In a message dated 98-07-05 03:46:42 EDT, you write:

<<
 I am a PCB fabricator in the UK and when we started using the electroless
 Nickel and Immersion Gold process we noticed a curious phenomenon. If the
 panels are immersed in DI water or mains water after processing, then
 exposed to air for a minute or two before drying, the gold has reddish brown
 stains in random areas. Although this did not seem to affect solderability
 to any noticeable extent, it was not cosmetically attractive.

I would like to have an explanation for this mechanism. The immersion gold
 is 0.15 microns max (6 millionths of an inch) over 4 microns (0.00016") of
 electroless nickel. As this occurs with DI or mains water, contamination of
 the water does not seem to be a factor, but simply exposure to air at room
 temperature when the surface is wet. >>


Paul:

Given the thiness of the EN (and Au), I would bet the problem is likely one of
porosity, and having some exposed Copper here and there.  And porosity driven
by our industry's great nemisis, galvanic corrosion, would give you exactly
what you are seeing.

Further, I would bet that thicker EN ( 2-3X) would stop the problem.

Rudy Sedlak
RD Chemical Company

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