good reply -- thanks for the help -- I'm sure he appreciated your input.

______________________________ Reply Separator _________________________________
Subject: Soldering Alloy 42 lead frames
Author:  [log in to unmask] at SMTPpost
Date:    9/23/96 12:11 PM


          To: Randy Johnson
              Woodward Governor Co.
              Loveland Co.
     
             Here at Smiths Industries, Grand Rapids, Mi. we are using 
          Intel TSOPs with Alloy 42 lead frames in a military avionics 
          environment.  Our typical thermal cycle is 5 hours from -55 
          to 95 deg C with 2 hour dwells at the extremes.  Early in 
          the program we found solder joint failures at as few as 28 
          thermal cycles.  Failure analysis directly attributed the 
          failures to the poor solderability of Alloy 42 and lack of 
          coefficient of thermal expansion(CTE) matching between the 
          device and PWB.
             We had Intel come in with their local rep and 2 factory 
          people.  We explained our problem and asked of they would 
          consider using copper lead frames. The response was that 
          their largest TSOP customer was AT&T and that AT&T had been 
          asking for the same change for the same problem.  They went 
          on to say there were no plans at Intel to ever change this 
          device's lead frame material.  (I have noticed that the new 
          suffix 'DD' part has a copper lead frame.)  One of the 
          factory people said we could improve solderability by using 
          a more active flux and higher soldering temperatures.  Being 
          a military product we have been restricted to RMA.
            We solved our CTE problem by adding copper-invar-copper 
          foil layers to the PWB.  We have since successfully 
          completed 500 thermal cycles, which we consider a life test. 
            We continue to have difficulty soldering to the Alloy 42 
          and have had to give extra training to the solder operators 
          and inspectors.
     
            I have spoken with a reliability engineer at Rockwell 
          Collins and was told they had problems with these parts and 
          have prohibited the use of TSOPs.
     
     
          S. Holen
          Packaging Engineer
          Smiths Industries
          email: [log in to unmask]
     
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