Reaction dynamics of diffusion soldering with the eutectic Au–Sn alloy on copper and silver substrates

The dynamics and the morphology of the intermetallic phase evolution for isothermal diffusion soldering with the eutectic Au–Sn alloy as the solder material on copper and silver substrates was investigated. The phases involved and the reaction parameters like the rate of the intermetallic layer growth and the activation energy could be determined by in-situ X-ray diffraction. Transmission electron microscopy and energy dispersive X-ray spectroscopy bring further insight into the morphology changes that occur during the process. The results contribute to a better understanding of this advanced joining method extensively used in semiconductor packaging.

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► Copper reacts with the eutectic Au/Sn alloy to form a ternary Au2Cu6Sn2 compound.
► Silver reacts with the eutectic Au/Sn alloy forming a binary Ag3Sn compound.
► The reaction progresses linear with time, indicating a reaction controlled process.
► Reaction can be described by Arrhenius law with an activation energy of 1.2 eV.
► Copper reacts 24 times faster than silver.