A system and method for assembling dual-die integrated circuit packages using thermocompression bonding or thermosonic bonding to bond a second die to a substrate opposite a first die bonded to the substrate. The second die is bonded using heat conducted through the first die to the substrate, and optionally through an underfill material. The first and second die are connected such that bumps are connected to common bonding pads on the substrate. Bumps on one of the die extend through openings in the substrate to connect to the common bonding pads. The bonding pads are within the perimeter of the first die.