Reliability studies of Sn–9Zn/Cu solder joints with aging treatment

Sn–9Zn (in wt.%) solder ball was bonded to Cu pad, and the effect of aging on shear reliability was investigated. After reflow, the intermetallic compound (IMC) phase formed at the interface was Cu5Zn8, and the as-reflowed Sn–9Zn/Cu joint had sufficient shear strength. In the isothermal aging test, only Cu5Zn8 IMC was observed in the samples aged at temperatures between 70 and 120 °C. On the other hand, after aging at 150 °C for 250 h, Cu6Sn5 phase was observed at the interface between the interfacial Cu5Zn8 IMC layer and the Cu substrate. And, the layer-type Cu5Zn8 IMC layer was disrupted locally at the interface. In the ball shear test conducted after aging treatment, the shear strength significantly decreased after aging at all temperatures for initial 100 h, and then remained constant by further prolonged aging. The fracture mainly occurred at the interface between the solder and Cu5Zn8 IMC layer. The aged Sn–9Zn/Cu solder joint had an inferior joint reliability.