High-thermal-conductivity insulating PVDF / BN ball and diamond composite thermal interface material and dry preparation method thereof

Abstract

The invention discloses a PVDF / BN (Polyvinylidene Fluoride / Boron Nitride) ball and diamond-based high-thermal-conductivity insulating composite thermal interface material for efficient heat dissipation of an electronic device and a dry preparation method of the high-thermal-conductivity insulating composite thermal interface material. The material is prepared from, by mass, 20%-30% of polyvinylidene fluoride (PVDF) and 70%-80% of a mixture of boron nitride balls (BN) and diamond powder through dry cold press molding, the heat conductivity reaches up to 14.8 W / m.K, and the volume resistivity is gt; the thickness is 1015 omega.cm. The preparation process comprises the steps of dry mixing of the BN balls and the diamond, vacuum ultrasonic mixing of the PVDF powder and the filler, cold press molding and the like, no solvent is needed, and the preparation process is environmentally friendly and low in cost. The obtained material has high thermal conductivity, electrical insulating property and flexibility, and is suitable for high-temperature scenes such as chip heat dissipation and 5G equipment.

Description

Technical Field

[0001] This invention belongs to the field of thermal management materials technology, specifically relating to a high thermal conductivity polymer-based composite thermal interface material for heat dissipation of electronic devices and its dry preparation process. Background Technology

[0002] With the rapid development of technologies such as 5G communication, artificial intelligence, and high-power chips, the integration and power density of electronic devices are growing exponentially. The problem of heat accumulation has become a key bottleneck restricting the performance and reliability of devices. Traditional thermal interface materials (TIMs) such as silicone grease and thermally conductive silicone face the following challenges: (1) Insufficient thermal conductivity: The thermal conductivity of traditional materials is mostly below 5W / m·K, which cannot meet the heat dissipation requirements of high-power chips (such as GPUs and AI chips), resulting in the device temperature exceeding the threshold and performance degradation; (2) Process pollution and high cost: Wet preparation processes (such as solution blending) require the use of toxic solvents (such as N-methylpyrrolidone), which not only pollute the environment, but the residual solvent will also increase the interfacial thermal resistance; (3) Performance imbalance due to high filling ratio: In order to improve thermal conductivity, the proportion of ceramic filler (such as BN) needs to be increased, but under traditional processes, high filling amount will lead to material powder shedding and increased brittleness, making it difficult to maintain structural stability; (4) Limited large-scale production: Hot pressing, casting and other process equipment are complex and energy-intensive, making it difficult to adapt to the needs of large-scale mass production.

[0003] Existing research indicates that boron nitride (thermal conductivity ≈300 W / m·K) and diamond (thermal conductivity ≈2000 W / m·K) are ideal high thermal conductivity insulating fillers. However, constructing an efficient thermally conductive network within a polymer matrix while maintaining processability remains a challenge. Therefore, developing an environmentally friendly, low-cost process for preparing thermal interface materials that combines high thermal conductivity with flexibility is of great significance. Summary of the Invention

[0004] Purpose of the invention: To provide an environmentally friendly, low-cost, and scalable high thermal conductivity PVDF / BN sphere@diamond composite thermal interface material and its dry preparation method, solving the problems of low thermal conductivity, process pollution, and insufficient flexibility of existing materials.

[0005] Technical solution

[0006] Filler premixing: 80%–90% by mass of BN spheres (90–110 μm) and 10%–20% by mass of diamond powder (50–60 μm) are dry-mixed to form a synergistic thermally conductive structure of “BN sphere skeleton-diamond filler”.

[0007] Vacuum ultrasonic mixing: 25%–30% by mass of PVDF powder and 70%–75% by mass of BN spheres-diamond mixture are dry-mixed under vacuum ultrasonic conditions for 30–60 min. The ultrasonic cavitation effect is used to promote uniform dispersion of the filler and enhance interfacial bonding; as shown in the table below:

[0008] Table 1: Range of PVDF and BN sphere-diamond mixture ratio

[0009] Option 1 Option 2 Option 3 Option 4 PVDF 25％ 25％ 30％ 30％ BN spheres (90-110μm) 60％ 67.5％ 56％ 63％ Diamond (50-60μm) 15％ 7.5％ 14％ 7％

[0010] Cold pressing: The mixture is loaded into a mold and cold pressed under a pressure of 10–30MPa for 5–15 minutes. This process can achieve the encapsulation and bonding of PVDF powder to fillers without heating.

[0011] Post-processing: After demolding, cut into sheet materials with a thickness of 0.5–2 mm.

[0012] Beneficial effects

[0013] 1. Breakthrough in thermal conductivity: Through the synergistic effect of dual fillers of BN spheres and diamond and the dry cold pressing process, the thermal conductivity reaches 14.8 W / m·K, which is more than 200% higher than that of traditional wet BN sphere / PVDF materials and surpasses similar polymer-based TIMs (the highest in the literature is ≈10 W / m·K).

[0014] 2. Environmental and technological advantages: The entire dry process eliminates the use of solvents, avoiding environmental pollution and thermal resistance from solvent residues. Cold pressing reduces energy consumption by 40% compared to hot pressing, and the equipment is simple and easy to scale up.

[0015] 3. Performance Balance: With 25%–30% PVDF as the binder phase, it maintains good flexibility (bending radius <5mm) even with a high filler ratio of 70%–80%, resolving the contradiction between high thermal conductivity and flexibility, while maintaining a volume resistivity >10. 15 Ω·cm, meeting electrical insulation requirements;

[0016] 4. Anti-powdering properties: Dry mixing and cold pressing form a tight interface between the filler and the PVDF matrix. Even when the filler content reaches 80%, there is no powdering phenomenon, and the structural stability is significantly improved. Attached Figure Description

[0017] Figure 1 Flowchart of dry preparation of high thermal conductivity insulating PVDF / BN spheres@diamond composite thermal interface material;

[0018] Figure 2 Comparison of thermal conductivity under different ratios of BN spheres to diamond;

[0019] Figure 3 Schematic diagram of the application of thermal interface materials in chip heat dissipation; Detailed Implementation

[0020] Example 1

[0021] (1) Weigh 58g of BN balls (particle size 90–110μm) and 15g of diamond powder (particle size 50–60μm), and dry mix them in a planetary ball mill for 20min to form a uniform filler mixture.

[0022] (2) Weigh 27g of PVDF powder and 73g of BN balls and diamond filler mixture, place them in a vacuum ultrasonic mixer, and ultrasonically stir for 40min under a vacuum of -0.08MPa;

[0023] (3) Load the mixture into a circular mold with a diameter of 50 mm and cold press and hold it under a pressure of 30 MPa for 10 min;

[0024] (4) After demolding, cut into 1mm thick sheets.

[0025] Test results: Thermal conductivity 14.8 W / m·K (laser flash method), volume resistivity 2 × 10⁻⁶ 15 Ω·cm, no powder shedding.

[0026] Example 2

[0027] (1) Adjust the BN ball content to 75% and the diamond powder content to 25%, and the rest are the same as in step (1) of Example 1;

[0028] (2) Adjust the PVDF powder content to 25%, the filler mixture content to 75%, and vacuum ultrasonically mix for 30 min;

[0029] (3) Cold pressing pressure 20MPa, pressure holding for 15min.

[0030] Test results: Thermal conductivity 14.5 W / m·K, volume resistivity 1.5 × 10⁻⁶ 15 Ω·cm, no powder shedding.

[0031] Example 3

[0032] (1) The ratio of BN balls to diamond powder is the same as in Example 1;

[0033] (2) The cold pressing pressure is reduced to 10MPa and held for 5 minutes.

[0034] Test results: Thermal conductivity 14.2 W / m·K, but still meets high heat dissipation requirements.

[0035] Comparative Example 1

[0036] (1) Use a single BN ball filler (particle size 90–110 μm), with a content of 80% and a PVDF content of 20%, using a wet process (PVDF is dissolved in NMP solvent and then blended);

[0037] (2) Hot pressing (110℃, 20MPa, 30min).

[0038] Test results: Thermal conductivity 2.5 W / m·K, volume resistivity 1×10⁻⁶ 15 The material exhibits powder shedding and is prone to cracking, and solvent residue increases interfacial thermal resistance.

[0039] Table 2: Comparison of Thermal Conductivity between Comparative Example and Example

[0040] Thermal conductivity (W / m·K) Example 1 14.8 Example 2 14.5 Example 3 14.2 Comparative Example 2.5

[0041] All the above embodiments were prepared within the specified ratio range of PVDF and BN sphere / diamond mixture as proposed in the technical solution. By comparing the proportions and embodiments, it can be concluded that this invention designs a dual-filler system of BN spheres and diamond powder, utilizing the complementary properties of the high insulation of BN spheres and the superconductivity of diamond. A multi-level thermally conductive network of "skeleton-filler" is constructed through particle size matching (BN spheres 90–110 μm, diamond 50–60 μm). The PVDF content is optimized to 25%–30%, achieving a balance between adhesion and flexibility at a high filler ratio. The cold-pressing process requires no heating, utilizing the cold rheological properties of PVDF powder to achieve a tight bond with the filler, reducing production costs and improving the feasibility of large-scale production. The thermal conductivity of 14.8 W / m·K reaches a leading level in the polymer-based TIMs field, while also possessing electrical insulation, resolving the contradiction of "high thermal conductivity - insulation" in traditional materials. It exhibits excellent anti-powdering performance, maintaining structural stability even with a filler content of 80%, making it suitable for harsh electronic device assembly environments.

[0042] 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 method for preparing a high thermal conductivity insulating PVDF / BN sphere@diamond composite thermal interface material, characterized in that, Includes the following steps: Step 1: Dry mix 80%–90% by mass of BN balls with 10%–25% by mass of diamond powder until homogeneous; Step 2: Mix 25%–30% by mass of PVDF powder with 70%–75% by mass of BN spherical diamond mixture by dry mixing under vacuum ultrasonic conditions until homogeneous; Step 3: Pour the mixture into the mold; Step 4: Cold press molding under pressure of 10–30 MPa; Step 5: After demolding, cut into sheet-like thermal conductive material.

2. The method according to claim 1, characterized in that, The BN spheres have a particle size of 90–110 μm, and the diamond powder has a particle size of 50–60 μm.

3. The method according to claim 1, characterized in that, The mixing conditions are vacuum ultrasonic mechanical stirring dry mixing, and the mixing time is 30–60 min.

4. The method according to claim 1, characterized in that, The holding time for the cold pressing process is 5–15 minutes.

5. The method according to claim 1, characterized in that, The thermal conductivity of the obtained thermal interface material is 12–14.8 W / m·K.

6. A PVDF / BN sphere@diamond composite thermal interface material prepared by any one of claims 1–5, characterized in that, Contains 20%–30% PVDF and 70%–80% BN spheres and diamond powder, with a thermal conductivity ≥14.8 W / m·K and a volume resistivity >10. 15 Ω·cm.

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