To Chris Stack:

The short answer is that the process being discussed is what you describe as
Soldermask over Tin/Nickle, and/or the "Santa Clara Process", although I have
never heard it described as such.  I suspect that it has been dubbed the
"Santa Clara Process" because Bob Mack, of Santa Clara Circuits (now defunct)
had a patent on such a process/finish.

>From a fabricators point of view, the principle problem with the process was
that the Tin Nickle finish tended to accelerate the Copper etching, because
of the galvanic effect, and if it was not compensated for, it caused slivers
of Tin/Nickle to shred from the sides of the traces, and cause shorting.

Tin/Nickle is also notoriously difficult to "activate" once it has gone
passive, and thus suspect that soldering to old boards was a challenge.

Rudy Sedlak
RD Chemical Co.

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