Fracture mechanical life-time investigation of glass-frit bonded MEMS sensors

The long-term mechanical stability of the wafer level package is an important aspect in the reliability approach of MEMS products.Glass frit bonding is one of the most widely used bonding technologies. Since the glass frit bond frame is subjected to thermal stresses due to different thermal expansion coefficients of glass and silicon it constitutes a potential weak link of the package. Therefore, a reliability approach of a glass frit bonded MEMS device has to consider carefully its possible long term failure mechanisms. In particular, crack corrosion of the glass intermediate layer might lead to delayed failure of the device. In this paper, newly developed fracture mechanical measurement techniques as well as the numerical modelling of the experiments that allow determination of the fracture toughness and the crack growth rates of glass frit bonded micro samples are presented. A first fracture mechanical lifetime approach based on subcritical crack growth of initial defects in the glass frit bond frame is discussed. The obtained results form the basis for the lifetime prediction of glass frit bonded MEMS devices.