Packaging Optimization For Tire Pressure Monitoring System

In order to improve the reliability of tire pressure monitoring system (TPMS), packaging design optimization is essential. In this paper, finite element method (FEM) is used to analyze the effect of packaging processes on the residual stresses of the sensor die and its packaging, The Young's modulus and thickness of the coating material, the dimension effect of the dies and the substrates on which the dies are attached are considered in this paper. Results show the thinner coating gel that has a lower Young's modulus generates lower residual stress and smaller zero offset as well as smaller temperature drift to the sensor. For a given coating soft gel, the thermal residual stress decreases with the thickness of adhesive layer decreasing, and the effect is not significant when the thickness of coating gel is smaller than 1.55mm, Therefore, this value can be decided as the technological parameter. Comparing stainless steel, Kovar and FR-4, the ceramic is more suitable for using as the substrate, The ceramic has lower CTE compared with steel, Kovar and FR-4, therefore the residual thermal stresses resulted from the CTE mismatch are much lower than that of steel, Kovar and FR-4, For a given coating soft gel and substrate, smaller dimension of the dies will benefit the sensor's performance on the residual stresses, For a given coating soft gel, the material of the shells has little effect on the residual stresses of the dies.The above simulation results can be used to guide the tire pressure sensor's packaging design optimization, Based on FEM results, the optimized die-attaching process parameters are proposed, The experiments indicate that the proposed pressure sensor has a stable output voltage and good linearity, and the zero offset and temperature drift of the sensors are also minor.