At our shop we do a secondary via hole plug after HAL
process.   This allows us to solder coat the barrel of the via
holes,  which makes for a more reliable surface than just
bare copper & a much higher percentage of the via holes get
plugged.   Also we have noted that when there is a Via hole
test point  on one side of the PWB and the opposite side is
to be flooded with mask,  there is a possibility of the mask
being exposed up to the test point side which then causes
problems for elec.  testing,  this becomes a non-issue when
plugging after HAL.   We have done (and still do for a few
customers)   a via hole flooding from both sides of the board
prior to HAL but we found via holes with entrapped liquids
would blow out at the thermal cure operation.    If you have
any further questions  let me know.

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