# First-principles study on elastic properties of Cu, (Cu1−x,Nix)3Sn and interfacial mechanical properties of (Cu1−x,Nix)3Sn/Cu in the lead-free solder joint

## TL;DR

This study uses first-principles calculations to show how adding nickel to a copper-tin alloy improves the mechanical properties of lead-free solder joints, but only up to a certain limit.

## Contribution

The study reveals the enhancement mechanism of interfacial mechanical properties in lead-free solder joints through Ni alloying in (Cu1−x,Nix)3Sn.

## Key findings

- Ni alloying improves the interfacial mechanical properties of (Cu1−x,Nix)3Sn/Cu within the thermodynamically stable domain.
- Higher Ni content beyond stability reduces reliability due to mechanical or thermodynamic deterioration.
- The results guide high-performance lead-free solder design for miniaturized and harsh-environment electronics.

## Abstract

In this study, the elastic properties of Cu and (CuxNi1−x)3Sn were calculated to reveal the effects of Ni alloying on the interfacial mechanical properties of (CuxNi1−x)3Sn/Cu in lead-free solder joints. The results reveal that, within the thermodynamically stable domain of (CuxNi1−x)3Sn, the increase of Ni content can enhance the interfacial mechanical properties of (CuxNi1−x)3Sn/Cu, and increase the reliability of the lead-free solder joints. The enhancement mechanism can be attributed to the simultaneous improvements of oriented Young’s modulus and ductility of (CuxNi1−x)3Sn, achieved by Ni alloying. But higher Ni content beyond the thermodynamically stable domain of (CuxNi1−x)3Sn will deteriorate the interfacial mechanical properties by mechanical or thermodynamic mechanisms 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 high-performance lead-free solder design by alloying strategies to meet the requirements for electronic device miniaturization and harsh environmental applications.