Patent Publication Number: US-10763025-B2

Title: Surface-mount inductor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of priority to Japanese Patent Application No. 2018-210837, filed Nov. 8, 2018, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a surface-mount inductor. 
     Background Art 
     Japanese Unexamined Patent Application Publication No. 2007-165779 proposes a coil-sealed-type magnetic component including a coil having a wound portion that is formed by winding a conductive wire in two stages in a state where both ends of the conductive wire are located on an outer periphery thereof and the two stages are connected to each other at an inner periphery thereof, and a pair of extended portions extended from the wound portion; terminal electrodes having engagement portions for connecting to the extended portions of the coil; and an element assembly that contains the coil and the engagement portions and that is obtained by pressure-molding a mixture of magnetic powder and a resin. In the coil-sealed-type magnetic component, the extended portions of the coil are connected to the terminal electrodes within the element assembly, and the terminal electrodes are extended from side surfaces of the element assembly, and the extended terminal electrodes are bent onto the bottom surface of the element assembly, and the coil-sealed-type magnetic component is used as a surface-mount inductor. 
     Regarding the existing surface-mount inductor, when the size of the inductor is reduced, the distance between the bottom surface of the wound portion of the coil and the mounting surface of the element assembly tends to be short, and thus it is difficult to obtain sufficient characteristics in some cases. Particularly, in the case of providing a recess called standoff at the mounting surface side from the viewpoint of mountability, the thickness of the element assembly that covers the bottom surface of the wound portion of the coil tends to be insufficient, resulting in a decrease in characteristics. 
     SUMMARY 
     Accordingly, the present disclosure provides a surface-mount inductor that allows an element assembly, which covers the bottom surface of a wound portion of a coil, to be formed with a desired thickness and that have good characteristics. 
     According to preferred embodiments of the present disclosure, a surface-mount inductor includes an element assembly having a core including a base portion having a lower surface at a mounting surface side, an upper surface at a side opposite to the mounting surface, side surfaces adjacent to the upper surface and the lower surface, and a columnar portion disposed on the upper surface of the base portion. The core contains magnetic powder in at least a partial region. The element assembly also includes a coil disposed on the base portion. The coil has a wound portion formed by winding a conductive wire, having an insulating coating and having a pair of flat surface portions opposing each other, on the columnar portion in two upper and lower stages such that a surface of an inner peripheral portion of the wound portion is in contact with the columnar portion and the flat surface portions oppose each other in a state where both ends of the wound portion are located at an outer peripheral portion of the wound portion and the two stages are connected to each other at the inner peripheral portion of the wound portion. The coil also has a pair of extended portions extended from the wound portion toward the side surface of the base portion. The element assembly further includes a magnetic material formed to include the coil, cover at least a part of the core, and contain magnetic powder. The surface-mount inductor further includes a pair of external terminals disposed on the mounting surface of the element assembly and connected to the pair of extended portions, respectively. In the surface-mount inductor, a curved portion that is curved toward the side opposite to the mounting surface is provided on a surface at the mounting surface side of the wound portion. 
     According to preferred embodiments of the present disclosure, it is possible to provide a surface-mount inductor that allows an element assembly, which covers the bottom surface of a wound portion of a coil, to be formed with a desired thickness and that have good characteristics. 
     Other features, elements, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of preferred embodiments of the present disclosure with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partly transparent perspective view, as viewed from the upper surface side, showing a surface-mount inductor according to a first embodiment; 
         FIG. 2  is a partly transparent perspective view, as viewed from the mounting surface side, showing the surface-mount inductor according to the first embodiment; 
         FIG. 3  is a partly transparent plan view, as viewed from the side surface, showing the surface-mount inductor according to the first embodiment; 
         FIG. 4  is a schematic cross-sectional view taken along a cross-section passing through a line A-A in  FIG. 1 ; 
         FIG. 5A  is a schematic top view of a mold for forming a core of the surface-mount inductor according to the first embodiment; 
         FIG. 5B  is a schematic cross-sectional view of the mold; 
         FIG. 6  is a cross-sectional view for explaining a process for producing the surface-mount inductor according to the first embodiment; 
         FIG. 7  is a schematic partly transparent plan view, as viewed from the upper surface side, for explaining different-shape portions of a pair of extended portions of the surface-mount inductor according to the first embodiment; 
         FIG. 8  is another schematic partly transparent plan view, as viewed from the upper surface side, for explaining the different-shape portions of the pair of extended portions of the surface-mount inductor according to the first embodiment; 
         FIG. 9  is a partly transparent perspective view, as viewed from the upper surface side, showing a modification of the surface-mount inductor according to the first embodiment; 
         FIG. 10  is a partly transparent perspective view, as viewed from the upper surface side, showing a surface-mount inductor according to a second embodiment; 
         FIG. 11  is a partly transparent perspective view, as viewed from the upper surface side, showing a surface-mount inductor according to a third embodiment; 
         FIG. 12  is a partly transparent perspective view, as viewed from the upper surface side, showing a surface-mount inductor according to a fourth embodiment; 
         FIG. 13  is a partly transparent perspective view, as viewed from the upper surface side, showing a modification of the surface-mount inductor according to the fourth embodiment; 
         FIG. 14  is a partly transparent perspective view, as viewed from the upper surface side, showing a surface-mount inductor according to a fifth embodiment; 
         FIG. 15  is a partly transparent perspective view, as viewed from the upper surface side, showing a modification of the surface-mount inductor according to the fifth embodiment; 
         FIG. 16  is a schematic cross-sectional view of a surface-mount inductor according to a sixth embodiment; 
         FIG. 17  is a schematic cross-sectional view of a modification of the surface-mount inductor according to the sixth embodiment; 
         FIG. 18  is a schematic cross-sectional view of a surface-mount inductor according to a seventh embodiment; 
         FIG. 19  is a schematic cross-sectional view of a modification of the surface-mount inductor according to the seventh embodiment; 
         FIG. 20  is a schematic cross-sectional view of a modification of the surface-mount inductor according to the seventh embodiment; 
         FIG. 21  is a schematic cross-sectional view of a surface-mount inductor according to an eighth embodiment; 
         FIG. 22  is a schematic cross-sectional view of a modification of the surface-mount inductor according to the eighth embodiment; 
         FIG. 23  is a schematic cross-sectional view of a modification of the surface-mount inductor according to the eighth embodiment; 
         FIG. 24  is a partly transparent plan view, as viewed from the upper surface side, showing a surface-mount inductor according to a ninth embodiment; 
         FIG. 25  is a schematic cross-sectional view of a surface-mount inductor according to a tenth embodiment; 
         FIG. 26  is a schematic cross-sectional view of a modification of the surface-mount inductor according to the tenth embodiment; and 
         FIG. 27  is a partly transparent plan view, as viewed from the mounting surface side, of a surface-mount inductor according to an eleventh embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A surface-mount inductor includes an element assembly having a core, a coil, and a magnetic material; and a pair of external terminals. The core includes a base portion having a lower surface at a mounting surface side, an upper surface at a side opposite to the mounting surface, and side surfaces adjacent to the upper surface and the lower surface, and a columnar portion disposed on the upper surface of the base portion, and contains magnetic powder in at least a partial region. The coil is disposed on the base portion and has a wound portion formed by winding a conductive wire, having an insulating coating and having a pair of flat surface portions opposing each other, on the columnar portion in two upper and lower stages such that a surface of an inner peripheral portion of the wound portion is in contact with the columnar portion and the flat surface portions oppose each other in a state where both ends of the wound portion are located at an outer peripheral portion of the wound portion and the two stages are connected to each other at the inner peripheral portion of the wound portion, and a pair of extended portions extended from the wound portion toward the side surface of the base portion. The magnetic material is formed to include the coil, cover at least a part of the core, and contain at least magnetic powder. The element assembly is formed by the core, the coil, and the magnetic material. The pair of external terminals are disposed on the mounting surface of the element assembly and connected to the pair of extended portions, respectively. In the surface-mount inductor, a curved portion that is curved toward the side opposite to the mounting surface is provided on a surface at the mounting surface side of the wound portion. 
     Since the curved portion is provided on the surface at the mounting surface side of the wound portion of the coil, even though a recess is provided on the mounting surface of the element assembly, it is possible for the base portion, which covers the surface at the mounting surface side of the wound portion, to maintain a predetermined thickness, and thus it is possible to form a surface-mount inductor having good characteristics. 
     The base portion may have at least one ridge portion at which the upper surface and the side surface are in linear contact with each other, and the pair of extended portions may each be disposed such that one of the flat surface portions is close to the ridge portion. Since the flat surface portion is close to the ridge portion, the position of each extended portion is stabilized. In addition, since each extended portion is extended such that only one of the flat surface portions is close to the ridge portion, it is possible to inhibit excessive stress from being generated at a connection portion between the wound portion and the extended portion. 
     The base portion may have at least one ridge portion at which the upper surface and the side surface are in linear contact with each other, one of the extended portions may be disposed such that one of the flat surface portions is close to the ridge portion, and the other of the extended portions may be disposed such that the other of the flat surface portions is close to the ridge portion. Since the flat surface portion is close to the ridge portion, the position of each extended portion is stabilized. In addition, since the pair of extended portions are extended so as to be twisted in the same direction, the production process is simplified, and the productivity improves. 
     The base portion may have at least one ridge portion at which the upper surface and the side surface are in linear contact with each other, the conductive wire forming the wound portion may have a cross-sectional shape, orthogonal to a length direction, which is a substantially square shape, and the pair of extended portions may have different-shape portions each having a surface that is adjacent to a surface of the conductive wire opposing the columnar portion and that is larger than the surface of the conductive wire opposing the columnar portion of the core, and may be disposed such that a surface of each different-shape portion connected to a surface adjacent to the surface of the conductive wire opposing the columnar portion is close to the ridge portion. Since the flat surface portion is close to the ridge portion, the position of each extended portion is stabilized. In addition, since the pair of extended portions are extended without being twisted, it is possible to inhibit stress from being generated at the connection portion between the wound portion and each extended portion. 
     The pair of extended portions may be extended toward the same side surface and disposed close to the ridge portion, and a distance between positions at which the extended portions are close to the ridge portion may be larger than a distance between positions at which the wound portion is connected to the extended portions. It is possible to finely adjust the number of turns of the conductive wire in the wound portion, and it is possible to easily obtain desired inductance. 
     The pair of extended portions may be extended toward the same side surface and disposed close to the ridge portion, and a distance between positions at which the extended portions are close to the ridge portion may be smaller than a distance between positions at which the wound portion is connected to the extended portions. It is possible to finely adjust the number of turns of the conductive wire in the wound portion, and it is possible to easily obtain desired inductance. 
     The pair of extended portions may be extended toward the same side surface and disposed close to the ridge portion, the base portion may have another ridge portion opposing the ridge portion, and the columnar portion may be disposed closer to the ridge portion, to which the pair of extended portions are disposed close, than to the other ridge portion. It is possible to the element assembly having a thickness corresponding to the number of turns of the coil around the wound portion, and it is possible to easily adjust the balance of a magnetic flux within the element assembly. In addition, even when the size is reduced, it is possible to inhibit the wound portion of the coil from being exposed from the side surface of the element assembly. 
     The base portion may have a plurality of ridge portions at which the upper surface and the side surfaces are in linear contact with each other, and the pair of extended portions may be disposed close to different ridge portions. It is possible to adjust the number of turns of the conductive wire in the wound portion in a unit of ¼ turn by adjusting the position from which each extended portion is extended, and it is possible to easily obtain desired inductance. 
     The core may be disposed such that the lower surface of the base portion and an end surface of the columnar portion at a side opposite to the base portion are exposed from the element assembly. When the magnetic permeability of the core is higher than the magnetic permeability of the element assembly, the region in which the magnetic permeability is high is relatively increased, so that it is possible to improve the inductance value even with the same size. 
     The wound portion may be disposed such that a surface thereof at the side opposite to the mounting surface is exposed from the element assembly, and a resin layer that does not contain magnetic powder may be provided on the surface at the side opposite to the mounting surface. Since the layer that intersects a magnetic flux and that does not contain magnetic powder is provided, it is possible to improve direct current superposition characteristics. 
     The base portion may have a region that does not contain magnetic powder. Since the region that intersects a magnetic flux and that does not contain magnetic powder is provided, it is possible to improve direct current superposition characteristics. 
     The columnar portion may have a region that does not contain magnetic powder. Since the region that intersects a magnetic flux and that does not contain magnetic powder is provided, it is possible to improve direct current superposition characteristics. 
     The magnetic powder may include metallic magnetic powder, and a high-insulation region having higher insulation properties than the other surface may be located in the mounting surface. Since the high-insulation region is located in the mounting surface, it is possible to improve a dielectric breakdown voltage between the wound portion of the coil and each external terminal. 
     The two stages of the wound portion may have different numbers of turns, and the stage closer to the base portion may have a larger number of turns. Since the number of turns at the upper stage side of the wound portion that is not covered with the base portion is smaller, it is possible to improve the sealability of the wound portion by the element assembly. 
     As used herein, the term “process” not only includes an independent process but also includes a process that is not clearly distinguishable from another process, as long as the initial object of the process is achieved. Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. It should be noted that the embodiments described below are intended to illustrate surface-mount inductors for embodying the technical idea of the present disclosure, and the present disclosure is not limited to the surface-mount inductors described below. Members recited in the claims are not limited to members of the embodiments at all. In particular, the scope of the present disclosure is not limited to dimensions, materials, shapes, relative arrangements, etc., of constituent parts described in the embodiments unless specifically described, and they are only explanatory examples. In each drawing, the same parts are designated by the same reference signs. Although the embodiments are separately described for convenience in consideration of the description of main points or ease of understanding, components described in different embodiments may be partially replaced or combined with each other. Description of points common to a first embodiment will be omitted and only the points different from the first embodiment will be described in second and subsequent embodiments. In particular, similar effects and advantages achieved by similar components are not duplicated in each embodiment. 
     EMBODIMENTS 
     First Embodiment 
     A surface-mount inductor  100  according to a first embodiment will be described with reference to  FIGS. 1 to 9 .  FIG. 1  is a schematic partly transparent perspective view of the surface-mount inductor  100  as viewed from an upper surface at the side opposite to a mounting surface, and  FIG. 2  is a schematic partly transparent perspective view of the surface-mount inductor  100  as viewed from the mounting surface side.  FIG. 3  is a partly transparent plan view of the surface-mount inductor  100  as viewed from the side surface.  FIG. 4  is a schematic cross-sectional view of the surface-mount inductor  100  taken along a cross-section passing through a line A-A in  FIG. 1 .  FIG. 5A  is a top view of a mold for forming a core  30 , and  FIG. 5B  is a cross-sectional view of the mold.  FIG. 6  is a cross-sectional view for explaining a part of a process for producing the surface-mount inductor  100 .  FIGS. 7 and 8  are each a partly transparent plan view, as viewed from the upper surface side, for explaining different-shape portions  28  and  29  of a pair of extended portions  24  and  25 .  FIG. 9  is a partly transparent plan view of a surface-mount inductor  102 , which is a modification of the first embodiment, as viewed from the upper surface side. 
     As shown in  FIG. 1 , the surface-mount inductor  100  includes an element assembly  10  having the core  30 , a coil  20 , and a magnetic material  11 ; and a pair of external terminals  40  and  41 . The core  30  includes a base portion  34  and a columnar portion  32 . The coil  20  includes a wound portion  22  formed by winding a conductive wire about a winding axis A; and the pair of extended portions  24  and  25  extended from an outer peripheral portion of the wound portion  22 . The magnetic material  11  covers the coil  20  and the core  30  and is formed to contain at least magnetic powder. The pair of external terminals  40  and  41  are disposed on the mounting surface of the element assembly  10  and electrically connected to the pair of extended portions  24  and  25 , respectively. In the surface-mount inductor  100 , the core  30 , the coil  20 , and the magnetic material  11  are integrally formed to form the element assembly  10 . The surface-mount inductor  100  has a substantially rectangular parallelepiped shape that is defined with a height T in a direction substantially orthogonal to the mounting surface and with a length L and a width W substantially parallel to the mounting surface and substantially orthogonal to each other. 
     The base portion  34  of the core  30  has a lower surface at the mounting surface side, an upper surface at the side opposite to the mounting surface, and four side surfaces adjacent to the upper surface and the lower surface. In addition, the base portion  34  has four ridge portions at which the upper surface and the side surfaces are in contact with each other. The columnar portion  32  of the core  30  is disposed on the upper surface of the base portion  34  such that the extension direction thereof intersects the upper surface. A cross-sectional shape orthogonal to the extension direction of the columnar portion  32  is substantially an oval or an ellipse. A recess  36  is provided on the lower surface of the base portion  34  so as to intersect the extension direction of the columnar portion  32  and extend in the width W direction of the surface-mount inductor  100 , and is formed as a standoff. A part of the upper surface of the base portion  34  is curved at the side opposite to the mounting surface side, so as to correspond to the recess  36 . Two cut portions  38  for housing and allowing the extended portions  24  and  25  of the coil  20  to extend to the lower surface side are provided on one of the side surfaces intersecting the direction in which the recess  36  of the base portion  34  extends. The core  30  is formed from a composite material containing magnetic powder and a resin, by pressure-molding into a state where the base portion  34  and the columnar portion  32  are integrated with each other. The core  30  is formed such that the filling ratio of the magnetic powder is, for example, not less than about 60% by weight and preferably not less than about 80% by weight. As the magnetic powder, iron-based metallic magnetic powder such as Fe, Fe—Si—Cr, Fe—Ni—Al, Fe—Cr—Al, Fe—Si, Fe—Si-A, Fe—Ni, and Fe—Ni—Mo, other composition-based metallic magnetic powder, metallic magnetic powder such as amorphous, metallic magnetic powder whose surface is coated with an insulator such as glass, metallic magnetic powder whose surface is modified, and nano-level minute metallic magnetic powder are used. As the resin, thermosetting resins such as an epoxy resin, a polyimide resin, and a phenol resin, and thermoplastic resins such as a polyethylene resin and a polyamide resin are used. 
     For the coil  20 , a conductive wire (a so-called rectangular wire) having an insulating coating and having a pair of flat surface portions opposing each other is used. The coil  20  has the wound portion  22  and the extended portions  24  and  25  extended from the outer peripheral portion of the wound portion  22 , and is disposed on the base portion  34 . The wound portion  22  is formed by winding the conductive wire on the columnar portion  32  in two upper and lower stages (in so-called alpha-winding) such that, in a state where both ends of the conductive wire are located at the outer peripheral portion and the two stages are connected to each other at an inner peripheral portion of the wound portion  22 , the surface of the inner peripheral portion is in contact with the columnar portion  32 , and the flat surface portions oppose each other. The extended portions  24  and  25  are continuously formed from both ends of the conductive wire, forming the wound portion  22 , which are located on the outer peripheral portion thereof, and the extended portions  24  and  25  are extended toward the side surface of the base portion  34 . A cross-section orthogonal to the length direction of the conductive wire has, for example, a substantially rectangular shape and is defined by the wire width of the flat surface portion corresponding to a long side of the rectangular and a thickness that is the distance, between the flat surface portions, corresponding to the short sides of the rectangular. The conductive wire is formed such that the wire width thereof is, for example, not less than about 120 μm and not greater than about 350 μm (i.e., from about 120 μm to about 350 μm) and the thickness thereof is, for example, not less than about 10 μm and not greater than about 150 μm (i.e., from about 10 μm to about 150 μm). In addition, the insulating coating of the conductive wire is formed from an insulating resin such as polyamide imide such that the thickness thereof is, for example, not less than about 2 μm and not greater than about 10 μm (i.e., from about 2 μm to about 10 μm) and is preferably about 6 μm. A self-fusing layer containing a self-fusing component such as a thermoplastic resin or a thermosetting resin is further provided on the surface of the insulating coating and formed such that the thickness thereof is not less than about 1 μm and not greater than about 3 μm (i.e., from about 1 μm to about 3 μm). 
     The wound portion  22  is formed such that the surface of the inner peripheral portion thereof is in contact with the surface of the columnar portion  32  of the core  30 . In addition, regarding the winding direction of the wound portion  22 , the wound portion  22  is wound clockwise from the extended portion  24  toward the extended portion  25  as viewed from the upper surface side. A curved portion  26  that projects at the upper surface side of the wound portion  22  is formed on the lower surface of the wound portion  22  that is in contact with the base portion  34  of the core  30 . That is, the curved portion  26  is curved at the side opposite to the base portion  34  side of the core  30 . In  FIG. 1 , only the lower surface of the lower stage of the wound portion  22  in which the conductive wire is wound in the two upper and lower stages has a curved portion. However, a curved portion may be formed such that the lower surface of the lower stage and the upper surface of the lower stage are curved. Furthermore, a curved portion may be formed such that the lower surface of the lower stage, the upper surface of the lower stage, and the lower surface of the upper stage are curved, or a curved portion may be further formed such that the lower surface of the lower stage, the upper surface of the lower stage, the lower surface of the upper stage, and the upper surface of the upper stage are curved. Moreover, as shown in  FIG. 4 , in at least a part of a region where the upper stage and the lower stage of the wound portion  22  are in contact with or oppose each other, a meandering surface at which the conductive wire at the upper stage side and the conductive wire at the lower stage side are arranged so as to be mutually nested is present.  FIG. 4  is a schematic cross-sectional view of the surface-mount inductor  100  in  FIG. 1  taken along a plane passing through a line A-A and parallel to the winding axis A of the wound portion  22 . That is, on a cross-section parallel to the winding axis A, in at least a part of the region where the upper stage and the lower stage are in contact with or oppose each other, the wound portion  22  has a boundary surface formed by the conductive wire at one of the upper stage side and the lower stage side being in contact with or opposing a plurality of portions of the conductive wire at the other side. In addition, the boundary surface may be formed on a part of any cross-section other than the cross-section parallel to the winding axis A and passing through the line A-A, and, for example, may be formed on a part in the circumferential direction of the wound portion  22  or in a direction away from the winding axis A. 
     The pair of extended portions  24  and  25  of the coil  20  are each extended from the outer periphery of the wound portion  22  toward a side surface  34 A of the base portion  34  on which the two cut portions  38  are provided. Since the two cut portions  38  are provided on the side surface  34 A, the side surface  34 A has a projecting portion  34 A 1 , recessed portions  34 A 2 , and portions  34 A 3  connecting the projecting portion  34 A 1  and the recessed portions  34 A 2 . The surface of the projecting portion  34 A 1 , the surfaces of the recessed portions  34 A 2 , and the surfaces of the portions  34 A 3  connecting the projecting portion  34 A 1  and the recessed portions  34 A 2  form one side surface, and a ridge portion at which the upper surface of the base portion  34  and the surface of the projecting portion  34 A 1  are in contact with each other, ridge portions at which the upper surface of the base portion  34  and the surface of the recessed portions  34 A 2  are in contact with each other, and ridge portions at which the upper surface of the base portion  34  and the surface of the portions  34 A 3  connecting the projecting portion  34 A 1  and the recessed portions  34 A 2  are in contact with each other form one ridge portion R. In this case, the pair of extended portions  24  and  25  have an angle difference of about 90 degrees or less between the extended direction of the extended portion  24  and the extended direction of the extended portion  25  with the winding axis A as an origin. 
     Of the pair of extended portions  24  and  25 , the extended portion  24  is extended from the upper stage of the wound portion  22 , and the extended portion  25  is extended from the lower stage of the wound portion  22 . The extended portion  24  is extended from the portion connected to the wound portion  22  toward the ridge portion R of the base portion  34  so as to be twisted by about 90° counterclockwise as viewed from the wound portion side. The extended portion  25  is extended from the portion connected to the wound portion  22  toward the ridge portion R of the base portion  34  so as to be twisted by about 90° clockwise as viewed from the wound portion side. That is, the pair of extended portions  24  and  25  are each disposed such that one of flat surface portions H of the conductive wire is close to the ridge portion R of the base portion  34 . In  FIG. 1 , the pair of extended portions  24  and  25  are each disposed such that the flat surface portion connected to the flat surface portion of the conductive wire that is in contact with the columnar portion  32 , that is, to the flat surface portion disposed at an inner side portion of the conductive wire located at the outer peripheral portion of the wound portion  22 , is close to the ridge portion R of the base portion  34 . Since each extended portion is disposed such that the flat surface portion connected to the flat surface portion disposed at the inner side portion of the conductive wire located at the outer peripheral portion R of the wound portion  22  is close to the ridge portion R of the base portion  34 , each extended portion is twisted toward the center of the side surface of the base portion  34 , a force in a winding-up direction along the winding direction of the wound portion  22  is applied between a connection portion between the wound portion  22  and one of the extended portions and a connection portion between the wound portion  22  and the other extended portion, and thus winding blister of the wound portion  22  is inhibited. In addition, in  FIG. 1 , the distance between the centers of the pair of extended portions  24  and  25  is set so as to be uniform regardless of the distance from the wound portion  22 . That is, the pair of extended portions  24  and  25  are extended such that a distance L 1  between the centers in the wire width direction at the positions of contact with the ridge portion R of the base portion  34  is substantially equal to a distance L 2  between the centers in the thickness direction at the positions at which the wound portion  22  is connected to the extended portions  24  and  25 . Furthermore, as shown in  FIGS. 1, 2, and 3 , the pair of extended portions  24  and  25  are housed in the cut portions  38  provided to the base portion  34 , turn back, and extend to the mounting surface side of the base portion  34 . Moreover, the pair of extended portions  24  and  25  may each be formed such that the wire width and the thickness thereof are substantially equal to the wire width and the thickness of the conductive wire  22  of the wound portion, or may each be formed such that at least either one of the wire width and the thickness thereof is different from that of the conductive wire of the wound portion  22 . In  FIG. 1 , the different-shape portions  28  and  29  are formed so as to be wider than the wire width of the conductive wire of the wound portion  22  and be thinner than the thickness of the conductive wire of the wound portion  22 . The different-shape portions  28  and  29  are each disposed such that a surface thereof connected to one of the flat surface portions H of the conductive wire is close to the ridge portion R of the base portion  34 . The different-shape portions  28  and  29  are each formed such that, at the position close to the ridge portion R of the base portion  34 , the wire width thereof is, for example, not less than about 1.4 times of the wire width of the conductive wire of the wound portion  22 , for example, not less than about 168 μm and not greater than about 490 μm (i.e., from about 168 μm to about 490 μm), and the thickness thereof is, for example, about 50% of the thickness of the conductive wire of the wound portion  22 , for example, not less than about 5 μm and not greater than about 75 μm (i.e., from about 5 μm to about 75 μm). Since the different-shape portions  28  and  29  are formed at the end portions of the extended portions  24  and  25 , the thicknesses thereof are smaller than the thickness of the conductive wire of the wound portion, and thus the extended portions  24  and  25  are more easily bent to the mounting surface side so as to be close to the ridge portion R of the base portion  34 . In addition, since the wire widths of the different-shape portions  28  and  29  are larger than the wire width of the conductive wire of the wound portion  22 , it is possible to lengthen the portion of contact with the ridge portion R of the base portion  34  and stabilize the bending position, and it is also possible to further improve the reliability of connection with the external terminals. 
     The magnetic material  11  is formed so as to cover the coil  20 , the columnar portion  32  of the core  30 , and at least the upper surface of the base portion  34  of the core  30 . In this case, the magnetic material  11  also covers the extended portions  24  and  25  and the cut portions  38  of the base portion  34 . The magnetic material  11  is formed by pressure-molding a composite material containing magnetic powder and a resin. The filling ratio of the magnetic powder in the composite material is, for example, not less than about 60% by weight and preferably not less than about 80% by weight (i.e., from about 60% by weight to about 80% by weight). As the magnetic powder, iron-based metallic magnetic powder such as Fe, Fe—Si—Cr, Fe—Ni—Al, Fe—Cr—Al, Fe—Si, Fe—Si-A, Fe—Ni, and Fe—Ni—Mo, other composition-based metallic magnetic powder, metallic magnetic powder such as amorphous, metallic magnetic powder whose surface is coated with an insulator such as glass, metallic magnetic powder whose surface is modified, and nano-level minute metallic magnetic powder are used. As the resin, thermosetting resins such as an epoxy resin, a polyimide resin, and a phenol resin, and thermoplastic resins such as a polyethylene resin and a polyamide resin are used. Materials having the same composition may be used as the composite material for forming the magnetic material  11  and the composite material for forming the core  30 . In addition, the filling ratio of the magnetic powder of the magnetic material  11  may be lower than the filling ratio of the magnetic powder in the core  30 . The element assembly  10  is formed by the coil  20 , the core  30 , and the magnetic material  11 . 
     As shown in  FIG. 2 , at the mounting surface side of the surface-mount inductor  100 , the recess  36  is formed at a position corresponding to the curved portion  26  formed on the lower surface of the wound portion  22  of the coil  20 , so as to penetrate in the width W direction, and serves as a standoff. In the regions at both sides of the recess  36 , the pair of extended portions  24  and  25  of the coil  20  are disposed, respectively, and the pair of external terminals  40  and  41  connected to the pair of extended portions  24  and  25 , respectively, are disposed. Furthermore, an exterior resin (not shown) is formed on the surface of the element assembly  10  other than the regions in which the external terminals  40  and  41  are disposed. The exterior resin contains a thermosetting resin such as an epoxy resin, a polyimide resin, and a phenol resin, or a thermoplastic resin such as a polyethylene resin and a polyamide resin, and may further contain a filler including silicon, titanium, etc. 
     The external terminals  40  and  41  are disposed so as to cover the extended portions  24  and  25 , respectively, which are disposed at the mounting surface side. Each of the external terminals  40  and  41  is formed, for example, by plating, and includes a first layer formed from nickel and a second layer that is formed on the first layer and that is formed from tin. The external terminals  40  and  41  are formed on the entire regions at both sides of the recess  36  in  FIG. 2 , but may be formed so as to be smaller than the regions at both sides of the recess  36 . In this case, the surfaces of the external terminals  40  and  41  are formed so as to be flush with the surface of the exterior resin formed on the mounting surface of the element assembly  10 . In addition, in this case, the side surfaces, of the external terminals  40  and  41 , which are in contact with the exterior resin, may be formed so as to extend onto the exterior resin formed on the mounting surface of the element assembly  10 . 
       FIG. 3  is a partly transparent plan view of the surface-mount inductor  100  as viewed from the side surface direction at the side at which the extended portions  24  and  25  are extended. As shown in  FIG. 3 , the base portion  34  is partially exposed from the side surface of the surface-mount inductor  100 , and the extended portions  24  and  25  are covered with the magnetic material  11 . The extended portion  24  is extended from the upper stage of the wound portion  22 , is bent such that the flat surface portion of the conductive wire that is at the inner side at the outer peripheral portion of the wound portion  22  is in contact with the base portion  34 , and is disposed so as to extend on the lower surface of the base portion  34 . The extended portion  25  is extended from the lower stage of the wound portion  22 , is bent such that the flat surface portion of the conductive wire that is at the inner side at the outer peripheral portion of the wound portion  22  is in contact with the base portion  34 , and is disposed so as to extend on the lower surface of the base portion  34 . The external terminals  40  and  41  are disposed on the extended portions  24  and  25 , respectively, which extend on the lower surface of the base portion  34 . The recess  36  is formed at the mounting surface side of the surface-mount inductor  100 , and the curved portion  26  is formed at the position corresponding to the lower surface of the wound portion  22 . Since the wound portion  22  has the curved portion  26 , even though the recess  36  is formed, it is possible to exhibit good magnetic characteristics, since the base portion  34  containing the magnetic powder is disposed with a sufficient thickness at the lower surface side of the wound portion  22 . 
     In the surface-mount inductor  100  in  FIG. 1 , the cross-sectional shape orthogonal to the extension direction of the columnar portion  32  is substantially an oval or an ellipse, but may be substantially a circle, a rectangle, a polygon, or the like. In  FIG. 1 , the shape of the cross-section orthogonal to the length direction of the conductive wire is the shape of a substantially rectangular flat wire, but each side surface in the thickness direction may be curved such as substantially semicircular or semielliptical, not linear. 
     Next, an example of a method for producing the surface-mount inductor  100  will be described. The method for producing the surface-mount inductor  100  includes, for example, a core forming step, a coil forming step, a different-shape portion forming step, an extended portion disposing step, a molding/curing step, an exterior resin forming step, an exterior resin removing step, and an external terminal forming step. 
     Core Forming Step 
     A composite material containing magnetic powder and a resin is loaded into the cavity of a mold capable of forming a columnar portion and a base portion. The mold  200  includes, for example, a cavity  230  having a first portion  210  having a shape and a depth for forming the base portion; and a second portion  220  that is provided on the bottom surface of the first portion  210  and that has a shape and a depth for forming the columnar portion, as shown in  FIGS. 5A and 5B . In a state where the composite material is heated within the mold to a temperature equal to or higher than the softening temperature of the resin (for example, not lower than 60° C. and not higher than 150° C.), a pressure of not lower than about 1 t/cm 2  and not higher than about 10 t/cm 2  is applied thereto for several seconds to several minutes to mold a core. Next, the core is heated to a temperature equal to or higher than the curing temperature of the resin (for example, not lower than 100° C. and not higher than 220° C.) to be cured to obtain a core that has a flat plate-shaped base portion and a columnar portion disposed on the base portion and that has two cut portions on one of four side surfaces of the base portion. The resin may not be fully cured and may be semi-cured. In such a case, the resin may be semi-cured into a desired state by adjusting the temperature (for example, not lower than 100° C. and not higher than 220° C.) and the curing time (for example, not shorter than 1 minute and not longer than 60 minutes). 
     Coil Forming Step 
     A coil having a wound portion and a pair of extended portions extended from the wound portion is formed by winding a conductive wire on the columnar portion of the obtained core. As the conductive wire, a flat wire having an insulating coating and having a substantially rectangular cross-section is used. The wound portion is formed by winding the conductive wire in two stages such that both ends of the conductive wire are located at the outer periphery thereof and the two stages are connected to each other at the inner periphery thereof. In addition, the wound portion is formed by winding the flat wire on the columnar portion such that the width direction of the flat wire is substantially parallel to the extension direction of the columnar portion and one of flat surface portions of the flat wire opposes the columnar portion. Accordingly, the core in which the coil is mounted is obtained. 
     Different-Shape Portion Forming Step 
     A different-shape portion that is wider than the wire width of the conductive wire of the wound portion and that is thinner than the thickness of the conductive wire is formed at an end portion of each of the pair of extended portions of the coil by crushing the end portion. 
     Extended Portion Disposing Step 
     Each of the pair of extended portions of the coil is extended toward the side surface, of the base portion of the core, on which the two cut portions are formed, and is disposed such that one of the flat surface portions of the conductive wire is close to a ridge portion of the base portion. The pair of extended portions are extended from the upper surface of the base portion of the core toward a side surface of the base portion so as to be twisted in directions different from each other. In the surface-mount inductor  100 , the pair of extended portions are each extended so as to be twisted such that the flat surface portion located at the inner side at the outer peripheral portion of the wound portion of the coil is close to the ridge portion of the base portion. The distance between the centers of the pair of extended portions is set so as to be substantially uniform regardless of the distance from the wound portion. The pair of extended portions are bent to the mounting surface side of the core via the cut portions, which are provided to the base portion of the core, and are disposed on the lower surface of the core. 
     Molding/Curing Step 
     As shown in  FIG. 6 , the core  30  in which the coil  20  is mounted is put in a cavity  310  of a mold  300  having a projection  320  on a bottom surface thereof, such that the lower surface of the base portion  34  opposes the bottom surface of the cavity  310  of the mold  300 , and the lower surface of the base portion  34  is brought into contact with the bottom surface of the cavity  310  of the mold  300 . A composite material containing magnetic powder and a resin is loaded into the cavity  310  of the mold  300  in which the core in which the coil is mounted is put. In a state where the composite material is heated within the mold  300  to a temperature not lower than the softening temperature of the resin (for example, not lower than 60° C. and not higher than 150° C.), a pressure of not lower than 100 kg/cm 2  and not higher than 500 kg/cm 2  is applied to the composite material, and the composite material is further heated to a temperature equal to or higher than the curing temperature of the resin (for example, not lower than 100° C. and not higher than 220° C.) to be molded and cured, whereby the coil and the core are covered with the magnetic material, and an element assembly is formed by the coil, the core, and the magnetic material. Curing may be carried out after molding. 
     As a result of the molding/curing step, a recess (standoff) is formed on the mounting surface of the element assembly, and a curved portion is formed on the lower surface of the base portion and the mounting surface side of the wound portion of the coil so as to correspond to the recess. 
     When pressing, molding, and curing the composite material that is loaded into the mold and that contains the magnetic powder and the resin, in a state where the composite material is heated to a temperature not lower than the softening temperatures of the resin of the composite material and the insulating coating and the self-fusing layer of the conductive wire (for example, not lower than 60° C. and not higher than 150° C.), the composite material is pressed under a pressure of not lower than 100 kg/cm 2  and not higher than 500 kg/cm 2 , and heated to a temperature equal to or higher than the curing temperature of the resin of the composite material (for example, not lower than 100° C. and not higher than 220° C.) to be molded and cured, whereby the boundary surface between the upper stage and the lower stage of the wound portion of the coil is formed by a meandering surface at which the upper stage and the lower stage are arranged so as to be mutually nested. The meandering surface may be formed in a part of a region where the upper stage and the lower stage of the wound portion of the coil are in contact with or oppose each other. 
     Exterior Resin Forming Step 
     Next, an exterior resin is formed on the entire surface of the obtained element assembly. The exterior resin is formed by providing a thermosetting resin such as epoxy resin, a polyimide resin, and a phenol resin, or a thermoplastic resin such as a polyethylene resin and a polyamide resin to the surface by a means such as application, and dip; and curing the resin. 
     Exterior Resin Removing Step 
     The insulating coating of the conductive wire and the exterior resin at the positions at which external terminals are to be formed are removed from the element assembly on which the exterior resin is formed. The removal of the exterior resin and the insulating coating is carried out by using a physical means such as laser, blast processing, and polishing. 
     External Terminal Forming Step 
     The external terminals are formed by plating at the portions where the exterior resin is removed. The external terminals are formed by causing plating growth on the magnetic powder exposed on the surface and the extended portions  24  and  25  of the coil. As a result of the plating growth, for example, a first layer formed from nickel is formed, and then a second layer formed from tin is formed on the first layer. 
       FIG. 7  is a schematic partly transparent plan view, as viewed from the upper surface side, for explaining the different-shape portions of the pair of extended portions  24  and  25  of the surface-mount inductor  100  according to the first embodiment. In  FIG. 7 , the different-shape portions  28  and  29  that are wider than the wire width of the conductive wire and that are thinner than the thickness of the conductive wire are formed at the end portions of the pair of extended portions  24  and  25 , are bent at the positions of the cut portions of the base portion  34  from the middle of the different-shape portions  28  and  29 , and extend to the mounting surface side of the base portion  34 . Roots S from which the different-shape portions  28  and  29  are formed extend between the side surfaces and the wound portion of the coil at the upper surface side of the base portion  34 . 
       FIG. 8  is a schematic partly transparent plan view, as viewed from the upper surface side, for explaining another example of arrangement of the different-shape portions of the pair of extended portions  24  and  25  of the surface-mount inductor  100  according to the first embodiment. In  FIG. 8 , the different-shape portions  28  and  29  that are wider than the wire width of the conductive wire and that are thinner than the thickness of the conductive wire are formed at the end portions of the pair of extended portions  24  and  25 , are bent at the roots S from which the different-shape portions  28  and  29  are formed, that is, at the cut portions of the base portion  34 , and extend to the mounting surface side of the base portion  34 . Since the different-shape portions are bent at the roots S thereof, the extended portions  24  and  25  are easily bent at the positions at which the wire width and the thickness of the conductive wire are different, and stress when bending is reduced. Thus, it is possible to reduce the thickness of the base portion. Accordingly, it is possible to make the thicknesses of upper and lower magnetic paths of the wound portion equal to each other, a more uniform magnetic flux is obtained, and good magnetic characteristics are obtained. 
       FIG. 9  is a partly transparent perspective view, as viewed from the upper surface side, showing the surface-mount inductor  102 , which is the modification of the first embodiment. The surface-mount inductor  102  is configured in the same manner as the surface-mount inductor  100 , except that the pair of extended portions  24  and  25  are each disposed such that the flat surface portion connected to the flat surface portion disposed at an outer side portion of the conductive wire located at the outer peripheral portion of the wound portion  22  is close to the ridge portion R of the base portion  34 . In the surface-mount inductor  102 , similar to the surface-mount inductor  100 , the pair of extended portions  24  and  25  are extended from the outer periphery of the wound portion  22  toward the side surface  34 A on which the two cut portions  38  of the base portion  34  are provided. However, the extended portion  24  is extended from the portion connected to the wound portion  22  toward the ridge portion R of the base portion  34  so as to be twisted by about 90° clockwise as viewed from the wound portion side. The extended portion  25  is extended from the portion connected to the wound portion  22  toward the ridge portion R of the base portion  34  so as to be twisted by about 90° counterclockwise as viewed from the wound portion side. That is, the pair of extended portions  24  and  25  are each disposed such that one of the flat surface portions H of the conductive wire is close to the ridge portion R of the base portion  34 . 
     Since the extended portion  24  is extended so as to be twisted by about 90° clockwise as viewed from the wound portion side, and the extended portion  25  is extended so as to be twisted by about 90° counterclockwise as viewed from the wound portion side, the pair of extended portions  24  and  25  are extended so as to be twisted in directions opposite to each other, so that excessive stress is inhibited from being generated at the extended portions  24  and  25 . 
     Second Embodiment 
     A surface-mount inductor  104  according to a second embodiment will be described with reference to  FIG. 10 .  FIG. 10  is a schematic partly transparent perspective view, as viewed from the upper surface side, showing the surface-mount inductor  104 . The surface-mount inductor  104  is configured in the same manner as the surface-mount inductor  100 , except that the extended portion  25  is disposed such that the flat surface portion connected to the flat surface portion disposed at the outer side portion of the conductive wire located at the outer peripheral portion of the wound portion  22  is close to the ridge portion R of the base portion  34 . 
     In the surface-mount inductor  104 , similar to the surface-mount inductor  100 , the pair of extended portions  24  and  25  are extended from the outer periphery of the wound portion  22  toward the side surface  34 A on which the two cut portions  38  of the base portion  34  are provided. However, the extended portion  24  is extended from the portion connected to the wound portion  22  toward the ridge portion R of the base portion  34  so as to be twisted by about 90° counterclockwise as viewed from the wound portion side. The extended portion  25  is extended from the portion connected to the wound portion  22  toward the ridge portion R of the base portion  34  so as to be twisted by about 90° counterclockwise as viewed from the wound portion side. That is, the pair of extended portions  24  and  25  are extended so as to be twisted in the same direction. Accordingly, one of the extended portions is disposed such that one of the flat surface portions is close to the ridge portion R, and the other extended portion is disposed such that the other flat surface portion is close to the ridge portion R. Since the pair of extended portions is extended so as to be twisted in the same direction, the production process is simplified, and the productivity improves. 
     In the surface-mount inductor  104  in  FIG. 10 , the pair of extended portions  24  and  25  are each extended from the portion connected to the wound portion  22  toward the ridge portion R of the base portion  34  so as to be twisted by about 90° counterclockwise as viewed from the wound portion side, but may be extended so as to be twisted by about 90° clockwise as viewed from the wound portion side as a modification. 
     Third Embodiment 
     A surface-mount inductor  106  according to a third embodiment will be described with reference to  FIG. 11 .  FIG. 11  is a schematic partly transparent perspective view, as viewed from the upper surface side, showing the surface-mount inductor  106 . The surface-mount inductor  106  is configured in the same manner as the surface-mount inductor  100 , except that the cross-section orthogonal to the length direction of the conductive wire, which forms the coil, has a substantially square shape having a ratio of wire width and thickness of about 1; different-shape portions  28 A and  29 A are formed in the pair of extended portions  24  and  25  such that the wire width that is a surface adjacent to the surface, of the conductive wire, which opposes the columnar portion  32  of the core is larger than the thickness that is the surface, of the conductive wire, which opposes the columnar portion  32  of the core, by pressing the surface adjacent to the surface, of the conductive wire, which opposes the columnar portion  32  of the core; surfaces, of the different-shape portions  28 A and  29 A, which are connected to the surface adjacent to the surface, of the conductive wire, which opposes the columnar portion  32  of the core are close to the ridge portion R of the base portion  34 . 
     In the surface-mount inductor  106 , since the pair of extended portions  24  and  25  are not twisted, excessive stress is not generated at the extended portions, so that the positions at which the different-shape portions  28 A and  29 A are in contact with the ridge portion R of the base portion  34  are more stabilized. 
     Fourth Embodiment 
     A surface-mount inductor  108  according to a fourth embodiment will be described with reference to  FIG. 12 .  FIG. 12  is a schematic partly transparent perspective view, as viewed from the upper surface side, showing the surface-mount inductor  108 . The surface-mount inductor  108  is configured in the same manner as the surface-mount inductor  100 , except that the extended portions  24  and  25  are disposed such that the interval L 1  between the contact positions at which the pair of extended portions  24  and  25  are in contact with the ridge portion R of the base portion  34  is larger than the interval L 2  between the positions at which the wound portion  22  is connected to the extended portions  24  and  25 . The interval L 1  between the contact positions is the distance between the centers in the wire width direction of the pair of extended portions  24  and  25  at the ridge portion R of the base portion  34 , and the interval L 2  between the positions at which the wound portion  22  is connected to the extended portions  24  and  25  is the distance between the centers in the thickness direction of the conductive wire at the positions at which the wound portion  22  is connected to the extended portions  24  and  25 . 
     In the surface-mount inductor  108 , similar to the surface-mount inductor  100 , the pair of extended portions  24  and  25  are extended from the outer periphery of the wound portion  22  toward the side surface  34 A on which the two cut portions  38  of the base portion  34  are provided, but the pair of extended portions  24  and  25  are disposed so as to be extended such that the distance L 1  between the centers in the wire width direction of the pair of extended portions  24  and  25  increases from the end portion of the wound portion  22 , which is a connection portion between the wound portion  22  and each extended portion, toward the ridge portion R of the base portion  34 , in accordance with the distance from the wound portion  22 . Accordingly, it is possible to finely adjust the number of turns of the wound portion  22 , so that it is possible to adjust the inductance value to a smaller value. 
       FIG. 13  is a partly transparent perspective view, as viewed from the upper surface side, showing a surface-mount inductor  110  that is a modification of the fourth embodiment. The surface-mount inductor  110  is configured in the same manner as the surface-mount inductor  100 , except that the extended portions  24  and  25  are disposed such that the interval L 1  between the contact positions at which the pair of extended portions  24  and  25  are in contact with the ridge portion R of the base portion  34  is smaller than the interval L 2  between the positions at which the wound portion  22  is connected to the extended portions. In the surface-mount inductor  110 , similar to the surface-mount inductor  100 , the pair of extended portions  24  and  25  are extended from the outer periphery of the wound portion  22  toward the side surface  34 A on which the two cut portions  38  of the base portion  34  are provided, but the pair of extended portions  24  and  25  are disposed so as to be extended such that the distance L 1  between the centers in the wire width direction of the pair of extended portions  24  and  25  decreases from the end portion of the wound portion  22 , which is a connection portion between the wound portion  22  and each extended portion, toward the ridge portion R of the base portion  34 , in accordance with the distance from the wound portion  22 . Accordingly, it is possible to finely adjust the number of turns of the wound portion  22 , so that it is possible to adjust the inductance value to a higher value. 
     Fifth Embodiment 
     A surface-mount inductor  112  according to a fifth embodiment will be described with reference to  FIG. 14 .  FIG. 14  is a schematic partly transparent perspective view, as viewed from the upper surface side, showing the surface-mount inductor  112 . The surface-mount inductor  112  is configured in the same manner as the surface-mount inductor  100 , except that the pair of extended portions  24  and  25  are extended toward different ridge portions of the base portion  34 . 
     In the surface-mount inductor  112 , cut portions  38 A and  38 B for housing the extended portions  24  and  25  of the coil  20  and allowing the extended portions  24  and  25  to extend to the lower surface side are formed on the side surface  34 A of the base portion  34  of the core  30  and a side surface  34 B orthogonal to the side surface  34 A. Regarding the pair of extended portions  24  and  25 , the extended portion  24  and the extended portion  25  are extended toward the side surface  34 B of the base portion  34  and the side surface  34 A of the base portion  34 , respectively, and are disposed close to ridge portions, of the base portion  34 , which are orthogonal to each other. At this time, the pair of extended portions  24  and  25  are each disposed such that one of the flat surface portions of the conductive wire is close to the ridge portion. In addition, at this time, the angular difference between the extended direction of the extended portion  24  and the extended direction of the extended portion  25  with the winding axis A as an origin is not less than about 90 degrees. The pair of extended portions  24  and  25  are housed in the cut portions  38 A and  38 B, respectively, turn back, and extend to the mounting surface side of the base portion  34 . 
     Since the pair of extended portions  24  and  25  are extended toward the ridge portions, of the base portion  34 , which are orthogonal to each other, it is possible to change the number of turns of the wound portion  22  of the coil per ¼ turn. 
       FIG. 15  is a partly transparent perspective view, as viewed from the upper surface side, showing a surface-mount inductor  114  that is a modification of the fifth embodiment. In the surface-mount inductor  114 , cut portions  38 B and  38 D for housing the extended portions  24  and  25  of the coil  20  and allowing the extended portions  24  and  25  to extend to the lower surface side are formed on side surfaces  34 B and  34 D that are orthogonal to the opposing side surfaces  34 A and  34 C of the base portion  34  of the core  30  and that oppose each other. Regarding the pair of extended portions  24  and  25 , the extended portion  24  and the extended portion  25  are extended toward the side surface  34 B of the base portion  34  and the side surface  34 D of the base portion  34 , respectively, and are disposed close to ridge portions, of the base portion  34 , which oppose each other. At this time, the pair of extended portions  24  and  25  are each disposed such that one of the flat surface portions of the conductive wire is close to the ridge portion. In addition, at this time, the angular difference between the extended direction of the extended portion  24  and the extended direction of the extended portion  25  with the winding axis A as an origin is not less than about 90 degrees and not greater than about 180 degrees (i.e., from about 90 degrees to about 180 degrees). The pair of extended portions  24  and  25  are housed in the cut portions  38 B and  38 D, respectively, turn back, and extend to the mounting surface side of the base portion  34 . 
     Since the pair of extended portions  24  and  25  are extended toward the ridge portions, of the base portion  34 , which oppose each other, it is possible to change the number of turns of the wound portion of the coil per ½ turn. In  FIG. 15 , the pair of extended portions  24  and  25  are extended in the length L direction of the surface-mount inductor  114 , but may be extended in the width W direction. 
     Sixth Embodiment 
     A surface-mount inductor  116  according to a sixth embodiment will be described with reference to  FIG. 16 .  FIG. 16  is a schematic cross-sectional view showing the surface-mount inductor  116 , and is a schematic cross-sectional view taken along a plane that is orthogonal to the length L direction of the surface-mount inductor  116 , that is parallel to the winding axis A of the wound portion  22  of the coil, and that longitudinally traverses a recess extending in the width W direction. The surface-mount inductor  116  is configured in the same manner as the surface-mount inductor  100 , except that the end surface, of a columnar portion  32 A of the core, at the side opposite to a first base portion  34 A is exposed on the surface of the element assembly  10 . In the surface-mount inductor  116 , when the magnetic permeability of the columnar portion  32 A is higher than those of the magnetic material  11  and the base portion  34 , since the columnar portion  32 A are extended to the upper surface of the surface-mount inductor  116 , the region in which the magnetic permeability is high is increased, so that, for example, the inductance value improves. 
     In other words, the surface-mount inductor  116  is configured to include the element assembly  10  having a core having the columnar portion  32 A and the first base portion  34 A that are formed from the same composite material under the same pressing condition; a coil having the wound portion  22 ; and the magnetic material  11  covering the wound portion  22 . The upper end surface of the columnar portion  32 A is exposed from the upper surface of the surface-mount inductor  116 , and the columnar portion  32 A extends between the upper surface and the lower surface of the surface-mount inductor  116 . The first base portion  34 A is formed in a flange shape so as to be continuous from the lower end surface of the columnar portion  32 A. The wound portion  22  of the coil is formed from a conductive wire wound such that the flat surface portion thereof is opposed to the columnar portion  32 A, and is disposed at the upper surface side of the first base portion  34 A. In the surface-mount inductor  116 , the upper surface and the side surface of the wound portion  22  are covered with the magnetic material  11  having lower magnetic permeability than the core. 
       FIG. 17  is a schematic cross-sectional view showing a surface-mount inductor  118  that is a modification of the sixth embodiment.  FIG. 17  is a schematic cross-sectional view taken along a plane that is orthogonal to the length L direction of the surface-mount inductor  118 , that is parallel to the winding axis A of the wound portion  22  of the coil, and that longitudinally traverses a recess extending in the width W direction. The surface-mount inductor  118  is configured in the same manner as the surface-mount inductor  100 , except that the end surface, of the core, at the side opposite to the first base portion  34 A of a columnar portion  32 B is exposed on the surface of the element assembly  10 , and the core has a second base portion  34 B that has an upper surface continuous from the end surface of the columnar portion  32 B, that has an area larger than that of the end surface and smaller than that of the first base portion  34 A, and that is formed in a flange shape to have a thickness less than the height of the columnar portion  32 B. Since the core has the second base portion  34 B, the second base portion  34 B serves as a guide at the upper stage side for the wound portion  22  when forming the wound portion  22 , so that it is possible to more efficiently and more easily form the wound portion  22 . 
     In other words, the surface-mount inductor  118  is configured to include the element assembly  10  having a core having the columnar portion  32 B, the first base portion  34 A, and the second base portion  34 B that are formed from the same composite material under the same pressing condition; a coil having the wound portion  22 ; and the magnetic material  11  covering the wound portion  22 . The upper end surface of the columnar portion  32 B is exposed from the upper surface of the surface-mount inductor  118 , and the columnar portion  32 B extends between the upper surface and the lower surface of the surface-mount inductor  118 . The first base portion  34 A is formed in a flange shape so as to be continuous from the lower end surface of the columnar portion  32 A. The second base portion  34 B has an upper surface continuous from the upper end surface of the columnar portion  32 B, has an area larger than that of the end surface of the columnar portion  32 B and smaller than that of the first base portion  34 A, and is formed in a flange shape to have a thickness less than the height of the columnar portion  32 B. The wound portion  22  of the coil is formed from a conductive wire wound such that the flat surface portion is opposed to the columnar portion  32 B, and is disposed between the upper surface of the first base portion  34 A and the second base portion  34 B. In the surface-mount inductor  118 , the side surface of the wound portion  22  is covered with the magnetic material  11  having lower magnetic permeability than the core. 
     The surface-mount inductor  118  is configured such that the second base portion  34 B is formed in a flat plate shape and the outermost peripheral surface of the wound portion  22  and the side surface in the thickness direction of the second base portion  34 B are substantially flush with each other. Accordingly, fillability of the composite material for forming the element assembly  10  is improved. In a modification of the surface-mount inductor  118 , the outermost peripheral surface of the wound portion  22  may be located inward or outward of the side surface of the second base portion  34 B. 
     Seventh Embodiment 
     A surface-mount inductor  120  according to a seventh embodiment will be described with reference to  FIG. 18 .  FIG. 18  is a schematic cross-sectional view showing the surface-mount inductor  120 , and is a schematic cross-sectional view taken along a plane that is orthogonal to the length L direction of the surface-mount inductor  120 , that is parallel to the winding axis A of the wound portion  22  of the coil, and that longitudinally traverses a recess extending in the width W direction. The surface-mount inductor  120  is configured in the same manner as the surface-mount inductor  100 , except that the end surface, of the columnar portion  32 A of the core, at the side opposite to the base portion  34  is exposed on the surface of the element assembly  10 , the upper surface of the wound portion  22  of the coil is exposed on the surface of the element assembly  10 , and a layer  12  that covers the end surface of the columnar portion  32 A, the upper surface of the wound portion  22 , and the upper surface of the element assembly  10  and that does not substantially contain magnetic powder is included. Since the layer  12  that does not substantially contain magnetic powder is included, a magnetic flux generated by the coil is blocked by the layer  12  that does not substantially contain magnetic powder, that is, a so-called open magnetic circuit is formed, so that the direct current superposition characteristics are further improved. 
     The layer  12  that does not substantially contain magnetic powder is formed from a resin that does not contain magnetic powder, but may contain a silica filler, an alumina filler, a non-magnetic ceramic filler, or the like instead of magnetic powder. Accordingly, the strength of the surface-mount inductor  120  is further improved. The layer  12  that does not substantially contain magnetic powder may be disposed by forming a known insulating film. 
       FIG. 19  is a schematic cross-sectional view showing a surface-mount inductor  122  that is a modification of the seventh embodiment.  FIG. 19  is a schematic cross-sectional view taken along a plane that is orthogonal to the length L direction of the surface-mount inductor  122 , that is parallel to the winding axis A of the wound portion  22  of the coil, and that longitudinally traverses a recess extending in the width W direction. The surface-mount inductor  122  is configured in the same manner as the surface-mount inductor  100 , except that a base portion  34 C does not substantially contain magnetic powder. Since the base portion  34 C that does not substantially contain magnetic powder is included, a magnetic flux generated by the coil is blocked by the base portion  34 C that does not substantially contain magnetic powder, that is, a so-called field path structure is formed, so that the direct current superposition characteristics are further improved. 
     The base portion  34 C is formed from a resin that does not contain magnetic powder, but may contain a silica filler, an alumina filler, a non-magnetic ceramic filler, or the like instead of magnetic powder. Accordingly, the strength of the surface-mount inductor  122  is further improved. In  FIG. 19 , the entirety of the base portion  34 C does not substantially contain magnetic powder, but the base portion  34 C may be formed such that a partial region of the base portion  34 C does not substantially contain magnetic powder and the other region contains magnetic powder, for example, by forming a region that penetrates the lower end surface of the columnar portion  32  and the base portion  34 C, that has an area equal to, smaller than, or larger than that of the lower end surface of the columnar portion  32 , and that does not substantially contain magnetic powder, by forming a region that does not substantially contain magnetic powder, in an upper portion of the base portion  34 C, or by forming a region that does not substantially contain magnetic powder, in a lower portion of the base portion  34 C. 
     The core including the base portion  34 C is produced, for example, as described below. A composite material containing magnetic powder and a resin is loaded into a second portion of a cavity of a mold that includes the cavity having a first portion capable of forming a columnar portion and a flat plate-shaped base portion and having a shape and a depth for forming the base portion and the second portion provided on the bottom surface of the first portion and having a shape and a depth for forming the columnar portion, as shown in  FIGS. 5A and 5B . Next, a non-magnetic composite material containing a resin and a filler such as a silica filler, an alumina filler, and a non-magnetic ceramic filler is loaded into the first portion of the cavity of the mold. Then, molding is performed using the mold. Accordingly, a core having a base portion in which a region that does not contain magnetic powder is formed and a columnar portion that contains the magnetic powder and the resin and that is integrally formed with the base portion, is produced. 
       FIG. 20  is a schematic cross-sectional view showing a surface-mount inductor  124  that is a modification of the seventh embodiment.  FIG. 20  is a schematic cross-sectional view taken along a plane that is orthogonal to the length L direction of the surface-mount inductor  124 , that is parallel to the winding axis A of the wound portion  22  of the coil, and that longitudinally traverses a recess extending in the width W direction. The surface-mount inductor  124  is configured in the same manner as the surface-mount inductor  100 , except that a columnar portion  32 C does not substantially contain magnetic powder. Since the columnar portion  32 C that does not substantially contain magnetic powder is included, a magnetic flux generated by the coil is blocked by the columnar portion  32 C that does not substantially contain magnetic powder, that is, a so-called field path structure is formed, so that the direct current superposition characteristics are further improved. 
     The columnar portion  32 C is formed from a resin that does not contain magnetic powder, but may contain a silica filler, an alumina filler, a non-magnetic ceramic filler, or the like instead of magnetic powder. Accordingly, the strength of the surface-mount inductor  124  is further improved. In  FIG. 20 , the entirety of the columnar portion  32 C does not substantially contain magnetic powder, but the columnar portion  32 C may be formed such that a partial region of the columnar portion  32 C does not substantially contain magnetic powder and the other region contains magnetic powder, by forming a region that extends in a direction orthogonal to the winding axis A of the wound portion  22  of the coil and that does not substantially contain magnetic powder. 
     The core including the columnar portion  32 C is produced, for example, as described below. A non-magnetic composite material containing a resin and a filler such as a silica filler, an alumina filler, and a non-magnetic ceramic filler is loaded into a second portion of a cavity of a mold that includes the cavity having a first portion capable of forming a columnar portion and a flat plate-shaped base portion and having a shape and a depth for forming the base portion and the second portion provided on the bottom surface of the first portion and having a shape and a depth for forming the columnar portion, as shown in  FIGS. 5A and 5B . Next, a composite material containing magnetic powder and a resin and a filler is loaded into the first portion within the cavity of the mold. Then, molding is performed using the mold. Accordingly, a core having a columnar portion in which a region that does not contain magnetic powder is formed and a base portion that contains magnetic powder and that is integrally formed with the columnar portion, is produced. 
     Eighth Embodiment 
     A surface-mount inductor  126  according to an eighth embodiment will be described with reference to  FIG. 21 .  FIG. 21  is a schematic cross-sectional view showing the surface-mount inductor  126 , and is a schematic cross-sectional view taken along a plane that is orthogonal to the length L direction of the surface-mount inductor  126 , that is parallel to the winding axis A of the wound portion  22  of the coil, and that longitudinally traverses a recess extending in the width W direction. The surface-mount inductor  126  is configured in the same manner as the surface-mount inductor  100 , except that the magnetic powder contained in the core includes metallic magnetic powder; and in a partial region at the mounting surface side of the base portion  34  of the core, a high-insulation region  34 D in which the content of the metallic magnetic powder is less than that in the other region of the base portion  34  or in which no metallic magnetic powder is contained is formed. Since the high-insulation region  34 D is provided at the mounting surface side of the base portion  34 , it is possible to further improve a dielectric breakdown voltage between the wound portion  22  and the external terminals  40  and  41  disposed at the mounting surface side. 
     In the core in which the content of the metallic magnetic powder in the high-insulation region  34 D is low, for example, the high-insulation region  34 D is formed by increasing the content of a resin. In addition, in the case of the core in which the content of the metallic magnetic powder in the high-insulation region  34 D is low, a filler having insulation properties may be contained. Furthermore, in the core in which the high-insulation region  34 D contains no metallic magnetic powder, for example, the high-insulation region  34 D is formed from an insulating material composed of only a resin, or an insulating material containing a resin and a filler having insulation properties such as a silica filler and a ferrite filler instead of the metallic magnetic powder. 
     The core including the high-insulation region  34 D is s produced, for example, as described below. A metallic magnetic material containing metallic magnetic powder and a resin is loaded into a second portion and the bottom surface side of a first portion within a cavity of a mold that includes the cavity having the first portion capable of forming a columnar portion and a flat plate-shaped base portion and having a shape and a depth for forming the base portion and the second portion provided on the bottom surface of the first portion and having a shape and a depth for forming the columnar portion, as shown in  FIGS. 5A and 5B . Next, a metallic magnetic material having an increased content ratio of a resin, an insulating material composed of only a resin, or an insulating material containing a resin and a filler having insulation properties such as a silica filler and a ferrite filler instead of the metallic magnetic powder, is loaded into the upper surface side of the first portion within the cavity of the mold. Then, molding is performed using the mold. Accordingly, a core having a base portion in which a high-insulation region is formed at the mounting surface side and a columnar portion that contains the metallic magnetic powder and the resin and that is integrally formed with the base portion, is produced. 
       FIG. 22  is a schematic cross-sectional view showing a surface-mount inductor  128  that is a modification of the eighth embodiment.  FIG. 22  is a schematic cross-sectional view taken along a plane that is orthogonal to the width W direction of the surface-mount inductor  128 , that is parallel to the winding axis A of the wound portion  22  of the coil, and that laterally traverses a recess extending in the width W direction. The surface-mount inductor  128  is configured in the same manner as the surface-mount inductor  100 , except that the magnetic powder contained in the core includes metallic magnetic powder and a high-insulation region  34 E is formed by disposing an insulating film at the mounting surface side of the base portion  34  of the core. Since the high-insulation region is formed by the insulating film, it is possible to easily and efficiently form a high-insulation region at the mounting surface side of the base portion  34  of the core. 
       FIG. 23  is a schematic cross-sectional view showing a surface-mount inductor  130  that is a modification of the eighth embodiment.  FIG. 23  is a schematic cross-sectional view taken along a plane that is orthogonal to the width W direction of the surface-mount inductor  130 , that is parallel to the winding axis A of the wound portion  22  of the coil, and that laterally traverses a recess extending in the width W direction. The surface-mount inductor  130  is configured in the same manner as the surface-mount inductor  100 , except that the magnetic powder contained in the core includes metallic magnetic powder and a high-insulation region  34 E is formed by disposing an insulating film at the mounting surface side of the base portion  34  of the core in the region in which the external terminals  40  and  41  are formed. Since the high-insulation region is formed by the insulating film, it is possible to easily and efficiently form a high-insulation region at the mounting surface side of the base portion  34  of the core. In addition, it is possible to make the area of the high-insulation region to be formed smaller, and thus the productivity improves. 
     In the surface-mount inductor  130 , the pair of extended portions  24  and  25  extending at the mounting surface side are disposed on the high-insulation region  34 E and separated from the base portion  34  of the core containing the metallic magnetic powder. The external terminals  40  and  41  are formed on the pair of extended portions  24  and  25  extending at the mounting surface side, for example, by plating. 
     Ninth Embodiment 
     A surface-mount inductor  132  according to a ninth embodiment will be described with reference to  FIG. 24 .  FIG. 24  is a schematic partly transparent plan view, as viewed from the upper surface side, showing the surface-mount inductor  132 . The surface-mount inductor  132  is configured in the same manner as the surface-mount inductor  100 , except that the columnar portion  32  of a core  30 A is disposed closer to a first linear portion  38  (ridge portion) at the side at which the pair of extended portions  24  and  25  are extended, than to a second linear portion  39  (another ridge portion) opposing the first linear portion  38 . Since the columnar portion  32  of the core  30 A is unevenly disposed at the linear portion side at which the pair of extended portions  24  and  25  are extended, the magnetic flux balance in the element assembly becomes better. 
     In the wound portion  22  of the coil of the surface-mount inductor  132 , the number of turns at the side that is closer to the second linear portion  39  and that is the side opposite to the first linear portion  38  of the base portion  34  at which the pair of extended portions  24  and  25  are extended, is larger than the number of turns at the side closer to the first linear portion  38 , by one. 
     In addition, in the surface-mount inductor  132 , the columnar portion  32  is disposed such that a straight line L 2  to which distances W 3  and W 4  from both side surfaces of the columnar portion  32  orthogonal to the width W direction of the surface-mount inductor  132  are equal to each other and that passes through the center of the columnar portion  32  is closer to the first linear portion  38  by at least a distance equal to the thickness of the conductive wire that forms the coil, than a straight line L 1  to which distances W 1  and W 2  from the first linear portion  38  and the second linear portion  39  of the base portion  34  of the core are equal to each other and that passes through the center of the base portion  34 . Accordingly, the wound portion  22  is disposed such that the shortest distances between the outer peripheral portion of the wound portion  22  and the first linear portion  38  and the second linear portion  39  are substantially equal to each other, and the balance of a magnetic flux in the surface-mount inductor  132  becomes good. In addition, the outer peripheral portion of the wound portion  22  is inhibited from being exposed from the side surface of the element assembly. 
     Tenth Embodiment 
     A surface-mount inductor  134  according to a tenth embodiment will be described with reference to  FIG. 25 .  FIG. 25  is a schematic cross-sectional view showing the surface-mount inductor  134 .  FIG. 25  is a schematic cross-sectional view taken along a cross-section that is orthogonal to the length L direction of the surface-mount inductor  134 , that is parallel to the winding axis A of the wound portion  22  of the coil, and that longitudinally traverses a recess extending in the width W direction. The surface-mount inductor  134  is configured in the same manner as the surface-mount inductor  100 , except that the number of turns at the upper stage side and the number of turns at the lower stage side of a wound portion  22 A of the coil wound in two upper and lower stages are different from each other. 
     In the surface-mount inductor  134 , the side of the coil at which the number of turns is larger is disposed in contact with the base portion  34  of the core. That is, the number of turns at the lower stage side is larger than the number of turns at the upper stage side. Since the number of turns at the upper stage side is smaller, when forming the element assembly  10 , the composite material is able to sufficiently flow around, and the fillability of the composite material improves, so that better magnetic characteristics are obtained. 
       FIG. 26  is a schematic cross-sectional view showing a surface-mount inductor  136  that is a modification of the tenth embodiment.  FIG. 26  is a schematic cross-sectional view taken along a cross-section that is orthogonal to the length L direction of the surface-mount inductor  136 , that is parallel to the winding axis A of the wound portion  22  of the coil, and that longitudinally traverses a recess extending in the width W direction. The surface-mount inductor  136  is configured in the same manner as the surface-mount inductor  100 , except that a columnar portion  32 D of the core is formed in two stages having different outer diameters and the number of turns at the upper stage side and the number of turns at the lower stage side of a wound portion  22 B of the coil wound in two upper and lower stages are different from each other. 
     In the surface-mount inductor  136 , since the columnar portion  32 D is formed such that the outer diameter of the columnar portion  32 D at the side closer to the base portion  34  of the core is larger, the strength of the core improves, so that it is possible to more stably wind the conductive wire. 
     Eleventh Embodiment 
     A surface-mount inductor  140  according to an eleventh embodiment will be described with reference to  FIG. 27 .  FIG. 27  is a partly transparent plan view of the surface-mount inductor  140  as viewed from the mounting surface side. The surface-mount inductor  140  is configured in the same manner as the surface-mount inductor  100 , except that, on the bottom surface of the base portion  34  of the core  30 , a first electrode covering a root portion of the extended portion  24  that is turned back from the upper surface of the base portion  34 , a second electrode covering an end portion of the extended portion  24 , a third electrode covering a root portion of the extended portion  25  that is turned back from the upper surface of the base portion  34 , and a fourth electrode covering an end portion of the extended portion  25  are formed, and an external terminal  40  covering the extended portion  24 , the first electrode, and the second electrode and an external terminal  41  covering the extended portion  25 , the third electrode, and the fourth electrode are formed. Each of the first to fourth electrodes is formed, for example, from a resin containing metallic particles such as silver powder. Accordingly, each external terminal is connected to the electrodes and the extended portion. In this case, the external terminals  40  and  41  may be formed by peeling off the exterior resin on a portion of the mounting surface of the element assembly on which each external terminal is to be formed, applying a resin containing metallic particles onto the extended portions  24  and  25  to form electrodes, and causing plating growth on these. 
     In the above embodiments, the shape of the upper surface of the base portion is substantially a rectangle having a cut portion, but may be substantially a square, a circle, an oval, an ellipse, a polygon, or the like. 
     The wound portion of the coil may be formed such that the winding direction thereof is counterclockwise as viewed from the upper surface side. 
     In the first to eleventh embodiments, the upper stage and the lower stage of the coil may be turned upside down and disposed on the base portion of the core. 
     In the first to tenth embodiments, as shown in  FIG. 27 , the pair of extended portions  24  and  25  may be disposed on regions of the bottom surface of the base portion  34  of the core  30  at both sides of the recess  36 , a first electrode covering a root portion of the extended portion  24  that is turned back from the upper surface of the base portion  34 , a second electrode covering an end portion of the extended portion  24 , a third electrode covering a root portion of the extended portion  25  that is turned back from the upper surface of the base portion  34 , and a fourth electrode covering an end portion of the extended portion  25  may be formed, on the bottom surface of the base portion  34  of the core  30 , and an external terminal  40  covering the first electrode, and the second electrode of the extended portion  24 , and an external terminal  41  covering the third electrode, and the fourth electrode of the extended portion  25  may be formed on the bottom surface of the base portion  34  of the core  30 . 
     While preferred embodiments of the disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The scope of the disclosure, therefore, is to be determined solely by the following claims.