Novel Stress Measurement System for Evaluation of Package Induced Stress

Increasing demands on accuracy and reliability of micro-system (MST) devices like inertial and magnetic sensors require to account for the impact of mechanical stress. Stress is induced by the packaging process as well as by package modifications due to the influence of environmental conditions. Micromechanic comb structures are widely used in inertial sensors. Their capacitance is a measure for inertial quantities like acceleration or yaw rate. If this structure is mechanically stressed it will be deflected by rotation and translation with 6 degrees of freedom. For a random choice of deflections we have calculated the capacitance change and achieved a functional description. So we were able to simulate the over all capacitance change of a complete sensing structure. As this change of capacitance directly corresponds to an offset of the sensor signal, the sensing accuracy of the device is reduced. By this evaluation of the impact of stress on the signal offset of inertial sensors we obtained the result that the sensor performance will be significantly decreased by package induced stress.