An Overmolded Pressure Sensor Package Using an Ultrathick Photoresist Sacrificial Layer

Abstract

This study presents a novel technique for an overmolded package of piezoresistive pressure sensors using an ultrathick photoresist sacrificial layer. A 150 μm photoresist block is placed just on the silicon membrane of the pressure sensor and removed after the molding transfer process. The removal of the photoresist block exposes and reserves a sensing channel in the overmolded pressure sensor package. Experimental observations reveal that the silicon membrane of the pressure sensor is completely free of any epoxy molding compound contamination after the transfer molding process. The effectiveness of the photoresist block in shielding the silicon membrane of the pressure sensor was confirmed. Experiment and finite element model results reveal that the packaged pressure sensor has similar sensing characteristics to those of an unpackaged pressure sensor at room temperature. However, the packaged pressure sensor exerts a thermomechanical stress on the silicon membrane of the pressure sensor, resulting in an undesired output voltage drift. Employing a proper package design can reduce the output voltage drift. The proposed packaging scheme has a small package volume and surface mount device compatible features, making it suitable for portable commercial devices.