Reseach On The Properties Of Substrate Material From CaO-B₂O₃-SiO₂ System LTCC With Low Loss At High Frequency

Low temperature co-fired ceramics?LTCC?technology,as an emerging high-density packaging passive microcircuit,has rather broad application prospects in fields such as military electronics,aerospace,wireless communication etc..Among LTCC materials,CaO-B₂O₃-SiO₂?CBS?system LTCC material,due to a low dielectric constant and low dielectric loss at high frequency,has a unique position in the military multi-chip module?MCM?based on LTCC technology.However,the development of CBS glass-ceramics in China is not so mature that it has hindered the development of information weaponry of military.In this paper,to meet the application needs of CBS glass-ceramic system LTCC materials,DSC,XRD,SEM and other research tools are used to study the effects of chemical composition of CBS glass?including changing the boron oxide content and CaO/SiO₂ molar ratio?on the properties of CBS glass-ceramics,to have a preliminary exploration of the effects of nucleating agent?doped with TiO₂ alone and doped with both TiO₂ and ZrO₂?on the properties of CBS glass-ceramic and to analyze the crystallization kinetics mechanism of CBS glass and the influence of sintering process on the characteristics of CBS glass-ceramics.The conclusions are as follows.The content of B₂O₃ has a major impact on the crystallization characteristics,sintering properties and dielectric properties of CBS glass-ceramics.With the increase of B₂O₃ content,the crystallization exothermic peak temperature of CaSiO3 crystal phase gradually increased,which leads to higher sintering temperature of CBS.The density of CBS samples firstly increased and then decreased slightly with increasing B₂O₃ content.When the B₂O₃ content is within the range of 14 wt%¹6 wt%,the density of CBS sample reached a maximum of 2.47 g/cm3,which means a high degree of densification.In terms of the dielectric properties of CBS samples,with the increasing addition of B₂O₃ content,the dielectric constant of CBS samples increased initially and reduced afterwards,reaching its maximum?7.12?as the CBS content increased to 18 wt%,while the dielectric loss decreased gradually but were overall slightly larger than 0.2%,getting the minimum of 2.09×10^-3 when the B₂O₃ content was 21 wt%.With the content of B₂O₃ Fixed at 16.4 wt%,changes of CaO/SiO₂ relative content make a difference to the properties of CBS samples.With the increase of CaO /SiO₂ molar ratio,the dielectric constant of the CBS sample reduced at first and then increased slightly,fluctuating at 6 in general.As the CaO/SiO₂ molar ratio varied from 1.06 to 1.08,the dielectric loss decreased significantly from 3.49×10^-3 to 1.35×10-4.But the dielectric loss almost unchanged when increasing CaO/SiO₂ molar ratio further.The addition of TiO₂ and ZrO₂ to CBS glass has an important influence in dielectric characteristics of CBS.After adding 1 wt% TiO₂ to CBS,the dielectric constant decreased slightly but the dielectric loss reduced greatly(from 2.45×10^-3 to 8.5×10-4),which indicates the addition of TiO₂ significantly improves the dielectric properties of CBS glass-ceramics.Increasing the TiO₂ content continually,the bulk density of the CBS sample further reduced and the glass phase and pores increased,resulting in the increase of the dielectric loss.When adding 1 wt% TiO₂ and 0.2 wt% ZrO₂ to CBS,the density and the dielectric constant of CBS samples decreased but the dielectric loss went up sharply.When continuing increasing the content of ZrO₂,The properties of the CBS samples experienced further deterioration in dielectric performance and densification.At the same sintering temperature,the dielectric constant of the CBS samples changed irregularly with the extension of crystallization time,mainly because of the inconsistency with the different species and contents of crystalline phase and the different levels of densification at different sintering temperatures.With the crystallization time of CBS samples fixed at 1h,the bulk density,the dielectric constant and the dielectric loss increased firstly and then decreased as the sintering temperature rose.Therefore choosing the appropriate sintering temperature and crystallization time can effectively promote the densification of CBS glass-ceramics.Sintered at 870? for 1h,the sample CBS#7 obtained the best performance,with a density of 2.7g/cm3,the dielectric constant of 6.17 and the dielectric loss of 2.47×10^-3?11 GHz?.