Packaged microelectronic assemblies, such as memory chips and microprocessor chips, typically include a microelectronic substrate die encased in a plastic, ceramic or metal protective covering. The die includes functional devices, such as memory cells, processor circuits, and interconnecting circuitry. The die also typically includes bond pads electrically coupled to the functional devices. The bond pads are coupled to pins or other types of terminals that extend outside the protective covering for connecting to buses, circuits and/or other microelectronic assemblies.
Conventional microelectronic assemblies are typically mounted on a circuit board or other support device that is incorporated into a computer, mobile phone or other larger electronic product. One drawback with this arrangement is that the packaged microelectronic assemblies can extend a substantial distance away from the surface of the circuit board. Accordingly, it may be difficult to fit the circuit board and the attached microelectronic assemblies into the housing of a compact, low profile electronic product.
One approach to address this problem is to reduce the thickness of the packaged microelectronic assembly by reducing the thickness of the die within the package. For example, in one conventional arrangement, the functional features of the die are formed on or proximate to one surface of a substrate wafer. After forming these features, the opposite surface of the wafer is ground down ("backgrinding") by chemical-mechanical planarization ("CMP") or other techniques to reduce the overall thickness of the wafer. The wafer is then placed on an adhesive film and cut or singulated to form individual dies. The adhesive film is stretched to separate adjacent dies from each other and a suction cup removes the singulated dies from the adhesive film. The singulated dies are then encapsulated in the protective covering to form a packaged die having a reduced thickness.
One drawback with the backgrinding approach is that the amount of material that can be removed from the wafer by this process is limited because the wafer must remain sturdy enough to withstand the stresses applied to the wafer during the backgrinding process and other subsequent steps, such as transporting the wafer, mounting the wafer to the adhesive film and cutting the wafer. For example, the conventional techniques known by the inventors for reducing the thickness of the die typically cannot produce wafers less than about 150 microns thick without causing an unacceptable increase in the number of broken or damaged wafers and/or dies.