Abstract
The interfacial reactions between solders and under bump metallization (UBM) are of highly interests recently in flip chip technology. Intermetallic compounds (IMCs), i.e. (Cu,Ni)6Sn5 and (Ni,Cu)3Sn4, formed between solders and UBM. To fully understand the interfacial reactions and phase transformation phenomenon, a suitable phase diagram concerning solder, IMCs and UBM material is required. As a result, Sn-riched phase in Sn-Cu-Ni ternary phase diagram is very critical in determining the concentration tendency of x and y values in (Ni1-x,Cux)3Sn4 and (Cu1-y,Niy)6Sn5 compounds. In this study, ternary Sn-Cu-Ni alloys were prepared and annealed at 240℃. Three equilibrium phases, Sn, Ni3Sn4 and Cu6Sn5, were identified by XRD analysis, and also evidenced in BEI micrograph. Using EPMA quantitave analysis, three acme compositions of the ternary region in the Sn-Cu-Ni isotherm near the Sn-riched corner were determined as 98.5 at.%Sn, (Ni0.80, Cu0.20)3Sn4 and (Cu0.59,Ni0.41)6Sn5. Furthermore, the degree of composition homogeneity and the distribution of the forming phases were evaluated by X-ray color mapping and phase analysis technique. By way of software program to convert the concentration measured with EPMA, the exact compositions could be mapped on the Sn-Cu-Ni ternary isotherm. In addition, the solubility of the Cu and Ni in (Ni,Cu)3Sn4 and (Cu,Ni)6Sn5 compounds was evaluated. Finally, the isothermal section of the ternary Sn-Cu-Ni system at 240℃ was proposed on the basis of experimental results in this study. Furthermore, the related phase transformation was also discussed with respect to the formation of the IMCs around 240℃.