Inductor and method for manufacturing inductor

Abstract

The occurrence of solder explosion when a plating layer is formed on a surface of an element body is prevented or reduced.　This inductor has: an element body which is formed of a metal magnetic powder and a resin and in which a coil formed by winding a conductive wire is embedded; a small particle layer which is formed of particles having an average particle diameter smaller than the average particle diameter of metal magnetic particles contained in the metal magnetic powder on an outer peripheral surface of the element body; and a lead-out part which is led out from the small particle layer with respect to the coil.

Description

Inductor and Method for Manufacturing Inductor

[0001] The present disclosure relates to an inductor and a method for manufacturing an inductor.

[0002] Conventionally, inductors are widely used in various electrical devices such as smartphones, for example, as chip inductors that can be surface-mounted. Patent Document 1 discloses a technique for an inductor in which a drawing end portion of a coil is exposed on the surface of a molded body (hereinafter referred to as a base body) in which the coil is sealed with a sealing material containing metal magnetic powder and resin, and a plating layer using a metal material such as Ni or Sn is formed on the surface of the base body to connect the coil to an external terminal.

[0003] Japanese Patent Application Laid-Open No. 2016-58418

[0004] Depressions depending on the particle diameter of the particles contained in the metal magnetic powder occur on the surface of the base body. Therefore, when a plating layer serving as an external electrode is formed on the surface of the base body with the drawing end portion of the coil exposed, the depressions generated on the surface of the base body cannot be completely covered by the plating, and solder explosion occurs when mounting on a customer's substrate.

[0005] An object of the present invention is to provide an inductor capable of suppressing the occurrence of solder explosion when forming a plating layer on the surface of a base body.

[0006] This specification includes all the contents of Japanese Patent Application No. 2024-184407, filed on October 18, 2024. An inductor according to one aspect of the present disclosure includes a base body formed of metal magnetic powder and resin and having a coil in which a conducting wire is wound embedded therein, a small particle layer formed of particles having an average particle diameter smaller than the average particle diameter of the metal magnetic particles contained in the metal magnetic powder on the outer peripheral surface of the base body, and a drawing portion drawn from the small particle layer rather than the coil.

[0007] According to the inductor according to the present invention, the occurrence of solder explosion when forming a plating layer on the surface of the base body can be suppressed.

[0008] Figure 1 is a perspective view of the inductor according to the first embodiment, viewed from the top. Figure 2 is a perspective view of the inductor according to the first embodiment, viewed from the bottom. Figure 3 is a perspective view showing the internal configuration of the inductor according to the first embodiment. Figure 4 is a cross-sectional view taken along line IV-IV of Figure 3. Figure 5 is a schematic diagram of the manufacturing process of the inductor according to the first embodiment. Figure 6 is a schematic cross-sectional view of the inductor according to the second embodiment. Figure 7 is a schematic cross-sectional view of the inductor according to the third embodiment.

[0009] Embodiments of the present invention will be described below with reference to the drawings. Note that some drawings may be schematic. Also, dimensions and proportions in schematic drawings may differ from actual values.

[0010] (First Embodiment) [Overall Inductor Configuration] Figure 1 is a perspective view of the inductor according to the first embodiment, viewed from the top. Figure 2 is a perspective view of the inductor according to the first embodiment, viewed from the bottom. As shown in Figures 1 and 2, the inductor according to the first embodiment is configured as a surface-mount type electronic component and comprises a substantially rectangular parallelepiped body 2, which is one aspect of a substantially hexahedral shape, and a pair of external electrodes 4 provided on the outer circumferential surface of the body 2.

[0011] Hereinafter, in the base body 2, the first main surface (also called the mounting surface) that faces the mounting substrate (not shown) during mounting is defined as the bottom surface 10. In the base body 2, the second main surface opposite the bottom surface 10 is defined as the top surface 12. In the base body 2, a pair of third main surfaces perpendicular to the bottom surface 10 are defined as end surfaces 14, and a pair of fourth main surfaces perpendicular to these bottom surfaces 10 and the pair of end surfaces 14 are defined as side surfaces 16. Note that the end surfaces 14 are also side surfaces of the base body 2, similar to the side surfaces 16, but are distinguished from the side surfaces 16 by being referred to as end surfaces because they are provided with terminals such as external electrodes 4.

[0012] As shown in Figure 1, the distance from the bottom surface 10 to the top surface 12 is defined as the thickness T of the base body 2. The distance between the pair of side surfaces 16 is defined as the width W of the base body 2. The distance between the pair of end surfaces 14 is defined as the length L of the base body 2. Furthermore, the direction of the thickness T is defined as the thickness direction DT, the direction of the width W is defined as the width direction DW, and the direction of the length L is defined as the length direction DL.

[0013] The nominal dimensions of the finished inductor 1 are, for example, a length L of 1.4 mm, a width W of 1.2 mm, and a thickness T of 0.8 mm.

[0014] Hereinafter, the surface along the length direction DL and the thickness direction DT (the surface perpendicular to the width direction DW) will be referred to as the LT surface, the surface along the thickness direction DT and the width direction DW (the surface perpendicular to the length direction DL) will be referred to as the TW surface, and the surface along the length direction DL and the width direction DW (the surface perpendicular to the thickness direction DT) will be referred to as the LW surface. Furthermore, the cross-sections of the inductor 1 along the LT surface, TW surface, and LW surface will be referred to as the LT cross-section, TW cross-section, and LW cross-section, respectively.

[0015] The base body 2 is formed of metallic magnetic powder (hereinafter referred to as magnetic powder) and resin, and a coil with a wire wound around it is embedded inside. A layer of small particles 6 is formed on the outer surface (bottom surface 10) of the base body 2, containing particles with an average particle size smaller than the average particle size of the metallic magnetic particles (hereinafter referred to as magnetic particles) contained in the magnetic powder inside the base body 2. An external electrode 4 is formed on top of the layer of small particles 6. Leads (extensions) from the coil extend from the layer of small particles 6, and the external electrode 4 formed on top of the layer of small particles 6 is connected to the leads from the coil (details will be described later).

[0016] Figure 3 is a perspective view showing the internal structure of the inductor 1 according to the first embodiment. As shown in Figure 3, the base body 2 comprises a coil conductor 20 and a substantially hexahedral core 30 in which the coil conductor 20 is embedded, and is configured as a molded inductor with the coil conductor 20 sealed in the core 30.

[0017] The core 30 is a molded body obtained by compressing a mixed powder, which is a mixture of magnetic powder with a predetermined average particle size and resin, into a roughly hexahedral shape by pressurizing and heating it while enclosing the coil conductor 20. In this specification, "average particle size" means the median diameter based on volume. The average particle size can be measured using a particle size analyzer before mixing the magnetic powder. Alternatively, when measuring the average particle size in the state of the core 30, it can be measured by analyzing electron microscope images of the cross-section of the magnetic particles obtained by polishing the core 30. For example, the equivalent circle diameter of the cross-section of each magnetic particle can be determined from the electron microscope image, and assuming that each magnetic particle is a sphere having the above equivalent circle diameter, the volume of each sphere can be determined, and the average particle size can be calculated from the median of the volume value distribution.

[0018] Furthermore, the magnetic particles in this embodiment are made of a soft magnetic material. The magnetic powder is a mixture of a first magnetic powder containing first magnetic particles, which have a relatively large average particle size, and a second magnetic powder containing second magnetic particles, which have a relatively small average particle size. The second magnetic powder has an average particle size smaller than that of the first magnetic powder. As a result, during compression molding, the second magnetic particles, which are small particles, are filled in between the first magnetic particles, along with the resin, thereby increasing the filling density of the magnetic particles in the core 30 and also increasing the magnetic permeability.

[0019] In this embodiment, the average particle size of the metal particles of the first magnetic particles is, for example, 50 μm or less. The average particle size of the metal particles of the second magnetic particles is, for example, 10 μm or less. The magnetic particles may also contain particles with different average particle sizes from the first and second magnetic particles (the average particle size of which is larger than that of the second magnetic particles), thereby containing three or more different particle sizes.

[0020] Both the first and second magnetic particles are particles having a metal particle, an oxide film covering the surface of the metal particle, and an insulating film covering the surface of the oxide film. The covering of the metal particle with the oxide film and insulating film increases its insulation resistance and dielectric strength.

[0021] For example, in the first magnetic particle, Fe-Si-B amorphous alloy powder is used as the metal particle. The oxide film of the first magnetic particle consists of two layers: an SiO layer and Fe2SiO4, with a total oxide film thickness of 20 nm to 155 nm. In addition, the insulating film of the first magnetic particle is formed of phosphate glass with a thickness of 10 nm to 100 nm.

[0022] Furthermore, for example, in the second magnetic particle, carbonyl iron powder is used as the metal particle. The oxide film of the second magnetic particle is iron oxide formed by surface oxidation of the carbonyl iron powder, which is the metal particle. In addition, the insulating film of the second magnetic particle is a sol-gel reaction product with silica as a component. This increases the slipperiness of the surface of the second magnetic particle, making it easier for the second magnetic particle to penetrate between the first magnetic particles during the molding and hardening process of the base body 2, which will be described later. As a result, the density of the magnetic material in the core 30 can be further increased, and the relative permeability of the core 30 can be further increased.

[0023] Furthermore, in the first magnetic particle, the metal particles may be Fe-Si-Cr alloy powder, Fe-Ni-Al alloy powder, Fe-Cr-Al alloy powder, Fe-Si-Al alloy powder, Fe-Ni alloy powder, or Fe-Ni-Mo alloy powder. In addition, in the first magnetic particle, the insulating film may be phosphoric acid, zinc phosphate, manganese phosphate, glass, or resin.

[0024] Furthermore, for example, the resin material contained in the mixed powder includes bisphenol A type epoxy resin and rubber-modified epoxy resin. This makes it possible to manufacture an inductor 1 in which both the strength and toughness of the base body 2 are improved.

[0025] Furthermore, for example, the magnetic powder contained in the mixed powder is such that, based on the total weight of the magnetic particles contained in the mixed powder, the first magnetic particles make up 70 wt% to 85 wt%, and the second magnetic particles make up 15 wt% to 30 wt%. The resin contained in the mixed powder is such that, based on the total weight of the magnetic powder and resin, it makes up 2.0 wt% to 3.5 wt%. Preferably, the first magnetic particles are 70 wt% to 80 wt%, and the second magnetic particles are 20 wt% to 30 wt%. The resin is preferably 2.7 wt% to 30 wt%.

[0026] As shown in Figure 3, the coil conductor 20 comprises a winding section 22 wound in a spiral shape along the winding shaft K in two stages, upper and lower, such that the conductors are located on the outer circumference and connected to each other on the inner circumference; a pair of lead-out sections 23 drawn out from the winding section 22; and a pair of external electrode connection sections 24 connected to each of the lead-out sections 23, which are conductor portions for connecting to the external electrodes 4. The winding section 22 includes two overlapping winding regions 22a and 22b along the winding shaft K. The conductors of the winding regions 22a and 22b are connected to each other in a portion of their inner circumference.

[0027] The winding portion 22 has a substantially rectangular shape when viewed from the direction of the winding shaft K. The coil conductor 20 is embedded in the base body 2 such that the winding shaft K is aligned with the thickness direction DT of the base body 2, and that, when viewed from the direction of the winding shaft K, each side of the winding portion 22, which has a substantially rectangular shape in plan view, aligns with each side of the base body 2, which has a substantially rectangular shape in plan view (for example, parallel to it).

[0028] The conductor constituting the coil conductor 20 consists of a conductor and a coating layer formed on the surface of the conductor. The conductor is a flat wire with a rectangular cross-section, and the conductor is a strip-shaped conductor with a rectangular cross-section made of copper. The thickness of the conductor is, for example, 60 μm to 100 μm, and the width is 160 μm to 200 μm. The coating layer consists of an insulating layer formed on the surface of the strip-shaped conductor and a fusion layer formed on the surface of the insulating layer for bonding the overlapping strip-shaped conductors in the winding portion 22. The insulating layer is, for example, made of polyimide amide resin and has a thickness of 3 μm. The fusion layer is, for example, made of polyamide resin and has a thickness of 1 μm to 25 μm.

[0029] Figure 4 is a cross-sectional view taken along line IV-IV of Figure 3. Figure 4 shows the LT cross-section of the inductor 1. As shown in Figure 4, the small particle layer 6 is formed to cover the bottom surface 10 of the base body 2, and to expose the external electrode connection portion 24 at the end of the lead portion 23 drawn out from the winding portion 22.

[0030] The small particle layer 6 is formed from magnetic powder and resin, similar to the base body 2. The average particle size of the magnetic particles contained in the magnetic powder within the small particle layer 6 is smaller than the average particle size of the magnetic particles contained in the magnetic powder within the base body 2. More specifically, the average particle size of the magnetic powder within the small particle layer 6 is smaller than the average particle size of the magnetic particles contained in the second magnetic powder of the base body 2. For example, the average particle size of the magnetic powder within the small particle layer 6 is 5 μm or less. The thickness of the small particle layer 6 is greater than or equal to the average particle size of the magnetic powder within the small particle layer 6, for example, about 10 μm.

[0031] The magnetic particles contained in the magnetic powder of the small particle layer 6 are, like the magnetic powder that forms the base body 2, particles having metal particles, an oxide film covering the surface of the metal particles, and an insulating film covering the surface of the oxide film. For example, the magnetic particles contained in the magnetic powder of the small particle layer 6 are particles with the same configuration as the second magnetic particles, except for the average particle size described above. The resin material contained in the small particle layer 6 may also be the same as the resin that forms the base body 2.

[0032] In the inductor 1 according to the first embodiment, an external electrode 4 is formed on a small particle layer 6 as a base, and the external electrode 4 is connected to the external electrode connection portion 24 at the end of the lead portion 23. Specifically, a pair of external electrodes 4 are formed to connect the external electrode connection portion 24 of the lead portion 23 drawn out from one side of the coil conductor 20, and the external electrode connection portion 24 of the lead portion 23 drawn out from the other side. The pair of external electrodes 4 formed on the bottom surface 10 (mounting surface) in this way are electrically connected to the wiring of the circuit board by appropriate mounting means such as soldering.

[0033] Furthermore, it is desirable that the small particle layer 6 be formed so as to extend between the pair of external electrodes 4 described above, for example, over the entire surface of the bottom surface 10 (mounting surface). By forming the small particle layer 6 so as to extend between the pair of external electrodes 4 in this way, the average particle diameter is smaller than that of the base material 2, and the number of particle interfaces of particles having an insulating film can be increased. As a result, the insulation resistance between the pair of external electrodes 4 can be increased, and the withstand voltage of the inductor 1 can be increased.

[0034] Furthermore, a protective layer (not shown) is formed on the surface of the substrate 2 excluding the area of ​​the external electrode 4 (for example, the top surface 12, the end surface 14, and the side surface 16). The protective layer is, for example, a resin obtained by adding phenoxy resin to a novolac resin, and contains nanosilica as a filler. The protective layer is formed on the surface of the substrate 2 with a thickness of, for example, 10 μm to 30 μm. The thickness of the protective layer is preferably 10 μm to 20 μm, and more preferably 15 μm or less.

[0035] Inductor 1 with this configuration can improve DC superposition characteristics by using soft magnetic material for the magnetic particles, and is therefore used as an electronic component in electrical circuits where large currents flow, as a choke coil in DC-DC converter circuits and power supply circuits, and as an electronic component in electronic devices such as personal computers, DVD players, digital cameras, TVs, mobile phones, smartphones, car electronics, and medical and industrial machinery. However, the applications of inductor 1 are not limited to these, and it can also be used in filter circuits and rectifier / smoothing circuits, for example.

[0036] [Overview of Inductor Manufacturing Process] Figure 5 is a schematic diagram of the manufacturing process of the inductor 1 according to the first embodiment. As shown in Figure 5, the manufacturing process of the inductor 1 includes a coil conductor formation process (S1), a pre-molded body formation process (S2), a base body molding and hardening process (S3), a base body grinding process (S4), and an external electrode formation process (S5).

[0037] The coil conductor formation step (S1) is a step in which a coil conductor 20 is formed from a wire. In this step, the coil conductor 20 is formed in a shape having the aforementioned winding portion 22, lead portion 23, and external electrode connection portion 24 by winding the wire using a winding method called "alpha winding". Alpha winding refers to a state in which the wire, which functions as a conductor, is wound in a spiral shape, for example in two stages, such that the lead portions 23 at the beginning and end of the winding are located on the outer circumference. The number of turns of the coil conductor 20 is not particularly limited.

[0038] The pre-molded body formation step (S2) is a step in which a pre-molded body called a tablet is formed. The pre-molded body is formed into an easy-to-handle solid by pressurizing the mixed powder, which is the material for the base body 2. In this embodiment, two types of tablets are formed: a first tablet with an appropriate shape (e.g., E-shaped, T-shaped, etc.) that has a structure that can hold the coil conductor 20, and a second tablet with an appropriate shape (e.g., I-shaped, plate-shaped, etc.) that covers the coil attached to the first tablet.

[0039] In the base body molding and hardening process (S3), when manufacturing the inductor shown in Figure 4, a T-shaped first tablet is used. The winding portion of the coil conductor 20 is inserted into the columnar portion of the first tablet, and the lead portion 23 of the coil conductor 20 is bent to the back surface of the plate-shaped portion of the first tablet to attach the coil conductor 20. This second tablet is then set in a molding die. At this point, when forming the first tablet, a layer of small particles 6 may be formed on the bottom surface of the plate-shaped portion of the first tablet, or a mixture of magnetic powder and resin powder for forming the layer of small particles 6 may be filled into the bottom surface 10 portion of the molding die. Next, while applying heat, pressure is applied in the overlapping direction of the first tablet and the second tablet to harden them, thereby integrating the first tablet, the coil conductor 20, and the second tablet. This forms a base body 2 with the coil conductor 20 enclosed in the core 30. In addition, a layer of small particles 6 is formed on the bottom surface 10 of the base body 2.

[0040] The method for forming the small particle layer 6 on the bottom surface 10 of the base body 2 is not limited to the method described above. For example, the method for forming the small particle layer 6 may be to place a sheet material, which is made by forming the mixed powder constituting the small particle layer 6 into a sheet, on the bottom surface 10 and heat-press it.

[0041] In the base body grinding process (S4), abrasive grains are applied to the side surface of the molded body obtained in the base body molding and hardening process to grind it down until the width W is a predetermined width. This process yields a base body 2 with the width W of the molded body downsized to a predetermined width. This downsizing reduces the distance between the coil conductor 20 inside the base body 2 and the side surface of the base body 2 (also called the side gap), thereby increasing the coil's occupancy rate in the radial direction of the winding portion 22 of the coil conductor 20. Furthermore, since the base body 2 is obtained by grinding the molded body obtained by compression molding to a predetermined size, dimensional variations in the base body 2 can be reduced compared to the case where the base body 2 is controlled to a predetermined size by compression molding alone. In the base body grinding process, polishing (e.g., barrel polishing) may be performed to chamfer the corners created by grinding the side surface of the base body 2. Note that if downsizing or the like is not required for the base body 2, the base body grinding process (S4) may be omitted. In the example shown in Figure 4, the bottom surface 10 (mounting surface) of the base body 2 is ground by the base body grinding process (S4), and the end faces of the wires constituting the external electrode connection portion 24 of the coil conductor 20 are exposed from the surface of the small particle layer 6.

[0042] The external electrode formation step (S5) is a step of forming the external electrode 4 on the base body 2, and includes a base body protective layer formation step (S5a), a surface treatment step (S5b), and a plating layer formation step (S5c).

[0043] The base material protective layer formation step (S5a) is a step of coating the entire surface of the base material 2 with an insulating resin.

[0044] The surface treatment step (S5b) is a step of modifying the surface of the electrode planned location on the surface where the small particle layer 6 is formed in the core 30 by irradiating laser light. Here, the electrode planned location refers to the range on the surface of the core 30 where the external electrode 4 is to be formed, including the portion where the external electrode connection portion 24 is exposed. Specifically, by irradiating laser light, in the range of the electrode planned location, the element protection layer on the surface of the element 2 and the coating layer of the external electrode connection portion 24 of the coil conductor 20 are removed, the resin on the surface of the core 30 is removed, and the insulating film on the surface of the magnetic particles exposed from the core 30 is removed. As a result, in the portion of the surface of the core 30 that is the electrode planned location, the exposed area of the metal of the magnetic particles per unit area of the surface of the core 30 becomes larger than other surface portions of the core 30. Note that after the irradiation of the laser light, a cleaning process (for example, an etching process) for cleaning the surface of the electrode planned location may be performed.

[0045] In the plating layer forming step (S5c), by plating the surface where the small particle layer 6 is formed in the core 30, a plating layer (external electrode 4) is formed at the electrode planned location irradiated with laser light. Specifically, in the plating layer forming step (S5c), a Ni plating underlayer and a Sn plating layer on its surface are formed at the electrode planned location by barrel plating. Note that the Ni plating underlayer may be not only Ni but also Cu, Ag, Au, Pd, etc.

[0046] The small particle layer 6 serving as the base for the external electrode 4 is formed of magnetic powder having an average particle diameter smaller than the average particle diameter of the magnetic powder constituting the element 2. More specifically, the small particle layer 6 is formed of magnetic powder having an average particle diameter smaller than the average particle diameter of the magnetic particles included in the second magnetic powder constituting the element 2. For this reason, the surface of the small particle layer 6 has a smaller magnitude of unevenness generated depending on the particle diameter than the surface of the element 2. Therefore, by forming the external electrode 4 with the small particle layer 6 as the base as in the present embodiment, the recesses generated on the surface can be completely covered with plating, and the occurrence of solder explosion can be suppressed.

[0047] For example, when the average particle diameter of the magnetic powder contained in the small particle layer 6 is set to 5 μm or less, the depressions formed on the surface can be generally suppressed to 5 μm or less. Since the Ni plating base layer only grows isotropically, it cannot cover depressions exceeding twice the plating thickness. Also, the thickness of the Ni plating base layer is generally about 2.5 μm. Therefore, by setting the average particle diameter of the magnetic powder contained in the small particle layer 6 to 5 μm or less, the depressions formed on the surface by the Ni plating base layer can be filled completely, and the occurrence of solder explosion can be suppressed.

[0048] In addition, the surface of the small particle layer 6 has a better plating spreadability because the inter-particle distance is smaller compared to the surface of the base body 2. Therefore, the plating time can be shortened compared to the case of directly plating on the surface of the base body 2.

[0049] (Second Embodiment) FIG. 6 is a schematic cross-sectional view of an inductor according to the second embodiment. As shown in FIG. 6, in the inductor 1a according to the second embodiment, not only the bottom surface 10 (mounting surface) of the base body 2 but also a small particle layer 6a is formed on the end surface 14 (side surface) side.

[0050] For example, in the example of FIG. 6, the base body molding and curing process (S3) is as follows. First, a small particle layer 6a is formed on the bottom surface and side surface of the E-shaped first tablet, and the coil conductor 20 is disposed in the recess of the E-shaped first tablet. Next, the second tablet is placed on the E-shaped first tablet, and they are disposed in the molding die so that the lead-out portion 23a of the coil conductor 20 is sandwiched between the first tablet and the side surface of the die. Then, while applying heat, pressure is applied in the overlapping direction of the first tablet and the second tablet to cure them, whereby the base body 2 containing the coil conductor 20 in the core 30 is molded. Also, a small particle layer 6a is formed on the bottom surface 10 and the end surface 14 (side surface) of the base body 2.

[0051] Furthermore, in the inductor 1a according to the second embodiment, the lead portion 23a of the coil conductor 20 is led out from the small particle layer 6a formed on the end face 14, and the side surface of the conductor constituting the external electrode connection portion 24a is exposed on the end face 14 side to the surface of the small particle layer 6a. In this way, in the inductor 1a, since the lead portion 23a is led out to the end face 14 side which is in the winding direction of the winding portion 22, no excessive force (such as twisting in a direction perpendicular to the winding direction) is applied to lead out the lead portion 23.

[0052] Furthermore, in the inductor 1a according to the second embodiment, the external electrode 4a is formed in an L-shape in cross-section, for example, to connect the external electrode connection portion 24a on the end face 14 side and the substrate on the bottom face 10 side. That is, the external electrode 4a is formed on the small particle layer 6a. Therefore, solder cracking can be suppressed in the inductor 1a as well.

[0053] (Third Embodiment) Figure 7 is a schematic cross-sectional view of an inductor according to the third embodiment. As shown in Figure 7, in the inductor 1b according to the third embodiment, the small particle layer 6b is formed to cover the entire surface of the base body 2 (bottom surface 10, end surface 14, side surface 16 and top surface 12).

[0054] For example, in the example shown in Figure 7, the base body molding and hardening process (S3) is as follows. First, a first E-shaped tablet with a small particle layer 6b formed on its bottom and side surfaces is used, and a second tablet with a small particle layer 6b formed on one main surface is used, and the coil conductor 20 is placed in the recess of the first E-shaped tablet. Next, the second tablet is placed on the first E-shaped tablet, and these are placed in the molding die so that the lead portion 23a of the coil conductor 20 is sandwiched between the first tablet and the side surface of the die. Then, while applying heat, pressure is applied in the overlapping direction of the first and second tablets to harden them, thereby molding a base body 2 with the coil conductor 20 enclosed in the core 30. In addition, a small particle layer 6b is formed on the entire surface of the base body 2 (bottom surface 10, end surface 14, side surface 16 and top surface 12).

[0055] Furthermore, in the inductor 1b according to the third embodiment, similar to the inductor 1a according to the second embodiment, the lead portion 23a is led out from the small particle layer 6b formed on the end face 14, and the external electrode connection portion 24a is exposed on the end face 14 side. In the inductor 1b, the external electrode 4a is formed, for example, in an L-shape in cross-section to connect the external electrode connection portion 24a on the end face 14 side and the substrate on the bottom face 10 side.

[0056] In this way, by forming a small particle layer 6b that covers the entire surface of the base body 2, the inductor 1b has a smaller average particle diameter than the base body 2, and the number of particle interfaces of particles having an insulating film can be increased. Therefore, the insulating resistance of the surface of the inductor 1b can be improved.

[0057] All embodiments and modifications described above illustrate one aspect of the present invention and can be arbitrarily modified and applied without departing from the spirit of the invention. Furthermore, any elements of the embodiments described above can be combined to form new embodiments.

[0058] Furthermore, unless otherwise specified, the directions such as horizontal, orthogonal, and vertical, as well as various numerical values, shapes, and materials in the embodiments described above, include a range that produces the same effects as those directions, numerical values, shapes, and materials (the so-called equivalence range).

[0059] 1, 1a, 1b...Inductor 2...Element 4, 4a...External electrode 6, 6a, 6b...Small particle layer 10...Bottom surface 12...Top surface 14...End surface 16...Side surface 20...Coil conductor 22...Winding section 22a, 22b...Winding region 23, 23a...Outlet section 24, 24a...External electrode connection section 30...Core DL...Length direction DT...Thickness direction DW...Width direction K...Winding shaft L...Length T...Thickness W...Width

Claims

1. An inductor comprising: a base body formed of metal magnetic powder and resin, with a coil wound around a conductor embedded inside; a layer of small particles formed on the outer surface of the base body, with particles having an average particle size smaller than the average particle size of the metal magnetic particles contained in the metal magnetic powder; and a lead portion drawn out from the coil and the layer of small particles.

2. The inductor according to claim 1, wherein the metal magnetic powder comprises a first metal magnetic powder and a second metal magnetic powder having a particle size smaller than the average particle size of the first metal magnetic powder, and the small particle layer is formed of particles having an average particle size smaller than the average particle size of the metal magnetic particles contained in the second metal magnetic powder.

3. The inductor according to claim 1 or 2, wherein the fine particle layer is formed on the outer circumferential surface on a mounting surface facing the mounting substrate and on a side surface perpendicular to the mounting surface, and the lead portion is led out from the fine particle layer formed on the side surface.

4. The inductor according to claim 1 or 2, wherein the fine particle layer is formed on the outer surface facing the mounting substrate, and the lead portion is led out from the fine particle layer formed on the mounting surface.

5. The inductor according to claim 1 or 2, wherein the fine particle layer is formed over the entire outer surface.

6. The inductor according to any one of claims 1 to 5, wherein the small particle layer is formed by a sheet attached to the outer circumferential surface.

7. An inductor according to any one of claims 1 to 6, wherein an external electrode connected to the extraction portion is formed on the small particle layer.

8. The inductor according to claim 7, wherein the fine particle layer extends between a first external electrode connected to a first lead portion drawn out from one side of the coil and a second external electrode connected to a second lead portion drawn out from the other side of the coil.

9. A method for manufacturing an inductor, comprising the steps of: exposing the lead portion drawn out from the coil on the outer surface of a base body formed of metal magnetic powder and resin, in which a coil with a wire wound inside is embedded, and forming a layer of small particles with an average particle size smaller than the average particle size of the metal magnetic particles contained in the metal magnetic powder; and forming an external electrode on the layer of small particles that connects to the lead portion.

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