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

Abstract

To provide a magnetic material having excellent mechanical strength.SOLUTION: A magnetic material includes a first particle 21 of a first alloy containing Fe and Cr, a second particle 22 of a second alloy containing at least one of Al and Mn, and a bonding portion 23 that contains at least one oxide of Al and Mn and binds the first particles to each other.EFFECT: A bond containing at least one oxide of Al and Mn can improve the mechanical strength of the magnetic material.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a magnetic body, a coil component including the magnetic body, and a method for manufacturing the magnetic body. [Background technology]

[0002] In coil components, the basic characteristics such as inductance are determined by the combination of magnetic body and conductor. In particular, the magnetic material that makes up the magnetic body has a large impact on the characteristics of the coil component, so it is common to use different materials depending on the structure of the coil component and the environment in which it is used. For example, coil components for automobiles are required to operate under high voltages, so ferrite-based magnetic materials with excellent dielectric strength have often been used.

[0003] However, in recent years, metallic magnetic materials have begun to replace ferrite-based materials in coil components for automobiles. This is because metallic magnetic materials are less susceptible to magnetic saturation than ferrite-based materials, allowing for the miniaturization of coil components. In recent years, with the increasing electronicization of automobiles, the number of electronic components used has tended to increase. On the other hand, since the installation space for electronic components and the circuit boards on which they are mounted is limited, there is a demand for miniaturization of each electronic component. Therefore, to meet this demand, coil components made of metallic magnetic materials have begun to be adopted.

[0004] Metallic magnetic materials have the advantage over ferrite-based materials in that they are less susceptible to magnetic saturation, but they are inferior in electrical insulation. Therefore, magnetic bodies made of metallic magnetic materials are at risk of becoming electrically conductive under high voltage. Magnetic bodies made of metallic magnetic materials are composed of metallic magnetic particles in contact with each other. Therefore, various methods have been studied to improve the electrical insulation of the magnetic bodies, focusing on electrically insulating the surfaces of the metallic magnetic particles.

[0005] Furthermore, because automotive coil components are exposed to vibrations and temperature differences, the magnetic bodies that make them up are also required to have high mechanical strength and durability. The mechanical strength and durability of magnetic bodies made of metal magnetic materials are mainly achieved by bonding between metal magnetic particles, and it is known that the surfaces of metal magnetic particles can be electrically insulated while simultaneously bonding the particles together.

[0006] For example, Patent Document 1 discloses that a compact of soft magnetic alloy particles containing iron, silicon, and an element that is more easily oxidized than iron is heat-treated in the atmosphere to form an oxide layer made of metal oxide on the surface of the particles, and the particles are bonded together via the oxide layer.

[0007] Furthermore, Patent Document 2 discloses that the particle surfaces of Fe-Si-Cr based soft magnetic alloy powder are coated or adhered with a Si compound such as TEOS or colloidal silica, and then molded, followed by heat treatment in the atmosphere to bond the particles together via an oxide phase. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-249774 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-126047 Summary of the Invention [Problem to be solved by the invention]

[0009] Thus, coil components are required to have magnetic materials with excellent mechanical strength.

[0010] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a novel magnetic body having excellent mechanical strength and a coil component including the magnetic body. [Means for solving the problem]

[0011] A magnetic body according to one or more embodiments of the present invention comprises first particles of a first alloy containing Fe and Cr, second particles of a second alloy containing at least one of Al and Mn, and a bonding portion containing an oxide of at least one of Al and Mn that bonds the first particles together.

[0012] In a magnetic body according to one or more embodiments of the present invention, the mass ratio of the sum of Al and Mn to the sum of metal elements and Si elements in the second particles is higher than the mass ratio of Cr to the sum of metal elements and Si elements in the first particles.

[0013] In a magnetic body according to one or more embodiments of the present invention, the mass ratio of Cr to the sum of metal elements and Si elements in the first particles is greater than the mass ratio of Al and Mn to the sum of metal elements and Si elements in the second particles.

[0014] In the magnetic body according to one or more embodiments of the present invention, the first particles are join The magnetic body according to one or more embodiments of the present invention has a first oxide film containing Si at a mass ratio relative to the total of the metal element and the Si element that is greater than the mass ratio of the first oxide film to the total of the metal element and the Si element.

[0015] In the magnetic body according to one or more embodiments of the present invention, the second particles are join The magnetic body according to one or more embodiments of the present invention has a second oxide film containing Si at a mass ratio relative to the total of the metal element and the Si element that is greater than the mass ratio of the first oxide film to the total of the metal element and the Si element. In the magnetic body according to one or more embodiments of the present invention, the second oxide film is a crystalline oxide layer containing an oxide of at least one of Al and Mn.

[0016] In the magnetic body according to one or more embodiments of the present invention, the number of the first particles is greater than the number of the second particles.

[0017] In the magnetic body according to one or more embodiments of the present invention, the number of the second particles is greater than the number of the first particles.

[0018] The magnetic body according to one or more embodiments of the present invention includes a filling portion including an oxide of Si, which is provided in the gap between the first particle, the second particle, and the bonding portion.

[0019] In the magnetic body according to one or more embodiments of the present invention, the second particles have an oxide layer containing an oxide of at least one of Al and Mn on the surface thereof.

[0020] A method for manufacturing a magnetic body according to one or more embodiments of the present invention includes the steps of preparing a first powder of a first alloy containing Fe and Cr, and a second alloy containing at least one of Al and Mn, mixing the first powder and the second powder to obtain a mixed powder, compacting the mixed powder to obtain a compacted body, and heating the compacted body to form bonding portions containing an oxide of at least one of Al and Mn that bond the first particles together.

[0021] In the method for producing a magnetic body according to one or more embodiments of the present invention, the compact is obtained by adding a silicone resin to the mixed particles. In the method for producing a magnetic body according to one or more embodiments of the present invention, the heating step heats the compact to form the bonding portion and the filling portion containing Si.

[0022] A coil component according to one or more embodiments of the present invention includes any one of the magnetic bodies described above or any one of the magnetic bodies manufactured by any one of the manufacturing methods described above, and a coil conductor provided on the magnetic body. A circuit board according to one or more embodiments of the present invention includes the coil component described above. [Effects of the Invention]

[0023] According to the embodiments of the present invention, it is possible to provide a magnetic body having excellent mechanical strength and a coil component including the magnetic body. [Brief explanation of the drawings]

[0024] [Figure 1] 1A and 1B are explanatory views schematically illustrating a microstructure (a contact state between different types of particles) in a magnetic body in a coil component according to one embodiment of the present invention. [Figure 2] 1 is an explanatory diagram showing a procedure for confirming whether an insulating layer is amorphous in the present invention. [Figure 3] 1 is an explanatory diagram schematically illustrating a magnetic body in which first particles are bonded to each other via bonding portions. [Figure 4] FIG. 1 is an explanatory diagram schematically illustrating a magnetic material in which voids between particles are blocked by bonding portions. [Figure 5] FIG. 2 is an explanatory diagram schematically showing a magnetic body in which voids between particles are blocked by bonding portions and filling portions. [Figure 6] 1A to 1C are schematic diagrams illustrating the appearance of coil components fabricated in examples of the present invention and comparative examples. [Figure 7] FIG. 2 is a schematic diagram showing the manner in which a test piece is supported and loaded in a three-point bending test carried out in examples and comparative examples of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] Various embodiments of the present invention will be described below with reference to the drawings. When a numerical range is stated (two numerical values ​​connected by "~"), it means that the stated lower and upper limits are included.

[0026] One aspect of the present invention relates to a magnetic body having soft magnetic alloy grains and excellent mechanical strength. Another aspect of the present invention relates to a coil component including such a magnetic body. A coil component according to one embodiment of the present invention includes a magnetic body including soft magnetic alloy grains and a coil conductor disposed inside or on the surface of the magnetic body. The magnetic body includes first particles containing Fe and Cr as alloying components, second particles containing at least one of Al and Mn as alloying components, and bonding portions containing an oxide of at least one of Al and Mn and bonding at least the first particles together. The first particles may contain Si as an alloying component. The second particles may contain Fe and Si as alloying components. In one or more embodiments of the present invention, the average particle size of the second particles may be smaller than the average particle size of the first particles. In one or more embodiments of the present invention, the average particle size of the second particles may be larger than the average particle size of the first particles. The first particles may have an amorphous oxide film containing Si and Cr on their surfaces. The second particles may have a crystalline oxide layer containing an oxide of at least one of Al and Mn on their surfaces.

[0027] 1, a magnetic body according to one embodiment of the present invention comprises first particles 21 each having an amorphous oxide film 212 on its surface, second particles 22 each having a crystalline oxide layer 222 on its surface, and bonding portions 23 each containing an oxide of at least one of Al and Mn. The average particle size of the second particles 22 may be smaller or larger than the average particle size of the first particles.

[0028] The first particles 21 contain Fe and Cr as alloy components. In one embodiment, the first particles 21 are essentially composed of Fe, Si, and Cr as alloy components. Here, "essentially composed" means that the first particles 21 do not contain any other components except for unavoidable impurities. The first particles 21 include an amorphous oxide film 212 formed on the surface and an alloy portion 211 located therein. Because the amorphous oxide film 212 is thin and the proportion of the alloy portion 211 in the first particles 21 is relatively high, the magnetic properties of the magnetic material are mainly provided by the first particles 21, which are primarily composed of Fe. While the proportion of the alloy components in the first particles 21 is not particularly limited, a higher Fe content results in better magnetic properties. Therefore, it is preferable to increase the Fe content as much as possible within a range that achieves the desired electrical insulation and oxidation resistance. The preferred Fe content is more preferably 50% by mass or more, and even more preferably 70% by mass or more. On the other hand, the Fe content is preferably 98% by mass or less. Furthermore, the Si content is preferably 1% by mass or more in order to increase the electrical resistance of the alloy portion 211 and suppress deterioration of magnetic properties due to eddy currents. Furthermore, the Cr content is preferably 0.2% by mass or more in order to suppress oxidation of Fe in the alloy portion 211 and maintain high magnetic properties. In one embodiment, the mass ratio of Cr to the total of metal elements and Si elements in the first particle 21 is higher than the mass ratio of the total of Al and Mn to the total of metal elements and Si elements in the second particle 22. This can improve the electrical insulation of the amorphous oxide film 212.

[0029] The amorphous oxide film 212 on the surface of the first particle 21 contains Cr and O as constituent elements and is amorphous. The amorphous oxide film 212 may contain Si as a constituent element. When the amorphous oxide film 212 is an amorphous film containing Si, the thin amorphous oxide film 212 can provide high electrical insulation to the magnetic material. When the amorphous oxide film 212 contains Cr, deterioration of characteristics due to oxidation of Fe in the alloy portion 211 can be suppressed. The amorphous oxide film 212 may contain elements other than Si, Cr, and O as long as the amorphous state is maintained, and the type and content of the elements are not particularly limited. Therefore, as described below, when the amorphous oxide film 212 is formed by adhering a Si-containing substance to the surface of the first particle, a Si-containing substance containing elements other than Si and Cr may be used. In one or more embodiments of the present invention, the mass ratio of Fe to the sum of metal elements and Si element in the amorphous oxide film 212 is lower than the mass ratio of the sum of the constituent elements of the amorphous carbon film 212 other than Fe to the sum of metal elements and Si element. If the content of Fe in the amorphous oxide film 212 is high, the amorphous oxide film 212 becomes more likely to crystallize, which significantly reduces the electrical insulation of the magnetic body or coil component. Therefore, it is preferable that the content of Fe in the amorphous oxide film 212 is low.

[0030] The amorphous nature of the insulating layer 212 can be confirmed by the following procedure. First, a thin sample cut from the magnetic material is observed using a high-resolution transmission electron microscope (HR-TEM). A reciprocal space diagram is obtained by Fourier transform of the insulating layer, which is identified by differences in contrast (brightness) in the electron microscope image (see (1) in Figure 2). This reciprocal space diagram can also be obtained using a measurement device other than HR-TEM, as long as it is obtained by nanobeam diffraction. Next, the average signal intensity Ir,avg is calculated for each distance r from the beam incident position in the obtained reciprocal space diagram. That is, the signal intensity Ir is measured at multiple points equidistant r from the beam incident position, and these are averaged. Next, a radial distribution function is obtained based on the obtained Ir,avg and r (see (2) in Figure 2). Next, the point rp at which the signal intensity is maximized is determined in the radial distribution function, other than r = 0 (see (3) in Figure 2). Finally, the signal intensity at each point at a distance rp from the beam incident position is plotted against the rotation angle θ, and the maximum signal intensity Irp,max is compared with the minimum signal intensity Irp,min (see (4) in Figure 2). If the value of Irp,max is less than 1.5 times the value of Irp,min, the observed insulating layer is determined to be amorphous.

[0031] The second particles 22 contain at least one of Al and Mn as an alloy component. The second particles 22 may contain Fe and Si as an alloy component in addition to at least one of Al and Mn. The second particles 22 include a crystalline oxide layer 222 formed on the surface and an alloy portion 221 located therein. Because the thickness of the crystalline oxide layer 222 is greater than the thickness of the amorphous oxide film 212, the second particles 22 are firmly bonded to adjacent soft magnetic alloy particles via the crystalline oxide layer 222. In this way, the second particles 22 contribute to improving the mechanical strength of the magnetic material. Generally, an increase in the thickness of the oxide layer formed on the surface of a soft magnetic alloy particle means a decrease in the proportion of the alloy portion, which is detrimental to magnetic properties. For this reason, in one embodiment, the average particle size of the second particles 22 is smaller than that of the first particles 21. The proportion of the alloy component in the second particles 22 is not particularly limited. However, in order to maintain magnetic properties, it is preferable to increase the Fe content as much as possible within the range in which the desired electrical insulation and oxidation resistance are obtained. The preferred Fe content is 30% by mass or more, more preferably 50% by mass or more, and even more preferably 70% by mass or more. On the other hand, the Fe content is preferably 98% by mass or less. The Si content is preferably 1% by mass or more in order to increase the electrical resistance of the alloy portion 221 and suppress deterioration of magnetic properties due to eddy currents. The total content of Al and Mn is preferably 0.2% by mass or more in order to suppress oxidation of Fe in the alloy portion 221 and the resulting deterioration of magnetic properties. In one embodiment, the mass ratio of the total of Al and Mn to the total of metal elements and Si element in the second particle 22 is higher than the mass ratio of Cr to the total of metal elements and Si element in the first particle 21. This results in a magnetic body with superior mechanical strength.

[0032] Oxides of Al and oxides of Mn have high mechanical strength. Therefore, by making the second particles contain at least one of Al and Mn as an alloy component, the crystalline oxide layer 222 containing at least one of an oxide of Al and an oxide of Mn and the crystalline oxide layer 222 described later can be formed. join The portion 23 can be strengthened.

[0033] The crystalline oxide layer 222 on the surface of the second particle 22 contains an oxide of at least one of Al and Mn. The crystalline oxide layer 222 is mainly composed of at least one of Al and Mn. In this specification, the term "main component" refers to the component with the highest content ratio by mass. As described above, the crystalline oxide layer 222 is firmly bonded to the adjacent first particle 21 or second particle 22, contributing to improving the mechanical strength of the magnetic material. The crystalline oxide layer 222 is preferably single crystal, since this allows for a magnetic material with higher strength to be obtained. Here, whether the crystalline oxide layer 222 is single crystal can be confirmed by the following procedure.

[0034] First, a 50-100 nm thick thin specimen was extracted from the center of the coil component using a focused ion beam (FIB) device. The magnetic portion was then immediately observed using a scanning transmission electron microscope (STEM) equipped with an annular dark-field detector and an energy-dispersive X-ray spectroscopy (EDS) detector. The alloy portion located inside the soft magnetic alloy particle was then identified based on the contrast (brightness) difference in the electron microscope image. The composition of a 200 nm x 200 nm region of the identified alloy portion was calculated using the ZAF method using EDS, and this was designated as the composition of the alloy portion. The STEM-EDS measurement conditions were an acceleration voltage of 200 kV, an electron beam diameter of 1.0 nm, and a measurement time set so that the integrated value of the signal intensity in the range of 6.22 keV to 6.58 keV at each point in the alloy portion was 25 counts or more. If the composition of the resulting alloy portion contained at least one of Al and Mn, the soft magnetic alloy particle containing the alloy portion was determined to be the second particle. Next, in the electron microscope image, a portion located near the surface of the soft magnetic alloy particle determined to be the second particle and having a contrast different from that of the alloy portion is determined to be a crystalline oxide layer, and the electron beam diffraction pattern of the layer is measured. If the diffraction pattern becomes a net pattern of a two-dimensional point array (a lattice-like spot), the layer is determined to be single crystal.

[0035] The above-described method for determining the composition of the alloy portion is also used to determine the composition of the amorphous oxide film 212 and the crystalline oxide layer 222.

[0036] The second particles 22 may have an average particle size smaller than that of the first particles 21. This makes it possible to suppress deterioration of the magnetic properties of the magnetic material even if a thick crystalline oxide layer 222 is formed on the surface of the second particles 22. The ratio of the average particle size of the second particles 22 to that of the first particles 21 is preferably 0.02 to 0.5. By setting this ratio to 0.02 or more, the bonding strength between the particles can be increased. On the other hand, by setting this ratio to 0.5 or less, adverse effects on the magnetic properties can be suppressed. The average particle size of each particle can be, for example, 5 μm to 20 μm for the first particles and 0.1 μm to 2 μm for the second particles. Here, the average particle size of each particle is calculated using the following procedure.

[0037] The magnetic body may include more first particles 21 than second particles 22. This increases the proportion of insulating amorphous oxide film 212 in the magnetic body, thereby improving the insulating properties of the magnetic body. In addition, since the abundance ratio of first particles 21 is higher than that of second particles 22, the magnetic properties of the magnetic body can be improved.

[0038] The magnetic body may include more second particles 22 than first particles 21. This increases the abundance ratio of the crystalline oxide layer 222 in the magnetic body, and the crystalline oxide layer 222 can firmly bond the particles together, thereby increasing the mechanical strength of the magnetic body.

[0039] First, the magnetic material of the coil component is polished to expose its cross section (polished surface). The polished surface is then observed using a scanning electron microscope. The accelerating voltage during observation is limited to approximately 2 kV to selectively obtain electronic information near the surface of the polished surface. The observation is performed using backscattered electron images to easily distinguish between the metal magnetic particle portions and the oxide film portions between the particles, and the obtained images are saved. The magnification is approximately 2000 to 5000 times. Next, the observed area is subjected to area analysis using EDS, and each particle is determined to be either a first particle or a second particle based on the differences in the elements contained therein. Next, the major and minor axes of the metal magnetic particles in the saved image are measured, and the average value is taken as the particle size of the metal magnetic particle. Finally, the arithmetic mean values ​​of the first particles 21 and the second particles 22 are calculated from the particle sizes of each particle obtained and the above-mentioned determination results, and these values ​​are taken as the average particle size of the first particles 21 and the average particle size of the second particles 22, respectively. Furthermore, the number of first particles 21 and the number of second particles 22 in the magnetic body can be determined by counting the number of first particles 21 and the number of second particles 22 in an image obtained by a scanning electron microscope (SEM image). The number of first particles 21 and the number of second particles 22 in the magnetic body may be determined by obtaining SEM images at five locations on the magnetic body and comparing the average number of first particles 21 and the average number of second particles 22 in each of the five SEM images.

[0040] Like the crystalline oxide layer 222, the bonding portions 23 contain an oxide of at least one of Al and Mn, and have at least one of Al and Mn as a main component. The bonding portions 23 are in contact with both adjacent first particles 21. This makes it possible to increase the bonding strength between the first particles 21. When the first particles 21 are bonded to each other via the amorphous oxide film 212, it is difficult to increase the bonding strength between the first particles 21. By bringing the bonding portions 23 into contact with both adjacent first particles 21, it is possible to improve the bonding strength between the first particles 21. This makes it possible to obtain a magnetic body with excellent mechanical strength. The bonding portions 23 may be arranged between the first particles 21, as shown in FIG. 3. In other words, the adjacent first particles 21 are not in direct contact with each other, joinThe first particles 21 may be separated by the bonding portions 23. In this case, adjacent first particles 21 are bonded by the bonding portions 23. This makes it possible to obtain a magnetic body with excellent mechanical strength.

[0041] FIG. 4 shows a first particle, a second particle 22, and a join 1 is a diagram showing a schematic arrangement of a portion 23. As shown in the figure, in one embodiment of the present invention, join The portions 23 can close the gaps between the first particles 21 and between the first particles 21 and the second particles 22. When the second particles 22 are adjacent to each other, join The portions 23 can close the gaps between the second particles 22. This reduces the void ratio of the magnetic material, making it possible to provide a magnetic material with even better mechanical strength.

[0042] In one embodiment of the present invention, the mass ratio of Si contained in the amorphous oxide film 212 to the sum of the metal element and Si element is greater than the mass ratio of Si contained in the bonding portion 23 to the sum of the metal element and Si element. This makes it possible to obtain an amorphous oxide film 212 with excellent electrical insulation. In one embodiment of the present invention, the mass ratio of Si contained in the crystalline oxide layer 222 to the sum of the metal element and Si element is greater than the mass ratio of Si contained in the bonding portion 23 to the sum of the metal element and Si element. This makes it possible to obtain a crystalline oxide layer 222 with excellent electrical insulation.

[0043] FIG. 5 is a diagram illustrating a filling portion included in a magnetic body according to one embodiment of the present invention. As shown in the figure, the magnetic body according to one embodiment of the present invention includes first particles 21, second particles 22, bonding portions 23, and filling portions 24. The filling portions 24 are amorphous materials containing an oxide of Si. In one or more embodiments of the present invention, the mass ratio of the metal element Si and element Si in the filling portions 24 is higher than the mass ratio of the metal element Si and element Si in the bonding portions 23. The filling portions 24 block the gaps between the first particles 21, the second particles 22, and the bonding portions 23. In the illustrated embodiment, the filling portions 24 are surrounded by the bonding portions 23. In another embodiment, at least a portion of the filling portions 24 may be in contact with at least one of the first particles 21 and the second particles 22. The filling portions 24, together with the bonding portions 23, can block the gaps between the first particles 21 and the second particles 22. The filling portions 24 containing the oxide of Si can reduce the porosity of the magnetic body. The porosity of the magnetic body can be, for example, 2 vol% or less. By reducing the porosity of the magnetic body, migration of metal atoms contained in the coil conductor and external electrodes can be suppressed during the manufacturing process of the coil conductor, which will be described later.

[0044] The magnetic body in each embodiment of the present invention may contain soft magnetic metal particles other than the first particles and second particles, various fillers, and the like, as long as the desired properties are obtained.

[0045] The material, shape, and arrangement of the coil conductor are not particularly limited and may be determined appropriately depending on the required characteristics. Examples of materials include silver, copper, or alloys thereof. Examples of shapes include linear, meander, planar coil, and spiral. Examples of arrangements include a coated conducting wire wound around a magnetic body, or various shaped conductors embedded within a magnetic body.

[0046] A method for manufacturing a magnetic body and a coil component including the magnetic body according to an embodiment of the present invention will be described. The manufacturing method includes the following processes or operations. (a) As soft magnetic alloy powders, a first powder whose alloy components are substantially composed of Fe, Si, and Cr, and a second powder whose alloy components include Fe, Si, and at least one of Al and Mn are prepared. (d) mixing the first powder and the second powder to obtain a mixed powder. (e) forming the mixed powder obtained in (d) to obtain a molded body. (f) The compact obtained in (e) is heat-treated at a temperature of 500° C. to 900° C. in an atmosphere having an oxygen concentration of 10 ppm to 800 ppm or less to obtain a magnetic material. (g) (1) In (e) above, a conductor or a precursor thereof is disposed inside or on the surface of the molded body, or (2) after (f) above, a conductor is disposed on the surface of the magnetic body. The essential processing operations and some optional processing operations that may be performed in addition to these will be described in detail below. It goes without saying that in the second embodiment, processing operations known to those skilled in the art other than the processing operations described in detail below may also be performed.

[0047] <Regarding processing operation (a)> The soft magnetic alloy powder uses a first powder essentially consisting of Fe, Si, and Cr, and a second powder containing Fe, Si, and at least one of Al and Mn as alloy components. This is based on the following findings made by the inventors during the process of completing the present invention. Specifically, the inventors discovered that soft magnetic alloy powders containing only Cr as an element other than Si, which is more easily oxidized than Fe, exhibit higher electrical insulation and form a thinner oxide layer when heat-treated in a low-oxygen atmosphere than soft magnetic alloy powders containing elements other than Cr. Furthermore, soft magnetic alloy powders containing at least one of Al and Mn contribute to improved magnetic and mechanical strength. Based on this finding, the inventors conceived a magnetic body comprising first particles of a first alloy containing Fe and Cr, second particles of a second alloy containing at least one of Al and Mn, and a bonding portion containing an oxide of at least one of Al and Mn that bonds the first particles to the second particles. This magnetic body exhibits excellent mechanical strength while maintaining its magnetic properties.

[0048] Fe, an alloying component common to the first and second powders, contributes to the magnetic properties of the soft magnetic alloy particles constituting each powder. Therefore, in both powders, it is preferable to increase the Fe content as much as possible within the range in which the desired oxides are formed on the surfaces of the soft magnetic alloy particles by the heat treatment described below. A suitable Fe content is more preferably 50% by mass or more, and even more preferably 70% by mass or more. On the other hand, if the Fe content is too high, the desired oxides may not be formed on the surfaces of the soft magnetic alloy particles constituting each powder due to the influence of oxidation. Therefore, the Fe content is preferably 98% by mass or less.

[0049] Si, an alloying component common to the first powder and the second powder, contributes to the electrical insulation of the soft magnetic alloy particles constituting each powder. Furthermore, in the first powder, Si is the main component of the highly electrically insulating amorphous oxide film formed on the surface of the soft magnetic alloy particles by heat treatment, which will be described later. To impart the desired electrical insulation to the soft magnetic alloy particles and to form an amorphous oxide film over the entire surface of the soft magnetic alloy particles (first particles) constituting the first powder, the Si content in each powder is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2% by mass or more. On the other hand, to maintain the magnetic properties of the soft magnetic alloy particles constituting each powder, the Si content is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0050] Cr, an essential component of the first powder, inhibits the oxidation of Fe in the soft magnetic alloy particles and the resulting degradation of magnetic properties. Additionally, the Cr in the soft magnetic alloy particles diffuses to the particle surface during the heat treatment described below and forms the amorphous oxide film 212 together with the Si. This inhibits oxygen diffusion into the alloy portion located inside the particle, suppressing crystallization of the amorphous oxide film 212 due to Fe oxidation and diffusion, thereby improving the stability of the amorphous oxide film. To fully exert the aforementioned effect, the Cr content in the first particles is preferably 0.2% by mass or more, more preferably 0.5% by mass or more. On the other hand, to increase the Fe content in the soft magnetic alloy particles and inhibit Cr segregation in the particles to obtain excellent magnetic properties, the Cr content in the first particles is preferably 3% by mass or less, more preferably 1.5% by mass or less.

[0051] At least one of Al and Mn, which are essential components of the second powder, acts to suppress the oxidation of Fe in the soft magnetic alloy particles and the resulting degradation of magnetic properties, similar to the aforementioned Cr. In addition, at least one of Al and Mn diffuses to the particle surface by the heat treatment described below, forming a crystalline oxide layer 222. This layer is formed thicker than the aforementioned amorphous oxide film 212. Therefore, the bonding strength between the second particles 22 and the adjacent soft magnetic alloy grain (first particle 21 or second particle 22) is higher than when the amorphous oxide films 212 are bonded together. By filling the gaps between the particles with the bonding portions 23, the volume of the gaps between the particles is reduced, thereby improving the mechanical strength of the magnetic body. By filling the gaps between the particles with the filling portions 24 in addition to the bonding portions 23, the volume of the gaps between the particles can be further reduced, thereby improving the mechanical strength of the magnetic body. Furthermore, since the mass ratio of Si to the sum of metal elements and Si elements in the filling portion 24 is higher than the mass ratio of Si to the sum of metal elements and Si elements in the bonding portion 23, the insulating properties of the magnetic material can be further improved by filling the gaps between particles with the filling portion 24 in addition to the bonding portion 23.

[0052] In one embodiment of the present invention, the Al and Mn content ratios and the Cr content ratios in the first powder and the second powder can be adjusted so that the mass ratio of the total of Al and Mn to the total of metal elements and Si elements in the second particles 22 is higher than the mass ratio of Cr to the total of metal elements and Si elements in the first particles 21. This increases the content ratio of at least one of Al and Mn in the magnetic body after heat treatment, thereby obtaining a magnetic body with excellent magnetic properties and excellent mechanical strength. In one embodiment, providing a crystalline oxide film of Al and / or Mn can reduce the porosity of the magnetic body to 5 vol% or less. Since Al and Mn have a lower reaction temperature and a faster reaction rate than Cr, by increasing the mass ratio of the total of Al and Mn to the total of metal elements and Si elements in the second particles 22 higher than the mass ratio of Cr to the total of metal elements and Si elements in the first particles 21, a larger amount of the crystalline oxide layer 222 containing an oxide of at least one of Al and Mn can be generated in the voids between the first particles 21 and the second particles 22 during the heating step to produce the magnetic body. This reduces the gap between the first particle 21 and the second particle 22. In the heating process for manufacturing the magnetic body, the crystalline oxide layer 222 is generated at a relatively low temperature, and as the temperature rises, the amorphous oxide film 212 is formed.

[0053] The second powder may have a smaller average particle size than the first powder. This can prevent adverse effects on magnetic properties even when a thick crystalline oxide layer is formed on the surface of the soft magnetic alloy particles by the heat treatment described below. The ratio of the average particle size of the second powder to that of the first powder is preferably 0.02 to 0.5. By setting this ratio to 0.02 or more, the effect of improving the bonding strength between particles due to the formation of the crystalline oxide layer can be fully exerted. On the other hand, by setting this ratio to 0.5 or less, adverse effects on magnetic properties can be prevented. The average particle sizes of the first particles can be, for example, 5 μm to 20 μm, and the second particles can be 0.1 μm to 2 μm. These average particle sizes can be measured, for example, using a particle size distribution analyzer using a laser diffraction / scattering method.

[0054] <Regarding processing operation (d)> In the process step (d), the first powder and the second powder are mixed to obtain a mixed powder. At this time, soft magnetic metal powders other than the first powder and the second powder, various fillers, etc. may be mixed within a range in which a magnetic material having the desired properties is obtained. The first powder and the second powder can be mixed by any method commonly used for mixing powders, such as by using a mixer such as a ribbon blender or a V-type mixer, or by mixing using a ball mill.

[0055] <Regarding processing operation (e)> In the treatment step (e), the mixed powder obtained in the step (d) is molded to obtain a molded body. The molding method is not particularly limited, and examples thereof include a method in which the mixed powder and a resin are mixed and supplied to a molding die such as a metal mold, and then the resin is hardened after being pressed by a press or the like. Alternatively, a method in which green sheets containing the mixed powder are laminated and pressure-bonded may be employed.

[0056] When a molded body is obtained by press molding using a mold or the like, the pressing conditions may be appropriately determined depending on the types of mixed powder and resin to be mixed therewith, their blending ratios, and the like. The resin to be mixed with the mixed powder is not particularly limited as long as it can bond the soft magnetic alloy particles constituting the mixed powder together, allowing for molding and shape retention, and volatilizes without leaving any carbon residue during the heat treatment (f) described below. Examples include acrylic resins, butyral resins, and vinyl resins, each with a decomposition temperature of 500°C or less. Lubricants such as stearic acid or its salts, phosphoric acid or its salts, and boric acid or its salts may be used together with or instead of the resin. The amount of resin or lubricant added can be determined appropriately taking into consideration moldability and shape retention, and can be, for example, 0.1 to 5 parts by mass per 100 parts by mass of the soft magnetic alloy powder. Silicone resin may also be used as the resin to be mixed with the mixed powder. The silicone resin is extruded into the gaps between the soft magnetic alloy particles constituting the mixed powder (so-called triple junctions surrounded by three particles in cross-section) by the pressure during molding, and is primarily present at these triple junctions.

[0057] When green sheets are laminated and pressed to obtain a molded body, a method can be adopted in which individual green sheets are stacked using a suction conveyor or the like and then thermocompressed using a press. When multiple coil components are to be obtained from the pressed laminate, the laminate may be divided using a cutting machine such as a dicing machine or a laser cutting machine. In this case, the green sheet is typically produced by applying a slurry containing soft magnetic alloy powder and a binder to the surface of a base film such as a plastic film using a coating machine such as a doctor blade or die coater, followed by drying. The binder used is not particularly limited, as long as it can form the soft magnetic alloy powder into a sheet, maintain the shape, and can be removed by heating without leaving any carbon residue. Examples include polyvinyl acetal resins such as polyvinyl butyral. The solvent used to prepare the slurry is also not particularly limited, and glycol ethers such as butyl carbitol can be used. The content of each component in the slurry can be adjusted appropriately depending on the green sheet forming method used, the thickness of the green sheet to be prepared, and other factors.

[0058] <Regarding processing operation (f)> In the treatment step (f), the compact obtained in the step (e) is heat-treated at 500°C to 900°C in an atmosphere with an oxygen concentration of 10 ppm to 800 ppm to obtain a magnetic material. This volatilizes and removes the resin (binder) in the compact, and also generates crystalline oxides on the surfaces of the soft magnetic alloy particles (second particles) constituting the second powder, bonding the soft magnetic alloy particles together. The heat treatment for volatilizing and removing the resin (binder) in the compact may be performed separately from the treatment step (f). In this case, the heat treatment atmosphere preferably has an oxygen concentration of 10 ppm or higher, and the heat treatment temperature is preferably 400°C or lower to suppress oxidation of Fe. If the compact contains a silicone resin, the silicone resin remains in the compact even when the binder in the compact is volatilized and removed by heating the compact. The silicone resin remaining in the molded body is gradually decomposed during the heat treatment process, but not all of it is decomposed and remains as filler containing Si in the region between the particles known as the triple point.

[0059] The oxygen concentration in the heat treatment atmosphere is 10 ppm to 800 ppm. By setting the oxygen concentration in the heat treatment atmosphere to 10 ppm or more, the surfaces of the soft magnetic alloy particles constituting the soft magnetic alloy powder are oxidized, electrically insulating the particles and bonding them together via the oxide. To promote the oxidation of at least one of Al and Mn in the soft magnetic alloy particles (second particles) constituting the second powder and generate a sufficient amount of crystalline oxide 222 to firmly bond the soft magnetic alloy particles together, the oxygen concentration is preferably 100 ppm or more, more preferably 200 ppm or more. On the other hand, by setting the oxygen concentration in the heat treatment atmosphere to 800 ppm or less, the oxidation of Fe in the soft magnetic alloy particles (first particles) constituting the first powder and the resulting generation of crystalline oxide 212 on the particle surfaces can be suppressed. The oxygen concentration is preferably 500 ppm or less, more preferably 300 ppm or less. In the heat treatment process, the silicon resin remaining at the triple junctions of the soft magnetic alloy particles becomes an amorphous filling portion 24 containing an oxide of Si as the heat treatment temperature increases. The filling portion 24 may be formed so as to be surrounded by a crystalline oxide 222 containing at least one of Al and Mn. Because the reaction temperature and reaction rate for the formation of an amorphous oxide film containing Al and Mn are low, the crystalline oxide layer 222 and the bonding portion 23 are formed on the surface of the second particles 22 from an early stage of the heat treatment (when the heat treatment temperature is low). As the heat treatment process progresses and the heat treatment temperature increases, an amorphous filling portion 24 containing an oxide of Si derived from the silicon resin remaining in this region is formed at the triple junctions between the particles after molding. In this way, in the heat treatment process, the crystalline oxide layer 222 and the bonding portion 23 are formed first, and then the filling portion 24 is formed. Therefore, the filling portion 24 is surrounded by the crystalline oxide 222 and the bonding portion 23.

[0060] The heat treatment temperature is 500°C to 900°C. By setting the heat treatment temperature to 500°C or higher, the surfaces of the soft magnetic alloy particles constituting the soft magnetic alloy powder are oxidized, electrically insulating the particles from each other and bonding the particles to each other via the oxide. The heat treatment temperature is preferably 550°C or higher, more preferably 600°C or higher. On the other hand, by setting the heat treatment temperature to 900°C or lower, oxidation of Fe in the soft magnetic alloy particles (first particles) constituting the first powder and the resulting generation of crystalline oxides on the particle surfaces can be suppressed. The heat treatment temperature is preferably 850°C or lower, more preferably 800°C or lower.

[0061] The heat treatment time may be any time that allows the crystalline oxide formed on the surfaces of the second particles to grow and reach the contact points between the first particles. For example, the heat treatment time may be 30 minutes or more, and preferably 1 hour or more. On the other hand, in order to prevent the formation of a crystalline oxide film on the surfaces of the first particles and to complete the heat treatment in a short time to improve productivity, the heat treatment time may be 5 hours or less, and preferably 3 hours or less.

[0062] Here, the oxidation of Fe in the soft magnetic alloy particles (first particles) constituting the first powder and the resulting generation of crystalline oxides on the particle surfaces can be suppressed by lowering at least one of the oxygen concentration in the heat treatment atmosphere or the heat treatment temperature, or by shortening the heat treatment time. Therefore, for example, if it is necessary to increase the oxygen concentration in the heat treatment atmosphere and it is desired to minimize the generation of crystalline oxides, the heat treatment temperature can be set low or the heat treatment time can be set short. Furthermore, if it is necessary to increase the heat treatment temperature, the oxygen concentration in the heat treatment atmosphere can be set low or the heat treatment time can be set short. Furthermore, if it is necessary to increase the heat treatment time, the oxygen concentration in the heat treatment atmosphere can be set low or the heat treatment temperature can be set low.

[0063] <Regarding processing operation (g)> In the processing step (g), a coil conductor or its precursor is placed. Hereinafter, the coil conductor may be simply referred to as a conductor. Here, a conductor is something that will become a conductor in the coil component as it is, and a conductor precursor is something that contains a binder resin in addition to a conductive material that will become a conductor in the coil component, and becomes a conductor by heat treatment. There are two methods for placing a conductor or its precursor:

[0064] (1) In (e) above, a conductor or a precursor thereof is disposed inside or on the surface of the molded body. When the compact is obtained by the above-mentioned press molding, a method can be employed in which a mixed powder of soft magnetic alloys is filled into a mold in which a conductor or a precursor thereof has been placed in advance, and then pressed, thereby placing the conductor or a precursor thereof inside the compact.

[0065] Furthermore, when a molded body is obtained by laminating and pressing the above-mentioned green sheets, a method can be used in which a conductor precursor is disposed on the green sheets by printing a conductor paste or the like, followed by lamination and pressing. This allows the conductor or its precursor to be disposed inside or on the surface of the laminate. Examples of the conductor paste used include those containing a conductor powder and an organic vehicle. Examples of the conductor powder include powders of silver, copper, or alloys thereof. The particle size of the conductor powder is not particularly limited, but for example, a powder with an average particle size (median diameter (D50)) calculated from the particle size distribution measured on a volume basis of 1 μm to 10 μm is used. The composition of the organic vehicle can be determined taking into account its compatibility with the binder contained in the green sheets. One example is a polyvinyl acetal resin such as polyvinyl butyral (PVB) dissolved or swollen in a glycol ether solvent such as butyl carbitol. The compounding ratio of the conductor powder and the organic vehicle in the conductor paste can be appropriately adjusted depending on the viscosity of the paste suitable for the printing machine used and the film thickness of the conductor pattern to be formed.

[0066] In either case, the deposited conductor precursor is subsequently processed to form the conductor (f).

[0067] (2) After carrying out (f), a conductor is disposed on the surface of the magnetic material. In this case, the conductor can be arranged by winding a coated conductor wire around the obtained magnetic body, or by arranging a conductor precursor on the surface of the magnetic body by printing a conductor paste, etc., and then performing a baking process using a heating device such as a baking furnace.

[0068] <Regarding processing operation (b)> In the second embodiment, prior to the above-mentioned process operation (d), a Si-containing substance may be attached to the surface of each particle (first particle) constituting the first powder prepared in the process operation (a) (process operation (b)).

[0069] In the treatment step (b), a Si-containing substance is attached to the surfaces of the soft magnetic alloy particles (first particles) that make up the first powder, which makes it easier to form an amorphous film with a uniform thickness on the surfaces of the first particles. Examples of the Si-containing substance to be used include silane coupling agents such as tetraethoxysilane (TEOS), silica fine particles such as colloidal silica, etc. The amount of the Si-containing substance to be used can be determined appropriately depending on the type of the Si-containing substance, the particle size of the soft magnetic alloy particles, etc. Examples of methods for attaching the Si-containing substance to the surfaces of the soft magnetic alloy particles (first particles) constituting the first powder include, when the substance is in liquid form, spraying the particles or immersing the particles in the substance and then drying. Also, when the Si-containing substance is in the form of fine particles, examples include dry mixing or contacting the particles with a slurry in which the Si-containing substance is dispersed (spraying or immersing) and then drying. Furthermore, coating by a sol-gel method using a silane coupling agent may also be employed.

[0070] <Regarding processing operation (c1)> When performing the treatment operation (b) above, the first powder after the treatment operation may be heat-treated in an inert gas atmosphere at a temperature of 100°C to 700°C, or in an atmosphere with an oxygen concentration of 100 ppm or less at a temperature of 100°C to 300°C (treatment operation (c1)). Here, the inert gas refers to N2 or a rare gas. This causes the Si-containing substance attached to the surfaces of the alloy particles (first particles) constituting the first powder to form an amorphous thin film containing Si and O, and improves the mechanical strength of the formed thin film and its adhesive strength to metal particles. The thin film functions as an insulating layer in the magnetic body in the coil component, providing electrical insulation between the soft magnetic alloy particles.

[0071] The heat treatment temperature is preferably 100°C or higher. This promotes the formation of the aforementioned amorphous thin film. It also improves the mechanical strength of the formed thin film and its adhesion strength to the metal particles. However, if the heat treatment temperature is too high, oxidation of the soft magnetic metal powder and crystallization of the amorphous thin film become significant, resulting in a deterioration in the properties of the resulting magnetic material. For this reason, when heat treatment is performed in an atmosphere containing 100 ppm or less of oxygen, the heat treatment temperature is preferably 300°C or lower. On the other hand, when heat treatment is performed in an inert atmosphere, oxidation of the soft magnetic metal powder hardly occurs, so the upper limit of the heat treatment temperature can be set to 700°C.

[0072] The holding time at the heat treatment temperature is not particularly limited, but from the viewpoint of sufficiently forming an amorphous thin film and sufficiently increasing the mechanical strength of the formed thin film and its adhesive strength to the metal particles, it is preferably 30 minutes or more, more preferably 50 minutes or more. On the other hand, from the viewpoint of suppressing the formation of a crystalline film and completing the heat treatment in a short time to improve productivity, the heat treatment time is preferably 2 hours or less, more preferably 1.5 hours or less.

[0073] <Regarding processing operation (c2) (1)> In the second embodiment, instead of the above-described process (c1), the first powder having the Si-containing substance adhered to its surface may be subjected to a heat treatment at a temperature of 300°C to 900°C in an atmosphere with an oxygen concentration of 3 ppm to 100 ppm (process (c2)). This causes Si or Cr in the alloy particles (first particles) constituting the first powder to diffuse to the particle surface and oxidize on the surface. At this time, an amorphous oxide thin film is formed on the surface of the first particles, which, in combination with the amorphous thin film derived from the Si-containing substance, forms an amorphous thin film of sufficient thickness. This thin film functions as an insulating layer in the magnetic body in the coil component, electrically insulating the first particles on which it is formed from other adjacent alloy particles. This allows for the production of a magnetic body or coil component with excellent electrical insulation and low loss during operation.

[0074] By setting the oxygen concentration in the heat treatment atmosphere to 3 ppm or more and the heat treatment temperature to 300°C or more, the reaction between oxygen and the alloy components Si and Cr is promoted. This allows the surfaces of the soft magnetic alloy particles (first particles) constituting the first powder to be covered with an amorphous film with high electrical insulation. On the other hand, by setting the oxygen concentration in the heat treatment atmosphere to 100 ppm or less and the heat treatment temperature to 900°C or less, excessive oxidation of Fe in the first particles and the resulting generation of crystalline oxides on the particle surfaces can be suppressed. This prevents deterioration of magnetic properties and electrical insulation. The oxygen concentration is preferably 5 ppm or more. The oxygen concentration is preferably 50 ppm or less, more preferably 30 ppm or less, and even more preferably 10 ppm or less. The heat treatment temperature is preferably 350°C or more, more preferably 400°C or more. The heat treatment temperature is preferably 850°C or less, more preferably 800°C or less.

[0075] The holding time at the heat treatment temperature is not particularly limited, but is preferably 30 minutes or more, more preferably 1 hour or more, from the viewpoint of obtaining an amorphous film with a sufficient thickness. On the other hand, from the viewpoint of suppressing the formation of a crystalline film and completing the heat treatment in a short time to improve productivity, the heat treatment time is preferably 5 hours or less, more preferably 3 hours or less.

[0076] Here, the aforementioned excessive oxidation of Fe in the first particles and the resulting generation of crystalline oxides on the surfaces of the first particles can be suppressed by lowering at least one of the oxygen concentration in the heat treatment atmosphere and the heat treatment temperature, or by shortening the heat treatment time. Therefore, for example, if it is necessary to increase the oxygen concentration in the heat treatment atmosphere and it is desired to minimize oxidation of Fe, the heat treatment temperature can be set low or the heat treatment time can be set short. Furthermore, if it is necessary to increase the heat treatment temperature, the oxygen concentration in the heat treatment atmosphere can be set low or the heat treatment time can be set short. Furthermore, if it is necessary to increase the heat treatment time, the oxygen concentration in the heat treatment atmosphere can be set low or the heat treatment temperature can be set low.

[0077] <Regarding processing operation (c2) (2)> The above-mentioned treatment operation (c2) may be performed on the first powder that has not been subjected to the above-mentioned treatment operation (b). This results in the formation of a uniformly thick amorphous oxide thin film containing Si, Cr, and O on the surfaces of the soft magnetic alloy particles (first particles) that make up the first powder. This thin film functions as an insulating layer in the magnetic body in the coil component, electrically insulating the soft magnetic alloy particles from each other. This allows for the production of a magnetic body or coil component with a uniform insulating layer thickness and excellent magnetic properties. Furthermore, in this case, the thickness of the insulating layer can be made thinner than when the above-mentioned treatment operation (b) is performed, thereby increasing the proportion of the alloy portion inside the first particles and resulting in the production of a magnetic body or coil component with even more excellent magnetic properties.

[0078] When a silicone resin is used as the resin to be mixed with the mixed powder, amorphous filler portions 24 containing Si oxide are disposed between the first particles 21, the second particles 22, and the bonding portions 23 in the magnetic body obtained by the heat treatment. The filler portions 24 containing Si oxide can reduce the porosity of the magnetic body compared to a case in which the filler portions 24 are not provided, and can be set to, for example, 2 vol% or less. This can suppress migration of metal atoms contained in the coil conductor and external electrode. Furthermore, since the mass ratio of Si to the total of the metal element and Si element in the filler portions 24 is higher than the mass ratio of Si to the total of the metal element and Si element in the bonding portions 23, the insulating properties of the magnetic body can be improved.

[0079] According to the manufacturing method described above, a magnetic body can be obtained in which first particles 21, each having a highly electrically insulating amorphous oxide film formed on its surface, and second particles 22 are joined by a crystalline oxide having high mechanical strength (crystalline oxide layer 222 and bonding portion 23). This makes it possible to obtain a magnetic body having excellent mechanical strength and a coil component including the magnetic body.

[0080] One aspect of the present invention relates to a circuit board on which a coil component according to one embodiment of the present invention is mounted. The structure of the circuit board is not limited, and any suitable structure may be adopted depending on the purpose. In the third embodiment, the coil component according to the first embodiment is used, making the circuit board less susceptible to damage even when subjected to vibration or impact. [Example]

[0081] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0082] [Example 1] <Production of coil components and test magnetic materials> First, a soft magnetic alloy powder with an average particle size of 4 μm was prepared as the first powder. The powder contained 95.0 wt% Fe, 2.0 wt% Si, and 3.0 wt% Cr, with the remainder consisting of unavoidable impurities. The second powder contained 97.0 wt% Fe, 2.0 wt% Si, and 1.0 wt% Al, with the remainder consisting of unavoidable impurities. The soft magnetic alloy powder with an average particle size of 2 μm was then prepared. The first powder was then heat-treated for 1 hour at 700°C in an atmosphere with an oxygen concentration of 7 ppm. Next, 90 parts by mass of the heat-treated first powder was mixed with 10 parts by mass of the second powder, a polyvinyl butyral (PVB) binder resin, and a dispersion medium to prepare a slurry. This slurry was then formed into a sheet using an automatic coating machine to obtain a green sheet. Next, Ag paste was printed on the green sheet to form a precursor for the internal electrodes. The green sheets were then stacked, pressed, and singulated to obtain a compact. Next, this compact was heat-treated at 800°C for 1 hour in an atmosphere with an oxygen concentration of 800 ppm to obtain a magnetic body with an internal conductor. Finally, external electrodes connected to the internal conductor were formed to obtain a coil component with the shape shown in Figure 6. In addition, the green sheets without the internal electrode precursors formed were stacked and pressed together, and the molded bodies were processed into disks. These were then heat-treated under the conditions described above to obtain disk-shaped test magnetic bodies with a diameter of 7 mm and a thickness of 0.5 mm to 0.8 mm. Furthermore, the green sheets without the internal electrode precursors formed thereon were stacked and pressed together, and the resulting molded body was processed into a rectangular parallelepiped shape. The molded body was then heat-treated under the conditions described above to obtain a rectangular parallelepiped test magnetic body measuring 50 mm in length, 5 mm in width, and 4 mm in thickness.

[0083] <Measuring the average particle size of soft magnetic alloy particles> When the average particle size of the first particles and second particles of the soft magnetic alloy of the obtained coil component was measured by the method described above, the first particles were 4 μm and the second particles were 2 μm.

[0084] <Confirmation of the structure and composition of the oxide film and oxide layer> The structure and composition of the oxide film or oxide layer formed on the surface of the soft magnetic alloy particles in the magnetic body of the obtained coil component were confirmed using the method described above. As a result, it was found that an amorphous oxide film containing Si and Cr was formed on the surface of the first particles. It was also found that a layer of crystalline oxide (Al2O3) mainly composed of Al was formed on the surface of the second particles. Furthermore, it was confirmed that an oxide similar to that on the surface of the second particles was formed at the contact points between the first particles, spanning the multiple contacting first particles.

[0085] <Measurement of magnetic permeability> The relative magnetic permeability of the obtained coil component was measured at a frequency of 10 MHz using an L chrome meter (4285A manufactured by Agilent Technologies) as a measuring device. The obtained relative magnetic permeability was 32.

[0086] <Evaluation of electrical insulation> The electrical insulation of the coil component was evaluated based on the volume resistivity and breakdown voltage of the disk-shaped test magnetic material described above. An Au film was formed by sputtering on the entire surface of both sides of the above-mentioned disk-shaped test magnetic body to prepare an evaluation sample. The volume resistivity of the obtained evaluation sample was measured in accordance with JIS-K6911. The Au films formed on both sides of the sample were used as electrodes, and a voltage was applied between the electrodes so that the field strength was 60 V / cm, and the resistance value was measured, and the volume resistivity was calculated from the resistance value. The volume resistivity of the evaluation sample was 500 Ω cm. The breakdown voltage of the obtained evaluation sample was measured by using the Au films formed on both sides of the sample as electrodes, applying a voltage between the electrodes, and measuring the current value. The applied voltage was gradually increased and the current value was measured. The breakdown voltage was determined as the electric field strength calculated from the voltage at which the current density calculated from the current value became 0.01 A / cm2. The breakdown voltage of the evaluation sample was 6.2 kV / cm.

[0087] <Mechanical strength evaluation> The mechanical strength of the coil component was evaluated by a three-point bending test of the rectangular parallelepiped test magnetic body (test piece) described above. The test piece was supported and loaded in the manner shown in Fig. 7, and the breaking stress σb was calculated from the maximum load W at which it broke, taking into consideration the bending moment M and the moment of inertia I, using the following (Equation 1). The above test was carried out on 10 test pieces, and the average value of the breaking stress σb was taken as the breaking stress of the magnetic material according to Example 1. The obtained breaking stress was 17 kgf / mm2.

[0088]

number

[0089] [Example 2] <Production of coil components and test magnetic materials> A coil component and a test magnetic body according to Example 2 were produced in the same manner as in Example 1, except for the following points. Prior to mixing with the second powder, binder resin, and dispersion medium, the first powder was dispersed in a mixed solution containing ethanol and ammonia water, and a treatment solution containing tetraethoxysilane (TEOS), ethanol, and water was mixed and stirred therewith. The first powder was then separated by filtration and dried. The treated first powder was then mixed with the second powder, binder resin, and dispersion medium. The molded body was heat-treated at 800°C for 1 hour in an atmosphere with an oxygen concentration of 800 ppm.

[0090] <Confirmation of the structure and composition of the oxide film and oxide layer> The structure and composition of the oxide film or oxide layer formed on the surface of the soft magnetic alloy particles in the magnetic body of the obtained coil component were confirmed in the same manner as in Example 1, and it was confirmed that an oxide film and oxide layer having the same structure and composition as in Example 1 had been formed.

[0091] <Evaluation of coil components and test magnetic materials> The properties of the obtained coil component and test magnetic body were measured in the same manner as in Example 1. The relative permeability of the coil component was 30, the resistivity of the evaluation sample was 510 Ω cm, the breakdown voltage was 5.6 kV / cm, and the fracture stress of the magnetic body in three-point bending was 16 kgf / mm.

[0092] [Example 3] <Production of coil components and test magnetic materials> The coil component and test magnetic body of Example 3 were produced in the same manner as Example 1, except that the first powder was mixed with the second powder, binder resin, and dispersant without being heat-treated to prepare a slurry.

[0093] <Confirmation of the structure and composition of the oxide film and oxide layer> The structure and composition of the oxide film or oxide layer formed on the surface of the soft magnetic alloy particles in the magnetic body of the obtained coil component were confirmed in the same manner as in Example 1, and it was confirmed that an oxide film and oxide layer having the same structure and composition as in Example 1 had been formed.

[0094] <Evaluation of coil components and test magnetic materials> The properties of the obtained coil component and test magnetic body were measured in the same manner as in Example 1. The relative permeability of the coil component was 34, the resistivity of the evaluation sample was 470 Ω cm, the breakdown voltage was 5.2 kV / cm, and the fracture stress of the magnetic body in three-point bending was 17 kgf / mm.

[0095] [Example 4] <Production of coil components and test magnetic materials> As the first powder, a soft magnetic alloy powder containing 97.8 wt% Fe, 2.0 wt% Si, and 0.2 wt% Cr, with the remainder being unavoidable impurities, and having an average particle size of 4 μm was prepared. As the second powder, a soft magnetic alloy powder containing 97.0 wt% Fe, 2.0 wt% Si, and 1.0 wt% Al, with the remainder being unavoidable impurities, and having an average particle size of 2 μm was prepared. Using these first and second powders, a coil component and a test magnetic body according to Example 4 were fabricated in the same manner as in Example 3.

[0096] <Confirmation of the structure and composition of the oxide film and oxide layer> The structure and composition of the oxide film or oxide layer formed on the surface of the soft magnetic alloy particles in the magnetic body of the obtained coil component were confirmed in the same manner as in Example 1, and it was confirmed that an oxide film and oxide layer having the same structure and composition as in Example 1 had been formed.

[0097] <Evaluation of coil components and test magnetic materials> The properties of the obtained coil component and test magnetic body were measured in the same manner as in Example 1. The relative permeability of the coil component was 34, the resistivity of the evaluation sample was 380 Ω cm, the breakdown voltage was 5.0 kV / cm, and the fracture stress of the magnetic body in three-point bending was 17 kgf / mm.

[0098] [Example 5] <Production of coil components and test magnetic materials> The coil component and test magnetic body of Example 5 were produced in the same manner as in Example 3, except that silicone resin was mixed into the slurry for producing the green sheets instead of the binder resin.

[0099] <Confirmation of the structure and composition of the oxide film and oxide layer> The structure and composition of the oxide film or oxide layer formed on the surface of the soft magnetic alloy particles in the magnetic body of the obtained coil component were confirmed in the same manner as in Example 1. It was confirmed that an oxide film and oxide layer having the same structure and composition as in Example 1 had been formed, and that an amorphous material containing Si had been formed between these oxide films and oxide layers.

[0100] <Evaluation of coil components and test magnetic materials> The properties of the obtained coil component and test magnetic body were measured in the same manner as in Example 1. The relative permeability of the coil component was 34, the resistivity of the evaluation sample was 600 Ω cm, the breakdown voltage was 10.0 kV / cm, and the fracture stress of the magnetic body in three-point bending was 18 kgf / mm.

[0101] [Comparative Example 1] <Production of coil components and test magnetic materials> A coil component and a test magnetic body according to Comparative Example 1 were produced in the same manner as in Example 3, except that the second powder was not used and only the first powder was used as the soft magnetic alloy powder.

[0102] <Confirmation of the structure and composition of the oxide film and oxide layer> The structure and composition of the oxide film or oxide layer formed on the surface of the soft magnetic alloy particles in the magnetic body of the obtained coil component were confirmed using the same method as in Example 1, and no crystalline oxide was found on the surface of the soft magnetic alloy particles or at the contact points between the particles.

[0103] <Evaluation of coil components and test magnetic materials> The properties of the obtained coil component and test magnetic body were measured in the same manner as in Example 1. The relative permeability of the coil component was 28, the resistivity of the evaluation sample was 10 Ω cm, the breakdown voltage was 0.92 kV / cm, and the fracture stress of the magnetic body in three-point bending was 7 kgf / mm.

[0104] Comparative Example 2 <Production of coil components and test magnetic materials> A coil component and a test magnetic body according to Comparative Example 2 were produced in the same manner as in Example 3, except that the first powder was not used and only the second powder was used as the soft magnetic alloy powder.

[0105] <Confirmation of the structure and composition of the oxide film and oxide layer> The structure and composition of the oxide film or oxide layer formed on the surface of the soft magnetic alloy particles in the magnetic body of the obtained coil component were confirmed using the same method as in Example 1, and no amorphous oxide film was found on the surface of the soft magnetic alloy particles.

[0106] <Evaluation of coil components and test magnetic materials> The properties of the obtained coil component and test magnetic body were measured in the same manner as in Example 1. The relative permeability of the coil component was 22, the resistivity of the evaluation sample was 20 Ω cm, the breakdown voltage was 1.0 kV / cm, and the fracture stress of the magnetic body in three-point bending was 9 kgf / mm.

[0107] The above results are summarized in Table 1.

[0108] [Table 1]

[0109] Comparing the Examples and Comparative Examples, it can be said that coil components having a magnetic body including first particles and second particles as soft magnetic alloy particles, with the particles bonded via an oxide film or oxide layer of a specific structure, have higher mechanical strength than coil components having a magnetic body that does not have this configuration. Furthermore, the above-mentioned configuration allows the Fe ratio of the obtained magnetic alloy particles to be increased compared to the Fe composition of the raw material, and by using this, the magnetic permeability is also increased, resulting in a coil component with excellent magnetic properties. Furthermore, the above-mentioned configuration also increases the resistivity and breakdown voltage, resulting in a coil component with excellent electrical insulation. [Industrial Applicability]

[0110] According to the present invention, a coil component with improved mechanical strength is provided. The coil component according to the present invention is resistant to damage even when subjected to vibration or impact, and is therefore suitable for use in automobiles and the like. Furthermore, according to a preferred embodiment of the present invention, a coil component with improved magnetic properties is provided, and therefore the present invention is also useful in that it enables the miniaturization of components. Furthermore, according to a preferred embodiment of the present invention, a coil component with improved electrical insulation is provided, and is therefore suitable for use in automobiles and the like to which high voltages are applied. [Explanation of symbols]

[0111] 1 Coil parts 2 Magnetic material 21 1st particle 211 (first particle) alloy part 212 Amorphous oxide film 22 2nd particle 221 (second particle) alloy part 222 Crystalline acid layer 23 Joint 3 External Electrodes

Claims

1. a first particle of a first alloy containing only Fe, Si, and Cr as another element more easily oxidized than Fe, the first particle having a first oxide film made of an oxide of the first alloy on the surface thereof and a first alloy portion provided inside the first oxide film; second particles of a second alloy containing at least one of Al and Mn, the second particles having a second oxide film on the surface thereof, the second oxide film being mainly composed of an oxide of at least one of Al and Mn and being thicker than the first oxide film, and the second particles having a second alloy portion provided inside the second oxide film; a bonding portion that contains an oxide of at least one of Al and Mn and bonds the first particles together, adjacent first particles are in contact with each other in the first oxide film, the bonding portion fills at least a part of the gap between the adjacent first particles; magnetic material.

2. a mass ratio of the sum of Al and Mn to the sum of metal elements and Si element in the second particles is higher than a mass ratio of Cr to the sum of metal elements and Si element in the first particles; The magnetic body according to claim 1 .

3. a mass ratio of Cr to the total of metal elements and Si elements in the first particles is greater than a mass ratio of Al and Mn to the total of metal elements and Si elements in the second particles; The magnetic body according to claim 1 .

4. the first oxide film contains Si at a mass ratio relative to the total mass of the metal element and the Si element that is larger than the bonding portion; The magnetic body according to any one of claims 1 to 3.

5. the first oxide film is an amorphous oxide film containing Si and Cr; The magnetic body according to claim 4.

6. the second oxide film contains Si at a mass ratio relative to the total of the metal element and the Si element that is larger than the bonding portion; The magnetic body according to any one of claims 1 to 4.

7. the second oxide film is a crystalline oxide layer containing an oxide of at least one of Al and Mn; The magnetic body according to claim 6.

8. the number of the first particles is greater than the number of the second particles; The magnetic body according to any one of claims 1 to 7.

9. the number of the second particles is greater than the number of the first particles; The magnetic body according to any one of claims 1 to 7.

10. a filling portion containing Si provided in a gap between the first particle, the second particle, and the bonding portion; The magnetic body according to any one of claims 1 to 9.

11. the second particles have an oxide layer containing an oxide of at least one of Al and Mn on their surfaces; The magnetic body according to any one of claims 1 to 10.

12. The magnetic body according to any one of claims 1 to 11, a coil conductor provided on the magnetic body; A coil component comprising:

13. A circuit board on which the coil component according to claim 12 is mounted.

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