Flat polyimide wire-based vehicle ethernet common mode inductor and manufacturing method

Abstract

The application discloses a vehicle-mounted Ethernet common mode inductor based on a polyimide flat wire and a manufacturing method, and relates to the technical field of magnetic components. The common mode inductor comprises a DR type skeleton magnetic core, a polyimide flat wire winding and an RI type magnetic shielding sleeve. The winding adopts a rectangular copper wire wrapped by a polyimide film, and high magnetic coupling is realized through vertical overlapping winding or single-layer parallel arrangement. The manufacturing method comprises the steps of raw material preparation, full-automatic winding, laser paint stripping and welding. In the application, the flat wire is used to replace the round wire, and the disorder problem during parallel winding of the round wire is eliminated. The geometric position of the coil is fixed by a machine and a wire shape, and the product consistency is very high. The structure design is fully compatible with the existing full-automatic winding machine, the manual link is removed, and the manufacturing cost is expected to be reduced by 30%-40% compared with the same specification manual annular inductor. The PI material has excellent chemical resistance and heat resistance, and cooperates with the laser welding process to perfectly solve the problems of automobile vibration wire breakage and high-temperature aging short circuit.

Description

Technical Field

[0001] This invention belongs to the field of magnetic components technology, and in particular relates to automotive Ethernet common mode inductors based on polyimide flat wires and their manufacturing methods. Background Technology

[0002] With the rapid development of intelligent connected vehicles, automotive Ethernet technology has gradually become popular due to its advantages of high bandwidth and low latency. The OPEN Alliance has put forward stringent requirements for the common mode inductor of automotive Ethernet interfaces, especially in terms of differential mode insertion loss (Sdd21), return loss (Sdd11), and longitudinal conversion loss (LCL / Ssd21).

[0003] The existing technology has the following core pain points: (1) High-frequency performance limitations of traditional enameled wires: Ordinary polyurethane enameled wires have a high dielectric constant (≥4.5) and uneven coating thickness, resulting in large and fluctuating distributed capacitance between wires when the two wires are wound in parallel, which seriously affects the quality of high-frequency signal transmission and makes it difficult to meet the high-frequency communication requirements of automotive Ethernet; (2) Poor consistency between winding and welding: Traditional round wires are prone to "disorder" when wound in parallel, the coil arrangement is irregular, and the solder depth is difficult to control precisely, which makes it difficult to stabilize the impedance matching within the range of 100Ω±10% during mass production, resulting in low product yield and high production costs; (3) Reliability risks of ordinary flat wires: Ordinary flat wires have poor insulation resistance and are prone to insulation damage at bends, which cannot meet the environmental reliability requirements of automotive electronics AEC-Q200 Grade 1 (-40℃~+125℃). Therefore, it is urgent to develop an automotive Ethernet common-mode inductor that takes into account high-frequency performance, production consistency and high reliability to solve the shortcomings of the existing technology. Summary of the Invention

[0004] The purpose of this invention is to provide a high-performance common-mode inductor that can effectively reduce interlayer parasitic capacitance, improve product consistency, reduce production costs, and fully meet the OPEN Alliance standard in high-frequency communication scenarios such as automotive Ethernet, while also providing a fully automated manufacturing method to achieve mass production.

[0005] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0006] The common-mode inductor structure design of this invention is as follows:

[0007] This invention uses polyimide (PI) coated flat copper wire with low dielectric constant and high temperature resistance as the winding material, combined with a magnetic circuit structure of "DR type skeleton magnetic core + RI type magnetic shielding sleeve", and achieves a balance between high coupling coefficient and low parasitic capacitance through precision winding process.

[0008] Magnetic core assembly: includes an "I"-shaped or "H"-shaped DR Core framework core and an RI Core magnetic shielding sleeve, made of high-permeability, low-frequency-loss nanocrystalline materials (such as Fe). 78 Si 13 B7Cu1Nb1, heat treatment process (such as annealing at 520℃ for 1 hour, followed by furnace cooling) or high-performance nickel-zinc ferrite (parameter range, such as initial permeability μi=1000±100, saturation magnetic flux density Bs≥400mT, Curie temperature Tc≥250℃, high-frequency loss Pcv≤200mW / cm³ at 1MHz / 100mT), to ensure magnetic circuit closure and low loss characteristics; the above parameters must meet the coupling coefficient k≥0.98 when the magnetic circuit is closed. Those skilled in the art can match specific grades (such as nickel-zinc ferrite grade NXO-100) according to conventional magnetic core selection manuals.

[0009] Coil winding: Two rectangular PI insulated flat wires are used. The dielectric constant of the PI insulation layer is ≤3.0, which is significantly lower than that of traditional enameled wire. Under the same wire spacing, the inter-wire parasitic capacitance can be greatly reduced.

[0010] Winding method: adopts double-wire vertical stacking or single-layer parallel arrangement process, utilizes flat wire large contact area to improve magnetic coupling coefficient (k value close to 0.99), and at the same time, the low dielectric constant of PI material offsets the increase in parasitic capacitance caused by the increase in contact area, ensuring the integrity of high frequency signal.

[0011] Fully automated manufacturing process

[0012] This process is fully compatible with existing automated equipment and requires no manual intervention. It includes five major steps: raw material preparation, fully automated winding, laser paint stripping and welding, magnetic circuit closure and shielding, testing and packaging. It solves the problems of low efficiency and poor consistency of traditional processes.

[0013] The fully automated manufacturing method for common mode inductors includes the following steps:

[0014] S1. Raw Material Preparation: Copper flat wires with a width-to-thickness ratio of 3:1 to 6:1 are prepared using a high-precision calendering process. A polyimide insulating layer is then coated onto the surface of the copper flat wire using electrostatic spraying or lamination processes, with the polyimide layer thickness controlled at 10μm-30μm. The lamination process employs hot-press lamination at a temperature of 160℃-190℃, a pressure of 0.3MPa-0.5MPa, and a traction speed of 5m / min-8m / min, ensuring that the PI layer thickness deviation is ≤±1μm. DuPont Kapton® 100HN series PI film is selected, with a dielectric constant of 2.8±0.1 and a dielectric loss tangent ≤0.002 (1GHz).

[0015] S2. Fully automatic winding: The “H”-shaped inner magnetic core is fixed to the main shaft of the fully automatic winding machine. Two polyimide flat wires are fed in synchronously with constant tension through the double guide needle mechanism. They are precisely wound in multiple layers in the middle column of the magnetic core, using vertical stacking or single-layer parallel arrangement.

[0016] Adjust according to the width-to-thickness ratio of the copper flat wire. When the width-to-thickness ratio is 3:1-4:1, the tension is 0.6N-0.8N, and when the width-to-thickness ratio is 5:1-6:1, the tension is 0.8N-1.0N.

[0017] Precision winding specifications: adjacent wire spacing deviation ≤3μm, winding concentricity deviation ≤0.08mm, and number of turns per layer ≤±0.5 turns;

[0018] Dual guide pin parameters: guide pin spacing = copper flat wire width + 0.1mm, wire feeding speed = winding speed × 1.02 (synchronous compensation for wire length loss).

[0019] S3. Laser stripping and welding: The polyimide insulation layer at the end of the winding is stripped using an ultraviolet laser, and the copper wire is connected to the metal end electrode by laser spot welding.

[0020] S4. Magnetic circuit closure and shielding: The wound magnetic core assembly is installed into an RI-type magnetic shielding sleeve, or injected with epoxy resin containing magnetic powder for encapsulation; Ni-Zn ferrite magnetic powder (particle size 2μm-3μm, μi=800) is selected, and the mass ratio of magnetic powder to bisphenol A type epoxy resin is 65:35.

[0021] S5. Testing and Packaging: 100% inspection of products is conducted, including testing for inductance, resistance, and high-frequency S-parameters in the 1MHz-1GHz band. Qualified products are then packaged.

[0022] The present invention has the following advantages over the prior art:

[0023] (1) Meets OPEN Alliance standards: The low dielectric loss tangent of polyimide (PI) enables the inductor to maintain high impedance in the 1MHz-100MHz frequency band, while at frequencies up to 1GHz, the differential mode insertion loss is extremely low and the mode conversion rejection ratio (Scd21) is excellent.

[0024] (2) Solving process problems: Using flat wire instead of round wire eliminates the "disorder" problem when round wire is wound together. The geometric position of the coil is fixed by the machine and the shape of the wire, resulting in extremely high product consistency.

[0025] (3) Cost and efficiency: The structural design is fully compatible with existing T-Core / DR-Core fully automatic winding machines, eliminating manual steps, and the manufacturing cost is expected to be 30%-40% lower than that of manual toroidal inductors of the same specifications;

[0026] (4) High reliability: PI material has excellent chemical resistance and heat resistance. Combined with laser welding process, it perfectly solves the problems of wire breakage due to automotive vibration and short circuit due to high temperature aging.

[0027] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is an exploded view of the overall structure of the common-mode inductor of the present invention;

[0030] Figure 2 This is a schematic diagram of a flat cross-section of polyimide;

[0031] Figure 3 This is a cross-sectional view of the winding structure of the magnetic core. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the description of this invention, it should be understood that the terms "diameter," "surface," "spacing," "width," "thickness," etc., which indicate orientation or positional relationship, are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the components or elements referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting this invention.

[0034] like Figure 1-3 As shown, an in-vehicle Ethernet common-mode inductor has the following specific structure:

[0035] The core is an "H" type DR Core nickel-zinc ferrite core with a central column diameter of 8mm and upper and lower wing plate dimensions of 12mm×12mm. The surface of the central column is provided with precision wire grooves with a spacing of 0.2mm to accommodate the thickness of polyimide flat wire.

[0036] Winding: Copper flat wire with a width-to-thickness ratio of 4:1 (width 1.2mm, thickness 0.3mm), with a 20μm thick PI insulation layer on the surface. The PI film has a dielectric constant of 2.8 and a temperature resistance of 220℃. The two flat wires are wound vertically, with the first wire close to the core column and the second wire stacked on top of the first wire. The number of turns is 6-12, preferably 8-10. The number of turns must match the length of the core column and the size of the flat wire to ensure that the coupling coefficient k≥0.98.

[0037] Magnetic shielding sleeve: RI type nanocrystalline magnetic shielding sleeve is adopted, the inner diameter of which matches the size of the skeleton magnetic core wing plate, and a closed magnetic circuit is formed after assembly;

[0038] Metal end electrodes: Made of brass, they are connected to the ends of the winding copper wires by laser spot welding, with a weld area of ​​0.5 mm².

[0039] This structure achieves a magnetic coupling coefficient k=0.99 through the large contact area of ​​the flat lines, and the low dielectric constant of the PI layer ensures that the inter-line parasitic capacitance is ≤1pF. At a frequency of 1GHz, the differential mode insertion loss is ≤0.5dB, meeting the requirements of 1000BASE-T1 vehicle Ethernet communication.

[0040] The fully automated manufacturing method for the aforementioned common-mode inductor comprises the following steps:

[0041] Raw material preparation: Oxygen-free copper ingots are rolled into copper flat wires with a width-to-thickness ratio of 4:1 (1.2mm×0.3mm) using a high-precision rolling mill. A 20μm thick PI insulation layer is uniformly wrapped on the surface of the copper flat wires by electrostatic spraying. The spraying temperature is controlled at 180℃ to ensure the adhesion of the PI layer.

[0042] Fully automatic winding: The "H" type DR Core magnetic core is fixed on the main shaft of the fully automatic winding machine. The winding tension is set to 0.8N. Two PI flat wires are simultaneously fed into the magnetic core's central guide wire groove through a double guide needle mechanism. Two layers are precisely stacked at a rate of 4 turns per layer, with a winding speed of 100r / min.

[0043] Laser stripping and welding: A 5W ultraviolet laser with a focused spot diameter of 0.1mm is used to strip 5mm of the PI insulation layer at the end of the winding in 1s. Then, the copper wire is connected to the metal end electrode by a laser spot welding device (10W power, welding time 0.3s).

[0044] Magnetic circuit closure and shielding: The wound magnetic core assembly is installed into the RI-type nanocrystalline magnetic shielding sleeve and fixed with epoxy resin. The curing temperature is 70℃-90℃ and the curing time is 20min-40min. After curing, the Shore hardness of the encapsulation is ≥85D. Specifically, the curing temperature is 80℃ and the curing time is 30min.

[0045] Shielding performance requirement: leakage flux ≤ 5% (at 1MHz) after encapsulation;

[0046] Testing and Packaging: 100% inspection of products is carried out using a network analyzer to test inductance (target value: 12μH±5%), DC resistance (≤0.1Ω) and S-parameters in the 1MHz-1GHz frequency band. Qualified products are individually packaged in anti-static bags.

[0047] Specific limits for the OPEN Alliance standard (taking 1000BASE-T1 as an example):

[0048] Differential-mode insertion loss (Sdd21): ≤0.5dB in the 1MHz-1GHz band;

[0049] Return loss (Sdd11): ≤-15dB in the 1MHz-1GHz band;

[0050] Longitudinal conversion loss (Ssd21): ≥30dB in the 1MHz-1GHz band;

[0051] Mode conversion rejection ratio (Scd21): ≥40dB in the 1MHz-1GHz band;

[0052] Testing equipment: Agilent N5247A network analyzer was used, with a test port impedance of 50Ω and a calibration method of SOLT (short-open-load-straight).

[0053] Vibration test: According to AEC-Q200-003 standard, frequency 10Hz-2000Hz, acceleration 20g, test for 2 hours in each of the XYZ directions, after the test, the inductance change rate ≤±5%, no open circuit or short circuit;

[0054] High temperature aging test: Aging at 125℃ and 50% RH for 1000h, the DC resistance change rate after the test is ≤±10%, and the dielectric strength is ≥1kV (AC, 1min).

[0055] High and low temperature cycling test: -40℃ to +125℃ for 50 cycles (1 hour per cycle), after the test, the coupling coefficient k≥0.98, with no insulation damage;

[0056] like Figure 1The diagram shown is an exploded view of the overall structure of a common-mode inductor, where: 10 - magnetic shielding sleeve (RI Core), 20 - polyimide flat wire winding, 30 - skeleton magnetic core (DR Core), and 40 - metal end electrode; Structural relationship: the skeleton magnetic core 30 is located at the center, the polyimide flat wire winding 20 is wound around the central column of the skeleton magnetic core 30, the magnetic shielding sleeve 10 is sleeved on the outside of the skeleton magnetic core 30, and the metal end electrode 40 is fixed to the end face of the upper and lower flanges of the skeleton magnetic core 30 and connected to the end of the winding 20; the wire slot width = flat wire thickness + 0.05mm, the slot depth = flat wire width + 0.05mm, and the slot spacing = flat wire thickness;

[0057] In this embodiment, the groove width is 0.35mm and the groove depth is 1.25mm, corresponding to the flat line thickness of 0.3mm and width of 1.2mm in the corresponding embodiment;

[0058] like Figure 2 The diagram shows a cross-sectional view of a polyimide flat wire; a-rectangular copper conductor, b-polyimide insulating layer; dimensional relationship: the width-to-thickness ratio of the rectangular copper conductor a is 4:1 (1.2mm × 0.3mm), and the polyimide insulating layer b has a uniform thickness of 20μm and wraps around the outer periphery of the copper conductor a;

[0059] like Figure 3 The diagram shows a cross-sectional view of the core post winding structure: 1-Core Post, 2-Wire A (first polyimide flat wire), 3-Wire B (second polyimide flat wire); Positional relationship: The first polyimide flat wire 2 is closely attached to the surface of the core post 1, and the second polyimide flat wire 3 is tightly stacked on top of the first polyimide flat wire 2. The contact area between the two is ≥95%, and the winding direction is consistent, demonstrating high coupling coefficient characteristics.

[0060] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. An automotive Ethernet common-mode inductor based on polyimide flat wire, characterized in that, include: The skeleton core is a ferrite core with a central column and upper and lower flanges. The surface of the central column is provided with precision wire grooves, and the core material is nanocrystalline or high-performance nickel-zinc ferrite. The coil winding is composed of two rectangular cross-section polyimide insulated flat wires wrapped with rectangular copper wires. The film thickness of the polyimide insulated flat wires is 10μm-30μm, the temperature resistance is ≥200℃, and the width-to-thickness ratio of the rectangular copper wires is 3:1 to 6:

1. The magnetic shielding sleeve is an RI-type magnetic shielding sleeve or an epoxy resin encapsulation structure containing magnetic powder, which forms a closed magnetic circuit with the skeleton magnetic core. The metal end electrodes are connected to the winding copper wires by laser spot welding; the windings are wound on the central column of the magnetic core in a double-wire vertical stacking or single-layer parallel arrangement manner, with a magnetic coupling coefficient k≥0.

98.

2. The automotive Ethernet common-mode inductor based on polyimide flat wire according to claim 1, characterized in that, The dielectric constant of the polyimide film is ≤3.0, and the dielectric loss tangent is ≤0.003 in the 1MHz-1GHz frequency band.

3. The automotive Ethernet common-mode inductor based on polyimide flat wire according to claim 1, characterized in that, The core is an "I" or "H" shaped inner core, and the spacing between the wire slots in the core is adapted to the thickness of the polyimide insulated flat wire.

4. A method for manufacturing an automotive Ethernet common-mode inductor based on polyimide flat wire, used to manufacture the automotive Ethernet common-mode inductor as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Raw material preparation: Copper flat wires with a width-to-thickness ratio of 3:1 to 6:1 are prepared using a high-precision rolling process. A polyimide insulating layer is wrapped on the surface of the copper flat wires by electrostatic spraying or film coating process, and the thickness of the polyimide layer is controlled to be 10μm-30μm. S2. Fully automatic winding: The "H"-shaped inner magnetic core is fixed to the main shaft of the fully automatic winding machine. Two polyimide flat wires are fed in synchronously with constant tension through the double guide needle mechanism. They are precisely wound in multiple layers in the middle column of the magnetic core, using vertical stacking or single-layer parallel arrangement. S3. Laser stripping and welding: The polyimide insulation layer at the end of the winding is stripped using an ultraviolet laser, and the copper wire is connected to the metal end electrode by laser spot welding. S4. Magnetic circuit closure and shielding: The wound magnetic core assembly is installed into an RI-type magnetic shielding sleeve, or encapsulated by injecting epoxy resin containing magnetic powder. S5. Testing and Packaging: 100% inspection of products is conducted, including testing for inductance, resistance, and high-frequency S-parameters in the 1MHz-1GHz band. Qualified products are then packaged.

5. The automotive Ethernet common-mode inductor based on polyimide flat wire and its manufacturing method according to claim 1, characterized in that, In step S3, the power of the ultraviolet laser is matched with the stripping time, so that the polyimide insulating layer is completely removed without damaging the copper conductor.

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