Abstract:Low cycle mechanical fatigue tests on 96.5Sn-3Ag-0.5Cu solder joints were carried out using micro-uniaxial fatigue testing system at 25℃ with different frequencies (1Hz~10Hz) and a wide range of strain (2%~8%). The results showed that the low cycle fatigue (LCF) life followed the Coffin-Manson equation in different strain ranges. Frequency-modified Coffin-Manson equation can describe the frequency effect well on the fatigue life of solder joints. The analysis of failure process showed that the fatigue cracks initiated at the interfaces between the solder and inter-metallic compound (IMC) around the edge of the joints, then the cracks propagated within the solder along the solder/IMC interfaces proximately. Fracture morphologies of solder joints with different frequencies were similar which mainly consisted of an initiated region, a propagation region and a final fracture region. The fracture mechanism of the final fracture region transformed from inter-granular fracture to trans-granular fracture with increasing frequency.