Thermal Relief Via Covering

Hi!

I'd like to add thermal relief vias to a QFN thermal pad, but since epoxy/copper filling is expensive, I want to ask if it is possible to use tented vias instead. To make sure the vias are covered, I left some clearance in the solder resist layer around them (see below).

Also, solder paste covering of the exposed pad surface is around 50% to prevent liftoff of the package during reflow.

Please advise me, is this a good idea? Thanks!