Formation of alternating interfacial layers in Au-12Ge/Ni joints

Au-Ge alloys are promising materials for high-power and high-frequency packaging, and Ni is frequently used as diffusion barriers. This study investigates interfacial reactions in Au-12Ge/Ni joints at 300 °C and 400 °C. For the reactions at 300 °C, typical interfacial morphology was observed and the diffusion path was (Au) + (Ge)/NiGe/Ni5Ge3/Ni. However, an interesting phenomenon--the formation of (Au,Ni,Ge)/NiGe alternating layers - was observed for the reactions at 400 °C. The diffusion path across the interface was liquid/(Au,Ni,Ge)/NiGe/· · ·/(Au,Ni,Ge)/NiGe/Ni2Ge/Ni. The periodic thermodynamic instability at the NiGe/Ni2Ge interface caused the subsequent nucleation of new (Au,Ni,Ge)/NiGe pairs. The thermodynamic foundation and mechanism of formation of the alternating layers are elaborated in this paper.