Packaged microelectronic assemblies, such as memory chips and microprocessor chips, typically include a microelectronic die mounted to a substrate and encased in a plastic protective covering.  The die includes functional features, such as memory cells, processor circuits, and interconnecting circuitry.  The die also typically includes bond pads electrically coupled to the functional features.  The bond pads are electrically connected to pins or other types of terminals that extend outside the protective covering for connecting the die to busses, circuits, or other microelectronic assemblies.  In one conventional arrangement, the die is mounted (e.g., face up or face down) to a supporting substrate (e.g., a printed circuit board), and the die bond pads are electrically coupled to corresponding bond pads of the substrate with wire bonds or metal bumps (e.g., solder balls or other suitable connections).  After encapsulation, additional metal bumps can electrically connect the substrate to one or more external devices.  Accordingly, the substrate supports the die and provides an electrical link between the die and the external devices. 
Die manufacturers have come under increasing pressure to reduce the volume occupied by the dies and yet increase the capacity of the resulting encapsulated assemblies.  To meet these demands, die manufacturers often stack multiple dies on top of each other to increase the capacity or performance of the device within the limited surface area on the circuit board or other element to which the dies are mounted.