Vibration fracture behavior of Sn-xCu lead-free solders

The effect of Cu content on the microstructure and the vibration deformation mechanisms of a potential lead-free solder, Sn-xCu (x=0.3, 0.6, 1.3, 1.7 wt.%), are examined in this study. The results show that proeutectic Sn-rich phase decreased, while Cu₆Sn₅ intermetallic compounds increased with increasing the Cu content. For the specimens with high Cu content (1.3Cu and 1.7Cu), hard massive Cu₆Sn₅ existed mostly amongst the proeutectic Sn-rich phase dendrites, increasing the tensile strength. Under a constant vibration force and constant initial-deflection testing, the 0.6Cu specimen with a higher damping capacity was able to absorb more vibration energy and thus possessed a greater vibration fracture resistance. In addition, the lamellar-deformed structures (LDS) and Cu ₆Sn₅ were able to increase the crack tortuosity, which in turn increased the crack propagation resistance.