Composite heat-conducting silicone grease of multi-stage diamond filler and preparation method of composite heat-conducting silicone grease

Abstract

The invention relates to the technical field of heat conduction, in particular to composite heat-conducting silicone grease of multistage diamond filler and a preparation method of the composite heat-conducting silicone grease. The embodiment of the invention provides composite heat-conducting silicone grease of multistage diamond filler, which comprises an organic silicon matrix and filler distributed in the organic silicon matrix, and the filler comprises diamond microspheres, nano heat-conducting bridges and heat-conducting whiskers; the nano heat-conducting bridge forms a heat-conducting bridge among the diamond microspheres, and the heat-conducting whiskers are filled in gaps between the diamond microspheres and the nano heat-conducting bridge. The embodiment of the invention provides composite heat-conducting silicone grease of a multistage diamond filler and a preparation method of the composite heat-conducting silicone grease. The composite heat-conducting silicone grease with excellent heat-conducting property can be provided.

Description

Technical Field

[0001] This invention relates to the field of thermal conductivity technology, and in particular to a composite thermal grease with multi-level diamond filler and its preparation method. Background Technology

[0002] With the rapid development of electronic technology, the power density of integrated circuits and power devices is constantly increasing, leading to a sharp increase in the heat generated during operation. Effective heat dissipation has become crucial for ensuring the reliability, stability, and lifespan of electronic devices. Thermal grease, as an important thermal interface material (TIM), is widely used to fill the microscopic gaps between heat-generating components (such as CPUs and GPUs) and heat sinks to eliminate air, reduce contact thermal resistance, and improve heat dissipation efficiency.

[0003] Traditional thermal greases primarily use silicone oil as the base oil and metal oxides (such as aluminum oxide and zinc oxide) or nitrides (such as boron nitride) as thermally conductive fillers. While these materials improve heat dissipation to some extent, their thermal conductivity (TC) is typically difficult to exceed 5 W / (m·K), making it increasingly difficult to meet the heat dissipation requirements of modern high-power chips. Diamond, the naturally occurring material with the highest known thermal conductivity (theoretically reaching 2000 W / (m·K)), is an ideal material for thermally conductive fillers.

[0004] Currently, the thermal conductivity of commercially available high-end thermal greases is typically limited to below 12 W / (m·K). Although some studies have attempted to add diamond powder, simple physical mixing has not significantly improved the thermal conductivity. Summary of the Invention

[0005] This invention provides a composite thermal grease with multi-level diamond filler and its preparation method, which can provide a composite thermal grease with excellent thermal conductivity.

[0006] In a first aspect, embodiments of the present invention provide a composite thermal grease with multi-level diamond filler, comprising an organosilicon matrix and fillers distributed within the organosilicon matrix, wherein the fillers include diamond microspheres, nano-thermal bridges, and thermally conductive whiskers. The nano-thermal bridges form thermally conductive bridges between the diamond microspheres, and the thermally conductive whiskers fill the gaps between the diamond microspheres and the nano-thermal bridges.

[0007] In one possible design, the diamond microspheres have a particle size of 15-45 μm, the nano-thermal bridge comprises thermally conductive nanosheets and / or nanodiamond particles, the thermally conductive nanosheets have a planar dimension of 0.5-2 μm and a thickness of 0.6-20 nm, the nanodiamond particles have a particle size of 5-100 nm, and the thermally conductive whiskers have a diameter of 0.1-0.5 μm and a length of 5-20 μm.

[0008] In one possible design, the filler accounts for 78-89 wt% of the composite thermally conductive silicone grease, the diamond microspheres account for 50-70 wt% of the filler, the nano-thermal bridges account for 20-35 wt% of the filler, and the thermally conductive whiskers account for 5-15 wt% of the filler.

[0009] In one possible design, the surface of the diamond microspheres is coated with a metal layer.

[0010] In one possible design, the nano-thermal bridge comprises boron nitride nanosheets.

[0011] In one possible design, the thermally conductive whiskers comprise aluminum nitride whiskers.

[0012] Secondly, embodiments of the present invention provide a method for preparing a composite thermal grease with multi-level diamond fillers, used to prepare any of the above-mentioned composite thermal greases with multi-level diamond fillers, the method comprising: S1, the organosilicon matrix, surfactant and coupling agent are stirred and mixed; S2, add the thermally conductive whiskers and continue stirring and mixing; S3, add the nano thermal bridge and continue stirring and mixing; S4, add the diamond microspheres and continue stirring and mixing.

[0013] In one possible design, the stirring speed of S1 is 200~500 rpm and the stirring time is 10~15 minutes; the stirring speed of S2 is 600~1000 rpm and the stirring time is 20~30 minutes; the stirring speed of S3 is 1200~1800 rpm and the stirring time is 40~60 minutes; and the stirring speed of S4 is 2000~2500 rpm and the stirring time is 70~100 minutes.

[0014] In one possible design, prior to S1, a 50-200 nm thick metal layer is deposited on the surface of the diamond microspheres by magnetron sputtering or chemical plating, and the nano-thermal bridge is functionalized with a silane coupling agent.

[0015] In one possible design, following S4, it also includes: The mixture is ground at low temperature.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: This invention constructs a three-level thermally conductive structure in an organosilicon matrix, comprising diamond microspheres, nano-thermal bridges connecting different diamond microspheres, and thermally conductive whiskers inserted between the diamond microspheres and the nano-thermal bridges. This creates a complex, high-strength, and highly stable heat dissipation system composed of spheres, sheets, and needles. The nano-thermal bridges form nano-channels for heat conduction, and the whiskers effectively fill the tiny gaps between other fillers, further densifying the thermally conductive network and improving the material's mechanical strength and anti-settling properties. Compared to traditional structures with pure particle point-to-point connections, the complex network structure of this application provides heat flow channels with low phonon scattering to the maximum extent, resulting in a significant improvement in heat dissipation. The three-dimensional network structure possesses strong mechanical strength and anti-settling properties. Even with a high filler content, this structure maintains good thixotropic properties and fluidity of the thermal grease, making it easy to apply without settling or separating. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a flowchart illustrating a method for preparing a composite thermal grease with multi-level diamond filler provided in an embodiment of the present invention. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] This invention provides a composite thermal grease with multi-level diamond filler, comprising an organosilicon matrix and fillers distributed within the organosilicon matrix, the fillers including diamond microspheres, nano-thermal bridges and thermally conductive whiskers; Nano-thermal bridges form thermally conductive bridges between diamond microspheres, and thermally conductive whiskers fill the gaps between the diamond microspheres and the nano-thermal bridges.

[0021] This invention constructs a three-level thermally conductive structure in an organosilicon matrix, comprising diamond microspheres, nano-thermal bridges connecting different diamond microspheres, and thermally conductive whiskers inserted between the diamond microspheres and the nano-thermal bridges. This creates a complex, high-strength, and highly stable heat dissipation system composed of spheres, sheets, and needles. The nano-thermal bridges form nano-channels for heat conduction, and the whiskers effectively fill the tiny gaps between other fillers, further densifying the thermally conductive network and improving the material's mechanical strength and anti-settling properties. Compared to traditional structures with pure particle point-to-point connections, the complex network structure of this application provides heat flow channels with low phonon scattering to the maximum extent, resulting in a significant improvement in heat dissipation. The three-dimensional network structure possesses strong mechanical strength and anti-settling properties. Even with a high filler content, this structure maintains good thixotropic properties and fluidity of the thermal grease, making it easy to apply without settling or separating.

[0022] In some embodiments of the present invention, the diamond microspheres have a particle size of 15-45 μm (e.g., 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, or 45 μm), and the nano-thermal bridge comprises thermally conductive nanosheets and / or nanodiamond particles. The planar dimensions of the thermally conductive nanosheets are 0.5-2 μm (e.g., 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, or 2 μm), and the thickness is 0.6-20 nm (e.g., 0.6 μm, 0.8 μm, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, or 20 μm). The nanodiamond particles have a particle size of 5-100 nm (e.g., 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, or 100 nm). The diameter of the thermally conductive whiskers is 0.1~0.5μm (e.g., 0.1μm, 0.2μm, 0.3μm, 0.4μm or 0.5μm), and the length is 5~20μm (e.g., 5μm, 8μm, 10μm, 12μm, 14μm, 16μm, 18μm or 20μm).

[0023] Different particle sizes can make the thermally conductive three-dimensional network formed by the three types of fillers more compact and stable, further improving thermal conductivity and mechanical properties.

[0024] In some embodiments of the present invention, the filler accounts for 78-89 wt% of the composite thermally conductive silicone grease (e.g., 78 wt%, 80 wt%, 82 wt%, 84 wt%, 86 wt%, 88 wt%, or 89 wt%), diamond microspheres account for 50-70 wt% of the filler (e.g., 50 wt%, 54 wt%, 58 wt%, 60 wt%, 64 wt%, 66 wt%, 68 wt%, or 70 wt%), nano-thermal bridges account for 20-35 wt% of the filler (e.g., 20 wt%, 22 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt%, 32 wt%, 34 wt%, or 35 wt%), and thermally conductive whiskers account for 5-15 wt% of the filler (e.g., 5 wt%, 8 wt%, 10 wt%, 12 wt%, 14 wt%, or 15 wt%).

[0025] A higher filler content can significantly improve thermal conductivity while having almost no impact on the flowability and thixotropy of composite thermal grease. The proportions of various substances in the filler can be rationally adjusted to regulate the morphology of the three-dimensional thermally conductive network, optimizing its thermal conductivity and mechanical properties.

[0026] In some embodiments of the present invention, the surface of the diamond microspheres is coated with a metal layer, the thickness of which may be 50 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm or 200 nm.

[0027] The surface of diamond microspheres can be coated with a metal layer (preferably silver or nickel) by magnetron sputtering or chemical plating. This layer greatly improves compatibility with the silicone grease substrate and significantly reduces interfacial contact thermal resistance. The metal layer on the surface of the diamond microspheres acts as a "thermal buffer layer," greatly improving the phonon coupling efficiency with the substrate and other fillers, fundamentally solving the interfacial thermal barrier problem.

[0028] In some embodiments of the present invention, the nano-thermal bridge comprises boron nitride nanosheets.

[0029] The metallic layer on the surface of diamond microspheres acts as a "thermal buffer layer," significantly improving the phonon coupling efficiency with the matrix and other fillers, fundamentally solving the interfacial thermal barrier problem. It possesses high thermal conductivity (up to approximately 2000 W / m·K in-plane), high temperature resistance (up to 2800℃), and a low coefficient of thermal expansion. It also exhibits excellent electrical insulation, a wide bandgap (approximately 5.97 eV), and high dielectric strength, making it suitable as a thermally conductive silicone grease filler for electronic products. Furthermore, it possesses high strength and good lubricity, providing excellent support for thermally conductive three-dimensional networks.

[0030] In some embodiments of the present invention, the thermally conductive whiskers comprise aluminum nitride whiskers.

[0031] Aluminum nitride whiskers have the following properties: High thermal conductivity: Due to its single-crystal structure, extremely low impurity content and few lattice defects, it has less phonon scattering and its thermal conductivity is expected to approach the theoretical value of aluminum nitride (about 320 W / m·K), which is much higher than that of ordinary polycrystalline aluminum nitride ceramics (usually <200 W / m·K).

[0032] High insulation: Excellent electrical insulation (volume resistivity up to 10). 10 (Ω·cm or above).

[0033] Excellent mechanical properties: high fracture strength, high elastic modulus, high temperature resistance, and corrosion resistance.

[0034] Low coefficient of thermal expansion: Compatible with silicon (Si) and silicon carbide (SiC), suitable for semiconductor packaging.

[0035] High aspect ratio: One-dimensional nanostructures with a large aspect ratio (usually greater than 10, and even up to 500) are easy to form three-dimensional networks in composite materials.

[0036] Please refer to Figure 1 This invention provides a method for preparing a composite thermal grease with multi-level diamond filler, used to prepare any of the above-mentioned composite thermal greases with multi-level diamond filler. The method includes: S1, the organosilicon matrix, surfactant and coupling agent are stirred and mixed; S2, add thermally conductive whiskers and continue stirring to mix; S3, add the nano thermal bridge and continue stirring to mix; S4, add diamond microspheres and continue stirring to mix.

[0037] In this embodiment, stirring can be carried out in a dual planetary mixer under vacuum conditions. The organosilicon matrix is ​​a compound system of high-phenyl-content phenyl silicone oil and low-viscosity methyl silicone oil, designed to balance heat resistance and flowability.

[0038] In step S1, the mass fraction of the surfactant and the coupling agent is 1-3%.

[0039] In some embodiments of the present invention, the stirring speed of S1 is 200-500 rpm and the stirring time is 10-15 minutes; the stirring speed of S2 is 600-1000 rpm and the stirring time is 20-30 minutes; the stirring speed of S3 is 1200-1800 rpm and the stirring time is 40-60 minutes; and the stirring speed of S4 is 2000-2500 rpm and the stirring time is 70-100 minutes.

[0040] In a dual planetary mixer, the gap between the impeller and the container wall is very small, creating a strong velocity gradient during high-speed rotation, which generates high shear stress. This high shear stress can break up packing agglomeration, promote the adhesion of nanofillers to the surface of microspheres, enhance the interfacial compatibility between the packing and the matrix, and help construct a continuous thermally conductive network.

[0041] In some embodiments of the present invention, before S1, a 50-200 nm thick metal layer is deposited on the surface of the diamond microspheres by magnetron sputtering or chemical plating, and the nano-thermal bridge is functionalized with a silane coupling agent.

[0042] In this embodiment, the silane coupling agent may be KH-792.

[0043] In some embodiments of the present invention, after S4, the method further includes: The mixture is ground at low temperature.

[0044] In this embodiment, a high-speed three-roll mill with forced water cooling is used for multi-pass grinding to ensure that the agglomerates are completely opened up without damaging the network structure. Finally, static degassing is performed in a vacuum degassing chamber to obtain the final product.

[0045] It should be noted that the temperature during cryogenic grinding should not exceed 45℃. Without temperature control, localized high temperatures may lead to degradation of the silicone matrix, damage to the surface modification layer, and filler agglomeration, resulting in material denaturation, decreased thermal conductivity, and deterioration of workability. Therefore, forced cooling is a process safety measure.

[0046] To more clearly illustrate the technical solution and advantages of the present invention, several embodiments are described in detail below.

[0047] Example 1 formula: Phenyl silicone oil (500cSt) / Methyl silicone oil (100cSt) (composite matrix): 15 wt% Multi-stage diamondized composite filler: 84 wt% Silver-coated diamond microspheres (D50=25μm): accounting for 60% of the total weight of the filler (i.e. 50.4 wt%); Surface KH-792 functionalized nanodiamond particles (30nm): accounting for 25% of the total weight of the filler (i.e., 21.0 wt%); Aluminum nitride whiskers (0.2 μm in diameter, 10 μm in length): accounting for 15% of the total weight of the filler (i.e., 12.6 wt%); Additives (dispersants, coupling agents): 1 wt%; Preparation method: 1. In a dual planetary mixer, mix the silicone oil matrix and additives, apply vacuum, and mix at 300 rpm for 10 minutes.

[0048] 2. Add tertiary AlN whiskers and stir at 800 rpm for 20 minutes.

[0049] 3. Add secondary nanodiamonds, increase the rotation speed to 1500 rpm, and vacuum stir for 40 minutes.

[0050] 4. Add the first-grade silver-coated diamond microspheres in three batches, stirring at 2200 rpm for 30 minutes after each batch to ensure thorough mixing.

[0051] 5. Grind the paste three times using a three-roll mill (roller gap 5μm).

[0052] 6. Finally, allow to stand at -0.1MPa and 60℃ for 2 hours to remove bubbles.

[0053] Test results: The thermal conductivity of the thermal grease prepared in this example was determined to be 35.2 W / (m·K) by laser flare method (LFA).

[0054] Analysis: The nanodiamond particles act as thermal bridges, forming a dense network with the silver-coated diamond microspheres and whiskers, resulting in low interfacial thermal resistance and excellent thermal conductivity.

[0055] Example 2 formula: Phenyl silicone oil (500cSt) / Methyl silicone oil (100cSt) (composite matrix): 15 wt% Multi-stage diamondized composite filler: 84 wt% Silver-coated diamond microspheres (D50=25μm): accounting for 60% of the total weight of the filler (i.e. 50.4 wt%); KH-792 functionalized boron nitride nanosheets (1.2 μm, 8 nm thick): accounting for 25% (21.0 wt%) of the total weight of the filler; Aluminum nitride whiskers (0.2 μm in diameter, 10 μm in length): accounting for 15% of the total weight of the filler (i.e., 12.6 wt%); Additives (dispersants, coupling agents): 1 wt%; Preparation method: 1. In a dual planetary mixer, mix the silicone oil matrix and additives, apply vacuum, and mix at 300 rpm for 10 minutes.

[0056] 2. Add tertiary AlN whiskers and stir at 800 rpm for 20 minutes.

[0057] 3. Add secondary boron nitride nanosheets, increase the speed to 1500 rpm, and vacuum stir for 40 minutes.

[0058] 4. Add the first-grade silver-coated diamond microspheres in three batches, stirring at 2200 rpm for 30 minutes after each batch to ensure thorough mixing.

[0059] 5. Grind the paste three times using a three-roll mill (roller gap 5μm).

[0060] 6. Finally, allow to stand at -0.1MPa and 60℃ for 2 hours to remove bubbles.

[0061] Test results: The thermal conductivity of the thermal grease prepared in this example was determined to be 36.5 W / (m·K) by laser flare method (LFA).

[0062] Example 2 is basically the same as Example 1, except that boron nitride nanosheets are used instead of nanodiamond particles.

[0063] Analysis: Boron nitride nanosheets have extremely high in-plane thermal conductivity (~2000 W / (m·K)), making them more effective as thermal bridges, with a thermal conductivity slightly higher than that of Example 1.

[0064] Example 3 formula: Phenyl silicone oil (500cSt) / Methyl silicone oil (100cSt) (composite matrix): 15 wt% Multi-stage diamondized composite filler: 84 wt% Silver-coated diamond microspheres (D50=25μm): accounting for 60% of the total weight of the filler (i.e. 50.4 wt%); KH-792-functionalized boron nitride nanosheets (1.2 μm, 8 nm thick) and KH-792-functionalized nanodiamond nanosheets (5-50 nm): each accounted for 12.5% ​​of the total weight of the filler (totaling 21.0 wt%). Aluminum nitride whiskers (0.2 μm in diameter, 10 μm in length): accounting for 15% of the total weight of the filler (i.e., 12.6 wt%); Additives (dispersants, coupling agents): 1 wt%; Preparation method: 1. In a dual planetary mixer, mix the silicone oil matrix and additives, apply vacuum, and mix at 300 rpm for 10 minutes.

[0065] 2. Add tertiary AlN whiskers and stir at 800 rpm for 20 minutes.

[0066] 3. Add secondary nanodiamonds and boron nitride nanosheets, increase the rotation speed to 1500 rpm, and vacuum stir for 40 minutes.

[0067] 4. Add the first-grade silver-coated diamond microspheres in three batches, stirring at 2200 rpm for 30 minutes after each batch to ensure thorough mixing.

[0068] 5. Grind the paste three times using a three-roll mill (roller gap 5μm).

[0069] 6. Finally, allow to stand at -0.1MPa and 60℃ for 2 hours to remove bubbles.

[0070] Test results: The thermal conductivity of the thermal grease prepared in this example was determined to be 38.0 W / (m·K) by laser flare method (LFA).

[0071] Example 3 is basically the same as Example 1, except that the nano-thermal bridge includes both nanodiamond and boron nitride nanosheets.

[0072] Analysis: The hybrid nano-thermal bridges (diamond + boron nitride) synergistically enhance the heat flow path, resulting in a more complete network structure and the highest thermal conductivity.

[0073] Comparative Example 1 formula: Phenyl silicone oil (500cSt) / Methyl silicone oil (100cSt) (composite matrix): 15 wt% Diamond microspheres (D50=25μm) filler: 84 wt% Additives (dispersants, coupling agents): 1 wt%; Preparation method: 1. In a dual planetary mixer, mix the silicone oil matrix and additives, apply vacuum, and mix at 300 rpm for 10 minutes.

[0074] 2. Add the diamond microspheres in three batches, stirring at 2200 rpm for 30 minutes after each batch to ensure thorough mixing.

[0075] 3. Grind the paste three times using a three-roll mill (5μm gap between the rollers).

[0076] 4. Finally, allow to stand at -0.1MPa and 60℃ for 2 hours to remove bubbles.

[0077] Test results: The thermal conductivity of the thermal grease prepared in this example was determined to be 12.5 W / (m·K) by laser flare method (LFA).

[0078] Comparative Example 1 is basically the same as Example 3, except that the filler consists only of diamond microspheres.

[0079] Analysis: The lack of nano-thermal bridges and whiskers results in discontinuous heat flow paths, high interfacial thermal resistance, and significantly reduced thermal conductivity.

[0080] Comparative Example 2 formula: Phenyl silicone oil (500cSt) / Methyl silicone oil (100cSt) (composite matrix): 15 wt% Multi-stage diamondized composite filler: 84 wt% Diamond microspheres (D50=25μm): accounting for 60% of the total weight of the filler (i.e. 50.4 wt%); KH-792-functionalized boron nitride nanosheets (1.2 μm, 8 nm thick) and KH-792-functionalized nanodiamond nanosheets (5-50 nm): each accounted for 12.5% ​​of the total weight of the filler (totaling 21.0 wt%). Aluminum nitride whiskers (0.2 μm in diameter, 10 μm in length): accounting for 15% of the total weight of the filler (i.e., 12.6 wt%); Additives (dispersants, coupling agents): 1 wt%; Preparation method: 1. In a dual planetary mixer, mix the silicone oil matrix and additives, apply vacuum, and mix at 300 rpm for 10 minutes.

[0081] 2. Add tertiary AlN whiskers and stir at 800 rpm for 20 minutes.

[0082] 3. Add secondary nanodiamonds and boron nitride nanosheets, increase the rotation speed to 1500 rpm, and vacuum stir for 40 minutes.

[0083] 4. Add the first-grade silver-coated diamond microspheres in three batches, stirring at 2200 rpm for 30 minutes after each batch to ensure thorough mixing.

[0084] 5. Grind the paste three times using a three-roll mill (roller gap 5μm).

[0085] 6. Finally, allow to stand at -0.1MPa and 60℃ for 2 hours to remove bubbles.

[0086] Test results: The thermal conductivity of the thermal grease prepared in this example was determined to be 26.0 W / (m·K) by laser flare method (LFA).

[0087] Comparative Example 2 is basically the same as Example 3, except that the diamond microspheres are not coated with a metal layer.

[0088] Analysis: The lack of a metal coating leads to a decrease in interfacial phonon coupling efficiency, an increase in contact thermal resistance, and a decrease in thermal conductivity of approximately 30%.

[0089] Comparative Example 3 formula: Phenyl silicone oil (500cSt) / Methyl silicone oil (100cSt) (composite matrix): 15 wt% Multi-stage diamondized composite filler: 84 wt% Silver-coated diamond microspheres (D50=25μm): accounting for 60% of the total weight of the filler (i.e. 50.4 wt%); Aluminum nitride whiskers (0.2 μm in diameter, 10 μm in length): account for 40% of the total weight of the filler (i.e., 33.6 wt%); Additives (dispersants, coupling agents): 1 wt%; Preparation method: 1. In a dual planetary mixer, mix the silicone oil matrix and additives, apply vacuum, and mix at 300 rpm for 10 minutes.

[0090] 2. Add tertiary AlN whiskers and stir at 800 rpm for 20 minutes.

[0091] 3. Add the first-grade silver-coated diamond microspheres in three batches, stirring at 2200 rpm for 30 minutes after each batch to ensure thorough mixing.

[0092] 4. Grind the paste three times using a three-roll mill (5μm gap between the rollers).

[0093] 5. Finally, allow to stand at -0.1MPa and 60℃ for 2 hours to remove bubbles.

[0094] Test results: The thermal conductivity of the thermal grease prepared in this example was determined to be 18.5 W / (m·K) by laser flare method (LFA).

[0095] Comparative Example 3 is basically the same as Example 3, except that no nano-thermal bridges were added.

[0096] Analysis: The lack of nano-thermal bridges interrupts the heat flow bridge. Although whiskers fill the gaps, the thermal network is incomplete and has poor performance.

[0097] Comparative Example 4 formula: Phenyl silicone oil (500cSt) / Methyl silicone oil (100cSt) (composite matrix): 15 wt% Multi-stage diamondized composite filler: 84 wt% Silver-coated diamond microspheres (D50=25μm): accounting for 60% of the total weight of the filler (i.e. 50.4 wt%); KH-792-functionalized boron nitride nanosheets (1.2 μm, 8 nm thick) and KH-792-functionalized nanodiamond nanosheets (5-50 nm): each account for 20% of the total weight of the filler (totaling 33.6 wt%). Additives (dispersants, coupling agents): 1 wt%; Preparation method: 1. In a dual planetary mixer, mix the silicone oil matrix and additives, apply vacuum, and mix at 300 rpm for 10 minutes.

[0098] 2. Add secondary nanodiamonds and boron nitride nanosheets, increase the speed to 1500 rpm, and vacuum stir for 40 minutes.

[0099] 3. Add the first-grade silver-coated diamond microspheres in three batches, stirring at 2200 rpm for 30 minutes after each batch to ensure thorough mixing.

[0100] 4. Grind the paste three times using a three-roll mill (5μm gap between the rollers).

[0101] 5. Finally, allow to stand at -0.1MPa and 60℃ for 2 hours to remove bubbles.

[0102] Test results: The thermal conductivity of the thermal grease prepared in this example was determined to be 22.0 W / (m·K) by laser flare method (LFA).

[0103] Comparative Example 4 is basically the same as Example 3, except that whiskers were not added.

[0104] Analysis: The lack of whisker filling and the presence of air gaps between microspheres and nanosheets increase thermal resistance and decrease thermal conductivity.

[0105] Comparative Example 5 formula: Phenyl silicone oil (500cSt) / Methyl silicone oil (100cSt) (composite matrix): 15 wt% Multi-stage diamondized composite filler: 84 wt% Silver-coated diamond microspheres (D50=25μm): accounting for 60% of the total weight of the filler (i.e. 50.4 wt%); KH-792-functionalized boron nitride nanosheets (1.2 μm, 8 nm thick) and KH-792-functionalized nanodiamond nanosheets (5-50 nm): each accounted for 12.5% ​​of the total weight of the filler (totaling 21.0 wt%). Aluminum nitride whiskers (0.2 μm in diameter, 10 μm in length): accounting for 15% of the total weight of the filler (i.e., 12.6 wt%); Additives (dispersants, coupling agents): 1 wt%; Preparation method: 1. In a dual planetary mixer, mix the silicone oil matrix and additives, apply vacuum, and mix at 300 rpm for 10 minutes.

[0106] 2. Add tertiary AlN whiskers and stir at 800 rpm for 20 minutes.

[0107] 3. Add secondary nanodiamonds and boron nitride nanosheets, increase the rotation speed to 1500 rpm, and vacuum stir for 40 minutes.

[0108] 4. Add the first-grade silver-coated diamond microspheres in three batches, stirring at 1500 rpm for 30 minutes after each batch.

[0109] 5. Grind the paste three times using a three-roll mill (roller gap 5μm).

[0110] 6. Finally, allow to stand at -0.1MPa and 60℃ for 2 hours to remove bubbles.

[0111] Test results: The thermal conductivity is 15.0 W / (m·K), and agglomeration is observed.

[0112] Comparative Example 5 is basically the same as Example 3, except that the nano-thermal bridge includes both nanodiamond and boron nitride nanosheets.

[0113] Analysis: Low shear force leads to uneven packing dispersion, and the agglomerates increase phonon scattering, resulting in a significant decrease in thermal conductivity.

[0114] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite thermal grease with multi-level diamond filler, characterized in that, It includes an organosilicon matrix and fillers distributed within the organosilicon matrix, wherein the fillers include diamond microspheres, nano-thermal bridges, and thermally conductive whiskers; The nano-thermal bridges form thermally conductive bridges between the diamond microspheres, and the thermally conductive whiskers fill the gaps between the diamond microspheres and the nano-thermal bridges.

2. The composite thermal grease according to claim 1, characterized in that, The diamond microspheres have a particle size of 15-45 μm, the nano-thermal bridges include thermally conductive nanosheets and / or nanodiamond particles, the thermally conductive nanosheets have a planar dimension of 0.5-2 μm and a thickness of 0.6-20 nm, the nanodiamond particles have a particle size of 5-100 nm, and the thermally conductive whiskers have a diameter of 0.1-0.5 μm and a length of 5-20 μm.

3. The composite thermal grease according to claim 1, characterized in that, The filler accounts for 78-89 wt% of the composite thermally conductive silicone grease, the diamond microspheres account for 50-70 wt% of the filler, the nano thermally conductive bridges account for 20-35 wt% of the filler, and the thermally conductive whiskers account for 5-15 wt% of the filler.

4. The composite thermal grease according to claim 1, characterized in that, The surface of the diamond microspheres is coated with a metal layer.

5. The composite thermal grease according to claim 1, characterized in that, The thermally conductive nanosheets include boron nitride nanosheets.

6. The composite thermal grease according to claim 1, characterized in that, The thermally conductive whiskers include aluminum nitride whiskers.

7. A method for preparing a composite thermal grease with multi-level diamond filler, characterized in that, The method for preparing the composite thermal grease with multi-level diamond filler as described in any one of claims 1-6 comprises: S1, the organosilicon matrix, surfactant and coupling agent are stirred and mixed; S2, add the thermally conductive whiskers and continue stirring and mixing; S3, add the nano thermal bridge and continue stirring and mixing; S4, add the diamond microspheres and continue stirring and mixing.

8. The method according to claim 7, characterized in that, The mixing speed for S1 is 200-500 rpm, and the mixing time is 10-15 minutes. The mixing speed for S2 is 600-1000 rpm, and the mixing time is 20-30 minutes. The mixing speed for S3 is 1200-1800 rpm, and the mixing time is 40-60 minutes. The mixing speed for S4 is 2000-2500 rpm, and the mixing time is 70-100 minutes.

9. The method according to claim 7, characterized in that, Before S1, the process includes depositing a 50-200 nm thick metal layer on the surface of the diamond microspheres by magnetron sputtering or chemical plating, and functionalizing the nano-thermal bridges with silane coupling agents.

10. The method according to claim 7, characterized in that, Following S4, it also includes: The mixture is ground at low temperature.

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