inductor

Abstract

In the present invention, by using metal magnetic particles having a circularity of 0.7 or more in an inductor, initial permeability can be improved and DC superposition characteristics can be improved.　This inductor comprises: a coil conductor including a winding part around which a conductive wire is wound and a pair of lead-out parts led out from the winding part; an element body that contains metal magnetic particles and a resin and includes the coil conductor; and an external electrode formed on the surface of the element body and connected to the lead-out part of the coil conductor. The metal magnetic particles have a circularity of 0.7 or more. The metal magnetic particles having no more than a 20° adjacent angle, which is formed by a line between adjacent metal magnetic particles and a line in the thickness direction of the element body, are present at an accumulation frequency of 20% or more in a portion of the element body surrounded by the winding part of the coil conductor.

Description

inductor

[0001] The present invention relates to an inductor.

[0002] Patent Document 1 describes a coil component that is less likely to short circuit and a method for manufacturing the same. The coil component according to Patent Document 1 has a core portion containing soft magnetic metal particles and a coil portion formed by winding a conductor in a coil shape, with the coil portion disposed inside the core portion. In Patent Document 1, the core portion has a center portion surrounded by the inner diameter of the coil portion, and the coil component is configured such that, where θ is the deflection angle of the soft magnetic metal particles with respect to the winding axis direction of the coil portion, the average value of cos2θ of the soft magnetic metal particles contained in the center portion is 0.1 or more and the average value of the aspect ratio of the soft magnetic metal particles contained in the center portion is 1.1 or more.

[0003] Japanese Patent Application Laid-Open No. 2023-164012

[0004] In an inductor having the above configuration, the deflection angle θ of the soft magnetic metal particles contained in the core and the aspect ratio of the soft magnetic metal particles are set, and the inductance of the coil component is improved by the shape magnetic anisotropy of the metal particles, assuming that the metal particles have a flat shape. However, when trying to improve inductance based on shape magnetic anisotropy, there is a problem in that the DC bias characteristics deteriorate significantly as the inductance improves.

[0005] One aspect of the present invention is an inductor comprising: a coil conductor having a winding portion around which a conductive wire is wound and a pair of lead portions drawn out from the winding portion; an element body containing metal magnetic particles and resin and enclosing the coil conductor; and an external electrode formed on the surface of the element body and connected to the lead portions of the coil conductor, wherein the metal magnetic particles have a circularity of 0.7 or more, and in a portion of the element body surrounded by the winding portion of the coil conductor, the metal magnetic particles have an adjacent angle formed by a line between adjacent metal magnetic particles and a line in the thickness direction of the element body of 20° or less at a cumulative frequency of 20% or more. Note that this specification is intended to include the entire content of Japanese Patent Application No. 2024-122432, filed on July 29, 2024.

[0006] According to the present invention, while using metal magnetic particles with a circularity of 0.7 or more, it is possible to improve the initial permeability of an inductor and also improve the DC bias characteristics.

[0007] FIG. 1 is a perspective view of the inductor according to this embodiment, viewed from the top. FIG. 2 is a perspective view of the inductor according to this embodiment, viewed from the bottom. FIG. 3 is a see-through perspective view showing the internal configuration of the inductor. FIG. 4 is a plan view showing the internal configuration of the inductor. FIG. 5 is a cross-sectional view taken along line V-V in FIG. 4. FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 4. FIG. 7 is a schematic diagram of the manufacturing process of the inductor. FIG. 8 is a cross-sectional view of the inductor according to this embodiment. FIG. 9 is an enlarged view of a main portion of FIG. 8, showing a cross-section of the central core of a magnetic core. FIG. 10 is an explanatory diagram of the predetermined adjacent angle conditions of large particles in the central core of a magnetic core. FIG. 11 is a diagram showing the distribution of large particles in the central core for three inductor models. FIG. 12 is a histogram showing the adjacent angles of large particles in the central core for three inductor models. FIG. 13 is a graph showing the relationship between the magnetic field and magnetic permeability when the applied magnetic field is increased for three inductor models. Fig. 14 is a graph showing the relationship between the initial permeability and the cumulative frequency of large particles that satisfy the specified adjacent angle condition for each inductor of Materials No. 1 to 14 shown in Table 1. Fig. 15 is a graph showing the relationship between the permeability and the cumulative frequency of large particles that satisfy the specified adjacent angle condition when a magnetic field of 50 [kA / m] is applied for each inductor of Materials No. 1 to 14 shown in Table 1. Fig. 16 is a graph showing the relationship between the circularity and the cumulative frequency of large particles that satisfy the specified adjacent angle condition for each inductor of Materials No. 1 to 14 shown in Table 1.

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] [Overall Configuration of Inductor] Fig. 1 is a perspective view of the inductor 1 according to this embodiment, viewed from the top surface 12 side. Fig. 2 is a perspective view of the inductor 1 according to this embodiment, viewed from the bottom surface 10 side. The inductor 1 of this embodiment is configured as a surface-mounted electronic component. The inductor 1 of this embodiment includes an element body 2 having a substantially rectangular parallelepiped shape, which is one form of a substantially hexahedral shape, a pair of external electrodes 4 provided on the surface of the element body 2, and an element body protective layer 6 that covers the outer surface of the element body 2 excluding the area of ​​the external electrodes 4 of the element body 2. Note that the element body protective layer 6 may be omitted.

[0010] Hereinafter, in the base body 2, the first main surface that faces the mounting substrate (not shown) during mounting is defined as the bottom surface 10, the second main surface opposite the bottom surface 10 is called the top surface 12, a pair of third main surfaces that are perpendicular to the bottom surface 10 are called end surfaces 14, and a pair of fourth main surfaces that are perpendicular to the bottom surface 10 and the pair of end surfaces 14 are called side surfaces 16.

[0011] 1 , the distance from the bottom surface 10 to the top surface 12 is defined as the thickness T of the element body 2, the distance between a pair of side surfaces 16 is defined as the width W of the element body 2, and the distance between a pair of end surfaces 14 is defined as the length L of the element body 2. 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. The nominal size of the inductor 1 as a finished product is, for example, a length L dimension of 2.0 mm, a width W dimension of 1.2 mm, and a thickness T dimension of 0.7 mm.

[0012] Hereinafter, a plane along the length direction DL and the thickness direction DT (a plane perpendicular to the width direction DW) will be referred to as an LT plane, a plane along the thickness direction DT and the width direction DW (a plane perpendicular to the length direction DL) will be referred to as a TW plane, and a plane along the length direction DL and the width direction DW (a plane perpendicular to the DT direction) will be referred to as an LW plane. Also, cross sections of the inductor 1 along the LT plane, TW plane, and LW plane will be referred to as an LT cross section, TW cross section, and LW cross section, respectively.

[0013] FIG. 3 is a perspective view showing the internal configuration of inductor 1. FIG. 4 is a plan view showing the internal configuration of inductor 1. The element body 2 includes a coil conductor 20 and a substantially hexahedral magnetic core 30 in which the coil conductor 20 is embedded. The element body 2 is configured as a molded inductor in which the coil conductor 20 is enclosed in the magnetic core 30. In this embodiment, the element body 2 has a length L dimension of 1.95 mm, a width W dimension of 1.15 mm, and a thickness T dimension of 0.65 mm. In other words, the element body 2 is smaller than the inductor 1. Furthermore, when viewed from above the element body 2 (see FIG. 4 ), the narrowest distance between the coil conductor 20 wound in a substantially rectangular shape (i.e., the winding portion 22) and the end face 14 or side face 16 of the element body 2 is referred to as the side gap of the element body 2.

[0014] Fig. 5 is a cross-sectional view taken along line V-V in Fig. 4. In other words, Fig. 5 shows the T-W cross section of the inductor 1. The magnetic core 30 is a molded body obtained by compression-molding a powder mixture of magnetic particles and resin into a substantially hexahedral shape by applying pressure and heat while the powder mixture contains the coil conductor 20. Here, the proportion of the resin is 2.0 wt% or more and 3.5 wt% or less based on the total weight of the magnetic particles and resin.

[0015] The magnetic particles of this embodiment are formed of a soft magnetic material. The magnetic particles are 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. By covering the metal particles with the oxide film and the insulating film, the insulation resistance and withstand voltage are increased. The magnetic particles may have one type of particle size, or may have two or more types of particle sizes. In the magnetic particles of this embodiment, carbonyl iron powder is used as the metal particles. The oxide film of the magnetic particles is iron oxide formed by surface oxidizing the carbonyl iron powder, which is a metal particle. Furthermore, the insulating film of the magnetic particles is formed from phosphate glass.

[0016] In the magnetic particles, the metal particles may be FeCo alloy instead of carbonyl iron powder. Furthermore, the metal particles may be Fe alloy with an Fe content of 93 wt % or more instead of carbonyl iron powder or FeCo alloy. Specifically, the metal particles may be Fe—Si alloy powder, 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. Furthermore, the insulating film may be formed of phosphoric acid, zinc phosphate, manganese phosphate, glass, or resin instead of phosphate glass.

[0017] The resin contained in the mixed powder includes an epoxy resin.

[0018] The resin material contained in the mixed powder may be a thermosetting resin other than epoxy resin, such as phenol resin, polyester resin, polyimide resin, polyolefin resin, etc. Note that phenoxy resin of bisphenol A, F, S type can be mentioned as a resin that may be considered as a substitute for bisphenol A type epoxy resin.

[0019] The coil conductor 20 is wound with a conducting wire 42 and is drawn out to the surface of the element body 2. The coil conductor 20 in this embodiment is alpha wound. Alpha winding refers to a state in which the coil conductor 20 is wound in two spiral stages so that the lead-out portions 23 at the start and end of the winding are located on the outer periphery. Note that the coil conductor 20 may be edgewise wound instead of alpha wound. In this case, the lead-out portion 23 of the coil conductor 20 is drawn out from the winding portion 22 to the end face 14 of the element body 2.

[0020] 3 and 4 , the coil conductor 20 of this embodiment, which is an alpha winding, includes a winding portion 22 in which a conductor wire 42 is wound spirally around a winding axis K in two upper and lower stages so that both ends of the conductor wire 42 are located on the outer periphery and connected to each other on the inner periphery, a pair of lead-out portions 23 led out from the winding portion 22, and a pair of external electrode connecting portions 24 which are conductor wire portions connected to the lead-out portions 23, respectively, for connection to the external electrodes 4. The winding portion 22 includes two winding regions 22a and 22b (see FIG. 3 ) that overlap along the winding axis K. The conductor wires of the winding region 22a and the winding region 22b are connected to each other at a portion of their inner peripheries.

[0021] The winding portion 22 is, for example, substantially rectangular in plan view (see FIG. 4 ) when viewed from the direction of the winding axis K. The coil conductor 20 is embedded in the element body 2 so that the winding axis K is along the thickness direction DT of the element body 2 and so that, in plan view when viewed from the direction of the winding axis K, each side of the substantially rectangular winding portion 22 is along (e.g., parallel to) each side of the substantially rectangular element body 2. The dimensions of the winding portion 22 are, for example, a thickness T dimension (height dimension) of 0.4 mm, an outer diameter in the width direction DW of 1.17 mm, and an inner diameter of 0.55 mm.

[0022] The lead portion 23 is drawn out from the winding portion 22. The lead portion 23 is electrically connected to the external electrode 4 via external electrode connecting portions 24 that are drawn out to and exposed on each of the pair of end faces 14.

[0023] Figure 6 is a cross-sectional view corresponding to line VI-VI in Figure 4. Figure 6 shows a cross section perpendicular to the extension direction of the external electrode connection portion 24 at the connection portion between the lead portion 23 and the external electrode 4. The conductor 42 constituting the coil conductor 20 is composed of a conductor 43 and a coating layer 45 formed on the surface of the conductor 43. The conductor 42 is a flat wire with a rectangular cross section. Using a flat wire makes it easy to wind the conductor 42 without gaps. The conductor 43 is a strip-shaped conductor with a rectangular cross section. Copper is preferred as the material for the conductor 43; however, instead of the copper conductor 43, a copper-clad aluminum conductor 42 or an aluminum conductor 42 with an insulating coating formed on its surface may be used.

[0024] The covering layer 45 is composed of an insulating layer formed on the surface of the conductor 43 and a bonding layer formed on the surface of the insulating layer. The insulating layer ensures insulation of the conductor 42. The insulating layer is made of, for example, polyimide amide resin. The thickness of the insulating layer is, for example, 4 μm. Although polyimide amide resin is preferable for the insulating layer, polyurethane resin, polyester resin, or epoxy resin may also be used instead of polyimide amide resin.

[0025] The fusion layer secures the conductive wires 42 together. That is, the fusion layer bonds the overlapping conductive wires 42 together in the winding portion 22. The fusion layer is made of, for example, a polyamide resin. The thickness of the fusion layer is preferably 1 μm or more and 25 μm or less, more preferably 2 μm or more and 25 μm or less, and even more preferably 2 μm or more and 4 μm or less.

[0026] The pair of external electrodes 4 are so-called L-shaped electrodes (see FIG. 3 ), which are composed of L-shaped members extending from each of the end faces 14 of the element body 2 to the bottom face 10. Each of the external electrodes 4 is connected to an external electrode connecting portion 24 of the coil conductor 20 at the end face 14, and a portion 4A (see FIG. 2 ) extending to the bottom face 10 is electrically connected to wiring on a circuit board by an appropriate mounting means such as solder.

[0027] A pair of external electrodes 4 provided on the surface of the element body 2 are connected to conductors 43 exposed by removing the coating layer of the external electrode connecting portions 24. The width W of the external electrodes 4 at the bottom surface 10 of the element body 2 is 0.88 mm to 1.12 mm, and the length L is 0.3 mm to 0.7 mm. The dimension of the external electrodes 4 in the thickness direction DT at the end surfaces 14 of the element body 2 is approximately 0.43 mm to 0.60 mm.

[0028] The thickness of the external electrode 4 was measured as follows. Diagonal lines were connected to the four corners of the top surface 12 of the inductor 1, and the points where the diagonal lines intersected were defined as intersections. A cross section of the element body 2 was cut parallel to the side surface 16 so as to intersect with the intersections, i.e., an LT cross section intersecting the intersections. The film thicknesses of the external electrode 4 formed on the bottom surface 10 of the element body 2 at points dividing the length direction DL into four equal parts were measured using a microscope at 1000x magnification. The average of the measured film thicknesses at the four equal parts was calculated as the measured value. These measurements were then taken for 10 different inductors 1, and the average of the measurements was defined as the thickness of the external electrode 4. A model VHX-7000 microscope manufactured by Keyence Corporation was used as the microscope.

[0029] As shown in Fig. 6, the external electrode 4 has a plated conductor 50. The plated conductor 50 of this embodiment has a copper plating layer 51 as a plating layer of the same metal component as the conductor 43. The copper plating layer 51 is a plating layer that plates the surface of the conductor 43. The copper plating layer 51 and the conductor 43 are connected to each other.

[0030] A Ni plating layer 52 is formed on the copper plating layer 51. A Sn plating layer 53 is formed on the Ni plating layer 52. The plated conductor 50 of this embodiment has the copper plating layer 51, the Ni plating layer 52, and the Sn plating layer 53. However, the Sn plating layer 53 may be omitted from the plated conductor 50. Furthermore, the Ni plating layer 52 may also be omitted from the plated conductor 50.

[0031] The copper plating layer 51 may be formed in a partial region of the lead portion 23 of the coil conductor 20, spanning the lead portion 23 of the coil conductor 20 and the element body 2. Instead of the copper plating layer 51, a copper layer may be formed by sputtering, conductive resin, or a metal plate. Furthermore, aluminum, silver, palladium, etc. may be used instead of copper.

[0032] Although the external electrode 4 has been described as having an L-shaped electrode configuration, instead of an L-shaped electrode, a five-sided electrode may be formed using resin electrodes on the end face 14 of the element body 2 and the four faces surrounding the end face 14, i.e., the end face 14, bottom face 10, top face 12, and pair of side faces 16, and the four faces of the top face 12, end face 14, and pair of side faces 16 may be coated with an insulator to form a bottom electrode. Furthermore, a portion of the lead-out portion 23 of the coil conductor 20 may be covered with resin electrodes, and a copper plating layer may be provided on top of that. The external electrode 4 may be a five-sided electrode or a bottom electrode.

[0033] As shown in Figure 5, an element body protective layer 6 is formed on the surface of the element body 2. The element body protective layer 6 covers the outer surface of the element body excluding the area of ​​the external electrodes 4. The element body protective layer 6 contains a resin and a filler. The thickness of the element body protective layer 6 is 10 µm or more and 30 µm or less, preferably 10 µm or more and 20 µm or less, and more preferably 15 µm. If the thickness of the element body protective layer 6 is 10 µm or more, even if the metal magnetic powder protruding from the element body 2 is exposed from the element body protective layer 6, plating can be prevented from being formed on the surface of this exposed metal magnetic powder. Furthermore, if the thickness of the element body protective layer 6 is 30 µm or less, the element body 2 can be prevented from becoming larger than a predetermined size.

[0034] The resin of the element protective layer 6 contains an epoxy resin as a main component. The resin of the element protective layer 6 contains a novolac resin to enhance heat resistance. Furthermore, phenoxy resin is added to the resin of the element protective layer 6 to provide toughness, so that the phenoxy resin ratio is 20% or more. Furthermore, adding carbon black as a pigment to the resin of the element protective layer 6 improves processability when forming the external electrode formation region. Furthermore, the resin of the element protective layer 6 does not need to contain a pigment. A solvent is added to the resin of the element protective layer 6 to adjust drying properties.

[0035] The inductor 1 having such a configuration can improve the DC bias characteristics by using a soft magnetic material for the magnetic particles, and is therefore used as an electronic component in electric circuits through which large currents flow, 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, medical and industrial machinery, etc. However, the uses of the inductor 1 are not limited to this, and it can also be used, for example, in tuning circuits, filter circuits, rectifying and smoothing circuits, etc.

[0036] 7 is a schematic diagram of the manufacturing process of the inductor 1. As shown in the figure, the manufacturing process of the inductor 1 includes a coil conductor forming process, a preform forming process, an element molding and hardening process, an element grinding process, and an external electrode forming process.

[0037] The coil conductor forming process is a process of forming the coil conductor 20 from a rectangular copper wire as a conductor. In this embodiment, in this process, the coil conductor 20 is formed into a shape having the above-mentioned winding portion 22, lead-out portion 23, and external electrode connection portion 24 by winding the conductor using a winding method called "alpha winding." Alpha winding refers to a state in which the conductor, which functions as a conductor, is wound in two stages in a spiral shape so that the lead-out portions 23 at the beginning and end of the winding are located on the outer periphery. The number of turns of the coil conductor 20 is not particularly limited, but is determined so as to achieve the desired inductance.

[0038] The preform formation step is a step of forming a preform called a tablet. The preform is formed by pressing the mixed powder, which is the material of the element body 2, into a solid form that is easy to handle. In this embodiment, two types of tablets are formed: a first tablet (i.e., first core portion 30a of the product (see FIG. 5 )) of an appropriate shape (e.g., E-shaped) having a groove into which the coil conductor 20 fits, and a second tablet (i.e., second core portion 30b of the product (see FIG. 5 )) of an appropriate shape (e.g., I-shaped or plate-shaped) that covers the groove of the first tablet.

[0039] In the element molding and hardening process, the first tablet, the coil conductor 20, and the second tablet are set in a molding die, and while applying heat, pressure is applied in the overlapping direction of the first tablet and the second tablet, and they are hardened to integrate the first tablet, the coil conductor 20, and the second tablet. This forms the element 2 in which the coil conductor 20 is enclosed in the magnetic core 30.

[0040] In the element grinding step, abrasive grains are applied to the side surfaces of the molded body obtained in the element molding and hardening step to grind away (i.e., grind) the side surfaces until the width W reaches a predetermined width.

[0041] This process results in an element body 2 in which the width W of the molded body is downsized to a predetermined width. This downsizing reduces the distance (also called the side gap) between the coil conductor 20 in the element body 2 and the side surface of the element body 2, thereby increasing the radial occupancy of the coil of the winding portion 22 of the coil conductor 20.

[0042] Furthermore, since the element body 2 is obtained by grinding the compact obtained by compression molding to a predetermined size, it is possible to reduce dimensional variation in the element body 2 compared to when the element body 2 is controlled to a predetermined size by compression molding alone. In the element body grinding step, polishing (for example, barrel polishing) may be performed to chamfer corners created by grinding the side surfaces of the element body 2.

[0043] The external electrode forming step is a step of forming the external electrodes 4 on the element body 2, and includes an element body protective layer forming step, a surface treatment step, and a plating layer forming step.

[0044] The element body protective layer forming step is a step of coating the entire surface of the element body 2 with an insulating resin. The element body protective layer 6 is formed by spraying a protective material onto the element body 2 using a rotary spray device. The element body protective layer 6 may also be formed by a method such as spraying or dipping.

[0045] The surface treatment process is a process of modifying the surface of the planned electrode area on the surface of the magnetic core 30 by irradiating the area with laser light. Here, the planned electrode area refers to the area on the surface of the magnetic 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 the area with laser light, the element body protective layer 6 on the surface of the element body 2 and the coating layer of the external electrode connection portion 24 of the coil conductor 20 are removed within the planned electrode area, the resin on the surface of the magnetic core 30 is removed, and the insulating film on the surface of the magnetic particles exposed from the magnetic core 30 is removed. As a result, the exposed metal area of ​​the magnetic particles per unit area of ​​the surface of the magnetic core 30 is larger in the planned electrode area than in other surface areas of the magnetic core 30. Furthermore, adjacent magnetic particles of the metal magnetic powder of the element body 2 in the laser-irradiated portion come into contact with each other. Note that after the laser irradiation, a cleaning process (e.g., etching) may be performed to clean the surface of the planned electrode area.

[0046] In the plating layer forming step, a copper plating layer is formed at the electrode locations irradiated with the laser light by barrel plating copper on the surface of the magnetic core 30. In addition, in this embodiment, the plating layer is formed by further providing a Ni plating layer and a Sn plating layer on the copper plating layer.

[0047] The inductor 1 of this embodiment will be further described in detail below.

[0048] 8 is a cross-sectional view of the inductor 1 according to this embodiment. The element body 2 of the inductor 1 includes a coil conductor 20 and a magnetic core 30 in which the coil conductor 20 is embedded.

[0049] The magnetic core 30 has a first core portion 30a on the bottom surface 10 side and a second core portion 30b on the top surface 12 side. As shown in FIGS. 5 and 8 , the first core portion 30a has a plate-shaped portion 30a1 that forms one end portion in the winding axis direction. In other words, the first core portion 30a has the plate-shaped portion 30a1 that forms the bottom surface 10. A core portion 30a2 that protrudes toward the top surface 12 is provided in the center of the plate-shaped portion 30a1. Furthermore, an outer peripheral portion 30a3 that protrudes toward the top surface 12 is provided on the outer periphery of the plate-shaped portion 30a1. The outer peripheral portion 30a3 forms the end surface 14 and the side surface 16. A coil conductor 20 is arranged between the core portion 30a2 and the outer peripheral portion 30a3 of the first core portion 30a.

[0050] The second core portion 30b is formed in a plate shape located at the other end in the winding axis direction. In other words, the second core portion 30b is formed in a plate shape that constitutes the upper surface 12. The second core portion 30b is arranged so as to cover the first core portion 30a and the coil conductor 20.

[0051] Here, the central core portion 30a2 of the magnetic core 30 is a portion of the magnetic core 30 located on the inner circumferential side of the coil conductor 20. The central core portion 30a2 is in contact with the inner circumferential surface of the coil conductor 20, specifically, with the conducting wire 42 on the inner circumferential side of the winding portion 22 of the coil conductor 20, at its outer circumferential portion.

[0052] FIG. 9 is an enlarged view of a main portion of FIG. 8 , showing a cross section of the central core portion 30a2 of the magnetic core 30. As shown in FIG. 9 , the magnetic core 30 is composed of a resin 31 and metal magnetic particles 32. The metal magnetic particles 32 have a circularity of 0.7 or more. More specifically, the metal magnetic particles 32 are spherical with a circularity of 0.7 or more. Here, an SEM image is taken of a cross section of the element body 2 cut from the top surface 12 to the bottom surface 10 in the width direction DW passing through the winding axis K of the coil conductor 20, i.e., a WT cross section passing through the winding axis K of the coil conductor 20. The region of the SEM image surrounded by the winding portion 22 of the coil conductor 20 is analyzed using predetermined image analysis software (e.g., image analysis software WinROOF2021 (manufactured by Mitani Corporation)), which makes it possible to determine whether the circularity and other characteristics satisfy predetermined conditions.

[0053] The circularity of metal magnetic particle 32 is determined as follows. That is, when the projected area of ​​metal magnetic particle 32 is S and the circumferential length of metal magnetic particle 32 is L, the circularity of metal magnetic particle 32 is 4×π×S divided by L×L. The circularity in this embodiment is the average value of multiple locations within the area surrounded by winding portion 22 of coil conductor 20. Various circularities can be achieved by changing the manufacturing method (atomization method) used to create the metal magnetic particles.

[0054] The metal magnetic particles 32 of this embodiment include large particles 32a as first metal magnetic particles and small particles 32b as second metal magnetic particles having an average particle size smaller than that of the first metal magnetic particles. The large particles 32a have an average particle size 3.3 or more times larger than that of the small particles 32b. Insulating films 32a1 and 32b1 are formed on the surfaces of the large particles 32a and the small particles 32b, respectively. In this embodiment, the large particles 32a are an FeCo alloy. Instead of an Fe alloy, the large particles 32a may be an Fe-based alloy with an Fe content of 93 wt% or more.

[0055] In the central core portion 30a2 of the magnetic core 30, the large particles 32a that satisfy the "predetermined adjacent angle condition" are distributed so as to account for 20% or more of the contained large particles 32a.

[0056] FIG. 10 is an explanatory diagram of the predetermined adjacent angle conditions for the large particles 32a in the central core portion 30a2 of the magnetic core 30. The top row of FIG. 10 shows the distribution of the large particles 32a in the cross section of the central core portion 30a2 of the inductor 1. In other words, the top row of FIG. 10 illustrates only the large particles 32a in the cross section of the central core portion 30a2 of the inductor 1. The photographed range of the cross section may be the entire central core portion 30a2 or a predetermined range of the central core portion 30a2. However, if the photographed range of the cross section is not the entire central core portion 30a2, it is desirable that the photographed range of the cross section include 13 or more large particles 32a.

[0057] The predetermined adjacent angle condition will be described with reference to Fig. 10. The predetermined adjacent angle condition is a condition that the adjacent angle θ of the large particles 32a is between 0° and 20°. Here, the adjacent angle θ is defined as follows:

[0058] That is, the center of gravity 32g is identified for each large particle 32a contained in the central core portion 30a2. Then, the circle-equivalent diameters of one large particle 32a and any other large particles 32a surrounding the one large particle 32a are calculated. This circle-equivalent diameter is defined as the diameter of a circle having the same area as the projected area of ​​the large particle 32a. Then, the average value of these, i.e., the average circle-equivalent diameter, is calculated. For the two large particles 32a whose average circle-equivalent diameters have been calculated, it is determined whether the distance between their centers of gravity 32g is 1.1 times or less the calculated average circle-equivalent diameter.

[0059] If the distance between their centers of gravity 32g is 1.1 times the average equivalent circular diameter or less, the large particles 32a are determined to be adjacent to each other, and a straight line λ is set between their centers of gravity 32g. If the distance between their centers of gravity 32g is not 1.1 times the average equivalent circular diameter or less, that is, if the distance between their centers of gravity 32g is greater than 1.1 times the average equivalent circular diameter, the large particles 32a are determined not to be adjacent to each other, and no straight line λ is set.

[0060] By determining whether large particles 32a are adjacent to each other based on whether the diameter is 1.1 times the average equivalent circle diameter, it is possible to include large particles 32a that are not in contact with each other but are close enough to affect the magnetic permeability μ as adjacent particles.

[0061] As shown in the bottom row of Figure 10, the angle between the set straight line λ and a line extending in the thickness direction DT from one of the centers of gravity 32g is defined as the adjacent angle θ. In this embodiment, in the WT cross section of the inductor 1 (see Figure 8), a perpendicular line H2 is set to a straight line H1 connecting both ends of the top surface 12 of the element body 2. This perpendicular line H2 corresponds to a line extending in the thickness direction DT, and the angle formed by the perpendicular line H2 and the straight line λ is defined as the adjacent angle θ. Note that the adjacent angle θ is set to the smaller of the two angles. Therefore, the adjacent angle θ is defined to be greater than or equal to 0° and less than or equal to 90°.

[0062] 10 shows a state in which a line λ is set as a result of determining whether or not all large particles 32a included in a predetermined photographing range are adjacent to each other and determining that they are adjacent. In this embodiment, the predetermined adjacent angle condition is a condition as to whether or not the adjacent angle θ of the large particles 32a is 20° or less. In other words, the predetermined adjacent angle condition is satisfied when the adjacent angle θ of the large particles 32a is 20° or less.

[0063] In this embodiment, the magnetic core 30 is formed so that, within the imaging range of a predetermined cross section, large particles 32a having an adjacent angle θ of 20° or less account for 20% or more of all the large particles 32a. That is, in this embodiment, the magnetic core 30 is formed so that, in the central core portion 30a2 of the magnetic core 30, large particles 32a that satisfy the predetermined adjacent angle condition account for 20% or more of the large particles 32a included therein.

[0064] The cumulative frequency of large particles 32a that satisfy the predetermined adjacent angle condition is calculated based on the number of lines λ. Therefore, when multiple large particles 32a are present around one large particle 32a and multiple lines λ are set, the cumulative frequency is calculated based on the total number of the multiple lines λ and the lines λ that satisfy the predetermined contact angle condition.

[0065] The adjacent angle θ and the adjacent frequency can be set or changed when manufacturing the inductor 1. Specifically, the adjacent frequency can be controlled by the stirring method used when mixing the metal magnetic particles 32 that make up the element body 2 with the resin. Furthermore, the adjacent angle θ can be controlled by tapping after filling the mold.

[0066] In the inductor 1 of this embodiment, the magnetic core 30 in the central core portion 30a2 is formed so that the large particles 32a that satisfy the predetermined adjacent angle condition account for 20% or more of the included large particles 32a. Therefore, in the central core portion 30a2, the large particles 32a are easily brought into contact with the direction of the magnetic field H generated by the coil conductor 20. Therefore, in this embodiment, the initial permeability μ' is easily increased, and the inductor 1 has improved direct superposition characteristics.

[0067] FIG. 11 shows the distribution of large particles 32a in the central core portion 30a2 for three models MOD1, MOD2, and MOD3 of the inductor 1. FIG. 12 shows histograms of the adjacent angle θ of the large particles 32a in the central core portion 30a2 for the three models MOD1, MOD2, and MOD3 of the inductor 1. In FIG. 12, the horizontal axis represents the frequency at 5° intervals of the adjacent angle θ, and the vertical axis represents the number of adjacent locations of the large particles 32a corresponding to the frequency (in other words, the number of lines λ). Also, FIG. 12 shows the cumulative frequency from 0° as a broken line, and the right vertical axis represents the percentage of the cumulative total, i.e., the cumulative frequency CF. From FIG. 12, it can be determined that for all models MOD1, MOD2, and MOD3, the cumulative frequency CF tends to increase at a substantially constant rate as the adjacent angle θ increases.

[0068] FIG. 13 is a graph showing the relationship between the magnetic field Hdc and the magnetic permeability μ when the applied magnetic field Hdc is increased for the three models MOD1, MOD2, and MOD3 of inductor 1. In FIG. 13, the horizontal axis represents the magnetic field Hdc, and the vertical axis represents the magnetic permeability μ. As shown in FIG. 13, for all models MOD1 to MOD3, the magnetic permeability μ was observed to be 6 [H / m] or more for a magnetic field Hdc of approximately 0 [kA / m]. Furthermore, for all models MOD1 to MOD3, a decrease in the magnetic permeability μ was observed as the magnetic field Hdc increased. Furthermore, for all models MOD1 to MOD3, the magnetic permeability μ was observed to be 4 [H / m] for a magnetic field Hdc of 100 [kA / m]. Therefore, it was found that in models MOD1 to MOD3, the permeability μ when the magnetic field Hdc is approximately 0 [kA / m], i.e., the initial permeability μ', is improved, and the DC superposition characteristics, which are the resistance to a decrease in permeability μ when a large magnetic field Hdc is applied, are improved.

[0069] As shown in Figure 13, improvements in initial permeability μ' and DC bias characteristics were observed in all of models MOD1 to MOD3. The results for model MOD2 were particularly desirable. Here, as shown in Figure 12, model MOD2 differs from models MOD1 and MOD3 in that a frequency peak is observed in the range of adjacent angle θ between 0° and 20°. From this, it is inferred that the frequency of metal magnetic particles 32 with adjacent angles θ of 20° or less influences the results in Figure 13. Furthermore, in the other models MOD1 and MOD3, the cumulative frequency of metal magnetic particles 32 with adjacent angles θ of 20° or less is 20% or more. Note that Figure 13 includes a boundary line T1 indicating whether the adjacent angle θ is 20° or less.

[0070] Here, the fact that the cumulative frequency CF of metal magnetic particles 32 with an adjacent angle θ of 20° or less is 20% or more indicates that a high proportion of large-diameter metal magnetic particles 32, i.e., large particles 32a, are in contact in the direction of application of the magnetic field H, and an improvement in the initial permeability μ', etc., can be predicted from a theoretical standpoint.

[0071] Therefore, in this embodiment, the magnetic core 30 is formed so that the central core portion 30a2 contains 20% or more of the large particles 32a having an adjacent angle θ of 20° or less.

[0072] Next, Table 1 shows the relationship between the measurement results of the example of this embodiment and the comparative example.

[0073]

[0074] In the measurements shown in Table 1, the central core portion 30a2 was observed with a scanning electron microscope (SEM) in a WT cross section obtained by cutting the inductor 1 at the center in the longitudinal direction DL so as to pass through the winding axis K of the winding portion 22 of the coil conductor 20. The SEM observation image was loaded into a specified imaging software and analyzed. Then, the line λ and the adjacent angle θ were determined based on the center of gravity 32g of the large particles 32a, and the cumulative frequency CF of the large particles 32a with an adjacent angle θ of 20° or less was calculated. An example of the specified imaging software is WinROOF2021 manufactured by Mitani Corporation.

[0075] For each of the inductors 1 of documents No. 1 to 14 for which the cumulative frequency CF was determined, the initial permeability μ′, the permeability μ when a magnetic field H of 50 [kA / m] was applied, and the circularity were measured.

[0076] Fig. 14 is a graph showing the relationship between the initial permeability μ' and the cumulative frequency CF of large particles 32a that satisfy the predetermined adjacent angle condition for each inductor 1 of documents No. 1 to 14 shown in Table 1. In Fig. 14, the horizontal axis represents the cumulative frequency CF, and the vertical axis represents the initial permeability μ'.

[0077] Fig. 15 is a graph showing the relationship between the magnetic permeability μ and the cumulative frequency CF of large particles 32a that satisfy the predetermined adjacent angle condition when a magnetic field H of 50 [kA / m] is applied for each of the inductors 1 of documents 1 to 14 shown in Table 1. In Fig. 15, the horizontal axis represents the cumulative frequency CF, and the vertical axis represents the magnetic permeability μ.

[0078] Figure 16 is a graph showing the relationship between circularity and the cumulative frequency of large particles satisfying the specified adjacent angle condition for each inductor of Materials No. 1 to 14 listed in Table 1. In Figure 16, the horizontal axis represents cumulative frequency CF, and the vertical axis represents circularity. In Figures 14 to 16, data from examples with circularity of 0.7 or greater are shown with black circles, while data from comparative examples with circularity of less than 0.7 are shown with white circles. In Figures 14 to 16, a boundary line T2 is conveniently illustrated at a position where the cumulative frequency CF is 20%. Boundary line T2 marks the boundary between the examples and the comparative examples. In Figure 16, a boundary line T3 is conveniently illustrated at a position where the circularity is 0.7. Boundary line T3 marks the boundary between the examples and the comparative examples.

[0079] As shown in Table 1 and Fig. 14, in the examples of this embodiment in which the circularity was 0.7 or more and the cumulative frequency CF of large particles 32a with an adjacent angle θ of 0° or more and 20° or less was 20% or more, the initial permeability μ' was observed to be 7.5 [H / m] or more. Furthermore, as shown in Table 1 and Fig. 15, when a magnetic field H of 50 [kA / m] was applied, the magnetic permeability μ was observed to be 5.5 [H / m] or more in the examples of this embodiment.

[0080] In contrast, as shown in Table 1 and Figures 14 and 15, the cumulative frequency CF of large particles 32a with an adjacent angle θ of 0° or more and 20° or less was less than 20%, and in comparative examples that did not satisfy the requirements of this embodiment, the initial permeability μ' was less than 7.0 [H / m], and when a magnetic field H of 50 [kA / m] was applied, the magnetic permeability μ was less than 5.5 [H / m]. Furthermore, as shown in Table 1 and Figures 14 and 15, in comparative examples with a circularity of less than 0.7 that did not satisfy the requirements of this embodiment, the initial permeability μ' was 7.0 [H / m] or less, and when a magnetic field H of 50 [kA / m] was applied, the magnetic permeability μ was less than 5.5 [H / m]. Therefore, even if the adjacent angle θ and cumulative frequency CF were equivalent to those in the examples, it was confirmed that a small circularity caused magnetic flux concentration within large particles 32a, resulting in poor DC bias characteristics. Therefore, it is recognized that the examples have better initial permeability μ' and permeability μ than the comparative examples.

[0081] As described above, the inductor 1 includes a coil conductor 20 having a winding portion 22 around which a conductive wire 42 is wound and a pair of lead-out portions 23 led out from the winding portion 22, an element body 2 containing metal magnetic particles 32 and a resin 31 and enclosing the coil conductor 20, and an external electrode 4 formed on the surface of the element body 2 and connected to the lead-out portion 23 of the coil conductor 20, wherein the metal magnetic particles 32 have a circularity of 0.7 or more, and in a central core portion 30a2 as a portion of the element body 2 surrounded by the winding portion 22 of the coil conductor 20, 20% or more of the metal magnetic particles 32 have an adjacent angle θ formed by a straight line λ between adjacent metal magnetic particles 32 and a line H2 in the thickness direction DT of the element body 2 of 20° or less, as determined by a cumulative frequency CF. Therefore, for the inductor 1, by using metal magnetic particles 32 having a circularity of 0.7 or more, it is possible to improve the initial permeability μ' and also improve the DC superposition characteristics.

[0082] In this embodiment, insulating films 32a1 and 32b1 are formed on the surfaces of metal magnetic particles 32. Therefore, insulating films 32a1 and 32b1 make it easy to ensure physical space around metal magnetic particles 32, which can improve DC bias characteristics, reduce eddy current loss, and improve voltage resistance.

[0083] In this embodiment, the metal magnetic particles 32 include large particles 32 a and small particles 32 b having an average particle size smaller than that of the large particles 32 a. Therefore, the small particles 32 b can easily fill the gaps between the large particles 32 a, improving the filling rate of the metal magnetic particles 32 in the magnetic core 30 and improving the magnetic permeability μ.

[0084] In this embodiment, the large particles 32 a are made of an FeCo alloy or an Fe-based alloy with an Fe content of 93 wt % or more, which improves the DC bias characteristics compared to when the large particles 32 a are not made of an FeCo alloy or an Fe-based alloy with an Fe content of 93 wt % or more.

[0085] [Other Embodiments] In the above-described embodiment, the metal magnetic particles 32 contained in the central core portion 30a2 are configured from large particles 32a and small particles 32b. However, the small particles 32b may be omitted, and the metal magnetic particles 32 contained in the central core portion 30a2 may be configured from only large particles 32a. That is, the metal magnetic particles 32 contained in the central core portion 30a2 may be configured from metal magnetic particles 32 of a single type with an average particle size. In this case, the adjacent angle θ and circularity are set to the values ​​in this embodiment for metal magnetic particles 32 having an average particle size (D50, which is the circle-equivalent diameter determined from cross-sectional observation) or larger of the metal magnetic particles 32.

[0086] All of the above-described embodiments and modifications are merely examples of one aspect of the present invention, and can be modified and applied as desired without departing from the spirit of the present invention. Furthermore, unless otherwise specified, the horizontal, vertical, and other directions, various numerical values, shapes, and materials in the above-described embodiments include a range that provides the same action and effect as those directions, numerical values, shapes, and materials (so-called equivalent ranges).

[0087] [Configurations Supported by the Above-described Embodiments] The above-described embodiments support the following configurations.

[0088] (Configuration 1) An inductor comprising: a coil conductor having a winding portion around which a conductive wire is wound and a pair of lead-out portions drawn out from the winding portion; an element body containing metal magnetic particles and resin and enclosing the coil conductor; and external electrodes formed on the surface of the element body and connected to the lead-out portions of the coil conductor, wherein the metal magnetic particles have a circularity of 0.7 or more, and in a portion of the element body surrounded by the winding portion of the coil conductor, the metal magnetic particles have an adjacent angle formed by a line between adjacent metal magnetic particles and a line in the thickness direction of the element body of 20° or less at a cumulative frequency of 20% or more. According to the inductor of Configuration 1, while using metal magnetic particles with a circularity of 0.7 or more, it is possible to improve the initial permeability of the inductor and to improve the DC superposition characteristics.

[0089] (Configuration 2) The inductor according to Configuration 1, wherein an insulating film is formed on the surface of the metal magnetic particles. According to the inductor of Configuration 2, the insulating film makes it easy to ensure physical space around the metal magnetic particles, thereby improving DC bias characteristics, reducing eddy current loss, and improving voltage resistance.

[0090] (Configuration 3) The inductor according to Configuration 1, wherein the metal magnetic particles include first metal magnetic particles and second metal magnetic particles having an average particle size smaller than that of the first metal magnetic particles. With the inductor of Configuration 3, the gaps between the first metal magnetic particles are easily filled with the second metal magnetic particles, thereby improving the filling rate of the metal magnetic particles in the magnetic core and improving the magnetic permeability.

[0091] (Configuration 4) The inductor according to Configuration 3, wherein the first metal magnetic particles are an FeCo alloy or an Fe-based alloy with an Fe content of 93 wt % or more. The inductor of Configuration 4 can achieve improved DC bias characteristics compared to when the first metal magnetic particles are not an FeCo alloy or an Fe-based alloy with an Fe content of 93 wt % or more.

[0092] 1...inductor, 2...element body, 4...external electrode, 4A...extending portion, 6...element body protective layer, 10...bottom surface, 12...upper surface, 14...end surface, 16...side surface, 20...coil conductor, 22...winding portion, 22a...winding region, 22b...winding region, 23...drawing portion, 24...external electrode connecting portion, 30...magnetic core, 30a...first core portion, 30a1...plate-shaped portion, 30a2...center portion, 30a3...periphery, 30b...second core portion, 31...resin, 32...metal magnetic particles, 32a...large particles (first metal magnetic particles), 32a1...insulating film, 32b...small particles (second metal magnetic particles), 32b1...insulating film, 32g...center of gravity, 42...conductor, 43...conductor, 45...coating layer, 50...plated conductor, 51...copper plating layer, 52...Ni plating layer, CF...cumulative frequency, H...magnetic field, H1...straight line, Hdc...magnetic field, K...winding axis, L...length, MOD1...model, MOD2...model, MOD3...model, T1...boundary line, T2...boundary line, θ...adjacent angle, λ...straight line, μ...magnetic permeability, μ'...initial permeability.

Claims

1. An inductor comprising: a coil conductor having a winding portion around which a conducting wire is wound and a pair of lead-out portions drawn out from the winding portion; an element body containing metal magnetic particles and resin and enclosing the coil conductor; and an external electrode formed on the surface of the element body and connected to the lead-out portions of the coil conductor, wherein the metal magnetic particles have a circularity of 0.7 or more, and in the part of the element body surrounded by the winding portion of the coil conductor, the metal magnetic particles have an adjacent angle of 20° or less formed between a line between adjacent metal magnetic particles and a line in the thickness direction of the element body, and the cumulative frequency of these metal magnetic particles is 20% or more.

2. The inductor according to claim 1, wherein an insulating film is formed on the surface of the metal magnetic particles.

3. The inductor according to claim 1, wherein the metal magnetic particles include first metal magnetic particles and second metal magnetic particles having an average particle size smaller than that of the first metal magnetic particles.

4. The inductor according to claim 3, wherein the first metal magnetic particles are an FeCo alloy or an Fe-based alloy with an Fe content of 93 wt % or more.

Images