No abstract

a b s t r a c tIn this study, the interfacial reactions on Sn, Sn-3.0Ag-0.5Cu, Sn-0.7Cu, Sn-58Bi and Sn-9Zn lead-free solders with the Au/Pd/Ni/Cu multilayer substrate at 240-270 • C for 20 min to 20 h were investigated. The experimental results showed that the (Ni, Cu) 3 Sn 4 phase is converted to the (Cu, Ni) 6 Sn 5 and Cu 3 Sn phases in the Sn/Au/Pd/Ni/Cu system when the reaction time is longer than 4 h. In Sn-3.0Ag-0.5Cu/Au/Pd/Ni/Cu and Sn-0.7Cu/Au/Pd/Ni/Cu systems, the (Cu, Ni) 6 Sn 5 and Cu 3 Sn phase were observed, and only the Ni 3 Sn 4 phase was formed at the Sn-58Bi/Au/Pd/Ni/Cu interface. Furthermore, the Pd 2 Zn 9 and NiZn phases were formed in the Sn-9Zn/Au/Pd/Ni/Cu system. When the reaction time was longer than 4 h, the Pd 2 Zn 9 , NiZn, and Ni 5 Zn 21 phases were formed at the interface. The reaction mechanism for all the reaction systems was diffusion-controlled. The Sn-58Bi/Au/Pd/Ni/Cu system was found to have the lowest activation energy when compared with other systems, and its value was 17.43 kJ/mol.

The interfacial reactions of molten Sn and molten In with solid Cu substrate were determined by studying their reaction couples. The annealing temperature was 300 ЊC. The phases formed at the interface were examined by optical microscopy, scanning electron microscopy, and electron probe microscopy analysis (EPMA). The thickness of the reaction layers was measured using an image analyzer. For Cu/Sn couples, two phases, ε and , were found. Only the Cu 11 In 9 phase was observed at the interface of the Cu/In couples. In comparison with the results of couples of solid Sn and solid In with solid Cu substrate, their phase formation sequences were similar; however, the interfacial morphology and the reaction rates were different. For the liquid/solid couples, the reaction rate was much faster and the interface was nonplanar. A mathematic model was also proposed to describe the dissolution of the Cu substrate and the growth of the intermetallic compounds. Fast dissolution of the substrate was observed in the beginning of the reaction and was followed by a relatively slow growth of the intermetallic compounds at the interface.

The effect of Cu added eutectic Sn–9Zn solder reacting with the Ag substrate has been investigated in this study. Three Ag–Zn intermetallic compounds (IMCs), ∈–AgZn3, γ–Ag5Zn8, and ζ–AgZn, were formed on the Sn–9Zn/Ag interface at 260 °C. While Cu was gradually added to the Sn–9Zn alloy, microstructures of intermetallic compounds changed dramatically. The intermetallic compound microstructures became loose and Sn and Cu atoms in the Ag-Zn intermetallic compounds increased. If more than 3 wt% of Cu was added to the Sn-9Zn alloy, Ag-Sn intermetallic compounds were formed on the Ag surface and massive spalling of Ag–Zn IMC layers from the Ag surface occurred in a short reaction time.

Ag-Sn alloys are one of the most promising lead-free solders. Their reactions with Au substrates have been examined by using the reaction couple technique. Sn-3.5wt.%Ag/Au and Sn-25wt.%Ag/Au couples have been prepared and reacted at 120, 150, 180 and 200∞C for various lengths of time. Three phases, d-AuSn, e 2 -AuSn 2 , and h-AuSn 4 , are found in all the couples. The thickness of the reaction layers increases with higher temperatures and longer reaction time, and their growth rates are described by using the parabolic law. Arrhenius equation is used to describe the temperature dependence of the growth rates. The activation energy of the growth of the intermetallic layers in both kinds of the reaction couples is similar and is determined to be 76.74 KJ/mole. Based on the reaction path knowledge and interfacial morphology, it is concluded that Sn is the fastest diffusion species in the couples.