In LTCC technology, printing is the most reliable and cost-effective process for line deposition on ceramic layers. An enhancement of resolution is required to realize modules in the highest frequency range which requires small lines and distances. The fine line print resolution is limited by two factors of processing. One is paste rheology itself, including viscosity particle size and thixotropic behavior. The other factor is the screen with limitations in mesh size, wire thickness, calendering, and angle of the screen fabric in the frame. From the viewpoint of the screen, the idea was to improve the fabric by coating. It can be shown that especially in concentric circles, even with fine line screens, arrays occur where no printing happens. These paste free areas exhibit a moiré effect and follow exactly the string angle of the screen. This is caused by the crossing of the strings of the fabric which does not allow a passing of the paste due to very narrow gaps. To facilitate the paste passing, the idea is to coat the fabric with a hydrophobic surface, so that the adhesion of the paste on the fabric wires becomes drastically reduced and therefore the detachment is enhanced. This coating is only appropriate for the bottom side of the screen and the spaces between the meshes. On the topside, the thixotropic effect of the paste requires good adhesion to achieve the necessary shear effect. Therefore, the topside of the screen should be coated hydrophilic to provide a significant paste adhesion to the screen, which is necessary for this shear stress. This development is supported by numeric simulation to predict the appropriate direction for these coated screens to improve the paste rheology.

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Low-temperature co-fired ceramic (LTCC) are widely acknowledged for wide-band and microwave circuits. Within the project consortium KERAMIS, implementation of higher functionality in LTCC substrates is being investigated. Among the applications considered are a 4 × 4 switch matrix [1], voltage-controlled oscillators [2], and amplifiers for multimedia satellite communications working in Ka-band. In order to add more functionality (e.g., filters, couplers) in LTCC, current patterning limits of line width and line separation need to be extended. Four different technologies were considered 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. Evaluation of patterning technologies is based on a test coupon that 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 μm. Two substrate materials, Du Pont tapes 951 and 943, are included in the study. In addition to the main frequency band of interest in the project (17–22 GHz), these structures have been characterized up to 50 GHz. Electrical results are correlated to physical measurements of the structures (line width, spaces, and tolerances) and are evaluated with respect to performance, manufacturability, and yield. Results show excellent performance for screen-printed structures and demonstrated the importance of mask tuning to achieve optimum resolution (under etching etc.).

KERAMIS is the acronym of a German research and development project funded by the German Space Agency (DLR) and the Federal Ministry of Economics and Technology (BMWI). The consortium is developing an RF circuit technology for Ka band multimedia satellite applications. A set of modules has been designed, manufactured, and tested by the partners of the consortium. The goal of this effort is to qualify the KERAMIS technology for space applications and to participate in an on-orbit-verification (OOV) program of the DLR. The launch of the technology verification satellite (TET) is scheduled for late 2010. This paper will give an overview of innovative circuit and module designs as well as the assembly, integration, and test results of the project. The authors will present a modular circuit concept for state-of-the-art transmitters and receivers in space at around 20 GHz. Selected modules are a 4 × 4 switch matrix, two synthesizers, and other RF modules. All circuits are based on multilayer ceramic (LTCC) including passive components, transitions, housings, and DC supply.