What is the cooling rate of the grainy looking joints? Dull solder joints  
was reported in the early days of vapor phase soldering, until Mather &  Hagge 
of Rockwell Collins found that it was an artifact of slow cooling of the  
joints which altered the grain structure of the solder joints. Accelerating the  
cooling rate solved the problem. Details can be found in their paper:
"Kinetics of Intermetallic Compound Formation and of Base Metal Dissolution  
into Molten Solder During Vapor Phase Soldering", John C. Mather and John K.  
Hagge, Collins Telecom Products Div'n., Cedar Rapids. 
 
Perhaps Doug Pauls, Dave Hillman or Roy Keen would have a publication  
citation where the paper can be found. I just have a photocopy of it.  

Bill  Kenyon
Global Centre Consulting
3336 Birmingham Drive
Fort Collins, CO  80526
Tel: 970.207.9586   Cell:  970.980.6373

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