The wafer-level vacuum sealing and electrical interconnection using electroplated gold bumps planarized by single-point diamond fly cutting

Wafer-level vacuum sealing and electrical interconnection are often critical for microelectromechanical systems (MEMS). This article presents a packaging and integration technology, which is applicable to non-planer (i.e. microstructured) and temperature-sensitive wafers by means of single-point diamond fly cutting of electroplated Au bumps and Au-Au diffusion bonding. The process condition was optimized by L18 Design of Experiments (DOE), and the bonding force and surface pre-treatment were extracted as dominant parameters. The crystal size of the Au bump enlarges after heat treatment for degassing at 300°C, but a smaller crystal size, which is preferred for bonding, is obtained by fly cutting, as observed by electron back scattering diffraction (EBSD). Finally, 100% yield of vacuum-sealing and a high bonding shear strength were achieved.