plating, anodizing, & finishing Q&As since 1989
Gold Plating Thickness vs. Porosity
Q. Chris James
Would you please identify what the minimum thickness of gold is required to reduce or eliminate gold plating porosity sufficiently to ensure corrosion free electrical contacts over a 24-year period in a "NAVAL SHELTERED" environment. Also, are there any other factors that cause gold plating porosity?
A. Hello Chris,
The minimum gold thickness you are inquiring about is usually called out in the Mil-Spec for the coating. It would also depend on whether the contacts to be plated are stationary or moveable. In stationary contacts a type 1 gold plating spec is used (99.7% purity), the higher the gold purity, the lower the contact resistance. In moveable contacts type 2(acid hard gold) is used, alloyed with cobalt or nickel. This coating offers excellent wear resistance. The minimum purity for type 2 is 99.0%. The spec will also specify the hardness grade as well. In printed circuits there are two thickness requirement classes, class 2 and 3. Class 3 is 50 µinches minimum, which is what we had to plate for the military. Porosity in gold is normally not a problem as long as the barrier layer (usually nickel) is thick enough and the proper gold and gold thickness is applied. Pulse plating for gold offers lower porosity than the conventional plating method, something I would consider for your application. Good Luck!
A. Hi Chris. If you wish to follow up / read more on Mark's suggestion of pulse plating, Topic 0014, "Pulse Plating of Gold", offers a lot of experienced input on the subject.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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