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PCB plating for Metal Dome applications

2004

Hi,

I would like to know what are the recommended PCB plating for metal dome applications. The metal dome application will be used under heavy load. Thus, is there any specific recommended surface or finishes that the PCB should use? I want a solution that is high resistivity to oxidation and tough enough to last about 3 million hits. I heard that Nickel provide excellent resistivity to oxidation.

In one article, I found out that in normal metal dome applications, the PCB uses nickel plating with 50 millionths thick, minimum of 40 Rockwell C hardness and measured with the Knoop process at 100 grams. What is Rockwell and Knoop?

Thanks,

Don Chew
Engineering - PJ, Selangor, Malaysia

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Sulphamate nickel does sound possible because it has good conductivity, reasonable resistance to tarnish, and low stress for good flexibility. But I think it's most common that silver is plated on top of the nickel plating. If it's for extremely low voltage and current though, only precious metals like gold, palladium and rhodium offer freedom from tarnish.

50 millionths of an inch (0.000 050) seems thin for functional nickel plating, but that is apparently considered thick for dome plating. Rockwell C is a hardness scale, but one where the testing method doesn't translate well to testing thin layers; Knoop is another hardness scale testing method more appropriate to electronics.

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