Hi Jerry - The component finish we use is either the Sn63 or Sn60 eutectic
(ok, near eutectic for any really picky metallurgists) alloys. BUT, we have
quite a bit of military products where the components have the alloy
specifically designated so that would "skew" my answer to your question.
The reason you are having trouble with the Sn85 alloy is most likely heavy
surface oxidation and a poor flux reaction to break that oxide down. The
300-800 thickness should eliminate the issue of intermetallic oxidation
unless the IC's are really old. Have you tried a different flux to see if
you get an improved fillet? I am not suggesting that you switch fluxes but
if a different flux creates good fillets than you have an additional data
point that the problem is surface oxidation. Good Luck.

Dave Hillman
Rockwell Collins
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Jerry Cupples <[log in to unmask]> on 11/11/98 05:36:59 PM

Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
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Subject:  [TN] Assy: QFP leadframe tin-lead finish




Hello, TechNet:

Reviewing an IC component specification here, we find the plated finish of
300-800 microinches 85/15 Sn-Pb. Many other spec sheets simply call for an
Sn-Pb finish. The part in question seems to wet poorly, forming very
shallow fillets.

Can anyone confirm the typical fusible tin-lead alloy for QFP leadframes is
more like eutectic composition?


thanks,



Jerry Cupples
Interphase Corporation
Dallas, TX USA
http://www.iphase.com

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