Oh, yeah, about stripping immersion Tin.

You can strip immersion Tin the same way you strip plated Tin, and there are
two basic systems in use, a Nitric/Ferric based system, and a
Peroxide/Bifluoride based system.

The Peroxide Bifluoride based system is "cleaner", in that all the Tin
actually goes into solution, however it is heavily chelated.

The Nitric/Ferric system is slower, and the Tin goes into true solution only
when it is fresh, it then is dispersed as the oxide in the solution.  This
system is sometimes chelated, depending on your vendor.

The Peroxide Biflouride system inherently does not attack the Copper to a
great extent. The Nitric/Ferric system attacks Copper a lot, but usually
contains anti-tarnish type ingredients to minimize that.

If either system were left on the board permenantly, the Peroxide/Biflouride
system probably has less tendency to continue attack.

Rudy Sedlak
RD Chemical Company

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