Preparation And Rsearch Of Degradable LTCC Low Temperature Co-fired Ceramics Based On Borosilicate/AlN

With the rapid development of electronic technology,LTCC?low-temperature co-fired ceramics?are widely used due to their superior dielectric properties and high integration,especially in today's popular wireless communication devices such as mobile phones,computers,routers,they contains many LTCC devices.precious metal Ag is widely used as a conductive medium and electrode in LTCC devices,which is expensive.And great pollution will be generated if they cannot be recycled and reprocessed,while the LTCC substrates on the market can not easily degraded,and it is difficult to reprocess after recycling.This experiment designed and prepared low-temperature co-fired ceramics that can be degraded by water and meet the performance requirements of LTCC as well.The ceramic substrate can be easily separated from the conductive medium Ag after degradation,which can simplify the recovery process,reduce environmental pollution,and it also has certain economy.significance.In this experiment,the B₂O₃-2SiO₂ eutectic was firstly composited with AlN ceramics with average particle diameters of 5?m and 10?m,respectively,and sintered at different temperatures using pressureless sintering,cold isostatic pressing before pressureless sintering and hot pressing sintering,exploring the best process.Then the K₂O-B₂O₃-2SiO₂/AlN composites were prepared by adding K₂O to the B₂O₃-2SiO₂eutectic.In this paper,the microstructure and phase composition of two composite materials were investigated,and the effects of AlN content,sintering temperature and sintering process on the flexural strength,thermal conductivity,dielectric properties and degradability of B₂O₃-2SiO₂/AlN composites were investigated.And the degradation mechanism of the material was discussed.The effects of K₂O content on the flexural strength,thermal conductivity,dielectric properties and degradability of K₂O-B₂O₃-2SiO₂/AlN composites were also investigated.The main results are as follows:?1?The pressureless sintering process of B₂O₃-2SiO₂ eutectic and AlN ceramics is non-reactive sintering.The microscopic morphology can be described as the liquid phase envelops the AlN particles,accompanied by a few pores,and the pores increases as the liquid phase reduces.When the AlN content is 40wt.%,the B₂O₃-2SiO₂ eutectic reacts with the AlN ceramic during the hot-pressing sintering process to form a whisker-like new phase Al₄B₂O₉,and the microscopic morphology can be described as liquid-phase encapsulated AlN ceramic particles.with whisker-like Al₄B₂O₉ between the liquid phase and AlN,and the pores are significantly less;?2?For composites with AlN average particle size of 5?m:AlN content seriously affects the flexural strength,thermal conductivity,degradability of the material,excessive AlN content leads to insufficient liquid phase,incomplete liquid phase sintering,there are many internal pore defects,so that the bending strength and thermal conductivity are not ideal.Low AlN content leads to excessive liquid phase,sample deformation,and slightly lower bending strength.High AlN content lead to worse degradability,more amount of liquid phase leads to better degradability;the sintering temperature also affects the properties of the material.When the sintering temperature is 950°C,the sample with more liquid phase appears to be over-fired.The performance deteriorates severely,when the sintering temperature is 800°C,it is insufficient to produce a sufficient liquid phase,which affects the material properties.When AlN?5?m?content is 40wt.%,the sample sintered at 850°C after cold isostatic pressing has good comprehensive properties:thermal conductivity of 1.76 W/mK,flexural strength of 68.32 MPa,and dielectric constant?_r of 5.92?1MHz?,the dielectric loss tan?of6.5?10^-3?1MHz?,and it can react with water in water,which means it has certain degradability;while the hot-pressed sintered material has higher bending strength and thermal conductivity than the material used pressureless sintering.When the AlN content is 50wt.%,the material sintered at 850°C has good comprehensive properties,the thermal conductivity of 4.2 W/mK,the flexural strength of 161.42MPa,the dielectric constant?_r of 4.27?1MHz?,and the dielectric loss tan?of 4.41?10^-3?1MHz?,but no degradation behavior is observed;the flexural strength,thermal conductivity,and dielectric properties of composites with an average particle size of 10?m are far less than that of composites with an average AlN particle size of 5?m.Which means they can not be applied as LTCC substrates.?3?The sintering process of K₂O-B₂O₃-2SiO₂ eutectic and AlN ceramics is non-reactive sintering.The content of K₂O has much effects on the flexural strength,thermal conductivity,dielectric properties and degradability of K₂O-B₂O₃-2SiO₂/AlN composites.When small amount of K₂O is added,[BO₃]units are changed to[BO₄]units,and the structure becomes more compact.Compared with the B₂O₃-2SiO₂/AlN composite material to which K₂O is not added,the material density,bending strength,thermal conductivity,and even dielectric properties are optimized.When 0.01mol K₂O is added to 1mol B₂O₃-2SiO₂ base powder,the sample with AlN content of 40%has good comprehensive performance:the thermal conductivity of 1.639 W/m K,the flexural strength of 59.7 MPa,and the dielectric constant?_r of 2.3?1MHz?,the dielectric loss tan?of 1.9?10^-3?1MHz?.Although its reaction rate with water is slower,it still has certain degradability.When the amount of K₂O is increased,K⁺enters the silicon oxygen network,and the liquid phase itself become loose,has poor performance,the bending strength and thermal conductivity of the sample become lower,the structure becomes loose leads to increases of the relaxation loss.The introduction of K⁺increases the number of charged particles,makes the conductance loss larger,and the total dielectric loss becomes larger.The degree of ionic polarization increases,resulting in an increase in the dielectric constant of the sample and a deterioration in dielectric properties.And because[BO₃]is converted to[BO₄]in the liquid phase,the chemical activity is lowered,the material is not dissolved in water,no degradation behavior can be observed,and the degradability is low.