A package comprises a die stack having at least two stacked dies coupled for contactless communications with each other. At least one of the stacked dies has a substrate joined to its major face. The substrate has a plurality of conductive traces in or on the substrate for conducting power to the dies and for conducting heat from the dies. At least one conductive pillar is joined to at least one of the conductive traces on at least a first edge of the substrate, for conducting power to the at least one die and for conducting heat from the at least one die.