Hi Bill - I don't think Scott's dull solder joint appearance is due to 
large lead dendrites formed by slow cooling as described by Mather and 
Hagge. The Ag/Pd/PT termination finish can produce some "interesting" 
microstructure phases which could be the root cause of the grainy, dull 
solder joint appearance. Same basic principle but just another 
microstructure phase root cause. Either way, your  recommendation of Scott 
chasing down the thermal history of the solder joints is spot on. I 
actually have the original Mather/Hagge  paper in our Technical Reference 
library! That paper was published at the 6th Annual China Lake Soldering 
Technology Seminar Proceedings in 1982. There is also an excellent 
photograph of a large lead dendrite (due to slow cooling) causing solder 
joint surface roughness in the International Tin Research Institutes 
"Metallurgy of Soldered Joints in Electronics" Publication #708, page 36.

Dave



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Re: [TN] Dull and Grainy Leaded Solder Joints






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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