Microwave dielectric ceramics is used in microwave (mainly 300mhz~30ghz frequency band) circuit as a dielectric material and complete one or more functions of ceramics, in modern communication is used as resonators, filters, dielectric substrates, dielectric antennas, dielectric waveguide loops, etc., In addition to the necessary mechanical strength and chemical stability, the dielectric ceramics used in microwave circuits should meet the following dielectric properties, the high q·f value of the relative permittivity of the c^2 and the frequency temperature coefficient of close to 0 at microwave frequencies.
Microwave dielectric ceramics can be classified according to their composition system, dielectric properties and application fields, which are commonly classified according to their dielectric constant, which can be classified as low dielectric constant ($number), Medium dielectric constant ($number) and high dielectric constant (>80). Low dielectric microwave ceramics are mainly used in communication systems such as microwave substrates, satellite communications and military applications.
At present, more and more low dielectric microwave ceramics are mainly used in $literal and Ain, and the ideal performance of insulating heat dissipation materials with low dielectric microwave ceramic substrates is good for both thermal conductivity and heat dissipation, as well as minimizing loss in high frequency microwave action. Beo Ceramics is the best material of insulating and radiating in ceramic base copper clad laminate, but because of the toxicity of beo powder, strict protective measures should be taken during manufacturing, and the production of Beo ceramics has been banned in developed countries such as USA and Japan. Therefore, it is urgent to develop a new type of insulating material for copper clad laminate which replaces Beo ceramics. Ain Ceramics is a kind of ceramic material with better heat dissipation and innocuity, and the theoretical value of thermal conductivity is 320w/(m· K),Microwave Dielectric Ceramics the theoretical value of the thermal conductivity of Beo ceramics $number/(m· K) Similar, and has developed thermal conductivity in the/(m· K) above ain ceramic material. Therefore, Ain ceramic materials are considered to be the most promising alternative to Beo ceramic insulation heat dissipation materials.
The dielectric constant of BN is small, but the h-bn is added to the Ain ceramics, the h-bn is added to Ain, and the dielectric constant of Ain can be reduced according to the formula of dielectric constant of multiphase materials. The aim of this paper is to develop a high thermal conductivity, low dielectric loss ain and Bn-ain ceramic materials to meet the requirements of ceramic substrates, in order to replace Beo ceramic materials.
Because Bn, ain are covalent compounds, difficult to sinter, in order to obtain high density ceramics, the need to add sintering additives. The selection of sintering auxiliaries should be considered from two aspects, firstly, it can form low melt phase, realize liquid phase sintering, promote densification, and second, can react with oxygen impurities in ain to make Ain lattice purification. Based on these two points,Microwave Dielectric Ceramics the $literal is selected as the sintering additive. Because $literal and ain surface of alumina formation y3ai5o12, y3ai5o12 liquid phase temperature of 1760 ℃, so that both promote the sintering and purify the crystal lattice. However, if the sintering auxiliaries are dispersed unevenly, it is difficult to burn the ceramic materials with dense structure.
Through the chemical process, the BN is wrapped to the ALN powder surface to achieve the aim of uniformly dispersing bn into the Ain matrix, and the composite ceramic with uniform microstructure is prepared by using the package compound powder, its thermal conductivity is $number. 1/(m· K),Microwave Dielectric Ceramics in Ka band dielectric constant is 7.2, the minimum value of dielectric constant is 13x10-4. By studying the microwave properties of ain and bn-ain complex ceramics in Ka-band, it is found that the dielectric constant of Ain ceramics is very small, but the dielectric loss of the material varies with the frequency, and there is a maximum and minimum value in the interval.
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