Confirmation of Creep and Fatigue Damage in Pb/Sn Solder Joints

Abstract

Solder joints of leadless surface mounted components, which were thermally cycled, were studied to determine their failure mode and to compare the results with work done on bulk solder specimens. Previous studies done on the characterization of the mechanical properties of cyclically tested bulk Pb/Sn solder of different compositions show that their deformation behavior is a result of an interaction between creep and fatigue damage processes. Fractographic forensics of the failed solder joints also showed damage due to both creep and fatigue processes. Fatigue striations were observed side by side with creep voids and extensive intergranular cracking. The crack growth rate (da/dn) was calculated to be around 0.25 μm/cycle. It is also established that the failure is crack propagation controlled. It was found that the crack initiation site on at least one of the joints was a tin rich area. The size of the voids varied from 0.1 μm to 0.5 μm.