Effects of CaO additive on sintering behaviour and properties of CaO–B2O3–SiO2 glass-ceramics for LTCC applications

The effects of CaO additive on the phase composition, sintering behaviour, microstructure, and properties of CaO–B 2 O 3 –SiO 2 (CBS) glass-ceramics were investigated. The results revealed that a small amount of added CaO (0.5 wt%, 1 wt%) facilitated the transformation of α-CaSiO 3 to β-CaSiO 3 and improved the crystallinity. When the amount was greater than 1 wt%, it weakened this transformation and also decreased the crystallinity. The pure CBS sample needed a sintering temperature of 850 °C for maximum densification, whereas the CaO-added samples achieved densification at a sintering temperature of 750–770 °C. The addition of an appropriate amount of CaO significantly enhanced the densification, dielectric properties , and flexural strength of CBS glass-ceramics. However, the addition of CaO had minimal impact on the coefficient of thermal expansion (CTE), which varied from 7.69 to 8.51 ppm/°C. The sample doped with 1 wt% CaO was sintered at 770 °C for 15 min, and it exhibited fairly ideal performance with a bulk density of 2.64 g/cm 3 , ε r of 6.43, tanδ of 0.9 × 10 −3 (15 GHz), and a CTE value of 7.69 ppm/°C.