Flip-chip on board packaging of a thermal wind sensor

Abstract

A two dimensional wind sensor was designed, fabricated and packaged on ceramic substrate instead of silicon substrate. The Ti/Pt heater and thermistors were fabricated using single lift-off process. The gold bumps were then sputtered and patterned on the chip using lift-off process again. Correspondingly, the Pb/Sn bumps were fabricated on the FR4 substrate using stencil printing method after metallization. The sensor chip was flip-chip packaged on the FR4 substrate, and the gap was filled with epoxy-based underfill to improve the structure strength and thermal isolation. The wind velocity and direction offsets of the sensor were analyzed and compensated using software and hardware calibration. The packaged sensor was tested in wind tunnel in constant power mode. Both the simulation and test results show that the thermal wind sensor can measure wind speeds up to 10 m/s with an accuracy of 0.5 m/s, and wind direction in a full range of 360deg with a resolution within 5deg.