Resonant characteristics of the microelectronic Sn–Cu solder

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 finer, 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 (β-Sn) phase dendrites and the fineness of Cu6Sn5 is advantageous to resonant life. Under both constant vibration force and a constant initial-deflection testing, the 0.3Cu specimen and 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) of β-Sn and the finer Cu6Sn5 were able to increase the crack tortuosity, which in turn increased the crack propagation resistance.