Material & process challenges for tire pressure monitoring sensor (TPMS) packaging

In packaging MEMS pressure sensor applications such as tire pressure sensors, silicone gels are widely used due to its unique characteristics in meeting specific automotive requirements. The device requires low stress die adhesive to protect the sensor dies from any mechanical stress during field application. Since the sensing device is directly mounted into the wheel's rim, another critical requirement is to withstand the centrifugal force while the tire is rotating at high speed as well as be able to withstand any harsh chemicals which the tire may be exposed to. The device must also withstand the harsh changes in environmental temperature which can go over 100degC in summer and far below zero in winter. The silicone gels selected to suit these requirements were found to have various assembly packaging as well as reliability challenges. This paper discusses the material and process challenges associated with the application of these gels. Comprehensive studies and process characterization were conducted to address these challenges.