Investigation On The Structure And Properties Of RE/AlN/MAS Glass-ceramics Composites

With the rapid development of microelectronics technology, the performance of substrate materials such as high thermal conductivity, low thermal expansion coefficient, low dielectric constant and good thermal stability, has put forward higher requirements. The main phase of crystallization is cordierite in MgO-Al2O3-SiO2 system glass-ceramics, which has high mechanical strength and low dielectric constants, thermal expansion coefficient and low sintering temperature, is a kind of excellent substrate materials. The disadvantage of cordierite-based glass-ceramics is low thermal conductivity. With high conductivity, low thermal expansion coefficient and excellent mechanical properties, AlN is considered a new generation of ideal substrate material. But the high sintering temperature which make its cost is higher, restricted its large-scale using in the substrate material. MgO-Al2O3-SiO2 system glass-ceramics and AlN ceramic composites were prepared by using LTCC technology, with excellent overall performance is expected to meet the requirements of the substrate material.In this paper, MgO-Al2O3-SiO2 system glass-ceramics and AlN/MAS glass-ceramics composites were prepared by sintering. The crystallization of glass-ceramics was investigated by heat-treatment. The effects of sintering atmosphere, sintering temperature, the composites composition were investigated on the phase composition, structure, relative density, thermal conductivity of AlN/MAS glass-ceramics composites. Through the AIN/MAS glass-ceramics composites doped rare earth oxides, the effects of different content rare earth oxides La2O3 and Y2O3 on the phase composition, microstructure, sintering properties, thermal properties, dielectric properties and mechanical properties of AIN/MAS glass-ceramics composites were investigated by the X-ray diffraction(XRD), scanning electron microscope(SEM), thermal conductivity, thermal expansion coefficient, dielectric constant, dielectric loss, flexural strength test. The results indicate that:1. Through designing the chemical composition of MgO-Al2O3-SiO2 system glass and adding suitable additives, prepared the main crystal phase of glass-ceramics was a-cordierite at the heat treatment temperature≤1000℃. The best crystallization temperature of glass-ceramics was 820℃/2h-1000℃/2h.2. AIN/MAS glass-ceramics composites sintered at 1000℃～1300℃, the main crystal phase of MAS glass-ceramics was stillα-cordierite. Doped Y2O3 and La2O3 respectively, the main crystal phase of composites were still a-cordierite and AlN. No new crystal phase or the occurrence of phase transition.3. The relative density of AlN/MAS glass-ceramics composites generally decreased, when composites sintered at 1000℃～1300℃. The low relative density of AlN/MAS glass-ceramics composites due to AlN sintered difficultly and hindered glass crystallization on.liquid phase sintering. The relative density of composites significantly reduced with increasing the content of Y2O3 and La2O3. When the Y2O3 content is 3.0wt%, the relative density of composites increased.4. The thermal conductivity of AlN/MAS glass-ceramics composites in the maximum when the AlN content is 20wt% and sintered at 1000℃and 1200℃. When the Y2O3 content was 3.0wt%, the thermal conductivity of composites appeared maximum aparameter. The thermal conductivity of composites decreased with content of La2O3 increasing. The thermal conductivity of composites doped Y2O3 and La2O3 changed broadly in line with the size of relative density. The coefficient of thermal expansion of composite doped Y2O3 and La2O3 appeared decline. With the increase of the content of rare earth oxides, the coefficient of thermal expansion of composites increased.5. The dielectric constant of AlN/MAS glass-ceramics composites increased with the increase of doped Y2O3 content. The dielectric constant of AlN/MAS glass-ceramics composites gradually decreased with the La2O3 content increasing. As the test frequency increasing, the dielectric constant decreased. The dielectric loss of composites increased with Y2O3 and La2O3 content increasing. Dielectric loss of samples decreased with test frequency increasing.6. Flexural strength of composites decreased with Y2O3 content increasing. But when mixed with 3.0wt% La2O3 content, the flexural strength of the composites increased. Flexural strength of composites doped Y2O3 and La2O3 in line with the size of relative density.7. AlN/MAS glass-ceramics composites prepared by hot-pressing had high relative density. The relative density of composites reduced with the content of AlN increasing. The thermal conductivity of AlN/MAS glass-ceramics composites increased with the content of AlN increasing.