Study On Formulation And Casting Of Low Dielectric LTCC Alumina-based Ceramics

With the advent of the 5G era,the miniaturization of electronic communication equipment is increasingly popular.Microwave dielectric materials,as representatives of key electronic functional materials,have been attracting considerable public attention.LTCC technology has the advantages of achieving high density of integrated devices,high reliability and low cost.Besides,Ag electrode,one of the high-conductivity electrode materials,can significantly lower the conductivity loss of electronic component.Therefore,efforts have been made to explore new electronic substrate materials with low sintering temperature?<950??and excellent comprehensive performances.The aims of this dissertation is lowering the sintering temperature of Al₂O₃ ceramics.Firstly,glasses?KBS,BZACMBS,ZBS?were prepared after quenching,and then,the glass ceramics composed of Al₂O₃ and glass frits with excellent properties were obtained using traditional solid-phase method.Sintering kinetics and crystallization kinetics were also investigated.For its application,KBS-Al₂O₃ glass ceramic powder was used to casted.When K₂O=3 wt.%and B/Si=2/3 mol.%,the low-temperature sintering effect of KBS glass is satisfied after adjusting the composition of KBS glass.In the composite ceramics,the liquid phase generated during the sintering process would fill in the grain boundary,leading to an increase of density.When the amount of glass reaches to 57.5wt.%and sintered at 850?for 30 min,the properties of the sample is:?_r=5.27,tan?=3.3×10^-3,?=2.57 g/cm³,?=140 MPa,?_L=4.9 ppm/?.In addition,Ag will not penetrate the interface of ceramics,which shows that the ceramics are compatible with Ag.In order to achieve the continuous variations of dielectric constant,SiO₂ and TiO₂were used to replace the Al₂O₃,and the dielectric constants varied from 4.18 to 4.96 and5.27 to 6.01,respectively.Furthermore,the low-temperature sintering effect of BZACMBS glass was investigated.XRD analysis revealed that new phases were observed,which means chemical reaction was occurred during the sintering process.After adding 55 wt.%BZACMBS glass,the sample sintered at 950?possessed properties of:?_r=7.4,tan?=2.4×10^-3,?=3.18 g/cm³,?=208 MPa.Phase compositions of the ceramics were:Al₂O₃,hexagonal BaAl₂Si₂O₈,monoclinic BaAl₂Si₂O₈,and ZnAl₂O₄.To further reduce the relatively high sintering temperature,a certain amount of BaO was added into the original glass formula.The results showed that BaO-BZACMBS glass with an addition of 4 wt.%BaO mixing with 45 wt.%Al₂O₃ exhibited excellent properties:?_r=7.6;tan?=2.6×10^-3,?=194 MPa;?:3.23 g/cm³,sintered at 875?for 2 h.The glass ceramics also can be compatible with Ag conductor materials.On the other hand,ZBS glass is prepared.The glass ceramic with 55ZBS-45Al₂O₃ can be sintered compact at 850?for 30 minutes,and its excellent dielectric properties are:?_r=6.3;tan?=6.8×10^-4.The reason for this phenomenon is that the wettability between the ZBS glass and the Al₂O₃ ceramic phase and the crystallinity are more satisfied.The sintering activation energies of 57.5KBS-42.5Al₂O₃ and 55 BaO-BZACMBS-45Al₂O₃ samples were calculated using a constant heating rate model based on Arrhenious relationship.The results show that the sintering activation energy of the former is 318.60±32.23 kJ/mol,and that of the latter is 701.57±98.59 kJ/mol.Although the sintering activation energy are different,both of the two glass ceramics can be sintered at 850?with high density.Since the chemical reaction occurred during the sintering process of BaO-BZACMBS and Al₂O₃,and the chemical reaction provided energy to the system,the glass ceramics can be sintered compact at a lower temperature.The influence of BaO-BZACMBS on the crystallization activation energy of glass ceramic system was calculated with Kissinger analysis method and Ozawa analysis method,respectively.The addition of BaO-BZACMBS glass can indeed promote the precipitation of crystals,which can significantly reduce the activation energy of crystallization.Finally,the KBS-Al₂O₃ glass ceramic powder was used as the based material to carry out the casting process.After comparing the substrate sedimentation experiments among organic solvents such as ethanol,acetone,and methyl ethyl ketone,ethanol was chosen as the suitable solvent.The optimal amount of dispersant was 0.8 wt.%;and the content of the composite binder composed of PVB60 and PVB30 was 8 wt.%,which shows the best casting effect.