Passive RF band-pass filters in an LTCC module made by fine-line thick-film pastes

Low-temperature co-fired ceramic (LTCC) materials offer a good possibility to bury passive components and to produce compact electronic circuits. These properties were utilised in this study to realise a passive band-pass RF filter in the LTCC module. The filter consisted of planar inductors, capacitors and microstrip lines. The component values of the filter structure were determined by using the APLAC circuit simulator. Commercial fine-line thick-film Au paste and shrinkage-matched LTCC Ag pastes were used to print narrow conductor lines by gravure-offset-printing on different LTCC sheets. Narrow conductor lines down to 50 μm wide were printed successfully without shrinkage mismatch during firing. A network analyser and different microscopes were used to study, respectively, the electrical and material properties of the patterns and filters. Variations of the printed line widths and of the electrical values of the patterns and filters were about ±10%. The highest centre frequency of the realised filters was about 2 GHz.