Randy,
It sounds like you are definately seeing a soldering ability problem(
won't make fillets on boards using your soldering process). Do you
also see solderability test rejects at incoming?( steam age/r flux/245
C solder temp,etc...). I like to also just do a no steam age
solderability test( r flux, 245C, etc...) as a guage of whether or not
the parts or the process are likely at fault. If you have been using
the TSOP's for a long time with no problem and this is a new issue,
and if the problem is bounded by date codes and has now disappeared,
that would be good to know. Also, if you choose to sample your stock
of TSOP's, be sure to use a sample size that will be big enough to
have a chance to see at least one reject. If your fraction non
conformant solder joints is large, then you can use a smaller sampling
than if you are talking a 1% type defect rate.
Good luck and regards,
Mark Kwoka
Harris Semiconductor
______________________________ Reply Separator _________________________________
Subject: ASSY: Solderability problems with Intel 28F004 TSOPs
Author: [log in to unmask] at smtp
Date: 9/20/96 4:40 PM
We are having a problem soldering Intel 28F004 TSOPs. On some chips, the
solder does not wet the leads properly and has a dull appearance. It
flakes off rather than scratches when probed with a pick and fractures when
temp cycled. The lead material is ALLOY 42 and we know there are issues
with that. Some packages solder OK and survive 10 cycles of a -40 to +100 C
(2 min. ramp) screen, some don't, even with the same date code. We don't
know if what we are seeing is a problem inherent with Alloy 42 or is a
solder coating process problem at the manufacturer or combination of both.
Does anyone have a similar complaint? Intel says no one else is
complaining. Any hints on special fluxes or tests for solderability on the
components would be appreciated. We have seen this problem on 28F004 date
codes between late 1995 and March of 1996 so far.
For those with Alloy 42 questions, a paper published in Soldering and
Surface Mount Technology No. 21, October 95 by W. Englemaier and B. Fuentes
gives results of an investigation into solder strength of devices using
Alloy 42 lead frames. In summary, it was found that at best , strength of
the solder joints was about half that of devices utilizing copper lead
frames. The authors recommended against use of Alloy 42 in plastic SOICs.
Thanks.
Randy Johnson
Reliability Engineer
Woodward Governor Company
Loveland, Colorado
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