I have also observed "selective non-plating" on substrates (both ceramic
and flex) when using electroless processes where two pads that are
electrically connected do not plate.

I have had suspicions that it may be due to some sort of galvanic couple. 
When one pad does not plate (due to contamination, oxidation or whatever),
the pad that is electrically connected also does not plate.  Perhaps the
fact that one pad does not plate somehow changes the potential for
everything electrically connected to it.  

Is this theory way out in left field?

Dave Anderson
Medtronic, Inc.

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