nRF52840-CKAA ground via

[Mike]

Referencing the recommended 52840 PCB layout for the WLCSP package, we noticed two thru-hole vias in the middle of the ground area (in the center of the package). Do these thru-hols vias create problems for the PCB manufacturing (bare board and SMT assembly)? This seems rather unconventional to add a thru-hole via in an array of pads on a 0.35mm pitch? Is this ground via backfilled with an epoxy resin or covered over to create a smooth surface for SMT assembly.

Any guidance or recommendations would be appreciated.

Thank You-

Mike Schell

[ketiljo]

The vias are filled. Else they will wick up the solder from the balls. As long as you are able to sufficiently ground the GND balls, it doesn't matter how you do it. You can use vias in the pads, as you would have to anyway to bring out the inner balls. The GND vias must connect to the ground plane directly. The reference layout used through hole vias because the ground plane is on the bottom side and the micro vias in the pads don't reach that far.

[Mike]

Thank you, that makes sense. We will instruct the PCB shop to fill the through-hole vias to avoid wicking away the solder.