Investigation On Sintering Crystallization And Properties Optimization Of La₂O₃-B₂O₃ Glass/Al₂O₃ Composites

LTCC technology is a multi-layer ceramic manufacturing technology that encapsulates complex circuits and passive devices in high density.It provides a new solution for miniaturization and high integration of passive devices,and plays an important role in national defense,communication and other fields.As the bearing structure of functional circuits,LTCC substrate materials play a dual role of structural support and electrical shielding,which is the key to the development of LTCC technology.At present,the widely used substrate materials mainly include glass-ceramics system and glass/ceramic system.In this paper,the Ca O-B₂O₃-La₂O₃（CBL）glass/Al₂O₃ system,which has good potential for development,was chosen as the object of study.The effects of glass composition,glass size,glass/Al₂O₃ ratio and sintering regime on the sintering precipitation behavior and properties of glass/Al₂O₃ complex phase materials were investigated.This work provides some references for the control of mechanical and dielectric properties of LTCC substrate materials.The introduction of P₂O₅ can change the structure and sintering precipitation behavior of CBL glasses.Appropriate amount of P₂O₅ can delay the crystallization of CBL glass and introduce a new phase La PO₄.The uniformly dispersed Al₂O₃ particles in Ca O-B₂O₃-La₂O₃-P₂O₅（CBLP）glass/Al₂O₃ composites and the lath like crystalline phase Ca Al₂B₂O₇ formed in the two-phase transition region can effectively improve the mechanical properties;The introduction of a small amount of P₂O₅ can reduce the porosity of CBL glass/Al₂O₃ composite materials,improve the microstructure,and effectively improve the flexural strength.However,low porosity leads to higher dielectric constants and low La BO₃ ratios lead to higher dielectric losses.The introduction of too much P₂O₅ leads to higher dielectric losses and lower flexural strength of the material.When P₂O₅ content is 6 mol%,the sample has the best comprehensive properties:the flexural strength is 222.6 MPa,at 20 GHz,ε_r=6.521 and tanδ=0.789×10^-3,at 40 GHz,ε_r=6.559 and tanδ=0.917×10^-3,CTE=5.402×10^-6/℃.And the material can be co-fired well with silver electrode.The introduction of SiO₂ and alkali metal oxides can affect the properties of CBLP/Al₂O₃ complex phase materials.SiO₂can improve the network structure of CBLP glass,change the precipitated crystal phase and inhibit the crystallization of glass.The introduction of SiO₂ increases the residual glass phase and reduces the precipitation of Ca Al₂B₂O₇ in the composite material,resulting in the increase of dielectric constant and dielectric loss and the decrease of flexural strength;The thermal expansion coefficient of the material is significantly increased due to the precipitation of calcite phase with high thermal expansion coefficient.Na₂O and Li₂O will enhance the precipitation tendency and promote the precipitation of the crystalline phase of the complex phase material,so that the dielectric constant and dielectric loss will be reduced.The best dielectric properties are found at 2mol%of Na₂O,withε_r=6.354 and tanδ=0.613×10^-3 at 20 GHz,ε_r=6.379 and tanδ=0.785×10^-3 at 40 GHz.Concentrated particle size distribution of glass powder is beneficial to densification and sintering.Optimizing the particle size distribution of glass powder can improve the density and obtain better mechanical and dielectric properties.Increasing the proportion of glass can reduce the porosity and significantly improve the flexural strength.When the glass content is 50 wt.%,the flexural strength is 253.4 MPa.Increasing the proportion of Al₂O₃ reduces the dielectric loss,which is 0.622×10^-3 for an Al₂O₃ content of 60 wt.%.If the heating rate is too high,the dielectric constant and dielectric loss of multiphase materials will increase.Selecting a suitable sintering temperature can effectively improve the dielectric properties of the material.Increasing the sintering temperature can reduce the dielectric constant by 10.2%and the dielectric loss by 41.2%for a complex phase material with a SiO₂ content of 6 mol%.