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.