A new simulation scheme for tape casting is presented and applied. The model allows considering both the macroscopic flow behavior and the orientation of individual particles inside the ceramic slurry. It is based on the smoothed particle hydrodynamics method, a particle‐based computational fluid dynamics solver, and Jeffery's equations of particle motion, which describe the rotation of rigid, ellipsoidal particles in a fluid. It is shown how different process parameters and the rheological behavior of the slurry influence its flow behavior, which in turn affects the orientation of nonspherical particles inside the slurry. The simulations predict that a preferred, anisotropic particle orientation develops in the green tapes, whose extent depends mainly on the powder properties. All simulations are performed with real tape‐casting data concerning geometry of casting unit, casting parameters, slurry rheology, and powder properties. The anisotropy results are confirmed by experimental analysis of cross sections of tape‐cast films made from different powders.
Cast green tapes exhibit an undesired shrinkage anisotropy attributed to particle alignment. In contrast, a high degree of particle alignment is desired for templated grain growth techniques. This paper investigates pure alumina and low temperature co-fired ceramic (LTCC) tapes, which were cast from powders of different morphology. It describes how the particle shape controls particle orientation and therefore anisotropic shrinkage. Special emphasis is given to the time dependent rotation behavior of the particles in the shear gradient during casting and to the casting parameters which influence the flow profile. This understanding is the key factor for the interpretation of particle orientation and anisotropic shrinkage.
Low Temperature Cofired Ceramic (LTCC) is used as a substrate material for microelectronic devices in satellite communication. Its dielectric properties and excellent variability allows a good compactness and a high level of integration. An LTCC antenna array for microwave signals operating at 30 GHz is presented. All components such as radio frequency distribution network, four waveguide phase shifters and horn antennas are integrated in one ceramic module. The phase shifters are implemented as high volume cavities in the LTCC. A tailored mixture of liquid crystal can be stored inside the cavities. By applying an electric field, the anisotropic LC-molecules are aligned. The field is provided through a biasing network with four electrodes and screen printed resistive layers with resistance values in the MΩ/□ range. The alignment and with it the phase shifting is nearly seamless. The antenna module is manufactured in multilayer technology and consists of more than 40 layers. Lamination is carried out by thermocompression in two steps. A water based adhesive is used in the second. The cofiring is done in a sintering press. Temperature and pressure profile are chosen carefully, considering the high volume of the laminate and the buried cavities inside the module. After sintering, the horn antennas are milled into the front side of the ceramic body, which is about 5 mm in height.
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