Coli device and method for manufacturing the same

Abstract

To provide a coil device capable of preventing temperature rise in a coil and deterioration in inductance characteristics, and a method for manufacturing the same.SOLUTION: A coil device 1 includes: a core 3 having a columnar core portion 30, a sidewall portion 32 surrounding the core portion 30, and a recessed portion 36 located between the core portion 30 and the sidewall portion 32; a wire having a winding portion 20 accommodated in the recessed portion 36 and having a plurality of layers along a radial direction of the core portion 30, and a lead-out portion led out from the winding portion 20; resins 6 attached to the winding portion 20; and a terminal 5a connected to the lead-out portion and provided on the sidewall portion 32. The winding portion 20 includes a dense portion 24 having a relatively large number of layers along a radial direction of the winding portion 20, and a sparse portion 25 having a relatively small number of layers along the radial direction. The resin 6 bonds the dense portion 24 and the side wall portion 32 without bonding the sparse portion 25 and the side wall portion 32.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a coil device and a method for manufacturing the same. [Background technology]

[0002] Conventionally, coil devices having a so-called pot core have been known (see, for example, Patent Document 1). The pot core is a cylindrical core with a bottom, and has a columnar core, a side wall surrounding the core, and a recess located between the core and the side wall. A coil is housed in the recess, and the core is inserted inside the coil. The lead-out portion drawn out from the coil is connected to a terminal provided on the side wall.

[0003] By filling the recess with resin, heat generated in the coil can be dissipated via the resin, thereby preventing the temperature of the coil from rising. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 10-4021 Summary of the Invention [Problem to be solved by the invention]

[0005] However, if there is variation in the amount of resin filled into the recess, the heat dissipation of the coil will be insufficient, which can cause a problem of temperature rise in the coil. Also, if the coil is entirely covered with resin, as in the coil device of Patent Document 1, stress (thermal load) is likely to occur due to differences in the thermal expansion coefficients of the coil, resin, and core, which can deteriorate the inductance characteristics of the coil device.

[0006] The present disclosure provides a coil device capable of preventing a rise in coil temperature and deterioration of inductance characteristics, and a method for manufacturing the same. [Means for solving the problem]

[0007] The coil device of the present disclosure is a core having a columnar core portion, a sidewall portion surrounding the core portion, and a recess portion located between the core portion and the sidewall portion; a wire housed in the recess and including a wound portion having a plurality of layers along a radial direction of the core portion, and an outgoing portion drawn out from the wound portion; a resin attached to the winding portion; a terminal connected to the lead-out portion and provided on the side wall portion, the winding portion has a dense portion having a relatively large number of layers along a radial direction of the winding portion and a sparse portion having a relatively small number of layers along the radial direction, The resin bonds the dense portion and the side wall portion together without bonding the sparse portion and the side wall portion together.

[0008] The resin may bond an outer peripheral surface of the dense portion and an inner peripheral surface of the side wall portion together.

[0009] The resin may further bond the bottom surface of the dense portion and the bottom of the recess.

[0010] The dense portion may be closer to the bottom of the recess than the sparse portion.

[0011] The dense portion may have a first dense portion and a second dense portion that is closer to the bottom of the recess than the first dense portion, the sparse portion may be located between the first dense portion and the second dense portion along the axial direction of the core portion, and the resin may bond the second dense portion and the side wall portion.

[0012] The resin may bond the second dense portion to the side wall portion without bonding the first dense portion to the side wall portion and without bonding the sparse portion to the side wall portion.

[0013] In a cross section parallel to the axial direction of the core portion, the surface of the resin may be recessed toward the bottom of the recess between the dense portion and the side wall portion, and may be raised as it approaches the dense portion and the side wall portion.

[0014] The surface of the resin may be raised more in the vicinity of the side wall portion than in the vicinity of the dense portion.

[0015] The resin does not necessarily bond the core portion and the dense portion together.

[0016] The dense portion may be in contact with the core portion but not in contact with the side wall portion and the bottom of the recess.

[0017] In a plan view, the resin may locally bond the dense portion and the side wall portion along a path that connects an outer peripheral surface of the winding portion and the terminal in the shortest distance.

[0018] The method for manufacturing a coil device according to the present disclosure includes: preparing a winding portion having a dense portion having a relatively large number of layers along a radial direction and a sparse portion having a relatively small number of layers along the radial direction; preparing a core having a columnar core portion, a sidewall portion surrounding the core portion, and a recess portion located between the core portion and the sidewall portion; applying a resin to the recess; and a step of accommodating the wound portion in the recess and allowing the resin to enter between the dense portion and the side wall portion. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a perspective view of a coil device according to a first embodiment. [Figure 2] FIG. 2 is a perspective view showing the internal configuration of the coil device of FIG. [Figure 3] FIG. 3 is a perspective view of the first core. [Figure 4] FIG. 4 is a perspective view of the terminal of FIG. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV shown in FIG. [Figure 6] FIG. 6 is a diagram showing a method of winding the wire. [Figure 7]FIG. 7 is an enlarged cross-sectional view of a part of the coil device of FIG. [Figure 8] FIG. 8 is a cross-sectional view of the coil device according to the second embodiment. [Figure 9A] FIG. 9A is a diagram showing the measurement results of the rate of change of the inductance characteristics of the coil device. [Figure 9B] FIG. 9B is a diagram showing the measurement results of the rate of change in the inductance characteristics of the coil device. [Figure 9C] FIG. 9C is a diagram showing the measurement results of the rate of change in the inductance characteristics of the coil device. [Figure 10] FIG. 10 is a cross-sectional view of the coil device according to the third embodiment. [Figure 11] FIG. 11 is a plan view of a coil device according to the fourth embodiment. [Figure 12] FIG. 12 is a cross-sectional view of a modified example of the coil device of FIG. [Figure 13] FIG. 13 is a cross-sectional view of a modified example of the coil device of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the contents shown in the drawings are merely schematic and illustrative for understanding the present disclosure, and the appearance and dimensional ratios may differ from the actual product. Furthermore, the present disclosure is not limited to the following embodiments.

[0021] (First embodiment) 1 functions as, for example, an inductor and is mounted in a filter circuit of an electronic device, etc. As shown in Figures 1 and 2, the coil device 1 has a wire 2, a first core 3, a second core 4, a terminal 5a, a terminal 5b, and a resin 6 (Figure 5).

[0022] The wire 2 is, for example, an insulating coated wire, and has a conductive core wire coated with an insulating coating. The wire 2 is a known wound wire such as AIW (polyamideimide copper wire), UEW (polyurethane copper wire), or PEW (polyester copper wire). The wire 2 is a round wire, but may also be a square wire, twisted wire, Litz wire, braided wire, or the like. The wire 2 may also be a self-bonding wire having a bonding layer. The material constituting the wire 2 is not particularly limited, but may be, for example, copper, a copper alloy, silver, or nickel. The diameter of the wire 2 is, for example, 10 to 400 μm. The coating is peeled off at both ends of the wire 2, exposing the conductive core wire.

[0023] As shown in Fig. 2, the wire 2 has a winding portion 20 and lead-out portions 21 and 22 drawn out from the winding portion 20. The winding portion 20 is an air-core coil and is housed inside the first core 3. The lead-out portions 21 and 22 are drawn out in the same direction, but may be drawn out in different directions (e.g., opposite directions). Furthermore, the lead-out portions 21 and 22 extend parallel to each other, but may also extend non-parallel.

[0024] The first core 3 is a so-called pot core. The first core 3 is formed of a material containing a magnetic material and a resin. The magnetic material constituting the first core 3 is not particularly limited, but may be, for example, ferrite (Ni-Zn ferrite, Mn-Zn ferrite, etc.) or a metallic magnetic material (Fe-Ni alloy, Fe-Si alloy, Fe-Si-Cr alloy, Fe-Co alloy, Fe-Si-Al alloy, amorphous iron, etc.). The resin constituting the first core 3 is not particularly limited, but may be, for example, epoxy resin, phenol resin, polyester resin, polyurethane resin, polyimide resin, etc. The first core 3 may be a sintered body of a metallic magnetic material.

[0025] As shown in FIG. 3, the first core 3 has a core portion 30, a side wall portion 32, a bottom wall portion 34, and a recess 36. The bottom wall portion 34 is located at the bottom of the first core 3, which has a cylindrical shape with a bottom. The core portion 30 has a cylindrical shape and protrudes from the bottom wall portion 34. The shape of the core portion 30 is not limited to a cylinder, and may be, for example, an elliptical cylinder or a polygonal cylinder. The core portion 30 penetrates the inside of the winding portion 20 (FIG. 2).

[0026] The recess 36 is located between the core 30 and the side wall 32. The recess 36 is formed in a ring shape in a plan view. The winding part 20 is housed in the recess 36 (the space between the outer peripheral surface 30a of the core 30 and the inner peripheral surface 32e of the side wall 32). As will be described later, the recess 36 is coated (filled) with resin.

[0027] The side wall portion 32 protrudes from the bottom wall portion 34 so as to surround the core portion 30 in all directions. The side wall portion 32 is formed in a ring shape. In a plan view, the inner peripheral surface 32e of the side wall portion 32 is circular. The outer peripheral surface of the side wall portion 32 has a first surface 32a, a second surface 32b, a third surface 32c, and a fourth surface 32d. The second surface 32b, the third surface 32c, and the fourth surface 32d are substantially flat surfaces. On the other hand, the first surface 32a has irregularities.

[0028] In the plan view of FIG. 3 , the ridge between the second surface 32b and the third surface 32c is curved, but the second surface 32b and the third surface 32c may be perpendicular to each other. Furthermore, in the plan view, the ridge between the second surface 32b and the fourth surface 32d is curved, but the second surface 32b and the fourth surface 32d may be perpendicular to each other. Furthermore, in the plan view, the ridge between the first surface 32a and the third surface 32c is chamfered, but the first surface 32a and the third surface 32c may be perpendicular to each other. Furthermore, in the plan view, the ridge between the first surface 32a and the fourth surface 32d is chamfered, but the first surface 32a and the fourth surface 32d may be perpendicular to each other.

[0029] In the following, the axis parallel to the axial direction of the core 30 is referred to as the Z axis. The axis perpendicular to the second surface 32b is referred to as the X axis. The axis perpendicular to the third surface 32c and the fourth surface 32d is referred to as the Y axis. The Y axis is an axis along the direction in which the third surface 32c and the fourth surface 32d face each other. The X axis, Y axis, and Z axis are mutually orthogonal. The length of the coil device 1 in the X axis direction is not particularly limited, but is, for example, 2 to 20 mm. The length of the coil device 1 in the Y axis direction is not particularly limited, but is, for example, 2 to 20 mm. The length of the coil device 1 in the Z axis direction is not particularly limited, but is, for example, 1 to 10 mm.

[0030] In the present disclosure, the negative side of the X-axis is referred to as "forward," and the positive side of the X-axis is referred to as "rearward." The positive and negative sides of the Y-axis are referred to as "sides." The positive side of the Z-axis is referred to as "upward," and the negative side of the Z-axis is referred to as "downward." However, upward in the Z-axis direction does not necessarily coincide with upward in the vertical direction. Furthermore, downward in the Z-axis direction does not necessarily coincide with downward in the vertical direction. A mounting board (not shown) for mounting the coil device 1 is disposed below the coil device 1. The winding axis of the winding unit 20 described above is oriented perpendicular to the mounting board.

[0031] Furthermore, in the present disclosure, "equal," "same," or "similar" does not only refer to a state in which the physical quantities of the objects being compared are exactly equal, identical, or similar, but also includes a state in which there is an error of ±Δ% or less (not particularly limited, for example, Δ=7, 5, or 3) between the physical quantities of the objects being compared.

[0032] Furthermore, in the present disclosure, "parallel" does not only refer to strict parallelism, but also includes a state in which there is an error of ±Δθ° (not particularly limited, for example, Δθ=3) or less from strict parallelism. Furthermore, "perpendicular" or "orthogonal" does not only refer to strict perpendicular or orthogonal, but also includes a state in which there is an error of ±Δθ° (not particularly limited, for example, Δθ=3) or less from strict perpendicular or orthogonal.

[0033] Cutouts 37a and 37b are formed in the upper surface of the side wall 32. When viewed in the X-axis direction, the cutouts 37a and 37b are spaced apart in the Y-axis direction. The cutouts 37a and 37b cut downward into the upper surface of the side wall 32. The cutouts 37a and 37b extend forward from the center of the side wall 32 in the X-axis direction. However, the center of the side wall 32 in the X-axis direction includes not only the exact center of the side wall 32 in the X-axis direction but also a position ±Δx away from the exact center of the side wall 32 in the X-axis direction. Δx is not particularly limited, but is equivalent to, for example, 5% of the length of the side wall 32 in the X-axis direction.

[0034] The depth of cutout portion 37a or 37b is not particularly limited, but is, for example, 1 / 5 to 1 / 2 of the height of side wall portion 32. The length (minimum length or maximum length) of cutout portion 37a or 37b in the X-axis direction as viewed from the Y-axis direction is not particularly limited, but is, for example, 1 / 4 to 1 / 3 or more of the length of side wall portion 32 in the X-axis direction. The length (minimum length or maximum length) of cutout portion 37a or 37b in the Y-axis direction as viewed from the X-axis direction is not particularly limited, but is, for example, 1 / 4 to less than 1 / 2 of the length of side wall portion 32 in the X-axis direction.

[0035] 2, the drawer 21 is drawn forward through the cutout 37a toward the outside of the side wall 32. The drawer 22 is drawn forward through the cutout 37b toward the outside of the side wall 32.

[0036] When viewed from the Y-axis direction, lead-out portion 21 is exposed laterally (toward the negative Y-axis direction) through cutout portion 37a. When viewed from the Y-axis direction, lead-out portion 22 is exposed laterally (toward the positive Y-axis direction) through cutout portion 37b. When viewed from the Y-axis direction, winding portion 20 is exposed laterally through cutout portions 37a and 37b.

[0037] When viewed from the X-axis direction, lead-out portion 21 is exposed forward through cutout portion 37a. When viewed from the X-axis direction, lead-out portion 22 is exposed forward through cutout portion 37b. When viewed from the X-axis direction, winding portion 20 is exposed forward through cutout portions 37a and 37b.

[0038] As shown in Fig. 3, recesses 39a and 39b are formed on the first surface 32a. When viewed from the X-axis direction, the recesses 39a and 39b are spaced apart in the Y-axis direction. The recesses 39a and 39b are recessed toward the rear of the side wall portion 32. As shown in Fig. 2, in a plan view, a portion of the terminal 5a is disposed in the recess 39a. Furthermore, in a plan view, a portion of the terminal 5b is disposed in the recess 39b.

[0039] As shown in FIG. 3, a protrusion 38 is formed between the recess 39a and the recess 39b. The protrusion 38 protrudes forward from the bottom of the recesses 39a and 39b. In the plan view of FIG. 3, the length of the protrusion 38 in the Y-axis direction becomes shorter toward the front and longer toward the rear. The length of the protrusion 38 in the Y-axis direction is not particularly limited, but is, for example, at least one-quarter or one-third of the length of the side wall 32 in the Y-axis direction. The length of the protrusion 38 in the X-axis direction (in other words, the depth of the recess 39a or 39b) is not particularly limited, but is, for example, at least one-tenth and at most one-third of the length of the side wall 32 in the X-axis direction.

[0040] 4, terminals 5a and 5b have a mounting portion 50, a first side portion 51, a second side portion 52, a connecting portion 53, and a crimping portion 54. Terminals 5a and 5b are made of a plate-shaped conductor such as a metal.

[0041] 2 and 4, the mounting section 50 is disposed along the bottom surface of the first core 3. The mounting section 50 is connected to a mounting board (not shown) by solder, a conductive adhesive, or the like.

[0042] The first side portion 51 of the terminal 5a is disposed along the third surface 32c. The first side portion 51 of the terminal 5b is disposed along the fourth surface 32d. The first side portion 51 is continuous with the mounting portion 50 so as to be perpendicular to the mounting portion 50. The length of the first side portion 51 in the X-axis direction is not particularly limited, but is longer than the length of the mounting portion 50 in the X-axis direction. A fillet of solder, conductive adhesive, or the like is formed on the first side portion 51.

[0043] The second side portion 52 is continuous with the first side portion 51 and perpendicular to the first side portion 51. The second side portion 52 is disposed along the first surface 32a. More specifically, the second side portion 52 of the terminal 5a is disposed along the first surface 32a so as to be received in the recess 39a. The second side portion 52 of the terminal 5b is disposed along the first surface 32a so as to be received in the recess 39b.

[0044] The connection portion 53 is continuous with the second side portion 52 so as to be perpendicular to the second side portion 52. In the plan view of FIG. 2, at least a portion of the connection portion 53 of the terminal 5a is housed in the recess 39a. In the plan view of FIG. 2, at least a portion of the connection portion 53 of the terminal 5b is housed in the recess 39b. The connection portion 53 of the terminal 5a is connected to the lead-out portion 21. The connection portion 53 of the terminal 5b is connected to the lead-out portion 22.

[0045] The crimped portion 54 is configured to be freely bendable relative to the connecting portion 53. The crimped portions 54 of terminals 5a and 5b can be bent in directions that approach each other, although this is not particularly limited. The crimped portion 54 of terminal 5a sandwiches the lead portion 21 that is drawn to the connecting portion 53 of terminal 5a. The crimped portion 54 of terminal 5b sandwiches the lead portion 22 that is drawn to the connecting portion 53 of terminal 5b. The lead portions 21 and 22 are connected to the connecting portions 53 of terminals 5a and 5b by, for example, laser welding, solder, conductive adhesive, thermocompression bonding, ultrasonic bonding, resistance brazing, or ultraviolet-curing resin bonding. When the connecting portion 53 is laser-welded, a weld bead is formed on the connecting portion 53.

[0046] As shown in Fig. 1, the second core 4 is a plate-shaped core that is flat in the Z-axis direction. The material that constitutes the second core 4 is the same as the material that constitutes the first core 3, but may be different. The second core 4 is adhered to the upper surface of the side wall portion 32 shown in Fig. 2 by, for example, an adhesive. In Fig. 2, the area where the adhesive is applied is indicated by a two-dot chain line, but the area where the adhesive is applied is not limited to the area shown in Fig. 2.

[0047] As shown in FIG. 5 , the winding portion 20 has a dense portion 24 and a sparse portion 25. The dense portion 24 has a relatively large number of layers along the radial direction of the core portion 30 (however, there are multiple layers along the radial direction of the core portion 30). The sparse portion 25 has a relatively small number of layers along the radial direction of the core portion 30 (however, there are multiple layers along the radial direction of the core portion 30). The number of layers of the dense portion 24 along the radial direction of the core portion 30 is greater than the number of layers of the sparse portion 25 along the radial direction of the core portion 30. The number of layers of the dense portion 24 and the sparse portion 25 along the radial direction of the core portion 30 are both odd numbers, but at least one of these may be an even number. In the example shown in FIG. 5 , the number of layers of the dense portion 24 along the radial direction of the core portion 30 is five, and the number of layers of the sparse portion 25 along the radial direction of the core portion 30 is three. However, the number of layers of the dense portion 24 and the number of layers of the sparse portion 25 along the radial direction of the core portion 30 is not particularly limited, and for example, the number of layers of the dense portion 24 along the radial direction of the core portion 30 may be four layers (even number of layers), and the number of layers of the sparse portion 25 along the radial direction of the core portion 30 may be three layers (odd number of layers).

[0048] Although not particularly limited, the dense portion 24 is formed of three layers along the axial direction of the core portion 30. Although not particularly limited, the sparse portion 25 is formed of four layers along the axial direction of the core portion 30. The number of layers of the dense portion 24 along the axial direction of the core portion 30 is less than the number of layers of the sparse portion 25 along the axial direction of the core portion 30, but it may be the same as or greater than this.

[0049] In this embodiment, the dense portion 24 is closer to the bottom (bottom surface 36a) of the recess 36 than the sparse portion 25. That is, the dense portion 24 is located lower than the sparse portion 25. As shown in FIG. 6 , the dense portion 24 and the sparse portion 25 are continuously connected by the connecting portion 23. The connecting portion 23 extends obliquely from the outermost layer (third layer) of the sparse portion 25 in the radial direction to the innermost layer (first layer) of the dense portion 24 in the radial direction.

[0050] 6, the wire 2 is wound so as to reciprocate up and down in the sparse portion 25. The wire 2 is also wound so as to reciprocate up and down in the dense portion 24. That is, in this embodiment, the wire 2 is first wound so as to form the sparse portion 25, and then the wire 2 is wound so as to form the dense portion 24.

[0051] After the outermost layer of the sparse portion 25 in the radial direction is formed, the wire 2 is drawn out to the innermost layer of the dense portion 24 in the radial direction. This drawn-out portion of the wire 2 is the connecting portion 23. The method of winding the wire 2 is not limited to the above-mentioned method. For example, the wire 2 may be wound up to the third radial layer of the winding portion 20 without distinguishing between the dense portion 24 and the sparse portion 25. Then, the wire 2 may be wound so that the dense portion 24 is formed from the fourth to fifth radial layers of the winding portion 20.

[0052] 5, the wound portion 20 (dense portion 24 and sparse portion 25) is in contact with the outer peripheral surface 30a of the core portion 30. More specifically, the inner peripheral surface 20a of the wound portion 20 is in contact with the outer peripheral surface 30a of the core portion 30. However, the wound portion 20 does not have to be in contact with the outer peripheral surface 30a of the core portion 30, and a gap may be formed between the inner peripheral surface 20a of the wound portion 20 and the outer peripheral surface 30a of the core portion 30.

[0053] The dense portion 24 does not contact the side wall portion 32 and the bottom (bottom surface 36a) of the recess 36. Furthermore, the sparse portion 25 does not contact the side wall portion 32. More specifically, the outer peripheral surface 24a of the dense portion 24 does not contact the inner peripheral surface 32e of the side wall portion 32. Furthermore, the bottom (bottom surface) of the dense portion 24 does not contact the bottom surface 36a of the recess 36. Furthermore, the outer peripheral surface 25a of the sparse portion 25 does not contact the inner peripheral surface 32e of the side wall portion 32. However, the bottom of the dense portion 24 may be in contact with the bottom surface 36a of the recess 36.

[0054] The recess 36 is coated (filled) with resin 6, and the resin 6 is attached to the winding portion 20. The resin 6 is not particularly limited, but may be, for example, an epoxy-based resin. The resin 6 is attached to the outer peripheral surface 24a of the dense portion 24 and covers the outer peripheral surface 24a. The resin 6 penetrates into the gap between the outer peripheral surface 24a of the dense portion 24 and the inner peripheral surface 32e of the side wall portion 32, and bonds (connects) the dense portion 24 (the outer peripheral surface 24a of the dense portion 24) and the side wall portion 32 (the inner peripheral surface 32e of the side wall portion 32). In the example shown in FIG. 5, the width of the gap between the outer peripheral surface 24a of the dense portion 24 and the inner peripheral surface 32e of the side wall portion 32 is narrower than the diameter of the wire 2. However, the width of the gap between the outer peripheral surface 24a of the dense portion 24 and the inner peripheral surface 32e of the side wall portion 32 may be equal to or wider than the diameter of the wire 2.

[0055] The resin 6 may bond the dense portion 24 and the side wall portion 32 in all directions in the plan view of FIG. 5. Alternatively, the resin 6 may bond the dense portion 24 and the side wall portion 32 locally in the plan view of FIG. 5. The resin 6 is attached to the outer peripheral surface 24a of the dense portion 24, but a portion of the resin 6 may penetrate into the dense portion 24. For example, the resin 6 may be attached not only to the fifth layer in the radial direction of the dense portion 24, but also to at least one of the first to fourth layers in the radial direction of the dense portion 24. Furthermore, the dense portion 24 may be entirely immersed in the resin 6.

[0056] The resin 6 may be filled without any gaps between the outer peripheral surface 24a of the dense portion 24 and the inner peripheral surface 32e of the side wall portion 32. Alternatively, the resin 6 may be filled so as to form a gap between the outer peripheral surface 24a of the dense portion 24 and the inner peripheral surface 32e of the side wall portion 32.

[0057] The resin 6 is filled between the dense portion 24 and the side wall portion 32 from the bottom surface 36a of the recess 36 to the third layer of the dense portion 24 in the Z-axis direction. However, the resin 6 may be filled between the dense portion 24 and the side wall portion 32 from the bottom surface 36a of the recess 36 to the second layer of the dense portion 24 in the Z-axis direction, without covering the third layer of the dense portion 24 in the Z-axis direction. Furthermore, the resin 6 may be filled between the dense portion 24 and the side wall portion 32 from the bottom surface 36a of the recess 36 to the first layer of the dense portion 24 in the Z-axis direction, without covering the second and third layers of the dense portion 24 in the Z-axis direction.

[0058] The resin 6 is also filled between the dense portion 24 and the bottom (bottom surface 36a) of the recess 36. The resin 6 bonds (connects) the dense portion 24 (bottom surface of the dense portion 24) and the bottom surface 36a of the recess 36. The resin 6 may be filled without any gaps between the dense portion 24 and the bottom surface 36a of the recess 36, or may be filled so that a gap is formed. The resin 6 between the dense portion 24 and the bottom surface 36a is bonded to the resin 6 between the dense portion 24 and the side wall portion 32. However, the resin 6 between the dense portion 24 and the bottom surface 36a and the resin 6 between the dense portion 24 and the side wall portion 32 may be discontinuous. The resin 6 does not have to be filled between the dense portion 24 and the bottom of the recess 36. Furthermore, when the resin 6 is filled between the dense portion 24 and the bottom of the recess 36, the resin 6 does not have to bond the dense portion 24 and the bottom of the recess 36.

[0059] The thickness of the resin 6 between the dense portion 24 and the side wall portion 32 (however, the thickness along the radial direction of the dense portion 24) is thicker than the thickness of the resin 6 between the dense portion 24 and the bottom (bottom surface 36a) of the recess 36 (however, the thickness along the Z-axis direction of the dense portion 24). However, the thickness of the resin 6 between the dense portion 24 and the side wall portion 32 may be equal to or thinner than the thickness of the resin 6 between the dense portion 24 and the bottom (bottom surface 36a) of the recess 36.

[0060] 5, the resin 6 is not attached to the upper surface of the dense portion 24, but may be attached to the upper surface of the dense portion 24. In addition, the resin 6 attached to the upper surface of the dense portion 24 may be connected to the resin 6 between the dense portion 24 and the side wall portion 32.

[0061] The resin 6 bonds the dense portion 24 to the side wall portion 32 without bonding (connecting) the sparse portion 25 (the outer peripheral surface 25a of the sparse portion 25) to the side wall portion 32 (the inner peripheral surface 32e of the side wall portion 32). Therefore, a gap is formed between the outer peripheral surface 25a of the sparse portion 25 and the inner peripheral surface 32e of the side wall portion 32. In the example shown in FIG. 5 , the resin 6 is not attached to the outer peripheral surface 25a of the sparse portion 25. However, the resin 6 may be attached to at least a portion of the outer peripheral surface 25a of the sparse portion 25 as long as the sparse portion 25 and the side wall portion 32 are not bonded together. In this case, the resin 6 attached to the outer peripheral surface 25a of the sparse portion 25 may be connected to the resin 6 between the dense portion 24 and the side wall portion 32.

[0062] The resin 6 does not bond (connect) the core portion 30 and the wound portion 20 (the dense portion 24 and the loose portion 25). This is because the outer peripheral surface 30a of the core portion 30 and the inner peripheral surface 20a of the wound portion 20 (the inner peripheral surface of the dense portion 24 and the inner peripheral surface of the loose portion 25) are in contact with each other, and the resin 6 cannot enter between the outer peripheral surface 30a of the core portion 30 and the inner peripheral surface 20a of the wound portion 20. However, the resin 6 may enter slightly between the outer peripheral surface 30a of the core portion 30 and the inner peripheral surface 20a of the wound portion 20 (the inner peripheral surface of the dense portion 24 and / or the inner peripheral surface of the loose portion 25).

[0063] 7, a recess 60 is formed on the surface 6a of the resin 6. The recess 60 is recessed toward the bottom of the recess 36 between the dense portion 24 and the side wall portion 32. The bottom of the recess 60 is located below the upper surface of the dense portion 24, although this is not particularly limited.

[0064] The surface 6a of the resin 6 rises as it approaches the dense portion 24 and the side wall portion 32. That is, the surface 6a of the resin 6 slopes upward as it approaches the dense portion 24 and slopes upward as it approaches the side wall portion 32. However, the surface 6a of the resin 6 may be a flat surface parallel to the bottom surface 36a of the recess 36. Alternatively, the surface 6a of the resin 6 may be an inclined surface that slopes upward as it approaches the side wall portion 32.

[0065] The surface 6a of the resin 6 is raised more in the vicinity of the side wall portion 32 than in the vicinity of the dense portion 24. Although not particularly limited, the surface 6a of the resin 6 in the vicinity of the side wall portion 32 is located higher than the upper surface of the dense portion 24.

[0066] Next, a method for manufacturing the coil device 1 will be described. First, a wire 2 having a winding portion 20 shown in Fig. 1 and Fig. 2, a first core 3, a second core 4, a terminal 5a, and a terminal 5b are prepared. Here, as shown in Fig. 5, the winding portion 20 has a dense portion 24 having a relatively large number of layers along the radial direction of the winding portion 20, and a sparse portion 25 having a relatively small number of layers along the radial direction of the winding portion 20. In addition, the first core 3 has a columnar core portion 30, a side wall portion 32 surrounding the core portion 30, and a recess 36 located between the core portion 30 and the side wall portion 32.

[0067] Next, as shown in FIG. 2, the terminals 5a and 5b are bonded to the outer peripheral surface of the first core 3, for example, by an adhesive. Next, as shown in FIG. 5, a predetermined amount of resin 6 is applied (filled) to the recess 36 (for example, the bottom surface 36a of the recess 36 or the inner peripheral surface 32e of the side wall portion 32), and then the winding portion 20 is accommodated in the recess 36. Then, the resin 6 is allowed to flow between the dense portion 24 (the outer peripheral surface 24a of the dense portion 24) and the side wall portion 32 (the inner peripheral surface 32e of the side wall portion 32). As a result, the resin 6 bonds the dense portion 24 to the side wall portion 32 and also bonds the dense portion 24 to the bottom of the recess 36. Alternatively, the winding portion 20 may be accommodated in the recess 36, and then a predetermined amount of resin 6 may be applied (filled) to the recess 36 (for example, the bottom surface 36a of the recess 36 or the inner peripheral surface 32e of the side wall portion 32).

[0068] 4, the lead-out portion 21 is sandwiched between the crimped portions 54 of the terminal 5a, and the lead-out portion 21 is welded to the connecting portion 53 and the crimped portion 54, for example. Also, the lead-out portion 22 is sandwiched between the crimped portions 54 of the terminal 5b, and the lead-out portion 22 is welded to the connecting portion 53 and the crimped portion 54, for example.

[0069] 1 and 2, the second core 4 is adhered to the upper surface of the side wall portion 32 by, for example, an adhesive. In this manner, the coil device 1 shown in FIG. 1 can be manufactured.

[0070] As shown in FIG. 5 , in the coil device 1 of this embodiment, the winding portion 20 has a dense portion 24 having a relatively large number of layers along the radial direction of the winding portion 20 and a sparse portion 25 having a relatively small number of layers along the radial direction of the winding portion 20. The resin 6 bonds the dense portion 24 to the side wall portion 32 without bonding the sparse portion 25 to the side wall portion 32. By forming the dense portion 24 in the winding portion 20, the distance between the dense portion 24 and the side wall portion 32 becomes relatively short, making it easier for the resin 6 to bond the dense portion 24 to the side wall portion 32. By bonding the dense portion 24 to the side wall portion 32 with the resin 6, heat generated in the winding portion 20 can be dissipated via the resin 6. In particular, because the dense portion 24 is more likely to generate heat than the sparse portion 25, bonding the dense portion 24 to the side wall portion 32 with the resin 6 can efficiently dissipate heat generated in the winding portion 20 via the resin 6. Furthermore, since a predetermined amount of resin 6 is filled (applied) into recess 36 so that dense portion 24 and side wall portion 32 are bonded by resin 6, the amount of resin 6 filled into recess 36 is less likely to vary. Furthermore, by always filling recess 36 with resin 6 so that resin 6 is always filled up to, for example, the vicinity of the upper surface of dense portion 24, it is possible to effectively prevent variation in the amount of resin 6 filled into recess 36. This makes it less likely that the amount of heat dissipation from winding portion 20 will vary, and it is possible to effectively prevent a temperature rise in winding portion 20.

[0071] Furthermore, the resin 6 does not bond the sparse portion 25 to the side wall portion 32. That is, the resin 6 does not cover the entire winding portion 20, and does not bond the entire outer circumferential surface of the winding portion 20 to the inner circumferential surface 32e of the side wall portion 32. Therefore, when the temperature changes, stress caused by the difference in the thermal expansion coefficients of the winding portion 20, the resin 6, and the first core 3 (stress or thermal load caused by expansion and contraction of the resin 6) is less likely to be generated, and fluctuations in the inductance of the coil device 1 can be prevented.

[0072] Furthermore, the resin 6 bonds the outer peripheral surface 24a of the dense portion 24 to the inner peripheral surface 32e of the side wall portion 32. Therefore, a heat dissipation path for dissipating heat from the dense portion 24 can be formed between the outer peripheral surface 24a of the dense portion 24 and the inner peripheral surface 32e of the side wall portion 32. This allows the heat from the dense portion 24, which is likely to generate heat, to be efficiently dissipated toward the side wall portion 32 via the resin 6.

[0073] The resin 6 also bonds the bottom surface of the dense portion 24 to the bottom of the recess 36. Therefore, a heat dissipation path for dissipating heat from the dense portion 24 can be further formed between the bottom surface of the dense portion 24 and the bottom of the recess 36. This allows the heat from the dense portion 24, which is likely to generate heat, to be efficiently dissipated toward the side wall portion 32 via the resin 6.

[0074] Furthermore, the dense portion 24 is closer to the bottom of the recess 36 than the sparse portion 25. Therefore, the resin 6 can bond the dense portion 24 to the bottom of the recess 36. This allows the heat generated in the winding portion 20 to be efficiently dissipated. Furthermore, the amount of resin 6 between the dense portion 24 and the side wall portion 32 can be visually confirmed through the opening of the recess 36. This makes it possible to determine whether the amount of resin 6 between the dense portion 24 and the side wall portion 32 is appropriate (constant).

[0075] 7, in a cross section parallel to the axial direction of the core portion 30, the surface 6a of the resin 6 is recessed toward the bottom of the recess 36 between the dense portion 24 and the side wall portion 32, and rises as it approaches the dense portion 24 and the side wall portion 32. The surface 6a of the resin 6 rises as it approaches the dense portion 24, thereby increasing the bonding strength between the resin 6 and the dense portion 24. The surface 6a of the resin 6 rises as it approaches the side wall portion 32, thereby increasing the bonding strength between the resin 6 and the side wall portion 32. This makes it easier for the winding portion 20 to be firmly fixed to the side wall portion 32 via the resin 6. Therefore, the position of the winding portion 20 is stabilized, and variations in the inductance characteristics of the coil device 1 can be prevented.

[0076] Furthermore, the surface 6a of the resin 6 is more elevated near the side wall portion 32 than near the dense portion 24. This further increases the bonding strength between the resin 6 and the side wall portion 32. This stabilizes the position of the winding portion 20, effectively preventing variations in the inductance characteristics of the coil device 1.

[0077] Furthermore, the resin 6 does not bond the core portion 30 and the dense portion 24. Therefore, stress caused by the expansion and contraction of the resin 6 is less likely to be generated, and fluctuations in the inductance of the coil device 1 can be prevented.

[0078] Furthermore, while the dense portion 24 is in contact with the core portion 30, it is not in contact with the side wall portion 32 or the bottom of the recess 36. By having the dense portion 24 in contact with the core portion 30, the position of the winding portion 20 is stabilized, and fluctuations in the inductance of the coil device 1 can be prevented. Furthermore, when the dense portion 24 is not in contact with the side wall portion 32 or the bottom of the recess 36, the resin 6 is more likely to enter between the dense portion 24 and the side wall portion 32. Furthermore, the resin 6 is more likely to enter between the dense portion 24 and the bottom of the recess 36. This allows heat generated in the winding portion 20 to be efficiently dissipated via the resin 6.

[0079] The manufacturing method of the coil device 1 of this embodiment also includes a step of applying (filling) the resin 6 into the recess 36. Furthermore, the manufacturing method of the coil device 1 of this embodiment also includes a step of accommodating the winding portion 20 in the recess 36 and allowing the resin 6 to infiltrate between the dense portion 24 and the side wall portion 32. Therefore, the resin 6 that has infiltrated between the dense portion 24 and the side wall portion 32 can bond the dense portion 24 and the side wall portion 32. In this case, a predetermined amount of resin 6 is filled into the recess 36 so that the dense portion 24 and the side wall portion 32 are bonded by the resin 6, which reduces variation in the amount of resin 6 filled into the recess 36. Furthermore, by always filling the recess 36 with the resin 6 so that the resin 6 reaches, for example, near the top surface of the dense portion 24, it is possible to effectively prevent variation in the amount of resin 6 filled into the recess 36. This reduces variation in the amount of heat dissipation from the winding portion 20, thereby effectively preventing a rise in temperature of the winding portion 20.

[0080] (Second embodiment) The coil device 1A of the second embodiment shown in Fig. 8 has the same configuration as the coil device 1 of the first embodiment, except for the following points. The same reference numerals are used to designate parts that overlap with the coil device 1 of the first embodiment, and detailed descriptions thereof will be omitted.

[0081] The coil device 1A has a winding portion 20A. The winding portion 20A has a dense portion 26 in addition to a dense portion 24 and a sparse portion 25. That is, the dense portion in this embodiment is composed of two dense portions. The number of layers of the dense portion 26 along the radial direction of the core portion 30 is equal to the number of layers of the dense portion 24 along the radial direction of the core portion 30, but may be greater than or less than the number of layers of the dense portion 24 along the radial direction of the core portion 30. The dense portion 24 is located lower than the dense portion 26 and closer to the bottom of the recess 36 than the dense portion 26. The sparse portion 25 is located between the dense portion 24 and the dense portion 26 along the axial direction of the core portion 30. The number of layers of the sparse portion 25 along the axial direction of the core portion 30 is not particularly limited, but is preferably three. The dense portion 24 and the sparse portion 25 are continuously connected by a connecting portion 23a. The dense portion 26 and the sparse portion 25 are continuously connected by a connecting portion 23b.

[0082] The resin 6 bonds (connects) the dense portion 24 (the outer peripheral surface 24a of the dense portion 24) and the side wall portion 32 (the inner peripheral surface 32e of the side wall portion 32). The resin 6 also bonds (connects) the dense portion 24 (the bottom of the dense portion 24) and the bottom of the recess 36. The resin 6 between the dense portion 24 and the side wall portion 32 is connected to the resin 6 between the dense portion 24 and the bottom of the recess 36. However, the resin 6 does not have to be filled between the dense portion 24 and the bottom of the recess 36. Furthermore, when the resin 6 is filled between the dense portion 24 and the bottom of the recess 36, the resin 6 does not have to bond the dense portion 24 and the bottom of the recess 36.

[0083] The resin 6 does not bond (connect) the dense portion 26 (the outer peripheral surface 26a of the dense portion 26) and the side wall portion 32 (the inner peripheral surface 32e of the side wall portion 32). Furthermore, the resin 6 does not bond the sparse portion 25 (the outer peripheral surface 25a of the sparse portion 25) and the side wall portion 32 (the inner peripheral surface 32e of the side wall portion 32). However, the resin 6 may be attached to the outer peripheral surface 25a of the sparse portion 25. Furthermore, the resin 6 may be attached to the outer peripheral surface 26a of the dense portion 26. In this case, the resin 6 attached to the outer peripheral surface 25a and / or 26a may be connected to the resin 6 between the dense portion 24 and the side wall portion 32. Furthermore, the resin 6 may bond the dense portion 26 (the outer peripheral surface 26a of the dense portion 26) and the side wall portion 32 (the inner peripheral surface 32e of the side wall portion 32).

[0084] In this embodiment, the coil device 1A shown in FIG. 8 can be manufactured by the same manufacturing method as in the first embodiment, except for the method of forming the winding portion 20A. That is, in this embodiment, to form the winding portion 20A, first, the wire 2 is wound back and forth in the up-and-down direction (see the arrows in FIG. 6) to form the dense portion 26. Next, the wire 2 is drawn from the outermost layer of the dense portion 26 (the outermost layer of the dense portion 26 along the radial direction of the core 30) to the innermost layer of the sparse portion 25 (the innermost layer of the sparse portion 25 along the radial direction of the core 30). This drawn-out portion of the wire 2 becomes the above-mentioned connecting portion 23b. Then, the wire 2 is further wound back and forth in the up-and-down direction (see the arrows in FIG. 6) to form the sparse portion 25. Next, the wire 2 is drawn from the outermost layer of the sparse portion 25 (the outermost layer of the sparse portion 25 along the radial direction of the core 30) to the innermost layer of the dense portion 24 (the innermost layer of the sparse portion 24 along the radial direction of the core 30). The drawn-out portion of the wire 2 becomes the above-mentioned connecting portion 23a. Then, by further winding the wire 2 back and forth in the up and down direction (see the arrows in FIG. 6), the dense portion 24 is formed.

[0085] This embodiment also achieves the same effects as the first embodiment. Additionally, in this embodiment, the dense portion of the winding portion 20A includes a dense portion 26 and a dense portion 24 that is closer to the bottom of the recess 36 than the dense portion 26. The sparse portion 25 is located between the dense portion 24 and the dense portion 26 along the axial direction of the core 30. The resin 6 bonds the dense portion 24 to the side wall portion 32. The formation of the dense portion 24, the dense portion 26, and the sparse portion 25 in the winding portion 20A reduces the inter-wire stray capacitance between the dense portion 24 and the sparse portion 25, and also reduces the inter-wire stray capacitance between the dense portion 26 and the sparse portion 25. This allows the coil device 1A to achieve a broadband impedance frequency characteristic in the high frequency band. Furthermore, since a predetermined amount of resin 6 is filled in the recess 36 so that the dense portion 24 and the side wall portion 32 are bonded by the resin 6, the amount of resin 6 filled in the recess 36 is less likely to vary. Furthermore, by always filling recesses 36 with resin 6 up to near the top surface of dense portion 24, it is possible to effectively prevent variation in the amount of resin 6 filled in recesses 36. This reduces variation in the amount of heat dissipation from winding portion 20A, making it possible to effectively prevent a temperature rise in winding portion 20A.

[0086] Furthermore, the resin 6 bonds the dense portion 24 to the side wall portion 32 without bonding the dense portion 26 to the side wall portion 32 and without bonding the sparse portion 25 to the side wall portion 32. Therefore, the amount of resin 6 between the dense portion 24 and the side wall portion 32 can be visually confirmed through the opening of the recess 36. This makes it possible to determine whether the amount of resin 6 between the dense portion 24 and the side wall portion 32 is an appropriate amount (a certain amount).

[0087] Here, the results of measuring the rate of change in inductance characteristics under the following conditions (i) to (iii) using the coil device 1A shown in FIG. 8 are shown in FIGS. 9A to 9C. The rate of change in inductance characteristics was measured by placing a mounting board on which the coil device 1A was mounted in a furnace at a reflow temperature of 260°C and removing it 10 times. There were 24 samples of the coil device 1A. In FIGS. 9A to 9C, the vertical axis represents the rate of change in inductance characteristics, and the horizontal axis represents the number of times the mounting board passed through the furnace. However, the number of times the mounting board passed through the furnace was only two points: 0 and 10 times. (i) As shown in FIG. 8, when the resin 6 bonds only the dense portion 24 and the side wall portion 32 (ii) Unlike the example shown in FIG. 8, the resin 6 bonds the dense portion 24 and the side wall portion 32, and further bonds the sparse portion 25 and the side wall portion 32. (iii) Unlike the example shown in FIG. 8, the resin 6 bonds the dense portion 24 and the side wall portion 32, further bonds the sparse portion 25 and the side wall portion 32, and further bonds the dense portion 26 and the side wall portion 32.

[0088] When the resin 6 bonded only the dense portion 24 to the side wall portion 32, the rate of change in inductance did not fall below the standard value of ±5% in any of the samples, as shown in FIG. 9A. On the other hand, when the resin 6 bonded the dense portion 24 to the side wall portion 32 and further bonded the sparse portion 25 to the side wall portion 32, only one sample showed a rate of change in inductance characteristics below the standard value, as shown in FIG. 9B. Furthermore, when the resin 6 bonded the dense portion 24 to the side wall portion 32, further bonded the sparse portion 25 to the side wall portion 32, and further bonded the dense portion 26 to the side wall portion 32, as shown in FIG. 9C, eight samples showed a rate of change in inductance characteristics below the standard value. From the above, it was confirmed that by bonding only the dense portion 24 to the side wall portion 32 with the resin 6, fluctuations in the inductance characteristics of the coil device 1A can be effectively prevented.

[0089] (Third embodiment) The coil device 1B of the third embodiment shown in Fig. 10 has the same configuration as the coil device 1 of the first embodiment, except for the following points. The same reference numerals are used to designate parts that overlap with the coil device 1 of the first embodiment, and detailed descriptions thereof will be omitted.

[0090] The coil device 1B has a winding portion 20B. The winding portion 20B differs from the winding portion 20 of the first embodiment in that the sparse portion 25 is located close to the bottom of the recess 36. That is, in this embodiment, the positions of the dense portion 24 and the sparse portion 25 are swapped in the vertical direction.

[0091] The resin 6 bonds (connects) the dense portion 24 and the side wall portion 32 without bonding (connecting) the sparse portion 25 and the side wall portion 32. The resin 6 may penetrate into the dense portion 24. The resin 6 may also be attached to the upper surface and / or the lower surface of the dense portion 24. The resin 6 may also be attached to the outer peripheral surface 25a of the sparse portion 25. In this case, the resin 6 attached to the outer peripheral surface 25a may be connected to the resin 6 between the dense portion 24 and the side wall portion 32.

[0092] A recess 60m is formed on the upper surface 6b of the resin 6. The recess 60m is recessed toward the bottom of the recess 36 between the dense portion 24 and the side wall portion 32. The bottom of the recess 60m is located below the upper surface of the dense portion 24, although this is not particularly limited.

[0093] The upper surface 6b of the resin 6 rises as it approaches the dense portion 24 and the side wall portion 32. That is, the upper surface 6b slopes upward as it approaches the dense portion 24 and slopes upward as it approaches the side wall portion 32. However, the upper surface 6b may be a flat surface parallel to the bottom surface 36a of the recess 36.

[0094] In the vicinity of the side wall portion 32, the upper surface 6b of the resin 6 is raised higher than in the vicinity of the dense portion 24. In the vicinity of the side wall portion 32, the upper surface 6b is located higher than the upper surface of the dense portion 24, although this is not particularly limited.

[0095] A recess 60n is formed in the lower surface 6c of the resin 6. The recess 60n is recessed toward the opening of the recess 36 between the dense portion 24 and the side wall portion 32. The bottom of the recess 60n is located above the lower surface of the dense portion 24, although this is not particularly limited.

[0096] The lower surface 6c of the resin 6 rises as it approaches the dense portion 24 and the side wall portion 32. That is, the lower surface 6c slopes downward as it approaches the dense portion 24 and slopes downward as it approaches the side wall portion 32. However, the lower surface 6c may be a flat surface parallel to the bottom surface 36a of the recess 36.

[0097] Near the side wall portion 32, the lower surface 6c of the resin 6 is raised higher than near the dense portion 24. Near the side wall portion 32, the lower surface 6c is located lower than the lower surface of the dense portion 24, although this is not particularly limited.

[0098] In this embodiment, the coil device 1B shown in FIG. 9B can be manufactured by the same manufacturing method as in the first embodiment, except for the method of forming the winding portion 20B and the method of applying the resin 6. That is, in this embodiment, to form the winding portion 20B, first, the wire 2 is wound back and forth in the up-and-down direction (see the arrows in FIG. 6) to form the dense portion 24. Next, the wire 2 is drawn from the outermost layer of the dense portion 24 (the outermost layer of the dense portion 24 along the radial direction of the core 30) to the innermost layer of the sparse portion 25 (the innermost layer of the sparse portion 25 along the radial direction of the core 30). This drawn portion of the wire 2 becomes the above-mentioned connecting portion 23a. Then, the wire 2 is further wound back and forth in the up-and-down direction (see the arrows in FIG. 6) to form the sparse portion 25. In this way, the winding portion 20B can be formed.

[0099] Furthermore, in this embodiment, unlike the first embodiment, the resin 6 is not applied to the bottom surface 36a of the recess 36, but is applied to the inner circumferential surface 32e of the side wall 32 (particularly, a position of the inner circumferential surface 32e facing the outer circumferential surface 24a of the dense portion 24). Thereafter, the wound portion 20B is accommodated in the recess 36. Then, the resin 6 is allowed to flow between the dense portion 24 (the outer circumferential surface 24a of the dense portion 24) and the side wall 32 (the inner circumferential surface 32e of the side wall 32). Note that the wound portion 20B may be accommodated in the recess 36, and then the resin 6 may be applied to the inner circumferential surface 32e of the side wall 32 (particularly, a position of the inner circumferential surface 32e facing the outer circumferential surface 24a of the dense portion 24).

[0100] In this embodiment, the same effects as in the first embodiment can be obtained. In addition, in this embodiment, the dense portion 24 is closer to the opening of the recess 36 than the sparse portion 25. This makes it easier to fill the resin 6 between the dense portion 24 and the side wall portion 32, and makes it easier for the resin 6 to bond the dense portion 24 and the side wall portion 32 together.

[0101] (Fourth embodiment) The coil device 1C of the fourth embodiment shown in Fig. 11 has the same configuration as the coil device 1 of the first embodiment, except for the following points. The same reference numerals are used to designate parts that overlap with the coil device 1 of the first embodiment, and detailed descriptions thereof will be omitted.

[0102] In this embodiment, unlike the first embodiment, the resin 6 bonds (connects) the dense portion 24 and the side wall portion 32 locally, rather than omnidirectionally. In particular, in the plan view of Fig. 11, the resin 6 locally bonds the dense portion 24 (the outer peripheral surface 24a of the dense portion 24) and the side wall portion 32 (the inner peripheral surface 32e of the side wall portion 32) along a path that connects the outer peripheral surface of the winding portion 20 and the terminal 5a or 5b over the shortest distance. Furthermore, the resin 6 locally bonds the dense portion 24 and the side wall portion 32 around the path, in addition to the path that connects the outer peripheral surface of the winding portion 20 and the terminal 5a or 5b over the shortest distance.

[0103] In the example shown in FIG. 11 , the path connecting the outer peripheral surface of the winding portion 20 and the terminal 5a or 5b over the shortest distance is, for example, the path connecting the outer peripheral surface 24a of the dense portion 24 and the second side portion 52 over the shortest distance in a plan view. However, the path connecting the outer peripheral surface of the winding portion 20 and the terminal 5a or 5b over the shortest distance may also be the path connecting the outer peripheral surface 24a of the dense portion 24 and the first side portion 51 over the shortest distance in a plan view. Alternatively, the path connecting the outer peripheral surface of the winding portion 20 and the terminal 5a or 5b over the shortest distance may also be the path connecting the outer peripheral surface 24a of the dense portion 24 and the connecting portion 53 over the shortest distance in a plan view. Alternatively, the path connecting the outer peripheral surface of the winding portion 20 and the terminal 5a or 5b over the shortest distance may also be the path connecting the outer peripheral surface 24a of the dense portion 24 and the crimping portion 54 over the shortest distance in a plan view.

[0104] This embodiment also achieves the same effects as the first embodiment. Additionally, in this embodiment, in the plan view of FIG. 11 , the resin 6 locally bonds the dense portion 24 and the side wall portion 32 along the path connecting the outer circumferential surface of the winding portion 20 and the terminal 5a or 5b over the shortest distance. Therefore, heat generated in the winding portion 20 is transferred to the side wall portion 32 via the resin 6 along the path connecting the outer circumferential surface of the winding portion 20 and the terminal 5a or 5b over the shortest distance. The heat transferred to the side wall portion 32 is then transferred to the mounting board (not shown) via the terminal 5a or 5b. Therefore, the heat generated in the winding portion 20 can be efficiently dissipated. Furthermore, by locally bonding the dense portion 24 and the side wall portion 32 with the resin 6, the amount of resin 6 filled (applied) in the recess 36 can be reduced. This reduces the variation in the amount of resin 6 filled in the recess 36.

[0105] The present disclosure is not limited to the above-described embodiments, and various modifications can be made within the scope of the present disclosure.

[0106] 12, in the first embodiment, the resin 6 that bonds (connects) the dense portion 24 and the side wall portion 32 may extend along the inner circumferential surface 32e of the side wall portion 32 to the side of the sparse portion 25. Also, as shown in FIG. 13, in the third embodiment, the resin 6 that bonds (connects) the dense portion 24 and the side wall portion 32 may extend along the inner circumferential surface 32e of the side wall portion 32 to the side of the sparse portion 25. [Explanation of symbols]

[0107] 1, 1A, 1B, 1C... Coil device 2...Wire 20, 20A, 20B...winding section 20a...Inner peripheral surface 24,26…Secret area 24a, 26a...outer surface 25...Sparse area 25a...Outer surface 21,22...Drawer part 23,23a,23b...Connection part 3...First core 30…core part 30a...Outer surface 32...Side wall 32a…First page 32b…Second side 32c...Side 3 32d…Side 4 32e…Inner peripheral surface 34...Bottom wall 36...recess 36a…Bottom surface 37a, 37b...Notch 38...Convex part 39a, 39b...recess 4...Second core 5a,5b…Terminal 50...Mounting section 51...First side 52...Second side 53...Connection section 54... Crimping part 6...Resin 6a…Surface 6b…Top surface 6c…Bottom surface 60, 60m, 60n...recess

Claims

1. a core having a columnar core portion, a sidewall portion surrounding the core portion, and a recess portion located between the core portion and the sidewall portion; a wire housed in the recess and including a wound portion having a plurality of layers along a radial direction of the core portion, and an outgoing portion drawn out from the wound portion; a resin attached to the winding portion; a terminal connected to the lead-out portion and provided on the side wall portion, the winding portion has a dense portion having a relatively large number of layers along a radial direction of the winding portion and a sparse portion having a relatively small number of layers along the radial direction, The resin bonds the dense portion to the side wall portion without bonding the sparse portion to the side wall portion.

2. The coil device according to claim 1 , wherein the resin bonds an outer peripheral surface of the dense portion and an inner peripheral surface of the side wall portion together.

3. The coil device according to claim 2 , wherein the resin further bonds a bottom surface of the dense portion and a bottom of the recess.

4. 4. The coil device according to claim 1, wherein the dense portion is closer to the bottom of the recess than the sparse portion.

5. the dense portion has a first dense portion and a second dense portion that is closer to the bottom of the recess than the first dense portion, the low density portion is located between the first dense portion and the second dense portion along the axial direction of the core portion, 4. The coil device according to claim 1, wherein the resin bonds the second dense portion and the side wall portion together.

6. The coil device according to claim 5, wherein the resin bonds the second dense portion to the side wall portion without bonding the first dense portion to the side wall portion and without bonding the sparse portion to the side wall portion.

7. A coil device as described in any one of claims 1 to 3, wherein in a cross section parallel to the axial direction of the core portion, the surface of the resin is concave toward the bottom of the recess between the dense portion and the side wall portion, and is raised as it approaches the dense portion and the side wall portion.

8. The coil device according to claim 7 , wherein the surface of the resin is raised more in the vicinity of the side wall portion than in the vicinity of the dense portion.

9. 4. The coil device according to claim 1, wherein the resin does not bond the core portion and the dense portion together.

10. 4. The coil device according to claim 1, wherein the dense portion is in contact with the core portion but is not in contact with the side wall portion or the bottom of the recess.

11. A coil device as described in any one of claims 1 to 3, wherein, in a plan view, the resin locally bonds the dense portion and the side wall portion along the path connecting the outer surface of the winding portion and the terminal in the shortest distance.

12. preparing a winding portion having a dense portion having a relatively large number of layers along a radial direction and a sparse portion having a relatively small number of layers along the radial direction; preparing a core having a columnar core portion, a sidewall portion surrounding the core portion, and a recess portion located between the core portion and the sidewall portion; applying a resin to the recess; a step of accommodating the winding portion in the recess and allowing the resin to enter between the dense portion and the side wall portion.

Images