Joe:

Deepest sympathy.  You are fighting a no-win battle.  There really is no
known answer.  As long as electrons can travel from a more active Copper
site, to a less active Gold site, and both touch the same etch solution,
you've got a terribly lopsided etch.

The reason, is that the reaction of the oxidizer, be it Peroxide, or
Persulfate, or Cupric, or???, tends to interfere with, and thus slow down the
metal dissolution.  When you have a gold pad electrically connected to a
Copper surface, the Peroxide/Persulfate reaction occurs all on the Gold pad,
and the Copper surface is free to dissolve unimpeded, and it does!

One wild, and weird way that one customer resolved this issue was to get rid
of microetching.  That involved some serious re-engineering, but it can be
done.

Save eliminating microetch, the only way to resolve this is to cover the Gold
with something non-conductive.  (This sounds expensive)

If you want to discuss, call me, or mail me at work.

Rudy Sedlak
RD Chemical Company
650-962-8004
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