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Strange corrosion products on gold coated copper

I have Cu conductors coated with Au to protect them from corrosion. During processing, the circuit is subject to numerous ionic contaminants, most notably K. In humid environments, a crystallite growth appears in some locations along the side of the Cu/Au conductors. Given the .35 V difference on the Anodic index, am I witnessing galvanic corrosion? The growth is more pronounced when the circuit is electrically biased. How about salt precipitation? EDS analysis shows K, Cu, O and other trace contaminants.

Peter Ladwig
electronics mfgr - Hutchinson, Minnesota, USA
2003

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The gold needs to be thick enough to be non-porous (can be tested with nitric acid). If it is, and if the temperature is low enough that the copper and gold are not interdiffusing, and if there is no bias that is de-plating the gold, I don't see why you should be detecting any copper. So, electrically biased in which direction and with respect to what, Peter?

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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2003

The conductors have a positive bias with respect to a stainless steel substrate (separated by a polymer dielectric). The gold coating is uniform except for a small crack which may exist at the base (the conductor/polymer interface). Here, some copper may indeed be exposed.

Peter Ladwig
- Hutchinson, Minnesota, USA
2003

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