| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系 === 102 === High-temperature materials are demanding for high-power electronics, so the material of soldering need to support the high temperature. Currently, Pb is proven to be harmful to the environment and human health, so the searching for high temperature lead-free solders becoming to be a demanding need. In this study, we choose Au-Ge eutectic alloy to be the solder, reactions between Au-Ge solders and Ni or Cu substrates have to be investigated to evaluate the Au-Ge based high-temperature solders.
In the results of the interfacial reaction between Au-12wt. % Ge (Au-12Ge) and Ni substrate, after a 8-hour reaction, the formation of F.C.C.-(Au, Ge, Ni)/NiGe alternating layers occurred in the interface. The stability diagrams and the 673 K isothermal section of the Au-Ge-Ni ternary system were calculated using the CALPHAD method to analyze the mechanism of alternating-layer formation. Ge was then determined to be the dominant diffusion specie. When Ge atoms accumulated at the NiGe/Ni2Ge interface, the interface became unstable and a new pair of F.C.C.-(Au, Ge, Ni)/NiGe would form, resulting in the previously-formed F.C.C.-(Au, Ge, Ni)/NiGe layers being separated from the original Ni2Ge/Ni substrate. The periodic thermodynamic instability caused subsequent nucleation of new alternating layers. The diffusion path across the interface is liquid/F.C.C.-(Au, Ge, Ni)/NiGe/⋯/F.C.C.-(Au, Ge, Ni)/NiGe/Ni2Ge/Ni. In the previous research, the alternating-layers structure was always found in the solid/solid interfacial reaction. Our research is the first diffusion couple that found this phenomenon only in the liquid/solid reaction, but not in the solid/solid reaction. In the past, the research of Au-12Ge/Cu interfacial reaction annealing at 400 oC and 300 oC, the unidentified “X” phase has been found and recognized as a ternary phase. The composition of X phase had a range from Au-74.72Cu-16.97Ge to Au-77.65Cu-15.58Ge. Therefore, we constructed the isothermal phase diagram of Au-Ge-Cu ternary system. We focus on the phase area near the ζ and ε1 phase. According to the new isothermal phase diagram, the “X” phase has been identified to be the ε1 phase.
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