Low temperature TLP bonding of Al2O3-ceramics using eutectic Au-(Ge, Si) alloys

In this study, Al2O3-ceramics were joined via TLP bonding using interlayers of eutectic Au-12Ge (wt%) and Au-3Si (wt%) solder alloys, respectively, with a melting temperature of 361 and 363°C and Ni wetting layers. The Ni layers were part of a metallic multilayer coating (Ti/W/Ni) applied on the ceramic surface to ensure wetting and adhesion during the joining process. For comparison, a soldering process was performed as well by changing the multilayer structure to Ti/W/Au. With respect to the different joining processes the influence of the variation in wetting layers on the interface reactions, mechanical properties and re-melting temperature was analyzed by scanning electron microscopy, shear testing, and differential scanning calorimetry. It is shown that sound joint can be produced at a joining temperature of 400°C, achieving reasonable shear strength and re-melting temperatures more than 550°C above the initial melting temperature of the filler meta

Joining of Cu, Ni, and Ti Using Au-Ge-Based High-Temperature Solder Alloys

Au-Ge-based solder alloys are promising alternatives to lead containing solders due to the fact that they offer a combination of interesting properties such as good thermal and electrical conductivity and high corrosion resistance in addition to a relatively low melting temperature (361°C for eutectic Au-28Ge at.%). By adding a third element to the eutectic Au-28Ge alloy not only the Au content could be reduced but also the melting temperatures could be further decreased. In this study, in addition to the eutectic Au-28Ge (at.%) two ternary alloys were chosen from the Au-Ge-Sb and Au-Ge-Sn system, respectively. The soldering behavior of these alloys in combination with the frequently used metals Cu, Ni, and Ti was investigated. The interface reactions and microstructures of the joints were characterized in detail by SEM and EDX analysis. For the determination of the mechanical properties, shear tests were conducted. Mean shear strength values up to 104MPa could be achieved

Characterization of the isothermal solidification process in the Ni/Au-Ge layer system

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