Look VERY closely around the pins on the "Solder Side" of the board. You are looking for any (almost microscopic) gap between the pins and the solder on them.

ALSO, any pin that is completely covered over with solder can be fractured under the solder (I am referring to a pin that is short and doesn't stick up far enough to be above the level of the flowed solder). What this means is that you must flow solder well on any such pin to be sure it has not failed.