Inductor and method for manufacturing the inductor

Abstract

To enhance insulation properties between a coil conductor and magnetic particles, and thereby enhance pressure resistance performance of an inductor.SOLUTION: An inductor includes an element assembly including a coil conductor around which a band-like conductor is wound, and a core including magnetic particles where the coil conductor is embedded and a resin, wherein the band-like conductor has a cross-sectional shape including a pair of parallel main surfaces and a pair of end faces connecting the main surfaces, the coil conductor is formed by winding the band-like conductor provided with a coating layer having an insulation layer coating a surface of the band-like conductor and a fusion layer coating the insulation layer, and an end face in an axial direction of the winding part around which the band-like conductor is wound is formed with a recess by the insulation layer, and at least a part of the recess is filled with a resin of the fusion layer.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an inductor and a method for manufacturing the inductor.

Background Art

[0002] In Patent Document 1, in the manufacturing process of a coil component having a base body (magnetic body part) containing magnetic particles and resin, a coil conductor embedded in the base body, and a pair of external electrodes electrically connected to the ends of the coil conductor, it is disclosed that a wire with an insulating coating is wound to form a wound part, and both ends of the wire are drawn out from the outer periphery of the wound part to form a coil conductor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the wound part of the coil conductor embedded in the base body, the conductors of each turn are arranged in the axial direction of the winding, and recesses are formed at the boundaries between the conductors of each turn. The rectangular flat wire used for the coil conductor has a part where the thickness of the insulating coating around the corners is thinner than other places. Therefore, at the deep position of the recess where the corners of the rectangular flat wire are located, the distance between the magnetic particles and the conductor becomes close, and there is a fear that the insulation property is lower than that in places other than the recess. Therefore, in order to improve the withstand voltage performance of the inductor, it has been required to improve the insulation property in the above-described recess.

[0005] An object of the present invention is to improve the withstand voltage performance of an inductor by enhancing the insulation between a coil conductor formed by winding a conductor having an insulating coating and magnetic particles contained in a base body.

Means for Solving the Problems

[0006] One aspect of the present invention includes an element body including a coil conductor formed by winding a strip conductor, and a core including magnetic particles and resin in which the coil conductor is embedded. The strip conductor has a cross-sectional shape including a pair of parallel main surfaces and a pair of end surfaces connecting between the main surfaces. The coil conductor is formed by winding the strip conductor provided with a coating layer having an insulating layer covering the surface of the strip conductor and a fusion layer covering the insulating layer. On the axial end surface of the winding portion around which the strip conductor is wound, Between two adjacent ones of the strip conductors by the insulating layer Opening axially a recess is formed, and in the recess Inside the resin of the fusion layer is Extending such that the surface connecting the axial vertices of the insulating layers of the two adjacent strip conductors is the boundary between the resin of the fusion layer and the core , which is an inductor. Another aspect of the present invention is Having a cross-sectional shape including a pair of parallel main surfaces and a pair of end surfaces connecting between the main surfaces a coil conductor forming step of forming a coil conductor by winding a strip conductor, embedding the coil conductor in a core including magnetic particles and resin such that the surface of the lead-out portion drawn from the winding portion of the coil conductor is exposed from the surface of the core, and molding the core under pressure to form an element body, a surface treatment step of performing surface treatment on the surface of the element body and the lead-out portion, and a plating step of forming an external electrode on the lead-out portion, The strip conductor has an insulating layer covering the surface of the strip conductor And the front a fusion layer covering the insulating layer And having a coating layer And in the coil conductor forming step, the strip conductor is wound such that the end surface of the strip conductor faces the axial direction of the winding portion in at least one of the coil conductor forming step and the element body molding step, Into the recess formed by the insulating layers of two adjacent strip conductors at the axial end surface of the winding portion filling the resin of the fusion layer By exuding, the resin of the fusion layer is made to enter the recess until the surface connecting the axial vertices of the insulating layers of the two adjacent strip conductors becomes the boundary between the resin of the fusion layer and the core , which is a method for manufacturing an inductor.

Advantages of the Invention

[0007] According to the present invention, by filling the resin of the fusion layer into the recess formed in the winding portion of the coil conductor, the intrusion of magnetic particles into the recess can be suppressed. Therefore, by enhancing the insulation between the coil conductor and the magnetic particles, the withstand voltage performance of the inductor can be improved.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view of the inductor according to this embodiment, viewed from the side of the upper surface 12, and FIG. 2 is a perspective view of the inductor, viewed from the side of the bottom surface 10. The inductor of this embodiment is configured as a surface-mounted electronic component, and includes a base body 2 having a substantially rectangular parallelepiped shape, which is one aspect of a substantially hexahedral shape, and a pair of external electrodes 4 provided on the surface of the base body 2.

[0010] Hereinafter, in the base body 2, the first main surface facing the mounting substrate (not shown) during mounting is defined as the bottom surface 10, the second main surface facing the bottom surface 10 is referred to as the upper surface 12, a pair of third main surfaces orthogonal to the bottom surface 10 are referred to as end surfaces 14, and a pair of fourth main surfaces orthogonal to the bottom surface 10 and the pair of end surfaces 14 are referred to as side surfaces 16. As shown in FIG. 1, the distance from the bottom surface 10 to the upper surface 12 is defined as the thickness T of the base body 2, the distance between the pair of side surfaces 16 is defined as the width W of the base body 2, and the distance between the pair of end surfaces 14 is defined as the length L of the base body 2. Also, the direction of the thickness T is defined as the thickness direction DT, the direction of the width W is defined as the width direction DW, and the direction of the length distance is defined as the length direction DL. The size of the inductor is, for example, a length L dimension of 2.0 mm, a width W dimension of 1.6 mm, and a thickness T dimension of 1.1 mm.

[0011] FIG. 3 is a perspective view showing the internal structure of the inductor. The base body 2 includes a coil conductor 20 and a substantially hexahedral core 30 in which the coil conductor 20 is embedded, and is configured as a molded inductor in which the coil conductor 20 is encapsulated in the core 30.

[0012] The core 30 is a molded body obtained by compression molding a mixed powder of magnetic particles and resin into a substantially hexahedral shape while enclosing the coil conductor 20.

[0013] In addition, the magnetic particles of the present embodiment include two types of particles with different particle sizes: first magnetic particles with relatively large average particle sizes and second magnetic particles with relatively small average particle sizes. As a result, during compression molding, the second magnetic particles, which are small particles, enter between the first magnetic particles, which are large particles, together with the resin, thereby increasing the filling rate of the magnetic particles in the core 30 and also increasing the magnetic permeability. In the present embodiment, the average particle sizes of the metal particles of the first magnetic particles and the second magnetic particles are 24.4 μm and 1.7 μm, respectively. The average particle size of the first magnetic particles is preferably 7 μm or more and 60 μm or less, and the average particle size of the second magnetic particles is preferably 1 μm or more and 4 μm or less. Further, by including magnetic particles with different average particle sizes from the first magnetic particles and the second magnetic particles, it may include particles with three or more types of particle sizes.

[0014] Both the first magnetic particles and the second magnetic particles are particles having metal particles and an insulating film with a film thickness of several nm or more and several tens of nm or less covering the surface thereof. By covering the metal particles with the insulating film, the insulation resistance and breakdown voltage are increased. In the first magnetic particles of this embodiment, Fe-Si-B amorphous alloy powder is used for the metal particles, and zinc phosphate glass with a thickness of 10 nm or more and 50 nm or less is used for the insulating film. In the second magnetic particles of this embodiment, carbonyl iron powder is used for the metal particles, and a silica film with a thickness of 5 nm or more and 15 nm or less is used for the insulating film.

[0015] In addition, in the mixed powder of this embodiment, an epoxy resin mainly composed of a phenolic alkyl type epoxy resin is used as the resin material. In this embodiment, the composition of the mixed powder is such that the first magnetic particles are 75 ± 10 wt%, the second magnetic particles are 25 ± 10 wt%, and the resin is 2.7 wt% or more and 3.5 wt% or less.

[0016] As shown in FIG. 3, the coil conductor 20 includes a winding portion 22 around which a conductive wire is wound and a pair of lead portions 24 drawn from the winding portion 22. The coil conductor 20 is composed of a conductive wire and a coating layer formed on the surface of the conductive wire. The conductive wire is a rectangular cross-section strip-shaped conductive wire (so-called flat wire) made of copper, with a thickness of 18 μm or more and 90 μm or less and a width of 240 μm or more and 340 μm or less. The coating layer is composed of an insulating layer formed on the surface of the strip-shaped conductive wire and a fusion layer formed on the surface of the insulating layer for bonding the strip-shaped conductive wires overlapping in the winding portion 22. The insulating layer is made of polyimide amide resin and has a thickness of 6 ± 2 μm. The fusion layer is made of polyimide resin and has a thickness of 2.5 ± 1.0 μm. Note that the thickness surface of the coil conductor may be a curved surface. When the thickness surface is a curved surface, the width of the conductive wire includes the curved portion of the thickness.

[0017] The winding portion 22 of the coil conductor 20 is formed by winding a strip-shaped conductor (hereinafter also simply referred to as a conductor) in a spiral shape such that both ends of the conductor are drawn out to the outer periphery and are connected to each other at the inner periphery. Inside the base body 2, the coil conductor 20 is embedded in the core 30 in a posture where the central axis of the winding portion 22 is along the thickness direction DT of the base body 2. The lead-out portion 24 is drawn out from the winding portion 22 to each of the pair of end faces 14, one main surface of the strip-shaped conductor is exposed from the base body 2, and the other main surface is embedded in the base body 2. One main surface of the strip-shaped conductor of the lead-out portion 24 that is exposed from the base body 2 is electrically connected to the external electrode 4. In FIG. 3, the axis of the winding portion 22 is indicated by the reference sign AX. The axis AX coincides with, for example, the thickness direction DT of the inductor 1. In the winding portion 22, the coil conductor 20 circulates around the axis AX, and the number of circulations of the coil conductor 20 is determined corresponding to the number of turns of the inductor 1.

[0018] The pair of external electrodes 4 are so-called L-shaped electrodes each constituted by an L-shaped member extending from each of the end faces 14 of the base body 2 to the bottom face 10. Each of the external electrodes 4 is connected to the lead-out portion 24 of the coil conductor 20 at the end face 14, and the portion 4A (FIG. 2) extending to the bottom face 10 is electrically connected to the wiring of the circuit board by an appropriate mounting means such as solder.

[0019] Also, a base body protective layer (not shown) is formed on the surface of the base body 2 excluding the range of the external electrode 4. The base body protective layer is, for example, a phenoxy resin and a novolak resin, and contains nanosilica as a filler. The base body protective layer is formed on the surface of the base body 2 with a thickness of 10 μm or more and 30 μm or less.

[0020] An inductor with such a configuration can improve the DC superposition characteristics by using a soft magnetic material for the magnetic particles, so it is used as an electronic component in an electric circuit where a large current flows, a choke coil in a DC-DC converter circuit or a power supply circuit, and also as an electronic component in electronic devices such as personal computers, DVD players, digital cameras, TVs, mobile phones, smartphones, automotive electronics, and medical and industrial machines. However, the uses of the inductor are not limited to this, and for example, it can also be used in tuning circuits, filter circuits, rectifier smoothing circuits, etc.

[0021] FIG. 4 is a schematic diagram of the manufacturing process of the inductor. As shown in the figure, the manufacturing process of the inductor includes a coil conductor forming process, a preform forming process, a thermoforming and curing process, a barrel polishing process, and an external electrode forming process.

[0022] The coil conductor forming process is a process of forming the coil conductor 20 from a conducting wire. In this process, the coil conductor 20 is formed into a shape having the above-described winding portion 22 and a pair of lead-out portions 24 by winding the conducting wire in a winding method called "alpha winding" (α winding). Alpha winding refers to a state in which the lead-out portions 24 at the start and end of winding of the conducting wire that functions as a conductor are located on the outer periphery and are wound in a spiral shape in two stages. The number of turns of the coil conductor 20 is not particularly limited.

[0023] The preform forming process is a process of forming a preform called a tablet. The preform is formed by pressing the above-mentioned mixed powder, which is the material of the base body 2, into a solid shape that is easy to handle. In this embodiment, two types of tablets are formed: a first tablet having a groove into which the coil conductor 20 can enter and having an appropriate shape (for example, E-shaped), and a second tablet having an appropriate shape (for example, I-shaped or plate-shaped) that covers the groove of the first tablet.

[0024] In the thermoforming and curing process, the first tablet, the coil conductor 20, and the second tablet are set in a molding die, and while applying heat, pressure is applied in the overlapping direction of the first tablet and the second tablet to cure them, thereby integrating the first tablet, the coil conductor 20, and the second tablet. As a result, the element body 2 with the coil conductor 20 encapsulated in the core 30 is molded. The thermoforming and curing process corresponds to the element body molding process in the present disclosure.

[0025] The barrel polishing process is a process of barrel-polishing this molded body, and by this process, rounding of the corners of the element body 2 is performed.

[0026] The external electrode forming process is a process of forming the external electrode 4 on the core 30, and includes an element body protective layer forming process, a surface treatment process, and a plating layer forming process.

[0027] The element body protective layer forming process is a process of coating the surface of this molded body with an insulating resin. By this process, an element body protective layer made of an insulating resin is formed, for example, on the entire surface of the molded body.

[0028] The surface treatment process is a process of modifying the surface of the electrode planned portion on the surface of the core 30 by irradiating the electrode planned portion with laser light. Here, the electrode planned portion refers to the range on the surface of the core 30 where the external electrode 4 is to be formed, and includes the portion where the lead-out portion 24 is exposed. Specifically, by irradiating laser light, in the range of the electrode planned portion, the element body protective layer on the surface of the core 30 and the coating layer of the lead-out portion 24 of the coil conductor 20 are removed, the resin on the surface of the core 30 is removed, and the insulating film on the surface of the magnetic particles exposed from the core 30 is removed. As a result, in the portion of the surface of the core 30 that is the electrode planned portion, the exposed area of the metal of the magnetic particles per unit area of the surface of the core 30 becomes larger than that of the other surface portions of the core 30. Note that after irradiating the laser light, a cleaning process (for example, an etching process) for cleaning the surface of the electrode planned portion may be performed.

[0029] In the plating layer formation step, a copper plating layer is formed at the planned electrode positions irradiated with laser light by barrel plating copper on the surface of the core 30. In addition to this, the plating layer may be formed by further providing a Ni plating layer and a Sn plating layer on the copper plating layer.

[0030] By the above-described external electrode formation step, the external electrode 4 composed of the plating layer is formed. Note that the external electrode 4 is not limited to an L-shaped electrode, and may be a so-called five-sided electrode provided from the entire surface of the end face 14 over a part of each of the bottom face 10, the top face 12, and the pair of side faces 16 adjacent to the end face 14. When the five-sided electrode is provided by immersing the core 30 in a conductive resin, the base body protective layer formation step is not necessarily required.

[0031] FIG. 5 is a cross-sectional view taken along a plane in the thickness direction (i.e., a plane orthogonal to the length direction) of the coil conductor 20 before winding used in the present embodiment. The coil conductor 20 includes a strip-shaped conductor 20a and a coating layer 20b formed on the surface of the strip-shaped conductor 20a. The coating layer 20b includes an insulating layer 25a formed on the surface of the strip-shaped conductor 20a and a fused layer 25b formed on the surface of the insulating layer 25a. Note that in FIG. 5, it should be noted that each point indicated by a white circle or a black circle extends in the direction of the paper surface normal to form a line.

[0032] The strip-shaped conductor 20a is configured such that, in a cross-sectional view in the thickness direction of the strip-shaped conductor 20a shown in FIG. 5, two opposing main surfaces 26 and two opposing side surfaces 27 adjacent to the main surfaces 26 protrude in a curved shape toward the outside of the strip-shaped conductor 20a to form a curved surface having a ridge line 27a (position indicated by a black circle in the figure). Here, the distance (height to the apex of the insulating layer 25a) from the reference plane RP to the insulating layer 25a on the ridge line 27a of the strip-shaped conductor, measured with respect to a plane passing through the boundary 26a (position indicated by a white circle in the figure) between the flat main surface 26 and the side surface 27 and orthogonal to the main surface 26 as the reference plane RP, is defined as the height h of the ridge line. The height h is, for example, 8 μm or more.

[0033] The coil conductor 20 is heated when being wound into a shape having a winding portion 22 and a lead-out portion 24 in the above-described coil conductor forming step. By being wound while being heated, the fusion layers 25b of the coil conductor 20 that constitute each turn of the winding portion 22 are pressure-bonded to each other, so that two adjacent coil conductors 20 are adhered by the fusion layer 25b and the winding portion 22 is integrated.

[0034] FIG. 6 is a cross-sectional view taken along line A-A of FIG. 3. As shown in FIG. 6, in the winding portion 22, a plurality of coil conductors 20 that constitute each turn of the winding portion 22 are arranged in a direction intersecting the axis AX. Further, on the end surface of the winding portion 22 in the direction of the axis AX, side surfaces 27 of the coil conductors 20 of each turn are arranged, and the side surfaces 27 are in contact with the mixture of the magnetic particles and the resin of the base body 2.

[0035] FIG. 7 is an enlarged view showing a portion P in FIG. 6. In FIG. 7, the center line in the width direction of the coil conductor 20 is indicated by reference numeral C. The reference numeral C is a straight line passing through a plane parallel to the main surface 26. The center line C has an inclination angle θ with respect to the axis AX. This inclination is caused by pressure being applied to the winding portion 22 in the coil conductor forming step and / or the thermoforming / curing step. The angle θ is, for example, -15° to +15°.

[0036] The coil conductor 20 has the insulating layer 25a adhered to the adjacent turns of the coil conductor 20 by the fusion layer 25b while maintaining the state where the strip-shaped conductor 20a is covered by the insulating layer 25a. In the coil conductor forming step, a part of the fusion layer 25b penetrates in the direction of the axis AX from between the adjacent coil conductors 20 and reaches the side surface 27. This deformation of the fusion layer 25b can occur not only in the coil conductor forming step but also in the thermoforming / curing step.

[0037] On the end face of the winding portion 22 in the axial direction of the axis AX, a recess 27c is formed between the side surface 27 of the coil conductor 20 that constitutes one turn and the side surface 27 of the coil conductor 20 that constitutes an adjacent turn. As described above, the side surface 27 of the strip conductor 20a is a curved surface that protrudes toward the outside of the strip conductor 20a. The recess 27c is a recess having a substantially triangular cross section formed due to the fact that the side surface 27 is a curved surface. For example, the recess 27c formed between two adjacent coil conductors 20 in the winding portion 22 is a space surrounded by the surface connecting the vertices of the insulating layer 25a on the side surfaces 27 of the two coil conductors 20 and the surfaces of the insulating layer 25a of these two coil conductors 20. Although not shown in the figure, the recess 27c extends along the side surface 27 in the direction orthogonal to the paper surface, that is, in the longitudinal direction of the coil conductor 20. Note that the side surface of the coil conductor 20 does not have to be a curved surface. For example, even if the side surface of the coil conductor 20 is linear or planar, unevenness such as the recess 27c can be formed simply by tilting the center line C in the width direction.

[0038] The magnetic particles 40 contained in the base body 2 include, as described above, the first magnetic particles 40a that are large particles and the second magnetic particles 40b and 40c that are small particles. Here, the second magnetic particles 40c refer to those with particularly small particle sizes among the small particles. This is just an example, and it is not essential for the magnetic particles 40 to include particles with different particle sizes corresponding to the second magnetic particles 40b and 40c. These magnetic particles 40 are mixed with resin after being adjusted in particle size to form the core 30. Since the recess 27c is, for example, a space larger than the second magnetic particles 40b and 40c, the second magnetic particles 40b and 40c enter the recess 27c in the thermoforming and curing process.

[0039] Since the coil conductor 20 is covered by the insulating layer 25a, even if the second magnetic particles 40b and 40c enter the recess 27c, the insulation of the coil conductor 20 is maintained. However, in the recess 27c, the thickness of the insulating layer 25a is thinner than other places, and the insulation between the magnetic particles 40 and the strip conductor 20a is likely to be lower than in places other than the recess 27c.

[0040] On the other hand, in the configuration shown in FIG. 7, the fused layer 25b that has penetrated from between adjacent coil conductors 20 in the winding portion 22 enters the recess 27c, and at least a part of the recess 27c is filled with the fused layer 25b. The penetration of the magnetic particles 40 into the recess 27c is inhibited by the amount by which the fused layer 25b fills the recess 27c. Therefore, since the insulation in the recess 27c is kept sufficiently high, the withstand voltage performance of the inductor 1 can be improved.

[0041] FIG. 8 is a micrograph of a region corresponding to the cross-sectional view shown in FIG. 7. In the micrograph shown in FIG. 8, since the boundary line between the insulating layer 25a and the fused layer 25b is thin, the contour of the recess 27c is shown by the dotted-line frame in FIG. 8. As appears in FIG. 8, in each of the plurality of recesses 27c formed in the outer peripheral portion of the winding portion 22, at least a part of the recess 27c is filled with the fused layer 25b. For this reason, the entry of the magnetic particles 40 into the deep positions of the recesses 27c is suppressed.

[0042] In the present embodiment, the recess 27c is filled with the fused layer 25b as a resin for inhibiting the entry of the magnetic particles 40 into the recess 27c. The fused layer 25b penetrates into the recess 27c from between two adjacent strip conductors 20a in the coil conductor forming step and / or the thermoforming and curing step. The amount or ratio of the cross-sectional area occupied by the penetrating fused layer 25b can be adjusted by the thicknesses of the fused layer 25b and the insulating layer 25a, the pressure during winding, the height h of the ridge line, and the like. Therefore, the step of filling the recess 27c with a material having insulating properties is unnecessary, and there is no need to prepare an insulating material separately from the coil conductor 20. Therefore, the withstand voltage performance of the inductor 1 can be improved by a method that does not involve an increase in the manufacturing process of the inductor 1.

[0043] The amount of the fused layer 25b filled in the recess 27c does not have to be an amount that fills the entire recess 27c, and it is sufficient that at least a part of the recess 27c is occupied by the fused layer 25b. For example, in the cross-section of the base body 2 shown in FIGS. 7 and 8, it is preferable that 30% or more of the cross-sectional area of the recess 27c is occupied by the fused layer 25b, and more preferably 50% or more of the cross-sectional area is occupied by the fused layer 25b.

[0044] Further, not all of the recesses 27c of the winding portion 22 need to be filled with the fusion layer 25b. Recesses 27c are formed at positions where the side surface 27 faces the magnetic particles 40 in the winding portion 22. In particular, at positions closer to the surface of the base body 2, an effect of enhancing insulation is expected. Specifically, regions E1 and E4 shown in FIG. 6 are located closer to the upper surface 12, and regions E2 and E3 are located closer to the bottom surface 10. It is effective to fill the recesses 27c with the fusion layer 25b in these regions E1 to E4.

[0045] For example, if the fusion layer 25b is filled in four or more recesses 27c randomly extracted from among the plurality of recesses 27c existing in the regions E1 to E4, an effect of enhancing the insulation between the coil conductor 20 and the magnetic particles 40 in the inductor 1 can be expected. Further, in the cross section of the four or more extracted recesses 27c, it is preferable that the cross-sectional area occupied by the fusion layer 25b is 30% or more on average, and more preferably, the fusion layer 25b occupies 50% or more of the cross-sectional area on average.

[0046] Furthermore, even when the fusion layer 25b is filled in at least one recess 27c in all of the regions E1, E2, E3, and E4, an effect of enhancing the insulation between the coil conductor 20 and the magnetic particles 40 in the inductor 1 can be expected. In this case, in the recess 27c filled with the fusion layer 25b, it is preferable that the cross-sectional area occupied by the fusion layer 25b is 30% or more, and more preferably, the fusion layer 25b occupies 50% or more of the cross-sectional area. Note that the cross-sectional area occupied by the fusion layer 25b in the recess 27c can be calculated, for example, from a microscopic photograph of the cross section of the inductor 1 as shown in FIG. 7.

[0047] All of the above-described embodiments and modifications illustrate one aspect of the present invention, and can be arbitrarily modified and applied without departing from the spirit of the present invention. For example, in the above embodiment, an example in which the coil conductor 20 is configured by winding a conductor wire in a winding method called α winding in the coil conductor forming step has been described. This is just an example, and the coil conductor 20 may be formed into a shape having a winding portion 22 by winding the conductor wire in another winding method. In addition, the horizontal, vertical, and other directions, various numerical values, shapes, and materials in the above-described embodiments include ranges (so-called equivalent ranges) that exhibit the same effects as those directions, numerical values, shapes, and materials, unless otherwise specified.

[0048] [Configuration supported by the above embodiment] The above-described embodiment supports the following configuration.

[0049] (Configuration 1) A base body including a coil conductor formed by winding a strip conductor, and a core including magnetic particles and resin in which the coil conductor is embedded, the strip conductor having a cross-sectional shape including a pair of parallel main surfaces and a pair of end surfaces connecting between the main surfaces, the coil conductor being formed by α-winding the strip conductor provided with a coating layer having an insulating layer covering the surface of the strip conductor and a fusion layer covering the insulating coating layer, and a recess covered by the insulating layer being formed at an end surface in the axial direction of the winding portion around which the strip conductor is wound, and at least a part of the recess being filled with the resin of the fusion layer, an inductor. According to the inductor of Configuration 1, by filling the recess formed by winding the strip conductor with a fusion layer that is a part of the coating layer of the strip conductor, the insulation between the strip conductor and the magnetic particles in the recess can be enhanced. Therefore, the withstand voltage performance of the inductor can be improved.

[0050] (Configuration 2) The inductor according to Configuration 1, wherein the end surface of the strip conductor forms a curved surface that protrudes in the axial direction. According to the inductor of Configuration 2, by filling the recess formed by the convex end face of the strip conductor with the fusion layer, the insulation between the strip conductor and the magnetic particles in the recess can be enhanced.

[0051] (Configuration 3) In the inductor according to Configuration 2, the height from the boundary point between the main surface and the end surface of the strip conductor to the apex of the insulating layer covering the end surface, measured with respect to the plane orthogonal to the main surface passing through the boundary point, is 8 μm or more. According to the inductor of Configuration 3, due to the curved end face of the strip conductor, in the configuration where the insulating layers of two adjacent strip conductors form a recess, the insulation between the strip conductor and the magnetic particles in the recess can be enhanced.

[0052] (Configuration 4) In the cross-section of the base body, the area of the resin of the fusion layer in the cross-sectional area of the recess is 30% or more in the inductor according to any one of Configurations 1 to 3. According to the inductor of Configuration 4, since the fusion layer occupies 30% or more of the cross-sectional area of the recess, the insulation between the strip conductor and the magnetic particles in the recess can be more reliably enhanced.

[0053] (Configuration 5) A coil conductor forming step of winding a strip conductor to form a coil conductor, embedding the coil conductor in a core containing magnetic particles and resin such that the surface of the lead-out portion drawn from the wound portion of the coil conductor is exposed from the surface of the core, a base body molding step of pressing the core to mold a base body, a surface treatment step of performing a surface treatment on the surface of the base body and the lead-out portion, and a plating step of forming an external electrode on the lead-out portion. In the coil conductor forming step, the coil conductor is formed by α-winding the strip conductor provided with a coating layer having an insulating layer covering the surface of the strip conductor and a fusion layer covering the insulating layer. In at least one of the coil conductor forming step and the base body molding step, a recess covered by the insulating layer is formed in the axial end face of the wound portion where the strip conductor is wound, and at least a part of the recess is filled with the resin of the fusion layer. A method for manufacturing an inductor. According to the method for manufacturing the inductor of Configuration 5, by filling the recess formed by winding the strip conductor with the fused layer which is a part of the coating layer of the strip conductor, the insulation between the strip conductor and the magnetic particles in the recess can be enhanced, and the withstand voltage performance of the inductor can be enhanced.

Explanation of Signs

[0054] 1... Inductor, 2... Element body, 4... External electrode, 10... Bottom surface, 12... Upper surface, 14... End face, 16... Side surface, 20... Coil conductor, 20a... Strip conductor, 20b... Coating layer, 22... Winding part, 24... Lead-out part, 25a... Insulation layer, 25b... Fused layer, 26... Main surface, 26a... Boundary, 27... Side surface, 27a... Ridge line, 27c... Recess, 30... Core, 40... Magnetic particles, 40a... First magnetic particles, 40b, 40c... Second magnetic particles.

Claims

1. A base body comprising: a coil conductor formed by winding a strip conductor; and a core including magnetic particles and resin in which the coil conductor is embedded. The strip conductor has a cross-sectional shape including a pair of parallel main surfaces and a pair of end surfaces connecting between the main surfaces. The coil conductor is formed by winding the strip conductor provided with a coating layer having an insulating layer covering the surface of the strip conductor and a fusion layer covering the insulating layer. On an end surface in the axial direction of a winding portion around which the strip conductor is wound, recesses that open in the axial direction are formed by the insulating layers of two adjacent strip conductors. An inductor, wherein resin of the fusion layer extends inside the recess, and a surface connecting apexes in the axial direction of the insulating layers of the two adjacent strip conductors is a boundary between the resin of the fusion layer and the core.

2. The end surface of the strip conductor forms a curved surface that protrudes in the axial direction. The inductor according to claim 1.

3. The height from a reference plane, which is a plane passing through a boundary point between the main surface and the end surface of the strip conductor and perpendicular to the main surface, to an apex of the insulating layer covering the end surface is 8 μm or more. The inductor according to claim 2.

4. In a cross-section of the base body, the area of the resin of the fusion layer in the cross-sectional area of the recess is 30% or more. The inductor according to any one of claims 1 to 3.

5. A coil conductor forming step of forming a coil conductor by winding a strip conductor having a cross-sectional shape including a pair of parallel main surfaces and a pair of end surfaces connecting between the main surfaces; A base body molding step of embedding the coil conductor in a core including magnetic particles and resin so that a surface of a lead-out portion drawn from a winding portion of the coil conductor is exposed from a surface of the core, and molding the base body by pressing the core; A surface treatment step of performing a surface treatment on surfaces of the base body and the lead-out portion; A plating step of forming an external electrode on the lead-out portion; and the strip conductor has a coating layer having an insulating layer covering the surface of the strip conductor and a fusion layer covering the insulating layer. In the coil conductor forming step, the strip conductor is wound so that the end surface of the strip conductor faces the axial direction of the winding portion. In at least one of the coil conductor forming step and the base body molding step, by causing the resin of the fusion layer to exude into recesses formed by the insulating layers of two adjacent strip conductors on an end surface in the axial direction of the winding portion. Fill the resin of the fusion layer into the concave portion until the surface connecting the axial vertices of the insulating layers of the two adjacent strip-shaped conductive wires becomes the boundary between the resin of the fusion layer and the core. Method for manufacturing an inductor.

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