A lot of it is based on common sense.  If the hole walls are bare copper and
you want to protect that bare copper from both board fab and assembly
chemicals, you need to completely plug or cover the via.  LPI can flow into the via,
but there is no guarantee that there will be a complete plug or even coverage
of the entire hole wall.

If the hole walls are an inert finish such as ENIG, then protecting them is
not the most important aspect of via protection.  You would then have to
consider what you are wanting to do and if an incomplete plug would suffice.

Susan Mansilla

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