Hi Bev - in theory, a shrinkage void in a solderball is the same physics 
as a shrinkage void in a aluminum or steel casting so no, the shrinkage 
void  would not have to necessarily always reach a surface. However, after 
looking at several hundred SAC BGA/CSP cross-sections, I have nearly 
always (99.999%)  found a path of a shrinkage void to the solderball 
surface. Because we have a very limited and very small molten solder 
"volume", I think you will find a surface connection.  And I guess I'll 
bite - why the question?

Dave Hillman
Rockwell Collins
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Bev Christian <[log in to unmask]> 
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[TN] SAC Shrinkage Voids in BGA Balls






TechNetters,
Do all SAC shrinkage voids in BGA balls reach/start at the surface of
the ball?  I realize I may be stumped by a 2D cross-section of a 3D
phenomenon, but I thought I would ask this august body.
Bev
RIM

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