Patent Publication Number: US-2022231003-A1

Title: Semiconductor light-emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-005191, filed on Jan. 15, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a semiconductor light-emitting device. 
     BACKGROUND 
     A semiconductor light-emitting device including a semiconductor light-emitting element as a light source is widely known in the related art. The semiconductor light-emitting device disclosed in the related art includes a semiconductor light-emitting element and a board on which the semiconductor light-emitting element is mounted. 
     When the semiconductor light-emitting device is used together with, for example, a switching element and a capacitor configured to operate the semiconductor light-emitting device, the switching element and the capacitor are arranged separately from the semiconductor light-emitting device, and the semiconductor light-emitting element, the switching element, and the capacitor are electrically connected to one another by using wirings or the like. In such a configuration, inductance caused by the wirings or the like is a concern. 
     SUMMARY 
     According to an embodiment of the present disclosure, a semiconductor light-emitting device includes: a board including a front surface, a back surface facing an opposite side of the front surface, a first wiring pattern formed on the front surface, and a second wiring pattern formed on the side of the back surface with respect to the first wiring pattern; and a light-emitting element, a switching element, and a capacitor, which are electrically connected to one another by both the first wiring pattern and the second wiring pattern, wherein a first predetermined element and a second predetermined element among the light-emitting element, the switching element, and the capacitor are arranged in a first direction when viewed in a thickness direction of the board, wherein, the second predetermined element and a third predetermined element among the light-emitting element, the switching element, and the capacitor are arranged in a second direction intersecting the first direction when viewed in the thickness direction of the board, and wherein with respect to a first current path of a first current flowing through the light-emitting element, the switching element, and the capacitor on the front surface, the second wiring pattern is configured to form a second current path through which a second current flows in an opposite direction to a direction in which the first current flows through the first current path, the second current path overlapping the first current path when viewed in the thickness direction of the board. 
     According to another embodiment of the present disclosure, a semiconductor light-emitting device includes: a board including a front surface, a back surface facing an opposite side of the front surface, a first wiring pattern formed on the front surface, and a second wiring pattern formed on the side of the back surface with respect to the first wiring pattern; and a light-emitting element, a switching element, and a capacitor, which are electrically connected to one another by both the first wiring pattern and the second wiring pattern, wherein a first predetermined element among the light-emitting element, the switching element, and the capacitor has a shape having a longitudinal direction and a lateral direction when viewed in a thickness direction of the board, wherein the first predetermined element and another element among the light-emitting element, the switching element, and the capacitor are arranged in a first direction intersecting the longitudinal direction when viewed in the thickness direction of the board, and wherein with respect to a first current path of a first current flowing through the light-emitting element, the switching element, and the capacitor on the front surface, the second wiring pattern is configured to form a second current path through which a second current flows in an opposite direction to a direction in which the first current flows through the first current path, the second current path overlapping the first current path when viewed in the thickness direction of the board. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view of a semiconductor light-emitting device according to a first embodiment of the present disclosure. 
         FIG. 2  is an exploded perspective view of the semiconductor light-emitting device of  FIG. 1 . 
         FIG. 3  is a plan view showing an internal structure of the semiconductor light-emitting device of  FIG. 1 . 
         FIG. 4  is a cross-sectional view taken along line  4 - 4 , showing the semiconductor light-emitting device of  FIG. 3 . 
         FIG. 5  is a perspective view showing a wiring pattern on a side of the substrate back surface of a first substrate constituting a board main surface of a multilayer board of the semiconductor light-emitting device of  FIG. 1 . 
         FIG. 6  is a plan view of a third substrate constituting a board back surface of the multilayer board. 
         FIG. 7  is a perspective view showing a wiring pattern on a side of the substrate back surface of the third substrate. 
         FIG. 8  is a schematic circuit diagram of a laser system including the semiconductor light-emitting device of  FIG. 1 . 
         FIG. 9  is a plan view showing a first current path and a second current path of a semiconductor light-emitting device. 
         FIG. 10  is a graph showing transition of a current flowing through a light-emitting element of a semiconductor light-emitting device. 
         FIG. 11  is a plan view showing an internal structure of a semiconductor light-emitting device according to a second embodiment of the present disclosure. 
         FIG. 12  is a perspective view showing a wiring pattern on a side of the substrate back surface of a first substrate constituting a board main surface of a multilayer board of the semiconductor light-emitting device of  FIG. 11 . 
         FIG. 13  is a plan view showing an internal structure of a semiconductor light-emitting device according to a third embodiment of the present disclosure. 
         FIG. 14  is a schematic circuit diagram of a laser system including the semiconductor light-emitting device of  FIG. 13 . 
         FIG. 15  is a plan view showing an internal structure of a semiconductor light-emitting device according to a fourth embodiment of the present disclosure. 
         FIG. 16  is a perspective view showing a wiring pattern on a side of the substrate back surface of a first substrate constituting a board main surface of a multilayer board of the semiconductor light-emitting device of  FIG. 15 . 
         FIG. 17  is a plan view showing an internal structure of a semiconductor light-emitting device according to a fifth embodiment of the present disclosure. 
         FIG. 18  is a perspective view showing a wiring pattern on a side of the substrate back surface of a first substrate constituting a board main surface of a multilayer board of the semiconductor light-emitting device of  FIG. 17 . 
         FIG. 19  is a plan view of a third substrate constituting a board back surface of the multilayer board. 
         FIG. 20  is a perspective view showing a wiring pattern of the third substrate on a side of the substrate back surface of the third substrate. 
         FIG. 21  shows a cross-sectional view showing a portion of a cross-sectional structure of the semiconductor light-emitting device taken along line  21 - 21  in  FIG. 17 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of a semiconductor light-emitting device will now be described with reference to the drawings. The following embodiments exemplify configurations and methods for embodying the technical ideas of the present disclosure, and the materials, structures, arrangements, dimensions, and the like of various components are not limited to those described below. 
     First Embodiment 
     A semiconductor light-emitting device  10  according to a first embodiment of the present disclosure will be described with reference to  FIGS. 1 to 10 .  FIGS. 5 to 7  are shown in perspective to make it easier to understand a positional relationship of conductive layers of a multilayer board  20  to be described later. Further, for the sake of convenience, a conductive bonding material to be described later is omitted in  FIG. 3 . 
     The semiconductor light-emitting device  10  shown in  FIG. 1  may be used in a laser system that measures a distance between the semiconductor light-emitting device  10  and an object by, for example, irradiating the object with a pulsed laser and measuring scattered light reflected from the object. That is, the semiconductor light-emitting device  10  may be used in a laser system as LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging), which is an example of three-dimensional distance measurement. Further, the semiconductor light-emitting device  10  may be used in a laser system configured to measure a two-dimensional distance. 
     As shown in  FIG. 1 , the semiconductor light-emitting device  10  is formed in, for example, a rectangular flat plate shape. In a plan view of the semiconductor light-emitting device  10 , a direction along one side is defined as an x direction, and a direction orthogonal to the x direction is defined as a y direction. Further, a direction orthogonal to both the x direction and the y direction is defined as a z direction. The z direction may be a height direction of the semiconductor light-emitting device  10 . In the present embodiment, a size of the semiconductor light-emitting device  10  in the x direction is about 5.65 mm, and a size thereof in they direction is about 5.35 mm. The plan view of the semiconductor light-emitting device  10  refers to viewing the semiconductor light-emitting device  10  from the z direction. Therefore, in the following description, “viewed from the z direction” means a plan view. 
     As shown in  FIGS. 1 and 2 , the semiconductor light-emitting device  10  includes: a multilayer board  20 ; a capacitor  70 , a switching element  80 , and a light-emitting element  90 , which are electronic components mounted on the multilayer board  20 ; and a case  100 . 
     The multilayer board  20  has a rectangular shape having a long side and a short side when viewed in the z direction. In the present embodiment, the multilayer board  20  is arranged so that the x direction is the long side direction and the y direction is the short side direction. The multilayer board  20  has a board main surface  20   s  and a board back surface  20   r  facing opposite sides in the z direction. The capacitor  70 , the switching element  80 , and the light-emitting element  90  are mounted on the board main surface  20   s.    
     The multilayer board  20  has the board side surfaces  21  to  24  intersecting both the board main surface  20   s  and the board back surface  20   r . In the present embodiment, the board side surfaces  21  to  24  are orthogonal to both the board main surface  20   s  and the board back surface  20   r . When viewed in the z direction, the board side surfaces  21  and  22  extend along the x direction, and the board side surfaces  23  and  24  extend along the y direction. 
     The case  100  accommodates the capacitor  70 , the switching element  80 , and the light-emitting element  90 . The case  100  is attached to the multilayer board  20 . The interior of the case  100  is, for example, hollow. However, the present disclosure is not limited thereto, and the case  100  may be filled with any member (for example, a sealing resin). 
     The case  100  includes a frame-shaped side wall  101  that opens on both sides in the z direction, and a light-transmitting plate  102  installed at the side wall  101 . The side wall  101  is made of, for example, a material having a light-shielding characteristic, such as a colored resin. Light from the light-emitting element  90  is shielded by the side wall  101 . The side wall  101  is formed in a rectangular shape that is slightly smaller than the multilayer board  20  when viewed in the z direction. 
     The side wall  101  includes a first side wall  101 A and a second side wall  101 B forming both side walls in they direction, and a third side wall  101 C and a fourth side wall  101 D forming both side walls in the x direction. When viewed in the z direction, the first side wall  101 A is arranged at a position adjacent to the board side surface  21  of the multilayer board  20  in the y direction, and the second side wall  101 B is arranged at a position adjacent to the board side surface  22  thereof in they direction. The third side wall  101 C is arranged at a position adjacent to the board side surface  23  of the multilayer board  20  in the x direction, and the fourth side wall  101 D is arranged at a position adjacent to the board side surface  24  thereof in the x direction. When viewed in the z direction, the first side wall  101 A and the second side wall  101 B are side walls extending in the x direction, and the third side wall  101 C and the fourth side wall  101 D are side walls extending in the y direction. 
     The light-transmitting plate  102  is formed in a rectangular flat plate shape that is slightly smaller than the side wall  101  when viewed in the z direction. The light-transmitting plate  102  is made of, for example, a transparent material such as glass. The light-transmitting plate  102  transmits light from the light-emitting element  90 . 
       FIG. 3  is a plan view of a state in which the light-transmitting plate  102  is omitted from the semiconductor light-emitting device  10 . As shown in  FIG. 3 , the frame-shaped side wall  101  surrounds the capacitor  70 , the switching element  80 , and the light-emitting element  90 . 
     The capacitor  70  stores electric power from an external power source of the semiconductor light-emitting device  10  and supplies the electric power to the light-emitting element  90  via the switching element  80 . As the capacitor  70 , for example, a ceramic capacitor or a Si (silicon) capacitor is used. In the present embodiment, the ceramic capacitor is used as the capacitor  70 . 
     When viewed in the z direction, the capacitor  70  is interposed between a center of the multilayer board  20  in the y direction and the board side surface  22 . The capacitor  70  is arranged closer to the board side surface  22  than the center of the multilayer board  20  in the y direction. The capacitor  70  is arranged at a position adjacent to the second side wall  101 B in the y direction. 
     As shown in  FIGS. 1 and 2 , the capacitor  70  is formed in substantially a rectangular parallelepiped shape. As shown in  FIG. 3 , when viewed in the z direction, the capacitor  70  has a shape having a longitudinal direction and a lateral direction. In the present embodiment, the shape of the capacitor  70  viewed from the z direction is substantially a rectangular shape having a long side and a short side. In the present embodiment, the capacitor  70  is arranged so that its longitudinal direction is along the x direction and its lateral direction is along the y direction. 
     The size of the capacitor  70  in the x direction is, for example, ½ or more of the size of the multilayer board  20  in the x direction. In the present embodiment, the size of the capacitor  70  in the x direction is larger than ½ of the size of the multilayer board  20  in the x direction, specifically, about ⅔ of the size of the multilayer board  20  in the x direction. The size relationship between the capacitor  70  and the multilayer board  20  may be arbitrarily changed. In one example, the size of the capacitor  70  in the x direction may be smaller than ½ of the size of the multilayer board  20  in the x direction. 
     The capacitor  70  includes a first electrode  71  and a second electrode  72 . The first electrode  71  and the second electrode  72  are arranged apart from each other in the longitudinal direction of the capacitor  70 . The first electrode  71  and the second electrode  72  are distributed at both ends of the capacitor  70 , respectively, in the longitudinal direction. That is, in the present embodiment, the first electrode  71  and the second electrode  72  are arranged apart from each other in the x direction to be aligned with each other in the y direction. The first electrode  71  is arranged closer to the fourth side wall  101 D than the second electrode  72 . Therefore, the first electrode  71  is arranged closer to the fourth side wall  101 D than the center of the multilayer board  20  in the x direction. The second electrode  72  is arranged closer to the third side wall  101 C than the center of the multilayer board  20  in the x direction. In the present embodiment, the capacitor  70  is arranged closer to the third side wall  101 C than the fourth side wall  101 D. That is, a distance between the second electrode  72  and the third side wall  101 C is smaller than a distance between the first electrode  71  and the fourth side wall  101 D in the x direction. 
     The switching element  80  is an element that drives the light-emitting element  90  by turning it on and off and includes, for example, a MOSFET or an IGBT. In the present embodiment, an n-type MOSFET is used as the switching element  80 . 
     The switching element  80  is formed in a flat plate shape. When viewed in the z direction, the switching element  80  has a shape having a longitudinal direction and a lateral direction. In the present embodiment, the shape of the switching element  80  viewed from the z direction is a rectangular shape having a long side and a short side. The switching element  80  is arranged so that its longitudinal direction is along the x direction and its lateral direction is along they direction. In the present embodiment, the size of the switching element  80  in the x direction is smaller than the size of the capacitor  70  in the x direction, and the size of the switching element  80  in they direction is smaller than the size of the capacitor  70  in the y direction. The size of the switching element  80  in the x direction is, for example, ½ or less of the size of the capacitor  70  in the x direction. In the present embodiment, the size of the switching element  80  in the x direction is ⅓ or less of the size of the capacitor  70  in the x direction. The size of the switching element  80  in they direction is about ½ of the size of the capacitor  70  in they direction. The size of the switching element  80  in the x direction may be larger than ½ of the size of the capacitor  70  in the x direction. Further, the size of the switching element  80  in they direction may be larger than ½ of the size of the capacitor  70  in the y direction. 
     As shown in  FIG. 4 , the switching element  80  has a switching element main surface  80   s  and a switching element back surface  80   r  facing opposite sides in the z direction. The switching element  80  is arranged so that the switching element main surface  80   s  faces the same side as the board main surface  20   s  of the multilayer board  20 . 
     As shown in  FIGS. 3 and 4 , the switching element  80  includes a drain electrode  81 , a source electrode  82 , and a gate electrode  83 . The drain electrode  81  is formed on the switching element back surface  80   r , and both the source electrode  82  and the gate electrode  83  are formed on the switching element main surface  80   s . The drain electrode  81  is formed over the entire switching element back surface  80   r . The source electrode  82  is formed over most of the switching element main surface  80   s . The gate electrode  83  is formed at one of four corners of the switching element main surface  80   s.    
     When viewed in the z direction, the switching element  80  is arranged apart from the capacitor  70  in the y direction. When viewed in the z direction, it may be said that the capacitor  70  and the switching element  80  are arranged in the y direction. In the present embodiment, a distance between the capacitor  70  and the switching element  80  in the y direction is about 0.15 mm. The switching element  80  is arranged closer to the first side wall  101 A than the capacitor  70  in the y direction. In the present embodiment, the switching element  80  is arranged at the center of the multilayer board  20  in they direction. 
     As shown in  FIG. 3 , the switching element  80  is interposed between the center of the multilayer board  20  in the x direction and the board side surface  23 . The switching element  80  is arranged closer to the board side surface  23  than the center of the multilayer board  20  in the y direction. The switching element  80  is arranged at a position adjacent to the third side wall  101 C in the x direction. 
     The capacitor  70  and the switching element  80  are arranged at positions where at least portions of the capacitor  70  and the switching element  80  overlap each other when viewed in the y direction. That is, when at least portions of the capacitor  70  and the switching element  80  overlap each other when viewed in the y direction, it may be said that the capacitor  70  and the switching element  80  are arranged in a first direction. In the present embodiment, the x direction corresponds to the “first direction.” Further, the capacitor  70  corresponds to a “first predetermined element,” and the switching element  80  corresponds to a “second predetermined element.” 
     In the present embodiment, the switching element  80  is arranged at a position where it overlaps the second electrode  72  of the capacitor  70  when viewed in they direction. When viewed in the y direction, a portion of the switching element  80  protrudes from the capacitor  70  in the x direction. More specifically, an end, which is closer to the third side wall  101 C, of both ends of the switching element  80  in they direction protrudes from the second electrode  72  of the capacitor  70  toward the third side wall  101 C when viewed in the y direction. In this manner, in the present embodiment, the capacitor  70  and the switching element  80  are arranged at positions where portions of the capacitor  70  and the switching element  80  overlap each other when viewed in the y direction. 
     A positional relationship between the switching element  80  and the capacitor  70  is not limited thereto, and the entire switching element  80  may be arranged to overlap the capacitor  70  when viewed in the y direction. That is, the switching element  80  may be arranged so that the end, between both ends of the switching element  80 , which is closer to the third side wall  101 C in the y direction does not protrude from the second electrode  72  of the capacitor  70  toward the third side wall  101 C when viewed in the y direction. For example, the end, between both ends of the switching element  80 , which is closer to the third side wall  101 C in they direction and the second electrode  72  of the capacitor  70  may be arranged at positions at which they are aligned with each other in the x direction. 
     The light-emitting element  90  is a light source in the semiconductor light-emitting device  10  and emits light in a predetermined wavelength band by electric power from the capacitor  70 . The specific configuration of the light-emitting element  90  is not particularly limited, and it may be a semiconductor light-emitting element such as a semiconductor laser element or an LED element. Therefore, a light-emitting diode may be used as the light-emitting element  90 . In the present embodiment, the light-emitting element is a semiconductor laser element, and particularly, a VCSEL (Vertical Cavity Surface Emitting LASER) element is adopted as the light-emitting element. The light from the light-emitting element  90  passes through the light-transmitting plate  102  (see  FIG. 4 ) and is emitted to the outside. 
     As shown in  FIGS. 3 and 4 , the light-emitting element  90  is formed in a rectangular plate shape. As shown in  FIG. 4 , the light-emitting element  90  includes a light-emitting element main surface  90   s  and a light-emitting element back surface  90   r  facing opposite sides in the z direction. The light-emitting element  90  is arranged so that the light-emitting element main surface  90   s  faces the same side as the board main surface  20   s  of the multilayer board  20 . 
     As shown in  FIG. 3 , when viewed in the z direction, the light-emitting element  90  has a shape having a longitudinal direction and a lateral direction. In the present embodiment, the shape of the light-emitting element  90  viewed from the z direction is substantially a rectangular shape having a long side and a short side. In the present embodiment, the light-emitting element  90  is arranged such that its longitudinal direction is along the x direction and its lateral direction is along the y direction. 
     The size of the light-emitting element  90  in the x direction is smaller than the size of the capacitor  70  in the x direction, and the size of the light-emitting element  90  in they direction is smaller than the size of the capacitor  70  in they direction. On the other hand, the size of the light-emitting element  90  in the x direction is larger than the size of the switching element  80  in the x direction, and the size of the light-emitting element  90  in the y direction is larger than the size of the switching element  80  in they direction. The size of the light-emitting element  90  in the x direction is ½ or less of the size of the capacitor  70  in the x direction. In the present embodiment, the size of the light-emitting element  90  in the x direction is about ⅓ of the size of the capacitor  70  in the x direction. Since the size of the light-emitting element  90  in the y direction is slightly larger than the size of the switching element  80  in the y direction, it is slightly larger than ½ of the size of the capacitor  70  in the y direction. 
     As shown in  FIG. 4 , the light-emitting element  90  includes an anode electrode  91  and a cathode electrode  92 . The anode electrode  91  is formed on the light-emitting element main surface  90   s . More specifically, the anode electrode  91  is formed at an end of both ends of the light-emitting element main surface  90   s  in the x direction. The cathode electrode  92  is formed on the light-emitting element back surface  90   r . More specifically, the cathode electrode  92  is formed over the entire light-emitting element back surface  90   r.    
     As shown in  FIG. 3 , the light-emitting element  90  includes a light-emitting part  93  that emits light. The light-emitting part  93  emits the light toward the light-transmitting plate  102  in the z direction. The light-emitting part  93  is formed on the light-emitting element main surface  90   s . The anode electrode  91  and the light-emitting part  93  are arranged apart from each other in the x direction. The light-emitting part  93  is formed over most of the light-emitting element main surface  90   s.    
     When viewed in the z direction, the light-emitting element  90  is arranged apart from the capacitor  70  in the y direction. When viewed in the z direction, it may be said that the capacitor  70  and the light-emitting element  90  are arranged in the y direction. In the present embodiment, a distance between the capacitor  70  and the light-emitting element  90  in the y direction is about 0.15 mm. That is, in the present embodiment, the distance between the capacitor  70  and the light-emitting element  90  in the y direction is equal to the distance between the capacitor  70  and the switching element  80  in the y direction. Here, in a case where a difference between the distance between the capacitor  70  and the light-emitting element  90  in the y direction and the distance between the capacitor  70  and the switching element  80  in the y direction is, for example, 20% or less of the distance between the capacitor  70  and the light-emitting element  90  in the y direction, it may be said that the distance between the capacitor  70  and the light-emitting element  90  in the y direction is equal to the distance between the capacitor  70  and the switching element  80  in the y direction. 
     The capacitor  70  and the light-emitting element  90  are arranged at positions where they overlap each other when viewed in the y direction. In the present embodiment, the light-emitting element  90  is arranged such that the entire light-emitting element  90  overlaps the capacitor  70  when viewed in the y direction. The light-emitting element  90  is arranged closer to the third side wall  101 C than the first electrode  71  of the capacitor  70  and closer to the fourth side wall  101 D than the second electrode  72  of the capacitor  70 . That is, it may be said that the light-emitting element  90  is arranged between the first electrode  71  and the second electrode  72  of the capacitor  70  when viewed in they direction. In the present embodiment, the light-emitting element  90  is arranged closer to the second electrode  72  than the first electrode  71  of the capacitor  70  in the x direction. 
     The light-emitting element  90  is arranged closer to the first side wall  101 A than the capacitor  70  in the y direction. That is, the light-emitting element  90  is arranged on the same side as the side on which the switching element  80  is arranged with respect to the capacitor  70  in the y direction. In the present embodiment, the light-emitting element  90  is arranged at the center of the multilayer board  20  in they direction. 
     The switching element  80  and the light-emitting element  90  are arranged at positions where at least portions of the switching element  80  and the light-emitting element  90  overlap each other when viewed in the x direction. In the present embodiment, the switching element  80  is arranged at a position where the entire switching element  80  overlaps the light-emitting element  90  when viewed in the x direction. Therefore, it may be said that the switching element  80  and the light-emitting element  90  are arranged apart from each other in the x direction to be aligned with each other in the y direction. The light-emitting element  90  is arranged at a position adjacent to the switching element  80  in the x direction. The light-emitting element  90  is arranged closer to the fourth side wall  101 D than the switching element  80 . That is, when viewed in the z direction, the light-emitting element  90  is arranged near the center of the multilayer board  20 . In the present embodiment, the light-emitting element  90  is arranged so that the center of the light-emitting element  90  in the x direction is closer to the third side wall  101 C than the center of the multilayer board  20  in the x direction. More specifically, the light-emitting element  90  is arranged such that an end, which is closer to the fourth side wall  101 D, of both ends of the light-emitting element  90  in the x direction is arranged at the center of the multilayer board  20  in the x direction. 
     Here, when at least portions of the switching element  80  and the light-emitting element  90  overlap with each other when viewed in the x direction, it may be said that the switching element  80  and the light-emitting element  90  are arranged in a second direction. In the present embodiment, they direction corresponds to the “second direction.” Further, the light-emitting element  90  corresponds to a “third predetermined element.” 
     In the present embodiment, when the y direction corresponds to the “second direction,” the first direction corresponding to the x direction and the second direction are orthogonal to each other, but the present disclosure is not limited thereto. The present disclosure may apply as long as the first direction and the second direction intersect each other. In a case where the capacitor  70  and the switching element  80  are arranged so that at least portions thereof overlap each other when viewed in the y direction and the switching element  80  and the light-emitting element  90  are arranged so that at least portions thereof overlap each other when viewed in the x direction, it may be said that the first direction, which is an arrangement direction of the capacitor  70  and the switching element  80 , intersects the second direction, which is an arrangement direction of the switching element  80  and the light-emitting element  90 . 
     The positional relationship between the switching element  80  and the light-emitting element  90  is not limited to the positional relationship shown in  FIG. 3 . For example, the switching element  80  may be arranged so that a portion thereof protrudes from the light-emitting element  90  when viewed in the x direction. 
     As shown in  FIG. 4 , the multilayer board  20  includes a plurality of substrates and a plurality of conductive layers and is a multilayer board in which the substrates and the conductive layers are alternately stacked. In the present embodiment, the multilayer board  20  includes a first substrate  20 A, a second substrate  20 B, and a third substrate  20 C as the plurality of substrates, and a first conductive layer  30 , a second conductive layer  40 , a third conductive layer  50 , and a fourth conductive layer  60  as the plurality of conductive layers. Each of the substrates  20 A to  20 C is made of a material having an electrical insulation characteristic such as an epoxy resin. In the present embodiment, the thicknesses of the substrates  20 A to  20 C are equal to each other, and a thickness dimension of each of the substrates  20 A to  20 C is about 0.1 mm. That is, in the present embodiment, a thickness dimension of the first substrate  20 A is smaller than both the distance between the capacitor  70  and the switching element  80  in the y direction and the distance between the capacitor  70  and the light-emitting element  90  in the y direction. Each of the conductive layers  30 ,  40 ,  50 , and  60  is made of a conductive material such as Cu (copper), Al (aluminum), Ti (titanium), or Au (gold). 
     The thickness of each of the substrate  20 A to  20 C may be arbitrarily changed. In one example, the thicknesses of the substrates  20 A to  20 C may be different from each other. Further, in one example, the thickness of the second substrate  20 B may be larger than the thicknesses of the first substrate  20 A and the third substrate  20 C. 
     The third substrate  20 C, the second substrate  20 B, and the first substrate  20 A are stacked in this order in the z direction. The first conductive layer  30  is formed on the first substrate  20 A, the second conductive layer  40  is formed between the first substrate  20 A and the second substrate  20 B, the third conductive layer  50  is formed between the second substrate  20 B and the third substrate  20 C, and the fourth conductive layer  60  is formed on the side opposite to the third conductive layer  50  in the z direction with respect to the third substrate  20 C. 
     The first substrate  20 A has a substrate main surface  20 As and a substrate back surface  20 Ar facing opposite sides in the z direction. The substrate main surface  20 As constitutes the board main surface  20   s  of the multilayer board  20 . Here, in the present embodiment, the substrate main surface  20 As (the board main surface  20   s ) corresponds to a “surface of the board.” 
     As shown in  FIG. 3 , the first conductive layer  30  is a wiring pattern formed on the substrate main surface  20 As. In other words, the first conductive layer  30  is a wiring pattern formed on the board main surface  20   s  of the multilayer board  20 . Here, the first conductive layer  30  corresponds to a “first wiring pattern.” 
     The first conductive layer  30  includes a first wiring  31 , a second wiring  32 , a third wiring  33 , a fourth wiring  34 , and a fifth wiring  35 . The first to fifth wirings  31  to  35  are arranged apart from each other. Here, the first wiring  31  corresponds to a “first front surface side wiring,” the second wiring  32  corresponds to a “second front surface side wiring,” and the third wiring  33  corresponds to a “third front surface side wiring.” 
     The first wiring  31  is a wiring on which the first electrode  71  of the capacitor  70  is mounted, and is formed near the board side surface  22  and the board side surface  24  of the board main surface  20   s . The first electrode  71  of the capacitor  70  is bonded to the first wiring  31  by a conductive bonding material such as solder or Ag (silver) paste. As a result, the first electrode  71  of the capacitor  70  is electrically connected to the first wiring  31 . 
     The first wiring  31  is arranged at a position adjacent to both the second side wall  101 B and the fourth side wall  101 D. The first wiring  31  has an extension wiring  31   a  extending beyond the first electrode  71  of the capacitor  70  toward the fourth side wall  101 D in the x direction. 
     The shape of the first wiring  31  viewed from the z direction is substantially a rectangular shape in which the x direction is a long side direction and the y direction is a short side direction. It may be said that the first wiring  31  extends in the x direction. A width dimension of the first wiring  31  (a dimension of the first wiring  31  in they direction) is substantially equal to a dimension of the first electrode  71  of the capacitor  70  in they direction. More specifically, in consideration of a deviation in mounting position of the first electrode  71  of the capacitor  70  on the first wiring  31 , the width dimension of the first wiring  31  is also set to be slightly larger than the dimension of the first electrode  71  of the capacitor  70  in they direction. 
     The second wiring  32  is a wiring on which the second electrode  72  of the capacitor  70  and the switching element  80  are mounted. The second electrode  72  of the capacitor  70  is bonded to the second wiring  32  by a conductive bonding material. Further, the switching element back surface  80   r  (see  FIG. 4 ) of the switching element  80  is bonded to the second wiring  32  by a conductive bonding material. As a result, both the second electrode  72  of the capacitor  70  and the drain electrode  81  (see  FIG. 4 ) of the switching element  80  are electrically connected to the second wiring  32 . 
     The second wiring  32  is formed near the board side surface  22  and the board side surface  23  of the board main surface  20   s . The second wiring  32  is formed at a position adjacent to both the second side wall  101 B and the third side wall  101 C. 
     The shape of the second wiring  32  viewed from the z direction is substantially a rectangular shape in which the y direction is a long side direction and the x direction is a short side direction. It may be said that the second wiring  32  extends in the y direction. The second wiring  32  includes an extension wiring  32   a  extending beyond the switching element  80  toward the first side wall  101 A in they direction. The extension wiring  32   a  is arranged closer to the first side wall  101 A than the center of the multilayer board  20  in they direction. When viewed in the x direction, the second wiring  32  extends in the y direction to overlap the first wiring  31 , the third wiring  33 , and the fifth wiring  35 . In the present embodiment, when viewed in the x direction, the second wiring  32  extends in they direction to overlap the entire first wiring  31 , the entire third wiring  33 , and a portion of the fifth wiring  35  in they direction. 
     A width dimension of the second wiring  32  (a dimension of the second wiring  32  in the x direction) is substantially equal to a dimension of the switching element  80  in the x direction. More specifically, in consideration of a deviation in mounting position of the switching element  80  on the second wiring  32 , the width dimension of the second wiring  32  is set to be slightly larger than the dimension of the switching element  80  in the x direction. 
     The third wiring  33  is a wiring on which the light-emitting element  90  is mounted. The light-emitting element back surface  90   r  (see  FIG. 4 ) of the light-emitting element  90  is bonded to the third wiring  33  by a conductive bonding material. As a result, the cathode electrode  92  (see  FIG. 4 ) of the light-emitting element  90  is electrically connected to the third wiring  33 . Further, the anode electrode  91  of the light-emitting element  90  is connected to the source electrode  82  of the switching element  80  by a wire W. As a result, the anode electrode  91  is electrically connected to the source electrode  82 . The wire W is a bonding wire made of a conductive material. Cu, Al, Au, and the like are appropriately selected as the conductive material. 
     The third wiring  33  is formed in the center of the board main surface  20   s  in the y direction and near the board side surface  24  in the x direction. The third wiring  33  is arranged at a position adjacent to the fourth side wall  101 D. The third wiring  33  is arranged apart from the second wiring  32  in the x direction. It may be said that the third wiring  33  is arranged at a position aligned with the switching element  80  in the y direction. The third wiring  33  is arranged apart from the first wiring  31  in the y direction. When viewed in the y direction, the third wiring  33  has a portion that overlaps the first wiring  31 . 
     The shape of the third wiring  33  viewed from the z direction is substantially a rectangular shape in which the x direction is a long side direction and the y direction is a short side direction. It may be said that the third wiring  33  extends in the x direction. The third wiring  33  includes an extension wiring  33   a  extending beyond the light-emitting element  90  toward the fourth side wall  101 D in the y direction. In other words, the light-emitting element  90  is arranged at one of both ends of the third wiring  33  that is closer to the second wiring  32  in the x direction. A dimension of the third wiring  33  in the x direction is larger than a dimension of the light-emitting element  90  in the x direction. In the x direction, the extension wiring  33   a  extends closer to the fourth side wall  101 D than the first electrode  71  of the capacitor  70 . The extension wiring  33   a  is formed so that its lead end is aligned with the leading end of the extension wiring  31   a  of the first wiring  31  in the x direction. 
     A width dimension of the third wiring  33  (a dimension of the third wiring  33  in the y direction) is substantially equal to a dimension of the light-emitting element  90  in the y direction. More specifically, in consideration of a deviation in mounting position of the light-emitting element  90  on the third wiring  33 , the width dimension of the third wiring  33  is set to be slightly larger than the dimension of the light-emitting element  90  in the y direction. 
     The fourth wiring  34  is a wiring that is electrically connected to the gate electrode  83  of the switching element  80 . The gate electrode  83  of the switching element  80  is connected to the fourth wiring  34  by a wire W. As a result, the gate electrode  83  is electrically connected to the fourth wiring  34 . 
     The fourth wiring  34  is formed near the board side surface  21  and the board side surface  23  of the board main surface  20   s . The fourth wiring  34  is formed at a position adjacent to both the first side wall  101 A and the third side wall  101 C. The fourth wiring  34  is arranged apart from the fourth wiring  34  in the y direction to be aligned with the second wiring  32  in the x direction. It may be said that the fourth wiring  34  is interposed between the second wiring  32  and the first side wall  101 A in they direction. The shape of the fourth wiring  34  viewed from the z direction is substantially a rectangular shape in which the x direction is a long side direction and they direction is a short side direction. A dimension of the fourth wiring  34  in the x direction is equal to the width dimension (dimension in the x direction) of a portion of the second wiring  32  on which the switching element  80  is mounted. 
     The fifth wiring  35  is a wiring connected to the ground. The source electrode  82  of the switching element  80  is connected to the fifth wiring  35  by a wire W. As a result, the source electrode  82  is electrically connected to the fifth wiring  35 . 
     The fifth wiring  35  is formed near the board side surface  21  and the board side surface  24  of the board main surface  20   s . The fifth wiring  35  is arranged at a position adjacent to both the first side wall  101 A and the fourth side wall  101 D. The fifth wiring  35  is arranged apart from the third wiring  33  in the y direction to be aligned with the third wiring  33  in the x direction. When viewed in the y direction, the fifth wiring  35  is arranged at a position where it overlaps both the first wiring  31  and the third wiring  33 . When viewed in the x direction, the fifth wiring  35  is arranged at a position where it overlaps the fourth wiring  34 . 
     The shape of the fifth wiring  35  viewed from the z direction is substantially a rectangular shape in which the x direction is a long side direction and the y direction is a short side direction. It may be said that the fifth wiring  35  extends in the x direction. A dimension of the fifth wiring  35  in the x direction is equal to the dimension of the third wiring  33  in the x direction. A width dimension of the fifth wiring  35  (a dimension of the fifth wiring  35  in they direction) is larger than the width dimension of the third wiring  33 . 
     A first current path of a current flowing through the light-emitting element  90 , the switching element  80 , and the capacitor  70  is formed on the board main surface  20   s  of the multilayer board  20  by the first conductive layer  30 , the light-emitting element  90 , the switching element  80 , and the capacitor  70 . The first current path is, for example, a path through which a current flows in the order of the first electrode  71  and the second electrode  72  of the capacitor  70 , the drain electrode  81  and the source electrode  82  of the switching element  80 , the wire W, and the anode electrode  91  and the cathode electrode  92  of the light-emitting element  90 . 
     As shown in  FIG. 5 , the second conductive layer  40  is an inner layer pattern formed in the multilayer board  20 . In the present embodiment, the second conductive layer  40  corresponds to a “second wiring pattern.” That is, the light-emitting element  90 , the switching element  80 , and the capacitor  70  are electrically connected to each other by both the conductive layers  30  and  40 . 
     The second conductive layer  40  is formed on the substrate back surface  20 Ar (see  FIG. 4 ) of the first substrate  20 A. That is, it may be said that the second conductive layer  40  is formed on the board back surface  20   r  of the multilayer board  20  with respect to the first conductive layer  30 . When viewed in the z direction, the second conductive layer  40  is provided at a position where it overlaps the first conductive layer  30  (see  FIG. 3 ). That is, the second conductive layer  40  is formed to overlap the first current path when viewed in the z direction. Further, the second conductive layer  40  is configured to form a second current path of a current flowing in a direction opposite to that of the first current path. 
     The second conductive layer  40  includes a first wiring  41 , a second wiring  42 , a third wiring  43 , and a fourth wiring  44 . The first to fourth wirings  41  to  44  are arranged apart from one another. In the present embodiment, the first wiring  41  corresponds to a “back surface side wiring.” 
     As shown in  FIGS. 3 and 5 , the first wiring  41  is a wiring that forms the second current path of the current flowing in a direction opposite to the direction of the current flowing in the first current path. Further, the first wiring  41  is a wiring connected to the first current path. 
     The first wiring  41  includes a first wiring portion  41   a  formed at a position where it overlaps both the first electrode  71  and the second electrode  72  of the capacitor  70  when viewed in the z direction, a second wiring portion  41   b  formed at a position where it overlaps both the light-emitting element  90  and the switching elements  80  when viewed in the z direction, and a third wiring portion  41   c  connecting the first wiring portion  41   a  and the second wiring portion  41   b  in they direction. 
     The first wiring portion  41   a  extends in the x direction. When viewed in the z direction, the first wiring portion  41   a  is formed so as to overlap both the first wiring  31  of the first conductive layer  30  and a portion of the second wiring  32  that overlaps the first wiring  31  when viewed in the x direction. A width dimension of the first wiring portion  41   a  (a dimension of the first wiring portion  41   a  in they direction) is equal to the dimension of the first wiring  31  of the first conductive layer  30  in they direction. Therefore, the width dimension of the first wiring portion  41   a  is equal to the dimension of the capacitor  70  in they direction. More specifically, in consideration of a deviation in a mounting position of the capacitor  70 , the width dimension of the first wiring portion  41   a  is slightly larger than the dimension of the capacitor  70  in the y direction. In a case where a difference between the width dimension of the first wiring portion  41   a  and the dimension of the capacitor  70  in they direction is within, for example, 10% of the width dimension of the first wiring portion  41   a , it may be said that the width dimension of the first wiring portion  41   a  is equal to the dimension of the capacitor  70  in the y direction. 
     When viewed in the z direction, both ends of the first wiring portion  41   a  in the x direction protrude from the capacitor  70 . That is, the length of the first wiring portion  41   a  in the x direction is longer than the length of the capacitor  70  in the x direction. 
     The second wiring portion  41   b  extends in the x direction. The second wiring portion  41   b  is arranged apart from the first wiring portion  41   a  in they direction. A width dimension of the second wiring portion  41   b  (a dimension of the second wiring portion  41   b  in they direction) is equal to the width dimension of the third wiring  33  (the dimension of the third wiring  33  in the y direction) of the first conductive layer  30 . Therefore, the width dimension of the second wiring portion  41   b  is equal to the dimension of the light-emitting element  90  in they direction. More specifically, in consideration of a deviation in mounting position of the light-emitting element  90 , the width dimension of the second wiring portion  41   b  is slightly larger than the dimension of the light-emitting element  90  in they direction. In a case where a difference between the width dimension of the second wiring portion  41   b  and the dimension of the light-emitting element  90  in they direction is within, for example, 10% of the width dimension of the second wiring portion  41   b , it may be said that the width dimension of the second wiring portion  41   b  is equal to the dimension of the light-emitting element  90  in the y direction. 
     In the present embodiment, a distance between the first wiring portion  41   a  and the second wiring portion  41   b  in the y direction is larger than 0.1 mm and smaller than 0.15 mm. That is, the distance between the first wiring portion  41   a  and the second wiring portion  41   b  in the y direction is smaller than both the distance between the capacitor  70  and the switching element  80  in the y direction and the distance between the capacitor  70  and the light-emitting element  90  in they direction. In the present embodiment, since the dimension of the light-emitting element  90  in the y direction is smaller than the dimension of the capacitor  70  in they direction, the width dimension of the second wiring portion  41   b  is smaller than the width dimension of the first wiring portion  41   a . Since the width dimension of the first wiring portion  41   a  is set according to the dimension of the capacitor  70  in the y direction and the width dimension of the second wiring portion  41   b  is set according to the dimension of the light-emitting element  90  in they direction, in a case where the dimension of the light-emitting element  90  in the y direction is larger than the dimension of the capacitor  70  in they direction, the width dimension of the second wiring portion  41   b  is larger than the width dimension of the first wiring portion  41   a.    
     The distance between the first wiring portion  41   a  and the second wiring portion  41   b  in the y direction may be arbitrarily changed. For example, the distance between the first wiring portion  41   a  and the second wiring portion  41   b  in they direction may be larger than 0.15 mm. That is, the distance between the first wiring portion  41   a  and the second wiring portion  41   b  in the y direction may be larger than both the distance between the capacitor  70  and the switching element  80  in the y direction and the distance between the capacitor  70  and the light-emitting element  90  in the y direction. 
     The dimension of the second wiring portion  41   b  in the x direction is equal to the dimension of the first wiring portion  41   a  in the x direction. The leading end of the second wiring portion  41   b  and the leading end of the first wiring  41  are formed to be aligned with each other in the x direction. 
     The third wiring portion  41   c  is interposed between the first wiring portion  41   a  and the second wiring portion  41   b  in the y direction. When viewed in they direction, the third wiring portion  41   c  is arranged at a position where it overlaps both an end, between both ends of the first wiring portion  41   a , which is closer to the board side surface  23  in the x direction and an end, between both ends of the second wiring portion  41   b , which is closer to the board side surface  23  in the x direction. 
     As shown in  FIGS. 3 and 5 , when viewed in the z direction, the second wiring  42  is arranged at a position where it overlaps the extension wiring  32   a  in the second wiring  32  of the first conductive layer  30 . That is, when viewed in the z direction, the third wiring  43  is arranged closer to the first side wall  101 A (the board side surface  21 ) than the switching element  80 . On the other hand, the third wiring  43  is arranged closer to the board side surface  23  than the fourth wiring  44 . The second wiring  42  is arranged at a position where it overlaps an end, between both ends of the first wiring  41 , which is closer to the board side surface  23  in the x direction when viewed in the y direction. 
     When viewed in the z direction, the third wiring  43  is arranged at a position where it overlaps the fourth wiring  34  of the first conductive layer  30 . The shape and size of the third wiring  43  viewed from the z direction are the same as the shape and size of the fourth wiring  34  viewed from the z direction. When viewed in the y direction, the third wiring  43  is arranged at a position where it overlaps the second wiring  42 . 
     When viewed in the z direction, the fourth wiring  44  is arranged at a position where it overlaps the fifth wiring  35  of the first conductive layer  30 . The shape and size of the fourth wiring  44  viewed from the z direction is the same as the shape and size of the fifth wiring  35  viewed from the z direction. When viewed in the x direction, the fourth wiring  44  is arranged at a position where it overlaps both the second wiring  42  and the third wiring  43 . 
     As shown in  FIG. 6 , both the third conductive layer  50  and the fourth conductive layer  60  are wiring patterns formed on the third substrate  20 C. The third substrate  20 C has a substrate main surface  20 Cs and a substrate back surface  20 Cr (see  FIG. 4 ) facing opposite sides in the z direction. The substrate back surface  20 Cr forms the board back surface  20   r  of the multilayer board  20 . Here, the substrate back surface  20 Cr (the board back surface  20   r ) corresponds to a “back surface of the board.” 
     As shown in  FIG. 4 , the third conductive layer  50  is formed on the substrate main surface  20 Cs of the third substrate  20 C. The fourth conductive layer  60  is formed on the substrate back surface  20 Cr of the third substrate  20 C. It may be said that the third conductive layer  50  is an inner layer pattern formed in the multilayer board  20 . 
     As shown in  FIG. 6 , the third conductive layer  50  includes a first wiring  51 , a second wiring  52 , a third wiring  53 , and a fourth wiring  54 . The first wiring  51  to the fourth wiring  54  are arranged apart from one another. 
     As shown in  FIGS. 5 and 6 , when viewed in the z direction, the first wiring  51  is arranged at a position where it overlaps the first wiring  41  of the second conductive layer  40  and does not overlap the second wiring  42 , the third wiring  43 , and the fourth wiring  44 . Further, when viewed in the z direction, the first wiring  51  is arranged at a position where it does not overlap the third wiring portion  41   c  of the first wiring  41 . The first wiring  51  is arranged near the board side surface  22  and the board side surface  24  of the substrate main surface  20 Cs. When viewed in the z direction, the first wiring  51  is arranged closer to the board side surface  24  than the light-emitting element  90  (see  FIG. 3 ). When viewed in the z direction, the first wiring  51  is arranged at a position where it overlaps the first electrode  71  (see  FIG. 3 ) of the capacitor  70 . 
     The shape of the first wiring  51  viewed from the z direction is substantially a rectangular shape in which the y direction is a long side direction and the x direction is a short side direction. An end, between both ends of the first wiring  51 , which is closer to the board side surface  23  in the x direction is located closer to the board side surface  23  than the first electrode  71  of the capacitor  70  when viewed in the z direction. 
     When viewed in the z direction, the second wiring  52  is arranged at a position where it overlaps the first wiring  41  and the second wiring  42  of the second conductive layer  40  and does not overlap the third wiring  43  and the fourth wiring  44 . The second wiring  52  is arranged near the board side surface  22  and the board side surface  23  of the substrate main surface  20 Cs. When viewed in the z direction, the second wiring  52  is arranged at a position where it overlaps the second electrode  72  of the capacitor  70 , the switching element  80 , and the light-emitting element  90  (see  FIG. 3  for both). On the other hand, when viewed in the z direction, the second wiring  52  is arranged at a position where it does not overlap the first electrode  71  of the capacitor  70 . 
     The shape of the second wiring  52  viewed from the z direction is substantially a rectangular shape having a recessed portion  52   a , in which the y direction is a long side direction and the x direction is a short side direction. The recessed portion  52   a  is provided at an end, between both ends of the second wiring  52 , which is closer to the board side surface  21  in the x direction, and is recessed from the board side surface  24  toward the board side surface  23 . 
     As shown in  FIGS. 5 and 6 , when viewed in the z direction, the third wiring  53  is arranged at a position where it overlaps the third wiring  43  of the second conductive layer  40 . The shape of the third wiring  53  viewed from the z direction is the same as the shape of the third wiring  43  viewed from the z direction. 
     As shown in  FIGS. 5 and 6 , when viewed in the z direction, the fourth wiring  54  is arranged at a position where it overlaps the fourth wiring  44  of the second conductive layer  40 . The shape of the fourth wiring  54  viewed from the z direction is the same as the shape of the fourth wiring  44  viewed from the z direction. When viewed in the x direction, a portion of the fourth wiring  54  enters the recessed portion  52   a  of the second wiring  52 . 
     As shown in  FIG. 7 , the fourth conductive layer  60  includes a first wiring  61 , a second wiring  62 , a third wiring  63 , and a fourth wiring  64 . As shown in  FIGS. 6 and 7 , the first wiring  61  is arranged at a position where it overlaps the first wiring  51  of the third conductive layer  50  when viewed in the z direction, and has the same shape as the first wiring  51 . When viewed in the z direction, the second wiring  62  is arranged at a position where it overlaps the second wiring  52  of the third conductive layer  50 , and has the same shape as the second wiring  52 . When viewed in the z direction, the third wiring  63  is arranged at a position where it overlaps the third wiring  53  of the third conductive layer  50 , and has the same shape as the third wiring  53 . When viewed in the z direction, the fourth wiring  64  is arranged at a position where it overlaps the fourth wiring  54  of the third conductive layer  50 , and has the same shape as the fourth wiring  54 . The wirings  61  to  64  of the fourth conductive layer  60  are exposed to the outside of the multilayer board  20 , and are configured as a plurality of external terminals connected to the outside. In this way, the semiconductor light-emitting device  10  has a surface mount type package structure. 
     As shown in  FIGS. 3 to 7 , the multilayer board  20  has through-wirings that penetrate one or more substrates in the thickness direction thereof. In this embodiment, the multilayer board  20  has first through-wirings  25 S and  25 R, a second through-wiring  26 , third through-wirings  27 S and  27 R, a fourth through-wiring  28 , and a fifth through-wiring  29 . Both the first through-wiring  25 S and the third through-wiring  27 S are wirings penetrating the first substrate  20 A in the z direction. The first through-wiring  25 S and the third through-wiring  27 S are formed of vias formed, for example, by burying a conductor in a through-hole penetrating the first substrate  20 A in the z direction. Both the first through-wiring  25 R and the third through-wiring  27 R are formed of vias formed, for example, by burying a conductor in a through-hole penetrating the third substrate  20 C in the z direction. Each of the through-wirings  26 ,  28 , and  29  is, for example, a wiring that penetrates the first to third substrates  20 A to  20 C. Each of the through-wirings  26 ,  28 , and  29  is formed of a via formed by, for example, burying a conductor in a through-hole penetrating the first substrate  20 A in the z direction. Each of the through-wirings  25 S,  25 R,  26 ,  27 S,  27 R,  28 , and  29  is made of a conductive material such as Cu or Al. Each of the through-wirings  25 S,  25 R,  26 ,  27 S,  27 R,  28 , and  29  may be formed by a through-hole. 
     As shown in  FIGS. 3 and 5 , both the first through-wiring  25 S and the third through-wiring  27 S are wirings that connect the first wiring  31  and the third wiring  33  of the first conductive layer  30  and the first wiring  41  of the second conductive layer  40 . That is, the first wiring  31 , the third wiring  33 , and the first wiring  41  are electrically connected by the first through-wiring  25 S and the third through-wiring  27 S. In other words, the first current path and the second current path are electrically connected via the first through-wiring  25 S and the third through-wiring  27 S. 
     As shown in  FIGS. 3 and 5 , the first through-wiring  25 S is a wiring that connects the first wiring  31  and the first wiring portion  41   a  of the first wiring  41 . As shown in  FIG. 3 , the first through-wiring  25 S is arranged at a position where it overlaps the extension wiring  31   a  of the first wiring  31  when viewed in the z direction. That is, when viewed in the z direction, the first through-wiring  25 S is arranged closer to the fourth side wall  101 D than the first electrode  71  of the capacitor  70 . As shown in  FIG. 5 , the first through-wiring  25 S is arranged at a position where it overlaps the leading end of the first wiring portion  41   a  of the first wiring  41  when viewed in the z direction. A plurality of first through-wirings  25 S (two first through-wirings  25 S in the present embodiment) are provided. The two first through-wirings  25 S are arranged apart from each other in the y direction to be aligned with each other in the x direction. 
     As shown in  FIGS. 3 and 5 , the third through-wiring  27 S is a wiring that connects the third wiring  33  and the second wiring portion  41   b  of the first wiring  41 . As shown in  FIG. 3 , the third through-wiring  27 S is arranged at a position where it overlaps the extension wiring  33   a  of the third wiring  33  when viewed in the z direction. That is, when viewed in the z direction, the third through-wiring  27 S is arranged closer to the fourth side wall  101 D than the light-emitting element  90 . As shown in  FIG. 5 , the third through-wiring  27 S is arranged at a position where it overlaps the leading end of the second wiring portion  41   b  of the first wiring  41  when viewed in the z direction. A plurality of third through-wirings  27 S (three third through-wirings  27 S in the present embodiment) are provided. The three third through-wirings  27 S are arranged apart from each other in the x direction. 
     As shown in  FIGS. 6 and 7 , both the first through-wiring  25 R and the third through-wiring  27 R are wirings that connect the first wiring  51  of the third conductive layer  50  and the first wiring  61  of the fourth conductive layer  60 . That is, the first wiring  51  and the first wiring  61  are electrically connected by the first through-wiring  25 R and the third through-wiring  27 R. 
     In the present embodiment, the arrangement position and shape of the first through-wiring  25 R are the same as those of the first through-wiring  25 S. The arrangement position and shape of the third through-wiring  27 R are the same as those of the third through-wiring  27 R. The arrangement position, shape, and number of both the first through-wiring  25 R and the third through-wiring  27 R may be arbitrarily changed as long as these through-wirings  25 R and  27 R overlap both the first wiring  51  and the first wiring  61  when viewed in the z direction. For example, at least one of the arrangement position, shape, and number of the first through-wiring  25 R may be different from that of the first through-wiring  25 S. At least one of the arrangement position, shape, and number of the third through-wiring  27 R may be different from that of the third through-wiring  27 S. 
     As shown in  FIGS. 3 to 7 , the second through-wiring  26  is a wiring that connects the second wiring  32  of the first conductive layer  30 , the second wiring  42  of the second conductive layer  40 , the second wiring  52  of the third conductive layer  50 , and the second wiring  62  of the fourth conductive layer  60 . When viewed in the z direction, the second through-wiring  26  is arranged at a position where it overlaps the extension wiring  32   a  of the second wiring  32 . That is, when viewed in the z direction, the second through-wiring  26  is arranged closer to the board side surface  21  than the switching element  80 . 
     As shown in  FIGS. 3 to 7 , the fourth through-wiring  28  is a wiring that connects the fourth wiring  34  of the first conductive layer  30 , the third wiring  43  of the second conductive layer  40 , the third wiring  53  of the third conductive layer  50 , and the third wiring  63  of the fourth conductive layer  60 . 
     As shown in  FIGS. 3 to 7 , the fifth through-wiring  29  is a wiring that connects the fifth wiring  35  of the first conductive layer  30 , the fourth wiring  44  of the second conductive layer  40 , the fourth wiring  54  of the third conductive layer  50 , and the fourth wiring  64  of the fourth conductive layer  60 . A plurality of fifth through-wirings  29  (ten fifth through-wirings  29  in the present embodiment) are provided. In the plurality of fifth through-wirings  29 , two rows of five fifth through-wirings  29  arranged apart from each other in the x direction so as to be aligned with each other in the y direction are provided to be apart from each other in the y direction. 
     Since the second wiring  32  of the first conductive layer  30  and the second wiring  62  of the fourth conductive layer  60  are connected via the second through-wiring  26 , the second wiring  62  constitutes a power supply terminal for connection to an external electrode. 
     Since the fourth wiring  34  of the first conductive layer  30  and the third wiring  63  of the fourth conductive layer  60  are connected via the fourth through-wiring  28  and the gate electrode  83  of the switching element  80  is connected to the four wirings  34  via the wire W, the third wiring  63  constitutes a control terminal to control the switching element  80 . 
     Since the fifth wiring  35  of the first conductive layer  30  and the fourth wiring  64  of the fourth conductive layer  60  are connected via the fifth through-wiring  29 , the fourth wiring  64  constitutes a ground terminal. Since the source electrode  82  of the switching element  80  is connected to the fifth wiring  35  by the wire W, it may be said that the fourth wiring  64  is a source terminal connected to the source electrode  82  of the switching element  80 . 
     A circuit configuration of the semiconductor light-emitting device  10  having such a configuration will be described with reference to  FIG. 8 .  FIG. 8  shows an example of a laser system LS including the semiconductor light-emitting device  10 . An example of such a laser system LS is LIDAR. 
     As shown in  FIG. 8 , the semiconductor light-emitting device  10  is connected to an external power supply VS which is a DC power supply. The positive terminal of the external power supply VS is electrically connected to the drain electrode  81  of the switching element  80  and the second electrode  72  of the capacitor  70 , and the negative terminal thereof is connected to the source electrode  82  of the switching element  80 . That is, the positive terminal of the external power supply VS is electrically connected to the second wiring  62  which is the power supply terminal. The negative terminal of the external power supply VS is electrically connected to the fourth wiring  64  which is the ground terminal. 
     The source electrode  82  is electrically connected to the anode electrode  91  of the light-emitting element  90 . The cathode electrode  92  of the light-emitting element  90  is electrically connected to the first electrode  71  of the capacitor  70 . 
     A gate driver circuit GD is electrically connected to the gate electrode  83  of the switching element  80 . The gate driver circuit GD is a circuit that controls an on/off operation of the switching element  80  by applying a gate voltage to the gate electrode  83  of the switching element  80 . 
     A protective diode DP is connected to the light-emitting element  90  in antiparallel. That is, the cathode electrode of the protective diode DP is connected to the anode electrode  91  of the light-emitting element  90 , and the anode electrode of the protective diode DP is connected to the cathode electrode  92  of the light-emitting element  90 . The protective diode DP is a protective element provided outside the semiconductor light-emitting device  10 . 
     In the semiconductor light-emitting device  10 , when the switching element  80  is turned off by the gate driver circuit GD, the capacitor  70  is charged by the external power supply VS. Then, when the switching element  80  is turned on by the gate driver circuit GD, the capacitor  70  is discharged to allow a current to flow through the switching element  80 . As a result, the light-emitting element  90  emits laser light. 
     (Operation) 
     The operation of the semiconductor light-emitting device  10  according to the present embodiment will be described. In  FIG. 9 , the first wiring  41  of the second conductive layer  40  is indicated by a broken line for the sake of convenience. Further, in order to make the first wiring  41  easier to see, the first wiring  41  is shown to be slightly larger than an actual width dimension of the first wiring  41  such that it does not overlap the first conductive layer  30 . Further, in  FIG. 9 , a solid-line arrow indicating a current flow direction indicates the first current path, and a broken line arrow indicates the second current path. 
     As shown in  FIG. 9 , when the switching element  80  is turned on, the first current path through which a current flows in the order of the first electrode  71  and the second electrode  72  of the capacitor  70 , the second wiring  32  of the first conductive layer  30 , the drain electrode  81  (see  FIG. 4 ) and the source electrode  82  of the switching element  80 , the wire W, the anode electrode  91  and the cathode electrode  92  (see  FIG. 4 ) of the light-emitting element  90 , and the third wiring  33  is formed. Then, a current flows in the order of the third through-wiring  27 S, the second wiring portion  41   b , the third wiring portion  41   c , and the first wiring portion  41   a  of the first wiring  41  of the second conductive layer  40 . That is, when a current flows along the first current path on the side of the substrate main surface  20 As of the first substrate  20 A, a current flows in the direction opposite to a direction in which the current flows through the first current path on the side of the substrate back surface  20 Ar of the first substrate  20 A. In other words, a current flows in the second current path. Therefore, a magnetic flux caused by the current flowing along the first current path and a magnetic flux caused by the current flowing along the second current path cancel each other out. As a result, an inductance in a loop of the current flowing through the capacitor  70 , the switching element  80 , and the light-emitting element  90  is reduced. 
     A graph of  FIG. 10  shows a transition of a current flowing when a light-emitting element emits light in Experimental Example 1 and a transition of a current flowing when a light-emitting element emits light in Experimental Example 2. A solid line graph corresponds to Experimental Example 1, and a broken line graph corresponds to Experimental Example 2. Experimental Example 1 is a configuration of the semiconductor light-emitting device  10  of the present embodiment, and Experimental Example 2 is a configuration of a semiconductor light-emitting device in which the loop of a current flowing through the capacitor  70 , the switching element  80 , and the light-emitting element  90  is formed on the board main surface  20   s  of the multilayer board  20 . 
     In Experimental Example 1, since the current flow in the first current path on the side of the board main surface  20   s  and the current flow in the second current path on the substrate back surface  20 Ar are opposite to each other, the loop of the current flowing through the capacitor  70 , the switching element  80 , and the light-emitting element  90  is a sum of the first current path, the second current path, the first through-wiring  25 S, and the third through-wiring  27 S. 
     In Experimental Example 2, since the current loop is formed on the board main surface  20   s , this loop is roughly equal to the sum of the first current path and a distance between the light-emitting element  90  and the first electrode  71  of the capacitor  70 . 
     In this way, the length of the loop in Experimental Example 1 is longer than the length of the loop in Experimental Example 2. However, as shown in  FIG. 10 , the time from when a current is supplied to the light-emitting element  90  until the magnitude of the current supplied to the light-emitting element  90  reaches a threshold value TX in Experimental Example 1 is shorter than the time from when a current is supplied to the light-emitting element  90  until the magnitude of the current supplied to the light-emitting element  90  reaches a threshold value TX in Experimental Example 2. That is, it may be seen that it is more effective in reducing an inductance in the semiconductor light-emitting device to reduce a magnetic flux generated in the loop than to reduce a length of the loop of the current flowing through the capacitor  70 , the switching element  80 , and the light-emitting element  90 . 
     From this result, when the semiconductor light-emitting device  10  is applied to LIDAR, an output waveform of LIDAR may rise faster, thereby making the output waveform closer to a square wave. Therefore, the accuracy of measurement of a distance to an object by LIDAR may be improved. 
     (Effects) 
     According to the semiconductor light-emitting device  10  of the present embodiment, the following effects may be obtained. 
     (1-1) The semiconductor light-emitting device  10  includes the multilayer board  20  having the board main surface  20   s , the board back surface  20   r  facing the side opposite to the board main surface  20   s , the first conductive layer  30  formed on the board main surface  20   s , and the second conductive layer  40  formed on the side of the board back surface  20   r  with respect to the first conductive layer  30 , and further includes the light-emitting element  90 , the switching element  80 , and the capacitor  70 , which are electrically connected to one another by the first conductive layer  30 . When viewed in the z direction, the capacitor  70  and the switching element  80  are arranged in the y direction, and the switching element  80  and the light-emitting element  90  are arranged in the x direction. The first wiring  41  is formed to overlap the first current path of the current flowing through the light-emitting element  90 , the switching element  80 , and the capacitor  70  on the board main surface  20   s  when viewed in the z direction and to form the second current path of the current flowing in the direction opposite to the direction in which the current flows through the first current path. 
     According to this configuration, the magnetic flux generated by the current flowing in the first current path and the magnetic flux generated by the current flowing in the second current path cancel each other out, such that the inductance caused by the loop of the current flowing through the capacitor  70 , the switching element  80 , and the light-emitting element  90  may be reduced. 
     (1-2) When viewed in the z direction, the first wiring portion  41   a  of the first wiring  41  of the second conductive layer  40  is formed to overlap the entire capacitor  70 , and the second wiring portion  41   b  thereof is formed to overlap both the entire switching element  80  and the entire light-emitting element  90 . 
     According to this configuration, in comparison with at least one of a configuration where a portion of the capacitor  70  is arranged to be deviated from the first wiring portion  41   a  when viewed in the z direction and a configuration where portions of both the switching element  80  and the light-emitting element  90  are arranged to be deviated from the second wiring portion  41   b  when viewed in the z direction, a region where the magnetic flux generated by the current flowing in the first current path and the magnetic flux generated by the current flowing in the second current path of the current flowing in the direction opposite to the direction in which the current flows through the first current path are opposed to each other in the z direction increases. Therefore, it is possible to enhance an effect of cancelling out the magnetic flux generated by the current flowing in the first current path and the magnetic flux generated by the current flowing in the second current path. Therefore, it is possible to further reduce an inductance caused by the loop of the current flowing through the capacitor  70 , the switching element  80 , and the light-emitting element  90 . 
     (1-3) When viewed in the z direction, the dimension of the second wiring portion  41   b  of the first wiring  41  of the second conductive layer  40  in they direction is equal to the dimension of the third wiring  33  of the first conductive layer  30  in the y direction, and the dimension of the first wiring portion  41   a  of the first wiring  41  in they direction is equal to the dimension of the capacitor  70  in the y direction. 
     According to this configuration, for example, in comparison with at least one of a configuration where the dimension of the second wiring portion  41   b  in they direction is different from the dimension of the third wiring  33  in they direction and a configuration where the dimension of the first wiring portion  41   a  in they direction is different from the dimension of the capacitor  70  in the y direction, a region where the magnetic flux generated by the current flowing through the first current path and the magnetic flux generated by the current flowing through the second current path of the current flowing in the direction opposite to the direction in which the current flows through the first current path do not overlap each other in the z direction decreases. Therefore, it is possible to reduce magnetic fluxes, among the magnetic fluxes generated by the current flowing in the first current path and the magnetic fluxes generated by the current flowing in the second current path, which do not cancel each other out. Therefore, it is possible to further reduce the inductance caused by the loop of the current flowing through the capacitor  70 , the switching element  80 , and the light-emitting element  90 . 
     (1-4) The multilayer board  20  has the first to third substrates  20 A to  20 C and the first to fourth conductive layers  30 ,  40 ,  50 , and  60 . The first substrate  20 A constituting the board main surface  20   s  of the multilayer board  20  has the substrate main surface  20 As constituting the board main surface  20   s , and the substrate back surface  20 Ar facing the side opposite to the substrate main surface  20 As. The first wiring  41  of the second conductive layer  40  constituting the wiring pattern is formed on the substrate back surface  20 Ar. 
     According to this configuration, in the z direction, the current flowing through the first current path and the current flowing in the second current path of the current flowing in the direction opposite to the direction in which the current flows through the first current path may be brought close to each other. As a result, it is possible to enhance the effect of cancelling out the magnetic flux generated by the current flowing through the first current path and the magnetic flux generated by the current flowing through the second current path. Therefore, it is possible to further reduce the inductance caused by the loop of the current flowing through the capacitor  70 , the switching element  80 , and the light-emitting element  90 . 
     (1-5) The semiconductor light-emitting device  10  includes the case  100  which includes the side wall  101  surrounding the capacitor  70 , the switching element  80 , and the light-emitting element  90 , and the light-transmitting plate  102  provided on the side wall  101  and arranged at a position where it overlaps the light-emitting element  90  when viewed in the z direction. The light-emitting element  90  emits light such that the light spreads away from the multilayer board  20  in the z direction. The light-emitting element  90  is mounted on the multilayer board  20  so that a light-emitting region between the light-transmitting plate  102  and the multilayer board  20  is formed at an inward side from the side wall  101  when viewed in the z direction. 
     According to this configuration, since the light emitted from the light-emitting element  90  toward the light-transmitting plate  102  does not interfere with the side wall  101 , all the light emitted from the light-emitting element  90  toward the light-transmitting plate  102  passes through the light-transmitting plate  102 . Therefore, it is possible to suppress the light-emitting region of the light-emitting element  90  from narrowing when viewed in the z direction. 
     (1-6) The switching element  80  and the light-emitting element  90  are arranged apart from each other in the y direction. The light-emitting element  90  is arranged closer to the center of the multilayer board  20  in the x direction than the switching element  80 . 
     According to this configuration, the light emitted from the light-emitting element  90  toward the light-transmitting plate  102  is surely not interfered by the side wall  101 . Therefore, it is possible to suppress the narrowing of the light-emitting region of the light-emitting element  90  when viewed in the z direction. 
     (1-7) The dimension of the capacitor  70  in the x direction is larger than the sum of the dimension of the switching element  80  in the x direction and the dimension of the light-emitting element  90  in the x direction. The switching element  80  and the light-emitting element  90  are arranged apart from each other in the y direction and are arranged apart from each other in the x direction with respect to the capacitor  70 . 
     According to this configuration, the multilayer board  20  may be miniaturized as compared with a configuration where the capacitor  70 , the switching element  80 , and the light-emitting element  90  are arranged, in a row, side by side in the y direction. 
     Second Embodiment 
     A semiconductor light-emitting device  10  according to a second embodiment of the present disclosure will be described with reference to  FIGS. 11 and 12 . The semiconductor light-emitting device  10  according to the second embodiment is different from the semiconductor light-emitting device  10  of the first embodiment in the arrangement positions of the switching element  80  and the light-emitting element  90  and the shapes of the plurality of conductive layers of the multilayer board  20 . In the following description, the same constituent elements as those of the semiconductor light-emitting device  10  of the first embodiment are denoted by the same reference numerals, and explanation thereof may be omitted. Further, the plurality of conductive layers of the multilayer board  20  will be described as a first conductive layer  30 A, a second conductive layer  40 A, a third conductive layer  50 , and a fourth conductive layer  60 . 
     As shown in  FIG. 11 , the capacitor  70 , the switching element  80 , and the light-emitting element  90  are arranged in the y direction. Here, also in the present embodiment, the y direction corresponds to the “first direction.” 
     The capacitor  70 , the switching element  80 , and the light-emitting element  90  are arranged at positions where they at least partially overlap each other when viewed in the y direction. That is, when the capacitor  70 , the switching element  80 , and the light-emitting element  90  are arranged at a position where they at least partially overlap each other when viewed in the y direction, it may be said that the capacitor  70 , the switching element  80 , and the light-emitting element  90  are arranged in the y direction. In the present embodiment, when viewed in they direction, a portion of the light-emitting element  90  and a portion of the switching element  80  protrude from the capacitor  70  in the x direction. When viewed in the y direction, the switching element  80  is arranged at a position where it entirely overlaps the light-emitting element  90 . 
     Further, when viewed in the y direction, the switching element  80  may be arranged to partially protrude from the light-emitting element  90 . That is, both the switching element  80  and the light-emitting element  90  may be arranged at positions where they at least partially overlap each other when viewed in the y direction. 
     The capacitor  70  is arranged in the same manner as in the first embodiment. That is, when viewed in the z direction, the capacitor  70  is arranged such that its longitudinal direction is along the x direction and its lateral direction is along the y direction. The first electrode  71  and the second electrode  72  of the capacitor  70  are arranged apart from each other in the x direction. In the present embodiment, the first electrode  71  of the capacitor  70  is arranged adjacent to the third side wall  101 C in the x direction, and the second electrode  72  thereof is arranged adjacent to the fourth side wall  101 D in the x direction. 
     The light-emitting element  90  is arranged closer to the capacitor  70  than the switching element  80  in the y direction. That is, the light-emitting element  90  is interposed between the capacitor  70  and the switching element  80  in the y direction. When viewed in the y direction, the light-emitting element  90  is arranged at a position where it overlaps the first electrode  71  of the capacitor  70 . 
     When viewed in the z direction, the light-emitting element  90  is arranged such that the x direction is a long side direction and the y direction is a short side direction. The anode electrodes  91  formed on the light-emitting element main surface  90   s  of the light-emitting element  90  are provided at an end, between both ends of the light-emitting element main surface  90   s , which is closer to the third side wall  101 C in the x direction. In the present embodiment, the anode electrode  91  is arranged closer to the third side wall  101 C than the first electrode  71  of the capacitor  70 . 
     The switching element  80  is arranged closer to the third side wall  101 C than the light-emitting element  90  in the x direction. More specifically, the switching element  80  is arranged so that its center in the x direction is closer to the third side wall  101 C than the center of the light-emitting element  90  in the x direction. In the present embodiment, an end, between both ends of the switching element  80 , which is closer to the third side wall  101 C in the x direction and an end, between both ends of the light-emitting element  90 , which is closer to the third side wall  101 C in the x direction are arranged at positions where they are aligned with each other. 
     As shown in  FIGS. 11 and 12 , the multilayer board  20  of the present embodiment is different from the multilayer board  20  of the first embodiment in the configurations of the first conductive layer and the second conductive layer. In the following description, the first conductive layer is referred to as the “first conductive layer  30 A,” and the second conductive layer is referred to as the “second conductive layer  40 A.” The third conductive layer  50  and the fourth conductive layer  60  have substantially the same configurations as those of the first embodiment, although the shape of each wiring is changed from the first embodiment, and therefore, explanation thereof will be omitted. 
     As shown in  FIG. 11 , the first conductive layer  30 A of the multilayer board  20  includes a first wiring  31 A, a second wiring  32 A, a third wiring  33 A, a fourth wiring  34 A, and a fifth wiring  35 A. Here, in the present embodiment, the first conductive layer  30 A corresponds to a “first wiring pattern.” Further, the first wiring  31 A corresponds to a “first front surface side wiring,” the second wiring  32 A corresponds to a “second front surface side wiring,” and the third wiring  33 A corresponds to a “third front surface side wiring.” 
     The first wiring  31 A is a wiring on which the second electrode  72  of the capacitor  70  is mounted. The second electrode  72  is bonded to the first wiring  31 A by a conductive bonding material. As a result, the second electrode  72  is electrically connected to the first wiring  31 A. When viewed in the z direction, the arrangement position and shape of the first wiring  31 A are the same as those of the first wiring  31  of the first embodiment. That is, the first wiring  31 A has an extension wiring  31 Aa. 
     The second wiring  32 A is a wiring on which both the first electrode  71  of the capacitor  70  and the light-emitting element  90  are mounted. The first electrode  71  of the capacitor  70  and the light-emitting element back surface  90   r  (not shown in  FIG. 11 ) of the light-emitting element  90  are bonded to the second wiring  32 A by a conductive bonding material. As a result, both the first electrode  71  of the capacitor  70  and the cathode electrode  92  (not shown in  FIG. 11 ) of the light-emitting element  90  are electrically connected to the second wiring  32 A. 
     The shape of the second wiring  32 A viewed from the z direction is substantially L-shaped. The first electrode  71  of the capacitor  70  is mounted on an end, between both ends of the second wiring  32 A, which is closer to the second side wall  101 B in the y direction, and the light-emitting element  90  is mounted on an end, between both ends of the second wiring  32 A, which is closer to the first side wall  101 A in the y direction. A dimension, in the x direction, of the end, between both ends of the second wiring  32 A, which is closer to the first side wall  101 A in the y direction is larger than a dimension in the x direction of the end, between both ends of the second wiring  32 A, which is closer to the second side wall  101 B in they direction. That is, the dimension, in the x direction, of the end, between both ends of the second wiring  32 A, which is closer to the first side wall  101 A in they direction is larger than the dimension, in the x direction, of another portion of the second wiring  32 A on which the light-emitting element  90  is mounted. In the present embodiment, the multilayer board  20  does not have the second through-wiring  26 . 
     The third wiring  33 A is a wiring on which the switching element  80  is mounted. The switching element back surface  80   r  of the switching element  80  is bonded to the third wiring  33 A by a conductive bonding material. As a result, the drain electrode  81  of the switching element  80  is electrically connected to the third wiring  33 A. 
     The third wiring  33 A is arranged closer to the first side wall  101 A than the second wiring  32 A. The third wiring  33 A is interposed between the second wiring  32 A and the fourth wiring  34 A in the y direction. 
     The shape of the third wiring  33 A viewed from the z direction is substantially a rectangular shape in which the x direction is a long side direction and the y direction is a short side direction. It may be said that the third wiring  33 A extends in the x direction. The switching element  80  is arranged at the end, between both ends of the third wiring  33 A, which is closer to the third side wall  101 C in the x direction. In other words, the third wiring  33 A includes an extension wiring  33 Aa extending along the x direction from the switching element  80  toward the fourth side wall  101 D when viewed in the z direction. When viewed in the y direction, the extension wiring  33 Aa is formed to be aligned with the light-emitting element  90  in the x direction. The third through-wiring  27  is arranged at a position where it overlaps the extension wiring  33 Aa when viewed in the z direction. 
     The fourth wiring  34 A is a wiring electrically connected to the gate electrode  83  of the switching element  80 . The gate electrode  83  of the switching element  80  is connected to the fourth wiring  34 A by a wire W. As a result, the gate electrode  83  is electrically connected to the fourth wiring  34 A. When viewed in the z direction, the arrangement position and shape of the fourth wiring  34 A are the same as those of the fourth wiring  34  of the first embodiment. Similar to the first embodiment, the fourth through-wiring  28  is arranged at a position where it overlaps the fourth wiring  34 A when viewed in the z direction. 
     The fifth wiring  35 A is a wiring connected to the ground. The source electrode  82  of the switching element  80  is connected to the fifth wiring  35 A by a wire W. As a result, the source electrode  82  is electrically connected to the fifth wiring  35 A. 
     The fifth wiring  35 A is formed near the board side surface  21  and the board side surface  24  of the board main surface  20   s . The fifth wiring  35 A is arranged at a position adjacent to both the first side wall  101 A and the fourth side wall  101 D. When viewed in they direction, the fifth wiring  35 A is arranged at a position where it overlaps the first wiring  31 A, the second wiring  32 A, and the third wiring  33 A. When viewed in the x direction, the fifth wiring  35 A is arranged at a position where it overlaps both the third wiring  33 A and the fourth wiring  34 A. 
     The shape of the fifth wiring  35 A viewed from the z direction is substantially a rectangular shape having a recessed portion  35 Aa, in which the x direction is a long side direction and the y direction is a short side direction. The recessed portion  35 Aa is formed at an end, which is closer to the third side wall  101 C, of both ends of the fifth wiring  35 A in the x direction. The third wiring  33 A enters the recessed portion  35 Aa. A dimension of the fifth wiring  35 A in the x direction is larger than the dimension of the third wiring  33 A in the x direction. A width dimension of the fifth wiring  35 A (a dimension of the fifth wiring  35 A in they direction) is larger than the width dimension of the third wiring  33 A (the dimension of the third wiring  33 A in they direction). Similar to the first embodiment, the plurality of fifth through-wirings  29  are arranged at positions where they overlap the fifth wiring  35 A when viewed in the z direction. 
     In the board main surface  20   s  of the multilayer board  20 , a first current path in which a current flows through the light-emitting element  90 , the switching element  80 , and the capacitor  70  is formed by the first conductive layer  30 A, the light-emitting element  90 , the switching element  80 , and the capacitor  70 . The first current path is a path through which a current flows in the order of, for example, the first electrode  71  of the capacitor  70 , the second wiring  32 A, the drain electrode  81  and the source electrode  82  of the switching element  80 , the wire W, the anode electrode  91  and the cathode electrode  92  of the light-emitting element  90 , and the third wiring  33 A. 
     As shown in  FIG. 12 , the second conductive layer  40 A is an inner layer pattern formed in the multilayer board  20 . Here, in the present embodiment, the second conductive layer  40 A corresponds to a “second wiring pattern.” That is, the light-emitting element  90 , the switching element  80 , and the capacitor  70  are electrically connected to one another by both the conductive layers  30 A and  40 A. 
     The second conductive layer  40 A is formed on the substrate back surface  20 Ar of the first substrate  20 A. When viewed in the z direction, the second conductive layer  40 A is formed to overlap the first current path and form a second current path of a current flowing in a direction opposite to a direction in which the current flows through the first current path. 
     The second conductive layer  40 A includes a first wiring  41 A, a second wiring  42 A, and a third wiring  43 A. The first to third wirings  41 A to  43 A are arranged apart from one another. The first wiring  41 A corresponds to a “back surface side wiring.” 
     When viewed in the z direction, the first wiring  41 A is a wiring provided at a position where it overlaps the first current path, and is electrically connected to both the first wiring  31 A and the third wiring  33 A of the first conductive layer  30 A. The first wiring  41 A is a wiring that forms the second current path. The first wiring  41 A is connected to the first wiring  31 A by a first through-wiring  25 S, and is connected to the third wiring  33 A by a third through-wiring  27 . Here, the third through-wiring  27  is a wiring that penetrates the multilayer board  20  in the z direction. That is, the third through-wiring  27  is connected to the third wiring  33  of the first conductive layer  30 A, the first wiring  41 A of the second conductive layer  40 A, the second wiring  52  of the third conductive layer  50 , and the second wiring  62  of the fourth conductive layer  60 . 
     As shown in  FIGS. 11 and 12 , the first wiring  41 A is provided at a position where it overlaps the first wiring  31 A, the second wiring  32 A, and the third wiring  33 A of the first conductive layer  30 A when viewed in the z direction. The first wiring  31 A, the second wiring  32 A, and the third wiring  33 A are wirings that form the first current path in the first conductive layer  30 A. 
     The first wiring  41 A includes a first wiring portion  41 Aa that overlaps both the first electrode  71  and the second electrode  72  of the capacitor  70  when viewed in the z direction, and a second wiring portion  41 Ab that overlaps both the light-emitting element  90  and the switching element  80  when viewed in the z direction. 
     The first wiring portion  41 Aa extends in the x direction. A width dimension of the first wiring portion  41 Aa (a dimension of the first wiring portion  41 Aa in the y direction) is equal to the width dimension of the first wiring  31 A of the first conductive layer  30 A (the dimension of the first wiring  31 A in they direction). Further, the width dimension of the first wiring portion  41 Aa is equal to the dimension of the capacitor  70  in they direction. Similar to the first embodiment, in consideration of a deviation of a mounting position of the capacitor  70 , even when the width dimension of the first wiring portion  41 Aa is slightly larger than the dimension of the capacitor  70  in the y direction, it may be said that the width dimension of the first wiring portion  41 Aa (the dimension of the first wiring portion  41 Aa in they direction) is equal to the dimension of the capacitor  70  in they direction. 
     When viewed in the z direction, both ends of the first wiring portion  41 Aa in the x direction protrude from the capacitor  70 . That is, the length of the first wiring portion  41 Aa in the x direction is longer than the length of the capacitor  70  in the x direction. The first wiring portion  41 Aa extends to a position where it overlaps the first wiring  31 A when viewed in the z direction. A portion of the first wiring portion  41 Aa that overlaps the first wiring  31 A when viewed in the z direction is connected to the first wiring  31 A via the first through-wiring  25 S. 
     The second wiring portion  41 Ab extends in they direction from one among both ends of the first wiring portion  41 Aa that is closer to the board side surface  23  in the x direction. The second wiring portion  41 Ab extends from the first wiring portion  41 Aa toward the board side surface  21 . The third through-wiring  27  is connected to the second wiring portion  41 Ab. That is, the second wiring portion  41 Ab is connected to the third wiring  33 A of the first conductive layer  30 A via the third through-wiring  27 . In the present embodiment, the third through-wiring  27  is a wiring that penetrates the multilayer board  20  in the z direction. The third through-wiring  27  is formed of, for example, a via formed by burying a conductor in a through-hole penetrating the multilayer board  20  in the z direction. The third through-wiring  27  may be formed by a through-hole. 
     The third through-wiring  27  is connected to the third wiring  33  of the first conductive layer  30 , the first wiring  41  of the second conductive layer  40 , the second wiring  52  of the third conductive layer  50 , and the second wiring  62  of the fourth conductive layer  60 . As a result, the third wiring  33 , the first wiring  41 , the second wiring  52 , and the second wiring  62  are electrically connected to each other. 
     Since the third through-wiring  27  is provided at a position where it does not overlap the switching element  80  when viewed in the z direction, the dimension, in the x direction, of an end, between both ends of the second wiring portion  41 Ab, which is closer to the board side surface  21  in the y direction is larger than the dimension, in the x direction, of another portion of the second wiring portion  41 Ab. The dimension, in the x direction, of another portion of the second wiring portion  41 Ab is substantially equal to the dimension of the switching element  80  in the x direction. 
     When viewed in the z direction, the second wiring  42 A is arranged at a position where it overlaps the fourth wiring  34 A of the first conductive layer  30 A. The shape and size of the second wiring  42 A viewed from the z direction are the same as the shape and size of the fourth wiring  34 A viewed from the z direction. The second wiring  42 A is connected to the fourth wiring  34 A by the fourth through-wiring  28 . 
     Since the fourth through-wiring  28  penetrates the multilayer board  20  in the z direction, the fourth through-wiring  28  is a wiring that connects the fourth wiring  34 A of the first conductive layer  30 A, the second wiring  42 A of the second conductive layer  40 A, the third wiring  53  of the third conductive layer  50 , and the third wiring  63  of the fourth conductive layer  60 . As a result, the fourth wiring  34 A, the second wiring  42 A, the third wiring  53 , and the third wiring  63  are electrically connected to one another. 
     When viewed in the z direction, the third wiring  43 A is arranged at a position where it overlaps the fifth wiring  35 A of the first conductive layer  30 A. The shape and size of the third wiring  43 A viewed from the z direction are the same as the shape and size of the fifth wiring  35 A viewed from the z direction. 
     Since the fifth through-wiring  29  penetrates the multilayer board  20  in the z direction, the fifth through-wiring  29  is a wiring that connects the fifth wiring  35 A of the first conductive layer  30 A, the third wiring  43 A of the second conductive layer  40 A, the fourth wiring  54  of the third conductive layer  50 , and the fourth wiring  64  of the fourth conductive layer  60 . As a result, the fifth wiring  35 A, the third wiring  43 A, the fourth wiring  54 , and the fourth wiring  64  are electrically connected to each other. 
     According to the semiconductor light-emitting device  10  having the aforementioned configuration, when the switching element  80  is turned on, the first current path through which a current flows in the order of the first electrode  71  of the capacitor  70 , the second wiring  32 A of the first conductive layer  30 A, the drain electrode  81  (not shown) and the source electrode  82  of the switching element  80 , the wire W, the anode electrode  91  and the cathode electrode  92  (not shown) of the light-emitting element  90 , and the third wiring  33 A is formed. Then, the current flowing through the first current path flows in the order of the third through-wiring  27 , the second wiring portion  41 Ab of the first wiring  41 A of the second conductive layer  40 A, and the first wiring portion  41 Aa thereof. That is, when the current flows in the first current path, a current flows in the second current path which is the same path but through which the current flows in the opposite direction. Therefore, a magnetic flux caused by the current flowing through the first current path and a magnetic flux caused by the current flowing through the second current path cancel each other out. As a result, an inductance in a loop of the current flowing through the capacitor  70 , the switching element  80 , and the light-emitting element  90  is reduced. 
     (Effects) 
     According to the semiconductor light-emitting device  10  of the present embodiment, the following effects may be obtained in addition to the effects of (1-2) to (1-5) of the first embodiment. 
     (2-1) The semiconductor light-emitting device  10  includes the multilayer board  20  having the board main surface  20   s , the board back surface  20   r  facing the side opposite to the board main surface  20   s , the first conductive layer  30 A formed on the board main surface  20   s , and the second conductive layer  40 A formed on the side of the board back surface  20   r  with respect to the first conductive layer  30 A, and further includes the light-emitting element  90 , the switching element  80 , and the capacitor  70 , which are electrically connected to one another by the first conductive layer  30 A. When viewed in the z direction, the capacitor  70  has a shape having a longitudinal direction and a lateral direction. The capacitor  70 , the switching element  80 , and the light-emitting element  90  are arranged in the y direction, which is the first direction orthogonal to the longitudinal direction when viewed in the z direction. The second conductive layer  40 A is formed to overlap the first current path of the current flowing through the light-emitting element  90 , the switching element  80 , and the capacitor  70  on the board main surface  20   s  when viewed in the z direction and to configure the second current path of the current flowing in the direction opposite to the direction in which the current flows through the first current path. 
     According to this configuration, the magnetic flux generated by the current flowing through the first current path and the magnetic flux generated by the current flowing through the second current path cancel each other out, so that the inductance caused by the loop of the current flowing through the capacitor  70 , the switching element  80 , and the light-emitting element  90  may be reduced. 
     (2-2) The light-emitting element  90  is arranged so that the x direction is the long side direction and the y direction is the short side direction. According to this configuration, the size of a parts arrangement region from the capacitor  70  to the switching element  80  in the y direction may be reduced. On the other hand, since the dimension of the light-emitting element  90  in the x direction is smaller than the dimension of the capacitor  70  in the x direction, a dead space is formed in the x direction. By reducing the size of the dead space in the y direction, it is possible to suppress an increase in the size of the multilayer board  20 . 
     Third Embodiment 
     A semiconductor light-emitting device  10  according to a third embodiment of the present disclosure will be described with reference to  FIGS. 13 and 14 . The semiconductor light-emitting device  10  according to the present embodiment is different from the semiconductor light-emitting device  10  of the first embodiment in that a protective diode  110  is added. In the following description, the same constituent elements as those of the semiconductor light-emitting device  10  of the first embodiment are denoted by the same reference numerals, and explanation thereof may be omitted. 
     The protective diode  110  is an element corresponding to the protective diode DP (see  FIG. 8 ) of the first embodiment and is built in the semiconductor light-emitting device  10 . More specifically, as shown in  FIG. 13 , the protective diode  110  is mounted on the board main surface  20   s  of the multilayer board  20 . The protective diode  110  is, for example, a fast recovery diode and is configured as a chip component. The protective diode  110  is formed in a rectangular flat plate shape. The protective diode  110  has a diode main surface  110   s  and a diode back surface (not shown) facing opposite sides in the z direction. The protective diode  110  is mounted on the board main surface  20   s  so that the diode main surface  110   s  faces the same side as the board main surface  20   s  of the multilayer board  20 . 
     The protective diode  110  includes an anode electrode  111  and a cathode electrode  112  (see  FIG. 14 ). The anode electrode  111  is formed on the diode main surface  110   s , and the cathode electrode  112  is formed on the diode back surface. 
     When viewed in the z direction, the protective diode  110  is mounted on the fifth wiring  35 . The diode back surface of the protective diode  110  is bonded to the fifth wiring  35  by a conductive bonding material. As a result, the cathode electrode  112  of the protective diode  110  is electrically connected to the fifth wiring  35 . 
     The anode electrode  111  is connected to the third wiring  33  by a wire W. As a result, the anode electrode  111  is electrically connected to the third wiring  33 . The protective diode  110  is arranged closer to the fourth side wall  101 D than the light-emitting element  90  in the x direction and is arranged closer to the first side wall  101 A than the light-emitting element  90  in they direction. When viewed in they direction, the protective diode  110  is arranged at a position where it partially overlaps the first electrode  71  of the capacitor  70 . In the present embodiment, a portion of the protective diode  110  in the x direction protrudes toward the fourth side wall  101 D with respect to the first electrode  71  of the capacitor  70 . 
     As shown in  FIG. 14 , the protective diode  110  is connected in antiparallel to the light-emitting element  90 . The cathode electrode  112  of the protective diode  110  is electrically connected to the source electrode  82  of the switching element  80 . The anode electrode  111  of the protective diode  110  is electrically connected to the first electrode  71  of the capacitor  70 . 
     (Effects) 
     According to the semiconductor light-emitting device  10  of the present embodiment, the following effects may be obtained in addition to the effects of the first embodiment. 
     (3-1) The semiconductor light-emitting device  10  includes the protective diode  110 . The protective diode  110  is connected in antiparallel to the light-emitting element  90 . According to this configuration, it is possible to suppress an excessive reverse voltage being applied to the light-emitting element  90 . 
     Fourth Embodiment 
     A semiconductor light-emitting device  10  according to the fourth embodiment of the present disclosure will be described with reference to  FIGS. 15 and 16 . The semiconductor light-emitting device  10  according to the present embodiment is different from the semiconductor light-emitting device  10  of the second embodiment in the arrangement positions of the switching element  80  and the light-emitting element  90  and the shapes of the plurality of conductive layers of the multilayer board  20 . In the following description, the same constituent elements as those of the semiconductor light-emitting device  10  of the second embodiment are denoted by the same reference numerals, and explanation thereof may be omitted. 
     As shown in  FIG. 15 , the switching element  80  and the light-emitting element  90  are arranged closer to the second electrode  72  than the first electrode  71  of the capacitor  70  in the x direction. In the present embodiment, both the switching element  80  and the light-emitting element  90  are interposed between the first electrode  71  and the second electrode  72  of the capacitor  70  in the x direction. In the present embodiment, when viewed in the y direction, the switching element  80  is arranged so that the entire switching element  80  overlaps the light-emitting element  90 . 
     Similar to the second embodiment, the light-emitting element  90  is arranged closer to the capacitor  70  than the switching element  80  in the y direction. In other words, the light-emitting element  90  is interposed between the capacitor  70  and the switching element  80  in the y direction. 
     As shown in  FIGS. 15 and 16 , the multilayer board  20  is different from the multilayer board  20  of the first embodiment in the configurations of the first conductive layer and the second conductive layer. In the following description, the first conductive layer is referred to as a “first conductive layer  30 B,” and the second conductive layer is referred to as a “second conductive layer  40 B.” Since the third conductive layer  50  and the fourth conductive layer  60  are the same as those in the first embodiment, explanation thereof will be omitted. 
     As shown in  FIG. 15 , the first conductive layer  30 B includes a first wiring  31 B, a second wiring  32 B, a third wiring  33 B, a fourth wiring  34 B, and a fifth wiring  35 B. The first wiring  31 B and the fourth wiring  34 B are the same as the first wiring  31 A and the fourth wiring  34 A of the second embodiment. Here, in the present embodiment, the first conductive layer  30 B corresponds to a “first wiring pattern.” Further, the first wiring  31 B corresponds to a “first front surface side wiring,” the second wiring  32 B corresponds to a “second front surface side wiring,” and the third wiring  33 B corresponds to a “third front surface side wiring.” 
     In the present embodiment, as compared with the second embodiment, as both the switching element  80  and the light-emitting element  90  move toward the fourth side wall  101 D in the x direction, shapes of the second wiring  32 B and the fourth wiring  34 B of the first conductive layer  30  differ from those of the second wiring  32 A and the fourth wiring  34 A of the second embodiment. Further, as the shape of the fourth wiring  34 B is changed, a shape of the fifth wiring  35 B is different from the shape of the fifth wiring  35 A of the second embodiment. 
     More specifically, a dimension, in the x direction, of an end, between both ends of the second wiring  32 B, which is closer to the third wiring  33 B in the y direction is larger than a dimension, in the x direction, of an end, between both ends of the second wiring  32 A, which is closer to the third wiring  33 A in the second embodiment in the y direction. 
     The dimension of the third wiring  33 B in the x direction is larger than the dimension of the third wiring  33 A of the second embodiment in the x direction. The fifth wiring  35 B has a recessed portion  35 Ba. The dimension of the recessed portion  35 Ba in the x direction is larger than the dimension of the recessed portion  35 Aa of the fifth wiring  35 A of the second embodiment in the x direction. Similar to the second embodiment, the third wiring  33 B enters the recessed portion  35 Ba. Further, when viewed in the z direction, the switching element  80  is arranged in the recessed portion  35 Ba. 
     As shown in  FIG. 16 , the second conductive layer  40 B includes a first wiring  41 B, a second wiring  42 B, and a third wiring  43 B. The second wiring  42 B is the same as the second wiring  42 A of the second embodiment. Here, the second conductive layer  40 B corresponds to a “second wiring pattern,” and the first wiring  41 B corresponds to a “back surface side wiring.” That is, the light-emitting element  90 , the switching element  80 , and the capacitor  70  are electrically connected to one another by both the conductive layers  30 B and  40 B. 
     The first wiring  41 B is formed to overlap the capacitor  70 , the switching element  80 , and the light-emitting element  90  when viewed in the z direction. That is, the first wiring  41 B is provided at a position where it overlaps the first current path when viewed in the z direction. 
     The first wiring  41 B includes a first wiring portion  41 Ba, a second wiring portion  41 Bb, and a third wiring portion  41 Bc. As shown in  FIGS. 15 and 16 , the first wiring portion  41 Ba is formed so as to overlap the first wiring  31 B of the first conductive layer  30 B, the capacitor  70 , and a portion of the second wiring  32 B on which the first electrode  71  of the capacitor  70  is mounted, when viewed in the z direction. 
     The first wiring portion  41 Ba extends in the x direction. A width dimension of the first wiring portion  41 Ba (a dimension of the first wiring portion  41 Ba in the y direction) is equal to the width dimension of the first wiring  31 B (the dimension of the first wiring  31 B in the y direction) of the first conductive layer  30 B. Further, the width dimension of the first wiring portion  41 Ba is equal to the dimension of the capacitor  70  in the y direction. Similar to the first embodiment, in consideration of a deviation of a mounting position of the capacitor  70 , even when the width dimension of the first wiring portion  41 Ba is slightly larger than the dimension of the capacitor  70  in the y direction, it may be said that the width dimension of the first wiring portion  41 Ba (the dimension of the first wiring portion  41 Ba in they direction) is equal to the dimension of the capacitor  70  in the y direction. 
     When viewed in the z direction, both ends of the first wiring portion  41 Ba in the x direction protrude from the capacitor  70 . That is, the length of the first wiring portion  41 Ba in the x direction is longer than the length of the capacitor  70  in the x direction. The first wiring portion  41 Ba extends to a position where it overlaps the first wiring  31 B when viewed in the z direction. A portion of the first wiring portion  41 Ba that overlaps the first wiring  31 B when viewed in the z direction is connected to the first wiring  31 A via the first through-wiring  25 S. 
     The second wiring portion  41 Bb is formed so as to overlap the second wiring  32 B of the first conductive layer  30 B and the light-emitting element  90  when viewed in the z direction. When viewed in the z direction, the second wiring portion  41 Bb is formed so as to overlap both the light-emitting element  90  and a portion of the second wiring  32 B on which the light-emitting element  90  is mounted. In the present embodiment, a leading end of the second wiring portion  41 Bb is located closer to the third side wall  101 C than an end, between both ends of the light-emitting element  90 , which is closer to the fourth side wall  101 D in the x direction. That is, when viewed in the z direction, a portion of the light-emitting element  90  protrudes from the second wiring portion  41 Bb in the x direction. 
     The third wiring portion  41 Bc is formed so as to overlap the switching element  80  and a portion of the third wiring  33 A on which the switching element  80  is mounted, when viewed in the z direction. When viewed in the z direction, the third wiring portion  41 Bc is formed to overlap both the switching element  80  and the third wiring  33 B. In the present embodiment, a portion of the third wiring  33 B closer to the third side wall  101 C than a portion where the third through-wiring  27  is formed protrudes from the third wiring portion  41 Bc when viewed in the z direction. 
     As shown in  FIGS. 15 and 16 , the second wiring  42 B is arranged at a position where it overlaps the fourth wiring  34 B of the first conductive layer  30 B. The shape of the second wiring  42 B viewed from the z direction is the same as the shape of the fourth wiring  34 B viewed from the z direction. The second wiring  42 B is connected to the third wiring  43 B by the fourth through-wiring  28 . 
     The third wiring  43 B is arranged at a position where it overlaps the fifth wiring  35 B of the first conductive layer  30 B in the z direction. The shape of the third wiring  43 B viewed from the z direction is the same as the shape of the fifth wiring  35 B viewed from the z direction. The third wiring  43 B is connected to the fifth wiring  35 B by the fifth through-wiring  29 . 
     (Effects) 
     According to the semiconductor light-emitting device  10  according to the present embodiment, the following effects may be obtained in addition to the effects of the second embodiment. 
     (4-1) The light-emitting element  90  is arranged near the center of the multilayer board  20  in the x direction and the y direction. According to this configuration, as compared with a case where the light-emitting element  90  is arranged at a position adjacent to the side wall  101 , light emitted from the light-emitting element  90  toward the light-transmitting plate  102  does not interfere with the side wall  101 . Therefore, it is possible to suppress the light-emitting region of the light-emitting element  90  from narrowing when viewed in the z direction. 
     Fifth Embodiment 
     A semiconductor light-emitting device  10  according to a fifth embodiment will be described with reference to  FIGS. 17 to 20 . The semiconductor light-emitting device  10  according to the present embodiment is different from the semiconductor light-emitting device  10  of the fourth embodiment in the shapes of the plurality of conductive layers of the multilayer board  20 . In the following description, the same constituent elements as those of the semiconductor light-emitting device  10  of the first embodiment are denoted by the same reference numerals, and explanation thereof may be omitted. Further, the plurality of conductive layers of the multilayer board  20  are referred to as a “first conductive layer  30 C,” a “second conductive layer  40 C,” a “third conductive layer  50 C,” and a “fourth conductive layer  60 C.” 
     As shown in  FIG. 17 , the first conductive layer  30 C is a conductive layer corresponding to the first conductive layer  30  of the first embodiment and includes a first wiring  31 C, a second wiring  32 C, a third wiring  33 C, a fourth wiring  34 C, and a fifth wiring  35 C. That is, in the present embodiment, the first conductive layer  30 C corresponds to a “first wiring pattern.” Further, the first wiring  31 C corresponds to a “first front surface side wiring,” the second wiring  32 C corresponds to a “second front surface side wiring,” and the third wiring  33 C corresponds to a “third front surface side wiring.” 
     An arrangement position and a shape of the first wiring  31 C are the same as those of the first wiring  31  of the first conductive layer  30 . An arrangement position and a shape of the third wiring  33 C are the same as those of the third wiring  33  of the first conductive layer  30 . Further, an arrangement form of the capacitor  70  with respect to the first wiring  31 C and the second wiring  32 C, an arrangement form of the switching element  80  with respect to the second wiring  32 C, and an arrangement form of the light-emitting element  90  with respect to the third wiring  33 C are similar to those in the first embodiment respectively. 
     An arrangement position of the second wiring  32 C is the same as the arrangement position of the second wiring  32  of the first conductive layer  30 . A dimension of the second wiring  32 C in they direction is larger than the dimension of the second wiring  32  of the first conductive layer  30  in the y direction. The second wiring  32 C is formed such that both ends thereof in they direction are adjacent to the first side wall  101 A and the second side wall  101 B. 
     The fourth wiring  34 C is arranged apart from the third side wall  101 C in the x direction. The fourth wiring  34 C is interposed between the second wiring  32 C and the fifth wiring  35 C in the x direction. The fourth wiring  34 C is arranged at a position adjacent to the first side wall  101 A in they direction. When viewed in they direction, the fourth wiring  34 C is arranged at a position where it overlaps the third wiring  33 C. 
     Similar to the first embodiment, the fourth wiring  34 C is connected to the gate electrode  83  of the switching element  80  via a wire W. That is, the fourth wiring  34 C is electrically connected to the gate electrode  83  of the switching element  80 . 
     An arrangement position of the fifth wiring  35 C is the same as the arrangement position of the fifth wiring  35  of the first conductive layer  30 . On the other hand, the fifth wiring  35 C has a recessed portion  35 Ca. The recessed portion  35 Ca is formed at an end, between both ends of the fifth wiring  35 C, which is closer to the second wiring  32 C in the x direction. The fourth wiring  34 C is arranged in the recessed portion  35 Ca. The end, between both ends of the fifth wiring  35 C, which is closer to the second wiring  32 C in the x direction is located between the third wiring  33 C and the fourth wiring  34 C. 
     Similar to the first embodiment, the fifth wiring  35 C is connected to the source electrode  82  of the switching element  80  via a wire W. The wire W connected to the source electrode  82  is connected to the end, between both ends of the fifth wiring  35 C, which is closer to the second wiring  32 C in the x direction. That is, the fifth wiring  35 C is electrically connected to the source electrode  82  of the switching element  80 . 
     As shown in  FIG. 18 , the second conductive layer  40 C is a conductive layer corresponding to the second conductive layer  40  of the first embodiment and includes a first wiring  41 C, a second wiring  42 C, a third wiring  43 C, and a fourth wiring  44 C. That is, the second conductive layer  40 C corresponds to a “second wiring pattern,” and the first wiring  41 C corresponds to a “back surface side wiring.” That is, the light-emitting element  90 , the switching element  80 , and the capacitor  70  are electrically connected to one another by both the conductive layers  30 C and  40 C. 
     Similar to the first wiring  41  of the second conductive layer  40  of the first embodiment, the first wiring  41 C includes a first wiring portion  41 Ca, a second wiring portion  41 Cb, and a third wiring portion  41 Cc. Arrangement positions and shapes of the first wiring portion  41 Ca and the third wiring portion  41 Cc are the same as those of the first wiring portion  41   a  and the third wiring portion  41   c  of the first wiring  41  of the first embodiment. The arrangement position of the second wiring portion  41 Cb is the same as the arrangement position of the second wiring portion  41   b  of the first wiring  41  of the first embodiment, whereas a shape of the second wiring portion  41 Cb is different from the shape of the second wiring portion  41   b  of the first embodiment. Specifically, a dimension of the second wiring portion  41 Cb in the x direction is smaller than the dimension of the second wiring portion  41   b  of the first embodiment in the x direction. That is, a leading end of the second wiring portion  41 Cb is formed at a position apart from the fourth side wall  101 D. 
     The second wiring  42 C is arranged near the board side surface  21  and the board side surface  23  of the substrate back surface  20 Ar of the first substrate  20 A. The second wiring  42 C is arranged apart from the second wiring portion  41 Cb of the first wiring  41 C in the y direction. As shown in  FIGS. 17 and 18 , the second wiring  42 C is arranged at a position where it overlaps an end, between both ends of the second wiring  32 C of the first conductive layer  30 C, which is closer to the first side wall  101 A in they direction when viewed in the z direction. 
     The third wiring  43 C is interposed between the second wiring  42 C and the fourth wiring  44 C in the x direction. The third wiring  43 C and the second wiring  42 C are arranged apart from each other in the x direction to be aligned with each other in the y direction. As shown in  FIGS. 17 and 18 , the third wiring  43 C is arranged at a position where it overlaps the fourth wiring  34 C of the first conductive layer  30 C when viewed in the z direction. 
     The fourth wiring  44 C is arranged near the board side surface  21  and the board side surface  24  of the substrate back surface  20 Ar of the first substrate  20 A. The fourth wiring  44 C is interposed between the third wiring  43 C and the board side surface  24  in the x direction. That is, the fourth wiring  44 C does not have a portion that overlaps the third wiring  43 C when viewed in they direction. As shown in  FIGS. 17 and 18 , the fourth wiring  44 C is arranged at a position where it overlaps the fifth wiring  35 C of the first conductive layer  30 C when viewed in the z direction. 
     As shown in  FIG. 19 , the third conductive layer  50 C is a conductive layer corresponding to the third conductive layer  50  of the first embodiment and includes a first wiring  51 C, a second wiring  52 C, and a third wiring  53 C. The first wiring  51 C is arranged near the board side surface  21  and the board side surface  23  of the substrate main surface  20 Cs of the third substrate  20 C. As shown in  FIGS. 18 and 19 , the first wiring MC is arranged at a position where it overlaps the second wiring  42 C of the second conductive layer  40 C when viewed in the z direction. 
     The second wiring  52 C is interposed between the first wiring MC and the third wiring  53 C in the x direction. The second wiring  52 C and the first wiring MC are arranged apart from each other in the x direction to be aligned with each other in the y direction. As shown in  FIGS. 18 and 19 , the second wiring  52 C is arranged at a position where it overlaps the third wiring  43 C of the second conductive layer  40 C when viewed in the z direction. 
     The third wiring  53 C is formed over most of the substrate main surface  20 Cs of the third substrate  20 C. As shown in  FIGS. 17 and 19 , the third wiring  53 C is formed to cover the capacitor  70 , the switching element  80 , and the light-emitting element  90  when viewed in the z direction. That is, the third wiring  53 C is formed to cover the first current path when viewed in the z direction. Further, as shown in  FIGS. 18 and 19 , the third wiring  53 C is formed to cover the first wiring  41 C of the second conductive layer  40 C when viewed in the z direction. That is, the third wiring  53 C is formed to overlap the first current path when viewed in the z direction and to cover the second current path of the current flowing in the direction opposite to the direction in which the current flows through the first current path. As shown in  FIGS. 18 and 19 , when viewed in the z direction, the third wiring  53 C is arranged at a position where it overlaps the fourth wiring  44 C of the second conductive layer  40 C when viewed in the z direction. 
     As shown in  FIG. 19 , a recessed portion  53 Ca is formed in the third wiring  53 C. The recessed portion  53 Ca is formed at an end, between both ends of the third wiring  53 C, which is closer to the board side surface  24  in the x direction, and at the center of the end in the y direction. 
     As shown in  FIG. 20 , the fourth conductive layer  60 C is a conductive layer corresponding to the fourth conductive layer  60  of the first embodiment and includes a first wiring  61 C, a second wiring  62 C, a third wiring  63 C, a fourth wiring  64 C, a fifth wiring  65 C, and a sixth wiring  66 C. 
     The first wiring  61 C is arranged near the board side surface  21  and the board side surface  23  of the substrate back surface  20 Cr of the third substrate  20 C. As shown in  FIGS. 19 and 20 , the first wiring  61 C is arranged at a position where it overlaps the first wiring  51 C of the third conductive layer  50 C when viewed in the z direction. 
     The second wiring  62 C is interposed between the first wiring  61 C and the third wiring  63 C in the x direction. The second wiring  62 C and the first wiring  61 C are arranged apart from each other in the x direction to be aligned with each other in the y direction. As shown in  FIGS. 19 and 20 , the second wiring  62 C is arranged at a position where it overlaps the second wiring  52 C of the third conductive layer  50 C when viewed in the z direction. 
     The third wiring  63 C is arranged near the board side surface  21  and the board side surface  24  of the substrate back surface  20 Cr of the third substrate  20 C. The shape of the third wiring  63 C viewed from the z direction is the same as the shape of the fourth wiring  64 C (see  FIG. 18 ) of the second conductive layer  40 C viewed from the z direction. As shown in  FIGS. 19 and 20 , the third wiring  63 C is arranged at a position where it overlaps the third wiring  53 C of the third conductive layer  50 C when viewed in the z direction. 
     As shown in  FIG. 19 , the fourth wiring  64 C, the fifth wiring  65 C, and the sixth wiring  66 C are arranged closer to the board side surface  22  than the first wiring  61 C, the second wiring  62 C, and the third wiring  63 C in the y direction, respectively. The fourth wiring  64 C, the fifth wiring  65 C, and the sixth wiring  66 C are arranged apart from each other in the x direction to be aligned with one another in the y direction. The fifth wiring  65 C is interposed between the fourth wiring  64 C and the sixth wiring  66 C in the x direction. The fourth wiring  64 C is arranged closer to the board side surface  23  than the fifth wiring  65 C. The sixth wiring  66 C is arranged closer to the board side surface  24  than the fifth wiring  65 C. 
     The fourth wiring  64 C is arranged apart from the first wiring  61 C in they direction so as to be aligned with the first wiring  61 C in the x direction. The shape of the fourth wiring  64 C viewed from the z direction is substantially a rectangular shape in which the y direction is a long side direction and the x direction is a short side direction. It may be said that the fourth wiring  64 C extends in the y direction. In the present embodiment, the width dimension of the fourth wiring  64 C (the dimension of the fourth wiring  64 C in the x direction) is equal to the dimension of the first wiring  61 C in the x direction. 
     The fifth wiring  65 C is arranged at a position where it overlaps the second wiring  62 C when viewed in the y direction. When viewed in the y direction, the fifth wiring  65 C is arranged at a position where it overlaps an end, between both ends of the third wiring  63 C, which is closer to the second wiring  62 C in the x direction. 
     The fifth wiring  65 C extends in the y direction. A recessed portion  65 Ca is formed in the fifth wiring  65 C. The recessed portion  65 Ca is formed at an end, between both ends of the fifth wiring  65 C, which is closer to the second wiring  62 C in the y direction. The end, between both ends of the third wiring  63 C, which is closer to the second wiring  62 C in the x direction enters the recessed portion  65 Ca. 
     The sixth wiring  66 C is arranged at a position where it overlaps the third wiring  63 C when viewed in they direction. The shape of the sixth wiring  66 C viewed from the z direction is a rectangular shape in which the y direction is a long side direction and the x direction is a short side direction. It may be said that the sixth wiring  66 C extends in the y direction. 
     As shown in  FIGS. 17 to 20 , the multilayer board  20  includes a plurality of through-wirings, similar to the first embodiment. In the present embodiment, the multilayer board  20  includes a first through-wiring  25 , a second through-wiring  26 , a third through-wiring  27 , a fourth through-wiring  28 , and a fifth through-wiring  29 . 
     The first through-wiring  25  is a wiring that connects the first wiring  31 C of the first conductive layer  30 C and the first wiring  41 C of the second conductive layer  40 C, similarly to the first through-wiring  25 S of the first embodiment. The first through-wiring  25  is connected to an end, between both ends of the first wiring portion  41 Ca of the first wiring  41 C, which is closer to the fourth side wall  101 D in the x direction. 
     In the present embodiment, the second through-wiring  26  is a wiring provided at a position where it overlaps the second wiring  32 C of the first conductive layer  30 C when viewed in the z direction. As shown in  FIG. 17 , a plurality of second through-wirings  26  (two second through-wirings  26  in the present embodiment) are provided. These second through-wirings  26  are arranged apart from each other in the y direction to be aligned with each other in the x direction. For the sake of convenience, of the two second through-wirings  26 , the second through-wiring  26  closer to the first side wall  101 A is referred to as a “second through-wiring  26 A,” and the second through-wiring  26  closer to the second side wall  101 B is referred to as a “second through-wiring  26 B.” 
     Similar to the second through-wiring  26  of the first embodiment, the second through-wiring  26 A is a wiring that connects the second wiring  32 C of the first conductive layer  30 C, the second wiring  42 C of the second conductive layer  40 C, the first wiring  51 C of the third conductive layer  50 C, and the first wiring  61 C of the fourth conductive layer  60 C. In this case, the first wiring  61 C of the fourth conductive layer  60 C constitutes a terminal (drain terminal) to which the drain electrode  81  of the switching element  80  is electrically connected. 
     The second through-wiring  26 B is a wiring that connects the second wiring  32 C of the first conductive layer  30 C and the fourth wiring  64 C of the fourth conductive layer  60 C. That is, the second through-wiring  26 B is not connected to the second conductive layer  40 C and the third conductive layer  50 C. In this way, the fourth wiring  64 C of the fourth conductive layer  60 C serves as a heat-radiating wiring configured to radiate heat from the second wiring  32 C of the first conductive layer  30 C. 
     In the present embodiment, the third through-wiring  27  is a wiring provided at a position where it overlaps the third wiring  33 C of the first conductive layer  30 C when viewed in the z direction. As shown in  FIG. 17 , a plurality of third through-wirings  27  (two third through-wirings  27  in the present embodiment) are provided. In the arrangement form of these third through-wirings  27 , a pair of third through-wirings  27 , which are apart from each other in the y direction to be aligned with each other in the x direction, is arranged in two rows apart from each other in the x direction. For the sake of convenience, of these pairs of third through-wirings  27 , the pair of third through-wirings  27  that are closer to the third side wall  101 C is referred to as a “pair of through-wirings  27 A,” and the pair of third through-wirings  27  that are closer to the fourth side wall  101 D is referred to as a “pair of through-wirings  27 B.” 
     As shown in  FIG. 21 , the pair of third through-wirings  27 A connects the third wiring  33 C of the first conductive layer  30 C and the first wiring  41 C of the second conductive layer  40 C, similar to the third through-wirings  27 S of the first embodiment. The pair of third through-wirings  27 A are connected to an end, between both ends of the second wiring portion  41 Cb of the first wiring  41 C, which is closer to the fourth side wall  101 D in the x direction, that is, a leading end of the second wiring portion  41 Cb. 
     As shown in  FIG. 21 , the pair of third through-wirings  27 B is a wiring that connects the third wiring  33 C of the first conductive layer  30 C and the sixth wiring  66 C of the fourth conductive layer  60 C. That is, the pair of third through-wirings  27 B is not connected to the second conductive layer  40 C and the third conductive layer  50 C. As shown in  FIG. 19 , the recessed portion  53 Ca of the third wiring  53 C of the third conductive layer  50 C is formed to avoid the pair of third through-wirings  27 B. In this way, the sixth wiring  66 C of the fourth conductive layer  60 C serves as a heat-radiating wiring configured to radiate heat from the third wiring  33 C of the first conductive layer  30 C. 
     As shown in  FIGS. 17 to 20 , the fourth through-wiring  28  is a wiring that connects the fourth wiring  34 C of the first conductive layer  30 C, the third wiring  43 C of the second conductive layer  40 C, the second wiring  52 C of the third conductive layer  50 C, and the second wiring  62 C of the fourth conductive layer  60 C, similar to the fourth through-wiring  28  of the first embodiment. In this case, the second wiring  62 C of the fourth conductive layer  60 C constitutes a terminal (gate terminal) to which the gate electrode  83  of the switching element  80  is electrically connected. 
     In the present embodiment, the fifth through-wiring  29  is a wiring provided at a position where it overlaps the fifth wiring  35 C of the first conductive layer  30 C when viewed in the z direction. As shown in  FIG. 17 , a plurality of fifth through-wirings  29  (seven fifth through-wirings  29  in the present embodiment) are provided. In the arrangement form of these fifth through-wirings  29 , two rows of fifth through-wirings  29 , which are apart from each other in the x direction to be aligned with each other in the y direction, are arranged apart from each other in the y direction. For the sake of convenience, among the plurality of fifth through-wirings  29 , the fifth through-wiring  29  provided at one end, between both ends of the fifth wiring  35 C, which is closer to the second wiring  32 C in the x direction is referred to as a “fifth through-wiring  29 B,” and each of the remaining fifth through-wirings  29  is referred to as a “fifth through-wiring  29 A.” 
     The fifth through-wiring  29 B is a wiring that connects the fifth wiring  35 C of the first conductive layer  30 C and the fifth wiring  65 C of the fourth conductive layer  60 C. That is, the fifth through-wiring  29 B is not connected to the second conductive layer  40 C and the third conductive layer  50 C. In this way, the fifth wiring  65 C of the fourth conductive layer  60 C serves as a heat-radiating wiring configured to radiate heat of the fifth wiring  35 C of the first conductive layer  30 C. 
     Similar to the fifth through-wiring  29  of the first embodiment, each of the fifth through-wirings  29 A is a wiring that connects the fifth wiring  35 C of the first conductive layer  30 C, the fourth wiring  44 C of the second conductive layer  40 C, the third wiring  53 C of the third conductive layer  50 C, and the third wiring  63 C of the fourth conductive layer  60 C. In this case, the third wiring  63 C of the fourth conductive layer  60 C constitutes a ground terminal. 
     Even with such a semiconductor light-emitting device  10 , a relationship between the current flowing in the first current path and the current flowing in the second current path of the current flowing in the direction opposite to the direction in which the current flows through the first current path is the same as that in the first embodiment. Further, a portion of the current flowing through the third wiring  63 C flows to the sixth wiring  66 C via the third through-wiring  27 . 
     (Effects) 
     According to the semiconductor light-emitting device  10  according to the present embodiment, the following effects may be obtained in addition to the effects of the first embodiment. 
     (5-1) The second through-wiring  26 B is connected to the fourth wiring  64 C of the fourth conductive layer  60 C while avoiding the second conductive layer  40 C and the third conductive layer  50 C. According to this configuration, when the semiconductor light-emitting device  10  is driven with the semiconductor light-emitting device  10  mounted on a drive substrate (not shown), the heat of the switching element  80  moves from the second wiring  32 C of the first conductive layer  30 C to the fourth wiring  64 C via the second through-wiring  26 B. That is, since the heat of the switching element  80  is more easily transferred to the fourth wiring  64 C of the fourth conductive layer  60 C than the second conductive layer  40 C and the third conductive layer  50 C, the heat of the switching element  80  moves more easily to the drive substrate. As a result, it is possible to improve the heat radiation performance of the semiconductor light-emitting device  10 . 
     (5-2) The third through-wiring  27 B is connected to the sixth wiring  66 C of the fourth conductive layer  60 C while avoiding the second conductive layer  40 C and the third conductive layer  50 C. According to this configuration, when the semiconductor light-emitting device  10  is driven with the semiconductor light-emitting device  10  mounted on a drive substrate (not shown), the heat of the light-emitting element  90  moves from the third wiring  33 C of the first conductive layer  30 C to the sixth wiring  66 C via the third through-wiring  27 B. That is, the heat of the light-emitting element  90  is more easily transferred to the sixth wiring  66 C of the fourth conductive layer  60 C than the second conductive layer  40 C and the third conductive layer  50 C, so that the heat of the light-emitting element  90  moves more easily to the drive substrate. As a result, it is possible to improve the heat radiation performance of the semiconductor light-emitting device  10 . 
     (5-3) The third wiring  53 C, which is the ground potential, covers both the first current path and the second current path. According to this configuration, it is possible to prevent noise caused by the current flowing through the first current path and the current flowing through the second current path from leaking to the outside of the multilayer board  20 . 
     [Modifications] 
     Each of the aforementioned embodiments is an example of a form that the semiconductor light-emitting device according to the present disclosure may take, and is not intended to limit the form. The semiconductor light-emitting device according to the present disclosure may take a form different from the form exemplified in each of the aforementioned embodiments. One example thereof is a form in which each of the aforementioned embodiments is partially replaced, changed, or omitted, or a form in which a new configuration is added to each of the aforementioned embodiments. The following modifications may be combined with each other unless technically contradictory. In each of the following modifications, the same parts as each of the aforementioned embodiments are denoted by the same reference numerals as each of the aforementioned embodiments, and explanation thereof will be omitted.
         In the first embodiment, the arrangement form of the capacitor  70  may be arbitrarily changed. For example, the capacitor  70  may be arranged apart from each other in the y direction such that the first electrode  71  and the second electrode  72  are aligned with each other in the x direction. In this case, for example, the light-emitting element  90  may be arranged at a position where it does not overlap the capacitor  70  when viewed in the y direction. Further, for example, the light-emitting element  90  may be arranged at a position where it partially overlaps the capacitor  70  when viewed in the y direction.   In the second embodiment, both the switching element  80  and the light-emitting element  90  are arranged at positions where they overlap the first electrode  71  of the capacitor  70  when viewed in the y direction, but the present disclosure is not limited thereto. For example, when viewed in the y direction, both the switching element  80  and the light-emitting element  90  may be arranged at positions where they overlap the second electrode  72  of the capacitor  70 . In this case, for example, the fourth wiring  34  of the first conductive layer  30  may be arranged at a position where it is aligned with the second electrode  72  of the capacitor  70  in the x direction.   In the first and fourth embodiments, the positional relationship between the first wirings  41  and  41 C of the second conductive layers  40  and  40 C and the capacitor  70 , the switching element  80 , and the light-emitting element  90  when viewed in the z direction may be arbitrarily changed. For example, when viewed in the z direction, the capacitor  70  may be arranged to partially protrude from the first wiring portions  41   a  and  41 Ca of the first wirings  41  and  41 C. When viewed in the z direction, the switching element  80  may be arranged to partially protrude from the second wiring portions  41   b  and  41 Cb of the first wirings  41  and  41 C. When viewed in the z direction, the light-emitting element  90  may be arranged to partially protrude from the second wiring portions  41   b  and  41 Cb of the first wirings  41  and  41 C. In short, when viewed in the z direction, the capacitor  70  may be arranged to at least partially overlap the first wiring portions  41   a  and  41 Ca of the first wirings  41  and  41 C. The switching element  80  may be arranged to at least partially overlap the second wiring portions  41   b  and  41 Cb of the first wirings  41  and  41 C. The light-emitting element  90  may be arranged to at least partially overlap the second wiring portions  41   b  and  41 Cb of the first wirings  41  and  41 C.   In the first and fourth embodiments, the positional relationship among the first wirings  41  and  41 C of the second conductive layers  40  and  40 C and the first wiring  31 , the second wiring  32 , and the third wiring  33  of the first conductive layer  30  may be arbitrarily changed. For example, when viewed in the z direction, the first wiring portions  41   a  and  41 Ca of the first wirings  41  and  41 C may be partially deviated from the first wiring  31  in the y direction. When viewed in the z direction, the second wiring portions  41   b  and  41 Cb of the first wirings  41  and  41 C may be partially deviated from the third wiring  33  in they direction.   In the second and fourth embodiments, the positional relationship between the first wirings  41 A and  41 B of the second conductive layers  40 A and  40 B, the capacitor  70 , the switching element  80 , and the light-emitting element  90  when viewed in the z direction may be arbitrarily changed. For example, when viewed in the z direction, the capacitor  70  may be arranged to partially protrude from the first wiring portions  41 Aa and  41 Ba of the first wirings  41 A and  41 B. When viewed in the z direction, the switching element  80  may be arranged to partially protrude from the second wiring portions  41 Ab and  41 Bb of the first wirings  41 A and  41 B. When viewed in the z direction, the light-emitting element  90  may be arranged to partially protrude from the second wiring portions  41 Ab and  41 Bb of the first wirings  41 A and  41 B. In short, when viewed in the z direction, the capacitor  70  may be arranged to at least partially overlap the first wiring portions  41 Aa and  41 Ba of the first wirings  41 A and  41 B. The switching element  80  may be arranged to at least partially overlap the second wiring portions  41 Ab and  41 Bb of the first wirings  41 A and  41 B. The light-emitting element  90  may be arranged to at least partially overlap the second wiring portions  41 Ab and  41 Bb of the first wirings  41 A and  41 B.   In each of the embodiments, the size of the capacitor  70  is larger than the sizes of the switching element  80  and the light-emitting element  90 , but the size relationship among the capacitor  70 , the switching element  80 , and the light-emitting element  90  is not limited thereto. For example, the size of the light-emitting element  90  may be larger than the size of the capacitor  70 . Further, for example, the size of the switching element  80  may be larger than the size of the capacitor  70 . In this case, the light-emitting element  90  corresponds to the “first predetermined element,” and the capacitor  70  corresponds to the “second predetermined element” or the “third predetermined element.”   In each of the aforementioned embodiments, the electrode configuration of the switching element  80  may be arbitrarily changed. For example, the switching element  80  may have a configuration in which the drain electrode  81 , the source electrode  82 , and the gate electrode  83  are formed on the switching element main surface  80   s  of the switching element  80 .   In each of the embodiments, the light-emitting direction of the light-emitting element  90  is not limited to the z direction, but may be arbitrarily changed. For example, the light-emitting direction of the light-emitting element  90  may be a direction orthogonal to the z direction. In this case, an opening is formed in a portion of the side wall  101  of the case  100  through which the light of the light-emitting element  90  passes. A light-transmitting plate may be installed at this opening. Further, a top wall, instead of the light-transmitting plate  102 , may be installed on the side wall  101 . That is, the shape of the case  100  may be a box shape that opens toward the multilayer board  20 .   In each of the embodiments, the electrode configuration of the light-emitting element  90  may be arbitrarily changed. For example, the light-emitting element  90  may have a configuration in which both the anode electrode  91  and the cathode electrode  92  are formed on one of the light-emitting element main surface  90   s  and the light-emitting element back surface  90   r.      In each of the embodiments, the light-transmitting plate  102  may be omitted from the case  100 .   In each of the embodiments, the case  100  may be omitted from the semiconductor light-emitting device  10 .   In each of the embodiments, the semiconductor light-emitting device  10  may include a translucent resin instead of the case  100 . The translucent resin is made of a material that transmits light and has an electrical insulation characteristic, and covers the capacitor  70 , the switching element  80 , and the light-emitting element  90 . The translucent resin may have a rectangular parallelepiped shape that covers the entire board main surface  20   s  of the multilayer board  20 .   In each of the embodiments, the configuration of the multilayer board  20  may be arbitrarily changed. For example, the second substrate  20 B and the third conductive layer  50  may be omitted from the multilayer board  20 .   In each of the embodiments, the semiconductor light-emitting device  10  may include a single-layer board instead of the multilayer board  20 . An example of this will be described with the semiconductor light-emitting device  10  of the first embodiment. The first conductive layer  30  is formed on the board front surface, and the second conductive layer  40 , which is a wiring pattern, and external terminals, are formed on the board back surface. Examples of the external terminals may include a power supply terminal configured to supply electric power to the semiconductor light-emitting device  10 , a ground terminal connected to the ground, and a control terminal electrically connected to the gate electrode  83  of the switching element  80 . These external terminals are formed by, for example, a wiring pattern. In this case, both the third conductive layer  50  and the fourth conductive layer  60  are omitted. The semiconductor light-emitting device  10  includes a through-wiring that penetrates the board in its thickness direction and connects the first conductive layer  30  and the fourth conductive layer  60 . The through-wiring includes a first through-wiring  25 S that connects the first wiring  31  and the first wiring  41 , a second through-wiring  26  that connects the second wiring  32  and the second wiring  62 , a third through-wiring  27 S that connects the third wiring  33  and the first wiring  41 , a fourth through-wiring  28  that connects the fourth wiring  34  and the third wiring  63 , and a fifth through-wiring  29  that connects the fifth wiring  35  and the fourth wiring  64 .   In the present disclosure, the semiconductor light-emitting device  10  including the capacitor  70 , the switching element  80 , and the light-emitting element  90  is used, but the present disclosure is not limited thereto, and electronic components including a first element, a second element, and a third element electrically connected to one another may be used.       

     The term “on” as used in the present disclosure includes the meanings of “on” and “above” unless clearly stated otherwise in the context. Therefore, the expression “A is formed on B” is intended to mean that A may be arranged directly on B while being in contact with B in the present embodiment, but as a modification, A may be arranged above B while not being in contact with B. That is, the term “on” does not exclude a structure in which other members are formed between A and B. 
     The z direction used in the present disclosure may not be the vertical direction, and may not be exactly the same as the vertical direction. Therefore, various structures according to the present disclosure are not limited to “upper” and “lower” in the z direction described herein as being “upper” and “lower” in the vertical direction. For example, the x direction may be the vertical direction, or the y direction may be the vertical direction. 
     (Supplementary Notes) 
     The technical ideas that may be understood from each of the aforementioned embodiments and each of the aforementioned modifications are described below. In addition, reference numerals of the constituent elements of the embodiments corresponding to the constituent elements described in the respective supplementary notes are shown in parentheses. The reference numerals are shown as examples to assist in understanding, and the constituent elements described in the respective supplementary notes should not be limited to the constituent elements denoted by the reference numerals. 
     (Supplementary Note A1) 
     A semiconductor light-emitting device ( 10 ) including:
         a board including a front surface ( 20   s ), a back surface ( 20   r ) facing an opposite side of the front surface, a first wiring pattern ( 30 / 30 C) formed on the front surface ( 20   s ), and a second wiring pattern ( 40 / 40 C) formed on the side of the back surface ( 20   r ) with respect to the first wiring pattern ( 30 / 30 C); and   a light-emitting element ( 90 ), a switching element ( 80 ), and a capacitor ( 70 ), which are electrically connected to one another by both the first wiring pattern and the second wring patterns ( 30 / 30 C and  40 / 40 C),   wherein, a first predetermined element ( 70 ) and a second predetermined element ( 80 ) among the light-emitting element ( 90 ), the switching element ( 80 ), and the capacitor ( 70 ) are arranged in a first direction (y direction) when viewed in a thickness direction (z direction) of the board,   wherein the second predetermined element ( 80 ) and a third predetermined element ( 90 ) among the light-emitting element ( 90 ), the switching element ( 80 ), and the capacitor ( 70 ), are arranged in a second direction (x direction) intersecting the first direction (y direction) when viewed in the thickness direction (z direction) of the board, and   wherein with respect to a first current path of a first current flowing through the light-emitting element ( 90 ), the switching element ( 80 ), and the capacitor ( 70 ) on the front surface ( 20   s ), the second wiring pattern ( 40 / 40 C) is configured to form a second current path through which a second current flows in an opposite direction to a direction in which the first current flows through the first current path, the second current path overlapping the first current path when viewed in the thickness direction (z direction) of the board.       

     (Supplementary Note A2) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A1, wherein the first predetermined element ( 70 ) and the second predetermined element ( 80 )) are arranged at positions where the first predetermined element ( 70 ) and the second predetermined element ( 80 ) at least partially overlap each other when viewed in the first direction (y direction). 
     (Supplementary Note A3) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A1 or A2, wherein the second predetermined element ( 80 ) and the third predetermined element ( 90 ) are arranged at positions where the second predetermined element ( 80 ) and the third predetermined element ( 90 ) at least partially overlap each other when viewed in the second direction (x direction). 
     (Supplementary Note A4) 
     The semiconductor light-emitting device ( 10 ) of any one of Supplementary Notes A1 and A3, wherein the first predetermined element ( 70 ) has a shape having a longitudinal direction and a lateral direction when viewed in the thickness direction (z direction) of the board, and is arranged so that the lateral direction is along the first direction (y direction) and the longitudinal direction is along the second direction (x direction),
         wherein the length of the first predetermined element ( 70 ) in the longitudinal direction is longer than each of a length of the second predetermined element ( 80 ) and a length of the third predetermined element ( 90 ) in the second direction, and   wherein both the second predetermined element ( 80 ) and the third predetermined element ( 90 ) are arranged at a position where the second predetermined element ( 80 ) and the third predetermined element ( 90 ) at least partially overlap the first predetermined element ( 70 ) when viewed in the first direction (y direction).       

     (Supplementary Note A5) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A4, wherein both the second predetermined element ( 80 ) and the third predetermined element ( 90 ) are arranged at positions where the second predetermined element ( 80 ) and the third predetermined element ( 90 ) entirely overlap the first predetermined element ( 70 ) when viewed in the first direction (y direction). 
     (Supplementary Note A6) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A4 or A5, wherein the first predetermined element is the capacitor ( 70 ),
         wherein the capacitor ( 70 ) includes a first electrode ( 71 ) and a second electrode ( 72 ), and   wherein the first electrode ( 71 ) and the second electrode ( 72 ) are arranged apart from each other in the longitudinal direction (x direction).       

     (Supplementary Note A7) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A6, wherein the second predetermined element is the switching element ( 80 ), the third predetermined element is the light-emitting element ( 90 ), and the light-emitting element ( 90 ) is a light-emitting diode,
         wherein a drain electrode ( 81 ) of the switching element ( 80 ) is electrically connected to the second electrode ( 72 ) of the capacitor ( 70 ),   wherein a source electrode ( 82 ) of the switching element ( 80 ) is electrically connected to an anode electrode ( 91 ) of the light-emitting diode ( 90 ),   wherein a cathode electrode ( 92 ) of the light-emitting diode ( 90 ) is electrically connected to the first electrode ( 71 ) of the capacitor ( 70 ), and   wherein the switching element ( 80 ) is arranged closer to the second electrode ( 72 ) than the light-emitting diode ( 90 ) in the second direction (x direction).       

     (Supplementary Note A8) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A7, wherein the first wiring pattern ( 30 / 30 C) includes: a first front surface side wiring ( 31 / 31 C) on which the first electrode ( 71 ) of the capacitor ( 70 ) is mounted; a second front surface side wiring ( 32 / 32 C) on which the second electrode ( 72 ) of the capacitor ( 70 ) and the switching element ( 80 ) are mounted; and a third front surface side wiring ( 33 / 33 C) on which the light-emitting diode ( 90 ) is mounted,
         wherein the second wiring pattern ( 40 / 40 C) includes a back surface side wiring ( 41 / 41 C) formed at a position where the back surface side wiring ( 41 / 41 C) overlaps each of the third front surface side wiring ( 33 / 33 C), the second front surface side wiring ( 32 / 32 C), and a portion of the first front surface side wiring ( 31 / 31 C), when viewed in the thickness direction (z direction) of the board, and   wherein the back surface side wiring ( 41 / 41 C) is electrically connected to the third front surface side wiring ( 33 / 33 C).       

     (Supplementary Note A9) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A8, wherein the back surface side wiring ( 41 / 41 C) includes: a first wiring portion ( 41   a / 41 Ca) that extends along the second direction (x direction) and overlaps both the first electrode ( 71 ) and the second electrode ( 72 ) of the capacitor ( 70 ) when viewed in the thickness direction (z direction) of the board; a second wiring portion ( 41   b / 41 Cb) that extends along the second direction (x direction) and overlaps the light-emitting diode ( 90 ) and the switching element ( 80 ) when viewed in the thickness direction (z direction) of the board; and a third wiring portion ( 41   c / 41 Cc) that connects the first wiring portion ( 41   a / 41 Ca) and the second wiring portion ( 41   b / 41 Cb) in the first direction (y direction), and
         wherein the third wiring portion ( 41   c / 41 Cc) connects an end, which is closer to the switching element ( 80 ), of both ends of the first wiring portion ( 41   a / 41 Ca) in the second direction (x direction) and an end, which is closer to the second electrode ( 72 ) of the capacitor ( 70 ), of both ends of the second wiring portion ( 41   b / 41 Cb) in the second direction (x direction).       

     (Supplementary Note A10) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A9, wherein when viewed in the thickness direction (z direction) of the board, the first wiring portion ( 41   a / 41 Ca) is formed to entirely overlap the capacitor ( 70 ), and the second wiring portion ( 41   b / 41 Cb) is formed to entirely overlap both the switching element ( 80 ) and the light-emitting element ( 90 ). 
     (Supplementary Note A11) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A10, wherein when viewed in the thickness direction (z direction) of the board, a dimension of the second wiring portion ( 41   b / 41 Cb) in the first direction (y direction) is equal to a dimension of the third front surface side wiring ( 33 / 33 C) in the first direction (y direction), and a dimension of the first wiring portion ( 41   a / 41 Ca) in the first direction (y direction) is equal to a dimension of the capacitor ( 70 ) in the first direction (y direction). 
     (Supplementary Note A12) 
     A semiconductor light-emitting device ( 10 ) including:
         a board including a front surface ( 20   s ), a back surface ( 20   r ) facing an opposite side of the front surface ( 20   s ), a first wiring pattern ( 30 A/ 30 B) formed on the front surface ( 20   s ), and a second wiring pattern ( 40 A/ 40 B) formed on the side of the back surface ( 20   r ) with respect to the first wiring pattern ( 30 A/ 30 B); and   a light-emitting element ( 90 ), a switching element ( 80 ), and a capacitor ( 70 ), which are electrically connected to one another by both the first wiring pattern and the second wiring pattern ( 30 A/ 30 B and  40 A/ 40 B),   wherein a first predetermined element ( 70 ) among the light-emitting element ( 90 ), the switching element ( 80 ), and the capacitor ( 70 ) has a shape having a longitudinal direction and a lateral direction when viewed in a thickness direction (z direction) of the board,   wherein the first predetermined element ( 70 ) and another element ( 80  and  90 ) among the light-emitting element ( 90 ), the switching element ( 80 ), and the capacitor ( 70 ) are arranged in a first direction (y direction) intersecting the longitudinal direction when viewed in the thickness direction (z direction) of the board, and   wherein with respect to a first current path of a first current flowing through the light-emitting element ( 90 ), the switching element ( 80 ), and the capacitor ( 70 ) on the front surface ( 20   s ), the second wiring pattern ( 40 A/ 40 B) is configured to form a second current path through which a second current flows in an opposite direction to a direction in which the first current flows through the first current path, the second current path overlapping the first current path when viewed in the thickness direction (z direction) of the board.       

     (Supplementary Note A13) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A12, wherein the light-emitting element ( 90 ), the switching element ( 80 ), and the capacitor ( 70 ) are arranged at positions where the light-emitting element ( 90 ), the switching element ( 80 ), and the capacitor ( 70 ) at least partially overlap one another when viewed in the first direction (y direction). 
     (Supplementary Note A14) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A12 or A13, wherein the first predetermined element is the capacitor ( 70 ), and wherein the light-emitting element ( 90 ) is arranged closer to the capacitor ( 70 ) than the switching element ( 80 ) in the first direction (y direction). 
     (Supplementary Note A15) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A14, wherein the capacitor ( 70 ) includes a first electrode ( 71 ) and a second electrode ( 72 ),
         wherein the first electrode ( 71 ) and the second electrode ( 72 ) are arranged apart from each other in the longitudinal direction,   wherein both the switching element ( 80 ) and the light-emitting element ( 90 ) are arranged at positions where both the switching element and the light-emitting element overlap the first electrode ( 71 ) of the capacitor ( 70 ) when viewed in the first direction (y direction), and   wherein a cathode electrode ( 92 ) of the light-emitting element ( 90 ) is electrically connected to the first electrode ( 71 ) of the capacitor ( 70 ).       

     (Supplementary Note A16) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A15, wherein the light-emitting element ( 90 ) is a light-emitting diode,
         wherein the first wiring pattern ( 30 A/ 30 B) includes: a first front surface side wiring ( 31 A/ 31 B) on which the second electrode ( 72 ) of the capacitor ( 70 ) is mounted; a second front surface side wiring ( 32 A/ 32 B) on which the first electrode ( 71 ) of the capacitor ( 70 ) and the light-emitting diode ( 90 ) are mounted; and a third front surface side wiring ( 33 A/ 33 B) on which the switching element ( 80 ) is mounted,   wherein the second wiring pattern ( 40 A/ 40 B) includes a back surface side wiring ( 41 A/ 41 B) formed at a position where the back surface side wiring ( 41 A/ 41 B) overlaps each of the third front surface side wiring ( 33 A/ 33 B), the second front surface side wiring ( 32 A/ 32 B), and a portion of the first front surface side wiring ( 31 A/ 31 B), when viewed in the thickness direction (z direction) of the board, and   wherein the back surface side wiring ( 41 A/ 41 B) is electrically connected to the third front surface side wiring ( 33 A/ 33 B).       

     (Supplementary Note A17) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A16, wherein the back surface side wiring ( 41 A/ 41 B) includes: a first wiring portion ( 41 Aa/ 41 Ba) that extends in the first direction (y direction) and overlaps the switching element ( 80 ), the light-emitting diode ( 90 ), and the first electrode ( 71 ) of the capacitor ( 70 ) when viewed in the thickness direction (z direction) of the board; and a second wiring portion ( 41 Ab/ 41 Bb) that extends from the first wiring portion ( 41 Aa/ 41 Ba) in the second direction (x direction) and overlaps the second electrode ( 72 ) of the capacitor ( 70 ) when viewed in the thickness direction (z direction) of the board. 
     (Supplementary Note A18) 
     The semiconductor light-emitting device ( 10 ) of any one of Supplementary Notes A1 to A17, wherein the board ( 20 ) is a multilayer board including a plurality of substrates ( 20 A to  20 C) having an insulation characteristic and a plurality of conductive layers ( 30 ,  30 A to  30 C,  40 ,  40 A to  40 C,  50 ,  50 C,  60 , and  60 C),
         wherein a front surface side substrate ( 20 A), among the plurality of substrates ( 20 A to  20 C), constituting the front surface ( 20   s ) of the board ( 20 ) has a substrate front surface ( 20 As) constituting the front surface ( 20   s ) of the board ( 20 ) and a substrate back surface ( 20 Ar) facing an opposite side of the substrate front surface ( 20 As),   wherein the first wiring pattern ( 30 ,  30 A to  30 C) is a conductive layer, among the plurality of conductive layers ( 30 ,  30 A to  30 C,  40 ,  40 A to  40 C,  50 ,  50 C,  60 , and  60 C), formed on the substrate front surface ( 20 As), and   wherein the second wiring pattern ( 40 ,  40 A to  40 C) is a conductive layer, among the plurality of conductive layers ( 30 ,  30 A to  30 C,  40 ,  40 A to  40 C,  50 ,  50 C,  60 , and  60 C), formed on the substrate back surface ( 20 Ar).       

     (Supplementary Note A19) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A18, wherein a plurality of external terminals ( 60  and  60 C) connected to an outside of the semiconductor light-emitting device are formed on the back surface ( 20   r ) of the board ( 20 ), and
         wherein at least one of the plurality of external terminals ( 60  and  60 C) is electrically connected to at least one of the switching element ( 80 ) and the light-emitting element ( 90 ) by a through-wiring ( 25 ,  25 S,  25 R,  26 ,  27 S,  27 R,  28 ,  29 ) that penetrates the board ( 20 ) in the thickness direction (z direction) of the board.       

     (Supplementary Note A20) 
     The semiconductor light-emitting device ( 10 ) of Supplementary Note A19, wherein the through-wiring ( 25 ,  25 S,  25 R,  26 ,  27 S,  27 R,  28 ,  29 ) is provided to avoid a conductive layer ( 40 ,  40 A to  40 C,  50 ,  50 C), among the plurality of conductive layers ( 30 ,  30 A to  30 C,  40 ,  40 A to  40 C,  50 ,  50 C,  60 , and  60 C), interposed among the plurality of substrates ( 20 A to  20 C). 
     (Supplementary Note A21) 
     The semiconductor light-emitting device ( 10 ) of any one of Supplementary Notes A1 to A20, further including:
         a side wall ( 101 ) provided on the board ( 20 ) and configured to surround the capacitor ( 70 ), the switching element ( 80 ), and the light-emitting element ( 90 ); and   a light-transmitting plate ( 102 ) provided on the side wall ( 101 ) and arranged at a position where the light-transmitting plate ( 102 ) overlaps the light-emitting element ( 90 ) when viewed in the thickness direction (z direction) of the board,   wherein the light-emitting element ( 90 ) emits light such that a light-emitting region expands as the light-emitting region becomes distant from the board ( 20 ) in the thickness direction (z direction) of the board, and   wherein the light-emitting element ( 90 ) is mounted on the board ( 20 ) such that the light-emitting region between the light-transmitting plate ( 102 ) and the board ( 20 ) is formed at an inward side from the side wall ( 101 ) when viewed in the thickness direction (z direction) of the board.       

     (Supplementary Note A22) 
     The semiconductor light-emitting device ( 10 ) of any one of Supplementary Notes A1 to A21, further including: a protective diode ( 110 ) configured to protect the light-emitting element ( 90 ). 
     (Supplementary Note B1) 
     An electronic component including:
         a board including a front surface, a back surface facing an opposite side of the front surface, a first wiring pattern formed on the front surface, and a second wiring pattern formed on the side of back surface with respect to the first wiring pattern; and   a first element, a second element, and a third element, which are electrically connected to one another by both the first wiring pattern and the second wiring pattern,   wherein the first element and the second element are arranged in a first direction when viewed in a thickness direction of the board,   wherein the second element and the third element are arranged in a second direction intersecting the first direction when viewed in the thickness direction of the board, and   wherein with respect to a first current path of a first current flowing through the first element, the second element, and the third element on the front surface, the second wiring pattern is configured to form a second current path through which a second current flows in an opposite direction to a direction in which the first current flows through the first current path, the second current path overlapping the first current path when viewed in the thickness direction of the board.       

     (Supplementary Note B2) 
     An electronic component including:
         a board including a front surface, a back surface facing an opposite side of the front surface, a first wiring pattern formed on the front surface, and a second wiring pattern formed on the side of the back surface with respect to the first wiring pattern; and   a first element, a second element, and a third element, which are electrically connected to one another by both the first wiring pattern and the second wiring pattern,   wherein the first element has a shape having a longitudinal direction and a lateral direction when viewed in a thickness direction of the board,   wherein the first element, the second element, and the third element are arranged in a first direction intersecting the longitudinal direction, and   wherein with respect to a first current path of a first current flowing through the first element, the second element, and the third element on the front surface, the second wiring pattern is configured to form a second current path through which a second current flows in an opposite direction to a direction in which the first current flows through the first current path, the second current path overlapping the first current path when viewed in the thickness direction of the board.       

     According to the present disclosure in some embodiments, it is possible to provide a semiconductor light-emitting device capable of electrically connecting a light-emitting element, a switching element, and a capacitor while reducing the inductance. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the embodiments described herein may be embodied in a variety of other forms. Furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.