I've got a conundrum wrapped in riddle inside an enigma.

We are planning to make an bondwire interconnection from a microwave RF
board that is copper/nickel gold plated to an epoxy PCB
that is copper/ immersion silver plated using 1 mil aluminum wire.   Our
plan is to silver epoxy a bimetallic copper/aluminum tab onto the microwave
RF board so that the aluminum faces up.  Then we plan to solder another
bimetallic copper/aluminum tab onto the
epoxy PCB by reflowing with solder paste, again, leaving the aluminum side
up.   Now we have aluminum pads on both boards that we can aluminum wire
bond.

 My concern is whether the all the dissimilar metals are a galvanic cell
waiting to happen!  I should mention that the end assembly is mounted in a
cast housing, which although leak tested, does not have either a hermetic
seal or an inert atmosphere.
The product will be located outdoors and must last 10 years.

Has anyone had past successes using a similar technique that they'd care to
share?

Thanks in advance.

Ron VandenDolder
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