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. © 2006 Elsevier B.V. All rights reserved.