Bill, 
        I have experienced the condition you are describing when we were 
     using similar process materials and equipment. 
        We found RANDOM granular solder joint occurred were there was large 
     thermal mass that resulted in very slow cooling of those joints. Solder 
     joints at heavy voltage or ground planes, buss bars, and components that 
     had large leads, would often result in this condition. 
        We were able to reduce this some by providing additional cooling at the 
     exit of the wave to help cool the assembly quicker and by dropping our 
     processing temperatures a little. 
     
     Dan Botts
     Hughes Training Inc.  
     
     
 ------------------------ INTERNET MAIL ------------------------
From:    "BROMLEY, Bill" <[log in to unmask]> 
Subject: ASSY:Grainy wave solder joints
Date:    Tue, 18 Mar 97 16:05 EST
     
---------------------------------------------------------------------------
     
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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