Thermodynamic Calculation of Phase Equilibria and Its Applications in the Sn-Ag-Cu-Ni-Au System

Sn-Ag-Cu base solders are the most potential candidates to substitute of Sn-Pb eutectic solder. Gold (Au) coatings are used to protect conductor surface from oxidation and thereby to promote the solderability, and nickel (Ni) is often used as a diffusion barrier layer between lead-free solders and substrates to restrict the growing of intermetallic compound layers. And the gold and nickel also are added to the Pb-free solders to improve their performance. In the present work, the thermodynamic calculations of phase equilibria in the Sn-Ag-Cu-Ni-Au system were carried out using the CALPHAD method. Some examples of application are presented, and it is shown that the CALPHAD method is a good tool to design Pb-free solders and understand the interfacial reaction.