FO-WLP multi-DOF inertial sensor for automotive applications
Fan-out wafer level packaging (FO-WLP) is the fastest growing packaging technology. Besides providing greater number of IOs than could be obtained by fan-in wafer level packaging (WLP) it also offers interesting opportunities for multi-die packaging with minimum package dimensions. Combined inertial sensor is an established category of automotive sensor components. with of two or more MEMS sensor dies for 3- 6 axis motion measurement and an interface circuit die. It is used for electronic chassis stability control (ESC) and for advanced driver assistant systems (ADAS). Currently the sensor is packaged in various standard or proprietary configurations: ceramic cavity packages, pre-molded plastic cavity packages, over-molded SOIC, PBGA. The demand is towards smaller foot print and smaller height, lower cost and better robustness to vibrations. FO-WLP offers some excellent characteristics like small size, compatible cost, vibration robustness and low stress to sensitive MEMS dies. Present work shows that it will also reach automotive reliability requirements and pass high temperature, thermal cycle and temperature-humidity tests. Three fracture mechanism of the solder ball IOs were identified at 2000 thermal cycles. Solder fatigue was no issue and by design changes two other mechanisms can be corrected. Two-fold redundancy will make an IO failure rate low enough. EMI and internal cross-talk protection was found better than with existing devices. Reversible humidity dependence due to moisture absorption by polyimide film was seen and a lay-out change was implemented to overcome it.