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An overview of the industry
Introduction:
Until the early 1990s, the automotive sector in India was highly protected. This was in the
form of steep import tariffs and measures that restricted the participation of foreign companies.
Hindustan Motors (HM) and Premier Automobile (PAL) that were set up in 1940's dominated the
vehicle market and industry. In the 1950s, the arrival of Tata Motors, Bajaj Auto, and Mahindra &
Mahindra led to steadily increasing vehicle production in India, while the 1960s witnessed the
establishment of the two- and three-wheeler industry in India. However, the automotive industry
witnessed tremendous growth after the entry of Maruti Udyog in the 1980s. In 1983, the
government permitted Suzuki - for some time, the only FDI player - to enter the market in a joint
venture with Maruti - a state operated enterprise at the time. Ten years later, as part of a broader
move to liberalize its economy, India de-licensed passenger car manufacturing and opened it up
further to foreign participation. That brought a wave of FDI to India's vehicle industry. Import
barriers have been progressively relaxed. Today, almost all of the major global players are present
in India. The automotive industry is today a key sector of the Indian economy and a major foreign
exchange earner for the country.
India is amongst the fastest growing economies, with stable macroeconomic indicators.
India clocked a GDP growth rate of 8.5% during the FY 2003-04. The government is targeting a
GDP growth rate of 8% over the next 5 years. The most significant aspect about the GDP is the
decreasing contribution of the agricultural sector to the GDP facilitated by a simultaneous
increase in the contribution of services & industrial sectors. This provides stability to the GDP
growth, as agricultural sector is largely dependent on the monsoons, which are unpredictable.
The country's foreign exchanges reserves are at an all-time high of around USD 130 bn.
Exports from India have been rising. The Balance of Trade (Exports - Imports), although, still
negative, has remained stable over the last few years. All these factors coupled with pro-reform
measures of the government have helped India absorb external shocks without any major impact
on the economic growth.
The interest rates have been falling consistently over the years while the government has
managed to keep the inflation rates at 4-5% levels. Thus, the real rate of interest has come down.
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Lower rate of interest along with easy availability of finance has spurred consumption demand
among households. Other demographic factors such as growing working population, favorable
urbanization trends, increase in two-income households, etc. have also contributed to the increase
in consumption demand.
Government Policies & Automotive Sector:
The auto sector is one of the main drivers of the economy. Every commercial vehicle
manufactured, creates 13.31 jobs, while every passenger car creates 5.31 jobs and every two-
wheeler creates 0.49 jobs in the country. Besides, the automobile industry has an output multiplier
of 2.24, i.e. for every additional rupee of output in the auto industry, the overall output of the
Indian economy increases by Rs. 2.24. Realizing this, successive governments have taken various
measures to provide the much-required push to the auto sector.
The road infrastructure, in particular, had been given special importance by the previous
government of NDA with the 'Golden Quadrilateral' project and the 'North-South" and "East-
West" corridor projects. This momentum has been maintained by the present Congress-led United
Progressive Alliance (UPA) government with its continued support to road infrastructure
development. The excise and customs duties on cars and auto-components have been
continuously declining over the past five years. All these factors have contributed in providing the
impetus to the auto sector.
The government has chalked out a plan regarding Bharat Stage IV (equivalent to Euro IV)
norms by 2010. The government is also planning to form auto clusters to improve international
competitiveness of domestic industries. First such cluster will be set up in the Pimpri-Chinchwad
area of Maharashtra at a cost of Rs. 67 crores.
In the 2004 Budget the government announced new incentives to facilitate Research &
Development activity in India, which has been continued in the 2005 budget.
All these efforts are directed towards increasing the competitiveness of Indian auto industries and
providing better, technologically advanced and environmental friendly products to the end user.
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Introduction to WOORY Automotive industry:
PRODUCT OVERVIEW:
HVAC ACTUATOR
Fig1 HVAC actuators
Actuators are a device for moving HVAC door flap to control temperature fan speed, and air
circulation inside of vehicle.
Controlling temperature inside of vehicle
Inlet Mode Temp
In-Take the exterior
fresh air and circulating
interior air
Controlling the blow in/outlet direction
of each mode, vent, vent/floor,
def./floor and def.
Actuator, Using for
inside
temperature adjustment
(AIRCON/HEATER)
Table No 1: Controlling modes inside of vehicle
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Basic Specifications
Inlet Rated Voltage (VDC) 11 ~ 14
Technical Data
No Load speed (RPM)
Rated Speed (RPM)
Rated Current (mA)
Stall Current (mA)
Stall Torque (NCm)
Noise Level (dBA)
Operating Temp (°C)
2.0 ~ 7.0
0.7 ~ 6.0
50 ~ 150
<200 ~ 500
100 ~ 250NCm
35 ~ 40
-40 ~ 85
Table 2: Basic specifications of actuators
CONTROL HEAD:
Fig 2: control heads
Control Head which driver fit heater and air conditioner for the most suitable atmosphere.
Improving dependability, easy and gentle control and high durability.
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MCU Compiler
Name Application Notes
Metro Works C-
HC08 68HC08 Family C, C++ IDE
COSMIC C
68HC12 Family
68HC08 Family
ST7 Family
ODS Version
CSC-PCM C PIC 15XX, PIC 16XX
PIC 17XX, PIC 18XX -
HITEC-C PIC 15XX, PIC 16XX
PIC 17XX, PIC 18XX -
METROWORKS
FOR ST7 MCU ST7 Family -
INTELCOMPILER Intel 80C196 -
TMS370Series
Compiler TMS370C756 8bit 16K-OTP
DALLAS 80
Series Compiler DS80C320 8bit
Table 3: MCU compiler data
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Chapter: 1
1.0Introduction:
The assembling process of PCBs can be by using technologies. They are THT and SMT.
Traditional through-hole Dual In-Line Package assemblies reached their limits in terms of
improvements in cost, weight, volume, and reliability at approximately 68L. SMT allows
production of more reliable assemblies with higher I/O, increased board density, and reduced
weight, volume, and cost. The weight of printed board assemblies (PBAs) using SMT is reduced
because surface mount components (SMCs) can weigh up to 10 times less than their conventional
counterparts and occupy about one-half to one-third the space on the printed board (PB) surface.
SMT also provides improved shock and vibration resistance due to the lower mass of components.
The smaller lead lengths of surface mount components reduce parasitic losses and provide more
effective decoupling. Surface mounting was originally called "planar mounting". Surface-mount
technology was developed in the 1960s and became widely used in the late 1980s. Much of the
pioneering work in this technology was by IBM. The design approach first demonstrated by IBM
in 1960 in a small-scale computer was later applied in the Launch Vehicle Digital Computer used
in the Instrument Unit. Components were mechanically redesigned to have small metal tabs or
end caps that could be directly soldered to the surface of the PCB. Components became much
smaller and component placement on both sides of a board became far more common with surface
mounting than through-hole mounting, allowing much higher circuit densities
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CHAPTER: 2
2.0 About SMT:
Surface Mount Technology is the latest technology used in the assembling of PCBs.In this
method both leaded and non-leaded electrical components attached to the surface of a conductive
pattern that does not utilize leads in feed through holes. In SMT both components and conductive
tracer (i.e. connections) are installed on the same side of substrate or surface. Substrate can be
ceramic, paper plastic, rigid and flexible PCB’s. Printed circuit board designing especially those
requiring high on board density. Fewer holes need to be drilled on abrasive boards. The errors in
the component placement also corrected easily. And components can be placed on the both sides of
the board. The components used in SMT are called Surface Mount Components and the devices
used in assembling them are called Surface Mount Devices.
2.1 Types of SMT:
SMT replaces DIPs with surface mount components. The assembly is soldered by reflow
and/or wave soldering processes depending on the mix of surface mount and through-hole mount
components. When attached to PBs, both active and passive SMCs form three major types of SMT
assemblies, commonly referred to as Type 1, Type II, and Type III (see Figure 1).
Type 1:
Type I is a full SMT board with parts on one or both sides of the board. In type1 both active
and passive components mounted on the primary and secondary side of the printed board.
Type 2:
Type 2 is the most common type SMT board. It has a combination of through-hole
components and SMT components. Often, surface mount chip components are located on the
secondary side of the Printed Board (PB). Active SMCs and DIPs are then found on the primary
side. Multiple soldering processes are required.
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Fig 2.1 Type1 SMT
Fig 2.2 Type 2 SMT
Fig 2.3 Type 3 SMT
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Type 3:
Type III assemblies are similar to Type II. They also use passive chip SMCs on
the secondary side, but on the primary side only DIPs are used.
2.2 Surface Mount Components:
Many but not all through whole components have a surface mountable counterpart. Due to
some physical limitations so conventional components cannot be manufactured as SMC (Surface
Mount Components). For example high capacity capacitor and power transformers, still most
circuit can be assembled, using SMT, even though some conventional through hole components
are required. It is important for SMT surface designer and service technician to know the general
physical configuration and operating parameters of various SMC’s. All SMC’s in familiar are
available separately SMC’s used for automatic assemblies are supplied in rills of paper or in
magazine.
DETAILS ABOUT SOME (SMC’S)
1. Chip resister:
These are most widely produced of all SMC’s. They are originally developed for used in
hybrid micro circuit. The chip registers are leadless registers. Constructionally deice is similar to
thick film resister.
2. Chip Capacitor:
There are originally developed from use in hybrid micro circuits. There are basically three
types of surface mountable chip capacitor.
a) Multi-layer Ceramic
b) Electrolytic
c) Tantalum
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Ceramic multi-layer chip capacitors are commonly used. They are stable and highly reliable.
The capacitance values available are from 1 PF to 1 F. Package style is identical to chip resister.
The size of chip capacitor depends on the value of capacitor.
For high capacity electrolytic and tantalum capacitor are used. Tantalum capacitors are
available for the values of 0.1 F to 100 F. Aluminum electrolytic capacitors are larger than that
of tantalum. Tantalum capacitors are available in the values of 1.5 F to 47 F.
3. Potentiometer:
Both single and multitier trimming potentiometers are available in surface mountable
configuration. They are made from ceramic or high temperature plastic so as to protect than from
emersion soldering. The dimension of smallest single term trimmer is 4 x 4 mm. Multi terms
trimmers are not designed for repeated adjustments. They can be adjusted mostly 10 times. The
trimmers are designed to be adjusted by means of miniature screw driver or special tools.
4. Inductors:
Much kind of surface mountable lead and leadless inductors and even transformers are
available. Inductance’s value ranges from few 10’s of Nano henry to 1 milli Henry ( 10’s of nano
to mh )
5. Descript Semiconductors :
Many diodes, transistors and descript semiconductors are available in miniature surface
mountable packages. The S O D ( Small outline Diode ) package is leadless cylinder used for
diodes. The SOT ( Small outline transistor ) packages are used for transistors, diodes various up
opto electronic components.
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6. Integrated Circuits (IC’s) :
Surface mountable IC’s are developed by Texel Instruments. The most popular surface
mountable IC packages is small – outlet (SO) configuration developed by Philips. It resembles, a
miniature (Dual In Line Package ) DIP. An 50 i.e. small outlet device occupies 1/4th
board space
of an equipment (Dual In Line Package) DIP.
7. Other Surface Mountable Components:
There are many other surface mountable devices available like photo transistor, infrared red
LED,PLCC, ceramic filter, switches. PLCC is used to mount nonleaded component
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CHAPTER: 3
3.0Process of assembling:
There are mainly five stages in the assembling of PCB
1) Solder paste printing and dispensing
2) Component placement
3) Soldering
4) Inspection
5) Rework
Fig 3.1 Type 1 assembling process
The process sequence for type1 is shown inn fig 3.1.For single sided type1 solder paste is
printed on the board and the components are placed later soldering and cleaning is done.For
double sided one the board is turned over and process is repeated.
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Fig 3.2 Type2&3 assembling process
In the type2 SMT is same as the type1 but in this due to the mix up of active and passive
components the board undergo two types of soldering. Passive components and low pin count gull
wing are exposed to wave soldering.
3.1 Surface Mount Design:
The manufacturing is gaining more recognition as it becomes clear that cost reduction of printed
wiring assemblies cannot be controlled by manufacturing engineers alone. Design for manufacturability-
which includes considerations of land pattern, placement, soldering, cleaning, repair, and test-is
essentially a yield issue. Thus, companies planning surface mount products face a challenge in creating
manufacturability designs.
Of all the issues in design for manufacturability, land pattern design and interpackage spacing are
the most important. Interpackage spacing controls cost-effectiveness of placement, soldering, testing,
inspection, and repair. A minimum interpackage spacing is required to satisfy all these manufacturing
requirements, and the more spacing that is provided, the better.
Land pattern
Function
Packing moisture sensitivity
Solder joints reliability
Test nodes placement
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Land Pattern Design:
The surface mount land patterns, also called footprints or pads, define the sites where components
are to be soldered to the PC board. The design of land patterns is very critical, because it determines
solder joint strength and thus the reliability of solder joints, and also impacts solder defects, lean ability,
testability, and repair or rework. In other words, the very producibility or success of SMT is dependent
upon the land pattern design.
Design for Testability:
In SMT boards, designing for testability requires that test nodes be accessible to automated test
equipment (ATE). This requirement naturally has an impact on board real estate. In addition, the
requirement impacts cost, which is dependent upon defects.
3.2 Types of soldering:
1) Hand soldering
2) Wave soldering
3) Infrared/convective reflow soldering
Hand soldering:
Hand soldering the soldering paste is applied to the board and the SMCs are placed on it by hand,
so it is called as hand soldering. In general the components that cannot withstand high temperature levels
in wave soldering or reflow soldering and the components which are not possible to solder inside the
machine are hand soldered.
Wave soldering:
It is done using a wave soldering machine which uses the ultraviolet energy. It is important to
avoid the possibility of thermal shock during soldering and carefully controlled preheat is therefore
required. The rate of preheat should not exceed 4°C/second and a target figure 2°C/second is
recommended. Although an 80°C to 120°C temperature differential is preferred, recent developments
allow a temperature differential between the component surface and the soldering temperature of 150°C
(Maximum) for capacitors of 1210 size and below with a maximum thickness of 1.25mm. The user is
cautioned that the risk of thermal shock increases as chip size or temperature differential increases.
Mildly activated rosin fluxes are preferred. The minimum amount of solder to give a good joint should
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be used. Excessive solder can lead to damage from the stresses caused by the difference in coefficients
of expansion between solder, chip and substrate.
Fig 3.3 wave soldering machine
Infrared/Convective Reflow Soldering:
There are basically two types of infrared reflow processes: focused (radiant) and non-focused
(convective). Focused IR, also known as Lamp IR, uses quartz lamps that produce radiant energy
to heat the product. In non- focused or diffused IR, the heat energy is transferred from heaters by
convection. A gradual heating of the assembly is necessary to drive off volatiles from the solder
paste. This is accomplished by various top and bottom heating zones that are independently
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controlled. After an appropriate time in preheat, the assembly is raised to the reflow temperature
for soldering and then cooled. The most widely accepted reflow is now "forced convection" reflow.
It is considered more suitable for SMT packages and has become the industry standard. The
advantage of forced convection reflow is better heat transfer from hot air that is constantly being
replenished in large volume thus supplying more consistent heating.. For wave soldering
components, must be spaced sufficiently far apart avoid ridriging or shadowing(inability of solder
to penetrate properly in to small spaces).This is less important for reflow soldering but sufficient
space must be allowed to enable rework should it be required.
Fig 3.4 Reflow soldering machine
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3.3Component placement:
Automatic placement equipment can select the position on circuit board from 1000 to 5 lakhs
components per hour .A pick and place machine is used to place the components.
Fig 3.5 Pick and place machine
Fig 3.6 Component loader
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Pick and place machine is the heart of surface mount .This machine pick and places the electronic
components onto the PCB prior to the soldering. This machine uses vacuum pick up to hold the
components. Few other had vision assisted alignment. In general pick and place machine offers
better speed and accuracy than through hole insertion machines. The components are loaded in the
rack shown in fig 3.6.
3.4 Inspection:
Due to small size of components SMT board requires very careful inspection particularly for
solder ball, improperly soldered joints and missed solder connections, etc.Some components are
specially difficult to inspect like quad PLCC’s (Plastic Loaded Chip Carrier) i.e. IC having J –
profile pins along each four sides and it has more than 28 pins. Complete SMT board can be tested
by hand or automatic testing equipment. Whether testing is done by hand or automatically the test
probes should be touch to SMC’s solder pad or their conductive traces. The test probes should not
be touch to terminals of SMC’s properly designed SMT boards have test point location.
AOI (automatic inspection machine):
This machine is visual inspection machine to detect the bad position of the components
mounted on the PCB.AOI machine detects bad component placement using the high resolution
camera and image processing technology. By this it can detect soldering status and mounting. It
display results on monitor and mark on defected components using ink (NG Marking) or others. It
has strong (OCR) optical character reorganization. Just with one camera it can provide examination
speed upto 2 fov (field of view)Teaching time can be reduced by ATT (auto teaching tool).It
supports laser lighting by which the high and loose mounting can be detected.
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Fig 3.7 AOI machine
System configuration:
1)PC Section:
It manages system operation and stores data.
-vision board it acquires digital video data from camera.
- Motion board it controls motors of X and Y axis.and signal processing of various kinds of
sensors and switches.
-Integrated motion: using the closed loop servo mechanism , it adjusts X and Y axes nad width of
the conveyor automatically and controls laser rotation etc.
2)Control section:
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-i/o board : it relays driving signal of the motion board and various kinds of I/O signals.
-light control: it supplies power to the light control and controls the 265 levels of brightness.
-it controls the interface b/w motion board and step driver /servo amp,and the inputs and output
ports are necessary for system operation.
3) MOTOR section:
Step motor: it moves or controls the motion section of X and Y axes.
Servo motor: it actuates the robots of X and Y axes.
Step motor : it actuates conveyor system and laser rotation.
4)Moniter :
It displays information necessary for system opration inspection.
5)Vision section:
Camera: it converts image inspection area into digital signals and send them to vision board.
Lighting device: light is controlled by the arrangement of white led of high brightness in 3
levels(coaxial,vertical and horizontal)
Lighting controller: it is connected to pc to control the power and brightness of vericsl ,coaxial and
horizontal lights.
6)laser:
It inspects and detects the soldering ,reverse insertion, by checking loose components and their
hight.
7)NG marker:
After insertion ,the locations of defects on the relavent PCB are markedby NG marker (Optional).
8)conveyor system:
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It supplies the pcb in the previous process to the location of inspection and fixes pcb for
inspection,then discharge pcb to the following process.
Fig 3.8 AOI configuration
3.5ADVANTAGES OF SMT:
There are various advantages of SMT.
1. Reduce Circuit Board Size : The compact size of SMC’s considerably reduces area of circuit
board.
2. Light in weight : SMC’s are lighter than their through hole counter port. e.g. 8 – pin DIP,
LM 308 M opamp weighs 600 mg. The so package vargen of same IC Weighs 60 gm.
3. The low weight of SMC’s and smaller circuit board together gives 5 to 1 weight advantages
over conventional board. Also SMT boards are thin therefore they gives 8:1 volume advantage
over conventional boards.
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4. Double – Sided Circuit Board : SMT can also used double sided board with an advantage that
components can be placed on the both sides.
5. Subminiature Circuits : SMT circuits are nearly as tiny as hybrid integrated circuits.
6. Automated assembly : SMCs are much more compacted with automatic assembly equipment.
The time consuming in drilling holes in circuit board is climinated. SMC’s have no wire leads
to cut, bend and insert. Therefore SMT boards can be automatically assemble quickly than
conventional boards.
7. Lower Cost : The SMC’s cost is generally more, till SMT can reduce over all board cost for
variety of reasons. e.g. saving of 40% cost results from elimination of drilling hole equipment.
8. Other Advantages : Some advantages of SMT are less obvious than above.
i) Compact size of SMT so it is used in mobile.
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CHAPTER-4
4.0 I CT:
Mechanical and chemical process challenges initially limited the acceptance of SMT. As
those challenges have been overcome the another electronic test access obstacle has been come
apparent. Testing is the crucial part of SMT process. The physical test access is allowed in THT.
But where as in SMT the packing density is increased so physical test access in denied. So some
new technologies are introduced to test SMT manufactured PCBs.
4.1In circuit test fixture basics:
In order to carry out the test it is necessary to gain access to each node on the board. The
most common way of achieving this is to generate a "bed of nails" fixture. The term bed of nails is
a rather graphic description of what many fixtures look like, having a large number of test points or
probes proud of a board that holds them in place. Although the concept of the in-circuit test fixture
or bed of nails is broadly the same whatever manufacturer is used, there are a number of variations
on the basic theme.
Fig4.0: Bed of nails ICT fixture
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Fig 4.1: Probe able test pad
The In-circuit test fixture is required to interface the main tester with the particular board
under test. It will have a main connector that interfaces to the tester and wires that are taken from
the connector to individual pins / probes / or "nails" that make contact with the required nodes on
the board under test. The probes are held in place by what may be termed a base-board. This is
precision drilled to ensure that the probes are held in exactly the right place for the fixture to make
contact with the required nodes on the board. The board is held in place accurately by the fixture
and pulled onto spring loaded pins that make contact with connections on the board. The board
may either be pulled down under the action of a vacuum or it may be achieved mechanically. At
one time when board component densities were much lower it was often possible to place special
ATE pads onto the board to enable good connection to be made. Nowadays with very much more
compact boards this is not possible. Instead connections are made onto the component pads. This is
obviously more difficult because of the solder and the component connection itself, but can still be
achieved to a high degree of reliability. Typically each spring exerts a force of between 100 and
200g to ensure that good contact is made. This obviously means that the total force required for all
the pins on a board can be very significant. Sometimes supports for the board are required to
ensure that it does not flex too much as this may result in cracking some delicate surface mount
components. Typically pins are placed on a 0.1 inch matrix. Many new surface mount IC packages
require a much finer pitch, and to achieve this adapter is often used.
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There are about three main methods for pulling the board onto the probes:
Vacuum: This form of fixture uses a vacuum to pull the board down onto the pins. It has
the advantage that as the vacuum exists over the whole area of the board, the board is
evenly pulled down onto the pins, but it does require any holes in the board to be sealed
before the in-circuit test stage of the production process.
Pneumatic: This form of fixture uses a compressed air source, present in most
manufacturing areas to be used.
Mechanical: This uses a simple lever or other mechanical arrangement to pull the board
down onto the pins.
Fig 4.2: ICT machine
4.2 Wireless In-circuit test fixtures:
Another form of ICT fixture is known as a wireless fixture. This does not mean that it uses
wireless / radio communications, but instead the fixture does not use traditional wires but it uses a
printed circuit board. This provides a number of advantages:
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Reduces complexity of fixture: Most ICT fixtures require many wires to run between the
individual probes and the fixture connector that interfaces to the main ICT system
connector. There can often be several hundred wires, making the fixture very complicated
and difficult to work upon.
Reduces spurious resistance: The wires within an ICT fixture need to be long enough to
allow the fixture to be opened to enable proper access. The length of the wires can
introduce a significant amount of resistance that can reduce the overall measurement
accuracy of the system. Using a wireless ICT fixture enables the track lengths to be
shortened and resistance level decreased.
Improves reliability: the large number of wires in an ICT fixture introduces a means of
failure. Wires can easily break and become disconnected. The use of a wireless fixture,
using PCB technology significantly improves the level of reliability.
Reduces fixture cost: Using modern software, it is possible to reduce the cost of the
fixture production by using a PCB. Using automatic routing of the tracks in the PCB layout
software means that PCB design is automated to a large degree. This means that the
complex wiring is removed from the fixture production process.
Test pins / probes for in-circuit test fixtures
There is a great variety of different types of pin or test probe that can be used for in-circuit
test fixtures.
The in -circuit test probes or test pins or probes are spring loaded and comprise a barrel
with its internal spring, and the plunger. The test probes fit into a socket that enables them
to be replaced when they become worn of damaged.
4.3Basic In-Circuit Test Probe or Contact:
The major design changes are within the head or tip that contacts the board under test. Each
type of head has a particular application for which it is best suited.
Concave tips: These in-circuit test probes are often used for connecting on to terminal
posts.
Spherical radius convex tips: These may be used when mating with an edge connection on
a printed circuit board.
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Cone tips: This format for an in circuit test probe is often used for mating with a PCB via
hole, or directly onto a PCB track..
Single pointed tips: These are often used for mating with solder joints as the tip is able to
penetrate the oxide film on the solder to make good contact.
Multi-pointed tips : These may be used when a connection is required through a larger
area of solder - the multiple serrations mean that several points of contact can be made
through the oxide layer on the solder. They may also be used to mate with the connection to
a conventional component, i.e. not surface mount. The probe serrations will connect to the
solder and wire that protrudes through the board.
The wiring in the fixtures is generally not neatly loomed together. Whilst this may not be as
aesthetically pleasing, it reduces the levels of cross-talk and spurious capacitance. It also reduces
the wire lengths within the fixture as the shortest route between two points can be taken within
reason.
4.4 New trends in ICT:
In circuit testing is still a valuable tool in today's electronics manufacturing environment.
While many thought ICT would be phased out many years ago because the smaller components
and more compact circuit boards have been proved wrong. However to be able to used ICT
satisfactorily, it is necessary design for in-circuit test right from the earliest concept of the board. In
this way sufficient access can be gained to provide a high test coverage for the printed circuit board
or assembly.
By adopting design for in-circuit test guidelines, it is often possible to provide a sufficiently
high level of access to test most of the components on the board.
Design guidelines for In Circuit Testing, ICT
In order to maximize the coverage and capability of an In Circuit Test, ICT system, it is
necessary to ensure that the board is sufficiently testable for the ICT system to provide a useful
test. Guidelines can be adopted to help ensure that the circuit can be tested satisfactorily.
The ideas mentioned below are some ideas that can be implemented to improve the ICT
performance:
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1. Provide accessible location holes: In order that the connections can be made to the
board, it is necessary to have accurate position or location holes that can be used to
accurately locate the PCB onto the test fixture. In this way the PCB can make accurate
location onto any probes or connections required. Requirements for the tooling holes may
include:
o Three preferred but a minimum of two, on opposite diagonal corners
o Tooling or location holes should not be plated to ensure their accuracy
o Tooling or location holes should not be obscured and they should be free from
components etc in the vicinity of the hole to enable any locating spigots on the test
fixture to mate with the hole.
o Location accuracy of the tooling or location holes should typically be within 0.05
mm, i.e. 0.002 inches, although with techniques changing all the time, check the
requirements for the actual tester..
2. Connect resets and other key lines via a resistor: One key design for ICT parameter is
to ensure that any key reset or other lines that might be taken to ground or the supply rail,
are taken there via a resistor. In this way if the In Circuit Tester needs to control these
points on the chip to undertake a performance check, then it is able to have control.
3. Provide a probe-able pad for each circuit node: When using in-circuit testing, it is
necessary to get access to each node in the circuit to enable sufficient test coverage to be
achieved. Probe-able test pads are ideally dedicated test pads, but with circuits becoming
much smaller this is not always possible. Often ICT manufacturers claim fixtures can probe
solder joints. Check this out as this technique can lead to lower reliability testing.
4. Probe-able test pads should all be on one side of the board: When possible test pads
for the test probes should all be on the same side (underside) of the PCB. This means that
single sided fixtures can be employed. These are cheaper, simpler and faster to use than
double sided fixtures.
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5. Test pad finish: Any test pads should have a good conductive finish. This will include
solder, but often the gold plating if used elsewhere in the board can be used, although it
adds cost.
6. Test pad size should be sufficient for the fixtures: The test pad size will need to balance
available space on the PCB with the size required for the test probes. They should be
sufficient to allow the probe to make contact, and should have space around them to take up
any tolerances in the fixture, PCB, etc, so that the probes do not cause shorts.
7. Test pad density must be considered: The density of the test pads should not be so great
that it becomes impossible to manufacture the fixture. It is necessary to check this with the
fixture manufacturer as figures vary according to the type of fixture that will be used.
8. Fill plated through holes: If there is a likelihood that vacuum fixtures will be used, it is
necessary to fill the plated through holes as part of the manufacturing process. Methods for
filling other holes will also be required.
4.5 MDA:
The Manufacturing Defect Analyzer, MDA is a basic form of In-Circuit Tester. As the name
implies, the MDA is aimed at only providing a straightforward test of the board to reveal
manufacturing defects. As the majority of manufacturing defects are simple connectivity issues, the
MDA is restricted to making measurements of continuity. This significantly reduces its cost
making it more viable in many areas of test. MDA basics The concept for the MDA is based
around the concept that the design of a board has been previously proven, and parts are reliable and
very few defective components will be delivered. Therefore it should only be manufacturing
defects that will impact the performance of a board or assembly. As most of the defects consist if
solder splashes and poor or open joints, then the majority of failures will be detected by testing for
a relatively simple spectrum of failure types.
While Manufacturing Defect Analyzers are primarily focused on the detection of the very basic
faults, even the most basic testers these days will also detect missing components, although the
exact functionality for any given MDA will only be revealed in the datasheet / specification. Often
the tester will be able to detect the presence of resistors, capacitors and transistors. The detection of
integrated circuits can also be achieved using the protection diodes to indicate whether the
component is correctly placed.
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The tester makes connection to the board under test using a bed of nails fixture, and this
means that a different fixture is generally required for each board. It needs to make contact with
specific points on the board, where often there may be a test point or land area for the probe.
Like other forms of In-Circuit Tester, an MDA will use the printed circuit board CAD data
for the generation of the fixture design and the test programme. This often allows up to around
80% of the test programme to be generated automatically.
4.6 MDA Advantages / Disadvantages:
Like any other technology the manufacturing defect analyzer has its advantages and
disadvantages. This need to be considered when choosing which type of tester and test technology
should be used.
SUMMARY OF ADVANTAGES AND DISADVANTAGES OF A
MANUFACTURING DEFECT ANALYZER, MDA
ADVANTAGES DISADVANTAGES
Machine is much less costly than
a full ICT
Can detect open and short
circuits which form the major
number of defects
Can detect some values
dependent upon the MDA
capability
Limited component diagnostics
Still requires bed of nails fixture
and its associated costs
Component access can be an
issue with current board density
levels
Table 4: Advantages and Disadvantages of MDA
An MDA machine is very much simpler than a full ICT. This makes it an attractive
proposition for many situations, particularly within smaller companies where the capital
expenditure investment of a full ICT machine may not be viable. In many other situations a
Manufacturing Defect Analyzer may be a viable option is where the fault spectrum does not
warrant a full In-Circuit test. This decision can only be made in the light of an analysis of existing
fault spectra for a given manufacturing line.
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CHAPTER-5
5.0 IEEE boundary scan test access:
As the bed of nails test fixture is not suitable for testing of high density boards as well it is
required to repair after testing few PCBs so it adds cost to the board development cost and MDA is
failed to ensure the continuity of component the SMT needs an accurate, speedy and reliable tester
Boundary-scan essential for dramatically reducing development and production costs, speeding test
development through automation, and improving product quality because of increased fault
coverage.
5.1What is Boundary-Scan?
Boundary-scan, as defined by the IEEE Std.-1149.1 standard, is an integrated method for
testing interconnects on printed circuit boards (PCBs) that are implemented at the integrated circuit
(IC) level. The inability to test highly complex and dense printed circuit boards using traditional in-
circuit testers and bed of nail fixtures was already evident in the mid-eighties. Due to physical
space constraints and loss of physical access to fine pitch components and BGA devices, fixturing
cost increased dramatically while fixture reliability decreased at the same time.
5.2A Brief History of Boundary-Scan:
In the 1980s, the Joint Test Action Group (JTAG) developed a specification for boundary-
scan testing that was standardized in 1990 as the IEEE Std. 1149.1-1990. In 1993 a new revision to
the IEEE Std. 1149.1 standard was introduced (titled 1149.1a) and it contained many clarifications,
corrections, and enhancements. In 1994, a supplement containing a description of the Boundary-
Scan Description Language (BSDL) was added to the standard. Since that time, this standard has
been adopted by major electronics companies all over the world. Applications are found in high
volume, high-end consumer products, telecommunication products, defense systems, computers,
peripherals, and avionics. In fact, due to its economic advantages, some smaller companies that
cannot afford expensive in-circuit testers are using boundary-scan.
The boundary-scan test architecture provides a means to test interconnects between
integrated circuits on a board without using physical test probes. It adds a boundary-scan cell that
includes a multiplexer and latches to each pin on the device.
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Fig 5.1 - Typical Boundary-Scan Cell
Boundary-scan cells in a device can capture data from pin or core logic signals, or force data
onto pins. Captured data is serially shifted out and externally compared to the expected results.
Forced test data is serially shifted into the boundary-scan cells. All of this is controlled from a
serial data path called the scan path or scan chain. Figure 1 depicts the main elements of a
boundary-scan cell. By allowing direct access to nets, boundary-scan eliminates the need for a
large number of test vectors, which are normally needed to properly initialize sequential logic.
Tens or hundreds of vectors may do the job that had previously required thousands of vectors.
Potential benefits realized from the use of boundary-scan are shorter test times, higher test
coverage, increased diagnostic capability and lower capital equipment cost.
The principles of interconnect test using boundary-scan are illustrated in Figure 5.2. Figure
5.2 depicts two boundary-scan compliant devices, U1 and U2, which are connected with four nets.
U1includes four outputs that are driving the four inputs of U2 with various values. In this case, we
assume that the circuit includes two faults: a short between Nets 2 and 3, and an open on Net 4.
We will also assume that a short between two nets behaves as a wired-AND and an open is sensed
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as logic 1. To detect and isolate the above defects, the tester is shifting into the U1 boundary-scan
register the patterns shown in Figure 5.2 and applying these patterns to the inputs of U2. The inputs
values of U2 boundary-scan register are shifted out and compared to the expected results. In this
case, the results (marked in red) on Nets 2, 3, and 4 do not match the expected values and,
therefore, the tester detects the faults on Nets 2, 3, and 4.Boundary-scan tool vendors provide
various types of stimulus and sophisticated algorithms, not only to detect the failing nets, but also
to isolate the faults to specific nets, devices, and pins.
Fig 5.2 - Interconnect Test Example
The IEEE-1149.1 standard defines test logic in an integrated circuit which provides applications to
perform:
Chain integrity testing
Interconnection testing between devices
Core logic testing (BIST)
In-system programming
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In-Circuit Emulation
Functional testing
Fig 5.3 Main building blocks of a JTAG
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Fig 5.4 Boundary-Scan Chain with Multiple Chips
Fig 5.5 Boundary-Scan Test Vectors
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5.3 JTAG TAP Interface Signals:
Abbreviation Signal Description
TCK Test Clock Synchronizes the internal state machine operations
TMS Test Mode State Sampled at the rising edge of TCK to determine the
next state
TDI Test Data In
Represents the data shifted into the device's test or
programming logic. It is sampled at the rising edge of
TCK when the internal state machine is in the correct
state.
TDO Test Data Out
Represents the data shifted out of the device's test or
programming logic and is valid on the falling edge of
TCK when the internal state machine is in the correct
state
TRST Test Reset An optional pin which, when available, can reset the
TAP controller's state machine
Required Test Instructions
Working in conjunction with the TAP controller is an IR (Instruction Register) providing
which type of test to perform. The 1149.1 Standard requires that all compliant devices must
perform the following three instructions:
EXTEST Instruction
The EXTEST instruction performs a PCB interconnect test, places an IEEE 1149.1
compliant device into an external boundary test mode, and selects the boundary scan
register to be connected between TDI and TDO. During EXTEST instruction, the boundary
scan cells associated with outputs are preloaded with test patterns to test downstream
devices. The input boundary cells are set up to capture the input data for later analysis.
SAMPLE/PRELOAD Instruction
The SAMPLE/PRELOAD instruction allows an IEEE 1149.1 compliant device to remain in
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its functional mode and selects the boundary scan register to be connected between the TDI
and TDO pins. During SAMPLE/PRELOAD instruction, the boundary scan register can be
accessed through a data scan operation, to take a sample of the functional data input/output
of the device. Test data can also be preloaded into the boundary-scan register prior to
loading an EXTEST instruction.
BYPASS Instruction
Using the BYPASS instruction, a device's boundary scan chain can be skipped, allowing
the data to pass through the bypass register. This allows efficient testing of a selected
device without incurring the overhead of traversing through other devices. The BYPASS
instruction allows an IEEE 1149.1 compliant device to remain in a functional mode and
selects the bypass register to be connected between the TDI and TDO pins. Serial data is
allowed to be transferred through a device from the TDI pin to the TDO pin without
affecting the operation of the device.
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CHAPTER-6
6.1 Boundary-Scan Applications:
While it is obvious that boundary-scan based testing can be used in the production phase of a
product, new developments and applications of the IEEE-1149.1 standard have enabled the use of
boundary-scan in many other product life cycle phases. Specifically, boundary-scan technology is
now applied to product design, prototype debugging and field service as depicted in Figure 6.1.
This means the cost of the boundary-scan tools can be amortized over the entire product life cycle,
not just the production phase.
To facilitate this product life cycle concept, boundary-scan tool vendors such as Corelli’s
offer an integrated family of software and hardware solutions for all phases of a product's life-
cycle. All of these products are compatible with each other, thus protecting the user's investment.
Fig 6.1 - Product Life Cycle Support
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6.2 Applying Boundary-Scan for Product Development:
The on-going marketing drive for reduced product size, such as portable phones and digital
cameras, higher functional integration, faster clock rates, and shorter product life-cycle with
dramatically faster time-to- market has created new technology trends. These trends include
increased device complexity, fine pitch components, such as surface-mount technology (SMT),
systems-in-package (SIPs), multi-chip modules (MCMs), ball-grid arrays (BGAs), increased IC
pin-count, and smaller PCB traces. These technology advances, in turn, create problems in PCB
development:
Many boards include components that are assembled on both sides of the board. Most of
the through-holes and traces are buried and inaccessible.
Loss of physical access to fine pitch components, such as SMTs and BGAs, makes it
difficult to probe the pins and distinguish between manufacturing and design problems.
Often a prototype board is hurriedly built by a small assembly shop with lower quality
control as compared to a production house. A prototype generally will include more
assembly defects than a production unit.
When the prototype arrives, a test fixture for the ICT is not available and, therefore,
manufacturing defects cannot be easily detected and isolated.
Small-size products do not have test points, making it difficult or impossible to probe
suspected nodes.
Many Complex Programmable Logic Devices (CPLDs) and flash memory devices (in BGA
packages) are not socketed and are soldered directly to the board.
Every time a new processor or a different flash device is selected, the engineer has to learn
from scratch how to program the flash memory.
When a design includes CPLDs from different vendors, the engineer must use different in-
circuit programmers to program the CPLDs.
Boundary-scan technology is the only cost-effective solution that can deal with the above
problems. In recent years, the number of devices that include boundary-scan has grown
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dramatically. Almost every new microprocessor that is being introduced includes boundary-scan
circuitry for testing and in-circuit emulation. Most of the CPLD and field programmable array
(FPGA) manufacturers, such as Altera, Lattice and Xilinx, to mention a few, have incorporated
boundary-scan logic into their components, including additional circuitry that uses the boundary-
scan four-wire interface to program their devices in-system.
As the acceptance of boundary-scan as the main technology for interconnect testing and in-
system programming (ISP) has increased, the various boundary-scan test and ISP tools have
matured as well. The increased number of boundary-scan components and mature boundary-scan
tools, as well as other factors that will be described later, provide engineers with the following
benefits:
Easy to implement Design-For- Testability (DFT) rules. A list of basic DFT rules is
provided later in this article.
Design analysis prior to PCB layout to improve testability.
Packaging problems are found prior to PCB layout.
Little need for test points.
No need for test fixtures.
More control over the test process.
Quick diagnosis (with high resolution) of interconnection problems without writing any
functional test code.
Program code in flash devices.
Design configuration data placement into CPLDs.
JTAG emulation and source-level debugging.
6.3 What Boundary-Scan Tools are needed?
In the previous section, we listed many of the benefits that a designer enjoys when
incorporating boundary-scan in his product development. In this section we describe the tools and
design data needed to develop boundary-scan test procedures and patterns for ISP, followed by a
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description of how to test and program a board. We use a typical board as an illustration for the
various boundary-scan test functions needed. A block diagram of such a board is depicted in Figure
6.2.
Fig 6.2 - Typical Board with Boundary-Scan Components
A typical digital board with boundary-scan devices includes the following main components:
Various boundary-scan components such as CPLDs, FPGAs, Processors, etc., chained
together via the boundary-scan path.
Non-boundary-scan components (clusters).
Various types of memory devices.
Flash Memory components.
Transparent components such as series resistors or buffers.
Most of the boundary-scan test systems are comprised of two basic elements: Test Program
Generation and Test Execution. Generally, a Test Program Generator (TPG) requires the netlist of
the Unit Under Test (UUT) and the BSDL files of the boundary-scan components. The TPG
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automatically generates test patterns that allow fault detection and isolation for all boundary-scan
testable nets of the PCB. A good TPG can be used to create a thorough test pattern for a wide range
of designs. For example, Scan Express TPG typically achieves net coverage of more than 60%,
even though the majority of the PCB designs are not optimized for boundary-scan testing. The
TPG also creates test vectors to detect faults on the pins of non-scan able components, such as
clusters and memories that are surrounded by scan able devices.
Some TPGs also generate a test coverage report that allows the user to focus on the non-
testable nets and determine what additional means are needed to increase the test coverage.
Test programs are generated in seconds. For example, when Corelis ScanExpress TPG™
was used, it took a 3.0 GHz Pentium 4 PC 23 seconds to generate an interconnect test for a UUT
with 5,638 nets (with 19,910 pins). This generation time includes netlist and all other input files
processing as well as test pattern file generation.
Test execution tools from various vendors provide means for executing boundary-scan tests
and performing in-system programming in a pre-planned specific order, called a test plan. Test
vectors files, which have been generated using the TPG, are automatically applied to the UUT and
the results are compared to the expected values. In case of a detected fault, the system diagnoses
the fault and lists the failures as depicted in Figure 6.3. Figure 6.3 shows the main window of the
Corelis test execution tool, scan Express Runner™. scan Express Runner gives the user an
overview of all test steps and the results of executed tests. These results are displayed both for
individual tests as well as for the total test runs executed. scan Express Runner provides the ability
to add or delete various test steps from a test plan, or re-arrange the order of the test steps in a plan.
Tests can also be enabled or disabled and the test execution can be stopped upon the failure of any
particular test.
Different test plans may be constructed for different UUTs. Tests within a test plan may be
re-ordered, enabled or disabled, and unlimited different tests can be combined into a test plan. scan
Express Runner can be used to develop a test sequence or test plan from various independent sub-
tests. These sub-tests can then be executed sequentially as many times as specified or continuously
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if desired. A sub-test can also program CPLDs and flash memories. For ISP, other formats, such as
SVF, JAM, and STAPL, are also supported. To test the board depicted in Figure 6.2, the user must
execute a test plan that consists of various test steps as shown in Figure 6.3.
Fig 6.3 - Scan Express Runner Main Window
The first and most important test is the scan chain infrastructure integrity test. The scan chain
must work correctly prior to proceeding to other tests and ISP. Following a successful test of the
scan chain, the user can proceed to testing all the interconnections between the boundary-scan
components. If the interconnect test fails, scan Express Runner displays a diagnostic screen that
identifies the type of failure (such as stuck-at, Bridge, Open) and lists the failing nets and pins as
shown in Figure 6.4. Once the interconnect test passes, including the testing of transparent
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components, it makes sense to continue testing the clusters and the memory devices. At this stage,
the system is ready for in-system programming, which typically takes more time as compared to
testing.
Fig 6.4 - Scan Express Runner Diagnostics Display
During the design phase of a product, some boundary-scan vendors will provide design
assistance in selecting boundary-scan-compliant components, work with the developers to ensure
that the proper BSDL files are used, and provide advice in designing the product for testability.
6.4 Applying Boundary-Scan for Production Test:
Production testing, utilizing traditional In-Circuit Testers that do not have boundary-scan
features installed, experiences similar problems that the product developer had and more:
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Loss of physical access to fine pitch components, such as SMTs and BGAs, reduces bed-of-
nails ICT fault isolation.
Development of test fixtures for ICTs becomes longer and more expensive.
Development of test procedures for ICTs becomes longer and more expensive due to more
complex ICs.
Designers are forced to bring out a large number of test points, which is in direct conflict
with the goal to miniaturize the design.
In-system programming is inherently slow, inefficient, and expensive if done with an ICT.
Assembling boards with BGAs is difficult and subject to numerous defects, such as solder
smearing.
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CHAPTER-7
7.0 JTAG Embedded Functional Test:
Recently, a test methodology has been developed which combines the ease-of-use and low
cost of boundary-scan with the coverage and security of traditional functional testing. This new
technique, called JTAG Emulation Test (JET), lets engineers automatically develop PCB
functional test that can be run at full speed., If the PCB has an on-board processor with a JTAG
port (common, even if the processor doesn't support boundary-scan), JET and boundary-scan tests
can be executed as part of the same test plan to provide extended fault coverage to further
complement or replace ICT testing. Corelli’s Scan Express JET™ provides JTAG embedded test
for a wide range of processors.
7.1 Production Test Flow:
Figure 7.1 shows different production flow configurations. The diagram shows two typical
ways that boundary-scan is deployed:
As a stand-alone application at a separate test station or test bench to test all the
interconnects and perform ISP of on-board flash and other memories. JTAG embedded
functional test (JET) may be integrated with boundary-scan.
Fig 7.1 - Typical Production Flow Configurations
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Integrated into the ICT system, where the JTAG control hardware is embedded in the ICT
system and the boundary-scan (and possibly JET) software is a module called from the ICT
software system.
In the first two cases, the test flow is sometimes augmented with a separate ICT stage after
the JTAG-based testing is completed, although it is becoming more common for ICT to be skipped
altogether or at least to be limited to analog or special purpose functional testing.
The following are major benefits in using boundary-scan test and in-system programming in
production:
No need for test fixtures.
Integrates product development, production test, and device programming in one
tool/system.
Engineering test and programming data is reused in Production.
Fast test procedure development.
Preproduction testing can start the next day when prototype is released to production.
Dramatically reduces inventory management – no pre-programmed parts eliminates device
handling and ESD damage.
Eliminates or reduces ICT usage time – programming and screening.
Production test is an obvious area in which the use of boundary-scan yields tremendous
returns. Automatic test program generation and fault diagnostics using boundary-scan software
products and the lack of expensive fixturing requirements can make the entire test process very
economical. For products that contain edge connectors and digital interfaces that are not visible
from the boundary-scan chain, boundary-scan vendors offer a family of boundary-scan controllable
I/Os that provide a low cost alternative to expensive digital pin electronics.
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7.2 Field Service and Installation:
The role of boundary-scan does not end when a product ships. Periodic software and
hardware updates can be performed remotely using the boundary-scan chain as a non-intrusive
access mechanism. This allows flash updates and reprogramming of programmable logic, for
example. Service centers that normally would not want to invest in special equipment to support a
product now have an option of using a standard PC or laptop for boundary-scan testing. A simple
PC-based boundary-scan controller can be used for all of the above tasks and also double as a fault
diagnostic system, using the same test vectors that were developed during the design and
production phase. This concept can be taken one step further by allowing an embedded processor
access to the boundary-scan chain. This allows diagnostics and fault isolation to be performed by
the embedded processor. The same diagnostic routines can be run as part of a power-on self-test
procedure.
7.3 Boundary-Scan Design-for-Test Basic Considerations:
As mentioned earlier in this article, the design for boundary-scan test guidelines are simple to
understand and follow compared to other traditional test requirements. It is important to remember
that boundary-scan testing is most successful when the design and test engineering teams work
together to ensure that testability is "designed in" from the start. The boundary-scan chain is the
most critical part of boundary-scan implementations. When that is properly implemented,
improved testability inevitably follows.
Below is a list of basic guidelines to observe when designing a boundary-scan-testable board:
If there are programmable components in a chain, such as FPGAs, CPLDs, etc., group them
together in the chain order and place the group at either end of the chain. It is recommended
that you provide access to Test Data In (TDI) and Test Data Out (TDO) signals where the
programmable group connects to the non-programmable devices.
All parts in the boundary-scan chain should have 1149.1-compliant test access ports
(TAPs).
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Use simple buffering for the Test Clock (TCK) and Test Mode Select (TMS) signals to
simplify test considerations for the boundary-scan TAP. The TAP signals should be
buffered to prevent clocking and drive problems.
Group similar device families and have a single level converter interface between them,
TCK, TMS, TDI, TDO, and system pins.
TCK should be properly routed to prevent skew and noise problems.
Use the standard JTAG connector on your board as depicted in Corelis documentation.
Ensure that BSDL files are available for each boundary-scan component that is used on
your board and that the files are validated.
Design for interconnect testing requires board-level system understanding to ensure higher test
coverage and elimination of signal level conflicts.
Determine which boundary-scan components are on the board. Change as many non-
boundary-scan components to IEEE 1149.1-compliant devices as possible in order to
maximize test coverage.
Check non-boundary-scan devices on the board and design disabling methods for the
outputs of those devices in order to prevent signal level conflicts. Connect the enable pins
of the conflicting devices to boundary-scan controllable outputs. Corelis tools will keep the
enable/disable outputs at a fixed disabling value during the entire test.
Ensure that your memory devices are surrounded by boundary-scan components. This will
allow you to use a test program generator, such as ScanExpress TPG, to test the
interconnects of the memory devices.
Check the access to the non-boundary-scan clusters. Make sure that the clusters are
surrounded by boundary-scan components. By surrounding the non-boundary-scan clusters
with boundary-scan devices, the clusters can then be tested using a boundary-scan test tool.
If your design includes transparent components, such as series resistors or non-inverting
buffers, your test coverage can be increased by testing through these components using
scan Express TPG.
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Connect all I/Os to boundary-scan controllable devices. This will enable the use of
boundary-scan, digital I/O module, such as the ScanIO-300LV, to test all your I/O pins,
thus increasing test coverage.
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Limitations
1. SMT target is to develop high density boards so we have to compromise in the rating of
boards.
2. Some components could not withstand very high temperatures in soldering oven, so we need
to solder them separately in THT process.
3. SMC Standardization: The same SMC from two different manufacturers may have different
dimensions, which may create a problem. Hence standardization is necessary. Till today no
standardization is made.
4. SMC Availability: Some 15,000 components are available as SMC but not all of them may
be available when needed i.e. wanted.
5. High startup expenses: The startup cost of SMT for both manufacturers and individual
experimenters can be high. For manufacturers automated production equipment is most
expensive investment. For experimenters requires new assembly tools and stock of surface
mountable resisters, capacitors, Diodes, transistors, ICs, etc.
6. Thus the overall cost is very high.
7. In MDA the continuity is the problem in testing of some components for different frequencies.
And in this we need to develop perfect patterns on probe able test pads.
8. In boundary scan test the perfect data isolation is the problem because of forced data out for
some occasions.
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Conclusion:
SMT is more advantages than the conventional circuit board. Because it reduces the size of
circuit board, cost, weight etc. And the new automated machines easier our work and make it more
accurate. Due to above advantages SMT circuit can be mount on the coin or on the postal stamp.
Also the circuit can be mounted on both sides of the circuit board. So now a day it is used in
mobile, calculator or the circuit where small space circuit is required. But it needed to overcome
the problems in soldering and testing of the PCBs. By using MDA in addition to the bed of nails
test fixture the faults can be easily detected. By using CAD software in designing of probe able test
pads the accuracy of the tester increases. But this physical test access does not give accurate results
for latest and some double sided PCBs so we need to adopt latest technology like boundary scan
test access which can detect line faults, short faults and open faults etc. The AOI machine can work
in integration with boundary scan test access which is very helpful in detecting faults in initial
stages itself. While it is obvious that boundary-scan based testing can be used in the production
phase of a product, new developments and applications of the IEEE-1149.1 standard have enabled
the use of boundary-scan in many other product life cycle phases. Specifically, boundary-scan
technology is now applied to product design, prototype debugging and field service .This means
the cost of the boundary-scan tools can be amortized over the entire product life cycle, not just the
production phase.
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Bibliography:
1) E-BOOK ON SURFACE MOUNT TECHNOLOGYCOMPILED BY DR. KANTESH
DOSS ELCOTEQ, INC.
2) MIRTEC automatic machines user manual.
3) www.logextechno.com
4) Non-Contact Test Access for Surface Mount Technology IEEE 1149.1-1990
5) www.radioelectronics.com
6) Surface Mount Technology: Principles and Practice by Ray P. Prasad
7) The Electronic Packaging Handbook edited by Glenn R. Blackwell
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