Characterization of the isothermal solidification process in the Ni/Au-Ge layer system
Weyrich, Nico ; Leinenbach, Christian
In: Journal of Materials Science, 2015, vol. 50, no. 10, p. 3835-3844
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- The eutectic Au28Ge (at.%) solder alloy in combination with Ni substrates or Ni coatings is interesting for applications in transient liquid phase (TLP) bonding. To achieve sound joints with high re-melting temperatures, it is necessary to gain profound knowledge about the joining process. In this work, the isothermal solidification behavior in the Ni-Au28Ge (at.%) system was analyzed by means of microstructure evolution and time to complete solidification. In short-time annealing experiments the early stage of the reaction (<300s over liquidus temperature) was investigated. It was observed that a continuous layer of Ni5Ge3 forms at the substrate-solder interface before scallop-like NiGe grains start to grow as solidification proceeds. Cyclic differential scanning calorimetry measurements were applied to estimate the time to complete solidification. Solidification was completed after less than 1h in the Ni-Au28Ge (at.%) system, which enables comparably short processing times for TLP bonding.