inductor

Abstract

The present invention relates to an inductor for improving the withstand voltage of the inductor while maintaining the level of permeability. The inductor has a coil conductor embedded in a green body containing resin and metal magnetic material particles, the internal C amount in the inside of the green body being 13.8 mass% or more and 15.2 mass% or less, and the ratio of the above internal C amount to the surface C amount in the surface of the green body, i.e., the surface C amount / internal C amount, being 2.5 or more.

Description

Technical Field

[0001] This invention relates to inductors. Background Technology

[0002] Patent document 1 discloses an inductor in which a wound coil conductor is embedded in a preform containing resin and metallic magnetic particles.

[0003] The amount of carbon, or C, in the resin contained in the preform can affect the voltage withstand capability and permeability of the inductor.

[0004] Patent document 1: Japanese Patent Application Publication No. 2022-157440. Summary of the Invention

[0005] The purpose of this invention is to improve voltage resistance and maintain the level of magnetic permeability in an inductor in which a wound coil conductor is embedded in a blank containing resin and metallic magnetic particles.

[0006] One aspect of the present invention is an inductor in which a wound coil conductor is embedded in a blank containing resin and metallic magnetic particles, wherein the internal carbon content inside the blank is 13.8% by mass or more and 15.2% by mass or less, and the ratio of the internal carbon content to the surface carbon content on the surface of the blank, i.e., surface carbon content / internal carbon content, is 2.5 or more.

[0007] Furthermore, this specification includes the entire contents of Japanese Patent Application No. 2024-051037, filed on March 27, 2024.

[0008] According to the present invention, in an inductor in which a wound coil conductor is embedded in a blank containing resin and metallic magnetic particles, the withstand voltage can be improved and the level of magnetic permeability can be maintained. Attached Figure Description

[0009] Figure 1 This is a perspective view of the inductor according to an embodiment of the present invention, viewed from the top surface side.

[0010] Figure 2 This is a three-dimensional view of the inductor viewed from the bottom side.

[0011] Figure 3 It is a perspective three-dimensional diagram showing the internal structure of an inductor.

[0012] Figure 4 yes Figure 3 The inductor shown is shown in a cross-sectional view along plane IV.

[0013] Figure 5 This is a diagram showing the manufacturing process of an inductor.

[0014] Figure 6This is a schematic diagram of the ring in the embodiment. Detailed Implementation

[0015] In an inductor in which a wound coil conductor is embedded in a blank containing resin and metallic magnetic particles, the amount of carbon (C) from the resin contained in the blank can affect the inductor's withstand voltage and permeability.

[0016] The inventors carefully studied the internal carbon content inside the billet, the surface carbon content on the surface of the billet, the withstand voltage, and the magnetic permeability, gaining insights into the influence of internal carbon content, internal carbon content, and surface carbon content on the withstand voltage and magnetic permeability of inductors. Specifically, the inventors obtained the following insights: although a higher internal carbon content increases the withstand voltage, there is a tendency for a decrease in magnetic permeability due to factors such as a reduced proportion of metallic magnetic particles.

[0017] The inventors confirmed that, when the internal C amount is a specified amount, if the ratio of the surface C amount to the internal C amount is increased, the withstand voltage can be improved while maintaining the level of magnetic permeability.

[0018] This invention is based on the above insights. In an inductor, by specifying the ratio of surface carbon quantity to internal carbon quantity, it is possible to improve the voltage withstand capability and maintain the level of magnetic permeability.

[0019] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0020] [1. Structure of an inductor]

[0021] First, the structure of the inductor 1 in this embodiment will be described.

[0022] [1.1 Overall Structure of the Inductor]

[0023] Figure 1 , Figure 2 as well as Figure 3 This is a diagram showing the overall structure of inductor 1.

[0024] Figure 1 This is a perspective view of inductor 1 as seen from the top surface 12. Figure 2 This is a three-dimensional view of inductor 1 as seen from the bottom 10 side.

[0025] The inductor 1 in this embodiment is configured as a surface-mount electronic component, having a blank 2 in a generally cuboid shape, which is generally hexahedral in shape, and a pair of external electrodes 4 disposed on the surface of the blank 2.

[0026] In the following, in the blank 2, the first main surface facing the mounting substrate (not shown) during installation is defined as the bottom surface 10, the second main surface opposite to the bottom surface 10 is called the upper surface 12, the pair of third main surfaces orthogonal to the bottom surface 10 are called the end surfaces 14, and the pair of fourth main surfaces orthogonal to these bottom surfaces 10 and the pair of end surfaces 14 are called the side surfaces 16.

[0027] like Figure 1 As shown, the distance from the bottom surface 10 to the top surface 12 is defined as the thickness T of the billet 2, the distance between a pair of side surfaces 16 is defined as the width W of the billet 2, and the distance between a pair of end faces 14 is defined as the length L of the billet 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.

[0028] The inductor's dimensions are, for example, a length L of 2.0 mm, a width W of 1.2 mm, and a thickness T of 0.9 mm.

[0029] Figure 3 It is a perspective three-dimensional diagram showing the internal structure of an inductor.

[0030] The blank 2 has a coil conductor 20 and a core 30 of approximately hexahedral shape 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.

[0031] The core 30 is a molded body formed by compressing and heating a mixture of metallic magnetic particles and resin powder inside the coil conductor 20, resulting in a roughly hexahedral shape. The mixture may also contain solvents and / or curing agents. The mixture may also contain additives such as lubricants.

[0032] The metallic magnetic particles of this embodiment include two particle sizes: large first magnetic particles with a relatively large average particle size and small second magnetic particles with a relatively small average particle size. Therefore, during compression molding, the small second magnetic particles, along with the resin, enter between the large first magnetic particles, thereby increasing the filling rate of the metallic magnetic particles in the core 30 and also improving the magnetic permeability.

[0033] In this embodiment, the D50 particle size (median particle size) of the metal particles in the first magnetic particle and the second magnetic particle are 30 μm and 1.5 μm, respectively. Furthermore, the D50 particle size of the first magnetic particle is preferably 10 μm or more and 50 μm or less, and the D50 particle size of the second magnetic particle is preferably 1 μm or more and 5 μm or less. Additionally, the magnetic particles can contain particles with average particle sizes different from the first and second magnetic particles, thereby including particles of three or more particle sizes.

[0034] Both the first and second magnetic particles are particles consisting of metal particles and an insulating film covering their surfaces. The insulating film covering the metal particles improves the insulation resistance and withstand voltage.

[0035] The metal particles of the first magnetic particle and the second magnetic particle are, for example, Fe-based metal magnetic particles such as Fe (pure iron) or Fe alloys. As an example of an Fe alloy, one or more alloys selected from the group consisting of alloys containing Fe and Ni, alloys containing Fe and Co, alloys containing Fe and Si, alloys containing Fe, Si and Cr, alloys containing Fe, Si and Al, alloys containing Fe, Si, B and Cr, and alloys containing Fe, P, Cr, Si, B, Nb and C can be used.

[0036] The composition of the metal particles in the first magnetic particle and the composition of the metal particles in the second magnetic particle can be the same or different.

[0037] The insulating film formed on the surface of the metal particles of the first magnetic particle and the second magnetic particle can be, for example, one or more insulating films selected from the group consisting of inorganic glass films, organic-inorganic mixed films, and inorganic insulating films formed by the sol-gel reaction of metal alkoxides.

[0038] In this embodiment, the first magnetic particle uses Fe-Si-B alloy particles as metal particles, and the second magnetic particle uses Fe particles as metal particles.

[0039] In the mixed powder of this embodiment, the resin material uses phenol-biphenyl aralkyl type epoxy resin as the main agent and phenol-biphenyl aralkyl resin as the curing agent.

[0040] Examples of main agents include cresol-phenolic varnish-type epoxy resins, phenolic phenolic varnish-type epoxy resins, bisphenol A type epoxy resins, bisphenol F type epoxy resins, stilbene type epoxy resins, biphenyl type epoxy resins, naphthalene type epoxy resins, triphenol-methane type epoxy resins, dicyclopentadiene type epoxy resins, and phenol-aralkyl type epoxy resins. Two or more resins can be used as the main agent instead of just one. Furthermore, in addition to epoxy resins, polyurethane resins can also be used as the main agent.

[0041] Examples of curing agents include phenolic varnish resins, phenolic aralkyl resins, naphthol aralkyl resins, biphenyl aralkyl resins, and other benzene resins, acid anhydrides, and imidazoles. Two or more resins can also be used as curing agents instead of just one.

[0042] The preferred ratio of the first magnetic raw material particles to the second magnetic raw material particles is a weight ratio of 60:40 or more and 90:10 or less. A more preferred ratio is a weight ratio of 70:30 or more and 80:20 or less.

[0043] If there are too many large-sized primary magnetic material particles, the filling rate will decrease, the proportion of metallic magnetic particles in the core 30 will decrease, and the magnetic permeability will decrease. If there are too many small-sized secondary magnetic material particles, the magnetic flux in the core 30 will easily concentrate, and the magnetic permeability will decrease.

[0044] The resin content, on a whole basis, is preferably 2.5% by weight or more and 3.5% by weight or less. More preferably, the resin content, on a whole basis, is 2.8% by weight or more and 3.2% by weight or less.

[0045] If the amount of resin is too small, the densification of the core 30 cannot proceed during heating, resulting in unfilled resin portions. This reduces the proportion of metallic magnetic particles in the core 30 and lowers the magnetic permeability. If the amount of resin is too large, the resin will remain as a non-magnetic component in the core 30 after molding, further reducing the proportion of metallic magnetic particles and lowering the magnetic permeability.

[0046] like Figure 3 As shown, the coil conductor 20 has a winding portion 22 formed by winding a wire, and a pair of lead-out portions 24 extending from the winding portion 22 and at least partially exposed from the blank body 2.

[0047] The coil conductor 20 consists of a wire and a sheathing layer formed on the surface of the wire. The wire is a rectangular strip wire made of copper (so-called a flat wire).

[0048] In addition, the coil conductor 20 does not necessarily need to be wound; it can also be in a straight shape, a zigzag shape, etc.

[0049] The winding portion 22 of the coil conductor 20 is formed by winding the wire into a spiral shape so that the two ends of the strip wire (hereinafter simply referred to as the wire) extend outward and are connected to each other on the inner periphery. Inside the blank body 2, the coil conductor 20 is embedded in the core body 30 in an orientation along the thickness direction DT of the blank body 2 with the central axis of the winding portion 22 in this orientation. The lead-out portion 24 extends from the winding portion 22 to each of a pair of end faces 14, one of which is exposed from the blank body 2 and the other is embedded in the blank body 2. The aforementioned main face of the lead-out portion 24 exposed from the blank body 2 is electrically connected to the external electrode 4.

[0050] A pair of external electrodes 4 are so-called L-shaped electrodes, each consisting of an L-shaped member extending from the end face 14 of the blank 2 to the bottom face 10. The external electrodes 4 are connected to the lead-out portion 24 of the coil conductor 20 at the end face 14, and the portion 4A extending and protruding to the bottom face 10 (…) Figure 2 It is electrically connected to the wiring of the circuit board through appropriate mounting methods such as solder.

[0051] Figure 4 yes Figure 3 A cross-sectional view of plane IV. Plane IV is a plane parallel to the thickness direction DT and located at the center of the width W.

[0052] A preform protective layer 5, serving as an insulating film, is formed on the surface of the preform 2, excluding the area covered by the external electrode 4. The preform protective layer 5 can be, for example, epoxy resin, phenoxy resin, or phenolic varnish resin, and materials containing metal oxide microparticles can be used as fillers. In this embodiment, the preform protective layer 5 comprises silica filler forming metal oxide microparticles and epoxy resin. Besides the materials described above, the preform protective layer 5 can also be polyurethane, acrylic, polyimide, polyimide amide, polyamide, or other resins, or it can be glass or an oxide film.

[0053] The preform protective layer 5 is an example of a "resin coating".

[0054] [1-2. Carbon content]

[0055] Inductors 1 using metallic magnetic particles tend to have lower voltage withstand capability compared to ferrite-based electronic components. To improve voltage withstand capability, one could consider increasing the amount of resin in the blank 2 of the inductor 1. However, if the amount of resin is increased, the occupancy of the metallic magnetic particles decreases, leading to a decrease in permeability.

[0056] The inventors have gained the following insight: For the blank 2, by setting the internal C content to 13.8% by mass or more and 15.2% by mass or less, and setting the value obtained by dividing the surface C content by the internal C content to 2.5 or more and 2.8 or less, it is possible to improve the withstand voltage and maintain the level of magnetic permeability.

[0057] In this embodiment, the blank 2 is made such that the internal C content is 13.8% by mass or more and 15.2% by mass or less.

[0058] The definition of internal carbon content is explained below. Internal carbon content is one of the indicators of the amount of carbon inside the blank body 2, expressed in units of mass %

[0059] like Figure 4As shown, the cross-section of the blank 2, which has been cut to a width W of 1 / 2, is ground. Next, a measuring unit 40 is set up at a total of 5 points: 4 points at the center between the corner of the blank 2 and the end of the coil conductor 20 closest to that corner, and 1 point at the center of the blank 2.

[0060] The carbon content in the measurement section 40 was quantitatively analyzed using an electron microscope via SEM (Scanning Electron Microscope)-EDX (Energy Dispersive X-ray Spectrometry). The electron microscope used was a Schottky field emission scanning electron microscope (model: JSM-7900F) manufactured by Nippon Electron Ltd. Hereinafter, "electron microscope" refers to this Schottky field emission scanning electron microscope.

[0061] The quantitative analysis was performed on four blanks 2. For each of the 20 measurement points 40, the C value was quantified within a 200μm×100μm imaging range. The arithmetic mean of the 20 C values ​​was defined as the internal C value.

[0062] In this embodiment, the blank 2 is made such that the value obtained by dividing the surface C amount by the internal C amount is 2.5 or more and 2.8 or less.

[0063] The definition of surface carbon content is explained below. Surface carbon content is one of the indicators of the amount of carbon on the surface of the blank 2, expressed in units of mass %

[0064] The blank 2 is prepared before the formation of the protective layer 5. This blank 2 is formed by the blank forming process (S3) described later, and is equivalent to the blank 2 before the tumbling grinding process (S4). Any four points on the surface of this blank 2 are designated as measuring points (not shown). The term "surface" is not limited to any one of the six surfaces. Furthermore, a total of four identical blanks 2 are prepared, and a total of 20 points are designated as measuring points.

[0065] For the C quantity in the measurement section, the same electron microscope used for measuring the internal C quantity was used. For each of the 20 measurement sections, the C quantity was quantified within a 200μm × 100μm imaging range, and the arithmetic mean of the 20 C quantity values ​​was defined as the surface C quantity.

[0066] The value obtained by dividing the surface C quantity by the internal C quantity is represented by surface C quantity / internal C quantity, and is a dimensionless quantity.

[0067] The inductors described above improve DC superposition characteristics by using soft magnetic materials in their magnetic particles. Therefore, they are used as electronic components in circuits carrying large currents, DC-DC converter circuits, and choke coils in power supply circuits. They are also used as electronic components in personal computers, DVD players, digital cameras, TVs, mobile phones, smartphones, automotive electronics, and medical / industrial machinery. However, the applications of inductors are not limited to these; for example, they can also be used in tuning circuits, filtering circuits, and rectifier smoothing circuits.

[0068] [2. Manufacturing process of inductors]

[0069] Inductor 1 can be made as follows.

[0070] Figure 5 This is a diagram showing the manufacturing process of inductor 1.

[0071] The manufacturing process of inductor 1 may include: coil conductor forming process (S1), preform forming process (S2), blank forming process (S3), roller grinding process (S4), surface treatment process (S5), and external electrode forming process (S6).

[0072] The coil conductor forming process (S1) is the process of forming a coil conductor 20 from a wire. In this process, the coil conductor 20 is formed by winding the wire using a winding method called "α-winding," thereby forming a shape having the aforementioned winding portion 22 and a pair of lead-out portions 24. α-winding refers to a state in which the wire, which functions as a conductor, is wound in a spiral shape into two layers, with the lead-out portions 24 at the beginning and end of the winding located on the outer periphery. The number of turns of the coil conductor 20 is not particularly limited.

[0073] The preform formation process (S2) is the process of forming a preform known as a flat plate.

[0074] The preform is a molded body formed by pressing the above-mentioned mixed powder, which is the material of the blank 2, into an easy-to-handle solid shape. In this embodiment, two types of plates are formed: a first plate with a suitable shape (e.g., E-type) for the groove into which the coil conductor 20 enters, and a second plate with a suitable shape (e.g., I-type, plate-shaped) for the groove covering the first plate.

[0075] In the blank forming process (S3), the first plate, the coil conductor, and the second plate are placed in a forming metal mold, and pressure is applied in the overlapping direction of the first and second plates while heating, so that they are solidified, thereby integrating the first plate, the coil conductor, and the second plate. Thus, the blank 2, in which the coil conductor 20 is enclosed within the core 30, is formed.

[0076] The molding metal mold is formed by combining multiple metal parts. The gap between these metal parts is set to 20 μm. The smaller the gap, the less likely the resin is to leak out from the gap, and the more likely the resin will accumulate on the surface of the blank 2, thus there is a tendency for the amount of resin on the surface of the blank 2 to increase.

[0077] In the tumbling grinding process (S4), multiple blanks 2 are filled inside the tumbling drum, and the drum is rotated to prevent excessive impact. Additionally, a coating liquid, serving as a protective layer 5 for the blanks, is sprayed using a sprayer. This rounds the corners of the blanks 2 and coats them with the coating liquid. In this embodiment, the coating liquid contains silica as a filler (metal oxide microparticles) and epoxy resin as an organic resin.

[0078] Next, the blank 2 coated with the coating liquid is removed from the roller and subjected to heat treatment, thereby forming a blank protective layer 5 on the surface of the blank 2.

[0079] Furthermore, the formation of the preform protective layer 5 is not limited to the above-described method. It can also be carried out by setting up a process independent of the roller grinding process (S4), such as spraying the coating liquid onto the preform 2, immersing the preform 2 in the coating liquid, supplying the coating liquid to the surface of the preform 2 using a dispenser, or printing the coating material onto the surface of the preform 2 based on various printing methods.

[0080] The surface treatment process (S5) is a process that modifies the surface of the electrode predetermined area on the surface of the core 30 by irradiating it with a laser. Here, the electrode predetermined area refers to the area on the surface of the core 30 where the external electrode 4 should be formed, including the portion where the lead-out portion 24 is exposed. Specifically, by irradiating with a laser, within the area of ​​the electrode predetermined area, the blank protective layer 5 on the surface of the core 30 and the coating layer of the lead-out portion 24 of the coil conductor 20 are removed, and the resin on the surface of the core 30 and the insulating film on the surface of the exposed metal magnetic particles from the core 30 are also removed. As a result, compared with other surface portions of the core 30, the exposed area of ​​the metal magnetic particles per unit area on the surface of the core 30 is larger in the portion of the electrode predetermined area.

[0081] The wavelength of the laser is, for example, 180 nm or more and 3000 nm or less, more preferably 532 nm or more and 1064 nm or less. Furthermore, the laser irradiation energy is preferably 1 W / mm². 2 Above and 30W / mm 2 The following is more preferably 5W / mm 2 Above and 12W / mm 2 the following.

[0082] In the external electrode formation process (S6), an external electrode 4 is formed on the predetermined electrode location on the core 30, i.e., within the range of the irradiated laser. Specifically, firstly, a Cu plating layer is formed on the predetermined electrode location on the core 30 by electroplating. Next, a Ni plating layer and a Sn plating layer are formed on the Cu plating layer by electroplating.

[0083] For methods of forming the Cu layer, such as electrolytic copper plating, copper sulfate plating, copper pyrophosphate plating, and copper cyanide plating can be used.

[0084] When forming Ni and Sn plating layers, additives such as gloss materials can also be added to the plating solution.

[0085] Example

[0086] [3. Example]

[0087] Next, an embodiment of inductor 1 will be described.

[0088] The embodiments and comparative examples shown in Table 1 were prepared to evaluate the voltage withstand index, which represents the voltage withstand capability of inductor 1, and the permeability index, which represents the permeability of inductor 1.

[0089] Examples 1, 2, 3 and Comparative Examples 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, through the above-described... Figure 5 The manufacturing process shown is followed. In each embodiment or comparative example, inductor 1 and ring 50 (described later) are manufactured. Figure 6 The samples are used as examples. In each embodiment or comparative example, the number of samples for inductor 1 is 10, and the number of samples for ring 50 is 10.

[0090] Furthermore, in each embodiment or comparative example, the gap of the forming metal mold, the mixing conditions of the powder in the blank 2, and the pressure forming conditions for solidifying the blank 2 differ in the blank forming process (S3). These conditions will be described later.

[0091]

[0092] [3.1 Preparation of Examples and Comparative Examples]

[0093] <Inductor and Ring Fabrication>

[0094] The structure of the inductor 1 used as a sample in Examples 1-3 and Comparative Examples 1-11 will be described.

[0095] The composition of the mixed powder, i.e. the mixed powder conditions, in the preform formation process (S2) is as follows.

[0096] As metallic magnetic particles, a first magnetic particle with a D50 particle size of 30 μm based on Fe-Si-B system and a second magnetic particle with a D50 particle size of 1.5 μm based on Fe system are mixed such that the weight ratio of the first magnetic material particle to the second magnetic material particle is 75:25.

[0097] As the resin, the main agent is phenolic biphenyl aralkyl type epoxy resin, and the curing agent is phenolic biphenyl aralkyl resin.

[0098] Regarding the weight ratio of the first magnetic particles, the second magnetic particles, and the resin in the mixed powder, based on the total amount of the mixed powder, the resin content is 2.5% by weight or more and 3.5% by weight or less. Thus, in each embodiment or comparative example, the amount of mixed powder in the preform 2 during the preform formation process (S2) varies within the range of 2.5% by weight or more and 3.5% by weight or less of the resin content, indicating different mixing conditions. Furthermore, the mixing conditions are identical in one embodiment or comparative example.

[0099] The more resin there is as a whole in the mixed powder, the greater the internal carbon content tends to be.

[0100] In the preform forming process (S2), the first plate is E-shaped and the second plate is I-shaped.

[0101] The pressure molding conditions for preform 2 in the preform forming process (S3) are set as a specified temperature, a specified pressure, and a specified pressure time. In each embodiment or comparative example, the specified temperature and specified pressure are appropriately varied. The higher the temperature or pressure, the greater the surface carbon content tends to be. The curing conditions are the same in each embodiment or comparative example.

[0102] In Example 2, the pressure molding conditions were as follows: temperature 180°C, pressure 20 MPa, and pressing time 100 seconds.

[0103] Regarding the gap in the forming metal mold in the blank forming process (S3), the gap is 20 μm in Examples 1-3 and Comparative Examples 1-4, and 40 μm in Comparative Examples 5-11.

[0104] Compared to the case with a gap of 40 μm, the ratio of surface carbon to internal carbon tends to be larger when the gap is 20 μm.

[0105] After forming a blank protective layer 5 on the surface of the blank 2 through the tumbling grinding process (S4), in the surface treatment process (S5), the electrode predetermined portion, including the exposed portion of the lead-out portion 24 of the coil conductor 20, on the surface of the blank 2 is subjected to laser irradiation. Furthermore, the external electrode 4 is formed through the aforementioned external electrode forming process (S6).

[0106] Regarding the dimensions of inductor 1, the length L is 2.0 mm, the width W is 1.6 mm, and the thickness T is 1.2 mm.

[0107] Next, the structure of the ring 50 used as a sample in Examples 1-3 and Comparative Examples 1-11 will be described.

[0108] Figure 6 This is a schematic diagram of ring 50 in the embodiment.

[0109] Without the coil conductor forming process (S1), ring 50 does not contain coil conductor 20. The powder mixing composition, i.e., the powder mixing conditions, in the preform forming process (S2) are the same as those of inductor 1 in each embodiment or comparative example. The flat plate in the preform forming process (S2) is toroidal. The toroidal shape can also be called a toroidal surface shape. The pressure forming conditions of the blank 2 in the blank forming process (S3) are the same as those of inductor 1 in each embodiment or comparative example. If the blank forming process (S3) is completed, ring 50, which is formed into a toroidal surface shape and does not contain external electrode 4 and coil conductor 20, is obtained.

[0110] Will Figure 6 The Ta direction is defined as the thickness of ring 50, and the La direction dimension is defined as the length. Furthermore, the dimension between the inner and outer circumferences of ring 50 is defined as the ring width WR. Regarding the size of ring 50, the length is 2.0 mm, the ring width WR is 1.2 mm, and the thickness is 0.9 mm.

[0111] [3.2 Evaluation]

[0112] For Examples 1-3 and Comparative Examples 1-11, the internal carbon content and surface carbon content were measured, the withstand voltage index was evaluated, and the relative permeability index was evaluated.

[0113] [3.2.1 Evaluation Methods]

[0114] The evaluation was conducted using the methods described below.

[0115] <Internal C content and surface C content>

[0116] The measurements of the internal C-value and surface C-value of the inductor 1 manufactured as described above are as explained in the embodiment. Furthermore, the four inductors 1 used in the measurements of the internal C-value and surface C-value were randomly selected from 10 samples.

[0117] The following explains the definition of the internal C quantity of ring 50. The unit of the internal C quantity of ring 50 is set as mass%.

[0118] The ring 50 is cut into two equal parts along the La-Ta direction. The two cross-sections 51 of the ring 50 exposed by this cut are ground, and the central portion of each cross-section 51 is designated as the measuring section 52. The C content in the measuring section 52 is quantitatively analyzed using SEM-EDX with the same electron microscope used for measuring the internal C content. Quantitative analysis is performed on 10 rings 50. For each of the 20 measuring sections 52, the C content is quantified within a 200 μm × 100 μm imaging range, and the arithmetic mean of the 20 C content values ​​is taken as the internal C content of the ring 50.

[0119] The following explains the definition of the surface C quantity of ring 50. The surface C quantity of ring 50 is expressed in units of mass%.

[0120] For ring 50, the measurement section 54 is defined as the portion located at the center of the ring width WR and opposite to each other in the flat surface 53 extending along the La direction. For one ring 50, the measurement section 54 consists of four points in one flat surface 53 and another flat surface 53 of the ring 50. The C quantity in the measurement section 54 is quantitatively analyzed by SEM-EDX using the same electron microscope as the internal C quantity measurement. Quantitative analysis is performed on five rings 50. For each of the 20 measurement sections 54, the C quantity is quantified within an imaging range of 200 μm × 100 μm, and the arithmetic mean of the 20 C quantity values ​​is taken as the surface C quantity of the ring 50. Furthermore, the five rings 50 used in the measurement of the surface C quantity of the rings 50 are arbitrarily selected from 10 samples.

[0121] The internal C value and the surface C value of ring 50 are approximately the same as those of inductor 1 under the same powder mixing conditions and pressure molding conditions.

[0122] <Voltage withstand rating>

[0123] Using an insulation resistance meter, set the charging time to 1 second and the discharging time to 1 second. Apply voltages in ascending order: 25V, 50V, 100V, 200V, 300V, 400V, and 500V. Use tweezers to probe and contact the pair of external electrodes 4 of inductor 1. Use an insulation resistance of 10... 5 The withstand voltage is measured by comparing the voltage of the previous voltage when it is below Ω. The unit of withstand voltage is V / mm. The insulation resistance meter used is a digital ultra-high resistance / micro-current meter (model R8340) manufactured by Advantest Co., Ltd.

[0124] Measure the withstand voltage of the 10 inductors 1 that were manufactured, calculate the arithmetic mean, and set the arithmetic mean as the average withstand voltage.

[0125] Furthermore, the withstand voltage index is calculated by dividing the average withstand voltage of each embodiment or comparative example by the arithmetic mean of the average withstand voltage of comparative examples 5-11 with a gap of 40 μm.

[0126] <Relative permeability index>

[0127] The relative permeability of ring 50 at a frequency of 1 MHz was measured using a permeability meter.

[0128] The relative permeability of the 10 fabricated rings (50) was measured, and the arithmetic mean was calculated. This arithmetic mean was set as the average relative permeability. The permeability measurement instrument used was an impedance analyzer (model E4990A) manufactured by Keysight Technologies Co., Ltd.

[0129] Furthermore, the average relative permeability of each embodiment or comparative example is divided by the average relative permeability of Comparative Example 5 to calculate the relative permeability index.

[0130] The internal and surface permeability values ​​of ring 50 are approximately the same as those of inductor 1 under the same powder mixing and pressing conditions. Therefore, the relative permeability index of inductor 1 is obtained by using ring 50. Consequently, the trend of the relative permeability of inductor 1 can be confirmed by measuring the relative permeability of ring 50.

[0131] [3.2.1 Evaluation Results]

[0132] As shown in Table 1, comparing Examples 1-3, Comparative Examples 1-4, and Comparative Examples 5-11, it can be confirmed that even if the internal C content increases, the surface C content is difficult to increase compared to the case with a gap of 20 μm when the gap is 40 μm.

[0133] Comparative Examples 5-11 confirm that even if the internal C content increases, the withstand voltage index does not increase if the surface C content does not increase. Examples 1-3 and Comparative Examples 1-4 confirm that if the internal C content increases to 13.8% by mass or more, and the surface C content also increases, the withstand voltage index increases. Therefore, if the internal C content is 13.8% by mass or more, and the surface C content / internal C content ratio is 2.45 or more, it can be confirmed that the possibility of obtaining sufficient withstand voltage for inductor 1 is high.

[0134] Based on Examples 1-3 and Comparative Examples 1-4, it can be confirmed that if the internal C content is excessively increased, the relative permeability index decreases. In particular, the relative permeability index of Comparative Examples 3-4 is less than 1.0. Therefore, if the internal C content is 13.8% by mass or more and 15.2% by mass or less, and the surface C content / internal C content is 2.5 or more and 2.8 or less, it can be confirmed that there is a high probability of obtaining sufficient voltage withstand capability for the inductor 1 and maintaining a certain level of relative permeability.

[0135] [4. Other implementation methods]

[0136] In the above embodiments, the resin material in the mixed powder is configured such that phenolic biphenyl aralkyl type epoxy resin is used as the main agent and phenolic biphenyl aralkyl resin is used as the curing agent, but it is not limited to this. The main agent and the curing agent can be appropriately changed as long as they are materials with high heat resistance.

[0137] Furthermore, all the above-described embodiments and examples illustrate one aspect of the present invention, which can be arbitrarily modified and applied without departing from the spirit of the present invention.

[0138] In addition, unless otherwise specified, the horizontal and vertical directions, various values, shapes, and materials in the above embodiments include the range that has the same effect as these directions, values, shapes, and materials (the so-called equilibrium range).

[0139] [5. Structures supported by the above-described embodiments and examples]

[0140] The above-described implementation methods and embodiments support the following structures.

[0141] (Structure 1) An inductor in which a wound coil conductor is embedded in a blank containing resin and metallic magnetic particles, wherein the internal carbon content inside the blank is 13.8% by mass or more and 15.2% by mass or less, and the ratio of the internal carbon content to the surface carbon content on the surface of the blank, i.e., surface carbon content / internal carbon content, is 2.5 or more.

[0142] According to the inductor of structure 1, due to the increase in internal C and the decrease in the proportion of metallic magnetic particles, the permeability is effectively prevented from decreasing, the withstand voltage is improved, and the permeability level is maintained.

[0143] (Structure 2) According to the inductor described in Structure 1, the surface C value / internal C value is 2.8 or less.

[0144] According to the inductor of structure 2, due to the increase in internal C and the decrease in the proportion of metallic magnetic particles, the permeability is effectively prevented from decreasing, the withstand voltage is improved, and the permeability level is maintained.

[0145] (Structure 3) According to the inductor described in Structure 1 or 2, the resin is a thermosetting resin made using a main agent and a curing agent, wherein the main agent is an epoxy resin.

[0146] According to the inductor of structure 3, a thermosetting resin with high heat resistance is used, which can improve the heat resistance of the inductor.

[0147] (Structure 4) According to the inductor described in Structure 3, the epoxy resin is at least one of the following: cresol phenolic varnish type epoxy resin, phenolic phenolic varnish type epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, stilbene type epoxy resin, biphenyl type epoxy resin, naphthalene type epoxy resin, triphenol methane type epoxy resin, dicyclopentadiene type epoxy resin, and phenol aralkyl type epoxy resin.

[0148] According to the inductor of structure 4, the heat resistance of the inductor can also be improved by using a main agent with high heat resistance.

[0149] (Structure 5) According to the inductor described in Structure 3 or 4, the curing agent is at least one of benzene resin, acid anhydride, or imidazole resin, such as phenolic varnish resin, phenolic aralkyl resin, naphthol aralkyl resin, biphenyl aralkyl resin, etc.

[0150] According to the inductor of structure 5, the heat resistance of the inductor can also be improved by using a curing agent with high heat resistance.

[0151] (Structure 6) According to any one of the structures 1 to 5, a portion of the surface of the blank is covered by a resin coating.

[0152] According to the inductor of structure 6, the withstand voltage can be further improved through resin coating.

[0153] Explanation of reference numerals in the attached figures

[0154] 1…Inductor; 2…Bulk body; 4…External electrode; 5…Bulk body protective layer (resin coating); 6…Intermediate layer; 10…Bottom surface; 12…Top surface; 14…End face; 16…Side surface; 20…Coil conductor; 22…Winding part; 24…Lead-out part; 30…Core; 50…Ring.

Claims

1. An inductor comprising a wound coil conductor embedded in a blank containing resin and metallic magnetic particles, wherein, The internal carbon content of the billet is above 13.8% by mass and below 15.2% by mass. The ratio of the internal carbon content to the surface carbon content of the blank, i.e., the surface carbon content / internal carbon content, is 2.5 or more.

2. The inductor according to claim 1, wherein, The surface carbon content / internal carbon content ratio is less than 2.

8.

3. The inductor according to claim 1 or 2, wherein, The resin is a thermosetting resin made using a main agent and a curing agent, wherein the main agent is an epoxy resin.

4. The inductor according to claim 3, wherein, The epoxy resin is at least one of the following: cresol phenolic varnish type epoxy resin, phenolic phenolic varnish type epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, stilbene type epoxy resin, biphenyl type epoxy resin, naphthalene type epoxy resin, triphenol methane type epoxy resin, dicyclopentadiene type epoxy resin, and phenol aralkyl type epoxy resin.

5. The inductor according to claim 3 or 4, wherein, The curing agent is at least one of the following: phenolic varnish resin, phenolic aralkyl resin, naphthol aralkyl resin, biphenyl aralkyl resin, etc., as well as acid anhydrides and imidazoles.

6. The inductor according to any one of claims 1 to 5, wherein, A portion of the surface of the blank is covered by a resin coating.

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