The Water-proofing Modification Of AlN Powder And Carbothermal Reduction Sintering Of AlN Ceramics

AIN ceramics have good thermal conductivity,high strength and low dielectric constant,and are widely used in the packaging materials of new generation semiconductor substrates and electronic devices.However,AIN powder is easy to hydrolyze and may be mixed with oxygen impurities that are difficult to be removed during production,transportation and storage.The sintering density and thermal conductivity of AIN ceramics have an important relationship with oxygen impurities.In this thesis,the waterproofing property of AIN powder was improved by organic acid coating method.The sintering density and thermal conductivity of AIN ceramics were improved by adding the sintering aid of CaO/Y2O3/C.Using oleic acid and palmitic acid as surface modifiers,the modified AIN powder was prepared by mechanical mixing method.The hydrolysis of modified AIN powder at different temperatures was studied in detail.It was found that the hydrolysis resistance of AIN powder coated with palmitic acid and Tween 80 was obviously better than that of AIN powder coated with oleic acid and Tween 80.The AIN powder coated with palmitic acid and Tween 80 existed stably in 100 0C water for more than 10 hours.In this thesis,AIN ceramics with thermal conductivity of 113.5 W/(m·K)were prepared by pressureless sintering with 98.96 wt.%AIN powder as the raw material.The addition of different sintering aids(CaO,Y2O3,CaO-Y2O3,CaO-Y2O3-C)was studied in detail.The effect of CaO-Y2O3-C on the sintering density and thermal conductivity of AIN ceramics was studied.It was found that the density of AIN ceramics was much lower than the theoretical density when the sintering temperature was lower than 1750 0C.The density of AIN ceramics added with CYCA(CaO-Y2O3-C)at the sintering temperature of 1800 0C was close to the theoretical density,which was higher than that of AIN ceramics added with other sintering aids.Moreover,the contents of second phase and oxygen element of AIN ceramics with C-containing of ternary sintering aids were obviously less than those of AIN ceramics with binary or single sintering aids.A small amount of carbon could remove lattice oxygen impurities in AIN,and could help the second phase formed by the reaction of the additive with AIN to be discharged in the form of gas.Using CYCA(CaO-Y2O3-C)as sintering aid,AIN ceramics with excellent thermal conductivity were prepared by hot pressing sintering method.The influence of CaO content(0.5 wt.%-1.5 wt.%)in CYCA(CaO-Y2O3-C)on the bulk density and thermal conductivity of AIN ceramics was investigated in detail.It was found that when the content of CaO varied from 0.5 wt.%to 1 wt.%,the density was close to the theoretical density,and the grain size of A1N ceramics tended to grow with the increase of sintering temperature;when the sintering temperature was 1800?,the thermal conductivity was higher than 180 W/(m K).When the content of CaO was 1.5 wt.%,the density was far more less than the theoretical density and the thermal conductivity was lower than other samples.This was due to the excessive addition of CaO,the excessive viscosity of liquid phase and the difficulty of liquid phase flow,that hindered the densification process of A1N ceramics and made it difficult for A1N ceramics to sintering densification...