High-power inductor heat dissipation structure with inner-wall functionalized hollow flat copper wire and preparation method

Abstract

The present application relates to the technical field of electronic component manufacturing, in particular to a high-power inductance heat dissipation structure of inner wall functionalized hollow flat copper wire and a preparation method thereof. The heat dissipation structure comprises a magnetic core and a winding, and the winding is wound by a hollow flat copper wire with a through fluid cooling channel. The inner wall of the fluid cooling channel is provided with a high-thermal-conductivity insulating composite coating, which is composed of a high-temperature-resistant resin matrix and a directional arrangement of flaky hexagonal boron nitride fillers. The filler sheet layer plane is perpendicular to the channel inner wall surface, and a continuous low-thermal-resistance heat conduction channel is formed in the radial direction perpendicular to the inner wall. The present application realizes heat dissipation near the heat source through internal liquid cooling, and simultaneously meets the high insulation and high radial heat conduction requirements by combining with the directional filler coating, thereby greatly reducing the inductance operating temperature rise, improving the power density, and being suitable for the fields of high-power-density electronic equipment such as aerospace and new energy vehicles.

Description

Technical Field

[0001] This invention relates to the field of electronic component manufacturing technology, specifically to a high-power inductor heat dissipation structure and preparation method with internally functionalized hollow flat copper wire. Background Technology

[0002] With the large-scale deployment of 5G communication base stations, the continuous increase in the power of electric drive systems for new energy vehicles, and the development of aerospace electronic equipment towards integration and miniaturization, the power density of electronic systems is growing exponentially, posing unprecedented challenges to the current-carrying capacity and heat dissipation performance of core passive components—power inductors. When high-power inductors operate under high current and high-frequency conditions, the Joule loss (I0) of the coil conductor... 2 The R loss, hysteresis loss and eddy current loss of the magnetic core will be converted into a large amount of heat. If the heat cannot be dissipated in time, it will cause the coil temperature to rise sharply, accelerate the aging of the insulation layer, reduce the performance of the magnetic core, and even cause the device to burn out and fail, becoming the core bottleneck restricting the improvement of power density.

[0003] In existing technologies, heat dissipation solutions for high-power inductors are mainly divided into two categories: external heat dissipation and internal heat dissipation. External heat dissipation solutions are the most widely used. For example, thermally conductive protrusions are placed on the inductor casing and mounted on the surface of a liquid cooling plate, or thermally conductive pads are placed on the outside of the coil and matched with external cooling channels. Heat is transferred from inside the coil through the insulation layer, magnetic core, potting compound, and casing to the external coolant via thermal conduction. However, this type of heat dissipation path has multiple layers of interfacial thermal resistance. Heat needs to pass through at least 4-5 layers of different media to transfer from the center of the coil to the coolant. The total thermal resistance is high, and the room for improvement in heat dissipation efficiency is limited, making it difficult to meet the heat dissipation requirements of high-power inductors of kW level and above.

[0004] To shorten the heat dissipation path, some technologies attempt to construct heat dissipation structures inside the conductor. For example, a closed cavity can be set up inside a flat copper wire and filled with a phase-change heat transfer medium such as paraffin or alkanes, utilizing the evaporation-condensation principle of heat pipes to achieve uniform temperature inside the conductor. However, this approach is essentially passive heat dissipation, only achieving a redistribution of heat within the conductor and failing to actively remove heat from the device. The cooling medium relies on an external condensation section for secondary heat dissipation, resulting in high overall heat dissipation power consumption and slow response speed. It cannot achieve active strong convection heat transfer, and its heat dissipation effect is limited under continuous high-power conditions.

[0005] Using hollow conductors and directly introducing coolant is an ideal way to achieve near-end heat dissipation, but this solution faces two major challenges: First, direct contact between the coolant and the inner copper wall can cause corrosion of the copper tube, and the conductivity of the coolant can easily cause inter-turn short circuits, posing a reliability risk; Second, if ordinary insulating varnish is applied to the inner wall, the thermal conductivity of traditional insulating resin is usually less than 0.3 W / mK, which will form an "insulation layer" between the tube wall and the coolant, thereby increasing thermal resistance, deteriorating the heat dissipation effect, and failing to take advantage of internal liquid cooling.

[0006] To improve the thermal conductivity of insulating coatings, the industry typically adds high thermal conductivity fillers such as alumina and boron nitride to the resin. However, in conventional blend coatings, the fillers are randomly distributed, failing to form continuous thermal conduction pathways, resulting in limited improvement in thermal conductivity. Existing research indicates that hexagonal boron nitride (h-BN) microplates exhibit significant anisotropy, with in-plane thermal conductivity exceeding 300 W / mK. By aligning the plates perpendicular to the tube wall, heat is forced to transfer along the in-plane direction of the h-BN plates in a direction perpendicular to the tube wall (i.e., radial), thus forming continuous, low-thermal-resistance radial thermal conduction channels. Simultaneously, this coating maintains excellent electrical insulation properties in the vertical direction (along the tube wall normal). If the h-BN plates can be oriented within the coating, a highly efficient thermal conduction network can be constructed in a specific direction. However, existing orientation technologies such as scraping, spin coating, and electric field orientation are all applicable to planar substrates. For hollow flat copper wires with their narrow microchannels, large aspect ratio, and high curvature inner wall surfaces, there is still a significant technological gap in how to achieve uniform coating and highly oriented alignment of fillers within a limited space, while ensuring a balance between the coating's adhesion to the inner wall, insulation performance, and thermal conductivity. There is currently no mature industrial solution. Summary of the Invention

[0007] To address the problems in existing technologies, this invention provides a high-power inductor heat dissipation structure and preparation method with functionalized hollow flat copper wires on the inner wall. It solves technical problems such as long heat dissipation paths of traditional solid conductors, high thermal resistance of existing external liquid cooling, difficulty in balancing insulation and thermal conductivity of the inner wall of hollow conductors, and difficulty in directional arrangement of high thermal conductivity fillers on the narrow curved inner wall. Under the premise of ensuring electrical insulation and structural reliability, it achieves efficient active liquid cooling near the inductor heat source, significantly improving the power density and operating stability of the device.

[0008] The technical solution adopted by this invention to solve its technical problem is: a high-power inductor heat dissipation structure with functionalized hollow flat copper wire in the inner wall, including a magnetic core and a winding wound on the magnetic core. The winding is made of at least one hollow flat copper wire with a fluid cooling channel running through the length direction. The inner wall of the fluid cooling channel is provided with a high thermal conductivity insulating composite coating. The composite coating includes a resin matrix and sheet-like high thermal conductivity electrically insulating filler dispersed in the resin matrix. The sheet-like high thermal conductivity electrically insulating filler is oriented in the composite coating, and the sheet plane of the filler is basically perpendicular to the inner wall surface of the fluid cooling channel, thereby forming a continuous low thermal resistance heat conduction channel in the radial direction perpendicular to the inner wall surface.

[0009] Specifically, the sheet-like high thermal conductivity electrical insulating filler is hexagonal boron nitride microflakes with an average particle size of 0.5μm to 15μm and an aspect ratio greater than 10; the volume filling ratio of the hexagonal boron nitride microflakes in the composite coating is 30% to 60%.

[0010] Specifically, the cross-section of the hollow flat copper wire is rectangular or racetrack-shaped, with a width-to-thickness ratio greater than 3:1; the copper matrix wall thickness of the hollow flat copper wire is 0.3mm to 1mm; and the cross-sectional area of ​​the fluid cooling channel accounts for 30% to 60% of the total cross-sectional area of ​​the hollow flat copper wire.

[0011] Specifically, the thickness of the composite coating is 15μm to 35μm, the radial equivalent thermal conductivity of the coating is ≥5W / mK, the breakdown voltage is ≥2000V, and the temperature resistance is ≥180℃.

[0012] Specifically, the resin matrix is ​​one of polyimide, modified epoxy resin or silicone resin; the outer surface of the hollow flat copper wire is provided with an outer insulation layer, and the winding turns are filled with a thermally conductive structural adhesive layer, which together with the internal fluid cooling channel forms a dual heat dissipation path.

[0013] The above-mentioned method for fabricating a high-power inductor heat dissipation structure with internally functionalized hollow flat copper wire includes the following steps: S1: Cleaning and surface roughening treatment of the inner wall of the fluid cooling channel of the hollow flat copper wire to remove oil stains and oxide layer and form a micro-rough interface. S2: Disperse the sheet-like high thermal conductivity insulating filler in the precursor solution of the resin matrix, and obtain a uniform insulating coating through dispersion treatment; S3: The insulating coating is uniformly adhered to the inner wall surface of the fluid cooling channel using an inner wall flow coating method or an electrophoretic deposition method; S4: The coated hollow flat copper wire is heated and cured in segments. During the curing process, the filler is kept in an oriented arrangement by fluid shear force or electric field force to form a dense, high thermal conductivity insulating composite coating. S5: The prepared hollow flat copper wire with internal wall functionalization is wound onto the magnetic core and assembled to obtain an inductive heat dissipation structure.

[0014] Specifically, in step S3, when using the inner wall flow coating method, the apparent viscosity of the insulating coating is controlled to be 150 mPa·s to 1200 mPa·s, the flow coating linear velocity is 5 cm / s to 50 cm / s, and the fluid shear rate is maintained at 10 s. -1 ~100s -1 Through laminar shear force combined with wall constraint effect, the sheet packing is induced to align perpendicular to the inner wall.

[0015] Specifically, in step S3, when electrophoretic deposition is used, the surface of the sheet-like high thermal conductivity insulating filler is first modified to make it chargeable. The insulating coating is prepared as an aqueous electrophoretic solution, a DC electric field of 10V / cm to 30V / cm is applied, and the deposition time is 5min to 20min. The charged filler is driven by the electric field force to oriented and deposited on the inner wall along the direction of the electric field.

[0016] Specifically, in step S4, the segmented heating and curing process is as follows: first, the temperature is raised to 80℃ to 120℃ at a heating rate of 0.5℃ / min to 5℃ / min, and held for 1h to 2h for pre-curing; then, the temperature is raised to 180℃ to 220℃ at the same heating rate, and held for 1h to 3h for post-curing; during the curing process, the solvent slowly evaporates, and the resin cross-linking shrinkage further promotes the orientation of the filler sheets perpendicular to the inner wall surface.

[0017] Specifically, in step S1, the cleaning and roughening treatment sequentially employs alkaline washing to remove oil, acid washing to remove oxidation, deionized water rinsing, and plasma roughening; in step S5, after winding, thermally conductive structural adhesive is filled between the winding turns, and fluid adapters are welded to both ends of the winding. The fluid adapters have built-in distribution grooves to evenly distribute the coolant to the fluid cooling channels of each turn.

[0018] The beneficial effects of this invention are: 1. Active heat dissipation at the near end results in extremely low thermal resistance and significant temperature rise / fall. The coolant flows directly inside the heated copper conductor, carrying away heat directly from the heat source. This significantly shortens the heat dissipation path and eliminates the interfacial thermal resistance of multiple media in traditional external heat dissipation. Combined with the high thermal conductivity directional coating on the inner wall, the heat conduction path of "copper substrate → insulating coating → coolant" is completely opened up. Actual measurement data shows that under 10kW operating conditions, the winding hot spot temperature rise of this invention is only 29°C, which is lower than that of solid flat wire inductance and lower than that of ordinary insulating coated hollow flat wire inductance, resulting in a significant improvement in heat dissipation.

[0019] 2. Achieving both insulation and thermal conductivity, breaking through the performance bottlenecks of traditional coatings. By cleverly utilizing the anisotropy of the highly oriented h-BN microsheets, both high radial thermal conductivity and high normal insulation are achieved simultaneously within the same coating, resolving the inherent contradiction of traditional insulating coatings where "good insulation equates to poor thermal conductivity, and vice versa." The optimally formulated coating achieves a radial thermal conductivity of up to 7.5 W / mK, which is 25 times that of ordinary non-oriented insulating coatings, while maintaining excellent electrical insulation performance.

[0020] 3. High power density, suitable for high-frequency operating conditions The flat wire winding window fill factor can reach over 90%, far exceeding that of round wire windings. Simultaneously, the skin effect under high-frequency conditions concentrates current on the conductor surface. The hollow structure effectively eliminates the non-conductive central material, reducing weight and saving copper without compromising current-carrying capacity. Furthermore, the internal channels can be directly used for heat dissipation, achieving a perfect balance between electrical and thermal performance. The overall inductor volume can be reduced compared to traditional solutions, resulting in a significant increase in power density.

[0021] 4. The process is highly controllable and suitable for industrial mass production. Continuous coating production of long-length hollow flat copper wires can be achieved using either flow coating or electrophoretic deposition processes. Process parameters are stable and controllable, resulting in excellent coating consistency. No complex equipment or harsh environments are required, production costs are low, and large-scale application is easy. It is adaptable to inductor products of different specifications and power ratings. Attached Figure Description

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] Figure 1 A schematic diagram of the heat dissipation structure of a high-power inductor with functionalized hollow flat copper wire inner wall provided by the present invention. Figure 2 A cross-sectional schematic diagram of the high-power inductor heat dissipation structure with functionalized hollow flat copper wire inner wall provided by the present invention. Figure 3 A schematic diagram of the microstructure of the inner wall coating of the high-power inductor heat dissipation structure with functionalized hollow flat copper wire provided by the present invention. Figure 4 Temperature field of transverse cross section of hollow flat copper wire inductor with different insulation layers provided by the present invention; Figure 5 Temperature field of transverse cross section of hollow flat copper wire inductor with different insulation layers provided by the present invention; Figure 6 Temperature field of longitudinal section of hollow flat copper wire inductor with different insulation layers provided by the present invention; Figure 7 Temperature field of longitudinal section of hollow flat copper wire inductor with different insulation layers provided by the present invention (II); Figure 8 This is a schematic diagram of the internal wall flow coating process provided by the present invention.

[0024] In the figure: 1. Hollow flat copper wire winding; 2. Rectangular amorphous magnetic ring; 11. Outer insulation layer; 12. Copper substrate; 13. Inner high thermal conductivity coating; 14. Hollow flow channel; 15. Microplate structure. Detailed Implementation

[0025] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0026] like Figures 1-8 As shown, the high-power inductor heat dissipation structure with internal wall functionalized hollow flat copper wire according to the present invention includes a magnetic core assembly and a winding. The winding is made of at least one hollow flat copper wire winding 1. The hollow flat copper wire winding 1 has a fluid cooling channel running through it along the length direction. The coolant can flow in the channel and directly remove Joule heat from the inside of the conductor.

[0027] The core innovation of this invention lies in the fact that the inner wall of the fluid cooling channel is provided with a functionalized composite coating that combines high electrical insulation and high radial thermal conductivity. This composite coating is composed of a high-temperature resistant resin matrix and sheet-like high thermal conductivity and electrical insulation fillers dispersed therein, wherein the sheet-like filler micro-flake structures 15 are highly oriented within the coating, and their sheet planes are substantially perpendicular to the inner wall surface of the channel.

[0028] Based on the anisotropic thermal conductivity of sheet-like fillers such as hexagonal boron nitride, when the sheets are perpendicular to the inner wall surface, radial heat transfer perpendicular to the inner wall will proceed along the in-plane high thermal conductivity direction of the filler. Through the overlap and contact between the fillers, a continuous, low thermal resistance radial heat conduction channel is formed throughout the entire coating thickness direction. In the tangential and axial directions along the pipe wall, heat transfer must pass through the direction perpendicular to the filler sheets, where the thermal conductivity is lower. At the same time, the coating still maintains excellent electrical insulation performance in the thickness direction. This structure cleverly utilizes the anisotropy of the filler to achieve the dual functions of "high radial thermal conductivity plus high radial insulation," completely solving the problem of poor thermal conductivity and becoming a thermal bottleneck in traditional insulating coatings.

[0029] Hollow flat copper wire conductor: The hollow flat copper wire winding 1 is made of oxygen-free copper with a rectangular or racetrack-shaped cross-section and a width-to-thickness ratio greater than 3:1, preferably 4:1, to ensure a high window fill factor (up to 90% or more) and improve the inductor volume utilization. The copper substrate 12 has a wall thickness of 0.3mm to 1mm. While ensuring the mechanical strength and current carrying capacity of the conductor, the wall thickness is reduced as much as possible to reduce the thermal resistance of the conductor itself. The internal fluid cooling channel is the hollow flow channel 14. The cross-sectional shape of the channel matches the outer contour. The cross-sectional area of ​​the hollow flow channel 14 accounts for 30% to 60% of the total cross-sectional area, balancing the current carrying area and cooling flow rate. A polyimide or polyurethane outer insulation layer 11 can be provided on the outer surface of the hollow flat copper wire winding 1 to ensure inter-turn electrical insulation.

[0030] High thermal conductivity insulating composite coating: (1) Resin matrix: High temperature resistant insulating resin is selected, including but not limited to polyimide, modified epoxy resin, silicone resin, etc., preferably polyimide, which has a temperature resistance of up to 200℃ and excellent bonding force with copper matrix 12, and can adapt to the high temperature environment and thermal shock of inductor operation.

[0031] (2) Functional filler: Hexagonal boron nitride (h-BN) microflakes, i.e., microflake structure 15, are used. Their crystal structure is hexagonal layered, which has significant anisotropic thermal conductivity and insulation properties. The average particle size of the filler is 0.5μm to 15μm, and the aspect ratio is greater than 10, preferably greater than 15. Fillers with a large aspect ratio are more likely to be oriented under shear force and are more likely to form a continuous thermally conductive network. The volumetric filling ratio of the filler in the coating is 30% to 60%, preferably 40% to 55%. If the filling ratio is too low, a continuous thermally conductive path cannot be formed. If the filling ratio is too high, the filler will easily agglomerate, and the coating density and adhesion will decrease.

[0032] (3) Coating structure and performance: The thickness of the inner high thermal conductivity coating 13 is controlled between 15μm and 35μm. If it is too thin, pinhole defects will easily occur, leading to insulation failure. If it is too thick, the thermal resistance of the coating itself will increase and the cross-sectional area of ​​the hollow flow channel 14 will decrease. The optimized inner high thermal conductivity coating 13 has a radial equivalent thermal conductivity ≥5W / mK, and can reach more than 8W / mK, which is more than 10 times that of ordinary random filler insulating coatings. At the same time, the breakdown voltage is ≥2000V, which fully meets the requirements of inter-turn insulation and coolant insulation. The temperature resistance is ≥180℃, which can work stably under high temperature conditions for a long time.

[0033] Filler directional alignment molding technology: This invention provides two industrially feasible directional forming processes for inner wall coatings: inner wall flow coating and electrophoretic deposition, which are applicable to hollow flat copper wire windings 1 with different specifications and aspect ratios.

[0034] (1) Inner wall flow coating method: based on the principle of fluid shear force induced orientation. When the hollow flat copper wire winding 1 is placed vertically, and the coating is injected from the bottom and flows upward along the inner wall, there is a velocity gradient in the fluid near the pipe wall in the laminar flow state, which generates shear force along the flow direction, causing the layers of the micro-plate structure 15 to turn along the flow direction and finally arrange themselves perpendicular to the inner wall surface. By adjusting parameters such as coating viscosity, flow rate, and solid content, the shear rate can be controlled within 10s. -1 ~100s -1 Within this range, the height orientation of the micro-sheet structure 15 is achieved. The process equipment is simple and enables continuous production of long-length pipes.

[0035] (2) Electrophoretic deposition method: based on the principle of electric field-induced orientation. First, the h-BN microplates (microplate structure 15) are surface modified to carry positive or negative charges on their surface, and dispersed in an aqueous resin solution to form an electrophoretic solution. The hollow flat copper wire winding 1 is used as an electrode. After applying a DC electric field, the charged microplate structure 15 migrates towards the tube wall and is deposited under the drive of the electric field. At the same time, the layers turn along the electric field direction perpendicular to the tube wall and finally arrange themselves perpendicular to the inner wall surface. This process has good coating uniformity and is especially suitable for hollow flow channels 14 with large aspect ratios and complex cross-sections, and the coating adhesion is higher.

[0036] Segmented curing process: The coated layer employs a segmented temperature-curing process. First, a low-temperature pre-curing stage allows the solvent to evaporate slowly, preventing rapid evaporation and bubble formation. Then, a high-temperature post-curing stage ensures complete resin cross-linking. The heating rate is controlled between 0.5℃ / min and 5℃ / min; slow curing helps maintain the oriented arrangement of the micro-plate structure 15, preventing rapid resin cross-linking and flow that could damage the orientation structure. During curing, the volume shrinkage caused by resin cross-linking further compresses the micro-plate structure 15, promoting a more regular orientation perpendicular to the inner wall surface, thus improving the degree of orientation and the continuity of the thermally conductive network.

[0037] Winding and integrated heat dissipation structure: A hollow flat copper wire winding 1 with functionalized inner walls is tightly wound onto a rectangular amorphous magnetic ring 2. The rectangular amorphous magnetic ring 2 can be made of amorphous alloy, ferrite, or nanocrystalline materials, selected according to the application scenario. Thermally conductive structural adhesive can be filled between the winding turns to improve the mechanical strength and shock resistance of the winding, and to conduct heat between the turns to the rectangular amorphous magnetic ring 2 and the outer shell. Together with the internal hollow flow channel 14, it forms a dual heat dissipation path of "internal main liquid cooling plus external auxiliary heat conduction", further improving the heat dissipation effect. Special fluid adapters are welded to both ends of the winding. The adapters have built-in flow dividers to ensure that the coolant is evenly distributed to the hollow flow channel 14 of each coil turn, avoiding local insufficient flow and overheating dead zones.

[0038] Example 1: Inductor heat dissipation structure for military vehicle-mounted filters: This embodiment provides a high-power inductor heat dissipation structure for military vehicle-mounted DC-DC filters, with a rated operating power of 10kW, an operating frequency of 20kHz, and an operating ambient temperature of -40℃ to 125℃, possessing high reliability and shock resistance.

[0039] The inductor heat dissipation structure of this embodiment includes two parts: a rectangular amorphous magnetic ring 2 and a hollow flat copper wire winding 1. The rectangular amorphous magnetic ring 2 is made of iron-based amorphous alloy with a permeability of 800 μH / m and a saturation magnetic flux density of 1.5T. It features low loss and high saturation, making it suitable for high-frequency and high-power applications. The hollow flat copper wire winding 1 is formed by continuously winding 12 turns of a single hollow flat copper wire with functionalized inner walls. The winding method is tight flat winding, with a window fill factor of 92%.

[0040] The hollow flat copper wire winding 1 is made of oxygen-free copper, with a rectangular cross-section, a width-to-thickness ratio of 4:1, and external dimensions of 8mm × 2mm. The copper substrate 12 has a wall thickness of 0.5mm, and the internal hollow flow channel 14 has a racetrack-shaped cross-section with channel dimensions of 7mm × 1mm. The cross-sectional area of ​​the hollow flow channel 14 accounts for 43.75% of the total cross-sectional area. The outer surface of the hollow flat copper wire winding 1 is provided with a 20μm thick polyimide outer insulation layer 11, with a breakdown voltage ≥3000V, ensuring inter-turn and ground insulation.

[0041] The inner wall of the hollow flow channel 14 is coated with a 25 μm thick inner high thermal conductivity coating 13. The resin matrix of the inner high thermal conductivity coating 13 is thermosetting polyimide, and the functional filler is hexagonal boron nitride (h-BN) microflakes, i.e., microflake structures 15. The average particle size of the microflake structures 15 is 5 μm, the aspect ratio is approximately 20, and the volumetric filling ratio is 50%. The microflake structures 15 are highly oriented within the inner high thermal conductivity coating 13, with the sheet planes essentially perpendicular to the inner wall surface of the hollow flow channel 14, and the orientation factor f ≥ 0.85. Testing showed that the radial equivalent thermal conductivity of this inner high thermal conductivity coating 13 is 7.5 W / mK, and the interfacial thermal resistance is as low as 3.33 × 10⁻⁶. -6 m 2 • K / W, breakdown voltage of 2800V, long-term temperature resistance up to 220℃.

[0042] Stainless steel fluid adapters are welded to both ends of the hollow flat copper wire winding 1. The adapters have built-in flow dividers to evenly distribute the inlet coolant into the hollow flow channels 14 of the 12-turn coil, ensuring that the flow rate deviation per turn is less than 5% to avoid localized overheating. The coolant used is deionized water + 5% ethylene glycol antifreeze, with a working flow rate of 1.0 L / min and an inlet water temperature controlled at 20℃. The turns of the hollow flat copper wire winding 1 are filled with silicone structural adhesive with a thermal conductivity of 2.0 W / mK. This not only enhances the mechanical strength of the winding and meets the vehicle's vibration resistance requirements, but also serves as an auxiliary heat dissipation path, transferring heat between the turns to the rectangular amorphous magnetic ring 2 and the outer shell.

[0043] To verify the heat dissipation performance of this embodiment, three sets of control samples were set up for comparative testing. The test conditions were: output power 10kW, ambient temperature 20℃, coolant flow rate 1.0L / min, inlet water temperature 20℃, and K-type thermocouples embedded in the winding hot spot were used for temperature measurement. Data were recorded after thermal equilibrium was reached.

[0044] Comparative Example 1-1: Solid flat copper wire windings of the same size are used, without liquid cooling, and heat dissipation is achieved through natural convection and heat conduction from the outer casing.

[0045] Comparative Examples 1-2: Hollow flat copper wire winding 1 of the same size is used, with the inner wall coated with ordinary pure epoxy resin insulation coating (thermal conductivity 0.25W / mK) with a thickness of 25μm, and internal liquid cooling is provided.

[0046] Comparative Examples 1-3: Hollow flat copper wire winding 1 of the same size is used, with random h-BN filled epoxy coating (filling ratio 50 vol%, non-directional arrangement) on the inner wall, with a thickness of 25 μm, and internal liquid cooling.

[0047] The test results show that: the steady-state hot spot temperature of the sample in this embodiment is 79℃, the temperature rise relative to the ambient temperature is 54℃, the thermal equilibrium time is 28min, and the axial temperature difference of the winding is 5℃; the steady-state hot spot temperature of Control Example 1-1 is 148℃, the temperature rise is 123℃, the thermal equilibrium time is 65min, and the axial temperature difference is 18℃; the steady-state hot spot temperature of Control Example 1-2 is 123℃, the temperature rise is 98℃, the thermal equilibrium time is 42min, and the axial temperature difference is 12℃; the steady-state hot spot temperature of Control Example 1-3 is 96℃, the temperature rise is 76℃, the thermal equilibrium time is 35min, and the axial temperature difference is 9℃.

[0048] The comparison shows that this embodiment, through the combination of internal liquid cooling and a directional high thermal conductivity coating, reduces the temperature rise by 69°C (56%) compared to a solid liquid-cooled solution; it reduces the temperature rise by 44°C (45%) compared to a conventional insulating coating liquid cooling solution; and even compared to a non-directional h-BN coating solution, the temperature rise is reduced by 22°C (29%), fully demonstrating the significant effect of the 15-directional arrangement of the microchip structure on improving heat dissipation performance. Simultaneously, the axial temperature difference of the windings in this embodiment is only 5°C, exhibiting excellent thermal uniformity, which avoids insulation aging caused by localized overheating and improves the overall lifespan and reliability of the device.

[0049] Example 2: Preparation of internally functionalized hollow flat copper wires by internal wall flow coating method: This embodiment describes in detail the process of preparing the above-mentioned internally functionalized hollow flat copper wire using the internal wall flow coating method. It is applicable to hollow flat copper wire windings 1 with a length of less than 1m and an aspect ratio of less than 50, and can realize batch continuous production.

[0050] Step S1, Inner wall cleaning and roughening treatment: A hollow oxygen-free flat copper wire winding 1 with a wall thickness of 8mm×2mm×0.5mm was selected, and a tube with a length of 500mm was cut as the substrate. First, alkaline cleaning and degreasing were performed: the tube was immersed in a 5% sodium hydroxide aqueous solution at 50℃ and ultrasonically cleaned for 10 minutes to remove rolling oil and lubricant from the inner wall; after removal, it was rinsed three times with deionized water. Next, acid cleaning and oxidation removal were performed: the tube was immersed in a 10% dilute sulfuric acid solution at room temperature for 5 minutes to remove the oxide layer on the inner wall, exposing the copper substrate 12 to a fresh substrate; after removal, it was immediately rinsed with deionized water until neutral. Finally, plasma roughening was performed: the tube was passed through a low-temperature oxygen plasma treatment chamber with a treatment power of 200W for 3 minutes, forming a nanoscale micro-roughened interface on the inner wall, improving the adhesion between the inner high thermal conductivity coating 13 and the copper substrate 12. The treated tube was then dried in a 100℃ oven for later use.

[0051] Step S2, Preparation of insulating coating: A polyamic acid-type polyimide precursor solution with a solid content of 30 wt% and N,N-dimethylacetamide (DMAc) as the solvent was selected. h-BN microflakes (microflake structure 15) with an average particle size of 5 μm and an aspect ratio of 20 were weighed and added to the precursor solution at a volumetric filling ratio of 50 vol%. The mixture was first mechanically stirred for 30 min for initial mixing, then ultrasonically dispersed in an ultrasonic disperser at 300 W for 20 min to ensure thorough separation and dispersion of the microflake structure 15, preventing agglomeration. Subsequently, 0.5 wt% of silane coupling agent KH550 was added, and stirring continued for 15 min to enhance the interfacial bonding between the filler and the resin. The final coating had an apparent viscosity of 500 mPa·s (25℃) and a solid content of 42 wt%. Testing showed that the filler was uniformly dispersed without significant agglomeration or precipitation.

[0052] Step S3, Inner wall flow coating: A vertical top-flow coating process is employed: the dried hollow flat copper wire winding 1 is vertically fixed on the coating rack, with the lower end connected to a precision metering pump and a coating tank. The metering pump is started, injecting the coating at a linear velocity of 20 cm / s from the lower end of the pipe. The coating flows upwards along the inner wall in a laminar flow state, filling the entire hollow flow channel 14 before overflowing from the upper end and flowing back to the tank. The coating environment temperature is controlled at 25℃, and the relative humidity is below 60% to prevent excessive solvent evaporation. During the flow process, a fluid layer near the pipe wall is formed for approximately 40 seconds. -1 Under the shear force, the microplates of the microplate structure 15 gradually turn and eventually align perpendicular to the inner wall surface, with the edges of the plates oriented along the flow direction. The coating is repeated twice to ensure uniform thickness of the inner high thermal conductivity coating 13.

[0053] Step S4: Segmented heat curing: The coated pipe was placed horizontally in a programmed temperature oven and cured using a segmented process: In the first stage, the temperature was increased from room temperature to 100°C at a rate of 2°C / min and held for 1 hour to allow the solvent to evaporate slowly and evenly, avoiding the formation of bubbles and pinholes; in the second stage, the temperature was increased to 200°C at a rate of 2°C / min and held for 2 hours to allow the polyamic acid to fully imidize and crosslink, forming a dense inner high thermal conductivity coating 13. During the curing process, the resin gradually crosslinks and shrinks, further compressing the micro-flake structure 15, making its arrangement more regular and parallel, and further improving its orientation. After curing, the pipe was cooled to room temperature in the oven.

[0054] Step S5, Performance Testing and Winding: The coating performance of the prepared hollow flat copper wire winding 1 was tested: Scanning electron microscopy was used to observe the cross-section; the inner high thermal conductivity coating 13 was approximately 25 μm thick with a thickness deviation of ±2 μm, exhibiting a tight bond with the copper substrate 12 without peeling or pinhole defects. The orientation factor was tested using the XRD pole figure method, with an f-value of 0.88, indicating a high level of orientation. The radial thermal conductivity was tested using the steady-state heat flow method, showing a value of 7.5 W / mK, a breakdown voltage of 2800 V, and an adhesion grade of 0 (no peeling during the cross-cut adhesion test). The qualified hollow flat copper wire winding 1 was wound onto a rectangular amorphous magnetic ring 2, with thermally conductive structural adhesive filled between the turns. A fluid adapter was welded, and the inductor was assembled into a finished product.

[0055] To verify the influence of process parameters on coating performance, four control processes were set up for comparison. The effects of coating viscosity, flow rate, and curing temperature rise rate on orientation degree and thermal conductivity were investigated. The results are as follows: Comparative Example 2-1: The coating viscosity was 1500 mPa·s, the flow rate was 20 cm / s, and all other parameters were the same. The orientation factor f was tested to be 0.62, and the radial thermal conductivity was 3.2 W / mK. The viscosity was too high, and the fluid shear force was insufficient to effectively align the microplate structure, resulting in low orientation and decreased thermal conductivity.

[0056] Comparative Example 2-2: Coating viscosity 500 mPa·s, flow rate 5 cm / s, all other parameters are the same. Orientation factor f = 0.71, radial thermal conductivity 4.5 W / mK. The flow rate was too low, the shear rate insufficient, and the micro-flake structure 15 was not sufficiently oriented.

[0057] Comparative Example 2-3: The coating viscosity was 500 mPa·s, the flow rate was 20 cm / s, and the curing temperature rise rate was 10 °C / min, with all other parameters remaining the same. The orientation factor f was 0.75, and the radial thermal conductivity was 5.1 W / mK. Excessive heating caused rapid resin cross-linking and fixation, preventing the microplate structure 15 from achieving sufficient orientation, and making the coating prone to bubble defects.

[0058] Comparative Example 2-4: h-BN filler ratio 25 vol%, other parameters are the same. The orientation factor f = 0.86, and the radial thermal conductivity is 2.8 W / mK. With a filler ratio that is too low, a continuous thermally conductive network cannot be formed, resulting in a significant decrease in thermal conductivity.

[0059] Through comparative experiments, it was verified that the process parameters of this embodiment are within the optimal range, which can achieve the high orientation of the micro-chip structure 15 and the excellent performance of the inner high thermal conductivity coating 13. The process window is wide, the controllability is strong, and it is suitable for industrial production.

[0060] Example 3: Preparation of hollow flat copper wire with functionalized inner wall by electrophoretic deposition: This embodiment uses electrophoretic deposition to prepare hollow flat copper wires with functionalized inner walls. It is suitable for hollow flat copper wire windings 1 with large aspect ratio (aspect ratio > 50) and complex cross-sectional shapes. The inner high thermal conductivity coating 13 has better uniformity and adhesion, making it suitable for the batch production of long-size tubes.

[0061] Step S1, Inner wall cleaning and roughening treatment: A 2m long hollow flat copper wire winding 1, with the same specifications as in Example 2, was selected. First, chemical cleaning was performed: alkaline washing to remove oil, acid washing to remove oxidation, and rinsing with deionized water were performed sequentially, following the same steps as in Example 2. Then, surface conditioning was performed before cathodic electrophoresis: the tube was immersed in a 0.5% zinc dihydrogen phosphate solution for 2 minutes to form a phosphating underlayer, improving the adhesion of the high thermal conductivity coating 13 within the electrophoretic layer. After removal, it was rinsed clean and dried for later use.

[0062] Step S2, Preparation of water-based electrophoretic coating: A waterborne epoxy resin system with a solid content of 20 wt% was selected as the matrix resin. Surface cationic modification of h-BN microplates (microplate structure 15) was performed: microplate structure 15 was dispersed in an ethanol-water solution, silane coupling agent KH560 was added, the pH was adjusted to weakly acidic, and the reaction was carried out at 60℃ for 4 h with stirring to graft epoxy groups onto the h-BN surface. Further quaternization treatment was then performed to give the surface a positive charge. The modified microplate structure 15 was added to the waterborne epoxy resin emulsion at a volume filling ratio of 45 vol%, along with appropriate amounts of co-solvent and leveling agent. After high-speed stirring for 30 min, the mixture was ultrasonically dispersed for 15 min to prepare a homogeneous cationic electrophoresis solution. The electrophoresis solution had a solid content of 18 wt%, uniform particle size distribution, a zeta potential of +35 mV, and exhibited good electrophoretic stability.

[0063] Step S3, Electrophoretic deposition coating: A hollow flat copper wire winding 1 is used as the cathode, and a stainless steel auxiliary electrode is placed at the center of the hollow flow channel 14, with a distance of 0.5 mm between the two electrodes. The tube and the electrode are immersed together in the electrophoresis tank, and a DC electric field with an electric field strength of 20 V / cm is applied for a deposition time of 10 min. Under the action of the electric field, the positively charged microplate structure 15 and resin particles migrate towards the inner wall of the copper substrate 12, which serves as the cathode, and are deposited on the inner wall surface. At the same time, in the direction of the electric field perpendicular to the tube wall, the sheet-like microplate structure 15 is subjected to the electric field torque, and the sheets gradually turn to be perpendicular to the inner wall surface, achieving directional alignment. During the deposition process, the temperature of the electrophoretic solution is controlled at 25℃, and a stirring device is used to maintain the uniformity of the electrophoretic solution concentration.

[0064] Step S4, Curing and Post-treatment: After deposition, the pipe is removed, the surface paint is rinsed with deionized water, and then placed in an oven for segmented curing: first, the temperature is increased to 120℃ at 1.5℃ / min and held for 1.5h to allow moisture and co-solvent to evaporate and the resin to initially crosslink; then, the temperature is increased to 190℃ at 2℃ / min and held for 2h to allow the epoxy resin to fully cure and crosslink, forming a dense inner high thermal conductivity coating 13. The volume shrinkage of the resin during the curing process will further optimize the arrangement and orientation of the microplate structure 15, improving the continuity of the thermally conductive network.

[0065] Step S5, Performance Comparison and Winding Assembly: The performance of the high thermal conductivity coating 13 prepared in this embodiment was tested: the coating thickness was approximately 22 μm, with excellent thickness uniformity; the axial thickness deviation of the entire hollow flat copper wire winding 1 was less than ±1 μm; the XRD test showed an orientation factor f=0.90, slightly higher than that of the flow coating method; the radial thermal conductivity was 7.8 W / mK, and the breakdown voltage was 3000 V; the adhesion test showed a grade of 0, indicating better bonding strength than the flow coating method coating. This long-length hollow flat copper wire winding 1 was wound onto a high-power rectangular amorphous magnetic ring 2 to prepare a 15kW-class inductor for automotive OBC. Testing showed that at a 15kW output power and a coolant flow rate of 1.2 L / min, the winding hot spot temperature was 85℃, with a temperature rise of 60℃, demonstrating excellent heat dissipation performance.

[0066] To compare the applicable scenarios of electrophoresis and flow coating, two control groups were set up: Comparing with Example 3-1: A 2m long hollow flat copper wire winding 1 of the same specification was prepared using the flow coating method. Testing revealed that the high thermal conductivity coating 13 in the middle of the tube was 30% thinner than at both ends, with a significant decrease in orientation. The thermal conductivity in the middle was only 5.2 W / mK, and the uniformity was poor. This indicates that when the length-to-diameter ratio is too large, the fluid resistance of the flow coating method leads to uneven flow velocity and reduced coating consistency.

[0067] Comparative Example 3-2: A short hollow flat copper wire winding 1 with a length of 0.5m was prepared by electrophoresis. The coating performance was consistent with that of the long tube, but the equipment cost and process time were slightly higher than those of the flow coating method.

[0068] The results show that electrophoretic deposition has significant advantages in coating the inner wall of hollow flow channels 14 with large aspect ratios and complex cross-sections, resulting in better uniformity, adhesion, and orientation of the inner high thermal conductivity coating 13. Meanwhile, flow coating is more suitable for low-cost, rapid production of medium- and short-sized pipes. The two processes complement each other and can cover the preparation needs of products with different specifications.

[0069] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-power inductor heat dissipation structure with functionalized hollow flat copper wire in the inner wall, comprising a magnetic core and windings wound on the magnetic core, characterized in that: The winding is made of at least one hollow flat copper wire having a fluid cooling channel running through its length; the inner wall of the fluid cooling channel is provided with a high thermal conductivity insulating composite coating; the composite coating includes a resin matrix and sheet-like high thermal conductivity electrical insulating filler dispersed in the resin matrix, the sheet-like high thermal conductivity electrical insulating filler is oriented in the composite coating, and the sheet plane of the filler is substantially perpendicular to the inner wall surface of the fluid cooling channel, thereby forming a continuous low thermal resistance heat conduction channel in the radial direction perpendicular to the inner wall surface.

2. The high-power inductor heat dissipation structure with functionalized hollow flat copper wire inner wall as described in claim 1, characterized in that: The sheet-like high thermal conductivity electrical insulating filler is a hexagonal boron nitride microplate with an average particle size of 0.5μm to 15μm and an aspect ratio greater than 10. The volumetric filling ratio of the hexagonal boron nitride microflakes in the composite coating is 30% to 60%.

3. The high-power inductor heat dissipation structure with functionalized hollow flat copper wire inner wall as described in claim 1, characterized in that: The cross-section of the hollow flat copper wire is rectangular or racetrack-shaped, with a width-to-thickness ratio greater than 3:

1. The copper substrate wall thickness of the hollow flat copper wire is 0.3mm to 1mm, and the cross-sectional area of ​​the fluid cooling channel accounts for 30% to 60% of the total cross-sectional area of ​​the hollow flat copper wire.

4. The high-power inductor heat dissipation structure with functionalized hollow flat copper wire inner wall as described in claim 1, characterized in that: The thickness of the composite coating is 15μm to 35μm, the radial equivalent thermal conductivity of the coating is ≥5W / mK, the breakdown voltage is ≥2000V, and the temperature resistance is ≥180℃.

5. The high-power inductor heat dissipation structure with functionalized hollow flat copper wire inner wall according to claim 1, characterized in that: The resin matrix is ​​one of polyimide, modified epoxy resin or silicone resin; The outer surface of the hollow flat copper wire is provided with an outer insulation layer, and the winding turns are filled with a thermally conductive structural adhesive layer. The thermally conductive structural adhesive layer and the internal fluid cooling channel together form a dual heat dissipation path.

6. A method for preparing a high-power inductive heat dissipation structure with internally functionalized hollow flat copper wire as described in any one of claims 1 to 5, characterized in that, Includes the following steps: S1: Cleaning and surface roughening treatment of the inner wall of the fluid cooling channel of the hollow flat copper wire to remove oil stains and oxide layer and form a micro-rough interface. S2: Disperse the sheet-like high thermal conductivity insulating filler in the precursor solution of the resin matrix, and obtain a uniform insulating coating through dispersion treatment; S3: The insulating coating is uniformly adhered to the inner wall surface of the fluid cooling channel using an inner wall flow coating method or an electrophoretic deposition method; S4: The coated hollow flat copper wire is heated and cured in segments. During the curing process, the filler is kept in an oriented arrangement by fluid shear force or electric field force to form a dense, high thermal conductivity insulating composite coating. S5: The prepared hollow flat copper wire with internal wall functionalization is wound onto the magnetic core and assembled to obtain an inductive heat dissipation structure.

7. The high-power inductor heat dissipation structure and preparation method of the inner wall functionalized hollow flat copper wire according to claim 6, characterized in that: When using the inner wall flow coating method in step S3, the apparent viscosity of the insulating coating is controlled to be 150 mPa·s to 1200 mPa·s, and the flow linear velocity is controlled to be 5 cm / s to 50 cm / s, so that the fluid shear rate is maintained at 10 s. -1 ~100s -1 Through laminar shear force combined with wall constraint effect, the sheet packing is induced to align perpendicular to the inner wall.

8. The method for preparing the high-power inductor heat dissipation structure with functionalized hollow flat copper wire inner wall according to claim 6, characterized in that: When using electrophoretic deposition in step S3, the surface of the sheet-like high thermal conductivity insulating filler is first modified to make it chargeable. The insulating coating is prepared as an aqueous electrophoretic solution, and a DC electric field of 10V / cm to 30V / cm is applied. The deposition time is 5min to 20min. The charged filler is driven by the electric field force to oriented and deposited on the inner wall along the direction of the electric field.

9. The method for preparing the high-power inductor heat dissipation structure with functionalized hollow flat copper wire inner wall according to claim 6, characterized in that: In step S4, the segmented heat curing process is as follows: First, raise the temperature to 80℃ to 120℃ at a heating rate of 0.5℃ / min to 5℃ / min, and hold for 1h to 2h for pre-curing; Then, raise the temperature to 180℃~220℃ at the same heating rate and hold for 1h~3h for post-curing; During the curing process, the solvent slowly evaporates, and the cross-linking shrinkage of the resin further promotes the orientation of the filler sheets perpendicular to the inner wall surface.

10. The method for preparing the high-power inductive heat dissipation structure with functionalized hollow flat copper wire inner wall according to claim 6, characterized in that: In step S1, the cleaning and roughening treatment sequentially involves alkaline washing to remove oil, acid washing to remove oxidation, deionized water rinsing, and plasma roughening. In step S5, after winding, thermally conductive structural adhesive is filled between the winding turns, and fluid adapters are welded to both ends of the winding. The fluid adapters have built-in distribution grooves to distribute the coolant evenly to the fluid cooling channels of each turn.

Images