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Ask the Experts

September 20, 2010 - Updated
September 20, 2010 - Originally Posted

Bottom Side Component Attachments

What is an acceptable percentage of bottom side attachments for components with a solder tab on the bottom? We have had several issues with a sub-contractor and we heard it depends on whether it is used for a ground connection or heatsinking, which doesn't sound correct. Can you comment?

D. R.

Expert Panel Responses

This question needs further clarification and possibly a few photos.

Bryan Kerr
Principal Engineer - CMA Lab, BAE Systems

Bryan Kerr has 35 years experience in providing technical support to PEC assembly manufacturing. His experience ranges from analysis of materials and components to troubleshooting and optimizing, selecting reflow, cleaning, coating and other associated processes.

This does kind of depend on the reason for the solder attach as suggested by your sub-contractor. For heatsinking you may need as large an area as possible to maximise the heat transfer whereas electrical continuity to ground may not be so critical. Personally I would try to satisfy both while including some tolerance for your production process and variation in component stand off etc. Aiming for a minimum of 50% solder coverage would seem to be a reasonable, achievable target however be aware that you are likely to get a level of voiding in such solder joints unless you are using a vacuum soldering process and you will have to decide whether the 75% includes or excludes any voiding. X-ray will be the only way to check it.

Bryan Kerr
Principal Engineer - CMA Lab, BAE Systems

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