PCB Training Report

Industrial Training Report

PCBWhat is PCB?

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board (PWB) or etched wiring board. A PCB populated with electronic components is a printed circuit assembly (PCA), also known as a printed circuit board assembly (PCBA). Printed circuit boards are used in virtually all but the simplest commercially produced electronic devices.

PCBs are inexpensive, and can be highly reliable. They require much more layout effort and higher initial cost than either wire wrap or point-to-point construction, but are much cheaper and faster for high-volume production; the production and soldering of PCBs can be done by totally automated equipment. Much of the electronics industry's PCB design, assembly, and quality control needs are set by standards that are published by the IPC organization.

History

Development of the methods used in modern printed circuit boards started early in the 20th century. In 1903, a German inventor, Albert Hanson, described flat foil conductors laminated to an insulating board, in multiple layers. Thomas Edison experimented with chemical methods of plating conductors onto linen paper in 1904. Arthur Berry in 1913 patented a print-and-etch method in Britain, and in the United States Max Schoop obtained a patent to flame-spray metal onto a board through a patterned mask. Charles Durcase in 1927 patented a method of electroplating circuit patterns. [2]

The inventor of the printed circuit was the Austrian engineer Paul Eisler who, while working in England, made one circa 1936 as part of a radio set. Around 1943 the USA began to use the technology on a large scale to make proximity fuses for use in World War II. After the war, in 1948, the USA released the invention for commercial use. Printed circuits did not become commonplace in consumer electronics until the mid-1950s, after the Auto-Sembly process was developed by the United States Army.

Before printed circuits (and for a while after their invention), point-to-point construction was used. For prototypes, or small production runs, wire wrap or turret board can be more efficient. Predating the printed circuit invention, and similar in spirit, was John Sargrove's 1936–1947 Electronic Circuit Making Equipment (ECME) which sprayed metal onto a Bakelite plastic board. The ECME could produce 3 radios per minute.

During World War II, the development of the anti-aircraft proximity fuse required an electronic circuit that could withstand being fired from a gun, and could be produced in quantity. The Centralab

Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib 1 | P a g e

http://en.wikipedia.org/wiki/Proximity_fuse

http://en.wikipedia.org/wiki/Bakelite

http://en.wikipedia.org/wiki/John_Sargrove

http://en.wikipedia.org/wiki/Turret_board

http://en.wikipedia.org/wiki/Wire_wrap

http://en.wikipedia.org/wiki/Point-to-point_construction

http://en.wikipedia.org/wiki/United_States_Army

http://en.wikipedia.org/wiki/World_War_II

http://en.wikipedia.org/wiki/Proximity_fuse

http://en.wikipedia.org/wiki/Radio

http://en.wikipedia.org/wiki/Paul_Eisler

http://en.wikipedia.org/wiki/Austria

http://en.wikipedia.org/wiki/Printed_circuit_board#cite_note-Harper03-1

http://en.wikipedia.org/wiki/Thomas_Edison

http://en.wikipedia.org/wiki/IPC_(electronics)

http://en.wikipedia.org/wiki/Point-to-point_construction

http://en.wikipedia.org/wiki/Wire_wrap

http://en.wikipedia.org/wiki/Laminated

http://en.wikipedia.org/wiki/Industrial_etching

http://en.wikipedia.org/wiki/Electrical_conductor

http://en.wikipedia.org/wiki/Electronic_component


Division of Globe Union submitted a proposal which met the requirements: a ceramic plate would be screenprinted with metallic paint for conductors and carbon material for resistors, with ceramic disc capacitors and subminiature vacuum tubes soldered in place.

Originally, every electronic component had wire leads, and the PCB had holes drilled for each wire of each component. The components' leads were then passed through the holes and soldered to the PCB trace. This method of assembly is called through-hole construction. In 1949, Moe Abramson and Stanislaus F. Danko of the United States Army Signal Corps developed the Auto-Sembly process in which component leads were inserted into a copper foil interconnection pattern and dip soldered. With the development of board lamination and etching techniques, this concept evolved into the standard printed circuit board fabrication process in use today. Soldering could be done automatically by passing the board over a ripple, or wave, of molten solder in a wave-soldering machine. However, the wires and holes are wasteful since drilling holes is expensive and the protruding wires are merely cut off.

In recent years, the use of surface mount parts has gained popularity as the demand for smaller electronics packaging and greater functionality has grown. Printed circuit boards came from electrical connection systems that were used in the 1850s. Originally metal strips or rods were used to connect large electric components mounted on wooden bases. The metal strips were replaced by wires connected to screw terminals, and wooden bases were replaced by metal frames. Smaller designs were still due to the increased size and complexity of the circuits they were hoping to build. In 1925, Charles Ducas of the United States submitted a patent application for a method of creating an electrical path directly on an insulated surface by printing through a stencil with electrically conductive inks. This method gave birth to the name "printed wiring" or "printed circuit."

In 1943, Paul Eisler of the United Kingdom patented a method of etching the conductive pattern, or circuits, on a layer of copper foil bonded to a glass-reinforced, non-conductive base. Eisler's technique was noticed by the US military and they started to use it in their new weapons in World War II. His idea did not come in to commercial use until the 1950s when the transistor was introduced. Up to that point, the size of vacuum tubes and other components were so large that the traditional mounting and wiring methods were all that was needed. With the introduction of transistors, however, the components became very small, and manufacturers turned to printed circuit boards to reduce the overall size of the electronic package.

Through-hole technology and its use in multi-layer PCBs were patented by the U.S. firm Hazeltyne in 1961. The resulting increase in the complexity and detailed paths started a new era in PCB design. Integrated circuit chips were introduced in the 1970s, and these components were quickly incorporated into printed circuit board design and manufacturing techniques. Today the Printed Circuit Board can have up to 8 layers in some applications.


http://simple.wikipedia.org/wiki/Transistor

http://en.wikipedia.org/wiki/Surface-mount_technology

http://en.wikipedia.org/wiki/Wave_soldering

http://en.wikipedia.org/wiki/Dip_soldering

http://en.wikipedia.org/wiki/United_States_Army_Signal_Corps

http://en.wikipedia.org/wiki/United_States_Army_Signal_Corps

http://en.wikipedia.org/wiki/Through-hole_technology


http://en.wikipedia.org/wiki/Solder

http://en.wikipedia.org/wiki/Resistor

http://en.wikipedia.org/wiki/Screenprinting


Some of early Circuits



Single Sided PCB’s

Single Sided PCB’s are called so because Components are connected to each other via copper tracks at only one side. While Components are mounted on another side. The side which contains tracks is called as bottom side while side which contains Components is called as top side. In Single Sided PCBs we can’t mount components on both sides. Single Sided PCBs are inexpensive, and can be highly reliable. They require layout effort and higher initial cost. But are much cheaper and faster for high-volume production. Single Sided PCB’s are mostly used for simple electronic circuitry where manufacturing cost have to be kept at minimum level. Originally, every electronic component had wire leads, and the PCB has holes drilled for each wire of each component. The components' leads were then passed through the holes and soldered to the PCB trace. This method of assembly is called through-hole construction and in India mostly this assembly method is commonly used.

But In recent years, the use of surface mount parts has gained popularity as the demand for smaller electronics packaging and greater functionality has grown.

Single sided PCB Scheme

Single Sided PCB Raw Material




http://en.wikipedia.org/wiki/Solder

Industrial Training Report A Single Sided Printed Circuit Board contains a small layer of copper at the bottom side of Board. This thickness of copper layer is usually 17 micron and the thickness of base Dielectric material is usually 2.4mm But the thickness of copper layer an dielectric layer may vary from application to application of PCB. The construction of single sided PCB raw material is as shown:-

The basic function of the laminate is to provide mechanical support for electronic components and to interconnect them electrically. To achieve this, the laminates should have good electrical, mechanical and environmental characteristics and meet the standard specifications of IPC, MIL ANSI. The laminates are divided into 3 groups according to their applications. They are Group A, Group B and Group C. Group A laminates are used in single side and double side manufacturing, Group B laminates are used in multilayer boards manufacturing and group C laminates are used in flexible board manufacturing. So, the insulating material which is the mixture of filler and resin on which all conductors and components are mounted is called the base material. This can be either rigid or flexible material.

Types of Laminates

Many types of copper clad material are available. The copper clad laminates most widely used in the manufacturing of Printed circuit boards, However, are FR2 , CEM-1, FR4 and GI etc. All these laminates has different properties and characteristics according


Industrial Training Reportto the base material used, like filler and resins. There are quite a few different dielectrics that can be chosen to provide different insulating values depending on the requirements of the circuit. Some of these dielectrics are polytetrafluoroethylene (Teflon). Well known materials used in the PCB industry are :-

FR-2 (Phenolic cotton paper) CEM-1 (Cotton paper and epoxy)

FR-3 (Cotton paper and epoxy) CEM-2 (Cotton paper and epoxy)

FR-4 (Woven glass and epoxy) CEM-3 (Woven glass and epoxy)

FR-5 (Woven glass and epoxy) CEM-4 (Woven glass and epoxy)

FR-6 (Matte glass and polyester) G-10 (Woven glass and epoxy)

CEM-5 (Woven glass and polyester)

Here FR means Fire Retardant. Thermal expansion is an important consideration especially with BGA and naked die technologies, and glass fiber offers the best dimensional stability. The Thickness of conventional Glass Epoxy Sheet is 1.5mm and copper of 17 micron thickness is coated on it.

COPPER FOIL

A thin layer of copper foil thickness of 17.5 microns, 35 microns or 70 microns are bonded to one side of the base material. Copper foils are available in two forms, namely

Rolled annealed copper foil & Electrolytic copper foil

The foil should be free from pin, holes, pits, scratches and nodules.

ROLLED ANNEALED COPPER FOIL

Electrolytically formed copper cathodes are made into large ingots by melting. The rolled copper is 99.9% pure and has good horizontal grain structure. The rolled copper is mainly used in flexible PCB Manufacturing Process.

ELECTROLYTIC COPPER FOIL

This is manufactured by electroplating method, the tank has either a lead or polished stainless steel rotating drum which is used as cathode and pure copper as the anode. The purity of the foil is around 99.5% .

FILLER


http://en.wikipedia.org/wiki/FR-4

http://en.wikipedia.org/wiki/FR-2

http://en.wikipedia.org/wiki/Polytetrafluoroethylene

Industrial Training Report These are continuous webs of base, such as organic, Non- organic, metallic or non- metallic form. The metallic and non metallic base fillers are used in thick and thin film technology and surface mount applications. The base itself used as a heat sink and has low coefficient of thermal expansion. Examples:-

Paper Sheet, Glass cloth

Cotton Fabric, Quartz Material

Asbestos Sheet, Ceramic Material etc.

RESINS

There are two types of resins.

1. Natural resins2. Synthetic resins

NATURAL RESINS:-

Resins are polymeric material which are obtained in their natural form from the trees. They are obtained from natural sources like plants and animals. On exposure to atmosphere, they dry into hard semi transparent masses.

SYNTHETIC RESINS:-

These are based on synthetic type of organic base materials, either thermoplastic or thermosetting plastic formed by polymerization reactions.

GLASS CLOTH

The glass cloth is used for the manufacture of epoxy resin reinforced glass cloth laminates. G-10, G-11, FR4, and FR5 types are some of the glass cloth laminates available. The glass fibers or filaments are usually 9.6 microns diameter and are bunched together and twisted 10 from thread and are woven to produce the glass fibers.

PCB Base Materials



Single Sided PCB Manufacturing Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib 9 | P a g e

Industrial Training Report The very first process in Manufacturing an PCB is making Design from Circuit Diagram. This process is done under Research and Development Section of Industry. There are many packages such as protel, OrCAD, NI Multisim, Ultiboard or express PCB to name a few, which allows to design you own PCB. We will discuss about this process later. Now we starts with Cutting.

SHEARING OR CUTTING The base material of PCB should cut according to the size required. First of all measure the required dimensions of PCB. Then add 10mm in its width & 16mm in its length. These dimensions should be added in every size of PCB. These dimensions are added as a margin in length & width which is then cut at last stage of manufacturing. Using margin it has a safety measure to protect the corners from any type of damage during processing.

5mm Margins are added 5mm

In dimensions

8mm

Photo Imaging and Screen Making

Line art or tracks may be printed onto the outer surfaces that is copper side of a PCB by screen printing. Screen printing is a printing technique that uses a woven mesh to support an ink-blocking stencil. The attached stencil forms open areas of


http://en.wikipedia.org/wiki/Stencil

http://en.wikipedia.org/wiki/Mesh

http://en.wikipedia.org/wiki/Woven

http://en.wikipedia.org/wiki/Screen-printing

Industrial Training Reportmesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate. A roller or squeegee is moved across the screen stencil, forcing or pumping ink past the threads of the woven mesh in the open areas.

Screen printing is also a stencil method of print making in which a design is imposed on a screen of silk or other fine mesh, with blank areas coated with an impermeable substance, and ink is forced through the mesh onto the printing surface. It is also known as silkscreen, seriography, and serigraph.

A screen is made of a piece of porous, finely woven fabric called mesh stretched over a frame of aluminium or wood. Originally human hair was used, then silk was woven to make a screen mesh; currently most mesh is woven of man-made materials such as steel, nylon, and polyester. Areas of the screen are blocked off with a non-permeable material to form a stencil, which is a negative of the image to be printed; that is, the open spaces are where the ink will appear.

Before ink is applied to the screen, the screen and frame must go through a process referred to as 'pre-press'. In this process, an emulsion is 'scooped' across the mesh and the 'exposure unit' burns away the unnecessary emulsion leaving behind a clean area in the mesh with the identical shape as the desired image. The screen is placed atop a substrate such as paper or fabric. Ink is placed on top of the screen, and a fill bar (also known as a floodbar) is used to fill the mesh openings with ink. The operator begins with the fill bar at the rear of the screen and behind a reservoir of ink. The operator lifts the screen to prevent contact with the substrate and then using a slight amount of downward force pulls the fill bar to the front of the screen. This effectively fills the mesh openings with ink and moves the ink reservoir to the front of the screen. The operator then uses a squeegee (rubber blade) to move the mesh down to the substrate and pushes the squeegee to the rear of the screen. The ink that is in the mesh opening is pumped or squeezed by capillary action to the substrate in a controlled and prescribed amount, i.e. the wet ink deposit is proportional to the thickness of the mesh and or stencil. As the squeegee moves toward the rear of the screen the tension of the mesh pulls the mesh up away from the substrate (called snap-off) leaving the ink upon the substrate surface.

PHOTOGRAPHIC EMULSION METHOD

Use polyester or other suitable synthetic fabric or screen material. Do not use silk or organdy if you wish to reclaim the screen. This is one of the most exciting methods of Screen Printing

because it offers the widest range of possibilities. It makes possible the printing of fine line drawings, various hand and commercial lettering techniques, as well as photographic half-tone positives.

All methods of photographic Screen Printing require three things: (1) a screen prepared with a light-sensitive coating, (2) a film positive, or equal, and (3) a Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib 11 | P a g e

http://en.wikipedia.org/wiki/Squeegee

http://en.wikipedia.org/wiki/Polyester

http://en.wikipedia.org/wiki/Nylon

http://en.wikipedia.org/wiki/Silk

http://en.wikipedia.org/wiki/Mesh

http://en.wikipedia.org/wiki/Porous

http://en.wikipedia.org/wiki/Squeegee

http://en.wikipedia.org/wiki/Roller_(brush)

http://en.wikipedia.org/wiki/Substrate_(materials_science)

Industrial Training Reportlight source that will enable you to transfer the opaque images on your positive to the light-Sensitive Screen you have made. Let's examine these requirements.

Step A--Mixing the photo emulsion Follow the mixing instructions given on both containers. Store the sensitized emulsion in a cool and dark place. Shelf life for the sensitized emulsion is 4 weeks at 90 Degrees F 8 weeks at 70 Degrees F and 4 months when refrigerated.

Step B Coating the screen

Coat the screen by first pouring a bead of the solution on one end of the bottom side of the screen. Spread it evenly and thinly with the squeegee or the plastic spreader. Use more solution where necessary. Pour a bead of the solution on one end of the inside of the screen and spread it evenly with the squeegee or the plastic spreader. Work to achieve an even continuous coating on both sides of the screen fabric. Perform the final spreading on the inside of the screen. Return any excess solution to your mixing container.

Step C-Drying the coated screen

In an area AWAY FROM LIGHT AND HEAT, set the screen to dry horizontally, bottom side down. This will provide the most even, flat "film" on the underside of the screen. It will, however, require your elevating the four corners of the underside of the frame during the drying stage with push pins or other suitable devices. An empty drawer, cupboard, closet, or under a cardboard box will work fine. Allow the screen to dry thoroughly. If more than 300 prints are to be run, it is best to apply a second coating of the sensitized Photo Emulsion to the bottom of the screen after the first coat is dry. Remember, work for a smooth, even THIN coating. Repeat the drying process away from heat and light. Once the sensitized screen is dry, it must remain in a darkened area until it is ready to be exposed. A fan in the dark area will greatly speed up the drying of the emulsion on the screen.

Step D- Positive making

A "positive" is any opaque image (usually black), on any transparent or translucent surface. There are many ways you may choose to prepare them. A excellent transparent film for this purpose is Wet Media Acetate . Wet Media is available in various sizes.

The printed sheets (positives) have copy and illustrations that may be used to create a picture or message. With the plain sheets, you may make art work of your own with Speedball Super Black Ink and an artists' brush or SPEEDBALL pens. Excellent results can also be obtained by using dry transfer or pressure sensitive letters and symbols . These can be applied directly on the tracing paper or clear plastic. The graphics must be opaque to light.


http://www.reuels.com/reuels/Vinyl_Lettering.html

http://www.reuels.com/reuels/Speedball_Super_Black_Ink_2oz.html

http://www.reuels.com/reuels/Speedball_Super_Black_Ink_2oz.html

http://www.reuels.com/reuels/Graphix_Wet_Media_Acetate_005.html

Industrial Training Report Another way of producing positives is through copy machines that have the capability of reproducing very opaquely on film, tracing paper, etc. In order to satisfactorily produce a positive using a copy machine, the following conditions must be met:

(1) Black and white line work-Must be opaque (2) Photographic print-Must have high contrast(3) Copy machine must have capability stated above.

You must check this out in advance. However, because of the half-tones (or continuous tones) which are in all photographs, a special type of "positive" must be prepared. This must be done by someone with photographic expertise and who has the necessary equipment. Essentially, this person will photographically transfer the halftones to Kodalith Ortho film. A dot patterned half-tone screen will be placed between the lens, and the ortho film. These "half-tone" dots will be exposed to the film simultaneously with the photograph.

The resulting "half-tone" negative will then be converted by the photographer to a "half-tone" positive. This is the same type of "conversion" that is made in the preparation of photographs for newspaper and magazine printing. The dot pattern breaks up the continuous tones into a half-tone interpretation that can be printed. Fine art half-tone screen printing involves a posterization process whereby a series of selected positives are produced through a process camera. With filters, the process camera can selectively identify specific colors in the original art. These are then, sequentially prepared for color registry. This is a highly technical procedure and should be attempted only by experienced printers.

IMAGE MAKING

EXPOSING:-

Film Master i.e. Positive is registered over the dry film with the emulsion side is in contact with photo resist. Then the panel is kept in a vacuum frame for intimate contact between surfaces . The proper Exposing time depends upon light intensity, temperature, thickness, photo polymer and type of equipment is used. Generally UV Tubes are used to expose the photo resist. To set up your "Light Station" place the screen on top of a piece of black paper and center it 12 inches directly below a 150W clear incandescent bulb or a BBA No.1 Photoflood (preferred) Bulb. Either

should be fitted with a foil-type pie tin as a reflector. The positive can be placed in contact with the coated (dry) screen by either of the above methods.

First method shows here does not require the foam rubber cushion and the positive will read "correctly" as it's positioned in the screen frame. But second method employs the use of a foam rubber cushion which is cut to the inside dimensions of the screen frame. The positive is placed in reverse (mirror image) on top of the underside of the screen.



Recommended Exposure Chart with 150 Watt Bulb, Clear Incandescent

(Screen Size . 150W Bulb Height . . Exposure Time)

8"x10". . . . . . 12 inches . . . . . . . . . . . . 45 minutes10"x14". . . . . . 12 inches . . . . . . . . . . . . 45 minutes12"x18" . . . . . 15 inches . . . . . . . . . 1 hr. 14 minutes16"x20 . . . . . . 17 inches . . . . . . . . . 1 hr. 32 minutes18"x20" . . . . . 17 inches . . . . . . . . . 1 hr. 32 minutes

DEVELOPING:-

Apply a forceful spray of water (body temperature) to both sides of the screen. DO NOT USE HOT WATER. Concentrate this spray on the light images on the top side of the screen. After a few minutes, these areas will become "open." Continue spraying until all unwanted emulsion is gone. Once you have completely washed the screen, let it dry thoroughly in a level flat position.Hold the dry frame to the light and check for pin-holes. These can be covered with Speedball Screen Filler or pieces of masking.

SCREEN PRINTING INKS:-

The inks used in screen printing process for etching and plate resist are mostly vinyl based and can be broadly classified into two groups:-

Solvent Soluble

Alkali Soluble


Industrial Training ReportSCREEN PRINTING PROCESS:-

The Image transferred screen is fixed on the printer table with the help of clamps. Then the laminate is positioned under the screen. Ink is applied on the screen and with the help of a squeeze ink is wiped across the screen. The pressure and speed of squeeze are controlled Manually or Automatically. For Printing purpose ink is mixed with other material for the purpose of making it bit thick. PCB is placed under the nylon sheet and ink is passed one time over the nylon sheet. Spoon out the ink across the end of the screen nearest to you. With the screen lifted slightly from the base, apply an even blanket of ink onto the print area. Be sure to use an easy, smooth stroke with the squeegee at a slight angle away from you. This is the flood stroke. Drop the screen onto your paper Lift the squeegee over the ridge of ink and make the print stroke by pulling towards yourself. Keep the squeegee at a 45 degree angle with enough pressure to scrape the ink from the screen. Lift the screen from the print, make the flood stroke, set the kick leg, remove the print and put it to dry on your rack or line. Insert new paper, release the kick leg and repeat the process.

Sharp clear prints can be produced provided you (1) maintain a generous quantity of ink on the screen, (2) use the flood stroke and (3) maintain adequate and even pressure on the squeegee during the print stroke.

Etching

One of the major steps in the chemical processing of subtractive printed board is etching, or removal of copper, to achieve the desired circuit pattern. Etching, is also used for surface preparations with minimal metal removal during inner layer oxide coating and electro less or electrolytic plating.

The most common etching system are based on alkaline ammonia, hydrogen peroxide, sulphuric acid and cupric chloride. Other systems include per sulfates , ferric chloride and chromic-sulphuric acids. Good etching results depends upon proper image transfer in both inner


Industrial Training Reportlayer print and etch and plated metal etch resists. Etch personnel must be familiar with screened, photosensitive and plated resists commonly used. The etching of printed boards must begin with suitable cleaning, inspection and pre-etch steps to ensure acceptable products. But Ferric hydroxide is mainly used for etching of Single Sided Printed Circuit boards.

ETCHING SOLUTION (FERRIC CHLORIDE)

Ferric chloride solution find widespread use as etchants for copper, copper alloys, Ni-fe alloys, and steel in printed circuit applications, electronics, photoengraving arts and metal finishing. Ferric chloride is used with screen inks, photo resist and gold patterns, but it cannot be used on solder or tin plated boards. Kovar and similar glass to metal sealing alloys are etched with FeCl3 by using photo resist techniques. Typical applications include leads on solid state microcircuit ceramic flat packages and fine line metallization masks. At one time ferric chloride was the most accepted and used etchants. That is because all the etchants were not commonly regenerated and Ferric Chloride had a high tolerance for dissolved copper as well as being lower cost. Ferric chloride still remains as an attractive batch etchants.

CHEMISTRY:-

At the copper surface, ferric ion oxidize copper to cuprous chloride with formation of green ferrous chloride.

FeCl3 + Cu FeCl2 + CuCl

In the body of the solution, Cuprous chloride is further Oxidized to CuCl2

FeCl3 + CuCl FeCl2 + CuCl2

As cupric chloride builds up the etching solution, a disproportionation reaction takes over.

CuCl2+Cu 2CuCl

MAIN INTEGRENTS:- Ferric Chloride + Hcl

USAGE OF INTEGRENTS:- FeCl3 (350-500gm/lt)+ HCl(10ml/lt)

TIME CONSUMED BY PCB:- 15 min for fresh solution and 30 min for old solution.



COLOUR OF THE SOLUTION:- Blackish Yellow Color

REQUIRED TEMPRATURE OF THE SOLUTION:- 250C-400C

EFFECT:- Bare Copper on PCB get Dissolved into Solution and we get etched PCB.

Caustic Soda & Drying Process

After etching process all the un wanted or extra copper get removed from the PCB and PCB left with only printed circuit but as we know we want copper coated circuit so we have to remove the blue paint or ink from the PCB . for this purpose we use caustic soda. Caustic soda get react with blue paint and only PCB left with copper coated circuit. For this process , we have to put the PCB in to the caustic soda and your PCB is ready but for any further process , we have to dry it in oven or by the source of sunlight .



MAIN INTEGRENTS:- Caustic Soda + Water

USAGE OF INTEGRENTS:- 50gm/lt

TIME CONSUMED BY PCB:- 5 min

COLOUR OF THE SOLUTION:- Transparent but changes to Circuit blue (colour of ink.)


EFFECT:- Ink printed on Copper surface get dissolved into solution.

Drilling & Scrubbing

Drilling operation is one of the mechanical processes by which circuit boards are drilled for different purposes. One purpose of the drilled hole is to provide components lead mounting and other is to establish an electrical interconnection between the top and bottom layer. The quality of a drilled hole depends upon the quality of laminates and drills, processes including machine accuracy, drilling techniques and operator skills in control and evaluation of hole quality and drill bits. When all the processes are properly followed high quality drilled holes are obtained.


Industrial Training Report Drills which are used for making holes in PCB’s are usually made of tungsten carbide. they are available in two shapes namely common shank and straight shank.

DRILL GEOMETRY

The function of drill bit is to cut and remove the base material and copper form laminate. It is therefore important to understand the function and geometry of each of the drills. The point angle determine the quality of the tool to cut the laminate material and it usually varies between 90 to 1300. For paper base material FR3, it is between 90 to 1100 and for glass base material FR4 etc. it is between 115 to 1300. The drill point has two primary edges which are parallel

to each other and are separated by the web. The cutting edge is called chisel edge.

A good drilling technique must satisfy following points

1. Constant High- Quality 2. Perfect through hole plating.3. Smaller diameter, shorter distance between the holes.4. Greater Production 5. Lower Cost and simple Storekeeping.

CARBIDE DRILL BIT:-

Carbides are non-ferrous metal which are hard in its natural state. Their hardness is determined by two factors namely the structure of the carbide and of bonding metal. The carbides are basically used to determine the wear resistance. The bonding metal determines the strength in accordance with the proportions. The hardness is 9.8 to 9.9 on the mohs scale of Hardness at temperature between 1300 to 16000C. Fine grained tungsten carbide cobalt alloys produced today are 94% tungsten Carbide and 6% Cobalt.

DRILLING PROBLEMS

The defective holes are formed due to improper drill bit geometry, drill speed , feed rate and improper curing of the base material. The following are the main defects:-

1. Resin Smear2. Nail Heating3. Roughness

Resin Smear problem occurs when the resin is heated beyond 1550C. Nail heating is caused due to excessive burring in the hole wall when the drill speed and feed are not balanced with the drill geometry. While Roughness is occurred due to more chipped drill hole and the rough hole walls are due to the poor quality of the drill bits.

Types of Drilling used for Single Sided PCBs:-


Industrial Training Report1. Manual Drilling.2. CNC Drilling.

MANUAL DRILLING Manual Drilling is done with the help of small manually operated motor based drilling machine. Motor is used to rotate bit and by pushing the handle of machine downwards the force can drill a hole into the surface of PCB. These types of machines are used for Drilling hole into Single Sided PCBs. This process is cheaper than CNC Drilling but with less accurate results.

Manual Drilling Machine

CNC DRILLING

Drilling of components mounting holes into PCB is important operational process. Thus drilling is used to create the components lead holes and through holes into PCB. Drilling of Single sided PCBs is also done with the help of CNC DRILLING MACHINES. Because using this machine the speed of manufacturing get fast & second it’s drilling is very accurate. The full form of CNC is CNC- COMPUTER NUMERICAL CONTROL

As clear from name this machine is controlled by computer based software. CNC machine has two or more drill slots where user can fix bit of appropriate size.


Industrial Training ReportThe size of bit may varies from 0.5mm to Several millimeters. Drilling bits are set according to drilling size requirements.

SURFACE SPEED AND SPINDLE SPEED

As holes are getting smaller, higher spindle speeds are required to achieve the desired surfacespeed that determines throughput. However, higher surface speeds result in higher drillingtemperatures that may increase heat-related hole defects such as smearing.Surface speed is a measure of how much distance is covered by the drill’s diameter while it is rotated by the spindle and is expressed in surface feet per minute (sfm). It is used to calculate spindle speed (rpm) for a given drill diameter. The formula to calculate spindle speed using the desired surface speed is shown:-spindle speed (rpm)= sfm × 12/ π × diam.where diam. = drill diameter (in) π = 3.1415The higher the surface speed, the higher the spindle speed, and subsequently the higher the frictional heat that is generated, translating into greater extents of heat-related hole defects and drill wear. Conversely, lower surface speeds imply lower spindle speeds and less frictional heat. When more abrasive materials (e.g., materials with higher Tg such as multifunctional FR-4, polyimide, or cyanate ester) are processed or drilled stack height is increased, drilling temperatures increase. To offset the resulting increase in temperature under such conditions or when excessive extents of heat-related hole defects are apparent, decrease the surface speed to lower the spindle speed.

SCRUBBING

Wooling and scrubbing is done after Drilling holes on PCB . This process is done manually with the help of steel wool But automatic machines are also available and highly efficient than manual processing. This process is done to clean the track so that masking can be done easily on tracks and scrubbing is process of removing oxidized layer of copper and sharp projections around the drilling holes .



CNC Drilling Machine

PCB Scrubbing Machine



Solder Masking

Masking is the process just same as the Screen printing process. In this process the solder masking ink is used to avoid any cause of short circuit. The master artwork for solder resist pattern is prepared and then the solder mask is applied to PCB by screen printing. The PCBs are dried in air and then thermally cured in the hot air electric oven at 120 C, for about 60 min. On a worldwide basis, the most popular coating method by far is single-sided open screen coating because it is relatively easy to do successfully and has a low entry cost. By its nature, however, screen coating tends to remove resist ink at the conductor edge that makes the first contact with the squeegee and leave spacing between densely spaced conductors uncovered, whether it is a single-sided or simultaneous double-sided coating to be explained in the next subsection. To overcome this weakness, the users of the screen-coating method normally screen the panel twice or even three times to ensure sufficient coverage at conductor edges and spacing, particularly at their bottom area. Users of PWBs usually demand that the thickness of the solder resist be about 0.6 mil (or 0.15 mm) at the edges of the conductors.



Postcure Bake:- Postcure bake is done at about 300°F (150°C) for 30 to 60 min in a convectionoven. LPISR makers also recommend IR bump at about 340°F (170°C) for 5 min. Some high-volume producers using fully automated line screen legends right after drying the panel, following the final rinse and before the final cure, and combine the final LPISR cure with the legend ink cure in one shot.

BAKING

Legend Printing & Tinning


Industrial Training Report To facilitate assembly and repair jobs, the position and the value of the component is marked on each side of the PCB. This process is same as masking and printing but white colored ink is used at the place of green and blue. All the steps as explained under screen printing are repeated. The PCBs are dried in air or thermally dried in an hot air electric oven at 150 C for about 30 min. This step is the final step of fabrication technique of PCBs.

Tinning

After baking PCB is ready to 80%. Then one of the most important process is tinning. It is the process in which uncoated or copper coated holes or pads are coated with tin. This coating of tin provides the good strength to the soldering. Before tinning the PCB it is washed with ‘hydrogen chloride’ for at least 10 times. If we don’t do this, it will gone to blackish in colour and their life

also decreases. Before tinning the PCB is dipped in tinning salt and then it is washed with water.

Final Cutting & Finishing


Industrial Training Report Cutting of PCBs to their Actual sizes is the second to last step. In this process actual size is made by cutting, punching, rounding etc. Several PCBs are joined together to reduce work load, time & cost also. After this process PCBs are send for BARE BOARD TESTING. After tinning PCB is almost ready but some of tin get stick into the holes that are on PCB so we need to clean the holes by a sharp edge pin so that components get easily assembled on the PCB. This process is called as finishing. After this finishing PCB is completely ready and finally the boards are checked for quality and packed for dispatching.

Double Sided PCB’s

By definition, double-sided boards (DBs) have circuitry on both sides of the boards. They canbe classified into two categories:1. Without through-hole metallization


Industrial Training Report2. With through-hole metallization

The category of through-hole metallization can be further broken into two types:1. Plated-through-hole (PTH)2. Silver-through-hole (STH)

PLATED-THROUGH-HOLE TECHNOLOGY. Metallization of holes by copper plating has been practiced since the mid-1950s. Since PWB substrate is an insulating material, and therefore nonconductive, holes must be metallized first before subsequent copper plating can take place. The usual metallization procedure is to catalyze the holes with palladium catalyst followed by electroless copper plating. Then, thicker plating is done by galvanic plating. Alternately, electroless plating can be used to plate all the way to the desired thickness, which is called additive plating. The biggest change in the manufacturing process of double-sided PTH boards, and also of multilayer boards (MLBs), is the use of direct metallization technologies. (See Chap. 30 for full discussion of electroless and direct metallization for through-hole boards.) Here, simply, it eliminates the electroless copper process. The hole wall is made conductive by palladium catalyst, carbon, or polymer conductive film, then copper is deposited by galvanic plating. The elimination of electroless copper, in turn, allows the elimination of environmentally hazardous chemicals, such as formaldehyde, and EDTA, which are two main components of electroless copper-plating solutions.

SILVER-THROUGH-HOLE TECHNOLOGY. STH boards are usually made of paper phenolic materials or composite epoxy paper and glass materials, such as CE-1 or CE-3. After doublesided copper-clad materials are etched to form conductor patterns on both sides of the panel, holes are formed by drilling. Then the panel is screened with silver-filled conductive paste. Instead of silver, copper paste can also be used. Since STHs have a relatively high electrical resistance compared with PTHs, the application of STH boards is limited. However, because of their economic advantage (the cost of TYPES OF PRINTED WIRING BOARDS STH boards is usually one-half to two-thirds that of functionally equivalent PTH boards), their application has spread to high-volume, low-cost products such as audio equipment, floppy disk controllers, car radios, remote controls, etc.

PTH TECHNOLOGIES:-In 1953, the Motorola Corporation developed a PTH process called the Placir method,1 in which the entire surface and hole walls of an unclad panel are sensitized with SnCl2 and metallized by spraying on silver with a two-gun spray. Next, the panel is screened with a reverse conductor pattern, using a plating resist ink, leaving metallized conductor traces uncovered. The panel is then plated with copper

by an electroplating method. Finally, the resist ink is stripped and the base silver removed to complete the PTH board. One problem associated with the use of silver is the migration caused by silver traces underneath the copper conductors. The Placir method was the forerunner of the semiadditive process, which is discussed afterwards. In 1955, Fred Pearlstein2 published a process involving electroless nickel plating for metalizing nonconductive materials. This catalyzer consists of two steps. First the panel is sensitized in SnCl2 solution, and then it is activated in PdCl2 solution.This process presented no problem for metallizing nonconductive materials. At the same


Industrial Training Reporttime that Pearlstein’s paper was published, copper-clad laminates were starting to become popular. Manufacturers of PWBs applied this two-step catalyzing process to making PTHs using copper-clad laminates. This process, however, turned out to be incompatible with the copper surface. A myriad of black palladium particles called smads were generated between copper foil and electrolessly deposited copper, resulting in poor adhesion between the electroless copper and the copper foil. These smads and electroless copper had to be brushed off with strong abrasive action before the secondary electroplating process could begin. To overcome this smad problem, around 1960 researchers began attempting to develop better catalysts; the products of their research were the predecessors of modern palladium catalysts.

Scheme of Double Sided PCB Base Material

Processes for making PTH PCB’s

In PTH plating method, after the copper reduction process, plating

resist layers of the reverse conductor image are formed on both sides of the panel by screening

resist inks. In most fineline boards, photosensitive dry film is used instead. There are some minor

variations in the pattern-plating method:

1. Catalyzing (preparing the nonconductive surface to cause copper to come out of solution


Industrial Training Reportonto that surface)

2. Thin electroless copper (0.00001 in) followed by primary copper electroplating; thick

electroless copper (0.0001 in)

3. Imaging (application of a plating resist in the negative of the desired finished circuit)

4. Final electroplating copper

5. Solder plating (as etching resist) 0.0002 or 0.0006 in

6. Stripping plating resist

7. Etching of base copper

8. Solder etching (0.0002-in case); solder reflow (0.0006-in case)

9. Solder mask followed by hot-air solder coater leveler if solder etching is used

10. Final fabrication and inspection

Most manufacturers of DSBs with relatively wide conductors employ thick electroless copper

plating. However, thin electroless copper followed by primary electroplating is preferred for boards

having fine-line conductors, because a considerable amount of surface is brushed off for better

adhesion of dry film. This provides a higher reliability for PTHs. Solder reflow boards had been

preferred by many customers, particularly in military and telecommunications applications, until the

emergence of hot-air solder coater levelers. Although the solder-over-copper conductors protect the

copper from oxidization, solder reflow boards have some limitations. Solder mask is hard to apply

over reflowed solder, and it tends to wrinkle and peel off in some areas when the boards go through

component soldering. A more serious problem is the solder bridging that occurs when the conductor

width and clearance become very small. In step 9, the entire surface of the board except for the pads

is covered by solder mask, and then the board is immersed into the hot-air solder coater leveler,

resulting in a thin coating of solder over the pads and the hole walls. The operation sounds simple,

but it requires constant fine-tuning and maintenance of the hot-air solder coater leveler; otherwise,

some holes may become heavily clogged with solder and are then useless for component insertion.

But the main problem is that it is difficult to design such type of PCBs. In double sided PCBs we

use FR4 type base material which is highly resistive to heat. It is a high quality base material made

of glass-epoxy sheets. The raw sheet of double sided PCB has 17µ to 70µ of copper on each side.

But 35µ copper layer is commonly used. the thickness of sheet is between 0.8mm to3.2mm. But we

commonly use 2.4mm sheet.

Shearing When copper-clad laminates are to be sheared, the shear should be set with only 0.001 to 0.002 in clearance between the square-ground blades.The thicker the material to be cut, the greater the rake or scissor angle between the top and bottom shear blade. The converse also is true: The thinner the material, the smaller the rake angle and the closer the blades. Hence, as in many metal shears, the rake angle and the blade gap are fixed; the cutoff piece can be twisted or curled. Paper-base material can also exhibit feathered cracks along the edge that are due to too wide a gap or too


Industrial Training Reporthigh a shear angle. That can be minimized by supporting both piece and cutoff piece during the shear operation and decreasing the rake angle. Epoxy glass laminate, because of its flexural strength, does not usually crack, but the material can be deformed if the blade clearance is too great or the shear angle is too large. As in blanking, the quality of a part produced from paper-base laminates by shearing can be improved by warming the material before performing the operation.

Giant PCB Shearing Cutter

CNC Drilling

As circuit density continues to increase, along with the demand for higher and higher accuracy in hole location, the drilling machines and the environment in which the machines operate must be tightly controlled in order to achieve success in the drilling operation. High-density interconnect (HDI) has been defined as referring to holes with diameters of ≤0.006 in. HDI holes generally are expected to be made by non mechanical means, such as lasers, plasma, or photoimaging. However, the bulk of holes continue to be created bymechanical means, and as the hole size approaches, or in some cases goes below, 0.006 in. ,special challenges face the mechanical drilling process. PCB technology requires drilled holes as small as 0.002 in (0.05 mm) with extremely high accuracy, particularly when drilling dense hole patterns. The processes and machines used to drill these holes now constitute a highly developed science. As


Industrial Training Reportthe drilling process approaches these HDI dimensions, numerous factors become increasingly critical, such as:● Hole location● Predrilling process issues● Drill room temperature/relative humidity● Vacuum● Drill bit condition● Dynamic spindle run-out● Backup and entry material (type and thickness)● Maximum spindle speed● Depth control.

CNC CONTROL:-

The best thing about PCB layout programs is that they automatically generate lists of coordinates of points where holes are to be drilled. If a computer-controlled drilling machine is used, the circuit board simply needs to be fixed to the table and the machine does the rest. The only intervention required is to change drills, which can however be quite tiresome. The program must be stopped, the drilling head must be moved to a specific position, or at least raised away from the board, in order to gain access to the chuck. The height of the drill must be correct, to ensure that the new bit is at the same height as the old one for this purpose rings can be marked on the drill spindles. Alternatively, drills ready-marked with rings can be bought — but all from the same manufacturer, since different manufacturers put their rings at different heights! And if, after all this effort, the new drill is only used for a few holes, the whole process will have to be repeated just a few seconds later. Manufacturers soon realised that this was a problem, and developed chucks which can be opened from above using a small handle. This is a great improvement over chucks, such as those frequently found on milling machines and mini-drills, which require a special tool to open them. Such chucks make a rather expensive addition to a small drilling machine, but for the perfect solution you can expect to pay as much as a thousand pounds: you will need an automatic compressed-air tool changer with tool magazine and a compressor, and everything will work as if by magic.

The control program will run a little slower, because the drilling head has to move over to the tool magazine to drop off the old drill and pick up the new one; even here, comfort has its price. But there is still a big step from the perfect machine to a satisfactorily drilled circuit board. Have you ever considered how registration is preserved through the process of circuit board manufacture? In the PCB layout program the drilling coordinates are known exactly. The positions appear on the film and are then transferred to the circuit board — but where is the reference point? Getting the film cleanly and accurately aligned with the edges of the circuit board is made impossible by the frequently dirty and roughly-cut base material. The circuit board is generally not rectangular, the material being cut after production using a guillotine. A computer-controlled drilling machine requires a device that guarantees that the drill lands repeatably at the specified point. This device should be firmly fixed to the machine and in any case designed to make precise alignment easy. There are many approaches to registration, using try-squares, predrilled holes (a real problem when modifying a circuit), optical registration devices, sticking the film to the circuit board, or ‘intelligent’ motion analysis systems using a camera, TeachIN and coordinate transformations according to reference marks, and many other wonderful methods. Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib 31 | P a g e


Two Spindle CNC Drilling Machine

SCRAPPING:

Scrapping is next process after drilling. In this process, the useless copper left over the surface of drilled hole of the PCB is disposed off. Scrapping is usually done with scrapping machine. This scrapping machine consist of a round shaped rotating wheel on which special sand paper is fixed. Image of scrapping machine is as shown:-



Electroless Process

Electroless process is divided into different following steps:-


CLEANING CLEANING

Micro Etching Micro Etching


CLEANING:-

Cleaning is done with the help of Cleaner solution. But before dipping the PCB’s into Cleaner Solution these are washed by water. Some information of process is written here:-

MAIN INTEGRENTS:- Caustic Soda, Soap

USAGE OF INTEGRENTS:- 150ml/lt

TIME CONSUMED BY PCB:- 3 min.

COLOUR OF THE SOLUTION:- Transparent


MAXIMUM PRODUCTION BY 10Lt Sol.:- 100Sqm

EFFECT:- This Cleans dust particles from surface of PCB.

Micro ETCH SOLUTION Bath:-

This solution is used for removal of copper surface pre-treatment’s, Oxidation and presentation of uniformly active copper. PCB’s from cleaner solution directly added into this solution. Some information of process is written here:- Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib 34 | P a g e

Pre-ACTIVATOR Pre-ACTIVATOR

ACTIVATOR ACTIVATOR

Post-ACTIVATOR Post-ACTIVATOR

COPPER SOLUTION COPPER SOLUTION

ELECTROPLATING ELECTROPLATING

Industrial Training ReportMAIN INTEGRENTS:- SALT(AD 1481) in powdered form + Sulphuric acid 99% pure form.

USAGE OF INTEGRENTS:- SALT(150 gm/lt) + H2SO4(10ml/lt)

TIME CONSUMED BY PCB:- 1 min for fresh solution and 3 min for old solution.

COLOUR OF THE SOLUTION:- Transparent(When solution is new) and Sky Blue (When solution is old.)


MAXIMUM PRODUCTION BY 10Lt Sol.:- 40 Sqm

EFFECT:- This slow acid etching is used for removal of copper surface pretreatments, oxidation and presentation of uniformly active copper.

PRE-ACTIVATOR Solution Bath:-

Pre Activator Solution is used to maintain balance of chemical reactions for activator solution. Some information of this process is written here:-

MAIN INTEGRENTS:- PC 1236 Solution + HCl

USAGE OF INTEGRENTS:- 150gm/lt (PC 1236) + 15ml/lt for HCl



REQUIRED TEMPRATURE OF THE SOLUTION:- Room Temprature.

MAXIMUM PRODUCTION BY 10Lt Sol.:- 100Sqm

EFFECT:- used for removal of pre sulphate residues and to maintain balance of next step.

ACTIVATOR Solution Bath:-

Activator Solution is the neutral solutions of palladium and tin are used deposit a thin layer of surface active palladium in the holes and on the surface. Some information of this process is written here:-

MAIN INTEGRENTS:- Palladium 2446 solution + Adaptive 443 Solution + PC1236 solution.

USAGE OF INTEGRENTS:- 40 ml/lt for Pd 2446 + 15ml/lt for Adaptive Sol. +150gm/lt (PC 1236)

After 1 Sqm Production, 5 ml of Pd 2446 and 7ml of adaptive 443 is mixed into solution again.


Industrial Training ReportTIME CONSUMED BY PCB:- 15 min.

COLOUR OF THE SOLUTION:- Black

REQUIRED TEMPRATURE OF THE SOLUTION:- Room Temperature.

MAXIMUM PRODUCTION BY 10Lt Sol.:- Written above.

COST Of THE SOL.:- Rs 11165/lt (Activator)

EFFECT:- Acid Solution of palladium and tin are used to deposit a thin layer of surface active palladium in the holes and on the surface.

POST ACTIVATOR Solution Bath:-

Post Activator Solution is used for the removal of colloidal tin on board surfaces and holes. Some information of this process is written here:-

MAIN INTEGRENTS:- Kemplate PA 1491

USAGE OF INTEGRENTS:- 150ml/lt (PA 1491)




MAXIMUM PRODUCTION BY 10Lt Sol.:- Unlimited (Very Large)

EFFECT:- Used for the removal of colloidal tin on board surfaces and holes.

Copper Solution Bath:-

Alkaline chelated copper is reducing solution that deposits thin copper in the holes (20 to 100mm)and surface. Some information of this process is written here:-

MAIN INTEGRENTS:- Cu2406A + Cu 2406B

USAGE OF INTEGRENTS:- 100ml/lt (2406A) + 100ml/lt (2406B)


COLOUR OF THE SOLUTION:- Blue


Industrial Training ReportREQUIRED TEMPRATURE OF THE SOLUTION:- Room Temperature.

MAXIMUM PRODUCTION BY 10Lt Sol.:- 100sqm

EFFECT:- This Solution deposit thin copper layer in the holes.

ELECTROPLATING or Cu Hardening Bath:-

Principle:- The passage of a unidirectional current through a solution associated with the movement through it of charged particles called ions. The terminal leading the current into the solution are electrodes. The pole at which the chemical reaction of reduction takes place is cathode and the pole at which chemical reaction of oxidation takes place is called anode. In the electrolytic cell, the total process of decomposition due to the passage of a current is called electrolysis.

MAIN INTEGRENTS:- Copper Sulphate + Sulphuric acid + Cupra max. HT Additive.

USAGE OF INTEGRENTS (for 200 litre TUB):- 35 ml/lt for CuSO4 + 100ml/lt for H2SO4 + 100ml/bath HT Additive. An DC Current is also flowed through solution according to per decimetre PCB Size. Eg- PCB SIZE CURRENT

10 Decimetre 20 A

20 Decimetre 40 A




MAXIMUM PRODUCTION BY 10Lt Sol.:- Depends upon Anode(Slab).

EFFECT:- Thick layer of copper i.e. near about 17 micron deposit on copper inside and outside holes as shown.



PCB After Plating

Negative Printing

The photographic image is transferred to copper clad laminate by the screen printing technique. This technique has been used for a long time for printing cloth, panels and so on, and reaches its maximum degree of accuracy when applied to PCB manufacture. The technique is particularly adopted for low cost print and etch and plated printed boards, when the ultimate resolution and definition are not very exacting. A screen comprises an aluminum frame, mesh, emulsion and adhesive bonding. The emulsion is removed by a photochemical process where deposition is required. A specification of 1:1 ratio of open area to board pad area is typical, but 10


Industrial Training Report% variations are not uncommon. The flexibility of the emulsion creates a good gasket against the PCB and aids print definition. It is basically a stencil operation, which depends on the transfer of resist to the copper clad laminate surface using a stencil image of the circuit design. The stencil is firmly attached to the surface of a silk, nylon or stainless steel screen. A liquid resist material is forced through the open areas of the screen mesh that are not protected by the stencil onto the copper clad substrate by the pressure of a squeegee wiped across the top surface of the screen. The squeegee pressure deflects the screen downward in point contact with the substrate. As the squeegee passes a given point, screen fabric tension snaps the screen back, leaving screen ink behind. The only difference between negative and positive printing is that positive printing is done with positive developed film in which circuit tracks and holes are black in colour, while in negative developed film the circuit tracks and holes are left blank (transparent) and all other portion is filled with black ink. In the process of negative printing the portion where tracks and pads are situated is kept open. Rest of the portion of PCB is covered with etch resistive ink. User can use any color of etch resist ink. The open areas then plated by copper by using electroplating method.

A Negative



Negative Printed PCB.

ELECTROPATING:-Principle:- The passage of a unidirectional current through a solution associated with the movement through it of charged particles called ions. The terminal leading the current into the solution are electrodes. The pole at which the chemical reaction of reduction takes place is cathode and the pole at which chemical reaction of oxidation takes place is called anode. In the electrolytic cell, the total process of decomposition due to the passage of a current is called electrolysis.

MAIN INTEGRENTS:- Copper Sulphate + Sulphuric acid + Cupra max. HT Additive.

USAGE OF INTEGRENTS (for 200 litre TUB):- 35 ml/lt for CuSO4 + 100ml/lt for H2SO4 + 100ml/bath HT Additive. An DC Current is also flowed through solution according to per decimetre PCB Size. Eg- PCB SIZE CURRENT

10 Decimetre 20 A

20 Decimetre 40 A



REQUIRED TEMPRATURE OF THE SOLUTION:- 240C - 320C


Anode is connected to Copper Slab and Cathode is connected into Solution.

TIN PATING:- Pure Tin is the most commonly used plated finish for printed circuits. Its advantage are good solder ability and easy plating control. But we use Tin Plating as etch resistive


Industrial Training Reportsubstance. In ammonia etching, copper is easily removed by ammonia solution but tin plated portion remains unaffected.

MAIN INTEGRENTS:- Tin Sulphate + Sulphuric acid

USAGE OF INTEGRENTS (for 200 litre TUB):- 30gm/lt of SnSO4 + 100ml/lt for H2SO4

An DC Current is also flowed through solution according to per decimetre PCB Size.

Eg- PCB SIZE CURRENT

10 Decimetre 20 A - 30A

20 Decimetre 40 A -60A


COLOUR OF THE SOLUTION:- Yellowish Brown.

REQUIRED TEMPRATURE OF THE SOLUTION:- 280C - 370C


Anode is connected to Tin Slab and Cathode is connected into Solution.

Ammonia Etching

Alkaline etching with ammonium hydroxide complexing is increasingly used because of its continuous operation, compatibility with most metallic and organic resists, high capacity for dissolved copper, and fast etch rates. Continuous (open-loop) spray machine chemical Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib 41 | P a g e

Industrial Training Reportcontrol systems are universally used. This operation provides constant etch rates, high work output, ease of control and replenishment, and improved pollution control. However, rinsing after etching is critical, and the ammonium ion introduced to the rinses presents a waste-treatment problem. On-site closed-loop regeneration with chemical recycling is commercially available but not routinely practiced because of facility requirements, capital cost, fluctuating economics depending on copper commodity pricing, and worker requirements.The general economical and environmentally appropriate operating strategy is to recycle the by-product etchant products under contract to a supplier who reclaims or reconstitutes the copper contained and regenerates the ammoniacal constituents into a reformulated replenisher solution for return to fabricators.

Chemistry. The main chemical constituents function as follows:1. Ammonium hydroxide (NH4OH) acts as a complexing agent and holds copper in solution.2. Ammonium chloride (NH4Cl) increases etch rate, copper-holding capacity, and solutionstability.3. Copper ion (Cu2+) is an oxidizing agent that reacts with and dissolves metallic copper.4. Ammonium bicarbonate (NH4HCO3) is a buffer and as such retains clean solder holes andsurface.5. Ammonium phosphate [(NH4)3PO4] retains clean solder and plated through-holes.6. Ammonium nitrate (NH4NO3) increases etch rate and retains clean solder.7. Additional additives are included in most formulations to enhance speed and/or sidewallprotection.8. Continuous operations consist of single-solution makeup buffered to a pH of 7.5 to 9.5.Alkaline etching solutions dissolve exposed field copper on printed boards by a chemicalprocess of oxidation, solubilizing, and complexing. Ammonium hydroxide and ammoniumsalts combine with copper ions to form cupric ammonium complex ions [Cu(NH3)4 2+], which hold the etched and dissolved copper in solution at 18 to 30 oz/gal. Typical oxidation reactions for closed-loop systems are shown by the reaction of cupric ion on copper, and air (O2) oxidation of the cuprous complex ion:

Cu + Cu(NH3)42+ → 2Cu(NH3)4

+

4Cu(NH3)2+ + 8NH3 + O2 + 2H2O → 4Cu(NH4)42+ + 4OH-



Alkaline etching system

Properties and ControlEarly versions of alkaline etchants were batch operated. They had a low copper capacity, and the etch rates dropped off rapidly as copper content increased.4,5,6 It was found to be necessary to add controlled amounts of dissolved oxidizing agents to speed up the rate and increase copper capacity at a constant temperature. Batch operation is no longer supported by commercial suppliers. Etching solutions are operated at 120 to 130°F and are well suited to spray etching. Efficient exhaust systems are required because ammonia fumes are released during operation. Etching machines must have a slight negative pressure and moderate exhausting to retain the ammonia necessary for holding dissolved copper in solution. Care must be taken that sufficient fresh air to supply needed O2 is introduced to balance the extraction. Currently available solutions offer constant etching of 1 oz (35 μm) copper in 1 min or less, with a dissolved copper content of 18 to 24 oz/gal.



AMMONIA ETCHING

Green Masking Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib 44 | P a g e

Industrial Training Report Masking is the process just same as the Screen printing process. In this process the solder masking ink is used to avoid any cause of short circuit. The master artwork for solder resist pattern is prepared and then the solder mask is applied to PCB by screen printing. The PCBs are dried in air and then thermally cured in the hot air electric oven at 120 C, for about 60 min. On a worldwide basis, the most popular coating method by far is single-sided open screen coating because it is relatively easy to do successfully and has a low entry cost. By its nature, however, screen coating tends to remove resist ink at the conductor edge that makes the first contact with the squeegee and leave spacing between densely spaced conductors uncovered, whether it is a single-sided or simultaneous double-sided coating to be explained in the next subsection. To overcome this weakness, the users of the screen-coating method normally screen the panel twice or even three times to ensure sufficient coverage at conductor edges and spacing, particularly at their bottom area. Users of PWBs usually demand that the thickness of the solder resist be about 0.6 mil (or 0.15 mm) at the edges of the conductors.

Post cure Bake:- Post cure bake is done at about 300°F (150°C) for 30 to 60 min in a convectionoven. LPISR makers also recommend IR bump at about 340°F (170°C) for 5 min. Some high-volume producers using fully automated line screen legends right after drying the panel, following the final rinse and before the final cure, and combine the final LPISR cure with the legend ink cure in one shot.

HAL (Hot Air Levelling)

The bare copper on the printed circuit board generally tends to deteriorate with time resulting in an inferior appearance and making soldering difficult. As such, bare copper boards are acceptable only for experimental and prototyping work. For high quality products, some type of


Industrial Training Reportcoating is applied to prevent the occurrence of these problems. The most common type of coating is the tinning of the copper tracks. This is done either by roller tinning or electroplating. A modified process of roller coating is the hot air levelling process. Hot air levelling is a process of applying a thin coating of eutectic tin-lead on the exposed portion on a printed circuit board. This deposition increases the solderability of the board during assembly operations. Solder has many advantages over any other conventional organic coatings. These solder coatings have very good shelf life, short solder wetting time during assembly and very high mechanical stability. The formation of an inter-metallic bond even before the PCB assembly is a unique characteristic of HAL. Due to the presence of solder on copper, the PCB can withstand multiple soldering and de-soldering operations during the assembly cycle, with no adverse effect on the solderability of the board.

HAL also offers many advantages in the field of SMD and fine pitched quad packs. The procedure involves dipping a board in pure molten solder and blowing off the excess air between air knives. The quality of solder deposition basically depends upon the cleanliness of the surface. Pre-cleaning is therefore necessary to remove oily deposits, fingerprints and other organic contaminants that may be present on the copper surface on the through-holes. The steps involved in hot air levelling are as shown. Pre-cleaning is generally done by using a mild acid or using per sulphate, followed by rinsing with clean water. Fluxing is done either externally or internally in the HAL machine itself, which has a heated chamber. The flux generally used is water soluble so that it is easy to remove it after solder coating. The board is then transferred to a solder pot in which solder is maintained at a temperature of 250 °C to 270 °C where the soldering action takes place. The solder coating is then hot air levelled by hot air knives whose angles can be fixed depending upon the density and geometrical distribution of the circuit pattern on the board. The boards are then allowed to cool followed by cleaning with a slightly warm detergent water which removes the excessive flux, that is left over the board.



HAL PROCESS

Legend Printing


Industrial Training Report To facilitate assembly and repair jobs, the position and the value of the component is marked on each side of the PCB. This process is same as masking and printing but white colored ink is used at the place of green and blue. All the steps as explained under screen printing are repeated. The PCBs are dried in air or thermally dried in an hot air electric oven at 150 C for about 30 min.

Automatic Screen Printing Machine

Final Shearing, Routing etc.

The quality of a part produced from paper-base laminates by shearing, piercing, or blanking can be improved by performing the operation on material which has been warmed. Caution should be exercised in heating over 100°F because the coefficient of thermal expansion may be high enough to cause the part to shrink out of tolerance on cooling. Paper-base Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib 48 | P a g e

Industrial Training Reportlaminates are particularly anisotropic with respect to thermal expansion; that is, they expand differently in the x and y dimensions. The manufacturer’s data on coefficient of expansion should be consulted before a die for close-tolerance parts is designed. Keep in mind that the precision of the manufacturer’s data is probably no better than ±25 percent. Paper-base material can also exhibit feathered cracks along the edge that are due to too wide a gap or too high a shear angle. That can be minimized by supporting both piece and cut off piece during the shear operation and decreasing the rake angle. Epoxy glass laminate, because of its flexural strength, does not usually crack, but the material can be deformed if the blade clearance is too great or the shear angle is too large. As in blanking, the quality of a part produced from paper-base laminates by shearing can be improved by warming the material before performing the operation.

Modern circuit board fabricators rely principally on routing to perform profiling operations. The high cost and extended lead times for blanking dies, combined with the problem of design inflexibility of hard tooling, limit the punching operation generally to very high volumes or designs specific to die applications. The applications of NC routing extend well beyond merely cutting board profiles. The ability to produce boards in multiple-image modules reduces handling, not only in the board shop, but in every subsequent operation from packing, component assembly, wave solder, and test. This is of special value when dealing with a postage-stamp-size part or wire-bondable gold surfaces. Where handling must be minimized, the module acts as a pallet throughout these operations. In addition, unusual or irregular shapes, small or large, can be palletized to simplify handling and conveyance.



CNC routing can provide a variety of board requirements including:1. Internal cut outs2. Slots3. Counter bores4. Board edge conditioning for platingThere are many benefits available through CNC routing beyond those of efficient part profiling. A little planning before the release to production can improve manufacturability aswell as provide many no-cost benefits to assembly, soldering, etc.

BBT (Bare Board Testing)

Bare board testing generally checks for short-circuits between tracks and continuity of tracks. These tests can be performed by fully automatic machines which


Industrial Training Reportcan test up to 50,000 nodes and networks. The cuts and shorts in case of single-sided and double-sided PCBs can also be detected by the age-old method of visual inspection by optical means. Visual inspection is a very manual approach in that it makes use of people, good lighting, some type of training defining what is acceptable and what is not, and good operator judgment. Usually a comparison to a known good product or the artwork is made. If the operator has seen the board often, he or she becomes more skilled at finding faults and looking for faults in likely locations. As product complexity has increased, we find that many modern products are not suited to this method. Many inner layer defects are completely undetectable, and even the external layer complexity is visually overwhelming. Visual inspection often remains appropriate for detecting cosmetic defects, such as poor solder masking or physical damage. Such defects generally fall outside the realm of electrical testing as they are not detected by electrical means. Electrical testing is the final test method frequently used to determine whether a board should be shipped. Electrical testing emulates the intended function of the board conductor and insulator patterns by passing currents through conductors and applying voltages across insulators. Such direct electrical measurement requires that the board come into physical contact with a measurement system. Two test types are almost universally performed continuity and isolation testing. Some other tests may be applied selectively, depending upon the product and customer requirements. Test order is usually such that the continuity test is performed first. This verifies that each network is intact within itself, and that contact is established between any test fixture and the product.

UNIVERSAL TESTING MACHINE The universal grid test system presents a rectangular array of equally spaced test points. Generally this is chosen to be large enough to cover the test area of the largest product type to be tested. It is common to speak of the density of test points presented. A single density system presents points spaced at 0.100 in (10 per inch).Thus, there are 100 points per square inch. Similarly, a double-density system has test points spaced at 0.0707 in and provides 200 points per square inch, and quad-density spacing is 0.050 in for a density of 400 points per square inch. As grid cost is largely a function of the number of test points, larger sizes and/or higher-density configurations become expensive.



Continuity test Algorithm

DC Continuity Test Method Continuity testing checks for the expected continuous path within each electrical network. This is done in a series of point-to-point measurements within each network. The resistance found in each measurement is compared to the selected continuity resistance threshold. If the measured value is higher than this threshold, then a fault report is generated. For complex networks, multiple measurements are required in order to ensure that all extremities of the network are interconnected.

EXCLUSION MASK FIXTURES FOR UNIVERSAL GRID SYSTEMS Occasionally, some applications involve product whose test point spacing exactly matches the grid pattern. This situation may permit use of a very simple fixture referred to as an exclusion mask. This is composed of a thin glass-epoxy sheet, perhaps



0.030 in thick, drilled at those locations where test probes are desired to pass through from the grid to make contact with the product.

Exclusion Mask Fixture



PCB Designing


Industrial Training Report The basic function of a printed circuit is to provide support for circuit components and to interconnect the components electrically. In order to achieve these objectives, various printed wiring types have been developed. They vary in base material (laminate), conductor type, number of conductor planes, rigidity, etc. It is therefore expected that the printed circuit designers are adequately familiar with the variations and their effect on cost, component placement, wiring density, delivery cycles and functional performance. Design and layout broadly includes the perspective of total system hardware, which includes not only the printed circuit but each and every component in its final form. Design and layout considerations must also address the relations between and interactions of the components and assemblies throughout the system.

The design inputs which should be provided by the equipment designer to the PCB designer are called design elements. They are:

Type of circuit (analog or digital, etc.); Board size Number of layers Pad stack sizes Hole sizes Layer thickness Board thickness External connections Mounting holes Supply and ground layer thickness and Component details with specifications.

When designing a layout, it is a good practice to provide for a 5 to 10 per cent area for anymodification which may be required on the board. But it is normally done at the prototyping orbatch production stage. The layout design is best worked out when the physical design of the final product shape is available to match the board profile and size according to the same requirements. While working on the board size, locational constraints in respect of the following components are encountered:

Connectors or connecting tabs; Fixtures or anchoring areas; and

Control or adjusting devices such as switches and potentiometers. Besides these, mounting holes along with the safety areas around them are fixed. In this way, PCB net area is worked out from the gross area, taking into consideration the following geometrical constraints:

Locating holes (for assembly): The preferred diameter is 3.175 mm, their position is usuallyclose to the longest edge of the board, with the widest possible span. Their centre should beat least 1.5 times the hole diameter from the edge of the board, but not less than 2 mm. The

safety area around them should be of circular form.

Mounting holes: Safety areas need to be provided around the fixing holes, keeping in viewthe size of the washers and screws, unless insulating washers are used.

Edges: Usually a 2–5 mm safety strip is provided along all edges. This is necessary becausetrimming of the board could cause de-lamination of copper areas too close to the edge.


Industrial Training ReportIt is generally not possible to prescribe a universally applicable standard for the board size,though the ideal board size should be neither very large nor very small. However, in industrialapplications, the generally adopted rack size is 19", and obviously the printed circuit board sizesshould follow this standard. Standard board sizes allow the interchange of cards and the production of a standard range of blank prototyping boards, frames, fittings and modules for packaging systems. Standard PCB sizes have been suggested by different organizations.

CONDUCTOR DIMENSIONS In former times, the current carrying capacity of PCB conductors was often disregarded because conductor dimensions were usually much larger than needed for carrying the currents involved. However, with higher packaging density and thermal considerations, the conductor width has to be determined or at least checked according to the required current carrying capacity. In most electronic circuits, comparatively small currents are normally flowing for which the conductor resistance can practically be neglected. However, when we deal with supply and ground lines, especially in case of high speed signals and in some cases, digital circuitry, much broader conductors than ohmically necessary have to be provided between the supply and ground lines. Therefore, it is necessary to understand the factors which govern the choice of appropriate conductor width which determines its current carrying capacity. Obviously, ohmic resistance of the conductor may be problem when conductive paths are unusually long or when voltage regulation is critical.

ResistanceThe copper printed tracks on a PCB have a finite resistance which introduces a voltage drop proportional to the current flowing in that particular conductor. The resistance of a conductorconsidered as a metal section having a rectangular cross-section depends upon the specific resistivity of copper, which is 1.724 \10–6 ohm cm at 20°C. It will be useful to know the resistance of a 1mm wide copper conductor per cm of length. A standard copper foil of 35 mm thickness (without any plating) may be assumed.R = pL /A ohmsp = resistivity (ohms cm \ 10–6)L = conductor length (cm)A = area of cross-section of the conductor (cm2)p (copper) = 1.724 * 10–6 (at 20° C)L = 1 cmA = 35 *10–4 *0.1 cm2

R = 1.724 *10–6* 1= 35 *10–4 * 0.1= 0.0049 ohms=0.005 ohms =5 m ohms

This shows that a 1 mm wide conductor of 1 cm length for standard copper foil of 35 mm thickness is 5 m ohms. Similarly, a 0.5 mm wide conductor of 10 cm length will have a resistance of 5 *10*2 = 100 m ohms, since half the conductor width gives double as high resistance.



Following are the rules for component placement: In a highly sensitive circuit, the critical components are placed first and in such a manner

as to require minimum length for the critical conductors. In a less critical circuit, the components are arranged exactly in the order of signal flow.

This will result in a minimum overall conductor length. In a circuit where a few components have considerably more connecting points than the

others, these key components have to be placed first and the remaining ones are grouped around them.

The general rule is to place first components, whose position is fixed for the final fitting and interconnections, e.g. connectors, heat sinks, etc. Then place the components which are connected to these fixed components.

Components should be placed on the grid of 2.5 mm. Among the components, larger components are placed first and the space in between is

filled with smaller ones. All the components should be placed in such a manner that disordering of other components

is not necessary if they have to be replaced. Components should be placed in a row or a column, so that it gives a good overview.

While deciding the layout, sharp covers and acute angle bends in conductors should be avoided as far as possible. The rounded contours will not only minimize conductor cracking, foil lifting and electrical breakdown, but also greatly facilitate solder distribution.

The process may be more expensive from the drafting standpoint. Rounded corners at conductor bends and smooth fillets at the junction of conductors and terminal areas are desirable. A trace that extends in a straight line is relatively clean, one that extends straight and then turns 180 degrees back on itself looks just like an antenna. A line that makes a right angle turn also begins to look like, and have the characteristics of, an antenna. It is admittedly not a really good antenna.



GROUND CONSIDRATION The primary consideration in a power or ground conductor is to provide a direct connection from the device to the power supply. As this is not always possible, the next best step is to increase the width of the conductor to provide enough mass to accomplish essentially the same results. It may be remembered that supply and ground lines on a printed circuit board are not just conductive links. The width of these conductors and their layout play an important role in imparting stability to the circuit voltages. In some cases, resistive losses in these conductors may result in unstable supply voltage or ground system. In order to provide adequate shielding, particularly in the case of high frequency shielding, it is desirable to provide a ground plane. In the PCB world, a plane is a solid sheet of copper. It is a ground plane if it is connected to ground and it is a power plane if it is connected to a power supply voltage. But since there are usually many bypass capacitors between power and ground, the distinction between power and ground has no significance for ac signals, ac which can and do travel on either type of plane. The provision of a ground plane ensures a high frequency return line of low inductance. Mutual capacitances can be minimized if the signal line is placed close to the ground plane or is laid in the latter.

DESIGN PROCEDURE


Industrial Training ReportThe fundamental requirement of a good layout design is that it should reflect the concept of the final equipment. Although the circuit complexity and packaging density dictate the planning of the layout, there are general steps which need to be taken into consideration for the development of a good printed board design layout. These steps are listed below.

Begin with a careful design of the electrical circuit and prepare a schematic or logic diagram.

Make an initial evaluation of the schematic diagram, parts list and special circuit requirements and rules, if any, and carry out a rough comparison of this data with the physical limits of the board size.

Compile a bill of materials, together with complete information on special environmental and performance requirements.

Study the components carefully to understand their function in the circuit, requirement of heat sinks, ground and voltage connections, special width requirements and critical short conductor lengths. The circuit design engineer must define critical circuit design

considerations such as capacitance coupling, feedback, current and clock signal . Understand the signal input and output connector interconnections and logical organization

of different functional parts. Consider the general practices followed in the company/organization concerning component

matrix location parameters, mechanical hardware and the automatic component insertion requirements.

Select the shape and size of the board to accommodate all components and to fit the available space within the enclosure or the available area.

Prepare a PCB layout as viewed from the component side. Double-sided designs may be represented on a single sheet by a coding system.

Develop the layout in the direction of the signal flow as far as possible. This shall help to achieve the shortest possible interconnections.

First place all components that need to be in specific locations. This includes connectors, switches, LEDs, mounting holes, heat sinks or any other item that mounts to an external location.

The larger components are then placed and the space in between is filled with smaller ones. Heavy components should be located over or near the supported areas.

Find out the method of fastening or mounting to be used, i.e. card guides, screws, standoffs, etc.

All components are placed in such a manner that de-soldering of other components is not necessary if they have to be replaced.

Divide the circuit into functional subunits. Each of these sub-units should be realized on a defined portion of the board. This shall ensure functional reliability, easier testing and quicker servicing of the board.

Find out specific information on the widths of conductors, spacing of conductors and terminal areas.

Obtain information on: Component case sizes and shapes; Distance between components;

Method of component lead termination;

Most suitable or critical routing of conductors; and Holes sizes and locations.


Industrial Training Report All packages, viz. transistors and ICs should be placed in a single-axis mode i.e. they

should have the same orientation, either vertically or horizontally. This would make assembly and inspection of boards much easier. Uniform orientation minimizes mistakes in deciding routing of conductors.

Position polarized parts (i.e. diodes and electrolytic caps) with the positive leads all having the same orientation. Also use a square pad to mark the positive leads of these components.

After the components are in place, the next step is to lay the power and ground traces. It is essential when working with ICs to have solid power and ground lines, using wide traces that connect to common rails for each supply. It is very important to avoid snaking or daisy chaining the power lines from part-to-part.

Draw the conductor lines only on grid lines. This will make spacing between the conductors uniform. All component hole locations and mounting holes should be laid on a grid system. The basic modular units of location are based on 0.1, 0.05 and 0.025" system applied along both the X and Y axes.

Draw the initial layout by plotting a rough sketch/layout of the circuitry to establish the most practical placement of components and wiring.

Give careful thought when placing components to minimize trace lengths. Put parts that connect with each other next to each other. Doing a good job here will make laying of the traces much easier.

Convert the rough sketch/layout to a grid system. Establish the conductor paths, components, holes, test points and all other features. The layout should be viewed from the component side.

Components, terminals, polarities and connector contacts should be labelled on the layout as they appear on the schematic. Marking of polarity is necessary in case of diodes, polarized capacitors and power terminals. The marking and identification marks should be as small as possible to be able to survive etching and still be legible. If possible, component reference designation markings should be considered to link the assembly with the documentation.

On a DIP (Dual-in-line-package) and TO-5 type integrated circuits, pin 1 should always be marked.

In addition, printed board assembly number serial number of assembly and company logo should be indicated on the component side. It is a good idea to place text such as a product or company name on the top layer of the board.

After completion of the layout drawing, an art master is prepared either by manually taping it or with a computer. The art master is made to an enlarged scale, generally 2 \ 1 or 4 \ 1. It is then photo-reduced to provide a 1 \ 1 scale film negative and positive (photomaster), which is a tool for manufacturing the PC board.

COMPONENT PLACEMENT

Component Spacing for Through-hole DevicesThe following tables provide minimum recommended spacing guidelines for discrete and ICthrough-hole devices.


Industrial Training Report Discrete THDs

Fig.1

Fig.2

Integrated circuit through-hole devices



Mixed discrete and IC through-hole devices

Holes and jumper wires

Component Spacing for Surface-Mounted Devices Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib 62 | P a g e

Industrial Training ReportThe following tables provide minimum recommended spacing guidelines for discrete and ICsurface-mount devices.

Discrete SMDs

Integrated-circuit SMDs

Mixed discrete and IC SMDsUse the greater of any of the preceding spacing rules for the components involved.

Footprint design for THT


Industrial Training ReportThrough-hole devices fall generally into one of two categories: axial-leaded and radial-leaded.An example of a radial-leaded capacitor is shown in Fig. The footprint design for this type of device is determined strictly by the construction of the device. Clearly the padstacks have tobe located where the leads extend from the body. Radial-leaded devices include pin grid arraysand many discrete transistor devices such as TO220 and TO92 packages. The only variable isthe padstack design with regard to the lead diameters.

PCB Design for Signal Integrity

Circuit design constraints are primarily the responsibility of the circuit design engineer andwill not be covered in detail here, but some of the issues will be mentioned briefly since thesymptoms of poor circuit design can be confused with PCB design problems.



NoiseNoise generally refers to any signal that interferes with or degrades a signal of interest. It isoften used with an adjective for problems, such as phase noise, switching noise, cross-talknoise, and reflection noise. In this text we will limit the term “noise” to mean random orpseudo-random, natural signals, which are generally not a result of the PCB design. Functionalproblems such as cross talk or ringing (which are PCB-related problems) will be namedas such. From this perspective there are two basic categories of noise: background noiseand intrinsic component noise. These noise problems are generally addressed by the circuitdesigner, not the PCB designer, but are discussed here briefly for completeness.

Background noiseBackground noise is an uncontrolled signal that originates from the system or environmentyour board is working in. For example, if your circuit is an audio amplifier that is supposedto amplify a speaker’s voice as he or she speaks into a microphone, but a crowd of people istalking around the speaker or a jet plane flies overhead, both the speaker’s voice and the backgroundsounds will be amplified and the signal would be considered noisy or said to sufferfrom a low signal-to-noise ratio. There is nothing you can do about it from the PCB designperspective. Sensors may also be noisy because of their sensitivity, but that is also a circuit design issue and needs to be handled long before the PCB is laid out.

Intrinsic noiseThere are four basic types of intrinsic noise: thermal noise, shot noise, contact noise, andpopcorn noise. Thermal noise (a.k.a. Johnson noise) is due to the motion of electrons in aconducting material. It is present in any material that exhibits a resistance to current flow andis a function of temperature. It is white noise (is constant over frequency) and is prominentin resistors and semiconductor devices. Shot noise is also white noise and is due to potentialbarriers and is also prevalent in semiconductor devices. Contact noise (also called excess noise in resistors and 1/f noise) is due to imperfect connections at contact junctions or interfaces. It is not constant over frequency and can be fairly large at low frequencies. Your best defense against this type of noise is good quality connectors and good solder joints.

DistortionDistortion is an issue more related to analog circuitry because of the nature of continuoussignals. In analog circuitry all voltages between the power supply rails may be of significance.

Digital signals are not continuous; they are either HI or LO and usually nothing in between

matters. As long as voltage levels meet threshold specifications there is no ambiguity andtherefore no quality issues. Ringing on the rising and falling edges of a square wave might

be considered distortion, but that is handled differently, as described below. Distortion of asinusoidal signal (which normally has a single spike on a frequency spectrum) begins tooccur in amplifiers as the sine waves either are clipped or experience a phase reversal.Op-amps have amplitude limits imposed by the power supplies, their drive capabilities, andtheir frequency response. If the amplitude of a sinusoidal output signal (as determined bythe input signal times the gain) exceeds the output capability of the op-amp, then the outputsignal will be clipped off and begin to resemble a square wave. Square waves are composed


Industrial Training Reportof many sine waves, which are primarily odd harmonics of the fundamental frequency of thesquare wave. The dominant harmonic is typically the third one, so as a sine wave begins toclip the onset of third harmonic distortion is observed. If the input signal exceeds the op-amp’s input limits (as imposed by the power supply rails) the output signal will also be distorted. Some amplifiers simply clip the signal (causing third harmonic distortion), while other op-amps experience phase inversion, which also causes harmonic distortion. These problems are caused by the circuit design and component selection and are not the fault of the PCB design. These effects are mentioned because if you are not used to them or do not know about them they can be confused with PCB layout problems. Along with harmonic distortion ringing will produce unwanted frequency components, which can be seen with a spectrum analyzer and may be confused with other forms of distortion or noise. Ringing is is caused by reflections, which in turn are caused by impedance mismatches on PCB traces which is a function of the PCB design.

Let’s Design a PCB

Initial design concept and preparationBefore you start a PCB design process, you will likely have some sort of preliminary design concept jotted down. Perhaps P Spice simulations of sections of the design have even been performed. The design concept for this example is shown in Fig.. The circuit is very simple, but it contains enough parts that it encompasses the same steps required for larger, more complicated designs. The circuit is a basic amplifier that consists of an active component (the op-amp) and several passive components (resistors and capacitors).



Drawing the schematic with CaptureFigure shows the design goal. You can use it as a reference through the design example or modify it to your liking. If you are using the Demo version, remember that you cannot save a design in Layout that has more than 10 parts or parts with more than 14 pins. This design example meets these requirements so that you can save your work. Components used in ckt are:-Reference Value Mounting/packaging MFR MFR P/N J1 5-pin Through-hole 0–100-in. AMP/Tyco Electronics 3-643816-5 pin spacing C1, C2 10uF Through-hole, radial lead Panasonic–ECG ECS-F1VE106K C3, C4 0.1uF SMD, size 1206 Panasonic–ECG ECJ-3YB2A104K U1 LM741 SOIC-8 Texas Instruments UA741CD R1–R4 1k SMD size 1210 (¼W) Panasonic ECG ERJ-14NF xxxxU



Making power and ground connections There are three ways of adding power connections to active parts depending on what type of power supply pins the part has. A part’s power supply pin can be a power-type pin and non visible, or a power-type pin and visible, or a non power-type pin (such as a passive or an input pin), which is always visible. The term “visible” specifically refers to whether the pin is visible to the Wire tool. However, in the general case, a non visible pin is also invisible from the user’s perspective. Digital parts typically have non visible power pins, while analog parts— particularly op-amps—commonly use either visible power pins or one of the non power-type pins (which are always visible). If a part’s power supply pin is a power pin and is not visible you cannot connect a wire (a net) to it directly. A non visible power pin is a net and it is global. You connect a part’s power pin to a power symbol by giving the pin and the power symbol the same name. To make the connection, you will need to place a power symbol, which is also global, some where on the schematic. Power symbols are always visible and are wired to either an off-board connector or a PSpice power supply. To make the names the same you can change the name of the power symbol, or the power pin, or both. An example of how to do this is given below. If a power supply pin is a power pin, and it is visible, you can either take advantage of the power pin’s global properties using power symbols or make direct

connections to it with wires. If you use the pin’s global nature, the pin name and the power symbol name must be the same as described above. If you make a direct connection to the power pin with a


Industrial Training Reportwire you do not have consider the naming convention. If you have a multipart package (e.g., a quad op-amp with shared power pins) all of the parts within the package that are placed on a schematic must have their power supply pins connected in the same way. So either they must all be global or they must all have wires connected to them. If a part’s power supply pin is a not a power pin, you must use a wire to connect the pin to some other object such as a power symbol or an off-board connector. If you place more than one part from a multipart package that has non power-type power pins, connections need to be made to only one of the part’s power supply pins (although you can make connections to all of them if you want).

Generating the Layout netlist (.MNL) Once you have all of your connections finished and footprints and groups assigned, etc., you can create the .MNL netlist for Layout. To create a netlist for Layout, select the Design

icon in the Project Manager and select Create Netlist... from the Tools menu. In the Create Netlist dialog box select the Layout tab and specify a netlist name or accept the default .MNL name. For new designs you can leave the Run ECO to Layout box unchecked (this is used to update an existing board design with new information from Capture). Click OK. For the time being, that completes your work in Capture. It is best to leave the Capture Project open while you work in Layout because Capture and Layout communicate with each other in real time (referred to as intertool communication). This will be demonstrated below.

Choosing a technology file (.TCH)


Industrial Training Report When you first open Layout and start a new design, Layout will ask what technology file you want to use. The technology file defines the board layer structure and sets default values for trace width and route spacing (e.g., trace-to-trace and trace-to pad-spacing), default grids, Pad stack descriptions, default colors, etc. lists the most commonly used technology files with some of their default values. A complete listing of all the technology files and their characteristics is given.

Placing parts

Placing parts is part art and part science. How you ultimately place the parts on the board depends on both mechanical and electrical factors. Mechanical factors include designing for manufacturability (assembly and soldering processes) and physical board constraints (size, shape, etc.). Electrical factors include functional signal flow, thermal management, signal integrity, and electromagnetic compliance. Usually all of these considerations are important, and in some cases they can conflict with one another.

These issues are discussed in greater detail in Chaps. 4, 5, and 6 and in the IPC standards. In this example, the parts will simply be placed so that the board layout is similar to the schematic. When you initially set up the .MAX file the parts will be placed in a pile off to the left of the origin. The first step is to find the desired parts and begin moving them from the pile to the inside of your board outline. There are a couple of things that can be helpful in making the pile look less confusing. The first is to turn off the Assembly layers (AST and ASB),


Industrial Training Reportand the second is to turn off the rat’s nest (the yellow net lines). The assembly layers do not tell us anything important for placing parts, and we are not ready to deal with the nets just yet, so they will just be a distraction.

Setting up the layers Once you have the parts in place, the next step is to set up the layers. In this design we said that we needed six layers—two power planes, two ground planes, and two routing layers. First, let’s take an inventory of what we have. Click the View Spreadsheets button on the toolbar and select the Layers option. shows the default layer configuration. Six layers are defined: two plane layers (power and ground) and four routing layers (top, bottom, and two inner layers). We need two more plane layers and two fewer routing layers.



Autorouting the board Once the power and ground connections and any critical traces have been prerouted and all errors eliminated, you can let the autorouter route the rest of the board. Before running the autorouter make sure to disable and lock the ground and power nets and enable the signal nets using the Nets spreadsheet. Once you are satisfied with the prerouting and the autorouter setup you can start the autorouter by selecting Auto → Autoroute → Board from the menu bar. The autorouter will begin routing the board. When the autorouter has finished routing the board, it will inform you, “All sweeps completed (or disabled).” This sets the “done” flag as described above.

An Auto Routed Board

Autorouters have been a part of printed circuit design systems for many years. An autorouter automatically places vias and traces on the printed circuit based on the schematic and part geometries. Elaborate configuration menus drive the appropriate placement of these features. A special autorouter is required for HDI structures, because many HDI processes employ mass via generation as utilized for surface laminar circuit (SLC) technologies. These processes produce all the vias simultaneously and at any desired diameter. Since the cost of vias is rather insignificant, the autorouter should have the capability of achieving a near-zero via cost.



Introduction to Multilayer PCB Processing

The structure of multilayer printed wiring board (PWB) has evolved immensely. While the building block processes of the PWB industry are still prevalent, the sequences and material utilization employed continue to emerge into new technologies. The driver for this is the “density revolution,” which is caused by changes in electronic component technology. Since the circuit board was born as a means to an end, that is, to

provide electrical connectivity between components, it has had to evolve to meet new demands as the components evolve. Nowhere is that more evident than in the materials and processes used to make multilayer PWBs. It is that need for interconnectivity that brings the challenge. One of the components most responsible for the enabling of advanced technologies is the ball grid array (BGA). The on-board density of the area array component family creates a unique challenge to the circuit routing of the multilayer configuration. This new configuration, known as high-density interconnect (HDI), drives the new structure of PWB. High density designs, driven by the need for smaller, faster, cheaper products in all fields, have common issues to deal with, e.g., high operating signal speeds (1 GHz and higher), thermal management, and mechanical fatigue, all of which affect multilayer construction. In addition, life cycle management is crtical in determining the correct


Industrial Training Reportmultilayer board technology (MLT) to employ. Product requirements place serious demand on all aspects of the MLT process, e.g., the materials employed, the design techniques used, and the process methods implemented.

Summary of Materials used for MLPCB Material properties affect PWB operation in many important ways. The preceding discussion is focused on thermal and electrical properties. The use of small, high-aspect-ratio holes, thick boards, and high-power devices drives the need for materials with improved thermal properties. Similarly, the use of high-speed devices, including the RF circuits in wireless applications, drives the need for improved electrical performance. Materials exist with improved properties, but the ideal material that combines low cost with improvements in both thermal and electrical properties does not exist. Therefore the designer must consider the needs of each design before selecting a cost-effective material. The need for improved thermal properties includes three needs: High Tg, high thermal decomposition temperature, and low moisture absorption. Polyimide meets the first two needs at the expense of increased moisture absorption and high cost. BT satisfies all three needs, but cost remains an issue. The most economical solutions are the multifunctional epoxies and the epoxy-PPO blends. Multifunctional epoxies are relatively inexpensive, provide a significant improvement in Tg, and, in some cases, provide small improvements in thermal degradation temperature and moisture absorption. The PPO blends provide significant improvement in all three areas at a slightly higher cost. If moisture absorption is an issue, the PPO blend may be the best choice; otherwise the multifunctional epoxies are likely to be the lowest-cost option.

ML-PWB PROCESSING AND FLOWS Attempting to visualize the process flow of the manufacture of multilayer printed wiring products can be overwhelming. One way to help picture the multiple paths a board travels is through the use of flowcharts.



It should be noted that alternative flows and methods are possible in HDI when employing alternative processes such as conductive hole fill. This discussion is limited to mostly conventional processing. Major aspects of these processes are discussed in detail in the following sections.

ML-PWB Tooling


Industrial Training Report The tooling system employed for ML-PWB fabrication is one of the most critical aspects of the process and requires much forethought. The investment of tooling is significant and not easily changed. Planning is required to determine the degree of flexibility required in a tooling system.

Typically, a minimum number of panel sizes are chosen in order to standardize the process and reduce cost. The two most common panel sizes are 12 × 18 in and 18 × 24 in. These two are prominent in industry because they yield the best material utilization from raw stock of the laminate supplier. Another panel size, 24 × 36 in, is popular in high-volume fabrication. The ML-PWB tooling system can be broken down into three aspects: the front-end tooling, the method of generating tooling holes, and the investment tooling plates.

Front-End Tooling.- The first aspect of the ML-PWB tooling is commonly called front-end tooling or simply computer automated manufacturing (CAM) tooling. The front end is where manufacturing personnel using a CAM software package generate all phototools and associated computer numerical control (CNC) electronic files. The computer CAM station mirrors the tooling method chosen for the shop and the job work order. The CAM software is capable of overlaying the tooling pattern on each circuit layer to produce the master pattern alignment. The master artwork pattern is then photoplotted to reproduce the artwork film tools. Several important manufacturing functions fall within the bounds of the front-end tooling responsibility.

Design Rule Check (DRC). Design rule check (DRC) is where the electronic design data are analyzed against a specific set of fabrication rules, a virtual design for manufacturing (DFM).The capabilities and attributes of these rules are based on sound, industry proven values that match the technology targeted for construction. The default values embedded into the CAM are input by the manufacture as technology files. These files should reflect the capability of the fabricator’s equipment and processes in light of how they are utilized against the ML-PWB type being produced.

Electrical Testing. The final aspect of the tooling set is preparation of the electrical design data to support an electrical testing routine. The purpose of the electrical testing within the ML-PWB production process is to verify the integrity of circuit continuity. Electrical testers can take on many forms, but are generally divided into two major categories, the “bed-of-nails” and the “flying probe.” The electrical data required for the test must be extracted from the circuit pattern unless a separate net list is provided that contains the connectivity. The standard data format for electrical testing is IPC-356.Tooling for a bed-of-nails tester consists of outputting data to manufacture a fixture to accommodate the pins, which make contact with the circuit nets. When a flying probe tester is employed, the net data are fed into the machine, which uses its own software to configure the routine to probe continuity and perform isolation. The throughput of a flying probe unit is less than that of a bed-of-nails tester, but the flying probe does not have the expense of the fixturing. The chosen method of test tooling requires an examination of the economics based on the volume and technology of the ML-PWB. Typically, when the technology type involves HDI features, the only alternative is to use a flying

probe due to the limitation of the grid spacing in a bed-of-nails tester. High density test requirements continue to drive the flying probe technology, with machine probe head counts increasing to 16 or more to achieve higher speed. Baba Banda Singh Bahadur Engineering College, Fatehgarh Sahib 77 | P a g e


DRILLING Standard buried via inner layers are drilled and plated prior to lamination using the same procedures as a finished ML-PWB. Buried via inner layers are typically thin, and it is easy to drill very small holes. Whereas an 8-mil hole is difficult to drill and plate in a 62-mil-thick ML-PWB, it is relatively easy in a 5- or 10-mil-thick inner layer. Some manufacturers report success with holes as small as 4 mils. However, very small bits are expensive and easy to break. Special handling is required to load the bits and the drill machine must be vibration free with very low run-out. For most ML-PWB shops, 8 mils is a practical lower limit for mechanically drilled buried and blind vias. At 8 mils it is generally possible to drill thin layers in stacks up to 100 mils thick, greatly increasing drill productivity. The major challenge in buried via processing is handling. Care must be taken in mechanical operations such as deburring to avoid mechanical damage or distortion. Often a frame is used to stiffen the layer during plating. Blind vias may be fabricated like buried vias and drilled prior to lamination, or controlled-depth drilling may be used after lamination.Controlled-depth drilling has the advantage that standard inner layer processing is used,including foil stacking. Controlled-depth drilling has several limitations:● Blind holes cannot be stack-drilled, severely limiting drill productivity.● It is difficult to plate a blind hole whose depth exceeds its diameter, limiting the maximumhole depth.● Drill depth tolerances make it easy to under- or overdrill a blind hole, producing a reliabilityrisk.

Multilayer PCB Summary:- The printed wiring board manufacturing industry is experiencing the highest rate of change ever. Not too many years ago, the only difference in ML-PWB manufacturing was related to what brand of chemistry was being run. Today’s global market has introduced innovative change to meet the technology demands of a robust electronics industry. The manufacturing flow no longer resembles a standard methodology. The discussion in this chapter is a review of tried-and-true manufacturing processes for insertion of some of the more recent packaging innovations. A successful implementation of any of the high-density constructs discussed should always be


Industrial Training Reportcomplemented with sound statistical process verification. Sound benchmarking standardization is one tool for establishing manufacturing capability. Additionally, design standardization is required to clearly communicate technologies based on application. This will provide the needed stability within the rapidly changing environment.

Internal Scheme of Multilayer PCB



An 8 layer PCB

Flexible Multilayer PCB

Introduction to Flexible PCB


Industrial Training Report Flexible circuits are a form of printed wiring interconnect structure built on thin, flexible substrates. They are also bendable to complete 3-D (three dimensional) wiring that cannot be made by rigid circuit boards. Because of this flexibility, flexible circuits have many advantages compared to other wiring methods and they have many applications in electronic equipment that requires high-density wiring in a small space.

Advantages and Disadvantages of Flexible Circuits A thin flexible circuit generates many supplemental advantages not available with other wiring methods. On the other hand, flexible circuits also have many disadvantages due to unstable thin constructions. It is necessary to consider how to avoid the disadvantages when a flexible circuit is used in a packaging system. Otherwise overall process yield and productivity will be low, and the final cost will be relatively very high.

Economics of Flexible Circuits The largest disadvantage of flexible circuits is that they cost more than rigid circuit boards of the same size. Usually, flexible circuits are larger than rigid circuit boards to allow 3-D wiring capability, and the total circuit cost increases but is often cheaper than using multiple rigid boards and associated connectors. That is, the cost of using flexible circuits must be compared to the total cost of rigid circuit boards in terms of:● Connectors● Wires● Additional assembly costs

Types of Flexible Circuits

There are a few basic constructions of flexible circuits but there is significant variation between the different types in terms of their construction. Following is a review of the most common types of flexible circuit constructions

Single-sided flex circuits

Single-sided flexible circuits have a single conductor layer made of either a metal or conductive (metal filled) polymer on a flexible dielectric film. Component termination features are accessible only from one side. Holes may be formed in the base film to allow component leads to pass through for interconnection, normally by soldering. Single sided flex circuits can be fabricated with or without such protective coatings as cover layers or cover coats, however the use of a protective coating over circuits is the most common practice. The development of surface mounted devices on sputtered

conductive films has enabled the production of transparent LED Films, which is used in LED Glass but also in flexible automotive lighting composites.


http://en.wikipedia.org/wiki/LED_Headliner

http://en.wikipedia.org/wiki/Transparent_LED_embedded_glass


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http://en.wikipedia.org/wiki/Soldering

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Double access or back bared flex circuits

Double access flex, also known as back bared flex, are flexible circuits having a single conductor layer but which is processed so as to allow access to selected features of the conductor pattern from both sides. While this type of circuit has certain benefits, the specialized processing requirements for accessing the features limits its use.

Sculptured flex circuits

Sculptured flex circuits are a novel subset of normal flexible circuit structures. The manufacturing process involves a special flex circuit multi-step etching method which yields a flexible circuit having finished copper conductors wherein the thickness of the conductor differs at various places along their length. (i.e., the conductors are thin in flexible areas and thick at interconnection points.)

Double-sided flex circuits

Double-sided flex circuits are flex circuits having two conductor layers. Theses flex circuits can be fabricated with or without plated through holes, though the plated through hole variation is much more common. When constructed without plated through holes and connection features are accessed from one side only, the circuit is defined as a “Type V (5)” according to military specifications. It is not a common practice but it is an option. Because of the plated through hole, terminations for electronic components are provided for on both sides of the circuit, thus allowing components to be placed on either side. Depending on design requirements, double-sided flex circuits can be fabricated with protective coverlayers on one, both or neither side of the completed circuit but are most commonly produced with the protective layer on both sides.



http://en.wikipedia.org/wiki/Copper

http://en.wikipedia.org/wiki/Manufacturing

Industrial Training ReportMultilayer flex circuits

Flex circuits having three or more layers of conductors are known as multilayer flex circuits. Commonly the layers are interconnected by means of plated through holes, though this is not a requirement of the definition for it is possible to provide openings to access lower circuit level features. The layers of the multilayer flex circuit may or may not be continuously laminated together throughout the construction with the obvious exception of the areas occupied by plated through-holes. The practice of discontinuous lamination is common in cases where maximum flexibility is required. This is accomplished by leaving unbonded the areas where flexing or bending is to occur.

Multilayer Flex

Rigid-flex circuits

Rigid-flex circuits are a hybrid construction flex circuit consisting of rigid and flexible substrates which are laminated together into a single structure. Rigid-flex circuits should not be confused with rigidized flex constructions are simply flex circuits to which a stiffener is attached to support the weight of the electronic components locally. A rigidized or stiffened flex circuit can have one or more conductor layers. Thus while the two terms may sound similar, they represent products that are quite different.

The layers of a rigid flex are also normally electrically interconnected by means of plated through holes. Over the years, rigid-flex circuits have enjoyed tremendous popularity among military product designer, however the technology has found increased use in commercial products. While often considered a specialty product for low volume applications because of the challenges, an impressive effort to use the technology was made by Compaq computer in the production of boards for a laptop computer in the 1990s.

Rigid-flex boards are normally multilayer structures, however, two metal layer constructions are sometimes used.



Polymer thick film flex circuits

Polymer thick film (PTF) flex circuits are true printed circuits in that the conductors are actually printed onto a polymer base film. They are typically single conductor layer structures, however two or more metal layers can be printed sequentially with insulating layers printed between printed conductor layers. While lower in conductor conductivity and thus not suitable for all applications, PTF circuits have successfully served in a wide range of low power applications at slightly higher voltages. Keyboards are a common application, however, there are a wide range of potential applications for this cost effective approach to flex circuit manufacture.

Flexible Materials

Base material

The base material is the flexible polymer film which provides the foundation for the laminate. Under normal circumstances, the flex circuit base material provides most primary physical and electrical properties of the flexible circuit. In the case of adhesiveless circuit constructions, the base material provides all of the characteristic properties. While a wide range of thickness is possible, most flexible films are provided in a narrow range of relatively thin dimension from 12 µm to 125 µm (1/2 mil to 5 mils) but thinner and thicker material are possible. Thinner materials are of course more flexible and for most material, stiffness increase is proportional to the cube of thickness. Thus for example, means that if the thickness is doubled, the material becomes eight times stiffer and will only deflect 1/8 as much under the same load. There are a number of different materials used as base films including: polyester (PET), polyimide (PI), polyethylene napthalate (PEN),


Industrial Training ReportPolyetherimide (PEI), along with various fluropolymers (FEP) and copolymers Polyimide films are most prevalent owing to their blend of advantageous properties electrical, mechanical, chemical and thermal.

Bonding adhesive

Adhesives are used as the bonding medium for creating a laminate. When it comes to temperature resistance, the adhesive is also typically is the performance limiting element of a laminate especially when polyimide is the base material. Because of the earlier difficulties associated with polyimide adhesives, many polyimide flex circuits presently employ adhesive systems of different polymer families. However some newer thermoplastic polyimide adhesives are making important in-roads. As with the base films, adhesives come in different thickness. Thickness selection is typically a function of the application. For example, different adhesive thickness is commonly used in the creation of cover layers in order to meet the fill demands of different copper foil thickness which may be encountered.

Metal foil

A metal foil is most commonly used as the conductive element of a flexible laminate. The metal foil is the material from which the circuit paths are normally etched. A wide variety of metal foils of varying thickness are available from which to choose and create a flex circuit, however copper foils, serve the vast majority of all flexible circuit applications. Copper’s excellent balance of cost and physical and electrical performance attributes make it an excellent choice. There are actually many different types of copper foil. The identifies eight different types of copper foil for printed circuits divided into two much broader categories, electrodeposited and wrought, each having four sub-types.) As a result, there are a number of different types of copper foil available for flex circuit applications to serve the varied purposes of different end products. With most copper foil, a thin surface treatment is commonly applied to one side of the foil to improve its adhesion to the base film. Copper foils are of two basic types: wrought (rolled) and electrodeposited and their properties are quite different. Rolled and annealed foils are the most common choice, however thinner films which are electroplated are becoming increasingly popular.



APPLICATIONS

Computers & peripherals

Dot matrix print heads

Disk drives

Ink jet print heads

Printer head cables

Consumer

Digital & video cameras

Personal entertainment

Exercise monitors

Hand-held calculators

Industrial controls

Laser measuring

Inductor coil pickups

Copy machines

Heater coils

Medical

Hearing aids

Heart pace-makers

Defibrillators

Ultrasound probe heads

Military & Aerospace

Satellites

Instrumentation panels

Plasma displays

Radar systems


Industrial Training Report Jet engine controls

Night vision systems

Smart weapons

Laser gyroscopes

Torpedoes

References


Industrial Training Reportwww.wikipedia.org

Printed Circuits Handbook 5th Ed by Clyde Coombs (McGraw-Hill, 2001)

The Art of Electronics by Paul Horowitz and Winfield Hill

Complete PCB Design Using OrCad Capture and Layout book

Printed Circuit Assembly Design by Leonard Marks, James Caterina (McGraw-Hill 2008)

The Circuit Designer's Companion, 2nd ed, 2005, Tim Williams

www.tech-etch.com

www.google.com


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http://www.tech-etch.com/

http://www.wikipedia.org/

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