Stress reduction method in fabrication of a multi-scale inertial switch with ultra-high aspect ratio

Abstract

Micro inertial switches are widely used in airbags, accessories and military weapons. SU-8 photoresist and electroforming based UV-LIGA process is an effective way to fabricate inertial switches. However, during the fabrication, the high stress in the SU-8 layers often causes them to detach from the substrate, which results in fabrication failure. To solve the detachment problem of SU-8 layers, a novel method was presented in this paper to release the internal stress in SU-8 layers by decreasing the area of electroforming layers. ANSYS simulation study was performed to verify the stress reduction effect of this method. The simulation and experiment results showed that stress in SU-8 layers can be reduced effectively. By using this method, a multi-scale inertial switch with ultra-high aspect ratio 17:1 was fabricated successfully. The overall size of the inertial switch is 14 × 11 × 0.6 mm. The inertial switch is fabricated by multi-layer UV-LIGA process. Fabrication error of the process is estimated in this paper. The stress reduction method and error estimate method presented in this paper can provide help to the fabrication of micro metal devices with large area and high aspect ratio.