The Aducm350 datasheet specifies a ball diameter of (0.25 | 0.30 | 0.35 )mm and the recommended footprint available for download has 0.305mm pad (copper, solder, paste all the same). Typically I've seen a pad size of ~80% of the nominal ball diameter used and believe non-soldermask defined is preferred. Is there a reason for such a large pad and no solder mask expansion?
My current design uses the below sizes for a slightly smaller pad and some solder mask expansion to make the pads non-solder mask defined. Is there any concern with this?
Pad = 0.26mm
Solder paste = 0.26mm
Solder mask = 0.36mm (0.05mm expansion)