A method for preparing aluminum nitride thermally conductive filler with high sphericity

Abstract

This invention relates to the field of thermally conductive filler preparation technology, and provides a method for preparing high-sphericity aluminum nitride thermally conductive filler, solving the problems of easy agglomeration between existing aluminum nitride thermally conductive fillers, relatively poor thermal conductivity, and relatively poor preparation efficiency and quality; the method includes the following steps: 1) mixing aluminum nitride powder, PVB and anhydrous ethanol and then wet ball milling, followed by spray granulation to obtain spherical aluminum nitride granulated powder; 2) degreasing treatment; 3) dry mixing to obtain precursor mixed powder; 4) high-temperature sintering; 5) preparation of thermally conductive modifier, and after modification reaction, obtaining the high-sphericity aluminum nitride thermally conductive filler.

Description

Technical Field

[0001] This invention relates to the field of thermally conductive filler preparation technology, and in particular to a method for preparing a high sphericity aluminum nitride thermally conductive filler. Background Technology

[0002] Aluminum nitride ceramics possess high thermal conductivity, high electrical insulation, high temperature resistance, and an expansion coefficient matching that of silicon, making them an ideal electronic packaging material. With the increasing density of electronic components and the widespread application of high-power integrated circuits, higher demands are placed on the temperature rise and heat dissipation performance of electronic products. Among these, spherical aluminum nitride ceramics, with their combined properties of high thermal conductivity, high dielectric properties, high filler content, and environmental friendliness, are widely used as thermally conductive fillers in thermal interface materials.

[0003] Currently, the main conventional method for preparing aluminum nitride thermally conductive fillers is to first granulate aluminum nitride powder to obtain spherical granulated powder, and then sinter the degreased granulated powder at high temperature to prepare aluminum nitride ceramic spheres. However, since the high-temperature sintering process of granulated powder is a physicochemical reaction process of densification and ceramic formation, a large number of atomic diffusion rearrangements occur in the direct contact parts between granulated powders, resulting in the sintered powder being an interconnected blocky sintered body. Subsequent processing is required through mechanical crushing and dispersion, which will cause a certain degree of damage to the ceramic body, reducing the sphericity, filling rate, and thermal conductivity of the thermally conductive filler. Moreover, the equipment and processes required for crushing and dispersion are relatively cumbersome, increasing the production cost of the thermally conductive filler.

[0004] Chinese Patent Application No. 202311836763.5 discloses a method for preparing densified spherical aluminum nitride, which uses the addition of materials such as graphite and carbon black as separators. Although this method can prevent the bonding phenomenon during the sintering process of aluminum nitride, it requires a decarburization step in the range of 500-800°C, which increases the energy consumption and process cost of preparation. Moreover, the decarburization process is carried out in an air or oxygen atmosphere, which poses a risk of oxidation on the surface of aluminum nitride particles, potentially leading to a decrease in the thermal conductivity of aluminum nitride.

[0005] In view of the above problems, the present invention provides a method for preparing spherical aluminum nitride thermally conductive fillers from the perspective of improving the sphericity of aluminum nitride thermally conductive fillers and reducing the cost of preparation process. This method can effectively simplify the preparation process of spherical aluminum nitride fillers and significantly improve the preparation efficiency and quality of spherical aluminum nitride fillers. Summary of the Invention

[0006] Therefore, in view of the above problems, the present invention provides a method for preparing aluminum nitride thermally conductive filler with high sphericity, which solves the problems that existing aluminum nitride thermally conductive fillers are prone to agglomeration, have relatively poor thermal conductivity, and have relatively poor preparation efficiency and quality.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for preparing a high-sphericity aluminum nitride thermally conductive filler includes the following steps:

[0009] S1. Mix 100-120 parts by weight of aluminum nitride powder, 5-10 parts by weight of PVB and 100-200 parts by weight of anhydrous ethanol, then perform wet ball milling, and then perform spray granulation to obtain spherical aluminum nitride granulated powder.

[0010] S2. The spherical aluminum nitride granulated powder obtained in step S1 is degreased to obtain degreased aluminum nitride granulated powder.

[0011] S3. Dry mix the defatted aluminum nitride granulated powder obtained in step S2 with the nitride isolation powder to obtain the precursor mixed powder.

[0012] S4. The precursor mixed powder obtained in step S3 is sintered at high temperature to obtain crude aluminum nitride thermally conductive filler with high sphericity.

[0013] S5. Mix anhydrous ethanol and thermally conductive modifier evenly and stir for 30-60 minutes. Then add the crude high sphericity aluminum nitride thermally conductive filler obtained in step S4 and continue stirring for 3-4 hours to carry out the modification reaction. After the reaction is completed, the first mixture is obtained. The first mixture is washed with anhydrous ethanol 3-5 times, filtered and dried for 16-24 hours to obtain the high sphericity aluminum nitride thermally conductive filler.

[0014] The nitride isolation powder is one or a mixture of two of the following in any proportion: boron nitride powder and high-temperature calcined aluminum nitride powder;

[0015] The preparation process of the thermal conductivity modifier is as follows:

[0016] Under N2 protection, sodium hydride and tetrahydrofuran were mixed in a mass ratio of 1:3-5, stirred until homogeneous, and the temperature was raised to 180-200℃. A mixed solution of castor oil and tetrahydrofuran was added dropwise, and the reaction was allowed to proceed for 2-4 hours. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, and the supernatant was collected. The supernatant was then distilled to remove excess tetrahydrofuran, thus obtaining the thermally conductive modifier.

[0017] Furthermore, in the mixed solution of castor oil and tetrahydrofuran, the mass ratio of castor oil to tetrahydrofuran is 1:1-3.

[0018] Furthermore, the wet ball milling time is 4-8 hours.

[0019] Furthermore, the spray granulation is carried out in a spray dryer with a feed rate of 2000-2500 mL / h, a spray pressure of 0.5-1 MPa, a hot air inlet temperature of 140-200℃, and an air outlet temperature of 80-100℃.

[0020] Furthermore, the particle size of the spherical aluminum nitride granulated powder in step S1 is 10-200 micrometers.

[0021] Furthermore, the degreasing process is carried out in air at a temperature of 450–600°C for 12–16 hours, and the carbon content of the degreased aluminum nitride granulated powder is <500 ppm.

[0022] Furthermore, the particle size of the nitride isolation powder is 0.5 to 10 micrometers, and the amount added is 1 to 10 wt% of the weight of the degreased aluminum nitride granulated powder.

[0023] Furthermore, the high-temperature sintering described in step S4 is carried out under a nitrogen atmosphere, with a heating rate of 5°C / min, a sintering temperature of 1700–1900°C, and a holding time of 5–6 h.

[0024] Furthermore, the calcination temperature of the high-temperature calcined aluminum nitride powder is higher than the high-temperature sintering temperature.

[0025] By adopting the aforementioned technical solution, the beneficial effects of the present invention are as follows:

[0026] 1. The thermally conductive modifier prepared using sodium hydride and castor oil as raw materials has a long-chain fatty acid ester structure, which helps the thermally conductive modifier to be adsorbed on the surface of aluminum nitride, thereby achieving effective modification of crude high sphericity aluminum nitride thermally conductive filler. It can reduce the surface energy of aluminum nitride filler and avoid agglomeration between fillers; at the same time, it can improve the dispersibility of filler and is more conducive to the formation of thermally conductive network, thereby improving thermal conductivity.

[0027] 2. By adding nitride isolating powder to the degreased aluminum nitride granulated powder, direct contact between granulated powders can be effectively avoided, preventing the sintered powder from forming a blocky sintered body. This eliminates the need for subsequent mechanical crushing and dispersion processes, and high sphericity aluminum nitride thermally conductive filler can be directly prepared after sintering.

[0028] 3. Boron nitride is used as a separating powder and mixed with aluminum nitride granulation powder. The melting point of boron nitride is 2700℃, which is much higher than the sintering temperature of aluminum nitride thermal conductive filler. This can prevent the melting reaction between boron nitride and aluminum nitride powder at the sintering temperature, thus effectively isolating the aluminum nitride granulation powder. After sintering, the aluminum nitride thermal conductive filler with added boron nitride separating powder is in a loose state and does not require crushing and dispersion treatment.

[0029] 4. High-temperature calcined aluminum nitride powder is used as a separating powder and mixed with aluminum nitride granulation powder. After high-temperature calcination, the activity of aluminum nitride powder is greatly reduced, and its calcination temperature is higher than the sintering temperature of aluminum nitride thermal conductive filler. This can avoid melting reaction with aluminum nitride powder at the sintering temperature, and effectively isolate the aluminum nitride granulation powder. After sintering, the aluminum nitride thermal conductive filler with added calcined aluminum nitride micron powder as a separating powder is in a loose state and does not require crushing and dispersion treatment. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the synthesis reaction of the thermally conductive modifier in Examples 1 to 3 of the present invention;

[0031] Figure 2 This is a test image of the high sphericity aluminum nitride thermally conductive filler in Embodiment 1 of the present invention;

[0032] Figure 3 This is a test image of the high sphericity aluminum nitride thermally conductive filler in Example 2 of the present invention. Detailed Implementation

[0033] Example 1

[0034] A method for preparing a high-sphericity aluminum nitride thermally conductive filler includes the following steps:

[0035] S1. Mix 100 parts by weight of aluminum nitride powder, 5 parts by weight of PVB and 100 parts by weight of anhydrous ethanol and then perform wet ball milling for 4 hours. Then perform spray granulation in a spray dryer with a feed rate of 2000 mL / h, a spray pressure of 0.5 MPa, a hot air inlet temperature of 200°C and an outlet temperature of 80°C to obtain spherical aluminum nitride granulated powder with a particle size of 10 micrometers.

[0036] S2. The spherical aluminum nitride granulated powder obtained in step S1 is subjected to degreasing treatment. The degreasing treatment is carried out in air at a temperature of 580°C for 16 hours. The carbon content of the degreased aluminum nitride granulated powder is 300 ppm, and the degreased aluminum nitride granulated powder is obtained.

[0037] S3. Dry mix the defatted aluminum nitride granulated powder obtained in step S2 with the nitride isolation powder to obtain the precursor mixed powder.

[0038] S4. The precursor mixed powder obtained in step S3 is subjected to high-temperature sintering. The high-temperature sintering is carried out in a nitrogen atmosphere, with a heating rate of 5℃ / min, a sintering temperature of 1700℃, and a holding time of 5h to obtain a crude high sphericity aluminum nitride thermally conductive filler.

[0039] S5. Mix anhydrous ethanol and thermally conductive modifier evenly and stir for 30 min. Then add the crude high sphericity aluminum nitride thermally conductive filler obtained in step S4 and continue stirring for 3 h to carry out the modification reaction. After the reaction is completed, the first mixture is obtained. The first mixture is washed three times with anhydrous ethanol, filtered and dried for 16 h to obtain the high sphericity aluminum nitride thermally conductive filler.

[0040] The nitride isolation powder is boron nitride powder with a particle size of 3 micrometers. The amount added is 3 wt% of the weight of the degreased aluminum nitride granulated powder. A V-type mixer is used to mix the boron nitride powder and the degreased aluminum nitride granulated powder for 4 hours.

[0041] refer to Figure 1 The preparation process of the thermal conductivity modifier is as follows:

[0042] Under N2 protection, sodium hydride and tetrahydrofuran were mixed in a mass ratio of 1:3 and stirred until homogeneous. The temperature was raised to 180°C, and a mixed solution of castor oil and tetrahydrofuran was added dropwise. The mass ratio of castor oil to tetrahydrofuran in the mixed solution was 1:1. The reaction was carried out for 2 hours. After the reaction was completed, the mixture was cooled to room temperature and centrifuged. The supernatant was collected and then distilled to remove excess tetrahydrofuran, thus obtaining the thermal conductivity modifier.

[0043] refer to Figure 2 The high sphericity aluminum nitride thermally conductive filler prepared in this embodiment was tested and found to have good sphericity. After sintering, it is in a loose state and does not require crushing or dispersion processes.

[0044] Example 2

[0045] A method for preparing a high-sphericity aluminum nitride thermally conductive filler includes the following steps:

[0046] S1. 110 parts by weight of aluminum nitride powder, 6 parts by weight of PVB and 165 parts by weight of anhydrous ethanol are mixed and then wet ball-milled for 6 hours. Then, spray granulation is performed in a spray dryer with a feed rate of 2200 mL / h, a spray pressure of 0.8 MPa, a hot air inlet temperature of 200°C and an outlet temperature of 90°C to obtain spherical aluminum nitride granulated powder with a particle size of 50 micrometers.

[0047] S2. The spherical aluminum nitride granulated powder obtained in step S1 is subjected to degreasing treatment. The degreasing treatment is carried out in air at a temperature of 550°C for 12 hours. The carbon content of the degreased aluminum nitride granulated powder is 300 ppm, and the degreased aluminum nitride granulated powder is obtained.

[0048] S3. Dry mix the defatted aluminum nitride granulated powder obtained in step S2 with the nitride isolation powder to obtain the precursor mixed powder.

[0049] S4. The precursor mixed powder obtained in step S3 is subjected to high-temperature sintering. The high-temperature sintering is carried out in a nitrogen atmosphere, with a heating rate of 5℃ / min, a sintering temperature of 1750℃, and a holding time of 5.5h to obtain a crude high sphericity aluminum nitride thermally conductive filler.

[0050] S5. Mix anhydrous ethanol and thermally conductive modifier evenly and stir for 45 min. Then add the crude high sphericity aluminum nitride thermally conductive filler obtained in step S4 and continue stirring for 3.5 h for modification reaction. After the reaction is completed, the first mixture is obtained. The first mixture is washed 4 times with anhydrous ethanol, filtered and dried for 20 min to obtain the high sphericity aluminum nitride thermally conductive filler.

[0051] The nitride isolation powder is high-temperature calcined aluminum nitride powder, and the calcination temperature of the high-temperature calcined aluminum nitride powder is 1900℃; the particle size of the nitride isolation powder is 5 micrometers, and the addition amount is 5wt% of the weight of the degreased aluminum nitride granulated powder; a V-type mixer is used to mix the high-temperature calcined aluminum nitride powder and the degreased aluminum nitride granulated powder, and the mixing time is 4 hours;

[0052] refer to Figure 1 The preparation process of the thermal conductivity modifier is as follows:

[0053] Under N2 protection, sodium hydride and tetrahydrofuran were mixed in a mass ratio of 1:4 and stirred until homogeneous. The temperature was raised to 190°C, and a mixed solution of castor oil and tetrahydrofuran was added dropwise. The mass ratio of castor oil to tetrahydrofuran in the mixed solution was 1:2. The reaction was carried out for 3 hours. After the reaction was completed, the mixture was cooled to room temperature and centrifuged. The supernatant was collected and then distilled to remove excess tetrahydrofuran, thus obtaining the thermal conductivity modifier.

[0054] refer to Figure 3 The high sphericity aluminum nitride thermally conductive filler prepared in this embodiment was tested and found to have good sphericity. After sintering, it is in a loose state and does not require crushing or dispersion processes.

[0055] Example 3

[0056] A method for preparing a high-sphericity aluminum nitride thermally conductive filler includes the following steps:

[0057] S1. 120 parts by weight of aluminum nitride powder, 10 parts by weight of PVB and 180 parts by weight of anhydrous ethanol are mixed and then wet ball-milled for 8 hours. Then, spray granulation is performed in a spray dryer with a feed rate of 2500 mL / h, a spray pressure of 1 MPa, a hot air inlet temperature of 200°C and an outlet temperature of 100°C to obtain spherical aluminum nitride granulated powder with a particle size of 200 micrometers.

[0058] S2. The spherical aluminum nitride granulated powder obtained in step S1 is subjected to degreasing treatment. The degreasing treatment is carried out in air at a temperature of 600°C for 12 hours. The carbon content of the degreased aluminum nitride granulated powder is 300 ppm, and the degreased aluminum nitride granulated powder is obtained.

[0059] S3. Dry mix the defatted aluminum nitride granulated powder obtained in step S2 with the nitride isolation powder to obtain the precursor mixed powder.

[0060] S4. The precursor mixed powder obtained in step S3 is subjected to high-temperature sintering. The high-temperature sintering is carried out in a nitrogen atmosphere, with a heating rate of 5℃ / min, a sintering temperature of 1850℃, and a holding time of 6h to obtain a crude high sphericity aluminum nitride thermally conductive filler.

[0061] S5. Mix anhydrous ethanol and thermally conductive modifier evenly and stir for 60 min. Then add the crude high sphericity aluminum nitride thermally conductive filler obtained in step S4 and continue stirring for 4 h to carry out the modification reaction. After the reaction is completed, the first mixture is obtained. The first mixture is washed 5 times with anhydrous ethanol, filtered and dried for 24 h to obtain the high sphericity aluminum nitride thermally conductive filler.

[0062] The nitride isolation powder is a mixture of boron nitride powder and high-temperature calcined aluminum nitride powder in equal proportions, wherein the calcination temperature of the high-temperature calcined aluminum nitride powder is 1900℃; the particle size of the nitride isolation powder is 2 micrometers, and the addition amount is 10wt% of the weight of the degreased aluminum nitride granulated powder; a V-type mixer is used to mix the nitride isolation powder and the degreased aluminum nitride granulated powder for 4 hours;

[0063] refer to Figure 1 The preparation process of the thermal conductivity modifier is as follows:

[0064] Under N2 protection, sodium hydride and tetrahydrofuran were mixed in a mass ratio of 1:5 and stirred until homogeneous. The temperature was raised to 200°C, and a mixed solution of castor oil and tetrahydrofuran was added dropwise. The mass ratio of castor oil to tetrahydrofuran in the mixed solution was 1:3. The reaction was carried out for 4 hours. After the reaction was completed, the mixture was cooled to room temperature and centrifuged. The supernatant was collected and then distilled to remove excess tetrahydrofuran, thus obtaining the thermal conductivity modifier.

[0065] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A method for preparing a high-sphericity aluminum nitride thermally conductive filler, characterized in that, Includes the following steps: S1. Mix 100-120 parts by weight of aluminum nitride powder, 5-10 parts by weight of PVB and 100-200 parts by weight of anhydrous ethanol, then perform wet ball milling, and then perform spray granulation to obtain spherical aluminum nitride granulated powder. S2. The spherical aluminum nitride granulated powder obtained in step S1 is degreased to obtain degreased aluminum nitride granulated powder. S3. Dry mix the defatted aluminum nitride granulated powder obtained in step S2 with the nitride isolation powder to obtain the precursor mixed powder. S4. The precursor mixed powder obtained in step S3 is sintered at high temperature to obtain crude aluminum nitride thermally conductive filler with high sphericity. S5. Mix anhydrous ethanol and thermally conductive modifier evenly and stir for 30-60 minutes. Then add the crude high sphericity aluminum nitride thermally conductive filler obtained in step S4 and continue stirring for 3-4 hours to carry out the modification reaction. After the reaction is completed, the first mixture is obtained. The first mixture is washed with anhydrous ethanol 3-5 times, filtered and dried for 16-24 hours to obtain the high sphericity aluminum nitride thermally conductive filler. The nitride isolation powder is one or a mixture of two of the following in any proportion: boron nitride powder and high-temperature calcined aluminum nitride powder; The preparation process of the thermal conductivity modifier is as follows: Under N2 protection, sodium hydride and tetrahydrofuran were mixed in a mass ratio of 1:3-5, stirred until homogeneous, and the temperature was raised to 180-200℃. A mixed solution of castor oil and tetrahydrofuran was added dropwise, and the reaction was allowed to proceed for 2-4 hours. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, and the supernatant was collected. The supernatant was then distilled to remove excess tetrahydrofuran, thus obtaining the thermally conductive modifier.

2. The method for preparing a high-sphericity aluminum nitride thermally conductive filler according to claim 1, characterized in that, In the mixed solution of castor oil and tetrahydrofuran, the mass ratio of castor oil to tetrahydrofuran is 1:1-3.

3. The method for preparing a high sphericity aluminum nitride thermally conductive filler according to claim 1, characterized in that, The wet ball milling time is 4-8 hours.

4. The method for preparing a high-sphericity aluminum nitride thermally conductive filler according to claim 1, characterized in that, The spray granulation is carried out in a spray dryer with a feed rate of 2000-2500 mL / h, a spray pressure of 0.5-1 MPa, a hot air inlet temperature of 140-200℃, and an air outlet temperature of 80-100℃.

5. The method for preparing a high-sphericity aluminum nitride thermally conductive filler according to claim 1, characterized in that, The particle size of the spherical aluminum nitride granulated powder in step S1 is 10-200 micrometers.

6. The method for preparing a high sphericity aluminum nitride thermally conductive filler according to claim 1, characterized in that, The degreasing process is carried out in air at a temperature of 450–600°C for 12–16 hours, and the carbon content of the degreased aluminum nitride granulated powder is <500 ppm.

7. The method for preparing a high sphericity aluminum nitride thermally conductive filler according to claim 1, characterized in that, The particle size of the nitride isolation powder is 0.5 to 10 micrometers, and the amount added is 1 to 10 wt% of the weight of the degreased aluminum nitride granulated powder.

8. The method for preparing a high sphericity aluminum nitride thermally conductive filler according to claim 1, characterized in that, The high-temperature sintering described in step S4 is carried out under a nitrogen atmosphere, with a heating rate of 5℃ / min, a sintering temperature of 1700~1900℃, and a holding time of 5-6h.

9. The method for preparing a high sphericity aluminum nitride thermally conductive filler according to claim 1, characterized in that, The calcination temperature of the high-temperature calcined aluminum nitride powder is higher than the high-temperature sintering temperature.

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