Mail*Link(r) SMTP               FWD>RE>ASSY: tinning of components

Darrell

You do want to use a high Pb coating to preserve solderability, the killer is
the Sn, in particular on Cu containing component leads.

One of our empolyees was doing graduate work and UC Berkeley, she did a paper
summarizing some of their work at Surface Mount International, San Jose, CA,
Aug 25-29, 1991.  The paper is on page 751 in Volume II of the proceedings and
was titled "Pre-Tinning and Flux Considerations on the Reliability of Solder
Surface", By Dr. Ann J Sunwoo, LLNL; Professor J. W. Morris, LBNL & UC
Berkeley; and G. K. Lucey, Henry Diamond Laboratories.  They used 170 degrees
C for 6 days for their thermal aging environment, the results may be useful to
you.

Ralph Hersey
email:  [log in to unmask]

--------------------------------------
Date: 4/3/96 9:29 AM
From: [log in to unmask]

     
     In soldering with lead-based solders (i.e. HMP, >90%Pb) is it 
     essential to pretin the components lead with a high Pb alloy for 
     component leads that are Sn85/Pb15 or Sn80/Pb20 plated, Sn60/Pb40 or 
     Sn63/Pb37 coated, and what about gold-plated? 
     
     What are the pro's/con's of not pretinning, undestanding the 
     propensity of leads (Pb) and tins (Sn) to lower the melting 
     points..How much I am not sure ! Is there a distinct advantage OF 
     pretinning with Pb ?
     
     One other note, the storage temps will be greater than 190degC.
     
     Thanks
     Darrell


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Subject: ASSY: tinning of components
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