Retardation of spalling by the addition of Ag in Sn–Zn–Bi solder with the Au/Ni metallization

The work presented in this paper focuses on the role of Ag addition in the Sn–8%Zn–3%Bi solder on the shear strengths and the interfacial reactions with Au/Ni/Cu pad metallization in ball grid array (BGA) applications. Sn–Zn–Bi(–Ag) solder alloys were kept in molten condition (240 °C) on the Au/electrolytic Ni/Cu bond pads for different time periods ranging from 1 to 60 min. After the shear test, fracture surfaces were investigated by scanning electron microscopy. Cross-sectional studies of the interfaces were also conducted to correlate with the fracture surfaces. The results indicated that the spalling of the Au–Zn intermetallic compound (IMC) layer was regulated by the addition of 0.3%Ag in Sn–Zn–Bi solder. The retardation of spalling of the initial IMC, limited the formation of Ni–Zn compound in the Ag doped Sn–Zn–Bi solder. The formation of thick Ni–Zn IMC layer in Sn–Zn–Bi alloy deteriorated the mechanical strength of the joints after extended reflow.