Printed circuit board embedded inductor and manufacturing method thereof

Abstract

The application discloses a printed circuit board buried layer inductor and a manufacturing method thereof. The buried layer inductor comprises an inductor body and a conductive coil. The conductive coil comprises a spiral line, an upper connecting line and a lower connecting line. The spiral line is embedded in the inside of the inductor body. The upper connecting line is connected with one end of the spiral line and is located on the surface of the inductor body. The lower connecting line is connected with the other end of the spiral line and is located on the surface of the inductor body. The spiral line spirally goes up from the inside bottom surface of the inductor body to the inside top surface of the inductor body in the vertical direction. The upper end surface of the spiral line is parallel to the top surface of the inductor body and is exposed. The lower end surface of the spiral line is parallel to the bottom surface of the inductor body and is exposed. The upper connecting line and the lower connecting line can be connected with the spiral line. The buried layer inductor of the application is buried in the interlayer of the circuit board. A large number of welding points are saved. The reliability of the whole circuit is improved. The inductor is asymmetrically designed. The large circle is connected to the high-voltage end. When a large voltage impact is encountered, the outermost coil is used to bear the impact. The breakdown probability is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of inductors, and more particularly to a buried inductor on a printed circuit board and a method for manufacturing it. Background Technology

[0002] Circuit boards contain numerous inductors used to stabilize DC power levels, prevent current pulses from damaging chips in signal lines, and eliminate the influence of high-frequency electromagnetic noise on signals. In these scenarios, inductors are indispensable. There are two ways to assemble inductors on a circuit board: one is to use discrete components that are through-hole or surface-mounted; the other is to integrate the inductor into the circuit board, commonly known as a buried inductor, which is essentially burying the inductor coil within the circuit board.

[0003] There are several methods for manufacturing buried inductors. One method involves soldering discrete inductor components into pre-designed recesses on the circuit board. This method is cumbersome in terms of creating the recesses and still requires surface mounting. Another method uses a multi-layer process to manufacture the inductor within the circuit board. This requires manufacturing the circuit board at the inductor location in multiple layers, which is complex and time-consuming. Furthermore, the via fabrication process between each layer is complex, and these vias pose a risk of short circuits and open circuits, resulting in poor reliability. Additionally, when faced with large voltage surges, the nearest coil experiences the highest voltage and is extremely prone to breakdown. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the existing technology of buried inductors, such as complex process and easy breakdown under high voltage, and to provide a buried inductor for printed circuit boards.

[0005] The technical solution adopted by this invention to solve its technical problem is a method for manufacturing buried inductors on printed circuit boards, comprising the following steps: S1. Composition of injection molding compound: magnetic powder accounts for 80-86 wt%, hollow glass microspheres with D50=10-15μm account for 4-5 wt%, coupling agent methacryloxysilane KH570 accounts for 0.1-1.0 wt%, and resin accounts for 9-16 wt% by mass. S2. Injection Molding Preparation: Magnetic powder is baked in a vacuum environment at 130-150℃ for 2-4 hours, then cooled to room temperature by purging with nitrogen; the coupling agent is mixed with anhydrous ethanol and deionized water at a ratio of 1:9:1 to 1:18:2 and hydrolyzed for 15-30 minutes to form a coupling agent hydrolysate. The magnetic powder is stirred and sprayed with the coupling agent hydrolysate, and the mixture is stirred until it no longer clumps. The temperature is controlled not to exceed 50℃. The mixture is then baked again in a vacuum or nitrogen environment at 80-100℃ for 2-4 hours; the resin and magnetic powder are mixed using a twin-screw mixer, and the melt temperature is controlled at 310-325℃; the melt is air-cooled and drawn into strips, and then granulated to a length of 2-4mm. The granules are baked in a vacuum environment at 130-150℃ for 2-4 hours, with the moisture content controlled to ≤0.03%. The granules are then poured into an injection molding hopper, and the hopper is kept at 120-130℃. S3. Coil fabrication: Take a rectangular metal sheet and punch and cut it along the spiral direction. Take the two ends that have been cut and insert them into the slots of the upper and lower mold plates. Pull the two mold plates apart at a uniform speed, controlling the pulling distance to be the design thickness of the buried layer where the inductor is located. The size of each turn of the pulled-out conductive coil is different. S4. Fabrication of Buried Inductor: The injection mold is closed from all sides, with the injection port on all sides. The temperature of the injection cylinder nozzle is controlled, and the mold temperature is controlled at 130-160℃. The injection speed is controlled at 20-50mm / s, the injection pressure is 100-150MPa, the holding pressure is 50-100MPa, the holding time is 8-20 seconds, and the cooling time is 20-50s before demolding. After cooling and demolding, the leads extending from the top and bottom ends are cut off to expose the cut surface. Copper clad laminate is used to make two copper layers on the top and bottom sides and they are connected to the cut surface respectively. The wiring on the top and bottom sides is etched according to the circuit design to form the buried inductor.

[0006] Further, in step S1, the magnetic powder is prepared using iron-silicon-chromium powder with a surface treated by phosphating insulation or by silicon dioxide and ceramic coating as raw material. The powder particle size ranges from D50 to 11 μm. Coarse powder is removed by sieving through an 800-mesh sieve. The powder is then uniformly mixed with nano-silica sol, nano-alumina, and nano-aluminum nitride sol, which have a solid content of 3-5 wt% of the powder mass. 1 wt% of dispersant is added, and the mixture is continuously kneaded in a kneader with the kneading temperature controlled at 60-70°C to evaporate a large amount of moisture and to fully coat the surface of the magnetic powder with nanoparticles. When the powder reaches a wet sandy texture, it is placed in a glass rotary kiln and heated to 100-120°C under nitrogen protection to fully dry the powder.

[0007] The solution to further solve the technical problem of the present invention is a buried inductor manufactured by a method for manufacturing buried inductors on printed circuit boards, which includes an inductor body and a conductive coil. The conductive coil includes a spiral wire, an upper connecting wire and a lower connecting wire. The spiral wire is embedded inside the inductor body. The upper connecting wire is connected to one end of the spiral wire and is located on the surface of the inductor body. The lower connecting wire is connected to the other end of the spiral wire and is located on the surface of the inductor body. The spiral line spirals vertically upwards from the bottom surface of the inductor body to the top surface of the inductor body. The upper surface of the spiral line is parallel to and exposed on the top surface of the inductor body, and the lower surface of the spiral line is parallel to and exposed on the bottom surface of the inductor body, so that the upper and lower connecting lines can be connected to the spiral line.

[0008] Furthermore, the upper and lower connecting lines are attached to the surface of the inductor body and extend to the edge of the inductor body.

[0009] Furthermore, the upper and lower connecting lines extend in opposite directions.

[0010] Furthermore, the projection of the spiral line onto the plane is square.

[0011] Furthermore, the spiral includes multiple transition blocks and multiple connecting blocks, with a connecting block connecting each transition block. Each transition block is located on a horizontal plane at a different height, causing the connecting block to be tilted, thereby enabling the spiral to connect the upper and lower surfaces inside the inductor body.

[0012] Furthermore, the transition block is located near a corner inside the inductor body, and the distance between the transition block and the axis of the inductor body gradually decreases until they coincide, so that the projection of the spiral is square and connects the upper and lower surfaces inside the inductor body.

[0013] Furthermore, the transition block located on the bottom surface inside the inductor body is positioned near the corner, while the transition block located on the top surface inside the inductor body is positioned at the center.

[0014] Furthermore, the length of each connecting block is different. The length of the connecting block near the bottom of the inductor body gradually decreases as the spiral line rises, while the connecting block gradually approaches the axis of the inductor body.

[0015] The present invention has the following beneficial technical effects: The buried inductor fabricated using this method eliminates the need for vias between multiple turns of the coil and the need for layer-by-layer dielectric material fabrication, reducing cumbersome processes and time. Furthermore, the reduction in vias improves the reliability of the buried inductor.

[0016] Furthermore, in the formulation of magnetic powder, the use of inorganic sol treatment can increase the material's ability to withstand high voltages, and the thermal conductivity can conduct the heat generated by the powder through the nanoparticle network. It can also play a certain role in fire prevention, so that the buried inductor can improve safety without adding complicated processes. In the injection molding formulation, the purpose of adding glass microspheres is to improve the voltage resistance, reduce the material density, reduce the weight of the circuit board, and at the same time reduce the dielectric constant of the material, reduce the distributed capacitance, and thus the inductor's resonant frequency is higher.

[0017] The buried inductor design embeds itself within the circuit board's interlayer via upper and lower interconnects, eliminating numerous solder joints and improving overall circuit reliability. Furthermore, the buried inductor's conductive coil features an asymmetrical design, with the larger coil connected to the high-voltage end. When encountering high-voltage surges, the outermost coil absorbs the load, significantly reducing the probability of breakdown (the outer coil has a larger turn spacing, while the inner coil has a smaller turn spacing). Additionally, the helix has a pyramidal design, with each coil layer unaligned, resulting in a much smaller distributed capacitance and a higher resonant frequency. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of a copper sheet used to fabricate a conductive coil, according to an embodiment of a method for fabricating a buried inductor on a printed circuit board according to the present invention. Figure 2 This is a schematic diagram of copper sheet segmentation in an embodiment of a method for manufacturing buried inductors on a printed circuit board according to the present invention; Figure 3 This is a schematic diagram of a mold according to an embodiment of a method for manufacturing buried inductors on a printed circuit board according to the present invention; Figure 4 This is a schematic diagram of a mold according to an embodiment of a method for manufacturing buried inductors on a printed circuit board according to the present invention; Figure 5 This is a schematic diagram of a conductive coil being stretched according to an embodiment of a method for manufacturing buried inductors on a printed circuit board according to the present invention. Figure 6 This is a schematic diagram of a conductive coil according to an embodiment of a method for fabricating a buried inductor on a printed circuit board according to the present invention. Figure 7 This is a schematic diagram of the inductor body after demolding, according to an embodiment of the method for manufacturing buried inductors on printed circuit boards of the present invention. Figure 8 This is a schematic diagram of the copper-clad laminate process of an embodiment of the buried inductor on a printed circuit board according to the present invention; Figure 9 This is a schematic diagram of the overall structure of an embodiment of a buried inductor on a printed circuit board according to the present invention.

[0019] Explanation of reference numerals in the attached figures: 1. Inductor body; 2. Conductive coil; 21. Spiral wire; 211. Transition block; 212. Connecting block; 22. Upper connecting wire; 23. Lower connecting wire; 3. Mold; 31. Slot; 32. Stop block. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0021] Reference Figure 6 and Figure 9 This embodiment includes an inductor body 1 and a conductive coil 2. The conductive coil 2 is divided into a spiral wire 21, an upper connecting wire 22 and a lower connecting wire 23. The spiral wire 21 is completely located inside the inductor body 1. The upper connecting wire 22 is connected to one end of the spiral wire 21 and is disposed on the top surface of the inductor body 1. The lower connecting wire 23 is connected to the other end of the spiral wire 21 and is disposed on the bottom surface of the inductor body 1.

[0022] Reference Figure 5 and Figure 6 Specifically, the spiral 21 is a three-dimensional spiral shape, spiraling vertically upwards from the bottom surface inside the inductor body 1 to the top surface inside the inductor body 1. That is, the height of the spiral 21 is the same as the height of the inductor body 1. At the same time, the upper surface of the spiral 21 is parallel to and exposed on the top surface of the inductor body 1. The upper connecting line 22 is connected to the upper surface of the spiral 21 exposed on the top surface of the inductor body 1. The lower surface of the spiral 21 is parallel to and exposed on the bottom surface of the inductor body 1. The lower connecting line 23 is connected to the lower surface of the spiral 21 exposed on the bottom surface of the inductor body 1, thereby forming a complete buried inductor.

[0023] Reference Figure 9 It should be noted that the upper connection 22 and the lower connection 23 extend towards the edge of the inductor body 1 while adhering to the surface of the inductor body 1, and the direction of extension is perpendicular to the edge line of the inductor body 1. The directions of extension of the upper connection 22 and the lower connection 23 are also opposite.

[0024] Reference Figure 6The spiral 21 is composed of multiple transition blocks 211 and multiple connecting blocks 212. The upper connecting line 22 and the lower connecting line 23 connect two different transition blocks 211 on the spiral 21. A connecting block 212 connects the two transition blocks 211. Two connecting blocks 212 are connected to one transition block 211. The transition block 211 is used to connect two connecting blocks 212 that are perpendicular to each other to achieve the spiral shape. The connecting block 212 is used to connect two transition blocks 211 to form a connecting line. Specifically, the transition block 211 is a square block and the connecting block 212 is a rectangular block. The height of each transition block 211 from the ground is different, so that the connecting block 212 between two transition blocks 211 presents an inclined state with one end higher and the other end lower, thereby realizing the gradual rise of the spiral 21. At the same time, two adjacent edges of the transition block 211 are connected to two mutually perpendicular connecting blocks 212, so that the spiral 21 presents a spiraling upward state.

[0025] Reference Figure 9 It should be noted that in this embodiment, a total of eleven transition blocks 211 and ten connecting blocks 212 are provided. The transition blocks 211 at the bottom and top layers are also located on the surface of the inductor body 1 and exposed for connection with the upper connecting line 22 and the lower connecting line 23. The bottom transition block 211 is located at one side edge of the bottom surface of the inductor body 1. The second bottom transition block 211 is located at the edge of a vertical side inside the inductor body 1, and this vertical side is the same as the side where the bottom transition block 211 is located, but the second bottom transition block 211 is closer to the adjacent side of this side, but is not located at the edge. The remaining transition blocks 211 are also not located at any one edge. At the edge of the side; the bottom transition block 211 is closest to the corner of the inductor body 1. As the transition block 211 gradually rises, it also gradually moves away from the corner. That is, the bottom transition block 211 is furthest from the axis of the inductor body 1. As the transition block 211 gradually rises, it also gradually moves closer to the axis until they coincide. However, the straight line formed by connecting two transition blocks 211 of similar height is parallel to the vertical side of the inductor body 1. Thus, when the spiral line 21 spirals upward inside the inductor body 1, the shape of the spiral is not a conventional circle. The projection of the spiral line 21 on the plane is square, and this projection can form a square.

[0026] Furthermore, since the heights of the two adjacent transition blocks 211 are different, and their distances from the axis of the inductor body 1 are also different, the connecting block 212 is tilted. At the same time, the lengths of the connecting blocks 212 between the two different transition blocks 211 are also different. As the transition block 211 rises, the distance of the connecting block 212 from the axis becomes closer, and the length of the connecting block 212 gradually decreases. Correspondingly, the connecting block 212 will also gradually approach the axis until the connecting block 212 connects to the transition block 211 on the top surface of the inductor body 1. This achieves that as the spiral 21 rises spirally, one end of the spiral 21 gradually approaches the center until it coincides with the center. The point of coincidence is located exactly at the center of the top surface of the inductor body 1. This also makes the projection of the spiral 21 on the plane a seamless square. In addition, through the setting of the positions of the transition block 211 and the connecting block 212, the spiral 21 has a spiral shape and, from a three-dimensional perspective, it is pyramid-shaped.

[0027] Reference Figure 3 As shown, the closer the connection blocks 212 are to the inner top surface of the inductor body 1, the closer the spacing between them, the shorter the length of the connection blocks 212, and the smaller the tilt angle, so that the shape and size of the connection block 212 at the top layer gradually approach that of the transition block 211.

[0028] By using the buried inductor design, the buried inductor is embedded in the circuit board interlayer through the upper connection 22 and the lower connection 23, which eliminates a large number of solder joints and improves the reliability of the entire circuit. At the same time, the conductive coil 2 of the buried inductor has an asymmetrical design, with the large coil connected to the high voltage end. When encountering a large voltage surge, the outermost coil bears the load, greatly reducing the probability of breakdown (the outer coil has a large turn spacing, while the inner coil has a small turn spacing). Meanwhile, the spiral 21 has a pyramidal design, and the coils of each layer are not aligned, which greatly reduces the distributed capacitance and makes the inductor's resonant frequency higher.

[0029] An embodiment of the present invention discloses a method for fabricating a buried inductor on a printed circuit board, comprising the following steps: S1. Magnetic Powder Treatment in Injection Molding: Using iron-silicon-chromium powder with surface phosphating insulation treatment or silica and ceramic coating as raw materials, the powder particle size ranges from D50=7-11μm. Coarse powder is removed using an 800-mesh sieve. The powder is then uniformly mixed with nano-silica sol, nano-alumina, and nano-aluminum nitride sol, with a solid content of 3-5w% by weight of the powder. 1wt% BYK110 is added to disperse the nanoparticles and prevent clumping. The mixture is continuously kneaded in a kneader, with the kneading temperature controlled at 60-70℃ to evaporate a large amount of moisture and ensure the nanoparticles fully coat the magnetic powder surface. When the powder reaches a wet, sandy consistency, it is placed in a glass rotary kiln and heated to 100-120℃ under nitrogen protection to fully dry the powder. (The key to using inorganic sol treatment is to increase the material's resistance to high voltage and its thermal conductivity, allowing the heat generated by the powder to be conducted away through the nanoparticle network, and also providing a certain degree of fire resistance.) S2. Injection molding formulation composition: Magnetic powder accounts for 80-86wt%, hollow glass microspheres with D50=10-15μm account for 4-5wt%, coupling agent methacryloxysilane KH570 accounts for 0.1-1.0wt%, and PPS (polyphenylene sulfide) resin accounts for 9-16wt%. The purpose of the glass microspheres is to improve the withstand voltage while reducing the density of the material, thereby reducing the weight of the circuit board, and at the same time reducing the dielectric constant of the material and reducing the distributed capacitance. S3. Bake the magnetic powder in a vacuum environment at 130-150℃ (pressure ≤ -0.085MPa) for 2-4 hours, and then cool it to room temperature by purging with nitrogen or other gases. S4. Mix the coupling agent with anhydrous ethanol and deionized water at a ratio of 1:9:1 to 1:18:2 and hydrolyze for 15-30 minutes to form a coupling agent hydrolysate. Spray the magnetic powder with the coupling agent hydrolysate while stirring. Continue stirring until no more clumps form. Control the temperature to not exceed 50°C. Bake again at 80-100°C in a vacuum or nitrogen environment for 2-4 hours. S5. Using a twin-screw mixer, start mixing by adding PPS and simultaneously adding 0-0.10wt% silicone to lubricate and reduce adhesion to mold 3. After kneading for 2 minutes, start gradually adding magnetic powder in batches. The whole process takes 5-8 minutes. S6. After addition, the temperature of the mixer is controlled at 285-315℃, the screw speed is controlled at 80-200 rpm, the temperature of the mixed melt is controlled at 310-325℃, and the internal pressure is controlled at 8-218MPa. S7. Air-cool the melt material, draw it into strips, and cut them into pellets with a length of 2-4mm. S8. Bake the cut granules in a vacuum environment at 130-150℃ (pressure ≤ -0.085MPa) for 2-4 hours, controlling the moisture content to ≤0.03%, and pour them into the injection molding hopper. Keep the hopper at 120-130℃. S9. Take a piece of copper sheet as follows: Figure 1 As shown, along as Figure 2 The cutting lines in the design are cut using a die-cutting process. S10. Secure both ends of the copper sheet into the slots 31 of the upper and lower mold plates 3, as shown in the image. Figure 3 As shown, the two ends of the copper sheet are secured in the slot 31. Figure 4 As shown; S11. Pull the two mold plates apart at a uniform speed, as shown. Figure 5 The control distance is determined by the design thickness of the buried layer where the inductor is located on the circuit board. Because the dimensions of each turn of this coil are different, if the tension at both ends is uniform, the resulting structure is an uneven structure with a large turn spacing on the outer layer and a small turn spacing on the inner layer. The coil configuration is as follows: Figure 6 ; S12. The injection mold closes from all sides, and the injection port is on all sides, thus preventing the coil from being squeezed from the top and bottom and avoiding short circuits. S13. The temperatures of the rear / middle / front / nozzle of the injection molding cylinder are controlled at 300 / 310 / 320 / 320℃ respectively. The temperature of mold 3 is controlled at 130-160℃. The injection speed is controlled at 20-50mm / s. The injection pressure is 100-150MPa. The holding pressure is 50-100MPa. The holding time is 8-20 seconds. The cooling time is 20-50s. Demolding is then performed. S14. After cooling and demolding, cut off the lead wires extending from the top and bottom ends to expose the cut surface as shown. Figure 7 The top and bottom surfaces are made using copper-clad laminate technology, with two copper layers connected to the cut surface respectively. Figure 8 ; S15. Etch the wiring on the top and bottom surfaces according to the circuit design, as follows: Figure 9 This allows the inductor to be embedded in a single layer of a circuit board.

[0030] In the above steps, S3~S8 is the process of injection molding, S9~S11 is the process of manufacturing conductive coil 2, and S12~S15 is the process of manufacturing inductor body 1 (including conductive coil 2).

[0031] It is important to note that the mold 3 in step S10 is specifically designed for stretching the conductive coil 2. The shape of the mold 3 is identical to that of the inductor body 1. A groove 31 is located at the center or edge of one side of the mold 3, and a stop block 32 is positioned at the opening of the groove 31. The shape of the groove 31 is identical to that of the transition block 211. Therefore, in step S10, the ductility of the copper sheet allows both ends to extend into the groove 31 and be stopped by the stop block 32, thus achieving a fit. The position of the transition block 211 on the bottom or top surface of the inductor body 1 corresponds to the location of the groove 31 in the mold 3. The mold closing in step S12 can use a standard ordinary mold 3; the key aspects are the mold closing mechanism and the location of the injection port.

[0032] Using the above method, a copper sheet is used to make the conductive coil 2. The square spiral 21 of the coil is cut out according to the spiral pattern using a die-cutting process. Then, the two ends of the coil are fixed in the slots 31 of the upper and lower molds 3. The coil is then stretched into a coil with uneven turn spacing by the natural tension of the upper and lower molds 3. The molds 3 are then closed from all sides. The molds 3 have injection channels. The injection molding process is used to inject injection plastic containing magnetic powder into the molds 3. The injection plastic is heated and cured in the molds 3. At this time, the coil embedded in the magnetic injection board is made. Then, the exposed copper wires at both ends are cut off to leave the cut surface. The wiring is made on the upper and lower surfaces using PCB technology to connect the coil cut surface, thus completing an inductor embedded in the circuit board. When in use, it is used as an intermediate layer of a multi-layer circuit board.

[0033] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Identical components are represented by the same reference numerals. It should be noted that the terms "front," "rear," "left," "right," "up," and "down" used in the following description refer to directions in the accompanying drawings, while the terms "inner" and "outer" refer to directions toward or away from the geometric center of a specific component. Therefore, all equivalent changes made to the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for fabricating buried inductors on a printed circuit board, characterized in that, Includes the following steps: S1. Composition of injection molding compound: magnetic powder accounts for 80-86 wt%, hollow glass microspheres with D50=10-15μm account for 4-5 wt%, coupling agent methacryloxysilane KH570 accounts for 0.1-1.0 wt%, and resin accounts for 9-16 wt% by mass. S2. Injection Molding Preparation: Magnetic powder is baked in a vacuum environment at 130-150℃ for 2-4 hours, then cooled to room temperature by purging with nitrogen; the coupling agent is mixed with anhydrous ethanol and deionized water at a ratio of 1:9:1 to 1:18:2 and hydrolyzed for 15-30 minutes to form a coupling agent hydrolysate. The magnetic powder is stirred and sprayed with the coupling agent hydrolysate, and the mixture is stirred until it no longer clumps. The temperature is controlled not to exceed 50℃. The mixture is then baked again in a vacuum or nitrogen environment at 80-100℃ for 2-4 hours; the resin and magnetic powder are mixed using a twin-screw mixer, and the melt temperature is controlled at 310-325℃; the melt is air-cooled and drawn into strips, and then granulated to a length of 2-4mm. The granules are baked in a vacuum environment at 130-150℃ for 2-4 hours, with the moisture content controlled to ≤0.03%. The granules are then poured into an injection molding hopper, and the hopper is kept at 120-130℃. S3. Coil fabrication: Take a rectangular metal sheet and punch and cut it along the spiral direction. Take the cut ends and place them in the slots (31) of the upper and lower mold (3) plates. Pull the two mold (3) plates apart at a uniform speed. Control the pulling distance to be the design thickness of the buried layer where the inductor is located. The size of each turn of the pulled-out conductive coil (2) is different. S4. Fabrication of Buried Inductor: The injection mold is closed from all sides, with the injection port on all sides. The temperature of the injection cylinder nozzle is controlled, and the mold temperature is controlled at 130-160℃. The injection speed is controlled at 20-50mm / s, the injection pressure is 100-150MPa, the holding pressure is 50-100MPa, the holding time is 8-20 seconds, and the cooling time is 20-50s before demolding. After cooling and demolding, the leads extending from the top and bottom ends are cut off to expose the cut surface. Copper clad laminate is used to make two copper layers on the top and bottom sides and they are connected to the cut surface respectively. The wiring on the top and bottom sides is etched according to the circuit design to form the buried inductor.

2. The method for fabricating a buried inductor on a printed circuit board according to claim 1, characterized in that, In step S1, the magnetic powder is prepared using iron-silicon-chromium powder with a surface treated by phosphating insulation or by silica and ceramic coating as raw material. The powder particle size ranges from D50 to 7-11 μm. Coarse powder is removed by sieving through an 800-mesh sieve. The powder is then uniformly mixed with nano-silica sol, nano-alumina, and nano-aluminum nitride sol, which have a solid content of 3-5 wt% of the powder mass. 1 wt% of dispersant is added, and the mixture is continuously kneaded in a kneader with the kneading temperature controlled at 60-70℃ to evaporate a large amount of moisture and to fully coat the surface of the magnetic powder with nanoparticles. When the powder reaches a wet sandy texture, it is placed in a glass rotary kiln and heated to 100-120℃ under nitrogen protection to fully dry the powder.

3. A buried inductor manufactured based on the method for manufacturing a buried inductor on a printed circuit board according to any one of claims 1-2, characterized in that, The inductor includes an inductor body (1) and a conductive coil (2). The conductive coil (2) includes a spiral (21), an upper connecting wire (22), and a lower connecting wire (23). The spiral (21) is fitted inside the inductor body (1). The upper connecting wire (22) is connected to one end of the spiral (21) and is located on the surface of the inductor body (1). The lower connecting wire (23) is connected to the other end of the spiral (21) and is located on the surface of the inductor body (1). The spiral (21) spirals vertically upward from the bottom surface of the inductor body (1) to the top surface of the inductor body (1). The upper surface of the spiral (21) is parallel to and exposed on the top surface of the inductor body (1), and the lower surface of the spiral (21) is parallel to and exposed on the bottom surface of the inductor body (1), so that the upper connecting line (22) and the lower connecting line (23) can be connected to the spiral (21).

4. The buried layer inductor of a printed circuit board according to claim 3, characterized in that, The upper connecting line (22) and the lower connecting line (23) are attached to the surface of the inductor body (1) and extend to the edge of the inductor body (1).

5. A buried layer inductor for a printed circuit board according to claim 4, characterized in that, The upper connecting line (22) and the lower connecting line (23) extend in opposite directions.

6. The buried layer inductor of a printed circuit board according to claim 3, characterized in that, The projection of the spiral (21) onto the plane is square.

7. A buried layer inductor for a printed circuit board according to claim 3, characterized in that, The spiral (21) includes multiple transition blocks (211) and multiple connecting blocks (212). A connecting block (212) connects each transition block (211), and each transition block (211) is located on a horizontal plane at a different height, so that the connecting block (212) is tilted, thereby realizing that the spiral (21) connects the upper and lower surfaces inside the inductor body (1).

8. The buried layer inductor of a printed circuit board according to claim 7, characterized in that, The transition block (211) is located near the corner inside the inductor body (1), and the axial distance between the transition block (211) and the inductor body (1) gradually decreases until they coincide, so that the projection of the spiral (21) is square and connects the upper and lower surfaces inside the inductor body (1).

9. A buried layer inductor for a printed circuit board according to claim 7, characterized in that, The transition block (211) located on the bottom surface inside the inductor body (1) is located near the corner, and the transition block (211) located on the top surface inside the inductor body (1) is located at the center.

10. A buried layer inductor for a printed circuit board according to claim 7, characterized in that, Each connecting block (212) has a different length. The length of the connecting block (212) closest to the bottom of the inductor body (1) gradually decreases as the spiral (21) rises, while the connecting block (212) gradually approaches the axis of the inductor body (1).

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