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Copper as a material with a high electrical and thermal conductivity awakes large interest for many applications in industry, e.g. thermal management of electronic components. Powderbased manufacturing techniques (e.g. Selective Laser Melting, Binder Jetting, Fused Filament Fabrication and Metal Injection Molding) enable the complex shaping of metals. Especially the methods without melting processes like Binder Jetting, Fused Filament Fabrication and Metal Injection Molding have a great potential for complex Cu structures. These techniques built up a powder-based green body and require a subsequent sintering step to reach a high density with maximum properties. This work reports the development of the heat conductivity during pressure-less sintering of Cu powder green bodies. The experimental results are compared to analytical models and a numerical simulation and show the limits of the reachable heat conductivity depending on the remaining porosity and the impurity concentration.

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This work will present possibilities for the characterization of copper powder green bodies and sintered copper microstructures during pressureless sintering. The introduction of new parameters to microstructural characterization based on qualitative and quantitative microstructural analysis will facilitate the systematic optimization of the sintering process. As a result of the specific evaluation of the microstructure evolution, conventional isothermal sintering could be successfully replaced by multi-step temperature profiles, thus achieving sintering densities of more than 99 % by simultaneously reducing process time. This systematic optimization of the sintering process of Cu through specific microstructural analysis may now be applied to sinter-based manufacturing technologies such as Binder Jetting and Metal Powder Injection Moulding, enabling the manufacture of complex and highly conductive Cu parts for applications in electronics.

The viscosity behavior of extrusion pastes comprised of a PVB melt and varying amounts of nano‐zirconia powder have been explored with special emphasis on the impact of a dispersant to reduce the viscosity. In contrast to suspensions with nanopowders, the maximum solid loading in the highly viscous extrusion pastes studied is not limited by attractive interparticle forces. However, at a solid loading >30 vol% the pastes had too high viscosity to be processed due to the high number of adsorbed polymer molecules. By adding a decoupling agent that reduced the work of adhesion of the polymer molecules on the zirconia particles, the viscosity of the pastes could be lowered significantly. The calculated work of adhesion is consistent with the viscosity behavior of the feedstock and is confirmed by wetting angles that have been experimentally determined. It is shown that the effect of the dispersant cannot be explained by electrostatic or steric stabilization of the particles in the melt. A unifying scheme is proposed where the limiting factors “agglomeration” and “adsorption” for a high solid loading combined with the necessary mode of function of the dispersant are illustrated as a function of the viscosity of the medium and the particle size. The viscosity‐lowering decoupling effect of the dispersant was a prerequisite for reaching a solid loading of 50 vol% in the additional feedstock development. The feedstock with 50 vol% nano‐zirconia could be extruded to a tape and sintered to a relative density of 97% at 1200°C.