Pan Pacific Symposium Conference Proceedings


Author: Heiko Thust
Company: Technical U. of Ilmenau
Date Published: 2/2/1999   Conference: Pan Pacific Symposium

Abstract: Low Temperature Cofired Ceramics (LTCC) offers a wide range of opportunities to the designer by its almost unlim-ited number of layers. The compatibility to thick-film and the manufacturing process permit integrating printed resis-tors also in LTCC-modules. Resistors inside the multilayer structures were fired together with the glass-ceramic body. They undergo additional firings with each postfire step. Cofired resistor pastes require a shrinkage match to the tape due to firing and must be chemically compatible to the surrounding tape material. The glass in the resistors tends to interact with the tape glass, which leads to a shift in ratio glass to resistive particles, resulting in a shift of resistor characteristics. But the main advantage of buried resistors is the increase in integration density: Despite these advantages, Low Temperature Cofired Ce-ramics is typically limited by the low thermal conductivity of about 3 W/(mK). There is however another factor that should not be ignored. That means the easy workability of this material and new design possibilities in multilayer LTCC structures. It would be possible to integrate different kinds of thermal vias and thermal layers for a better heat distribution. Several configurations were tested and com-pared. Different patterns of thermal vias in the same area were fabricated. In addition to this, areas of silver paste for a definable heat convection were added in each layer. Equally, the enormous influence of a small metal plate at the backside will be demonstrated. Using a new manufacturing process it is possible to improve three times the amount of the current-carrying capacity of lines compared with conventional thick-film technology. In addition to this, the thermal conductivity would be also improved three times. The laser-scraping of ditches permits the fabrication of any cross section. This is followed by the filling process. Differ-ent methods were tested and compared. In contrast to the top layer, buried ditches must be completely filled. Furthermore, the ingredients of the used paste play a deci-sive part.

Keywords: LTCC, thick-film, laser, thermal vias, heat dissipation

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