Hi Bill and Mike!
     
     Let me describe two conditions and then you will have to decide which 
     you have:
     
     1) a "disturbed" solder joint: a solder joint that has an "angular, 
     faceted" appearance that is caused by the solder joint being moved as 
     it solidified.
     
     2) a "grainy" solder joint: a solder joint that has a rough, gritty 
     appearance that is caused by the solder microstructure giving the 
     solder joint surface relief.
     
     I am an advocate of NOT using visual appearance to define what a good 
     and bad solder joint looks like - the number of hours spent by the 
     specification community trying to define what a "disturbed or grainy" 
     solder joint is would/should make all of us disturbed! But if you 
     think you have a 'disturbed' situation go looking for equipment or 
     fixture causes for the movement. If you have a 'grainy' situation you 
     have two options: try to find a way to cool the solder joint faster 
     and/or not get it so hot in the first place so that the solder joint 
     microstructure is finer thus not giving you little solder joint 
     surface relief or use some cross section analysis to prove that the 
     'graininess' is not a reliability issue. We did some extensive work in 
     the 80's showing that a 'grainy' solder joint is not a bad solder 
     joint - only different, reflecting some process or design parameter 
     influence. 
     
     Good luck.
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: ASSY:Grainy wave solder joints
Author:  [log in to unmask] at ccmgw1
Date:    3/18/97 4:27 PM


     
We are currently experiencing random grainular solder joints on double 
sided rigid PWB assemblies after wave solder. Our wave solder machine is an 
Electrovert Econopak 229, and we are using Alpha 615-25 (RMA-type) flux 
with Sn6337 solder per QQ-S-571. The PWB is GHN type per Mil-P-13949/5 with 
"C" type copper, and solder coated, with a dry film soldermask. We have 
made many process adjustments, including speed, top-side board temperature, 
wave bath temperature, etc. We have very recently verified that solder 
purity is within specifications. The graininess we are seeing in the solder 
joint (including the fillet area) is randomly distributed, and in some 
cases located one pad from a perfect solder joint. There is no consistent 
pattern from board to board. Can anyone offer some advice?
     
Bill Bromley/Mike Polifrone
Lucas Aerospace PSA
777 Lena Dr.
Aurora OH 44202 USA
voice: 216-995-1000 ex 7036
email: [log in to unmask]
     
     
     
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