1- Do people put a lot of vias under BGAs to perform ICT or do they just
perform functional tests ?

We ICT all of out assemblies from the solder side, so we fan out test points
for the BGAs (and for all test nodes, for that matter).

2- How do you guys inspect your BGA solder joints once on the card ?  Are
X-ray practical and reliable in a production mode ?  What about Scanning
Acoustic Microscopy (like a system from Sonoscan) ?

We do a courtesy x-ray on the BGAs to look for bridges, since that's the only
thing you'd probably see.  As was previously stated, you need good process
control to ensure an acceptable assembly.  We rely on ICT for added insurance.

3- And what about repairs ?  Are they easily done with a high success rate ?

Repairs?  Who does that?  Repairs aren't that difficult, once you've selected
the proper equipment and done your process development (so I've heard).  We
even went ahead and developed a re-balling process so we could re-use more
expensive BGAs.

Jim Marsico
AIL Systems, Inc.

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