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The advantages of Aluminium nitride (AlN) ceramics are a high bulk thermal conductivity, insulating resistance, dielectric strength, flexural strength and a coefficient of thermal expansion, which is well matched to semiconductor materials, like silicon carbide. AlN ceramics show high potential as substrate materials for thick film- / hybrid applications in the field of power electronics and multichip modules. These applications require metallisations with high ampacity. Herein, the direct copper bond technology (DBC) is state of the art. Nevertheless, DBC shows several disadvantages in the circuit building process, for instance the etching process for patterning the foil, what limits the structure resolution on the one hand. On the other hand, this subtractive process is expensive along with a high chemicals consumption. The use of copper thick film pastes (thick print copper-TPC) instead of DBC results in higher structure resolutions, is an easier industrial applicable, energy-saving and environmentally friendlier process [Gun16]. Due to the fact that copper thick films have to be fired in nitrogen atmosphere and the actual bottlenecks in copper production, what might rise the copper price [Wie17], thick print silver (TPS) seems to be a promising alternative to TPC. Moreover, the conductivity of silver is slightly higher than those of copper and silver can be fired in air. The aim of this study is to get insight the silver films sinter kinetics and the interface formation on AlN. Therefore, systematic variations in the paste recipe where done and the resulting film shrinkage, blister behaviour, solderability and adhesion strength where correlated with the sintering kinetics and the microstructure of the films. A significant role in this process play the inorganic components bismuth oxide and the glass. This is because of the ability of bismuth oxide solution in the glass matrix, what shifts the softening down to lower temperatures. The influence of the glass and bismuth oxide volume fractions on the glass-viscosity, sintering behaviour of silver pastes as well as the interfacial reactions with AlN were investigated by means of thermomechanical analysis, FESEM-cross sections of fired films and XRD. Phase transformation mechanisms and root causes for blister formation are investigated. It was found out that sinter kinetics in combination with the simultaneous glas softening and phase redistribution are crucial for the interface reaction, film adhesion and blistering. Ways to attain evaporation possibilities via controlled sintering retardation of the thick films are examined

The realization of high current conductors in LTCC multilayer architectures was studied. By mixtures of spherical silver powders, maximum tap densities above 7 g/cm3 could be obtained. On pressed cylinders a good correlation between tap density and total shrinkage was found. Pastes were made of the highly packed silver powders and detailed investigations regarding paste sintering kinetics and interactions between paste ingredients among one another as well as between paste ingredients and LTCC substrates were made. The pastes did not show a pronounced correlation between tap density and total densification. With increasing solid content of the pastes, the shrinkage printed-dry, the shrinkage dry-fired and the specific sheet resistance decreases. These findings can be used to control the filling degree of channels or grooves as well as the properties of the fired conductor. Expansion effects of the pure silver powders during sintering could be correlated to gas pressure effects, whereby there are obviously different kinds of gas formation in fine and coarse powders. Avoiding of camber of freely sintered LTCC should be attained if new LTCC materials are showing different sintering behavior, e. g. strong and early crystallization building of diffusion barriers or the possession of a glass phases which will not incorporate silver oxide. Research on this target should be done. The realization of high current conductors in constrained sintered LTCC was successfully shown. A paste comparable to standard values for direct copper bond (DCB) substrates with a thickness 35 μm of 0,48 mOhm/sq is introduced

The focus of this work was the optimization of a 10 Ω/□ thick film resistor (TFR) paste composition to obtain increased power capability, aging stability and minimum use of ruthenium oxide for cost savings without changing the defined narrow sheet resistance (R□) and temperature coefficient of resistance (TCR) specifications. In times of highly fluctuating precious metal costs, the use of a minimum of the precious metal ruthenium respectively ruthenium dioxide is one essential part for cost-effectiveness. The thick film paste formulation consists of the electrically conducting phase ruthenium dioxide, a lead-free glass phase and two inorganic additives for tuning thermo-mechanical and electrical properties of the formed films. A phthalate free organic vehicle with ethyl cellulose polymer was used to formulate a screen printable ceramic thick film paste. For this paper, RuO2 powders with various specific surface area values (BET) were prepared by thermal annealing of a precipitated fine ruthenium dioxide powder. All other solid and liquid components of the paste were the same as used for IKTS 10 Ω/□ TFR paste FK9611 for AlN substrates. Furthermore, the content of ruthenium dioxide in the paste compositions was changed systematically around an assumed target content to achieve the desired sheet resistivity. Concurrent to the variation of the ruthenium dioxide content the inorganic additives had to be adapted too. The influence of the variations of raw material and paste composition on the film properties were investigated by screen printing 24 resistors of 2 mm × 1 mm dimension on an 1” × 1” AlN substrate, firing at 850 °C for 10 minutes in air atmosphere and subsequently measuring R□, TCR, the stability of resistance ΔR/R0 effected by artificial aging of the resistors (stored 100 up to 1000 hours @ 200°C) and the maximum rated power dissipation (MRPD) as well as short term overload voltage (STOL). The results are discussed in regard to find an optimum between all demands of the most important electrical film properties.