In a message dated 4/17/2007 8:33:13 AM Pacific Daylight Time,  
[log in to unmask] writes:

The  improved reliability should not have come as a surprise. Consider what 
is  
happening: 
(1) the solder balls are at their full diameter when BGA is  placed,
(2) the epoxy fixes the distance between PCB and BGA at that  diameter value,
(3) during reflow, the epoxy expands opening the solder gap  further,
(4) on cooling, that solder balls are prevented by the epoxy from  collapsing,
(5) you have the equivalent reliability of using non-melting  10Sn90 Pb 
solder 
balls,
and (6) this results in the reliability  improvement observed.
I have been pushing this for   ceramic  chipp components for some time.





Very crisp summary, Werner. Thanks
 
All the best, 
Joe 



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