Joe,

The advise from Mike (Fluke) is right on line.  I would add one note.  I have
seen this in the past when there is an exposed pad/via close to the gold tab.
 The soldermask clearance/opening was exposing the trace that lead to the
gold tab.  This trace was always etching "open".  To make matters worse, this
was happening in a final finish after E.T., so the opens were getting to the
customer (ouch!).

The solution was to either get the customer to move the via, or change the
soldermask artwork to decrease the galvanic reaction.

By the way, this was on a SIM card board where there are a lot of tabs and a
lot of vias.

I hope this is helpful.

Scott Griggs
Senior Applications Engineer
RBP Chemical Corp.
MPLS, MN
(612) 825-6113

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