An ultrathin power inductor and a preparation process thereof

Abstract

This application relates to an ultrathin power inductor and its fabrication process, comprising a multilayer magnet composed of stacked magnetic layers; a coil disposed within the multilayer magnet; and terminal electrodes disposed at opposite end faces of the multilayer magnet and electrically connected to the coil. The magnetic layers are formed by sintering FeSiCr alloy powder, and the surface of the magnetic layer particles is coated with a chromium oxide insulating layer, which is then coated with a phosphate-silane composite insulating layer. The interaction between the chromium oxide insulating layer and the phosphate-silane composite insulating layer insulates the metal particles constituting the magnetic layer. The chromium oxide insulating layer is formed on the surface of the metal particles during high-temperature sintering of the magnetic layer through the reaction between Cr and O2 in the FeSiCr alloy powder. This chromium oxide insulating layer, together with the phosphate-silane composite insulating layer pre-coated on the surface of the metal particles, fills gaps, ensuring both insulation performance and a thin magnetic layer while minimizing resistance to heat conduction.

Description

Technical Field

[0001] This application relates to the technical field of power inductors, and in particular to an ultrathin power inductor and its fabrication process. Background Technology

[0002] As consumer electronic devices evolve towards thinner, lighter, and higher-performance designs, more stringent requirements are being placed on the electronic components within these devices, demanding miniaturization, high heat dissipation, and high reliability.

[0003] To meet the ultra-thin size requirements of power inductors with a thickness of less than 1.0 mm for current consumer electronic devices, power inductors are usually manufactured using a multilayer molding technology. FeSiCr alloy has become the mainstream magnetic material for this type of multilayer power inductor due to its high saturation magnetic induction intensity and excellent DC bias characteristics.

[0004] In order to suppress high-frequency eddy current losses, an effective insulation system must be constructed inside the multilayer magnet, especially between adjacent magnetic layers, when fabricating FeSiCr power inductors using conventional multilayer processes.

[0005] One approach is to introduce an independent insulating dielectric layer into the laminated structure. In this regard, Chinese patent CN104380402A discloses a manufacturing method for a laminated coil component, which discloses an insulation method using glass material to cover the surface of the FeSiCr magnetic layer.

[0006] Another approach is to achieve interlayer indirect isolation by coating the surface of the magnetic powder with an insulating layer, such as a phosphate, silane coupling agent, or oxide coating, through the powder's own insulation.

[0007] However, the first method suffers from poor thermal conductivity of the traditional insulation layer, and in order to ensure the insulation effect, the traditional insulation layer needs to be designed to be thicker. This makes it impossible for the power inductor using the first method to simultaneously meet the three requirements of miniaturization, good insulation performance, and high heat dissipation performance.

[0008] The second method involves an insulating layer coating the powder surface that is prone to decomposition, diffusion, or detachment during high-temperature sintering, leading to decreased interlayer insulation performance, increased eddy current losses, and reduced device lifespan. Summary of the Invention

[0009] To address the issue that existing power inductor manufacturing processes cannot meet the dual requirements of high heat dissipation and high performance in miniaturized power inductors, this application provides an ultrathin power inductor and its fabrication process.

[0010] Firstly, the ultra-thin power inductor provided in this application adopts the following technical solution: An ultra-thin power inductor, comprising: A multilayer magnet, comprising multiple layers of magnetic material stacked together; A coil is disposed inside the stacked magnet; End electrodes are located on opposite end faces of the stacked magnet and are electrically connected to the coil. The magnetic layer is formed by sintering FeSiCr alloy powder. The surface of the magnetic layer particles is coated with a chromium oxide insulating layer, and the chromium oxide insulating layer is coated with a phosphate-silane composite insulating layer.

[0011] Through the above technical solution, the metal particles that make up the magnetic layer are insulated by the interaction between the chromium oxide insulating layer and the phosphate-silane composite insulating layer. While ensuring that the magnetic layer is thin and light, the chromium oxide insulating layer is generated on the surface of the metal particles during the high-temperature sintering of the magnetic layer through the reaction between Cr and O2 in FeSiCr alloy powder. It works together with the phosphate-silane composite insulating layer that is pre-coated on the surface of the metal particles to fill the gaps. This ensures that the insulation effect is guaranteed, and the thermal conduction of the magnetic layer is reduced. The thermal conductivity of the multilayer magnet composed of the magnetic layers meets the requirements of the miniaturized power inductor.

[0012] Optionally, the gaps between the particles constituting the magnetic layer are filled with silicone resin.

[0013] Optionally, the outer surface of the stacked magnet is covered with an insulating coating, which is made of nano-sized silicone resin.

[0014] Optionally, the magnetic layer has a compensation gap inside, which is used to compensate for the collapse or overflow of material that occurs during the fabrication of the magnetic layer.

[0015] Optionally, the thickness of the composite insulating layer is ≥50nm and ≤200nm.

[0016] Optionally, the total thickness of the stacked magnets is ≤1.0mm.

[0017] Optionally, the terminal electrode, along the direction of the original stacked magnet, sequentially includes a silver layer, an electroplated nickel layer, and an electroplated tin layer.

[0018] Secondly, this application provides a method for fabricating the above-mentioned ultrathin power inductor, characterized by comprising the following steps: S1. Ingredients: FeSiCr alloy powder, high thermal conductivity insulating filler particles, phosphate and dispersant are mixed in an organic solvent. The high thermal conductivity insulating filler particles and quaternary ammonium salt are uniformly coated on the surface of FeSiCr alloy powder particles through a dispersion process. Then, silane coupling agent is added and stirring is continued to form a powder with a phosphate-silane composite insulating coating layer. Finally, binder, plasticizer and organic solvent are added and stirred to form a magnetic slurry for later use. S2, Casting: Cast the magnetic paste in S1 into a magnetic green sheet of a specified thickness, and complete the opening of the through holes in the magnetic green sheet. S3, Printing: Conductive paste is printed onto the surface of the magnetic green sheet raised in S2 using screen printing to form a spiral coil. At the same time, conductive paste is filled into the through holes to serve as a conductive path between two adjacent coils. S4. Lamination: The magnetic green sheets with printed coils and insulation layers are alternately stacked in the designed order to complete the lamination process. S5, lamination, is the pressing of the laminated blank under specified pressure and time. S6. Preparation: The laminated blank is divided into individual device blanks, and chamfering and debinding are performed simultaneously. Finally, the device blanks are sintered in a reducing atmosphere, and the oxygen partial pressure is controlled to be below 10 ppm, so that Cr in the FeSiCr alloy powder is selectively oxidized and chromium oxide insulating underlayer is generated in situ. S7. Silvering: The silvering process is used to immerse both ends of the sintered green body into the silver paste to ensure that the silver paste evenly covers the end face of the green body (avoiding non-electrode areas). S8. Silvering: The silver-coated blank is placed in a sintering furnace to complete the silvering process and form the bottom silver electrode. S9. Impregnation: The device surface (except for the terminal silver electrode) is coated with nano-silicone resin to form a surface insulating layer; S10, Electroplating: First, electroplat a nickel layer on the surface of the device after impregnation and curing, and then electroplat a tin layer; S11. Rust prevention treatment: The electroplated parts are subjected to rust prevention treatment.

[0019] Optionally, in the S3 printing step, the magnetic paste from S1 is printed onto the surface of the magnetic green sheet using a screen printing process, which is complementary to the coil pattern, so that the coil is embedded in the magnetic green sheet. A compensation gap is provided between the printed magnetic paste and the through hole to compensate for the collapse or overflow of the magnetic paste during lamination.

[0020] Optionally, the high thermal conductivity insulating filler includes boron nitride nanosheets and aluminum nitride nanoparticles.

[0021] Optionally, after the S6 sintering is completed, the silicone resin is drawn into the gaps between the particles constituting the magnetic sheet using a negative pressure process.

[0022] In summary, this application utilizes the synergy between a chromium oxide insulating layer and a phosphate-silane composite insulating layer to insulate the metal particles that make up the magnetic layer. While ensuring the magnetic layer is thin and lightweight, the chromium oxide insulating layer is formed on the surface of the metal particles during high-temperature sintering of the magnetic layer through the reaction between Cr and O2 in the FeSiCr alloy powder. This synergy with the phosphate-silane composite insulating layer pre-coated on the surface of the metal particles fills the gaps, thus ensuring insulation while reducing the barrier to thermal conduction of the magnetic layer. The thermal conductivity of the multilayer magnet composed of the magnetic layers meets the requirements of miniaturized power inductors. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the power inductor of this application.

[0024] Figure 2 This is a partial exploded structural diagram of the stacked magnet of this application.

[0025] Those skilled in the art will understand that the elements in the accompanying drawings are shown for simplicity and clarity and are not necessarily drawn to scale. For example, the size and position of some elements in the drawings may be enlarged relative to other elements to aid in understanding the embodiments of the invention.

[0026] Reference numerals: 1. Stacked magnet; 11. Magnetic layer; 2. Coil; 3. Terminal electrode; 4. Through hole. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments. It should be noted that, unless otherwise specified, the technical means used in the following examples are conventional means well known to those skilled in the art, and the raw materials used are all commercially available conventional products. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various modifications or alterations to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0028] In a first aspect, embodiments of this application disclose an ultra-thin power inductor, referring to... Figure 1 and Figure 2 It includes a multilayer magnet 1, a coil 2, a terminal electrode 3, and a ceramic substrate.

[0029] Reference Figure 1 and Figure 2The multilayer magnet 1 includes several magnetic layers 11 with a thickness of 10 μm and several magnetic layers 11 with a thickness of 35 μm. The coil 2 has a thickness of 23 μm and is provided with several coils. All magnetic layers 11 are made of FeSiCr alloy powder sintered together.

[0030] Coil 2 is a planar spiral coil 2, which is printed one-to-one with the 10μm thick magnetic layer 11 using silver paste. The coil 2 and the 10μm thick magnetic layer 11 are arranged alternately. On the 10μm thick magnetic layer 11 outside the coil 2 area, the coil 2 is filled by printing with a screen with the opposite pattern to the coil 2, and then sintered to form a 23μm thick magnetic layer 11 inlaid with the coil 2.

[0031] A 10μm magnetic layer 11 and a 23μm magnetic layer 11 thereon are stacked to form a preliminary stacked magnet 1, and the coil 2 is located inside the preliminary stacked magnet 1.

[0032] The initial stacked magnet 1 is rectangular. After the initial stacked magnet 1 is placed horizontally, several 35μm magnetic layers 11 are fixed on the top and bottom walls of the initial stacked magnet 1, thus forming the finished stacked magnet 1. In the following text, the stacked magnet 1 refers to the finished stacked magnet 1.

[0033] The number of 35μm magnetic layers 11 at the top wall of the laminated magnet 1 is less than the number of 35μm magnetic layers 11 at the bottom wall of the laminated magnet 1. The 35μm magnetic layers 11 are integral after sintering.

[0034] The number of magnetic layers 11 of various thicknesses can be selected according to specific circumstances. The sidewalls of each magnetic layer 11 are flush, ensuring that the total thickness of the stacked magnet 1 is not greater than 0.8 mm.

[0035] The FeSiCr alloy powder particles of magnetic layer 11 are coated with a chromium oxide insulating layer, and the chromium oxide insulating layer is coated with a phosphate-silane composite insulating layer. The thickness of the composite insulating layer is ≥50nm and ≤200nm. Meanwhile, the gaps between the particles constituting magnetic layer 11 are filled with silicone resin particles. The ceramic substrate is fixedly mounted on the terminal electrode 3, and the ceramic substrate is provided with pads for docking with external devices.

[0036] The outer surface of the laminated magnet 1 is covered with an insulating coating made of nano-sized silicone resin. Simultaneously, a compensation gap is provided inside the magnetic layer 11 to compensate for material collapse or spillage that occurs during the fabrication of the magnetic layer 11.

[0037] The terminal electrode 3 includes a silver layer, a nickel plating layer, and a tin plating layer in sequence. The magnetic layer 11 is rectangular in shape, and the silver layer is fixedly connected to both ends of the stacked magnet 1 along its length.

[0038] The magnetic layer 11 has a through hole 4. Adjacent coils 2 are connected by pillars filled with solidified silver paste in the through hole 4. The ends of the coils 2 located at both ends of the stacked magnet 1 are electrically connected to the end electrodes 3.

[0039] Secondly, this application discloses a fabrication process for an ultrathin power inductor.

[0040] The following are the test methods for the relevant performance indicators in each embodiment and comparative example: Inductance and quality factor: Measured using an impedance analyzer (Keysight E4991B) at a test frequency of 1 MHz.

[0041] DC resistance: Measured using a four-wire DC resistance tester (HIOKI RM3545).

[0042] Insulation resistance: A high resistance meter (HIOKI ST5520) was used to measure the resistance between the two electrodes of the device by applying a 50V DC voltage.

[0043] Withstand voltage strength: A withstand voltage tester (Chroma 19032) was used to apply a gradually increasing DC voltage between the two electrodes until breakdown occurred. The breakdown voltage was recorded and divided by the insulation layer thickness for calculation.

[0044] Thermal resistance: The device is soldered onto a standard test board and placed in a sealed constant temperature chamber. The rated current is applied to it to achieve thermal equilibrium. The thermal resistance is calculated by measuring the temperature rise of the device surface and the temperature difference with the environment, combined with the power consumption.

[0045] Saturation current: Using an inductance tester (Wenke 1J6510B+1J6565-10), the current value when the inductance value drops to 30% of the initial value is monitored under the condition that the DC bias current gradually increases.

[0046] Temperature rise current: The current required to raise the surface temperature of a device by 40°C when a current is applied at 25°C.

[0047] Secondly, this application discloses a fabrication process for an ultrathin power inductor, comprising the following steps: Example 1

[0048] S1. Ingredients: Weigh 100 parts by weight of FeSiCr alloy powder (chemical composition by mass percentage: Fe 89%, Si 4.5%~7%, Cr 0.5%~4%, in this example Fe 89%, Si 6.0%, Cr 3.0%) and disperse it in a mixed solvent of ethanol and toluene (volume ratio 1:1). Add 1.2 parts of aluminum dihydrogen phosphate, 0.5 parts of hexadecyltrimethylammonium bromide (dispersant), and 0.5 parts of boron nitride (BN) nanosheets with an average particle size of 200 nm (i.e., doping amount of 0.5 wt% of alloy powder). React in a constant temperature water bath at 30-70℃ (50℃ in this example) with stirring at 800 rpm for 0.5-2 hours (1.5 hours in this example). After cooling to room temperature, 1.0 part of γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560) was added, and stirring was continued for 3-20 hours (8 hours in this example) to allow the high thermal conductivity filler, phosphate, and silane coupling agent to form a preliminary composite insulating layer on the surface of the alloy powder. The thickness of this coating layer was approximately 100 nm as measured by SEM. Finally, 7 parts of polyvinyl acetate (PVB) and 3.5 parts of dibutyl phthalate (DBP) were added to the system, and an appropriate amount of ethanol was added to adjust the viscosity. Stirring was continued for 24 hours to finally obtain a magnetic slurry with a viscosity of approximately 5000~8000 mPa·s.

[0049] S2. Preparation of raw slices: The slurry in S1 is cast onto a polyester film carrier using a casting machine and dried in an oven at 60-85℃ (80℃ in this embodiment) to form a magnetic green sheet with a thickness of 10-100μm (60μm in this embodiment). Then, a through hole 4 with a diameter of 80-200μm (100μm in this embodiment) is punched on the magnetic green sheet using an ultraviolet laser.

[0050] Using a first screen, a spiral coil 2 is printed with silver paste on the surface of the magnetic green sheet to form a planar spiral coil 2, and the through holes 4 are filled to form interlayer connection points. Then, using a second screen complementary to the coil 2 pattern, the magnetic paste in S1 is printed into the gap areas between the coil 2 patterns to form a filling layer.

[0051] During printing, an annular compensation gap with a width of 25-60μm (40μm in this embodiment) is reserved in the connection area corresponding to the lead-out end of terminal electrode 3. This structure of "printed coil 2 + printed filler" is defined as a printing unit. Printing units of 4-23 layers (8 layers in this embodiment) are sequentially aligned and stacked with two pure magnetic green sheets (without patterns) serving as the top and bottom layers to form a stacked structure with a total green sheet thickness of approximately 1.1mm.

[0052] S3, Lamination: The stacked billets are placed in a warm water press and pressed for 30-120 minutes at 550-600MPa pressure and 120℃ warm water environment (in this embodiment, it is pressed for 60 minutes at 580MPa and 120℃) to obtain the whole billet.

[0053] S4, Slicing: The large blank in S3 is divided into individual device blanks with dimensions of 2.0mm × 1.6mm, and the edges of the blanks are chamfered.

[0054] S5. Debinding and Sintering: The green body is placed in a debinding furnace and heated to 320°C at a rate of 1°C / min in a nitrogen atmosphere containing 5% oxygen, and held at that temperature for 1-4 hours (2 hours in this embodiment) to remove the binder. After debinding, the green body is transferred to a bell-type sintering furnace and sintered in a nitrogen-hydrogen mixed reducing atmosphere, with the oxygen partial pressure controlled below 10 ppm (8 ppm in this embodiment), and heated to 650-720°C (680°C in this embodiment) at a rate of 5°C / min, and held at that temperature for 2 hours. During this process, Cr in the FeSiCr alloy powder is selectively oxidized, forming a dense chromium oxide (Cr2O3) insulating underlayer in situ on the surface of the powder particles. After sintering, a sintered body with a total thickness of approximately 0.8 mm is obtained.

[0055] S6, Negative pressure impregnation filling: The sintered body was placed in a vacuum impregnation apparatus and evacuated to -0.095 MPa. Low-viscosity methylphenyl vinyl silicone resin was then injected. The negative pressure was maintained for 20 minutes to allow the silicone resin to fully penetrate all microscopic voids between the FeSiCr alloy powder particles inside the sintered body. After the vacuum was released, the mixture was cured at 180°C for 1 hour.

[0056] S7, End Electrode 3 Fabrication: A silver-plating process is employed, immersing both ends of the device in silver paste and holding it at 580-625℃ (625℃ in this embodiment) for 15-30 minutes (20 minutes in this embodiment) to complete the silver plating process and form the bottom silver electrode. Then, the entire device is immersed in a nano-scale silicone resin solution, pulled out, and cured at 180℃ to form an outer insulating coating. Taking advantage of the strong adhesion between this nano-silicone resin coating and the ceramic surface, but weak adhesion to the silver electrode layer, a precision polishing machine is used to polish the electrode areas at both ends of the device, completely removing the nano-silicone resin coating in these areas and exposing the clean silver electrode surface. Finally, a nickel layer with a thickness of 2-5μm (3μm in this embodiment) and a tin layer with a thickness of 5-10μm (7μm in this embodiment) are sequentially electroplated onto the exposed silver electrode layer, forming a complete Ag / Ni / Sn three-layer electrode structure.

[0057] Finally, the performance of the manufactured power inductor was tested.

[0058]

[0059] The table above shows the test results, specifically: inductance (L) is 1.0 μH, DC resistance (DCR) is 45 mΩ, quality factor (Q) is 25, saturation current (Isat) is 1.5 A, and temperature rise current (Irms) is 1.3 A. Insulation resistance is 2.5 × 10⁻⁶. 9 The device has a withstand voltage of 650V / μm and a thermal resistance of 18℃ / W. The total thickness of the device is 0.81mm, and the total thickness of the multilayer magnet 1 is ≤1.0mm. Example 2

[0060] S1. Ingredients: Weigh 100 parts by weight of FeSiCr alloy powder (chemical composition: Fe 91%, Si 4.5%, Cr 2.5%). Disperse it in ethyl acetate. Add 1.0 part of aluminum dihydrogen phosphate, 0.3 parts of trimeric cashew phenol polyoxyethylene ether, and 0.8 parts (0.8 wt%) of aluminum nitride (AlN) nanoparticles. Stir at 40°C for 2 hours. After cooling, add 0.8 parts of KH-550 silane coupling agent and stir for 6 hours. Finally, add 8 parts of PVB and 4 parts of DBP to adjust the viscosity and obtain a magnetic slurry.

[0061] S2, Flowing: A 50μm thick green sheet is cast and laser-drilled. After printing silver paste coil 2, magnetic paste is filled using complementary screen printing, leaving a 30μm compensation gap. The 6-layer printing unit is then stacked with the upper and lower cast green sheets.

[0062] S3, Subsequent Processes: After being subjected to 550 MPa / 120℃ warm water pressure for 50 minutes, the blanks were cut into 1.6 mm × 0.8 mm pieces and chamfered. The binder was removed at 300℃ for 2.5 hours. Sintering was then carried out at 660℃ for 2.5 hours under an oxygen partial pressure of 5 ppm. The blanks were then impregnated with silicone resin under negative pressure and cured at 180℃ for 1 hour. After silvering, the blanks were fired at 600℃ for 25 minutes, followed by coating with nano-silicone resin and polishing the electrode areas. Finally, Ni (2 μm) / Sn (5 μm) plating was performed.

[0063] Performance testing: The resulting inductor measures 1.6mm × 0.8mm × 0.55mm. L = 0.47μH, DCR = 28mΩ, Q = 30, Isat = 1.8A, Irms = 1.5A. Insulation resistance is 2.0 × 10⁻⁶. 9 Ω, withstand voltage 600V / μm, thermal resistance 20℃ / W.

[0064] Comparative Example 1: The preparation method is the same as in Example 1, except that boron nitride (BN) nanosheets are not added during the formulation. All other steps and parameters are exactly the same.

[0065] Performance test results: Inductance 1.0μH, DC resistance 45mΩ, saturation current 1.3A, temperature rise current 1.1A. Insulation resistance 5.0×10⁻⁶. 8 Ω, withstand voltage 320V / μm, thermal resistance 42℃ / W.

[0066] Comparative Example 2: The preparation method is the same as in Example 1, except that the "negative pressure impregnation and filling" step is omitted, that is, no silicone resin is filled after sintering.

[0067] Performance test results: Inductance 1.0μH, DC resistance 45mΩ, saturation current 1.4A, temperature rise current 1.2A. Insulation resistance 3.0×10⁻⁶. 8 Ω, withstand voltage 380V / μm, thermal resistance 26℃ / W.

[0068] Comparative Example 3: The preparation method is the same as in Example 1, except that the oxygen partial pressure is controlled at 1000 ppm (0.1%) in the sintering step, while the other conditions remain unchanged.

[0069] Performance test results: The device turned black, and its magnetic properties deteriorated. The inductance dropped to 0.7 μH, the DC resistance increased to 60 mΩ, and the insulation resistance was 1.0 × 10⁻⁶. 8 Ω indicates that excessively high oxygen partial pressure leads to over-oxidation.

[0070] In summary, the experimental methods and data results demonstrate that this invention, through the synergistic effect of three technologies—"in-situ generation of chromium oxide insulating underlayer," "coating with a phosphate-silane composite insulating layer containing highly thermally conductive filler," and "negative-pressure impregnation with silicone resin to fill gaps"—combined with a "printing-casting hybrid structure" and "compensation gap design," effectively solves the core contradiction of achieving both "high insulation reliability" and "high heat dissipation efficiency" in FeSiCr ultrathin multilayer power inductors. The products in Examples 1-2, with their ultrathin dimensions (≤1.0 mm), all achieved high insulation resistance (≥2.0 × 10⁻⁶). 9 It boasts high voltage resistance (≥600V / μm), low thermal resistance (≤20℃ / W), and excellent overall electrical performance, significantly outperforming comparative examples 1-3, demonstrating remarkable superiority.

[0071] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. An ultrathin power inductor, characterized in that, include: A stacked magnet (1) includes several stacked magnetic layers (11). Coil (2) is located inside the stacked magnet; The end electrodes (3) are located on opposite end faces of the stacked magnet (1) and are electrically connected to the coil (2); The magnetic layer (11) is formed by sintering FeSiCr alloy powder. The surface of the magnetic layer (11) particles is covered with a chromium oxide insulating layer, and the chromium oxide insulating layer is covered with a phosphate-silane composite insulating layer.

2. The ultrathin power inductor of claim 1, wherein: The gaps between the particles constituting the magnetic layer (11) are filled with silicone resin.

3. The ultrathin power inductor of claim 1, wherein: The outer surface of the stacked magnet (1) is covered with an insulating coating, which is made of nano-sized silicone resin.

4. The ultrathin power inductor of claim 1, wherein: The magnetic layer (11) has a compensation gap inside, which is used to compensate for the collapse or overflow of material that occurs during the fabrication of the magnetic layer (11).

5. The ultrathin power inductor of claim 1, wherein: The thickness of the composite insulating layer is ≥50nm and ≤200nm.

6. The ultrathin power inductor of claim 1, wherein: The total thickness of the stacked magnet (1) is ≤1.0mm.

7. The ultrathin power inductor of claim 1, wherein: The terminal electrode (3) consists of a silver layer, an electroplated nickel layer, and an electroplated tin layer in sequence along the direction of the stacked magnet.

8. A process for the preparation of an ultrathin power inductor, characterized in that, Includes the following steps: S1. Ingredients: FeSiCr alloy powder, high thermal conductivity insulating filler particles, phosphate and dispersant are mixed in an organic solvent. The high thermal conductivity insulating filler particles and quaternary ammonium salt are uniformly coated on the surface of FeSiCr alloy powder particles through a dispersion process. Then, silane coupling agent is added and stirring is continued to form a powder with a phosphate-silane composite insulating coating layer. Finally, binder, plasticizer and organic solvent are added and stirred to form a magnetic slurry for later use. S2, casting, casting the magnetic paste in S1 into a magnetic green sheet of a specified thickness, and completing the opening of the through holes (4) of the magnetic green sheet; S3, Printing: Conductive paste is printed onto the surface of the magnetic green sheet generated in S2 using screen printing process to form a spiral coil (2). At the same time, conductive paste is filled into the through hole (4) to serve as a conduction path between two adjacent coils (2). S4. Stacking: The magnetic green sheets with printed coils (2) and insulation layers are stacked alternately in the design order to complete the stacking process. S5, lamination, is the pressing of the laminated blank under specified pressure and time. S6. Preparation: The laminated blank is divided into individual device blanks, and chamfering and debinding are performed simultaneously. Finally, the device blanks are sintered in a reducing atmosphere, and the oxygen partial pressure is controlled to be below 10 ppm, so that Cr in the FeSiCr alloy powder is selectively oxidized and chromium oxide insulating underlayer is generated in situ. S7. Silvering: The silvering process is used to immerse both ends of the sintered green body into the silver paste to ensure that the silver paste evenly covers the end face of the green body (avoiding non-electrode areas). S8. Silvering: The silver-coated blank is placed in a sintering furnace to complete the silvering process and form the bottom silver electrode. S9. Impregnation: The device surface (except for the terminal silver electrode) is coated with nano-silicone resin to form a surface insulating layer; S10, Electroplating: First, electroplat a nickel layer on the surface of the device after impregnation and curing, and then electroplat a tin layer; S11. Rust prevention treatment: The electroplated parts are subjected to rust prevention treatment.

9. The process for making an ultrathin power inductor of claim 1, wherein: In the S3 printing step, the magnetic paste in S1 is printed onto the surface of the magnetic green sheet through the screen printing process, which is complementary to the pattern of the coil (2), so that the coil (2) is embedded in the magnetic green sheet. A compensation gap is provided between the printed magnetic paste and the through hole (4) to compensate for the collapse or overflow of the magnetic paste during lamination. The high thermal conductivity insulating filler includes boron nitride nanosheets and aluminum nitride nanoparticles.

10. The process for making an ultrathin power inductor of claim 1, wherein: After the S6 sintering is completed, the silicone resin is drawn into the gaps between the particles that make up the magnetic sheet through a negative pressure process.

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