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|Development of an AlN HTCC Multilayer System with a Tungsten Cofiring Metallization|
|Keywords: HTCC, AlN, multilayer|
|AlN ceramic materials exhibit a high value of thermal conductivity and are therefore of interest in various microelectronic applications, where power and heat dissipation are important (e.g. power electronics, hermetic packaging). The opportunity to use AlN with tungsten metallization in a multilayer system with a cofiring process (HTCC – high temperature cofired ceramic), possess the possibility to realize miniaturized three dimensional designed components. Tape casted AlN tapes exhibit a high homogeneity and quality, which is characterized by microscopic observations. Tungsten thick film pastes are developed for cofiring and screen printed on the green tapes. Laminating to a multilayer is possible by standard isostatic or uniaxial pressing processes. The debindering and the following sintering are the main process steps to get a proper HTCC component. For pure AlN multilayers a high quality in density, flatness and thermal conductivity (up to 180 W/mK) can be reached. A key factor for cofiring AlN with W metallization is the proper adaption of the shrinkage behavior of both to realize components with a low warpage. Systematic analysis of the shrinkage values in the temperature field of 1600..1830 °C with respect to the paste formulations and technological aspects will demonstrate possibilities to adapt the shrinkage of the paste to the tape during sintering. Furthermore different analyses will demonstrate that small residues of carbon after debindering will lead to a shift in the outbuilding of the liquid phases in the AlN tape as well as the building of tungsten carbide with the metallization. Such effects show a negative influence on the homogeneity of flat multilayers and of the electronic conductivity of the metallization. The optimizations of the debindering process as well as the formulation of the AlN tape and W paste composition are discussed together with microstructural and technological aspects.|
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