In order to evaluate the feasibility of replacing the traditional Ni-P with the amorphous Ni-Cu-P barrier layer, soldering experiments were conducted on self-manufactured Ni-P and Ni-Cu-P amorphous coatings. Notably, after soldering with pure Sn, the Ni-Cu-P coating reveals only two layers of thin and contiguous intermetallic compounds (IMCs). In contrast, there are not only two layers of IMC, but also a significant amount of irregular \({\text{Ni}}_{3}{{\text{Sn}}}_{4}\) in the Ni-P coating, which tends to cause stress concentration at the interface, thereby accelerating the failure of solder joints during service. Furthermore, the addition of Cu can improve the wettability of the Ni-Cu-P coating, reduce the thickness of the \({\text{Ni}}_{3}{{\text{Sn}}}_{4} {\text{and}} {\text{Ni}}_{3}{\text{P}}\) -IMC formed, and decrease the consumption rate during the soldering process. During the kinetic studies, it is noteworthy that the amorphous Ni-Cu-P layer displays a much higher activation energy (120 kJ/mol) for IMC growth during soldering, which is in a sharp contrast to the Ni-P layer (42 kJ/mol). Therefore, we can assert that the amorphous Ni-Cu-P exhibits superior diffusion barrier properties compared to the traditional Ni-P layer.
