Study of Fatigue Crack Propagation Behavior of Film Materials : Fatigue Testing Method and Factors Controlling Fatigue Crack Propagation Rates

At present, materials with small dimensions such as thin films are often used in electronic packaging. This study concerns a film fatigue testing method, which makes it possible to observe the fatigue crack propagation behavior on a film bonded to a through-hole in a base plate subjected to push-pull cyclic loads. An analytical model for this testing method is presented using a boundary element method, so that the film fatigue fracture can be treated quantitatively in terms of fracture mechanics (K-values and J-integrals). The fatigue crack growth properties were examined for commercial-grade iron films with 100 μm thickness bonded to either a circular or an elliptical hole in the base plate. As a result, using the stress intensity factor based on the measured crack opening displacement, ΔK est , the fatigue crack propagation behavior of the film could be understood in terms of the effective stress intensity factor widely used in the bulk specimen, ΔK eff .