Patent Publication Number: US-2021193364-A1

Title: Coil structure

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Japanese Patent Application No. 2019-232038 filed on Dec. 23, 2019, the entire contents of which are incorporated by reference herein. 
     TECHNICAL FIELD 
     The present disclosure relates to a coil structure. 
     BACKGROUND 
     Conventionally, as a coil structure, one described in PCT International Publication No. WO 2018/193504 is known. This coil structure includes a substrate having a coil conductor, a first core disposed on one side of the substrate, and a second core disposed on the other side of the substrate. The first core is an E-type core and the second core is an I-type core. 
     SUMMARY 
     Here, in the coil structure as described above, it is required to reduce the size and improve the performance. 
     An objective of the present disclosure is to provide a coil structure in which reduction in size can be achieved and a performance can be improved. 
     A coil structure according to the present disclosure includes a substrate including a coil conductor, a first core disposed on one main surface side of the substrate, a second core disposed on other main surface side of the substrate; and an insulating member made of an insulating material, in which the first core includes a main body part extending in a first direction along a main surface of the substrate, a first foot part extending from the main body part to the second core through the substrate, and a second foot part extending from the main body part to the second core through the substrate at a position at which the coil conductor is sandwiched between the second foot part and the first foot part in the first direction, and the insulating member includes a bottom wall part interposed between at least the first foot part and the second core, and a side wall part extending along at least either of the first foot part and the second foot part and interposed between either of the foot parts and the coil conductor. 
     In the coil structure according to the present disclosure, the insulating member includes the bottom wall part interposed between the first foot part and the second core. Thereby, the insulating member can adjust an L value between the first core and the second core. Here, the insulating member includes a side wall part extending along at least either of the first foot part and the second foot part and interposed between either of the foot parts and the coil conductor. In this case, the side wall part can function as a positioning part for the first core. Therefore, when a gap is formed between the first foot part of the first core and the second core, fixing, positioning, and checking of the insulating member can be easily performed. As described above, since the processing can be easily performed, deviations or the like between the members can be prevented and a performance of the coil structure can be improved. Also, the side wall part is interposed between either of the foot parts and the coil conductor. In this case, when it is necessary to secure an insulating distance between the foot parts and the coil conductor, since the insulating member is disposed between the foot parts and the coil conductor, a distance between the foot parts and the coil conductor can be decreased. Thereby, reduction in size of the coil structure can be achieved. 
     A pair of the first foot parts may extend from both end sides of the main body part in the first direction, and the second foot part may be disposed on an inner circumferential side of the coil conductor between the pair of first foot parts. In this case, the coil structure of the present disclosure can be applied to an EI core. 
     The insulating member may include a first side wall part extending along a side surface on an inner side in the first direction of the first foot part and interposed between the first foot part and the coil conductor. Thereby, a distance between the first foot part and the coil conductor in the first direction can be decreased. 
     The insulating member may include a second side wall part extending along a side surface in the first direction of the second foot part and interposed between the second foot part and the coil conductor. Thereby, a distance between the second foot part and the coil conductor in the first direction can be decreased. 
     A direction extending along the main surface of the substrate and intersecting the first direction is a second direction, and the insulating member may include a third side wall part extending along a side surface in the second direction of the second foot part and interposed between the second foot part and the coil conductor. In this case, a distance between the second foot part and the coil conductor in the second direction can be decreased. 
     The insulating member may include an upper wall part extending in the first direction along the main body part between the first foot part and the second foot part. In this case, a distance between the main body part and the coil conductor can be decreased. 
     The insulating member may include a fourth side wall part extending along a side surface on an outer side in the first direction of the first foot part. In this case, when another conductor is present on the outer side in the first direction of the first foot part, a distance between the conductor and the first foot part in the first direction can be decreased. 
     A heat dissipation material may be disposed in a gap between the second foot part and the second core. Thereby, the heat dissipation path can be formed between the second foot part and the second core in which heat is easily accumulated. 
     The insulating member may include a second side wall part extending along a side surface in the first direction of the second foot part and interposed between the second foot part and the coil conductor, and the second side wall part may extend to the second core side with respect to a lower surface of the second foot part. In this case, a vicinity of an end portion of the second side wall part on the second core side can block the heat dissipation material. 
     According to the present disclosure, it is possible to provide a coil structure in which reduction in size can be achieved and a performance can be improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a coil structure according to an embodiment of the present disclosure. 
         FIG. 2  is an exploded perspective view of the coil structure. 
         FIG. 3  is an enlarged perspective view of a first core and an insulating member illustrated in  FIG. 2 . 
         FIG. 4  is an enlarged cross-sectional view along line IV-IV of  FIG. 1 . 
         FIG. 5  is an enlarged cross-sectional view of a coil structure according to a comparative example. 
     
    
    
     DETAILED DESCRIPTION 
     A coil structure according to an embodiment of the present disclosure will be described with reference to  FIGS. 1 to 4 .  FIG. 1  is a perspective view illustrating a coil structure  100  according to an embodiment of the present disclosure.  FIG. 2  is an exploded perspective view of the coil structure  100 .  FIG. 3  is an enlarged perspective view of a first core  1  and an insulating member  3  illustrated in  FIG. 2 .  FIG. 4  is an enlarged cross-sectional view along line IV-IV of  FIG. 1 . 
     As illustrated in  FIGS. 1 and 2 , the coil structure  100  includes a substrate  50 , a first core  1 , a second core  2 , and an insulating member  3 . A facing direction in which the first core  1  and the second core  2  face each other is referred to as a Z-axis direction. Further, the first core  1  side is referred to as a positive side in the Z-axis direction. A direction perpendicular to the Z-axis direction, that is, a direction along the substrate  50  is referred to as an X-axis direction, and a direction perpendicular to the Z-axis direction and the X-axis direction is referred to as a Y-axis direction. Further, in the present embodiment, the X-axis direction corresponds to a “first direction” in the claims, and the Y-axis direction corresponds to a “second direction” in the claims. However, the present disclosure is not limited to this correspondence relationship. 
     The substrate  50  is a plate-shaped member that extends in an XY plane. The substrate  50  includes a main surface  50   a  on the positive side in the Z-axis direction and a main surface  50   b  on a negative side in the Z-axis direction. A rectangular penetration part  51  is formed in the substrate  50 . Also, the substrate  50  includes a rectangular penetration part  52 A formed at a position separated from the penetration part  51  on a negative side in the X-axis direction. The substrate  50  includes a rectangular penetration part  52 B formed at a position separated from the penetration part  51  on a positive side in the X-axis direction. The substrate  50  includes a coil conductor  53  on the main surface  50   a . The coil conductor  53  forms a winding part that is wound in a rectangular shape to surround the penetration part  51 . 
     Specifically, as illustrated in  FIG. 2 , the coil conductor  53  includes side parts  53   a ,  53   b ,  53   c , and  53   d . The side part  53   a  is disposed on the negative side of the penetration part  51  in the X-axis direction. The side part  53   b  is disposed on the positive side of the penetration part  51  in the X-axis direction. The side part  53   c  is disposed on the negative side of the penetration part  51  in the Y-axis direction. The side part  53   d  is disposed on the positive side of the penetration part  51  in the Y-axis direction. Further, portions of the side parts  53   c  and  53   d  extend to positions corresponding to the penetration parts  52 A and  52 B in the X-axis direction. 
     The first core  1  is an E-shaped core. The first core  1  is disposed on the main surface  50   a  side of the substrate  50 . The first core  1  includes a main body part  6 , a pair of first foot parts  7 A and  7 B, and a second foot part  8 . The first foot parts  7 A and  7 B penetrate the substrate  50  and extend to the second core  2 . The first foot parts  7 A and  7 B are inserted into the penetration parts  52 A and  52 B of the substrate  50 . The second foot part  8  penetrates the substrate  50  and extends to the second core  2 . The second foot part  8  is inserted into the penetration part  51  of the substrate  50 . 
     The first foot parts  7 A and  7 B protrude from the main body part  6  toward the negative side in the Z-axis direction. The first foot part  7 A is provided at an end portion of the main body part  6  on the negative side in the X-axis direction. The first foot part  7 B is provided at an end portion of the main body part  6  on the positive side in the X-axis direction. The first foot part  7 A and the first foot part  7 B are separated from each other in the X-axis direction. The second foot part  8  protrudes from the main body part  6  toward the negative side in the Z-axis direction between the first foot parts  7 A and  7 B. The second foot part  8  is disposed at a center position of the main body part  6  in the X-axis direction. The second foot part  8  is disposed at a position separated from the first foot part  7 A on the positive side in the X-axis direction. The second foot part  8  is disposed at a position separated from the first foot part  7 B on the negative side in the X-axis direction. A more detailed description of the first core  1  will be described below. 
     The second core  2  is an I-shaped core. The second core  2  is disposed on the main surface  50   b  side of the substrate  50 . The second core  2  is magnetically connected to the first core  1  via the foot parts  7 A,  7 B, and  8 . The second core  2  has a rectangular plate shape extending parallel to the XY plane. The second core  2  includes an upper surface  2   a , a lower surface  2   b , and side surfaces  2   c ,  2   d ,  2   e , and  2   f . The upper surface  2   a  extends parallel to the XY plane at a position on the positive side in the Z-axis direction. The lower surface  2   b  extends parallel to the XY plane at a position on the negative side in the Z-axis direction. The side surfaces  2   c  and  2   d  extend parallel to an XZ plane at positions on the positive side and the negative side in the Y-axis direction. The side surfaces  2   e  and  2   f  extend parallel to a YZ plane at positions on the positive side and the negative side in the X-axis direction. 
     The insulating member  3  is a member made of an insulating material. The “insulating material” is a material constituting an insulator, and for example, a phenol resin or the like may be employed. The insulating member  3  is a member for securing insulation between the first core  1  and other parts. Also, the insulating member  3  is a member that forms gaps between the first foot parts  7 A and  7 B of the first core  1  and the second core  2  and allows positioning of the first core  1 . The insulating member  3  includes a pair of accommodating parts  11 A and  11 B, an accommodating part  12 , and a pair of connecting parts  13 A and  13 B. The first accommodating parts  11 A and  11 B are portions that accommodate the first foot parts  7 A and  7 B of the first core  1 . The second accommodating part  12  is a portion that accommodates the second foot part  8  of the first core  1 . The connecting part  13 A is a portion connecting the first accommodating part  11 A and the second accommodating part  12 . The connecting part  13 B is a portion connecting the first accommodating part  11 B and the second accommodating part  12 . A more detailed description of the insulating member  3  will be described below. 
     Next, a detailed configuration of the first core  1  will be described with reference to  FIG. 3 . The main body part  6  is formed in a rectangular parallelepiped shape having a longitudinal direction in the X-axis direction. The main body part  6  includes a lower surface  6   a , an upper surface  6   b , side surfaces  6   c  and  6   d , and end surfaces  6   e  and  6   f . The lower surface  6   a  extends parallel to the XY plane at a position on the negative side in the Z-axis direction. The upper surface  6   b  extends parallel to the XY plane at a position on the positive side in the Z-axis direction. The side surfaces  6   c  and  6   d  extend parallel to the XZ plane at positions on the positive side and the negative side in the Y-axis direction. The end surfaces  6   e  and  6   f  extend parallel to the YZ plane at positions on the positive side and the negative side in the X-axis direction. 
     The first foot parts  7 A and  7 B each have a rectangular shape when viewed from the Z-axis direction. The first foot parts  7 A and  7 B each have side surfaces  7   a ,  7   b ,  7   c , and  7   d , and a lower surface  7   e . The side surfaces  7   a  and  7   b  extend parallel to the XZ plane at positions on the positive side and the negative side in the Y-axis direction. The side surfaces  7   c  and  7   d  extend parallel to the YZ plane at positions on an outer side and an inner side in the X-axis direction. Further, the “outer side in the X-axis direction” is based on the longitudinal direction of the main body part  6  and indicates the end surfaces  6   e  and  6   f  sides. The lower surface  7   e  extends parallel to the XY plane at a position on the negative side of the substrate  50  in the Z-axis direction. In the present embodiment, the side surfaces  7   a  and  7   b  of the first foot parts  7 A and  7 B form the same plane as the side surfaces  6   c  and  6   d  of the main body part  6 , respectively. The side surface  7   c  of the first foot part  7 A forms the same plane as the end surface  6   e  of the main body part  6 . The side surface  7   c  of the first foot part  7 B forms the same plane as the end surface  6   f  of the main body part  6 . 
     The second foot part  8  has a rectangular shape when viewed from the Z-axis direction. The second foot part  8  includes side surfaces  8   a ,  8   b ,  8   c , and  8   d , and a lower surface  8   e . The side surfaces  8   a  and  8   b  extend parallel to the XZ plane at positions on the positive side and the negative side in the Y-axis direction. The side surfaces  8   c  and  8   d  extend parallel to the YZ plane at positions on the positive side and the negative side in the X-axis direction. The lower surface  8   e  extends parallel to the XY plane at a position on the negative side of the substrate  50  in the Z-axis direction. In the present embodiment, the side surfaces  8   a  and  8   b  of the second foot part  8  form the same plane as the side surfaces  6   c  and  6   d  of the main body part  6 , respectively. However, shapes of the first foot parts  7 A and  7 B and the second foot part  8  and positional relationships thereof with the main body part  6  are not particularly limited. 
     The lower surfaces  7   e  of the first foot parts  7 A and  7 B and the lower surface  8   e  of the second foot part  8  of the first core  1  are disposed to be parallel to and close to the upper surface  2   a  of the second core  2 . Further, positions of the lower surfaces  7   e  of the first foot parts  7 A and  7 B and the lower surface  8   e  of the second foot part  8  in the Z-axis direction may be the same as each other but may also be slightly deviated from each other. 
     Next, a detailed configuration of the insulating member  3  will be described with reference to  FIGS. 3 and 4 . Further, the insulating member  3 , the first core  1 , and the second core  2  have a configuration that is line-symmetric with respect to a center line in the X-axis direction when viewed from the Y-axis direction. Therefore, although only a configuration thereof on the negative side in the X-axis direction is illustrated in  FIG. 4 , a configuration thereof on the positive side in the X-axis direction also has the same effect. Further, in the following description, a state in which the insulating member  3  is assembled to the first core  1  (states illustrated in  FIGS. 1 and 4 ) will be described. 
     As illustrated in  FIG. 3 , the accommodating part  11 A includes a side wall part  21  (side wall part, first side wall part), a side wall part  22  (fourth side wall part), side wall parts  23  and  24  (side wall parts), and a bottom wall part  25 . 
     The side wall part  21  of the accommodating part  11 A extends along the side surface  7   d  on the inner side in the X-axis direction of the first foot part  7 A and is interposed between the first foot part  7 A and the coil conductor  53 . The side wall part  21  extends parallel to the YZ plane to cover the side surface  7   d  at a position on the positive side of the side surface  7   d  in the X-axis direction. The side wall part  21  of the accommodating part  11 A is interposed between the side surface  7   d , and an edge portion of the penetration part  51  and the side part  53   a  of the coil conductor  53  (see  FIG. 2 ). 
     The side wall part  22  of the accommodating part  11 A extends along the side surface  7   c  on the outer side in the X-axis direction of the first foot part  7 A. The side wall part  22  extends parallel to the YZ plane to cover the side surface  7   c  at a position on the negative side of the side surface  7   c  in the X-axis direction. 
     The side wall part  23  of the accommodating part  11 A extends along the side surface  7   a  on the positive side in the Y-axis direction of the first foot part  7 A. The side wall part  23  extends parallel to the XZ plane to cover the side surface  7   a  at a position on the positive side of the side surface  7   a  in the Y-axis direction. Both end portions of the side wall part  23  in the X-axis direction are connected to end portions of the side wall parts  21  and  22  on the positive side in the Y-axis direction. The side wall part  23  of the accommodating part  11 A is interposed between the side surface  7   a , and an edge portion of the penetration part  52 A and an extended portion of the side part  53   d  of the coil conductor  53  (see  FIG. 2 ). Therefore, in the present embodiment, the side wall part  23  of the accommodating part  11 A is interposed between the first foot part  7 A and the coil conductor  53 . 
     The side wall part  24  of the accommodating part  11 A extends along the side surface  7   b  on the negative side in the Y-axis direction of the first foot part  7 A. The side wall part  24  extends parallel to the XZ plane to cover the side surface  7   b  at a position on the negative side of the side surface  7   b  in the Y-axis direction. Both end portions of the side wall part  24  in the X-axis direction are connected to end portions of the side wall parts  21  and  22  on the negative side in the Y-axis direction. The side wall part  24  of the accommodating part  11 A is interposed between the side surface  7   b , and an edge portion of the penetration part  52 A and an extended portion of the side part  53   c  of the coil conductor  53  (see  FIG. 2 ). Therefore, in the present embodiment, the side wall part  24  of the accommodating part  11 A is interposed between the first foot part  7 A and the coil conductor  53 . 
     The bottom wall part  25  of the accommodating part  11 A extends along the lower surface  7   e  of the first foot part  7 A. The bottom wall part  25  is interposed between the first foot part  7 A and the second core  2 . The bottom wall part  25  extends parallel to the XY plane to cover the lower surface  7   e  at a position on the negative side of the lower surface  7   e  in the Z-axis direction. The bottom wall part  25  is in contact with the lower surface  7   e  of the first foot part  7 A on an upper surface side and in contact with the upper surface  2   a  of the second core  2  on a lower surface side. Both end portions of the bottom wall part  25  in the X-axis direction are connected to end portions of the side wall parts  21  and  22  on the negative side in the Z-axis direction. Both end portions of the bottom wall part  25  in the Y-axis direction are connected to end portions of the side wall parts  23  and  24  on the negative side in the Z-axis direction. 
     The accommodating part  11 B includes a side wall part  21  (side wall part, first side wall part), a side wall part  22  (fourth side wall part), side wall parts  23  and  24  (side wall parts, third side wall parts), and a bottom wall part  25 . The accommodating part  11 B has a configuration of the same effect as that of the accommodating part  11 A except that the side wall part  21  is disposed on the negative side of the first foot part  7 B in the X-axis direction, and the side wall part  22  is disposed on the positive side of the first foot part  7 B in the X-axis direction. 
     The accommodating part  12  includes side wall parts  31  and  32  (side wall parts, second side wall parts), and side wall parts  33  and  34  (side wall parts, third side wall parts). 
     The side wall part  31  of the accommodating part  12  extends along the side surface  8   c  on the negative side in the X-axis direction of the second foot part  8 , and is interposed between the second foot part  8  and the coil conductor  53 . The side wall part  31  extends parallel to the YZ plane to cover the side surface  8   c  at a position on the negative side of the side surface  8   c  in the X-axis direction. The side wall part  31  of the accommodating part  12  is interposed between the side surface  8   c , and an edge portion of the penetration part  51  and the side part  53   a  of the coil conductor  53  (see  FIG. 2 ). 
     The side wall part  32  of the accommodating part  12  extends along the side surface  8   d  on the positive side in the X-axis direction of the second foot part  8  and is interposed between the second foot part  8  and the coil conductor  53 . The side wall part  32  extends parallel to the YZ plane to cover the side surface  8   d  at a position on the positive side of the side surface  8   d  in the X-axis direction. The side wall part  32  of the accommodating part  12  is interposed between the side surface  8   d , and an edge portion of the penetration part  51  and the side part  53   b  of the coil conductor  53  (see  FIG. 2 ). 
     The side wall part  33  of the accommodating part  12  extends along the side surface  8   a  on the positive side in the Y-axis direction of the second foot part  8  and is interposed between the second foot part  8  and the coil conductor  53 . The side wall part  33  extends parallel to the XZ plane to cover the side surface  8   a  at a position on the positive side of the side surface  8   a  in the Y-axis direction. Both end portions of the side wall part  33  in the X-axis direction are connected to end portions on the positive side of the side wall parts  31  and  32  in the Y-axis direction. The side wall part  33  of the accommodating part  12  is interposed between the side surface  8   a , and an edge portion of the penetration part  51  and the side part  53   d  of the coil conductor  53  (see  FIG. 2 ). 
     The side wall part  34  of the accommodating part  12  extends along the side surface  8   b  on the negative side in the Y-axis direction of the second foot part  8  and is interposed between the second foot part  8  and the coil conductor  53 . The side wall part  34  extends parallel to the XZ plane to cover the side surface  8   b  at a position on the negative side of the side surface  8   b  in the Y-axis direction. Both end portions of the side wall part  34  in the X-axis direction are connected to end portions on the negative side of the side wall parts  31  and  32  in the Y-axis direction. The side wall part  34  of the accommodating part  12  is interposed between the side surface  8   b , and an edge portion of the penetration part  51  and the side part  53   c  of the coil conductor  53  (see  FIG. 2 ). 
     End portions on the negative side of the side wall parts  31 ,  32 ,  33 , and  34  in the Z-axis direction are free end portions without being provided with a bottom wall part. Thereby, an opening  35  is formed on a bottom surface side of the accommodating part  12 . The lower surface  8   e  of the second foot part  8  and the upper surface  2   a  of the second core  2  face each other via the opening  35  in a state in which they are separated from each other in the Z-axis direction. Thereby, a gap GP is formed between the second foot part  8  and the second core  2 . As illustrated in  FIG. 4 , a heat dissipation material  60  is disposed in the gap GP. The heat dissipation material  60  is in contact with the lower surface  8   e  of the second foot part  8  and the upper surface  2   a  of the second core  2 . The heat dissipation material  60  is formed to thermally connect the lower surface  8   e  of the second foot part  8  and the upper surface  2   a  of the second core  2 . The heat dissipation material  60  is formed by being filled into the gap GP in a state of having fluidity and is then cured. Further, the heat dissipation material  60  is made of a material having a higher thermal conductivity than the insulating member  3  and a general gap sheet, and for example, a gap filler or the like may be employed. 
     The side wall parts  31 ,  32 ,  33 , and  34  extend to the second core  2  side (that is, the negative side in the Z-axis direction) with respect to the substrate  50  and the lower surface  8   e  of the second foot part  8 . Lower end portions of the side wall parts  31 ,  32 ,  33 , and  34  are disposed at positions slightly separated from the upper surface  2   a  of the second core  2 . Thereby, the side wall parts  31 ,  32 ,  33 , and  34  protrude in the Z-axis direction from four edge portions of the lower surface  8   e . The side wall parts  31 ,  32 ,  33 , and  34  are disposed to surround and partition the gap GP. Therefore, the side wall parts  31 ,  32 ,  33 , and  34  can inhibit the heat dissipation material  60  flowing out before it is cured when the heat dissipation material  60  is filled into the gap GP. 
     As illustrated in  FIG. 3 , the connecting part  13 A includes an upper wall part  41  and side wall parts  43  and  44 . The connecting part  13 B includes an upper wall part  41  and side wall parts  43  and  44 . Since a configuration of the connecting part  13 B has the same effect as that of the connecting part  13 A, description thereof will be omitted. 
     The upper wall part  41  extends in the X-axis direction along the main body part  6  between the first foot part  7 A and the second foot part  8 . The upper wall part  41  is interposed between the main body part  6  and the coil conductor  53 . The upper wall part  41  extends parallel to the XY plane to cover the lower surface  6   a  at a position on the negative side of the lower surface  6   a  of the main body part  6  in the Z-axis direction. Both end portions of the upper wall part  41  in the X-axis direction are connected to end portions of the side wall parts  21  and  31  on the positive side in the Z-axis direction. The upper wall part  41  is interposed between the lower surface  6   a  and the side part  53   a  of the coil conductor  53  (see  FIG. 2 ). 
     The side wall part  43  rises from an end portion of the upper wall part  41  on the positive side in the Y-axis direction to the positive side in the Z-axis direction. The side wall part  43  faces the side surface  6   c  of the main body part  6  in the Y-axis direction. The side wall part  43  is connected to the side wall parts  23  and  33  to form the same plane as the side wall part  23  and the side wall part  33 . The side wall part  44  rises from an end portion of the upper wall part  41  on the negative side in the Y-axis direction to the positive side in the Z-axis direction. The side wall part  44  faces the side surface  6   d  of the main body part  6  in the Y-axis direction. The side wall part  44  is connected to the side wall parts  24  and  34  to form the same plane as the side wall part  24  and the side wall part  34 . 
     Next, the operation and effects of the coil structure  100  according to the present embodiment will be described. 
     In the coil structure  100  according to the present disclosure, the insulating member  3  includes the bottom wall parts  25  each interposed between the pair of first foot parts  7 A and  7 B and the second core  2 . Thereby, the insulating member  3  can adjust an L value between the first foot parts  7 A and  7 B and the second core  2 . 
     Here, in a coil structure according to a comparative example illustrated in  FIG. 5 , a gap sheet  130  is used to adjust gaps between the first foot parts  7 A and  7 B and the second core  2 . However, when such a gap sheet  130  is used, it is difficult for the first core  1  to be positioned and fixed with respect to the gap sheet  130 . Therefore, there is a possibility that a position of the first core  1  with respect to the second core  2  will be deviated. Also, it becomes difficult to check the positional deviation. 
     In contrast, in the present embodiment, the insulating member  3  extends along the pair of first foot parts  7 A and  7 B and the second foot part  8 , and includes the side wall parts  21 ,  23 ,  24 ,  31 ,  32 ,  33 , and  34  interposed between these foot parts  7 A,  7 B, and  8  and the coil conductor  53 . In this case, the side wall parts  21 ,  23 ,  24 ,  31 ,  32 ,  33 , and  34  can function as positioning parts for the first core  1 . Therefore, when a gap is formed between the first foot parts  7 A and  7 B of the first core  1  and the second core  2 , fixing, positioning, and checking of the insulating member  3  can be easily performed. As described above, since the processing can be easily performed, deviations or the like between the members can be prevented and a performance of the coil structure  100  can be improved. 
     Here, for example, in a structure of a DC-DC converter for vehicles, the cores  1  and  2  and the coil conductor  53  should all be set to a primary side voltage (dangerous voltage) of a circuit from a viewpoint of safety standards. However, for heat dissipation of the cores  1  and  2 , it is necessary to bring the cores  1  and  2  into contact with a heat dissipation member (provided on a lower surface side of the second core  2 ). Therefore, a portion of the coil conductor  53  becomes a primary side voltage, and the cores  1  and  2  become a secondary side voltage (safety voltage). Here, there are cases in which a safety distance standard of the DC-DC converter is determined to be, for example, 2.6 mm. In the coil structure according to the comparative example illustrated in  FIG. 5 , only a space is formed between the coil conductor  53  and the first core  1 . Therefore, it is necessary to secure a safety distance according to the standard between the coil conductor  53  and each side surface of the foot parts  7 A,  7 B, and  8 . For example, as the distances illustrated in  FIG. 5 , it is necessary to secure large distances between the side surface  7   d  of the first foot part  7 A and the coil conductor  53 , between the second foot part  8  and the coil conductor  53 , and between the lower surface  6   a  of the main body part  6  and the coil conductor  53 . Thereby, a problem occurs in that the coil structure becomes large. 
     In contrast, in the present embodiment, the side wall parts  21 ,  23 ,  24 ,  31 ,  32 ,  33 , and  34  are interposed between the foot parts  7 A,  7 B, and  8  and the coil conductor  53 . In this case, since the insulating member  3  is disposed between the foot parts  7 A,  7 B, and  8  and the coil conductor  53 , distances between the foot parts  7 A,  7 B, and  8  and the coil conductor  53  can be decreased. Thereby, reduction in size of the coil structure  100  can be achieved. 
     The pair of first foot parts  7 A and  7 B may extend from both end sides of the main body part  6  in the X-axis direction, and the second foot part  8  may be disposed on an inner circumferential side of the coil conductor  53  between the pair of first foot parts  7 A and  7 B. In this case, the coil structure  100  of the present disclosure can be applied to an EI core. 
     The insulating member  3  includes the side wall parts  21  which extend along the side surfaces  7   d  on the inner side in the X-axis direction of the first foot parts  7 A and  7 B and are interposed between the first foot parts  7 A and  7 B and the coil conductor  53 . Thereby, distances between the first foot parts  7 A and  7 B and the coil conductor  53  in the X-axis direction can be decreased. 
     The insulating member  3  includes the side wall parts  31  and  32  which extend along the side surfaces  8   c  and  8   d  in the X-axis direction of the second foot part  8  and are interposed between the second foot part  8  and the coil conductor  53 . Thereby, a distance between the second foot part  8  and the coil conductor  53  in the X-axis direction can be decreased. 
     The insulating member  3  includes the side wall parts  33  and  34  which extend along the side surfaces  8   a  and  8   b  in the Y-axis direction of the second foot part  8  and are interposed between the second foot part  8  and the coil conductor  53 . In this case, a distance between the second foot part  8  and the coil conductor  53  in the Y-axis direction can be decreased. 
     The insulating member  3  includes the upper wall parts  41  which extend in the X-axis direction along the main body part  6  between the first foot parts  7 A and  7 B and the second foot part  8 . In this case, a distance between the main body part  6  and the coil conductor  53  can be decreased. 
     The insulating member  3  includes the side wall parts  22  which extend along the side surfaces  7   c  on the outer side in the X-axis direction of the first foot parts  7 A and  7 B. In this case, when other conductors are present on the outer side of the first foot parts  7 A and  7 B in the X-axis direction, distances between the conductors and the first foot parts  7 A and  7 B in the X-axis direction can be decreased. 
     The heat dissipation material  60  may be disposed in the gap GP between the second foot part  8  and the second core  2 . Thereby, a heat dissipation path can be formed between the second foot part  8  and the second core  2  in which heat is easily accumulated. 
     The insulating member  3  includes the side wall parts  31  and  32  which extend along the side surfaces  8   c  and  8   d  in the X-axis of the second foot part  8  direction and are interposed between the second foot part  8  and the coil conductor  53 , and the side wall parts  31  and  32  extend to the second core  2  side with respect to the lower surface  8   e  of the second foot part  8 . In this case, vicinities of the end portions of the side wall parts  31  and  32  on the second core  2  side can block the heat dissipation material  70 . 
     The present disclosure is not limited to the embodiment described above. 
     The configuration of the insulating member  3  is not limited to the above-described embodiment. For example, the side wall parts  22 ,  23 ,  24 ,  43 , and  44  may be omitted from the insulating member  3 . Also, the insulating member  3  need only include at least one side wall part which extends along at least either of the first foot part and the second foot part and is interposed between either of the foot parts and the coil conductor  53 . 
     In the embodiment described above, the EI core has been described as an example. However, the coil structure of the present disclosure is not particularly limited in types of core, and can also be applied to UI cores, EE cores, UU cores, or the like. 
     A coil structure in a case of a UI core has a configuration in which portions of the first foot part  7 B and the corresponding insulating member  3  are removed from the above-described embodiment. Specifically, the first foot part  7 B and a portion on the positive side of the second foot part  8  in the X-axis direction in the main body part  6  are omitted from the first core  1 , and thereby a U-shaped first core is formed. Also, the first accommodating part  11 B and the connecting part  13 B are omitted from the insulating member  3 . 
     As a coil structure in a case of an EE core, in the above-described embodiment, an E-shaped core having the same configuration as the first core  1  is employed as the second core instead of the I-shaped core. In this case, the second core is disposed with the first core  1  inverted upside down in the Z-axis direction. Thereby, the foot parts  7 A,  7 B, and  8  of the first core  1  are connected to the foot parts  7 A,  7 B, and  8  of the second core. Further, the insulating member  3  may be provided also with respect to the second core. A coil structure in a case of a UU core has a configuration in which the U-shaped core described in the UI core is used as the first coil and the second coil. 
     Embodiment 1. A coil structure comprising:
         a substrate including a coil conductor;   a first core disposed on one main surface side of the substrate;   a second core disposed on the other main surface side of the substrate; and   an insulating member made of an insulating material, wherein the first core includes:   a main body part extending in a first direction along a main surface of the substrate;   a first foot part extending from the main body part to the second core through the substrate; and   a second foot part extending from the main body part to the second core through the substrate at a position at which the coil conductor is sandwiched between the second foot part and the first foot part in the first direction, and   the insulating member includes:   a bottom wall part interposed between at least the first foot part and the second core; and   a side wall part extending along at least either of the first foot part and the second foot part and interposed between either of the foot parts and the coil conductor.
 
Embodiment 2. The coil structure according to embodiment 1, wherein
   a pair of the first foot parts extend from both end sides of the main body part in the first direction, and   the second foot part is disposed on an inner circumferential side of the coil conductor between the pair of first foot parts.
 
Embodiment 3. The coil structure according to embodiment 1 or 2, wherein the insulating member includes a first side wall part extending along a side surface on an inner side in the first direction of the first foot part and interposed between the first foot part and the coil conductor.
 
Embodiment 4. The coil structure according to any one of embodiments 1 to 3, wherein the insulating member includes a second side wall part extending along a side surface in the first direction of the second foot part and interposed between the second foot part and the coil conductor.
 
Embodiment 5. The coil structure according to any one of embodiments 1 to 4, wherein
   a direction extending along the main surface of the substrate and intersecting the first direction is a second direction, and   the insulating member includes a third side wall part extending along a side surface in the second direction of the second foot part and interposed between the second foot part and the coil conductor.
 
Embodiment 6. The coil structure according to any one of embodiments 1 to 5, wherein the insulating member includes an upper wall part extending in the first direction along the main body part between the first foot part and the second foot part.
 
Embodiment 7. The coil structure according to any one of embodiments 1 to 6, wherein the insulating member includes a fourth side wall part extending along a side surface on an outer side in the first direction of the first foot part.
 
Embodiment 8. The coil structure according to any one of embodiments 1 to 7, wherein a heat dissipation material is disposed in a gap between the second foot part and the second core.
 
Embodiment 9. The coil structure according to embodiment 8, wherein
   the insulating member includes the second side wall part extending along a side surface in the first direction of the second foot part and interposed between the second foot part and the coil conductor, and   the second side wall part extends to the second core side with respect to a lower surface of the second foot part.       

     REFERENCE SIGNS LIST 
     
         
         
           
               1  First core 
               2  Second core 
               3  Insulating member 
               7 A,  7 B First foot part 
               6  Main body part 
               8  Second foot part 
               21  Side wall part (side wall part, first side wall part) 
               22  Side wall part (fourth side wall part) 
               23 ,  24  Side wall part (side wall part) 
               25  Bottom wall part 
               31 ,  32  Side wall part (side wall part, second side wall part) 
               33 ,  34  Side wall part (side wall part, third side wall part) 
               41  Upper wall part 
               100  Coil structure