How do we prevent blistering of nickel plated copper parts?

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Q. Recently we observed blistering of nickel plated copper parts. The parts were plated in a sulfamate bath by our supplier. We use these parts to prepare electronics for the automotive industry. Our vendor does not have any answers to this problem. Can you help us? —D.O.

A. I would say that the copper under layer had a pit or hole that trapped some of the sulfamate plating solution during the nickel plating step. The liquid in this defect worked its way out of the pit and caused the blister you observed.

You mentioned in a follow-up email that you have observed this on two or three parts out of 1,000 parts examined. This is not a large percentage of the parts and it speaks well for your inspection process that you are able to catch these defective parts. I would suggest to your vendor that they investigate their copper plating process. Depending on the type of copper plating they are doing, this pitting may be caused by a high free cyanide (if using a cyanide-based copper plating bath) or organic contaminants.

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