Interfacial reactions between lead-free solders and the multilayer Au/Ni/SUS304 substrate

Interfacial reactions between Sn, Sn-3.0 wt.% Ag-0.5 wt.% Cu (SAC) and an Au/Ni/SUS304 stainless steel (SUS304) substrate were conducted using the reaction couple technique at 240, 255 and 270 degrees C for 1-5 h. In the earliest stage of the reaction, only the Ni3Sn4 phase was formed on the Sn/Au/Ni/SUS304 interface. As the reaction time increased to 4 h, the Ni layer was gradually consumed and the Ni3Sn4 phase detached from the interface. Meanwhile, the Sn reacted with the SUS304 to form the FeSn2 phase. In the SAC/Au/Ni/SUS304 reaction couple, both Ni3Sn4 and CU6Sn5 phases were formed on the interface. When the reaction time exceeded 4 h, the Ni3Sn4 phase disappeared; the CU6Sn5 phase was spread over the SUS304 surface and the FeSn2 phase was formed on the SUS304 surface. The growth of intermetallic compounds can be described by the parabolic law and the reactions were diffusion-controlled.