The SMD and NSMD solder pads are usually associated with ICs footprints especially for BGA
SMD(Solder mask Defined ) pads have the solder mask covering or overlapping a bit of the Solder pad . ie the solder will not wet the entire solder pad .
NSMD(Non Solder mask Defined ) pads will have a small gap between the solder pad and the solder mask . Solder can wet the entire pad and also flow and fill the edges of the Solder pad
This gives better connectivity and more solder area. Hence this is the most recommended pad configuration.
