Size effect on tensile performance of microscale Cu/Sn3.0Ag0.5Cu/Cu joints at low temperatures

For the reliability of cryoelectronics, the tensile performance and fracture behavior of microscale Cu/Sn3.0Ag0.5Cu/Cu joints with shrinking size were investigated at decreasing temperature ranging from 25 degrees C to -120 degrees C. The experimental results showed that the tensile behavior of solder joints was greatly influenced by temperature and joint size. The tensile strength of the solder joint increased with decreasing temperature. At a same temperature, the joint tensile strength increased with decreasing thickness-to-diameter ratio (R = t/d, 1, 1/2 and 1/4). In addition, at a same R, the joint with a smaller diameter had a higher tensile strength. In general, the tensile strength showed an inversely proportional function of solder volume. Moreover, as temperature decreased, the fracture position changed from the solder matrix to the interface between solder and intermetallic compound layer, showing a ductile-to-brittle transition. The ductile-to-brittle transition temperature increased with decreasing R in the solder joints with a same diameter, and it decreased with decreasing joint diameter in the solder joints with a same R.