Analysis of Stress-Strain Hysteresis Loop and Prediction of Thermal Fatigue Life for Chip Size Package Solder Joints

Abstract

The aim of this study is to investigate the relationship between the inelastic strain range and the thermal fatigue lives of chip size package solder joints with Sn-Pb and Sn-Ag-Cu solder balls. The inelastic strain range was examined by finite element analysis. In both solder joints, the exponential terms in the inelastic strain range term in the Coffin-Manson equation were evaluated as 1.8 - 2.3. These values are very close to the conventional one used in Sn-Pb and the Pb containing solders. The inelastic strain range is almost proportional to the temperature range in the Sn-Pb solder joint. On the contrary, the inelastic strain range is proportional to approximately the square root of the temperature range in the Sn-Ag-Cu solder joint. The deference depends on the change of the stress-strain hysteresis curve in the thermal cycle.