The Navy did a surface mount repair study in June 1987.    The conclusion of 
this study is that the "long term reliability of a solder joint will be 
jeopardized with multiple rework cycles. With copper dissolving away during 
thermal processing, the pads will inherently lose their structural 
compliancy.  The copper goes into solution forming brittle compounds such as 
Cu6Sn6.  These brittle intermetallic layers may cause long-term solder joint 
fatiguing problems."  They state that on 2 oz copper  100% of the pad would 
dissolve in 12 cycles.

 My question does anybody know of any recent studies that would support or 
counter this study.  Do other companies limit the number of heat cycle on a 
pad?



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