Packaging effect investigation of WL-CSP with a central opening: A case study on pressure sensors

This study reports the packaging effects of wafer-level chip scale packaging (WL-CSP) with a central opening on piezoresistive pressure sensors. A regular pressure sensor with calculated sensitivity of 3.1 × 10−2 mVV−1 kPa−1 and a sensitive pressure sensor with calculated sensitivity of 32.0 × 10−2 mVV−1 kPa−1 are investigated. A finite element (FE) model validated by experimental measurements is used to explore the sensing characteristics of the pressure sensors. The results show that the output variation of the packaged pressure sensor is dominated by the CTE mismatch not the piezoresistive coefficient change as temperature varies. WL-CSP with small polyimide (PI) thickness and large PI opening produces small packaging induced stress, making it ideal for precision sensing for both regular and sensitive pressure sensors.