High-pressure molded copper-iron co-fired inductor and preparation method thereof

Abstract

The invention relates to the technical field of magnetic functional materials, in particular to a high-pressure molded copper-iron co-fired inductor and a preparation method thereof. The preparation method comprises the following steps: S1, pretreating a copper sheet; s2, coating an insulating layer; s3, preparing soft magnetic metal powder; s4, preparing a magnetic powder core; and S5, preparing the copper-iron co-fired inductor: performing two-way compression molding on the magnetic powder core through a mold, performing gradient annealing on the magnetic powder core by using a reducing atmosphere, finally soaking the magnetic powder core in an epoxy resin acetone solution under the vacuum degree of 0.05 MPa, washing the magnetic powder core with acetone for three times, and baking the magnetic powder core to obtain the high-pressure molded copper-iron co-fired inductor. Through deep combination of material innovation (passivation / coating / lubrication system) and process optimization (stepped curing-bidirectional pressing-gradient annealing), breakthrough improvement of the high-pressure molded copper-iron co-fired inductor in the aspects of loss, voltage resistance, reliability and the like is realized, meanwhile, the production cost is remarkably reduced, and a core device is provided for upgrading of high-frequency power electronic equipment.

Description

Technical Field

[0001] This application relates to the field of magnetic functional materials technology, and in particular to a high-pressure molded copper-iron co-fired inductor and its preparation method. Background Technology

[0002] Chip inductors are a key component of chip power supply modules, providing power to the front-end of chips such as GPUs and CPUs. As electronic products evolve towards higher efficiency, higher power density, and miniaturization, improving chip inductor performance and optimizing its size have become urgent issues to address.

[0003] The latest type of chip inductor is the copper-iron co-fired inductor. This technology combines a magnetic powder core with a molded inductor. Copper wires or sheets embedded within soft magnetic metal powder are pressed together under high pressure. This achieves both the high density and high permeability of the magnetic powder core material and the "iron-clad copper" magnetic shielding and mechanized mass production advantages of the molded inductor. However, due to the immaturity of the copper-iron co-fired inductor technology, its inductor performance still needs improvement. The most obvious drawbacks are the low inductance value and inductance loss of copper-iron co-fired inductors. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a high-voltage formed copper-iron co-fired inductor and its preparation method. The preparation method of this application is simple, the reaction conditions are mild, and the cost is low. The high-voltage formed copper-iron co-fired inductor prepared by this application has excellent loss performance, inductance value, insulation withstand voltage, and reliability.

[0005] In a first aspect, this application provides a method for preparing a high-voltage molded copper-iron co-fired inductor, which adopts the following technical solution: A method for preparing a high-voltage molded copper-iron co-fired inductor includes the following steps: S1. Copper sheet pretreatment: After degreasing, acid activation, and nitrogen drying of the copper sheet surface, oxygen plasma treatment is used to enhance surface roughness and adhesion, resulting in pretreated copper sheets. S2. Coating the insulating layer: After completely immersing the pretreated copper sheet in the polyimide coating for 5-8 minutes, remove it and dry it in an 80℃ oven for 30-40 minutes. Then, under nitrogen protection, cure it by step-by-step heating and cool it to room temperature to obtain a copper sheet coated with a polyimide insulating layer. The step-by-step heating and curing process conditions are as follows: heat up to 150℃ and hold for 1 hour, then heat up to 250℃ and hold for 1 hour, and finally heat up to 330℃ and hold for 2 hours. S3. Preparation of soft magnetic metal powder: First, mix gas-atomized iron-silicon-chromium alloy powders of different particle sizes to obtain mixed powder, and then mix them with passivating agent, coating agent and lubricant in sequence to obtain soft magnetic metal powder. S4. Preparation of magnetic powder core: A copper sheet coated with a polyimide insulating layer is placed in the center of a soft magnetic metal powder. The soft magnetic metal powder is present on both the top and bottom surfaces of the copper sheet coated with the polyimide insulating layer. The two ends of the copper sheet coated with the polyimide insulating layer extend beyond the soft magnetic metal powder to obtain a magnetic powder core. S5. Preparation of copper-iron co-fired inductor: The magnetic powder core is bidirectionally pressed into shape using a mold, then subjected to gradient annealing in a reducing atmosphere, and finally immersed in an epoxy resin acetone solution under a vacuum of 0.05 MPa. After washing with acetone three times and baking, a high-pressure molded copper-iron co-fired inductor is obtained.

[0006] By adopting the above technical solutions, the S1 copper sheet pretreatment removes surface impurities through degreasing and acid activation, while oxygen plasma treatment increases surface roughness, significantly improving the adhesion of the subsequent polyimide coating. This provides a clean and highly active surface for the S2 insulating layer coating, avoiding the risk of coating peeling. The S2 insulating layer is coated, with polyimide forming a dense insulating layer through stepped curing (150℃→250℃→330℃); nitrogen protection prevents copper oxidation and ensures the thermal stability of the coating. S3 prepares soft magnetic metal powder, with multi-particle-size mixing optimizing the filling density (reducing air gaps); a passivating agent generates an iron oxide insulating layer, a coating agent constructs a high-temperature resistant protective layer, and a lubricant improves pressing flowability. This provides a high-permeability, low-loss magnetic medium for the S4 magnetic powder core, while ensuring the operability of the pressing process. The S4 magnetic powder core is prepared with centrally symmetrically distributed copper sheets to achieve a uniform magnetic field; the exposed ends of the copper sheets provide interfaces for subsequent welding. The structure, combined with the S5 bidirectional pressing process, avoids pressing misalignment and ensures precise positioning of the inductor coil and magnetic core. S5 copper-iron co-fired inductors are formed using bidirectional pressing to achieve a high-density magnetic core; gradient annealing eliminates stress and stabilizes the coating layer; epoxy resin impregnation fills micropores and enhances mechanical strength. Through a combination of processes (pressing-annealing-encapsulation), low loss and high reliability are ultimately achieved. Passivating agents (such as phosphoric acid + oxalic acid): Phosphoric acid: The acidic environment accelerates metal surface oxidation, promoting the reaction of oxalic acid with Fe, Si, and Cr to form an oxalate passivation film. Oxalic acid: Reacts with the metal to form iron oxalate, which decomposes into a uniform iron oxide insulating layer after annealing, reducing eddy current losses. The dual-acid system achieves rapid passivation and uniform oxide layer formation, improving passivation efficiency. Coating agents (such as RF-901 fluorosilicone resin + titanium trifluoride + aluminum hexafluoroacetylacetonate): RF-901 fluorosilicone resin: Its hydrophobicity and chemical inertness provide a corrosion-resistant barrier, reducing insulation failure caused by moisture absorption. Titanium trifluoride (TiF3): Its negative thermal expansion characteristics offset high-temperature volume expansion stress, preventing coating layer cracking; its high insulation suppresses leakage current. Aluminum hexafluoroacetylacetonate: Annealing decomposes into alumina nanoparticles, filling coating layer defects and improving withstand voltage. The three components form a gradient coating structure (fluorosilicone resin outer layer - TiF3 intermediate layer - Al2O3 inner layer), enhancing insulation withstand voltage. Lubricant (e.g., fumed alumina + hexagonal boron nitride): Fumed alumina nanoparticles adsorb onto the powder surface, reducing van der Waals forces and improving flowability. Hexagonal boron nitride (h-BN): Forms a liquid lubricating film during pressing, reducing mold friction loss. Alumina improves room temperature flowability, while h-BN provides high-temperature lubrication, increasing pressing density. Gas-atomized iron-silicon-chromium alloy powder, multi-particle size mixing: Mixing gas-atomized iron-silicon-chromium alloy powders of different particle sizes results in better sphericity, increasing dense contact between powder particles, enabling high-density filling of magnetic powder and achieving high inductance performance.In summary, this method achieves the integrated fabrication of high-density, low-loss inductors through precise coordination between steps (pretreatment-coating-magnetic powder design-molding) and complementary component functions (insulation-lubrication-thermal stability), with comprehensive performance meeting the requirements of high-frequency, high-current applications (such as 5G base station power supplies and new energy vehicle electronic control systems).

[0007] Preferably, in step S1, the copper sheet has a thickness of 40-65 μm and a width of 2-4 mm; the degreasing of the copper sheet surface refers to ultrasonically cleaning the copper sheet in acetone for 10-15 minutes to remove grease and residual contaminants; the acid activation process is: ultrasonic activation in 5% dilute sulfuric acid solution for 1-1.5 minutes to remove surface oxides; the oxygen plasma treatment process is: treatment in an oxygen atmosphere at a power of 300W for 3-5 minutes.

[0008] Preferably, in step S2, the polyimide coating comprises the following components by mass percentage: 38-42% polyimide resin, 1-2% silane coupling agent (KH-550), and the balance being N-methylpyrrolidone; the thickness of the polyimide insulating layer is 10-20 μm.

[0009] By employing the above technical solutions, polyimide resin, as the film-forming matrix, provides high insulation, high temperature resistance, and mechanical strength. Its prepolymer solution can form a uniform film through dip coating, and after step-curing, cross-linking forms a dense structure that resists stress during subsequent pressing and annealing processes. The silane coupling agent KH-550: the amino group (-NH2) in the molecule reacts with the hydroxyl group (-OH) treated by oxygen plasma on the copper sheet surface to form a chemical bond; the other end couples with the imide group of the polyimide resin, improving coating adhesion. The hydrophobic group (-Si-O-) of the coupling agent reduces the coating's water absorption, enhancing insulation stability under humid and hot environments. The strong dissolving power of N-methylpyrrolidone ensures uniform resin dispersion and a moderate evaporation rate, preventing skinning or internal bubbles on the coating surface, forming a defect-free film. KH-550 forms a "chemical bridge" between the resin and the copper sheet, improving the peel strength between the polyimide insulation layer and the copper sheet, while reducing interfacial thermal stress cracking during high-temperature curing. The high solubility of NMP ensures that the resin molecular chains are fully extended, resulting in a more ordered molecular arrangement after curing. Furthermore, the gradual evaporation of the solvent during stepped temperature curing avoids micropores caused by sudden boiling. The thermal expansion coefficient of polyimide is close to that of copper, reducing the risk of interfacial delamination under temperature cycling, and thickness control further alleviates thermal stress concentration. This polyimide coating, through precise component ratios (resin-KH-550-NMP) and thickness control (10-20μm), achieves a combination of a high-adhesion insulation layer and process compatibility, contributing to improved inductance performance, inductance value, insulation withstand voltage, and reliability.

[0010] Preferably, in step S3, the different particle sizes are D50 = 25-30 μm, D50 = 8-10 μm and D50 = 1-3 μm, and the gas-atomized iron-silicon-chromium alloy powders of different particle sizes account for 50%, 35% and 15% of the mixed powder, respectively.

[0011] By adopting the above technical solution, the gas-atomized iron-silicon-chromium alloy powders of different particle sizes are mixed to achieve better sphericity and increase the dense contact between powder particles. The gas-atomized iron-silicon-chromium alloy powders of this application with the mass ratio and particle size ratio can achieve high-density filling of magnetic powder and achieve high inductance performance.

[0012] Preferably, in step S3, the passivating agent is a mixed solution of phosphoric acid and oxalic acid; the amount of phosphoric acid used is 0.4-0.6 wt% of the mass of the mixed powder; and the amount of oxalic acid used is 0.2-0.3 wt% of the mass of the mixed powder.

[0013] By adopting the above technical solution, a mixed solution of phosphoric acid and oxalic acid is used as a passivating agent. Phosphoric acid provides acidity and oxidizing properties, which promotes the passivation reaction between oxalic acid and gas-atomized iron-silicon-chromium alloy powder. The generated iron oxalate will decompose into iron oxide during high-temperature annealing. This can uniformly coat the powder surface, improve the insulation performance of the powder, reduce eddy current losses between powders, and thus reduce the total inductance loss.

[0014] Preferably, in step S3, the coating agent is composed of RF-901 solvent-based fluorosilicone resin, titanium trifluoride, aluminum hexafluoroacetylacetonate, and acetone; wherein the amount of RF-901 solvent-based fluorosilicone resin is 2-3 wt% of the mass of the mixed powder; the amount of titanium trifluoride is 0.02-0.04 wt% of the mass of the mixed powder; the amount of aluminum hexafluoroacetylacetonate is 0.6-0.8 wt% of the mass of the mixed powder; and the amount of acetone is 7-7.5 wt% of the mass of the mixed powder.

[0015] By adopting the above technical solution, RF-901 solvent-based fluorosilicone resin, as the main film-forming material for coating, forms a continuous hydrophobic film layer after solvent evaporation, blocking the penetration of moisture and corrosive media and improving pressure resistance. The high chemical inertness (resistance to acids / alkalis / solvents) of the fluorosilicone resin protects the soft magnetic powder from environmental corrosion, ensuring long-term reliability. Aluminum hexafluoroacetylacetonate also decomposes into aluminum oxide during high-temperature annealing and grows uniformly on the powder surface, effectively reducing inductance loss. Furthermore, Al₂O and TiF₃ form Al-O-Ti bonds during annealing, enhancing the interfacial bonding between the coating layer and the passivation layer (Fe₂O₃ / Cr₂O₃). Titanium trifluoride possesses excellent insulation and thermal stability, and it does not decompose during high-temperature annealing, ensuring the stability of the coating layer. More importantly, titanium trifluoride has a certain negative coefficient of thermal expansion, meaning that it does not expand in volume during high-temperature annealing but rather shrinks slightly. This effectively avoids film rupture caused by coating expansion, ensuring the integrity of the coating layer. In summary, this coating agent, through precise formulation of resin, nanofiller, and solvent, constructs a composite coating layer that combines high insulation, thermal stability, and process compatibility.

[0016] Preferably, in step S3, the lubricant is composed of fumed alumina and hexagonal boron nitride in a mass ratio of 4:3; the amount of lubricant used is 0.1-0.3 wt% of the mass of the mixed powder.

[0017] By employing the above technical solution, fumed alumina and atomized iron-silicon-chromium alloy powder, after being mixed, can be orderly bonded to the surface of powder particles, forming a shell layer. This shell layer effectively reduces the electrostatic attraction between particles, preventing powder adhesion caused by van der Waals forces, moisture absorption, and particle friction, thereby improving powder flowability and increasing the inductance value of the inductor. Hexagonal boron nitride is used as the lubricant. During the bidirectional pressing process of the magnetic powder core, hexagonal boron nitride rapidly transforms into a liquid lubricating film due to the rapid increase in pressure and temperature, thus providing lubrication. These two synergistic effects further improve the inductor's loss performance, inductance value, insulation withstand voltage, and reliability.

[0018] Preferably, in step S5, the pressure of the bidirectional pressing is 2000-2200 MPa; the reducing atmosphere is a mixture of hydrogen and argon, wherein the volume of hydrogen accounts for 11-15% of the volume of the mixture; the gradient annealing process conditions are as follows: the temperature is gradually increased in the following stages: the first stage is 40 min from room temperature to 180℃ and held for 30 min; the second stage is 40 min from room temperature to 320℃ and held for 30 min; the third stage is 40 min from room temperature to 480℃ and held for 30 min; the fourth stage is 40 min from room temperature to 620℃ and held for 30 min; the fifth stage is the last 40 min from room temperature to 720℃-780℃ and held for 120 min, followed by natural cooling to room temperature.

[0019] Preferably, in step S5, the baking temperature is 180-200℃ and the baking time is 60-70 minutes.

[0020] Secondly, this application provides a high-voltage formed copper-iron co-fired inductor, which adopts the following technical solution: As a general technical concept, this application also provides a high-voltage formed copper-iron co-fired inductor prepared by the above-mentioned high-voltage formed copper-iron co-fired inductor preparation method.

[0021] In summary, this application includes at least one of the following beneficial technical effects: 1. Performance Improvement: Low loss: The inductance loss is effectively reduced through specially treated insulation and coating layers.

[0022] High inductance: The use of alloy powders with different particle sizes improves the stability of the inductance value.

[0023] High insulation and withstand voltage: The polyimide coating and overlay together enhance the insulation performance.

[0024] 2. Process simplification and cost optimization: Mild process conditions: Stepped curing and reducing atmosphere annealing reduce energy consumption and equipment investment.

[0025] High-efficiency molding: The application of lubricant reduces wear during the pressing process and improves molding efficiency.

[0026] High material utilization rate: The pre-embedded copper sheet design reduces material waste.

[0027] 3. Reliability and environmental adaptability: High mechanical strength: The flexural strength is improved by impregnation with epoxy resin.

[0028] Corrosion resistance: The use of fluorosilicone resin and alumina enhances corrosion resistance.

[0029] Long life design: Gradient annealing process improves long-term reliability.

[0030] 4. Wide range of applications: High-frequency, high-current applications: suitable for 5G base stations, new energy vehicles, and photovoltaic inverters, etc.

[0031] Miniaturization potential: Enables miniaturized inductor designs, increasing power density. Detailed Implementation

[0032] The embodiments of this application will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of this application. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available products. RF-901 solvent-based fluorosilicone resin was purchased from Fuxin Ruifeng Fluorochemical Co., Ltd.

[0033] In the following embodiments, the copper sheet has a thickness of 50 μm, a width of 3 mm, and a length of 36 mm.

[0034] Example 1 A method for preparing a high-pressure molded copper-iron co-fired inductor includes the following steps: S1. Copper sheet pretreatment: The copper sheet is placed in acetone and ultrasonically cleaned for 10 minutes to remove grease and residual contaminants; then it is placed in a 5% dilute sulfuric acid solution and ultrasonically activated for 1 minute to remove surface oxides; after being dried with nitrogen, it is treated with oxygen plasma. The oxygen plasma treatment process is as follows: in an oxygen atmosphere, the power is 300W and the treatment time is 3 minutes to enhance the surface roughness and adhesion, thus obtaining the pretreated copper sheet. S2. Coating the insulating layer: After completely immersing the pretreated copper sheet in the polyimide coating for 5 minutes, remove it and dry it in an 80°C oven for 30 minutes. Then, under nitrogen protection, cure it by step-by-step heating and cool it to room temperature to obtain a copper sheet with a polyimide insulating layer of 10 μm thickness. The step-by-step heating curing process conditions are: heating to 150°C and holding for 1 hour, then heating to 250°C and holding for 1 hour, and finally heating to 330°C and holding for 2 hours. The polyimide coating comprises the following components by mass percentage: 38% polyimide resin, 1% silane coupling agent (KH-550), and the balance being N-methylpyrrolidone. S3. Preparation of soft magnetic metal powder: First, mix 50g of gas-atomized iron-silicon-chromium alloy powder with D50=25μm, 35g of D50=8μm and 15g of D50=1μm to obtain a mixed powder. Add 0.4g of phosphoric acid, 0.2g of oxalic acid and 10g of distilled water to the mixed powder, stir and heat to 120℃ and keep warm for 30 minutes. After the powder is dried, cool to room temperature. Add 2g of RF-901 solvent-based fluorosilicone resin, 0.02g of titanium trifluoride, 0.6g of aluminum hexafluoroacetylacetonate and 7g of acetone to the cooled powder, stir and heat to 93℃. After the powder is dried, cool to room temperature to obtain a coated powder. Add 0.1g of lubricant to the coated powder and mix evenly. The lubricant is composed of fumed alumina and hexagonal boron nitride in a mass ratio of 4:3 to obtain soft magnetic metal powder. S4. Preparation of magnetic powder core: A copper sheet coated with a polyimide insulating layer is placed in the center of a soft magnetic metal powder. The soft magnetic metal powder is present on both the top and bottom surfaces of the copper sheet coated with the polyimide insulating layer. The two ends of the copper sheet coated with the polyimide insulating layer extend beyond the soft magnetic metal powder to obtain a magnetic powder core. S5. Preparation of Copper-Iron Co-fired Inductors: Magnetic powder cores are placed in a mold and subjected to bidirectional pressing at 2000 MPa to obtain a pressed product. The pressed product is then subjected to gradient annealing in a mixture of hydrogen and argon, where the hydrogen volume accounts for 11% of the mixed gas volume. The gradient annealing process conditions are as follows: The temperature is gradually increased in the following stages: Stage 1: 40 min at room temperature to 180℃, held for 30 min; Stage 2: 40 min at room temperature to 320℃, held for 30 min; Stage 3: 40 min at 480℃, held for 30 min; Stage 4: 40 min at 620℃, held for 30 min; Stage 5: 40 min at 720℃, held for 120 min, and then naturally cooled to room temperature. Finally, under a vacuum of 0.05 MPa, the product is immersed in a 50% solids epoxy resin acetone solution for 10 minutes, washed three times with acetone, and baked at 180℃ for 70 minutes to obtain a high-pressure molded copper-iron co-fired inductor.

[0035] Example 2 A method for preparing a high-pressure molded copper-iron co-fired inductor includes the following steps: S1. Copper sheet pretreatment: The copper sheet is placed in acetone and ultrasonically cleaned for 15 minutes to remove grease and residual contaminants; then it is placed in a 5% dilute sulfuric acid solution and ultrasonically activated for 1.5 minutes to remove surface oxides; after being dried with nitrogen, it is treated with oxygen plasma. The oxygen plasma treatment process is as follows: in an oxygen atmosphere, the power is 300W and the treatment time is 5 minutes to enhance the surface roughness and adhesion, thus obtaining the pretreated copper sheet. S2. Coating the insulating layer: After completely immersing the pretreated copper sheet in the polyimide coating for 8 minutes, remove it and dry it in an oven at 80°C for 40 minutes. Then, under nitrogen protection, cure it by step-by-step heating and cool it to room temperature to obtain a copper sheet with a polyimide insulating layer of 20 μm thickness. The step-by-step heating curing process conditions are: heating to 150°C and holding for 1 hour, then heating to 250°C and holding for 1 hour, and finally heating to 330°C and holding for 2 hours. The polyimide coating comprises the following components by mass percentage: 42% polyimide resin, 2% silane coupling agent (KH-550), and the balance being N-methylpyrrolidone. S3. Preparation of soft magnetic metal powder: First, mix 50g of gas-atomized iron-silicon-chromium alloy powder with D50=30μm, 35g of D50=10μm and 15g of D50=3μm to obtain a mixed powder. Add 0.6g of phosphoric acid, 0.3g of oxalic acid and 10g of distilled water to the mixed powder, stir and heat to 120℃ and keep warm for 30 minutes. After the powder is dried, cool to room temperature. Add 3g of RF-901 solvent-based fluorosilicone resin, 0.03g of titanium trifluoride, 0.8g of aluminum hexafluoroacetylacetonate and 7.5g of acetone to the cooled powder, stir and heat to 93℃. After the powder is dried, cool to room temperature to obtain a coated powder. Add 0.3g of lubricant to the coated powder and mix evenly. The lubricant is composed of fumed alumina and hexagonal boron nitride in a mass ratio of 4:3 to obtain soft magnetic metal powder. S4. Preparation of magnetic powder core: A copper sheet coated with a polyimide insulating layer is placed in the center of a soft magnetic metal powder. The soft magnetic metal powder is present on both the top and bottom surfaces of the copper sheet coated with the polyimide insulating layer. The two ends of the copper sheet coated with the polyimide insulating layer extend beyond the soft magnetic metal powder to obtain a magnetic powder core. S5. Preparation of Copper-Iron Co-fired Inductors: Magnetic powder cores are placed in a mold and subjected to bidirectional pressing at 2200 MPa to obtain a pressed product. The pressed product is then subjected to gradient annealing in a mixture of hydrogen and argon, where the hydrogen volume accounts for 15% of the mixed gas volume. The gradient annealing process conditions are as follows: The temperature is gradually increased in the following stages: Stage 1: 40 min at room temperature to 180℃, held for 30 min; Stage 2: 40 min at room temperature to 320℃, held for 30 min; Stage 3: 40 min at 480℃, held for 30 min; Stage 4: 40 min at 620℃, held for 30 min; Stage 5: 40 min at 780℃, held for 120 min, and then naturally cooled to room temperature. Finally, under a vacuum of 0.05 MPa, the product is immersed in a 50% solids epoxy resin acetone solution for 10 minutes, washed three times with acetone, and baked at 200℃ for 60 minutes to obtain a high-pressure molded copper-iron co-fired inductor.

[0036] Example 3 A method for preparing a high-pressure molded copper-iron co-fired inductor includes the following steps: S1. Copper sheet pretreatment: The copper sheet is placed in acetone and ultrasonically cleaned for 13 minutes to remove grease and residual contaminants; then it is placed in a 5% dilute sulfuric acid solution and ultrasonically activated for 1.2 minutes to remove surface oxides; after drying with nitrogen, it is treated with oxygen plasma. The oxygen plasma treatment process is as follows: in an oxygen atmosphere, the power is 300W and the treatment time is 4 minutes to enhance the surface roughness and adhesion, thus obtaining the pretreated copper sheet. S2. Coating the insulating layer: After the pretreated copper sheet is completely immersed in the polyimide coating for 6 minutes, it is taken out and dried in an oven at 80°C for 35 minutes. Then, under nitrogen protection, it is cured by step-by-step heating and cooled to room temperature to obtain a copper sheet with a polyimide insulating layer with a thickness of 13μm. The step-by-step heating process conditions are: heating to 150°C and holding for 1 hour, then heating to 250°C and holding for 1 hour, and finally heating to 330°C and holding for 2 hours. The polyimide coating comprises the following components by mass percentage: 40% polyimide resin, 1.2% silane coupling agent (KH-550), and the balance being N-methylpyrrolidone. S3. Preparation of soft magnetic metal powder: First, mix 50g of gas-atomized iron-silicon-chromium alloy powder with D50=28μm, 35g of D50=9μm and 15g of D50=2μm to obtain a mixed powder. Add 0.5g of phosphoric acid, 0.25g of oxalic acid and 10g of distilled water to the mixed powder, stir and heat to 120℃ and keep warm for 30 minutes. After the powder is dried, cool to room temperature. Add 2.3g of RF-901 solvent-based fluorosilicone resin, 0.025g of titanium trifluoride, 0.7g of aluminum hexafluoroacetylacetonate and 7.3g of acetone to the cooled powder, stir and heat to 93℃. After the powder is dried, cool to room temperature to obtain a coated powder. Add 0.2g of lubricant to the coated powder and mix evenly. The lubricant is composed of fumed alumina and hexagonal boron nitride in a mass ratio of 4:3 to obtain soft magnetic metal powder. S4. Preparation of magnetic powder core: A copper sheet coated with a polyimide insulating layer is placed in the center of a soft magnetic metal powder. The soft magnetic metal powder is present on both the top and bottom surfaces of the copper sheet coated with the polyimide insulating layer. The two ends of the copper sheet coated with the polyimide insulating layer extend beyond the soft magnetic metal powder to obtain a magnetic powder core. S5. Preparation of Copper-Iron Co-fired Inductors: Magnetic powder cores are placed in a mold and subjected to bidirectional pressing at 2100 MPa to obtain a pressed product. The pressed product is then subjected to gradient annealing in a mixture of hydrogen and argon, where the hydrogen volume accounts for 12% of the mixed gas volume. The gradient annealing process conditions are as follows: The temperature is gradually increased in the following stages: Stage 1: 40 min at room temperature to 180℃, held for 30 min; Stage 2: 40 min at room temperature to 320℃, held for 30 min; Stage 3: 40 min at 480℃, held for 30 min; Stage 4: 40 min at 620℃, held for 30 min; Stage 5: 40 min at 750℃, held for 120 min, and then naturally cooled to room temperature. Finally, under a vacuum of 0.05 MPa, the product is immersed in a 50% solids epoxy resin acetone solution for 10 minutes, washed three times with acetone, and baked at 190℃ for 65 minutes to obtain a high-pressure molded copper-iron co-fired inductor.

[0037] Comparative Example 1 Similar to Example 3, except that step S2, coating the insulating layer, is omitted, and in step S4, preparing the magnetic powder, the pretreated copper sheet is placed directly in the center of the soft magnetic metal powder.

[0038] Comparative Example 2 Similar to Example 3, except that in S3, the soft magnetic metal powder is prepared as follows: 50g of gas-atomized iron-silicon-chromium alloy powder with D50 = 28μm, 35g of D50 = 9μm and 15g of D50 = 2μm are mixed to obtain a mixed powder. 0.75g of phosphoric acid and 10g of distilled water are added to the mixed powder, stirred and heated to 120°C for 30 minutes. After the powder dries, it is cooled to room temperature. 2.3g of RF-901 solvent-based fluorosilicone resin, 0.025g of titanium trifluoride, 0.7g of aluminum hexafluoroacetylacetonate and 7.3g of acetone are added to the cooled powder, stirred and heated to 93°C. After the powder dries, it is cooled to room temperature to obtain a coated powder. 0.2g of lubricant is added to the coated powder and mixed evenly. The lubricant is composed of fumed alumina and hexagonal boron nitride in a mass ratio of 4:3 to obtain the soft magnetic metal powder.

[0039] Comparative Example 3 Similar to Example 3, except that in S3, the soft magnetic metal powder is prepared as follows: 50g of gas-atomized iron-silicon-chromium alloy powder with D50 = 28μm, 35g of D50 = 9μm and 15g of D50 = 2μm are mixed to obtain a mixed powder. 0.75g of oxalic acid and 10g of distilled water are added to the mixed powder, stirred and heated to 120°C for 30 minutes. After the powder dries, it is cooled to room temperature. 2.3g of RF-901 solvent-based fluorosilicone resin, 0.025g of titanium trifluoride, 0.7g of aluminum hexafluoroacetylacetonate and 7.3g of acetone are added to the cooled powder, stirred and heated to 93°C. After the powder dries, it is cooled to room temperature to obtain a coated powder. 0.2g of lubricant is added to the coated powder and mixed evenly. The lubricant is composed of fumed alumina and hexagonal boron nitride in a mass ratio of 4:3 to obtain the soft magnetic metal powder.

[0040] Comparative Example 4 Similar to Example 3, except that in S3, the soft magnetic metal powder is prepared as follows: 50g of gas-atomized iron-silicon-chromium alloy powder with D50 = 28μm, 35g of D50 = 9μm and 15g of D50 = 2μm are mixed to obtain a mixed powder. 0.5g of phosphoric acid, 0.25g of oxalic acid and 10g of distilled water are added to the mixed powder, stirred and heated to 120°C for 30 minutes. After the powder dries, it is cooled to room temperature. 2.3g of RF-901 solvent-based fluorosilicone resin and 7.3g of acetone are added to the cooled powder, stirred and heated to 93°C. After the powder dries, it is cooled to room temperature to obtain a coated powder. 0.2g of lubricant is added to the coated powder and mixed evenly. The lubricant is composed of fumed alumina and hexagonal boron nitride in a mass ratio of 4:3 to obtain the soft magnetic metal powder.

[0041] Comparative Example 5 Similar to Example 3, except that in S3, the soft magnetic metal powder is prepared as follows: 50g of gas-atomized iron-silicon-chromium alloy powder with D50 = 28μm, 35g of D50 = 9μm and 15g of D50 = 2μm are mixed to obtain a mixed powder. 0.5g of phosphoric acid, 0.25g of oxalic acid and 10g of distilled water are added to the mixed powder, stirred and heated to 120°C for 30 minutes. After the powder dries, it is cooled to room temperature. 2.3g of RF-901 solvent-based fluorosilicone resin, 0.7g of aluminum hexafluoroacetylacetonate and 7.3g of acetone are added to the cooled powder, stirred and heated to 93°C. After the powder dries, it is cooled to room temperature to obtain a coated powder. 0.2g of lubricant is added to the coated powder and mixed evenly. The lubricant is composed of fumed alumina and hexagonal boron nitride in a mass ratio of 4:3 to obtain the soft magnetic metal powder.

[0042] Comparative Example 6 Similar to Example 3, except that in S3, the soft magnetic metal powder is prepared as follows: 50g of gas-atomized iron-silicon-chromium alloy powder with D50 = 28μm, 35g of D50 = 9μm and 15g of D50 = 2μm are mixed to obtain a mixed powder. 0.5g of phosphoric acid, 0.25g of oxalic acid and 10g of distilled water are added to the mixed powder, stirred and heated to 120°C for 30 minutes. After the powder dries, it is cooled to room temperature. 2.3g of RF-901 solvent-based fluorosilicone resin, 0.025g of titanium trifluoride and 7.3g of acetone are added to the cooled powder, stirred and heated to 93°C. After the powder dries, it is cooled to room temperature to obtain a coated powder. 0.2g of lubricant is added to the coated powder and mixed evenly. The lubricant is composed of fumed alumina and hexagonal boron nitride in a mass ratio of 4:3 to obtain the soft magnetic metal powder.

[0043] Comparative Example 7 Similar to Example 3, except that in S3, in the preparation of soft magnetic metal powder, the lubricant is fumed alumina.

[0044] Comparative Example 8 Similar to Example 3, except that in S3, in the preparation of soft magnetic metal powder, the lubricant is hexagonal boron nitride.

[0045] Performance testing The high-voltage formed copper-iron co-fired inductors prepared in Examples 1-3 and Comparative Examples 1-8 were tested for inductance and power loss performance according to standard SJ20966-2006. The inductance value was tested using a Wink WK6500B precision impedance analyzer, and the power loss value was tested using an Iwasaki SY8218BH analyzer. The withstand voltage value was tested according to the national standard GB4706 (IEC1010) using a withstand voltage tester. The test results are shown in Table 1.

[0046] Table 1 Performance Tests Analyzing the data in Table 1, we can see that: 1) The high-voltage molded copper-iron co-fired inductors prepared in Examples 1-3 have excellent loss performance, inductance value, insulation withstand voltage and reliability.

[0047] 2) The performance comparison analysis of the high-voltage molded copper-iron co-fired inductors prepared in Example 3 and Comparative Example 1 shows that coating the copper sheet with a polyimide insulating layer helps to improve the inductor's loss performance, inductance value and insulation withstand voltage.

[0048] 3) The performance comparison analysis of the high-pressure molded copper-iron co-fired inductors prepared in Example 3 and Comparative Examples 2-3 shows that the use of a mixed solution of phosphoric acid and oxalic acid as a passivating agent, in which phosphoric acid provides acidity and oxidizing properties, promotes the passivation reaction of oxalic acid with gas-atomized iron-silicon-chromium alloy powder. The generated iron oxalate will decompose into iron oxide during high-temperature annealing, which can uniformly coat the powder surface, improve the insulation performance of the powder, reduce eddy current losses between powders, and thus improve the overall performance of the inductor.

[0049] 4) The performance comparison analysis of the high-voltage molded copper-iron co-fired inductors prepared in Example 3 and Comparative Examples 4-6 shows that the coating agent is composed of RF-901 solvent-based fluorosilicone resin, titanium trifluoride, aluminum hexafluoroacetylacetonate and acetone. The combined effect of RF-901 solvent-based fluorosilicone resin, titanium trifluoride and aluminum hexafluoroacetylacetonate significantly improves the loss performance, inductance value and insulation withstand voltage of the inductor.

[0050] 5) The performance comparison analysis of the high-pressure molded copper-iron co-fired inductors prepared in Example 3 and Comparative Examples 7-8 shows that the use of a lubricant composed of fumed alumina and hexagonal boron nitride in a mass ratio of 4:3, and the synergistic effect between them, can further improve the overall performance of the inductor.

[0051] The above embodiments are only used to explain the technical solutions of this application and are not intended to limit it. Although the above embodiments have provided specific descriptions of this application, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation methods of this application. Any modifications and equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of this application.

Claims

1. A method for preparing a high-pressure molded copper-iron co-fired inductor, characterized in that, Includes the following steps: S1. Copper sheet pretreatment: After degreasing, acid activation, and nitrogen drying of the copper sheet surface, oxygen plasma treatment is used to enhance surface roughness and adhesion, resulting in pretreated copper sheets. S2. Coating the insulating layer: After completely immersing the pretreated copper sheet in the polyimide coating for 5-8 minutes, remove it and dry it in an 80℃ oven for 30-40 minutes. Then, under nitrogen protection, cure it by step-by-step heating and cool it to room temperature to obtain a copper sheet coated with a polyimide insulating layer. The step-by-step heating and curing process conditions are as follows: heat up to 150℃ and hold for 1 hour, then heat up to 250℃ and hold for 1 hour, and finally heat up to 330℃ and hold for 2 hours. S3. Preparation of soft magnetic metal powder: First, mix gas-atomized iron-silicon-chromium alloy powders of different particle sizes to obtain mixed powder, and then mix them with passivating agent, coating agent and lubricant in sequence to obtain soft magnetic metal powder. S4. Preparation of magnetic powder core: A copper sheet coated with a polyimide insulating layer is placed in the center of a soft magnetic metal powder. The soft magnetic metal powder is present on both the top and bottom surfaces of the copper sheet coated with the polyimide insulating layer. The two ends of the copper sheet coated with the polyimide insulating layer extend beyond the soft magnetic metal powder to obtain a magnetic powder core. S5. Preparation of copper-iron co-fired inductor: The magnetic powder core is bidirectionally pressed into shape using a mold, then subjected to gradient annealing in a reducing atmosphere, and finally immersed in an epoxy resin acetone solution under a vacuum of 0.05 MPa. After washing with acetone three times and baking, a high-pressure molded copper-iron co-fired inductor is obtained.

2. The method for preparing a high-pressure molded copper-iron co-fired inductor according to claim 1, characterized in that, In step S1, the copper sheet has a thickness of 40-65 μm and a width of 2-4 mm; the degreasing of the copper sheet surface refers to ultrasonically cleaning the copper sheet in acetone for 10-15 minutes to remove grease and residual contaminants; the acid activation process is ultrasonic activation in a 5% dilute sulfuric acid solution for 1-1.5 minutes to remove surface oxides; the oxygen plasma treatment process is treatment in an oxygen atmosphere at a power of 300W for 3-5 minutes.

3. The method for preparing a high-pressure molded copper-iron co-fired inductor according to claim 1, characterized in that, In step S2, the polyimide coating comprises the following components by mass percentage: 38-42% polyimide resin, 1-2% silane coupling agent (KH-550), and the balance being N-methylpyrrolidone; the thickness of the polyimide insulating layer is 10-20 μm.

4. The method for preparing a high-pressure molded copper-iron co-fired inductor according to claim 1, characterized in that, In step S3, the different particle sizes are D50=25-30μm, D50=8-10μm and D50=1-3μm, and the gas-atomized iron-silicon-chromium alloy powders of different particle sizes account for 50%, 35% and 15% of the mixed powder, respectively.

5. The method for preparing a high-pressure molded copper-iron co-fired inductor according to claim 1, characterized in that, In step S3, the passivating agent is a mixed solution of phosphoric acid and oxalic acid; the amount of phosphoric acid used is 0.4-0.6 wt% of the mass of the mixed powder; and the amount of oxalic acid used is 0.2-0.3 wt% of the mass of the mixed powder.

6. The method for preparing a high-pressure molded copper-iron co-fired inductor according to claim 1, characterized in that, In step S3, the coating agent is composed of RF-901 solvent-based fluorosilicone resin, titanium trifluoride, aluminum hexafluoroacetylacetonate, and acetone; wherein the amount of RF-901 solvent-based fluorosilicone resin is 2-3 wt% of the mass of the mixed powder; the amount of titanium trifluoride is 0.02-0.04 wt% of the mass of the mixed powder; the amount of aluminum hexafluoroacetylacetonate is 0.6-0.8 wt% of the mass of the mixed powder; and the amount of acetone is 7-7.5 wt% of the mass of the mixed powder.

7. The method for preparing a high-pressure molded copper-iron co-fired inductor according to claim 1, characterized in that, In step S3, the lubricant is composed of fumed alumina and hexagonal boron nitride in a mass ratio of 4:3; the amount of lubricant used is 0.1-0.3 wt% of the mass of the mixed powder.

8. The method for preparing a high-pressure molded copper-iron co-fired inductor according to claim 1, characterized in that, In step S5, the pressure of the bidirectional pressing is 2000-2200MPa; the reducing atmosphere is a mixture of hydrogen and argon, wherein the volume of hydrogen accounts for 11-15% of the volume of the mixture; the gradient annealing process conditions are as follows: the temperature is gradually increased in the following stages, the first stage is 40 minutes to increase from room temperature to 180℃, and then held for 30 minutes. The second stage involves raising the temperature to 320℃ for 40 minutes and holding it for 30 minutes; the third stage involves raising the temperature to 480℃ for 40 minutes and holding it for 30 minutes; the fourth stage involves raising the temperature to 620℃ for 40 minutes and holding it for 30 minutes; and the fifth stage involves raising the temperature to 720℃-780℃ for the last 40 minutes and holding it for 120 minutes, followed by natural cooling to room temperature.

9. The method for preparing a high-pressure molded copper-iron co-fired inductor according to claim 1, characterized in that, In step S5, the baking temperature is 180-200℃ and the time is 60-70 minutes.

10. A high-pressure molded copper-iron co-fired inductor, characterized in that, The high-pressure molded copper-iron co-fired inductor is prepared by the preparation method of the high-pressure molded copper-iron co-fired inductor according to any one of claims 1-9.

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