Technology And Mechanism Of Sintering Of AlN For Electronic Packaging

With high theoretical thermal conductivity, aluminum nitride ceramic is the ideal material of integrated circuit substrates and electronic packaging. But aluminum nitride is covalent bond compound with high melting point and low self-diffusion coefficient, and usually it can be used to prepare high dense aluminum nitride ceramic by hot pressing sintering. Aluminum nitride also has strong affinity to oxygen, easily introduces oxygen impurity in ceramic preparation and causes decline of thermal conductivity. By sintering aluminum nitride under normal pressure, this paper has studied the influence of different preparation technology and selected different sintering reagent promoter on the sintering process of aluminum nitride ceramic.By analyzing the impurity introduced in the preparation process of aluminum nitride ceramic, powder thermal oxidation and hydrolysis oxidation of aluminum nitride were studied, on the basis of which, the influence of aluminum nitride ceramic"s preparation technology on oxidation of aluminum nitride was researched. The results showed that thermal oxidation of aluminum nitride could be completed at 800℃, aluminum nitride powder with smaller particle size could be oxidized more easily. There was a long initial phase in the hydrolysis oxidation of aluminum nitride, which was comparatively slow. In the process of ceramic sintering, using carbon black for powder bed could generate carbothermal reduction action, which avoided oxidation of aluminum nitride.The preparation technology was changed to sinter aluminum nitride ceramic at low temperature and study the influence of different conditions on aluminum nitride ceramic's density. The results showed that In low-temperature sintering of aluminum nitride ceramic, only adding Y1O3 as sintering auxiliary couldn't promote effectively volume contraction of ceramic and improvement of density, in addition, sintering process was realized still depending on diffusion. Improving body briquetting pressure could promote densification of nanometer-level aluminum nitride, but such influence gradually became weak with improvement of sintering temperature. The surface diffusion-volume diffusion transformation of micron-level aluminum nitride raw materials was completed at temperature of 1500℃-1550℃. The diffusion transformation temperature of nanometer-level aluminum nitride raw materials was comparatively low, which could improve its density at comparatively low temperature.With liquid phase sintering mechanism and phase diagram as theoretical basis, the influence of sintering auxiliary on high-temperature sintering of aluminum nitride was studied. The results showed that only adding Y2O3 as sintering auxiliary was not enough to promote sintering, the microcosmic appearance of sintered compacts had defect, and ceramic wasn't completely densified. Combining CaF2 or CaO with Y2O3 as complex auxiliary could effectively lower the lowest eutectic temperature with Al2O3 in sintering process, make liquid phase generated earlier and aluminum nitride ceramic completely densified. Selecting CaF2 to combine with Y2O3 was better for aluminum nitride ceramic sintering than selecting CaO. With 3wt% Y2O3-2wt% CaF2 added as complex sintering auxiliary, the microstructure of aluminum nitride samples sintered at 1800℃was good, and the second phase was distributed at triangle crystal boundary. The density of sintered compacts was as high as 3.35 g/cm3.Aluminum nitride powder with comparatively high anti-hydrolysis ability was prepared through acid-cleaning aluminum nitride powder with phosphoric acid. The influence of preprocessing with phosphoric acid on the process of aluminum nitride's high-temperature sintering was studied. The result showed that acid-cleaning with phosphoric acid improved water resistance of aluminum nitride powder, optimized sintering property of powder, which was good for preparation of aluminum nitride ceramic, in addition, the density of sintered aluminum nitride ceramic at 1800℃was 3.223 g/cm3. The new phase of sintered products wasn't generated after aluminum nitride powder was cleaned with phosphoric acid, and any bad negative impact of acid-cleaning with phosphoric acid on the sintered microstructure phase wasn't found in the experiment.