High-thermal-conductivity insulating PTFE / surface modified hexagonal BN sheet and diamond and PBO composite heat-conducting gasket and preparation method thereof

Abstract

The invention discloses a high-thermal-conductivity insulating PTFE (polytetrafluoroethylene) / surface modified hexagonal BN (boron nitride) sheet and diamond and PBO (poly-p-phenylenebenzobisoxazole) composite heat-conducting gasket and a preparation method thereof. A titanate coupling agent is adopted for carrying out surface modification on a hexagonal BN sheet with the thickness of 10-20 micrometers, and the composite material is prepared through water-phase ultrasonic homogenization, casting-like extrusion orientation and high-temperature hot press molding on the hexagonal BN sheet, diamond powder, PBO fibers and PTFE water-based dispersion liquid. The modified BN sheet is uniformly dispersed in a water phase and forms strong interface bonding with the PTFE matrix, the in-plane thermal conductivity of the obtained pad reaches more than 30W / m.K, and the volume resistivity is gt; the heat dissipation material has high heat conductivity and weather resistance, and is suitable for heat dissipation of high-power electronic devices. The water-based dispersion process is environment-friendly and efficient, and large-scale production can

Description

Technical Field

[0001] This invention belongs to the field of electronic packaging thermal management materials technology, and relates to a polytetrafluoroethylene (PTFE) based composite thermal interface material suitable for heat dissipation of high-power chips and its surface modification preparation process, and particularly to a high thermal conductivity insulating pad that constructs a multi-level thermally conductive network through an aqueous dispersion system. Background Technology

[0002] With the rapid development of third-generation semiconductor technology, edge computing, and high-density packaging technology, the integration density and heat dissipation power of power devices are increasing exponentially. Taking SiC / GaN power modules as an example, their thermal density per unit area has exceeded 500 W / cm². 2 Traditional heat dissipation solutions face thermal resistance bottlenecks. Polymer-based composite thermal interface materials, acting as a heat conduction bridge between the chip and the heat sink, directly determine the device's junction temperature control capability. Traditional PTFE-based thermal conductive materials suffer from uneven filler dispersion and high interfacial thermal resistance, resulting in in-plane thermal conductivity generally below 15 W / m·K, which is insufficient to meet the heat dissipation requirements of advanced packaging scenarios. Therefore, there is an urgent need to develop novel composite systems that combine high thermal conductivity, low dielectric constant, and weather resistance.

[0003] Hexagonal boron nitride (h-BN), as a typical layered ceramic filler, has an intrinsic thermal conductivity of up to 300 W / m·K and excellent electrical insulation properties (volume resistivity > 10). 15 BN (with a surface area of ​​Ω·cm) is an ideal thermally conductive reinforcing phase for PTFE-based composites. When the BN flake diameter is controlled within 10-20 μm, its specific surface area and flake packing efficiency reach an optimal balance. However, the following technical obstacles still exist in practical applications:

[0004] 1. Insufficient interface compatibility: The non-polar properties of PTFE molecular chains and the polar surface of BN sheets form a thermodynamically incompatible system, resulting in severe phonon scattering at the interface;

[0005] 2. Poor dispersion stability: In aqueous systems, unmodified BN flakes are prone to agglomeration due to hydrogen bond formation on the hydroxylated surface, resulting in a high sedimentation rate in PTFE dispersions and making it difficult to achieve uniform dispersion.

[0006] 3. Difficulty in constructing the heat conduction network: In traditional wet mixing processes, the aqueous medium easily leads to enhanced hydration between BN sheets, forming a "card house" type agglomeration structure, which damages the continuity of the heat conduction pathway;

[0007] Studies have shown that modifying the surface energy and polarity of BN sheets through coupling agent surface modification, combined with multi-level filler synergistic design and orientation process optimization, is an effective way to overcome the thermal conductivity bottleneck of PTFE-based composite materials. In particular, the introduction of an aqueous dispersion system can avoid the problem of organic solvent pollution, which is in line with the green manufacturing trend of electronic packaging materials, but the matching problem of the filler-water-PTFE three-phase interface needs to be solved. Summary of the Invention

[0008] Technical solution

[0009] To address the aforementioned technical bottlenecks, this invention proposes a multi-dimensional design strategy of "surface polarity regulation - multi-level network construction - aqueous phase rheometry molding," and develops a high thermal conductivity insulating PTFE / surface-modified hexagonal BN sheet@diamond@PBO composite thermal conductive pad. The specific technical solution is as follows:

[0010] Surface modification design

[0011] The surface of 10-20 μm hexagonal BN sheets was modified using the titanate coupling agent NDZ-101. The reaction mechanism is as follows:

[0012] BN-OH+(RO)3Ti(OCOR')→BN-O-Ti(OCOR')(RO)2+ROH

[0013] After modification, organotitanate segments are grafted onto the surface of the BN sheet, which improves the properties of the composite material through a triple effect:

[0014] 1. Polarity matching optimization: The nonpolar alkyl groups of the titanate ester segment form hydrophobic interactions with the PTFE molecular chain, reducing the interfacial polarity difference from Δδ=12 (J / cm) 3 ) 1 / 2 Reduced to Δδ=5 (J / cm) 3 ) 1 / 2 ;

[0015] 2. Interfacial chemical bonding: The Ti-OC covalent bonds on the surface of the BN sheet form a chemical anchor with the PTFE matrix, increasing the interfacial shear strength by 40%.

[0016] 3. Enhanced dispersion stability: The sedimentation rate of the modified BN flakes in the aqueous system is reduced to 0.1 cm / h, achieving stable nanoscale dispersion.

[0017] Key process optimization

[0018] 1. Aqueous phase dispersion process: A PTFE aqueous dispersion with a solid content of 50% (particle size 0.2-0.5μm) is used, combined with vacuum ultrasonic treatment at -0.09MPa (600W, 30min) to break the hydrogen bond aggregation of BN sheets by utilizing the cavitation effect, while promoting the coating of modified BN sheets by PTFE particles.

[0019] 2. Orientation molding technology: During the similar casting extrusion process, a back pressure of 12MPa is applied, and in an aqueous system at 60-80℃, shear force is used to induce the BN sheets to align in the extrusion direction, with an orientation degree of 0.92 (measured by X-ray diffraction).

[0020] 3. Multi-level filler synergy: Constructing a three-dimensional network of "modified BN sheet (65%) - diamond (18%) - PBO fiber (10%)": Diamond particles (10-30μm) fill the interlayer pores of BN sheet, forming "point-to-surface" thermally conductive contact; PBO fiber (200-400μm) runs through the BN sheet network, constructing a cross-scale heat conduction channel, improving the continuity of the heat conduction path by 35%.

[0021] Beneficial effects

[0022] 1. Significantly improved thermal conductivity: The in-plane thermal conductivity reaches 30.5 W / m·K, which is 52% higher than that of the unmodified PTFE system, and the thermal resistance is reduced to 0.12℃·cm. 2 / W, to meet the heat dissipation requirements of high-power devices;

[0023] 2. Enhanced interfacial bonding: The modified BN sheet forms a chemical cross-link with the PTFE matrix, achieving a tensile strength of up to 25MPa, making it suitable for flexible heat dissipation modules;

[0024] 3. Excellent insulation and weather resistance: volume resistivity reaches 3.2×10⁻⁶. 15 Ω·cm, and the internal thermal conductivity retention rate is >95% after aging at 200℃;

[0025] 4. Advantages of green process: The water-based dispersion system avoids the use of organic solvents, reduces VOC emissions by 90%, and reduces the energy consumption of hot pressing molding by 25% compared with traditional processes, making it suitable for large-scale mass production. Attached Figure Description

[0026] Figure 1 Flowchart for the preparation of high thermal conductivity insulating PTFE / surface modified hexagonal BN sheet@diamond@PBO composite thermal conductive pad; Detailed Implementation

[0027] Example 1

[0028] (1) Modification of BN sheets: 60g of 10-20μm hexagonal BN sheets were added to 600mL of 3% NDZ-101 ethanol aqueous solution (ethanol:water = 7:3), and the mixture was magnetically stirred at 50℃ for 3h. After filtration, the mixture was vacuum dried at 60℃ for 15h.

[0029] (2) Filler mixing: Weigh 65g of modified BN sheet and 18g of diamond powder (10-30μm) and mix dry for 30min. Add 10g of PBO fiber (300μm in length) and continue mixing for 15min.

[0030] (3) Aqueous phase dispersion: Add 22g of PTFE aqueous dispersion (solid content 60%) and deionized water to prepare a slurry with a solid content of 45%, and ultrasonically treat it at 600W under a vacuum of -0.09MPa for 30min.

[0031] (4) Cast-type extrusion: Extruded at 0.8 mm / s through a 0.8 mm slit nozzle at 70 °C, with a back pressure of 12 MPa applied;

[0032] (5) Hot pressing: Hot pressing at 320℃ and 25MPa for 8 minutes to obtain a 0.8mm thick gasket.

[0033] Test results: In-plane thermal conductivity 30.5 W / m·K, volume resistivity 3.2 × 10⁻⁶ 15 Ω·cm, thermal resistance 0.12℃·cm 2 / W.

[0034] Comparative Example 1

[0035] Use 60g of unmodified 10-20μm hexagonal BN sheets directly, and follow the same steps as in Example 1.

[0036] After ultrasonic treatment, the BN flakes in the slurry formed obvious flocculent aggregates.

[0037] Test results: In-plane thermal conductivity 20.1 W / m·K, volume resistivity 2.1 × 10⁻⁶ 15 Ω·cm, thermal resistance 0.28℃·cm 2 / W.

[0038] Comparative Example 2

[0039] The traditional aqueous solution mixing process was used, but no casting orientation process was used; otherwise, it was the same as in Example 1.

[0040] Test results: In-plane thermal conductivity 24.3 W / m·K, volume resistivity 2.5 × 10⁻⁶ 15 Ω·cm, thermal resistance 0.19℃·cm 2 / W.

[0041] Table 1. Performance Comparison of Examples and Comparative Examples

[0042] sample Volume resistivity (Ω·cm) <![CDATA[Thermal resistance (°C·cm 2 / W)]]> In-plane thermal conductivity (W / m·K) Example 1 (Modified) <![CDATA[3.2×10 15 ]]> 0.12 30.5 Comparative Example 1 <![CDATA[2.1×10 15 ]]> 0.28 20.1 Comparative Example 2 <![CDATA[2.5×10 15 ]]> 0.19 24.3

[0043] This invention utilizes the titanate coupling agent NDZ-101 to surface-modify hexagonal boron nanosheets, effectively solving the agglomeration problem of boron nanosheets in aqueous PTFE systems. Combined with a cast extrusion-like directional process and a multi-level thermally conductive network design of "boron nanosheet-diamond-PBO fiber," the in-plane thermal conductivity exceeds 30 W / m·K. Simultaneously, the aqueous dispersion process avoids organic solvent contamination, and the hot-pressing temperature matches the melting characteristics of PTFE. The resulting gasket possesses high thermal conductivity, high insulation, and weather resistance, making it suitable for heat dissipation requirements in high-heat-dissipation scenarios such as 5G base stations and electric drives for new energy vehicles.

[0044] 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 PTFE / surface-modified hexagonal BN sheet@diamond@PBO composite thermal conductive pad, characterized in that... Includes the following steps: Step 1: Surface modification of 10-20μm hexagonal BN sheets using titanate coupling agent NDZ-101: The hexagonal BN sheets were placed in a 3% NDZ-101 ethanol aqueous solution, magnetically stirred at 50℃ for 3h, filtered and dried to obtain surface-modified BN sheets. Step 2: Dry mix 60%-70% by mass of modified hexagonal BN sheets with 15%-20% by mass of diamond powder (particle size 10-30μm) until homogeneous; Step 3: Mix 8%-12% by mass of PBO fibers (200-400 μm in length) with the mixture obtained in Step 2 until homogeneous; Step 4: Add the 18%-22% mass fraction of PTFE aqueous dispersion and the mixture obtained in Step 3 to deionized water, and homogenize it by ultrasonication at 600W power for 30 minutes under a vacuum of -0.09MPa. Step 5: Apply 12MPa pressure to the ultrasonically treated paste mixture through the nozzle and extrude it at a speed of 0.8mm / s at 60-80℃ in a cast-cast manner to achieve directional alignment of PBO fibers and modified BN sheets; Step 6: Hot press at 320℃ and 25MPa pressure for 8 minutes, then demold and cut into sheet-shaped thermal pads.

2. The method according to claim 1, characterized in that... The temperature is maintained at 60-80℃ during the pressurized extrusion process at the nozzle.

3. The method according to claim 1, characterized in that... The resulting thermal pad has an in-plane thermal conductivity ≥30 W / m·K and a volume resistivity >10. 15 Ω·cm.

4. A PTFE / surface-modified hexagonal BN sheet@diamond@PBO composite thermal pad prepared by any one of claims 1-3, characterized in that... It contains 18%-22% PTFE, 60%-70% surface-modified hexagonal BN sheets (10-20μm), 15%-20% diamond powder and 8%-12% PBO fiber, with an in-plane thermal conductivity of over 30W / m·K.

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