Ultrathin Packaging of Multiple Integrated-Circuit Chips

A process being developed for ultrathin packaging of multiple integrated-circuit chips and associated microelectromechanical components makes it possible to fabricate a minimally invasive pressure-measuring instrument to be used in characterizing a boundary-layer flow inside a turbomachine. Such an instrument must be thin enough not to appreciably perturb the flow; according to specifications supplied by NASA researchers, this means that the entire instrument package must be less than 5 mils (127 µm) thick. In comparison, a piece of copy paper is about 4 mils (102 µm) thick. To achieve the needed capabilities for collection, storage, and processing of measurement data, it is necessary to integrate sensor, microcontroller, and memory chips into a single package. In addition to conforming to the stringent specification regarding overall thickness, the packaging is required to provide mechanical and electrical connections for all of the chips and for a rechargeable battery, protect the electronic components on the chips, hermetically seal the battery, expose a pressure-sensor diaphragm while preventing exposure of electronic circuits to the environment, provide means for charging the battery, and enable communication between the microcontroller and external data-processing equipment. Moreover, the thermal limits of the components must not be exceeded during the packaging process.