Preparation And Properties Of AlN Ceramics With High Thermal Conductivity

AlN ceramic with high thermal conductivity showed a great prospects in the substrate and electronic packaging materials.In recent years,the preparation process and performance of AlN ceramic have been widely studied.AlN ceramics were mainly prepare by hot pressing.In order to reduce costs and improve performance,this dissertation was focused on the low temperature pressureless sintering process of highly thermal conductivity AlN ceramics by adding new sintering additives.This dissertaion was summarized as follows:AlN ceramics were prepared by Pressureless Sintering in N₂ atmosphere with LaF₃ as sintering additives.The effect of heating rate,sintering temperature,sintering time and the doping amount on AlN ceramics were respectively discusses in this dissertation.A high relative density?99.2%?and nomal thermaml conductivity(113.61 W?m^-1?K^-1)of AlN ceramics could be achieved at 1750oC for 3 h with doping 1 wt%LaF₃.AlN ceramics were prepared by Pressureless Sintering in N₂ atmosphere with doping Y₂O₃-LaF₃ and CaO-LaF₃.In the meantime,the density,phase,morphology,thermal conductivity and dielectric properties of AlN ceramics were investigated.The results showed that Y₂O₃-LaF₃ was better than CaO-LaF₃ for promoting the sintering.A high relative density?99.08%?and thermaml conductivity(200.01 W?m^-1?K^-1)of AlN ceramics could be achieved at 1700oC for 3 h with doping 2 wt%Y₂O₃-1 wt%LaF₃.At-50oC²00oC,the dielectric constant of AlN ceramics was 9.7⁹.9 in 1 MHz,and the dielectric loss was about 1×10^-3.Based on the previous research,the influence of moisture content on the composition and morphology of AlN powder was discussed by respectively stored in the wet and dry environment.Two different AlN powders were doped with 2 wt%Y₂O₃-1 wt%LaF₃ and sintered at 1700oC for 3 h.The phase,morphology and thermal conductivity of AlN ceramics were researched in detail.And we found that the AlN powder stored in wet environment was hydrolyzed and agglomerated,and the surface generated a layer of porous amorphous material.Eventually,the AlN powder activity was decreased,and oxygen content was increased.And then,the thermal conductivity of AlN ceramic for non hydrolytic and hydrolytic powder as raw materials were respectively 200.01 W?m^-1?K^-1 and163.968 W?m^-1?K^-1.