Good question Jack,
The property that makes it uncorrodable (a very thick-non porous oxide
film) also makes it very difficult to solder.  In the old days we could
use an active acid flux but that is no longer true.  The current non-clean
type of flux would not even penetrate the oxide on a tin-nickel pad and it
would end up non-wetted (not even de-wetted).  Gold, tin, tin-lead,
silver, Pd, etc all solder very nicely, so they need to be put over the
tin-nickel to prevent the oxides from forming.

The other factor is that the plating bath is difficult to control and you
have to watch it to make sure it does not plate stressed.  I once saw the
traces 'jump' off the boards after etching, the tin-nickel was so
stressed.  But like I said, the sail boat metal parts are remarkable!

Happy





"Jack C. Olson" <[log in to unmask]>
05/23/2003 09:32 AM


        To:     TechNet <[log in to unmask]>
        cc:     [log in to unmask]
        Subject:        Re: Sn-Ni PCB plating



Ok, I'm probably showing my ignorance here,
but with a stable non-corrodable finish like
Sn-Ni, why do you need the gold?

Jack (a PCB layout guy)









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