Preparation method and application of aluminum nitride powder

Abstract

The application discloses a preparation method and application of aluminum nitride powder, and the preparation method comprises the following steps: S1: coating organic matter on the surface of aluminum oxide and carbonizing to obtain a carbon-coated precursor; S2: mixing and grinding the carbon-coated precursor with carbon material, and then sintering in a nitrogen atmosphere to obtain a sintered product; and S3: mixing the sintered product with a separation liquid, and separating to obtain the aluminum nitride powder; the separation liquid comprises solvent A and solvent B, the polarity of the solvent A is greater than that of the solvent B, the density of the solvent A is greater than that of the solvent B, and the polarity difference between the solvent A and the solvent B is greater than 5. The preparation method of the application can promote complete nitriding, avoid agglomeration between aluminum nitride particles, and thus prepare the aluminum nitride powder with a higher specific surface area, low oxygen content and low carbon impurity content by closely contacting the organic matter with the aluminum oxide particles and carbonizing, and then grinding and sintering with the carbon material.

Description

Technical Field

[0001] This invention relates to the field of materials, specifically to a method for preparing aluminum nitride powder and its application. Background Technology

[0002] With the continuous development of microelectronics technology, the increased integration of electronic systems has led to higher power density, resulting in increased heat generation during operation. Traditional alumina ceramic substrate materials are no longer sufficient to meet the increasingly demanding heat dissipation requirements of the electronic packaging industry. Aluminum nitride ceramics, with their high thermal conductivity, strong heat dissipation capabilities, and thermal expansion coefficients matching those of Si and GaAs semiconductor devices, along with good insulation and high dielectric properties, have become a replacement material for alumina ceramics. They are widely used in electronics, metallurgy, machinery, military, and many other fields, showing extremely promising prospects.

[0003] With the rapid development of new energy, communication technology and other fields, the heat dissipation requirements of electronic components have further increased, placing higher demands on the thermal conductivity of aluminum nitride ceramics, requiring a thermal conductivity >200W / (m·K). However, aluminum nitride ceramics prepared by existing methods cannot meet this performance requirement. On the one hand, existing preparation processes require complex precursor preparation procedures, resulting in complex processes, high production costs, and difficulty in industrial mass production. On the other hand, the carbothermic reduction method requires the addition of excessive carbon black to ensure complete nitridation. After the powder nitridation, the excess carbon black needs to be removed. The commonly used method for removing carbon black in the industry is to heat to 600-900℃ in an oxygen atmosphere, which leads to oxidation of the powder particle surface, increases the oxygen content, and requires the addition of more flux to migrate oxygen impurities, resulting in a decrease in thermal conductivity. Moreover, existing carbon removal methods convert carbon black into carbon dioxide and emit it, which does not conform to the green, low-carbon and environmentally friendly development concept. Summary of the Invention

[0004] In order to overcome at least one of the technical problems existing in the prior art, one of the objectives of the present invention is to provide a method for preparing aluminum nitride powder.

[0005] The second objective of this invention is to provide a ceramic substrate.

[0006] A third objective of this invention is to provide a method for preparing aluminum nitride powder and / or the application of the aluminum nitride powder prepared by the method in the preparation of electronic packaging ceramic materials.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] The first aspect of this invention provides a method for preparing aluminum nitride powder, comprising the following steps:

[0009] S1: Coating organic matter onto the surface of alumina and carbonizing it to obtain a carbon-coated precursor;

[0010] S2: The carbon-coated precursor is mixed and ground with carbon material, and then sintered in a nitrogen atmosphere to obtain a sintered product;

[0011] S3: The sintering product is mixed with the separation liquid to separate and obtain the aluminum nitride powder;

[0012] The separation liquid includes solvent A and solvent B, wherein the polarity of solvent A is greater than that of solvent B and the density of solvent A is greater than that of solvent B, and the polarity difference between solvent A and solvent B is greater than 5.

[0013] The preparation method of this invention solves the technical problem of reduced specific surface area of ​​aluminum nitride powder caused by the agglomeration and growth of aluminum nitride powder particles during sintering by coating the surface of aluminum oxide with organic matter. In addition, this invention removes carbon materials from aluminum nitride powder by mixing solvents of different polarities and densities. It utilizes the differences in solubility, dispersibility and density between carbon black and aluminum nitride powder to achieve the invention's objective of efficient and rapid separation of carbon black and aluminum nitride powder. Moreover, during the carbon removal process, the aluminum nitride powder is always located in the lower separation liquid, which solves the technical problem of aluminum nitride powder oxidation caused by contact with oxygen or water vapor during the carbon removal process.

[0014] In this invention, the separation liquid can be a partially miscible two-liquid system or a completely immiscible mixed solvent system. After the carbon material undergoes a nitriding reaction (nitrogen atmosphere, sintering at 1500-1700℃), the groups attached to the carbon black are decomposed and volatilized, and the carbon black is in a non-polar state, which results in better dispersibility in solvent B, which has a smaller polarity. If the polarity difference between solvent A and solvent B is too small, the two solvents will have no difference in the dispersibility of carbon black and aluminum nitride powder, which will seriously reduce the separation efficiency of carbon black and aluminum nitride powder, and ultimately make it impossible to achieve complete separation of carbon black and aluminum nitride powder. After high-temperature treatment during nitriding, the polar groups in carbon black decompose and volatilize, making it easier to disperse in non-polar solvents. Utilizing the difference in carbon black's dispersibility in different solvents, incompatible low-polarity solvents can be used to extract carbon black from poorly dispersible high-polarity solvents. Simultaneously, carbon black and aluminum nitride powder have density differences and inconsistent sedimentation rates. Using an incompatible solvent system can increase the sedimentation distance, better separating aluminum nitride powder and carbon black. Therefore, two or more liquids with immiscible temperature ranges between 0-80℃ can be used, preferably partially miscible or completely immiscible solvent systems at room temperature. The mixed solvents should have a density difference greater than 0.01 g / cm³. 3 By using high-speed stirring or ultrasound, the contact and attraction between carbon black and aluminum nitride powder are disrupted, thus efficiently separating carbon black and aluminum nitride powder.

[0015] Preferably, the separation step in step S3 is as follows: removing the upper mixture and then removing solvent A from the lower mixture to obtain the aluminum nitride powder. In this invention, the sintered product and the separation liquid will separate into layers. The upper mixture consists of solvent B and carbon black impurities, while the lower mixture consists of solvent A and aluminum nitride powder. In the separation step, removing the upper mixture and then removing solvent A from the lower mixture yields the aluminum nitride powder. The carbon removal step is simple and easy to operate, and the carbon removal effect is good, resulting in a carbon content of ≤500ppm in the obtained aluminum nitride powder.

[0016] Preferably, the specific surface area of ​​the aluminum nitride powder is ≥2.9 m². 2 / g; More preferably, the specific surface area of ​​the aluminum nitride powder is 2.9m². 2 / g~3.92m 2 / g.

[0017] Preferably, the carbon content of the aluminum nitride powder is ≤500ppm; more preferably, the carbon content of the aluminum nitride powder is ≤300ppm; even more preferably, the carbon content of the aluminum nitride powder is 252-289ppm.

[0018] Preferably, the oxygen content of the aluminum nitride powder is ≤0.4%; more preferably, the oxygen content of the aluminum nitride powder is 0.21-0.39%.

[0019] Preferably, the particle size D of the aluminum nitride powder is... 50 It ranges from 1 to 2.5 μm.

[0020] Preferably, the mass ratio of the organic matter to alumina is (0.2-15):100. In this invention, the organic matter is uniformly dispersed and comes into contact with alumina powder particles. During spray granulation, the organic matter coats the surface of the alumina particles and adheres to the surface for carbonization, forming tight carbon-alumina binding sites. During nitriding, these sites preferentially form active centers, and subsequently, aluminum nitride particles grow based on these active centers. If the amount of organic matter added is less than 0.2 wt% (based on the total mass percentage of alumina as 100%), the pre-coating effect on alumina powder is not obvious, the number of active centers is insufficient, resulting in a smaller specific surface area of ​​aluminum nitride powder and reduced sintering activity. The aluminum nitride ceramic substrate prepared from this aluminum nitride powder requires a higher sintering temperature to achieve densification. If the amount of organic matter added is greater than 15 wt% (based on the total mass percentage of alumina as 100%), the surface of some alumina powder particles is completely coated with organic matter, and N2 cannot contact alumina. In the early stage of nitriding, effective active sites cannot be formed, which hinders the nitriding process. This results in a high oxygen content in the aluminum nitride powder and a low thermal conductivity of the ceramic substrate prepared from this aluminum nitride powder.

[0021] Preferably, the volume ratio of solvent A to solvent B is 1:(2-5); the ratio of solvent A to solvent B can be adjusted in any proportion as needed. When the volume ratio of solvent A to solvent B is 1:(2-5), the separation effect is better, the amount of solvent used is less, the separation efficiency is higher, and the economy is better.

[0022] Preferably, solvent A is selected from acetonitrile, dimethylformamide, or a combination thereof.

[0023] Preferably, solvent B is selected from n-hexane, cyclohexane, or a combination thereof.

[0024] Preferably, the ratio of the mass of the carbon material to the mass of the carbon-coated precursor is greater than 0.3.

[0025] Preferably, the purity of the alumina is greater than 99%; more preferably, the purity of the alumina powder is greater than 99.95%.

[0026] Preferably, the purity of the carbon material is greater than 99.9%.

[0027] Preferably, the carbon material is selected from at least one of conductive carbon black, pigment carbon black, and rubber-filled carbon black.

[0028] Preferably, the organic compound is selected from at least one of carboxylic acids, carboxylates, polyvinyl alcohol, aldehydes, and esters.

[0029] Preferably, the carboxylic acid is selected from polyacrylic acid, oxalic acid, or a combination thereof.

[0030] Preferably, the carboxylate is selected from at least one of polyacrylate, oxalate, and stearate.

[0031] Preferably, the polyacrylate is selected from at least one of ammonium polyacrylate, sodium polyacrylate, and potassium polyacrylate.

[0032] Preferably, the aldehyde is selected from at least one of polyvinyl butyral, polyvinyl formaldehyde, polyvinyl alcohol formaldehyde, and polyvinyl alcohol butyral.

[0033] Preferably, the ester is selected from at least one of polymethyl methacrylate, polyalkylene carbonate, and ethyl methacrylate. Preferably, the organic compound is a water-soluble organic compound or an organic compound soluble in an organic solvent; more preferably, the organic compound is a water-soluble organic compound.

[0034] Preferably, the mass ratio of the carbon material to the carbon-coated precursor is (0.3-0.6):1. In this invention, if the amount of carbon material is lower than the above range, the amount of carbon material is insufficient to fully convert the alumina powder into aluminum nitride powder; if the amount of carbon material is higher than the above range, the increased carbon material has no effect on the properties of the obtained aluminum nitride powder, but the amount of residual carbon black in the aluminum nitride powder after sintering increases, the carbon removal cost is high, the economic efficiency is poor, and the carbon removal efficiency is low.

[0035] Preferably, the mass ratio of the organic matter to alumina is (0.5-5):100.

[0036] Preferably, the sintering temperature is 1500-1700℃.

[0037] Preferably, the sintering time is 0.5-5 hours.

[0038] Preferably, step S1 involves mixing alumina, organic matter, and solvent C, and then spray-drying the mixture at a temperature not lower than 260°C to obtain a carbon-coated precursor. After the organic matter is coated onto the surface of the alumina, it is spray-dried at a temperature not lower than 260°C. During the spray-drying process, the organic matter carbonizes and coats the surface of the alumina, thus obtaining the carbon-coated precursor.

[0039] Preferably, solvent C is water. When solvent C is water, the organic matter is a water-soluble organic matter, and water is mainly used as a dispersion and mixing medium for water-soluble organic matter. In this invention, solvent C can also be an organic solvent, in which case the organic matter is an organic matter that can be dissolved in the organic solvent.

[0040] Preferably, the mass ratio of alumina to solvent C is 1:(0.6-4); more preferably, the mass ratio of alumina to solvent C is 1:(0.6-2).

[0041] Preferably, the grinding step in step S2 is grinding using grinding balls.

[0042] Preferably, the grinding step in step S2 is dry grinding or wet grinding.

[0043] Preferably, the grinding time in step S2 is 0.2-2 hours.

[0044] Preferably, the mixing step in step S3 is stirring or ultrasonic mixing.

[0045] Preferably, step S3 involves: pouring the sintered product into a separation liquid and stirring or ultrasonically mixing to separate the carbon powder and aluminum nitride powder particles; after standing, separating the upper carbon powder mixture solution and the lower aluminum nitride powder mixture solution; and drying the lower aluminum nitride powder mixture solution to obtain the aluminum nitride powder. More preferably, step S3 involves: pouring the sintered product into a separation liquid and stirring or ultrasonically mixing to separate the carbon powder and aluminum nitride powder particles; after standing, separating the upper carbon powder mixture solution... The upper carbon powder mixture and the lower aluminum nitride powder mixture are dried at a temperature below 200°C to obtain the aluminum nitride powder. More preferably, step S3 is as follows: the sintered product is poured into a separation liquid and stirred or ultrasonically mixed to separate the carbon powder and aluminum nitride powder particles. After standing, the upper carbon powder mixture and the lower aluminum nitride powder mixture are separated. The lower aluminum nitride powder mixture is dried under negative pressure at 50-100°C to obtain the aluminum nitride powder. The carbon black powder and solvent system after nitriding are mixed by stirring or ultrasound. The upper solution (i.e., solvent B) has low polarity, resulting in better dispersion of carbon black in the upper solution. Moreover, the density of carbon black is much lower than that of aluminum nitride powder, making it easier for carbon black to remain in the upper layer during the initial settling process. The upper carbon black solvent and the lower aluminum nitride powder solvent can be separated at an appropriate time point. After drying in an oxygen-free atmosphere, high-purity aluminum nitride powder is obtained. The drying temperature is <200℃, preferably 50-100℃. Solvent removal is carried out under negative pressure adsorption conditions. Using a mixed solvent system to remove carbon black from the nitrided powder has the advantages of energy saving and emission reduction, and it can also recover carbon black while preventing the aluminum nitride powder from oxidizing under high temperature conditions.

[0046] The preparation method of this invention brings water-soluble organic matter into close contact with alumina particles. During spray drying, the water-soluble organic matter is carbonized, achieving uniform carbon coating. Compared with commonly used carbon coating processes, current methods such as CVD and pyrolysis have the following problems: for example, alumina powder particles agglomerate during the coating process, causing multiple alumina particles to be encapsulated together by carbon (abnormal growth of multiple alumina particles during sintering leads to the growth of aluminum nitride particles); uneven coating in the microscopic layer; and other carbon coating methods are complex and inefficient. This invention provides a simple and efficient carbon coating pretreatment method. This method effectively avoids the agglomeration of alumina particles during the carbon coating process, which leads to abnormal growth of the prepared aluminum nitride powder particles. On the other hand, commonly used carbon coating methods cannot effectively and uniformly coat the alumina particles, resulting in some alumina particles being completely encapsulated by carbon, hindering the entry of nitrogen gas, and preventing the nitriding reaction from proceeding. This results in incomplete nitriding of the produced aluminum nitride powder, high oxygen content, and low thermal conductivity of the produced substrate. This invention, by controlling the addition ratio of organic matter, can effectively prevent alumina particles from being completely encapsulated by carbon. At the same time, through process control, the produced aluminum nitride has a high specific surface area and good carbon content uniformity, effectively preventing the situation where carbon completely encapsulates alumina particles.

[0047] A second aspect of the present invention provides a ceramic substrate, wherein the raw materials for preparing the ceramic substrate include aluminum nitride powder obtained by the preparation method provided in the first aspect of the present invention.

[0048] Preferably, the thermal conductivity of the ceramic substrate is ≥200 W / (m·K); more preferably, the thermal conductivity of the ceramic substrate is 201~234 W / (m·K).

[0049] Preferably, the strength of the ceramic substrate is ≥400MPa; more preferably, the strength of the ceramic substrate is 400-507MPa.

[0050] The third aspect of the present invention provides a method for preparing aluminum nitride powder provided in the first aspect of the present invention and / or the application of aluminum nitride powder prepared by the method described in the first aspect of the present invention in the preparation of electronic packaging ceramic materials.

[0051] The beneficial effects of this invention are as follows: The preparation method of this invention involves bringing organic matter into close contact with alumina particles and carbonizing the surface of the alumina particles. Then, the mixture is ground and sintered with carbon materials. This reduces the amount of carbon materials used and promotes complete nitriding, lowering the oxygen content in the aluminum nitride powder and preventing agglomeration between aluminum nitride particles. This results in aluminum nitride powder with a high specific surface area, low oxygen content, and low carbon impurity content. Furthermore, this invention achieves efficient and rapid separation of carbon black powder and aluminum nitride powder using a separation liquid. During the separation process, aluminum nitride does not come into contact with oxygen or water vapor, thus avoiding the problems of increased oxygen content in the aluminum nitride powder and incomplete separation during the separation process.

[0052] The ceramic substrate prepared using aluminum nitride powder obtained by the preparation method of this invention as raw material has high strength and high thermal conductivity, which can meet the requirements of electronic packaging ceramic materials. Detailed Implementation

[0053] The following examples provide a more detailed description of the specific implementation of the present invention, but the implementation and protection of the present invention are not limited thereto. It should be noted that any processes not specifically described below are methods that can be implemented or understood by those skilled in the art by referring to existing technology. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0054] Example 1

[0055] This example provides a method for preparing aluminum nitride powder, the specific steps of which are as follows:

[0056] S1: Weigh 3wt% of ammonium polyacrylate (i.e., water-soluble organic matter) and 2 times the weight of alumina powder, based on the mass percentage of alumina powder being 100wt% of alumina powder. Then mix them evenly and spray dry them to carbonize the organic matter. The spray drying temperature is 300℃ to prepare a carbon-coated precursor.

[0057] S2: Mix the carbon-coated precursor obtained in S1 and conductive carbon black (i.e. carbon powder) at a ratio of 1:0.4, and then dry ball mill the mixture for 2 hours.

[0058] S3: The material obtained in S2 is placed in a high-purity graphite sagger and sintered in a nitrogen atmosphere at a temperature of 1650℃ for 2.5 hours.

[0059] S4: Pour the sintered powder obtained in S3 into a mixed solvent of acetonitrile (i.e., solvent A) and n-hexane (i.e., solvent B) with a volume ratio of 2:7. Stir at a high speed of 7500 rpm for 30 minutes. After standing for 2-5 minutes, pour out the upper layer of mixed solution of n-hexane and carbon black to obtain the lower layer of clear mixed solution of acetonitrile and aluminum nitride powder.

[0060] The polarity difference between acetonitrile and n-hexane is 6.4, and they are immiscible. The density of acetonitrile is 0.786 g / mL, and the density of n-hexane is 0.659 g / mL, with a density difference of 0.127 g / mL.

[0061] S5: The mixed solution of acetonitrile and aluminum nitride powder obtained in S4 is dried at 60°C and under a vacuum of -8KPa for 20 minutes to obtain the high-purity aluminum nitride powder in this example.

[0062] Examples 2-6

[0063] The only difference between the preparation methods of aluminum nitride powder in Examples 2-6 and Example 1 is the addition ratio of water-soluble organic matter, as shown in Table 1.

[0064] Examples 7-9

[0065] The only difference between the preparation methods of aluminum nitride powder in Examples 7-9 and Example 1 is that the ratio of carbon-coated precursor to carbon powder is different, as shown in Table 1.

[0066] Examples 10-11

[0067] The only difference between the preparation methods of aluminum nitride powder in Examples 10 and 11 and those in Example 1 is that the types of water-soluble organic compounds are different, as shown in Table 1.

[0068] Examples 12-13

[0069] The preparation methods of aluminum nitride powder in Examples 12 and 13 differ from those in Example 1 only in the types of solvent A and solvent B, the difference in solvent polarity, and the difference in solvent density, as shown in Table 1.

[0070] Comparative Examples 1-2

[0071] The only difference between the preparation methods of aluminum nitride powder in Comparative Examples 1 and 2 and those in Example 1 is the addition ratio of water-soluble organic matter, as shown in Table 1.

[0072] Comparative Example 3

[0073] The only difference between the preparation method of aluminum nitride powder in Comparative Example 3 and Example 1 is that the ratio of carbon-coated precursor to carbon powder is different, as shown in Table 1.

[0074] Comparative Example 4

[0075] The only difference between the preparation method of aluminum nitride powder in Comparative Example 4 and Example 1 is that the types of solvent A and solvent B, the difference in solvent polarity, and the difference in solvent density are different, as shown in Table 1.

[0076] Comparative Example 5

[0077] This example provides a method for preparing aluminum nitride powder, the specific steps of which are as follows:

[0078] S1: Mix 99.99% high-purity alumina powder and conductive carbon black (i.e., carbon powder) in a ratio of 1:0.4, and then dry ball mill the mixture for 2 hours;

[0079] S2: The material obtained in S1 is placed in a high-purity graphite sagger and sintered in a nitrogen atmosphere at a temperature of 1650℃ for 2.5 hours.

[0080] S3: Pour the sintered powder obtained in S2 into a mixed solvent of acetonitrile (i.e., solvent A) and n-hexane (i.e., solvent B) with a volume ratio of 2:7. Stir at a high speed of 7500 rpm for 30 minutes. After standing for 2-5 minutes, pour out the upper layer of mixed solution of n-hexane and carbon black to obtain the lower layer of clear mixed solution of acetonitrile and aluminum nitride powder.

[0081] The polarity difference between acetonitrile and n-hexane is 6.4, and they are immiscible. The density of acetonitrile is 0.786 g / mL, and the density of n-hexane is 0.659 g / mL, with a density difference of 0.127 g / mL.

[0082] S4: The mixed solution of acetonitrile and aluminum nitride powder obtained in S3 is dried at 60°C and under a vacuum of -8KPa for 20 minutes to obtain the high-purity aluminum nitride powder in this example.

[0083] Comparative Example 6

[0084] The only difference between the preparation method of aluminum nitride powder in Comparative Example 6 and Example 1 is that step S4 in this example is to remove carbon from the sintered powder obtained in S3 by holding it at 650°C for 4 hours to obtain aluminum nitride powder. Step S5 is not included in this example. The details are shown in Table 1.

[0085] Comparative Example 7

[0086] The only difference between the preparation method of aluminum nitride powder in Comparative Example 7 and Comparative Example 5 is that step S3 in this example is to remove carbon from the sintered powder obtained in S2 by holding it at 650°C for 4 hours to obtain aluminum nitride powder. Step S4 is not included in this example. The details are shown in Table 1.

[0087] Table 1. Data on the amount of raw materials used in Examples 1-13 and Comparative Examples 1-7.

[0088]

[0089] Performance testing

[0090] The aluminum nitride powder, sintering aid Y2O3, and PVB resin from Examples 1-13 and Comparative Examples 1-7 were mixed at a weight ratio of 90%, 1.8%, and 8.2%, respectively. The mixture was then placed in a ball mill jar with anhydrous ethanol and ball milled for 960 min. The mixture was then cast into a green blank with a width of 160 mm and a thickness of 0.6-0.7 mm using a casting machine. The green blank was cut into 155*155 mm blanks and held at 580°C for 360 min in a debinding furnace to remove the binder. The blanks were then placed in a graphite atmosphere furnace and sintered in a N2 protective atmosphere. The specific sintering process was as follows: sintering temperature of 1800°C, holding temperature for 4 h, and heating and cooling rate of 4°C / min. The sintered aluminum nitride substrate was ground into ceramic wafers with a thickness of 0.38 mm using a grinding machine. Test samples with dimensions of 114 mm * 114 mm * 0.38 mm and 40 mm * 24 mm * 0.38 mm were prepared using a laser scribing machine. Then, the various properties of the alumina powder and the test samples were tested according to the following test methods:

[0091] A. Carbon coating uniformity test: Use a carbon-sulfur meter to test the difference in carbon content of aluminum nitride powder at different locations. Use 5-10 pretreated alumina powders from different locations randomly selected, test the carbon content with a carbon-sulfur meter and calculate the standard deviation of carbon content. The standard is: standard deviation of carbon content ≤ 0.1.

[0092] B. Oxygen content test: Using an oxygen-nitrogen analyzer, weigh 0.02-0.03g of the powder to be tested, put the aluminum nitride powder in a high-purity tin bag and nickel basket, place it in a high-purity graphite crucible (dried at 120℃ before use), and heat it at high frequency (6400W) under helium protection. The O in the aluminum nitride powder combines with the carbon in the graphite crucible to form CO2, which is then introduced into the detection cell. The standard is that the oxygen content of the aluminum nitride powder is ≤0.4%.

[0093] C. Specific Surface Area: BET method, using standard carbon black samples as the standard, test quantity 0.8-1.2g, the standard for compliance is: aluminum nitride powder specific surface area ≥ 2.9m². 2 / g;

[0094] D. Carbon content test: A carbon-sulfur analyzer is used. Weigh 0.2-0.3g of the powder to be tested, use iron powder and nickel powder as binary flux, and use an alumina ceramic crucible (calcined at 750℃ before use). Heat at high frequency (800W) under pure oxygen (5N purity oxygen) conditions to oxidize the C in the ceramic powder into CO2 and pass it into the detection cell. The standard is: carbon content ≤500ppm.

[0095] E. Substrate thermal conductivity: Transient planar heat source method test, sample size 114*114*0.38mm, test equipment: Hotdisk TPS2500S, the standard is: thermal conductivity of substrate ≥200W / (m·K);

[0096] F. Strength: Three-point bending test, span 30mm, loading rate 0.05mm / min, sample size: 40mm*24mm*0.38mm; testing instrument: universal testing machine, the standard for compliance is: substrate strength ≥400MPa;

[0097] G. Particle size test: A laser particle size analyzer is used to test the particle size of aluminum nitride powder. 0.5-1g samples are randomly selected from 3 locations. Alcohol is used as the solvent to test the median diameter D50. The standard is that the particle size D50 of aluminum nitride powder is 1.0-2.5μm.

[0098] The various properties of aluminum nitride powder in Examples 1-13 and Comparative Examples 1-7 were tested according to the above test methods, and the specific test results are shown in Table 2.

[0099] Table 2. Performance test results of aluminum nitride powder in Examples 1-13 and Comparative Examples 1-7

[0100]

[0101]

[0102] As shown in Table 2, compared with Comparative Example 1, the addition of water-soluble organic matter in Examples 1-6 gradually increased the effective carbon coating sites of aluminum nitride powder, reaching a peak and then gradually decreasing. Oxygen content was improved to varying degrees, and the thermal conductivity and strength of the substrate were also improved. Comparative Example 2 used more than 15% water-soluble organic matter, resulting in some alumina powder particles being completely coated, leading to incomplete nitriding during the nitriding process and a significant decrease in thermal conductivity. Comparison of Examples 7-9 shows that once the proportion of carbon black increases to a certain level, further increases in carbon black do not significantly improve the performance of the powder and substrate, and may even affect the carbon content after decarbonization, leading to a decrease in substrate performance. Comparative Example 3 used less than 0.3 times the amount of carbon black, which was insufficient to fully convert the alumina powder into aluminum nitride powder, resulting in a high oxygen content in the aluminum nitride powder and low thermal conductivity of the prepared aluminum nitride substrate. In Comparative Example 4, the solvent system was replaced with a solvent with a higher polarity, whose density was lower than that of a solvent with lower polarity (i.e., the upper layer solvent was more polar than the lower layer solvent). This resulted in ineffective extraction and separation of carbon black, rendering it unusable for substrate production. Comparative Example 5 did not use water-soluble organic coating, leaving the alumina surface uncoated with carbon. While the organic solvent system effectively reduced oxygen content, the specific surface area was relatively small. Although thermal conductivity was improved to some extent, the strength was relatively low. Comparative Example 6 used a traditional decarbonization method. Carbon coating increased the specific surface area of ​​the aluminum nitride powder and simultaneously improved the strength of the aluminum nitride substrate. However, with existing decarbonization methods, a high specific surface area meant high oxygen content, leading to decreased substrate thermal conductivity. Comparative Example 7 did not use either water-soluble organic coating or the decarbonization method described in this invention, resulting in the same adverse effects as Comparative Examples 6 and 7.

[0103] In summary, the aluminum nitride powder preparation method of this invention can rapidly and efficiently prepare carbon-coated precursors. Simultaneously, a mixed solvent system is used to separate carbon black and aluminum nitride powder, resulting in aluminum nitride powder with high specific surface area and low impurity content, thereby obtaining a high thermal conductivity aluminum nitride substrate. Water-soluble organic matter is used to uniformly pre-coat alumina powder, and partial carbonization is achieved through a spray tower, forming more carbon sites in close contact with alumina particles. During the nitriding reaction, a large number of nitriding reaction sites are formed and nitriding growth occurs simultaneously, achieving the effect of pyrolyzing alumina particles and reducing dependence on alumina powder raw materials. Furthermore, by controlling the ratio of alumina to water-soluble organic matter, the phenomenon of excessive carbon sites coating the surface of alumina particles, thus preventing nitrogen from effectively entering and hindering the carbothermic reduction reaction, can be prevented. Furthermore, this invention uses a two-liquid system combined with sedimentation to separate carbon black and aluminum nitride powder particles. Conventional sedimentation methods for separating carbon black are inefficient and suffer from incomplete separation. This invention uses an immiscible solution system to achieve rapid and efficient separation of aluminum nitride powder and carbon black. This method avoids contact between aluminum nitride powder and an oxygen atmosphere, and the subsequent processing temperature is low, which can effectively prevent the oxidation of aluminum nitride powder and is beneficial for preparing aluminum nitride powder with low oxygen content.

[0104] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for preparing aluminum nitride powder, characterized in that: Includes the following steps: S1: Coating organic matter onto the surface of alumina and carbonizing it to obtain a carbon-coated precursor; S2: The carbon-coated precursor is mixed and ground with carbon material, and then sintered in a nitrogen atmosphere to obtain a sintered product; S3: The sintering product is mixed with the separation liquid to separate and obtain the aluminum nitride powder; The separation liquid includes solvent A and solvent B, wherein the polarity of solvent A is greater than that of solvent B and the density of solvent A is greater than that of solvent B, and the polarity difference between solvent A and solvent B is greater than 5. The mass ratio of the organic matter to alumina is (0.2-15):100; Solvent A is selected from acetonitrile, dimethylformamide, or a combination thereof; Solvent B is selected from n-hexane, cyclohexane, or a combination thereof; The sintering temperature is 1500-1700℃; The carbon material is selected from at least one of conductive carbon black, pigment carbon black, and rubber filler carbon black; The organic compound is selected from at least one of carboxylic acids, carboxylates, polyvinyl alcohol, esters, and aldehydes; The mass ratio of the carbon material to the carbon-coated precursor is (0.3-0.6):

1.

2. The method for preparing aluminum nitride powder according to claim 1, characterized in that: The volume ratio of solvent A to solvent B is 1:(2-5).

3. The method for preparing aluminum nitride powder according to claim 1, characterized in that: The alumina has a purity greater than 99%; and / or, the carbon material has a purity greater than 99.9%.

4. The method for preparing aluminum nitride powder according to claim 1, characterized in that: The mass ratio of the organic matter to alumina is (0.5-5):

100.

5. The method for preparing aluminum nitride powder according to claim 1, characterized in that: The sintering time is 0.5-5 hours.

6. The method for preparing aluminum nitride powder according to claim 1, characterized in that: Step S1 is as follows: after mixing alumina, organic matter and solvent C, spray drying is carried out at a temperature of not less than 260°C to obtain carbon-coated precursor.

7. The method for preparing aluminum nitride powder according to claim 6, characterized in that: The mass ratio of alumina to solvent C is 1:(0.6~4).

8. A ceramic substrate, characterized in that: The raw materials for preparing the ceramic substrate include aluminum nitride powder prepared by the preparation method according to any one of claims 1 to 7.

9. The method for preparing aluminum nitride powder according to any one of claims 1 to 7, or the application of aluminum nitride powder prepared by the method according to any one of claims 1 to 7 in the preparation of electronic packaging ceramic materials.

Images