Sevgi ŞENGÜL, BSc. Student
Metallurgy and Materials Engineering
Yıldız Technical University
Faculty of Chemistry - Metallurgy
Development of Pb-Free Glass Ceramics for ULTCCs
ULTCC (Ultra-low Temperature Co-fired Ceramics) is an emerging material which is used in multilayer ceramic technology that, can be sintered at temperatures less than 700 °C. Ultra-low temperature enables some advantages compared to materials with higher sintering temperature such as lower energy consumption, low fabrication temperature, low-cost investments for firing furnace, reduction of processing time, enabling of further integration of passive components and further integration of low melting point materials (e.g., nanosilver inks for ink-jet printing of substrates). Ultra-low temperature co-fired ceramics require some significant properties to meet the application demand such as low dielectric constant (ε), high quality factor value, a near-zero temperature coefficient of the resonant frequency, thermal expansion matched with silicon, good chemical stability and superior chemical compatibility with electrodes. The sintering temperature must be less than melting temperatures of the inner electrodes. ULTCCs are extensively used in military and radar applications because of their high reliability and design flexibility. ULTCCS are also used in wireless and satellite communication technologies and in many applications such as antennas, multi-chip modules, substrates, packages, Internet of Things (IoT), Tactile Internet (5G), electronic warfare, and intelligent transport system. ULTCC is manufactured through two different routes. The first one includes a glass-ceramic composition which devitrifies at sintering temperature to form crystal phases such as anorthite, cordierite, etc. The second one includes the composite of glass and a ceramic filler such as Al2O3. In both routes, mixed powders are tape casted, stacked, laminated, screen printed with desired wiring pattern and then co-fired with metal electrodes.
In this study, the second route was used with 50 wt% Al2O3 – 50 wt% glass composite. Glass frits were wet-milled with 450 rpm for 3h to obtain glass powder. Dried glass powders were pressed at 300 MPa by CIP (Cold Isostatic Pressing) technique and sintered at 770 °C. The dielectric constant and dielectric loss of glass composition was measured by an Impedance Analyzer. For the tape casting process, Al2O3 and milled glass powders were mixed homogeneously with a ball mill for 1h. LTCC tapes were produced by tape casting. 10 sheets of Al2O3 – glass composite was stacked and laminated at 70 °C for 30 min under 30 MPa pressure.