Package-on-package structures

Embodiments of the present disclosure provide a first package configured to be coupled to a second package, wherein the first package comprises: a ball grid array substrate; a die coupled to the ball grid array substrate; two rows of ball pads arranged around a periphery of the ball grid array substrate, wherein the ball pads of the two rows of ball pads are configured to receive solder balls to couple the first package to the second package, wherein an outer row of the two rows of ball pads comprises at least some ball pads configured as a first type of ball pad, wherein an inner row of the two rows of ball pads comprises at least some ball pads configured as a second type of ball pad, wherein the first type of ball pad is different than the second type of ball pad.