Dynamic response of a plastic encapsulated high-g MEMS accelerometer

Abstract

A high-g MEMS accelerometer with double cantilever beams is sandwiched between a glass substrate and a protective cap using wafer level packaging technology, and then die attached and encapsulated in a Kovar header. Encapsulation is a key step to ensure the reliability of high-g MEMS accelerometer. There are currently few detailed reports on the encapsulation of high-g MEMS accelerometers. In this work, the dynamic response of the package structure under high-g shock acceleration is simulated using finite element method. By applying a 50 /spl mu/s half-sine pulse of acceleration with 100,000 g's peak (1 g = 9.8 m/s/sup 2/), results show that the effect of modulus of encapsulant on the output voltage and beam deflection can be ignored. The peak value of output voltage was close to the analytic solution, also for the equivalent stress at the root of beam. The cantilever beams of accelerometer still behave as damped free vibration, but the peak values of output voltage and beam deflection show well linearity with the peak acceleration applied. Encapsulant with elastic modulus > 4 GPa is rigid enough to encapsulate the chip.