Given the pitch of the BGA is so fine (0.35mm or 13.8mil), how the heck are traces routed out from this part? I assume microvias are used but what size drill hole and pad size are needed and who can manufacture such small diameters?
Further, the downloadable footprints under "Symbols and footprints" at www.analog.com/en/products/adau1787.html define footprints that are larger than specified on the last page of the data sheet for the adau1787. The data sheet shows 0.24mm [9.4mil] (0.2mm to 0.28mm worst case) balls yet the downloadable footprint has pads that are 0.3mm (11.8mil) in size. This makes the area in between the pads only 0.19mm (7.5mil) in diameter which means the via needs to be smaller than that in order to not short with the adjacent pads.
So what size drill hole and what size annular ring are needed and can be manufactured in order to fit in between the pads?
This size of BGA requires vias-in-pads to get the signals to and from the internal pads. Consult the evaluation board user guide for fabrication details. It is in there now and there will be an update to it in the near future to add a few more details.