Study On Modification Of K₂O-B₂O₃-SiO₂ Glass Ceramics

With the coming of 5th-Generation into our lives,electronic communication industry has achieved comprehensive development.Miniaturization and integration are the main trends of electronic components.In order to achieve a better integration and packaging of devices,low temperature co-fired ceramics（LTCC）is an excellent solution.As a branch of LTCC materials,glass/ceramic composites have attracted a widespread attention due to their low dielectric constant,low loss,high flexural strength and good thermal expansion.In this paper,SiO₂-B₂O₃-K₂O based glass-ceramics are investigated by pre-sintering process and glass/ceramic route.The first process is pre-sintering process.Without the addition of glass,the effects of pre-sintering temperature,K₂O content,Na₂O content,CaO content,and BaO content on the properties of composites are considered systematically.In the second process,a mixture of K₂O–B₂O₃–SiO₂–Al₂O₃ glass and ZnO-B₂O₃-SiO₂ glass is introduced as as a sintering aid of Al₂O₃,and the effects of glass mixture component on the properties of the composites are studied.In the first pre-sintering process,the appropriate pre-sintering temperature is helpful for the initial chemical reaction of various oxides,thus improving the efficiency of solid-state reaction.K₂O and Na₂O can break the glass network,thus reducing the softening point of glass and promoting the efficiency of liquid phase sintering.However,too many two oxides can easily lead to higher dielectric loss,making the addition of the two metal oxides light.The main purpose of BaO in this study is to limit the ion movement of alkali metal ions according to the pressure-alkali effect,thus adjusting dielectric loss of composites.The addition of calcium oxide significantly increases sintering density and reduces the porosity of the composites.In addition,the increase of density leads to the increase of mechanical properties and the decrease of thermal expansion coefficient.Ca²⁺restrains the ion movement of alkali metal ions,thus reducing dielectric loss of the composites.As CaO content increases up to 2.8 wt.%,the composites sintered at 850℃ have a dielectric constant of 4.94 and tanδof 8×10^-4 at 1 MHz,thermal expansion coefficient（TEC）of 8.5 ppm/℃,and flexural strength of 150 MPa..The excellent properties make the K₂O-B₂O₃-SiO₂-Al₂O₃ composite a promising candidate for LTCC applications.For the second process,glass/Al₂O₃ composites with low dielectric constant less than5 were successfully prepared by liquid phase sintering using a novel glass mixture of K-Al-B-Si（KABS）and Zn-B-Si（ZBS）.The XRD results shows a crystalline phase of ZnAl₂O₄ spinel by adjusting the component of the glass mixture.The dielectric constant shows low values between 4.56 and 5.14 due to the addition of Si-rich KABS glass as well as the formation of ZnAl₂O₄ having a low dielectric constant.The formation of ZnAl₂O₄ and the decreasing amount of KABS glass are corresponded to the increase of Q×f.The dense microstructure and ZnAl₂O₄ crystal phases are deemed to enhance the flexural strength.Meanwhile,the increasing values of TEC is due to the enhanced ZnAl₂O₄ crystal phases as well as decreasing liquid phase.The composite with mass ratio of KABS:ZBS equal to 6:4 exhibits good sintering capability at 850℃,with high densification（2.89 g/cm3）,low dielectric constant（4.92）and Q×f（6873 GHZ）,thermal expansion（5.5 ppm/℃）,which makes the novel composites a promising candidate for LTCC applications.