Low dielectric constant high thermal conductivity composite powder, and preparation method and use thereof

Abstract

The application discloses a kind of low dielectric constant high thermal conductivity composite powder and its preparation method and use.The composite powder is micron grade particle, the micron grade particle has core-shell structure, with silica microsphere as core layer, with alumina as shell layer, and the alumina includes alpha-Al2O3.The composite powder of the application has core-shell structure, a continuous dense alpha-Al2O3 film is coated on the surface of silica microsphere, which can improve the thermal conductivity and volume resistivity while ensuring the low dielectric constant, low dielectric loss characteristics of silica microsphere, can meet the requirements of high heat dissipation, high insulation, low dielectric constant and low dielectric loss required by subsequent microelectronic substrate, and is suitable for 5G / 6G high frequency high speed copper clad plate, chip packaging and other application fields.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a composite powder with low dielectric constant and high thermal conductivity, its preparation method, and its applications. Background Technology

[0002] With the breakthrough development of microelectronics integration technology, the integration and complexity of electronic components have increased dramatically. Modern electronic devices are gradually trending towards higher power, miniaturization, thinner and lighter designs, greater intelligence, and enhanced functionality. The development of the electronic information industry largely depends on large-scale integrated circuit (LSI) and very large-scale integrated circuit (VLSI) packaging technologies. High frequency, high speed, and high thermal conductivity are essential requirements for chip packaging in next-generation high-frequency communication. Polymer composite materials are one of the three main materials for back-end packaging of integrated circuits. Epoxy molding compounds have become the mainstream for packaging VLSIs both domestically and internationally, with over 95% of microelectronic devices being plastic-encapsulated devices. In the composition of epoxy molding compounds, inorganic powder fillers account for 70%–90% of the total weight, in addition to the epoxy resin matrix.

[0003] Spherical fused silica powder made from high-purity quartz or spherical silica prepared by chemical synthesis has become an irreplaceable key functional filler in epoxy molding compounds due to its low dielectric constant, low dielectric loss, and low linear expansion coefficient, which match the requirements of high-frequency and high-speed technologies. However, the thermal conductivity of high-purity spherical silica (1.2 W / (m·K)) is poor, making it difficult for electronic packaging materials to meet the requirements of next-generation high-frequency communication for efficient chip heat dissipation. The thermal conductivity of composite powders is usually improved by introducing high thermal conductivity fillers. Currently, thermally conductive fillers are mainly carbon-based materials and metallic materials, such as graphene, carbon nanotubes, silver / silver nanowires, and copper / copper nanowires. However, most of these materials are conductive, and under high loads, they inevitably reduce the low dielectric and high insulation properties of the composite powder. Furthermore, carbon-based materials such as graphene or carbon nanotubes have significant drawbacks in polymer matrices, such as poor dispersibility and high viscosity. Therefore, these fillers are not the preferred materials in the field of thermal conductivity and insulation. However, ceramic materials possess excellent properties of high thermal conductivity and high insulation. Currently, the most commonly used ceramic materials on the market are α-alumina, aluminum nitride, and boron nitride. Aluminum nitride readily hydrolyzes to produce aluminum hydroxide, resulting in a significant decrease in thermal conductivity. Boron nitride, due to its strong surface inertness, has poor affinity with resins, severely affecting the overall performance of the composite powder. α-alumina, with its excellent properties such as high thermal conductivity, low dielectric constant, and high volume resistivity, as well as its simple preparation process and high cost-effectiveness, is an ideal choice for inorganic fillers in high-performance electronic packaging.

[0004] However, the current binary mixed filler system using high-purity spherical silica powder / spherical α-alumina has interfacial polarization and interfacial thermal resistance effects caused by the multiphase interface and the difference in filler modulus. Although the thermal conductivity of the binary mixed filler system is improved, the excellent low dielectric constant of high-purity silica is sacrificed.

[0005] Therefore, there is a need to provide a composite powder material that combines low dielectric constant and high thermal conductivity, while also possessing the advantages of both low dielectric constant and high thermal conductivity. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a composite powder with low dielectric constant and high thermal conductivity, its preparation method and application, so as to solve the problem that it is difficult to simultaneously achieve low dielectric constant and high thermal conductivity in the composite powder materials of the prior art.

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

[0008] The first aspect of the present invention protects a composite powder with low dielectric constant and high thermal conductivity, wherein the composite powder is micron-sized particles, the micron-sized particles having a core-shell structure, with silica microspheres as the core layer and alumina as the shell layer, wherein the alumina contains α-Al2O3.

[0009] The low dielectric constant and high thermal conductivity composite powder of the present invention has a core-shell structure, in which a continuous and dense α-Al₂O₃ film is coated on the surface of silica microspheres. This ensures that the composite powder possesses the low dielectric constant and low dielectric loss characteristics of silica microspheres, while also exhibiting the high thermal conductivity and high volume resistivity of alumina. The composite powder material of the present invention can meet the requirements of high heat dissipation, high insulation, low dielectric constant, and low dielectric loss for subsequent microelectronic substrates, and is suitable for applications such as 5G / 6G high-frequency and high-speed copper-clad laminates and chip packaging.

[0010] Preferably, the D of the silica microspheres 50 (50% average particle size) Particle size can be 0.5–3.5 μm, or 0.5–3.5 μm, or 3.5 μm, 1.0 μm, or 2.2 μm. D 50 It refers to the particle size corresponding to a cumulative particle size distribution percentage of 50%.

[0011] Preferably, the thickness of the shell layer can be 10-150nm, 10-85nm, 80-120nm, 100-150nm, or 150nm, 120nm, 100nm, or 80nm.

[0012] Preferably, the alumina is formed by calcining an alumina precursor.

[0013] More preferably, the alumina precursor is selected from fusiform boehmite.

[0014] More preferably, the calcination temperature is 900–1200°C, or 900–1000°C, or 950–1100°C, or 1050–1200°C, specifically 900°C.

[0015] More preferably, the calcination time can typically be 1–6 hours, or 1–3 hours, or 2–5 hours, or 4–6 hours, specifically 3 hours.

[0016] More preferably, the preparation method of the spindle-shaped boehmite is as follows: under the action of a surfactant, an aluminum source and an ammonium salt undergo a hydrothermal reaction in water, followed by drying. The ammonium salt and aluminum source of this application can be processed in a one-step hydrothermal method using a surfactant to obtain a high-purity, highly crystalline spindle-shaped boehmite material with uniform morphology and size, exhibiting a spindle-shaped structure that is wider in the middle and narrower at both ends, with an average length of 500–800 nm and a width of approximately 100–200 nm.

[0017] More preferably, the temperature of the hydrothermal reaction can typically be 120–180°C, or 120–150°C, or 140–170°C, or 150–180°C, specifically 150°C, 120°C, 180°C, 160°C, or 170°C.

[0018] More preferably, the hydrothermal reaction time can typically be 12–24 h, 12–18 h, 16–20 h, or 17–24 h, specifically 24 h, 12 h, 20 h, or 18 h.

[0019] More preferably, the drying temperature is 50-100℃, or 50-65℃, or 60-75℃, or 65-80℃, or 75-90℃, or 80-100℃, specifically 80℃.

[0020] More preferably, the drying time can typically be 8–24 hours, or 8–16 hours, or 14–20 hours, or 17–24 hours, specifically 12 hours, 20 hours, or 18 hours.

[0021] Further preferably, the hydrothermal reaction includes solid-liquid separation and washing. The solid-liquid separation is filtration, and the washing uses water or ethanol as the detergent. Specifically, washing is performed at least once with water and once with ethanol, such as twice or three times, which can be selected by those skilled in the art according to actual needs.

[0022] More preferably, the aluminum source is selected from aluminum nitrate.

[0023] More preferably, the ammonium salt is selected from urea.

[0024] More preferably, the mass ratio of the aluminum source to the ammonium salt can typically be (1-10):1, (2-8):1, (1-5):1, (3-7):1, or (4-10):1, specifically 4.26:2.16, 8.2:1, or 1.5:1.

[0025] More preferably, the mass ratio of the aluminum source to the surfactant is typically (2-4):1, or (2-2.5):1, or (2.2-3.5):1, or (3.1-4):1, specifically 4.26:1.5, 3.8:1, or 2:1.

[0026] More preferably, the surfactant is selected from one or more of PEG-600 and PEG-4000.

[0027] More preferably, the mass ratio of PEG-600 to PEG-4000 is 1:(1-5), or it can be 1:(1-2.6), or it can be 1:(2.2-3.6), or it can be 1:(3.2-5), specifically 1:2, 1:5, or 1:1.

[0028] In one specific embodiment, an aluminum source and water are mixed, an ammonium salt is added, and then a surfactant is added to carry out a hydrothermal reaction.

[0029] Preferably, the silica microspheres are derived from silica powder, which is selected from fused silica powder or chemically synthesized silica.

[0030] More preferably, the fused silica powder comprises spherical fused silica powder, and the chemically synthesized silica comprises spherical silica.

[0031] More preferably, the SiO2 content in the fused silica powder is ≥99.995%, and the SiO2 content in the chemically synthesized silicon dioxide is ≥99.9999%.

[0032] The fused silica powder or chemically synthesized silica used in this invention are both known products. The spherical fused silica powder is an amorphous form of silica (quartz, silicon), produced by melting natural high-purity quartz at a temperature above 1760°C, followed by rapid cooling. During this process, crystalline silica is transformed into an amorphous glass melt. In one specific embodiment, the fused silica powder is prepared from angular quartz powder using a flame spheroidization process, with the suspension spheroidization temperature above 2500°C during the preparation process.

[0033] The chemically synthesized silica in this invention refers to silica synthesized using chemical methods, which typically involve reacting a silicon source with other reactive materials under appropriate, artificially controlled conditions to obtain chemically synthesized silica. Chemically synthesized silica may include, but is not limited to, silica melting methods, sol-gel methods, gas-phase methods, and hydrothermal methods. Other steps and conditions involved in the synthesis of chemically synthesized silica applicable to this invention can be determined by those skilled in the art without excessive experimentation. In one embodiment, the sol-gel method involves: dissolving a silicon source in an organic solvent to form a colloidal solution; then, through hydrolysis and condensation reactions, gradually polymerizing the silicon source in the colloidal solution into a silica gel; finally, heat-treating the gel to remove organic matter, obtaining chemically synthesized silica. The silicon source includes, but is not limited to, silanols, silicates, methyl silicate, propyl silicate, etc., and the organic solvent includes, but is not limited to, ethanol. A specific embodiment involves: adding alcohol, water, and concentrated ammonia to a container; after the solution is mixed evenly, adding a mixture of tetraethyl orthosilicate and alcohol dropwise, reacting to obtain chemically synthesized silica. More specifically, the chemically synthesized silica may be purchased from, for example, but not limited to, spherical silica sold by Glass New Materials Innovation Center (Anhui) Co., Ltd.

[0034] The second aspect of this invention protects a method for preparing the composite powder as described above, comprising the following:

[0035] The alumina precursor and silica powder were ball-milled and calcined to obtain the composite powder.

[0036] This application uses ball milling to generate numerous defects and dangling bonds on the surface of the alumina precursor, namely fusiform boehmite, thus accumulating a large amount of surface energy. The greater the surface energy, the more effectively the phase transition temperature of α-Al2O3 can be reduced. Furthermore, ball milling creates a distinct interface at the core-shell junction of the micron-sized particles in the composite powder. The interface has a large surface energy, which is conducive to phase transition and induces the transformation of fusiform boehmite (γ-AlOOH) into α-Al2O3, while effectively reducing the phase transition temperature of α-Al2O3.

[0037] Preferably, the volume ratio of the alumina precursor to the silica powder can be (10-3):1, (6.2-3):1, (7.5-4.5):1, (10-6):1, or 3:1, 4:1, 6:1, 7:1, 8:1, or 10:1.

[0038] Preferably, during ball milling, the rotation speed can typically be 50–200 rpm, or 50–100 rpm, or 80–180 rpm, or 160–200 rpm, specifically 100 rpm.

[0039] Preferably, the ball milling time can be 30-60 min, 30-45 min, 40-55 min, or 50-60 min, specifically 45 min.

[0040] Preferably, during ball milling, the ball-to-material ratio is (3-5)g:1g.

[0041] Preferably, the milling media is quartz glass balls.

[0042] More preferably, the quartz glass sphere is selected from one or more of glass spheres with a diameter of 8 mm, 5 mm, and 3 mm.

[0043] More preferably, the mass ratio of the glass spheres with a diameter of 8 mm, 5 mm, and 3 mm is 3:(1-5):1.

[0044] Preferably, the calcination temperature can be 900-1200℃, 900-1000℃, 950-1100℃, or 1050-1200℃, specifically 900℃.

[0045] Preferably, the calcination time can typically be 1-6 hours, 1-3 hours, 2-5 hours, or 4-6 hours, specifically 3 hours.

[0046] Preferably, the silica powder is selected from fused silica powder or chemically synthesized silica.

[0047] More preferably, the fused silica powder comprises spherical fused silica powder, and the chemically synthesized silica comprises spherical silica.

[0048] More preferably, the SiO2 content in the fused silica powder is ≥99.995%, and the SiO2 content in the chemically synthesized silicon dioxide is ≥99.9999%.

[0049] The fused silica powder or chemically synthesized silica used in this invention are both known products. The spherical fused silica powder is an amorphous form of silica (quartz, silicon), produced by melting natural high-purity quartz at a temperature above 1760°C, followed by rapid cooling. During this process, crystalline silica is transformed into an amorphous glass melt. In one specific embodiment, the fused silica powder is prepared from angular quartz powder using a flame spheroidization process, with the suspension spheroidization temperature above 2500°C during the preparation process.

[0050] The chemically synthesized silica in this invention refers to silica synthesized using chemical methods, which typically involve reacting a silicon source with other reactive materials under appropriate, artificially controlled conditions to obtain chemically synthesized silica. Chemically synthesized silica may include, but is not limited to, silica melting methods, sol-gel methods, gas-phase methods, and hydrothermal methods. Other steps and conditions involved in the synthesis of chemically synthesized silica applicable to this invention can be determined by those skilled in the art without excessive experimentation. In one embodiment, the sol-gel method involves: dissolving a silicon source in an organic solvent to form a colloidal solution; then, through hydrolysis and condensation reactions, gradually polymerizing the silicon source in the colloidal solution into a silica gel; finally, heat-treating the gel to remove organic matter, obtaining chemically synthesized silica. The silicon source includes, but is not limited to, silanols, silicates, methyl silicate, propyl silicate, etc., and the organic solvent includes, but is not limited to, ethanol. A specific embodiment involves: adding alcohol, water, and concentrated ammonia to a container; after the solution is mixed evenly, adding a mixture of tetraethyl orthosilicate and alcohol dropwise, reacting to obtain chemically synthesized silica. More specifically, the chemically synthesized silica may be purchased from, for example, but not limited to, spherical silica sold by Glass New Materials Innovation Center (Anhui) Co., Ltd.

[0051] Preferably, the alumina precursor is selected from fusiform boehmite.

[0052] More preferably, the preparation method of the spindle-shaped boehmite is as follows: under the action of a surfactant, an aluminum source and an ammonium salt undergo a hydrothermal reaction in water, followed by drying. The ammonium salt and aluminum source of this application can be processed in a one-step hydrothermal method using a surfactant to obtain a high-purity, highly crystalline spindle-shaped boehmite material with uniform morphology and size, exhibiting a spindle-shaped structure that is wider in the middle and narrower at both ends, with an average length of 500–800 nm and a width of approximately 100–200 nm.

[0053] More preferably, the temperature of the hydrothermal reaction can typically be 120–180°C, or 120–150°C, or 140–170°C, or 150–180°C, specifically 150°C, 120°C, 180°C, 160°C, or 170°C.

[0054] More preferably, the hydrothermal reaction time can typically be 12–24 h, 12–18 h, 16–20 h, or 17–24 h, specifically 24 h, 12 h, 20 h, or 18 h.

[0055] More preferably, the drying temperature is 50-100℃, or 50-65℃, or 60-75℃, or 65-80℃, or 75-90℃, or 80-100℃, specifically 80℃.

[0056] More preferably, the drying time can typically be 8–24 hours, or 8–16 hours, or 14–20 hours, or 17–24 hours, specifically 12 hours, 20 hours, or 18 hours.

[0057] Further preferably, the hydrothermal reaction includes solid-liquid separation and washing. The solid-liquid separation is filtration, and the washing uses water or ethanol as the detergent. Specifically, washing is performed at least once with water and once with ethanol, such as twice or three times, which can be selected by those skilled in the art according to actual needs.

[0058] More preferably, the aluminum source is selected from aluminum nitrate.

[0059] More preferably, the ammonium salt is selected from urea.

[0060] More preferably, the mass ratio of the aluminum source to the ammonium salt can typically be (1-10):1, (2-8):1, (1-5):1, (3-7):1, or (4-10):1, specifically 4.26:2.16, 8.2:1, or 1.5:1.

[0061] More preferably, the mass ratio of the aluminum source to the surfactant is typically (2-4):1, or (2-2.5):1, or (2.2-3.5):1, or (3.1-4):1, specifically 4.26:1.5, 3.8:1, or 2:1.

[0062] More preferably, the surfactant is selected from one or more of PEG-600 and PEG-4000.

[0063] More preferably, the mass ratio of PEG-600 to PEG-4000 is 1:(1-5), or it can be 1:(1-2.6), or it can be 1:(2.2-3.6), or it can be 1:(3.2-5), specifically 1:2, 1:5, or 1:1.

[0064] In one specific embodiment, an aluminum source and water are mixed, an ammonium salt is added, and then a surfactant is added.

[0065] A third aspect of the present invention protects a polymer composite material comprising the composite powder and the polymer as described above.

[0066] Preferably, the polymer is selected from one or more of epoxy resin, polytetrafluoroethylene (PTFE) resin, polyimide resin, bismaleimide (BMI) resin, polyphenylene oxide (PPO) resin, and polyolefin resin.

[0067] More preferably, the polymer is an epoxy resin.

[0068] More preferably, the epoxy resin has an epoxy value of 0.48–0.54 eq / 100g. Specifically, it is bisphenol A type E-51 epoxy resin.

[0069] Preferably, the filling amount of the composite powder is 10-60 vol%, based on the total volume of the polymer composite material.

[0070] Preferably, it also includes a curing agent. The curing agent is selected from dicyandiamide.

[0071] Preferably, it also includes an accelerator. The curing agent is selected from 2-ethyl-4-methylimidazole.

[0072] The polymer composite material of the present invention has a thermal conductivity of 0.578–1.034 W / (m·K) and a volume resistivity of 2.11–8.04 × 10⁻⁶. 14 Ω·cm and superior to ordinary insulating materials (the volume resistivity of ordinary insulating materials is ≥1×10 Ω·cm). 9 With a dielectric constant of 4.16–4.25 (1MHz) and a dielectric loss of 0.0148–0.0182, it can ensure good heat dissipation and insulation performance when used in 5G / 6G high-frequency and high-speed copper-clad laminates and chip packaging. In addition, its dielectric constant is low, ranging from 4.16 to 4.25, and its dielectric loss is low, ranging from 0.0148 to 0.0182, which can meet the requirements of microelectronic substrates and is suitable for applications such as 5G / 6G high-frequency and high-speed copper-clad laminates and chip packaging.

[0073] The processing and molding method of the composite material described above includes the following steps: The composite powder, polymer, fixative, and curing accelerator described above are stirred in a solvent, and a first curing is performed at 160–180°C, followed by a second curing at 140–160°C. The first curing time is 0.5–1.5 hours, and the second curing time is 2–4 hours. In one specific embodiment, after stirring the composite powder, polymer, fixative, and curing agent in a solvent, a first curing is performed at 170°C for 1 hour, followed by a second curing at 150°C for 3 hours.

[0074] The fourth aspect of this invention protects the use of the composite powder or polymer composite material described above in 5G / 6G communication and semiconductor chip packaging.

[0075] The essence of 5G / 6G communication technology is to process and transmit large-capacity signals at high frequencies (above 3GHz). High-frequency copper-clad laminates used in printed circuit boards are key components of 5G communication. High-frequency and high-speed copper-clad laminates generally require good thermal performance, typically requiring a thermal decomposition temperature above 400℃, a glass transition temperature above 180℃, a high thermal conductivity, and a low coefficient of thermal expansion.

[0076] The composite powder and polymer composite materials of the present invention have the characteristics of low dielectric constant, low dielectric loss, high thermal conductivity and high volume resistivity, and can be used as irreplaceable key functional fillers in the composition of epoxy molding compounds for 5G / 6G communication or high-frequency and high-speed copper clad laminates.

[0077] Compared with the prior art, the present invention has the following beneficial effects:

[0078] 1) This invention uses a one-step hydrothermal synthesis method to prepare high-purity, high-crystallinity spindle-shaped boehmite material.

[0079] 2) The composite powder of the present invention, through ball milling and coating, generates a large number of defects and dangling bonds on the surface of the alumina precursor spindle boehmite (γ-AlOOH), accumulating a large amount of surface energy. The greater the surface energy, the more effectively the phase transition temperature of α-Al2O3 is reduced.

[0080] 3) The composite powder of the present invention has a core-shell structure with a clear interface at the core-shell junction. The surface energy at the interface is large, which is conducive to phase transformation and induces the transformation of fusiform boehmite (γ-AlOOH) into α-Al2O3, further reducing the phase transformation temperature of α-Al2O3.

[0081] 4) Compared with the simple binary mixed filler system formed by silicon dioxide and alumina, the composite powder with core-shell structure of the present invention effectively reduces the interfacial polarization and interfacial thermal resistance effects caused by the multiphase interface and the difference in filler modulus.

[0082] 5) The composite powder of the present invention can achieve efficient optimization and control of dielectric and thermal conductivity by effectively adjusting the coating amount of α-alumina.

[0083] 6) The low dielectric constant and high thermal conductivity composite powder of the present invention has a core-shell structure and low dielectric constant and high thermal conductivity. It has insulation properties while providing high heat dissipation, and is especially suitable for applications such as high frequency and high speed copper clad laminates and chip packaging.

[0084] 7) The preparation method of the present invention is simple, easy to industrialize, and has broad application prospects. Attached Figure Description

[0085] Figure 1 The image shown is the XRD pattern of the spindle-shaped boehmite (γ-AlOOH) of this invention.

[0086] Figure 2 The images shown are SEM and TEM images of the fusiform boehmite (γ-AlOOH) of this invention.

[0087] Figure 3The image shown is a SEM image and elemental mapping image of the SiO2@α-Al2O3 composite powder in Example 3 of this invention.

[0088] Figure 4 The XRD patterns of SiO2 and SiO2@γ-AlOOH at different calcination temperatures are shown. Detailed Implementation

[0089] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0090] Before further describing specific embodiments of the present invention, it should be understood that the scope of protection of the present invention is not limited to the specific embodiments described below; it should also be understood that the terminology used in the embodiments of the present invention is for describing specific embodiments and not for limiting the scope of protection of the present invention. Test methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the respective manufacturers.

[0091] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. In addition to the specific methods, apparatus, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, apparatus, and materials similar to or equivalent to those described, apparatus, and materials in the embodiments of this invention may be used to implement the present invention.

[0092] In the following embodiments of this application, the fused silica powder is prepared by processing angular silica powder through a flame spheroidization process. Specifically, the angular silica powder is melted by a high-temperature flame to form small droplets, and then rapidly cooled to obtain spherical particles. The high temperature is 2500°C, and the SiO2 content is ≥99.9999%.

[0093] Example 1

[0094] This embodiment 1 provides a composite powder with low dielectric constant and high thermal conductivity, as well as a method for its preparation. The method includes the following steps:

[0095] 1) Synthesis of fusiform boehmite (abbreviated as γ-AlOOH)

[0096] Weigh 4.26 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O) (0.01 mol) and dissolve it in 35 mL of deionized water to prepare a 0.32 mol / L Al(NO3)3·9H2O solution. Then add 2.16 g of urea (CO(NH2)2) (0.04 mol). After it is completely dissolved, add 1.5 g of surfactant and stir on a magnetic stirrer for 45 min. Then pour the mixed solution into a 45 mL polytetrafluoroethylene hydrothermal reactor and hydrothermally react at 150 °C for 24 h. After natural cooling, filter and wash three times with deionized water and ethanol. Place it in an oven and dry at 80 °C for 12 h to obtain a white boehmite powder with a length of 300-400 nm.

[0097] The mass ratio of aluminum nitrate nonahydrate to urea is 4.26g:2.16g, and the molar ratio is 1:4. The surfactant is composed of PEG-600 and PEG-4000, and the mass ratio of surfactant to aluminum nitrate nonahydrate is 1.5g:4.26g. Among the surfactants, the mass ratio of PEG-600 to PEG-4000 is 1:2.

[0098] 2) Ball mill

[0099] Spherical fused silica powder and the spindle-shaped boehmite obtained in step 1) were added to a polytetrafluoroethylene high-energy ball mill jar. The grinding balls were quartz glass balls, the ball-to-material ratio was 3g:1g, the ball milling speed was 100rpm, and the ball milling time was 45min, to obtain a white SiO2@γ-AlOOH powder material. The spherical fused silica powder and spindle-shaped boehmite were ball-milled at a volume ratio of 10:1.

[0100] The quartz glass spheres consist of quartz glass spheres with diameters of 8mm, 5mm, and 3mm, in a mass ratio of 1:1:1.

[0101] 3) Calcination

[0102] The SiO2@γ-AlOOH white powder material from step 2) was placed in a muffle furnace and calcined at 1050℃ for 3 hours to obtain SiO2@α-Al2O3 white powder material, which is a composite powder with low dielectric constant and high thermal conductivity.

[0103] The fusiform boehmite synthesized in step 1) was characterized by XRD, SEM, and TEM. XRD data can be found in the figure below. Figure 1 SEM and TEM are shown. Figure 2 .

[0104] XRD characterization: The experimental raw materials and samples were characterized by phase analysis using a Burker D8 Advance X-ray diffractometer (XRD) from Germany. During the test, Cu Kα target material was used, with an accelerating voltage of 40 kV and a current of 250 mA. The diffraction angle range was 5–80°, and the diffraction target was Cu-Ka.

[0105] TEM characterization: The microstructure, crystal structure, and elemental distribution of the samples were characterized and analyzed using a Thermo Fisher JEOL JEM-2100F field emission transmission electron microscope (TEM) and an Oxford X-Max 20mm² energy dispersive spectrometer (EDX). The operating voltage during testing was 200kV.

[0106] from Figure 1 It can be seen that the synthesized spindle-shaped boehmite is a highly crystalline boehmite.

[0107] from Figure 2 It can be seen that the synthesized spindle-shaped boehmite has a uniform morphology and size, and is a spindle-shaped structure that is wide in the middle and narrow at both ends, with an average length of 500-800 nm and a width of about 100-200 nm.

[0108] In this embodiment, the low dielectric constant and high thermal conductivity composite powder consists of micron-sized particles with a core-shell structure and a D-type silica microsphere core layer. 50 The particle size is 3.5 μm, the thickness of the alumina shell is 150 nm, and the alumina contains α-Al2O3.

[0109] Example 2

[0110] The difference between Example 2 and Example 1 is that in step 2), the spherical fused quartz powder and the spindle-shaped boehmite are ball-milled at a volume ratio of 8:1; the rest are the same as in Example 1.

[0111] The composite powder obtained in this embodiment consists of micron-sized particles with a core-shell structure, and the core layer is composed of silica microspheres with a D... 50 The particle size is 3.5 μm, the thickness of the alumina shell is 120 nm, and the alumina contains α-Al2O3.

[0112] Example 3

[0113] The difference between Example 3 and Example 1 is that: in 2), the spherical fused silica powder and spindle-shaped boehmite are ball-milled at a volume ratio of 6:1; the rest are the same as in Example 1.

[0114] The composite powder obtained in this embodiment consists of micron-sized particles with a core-shell structure, and the core layer is composed of silica microspheres with a D... 50The particle size is 3.5 μm, the thickness of the alumina shell is 100 nm, and the alumina contains α-Al2O3.

[0115] The composite powder of this embodiment was characterized, including SEM and elemental mapping. The results are shown in [Figure number missing]. Figure 3 .

[0116] from Figure 3 It can be seen that the composite powder obtained after calcination is still spherical particles, and a thin film is clearly visible on the surface. A continuous and dense film structure is clearly formed on the surface of the composite powder after calcination. This is mainly because γ-AlOOH continuously removes water molecules during the phase transition, forming Al–O–Al oxygen bridge structures, resulting in a dense and continuous film structure. Furthermore, during the transformation of γ-Al2O3 to α-Al2O3, the grain size rapidly grows and aggregates, promoting further densification of the surface film structure. This is the typical worm-like necking phenomenon of α-Al2O3 (i.e., after the phase transition, vacancies accumulate at the junction of the two phases, and these accumulated vacancies connect to form worm-like pore channels), ultimately constructing a typical SiO2@α-Al2O3 core-shell structure material. Elemental mapping analysis shows that α-Al2O3 is uniformly coated on the SiO2 surface, with no obviously uncoated areas.

[0117] Example 4

[0118] The difference between Example 4 and Example 1 is that the spherical fused quartz powder and spindle-shaped boehmite in step 2) are ball-milled at a volume ratio of 4:1; the rest are the same as in Example 1.

[0119] The composite powder obtained in this embodiment consists of micron-sized particles with a core-shell structure, and the core layer is composed of silica microspheres with a D... 50 The particle size is 3.5 μm, the thickness of the alumina shell is 80 nm, and the alumina contains α-Al2O3.

[0120] Example 5

[0121] The difference between Example 5 and Example 3 is that the calcination temperature is different, as detailed below:

[0122] Spherical fused silica powder and fusiform boehmite were ball-milled at a volume ratio of 6:1, and then calcined at 750℃ for 3 hours. Samples were then analyzed at different calcination temperatures. XRD patterns of the composite powder at different calcination temperatures are shown in [Figure 1]. Figure 4 .

[0123] Among the many crystalline phases of alumina, except for the α phase which is stable at high temperatures, the rest are metastable phases, collectively referred to as transition phases. Transition phase alumina can be divided into two main categories according to the different oxygen ion stacking modes: FCC (such as γ-Al₂O₃) and HCP (such as k-Al₂O₃).

[0124] In homogeneous nucleation during solid-state phase transitions, the difference in free energy between the new phase and the parent phase drives nucleation, while interfacial energy and strain energy hinder it. The critical nucleation work, or nucleation barrier, is crucial; lowering this barrier favors the nucleation of the new phase. Transitions between phases are often continuous. Since the oxygen ion packing pattern remains unchanged during this period, only aluminum ions undergo local migration, thus preserving the original crystal morphology and requiring less energy, allowing for low-temperature occurrence. Notably, the α-phase transition from γ-AlOOH to α-Al₂O₃ represents a shift from an intermediate fcc framework to an hcp framework, a lattice reconstruction phase transition. This process involves O atom lattice migration, and aluminum ions change from a random distribution in octahedral or tetrahedral voids to a uniform distribution. Therefore, this phase transition requires a significant amount of energy, with most of it used to overcome the nucleation barrier and form the α-phase nucleus, and the remaining energy used for grain growth. Therefore, if a phase transition to α-Al2O3 occurs, the calcination temperature must be at least 1150℃ for γ-Al2O3 to overcome the potential energy required to transform into α-Al2O3.

[0125] from Figure 4 It was found that when the calcination temperature was 1050℃, typical diffraction peaks of α-Al2O3 appeared at 36.23°, 46.12°, and 67.23°, indicating that α-Al2O3 was successfully coated on the surface of SiO2 and had high crystallinity, forming a dense SiO2@α-Al2O3 core-shell structure. Secondly, when the temperature of the SiO2@γ-AlOOH material increased from 750℃ to 1050℃, the spindle-shaped boehmite (γ-AlOOH) underwent a transformation from γ-Al2O3 to θ-Al2O3 and then to α-Al2O3. Since the temperature is controlled above 2500℃ during the preparation of spherical fused silica powder, the SiO2 in the composite powder remains an amorphous stable phase at 1050℃, and the phase transformation during calcination will not affect the preparation of the core-shell structure.

[0126] The phase transition temperature of α-Al₂O₃ prepared in this invention is 1050℃. The reduction in the α-Al₂O₃ phase transition temperature is mainly due to two reasons: First, during ball milling, a large number of defects and dangling bonds are generated on the surface of the spindle-shaped boehmite (γ-AlOOH), accumulating a large amount of surface energy; the greater the surface energy, the lower the phase transition temperature. Second, there is a clear interface at the core-shell junction of the SiO₂@γ-AlOOH material, where the surface energy is relatively large, which is conducive to phase transition and induces the transformation of γ-AlOOH into α-Al₂O₃. Therefore, the technical strategy of constructing a core-shell structure SiO₂@α-Al₂O₃ through ball milling can effectively reduce the phase transition temperature of α-Al₂O₃.

[0127] Example 6

[0128] The difference between Example 6 and Example 3 is that the D of the spherical fused silica powder... 50 The spherical fused silica powder and fusiform boehmite with a particle size of 1.0 μm were ball-milled at a volume ratio of 6:1; the rest were the same as in Example 3.

[0129] Example 7

[0130] The difference between Example 7 and Example 3 is that the D of the spherical fused silica powder... 50 The spherical fused silica powder and fusiform boehmite with a particle size of 2.2 μm were ball-milled at a volume ratio of 6:1; the rest were the same as in Example 3.

[0131] Example 8

[0132] The differences between Example 8 and Example 3 are as follows: the ball-to-material ratio, ball milling speed, and ball milling time in step 1) are different. Specifically, the ball-to-material ratio is 4g:1g, the speed is 200rpm, and the ball milling time is 30min; the synthesis method of fusiform boehmite (abbreviated as γ-AlOOH) is different; the rest are the same as in Example 3.

[0133] The specific method for synthesizing fusiform boehmite in this embodiment is as follows:

[0134] Aluminum nitrate nonahydrate (Al(NO3)3·9H2O) was weighed and dissolved in 35 mL of deionized water to prepare an Al(NO3)3·9H2O aqueous solution. Urea (CO(NH2)2) was then added, and after complete dissolution, a surfactant was added. The mixture was stirred on a magnetic stirrer for 45 min. The resulting solution was then poured into a polytetrafluoroethylene hydrothermal reactor and hydrothermally reacted at 120 °C for 20 h. After natural cooling, the solution was filtered, washed three times with deionized water and ethanol, and dried in an oven at 80 °C for 12 h to obtain a white boehmite powder with a length of 300–400 nm. The mass ratio of aluminum nitrate nonahydrate to urea was 8.2:1; the surfactant consisted of PEG-600 and PEG-4000, with a mass ratio of aluminum nitrate nonahydrate to surfactant of 3.8:1; and the mass ratio of PEG-600 to PEG-4000 was 1:1.

[0135] Example 9

[0136] The differences between Example 9 and Example 3 are as follows: the ball-to-material ratio, ball milling speed, and ball milling time in step 1) are different. Specifically, the ball-to-material ratio is 5g:1g, the speed is 150rpm, and the ball milling time is 60min; the synthesis method of fusiform boehmite (abbreviated as γ-AlOOH) is different; the rest are the same as in Example 3.

[0137] The specific details of the spindle-shaped boehmite in this embodiment are as follows:

[0138] Aluminum nitrate nonahydrate (Al(NO3)3·9H2O) was weighed and dissolved in 35 mL of deionized water to prepare an Al(NO3)3·9H2O aqueous solution. Urea (CO(NH2)2) was then added, and after complete dissolution, a surfactant was added. The mixture was stirred on a magnetic stirrer for 45 min. The resulting solution was then poured into a 45 mL polytetrafluoroethylene hydrothermal reactor and hydrothermally reacted at 180 °C for 12 h. After natural cooling, the solution was filtered, washed three times with deionized water and ethanol, and then dried in an oven at 80 °C for 12 h to obtain a white boehmite powder with a length of 300–400 nm in spindle-shaped particles. The mass ratio of aluminum nitrate nonahydrate to urea was 1.5:1; the surfactant consisted of PEG-600 and PEG-4000, with a mass ratio of aluminum nitrate nonahydrate to surfactant of 2:1; and the mass ratio of PEG-600 to PEG-4000 in the surfactant was 1:5.

[0139] Example 10

[0140] The difference between Example 10 and Example 3 is that the core layer is high-purity chemically synthesized silica, and the high-purity chemically synthesized silica and fusiform boehmite are ball-milled at a volume ratio of 6:1; the rest is the same as in Example 3. The preparation method of high-purity chemically synthesized silica can be referred to in Reference 1 (Zhao Li, Yu Jiaguo et al. Preparation and formation mechanism of monodisperse silica spherical particles [J]. Acta Chimica Sinica, 2003, 4: 562-566), and the SiO2 content in the chemically synthesized silica is ≥99.9999%.

[0141] The composite powder obtained in this embodiment consists of micron-sized particles with a core-shell structure. The silica microspheres in the core layer have a D... 50 The particle size is 2.2 μm, the thickness of the alumina shell is 120 nm, and the alumina contains α-Al2O3.

[0142] Comparative Example 1

[0143] The difference between Comparative Example 1 and Example 3 is that the powder is only obtained by ball milling and calcining spherical fused quartz powder, without being coated by ball milling of spindle-shaped boehmite.

[0144] Comparative Example 2

[0145] The difference between Comparative Example 2 and Example 3 is that the calcination temperature in step 2) is 700°C and the calcination time is 3 hours; the rest is the same as in Example 3, and powder is obtained.

[0146] Comparative Example 3

[0147] The difference between Comparative Example 3 and Example 3 is that: D... 50 It consists of 3.5μm spherical fused silica powder and D 50 A binary mixed filler system of 1.2μm α-Al2O3 powder (purchased from Bengbu Zhongheng New Material Technology Co., Ltd.) was mixed at a volume ratio of 6:1 without ball milling or calcination, and the rest was the same as in Example 3.

[0148] Polymer composite material and its preparation: The low dielectric constant and high thermal conductivity composite powder SiO2@α-Al2O3 obtained in Examples 1-10 and the materials of Comparative Examples 1-3 were added to epoxy resin (bisphenol A type E-51 epoxy resin) according to the volume filling amount. Then, 8% by mass of the epoxy resin curing agent dicyandiamide (DICY) was added, followed by 5% by mass of the curing agent curing accelerator 2-ethyl-4-methylimidazolium (EMI-2,4). Then, the polar solvent N,N-dimethylformamide (DMF) was added. The mixture was placed in a vacuum degassing mixer and mixed three times under the conditions of 2000 rpm and vacuum degassing for 15 min. Then, it was poured into a stainless steel mold coated with dimethyl silicone oil release agent, pre-cured at 170℃ for 1 h, and then post-cured at 150℃ for 3 h to prepare the polymer composite material (an epoxy resin composite material filled with inorganic filler, also known as SiO2@α-Al2O3 / epoxy resin composite material). The dielectric constant, dielectric loss, thermal conductivity, and volume resistivity of the obtained polymer composite material were determined. The results are shown in Table 1.

[0149] Dielectric constant and dielectric loss determination: The dielectric constant and dielectric loss of the inorganic filler-filled epoxy resin composite material were tested using an Agilent 4294A precision impedance analyzer. The test sample was a cylinder with a diameter of 5 cm and a thickness of 3 mm, and the mold was made of stainless steel. The test was conducted at room temperature, and the test frequency range was 10 Hz. 2 -10 7 Hz.

[0150] Volume resistivity determination: The volume resistivity of the epoxy resin composite material filled with inorganic filler was measured using a BEST-212 volume resistivity tester from Beijing Beiguang Precision Instrument Co., Ltd. Samples were prepared and tested according to the requirements of the national standard GB / T 31838.2-2019 "Dielectric and resistive properties of solid insulating materials - Part 2: Resistive properties (DC method) - Volume resistivity and volume resistivity".

[0151] Thermal conductivity determination: The thermal conductivity of the inorganic filler-filled epoxy resin composite was tested using a Longwin TIM LW-9389 thermal conductivity meter. The test sample was a cube with a diameter of 2.8 cm and a thickness of 2.8 mm. The thermal conductivity properties of homogeneous and heterogeneous thermally conductive electrical insulating materials were determined according to the standard test method for thermal conductivity electrical insulating materials (ASTM D 5470-2012).

[0152] Table 1

[0153]

[0154] Note: The volumetric filling amount of the core-shell composite powder is 50 vol%, and the resin system is bisphenol A type E-51 epoxy resin. / indicates that no testing was performed.

[0155] As shown in Table 1, compared with Comparative Example 1 using spherical fused silica powder, the polymer composite material filled with the low dielectric constant and high thermal conductivity composite powder of the present invention maintains low dielectric constant and low dielectric loss while also possessing the advantages of high thermal conductivity and high volume resistivity. Its dielectric constant (1 MHz) is 4.16–4.25 (while the dielectric constant of alumina is reported to be 10–15), dielectric loss (1 MHz) is 0.0148–0.0182; thermal conductivity is 0.578–1.034 W / (m·K), and volume resistivity is (2.11–8.04) × 10⁻⁶. 14 The thermal conductivity is significantly higher than that of Comparative Example 1, which uses single-spherical fused silica powder, at Ω·cm. Furthermore, it can be seen that the core-shell structured composite powder filler, with spherical silica as the core layer and alumina (α-alumina) as the shell layer, effectively reduces interfacial polarization and interfacial thermal resistance caused by the multiphase interface and the difference in filler modulus, compared to the binary mixed filler system (Comparative Example 3). The composite powder of this invention achieves the α-alumina coating amount by adjusting the volume ratio of the alumina precursor and silica raw materials, while simultaneously achieving efficient optimization and control of low dielectric constant and high thermal conductivity.

[0156] In summary, the polymer composite material formed by the core-shell structured low dielectric constant and high thermal conductivity composite powder of the present invention has excellent dielectric constant and thermal conductivity in the millimeter wave band, and is suitable as an irreplaceable key functional filler in the composition of epoxy molding compounds for 5G / 6G communication or high-frequency and high-speed copper clad laminates.

[0157] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A composite powder with low dielectric constant and high thermal conductivity, characterized in that, The composite powder is micron-sized particles with a core-shell structure, using silica microspheres as the core layer and alumina as the shell layer, wherein the alumina contains α-Al2O3. The alumina is formed by calcining an alumina precursor; the alumina precursor is selected from fusiform boehmite. The preparation method of the spindle-shaped boehmite is as follows: under the action of a surfactant, an aluminum source and an ammonium salt undergo a hydrothermal reaction in water; the aluminum source is selected from aluminum nitrate, the ammonium salt is selected from urea, and the surfactant is PEG-600 and PEG-4000, with a mass ratio of PEG-600 and PEG-4000 of 1:(1~5). The mass ratio of the aluminum source to the ammonium salt is (1-10):1, and the mass ratio of the aluminum source to the surfactant is (2-4):

1. The temperature of the hydrothermal reaction is 120–180°C; The composite powder is prepared by ball milling an alumina precursor and a silica powder, followed by calcination to obtain the composite powder; the calcination temperature is 900–1200°C.

2. The composite powder as described in claim 1, characterized in that, The D of the silica microspheres 50 The particle size is 1.0–3.5 μm; And / or, the thickness of the shell is 10–150 nm; And / or, the silica microspheres are selected from silica powder, which is selected from fused silica powder or chemically synthesized silica; And / or, the calcination time is 1 to 6 hours; And / or, the hydrothermal reaction time is 12 to 24 hours.

3. The composite powder as described in claim 2, characterized in that, The SiO2 content in the fused silica powder is ≥99.995%, or the SiO2 content in the chemically synthesized silicon dioxide is ≥99.9999%.

4. The method for preparing the composite powder according to any one of claims 1-3, characterized in that, The steps include the following: The alumina precursor and silica powder are ball-milled and calcined to obtain the composite powder, wherein the calcination temperature is 900-1200℃.

5. The preparation method according to claim 4, characterized in that, The ball mill rotates at a speed of 50–200 rpm; And / or, the ball milling time is 30 to 60 minutes; And / or, during ball milling, the ball-to-material ratio is (3-5) g: 1 g; And / or, the calcination time is 1 to 6 hours.

6. A polymer composite material, characterized in that, It comprises the composite powder and polymer as described in any one of claims 1-3.

7. The use of the composite powder as described in any one of claims 1-3 or the polymer composite material as described in claim 6 in 5G / 6G communication and semiconductor chip packaging.

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