A current design in our CAD department has vias inbetween BGA pads.  They want
to tent the vias.  I was thinking
of covering half of the pad of the vias with solder mask to increase the solder
mask wall between a via and solder pad
while still leaving the via open.

Otherwise I have a question concerning via tenting.  I know that the best
situation is to leave the vias open.  I know that you
shouldn't tent only one side to avoid possible entrapment of flux.  I know that
if you tent both sides there is a
chance of blow-out.  What exactly happens to the PCB if there is blow-out and
what is the actual cause of via blowout.
Thank you.

Best Regards,

Mike Forrester
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