Yannick,

I would advise that you go back to the OEM who designed the board to ask
them to have a requirement for "plugged" vias for those holes. It will
entail, typically, that they issue a mask layer with apertures for the
plug  for  those specific holes, and add a note to the print indicating
that there are plugged vias from Side 2 using mask artwork supplied. The
plug is not the same as "filling"  - to totally fill the hole with
material is more difficult and more expensive (although technically
available). The least costly way out is with plugging with non-LPI
soldermask material from the back side of the via. There is one caveat: if
the board has an OSP for a surface finish it is not compatible with the
via plug process. In that case the vias will need to be filled with
material ... which gets into a larger discussion about how best to effect
that.

Good luck,

Valerie

ps: IPC is working on a complete guide (discussion, terms, guidance, etc.)
for the ways through holes can be "protected" (filled, capped, plugged
etc) but while it is close I don't think it is quite ready; you might want
to make yourself a note to check on it periodically.

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