Good morning!

Bright-eyed and bushy tailed are we?  :)

I have some questions about underfill.
1) I know that voids next to solder balls in underfills for flip chips
are no-nos because the pressure the cured underfill exerts on the solder
balls is enough to actually make them flow into the voids.  My question
is: does this same concern exist for the larger solder balls of BGAs or
do they have enough strength to be resistant to this?  
2) What do people allow for % voiding in underfills?
3) If a component has too many layers for acoustic microscopy to be used
and the underfill has no x-ray retarding character, how in the world
does one determine the amount of voiding in the underfill, short of
prying the part off the board?
4) What is the best course anyone has taken at APEX/SMTAI/ECTC, etc.
that was on underfilling or at least spent quite a bit of time on it?
5) Any particular book people would recommend?

Thanks.

Bev
RIM




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