INSITU CALIBRATION OF STRESS CHIPS

Growing use of stress chips as a tool to address reliability concerns in encapsulated integrated circuits (IC's) necessitated the need for an accurate calibration procedure to properly interpret gauge readings. A special test chip having several silicon diffused piezoresistive strain gauges was used to demonstrate a new in situ calibration procedure for the gauges. It is based on the use of a high sensitivity strain measuring technique called Moiré Interferometry to monitor mechanical strains at the same locations where the gauges are, thus providing a direct correlation between measured resistance changes of the gauges and actual strains. Many of the limitations and drawbacks of the currently employed calibration techniques have been eliminated by this new approach which proved to be direct, simple, and highly reliable. Moreover, it is applicable to new as well as existing stress chips. © 1990 IEEE