Interfacial reactions of Sn-0.7Cu, Sn-58Bi and Sn-9Zn lead-free solders with the Au/Ni/SUS 304 substrate

This study investigates the interfacial reactions between three kinds of lead-free solders, Sn-0.7 wt%Cu (SC), Sn-58 wt%Bi (SB) and Sn-9 wt%Zn (SZ), and Au/Ni/SUS 304 substrates. The reaction temperatures were at 240, 255 and 270 °C, and the reactions times were varied between 1 to 5 hours. According to experimental results, only the (Cu,Ni)6Sn5 phase was found in the SC/Au/Ni/SUS 304 couples. When the Ni layer was completely consumed, the massive spalling of the (Cu,Ni)6Sn5 phase was found in the solder. And then the FeSn2 phase was formed at the SUS 304 surface. Only the Ni3Sn4 phase was found at the SB/Au/Ni/SUS 304 interface. In the SZ/Au/Ni/SUS 304 couple, the Ni5Zn21 phase was formed at the interface. The thickness of the IMC in the SB/Au/Ni/SUS 304 and SZ/Au /Ni/SUS 304 couples increased with increasing the reaction time.