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How to evaluate quality of Gold plating

We would like to know how the quality of Gold plating could be evaluated for the contact pins made in Brass. We had some contacts gold plated from a agency and after a month's usage we find that the contacts are having higher resistance problem. The plated surface is turning blackish.

Baburao C. Arnalkar
- Pune, Maharashtra, India
2006

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The common practice in gold plating is to have a diffusion barrier plate between the substrate and the gold. Nickel is often chosen as the barrier plate, without one you are asking for trouble. You did not mention if the pins are leaded brass. Without a barrier plate zinc and or lead (to name a few) will migrate through the surface of the gold causing the discoloration. If the gold thickness is minimal, migration occurs at a more rapid rate, contact resistance will rise because of these undesirable metals migrating to the surface.
First, I would talk to another plater. Let them know of your current problem, alloy of your brass, and that you want documentation sent with the parts regarding gold thickness measurements. Have someone with good plating experience visit the plating facility on your company's behalf to see what kind of operation they run. Good Luck!

Mark Baker
process engineer - Malone, New York
2006