Drift of magnetic sensitivity of smart Hall sensors due to moisture absorbed by the IC-package [automotive applications]

For automotive applications like cam-shaft, crank-shaft, throttle valve or accelerator pedal position sensing, Hall probes are integrated together with biasing and complex signal processing circuits into tiny plastic packages. Instabilities of magnetic switching points and magnetic sensitivity have been observed for some time. We show by way of experiments that the main contribution to this sensitivity drift originates from moisture absorption by the mold compound of the plastic package which changes the mechanical stress on the die. The mechanical stress affects the Hall factor of the Hall probe (piezo-Hall effect) and the current through the Hall probe (piezo-resistance effect) which finally leads to a drift of the overall magnetic sensitivity.