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TO-220 Chip Package - Bridges

Views: 2316

#69198

TO-220 Chip Package - Bridges | 7 June, 2013

We use a Wave Solder Plated Through Hole (PTH) assembly process to install a TO-220 Chip Package in the PCB board that we manufacture and have experienced lower yields on a number of boards with this component due to Bridges. The bridges on the TO-220 Chip Package account for 35% of our overall Wave Solder bridges.

Can anyone discuss successes related to reducing bridges with the TO-220 Chip Package. The TO-220 Package board design is a 50 mils PTH with 30 mils clearance between pads except for the kicked-out pin.

We have already attempted the basics to reduce bridges including: Dross removal on regular basis, Preventive Maintenance including machine level/conveyor angle/solder pot angle, Profile Optimization of flux amount/dwell time/conveyor speed, Board Rotation of 90 degree & 180 degree, Lead Length reduction, and Board Warp reduction.

Some of our pad designs already incorporate an oval pad – although we are currently looking at the possibility that a more optimized oval pad may improve our situation. We are also looking at better control and optimization of our flux process. Thank you for your help!

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#69201

TO-220 Chip Package - Bridges | 7 June, 2013

Run the board at 90* from the direction that you currently run it through the wave

BR, davef

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#69258

TO-220 Chip Package - Bridges | 12 June, 2013

Dan,

Can you upload a picture of the bridging?

Why oval pads? Have you considered using round pads with the smallest practical annular ring? In my opinion, an oval pad would potentially hold more solder because there is more exposed area, and the more molten solder, the greater chance of bridging.

It is mainly the solder within the plated through hole that gives the strength, not so much the top/bottom side fillets.

Before you redesign you boards, try putting some Kapton tape on part of the pads to reduce the exposed area as a test.

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#69260

TO-220 Chip Package - Bridges | 12 June, 2013

daveF - thank you for your reply. We ave tried both the 90 and 180 degree rotation in addition to other solutions mentioned in previous post but with no or minimal success.

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#69264

TO-220 Chip Package - Bridges | 12 June, 2013

DeanM - thank you for your response. I will work on uploading a picture of the bridges. We are focusing our efforts on nine boards that use the TO-220 package.

I will also pass along your idea of Oval Pads to our Manufacturing and Design Engineers and also the idea of testing before-hand with Kapton tape. Thanks again.

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#69269

TO-220 Chip Package - Bridges | 13 June, 2013

put the silk screen mask between pads.Add drain pads after TO220.

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