Mechanical properties of glass frit bonded micro packages
Frit glass bonding is a widely used technology for encapsulation of surface micro-machined structures like inertial sensors or gyroscopes on wafer level. Since for sensors in automotive applications, a lifetime of 15-20 years has to be guaranteed for, a reliable lifetime prediction is necessary. Different material parameters have to be known for a lifetime estimation based on stress corrosion cracking, which determines the longterm strength behaviour of most bonded interfaces of microsystems. Parameters needed for lifetime prediction have to describe the material's resistance against crack propagation (fracture toughness KIC), the stress situation in a micro package and the long-term strength behaviour. Results for fracture toughness investigations presented in this paper were determined by the micro chevron test. The stress situation in a micro package was calculated by a thermo-mechanical Finite Element Analysis. Furthermore the residual stress in the glass layer and linear thermal expansion coefficient were determined by a crack width measurement in an environmental scanning electron microscope.