Method of Estimating Fatigue-Crack Propagation Properties Based on Accumulated Damage Model

We previously developed a crack propagation model to calculate crack paths using accumulated damage in microsolder joints in semiconductor structures. We have now developed a method based on the crack propagation model, which is named accumulated damage model, to predict fatigue-crack propagation properties of solders. Generally, there is a correlation between crack propagation rates, da/dN, of solders and J-integral ranges, ΔJ. The correlation can be represented in an equation as a simple power relationship, given by da/dN=B [ΔJ] q. We derive this simple power equation from our crack propagation model and Hutchinson-Rice-Rosengren singularity theory. The equation enabled us to estimate fatigue-crack propagation properties from cyclic stress-strain curves and fatigue strength properties. We used the method to predict fatigue-crack propagation properties for center-cracked plate specimens made of Sn-40Pb and Sn-3.5Ag-1Cu. The predictions agreed well with actual fatigue-crack propagation properties determined by experiment for center-cracked plate specimens made of Sn-40Pb and Sn-3.5Ag-1Cu, indicating that our method effectively predicts solder fatigue-crack propagation properties.