Creep and mechanical properties of Cu₆Sn₅ and (Cu,Ni)₆Sn₅ at elevated temperatures

Cu₆Sn₅ is the most common and important intermetallic compound (IMC) formed between Sn-based solders and Cu substrates during soldering. The Cu₆Sn₅ IMC exhibits significantly different thermomechanical properties from the solder alloys and the substrate. The progress of high-density three-dimensional (3D) electrical packaging technologies has led to increased operating temperatures, and interfacial Cu₆Sn₅ accounts for a larger volume fraction of the fine-pitch solder joints in these packages. Knowledge of creep and the mechanical behavior of Cu₆Sn₅ at elevated temperatures is therefore essential to understanding the deformation of a lead-free solder joint in service. In this work, the effects of temperature and Ni solubility on creep and mechanical properties of Cu₆Sn₅ were investigated using energy-dispersive x-ray spectroscopy and nanoindentation. The reduced modulus and hardness of Cu₆Sn₅ were found to decrease as temperature increased from 25 C to 150 C. The addition of Ni increased the reduced modulus and hardness of Cu₆Sn₅ and had different effects on the creep of Cu₆Sn₅ at room and elevated temperatures.