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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