JP7735992B2 - Inductor manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing an inductor and to an inductor.

Patent Document 1 discloses a surface-mount inductor that includes a coil formed by winding a conductive wire and a molded body that incorporates the coil using a sealing material containing resin and magnetic material. This inductor is manufactured by placing the coil and a tablet with a flat, plate-shaped periphery and columnar protrusions inside the cavity of a molding die, and then heating and compressing the molded body using a resin molding method.

JP 2010-245473 A

In order to achieve miniaturization, the manufacturing method for this type of inductor leaves room for improvement in the precision of positioning the coil conductor inside the molded body. Furthermore, because the characteristics of an inductor are affected by the position of the coil conductor inside the molded body, there is also room for improvement in suppressing the variation in characteristics between manufactured inductors.

One aspect of the present invention is a method for manufacturing an inductor including an element body having a coil conductor having a winding portion around which a conducting wire is wound and a lead-out portion led out from the winding portion, and a core containing metal magnetic powder and resin and in which the coil conductor is embedded, wherein the element body is formed by arranging a preform and the coil conductor arranged in the preform inside a cavity formed in a molding die and compression molding the preform, and the molding die is formed so that the cavity is rectangular when viewed from above, and the cavity is formed by compressing the preform and the core. a pair of first inner wall surfaces facing each other, a pair of second inner wall surfaces facing each other, and first protrusions formed on each of the pair of first inner wall surfaces at opposing positions , wherein the first protrusions protrude toward the inside of the cavity and extend parallel to the first inner wall surfaces, and the coil conductor is arranged inside the cavity with the winding axis of the coil conductor parallel to the direction in which the first protrusions extend, the coil conductor is close to the first protrusions , and the wide surface of the lead-out portion is in contact with the second inner wall surfaces .

This invention makes it easier to suppress variations in characteristics between inductors.

1 is a perspective view of an inductor according to a first embodiment of the present invention, viewed from the top side; FIG. 2 is a perspective view of the inductor according to the first embodiment, viewed from the bottom side. FIG. 2 is a perspective view showing the internal configuration of the inductor according to the first embodiment. 3A to 3C are schematic diagrams illustrating a manufacturing process of the inductor according to the first embodiment. FIG. 2 is a cross-sectional view of the molding die according to the first embodiment. FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 5 according to the first embodiment. FIG. 2 is a plan view of the element body according to the first embodiment as viewed from the top surface side. FIG. 2 is a side view of the element body according to the first embodiment, viewed from the side. 10 is a graph showing the results of a simulation according to an example. FIG. 10 is a cross-sectional view of an upper mold according to a second embodiment. FIG. 10 is a plan view of an element body according to a second embodiment, viewed from the top side. FIG. 10 is a cross-sectional view of a basic molding die according to a third embodiment.

[Embodiment 1]
A method for manufacturing the inductor 1 according to the first embodiment and the inductor 1 will be described below.
(Overall inductor configuration)
FIG. 1 is a perspective view of an inductor 1 according to this embodiment as viewed from a top surface 12 side, and FIG. 2 is a perspective view of the inductor 1 as viewed from a bottom surface 10 side.
The inductor 1 of this embodiment is configured as a surface-mounted electronic component, and includes a base body 2 having an approximately rectangular parallelepiped shape, which is one form of an approximately hexahedral shape, and a pair of external electrodes 4 provided on the surface of the base body 2.

Hereinafter, in the element body 2, a first main surface that faces a mounting substrate (not shown) during mounting will be defined as a bottom surface 10, a second main surface opposite the bottom surface 10 will be referred to as a top surface 12, a pair of third main surfaces that are perpendicular to the bottom surface 10 will be referred to as end surfaces (second side surfaces) 14, and a pair of fourth main surfaces that are perpendicular to the bottom surface 10 and the pair of end surfaces 14 will be referred to as side surfaces (first side surfaces) 16. The pair of end surfaces 14 are disposed opposite each other. The pair of side surfaces 16 are also disposed opposite each other. A pair of first grooves 16a that are parallel to each other are formed in each of the pair of side surfaces 16. Details of the first grooves 16a will be described later.
1, the distance from the bottom surface 10 to the top surface 12 is defined as the thickness T of the element body 2, the distance between a pair of side surfaces 16 is defined as the width W of the element body 2, and the distance between a pair of end surfaces 14 is defined as the length L of the element body 2. Furthermore, 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 nominal size of the inductor 1 as a finished product is, for example, a length L of 1.4 mm, a width W of 1.2 mm, and a thickness T of 0.65 mm.

Hereinafter, a plane along the DL direction and DT direction (a plane perpendicular to the DW direction) will be referred to as an LT plane, a plane along the DT direction and DW direction (a plane perpendicular to the DL direction) will be referred to as a TW plane, and a plane along the DL direction and DW direction (a plane perpendicular to the DT direction) will be referred to as an LW plane. Furthermore, cross sections of inductor 1 along the LT plane, TW plane, and LW plane will be referred to as the LT cross section, TW cross section, and LW cross section, respectively.

FIG. 3 is a perspective view showing the internal configuration of the inductor 1. As shown in FIG.
The element 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 sealed in the core 30 .

The core 30 is a molded body formed by compressing and heating a powder mixture of magnetic particles (metallic magnetic powder) and resin, with the coil conductor 20 enclosed inside, into an approximately hexahedral shape.

The magnetic particles of this embodiment are made of a soft magnetic material and contain particles of two different particle sizes: first magnetic particles that are large particles with a relatively large average particle size, and second magnetic particles that are small particles with a relatively small average particle size. As a result, during compression molding, the second magnetic particles, which are small particles, enter between the first magnetic particles, along with the resin, thereby increasing the filling rate of the magnetic particles in the core 30 and also increasing the magnetic permeability.
In this embodiment, the average particle size of the metal particles of the first magnetic particles is 20 μm or more and 28 μm or less, and the average particle size of the metal particles of the second magnetic particles is 1 μm or more and 6 μm or less. The average particle size of the first magnetic particles is preferably 21.4 μm or more and 27.4 μm or less, and the average particle size of the second magnetic particles is preferably 1.5 μm or more and 1.8 μm or less. Furthermore, the magnetic particles may contain particles with different average particle sizes from the first magnetic particles and the second magnetic particles, thereby containing particles of three or more different particle sizes.

The first magnetic particles and the second magnetic particles are both particles having a metal particle, an oxide film covering the surface of the metal particle, and an insulating film covering the surface of the oxide film. By covering the metal particle with the oxide film and the insulating film, the insulation resistance and the withstand voltage are increased.
In the first magnetic particles of this embodiment, Fe-Si-B amorphous alloy powder is used as the metal particles. The oxide film of the first magnetic particles is composed of two layers, an SiO layer and an Fe ₂ SiO ₄ layer, and the total thickness of the oxide film is 20 nm to 155 nm. The insulating film of the first magnetic particles is made of phosphate glass and has a thickness of 10 nm to 50 nm.

In addition, in this embodiment, the second magnetic particles use carbonyl iron powder as the metal particles. The oxide film of the second magnetic particles is iron oxide formed by surface oxidation of the carbonyl iron powder, which is a metal particle. Furthermore, the insulating film of the second magnetic particles is a sol-gel reaction product containing silica. This increases the slipperiness of the surface of the second magnetic particles, making it easier for the second magnetic particles to penetrate between the first magnetic particles during the element molding and hardening process of the element body 2, which will be described later. As a result, the density of the magnetic material in the core 30 can be further increased, further increasing the relative permeability of the core 30.

In addition, in the first magnetic particles, the metal particles may be Fe—Si—Cr alloy powder, Fe—Ni—Al alloy powder, Fe—Cr—Al alloy powder, Fe—Si—Al alloy powder, Fe—Ni alloy powder, or Fe—Ni—Mo alloy powder.
In the first magnetic particles, the insulating film may be made of phosphoric acid, zinc phosphate, manganese phosphate, glass, or resin.

The resin material contained in the mixed powder of this embodiment includes bisphenol A-type epoxy resin and rubber-modified epoxy resin. This makes it possible to manufacture an inductor 1 with improved element body 2 strength and toughness.

In this embodiment, the magnetic powder contained in the mixed powder is such that the first magnetic particles account for 70 wt% to 85 wt% and the second magnetic particles account for 15 wt% to 30 wt% of the total weight of the magnetic particles contained in the mixed powder. Furthermore, the resin contained in the mixed powder is 2.0 wt% to 3.5 wt% of the total weight of the magnetic powder and resin. The first magnetic particles are preferably 70 wt% to 80 wt%, and the second magnetic particles are preferably 20 wt% to 30 wt%. Furthermore, the resin is preferably 2.7 wt% to 30 wt%.

As shown in Figure 3, the coil conductor 20 comprises a winding portion 22 in which a conductor wire is wound spirally around the winding axis K in two layers, one above the other, with both ends positioned on the outer periphery and connected to each other on the inner periphery; a pair of lead-out portions 23 drawn out from the winding portion 22; and a pair of external electrode connection portions 24, which are conductor wire portions connected to the lead-out portions 23, respectively, for connection to external electrodes described below. The winding portion 22 includes two winding regions 22a and 22b overlapping along the winding axis K. The conductor wires of the winding regions 22a and 22b are connected to each other along part of their inner peripheries.

The coil conductor 20 is embedded within the element body 2 so that the winding axis K is aligned with the thickness direction DT of the element body 2.

The wire that makes up the coil conductor 20 is composed of a conductor and a coating layer formed on the surface of the conductor. The conductor is a flat, rectangular wire with a cross section, and the conductor is a copper strip conductor with a rectangular cross section. The conductor has a thickness of 52 μm to 118 μm and a width of 110 μm to 180 μm. The coating layer is composed of an insulating layer formed on the surface of the strip conductor and a fusion layer formed on the surface of the insulating layer to bond the overlapping strip conductors together in the winding portion 22. The insulating layer is made of, for example, polyimide amide resin and has a thickness of 3 μm. The fusion layer is made of, for example, polyamide resin and has a thickness of 1 μm to 25 μm.

The lead-out portion 23 is drawn out from the winding portion 22 and electrically connected to the external electrode 4 via external electrode connecting portions 24 that are drawn out and exposed to each of the pair of end faces 14 .
The pair of external electrodes 4 are so-called L-shaped electrodes, consisting of L-shaped members extending from each of the end faces 14 of the element body 2 to the bottom face 10. Each of the external electrodes 4 is connected to an external electrode connecting portion 24 of the coil conductor 20 at the end face 14, and a portion 4A (FIG. 2) extending to the bottom face 10 is electrically connected to wiring on a circuit board by an appropriate mounting means such as solder.

An element protective layer (not shown) is formed on the surface of the element body 2 excluding the area of the external electrodes 4. The element protective layer is, for example, a resin made by adding phenoxy resin to novolac resin, and contains nanosilica as a filler. The element protective layer is formed on the surface of the element body 2 to a thickness of 10 μm or more and 30 μm or less. The thickness of the element protective layer is preferably 10 μm or more and 20 μm or less, and more preferably 15 μm or less.

The inductor 1 configured as described above can improve DC bias characteristics by using a soft magnetic material for the magnetic particles, and is therefore used as an electronic component in electrical circuits through which large currents flow, as a choke coil in DC-DC converter circuits and power supply circuits, and as an electronic component in electronic devices such as personal computers, DVD players, digital cameras, TVs, mobile phones, smartphones, car electronics, and medical and industrial machinery. However, the uses of inductor 1 are not limited to these, and it can also be used in tuning circuits, filter circuits, rectifying and smoothing circuits, etc.

(Outline of inductor manufacturing process)
FIG. 4 is a schematic diagram of the manufacturing process of the inductor 1.
As shown in the figure, the manufacturing process of the inductor 1 includes a coil conductor forming step, a preform forming step, an element molding and hardening step, and an external electrode forming step.

The coil conductor formation process is a process for forming the coil conductor 20 from a conducting wire. In this process, the coil conductor 20 is formed into a shape having the aforementioned winding portion 22, lead-out portion 23, and external electrode connection portion 24 by winding the conducting wire using a method known as "alpha winding." Alpha winding refers to a state in which the conducting wire, which functions as a conductor, is wound in two stages in a spiral shape so that the lead-out portions 23 at the beginning and end of the winding are located on the outer periphery. There is no particular limitation on the number of turns in the coil conductor 20.

The preform forming step is a step 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 form that is easy to handle.In this embodiment, two types of tablets are formed: a first tablet of an appropriate shape (e.g., T-shaped) in which the coil conductor 20 is placed, and a second tablet of an appropriate shape (e.g., I-shaped or plate-shaped) in which the coil conductor 20 is sandwiched between the first tablet and the second tablet.

In the element molding and hardening process, the first tablet, coil conductor, and second tablet are placed in a molding die, and while applying heat, pressure is applied in the overlapping direction of the first tablet and second tablet, hardening them to integrate the first tablet, coil conductor, and second tablet. This results in the formation of an element 2 in which the coil conductor 20 is enclosed in the core 30. Details of the element molding and hardening process will be described later. The element 2 obtained in this process may also be subjected to barrel polishing to remove burrs and the like that have formed on the element 2 and to chamfer the corners of the element 2.

The external electrode formation process is a process for forming the external electrodes 4 on the element body 2, and includes an element body protective layer formation process, a surface treatment process, and a plating layer formation process.

The element body protection layer formation process is a process in which the entire surface of the element body 2 is coated with an insulating resin.

The surface treatment process involves modifying the surface of the planned electrode locations on the surface of the core 30 by irradiating the locations with laser light. Here, the planned electrode locations refer to the areas on the surface of the core 30 where the external electrodes 4 are to be formed, including the areas where the external electrode connection portions 24 are exposed. Specifically, by irradiating the laser light, the element body protective layer on the surface of the element body 2 and the coating layer on the external electrode connection portions 24 of the coil conductor 20 are removed within the planned electrode locations, the resin on the surface of the core 30 is removed, and the insulating film on the surfaces of the magnetic particles exposed from the core 30 is removed. As a result, the exposed area of the metal of the magnetic particles per unit area of the core 30's surface is larger in the planned electrode locations than in other surface areas of the core 30. After irradiating the laser light, a cleaning process (e.g., etching) may be performed to clean the surfaces of the planned electrode locations.

In the plating layer formation process, copper is barrel-plated onto the surface of the core 30, forming a copper plating layer at the electrode locations irradiated with laser light. In addition, the plating layer may be formed by providing a Ni plating layer and a Sn plating layer on top of the copper plating layer.

The manufacturing method of the inductor 1 in this embodiment and the details of the inductor 1 are further explained below.

(Details of the element molding and hardening process)
Figure 5 is a cross-sectional view of the molding die 50 in the element molding and curing step, showing the molding die 50 in the T-W cross section. Figure 6 is a cross-sectional view taken along the VI-VI cross section of Figure 5. The molding die 50 has an upper die 51 in which a cavity 51a is formed, a lower die 53 that closes one end of the cavity 51a, and a punch 55 that is inserted into the cavity 51a from the opposite side of the lower die 53. The molding die 50 compression-molds the element 2 by using the punch 55 to compress the components of the element 2 placed on the lower die 53 inside the cavity 51a.

The upper mold 51 is a mold having an outer shape of a rectangular parallelepiped. The cavity 51a is a hole formed through the upper mold 51 in the thickness direction DT and has a substantially rectangular shape when viewed from the thickness direction DT. The upper mold 51 has a pair of opposing first inner wall surfaces 56 and a pair of opposing second inner wall surfaces 54 formed therein, and the cavity 51a is a hole formed by being surrounded by the pair of first inner wall surfaces 56 and the pair of second inner wall surfaces 54. The first inner wall surfaces 56 and the second inner wall surfaces 54 are perpendicular to each other. As shown in FIG. 6 , the pair of first inner wall surfaces 56 are spaced apart by a width W0. The pair of second inner wall surfaces 54 are spaced apart by a length L0. The width W0 corresponds to the dimension of the element body 2 of the inductor 1 in the width direction DW, and is 1.15 mm in the first embodiment. Furthermore, length L0 corresponds to the dimension of element body 2 in the longitudinal direction DL, and is 1.35 mm in embodiment 1. The first inner wall surface 56 and second inner wall surface 54 form the side surface 16 and end surface 14 of element body 2, respectively, during compression molding of element body 2.

First protrusions 56a are formed on each of the pair of first inner wall surfaces 56, protruding toward the inside of the cavity 51a. The protrusion amount of the first protrusions 56a is, for example, approximately 50 μm. The first protrusions 56a extend parallel to the thickness direction DT. The pair of first protrusions 56a are provided at opposing positions on the pair of first inner wall surfaces 56, and the distance between their tips is set to W1. The first protrusions 56a are formed so that their average dimension in the length direction DL is smaller than their dimension in the thickness direction DT. The pair of first protrusions 56a each form a first groove 16a, described below, during compression molding of the base body 2.

The lower mold 53 is a generally rectangular plate-like member. The lower mold 53 closes one end of the cavity 51a in the thickness direction DT, which opens to the outside of the upper mold 51, from the outside of the cavity 51a. The lower mold 53 forms the bottom surface 10 of the element body 2 during compression molding of the element body 2.

The punch 55 is a member having a cross-section similar to the shape of the cavity 51a when viewed along the thickness direction DT, and is movable along the thickness direction DT. The punch 55 is inserted into the cavity 51a from the other end of the cavity 51a that is not blocked by the lower die 53. The outer edge of the punch 55 inserted into the cavity 51a follows the first inner wall surface 56, the second inner wall surface 54, and the first protrusion 56a of the upper die 51, respectively.

As shown in Figures 5 and 6, a first tablet 71, a coil conductor 20, and a second tablet 73 are arranged inside the cavity 51a.

The first tablet 71 is a preform formed by compression molding the mixed powder and is placed on the lower mold 53. The first tablet 71 is a so-called T-shaped preform and has a flat portion 71a and a shaft portion 71b. The flat portion 71a is a roughly rectangular plate-like portion, and its dimension along the length direction DL is smaller than the length L0. The dimension of the flat portion 71a in the width direction DW is set to be equal to the distance W1 between the first protrusions 56a. Therefore, the flat portion 71a placed in the cavity 51a is positioned along the pair of first protrusions 56a and is positioned in the width direction DW by the first protrusions 56a. The shaft portion 71b is formed in the center of the flat portion 71a when viewed in the thickness direction DT and protrudes toward the thickness direction DT.

The coil conductor 20 is placed on the flat plate portion 71a at a position where the shaft portion 71b is inserted into the winding portion 22. The coil conductor 20 is arranged in the cavity 51a with the winding axis K aligned along the thickness direction DT of the upper mold 51 and the external electrode connection portion 24 aligned along the second inner wall surface 54. That is, the coil conductor 20 is arranged in the cavity 51a with the winding axis K parallel to the extension direction of the pair of first protrusions 56a. Furthermore, the dimension of the winding portion 22 in the width direction DW is equal to the distance W1 between the tips of the pair of first protrusions 56a in the width direction DW. In other words, the distance W1 between the tips of the pair of first protrusions 56a is set to be equal to the dimension of the winding portion 22 in the width direction DW. The outer periphery of the winding portion 22 is arranged in a position where it contacts the tips of the pair of first protrusions 56a.

The second tablet 73 is a preformed body obtained by compression molding the mixed powder, and is arranged between the first tablet 71 and the second tablet 73, with the coil conductor 20 sandwiched between them. The second tablet 73 is a so-called I-shaped preformed body in a flat plate shape, and is arranged in a direction perpendicular to the thickness direction DT.

In the element molding and curing process, while heat is being applied to the molding die 50, the components of the element 2 arranged inside the cavity 51a as described above are compressed by a punch 55 moving toward the lower die 53 to form the core 30 in which the coil conductor 20 is embedded. This results in the formation of the element 2 having the coil conductor 20 and the core 30.

At this time, movement of the winding portion 22 in the width direction DW is restricted by the pair of first protrusions 56a. As a result, in the element body 2 molded in the element body molding and curing process, the position of the coil conductor 20 in the width direction DW is less likely to vary from one element body 2 to another. As described in the examples below, the position of the coil conductor 20 in the element body 2 affects the characteristics of the inductor 1, such as the DC superimposed rated current (hereinafter referred to as Isat) and inductance value (hereinafter referred to as L value). Therefore, positioning the coil conductor 20 using the pair of first protrusions 56a makes it easier to suppress variation in the characteristics of the inductor 1.

Furthermore, as described above, the coil conductor 20 in embodiment 1 is made of a flat rectangular conductor wire, so the area of the winding portion 22 that comes into contact with the first protrusion 56a is likely to be larger than when a round wire is used as the conductor wire. Therefore, by using a flat rectangular conductor wire for the coil conductor 20, the position of the coil conductor 20 within the element body 2 is less likely to vary, making it easier to suppress variation in the characteristics of the inductor 1.

After the element body 2 has been molded, the lower die 53 is removed from the molding die 50, and the element body 2 is pushed out of the cavity 51a by the punch 55.

In embodiment 1, a T-shaped preform is used as the first tablet 71, and the coil conductor 20 is positioned by the first protrusion 56a, which differs from conventional element molding and curing processes. Unlike embodiment 1, conventionally, an E-shaped preform having two protrusions along both outer sides of the periphery of the winding portion 22 in the width direction DW was used as the first tablet 71, and the winding portion 22 was positioned by the shaft portion 71b and the two protrusions of the E-shaped preform. In this case, the molding die 50 did not have the first protrusion 56a that could position the coil conductor 20. In such a conventional molding die 50, if a T-shaped preform as in this embodiment was used as the first tablet 71 to reduce the size of the element 2, the coil conductor 20 was not positioned from the outside, leaving room for improvement in preventing misalignment. In contrast, in embodiment 1, by using a molding die 50 on which a pair of first protrusions 56a are formed, the coil conductor 20 is less likely to shift position even when a T-shaped preform without protrusions sandwiching the winding portion 22 from both sides in the width direction DW is used as the first tablet 71. This makes it easier to reduce the dimension of the element body 2 in the width direction DW compared to conventional methods. Furthermore, in embodiment 1, unlike conventional methods, the coil conductor 20 can be positioned by the first protrusions 56a, which do not move within the cavity 51a, thereby improving the positioning accuracy of the coil conductor 20 compared to conventional methods.

(Configuration of molded element body)
FIG. 7 is a plan view of the element body 2 as viewed from the top surface 12. FIG. 8 is a side view of the element body 2 as viewed from the side surface 16. Note that FIG. 8 also shows a bisector C of the dimension of the side surface 16 in the thickness direction DT. As shown in FIGS. 7 and 8 , one first groove 16a is formed in each of a pair of opposing side surfaces 16 of the element body 2 molded in the element body molding and hardening process. The pair of first grooves 16a extend along the winding axis K of the coil conductor 20, with the thickness direction DT as their longitudinal direction, and are recessed toward the inside of the core 30. The first groove 16a is formed by the first protrusions 56a pushing aside the mixed powder in the element body molding and hardening process. The LW cross-sectional shape of the first groove 16a is the same as the LW cross-sectional shape of the first protrusions 56a.

As shown in Figure 8, exposed portion 22a1, which is part of the upper winding region 22a, and exposed portion 22b1, which is part of the lower winding region 22b, are exposed from the surface of core 30 via first groove 16a. In other words, the element body 2 uses a coil conductor 20 having a winding portion 22 with a large dimension in the width direction DW, such that it is exposed to the outside of element body 2 through first groove 16a. This makes it easier to increase the cross-sectional area of the winding portion 22 and the L value of inductor 1.

8 , when viewed along the width direction DW, the coil conductor 20 is formed at a position overlapping the bisector C of the side surface 16 in the thickness direction DT, and the exposed portions 22a1, 22b1 overlap the bisector C. That is, the exposed portions 22a1, 22b1 are formed at the center in the direction in which the first groove 16a extends. The exposed portions 22a1, 22b1 are portions that were in contact with the center of the winding regions 22a, 22b in the direction in which the first protrusion 56a extends during the element molding and curing process. Therefore, when the exposed portions 22a1, 22b1 are formed at the center in the direction in which the first groove 16a extends, it becomes easier to position the winding portion 22 within the element body 2.
Furthermore, by coating this molded element body 2 with a thin insulating resin in the element body protective layer forming step, exposed portions 22a1, 22b1 are covered with the thin insulating resin. That is, exposed portions 22a1, 22b1 of winding portion 22 in embodiment 1 are exposed from core 30 that constitutes element body 2, but are not exposed on the outer surface of inductor 1, which has an additional insulating resin coating on the surface of element body 2. This coating can cover and conceal exposed portions 22a1, 22b1 exposed on the outside of core 30, thereby eliminating the strange appearance caused by the exposed winding portion 22.

[Example]
The inventors conducted an experiment to verify the effect that misalignment of the coil conductor 20 in the element body 2 has on the characteristics of the inductor 1. In the experiment, the inventors created an inductor 1 and, based on the Isat and L values of the created inductor 1, estimated the effect that misalignment of the coil conductor 20 has on the Isat and L values through simulation. Details of the experiment conducted by the inventors will be described below in the examples.

(Creating an inductor)
First, the inventors created an inductor 1 to obtain the Isat and L values to be input into the simulation.

The inventors used a mixed powder for the core 30, consisting of a metal magnetic powder containing Fe-Si-Cr alloy powder as the first magnetic particles and carbonyl iron powder as the second magnetic particles. Measurements using a particle size distribution analyzer revealed that the metal magnetic powder in this example had an average particle size of 25.3 μm for the first magnetic particles and 1.7 μm for the second magnetic particles. The resin in this example contained bisphenol A epoxy resin and rubber-modified epoxy resin, accounting for 2.7 wt% of the mixed powder. According to measurements by the inventors, the mixed powder had a relative permeability of 34 and a saturation magnetic flux density of 1.36 T. The relative permeability was measured using a BH analyzer and an impedance material analyzer with a high-frequency signal at 1 MHz. The saturation magnetic flux density was determined by measuring the inductance change during superposition using an LCR meter and a DC power source, and then back-calculating the BH data to determine the value at which the magnetic flux became saturated.

In the example, the inventors created the coil conductor 20 using a rectangular conductor wire with cross-sectional dimensions of 0.128 mm in length and 0.083 mm in width.

In the example, the element body 2 was compression molded to have dimensions of 1.52 mm in the length direction DL, 1.35 mm in the width direction DW, and 0.57 mm in the thickness direction DT. Furthermore, in the element body 2, the side gaps WSG1 and WSG2 (see Figure 7), which are the distances in the width direction DW between the outer periphery of the winding portion 22 and a pair of side surfaces 16, were each 50 μm.

The inventors measured the Isat and L value of the inductor 1 having the element body 2 fabricated as described above. The inventors measured the inductance value with an LCR meter while increasing the DC current value applied to the coil conductor 20 of the fabricated inductor 1, and defined the current value at which the inductance value decreased by 30% from its initial value as the Isat. The inventors also measured the inductance value at 1 Hz with the LCR meter, and defined this value as the L value. According to the inventors' measurements, the inductor 1 of the example had an L value of 0.32 μH and an Isat of 6.5 A.

(simulation)
The inventors input the L value and Isat of the inductor 1 created as described above into simulation software and estimated the L value and Isat when the side gaps WSG1 and WSG2 were changed. Note that in order to evaluate the influence of misalignment of the coil conductor 20 in the element body 2 along the width direction DW, the inventors performed the simulation with the total of the side gaps WSG1 and WSG2 fixed at 100 μm.

Figure 9 is a graph showing the results of the simulation. As shown in Figure 9, it was found that the L value was greatest when the side gaps WSG1 and WSG2 were both 50 μm. The L value was also smallest when the side gap WSG1 was 0 μm, a decrease of approximately 0.015 μH at most compared to when the side gaps WSG1 and WSG2 were both 50 μm. Furthermore, Isat increased by approximately 0.1 A when the side gap WSG1 was 0 μm compared to when the side gaps WSG1 and WSG2 were both 50 μm.

These results indicate that displacement of the coil conductor 20 in the element body 2 in the width direction DW changes the L value by a maximum of approximately 0.015 μH and the Isat by a maximum of approximately 0.1 A. Therefore, the inventors' experiments in the examples suggest that suppressing variation in the coil conductor 20 in the element body 2 in the width direction DW can suppress variation in the characteristics of the inductor 1.

[Embodiment 2]
Next, a second embodiment will be described with reference to Figures 10 and 11. Note that only differences from the first embodiment will be described below, and the same description will be omitted.

(Body molding/hardening process)
FIG. 10 is a cross-sectional view of the upper mold 151 of the second embodiment, showing the LW cross section of the upper mold 151 corresponding to FIG. 6 . As shown in FIG. 10 , a pair of second inner wall surfaces 154 of the upper mold 151 of the second embodiment, which face each other and are perpendicular to the first inner wall surface 56, each have a second protrusion 154a formed thereon. The pair of second protrusions 154a extend parallel to each other along the thickness direction DT and protrude toward the inside of the cavity 51a. The distance L1 between the second protrusions 154a in the length direction DL is equal to the dimension of the winding portion 22 of the coil conductor 20 in the length direction DL, and the outer periphery of the winding portion 22 is in contact with the second protrusion 154a. In the second embodiment, the dimension of the flat portion 171a of the first tablet 71 in the length direction DL is set equal to the dimension of the winding portion 22 in the length direction DL, and the flat portion 171a is arranged along the second protrusion 154a.

In embodiment 2, the winding portion 22 of the coil conductor 20 and the first tablet 71 are positioned in the longitudinal direction DL by a pair of second protrusions 154a, and movement during compression molding is restricted.

(Configuration of molded element body)
11 is a plan view of the element body 102 of embodiment 2 as viewed from the top surface 12. As shown in Fig. 11, the core 130 of the element body 102 has parallel second grooves 114a on a pair of end surfaces (second side surfaces) 114 that are perpendicular to the side surfaces 16 and face each other. The pair of second grooves 114a are grooves that extend along the thickness direction DT over the entire length of the end surfaces 114 and are parallel to the winding axis K of the winding part 22, and are recessed toward the inside of the core 130.

In this way, by providing the second protrusions 154a on the upper mold 151 and forming the second grooves 114a in the element body 102, the position of the coil conductor 20 in the element body 102 is less likely to vary from element body 102 to element body 102, even in the longitudinal direction DL. Therefore, in embodiment 2, it is easier to suppress variation in the characteristics of the inductor 1.

[Embodiment 3]
Next, a third embodiment will be described with reference to Fig. 12. Below, only the method for manufacturing the inductor 1 of the first embodiment and the differences from the inductor 1 will be described, and the same description will be omitted. Fig. 12 is a cross-sectional view of an upper mold 251 in the third embodiment, showing the LW cross section of the upper mold 251 corresponding to Fig. 6.

As shown in FIG. 12, the upper mold 251 has a pair of first inner wall surfaces 56, 256 facing each other. A first protrusion 56a is formed on the first inner wall surface 56, and no first protrusion 56a is formed on the first inner wall surface 256. Furthermore, the distance W1 in the width direction DW between the tip of the first protrusion 56a and the first inner wall surface 256 is equal to the dimension of the winding portion 22 in the width direction.

In embodiment 3, the winding portion 22 of the coil conductor 20 is positioned in the width direction DW by the first protrusion 56a and the first inner wall surface 256, and movement during compression molding is restricted. In this way, even by providing only one first protrusion 56a on one of the first inner wall surfaces 56, variation in the position of the coil conductor 20 within the element body can be suppressed, and variation in the characteristics of the inductor 1 can be suppressed. Furthermore, the element body molded using the upper mold 251 in Figure 12 has the first groove 16a only on one side surface 16, making it less likely that the position of the coil conductor 20 will vary within the element body.

Other Embodiments
In the above-described first embodiment, the element body 2 is coated with insulating resin in the element body protective layer forming step, but this is merely an example. Depending on the intended use of the inductor 1, the surface of the element body 2 may not be coated with resin. In this case, the exposed portions 22a1, 22b1 are not covered with insulating resin until the end of the manufacturing method of the inductor 1, and the winding portion 22 of the coil conductor 20 remains exposed on the outer surface of the inductor 1.

In addition, in embodiments 1 to 3, it has been described that the pair of first grooves 16a formed in the element body 2, 102 are formed over the entire length of the side surface 16 in the thickness direction DT. Also, it has been described that the pair of second grooves 114a formed in the element body 102 are formed over the entire length of the end surface 14 in the thickness direction DT, but this is just an example. The first grooves 16a and second grooves 114a may each be formed in a shape that allows the element body 2 to be removed from the cavity 51a. For example, when the element body 2, 102 is removed from the cavity 51a toward the lower mold 53 that molds the bottom surface 10 of the element body 2, 102, the first grooves 16a and second grooves 114a of the element body 2, 102 do not have to extend to the bottom surface 10.

In addition, in embodiments 1 to 3, the upper mold 51, 151, 251, which is configured as a single member, is used when compression molding the element body 2, but this is just one example. The upper mold 51, 151, 251 may be configured to be separable into multiple parts. Furthermore, the molding die 50 may not have the lower mold 53, and may be configured to compression mold the element body 2, 102 using two punches 55. Furthermore, when compression molding the element body 2, the first tablet 71, which is a T-shaped preform, the coil conductor 20, and the second tablet 73, which is an I-shaped preform, are placed in the cavity 51a. However, this is just one example. For example, instead of the second tablet 73, a mixed powder of magnetic particles and resin may be filled into the cavity 51a from above the first tablet 71 and the coil conductor 20, and the element body 2 may be compression molded.

In addition, in embodiments 1 to 3, the coil conductor 20 arranged inside the cavity 51a is described as being in contact with the first protrusion 56a and the second protrusion 154a, but this is merely an example. Even if the first protrusion 56a and the second protrusion 154a are close to the coil conductor 20 but do not contact it, they can still prevent the coil conductor 20 from shifting position. Providing a gap between the first protrusion 56a and the second protrusion 154a and the coil conductor 20 in this way makes it easier to position the coil conductor 20 within the cavity 51a by the amount of the gap. Furthermore, when the element body 2 is compression molded in this way without the first protrusion 56a and the second protrusion 154a contacting the coil conductor 20, no exposed portions of the winding portion 22 from the core 30, such as the exposed portions 22a1 and 22b1, are formed, and the entire winding portion 22 is embedded in the core 30.

All of the above-described embodiments and modifications are merely examples of aspects of the present invention, and any modifications and applications are possible without departing from the spirit of the present invention. In addition, any elements of the above-described embodiments may be combined to form a new embodiment.
Furthermore, unless otherwise specified, the horizontal, perpendicular, vertical, and other directions, various numerical values, shapes, and materials in the above-described embodiments include a range (so-called equivalent range) that produces the same effect as those directions, numerical values, shapes, and materials.

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

(Configuration 1) A method for manufacturing an inductor comprising an element body having a coil conductor formed by winding a conductive wire, and a core containing metal magnetic powder and resin and in which the coil conductor is embedded, wherein the element body is formed by placing a pre-molded body and the coil conductor placed on the pre-molded body inside a cavity formed in a molding die and compression molding the pre-molded body, the molding die having a pair of opposing first inner wall surfaces and a pair of opposing second inner wall surfaces that form the cavity, and a first protrusion formed on at least one of the pair of first inner wall surfaces, the first protrusion protruding toward the inside of the cavity and extending parallel to the first inner wall surface, the coil conductor being placed inside the cavity with the winding axis of the coil conductor parallel to the extension direction of the first protrusion, and the coil conductor being close to the first protrusion.
According to the method for manufacturing an inductor as set forth in configuration 1, the first protrusion formed on the molding die can suppress misalignment of the coil conductor inside the cavity, which makes it easier to suppress variations in the characteristics of the inductor.

(Configuration 2) The method for manufacturing an inductor according to Configuration 1, wherein the first protrusions are formed on the pair of first inner wall surfaces, respectively.
According to the method for manufacturing an inductor of configuration 2, the pair of first protrusions can suppress misalignment of the coil conductor inside the cavity, which makes it easier to suppress variations in the characteristics of the inductor.

(Configuration 3) The method for manufacturing an inductor according to configuration 1 or 2, wherein the coil conductor is in contact with the first protrusion.
According to the method for manufacturing an inductor of the third aspect, the first protrusions in contact with the coil conductor make it easier to suppress misalignment of the coil conductor, thereby making it easier to suppress variations in the characteristics of the inductor.

(Configuration 4) The method for manufacturing an inductor according to Configuration 3, wherein the coil conductor is in contact with the first protrusion at the center of the first protrusion in the direction in which the first protrusion extends.
According to the inductor manufacturing method of configuration 4, the first protrusions contact the coil conductor at the centers thereof in the direction in which the first protrusions extend, which makes it easier to suppress misalignment of the coil conductor and therefore easier to suppress variations in the characteristics of the inductor.

(Configuration 5) A method for manufacturing an inductor described in any one of configurations 1 to 4, wherein the molding die further has second protrusions formed on a pair of second inner wall surfaces, protruding toward the inside of the cavity and extending parallel to the second inner wall surfaces, and the coil conductor is in close proximity to the second protrusions.
According to the method for manufacturing an inductor as set forth in configuration 5, the second protrusion formed on the molding die can suppress misalignment of the coil conductor inside the cavity, which makes it easier to further suppress variations in the characteristics of the inductor.

(Configuration 6) The method for manufacturing an inductor according to Configuration 5, wherein the coil conductor is in contact with the second protrusion.
According to the method for manufacturing an inductor as set forth in configuration 6, the second protrusions in contact with the coil conductor make it easier to suppress misalignment of the coil conductor, thereby making it easier to suppress variations in the characteristics of the inductor.

(Configuration 7) A method for manufacturing an inductor according to any one of configurations 1 to 6, wherein the element body formed by the compression molding is covered with an insulating resin.
According to the method for manufacturing an inductor as set forth in configuration 7, it becomes easier to suppress magnetic flux leakage in the manufactured inductor.

(Structure 8) An inductor comprising: an element body having a coil conductor formed by winding a conductive wire; and a core containing metal magnetic powder and resin and in which the coil conductor is embedded, wherein the core has a pair of first side surfaces parallel to the winding axis of the coil conductor, a pair of second side surfaces that intersect the first side surfaces and are parallel to the winding axis, and a first groove formed in at least one of the pair of first side surfaces, wherein the pair of first side surfaces are surfaces that face each other in the core, and the first groove is recessed toward the inside of the core and extends parallel to the winding axis.
According to the inductor of configuration 8, the first groove makes it difficult for the position of the coil conductor to vary within the core, which makes it easier to suppress variations in the characteristics of the inductor.

(Configuration 9) The inductor according to Configuration 8, wherein the first grooves are formed on each of the pair of first side surfaces.
According to the inductor of configuration 9, the pair of first grooves makes it difficult for the position of the coil conductor to vary within the core, which makes it easier to suppress variations in the characteristics of the inductor.

(Configuration 10) An inductor according to configuration 8 or 9, wherein the core further has a second groove recessed toward the inside of the core on the second side surface and extending parallel to the winding axis.
According to the inductor of configuration 10, the second groove makes it difficult for the position of the coil conductor to vary within the core, which makes it easier to suppress variations in the characteristics of the inductor.

(Configuration 11) An inductor according to any one of configurations 8 to 10, wherein the conductor is a flat rectangular conductor.
According to the inductor of configuration 11, the coil conductor can be easily positioned by using a rectangular conductor as the conductor, and variations in the characteristics of the inductor can be easily suppressed.

(Configuration 12) An inductor described in any one of configurations 8 to 11, wherein the coil conductor has a winding portion around which the conductive wire is wound, and a portion of the winding portion is exposed to the outside of the core through the first groove.
According to the inductor of configuration 12, the winding portion of the coil conductor can be made larger, which makes it easier to improve the characteristics of the inductor.

(Configuration 13) An inductor according to configuration 12, wherein a portion of the winding portion is exposed to the outside of the core at the center of the first groove in the direction in which the first groove extends.
According to the inductor of configuration 13, the coil conductor can be easily positioned by the first groove, and variations in the characteristics of the inductor can be easily suppressed.

1...inductor, 2...element body, 4...external electrode, 10...bottom surface, 12...top surface, 14...end surface (second side surface), 16...side surface (first side surface), 16a...first groove, 20...coil conductor, 22...winding portion, 22a1...exposed portion, 22b1...exposed portion, 24...external electrode connection portion, 30...core, 50...molding die, 51a...cavity, 54...second inner wall surface, 56...first inner wall surface, 56a...first protrusion, 71...first tablet (preformed body), 73...second tablet (preformed body), 102...element body, 114...end surface (second side surface), 114a...second groove, 130...core, 154...second inner wall surface, 154a...second protrusion, 256...first inner wall surface, K...winding shaft.

Claims (6)

A method for manufacturing an inductor including an element body having a coil conductor having a winding portion around which a conducting wire is wound and a lead portion drawn out from the winding portion , and a core containing metal magnetic powder and resin and in which the coil conductor is embedded, comprising:
the element body is formed by placing a preform and the coil conductor disposed on the preform inside a cavity formed in a molding die, and compression molding the preform and the coil conductor;
The molding die has a cavity formed in a rectangular shape when viewed from above, and includes a pair of first inner wall surfaces facing each other, a pair of second inner wall surfaces facing each other, and first protrusions formed at opposing positions on the pair of first inner wall surfaces,
the first protrusion protrudes toward the inside of the cavity and extends parallel to the first inner wall surface,
the coil conductor is disposed inside the cavity with the winding axis of the coil conductor parallel to the direction in which the first projection extends, the coil conductor is close to the first projection , and the wide surface of the lead-out portion is in contact with the second inner wall surface;
How to manufacture an inductor. the coil conductor is in contact with the first protrusion;
The method for manufacturing the inductor according to claim 1 . the coil conductor is in contact with the first protrusion at a center of the first protrusion in an extending direction of the first protrusion;
The method for manufacturing the inductor according to claim 2 . the molding die further includes second protrusions formed on the pair of second inner wall surfaces, the second protrusions protruding toward the inside of the cavity and extending parallel to the second inner wall surfaces,
the coil conductor is in close proximity to the second protrusion;
The method for manufacturing the inductor according to any one of claims 1 to 3 . The coil conductor is in contact with the second protrusion.
The method for manufacturing an inductor according to claim 4 . The element body formed by the compression molding is covered with an insulating resin.
The method for manufacturing the inductor according to any one of claims 1 to 3 .