Intermetallic Compounds Formation in Transient Liquid Phase Sn−Ag−Ni Alloys via Multiple Reflow Cycles

Abstract

This study qualitatively demonstrates the role of Ni addition on transient liquid phase (TLP) Sn−Ag−Ni solder alloy through multiple reflow cycles, focusing on the formation, stability, and transformation of intermetallic compounds (IMCs). The optimal incorporation of 0.3 wt.% nickel (Ni) into the Sn−Ag solder alloy promotes the formation of thermally stable, high-melting-point IMCs, enhancing the structural integrity of the solder joint. Phase diagram analysis using Thermo-Calc software qualitatively confirms the coexistence of Ag3Sn, Ag4Sn, and Ni3Sn4 with the β-Sn phase, supporting their structural role in solder joint stability. Thermodynamic analysis shows that Ag3Sn IMC has the highest favorability for formation and stability at room temperature, while Ni3Sn4 IMC enhances high-temperature performance. Differential Scanning Calorimetry (DSC) analysis qualitatively supports these findings, revealing two distinct melting peaks. The first peak relates to the eutectic melting temperature, while the second peak relates to the high melting temperature. The Sn−Ag−Ni solder alloy is more thermally stable than Sn−Ag. Heat flow data indicate enhanced phase transformations and improved thermal stability in Ni-containing solder alloy. This study provides a qualitative understanding of the addition of Ni and its effects on the IMC evolution, phase inter-reaction, and high-temperature reliability critical for optimizing lead-free solder alloys in electronic packaging applications.