Just for the record, the reason the semiconductor assemblers have gone to an
Sn85/Pb15 or a Sn90/Pb10 lead finish on PQFPs is because of their trim and
form systems.  The Sn63 alloys are too soft and and the soft metals build up
on the tooling causing major headaches.  The plating operation is done in
strip form with the shorting bar between leads to provide electrical
continuity during the plating operation.  Since the plating must be done
before trim & form, which removes the shorting bar, they have little choice
but to increase the tin content to make the finish (and the tooling)
survive.  If you need a fused leadfinish then I suggest that you solder dip
the components prior to board assembly.  This will not only improve the
solderability of a marginal component but also provide a nice new eutectic
(Sn63/Pb37) finish.  If you don't need a "fused" finish then just test the
solderability of the components.  If its lousy then send them back to the
manufacturer and tell them to get their act together.

Hope this helps

Russ Winslow
Six Sigma
(We specialize in lead finish)

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