Modification of CaO–B2O3–La2O3 glass powder and its application in low-temperature co-fired ceramic substrate

Abstract

CaO–B2O3–La2O3 (CBL) glass is widely used in high-frequency packaging and co-firing with highly conductive metal electrodes as a new lead-free glass/ceramic system in low-temperature co-fired ceramic (LTCC) materials due to its multiple advantages, such as low softening point, controllable crystallisation properties, and chemical stability. The silane coupling agent, KH-570, was used as a surface modifier for preparing modified CBL glass powder to obtain a tape-casting slurry with low viscosity and excellent stability in a polymethyl methacrylate binder system; this system achieved better co-firing compatibility between the composite and Ag electrodes. In this study, the modification mechanism of the silane coupling agent with the powder is elucidated. The effects of the modified powder on the kinetic stability and rheological properties of the slurries were investigated. A slurry with a solid content of 39.6 vol% and lowest viscosity of 1500 mPa s could be obtained with the addition of 2 wt% KH-570. In particular, the uniformity of tape-casting slurry was observed during tape casting, leading to a difference in the density of green tapes, which increased from 2.45 (without KH-570) to 2.61 g/cm3 (with 2 wt% KH-570), and the tensile strength increased to 5.11 MPa. Simultaneously, the micromorphology and surface roughness of the green tapes and substrate were analysed by scanning electron microscopy and atomic force microscopy. The results showed an improvement in densification and a decrease in Ra after modification, resulting in the sintered substrate obtaining a higher density of 3.06 g/cm3 and a lower dielectric loss of 9.8 × 10−4 (12 GHz). The excellent co-firing compatibility between green tapes and silver paste at 850 °C was confirmed by energy-dispersive X-ray spectroscopy. In this study, high-quality LTCC materials were manufactured by coupling modification, with their stable performance ensuring their wide application.