Abstract
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) 6 Sn 5 and (Ni,Cu) 3 Sn 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 ) 3 Sn 4 and (Cu 1-y , Ni y ) 6 Sn 5 compounds. In this study, ternary Sn-Cu-Ni alloys were prepared and annealed at 240 °C. Three equilibrium phases, Sn, Ni 3 Sn 4 , and Cu 6 Sn 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. % Sn, (Ni 0.80 , Cu 0.20 ) 3 Sn 4 and (Cu 0.59 , Ni 0.41 ) 6 Sn 5 . In addition, the solubility of Cu and Ni in (Ni,Cu) 3 Sn 4 and (Cu,Ni) 6 Sn 5 compounds was evaluated. Finally, the isothermal section of the ternary Sn-Cu-Ni system at 240 °C was proposed on the basis of experimental results in this study. © 2005 Materials Research Society.