Magnetic substrate, coil component including magnetic substrate, and method for manufacturing magnetic substrate

Abstract

To suppress core loss in a magnetic substrate.SOLUTION: A coil component according to an aspect of the present invention includes a plurality of metal magnetic particles containing Fe and an element M (the element M is at least one element selected from the group consisting of Si, Cr, and Al) which is more easily oxidized than Fe, and an oxide coating provided on the surface of each of the plurality of metal magnetic particles. The plurality of metal magnetic particles includes a plurality of first metal magnetic particles. Each of the plurality of first metal magnetic particles contains a precipitate containing the element M.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The disclosure in this specification mainly relates to a magnetic substrate, a coil component including the magnetic substrate, and a method for manufacturing the magnetic substrate. [Background technology]

[0002] A magnetic substrate containing a large number of metallic magnetic particles made of a magnetic metal material is used as a magnetic substrate for coil components. The surface of each of the metallic magnetic particles contained in the magnetic substrate is covered with an insulating film, and adjacent metallic magnetic particles are bonded to each other via the insulating film.

[0003] The metal magnetic particles are composed of, for example, a soft magnetic material mainly composed of Fe. The soft magnetic material for producing the Fe-based metal magnetic particles contains additive elements such as Si, Cr, and Al in addition to Fe in order to improve the magnetic properties and insulating properties.

[0004] The magnetic substrate is produced, for example, by mixing a metal magnetic powder (raw material powder) made of a soft magnetic material with a resin to produce a mixed resin composition, and then heating this mixed resin composition. During the heat treatment, the additive elements (e.g., Si, Cr, Al) contained in the raw material powder particles are oxidized on the surface of each raw material powder particle. As a result, an oxide film containing oxides of the elements contained in the raw material powder is formed on the surface of the metal magnetic particles. This oxide film electrically insulates adjacent metal magnetic particles.

[0005] Magnetic substrates containing Fe-based metal magnetic particles are described in the following Patent Documents 1 to 3. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2013-046055 A [Patent Document 2] International Publication No. 2018 / 180659 [Patent Document 3] JP 2012-238842 A Summary of the Invention [Problem to be solved by the invention]

[0007] It is desirable to suppress iron loss in a magnetic substrate, and particularly when the magnetic substrate is used for a coil component incorporated in a high-frequency circuit, it is desirable to suppress iron loss.

[0008] It is an object of the invention disclosed herein to solve or mitigate at least some of the problems mentioned above. One more specific object of the invention is to suppress iron loss in a magnetic substrate. One more specific object of the invention is to suppress eddy current loss in a magnetic substrate.

[0009] The object of the present invention other than the above will become clear throughout the entire description of the specification. The invention described in the claims may solve problems other than those grasped from the "Problem to be solved by the invention." [Means for solving the problem]

[0010] The magnetic substrate according to one embodiment of the present invention comprises a plurality of metal magnetic particles containing Fe and an element M which is more easily oxidized than Fe (wherein the element M is at least one element selected from the group consisting of Si, Cr, and Al), and an oxide coating provided on the surface of each of the plurality of metal magnetic particles. The plurality of metal magnetic particles include a plurality of first metal magnetic particles. Each of the plurality of first metal magnetic particles contains a precipitate containing the element M. Effect of the Invention

[0011] According to the embodiments of the invention disclosed herein, it is possible to provide metallic magnetic particles that suppress eddy current losses in a magnetic substrate. [Brief description of the drawings]

[0012] [Figure 1]FIG. 1 is a perspective view illustrating a coil component including a magnetic composite according to an embodiment. [Diagram 2] FIG. 2 is an exploded perspective view of the coil component of FIG. [Diagram 3] 2 is a cross-sectional view that illustrates a cross section of the coil device of FIG. 1 taken along line II. [Figure 4] 2 is an enlarged cross-sectional view showing a schematic enlargement of a region A in the cross section of the base body. FIG. [Diagram 5] FIG. 2 is a cross-sectional view that typically shows a cross section of a first metal magnetic particle that contains a precipitate. [Figure 6] FIG. 3 is a cross-sectional view that typically shows a cross section of a second metal magnetic particle. [Figure 7] FIG. 4 is a flow chart showing a manufacturing process of the coil component according to the embodiment of the present invention. [Figure 8] FIG. 13 is a front view showing a coil component according to another embodiment. [Figure 9] FIG. 6 is a flow diagram showing a manufacturing process of a coil component according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Various embodiments of the present invention will be described below with reference to the drawings as appropriate. Components common to multiple drawings are given the same reference numerals. Please note that the drawings are not necessarily drawn to scale for the sake of convenience. The embodiments of the present invention described below do not necessarily limit the invention according to the claims. Elements described in the following embodiments are not necessarily essential to the solution of the invention.

[0014] One embodiment of the invention disclosed in this specification relates to a magnetic substrate. The magnetic substrate is used, for example, in a coil component. The magnetic substrate includes a plurality of metal magnetic particles. The metal magnetic particles are mainly composed of Fe. The metal magnetic particles contain element M in addition to Fe. The element M is at least one element selected from the group consisting of Si, Cr, and Al. Each of the plurality of metal magnetic particles is covered with an oxide film having excellent insulating properties. Adjacent ones of the plurality of metal magnetic particles are bonded to each other via the oxide film.

[0015] In the following, first, a coil component 1 including a magnetic base according to one embodiment will be described with reference to FIGS. 1 to 3, and then the microstructure of the magnetic base will be described with reference to FIGS.

[0016] Fig. 1 is a perspective view that shows a schematic diagram of the coil component 1, and Fig. 2 is an exploded perspective view of the coil component 1. Fig. 3 is a schematic cross-sectional view of the coil component 1, in which the coil component 1 is cut along line II in Fig. 1. For ease of explanation, external electrodes are omitted from Fig. 2.

[0017] 1 to 3 show a laminated inductor as an example of a coil component 1. The illustrated laminated inductor is one example of a coil component 1 to which the present invention can be applied, and the present invention can be applied to various types of coil components other than laminated inductors. For example, the coil component 1 can also be applied to a wire-wound coil component or a planar coil.

[0018] As shown in the figure, the coil component 1 includes a base 10, a coil conductor 25 provided inside the base 10, an external electrode 21 provided on the surface of the base 10, and an external electrode 22 provided on the surface of the base 10 at a position spaced apart from the external electrode 21. The base 10 is a magnetic base made of a magnetic material. The base 10 is an example of a "magnetic base" described in the claims. In this specification, the base 10 may also be referred to as a magnetic base 10. As described below, the base 10 includes a large number of metal magnetic particles.

[0019] The external electrode 21 is electrically connected to one end of the coil conductor 25 , and the external electrode 22 is electrically connected to the other end of the coil conductor 25 .

[0020] The coil component 1 can be mounted on a mounting board 2a. In the illustrated embodiment, the mounting board 2a is provided with land portions 3a and 3b. The coil component 1 is mounted on the mounting board 2a by joining an external electrode 21 to the land portion 3a and connecting an external electrode 22 to the land portion 3b. A circuit board 2 according to an embodiment of the present invention includes the coil component 1 and a mounting board 2a on which the coil component 1 is mounted. The circuit board 2 can be mounted on various electronic devices. Electronic devices on which the circuit board 2 can be mounted include smartphones, tablets, game consoles, automotive electrical equipment, servers, and various other electronic devices.

[0021] The coil component 1 may be an inductor, a transformer, a filter, a reactor, an inductor array, or any other of various coil components. The coil component 1 may be a coupled inductor, a choke coil, or any other of various magnetically coupled coil components. Applications of the coil component 1 are not limited to those explicitly described in this specification.

[0022] In one embodiment, the base 10 is configured such that the dimension in the L-axis direction (length dimension) is greater than the dimension in the W-axis direction (width dimension) and the dimension in the T-axis direction (height dimension). For example, the length dimension is in the range of 1.0 mm to 6.0 mm, the width dimension is in the range of 0.5 mm to 4.5 mm, and the height dimension is in the range of 0.5 mm to 4.5 mm. The dimensions of the base 10 are not limited to the dimensions specifically described in this specification. In this specification, the term "rectangular parallelepiped" or "rectangular parallelepiped shape" does not mean only "rectangular parallelepiped" in the mathematically strict sense. The dimensions and shape of the base 10 are not limited to those explicitly described in this specification.

[0023] The base 10 has a first main surface 10a, a second main surface 10b, a first end surface 10c, a second end surface 10d, a first side surface 10e, and a second side surface 10f. The outer surface of the base 10 is defined by these six surfaces. The first main surface 10a and the second main surface 10b form the surfaces at both ends of the base 10 in the height direction, the first end surface 10c and the second end surface 10d form the surfaces at both ends of the base 10 in the length direction, and the first side surface 10e and the second side surface 10f form the surfaces at both ends of the base 10 in the width direction. As shown in FIG. 1, the first main surface 10a is located on the upper side of the base 10, so the first main surface 10a may be referred to as the "upper surface". Similarly, the second main surface 10b may be referred to as the "lower surface" or "bottom surface". The coil component 1 is disposed so that the second main surface 10b faces the mounting board 2a, and therefore the second main surface 10b is sometimes called the "mounting surface." The upper surface 10a and the lower surface 10b are spaced apart by the height dimension of the base 10, the first end surface 10c and the second end surface 10d are spaced apart by the length dimension of the base 10, and the first side surface 10e and the second side surface 10f are spaced apart by the width dimension of the base 10.

[0024] 2, the substrate 10 has a magnetic film 20, a lower cover layer 19 provided on the lower surface of the magnetic film 20, and an upper cover layer 18 provided on the upper surface of the magnetic film 20. The upper cover layer 18, the lower cover layer 19, and the magnetic film 20 are components of the substrate 10.

[0025] The magnetic film 20 includes magnetic films 11 to 17. In the magnetic film 20, the magnetic film 17, the magnetic film 16, the magnetic film 15, the magnetic film 14, the magnetic film 13, the magnetic film 12, and the magnetic film 11 are laminated in this order from the negative side to the positive side in the T-axis direction.

[0026] Conductive patterns C11 to C17 are formed on the upper surfaces of the magnetic films 11 to 17, respectively. Each of the conductive patterns C11 to C17 extends around the coil axis Ax1 (see FIG. 3) in a plane (LW plane) perpendicular to the coil axis Ax1. The conductive patterns C11 to C17 are formed, for example, by printing a conductive paste made of a metal or alloy with excellent conductivity by a screen printing method. The conductive paste may be made of Ag, Pd, Cu, Al, or an alloy thereof. The conductive paste is produced by kneading a conductive powder made of a conductive material with excellent conductivity, such as Ag, Pd, Cu, Al, or an alloy thereof, with a binder resin and a solvent. When Cu powder is used as the conductive powder, a thermally decomposable resin such as an acrylic resin may be used as the binder resin in order to suppress excessive oxidation of the Cu powder during degreasing. The thermally decomposable resin is decomposed without a combustion reaction with oxygen. The thermally decomposable resin is thermally decomposed when heated in a non-oxygen atmosphere (for example, a nitrogen atmosphere), and no residue is left behind. Therefore, by using a thermally decomposable resin as a binder resin, the degreasing treatment can be performed in a non-oxygen atmosphere. As the acrylic resin for the conductive paste, for example, a (meth)acrylic acid copolymer, a (meth)acrylic acid-(meth)acrylic acid ester copolymer, a styrene-(meth)acrylic acid copolymer, or a styrene-(meth)acrylic acid-(meth)acrylic acid ester copolymer can be used. As the solvent, toluene, ethanol, terpineol, or a mixture thereof can be used. The conductive paste can contain an adjusting agent for adjusting the thixotropy. The conductive patterns C11 to C17 may be formed by other materials and methods. The conductive patterns C11 to C17 may be formed by, for example, a sputtering method, an inkjet method, or other known methods.

[0027] Vias V1 to V6 are formed at predetermined positions of the magnetic films 11 to 16, respectively. The vias V1 to V6 are formed by forming through holes penetrating the magnetic films 11 to 16 in the T-axis direction at predetermined positions of the magnetic films 11 to 16, and filling the through holes with a conductive material.

[0028] Each of the conductor patterns C11 to C17 is electrically connected to the adjacent conductor patterns through the vias V1 to V6. The conductor patterns C11 to C17 and the vias V1 to V6 connected in this way form a spiral coil conductor 25. That is, the coil conductor 25 has the conductor patterns C11 to C17 and the vias V1 to V6.

[0029] The end of the conductor pattern C11 opposite to the end connected to the via V1 is connected to an external electrode 22. The end of the conductor pattern C17 opposite to the end connected to the via V6 is connected to an external electrode 21.

[0030] The upper cover layer 18 includes magnetic films 18a-18d made of a magnetic material, and the lower cover layer 19 includes magnetic films 19a-19d made of a magnetic material. In this specification, the magnetic films 18a-18d and the magnetic films 19a-19d may be collectively referred to as the "cover layer magnetic film."

[0031] As shown in Figure 3, the coil conductor 25 has a winding portion 25a wound around a coil axis Ax1 extending along the thickness direction (T-axis direction), a pull-out portion 25b1 extending from one end of the winding portion 25a to the first end face 10c of the base 10, and a pull-out portion 25b2 extending from the other end of the winding portion 25a to the second end face 10d of the base 10.

[0032] Next, the microstructure of the base 10 will be described with reference to Fig. 4. Fig. 4 is an enlarged cross-sectional view that shows a schematic view of region A shown in Fig. 3. Region A is a part of a cross section of the base 10 cut along the T axis. Region A can be any region that occupies a part of a cross section of the base 10 cut along the T axis.

[0033] As shown in Fig. 4, the substrate 10 includes a plurality of metal magnetic particles. The metal magnetic particles included in the substrate 10 include first metal magnetic particles 31 and second metal magnetic particles 32. The first metal magnetic particles 31 and the second metal magnetic particles 32 are distinguished from each other in that the first metal magnetic particles 31 include element M precipitates that include the element M, whereas the second metal magnetic particles 32 do not include element M precipitates. The element M is at least one element selected from the group consisting of Si, Cr, and Al. Details of the element M precipitates that include the element M will be described later.

[0034] In one embodiment, the ratio of the number of the first metal magnetic particles 31 to the total number of the metal magnetic particles contained in the base 10 (the sum of the number of the first metal magnetic particles 31 and the number of the second metal magnetic particles 32) (hereinafter, sometimes simply referred to as "precipitate occurrence ratio") is, for example, 1% or more and 10% or less. In other words, 1% to 10% of the metal magnetic particles contained in the base 10 may contain element M precipitates. In one embodiment, the precipitate occurrence ratio may be 1% or more and 10% or less, 1% or more and 9% or less, 1% or more and 8% or less, 1% or more and 7% or less, 1% or more and 6% or less, 1% or more and 5% or less, 1% or more and 4% or less, or 1% or more and 3% or less. The lower limit of the precipitate occurrence ratio may be 2%. The ratio of the number of the first metal magnetic particles 31 to the total number of the metal magnetic particles contained in the base 10 (precipitate occurrence ratio) is determined as follows. First, the substrate 10 is cut along its thickness direction (T-axis direction) to expose a cross section, and the cross section is photographed with a scanning electron microscope (SEM) at a predetermined magnification (for example, a magnification ranging from 5000 times to 30000 times) to obtain an SEM image with a part of the cross section of the substrate 10 as an observation field. Next, the metal magnetic particles contained in the SEM image obtained by this photographing are classified into the first metal magnetic particles 31 and the second metal magnetic particles 32 depending on whether or not they contain element M precipitates. When element mapping shows that there is a region in which the element M is aggregated inside the metal magnetic particle, it can be determined that the metal magnetic particle contains an element M precipitate portion. As one method of determination, in an SEM image obtained by photographing the cross section of the substrate 10, the region in which the element M is aggregated (element M precipitate) can be distinguished from the region other than the region in which the element M is aggregated by contrast. More specifically, in the SEM image of the cross section of the substrate 10, the element M precipitate formed by aggregation of the element M appears darker than other regions. Furthermore, the concentration of element M in a region where element M is aggregated (element M precipitate) is higher than in other regions. Therefore, when the concentration of element M in a region that appears dark in the SEM image is higher than the concentration of element M around that region, the region that appears dark in the SEM image can be determined to be an element M precipitate. Furthermore, when the element M precipitate is a nitride, element N is detected. Furthermore, when the element M precipitate is an oxide, element O is detected.The number of first metal magnetic particles 31 included in the observation field divided by the total number of metal magnetic particles can be regarded as the ratio of the number of first metal magnetic particles 31 to the total number of metal magnetic particles included in base 10 (precipitate occurrence ratio). A plurality of observation fields are set on the cross section of base 10, and the ratio of the number of first metal magnetic particles 31 to the total number of metal magnetic particles included in each observation field is determined, and the average value of the ratios determined for each observation field may be regarded as the precipitate occurrence ratio. The number of observation fields can be set arbitrarily between 5 and 10, for example.

[0035] The surface of the first metal magnetic particle 31 is covered with an oxide film 41 having excellent insulating properties. Similarly, the surface of the second metal magnetic particle 32 is covered with an oxide film 42 having excellent insulating properties. The oxide film 41 desirably covers the entire surface of the first metal magnetic particle 31, and the oxide film 42 desirably covers the entire surface of the second metal magnetic particle 32. In the base 10, each metal magnetic particle is bonded to an adjacent metal magnetic particle via an oxide film provided on each surface. That is, the oxide films provided on the surfaces of adjacent metal magnetic particles are bonded to each other, and the metal magnetic particles covered with the oxide film are bonded to each other by the bond between the oxide films. For example, the first metal magnetic particle 31 is bonded to the second metal magnetic particle 32 adjacent to the first metal magnetic particle 31 via the oxide film 41 provided on the surface of the first metal magnetic particle 31 and the oxide film 42 provided on the surface of the second metal magnetic particle 32. The oxide films 41 and 42 provide electrical insulation between the first metal magnetic particles 31 , between the second metal magnetic particles 32 , or between the first metal magnetic particles 31 and the second metal magnetic particles 32 .

[0036] The metal magnetic particles contained in the base 10 are obtained by heating the raw material metal magnetic powder (raw material powder). As described in detail below, the base 10 can be produced by mixing the metal magnetic powder with a resin to produce a mixed resin composition, and then heating this mixed resin composition. By the heat treatment in the manufacturing process of this base 10, metal magnetic particles having an oxide film on the surface are obtained from the metal magnetic powder.

[0037] In this specification, the "metal magnetic particles contained in the base 10" includes both the first metal magnetic particles 31 and the second metal magnetic particles 32. In other words, the explanation of the "metal magnetic particles contained in the base 10" applies to both the first metal magnetic particles 31 and the second metal magnetic particles 32, unless otherwise required by the context.

[0038] The raw material powder of the metal magnetic particles contained in the base 10 is mainly composed of Fe. The raw material powder of the metal magnetic particles contained in the base 10 contains element M in addition to Fe. Element M is an element that is more easily oxidized than Fe. For example, element M is at least one selected from the group consisting of Si, Cr, and Al. That is, the raw material powder of the metal magnetic particles contained in the base 10 can contain one or more elements of Si, Cr, and Al in addition to Fe. In the metal magnetic particles obtained by heating this raw material powder, the ratio of Fe to the total of Fe and element M can be 95 at % or more. The raw material powder of the metal magnetic particles contained in the base 10 can contain trace amounts of elements other than Fe and element M. Elements that can be contained in trace amounts in the raw material powder of the metal magnetic particles include zinc (Zr), boron (B), carbon (C), and nickel (Ni).

[0039] The oxide film provided on the surface of the metal magnetic particles contained in the base 10 contains an oxide of an element contained in the raw material powder. The "oxide film provided on the surface of the metal magnetic particles contained in the base 10" includes the oxide film 41 provided on the surface of the first metal magnetic particles 31 and the oxide film 42 provided on the surface of the second metal magnetic particles 32. For ease of explanation, the oxide film provided on the surface of the metal magnetic particles contained in the base 10 may be simply referred to as the "oxide film". Since the element M is more easily oxidized than Fe, when the raw material powder contains Fe and the element M, the oxide film contains an oxide of the element M. The oxide film may also contain an oxide of Fe.

[0040] The average particle size of the metal magnetic particles contained in the base 10 can be, for example, in the range of 1 μm to 50 μm. The average particle size of the metal magnetic particles contained in the base 10 is determined based on a volume-based particle size distribution obtained by cutting the base 10 along its thickness direction (T-axis direction) to expose a cross section and taking an SEM image of the cross section with a scanning electron microscope (SEM). For example, the average particle size (median diameter (D50)) calculated from the volume-based particle size distribution obtained based on the SEM image can be used as the average particle size of the metal magnetic particles contained in the base 10.

[0041] Next, the first metal magnetic particle 31 will be further described with reference to FIG. 5. FIG. 5 shows a schematic cross section of one of the plurality of first metal magnetic particles 31 contained in the base 10. In FIG. 5, the cross section of the first metal magnetic particle 31 is drawn as a circle for convenience. As shown in FIG. 4, the first metal magnetic particle 31 contained in the base 10 can have various shapes other than a circle. FIG. 5 also shows an oxide film 41 provided on the surface of the first metal magnetic particle 31.

[0042] As shown in Fig. 5, the first metal magnetic particle 31 is divided into a central region 31a and a surface region 31b. The central region 31a includes a geometric center C1 of the cross section of the first metal magnetic particle 31 shown in Fig. 5. The surface region 31b is located radially outward from the central region 31a. The surface region 31b covers the outer peripheral surface of the central region 31a. Thus, the surface region 31b extends along the surface of the first metal magnetic particle 31 radially outward from the central region 31a.

[0043] In the radial direction of the first metal magnetic particle 31, the surface region 31b has a width d12. In one embodiment, the width d12 of the surface region 31b is 10% of the Heywood diameter of the first metal magnetic particle 31. The width d12 of the surface region 31b may be 10% or less of the Heywood diameter of the first metal magnetic particle 31. The radial dimension d11 of the central region 31a corresponds to the difference between the dimension between the geometric center C1 of the first metal magnetic particle 31 and its surface, and the width d12 of the surface region 31b.

[0044] The metal magnetic particle included in the substrate 10 may have a plurality of metal crystal grains in the grain. The first metal magnetic particle 31 may have a plurality of crystal grains. As shown in FIG. 5, when the first metal magnetic particle 31 has a plurality of crystal grains CP1 to CP3, a crystal grain boundary region 31c is defined along the boundary between the crystal grains CP1 to CP3 in the first metal magnetic particle 31. The width d13 of the crystal grain boundary region 31c is the same as the width d12 of the surface region 31b. In each of the crystal grains CP1 to CP3, the region inside the crystal grain boundary region 31c and surrounded by the crystal grain boundary region 31c is called a crystal grain inner region 31d. The crystal grain inner region 31d is included in the central region 31a. The crystal grain inner region 31d does not overlap with the surface region 31b and the crystal grain boundary region 31c.

[0045] The first metal magnetic particle 31 may contain 95 at% or more of Fe in the crystal grain inner region 31d. In this case, the content ratio of Fe in the crystal grain inner region 31d may be 97 at% or more, 98 at% or more, or 99 at% or more. In a plurality of metal magnetic particles contained in a known magnetic base, the content ratio of Fe is at most about 92 at% and a content ratio of Fe exceeding 95 at% has not been realized. The content ratio of Fe in the crystal grain inner region 31d of the first metal magnetic particle 31 is higher than the content ratio of about 92 at% that has been realized so far. When the first metal magnetic particle 31 is generated from the raw material powder, an oxide film is formed on the surface of the raw material powder, and this oxide film prevents oxygen from penetrating into the raw material powder. However, when the content ratio of Fe in the raw material powder becomes high, for example, to about 95 at% or more, the content ratio of the additive element decreases, so that it becomes difficult to form an oxide film having a sufficient thickness to prevent oxygen from penetrating on the surface of the raw material powder. As a result, oxygen penetrates into some of the raw material powders (e.g., 1% to 10% of the total number of raw material powders) where an oxide film with a sufficient thickness is not formed. The oxygen that penetrates into the raw material powder in this way combines with element M present in surface region 31b to become element M precipitates 50. The element M precipitates 50 formed in this way contain elements M and O. In this way, the element M present in surface region 31b captures the oxygen that has penetrated into the raw material powder, thereby preventing the oxygen from reaching central region 31a and oxidizing Fe in crystal grain inner region 31d in central region 31a.

[0046] The content ratio of Fe contained in the first metal magnetic particles 31 is measured by exposing a cross section of the substrate 10 by cutting the substrate 10 along the coil axis Ax and performing energy dispersive X-ray spectroscopy (EDS) analysis on the cross section. The content ratio of Fe can be measured by a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDS) detector. EDS analysis using an SEM equipped with an EDS detector is called SEM-EDS analysis. The content ratio of Fe is measured, for example, using a scanning electron microscope SU7000 manufactured by Hitachi High-Tech Corporation and an energy dispersive X-ray spectroscopy detector Octane Elite manufactured by Ametech Co., Ltd. at an acceleration voltage of 5 kV. The content ratios of elements other than Fe contained in the first metal magnetic particles 31 are also measured by SEM-EDS analysis in the same manner as the content ratio of Fe.

[0047] The first metal magnetic particle 31 may contain element M in addition to Fe in the central region 31a. The content ratio of element M in the central region 31a may be 0.01 at% or more and 1.0 at% or less. The element M may not be contained in the crystal grain inner region 31d in the central region 31a of the first metal magnetic particle 31. The content ratio of element M in the crystal grain inner region 31d is measured by SEM-EDS analysis as described above. When element M is not detected in the crystal grain inner region 31d by SEM-EDS analysis, it is determined that element M is not contained in the central region 31a, although element M may actually be contained below the detection limit of SEM-EDS analysis. In the SEM-EDS analysis of the first metal magnetic particle 31, an integrated measurement is performed so that the acquisition count of the L-line peak of the Fe element is 100,000 counts or more, and it can be determined that the quantified element is present when the peak intensity of the quantified element exceeds a position where the standard deviation σ of the background level is three times, i.e., 3σ. Specifically, since the standard deviation σ of the background level is the square root of the background level, it can be determined that the quantified element is present at a position where the count value of the quantified element is three times or more than the square root of the background level. In other words, the count value three times the square root of the background level is set as the detection limit. Whether or not the element M is present in the crystal grain inner region 31d can be determined by performing an EDS analysis on the SEM image of the cross section of the first metal magnetic particle 31 to obtain mapping data of the element M, and if there is a position in the crystal grain inner region 31d that shows a peak intensity of the element M equal to or greater than the detection limit in this mapping data, it can be determined that the element M is present at that position. Conversely, if the peak intensity of the element M is less than the detection limit in all regions of the crystal grain inner region 31d, it is determined that the element M is not contained in the central region 31a. It can be determined that the element M is present at a position that shows a detection value three times or more than the square root of the detection value of the element M in the background.

[0048] The central region 31a may contain Cr at an atomic ratio less than that of Si. The central region 31a may contain Al at a ratio less than that of Si. The central region 31a may contain Cr and Al. In this case, the content ratio of Cr and the content ratio of Al are both less than the content ratio of Si. The central region 31a may not contain Cr. The central region 31a may not contain Al. The central region 31a may not contain any element M. When Cr is not detected in the central region 31a by SEM-EDS analysis, it can be determined that Cr is not contained in the central region 31a. Similarly, when Al is not detected in the central region 31a by SEM-EDS analysis, it can be determined that Al is not contained in the central region 31a. In this specification, when the amount of the content ratio of an element is described, the content ratio of the element is expressed as the molar ratio (atomic percentage) of the element, unless otherwise specified.

[0049] The surface region 31b and the grain boundary region 31c contain the element M at a higher atomic ratio than the central region 31a. The element M is precipitated as element M precipitates 50 in the surface region 31b and the grain boundary region 31c. In element mapping obtained by SEM-EDS analysis, it can be determined that the element M precipitate portion 50 exists in a region where the element M aggregates in the surface region 31b or the grain boundary region 31c. The element M precipitates 50 may contain an oxide of the element M. Specifically, the element M and oxygen combine to generate MO, and the generated MO gather and precipitate as the element M precipitates 50. When the element M precipitates 50 contain an oxide of the element M, the elements M and O are detected at the same detection position in the surface region 31b or the grain boundary region 31c in the element mapping obtained by SEM-EDS analysis. The element M precipitates 50 may contain a nitride of the element M. Specifically, element M and nitrogen combine to generate MN, and the generated MN gather together and precipitate as element M precipitate 50. When element M precipitate 50 contains a nitride of element M, element M and N are detected at the same detection position in surface region 31b or grain boundary region 31c in element mapping obtained by SEM-EDS analysis. Element M precipitate 50 may contain both an oxide of element M and a nitride of element M.

[0050] As described above, the element M precipitates 50 are contained in the surface region 31b of the first metal magnetic particle 31. The surface region 31b may contain a plurality of element M precipitates 50. The surface region 31b may contain several to several hundred element M precipitates 50. The plurality of element M precipitates 50 are spaced apart from each other. That is, the element M precipitates 50 are not precipitated in a continuous layer shape in the surface region 31b, but in the form of particles spaced apart from each other. The element M present in the surface region 31b combines with oxygen and / or nitrogen that has penetrated into the first metal magnetic particle 31 and precipitates as the element M precipitates 50, so that the content of element M is reduced in the region other than the element M precipitates 50 in the surface region 31b. For this reason, during the manufacture of the magnetic substrate 10, a concentration gradient of element M is generated between the central region 31a and the surface region 31b, and this concentration gradient makes it easier for the element M to move from the central region 31a to the surface region 31b. As a result, the content of element M in the central region 31a also decreases. As a result of the decrease in element M in the central region 31a, the content ratio of Fe in the central region 31a increases.

[0051] As described above, in the first metal magnetic particle 31 including a plurality of crystal grains, element M precipitates are precipitated not only in the surface region 31b but also in the crystal grain boundary region 31c. Since oxygen and / or nitrogen easily penetrate into the crystal grain boundaries of the first metal magnetic particle 31, element M contained in the crystal grain boundary region 31c near the crystal grain boundaries is bonded with oxygen or nitrogen, and element M precipitates 50 are precipitated in the crystal grain boundary region 31c. The crystal grain boundary region 31c may contain several to several hundred element M precipitates 50. Since the penetration distance of oxygen is larger in the crystal grain boundary region 31c than in the surface region 31b, the element M precipitates 50 contained in the crystal grain boundary region 31c are smaller than the element M precipitates 50 contained in the surface region 31b. The element M precipitates 50 contained in the crystal grain boundary region 31c are also spaced apart from each other. That is, the element M precipitates 50 are not in a continuous layer shape but are separated from each other in the grain boundary region 31c. The element M that existed in the surface region 31b before bonding with oxygen and / or nitrogen is bonded with oxygen or nitrogen that has entered the grain boundary region 31c and precipitates as the element M precipitates 50, so that the content of the element M is reduced in the region other than the element M precipitates 50 in the grain boundary region 31c. Therefore, during the manufacture of the magnetic base 10, a concentration gradient of the element M is generated between the grain inner region 31d of the crystal grains CP1 to CP3 and the grain boundary region 31c, and this concentration gradient makes it easier for the element M to move from the grain inner region 31d of the crystal grains CP1 to CP3 to the grain boundary region 31c. As a result, the content of the element M in the grain inner region 31d of the crystal grains CP1 to CP3 is reduced. As a result of the reduction in the element M in the grain inner region 31d, the content ratio of Fe in the grain inner region 31d is improved.

[0052] The first metal magnetic particles 31 and the second metal magnetic particles 32 may each have a flat shape. The aspect ratio of the first metal magnetic particles 31 may be 1.2 or more. The aspect ratio of the first metal magnetic particles 31 and the second metal magnetic particles 32 can be increased by applying a large compressive stress to a slurry containing raw material powder of the first metal magnetic particles 31 and the second metal magnetic particles 32 during the manufacture of the magnetic base 10. The first metal magnetic particles 31 may be formed by heating raw material powder that has been significantly deformed by compressive stress to have an aspect ratio of 1.2 or more. The aspect ratio of each metal magnetic particle is expressed as the ratio of the length of the longest axis of each particle to the length of the shortest axis.

[0053] In the manufacturing process of the magnetic base 10, the raw powder of the first metal magnetic particles 31 having an aspect ratio of 1.2 or more has a larger distortion than the raw powder of the first metal magnetic particles 31 having an aspect ratio of less than 1.2. Therefore, nitrogen and oxygen in the heating atmosphere easily penetrate into the raw powder of the first metal magnetic particles 31 having an aspect ratio of 1.2 or more, so that the element M contained in the first metal magnetic particles 31 having an aspect ratio of 1.2 or more is easily precipitated as a nitride or oxide. Therefore, the element M precipitate 50 contained in the first metal magnetic particles 31 having an aspect ratio of 1.2 or more has a high content of nitride or oxide of element M. Since the nitride or oxide of element M has a lower magnetic permeability than Fe, it functions as a magnetic gap in the magnetic base, so that the DC superposition characteristics of the coil component 1 including the magnetic base 10 can be improved by increasing the aspect ratio of the first metal magnetic particles 31 (for example, 1.2 or more). In addition, the first metal magnetic particle 31 having an aspect ratio of 1.2 or more is more likely to generate element M precipitates 50 in the central region 31a than the first metal magnetic particle 31 having an aspect ratio of less than 1.2. In addition, the first metal magnetic particle 31 having an aspect ratio of 1.2 or more can increase the ratio of element M precipitates 50 in the central region 31a compared to the surface region 31b. In other words, when observing the cross section of the first metal magnetic particle 31 in a cross section obtained by cutting the substrate 10, the area of ​​the element M precipitates 50 included in the central region 31a can be made larger than the area of ​​the element M precipitates 50 included in the surface region 31b (here, this means a region having a width of 10% of the Heywood diameter of the first metal magnetic particle 31 from the surface of the first metal magnetic particle 31). This can reduce the eddy current loss of the magnetic substrate 10.

[0054] On the other hand, when the aspect ratio of the first metal magnetic particles 31 is less than 1.2, the raw material powder of the first metal magnetic particles 31 does not undergo large distortion during the manufacturing process, so that nitrogen and oxygen are less likely to penetrate into the raw material powder. Therefore, the content ratio of element M that is not nitrided or oxidized is high in the element M precipitate 50 contained in the first metal magnetic particles 31 with an aspect ratio of less than 1.2. Since the nitride and oxide of element M are non-magnetic materials, if the content ratio of nitride and oxide of element M in the element M precipitate 50 is high, it causes a decrease in the magnetic permeability of the magnetic base 10. By making the aspect ratio of the first metal magnetic particles 31 less than 1.2, there are parts with a high content ratio of Cr and Al as unoxidized metals in the element M precipitate 50, and this makes it possible to suppress the decrease in the magnetic permeability of the magnetic base 10 due to the element M precipitate 50. In addition, the element M precipitate 50 can include an oxide of element M, a nitride of element M, or a condensate in which element M condenses without combining with oxygen or nitrogen (metal if element M is a metal element), or a mixture thereof.

[0055] The element M contained in the raw material powder has a property of easily diffusing to the surface of the raw material powder when the raw material powder is heated in the manufacturing process of the magnetic base 10. For example, the element M is Si, Al, or Cr. Since Si is easily oxidized and easily precipitates as silica (SiO2) with excellent insulating properties when oxidized, the insulating properties of the oxide film 41 can be improved by increasing the content ratio of Si contained in the raw material powder as the element M. Furthermore, by increasing the content ratio of Si contained in the raw material powder as the element M, oxygen that has entered the raw material powder is easily trapped by Si that has thermally diffused to the vicinity of the powder surface (the region corresponding to the surface region 31b of the first metal magnetic particle 31) when the raw material powder is heated, so that the oxidation of Fe contained in the central region 31a can be suppressed. This makes it possible to suppress the decrease in the magnetic permeability of the magnetic base 10 due to the oxidation of Fe. Al is also easily oxidized, and the oxide of Al (Al2O3) has excellent insulating properties, so that, like Si, the insulating properties of the oxide film 41 can be improved and the oxidation of Fe contained in the central region 31a can be suppressed.

[0056] When strain occurs in the raw material powder, the thermal diffusion of elements contained in the raw material powder is promoted in the direction of strain. Therefore, Si and Al are also likely to thermally diffuse into the grain boundary region 31c. In addition, the grain boundary region 31c traps oxygen and nitrogen that enter the raw material powder and precipitates them as element M precipitates 50, thereby suppressing the oxidation of Fe in the grain inner region 31d.

[0057] As described above, the Si and Al contained in the raw material powder are easily thermally diffused when the raw material powder is heated. Therefore, by increasing the content ratio of Si and Al in the element M added to the raw material powder, the amount of element M remaining in the crystal grain inner region 31d of the first metal magnetic particle 31 can be reduced, and as a result, the content ratio of Fe in the crystal grain inner region 31d can be increased.

[0058] When the raw material powder contains Cr, the crystallization temperature of the raw material powder is close to the diffusion temperature of Cr (the temperature required for Cr to thermally diffuse in the raw material powder), so that thermal diffusion of Cr occurs in parallel with the crystallization of the raw material powder, and the thermally diffused Cr tends to aggregate in the grain boundary region 31c, forming Cr aggregates in the grain boundary region 31c. The Cr aggregates precipitated in the grain boundary region 31c can inhibit the growth of the crystal grains, so that when the raw material powder contains Cr, the size of the crystal grains is suppressed.

[0059] 5, when element M precipitates 50 are formed in surface regions 31b and grain boundary regions 31c of first metal magnetic grains 31, the Fe content in grain inner regions 31d is increased. In this case, the Fe content in grain inner regions 31d may be 97 at% or more, 98 at% or more, or 99 at% or more.

[0060] It can be confirmed that the element M precipitates 50 precipitated in the surface region 31b and the grain boundary region 31c contain an oxide of element M and / or a nitride of element M as follows. First, the substrate 10 is cut along the T-axis direction to expose a cross section, and the cross section is photographed at a predetermined magnification by a scanning electron microscope (SEM) to obtain an SEM image. EDS analysis is performed on this SEM image to obtain a distribution image of element M and O element and / or N element (a mixed map of elements M and O, a mixed map of elements M and N, or a mixed map of elements M, O and N). In this distribution image, it can be determined that element M precipitates 50 containing an oxide of element M are present in a region where elements M and O are distributed in a particulate form. In addition, it can be determined that element M precipitates 50 containing a nitride of element M are present in a region where elements M and N are distributed in a particulate form in this distribution image.

[0061] The oxide film 41 covers the surface region 31b of the first metal magnetic particle 31. The oxide film 41 contains an oxide having excellent insulating properties. The oxide film 41 contains an oxide of element M (e.g., an oxide of Si, an oxide of Cr, and / or an oxide of Al). All oxides of element M have excellent insulating properties. The oxide film 41 may contain an oxide of Fe. The oxide film 41 preferably covers the entire surface region 31b of the first metal magnetic particle 31. The oxide film 41 preferably has a thickness (diameter dimension) of 5 nm or more.

[0062] Next, the second metal magnetic particle 32 will be further described with reference to Fig. 6. Fig. 6 shows a schematic cross section of one of the plurality of second metal magnetic particles 32 contained in the base 10. In Fig. 6, the cross section of the second metal magnetic particle 32 is drawn as a circle for convenience. The second metal magnetic particle 32 contained in the base 10 can have various shapes other than a circle, as shown in Fig. 4. Fig. 6 also shows an oxide film 42 provided on the surface of the second metal magnetic particle 32.

[0063] As shown in Fig. 6, the second metal magnetic particle 32 is divided into a central region 32a and a surface region 32b. The central region 32a includes a geometric center C2 of the cross section of the second metal magnetic particle 32 shown in Fig. 6. The surface region 32b is located radially outward from the central region 32a. The surface region 32b covers the outer peripheral surface of the central region 32a. Thus, the surface region 32b extends along the surface of the second metal magnetic particle 32 radially outward from the central region 32a.

[0064] In the radial direction of the second metal magnetic particle 32, the surface region 32b has a width d22. In one embodiment, the width d22 of the surface region 32b is 10% of the Heywood diameter of the second metal magnetic particle 32. The width d22 of the surface region 32b may be 10% or less of the Heywood diameter of the second metal magnetic particle 32. The dimension d21 in the radial direction of the central region 32a corresponds to the difference between the dimension between the geometric center C2 of the second metal magnetic particle 32 and its surface, and the width d22 of the surface region 32b.

[0065] As described above, the second metal magnetic particles 32 differ from the first metal magnetic particles 31 in that they do not contain precipitates of element M. In one embodiment, the particle size of the second metal magnetic particles 32 is larger than the particle size of the first metal magnetic particles 31. For example, in an observation field of a cross section of the substrate 10 (for example, an observation field when observed at a magnification of 10,000 times), the average particle size of the second metal magnetic particles 32 is larger than the average particle size of the first metal magnetic particles 31. In addition, the aspect ratio of the first metal magnetic particles 31 may be larger than the aspect ratio of the second metal magnetic particles 32.

[0066] The composition of the second metal magnetic particle 32 may be the same as that of the first metal magnetic particle 31, except for the element M precipitate. The second metal magnetic particle 32 contains 95 at% or more of Fe in the central region 32a. The second metal magnetic particle 32 may contain 97 at% or more of Fe in the central region 32a, similar to the first metal magnetic particle 31. The content ratio of Fe in the central region 31a may be 98 at% or more, or may be 99 at% or more. The second metal magnetic particle 32 may contain the element M in addition to Fe in the central region 32a. The content ratio of the element M in the central region 32a may be 0.01 at% or more and 1.0 at% or less. Since the second metal magnetic particle 32 does not contain the element M precipitate portion 50, the element M contained in the second metal magnetic particle 32 is dispersed without agglomeration within the second metal magnetic particle 32. The element M may not be contained in the central region 32a. The central region 32a may contain Cr at an atomic ratio less than that of Si. The central region 32a may contain Al at a ratio less than that of Si. The central region 32a may contain Cr and Al. The central region 32a may not contain Cr. The central region 32a may not contain Al. The central region 32a may not contain any element M. Whether the element M is present in the central region 32a or not can be determined by performing an EDS analysis on an SEM image of a cross section of the second metal magnetic particle 32 to obtain mapping data of the element M, and if there is a position in the central region 32a in this mapping data that shows a peak intensity of the element M equal to or greater than the detection limit, it can be determined that the element M is present at that position. Conversely, if the peak intensity of the element M is less than the detection limit in all regions of the central region 32a, it is determined that the element M is not contained in the central region 32a. The detection limit for the element M is determined to be three times the standard deviation σ of the background level, that is, three times the square root of the background level. The atomic ratio of the element M contained in the surface region 32b is higher than the atomic ratio of the element M contained in the central region 32a.

[0067] The oxide film 42 covers the surface region 32b of the second metal magnetic particle 32. The oxide film 42 contains an oxide having excellent insulating properties. Like the oxide film 41, the oxide film 42 contains an oxide of element M (an oxide of Si, an oxide of Cr, and / or an oxide of Al). The oxide film 42 may contain an oxide of Fe. The oxide film 42 preferably covers the entire surface region 32b of the second metal magnetic particle 32. The oxide film 42 preferably has a thickness (diameter dimension) of 5 nm or more.

[0068] Next, an example of a method for manufacturing the coil component 1 will be described with reference to FIG. 7. Since the manufacturing process of the coil component 1 includes a manufacturing process of the base 10, the manufacturing method of the base 10 will also be described with reference to FIG. 7. FIG. 7 is a flow diagram showing a method for manufacturing the coil component 1 according to an embodiment of the present invention. In the following description, it is assumed that the coil component 1 is manufactured by a sheet lamination method. The coil component 1 may be manufactured by a known method other than the sheet lamination method. For example, the coil component 1 can be manufactured by a lamination method such as a print lamination method, a thin film process method, or a slurry build method.

[0069] First, in step S1, a magnetic sheet is produced. The magnetic sheet is produced from a magnetic material paste obtained by kneading a metal magnetic powder (raw material powder) that is the raw material of the first metal magnetic particles 31 and the second metal magnetic particles 32 with a binder resin and a solvent. The first metal magnetic particles 31 and the second metal magnetic particles 32 can be produced from a common raw material powder. The metal magnetic powder contains Fe and the element M. In the metal magnetic powder, Fe and the element M are distributed almost uniformly. The Fe content in the raw material powder is different from the Fe content in the crystal grain inner region 31d of the first metal magnetic particles 31 and the Fe content in the central region 32a of the second metal magnetic particles 32 after heat treatment.

[0070] The binder resin for the magnetic material paste is, for example, an acrylic resin. The binder resin for the magnetic material paste may be an epoxy resin, a polyimide resin, a resin known as a binder resin other than the above, or a mixture thereof. The solvent is, for example, toluene. This magnetic material paste is applied to the surface of a plastic base film by a doctor blade method or other general method. A sheet-shaped molded body is obtained by drying the magnetic material paste applied to the surface of the base film. A plurality of magnetic sheets are produced by pressurizing and molding this sheet-shaped molded body in a mold at a molding pressure of about 10 to 100 MPa.

[0071] Next, in step S2, a conductive paste is applied to some of the magnetic sheets prepared in step S1. The conductive paste is produced by kneading a conductive powder made of a conductive material with excellent conductivity, such as Ag, Pd, Cu, Al, or an alloy thereof, with a binder resin and a solvent. The binder resin for the conductive paste may be the same type of resin as the binder resin for the magnetic material paste. Both the binder resin for the conductive paste and the binder resin for the magnetic material paste may be acrylic resin.

[0072] By applying a conductive paste to the magnetic sheet, an unfired conductive pattern that will become the conductive patterns C11 to C17 after firing is formed on the magnetic sheet. Through holes penetrating in the stacking direction are formed in parts of the magnetic sheet. When the conductive paste is applied to a magnetic sheet having through holes, the conductive paste is also embedded in the through holes. In this way, unfired vias that will become the vias V1 to V5 after firing are formed in the through holes of the magnetic sheet. The conductive paste is applied to the magnetic sheet by, for example, a screen printing method.

[0073] Next, in step S3, the magnetic sheets prepared in step S1 are stacked to prepare an upper laminate which becomes the upper cover layer 18, an intermediate laminate, and a lower laminate which becomes the lower cover layer 19. The upper laminate and the lower laminate are each formed by stacking four of the magnetic sheets prepared in step S1 on which no unsintered conductor pattern is formed. The four magnetic sheets of the upper laminate become the magnetic films 18a to 18d in the finished coil component 1, and the four magnetic sheets of the lower laminate become the magnetic films 19a to 19d in the finished coil component 1. The intermediate laminate is formed by stacking seven magnetic sheets on which unsintered conductor patterns are formed in a predetermined order. The seven magnetic sheets of the intermediate laminate become the magnetic films 11 to 17 in the finished coil component 1. The intermediate laminate prepared as described above is sandwiched between the upper laminate and the lower laminate from above and below, and the upper laminate and the lower laminate are thermocompressed to the intermediate laminate to obtain a main laminate. Next, the main laminate is divided into pieces of a desired size using a cutting machine such as a dicing machine or a laser processing machine to obtain a chip laminate. The chip laminate is an example of a molded body including an element that becomes the base 10 after heat treatment and an unfired conductor pattern that becomes the coil conductor 25 after heat treatment. The element that becomes the base 10 after heat treatment and the molded body including an unfired conductor pattern that becomes the coil conductor 25 after heat treatment may be produced by a method other than the sheet lamination method.

[0074] The raw material powder contained in the chip stack is compressed in the process of forming the chip stack. For example, the raw material powder is compressed in a process of forming a magnetic sheet by pressure molding a sheet-shaped molded body containing the raw material powder, or in a process of thermocompression bonding an intermediate stack. By compressing the raw material powder, the contact area between adjacent raw material powders increases. In addition, strain occurs in the compressed raw material powder. By increasing the Fe content in the raw material powder, the raw material powder is more likely to be plastically deformed by compression stress, so that the contact area between adjacent raw material powders can be increased and the strain generated in the raw material powder contained in the chip stack can be increased.

[0075] Next, in step S4, the molded body produced in step S3 is degreased. When a thermally decomposable resin is used as the binder resin for the magnetic material paste and the conductive paste, the molded body can be degreased in a non-oxygen atmosphere such as a nitrogen atmosphere. By performing the degreasing in a non-oxygen atmosphere, it is possible to prevent Fe contained in the metal magnetic powder from being oxidized during the degreasing. The degreasing is performed at a temperature higher than the thermal decomposition start temperature of the binder resin for the magnetic material paste. When an acrylic resin is used as the binder resin for the magnetic material paste, the degreasing is performed at a temperature higher than the thermal decomposition start temperature of the acrylic resin, for example, 300°C to 500°C. The thermally decomposable resin contained in the molded body is decomposed by the degreasing, so that no thermally decomposable resin remains in the molded body after the degreasing is completed. When the degreasing is performed in a temperature range of 300°C to 500°C, there is almost no movement of elements (for example, element M) in the metal magnetic powder due to thermal diffusion. By using the same thermally decomposable resin for the binder resin for the conductive paste as the binder resin for the magnetic material paste, the thermally decomposable resin contained in the unsintered conductor pattern is also thermally decomposed in the degreasing process in step S4. Thus, in step S4, both the magnetic sheet and the unsintered conductor pattern that constitute the molded body are degreased.

[0076] Next, in step S5, the degreased molded body is subjected to a first heat treatment. The first heat treatment is performed at a first temperature in a reducing atmosphere such as hydrogen gas diluted with nitrogen. The hydrogen concentration of the reducing atmosphere in the first heat treatment is, for example, 0.5% to 4.0%. The first temperature can be a temperature between 600°C and 800°C. By heating the metal magnetic powder at 600°C to 900°C, the element M in each metal magnetic powder moves to the vicinity of the surface of the metal magnetic powder by thermal diffusion. In addition, since the metal magnetic powder is distorted as described above, the element M diffuses to the crystal grain boundaries between the multiple crystal grains contained in the metal magnetic powder by thermal diffusion promoted by this distortion. Since the first heat treatment is performed in a reducing atmosphere, the elements contained in the metal magnetic powder are not oxidized in the first heat treatment. Since the atmosphere in which the first heat treatment is performed contains nitrogen, in the first heat treatment, the element M thermally diffused near the surface or to the grain boundaries of the metal magnetic powder may combine with the nitrogen that has penetrated into the raw material powder, and a nitride of the element M may be generated in the grain boundary region 31c. The first heating time during which the first heat treatment is performed may be between 1 hour and 6 hours. The first heating time may be, for example, 1 hour. In the case of Fe-based metal magnetic powder having an average particle size of about 1 μm to 50 μm, the additive element such as the element M can be moved to the vicinity of the surface of each metal magnetic powder particle by heating at a heating temperature of 600° C. or higher for 1 hour or more.

[0077] Next, in step S6, the molded body after being heated in the first heat treatment is subjected to a second heat treatment in a low-oxygen atmosphere. The second heat treatment is performed in a low-oxygen atmosphere containing oxygen in the range of 5 to 1000 ppm, for example. Since the second heat treatment is performed in a low-oxygen atmosphere, the elements contained in the metal magnetic powder are oxidized in the second heat treatment. Since the element M moves to the vicinity of the surface of the metal magnetic powder in the first heat treatment, an oxide film containing an oxide of the element M is formed on the surface of the metal magnetic powder in the second heat treatment. In addition, oxygen penetrates into the interior of some particles of the metal magnetic powder, and the oxygen that penetrates into the interior bonds with the element M in a region slightly inside the surface of the metal magnetic powder, generating an element M precipitate 50. In addition, the element M that has been thermally diffused into the crystal grain boundary may bond with the oxygen that has penetrated into the crystal grain boundary of the metal magnetic powder, generating an oxide of the element M in the crystal grain boundary region 31c. In this second heat treatment, a part of the metal magnetic powder becomes the first metal magnetic particles 31 with an oxide film 41 formed on the surface and element M precipitates 50 precipitated near the surface, and the remaining part of the metal magnetic powder becomes the second metal magnetic particles 32 with an oxide film 42 formed on the surface. As described above, the second metal magnetic particles 32 do not contain element M precipitates 50. When the first metal magnetic particles 31 are adjacent to each other, the oxide films 41 provided on the respective surfaces are bonded to each other. When the first metal magnetic particle 31 and the second metal magnetic particle 32 are adjacent to each other, the oxide film 41 of the first metal magnetic particle 31 and the oxide film 42 of the second metal magnetic particle 32 are bonded to each other.

[0078] As shown in FIG. 5, element M precipitates 50 are precipitated in the crystal grain boundary regions 31c inside the first metal magnetic particles 31 formed by the second heat treatment in step S6. The element M precipitates 50 inhibit the crystallization reaction of the crystal grains (e.g., crystal grains CP1 to CP3) in the first metal magnetic particles 31, so the first metal magnetic particles 31 containing the element M precipitates 50 contain a plurality of crystal grains even after the first heat treatment and the second heat treatment. The eddy current loss in the metal magnetic particles is divided into macro eddy current loss caused by macro eddy current flowing through the entire metal magnetic particle, and local eddy current loss caused by the movement of domain walls in the metal magnetic particles. The local eddy current loss is smaller as the number of domain walls increases, in other words, as the first metal magnetic particles 31 are divided into smaller magnetic domains. The magnetic domains become larger as the crystal grain size increases. Therefore, by suppressing the recrystallization of the crystal grains contained in the raw material powder and making the first metal magnetic particle 31 contain a plurality of crystal grains, it is possible to suppress the crystal grain size in the first metal magnetic particle 31 from increasing in size due to recrystallization, and thus to suppress local eddy current loss. Since the first metal magnetic particle 31 has a plurality of crystal grains (e.g., crystal grains CP1 to CP3), the eddy current loss in the first metal magnetic particle 31 is smaller than the eddy current loss in a metal magnetic particle composed of a single crystal grain of the same diameter as the first metal magnetic particle 31. In this way, by precipitating element M precipitate 50 in the crystal grain boundary region 31c in the heat treatment of the raw material powder to inhibit the recrystallization of the crystal grains, the first metal magnetic particle 31 after the first heat treatment and the second heat treatment contains a plurality of crystal grains (e.g., crystal grains CP1 to CP3), it is possible to suppress local eddy current loss.

[0079] As described above, a nitride of element M may be generated in step S5, and an oxide of element M may be generated in step S6. By increasing the first temperature in the first heating treatment in step S5, the generation of the nitride of element M can be promoted. Furthermore, by increasing the second temperature in the second heating treatment in step S6, the generation of the oxide of element M can be promoted.

[0080] In the second heat treatment, in addition to the oxidation of the metal magnetic powder, the conductor powder in the unsintered conductor pattern is also sintered. The conductor powder in the unsintered conductor pattern is sintered to obtain the coil conductor 25. When copper powder is used as the conductor powder, the copper crystals are densely sintered to become the coil conductor 25.

[0081] The second heating process is performed at the second heating temperature for only the second heating time. The second heating temperature and the second heating time are determined so that an oxide film having a sufficient thickness to ensure insulation is formed on the surface of the metal magnetic powder, and so that 1% to 10% of the metal magnetic powder contained in the molded body becomes the first metal magnetic particles 31 and the remainder becomes the second metal magnetic particles 32. The second heating temperature is preferably a temperature at which the conductor powder contained in the conductive paste can grow grains. When the conductor powder is Cu or Ag, crystal grain growth can be caused in the conductor powder at 600°C or higher. From this perspective, the second heating temperature can be set to, for example, a temperature between 600°C and 700°C. The higher the second heating temperature, the faster the oxidation progresses, so the second heating time varies depending on the second heating temperature. When the second heating temperature is 600°C, the second heating time can be set to a value between 1 hour and 6 hours. When the second heating temperature is 700°C, the second heating time can be set to a value between 30 minutes and 1 hour.

[0082] In this manner, the coil conductor 25 is produced from the unsintered conductor pattern by the second heating treatment. Furthermore, the metal magnetic powder contained in the molded body is oxidized by the second heating treatment to produce the first metal magnetic particles 31 or the second metal magnetic particles 32, and the base 10 in which the first metal magnetic particles 31 and the second metal magnetic particles 32 are bonded is obtained. In this manner, a molded body in which the coil conductor 25 is provided within the base 10 is obtained.

[0083] Next, in step S7, the external electrodes 21 and 22 are formed on the surface of the molded body obtained in step S6. The external electrode 21 is connected to one end of the coil conductor 25, and the external electrode 22 is connected to the other end of the coil conductor 25. Before forming the external electrodes 21 and 22, the molded body after the second heat treatment may be impregnated with a resin. The molded body is impregnated with a thermosetting resin such as an epoxy resin. This allows the resin to permeate into the gaps between the metal magnetic particles in the base 10. Then, by hardening the resin impregnated in the base 10, the mechanical strength of the base 10 can be improved.

[0084] Through the above steps, the coil component 1 is obtained.

[0085] Next, a coil device 101 according to another embodiment will be described with reference to Fig. 8. Fig. 8 is a front view showing a coil device 101 according to another embodiment.

[0086] 8, the coil device 101 includes a base 110, a winding 125 wound around a winding core of the base 110, an external electrode 121, and an external electrode 122. The winding 125 is an example of a coil conductor. The external electrode 121 is provided on one flange of the base 110, and the external electrode 122 is provided on the other flange of the base 110. The winding 125 is configured such that one end thereof is electrically connected to the external electrode 121, and the other end thereof is electrically connected to the external electrode 122.

[0087] Similar to the base 10, the base 110 includes a plurality of metal magnetic particles. The metal magnetic particles included in the base 110 include first metal magnetic particles 31 and second metal magnetic particles 32. The first metal magnetic particles 31 include element M precipitates 50, whereas the second metal magnetic particles 32 do not include element M precipitates 50. The explanation regarding the base 10 also applies to the base 110 unless the context requires otherwise.

[0088] Next, an example of a method for producing the coil component 101 by compression molding will be described with reference to FIG.

[0089] When manufacturing the coil component 101 by the compression molding method, first, in step S11, a mixed magnetic material is generated by kneading a metal magnetic powder (raw material powder) that is the raw material of the first metal magnetic particles 31 and the second metal magnetic particles 32 with a binder resin and a solvent. The mixed magnetic material may be in the form of a paste or granulated magnetic powder.

[0090] Next, in step S12, the mixed magnetic material prepared in step S11 is charged into a metal mold and compression molded in the metal mold to obtain a molded body.

[0091] Next, in step S13, the molded body obtained in step S12 is degreased. The degreasing in step S13 is performed in the same manner as the degreasing in step S4 in the lamination method.

[0092] Next, in step S14, a first heating process is performed on the molded body degreased in step S13. The first heating process in step S14 is performed in the same manner as the first heating process in step S5 in the lamination method.

[0093] Next, in step S15, a second heat treatment is performed on the molded body that has been subjected to the first heat treatment in step S14. The second heat treatment in step S15 is performed in the same manner as the second heat treatment in step S6 in the lamination method. By this second heat treatment, the base body 110 is obtained from the molded body.

[0094] Next, in step S16, the winding 125 is wound around the winding core of the base 110 obtained in step S15.

[0095] Next, in step S17, external electrodes 121, 122 are formed on base 110. Both ends of winding 125 wound around base 110 in step S16 are connected to the corresponding external electrodes. In this manner, coil component 101 having base 110 produced by compression molding is produced.

[0096] The substrate 10 according to one embodiment includes a plurality of first metal magnetic particles 31 containing element M precipitates 50, and a plurality of second metal magnetic particles 32 not containing element M precipitates 50. The first metal magnetic particles 31 contain element M precipitates 50 therein, and are partitioned into a plurality of crystal grains (crystal grains CP1 to CP3 in the example of FIG. 5) by crystal grain boundary regions 31c containing the element M precipitates 50. For this reason, in the first metal magnetic particles 31, the crystal grain size can be made smaller than that of metal magnetic particles containing a single crystal grain, thereby suppressing local eddy current loss.

[0097] The present inventors have noticed that the raw material powder of the metal magnetic particles includes a mixture of easily oxidizable particles into which oxygen easily penetrates and hardly oxidizable particles into which oxygen does not easily penetrate. For example, raw material powder particles having a relatively small particle size have a larger specific surface area than raw material powder particles having a relatively large particle size. For this reason, when the element M moves to the vicinity of the surface of each metal magnetic powder particle by thermal diffusion in the first heat treatment, the amount of element M per surface area in the raw material powder having a relatively small particle size is smaller than that in the raw material powder having a relatively large particle size, so that oxygen easily penetrates into the raw material powder. For this reason, the raw material powder particles having a relatively small particle size are more likely to have oxygen penetrate into the inside than the raw material powder particles having a relatively large particle size. In addition, in the manufacturing process of the magnetic base (for example, during compression molding to produce a magnetic sheet), some raw material powder particles may be relatively distorted. Oxygen easily penetrates into the inside of raw material powder particles in which large distortion occurs. When an oxide film containing the element M is formed on the surface of the raw material powder with a sufficient thickness, the raw material powder becomes a hardly oxidizable particle into which oxygen does not easily penetrate. This oxide film is formed during the second heat treatment, but if the ratio of Fe in the raw material powder is very high, for example 95 at% or more, the amount of element M required to form the oxide film is small, making it difficult to form an oxide film of sufficient thickness. If an oxide film of sufficient thickness is not formed on the surface of some of the raw material powder, the raw material powder becomes easily oxidized particles into which oxygen can easily penetrate.

[0098] In the second heat treatment, oxygen may penetrate into the raw material powder composed of a plurality of crystal grains along the grain boundaries, which are the boundaries between the plurality of crystal grains. The element M may be present in the vicinity of the grain boundaries of the crystal grains (the region corresponding to the grain boundary region 31c). The oxygen that penetrates into the grain boundaries of the crystal grains combines with the element M in the vicinity of the grain boundaries, and the element M precipitates in the grain boundary region 31c. Therefore, the first metal magnetic particle 31 contains the element M precipitate in the grain boundary region 31c in addition to the surface region 31b. In this way, during the second heat treatment, the oxygen that penetrates into the raw material powder particles from the surface is captured by the element M ubiquitously present in the surface region 31b, and the oxygen that penetrates into the raw material powder particles from the grain boundaries is captured by the element M in the vicinity of the grain boundaries, so that the oxidation of Fe in the center region 31a is suppressed.

[0099] If the amount of oxygen penetrating into the raw material powder in the second heat treatment becomes excessive, then all of the element M present in the surface region 31b will bond with oxygen, and the oxygen will pass through the surface region 31b and penetrate into the central region 31a. The oxygen that penetrates into the central region 31a oxidizes the Fe present in the central region 31a, so if the amount of oxygen that penetrates into the raw material powder is excessive, the magnetic properties (magnetic permeability) of the base 10 will deteriorate. Whether or not the amount of oxygen that penetrates into the raw material powder is excessive can be determined based on the percentage of particles in which element M precipitates 50 are precipitated among the metal magnetic particles contained in the base 10 (i.e., based on the precipitate occurrence rate). For example, if element M precipitates 50 are precipitated in 1% to 10% of the metal magnetic particles contained in the base 10 (i.e., if the precipitate occurrence rate is in the range of 1% to 10%), it can be determined that an appropriate amount of oxygen has penetrated into the raw material powder. When the precipitate generation rate exceeds 10%, oxygen also penetrates into a part of the hardly oxidizable particles, so that the oxygen that penetrates into the easily oxidizable particles becomes excessive, and oxygen reaches the central region 31a. On the other hand, when the precipitate generation rate is less than 1%, the raw material powder may not be oxidized sufficiently, and the oxide film 41 may not be formed to a sufficient thickness for electrical insulation between the metal magnetic particles, which may deteriorate the insulating properties of the base 10. In this way, by performing the second heat treatment under conditions where the element M precipitate 50 is generated in the easily oxidizable particles but the element M precipitate 50 is not generated in the hardly oxidizable particles (specifically, by performing the second heat treatment under heating conditions where the precipitate generation rate is in the range of 1% to 10%), it is possible to suppress the penetration of excessive oxygen into the central region of the easily oxidizable particles and suppress the oxidation of Fe in the central region 31a. In this case, the penetration of excessive oxygen into the central region of the hardly oxidizable particles is also suppressed. Therefore, a high Fe content can be realized in each of the metal magnetic particles contained in the base 10.

[0100] In addition, since oxygen penetrates into the easily oxidizable particles during the manufacturing process of the coil components 1 and 101, the oxidation of the additive elements is sufficiently advanced on the surface of each raw material powder particle, and therefore, oxide films 41 and 42 having a thickness required to ensure insulation can be formed on the surface of each metal magnetic particle.

[0101] Furthermore, since the nitride or oxide of element M contained in the element M precipitate 50 has a lower magnetic permeability than Fe, it functions as a magnetic gap in the magnetic base. In the above embodiment, the element M precipitate 50 is present in the surface region 31b of the first metal magnetic particle 31, and the element M precipitate 50 functions as a magnetic gap, thereby improving the DC superposition characteristics of the coil component 1, 101. When the element M precipitate 50 is present in both the surface region 31b and the grain boundary region 31c of the first metal magnetic particle 31, the region that functions as a magnetic gap increases, and therefore the DC superposition characteristics of the coil component 1, 101 can be further improved.

[0102] Some of the steps included in the manufacturing method described in this specification may be omitted as appropriate. In the manufacturing method of the coil component 1, steps not explicitly described in this specification may be performed as necessary. Some of the steps included in the manufacturing method of the coil component 1 described above may be performed in a different order as needed, as long as this does not deviate from the spirit of the present invention. Some of the steps included in the manufacturing method of the coil component 1 described above may be performed simultaneously or in parallel, if possible.

[0103] The dimensions, materials, and arrangements of each component described in the various embodiments above are not limited to those explicitly described in each embodiment, and each component can be modified to have any dimensions, materials, and arrangements that may fall within the scope of the present invention.

[0104] Components not explicitly described in this specification may be added to each of the above-described embodiments, and some of the components described in each embodiment may be omitted.

[0105] The designations "first," "second," "third," and the like in this specification are given to identify components, and do not necessarily limit the number, order, or content. Furthermore, numbers for identifying components are used in different contexts, and a number used in one context does not necessarily indicate the same configuration in another context. Furthermore, a component identified by a certain number does not prevent the component from also having the function of a component identified by another number.

[0106] This specification also discloses the following techniques. [Appendix 1] A plurality of metal magnetic particles containing Fe and an element M which is more easily oxidized than Fe (wherein the element M is at least one element selected from the group consisting of Si, Cr, and Al); an oxide film provided on a surface of each of the plurality of metal magnetic particles; Equipped with The plurality of metal magnetic particles include a plurality of first metal magnetic particles containing precipitates including the element M. Magnetic substrate. [Appendix 2] the plurality of metal magnetic particles further includes a plurality of second metal magnetic particles that do not contain the precipitates; 2. The magnetic substrate according to claim 1. [Appendix 3] The precipitate contains a metal containing the element M. 3. The magnetic substrate according to claim 1 or 2. [Appendix 4] The precipitates contain at least one of Cr and Al. 4. The magnetic substrate according to claim 3. [Appendix 5] The precipitate contains an oxide of the element M. 5. The magnetic substrate according to claim 1 , [Appendix 6] The precipitates contain at least one of Cr and Al. 6. The magnetic substrate according to claim 5. [Appendix 7] The precipitate contains a nitride of the element M. 7. The magnetic substrate according to claim 1 , [Appendix 8] The precipitates contain at least one of Cr and Al. 8. The magnetic substrate according to claim 7. [Appendix 9] At least one of the first metal magnetic particles has a plurality of crystal grains and contains the precipitate in a crystal grain boundary region in the vicinity of the crystal grain boundaries of the plurality of crystal grains. 9. The magnetic substrate according to claim 1, [Appendix 10] Each of the plurality of metal magnetic grains contains 95 at % or more of Fe in a grain inner region surrounded by the grain boundary region. 10. The magnetic substrate according to claim 1, [Appendix 11] Each of the plurality of first metal magnetic grains contains 97 at % or more of Fe in the crystal grain inner region. 11. The magnetic substrate according to claim 10. [Appendix 12] Each of the plurality of first metal magnetic grains contains 98 at % or more of Fe in the crystal grain inner region. 12. The magnetic substrate according to claim 11. [Appendix 13] Each of the first metal magnetic grains contains 99 at % or more of Fe in the crystal grain inner region. 13. The magnetic substrate according to claim 12. [Appendix 14] Each of the plurality of metal magnetic grains contains 0.01 at % or more and 1.0 at % or less of element M in the crystal grain boundary region. 14. The magnetic substrate according to claim 1. [Appendix 15] The first metal magnetic particles account for 1% to 10% of the total number of the plurality of metal magnetic particles included in the observation field of view. 15. The magnetic substrate according to any one of claims 1 to 14. [Appendix 16] The oxide film contains an oxide of Fe. 16. The magnetic substrate according to claim 1 , [Appendix 17] the plurality of metal magnetic particles include one metal magnetic particle and another metal magnetic particle adjacent to the one metal magnetic particle, and the one metal magnetic particle and the other metal magnetic particle are bonded to each other by the oxide coating covering the surface of the one metal magnetic particle and the oxide coating covering the surface of the other metal magnetic particle; 17. The magnetic substrate according to any one of claims 1 to 16. [Appendix 18] A step of obtaining a molded body from a mixed resin composition obtained by mixing a plurality of metal magnetic powders containing Fe and an element M which is more easily oxidized than Fe (wherein the element M is at least one element selected from the group consisting of Si, Cr, and Al) with a resin; a first heating step of heating the molded body at a first temperature in a reducing atmosphere; a second heating step in which, after the first heating step, the molded body is heated in a low-oxygen atmosphere containing oxygen, thereby forming an oxide film containing an oxide of the element M on the surface of each of the plurality of metal magnetic powder particles and precipitating a precipitate containing the element M inside the plurality of metal magnetic powder particles; A method for manufacturing a magnetic substrate comprising the steps of: [Explanation of symbols]

[0107] 1, 101 Coil parts 10, 110 Substrate (magnetic substrate) 21, 22, 121, 122 external electrode 31 First metal magnetic particles 31a, 32a central area 31b, 32b surface area 32 Second metal magnetic particles 41, 42 Oxide film 50 Precipitates

Claims

1. A plurality of metal magnetic particles containing Fe and an element M which is more easily oxidized than Fe (wherein the element M is at least one element selected from the group consisting of Si, Cr, and Al); an oxide film provided on a surface of each of the plurality of metal magnetic particles; Equipped with The plurality of metal magnetic particles include a plurality of first metal magnetic particles containing a precipitate including the element M. Magnetic substrate.

2. The plurality of metal magnetic particles further includes a plurality of second metal magnetic particles that do not contain the precipitate. The magnetic substrate according to claim 1 .

3. The precipitate contains a metal containing the element M.

3. The magnetic substrate according to claim 1 or 2.

4. The precipitates contain at least one of Cr and Al. The magnetic substrate according to claim 3.

5. The precipitate contains an oxide of the element M.

3. The magnetic substrate according to claim 1 or 2.

6. The precipitates contain at least one of Cr and Al. The magnetic substrate according to claim 5 .

7. The precipitate contains a nitride of the element M.

3. The magnetic substrate according to claim 1 or 2.

8. The precipitates contain at least one of Cr and Al. The magnetic substrate according to claim 7.

9. At least one of the first metal magnetic particles has a plurality of crystal grains and contains the precipitate in a crystal grain boundary region in the vicinity of the crystal grain boundaries of the plurality of crystal grains. The magnetic substrate according to claim 1 .

10. Each of the plurality of metal magnetic grains contains 95 at % or more of Fe in a crystal grain inner region surrounded by the crystal grain boundary region. The magnetic substrate according to claim 9.

11. Each of the first metal magnetic grains contains 97 at % or more of Fe in the crystal grain inner region. The magnetic substrate according to claim 10.

12. Each of the first metal magnetic grains contains 98 at % or more of Fe in the crystal grain inner region. The magnetic substrate according to claim 11.

13. Each of the first metal magnetic grains contains 99 at % or more of Fe in the crystal grain inner region. The magnetic substrate according to claim 12.

14. Each of the plurality of metal magnetic grains contains the element M in an amount of 0.01 at % or more and 1.0 at % or less in the crystal grain boundary region. The magnetic substrate according to claim 9.

15. The first metal magnetic particles account for 1% to 10% of the total number of the plurality of metal magnetic particles included in the observation field of view.

3. The magnetic substrate according to claim 1 or 2.

16. The oxide film contains an oxide of Fe.

3. The magnetic substrate according to claim 1 or 2.

17. the plurality of metal magnetic particles include one metal magnetic particle and another metal magnetic particle adjacent to the one metal magnetic particle, and the one metal magnetic particle and the other metal magnetic particle are bonded to each other by the oxide coating covering the surface of the one metal magnetic particle and the oxide coating covering the surface of the other metal magnetic particle; 3. The magnetic substrate according to claim 1 or 2.

18. A step of obtaining a molded body from a mixed resin composition obtained by mixing a plurality of metal magnetic powders containing Fe and an element M which is more easily oxidized than Fe (wherein the element M is at least one element selected from the group consisting of Si, Cr, and Al) with a resin; a first heating step of heating the molded body at a first temperature in a reducing atmosphere; a second heating step in which, after the first heating step, the molded body is heated in a low-oxygen atmosphere containing oxygen, thereby forming an oxide film containing an oxide of the element M on a surface of each of the plurality of metal magnetic powders and precipitating a precipitate containing the element M inside the plurality of metal magnetic powders; A method for manufacturing a magnetic substrate comprising the steps of:

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