Characterization of Packaging Stress with a Capacitive Stress Sensor Array

This paper presents a high-resolution capacitive stress sensor array to precisely characterize the distributed MEMS packaging stress, for the first time. The unit stress measurement cell utilizes a bridge-type mechanical amplifier that converts the substrate strain into capacitance variations. We have measured and compared the MEMS die stress over temperature for different die attaches with a custom designed PCB housing an on-chip heater. The proposed approach significantly simplifies the evaluation and selection of packaging materials. Comparing the temperature responses of a soft silicone-based and stiffer silver-filled epoxy reveals difficult to predict results.