CN113173586A

CN113173586A - Cordierite microcrystalline powder and preparation method thereof, and alumina ceramic substrate and preparation method thereof

Info

Publication number: CN113173586A
Application number: CN202110472771.0A
Authority: CN
Inventors: 高朋召; 刘小磐; 郑航博; 李玉玲
Original assignee: Hunan University
Current assignee: Hunan University
Priority date: 2021-04-29
Filing date: 2021-04-29
Publication date: 2021-07-27
Anticipated expiration: 2041-04-29
Also published as: CN113173586B

Abstract

The invention discloses a cordierite microcrystalline powder, alumina ceramic substrate and a preparation method thereof, wherein the preparation method comprises the following steps: carrying out ball milling on micron alumina, a sintering aid, a dielectric loss regulator, cordierite microcrystalline powder and a forming aid to obtain slurry; preparing a green body: preparing a green sheet by adopting a tape casting method; and (3) glue discharging and sintering of green bodies: and sintering the green sheet after the binder removal, wherein the temperature range of the sintering process is from 650 ℃ to the highest temperature, and the highest temperature is from 1000 ℃ to 1450 ℃. The method utilizes cordierite microcrystalline powder to improve Al₂O₃Strength of the substrate, lowering itCoefficient of thermal expansion and dielectric constant; reducing the sintering temperature of the substrate by using a sintering aid; the dielectric loss regulator is utilized to reduce the dielectric loss of the substrate under high frequency, and the Al prepared by the prior art is effectively solved₂O₃The substrate has high dielectric constant and dielectric loss, high thermal expansion coefficient and poor thermal shock resistance, and greatly widens the range of Al₂O₃The substrate has a wide application range and a simple and stable process.

Description

Cordierite microcrystalline powder and preparation method thereof, and alumina ceramic substrate and preparation method thereof

Technical Field

The invention relates to the technical field of alumina ceramics, in particular to cordierite microcrystalline powder and a preparation method thereof, an alumina ceramic substrate which is sintered at low temperature, has adjustable dielectric constant, low dielectric loss and thermal expansion coefficient and high strength, and a preparation method thereof.

Background

The development of electronic technology has led to a rapid growth in the industry of carrier-insulating substrates as circuit components. The high power, high density and high integration of electronic components have put increasing demands on the mechanical, thermal and electrical properties of the substrate materials. Tape casting is an important forming process for thin ceramic materials, is suitable for forming large and thin ceramic parts, is particularly easy to form thin parts with complex shapes and sizes, and has stable blank quality, and the parts are almost impossible or difficult to form by pressing or extruding. Tape casting has now become a technology of pillars for producing ceramic substrates and capacitors, both of which are important in the increasingly developed electronic ceramic industry.

Al₂O₃Ceramics have excellent properties in strength, heat resistance, thermal shock resistance, electrical insulation, corrosion resistance and the like, and are widely applied to electronic industry packaging and integrated circuits, and the raw materials are sufficient and cheap. Production of Al by tape casting₂O₃The ceramic substrate is generally made of Al with high purity₂O₃The raw materials can form a compact structure only by sintering at high temperature (more than 1600 ℃), the requirements on sintering equipment are high, the production cost is high, and the application of the raw materials is severely limited.

Chinese patent (application number) CN201911361168.4 proposes a method for preparing high-purity Al at low temperature₂O₃Method of preparing ceramic substrate, nano-scale Al₂O₃Powder and micron-sized Al₂O₃Mixing the powder according to a certain proportion, using alcohol as solvent, adding adjuvant, ball-milling and mixing to obtain slurry, then mixing the slurryCarrying out material casting molding, standing and drying to obtain a raw material belt, cutting the raw material belt, carrying out isostatic pressing molding to obtain a blank sheet, and finally sintering the blank sheet to obtain the low-temperature prepared high-purity Al₂O₃A ceramic substrate. The sintering temperature is 1600-1800 ℃, and the density of the prepared ceramic substrate is 3.75 g-cm^-3Porosity 1.10%, bending strength 325 MPa. The Al₂O₃The ceramic film substrate has high sintering temperature and long sintering time.

Chinese patent (application number) CN201910832623.8 proposes an ultrathin Al₂O₃A method of preparing a ceramic substrate comprising the steps of: (1) al (Al)₂O₃Modifying the surface of the powder; (2) preparing slurry; (3) tape casting; (4) stamping: stamping the green belt obtained in the step (3) to obtain a green sheet; (5) rubber discharging: putting the green sheet into a glue discharging furnace, performing first glue discharging in nitrogen atmosphere at 0.8-2 ℃ for min^-1Raising the temperature to 450 ℃. 550 ℃ at the temperature raising rate, preserving the heat for 35-60min, and then performing secondary glue removal at the temperature of 2-5 ℃ for min in the air atmosphere^-1The temperature is increased to 180 ℃ and 250 ℃, and the temperature is kept for 80-120 min; (5) and (3) sintering: and (4) placing the green sheet subjected to the glue discharging in the step (5) into a sintering furnace for sintering for 12-20h, wherein the sintering temperature is 1550-. The method has the advantages of powder surface modification and 2 times of rubber discharge, and the preparation process is relatively complex.

Chinese patent (application number) CN201711363239.5 proposes a high-strength Al₂O₃Method for preparing ceramic substrates by reacting CO₂Ultrafine aluminum hydroxide grains can be formed after the sodium aluminate solution is introduced, precursor sol is doped for tape casting to obtain a tape casting raw material tape with good cohesiveness, and the sol has a high thermal expansion coefficient and plays a role in binding and toughening, so that Al is prevented from being formed₂O₃Cracking deformation occurs when the ceramic substrate is sintered and molded; wherein Al is₂O₃The sol in the micro-perforation of the ceramic substrate is sintered and then cooled to grow mullite whisker so as to ensure that Al is₂O₃Al of ceramic substrate₂O₃The particles are wound by crystal wires, and the crystal wires are favorable for uniform distribution of internal stress, so that Al is ensured₂O₃Relative displacement between the crystal grains of silicate is reduced, and the crystal grainsThe wire can inhibit the aggregation and growth of crystal grains and effectively reduce pores in the ceramic, thereby improving the compactness of the sintered body and enabling Al to be in contact with the sintered body₂O₃The ceramic substrate has homogeneous crystal grain distribution, compact crystal grain distribution and high mechanical strength. The patent not only has complex slurry preparation process, but also has the defects of twice sintering and the like.

Chinese patent (application number) cn201710006821.x proposes a preparation method of a low-cost high-strength alumina ceramic substrate for electronic packaging. The preparation process comprises the following steps: (1) preparation of Al₂O₃Fine powder; (2) mixing Al₂O₃Mixing the powder with a solvent to prepare a slurry with good stability, and removing Al by a high-gradient magnetic separator₂O₃Iron impurities in the fine powder; (3) purifying the Al₂O₃Adding the fine powder, the solvent, the dispersant, the binder, the plasticizer and the sintering aid into a ball milling tank, mixing by a ball mill, and preparing Al by a tape casting method₂O₃Ceramic biscuit, sintering to obtain high-strength Al₂O₃A ceramic substrate. The substrate is sintered for 2.0h at 1650 ℃ to obtain the alumina ceramic substrate. The bending strength is 509MPa, and the fracture toughness is 4.8 MPa.m^1/2Dielectric constant of 9.2 and dielectric loss tangent of 9.5X 10^-4. The resistance card has excellent mechanical properties, but has the problems of high dielectric constant, high dielectric loss, high sintering temperature and the like.

Cordierite has a low dielectric constant and a low thermal expansion coefficient, and has good mechanical strength and electrical insulation performance, and is considered to be a promising dielectric material, and is widely applied to the fields of power electronics and the like, such as manufacturing various types of circuit boards, insulators, capacitors, filters, mixers and the like. Commercial cordierite generally has larger grain diameter and complete crystal development, can be completely and directly used for preparing an alumina substrate and mainly has the function of reducing the thermal expansion coefficient and the dielectric constant of the substrate. However, commercial cordierite powder has high inertia, is difficult to be fused with sintering aid powder to produce a glass phase under a sintering condition, cannot promote the development of alumina plate-shaped crystals in the substrate, does not promote the improvement of the mechanical property of the substrate, and simultaneously has low density and low strength of the corresponding substrate after sintering because commercial cordierite has high inertia and large addition amount.

Disclosure of Invention

The invention aims to solve the technical problem that aiming at the defects of the prior art, provides cordierite microcrystalline powder and a preparation method thereof, wherein the microcrystalline powder has small particle diameter, more surface defects and higher activity, and is suitable for being added into Al₂O₃Preparing an alumina ceramic substrate in the powder.

The invention also provides an alumina ceramic substrate and a preparation method thereof, and the alumina ceramic substrate with adjustable dielectric constant, low dielectric loss and thermal expansion coefficient and high strength, which is sintered at low temperature, is prepared.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows: a preparation method of cordierite microcrystalline powder comprises the following steps:

weighing three powder materials of micron magnesia, micron silica and micron alumina according to the stoichiometric ratio of cordierite, ball-milling the three powder materials by taking water as a medium, drying, synthesizing at the temperature of 700-1500 ℃ after drying, wherein the heating rate in the synthesis process is 0.5-6 ℃ mim^-1The synthesis time is 0.5-8h, and cordierite microcrystalline powder is obtained after cooling. Preferably, the synthesis is carried out at the temperature of 900-1300 ℃ after drying, and the heating rate of the synthesis temperature is 1-5 ℃ mim^-1The synthesis time is 1.5-4 h.

Commercial cordierite powder and cordierite microcrystalline powder prepared by the method have the same raw material ratio, and the main difference is reaction temperature and heat preservation time. The synthesis reaction temperature is low, the heat preservation time is short, the grain size of the microcrystal powder is small, and the activity is improved.

Adding the cordierite microcrystalline powder prepared by the method into Al₂O₃In the middle, the sintering process can induce the matrix Al₂O₃The directional growth of crystal grains obtains plate-shaped crystals, thereby improving the strength of the substrate, and commercial cordierite powder does not have the effect because the crystals are completely developed.

Furthermore, the particle size of the micron magnesium oxide is 0.5-1.5 microns, the particle size of the micron silicon oxide is 0.5-1.5 microns, and the particle size of the micron aluminum oxide is 0.5-1.5 microns. The particle size of the raw material powder used for synthesis is small, so that the granularity of the microcrystalline powder is small, and the activity is improved.

Furthermore, the drying temperature is 40-120 ℃, and the drying time is 12-60 h. Preferably, the drying temperature is 60-100 ℃, and the drying time is 24-50 h.

Furthermore, the ball milling time is 5-60h, and the rotating speed of the ball mill is 100-^-1. Preferably, the ball milling time is 10-40h, and the rotation speed of the ball mill is 200-^-1。

Further, the proportion of the various powders is (mass percent): the content of the μm-MgO powder is 0-20% (preferably 0-15%), μm-SiO₂The powder is 0-80% (preferably 0-60%), μm-Al₂O₃The powder is 0-60% (preferably 0-40%). Preferably, W (μm-MgO) ═ 14.0%, W (μm-SiO₂)＝51.0％、W(μm-Al₂O₃) 35.0%. The ball milling process is to put the three powder materials into a ball milling tank, take water as a medium and corundum balls as an abrasive material, and ball mill for a period of time.

The invention also discloses cordierite microcrystalline powder prepared by the preparation method.

The invention also discloses a preparation method of the alumina ceramic substrate, which comprises the following steps:

preparing slurry: adding 30-99 parts by mass of micron alumina, 0-15 parts by mass of a sintering aid, 0-15 parts by mass of a dielectric loss regulator, 5.6-33 parts by mass of a forming aid and 5-15 parts by mass of cordierite microcrystalline powder in claim 4 into a ball milling tank, and carrying out ball milling to obtain slurry;

preparing a green body: preparing a green sheet from the slurry by adopting a tape casting method;

and (3) glue discharging and sintering of green bodies: sintering the green sheet after removing the glue, wherein the sintering temperature control process comprises the following steps: at the temperature of 650 plus 1000 ℃, the heating rate is 0.5-5.0 ℃ mim^-1(ii) a The maximum temperature is 1300-1600 ℃, and the heating speed from 1000 ℃ to the maximum temperature is 0.5-6.0 ℃ mim^-1And keeping the temperature at the highest temperature for 0.2-4h to obtain the alumina ceramic substrate.

Preferably, the temperature control process of sintering is as follows: at the temperature of 650 plus 1000 ℃, the heating rate is 1.5-4.0 ℃ mim^-1(ii) a Maximum temperatureThe temperature is 1350-^-1The heat preservation time of the highest temperature is 0.5-3.0 h. Further preferably, the maximum temperature is 1350-.

Part of Al is promoted in the sintering process by utilizing the high activity of cordierite microcrystalline powder₂O₃The grains grow into plate-shaped crystals to increase Al₂O₃Substrate strength, Al reduction by cordierite low coefficient of thermal expansion₂O₃The thermal expansion coefficient of the substrate, thereby increasing Al₂O₃The thermal shock resistance of the substrate; al reduction by using cordierite with lower dielectric constant₂O₃The dielectric constant of the substrate.

Furthermore, the mass parts of the micron alumina, the sintering aid, the dielectric loss regulator, the forming aid and the cordierite microcrystalline powder are 55-95 parts, 0-15 parts, 0-10 parts, 8.5-21 parts and 4-12 parts respectively.

Further, the sintering aid includes one of CaO, SrO, and BaO.

Further, the dielectric loss adjuster comprises ZnO and Fe₂O₃MnO and Cr₂O₃One of (1);

the forming auxiliary agent comprises 2-10 parts by mass, 1.4-7.0 parts by mass and 0.2-6.0 parts by mass of dispersing agent, binder, plasticizer and film-forming agent. Preferably, the forming aid comprises 3-7 parts by mass, 3-5 parts by mass, 2.0-4.0 parts by mass and 0.5-5.0 parts by mass of a dispersing agent, a binder, a plasticizer and a film forming agent.

Further, the temperature of the binder removal of the green body is raised to 400 ℃ from room temperature, and the heating speed is 0.2-4 ℃ mim^-1400-650 ℃, the temperature rising speed is 0.5-5 ℃ mim^-1. Preferably, the temperature of the discharged rubber is raised to 400 ℃ from room temperature, and the raising speed is 0.5-2.0 ℃ mim^-1400-650 ℃ and the heating rate of 1.0-3 ℃ mim^-1。

The invention also discloses an alumina ceramic substrate prepared by the preparation method of the alumina ceramic substrate.

Preferably, the grain diameter of the micron alumina is 1.0 +/-0.5 micron, the grain diameter of the sintering aid is 0.6 +/-0.2 micron, the grain diameter of the dielectric loss regulator is 0.6 +/-0.2 micron, and the purity of the powder is more than or equal to 99 percent. And drying the powder, and weighing, wherein the drying temperature is 40-100 ℃ (preferably 50-90 ℃), and the drying time is 12-36h (preferably 16-30 h).

The detailed process of the slurry preparation is as follows:

mixing cordierite microcrystal powder and micron-Al₂O₃Adding powder, sintering aid, dielectric loss regulator, water and dispersant into the mixture according to a certain proportion, placing the mixture into a ball milling tank, taking water as a medium and corundum balls as an abrasive, and firstly carrying out ball milling for a period of time; then adding a binder, a plasticizer and a film-forming agent, then carrying out ball milling for a period of time to obtain stable slurry, and carrying out vacuum stirring on the slurry to remove bubbles so as to obtain the slurry with good fluidity and stability.

The dispersant is any one of phosphate, polyacrylic acid and polymethacrylic acid, the first ball milling time is 5-24h (preferably 10-20h), and the rotating speed of the ball mill is 50-600 r.min^-1(preferably 100-^-1) (ii) a The binder is any one of polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC); the plasticizer is polyethylene glycol (PEG); the film forming agent is glycerol; the secondary ball milling time is 5-40h (preferably 10-30h), and the rotating speed of the ball mill is 50-600 r.min^-1(preferably 100-^-1)。

The detailed process of green body preparation is as follows: and (2) feeding the prepared slurry into a casting machine, forming a thin-layer green belt on a conveying belt of the casting machine by the slurry, controlling the thickness of the green belt by controlling the flow rate of the slurry and the distance between a scraper and the conveying belt, drying the green belt by a drying chamber, and putting the dried green belt on a sheet punching machine for punching and cutting to obtain a green sheet with the required shape and size.

The detailed process of green body binder removal and sintering is as follows: putting the green sheet into a continuous kiln, discharging glue in the air according to a certain heat treatment system, and sintering according to a certain heat treatment system to obtain the target Al₂O₃A substrate.

Compared with the prior art, the invention has the beneficial effects that:

1. the raw material powder for synthesis has small particle size, low reaction temperature and short heat preservation time, and the cordierite microcrystalline powder has small particle size, more surface defects and high activity.

2. Part of Al is promoted in the sintering process by utilizing the high activity and many surface defects of cordierite microcrystalline powder₂O₃The grains grow into plate-shaped crystals to increase Al₂O₃Substrate strength, Al reduction by cordierite low coefficient of thermal expansion₂O₃The thermal expansion coefficient of the substrate, thereby increasing Al₂O₃The thermal shock resistance of the substrate; al reduction by using cordierite with lower dielectric constant₂O₃The dielectric constant of the substrate;

3. by adding a sintering aid (abbreviated as RO), Al is promoted by liquid phase sintering₂O₃The densification and sintering of the particles reduce the sintering temperature, improve the density of the substrate and simultaneously improve the dielectric constant of the substrate;

4. by adding trace dielectric loss regulator (XO) to Al₂O₃The crystal lattice surface of the particles forms solid solution, distorts the crystal lattice and hinders Al in the polarization process³⁺Thereby reducing Al₂O₃Dielectric loss of the substrate;

5、Al₂O₃the sintering temperature and the sintering time of the substrate are obviously reduced, and the production cost is reduced.

Drawings

FIG. 1 is a scanning electron micrograph of substrates obtained in example 1 of the present invention and comparative example 1.

FIG. 2 is a thermal expansion curve of the substrates obtained in examples 1, 2 and 3 of the present invention.

FIG. 3 is a stress-strain curve of the substrates obtained in examples 1, 2 and 3 of the present invention.

Fig. 4 is a stress-strain curve of the substrates obtained in comparative examples 1, 2 and 3.

Detailed Description

Example 1

A low-temperature sintered ultrathin alumina ceramic substrate with adjustable dielectric constant, low dielectric loss and thermal expansion coefficient and high strength and a preparation method thereof comprise the following steps:

(1) preparing and drying raw materials: drying the used powder for 24 hours at the temperature of 80 ℃, and respectively weighing 14g of micron magnesium oxide (mum-MgO) and 14g of micron silicon oxide (mum-SiO)₂)51g, micron alumina (. mu.m-Al)₂O₃)910g of CaO powder, 20g of CaO powder and 5g of ZnO powder.

(2) Pre-synthesizing cordierite microcrystal powder: separately mixing mu m-MgO14 g, mu m-SiO₂51g and μm-Al₂O₃Adding 35g of the mixture into a ball milling tank, taking water as a medium, taking corundum balls as an abrasive, and performing ball milling for 30 hours at the ball milling speed of 400 r.min^-1The slurry was dried at 90 ℃ for 48h and then in a box furnace at 4 ℃ mim^-1Raising the temperature to 1050 ℃ and preserving the heat for 4 hours, and then cooling the cordierite microcrystalline powder along with the furnace to obtain cordierite microcrystalline powder;

(3) preparing slurry: the obtained cordierite microcrystalline powder is separated by 875g of mu m-Al₂O₃Adding 20g of powder, 20g of CaO powder, 5g of ZnO powder and 30g of polyacrylic acid dispersant into a ball milling tank, taking water as a medium and corundum balls as an abrasive, and ball milling for 12 hours at the ball milling speed of 300 r.min^-1(ii) a Then adding 35g of polyvinyl alcohol binder, 24.5g of polyethylene glycol plasticizer and 20g of glycerol film forming agent, and then carrying out ball milling for 24 hours at the rotating speed of 200 r.min^-1Obtaining stable slurry, and defoaming the slurry under vacuum stirring to obtain the slurry with good fluidity and stability;

(4) preparing a green body: feeding the prepared slurry into a casting machine, forming a thin-layer green belt on a conveying belt of the casting machine by the slurry, controlling the thickness of the green belt by controlling the flow rate of the slurry and the distance between a scraper and the conveying belt, drying the green belt by a drying chamber, and putting the dried green belt on a sheet punching machine for punching and cutting to obtain a green sheet with required shape and size;

(5) and (3) glue discharging and sintering of green bodies: putting the green sheets into a continuous kiln, and in an air atmosphere, performing a glue discharging process: the temperature is raised to 400 ℃ at a rate of 1.0 ℃ mim^-1400-650 ℃ and a heating rate of 1.5 ℃ mim^-1(ii) a The sintering process comprises the following steps: 650-1000 ℃ interval, the temperature rise rate is 2.0 ℃ mim^-1，1000℃-1350 ℃ interval, and the heating-up speed is 2.5 ℃ mim^-1Keeping the temperature for 1.0h to obtain the target Al₂O₃A substrate.

The resulting substrate had a flexural strength of 312MPa and a thermal expansion coefficient of 6.87X 10^-6℃^-1(800 ℃ C.), a dielectric constant of 7.54 and a dielectric loss tg delta (10. times.^-4The frequency range: 1Hz-1MHz) ═ 1.2.

Example 2

(1) preparing and drying raw materials: drying the used powder for 24 hours at the temperature of 80 ℃, and respectively weighing 11.2g of mum-MgO and 11.2g of mum-SiO₂ 40.8g，μm-Al₂O₃898g, CaO powder 40g and ZnO powder 10 g.

(2) Pre-synthesizing cordierite microcrystal powder: respectively mixing mu m-MgO 11.2g, mu m-SiO₂40.8g and μm-Al₂O₃28g of the mixture is added into a ball milling tank, water is used as a medium, corundum balls are used as abrasive materials, the ball milling time is 30 hours, and the rotating speed of the ball mill is 400 r.min^-1The slurry was dried at 90 ℃ for 48h and then in a box furnace at 4 ℃ mim^-1Raising the temperature to 1100 ℃ and preserving the heat for 2h, and then cooling the cordierite microcrystalline powder along with the furnace to obtain cordierite microcrystalline powder;

(3) preparing slurry: the obtained cordierite microcrystalline powder was mixed with 870g of a-. mu.m-Al powder₂O₃Adding 40g of powder, 40g of CaO powder, 10g of ZnO powder and 40g of polyacrylic acid dispersing agent into a ball milling tank, taking water as a medium and corundum balls as an abrasive, and ball milling for 12 hours at the ball milling speed of 300 r.min^-1(ii) a Then adding 40g of polyvinyl alcohol binder, 28g of polyethylene glycol plasticizer and 25g of glycerol film-forming agent, and then carrying out ball milling for 24 hours at the rotating speed of 200 r.min^-1Obtaining stable slurry, and defoaming the slurry under vacuum stirring to obtain the slurry with good fluidity and stability;

(5) and (3) glue discharging and sintering of green bodies: putting the green sheets into a continuous kiln, and in an air atmosphere, performing a glue discharging process: the temperature is raised to 400 ℃ at a rate of 1.0 ℃ mim^-1400-650 ℃ and a heating rate of 1.5 ℃ mim^-1(ii) a The sintering process comprises the following steps: 650-1000 ℃ interval, the temperature rise rate is 2.0 ℃ mim^-1Temperature rise speed of 2.5 ℃ mim between 1000 ℃ and 1400 DEG C^-1Keeping the temperature for 0.8h to obtain the target Al₂O₃A substrate.

The resulting substrate had a flexural strength of 325MPa and a thermal expansion coefficient of 7.32X 10^-6℃^-1Dielectric constant of 7.86 and dielectric loss tg delta (x 10)^-4The frequency range: 1Hz-1MHz) ═ 1.9.

Example 3

(1) preparing and drying raw materials: drying the used powder for 24 hours at the temperature of 80 ℃, and respectively weighing 7g of mum-MgO and 7g of mum-SiO₂25.5g，μm-Al₂O₃892.5g, CaO powder 60g and ZnO powder 15 g.

(2) Pre-synthesizing cordierite microcrystal powder: respectively mixing mu m-MgO 7g, mu m-SiO₂25.5g and μm-Al₂O₃Adding 17.5g of the mixture into a ball milling tank, taking water as a medium, taking corundum balls as an abrasive, and performing ball milling for 30 hours at the ball milling speed of 400 r.min^-1The slurry was dried at 90 ℃ for 48h and then in a box furnace at 4 ℃ mim^-1Raising the temperature to 1150 ℃ and preserving the heat for 1.5h, and then cooling the cordierite microcrystalline powder along with the furnace to obtain cordierite microcrystalline powder;

(3) preparing slurry: the obtained cordierite microcrystalline powder is separated by 875g of mu m-Al₂O₃Adding 60g of powder, 60g of CaO powder, 15g of ZnO powder and 50g of polyacrylic acid dispersant into a ball milling tank, taking water as a medium and corundum balls as an abrasive, wherein the ball milling time is 12 hours, and the rotating speed of the ball mill is 300 r.min^-1(ii) a Then theAdding 45g of polyvinyl alcohol binder, 32g of polyethylene glycol plasticizer and 30g of glycerol film-forming agent, and then carrying out ball milling for 24 hours at the rotating speed of 200 r.min^-1Obtaining stable slurry, and defoaming the slurry under vacuum stirring to obtain the slurry with good fluidity and stability;

(5) and (3) glue discharging and sintering of green bodies: putting the green sheets into a continuous kiln, and in an air atmosphere, performing a glue discharging process: the temperature is raised to 400 ℃ at a rate of 1.0 ℃ mim^-1400-650 ℃ and a heating rate of 1.5 ℃ mim^-1(ii) a The sintering process comprises the following steps: 650-1000 ℃ interval, the temperature rise rate is 2.0 ℃ mim^-1In the range of 1000-1450 deg.C, the temp. raising speed is 2.5 deg.C.mim^-1Keeping the temperature for 0.5h to obtain the target Al₂O₃A substrate.

The resulting substrate had a flexural strength of 335MPa and a thermal expansion coefficient of 7.34X 10^-6℃^-1Dielectric constant of 8.06, dielectric loss tg delta (x 10)^-4The frequency range: 1Hz-1MHz) ═ 2.5.

Comparative example 1-commercial cordierite powder (median particle size 2.5 μm, purity 99% or more) was used

(1) preparing and drying raw materials: drying the used powder for 24 hours at the temperature of 80 ℃, and respectively weighing 100g of cordierite powder and mu m-Al₂O₃875g of CaO powder, 20g of ZnO powder and 5g of ZnO powder;

(2) preparing slurry: mixing cordierite powder, μm-Al₂O₃Adding 30g of powder, CaO powder, ZnO powder and polyacrylic acid dispersant into a ball milling tank, taking water as a medium and corundum balls as an abrasive material, and carrying out ball milling for 12 hoursThe rotating speed of the machine is 300 r.min^-1(ii) a Then adding 35g of polyvinyl alcohol binder, 24.5g of polyethylene glycol plasticizer and 20g of glycerol film forming agent, and then carrying out ball milling for 24 hours at the rotating speed of 200 r.min^-1Obtaining stable slurry, and defoaming the slurry under vacuum stirring to obtain the slurry with good fluidity and stability;

(5) and (3) glue discharging and sintering of green bodies: putting the green sheets into a continuous kiln, and in an air atmosphere, performing a glue discharging process: the temperature is raised to 400 ℃ at a rate of 1.0 ℃ mim^-1400-650 ℃ and a heating rate of 1.5 ℃ mim^-1(ii) a The sintering process comprises the following steps: 650-1000 ℃ interval, the temperature rise rate is 2.0 ℃ mim^-1In the range of 1000-1350 deg.C, the temp. raising speed is 2.5 deg.C.mim^-1Keeping the temperature for 1.0h to obtain the target Al₂O₃A substrate.

The resulting substrate had a flexural strength of 295MPa and a coefficient of thermal expansion of 6.95X 10^-6℃^-1Dielectric constant of 7.26, dielectric loss tg δ (× 10)^-4The frequency range: 1Hz-1MHz) ═ 1.1.

Comparative example 2-No sintering aid addition

(1) preparing and drying raw materials: drying the used powder for 24 hours at the temperature of 80 ℃, and respectively weighing 14g of mum-MgO and 14g of mum-SiO₂51g，μm-Al₂O₃930g and ZnO powder 5 g.

(2) Pre-synthesizing cordierite microcrystal powder: respectively mixing mu m-MgO14 g, mu m-SiO₂51g and μm-Al₂O₃Adding 35g of the mixture into a ball milling tank, taking water as a medium and corundum balls as an abrasive, and performing ball milling for 30 hours,the rotating speed of the ball mill is 400 r.min^-1The slurry was dried at 90 ℃ for 48h and then in a box furnace at 4 ℃ mim^-1Raising the temperature to 1050 ℃ and preserving the heat for 4 hours, and then cooling the heated material along with the furnace to obtain cordierite microcrystalline powder;

(3) preparing slurry: the cordierite microcrystalline powder obtained was treated to leave 895g of mu m-Al₂O₃Adding 5g of powder, 5g of ZnO powder and 30g of polyacrylic acid dispersant into a ball milling tank, taking water as a medium and corundum balls as an abrasive, and ball milling for 12 hours at the ball milling speed of 300 r.m.min^-1(ii) a Then adding 35g of polyvinyl alcohol binder, 24.5g of polyethylene glycol plasticizer and 20g of glycerol film forming agent, and then carrying out ball milling for 24 hours at the rotating speed of 200 r.min^-1Obtaining stable slurry, and defoaming the slurry under vacuum stirring to obtain the slurry with good fluidity and stability;

The resulting substrate had a flexural strength of 276MPa and a thermal expansion coefficient of 6.45X 10^-6℃^-1Dielectric constant of 7.24, dielectric loss tg δ (× 10)^-4The frequency range: 1Hz-1MHz) ═ 2.7.

Comparative example 3 No dielectric loss modifier

(1) preparing and drying raw materials: drying the used powder for 24 hours at the temperature of 80 ℃, and respectively weighing 14g of mum-MgO and 14g of mum-SiO₂51g，μm-Al₂O₃915g and 20g of CaO powder.

(2) Pre-synthesizing cordierite microcrystal powder: respectively mixing mu m-MgO14 g, mu m-SiO₂51g and μm-Al₂O₃Adding 35g of the mixture into a ball milling tank, taking water as a medium, taking corundum balls as an abrasive, and performing ball milling for 30 hours at the ball milling speed of 400 r.min^-1The slurry was dried at 90 ℃ for 48h and then in a box furnace at 4 ℃ mim^-1Raising the temperature to 1050 ℃ and preserving the heat for 4 hours, and then cooling the heated material along with the furnace to obtain cordierite microcrystalline powder;

(3) preparing slurry: the cordierite microcrystalline powder obtained was made to remain 880g of μm-Al₂O₃Adding 20g of powder, 20g of CaO powder and 30g of polyacrylic acid into a ball milling tank, taking water as a medium, taking corundum balls as an abrasive, and milling for 12 hours at the ball milling speed of 300 r.m.min^-1(ii) a Then adding 35g of polyvinyl alcohol binder, 24.5g of polyethylene glycol plasticizer and 20g of glycerol film forming agent, and then carrying out ball milling for 24 hours at the rotating speed of 200 r.min^-1Obtaining stable slurry, and defoaming the slurry under vacuum stirring to obtain the slurry with good fluidity and stability;

The resulting substrate had a flexural strength of 322MPa and a coefficient of thermal expansion of 6.85X 10^-6℃^-1Dielectric constant of 7.62, dielectric loss tg δ (× 10)^-4The frequency range: 1Hz-1MHz) ═ 5.6.

Comparative example 4 No cordierite powder addition

(1) preparing and drying raw materials: drying the used powder for 24 hours at the temperature of 80 ℃, and respectively weighing mum-Al₂O₃975g, CaO powder 20g and ZnO powder 5 g;

(2) preparing slurry: 975g of μm-Al₂O₃Adding 20g of powder, 20g of CaO powder, 5g of ZnO powder and 30g of polyacrylic acid dispersant into a ball milling tank, taking water as a medium and corundum balls as an abrasive, and ball milling for 12 hours at the ball milling speed of 300 r.min^-1(ii) a Then adding 35g of polyvinyl alcohol binder, 24.5g of polyethylene glycol plasticizer and 20g of glycerol film forming agent, and then carrying out ball milling for 24 hours at the rotating speed of 200 r.min^-1Obtaining stable slurry, and defoaming the slurry under vacuum stirring to obtain the slurry with good fluidity and stability;

The resulting substrate had a flexural strength of 152MPa and a thermal expansion coefficient of 8.04X 10^-6℃^-1(800 ℃ C.), a dielectric constant of 8.25 and a dielectric loss tg.delta (. times.10)^-4The frequency range: 1Hz-1MHz) ═ 2.3.

Matrix Al for the non-added Components in comparative examples 1-4₂O₃Replacing the micro-rice flour, and ensuring that the total mass of all powder is 100 percent.

TABLE 1 parameters tested in examples 1-3 and comparative examples 1-4

The test method comprises the following steps:

and (3) appearance observation: and (2) directly taking the fracture of the sintered substrate, cleaning, spraying gold, and carrying out scanning electron microscope morphology observation, wherein as shown in figure 1, a figure is a microstructure photograph of the substrate in example 1, and b figure is a microstructure photograph of the substrate in comparative example 1.

Testing thermal expansion coefficient and mechanical property:

drying the substrate slurry, preparing a strip sample by compression molding, sintering according to the sintering temperature of the substrate with corresponding composition, and testing the thermal expansion coefficient and the bending strength of the obtained sample strip;

dielectric properties and dielectric loss measurements:

drying the substrate slurry, preparing a sheet green body by compression molding, sintering according to the sintering temperature of the corresponding composition substrate, and then testing the dielectric property and dielectric loss of the obtained sample sheet;

in example 1, MgO and SiO were used₂、Al₂O₃Keeping the temperature at 1050 ℃ after ball milling to obtain cordierite microcrystalline powder, wherein commercial cordierite powder is adopted in comparative example 1. Commercial cordierite powder and cordierite microcrystalline powder prepared by the method have the same raw material ratio, and the main differences are the raw material particle size, the reaction temperature and the heat preservation time. The raw material powder for synthesis has small particle size, low reaction temperature and short heat preservation time, and therefore, the microcrystal powder has small particle size and many surface defects. As can be seen from FIG. 1, the substrate obtained in example 1 had plate-like crystal grains, andno platelets appeared in the substrates made with commercial cordierite powders. The reason is that the self-made cordierite microcrystalline powder has small size and a plurality of surface defects, and the sintering process can induce the matrix Al₂O₃The directional growth of crystal grains obtains plate-shaped crystals, thereby improving the strength of the substrate, and commercial cordierite powder does not have the effect because the crystals are completely developed.

Generally, for a substrate, the lower the dielectric constant, the better. But is influenced by material composition and density, the same composition is adopted, the higher the density is, the larger the dielectric constant is; substrates of different compositions, primarily in terms of the magnitude of the dielectric constant of each component in the constituent substrate, are due to the fact that cordierite has a dielectric constant (5-7) that is significantly lower than alumina (8-9), both of which factors contribute to the dielectric constant of the final substrate. In comparative example 1 of the commercial cordierite powder, the commercial cordierite powder has a high inertness, and is difficult to be fused with sintering aid powder to produce a glass phase under a sintering condition, so that the final substrate has a low density. When the ceramic material has the same composition, the dielectric constant of the ceramic material has a positive relation with the compactness thereof, and the denser the ceramic material is, the higher the dielectric constant is. Since commercial cordierite is more inert, it also results in a corresponding resistor having lower density, lower strength, and lower dielectric constant, such that the dielectric constant in comparative example 1 is lower than that of example 1.

The bending strength of the substrate in the comparative example 2 is not as good as that of the substrate in the example 1 because the sintering aid is not added in the comparative example 2, compared with the example 1, the bending strength of the substrate in the comparative example 2 is proved to be improved by adding the sintering aid in the example 1 and improving the compactness of the substrate in the same sintering temperature and sintering time;

comparative example 3, to which no dielectric loss adjusting agent was added, had a dielectric loss of 5.6tg δ (× 10)^-4The frequency range: 1Hz-1MHz), and dielectric loss in example 1 was 1.2 tg. delta (. times.10)^-4The frequency range: 1Hz-1MHz) in Al by adding a dielectric loss modifier₂O₃The crystal lattice surface of the particles forms solid solution, distorts the crystal lattice and hinders Al in the polarization process³⁺Thereby reducing Al₂O₃Dielectric loss of the substrate.

Comparative example 4, in which no cordierite was added, had a bending strength significantly lower than that of example 1, and the thermal expansion coefficient, dielectric constant and dielectric loss were significantly higher than those of example 1.

FIG. 2 is a thermal expansion curve of the substrates obtained in examples 1, 2 and 3, wherein the thermal expansion curves of the substrates obtained in examples 1, 2 and 3 mainly differ in the cordierite content and the compactness of the substrate, and generally speaking, the denser the ceramic material, the higher the thermal expansion coefficient; in addition, since the thermal expansion coefficient of cordierite is significantly smaller than that of alumina, the higher the amount of cordierite added to the substrate, the lower the thermal expansion coefficient of the substrate.

Fig. 3 is a stress-strain curve of the substrates obtained in examples 1, 2 and 3, and fig. 4 is a stress-strain curve of the substrates obtained in comparative examples 1, 2, 3 and 4, the stress-strain curve being mainly influenced by the compactness of the material, the amount of cordierite added, the denser the higher the strength, the less the cordierite added, the higher the strength.

Claims

1. A preparation method of cordierite microcrystalline powder is characterized by comprising the following steps:

weighing three powder materials of micron magnesia, micron silica and micron alumina according to the stoichiometric ratio of cordierite, ball-milling the three powder materials by taking water as a medium, drying, synthesizing at the temperature of 700-1500 ℃ after drying, wherein the heating rate in the synthesis process is 0.5-6 ℃ mim^-1The synthesis time is 0.5-8h, and cordierite microcrystalline powder is obtained after cooling.

2. The method of producing cordierite microcrystal powder according to claim 1, wherein the particle size of the micro magnesia is 0.5 to 1.5 μm, the particle size of the micro silica is 0.5 to 1.5 μm, and the particle size of the micro alumina is 0.5 to 1.5 μm.

3. The method of producing cordierite microcrystal powder according to claim 1, wherein the baking temperature is 40-120 ℃ and the baking time is 12-60 hours.

4. A cordierite microcrystalline powder produced by the production method according to any one of claims 1 to 3.

5. A preparation method of an alumina ceramic substrate is characterized by comprising the following steps:

and (3) glue discharging and sintering of green bodies: the green sheet is sintered after binder removal, and the temperature rise speed is 0.5-5.0 ℃ and mim when the sintering temperature control process is 650-^-1(ii) a The maximum temperature is 1300-1600 ℃, and the heating speed from 1000 ℃ to the maximum temperature is 0.5-6.0 ℃ mim^-1And keeping the temperature at the highest temperature for 0.2-4h to obtain the alumina ceramic substrate.

6. The preparation method according to claim 5, wherein the mass parts of the micron alumina, the sintering aid, the dielectric loss modifier, the forming aid and the cordierite microcrystalline powder are 55-95 parts, 0-15 parts, 0-10 parts, 8.5-21 parts and 4-12 parts, respectively.

7. The production method according to claim 5, wherein the sintering aid includes one of CaO, SrO, and BaO.

8. The method according to claim 5, wherein the dielectric loss modifier comprises ZnO, Fe₂O₃MnO and Cr₂O₃One of (1);

the forming auxiliary agent comprises 2-10 parts by mass, 1.4-7.0 parts by mass and 0.2-6.0 parts by mass of dispersing agent, binder, plasticizer and film-forming agent.

9. The method according to any one of claims 5 to 7, wherein the green body is removed at a temperature of from room temperature to 400 ℃ at a rate of from 0.2 to 4 ℃ mim^-1400-650 ℃, the temperature rising speed is 0.5-5 ℃ mim^-1。

10. An alumina ceramic substrate obtained by the production method according to any one of claims 5 to 9.