Tagungsbeiträge

Die Via- Gestaltung von HF-Multilayer-Leitungsstrukturen wird bezüglich möglicher Leitungs-Moden und der Grenzfrequenz untersucht und bewertet. Mit diesen Ergebnissen werden Leitungsübergänge und Filter für das K-Band optimal gestaltet. Bei der Realisierung werden verschiedene Technologievarianten eingesetzt und die Ergebnisse verglichen. Für die Fine-Line Strukturierung wird die Fodel-Technologie eingesetzt. Zum Vergleich und zur Verbesserung der Leitfähigkeit wird eine Direkt-Vollmetall-Beschichtung in 0-Schrumpfungs-cofire-LTCC-Technologie angewendet, die mittels Ätztechnik strukturiert wird.

Over the last years, the thickfilm technology for LTCC (Low Temperature Cofired Ceramics) has constantly been improved. Using fine-line and photo-imageable techniques, the possible resolution increased up to 30 mm. However, the problem is that the thickfilm technology is based on bastes or inks, which limits conductivity, accuracy, resolution and chemical processability. The reason for this ist the particle structure of the pastes and inks. For both screen printing and jet printing, well-defined properties are necessary. Furthermore, the typical cofiring process requires special sintering conditions. Therefore, the particle size and the material composition are limited. In this work, various zero-shrinkage techniques for LTCC and especially PAS (Pressure Assisted Sintering) are described, and their features are compared with one another for standard thickfilm applications. Furthermore, the possibilities of the realization of buries bulk materials are explained. Structures of such a kind are compared with screen printed structures. Furthermore, structured metallic bulk materials can be used to realize special kinds of cavities. In contrast to organic inlays, they are removed by etching after sintering, which ensures that the cavities maintain their accuracy during the whole process. This helos to produce large and filigree menbranes and channels as well as to modify the inner surface of the cavities. The new technologies can help to provide the inner layers with more functions and despite the higher production effort, they can increase the spectrum of LTCC multilayers especially in the fields of radio frequency, power and fluidic applications.

The size of printed structures on LTCC modules has been considerably reduced in the last years. New printing technologies and photo sensible inks allow lines and spaces of 50 æm and less. Very often the complexity of LTCC modules is limited by the dimension of the vias. Therefore it is desirable to reduce the diameter of the vias to the same order of size. Vias in LTCC can be manufactured by mechanical punching or laser drilling. It is also possible to use both technologies to cut cavities and notches of different shapes. Progresses have been achieved recently in both technologies. Today mechanical punching is the standard technology. The main advantage of laser drilling, milling and cutting is that the laser tool shows no wear and tear. There is no need to change tools and all changes of designs lead only to changes of CAD-files. For drilling we have used a tripled YAG-Laser with a trepanning optics. Cutting is also possible with this machine using a highly dynamic XY precision table. The UV-laser was chosen because the diameter of the laser spot may be reduced to 20 æm and below. The laser was used to manufacture microvias, small ditches and notches. First experiences showed, that the ?technological window? for the process is relatively small. To avoid burned structures on the surface and melting of the glass particles the?tool parameters? like laser power and cutting speed have to be chosen very carefully. Test structures with microvias, notches and ditches were manufactured using different LTCC materials of different thicknesses. The first applications were small inductors for RF- and microwave circuits. The investigations were done within the KERAMIS project. This project is funded by the German Ministry of Education and Technology. The project consortium consists of six companies, research institutes and universities and is developing ceramic based microwave packages for satellite applications.

Within the project KERAMIS (Ceramic Microwave Circuits for Satellite Communications), which is funded by the German Ministry of Education and Technology, a consortium of six companies, research institutes and universities are developing ceramic based microwave circuits and modules for satellite applications. Examples of them are a Reconfigurable Switch Matrix and Hermetic Microwave Packages. - Our investigations are focused on developing, manufacturing and optimizing several types of broadband line transitions, different types of microwave interconnections to other modules or to the motherboard and matching networks and Filters. - Fodel® inks from DuPont were used to realize these multi-layer LTCC elements. Some of these elements include laser-structured micro-vias. - All line transitions and microwave interconnections are required to have a wide bandwidth and a very good impedance matching over the desired frequency range. The bandwidth limitations of the used arrangements depending on their geometrical properties was analyzed, evaluated and optimized and was applied to : - &hahog; design a LGA connection and a coplanar-embedded coplanar-coplanar line transition - &hahog; demonstrate the need for fine line structuring techniques, such us the well known Fodel® Technology, and micro vias when the modules are supposed to work at frequencies over 20 GHz (depending on the application) - 3D S-Parameter Simulations as well as S-Parameter measurements of all manufactured structures are going to be presented and explained.