Pin in Paste

GS-20-024Rev: A of 13

Pin-in-pasteApplication guide

(Pin-in-paste, Paste-in hole, intrusion reflow etc.)

Pin-in-pasteApplication guide

(Pin-in-paste, Paste-in hole, intrusion reflow etc.)

GS-20-024Rev: A of 13

We believe that the information contained in this publication is thebest currently available on the subject. It is offered as a possiblehelpful suggestion in any experimentation you may care toundertake and is subject to revision as additional knowledge andexperience is gained. FCI makes no guarantee of results and assumesno obligation or liability whatsoever in connection with thisinformation. This publication is not a license to operate under, orintended to suggest infringement of, any existing patent.

Information given on the drawings in this document is not suitablefor tooling design and construction. To obtain the correct drawingsfor these purposes, contact your local FCI representative.

About FCICreated in 1989, FCI rapidly secured its place among the world’s top three manufacturers & suppliers of connectors and interconnectsystems. With a turnover of 1.97 billion Euros (1.8 billion dollars) in 2001, FCI is operating all around the world, with activities gearedtowards major markets: communications, data, consumer, industrial, military and aerospace, automotive and electrical powerinterconnect. FCI has its headquarters in Paris, France and employs 16 000 people in Europe, Asia and the Americas. The companyis a member of the AREVA group, which also includes COGEMA, Framatome ANP and an 11% interest in ST Microelectronics.

For more information: www.fciconnect.com.

IntroductionSMT process description 3

The pin-in-paste technologyIntroduction 4Paste application 4Stancil apertures 5Component feeding and package 6Component picking and assembly 6Reflow 7Inspection, quality references 7Micro sectioning of solder joints 8

Pin-in-paste connectorsGeneral 9Ability to carry forces 9Positioning 9Board layout 10Solder mask application 10Solder paste application 10Utilization of area for paste printing 11Paste application close to the connector 11Guiding wafer stand-offs 12Hold down features 12Repair/replacement 13

This application guide is a handbook in implementing board edgeand front I/O connectors to SMT-processes. The aim is to giveinformation to all people involved in the process of developingand manufacturing electronic hardware.For further specific information, please contact your local salesoffice as listed on the rear cover.

Introduction of this publication

Content

Liability

Pin-in pasteApplication guide

AW: KM

GS-20-024Rev: A of 13

SMT process description

A typical SMT-process is in principle 3 steps, application of solder paste on the bare boards, assembly of components and reflowsoldering. To achieve high efficiency the process in reality is more complicated.

The boards are automatically handled into the screen printing equipment for solder paste application. A screen printing stencil isprovided with openings(apertures) to control the paste printing. The stencil thickness may vary, but typical values are 0,125 and 0,15mm. The paste is pressed into the apertures with a squeegee, or with a special paste head providing vertical pressure on the paste whilepassing over the stencil (e.g. ProCon). The screen printing can be made in one or more strokes to provide wanted aperture filling

After the paste application vision-based automatic inspection equipment can inspect crucial areas for defects in the paste application.The boards are carried on a conveyor through the process steps.

The first component assembly station normally handles the smallest components with a very high mounting speed. They are placed inthe paste, and a vision inspection may be placed after the assembly, or after some more assembly steps. Further assembly stations maybe used, depending on type of boards and components involved.

The final assembly normally deals with larger and odd shape components. After final assembly and optional vision inspection, theboards pass through the solder reflow oven. The final inspection is either manual or automatic.

Introduction

Figure 1Typical SMT process overview.

Pas

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Bare board 1st a

ssem

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2 nd

ass

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Larg

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com

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ntas

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Ref

low

sold

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Check/inspection

Componentson reels/trays

Assembled andsoldered board


GS-20-024Rev: A of 13

The Pin-in-paste (PIP) technology

Introduction

The principle for PIP is that solder-through-hole componentposts are placed in holes with SMT-solder paste and thenreflow soldered in the same operation as the SMT components.

Especially for connectors in backplane systems the positionrequirements and the external forces need special attention.Pin-in paste connectors are therefore provided with locationand in some cases also hold-down features (HDF) for properadaptation to the SMT process.

Board with hole Solderpaste

Stencil

Component assembled Reflow soldered

squeegee

Process parameters are hole size, pin size, board thickness,stencil aperture, stencil thickness, paste filling into hole andpaste properties.Compared with wave soldering the process normally showsbetter result in wetting and less bridging, but for componentswith thin pins in large holes with thick boards it may sometimesbe hard to put enough paste on to get 100 % filling. Industrystandard quality requirements has taken these into account,and permit less filling for pin-in paste soldering. (see furtherin section Inspection, quality references).

45

Paste application

The amount of paste necessary to give an appropriate solderjoint can be calculated. Normally there is a need to print pastealso on the board surface (overprinting), not only in the holeitself, so the stencil apertures are larger than the land of the hole.Paste applied on the board surface will later be sucked into thehole in the reflow process.

Stencil

Squeegee

Figure 3Paste application squeegee


Figure 2Pin-in-paste process sequence

GS-20-024Rev: A of 13

Stencil apertures

In principle the hole grid for connectors can be printed with pasteall over, but then the amount of solder sucked into the holes willdiffer from joint to joint depending on where the melting of thepaste starts.It is therefore recommended to let each hole have its own definedpaste printing shape. In the case with connector solder tail grids,the paste amount is often maximised by the grid size, e.g. 2 x 2mm. Separating space should normally be equal or more than 0,3mm. (see figure 16). The apertures in connector grids may verywell be optimised in size using unsymmetrical placing of pasteapertures (see figure 22).

The amount of paste in the hole will depend on which verticalpressure the paste applicator can provide. A normal squeegee willimprove the vertical pressure if the angle is reduced from 60° to45° (see figure 3).Improved filling can also be achieved with applicators providing astatic pressure against the board/stencil.

The filling degree (Fd) of a joint can be calculated according tofollowing:

Fd = P/V P= metal volume in applied pasteV= volume to fill (hole - post)

P = {(Y * X* T) + [(D/2)2 * p] * Z}* m

m= metal volume in paste.(normally about 50% = 0,5)Z =paste filling in hole, dimension fromboard surface and into the hole

Figure 5Paste volume calculation definitionsCalculations will show that the length ”Z” is important for the

filling degree, as well as not having the hole oversized.

Additional paste can also be applied with dispensing units. AsSMT-lines are not often equipped with dispensing units this willbe used in special cases. In addition to the possibility to add morepaste, the paste can also have different properties (viscosity, metalcontent) to give better filling degree.

Screen-printing stencils may also have partially thicker areas toincrease the paste volume at the connector positions. Somelimitation must be taken into account as squeegee movingdirection, connector positions, more expensive stencil etc.

land

hole

paste printing aperture

Figure 4Stencil aperture principle


X

Z

T

D

Y

Solder paste

GS-20-024Rev: A of 13

Component feeding and package

For SMT components the package is a part of the product. It isimportant that the component is fed into and presented to theassembly process in a proper way. Normally the preferred packageis tape according to EIA 481 specifications. This allows for use inmost SMT-equipment. Metral connector tape is shown infigure 6.

Figure 6Tape-and-reel packaged connectors

Component picking and assembly

The assembly equipment normally has a vacuum nozzle as pickingand handling tool. Special designed mechanical grippers couldalso be used.To allow for a proper use of the vacuum nozzle the componentmust be provided with a flat surface of enough area, and thissurface must be parallel to board mounting plane.It is recommended to use vacuum nozzle without rubber edge inorder to allow the connector to self-correct position during thefinal part of the mounting cycle.

The handling cycle normally includes a vision inspection, wherethe position of the component is controlled, and parameters givento the control system to adjust position for the board assembly.The vision system may also be able to check features like solderterminals etc. A connector, often having features for locating toboard holes, shall normally have visible reference features to controlthe position.For connectors, in general the placement on the board shall bemade with only z-movement (vertically). This is to avoidinterference with already assembled adjacent connectors.If the connector assembly needs force due to locating/fixingfeatures, a board support has to be installed.

A large component/odd shape component assembly machineprinciple is shown in figure 8.

Board

rodLongituditional

Transversepositioning

Vision inspectionTape

Assembly head(longituditionalposition)

Feeder

Component

picking areaTray/tube

Figure 8Last step component assembly machine principle

Figure 7Vacuum nozzle picking connector from tape package


GS-20-024Rev: A of 13

Reflow

The assembled board will be fed through the reflow oven. Theoven consists of several zones with different temperature. This isto ensure even temperature distribution and minimise risk ofcomponent failure due to temperature stresses. A typicaltemperature profile is shown in figure 9.

During the reflow process the flux content in the paste isevaporating while cleaning the joint surfaces, the small balls of tin(tin/lead) start to melt and the liquid metal pulled towards theclean metal surfaces (e.g. pads and posts) by surface tension. Asolder mask on the board prevents the tin to creep out from thepads and remain creating solder balls.

The conveyor speed in the oven is normally 500 to 1000 mm/min. Length (m)

Temperature

200

100

On board measured temperature

Zone temperature

2 4

Figure 9Reflow oven temperature zones

Inspection, quality references

The most used quality standards published by IPC (The Institutefor Interconnecting and Packaging Electronic Circuits), outlinethe acceptance of solder joints with minimum 75 % filling degree.

The quality is mainly secured by process control. The main toolsfor controlling the process is x-ray and micro sectioning.For judging and approval of soldering in tuning the processparameters the filling degree at a micro sectioned soldering asexpressed in figure 10 and 11 can be helpful.

Quality/inspection criteria must be considered differently thanfor normal wave soldering. The most important is that the amountof solder paste is controlled by the process by specifying hole,post, paste, stencil aperture and paste applicator serviceparameters. The remaining inspection can be reduced to checkproper assembly and wetting.

ba t

Figure 11Filling degree with voids

a tb1b2

Figure 10Filling degree calculation units

Calculation 1 (for figure 10)(a+b)/2t ≥ 0,75 (for t less or equal to 2.4 mm)

If voids are indicated, the whole filling shall be measured (b1) andthe effective unsoldered high (b2) of the void deducted from thedimension as shown in figure xxx.Voids not touching any or only one of the sides (pin or hole) shallnot be taken in account.

Calculation 2 (for figure 11) [a+(b1-b2)]/2t ≥ 0,75 (for t less or equal to 2.4 mm)


GS-20-024Rev: A of 13

Filling degree according to calculation below gives the averagefilling as the soldering very seldom is symmetric (as shown inIPC-requirements)

Board thickness t =2 mm (in this case equal to ”b”).a = 1,2 mmb = 2 mmFilling degree(a+b)/2t

(1,2+2)/4 = 0,8 (80%).

Figure 12Solder joints in 1,7 mm thick board. Paste screen aperture 1,7x1,8mm. 100% filling and approved wetting

According to quality standard used in industry (IPC) it is notneed for solder post to have protrusion on thicker boards than2,3 mm. For thick boards, or in general if solder posts are shorterthan the board thickness, soldering not necessary need to gothrough the hole as indicated in figure14. Filling degree couldthan be calculated as having a board thickness of 2,3 mm, orhaving the board thickness equal to solder post hole penetra-tion. This issues is up to each user to evaluate and decide on.

Figure 14Solder posts shorter than board thickness

Micro-sectioning of solder joints

The following figures from actual Pin-in paste soldering give someexample of the results.

ab

Figure 13Solder joints with partial filling.


GS-20-024Rev: A of 13

GeneralBoard connectors like Metral and Sofix brings some specificrequirements for appropriate SMT-compatibility.These are: - Ability to carry forces - Position after assembly

Vertical (board level related)Horizontal (board position related)

Special attention has been taken in the development of SMTcompatible connectors to fulfil these requirements.

Ability to carry forcesThe forces exposed to the connectors come from handling, matingand unmating. Normally the locating pegs and the solderings ofthe tails carry those forces well. In some cases depending on theconnector design, additiononal features for force retention is used.On Metral connectors an optional hold-down feature (HDF)has been developed (see fig 15), for e.g. DIN and D-sub connectorsa harpoon feature is used (figure 18).

The HDF shall be soldered to a corresponding pad at the board,and the harpoon is soldered in the a plated through mountinghole.

PositioningNormally SMT components are self-aligning to their pads byallowing them to float. For a connector with its references to theboard pattern/surface, housing placed on the board surface andsometimes rather heavy, it is necessary to control the position. Acompliant locating peg has been developed to cope with bothlimitations in mounting force (max 20 N) and to keep theconnector in place after mounting prior to soldering(minimum 5 N).

For positioning versus board surface, the recommended layoutfor Metral connectors with HDF are provided with 4 levelreference pads (1x1 mm) touching the housing in each of thecorners (see figure 17). These pads shall be surface treated (tin,gold, OSP etc) the same as the pads of the whole board, but nosolder paste shall be applied. The reference pads bring the connectorto the reference level of the board (primary side). This is importantfor co-planarity if the connector has a hold-down feature (HDF)as described above. Also in case of mixed Metral on same boardedge it is recommended to have reference pads also on those nothaving HDF.

Figure 15Hold-down and location features at Metral

Figure 17Hold down and reference pads at Metral connectors

Pin-in paste connectors

Figure 18Harpoon type hold down feature (DIN 41626-connector)

Compliant locatingpegs

HDF-plate(optional)


Figure 16Location and force retention peg at Metral TINT

Location and forceretention peg

retention padHold down and Reference pads

GS-20-024Rev: A of 13

Board layout

The recommended board layout is shown on the CustomerDrawings of each product (If not available, ask for it from yourlocal sales office or look into www.fciconnect.com).

Pay attention to the hole size tolerances for the compliant locatingpegs (often 1,55 +0/-0,05 mm) as the control of retention force atassembly is maintained by those holes.

Solder mask application

To avoid disturbance in the reference surface of connector/boardit is recommended that solder mask is never printed on thereference pads underneath the housing. To achieve that the areacan be without solder mask. See figure 19. (only applicable atMetral connectors when using reference pads).

Solder mask has to be applied on all surfaces where solder paste isprinted except on the solder pads.

housing areanear the connectorSolder mask coverage

12,2 minimum

Board edge

2,2

min

imum

Figure 19Recommended solder mask opening

Solder paste application

Solder paste at the hole grid is recommended as in figures 20 for 4row Metral connectors. It is preferred to utilize the area withrectangular shaped pads, maximum sizes as shown.For other connector types see actual customer drawing.

It is important that the paste pad configuration is adapted toactual connector, board thickness, hole size, paste applicator, stencilthickness etc. What is recommended below and/or at our customerdrawing is general advice.

Figure 20Proposal for maximum amount of paste applied at the pin grid of the4-row Metral connectors.

4,65

4,65

Board edge

0,3

0,3

2,1

1,7Land diameter to be minimized

1,0

2,25

2,25

Stencil aperture


GS-20-024Rev: A of 13

Some caution needs to be taken if the aperture edge of the screenprinting stencil is resting on the land of a hole; leakage is a risk. Itis therefore recommended to minimise land diameter (Nominalhole diameter + 0,4 mm) . Apertures could also have a shapeavoiding the land (see figure 21).

Figure 21Screen printing stencil apertures to reduce paste leakage. Lands to beminimized (Nominal hole diameter + 0,4 mm)

Utilization of area for printing paste

In some cases, especially on connectors with few solder posts, thearea can be utilized as much as possible, as long as the meltingpaste have a distance to be sucked into the hole less than 2 mm. Infigure 22 the maximum paste printing is shown for Sofix ShieldedI/O 8 pos connector.

Housing

Paste pads 2,70 x 1,95 mm

Space between pads 0,3 mm

Figure 22Maximum use for printing paste with unsymmetrically placed sol-der paste pads.

Paste application close to the connector

Some of the connector housings is provided with a recess to allowfor paste to be applied for soldering close to the housing. A recessis also normally present for a hole having a harpoon typemounting. The customer drawing is providing the actual infor-mation.

Figure 23Housing recess for solder paste


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GS-20-024Rev: A of 13

Guiding wafer stand-offs

Some connectors are equipped with a guiding wafer to ensureproper true position of the solder tails. To give space for solderpaste to move and reflow correctly, such guiding wafer has stand-offs placed in the space between the proposed solder paste pads.The position of the stand-offs can be found on the customerdrawing of the connector.To avoid disturbance in the paste pads it is recommended to makesmall adjustments in the apertures as shown in figure 24 and 25.

Figure 24Reduction of paste pad in the intersection (recommended) due towafer stand-off

Figure 25Reduction of paste if stand-off is not fitting in the intersection

R 1,3

0,6

9,0

R 2,0 40

5,01,

9

Reference pads (no paste)

0,3

2,6

20

Figure 26Proposal for paste application on the hold-down feature area

0,6

0,6

Hold down features

Hold down features (HDF) are in some cases shaped as seen infigure 15. A corresponding pad at the board for soldering to theHDF-plate is recommended in the actual customer drawing. Thepaste printing stencil apertures are recommended as in figure 26.In the case with a hole in size 2 mm it is not recommended to printover the hole, but make the apertures divided in smaller portions.It is however important that it will be soldered almost around thewhole hole.

For paste printing on harpoon holes, often of 2,5 mm diameter, itmay be necessary to have a beam in the stencil to avoid too muchleakage of paste through the hole.


GS-20-024Rev: A of 13

Repair/replacing

If a connector must be replaced, the following method can beused:

1Cut off all terminals close to the guiding wafer with a cutting tool.

2Warm up the visible part of the HDF (if present) solder plateunderneath the connector. Use a flat iron or hot air. When solderjoint is melted, lift off the connector body.

4Clean up the terminal area by desoldering the remainings of thesolder tails, and clean the holes from solder. Clean also the HDFpad.

5Alternative 1Apply new solder paste on the HDF-pad.Put a new SMT PIP connector on place. Make sure it is leaning onthe 4 reference pads. Otherwise it can indicate that the old solderon the HDF pad is not fully removed. Reflow the paste w i t hhot air or an iron.Alternative 2Use a connector with heat stake or press-peg mounting.

6Solder the terminals with a solder iron

7Inspect the connector with respect to placement and solder joints.

Your own notes


Revision record:

Rev Page Description EC# Date

A All New document ECP H20129 2002-07-01

Pin in Paste

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