Steve:

Presume you mean stripping resist from Tin/Lead plated boards using Caustic
Soda.

Tin/Lead is about the only thing you can strip well using caustic, other than
innerlayers, as the Tin is so readily attacked using Caustic.  However, when
the Caustic gets to the Lead it stops, so you get a buildup of Tin in the
Caustic, which then can immersion plate on to the exposed Copper.

Caustic is the slowest, worst stripper for photoresist that you can use, and
if you overplate at all, it becomes a near miracle that you can strip the
photoresist cleanly enough to etch properly.

All around, there is a good reason why most shops in the US strip outers
using proprietary strippers, and I suspect you are more familiar with these
reasons than most people.  There has been some movement in the direction of
making additives for Caustic to assist in alleviating some of these issues,
and with Tin/Lead, they turn it into a manageable situation.

Are there any more specific questions that we can answer?

Rudy Sedlak
RD Chemical Company

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