Hi Genny,
The real problem is not solder joint reliability at all, but the reliability 
threat posed by the through vias in the PCB. Depending on the details, each 
excursion to soldering temperatures consumes about 3 to 6% of the fatigue life 
of the vias, starting with HASL. The higher percentage consumptions apply to 
LF-soldering. Thus, 1 HASL+2 reflow+3 repair/rework can cost you between 18 and 
36% of the life of the vias--and this is assuming good quality vias. But even 
this much accumulated fatigue damage is not a real issue--assuming of course, 
that failure did not occur during any of these solder excursions--unless the 
operating environment produced cyclic delta-T's in excess of 35°C.

Regards,
Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL 32174 USA
Phone: 386-437-8747, Fax: 386-437-8737, Cell: 386-316-5904
E-mail: [log in to unmask], Website: www.engelmaier.com

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