Magnetic substrate and coil component including magnetic substrate

Abstract

To provide a magnetic substrate in which the insulating properties of metal magnetic particles are improved.SOLUTION: A magnetic substrate according to an embodiment includes a plurality of metal magnetic particles containing Fe, Si, and the element α, a first oxide film covering the surface of each of the plurality of metal magnetic particles, and a second oxide film covering the surface of the first oxide film. The first oxide film is primarily composed of an oxide of Si. The second oxide film is primarily composed of an oxide of the element α. A first thickness indicating the thickness of the first oxide film is thicker than a second thickness indicating the thickness of the second oxide film.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The disclosure herein primarily relates to a magnetic substrate and a coil component including the magnetic substrate. [Background technology]

[0002] A soft magnetic substrate consisting of a plurality of bonded metal magnetic particles is used as a magnetic substrate for coil components. The surface of each metal magnetic particle contained in the soft magnetic substrate is covered with an insulating film, and adjacent metal magnetic particles are bonded to each other via the insulating film. Because soft magnetic substrates are less susceptible to magnetic saturation than magnetic substrates made of ferrite, they are suitable as magnetic substrates for coil components used in circuits through which large currents flow.

[0003] The metal magnetic particles are produced from an Fe-based raw material powder whose main component is Fe. This Fe-based raw material powder contains additive elements such as Si, Cr, and Al in addition to Fe to improve magnetic and insulating properties.

[0004] An insulating coating film applied to the surface of raw material powder is sometimes used as an insulating film on the surface of metal magnetic particles. The coating film that covers the surface of the raw material powder is formed, for example, by applying a mixed liquid of TEOS (tetraethoxysilane) and ethanol to the surface of the raw material powder. Due to limitations in the manufacturing process, it is difficult to form a thin, uniform coating film on the surface of the raw material powder. For this reason, the coating film provided on the surface of the metal magnetic particles can cause deterioration of the magnetic properties (e.g., magnetic permeability) of the magnetic substrate.

[0005] To obtain a magnetic substrate with excellent magnetic properties, it is more desirable to cover the surfaces of metal magnetic particles with an insulating oxide film obtained by oxidizing elements contained in the raw material powder, rather than using a coating film, which is difficult to thin. JP 2014-143301 A (Patent Document 1) describes a magnetic substrate containing metal magnetic particles on whose surfaces an oxide film containing Si oxide and Cr oxide is formed. The metal magnetic particles are produced by heat-treating a soft magnetic alloy powder containing Fe, Si, and Cr at 750°C. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-143301 Summary of the Invention [Problem to be solved by the invention]

[0007] As described in Patent Document 1, a first oxide film mainly composed of silica (SiO2) is formed on the surface of metal magnetic particles produced by heat-treating raw material powder containing Fe, Si, and Cr, and a second oxide film mainly composed of chromium oxide (III) (Cr2O3) is formed on the outer surface of this first oxide film.

[0008] The raw material powder may contain Al. A first oxide film, primarily composed of silica (SiO2), is formed on the surface of the metal magnetic particles produced by heat-treating the raw material powder containing Fe, Si, and Al, and a second oxide film, primarily composed of alumina (Al2O3), is formed on the outer surface of this first oxide film.

[0009] The oxide film formed on the surface of the metal magnetic particles is thinner than the coating film, and therefore may not provide sufficient insulation to the magnetic substrate. In soft magnetic substrates in which the metal magnetic particles are insulated by the oxide film, further improvement in the insulation between the metal magnetic particles is desired.

[0010] It is an object of the invention disclosed herein to solve or alleviate at least some of the problems mentioned above, and one more specific object of the invention is to provide a magnetic substrate having improved insulating properties.

[0011] Objects of the present invention other than those mentioned above will become clear throughout the entire description of the specification. The inventions described in the claims may solve problems other than those grasped from the "problem to be solved by the invention." The various inventions disclosed in this specification may be collectively referred to as "the present invention." [Means for solving the problem]

[0012] In one embodiment, the magnetic substrate comprises a plurality of metal magnetic particles containing Fe, Si, and the element α, a first oxide film covering the surface of each of the plurality of metal magnetic particles, and a second oxide film covering the surface of the first oxide film. The first oxide film is primarily composed of an oxide of Si. The second oxide film is primarily composed of an oxide of the element α. A first thickness indicating the thickness of the first oxide film is thicker than a second thickness indicating the thickness of the second oxide film. [Effects of the Invention]

[0013] According to the embodiments of the invention disclosed herein, a magnetic substrate with improved insulating properties can be obtained. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view schematically illustrating a coil component including a magnetic composite according to an embodiment. [Figure 2] FIG. 2 is an exploded perspective view of the coil component of FIG. 1. [Figure 3] 2 is a cross-sectional view schematically showing a cross section of the coil device of FIG. 1 taken along line II. [Figure 4] 1 is an enlarged cross-sectional view schematically illustrating a partial region of a cross section of a magnetic substrate according to an embodiment. [Figure 5] 1 shows a line profile obtained by EDS analysis along scan line SL1. [Figure 6] FIG. 3 is a flow chart showing a manufacturing process of a coil component according to an embodiment of the present invention. [Figure 7] FIG. 10 is a flowchart showing a manufacturing process for a coil component according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Various embodiments of the present invention will be described below with appropriate reference to the drawings. Components common to multiple drawings are designated by 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.

[0016] Some embodiments disclosed herein relate to a magnetic substrate of a coil component. The magnetic substrate includes a plurality of metal magnetic particles. Hereinafter, a coil component 1 including a magnetic substrate 10 according to one embodiment will be described first with reference to FIGS. 1 to 3 , and then the microstructure of the magnetic substrate will be described with reference to FIGS. 4 and 5 .

[0017] Fig. 1 is a perspective view that schematically shows 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 taken along line II in Fig. 1. For ease of explanation, external electrodes are not shown in Fig. 2.

[0018] 1 to 3 show a laminated inductor as an example of a coil component 1. The illustrated laminated inductor is an 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.

[0019] As shown in the figure, the coil device 1 includes a base 10, a coil conductor 25 disposed inside the base 10, a first external electrode 21 disposed on the surface of the base 10, and a second external electrode 22 disposed on the surface of the base 10 at a position spaced apart from the first 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" as defined in the claims. When the base has poor insulation properties, the external electrodes are attached to the surface of the base via an insulating film with excellent insulation properties. As described below, the metal magnetic particles contained in the base 10 to which the present invention is applied have improved insulation properties, so the first external electrode 21 and the second external electrode 22 can be attached directly to the base 10 without an insulating film. In other words, the first external electrode 21 and the second external electrode 22 may be attached directly to the surface of the base 10.

[0020] The substrate 10 includes a plurality of metal magnetic particles. The average particle size of the plurality of metal magnetic particles included in the substrate 10 is, for example, in the range of 1 to 20 μm. The average particle size of the metal magnetic particles included in the substrate 10 may be 1 to 10 μm, or may be 2 to 8 μm. The average particle size of the metal magnetic particles included in the substrate 10 can be determined, for example, as follows. First, the substrate 10 is cut or polished along its thickness direction (T-axis direction) to expose a cross section, and an SEM image of the cross section is obtained by photographing the cross section with a scanning electron microscope (SEM) at a magnification of approximately 10,000 to 50,000 times. Next, the circle-equivalent diameter (Heywood diameter) of each metal magnetic particle is determined by image analysis of the SEM image. The average circle-equivalent diameter of each metal magnetic particle in the SEM image can then be determined as the average particle size of the metal magnetic particles.

[0021] The first external electrode 21 is electrically connected to one end of the coil conductor 25 , and the second external electrode 22 is electrically connected to the other end of the coil conductor 25 .

[0022] 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 the first external electrode 21 to the land portion 3a and connecting the second external electrode 22 to the land portion 3b. A circuit board 2 according to one 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 in various electronic devices. Electronic devices on which the circuit board 2 can be mounted include smartphones, tablets, game consoles, automotive electrical components, servers, and various other electronic devices. The coil component 1 can also be built into the board.

[0023] The coil component 1 may be an inductor, a transformer, a filter, a reactor, an inductor array, or any of various other coil components. The coil component 1 may be a coupled inductor, a choke coil, or any of various other magnetically coupled coil components. The uses of the coil component 1 are not limited to those explicitly described in this specification.

[0024] When the coil component 1 is an inductor array or a magnetically coupled coil component, the coil conductor 25 is composed of two or more conductor portions that are electrically insulated from each other within the base 10.

[0025] In one embodiment, the base 10 is configured so 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 terms "rectangular parallelepiped" or "rectangular parallelepiped shape" do not necessarily mean "rectangular parallelepiped" in the strict mathematical sense. The dimensions and shape of the base 10 are not limited to those explicitly described in this specification.

[0026] The substrate 10 has a first major surface 10a, a second major 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 substrate 10 is defined by these six surfaces. The first major surface 10a and the second major surface 10b form the two ends of the substrate 10 in the height direction, the first end surface 10c and the second end surface 10d form the two ends of the substrate 10 in the length direction, and the first side surface 10e and the second side surface 10f form the two ends of the substrate 10 in the width direction. As shown in FIG. 1 , the first major surface 10a, which is located on the upper side of the substrate 10, may be referred to as the "upper surface" in this specification. Similarly, the second major 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 substrate 2a, and therefore the second main surface 10b is sometimes called the "mounting surface." The top surface 10a and the bottom 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.

[0027] 2, the substrate 10 has a body layer 20, a lower cover layer 19 provided on the lower surface of the body layer 20, and an upper cover layer 18 provided on the upper surface of the body layer 20. The upper cover layer 18, the lower cover layer 19, and the body layer 20 are components of the substrate 10.

[0028] The main body layer 20 includes magnetic films 11 to 17. In the main body layer 20, magnetic film 17, magnetic film 16, magnetic film 15, magnetic film 14, magnetic film 13, magnetic film 12, and magnetic film 11 are stacked in this order from the negative side to the positive side in the T-axis direction.

[0029] 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 using a screen printing method. 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 may be a PVB resin, a phenolic resin, or a resin known as a binder resin other than the above, or a mixture thereof. 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 to suppress excessive oxidation of the Cu powder during degreasing. The conductive paste may contain an adjuster for adjusting thixotropy. The conductive patterns C11 to C17 may be formed using other materials and methods, for example, sputtering, inkjet printing, or other known methods.

[0030] 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 that penetrate 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. Each of the conductor patterns C11 to C17 is electrically connected to an adjacent conductor pattern via the vias V1 to V6.

[0031] The end of the conductor pattern C11 opposite to the end connected to the via V1 is connected to the second external electrode 22. The end of the conductor pattern C17 opposite to the end connected to the via V6 is connected to the first external electrode 21.

[0032] 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 are sometimes collectively referred to as "cover layer magnetic films." Furthermore, the components of the substrate 10 do not necessarily have a laminated structure in which multiple magnetic films are stacked. For example, the upper cover layer 18 may be a molded body made of a magnetic material, rather than a laminate in which multiple magnetic films 18a-18d are stacked.

[0033] 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 lead-out portion 25b1 extending from one end of the winding portion 25a to the first end face 10c of the base 10, and a lead-out portion 25b2 extending from the other end of the winding portion 25a to the second end face 10d of the base 10. Conductor patterns C11 to C17 and vias V1 to V6 form the spiral winding portion 25a. That is, the winding portion 25a has the conductor patterns C11 to C17 and the vias V1 to V6.

[0034] Next, the microstructure of the substrate 10 will be described with reference to Figures 4 and 5. Figure 4 is an enlarged cross-sectional view that schematically shows a partial region (region A1) of the cross section shown in Figure 3. Figure 4 also shows a schematic representation of a portion of each of two of the numerous metal magnetic particles contained in the substrate 10. Figure 5 shows a line profile obtained by EDS analysis along the scan line SL1 shown in Figure 4.

[0035] As shown in FIG. 4, the multiple metal magnetic particles constituting the base 10 include first metal magnetic particles 30a and second metal magnetic particles 30b. The first metal magnetic particles 30a and the second metal magnetic particles 30b are arranged adjacent to each other. In FIG. 4, the cross sections of the first metal magnetic particles 30a and the second metal magnetic particles 30b are depicted as circular for convenience. The metal magnetic particles contained in the base 10 can have various cross-sectional shapes other than circular. The metal magnetic particles contained in the base 10 are mainly composed of Fe. The first metal magnetic particles 30a and the second metal magnetic particles 30b are examples of metal magnetic particles contained in the base 10. The description of the first metal magnetic particles 30a and the second metal magnetic particles 30b also applies to metal magnetic particles other than the first metal magnetic particles 30a or the second metal magnetic particles 30b contained in the base 10.

[0036] The metal magnetic particles contained in the substrate 10 preferably contain Fe at a content ratio of 94 wt% or more so that the substrate 10 has high magnetic saturation characteristics. The Fe content ratio of the metal magnetic particles contained in the substrate 10 is measured by cutting the substrate 10 along the coil axis Ax to expose a cross section of the substrate 10 and performing energy dispersive X-ray spectroscopy (EDS) analysis on this cross section. The Fe content ratio can be measured using 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 Fe content ratio 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 Ametec Co., Ltd. at an acceleration voltage of 5 kV. The contents of elements other than Fe contained in the first metal magnetic particles 30a are also measured by SEM-EDS analysis, similar to the Fe content ratio.

[0037] In one embodiment of the present invention, the crystalline regions of the metal magnetic particles contained in the substrate 10 occupy a larger area than the amorphous regions. Increasing the crystalline regions of the metal magnetic particles can improve the magnetic permeability of the substrate 10. In one embodiment of the present invention, the metal magnetic particles contained in the substrate 10 have a small number of crystals, specifically, three or less. It is desirable that at least a portion of the metal magnetic particles contained in the substrate 10 are single crystals having a single crystal structure. When an electron diffraction pattern is measured for a sample containing the metal magnetic particles removed from the substrate 10, and this diffraction pattern forms a two-dimensional point array net pattern (lattice-like spots), it can be determined that the metal magnetic particles contained in the sample are single crystals. By forming the metal magnetic particles from a small number of crystals, the magnetic permeability of the substrate 10 can be further improved.

[0038] The surface of each metal magnetic particle included in the substrate 10 is coated with multiple layers of oxide films with excellent insulating properties. Therefore, the metal magnetic particles included in the substrate 10 are electrically insulated from one another. For example, at least between the first metal magnetic particle 30a and the second metal magnetic particle 30b, the surface 31a of the first metal magnetic particle 30a is covered with a first inner oxide film 41a, and the surface of the first inner oxide film 41a is covered with a first outer oxide film 42a. The surface 31b of the second metal magnetic particle 30b is covered with a second inner oxide film 41b, and the surface of the second inner oxide film 41b is covered with a second outer oxide film 42b. The first inner oxide film 41a preferably covers the entire surface of the first metal magnetic particle 30a, and the second inner oxide film 41b preferably covers the entire surface of the second metal magnetic particle 30b. The first inner oxide film 41a is in direct contact with the outer surface of the first metal magnetic particle 30a. The second inner oxide film 41b is in direct contact with the outer surface of the second metal magnetic particle 30b.

[0039] In the substrate 10, each metal magnetic particle is bonded to an adjacent metal magnetic particle via an oxide film formed on the surface of each particle. That is, the oxide films formed on the surfaces of adjacent metal magnetic particles are bonded to each other, and the oxide film-covered metal magnetic particles are bonded to each other through the bonding of the oxide films. For example, a first metal magnetic particle 30a is bonded to a second metal magnetic particle 30b adjacent to the first metal magnetic particle 30a via at least one of a first outer oxide film 42a and a second outer oxide film 42b.

[0040] The metal magnetic particles contained in the base 10 can be obtained, for example, by heating raw material powder made of a soft magnetic material. As described in detail below, the base 10 can be produced by mixing soft magnetic metal powder made of a soft magnetic material with a resin to produce a mixed resin composition, and then heating this mixed resin composition. The heat treatment in the manufacturing process of the base 10 causes the additive elements contained in the raw material powder to diffuse to the surface of the raw material powder and oxidize on the surface of the raw material powder, thereby forming oxide films containing oxides of the elements contained in the raw material powder on the surfaces of the metal magnetic particles. For example, the first inner oxide film 41a, the first outer oxide film 42a, the second inner oxide film 41b, and the second outer oxide film 42b described above are all oxide films containing oxides of the additive elements contained in the raw material powder.

[0041] 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 two or more additive elements in addition to Fe. For example, the raw material powder of the metal magnetic particles contained in the base 10 contains Si and at least one element α as additives in addition to Fe. As described above, the content of Fe in the raw material powder can be 94 wt% or more. The content of Si in the raw material powder can be 3 wt% or more. The content of element α in the raw material powder can be less than 3 wt%. The content of element α in the raw material powder can be 1 wt% or more.

[0042] In one embodiment, the element α is, for example, an element that has a slower diffusion rate in Fe than Si. Also, the element α is an element that is more easily oxidized than Fe (i.e., has a smaller standard Gibbs energy of reaction of the oxide than Fe). For example, the element α is Cr or Al.

[0043] Both Si and element α are more easily oxidized than Fe. Therefore, when the raw material powder contains Si and element α in addition to Fe, oxidation of Fe in the raw material powder is suppressed during heat treatment. The raw material powder of metal magnetic particles may contain trace amounts of elements other than Fe, Si, and element α. Elements that may be contained in trace amounts in the raw material powder of metal magnetic particles may include vanadium (V), zinc (Zn), boron (B), carbon (C), and nickel (Ni).

[0044] The oxide films formed on the surfaces of the metal magnetic particles contained in the base 10 contain oxides of elements contained in the raw material powder. The "oxide films formed on the surfaces of the metal magnetic particles contained in the base 10" include the first inner oxide film 41a and the first outer oxide film 42a formed on the surfaces of the first metal magnetic particles 30a, and the second inner oxide film 41b and the second outer oxide film 42b formed on the surfaces of the second metal magnetic particles 30b. For ease of explanation, the oxide films formed on the surfaces of the metal magnetic particles contained in the base 10 may be simply referred to as "oxide films." Since Si and element α are more easily oxidized than Fe, when the raw material powder contains Si and element α in addition to Fe, the oxide film contains an oxide of Si and an oxide of element α. In addition to the above oxides, the insulating film may also contain an oxide of at least one of vanadium (V), zinc (Zn), boron (B), carbon (C), and nickel (Ni).

[0045] The first inner oxide film 41a and the second inner oxide film 41b contain silica (SiO2), an oxide of Si, as their main component. When EDS analysis reveals that the abundance of Si (atomic percentage (at%) of Si) is the highest among all elements other than oxygen contained in the first inner oxide film 41a, the first inner oxide film 41a can be said to contain silica as its main component. The first inner oxide film 41a has high insulating properties because it contains silica, which has a high volume resistivity, as its main component. The description of the first inner oxide film 41a also applies to the second inner oxide film 41b. In this specification, an oxide film covering the surface of a metal magnetic particle and containing silica as its main component may be referred to as a "Si oxide film." Si oxide films are also provided on the surfaces of metal magnetic particles contained in the substrate 10 other than the first metal magnetic particles 30a and the second metal magnetic particles 30b.

[0046] The silica contained in the first inner oxide film 41a and the second inner oxide film 41b is produced by the oxidation of Si contained in the raw material powder during heat treatment. Since Si has a fast diffusion rate in Fe and a small standard Gibbs energy of reaction of oxides, Si diffuses to the surface of the raw material powder during heat treatment of the raw material powder mainly composed of Fe. Then, Si combines with oxygen on the surface of the raw material powder to form silica.

[0047] The first outer oxide film 42a and the second outer oxide film 42b contain an oxide of the element α as a primary component. When the element α is Cr, the primary component of the first outer oxide film 42a and the second outer oxide film 42b is chromium (III) oxide (Cr2O3). When the element α is Al, the primary component of the first outer oxide film 42a and the second outer oxide film 42b is alumina (Al2O3). When the abundance (at%) of the element α is the highest among elements other than oxygen contained in the first outer oxide film 42a in EDS analysis, it can be said that the first outer oxide film 42a contains an oxide of the element α as a primary component. The description of the first outer oxide film 42a also applies to the second outer oxide film 42b. In this specification, an oxide film containing chromium (III) oxide as a primary component, which is formed on the outer surface of a Si oxide film provided on the surface of a metal magnetic particle, is referred to as a "Cr oxide film." Furthermore, an oxide film containing alumina as its main component, which is formed on the outer surface of a Si oxide film provided on the surface of a metal magnetic particle, is sometimes called an “Al oxide film.” A Cr oxide film or an Al oxide film is also provided on the surface of metal magnetic particles contained in base 10 other than first metal magnetic particles 30a and second metal magnetic particles 30b.

[0048] The oxide of element α contained in the first outer oxide film 42a and the second outer oxide film 42b is generated by the oxidation of element α contained in the raw material powder during heat treatment. Because the diffusion rate of element α in Fe is slower than that of Si, element α is oxidized after Si is oxidized on the surface of the raw material powder. Therefore, the first outer oxide film 42a and the second outer oxide film 42b are formed outside the first inner oxide film 41a and the second inner oxide film 41b, which are mainly composed of silica, respectively.

[0049] As shown in FIG. 4, the first inner oxide film 41a is thicker than the first outer oxide film 42a. The second inner oxide film 41b is thicker than the second outer oxide film 42b. More generally, in the metal magnetic particles contained in the base 10, the Si oxide film is thicker than an oxide film (Cr oxide film or Al oxide film) whose main component is an oxide of element α. Silica has a higher volume resistivity than chromium (III) oxide or alumina. Therefore, by making the first inner oxide film 41a and the second inner oxide film 41b, which are mainly composed of silica, thicker than the first outer oxide film 42a and the second outer oxide film 42b, which are mainly composed of chromium (III) oxide or alumina, the insulating properties of the first metal magnetic particles 30a and the second metal magnetic particles 30b can be improved.

[0050] In conventional magnetic substrates, the Si oxide film is thinner than the Cr oxide film on the surface of the metal magnetic particles. For example, Patent Document 1 (see FIG. 6(b)) shows the results of EDS analysis of the surfaces of metal magnetic particles obtained by heating Fe-Si-Cr-based raw material powder. The EDS analysis results reveal that the Cr oxide film is thicker than the Si oxide film on the surface of the metal magnetic particles. As described above, when the raw material powder is heated, Fe, Si, and Cr or Al contained in the raw material powder diffuse toward the surface of the raw material powder. Because Si has the fastest diffusion rate among the major elements contained in the raw material powder, silica is formed on the surface of the raw material powder. However, as the heat treatment progresses, chromium (III) oxide and alumina are also formed. As the amount of chromium (III) oxide and alumina produced increases, a passive film of chromium (III) oxide or alumina is formed on the surface of the raw material powder. When this passive film is formed, the Si on the surface of the raw material powder cannot bond with oxygen, and the passive film inhibits the growth of the Si oxide film. On the other hand, the passive film of chromium (III) oxide or alumina grows as long as the Cr and Al continue to diffuse outward from the inside of the raw material powder. Because the passive film of chromium (III) oxide or alumina inhibits the growth of the Si oxide film, the Cr oxide film or Al oxide film on the surface of conventional metal magnetic particles becomes thicker than the Si oxide film.

[0051] In contrast, in one embodiment of the present invention, as described above, the first inner oxide film 41a, which is primarily composed of silica, is thicker than the first outer oxide film 42a, which is primarily composed of chromium (III) oxide or alumina, and the second inner oxide film 41b, which is primarily composed of silica, is thicker than the second outer oxide film 42b, which is primarily composed of chromium (III) oxide or alumina. The inventors of the present invention have noticed that the diffusion rate of Si in Fe is faster than that of the element α (Cr or Al) and that the diffusion rate is strongly dependent on temperature according to the Arrhenius equation, and have discovered that by heating at a temperature lower than conventional temperatures at which the thermal diffusion of Si is active but the thermal diffusion of Cr or Al is not active, a thick Si oxide film can be formed before Cr or Al form a passivation film on the surface of the raw material powder. Using this principle, in one embodiment of the present invention, the raw material powder is first heated at a relatively low temperature (500 to 700°C, as described below) in a first stage of heat treatment to form a thick Si oxide film on the surface of the raw material powder, and after the thick Si oxide film has formed on the surface of the raw material powder, the raw material powder is heated at a relatively high temperature (750 to 900°C, as described below) in a second stage of heat treatment to make the Si oxide film (e.g., first inner oxide film 41a and second inner oxide film 41b) formed on the surface of the metal magnetic particles thicker than the Cr oxide film or Al oxide film (e.g., first outer oxide film 42a and second outer oxide film 42b). This improves the insulating properties of the metal magnetic particles contained in the substrate 10.

[0052] A first inner oxide film 41a, a first outer oxide film 42a, a second inner oxide film 41b, and a second outer oxide film 42b are interposed between adjacent first metal magnetic grains 30a and second metal magnetic grains 30b within the substrate 10. By making the first inner oxide film 41a and the second inner oxide film 41b, which are primarily composed of silica, which has a high volume resistivity, thicker than the first outer oxide film 42a and the second outer oxide film 42b, the total thickness of the oxide films provided on the surfaces of the metal magnetic particles can be reduced to ensure the insulation required for the substrate 10. By reducing the total thickness of the oxide films interposed between adjacent metal magnetic particles, the filling rate of the metal magnetic particles in the substrate 10 can be increased, thereby improving the magnetic permeability of the substrate 10. Therefore, by making the Si oxide film provided on the surfaces of the metal magnetic particles thicker than the Cr oxide film and the Al oxide film, the magnetic permeability of the substrate 10 can be improved while ensuring the insulation of the substrate 10.

[0053] When the raw material powder is heated, Si has the property of being less likely to diffuse into grain boundaries than Cr or Al. Therefore, the thickness of the Si oxide film (e.g., the first inner oxide film 41a and the second inner oxide film 41b) can be precisely controlled by the Si content in the raw material powder, the temperature during the heat treatment, and the heating time.

[0054] The presence and thickness of each oxide film can be confirmed as follows. Specifically, an analytical sample is prepared by thinning the substrate 10 so that the observation surface is a plane parallel to a plane extending along the coil axis (e.g., the LT plane). An observation area spanning two metal magnetic particles is set on the observation surface of this thinned analytical sample. SEM-EDS is then performed on this observation area to obtain mapping data for Fe, Si, the element α, and O (oxygen). The presence of each oxide film can be confirmed based on this mapping data.

[0055] FIG. 4 shows a cross section along the LT plane of the substrate 10 containing two metal magnetic particles (first metal magnetic particle 30a and second metal magnetic particle 30b). Hereinafter, we will further describe the detection of oxide films based on mapping data, assuming that the region A1 shown in FIG. 4 represents the observation surface of a thin-sectioned analytical sample. Detection of each oxide film by SEM-EDS analysis in the observation region A1 shown in FIG. 4 can be performed, for example, as follows: First, SEM-EDS is performed on the observation region A1 to obtain mapping data for the quantified elements contained in the observation region A1 of the analytical sample. The observation region A1 is, for example, a square region measuring 200 nm on each side. The quantified elements include Fe, Si, element α, and O. Next, line analysis is performed based on the obtained mapping data. Specifically, a scanning line SL1 extending from the first metal magnetic particle 30a to the second metal magnetic particle 30b is set within the observation region A1, and the mapping data for the quantified elements is reconstructed along this scanning line SL1 to create a line profile for each of the quantified elements. The length of the scanning line SL1 is set to, for example, 50 nm, and the length of the scanning line SL1 for obtaining a line profile can be changed as appropriate.

[0056] Figure 5 shows an example of a line profile reconstructed along scan line SL1 from mapping data acquired by SEM-EDS in region A1 of the analytical sample. The line profile in Figure 5 is an example of a graph reconstructed along scan line SL1 from mapping data of the elements Fe, Si, Cr, and O obtained by performing SEM-EDS on an analytical sample prepared from a substrate 10 containing metal magnetic particles produced by heating an Fe-Si-Cr-based raw material powder. In Figure 4, the horizontal axis indicates the detection position on scan line SL1, and the vertical axis indicates the detection intensity calculated based on the count numbers of Fe, Si, Cr, and O at each detection position.

[0057] The ends of the horizontal axis of the graph in Fig. 5 correspond to the ends of the scan line SL1 in Fig. 4, so the regions near the ends of the horizontal axis of the graph in Fig. 5 correspond to the first metal magnetic particles 30a and the second metal magnetic particles 30b, respectively. In the graph shown in Fig. 5, there are regions near the ends of the scan line SL1 where Fe is contained as a main component at approximately 94 at % or more, so it can be determined that the region near the left end of the graph corresponds to the first metal magnetic particles 30a, and the region near the right end of the graph corresponds to the second metal magnetic particles 30b.

[0058] In FIG. 5, moving to the right along the horizontal axis from the region corresponding to the first metal magnetic particle 30a, the detected intensity of Si increases and conversely, the detected intensity of Fe decreases. The line profile of Si intersects with the line profile of Fe at a position approximately 9 nm from the viewpoint of the scan line SL1. In a region approximately 20 nm wide to the right of the intersection of the line profile of Fe and the line profile of Si, the Si content ratio is highest among Fe, Si, and Cr. This region with the highest Si content ratio corresponds to the first inner oxide film 41a. Moving further right along the horizontal axis from the region corresponding to the first inner oxide film 41a, the detected intensity of Si decreases and conversely, the detected intensity of Cr increases, and the line profile of Si intersects with the line profile of Fe. The intersection of the line profile of Si and the line profile of Cr marks the boundary between the first inner oxide film 41a and the first outer oxide film 42a located outside it. Similarly, by moving from the right end of the graph in Figure 5 to the left while focusing on the content ratios of Fe, Si, and Cr, the boundary between the second metal magnetic grain 30b and the second inner oxide film 41b, and the boundary between the second inner oxide film 41b and the second outer oxide film 42b can be determined.

[0059] The thickness of each oxide film can be determined by measuring the horizontal length of the first inner oxide film 41a, the first outer oxide film 42a, the second inner oxide film 41b, and the second outer oxide film 42b. In the example shown in FIG. 5, the thicknesses of the first inner oxide film 41a, the first outer oxide film 42a, the second inner oxide film 41b, and the second outer oxide film 42b are D1a, D2a, D1b, and D2b, respectively. The thickness D1a of the first inner oxide film 41a is greater than the thickness D2a of the first outer oxide film 42a. The thickness D1b of the second inner oxide film 41b is greater than the thickness D2b of the second outer oxide film 42b.

[0060] In one embodiment of the present invention, the thickness D1a of the first inner oxide film 41a is preferably at least twice the thickness D2a of the first outer oxide film 42a. Furthermore, the thickness D1b of the second inner oxide film 41b is preferably at least twice the thickness D2b of the second outer oxide film 42b. By making the thickness D1a of the first inner oxide film 41a at least twice the thickness D2a of the first outer oxide film 42a and the thickness D1b of the second inner oxide film 41b at least twice the thickness D2b of the second outer oxide film 42b, the first inner oxide film 41a and the second inner oxide film 41b, which are primarily composed of silica with high volume resistivity, can improve the insulation of the first metal magnetic particles 30a and the second metal magnetic particles 30b.

[0061] In one embodiment of the present invention, the thickness D1a of the first inner oxide film 41a is preferably four times or less the thickness D2a of the first outer oxide film 42a. Furthermore, the thickness D1b of the second inner oxide film 41b is preferably four times or less the thickness D2b of the second outer oxide film 42b. By setting the thickness D1a of the first inner oxide film 41a to four times or less the thickness D2a of the first outer oxide film 42a and the thickness D1b of the second inner oxide film 41b to four times or less the thickness D2b of the second outer oxide film 42b, a decrease in the filling rate of the metal magnetic particles in the base 10 can be suppressed.

[0062] In one embodiment of the present invention, the thickness D1a of the first inner oxide film 41a and the thickness D2a of the second outer oxide film 42a can be set to 10 to 25 nm, provided that the thickness D2a is smaller than the thickness D1a of the first inner oxide film 41a and the thickness D2b of the second outer oxide film 42b.

[0063] It is desirable that the insulation between the first metal magnetic grains 30a and the second metal magnetic grains 30b be ensured mainly by the first inner oxide film 41a and the second inner oxide film 41b. In other words, it is desirable that the first metal magnetic grains 30a and the second metal magnetic grains 30b be electrically insulated by the first inner oxide film 41a and the second inner oxide film 41b, regardless of the thicknesses of the first outer oxide film 42a and the second outer oxide film 42b. By ensuring electrical insulation between the first metal magnetic grains 30a and the second metal magnetic grains 30b by the first inner oxide film 41a and the second inner oxide film 41b, the thicknesses of the first outer oxide film 42a and the second outer oxide film 42b can be reduced, thereby improving the filling rate of the metal magnetic particles in the base 10. Furthermore, because Cr and Al tend to diffuse into grain boundaries during heat treatment of the magnetic powder, it is difficult to accurately control the thicknesses of the first outer oxide film 42a and the second outer oxide film 42b. Therefore, regardless of the thickness of the first outer oxide film 42a and the second outer oxide film 42b, the first inner oxide film 41a and the second inner oxide film 41b provide the resistance required for insulation, thereby more reliably insulating the first metal magnetic grains 30a and the second metal magnetic grains 30b.

[0064] If the thickness of the first inner oxide film 41a or the second inner oxide film 41b varies significantly, dielectric breakdown may occur in the thin portions of the first inner oxide film 41a or the second inner oxide film 41b. Therefore, it is desirable that the thicknesses of the first inner oxide film 41a and the second inner oxide film 41b be highly uniform. In one embodiment of the present invention, it is desirable that the standard deviation Cv1 of the thickness of the first inner oxide film 41a and the standard deviation Cv2 of the thickness of the second inner oxide film 41b are both 3 nm or less. The standard deviation Cv1 of the thickness of the first inner oxide film 41a refers to the standard deviation calculated from measurements of the thickness of the first inner oxide film 41a at five different circumferential positions around the geometric center of the first metal magnetic particle 30a. The standard deviation Cv2 of the film thickness of the second inner oxide film 41b means the standard deviation calculated from the measured values ​​of the film thickness of the second inner oxide film 41b measured at five different circumferential positions around the geometric center of the second metal magnetic grain 30b.

[0065] By fabricating a substrate from raw material powder coated with a mixture of tetraethoxysilane (TEOS) and ethanol, a silica-based coating film can be formed on the surface of the metal magnetic particles. In one embodiment of the present invention, the Si oxide films (e.g., the first inner oxide film 41a and the second inner oxide film 41b) formed on the surface of the metal magnetic particles constituting the substrate 10 are silica-based oxide films formed by the oxidation of Si contained in the raw material powder on the surface of the raw material powder during heat treatment of the raw material powder containing Fe and Si. These films are not coating films formed by applying a coating liquid. As shown in the graph of FIG. 5, the first inner oxide film 41a and the second inner oxide film 41b are silica-based oxide films, but also contain Fe and Cr diffused during the heat treatment of the raw material powder. On the other hand, silica coating films typically do not contain any constituent elements of the raw material powder other than Si. Therefore, the first inner oxide film 41a and the second inner oxide film 41b can be distinguished from silica-containing coating films in that they contain elements derived from the raw material powder other than Si (Fe and Cr in the example of FIG. 5).

[0066] Next, an example of a method for manufacturing the coil component 1 will be described with reference to FIG. 6. Because the base 10 is produced in the process of manufacturing the coil component 1, the method for manufacturing the base 10 will also be described with reference to FIG. 6. In the following description, it is assumed that the coil component 1 is manufactured by a sheet lamination method. The coil component 1 may also 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.

[0067] First, in step S1, a magnetic sheet is produced. The magnetic sheet is produced from a magnetic material paste obtained by kneading soft magnetic metal powder (raw material powder), which is the raw material for metal magnetic particles, with a binder resin and a solvent. This raw material powder is made of a soft magnetic metal material. The raw material powder contains Fe, Si, and the element α. In the following description of the manufacturing method, for ease of understanding, it is assumed that the raw material powder contains Cr as the element α. The raw material powder can contain 94 wt% or more of Fe. The raw material powder contains more Si than Cr on a mass basis. The raw material powder contains, for example, 3 wt% or more of Si.

[0068] The binder resin for the magnetic material paste is, for example, an acrylic resin. The binder resin for the magnetic material paste may be a PVB resin, a phenolic resin, a resin known as a binder resin other than those mentioned 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 common method. A sheet-shaped molded body is obtained by drying the magnetic material paste applied to the surface of this base film. A plurality of magnetic sheets are produced by pressure-molding this sheet-shaped molded body in a mold at a molding pressure of about 10 to 100 MPa.

[0069] 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.

[0070] By applying a conductive paste to a magnetic material sheet, unsintered conductor patterns that will become conductor patterns C11 to C17 after firing are formed on the magnetic material sheet. Multiple unsintered conductor patterns are formed on each magnetic material sheet. For example, multiple unsintered conductor patterns that will become conductor pattern C11 after firing are formed on a certain magnetic material sheet. Through holes that penetrate the magnetic material sheet in the stacking direction are formed in some of the magnetic material sheets. When a conductive paste is applied to a magnetic material sheet with through holes, the conductive paste is also embedded in the through holes. In this way, unsintered vias that will become vias V1 to V5 after firing are formed in the through holes of the magnetic material sheet. The conductive paste is applied to the magnetic material sheet by, for example, a screen printing method.

[0071] Next, in step S3, the magnetic sheets prepared in step S1 are stacked to prepare an upper laminate that will become the upper cover layer 18, an intermediate laminate that will become the main layer 20, and a lower laminate that will become 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 that do not have unsintered conductor patterns formed thereon. The four magnetic sheets of the upper laminate will become magnetic films 18a-18d in the finished coil component 1, and the four magnetic sheets of the lower laminate will become magnetic films 19a-19d in the finished coil component 1. The intermediate laminate is formed by stacking seven magnetic sheets with unsintered conductor patterns formed thereon in a predetermined order. The seven magnetic sheets of the intermediate laminate will become magnetic films 11-17 in the finished coil component 1. The intermediate laminate prepared as described above is sandwiched between the upper laminate and the lower laminate, and the upper laminate and the lower laminate are thermocompression bonded to the intermediate laminate to obtain the main laminate. Next, the main laminate is divided into individual pieces 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 will become base 10 after heat treatment and an unfired conductor pattern that will become coil conductor 25 after heat treatment. The molded body including the element that will become base 10 after heat treatment and an unfired conductor pattern that will become coil conductor 25 after heat treatment may be produced by a method other than the sheet lamination method.

[0072] Next, in step S4, the green body produced in step S3 is degreased. The degreasing of the green body can be performed in a non-oxygen atmosphere such as a nitrogen atmosphere. By performing the degreasing in a non-oxygen atmosphere, it is possible to prevent the Fe contained in the raw material powder from being oxidized during the degreasing. The degreasing is performed, for example, at 300 to 500°C for 30 to 60 minutes. The degreasing decomposes the heat-decomposable resin contained in the green body, so no heat-decomposable resin remains in the green body after the degreasing is completed. By using the same heat-decomposable resin for the binder resin for the conductive paste as for the magnetic material paste, the binder resin contained in the unsintered conductor pattern is also thermally decomposed during the degreasing of step S4. In this way, in step S4, both the magnetic material sheet and the unsintered conductor pattern that constitute the green body are degreased.

[0073] In the debinding process of step S4, the raw material powder is heated to a temperature of about 300 to 500°C, causing elements in the raw material powder to thermally diffuse toward the outer surface of each powder. The raw material powder is mainly composed of Fe. The diffusion rate of Si in Fe is faster than the diffusion rate of Cr in Fe. Therefore, the debinding process increases the concentration of Si, which has a faster diffusion rate in Fe, near the surface of each powder constituting the raw material powder.

[0074] Next, in step S5, the degreased compact is subjected to a first heating treatment. The first heating treatment is performed at a first heating temperature of 500 to 700°C in a low-oxygen atmosphere containing oxygen in the range of 5 to 1000 ppm. By heating the raw material powder at 500 to 700°C in an oxygen-containing atmosphere, thermal diffusion of Si toward the surface of each raw material powder is further promoted. The Si diffused near the surface combines with oxygen in the atmosphere, producing silica on the surface of each powder. Cr in the raw material powder also diffuses near the surface of each powder, but because its diffusion rate in Fe is slower than that of Si, the Cr concentration near the surface of each powder is lower than the Si concentration during the first heating treatment. Therefore, oxidation of Si occurs more actively than oxidation of Cr during the first heating treatment. Therefore, among the additive elements contained in each raw material powder, Si oxide, which has a high concentration near the surface and is easily oxidized, is mainly produced during the first heating treatment. A Si oxide film composed mainly of Si oxide is formed on the surface of the raw material powder by the first heating treatment. The first heating time for the first heat treatment is set to be sufficient to form a Si oxide film of a desired thickness on the surface of the raw material powder. The first heating time can be, for example, between 1 hour and 6 hours. As described above, the film thickness D1a of the Si oxide film (e.g., first inner oxide film 41a or second inner oxide film 41b) formed on the surface of the metal magnetic particle can be set to 10 to 50 nm. By extending the first heating time, the film thickness of the Si oxide film can be increased.

[0075] Next, in step S6, the compact after the first heating treatment is subjected to a second heating treatment at a second heating temperature higher than the first heating temperature for a second heating time. The second heating treatment is preferably performed in an atmosphere with a higher oxygen concentration than the atmosphere in which the first heating treatment was performed to promote the formation of a Cr oxide film. For example, the second heating treatment is performed in an atmosphere containing oxygen in the range of 500 to 10,000 ppm. The second heating temperature and second heating time are determined so that a Cr oxide film is formed on the surface of the raw material powder on which the Si oxide film was formed in step S5. The second heating temperature can be, for example, a temperature between 750 and 900°C. During the second heating treatment, the raw material powder is heated at the second heating temperature, so the diffusion rate of Cr is increased, and a sufficient amount of Cr is diffused on the surface of the raw material powder to form a Cr oxide film. Therefore, Cr comes into contact with oxygen on the surface of the raw material powder on which the Si oxide film has been formed (the outer surface of the Si oxide film) through the second heating treatment, generating chromium (III) oxide. The chromium (III) oxide thus generated forms the Cr oxide film.

[0076] In the second heat treatment in step S6, if unoxidized Si is present on the surface of the raw material powder, SiO2 is generated on the surface of the raw material powder, and the Si oxide film grows further. Also, in the second heat treatment, if magnetite is present near the Cr that has diffused on the surface of the raw material powder, the Cr and magnetite combine to generate chromite (FeCr2O4).

[0077] Since the standard reaction Gibbs energy of Cr oxide is larger (its absolute value is smaller) than that of Si oxide, the second heat treatment may be performed in an oxygen concentration higher than that of the first heat treatment to promote the oxidation of Cr. For example, the second heat treatment may be performed in a low-oxygen atmosphere of 1000 to 10000 ppm.

[0078] In the second heat treatment, in addition to oxidation of the raw material powder, sintering of the conductor powder in the unsintered conductor pattern also occurs. The sintering of the conductor powder in the unsintered conductor pattern results in the coil conductor 25. When copper powder is used as the conductor powder, the copper crystals are densely sintered to form the coil conductor 25.

[0079] By the second heat treatment, adjacent metal magnetic particles are bonded to each other via the insulating films (specifically, Cr oxide films) formed on their surfaces, thereby obtaining a base 10 in which the metal magnetic particles are bonded to each other.

[0080] In this way, by heating the raw material powder at a relatively low first heating temperature in the first heating treatment and then continuing to heat the raw material powder at a relatively high second heating temperature in the second heating treatment, thick Si oxide films (first inner oxide film 41a and second inner oxide film 41b) can be formed on the surfaces of the raw material powder, and then Cr oxide films (first outer oxide film 42a and second outer oxide film 42b) can be formed on the surfaces of the Si oxide films. The thickness of the Si oxide films can be increased by extending the first heating time for the first heating treatment or by increasing the Si content in the raw material powder.

[0081] As described above, the thickness of the Si oxide film can be set to 10 to 50 nm. By setting the thickness of the Si oxide film to 10 nm or more, the substrate 10 can be 5 A high volume resistivity of Ω·cm or more can be achieved. The volume resistivity of the substrate 10 can be measured in accordance with JIS-K6911.

[0082] The second heat treatment forms a thin Cr oxide film, which is a passive film, on the surface of the Si oxide film, and this Cr oxide film suppresses excessive growth of the Si oxide film. Furthermore, by adjusting the parameters of the second heat treatment (e.g., heating time), the Cr oxide film itself can be made thin. This prevents the oxide film on the surface of the metal magnetic particles from becoming excessively thick.

[0083] Next, in step S7, a first external electrode 21 and a second external electrode 22 are formed on the surface of the base 10 obtained in step S6. The first external electrode 21 is connected to one end of the coil conductor 25, and the second external electrode 22 is connected to the other end of the coil conductor 25. Before forming the first external electrode 21 and the second external electrode 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 penetrate into the gaps between the metal magnetic particles in the base 10. Then, by curing the resin impregnated into the base 10, the mechanical strength of the base 10 can be improved.

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

[0085] When the raw material powder contains Al instead of Cr as the element α, a similar mechanism occurs in which a Si oxide film of a sufficient thickness to ensure insulation is formed on the surface of the raw material powder by the first heat treatment, and then an Al oxide film mainly composed of alumina is formed on the surface of the Si oxide film by the second heat treatment.

[0086] Next, another embodiment of the method for manufacturing the coil device 1 will be described with reference to Fig. 7. The manufacturing method shown in Fig. 7 differs from the manufacturing method shown in Fig. 6 in that the raw material powder is preheated before the magnetic sheet is produced, and a Si oxide film is formed on the surface of the raw material powder by this preheating.

[0087] As shown in FIG. 7, first, in step S21, raw material powder, which is the raw material for the metal magnetic particles, is prepared and preheated. Preheating is performed at 300 to 700°C for 30 minutes to 1 hour. This preheating forms a Si oxide film on the surface of the raw material powder. Using the raw material powder with the Si oxide film formed on its surface in this way, steps S1 to S3 are performed as in FIG. 6, and a compact in which magnetic sheets are laminated is produced. In step S4, this compact is degreased.

[0088] Next, in step S22, the degreased compact is subjected to a heat treatment. The heat treatment in step S22 is performed under the same conditions as the second heat treatment in step S6 of FIG. 6. This second heat treatment causes a Cr oxide film to be further formed on the surface of the raw material powder covered with the Si oxide film contained in the compact, thereby turning the raw material powder into metal magnetic particles. The heat treatment in step S22 bonds adjacent metal magnetic particles together via the Cr oxide films formed on their surfaces. In this way, a base 10 in which metal magnetic particles are bonded together is obtained.

[0089] Next, in step S7, the first external electrode 21 and the second external electrode 22 are formed on the surface of the base 10 obtained in step S22. Through the above steps, the coil component 1 is produced.

[0090] In this way, by heating the raw material powder at a relatively low temperature in the preheating in step S21, a thick Si oxide film is formed on the surface of the raw material powder, and then by further heating the raw material powder at a relatively high temperature in the heat treatment in step S22, a Cr oxide film can be formed on the outside of the Si oxide film. [Example]

[0091] According to the flow chart shown in FIG. 6, a coil component 1 was fabricated from raw material powder containing Fe, Si, and Cr. The raw material powder had a composition ratio of Fe: 95 wt%, Si: 45 wt%, and Cr: 1%. A compact containing this raw material powder and a binder resin was fabricated according to the procedure in step S3. Next, this compact was subjected to a debinding treatment. In the debinding treatment, the compact was heated at 350°C for 60 minutes in a nitrogen atmosphere. Next, the debinding-treated compact was subjected to a first heat treatment. The first heat treatment was performed at 600°C for 2 hours in an atmosphere containing 500 ppm oxygen. Next, the heat-treated compact was subjected to a second heat treatment. The second heat treatment was performed in an atmosphere containing 5000 ppm oxygen. EDS analysis was performed on the substrate obtained by this second heat treatment. Specifically, the substrate was sliced ​​to prepare an analytical sample. An observation area spanning two metal magnetic particles was set on the observation surface of the sliced ​​analytical sample. SEM-EDS was performed on this observation area to obtain mapping data for Fe, Si, Cr, and O (oxygen). Next, a scan line extending across two adjacent metal magnetic particles was set within the observation area, and the mapping data for Fe, Si, Cr, and O were reconstructed along this scan line to create a line profile for each of the quantified elements. The line profile created in this manner is shown in Figure 5. As shown in Figure 5, it was confirmed that a silicon oxide film approximately 15 to 20 nm thick was formed on the surface of the metal magnetic particle, and a chromium oxide film approximately 10 nm thick, thinner than the silicon oxide film, was formed on the outer surface of this silicon oxide film.

[0092] It was confirmed that, even if the conditions were changed within the range of conditions shown in the explanation of the manufacturing process in Figure 6, a Si oxide film 10 to 50 nm thick was formed on the surface of the metal magnetic particles, and a Cr oxide film thinner than the Si oxide film was formed on the outer surface of this Si oxide film. Furthermore, when Cr was replaced with Al, it was confirmed that a Si oxide film 10 to 50 nm thick was formed on the surface of the metal magnetic particles, and an Al oxide film thinner than the Si oxide film was formed on the outer surface of this Si oxide film.

[0093] 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.

[0094] 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.

[0095] The designations "first," "second," "third," etc. in this specification are used to identify components and do not necessarily limit the number, order, or content thereof. Furthermore, numbers used to identify components are used in different contexts, and numbers used in one context do not necessarily indicate the same configuration in another context. Furthermore, this does not prevent a component identified by a certain number from also serving the function of a component identified by another number.

[0096] This specification also discloses the following techniques. [Appendix 1] a plurality of metal magnetic particles containing Fe, Si, and an element α; a first oxide film (41a) covering the surface of each of the plurality of metal magnetic particles and containing an oxide of Si as a main component; a second oxide film (42a) covering the surface of the first oxide film and containing an oxide of element α as a main component; Equipped with a first thickness indicating a thickness of the first oxide film is greater than a second thickness indicating a thickness of the second oxide film; Magnetic substrate. [Appendix 2] The first thickness is at least twice the second thickness. The magnetic substrate according to [Appendix 1]. [Appendix 3] The first thickness is four times or less than the second thickness. The magnetic substrate according to [Appendix 1] or [Appendix 2]. [Appendix 4] The standard deviation of the thickness of the first oxide film is 3 nm or less. The magnetic substrate according to any one of [Appendix 1] to [Appendix 3]. [Appendix 5] The element α is Cr; The magnetic substrate according to any one of [Appendix 1] to [Appendix 4]. [Appendix 6] The element α is Al. The magnetic substrate according to any one of [Appendix 1] to [Appendix 5]. [Appendix 7] The thickness of the first oxide film is 10 nm or more and 50 nm or less. The magnetic substrate according to any one of [Appendix 1] to [Appendix 6]. [Appendix 8] A magnetic substrate according to any one of [Appendix 1] to [Appendix 7]; a coil conductor provided on the magnetic substrate; A coil component comprising: [Appendix 9] A circuit board including the coil component described in [Appendix 8]. [Appendix 10] An electronic component including the circuit board described in [Appendix 9]. [Explanation of symbols]

[0097] 1 Coil parts 10 Base 21 1st external electrode 22 2nd external electrode 30a First metal magnetic particles 30b Second metal magnetic particles 41a First inner oxide film (Si oxide film) 41b Second inner oxide film (Si oxide film) 42a First outer oxide film (Cr oxide film or Al oxide film) 42b Second outer oxide film (Cr oxide film or Al oxide film)

Claims

1. a plurality of metal magnetic particles containing Fe, Si, and the element α; a first oxide film covering the surface of each of the plurality of metal magnetic particles and containing an oxide of Si as a main component; a second oxide film covering the surface of the first oxide film and containing an oxide of element α as a main component; Equipped with a first thickness indicating a thickness of the first oxide film is greater than a second thickness indicating a thickness of the second oxide film; Magnetic substrate.

2. The first thickness is at least twice the second thickness. The magnetic substrate according to claim 1 .

3. The first thickness is less than or equal to four times the second thickness.

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

4. The standard deviation of the thickness of the first oxide film is 3 nm or less.

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

5. The element α is Cr.

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

6. The element α is Al.

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

7. The thickness of the first oxide film is 10 nm or more and 50 nm or less.

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

8. The magnetic substrate according to claim 1 or 2; a coil conductor provided on the magnetic substrate; A coil component comprising:

9. A circuit board comprising the coil component according to claim 8.

10. An electronic component comprising the circuit board according to claim 9.

Images