Characteristics of Reactive Ni₃Sn₄ Formation and Growth in Ni-Sn Interlayer Systems

The near-isothermal growth and formation of Ni₃Sn₄ intermetallic compounds (IMC) in Ni-Sn interlayer systems was studied in the solid state at 473 K (200 °C) and under solid–liquid conditions at 523 and 573 K (250 °C and 300 °C) from an initial state of a few seconds. Scalloped solid-state IMC formation was mainly driven by grain boundary diffusion of Ni through the IMC layer combined with the grain coarsening of the IMC layer. Under solid–liquid conditions, the formation of faceted and needle-shaped Ni₃Sn₄ grains as well as an atypical IMC growth behavior with similar parabolic growth constants for 523 K and 573 K (250 °C and 300 °C) was observed within the first 180 seconds of the holding time, and IMC growth occurred as an isothermal solidification from the Ni-saturated Sn melt. Due to the progressive densification of the IMC layer and the diffusion-controlled growth, the kinetics slowed down by approximately one order of magnitude after 180 seconds of annealing. The final stage was characterized by the formation of IMC islands ahead of the interfacial Ni₃Sn₄ layer. Needle-like IMC growth was effectively suppressed under combined solid-state and solid–liquid conditions. Textured Ni₃Sn₄ IMC formation at the Ni-Sn interface was approved with pole figure measurements. The activation energy Q for solid–liquid IMC formation was calculated as 43.3 kJ/mol, and processing maps for IMC growth and Sn consumption were derived as functions of temperature and time, respectively.