Effects of Ga Addition on Interfacial Reactions Between Sn-Based Solders and Ni

Abstract

The use of Ga as a micro-alloying element in Sn-based solders can change the microstructure of solder joints to improve the mechanical properties, and even suppress the interfacial intermetallic compound (IMC) growth. This research investigated the effects of Ga addition (0.2–1 wt.%Ga) on the IMC formation and morphological evolution in the Sn-based solder joints with Ni substrate. In the soldering reaction at 250°C and with less than 0.2 wt.%Ga addition, the formed phase was Ni₃Sn₄. When the Ga addition increased to 0.5 wt.%, it changed to a thin Ni₂Ga₃ layer of ∼1 μm thick, which stably existed at the interface in the initial 1-h reaction. Subsequently, the whole Ni₂Ga₃ layer detached from the Ni substrate and drifted into the molten solder. The Ni₃Sn₄ phase became dominant in the later stage. Notably, the Ga addition significantly reduced the grain size of Ni₃Sn₄, resulting in the massive spalling of Ni₃Sn₄ grains. With 1 wt.%Ga addition, the Ni₂Ga₃ layer remained very thin with no significant growth, and it stably existed at the interface for more than 10 h. In addition, the solid-state reactions were examined at temperatures of 160°C to 200°C. With addition of 0.5 wt.%Ga, the Ni₃Sn₄ phase dominated the whole reaction. By contrast, with increasing to 1 wt.%Ga, only a thin Ni₂Ga₃ layer was found even after aging at 160°C for more than 1200 h. The 1 wt.%Ga addition in solder can effectively inhibit the Ni₃Sn₄ formation in soldering and the long-term aging process.