Tensile and Fatigue Behaviors of Aged Cu/Sn-4Ag Solder Joints

Tensile properties and stress-controlled fatigue fracture behaviors of Cu/Sn-4Ag solder joints aged at 180A degrees C for different times were systematically investigated. It was found that the tensile strength of the solder joints decreased with increasing aging time and that the fracture mode changed from ductile to brittle. The fatigue life of the solder joints also decreased with increasing aging time. For most of the solder joints, fatigue cracks tended to initiate around the Cu/Cu6Sn5 interfaces due to the strain incompatibility and local strain concentration on a micro-scale, and they then propagated within the solder proximately along the Cu/Cu6Sn5 interfaces. The samples aged fora different pound times or tested under different stress amplitudes had similar fractography morphologies, which consisted mainly of a propagation region, covered by solder, and a final fracture region. Based on the experimental observations above, the corresponding interfacial fatigue failure mechanisms were discussed in terms of different influencing factors.