Nucleation behaviors of the intermetallic compounds at the initial interfacial reaction between the liquid Sn3.0Ag0.5Cu solder and Ni substrate during reflow

► NiSn compound nucleated heterogeneously during the liquid solder/solid Ni reaction. ► A ternary Sn-Cu-Ni amorphous diffusion zone formed at the SnAgCu/Ni interface. ► Base structure, atom cluster and SRO structure were observed in an amorphous zone. ► Metastable NiSn and Cu6Sn5 nano cells were also observed within the amorphous zone. ► The formations of both compounds take place through the homogeneous nucleation.