Inductor and production method for inductor

Abstract

Provided are an inductor that has improved magnetic characteristics and a production method for the inductor. This inductor 1 comprises: an element body 10 that comprises a plurality of metal magnetic powders MP; and a coil that is provided inside the element body 10. The metal magnetic powders MP comprise: metal magnetic particles DP that include Fe; and an oxide coating film OL that includes an easily oxidized material that is more easily oxidized than Fe. When a region in which the distance between the surface of a first metal magnetic particle DP and the surface of a second metal magnetic particle DP that is adjacent to the metal magnetic particle DP decreases is an interparticle layer region R1 and a region in which the distance increases is a non–interparticle layer region R2, the concentration of the easily oxidized material in the non–interparticle layer region R2 is greater than the concentration of the easily oxidized material in the interparticle layer region R1.

Description

Inductor and method for manufacturing the same

[0001] The present disclosure relates to inductors and methods for manufacturing inductors.

[0002] Patent Document 1 discloses a coil component in which a spiral coil part covered with a magnetic material part is in direct contact with the magnetic material part, the magnetic material part being mainly composed of magnetic alloy grains and not containing a glass component, and an oxide film of the magnetic alloy grains is present on the surface of each magnetic alloy grain. ３ O ４ and Fe, which belongs to the non-magnetic material ２ O ３ and Cr ２ O ３ It is disclosed that the above at least includes the following.

[0003] JP 2012-164958 A

[0004] The coil component described in Patent Document 1 contains a non-magnetic component, Cr, as an oxide film between magnetic alloy grains, and therefore required further improvement in magnetic properties. More specifically, it was discovered that the magnetic properties of the inductor could be improved by improving the concentration of the non-magnetic component in the oxide film.

[0005] Therefore, an object of the present disclosure is to provide an inductor with improved magnetic properties and a method for manufacturing the inductor.

[0006] The inductor according to the present disclosure comprises: an element body including a plurality of metal magnetic powders; and a coil provided within the element body; the metal magnetic powders include metal magnetic particles containing Fe and an oxide film containing an oxidizable material that is more easily oxidized than Fe; and when a region where the distance between a surface of a first metal magnetic particle and a surface of a second metal magnetic particle adjacent to the first metal magnetic particle becomes smaller is defined as an intergranular layer region, and a region where the distance becomes larger is defined as a non-intergranular layer region, the concentration of the oxidizable material in the non-intergranular layer region is higher than the concentration of the oxidizable material in the intergranular layer region.

[0007] The method for manufacturing an inductor according to the present disclosure is a method for manufacturing the above-described inductor, and includes: a preparation step of adding the easily oxidizable material to the metal magnetic particles to prepare a magnetic material that constitutes an element body; a pressurization step of pressurizing an element body precursor formed using the magnetic material, thereby distributing the easily oxidizable material more in the non-intergranular layer region than in the intergranular layer region; and a heat treatment step of heating the magnetic material to form an oxide film containing the easily oxidizable material on the surface of the metal magnetic particles.

[0008] According to the present disclosure, it is possible to provide an inductor with improved magnetic properties and a method for manufacturing an inductor.

[0009] FIG. 1 is a perspective view of an inductor according to the present disclosure. FIG. 2 is an exploded perspective view of an embodiment of an inductor according to the present disclosure. FIG. 3 is a cross-sectional view of a central portion of the cross section taken through the center of the element body and the winding axis of the coil in FIG. 1 , perpendicular to the mounting surface and end surfaces of the element body. FIG. 4 is an enlarged cross-sectional view of the region bounded by the dashed line in FIG. 3. FIG. 5A is a graph showing the concentration distribution of Si, Fe, and Zn in the intergranular layer region. FIG. 5B is a graph showing the concentration distribution of Si, Fe, and Zn in the non-intergranular layer region. FIG. 5C is a graph showing the concentration distribution of Si, Fe, and Zn at other positions in the non-intergranular layer region. FIG. 6 is a manufacturing flow illustrating the manufacturing process of an inductor according to the present disclosure. FIG. 7 is an element mapping image of an inductor according to a comparative example. FIG. 8 is an element mapping image of an inductor according to an example. FIG. 9 is a graph showing the change in magnetic permeability before and after heat treatment. FIG. 10 is a table showing the change in magnetic permeability for the comparative example and examples 1 to 4, which are the basis for the graph in FIG. 9 .

[0010] The inductor of the present disclosure will be described below. Note that the present disclosure is not limited to the following configurations and may be modified as appropriate without departing from the spirit of the present disclosure. In addition, a combination of multiple individual preferred configurations described below also constitutes the present disclosure.

[0011] The inductor of the present disclosure is used in, for example, a DC-DC converter, but can also be used in applications other than DC-DC converters.

[0012] In this specification, terms indicating the relationship between elements (e.g., "parallel," "orthogonal," etc.) and terms indicating the shape of elements do not only mean the strict literal form, but also mean a range that is substantially equivalent, for example, a range that includes a difference of about a few percent. Note that in this specification, the direction in which the magnetic layers and coil conductors that make up the element body are stacked is referred to as the "stacking direction."

[0013] Furthermore, in the description of this specification, references to directions or orientations are made merely for the convenience of explanation and are not intended to limit the scope of the present disclosure unless otherwise explicitly stated. For example, relative terms such as "outside (or outer, external, or outer circumference)" and "inside (or inner, internal, or inner circumference)" and their derivatives should be understood to refer to the direction as described or illustrated. In other words, unless otherwise explicitly stated, the invention is not necessarily limited to a specific direction, orientation, form, or the like. Similarly, terms such as "provided" and "connected" and their derivatives may refer to a configuration in which other elements, such as intervening elements, are present, rather than being limited to a direct configuration, unless otherwise explicitly stated.

[0014] The drawings shown below are schematic diagrams, and the dimensions, aspect ratio, scale, etc. may differ from those of the actual product.

[0015] 1 to 5C, the inductor of the present disclosure includes an element body 10 including a plurality of metal magnetic powder particles MP (see FIG. 3), and a coil provided within the element body 10.

[0016] The element body 10 has, for example, a rectangular parallelepiped or approximately rectangular parallelepiped shape having six sides (see FIG. 1 ). The corners and ridges of the element body 10 may be rounded. A corner is a portion where three sides of the element body 10 intersect, and a ridge is a portion where two sides of the element body 10 intersect.

[0017] 1, the length direction, width direction, and height direction of the inductor 1 and the element body 10 are shown as L direction, W direction, and T direction, respectively. The length direction L, width direction W, and height direction T are perpendicular to each other. The mounting surface of the inductor 1 is, for example, a surface (LW surface) parallel to the length direction L and width direction W.

[0018] 1 has a first main surface 11 and a second main surface 12 that face each other in a height direction T, a first end surface 13 and a second end surface 14 that are perpendicular to the height direction T and face each other in a length direction L, and a first side surface 15 and a second side surface 16 that face each other in a width direction W that is perpendicular to the length direction L and the height direction T. In the example shown in FIG. 1 , the first main surface 11 of the element body 10 corresponds to the mounting surface (bottom surface) of the element body 10. Note that the second main surface 12 may also be the mounting surface of the element body 10.

[0019] The element body 10 has a laminated structure in which a plurality of element layers, each having a magnetic layer ML and a coil conductor CD (see FIG. 2), are stacked in a stacking direction (e.g., height direction T). In this embodiment, the element body 10 is constructed by stacking element layers G1 to G8 as shown in FIG. 2. A coil is then constructed by stacking a plurality of coil conductors CD. By constructing a coil by stacking coil conductors CD, it is possible to make it smaller than a wire-wound coil in which a conductor wire is wound. Note that the boundaries between the layers in the laminated structure of the element body 10 disappear. Furthermore, each of the element layers G1 to G8 may be constructed by stacking a plurality of identical patterns.

[0020] A coil formed by stacking multiple coil conductors CD is provided within the element body 10. In the example shown in FIG. 2, two coils (a first coil and a second coil) are provided within the element body 10 along the stacking direction. More specifically, the first coil is formed by the coil conductors CD of element body layers G4 and G5, and the second coil is formed by the coil conductors CD of element body layers G2 and G3. The inductor 1 of the first embodiment is not limited to this example; for example, three or more coils may be provided along the stacking direction. Furthermore, a coil array may be formed by arranging multiple coils side by side within the element body 10 in a direction intersecting the stacking direction (direction L in FIG. 1).

[0021] External electrodes E are provided on the mounting surface (first main surface 11) of the element body 10. In the example shown in Fig. 2, the external electrodes E include a first external electrode E1 and a second external electrode E2 connected to the respective ends of the first coil, and a third external electrode E3 and a fourth external electrode E4 connected to the respective ends of the second coil. Two external electrodes are provided for each coil. Therefore, if the number of coils is three, the number of external electrodes may be six.

[0022] Through-hole conductors TH are used to connect the coil (coil conductor CD) and the external electrodes E. That is, first through-hole conductors TH1 to TH4 are provided corresponding to the first external electrodes E1 to E4. The first through-hole conductors TH1 to TH4 extend in the stacking direction.

[0023] The magnetic layer ML of each of the element layers G1 to G8 includes metal magnetic powder MP (see FIG. 3) made of a magnetic material. The metal magnetic powder MP includes metal magnetic particles DP, an oxide film OL, and a resin.

[0024] The average particle size of the metal magnetic powder MP may be preferably 0.2 μm or more and 20 μm or less, more preferably 0.2 μm or more and 15 μm or less, and even more preferably 1 μm or more and 6 μm or less.

[0025] The average particle size of the metal magnetic powder MP can be measured using the following procedure. An inductor sample is cut to obtain a cross section. Specifically, the sample cross section is obtained by cutting the sample through the center of the element body and the winding axis of the coil, perpendicular to the mounting surface and end surface of the element body. The cross section may be flattened by ion milling or the like. Three randomly selected locations in the center of the cut surface, which corresponds to the center of the element body 10, are photographed using an SEM (at approximately 1000x magnification) and subjected to composition analysis using EDX. The location of the metal magnetic powder MP in the SEM image can be identified by confirming the location of Fe in the field of view from the EDX composition analysis results. The average value of the obtained circle-equivalent diameters for the identified metal magnetic powder MP is then used as the average particle size of the metal magnetic particles. Note that the term "average particle size" used herein may refer to the average particle size D50 (particle size equivalent to a cumulative percentage of 50% by volume).

[0026] The metal magnetic particles DP contain at least Fe (iron). More specifically, they may be particles or alloy particles containing Fe and Si. Examples of metal magnetic particles DP include Fe-Si alloys, Fe-Si-Cr (chromium) alloys, Fe-Si-Al (aluminum) alloys, Fe-Si-B (boron)-P (phosphorus)-Cu (copper)-C (carbon) alloys, and Fe-Si-B-Nb (niobium)-Cu alloys. The metal magnetic particles DP may also contain impurities such as Cr, Mn (manganese), Cu, Ni (nickel), P, S (sulfur), or Co (cobalt) that are not intended in the manufacturing process. The metal magnetic particles DP may also be contained in a magnetic paste, as will be described in detail in the description of the manufacturing method. The magnetic paste may contain an easily oxidizable material that is more easily oxidized than Fe (for example, any of Zn (zinc), Zr (zirconium), Al (aluminum), Ti (titanium), Mg (magnesium), Cr (chromium), and Mo (molybdenum)). By including an easily oxidizable material in the magnetic paste, the easily oxidizable material can be attached to the surface of the metal magnetic particles DP, and the easily oxidizable material on the surface of the metal magnetic particles DP is preferentially oxidized, leaving oxides of the easily oxidizable material on the surface of the metal magnetic particles DP, thereby reducing oxidation of the Fe element contained in the metal magnetic particles. This prevents a decrease in magnetic permeability due to oxidation of the Fe element, thereby further increasing the magnetic permeability of the inductor 1. The resin component contained in the magnetic paste may disappear or remain due to heat treatment of the element body. Furthermore, the material of the easily oxidizable material that is more easily oxidized than Fe is selected to be different from the material contained in the metal magnetic particles DP, for example, if the material of the metal magnetic particles DP is an Fe-Si-Cr alloy, a material other than Si or Cr is selected as the easily oxidizable material.

[0027] The surfaces of the metal magnetic particles DP are covered with an insulating coating. In this specification, "insulating" refers to a volume resistivity of 1 MΩcm or more. When the surfaces of the metal magnetic particles DP are covered with an insulating coating, the insulation between the metal magnetic particles DP can be improved. A specific example of the insulating coating is an oxide coating OL, as shown in FIG. 3. Note that a configuration in which an insulating material is provided outside the oxide coating OL may also be used, in other words, the metal magnetic particles DP and the oxide coating OL may be coated with an insulating material (not shown).

[0028] The oxide film OL is a film produced by oxidation of an element contained in the metal magnetic particles DP that is more easily oxidized than Fe. In other words, the oxide film OL may contain an oxide of the above-mentioned oxidizable material that is more easily oxidized than Fe and an oxide of a raw material derived from the metal magnetic particles DP. As used herein, the term "oxidizable material that is more easily oxidized than Fe" refers to a material that has a greater ionization tendency than Fe. The thickness of the oxide film OL may be preferably 1 nm to 100 nm, more preferably 1 nm to 50 nm, and even more preferably 1 nm to 20 nm. The thickness of the oxide film OL can be measured, for example, by photographing a cross section obtained by polishing an inductor sample with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and measuring the thickness of the oxide film OL covering the surface of the metal magnetic particles DP from the obtained SEM image. The thickness of the oxide film OL is measured by photographing any three locations in the center of a cross section obtained by cutting the element body through the center and the coil winding axis, perpendicular to the mounting surface and end surface of the element body. The thickness of the oxide coating OL is measured at three arbitrary positions in the center of each visual field, and the average of these nine positions (three arbitrary positions in the center of the cut surface) x (three arbitrary positions in the center of each visual field) may be used as the thickness of the oxide coating OL.

[0029] A suitable easily oxidizable material may include at least one selected from the group consisting of Zr, Al, Ti, Mg, Cr, and Mo. More specifically, a metal with a greater ionization tendency than Fe may be used. If such a material is used as the easily oxidizable material, the easily oxidizable material is oxidized preferentially over the metal magnetic powder, thereby reducing oxidation of the Fe-containing metal magnetic particles DP.

[0030] To increase the strength of the element body 10, the element body 10 may be formed by stacking the above-mentioned element body layers G1 to G8, and then heat-treated, and then the element body 10 may be impregnated with the resin, so that the resin is present between adjacent metal magnetic powder particles MP bonded by an insulating coating. As an example, the resin impregnated into the element body 10 after heat-treatment may be one or more resins selected from the group consisting of epoxy resin, phenolic resin, polyester resin, polyimide resin, polyolefin resin, silicone resin, acrylic resin, polyvinyl butyral resin, cellulose resin, alkyd resin, etc.

[0031] In the inductor 1 of this embodiment, a cut surface is obtained by cutting the element body through the center and the winding axis of the coil perpendicular to the mounting surface and end surface of the element body, and photographing three arbitrary points in the center of the cut surface. As shown in Figure 3, in each field of view, it can be seen that there are areas where resin impregnated into the element body or voids are present, indicated by dots around multiple metal magnetic powder particles MP, as shown in Figure 3. Image analysis software (for example, image analysis software WinROOF2021 (manufactured by Mitani Corporation)) is used to select from the multiple metal magnetic powder particles MP those where the distance between the center of gravity of two metal magnetic particles DP is 100 nm or less, thereby identifying one metal magnetic particle DP and the other metal magnetic particle DP adjacent to that metal magnetic particle DP. As shown in Figure 4, when observing the relationship between one metal magnetic particle DP and the other metal magnetic particle DP, the region where the distance between the surface of one metal magnetic particle DP and the surface of the other metal magnetic particle DP adjacent to the metal magnetic particle DP becomes small is defined as the intergranular layer region R1, and the region where the distance between the surface of one metal magnetic particle DP and the surface of the other metal magnetic particle DP adjacent to the metal magnetic particle DP becomes large is defined as the non-intergranular layer region R2. The concentration of the easily oxidizable material in the non-intergranular layer region R2 is higher than the concentration of the easily oxidizable material in the intergranular layer region R1. As used herein, the "intergranular layer region" refers to the region between two particles facing each other, as shown in Figure 4, where the line segment connecting the centers of gravity of adjacent particles is defined as a virtual line L1, and virtual lines L2 are drawn on both sides of the virtual line L1 at ±10° from the center of gravity of the metal magnetic particle. In Figure 4, the maximum distance between the two particles is, for example, 50 nm or less. Here, the imaginary lines L1 and L2 can be drawn using image analysis software (for example, image analysis software WinROOF2021 (manufactured by Mitani Shoji Co., Ltd.)) when determining the circle-equivalent diameter of the above-mentioned metal magnetic powder MP. Furthermore, the term "non-intergranular layer region" in this specification refers to a region other than the intergranular layer region, where the interparticle distance is greater than that in the intergranular layer region.

[0032] Furthermore, the "concentration of the easily oxidizable material" in this specification can be measured by the procedure described below. A cross section is created by cutting the element body 10 in the thickness direction along the length of the element body 10 from the mounting surface (first main surface 11) side of the element body 10 at a position passing through the coil winding axis. This cross section is photographed using a TEM (magnification of approximately 600,000 times) so that the metal magnetic powder MP is within the coil winding axis portion of the photographic field, and the location of the metal magnetic powder MP is identified. Quantitative analysis is performed at the identified position using EDX. In quantitative analysis using EDX, composition analysis is performed by line analysis so as to straddle the outer edge of the metal magnetic particles DP, and the maximum concentration value of the concentration of the easily oxidizable material in the obtained composition analysis graph is measured. The "concentration of the easily oxidizable material in the intergranular layer region" is measured at two locations inside the virtual line L1 and the virtual line L2 and equally spaced from the virtual line L1, and the average of the maximum concentration values ​​is taken as the concentration of the easily oxidizable material in the intergranular layer region. Furthermore, the "concentration of the easily oxidizable material in the non-intergranular layer region" is measured at two equally spaced locations, one outside one imaginary line L2 and the other outside the other imaginary line L2, and the average of the maximum concentration values ​​is taken as the concentration of the easily oxidizable material in the non-intergranular layer region. Details of the analysis will be described in detail in the "Examples" below, but the line analysis results for the intergranular layer region R1 are as shown in FIG. 5A, and the line analysis results for the non-intergranular layer region R2 are as shown in FIGS. 5B and 5C. Note that the "concentration of the easily oxidizable material" in this specification does not include O (oxygen), C (carbon), or other impurities.

[0033] The line analysis results show that the concentration of the easily oxidizable material in the non-intergranular layer region R2 (the maximum value of the Zn concentration in FIG. 5B or 5C ) is higher than the concentration of the easily oxidizable material in the intergranular layer region R1 (the maximum value of the Zn concentration in FIG. 5A ). One reason for this line analysis result is thought to be that the magnetic material is pressed in the pressurizing step of the "inductor manufacturing method" described below, which pressurizes the magnetic material and pushes the easily oxidizable material in the intergranular layer region R1 toward the non-intergranular layer region R2, resulting in such a concentration of the easily oxidizable material.

[0034] In the inductor 1 of this embodiment, the concentration of the oxidizable material in the non-intergranular layer region R2 is higher than the concentration of the oxidizable material in the intergranular layer region R1. As a result, in the non-intergranular layer region R2, the oxidizable material, which is more easily oxidized than Fe, is oxidized preferentially over Fe, thereby reducing the oxidation of Fe. Furthermore, since the concentration of the oxidizable material is low in the intergranular layer region R1, nonmagnetic components are reduced, thereby improving the magnetic properties.

[0035] A suitable range of the intergranular layer region is that the distance between one metal magnetic particle DP and the other metal magnetic particle DP adjacent to the metal magnetic particle DP is at least 20 nm to 100 nm. If the distance between the metal magnetic particles DP is 20 nm to 100 nm, appropriate magnetic properties can be ensured while appropriate insulation between the metal magnetic powder particles MP can be achieved.

[0036] Furthermore, in a preferred non-intergranular layer region R2, the surface roughness of the oxide coating film OL may be 10 nm or more and 70 nm or less. The term "surface roughness" as used herein refers to the ten-point average roughness defined in JIS B0601:1994. The measurement position for measuring the surface roughness is the non-intergranular layer region R2, where the surface roughness is measured between two locations where the concentration of the easily oxidizable material is measured, and the ten-point average roughness is calculated. For metal magnetic powder MP on the order of several μm, if the surface roughness of the oxide coating film OL is 10 nm or more and 70 nm or less, the metal magnetic particles DP can be adequately covered by the oxide coating film OL, thereby increasing mechanical strength.

[0037] Regarding the preferred concentration of the oxidizable material of the present disclosure, the concentration (maximum concentration) of the oxidizable material in the intergranular layer region R1 may be 0.6 atom % or less, and the concentration (maximum concentration) of the oxidizable material in the non-intergranular layer region R2 may be 5 atom % or more and 30 atom % or less. With these concentrations, the concentration of the oxidizable material in the intergranular layer region R1 is relatively low at 0.6 atom % or less, thereby reducing nonmagnetic components and improving magnetic properties. Furthermore, the concentration of the oxidizable material in the non-intergranular layer region R2 is relatively high at 5 atom % or more and 30 atom % or less, thereby preferentially oxidizing the oxidizable material over Fe, thereby reducing Fe oxidation.

[0038] <Method for Manufacturing an Inductor According to the Present Disclosure> Next, a method for manufacturing an inductor according to the present disclosure will be described with reference to Fig. 6. The method for manufacturing an inductor according to the present disclosure includes a preparation step, a pressurizing step, and a heat treatment step. As will be described later, the method may optionally include a degreasing step.

[0039] - Preparation Step - First, the magnetic material (magnetic paste) for forming the magnetic layers ML of the element layers G1 to G8 described with reference to FIG. 2 and the conductor paste for forming the coil conductor CD are prepared.

[0040] As an example of a method for producing a magnetic paste, a metal powder such as an Fe-Si alloy or an Fe-Si-Cr alloy with a cumulative 50% particle diameter (D50) on a volume basis of 2 μm or more and 20 μm or less is prepared. An easily oxidizable material (e.g., Zn particles: 0.5 wt% or more) that oxidizes more easily than Fe is added to this metal powder, and a binder such as cellulose or polyvinyl butyral (PVB) and a solvent such as a mixture of terpineol and butyl diglycol acetate (BCA) are added, and the mixture is kneaded to produce a magnetic paste.

[0041] When an Fe—Si alloy is used as the metal magnetic material, the Si content is preferably 2.0 atom % or more and 8.0 atom % or less. When an Fe—Si—Cr alloy is used as the metal magnetic powder, the Si content is preferably 2.0 atom % or more and 8.0 atom % or less. Furthermore, when an Fe—Si—Cr alloy is used as the metal magnetic powder, the Cr content is preferably 0.2 atom % or more and 6.0 atom % or less.

[0042] As the conductive paste, for example, a paste containing Ag as a conductive material is prepared.

[0043] The above-mentioned magnetic paste and conductive paste are used to prepare and stack the element layers G1 to G8 shown in FIG. 2 by screen printing or the like.

[0044] - Pressurizing step - After the element layers G1 to G8 are stacked, the element layers G1 to G8 are pressurized. By pressing the magnetic material and the easily oxidizable material, the easily oxidizable material is distributed more in the non-intergranular layer regions R2, where the distance between the metal magnetic particles is 100 nm or more, than in the intergranular layer regions R1, where the distance between the metal magnetic particles is 100 nm or less. By applying the pressure of 300 MPa or more, the concentration of the easily oxidizable material can be adjusted to the desired concentration.

[0045] In a preferred embodiment of the pressurizing step, the pressurizing step may be performed while heating at a temperature lower than the temperature of the heat treatment step described below. Specifically, by applying pressure while heating at a temperature of about 70° C., the concentration of the easily oxidizable material can be adjusted to a desired concentration.

[0046] - Degreasing step (optional step) - A manufacturing process of a preferred inductor manufacturing method may include a degreasing step. The degreasing step is a step of removing binders contained in the magnetic paste and conductive paste. As an example, degreasing is performed at a temperature of about 300°C or higher and 500°C or lower. This removes the binders contained in the magnetic paste and conductive paste.

[0047] Heat Treatment Step After the degreasing step, a heat treatment is performed. The heat treatment temperature is a temperature at which the coil conductor is sintered, and may be, for example, about 700°C or higher and 900°C or lower. The heat treatment step of the present disclosure may be performed in an air atmosphere or a low-oxygen concentration atmosphere.

[0048] Furthermore, to increase the strength of the element body, the element body may be impregnated with a resin and then cured. The resin impregnated into the element body is typically an epoxy resin, but one or more resins selected from the group consisting of phenolic resin, polyester resin, polyimide resin, polyolefin resin, silicone resin, acrylic resin, polyvinyl butyral resin, cellulose resin, and alkyd resin may also be used. Through the above steps, the inductor element body of the present disclosure is formed.

[0049] External electrodes electrically connected to the coil conductors are then formed on the formed element body. The external electrodes are formed by electrolytic plating at the positions where the through-hole conductors are exposed on the mounting surface (first main surface 11) of the element body 10. The plating material may be Cu plating. Other examples include, but are not limited to, Ni-Sn, Ni-Au, Ni-Cu, and / or Cu-Ni-Au. After the external electrodes are formed, the inductor of this embodiment can be manufactured by cutting into individual elements.

[0050] As described above, according to the inductor manufacturing method described in this embodiment, an inductor can be manufactured in which the concentration of the oxidizable material in the non-intergranular layer region is higher than the concentration of the oxidizable material in the intergranular layer region.

[0051] The soft magnetic metal powder of the present disclosure was subjected to a verification test, and the inductors described in the following examples and comparative examples were manufactured.

[0052] -Description of Inductor of Example- A magnetic material was prepared by preparing an Fe-Si alloy metal powder having a cumulative 50% particle diameter (D50) of 2 μm or more and 20 μm or less, and adding Zn to a magnetic paste as an easily oxidizable material that oxidizes more easily than Fe. The amount of Zn added was 0.5% relative to the Fe-Si alloy metal powder.

[0053] As explained in the preparation step of the inductor manufacturing method of the present disclosure, a conductor paste was prepared, and element layers G1 to G8 shown in Figure 2 were formed. Then, the element precursor formed by stacking element layers G1 to G8 was heated and pressed. After that, a degreasing step and a heat treatment step were performed, and the inductor of the example was manufactured.

[0054] - Explanation of Inductor of Comparative Example - The inductor of the comparative example was manufactured in the same manner as the inductor of the example, except that Zn was not added as an easily oxidizable material.

[0055] - Evaluation of inductors (part 1) - The "concentration of easily oxidizable materials" was evaluated for the manufactured inductors.

[0056] First, composition analysis was performed on the intergranular layer region R1 using EDX (Noran, System 7) across the outer edge of the metal magnetic particles DP. As described above, the composition analysis was performed at nine locations: (any three locations in the center of the cut surface) x (any three locations in the center of each field of view). As an example, FIG. 5A shows a graph of the composition distribution along line A1 shown in FIG. 4. In the graph shown in FIG. 5A, the horizontal axis corresponds to the measurement position in the line analysis, and the vertical axis corresponds to the amount of element. In the graph of FIG. 5A, positions P1 and P2 of the peak concentration value of Si, an oxide of an element derived from the metal magnetic particles DP, correspond to positions near the outer edges of adjacent metal magnetic particles DP. The region between the two peak concentration value positions P1 and P2 of Si corresponds to the intergranular layer region R1. According to the graph in FIG. 5A, the maximum concentration of Zn in the intergranular layer region R1 was 0.4 atom%. The maximum concentration of the easily oxidizable material was the average value of the measurements at the nine locations described above.

[0057] Next, composition analysis was performed on the non-intergranular layer region R2 using EDX (Noran, System 7) across the outer edge of the metal magnetic particles DP. As an example, graphs of the composition distribution along lines A2 and A3 shown in FIG. 4 are shown in FIGS. 5B and 5C, respectively. In the graphs shown in FIGS. 5B and 5C, the horizontal axis corresponds to the measurement position in the line analysis, and the vertical axis corresponds to the amount of element. Note that in the graphs of FIGS. 5B and 5C, positions P3 and P4 of the peak concentration value of Si, which is an oxide of an element derived from the metal magnetic particles DP, correspond to positions near the outer edge of the metal magnetic particles DP. The position on the positive side of the horizontal axis from positions P3 and P4 corresponds to the non-intergranular layer region R2. FIG. 5B shows the measurement results up to a certain point, and as a result of analyzing the non-intergranular layer region R2 from one end to the other, the maximum Zn concentration in the non-intergranular layer region R2 was 22.8 atom %. FIG. 5C shows the measurement results up to a certain point, and as a result of analyzing the non-intergranular layer region R2 from one end to the other, the maximum Zn concentration in the non-intergranular layer region R2 was 22.0 atom %.

[0058] - Evaluation of inductors (part 2) - Fe (iron) composition analysis and O (oxygen) composition analysis were performed using EDX on the inductors of the example and the comparative example. Fig. 7 shows an SEM image of the measurement point on the inductor of the comparative example and elemental mapping images of Fe and O, and Fig. 8 shows an SEM image of the measurement point on the inductor of the example and elemental mapping images of Fe and O.

[0059] According to the Fe element mapping image of the inductor of the comparative example shown in Figure 7, it can be seen that a faint Fe component is present in the oxide film portion outside the outer edge of the metal magnetic particles DP, as well as the presence of O, so it can be seen that oxidation of Fe has occurred in this portion. On the other hand, according to the Fe element mapping image of the inductor of the example shown in Figure 8, the Fe component is clearly present in the outer edge portion of the metal magnetic particles DP compared to Figure 7, and the presence of the Fe component can hardly be confirmed in the oxide film portion outside the outer edge of the metal magnetic particles DP, so it can be seen that oxidation of Fe is reduced compared to the inductor of the comparative example.

[0060] -Inductor Evaluation (Part 3)- To evaluate the inductors, the magnetic permeability of the comparative example and the example was measured. The magnetic permeability of the samples was measured using an impedance analyzer (Keysight 4991A). For the example inductors, samples were prepared with ZnO addition amounts ranging from 0.2 wt% to 0.5 wt%. That is, in Example 1, the ZnO addition amount was 0.2 wt%, in Example 2, the ZnO addition amount was 0.3 wt%, in Example 3, the ZnO addition amount was 0.4 wt%, and in Example 4, the ZnO addition amount was 0.5 wt%. In this evaluation, the magnetic permeability of the inductor before sintering the coil conductor (before heat treatment) and after sintering the coil conductor (after heat treatment) were measured, and the rate of change was graphed. A graph of the rate of change in magnetic permeability is shown in Figure 9, and the data on which this graph was based is shown in Figure 10. The impedance analyzer may be any that can perform measurements at 1 MHz, and Keysight products such as 4991B, 4990A, and 4294A can be used.

[0061] According to the evaluation results shown in Figures 9 and 10, the magnetic permeability of the inductor of the comparative example did not change before and after the heat treatment, but the magnetic permeability of the inductors of Examples 1 to 4 showed a significant improvement before and after the heat treatment.

[0062] As described above, the evaluation results of the inductor confirmed that the maximum Zn concentration in the non-intergranular layer region R2 was higher than the maximum Zn concentration in the intergranular layer region R1. Therefore, in the non-intergranular layer region R2, the easily oxidizable material, which is more easily oxidized than Fe, oxidizes preferentially over Fe, thereby reducing Fe oxidation compared to conventional inductors. Furthermore, because the concentration of the easily oxidizable material in the intergranular layer region R1 is low, nonmagnetic components are reduced, resulting in improved magnetic properties compared to conventional inductors.

[0063] It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be defined based on the claims. The technical scope of the present disclosure also includes all modifications within the scope and meaning equivalent to the claims.

[0064] The present disclosure provides an inductor and a method for manufacturing an inductor as follows: <1> An inductor comprising: an element body including a plurality of metal magnetic powders; and a coil provided within the element body, wherein the metal magnetic powder comprises metal magnetic particles containing Fe and an oxide film containing an oxidizable material that oxidizes more easily than Fe, wherein a region where the distance between a surface of a first metal magnetic particle and a second metal magnetic particle adjacent to the first metal magnetic particle is small is defined as an intergranular layer region, and a region where the distance is large is defined as a non-intergranular layer region, and the concentration of the oxidizable material in the non-intergranular layer region is higher than the concentration of the oxidizable material in the intergranular layer region. <2> The inductor according to <1>, wherein the oxidizable material includes at least one selected from the group consisting of Zn, Zr, Al, Ti, Mg, Cr, and Mo. <3> The inductor according to <1> or <2>, wherein the concentration of the easily oxidizable material in the intergranular layer region is 0.6 atom% or less, and the concentration of the easily oxidizable material in the non-intergranular layer region is 5 atom% or more and 30 atom% or less. <4> The inductor according to any one of <1> to <3>, wherein the distance in the intergranular layer region is 20 nm or more and 100 nm or less. <5> The inductor according to any one of <1> to <4>, wherein the surface roughness of the oxide film in the non-intergranular layer region is 10 nm or more and 70 nm or less. <6> The inductor according to any one of <1> to <5>, wherein the average particle size of the metal magnetic particles is 1 μm or more and 6 μm or less. <7> A method for manufacturing the inductor described in any one of <1> to <6>, comprising: a preparation step of adding the easily oxidizable material to the metal magnetic particles to prepare a magnetic material that constitutes an element body, a pressurizing step of pressurizing an element body precursor formed using the magnetic material to distribute the easily oxidizable material more in the non-proximal region than in the intergranular layer region, and a heat treatment step of heating the magnetic material to form an oxide film containing the easily oxidizable material on the surface of the metal magnetic particles.<8> The method for manufacturing an inductor described in <7>, wherein the pressurizing step is performed while heating at a temperature lower than the temperature in the heat treatment step.

[0065] The inductor and the method for manufacturing the inductor according to the present disclosure can be suitably used as an electronic component with improved magnetic properties.

[0066] REFERENCE SIGNS LIST 1 inductor 10 element body 11 first main surface 12 second main surface 13 first end surface 14 second end surface 15 first side surface 16 second side surface MP metal magnetic powder DP metal magnetic particle OL oxide film C coil CD coil conductor E external electrode E1 to E4 first external electrode to fourth external electrode G1 to G8 element body layer ML magnetic layer TH through-hole conductor TH1 to TH4 first through-hole conductor to fourth through-hole conductor R1 inter-grain layer region R2 non-inter-grain layer region

Claims

1. An inductor comprising: a body including a plurality of metal magnetic powders; and a coil provided in the body, wherein the metal magnetic powders include metal magnetic particles containing Fe and an oxide film containing an easily oxidizable material that is more easily oxidized than Fe. When a region where the distance between the surface of the first metal magnetic particle and the surface of the second metal magnetic particle adjacent to the first metal magnetic particle is small is defined as an intergranular layer region, and a region where the distance is large is defined as a non-intergranular layer region, the concentration of the easily oxidizable material in the non-intergranular layer region is higher than the concentration of the easily oxidizable material in the intergranular layer region.

2. The inductor according to claim 1, wherein the easily oxidizable material includes at least one selected from the group consisting of Zn, Zr, Al, Ti, Mg, Cr, and Mo.

3. The inductor according to claim 1 or 2, wherein the concentration of the easily oxidizable material in the intergranular layer region is 0.6 atom% or less, and the concentration of the easily oxidizable material in the non-intergranular layer region is 5 atom% or more and 30 atom% or less.

4. The inductor according to any one of claims 1 to 3, wherein the intergranular layer region has a distance of 20 nm or more and 100 nm or less.

5. The inductor according to any one of claims 1 to 4, wherein the surface roughness of the oxide film in the non-intergranular layer region is 10 nm or more and 70 nm or less.

6. The inductor according to any one of claims 1 to 5, wherein the average particle diameter of the metal magnetic powders is 1 μm or more and 6 μm or less.

7. A method for manufacturing an inductor according to any one of claims 1 to 6, comprising: a preparation step of adding the easily oxidizable material to the metal magnetic particles to prepare a magnetic material constituting a body; a pressing step of pressing a body precursor formed using the magnetic material to distribute the easily oxidizable material more in the non-proximity region than in the intergranular layer region; and a heat treatment step of heating the magnetic material to form an oxide film containing the easily oxidizable material on the surface of the metal magnetic particles.

8. The method for manufacturing an inductor according to claim 7, wherein the pressing step is performed while heating at a temperature lower than the temperature of the heat treatment step.