A novel method for packaging of micromachined piezoresistive pressure sensor

Abstract

A novel method for wafer level packaging of the piezoresistive pressure sensor is proposed. At present, the wire bonding technology is employed for interconnections. Hence, a coating is necessary to protect the wires and the device. To transmit the applied pressure to the sensor diaphragm this coating must be elastic. This elastic property of coating transfers the applied pressure not only onto the diaphragm, but also to the bonded wires. In other words, this movement of elastic coating causes a mechanical movement directly onto the wire bonding. The consequence is reduced lifetime of wire bonding, which is main disadvantage for present packaging methods. The proposed method that is designed for the measurement of automotive engine oil pressure, resolves above-mentioned problems. This method is based on flip chip technology that substitute bumps with the wire bonding. Due to the underfill material used in flip chip technology, the mechanical movement will be negligible. Major advantage of this work is the wafer level packaging method that reduces the packaging cost. The device is simulated using ANSYS software by the finite element method. This analysis considers thermal effect; stress and lifetime, such as the pressure sensor sensitivity changed due to new package, effect of bump height on the package lifetime, CTE mismatch between underfill, bump and die.