Synthesis and Characterization of CaO-Al2O3-SiO2 Glass/Al2O3 Composites via Sol-Gel Method for Electronic Packaging Applications

In this study, CaO–Al2O3–SiO2 (CAS) glass-ceramic composites were synthesized via the sol-gel method to develop novel substrate materials for Low-Temperature Co-fired Ceramic (LTCC) applications. The CAS glass powder, synthesized using TEOS, aluminum nitrate, and calcium nitrate precursors, was mixed with 40 wt. % commercial alumina (Al2O3) powder to fabricate C6A4 composites. The effects of sintering temperatures ranging from 850 to 950 °C on the densification, microstructural evolution, phase composition, and dielectric properties were systematically investigated. Thermal analysis (DSC-TGA) of the CAS precursor revealed a glass transition temperature (Tg) of approximately 770 °C and a crystallization peak at 952 °C. X-ray diffraction (XRD) analysis indicated that corundum constituted the primary crystalline phase, while anorthite (CaAl2Si2O8) precipitated as the secondary phase during sintering. Scanning Electron Microscopy (SEM) observations confirmed that a dense microstructure with minimal porosity was achieved at 950 °C, supported by the liquid-phase sintering mechanism. The bulk density increased with temperature, reaching a saturation value of 2.40 g/cm³, whereas water absorption decreased to negligible levels (<1%). Commensurate with densification and anorthite crystallization, a significant improvement in Vickers hardness was recorded. The composite sintered at 950 °C exhibited favorable dielectric properties, with a dielectric constant (εr) of 7 and a dielectric loss (tan δ) of 0.005 at 1 MHz. In conclusion, the sol-gel-derived CAS/Al2O3 composites exhibited promising thermal, mechanical, and electrical characteristics suitable for high-frequency electronic packaging and LTCC substrate applications.