John:

Whether the Tin is 15 or 50 millionths thick, and whether it has another part
of the deposit that impedes intermetallic formation, there comes a time when
the deposit is all intermetalic, and no more pure Tin, and when that occurs
you will get dewetting.

This is the big drawback to immersion Tin, it has a limited shelf life.

You can get different deposit thicknesses depending on temperature of
application, and whether or not you have certain ingredients in the Tin bath,
which promote corrosion of the Copper.  When the Copper is corroded, the
surface is roughened, and the Tin thickness is increased.

Rudy Sedlak
RD Chemical Company

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