We are experiencing the common mechanical stress induced BGA corner 
cracking in our assembly plant.  I have identified a number of potential 
corroctive actions, but I can't realistically expect the problem to be 
eliminated.  What I am being asked to provide in order to allow the product to 
be released is reliability projections for the BGAs.

We have experienced <5% failure rate due to fully fractured joints.  What we 
can't determine is how many partially fractured joints are being created, and 
what may progress in these joints in use.

The product will not see severe environmental conditions, as they are used in 
indoor retail locations.  Do I need to be worried about potential corrosion in 
partially fractured joints?  Should I be concerned about partial fractures 
continuing to grow until they create an open joint?

Cross section SEM and EDX testing shows that the joints (Hi-P ENiG and SAC) 
are very good, IMCs are formed, <10% P.

I'm not finding too many studies on long term reliabliity assessment, and I 
don't know that I will be able to convince anyone to do regular cross sectional 
analysis.  But they're going to want my yea/nay on continuing production.

Thanks,

Pete

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