Reliability of flip-chip technologies for SiC-MEMS operating at 500 °C

The flip-chip technology has many advantages over standard wire bonding processes especially as interconnection technique for MEMS operating in harsh environments. In this paper, silver based micro contact bumps are investigated with test assemblies on their reliability for an operating temperature of 500 °C. The contact bump materials are a nano-silver sinter paste and a glass-solder filled with silver particles. Our experiments showed an optimal mixture ratio of silver and glass of 80/20 with regard to stability and electrical performance of the contact material. Silicon based test-chips mounted on Al₂O₃, AlN and Si₃N₄ substrates, metallized with platinum were the test devices for process optimization and reliability measurements. The stability and electrical performance of the contact materials were investigated. We used an analytical approach to identify material and process parameters that influence the stress inside a contact bump after processing. Our experimental results indicate a high influence of the sensor substrate CTE and the process temperature on the lifetime in the micro contact. After processing the test-assemblies were exposed to extreme thermal shock cycles with ΔT = 470 K. We analyzed the lifetime of the micro contacts during the cycles with in-situ resistance measurements of the test-structures. Sintered silver and conductive glass contacts are both promising high-temperature flip-chip interconnections. Longer lifetimes of contact bumps with sintered silver were detected. We observed early contact failures after 10 to 20 thermal shocks for the devices with Al₂O₃ and AlN substrates. A test assembly contacted by silver-sintering on Si₃N₄ had the first contact failure after 54 thermal shock cycles.