Electrical connection using submicron porous gold bumps for wafer-level packaging of mems using anodically-bondable LTCC wafer

An anodically-bondable low temperature cofired ceramic (LTCC) wafer offers a versatile, clean and reliable wafer-level hermetic packaging for MEMS. This paper reports electrical connection in parallel with anodic bonding between MEMS on a Si wafer and vias in the LTCC wafer using porous Au bump. The Au bump is made of submicron Au particles, and so compliant as it easily absorbs large height difference. The LTCC wafer with the Au bumps and an SOI wafer with Au/Pt/Cr pads and diaphragms were anodically bonded. 100% yield of both electrical connection and hermetic sealing was demonstrated. Heat cycle test confirmed the reliability of both electrical connection and hermeticity. In addition, the transfer of the porous Au bumps from a mother glass wafer to a target LTCC wafer was demonstrated. This method dispenses with the fabrication of the porous Au bumps by users, which includes non-standard processes.