Open vias in pads are not an industry-accepted practice. In a perfect world, we'd like to never see
one. However, the real-world is saying otherwise. Manufacturers of QFN parts are starting to
recommend vias in the heat-slug pad for improved thermal conductivity. High frequency designs
benefit from the shortest possible routing, which may indicate via in pad. Super fine pitch BGAs
may not leave any other options.
Our first recommendation would be to re-design the boards so the vias are in between the pads,
plug or cap the vias at the board house or to use microvias that don't go all the way through the
board. If you can't do any of that, we would suggest that you use as small a diameter as the design
will allow and follow the component manufacturer's guidelines for placement and via capping or
filling.
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small a diameter as the design
will allow

Напомнить, какие дырки могут делать на западе, и сколько такое удовольствие обойдется у нас?