Hi David,
Macro-voids [micro-voids is a different story, however] as a whole do not 
increase the threat to reliability—this has been shown both with analysis and 
testing. This is true for voids caused by gaseous inclusion or for shrinkage 
voids [shrinkage voids existed long before LF-solders, but were rarely observed 
because nobody was looking for them and they were all internal]. Indeed, in 
ductile materials, voids have ablunting effect on crack propagation. however, the 
effect is highly localized because of the 3D-goemetry of the SJs and has no 
significant impact on SJ reliability.
Most of what is now called 'shrinkage voids' are more properly called 
'shrinkage fissures' or 'hot tearing', and even 'fillet liftying,' 'pad lifting' and 
'fillet cracking' are related.
There may indeed be special circumstances, where there is a possible 
reliability impact, but I have not seen one as yet.

Werner



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