Investigation of ultrasonic platinum and palladium wire bonding as interconnection technology for high-temperature SiC-MEMS

The objective of this study is to develop and investigate a reliable electrical interconnection for SiC-MEMS, which can sustain high mechanical and thermal loads in harsh environments. Platinum and palladium wire bonds, with a diameter of 25 microns, are used for interconnection of sensors with an operating temperature of 500 °C. Silicon testsensors with TiW/Pt bond pad metallization are processed in thin film technology. The test-chips are mounted with temperature stable assembly techniques on ceramic substrates for reliability evaluation of the package. Ultrasonic bonding process for sensor interconnection is developed in this work and the optimized process parameters are given for both materials. Wire-pull tests with initial devices, after aging and at 300 °C are performed to investigate the stability of the interconnections. An O2-plasma cleaning process of the bond metallization showed significant improvement of the bond reliability. Maximal pull forces up to 20 gf for Pt wires were measured. An increase of the average pull force values compared to untreated specimen for Pt wires of 75 %, for Pd wires of 40 % was observed. The fracture surfaces of devices after the pull-tests were examined by microscope and SEM. Bond-neck break and bond interface fracture were the main bond failure modes. After storage of 200 hours at 500 °C the electrical contact was ensured but a degradation of the bond metallization was observed that leaded to a decrease of obtained pull forces for Pt and Pd. High pull forces of bonds tested at 300 °C were observed with a reduction only by 8 to 10 % for both materials from the initial value.