Patent Publication Number: US-2019172630-A1

Title: Coil device

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a coil device used for example as a coil type common mode field and the like. 
     As a common mode choke coil used as the coil type common field filter and the like, for example a coil device shown in following Patent document 1 is known. In this coil device, an improvement of a mode conversion property is proposed. 
     In the coil device used as a conventional common mode filter and the like, many of them are structured to have a wire connecting part on the mounting face as shown in Patent document 1. When the wire connecting part is present on the mounting face, heat of a solder during mounting may have adverse effect on the wire connecting part, thus a heat-resistant wire needs to be used. Also, it is difficult to attain a structure having strong thermal shock resistance. 
     Thus, a coil device in which wires are connected at an opposite face of the mounting face is proposed. However, when using the coil device in which the wires are connected at the opposite face of the mounting face to the common field filter and the like, a risk of compromising the mode conversion property was confirmed. 
     Patent document 1: JP Patent Application Laid Open No. 2017-112156 
     SUMMARY OF THE INVENTION 
     The present invention is attained in view of such circumstances, and the object thereof is to provide a coil device capable of being suitably used as a common mode filter having excellent mode conversion property. 
     In order to attain the above object, the coil device according to the present invention has 
     a core, 
     a first collar part and a second collar part each provided at both sides along the axis direction of the core, 
     a coil part at least having a first wire and a second wire which are wound around the core, 
     a first terminal connected with one lead part of the first wire and provided to the first collar part, 
     a second terminal connected with one lead part of the second wire and provided apart from the first terminal to the first collar part, 
     a third terminal connected with other lead part of the first wire and provided to the second collar part, 
     a fourth terminal connected with other lead part of the second wire and provided apart from the third terminal to the second collar part, wherein 
     the one lead part of the first wire heading towards the coil part from the first terminal and the one lead part of the second wire heading towards the coil part from the second terminal are placed in close proximity at least between the coil part and an inner face of the first collar part, and 
     the first wire and the second wire form a crossing part of which the first wire and the second wire are crossing against each other in the middle of the core. 
     As a result of keen study regarding the coil device such as the common field filter and the like by the present inventors, it was found that by placing the one lead part of the first wire heading towards the coil part from the first terminal and the one lead part of the second wire heading towards the coil part from the second terminal in close proximity at least between the inner face of the first collar part and the coil part, and also by providing a crossing part in the middle of the coil part, the mode conversion property can be improved. Thereby, the present invention was attained. 
     As an index relating to a noise property and a signal quality of the common mode filter, the mode conversion property is used. When the mode conversion property is good, this means that a differential signal is not converted to a common mode and a property as the common mode filter is good. Particularly recently, a data transfer rate is improved, and an excellent mode conversion property is demanded at the data transfer rate of 100 Mbps or more. Particularly, the common mode filter used for Automotive Ethernet™ and the like is demanded to attain a higher performance. According to the coil device of the present invention, the common mode filter capable of corresponding to such demands can be attained. 
     According to the coil device of the present invention, the mode conversion property improves even when the wire connecting part is placed other than the mounting face. Therefore, the adverse effect to the wire connecting part by heat of a solder during mounting decreases, and the heat resistant wire does not necessarily have to be used as the wire constituting the coil part. Also, since the wire does not necessarily have to be connected to the mounting part, for example a metallic terminal can be provided to the collar part, and the structure having a strong thermal shock resistance can be easily attained. Therefore, for example, it can be suitably used as a coil device for automobile. 
     Also, the wires do not have to be connected to the mounting part, thus even in case of coating a moisture proof material to the coil device, a stress acting on the wire connecting part is relieved, and a durability of the wire connecting part improves. Further, in image recognition of a solder fillet after mounting, the connecting part is suppressed from appearing in the image, and the image recognition becomes easy, thus an image recognition evaluation is stabilized. 
     Preferably, the other lead part of the first wire heading towards the coil part from the third terminal and the other lead part of the second wire heading towards the coil part from the fourth terminal are placed in close proximity at least between the inner face of the second collar part and the coil part. By constituting as such, the mode conversion property is further improved. 
     Preferably, the first collar part is provided with a first common guiding passage which guides the one lead part of the first wire and the one lead part of the second wire towards outside from the inner face of the first collar part. By constituting as such, the lead parts of both wires can be easily placed in close proximity between the coil part and the inner face of the collar part. The lead parts of the first wire and second wire extending out from the first common guiding passage respectively extend towards the wire connecting part of the first terminal and the wire connecting part of the second terminal, and the wires are connected there. 
     Preferably, the second collar part is provided with a second common guiding passage which guides the other lead part of the first wire and the other lead part of the second wire towards outside from the inner face of the second collar part. By constituting as such, the lead parts of both wires can be easily placed in close proximity between the coil part and the inner face of the collar part. The lead parts of the first wire and second wire extending out from the second common guiding passage respectively extend towards the wire connecting part of the third terminal and the wire connecting part of the fourth terminal, and the wires are connected there. 
     A first terminal guiding passage which guides the one lead part of the first wire towards outside from the inner face of the first collar part and a second terminal guiding passage which guides the one lead part of the second wire towards outside from the inner face of the first collar part may be formed to the first collar part, and the first terminal guiding passage and the second guiding passage may be in close proximity at the inner face of the first collar part. By constituting as such, the lead parts of both wires can be placed in close proximity between the inner face of the first collar part and the coil part, and in such case the mode conversion property improves as well. 
     A third terminal guiding passage which guides the other lead part of the first wire towards outside from the inner face of the second collar part and a fourth terminal guiding passage which guides the other lead part of the second wire towards outside from the inner face of the second collar part may be formed to the second collar part, and the third terminal guiding passage and the fourth guiding passage may be in close proximity at the inner face of the second collar part. By constituting as such, the lead parts of both wires can be placed in close proximity between the inner face of the collar part and the coil part, and in such case the mode conversion property improves as well. 
     Preferably, the coil device further has a board which extends between an opposite face of the mounting face of the first collar part and an opposite face of the mounting face of the second collar part. The board is preferably constituted by a magnetic material as similar to a magnetic core made from a coil and a core part, but the board does not necessarily have to be a magnetic material. By constituting the board by a magnetic material, a closed magnetic path circuit can be formed together with the magnetic core, and a magnetic property of the coil device improves. 
     The board may be provided with a board first common guiding passage which guides the one lead part of the first wire and the one lead part of the second wire together towards outside from the inner face of the first collar part. Also, the board may be provided with a board second common guiding passage which guides the other lead part of the first wire and the other lead part of the second wire together towards outside from the inner face of the second collar part. By forming the guiding passages to the board, a guiding passage does not have to be formed to the guiding passage, and a volume reduction of the magnetic core is suppressed, thus the magnetic property can be improved. 
     A length of the one lead part of the first wire from the coil part to the first terminal and a length of the one lead part of the second wire from the coil part to the second terminal may be about the same, or may be different. Preferably, a number of windings of the first wire around the coil part and a number of windings of the second wire around the coil part are the same. By constituting as such, the mode conversion property can be further improved. 
     Preferably, a winding density of the first wire and a winding density of the second wire decrease in the middle of the core and form an exposed area in which a surface of the core is exposed, and the crossing part is formed to the exposed area. By constituting as such, the mode conversion property further improves. 
     In the coil device of the present invention, even in case wire connecting parts of the first terminal, second terminal, third terminal, and fourth terminal are placed other than the mounting face of the first collar part and the second collar part, the mode conversion property can be improved. Particularly, in case the coil device has the board, the mode conversion property can be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of the coil device according to an embodiment of the present invention. 
         FIG. 2  is a plan view of the coil device shown in  FIG. 1 . 
         FIG. 3  is an exploded perspective view of the coil device shown in  FIG. 1 . 
         FIG. 4A  is a perspective view of the coil device according to other embodiment of the present invention. 
         FIG. 4B  is a perspective view of the coil device according to further other embodiment of the present invention. 
         FIG. 4C  is a perspective view of the coil device according to further other embodiment of the present invention. 
         FIG. 4D  is a perspective view of the coil device according to a comparative example of the present invention. 
         FIG. 5  is a graph showing an effect of the coil device according to an example of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, the present invention will be described based on an embodiment. 
     First Embodiment 
     A coil device  10  according to an embodiment of the present invention shown in  FIG. 1  is preferably used as a coil type common mode filter and the like, and the use thereof is not particularly limited. For example, it may be used as a balun, a dual inductor, and the like. 
     The coil device  10  has a drum core  20 , a coil part  40  wound around a core  22  of the drum core  20 , and a board  30  placed on upper part of the drum core  20 . Note that, when explaining the coil device  10 , X-axis direction is on a parallel plane with a mounting face where the coil device  10  is mounted and also X-axis direction is parallel to a coil axis of the core  22  of the drum core  20 , Y-axis direction is on a parallel plane with a mounting face as similar to X-axis and is perpendicular to X-axis; and Z-axis direction is a normal direction to the mounting face. 
     The drum core  20  has the core  22  of rod shape and a pair of first collar part  24  and second collar part  26  as a pair of end part of the core provided to both ends of the core  22 . An outer shape of the first collar part  24  is approximately rectangular parallelepiped shape, the first collar part  24  and the second collar part  26  are placed to be approximately parallel to each other taking predetermined space in X-axis direction between each other. The core  22  is connected to approximately center part of each faces of the pair of first and second collar parts  24  and  26  which are facing against each other, and the core  22  is integrally formed with the pair of first and second collar parts  24  and  26  as one body. A transverse cross section shape of the core  22  is rectangle shape in the present embodiment, but the cross section shape is not particularly limited and it may be a circular shape. 
     At an upper end part in Z-axis direction of the drum core  20 , a board  30  is preferably adhered. The flat board  30  extends between an opposite face  24   b  of the mounting face  24   a  of the first collar  24  and an opposite face  26   b  of the mounting face  26   a  of the second collar  26 , and the board  30  preferably connects with these opposite faces of the mounting face. 
     As shown in  FIG. 3 , in the present embodiment, the first collar  24  is constituted in a rectangular parallelepiped shape as a whole. The first collar part  24  has a mounting face  24   a  which is a lower face in Z-axis direction, the opposite face  24   b  which is opposite to the mounting face  24   a , an outer end face  24   c  in X-axis direction, an inner face  24   d  facing towards the core  22 , and a pair of side faces  24   e  and  24   e  which are positioned opposite to each other in Y-axis direction. At the center part in Y-axis direction of the opposite face  24   b  of the mounting face  24   a , a first common guiding passage  24   b   1  of a groove shape is formed, which is opened in X-axis direction. 
     Also, at outer side in X-axis direction of the opposite face  24   b  of the mounting face  24   a , a guiding face  24   b   2  is formed approximately on the same level in Z-axis direction of the first common guiding passage  24   b   1 . Also, at both sides in Y-axis direction of the opposite face  24   b  of the mounting face  24   a , a wire connection step face  24   b   3  is formed which is slightly lower in Z-axis direction with respect to the guiding step face  24   b   2 . 
     The depth of the first common guiding passage  24   b   1  in Z-axis direction only needs to be a depth so that the one lead part  41   a  of the first wire  41  and the one lead part  42   a  of the second wire  42  which are constituting the coil part  40  shown in  FIG. 1  can pass through the first common guiding passage  24   b   1  without being interfered by the board  30 . Also, a width in Y-axis direction of the first common guiding passage  24   b   1  only needs to be a width so that the one lead part  41   a  of the first wire  41  and the one lead part  42   a  of the second wire  42  can pass through the first common guiding passage  24   b   1  without being interfered by the board  30 . Note that, a position where the first common guiding passage  24   b   1  is formed does not necessarily have to be at a center in Y-axis direction of the opposite face  24   b  of the mounting face  24   a , and it may be shifted towards either one of the side faces  24   e.    
     A width in X-axis direction of the guiding face  24   b   2  dented in X-axis direction from the outer end face  24   c  is not particularly limited as long as each of lead parts  41   a  and  42   a  can be guided to outside in Y-axis direction. As shown in  FIG. 2 , the lead parts  41   a  and  42   a  together extend out from the coil part  40  to the inner face  24   d  of the first collar part  24 , and extend to outside in X-axis direction by together passing through the first common guiding passage  24   b   1 . Then, the lead parts  41   a  and  42   a  respectively extend to opposite direction with each other towards outside in Y-axis direction of the guiding face  24   b   2 . 
     As shown in  FIG. 3 , at both sides in Y-axis direction of the outer end face  24   c , a terminal installation face  24   c   1  is formed to each side which is dented towards the inner side in X-axis direction (a center side of the core  20 ) than the outer end face  24   c . A width of each terminal installation face  24   c   1  is about the same as the width in Y-axis direction of the wire connection step face. An inner face of a terminal main body  51   c  of the first terminal  51  and an inner face of a terminal main body  52   c  of the second terminal  52  are respectively installed to each terminal installation face  24   c , and if needed, it is adhered. 
     The terminal installation face  24   c   1  is dented towards inside in X-axis direction with respect to the outer end face  24   c  preferably in a level about the same as the thickness of the first terminal  51  or the second terminal  52 . Also, the wire connection step face  24   b   3  is lower in Z-axis direction with respect to the guiding face  24   b   2 , and it is preferably lower in a level about the same as the thickness of the first terminal  51  or the second terminal  52 . 
     The first terminal  51  is constituted by a conductive board material such as metal and the like. In the first terminal  51 , a bended part which becomes the mounting part  51   a  is integrally formed to the terminal main body  51   c  at a lower side in Z-axis direction of the rectangle shaped terminal main body  51   c ; and a bended part which becomes the wire connection part  51   b  is integrally formed to the terminal main body  51   c  at an upper side in Z-axis direction of the terminal main body  51   c . The mounting part  51   a  is constituted to be about the same shape as the wire connection part  51   b , and it is installed by attaching to the mounting face  24   a  of the first collar part  24 . The wire connection part  51   b  is installed by attaching to the wire connection step face  24   b   3 . 
     The wire connection step face  24   b   3  and the mounting face  24   a  positioned opposite thereof are held by the wire connection part  51   b  and the mounting part  51   a , thereby the terminal main body  51   c  of the first terminal  51  is installed to the terminal installation face  24   c   1 . Thus, the first terminal  51  is easily installed to the first collar part  24 , and an installation strength improves. 
     As similar to the first terminal  51 , the second terminal  52  is also constituted by a conductive board material such as metal and the like. In the second terminal  52 , a bended part which becomes the mounting part  52   a  is integrally formed to the terminal main body  52   c  at a lower side in Z-axis direction of the rectangle shaped terminal main body  52   c ; and a bended part which becomes the wire connection part  52   b  is integrally formed to the terminal main body  52   c  at an upper side in Z-axis direction of the terminal main body  52   c . The mounting part  52   a  is constituted to be about the same shape as the wire connection part  52   b  and it is installed by attaching to the mounting face  24   a  of the first collar part  24 . The wire connection part  52   b  is installed by attaching to the wire connection step face  24   b   3 . 
     The wire connection step face  24   b   3  and the mounting face  24   a  positioned opposite thereof are held by the wire connection part  52   b  and the mounting part  52   a , thereby the terminal main body  52   c  of the second terminal  52  is installed to the terminal installation face  24   c   1 . Thus, the second terminal  52  is easily installed to the first collar part  24 , and an installation strength improves. 
     In the present embodiment, the second collar part  26  has similar constitution as the first collar part  24 , but it does not necessarily have to be the same. In the present embodiment, the second collar part  26  is constituted in a rectangular parallelepiped shape as a whole, and the second collar part  26  has the mounting face  26   a  which is the lower face in Z-axis direction, and an opposite face  26   b  of the mounting face  26   a , an outer end face  26   c  in X-axis direction, an inner face  26   d  facing towards the direction of the core  22 , and a pair of side faces  26   e  and  26   e  positioned opposite to each other in Y-axis direction. At a center part in Y-axis direction of the opposite face  26   b  of the mounting face  26   a , a second guiding passage  26   b   1  of a groove shape is formed, which is opened in X-axis direction. 
     Also, at outer side in X-axis direction of the opposite face  26   b  of the mounting face  26   a , a guiding face  26   b   2  is formed approximately on the same level in Z-axis direction of the second common guiding passage  26   b   1 . Also, at both sides in Y-axis direction of the opposite face  26   b  of the mounting face  26   a , a wire connection step face  26   b   3  is formed which is slightly lower in Z-axis direction with respect to the guiding step face  26   b   2 . 
     The depth of the second common guiding passage  26   b   1  in Z-axis direction only needs to be a depth so that the other lead part  41   b  of the first wire  41  and the other lead part  42   b  of the second wire  42  which are constituting the coil part  40  shown in  FIG. 2  can pass through the second common guiding passage  26   b   1  without being interfered by the board  30  shown in  FIG. 1 . Also, a width in Y-axis direction of the second common guiding passage  26   b   1  only needs to be a width so that the other lead part  41   b  of the first wire  41  and the other lead part  42   b  of the second wire  42  can pass through the second common guiding passage  26   b   1  without being interfered by the board  30 . Note that, a position where the second common guiding passage  26   b   1  is formed does not necessarily have to be at a center in Y-axis direction of the opposite face  26   b  of the mounting face  26   a , and it may be shifted towards either one of the side faces  26   e.    
     As shown in  FIG. 3 , a width in X-axis direction of the guiding face  26   b   2  dented in X-axis direction from the outer end face  26   c  is not particularly limited as long as each of lead parts  41   b  and  42   b  shown in  FIG. 2  can be guided to outside in Y-axis direction. The lead parts  41   b  and  42   b  together extend out from the coil part  40  to the inner face  26   d  of the second collar part  26 , and extend to outside in X-axis direction by together passing through the second common guiding passage  26   b   1 . Then, the lead parts  41   b  and  42   b  respectively extend in opposite direction with respect to each other towards outside in Y-axis direction of the guiding face  26   b   2 . 
     As shown in  FIG. 3 , at both sides in Y-axis direction of the outer end face  26   c , a terminal installation face  26   c   1  is formed on each side which is dented towards the inner side in X-axis direction (a center side of the core  20 ) than the outer end face  26   c . A width of each terminal installation face  26   c   1  is about the same as the width in Y-axis direction of the wire connection step face  26   b   3 . An inner face of a terminal main body  53   c  of the third terminal  53  and an inner face of a terminal main body  54   c  of the fourth terminal  54  are respectively installed to each terminal installation face  26   c   1 , and if needed, it is adhered. 
     The terminal installation face  26   c   1  is dented towards inside in X-axis direction with respect to the outer end face  26   c  preferably in a level about the same as the thickness of the third terminal  53  or the fourth terminal  54 . Also, the wire connection step face  26   b   3  is lower in Z-axis direction with respect to the guiding face  26   b   2 , and it is preferably lower in a level about the same as the thickness of the third terminal  53  or the fourth terminal  54 . 
     The third terminal  53  is constituted by a conductive board material such as metal and the like. In the third terminal  53 , a bended part which becomes the mounting part  53   a  is integrally formed to the terminal main body  53   c  at a lower side in Z-axis direction of the rectangle shaped terminal main body  53   c ; and a bended part which becomes the wire connection part  53   b  is integrally formed to the terminal main body  53   c  at an upper side in Z-axis direction of the terminal main body  53   c . The mounting part  53   a  is constituted to be about the same shape as the wire connection part  53   b , and it is installed by attaching to the mounting face  26   a  of the second collar part  26 . The wire connection part  53   b  is installed by attaching to the wire connection step face  26   b   3 . 
     The wire connection step face  26   b   3  and the mounting face  26   a  positioned opposite thereof are held by the wire connection part  53   b  and the mounting part  53   a , thereby the terminal main body  53   c  of the third terminal  53  is installed to the terminal installation face  26   c   1 . Thus, the third terminal  53  is easily installed to the second collar part  26 , and an installation strength improves. 
     The fourth terminal  54  is constituted by a conductive board material such as metal and the like as similar to the first terminal  51 , the second terminal  52 , and the third terminal  53 . In the fourth terminal  54 , a bended part which becomes the mounting part  54   a  is integrally formed to the terminal main body  54   c  at a lower side in Z-axis direction of the rectangle shaped terminal main body  54   c ; and a bended part which becomes the wire connection part  54   b  is integrally formed to the terminal main body  54   c  at an upper side in Z-axis direction of the terminal main body  54   c . The mounting part  54   a  is constituted to be about the same shape as the wire connection part  54   b , and it is installed by attaching to the mounting face  26   a  of the second collar part  26 . The wire connection part  54   b  is installed by attaching to the wire connection step face  26   b   3 . 
     The wire connection step face  26   b   3  and the mounting face  26   a  positioned opposite thereof are held by the wire connection part  54   b  and the mounting part  54   a , thereby the terminal main body  54   c  of the fourth terminal  54  is installed to the terminal installation face  26   c   1 . Thus, the fourth terminal  54  is easily installed to the second collar part  26 , and an installation strength improves. 
     As shown in  FIG. 2 , a tip part of the one lead part  41   a  of the first wire  41  is attached to the wire connection part  51   b  of the first terminal  51 , and a tip part of the one lead part  42   a  of the second wire  42  is attached to the wire connection part  52   b  of the second terminal  52 . Also, a tip part of the other lead part  41   b  of the first wire  41  is attached to the wire connection part  53   b  of the third terminal  53 , and a tip part of the other lead part  42   b  of the second wire  42  is attached to the wire connection part  54   b  of the fourth terminal  54 . As a means for attaching these, it is not particularly limited, and a solder, a thermal compression, a laser welding, and the like may be mentioned. 
     As shown in  FIG. 1 , the coil part  40  is formed at the core  22  of the drum core  20 . In the present embodiment, the coil part  40  is constituted by two wires  41  and  42 . The wires  41  and  42  are for example constituted by a coated conductive wire, and have a constitution in which the core made of a good conductor being coated with an insulating coating film. For example, the wires  41  and  42  are wound around the core  22  in two layer structure. In the present embodiment, each of the wires  41  and  42  has the same transverse cross section area of the conductor part. 
     In the present embodiment, as shown in  FIG. 2 , a winding density of the first wire  41  and a winding density of the second wire  42  decrease in the middle of the core  22  in X-axis direction and forms an exposed area in which a surface of the core is exposed, and at the exposed area, a crossing part  43  is present where the first wire  41  and the second wire  42  cross with each other. 
     In the present embodiment, the first wire  41  and the second wire  42  form a usual bifilar-wound around the core  22 , and the crossing part  43  is formed at a predetermined position along an axis direction of the core  22 . 
     For a production of the coil device  10 , first, the drum core  20  provided with the terminals  51  to  54 , the board  30 , and the wires  41  and  42  are prepared. The drum core  20  is constituted by a magnetic material, and for example it is produced by molding and sintering magnetic powder constituted for example by a magnetic material having relatively high magnetic permeability such as Ni—Zn based ferrite, Mn—Zn based ferrite, magnetic metal, or the like. Preferably, the board  30  is constituted by a magnetic material which may be same or different from the drum core  20 , but the board  30  does not necessarily have to be constituted by a magnetic material. 
     The first to fourth terminals  51  to  54  made of metal are fixed at a predetermined position of the collar parts  24  and  26  of the drum core  20  by adhesion and the like. Note that, the terminals  51  to  54  may be provided to the collar part  24  by forming a conductive film to the drum core  20  by printing, plating, and the like, then by firing the conductive film. 
     As the wires  41  to  42 , for example, the core material made of a good conductor such as copper (Cu) and the like may be coated by an insulation material such as imide modified polyurethane and the like, then an outer most face may be coated by a thin resin film such as polyester and the like, thereby this may be used as the wires  41  to  42 . The prepared drum core  20  provided with the terminals  51  to  54  and the wires  41  and  42  are set to a coil winding machine, and the wires  41  and  42  are wound around the core  22  of the drum core  20  in predetermined sequence. 
     In the present embodiment, in a first section, the bifilar-wound of the first wire  41  and the second wire  42  is formed, and then in a second section, the bifilar-wound is formed by reversing the layer order of the first wire  41  and the second wire  42 . The lead parts  41   a ,  42   a ,  41   b , and  42   b  which are wire ends of the wound wires  41  and  42  are fixed to the wire connection parts  51   b  to  54   b  of the predetermined terminals  51  to  54  shown in  FIG. 2  by a silver solder, a thermal compression, a laser bonding, or the like. Note that, a method of winding the wires  41  and  42  is not particularly limited. Also, the winding may start from the second section which is closer to the second collar part  26  then to the first section direction which is closer to the first collar part  24 . 
     After winding the wires  41  and  42  around the core  22 , the board  30  is attached to the opposite faces  24   b  and  26   b  of the mounting faces  24   a  and  26   a  of the collar parts  24  and  26 . A means for attaching is not particularly limited, and for example a method of adhering may be mentioned. 
     In the coil device  10  according to the present embodiment, the one lead part  41   a  of the first wire  41  heading towards the coil part  40  from the first terminal  51  and the one lead part  42   a  of the second wire  42  heading towards the coil part  40  from the second terminal  52  are placed in close proximity at least between the inner face of the first collar part  24  and the coil part  40 . Note that, in the present embodiment, the two lead parts placed in close proximity means that each of the lead parts are in contact or in case it is away from each other the distance between the two is 1.6 mm or less. 
     Also, the other lead part  41   b  of the first wire  41  heading towards the coil part  40  from the third terminal  53  and the other lead part  42   b  heading towards the coil part  40  from the fourth terminal  54  are placed in close proximity at least between the inner face of the second collar part  26  and the coil part  40 . 
     That is, as shown in  FIG. 2 , the one lead part  41   a  of the first wire  41  and the one lead part  42   a  of the second wire  42  extending from the coil part  40  together extend out from the coil part  40  through the inner face  24   d  of the first collar part  24 , and guided towards the first common guiding passage  24   b   1 . The lead part  41   a  and the lead part  42   a  extend away from each other to the opposite direction in Y-axis direction at outside in X-axis direction of the first common guiding passage  24   b   1 . 
     Similarly, the other lead part  41   b  of the first wire  41  and the other lead part  42   b  of the second wire  42  extending from the coil part  40  together extend out from the coil part  40  through the inner face  26   d  of the second collar part  26 , and guided towards the second common guiding passage  26   b   1 . The lead part  41   b  and the lead part  42   b  extend away from each other to the opposite direction in Y-axis direction at outside in X-axis direction of the second common guiding passage  26   b   1 . Further in the present embodiment, the crossing part  43  is formed at a predetermined position along the axis direction of the core  22 . 
     The present inventors have found that by constituting as such, when the coil device  10  is used as the common mode filter, the mode conversion property improves. 
     As an index regarding the noise property and signal quality of the common mode filter, the mode conversion property is used. In case the mode conversion property is good, a differential signal is not converted to a common mode, thus this indicates that a property as the common mode filter is good. Particularly recently, the data transfer rate has improved, and an excellent mode conversion property at a transfer rate of 100 Mbps or more is demanded. Particularly, as the common mode filter used for Automotive Ethernet™ and the like, higher performance is demanded. According to the coil device  10  of the present embodiment, the common mode filter capable of complying with such demands can be attained. 
     According to the coil device  10  of the present embodiment, the wire connection parts  51   b  to  54   b  to which the wire  41  or  42  shown in  FIG. 2  is connected are not connected to the mounting faces  24   a  and  26   a  of the collar parts  24  or  26 , but are placed to the sides of the opposite faces  24   b  and  26   b  of the mounting faces  24   a  and  24   b  as shown in  FIG. 3 . Even in such case, the mode conversion property improves. Therefore, the wire connection parts  51   b  to  54   b  receives less adverse effect which is caused by heat of solder during mounting applied to the mounting parts  51   a  to  54   a  of the terminals  51  to  54 , thus the heat resistance wire does not necessarily have to be used as the wires  41  and  42  constituting the coil parts  40 . 
     Also, since there is no need to connect the wires  41  and  42  to the mounting parts  51   a  to  54   a , for example the metal terminals  51  to  54  can be installed to the collar parts  24  and  26 , thus a structure having strong thermal shock resistance can be attained. Therefore, for example it can be suitably used as the coil device  20  for automobile. 
     Also, since there is no need to connect the wires  41  and  42  to the mounting parts  51   a  to  54   a , even in case the moisture proof material is coated to the coil device  10 , the stress acting on the wire connection parts  51   b  to  54   b  of the wires  41  and  42  is relieved, thus the durability of the wire connection parts  51   b  to  54   b  of the wires  41  and  42  is improved. Further, in image recognition of a solder fillet after mounting, the wire connecting part is suppressed from appearing in the image, and the image recognition becomes easy, thus an image recognition evaluation is stabilized. 
     Also, in the present embodiment, as shown in  FIG. 2 , the first collar part  24  is provided with the first common guiding passage  24   b   1  which guides the one lead part  41   a  of the first wire  41  and the one lead part  42   a  of the wire  42  together towards outside from the inner face  24   d  of the first collar part  24 . By constituting as such, the lead parts  41   a  and  42   a  of the wires  41  and  42  can be placed in close proximity to each other between the inner face  24   d  of the collar part  24  and the coil part  40 . 
     Also, similarly, the second collar part  26  is provided with the second common guiding passage  26   b   1  which guides the other lead part  41   b  of the first wire  41  and the other lead part  42   b  of the second wire  42  together towards outside from the inner face  26   d  of the second collar part  26 . By constituting as such, the lead parts  41   b  and  42   b  of the wires  41  and  42  can be easily placed in close proximity to each other between the inner face  26   d  of the second collar part  26  and the coil part  40 . The lead parts  41   b  and  42   b  of the first wire  41  and the second wire  42  which extend from the second common guiding passage  26   b   1  further extend towards the wire connection part  53   b  of the third terminal  53  and the wire connection part  54   b  of the fourth terminal  54  respectively, and then the wire connection treatment is carried out. 
     Further, the present embodiment further has the board  30  which extends between the opposite face  24   b  of the mounting face  24   a  of the first collar part  24  and the opposite face  26   b  of the mounting face  26   a  of the second collar part  26 . The board  30  may be constituted by a magnetic material, thereby a closed magnetic path circuit can be formed together with the drum core  20  which is constituted by a magnetic material, and a magnetic property of the coil device  20  improves. 
     Further in the present embodiment, the wire length of the one lead part  41   a  of the first wire  41  from the coil part  40  to the wire connection part  51   b  of the first terminal  51  and the wire length of the one lead part  42   a  of the second wire  42  from the coil part  40  to the wire connection part  52   b  of the second terminal  52  are preferably about the same, but these may be different. Also, preferably, the number of windings of the first wire  41  and the number of winding of the second wire  42  around the coil  40  are the same. By constituting as such, the mode conversion property further improves. 
     In the coil device  10  of the present embodiment, the wire connection parts  51   b  to  54   b  of the wires of the first terminal  51 , second terminal  52 , third terminal  53 , and fourth terminal  54  are not positioned on the mounting face  24   a  of the first collar part  24  and the mounting face  26   a  of the second collar part  26 , but are positioned near the bonding part of the board  30  at the sides of the opposite faces  24   b  and  26   b  of the mounting faces  24   a  and  26   a.    
     In the present embodiment, the lead part  41   a  of the wire  41  heading towards the coil part  40  from the first terminal  51  and the lead part  42   a  of the wire  42  heading towards the coil part  40  from the second terminal  52  are placed in close proximity at least between the inner face  24   d  of the collar part  24  and the coil part  40 . Further, the crossing part  43  is formed at the predetermined position along the core axis direction of the core  22 . By constituting as such, the mode conversion property can be improved. Also, in the present embodiment, the lead part  41   b  of the wire  41  heading towards the coil part  40  from the third terminal  53  and the lead part  42   b  of the wire  42  heading towards the coil part  40  from the fourth terminal  54  are placed in close proximity at least between the inner face  26   d  of the second collar part  26  and the coil part  40 . Further, the crossing part  43  is formed at the predetermined position along the core axis direction of the core  22 . By constituting as such, the mode conversion property is further improved. 
     Also, in the present embodiment, as shown in  FIG. 2 , the lead peats  41   a  and  42   a  ( 41   a  and  42   b ) extend together between the coil part  40  and the inner face  24   d  ( 26   d ) of the first collar part  24  (the second collar part  26 ), and then passes through the first common guiding passage  24   b   1  ( 26   b   1 ) together. Then, the lead parts  41   a  and  42   a  ( 41   b  and  42   b ) extend towards outside in X-axis direction, and extend in opposite direction against each other towards outside in Y-axis direction on the guiding face  24   b   2  ( 26   b   2 ). Thus, lead parts  41   a  and  42   a  ( 41   b  and  42   b ) of the wire  41  ( 42 ) do not expose to outside of the coil device  10 , hence the lead parts  41   a  and  42   a  ( 41   b  and  42   b ) are unlikely to contact other members and cause damage while handling the coil device. 
     Further, in the present embodiment, as shown in  FIG. 3 , by fitting the terminals  51  to  54  to the collar parts  24  and  26 , the thermal shock resistance of the coil device  10  can be improved. Further, by providing a projection part and a dented part for fitting the terminals  51  to  54  and the collar parts  24  and  26  respectively, the position of the terminals  51  to  54  is stabilized; hence there is a merit from the point of the production. 
     Second Embodiment 
     The coil device according to the second embodiment of the present invention is same as the aforementioned first embodiment other than the constitutions mentioned in below, and the same effect is attained, thus the overlapping section is omitted from describing. Also, in the figures, the same members as the first embodiment are given with the same numerical references. 
     As shown in  FIG. 4A , a coil device  110  of this embodiment has a drum core  120 . An area of the opposite face  24   b  of the mounting face of the first collar part  24  of the drum core  120  is about the same as X-Y cross section of the first collar part  24 , and an bonding area with the board  30  is relatively larger compared to the coil device  10  of the embodiment shown in  FIG. 1 . 
     At approximately center part in Y-axis direction of the opposite face  24   b  of the mounting face  24   a , the first common guiding passage  24   b   1  is formed which is opened from the inner face  24   d  of the collar part  24  to the outer end face  24   c . The lead part  41   a  of the first wire and the lead part  42   a  of the second wire which are guided from the coil part  40  to the first common guiding passage  24   b   1  extend out to separate directions at an end part of the first common guiding passage  24   b   1 . A tip part of the lead part  41   a  of the first wire which extended out from the first common guiding passage  24   b   1  then heads towards a wire connection part  151   b  of a first terminal  151 , and the wire connection treatment such as soldering and the like is carried out. Also, a tip part of the lead part  42   a  of the second wire which extended out from the first common guiding passage  24   b   1  then heads towards a wire connection part  152   b  of the second terminal  152 , and the wire connection treatment such as soldering and the like is carried out. 
     In the present embodiment, the first terminal  151  and the second terminal  152  have the same shape, and each of them has the mounting parts  151   a  and  152   a , and the wire connection parts  151   b  and  152   b . These terminals  151  and  152  are for example formed by a metal board of which the cross section is L shaped, and each of them has the mounting parts  151   a  and  152   a , and the wire connection parts  151   b  and  152   b.    
     The mounting parts  151   a  and  152   a  of the terminals  151  and  152  are adhered to the mounting face  24   a  positioned near the outer end face  24   c  of the collar part  24  and away from each other taking predetermined distance in Y-axis direction. Also, the wire connection parts  151   b  and  152   b  of the terminals  151  and  152  are adhered to the outer end face  24   c  positioned near the mounting face  24   a  of the collar part  24  and away from each other taking predetermined distance in Y-axis direction. 
     Note that, although it is not shown in  FIG. 4A , the third terminal and the fourth terminal are in similar relation as in case of the first terminal  151  and the second terminal  152 , and have same shape and respectively has the mounting part and the wire connection part. 
     The mounting parts of the third terminal and the fourth terminal are adhered to the mounting face  26   a  positioned near the outer end face  26   c  of the collar part  26  and away from each other taking predetermined distance in Y-axis direction. Also, the wire connection parts of the third terminal and the fourth terminals are adhered to the outer end face  26   c  positioned near the mounting face  26   a  of the collar part  26  and away from each other taking predetermined distance in Y-axis direction. 
     In the present embodiment, the second collar part  26  has similar constitution as the first collar part  24 , and at approximately center part in Y-axis direction of the opposite face  26   b  of the mounting face  26   a , the second common guiding passage  26   b   1  is formed which is opened from the inner face  26   d  of the collar part  26  to the outer end face  26   c . The lead part  41   b  of the first wire and the lead part  42   b  of the second wire which are guided to the second common guiding passage  26   b   1  from the coil part  40  extend out in separate directions from the end part of the second common guiding passage  26   b   1 . This end part of the second common guiding passage  26   b   1  is formed between the edge of the outer end face  26   c.    
     The tip part of the lead part  41   b  of the first wire which extended out heads towards the wire connection part of the third terminal and then the wire connection treatment is carried out by soldering and the like. Also, the tip part of the lead part  42   b  of the second wire which extended out heads towards the wire connection part of the fourth terminal and then the wire connection treatment is carried out. 
     In the coil device  110  of the present embodiment, the wire connection parts ( 151   b  and  152   b  are only shown in the figure) of the wires  41  and  42  are not positioned on the mounting face  24   a  of the first collar part  24  and the mounting face  26   a  of the second collar part  26 , but are positioned to the outer end faces  24   c  and  26   c  of the collar parts  24  and  26 . 
     In the present embodiment, the lead parts  41   a  of the wire  41  heading towards the coil part  40  from the first terminal  151  and the lead part  42   a  of the wire  42  heading towards the coil part  40  from the second terminal  52  are placed in close proximity at least between the inner face  24   d  of the collar part  24  and the coil  40 . Further, the crossing part  43  is formed at a predetermined position along the core axis direction of the core  22 . By constituting as such, the mode conversion property is improved. Also, in the present embodiment, the lead part  41   b  of the wire heading towards the coil part  40  from the third terminal and the lead part  42   b  of the wire  42  heading towards the coil part  40  from the fourth terminal are placed in close proximity at least between the inner face  26   d  of the collar part  26  and the coil part  40 . Further, the crossing part  43  is formed at the predetermined position along the core axis direction of the core  22 . By constituting as such, the mode conversion property is improved. 
     Third Embodiment 
     The coil device according to the third embodiment of the present invention is same as the aforementioned first and second embodiments other than the constitutions mentioned in below, and the same effect is attained, thus the overlapping section is omitted from describing. Also, in the figures, the same members as the first and second embodiments are given with the same numerical references. 
     As shown in  FIG. 4B , a coil device  210  of this embodiment has a drum core  220 . An area of the opposite face  24   b  of the mounting face of the first collar part  24  of the drum core  220  is about the same as X-Y cross section of the first collar part  24 , and an bonding area with the board  30  is larger compared to the coil device  110  of the embodiment shown in  FIG. 4A . 
     The entire face of the opposite face  24   b  and  26   b  of the mounting face  24   a  and  26   a  are attached with the board  30 . In the present embodiment, a first common guiding passage  24   e   1  of a groove shape formed to each of both side faces  24   e  of the first collar part  24  positioned near the opposite face  24   b  of the mounting face. The lead part  41   a  of the first wire and the lead part  42   a  of the second wire which are together guided to either one of the first common guiding passage  24   e   1  from the coil part  40  and extend out to separate direction at an end part of the first common guiding passage  24   e   1 . This end part of the first common guiding passage  24   e   1  is formed to the edge of the outer end face  24   c.    
     The tip part of the lead part  41   a  of the first wire which extended out heads towards the wire connection part  151   b  of the first terminal  151 , and then the wire connection treatment such as soldering and the like is carried out. The tip part of the lead part  42   a  of the second wire which extended out heads towards the wire connection part  152   b  of the first terminal  152 , and then the wire connection treatment such as soldering and the like is carried out. 
     In the present embodiment, the first terminal  151  and the second terminal  152  are the same as the terminals  151  and  152  shown in  FIG. 4A . The mounting parts  151   a  and  152   a  of the terminals  151  and  152  are adhered to the mounting face  24   a  positioned near the outer end face  24   c  of the collar part  24 , and separate from each other in predetermined distance in Y-axis direction. Also, the wire connection parts  151   b  and  152   b  of the terminals  151  and  152  are adhered to the outer end face  24   c  positioned near the mounting face  24   a  of the collar part  24 , and separate from each other in predetermined distance in Y-axis direction. 
     Note that, although it is not shown in  FIG. 4B , the third terminal and the fourth terminal are in similar relation as in case of the first terminal  151  and the second terminal  152 , and have same shape and each of them have the mounting part and the wire connection part. 
     The mounting part of the third and fourth terminals are adhered to the mounting face  26   a  positioned near the outer end face  26   c  of the collar part  26 , and separate from each other in predetermined distance in Y-axis direction. Also, the wire connection part of the third and fourth terminals are adhered to the outer end face  26   c  positioned near the mounting face  26   a  of the collar part  26 , and separate from each other in predetermined distance in Y-axis direction. 
     In the present embodiment, a second common guiding passage  26   e   1  of a groove shape is formed to each of both side faces  26   e  of the second collar part  26  having similar constitution as the first collar part  24  and positioned near the opposite face  26   b  of the mounting face. The lead part  41   b  of the first wire and the lead part  42   b  of the second wire which are together guided to either one of the second common guiding passage  26   e   1  from the coil part  40  extend out to separate directions at an end part of the second common guiding passage  26   e   1 . This end part of the second common guiding passage  26   e   1  is formed to the edge of the outer end face  26   c.    
     Note that, in the present embodiment, the first common guiding passage  24   e   1  of which the lead parts  41   a  and  42   a  of the wires are guided together, and the second common guiding passage  26   e   1  of which the lead parts  41   b  and  42   b  of the wires are guided together are preferably positioned in opposite direction in Y-axis direction. 
     The tip part of the lead part  41   b  of the first wire which extended out heads towards the wire connection part of the third terminal, and then the wire connection treatment such as soldering and the like is carried out. The tip part of the lead part  42   b  of the second wire which extended out heads towards the fourth terminal, and then the wire connection treatment such as soldering and the like is carried out. 
     In the coil device  210  of the present embodiment, the wire connection parts ( 151   b  and  152   b  are only shown in the figure) of the wires  41  and  42  are not positioned to the mounting face  24   a  of the first collar part  24  and the mounting face  26   a  of the second collar part  26 , but are positioned to the outer end faces  24   c  and  26   c  of the collar parts  24  and  26 . 
     In the present embodiment, the lead part  41   a  of the wire  41  heading towards the coil part  40  from the first terminal  151  and the lead part  42   a  of the wire  42  heading towards the coil part  40  from the second terminal  152  are placed in close proximity at least between the inner face  24   d  of the collar part  24  and the coil part  40 . Further, the crossing part  43  is formed at the predetermined position along the core axis direction of the core  22 . By constituting as such, the mode conversion property is improved. Also, in the present embodiment, the lead part  41   b  of the wire  41  heading towards the coil part  40  from the third terminal and the lead part  42   b  of the wire  42  heading towards the coil part  40  from the fourth terminal are placed in close proximity at least between the inner face  26   d  of the collar part  26  and the coil part  40 . Further, the crossing part  43  is formed at the predetermined position along the core axis direction of the core  22 . By constituting as such, the mode conversion property is improved. 
     Further, in the present embodiment, the first common guiding passage  24   e   1  of a groove shape is formed to both side faces  24   e  ( 26   e ) of the first collar part  24  (the second collar part  26 ) positioned near the opposite face  24   b  of the mounting face. Thus, the bonding area between the board  30  and the collar part  24  ( 26 ) can be made larger. Hence, an inductance of the coil device  210  can improve. 
     Fourth Embodiment 
     The coil device according to the fourth embodiment of the present invention is same as the aforementioned first to third embodiments other than the constitutions mentioned in below, and the same effect is attained, thus the overlapping section is omitted from describing. Also, in the figures, the same members as the first to third embodiments are given with the same numerical references. 
     As shown in  FIG. 4C , the coil device  310  of this embodiment has a drum core  320 . An area of the opposite face  24   b  of the mounting face of the first collar part  24  of the drum core  320  is about the same as X-Y cross section of the first collar part  24 , and an bonding area with the board  30  is larger compared to the coil device  10  of the embodiment shown in  FIG. 1 . 
     A first terminal guiding passage  24   b   4  is formed at the center part of an edge along Y-axis direction formed between the opposite face  24   b  of the mounting face and the inner face  24   d  of the first collar part  24 . The first terminal guiding passage  24   b   4  is formed in an angle on the opposite mounting face  24   b  of the mounting face from the edge of the inner face  24   d  of the first collar part  24  towards the edge of the outer end face  24   c  where the first terminal  151  is provided. Also, a second terminal guiding passage  24   b   5  is formed at the center part of an edge along Y-axis direction formed between the opposite face  24   b  of the mounting face and the inner face  24   d  of the first collar part  24 . The second terminal guiding passage  24   b   5  is formed in an angle on the opposite mounting face  24   b  of the mounting face from the edge of the inner face  24   d  of the first collar part  24  towards the edge of the outer end face  24   c  where the second terminal  152  is provided. These passages  24   b   4  and  24   b   5  intersect at the center part of the edge along Y-axis direction formed between the opposite face  24   b  of the mounting face and the inner face  24   d  of the first collar part  24 , and are separated at an edge formed between the opposite face  24   b  of the mounting face and the outer end face  24   c.    
     The lead part  41   a  of the first wire guided to the first terminal passage  24   b   4  from the coil part  40  extends downwards in Z-axis direction along the outer end face  24   c . The tip part of the lead part  41   a  of the first wire which extended out heads towards the wire connection part  151   b  of the first terminal  151 , then the wire connection treatment such as soldering and the like is done. Also, the lead part  42   a  of the second wire guided to the second terminal passage  24   b   5  from the coil part  40  extends downwards in Z-axis direction along the outer end face  24   c . The tip part of the lead part  42   a  of the second wire which extended out heads towards the wire connection part  152   b  of the second terminal  152 , then the wire connection treatment such as soldering and the like is done. 
     In the present embodiment, the first terminal  151  and the second terminal  152  are same as the terminals  151  and  152  shown in  FIG. 4A  or  FIG. 4B . The mounting parts  151   a  and  152   a  of the terminals  151  and  152  are adhered to the mounting face  24   a  positioned near the outer end face  24   c  of the collar part  24  and separate from each other in predetermined distance along Y-axis direction. Also, the wire connection parts  151   b  and  152   b  of the terminals  151  and  152  are adhered to the outer end face  24   c  positioned near the mounting face  24   a  of the collar part  24 , and separate from each other in predetermined distance along Y axis direction. 
     Note that, although it is not shown in  FIG. 4C , the third terminal and the fourth terminal are in similar relation as in case of the first terminal  151  and the second terminal  152 , and these have same shape and have mounting part and the wire connection part. 
     The mounting parts of the third terminal and the fourth terminal are adhered to the mounting face  26   a  positioned near the outer end face  26   c  of the collar part  26 , and are separated in predetermined distance along Y-axis direction. Also, the wire connection parts of the third terminal and the fourth terminal are adhered to the outer end face  26   c  positioned near the mounting face  26   a  of the collar part  26 , and are separated in predetermined distance along Y-axis direction. 
     In the present embodiment, a third terminal guiding passage  26   b   4  is formed at the center part of an edge along Y-axis direction formed between the opposite face  26   b  of the mounting face and the inner face  26   d  of the second collar part  26 . The third terminal guiding passage  26   b   4  is formed in an angle on the opposite mounting face  26   b  of the mounting face from the edge of the inner face  26   d  of the second collar part  26  towards the edge of the outer end face  26   c  where the third terminal is provided. Also, a fourth terminal guiding passage  26   b   5  is formed at the center part of an edge along Y-axis direction formed between the opposite face  26   b  of the mounting face and the inner face  26   d  of the second collar part  26 . The fourth terminal guiding passage  26   b   5  is formed in an angle on the opposite mounting face  26   b  of the mounting face from the edge of the inner face  26   d  of the second collar part  26  towards the edge of the outer end face  26   c  where the fourth terminal is provided. These passages  26   b   4  and  26   b   5  intersect at the center part of the edge along Y-axis direction formed between the opposite face  26   b  of the mounting face and the inner face  26   d  of the second collar part  26 , and are separated at an edge formed between the opposite face  26   b  of the mounting face and the outer end face  26   c.    
     The lead part  41   b  of the first wire guided to the third terminal passage  26   b   4  from the coil part  40  extends downward in Z-axis direction along the outer end face  26   c . The tip part of the lead part  41   b  of the first wire which extended out heads towards the wire connection part of the third terminal, then the wire connection treatment such as soldering and the like is done. Also, the lead part  42   b  of the second wire guided to the fourth terminal passage  26   b   5  from the coil part  40  extends downward in Z-axis direction along the outer end face  26   c . The tip part of the lead part  42   b  of the second wire which extended out heads towards the wire connection part of the fourth terminal, then the wire connection treatment such as soldering and the like is done. 
     In the coil device  310  of the present embodiment, the wire connection parts ( 151   b  and  152   b  are only shown in the figure) of the wires  41  and  42  are not positioned to the mounting face  24   a  of the first collar part  24  and the mounting face  26   a  of the second collar part  26 , but are positioned to the outer end faces  24   c  and  26   c  of the collar parts  24  and  26 . 
     In the present embodiment, the lead part  41   a  of the wire  41  heading towards the coil part  40  from the first terminal  151  and the lead part  42   a  of the wire  42  heading towards the coil part  40  from the second terminal  152  are placed in close proximity at least between the inner face  24   d  of the collar part  24  and the coil part  40 . Further, the crossing part  43  is formed at the predetermined position along the core axis direction of the core  22 . By constituting as such, the mode conversion property is improved. Also, in the present embodiment, the lead part  41   b  of the wire  41  heading towards the coil part  40  from the third terminal and the lead part  42   b  of the wire  42  heading towards the coil part  40  from the fourth terminal are placed in close proximity at least between the inner face  26   d  of the collar part  26  and the coil part  40 . Further, the crossing part  43  is formed at the predetermined position along the core axis direction of the core  22 . By constituting as such, the mode conversion property is improved. 
     Note that, the present invention is not to be limited to the aforementioned embodiments, and it may be modified variously within the scope of the present invention. 
     For example, in the above mentioned embodiments, the first collar part  24  and the second collar part  26  have the same constitution, but these may have different constitution. For example, the first collar part  24  may have the constitution shown in  FIG. 1  and  FIG. 2 , and the second collar part  26  may be constituted as any one of  FIG. 4A  to  FIG. 4C . Alternatively, the first collar part  24  may be constituted as any one of  FIG. 4A  to  FIG. 4C , and the second collar part  26  may be constituted as any one of  FIG. 4A  to  FIG. 4C  but different from the first collar part  24 . Also, either one of the first collar part  24  and the second collar part  26  may be constituted as shown in  FIG. 1  and  FIG. 2 , or as any one of  FIG. 4A  to  FIG. 4C , and the other collar part may be constituted as conventional collar part. 
     Further, in the aforementioned embodiments, the common guiding passages  24   b   1 ,  26   b   1 ,  24   e   1 , and  26   e   1  or the terminal guiding passages  24   b   4 ,  24   b   5 ,  26   b   4 , and  26   b   5  which are formed to the collar part  24  or  26  may be formed to inner face or side face of the board  30 . By forming the guiding passages to the board  30 , there is no need to form the guiding passages to the collar parts  24  and  26  hence the volume reduction of the magnetic core is suppressed, and the magnetic properties can be improved. 
     EXAMPLE 
     Hereinafter, the present invention is further described based on detailed examples, but the present invention is not to be limited thereto. 
     Example 1 
     As similar to the second embodiment, the coil device  110  shown in  FIG. 4A  was produced. For this coil device  110 , S parameter property, particularly Ssd21which indicates the mode conversion property was measured by a test defined by OPEN ALLIANCE. The result is shown in a bold line of  FIG. 5 . 
     Example 2 
     As similar to the third embodiment, the coil device  210  shown in  FIG. 4B  was produced. For this coil device  210 , as similar to Example 1, Ssd21 was measured by a test defined by OPEN ALLIANCE. The result is shown in a dot-dash line of  FIG. 5 . 
     Comparative Example 1 
     The coil device  410  shown in  FIG. 4D  was produced as similar to Example 2 except for following. For the coil device  410 , the one lead part  41   a  of the first wire and the one lead part  42   a  of the second wire were respectively guided to passages  24   e   1  and  24   e   1  of the first collar part  24 . Also, the other lead part  41   b  of the first wire and the other lead part  42   b  of the second wire were respectively guided to the passages  26   e   1  and  26   e   1  of the second collar part  26 . 
     For the coil device  410 , Ssd21 was measured as similar to Example 1. The result is shown in a dot line of  FIG. 5 . 
     Comparative Example 2 
     The coil device was produced as same as Example 1 except for the following. For this coil device, the crossing part  43  was not formed of which the first wire  41  and the second wire  42  cross against each other in the middle of the core  22  of the coil device shown in  FIG. 4A  according to Example 1. For this coil device, Ssd21 was measured as similar to Example 1. The result is shown in two-dot chain line. 
     Evaluation 
     Examples 1 and 2 compared to Comparative examples 1 and 2 were able to reduce Ssd21 across the range of low frequency and high frequency which is indicated in a horizontal axis. Since Ssd21 can be reduced, for the coil device of Examples, differential signals were not converted to common mode, thus exhibited good property as a common mode filter. 
     Also, by comparing Examples 1 and 2 with Comparative examples 1 and 2, the present inventors have found following. That is, the mode conversion property was improved as the lead part heading towards the coil part from the terminal and the lead part heading towards the coil part from the terminal were placed in close proximity at least between the inner face of the collar part and the coil part (Examples 1 and 2), and also by providing the crossing part in the middle of the core part. 
     Note that, in the aforementioned Examples 1, 2 and Comparative example 1, the crossing part  43  is formed in the middle of the coil part  40 , but in Comparative example 2, the crossing part  43  is not provided in the middle of the coil part. Also, for the coil device shown in  FIG. 1 to 3  and  FIG. 4C , it has been confirmed that the same result as the coil device of  FIG. 4A  can be obtained. 
     DESCRIPTION OF THE REFERENCE NUMERAL 
       10 ,  110 ,  210 ,  310 ,  410  . . . Coil device 
       20 ,  120 ,  220 ,  320  . . . Drum core 
       22  . . . Core 
       24  . . . First collar part 
       24   a  . . . Mounting face 
       24   b  . . . Opposite face of mounting face 
       24   b   1  . . . First common guiding passage 
       24   b   2  . . . Guiding face 
       24   b   3  . . . Wire connection step face 
       24   b   4  . . . First terminal guiding passage 
       24   b   5  . . . Second terminal guiding passage 
       24   c  . . . Outer end face 
       24   c   1  . . . Terminal installation face 
       24   d  . . . Inner face 
       24   e  . . . Side face 
       24   e   1  . . . First common guiding passage 
       26  . . . Second collar part 
       26   a  . . . Mounting face 
       26   b  . . . Opposite face of mounting face 
       26   b   1  . . . Second guiding passage 
       26   b   2  . . . Guiding face 
       26   b   3  . . . Wire connection step face 
       26   c  . . . Outer end face 
       26   c   1  . . . terminal installation face 
       26   d  . . . Inner face 
       26   e  . . . Side face 
       26   e   1  . . . Second common guiding passage 
       30  . . . Board 
       40  . . . Coil part 
       41  . . . First wire 
       41   a  . . . One lead part 
       41   b  . . . Other lead part 
       42  . . . Second wire 
       42   a  . . . One lead part 
       42   b  . . . Other lead part 
       43  . . . Crossing part 
       51 ,  151  . . . First terminal 
       51   a ,  151   a  . . . Mounting part 
       51   b ,  151   b  . . . Wire connection part 
       51   c  . . . Terminal main body 
       52 ,  152  . . . Second terminal 
       52   a ,  152   a  . . . Mounting part 
       52   b ,  152   b  . . . Wire connection part 
       52   c  . . . Terminal main body 
       53 ,  153  . . . Third terminal 
       53   a ,  153   a  . . . Mounting part 
       53   b ,  153   b  . . . Wire connection part 
       53   c  . . . Terminal main body 
       54 ,  154  . . . Fourth terminal 
       54   a ,  154   a  . . . Mounting part 
       54   b ,  154   b  . . . Wire connection part 
       54   c  . . . Terminal main body