First, a 12 layer board .062" thick? Don't think so if it's a serious board
requiring hole to pad registration and no breakout, etc. What are you
specifying for preg/core - 80% resin content with no glass? 10 layer boards
enjoy this privelage - not 12's without serious yield problems.

The silver fill stuff is touted by some like Sanmina/Hadco but often for
capped vias that you might consider only when using sequential lamination.
This ensures micro vias or others be plated over the hole forming a flat
surface on the BGA pads. It's sort of like having vias in pads without
knowing it. You know the drill.

Everyone, since 1980 has had this goal in mind and many of us did it then
as now. You must assess supplier process capabilities and your design
objectives, together with a cost picture, to make the right decision. The
whole concept is admirable but compromises can cost a bundle.

Earl Moon

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