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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