Package Design for Multiphysics MEMS Sensor

In the field of MEMS and sensors, package plays a primary role since it strongly affects device behavior and performance. Depending on the application and industrial domain, the design needs to be targeted toward the given requirements. The same sensor, thought for different applications, may require completely different packaging technology and design. In this context, mechanical, thermal and thermo-mechanical simulations are the driving forces of design, especially when stringent size/performance constraints and multi-sensor integration are introduced. This work presents a full-mold LGA package integrating a tri-axial MEMS accelerometer for motion sensing and a temperature sensor to monitor a device connected through a thermal path routed in the PCB. Currently, the motion sensor is assembled in a 2×2 mm2 LGA package while the temperature sensor in a 2×2 mm2 DFN package with exposed pad. The proposed package is based on a 3 dice stack-up: temperature sensor die bottom, MEMS die, ASIC die on top. Since the temperature sensor die footprint is smaller than the MEMS, an overhang die bonding follows. A 2-layers organic substrate has been designed to manage the signals and optimized to replicate the thermal behavior of the DFN exposed pad. By means of a high thermal conductivity die attach glue and vias connecting the temperature sensor die to the exposed metal pad in the bottom of the package, the thermal resistance “junction - case bottom” is aligned to the target. Numerical analysis has been performed on package. Main focus is given to the thermal simulations to evaluate the performance gap of the temperature sensor with respect to the DFN solution. Thermo-mechanical simulations have been carried out to assess the influence of molding and soldering processes on the accelerometer.