Hi TechNet!
     
     Dennis - just to add to Hector's comments: if you are using the same 
     solder alloy and only the form changes (solder paste versus  solder 
     preform) then having solder joint problems with only one of the solder 
     "form" choices is an indication that your processing is suspect. 
     Processing could be reflow method, handling, flux, temperatures, etc - 
     all relating to process type variables. Take a look at those things 
     rather than spending lots of time chasing solder alloy questions. Good 
     Luck.
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: General Soldering
Author:  [log in to unmask] at ccmgw1
Date:    5/12/97 9:43 AM


Dennis,
     
What your are getting is more voiding in the solder paste than in the 
solid solder. I would suggest you xray your samples, and assure you 
minimize the voiding.  I think you may find out that the solderpaste is 
much more sensitive process.
     
Hector Valladares
[log in to unmask]
Honeywell Space Systems
813-539-3683
     
Subject: GEN: Soldering Problem
Author:  [log in to unmask] at internet-mail 
Date:    5/12/97 8:49 AM
     
     
I have a customer that states that they solder a silver tab to a solar 
cell 
with Sn95 5Ag and that when thermal cycling the resistance of the joint 
goes 
high.  The resulting voltage drop is unacceptable.  The customer states 
that 
the drop is due to a change in the resistance in the solder joint.  When 
the 
tab is soldered with a preform the problem does not occur.  Only when 
soldered with solder paste.  The thermal cycle is +150 to -170 degrees 
C. 
The problem occurs when cold.  Any suggestions?
     
Thanks to all!!
Denis Meloche
Technical Sales Engineer
Heraeus Cermalloy Division
24 Union Hill Rd
West Conshohocken Pa., 19428
610-825-6050 Fax 610-825-7061
E-Mail [log in to unmask]
     
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