Packaging of Ultrathin Flexible Magnetic Field Sensors With Polyimide Interposer and Integration in an Active Magnetic Bearing

Ultrathin sensors enable various scopes for measuring signals in restricted geometries. One example is the use of magnetic field sensors in active magnetic bearings (AMBs). Here, the thin sensor will allow measuring the magnetic flux directly in the air gap between the rotor and the stator of the AMB, which allows controlling the AMB faster and more precisely. This also results in a higher stiffness of the AMB. Therefore, the sensor has to be thinner than 150 μm. In this article, previous experiences with polyimideand silicon-based Hall sensors which rely on thin bismuth films were used to realize a reliable sensor with suitable interconnection technologies. Especially the adhesive flipchip technology, which was used with silicon interposers, has to be adapted and optimized for the packaging of polyimide-based sensors. The technologies and the materials were optimized for this approach with a special test design setup. Afterward, the working sensor systems were manufactured. These sensors show very promising results and could be successfully integrated into an AMB setup for preliminary tests.