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2012
Conference Paper
Titel
Towards highly conductive silver pastes for LTCC power electronics
Abstract
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.