Inductor

Abstract

The purpose of the present invention is to easily suppress the existence of a gap between a coil conductor and a center portion, and to easily improve the inductance of the inductor.　The inductor comprises a magnetic core that is composed of a resin and metal magnetic particles, and a coil conductor that is embedded in the magnetic core. The magnetic core includes a center part that is positioned on the inner peripheral side of the coil conductor. The coil conductor is in contact with the surfaces of the metal magnetic particles of the magnetic core at a contact rate of 80% or more at a portion that is in contact with the center part. Among the metal magnetic particles of the center part, the metal magnetic particles that are in contact with the coil conductor are flat and exhibit an average value of θ of 60° or less, where θ represents the deflection angle with respect to the thickness direction as a surface 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 portion and the aspect ratio of the soft magnetic metal particles are set, but the aspect ratio of the soft magnetic metal particles is an index of the flattening of the soft magnetic metal particles, and the deflection angle θ is an index of whether the long axis of the soft magnetic metal particles is aligned with the direction of the magnetic field of the inductance. Therefore, in an inductor having the above configuration, no provision is made for the gap between the coil conductor and the core portion, and the presence of the gap between the coil conductor and the core portion makes it difficult to improve the inductance.

[0005] One aspect of the present invention is an inductor including a magnetic core made of resin and metal magnetic particles and a coil conductor embedded in the magnetic core, wherein the magnetic core includes a center core located on the inner periphery of the coil conductor, and the coil conductor has a contact rate of 80% or more of the portion that contacts the center core contacting the surface of the metal magnetic particles of the magnetic core, and the metal magnetic particles in the center core that contact the coil conductor are flat, and when the deflection angle of the surface of the coil conductor with respect to the thickness direction is θ, the average value of θ is 60° or less. This specification is intended to include the entire contents of Japanese Patent Application No. 2024-107507, filed on July 3, 2024.

[0006] According to the present invention, it is easy to suppress the presence of a gap between the coil conductor and the central core portion, and it is easy to improve the inductance of the inductor.

[0007] FIG. 1 is a perspective view of an inductor according to this embodiment, viewed from the top side. FIG. 2 is a perspective view of an inductor according to this embodiment, viewed from the bottom side. 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 corresponding to line VI-VI in FIG. 4. FIG. 7 is a schematic diagram of a manufacturing process for an inductor. FIG. 8 is a cross-sectional view of an inductor according to this embodiment. FIG. 9 is a cross-sectional view of an inductor corresponding to a rectangular region indicated by arrow IX in FIG. 8. FIG. 10 is a cross-sectional view of an inductor corresponding to a rectangular region indicated by arrow X in FIG. 8. FIG. 11 is a cross-sectional view of an inductor corresponding to a rectangular region indicated by arrow XI in FIG. 8. FIG. 12 is a cross-sectional view of an inductor corresponding to a rectangular region indicated by arrow XII in FIG. 8.

[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 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 instead of carbonyl iron powder. Also, 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 multiple types of resin materials. The resin material contained in the mixed powder of this embodiment includes at least bisphenol A epoxy resin and rubber-modified epoxy resin. This makes it possible to manufacture an inductor 1 with improved both the strength and toughness of the element body 2. Furthermore, the resin material contained in the mixed powder may include phenol novolac epoxy resin in addition to bisphenol A epoxy resin and rubber-modified epoxy resin.

[0018] Here, when the resin is composed of bisphenol A epoxy resin and rubber-modified epoxy resin, the bisphenol A epoxy resin accounts for 50 wt% to 90 wt% and the rubber-modified epoxy resin accounts for 10 wt% to 50 wt% of the total weight of the resins contained in the mixed powder. In this case, by setting the ratio of bisphenol A resin to rubber-modified epoxy resin in the resins contained in the mixed powder and molding the element body 2 with the coil conductor 20 sealed in by the element molding and curing process, it is possible to manufacture an inductor 1 that combines strength and toughness.

[0019] On the other hand, when the resin is composed of bisphenol A epoxy resin, rubber-modified epoxy resin, and phenol novolac epoxy resin, the bisphenol A epoxy resin is 40 wt % to 80 wt %, the rubber-modified epoxy resin is 10 wt % to 50 wt %, and the phenol novolac epoxy resin is 1 wt % to 30 wt %, based on the total weight of the resins contained in the mixed powder. In this case, the phenol novolac epoxy resin adjusts the viscosity when the mixed powder is flowed to form the element body 2 in the element molding and curing process, and adjusts the glass transition temperature of the element body 2, thereby improving the strength of the element body 2 at high temperatures. Therefore, by appropriately blending the phenol novolac epoxy resin, it is possible to manufacture an inductor 1 that has both strength and toughness, while improving the strength of the element body 2 against heat during molding of the element body 2.

[0020] The resin material contained in the mixed powder may be a thermosetting resin such as a phenol resin, a polyester resin, a polyimide resin, or a polyolefin resin, in addition to an epoxy resin. Resins that may be considered as a replacement for bisphenol A-type epoxy resin include bisphenol A, F, and S-type phenoxy resins. Resins or rubbers that may be considered as a replacement for rubber-modified epoxy resin include urethane-modified, NBR (Acrylonitrile Butadiene Rubber) rubber-modified, CTBN (Carboxyl Terminated Butadiene Acrylonitrile) rubber-modified, and CTBN rubber.

[0021] Furthermore, resins that may be considered as substitutes for phenol novolac epoxy resins include, if limited to novolac types, cresol, dicyclopentadiene, phenol aralkyl, biphenyl, naphthol, xylylene, triphenylmethane, and tetrakisphenolethane, and if not limited to novolac types, also include naphthalene, biphenyl, and triazine.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The inductor 1 of this embodiment will be further described in detail below.

[0051] [Detailed Inductor Configuration] Fig. 8 is a cross-sectional view of the inductor 1 according to this embodiment. Fig. 9 is a cross-sectional view of the inductor 1 corresponding to the rectangular area indicated by arrow IX in Fig. 8. Fig. 10 is a cross-sectional view of the inductor 1 corresponding to the rectangular area indicated by arrow X in Fig. 8. Fig. 11 is a cross-sectional view of the inductor 1 corresponding to the rectangular area indicated by arrow XI in Fig. 8. Fig. 12 is a cross-sectional view of the inductor 1 corresponding to the rectangular area indicated by arrow XII in Fig. 8. The magnetic core 30 is made of resin 31 and metal magnetic particles 32.

[0052] 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.

[0053] 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.

[0054] Here, the central core portion 30 a 2 of the magnetic core 30 is in contact with the inner peripheral surface of the coil conductor 20 , specifically, with the conducting wire 42 on the inner peripheral side of the winding portion 22 of the coil conductor 20 .

[0055] In this embodiment, as shown in Figures 8 to 10, 80% or more of the surface area (contact rate) of the portion of the coil conductor 20 that contacts the central core portion 30a2 of the magnetic core 30 is in contact with the surfaces of the metal magnetic particles 32 of the magnetic core 30. Hereinafter, this may be simply referred to as a contact rate of 80% or more. In other words, the proportion of the surface portion of the coil conductor 20 that contacts the central core portion 30a2 of the magnetic core 30 that is in contact with the surfaces of the metal magnetic particles 32 of the magnetic core 30 in the cross section of the inductor 1 is also referred to as the contact rate. Specifically, as shown in Figure 10, this contact rate is calculated as Lp / Lc by measuring the length Lc of the surface of the coil conductor 20 and the length Lp of the surface of the metal magnetic particles 32 that contacts the surface of the coil conductor 20.

[0056] The metal magnetic particles 32 in the central core portion 30a2 include flat metal magnetic particles 32. In particular, of the metal magnetic particles 32 in the central core portion 30a2, the metal magnetic particles 32 that come into contact with the coil conductor 20 are flat. That is, when the metal magnetic particles 32 are viewed in cross section, a major axis m is set in the longer length direction, and a minor axis n is set in the shorter length direction. The major axis m is set at the longest position in the longitudinal direction of the metal magnetic particle 32 when viewed in cross section. The minor axis n is set at the longest position in the lateral direction of the metal magnetic particle 32 when viewed in cross section. Of the metal magnetic particles 32 in the central core portion 30a2, the metal magnetic particles 32 that come into contact with the coil conductor 20 have an average deflection angle θ of 60° or less, where θ is the deflection angle with respect to the thickness direction DT of the surface of the coil conductor 20. In this embodiment, in the WT cross section of the inductor 1 (see FIG. 8 ), a perpendicular line H2 is set to a 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 as the surface of the coil conductor 20, and the angle formed by the perpendicular line H2 and the major axis m of the metal magnetic particle 32 is defined as the deflection angle θ. The deflection angle θ is set to the smaller of the two angles.

[0057] The contact rate and deflection angle θ can be set by controlling the pressure applied during the element molding and hardening process when manufacturing the inductor 1. That is, when pressure is applied during the element molding and hardening process, a force acts on the center side of the center core portion 30a2 toward the plate-shaped portion 30a1. In contrast, on the outer periphery of the center core portion 30a2, i.e., the portion of the center core portion 30a2 that contacts the coil conductor 20, a force acts that makes it difficult for the center core portion 30a2 to move due to friction. Therefore, the amount of movement in the pressure direction differs between the center side and the outer periphery of the center core portion 30a2, and the contact rate and deflection angle θ of the metal magnetic particles 32 of the center core portion 30a2 near the surface of the coil conductor 20 can be controlled.

[0058] The metal magnetic particles 32 of the first core portion 30a include metal magnetic particles 32 with an aspect ratio of 1.10 or more. Here, the aspect ratio of the metal magnetic particles 32 is defined as follows: When the metal magnetic particle 32 is viewed in cross section, the major axis m is set in the direction of the longer length. When the metal magnetic particle 32 is viewed in cross section, the major axis m is set at the longest position in the longitudinal direction of the metal magnetic particle 32. Then, a virtual circumscribing rectangle S1 that circumscribes the metal magnetic particle 32 is set so that the major axis m becomes the center line of symmetry. The perpendicular line to the major axis m, which is the length of the short side of this circumscribing rectangle S1, is set as the minor axis n. In this way, the major axis m and the minor axis n are set.

[0059] The aspect ratio of the metal magnetic particles 32 is set based on the lengths of the major axis m and minor axis n. That is, the aspect ratio of the metal magnetic particles 32 in the first core portion 30a is calculated as the average value of the metal magnetic particles 32 that appear in the field of view. Specifically, when N metal magnetic particles 32 appear in the field of view, the length Li of the major axis m and the length Di of the minor axis n of the i-th metal magnetic particle 32 among the N metal magnetic particles 32 are measured, and the aspect ratio of the metal magnetic particles 32 in the first core portion 30a is calculated by the following formula: Σ(Li / Di) / N, where i = 1, 2, ..., N.

[0060] 12, the second core portion 30b contains metal magnetic particles 32 with an aspect ratio of 1.80 or less. In the second core portion 30b of this embodiment, the metal magnetic particles 32 are composed of spherical metal magnetic particles 32b and flat metal magnetic particles 32a. The aspect ratio of the flat metal magnetic particles 32a is 1.10 or more. The aspect ratio of the spherical metal magnetic particles 32b is 1.80 or less. Therefore, since the second core portion 30b of this embodiment contains spherical metal magnetic particles 32, the aspect ratio of the flat metal magnetic particles 32a does not need to be 1.80 or less. In this embodiment, spherical refers to an aspect ratio of less than 1.10.

[0061] In the inductor 1 of this embodiment, the high contact rate easily prevents the presence of gaps between the coil conductor 20 and the central core portion 30a2 of the magnetic core 30. Furthermore, the average value of the deflection angle θ is 60° or less, and the long axes m of the metal magnetic particles 32a tend to align with the direction of the magnetic field generated by the inductor 1, making it easy to increase the magnetic permeability and improve the inductance.

[0062] Next, Table 1 shows the relationship between the measurement results of the example of this embodiment and the comparative example.

[0063]

[0064] 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 predetermined imaging software and analyzed to define the major axis m of the metal magnetic particles 32 in contact with the coating layer 45 of the conductive wire 42 of the coil conductor 20. An example of the predetermined imaging software is WinROOF2021 manufactured by Mitani Corporation.

[0065] If the shortest distance from the surface of the metal magnetic particle 32 to the surface of the conductor 42 is less than one-tenth of the length of the minor axis n, the metal magnetic particle 32 is determined to be in contact with the surface of the conductor 42 of the coil conductor 20.

[0066] The average value of the deflection angle θ is calculated by the following formula, i.e., Σθi / N (i=1, 2, ..., N). At this time, the range of the SEM observation image is set so that N metal magnetic particles 32, where N≧10, are observed.

[0067] Specifically, a case where N = 10 is illustrated using Figures 9 and 10. A metal magnetic particle 32 close to the surface of the conductor 42 of the coil conductor 20 is identified. Then, a major axis m is appropriately defined. A circumscribing rectangle S1 based on this major axis m is set to obtain a minor axis n. If the shortest distance from the surface of the metal magnetic particle 32 to the surface of the conductor 42 is less than one-tenth the length of the minor axis n, the metal magnetic particle 32 is determined to be in contact with the coil conductor 20 and adopted. If the shortest distance is greater than one-tenth the length of the minor axis n, the metal magnetic particle 32 is determined not to be in contact with the coil conductor 20, and similar major axes m and minor axes n are set for other candidate metal magnetic particles 32 to determine whether they are in contact. In this way, major axes m1, m2, ..., m10, minor axes n1, n2, ..., n10, and deflection angles θ1, θ2, ..., θ10 are set for 10 metal magnetic particles 32. Then, the average value of the deflection angles θ of these 10 metal magnetic particles 32 can be obtained by the above formula.

[0068] Furthermore, the contact rate is calculated by measuring the length Lp1, Lp2, ..., Lp10 of each of the 10 metal magnetic particles 32 that are in contact with the coating layer 45 of the coil conductor 20. The overall length Lp is then calculated by Lp = ΣLpi (i = 1, 2, ..., 10). Meanwhile, the length Lc of the surface of the coil conductor 20 is measured as the length from the contact start position of the first metal magnetic particle 32 to the contact end position of the tenth metal magnetic particle 32. The contact rate is then calculated by Lp / Lc. The lengths Lp1, Lp2, ..., Lp10 are schematically shown as straight lines in FIG. 10. Since the surface of the metal magnetic particle 32 is uneven, each length Lpi is determined by determining the outline of the metal magnetic particle 32 and the outline of the coating layer 45 of the coil conductor 20 using WinROOF2021, measuring the distance from the first point of contact to the coating layer 45 of the coil conductor 20 on the surface of the metal magnetic particle 32 to the last point of contact, and then determining the length between the first and last points of contact.

[0069] 10, the lines indicating lengths Lp1, Lp2, ..., Lp10 are continuous and length Lp is measured as the length of one line, but the lines indicating lengths Lp1, Lp2, ..., Lp10 may be spaced apart. That is, if a metal magnetic particle 32 that is determined to be not in contact is located between adjacent metal magnetic particles 32 that are in contact with coil conductor 20, the lines indicating lengths Lp1, Lp2, ..., Lp10 may be spaced apart.

[0070] As shown in Table 1, when the contact rate is 80% or more, the average deflection angle θ is 60° or less, and the aspect ratio is 1.10 or more, an L value (inductance value) of 0.30 or more is obtained. In contrast, in the comparative examples that do not satisfy the requirements of this embodiment, the L value is 0.20 or less, which is 0.1 or more smaller than the L value of the examples. Conversely, the L value of the examples is 0.10 or more larger than the comparative examples, and the inductance is improved compared to the comparative examples.

[0071] As described above, the inductor 1 includes a magnetic core 30 made of resin 31 and metal magnetic particles 32, and a coil conductor 20 embedded in the magnetic core 30. In this inductor 1, the magnetic core 30 includes a center core 30a2 located on the inner periphery of the coil conductor 20, and 80% or more of the contact rate of the portion of the coil conductor 20 that contacts the center core 30a2 contacts the surfaces of the metal magnetic particles 32 of the magnetic core 30. Of the metal magnetic particles 32 of the center core 30a2, the metal magnetic particles 32 that contact the coil conductor 20 are flat, and when the deflection angle θ of the surface of the coil conductor 20 with respect to the thickness direction DT of the magnetic core 30 is θ, the average value of θ is 60° or less. This makes it easier to suppress the presence of gaps between the coil conductor 20 and the center core 30a2, making it easier to improve the inductance of the inductor 1.

[0072] Furthermore, in the inductor 1 of this embodiment, the metal magnetic particles 32 of the magnetic core 30 include metal magnetic particles with an aspect ratio of 1.10 or more. Therefore, the magnetic core 30 can include metal magnetic particles that are flattened and can define a major axis m and a minor axis n.

[0073] Furthermore, in the inductor 1 of this embodiment, the magnetic core 30 includes a first core portion 30a having a center core portion 30a2 and a plate-like portion 30a1 formed at one end of the center core portion 30a2 in the winding axis direction, and a second core portion 30b located at the other end of the center core portion 30a2 in the winding axis direction and covering the first core portion 30a and the coil conductor 20. The metal magnetic particles 32 of the first core portion 30a are metal magnetic particles with an aspect ratio of 1.10 or greater. Therefore, the center core portion 30a2 of the first core portion 30a can be composed of metal magnetic particles that are flattened so that a major axis m and a minor axis n can be defined, making it easier to improve magnetic permeability.

[0074] In the inductor 1 of this embodiment, the metal magnetic particles 32 of the second core portion 30b include metal magnetic particles with an aspect ratio of 1.10 or more. Therefore, the second core portion 30b can include metal magnetic particles that are flattened and can define a major axis m and a minor axis n.

[0075] In the inductor 1 of this embodiment, the metal magnetic particles 32 of the second core portion 30b include spherical metal magnetic particles 32b as an example of metal magnetic particles having an aspect ratio of 1.80 or less. This allows the second core portion 30b to contain the metal magnetic particles 32b having an aspect ratio of 1.80 or less.

[0076] [Other Embodiments] In the above-described embodiment, the metal magnetic particles 32 of the second core portion 30b include spherical metal magnetic particles 32b, but the spherical metal magnetic particles 32b are metal magnetic particles 32b of one type of particle size. However, the spherical metal magnetic particles 32b may be metal magnetic particles 32b of multiple types with different average particle sizes. In this embodiment, the average particle size is calculated as the average value of the length of the major axis m and the length of the minor axis n. In this way, by being composed of multiple types of metal magnetic particles 32b with different average particle sizes, it is possible to easily manufacture the second core portion 30b according to the desired characteristics.

[0077] 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).

[0078] [Configurations Supported by the Above-described Embodiments] The above-described embodiments support the following configurations.

[0079] (Configuration 1) An inductor including a magnetic core made of resin and metal magnetic particles, and a coil conductor embedded in the magnetic core, wherein the magnetic core includes a center portion located on the inner periphery of the coil conductor, and the coil conductor has a contact rate of 80% or more of the portion that contacts the center portion contacting the surface of the metal magnetic particles of the magnetic core, and the metal magnetic particles in the center portion that contact the coil conductor are flat, and when the deflection angle θ is the deflection angle of the surface of the coil conductor with respect to the thickness direction, the average value of θ is 60° or less. The inductor of Configuration 1 makes it easy to suppress the presence of voids between the coil conductor and the center portion, making it easy to improve the inductance of the inductor.

[0080] (Configuration 2) The inductor according to Configuration 1, wherein the metal magnetic particles of the magnetic core include metal magnetic particles having an aspect ratio of 1.10 or more. According to the inductor of Configuration 2, the magnetic core can include metal magnetic particles that are flattened to define a major axis and a minor axis.

[0081] (Configuration 3) The inductor according to Configuration 1 or 2, wherein the magnetic core has a first core portion having the center core portion and a plate-shaped portion formed at one end of the center core portion in the winding axis direction, and a second core portion located at the other end of the center core portion in the winding axis direction and covering the first core portion and the coil conductor, and the metal magnetic particles of the first core portion are metal magnetic particles with an aspect ratio of 1.10 or more. According to the inductor of Configuration 3, the center core portion of the first core portion can be made of metal magnetic particles that are flattened so that the major axis and the minor axis can be defined, making it easier to improve magnetic permeability.

[0082] (Configuration 4) The inductor according to Configuration 3, wherein the metal magnetic particles of the second core portion include metal magnetic particles having an aspect ratio of 1.10 or more. According to the inductor of Configuration 4, the second core portion can include metal magnetic particles that are flattened to define a major axis and a minor axis.

[0083] (Configuration 5) The inductor according to Configuration 3 or 4, wherein the metal magnetic particles of the second core portion include metal magnetic particles having an aspect ratio of 1.80 or less. According to the inductor of Configuration 5, the second core portion can include metal magnetic particles having an aspect ratio of 1.80 or less.

[0084] (Configuration 6) The inductor according to Configuration 5, wherein the metal magnetic particles of the second core portion are composed of multiple types of metal magnetic particles with different average particle sizes. According to the inductor of Configuration 6, the second core portion is composed of multiple types of metal magnetic particles with different average particle sizes, which makes it easier to manufacture the second core portion according to the desired characteristics.

[0085] 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 2 core portion, 31...resin, 32...metal magnetic particle, 32a...metal magnetic particle, 32b...metal magnetic particle, 42...conductor, 43...conductor, 45...coating layer, 50...plated conductor, 51...copper plating layer, 52...Ni plating layer, Di...length, H1...straight line, H2...perpendicular line, Lc...length, Li...length, Lp...length, K...winding axis, S1...circumscribed rectangle, T...thickness, W...width, m...major axis, n...minor axis, θ...deflection angle.

Claims

1. An inductor comprising a magnetic core made of resin and metal magnetic particles, and a coil conductor embedded in the magnetic core, wherein the magnetic core includes a center portion located on the inner periphery of the coil conductor, and the coil conductor has a contact rate of 80% or more of the contact area with the center portion that contacts the surface of the metal magnetic particles of the magnetic core, and the metal magnetic particles in the center portion that contact the coil conductor are flat, and when the deflection angle of the surface of the coil conductor with respect to the thickness direction is θ, the average value of θ is 60° or less.

2. The inductor according to claim 1, wherein the metal magnetic particles of the magnetic core include metal magnetic particles having an aspect ratio of 1.10 or more.

3. An inductor as described in claim 1 or 2, wherein the magnetic core has a first core portion having the central core portion and a plate-shaped portion formed at one end of the central core portion in the winding axis direction, and a second core portion located at the other end of the central core portion in the winding axis direction and covering the first core portion and the coil conductor, and the metal magnetic particles of the first core portion are metal magnetic particles with an aspect ratio of 1.10 or more.

4. The inductor according to claim 3, wherein the metal magnetic particles of the second core portion include metal magnetic particles having an aspect ratio of 1.10 or more.

5. The inductor according to claim 3 or 4, wherein the metal magnetic particles of the second core portion include metal magnetic particles having an aspect ratio of 1.80 or less.

6. The inductor according to claim 5, wherein the metal magnetic particles of the second core portion are composed of multiple types of metal magnetic particles with different average particle sizes.

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