Sintering characteristics, microstructures and dielectric properties of borosilicate-based glass/alpha-Al₂O₃ composites for LTCC application with different MgO and Na₂O contents

The sintering characteristics, microstructures and dielectric properties of Ca–B–Si–O glass/alpha-Al₂O₃ materials at different MgO and Na₂O contents were studied. The addition of MgO and Na₂O in glass could regulate and manage the glass softening and crystallization, and further improved the sintering characteristics and dielectric properties of Ca–B–Si–O/Al₂O₃ glass + ceramic composites. The bulk density, thermal conductivity and dielectric constant curves elevated from 0 to 2 wt% at MgO and Na₂O content, and then declined with the further increase of MgO and Na₂O content, while the dielectric loss curve exhibited the converse varying trend. Phases and microstructures analysis showed that Ca–B–Si–O/Al₂O₃ glass + ceramic composites with 2 wt% MgO and Na₂O content were composed of glass with amorphous structure, pores, crystalline phases of alpha-Al₂O₃ and CaAl₂SiO₈ with the triclinic unit cell that was formed by the typical chemical reaction of Ca²⁺, Al³⁺, Si⁴⁺, O²⁻ ions in the glass. By contrast, Ca–B–Si–O /Al₂O₃ glass + ceramic composites with 2 wt% MgO and Na₂O content at 850 °C exhibited better properties of ρ = 3.06 g/cm³, λ = 3.23 W/m K, ε_r = 7.82 (at 7 GHz), tan δ = 1.3 × 10^{− 3} (at 7 GHz), and a well chemical and co-fired compatibility between glass + ceramic composites and Ag electrodes.