Using Through Vias on a 0.4mm BGA
It is quite possible to use through vias with via-pad design on a 0.4mm BGA. These vias are silver filled to provide a flat finish. The via size used in this instance is a 4 mil drill with a 7.5 mil pad and 12.7 mil anti-pad. The only limiting factor in this scenario is the maximum thickness of the board. With a 4-mil drill, most fab shops can only produce up to a 0.062" thick board. The layer count of the board used as an example shown here:
Fan-out of a 0.4mm BGA shown here using through vias. Vias which are placed directly on the BGA pad, are called silver-filled vias.