Thermal via in pads

I have a IC with a large contact pad underneath it. The IC will consume a lot of power during operation, so it's highly desirable to increase the PCB area to accommodate it. I plan to use thermal vias in its center contact pad to connect to the ground plane underneath.

I also plan to use a PCBA service to solder the IC to the board.

Are there any recommendations for the geometry of the thermal vias or other considerations?