Thanks, we would like indeed to fill the vias with solder instead of epoxy, but we presume this is more expensive?
The “lattice” I described was put forward by our PCB manufacturer.
We used to just have a few 0.3mm thermal vias in the pad (16), and not plated over, but we found that solder would leak through the vias during reflow and make bumpy, often sharp protrusions on the bottom side of the PCB, which is a very bad situation, so we don’t want to do that any more.
So basically, we don’t see how we can fill the vias with solder without the solder protruding out of the bottom side.