Patent Publication Number: US-2021166862-A1

Title: Coil device

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a winding-type coil device. 
     As a winding-type coil device, for example, a coil device shown in Patent Document 1 is known. In the coil device of Patent Document 1, terminal fittings are attached to flanges, a lead end of a wire is connected to the terminal fittings, and the coil device can be mounted on a board via the terminal fittings. In the coil device of Patent Document 1, however, the terminal fittings are fixed to the flanges only via adhesive and may come off from the flanges when the board vibrates or deforms after mounting. 
     Patent Document 1: JP2018056399 (A) 
     BRIEF SUMMARY OF INVENTION 
     The present invention has been achieved under such circumstances. It is an object of the invention to provide a coil device capable of improving the reliability of fixation between a terminal fitting and a flange. 
     To achieve the above object, a coil device according to the present invention includes: 
     a winding core wound by a wire; 
     a flange formed at an end of the winding core in its axial direction; and 
     a terminal fitting attached to the flange, 
     wherein the terminal fitting includes an engagement part engaged with a circumferential wall part of the flange. 
     In the coil device according to the present invention, the terminal fitting includes an engagement part engaged with a circumferential wall part of the flange. Since the engagement part is engaged with the circumferential wall part of the flange, the terminal fitting can firmly be fixed to the flange and is hard to come off from the flange even if a board (a board for mounting the coil device) vibrates or deforms after mounting. Thus, the coil device according to the present invention can improve the reliability of fixation between the terminal fitting and the flange. 
     Preferably, the engagement part includes a pair of clamping pieces, and the pair of clamping pieces clamps the circumferential wall part of the flange from outside. In this structure, the engagement strength of the engagement part for the flange can be increased, and the terminal fitting can be fixed to the flange more firmly. 
     Preferably, the pair of clamping pieces clamps an inner end surface and an outer end surface of the flange from a side of the flange. In this structure, the terminal fitting can be fixed to the side of the flange, the coil device can be prevented from being larger due to the attachment of the terminal fitting, and the low profile of the coil device can be achieved. 
     Preferably, the terminal fitting includes a protrusion plate part including a wire connection surface to which a lead end of the wire is connected and a main mounting surface located opposite to the wire connection surface and being connectable to an external circuit. In this structure, the connection surface and the main mounting surface are substantially close to each other only with the thickness of the protrusion plate part, and it is possible to extremely reduce a DC resistance of the terminal fitting from the connection part of the lead end of the wire to an external circuit and to extremely reduce a DC resistance of the coil device as a whole. Thus, the coil device according to the present invention can also favorably be used for power supply applications. 
     Even when the coil device according to the present invention is used for signal system applications, the increase in insertion loss (IL) can be restrained, and the coil device according to the present invention can also favorably be used for signal system applications. 
     Preferably, the protrusion plate part includes a mounting base part extending in parallel to the external circuit and a tip bending part bending in turn back manner at a tip of the base part, and the lead end of the wire is sandwiched between the mounting base part and the tip bending part. When the lead end of the wire is sandwiched between the tip bending part and the mounting base part, the lead end is easily connected to the terminal fitting. 
     Preferably, the protrusion plate part includes a connection base part connecting the engagement part and the mounting base part. In this structure, a stress generated by vibration, deformation, etc. of the board can be reduced (absorbed) via the connection base part, and it is possible to effectively prevent the terminal fitting from coming off from the flange. In addition, when the connection base part is disposed between the engagement part and the mounting base part, the engagement part and the mounting base part can be separated from each other, and the above-mentioned reduction effect on the stress can be obtained effectively. 
     Preferably, a slit is formed near the engagement part. In this structure, a stress generated by vibration, deformation, etc. of the board can be prevented from traveling to the engagement part or so, and it is possible to effectively prevent the terminal fitting from coming off from the flange. 
     Preferably, the terminal fitting is narrow at a location of the slit. In this structure, the above-mentioned stress can effectively be prevented from traveling at the location of the slit, and the reduction effect of the slit can be enhanced. 
     Preferably, the flange is partly contacted with a rear surface of the terminal fitting located opposite to an external circuit. In this structure, the terminal fitting can be supported from behind by a part of the flange, and it is possible to prevent the deformation of the terminal fitting due to a stress generated by vibration, deformation, or the like of the board. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1A  is a perspective view of a coil device according to First Embodiment of the present invention; 
         FIG. 1B  is a lateral view of the coil device shown in  FIG. 1A ; 
         FIG. 1C  is a front view of the coil device shown in  FIG. 1A ; 
         FIG. 1D  is a bottom view of the coil device shown in  FIG. 1A ; 
         FIG. 2A  is a perspective view of a drum-type core of the coil device shown in  FIG. 1A ; 
         FIG. 2B  is a perspective view of the drum-type core shown in  FIG. 2A  from below; 
         FIG. 3  is a perspective view of a terminal metal fitting of the coil device shown in  FIG. 1A ; 
         FIG. 4  is a perspective view of a coil device according to Second Embodiment of the present invention; 
         FIG. 5A  is a perspective view of a drum-type core of the coil device shown  FIG. 4 ; 
         FIG. 5B  is a perspective view of the drum-type core shown in  FIG. 5A  from below; 
         FIG. 6A  is a perspective view of a coil device according to Third Embodiment of the present invention; 
         FIG. 6B  is a lateral view of the coil device shown in  FIG. 6A ; 
         FIG. 6C  is a front view of the coil device shown in  FIG. 6A ; and 
         FIG. 7  is a perspective view of a terminal metal fitting of the coil device shown in  FIG. 6A . 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     Hereinafter, the present invention is explained based on the embodiments shown in the figures. 
     First Embodiment 
     A coil device  10  according to First Embodiment of the present invention shown in  FIG. 1A  is used for any purposes and is used as, for example, a winding-type common mode filter. The coil device  10  can also be used as a balun, a dual inductor, etc. 
     The coil device  10  includes a drum core  20 , a coil unit  40  wound around a winding core  22  of the drum core  20 , and a flat plate-like member  30  disposed on the drum core  20 . In the explanation of the coil device  10 , the X-axis direction is a direction parallel to a main mounting surface for the coil device  10  and to the winding axis of the winding core  22  of the drum core  20 , the Y-axis direction is a direction parallel to the main mounting surface as similarly to the X-axis and perpendicular to the X-axis, and the Z-axis is a normal direction of the main mounting surface. 
     As shown in  FIG. 2A  and  FIG. 2B , the drum core  20  includes the winding core  22  having a bar shape extending in the X-axis direction and a first flange  24  and a second flange  26  as a pair of core ends arranged on both ends of the winding core  22 . The first flange  24  and the second flange  26  have substantially the same shape and are arranged in the winding core  22  so as to substantially be parallel to each other with a predetermined space in the X-axis direction. 
     The winding core  22  is connected to a substantially central area of each of surfaces of the pair of flanges  24  and  26  facing each other and is integrated with the pair of flanges  24  and  26 . In the present embodiment, the winding core  22  has a rectangular cross-sectional shape, but may have any cross-sectional shape, such as circular. 
     Preferably, a plate-like member  30  shown in  FIG. 1A  is attached to an upper end of the drum core  20  in the Z-axis direction. Preferably, the plate-like member  30  is attached to an anti-mounting-side core surface  24   b  of the first flange  24  and an anti-mounting-side core surface  26   b  of the second flange  26  so as to bridge these anti-mounting-side core surfaces. 
     In the present embodiment, as shown in  FIG. 2A  and  FIG. 2B , the first flange  24  is structured by a substantially rectangular parallelepiped as a whole, and notches  24   c   1  and notches (steps)  24   f   2  are formed at lower parts (or central parts) of the substantially rectangular parallelepiped shape on both sides in the Y-axis direction. The first flange  24  includes a mounting-side core surface  24   a  (lower surface in the Z-axis direction), the anti-mounting-side core surface  24   b  located opposite to the mounting-side core surface  24   a,  an outer end surface  24   c  in the X-axis direction, an inner surface (inner end surface)  24   d  facing the winding core  22 , a pair of lateral surfaces  24   e  and  24   e  located opposite to each other in the Y-axis direction, and a pair of step surfaces  24   f  and  24   f  formed at central parts on both sides in the Y-axis direction. 
     The notches  24   c   1  are formed on the outer end surface  24   c.  As shown in  FIG. 1C , a protrusion plate part  51   b  of a terminal  51  can partly be disposed (contained) in each of the notches  24   c   1 . 
     As shown in  FIG. 2A  and  FIG. 2B , a terminal attachment surface  24   f   1  is formed on the step surfaces  24 . The terminal attachment surface  24   f   1  is formed by forming the notches (steps)  24   f   2  on the outer end surface  24   c,  the inner surface  24   d,  and the lateral surfaces  24   e  and  24   e.  The terminal attachment surface  24   f   1  of the outer end surface  24   c  and the inner surface  24   d  is dented inward in the X-axis direction (toward the central part of the flange  24  in the X-axis direction), and the terminal attachment surface  24   f   1  of the lateral surfaces  24   e  is dented toward the inner side of the flange  24  in the Y-axis direction (toward the central part of the flange  24  in the Y-axis direction). The step depth of the terminal attachment surface  24   f   1  dented from the outer end surface  24   c  and the inner surface  24   d  toward the inner side in the X-axis direction is preferably as large as a plate thickness of the terminal  51  (engagement part  51   a ) shown in  FIG. 3 , but may be smaller or larger than the plate thickness. This is also the case with the step depth of the terminal attachment surface  24   f   1  dented from the lateral surfaces  24   e  and  24   e  toward the inner side in the Y-axis direction. 
     Incidentally, each surface constituting the terminal attachment surface  24   f   1  is regarded as a part of the outer end surface  24   c,  the inner surface  24   d,  and the lateral surfaces  24   e.  Thus, the terminal attachment surface  24   f   1  is formed over the outer end surface  24   c,  the inner surface  24   d,  and the lateral surfaces  24   e.  The terminal attachment surface  24   f   1  is engaged with engagement parts  51   a  of the terminals  51  shown in  FIG. 3 . If necessary, the fixation of the engagement parts  51   a  to the terminal attachment surface  24   f   1  is reinforced by adhesion. 
     As shown in  FIG. 3 , each of the terminals  51  is structured by a conductive terminal plate or so and includes the engagement part  51   a  and the protrusion plate part  51   b  formed by bending a sheet of conductive plate-like member of a metal plate or so. 
     Each of the engagement part  51   a  has a substantially C shape and is engaged with the terminal attachment surface  24   f   1  formed on each of the step surfaces  24   f  shown in  FIG. 2A  and  FIG. 2B . As shown in  FIG. 1A , each of the engagement parts  51   a  is engaged with a circumferential wall part (peripheral part) of the flange  24  and is attached over a lateral part (lateral surface  24   e ), an inner part (inner surface  24   d ), and an outer part (outer end surface  24   c ) of the terminal attachment surface  24   f   1  shown in  FIG. 2A  and  FIG. 2B . As shown in  FIG. 1C , the lower ends of the engagement parts  51   a  in the Z-axis direction protrude from those of the step surfaces  24   f  and  24   f  in the Z-axis direction. 
     As shown in  FIG. 3 , each of the engagement parts  51   a  includes a pair of clamping pieces  51   a   1  and  51   a   1 . The pair of clamping pieces  51   a   1  and  51   a   1  clamps a circumferential wall part of the flange  24  shown in  FIG. 1A  from outside. For more detail, the pair of clamping pieces  51   a   1  and  51   a   1  clamps the inner surface  24   d  and the outer end surface  24   c  of the flange  24  shown in  FIG. 2A  and  FIG. 2B  from the side of the flange  24  (surfaces on both sides of the terminal attachment surface  24   f   1  in the X-axis direction). The distance between the clamping pieces  51   a   1  and  51   a   1  in the X-axis direction is as large as or smaller than a width of the terminal attachment surface  24   f   1  in the X-axis direction. 
     In the example of  FIG. 3 , the distance between the pair of clamping pieces  51   a   1  and  51   a   1  in the X-axis direction is constant in the protrusion direction of the pair of clamping pieces  51   a   1  and  51   a   1 , but may be smaller toward the tips of the pair of clamping pieces  51   a   1  and  51   a   1 . This structure can increase the clamping strength of the clamping pieces  51   a   1  and  51   a   1  for the terminal attachment surface  24   f   1  (the engagement strength of the engagement parts  51   a  for the terminal attachment surface  24   f   1 ). 
     In the present embodiment, the thickness part of the flange  24  in its thickness direction (X-axis direction) shown in  FIG. 2A  and  FIG. 2B  is clamped by the pair of clamping pieces  51   a   1  and  51   a   1  shown in  FIG. 3  from the ends of the flange  24  (lateral ends), and the engagement parts  51   a  can thereby be engaged with the terminal attachment surface  24   f   1 . The length of the pair of clamping pieces  51   a   1  and  51   a   1  in its longitudinal direction (protrusion length) is not limited as long as the lateral part of the terminal attachment surface  24   f   1  (lateral surface  24   e ) can be clamped. 
     Each of the protrusion plate parts  51   b  has a substantially L shape and extends downward in the Z-axis direction from the lower end of each of the engagement parts  51   a  in the Z-axis direction. In addition, each of the protrusion plate parts  51   b  is formed by bending in the Y-axis direction and protrudes toward the inner side of the flange  24  in the Y-axis direction. 
     Each of the protrusion plate parts  51   b  includes a mounting base part  51   c  extending in parallel to an external circuit board (not shown), a tip bending part  51   d  bending in turn back manner at the tip of the mounting base part  51   c,  and a connection base part  51   e  formed integrally with the lower end of each of the engagement parts  51   a  in the Z-axis direction and extending downward in the Z-axis direction. 
     The connection base part  51   e  functions as a leaf spring-like support and integrally connects the engagement part  51   a  and the mounting base part  51   c.  Even if an external circuit board (not shown) connected to the main mounting surface  51   c   1  bends or vibrates due to external force, thermal deformation, or the like, the deformation of the connection base part  51   e  absorbs the deformation (force) or the vibration and can effectively protect the coil device  110 . 
     A pair of slits  51   f  and  51   f  is formed near the boundary between the engagement part  51   a  and the connection base part  51   e  (near the engagement part  51   a ). Each of the pair of slits  51   f  and  51   f  is made of a groove dented toward the inner side of the connection base part  51   e  in its width direction (X-axis direction). The terminal  51  is narrow in the X-axis direction at a location of the pair of slits  51   f  and  51   f.  A narrow part  51   g  is formed in the connection base part  51   e  at the location with a small width in the X-axis direction (between the pair of slits  51   f  and  51   f ). Preferably, the width of the narrow part  51   g  in the X-axis direction is ¼-¾ of the width of the connection base part  51   e  in the X-axis direction where the narrow part  51   g  is not formed. 
     The mounting base part  51   c  is formed integrally with the lower end of the connection base part  51   e  in the Z-axis direction and extends toward the inner side of the flange  24  in the Y-axis direction. For more detail, as shown in  FIG. 1C , each of the mounting base parts  51   c  protrudes toward the inner side of the flange  24  in the Y-axis direction in the space formed below the notches  24   c   1  and the step surfaces  24   f.  The mounting base parts  51   c  are substantially perpendicular to the connection base parts  51   e  and extend substantially in parallel to the anti-mounting-side core surface  24   b.    
     As shown in  FIG. 3 , the tip bending part  51   d  bends upward in the Z-axis direction and turns back at the tip of the mounting base parts  51   c,  the outer surface of the mounting base part  51   c  located opposite to the tip bending part  51   d  is a main mounting surface  51   c   1 , and the inner surface of the mounting base part  51   c,  which the tip bending part  51   d  is located, is a connection surface (wire connection surface)  51   c   2 . A lead end  41   a  ( 42   a,    41   b,    42   b ) (lead portion) of the wire  41  ( 42 ) is connected to the connection surface  51   c   2 . When the lead end  41   a  ( 42   a,    41   b,    42   b ) (lead portion) of the wire  41  ( 42 ) is being connected, the tip bending part  51   d  is bent in turn back manner toward one side in the Y-axis direction (outside the flange  24  in the Y-axis direction) and extends substantially in parallel to the mounting base part  51   c.  The main mounting surface  51   c   1  is located opposite to the connection surface  51   c   2  and is connected to an external circuit. 
     In the present embodiment, the lead end  41   a  ( 42   a,    41   b,    42   b ) (lead portion) of the wire  41  ( 42 ) is sandwiched between the mounting base part  51   c  and the tip bending part  51   d.  For more detail, as shown in  FIG. 1C , the lead end  41   a  (one lead end) of the first wire  41  (one wire) constituting the coil unit  40  shown in  FIG. 1B  is sandwiched and caulked by the connection surface  51   c   2  of the mounting base part  51   c  and the tip bending part  51   d.  This is also the case with the lead ends  42   a,    41   b,  and  42   b.  After the caulking, the terminal  51  and the lead end  41   a  of the wire  41  may be connected by soldering, laser welding, etc. 
     The main mounting surface  51   c   1  is connected to a circuit pattern of an external circuit board (not shown). The connection to the circuit pattern of the external circuit board is carried out in any manner, such as solder connection. 
     In the present embodiment, the second flange  26  has a similar structure to the first flange  24 , but may not necessarily have the same structure. In the present embodiment, as shown in  FIG. 2A  and  FIG. 2B , the second flange  26  is structured by a substantially rectangular parallelepiped as a whole, and notches  26   c   1  and notches (steps)  26   f   2  are formed at lower parts (or central parts) of the rectangular parallelepiped shape on both sides in the Y-axis direction. The second flange  26  includes a mounting-side core surface  26   a  (lower surface in the Z-axis direction), the anti-mounting-side core surface  26   b  located opposite to the mounting-side core surface  26   a,  an outer end surface  26   c  in the X-axis direction, an inner surface  26   d  facing the winding core  22 , a pair of lateral surfaces  26   e  and  26   e  located opposite to each other in the Y-axis direction, and a pair of step surfaces  24   f  and  24   f  formed at central parts on both sides in the Y-axis direction. 
     The notches  26   c   1  are formed on the outer end surface  26   c.  The protrusion plate part  51   b  of the terminal  51  can partly be disposed (contained) in each of the notches  26   c   1  (see  FIG. 1C ). 
     As shown in  FIG. 2A  and  FIG. 2B , a terminal attachment surface  26   f   1  is formed on step surfaces  26   f.  The terminal attachment surface  26   f   1  is formed by forming the notches (steps)  26   f   2  on the outer end surface  26   c,  the inner surface  26   d,  and the lateral surfaces  26   e  and  26   e.  The terminal attachment surface  26   f   1  of the outer end surface  26   c  and the inner surface  26   d  are dented inward in the X-axis direction (toward the central part of the flange  26  in the X-axis direction), and the terminal attachment surfaces  26   f   1  of the lateral surfaces  26   e  are dented toward the inner side of the flange  26  in the Y-axis direction (toward the central part of the flange  26  in the Y-axis direction). The step depth of the terminal attachment surface  26   f  dented from the outer end surface  26   c  and the inner surface  26   d  toward the inner side in the X-axis direction is preferably as large as a plate thickness of the terminal  51  (engagement part  51   a ) shown in  FIG. 3 , but may be smaller or larger than the plate thickness. This is also the case with the step depth of the terminal attachment surface  26   f  dented from the lateral surfaces  26   e  and  26   e  toward the inner side in the Y-axis direction. 
     Incidentally, each surface constituting the terminal attachment surface  26   f   1  is regarded as a part of the outer end surface  26   c,  the inner surface  26   d,  and the lateral surfaces  26   e.  Thus, the terminal attachment surface  26   f   1  is formed over the outer end surface  26   c,  the inner surface  26   d,  and the lateral surfaces  26   e.  The terminal attachment surface  26   f   1  is engaged with engagement parts  51   a  of the terminal  51  shown in  FIG. 3 . If necessary, the fixation of the engagement parts  51   a  to the terminal attachment surface  26   f   1  is reinforced by adhesion. 
     The attachment structure of the terminal  51  shown in  FIG. 3  to the second flange  26  shown in  FIG. 2A  and  FIG. 2B  is similar to that to the first flange  24  shown in  FIG. 2A  and  FIG. 2B  mentioned above and is thereby not explained in detail. 
     As shown in  FIG. 1C , the lead ends  41   a  and  42   a  (one leading portions) of the wires  41  and  42  are connected to the connection surfaces  51   c   2  of the terminals  51 . The lead ends  41   b  and  42   b  (the other leading portions) of the wires  41  and  42  shown in  FIG. 1D  are connected to the connection surfaces  51   c   2  of the terminals  51  on the back in the X-axis direction shown in  FIG. 3 . These are connected by any method, such as welding, resistance welding, ultrasonic welding, caulking, thermocompression bonding, and heat welding (preferably, laser welding, soldering, etc.). Incidentally, the four terminals  51  shown in  FIG. 3  have a similar structure. 
     As shown in  FIG. 1A ,  FIG. 1B , and  FIG. 1D , the coil unit  40  is formed around the winding core  22  of the drum core  20 . In the present embodiment, the coil unit  40  is structured by two wires  41  and  42 . The wires  41  and  42  are structured by, for example, a coated wire formed by covering a core made of a good conductor (e.g., copper wire) with an insulating coverage film and are wound around the winding core  22 , for example, in a double-layer structure. In the present embodiment, the cross-sectional areas of conductive parts of the wires  41  and  42  are the same as each other. 
     In the present embodiment, the first wire  41  and the second wire  42  are wound around the winding core  22  by a normal bifilar winding, but a cross part may be formed at a predetermined location in the winding axis of the winding core  22 . 
     In the manufacture of the coil device  10 , the four terminals  51  shown in  FIG. 3  are initially attached to the drum core  20  shown in  FIG. 2A  and  FIG. 2B . The terminals  51  are attached by engaging the engagement parts  51   a  of the terminals  51  with the terminal attachment surfaces  24   f   1  and  26   f   1  of the flanges  24  and  26 . The engagement parts  51   a  are attached to the terminal attachment surfaces  24   f   1  and  26   f   1  by pushing the engagement parts  51   a  against the terminal attachment surfaces  24   f   1  and  26   f   1  from the outer side to the inner side in the Y-axis direction. 
     Prepared are the drum-type drum core  20  with the terminals  51  manufactured in such a manner, the flat plate-like member  30 , and the wires  41  and  42 . The drum core  20  is made of magnetic material and can be manufactured by, for example, pressing and sintering a magnetic material with a comparatively high permeability (e.g., Ni—Zn based ferrite, Mn—Zn based ferrite) or a magnetic powder composed of metal magnetic material or so. The flat plate-like member  30  is preferably made of the same or different magnetic material from the drum core  20 , but is not necessarily made of magnetic material. 
     The terminals  51  are structured by a metal terminal made of phosphor bronze, tough pitch copper, pure copper, brass, silver, gold, metallic alloys with solder bondability, etc. Each of the terminals  51  has any thickness, but preferably has a thickness of 50-300 μm. 
     For example, the wires  41  and  42  can be formed by covering a core made of a good conductor of copper (Cu) or so with an insulating material made of imide-modified polyurethane or so and further covering the outermost surface with a thin resin film of polyester or so. The drum core  20  on which the terminals  51  are installed and the wires  41  and  42  are set to a winding machine, and the wires  41  and  42  are wound around the winding core  22  of the drum core  20  in a predetermined order. Each of the wires  41  and  42  has any diameter, but preferably has a diameter of 10-300 μm. 
     In the present embodiment, the first wire  41  and the second wire  42  are wound by bifilar winding. The lead ends  41   a,    42   a,    41   b,  and  42   b  of the lead portions (wire ends) of the wound wires  41  and  42  are connected after the tip bending part  51   d  is caulked to the connection surfaces  51   c   2  of the predetermined terminals  51  shown in  FIG. 3 . 
     After the winding operation of the wires  41  and  42  to the winding core  22 , the flat plate-like member  30  is connected to the anti-mounting-side core surfaces  24   b  and  26   b  of the flanges  24  and  26  by any method, such as adhesion. 
     In the coil device  10  according to the present embodiment, the wire length of the lead end  41   a  (one lead portion) of the first wire  41  from the coil unit  40  to the connection surface  51   c   2  of the terminal  51  and the wire length of the lead end  42   a  (one lead portion) of the second wire  42  from the coil unit  40  to the connection surface  51   c   2  of the terminal  51  are preferably substantially the same, but may be different from each other. Preferably, the winding number of the first wire  41  and the winding number of the second wire  42  in the coil unit  40  are the same as each other. This structure further improves mode conversion characteristics. 
     In the coil device  10  according to the present embodiment, each of the terminals  51  includes the engagement part  51   a  engageable with a circumferential wall part of the flange  24  (or the flange  26 ; the same applies hereinafter). Since the engagement part  51   a  is engaged with the circumferential wall part of the flange  24 , the terminals  51  can firmly be fixed to the flange  24  and are hard to come off from the flange  24  even if an external circuit board vibrates or deforms after mounting. Thus, the coil device  10  according to the present embodiment can improve the reliability of fixation between the terminals  51  and the flange  24 . 
     In the present embodiment, each of the engagement parts  51   a  includes a pair of clamping pieces  51   a   1  and  51   a   1 , and the pair of clamping pieces  51   a   1  and  51   a   1  clamps the circumferential wall part of the flange  24  from outside. Thus, the engagement strength of the engagement part  51   a  for the flange  24  can be increased, and the terminals  51  can be fixed to the flange  24  more firmly. Moreover, for example, since the pair of clamping pieces  51   a   1  and  51   a   1  does not clamp the mounting-side core surface  24   a  or the anti-mounting-side core surface  24   b  of the flange  24 , but clamps parts of the flange  24  in its thickness direction (X-axis direction), these parts can strongly be clamped by the pair of clamping pieces  51   a   1  and  51   a   1 . 
     In the present embodiment, the pair of clamping pieces  51   a   1  and  51   a   1  clamps the inner surface (inner end surface)  24   d  and the outer end surface  24   c  of the flange  24  from the side of the flange  24 . Thus, the terminals  51  can be fixed to the side of the flange  24 , the coil device  10  can be prevented from being larger due to the attachment of the terminals  51 , and the low profile of the coil device  10  can be achieved. 
     In the present embodiment, each of the terminals  51  includes a protrusion plate part  41   c  including: a connection surface (wire connection surface)  51   c   2  to which the lead end  41   a  ( 42   a,    41   b,    42   b ) (lead portion) of the wire  41  ( 42 ) is connected; and a main mounting surface  51   c   1  located opposite to the wire connection surface and being connectable to an external circuit. Thus, the connection surface  51   c   2  and the main mounting surface  51   c   1  are substantially close to each other only with the thickness of the protrusion plate part  51   b,  and it is possible to extremely reduce a DC resistance of each of the terminals  51  from the connection part of the lead end  41   a  ( 42   a,    41   b,    42   b ) (lead portion) of the wire  41  ( 42 ) to an external circuit and to extremely reduce a DC resistance of the coil device  10  as a whole. Thus, the coil device  10  according to the present embodiment can also favorably be used for power supply applications. 
     Even when the coil device  10  according to the present embodiment is used for signal system applications, the increase in insertion loss (IL) can be restrained, and the coil device  10  according to the present embodiment can also favorably be used for a high frequency signal system application of, for example, 100 MHz or more. 
     In the present embodiment, the protrusion plate part  51   b  includes: a mounting base part  51   c  extending in parallel to the external circuit; and a tip bending part  51   d  bending in turn back manner at a tip of the base part  51   c,  and the lead end  41   a  ( 42   a ,  41   b,    42   b ) (lead portion) of the wire  41  ( 42 ) is sandwiched between the mounting base part  51   c  and the tip bending part  51   d.  When the lead end  41   a  ( 42   a,    41   b,    42   b ) (lead portion) of the wire  41  ( 42 ) is sandwiched between the tip bending part  51   d  and the mounting base part  51   c,  the lead end  41   a  ( 42   a,    41   b,    42   b ) is easily connected to the terminal  51 . 
     In the present embodiment, the protrusion plate part  51   b  includes a connection base part  51   e  connecting the engagement part  51   a  and the mounting base part  51   c . Thus, a stress generated by vibration, deformation, etc. of the board can be reduced (absorbed) via the connection base part  51   e,  and it is possible to effectively prevent the terminals  51  from coming off from the flange  24 . In addition, when the connection base part  51   e  is disposed between the engagement part  51   a  and the mounting base part  51   c , the engagement part  51   a  and the mounting base part  51   c  can be separated from each other, and the above-mentioned reduction effect on the stress can be obtained effectively. 
     In the present embodiment, a pair of slits  51   f  and  51   f  is formed near the engagement part  51   a.  Thus, a stress generated by vibration, deformation, etc. of the board can be prevented from traveling to the engagement part  51   a  or so, and it is possible to effectively prevent the terminals  51  from coming off from the flange  24 . 
     In the present embodiment, each of the terminals  51  is narrow at a location of the pair of slits  51   f  and  51   f.  Thus, the above-mentioned stress can effectively be prevented from traveling at the location of the pair of slits  51   f  and  51   f,  and the reduction effect of the slits  51   f  and  51   f  can be enhanced. 
     In the present embodiment, as shown in  FIG. 1C , a gap distance Z 1  between the tip bending part  51   d  of the protrusion plate part  51   b  and the flange  24  ( 26 ) in the Z-axis direction perpendicular to the main mounting surface  51   c   1  is twice or larger than a thickness of the protrusion plate part  51   b  at a location where the lead end  41   a  ( 42   a ) of the wire  41  ( 42 ) is connected. In this structure, for example, the lead end  41   a  ( 42   a ) of the wire  41  ( 42 ) can easily be connected to the protrusion plate part  51   b  by laser welding, soldering, or the like. In addition, a thermal deformation stress of a circuit board (not shown) or so is hard to travel to the flanges, and the connection strength of the coil device  10  to the circuit board is improved. 
     In the present embodiment, as shown in  FIG. 1C , the main mounting surfaces  51   c   1  of the mounting base parts  51   c  protrude downward in the Z-axis direction from the mounting-side core surface  24   a  by a predetermined distance Z 2 . Preferably, the predetermined distance Z 2  is larger than zero and is about twice or less (more preferably, once or less) of the thickness of each of the plate-like members constituting the terminal  51 . 
     In the present embodiment, as shown in  FIG. 1A , the coil device  10  according to the present embodiment further includes a flat plate-like member  30  bridging the anti-mounting-side core surface  24   b  of the first flange  24  and the anti-mounting-side core surface  26   b  of the second flange  26 . When the flat plate-like member  30  is made of magnetic material, a closed magnetic circuit can be formed by combination with the drum core  20  made of magnetic material, and magnetic characteristics of the coil device  10  are improved. 
     Incidentally, the plate-like member  30  may be a nonmagnetic member. In addition, the plate-like member  30  may be a member formed by application of resin. Preferably, such plate-like members  30  have a flat surface. A suction member for pickup can detachably be attached to the flat surface. This improves the handling performance. 
     Second Embodiment 
     A coil device according to Second Embodiment of the present invention is different from the coil device  10  according to First Embodiment only in the following structure and demonstrates effects similar to those of First Embodiment. The overlapping matters with First Embodiment are not explained. In the figures, common components with First Embodiment are given common references. 
     In a coil device  110  according to the present embodiment, as shown in  FIG. 4 , the core  20  of the coil device  10  according to First Embodiment shown in  FIG. 1A  to  FIG. 1D  is replaced with a core  120 . The core  120  includes flanges  124  and  126 . The flange  124  ( 126 ) includes protrusion parts  124   g  ( 126   g ). 
     The protrusion parts  124   g  ( 126   g ) constitute a part of the flange  124  ( 126 ) and protrude downward in the Z-axis direction. Each of the protrusion parts  124   g  ( 126   g ) includes a step surface  124   f  ( 126   f ). The step surfaces  124   f  ( 126   f ) are formed by extending the step surfaces  24   f  ( 26   f ) shown in  FIG. 2A  and  FIG. 2B  downward in the Z-axis direction. 
     As shown in  FIG. 5A  and  FIG. 5B , the lower ends of the protrusion parts  124   g  ( 126   g ) in the Z-axis direction are arranged at substantially the same location as the mounting-side core surface  24   a  ( 26   a ) of the flange  124  ( 126 ) or arranged above the mounting-side core surface  24   a  ( 26   a ) of the flange  124  ( 126 ). The protrusion parts  124   g  ( 126   g ) are contacted with rear surfaces (connection surfaces  51   c   2 ) of the terminals  51  located opposite to an external circuit board (not shown). Thus, the terminals  51  can be fixed to the protrusion parts  124   g  ( 126   g ) at least at two points (the engagement parts  51   a  and the connection surfaces  51   c   2 ). 
     In the present embodiment, the flange  124  ( 126 ) is partly (protrusion parts  124   g  ( 126   g )) contacted with the rear surfaces (connection surfaces  51   c   2 ) of the terminals  51  located opposite to an external circuit board (not shown). Thus, the terminals  51  can be supported from behind by the protrusion parts  124   g  ( 126   g ), and it is possible to prevent the deformation of the terminals  51  due to a stress generated by vibration, deformation, or the like of an external circuit board (not shown). 
     Third Embodiment 
     A coil device according to Third Embodiment of the present invention is different from the coil device  10  according to First Embodiment only in the following structure and demonstrates effects similar to those of First Embodiment. The overlapping matters with First Embodiment are not explained. In the figures, common components with First Embodiment are given common references. 
     In a coil device  210  according to the present embodiment, as shown in  FIG. 6 , the terminals  51  of the coil device  10  according to First Embodiment shown in  FIG. 1A  to  FIG. 1D  are replaced with terminals  251 . Each of the terminals  251  includes an engagement part  251   a  and a protrusion plate part  251   b.    
     As shown in  FIG. 7 , the engagement parts  251   a  are different from the engagement parts  51   a  according to First Embodiment in that the length of the engagement parts  251   a  in the Z-axis direction is smaller than that of the engagement parts  51   a  shown in  FIG. 3 . As shown in  FIG. 6B , the lower ends of the engagement parts  251   a  in the Z-axis direction do not protrude from those of the terminal attachment surfaces  24   f   1  ( 26   f   1 ) in the Z-axis direction, but are arranged on the inner sides of the lower ends of the terminal attachment surfaces  24   f   1  ( 26   f   1 ) in the Z-axis direction. 
     The protrusion plate part  251   b  is different from the protrusion plate part  51   b  shown in  FIG. 3  in that the protrusion plate part  251   b  includes a tip bending part  251   d,  a connection base part  251   e,  and a standing piece  251   h.  The connection base part  251   e  is different from the connection base part  51   e  in that the length of the connection base part  251   e  in the Z-axis direction is larger than that of the connection base part  51   e  according to First Embodiment in the Z-axis direction. The standing piece  251   h  is bent to stand upward in the Z-axis direction at the tip of the mounting base part  51   c.  In the illustrated example, the standing piece  251   h  stands substantially perpendicularly to the mounting base part  51   c.    
     The tip bending part  251   d  is bent downward in the Z-axis direction at the tip of the standing piece  251   h  in the Z-axis direction. The tip bending part  251   d  extends substantially in parallel to the standing piece  251   h  and the connection base part  251   e . The lead end  41   a  ( 42   a,    41   b,    42   b ) (lead portion) of the wire  41  ( 42 ) can be sandwiched between the standing piece  251   h  and the tip bending part  251   d.  As shown in  FIG. 6C , the standing piece  251   h  and the tip bending part  251   d  sandwich the lead end  41   a  ( 42   a ,  41   b,    42   b ) (lead portion) of the wire  41  ( 42 ) on the inner side of the notches  24   c  ( 26   c ) of the flange  24  ( 26 ). 
     Effects similar to those of First Embodiment are also obtained in the present embodiment. That is, the terminals  51  are hard to come off from the flange  24  ( 26 ) even if an external circuit board vibrates or deforms after mounting, and the reliability of fixation between the terminals  51  and the flange  24  ( 26 ) can be improved. 
     Incidentally, the present invention is not limited to the above-mentioned embodiments and can variously be modified within the scope of the present invention. 
     In the above-mentioned embodiments, for example, the first flange  24  and the second flange  26  have the same structure, but may have different structures. The notches  24   c   1  formed at the lower parts of the flange  24  ( 26 ) of the drum core  20  shown in  FIG. 2A  and  FIG. 2 b    on both sides in the Y-axis direction may be wide in the Y-axis direction. For example, the notches  24   c   1  on both sides may be connected in the Y-axis direction. 
     In the above-mentioned embodiments, the engagement part  51   a  of the terminal  51  is engaged with the lateral surfaces  24   e  ( 26 ) of the flange  24  ( 26 ), but may be engaged with another part of the circumferential wall part of the flange  24  ( 26 ). For example, the engagement part  51   a  may be engaged with the anti-mounting-side core surface  24   b  ( 26   b ) of the flange  24  ( 26 ). 
     In the above-mentioned embodiments, the engagement parts  51   a  may directly be engaged with the lateral surfaces  24   e  ( 26 ) without forming the step surfaces  24   f  ( 26   f ). The main mounting surfaces  51   c  of the terminals  51  may be formed below the mounting-side core surface  24   a  ( 26   a ) of the flange  24  ( 26 ) in the Z-axis direction without forming the notches  24   c   1  ( 26   c   1 ). 
     In the above-mentioned embodiments, the connection base part  51   e  is not an essential component and may not be formed. In this case, the mounting base part  51   c  may be formed by bending the lower end of the engagement part  51   a  in the Z-axis direction to the Y-axis direction and protrude toward the inner side of the flange  24  in the Y-axis direction. In this case, if necessary, the lower end of the engagement part  51   a  in the Z-axis direction may be extended downward, or the engagement location of the engagement part  51   a  may be shifted downward in the Z-axis direction. 
     In Third Embodiment, the length of the engagement part  251   a  and the connection base part  251   e  in the Z-axis direction may be similar to that of the engagement part  51   a  and the connection base part  51   e  in the Z-axis direction according to First Embodiment. 
     In the above-mentioned embodiments, the pair of slits  51   f  and  51   f  is structured by forming a pair of grooves on both sides of the terminal  51  in the X-axis direction, but the slits  51   f  and  51   f  may be structured by, for example, forming a linear groove (a groove extending in the X-axis direction) connecting between one end and the other end in the X-axis direction on the surface of the terminal  51 . 
     In the above-mentioned embodiments, the clamping strength of the pair of clamping pieces  51   a   1  and  51   a   1  for the terminal attachment surface  24   f   1  ( 26   f   1 ) may be improved by providing projections on the inner surfaces of the pair of clamping pieces  51   a   1  and  51   a   1  or further providing recesses being engageable with the projections on the terminal attachment surface  24   f   1  ( 26   f   1 ). 
     DESCRIPTION OF THE REFERENCE NUMERICAL 
     
         
           10 ,  110 ,  210  . . . coil device 
           20 ,  120  . . . drum core 
           22  . . . winding core 
           24 ,  124  . . . first flange 
           24   a  . . . mounting-side core surface 
           24   b  . . . anti-mounting-side core surface 
           24   c  . . . outer end surface 
           24   c    1  . . . notch 
           24   d  . . . inner surface 
           24   e  . . . lateral surface 
           24   f  . . . step surface 
           24   f   1  . . . terminal attachment surface 
           24   f   2  . . . notch 
           124   g  . . . protrusion part 
           26  . . . second flange 
           26   a  . . . mounting-side core surface 
           26   b  . . . anti-mounting-side core surface 
           26   c  . . . outer end surface 
           26   c    1  . . . notch 
           26   d  . . . inner surface 
           26   e  . . . lateral surface 
           26   f  . . . step surface 
           26   f   1  . . . terminal attachment surface 
           26   f   3  . . . notch 
           126   g  . . . protrusion part 
           30  . . . flat plate-like member 
           40  . . . coil unit 
           41  . . . first wire 
           41   a  . . . one lead portion (lead end) 
           41   b  . . . the other lead portion (lead end) 
           42  . . . second wire 
           42   a  . . . one lead portion (lead end) 
           42   b  . . . the other lead portion (lead end) 
           51 ,  251  . . . terminal (terminal fitting) 
           51   a,    251   a  . . . engagement part 
           51   a   1 ,  251   a   1  . . . clamping piece 
           51   b,    251   b  . . . protrusion plate part 
           51   c  . . . mounting base part 
           51   c   1  . . . main mounting surface 
           51   c   2  . . . connection surface (wire connection surface) 
           51   d,    251   d  . . . tip bending part 
           51   e,    251   e  . . . connection base part 
           51   f  . . . slit 
           51   g  . . . narrow part 
           251   h  . . . standing piece