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.
The packaging process, being developed to satisfy the foregoing requirements, is a highly modified flip-chip process that involves a novel extension of conventional packaging techniques.
The figure presents a simplified cross section of the finished instrument package adhesively bonded to a surface exposed to the flow to be measured, showing the battery and a few of the chips connected to the cover substrate. Note that the overall thickness of the package plus the adhesive is 130 µm, and could be reduced to less than the maximum allowable thickness of 127 µm by thinning the adhesive layer to 22 µm or less.
This work was done by Daniel A. Pruzan of Nielsen Engineering &Research for Lewis Research Center. Inquiries concerning rights for the commercial use of this invention should be addressed to
NASA Lewis Research Center, Commercial Technology Office, Attn: Tech Brief Patent Status, Mail Stop 7-3, 21000 Brookpark Road, Cleveland, Ohio 44135
Refer to LEW-16545.