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Corrosion on gold plated PCB edge

I have many PCBs (circuit boards) of my design which were fabricated and assembled by another company under contract. I received these boards about three months ago and on inspection (about 10 percent) noticed that some boards had small dark spots on the gold plated edge fingers. Now, three months later, I'm going through the boards an find some of the gold fingers have deteriorated further.

 

I will speak to the manufacturer about this, but as I know almost nothing about metalurgy I would prefer to find an unbiased opinion first. The gold fingers were specified to be 28 micro" gold over nickel (of unknown thickness).

Can anybody tell me what might be happening to the gold plated edge contacts to make them look like these pictures?

John Ermington
Product Designer - Perth, Australia
February 27, 2011

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The purpose of the nickel is to keep the underlying copper from migrating right through the gold and leaving a copper rich corrosion spot on top of the gold. So, first be sure he even laid down some nickel, then find out how thick, then call for 0.0003 inch thick to block the copper from migrating to the top and the corroding. Then check on the purity of the gold deposit.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

March 1, 2011

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March 2, 2011

Dear John,
It seems the issue is related to porosity and this is a vast subject. care should be taken from base preparation to thickness of plating of different layers of plating.
An audit in your vendors place in the presence of plating chemistry supplier may help.
p.s. Gold is very costly - now-a-days!
Regards

T.K. Mohan
plating process supplier - Mumbai, India