First-principles study on elastic properties of Cu, (Cu 1-x Ni x ) 3 Sn and interfacial mechanical properties of (Cu 1-x Ni x ) 3 Sn/Cu in the lead-free solder joint

In this study, the elastic properties of Cu and (Cu x Ni 1-x ) 3 Sn are calculated to reveal the effects of Ni alloying on the interfacial mechanical properties of (Cu x Ni 1-x ) 3 Sn/Cu in lead-free solder joints. The results reveal that, within the thermodynamically stable domain of (Cu x Ni 1-x ) 3 Sn, the increase of Ni content can enhance the interfacial mechanical properties of (Cu x Ni 1-x ) 3 Sn/Cu, and increase the reliability of the lead-free solder joints. The enhancement mechanism can be attributed the improvements of orientated Young's modulus and ductility of (Cu x Ni 1-x ) 3 Sn achieved by Ni alloying. But higher Ni content beyond the thermodynamically stable domain of (Cu x Ni 1-x ) 3 Sn will deteriorate the interfacial mechanical properties by mechanical mechanism or thermodynamical mechanism, and decrease the reliability of the lead-free solder joints. The results presented in this study will not only unveil the effects of Ni alloying on the interfacial properties of lead-free solder joints, but also will provide a guidance for the high-performed lead-free solder design by alloying strategies to meet the requirements for electronic device miniaturization and harsh environmental applications.