Coil device

Abstract

To provide a coil device excellent in DC superposition characteristics and improved in mechanical strength.SOLUTION: A coil device includes a first core 20 having a first magnetic body 20a, a second core 30 having a second magnetic body 30a higher in porosity than the first magnetic body 20a, and a bonding layer 32 that bonds a first bonding surface 20α of the first core 20 and a second bonding surface 30α of the second core 30. The second magnetic body 30a has a coating 30b that fills a gap on the surface of the second magnetic body 30a at least at a position that serves as the second adhesion surface 30α, and the surface of the coating 30b serves as the second adhesion surface 30α in contact with the adhesion layer 32.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a coil device having excellent DC superposition characteristics and improved mechanical strength.

Background Art

[0002] For example, as shown in Patent Document 1 below, it has been proposed to improve the DC superposition characteristics of a coil device by configuring it with materials having different magnetic permeabilities along the axial direction of the core portion. However, in conventional coil devices, the adhesive strength between core portions made of materials with different magnetic permeabilities has been a problem.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In view of such a situation, the present invention has been made, and its object is to provide a coil device having excellent DC superposition characteristics and improved mechanical strength.

Means for Solving the Problems

[0005] In order to achieve the above object, the coil device according to the present invention includes a first core having a first magnetic body, a second core having a second magnetic body with a higher porosity than the first magnetic body, and an adhesive layer that adheres a first adhesive surface of the first core and a second adhesive surface of the second core, and is a coil device having the second magnetic body having a film that fills voids present on the surface of the second magnetic body at least at a position that becomes the second adhesive surface, and the surface of the film becomes the second adhesive surface and contacts the adhesive layer.

[0006] In this coil device, even if the porosity of the second magnetic material becomes higher than that of the first magnetic material in order to lower the permeability of the second magnetic material compared to that of the first magnetic material, it becomes easy to reliably and firmly bond the first and second magnetic materials with a small amount of adhesive. As a result, the mechanical strength of the coil device is improved. Furthermore, it becomes easier to construct the core of the coil device with a combination of materials with different permeability, and the DC superposition characteristics are also improved.

[0007] According to the inventors' new findings, when attempting to directly join a second magnetic material with high porosity and a first magnetic material with low porosity using an adhesive, the adhesive is absorbed into the surface of the second magnetic material with high porosity, making it difficult to properly connect the first and second magnetic materials and resulting in poor bonding. Increasing the amount of adhesive to avoid poor bonding may adversely affect the high-frequency characteristics of the coil device.

[0008] In the coil device of the present invention, the second magnetic material, which has a high porosity, has a coating that fills the voids on the surface of the second magnetic material at the position that becomes the second bonding surface. Therefore, the adhesive for forming the bonding layer is prevented from seeping into the interior of the second magnetic material from the surface because the surface of the second magnetic material is blocked by the coating. In addition, the adhesive for forming the bonding layer is less likely to seep into the interior of the first magnetic material from the surface of the first magnetic material, which has a low porosity.

[0009] Therefore, it becomes easier to form an adhesive layer with a small amount of adhesive, and the adhesive layer reliably and firmly bonds the surface of the second magnetic material coating to the surface of the first magnetic material, thereby improving the mechanical strength of the coil device.

[0010] Preferably, the coating has a glass film containing glass. The coating can also be made of a resin or the like that has properties that do not penetrate deeply from the surface to the interior of the second magnetic material, but preferably it is made of a glass film, which improves the high-frequency characteristics of the coil device. This is because the glass component has superior impedance characteristics on the high-frequency side compared to the resin component.

[0011] Preferably, the surface roughness Ra of the second adhesive surface of the coating is 0.2 μm or more. The adhesive strength between the coating and the adhesive layer is improved when the surface roughness Ra of the coating in contact with the adhesive layer is above a predetermined value. It is also preferable that the surface roughness Ra of the coating in contact with the adhesive layer is close to the surface roughness Ra of the first adhesive surface of the first magnetic material.

[0012] Preferably, the thickness of the coating present on the surface of the second magnetic material at the location of the second adhesive surface is in the range of 1 to 11 μm, more preferably in the range of 3 to 9 μm, and particularly preferably in the range of 4 to 8 μm. The thickness of the coating present on the surface of the second magnetic material at the location of the second adhesive surface may be partially 0, but preferably a coating of 1 μm or more is formed at least partially.

[0013] Preferably, the penetration depth of the coating that extends from the surface of the second magnetic material into the interior of the second magnetic material is 15 μm or less, more preferably 10 μm or less, and particularly preferably 8 μm or less.

[0014] Preferably, the first magnetic material is made of ferrite. By making the first magnetic material of ferrite, the permeability of the first magnetic material can be improved. Also preferably, the second magnetic material is made of a metallic magnetic material. By making the second magnetic material of a metallic magnetic material, the permeability of the second magnetic material can be set low. By combining these ferrite and metallic magnetic materials by bonding them with an adhesive layer to form a core, the DC superposition characteristics of the coil device can be further improved.

[0015] Preferably, the first core is made of the first magnetic material and has a winding core around which a wire can be wound. By making the entire winding core around which the wire is wound out of the first magnetic material, the inductance of the coil device can be improved.

[0016] The first core may be integrally formed with the bobbin portion from a first magnetic material, and may further include flange portions respectively formed at both axial ends of the bobbin portion. Preferably, the second core has the plate-shaped second magnetic material disposed so as to connect these flange portions. By forming the second core from the plate-shaped second magnetic material and firmly joining the second core to the first magnetic material via an adhesive layer, the mechanical strength of the coil device with further improved DC superposition characteristics can be further enhanced.

Brief Description of the Drawings

[0017] [Figure 1A] FIG. 1A is a perspective view of a coil device according to an embodiment of the present invention. [Figure 1B] FIG. 1B is a side view of the coil device shown in FIG. 1A. [Figure 1C] FIG. 1C is a front view of the coil device shown in FIG. 1A. [Figure 1D] FIG. 1D is a bottom view of the coil device shown in FIG. 1A. [Figure 2] FIG. 2 is a perspective view of the drum-type core of the coil device shown in FIG. 1A. [Figure 3] FIG. 3 is a perspective view of the terminal fitting of the coil device shown in FIG. 1A. [Figure 4] FIG. 4 is a partial cross-sectional view of the core along the line IV-IV shown in FIG. 1B. [Figure 5A] FIG. 5A is an enlarged photograph of the surface of the drum core before the adhesive layer is formed. [Figure 5B] FIG. 5B is an enlarged photograph of the surface of the flat core before the adhesive layer is formed.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, the present invention will be described based on the embodiments shown in the drawings.

[0019] First Embodiment The coil device 10 according to one embodiment of the present invention shown in Figure 1A can be used, for example, as a wound-type common-mode filter, but its applications are not particularly limited, and it can also be used as a balun, a dual inductor, or the like.

[0020] The coil device 10 includes a drum core (first core) 20, a coil portion 40 wound around the winding core portion 22 of the drum core 20, and a flat plate core 30 positioned on the upper part of the drum core 20. In describing the coil device 10, the direction parallel to the winding axis of the winding core portion 22 of the drum core 20, which lies in a plane parallel to the main mounting surface on which the coil device 10 is mounted, is defined as the X-axis, the direction perpendicular to the X-axis, which lies in a plane parallel to the main mounting surface, is defined as the Y-axis, and the direction normal to the main mounting surface is defined as the Z-axis.

[0021] As shown in Figure 2, the drum core 20 has a rod-shaped winding core portion 22 extending in the X-axis direction, and a pair of core ends, a first flange portion 24 and a second flange portion 26, provided at both ends of the winding core portion 22. The first flange portion 24 and the second flange portion 26 have substantially the same shape and are provided on the winding core portion 22 at a predetermined distance in the X-axis direction and substantially parallel to each other.

[0022] The core portion 22 is connected to the approximate center of each of the opposing surfaces of the pair of flange portions 24 and 26, and is integrated with the pair of flange portions 24 and 26. In this embodiment, the cross-sectional shape of the core portion 22 is rectangular, but it may also be circular, and its cross-sectional shape is not particularly limited.

[0023] A flat plate core (second core) 30, as shown in Figure 1A, is joined to the upper end of the drum core 20 in the Z-axis direction. The flat plate core 30 is joined to the non-mounting side core surface (first bonding surface) 24b of the first flange portion 24 and the non-mounting side core surface (first bonding surface) 26b of the second flange portion 26, so as to span across these two non-mounting side core surfaces. It is preferable that the flat plate core 30 has a flat surface on its upper surface. A suction member for pickup can be attached to and detachably attached to the flat surface, improving handling.

[0024] As shown in Figure 2, in this embodiment, the first flange portion 24 is composed as a rectangular parallelepiped, with rectangular notches 24c3 formed on the lower sides of both sides in the Y-axis direction of the rectangular parallelepiped. The first flange portion 24 has a mounting-side core surface 24a which is the lower surface in the Z-axis direction, a non-mounting-side core surface 24b on the opposite side, an outer end surface 24c in the X-axis direction, an inner surface 24d facing the direction of the winding core portion 22, and a pair of sides 24e, 24e located on mutually opposite sides in the Y-axis direction.

[0025] Terminal mounting surfaces 24c1 are formed on both the lower sides of the outer end surface 24c in the Y-axis direction, recessed inward in the X-axis direction (towards the center of the core 20) compared to the outer end surface 24c. A terminal insulating projection 24c2 is formed in the center of each terminal mounting surface 24c1 in the Y-axis direction, insulating the first terminal (terminal fitting) 51 and the second terminal (terminal fitting) 52, which are attached as shown in Figure 1A.

[0026] The inner surface of the outer end surface contact portion 51a1 of the terminal body 51a of the first terminal 51 and the inner surface of the outer end surface contact portion 52a1 of the terminal body 52a of the second terminal 52 are attached to each terminal mounting surface 24c1 shown in Figure 2, and are bonded together as needed.

[0027] The depth of the step in which the terminal mounting surface 24c1 is pulled inward in the X-axis direction relative to the outer end surface 24c shown in Figure 2 is preferably about the thickness of the first terminal 51 or the second terminal 52 shown in Figure 3, but it may be shallower or deeper. The shapes of the first terminal 51 and the second terminal 52 shown in Figure 3 are symmetrical to each other.

[0028] The first terminal 51 is made of a conductive terminal plate or the like, and has a terminal body 51a and a protruding plate portion 51b, which are formed by bending a single conductive plate material such as a metal plate. The terminal body 51a has a substantially L-shaped outer end surface contact portion 51a1 which is attached with adhesive or the like to one terminal mounting surface 24c1 formed on the outer end surface 24c of the flange portion 24 shown in Figure 2. The terminal body 51a further has a rectangular plate-shaped mounting side contact portion 51a2 which is formed by bending the outer end surface contact portion 51a1 in the X direction from the lower end in the Z direction.

[0029] The outer end surface contact portion 51a1 of the terminal body 51a shown in Figure 3 is fixed to the terminal mounting surface 24c1 of the flange portion 24 shown in Figure 2 with adhesive or the like, and the mounting side contact portion 51a2 shown in Figure 3 is in close contact with the mounting side core surface 24a shown in Figure 2 with a predetermined gap (the gap may be 0). The outer surface of the mounting side contact portion 51a2 located on the opposite side from the surface that is in contact with the mounting side core surface 24a shown in Figure 2 is the sub-mounting surface 51a3. The role of the sub-mounting surface 51a3 will be described later.

[0030] The mounting-side contact portion 51a2 of the terminal body 51a shown in Figure 3 is integrally molded with a protruding plate portion 51b shown in Figure 3, which protrudes outward in the Y-axis direction from the mounting-side core surface 24a of the flange portion 24 shown in Figure 2, at the lower end of the flange portion 24. The protruding plate portion 51b has a base portion 51c that extends outward in the Y-axis direction flush with the mounting-side contact portion 51a2 of the terminal body 51a, and a bent tip portion 51d that is folded back and bent from the tip of the base portion 51c.

[0031] In this embodiment, the tip of the base 51c is bent so as to fold back upward in the Z-axis direction, and the outer surface of the base 51c located on the opposite side of the tip bent portion 51d becomes the main mounting surface 51c1, and the inner surface of the base 51c where the tip bent portion 51d is located becomes the splicing surface (wire connection surface) 51c2. As shown in Figure 1C, the lead end 41a of one of the leading wires 41 that constitute the coil portion 40 shown in Figure 1B is sandwiched and crimped between the splicing surface 51c2 of the base 51c and the tip bent portion 51d. After crimping, the terminal 51 and the lead end 41a of the wire 41 may be connected by soldering or laser welding.

[0032] In this embodiment, as shown in Figure 1C, the main mounting surface 51c1 and the sub-mounting surface 51a3 of the first terminal 51 are flush outer surfaces. Primarily, the main mounting surface 51c1 is connected to the circuit pattern of an external circuit board (not shown), but the sub-mounting surface 51a3 may also be connected at the same time. The method of connecting to the circuit pattern of the external circuit board (not shown) is not particularly limited, but soldering is an example.

[0033] The second terminal 52, like the first terminal 51, is made of a conductive terminal plate or the like, and has a terminal body 52a and a protruding plate portion 52b, which are formed by bending a single conductive plate material such as a metal plate. The terminal body 52a has a substantially L-shaped outer end surface contact portion 52a1 which is attached with adhesive or the like to the other terminal mounting surface 24c1 formed on the outer end surface 24c of the flange portion 24 shown in Figure 2. The terminal body 52a further has a rectangular plate-shaped mounting side contact portion 52a2 which is formed by bending the outer end surface contact portion 52a1 in the X direction from the lower end in the Z direction.

[0034] The outer end contact portion 52a1 of the terminal body 52a shown in Figure 3 is fixed to the terminal mounting surface 24c1 of the flange portion 24 shown in Figure 2 with adhesive or the like, and the mounting side contact portion 52a2 shown in Figure 3 is in close contact with the mounting side core surface 24a shown in Figure 2 with a predetermined gap (the gap may be 0). The outer surface of the mounting side contact portion 52a2 located on the opposite side from the surface that is in contact with the mounting side core surface 24a shown in Figure 2 is the sub-mounting surface 52a3. The role of the sub-mounting surface 52a3 is the same as that of the sub-mounting surface 51a3.

[0035] The mounting-side contact portion 52a2 of the terminal body 52a shown in Figure 3 is integrally molded with a protruding plate portion 52b shown in Figure 3, which protrudes outward in the Y-axis direction from the mounting-side core surface 24a of the flange portion 24 shown in Figure 2, at the lower end of the flange portion 24. The protruding plate portion 52b has a base portion 52c that extends outward in the Y-axis direction flush with the mounting-side contact portion 52a2 of the terminal body 52a, and a bent tip portion 52d that is folded back and bent from the tip of the base portion 52c.

[0036] In this embodiment, the tip of the base 52c is bent so as to fold back upward in the Z-axis direction, and the outer surface of the base 52c located on the opposite side of the tip bent portion 52d becomes the main mounting surface 52c1, and the inner surface of the base 52c where the tip bent portion 52d is located becomes the splicing surface (wire connection surface) 52c2. As shown in Figure 1C, the lead end 42a, which is one of the leads of the other second wire 42 constituting the coil portion 40 shown in Figure 1B, is sandwiched between the splicing surface 52c2 of the base 52c and the tip bent portion 52d and crimped. After crimping, the terminal 52 and the lead end 42a of the wire 42 may be connected by laser welding or soldering.

[0037] In this embodiment, as shown in Figure 1C, the main mounting surface 52c1 and the sub-mounting surface 52a3 of the second terminal 52 are flush outer surfaces. Primarily, the main mounting surface 52c1 is connected to the circuit pattern of an external circuit board (not shown), but the sub-mounting surface 52a3 may also be connected at the same time. The method of connecting to the circuit pattern of the external circuit board (not shown) is not particularly limited, but soldering is an example.

[0038] In this embodiment, as shown in Figure 2, the second flange portion 26 has a similar configuration to the first flange portion 24, but it does not necessarily have to be the same. In this embodiment, the second flange portion 26 is composed of a rectangular parallelepiped as a whole, and rectangular notches 26c3 are formed on the lower sides of both sides in the Y-axis direction of the rectangular parallelepiped. The second flange portion 26 has a mounting-side core surface 26a which is the lower surface in the Z-axis direction, a non-mounting-side core surface 26b on the opposite side, an outer end surface 26c in the X-axis direction, an inner surface 26d facing the direction of the winding core portion 22, and a pair of sides 26e, 26e located on mutually opposite sides in the Y-axis direction.

[0039] Terminal mounting surfaces 26c1 are formed on both sides of the outer end surface 26c in the Y-axis direction, recessed inward in the X-axis direction (towards the center of the core 20) compared to the outer end surface 26c. A terminal insulating protrusion (not shown / corresponding to terminal insulating protrusion 24c2) is formed in the center of each terminal mounting surface 26c1 in the Y-axis direction, insulating the first terminal 51 and the second terminal 52 on the far side along the X-axis as shown in Figure 3. The inner surface of the outer end surface contact portion 51a1 of the terminal body 51a of the first terminal 51 and the inner surface of the outer end surface contact portion 52a1 of the terminal body 52a of the second terminal 52 are attached to each terminal mounting surface 26c1 shown in Figure 2, and bonded together as needed.

[0040] The mounting structure of the first terminal 51 and the second terminal 52 on the far side along the X-axis, as shown in Figure 3, to the second flange portion 26 shown in Figure 2, is the same as the mounting structure of the first terminal 51 and the second terminal 52 to the first flange portion 24 shown in Figure 2, as described above, so a detailed explanation is omitted.

[0041] As shown in Figure 1C, one lead end 41a of the first wire 41 is joined to the joint surface 51c2 of the first terminal 51, and one lead end 42a of the second wire 42 is joined to the joint surface 52c2 of the second terminal 52. The other lead end 41b of the first wire 41 is joined to the joint surface 52c2 of the second terminal 52 on the far side in the X-axis direction as shown in Figure 3, and the other lead end 42b of the second wire 42 as shown in Figure 1C is joined to the joint surface 51c2 of the first terminal 51 on the far side in the X-axis direction as shown in Figure 3. The means for these joining are not particularly limited, and laser welding and soldering are preferred, but are not limited to these, and examples include welding, resistance welding, ultrasonic welding, crimping, thermocompression bonding, and thermal fusion bonding.

[0042] As shown in Figures 1A, 1B, and 1D, a coil portion 40 is formed in the winding core portion 22 of the drum core 20. In this embodiment, the coil portion 40 is composed of two wires 41 and 42. The wires 41 and 42 are made of, for example, insulated conductors, and have a structure in which a core material made of a good conductor (for example, copper wire) is covered with an insulating coating film, and are wound around the winding core portion 22 in, for example, a two-layer structure. In this embodiment, the cross-sectional area of ​​the conductor portion of each wire 41 and 42 is the same.

[0043] In this embodiment, the first wire 41 and the second wire 42 are wound in a conventional bifilar manner on the winding core 22, but a cross portion may be formed at a predetermined position along the winding axis direction of the winding core 22.

[0044] In the manufacturing of the coil device 10, first, each pair of terminals 51 and 52 shown in Figure 3 are attached to the drum core 20 shown in Figure 2. Preferably, only the inner surfaces of the outer end contact portions 51a1 and 52a1 of each terminal 51 and 52 are bonded to the terminal mounting surface 24c1 or 26c1, respectively. Preferably, the mounting-side contact portions 51a2 and 52a2 of each terminal 51 and 52 are not bonded to the mounting-side core surfaces 24a and 26a of each flange portion 24 and 26. This is to prevent vibrations from an external circuit board (not shown) from being directly transmitted to the mounting-side core surfaces 24a and 26a of each flange portion 24 and 26.

[0045] Terminals 51 and 52 are made of metal, such as phosphor bronze, tough pitch steel, pure copper, brass, silver, gold, or a metal alloy that is solderable. The thickness of terminals 51 and 52 is not particularly limited, but is preferably 50 to 300 μm.

[0046] As wires 41 and 42, for example, a core material made of a good conductor such as copper (Cu) can be covered with an insulating material such as imide-modified polyurethane, and the outermost surface can be covered with a thin resin film such as polyester. The drum core 20 with the prepared terminals 51 and 52 installed and the wires 41-42 are set in a winding machine, and the wires 41-42 are wound around the winding core portion 22 of the drum core 20 in a predetermined order. The diameter of each wire 41 and 42 is not particularly limited, but is preferably 10-300 μm.

[0047] In this embodiment, a bifilar winding is performed on the first wire 41 and the second wire 42. The lead ends 41a, 42a, 41b, and 42b of the wire ends of the wound wires 41 and 42 are connected to the joint surface 51c2 or 52c2 of predetermined terminals 51 and 52 shown in Figure 3 after the bent tip pieces 51d or 52d are crimped onto them.

[0048] After winding the wires 41 and 42 onto the core 22, the flat core 30 is joined to the non-mounting side core surfaces 24b and 26b of the flanges 24 and 26 of the drum core 20. In this embodiment, as shown in Figure 4, the flat core 30 consists of a second magnetic material 30a composed of a plurality of second magnetic particles 30a1 and a coating 30b covering the entire surface of the flat-shaped second magnetic material 30a. The drum core 20 consists of a first magnetic material 20a composed of a plurality of first magnetic particles 20a1.

[0049] As shown in Figure 4, the first adhesive surface 20α of the first magnetic material 20a constituting the drum core 20 and the second adhesive surface 30α of the coating 30b formed on the surface of the flat core 30 are bonded together by the adhesive layer 32, thereby joining the drum core 20 and the flat core 30. The first adhesive surface 20α of the first magnetic material 20a constituting the drum core 20 corresponds to the two non-mounting side core surfaces 24b and 26b shown in Figure 1A. The second adhesive surface 30α of the coating 30b formed on the surface of the flat core 30 shown in Figure 4 corresponds to two locations on the inner surface of the flat core 30 that correspond to the non-mounting side core surface 24b shown in Figure 1A.

[0050] In this embodiment, the first magnetic material 20a shown in Figure 4 is, for example, a Mn-Zn or Ni-Zn ferrite, and the first magnetic material particles 20a1 are ferrite particles. The second magnetic material 30a is, for example, a metallic magnetic material, and the second magnetic material particles 30a1 are metallic magnetic material particles.

[0051] The metallic magnetic material is not particularly limited, but examples include Co-based amorphous alloys, Sendust (Fe-Si-Al; iron-silicon-aluminum), Fe-Si-Cr (iron-silicon-chromium), Permalloy (Fe-Ni), carbonyl iron-based materials, carbonyl Ni-based materials, and nanocrystals. The first magnetic material 20a has a higher relative permeability than the second magnetic material 30a, having a relative permeability 10 to 20 times or more than that of the second magnetic material 30a.

[0052] As shown in Figure 4, the second magnetic material 30a, which is made of a metallic magnetic material, has wider gaps between particles 30a1 and a higher porosity compared to the first magnetic material 20a, which is made of ferrite. For example, the porosity (B1) in the cross-section or on the surface of the first magnetic material 20a is preferably 5% or less, and more preferably 3% or less. Also, the porosity (B2) in the cross-section or on the surface of the second magnetic material 30a may be 3 times or more, 5 times or more, or 8 times or more, the porosity (B1) of the first magnetic material 20a. For example, the porosity (B2) of the second magnetic material 30a may be 10% or more, 15% or more, or 18% or more.

[0053] The porosity of the first magnetic material 20a and the second magnetic material 30a can be expressed, for example, as the area ratio of voids observed within a predetermined field of view when observing the polished surface (or cross-section) of the magnetic material under a microscope. Figure 5A is a micrograph of the polished surface of the first magnetic material composed of ferrite, and Figure 5B is a micrograph of the polished surface of the second magnetic material composed of metallic magnetic material, where the black areas represent voids. The void ratio can be calculated by performing a binarization process or the like on the photographic images shown in Figure 5A or Figure 5B. Metallic magnetic materials and ferrite can be molded into predetermined shapes using conventionally known methods.

[0054] As shown in Figure 4, a coating 30b is formed on the surface of the second magnetic material 30a, which is made of a metallic magnetic material. In this embodiment, it is preferable that the coating 30b is composed of a glass film containing glass, such as a glass coating film. The glass coating film can be formed, for example, by applying a glass slurry containing glass powder, a binder, and a solvent to the surface of the second magnetic material 30a and curing it. The application method is not particularly limited, and examples include spray coating and barrel coating.

[0055] The glass powder is not particularly limited, but for example, silica-boron glass is preferred among silica-based glasses, and examples include amorphous glass powders and crystalline glass powders such as lead borosilicate glass, bismuth borosilicate glass, and zinc borosilicate glass. The binder and solvent are not particularly limited.

[0056] As shown in Figure 4, the thickness t1 of the coating 30b present on the surface of the second magnetic material 30a is preferably in the range of 1 to 11 μm, more preferably in the range of 3 to 9 μm, and particularly preferably in the range of 4 to 8 μm. The thickness of the coating 30b present on the surface of the second magnetic material 30a at the position of the second adhesive surface 30α may be partially 0, but it is preferable that a coating 30b of 1 μm or more is formed at least partially. If the thickness t1 of this coating 30b is too thin, the adhesive constituting the adhesive layer 32 tends to seep from the surface into the interior of the second magnetic material 30a, and if the thickness t1 of the coating 30b is too thick, the characteristics of the coil device 10, such as the inductance, tend to deteriorate.

[0057] Preferably, the average thickness of the coating present on the surface of the second magnetic material at the position of the second adhesive surface is 2 to 10 μm, more preferably 2 to 8 μm, and particularly preferably 2 to 7 μm. The average thickness of the coating is calculated, for example, as the average of measurements taken at 10 or more measurement points spaced 5 μm apart along the direction of the coating's extension in a cross section perpendicular to the coating.

[0058] Preferably, the penetration depth t2 of the coating 30b that penetrates from the surface of the second magnetic material 30a into the interior of the second magnetic material 30a is 15 μm or less, more preferably 10 μm or less, and particularly preferably 8 μm or less. The penetration depth t2 of the coating may be 0 as long as the thickness of the coating 30b present on the surface of the second magnetic material 30a at the position of the second adhesive surface 30α is ensured.

[0059] However, due to the manufacturing process of the coating 30b, it is difficult to make the penetration thickness of the coating 30b zero. It may be greater than or equal to the particle size of the magnetic particles 30a1 located on the surface of the second magnetic material 30a, or more than twice or three times the particle size. If the penetration thickness t2 of the coating is too thick, the characteristics of the coil device, such as impedance, tend to deteriorate.

[0060] The penetration thickness t2 of the coating 30b can be controlled, for example, by adjusting the viscosity of the paste used to form the coating 30b. Similarly, the total thickness t0 of the coating 30b can also be controlled, for example, by adjusting the viscosity of the paste used to form the coating 30b. The total thickness t0 of the coating 30b is the thickness of the coating 30b present on the surface of the second magnetic material 30a plus the penetration thickness t2 of the coating 30b. This total thickness t0 of the coating 30b varies somewhat depending on the position of the second adhesive surface 30α, but is preferably 1 to 25 μm, more preferably 3 to 15 μm, or 5 to 15 μm.

[0061] In this embodiment, the surface of the coating 30b that contacts the adhesive layer 32 becomes the second adhesive surface and has a predetermined surface roughness Ra. The surface roughness Ra of the second adhesive surface, which is the surface of the coating 30b, is the arithmetic mean roughness as defined in JIS B0601, and is preferably 0.2 μm or more, and more preferably 0.3 μm or more.

[0062] The surface roughness Ra of the coating 30b in contact with the adhesive layer 32 is greater than or equal to a predetermined value, thereby improving the adhesive strength between the coating 30b and the adhesive layer 32. It is also preferable that the surface roughness Ra of the coating 30Bb in contact with the adhesive layer 32 is close to the surface roughness Ra of the first adhesive surface 20α of the first magnetic material 20a.

[0063] The surface roughness Ra of the coating 30b in contact with the adhesive layer 32 can be controlled by, for example, the composition and viscosity of the paste used to form the coating 30b, or by heat treatment conditions and post-treatment conditions.

[0064] The adhesive constituting the adhesive layer 32 shown in Figure 4 is not particularly limited, and for example, epoxy adhesives, silicone adhesives, modified acrylic resins, urethane resins, polyimide resins, etc., can be used. The adhesive may also contain fillers. The thickness t3 of the adhesive layer 32 shown in Figure 4 is preferably 2 to 10 μm, more preferably 2 to 8 μm or 2 to 4 μm. The value obtained by adding the surface thickness t1 of the coating 30b to the thickness t3 of the adhesive layer (t1 + t3) becomes the gap between the first magnetic material 20a and the second magnetic material 30a, and is preferably 20 μm or less. If the thickness t3 of the adhesive layer 32 is too thin, the adhesive strength tends to decrease, and if it is too thick, the gap becomes large, and the coil characteristics (inductance, etc.) tend to deteriorate.

[0065] In the coil device 10 according to this embodiment, the permeability of the second magnetic material 30a, which is made of a metallic magnetic material, is lower than that of the first magnetic material 20a, which is made of ferrite. However, the porosity of the second magnetic material 30a is higher than that of the first magnetic material 20a.

[0066] In this embodiment, a coating 30b made of a glass coating film is formed on the surface of the second magnetic material 30a at least at a position corresponding to the second adhesive surface 30α. The coating 30b blocks the adhesive components contained in the adhesive layer 32 from penetrating into the interior of the second magnetic material 30a. Therefore, it becomes easy to reliably and firmly bond the first magnetic material 20a and the second magnetic material 30a with a small amount of adhesive. As a result, the mechanical strength of the coil device 10 is improved. In addition, it becomes easy to construct the core of the coil device with a combination of materials with different magnetic permeability, and the DC superposition characteristics are also improved.

[0067] It was found that when attempting to directly bond a second magnetic material with high porosity to a first magnetic material with low porosity using an adhesive, the adhesive is absorbed into the surface of the second magnetic material, making it difficult to properly connect the first and second magnetic materials and resulting in a poor bond. Increasing the amount of adhesive to avoid the poor bond may adversely affect the high-frequency characteristics of the coil device.

[0068] In the coil device 10 of this embodiment, the second magnetic material 30a, which has a high porosity, has a coating 30b that fills the voids on the surface of the second magnetic material 30a at the position that becomes the second adhesive surface 30α. Therefore, the adhesive for forming the adhesive layer 32 is prevented from seeping into the interior of the second magnetic material 30a from the surface because the surface of the second magnetic material is blocked by the coating 30b. In addition, the adhesive for forming the adhesive layer 32 is less likely to seep into the interior of the first magnetic material 20a from the surface of the first magnetic material 20a, which has a low porosity.

[0069] Therefore, it becomes easier to form an adhesive layer with a small amount of adhesive, and the adhesive layer 32 reliably and firmly bonds the surface of the coating 30b of the second magnetic material 30a (second adhesive surface 30α) to the surface of the first magnetic material 20a (first adhesive surface 20α), thereby improving the mechanical strength of the coil device 10.

[0070] Furthermore, the coating 30b has a glass film containing glass. The coating 30b can also be made of a resin or other material that does not penetrate deeply into the interior from the surface of the second magnetic material 30a, but by using a glass film, the high-frequency characteristics of the coil device 10 are improved. This is because the glass component has superior impedance characteristics on the high-frequency side compared to the resin component.

[0071] Furthermore, in this embodiment, the first magnetic material 20a is made of ferrite. By making the first magnetic material ferrite, the permeability of the first magnetic material can be improved. Also, the second magnetic material 30a is made of metallic magnetic material. By making the second magnetic material 30a a metallic magnetic material, the permeability of the second magnetic material 30a can be set low. By combining these ferrite and metallic magnetic material by bonding them with an adhesive layer 32 to form a core, the DC superposition characteristics of the coil device 10 are further improved.

[0072] Furthermore, the drum core 20 is made of a first magnetic material 20a and has a winding core portion 22 around which the wires 41 and 42 shown in Figure 1A can be wound. By making the entire winding core portion 22 around which the wires 41 and 42 are wound out of the first magnetic material 20a of ferrite, the inductance of the coil device 10 can be improved.

[0073] Furthermore, the drum core 20, which consists of the first core, is integrally formed with the winding core portion 22 by the first magnetic material 20a, and further has flange portions 24 and 26 formed at both ends in the axial direction of the winding core portion 22. The flat plate core 30, which consists of the second core, has a plate-shaped second magnetic material 30a arranged to connect these flange portions 24 and 26. By constructing the second core with a plate-shaped second magnetic material 30a and firmly bonding the second core to the first magnetic material 20a via an adhesive layer 32, the mechanical strength of the coil device 10, which has further improved DC superposition characteristics, can be further improved.

[0074] It should be noted that the present invention is not limited to the embodiments described above, and can be modified in various ways within the scope of the present invention.

[0075] For example, in the embodiment described above, the flat core 30 has a second magnetic material 30a and its entire surface is covered with a coating 30b, but it is sufficient if at least the portion that becomes the second adhesive surface 30α is covered with the coating 30b. Also, in the embodiment described above, the coating 30b is composed of a glass coating film, but it is not limited to this and may be other coatings, such as a resin film, silicone, parylene, etc.

[0076] Furthermore, in the embodiment described above, multiple wires, including the first wire 41 and the second wire 42, are wound around the winding core portion 22 of the drum core 20. However, a single wire, for example, only the first wire 41, may also be wound around the winding core portion 22 of the drum core 20.

[0077] Furthermore, in the embodiment described above, the first terminal and the second terminal attached to the flange portions 24 and 26, respectively, are insulated from each other. However, when only a single wire, for example, the first wire 41, is wound around the winding core portion 22 of the drum core 20, the first terminal and the second terminal attached to the same flange portion 24 or 26 may be electrically connected.

[0078] Furthermore, although the above-described embodiment illustrates the case where a drum core 10 as the first core and a flat plate core 30 as the second core are joined with an adhesive layer 32, the invention is not limited to this, and a coil device can also be constructed by joining cores of other shapes via the adhesive layer 32. In any case, as shown in Figure 4, the second magnetic material 30a of the second core, which has a large porosity, has a coating 30b that fills the voids on the surface of the second magnetic material 30a at least at the position that becomes the second adhesive surface 30α, and the surface of the coating 30b becomes the second adhesive surface 30α and comes into contact with the adhesive layer 32. [Examples]

[0079] The present invention will be described below based on more detailed examples, but the present invention is not limited to these examples.

[0080] Example 1 A drum core 20 and a flat plate core 30 were prepared as shown in Figure 1A. The drum core 20 was composed of a first magnetic material 20a made of Ni-Zn ferrite. The porosity of the first magnetic material 20a was 2%. The surface roughness Ra of the first adhesive surface 20α of the first magnetic material 20a was 0.43 μm.

[0081] The flat core 30 was composed of a second magnetic material made of an Fe-Si-Cr metallic magnetic material. The porosity of the second magnetic material 30a was 20%. A coating 30b made of a silica-boron glass coating film was formed over the entire surface of the second magnetic material. The average thickness t1 of the coating 30b was 2 μm, with variations observed within a range of ±1 μm. The penetration depth t2 of the coating 30b was 5 μm or less. The surface roughness Ra of the coating 30b corresponding to the second adhesive surface 30α was 0.32.

[0082] Next, epoxy adhesive was applied to the position corresponding to the first adhesive surface 20α located on the upper surface of the flange portions 24 and 26 of the drum core 20. The second adhesive surface 30α of the flat core 30 (second magnetic material 30a with coating 30b) was then pressed against the adhesive-coated surface to cure the adhesive and form an adhesive layer 32. The thickness t3 of the cured adhesive layer 32 was 2 to 4 μm.

[0083] Five samples of the obtained coil device were prepared, and for each sample, the tensile shear adhesive strength between the drum core 20 and the flat plate core 30 was measured in accordance with JIS-K6850. This value was defined as the adhesive strength, and the average was calculated. The average adhesive strength of the samples in Example 1 was 40.0 N, as shown in Table 1.

[0084] [Table 1]

[0085] The porosity of the magnetic material was calculated by polishing the surface or cross-section of each magnetic material sample, observing the polished surface with a SEM, binarizing the obtained image to determine the ratio of the area occupied by voids to the entire image area, and then determining this ratio as the porosity. The surface roughness of each magnetic material was calculated as the arithmetic mean roughness for each magnetic material sample in accordance with JIS B 0601-2001. The thickness t1 of the coating 30b and the thickness t3 of the adhesive layer 32 were determined by cutting the area near the joint surface of the first magnetic material 20a and the second magnetic material 30a with a cross-section approximately perpendicular to the adhesive layer 32, and observing the cross-section with an SEM image.

[0086] Example 2 A sample of a coil device was prepared in the same manner as in Example 1, except that a flat core 30 was fabricated by forming a coating 30b consisting of a glass coating film on the surface of a second magnetic material 30a such that the average thickness t1 of the coating 30b was 5 μm (with a variation of ±1 μm) and the penetration depth t2 of the coating 30b was 5 μm or less. Measurements were performed in the same manner as in Example 1. The results are shown in Table 1.

[0087] Comparative Example 1 A sample of the coil device was prepared in the same manner as in Example 1, except that a second magnetic material without a coating 30b was used as the flat core 30. Measurements were performed in the same manner as in Example 1. The results are shown in Table 1.

[0088] Rating 1 Compared to Comparative Example 1, Example 1 achieved more than 1.5 times the adhesive strength. Furthermore, compared to Comparative Example 1, Example 2 achieved more than 3 times the adhesive strength.

[0089] Example 3 The DC superposition characteristics of a sample of the coil device from Example 1 were measured under normal temperature conditions.

[0090] Example 4 The DC superposition characteristics of a sample of the coil device from Example 2 were measured under the same conditions as in Example 3.

[0091] Comparative Example 2

[0092] A sample of the coil device was prepared in the same manner as in Example 3, except that a second magnetic material made of an Fe-Si-Cr-based metallic magnetic material without a coating 30b was used as the flat plate core 30. The DC superposition characteristics of the sample were measured under the same conditions as in Example 3.

[0093] Rating 2 Compared to Comparative Example 2, Examples 3 and 4 showed improvements in DC superposition characteristics of 1.07 times in Example 3 and 1.11 times or more in Example 4 compared to Comparative Example 2. [Explanation of Symbols]

[0094] 10… Coil device 20… Drum core (1st core) 20α... 1st adhesive surface 20a... first magnetic body 20a1... first magnetic particle 22… Core section 24… First guard section 24a… Core side of implementation 24b… Non-implementation side core 24c… Outer end surface 24c1… Terminal mounting surface 24c2… Terminal insulation protrusion 24c3… Notch 24d… Inner self 24e…side 26... Second guard section 26a… Core side of implementation 26b… Core surface on the non-implementation side 26c… Outer end surface 26c1… Terminal mounting surface 26c3… Notch 26d… Inner self 26e…side 30… Flat core (second core) 30α…Second adhesive surface 30a…Second magnetic body 30a1… Second magnetic particle 30b… Coating 32… Adhesive layer 40… Coil section 41… First wire 41a... One of the lead ends 41b... The other lead end 42… Second wire 42a... One of the lead ends 42b... The other lead end 51... 1st terminal (terminal fitting) 51a… Terminal body 51a1... Outer end surface contact area 51a2… Mounting side contact area 51a3… Sub-implementation surface 51b...Protruding plate part 51c... base 51c1… Main implementation surface 51c2… Wire connection surface (wire connection surface) 51d... Bent tip 52... 2nd terminal (terminal fitting) 52a… Terminal body 52a1… Outer end surface contact area 52a2… Mounting side contact area 52a3… Sub-implementation surface 52b...Protruding plate part 52c…base 52c… Main implementation side 52c2… Wire connection surface (wire connection surface) 52d... Bent tip

Claims

1. A first core having a first magnetic material, A second core having a second magnetic material with a higher porosity than the first magnetic material, A coil device having an adhesive layer that bonds the first adhesive surface of the first core and the second adhesive surface of the second core, The porosity of the second magnetic material is higher than that of the first magnetic material. The second magnetic material has a coating that fills the voids present on the surface of the second magnetic material, at least at the position that becomes the second adhesive surface. The aforementioned coating is a glass film containing glass, The penetration depth of the coating that extends from the surface of the second magnetic material into the interior of the second magnetic material is 15 μm or less. The thickness of the adhesive layer is 2 to 10 μm. At the second adhesive surface, the sum of the thickness of the coating present on the surface of the second magnetic material and the thickness of the adhesive layer is 20 μm or less. Coil device.

2. The coil device according to claim 1, wherein the surface roughness Ra of the second adhesive surface of the coating is 0.2 μm or more.

3. The coil device according to claim 1 or 2, wherein the thickness of the coating present on the surface of the second magnetic material at the position of the second adhesive surface is in the range of 1 to 11 μm.

4. The coil device according to any one of claims 1 to 3, wherein the penetration depth of the coating is greater than or equal to the particle size of the magnetic particles located on the surface of the second magnetic material.

5. The coil device according to any one of claims 1 to 4, wherein the first magnetic material is made of ferrite.

6. The coil device according to any one of claims 1 to 5, wherein the second magnetic material is made of a metallic magnetic material.

7. The coil device according to any one of claims 1 to 6, wherein the first core is made of the first magnetic material and has a winding core portion on which a wire can be wound.

8. The first core is integrally formed of the first magnetic material with respect to the winding core, and further has flanges formed at both ends of the winding core in the axial direction, The coil device according to claim 7, wherein the second core has a plate-shaped second magnetic material arranged to connect these flange portions.

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