I have a question concerning plugged via holes under BGA components.
During the SMT process of assembling a PCB I noticed clogged or plugged
vias. I assumed it may have been from improper cleaning of misprinted PCBs.
Upon further investigation I verified 98% of the bare PCBs had plugged vias.
I am currently placing two BGA components ( 272, and 350 ball count,
parameter array). In the case of all the PCBs the plugged vias are under
both BGA components.
        I am concerned that not all the plugged vias are plated on the top
or bottom of the PCBs. None are masked vias. I am concerned during the wave
solder process I may have some trapped flux in a via that is not completely
plugged resulting in outgasing and possible micro explosions under the BGA
components.
        I contacted the PCB vender and was informed that plugged vias were
industry standard and acceptable. Now to my question, it maybe acceptable
for plugged vias on a PCB but what about under BGA components? Is there any
information that addresses this issue? If so where can I find it?

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