Glenn-

Hadco (Watsonville CA) recently talked us into 30 microinches Au, vs.
our original 50 microinch callout, on BT laminate. We established that
reliable Au wire wedge bonds could be made at 30, before we approved the
order. We're now thinking that we could make good wire bonds to
something less than 30, but we haven't tried. Maybe Hadco (or someone
else) can recommend minimum Au plating for Au wire bonding AND
(eutectic) soldering.

-Michael Alderete


You wrote...
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Date:    Wed, 30 Sep 1998 10:31:54 PDT
From:    glenn pelkey <[log in to unmask]>
Subject: Fab:  Multiple surface finishes

Hello all,

     I'm looking for information on how to build a board with both soft
gold and solder as outer layer surface finishes.  We want to make sure
it is manufacturable before designing it.  The only thing I have now are
examples with edge connectors.  The gold and solder would be at select
locations throughout the board.

     In case you're wondering why, I'll tell you.  We want to increase
the gold thickness to greater than 70 microinches for wire bonding.
But, this product also has screened solder for SMT.  Since sceening
limits the amount of solder, gold embrittlement becomes an issue.  I
calculated 3.7% of gold by weight at 70 microinches.  I know opinions
vary here, but I think everyone can agree that this is at least a
concern.

      What do you think?  How hard is this to do?  Contamination,
increased cost, other reliabilty or quality issues to trade off?

Thanks for all your help.

Glenn Pelkey
Maxtek Components Corp.
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