Preparation method of high-strength, high-toughness and high-thermal-conductivity aluminum nitride ceramic substrate with synergistic effect

Abstract

The invention discloses a preparation method of a high-strength, high-toughness and high-thermal-conductivity aluminum nitride ceramic substrate with a synergistic effect, and relates to the technical field of aluminum nitride ceramic materials. Large-particle aluminum nitride powder and crystal whiskers are subjected to surface modification to solve the sintering activity problem, aluminum nitride fine powder is subjected to dispersion modification to avoid the dispersion and viscosity problems during ceramic slurry ball-milling blending, cold isostatic pressing is used for improving the casting blank sheet density and eliminating uneven stress, and a multi-element composite sintering aid is matched to improve the sintering performance of the ceramic slurry. A synergistic effect is achieved through multiple strengthening means of strengthening heat conduction through the graded large-particle aluminum nitride powder, toughening through the aluminum nitride whiskers and strengthening through the nanometer dispersed zirconium nitride particles, the strengthening defects are mutually compensated, the strengthening effects are mutually promoted, and the obtained aluminum nitride ceramic substrate has very high comprehensive performance and has high commercial value and practical significance.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum nitride ceramic materials, and particularly relates to a high-strength, high-toughness, and high-thermal-conductivity aluminum nitride ceramic substrate material with a synergistic effect. Background Art

[0002] With the continuous progress of integrated circuit chip technology, while the chip performance is improved, its power and heat generation are also significantly increased. The chip size and packaging volume are developing towards miniaturization, posing new challenges to packaging technology, packaging materials, and the heat dissipation performance of the system.

[0003] As an emerging packaging system material, ceramic substrates generally have excellent insulation performance, high thermal conductivity, high chemical stability, and high strength, and are more suitable for power electronic product packaging. Currently, the commonly used ceramic substrate materials mainly include: alumina, zirconia toughened alumina, beryllium oxide, aluminum nitride, silicon nitride, etc.

[0004] Aluminum nitride has a relatively high thermal conductivity base, generally reaching 170 - 220 W / m·K, is non-toxic and environmentally friendly, has a high breakdown voltage, low dielectric constant and dielectric loss. However, its toughness is poor, the flexural strength generally reaches 300 - 400 MPa, and the fracture toughness generally reaches 2 - 4 MPa·m 1 / 2 , in the actual application of aluminum nitride ceramic substrates, it may be required to withstand impacts, vibrations, high-temperature differential thermal cycles, etc. It is necessary to enhance the aluminum nitride ceramic material, explore new strengthening means and optimize the preparation process to meet its actual use requirements.

[0005] CN108863393 discloses a preparation method of a high-strength and high-thermal-conductivity aluminum nitride ceramic material. Using 200nm ultrafine aluminum nitride powder as the basis, adding a composite additive, pre-sintering at 1300°C - 1500°C for 1 - 5 hours in an atmospheric-pressure nitrogen-containing reducing atmosphere, and then sintering at 1500°C - 1800°C for 3 - 10 hours in a nitrogen atmosphere to prepare fine-grained ceramics with a thermal conductivity of 180 W / m·k and a flexural strength of 550 MPa.

[0006] CN105777169 discloses an aluminum nitride whisker-reinforced aluminum nitride ceramic material for electronic parts. Adding 5 - 32wt% of aluminum nitride whiskers to the aluminum nitride ceramic, using the characteristics of high fracture strength and large elastic modulus of ceramic whiskers to improve the mechanical properties of the aluminum nitride ceramic material, making it have higher reliability when used as an electronic packaging substrate, and the preparation method is simple and easy to realize industrial production.

[0007] CN103553691 discloses a method for preparing a particle-dispersed toughened aluminum nitride ceramic substrate for high-power LED lighting packaging, wherein 3-12wt% of a toughening phase is added, and the toughening phase is one or a composite of any of molybdenum, tungsten, niobium, molybdenum carbide, tungsten carbide, and niobium carbide. The fracture toughness of the AlN substrate is effectively improved through the toughening mechanisms of crack deflection bending, crack bridging, and residual stress.

[0008] The above methods have their own advantages, but there are also some problems, such as the need for waterproofing of nano-scale ultrafine aluminum nitride powder, the use of highly dangerous gas sources such as hydrogen cyanide, the shortening of the aspect ratio of the whiskers after long-term ball milling, the loss of their whisker structural characteristics and strengthening capabilities, and the toughening effect of the toughening phase is not obvious enough. Summary of the invention

[0009] In view of the problems existing in the above-mentioned background technology, the present invention aims to provide a method for preparing a high-strength, high-toughness, and high-thermal conductivity aluminum nitride ceramic substrate with a synergistic effect of multiple strengthening means.

[0010] The key technical principle of the present invention is:

[0011] Introducing aluminum nitride whiskers into aluminum nitride ceramics, the structural characteristics of the whiskers make them a heat conduction path in aluminum nitride ceramics, which can improve the intrinsic thermal conductivity of the ceramics, and greatly enhance the fracture toughness of the ceramics through crack deflection effect, whisker debonding effect, whisker pull-out effect, and whisker bridging effect. However, due to the bridging effect of whiskers in the ceramic body structure, the liquid phase of the sintering aid cannot diffuse, migrate, and coat well during the sintering process, resulting in a decrease in the sintering activity of the ceramics. After sintering, there are some non-densified areas and sintering defects in the ceramics, which reduce the density and bending strength and need to be reinforced.

[0012] A certain amount of sintering aid phase is coated on the surface of the whisker, the corresponding nitrate of the selected auxiliary phase component is dissolved in ethanol, and then precipitated and coated on the surface of the whisker, and nitrogen is passed through at the decomposition temperature corresponding to the nitrate to keep it warm, so as to obtain a loose, highly active and uniform auxiliary phase coating.

[0013] Introducing dispersed zirconium nitride particles into aluminum nitride ceramics can strengthen the grain boundaries of aluminum nitride ceramics, change the crack propagation path, induce more transgranular fractures, and improve the strength and fracture toughness of the ceramics. However, the intrinsic thermal conductivity of zirconium nitride is very low, about 20W / m·K, and it enters aluminum nitride ceramics as a composite phase, so its morphology, existence position and total amount of addition need to be controlled.

[0014] The amount of zirconium nitride added should not be too high to reduce its adverse effect on the thermal conductivity of aluminum nitride ceramics. After a trace amount is added, the dispersion of zirconium nitride will increase, making it less likely to self-agglomerate. It should also be controlled to exist only at the aluminum nitride grain boundary and not grow into the interior of the aluminum nitride grains.

[0015] The introduction of zirconium nitride is carried out by a method of in-situ reaction of zirconia to generate dispersed zirconium nitride particles. The reaction precursor can be selected from one or more of zirconia, 3mol% yttrium-stabilized zirconia, zirconium carbonate, and zirconium nitrate, which are prepared by the sol-gel method or directly used as nanopowders, D 50 <300nm.

[0016] The introduced precursor will decompose into zirconia at high temperature. Zirconia has good chemical stability and will not diffuse into the aluminum nitride lattice. Zirconia will react in-situ with aluminum nitride at about 1500 - 1700 °C to generate nano-zirconium nitride microspheres, which are dispersed between aluminum nitride particles, pinning and strengthening the aluminum nitride grain boundaries, and can have a significant strengthening effect on the ceramic. However, a small amount of alumina will be generated simultaneously, increasing the oxygen content of the additive phase, from Y 4 Al 2 O 9 (YAM) to Y 3 Al 5 O 12 (YAG) conversion, which can improve the sintering activity, but will also reduce the thermal conductivity of the ceramic to a certain extent.

[0017] 8AlN + 6ZrO 2 →6ZrN + 4Al 2 O 3 +N 2

[0018] 2Y 2 O 3 +Al 2 O 3 →Y 4 Al 2 O 9 (YAM)

[0019] 3Y 2 O 3 +5Al 2 O 3 →2Y 3 Al 5 O 12 (YAG)

[0020] Using aluminum nitride ceramic powder with particle size grading can increase the density of the ceramic green body, introduce large particle high thermal conductivity grains, and improve the thermal conductivity of the ceramic. However, the sintering activity of large particle aluminum nitride ceramic powder is low, and the increase in the average grain size after sintering will reduce the flexural strength of the ceramic.

[0021] To solve the problem of poor sintering activity of large-sized aluminum nitride powder, it is pre-oxidized and then coated with a certain amount of sintering aid phase: the corresponding nitrates of the sintering aid phase components are dissolved in ethanol and then precipitated to coat the surface of the large-sized aluminum nitride. Nitrogen is introduced and kept warm at the decomposition temperature of the corresponding nitrates to obtain a loose, highly active and uniform coating of the sintering aid phase.

[0022] The large-sized aluminum nitride powder is first pre-oxidized to form a nano-oxide film on its surface. The composition of the oxide film is a non-stoichiometric compound AlO x (x < 1.5) of aluminum and oxygen. After the coating of the nitrates of the sintering aid phase, they are calcined and decomposed into the oxides of the sintering aid phase at high temperature, which can combine well with the oxide film on the surface of the aluminum nitride particles and improve the sintering activity of the large-sized aluminum nitride powder during the sintering process.

[0023] 2AlN + xO 2 → 2AlO x + N 2

[0024] 2Y(NO 3 ) 3 → Y 2 O 3 + 3N 2 O 5

[0025] mY 2 O 3 + nAlO x → Y 4 Al 2 O 9 (YAM) / YAlO 3 (YAP) / Y 3 Al 5 O 12 (YAG)

[0026] The surface-modified large-sized aluminum nitride powder is used for secondary or tertiary grading with sub-micron-sized aluminum nitride fine powder. The sub-micron-sized aluminum nitride fine powder only undergoes dispersion modification to avoid its difficulty in being dispersed in the composite solvent at the initial stage of preparing the ball-milling slurry, and there is no need to add an excessive amount of composite solvent for the dispersion of the aluminum nitride fine powder to avoid difficulties in adjusting the viscosity of the slurry.

[0027] Aluminum nitride whiskers and graded large-particle aluminum nitride powders can improve the thermal conductivity and toughness of ceramics, but will reduce the strength and sintering activity; dispersed zirconium nitride particles can improve the strength and toughness of ceramics and enhance the sintering activity of the additive phase, but will reduce the thermal conductivity of ceramics. Each single strengthening method has its own advantages and disadvantages, and has different degrees of improvement or reduction in different performance directions of ceramics. By combining them, the disadvantages of strengthening can be compensated for each other, and the strengthening effects can promote each other. And for different application targets and directions, through the control of the ceramic preparation process, the synergistic effect of strengthening, toughening, and high thermal conductivity can be realized.

[0028] To achieve the above object, the present invention also optimizes some key technical processes, and the specific technical solutions are as follows:

[0029] S1 Dispersion modification of aluminum nitride fine powder: Put 100 parts of aluminum nitride fine powder, 60 - 70 parts of absolute ethanol, 0.2 - 2 parts of dispersion modifier, and 500 parts of zirconia grinding balls into a ball mill tank, ball mill eight times, with each time being thirty minutes and the intermittent time being ten minutes, and the ball mill rotation speed being 200 - 400 r / min. After ball milling, place the slurry in a 45°C vacuum oven for drying, and after drying, pass it through a 60-mesh sieve to obtain the modified aluminum nitride fine powder for standby;

[0030] Preferably, in step S1, the oxygen content of the aluminum nitride fine powder is less than 1 wt%, the particle size distribution is narrow, and 0.5μm ≤ D 50 ≤5μm.

[0031] Preferably, in step S1, the dispersion modifier is one or more of castor oil, fish oil, polyethylene glycol 2000, oleic acid, paraffin wax, and titanate coupling agent.

[0032] Preferably, in step S1, the material of the ball mill tank is organic materials such as nylon and polytetrafluoroethylene, and materials such as stainless steel and agate are not used.

[0033] S2 Surface modification of large-particle aluminum nitride powder: First, perform high-temperature calcination on the large-particle aluminum nitride powder under an air atmosphere condition, then dissolve 0.5 - 3 parts of the composite sintering aid nitrate in 20 - 35 parts of ethanol, add 100 parts of the calcined large-particle aluminum nitride powder, stir ultrasonically and heat at 60°C to evaporate the ethanol, heat to 900 - 1000°C at 2.5°C / min under a nitrogen atmosphere and calcine for one hour, and set insulation at the decomposition temperature point of the corresponding nitrate to obtain the modified large-particle aluminum nitride powder for standby;

[0034] Preferably, in step S2, the oxygen content of the large-particle aluminum nitride powder is less than 1 wt%, the particle size distribution is narrow, and 5μm ≤ D 50 ≤100μm.

[0035] Preferably, the maximum holding temperature range of the calcination in step S2 is between 500 and 750 °C, and the holding time is between 20 and 60 minutes.

[0036] Preferably, the composite sintering aid nitrate in step S2 is selected from two or more of yttrium nitrate, calcium nitrate, lanthanum nitrate, lithium nitrate, and magnesium nitrate.

[0037] S3 Surface modification of aluminum nitride whiskers: Dissolve 0.5 - 3 parts of the composite sintering aid nitrate in 30 parts of ethanol, add 100 parts of aluminum nitride whiskers, stir ultrasonically and heat at 60 °C to evaporate the ethanol. Calcinate at 2.5 °C / minute to 900 - 1000 °C for one hour under a nitrogen atmosphere, and set the holding temperature at the decomposition temperature point of the corresponding nitrate to obtain modified aluminum nitride whisker powder for standby.

[0038] Preferably, the oxygen content of the aluminum nitride whiskers in step S3 is less than 1 wt%, the length is between 5 and 250 μm, and the aspect ratio is between 10 and 50. It can be seen that Figure 1 。

[0039] Preferably, the composite sintering aid nitrate in step S3 is selected from two or more of yttrium nitrate, calcium nitrate, lanthanum nitrate, lithium nitrate, and magnesium nitrate.

[0040] S4 Ball milling and mixing: Put 85 - 97 parts of graded aluminum nitride powder, 15 - 25 parts of composite organic solvent, 3 - 5 parts of dispersant dissolved in advance, 0.5 - 3 parts of composite sintering aid, 0.5 - 2 parts of zirconia reaction precursor, and 500 parts of zirconia grinding balls into the ball mill tank. The ball milling time for each time is thirty minutes, the intermittent time is ten minutes, the ball milling speed is 200 - 400 r / minute, ball mill four times, add 3 - 5 parts of plasticizer, then ball mill four times, add 8 - 12 parts of binder. The binder needs to be dissolved in 21 - 42 parts of ethanol in advance to form a sol, then ball mill four times, add 3 - 15 parts of modified aluminum nitride whisker powder, and finally ball mill for fifteen minutes. Filter out the grinding balls, and vacuum stir and defoam the casting slurry for one hour;

[0041] Preferably, in the graded aluminum nitride powder in step S4, the modified fine aluminum nitride powder accounts for 10 - 90 wt%, and the modified large particle aluminum nitride powder accounts for 10 - 90 wt%.

[0042] Preferably, in the composite organic solvent in step S4, ethanol accounts for 40 - 60 parts, and n-butanol accounts for 40 - 60 parts.

[0043] Preferably, the dispersant in step S4 is selected from one of castor oil and fish oil.

[0044] Preferably, the composite sintering aid in step S4 is selected from two or more of yttrium oxide, calcium carbonate, lanthanum oxide, lithium carbonate, and magnesium oxide, and nanometer powder is used. D 50<300 nm.

[0045] Preferably, the zirconia reaction precursor in step S4 can be selected from one or more of zirconia, 3 mol% yttria-stabilized zirconia, zirconium carbonate, and zirconium nitrate, prepared by the sol-gel method, or directly used as nanopowder, D 50 <300 nm.

[0046] Preferably, the plasticizer in step S4 can be dibutyl phthalate.

[0047] Preferably, the binder in step S4 can be polyvinyl butyral.

[0048] S5 Tape casting: Cast the degassed tape-casting slurry to obtain a tape-cast green sheet of a certain thickness, or continue to dry, cut, and hot-press laminate to reach the required thickness;

[0049] Preferably, in the tape casting in step S5, the height of the tape-casting doctor blade is 0.5 - 1 mm, and the tape-casting speed is 0.5 m / minute.

[0050] Preferably, in the hot-press lamination in step S5, the heating temperature is 50 - 150 °C, the pressing pressure is 10 - 30 MPa, and the holding pressure time is 20 - 40 minutes.

[0051] S6 Cold isostatic pressing: Stack the tape-cast green sheets with a plastic film in between, and perform cold isostatic pressing after soft sealing;

[0052] Preferably, in the cold isostatic pressing in step S6, the pressure increase and decrease rates are both 100 MPa / minute, and the maximum holding pressure is 200 MPa for 5 minutes.

[0053] S7 Debinding: Spray boron nitride release agent on the tape-cast green sheets for lamination, press a boron nitride ceramic plate on top, and perform debinding in a flowing air atmosphere. The heating rate is 1 °C / minute, the maximum holding temperature is 600 °C, and the holding time is 2 - 5 hours. Set the holding temperature according to the selected organic components at their volatilization temperature points. The process temperature curve is shown in Figure 2 ;

[0054] S8 Ceramic sintering: Spray boron nitride on the tape-cast green sheets for lamination, press a boron nitride ceramic plate on top, and perform stepwise sintering in a nitrogen atmosphere. When a non-oxide form is selected in the sintering aid, set the holding temperature at its corresponding decomposition temperature point. The process temperature curve is shown in Figure 3 ;

[0055] Preferably, the sintering holding temperature in step S8 can be selected from 1650 °C to 1850 °C, and the holding time can be selected from 2 to 4 hours.

[0056] After-treatment and performance testing of S9: The sintered ceramic substrates are polished, cut into the required sizes, and tested for thermal conductivity, flexural strength, fracture toughness, hardness, etc.

[0057] Preferably, the thermal conductivity of the obtained aluminum nitride ceramic product > 150 W / m·K, the flexural strength > 450 MPa, and the fracture toughness > 9 MPa·m 1 / 2 , and for different application targets and directions, individual performance indicators can be higher.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] By synergistically using various performance enhancement means such as strengthening heat conduction with graded large-particle aluminum nitride powder, toughening with aluminum nitride whiskers, and dispersion strengthening with second-phase particles, the disadvantages of strengthening are mutually compensated, the strengthening effects are mutually promoted, and some detailed processes in ceramic tape casting are optimized, making the entire ceramic preparation process more stable and further improving the comprehensive performance of the aluminum nitride ceramic substrate. Description of the Drawings

[0060] Figure 1 SEM photograph of aluminum nitride whiskers.

[0061] Figure 2 General temperature curve of debinding and degreasing process.

[0062] Figure 3 Temperature curve of sintering process (Example 2).

[0063] Figure 4 Internal zirconium nitride microspheres in the ceramic after sintering.

[0064] Figure 5 SEM photograph of the ceramic fracture surface after sintering. Detailed Embodiments

[0065] The present invention will be further described below in conjunction with embodiments and drawings, but should not be construed as a limitation of the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative efforts fall within the scope of protection of the present invention.

[0066] Example 1

[0067] Put 100 parts of D 50 0.9 μm aluminum nitride fine powder, 60 parts of anhydrous ethanol, 1 part of castor oil, and 500 parts of zirconia grinding balls into a ball mill tank, ball mill for four hours, dry and pass through a 60-mesh sieve to obtain modified aluminum nitride fine powder for standby.

[0068] Put D 50The 5-μm large particle aluminum nitride powder is calcined in an air atmosphere at a heating rate of 10 °C / minute, with a maximum holding temperature of 700 °C and a holding time of 30 minutes.

[0069] Dissolve 0.2 parts of yttrium nitrate, 0.2 parts of lanthanum nitrate, and 0.1 part of calcium nitrate in 25 parts of ethanol. Add 100 parts of the calcined large particle aluminum nitride powder, stir ultrasonically, and heat at 60 °C to evaporate the ethanol. In a nitrogen atmosphere, heat at a rate of 2.5 °C / minute, hold for one hour at 130 °C, 500 °C, 550 °C, and 800 °C respectively, with a maximum calcination temperature of 1000 °C and hold for one hour to obtain the modified large particle aluminum nitride powder for standby.

[0070] Dissolve 0.2 parts of yttrium nitrate, 0.2 parts of lanthanum nitrate, and 0.1 part of calcium nitrate in 25 parts of ethanol. Add 100 parts of aluminum nitride whiskers, stir ultrasonically, and heat at 60 °C to evaporate the ethanol. In a nitrogen atmosphere, heat at a rate of 2.5 °C / minute, hold for one hour at 130 °C, 500 °C, 550 °C, and 800 °C respectively, with a maximum calcination temperature of 1000 °C and hold for one hour to obtain the modified aluminum nitride whisker powder for standby.

[0071] Put 95 parts of graded aluminum nitride powder, including 90 wt% of modified fine aluminum nitride powder, 10 wt% of modified large particle aluminum nitride powder, 15 parts of ethanol, 10 parts of n-butanol, 3 parts of castor oil, 1 part of yttrium oxide, 1 part of lanthanum oxide, 0.5 part of calcium carbonate, 1.5 parts of 3 mol% yttrium-stabilized zirconia, and 500 parts of zirconia grinding balls into a ball mill can. The ball mill rotates at 200 r / minute for two hours, add 4 parts of dibutyl phthalate, ball mill for two hours, add 10 parts of polyvinyl butyral (polyvinyl butyral needs to be dissolved in 35 parts of ethanol in advance to form a sol), ball mill for two hours, add 5 parts of modified aluminum nitride whisker powder, ball mill for 15 minutes, filter out the grinding balls, and vacuum stir and defoam the casting slurry for one hour.

[0072] Perform tape casting on the defoamed casting slurry, dry, cut, and hot press and laminate to 0.7 mm.

[0073] Stack the tape-cast green sheets with a plastic film in between, perform soft sealing, and then carry out cold isostatic pressing at 200 MPa for five minutes.

[0074] Spray boron nitride release agent on the tape-cast green sheets for lamination, place a boron nitride ceramic plate on the top, and perform debinding and degassing in a flowing air atmosphere at a heating rate of 1 °C / minute. Hold for one hour at 200 °C and 350 °C respectively, hold for two hours at 600 °C, and then cool down with the furnace.

[0075] The tape-cast green sheets are sprayed with boron nitride and laminated, and a boron nitride ceramic plate is pressed on top. Sintering is carried out in a nitrogen atmosphere using a segmented heating method. It is heated to 850°C at a rate of 5°C per minute, held for one hour, then heated to 1500°C at a rate of 5°C per minute and held for one hour, then heated to 1650°C at a rate of 2.5°C per minute and held for four hours, then cooled to 1200°C at a rate of 5°C per minute and then to room temperature at a rate of 10°C per minute to complete sintering. It is then polished to a thickness of 0.4 mm.

[0076] Example 2

[0077] Add D 50 100 parts of 0.9 μm aluminum nitride fine powder, 60 parts of anhydrous ethanol, 1 part of castor oil, and 500 parts of zirconia grinding balls are placed in a ball mill and milled for four hours. After drying, it is passed through a 60-mesh sieve to obtain modified aluminum nitride fine powder for standby.

[0078] Add D 50 5 μm large particle aluminum nitride powder is calcined in an air atmosphere at a heating rate of 10°C per minute, with a maximum holding temperature of 700°C and a holding time of 30 minutes.

[0079] 0.2 parts of yttrium nitrate, 0.2 parts of lanthanum nitrate, and 0.1 part of calcium nitrate are dissolved in 25 parts of ethanol. 100 parts of the calcined large particle aluminum nitride powder are added, and it is ultrasonically stirred and heated at 60°C to evaporate the ethanol. In a nitrogen atmosphere, the heating rate is 2.5°C per minute, and it is held for one hour at 130°C, 500°C, 550°C, and 800°C respectively. The maximum calcination temperature is 1000°C and it is held for one hour to obtain modified large particle aluminum nitride powder for standby.

[0080] 0.2 parts of yttrium nitrate, 0.2 parts of lanthanum nitrate, and 0.1 part of calcium nitrate are dissolved in 25 parts of ethanol. 100 parts of aluminum nitride whiskers are added, and it is ultrasonically stirred and heated at 60°C to evaporate the ethanol. In a nitrogen atmosphere, the heating rate is 2.5°C per minute, and it is held for one hour at 130°C, 500°C, 550°C, and 800°C respectively. The maximum calcination temperature is 1000°C and it is held for one hour to obtain modified aluminum nitride whisker powder for standby.

[0081] 90 parts of graded aluminum nitride powder, including 70 wt% of modified aluminum nitride fine powder, 30 wt% of modified large particle aluminum nitride powder, 15 parts of ethanol, 10 parts of n-butanol, 3 parts of castor oil, 1 part of yttrium oxide, 1 part of lanthanum oxide, 0.5 part of calcium carbonate, 1.5 parts of 3 mol% yttrium-stabilized zirconia, and 500 parts of zirconia grinding balls are placed in a ball mill. The ball mill speed is 200 r / min, and it is milled for two hours. 4 parts of dibutyl phthalate are added and milled for two hours. 10 parts of polyvinyl butyral are added, and the polyvinyl butyral needs to be dissolved in 35 parts of ethanol in advance to form a sol. It is milled for two hours. 10 parts of modified aluminum nitride whisker powder are added and milled for 15 minutes. The grinding balls are filtered off, and the tape-casting slurry is vacuum stirred and degassed for one hour.

[0082] The defoamed casting slurry is subjected to casting forming, drying, cutting, and hot pressing and laminating to 0.7 mm.

[0083] The cast green sheets are laminated with a plastic film in between, and after soft sealing, they are subjected to cold isostatic pressing at 200 MPa for five minutes.

[0084] The cast green sheets are sprayed with boron nitride release agent for lamination, a boron nitride ceramic plate is pressed on top, and debinding is carried out in a flowing air atmosphere. The heating rate is 1 °C per minute, and it is held at 200 °C and 350 °C for one hour respectively, and held at 600 °C for two hours, and then cooled with the furnace.

[0085] The cast green sheets are sprayed with boron nitride for lamination, a boron nitride ceramic plate is pressed on top, and sintering is carried out in a nitrogen atmosphere. A segmented heating method is adopted, heating to 850 °C at 5 °C per minute, holding for one hour, heating to 1500 °C at 5 °C per minute, holding for one hour, heating to 1700 °C at 2.5 °C per minute, holding for four hours, cooling to 1200 °C at 5 °C per minute, and cooling to room temperature at 10 °C per minute to complete sintering, and then grinding and polishing to a thickness of 0.4 mm.

[0086] Example 3

[0087] Add 50 100 parts of 0.9 μm aluminum nitride fine powder, 60 parts of absolute ethanol, 1 part of castor oil, and 500 parts of zirconia grinding balls into a ball mill tank, ball mill for four hours, dry and then pass through a 60-mesh sieve to obtain modified aluminum nitride fine powder for standby.

[0088] Add 50 10 μm large particle aluminum nitride powder is calcined in an air atmosphere, the heating rate is 10 °C per minute, the maximum holding temperature is 700 °C, and the holding time is 30 minutes.

[0089] Dissolve 0.2 part of yttrium nitrate, 0.2 part of lanthanum nitrate, and 0.1 part of calcium nitrate in 25 parts of ethanol, add 100 parts of the calcined large particle aluminum nitride powder, stir ultrasonically and heat at 60 °C to evaporate the ethanol. In a nitrogen atmosphere, the heating rate is 2.5 °C per minute, and it is held at 130 °C, 500 °C, 550 °C, and 800 °C for one hour respectively, the maximum calcination temperature is 1000 °C, and it is held for one hour to obtain modified large particle aluminum nitride powder for standby.

[0090] Dissolve 0.2 part of yttrium nitrate, 0.2 part of lanthanum nitrate, and 0.1 part of calcium nitrate in 25 parts of ethanol, add 100 parts of aluminum nitride whiskers, stir ultrasonically and heat at 60 °C to evaporate the ethanol. In a nitrogen atmosphere, the heating rate is 2.5 °C per minute, and it is held at 130 °C, 500 °C, 550 °C, and 800 °C for one hour respectively, the maximum calcination temperature is 1000 °C, and it is held for one hour to obtain modified aluminum nitride whisker powder for standby.

[0091] Put 95 parts of graded aluminum nitride powder, including 60wt% of modified fine aluminum nitride powder and 40wt% of modified large particle aluminum nitride powder, 15 parts of ethanol, 10 parts of n-butanol, 3 parts of castor oil, 1 part of yttrium oxide, 1 part of lanthanum oxide, 0.5 part of calcium carbonate, 0.5 part of 3mol% yttrium-stabilized zirconia, and 500 parts of zirconia grinding balls into a ball mill tank. The ball mill speed is 200r / min, and ball mill for two hours. Then add 4 parts of dibutyl phthalate and ball mill for another two hours. Add 10 parts of polyvinyl butyral. Polyvinyl butyral needs to be dissolved in 35 parts of ethanol in advance to form a sol, then ball mill for two hours. Add 10 parts of modified aluminum nitride whisker powder and ball mill for 15 minutes. Filter out the grinding balls, and vacuum stir and defoam the tape casting slurry for one hour.

[0092] Perform tape casting on the defoamed tape casting slurry, dry it, cut it, and hot press and laminate it to 0.7mm.

[0093] Stack the tape casting green sheets with a plastic film in between, and after soft sealing, perform cold isostatic pressing at 200MPa for five minutes.

[0094] Spray boron nitride release agent on the tape casting green sheets for lamination, press a boron nitride ceramic plate on the top, and perform debinding and degreasing in a flowing air atmosphere. The heating rate is 1℃ / min. Keep it at 200℃ and 350℃ for one hour respectively, keep it at 600℃ for two hours, and then cool it down with the furnace.

[0095] Spray boron nitride on the tape casting green sheets for lamination, press a boron nitride ceramic plate on the top, and perform sintering in a nitrogen atmosphere. Adopt a segmented heating method: heat up to 850℃ at 5℃ / min and keep it for one hour, heat up to 1500℃ at 5℃ / min and keep it for one hour, heat up to 1850℃ at 2.5℃ / min and keep it for four hours, cool down to 1200℃ at 5℃ / min, and then cool down to room temperature at 10℃ / min to complete sintering, and grind and polish it to a thickness of 0.4mm.

[0096] Perform performance tests on the aluminum nitride ceramic substrates prepared in the above three examples, and the results are shown in the following table. The thermal conductivity is tested by the thin film radial method, the flexural strength is tested by the three-point bending method, and the fracture toughness is tested by the single-edge V-notch beam method.

[0097] Thermal conductivity W / m·k Flexural strength MPa <![CDATA[Fracture toughness MPa·m 1 / 2 > Example 1 149 474 9.55 Example 2 158 463 10.32 Example 3 192 430 8.68

Claims

1. A method for preparing a high-strength, high-toughness, and high-thermal-conductivity aluminum nitride ceramic substrate having a synergistic effect, characterized in that The following steps are involved: The parts in the following text all represent the mass parts, D 50 is the volume median diameter of the particle size; S1: Dispersion modification of aluminum nitride fine powder: 100 parts of aluminum nitride fine powder, 0.2-2 parts of dispersion modifier, and 60-70 parts of ethanol solvent are mixed and ball milled for a total of four hours, and then dried and passed through a 60-mesh sieve to obtain modified aluminum nitride fine powder; S2 large-particle aluminum nitride powder surface modification, the large-particle aluminum nitride powder is first calcined at high temperature under air atmosphere conditions, the air atmosphere calcination heating rate is 2.5℃ / min, the maximum insulation temperature range is between 500 and 750℃, and the insulation time is between 20 and 60 minutes; then 0.5 to 3 parts of composite sintering aid nitrate are dissolved in 20 to 35 parts of ethanol, 100 parts of calcined large-particle aluminum nitride powder are added, ultrasonic stirring and heating at 60℃ to volatilize ethanol, heating to 900 to 1000℃ under nitrogen atmosphere at 2.5℃ / min and calcining for one hour, and insulation is set at the decomposition temperature point corresponding to the nitrate to obtain modified aluminum nitride whisker powder for use; S3 aluminum nitride whisker surface modification, dissolving 0.5-3 parts of composite sintering aid nitrate in 20-35 parts of ethanol, adding 100 parts of aluminum nitride whiskers, ultrasonically stirring and heating at 60°C to volatilize the ethanol, heating to 900-1000°C at 2.5°C / min in a nitrogen atmosphere and calcining for one hour, and setting insulation at the corresponding decomposition temperature of the nitrate to obtain modified aluminum nitride whisker powder for use; S4 ball milling mixing, 85-97 parts of graded aluminum nitride powder, 15-25 parts of composite organic solvent, 3-5 parts of dispersant dissolved in advance, 0.5-3 parts of composite sintering aid, 0.5-2 parts of zirconium oxide reaction precursor are ball milled, 3-5 parts of plasticizer are added after ball milling for two hours, 8-12 parts of binder are added after ball milling for two hours, and the binder needs to be dissolved in 21-42 parts of composite organic solvent in advance to form a sol, 3-15 parts of modified aluminum nitride whisker powder are added after ball milling for two hours, and finally ball milling for fifteen minutes, filtering out the grinding balls, and vacuum stirring the casting slurry for degassing for one hour; S5 tape casting, tape casting the degassed tape casting slurry to obtain a tape casting blank of a certain thickness, or continue drying, cutting, hot pressing and laminating to reach a desired thickness; S6 cold isostatic pressing, laminating the cast green sheet with a plastic film, soft-sealing and then cold isostatic pressing; S7 degreasing and debinding, spraying boron nitride release agent on the cast green sheet for lamination, pressing boron nitride ceramic plate on it, and degreasing and debinding in flowing air atmosphere; S8 ceramic sintering, spray boron nitride on the cast green sheet for stacking, press boron nitride ceramic plate on top, and perform segmented sintering in a nitrogen atmosphere. When a non-oxide form is selected in the sintering aid, insulation is set at its corresponding decomposition temperature point.

2. The preparation method according to claim 1, characterized in that The particle size distribution of the aluminum nitride fine powder in step S1 is narrow and 0.5 μm ≤ D 50 ≤5μm; the dispersion modifier is one or more of castor oil, fish oil, polyethylene glycol 2000, oleic acid, paraffin, and titanate coupling agent.

3. The preparation method according to claim 1, characterized in that: The particle size distribution of the large-particle aluminum nitride powder in step S2 is narrow and 5μm≤D 50 ≤100μm; the sintering aid nitrate is selected from two or more of yttrium nitrate, calcium nitrate, lanthanum nitrate, lithium nitrate and magnesium nitrate.

4. The preparation method according to claim 1, characterized in that: In step S3, the length of the aluminum nitride whisker is between 5 and 250 μm, and the aspect ratio is between 10 and 50; the sintering aid nitrate is selected from two or more of yttrium nitrate, calcium nitrate, lanthanum nitrate, lithium nitrate, and magnesium nitrate.

5. The preparation method according to claim 1, characterized in that: In step S4, the modified aluminum nitride fine powder accounts for 10-90wt% of the intermediate aluminum nitride powder, and the modified large-particle aluminum nitride powder accounts for 10-90wt%; the composite organic solvent, ethanol accounts for 40-60 parts, and n-butanol accounts for 40-60 parts; the dispersant is selected from castor oil and fish oil; the composite sintering aid is selected from two or more of yttrium oxide, calcium carbonate, lanthanum oxide, lithium carbonate, and magnesium oxide, and nanopowder is used, D 50 <300nm; the zirconium oxide reaction precursor is selected from one or more of zirconium dioxide, 3mol% yttrium-stabilized zirconium oxide, zirconium carbonate, and zirconium nitrate, and is prepared by a sol-gel method, or directly using nanopowder, D 50 <300nm; dibutyl phthalate is used as plasticizer; polyvinyl butyral is used as binder.

6. The preparation method according to claim 1, characterized in that: In step S5, the casting scraper height is 0.2-2 mm, and the casting speed is 0.5 m / min; in the hot pressing lamination, the heating temperature is 50-150° C., the pressing pressure is 10-30 MPa, and the holding time is 20-40 minutes.

7. The preparation method according to claim 1, characterized in that: In the cold isostatic pressing in step S6, the pressure increase and decrease rates are both 100 MPa / min, and the maximum pressure is maintained at 200 MPa for five minutes.

8. The preparation method according to claim 1, characterized in that: In step S7, the degreasing and debinding heating rate is 1°C / min, the maximum insulation temperature is 600°C, the insulation time is 2 to 5 hours, and the insulation is set at the volatilization temperature point of the selected organic component.

9. The preparation method according to claim 1, characterized in that: In step S8, the sintering holding temperature can be selected from 1650° C. to 1850° C., and the holding time can be selected from 2 to 4 hours.

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