Preparation And Properties Of LTCC Alumina Ceramic Substrates Doped With Rare Earth

Low Temperature Co-fired Ceramics（LTCC）materials play a very important role in the field of electronic packaging technology,which have a very important impact on the performance and quality of electronic packaging modules and the selection of related process materials.In order to meet the requirements of high integration density,high transmission rate,versatility,high reliability and low cost of today’s electronic devices and components,the development of LTCC materials with low dielectric and high performance is in line with the rapid development trend of current electronic products to high frequency and high speed.In this thesis,LTCC alumina ceramic substrate materials doped with rare earth as the research object,from rare earth glass,rare earth glass and alumina ceramic composite material,rare earth doped LTCC alumina ceramic casting substrate were studied.Firstly,aluminobosilicate glass materials containing different rare earth elements（Dy₂O₃,Eu₂O₃and La₂O₃）and different rare earth contents were synthesized by sol-gel method with aluminobosilicate glass as the matrix raw material,through the single and co doping of rare earth elements.The results showed that glasses doped with 2.0 wt.%La₂O₃contained more[BO₄]and[Al O₄],which optimized the polymerization degree of the glass network,and strengthened the structure.This glass had a lower dielectric constant（ε_r=2.27）and dielectric loss（tanδ=0.0019）at 13GHz.Additionally,the glass transition temperature（T_g）,initial crystallization temperature（T_c）,and thermal stability（△T）all increased with higher rare earth ionic radius(Dy³⁺,Eu³⁺,La³⁺),due to decreased non-bridging oxygen levels（NBO）of[Si O₄]and increased[BO₄]and[Al O₄]in the glass grid.However,co-doped rare earth oxide glasses inhibited conversion from[BO₃]to[BO₄]when equal amounts of La₂O₃and Dy₂O₃or Eu₂O₃were added,which resulted in a looser glass network and a higher dielectric constant.As La₂O₃gradually replaced Dy₂O₃or Eu₂O₃,the dielectric constant initially increased and then decreased,ascribed to the shift polarization of RE³⁺in the glass structure.Secondly,the prepared rare-earth doped aluminum-borosilicate glass with low dielectric constant and low dielectric loss and excellent comprehensive performance was selected for co-firing with alumina ceramics.By adjusting the ratio of glass powder and alumina powder and sintering temperature,the influence rule of these on the structure and properties of alumina based ceramics was explored.It was found that in addition to the main phase Al₂O₃,there were a small amount of Al₂Si O₅and(Al_xSi_1-x)O₂precipitated during the high temperature chemical reaction between the glass phase and Al₂O₃in the sintered rare earth doped alumina base ceramic material.With the increase of sintering temperature and doped glass phase content,the degree of sintering densification increases.When the sintering temperature continues to rise to 950℃,the sample would appear sintering overheating phenomenon,resulting in the increase of pores in the sample and the decrease of densification.When the doped glass phase content reaches 60 wt.%,there would be excessive liquid phase covering Al₂O₃ceramic particles in the sample,resulting in multiple pores in the sample,and the relative density decreases.The dielectric constant firstly decreased and then increased with the increase of sintering temperature and the doping amount of glass phase.The dielectric constant reached the lowest when the sample structure is the densest.When the sintering temperature was 900℃and the glass phase content was50 wt.%,the rare-earth doped LTCC alumina ceramic sample was the densiest,ρ=3.41 g/cm³,the dielectric constant was as low as 2.98 at 13 GHz,and the dielectric loss(tanδ=0.64×10^-3).Finally,under the sintering temperature of 900℃and the glass phase ratio of50 wt.%,multilayer rare-earth doped alumina base ceramic substrate was prepared by casting,slicing,superpressing and sintering,and was co-fired with Cu.The viscosity of the fluidized slurry decreased exponentially with time,which was related to the dispersing agent in the slurry.During the slurry mixing process,dispersion and deflocculation continued.When the concentration of the dispersing agent was just enough to completely deflocculate the particles,the relative stability wuold be reached.It was found that the raw ceramic chips with uniform film thickness and no defects in appearance were obtained by fluidized casting,and were compact sintered at 900℃.Al,Si,Mg,Ca and rare earth elements were uniformly distributed in the samples.After the raw porcelain and copper foil were superpressed into multilayer ceramic and sintered at 900℃,the metal Cu and alumina substrate ceramic were closely fitted and stably exist in the ceramic substrate.The rare earth doped alumina base ceramic material had good chemical compatibility with metal Cu.The controllable preparation of multilayer rare earth doped LTCC alumina ceramic substrate is realized,and it would become a new LTCC candidate material with great development prospect and application range.