Inductors and methods for manufacturing inductors

Description

Technical Field

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[0001] This disclosure relates to an inductor and a method for manufacturing the inductor.

Background Art

[0002] Patent Document 1 discloses a coil component in which a spiral coil portion covered by a magnetic body portion is in direct contact with the magnetic body portion. In the magnetic body portion, the main component is a group of magnetic alloy particles and does not contain a glass component, and an oxide film of the magnetic alloy particles is present on the surface of each magnetic alloy particle. Further, it is disclosed that the oxide film contains at least Fe3O4 belonging to the magnetic body and Fe2O3 and Cr2O3 belonging to the non-magnetic body.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since the coil component described in Patent Document 1 contains Cr, which is a non-magnetic component, as an oxide film between the magnetic alloy particles, further improvement in magnetic properties is required. More specifically, by improving the concentration mode of the non-magnetic component in the oxide film, a finding that the magnetic properties of the inductor become good has been obtained.

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

Means for Solving the Problems

[0006] The inductor according to this disclosure is a body including a plurality of metal magnetic powders, and a coil provided in the body. The aforementioned metal magnetic powder comprises metal magnetic particles containing Fe and an oxide film containing an easily oxidizable material that is more readily oxidized than Fe. When the region where the distance between the surface of a first metallic magnetic particle and the surface of a second metallic magnetic particle adjacent to the first metallic magnetic particle is small is defined as the intergranular layer region, and the region where the distance is large is defined as the 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.

[0007] The method for manufacturing an inductor relating to this disclosure is: A method for manufacturing the above-mentioned inductor, A preparation step of preparing a magnetic material constituting a base body by adding the easily oxidizable material to the aforementioned metallic magnetic particles, A pressurizing step involves pressurizing a substrate precursor formed using the magnetic material to distribute the easily oxidizable material more in the non-intergranular layer region than in the intergranular layer region, The method comprises a heat treatment step of heating the magnetic material to form an oxide film containing the easily oxidizable material on the surface of the metallic magnetic particles. [Effects of the Invention]

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

[0009] [Figure 1] Figure 1 is a perspective view of the inductor of this disclosure. [Figure 2] Figure 2 is an exploded perspective view of one embodiment of the inductor of the present disclosure. [Figure 3] Figure 3 is a cross-sectional view showing one field of view of the central part of the cross-section, obtained by cutting the base body shown in Figure 1 through the center and the coil winding axis, perpendicular to the mounting surface and end face of the base body. [Figure 4] Figure 4 is an enlarged cross-sectional view of the area demarcated by the dashed line in Figure 3. [Figure 5A]FIG. 5A is a graph showing the concentration distributions of Si, Fe, and Zn in the intergranular layer region. [Figure 5B] FIG. 5B is a graph showing the concentration distributions of Si, Fe, and Zn in the non-intergranular layer region. [Figure 5C] FIG. 5C is a graph showing the concentration distributions of Si, Fe, and Zn at other positions in the non-intergranular layer region. [Figure 6] FIG. 6 is a manufacturing flow explaining the manufacturing process of the inductor of the present disclosure. [Figure 7] FIG. 7 is an elemental mapping image of the inductor of the comparative example. [Figure 8] FIG. 8 is an elemental mapping image of the inductor of the example. [Figure 9] FIG. 9 is a graph showing the change in permeability before and after heat treatment. [Figure 10] FIG. 10 is a table showing the change in permeability of the comparative example and Examples 1 to 4 on which the graph of FIG. 9 is based.

DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, the inductor of the present disclosure will be described. Note that the present disclosure is not limited to the following configuration and may be appropriately changed without departing from the gist of the present disclosure. Also, a combination of a plurality of the individual preferred configurations described below is also within the scope of the present disclosure.

[0011]

[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 a strictly literal aspect, but also mean a substantially equivalent range, for example, a range including a difference of about several percent. In this specification, the direction in which the magnetic layer and the coil conductor constituting the element body are laminated is defined as the "lamination direction".

[0013] Also, in the description of this specification, references to directions or orientations, etc. are for the convenience of explanation only and are not intended to limit the scope of the present disclosure unless specifically stated otherwise. For example, relative terms such as "outer (or outside, external or outer periphery)", "inner (or inside, internal or inner periphery)", etc., as well as their derivative terms, etc. should be construed as referring to the directions as described or illustrated. That is, unless specifically stated otherwise, the invention need not be limited to a specific direction, orientation, form, etc. Also, terms such as "provided" and "connected", etc., as well as their derivative terms are the same. Unless specifically stated otherwise, they are not limited to a direct mode, and other elements such as intervening objects may be involved.

[0014] The drawings shown below are schematic diagrams, and their dimensions, scales of aspect ratios, etc. may differ from those of actual products.

[0015] <The inductor of the present disclosure> The inductor of the present disclosure will be described with reference to FIGS. 1 to 5C. The inductor of the present disclosure includes a body 10 including a plurality of metal magnetic powders MP (see FIG. 3) and a coil provided in the body 10.

[0016] The body 10 is, for example, in a rectangular parallelepiped shape or a substantially rectangular parallelepiped shape having six faces (see FIG. 1). The body 10 may have rounded corners and edges. A corner is a portion where three faces of the body 10 intersect, and an edge is a portion where two faces of the body 10 intersect.

[0017] In FIG. 1, the length direction, width direction, and height direction of the inductor 1 and the body 10 are shown as the 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 the width direction W.

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

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

[0020] The element 10 contains a coil formed by stacking multiple coil conductors CD. In the example shown in Figure 2, two coils (a first coil and a second coil) are provided within the element 10 along the stacking direction. More specifically, the first coil is formed by the coil conductors CD of element layers G4 and G5, and the second coil is formed by the coil conductors CD of element layers G2 and G3. Note that the inductor 1 of the first embodiment is not limited to this example, and 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 in a direction intersecting the stacking direction (direction L in Figure 1) inside the element 10.

[0021] External electrodes E are provided on the mounting surface (first main surface 11) of the base body 10. In the example shown in Figure 2, the external electrodes E include a first external electrode E1 and a second external electrode E2 connected to each end of the first coil, and a third external electrode E3 and a fourth external electrode E4 connected to each end of the second coil. Note that 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) to the external electrode E. In other words, the first through-hole conductors TH1 to TH4 are provided corresponding to the first external electrode E1 to 4 external electrode E4. Furthermore, the first through-hole conductors TH1 to TH4 extend along the lamination direction.

[0023] The magnetic layer ML of each elemental layer G1 to G8 comprises a metallic magnetic powder MP (see Figure 3) composed of a magnetic material. The metallic magnetic powder MP includes metallic magnetic particles DP, an oxide film OL, and a resin.

[0024] The average particle size of the metal magnetic powder MP is 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 by the procedure described below. A sample of the inductor is cut to obtain a sample cross-section. Specifically, the sample cross-section is obtained by cutting the sample perpendicular to the mounting surface and end face of the inductor, passing through the center of the inductor and the winding axis of the coil. The sample cross-section may be made flat by ion milling or the like. For the obtained cross-section, three arbitrary locations in the center of the cut surface, which corresponds to the central part of the inductor 10, are photographed by SEM (at a magnification of approximately 1000x) and compositional analysis is performed by EDX. By confirming the position of Fe in the field of view from the compositional analysis results by EDX, the position of the metal magnetic powder MP in the SEM image can be identified. Then, the average value of the obtained equivalent circle diameter for the identified metal magnetic powder MP is taken as the average particle size of the metal magnetic particles. In this specification, the average particle size may mean the average particle size D50 (particle size equivalent to 50% cumulative percentage by volume).

[0026] The metallic magnetic particles DP contain at least Fe (iron). More specifically, they may be particles or alloy particles containing Fe and Si. Examples of metallic 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, Fe-Si-B (niobium)-Cu alloys, etc. The metallic 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 during manufacturing. Furthermore, the metallic magnetic particles DP may be contained in a magnetic paste, as will be described in detail in the manufacturing method description. The magnetic paste may contain an easily oxidizable material that oxidizes more readily than Fe (for example, any of Zn (zinc), Zr (zirconium), Al (aluminum), Ti (titanium), Mg (magnesium), Cr (chromium), or Mo (molybdenum)). By including an easily oxidizable material in the magnetic paste, it can adhere to the surface of the metal magnetic particles DP, and the easily oxidizable material on the surface of the metal magnetic particles DP will oxidize preferentially, leaving oxides of the easily oxidizable material on the surface of the metal magnetic particles DP, thereby reducing the oxidation of the Fe element contained in the metal magnetic particles. This suppresses the decrease in permeability due to the oxidation of the Fe element and allows for a higher permeability of the inductor 1. The resin component contained in the magnetic paste may disappear or remain after the heat treatment of the base material. Furthermore, the material of the easily oxidizable material that oxidizes more readily than Fe may 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, the easily oxidizable material may be a material other than Si or Cr.

[0027] The surface of the aforementioned metallic magnetic particles DP is covered with an insulating coating. In this specification, "insulating" means that the volume resistivity is 1 MΩcm or more. Covering the surface of the metallic magnetic particles DP with an insulating coating increases the insulating properties between the metallic magnetic particles DP. A specific example of the insulating coating is the oxide film OL, as shown in Figure 3. Note that an insulating material may be provided outside the oxide film OL; that is, the metallic magnetic particles DP and the oxide film OL may be coated with an insulating material not shown.

[0028] The oxide film OL is a film produced by the oxidation of elements that are more easily oxidized than Fe contained in the metal magnetic particles DP. In other words, the oxide film OL may contain oxides of easily oxidized materials that are more easily oxidized than Fe as described above, and oxides of raw materials derived from the metal magnetic particles DP. In this specification, "easily oxidized materials that are more easily oxidized than Fe" refers to materials that have a greater ionization tendency than Fe. The thickness of the oxide film OL is 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 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 three arbitrary locations in the center of the cross-section obtained by cutting the sample so as to be perpendicular to the mounting surface and end face of the sample through the center of the sample body and the winding axis of the coil. In each field of view, the thickness of the oxide film OL is measured at three arbitrary locations in the center. The thickness of the oxide film OL can be calculated by taking the average of these nine points: (any three points in the center of the cross section) × (any three points in the center of each field of view).

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

[0030] To increase the strength of the base body 10, the resin may be present between adjacent metal magnetic powders MP bonded by an insulating film by impregnating the base body 10 with resin after heat treatment of the base body 10, which is constructed by laminating the above-described base body layers G1 to G8. As an example, the resin impregnated after heat treatment of the base body 10 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, and alkyd resin.

[0031] In the inductor 1 of this embodiment, the body is cut perpendicular to the mounting surface and end face of the body, passing through the center of the body and the winding axis of the coil, and a cross-section is obtained. When three arbitrary locations in the center of the cross-section are photographed, it can be seen in each field of view, as shown in Figure 3, that there are regions around multiple metal magnetic powders MP where resin impregnated in the body and voids exist, indicated by dots. Here, using image analysis software (for example, image analysis software WinROOF2021 (manufactured by Mitani Corporation)), one metal magnetic particle DP and the other metal magnetic particle DP adjacent to it are identified by selecting from the multiple metal magnetic powders MP in which the distance between the centroid points of two metal magnetic particles DP is 100 nm or less. As shown in Figure 4, when observing between one metallic magnetic particle DP and the other metallic magnetic particle DP, the region where the distance between the surface of one metallic magnetic particle DP and the surface of the other metallic magnetic particle DP adjacent to it is small is defined as the intergranular layer region R1, and the region where the distance between the surface of one metallic magnetic particle DP and the surface of the other metallic magnetic particle DP adjacent to it is large is defined as the non-intergranular layer region R2. In this specification, the concentration of easily oxidizable material in the non-intergranular layer region R2 is higher than the concentration of easily oxidizable material in the intergranular layer region R1. As shown in Figure 4, the "intergranular layer region" refers to the region between two particles facing each other between two virtual lines L2, where virtual line L1 is a line segment connecting the centroid points of adjacent particles, and virtual lines L2 are drawn on both sides of virtual line L1 with the centroid points of the metallic magnetic particles at ±10° from the centroid point of the metallic magnetic particles. In Figure 4, the maximum distance between two particles is, for example, 50 nm or less. Here, the virtual lines L1 and L2 can be drawn using image analysis software (for example, WinROOF2021 image analysis software (manufactured by Mitani Corporation)) when determining the equivalent circular diameter of the metal magnetic powder MP mentioned above. Furthermore, the "non-intergranular layer region" in this specification refers to a region other than the intergranular layer region where the inter-particle distance is greater than that of the intergranular layer region.

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

[0033] Line analysis results show that the concentration of easily oxidizable material in the non-intergranular layer region R2 (the maximum value of Zn concentration in Figure 5B or Figure 5C) is higher than the concentration of easily oxidizable material in the intergranular layer region R1 (the maximum value of Zn concentration in Figure 5A). One reason for this line analysis result is thought to be that in the pressurization step of the "Inductor Manufacturing Method" described later, the magnetic material is pressurized, pushing the easily oxidizable material in the intergranular layer region R1 toward the non-intergranular layer region R2, resulting in this concentration of easily oxidizable material.

[0034] In the inductor 1 of this embodiment, 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 a result, in the non-intergranular layer region R2, the easily oxidizable material, which is more easily oxidized than Fe, is preferentially oxidized over Fe, thereby reducing the oxidation of Fe. Furthermore, in the intergranular layer region R1, the concentration of the easily oxidizable material is low, which reduces the non-magnetic component and improves the magnetic properties.

[0035] A suitable range for the intergranular layer region is when the distance between one metallic magnetic particle DP and the other metallic magnetic particle DP adjacent to it is at least 20 nm to 100 nm. If the distance between metallic magnetic particles DP is 20 nm to 100 nm, appropriate insulation between metallic magnetic powders MP can be ensured while maintaining appropriate magnetic properties.

[0036] Furthermore, in the suitable non-intergranular layer region R2, the surface roughness of the oxide film OL may be between 10 nm and 70 nm. In this specification, "surface roughness" refers to the ten-point average roughness as defined in JIS B0601:1994. The surface roughness is measured in the non-intergranular layer region R2, by measuring the surface roughness between two locations where the concentration of the easily oxidizable material is measured, and then calculating the ten-point average roughness. For metal magnetic powder MP on the order of several μm, if the surface roughness of the oxide film OL is between 10 nm and 70 nm, the oxide film OL can adequately cover the metal magnetic particles DP, thereby increasing their mechanical strength.

[0037] Furthermore, regarding the preferred concentrations of the easily oxidizable material in this disclosure, the concentration (maximum concentration) of the easily oxidizable material in the intergranular layer region R1 may be 0.6 atom% or less, and the concentration (maximum concentration) of the easily oxidizable material in the non-intergranular layer region R2 may be 5 atom% or more and 30 atom% or less. With such concentrations, in the intergranular layer region R1, the concentration of the easily oxidizable material is relatively low at 0.6 atom% or less, so the non-magnetic component can be reduced and the magnetic properties can be improved. In the non-intergranular layer region R2, the concentration of the easily oxidizable material is relatively high at 5 atom% or more and 30 atom% or less, so the easily oxidizable material is preferentially oxidized over Fe, and the oxidation of Fe can be reduced.

[0038] <Method for manufacturing an inductor in this disclosure> Next, the method for manufacturing the inductor of this disclosure will be described with reference to Figure 6. The method for manufacturing the inductor of this disclosure comprises a preparation step, a pressurization step, and a heat treatment step. As will be described later, a degreasing step may be optionally included.

[0039] -Preparation process- First, prepare the magnetic material (magnetic paste) that constitutes the magnetic layer ML of the base layers G1 to G8 as explained in Figure 2, and the conductive paste that constitutes the coil conductor CD.

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

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

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

[0043] Using the magnetic paste and conductive paste described above, the base layers G1 to G8 shown in Figure 2 are prepared and laminated by screen printing or the like.

[0044] -Pressurization process- After stacking the base layers G1 to G8, the base layers G1 to G8 are pressurized. Pressurizing the magnetic material and the easily oxidizable material causes the easily oxidizable material to be more abundant in the non-intergranular layer region R2, where the distance between metallic magnetic particles is 100 nm or more, than in the intergranular layer region R1, where the distance between metallic magnetic particles is 100 nm or less. By performing this pressurization at a pressure of 300 MPa or higher, the concentration of the easily oxidizable material can be set to the desired concentration.

[0045] A preferred configuration for the pressurization process is to perform the pressurization process while heating at a temperature lower than that of the heat treatment process described later. Specifically, by pressurizing while heating at a temperature of about 70°C, the concentration of the easily oxidizable material can be adjusted to the desired concentration.

[0046] -Degreasing process (optional additional process)- A suitable manufacturing process for an inductor may include a degreasing step. The degreasing step is a process of removing the binder contained in the magnetic paste and conductive paste. For example, degreasing is performed at a temperature of approximately 300°C to 500°C. This removes the binder contained in the magnetic paste and conductive paste.

[0047] • Heat treatment process A heat treatment is performed after the degreasing process. The heat treatment temperature is such that the coil conductor sintersects, and may be, for example, between 700°C and 900°C. The heat treatment process of this disclosure may be carried out in an air atmosphere or in a low-oxygen concentration atmosphere.

[0048] Furthermore, to increase the strength of the base material, the base material may be impregnated with a resin and cured. The resin used to impregnate the base material is 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. By going through the above steps, the base material of the inductor of this disclosure is formed.

[0049] Subsequently, external electrodes electrically connected to the coil conductor are formed on the formed body. The external electrodes are formed by electroplating at the positions where the through-hole conductors are exposed on the mounting surface (first main surface 11) of the body 10. The plating material may be Cu plating. Other materials include, but are not limited to, Ni-Sn, Ni-Au, Ni-Cu and / or Cu-Ni-Au. After forming the external electrodes, the element can be cut into individual components to manufacture the inductor of this embodiment.

[0050] As described above, the inductor manufacturing method described in this embodiment makes it possible to manufacture an inductor in which the concentration of easily oxidizable material in the non-intergranular layer region is higher than the concentration of easily oxidizable material in the intergranular layer region. [Examples]

[0051] The demonstration tests concerning the soft magnetic metal powder of this disclosure are described in detail. Specifically, the inductors described in the following examples and comparative examples were manufactured.

[0052] -Description of the inductor in the example- A metal powder of Fe-Si alloy with a cumulative 50% particle size (D50) of 2 μm or more and 20 μm or less was prepared. Zn was added to the magnetic paste as an easily oxidizable material, which oxidizes more readily than Fe, to prepare the magnetic material. The amount of Zn added was 0.5% relative to the Fe-Si alloy metal powder.

[0053] As described in the preparation steps for the manufacturing method of the inductor of this disclosure, a conductor paste was prepared and the elemental layers G1 to G8 shown in Figure 2 were formed. Then, the elemental precursor formed by stacking the elemental layers G1 to G8 was heated and pressurized. Subsequently, the inductor of the example was manufactured through a degreasing step and a heat treatment step.

[0054] -Explanation of the inductor in the comparative example- The comparative inductor was manufactured in the same manner as the inductor in the example, except that it did not contain Zn as an easily oxidizable material.

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

[0056] First, compositional analysis was performed on the intergranular layer region R1 using EDX (Noran System 7), straddling the outer edge of the metallic magnetic particle DP. As described above, the compositional analysis was performed at 9 locations: (3 arbitrary locations in the center of the cross section) × (3 arbitrary locations in the center of each field of view). As an example, Figure 5A shows a graph of the compositional distribution along line A1 shown in Figure 4. In the graph in Figure 5A, the horizontal axis corresponds to the measurement position in the line analysis, and the vertical axis corresponds to the elemental amount. In the graph in Figure 5A, the peak concentration values ​​of Si, an oxide of the element derived from the metallic magnetic particle DP, at positions P1 and P2 correspond to the vicinity of the outer edge of the metallic magnetic particle DP, which are adjacent to each other. The region between the two Si peak concentration values ​​at positions P1 and P2 corresponds to the intergranular layer region R1. According to the graph in Figure 5A, the maximum concentration of Zn in the intergranular layer region R1 was 0.4 atom%. The maximum concentration of easily oxidizable material is the average value of the measurements at the 9 locations mentioned above.

[0057] Next, compositional analysis was performed on the non-intergranular layer region R2 using EDX (Noran System 7), straddling the outer edge of the metallic magnetic particle DP. As an example, graphs of the compositional distribution along lines A2 and A3 shown in Figure 4 are shown in Figures 5B and 5C, respectively. In the graphs shown in Figures 5B and 5C, the horizontal axis corresponds to the measurement position in the line analysis, and the vertical axis corresponds to the elemental amount. In the graphs in Figures 5B and 5C, the peak concentration values ​​of Si, an oxide of the element derived from the metallic magnetic particle DP, at positions P3 and P4 correspond to the vicinity of the outer edge of the metallic magnetic particle DP. The area on the positive side of the horizontal axis from positions P3 and P4 corresponds to the non-intergranular layer region R2. Figure 5B shows the measurement results up to a certain point. Analysis from end to end of the non-intergranular layer region R2 revealed that the maximum Zn concentration within the non-intergranular layer region R2 was 22.8 atom%, and Figure 5C also shows the measurement results up to a certain point. Analysis from end to end of the non-intergranular layer region R2 revealed that the maximum Zn concentration within the non-intergranular layer region R2 was 22.0 atom%.

[0058] -Inductor Evaluation (Part 2)- Compositional analysis of Fe (iron) and O (oxygen) was performed on the inductors of the example and the comparative example using EDX. Figure 7 shows the SEM image of the measurement location for the comparative example inductor, as well as the elemental mapping images of Fe and O. Figure 8 shows the SEM image of the measurement location for the example inductor, as well as the elemental mapping images of Fe and O.

[0059] According to the Fe elemental mapping image of the comparative example inductor shown in Figure 7, it can be confirmed that a faint Fe component is present in the oxide film portion outside the outer edge of the metal magnetic particle DP, and that O is also present, indicating that Fe oxidation has occurred in that portion. On the other hand, according to the Fe elemental mapping image of the example inductor shown in Figure 8, the Fe component is clearly present in the outer edge of the metal magnetic particle DP compared to Figure 7, and the presence of the Fe component is almost not confirmed in the oxide film portion outside the outer edge of the metal magnetic particle DP, indicating that Fe oxidation has been reduced compared to the comparative example inductor.

[0060] -Inductor Evaluation (Part 3)- As part of the evaluation of the inductors, the permeability of the comparative example and the example was measured. The permeability was measured using an impedance analyzer (Keysight 4991A). For the example inductors, samples were prepared with varying amounts of ZnO added from 0.2 wt% to 0.5 wt%. Specifically, Example 1 used 0.2 wt% ZnO, Example 2 used 0.3 wt%, Example 3 used 0.4 wt%, and Example 4 used 0.5 wt% ZnO. In this evaluation, the permeability of the inductor before coil conductor sintering (before heat treatment) and after coil conductor sintering (after heat treatment) were measured, and the rate of change was graphed. The graph of the rate of change of permeability is shown in Figure 9, and the data on which the graph was based is shown in Figure 10. The impedance analyzer only needs to be able to measure at 1 MHz; if using a Keysight product, models such as the 4991B, 4990A, or 4294A can be used.

[0061] According to the evaluation results shown in Figures 9 and 10, the comparative inductor showed no change in magnetic permeability before and after heat treatment, while the inductors of Examples 1 to 4 showed a significant improvement in magnetic permeability before and after heat treatment.

[0062] Based on the evaluation results of the inductor, it was confirmed that the maximum concentration of Zn in the non-intergranular layer region R2 was higher than the maximum concentration of Zn in the intergranular layer region R1. Therefore, in the non-intergranular layer region R2, easily oxidizable materials that are more readily oxidized than Fe are preferentially oxidized over Fe, thus reducing Fe oxidation compared to conventional inductors. Furthermore, in the intergranular layer region R1, the low concentration of easily oxidizable materials reduces the non-magnetic component, improving magnetic properties compared to conventional inductors.

[0063] The embodiments disclosed herein are illustrative in all respects and do not constitute a limiting interpretation. Therefore, the technical scope of this disclosure is not construed solely by the embodiments described above, but is defined based on the claims. Furthermore, the technical scope of this disclosure includes all modifications within the meaning and scope of equivalence to the claims.

[0064] The embodiments of the inductor and the method for manufacturing the inductor described herein are as follows. <1> A base body containing multiple metal magnetic powders, The body comprises a coil provided within the aforementioned body, The aforementioned metal magnetic powder comprises metal magnetic particles containing Fe and an oxide film containing an easily oxidizable material that is more readily oxidized than Fe. The surface of the first metallic magnetic particle and the second metallic magnetic particle adjacent to the first metallic magnetic particle surface An inductor in which, when the region where the distance between the two is small is defined as the intergranular layer region, and the region where the distance is large is defined as the 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 easily oxidizable material includes at least one selected from the group consisting of Zn, Zr, Al, Ti, Mg, Cr, and Mo. <1> The inductor described above. <3> The concentration of the easily oxidizable material in the intergranular layer region is 0.6 atom% or less. The concentration of the easily oxidizable material in the non-intergranular layer region is 5 atom% or more and 30 atom% or less. <1> or <2> The inductor described above. <4> The intergranular layer region has a distance of 20 nm or more and 100 nm or less. <1> ~ <3> An inductor listed in any one of the following. <5> The surface roughness of the oxide film in the non-granular layer region is 10 nm or more and 70 nm or less. <1> ~ <4> An inductor listed in any one of the following. <6> The aforementioned metal magnetism powder The average particle size is between 1 μm and 6 μm. <1> ~ <5> An inductor listed in any one of the following. <7> <1> ~ <6> A method for manufacturing an inductor as described in any one of the following: A preparation step of preparing a magnetic material constituting a base body by adding the easily oxidizable material to the aforementioned metallic magnetic particles, By pressurizing the substrate precursor formed using the magnetic material, the easily oxidizable material is made more non-oxidizable than the intergranular layer region. intergranular layer A pressurization process that distributes pressure widely across the region, A method for manufacturing an inductor, comprising a heat treatment step of heating the magnetic material to form an oxide film containing the easily oxidizable material on the surface of the metallic magnetic particles. <8> The pressurization step is carried out while heating at a temperature lower than the temperature of the heat treatment step. <7> The method for manufacturing an inductor as described above. [Industrial applicability]

[0065] The inductor and method for manufacturing the inductor described herein can be suitably used as electronic components with improved magnetic properties. [Explanation of Symbols]

[0066] 1 Inductor 10 Base Body 11. First Main Surface 12 Second Main Surface 13 First end surface 14 Second end face 15 First aspect 16 Second aspect MP metal magnetic powder DP metal magnetic particles OL oxide film C coil CD coil conductor E External electrode E1~E4 1st external electrode ~ 4th external electrode G1-G8 Base Layer ML magnetic layer TH Through-Hole Conductor TH1~TH4 First through-hole conductor~Fourth through-hole conductor R1 Intergranular layer region R2 Non-intergranular layer region

Claims

1. A base body containing multiple metal magnetic powders, The body comprises a coil provided within the aforementioned body, The aforementioned metal magnetic powder comprises metal magnetic particles containing Fe and an oxide film containing an easily oxidizable material that is more readily oxidized than Fe. An inductor wherein, when the region where the distance between the surface of a first metallic magnetic particle and the surface of a second metallic magnetic particle adjacent to the first metallic magnetic particle is small is defined as an intergranular layer region, and the 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 concentration of the easily oxidizable material in the intergranular layer region is 0.6 atom% or less. The inductor according to claim 1, wherein 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 claim 1, wherein the intergranular layer region has a distance of 20 nm or more and 100 nm or less.

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

6. The inductor according to claim 1, wherein the average particle size of the metal magnetic powder is 1 μm or more and 6 μm or less.

7. A method for manufacturing an inductor according to claim 1, A preparation step of preparing a magnetic material constituting a base body by adding the easily oxidizable material to the aforementioned metallic magnetic particles, A pressurizing step involves pressurizing a precursor body formed using the magnetic material to distribute the easily oxidizable material more in the non-intergranular layer region than in the intergranular layer region, A method for manufacturing an inductor, comprising a heat treatment step of heating the magnetic material to form an oxide film containing the easily oxidizable material on the surface of the metallic magnetic particles.

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

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