Influence of P Content in Electroless Plated Ni-P Alloy Film on Interfacial Structures and Strength between Sn-Zn Solder and Plated Au/Ni-P Alloy Film

Abstract

The interfacial structure and strength of solder joints between Sn–9 mass%Zn solder and plated Au/Ni–P alloy film on a Cu substrate have been investigated. Three reaction layers with 0.2 to 0.5 \\micron thickness were formed along the interface between the plated Ni–P alloy films and Sn–9 mass%Zn solder. The outermost layer contains a Ni–Sn intermetallic compound. The middle layer contains approximately 40 mass%Au, 35 mass%Zn, 20 mass%Ni and 5 mass%Sn. The thickness of the Au layer is 0.1 \\micron, so the Au layer does not dissolve. The innermost layer contains about 63 mass%Zn, 25 mass%Ni, 10 mass%Au and 2 mass%Sn. The strength of the Sn–9 mass%Zn solder joints take almost the same values independent of P concentration. The strength of Sn–Zn solder joints with Sn–Zn/Ni–2 mass%P, Sn–Zn/Ni–4 mass%P and Sn–Zn/Ni–8 mass%P joints were found to be almost constantly independent of reflow cycles. Therefore, Sn–9 mass%Zn solder is considered to be an excellent solder material for plated Ni–P alloy films.