Composite metal magnetic body, inductor, and method for manufacturing composite metal magnetic body

Abstract

The present disclosure provides a composite metal magnetic body that further reduces deterioration of oxide films covering metal magnetic particles, an inductor, and a method for manufacturing the composite metal magnetic body. According to the present disclosure, composite metal magnetic bodies CP1-CP3 have metal magnetic particles DP and oxide films OL that cover the metal magnetic particles DP, and in each of the composite metal magnetic bodies CP1-CP3, a plurality of the metal magnetic particles DP are bonded to each other via the oxide films OL. Each oxide film OL comprises: an inner oxide film OLi that is in contact with the metal magnetic particle DP and has Si as a main component; and an outer oxide film OLo that is located outside the inner oxide film OLi, has an element that is more easily oxidized than Fe as a main component, and is an oxide containing Si.

Description

Composite metal magnetic material, inductor, and method for manufacturing a composite metal magnetic material

[0001] This disclosure relates to a composite metal magnetic material, an inductor, and a method for manufacturing a composite metal magnetic material.

[0002] Patent Document 1 discloses a coil component of the type in which a spiral coil portion covered by a magnetic material portion is in direct contact with the magnetic material portion, wherein the magnetic material portion mainly consists of a group of magnetic alloy particles and does not contain a glass component, and an oxide film of magnetic alloy particles exists on the surface of each magnetic alloy particle (see Claim 1 of Patent Document 1). Furthermore, the oxide film contains Fe, which belongs to the magnetic material. ３ O ４ And Fe, which belongs to the non-magnetic material ２ O ３ and Cr ２ O ３ The document discloses at least the following (see paragraph

[0018] of Patent Document 1).

[0003] Japanese Patent Publication No. 2012-164958

[0004] The oxide film described in Patent Document 1 was susceptible to degradation of its insulating properties due to reduction of the oxide film under load during inductor use. Therefore, the present disclosure aims to provide a composite metal magnetic material, an inductor, and a method for manufacturing the composite metal magnetic material that further reduces the degradation of the oxide film coating the metal magnetic particles.

[0005] The composite metallic magnetic material of the present disclosure comprises metallic magnetic particles and an oxide film coating the metallic magnetic particles, wherein a plurality of the metallic magnetic particles are bonded together via the oxide film, and the oxide film comprises an inner oxide film mainly composed of Si in contact with the metallic magnetic particles and an outer oxide film located outside the inner oxide film, which is an oxide mainly composed of an element that is more easily oxidized than Fe and contains Si.

[0006] The inductor of this disclosure comprises the composite metal magnetic material described above.

[0007] The present disclosure provides a method for producing a composite metal magnetic material, comprising: a formation step of adding a metal-organic compound containing an element more easily oxidized than Fe to the surface of metal magnetic particles to form a metal magnetic precursor; and a heat treatment step of heat-treating the metal magnetic precursor to form an oxide film on the surface of the metal magnetic particles and bonding a plurality of the metal magnetic particles via the oxide film, wherein the formation step of forming the metal magnetic precursor includes a step of pressurizing the metal magnetic precursor.

[0008] The composite metallic magnetic material of this disclosure can further reduce the deterioration of the insulating properties of the oxide film coating the metallic magnetic particles. Specifically, the oxide film has at least a two-layer structure comprising an inner oxide film mainly composed of Si that is in contact with the metallic magnetic particles, and an outer oxide film located outside the inner oxide film, which is an oxide mainly composed of an element that is more easily oxidized than Fe and contains Si. This makes it possible to ensure insulating properties with the inner oxide film while reducing the reduction of the oxide film with the outer oxide film.

[0009] Figure 1 is a perspective view of the inductor of this disclosure. Figure 2 is an exploded perspective view of the inductor of this disclosure. Figure 3 is a dashed cross-sectional view taken in the direction of the arrow III-III in Figure 2. Figure 4 is a graph showing the compositional analysis results of the composite metal magnetic material shown in Figure 3. Figure 5 is a dashed cross-sectional view in another embodiment. Figure 6 is a graph showing the compositional analysis results of the composite metal magnetic material shown in Figure 5. Figure 7 is a dashed cross-sectional view in yet another embodiment. Figure 8 is a graph showing the compositional analysis results of the composite metal magnetic material shown in Figure 7. Figure 9 is a flowchart showing the manufacturing flow of the method for manufacturing the composite metal magnetic material of this disclosure. Figure 10 is a table showing the results of the verification test related to the composite metal magnetic material.

[0010] The composite metal magnetic material and inductor, as well as the method for manufacturing the composite metal magnetic material, will be described in detail below. While the drawings will be referenced as necessary, the illustrations are provided for illustrative purposes only to aid in understanding this disclosure, and their appearance and dimensional ratios may differ from those of the actual product.

[0011] <Description of the Composite Metal Magnetic Material of the First Embodiment> First, the composite metal magnetic material CP1 of the first embodiment will be described. In this specification, "composite metal magnetic material" refers to a configuration in which metal magnetic powders MP, each composed of metal magnetic particles DP coated with an oxide film OL, are bonded together via the oxide film OL, as shown in Figure 3. However, it is not limited to the configuration shown in Figure 3, and for example, at least a portion of the material may have metal magnetic powders MP bonded together via a resin R without an oxide film. In other words, "multiple bonding" in this specification refers to a configuration in which multiple (two or more) metal magnetic powders MP are directly bonded together or partially indirectly bonded together.

[0012] The metal magnetic powder MP comprises metal magnetic particles DP and an oxide film OL. As shown in Figure 3, a resin R may be present in the gaps between the oxide films OL of the metal magnetic particles DP, which are bonded together by the oxide film OL. As will be described later, epoxy resin is used for the resin R, 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 be used. Furthermore, the oxide film OL may contain a resin component depending on the method of forming the oxide film OL.

[0013] The average particle size of the metal magnetic particles DP is preferably 0.2 μm or more and 20 μm or less, more preferably 0.5 μm or more and 15 μm or less, and even more preferably 1 μm or more and 6 μm or less.

[0014] The average particle size of the metallic magnetic particles DP 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 main body 10 (see Figure 1) through the center and the winding axis of the coil, perpendicular to the mounting surface and end face of the main body. 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 corresponding to the central part of the main body 10 are photographed with an SEM (magnification of approximately 2000 to 3000 times). Then, in each field of view, the obtained SEM images are analyzed at three arbitrary locations in the center using image analysis software (for example, image analysis software WinROOF2021 (manufactured by Mitani Corporation)) to identify the metallic magnetic particles DP and determine the equivalent circle diameter of the metallic magnetic particles. The average value of the obtained equivalent circle diameters is taken as the average particle size of the metallic magnetic particles. In this specification, the average particle size may mean the average particle size D50 (particle size equivalent to 50% of the cumulative percentage by volume).

[0015] The metallic magnetic particles DP may be an Fe-Si alloy. The metallic magnetic particles DP may be contained in the magnetic paste. The resin components contained in the magnetic paste may be removed by heat treatment or may remain.

[0016] The oxide film OL covers the surface of the metal magnetic particles DP, providing insulation between them. When the surface of the metal magnetic particles DP is covered with the oxide film OL, the insulation between the metal magnetic particles DP can be increased.

[0017] The oxide film OL is a film produced by the oxidation of the metallic magnetic particles DP. In other words, it may contain oxygen and elements that are more easily oxidized than Fe (e.g., Zr, Ti, Al, Cr, Mg, Mn, Zn) added during the production of the magnetic paste, as well as oxides formed by the oxidation of these elements that are more easily oxidized than Fe. The total thickness of the oxide film OL is preferably 5 nm to 100 nm, more preferably 5 nm to 50 nm, and even more preferably 5 nm to 20 nm. The thickness of the oxide film OL can be measured, for example, by taking a scan electron microscope (SEM) or transmission electron microscope (TEM) image of a cross-section obtained by polishing an inductor sample, and measuring the thickness of the oxide film OL covering the surface of the metallic magnetic particles DP from the obtained SEM image. The thickness of the oxide film OL is measured by taking images of three arbitrary locations in the center of a cross-section cut perpendicular to the mounting surface and end face of the base body 10, passing through the center of the base body 10 and the winding axis of the coil. In each field of view, the thickness of the oxide film OL is measured at three arbitrary points in the center. The average of these nine points ((three arbitrary points in the center of the cross section) × (three arbitrary points in the center of each field of view)) can be used as the thickness of the oxide film OL.

[0018] The oxide film OL comprises at least an inner oxide film OLi and an outer oxide film OLo. Furthermore, in the embodiment shown in Figure 3, an intervening oxide film OLm may be included. The boundary between the inner oxide film OLi, the intervening oxide film OLm, and the outer oxide film OLo is determined by the compositional analysis results of the metal magnetic powder MP. Specifically, a cross-section obtained by polishing an inductor sample is photographed with a transmission electron microscope (TEM) at a magnification of approximately 800,000 times, and the composition is determined from the results of quantitative compositional analysis performed on the cross-section by line analysis along the arrows shown in the illustrated example (Figure 3, etc.). The compositional analysis results of the composite metal magnetic material CP1 of the first embodiment are shown in Figure 4.

[0019] The inner oxide film OLi is in contact with the metallic magnetic particles DP and is mainly composed of Si. In this specification, "main component" refers to the component that is most abundant among the metallic elements and Si in the inner oxide film OLi. The inner oxide film OLi in this embodiment is SiO ２ This may be the intended meaning. More preferably, SiO2 with a higher O content than Si content.２ This may be intended. Further, the inner oxide film OLi may contain a metal element (for example, Zr) resulting from the oxide described later.

[0020] The boundary between the inner oxide film OLi and the metal magnetic particles DP may be intended to be at a position P1 where the Si content is higher than the Fe content in the graph of the compositional analysis (see FIG. 4). Also, the boundary between the inner oxide film OLi and the intervening oxide film OLm may be intended to be at a position P2 where the Fe content is higher than the Si content in the graph of the compositional analysis (see FIG. 4).

[0021] The intervening oxide film OLm is disposed outside the inner oxide film OLi and may have Fe as the main component. The "main component" in this specification refers to the component with the highest content among the metal elements and Si of the intervening oxide film OLm. More specifically, in the intervening oxide film OLm of the present embodiment, FeO, Fe ２ O ３ 、Fe ３ O ４ may be intended. Further, the intervening oxide film OLm may contain the aforementioned Si or a metal element (for example, Zr) resulting from the oxide.

[0022] The boundary between the intervening oxide film OLm and the outer oxide film OLo may be intended to be at a position P3 where the content of an element "more easily oxidized than Fe" described later is higher than the Fe content in the graph of the compositional analysis (see FIG. 4).

[0023] The outer oxide film OLo is located outside the inner oxide film OLi, is an oxide having an element more easily oxidized than Fe as the main component, and contains Si. Note that a plurality of elements more easily oxidized than Fe may be contained. The "element more easily oxidized than Fe" in this specification may be an index determined by referring to the Ellingham diagram. As an example, it may be Zr, Ti, Al, Cr, Mg, Mn, and / or Zn. In the present embodiment, the "element more easily oxidized than Fe" will be described as Zr. Therefore, as an example of the outer oxide film OLo, ZrO ２ and ZrSiO ４ may be. More preferably, ZrO where the O content is higher than the Zr content ２ and ZrSiO４ It may be intended. Note that the outer edge of the outer oxide film OLo may be intended at the position P4 where the Zr content no longer corresponds to the main component in the composition analysis graph (see FIG. 4), or the outer edge of the outer oxide film OLo may be determined from the SEM image or TEM image. Also, the "main component" in this specification refers to the component with the highest content among the metal elements of the outer oxide film OLo. Further, the outer oxide film OLo may contain oxides other than ZrO ２ and ZrSiO ４ For example, SiO ２ , FeO, Fe ２ O ３ , Fe ３ O ４ and other oxides can be determined from the overlapping regions of the compositions constituting them in the mapping image by composition analysis.

[0024] Further, ZrSiO in the outer oxide film OLo ４ may be present discretely in the film. As used in this specification, "discrete" means that ZrSiO ４ is scattered and present in the film, and the state of this discreteness can be determined from the presence or absence of crystals by XRD (X-ray diffraction method) and the overlapping region by TEM-EDX (energy dispersive X-ray spectroscopy). It can also be confirmed by EELS (electron energy loss spectroscopy) or XPS (X-ray photoelectron spectroscopy).

[0025] According to the composite metal magnetic body CP1 of the first embodiment described above, the oxide film OL includes at least an inner oxide film OLi having Si as a main component and in contact with the metal magnetic particles DP, and an outer oxide film OLo located outside the inner oxide film OLi and having an element more easily oxidized than Fe as a main component and containing Si. Therefore, while ensuring insulation by the inner oxide film OLi which is an oxide film having Si as a main component, an oxide containing Si and having an element more easily oxidized than Fe as a main component is chemically stable and reduces the reduction of the oxide film, so that the deterioration of insulation due to the reduction reaction can be reduced.

[0026] In the more preferred first embodiment of the composite metallic magnetic material CP1, the metallic magnetic particles DP are an alloy containing Fe and Si, and the outer oxide film OLo contains an oxide in which an element more easily oxidized than Fe and Si are bonded. By configuring the metallic magnetic particles DP as an alloy containing Fe and Si in this way, the Si element in the metallic magnetic particles DP can be reacted with the inner oxide film OLi and the outer oxide film OLo during the manufacturing of the composite metallic magnetic material (for example, during heat treatment) to form the desired inner oxide film OLi and outer oxide film OLo.

[0027] In a more preferred embodiment of the composite metal magnetic material CP1, the "element that is more easily oxidized than Fe" is preferably Zr. Zr oxides have higher insulation resistance, are chemically stable, and are less easily reduced than Fe oxides. From this viewpoint, the oxide is ZrO ２ or ZrSiO ４ This configuration may include the following. With this configuration, the outer oxide film OLo has high insulation resistance, is chemically stable, and is difficult to reduce, thus further reducing the deterioration of insulation due to reduction reactions.

[0028] In the first embodiment, the composite metal magnetic material CP1 may have an intervening oxide film OLm, mainly composed of Fe, provided between the outer oxide film OLo and the inner oxide film OLi.

[0029] Furthermore, in the composite metal magnetic material CP1 of the first embodiment, the thickness To of the outer oxide film OLo may be thicker than the thickness Ti of the inner oxide film OLi. More specifically, in Figure 4, the thickness To from position P3 to position P4, which corresponds to the thickness of the outer oxide film OLo, may be thicker than the thickness Ti from position P1 to position P2, which corresponds to the thickness of the inner oxide film OLi. In this way, by making the thickness To of the outer oxide film OLo, which is chemically stable and acts to reduce the reduction of the oxide film, thicker than the thickness Ti of the inner oxide film OLi, the deterioration of insulating properties due to reduction reactions can be further reduced.

[0030] Furthermore, in the composite metal magnetic material CP1 of the first embodiment, the Fe peak position M1, which is the peak of the Fe content in the oxide film OL, is located at a position corresponding to the intervening oxide film OLm, and the Fe content may decrease as one moves outward from the Fe peak position M1 (see Figure 4). If the Fe content in the oxide film OL decreases as one moves outward from the Fe peak position M1, the reduction of the oxide film (e.g., iron oxide) becomes less likely to occur, and the deterioration of insulating properties can be further reduced.

[0031] Furthermore, as a specific composition of the outer oxide film OLo in the composite metal magnetic material CP1 of the first embodiment, the total content of Zr and Si contained in the outer oxide film OLo may be 50 atom% or more relative to the total of all metal elements and Si. It should be noted that this content relationship is not limited to being satisfied throughout the entire outer oxide film OLo, but is intended to be satisfied in only a portion of the outer oxide film OLo. This content relationship may be calculated from the composition analysis results graph shown in Figure 4. Also, this content relationship can be adjusted by the heat treatment process in the manufacturing method of the composite metal magnetic material described later. With such a total content of Zr and Si, the chemical stability is maintained, and Zr and Si act to reduce the reduction of the oxide film, thus further reducing the deterioration of insulation due to reduction reactions.

[0032] Furthermore, in the composite metal magnetic material CP1 of the first embodiment, as shown in Figure 3, when multiple bonded positions via the outer oxide film OLo are designated as bonded positions BP, and a desired position between each bonded position BP in the outer oxide film OLo is designated as the interbonded position IP, the Zr content in the interbonded position IP may be greater than the Zr content in the bonded positions BP. In this specification, "bonded position BP" refers to the region between two opposing metal magnetic powders MP, as shown in Figure 3, where a line segment L1 is drawn connecting the centroids of adjacent metal magnetic powders MP, and virtual lines L2 are drawn on both sides of the virtual line L1 with the centroids of the metal magnetic powders MP at ±10°, with the virtual line L2 as the reference. In addition, in this specification, "interbonded position IP" refers to the position between the contacting parts when multiple metal magnetic powders MP are in contact with one metal magnetic powder MP. The Zr content can also be adjusted by the heat treatment process in the manufacturing method of the composite metal magnetic material described later. With such a Zr content, the Zr content of the outermost surface film is higher in the interbonding position IP that is in contact with the external environment, and the Fe content is relatively lower, thus reducing the influence of the reduction reaction of Fe oxides.

[0033] <Description of the Composite Metal Magnetic Material of the Second Embodiment> Next, the composite metal magnetic material CP2 of the second embodiment will be described with reference to Figures 5 and 6. In describing the composite metal magnetic material CP2 of the second embodiment, explanations of points that are common with the configuration of the composite metal magnetic material CP1 of the first embodiment will be omitted as appropriate. In other words, the following description will focus on the configurations that differ from the composite metal magnetic material CP1 of the first embodiment.

[0034] In the second embodiment of the composite metal magnetic material CP2, the thickness Ti of the inner oxide film OLi may be greater than the thickness To of the outer oxide film OLo. More specifically, in Figure 6, the thickness Ti from position P1 to position P2, which corresponds to the thickness of the inner oxide film OLi, may be greater than the thickness To from position P3 to position P4, which corresponds to the thickness of the outer oxide film OLo. By making the thickness Ti of the inner oxide film OLi, which is an oxide film mainly composed of Si, greater than the thickness To of the outer oxide film OLo, it is possible to reduce the reduction reaction caused by the outer oxide film OLo while obtaining high insulation properties due to the influence of the inner oxide film OLi, which has good insulating properties.

[0035] In the composite metal magnetic material CP2 of the second embodiment, the thickness Tm of the intervening oxide film OLm may be thinner than the thickness To of the outer oxide film OLo or the thickness Ti of the inner oxide film OLi. More specifically, in Figure 6, the thickness Tm from position P2 to position P3 corresponding to the thickness of the intervening oxide film OLm may be thinner than the thickness To from position P3 to position P4 corresponding to the thickness of the outer oxide film OLo, or the thickness Ti from position P1 to position P2 corresponding to the thickness of the inner oxide film OLi. By making the thickness Tm of the intervening oxide film OLm thinner, the amount of FeO and Fe contained in the intervening oxide film OLm can be reduced. ２ O ３ Fe ３ O ４ This reduces the degree of reduction and further minimizes the deterioration of insulation due to the reduction reaction.

[0036] Furthermore, in the composite metal magnetic material CP2 of the second embodiment, the Si content in the inner oxide film OLi may be 90 atom% or more relative to the total of all metal elements and Si at the Si peak position M2 shown in Figure 6. Preferably, it may be 95 atom% or more, and more preferably 98 atom% or more. This content relationship may be calculated from the graph showing the composition analysis results shown in Figure 6. In addition, this content relationship can be adjusted by the heat treatment process in the manufacturing method of the composite metal magnetic material described later. With such a Si content, the Fe content is lower than that of the inner oxide film OLi of the composite metal magnetic material CP1 of the first embodiment, and good insulation properties can be obtained.

[0037] <Description of the Composite Metal Magnetic Material of the Third Embodiment> Next, the composite metal magnetic material CP3 of the third embodiment will be described with reference to Figures 7 and 8. In describing the composite metal magnetic material CP3 of the third embodiment, explanations of points common to the configuration of the composite metal magnetic material CP1 of the first embodiment and the configuration of the composite metal magnetic material CP2 of the second embodiment will be omitted as appropriate. In other words, the following description will focus on the configurations that differ from the composite metal magnetic materials CP1 and CP2 of the above embodiments.

[0038] The composite metal magnetic material CP3 of the third embodiment comprises at least an inner oxide film OLi and an outer oxide film OLo as the oxide film OL. Specifically, the outer oxide film OLo and the inner oxide film OLi are in contact. In other words, unlike the composite metal magnetic material CP1 of the first embodiment and the composite metal magnetic material CP2 of the second embodiment, it does not have an intervening oxide film. Therefore, according to the composite metal magnetic material CP3 of the third embodiment, since it does not have an oxide film mainly composed of Fe, the reduction of Fe is further reduced, thus further improving insulation and reducing the deterioration of insulation due to reduction reactions.

[0039] Furthermore, as a specific configuration of the outer oxide film OLo in the composite metal magnetic material CP3 of the third embodiment, the total content of Zr and Si contained in the outer oxide film OLo may be 90 atom% or more relative to the total amount of all metal elements Si. More preferably, it may be 95 atom% or more. Note that this content relationship is not limited to being satisfied throughout the entire outer oxide film OLo, but is intended to be satisfied in only a part of the outer oxide film OLo. This content relationship may be calculated from the graph showing the composition analysis results shown in Figure 8. In addition, this content relationship can be adjusted by the heat treatment process in the manufacturing method of the composite metal magnetic material described later. With such a total content of Zr and Si, the chemical stability is maintained and Zr and Si act to reduce the reduction of the oxide film, thus further reducing the deterioration of insulation due to reduction reactions.

[0040] <Description of the Inductor of the Disclosure> Next, the inductor of the Disclosure will be described with reference to Figures 1 and 2. The inductor of the Disclosure comprises a base body 10 having the composite metal magnetic material described above, and a coil provided within the base body 10.

[0041] The base body 10 is, for example, a rectangular prism shape or a roughly rectangular prism shape having six faces. The corners and edges of the base body 10 may be rounded. The corners are the parts where three faces of the base body 10 intersect, and the edges are the parts where two faces of the base body 10 intersect.

[0042] Figure 1 shows the length, width, and height directions of the inductor 1 and the base body 10 as the L, W, and T directions, respectively. The length L, width W, and height T are orthogonal to each other. The mounting surface of the inductor 1 is, for example, a surface parallel to the length L and width W (LW surface).

[0043] The base body 10 shown in Figure 1 has a first main surface 11 and a second main surface 12 facing the height direction T, a first end surface 13 and a second end surface 14 perpendicular to the height direction T and facing the length direction L, and a first side surface 15 and a second side surface 16 perpendicular to the width direction W, which is perpendicular to both the length direction L and the height direction T. 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.

[0044] The base body 10 has a laminated structure in which multiple magnetic layers, each having a magnetic layer ML and a coil conductor CD, are stacked in the stacking direction (for example, the height direction T). In this embodiment, the base body 10 is constructed by stacking magnetic layers G1 to G8 as shown in Figure 2. A coil is formed by stacking multiple coil conductors CD and connecting the coil conductors CD between the magnetic layers ML. Constructing a coil by stacking coil conductors CD contributes to miniaturization. Note that the boundaries between each layer of the laminated structure of the base body 10 have disappeared.

[0045] The base body 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 base body 10 along the stacking direction. More specifically, the first coil is formed by the coil conductors CD of magnetic layers G4 and G5, and the second coil is formed by the coil conductors CD of magnetic layers G2 and G3. The coil conductors CD mainly consist of Ag. Using Ag can improve the inductance characteristics. As an example of the material for the coil conductors CD, metal conductors such as Cu, Au, or their alloys may be used instead of Ag. Furthermore, the inductor 1 of the first embodiment is not limited to this example, and for example, the base body 10 may contain only one coil. Alternatively, multiple coils may be arranged side by side inside the base body 10 in a direction intersecting the stacking direction (direction L in Figure 1) to form a coil array.

[0046] 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.

[0047] A through-hole conductor TH may be used to connect the coil to the external electrode E. That is, the first through-hole conductor TH1 to the fourth through-hole conductor TH4 may be provided corresponding to the first external electrode E1 to the fourth external electrode E4. Furthermore, the first through-hole conductor TH1 to the fourth through-hole conductor TH4 may extend along the lamination direction.

[0048] According to the inductor of this disclosure, since it comprises one of the above-mentioned composite metal magnetic materials CP1 to CP3, insulation can be ensured by the inner oxide film OLi, while the reduction of the oxide film can be reduced by the outer oxide film OLo.

[0049] <Description of the manufacturing method of the composite metal magnetic material of the first embodiment> Next, the manufacturing method of the composite metal magnetic material of the present disclosure will be described. Since the composite metal magnetic material of the present disclosure is intended to be used in an inductor, the description will be mainly given as a method for manufacturing an inductor. First, the manufacturing method of the composite metal magnetic material of the first embodiment shown in Figures 3 and 4 will be described with reference to Figure 9.

[0050] The method for manufacturing an inductor comprising a composite metal magnetic material according to the first embodiment comprises a forming step for forming a metal magnetic precursor and a heat treatment step (see Figure 9). In this specification, for convenience, the step for forming the metal magnetic precursor may include a preparation step, a pressurization step, and a degreasing step for forming the metal magnetic precursor. The details of each step will be described below.

[0051] -Preparation Process- Prepare the magnetic material (magnetic paste) that constitutes the magnetic layer ML of the magnetic layers G1 to G8 as explained in Figure 2, and the conductive paste that constitutes the coil conductor CD.

[0052] As an example of a method for producing a magnetic paste, a metallic magnetic powder containing Fe and Si with a D50 (cumulative 50% particle size by volume) of 2 μm to 20 μm is prepared. When producing a magnetic paste using this metallic magnetic powder, a metal-organic compound mainly composed of an element that is more easily oxidized than Fe (for example, Zr resinate) is added to the metallic magnetic powder at a concentration of, for example, 0.5 wt%, 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 kneaded to produce the magnetic paste.

[0053] As a conductive paste, for example, a paste containing Ag as a conductive material is prepared. However, the conductive material is not limited to Ag; a paste made from conductive materials such as Cu, Au, or their alloys may also be used.

[0054] Using the magnetic paste and conductive paste described above, the magnetic layers G1 to G8 shown in Figure 2 are prepared and laminated by screen printing or the like.

[0055] -Pressurization Process- After laminating the magnetic layers G1 to G8, the magnetic layers G1 to G8 are subjected to pressurization. This pressurization may be performed at a pressure of 300 MPa or higher. Pressurizing the magnetic layers G1 to G8 improves the packing density of the metal magnetic powder MP within the laminate of magnetic layers G1 to G8. Furthermore, this pressurization pushes the metal-organic compound, which is the material of the outer oxide film of the metal magnetic particles, from the bonding positions of multiple adjacent metal magnetic particles to the interbonding positions.

[0056] - Degreasing Process - A degreasing process may be included as a manufacturing process for a suitable inductor. The degreasing process is a process for removing binders contained in magnetic paste and conductive paste. For example, degreasing is performed in an air atmosphere at a temperature of about 300°C to 500°C. This removes the binders contained in magnetic paste and conductive paste.

[0057] - Heat treatment process: Heat treatment is performed after the degreasing process. The inside of the heat treatment furnace is heated to 99% N. ２ +1%H ２ Nitrogen and hydrogen are injected to achieve the desired result. The heat treatment temperature is such that the coil conductor sintersects, and can be, for example, between 400°C and 1000°C. Furthermore, to achieve both a reduction in coercivity and suppression of thermal diffusion of the coil conductor material components into the base body, it is desirable to set the temperature between 600°C and 800°C. Through this heat treatment, adjacent metal magnetic powders MP are bonded together by an oxide film OL. At this time, the oxidation of Fe is reduced, and Si and Zr are selectively oxidized, resulting in the formation of a base body 10 with a composite metal magnetic material CP1 mainly composed of Zr on the outermost surface. In other words, as shown in Figures 3 and 4, an inner oxide film OLi mainly composed of Si is formed in contact with the metal magnetic particles DP, and an outer oxide film OLo is located outside the inner oxide film OLi and is an oxide mainly composed of an element (Zr) that is more easily oxidized than Fe, and also contains Si.

[0058] Furthermore, in order to increase the strength of the base material, resin may be impregnated into the gaps between the oxide films of adjacent metal magnetic particles within the base material 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.

[0059] 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 conductor is 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 the external electrodes are formed, the element can be cut into individual pieces to manufacture the inductor of this embodiment.

[0060] <Description of the Method for Manufacturing a Composite Metal Magnetic Material in the Second Embodiment> Next, the method for manufacturing a composite metal magnetic material in the second embodiment shown in Figures 5 and 6 will be described. The method for manufacturing a composite metal magnetic material in the second embodiment differs from the method for manufacturing a composite metal magnetic material in the first embodiment in the conditions of the heat treatment process. Therefore, explanations of points common to the method for manufacturing a composite metal magnetic material in the first embodiment will be omitted as appropriate, and the following description will focus on the heat treatment process that differs from the method for manufacturing a composite metal magnetic material in the first embodiment.

[0061] • Heat treatment process: In this embodiment, the heat treatment process involves heating the inside of the furnace of the heat treatment apparatus to 97% N2. ２ +3%H ２Nitrogen and hydrogen are injected to achieve the desired result. The heat treatment temperature is such that the coil conductor sintersects, for example, it may be between 400°C and 1000°C. Furthermore, to achieve both a reduction in coercivity and suppression of thermal diffusion of the coil conductor material components into the base material, it is desirable to set the temperature between 600°C and 800°C. Through this heat treatment, as shown in Figures 5 and 6, the thickness of the inner oxide film OLi, which is an oxide film mainly composed of Si, is made thicker than the outer oxide film OLo. This reduces the reduction reaction caused by the outer oxide film OLo, while high insulation properties can be obtained due to the influence of the inner oxide film OLi, which has good insulating properties.

[0062] Furthermore, the amount of hydrogen injected during the heat treatment process is limited to the upper limit of industrially safe usage (3%). Therefore, it is preferable to supply hydrogen in such a way that the hydrogen concentration in the atmosphere is between 1% and 3%. By setting the heat treatment process in this way, insulation can be ensured by the inner oxide film OLi, while the reduction of the oxide film can be reduced by the outer oxide film OLo.

[0063] Furthermore, the nitrogen injected during the heat treatment process may be in a nitrogen atmosphere of 97% to 99%. By setting the heat treatment process in this way, insulation can be ensured by the inner oxide film OLi, while the reduction of the oxide film can be reduced by the outer oxide film OLo.

[0064] <Description of the Method for Manufacturing a Composite Metal Magnetic Material in the Third Embodiment> Next, the method for manufacturing a composite metal magnetic material in the third embodiment shown in Figures 7 and 8 will be described. The method for manufacturing a composite metal magnetic material in the third embodiment differs from the method for manufacturing a composite metal magnetic material in the second embodiment in the conditions of the degreasing step. Therefore, explanations of points common to the method for manufacturing a composite metal magnetic material in the second embodiment will be omitted as appropriate, and the following description will focus on the degreasing step that differs from the method for manufacturing a composite metal magnetic material in the second embodiment.

[0065] - Degreasing process - The degreasing process in this embodiment may be carried out in an oxygen atmosphere of 2 ppm to 200 ppm. After undergoing such a degreasing process in a low-oxygen atmosphere, the heat treatment process described in the method for manufacturing a composite metal magnetic material of the second embodiment is performed, and as shown in Figures 7 and 8, the oxide film OL is configured such that the outer oxide film OLo and the inner oxide film OLi are in contact with each other. Since it does not have an oxide film mainly composed of Fe, the deterioration of insulating properties due to reduction reactions can be reduced.

[0066] The demonstration tests concerning the composite metallic magnetic materials of this disclosure are described in detail. Specifically, the composite metallic magnetic materials described in the following examples and comparative examples were manufactured.

[0067] -Composite Metal Magnetic Material of the Example- Following the method for manufacturing the composite metal magnetic material of the first embodiment, as described in the preparation step, a magnetic paste was prepared by adding 0.5 wt% of Zr resinate to a metal magnetic powder containing Fe and Si. Then, a pressurization step, a degreasing step, and a heat treatment step were performed.

[0068] Here, the composite metal magnetic material of Example 1 is used to maintain 99% N inside the furnace of the heat treatment apparatus. ２ +1%H ２ The atmosphere was set to 99% N2, and the heat treatment temperature was 650°C. In Example 2, the inside of the furnace of the heat treatment apparatus was set to 99% N2. ２ +1%H ２ The atmosphere was set to 99% N₂. In Example 3, the inside of the furnace of the heat treatment apparatus was set to 99% N₂. ２ +1%H ２ The atmosphere was set as described above, and the heat treatment temperature was set to 750°C.

[0069] -Comparative example of a composite metal magnetic material- A composite metal magnetic material was manufactured in accordance with the manufacturing method of the composite metal magnetic material of the first embodiment, except that Zr resinate was not added.

[0070] Here, the composite metal magnetic material of Comparative Example 1 has a 99% N content inside the furnace of the heat treatment apparatus. ２ +1%H ２ The atmosphere was set to 99% N2, and the heat treatment temperature was 650°C. Comparative Example 2 was a heat treatment apparatus with a furnace atmosphere of 99% N2. ２ +1%H ２The atmosphere was set to 99% N in the heat treatment furnace, and the heat treatment temperature was set to 700°C. Comparative Example 3 was set to 99% N in the furnace of the heat treatment apparatus. ２ +1%H ２ The atmosphere was set as described above, and the heat treatment temperature was set to 750°C.

[0071] -Evaluation of Insulation Resistance of Composite Metal Magnetic Materials- The insulation resistance of the composite metal magnetic materials of Examples 1 to 3 and Comparative Examples 1 to 3 was evaluated.

[0072] To evaluate the insulation resistance, a composite magnetic substrate with a diameter of 8 mm and a thickness of 1 mm was fabricated using a composite metallic magnetic material. Conductive electrodes were formed on the top and bottom surfaces of the composite magnetic substrate, and the insulation resistance was measured using an insulation resistance meter (Advantest Corporation, model number: R8340).

[0073] The insulation resistance evaluation is shown in Figure 10. According to the insulation resistance evaluation, when the insulation resistance of the composite metal magnetic materials of Comparative Examples 1 to 3 was measured and compared before and after thermal loading, a decrease in the insulation resistance value occurred after thermal loading, confirming deterioration of insulation due to the reduction reaction. On the other hand, when the insulation resistance of the composite metal magnetic materials of Examples 1 to 3 was measured and compared before and after thermal loading, no decrease in the insulation resistance value occurred, confirming that good insulation properties can be obtained. From this insulation resistance evaluation, it can be concluded that the composite metal magnetic materials of this disclosure can further reduce the deterioration of the oxide film coating the metal magnetic particles.

[0074] 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.

[0075] Embodiments of the composite metal magnetic material, inductor, and method for manufacturing the composite metal magnetic material of the present disclosure are as follows: <1> A composite metal magnetic material having metallic magnetic particles and an oxide film covering the metallic magnetic particles, wherein a plurality of metallic magnetic particles are bonded together via the oxide film, wherein the oxide film comprises: an inner oxide film mainly composed of Si in contact with the metallic magnetic particles, and an outer oxide film located outside the inner oxide film, which is an oxide mainly composed of an element that is more easily oxidized than Fe and contains Si. <2> The composite metal magnetic material according to <1>, wherein the metallic magnetic particles are an alloy containing Fe and Si, and the outer oxide film contains an oxide in which an element that is more easily oxidized than Fe and Si are bonded together. <3> The oxide of the outer oxide film is ZrO ２ or ZrSiO ４A composite metallic magnetic material according to <1> or <2>, including <4> an intervening oxide film mainly composed of Fe is provided between the outer oxide film and the inner oxide film, the composite metallic magnetic material according to any one of <1> to <3>. <5> A composite metallic magnetic material according to <4>, wherein the thickness of the intervening oxide film is thinner than the thickness of the outer oxide film or the thickness of the inner oxide film. <6> A composite metallic magnetic material according to any one of <1> to <5>, wherein the thickness of the outer oxide film is thicker than the thickness of the inner oxide film. <7> A composite metallic magnetic material according to any one of <1> to <5>, wherein the thickness of the inner oxide film is thicker than the thickness of the outer oxide film. <8> A composite metallic magnetic material according to <4>, wherein the Fe peak position, which is the peak of the Fe content in the oxide film, is located at a position corresponding to the intervening oxide film, and the Fe content decreases as you move outward from the Fe peak position. <9> A composite metallic magnetic material according to any one of <1> to <3>, wherein the outer oxide film and the inner oxide film are in contact. <10> A composite metallic magnetic material according to <8>, wherein the total content of Zr and Si in the outer oxide film is 50 atom% or more relative to the total of all metal elements and Si. <11> A composite metallic magnetic material according to <8>, wherein the total content of Zr and Si in the outer oxide film is 90 atom% or more relative to the total of all metal elements and Si. <12> A composite metallic magnetic material according to any one of <1> to <11>, wherein when multiple bonded positions via the outer oxide film are designated as bond positions, and a desired position between each bond position in the outer oxide film is designated as an inter-bond position, the Zr content at the inter-bond position is greater than the Zr content at the bond positions. <13> An inductor comprising any one of the composite metallic magnetic materials according to <1> to <12>. <14> A method for producing a composite metal magnetic material, comprising: a forming step of adding a metal organic compound containing an element that is more easily oxidized than Fe to the surface of metal magnetic particles to form a metal magnetic precursor; and a heat treatment step of heat-treating the metal magnetic precursor to form an oxide film on the surface of the metal magnetic particles and bonding a plurality of metal magnetic particles via the oxide film, wherein the forming step of forming the metal magnetic precursor includes a step of pressurizing the metal magnetic precursor.<15> The method for producing a composite metal magnetic material according to <14>, wherein the heat treatment step is performed to form an inner oxide film mainly composed of Si in contact with the metal magnetic particles, and an outer oxide film located outside the inner oxide film, which is an oxide mainly composed of an element that is more easily oxidized than Fe and contains Si. <16> The method for producing a composite metal magnetic material according to <14> or <15>, wherein the heat treatment step is performed in a nitrogen atmosphere of 97% to 99%. <17> The method for producing a composite metal magnetic material according to any one of <14> to <16>, wherein the heat treatment step is performed by supplying hydrogen in the atmosphere to a concentration of 1% to 3%. <18> The method for producing a composite metal magnetic material according to any one of <14> to <17>, wherein degreasing is performed in an oxygen atmosphere of 2 ppm to 200 ppm before the heat treatment step.

[0076] The composite metal magnetic material, inductor, and method for manufacturing the composite metal magnetic material described herein can be suitably used as electronic components that further reduce the degradation of the oxide film coating the metal magnetic particles.

[0077] 1 Inductor 10 Base 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 CD Coil conductor CP1-CP3 Composite metal magnetic material DP Metal magnetic particles E External electrodes E1-E4 First external electrode to fourth external electrode G1-G8 Magnetic layer ML Magnetic layer MP Metal magnetic powder OL Oxide film OLi Inner oxide film OLm Interposed oxide film OLo Outer oxide film R Resin TH Through-hole conductor TH1-TH4 First through-hole conductor to fourth through-hole conductor M1, M2 Peak position P1-P4 Position BP Coupling position IP Inter-coupling position

Claims

1. A composite metallic magnetic material comprising metallic magnetic particles and an oxide film coating the metallic magnetic particles, wherein a plurality of the metallic magnetic particles are bonded together via the oxide film, the oxide film comprising: an inner oxide film mainly composed of Si in contact with the metallic magnetic particles; and an outer oxide film located outside the inner oxide film, mainly composed of an element more easily oxidized than Fe and containing Si.

2. The composite metallic magnetic material according to claim 1, wherein the metallic magnetic particles are an alloy containing Fe and Si, and the outer oxide film contains an element that is more easily oxidized than Fe and an oxide of Si.

3. The oxide of the outer oxide film is ZrO ２ or ZrSiO ４ A composite metallic magnetic material according to claim 1 or 2, comprising:

4. The composite metallic magnetic material according to any one of claims 1 to 3, wherein an intervening oxide film mainly composed of Fe is provided between the outer oxide film and the inner oxide film.

5. The composite metallic magnetic material according to claim 4, wherein the thickness of the intervening oxide film is thinner than the thickness of the outer oxide film or the thickness of the inner oxide film.

6. The composite metallic magnetic material according to any one of claims 1 to 5, wherein the thickness of the outer oxide film is greater than the thickness of the inner oxide film.

7. The composite metallic magnetic material according to any one of claims 1 to 5, wherein the thickness of the inner oxide film is greater than the thickness of the outer oxide film.

8. The composite metallic magnetic material according to claim 4, wherein the Fe peak position, which represents the peak of Fe content in the oxide film, is located at a position corresponding to the intervening oxide film, and the Fe content decreases as one moves outward from the Fe peak position.

9. The composite metallic magnetic material according to any one of claims 1 to 3, wherein the outer oxide film and the inner oxide film are in contact.

10. The composite metallic magnetic material according to claim 8, wherein the total content of Zr and Si in the outer oxide film is 50 atom% or more relative to the total of all metal elements and Si.

11. The composite metallic magnetic material according to claim 8, wherein the total content of Zr and Si in the outer oxide film is 90 atom% or more relative to the total of all metal elements and Si.

12. The composite metallic magnetic material according to any one of claims 1 to 11, wherein when the multiple bonded positions via the outer oxide film are defined as bonded positions, and the spaces between each bonded position in the outer oxide film are defined as interbonded positions, the Zr content at the interbonded positions is greater than the Zr content at the bonded positions.

13. An inductor comprising a composite metallic magnetic material according to any one of claims 1 to 12.

14. A method for producing a composite metal magnetic material, comprising: a forming step of adding a metal-organic compound containing an element that is more easily oxidized than Fe to the surface of metal magnetic particles to form a metal magnetic precursor; and a heat treatment step of heat-treating the metal magnetic precursor to form an oxide film on the surface of the metal magnetic particles and bonding a plurality of the metal magnetic particles via the oxide film, wherein the forming step of forming the metal magnetic precursor includes a step of pressurizing the metal magnetic precursor.

15. The method for producing a composite metal magnetic material according to claim 14, wherein the heat treatment step forms an inner oxide film mainly composed of Si in contact with the metal magnetic particles, and an outer oxide film located outside the inner oxide film, which is an oxide mainly composed of an element that is more easily oxidized than Fe and contains Si.

16. The method for producing a composite metal magnetic material according to claim 14 or 15, wherein the heat treatment step is carried out in a nitrogen atmosphere of 97% or more and 99% or less.

17. The method for producing a composite metal magnetic material according to any one of claims 14 to 16, wherein the heat treatment step is carried out by supplying hydrogen in an atmosphere such that it is 1% or more and 3% or less.

18. A method for producing a composite metal magnetic material according to any one of claims 14 to 17, wherein degreasing is performed in an oxygen atmosphere of 2 ppm to 200 ppm before the heat treatment step.

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