Low-Cycle Fatigue Life Definition for Sn-3.5Ag and Sn-0.7Cu Lead-free Solders Using Surface Deformation

Abstract

The low-cycle fatigue behavior and the relationship between the surface features in the low-cycle fatigue testing and the fatigue life of Sn-3.5Ag and Sn-0.7Cu lead-free solders were investigated at strain rate of 0.1%/s with a non-contact extensometer at room temperature ( 22 o C), 80 o C and 120 o C. In addition the fatigue life using the surface deformation of those solders were defined and estimated from the surface features of solders investigated by image processing and compared with Coffin-Manson type of fatigue behavior of solders. The fatigue life of Sn-3.5Ag solder was superior to that of Sn-0.7Cu solder under temperatures of 80 o C and 120 o C. The fatigue life defined from surface deformation indicated a close behavior to Coffin-Manson type of fatigue behavior in those solders. This method could identify the low-cycle fatigue life of solders from the surface deformation.