Synthesis and characterization of low CTE value La2O3-B2O3-CaO-P2O5 glass/cordierite composites for LTCC application

Low-softening-point La2O3-B2O3-CaO-P2O5 (LBCP) glass-ceramic/cordierite composite systems have been prepared in this work. Influence of the ratio of La2O3 to B2O3 and the content of cordierite on the sintering behavior, microstructure, sintering quality, thermal properties and dielectric properties of composites are studied. The results show that high La2O3/B2O3 ratio improves the crystalline quality of LBCP glass-ceramic, but also narrows its process window. The increase of cordierite content reduces the coefficient of thermal expansion (CTE) value of composites obviously. However, excess cordierite is detrimental to the densification of the composite microstructure, and too low cordierite content causes serious foaming. Sample containing 30 wt% LBCP1 glass ceramic and 70 wt% cordierite sintered at 850 degrees C shows excellent properties: relative density of 95.26%, CTE value of 4.12 ppm/degrees C, dielectric constant of 4.78 (1 MHz)/4.52 (12.8 GHz), dielectric loss of 2.3 x 10(-3) (1 MHz)/2.5 x 10(-3) (12.8 GHz) and the ability to co-fire with silver, which suggests that LBCP glass/cordierite composite system has potential to meet the requirements of LTCC substrate material.