Fatigue damage mechanisms of copper single crystal/Sn–Ag–Cu interfaces

Sn–Ag–Cu solder/copper single crystal joints were prepared to reveal the interfacial fatigue damage mechanisms. Scallop-type Cu6Sn5 and planar-type Cu6Sn5/Cu3Sn intermetallic compounds (IMCs) interfaces were formed between SnAgCu solder and copper single crystal after re-flowing at 240 °C and subsequent aging at 170 °C, respectively. Under cyclic loading, persistent slip bands (PSBs) were activated in copper single crystal and continuously impinged the interfaces of the SnAgCu solder/copper single crystal joint. Two types of fatigue cracking modes, i.e. interfacial cracking between solder and IMC and fracture within IMC, were observed. Based on the experimental observations above, the corresponding interfacial fatigue cracking mechanisms were discussed.