Adam -

Alkaline etchant is used with tin plating all the time.  Acid etchants are
based on sulfate or chloride chemistry - peroxide sulfuric, persulfate,
cupric chloride, and ferric chloride.  All attack tin - makes sense when you
think that you plate tin from sulfate or chloride baths - that's what
dissolves the anodes so you can plate.

Couple of advantages of stripping tin for all copper circuitry -

- Your assembly process might be hot enough to relow tin (watch out for
temperature sensitive components) and cause the mask to wrinkle over the
molten tin

- Copper circuitry can be treated with oxide or one of the new "adhesion
promoters" for extra strong mask adhesion when plating harsh final finishes
such as ENIG  or immersion tin.  In fact, you must strip the tin to get to
any of these other final finishes

Denny Fritz
MacDermid, Inc

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