Phase equilibria in the Sn-rich corner of the Sn-Cu-Ni ternary alloy system at 240 deg C

摘要

The interfacial reactions between solders and under bump metallization (UBM) have been of great interest recently in flip chip technology. Intermetallic compounds (IMCs), i.e., (Cu,Ni)_6Sn_5 and (Ni,Cu)_3Sn_4, usually formed between solders and UBM. To fully understand the interfacial reactions and phase transformation phenomenon, a suitable phase diagram concerning solders, IMCs, and UBM materials is required. In particular, a Sn-rich phase region in the Sn-Cu-Ni ternary diagram is very critical in determining the concentration tendency of x and y values in (Ni_(1-x),Cu_x)_3Sn_4 and (CU_(1-y)Ni_y)_6Sn_5 compounds. In this study, ternary Sn-Cu-Ni alloys were prepared and annealed at 240 deg C. Three equilibrium phases, Sn, Ni_3Sn_4, and Cu_6Sn_5, were identified by x-ray diffraction analysis and also showed in backscattered electron imaging. Using electron probe microanalysis quantitative analysis, three acme compositions of the ternary region in the Sn-Cu-Ni isotherm near the Sn-rich corner were determined as 98.5 at. percent Sn, (Ni_(0.80), Cu_(0.20))_3Sn_4 and (Cu_(0.59),Ni_(0.41))_5Sn_5. In addition, the solubility of Cu and Ni in (Ni,Cu)_3Sn_4 and (Cu,Ni)_6Sn_5 compounds was evaluated. Finally, the isothermal section of the ternary Sn-Cu-Ni system at 240 deg C was proposed on the basis of experimental results in this study.