Wafer-level vacuum packaging for hetero-integration by thermo-compression bonding using planarized-electroplated gold bumps

Wafer-level vacuum sealing and electrical interconnection are often crucial for advanced device packaging. This article presents a novel packaging and integration technology, which is applicable to non-planar (i.e. microstructured) and/or temperature-sensitive wafers, by means of Au-Au low-temperature thermo-compression bonding utilizing electroplated Au microbump that surface has been planarized by single-point diamond fly-cut. Device integration, vacuum encapsulation, and electrical interconnection at the same time is the major advantage offered by the proposed technology. In this study, the sealing pressure was evaluated under various bonding conditions by the zero-balance method utilizing diaphragm-structured devices for bonding test. The vacuum sealing pressure was obtained as a few kPa, or even better without introducing any getter materials. The bonding shear strength was also measured to be higher than 100 MPa.