Effect of moisture swelling on MEMS packaging and integrated sensors

In MEMS packaging moisture uptake of packaging materials may lead to severe changes in sensor behavior and package reliability. Knowledge and understanding of the effect of moisture swelling on the overall package deformation and on the sensor system is therefore inevitable for a successful MEMS design and packaging solution. The paper shows a design optimization of a pressure sensor packaging towards minimization of sensor drift due to stresses induced by moisture uptake. The work was done in a combined experimental and simulative approach. Experimental data clearly shows the sensor sensitivity to moisture uptake of polymer based packaging material. Based on the experimental findings the complete sensor package was modeled by means of finite element analysis. In a second step a new packaging geometry was defined to reduce the effect of moisture swelling to sensor signal. Additionally sensitivity of the sensor output signal to viscoelastic properties of three different moulding compounds was simulated. In the result of the work an optimized package design was achieved.