Inductor

Abstract

The present invention improves the withstand voltage of an inductor and maintains the level of magnetic permeability.　Provided is an inductor in which embedded is a coil conductor wound in an element body containing resin and metal magnetic material particles. An internal C amount inside the element body is 13.8 mass% to 15.2 mass%. The ratio of the internal C amount and a surface C amount on the surface of the element body, or surface C amount / internal C amount, is 2.5 or more.

Description

inductor

[0001] The present invention relates to an inductor.

[0002] Patent Document 1 discloses an inductor in which a wound coil conductor is embedded in an element body containing resin and metal magnetic particles.

[0003] The amount of C, which is the amount of carbon derived from the resin contained in the element body, can affect the withstand voltage and magnetic permeability of the inductor.

[0004] Japanese Patent Application Laid-Open No. 2022-157440

[0005] An object of the present invention is to improve the withstand voltage and maintain a certain level of magnetic permeability in an inductor having a wound coil conductor embedded in an element containing resin and metal magnetic particles.

[0006] One aspect of the present invention is an inductor having a wound coil conductor embedded in an element body containing resin and metal magnetic particles, wherein the internal C content inside the element body is 13.8 mass% or more and 15.2 mass% or less, and the ratio of the internal C content to the surface C content on the surface of the element body, i.e., surface C content / internal C content, is 2.5 or more. This specification includes the entire content of Japanese Patent Application No. 2024-051037, filed on March 27, 2024.

[0007] According to the present invention, in an inductor having a wound coil conductor embedded in an element containing resin and metal magnetic particles, it is possible to improve the withstand voltage and maintain a certain level of magnetic permeability.

[0008] Fig. 1 is a perspective view of an inductor according to an embodiment of the present invention, viewed from the top side. Fig. 2 is a perspective view of the inductor, viewed from the bottom side. Fig. 3 is a see-through perspective view showing the internal structure of the inductor. Fig. 4 is a cross-sectional view of the inductor shown in Fig. 3 in the IV plane. Fig. 5 is a diagram showing a manufacturing process of the inductor. Fig. 6 is a schematic diagram of a ring in an example.

[0009] In an inductor in which a wound coil conductor is embedded in a base body containing resin and metal magnetic particles, the amount of C, which is the amount of carbon derived from the resin contained in the base body, can affect the inductor's withstand voltage and magnetic permeability.

[0010] The inventors have conducted extensive research into the amount of internal C inside the element body, the amount of surface C on the surface of the element body, and the withstand voltage and magnetic permeability, and have found that the amount of internal C and the amounts of internal and surface C affect the withstand voltage and magnetic permeability of an inductor. Specifically, the inventors have found that the withstand voltage increases as the amount of internal C increases, but the permeability tends to decrease due to factors such as a decrease in the content of metal magnetic particles. The inventors have confirmed that, when the amount of internal C is a predetermined amount, increasing the ratio of the amount of surface C to the amount of internal C can improve the withstand voltage while maintaining a certain level of magnetic permeability.

[0011] The present invention was made based on the above findings, and by specifying the ratio of the amount of surface C to the amount of internal C in an inductor, it is possible to improve the withstand voltage and maintain the same level of magnetic permeability.

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [1. Inductor Configuration] First, the configuration of an inductor 1 according to this embodiment will be described. [1.1 Overall Configuration of Inductor] Figures 1, 2, and 3 are diagrams showing the overall configuration of the inductor 1. Figure 1 is a perspective view of the inductor 1 viewed from the top surface 12 side, and Figure 2 is a perspective view of the inductor 1 viewed from the bottom surface 10 side. The inductor 1 of this embodiment is configured as a surface-mount electronic component, and includes an element body 2 having a substantially rectangular parallelepiped shape, which is one form of a substantially hexahedral shape, and a pair of external electrodes 4 provided on the surface of the element body 2.

[0013] Hereinafter, in the element body 2, the first main surface facing the mounting substrate (not shown) during mounting is defined as the bottom surface 10, the second main surface opposite the bottom surface 10 is defined as the top surface 12, a pair of third main surfaces perpendicular to the bottom surface 10 are defined as end surfaces 14, and a pair of fourth main surfaces perpendicular to the bottom surface 10 and the pair of end surfaces 14 are defined as side surfaces 16. As shown in FIG. 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 the pair of side surfaces 16 is defined as the width W of the element body 2, and the distance between the 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 size of the inductor is, for example, the length L dimension is 2.0 mm, the width W dimension is 1.2 mm, and the thickness T dimension is 0.9 mm.

[0014] 3 is a perspective view showing the internal structure of the inductor. 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.

[0015] The core 30 is a molded body obtained by compression molding a mixed powder of metal magnetic particles and resin into a substantially hexahedral shape by applying pressure and heat while the mixed powder contains the coil conductor 20. The mixed powder may contain a solvent and / or a hardener. The mixed powder may further contain additives such as a lubricant.

[0016] The metal magnetic particles of this embodiment include particles of two 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 metal magnetic particles in the core 30 and also increasing the magnetic permeability.

[0017] In this embodiment, the D50 particle size (median diameter) of the metal particles of the first magnetic particles and the second magnetic particles is 30 μm and 1.5 μm, respectively. The D50 particle size of the first magnetic particles is preferably 10 μm or more and 50 μm or less, and the D50 particle size of the second magnetic particles is preferably 1 μm or more and 5 μm or less. Furthermore, the magnetic particles may contain particles with an average particle size different from that of the first magnetic particles and the second magnetic particles, thereby containing particles of three or more particle sizes.

[0018] The first magnetic particles and the second magnetic particles are both particles having a metal particle and an insulating film covering the surface of the metal particle. By covering the metal particle with the insulating film, the insulation resistance and the withstand voltage are increased.

[0019] The metal particles of the first magnetic particles and the second magnetic particles are, for example, Fe-based metal magnetic particles such as Fe (pure iron) or Fe alloys. Examples of Fe alloys include one or more alloys selected from the group consisting of an alloy containing Fe and Ni, an alloy containing Fe and Co, an alloy containing Fe and Si, an alloy containing Fe, Si and Cr, an alloy containing Fe, Si and Al, an alloy containing Fe, Si, B and Cr, and an alloy containing Fe, P, Cr, Si, B, Nb and C.

[0020] The composition of the metal particles of the first magnetic particles and the composition of the metal particles of the second magnetic particles may be the same or different from each other. The insulating film formed on the surfaces of the metal particles of the first magnetic particles and the second magnetic particles may be, for example, one or more insulating films selected from the group consisting of inorganic glass films, organic-inorganic hybrid films, and inorganic insulating films formed by the sol-gel reaction of metal alkoxides.

[0021] In this embodiment, the first magnetic particles are made of Fe—Si—B alloy particles as metal particles, and the second magnetic particles are made of Fe particles as metal particles.

[0022] In the mixed powder of this embodiment, a phenol biphenyl aralkyl type epoxy resin is used as the main resin material, and a phenol biphenyl aralkyl resin is used as the curing agent.

[0023] Examples of the base resin include cresol novolac epoxy resin, phenol novolac epoxy resin, bisphenol A epoxy resin, bisphenol F epoxy resin, stilbene epoxy resin, biphenyl epoxy resin, naphthalene epoxy resin, triphenolmethane epoxy resin, dicyclopentadiene epoxy resin, and phenol aralkyl epoxy resin. Two or more types of resins may be used as the base resin, rather than one type. Furthermore, in addition to epoxy resin, urethane resin may also be used as the base resin.

[0024] Examples of the curing agent include phenolic resins such as phenol novolac resin, phenol aralkyl resin, naphthol aralkyl resin, and biphenyl aralkyl resin, acid anhydrides, and imidazoles. Two or more types of resins may be used as the curing agent, instead of one type.

[0025] The ratio of the first magnetic raw particles to the second magnetic raw particles is preferably 60:40 or more and 90:10 or less, in terms of weight of the first magnetic raw particles:weight of the second magnetic raw particles, and more preferably 70:30 or more and 80:20 or less, in terms of weight of the first magnetic raw particles:weight of the second magnetic raw particles.

[0026] If there are too many first magnetic raw material particles with large particle sizes, the filling rate decreases, the proportion of metal magnetic particles in the core 30 decreases, and the magnetic permeability decreases. If there are too many second magnetic raw material particles with small particle sizes, the magnetic flux in the core 30 tends to concentrate, and the magnetic permeability decreases.

[0027] The resin content is preferably 2.5% by weight or more and 3.5% by weight or less based on the total weight, and more preferably 2.8% by weight or more and 3.2% by weight or less based on the total weight.

[0028] If the amount of resin is too small, the core 30 does not densify during heating, resulting in unfilled resin areas, a decrease in the proportion of metal magnetic particles in the core 30, and a decrease in magnetic permeability.If the amount of resin is too large, the resin remains in the core 30 as a non-magnetic area after molding, a decrease in the proportion of metal magnetic particles in the core 30, and a decrease in magnetic permeability.

[0029] As shown in Fig. 3, the coil conductor 20 includes a winding portion 22 around which a conductor wire is wound, and a pair of lead-out portions 24 that are drawn out from the winding portion 22 and at least partially exposed from the element body 2. The coil conductor 20 is composed of a conductor wire and a coating layer formed on the surface of the conductor wire. The conductor wire is a strip-shaped conductor wire made of copper and having a rectangular cross section (so-called flat conductor wire). Note that the coil conductor 20 does not necessarily have to be wound, and may be linear, meandering, or the like.

[0030] The winding portion 22 of the coil conductor 20 is formed by spirally winding a strip-shaped conductor wire (hereinafter simply referred to as conductor wire) such that both ends are drawn out to the outer periphery and connected to each other at the inner periphery. Inside the element body 2, the coil conductor 20 is embedded in the core 30 with the central axis of the winding portion 22 oriented along the thickness direction DT of the element body 2. The lead-out portions 24 are drawn out from the winding portion 22 to each of a pair of end faces 14, with one main surface exposed from the element body 2 and the other main surface embedded in the element body 2. The one main surface of the lead-out portion 24 exposed from the element body 2 is electrically connected to the external electrode 4.

[0031] 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 the lead-out portion 24 of the coil conductor 20 at the end face 14, and the portion 4A (FIG. 2) extending to the bottom face 10 is electrically connected to wiring on the circuit board by an appropriate mounting means such as solder.

[0032] FIG. 4 is a cross-sectional view taken along plane IV in FIG. 3 . The plane IV is parallel to the thickness direction DT and is located at the center of the width W. An insulating film, i.e., an element body protective layer 5, is formed on the surface of the element body 2 excluding the area of ​​the external electrodes 4. The element body protective layer 5 is made of, for example, epoxy resin, phenoxy resin, or novolac resin, and may contain metal oxide fine particles as a filler. In this embodiment, the element body protective layer 5 contains a silicon dioxide filler, which serves as metal oxide fine particles, and an epoxy resin. In addition to the above materials, the element body protective layer 5 may be made of a resin such as urethane, acrylic, polyimide, polyimideamide, or polyamide, or may be glass or an oxide film. The element body protective layer 5 is an example of a "resin coating layer."

[0033] [1-2. Carbon Amount] Inductors 1 using metal magnetic particles tend to have a lower withstand voltage compared to, for example, ferrite-based electronic components. One possible way to improve the withstand voltage is to increase the amount of resin in the body 2 of the inductor 1, but increasing the amount of resin reduces the occupancy rate of the metal magnetic particles, which in turn reduces the magnetic permeability.

[0034] The inventors have discovered that the element body 2 can improve its withstand voltage and maintain a certain level of magnetic permeability by having an internal C content of 13.8 mass % or more and 15.2 mass % or less, and by having the surface C content divided by the internal C content of 2.5 or more and 2.8 or less.

[0035] In this embodiment, the element body 2 is produced so that the internal C content is 13.8 mass % or more and 15.2 mass % or less.

[0036] The definition of the internal C content will be explained below. The internal C content, expressed in units of mass %, is one indicator of the amount of carbon inside the element body 2. As shown in Figure 4, the cross section of the element body 2 cut to half its width W is polished. Next, a total of five points are measured as measurement points 40: four points in the center between the corners of the element body 2 and the ends of the coil conductor 20 closest to those corners, and one point in the center of the element body 2.

[0037] The amount of carbon in the measuring section 40 is quantitatively analyzed by SEM (Scanning Electron Microscope)-EDX (Energy Dispersive X-ray spectrometry) using an electron microscope. The electron microscope used is a Schottky field emission scanning electron microscope (model number: JSM-7900F) manufactured by JEOL Ltd. Hereinafter, the electron microscope refers to this Schottky field emission scanning electron microscope.

[0038] The quantitative analysis was performed on four elements 2, and the C amount was quantified in an imaging range of 200 μm×100 μm for each of the 20 measurement points 40, and the arithmetic mean value of the 20 C amount values ​​was defined as the internal C amount.

[0039] In this embodiment, the element body 2 is fabricated so 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.

[0040] The definition of the surface C amount will be explained below. The surface C amount, expressed in mass %, is one indicator of the amount of carbon on the surface of the element body 2. An element body 2 is prepared before the element body protective layer 5 is formed. This element body 2 is formed in the element body molding step (S3) described below, and corresponds to the element body 2 before the barrel polishing step (S4). Any four points on the surface of the element body 2 are used as measurement points (not shown). The surface may be any of the six faces. Furthermore, a total of four similar element bodies 2 are prepared, making a total of 20 measurement points.

[0041] The C amount in the measurement area is quantified in an imaging range of 200 μm × 100 μm for each of the 20 measurement areas using the same electron microscope as used for measuring the internal C amount, and the arithmetic mean of the 20 C amount values ​​is defined as the surface C amount.

[0042] The value obtained by dividing the amount of surface C by the amount of internal C is expressed as the amount of surface C / the amount of internal C, and is a dimensionless quantity.

[0043] Inductors with such a configuration can improve DC bias characteristics by using a soft magnetic material for the magnetic particles, and are therefore used as electronic components in electric circuits through which large currents flow, as choke coils in DC-DC converter circuits and power supply circuits, and as electronic components in electronic devices such as personal computers, DVD players, digital cameras, TVs, mobile phones, smartphones, car electronics, medical and industrial machinery, etc. However, the uses of inductors are not limited to these, and they can also be used, for example, in tuning circuits, filter circuits, rectifying and smoothing circuits, etc.

[0044] [2. Manufacturing Process of Inductor] The inductor 1 can be produced as follows. Figure 5 is a diagram showing the manufacturing process of the inductor 1. The manufacturing process of the inductor 1 can include a coil conductor forming step (S1), a preform forming step (S2), an element molding step (S3), a barrel polishing step (S4), a surface treatment step (S5), and an external electrode forming step (S6).

[0045] The coil conductor forming step (S1) is a step of forming a coil conductor 20 from a conductive wire. In this step, the coil conductor 20 is formed into a shape having the above-mentioned winding portion 22 and a pair of lead-out portions 24 by winding the conductive wire using a winding method known as "alpha winding." Alpha winding refers to a state in which the conductive wire, which functions as a conductor, is wound in two stages in a spiral shape so that the lead-out portions 24 at the beginning and end of the winding are located on the outer periphery. The number of turns of the coil conductor 20 is not particularly limited.

[0046] The preform formation step (S2) is a step of forming a preform called a tablet. The preform is formed by pressing the mixed powder, which is the material of the element 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., E-shaped) having a groove into which the coil conductor 20 fits, and a second tablet of an appropriate shape (e.g., I-shaped or plate-shaped) that covers the groove of the first tablet.

[0047] In the element molding step (S3), the first tablet, the coil conductor, and the second tablet are set in a molding die, and while applying heat, pressure is applied in the overlapping direction of the first tablet and the second tablet, and they are hardened to integrate the first tablet, the coil conductor, and the second tablet. This results in the molding of the element 2, in which the coil conductor 20 is enclosed in the core 30. The molding die is made up of a plurality of metal parts. The clearance between the metal parts is set to 20 μm. The smaller the clearance, the less likely resin is to leak from the gap and the more likely resin is to accumulate on the surface of the element 2, and therefore the amount of resin on the surface of the element 2 tends to be greater.

[0048] In the barrel polishing step (S4), a plurality of element bodies 2 are loaded into a drum, and the drum is rotated so as not to apply excessively strong impacts. A coating liquid that will become the element body protective layer 5 is sprayed onto the element bodies 2. This rounds the corners of the element bodies 2 and applies the coating liquid to the element bodies 2. In this embodiment, the coating liquid contains a silicon dioxide filler that serves as metal oxide microparticles and an epoxy resin that serves as an organic resin.

[0049] Next, the element body 2 coated with the coating liquid is taken out of the drum and heat treated to form an element body protective layer 5 on the surface of the element body 2 .

[0050] The formation of the element body protective layer 5 is not limited to the above, and can be performed by various methods, such as spraying a coating liquid onto the element body 2, dipping the element body 2 into the coating liquid, supplying the coating liquid to the surface of the element body 2 via a dispenser, and / or printing a coating material onto the surface of the element body 2 using various printing methods, in a separate step from the barrel polishing step (S4).

[0051] The surface treatment step (S5) is a step of 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 lead-out portions 24 are exposed. Specifically, by irradiating with laser light, the element body protective layer 5 on the surface of the core 30 and the coating layer on the lead-out 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 metal magnetic particles exposed from the core 30 is removed. As a result, the exposed area of ​​the metal of the metal magnetic particles per unit area of ​​the surface of the core 30 is larger in the planned electrode locations on the surface of the core 30 than in other surface areas of the core 30.

[0052] The wavelength of the laser light is, for example, 180 nm or more and 3000 nm or less, more preferably 532 nm or more and 1064 nm or less. The irradiation energy of the laser light is 1 W / mm ２ More than 30W / mm ２ Preferably, 5 W / mm or less ２ 12W / mm or more ２ The following is more preferred:

[0053] In the external electrode formation step (S6), the external electrodes 4 are formed in the areas irradiated with the laser light, which are the planned electrode locations on the core 30. Specifically, first, a Cu plating layer is formed by electrolytic plating in the planned electrode locations on the core 30. Subsequently, a Ni plating layer and a Sn plating layer can be formed by electrolytic plating on the Cu plating layer.

[0054] The Cu plating layer can be formed by electrolytic copper plating, such as copper sulfate plating, copper pyrophosphate plating, or copper cyanide plating.

[0055] When forming the Ni plating layer and the Sn plating layer, an additive such as a brightener may be added to the plating solution.

[0056] [3. Examples] Next, examples of the inductor 1 will be described. Examples and comparative examples shown in Table 1 were fabricated, and the withstand voltage index representing the magnitude of the withstand voltage of the inductor 1 and the magnetic permeability index representing the magnitude of the magnetic permeability of the inductor 1 were evaluated. Examples 1, 2, and 3 and comparative examples 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11 were fabricated using the manufacturing process shown in FIG. 5 described above. In each example or comparative example, the inductor 1 and a ring 50 (see FIG. 6 ), which will be described later, were fabricated as samples. In each example or comparative example, the number of samples of the inductor 1 was 10, and the number of samples of the ring 50 was 10. Furthermore, each example or comparative example differed in the clearance of the molding die in the element molding step (S3), the mixed powder conditions for the element body 2, and the pressure molding conditions for hardening the element body 2. These conditions will be described later.

[0057]

[0058] [3.1 Fabrication of Examples and Comparative Examples] <Fabrication of Inductors and Chips> The configuration of inductor 1 as a sample in Examples 1-3 and Comparative Examples 1-11 will be described. The mixed powder conditions, which are the configuration of the mixed powder in the preform formation step (S2), are as follows. As the metal magnetic particles, Fe-Si-B-based first magnetic particles with a D50 particle size of 30 μm and Fe-based second magnetic particles with a D50 particle size of 1.5 μm were mixed so that the weight of the first magnetic raw material particles: the weight of the second magnetic raw material particles = 75:25. As the resin, a phenol biphenyl aralkyl type epoxy resin was used as the base resin, and a phenol biphenyl aralkyl resin was used as the curing agent.

[0059] The weight ratio of the first magnetic particles, the second magnetic particles, and the resin in the mixed powder was set to 2.5% by weight or more and 3.5% by weight or less of the resin based on the total mixed powder. Thus, in each example or comparative example, the amount of mixed powder in the element body 2 in the preform formation step (S2) varies within the range of 2.5% by weight or more and 3.5% by weight or less of the resin based on the total mixed powder, and the mixed powder conditions are different. Note that the mixed powder conditions are the same in one example or one comparative example. The more resin there is based on the total mixed powder, the greater the internal C content tends to be.

[0060] In the preform forming step (S2), the shape of the first tablet is I-shaped, and the shape of the second tablet is E-shaped.

[0061] The pressure molding conditions for the element body 2 in the element body molding step (S3) were set to a predetermined temperature, a predetermined pressure, and a predetermined pressure time. In each example or comparative example, the predetermined temperature and predetermined pressure were changed as appropriate. The higher the temperature or pressure applied, the greater the amount of C on the surface tends to be. Note that the curing conditions in one example or one comparative example are the same. In Example 2, the pressure molding conditions were a temperature of 180°C, a pressure of 20 MPa, and a pressure time of 100 seconds.

[0062] The clearance of the molding die in the element molding step (S3) was 20 μm in Examples 1 to 3 and Comparative Examples 1 to 4, and 40 μm in Comparative Examples 5 to 11. When the clearance was 20 μm, the ratio of the surface C amount to the internal C amount tended to be larger than when the clearance was 40 μm.

[0063] After forming an element body protective layer 5 on the surface of the element body 2 in the barrel polishing step (S4), in the surface treatment step (S5), laser light was irradiated to planned electrode locations on the surface of the element body 2, including exposed locations of the lead-out portions 24 of the coil conductors 20. Furthermore, in the external electrode formation step (S6) described above, external electrodes 4 were formed. The dimensions of the inductor 1 were a length L of 2.0 mm, a width W of 1.6 mm, and a thickness T of 1.2 mm.

[0064] Next, the configuration of the ring 50 as a sample in Examples 1 to 3 and Comparative Examples 1 to 11 will be described. Fig. 6 is a schematic diagram of the ring 50 in the examples.

[0065] There is no coil conductor forming step (S1), and the ring 50 does not include a coil conductor 20. The mixed powder conditions, which are the composition of the mixed powder in the preform forming step (S2), are the same as those of the inductor 1 in each example or comparative example. The tablet in the preform forming step (S2) is ring-shaped. The ring shape can also be called a torus shape. The pressure molding conditions of the element body 2 in the element molding step (S3) are the same as those of the inductor 1 in each example or comparative example. When the element molding step (S3) is completed, a ring 50 formed in a torus shape and not including an external electrode 4 or a coil conductor 20 is obtained.

[0066] 6 is defined as the thickness of the ring 50, and the dimension in the La direction is defined as the length. The dimension between the inner and outer circumferences of the ring 50 is defined as the ring width WR. The ring 50 has a length of 2.0 mm, a ring width WR of 1.2 mm, and a thickness of 0.9 mm.

[0067] [3.2 Evaluation] For the fabricated Examples 1 to 3 and Comparative Examples 1 to 11, the internal C amount and surface C amount were measured, and the withstand voltage index and the relative permeability index were evaluated.

[0068] [3.2.1 Evaluation Method] Evaluation was performed by the following method. <Internal C Amount and Surface C Amount> The internal C amount and surface C amount of the inductor 1 fabricated as described above were measured as described in the embodiment. The four inductors 1 used in measuring the internal C amount and surface C amount were randomly selected from the ten samples.

[0069] The definition of the internal C amount of the ring 50 will be explained below. The internal C amount of the ring 50 is expressed in units of mass %. The ring 50 is cut into two equal parts along a plane extending in the La-Ta direction. The two cross sections 51 of the ring 50 exposed by the cut are polished, and the center of the cross section 51 is designated as the measurement section 52. The C amount in the measurement section 52 is quantitatively analyzed by SEM-EDX using the same electron microscope as used to measure the internal C amount. Quantitative analysis was performed on 10 rings 50, and the C amount was quantified in an imaging range of 200 μm × 100 μm for each of the 20 measurement sections 52, and the arithmetic mean of the 20 C amount values ​​was measured as the internal C amount of the ring 50.

[0070] The definition of the surface C amount of the ring 50 will be explained below. The unit of the surface C amount of the ring 50 is mass %. The measurement points 54 are located at the center of the ring width WR and facing each other on the flat surfaces 53 extending in the La direction of the ring 50. For one ring 50, the measurement points 54 are four points on one flat surface 53 of the ring 50 and the other flat surface 53. The C amount in the measurement points 54 is quantitatively analyzed by SEM-EDX using the same electron microscope as used to measure the internal C amount. Quantitative analysis was performed on five rings 50, and the C amount was quantified in an imaging range of 200 μm × 100 μm for each of the 20 measurement points 54. The arithmetic mean of the 20 C amount values ​​was measured as the surface C amount of the ring 50. The five rings 50 used to measure the surface C amount of the ring 50 were randomly selected from 10 samples.

[0071] The amount of C inside the ring 50 and the amount of C on the surface of the ring 50 were approximately equal to the amount of C inside and the amount of C on the surface of the inductor 1, which was produced under the same mixed powder conditions and pressure molding conditions.

[0072] <Withstand voltage index> Using an insulation resistance meter, a charge time of 1 second and a discharge time of 1 second were applied, with voltages of 25 V, 50 V, 100 V, 200 V, 300 V, 400 V, and 500 V applied in ascending order. The pair of external electrodes 4 of the inductor 1 were brought into contact with tweezers probes, and the insulation resistance was measured to see if it was 10 ５The voltage immediately preceding the voltage at which the resistance fell below Ω was used to measure the withstand voltage. The withstand voltage is measured in units of V / mm. An Advantest Digital Ultra-High Resistance / Micro-Current Meter (Model R8340) was used as the insulation resistance meter.

[0073] The withstand voltages of the ten fabricated inductors 1 were measured, and the arithmetic mean value was calculated. The arithmetic mean value was used as the average withstand voltage. Furthermore, the withstand voltage index was calculated by dividing the average withstand voltage of each example or comparative example by the arithmetic mean value of the average withstand voltages of comparative examples 5 to 11, which had a clearance of 40 μm.

[0074] <Relative Permeability Index> The relative permeability of the ring 50 at a frequency of 1 MHz was measured using a permeability measuring device. The relative permeabilities of the ten produced rings 50 were measured, and the arithmetic mean value was calculated, and this arithmetic mean value was used as the average relative permeability. The permeability measuring device used was an impedance analyzer (model number E4990A) manufactured by Keysight Technologies, Inc.

[0075] Furthermore, the average relative permeability of each example or comparative example was divided by the average relative permeability of comparative example 5 to calculate a relative permeability index.

[0076] The internal C amount and surface C amount of the ring 50 were almost identical to the internal C amount and surface C amount of the inductor 1, which was manufactured under the same mixed powder conditions and pressure molding conditions. Therefore, the relative permeability index of the inductor 1 can be obtained by using the ring 50. Therefore, the tendency of the relative permeability of the inductor 1 can be confirmed by measuring the relative permeability using the ring 50.

[0077] [3.2.1 Evaluation Results] As shown in Table 1, by comparing Examples 1-3 and Comparative Examples 1-4 with Comparative Examples 5-11, it was confirmed that when the clearance was 40 μm, the amount of surface C was less likely to increase even if the amount of internal C increased, compared to when the clearance was 20 μm.

[0078] From Comparative Examples 5-11, it was confirmed that even if the internal C content increases, the withstand voltage index does not increase unless the surface C content increases. From Examples 1-3 and Comparative Examples 1-4, it was confirmed that when the internal C content increases to 13.8 mass% or more and the surface C content also increases, the withstand voltage index increases. This confirmed that when the internal C content is 13.8 mass% or more and the surface C content / internal C content ratio is 2.45 or more, there is a high possibility that a sufficient withstand voltage of the inductor 1 can be obtained.

[0079] From Examples 1-3 and Comparative Examples 1-4, it was confirmed that if the internal C content is too high, the relative permeability index decreases. In particular, the relative permeability index of Comparative Examples 3-4 is less than 1.0. This confirms that if the internal C content is 13.8 mass% or more and 15.2 mass% or less, and the surface C content / internal C content ratio is 2.5 or more and 2.8 or less, it is highly likely that the inductor 1 can achieve a sufficient withstand voltage and maintain a high level of relative permeability.

[0080] [4. Other Embodiments] In the above-described embodiment, the resin material in the mixed powder is configured to use a phenol biphenyl aralkyl type epoxy resin as the base agent and a phenol biphenyl aralkyl resin as the curing agent, but this is not limited thereto. The base agent and the curing agent can be changed as appropriate as long as they are materials with high heat resistance.

[0081] It should be noted that all of the above-described embodiments and examples are merely examples of one aspect of the present invention, and can be modified and applied as desired without departing from the spirit of the present invention. Furthermore, unless otherwise specified, the horizontal, vertical, and other directions, various numerical values, shapes, and materials in the above-described embodiments include a range that provides the same action and effect as those directions, numerical values, shapes, and materials (so-called equivalent ranges).

[0082] 5. Configurations Supported by the Above-described Embodiments and Examples The above-described embodiments and examples support the following configurations.

[0083] (Configuration 1) An inductor having a wound coil conductor embedded in an element body containing resin and metal magnetic particles, wherein the internal C content inside the element body is 13.8 mass% or more and 15.2 mass% or less, and the ratio of the internal C content to the surface C content on the surface of the element body, i.e., surface C content / internal C content, is 2.5 or more. The inductor of Configuration 1 effectively prevents a decrease in magnetic permeability due to a decrease in the content of metal magnetic particles caused by an increase in the internal C content, thereby improving the withstand voltage and maintaining the level of magnetic permeability.

[0084] (Configuration 2) The inductor according to Configuration 1, wherein the surface C content / internal C content is 2.8 or less. The inductor of Configuration 2 effectively prevents a decrease in magnetic permeability due to a decrease in the proportion of metal magnetic particles contained due to an increase in the internal C content, thereby improving the withstand voltage and further maintaining the level of magnetic permeability.

[0085] (Configuration 3) The inductor according to Configuration 1 or 2, wherein the resin is a thermosetting resin made using a base material and a curing agent, and the base material is an epoxy resin. According to the inductor of Configuration 3, since a thermosetting resin with high heat resistance is used, the heat resistance of the inductor can be improved.

[0086] (Configuration 4) The inductor according to Configuration 3, wherein the epoxy resin is at least one of cresol novolac epoxy resin, phenol novolac epoxy resin, bisphenol A epoxy resin, bisphenol F epoxy resin, stilbene epoxy resin, biphenyl epoxy resin, naphthalene epoxy resin, triphenolmethane epoxy resin, dicyclopentadiene epoxy resin, and phenol aralkyl epoxy resin. According to the inductor of Configuration 4, a base resin with high heat resistance is used, thereby further improving the heat resistance of the inductor.

[0087] (Configuration 5) The inductor according to Configuration 3 or 4, wherein the curing agent is at least one of a phenolic resin such as a phenol novolac resin, a phenol aralkyl resin, a naphthol aralkyl resin, or a biphenyl aralkyl resin, an acid anhydride, or an imidazole. According to the inductor of Configuration 5, a curing agent with high heat resistance is used, thereby further improving the heat resistance of the inductor.

[0088] (Configuration 6) The inductor according to any one of configurations 1 to 5, wherein a portion of the surface of the element body is covered with a resin coating layer. According to the inductor of configuration 6, the resin coating layer can further improve the withstand voltage.

[0089] 1...inductor, 2...element body, 4...external electrode, 5...element body protective layer (resin coating layer), 6...intermediate layer, 10...bottom surface, 12...top surface, 14...end surface, 16...side surface, 20...coil conductor, 22...winding portion, 24...drawing portion, 30...core, 50...ring.

Claims

1. An inductor having a wound coil conductor embedded in an element body containing resin and metal magnetic particles, wherein the internal C content inside the element body is 13.8% by mass or more and 15.2% by mass or less, and the ratio of the internal C content to the surface C content on the surface of the element body, i.e., surface C content / internal C content, is 2.5 or more.

2. The inductor according to claim 1, wherein the surface C amount / internal C amount is 2.8 or less.

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

4. The inductor according to claim 3, wherein the epoxy resin is at least one of cresol novolac type epoxy resin, phenol novolac 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, triphenolmethane 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 a phenolic resin such as a phenol novolac resin, a phenol aralkyl resin, a naphthol aralkyl resin, or a biphenyl aralkyl resin, an acid anhydride, or an imidazole.

6. The inductor according to any one of claims 1 to 5, wherein a portion of the surface of the element body is covered with a resin coating layer.

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