Integration of polymer bonded magnets into magnetic sensors

This paper introduces a novel assembly and manufacturing technology for integrating permanent magnets into magnet sensor modules by use of plastic bonded magnets. High precision speed sensors in automotive applications, e.g. in anti-blocking-system or engine management, are based on a magnetic measurement principle [1]. Typical sensor modules contain a semiconductor based sensor chip and a permanent magnet providing the necessary bias field (see Fig. 1). This field is modulated by a passing external gear wheel out of material with high magnetic permeability, which is part of the magnetic circuit. The wheel speed can directly be determined by measuring the frequency of the magnetic field modulation. Permanent magnets are often assembled in a sequential pick and place process. We report a novel assembly technology by direct molding of thermoplast bonded magnets onto a chip carrier containing pre-assembled sensors. We will show, that this offers the following advantages: - Highest accuracy - Optimum working point, in particular for GMR sensors - High throughput by efficient parallel process - Simplification of the module assembly.