JP2020004945A - Inductor and manufacturing method thereof - Google Patents

Abstract

To provide an inductor that can be miniaturized with little leakage flux.SOLUTION: An inductor 100 includes an element body 10 including metal magnetic powder and resin, a coil constituted by a wound portion and a pair of drawn portions 22 drawn out at both ends of the wound portion, and buried in the element body 10, a pair of external terminals 30 electrically connected to each of the drawn portions 22, and a conductor layer 40 disposed on the surface of the element body intersecting the winding axis of the coil. The conductor layer 40 includes a first metal layer formed by fusing the metal magnetic powder on the surface of the element body to each other, and a second metal layer plated on the first metal layer, and the electrical resistivity of the second metal layer is configured to be lower than the electrical resistivity of the first metal layer.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an inductor and a method for manufacturing the inductor.

  2. Description of the Related Art There is known an electronic component in which a coil is embedded in a body made of a composite material of a resin material and a metal powder.

US Patent Application Publication No. 2017/0309394

  In an inductor in which a coil is built in a body made of a composite material containing a magnetic powder and a resin, since the relative permeability of the composite material is low, magnetic flux leaks out of the body, and leakage magnetic flux poses a problem. Since the leakage magnetic flux is a cause of radiation noise radiated from the inductor, as a method for suppressing the leakage magnetic flux, a structure in which a metal case is provided on an element body and the leakage magnetic flux is consumed as eddy current in the metal case (for example, see Patent Document 1). Are known. However, there is a problem that providing the exterior of the metal case increases the outer shape of the element. SUMMARY OF THE INVENTION An object of the present invention is to provide a small-sized inductor having a small leakage magnetic flux.

  The inductor according to the present invention includes a body including metal magnetic powder and resin, a wound portion, and a pair of lead portions drawn out at both ends of the wound portion, a coil embedded in the body, and a lead portion. And a conductor layer disposed on a surface of the element crossing the winding axis of the coil. The conductor layer includes a first metal layer in which metal magnetic powders near the surface of the element are fused to each other, and a second metal layer plated on the first metal layer. The electrical resistivity of the second metal layer is lower than the electrical resistivity.

  According to the invention, it is possible to provide a small-sized inductor having a small leakage magnetic flux.

FIG. 2 is a schematic partially transparent perspective view of the inductor according to the first embodiment. FIG. 2 is a schematic partially transparent perspective view of the inductor shown in FIG. 1. FIG. 2 is a schematic cross-sectional view illustrating a method for forming a conductor layer of the inductor shown in FIG. 1. FIG. 2 is a perspective view illustrating a distribution of an eddy current generated in a conductor layer of the inductor illustrated in FIG. 1. FIG. 7 is a schematic partially transparent perspective view of an inductor according to a second embodiment. FIG. 10 is a schematic partially transparent perspective view of an inductor according to a third embodiment. FIG. 14 is a schematic oblique partial transparent view of the inductor according to the fourth embodiment. FIG. 8 is a diagram illustrating a magnetic field noise distribution in the inductor illustrated in FIG. 7. FIG. 4 is a diagram illustrating a magnetic field noise distribution in an inductor having no conductor layer. FIG. 14 is a schematic partially transparent perspective view of an inductor according to a fifth embodiment. FIG. 14 is a schematic partially transparent perspective view of an inductor according to a sixth embodiment.

  The inductor according to the present embodiment has a body including metal magnetic powder and resin, a winding part and a pair of lead parts drawn out at both ends of the winding part, and a coil embedded in the body. And a pair of external terminals electrically connected to each of the lead portions, and a conductor layer disposed on a surface of the element body that intersects the winding axis of the coil. The conductor layer includes a first metal layer in which metal magnetic powders near the surface of the element are fused to each other, and a second metal layer plated on the first metal layer. The electrical resistivity of the second metal layer is lower than the electrical resistivity.

  The first metal layer may be formed inside the element body. Thereby, the leakage magnetic flux can be further reduced.

  The conductor layer may be arranged so as to cover at least a part of the winding portion of the coil when viewed from the winding axis direction of the coil. Thereby, the leakage magnetic flux can be further reduced.

  The conductor layer may be arranged inside the outer periphery of the winding part of the coil when viewed from the winding axis direction of the coil. Thereby, the leakage magnetic flux can be further reduced.

  The conductor layer may include an annular conductor layer disposed between an outer peripheral portion and an inner peripheral portion of the winding portion of the coil when viewed from the winding axis direction of the coil. Thereby, it is possible to achieve both the suppression of the leakage magnetic flux and the suppression of the deterioration of the characteristics of the inductor.

  The conductor layer may include a plurality of annular conductor layers that do not cross each other. Thereby, it is possible to achieve both the suppression of the leakage magnetic flux and the suppression of the deterioration of the characteristics of the inductor.

  The plurality of annular conductor layers may be electrically connected to each other. Thereby, the productivity of forming the conductor layer is further improved.

  The conductor layer may be electrically connected to a ground terminal connected to the ground of the board on which the conductive layer is mounted. Thereby, electric field noise can be suppressed more effectively.

  The inductor may further include an insulating layer covering the conductor layer. Thereby, the oxidation of the conductor layer is suppressed, and the reliability is further improved.

  The method for manufacturing an inductor according to the present embodiment includes embedding a coil formed of a wound portion and a pair of lead portions drawn out at both ends of the wound portion in a composite material containing metal magnetic powder and resin. Forming a body, and providing, on the surface of the body intersecting the winding axis of the coil, a first metal layer in which metal magnetic powder is melted and fused to each other near the surface of the body, Forming a second metal layer on the first metal layer. As a result, it is possible to obtain a small-sized inductor having a small leakage magnetic flux.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies an inductor for embodying the technical idea of the present invention, and the present invention is not limited to the inductor described below. The members described in the claims are by no means limited to the members of the embodiment. In particular, the dimensions, materials, shapes, relative arrangements, and the like of the components described in the embodiments are not intended to limit the scope of the present invention thereto, unless otherwise specified. It's just In the drawings, the same portions are denoted by the same reference numerals. Although the embodiments are shown separately for the sake of convenience in consideration of the explanation of the main points or the ease of understanding, partial replacement or combination of the configurations shown in different embodiments is possible. In the second and subsequent embodiments, description of matters common to the first embodiment will be omitted, and only different points will be described. In particular, the same operation and effect of the same configuration will not be sequentially described for each embodiment.

(Example 1)
First Embodiment An inductor 100 according to a first embodiment will be described with reference to FIGS. FIG. 1 is a schematic partially transparent perspective view illustrating the internal structure of the inductor 100 according to the first embodiment, and FIG. 2 is a schematic partially transparent perspective view illustrating the outer shape of the inductor.

  As shown in FIGS. 1 and 2, an inductor 100 includes a body 10 containing metal magnetic powder and resin, a coil 20 embedded in the body 10, and a pair of coils electrically connected to both ends of the coil 20. And a conductor layer 40 arranged on the surface of the element body 10. The element body 10 has a bottom surface on the mounting surface side intersecting with the winding axis of the coil 20, an upper surface facing the bottom surface, and four side surfaces adjacent to the bottom surface and the upper surface. The coil 20 has a wound part 21 and a pair of drawn parts 22 drawn out at both ends of the wound part 21. In the inductor 100, the conductor layer 40 is disposed on the upper surface of the element body opposite to the mounting surface side intersecting with the winding axis of the coil 20, and on two opposing side surfaces. From the other two opposing side surfaces where the conductor layer is not disposed, the end surface of the lead portion 22 is exposed, and an external terminal 30 electrically connected to the lead portion 22 is provided. The external terminal 30 extends from the side surface to the bottom surface of the element body 10. In the inductor 100, the external terminal 30 is provided on the entire side surface and a part of the bottom surface of the element body 10, and the external terminal 30 provided on the bottom surface is shown as a partially transparent view in FIG. 2, and is omitted in FIG. The external terminal 30 can be formed, for example, in the same manner as the conductor layer 40, and may be formed simultaneously with the conductor layer 40.

  The element body 10 is formed, for example, by applying pressure to the composite material in which the coil 20 is embedded. The composite material forming the element body 10 includes, for example, a magnetic metal powder and a binder such as a resin. Examples of the metal magnetic powder include iron (Fe), Fe-Si, Fe-Si-Cr, Fe-Si-Al, Fe-Ni-Al, and Fe-Cr-Al based irons. Metal magnetic powder, metal magnetic powder of a composition not containing iron, metal magnetic powder of another composition containing iron, metal magnetic powder in an amorphous state, metal magnetic powder whose surface is covered with an insulator such as glass, surface A magnetic metal powder modified from, a fine metal magnetic powder of a nano level, or the like can be used. Further, as the binder, a thermosetting resin such as an epoxy resin, a polyimide resin, and a phenol resin, and a thermoplastic resin such as a polyester resin and a polyamide resin are used.

  The coil 20 is formed by edgewise winding a conductor having a rectangular cross section (hereinafter, also referred to as a flat wire) having an insulating coating along a unidirectional winding axis. The insulating coating includes, for example, a polyurethane resin, a polyester resin, an epoxy resin, and a polyamideimide resin. The coil 20 is built in the element body 10 with the winding axis crossing the bottom surface and the upper surface of the element body 10 on the mounting surface side.

  The conductor layer 40 includes a first metal layer in which metal magnetic powder contained in the composite material constituting the element body 10 is melted near the surface of the element body and fused together, and a first metal layer formed by plating the first metal layer. A second metal layer formed as a seed layer and disposed on the surface of the element body 10. In the inductor 100, the conductor layers disposed on the upper surface and the side surfaces of the element body 10 each have a rectangular shape, and are disposed on three surfaces continuous from the upper surface to the side surfaces. In the inductor 100, the conductor layer 40 is formed to have a width smaller than the width between the side surfaces where the end surfaces of the lead portions 22 of the element body 10 are exposed.

  A method for forming the conductor layer will be described with reference to FIG. FIG. 3A is a schematic cross-sectional view schematically showing the vicinity of the surface of the element body 10. The element body 10 is formed by pressure molding a composite material containing metal magnetic powder containing metal magnetic particles 11 covered with an insulator layer 12 and a resin 13. In FIG. 3A, the metal magnetic powder is an aggregate of at least two types of metal magnetic particles 11 having different average particle sizes and different particle size distributions. The metal magnetic powder may be an aggregate of the metal magnetic particles 11 having a single average particle diameter and a single particle size distribution. When the metal magnetic powder includes the metal magnetic particles 11 having different average particle diameters, the density of the metal magnetic powder included in the element body 10 can be increased.

  In FIG. 3B, the first metal layer 14 is formed near the surface of the element body 10 by irradiating the surface of the element body 10 with a laser beam, for example, in the direction of the arrow in the figure. By irradiating the surface of the element body 10 with a laser beam, a portion of the resin 13 on the surface of the element body 10 and the vicinity thereof and the insulating layer 12 provided around the metal magnetic particles 11 existing on the surface and the vicinity thereof are provided. Is partially removed. Further, the surface of the metal magnetic particles 11 is melted by the laser beam, and the metal magnetic particles 11 are mutually fused to form the first metal layer 14. That is, the compositions of the metal magnetic particles 11 and the first metal layer 14 are substantially equal. The first metal layer 14 is formed inside the outermost surface of the element body 10, and the surface is exposed outside the element body 10. Since the first metal layer 14 is formed by partially fusing the metal magnetic particles 11 to each other, the continuity may be incomplete and the thickness may be small. Therefore, the electrical resistivity of the first metal layer 14 may be relatively large. For example, on a composite material using iron as the metal magnetic powder, the electric resistance of the first metal layer formed in a C-shape in which a part of a ring having a width of 0.25 mm and a gap of 0.5 mm between open ends is missing is formed. , Φ9 mm, and about 14 Ω, and φ5 mm, about 8 Ω.

  In FIG. 3C, a second metal layer 16 is formed by a plating method on the first metal layer 14 formed by exposing the surface from the element body 10, and the conductor layer 40 is formed. Since the second metal layer 16 is formed by growing plating using the first metal layer 14 as a seed layer, the second metal layer 16 has a lower electrical resistivity than the first metal layer 14. For example, a first metal layer is formed in a C shape with a width of 0.25 mm and a gap between opening ends of 0.5 mm on a composite material using iron as a metal magnetic powder, and further, a copper-plated conductor having a thickness of 52 μm is formed. The layer electrical resistance was about 36 mΩ for φ9 mm and about 20 mΩ for φ5 mm. Note that the second metal layer may protrude from the element body 10.

  In the first metal layer included in the conductor layer disposed on the surface of the element body of the inductor, the generation of the eddy current is suppressed because the electric resistivity is relatively large. On the other hand, since the second metal layer has a relatively low electric resistivity, it is considered that most of the eddy current generated in the conductor layer flows through the second metal layer. Therefore, a substantial conductor portion in the conductor layer is formed only on the surface of the element body. By forming the conductor layer substantially on the surface of the element body, it is possible to reduce the eddy current loss while reducing the leakage flux of the inductor.

  In the above-described embodiment, since the conductor layer is formed on substantially the entire three surfaces of the element body, efficient manufacturing may be difficult by laser beam irradiation. For efficient manufacture, it is preferable to reduce the area of the conductor layer as much as possible. FIG. 4 is a simulation result of a distribution of an eddy current generated in the conductor layer 40 when a current of 1 MHz / 5 A flows through the coil 20 of the inductor 100 according to the first embodiment. The simulation was performed using the finite element method analysis software Femtet (registered trademark) manufactured by Murata Software with the outer diameter of the coil being 9 mm and the inner diameter being 5 mm. In FIG. 4, the eddy current is concentrated in the annular region of the winding portion 21 of the coil 20 in plan view from the winding axis direction of the coil. Therefore, the main leakage magnetic flux can be suppressed only by forming the conductor layer in an annular shape on the upper surface of the element body in accordance with the distribution of the eddy current obtained by the simulation.

(Example 2)
Second Embodiment An inductor 110 according to a second embodiment will be described with reference to FIG. FIG. 5 is a schematic partially transparent perspective view of the inductor 110, and the coil built in the element body 10 is not shown. The inductor 110 has the same configuration as that of the inductor 100 except that the conductor layer 40a is disposed on the upper surface of the element body 10 as an annular conductor layer, and the conductor layer is not disposed on the side surface.

  In the inductor 110, the conductor layer 40 a formed in an annular shape is arranged substantially coincident with the winding part 21 of the coil when viewed from the direction of the winding axis of the coil. Since the conductor layer 40a is arranged only in the region where the leakage magnetic flux generated from the coil is strong, a sufficient leakage flux reduction effect can be obtained, and the conductor layer 40a can have a small area to form a conductor layer with good productivity. .

  In the inductor of the present invention, the conductor layer is disposed substantially on the surface of the element body. Thus, the reason why the eddy current loss can be reduced while reducing the leakage magnetic flux of the inductor can be explained as follows, for example.

  Leakage magnetic flux can be evaluated by measuring the magnetic flux density on a plane separated by a predetermined distance from the surface of the body of the inductor in the direction of the winding axis of the coil, and evaluating the maximum magnetic flux density in the plane. That is, a small value of the maximum magnetic flux density means that the leakage magnetic flux radiated from the inductor is small. On the other hand, eddy current loss cannot be measured directly. However, when the magnetic flux generated from the coil crosses the conductor layer, an eddy current is generated in the conductor layer. Due to this eddy current, a secondary magnetic flux is generated in a direction opposite to the original magnetic flux generated from the coil. A part of the magnetic flux generated from the coil is offset by the secondary magnetic flux generated by the eddy current, so that the inductance value decreases. Since the inductance value decreases as the eddy current increases, the magnitude of the eddy current loss can be indirectly evaluated from the rate of change of the inductance value. That is, a small change rate of the inductance value means that the eddy current loss is small.

  Thus, for an inductor having an annular conductor layer such as the inductor 110, the relationship between the formation position of the conductor layer and the maximum magnetic flux density Bmax and the inductance value was evaluated by simulation. Table 1 shows the results. In the simulation, the inner diameter of the winding portion of the coil is 5 mm, the outer diameter is 9 mm, and the conductor layer is a 50 μm-thick annular member which is overlapped on the winding portion of the coil when viewed from the coil axis direction. The position where the layer was arranged was changed from the surface of the element body to a depth of 150 μm from the element body surface every 50 μm. Here, the current flowing through the coil was 1 MHz / 5 A. As for the maximum magnetic flux density, the maximum magnetic flux density was calculated for a plane having a distance of 0.5 mm and a plane having a distance of 1.0 mm from the upper surface of the element body in the winding axis direction of the coil. Table 1 shows, as a comparative example, an inductor in which the conductor layer 40a is not formed, a change rate (%) of the inductance value L based on the inductance value L of the comparative example (100%), and a maximum magnetic flux of the inductor of the comparative example. The relative value (%) of the maximum magnetic flux density Bmax based on the density (100%) is shown. The simulation was performed using Femtet.

  From Table 1, it can be seen that the maximum magnetic flux density Bmax decreases irrespective of the depth at which the annular conductor layer is embedded in the body. Therefore, by providing the conductor layer, the leakage flux of the inductor can be reduced. On the other hand, it can be seen that the absolute value of the change rate of the inductance value L is significantly increased according to the depth at which the annular conductor layer is embedded in the body. This is because, when the annular conductor layer is embedded in the body, in addition to the increase in the inductance of the annular conductor layer, the magnetic coupling between the winding portion of the coil and the annular conductor layer increases, and as a result, It is considered that the eddy current loss increases. Therefore, eddy current loss can be reduced by providing the conductor layer closer to the surface of the element body.

(Example 3)
Third Embodiment An inductor 120 according to a third embodiment will be described with reference to FIG. FIG. 6 is a schematic partially transparent perspective view of the inductor 120. In the inductor 120, a disc-shaped conductor layer 40b having an outer diameter substantially matching the outer diameter of the winding portion of the coil is arranged on the upper surface of the element body 10, and no conductor layer is arranged on the side surface of the element body 10. Except for this, the configuration is the same as that of the inductor 100.

  In the inductor 120, when viewed from the direction of the winding axis of the coil, the outer peripheral portion of the disc-shaped conductor layer 40b is disposed so as to substantially match the outer peripheral portion of the winding portion of the coil embedded in the element body 10. Since the conductor layer 40b is arranged only in a region where the leakage magnetic flux generated from the coil is strong, a sufficient leakage flux reduction effect is obtained, and the area of the conductor layer 40b is reduced to form a conductor layer with better productivity. it can.

(Example 4)
Fourth Embodiment An inductor 130 according to a fourth embodiment will be described with reference to FIGS. FIG. 7 is a schematic partially transparent perspective view of the inductor 130. In the inductor 130, on the upper surface of the element body 10, an annular conductor layer 40c substantially coincident with the inner periphery of the coil winding portion, and an annular conductor layer 40d substantially coincident with the outer periphery of the coil winding portion Are arranged, and the configuration is the same as that of the inductor 100 except that the conductor layer is not arranged on the side surface of the element body 10. In addition, the inductor 130 is configured such that one annular conductor layer 40a of the inductor 110 is divided into an annular conductor layer 40c provided on the inner peripheral portion of the winding portion of the coil and an annular conductor layer 40d provided on the outer peripheral portion. The configuration is the same as that of the inductor 110, except that the inductor 110 is divided and the conductor layer is not arranged between the conductor layers 40c and 40d.

  In the inductor 130, the inner diameter of the annular conductor layer 40c is substantially equal to the inner diameter of the winding portion of the coil embedded in the element body 10 when viewed from the coil axis direction. Further, the outer diameter of the annular conductor layer 40 d is substantially equal to the outer diameter of the winding portion of the coil embedded in the element body 10. The conductor layers 40c and 40d are arranged as concentric circles around the winding axis of the coil. Since the conductor layers 40c and 40d are arranged only in a region where the leakage magnetic flux generated from the coil is particularly strong, a sufficient effect of reducing the leakage magnetic flux can be obtained while reducing the area of the conductor layer. The width of the conductor layer 40c is, for example, about 0.25 mm when the inner diameter of the winding portion of the coil is 5 mm and the outer diameter is 9 mm.

  8 and 9 are graphs showing actual measurement results of magnetic field noise generated from the inductor. FIG. 8 shows the measurement result of the inductor 130 of the fourth embodiment, and FIG. 9 shows the measurement result of the inductor having no annular conductor layer for comparison. The measurement was performed by mounting the inductor on a DC-DC converter driven at 1 MHz and measuring the distribution of excitation voltage due to magnetic field noise in a plane 1 mm away from the top surface of the inductor using an EMI tester device (Peritec Co., Ltd., EMV-100). The measurement was performed using 8 and 9, the X axis and the Y axis indicate the relative position of the coil on the inductor from the winding axis, and the vertical axis indicates the excitation voltage. In the inductor used for the measurement, the inner diameter of the winding portion of the coil was 5 mm, the outer diameter was 9 mm, and the width of each of the annular conductor layers 40c and 40d was 0.25 mm.

  As shown in FIG. 9, the maximum value of the excitation voltage of the inductor having no annular conductor layer for comparison was about 53 dBμV. On the other hand, as shown in FIG. 8, the maximum value of the excitation voltage of the inductor 130 of Example 4 was about 48.1 dBμV, and the difference between the excitation voltages was 4.9 dBμV. That is, about 44% of the magnetic field noise could be suppressed by the two annular conductor layers arranged as concentric circles.

(Example 5)
Fifth Embodiment An inductor 140 according to a fifth embodiment will be described with reference to FIG. FIG. 10 is a schematic partially transparent perspective view of the inductor 140. In the inductor 140, on the upper surface of the element body 10, an annular conductor layer 40c substantially coincident with the inner periphery of the coil winding portion, and an annular conductor layer 40d substantially coincident with the outer periphery of the coil winding portion Are arranged, and the conductor layer 40c and the conductor layer 40d are configured similarly to the inductor 100 except that the conductor layer 40c and the conductor layer 40d are electrically connected to each other by the connection conductor 42, and that the conductor layer is not arranged on the side surface of the element body 10. You. The inductor 140 is configured in the same manner as the inductor 130 except that the conductor layer 40c and the conductor layer 40d of the inductor 130 are electrically connected to each other by the connection conductor 42.

  In the inductor 140, the annular conductor layer 40c is disposed such that the inner peripheral portion thereof substantially coincides with the inner peripheral portion of the winding portion of the coil embedded in the element body 10, as viewed from the coil winding axis direction. In addition, the outer peripheral portion of the ring-shaped conductor layer 40 d is arranged so as to substantially coincide with the outer peripheral portion of the winding portion of the coil embedded in the element body 10. The conductor layers 40c and 40d are arranged as concentric circles around the winding axis of the coil, and are electrically connected to each other by the connection conductor 42. The connection conductor 42 can be formed, for example, in the same manner as the conductor layers 40c and 40d, and may be formed simultaneously with the conductor layers 40c and 40d.

  The second metal layer included in the conductor layers 40c and 40d is formed by, for example, electroplating. In the inductor 130, since the first metal layer to be plated is divided into a plurality, the productivity of electroplating may be reduced. The inductor 140 is electrically connected through a plurality of first metal layers connected by the connection conductor 42. Therefore, in the barrel plating method, the chance of contact between the metal ball and the plating portion can be increased, and in the plating method in which the electrode is connected to the plating portion, only one connection point is required, and the efficiency of the second metal layer is reduced. Well formed. Note that even if an eddy current flows in the annular conductor layer, the conductor layer is electrically floating, so that there is no effect on the effect of reducing the leakage magnetic flux.

(Example 6)
Sixth Embodiment An inductor 150 according to a sixth embodiment will be described with reference to FIG. 11 is a schematic partially transparent perspective view of the inductor 150. In the inductor 150, on the upper surface of the element body 10, an annular conductor layer 40c substantially coinciding with the inner periphery of the coil winding portion, and an annular conductor layer 40d substantially coincident with the outer periphery of the coil winding portion Are arranged, the conductor layer and the conductor layer 40d are electrically connected to each other by the connection conductor 42, and the conductor layer 40c and the conductor layer 40d are electrically connected to the ground terminal 32 via the connection conductor 44. , And a configuration similar to that of inductor 100 except that no conductor layer is disposed on the side surface of element body 10. The inductor 150 is configured in the same manner as the inductor 140 except that the conductor layer 40c and the conductor layer 40d of the inductor 140 are electrically connected to the ground terminal 32 via the connection conductor 44.

  In the inductor 150, the ground terminal 32 connected to the ground on the substrate on which the inductor is mounted is continuously arranged on the bottom surface of the element body 10 and on the side surface adjacent to the bottom surface and where the end of the coil is not exposed. Is done. The ground terminal 32 can be formed, for example, in the same manner as the conductor layers 40c and 40d, and may be formed simultaneously with the conductor layers 40c and 40d. The ground terminal 32 is connected to the conductor layer 40d via the connection conductor 44 continuously arranged on the upper surface and the side surface of the element body 10. The conductor layer 40d is connected to the conductor layer 40c via the connection conductor 42. The connection conductor 44 can be formed, for example, similarly to the conductor layers 40c and 40d, and may be formed simultaneously with the conductor layers 40c and 40d. By connecting the conductor layers 40c and 40d to the ground, electric field noise can be reduced in addition to electromagnetic noise due to leakage magnetic flux.

  For the inductors 100 to 130 shown in the first to fourth embodiments, the change rate of the inductance value L and the maximum magnetic flux density Bmax for a plane having a distance of 0.5 mm and 1.0 mm from the upper surface of the inductor in the winding axis direction of the coil are shown. Table 2 shows the results of the evaluation by simulation. The winding portion of the coil embedded in the element had an inner diameter of 5.0 mm and an outer diameter of 9.0 mm.

  In the inductor 100 according to the first embodiment, as shown in FIG. 2, rectangular conductor layers covering the upper surface and two side surfaces of the element body are provided continuously with a thickness of 50 μm. In the inductor 110 according to the second embodiment, as shown in FIG. 5, one wide annular conductor layer is provided with a thickness of 50 μm so as to coincide with the winding part. In the inductor 120 according to the third embodiment, as shown in FIG. 6, a disc-shaped conductor layer is provided with a thickness of 50 μm, which matches the outer diameter of the winding portion. As for the inductor 130 of the fourth embodiment, as shown in FIG. 7, the two annular conductor layers each have the outer diameter of the outer conductor layer equal to the outer diameter of the winding portion, and the inner diameter of the inner conductor layer. Corresponds to the inner diameter of the winding portion, and has a conductor width of 0.25 mm and a thickness of 50 μm.

  In Table 2, an inductor having no conductor layer is used as a comparative example, a rate of change (%) of the inductance value L based on the inductance value L of the comparative example (100%), and a maximum magnetic flux of the inductor of the comparative example. It is shown as a relative value (%) of the maximum magnetic flux density Bmax based on the density (100%). Note that the simulation was performed using Femtet at a coil current of 1 MHz / 5A.

  From Table 2, it can be seen that the effect of reducing the leakage magnetic flux is improved in the order of the inductors of Examples 4, 2, 3, and 1, and the absolute value of the rate of change of L is increased. In addition, when the conductor layer is disposed on the surface of the inductor element, it is difficult to achieve both the effect of reducing the leakage flux and the suppression of the eddy current loss. In other words, the conductor layer pattern may be selected from various conductor layer patterns according to the characteristics of the leakage magnetic flux and the power loss required for the inductor. Further, even if the shape of the conductor layer is the same, the electric resistivity of the second metal layer is adjusted by adjusting the thickness of the second metal layer, and the balance between the effect of reducing the leakage flux and the suppression of the eddy current loss is adjusted. Can also be adjusted.

In the above-described embodiment, a coil having a circular winding portion in which a conductor is edgewise wound as a coil is used, but the shape of the winding portion is elliptical, rectangular, track-shaped, elliptical, and the like. Shapes may be used. The winding method is not limited to edgewise winding, but may be another winding method such as α winding, or a coil may be formed by laminating conductor patterns.
In FIGS. 5 and 6, the outer shape of the conductor layer is circular, but may be elliptical, rectangular, track-shaped, oval, or the like in accordance with the shape of the winding portion of the coil.
In FIGS. 7, 10, and 11, two ring-shaped conductor layers are used as the conductor layers, but the number of ring-shaped conductor layers may be more than two.
An insulating layer may be further provided on the conductor layer. The insulating layer has the effect of preventing oxidation of the conductor layer and the effect of preventing short-circuit with the terminal of the coil conductor.
In the above-described embodiment, the conductor layer is provided on the upper surface of the body. However, the conductor layer may be further provided on the bottom surface on the mounting surface side of the body. Generally, in an inductor mounted on a substrate, a leakage magnetic flux is cut off because a conductor pattern exists around or on the back surface of the inductor on the substrate. However, when the conductor pattern is small, the leakage magnetic flux radiated from the bottom surface of the inductor can be reduced by providing the conductor layer also on the bottom surface of the element body.

DESCRIPTION OF SYMBOLS 100 Inductor 10 Element body 20 Coil 21 Winding part 22 Leader part 30 External terminal 32 Ground terminal 40 Conductive layer

Claims (10)

A body including metal magnetic powder and resin, a winding part and a pair of lead parts drawn out at both ends of the winding part, each of the coil embedded in the body and the lead part A pair of external terminals that are electrically connected, and a conductor layer disposed on a surface of the element body that intersects with a winding axis of the coil,
The conductor layer includes a first metal layer formed by fusing metal magnetic powders near the surface of the element body to each other, and a second metal layer plated on the first metal layer,
An inductor having an electric resistivity of the second metal layer lower than an electric resistivity of the first metal layer.   The inductor according to claim 1, wherein the first metal layer is formed inside the element body.   3. The inductor according to claim 1, wherein the conductor layer is disposed so as to cover at least a part of the winding portion when viewed from a winding axis direction of the coil. 4.   4. The inductor according to claim 1, wherein the conductor layer is disposed inside an outer peripheral portion of the winding portion when viewed from a winding axis direction of the coil. 5.   The inductor according to any one of claims 1 to 4, wherein the conductor layer includes an annular conductor disposed between an outer peripheral portion and an inner peripheral portion of the winding portion when viewed from a winding axis direction of the coil. .   The inductor according to claim 5, wherein the conductor layer includes a plurality of annular conductor layers that do not cross each other.   The inductor according to claim 6, wherein the plurality of annular conductor layers are electrically connected to each other.   The inductor according to any one of claims 1 to 7, further comprising a ground terminal connected to a ground of a board to be mounted, wherein the conductor layer is electrically connected to the ground terminal.   The inductor according to claim 1, further comprising an insulating layer covering the conductor layer. A coil composed of a wound portion and a pair of drawn portions drawn out at both ends of the wound portion, burying in a composite material containing metal magnetic powder and resin to form a body,
Providing a first metal layer on the surface of the body intersecting the winding axis of the coil, wherein the metal magnetic powder is melted near the surface of the body and fused to each other;
Forming a second metal layer on the first metal layer;
A method for manufacturing an inductor, comprising:

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