Inductor and method for manufacturing inductor

Abstract

The purpose of the present invention is to inexpensively provide a large-current inductor having low inductance.　This inductor comprises: a coil conductor having a pair of leads, the coil conductor comprising a conductive wire having a conductor and an insulating film covering the outer periphery of the conductor; an element containing metallic magnetic particles and a resin and enclosing the coil conductor; and an external electrode connected to the exposed portion of the lead that is exposed from the surface of the element body. The element has a mounting surface facing the side of a mounting substrate when mounted. The coil conductor has a winding part in which a conductive wire is wound in a helix. A winding shaft of the winding part is embedded in the element in an orientation following a direction substantially parallel to the mounting surface of the element. Each of the two leads is led out from the outer periphery on the mounting surface side of the winding part to the mounting surface while a part of the outer periphery of the conductive wire faces the mounting surface.

Description

Inductor and method for manufacturing the same

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

[0002] For use in automotive power supply circuits, there is a demand for so-called low-L, large-current inductors having a low inductance of 100 nH or less and a large DC bias allowable current of about 30 A to 50 A.

[0003] Patent Document 1 describes a surface-mount inductor in which a coil conductor made of a rectangular conductor wire wound in an alpha winding (outside-outside winding) is embedded in an element containing metal magnetic particles and resin.

[0004] In alpha winding, the conductor is wound in two stages along the winding axis so that the beginning and end of the winding are located on the outer periphery, and the innermost conductor is wound in a cross-like manner to connect the stages. However, forming a coil conductor with a total number of turns using alpha winding is difficult.

[0005] Patent Document 2 discloses a coil that does not use a conducting wire as the coil conductor but uses a tube made of a conductive material. In this coil, a helical conductor is formed by forming a helical groove along the central axis of the tube in the wall of the tube using laser processing technology. However, a coil that uses a conducting material tube requires special processing using a laser, which increases manufacturing costs compared to a configuration that uses a conducting wire as the coil conductor.

[0006] International Publication No. 2012 / 105489 Japanese Patent Application Laid-Open No. 2023-139185

[0007] An object of the present invention is to realize a low-inductance inductor for large currents at low cost.

[0008] One aspect of the present invention is an inductor comprising: a coil conductor having a pair of lead-out portions, the lead-out portion being made of a conductive wire having a conductor and an insulating coating covering the outer periphery of the conductor; an element body containing metal magnetic particles and resin and containing the coil conductor; and an external electrode connected to an exposed portion of the lead-out portion that is exposed from the surface of the element body, wherein the element body has a mounting surface that faces a mounting board when mounted; the coil conductor has a winding portion in which the conductive wire is wound helically, the winding axis of the winding portion being embedded in the element body in an orientation that is approximately parallel to the mounting surface of the element body; and each of the two lead-out portions is drawn out from the outer periphery of the winding portion on the mounting surface side to the mounting surface while a portion of the outer periphery of the conductive wire faces the mounting surface. Another aspect of the present invention is a method for manufacturing an inductor, comprising: a coil conductor forming process for producing a coil conductor having a winding portion in which a conductive wire having a conductor and an insulating coating covering the outer periphery of the conductor is helically wound, and a pair of lead-out portions drawn out from the winding portion; a body molding process for embedding the coil conductor in an element body containing metal magnetic particles and resin so that the lead-out portions are exposed from the surface of the element body; and an external electrode forming process for forming an external electrode by plating in a predetermined area of ​​the surface of the element body including the portion where the lead-out portions are exposed, wherein in the element body molding process, the coil conductor is embedded in the element body so that the winding axis of the winding portion is oriented in a direction approximately parallel to the mounting surface of the element body that faces the mounting board when mounted, and the two lead-out portions are each drawn out from the outer periphery of the winding portion on the mounting surface side to the mounting surface while facing the mounting surface and being exposed. This specification includes the entire contents of Japanese Patent Application No. 2024-075167, filed on May 7, 2024.

[0009] According to the present invention, a large current inductor having low inductance can be realized at low cost.

[0010] Fig. 1 is a perspective view of an inductor according to an embodiment of the present invention, viewed from the top side. Fig. 2 is a perspective view of the inductor, viewed from the mounting surface side. Fig. 3 is a see-through perspective view showing the internal configuration of the inductor. Fig. 4 is a see-through view of the inductor viewed along the direction of the winding axis. Fig. 5 is a diagram showing the configuration of an inductor according to a first modified example. Fig. 6 is a diagram showing the configuration of an inductor according to a second modified example. Fig. 7 is a diagram showing the configuration of an inductor according to a third modified example. Fig. 8 is a diagram showing a manufacturing process of the inductor.

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [1. Inductor Configuration] Fig. 1 is a perspective view of an inductor 1 according to this embodiment as viewed from the top surface 12 side, and Fig. 2 is a perspective view of the inductor 1 as viewed from the mounting surface 10 side. The inductor 1 of this embodiment is configured as a surface-mount electronic component, and includes an element body 2 having a substantially rectangular parallelepiped shape, which is one form of a substantially hexahedral shape, and a pair of external electrodes 4 provided on the surface of the element body 2.

[0012] Hereinafter, in the base body 2, the first main surface that faces the mounting board (not shown) during mounting is defined as the mounting surface 10, the second main surface opposite the mounting surface 10 is referred to as the top surface 12, a pair of third main surfaces that are perpendicular to the mounting surface 10 are referred to as end surfaces 14, and a pair of fourth main surfaces that are perpendicular to the mounting surface 10 and the pair of end surfaces 14 are referred to as side surfaces 16.

[0013] 1 , the distance from the mounting 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 distance is defined as the length direction DL. The size of the inductor 1 is, for example, a length L dimension of 2.0 mm, a width W dimension of 2.5 mm, and a thickness T dimension of 1.8 mm.

[0014] Fig. 3 is a see-through perspective view showing the internal configuration of the inductor 1. Fig. 4 is a see-through view of the inductor 1, looking at an end face 14 from outside the element body 2 along the direction of the winding axis Q. The element body 2 includes a coil conductor 20 and a substantially hexahedral core 30 in which the coil conductor 20 is embedded, and is configured as a molded inductor in which the coil conductor 20 is sealed in the core 30.

[0015] The core 30 is a molded body obtained by compressing and molding a powder mixture of magnetic particles and resin into a substantially hexahedral shape by applying pressure and heat while the coil conductor 20 is enclosed therein.

[0016] The magnetic particles of this embodiment include particles of two particle sizes: first magnetic particles that are large particles with a relatively large average particle size, and second magnetic particles that are small particles with a relatively small average particle size. As a result, during compression molding, the second magnetic particles, which are small particles, enter between the first magnetic particles, along with the resin, thereby increasing the filling rate of the magnetic particles in the core 30 and also increasing the magnetic permeability.

[0017] The average particle size (D50) of the first magnetic particles is preferably 20 μm or more and 68 μm or less, more preferably 21.4 μm or more and 27.4 μm or less. The average particle size (D50) of the second magnetic particles is preferably 1 μm or more and 6 μm or less, more preferably 1.5 μm or more and 1.8 μm or less. The magnetic particles may contain particles of three or more different particle sizes by including particles having an average particle size different from that of the first magnetic particles and the second magnetic particles.

[0018] The first magnetic particles and the second magnetic particles are both particles having a metal particle and an insulating film covering the surface of the metal particle, the insulating film having a thickness of several nanometers to several tens of nanometers. By covering the metal particle with the insulating film, the insulation resistance and the withstand voltage are increased.

[0019] For example, the first magnetic particles of this embodiment use Fe—Si—B amorphous alloy powder as the metal particles and zinc phosphate glass with a thickness of 10 nm to 50 nm as the insulating film, while the second magnetic particles of this embodiment use carbonyl iron powder as the metal particles and a silica film with a thickness of 5 nm to 15 nm as the insulating film.

[0020] In the mixed powder of this embodiment, the resin material is an epoxy resin whose main component is a phenol alkyl epoxy resin. The amount of second magnetic particles contained in the mixed powder is, for example, 15 wt% to 30 wt% and preferably 20 wt% to 30 wt% based on the total weight of the magnetic particles. The resin content in the mixed powder is 2.0 wt% to 3.5 wt% based on the total weight of the mixed powder.

[0021] As shown in FIG. 3 , the coil conductor 20 has a winding portion 22 around which a conducting wire is wound, and a pair of lead-out portions 24 that are led out from the winding portion 22 .

[0022] The conducting wire forming the coil conductor 20 has a copper conductor and an insulating coating covering the outer periphery of the conductor. The insulating coating is made of, for example, polyurethane resin, polyester resin, epoxy resin, or polyimideamide resin, preferably polyimideamide resin. The insulating coating has a thickness of, for example, 3 μm. The conducting wire may have a bonding layer on the insulating coating to bond the overlapping conducting wires together in the winding portion 22.

[0023] In this embodiment, the conductor of the conductor has a rectangular cross-sectional shape. The conductor may also be composed of a conductor having a circular or square cross-section. However, when a conductor with a rectangular cross-sectional shape is used as in this embodiment, the occupancy rate of the conductor in the element body can be increased, thereby reducing DC resistance. In this embodiment, for example, the conductor has a rectangular cross-sectional shape with one side having a length of 50 μm or more and 450 μm or less, and the other side having a length of 100 μm or more and 800 μm or less. Furthermore, the ratio of the length of the short side to the length of the long side of the rectangular cross-sectional shape of the conductor is 0.3 or more and 1.0 or less. In this embodiment, a low-inductance, large-current inductor can be realized at low cost using such a rectangular cross-sectional shape conductor, which is difficult to form an alpha winding.

[0024] 3 , in this embodiment, in particular, the winding portion 22 has a conductor wound helically (i.e., spirally) along a winding axis Q. Furthermore, inside the element body 2, the coil conductor 20 is embedded in the core 30 with the winding axis Q, which is the central axis of the winding portion 22, extending along a direction substantially parallel to the mounting surface 10 of the element body 2. In this embodiment, for example, the coil conductor 20 is embedded in the core 30 with the winding axis Q extending along a direction substantially parallel to the mounting surface 10 and the side surface 16 and substantially perpendicular to the end face 14.

[0025] 3 and 4 , in this embodiment, each of the two lead-out portions 24 is led from position B on the outer periphery of the winding portion 22 on the mounting surface 10 side to the mounting surface 10, with a portion of the conductor's outer periphery facing the mounting surface 10, and connected to the external electrode 4. In this embodiment, the conductor constituting the coil conductor 20 is a rectangular wire, and therefore the portion of the conductor's outer periphery facing the mounting surface 10 in the lead-out portion 24 is, for example, one of two widthwise side surfaces, front and back, along the width direction of the rectangular wire (the widthwise side surface facing the mounting surface 10 at outer periphery position B of the winding portion 22).

[0026] 4, in this embodiment, the cross-sectional area of ​​the lead portion 24 increases so that the cross-sectional area of ​​the portion that connects to the external electrode 4 decreases toward the tip of the lead portion 24. For example, in the example of Fig. 4, the thickness of the portion that connects to the external electrode 4 of the lead portion 24 decreases toward the tip of the lead portion 24. This increases the connection area between the external electrode and the conductor, improving connection reliability.

[0027] In this embodiment, the two lead-out portions 24 are led out from the same position B on the outer periphery of the winding portion 22 on the side of the mounting surface 10 as shown in Fig. 4, but each of the lead-out portions 24 may be led out from a different position on the outer periphery on the side of the mounting surface 10. Furthermore, the number of turns in the winding portion 22 is two in the example shown in Fig. 3, but the number of turns may be fewer or more.

[0028] Furthermore, in this embodiment, the shape of the element body 2 when viewed from the direction of the winding axis Q, i.e., the shape of a cross section perpendicular to the winding axis Q, is a substantially rectangular shape with long sides along the mounting surface 10. The shape of the winding portion 22 of the coil conductor 20 when viewed from the direction of the winding axis Q is an ellipse with a diameter along the mounting surface 10 longer than the diameter in the direction perpendicular to the mounting surface 10. This allows magnetic flux to pass through the entire element body 2, making it easy to achieve the desired inductance, even in an element body 2 with a substantially rectangular cross section perpendicular to the winding axis Q.

[0029] 3 , the pair of external electrodes 4 extend in the direction of the winding axis Q (the DL direction in this embodiment) along two sides that face each other in a direction perpendicular to the winding axis Q (the DW direction in this embodiment) on the mounting surface 10. This allows the external electrodes 4 to be formed along the direction of the magnetic flux, thereby suppressing manufacturing variations in inductance characteristics.

[0030] Furthermore, the mounting surface 10 of the element body 2 on which the external electrodes 4 are formed is formed to have a rougher surface than the top surface 12 opposite the mounting surface 10. This increases the surface roughness of the boundary surface between the mounting surface 10, including the end faces of the lead-out portions 24, and the external electrodes 4, and therefore the anchor effect that can occur at this boundary surface can improve the fixing strength of the external electrodes 4 on the mounting surface 10 of the element body 2.

[0031] Here, the surface roughness of the mounting surface 10 and the top surface 12 can be determined, for example, by scanning the center of the surface of the top surface 12 and the mounting surface 10 of the inductor 1 along the direction of the winding axis Q and a direction perpendicular to the direction of the winding axis Q using a shape analysis laser microscope, and measuring the maximum height (Sz).

[0032] From the viewpoint of improving the fixing strength of the external electrodes 4, the maximum height Sz of the mounting surface 10 is preferably higher than the maximum height Sz of the upper surface 12 and in the range of 40 μm to 60 μm.

[0033] An element body protective layer (not shown in FIGS. 1 to 5 ) may be formed on the surface of the element body 2 excluding the area of ​​the external electrodes 4. The element body protective layer may be made of, for example, a phenoxy resin or a novolac resin, and may contain nanosilica as a filler. The thickness of the element body protective layer may be, for example, 10 μm or more and 30 μm or less.

[0034] In the inductor 1 having the above configuration, the winding portion 22 of the coil conductor 20 is formed by helically winding a conductor wire. The coil conductor 20 is embedded in the element body 2 so that the winding axis Q is substantially parallel to the mounting surface 10 and the lead-out portion 24 is exposed on the mounting surface 10. This allows the inductor 1 to easily achieve low inductance characteristics using a thick conductor wire that can carry a small DC current and a large current without using a special process such as laser precision machining of a metal tube. Furthermore, because the coil conductor 20 is embedded in the element body 2 during pressure molding of the element body 2, which contains metal magnetic particles and a resin, a large-current inductor having the above low inductance characteristics can be easily manufactured at low cost and with a desired outer size. The manufacturing process for the inductor 1 will be described later.

[0035] [2. Modifications] The following describes modifications of the inductor 1. [2.1. First Modification] In a first modification, the element body 2 is configured such that the metal filling rate, which is the weight of metal magnetic particles per unit weight, in a portion of the element body 2 is lower than the metal filling rate in other portions.

[0036] Fig. 5 is a diagram showing the configuration of an element body 2 according to a first modified example of the inductor 1. (a) shown in the upper part of Fig. 5 is a perspective view of an end face 14 of the element body 2 as viewed from the outside of the element body 2 along the direction of the winding axis Q, and corresponds to Fig. 4 described above. (b) shown in the lower part of Fig. 5 is a perspective view of the element body 2 as viewed from the mounting surface 10.

[0037] In this modified example, as shown in FIG. 5 , element body 2 has a columnar portion P (i.e., the hatched portion in FIGS. 5A and 5B ) that is a portion of element body 2 and has a cross section defined by an area surrounded by at least two lead-out portions 24 and mounting surface 10 in a projected view of element body 2 seen from the direction of winding axis Q ( FIG. 5A ), and that extends along winding axis Q. The metal filling rate of this columnar portion P is lower than the metal filling rate of other portions (non-hatched portions).

[0038] As shown in Figure 4, in the portion of element body 2 between winding portion 22 and mounting surface 10, two lead-out portions 24 are present in the projected view seen from winding axis Q, and therefore the projected cross-sectional area through which magnetic flux passes (the projected area that does not overlap with winding portion 22 and lead-out portion 24 in the projected view) is narrower than between winding portion 22 and top surface 12. For this reason, in columnar portion P of element body 2 shown in Figure 5, the magnetic flux density can be higher than in other portions. As a result, magnetic saturation is more likely to occur in columnar portion P than in other portions, which can be a factor in limiting the allowable DC superimposition current.

[0039] In the first modified example shown in FIG. 5 , as described above, the element body 2 is configured so that the metal filling rate in the columnar portion P is lower than the metal filling rate in other portions. Therefore, the magnetic flux density in the columnar portion P can be adjusted to be approximately the same as the magnetic flux density in other portions, thereby improving the DC superimposition allowable current of the inductor 1.

[0040] The amount of metal filled in the columnar portion P can be adjusted by, for example, adjusting the fluidity of the mixed powder.

[0041] [2.2. Second Modification] As a second modification, top surface 12 of element body 2, which faces mounting surface 10, has a shape in which ridges parallel to the direction of winding axis Q are chamfered. Fig. 6 is an outline drawing of inductor 1 according to a third modification, and corresponds to Fig. 1 described above. As shown in Fig. 6, top surface 12 of element body 2 has curved portions C11 and C12 in which two ridges parallel to the DL direction, which is the direction of winding axis Q, are chamfered. Note that the shape of the chamfer may be a flat C-chamfer in addition to the curved R-chamfer shown in Fig. 6.

[0042] As a result, during the manufacturing process, when the element bodies 2 are placed in a tray provided with a plurality of recesses into which the element bodies 2 fit, by shaping the recesses to correspond to the chamfering, it becomes easy to align the plurality of element bodies 2 in the tray so that the winding axis Q faces in the same direction. Also, costs can be reduced by saving material for the portions of the element bodies 2 that do not affect the inductor.

[0043] [2.3. Third Modification] In a third modification, the top surface 12 of the element body 2, which faces the mounting surface 10, has a shape in which ridges perpendicular to the direction of the winding axis Q are chamfered. FIG. 7 is an outline drawing of an inductor 1 according to a fourth modification, and corresponds to FIG. 1 described above. As shown in FIG. 7, the top surface 12 of the element body 2 has curved portions C21 and C22 in which two ridges extending in the DW direction, which is perpendicular to the DL direction, which is the direction of the winding axis Q, are chamfered. This allows the third modification to achieve the same effects as the second modification described above. Note that the shape of the chamfer may be a curved R-chamfer as shown in FIG. 7, or a flat C-chamfer.

[0044] The chamfers shown in FIG. 6 or 7 can be formed, for example, by adjusting the groove shape of the cavity used to mold element body 2 in the element body molding step (S3) of the inductor manufacturing process described below.

[0045] 8 is a diagram showing the manufacturing process of the inductor 1. As shown in the figure, the manufacturing process of the inductor 1 includes a coil conductor forming step (S1), a preform forming step (S2), an element molding step (S3), a mounting surface polishing step (S4), a barrel polishing step (S5), and an external electrode forming step (S6).

[0046] The coil conductor forming step (S1) is a step of forming the coil conductor 20 from a conductive wire. In this step, the coil conductor 20 is produced, which has a winding portion 22 in which a conductive wire having a conductor and an insulating coating covering the outer periphery of the conductor is helically wound, and a pair of lead-out portions 24 led out from the winding portion 22.

[0047] The preform formation step (S2) 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 of an appropriate shape (e.g., E-shaped) having a groove into which the coil conductor 20 fits, and a second tablet of an appropriate shape (e.g., I-shaped or plate-shaped) that covers the groove of the first tablet.

[0048] In the element molding step (S3), 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 cured to integrate the first tablet, the coil conductor 20, and the second tablet. As a result, the coil conductor 20 is embedded in the element 2 containing metal magnetic particles and resin, so that the lead-out portion 24 is exposed from the surface of the element 2.

[0049] In this embodiment, particularly in the element molding step (S3), the coil conductor 20 is embedded in the element 2 with the direction of the winding axis Q of the winding portion 22 parallel to the mounting surface 10 of the element 2, and the two lead-out portions 24 are embedded in the element 2 so that part of the outer periphery of the conductor is drawn out from the outer periphery of the winding portion 22 on the mounting surface 10 side to the mounting surface 10 and exposed while facing the mounting surface 10. As described above, in this embodiment, the conductor constituting the coil conductor 20 is a rectangular wire, and therefore the part of the outer periphery of the conductor that faces the mounting surface 10 in the lead-out portions 24 is one of the two widthwise side surfaces, front and back, of the rectangular wire.

[0050] In the mounting surface polishing step (S4), the mounting surface 10 of the element body 2 is ground or polished with the lead-out portion 24 exposed from the mounting surface 10. As a result, the end faces of the lead-out portion 24 and the mounting surface 10 of the element body 2 are ground, and the element body 2 is processed so that the thickness T measured from the top surface 12 has a desired value and so that the surface roughness of the mounting surface 10 is rougher than that of the top surface 12. The surface roughness of the mounting surface 10 can be adjusted by the roughness of the grinding stone used for the grinding or polishing.

[0051] The barrel polishing step (S5) is a step of barrel polishing the element body 2, and by this step, the corners of the element body 2 are slightly chamfered.

[0052] The external electrode forming step (S6) is a step of forming the external electrodes 4 on the core 30, and includes an element body protective layer forming step (S61), a surface treatment step (S62), and a plating layer forming step (S63).

[0053] The element body protective layer forming step (S61) is a step of coating the entire surface of the core 30 of the element body 2 with an insulating resin.

[0054] The surface treatment step (S62) is a step of modifying the surface of the planned electrode area by irradiating the area with laser light. Here, the planned electrode area refers to the area on the surface of the core 30 where the external electrode 4 is to be formed, including the area where the lead-out portion 24 is exposed. Specifically, by irradiating the laser light, the element body protective layer on the surface of the core 30 and the coating layer on the lead-out portion 24 of the coil conductor 20 are removed within the planned electrode area, the resin on the surface of the core 30 is removed, and the insulating film on the surface of the magnetic particles exposed from the core 30 is removed. As a result, the exposed area of ​​the metal of the magnetic particles per unit area of ​​the surface of the core 30 is larger in the planned electrode area than in other surface areas of the core 30. After irradiating the laser light, a cleaning process (e.g., etching) may be performed to clean the surface of the planned electrode area.

[0055] In the plating layer forming step (S63), copper is barrel-plated on the surface of the core 30 to form a copper plating layer at the electrode-planed location irradiated with the laser light, thereby forming the external electrode 4. The external electrode 4 may be formed by further providing a Ni plating layer and a Sn plating layer on the copper plating layer.

[0056] 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).

[0057] 4. Configurations Supported by the Above-Described Embodiments The above-described embodiments and modifications support the following configurations.

[0058] (Configuration 1) An inductor comprising: a coil conductor having a pair of lead-out portions, the lead-out portion being made of a conductive wire having a conductor and an insulating coating covering the outer periphery of the conductor; an element body containing metal magnetic particles and resin and encapsulating the coil conductor; and an external electrode connected to an exposed portion of the lead-out portion that is exposed from a surface of the element body, the element body having a mounting surface that faces a mounting board when mounted; the coil conductor having a winding portion in which the conductive wire is helically wound, the winding axis of the winding portion being embedded in the element body with an orientation along a direction substantially parallel to the mounting surface of the element body; and two lead-out portions each extending from the outer periphery of the winding portion toward the mounting surface to the mounting surface while a portion of the outer periphery of the conductive wire faces the mounting surface. According to Configuration 1, a large-current inductor having low inductance characteristics can be inexpensively produced using a thick conductive wire that has low DC resistance and can carry a large current, without using a special process such as laser precision machining of a conductive material.

[0059] (Configuration 2) The inductor according to Configuration 1, wherein a columnar portion of the element body, the columnar portion having a cross section defined by an area surrounded by at least two of the lead-out portions and the mounting surface in a projected view from the direction of the winding axis and extending along the winding axis, has a metal filling rate, which is the weight of the metal magnetic particles per unit weight, lower than the metal filling rate of other portions. According to Configuration 2, it is possible to suppress imbalance in the magnitude of magnetic flux density between the portion of the element body between the winding portion and the mounting surface and the portion of the element body between the winding portion and the top surface, thereby improving the DC superimposition allowable current.

[0060] (Configuration 3) The inductor according to Configuration 1 or 2, wherein the cross-sectional area of ​​the lead portion connected to the external electrode decreases toward the tip of the lead portion. According to Configuration 3, the connection area between the external electrode and the conductor can be increased, improving connection reliability.

[0061] (Configuration 4) The inductor according to any one of Configurations 1 to 3, wherein the external electrodes extend in the direction of the winding axis on the mounting surface. According to Configuration 4, the external electrodes are formed along the direction of magnetic flux, thereby suppressing manufacturing variations in inductance characteristics.

[0062] (Configuration 5) An inductor according to any one of Configurations 1 to 4, wherein the upper surface of the element body facing the mounting surface has a chamfered ridgeline parallel to the winding axis direction or a chamfered ridgeline perpendicular to the winding axis direction. According to Configuration 5, when the element bodies are placed in a tray having a plurality of recesses into which the element bodies fit during a manufacturing process, by shaping the recesses to accommodate the chamfering, it becomes easy to align the plurality of element bodies in the tray so that their winding axis directions are the same. Furthermore, costs can be reduced by saving material in the element body portions that do not affect the inductor.

[0063] (Configuration 6) An inductor according to any one of Configurations 1 to 5, wherein the mounting surface of the element body has a surface roughness greater than that of the upper surface opposite the mounting surface. According to Configuration 6, the surface roughness of the boundary surface between the mounting surface, including the end surfaces of the lead-out portions, and the external electrodes is increased, and the anchor effect that can occur at the boundary surface can improve the fixing strength of the external electrodes to the mounting surface.

[0064] (Configuration 7) The inductor according to any one of Configurations 1 to 6, wherein the cross section of the element body perpendicular to the winding axis has a generally rectangular shape with long sides along the mounting surface, and the coil conductor has a winding portion with an elliptical shape when viewed from the direction of the winding axis, the diameter along the mounting surface being longer than the diameter in the direction perpendicular to the mounting surface. According to Configuration 7, even in an element body having a generally rectangular cross section perpendicular to the winding axis, magnetic flux can pass through the entire element body, making it possible to easily achieve a desired inductance.

[0065] (Configuration 8) The inductor according to any one of Configurations 1 to 7, wherein the conductor of the conductor wire has a rectangular cross section, one side of the rectangular cross section has a length of 50 μm or more and 450 μm or less, the other side has a length of 100 μm or more and 800 μm or less, and the ratio of the length of the short side to the length of the long side of the rectangular cross section is 0.3 or more and 1.0 or less. According to Configuration 8, a low-inductance, large-current inductor can be realized at low cost using a conductor wire with a rectangular cross section, which is difficult to wind with an alpha winding.

[0066] (Configuration 9) A method for manufacturing an inductor, comprising: a coil conductor forming step for fabricating a coil conductor having a winding portion formed by helically winding a conducting wire having a conductor and an insulating coating covering the outer periphery of the conductor, and a pair of lead-out portions drawn out from the winding portion; an element molding step for embedding the coil conductor in an element containing metal magnetic particles and resin so that the lead-out portions are exposed at a surface of the element body; and an external electrode forming step for forming external electrodes by plating in predetermined areas of the surface of the element body including the exposed portions of the lead-out portions, wherein in the element molding step, the coil conductor is embedded in the element body such that the winding axis of the winding portion is oriented in a direction substantially parallel to a mounting surface of the element body that faces a mounting board when mounted, and the two lead-out portions each extend from the outer periphery of the winding portion toward the mounting surface and expose a portion of the outer periphery of the conducting wire to the mounting surface while facing the mounting surface. Configuration 9 can achieve the same effect as configuration 1.

[0067] 1...inductor, 2...element body, 4...external electrode, 10...mounting surface, 12...upper surface, 14...end surface, 16...side surface, 20...coil conductor, 22...winding portion, 24...lead-out portion, 30...core, Q...winding axis.

Claims

1. An inductor comprising: a coil conductor having a pair of lead-out portions, the lead-out portion being made of a conducting wire having a conductor and an insulating coating covering the outer periphery of the conductor; an element body containing metal magnetic particles and resin and containing the coil conductor; and an external electrode connected to the exposed portion of the lead-out portion that is exposed from the surface of the element body, wherein the element body has a mounting surface that faces the mounting board when mounted, the coil conductor has a winding portion where the conducting wire is wound helically, and the winding axis of the winding portion is embedded in the element body in an orientation that is approximately parallel to the mounting surface of the element body, and each of the two lead-out portions is drawn out from the outer periphery of the winding portion on the mounting surface side to the mounting surface while a portion of the outer periphery of the conducting wire faces the mounting surface.

2. An inductor as described in claim 1, wherein a columnar portion of the element body, which has a cross section defined by an area surrounded by at least two of the lead-out portions and the mounting surface when viewed from the direction of the winding axis and which extends along the winding axis, has a metal filling rate, which is the weight of the metal magnetic particles per unit weight, that is lower than the metal filling rate of other portions.

3. The inductor according to claim 1 or 2, wherein the cross-sectional area of ​​the portion of the lead-out portion that connects to the external electrode decreases toward the tip of the lead-out portion.

4. The inductor according to any one of claims 1 to 3, wherein the external electrodes extend in the direction of the winding axis on the mounting surface.

5. The inductor according to any one of claims 1 to 4, wherein an upper surface of the element body facing the mounting surface has ridges that are parallel to the direction of the winding axis or ridges that are perpendicular to the direction of the winding axis chamfered.

6. The inductor according to any one of claims 1 to 5, wherein the mounting surface of the element body has a rougher surface than an upper surface opposite to the mounting surface.

7. An inductor according to any one of claims 1 to 6, wherein the cross section of the element body perpendicular to the winding axis is a substantially rectangular shape with long sides along the mounting surface, and the coil conductor has a winding portion with an elliptical shape when viewed from the direction of the winding axis, the diameter of which along the mounting surface is longer than the diameter of which in a direction perpendicular to the mounting surface.

8. An inductor according to any one of claims 1 to 7, wherein the conductor of the conducting wire has a rectangular cross section, one side of the rectangular cross section has a length of 50 μm or more and 450 μm or less, the other side has a length of 100 μm or more and 800 μm or less, and the ratio of the length of the short side to the length of the long side of the rectangular cross section is 0.3 or more and 1.0 or less.

9. A method for manufacturing an inductor, comprising: a coil conductor forming step of fabricating a coil conductor having a winding portion formed by helically winding a conducting wire having a conductor and an insulating coating covering the outer periphery of the conductor, and a pair of lead-out portions drawn out from the winding portion; a body molding step of embedding the coil conductor in an element body containing metal magnetic particles and resin so that the lead-out portions are exposed from the surface of the element body; and an external electrode forming step of forming external electrodes by plating in predetermined areas of the surface of the element body including the portions where the lead-out portions are exposed, wherein in the element body molding step, the coil conductor is embedded in the element body such that the winding axis of the winding portion is oriented in a direction approximately parallel to the mounting surface of the element body that faces the mounting board when mounted, and the two lead-out portions are each drawn out from the outer periphery of the winding portion on the mounting surface side to the mounting surface while facing the mounting surface and being exposed.

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