Preparation and properties of crystallizable glass/Al ₂O ₃ composites for LTCC material

The investigated low temperature Co fired ceramics(LTCC) composite of 60wt% CaO-Al ₂O ₃-B ₂O ₃-SiO ₂ glass and 40wt% α-Al ₂O ₃ as a filler is a non-reactive system, which is a critical part of the low temperature Co fired ceramics process. Through a study on densification process, the phase transformation and microstructure can be revealed. Its composites typically consist of CaO-Al ₂O ₃-B ₂O ₃-SiO ₂ glass and α-Al ₂O ₃ powders of average particle size (D ₅₀=3.49 μm). The sintering behavior, phase evaluation, sintered morphology, and microwave dielectric properties were investigated. In the fire range of 800 to 900 °C, the composites were crystallized after completion of densification. It is found that the composites start to densify at 825 °C, simultaneously, the dielectric constant (ε _r) reaches its maximum. With increasing heat-treatment temperatures, due to the loose microstructure of the material, tanδ increases slightly. The last of the sintered samples were identified as partly Anorthite at 850 °C. At that temperature it has ε _r of 7.9 and tanδ less than 1×10∼ ³, and can be used as a promising LTCC material.