Heat-conducting filler as well as preparation method and application thereof

Abstract

The embodiment of the invention provides a heat-conducting filler and a preparation method and application thereof, and the preparation method comprises the following steps: mixing silica powder and an activator, carrying out ultrasonic treatment to activate the surface of the silica powder, and drying to obtain activated powder. Mixing a boron-containing compound and a nitrogen-containing compound to obtain a mixed solution, mixing the activated powder with the mixed solution, and heating to form a precursor layer on the surface of the activated powder to obtain an intermediate solution; nitrogen-containing reaction gas is introduced into the intermediate solution for chemical vapor deposition, a boron nitride coating layer is formed on the surface of the activated powder after the nitrogen-containing reaction gas reacts with the precursor layer, and the heat-conducting filler is obtained after drying. The preparation method comprises the following steps: firstly activating the surface of silica powder, then coating the surface of the silica powder with boron nitride through a chemical vapor deposition method, and finally modifying the boron nitride coating the surface of the silica powder, so that the heat-conducting filler with a stable structure is finally obtained, and meanwhile, the heat-conducting filler also has the comprehensive properties of low dielectric constant, low dielectric loss, high heat conductivity and low water absorption rate.

Description

Technical Field

[0001] The present application relates to the technical field of material preparation, and in particular to a thermally conductive filler and a preparation method and application thereof. Background Art

[0002] With the rapid development of high-performance computing, high-frequency and high-speed copper clad laminates have higher requirements for dielectric properties and thermal conductivity. Currently, silicon dioxide is mainly used as the thermal conductive filler system for copper clad laminates, but there are still some problems, such as the difficulty in synergistic optimization between dielectric constant and dielectric loss, low thermal conductivity, and the fragility of fillers during mixing. Summary of the invention

[0003] In view of this, in order to solve at least one of the above technical problems, an embodiment of the present application provides a thermally conductive filler.

[0004] In addition, the embodiments of the present application also provide a method for preparing the aforementioned thermally conductive filler, and a copper clad laminate using the thermally conductive filler.

[0005] The present application provides a method for preparing a thermally conductive filler, including: mixing silicon micropowder and an activator and ultrasonically treating the silicon micropowder surface to activate the silicon micropowder surface, and obtaining an activated powder after drying. Mixing a boron-containing compound and a nitrogen-containing compound to obtain a mixed solution, and mixing the activated powder with the mixed solution, heating to form a precursor layer on the surface of the activated powder to obtain an intermediate solution. Passing a nitrogen-containing reaction gas into the intermediate solution for chemical vapor deposition, so that the nitrogen-containing reaction gas reacts with the precursor layer to form a boron nitride coating layer on the surface of the activated powder, and drying to obtain a thermally conductive filler.

[0006] In some embodiments of the present application, the temperature of chemical vapor deposition is 900° C. to 1000° C., and the reaction time is 2 h to 4 h.

[0007] In some embodiments of the present application, the nitrogen-containing reaction gas includes hydrogen and nitrogen, wherein the volume proportion of hydrogen in the nitrogen-containing reaction gas is 5% to 15%.

[0008] In some embodiments of the present application, the activator includes any one of a hydrochloric acid solution, a nitric acid solution, and a sulfuric acid solution with a mass fraction of 5% to 15%; or any one of a sodium hydroxide solution and a potassium hydroxide solution with a mass fraction of 1% to 5%.

[0009] In some embodiments of the present application, the mass ratio of the activator to the silicon powder is 2% to 10%.

[0010] In some embodiments of the present application, the molar ratio of the boron-containing compound to the nitrogen-containing compound is 1:2 to 1:4.

[0011] In some embodiments of the present application, the mass ratio of the mixed solution to the silicon powder is 10% to 20%.

[0012] In some embodiments of the present application, the mass ratio of the coupling agent to the activated powder having a boron nitride coating layer is 1% to 3%.

[0013] In some embodiments of the present application, the boron-containing compound includes one or more of boric acid, boron chloride and sodium borate tetradecahydrate, and the nitrogen-containing compound includes one or more of urea, melamine, hexamethylenetetramine, ethylenediamine and ammonia water.

[0014] In some embodiments of the present application, after chemical vapor deposition, the preparation method further comprises:

[0015] The thermally conductive filler is mixed with a coupling agent, which includes a silane coupling agent containing an amino group.

[0016] The embodiment of the present application also provides a thermally conductive filler, which is prepared by the aforementioned preparation method. The thermally conductive filler includes a core and a coating layer provided on at least a portion of the surface of the core, wherein the core includes silicon powder and the coating layer includes boron nitride.

[0017] In some embodiments of the present application, the mass ratio of boron nitride to silicon powder is 5% to 15%.

[0018] In some embodiments of the present application, the boron nitride includes hexagonal boron nitride.

[0019] The embodiment of the present application further provides a copper clad laminate, comprising a copper foil layer and a dielectric layer stacked in layers, wherein the dielectric layer comprises the aforementioned thermal conductive filler.

[0020] Compared with the prior art, the preparation method provided in the embodiment of the present application is to first activate the surface of silicon micropowder, then coat boron nitride on the surface of silicon micropowder by chemical vapor deposition, and finally modify the boron nitride coated on the surface of silicon micropowder, and finally obtain a thermally conductive filler with a stable structure. The dielectric anisotropy is reduced by directional arrangement of the boron nitride crystal plane, and the strength of the filler during the mixing process can also be improved. The thickness of the surface-coated boron nitride is controllable without using a catalyst, and the comprehensive performance of low dielectric constant, low dielectric loss, high thermal conductivity and low water absorption is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A process flow chart of the method for preparing the thermally conductive filler provided in an embodiment of the present application. DETAILED DESCRIPTION

[0022] The following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0023] In order to improve the thermal conductivity of existing copper-clad laminates, silicon dioxide is widely used in the dielectric layer of copper-clad laminates due to its good insulation and low thermal expansion coefficient. 2 The dielectric constant of fillers is generally higher than 4.0, which makes it difficult to meet the stringent requirements of dielectric constant ≤3.5 in high-frequency scenarios. Although hollow silica powder can reduce the overall dielectric constant by introducing an air phase, the surface of silica powder is rich in hydroxyl groups and easily adsorbs water molecules in a hot and humid environment, resulting in a sharp increase in dielectric loss. Experimental data show that the dielectric loss value of untreated hollow silica powder increases by more than 40% at 85% humidity, which seriously restricts its reliability in humid environments. The traditional process physically mixes boron nitride and SiO 2 Powder improves thermal conductivity, but due to the boron nitride and SiO 2 There is a lack of chemical bonding between the two, and the interface thermal resistance is extremely high, and the thermal conductivity of the composite material is usually less than 1.5W / (m·K). Especially at high filler loading (>60wt%), the random dispersion of boron nitride particles will lead to deterioration of the fluidity of the resin matrix and aggravate interface defects.

[0024] Therefore, it is necessary to coat the surface of silicon micropowder. The inventors of the present application have found that although existing coating technologies such as metal catalytic vapor deposition can achieve boron nitride coating of silicon micropowder, they require the use of precious metal catalysts such as palladium and platinum, and residual metal ions will cause dielectric loss to deteriorate. The catalyst-free physical vapor deposition (PVD) method faces problems such as uneven coating layer and high equipment investment, making it difficult to apply on a large scale.

[0025] Based on this, one embodiment of the present application provides a method for preparing a thermally conductive filler. Figure 1 , the preparation method comprises:

[0026] Step S1, mixing silicon micropowder and an activator and subjecting the mixture to ultrasonic treatment to activate the surface of the silicon micropowder, and obtaining activated powder after drying.

[0027] In some embodiments, the activator includes any one of hydrochloric acid solution, nitric acid solution, and sulfuric acid solution with a mass fraction of 5% to 15%; or any one of sodium hydroxide solution and potassium hydroxide solution with a mass fraction of 1% to 5%, that is, the surface of the silicon micropowder can be activated by acid treatment with an appropriate concentration, and the surface of the silicon micropowder can be activated by H + The Si-O-Si bond on the surface of the silicon micropowder is hydrolyzed to generate a new -Si-OH group. Alkali treatment can expose the hydroxyl group by corroding the structure of the surface of the silicon micropowder, making the surface of the silicon micropowder hydroxylated, which is beneficial to improve the interface affinity of the silicon micropowder and enhance the subsequent bonding between the silicon micropowder and the coating.

[0028] In some embodiments, the silicon micropowder is hollow silicon micropowder, wherein the particle size of the hollow silicon micropowder is 5 μm to 10 μm, the wall thickness is 0.2 μm to 0.5 μm, and the SiO 2 The mass content accounts for >99%.

[0029] In some embodiments, the activator may be a hydrochloric acid solution with a mass fraction of 5% to 15%. For example, the mass fraction of the hydrochloric acid solution may be 5%, 8%, 10%, 11%, 15% or any value within the range formed by any two of the above values.

[0030] In some embodiments, the activator can be a sodium hydroxide solution with a mass fraction of 1% to 5%. For example, the mass fraction of the sodium hydroxide solution can be 1%, 2%, 3%, 4%, 5%, or any value within the range formed by any two of the above values.

[0031] In some embodiments, the ultrasonic treatment time is 20 min to 40 min. For example, the ultrasonic treatment time can be 20 min, 22 min, 25 min, 28 min, 30 min, 32 min, 35 min, 38 min, 40 min or any value within the range formed by any two of the above values. Controlling the ultrasonic treatment time within the above range is beneficial to the completeness of the hydroxylation of the silicon micropowder surface.

[0032] In some embodiments, the mass ratio of the activator to the silicon micropowder is 2% to 10%. For example, the mass ratio can be 2%, 4%, 5%, 6%, 8%, 10%, or any value within the range formed by any two of the above values. Controlling the mass ratio within the above range is conducive to the surface hydroxylation of the hollow silicon micropowder.

[0033] Step S2, mixing the boron-containing compound and the nitrogen-containing compound to obtain a mixed solution, mixing the activated powder with the mixed solution, and heating to form a precursor layer on the surface of the activated powder to obtain an intermediate solution.

[0034] Among them, through the sol-gel method, the boron element in the boron-containing compound can self-assemble on the surface of the silicon micropowder to form BO-Si chemical bonds, so as to facilitate the combination of boron nitride and silicon micropowder in the subsequent chemical vapor deposition process.

[0035] In some embodiments, the boron-containing compound includes one or more of boric acid, boron chloride and sodium borate tetradecahydrate, and the nitrogen-containing compound includes one or more of urea, melamine, hexamethylenetetramine, ethylenediamine and ammonia water. In this embodiment, the boron-containing compound includes boric acid, the nitrogen-containing compound includes urea, and the molar ratio of boric acid to urea is 1:2 to 1:4. For example, the molar ratio can be 1:2, 1:3, 1:4 or any value within the range of any two of the above ratios.

[0036] In some embodiments, the mass ratio of the mixed solution to the silicon powder is 10% to 20%. For example, the mass ratio can be 10%, 12%, 14%, 16%, 18%, 20%, or any value within the range formed by any two of the above values.

[0037] In some embodiments, the heating temperature of the sol-gel method is 100° C. to 120° C. For example, the temperature can be 100° C., 110° C., 120° C., or any value within the range formed by any two ratios of the above. Controlling the temperature within the above range is conducive to the self-assembly of the silicon powder surface to form BO-Si chemical bonds.

[0038] Step S3, introducing nitrogen-containing reaction gas into the intermediate solution for chemical vapor deposition, so that the nitrogen-containing reaction gas reacts with the precursor layer to form a boron nitride coating layer on the surface of the activated powder, and drying to obtain a thermally conductive filler.

[0039] In some embodiments, the vapor deposition reaction is carried out at 900°C to 1000°C for 2h to 4h. For example, the temperature of the vapor deposition reaction can be 900°C, 920°C, 930°C, 950°C, 980°C, 1000°C, or any value within the range formed by any two of the above values. The time of the vapor deposition reaction can be 2h, 3h, 4h, or any value within the range formed by any two of the above values. Controlling the temperature within the above range is conducive to the formation of uniform hexagonal boron nitride in the coating.

[0040] In some embodiments, the nitrogen-containing reaction gas includes hydrogen and nitrogen, wherein the volume percentage of hydrogen in the nitrogen-containing reaction gas is 5% to 15%. For example, the volume percentage may be 5%, 8%, 10%, 12%, 13%, 15%, or any value within the range formed by any two of the above values.

[0041] After chemical vapor deposition, the preparation method further comprises step 4, mixing the activated powder with the boron nitride coating layer, the organic solvent and the coupling agent, and drying to obtain the thermal conductive filler. Surface modification of the boron nitride coating layer helps to improve the compatibility between the thermal conductive filler and the copper clad laminate.

[0042] In some embodiments, the mass ratio of the coupling agent to the activated powder having a boron nitride coating is 1% to 3%. For example, the mass ratio can be 1%, 2%, 3%, or any value within the range formed by any two of the above values.

[0043] In some embodiments, the coupling agent includes a silane coupling agent containing an amino group. Specifically, the silane coupling agent can be one of KH550, KH792, and KH602, or a mixture of several thereof.

[0044] In some embodiments, the organic solvent is ethanol.

[0045] In some embodiments, the stirring temperature of the activated powder having a boron nitride coating, the organic solvent and the coupling agent is 50° C. to 70° C., and the stirring time is 3 h to 5 h. For example, the stirring temperature can be 50° C., 60° C., 70° C., or any value within the range of any two of the above values. The stirring time can be 3 h, 4 h, 5 h, or any value within the range of any two of the above values.

[0046] Compared with the prior art, the thermally conductive filler provided in the embodiment of the present application has the following beneficial effects: by first activating the surface of silicon micropowder, forming a precursor coating on the surface of silicon micropowder by a sol-gel method, and then converting the precursor coating into a boron nitride coating by a chemical vapor deposition method, and finally modifying the boron nitride coated on the surface of silicon micropowder, a thermally conductive filler with a stable structure is finally obtained. The dielectric anisotropy is reduced by directional arrangement of the boron nitride crystal plane. Moreover, the thickness of the boron nitride coated on the surface is controllable without using a catalyst, and the comprehensive performance of low dielectric constant, low dielectric loss, high thermal conductivity and low water absorption is achieved.

[0047] The embodiment of the present application also provides a thermally conductive filler, which is prepared by the above-mentioned preparation method. The thermally conductive filler includes a core and a coating provided on at least a portion of the surface of the core, the core includes silicon micropowder, and the coating includes boron nitride.

[0048] In the thermal conductive filler of the present application, silicon powder and boron nitride form a specific structural relationship, which is conducive to better combining the advantages of silicon powder insulation and boron nitride high thermal conductivity, low dielectric constant, etc. Silicon powder and boron nitride can more fully realize the complementary optimization of the performance of the two materials through the preset structural relationship compound; wherein, the hydroxyl group on the surface of silicon powder is conducive to enhancing the binding force between the hollow silicon powder in the core and the boron nitride of the coating, making the structure of the thermal conductive filler more stable. Applied in copper clad laminates, it is conducive to improving the insulation performance of copper clad laminates, reducing signal transmission loss, and meeting high-frequency and high-speed communication requirements. At the same time, it is also conducive to improving thermal conductivity, better improving thermal stability, reducing thermal expansion coefficient, reducing warping and delamination, and can also enhance the mechanical strength of copper clad laminates and improve their anti-deformation ability. In addition, the present application performs surface modification on the coating layer boron nitride, and the thermal conductive filler has good binding properties with the resin matrix of the copper clad laminate, which is conducive to improving the compatibility of the interface between the copper clad laminate filler and the resin matrix, thereby helping to better improve the comprehensive performance of the copper clad laminate.

[0049] In some embodiments, the mass ratio of boron nitride to silicon powder is 5% to 15%. For example, the mass ratio of boron nitride to silicon powder can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any value within the range formed by any two of the above values. Controlling the mass ratio of boron nitride to silicon powder within the above range is conducive to better exerting the advantages of silicon powder and boron nitride, and more fully realizing the complementary optimization of the performance of the two materials, thereby helping to improve the performance of the thermal conductive filler.

[0050] In some embodiments, the boron nitride includes hexagonal boron nitride. The coating of the thermal conductive filler can be selected from the above-mentioned types of boron nitride, which can achieve the effect of complementary optimization of material properties, and the coating is conducive to improving the thermal conductivity and thermal stability of the copper clad laminate.

[0051] The embodiment of the present application also provides a copper clad laminate, which is a laminated copper foil layer and a dielectric layer. The dielectric layer includes the aforementioned thermal conductive filler. The thermal conductive filler of the present application has good bonding with the copper clad laminate resin, which is beneficial to improving the compatibility of the interface between the copper clad laminate filler and the resin matrix. Therefore, the copper clad laminate whose dielectric layer includes the thermal conductive filler has improved comprehensive performance.

[0052] The scheme of the present application will be explained below in conjunction with the embodiments. Those skilled in the art will understand that the following examples are only used to explain the present application and cannot be construed as limiting the present application. Unless otherwise stated, the reagents, software and instruments not specifically stated in the following embodiments are all conventional commercial products or open source.

[0053] Example 1

[0054] (1) The preparation method of the thermally conductive filler comprises:

[0055] Step S1, taking 20 portions of hollow spherical silicon powder with a particle size of 5 μm, placing them in a 5% sodium hydroxide solution for ultrasonic treatment for 30 minutes, and centrifugally drying them after the reaction to obtain activated powder.

[0056] Step S2, mixing boric acid and urea to obtain a mixed solution, immersing the above-mentioned activated powder in a boric acid-urea mixed solution at a mass ratio of 10%-20%, wherein the molar ratio of boric acid to urea is 1:3, heating to 120°C to allow the surface of the activated powder to self-assemble to form a precursor layer, and introducing a reaction gas of hydrogen and nitrogen in a volume ratio of 1:9 into a tubular furnace, reacting at a temperature of 950°C for 2h to obtain an activated powder with a boron nitride coating layer.

[0057] Step S3, dispersing the activated powder with a boron nitride coating layer in an ethanol solution, adding 2 wt % of a silane coupling agent KH792 for surface modification, stirring and reacting at 60° C. for 4 h, filtering and drying after the reaction to obtain a thermal conductive filler.

[0058] (2) The method for preparing the copper clad laminate comprises:

[0059] The first step: fully mix the synthesized thermal conductive filler and the PTFE emulsion to obtain co-coagulation powder.

[0060] Step 2: The co-coagulated powder is subjected to aging, extrusion and calendaring to obtain a raw base film (i.e., a dielectric layer).

[0061] Step 3: Copper foils are coated on both sides of the raw base film and vacuum pressed at high temperature to obtain a copper clad laminate.

[0062] Example 2

[0063] (1) Preparation of thermally conductive filler, the preparation method comprising:

[0064] Step S1, taking 20 portions of hollow spherical silicon powder with a particle size of 8 μm, placing them in a 10% hydrochloric acid solution for ultrasonic treatment for 30 minutes, and centrifugally drying after the reaction to obtain activated powder.

[0065] Step S2, mixing boric acid and urea to obtain a mixed solution, immersing the above-mentioned activated powder in a boric acid-urea mixed solution at a mass ratio of 10%-20%, wherein the molar ratio of boric acid to urea is 1:4, heating to 120°C to allow the surface of the activated powder to self-assemble to form a precursor coating, and introducing a reaction gas of hydrogen and nitrogen in a volume ratio of 1:9 into a tubular furnace, reacting at a temperature of 920°C for 3h to obtain an activated powder with a boron nitride coating layer.

[0066] Step S3, dispersing the activated powder with a boron nitride coating layer in an ethanol solution, adding 2 wt % of a silane coupling agent KH792 for surface modification, stirring and reacting at 60° C. for 4 h, filtering and drying after the reaction to obtain a thermal conductive filler.

[0067] (2) A copper clad laminate, the preparation method of which is basically the same as that of Example 1.

[0068] Example 3

[0069] (1) Preparation of thermally conductive filler, the preparation method comprising:

[0070] Step S1, taking 20 portions of hollow spherical silicon powder with a particle size of 5 μm, placing them in a 10% hydrochloric acid solution for ultrasonic treatment for 30 minutes, and centrifugally drying after the reaction to obtain activated powder.

[0071] Step S2, mixing boric acid and urea to obtain a mixed solution, immersing the above-mentioned activated powder in a boric acid-urea mixed solution at a mass ratio of 10%-20%, wherein the molar ratio of boric acid to urea is 1:3, heating to 120°C to allow the surface of the activated powder to self-assemble to form a precursor coating, and introducing a reaction gas of hydrogen and nitrogen in a volume ratio of 1:9 into a tubular furnace, reacting at a temperature of 920°C for 3h to obtain an activated powder with a boron nitride coating layer.

[0072] Step S3, dispersing the activated powder with a boron nitride coating layer in an ethanol solution, adding 1wt% of silane coupling agent KH792 and 1wt% of silane coupling agent KH602, stirring and reacting at 60°C for 4h, filtering and drying after the reaction to obtain a thermal conductive filler.

[0073] (2) A copper clad laminate, the preparation method of which is basically the same as that of Example 1.

[0074] Comparative Example 1:

[0075] A conventional copper clad laminate, the preparation method of which comprises:

[0076] The first step is to adjust the glue: add bisphenol A epoxy resin into the reactor, heat it to 50℃ to 70℃, stir it to make it completely dissolved, add curing agent, initiator, and flame retardant in turn, and continue stirring for 30 minutes to 60 minutes. The speed is controlled at 50r / min to 300r / min to ensure that the additives are evenly dispersed to form a uniform and stable epoxy resin glue solution, among which the curing agent accounts for 5% to 15% of the epoxy resin mass percentage, the accelerator accounts for 0.5% to 3%, and the flame retardant accounts for 10% to 30%.

[0077] The second step is to dip the glass fiber cloth into the epoxy resin glue and control the dipping speed from 0.5m / min to 2m / min to ensure sufficient dipping.

[0078] The third step is scraping glue and drying: Use a scraper or squeeze roller to remove excess glue on the surface of the glass fiber cloth to control the resin content of the prepreg to 40% to 60%. Then send it to the drying furnace and dry it at 120℃ to 150℃ for 10 minutes to 30 minutes to fully volatilize the solvent to obtain a prepreg.

[0079] Step 4: Lamination: Laminating the copper foils on both sides of the prepreg obtained above by high temperature vacuum lamination to obtain a copper clad laminate.

[0080] Comparative Example 2

[0081] (1) The preparation of the thermally conductive filler differs from that of Example 1 in that the hollow silicon micropowder and the flaky boron nitride are directly mixed by mechanical stirring without going through step S1 and step S2, with a mass ratio of 3:1, and the remaining steps are consistent with those of Example 1.

[0082] (2) A copper clad laminate, the preparation method of which is basically the same as that of Example 1.

[0083] The present application also conducted the following performance tests on the copper clad laminates of Examples 1-3 and Comparative Examples 1-2:

[0084] (1) Dielectric constant and dielectric loss factor test: The dielectric properties are tested using the Split Cylindrical Resonator (SPDR) method (a standard of the American Society for Testing and Materials, method number ASTM2520). First, connect the 10 GHz test fixture to the network analyzer and measure the center frequency f of the cavity. c And the quality factor Q c Then, insert the sample and measure the center frequency f again after loading the sample. s And the loaded quality factor Q s . Then through the following formula:

[0085]

[0086] Calculate the dielectric constant and dielectric loss, where f c is the center frequency of the cavity, f s is the center frequency of the sample, Q c is the cavity quality factor, Q s is the sample quality factor, V c is the volume of the cavity, V s is the volume of the sample.

[0087] (2) Thermal expansion coefficient test: Thermomechanical analysis method, IPC TM 650 2.4.24.4 (-55~288℃), the thermal mechanical analyzer heats the sample and calculates the thermal expansion coefficient α by measuring the change in length of the sample at different temperatures. i :

[0088]

[0089] Among them, α i It is the thermal expansion coefficient of the material in the i direction (i = X, Y, Z), in ppm / ℃, ΔL i It is the change in length of the material in the i direction (i = X, Y, Z), in μm, L 0i is the initial length of the material in the i direction (i=X, Y, Z), in meters, and ΔT is the change in temperature, in degrees Celsius.

[0090] (3) Thermal conductivity test: Using the steady-state heat flow method, a certain heat flow (heat flow output is detected by a heat flow sensor) and pressure are applied to the sample above and below the sample, and the thickness of the sample and the temperature difference between the hot plate and the cold plate are tested to obtain the thermal conductivity λ of the sample:

[0091]

[0092] Where λ is the thermal conductivity of the sample in W / Mk, Q h is the heat flux output of the upper sensor in W / m 2 , Q c is the heat flux output of the lower sensor in W / m 2 , L is the thickness of the sample, in m, and ΔT is the temperature difference between the upper and lower surfaces of the sample, in K.

[0093] (4) Peel strength test:

[0094] ① Sample preparation: Cut a sample with a length of 120 mm and a width of 70 mm from the area 2.54 mm or more from the edge of the laminated copper clad board, stick an anti-corrosion tape on the sample, and use ferric chloride etching solution to make three test strips with a width of 3.18 mm and a length of 100 mm in the sample area.

[0095] ② Sample measurement: Use a universal testing machine, with the copper foil side of the test strip facing up, align the test strip with the center of the sample holder, place the pinhole plate on the test strip, place the clamping head in the hole, align the copper foil strip with the inclined slot, clamp the copper foil strip with the sample clamp, make the peeling direction 90 degrees to the insulating substrate, and start peeling at a rate of 50.8mm / min.

[0096] ③ Calculate the peel strength: Peel strength = minimum peel force / sample width.

[0097] Please refer to Table 1 for the above test results.

[0098] Table 1. Performance test results of copper clad laminates of Examples 1-3 and Comparative Examples 1-2 of the present application

[0099]

[0100]

[0101] Embodiments 1-3 of the present application are first activated on the surface of silicon micropowder, then coated with boron nitride on the surface of silicon micropowder by chemical vapor deposition, and finally the boron nitride coated on the surface of silicon micropowder is modified to finally obtain a thermally conductive filler with a stable structure. The dielectric anisotropy is reduced by directional arrangement of the boron nitride crystal plane. The thickness of the surface-coated boron nitride is controllable without using a catalyst, and the comprehensive performance of low dielectric constant, low dielectric loss, high thermal conductivity and low water absorption is achieved. Therefore, the copper-clad laminate obtained by embodiments 1-3 of the present application improves insulation, and the signal transmission loss is low, which meets the requirements of high-frequency and high-speed communication. At the same time, it also has the comprehensive performance of low dielectric constant, low dielectric loss, high thermal conductivity and low water absorption.

[0102] Compared with Example 1, Comparative Example 1 is a traditional copper clad laminate, and its performance is obviously inferior to that of Example 1 of the present application, which shows that the application of the thermal conductive filler of the present application to the copper clad laminate can significantly improve the comprehensive performance of the copper clad laminate.

[0103] Compared with Example 1, the composite material of Comparative Example 2 simply mixes silicon micropowder with boron nitride, and the thermally conductive filler of the present application cannot be obtained. The performance of the copper-clad laminate obtained is not as good as that of Example 1 of the present application, indicating that the thermally conductive filler of the present application has good bonding with the copper-clad laminate resin, which is conducive to improving the compatibility of the interface between the copper-clad laminate filler and the resin matrix. Therefore, the copper-clad laminate in which the dielectric layer includes the thermally conductive filler has improved comprehensive performance. In the thermally conductive filler obtained by the preparation method of the present application, the surface of the silicon micropowder is first activated, and then the surface of the silicon micropowder is coated with boron nitride by chemical vapor deposition, and finally the boron nitride coated on the surface of the silicon micropowder is modified, and finally a thermally conductive filler with a stable structure is obtained. The dielectric anisotropy is reduced by directional arrangement of the boron nitride crystal plane, and the strength of the filler in the mixing process can also be improved. Moreover, the preparation process can realize the controllable thickness of the surface-coated boron nitride without using a catalyst, and realizes the comprehensive performance of having both low dielectric constant, low dielectric loss, high thermal conductivity and low water absorption.

[0104] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a thermally conductive filler, characterized in that: The preparation method comprises: Mixing silicon micropowder and activator and ultrasonically treating to activate the surface of silicon micropowder, and obtaining activated powder after drying; Mixing a boron-containing compound and a nitrogen-containing compound to obtain a mixed solution, mixing the activated powder with the mixed solution, and heating to form a precursor layer on the surface of the activated powder to obtain an intermediate solution; A nitrogen-containing reaction gas is introduced into the intermediate solution for chemical vapor deposition, so that the nitrogen-containing reaction gas reacts with the precursor layer to form a boron nitride coating layer on the surface of the activated powder, and the thermal conductive filler is obtained by drying.

2. The method for preparing the thermally conductive filler according to claim 1, characterized in that: The temperature of the chemical vapor deposition is 900° C. to 1000° C., and the reaction time is 2 h to 4 h.

3. The method for preparing the thermally conductive filler according to claim 1, characterized in that: The nitrogen-containing reaction gas includes hydrogen and nitrogen, wherein the volume proportion of the hydrogen in the nitrogen-containing reaction gas is 5% to 15%.

4. The method for preparing the thermally conductive filler according to claim 1, characterized in that: The activator includes any one of hydrochloric acid solution, nitric acid solution and sulfuric acid solution with a mass fraction of 5% to 15%; or any one of sodium hydroxide solution and potassium hydroxide solution with a mass fraction of 1% to 5%.

5. The method for preparing the thermally conductive filler according to claim 1, characterized in that: The preparation method satisfies at least one of the following conditions: (1) The mass ratio of the activator to the silicon powder is 2% to 10%; (2) the molar ratio of the boron-containing compound to the nitrogen-containing compound is 1:2 to 1:4; (3) The mass ratio of the mixed solution to the silicon powder is 10% to 20%; (4) The mass ratio of the coupling agent to the activated powder having the boron nitride coating layer is 1% to 3%.

6. The method for preparing the thermally conductive filler according to claim 1, characterized in that: The boron-containing compound includes one or more of boric acid, boron chloride and sodium borate tetradecahydrate, and the nitrogen-containing compound includes one or more of urea, melamine, hexamethylenetetramine, ethylenediamine and ammonia water.

7. The method for preparing a thermally conductive filler according to claim 1, characterized in that: After the chemical vapor deposition, the preparation method further comprises: The thermally conductive filler is mixed with a coupling agent, wherein the coupling agent includes a silane coupling agent containing an amino group.

8. A thermally conductive filler, characterized in that: The thermally conductive filler is prepared by the preparation method according to any one of claims 1 to 7, wherein the thermally conductive filler comprises a core and a coating layer provided on at least a portion of the surface of the core, the core comprises silicon powder, and the coating layer comprises boron nitride.

9. The thermally conductive filler according to claim 8, characterized in that: The thermally conductive filler satisfies at least one of the following conditions: (1) The mass ratio of the boron nitride to the silicon powder is 5% to 15%; (2) The boron nitride includes hexagonal boron nitride.

10. A copper-clad laminate, comprising a copper foil layer and a dielectric layer stacked together, characterized in that: The dielectric layer includes the thermally conductive filler as claimed in claim 8 or 9.

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