Effects of MgO/CaO ratio on the crystal phase composition and performance of MgO-CaO-B₂O₃-SiO₂ glass–ceramics for LTCC applications

The MgO-CaO-B₂O₃-SiO₂ (MCBS) glass–ceramics with different MgO/CaO ratio were designed and prepared. The phase transition, microstructure, dielectric properties and flexural strength of the MCBS system were investigated. The quantitative calculations results showed that the MgO/CaO ratio favored the formation of CaMgSi₂O₆ phase but hindered the formation of CaSiO₃ and CaB₂O₄ phases. With increasing MgO/CaO ratio, the microstructure of sample changes from dendritic to polygonal shape. The MgO/CaO ratio also affected the properties of matrix. In this study, the 5MgO-36CaO-18B₂O₃-41SiO₂ (mol%) sample sintered at 825 °C for 15 min exhibited superior performance: the density of 2.64 g cm⁻³, a moderate dielectric constant of 5.92, the dielectric loss of 1.54 × 10^–3 (10 GHz), the thermal expansion coefficient of 9.61 ppm K⁻¹, the thermal conductivity of 3.02 W m⁻¹ K⁻¹, and a high flexural strength of 208.7 MPa, which might be a potential material for LTCC applications.