Patent Publication Number: US-2021166858-A1

Title: Coil component

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-218752, filed on 3 Dec. 2019, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a coil component. 
     BACKGROUND 
     Japanese Unexamined Patent Publication No. 2017-92444 (Patent Literature 1) discloses a coil component in which a double coil is formed by a pair of coil patterns provided on one surface of a substrate and a pair of coil patterns provided on the other surface of the substrate. 
     SUMMARY 
     In the configuration of the coil component according to the above-described conventional technique, it has been difficult to obtain a high coupling coefficient in the double coil. After diligent research, the inventors have found a new technology which can realize a high coupling coefficient in a double coil. 
     According to the disclosure, a coil component having an improved coupling coefficient in a double coil is provided. 
     A coil component according to an aspect of the disclosure includes an elementary body having a first end surface and a second end surface parallel to each other; an insulating substrate provided in the elementary body, the insulating substrate being orthogonal to the first end surface and the second end surface and extending between the first end surface and the second end surface; a first coil portion including a first planar coil pattern, a second planar coil pattern, and a first through conductor, the first planar coil pattern provided on one surface of the insulating substrate and wound around a magnetic core located on an equidistant line in which a distance from the first end surface and a distance from the second end surface are equal when seen in a thickness direction of the insulating substrate and having an inner end portion located on the equidistant line and an outer end portion extending to the first end surface of the elementary body, the second planar coil pattern provided on the other surface of the insulating substrate and having an inner end portion overlapping the inner end portion of the first planar coil pattern and an outer end portion extending to the second end surface of the elementary body when seen in the thickness direction of the insulating substrate, the first through conductor piercing the insulating substrate in the thickness direction on the equidistant line when seen in the thickness direction of the insulating substrate and connecting the inner end portion of the first planar coil pattern to the inner end portion of the second planar coil pattern; a second coil portion including a third planar coil pattern, a fourth planar coil pattern, and a second through conductor, the third planar coil pattern provided on the one surface of the insulating substrate to be wound parallel to the first planar coil pattern and having an inner end portion adjacent to the inner end portion of the first planar coil pattern on an outer peripheral side of the first planar coil pattern and an outer end portion extending to the first end surface of the elementary body on the equidistant line when seen in the thickness direction of the insulating substrate, the fourth planar coil pattern provided on the other surface of the insulating substrate and having an inner end portion overlapping the inner end portion of the third planar coil pattern and an outer end portion extending to the second end surface of the elementary body when seen in the thickness direction of the insulating substrate, the second through conductor piercing the insulating substrate in the thickness direction to be adjacent to the first through conductor on the equidistant line when seen in the thickness direction of the insulating substrate and connecting the inner end portion of the third planar coil pattern to the inner end portion of the fourth planar coil pattern; a first external terminal electrode provided on the first end surface of the elementary body and connected to the outer end portion of the first planar coil pattern; a second external terminal electrode provided on the second end surface of the elementary body and connected to the outer end portion of the second planar coil pattern; a third external terminal electrode provided on the first end surface of the elementary body and connected to the outer end portion of the third planar coil pattern; and a fourth external terminal electrode provided on the second end surface of the elementary body and connected to the outer end portion of the fourth planar coil pattern. 
     In the coil component, a double coil is configured of the first coil portion and the second coil portion, and the first through conductor of the first coil portion and the second through conductor of the second coil portion are adjacent to each other. Thus, magnetic coupling is enhanced at locations (that is, the first through conductor and the second through conductor) at which the planar coil patterns on one surface of the insulating substrate and the planar coil patterns on the other surface of the insulating substrate are connected, and a coupling coefficient between the first coil portion and the second coil portion is improved. 
     In the coil component according to another aspect of the disclosure, the number of turns of the first coil portion may be larger than the number of turns of the second coil portion. In this case, a value of inductance of the first coil portion and a value of inductance of the second coil portion can be made different from each other. 
     In the coil component according to another aspect of the disclosure, a pattern shape of the first planar coil pattern and a pattern shape of the second planar coil pattern may be line symmetric with respect to the equidistant line, and a pattern shape of the third planar coil pattern and a pattern shape of the fourth planar coil pattern may be line symmetric with respect to the equidistant line when seen in the thickness direction of the insulating substrate. When the pattern shapes have symmetry in this way, a manufacturing process can be simplified. 
     In the coil component according to another aspect of the disclosure, the first planar coil pattern, the second planar coil pattern, the third planar coil pattern, and the fourth planar coil pattern may be configured by plating, and the first planar coil pattern and the third planar coil pattern provided on the one surface of the insulating substrate, and the second planar coil pattern and the fourth planar coil pattern provided on the other surface of the insulating substrate may be separated by resin walls. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of a coil component according to an embodiment. 
         FIG. 2  is an exploded view of the coil component shown in  FIG. 1 . 
         FIG. 3  is a sectional view taken along line III-III of the coil component shown in  FIG. 1 . 
         FIG. 4  is a view showing a planar coil pattern provided on an upper surface of a substrate. 
         FIG. 5  is a view showing only a first planar coil pattern. 
         FIG. 6  is a view showing only a third planar coil pattern. 
         FIG. 7  is a view showing a second planar coil pattern provided on a lower surface of the substrate. 
         FIG. 8  is a view showing a fourth planar coil pattern provided on the lower surface of the substrate. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and duplicate description thereof will be omitted. 
     A structure of a coil component  10  according to an embodiment will be described with reference to  FIGS. 1 to 4 . 
     The coil component  10  is configured of a main body  12  (an elementary body) having a rectangular parallelepiped shape, and two pairs of external terminal electrodes  14 A,  14 B,  14 C, and  14 D provided on a surface of the main body  12 . The two pairs of external terminal electrodes  14 A,  14 B,  14 C, and  14 D are respectively provided on end surfaces  12   a  and  12   b  of the main body  12  which are parallel to each other. As an example, the coil component  10  is designed with dimensions of a long side of 2.5 mm, a short side of 2.0 mm, and a height of 0.8 to 1.0 mm. 
     Hereinafter, for convenience of explanation, XYZ coordinates are set as shown in the drawing. That is, a thickness direction of the main body is set to a Z direction, a facing direction of the end surfaces  12   a  and  12   b  on which the external terminal electrodes are provided is set to an X direction, and a direction orthogonal to the Z direction and the X direction is set to a Y direction. 
     As shown in  FIG. 2 , the main body  12  includes an insulating substrate  20 , a coil C provided on the insulating substrate  20 , and a magnetic body  30 . 
     The insulating substrate  20  is a plate-shaped member having a rectangular shape provided inside the main body  12 , and is made of a non-magnetic insulating material. The insulating substrate  20  extends between the end surfaces  12   a  and  12   b  and is designed to be orthogonal to the end surfaces  12   a  and  12   b . An elliptical through hole  20   c  is provided in a central portion of the insulating substrate  20 . A substrate in which a glass cloth is impregnated with an epoxy resin and which has a plate thickness of 10 μm to 60 μm can be used as the insulating substrate  20 . In addition to an epoxy resin, a BT resin, polyimide, aramid and the like can also be used. Ceramic or glass can also be used as the material of the insulating substrate  20 . The material of the insulating substrate  20  may be a mass-produced printed circuit board material, and may be a resin material, in particular, one used for a BT printed circuit board, a FR4 printed circuit board, or an FR5 printed circuit board. 
     The coil C includes a first coil portion C 1  and a second coil portion C 2  which form a double coil structure. The first coil portion C 1  includes a first planar coil pattern  22 A having a planar spiral shape and provided on an upper surface  20   a  (one surface) of the insulating substrate  20 , a second planar coil pattern  22 B having a planar spiral shape and provided on a lower surface  20   b  (the other surface) of the insulating substrate  20 , and a first through conductor  26  which connects the first planar coil pattern  22 A to the second planar coil pattern  22 B. The second coil portion C 2  includes a third planar coil pattern  22 C having a planar spiral shape and provided on the upper surface  20   a  of the insulating substrate, a fourth planar coil pattern  22 D having a planar spiral shape and provided on the lower surface  20   b  of the insulating substrate  20 , and a second through conductor  27  which connects the third planar coil pattern  22 C to the fourth planar coil pattern  22 D. 
     The first planar coil pattern  22 A of the first coil portion C 1  and the third planar coil pattern  22 C of the second coil portion C 2  are wound on the upper surface  20   a  of the insulating substrate  20  to be adjacent and parallel to each other. Further, the second planar coil pattern  22 B of the first coil portion C 1  and the fourth planar coil pattern  22 D of the second coil portion C 2  are wound on the lower surface  20   b  of the insulating substrate  20  to be adjacent and parallel to each other. 
     Each of the planar coil patterns  22 A,  22 B,  22 C, and  22 D has a rectangular cross section and is designed so that heights from the insulating substrate  20  are the same as each other. Each of the through conductors  26  and  27  is provided to pierce the insulating substrate  20  in the thickness direction and has, for example, a substantially cylindrical or substantially prismatic exterior. Each of the through conductors  26  and  27  may be configured of a hole provided in the insulating substrate  20  and a conductive material (for example, a metal material such as Cu) filled into the hole. 
     Resin walls  24  are provided between the first planar coil patterns  22 A and the third planar coil patterns  22 C wound parallel to each other on the upper surface  20   a  of the insulating substrate, and the first planar coil patterns  22 A and the third planar coil patterns  22 C are physically and electrically separated from each other by the resin walls  24 . Further, the resin walls  24  are also provided on the outer side of the outermost turn and the inner side of the innermost turn of the first planar coil patterns  22 A. In the embodiment, the resin walls  24  located on the outer side of the outermost peripheral turn and the inner side of the innermost peripheral turn of the first planar coil pattern  22 A are designed to be thicker than the resin walls  24  located between the first planar coil pattern  22 A and the third planar coil pattern  22 C. 
     Each of the resin walls  24  is also provided between the second planar coil pattern  22 B and the fourth planar coil pattern  22 D wound parallel to each other on the lower surface  20   b  of the insulating substrate, and the second planar coil pattern  22 B and the fourth planar coil pattern  22 D are physically and electrically separated from each other by each of the resin walls  24 . Further, the resin walls  24  are also provided on the outer side of the outermost peripheral turn and the inner side of the innermost peripheral turn of the second planar coil pattern  22 B. In the embodiment, the resin walls  24  located on the outer side of the outermost peripheral turn and the inner side of the innermost peripheral turn of the second planar coil pattern  22 B are designed to be thicker than the resin walls  24  located between the second planar coil pattern  22 B and the fourth planar coil pattern  22 D. 
     The resin walls  24  are made of an insulating resin material. The resin walls  24  can be provided on the insulating substrate  20  before each of the planar coil patterns  22 A,  22 B,  22 C, and  22 D is formed, and in this case, each of the planar coil patterns  22 A,  22 B,  22 C, and  22 D is plated and grown between walls defined in the resin walls  24 . That is, formation regions of the planar coil patterns  22 A,  22 B,  22 C, and  22 D are defined by the resin walls  24  provided on the insulating substrate  20 . The resin walls  24  can be provided on the insulating substrate  20  after the planar coil patterns  22 A,  22 B,  22 C, and  22 D are formed, and in this case, the resin walls  24  are provided on the planar coil patterns  22 A,  22 B,  22 C, and  22 D by filling or coating. 
     A height of each of the resin walls  24  (that is, heights with respect to the insulating substrate  20 ) is designed to be higher than the heights of the planar coil patterns  22 A,  22 B,  22 C, and  22 D. Therefore, a creepage distance between adjacent planar coil patterns  22 A,  22 B,  22 C, and  22 D via the resin wall  24  is increased, as compared with a case in which the height of the resin wall  24  and the heights of the planar coil patterns  22 A,  22 B,  22 C, and  22 D are the same. Thus, it is possible to curb situations in which short circuiting occurs between adjacent planar coil patterns  22 A,  22 B,  22 C, and  22 D. 
     An insulating layer  25  is interposed between adjacent resin walls  24 . The insulating layer  25  is provided over the entire upper surface of each of the planar coil patterns  22 A,  22 B,  22 C, and  22 D between adjacent resin walls  24 . The insulating layer  25  is made of a resin such as an epoxy resin or a polyimide resin and is formed using a photolithography method. 
     The magnetic body  30  integrally covers the insulating substrate  20  and the coil C. More specifically, the magnetic body  30  covers the insulating substrate  20  and the coil C from above and below and covers the outer periphery of the insulating substrate  20  and the coil C. Further, the magnetic body  30  fills the inside of the through hole  20   c  of the insulating substrate  20  and an inner region of the coil C. 
     The magnetic body  30  is made of a metal magnetic component-containing resin. The metal magnetic component-containing resin is a binder powder in which metal magnetic powder is bound by a binder resin. The metal magnetic powder of the metal magnetic component-containing resin constituting the magnetic body  30  is configured of, for example, an iron-nickel alloy (a Permalloy alloy), carbonyl iron, an amorphous or crystalline FeSiCr-based alloy, Sendust, or the like. The binder resin is, for example, a thermosetting epoxy resin. In the embodiment, a content of the metallic magnetic powder in the binder powder is 80 to 92 vol % in percentage by volume and 95 to 99 wt % in percentage by mass. From the viewpoint of magnetic properties, the content of the metal magnetic powder in the binder powder may be 85 to 92 vol % in percentage by volume and 97 to 99 wt % in percentage by mass. The magnetic component of the metal magnetic component-containing resin constituting the magnetic body  30  may be a powder having one kind of average particle diameter, or may be a mixed powder having a plurality of kinds of average particle diameter. In the embodiment, the magnetic component of the metal magnetic component-containing resin constituting the magnetic body  30  is a mixed powder having three kinds of average particle diameter. When the magnetic component of the metal magnetic component-containing resin constituting the magnetic body  30  is a mixed powder, the kinds of magnetic components having different average particle diameters may be the same as or different from each other. 
     The two pairs of external terminal electrodes  14 A,  14 B,  14 C, and  14 D provided on the end surfaces  12   a  and  12   b  of the main body  12  are respectively connected to outer end portions  22   a  of the corresponding planar coil patterns  22 A,  22 B,  22 C, and  22 D. That is, the first external terminal electrode  14 A provided on the end surface  12   a  (a first end surface) is connected to the outer end portion  22   a  of the first planar coil pattern  22 A, the second external terminal electrode  14 B provided on the end surface  12   b  (a second end surface) is connected to the outer end portion  22   a  of the second planar coil pattern  22 B, the third external terminal electrode  14 C provided on the end surface  12   a  is connected to the outer end portion  22   a  of the third planar coil pattern  22 C, and the fourth external terminal electrode  14 D provided on the end surface  12   b  is connected to the outer end portion  22   a  of the fourth planar coil pattern  22 D. 
     The first external terminal electrode  14 A and the second external terminal electrode  14 B face each other in the X direction, and the third external terminal electrode  14 C and the fourth external terminal electrode  14 D face each other in the X direction. 
     Next, a pattern shape of each of the planar coil patterns  22 A,  22 B,  22 C, and  22 D will be described in more detail with reference to  FIGS. 4 to 8 . Alternate long and short dash lines in  FIGS. 4 to 8  indicate equidistant lines L having the same distance from the end surface  12   a  and the same distance from the end surface  12   b  when seen in the thickness direction of the insulating substrate  20 . 
     All of the four planar coil patterns  22 A,  22 B,  22 C, and  22 D are wound around the through hole  20   c  provided in the central portion of the insulating substrate  20 . A magnetic core of the coil C is configured of the magnetic material  30  which fills the inside of the through hole  20   c  of the insulating substrate  20  and the inner region of the coil C, and the magnetic core of the coil C is located on the equidistant line L. 
     Each of the planar coil patterns  22 A,  22 B,  22 C, and  22 D has the outer end portion  22   a  which reaches the end surface  12   a  or the end surface  12   b  of the main body  12  and is exposed, an inner end portion  22   b  provided on a peripheral edge of the through hole  20   c , a winding portion  22   c  which connects the outer end portion  22   a  to the inner end portion  22   b.    
     As shown in  FIGS. 4 and 5 , the inner end portion  22   b  of the first planar coil pattern  22 A is located on the equidistant line L at the peripheral edge of the through hole  20   c . In the form shown in  FIGS. 4  and  5 , the inner end portion  22   b  of the first planar coil pattern  22 A is located on the left side of the through hole  20   c . The first through conductor  26  which extends in the thickness direction of the insulating substrate  20  is provided at a position at which it overlaps the inner end portion  22   b  of the first planar coil pattern  22 A. That is, the first through conductor  26  is located on the equidistant line L. The first through conductor  26  is in contact with the first planar coil pattern  22 A on an upper end surface thereof and is in contact with the second planar coil pattern  22 B on a lower end surface thereof. 
     The outer end portion  22   a  of the first planar coil pattern  22 A extends to the end surface  12   a  and is connected to the first external terminal electrode  14 A at the end surface  12   a.    
     The winding portion  22   c  of the first planar coil pattern  22 A constitutes the innermost and outermost turns of the planar coil patterns  22 A and  22 C provided on the upper surface  20   a  of the insulating substrate  20 . The number of turns of the winding portion  22   c  of the first planar coil pattern  22 A is about two turns (two turns). 
     As shown in  FIGS. 4 and 6 , the inner end portion  22   b  of the third planar coil pattern  22 C is located on the outer peripheral side (left side in the aspect shown in  FIG. 4 ) of the first planar coil pattern  22 A in the inner end portion  22   b  of the first planar coil pattern  22 A on the equidistant line L at the peripheral edge of the through hole  20   c , and is adjacent to the inner end portion  22   b  of the first planar coil pattern  22 A. 
     The second through conductor  27  which extends in the thickness direction of the insulating substrate  20  is provided at a position at which it overlaps the inner end portion  22   b  of the third planar coil pattern  22 C. That is, the second through conductor  27  is located on the equidistant line L and is adjacent to the first through conductor  26 . The second through conductor  27  is in contact with the third planar coil pattern  22 C on an upper end surface thereof and is in contact with the fourth planar coil pattern  22 D on a lower end surface thereof. 
     The outer end portion  22   a  of the third planar coil pattern  22 C extends to the end surface  12   a  and is connected to the third external terminal electrode  14 C at the end surface  12   a . In the form shown in  FIG. 4 , the outer end portion  22   a  of the third planar coil pattern  22 C is located on the right side of the outer end portion  22   a  of the first planar coil pattern  22 A. 
     The winding portion  22   c  of the third planar coil pattern  22 C is wound to be adjacent to the winding portion  22   c  of the first planar coil pattern  22 A. The number of turns of the winding portion  22   c  of the third planar coil pattern  22 C is less than the number of turns of the winding portion  22   c  of the first planar coil pattern  22 A, and is about one turn (one turn). Therefore, the winding portion  22   c  of the third planar coil pattern  22 C is wound to be sandwiched between the winding portions  22   c  of the first planar coil pattern  22 A. 
     As shown in  FIGS. 5 and 7 , the pattern shape of the first planar coil pattern  22 A and the pattern shape of the second planar coil pattern  22 B have a line-symmetrical relationship with respect to the equidistant line L. 
     The inner end portion  22   b  of the second planar coil pattern  22 B is located on the equidistant line L at the peripheral edge of the through hole  20   c , and overlaps the inner end portion  22   b  of the first planar coil pattern  22 A when seen in the thickness direction of the insulating substrate  20 . 
     The outer end portion  22   a  of the second planar coil pattern  22 B extends until it reaches the end surface  12   b , and is connected to the second external terminal electrode  14 B at the end surface  12   b . The second external terminal electrode  14 B is provided on the end surface  12   b  at a position corresponding to the first external terminal electrode  14 A provided on the end surface  12   a.    
     The winding portion  22   c  of the second planar coil pattern  22 B constitutes the innermost and outermost turns of the planar coil patterns  22 B and  22 D provided on the lower surface  20   b  of the insulating substrate  20 . The number of turns of the winding portion  22   c  of the second planar coil pattern  22 B is about two turns, similar to the number of turns of the winding portion  22   c  of the first planar coil pattern  22 A. 
     As shown in  FIGS. 6 and 8 , the pattern shape of the third planar coil pattern  22 C and the pattern shape of the fourth planar coil pattern  22 D have a line-symmetrical relationship with respect to the equidistant line L. 
     The inner end portion  22   b  of the fourth planar coil pattern  22 D is located on the equidistant line L at the peripheral edge of the through hole  20   c , and overlaps the inner end portion  22   b  of the third planar coil pattern  22 C when seen in the thickness direction of the insulating substrate  20 . 
     The outer end portion  22   a  of the fourth planar coil pattern  22 D extends until it reaches the end surface  12   b , and is connected to the fourth external terminal electrode  14 D at the end surface  12   b . The fourth external terminal electrode  14 D is provided on the end surface  12   b  at a position corresponding to the third external terminal electrode  14 C provided on the end surface  12   a.    
     The winding portion  22   c  of the fourth planar coil pattern  22 D is wound to be sandwiched between the winding portions  22   c  of the third planar coil pattern  22 C, and does not constitute the innermost and outermost turns of the planar coil patterns  22 B and  22 D provided on the lower surface  20   b  of the insulating substrate  20 . The number of turns of the winding portion  22   c  of the fourth planar coil pattern  22 D is about one turn (one turn), similar to the number of turns of the winding portion  22   c  of the third planar coil pattern  22 C. 
     In the above-described coil component  10 , the double coil is configured of the first coil portion C 1  and the second coil portion C 2 , and the first through conductor  26  of the first coil portion C 1  and the second through conductor  27  of the second coil portion C 2  are adjacent to each other. Thus, the first coil portion C 1  and the second coil portion C 2  have enhanced magnetic coupling at locations (that is, the first through conductor  26  and the second through conductor  27 ) at which the planar coil patterns  22 A,  22 B,  22 C, and  22 D of the upper and lower surfaces  20   a  and  20   b  of the insulating substrate  20  are connected, in addition to magnetic coupling in the planar coil patterns  22 A,  22 B,  22 C, and  22 D wound around the through hole  20   c . Therefore, according to the coil component  10 , a high coupling coefficient between the first coil portion C 1  and the second coil portion C 2  is realized. 
     Further, in the coil component  10 , the number of turns of the first coil portion C 1  is the sum of the number of turns of the winding portion  22   c  of the first planar coil pattern  22 A and the number of turns of the winding portion  22   c  of the second planar coil pattern  22 B, and is about 4 turns. On the other hand, the number of turns of the second coil portion C 2  is the sum of the number of turns of the winding portion  22   c  of the third planar coil pattern  22 C and the number of turns of the winding portion  22   c  of the fourth planar coil pattern  22 D, and is about two turns. That is, the number of turns of the first coil portion C 1  and the number of turns of the second coil portion C 2  are different, and specifically, the number of turns of the first coil portion C 1  is larger than the number of turns of the second coil portion C 2 . In the coil component  10 , a value of inductance of the first coil portion C 1  and a value of inductance of the second coil portion C 2  are different from each other by making the number of turns of the first coil portion C 1  and the number of turns of the second coil portion C 2  different from each other. 
     Furthermore, in the coil component  10 , when seen in the thickness direction (the Z direction) of the insulating substrate  20 , as shown in  FIGS. 5 and 7 , the pattern shape of the first planar coil pattern  22 A and the pattern shape of the second planar coil pattern  22 B are line symmetric with respect to the equidistant line L, and as shown in  FIGS. 6 and 8 , the pattern shape of the third planar coil pattern  22 C and the pattern shape of the fourth planar coil pattern  22 D are line symmetric with respect to the equidistant line L. Since the pattern shapes of the planar coil patterns  22 A,  22 B,  22 C, and  22 D have symmetry in this way, a manufacturing process can be simplified. For example, types of mask patterns used during manufacturing can be reduced, the number of work processes can be reduced, and work time can be shortened. Further, when the planar coil patterns  22 A,  22 B,  22 C and  22 D are plated and molded, the planar coil patterns  22 A,  22 B,  22 C and  22 D can be plated and grown at a uniform speed by making plating formation regions on the upper and lower surfaces  20   a  and  20   b  of the insulating substrate  20  have the same area, and thus the planar coil patterns  22 A,  22 B,  22 C, and  22 D can be formed with high dimensional accuracy. 
     Further, in the coil component  10 , the planar coil patterns  22 A,  22 B,  22 C, and  22 D formed on the respective surfaces of the insulating substrate  20  are separated from each other by the resin walls  24 , and a region sandwiched between the adjacent resin walls  24  is the plating formation region of each of the planar coil patterns  22 A,  22 B,  22 C, and  22 D. An area of the plating formation region can be designed with high accuracy by defining the plating formation regions with the resin walls  24  in this way, and thus, the planar coil patterns  22 A,  22 B,  22 C, and  22 D can be formed with high dimensional accuracy. 
     The disclosure is not limited to the above-described embodiment, and may take various aspects. 
     For example, the planar coil patterns formed on the upper and lower surfaces of the insulating substrate do not have to be line symmetric with respect to the equidistant line. Further, the number of turns of the first coil portion and the number of turns of the second coil portion can be increased or decreased as appropriate. Further, a position of the outer end portion of each of the planar coil patterns (that is, a position at which the external terminal electrode is formed) can be appropriately changed.