Hi Günter & All,
I am in full agreement with everything Günter said.
There was some work done by chuck Schmidt at SRI, many years back now and not 
openly published to my knowledge, that showed that locally and temporarily a 
voids would retard crack growth. This however, had no effect in the 
reliability if the SJ--the important information here is, that the voids did 
not reduce reliability.
An other issue is solder balls. you definiitely do not want to have voids in 
the balls prior to reflow, because that would give you a lower solder volume. 
However, after reflow voids actually can enhance reliability since for a 
givensolder volume, voids will gove you a larger solder joint height and thus 
lower strains for the same displacement.

Werner Engelmaier
Engelmaier Associates, L.C.
Electronic Packaging, Interconnection and Reliability Consulting
7 Jasmine Run
Ormond Beach, FL  32174  USA
Phone: 904-437-8747, Fax: 904-437-8737
E-mail: [log in to unmask], Website: www.engelmaier.com 

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