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From [log in to unmask] Mon Sep 23 17: |
46:02 1996 |
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Hi Randy-
As for a solderability test try using one of the methods in ANSIJ-STD-002
Solderability tests for components. The dip and look test (method A) would give
you a good gauge of solderability. I would also print some paste on a
nonwettable surface (ie.teflon or ceramic), place the TSOP in the pattern and
run it through reflow to see how the leads wet (this is the proposed surface
mount use test in 002 draft 2, rev B) . You mention that the finish "flakes" off
of the leads rather than scratching - it sounds like you have a contaminated
alloy 42 surface. No metallurgical bond was formed between the solder finish and
the alloy 42 surface. If this is true you will need an aggressive flux chemistry
to remove the oxides on the alloy 42 surface to allow solder to wet. Good luck.
Dave Hillman
Rockwell Collins
[log in to unmask]
______________________________ Reply Separator _________________________________
Subject: ASSY: Solderability problems with Intel 28F004 TSOPs
Author: [log in to unmask] at ccmgw1
Date: 9/20/96 5:50 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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