LTCC - Glass-ceramic tapes und multilayer technology for packaging and passive integration in microsystem technology applications

LTCC multilayer technology based on glass-ceramic tapes sintered at low temperatures allows innovative packaging solutions for hybrid microelectronics and microsystems technology. Due to it's miniaturisation possibilities, the potential for integrating passive

components, and the high reliability of the ceramic material even under extreme conditions, the concept exhibits great potential, among other things, for fabricating microsystems, intelligent sensors and multicomponent modules for communication technology and automotive electronics. Due to local differences in shrinkage during sintering, with increasing size of the LTCC multilayers it becomes more and more difficult to ensure precise positioning of vertical structures, e.g. vias. This precision - ensured over the complete LTCC laminate surface - is mandatory for automated assembly techniques (e.g. flip chip mounting). Therefore, a sintering technology which avoids shrinkage in lateral (x-y) direction is necessary. The new zero shrinkage concept which is part of this project is based upon multilayers made from two LTCC tapes (for inner and outer layers) of different composition and distinct sintering temperature. Hence, both tapes of the compound fulfil different functions, during sintering and application. For LTCC applications, the substrate surface (the outer layer) shall be compatible with thin film processes, the inner layer in contrast shall assure the refiring stability of the compound. Starting from the development of suitable glasses for glass-ceramic compound materials, different varieties for outer layers were developed and successfully tested. The essential parameter for the inner layers was a low sintering temperature as well as obtaining an almost complete crystallisation of the material's glassy phase. Thus, the refiring stability of the compound's inner layers could be achieved. Varieties of both layers were processed to LTCC multilayers. The outer layer shows very small grain and pore size and a very smooth surface. The small roughness guarantees the desired compatibility with thin film processes. Lateral shrinkage could be reduced down to 1%. Project partners are the BAM division V.4 and the companies W.C. Heraeus, Siegert TFT und VIA electronic. The project is funded by the German Ministry of Economy and Labour.