Accurate assessment of packaging stress effects on MEMS sensors by measurement and sensor-package interaction Simulations

n this paper, packaging-induced stress effects are assessed for microelectromechanical systems (MEMS) sensors. A packaged MEMS sensor may experience output signal shift (offset) due to the thermomechanical stresses induced by the plastic packaging assembly processes and external loads applied during subsequent use in the field. Modeling and simulation to minimize the stress-induced offset shift are essential for high-precision accelerometers, gyroscopes, and many other MEMS devices. Improvement of plastic package modeling accuracy is accomplished by correlating finite-element analysis package models using measured material properties and package warpage. Using a refined reduced-order MEMS sensor and package interaction model, device offset is simulated, optimized, and compared with data collected from a unique three-axis accelerometer, which uses a single mass for all three axes sensing. As a result, this accelerometer has achieved very low offset (< 1 mg/degrees C) in all XYZ axes over device operation temperature range of -40 degrees C to +80 degrees C. Device offset performance was improved by at least five times after the MEMS design optimization as compared with the one prior to the optimization.