Research On Alumina Ceramic Metallization And Brazing With Kovar Alloy

This paper consists of two parts:The first one is alumina ceramic metalizaion.A screen-printing deposition method was used to explore the metallization process.The adhesion,surface resistivity,sheet resistance and other related properties were measured.On the basis of macroscopic performance and microscopic observation of the metallization layer,the influence factors of metallization were discussed.Firstly we set three variablesand choose two different silver pastes.Different holding time of metal sintering,as well as d ifferent pretreatment conditions were carried out on the ceramic surfaces.By adjusting the metal sintering holding time the optimum sintering process conditions were obtained.This study identified the best keeping time of metal sintering for two metallization pastes.For the medium-temperature silver paste it takes 120 min from room temperature up to 600 ℃,then the samples were kept for 20 min at 600 ℃,finally furnace cooled to room temperature.For the silver-palladium paste,it takes 170 min from room temperature up to 850 ℃,then the samples were kept for40 min at 850 ℃,finally furnace cooled to room temperature.Based on the optimum sintering process for the metallization,the surface of alumina ceramics was heat treated with different concentration of Na OH.It is indicated that with the increase of sodium hydroxide concentration,the adhesion strength is gradually increases.But for its electrochemical properties,surface resistivity and sheet resistance does not decrease correspondingly,because th e electrochemical performance also depends on the thickness of the metal layer.However,at the maximum concentration,the surface resistivity of the square resistance is minimal.In addition,the thermocycling experiment was carried on the two metal layers formed by the two kinds of pvastes.The results demonstrate that both the surface resistivity and square resistance have no obvious change,indicating the conductive metal layers have excellent performance.To sum up,in 850 ℃,the heat preservation 40 min,palladium silver paste with 30% sodium hydroxide concentration,metallization for best performance.The second main research content is alumina ceramic and Kovar sealing through direct and indirect brazing process.Finally,the performance of joints which are sealed by indirect brazing welding meets the requirements of our research.