I am observing a variation in the color of gold immersion finished boards. My theory is the gold finish is being contaminated by subsequent cleaning processes prior to assembly.

Does anyone have any experience with copper contamination of immersion gold? I know that nickel is used as a barrier between the copper SMT pad and the gold finish. Without the Nickel barrier the copper would migrate into the gold creating an unsolderable finish. So there is a chemical reaction possible between copper and gold.

So what if the gold immersion finish is subjected to subsequent processes in the fabrication facility that have copper in solution. Is the copper attracted to the gold surface out of solution? Can the concentration of copper in solution be so high as to make the gold finish unsolderable? Is there an acceptable limit of copper contamination in an immersion gold finish from an assemblers solderability viewpoint? 

Doug Smith
Technical Support Engineer
Yamamoto Mfg. (USA), Inc.

(408)944-8308
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