Technology Benchmarking of High Resolution Structures on LTCC for Microwave Circuits

Low temperature co-fired ceramics (LTCC) is being widely used for microwave circuits. The BMBF funded R&D-project KERAMIS focuses on larger implementation of functionality in LTCC substrates to allow designs with "standard" MMICs. Target applications are circuits for multimedia satellite communications. In order to add more functionality in LTCC, current patterning limits of line width and line separation (100 mum) need to be extended. Four different technologies are considered candidates for higher resolution: a) fine line printing technology with special screens, b) photo-imageable pastes, c) etching of thick film conductors (co- and post-fired) and d) thin films on LTCC. For this purpose, a test coupon was designed and manufactured by the consortium members. The artwork contains lines, line transitions, ring resonators (microstrip and stripline), edge-coupled filters, DC blocking structures, and various lines for DC resistance testing. The smallest gap definition is 50 mum. Two substrate materials, Du Pont tape 951 and 943, are included in the study. Besides the main frequency band of interest in the project (17-22 GHz), these structures have been characterised up to 50 GHz. Electrical results are correlated to physical measurements of the features (line width, spaces and tolerances). Data are evaluated with respect to performance, manufacturability, and yield