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|Material Behavior of Low Temperature Co-Fired Ceramics at Elevated Temperatures and its Impact on Applications|
|Keywords: LTCC, high temperature behavior, glass softening|
|To enable the usage of metals of improved conductivity like Ag, AgPd, Au or Cu as conducting pastes and take advantage of material properties of its ceramic filler material, Low-Temperature Co-Fired Ceramics (LTCC) are densified at temperatures below 900°C via glass assisted sintering. The densification mechanism is controlled by viscous sintering in combination with the crystallization of the glass matrix. Hence, the glass composition and its corresponding softening behavior are of utmost importance. The transition range of the remaining amorphous phase as well as the intermediate and final crystallization products have great influence on possible lifetime predictions and the extension of the application range to elevated temperatures. However, since multilayer ceramics based on LTCC composites are more and more in focus for manufacturing of highly integrated devices for sensor applications, their material behavior at elevated temperature gains more and more interest. Material characterization in this case comprises the mechanical behavior as well as the insulating performance of LTCC substrate materials at elevated temperatures. This is necessary, since with increasing temperature, the electrical resistance of dielectric materials such as ceramics decreases. Therefore, leakage currents through the substrate as well as softening of the material limit the application temperature of each LTCC material system. In this study, four commercial LTCC substrate materials in the sintered state were investigated in respect to the temperature dependence of their mechanical and electrical properties. Characterization included 3-point bending tests of single layer substrates, determination of sintering viscosities and investigation of visco-elastic behavior as well as their electrical resistivity in dependence on temperature. These results were then correlated to the composition of the glasses, determined by ICP analysis, as well as their crystallization products apparent in the composite, which were determined by XRD of sintered substrates, and microstructure analysis. Based on the understanding gained from these results, a novel LTCC composition with improved electrical behavior and good temperature stability up to 650°C will be presented and its properties will be discussed.|
|Christian Bienert, Student
University of Erlangen-Nuremberg
Erlangen, Bayern 91058,