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

Abstract

The present invention provides: a composite metal magnetic body and an inductor, in each of which the filling rate of metal magnetic particles is improved by making the Vickers hardness thereof smaller than ever before; and a method for manufacturing the composite metal magnetic body and a method for manufacturing the inductor. A composite metal magnetic body CP according to the present disclosure is obtained by combining a plurality of metal magnetic powders MP each having a metal magnetic particle DP that contains Fe and a passivation element that is more easily oxidized than Cr and an oxide film OL that covers the metal magnetic particle DP via the oxide film OL, wherein the Vickers hardness of the metal magnetic particle DP is 67 HV to 191 HV inclusive.

Description

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

[0001] The present disclosure relates to a composite metal magnetic body, an inductor, a method for manufacturing a composite metal magnetic body, and a method for manufacturing an inductor.

[0002] Patent Document 1 discloses a coil component in which a spiral coil portion covered with a magnetic material portion is in direct contact with the magnetic material portion, the magnetic material portion being mainly composed of magnetic alloy particles and not containing a glass component, and each magnetic alloy particle has an oxide film of the magnetic alloy particle on its surface (see claim 1 of Patent Document 1). Patent Document 1 further discloses that the magnetic alloy particles are Fe-Cr-Si alloy particles (see claim 3 of Patent Document 1).

[0003] JP 2012-164958 A

[0004] The magnetic alloy particles described in Patent Document 1 contain Si, which results in a high Vickers hardness. Magnetic alloy particles with high Vickers hardness are less likely to undergo plastic deformation even when pressed at a desired molding pressure, making it difficult to increase the metal occupancy rate within the magnetic body. As a result, it was not possible to improve the magnetic permeability.

[0005] Furthermore, even when pressed at a desired molding pressure, surface contact between the Si-containing magnetic alloy particles is difficult to occur, resulting in the generation of magnetic field concentration points, which deteriorates the DC superposition characteristics of the inductor.

[0006] Furthermore, the oxide film that coats the magnetic alloy particles mainly composed of Fe-Cr-Si has poor corrosion resistance, and when heat treatment is performed during the production of the metal magnetic body, the oxide film has the property of being easily reduced.

[0007] In view of these points, the present disclosure aims to provide a composite metal magnetic body and an inductor that have a lower Vickers hardness than conventional bodies and an improved filling rate of metal magnetic particles, as well as a method for manufacturing a composite metal magnetic body and a method for manufacturing an inductor.

[0008] The composite metal magnetic body of the present disclosure is a composite metal magnetic body in which a plurality of metal magnetic powders each having metal magnetic particles containing a passivation element and Fe that are more easily oxidized than Cr, and an oxide film that covers the metal magnetic particles, are bonded together via the oxide film, and the Vickers hardness of the metal magnetic particles is 67 HV or more and 191 HV or less.

[0009] The inductor of the present disclosure includes the composite metal magnetic body described above.

[0010] The method for producing a composite metal magnetic body of the present disclosure includes a heat treatment step of heating the metal magnetic particles in a low-oxygen atmosphere or a reducing atmosphere to form an oxide film on the surface of the metal magnetic particles.

[0011] The method for manufacturing an inductor according to the present disclosure includes a heat treatment step of heating the metal magnetic particles in a low-oxygen atmosphere or a reducing atmosphere to form an oxide film on the surface of the metal magnetic particles.

[0012] According to the present disclosure, it is possible to provide a composite metal magnetic body and an inductor that have a lower Vickers hardness than conventional ones and an improved filling rate of metal magnetic particles, as well as a method for manufacturing a composite metal magnetic body and a method for manufacturing an inductor.

[0013] FIG. 1 is a perspective view of an inductor according to the present disclosure. FIG. 2 is an exploded perspective view of the inductor according to the present disclosure. FIG. 3 is a cross-sectional view taken along the arrow III-III in FIG. 2. FIG. 4A is a cross-sectional view of a composite metal magnetic body according to the present disclosure. FIG. 4B is a cross-sectional view of a modified example of a composite metal magnetic body according to the present disclosure. FIG. 5 is a table showing the results of a demonstration test. FIG. 6 is a graph showing the results of a demonstration test relating to Vickers hardness. FIG. 7 is a graph showing the results of a demonstration test relating to bulk density. FIG. 8 is a graph showing the results of a demonstration test relating to real permeability μ'. FIG. 9 is a graph showing the results of a demonstration test relating to tan δ, which corresponds to core loss. FIG. 10 is a graph showing the relationship between real permeability μ' and the Ni composition amount.

[0014] The composite metal magnetic body and inductor, as well as the manufacturing method of the composite metal magnetic body and the manufacturing method of the inductor according to the present disclosure, will be described in detail below. While the description will be made with reference to the drawings as necessary, the contents shown in the drawings are merely shown as schematic examples for the purpose of understanding the present disclosure, and the appearance and dimensional ratios may differ from the actual products.

[0015] <Description of the composite metal magnetic body of the present disclosure> First, the composite metal magnetic body CP of the present disclosure will be described. Note that the "composite metal magnetic body" referred to in this specification refers to a configuration in which metal magnetic powders MP formed by coating metal magnetic particles DP with an oxide film OL are bonded together via the oxide film OL, as shown in Fig. 4A, and may also have regions in which metal magnetic powders MP are bonded together via a resin R without an oxide film as shown in Fig. 4B. In other words, the "composite metal magnetic body" refers to a configuration in which multiple (two or more) metal magnetic powders MP are bonded directly or indirectly.

[0016] The metal magnetic powder MP includes metal magnetic particles DP and an oxide film OL. Depending on the method for forming the oxide film OL, the oxide film OL may contain a resin component.

[0017] The average particle size of the metal magnetic particles DP is preferably 0.2 μm to 20 μm, more preferably 1 μm to 15 μm, and even more preferably 1 μm to 10 μm, which allows for high magnetic permeability and low core loss.

[0018] The average particle size of the metal magnetic particles DP can be measured using the procedure described below. An inductor sample is cut to obtain a cross section. Specifically, the sample cross section is obtained by cutting the sample through the center of the element body and the winding axis of the coil, perpendicular to the mounting surface and end surface of the element body. The sample cross section may be flattened by ion milling or the like. Three randomly selected central locations on the cut surface, which corresponds to the center of the element body 10, are photographed using an SEM (approximately 1000x magnification) and subjected to composition analysis using EDX. The position of the metal magnetic particles DP in the SEM image can be identified by confirming the position of Fe in the photographed field of view using the EDX composition analysis results. Then, the obtained SEM images are analyzed at three randomly selected central locations in each field of view using image analysis software (e.g., image analysis software WinROOF2021 (manufactured by Mitani Corporation)), and the identified metal magnetic particles DP are analyzed to determine the circle-equivalent diameter of the metal magnetic particles DP. The average of the obtained circle-equivalent diameters is taken as the average particle size of the metal magnetic particles DP. The average particle size in this specification may refer to the average particle size D50 (particle size corresponding to a cumulative percentage of 50% on a volume basis).

[0019] The metal magnetic particles DP contain at least Fe (iron). Furthermore, the metal magnetic particles DP do not contain Si. As used herein, "does not contain Si" may mean that the metal magnetic particles DP contain 1 wt% or less of Si as an impurity, based on the total metal and metalloid elements constituting the metal magnetic particles DP. Furthermore, the metal magnetic particles DP may contain Ni. More specifically, they may contain elements that are less susceptible to oxidation than the passivation elements described below. Furthermore, the metal magnetic particles DP contain a passivation element that is more easily oxidized than Cr. In this specification, the term "passivation element that is more easily oxidized than Cr" may be an index determined with reference to the Ellingham diagram.

[0020] As an example of a preferred passivation element, the passivation element may include at least one element selected from the group consisting of Al, Zr, and Ti. Among the passivation elements, Al is the element that is most easily oxidized, followed by Zr and Ti in order of least oxidization. In the following description, the passivation element will be described as Al.

[0021] The metal magnetic particles DP may be contained in the magnetic paste, as will be described in detail in the explanation of the manufacturing method. The resin component contained in the magnetic paste may be lost by the heat treatment, or may remain.

[0022] The surfaces of the metal magnetic particles DP are covered with an insulating coating (oxide coating OL) produced by oxidizing the metal magnetic particles DP through heat treatment of the metal magnetic particles DP. As used herein, "insulating" refers to a volume resistivity of 1 MΩcm or more. When the surfaces of the metal magnetic particles DP are covered with an insulating coating, the insulation between the metal magnetic particles DP can be improved. A specific example of the insulating coating is an oxide coating OL, as shown in FIG. 3. Adjacent metal magnetic particles DP are bonded via this oxide coating OL. Between the metal magnetic particles DP bonded by the oxide coating OL, a resin R is present in the gap between the oxide coating OL of the metal magnetic particles DP and the oxide coating OL of the metal magnetic particles DP. As described below, an epoxy resin is used as 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, alkyd resin, etc. may also be used.

[0023] The oxide film OL is a film generated by the oxidation of the metal magnetic particles DP. In other words, it may contain oxygen. Furthermore, it may contain a passivating element and may contain an oxide derived from the passivating element. For example, when Al is used as the passivating element, the oxide film OL may contain aluminum oxide. The thickness of the oxide film OL may be 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 photographing a cross section obtained by polishing an inductor sample with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and measuring the thickness of the oxide film OL covering the surface of the metal magnetic particles DP from the obtained SEM image. The thickness of the oxide film OL is measured by photographing three arbitrary central locations on a cross section cut perpendicular to the mounting surface and end surface of the element body through the center of the element 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 central locations. The thickness of the oxide film OL may be determined by averaging these nine points (any three points in the center of the cut surface) x (any three points in the center of each field of view).

[0024] The resin R may be used to increase the strength of the inductor element, which will be described later. As an example, the element 10, which is formed by stacking magnetic layers G1 to G8 (see FIG. 2), which will be described later, may be heat-treated and then impregnated with the resin, so that the resin R is present between adjacent metal magnetic powder particles MP bonded by an insulating coating. Examples of the resin impregnated into the element 10 after heat-treatment include epoxy resin and silicone resin. Other resins that may be used include one or more resins selected from the group consisting of phenolic resin, polyester resin, polyimide resin, polyolefin resin, acrylic resin, polyvinyl butyral resin, cellulose resin, alkyd resin, and the like.

[0025] The composite metal magnetic body CP of the present disclosure is manufactured by a heat treatment process, such as sintering in a low-oxygen atmosphere or a reducing atmosphere, as described in detail in the manufacturing method of the composite metal magnetic body below. After manufacturing the composite metal magnetic body CP, the Vickers hardness is measured. The Vickers hardness can be measured using the procedure described below. First, a measurement sample is prepared by cutting the element body along its length in the thickness direction from the mounting surface side at a position passing through the coil winding axis. The measurement sample is hardened with a curing resin so that the cut surface is exposed to the outside. After the resin is hardened, the cut surface is mechanically polished or electrolytically polished. The measurement sample is then placed in a dynamic ultra-microhardness tester (DUH series, manufactured by Shimadzu Corporation). The Vickers hardness is measured using a triangular pyramidal indenter (made of diamond) with a 115° edge-to-edge angle as the measuring indenter. The indenter size is 10 μm, the test load is 100 mN, the load holding time is 10 seconds, and the spacing between indentations is 100 μm or more.

[0026] When the Vickers hardness of the composite metal magnetic body CP of the present disclosure is measured, it is found that the composite metal magnetic body CP of the present disclosure does not contain Si element, and therefore has a reduced Vickers hardness compared to Fe-Si alloy particles of the prior art. As will be explained in detail in the Examples, the Vickers hardness of the metal magnetic particles DP in the composite metal magnetic body CP of the present disclosure is 67 HV or more and 191 HV or less. With such a Vickers hardness, plastic deformation is more likely to occur when pressurized at a desired molding pressure in the pressurizing step when manufacturing an inductor, and the filling rate of the metal magnetic particles DP within the element can be improved, thereby increasing magnetic permeability. Note that with regard to the unit "HV" of Vickers hardness, 1 HV is 1 kgf / mm ２ The units can be converted as follows.

[0027] In the manufactured composite metal magnetic material CP, the Al content of the suitable metal magnetic particles DP may be 0.7 wt% or more and 5 wt% or less. The content of the metal element or semi-metal element in the metal magnetic particles DP is as explained in the measurement of the average particle size of the metal magnetic particles DP above, and is determined by composition analysis using EDX. Details of this numerical range will be explained in the examples below, but with such an Al content in the metal magnetic particles DP, the Vickers hardness can be further reduced compared to Fe-Si alloy particles of the prior art. Furthermore, a chemically stable oxide film can be formed on the surface of the metal magnetic particles, and by controlling the atmosphere during sintering, the magnetic permeability can be improved.

[0028] Furthermore, in the manufactured composite metal magnetic material CP, the Ni content of the metal magnetic particles may be preferably 0 wt % or more and 52 wt % or less. Details of this range will be explained in the examples below, but with such a Ni content of the metal magnetic particles, good magnetic permeability can be obtained.

[0029] Furthermore, the manufactured composite metal magnetic body CP may contain Fe, Ni, and Al as the metal magnetic particles DP, and the metal magnetic particles DP may have a Vickers hardness of 67 HV or more and 191 HV or less. With such metal magnetic particles DP, the filling rate of the metal magnetic particles DP within the element body 10 can be improved, thereby increasing the magnetic permeability.

[0030] 1 to 4B, the inductor of the present disclosure will be described. The inductor of the present disclosure includes a base body 10 including the composite metal magnetic body CP described above, and a coil provided within the base body 10.

[0031] The inductor of the present disclosure may be an inductor constructed by stacking multiple magnetic layers G1 to G8 each having a coil conductor CD and a magnetic layer ML as shown in Figure 2 (hereinafter referred to as inductor 1A of this embodiment), or may be an inductor constructed by winding a conductor wire.

[0032] Description of the Inductor of the Present Embodiment The element body 10 has, for example, a rectangular parallelepiped shape or a substantially rectangular parallelepiped shape having six sides. The element body 10 may have rounded corners and ridges. A corner is a portion where three sides of the element body 10 intersect, and a ridge is a portion where two sides of the element body 10 intersect.

[0033] 1, the length direction, width direction, and height direction of the inductor 1A and the element body 10 are shown as L direction, W direction, and T direction, respectively. The length direction L, width direction W, and height direction T are perpendicular to each other. The mounting surface of the inductor 1A is, for example, a surface (LW surface) parallel to the length direction L and width direction W.

[0034] 1 has a first main surface 11 and a second main surface 12 that face each other in a height direction T, a first end surface 13 and a second end surface 14 that are perpendicular to the height direction T and face each other in a length direction L, and a first side surface 15 and a second side surface 16 that face each other in a width direction W that is perpendicular to the length direction L and the height direction T. In the example shown in FIG. 1 , the first main surface 11 of the element body 10 corresponds to the mounting surface (bottom surface) of the element body 10. Note that the second main surface 12 may also be the mounting surface of the element body 10.

[0035] The element body 10 includes a magnetic body formed of a composite metal magnetic body CP and a coil formed by laminating a coil conductor CD therein. Here, the magnetic body is formed by laminating multiple magnetic layers ML shown in FIG. 2 in a lamination direction (e.g., height direction T), and the coil is formed by laminating multiple coil conductors CD in the lamination direction. In this embodiment, the element body 10 is formed by laminating magnetic layers G1 to G8 as shown in FIG. 2. Note that the boundaries between the layers in the layered structure of the element body 10 disappear. Furthermore, each of the magnetic layers G1 to G8 may be formed by laminating multiple identical patterns. Furthermore, to increase the element strength of the inductor, multiple metal magnetic particles DP contained in the magnetic body may be bonded via a resin R such as epoxy resin or silicone resin (see FIG. 3).

[0036] In the example shown in FIG. 2 , two coils (a first coil and a second coil) are arranged in the element body 10 along the stacking direction. More specifically, the first coil is formed by the coil conductor CD of the magnetic body layers G4 and G5, and the second coil is formed by the coil conductor CD of the magnetic body layers G2 and G3. The coil conductor CD is mainly composed of Cu. The use of Cu can improve inductance characteristics. Note that, as an example of the material for the coil conductor CD, a metal conductor such as Ag, Au, or an alloy thereof may also be used instead of Cu. The inductor 1A of this embodiment is not limited to this example, and for example, three or more coils may be arranged along the stacking direction. Furthermore, a coil array may be formed by arranging multiple coils side by side inside the element body 10 in a direction intersecting the stacking direction (the L direction in FIG. 1 ).

[0037] External electrodes E are provided on the mounting surface (first main surface 11) of the element body 10. In the example shown in Fig. 2, the external electrodes E include a first external electrode E1 and a second external electrode E2 connected to the respective ends of the first coil, and a third external electrode E3 and a fourth external electrode E4 connected to the respective ends of the second coil. Two external electrodes are provided for each coil. Therefore, if the number of coils is three, the number of external electrodes may be six.

[0038] The through-hole conductors TH may be used to connect the coil and the external electrodes E. That is, the first through-hole conductors TH1 to TH4 may be provided corresponding to the first external electrode E1 to the fourth external electrode E4. The first through-hole conductors TH1 to TH4 may extend along the stacking direction.

[0039] According to the inductor 1A of this embodiment, a composite metal magnetic material CP is used in which the Vickers hardness of the above-mentioned metal magnetic particles DP is 67 HV or more and 191 HV or less, and therefore it is possible to improve the filling rate of the metal magnetic particles DP within the base body 10, thereby increasing the magnetic permeability and obtaining good DC superposition characteristics.

[0040] In a preferred embodiment of the inductor 1A of the present disclosure, the starting frequency at which the real permeability μ' begins to decrease may be 10 MHz or higher, and the frequency at which tanδ becomes 0.05 or higher may be 10 MHz or higher. The term "real permeability μ'" as used herein refers to the real part of the complex permeability of the inductor. Furthermore, the term "tanδ" as used herein refers to the value calculated by tanδ = μ" / μ', where μ" is the imaginary part of the complex permeability of the inductor. The term "complex permeability" as used herein refers to the ratio of B to H, expressed in complex terms as μ = B / H = μ'-jμ'', when an alternating magnetic field H (a magnetic field whose magnitude and direction repeatedly change over time) is applied to a magnetic material, and a phase delay occurs in the change in magnetic flux density B. The numerical range of the start frequency will be described in detail in the examples below, but an inductor 1A having such a start frequency can provide good frequency characteristics.

[0041] <Method for manufacturing a composite metal magnetic body and a method for manufacturing an inductor according to the present disclosure> Next, a method for manufacturing an inductor according to the present disclosure will be described. Note that the method for manufacturing a composite metal magnetic body is included in the method for manufacturing an inductor, so description thereof will be omitted.

[0042] The method for manufacturing an inductor according to the present disclosure includes a preparation step, a pressurizing step, and a heat treatment step. As will be described later, the method may also include an optional degreasing step.

[0043] - Preparation Step - A magnetic material (magnetic paste) for forming the magnetic layers ML of the magnetic layers G1 to G8 described with reference to FIG. 2 and a conductor paste for forming the coil conductor CD are prepared.

[0044] As an example of a method for producing a magnetic paste, a metal magnetic powder containing Fe with a cumulative 50% particle diameter (D50) of 2 μm to 20 μm is prepared. A passivating element that is more easily oxidized than Cr (for example, Al: 0.7 wt% to 5 wt%) is added to this metal magnetic powder, and a binder such as cellulose or polyvinyl butyral (PVB) and a solvent such as a mixture of terpineol and butyl diglycol acetate (BCA) are added, and the mixture is kneaded to produce a magnetic paste.

[0045] The conductive paste may be, for example, a paste containing Cu as a conductive material. Note that the conductive material is not limited to Cu, and a conductive material such as Ag, Au, or an alloy thereof may be formed into a paste.

[0046] The magnetic layers G1 to G8 shown in FIG. 2 are prepared and laminated by screen printing or the like using the magnetic paste and conductive paste described above.

[0047] - Pressurizing step (optional step) - After the magnetic layers G1 to G8 are stacked, the magnetic layers G1 to G8 are pressurized. This pressurization may be performed at a pressure of 300 MPa or more. By pressing the magnetic layers G1 to G8, two or more metal magnetic powders MP are bonded to form a composite metal magnetic body CP.

[0048] - Degreasing step (optional step) - A manufacturing process of a preferred inductor manufacturing method may include a degreasing step. The degreasing step is a step of removing binders contained in the magnetic paste and conductive paste. As an example, degreasing is performed at a temperature of about 300°C or higher and 500°C or lower. This removes the binders contained in the magnetic paste and conductive paste.

[0049] Heat Treatment Step Heat treatment is performed after the degreasing step. As an example of heat treatment conditions, nitrogen is injected into the furnace of the heat treatment device at a flow rate of 19 L / min, thereby creating a low-oxygen atmosphere inside the furnace. As another example of heat treatment conditions, nitrogen is injected into the furnace of the heat treatment device at a flow rate of 19 L / min and hydrogen is injected into the furnace of the heat treatment device at a flow rate of 0.19 L / min, thereby creating a reducing atmosphere inside the furnace. The heat treatment temperature is a temperature at which the coil conductor is sintered, and may be, for example, between 400°C and 1000°C. Furthermore, it is desirable to set the temperature to between 700°C and 900°C in order to simultaneously reduce the coercive force and suppress the thermal diffusion of the coil conductor material components into the base body. In particular, FeAl ２ O ４ When forming a highly corrosion-resistant composite oxide such as those mentioned above, the temperature is preferably set to 750° C. or higher and 900° C. This heat treatment forms an oxide coating mainly composed of Al oxide on the surface of the metal magnetic particles within the element, and adjacent metal magnetic particles can be bonded together by an insulating coating.

[0050] Here, the background to the implementation of the heat treatment process in a low-oxygen atmosphere and a reducing atmosphere according to the present disclosure will be explained. In the prior art, Fe—Cr—Si alloy particles contain at least Si. As described in paragraph

[0032] of the prior art (JP 2012-164958 A), binder removal and oxide film formation have been achieved by performing a heat treatment in an oxidizing atmosphere such as air. However, because the prior art contains Si, the Vickers hardness is high, making it difficult to increase the filling rate of metal magnetic particles within the magnetic body.

[0051] Therefore, the inventors of the present application came up with the idea of ​​a metal magnetic body that is substantially free of Si, thereby reducing the Vickers hardness and increasing the packing density of the metal magnetic particles within the magnetic body. However, when metal magnetic particles that are substantially free of Si are subjected to a heat treatment in an oxidizing atmosphere such as air, as disclosed in the prior art, the degree of oxidation of the metal magnetic particles increases, and it is not possible to obtain the desired magnetic permeability and DC bias characteristics.

[0052] The present inventors conducted extensive research into optimal heat treatment conditions for a composite metal magnetic body substantially free of Si, and discovered that the desired magnetic permeability and DC bias characteristics can be obtained by performing the heat treatment process in the low-oxygen and reducing atmospheres described above. In other words, the heat treatment process described above allows for the appropriate formation of oxide coatings on the surfaces of the metal magnetic particles, resulting in a composite metal magnetic body having a Vickers hardness of 67 HV to 191 HV. Furthermore, the packing density of the metal magnetic particles within the base body 10 can be improved, thereby increasing magnetic permeability. Note that, in this specification, a low-oxygen atmosphere refers to an atmosphere with an oxygen concentration of 2 ppm to 200 ppm. A reducing atmosphere refers to an atmosphere that causes a reaction in which oxygen is removed from a substance.

[0053] Additional Processes After the Heat Treatment Process After the above-described heat treatment process, the gaps between the oxide films of adjacent metal magnetic particles may be impregnated with a resin and cured in order to further increase the strength of the element body. The resin impregnated into the element body is typically an epoxy resin, but one or more resins selected from the group consisting of phenolic resin, polyester resin, polyimide resin, polyolefin resin, silicone resin, acrylic resin, polyvinyl butyral resin, cellulose resin, alkyd resin, etc. may also be used. Through the above process, the inductor element body of the present disclosure is formed.

[0054] External electrodes electrically connected to the coil conductors are then formed on the formed element body. The external electrodes are formed by electrolytic plating at the positions where the through-hole conductors are exposed on the mounting surface (first main surface 11) of the element body 10. The plating material may be Cu plating. Other examples include, but are not limited to, Ni-Sn, Ni-Au, Ni-Cu, and / or Cu-Ni-Au. After the external electrodes are formed, the inductor of this embodiment can be manufactured by cutting into individual elements.

[0055] As described above, according to the inductor manufacturing method described in this embodiment, by heating the metal magnetic particles in a low-oxygen atmosphere or a reducing atmosphere in the heat treatment step, it is possible to appropriately form an oxide film on the surface of the metal magnetic particles, and to obtain a composite metal magnetic body in which the metal magnetic particles have a Vickers hardness of 67 HV to 191 HV. Therefore, it is possible to improve the packing rate of the metal magnetic particles within the element body 10 and increase the magnetic permeability.

[0056] The following describes in detail the demonstration tests for the composite metal magnetic body of the present disclosure. Specifically, the inductors described in the following Examples 1 to 15 and Comparative Example were manufactured (see FIG. 5).

[0057] -Explanation of the inductor of Example 1- (1) A magnetic paste (Fe-50Ni-3Al) was prepared by kneading a metal magnetic powder containing Ni (50 wt%), Al (3 wt%), and Fe (bal) with a D50 of 5 μm, with ethyl cellulose as a binder and a mixture of terpineol and butyl diglycol acetate (BCA) as a solvent (preparation process). (2) As shown in Figure 2, the magnetic layers G1 to G8 were stacked, and then the magnetic layers were pressurized at approximately 300 MPa and degreased (pressurization process and degreasing process). (3) A heat treatment was performed at 750°C in a reducing atmosphere (nitrogen flow rate 19 L / min, hydrogen flow rate 0.19 L / min) in the furnace of the heat treatment device.

[0058] -Description of Inductors of Examples 2 to 15- For the inductor of Example 2, a magnetic paste (Fe-50Ni-5Al) containing Ni (50 wt%), Al (5 wt%), and Fe (bal) was used in the preparation process. For the inductor of Example 3, a magnetic paste (Fe-10Ni-5Al) containing Ni (10 wt%), Al (5 wt%), and Fe (bal) was used in the preparation process. For the inductor of Example 4, a magnetic paste (Fe-1Al) containing Al (1 wt%) and Fe (bal) was used in the preparation process. For the inductor of Example 5, a magnetic paste (Fe-3Al) containing Al (3 wt%) and Fe (bal) was used in the preparation process. For the inductor of Example 6, a magnetic paste (Fe-5Al) containing Al (5 wt%) and Fe (bal) was used in the preparation process. For the inductor of Example 7, a magnetic paste (Fe-50Ni-0.7Al) containing Ni (50 wt%), Al (0.7 wt%), and Fe (bal) was used in the preparation process. For the inductor of Example 8, a magnetic paste (Fe-52Ni-5Al) containing Ni (52 wt%), Al (5 wt%), and Fe (bal) was used in the preparation process. For the inductor of Example 9, a magnetic paste (Fe-52Ni-6Al) containing Ni (52 wt%), Al (6 wt%), and Fe (bal) was used in the preparation process. For the inductor of Example 10, a magnetic paste (Fe-10Ni-1Zr) containing Ni (10 wt%), Zr (1 wt%), and Fe (bal) was used in the preparation process. For the inductor of Example 11, a magnetic paste (Fe-10Ni-3Zr) containing Ni (10 wt%), Zr (3 wt%), and Fe (bal) was used in the preparation process. For the inductor of Example 12, a magnetic paste (Fe-10Ni-5Zr) containing Ni (10 wt%), Zr (5 wt%), and Fe (bal) was used in the preparation process. For the inductor of Example 13, a magnetic paste (Fe-10Ni-1Ti) containing Ni (10 wt%), Ti (1 wt%), and Fe (bal) was used in the preparation process. For the inductor of Example 14, a magnetic paste (Fe-10Ni-3Ti) containing Ni (10 wt%), Ti (3 wt%), and Fe (bal) was used in the preparation process.For the inductor of Example 15, a magnetic paste (Fe-10Ni-5Ti) containing Ni (10 wt%), Ti (5 wt%), and Fe (bal) was used in the preparation process. The other steps were the same as those in Example 1. In this specification, wt% refers to percentage by weight.

[0059] - Explanation of the inductor of the comparative example - (1) A magnetic paste (Fe-6.5Si) was produced by adding ethyl cellulose as a binder to a metal magnetic powder containing Si (6.5 wt%) and Fe (bal) with a D50 of 5 μm, and adding a mixture of terpineol and butyl diglycol acetate (BCA) as a solvent, and kneading it (preparation process). (2) As shown in Figure 2, the magnetic layers G1 to G8 were stacked, and then the magnetic layers were pressurized at about 300 MPa and degreased (pressurization process and degreasing process). (3) A heat treatment was performed at 700°C with the furnace of the heat treatment device in an air atmosphere.

[0060] - Vickers Hardness Evaluation - Vickers hardness evaluation was performed on the inductors of Examples 1 to 15 and the Comparative Example. The specific evaluation procedure was as described above in <Description of the Composite Metal Magnetic Body of the Present Disclosure>. The evaluation results are shown in Figures 5 and 6. Note that the Vickers hardness values ​​in the table of Figure 5 are the average values ​​when five measurements were taken.

[0061] 5 and 6, the Vickers hardness of the inductor of the comparative example was 210 HV or more on average, while the Vickers hardness of the inductors of Examples 1 to 15 was approximately 67 to 191 HV on average. Even when taking into account the measurement variations shown in Fig. 6, the Vickers hardness of the inductor of the comparative example was greater than 191 HV, while the Vickers hardness of the inductors of Examples 1 to 15 was 191 HV or less. Furthermore, the Vickers hardness of the inductors of Examples 1 to 15 was lower than the Vickers hardness of the metal magnetic powder before heat treatment.

[0062] According to the above results, a composite metal magnetic body with a Vickers hardness of 191 HV or less undergoes moderate plastic deformation, allowing for surface contact between the metal magnetic particles, improving the metal space factor and improving the magnetic permeability described below. Furthermore, if the Vickers hardness is less than 67 HV, the metal magnetic particles undergo excessive deformation, resulting in areas where the insulating coating is not formed and cracks in the metal magnetic particles. Therefore, it was confirmed that insulation deterioration and corrosion resistance decrease. In light of the above, it was appropriate to set the Vickers hardness range to 67 HV or more and 191 HV or less.

[0063] -Bulk Density Evaluation- Bulk density evaluation was performed on the inductors of Examples 1 to 3, 6, and the Comparative Example. In this specification, "bulk density" refers to the weight per volume of a molded body made of metal magnetic particles. The specific evaluation procedure is as follows: (1) Using a dimension measuring device: an image measure (Keyence Corporation, model number: IM-6700+6025) and a thickness measuring device: a micrometer (Mitutoyo Corporation, model number: SPM-25MJ), the length, width, and height of the molded body were measured at four locations. (2) The volume of the molded body was calculated using the average length, width, and height of the molded body. (3) Weighing device: an electronic balance (AS ONE Corporation, model number: IUX-200) was used to determine the weight of the molded body. (4) The bulk density was calculated from the volume and weight of the molded body. The evaluation results are shown in Figures 5 and 7.

[0064] 5 and 7, the inductors of Examples 1 to 3 and 6 have a higher bulk density than the inductor of the comparative example. This result indicates that the inductors of Examples 1 to 3 and 6 have a higher filling rate of metal magnetic particles than the inductor of the comparative example. This allows for an improvement in magnetic permeability, as described below.

[0065] - Complex Permeability Evaluation - Complex permeability was evaluated for the inductors of Examples 1 to 3, 6, and 7 and the Comparative Example. Specific evaluation procedures involved using an impedance analyzer (manufactured by Keysight Technologies, Inc., model number: E4990A) at measurement frequencies of 1 kHz to 100 MHz. The evaluation results are shown in Figure 5 and Figures 8 to 10.

[0066] First, referring to Figure 8, the evaluation results for the real part permeability μ' of the complex permeability are shown. At a frequency of 10 MHz, the real part permeability μ' of the inductors of Examples 1 to 3 and 6, excluding Example 7, was found to be higher than the real part permeability μ' of the inductor of the comparative example. Note that although the real part permeability μ' of the inductor of Example 7 is lower than the real part permeability μ' of the inductor of the comparative example, the tan δ corresponding to the core loss shown in Figure 9 was found to be higher for the inductor of Example 7 than for the inductor of the comparative example, at a frequency of 10 MHz.

[0067] According to Figure 8, the starting frequency at which the real permeability μ' begins to decrease is 10 MHz or higher. Here, the "starting frequency at which the real permeability μ' begins to decrease" as used herein refers to the frequency at which a decrease of 20% or more is observed from the value of the real permeability μ' at 1 MHz. Since the inductor of the present disclosure starts to decrease in the real permeability μ' at 10 MHz or higher, it can function properly as an inductor at a frequency of at least 10 MHz. For example, by being able to maintain the real permeability μ' up to a high frequency band, the usable frequency band can be expanded.

[0068] Next, referring to FIG. 9 , the evaluation results for tan δ, which corresponds to magnetic core loss, are shown. According to the evaluation results in FIG. 9 , the frequency at which tan δ is 0.05 or greater can be set to 10 MHz or greater for all of the Comparative Example and Examples 1 to 3, 6, and 7. This reduces power consumption and heat generation up to high frequency bands, thereby expanding the usable frequency band. Furthermore, at a frequency of 10 MHz, the results showed that the inductors of Examples 1 to 3, 6, and 7 have better tan δ than the Comparative Example. This means that at least at a frequency of 10 MHz, the inductors of Examples 1 to 3, 6, and 7 can function as inductors more appropriately than the Comparative Example.

[0069] Furthermore, Figure 10 shows a graph showing the relationship between the real permeability μ' and the Ni content. From this graph, it can be seen that the real permeability μ' increases as the Ni content increases. On the other hand, when the Ni content exceeds 52 wt%, the Fe content decreases, resulting in a deterioration in the DC bias characteristics. Therefore, it was found that it is preferable for the Ni content of the metal magnetic particles to be 52 wt% or less.

[0070] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. For example, the inductor 1A of the first embodiment described above is formed by laminating a plurality of coil conductors CD in the lamination direction, but is not limited to this. The inductor may include an element body having a magnetic body formed of a composite metal magnetic body and a coil wound around the outer periphery of the magnetic body, and an epoxy resin or silicone resin may be present between metal magnetic particles bonded via an oxide film. The magnetic body may be formed in a rod or drum shape.

[0071] The coil may be formed by winding a conductor. The conductor is preferably formed of a rectangular wire, which has the effect of enabling the wires to be wound densely without gaps between them and reducing DC resistance. Note that the conductor is not limited to this example, and for example, a round wire or the like may also be used.

[0072] The conductor is preferably made of a metal wire (e.g., copper wire) covered with an insulating material such as resin, which, together with the resin (e.g., epoxy resin) contained in the element, allows the coil to be firmly molded into the element.

[0073] Even in the above-described inductor configuration, the base body has a composite metal magnetic material in which the Vickers hardness of the metal magnetic particles is 67 HV or more and 191 HV or less, so that the filling rate of the metal magnetic particles within the base body can be improved, thereby increasing the magnetic permeability.

[0074] The composite metal magnetic body and inductor, as well as the method for manufacturing the composite metal magnetic body and the method for manufacturing the inductor, according to the present disclosure, are as follows: <1> A composite metal magnetic body in which a plurality of metal magnetic powders are bonded via an oxide film, the metal magnetic particles including a passivation element that is more easily oxidized than Cr and Fe, and an oxide film that coats the metal magnetic particles, the metal magnetic particles having a Vickers hardness of 67 HV or more and 191 HV or less. <2> The composite metal magnetic body according to <1>, in which the passivation element is at least one element selected from the group consisting of Al, Zr, and Ti. <3> The composite metal magnetic body according to <1> or <2>, in which the metal magnetic particles contain at least Fe and Al, or Fe, Ni, and Al. <4> The composite metal magnetic body according to any one of <1> to <3>, in which the metal magnetic particles have an average particle size of 1 μm or more and 10 μm or less. <5> An inductor comprising the composite metal magnetic body according to any one of <1> to <4>. <6> The inductor according to <5>, comprising an element body having a magnetic body formed from the composite metal magnetic body and a coil formed by laminating a coil conductor inside, wherein the coil conductor contains Ag or Cu, and an epoxy resin or silicone resin is present between the metal magnetic particles bonded via the oxide film. <7> The inductor according to <5>, comprising an element body having a magnetic body formed from the composite metal magnetic body and a coil wound around the outer periphery of the magnetic body, wherein an epoxy resin or silicone resin is present between the metal magnetic particles bonded via the oxide film. <8> The inductor according to any one of <5> to <7>, wherein the start frequency at which the real part of magnetic permeability μ' begins to decrease is 10 MHz or higher, and the frequency at which tan δ becomes 0.05 or higher is 10 MHz or higher. <9> A method for producing a composite metal magnetic body according to any one of <1> to <4>, comprising a heat treatment step of heating the metal magnetic particles in a low-oxygen atmosphere or a reducing atmosphere to form an oxide film on the surface of the metal magnetic particles.<10> A method for manufacturing an inductor according to any one of <5> to <8>, comprising a heat treatment step of heating the metal magnetic particles in a low-oxygen atmosphere or a reducing atmosphere to form an oxide film on the surface of the metal magnetic particles.

[0075] The composite metal magnetic body and inductor, as well as the manufacturing method thereof, of the present disclosure can be suitably used as electronic components having a Vickers hardness lower than conventional ones and an improved filling rate of metal magnetic particles.

[0076] 1A, 1B Inductor 10 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 C Coil CD Coil conductor CP Composite metal magnetic material DP Metal magnetic particles E External electrodes E1 to E4 First external electrode to fourth external electrode G1 to G8 Magnetic layer ML Magnetic layer MP Metal magnetic powder OL Oxide coating R Resin

Claims

1. A composite metal magnetic body in which multiple metal magnetic powders are bonded together via an oxide film, the metal magnetic powders having metal magnetic particles containing Fe and a passivation element that is more easily oxidized than Cr, and an oxide film that covers the metal magnetic particles, wherein the Vickers hardness of the metal magnetic particles is 67 HV or more and 191 HV or less.

2. The composite metal magnetic body according to claim 1, wherein said passivating element is at least one element selected from the group consisting of Al, Zr, and Ti.

3. A composite metal magnetic body according to claim 1 or 2, wherein the metal magnetic particles contain at least Fe and Al, or Fe, Ni and Al.

4. A composite metal magnetic body according to any one of claims 1 to 3, wherein the average particle size of the metal magnetic particles is 1 μm or more and 10 μm or less.

5. An inductor comprising the composite metal magnetic body according to any one of claims 1 to 4.

6. An inductor according to claim 5, comprising an element body having a magnetic body formed from the composite metal magnetic body and a coil formed by laminating a coil conductor inside, wherein the coil conductor contains Ag or Cu, and an epoxy resin or silicone resin is present between the metal magnetic particles bonded via the oxide film.

7. An inductor according to claim 5, comprising an element body having a magnetic body formed from the composite metal magnetic body and a coil wound around the outer periphery of the magnetic body, wherein epoxy resin or silicone resin is present between the metal magnetic particles bonded via the oxide film.

8. An inductor according to any one of claims 5 to 7, wherein the starting frequency at which real permeability μ' begins to decrease is 10 MHz or higher, and the frequency at which tan δ becomes 0.05 or higher is 10 MHz or higher.

9. A method for producing a composite metal magnetic body according to any one of claims 1 to 4, comprising a heat treatment step of heating the metal magnetic particles in a low-oxygen atmosphere or a reducing atmosphere to form an oxide film on the surface of the metal magnetic particles.

10. A method for manufacturing an inductor according to any one of claims 5 to 8, comprising a heat treatment step of heating the metal magnetic particles in a low-oxygen atmosphere or a reducing atmosphere to form an oxide film on the surface of the metal magnetic particles.

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