Towards highly conductive silver pastes for LTCC power electronics

摘要

The realization of high current conductors in LTCC multilayer architectures was studied. By mixturesof spherical silver powders, maximum tap densities above 7 g/cm~3 could be obtained. On pressedcylinders a good correlation between tap density and total shrinkage was found. Pastes were made ofthe highly packed silver powders and detailed investigations regarding paste sintering kinetics andinteractions between paste ingredients among one another as well as between paste ingredients andLTCC substrates were made. The pastes did not show a pronounced correlation between tap densityand total densification. With increasing solid content of the pastes, the shrinkage printed-dry, theshrinkage dry-fired and the specific sheet resistance decreases. These findings can be used to controlthe filling degree of channels or grooves as well as the properties of the fired conductor. Expansioneffects of the pure silver powders during sintering could be correlated to gas pressure effects, wherebythere are obviously different kinds of gas formation in fine and coarse powders. Avoiding of camberof freely sintered LTCC should be attained if new LTCC materials are showing different sinteringbehavior, e. g. strong and early crystallization building of diffusion barriers or the possession of aglass phases which will not incorporate silver oxide. Research on this target should be done. Therealization of high current conductors in constrained sintered LTCC was successfully shown. A pastecomparable to standard values for direct copper bond (DCB) substrates with a thickness 35 μm of0,48 mOhm/sq is introduced.