I need more then 6 IO pins for my application with the WLCSP footprint. Since micro vias, i.e. 0.1mm Φ, are expensive here, is it possible to use normal vias （0.2 mmΦ）in the WLCSP empty area as shown in this figure?
Placing vias at the left open places is a little bit risky. We left those positions open by purpose, because RF inductors are placed at this position on the die. So, strongly recommend you to NOT use either micro vias or normal vias in those positions.
Ok. Thank you for reminding me.