Metalization And Co-sintering Of The Alumina Ceramic Substrate

Ceramic/metal composite material not only has good electrical and thermal conductivities, but also has heat resistance and high mechanical strength, with a wide range of applications in hybrid integrated circuits and electronic devices in vacuum. But it is difficult to connect the metal and ceramic well. Therefore, the paper studied the metallization process of alumina ceramic and the sintering matches of metallization slurry.In this paper, alumina ceramic substrate was firstly prepared by casting to determine the process parameters of preparation of the alumina ceramic substrate. Secondly, properties of tungsten metalized slurry and process parameters of screen printing were studied to determine the optimal viscosity of tungsten metalized slurry and the optimal process parameters of printing process. Thirdly, the degreasing temperature-time curve and maximum sintering temperature were analyzed by the thermal analysis of alumina substrate and tungsten powder. Finally, the performances of the product were tested and analyzed.Through the study of alumina ceramic substrate casting slurry properties and casting process conditions, determined that the slurry solids range of the alumina ceramic substrate was between 73-75wt%, the viscosity range at 1.0-1.5 Pa·s, which was suitable for the casting. And when the apparatus temperature was at 30±0.5℃, the height of hopper at 20±2mm, the green alumina substrate had smooth surface and had no macroscopic defects.Properties of tungsten metalized slurry and process parameters of screen printing were studied to determined that: when the slurry solids content at 80%,the viscosity at 110 Pa·s; the distance from the screen at 1.75 mm, blade angle at 65° and blade crooked degree at 20°. In this time, the screen printing pattern could be smooth surface, sharp edges, void-free and uniform thickness.The degreasing temperature-time curve was determined by the thermal analysis of the alumina ceramic substrate and the tungsten powder. That was from 25 to ℃ 350℃, the heating rate was 1℃/min, in 215 and 350 h℃ ℃ eat preservation was set for 15 min, from 350 to 600℃ ℃, the heating rate was 1.7℃/min, in 600 ℃heat preservation was set for 15 min. The wet hydrogen atmosphere was used for degreasing to avoid excessive oxidation of the tungsten powder. And the sintering temperature was 1550℃.The sintered shrinkage of alumina substrate was 16.5%, while that of metallized layer adding an appropriate amount of reducing tungsten powder was 13.8%. They match substantially after co-firing, without obvious defects. The square resistance of the sample was less than 0.05Ω/□, which met the standard of thick film conductor paste conductive properties.