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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