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Solder balls up on zinc and chromate screws

2003

We use #4- 20 Plastite thread with Phillips Head screw with Zinc with Yellow Chromate coating to fasten connectors to PCB. One of the issues which we face with is solder/solder balls adhering to screws when we run it through our Wave solder process which is a concern for our customer.

We have come across 2 types of Organic coating (Ford Spec - S424 and a GM Spec) which seem to be solder resistant. The issue is that the plater we have called are hesitant to plate because of concerns of over filling the recess on the Phillips head and maintaining the dimensions.

Any help? We also want to get out of the hexavalent chromium with this effort.

Karthik Thilakarajan (KT)
1st tier automotive Electronics supplier Tampa, Florida

We are having the same problem albeit using different screws and possibly exacerbated by our solder pot containing lead free solder due to RoHS compliancy requirements. This means that our solder has a silver component. The screws we are using are steel, zinc plated and Cr3 passivated, also for RoHS requirements. This has the potential of being a serious problem in an electrical environment. Any suggestions for alternative screw finishes which still meet RoHS requirements would be most helpful. Watching with interest.

Lee Braden
power supply manufacturer - Melbourne, Victoria, Australia
2006

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Hi. It would seem that you need something that is less amenable to having solder stick to it. Stainless steel screws may or may not be practical, but generally are passive enough that the older probably won't stick. Other than that, it would seem that a temporary (masking) or permanent organic coating (Teflon?) would keep the solder from sticking. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 24, 2009