Fabrication and characterization of a low-temperature hermetic MEMS package bonded by a closed loop AuSn solder-line

This paper presents a hermetic MEMS package bonded by a closed-loop AuSn solder-line. We design three different test specimens including substrate heated specimen without interconnection-line (SHX), substrate heated specimen with interconnection-line (SHI) and locally heated specimen with interconnection-line (LHI). Pressurized helium leak tests are carried out for hermetic seal evaluation with the critical pressure test for bonding strength measurement. In hermeticity tests, SHX, SHI and LHI show leak rates of 8.4±6.7×10^-10 mbar-l/s, 13.5±9.8×10^-10 mbar-l/s and 18.8±9.9×10^-10 mbar-l/s with the same internal volume of 6.89±0.2×10^-6 l, respectively. The specimens of SHX and SHI, bonded by the substrate heater, show leak rates lower than that of LHI. However, the three test specimens satisfy MIL-STD-883E for hermeticity test of microcircuits. In the additional critical pressure test, no fracture is found in the bonded specimens at applied pressure of 1±0.1MPa. From these results, we approximately extract the bonding strength of the test specimen of 3.53±0.07 MPa. We experimentally verify that the LHI shows potential for hermetic MEMS packaging with interconnection-line and short-time bonding processes for mass production.