Coil member, circuit board, and electronic device

Abstract

A coil component, a circuit board, and an electronic device are provided. A coil component of one embodiment includes a magnetic core including a plurality of ferrite crystal grains and a plurality of Bi-segregation regions existing at grain boundaries of the plurality of ferrite crystal grains, and a winding wound around the magnetic core. In one embodiment, a plurality of line profiles obtained by detecting the content of Bi along a plurality of scan lines intersecting the grain boundaries includes at least one first line profile including a detected peak of Bi at the grain boundary, and a plurality of second line profiles not including the detected peak.

Description

Technical Field

[0001] This invention relates to coil components, circuit boards, and electronic devices. Background Technology

[0002] Various types of coil components are used in electronic devices. Examples of coil components include inductors and transformers used to remove noise from signals. Wire-wound coil components are known as examples of coil components. Wire-wound coil components include: a sintered body of ferrite material, i.e., a magnetic core; a winding wound around the core; and multiple external electrodes electrically connected to the ends of the winding. During the reflow soldering process when mounting such coil components on a circuit board, there is a possibility that the magnetic core may crack due to thermal shock.

[0003] To suppress the formation of cracks in ferrite cores caused by thermal shock, the addition of Bi-containing byproducts has been proposed in the past. For example, Japanese Patent Application Publication No. 4-325458 (Patent Document 1) discloses a ferrite material containing 0.03 mol% to 2 wt% Bi₂O₃ as a byproduct relative to the main component. In the ferrite sintered body formed from the ferrite material of Patent Document 1, an amorphous layer composed of the byproduct and impurities is formed at the grain boundaries of the ferrite crystals with a thickness of 2 to 50 nm. According to Patent Document 1, by providing an amorphous layer at the grain boundaries, sintered ferrite with excellent thermal shock resistance can be obtained.

[0004] Japanese Patent Application Publication No. 11-35369 (Patent Document 2) discloses a ferrite material containing, relative to the main components, 0.05 wt% to 2.0 wt% bismuth oxide (Bi₂O₃), 0.05 wt% to 1.0 wt% silicon dioxide (SiO₂), and 0.05 wt% to 1.5 wt% chromium oxide (Cr₂O₃). According to Patent Document 2, a glassy stress-relieving layer containing these secondary components is formed at the grain boundaries of the ferrite particles. This stress-relieving layer can prevent crack propagation, thus enabling the acquisition of sintered ferrite with excellent thermal shock resistance.

[0005] Japanese Patent Application Publication No. 1-228108 (Patent Document 3) discloses a Ni-Cu-Zn type ferrite material containing 0.03 wt% or less of SiO2, 0.10 wt% or less of MnO, 0.10 wt% or less (excluding 0) of Bi2O3, and 1.0 wt% or less (excluding 0) of MgO as secondary components. The sintered body of the ferrite material in Patent Document 3 has a stress-relieving layer composed of these secondary components at the grain boundaries of the crystal particles. Patent Document 3 discloses that when stress is applied to the sintered ferrite from the outside, this stress-relieving layer can alleviate the stress, thus contributing to improving the material strength of the sintered ferrite.

[0006] As described above, it is known that by using a Bi oxide as a byproduct in a ferrite material, a Bi-containing film can be formed between the crystal grains in the sintered body of the ferrite material, and this film can be used to suppress the generation and propagation of cracks caused by thermal shock or external stress.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 4-325458

[0010] Patent Document 2: Japanese Patent Application Publication No. 11-35369

[0011] Patent Document 3: Japanese Patent Application Publication No. 1-228108 Summary of the Invention

[0012] The technical problem that the invention aims to solve

[0013] However, in ferrite cores with a stress-relief layer containing Bi oxide formed at the grain boundaries, the crystals are bonded together by the soft stress-relief layer. Therefore, ferrite cores with a stress-relief layer containing Bi oxide formed at the grain boundaries have lower mechanical strength relative to external forces compared to ferrite cores without this stress-relief layer.

[0014] The object of this invention is to solve or mitigate the aforementioned problems. One more specific object of this invention is to provide a coil component having a ferrite core capable of suppressing the formation of cracks caused by thermal shock and improving mechanical strength relative to external forces. Other objects of this invention will become apparent from the entire description of the specification.

[0015] Means for solving technical problems

[0016] One aspect of the coil component of the present invention includes: a magnetic core having a plurality of ferrite grains and a plurality of Bi segregation regions present at the grain boundaries of the plurality of ferrite grains; and a winding wound on the magnetic core. In one embodiment, a plurality of line distributions obtained by detecting the Bi element content along a plurality of scan lines intersecting the grain boundaries include: at least one first line distribution containing a detection peak of Bi element at the grain boundaries; and a plurality of second line distributions not containing the detection peak.

[0017] In one embodiment, the plurality of scan lines includes: at least one first scan line corresponding to the at least one first line distribution; and two second scan lines corresponding to the plurality of second line distributions, wherein at least one of the at least one first scan line is sandwiched between the two second scan lines.

[0018] In one embodiment, the plurality of scan lines are set at equal intervals.

[0019] In one embodiment, the magnetic core contains more than 0.03 wt% and less than 0.1 wt% Bi in oxide form.

[0020] In one embodiment, the magnetic core contains more than 0.05 wt% and less than 0.075 wt% Bi in oxide form.

[0021] One aspect of the present invention includes a coil component comprising: a magnetic core having a plurality of ferrite grains and a plurality of Bi segregation regions present at the grain boundaries of the plurality of ferrite grains; and a winding wound on the magnetic core, the plurality of Bi segregation regions being spaced apart from each other.

[0022] One embodiment of the circuit board of the present invention includes the coil component described above.

[0023] An electronic device according to one aspect of the present invention includes the circuit board.

[0024] Invention Effects

[0025] By employing various embodiments of the present invention, it is possible to provide a coil component having a ferrite core capable of suppressing the generation of cracks caused by thermal shock and improving mechanical strength relative to external forces. Attached Figure Description

[0026] Figure 1 This is a perspective view of a coil component according to one embodiment of the present invention.

[0027] Figure 2 yes Figure 1 The front view of the coil component shown.

[0028] Figure 3 yes Figure 1 The right side view of the coil component shown.

[0029] Figure 4 yes Figure 1 The bottom view of the coil component is shown.

[0030] Figure 5 Using the surface through line II Figure 1 The cross-sectional view obtained by cutting the coil component shown.

[0031] Figure 6 yes Figure 1 The diagram shows a three-dimensional view of a drum-shaped magnetic core.

[0032] Figure 7 This is a schematic diagram showing an image obtained by observing a cross-section of a magnetic substrate according to an embodiment of the present invention using a scanning transmission electron microscope.

[0033] Figure 8 It is used to explain the Figure 7 A schematic diagram of the EDS element-based image analysis (EDS mapping) method performed on the image.

[0034] Figure 9 This is an example of a first-line distribution obtained through EDS elemental image analysis.

[0035] Figure 10 This is an example of a second-line distribution obtained through EDS elemental image analysis.

[0036] Explanation of reference numerals in the attached figures

[0037] 1……coil component, 10……drum-shaped magnetic core, 11……winding core, 12a, 12b……flange, 20……winding, 40……covering part. Detailed Implementation

[0038] Various embodiments of the present invention will now be described with appropriate reference to the accompanying drawings. Identical components in the multiple drawings are labeled with the same reference numerals in those drawings. It should be noted that, for ease of explanation, the drawings are not necessarily shown at an exact scale.

[0039] Figure 1 This is a perspective view of a coil component 1 according to one embodiment of the present invention. Figure 2 This is a front view of coil component 1. Figure 3 This is a right-side view of coil component 1. Figure 4 This is a bottom view of coil component 1. Figure 5 This is a cross-sectional view obtained by cutting coil component 1 with cut wire II. Figure 6 This is a three-dimensional view of the magnetic core of coil component 1.

[0040] In the illustrated embodiment, the coil component 1 is mounted on the circuit board 2 via a first pad portion 3a and a second pad portion 3b. The coil component 1 is, for example, an inductor used to remove noise in an electronic circuit. The coil component 1 may also be a power inductor assembled in a power line, or an inductor used in a signal line.

[0041] Figure 1 The figure shows the mutually orthogonal X, Y, and Z directions. In this specification, the figures are sometimes used... Figure 1The orientation and arrangement of the constituent components of coil component 1 are explained using the X, Y, and Z directions as references. Specifically, the direction in which the core A of the winding core 11 extends is defined as the X direction, the direction perpendicular to the core A of the winding core 11 and parallel to the mounting surface of the circuit board 2 is defined as the Y direction, and the direction orthogonal to the X and Y directions is defined as the Z direction. In this specification, the X direction is sometimes referred to as the width direction of coil component 1, the Y direction as the length direction of coil component 1, and the Z direction as the height direction of coil component 1.

[0042] In one embodiment of the present invention, the coil component 1 is formed in a cuboid shape. The coil component 1 has a first end face 1a, a second end face 1b, a first main face 1c (upper surface 1c), a second main face 1d (bottom surface 1d), a first side face 1e, and a second side face 1f. More specifically, the first end face 1a is the end face of the coil component 1 in the negative X-axis direction, the second end face 1b is the end face of the coil component 1 in the positive X-axis direction, the first main face 1c is the end face of the coil component 1 in the positive Z-axis direction, the second main face 1d is the end face of the coil component 1 in the negative Z-axis direction, the first side face 1e is the end face of the coil component 1 in the positive Y-axis direction, and the second side face 1f is the end face of the coil component 1 in the negative Y-axis direction.

[0043] As shown in the figure, the coil component 1 includes a drum core 10 formed of ferrite material, a winding 20, a first external electrode 30a, a second external electrode 30b, and a resin part 40.

[0044] The drum-shaped magnetic core 10 includes: a core 11 extending in a direction parallel to the mounting surface of the circuit board 2; a cuboid flange 12a disposed at one end of the core 11; and a cuboid flange 12b disposed at the other end of the core 11. The core 11 connects the flanges 12a and 12b. The flanges 12a and 12b are arranged such that their inner surfaces face each other.

[0045] The drum-shaped magnetic core 10 has a first end face 10a, a second end face 10b, a first main face 10c (upper surface 10c), a second main face 10d (bottom surface 10d), a first side face 10e, and a second side face 10f.

[0046] In the illustrated embodiment, the core 11 is approximately square prism in shape. The core 11 can take any shape suitable for winding the winding 20. For example, the core 11 can take the shape of a triangular prism, pentagonal prism, hexagonal prism, or other polygonal prism, cylindrical, elliptical, or frustum conical.

[0047] The drum-shaped magnetic core 10 is a sintered ferrite body obtained by sintering ferrite material. The ferrite material used in the drum-shaped magnetic core 10 comprises, for example, oxides with Fe₂O₃, ZnO, CuO, and NiO as the main components and Bi₂O₃ as the secondary component. More specifically, the ferrite material used in the drum-shaped magnetic core 10 contains 49.3 mol% Fe₂O₃, 23.1 mol% ZnO, 6.6 mol% CuO, and 21 mol% NiO₂ as the main components, and 0.03 wt% to 0.1 wt% Bi₂O₃ as the secondary component. The content ratio of each component can be varied. For example, the content ratio of Bi₂O₃ can be 0.05 wt% to 0.075 wt%.

[0048] The drum-shaped magnetic core 10 can be manufactured based on the aforementioned ferrite material using conventional methods. An example of the manufacturing method for the drum-shaped magnetic core is described below. First, powders of Fe2O3, ZnO, CuO, and NiO, which are the main components, are mixed, and the mixed powder is pre-fired at approximately 850°C. Next, the pre-fired mixed powder is pulverized using a wet mill to obtain ferrite powder with an average particle size of 2 μm. Then, the ferrite powder is mixed with water to prepare a slurry, and Bi2O3 powder is added to the slurry. The amount of Bi2O3 powder added is, for example, 0.03 wt% to 0.1 wt%, as described above. Next, the slurry containing the Bi2O3 powder is stirred using a disperser at a speed of 500 rpm to 1000 rpm for at least 5 minutes. A binder is added to the stirred slurry to form granules. Then, the granules are compressed and shaped to obtain a molded body having the shape of the drum-shaped magnetic core 10. Next, the formed body is fired in the atmosphere at approximately 1050°C to produce the drum-shaped magnetic core 10. The main composition of the ferrite material used for the drum-shaped magnetic core 10 is not limited to the composition described above. The content ratio of oxides contained as the main component can be appropriately changed. In addition, various parameters in the manufacturing process can be appropriately changed.

[0049] A winding 20 is wound on the core 11. The winding 20 is constructed by covering an insulating film around a conductor made of a highly conductive metal material. The metal material used for the winding 20 can be, for example, one or more metals selected from Cu (copper), Al (aluminum), Ni (nickel), and Ag (silver), or an alloy containing any of these metals.

[0050] An external electrode 30a is provided on flange 12a, and an external electrode 30b is provided on flange 12b. The shape and configuration of the external electrodes 30a and 30b shown in the figure are merely illustrative, and the external electrodes 30a and 30b can take various shapes and configurations.

[0051] One end of the winding 20 is electrically connected to the external electrode 30a, and the other end of the winding 20 is electrically connected to the external electrode 30b.

[0052] The resin portion 40 is formed by filling the space between flanges 12a and 12b with resin. The resin portion 40 covers at least a portion of the winding 20. For example, the resin portion 40 may only cover the upper surface of the winding 20, thereby ensuring or improving adhesion during installation. The resin portion 40 is, for example, made of resin or a resin containing filler. As the material of the resin portion 40, any resin material used for covering windings in wound coil components can be used. As the filler, magnetic or non-magnetic materials can be used. By using ferrite powder, metallic magnetic particles, alumina particles, or silica particles as fillers, the coefficient of linear expansion of the resin portion 40 can be reduced, and its mechanical strength improved.

[0053] Next, refer to Figure 7 The crystal structure contained in the drum-shaped magnetic core 10 is described. Figure 7 This is a schematic diagram showing a STEM image obtained by observing a cross-section of a drum-shaped magnetic core 10 according to an embodiment of the present invention using a STEM (scanning transmission electron microscope). Figure 7 The image shows a STEM image of a 1.3 μm × 1.3 μm region 50 in a cross-section of the drum-shaped magnetic core 10. Region 50 was selected such that grain boundaries are included in the field of view for analysis using EDS elemental imaging techniques described later. Region 50 is selected, for example, to include the triangular points of the grains. As shown, region 50 contains three ferrite grains 60 and grain boundaries 70 present between these grains 60.

[0054] like Figure 7 As shown, at the grain boundaries 70 of each ferrite grain 60, a composition containing Bi as the main component segregates, and this composition exists in multiple regions. In this specification, the composition containing Bi as the main component segregated at the grain boundaries 70 of the ferrite grain 60 is referred to as "Bi segregation," and the region where the Bi segregation exists is referred to as "Bi segregation region." Figure 7 In the figure, Bi segregation region 90 is indicated by reference numeral 90. At the grain boundary 70, the Bi segregation region 90 is not segregated as a film but as an island. In other words, at the grain boundary 70, multiple Bi segregation regions 90 exist spaced apart from each other. Figure 7 This is an example of an image obtained by observing the cross-section of the drum-shaped magnetic core 10 using STEM. Even when observing other cross-sections of the drum-shaped magnetic core 10, multiple Bi segregation regions 90 are spaced apart from each other at the grain boundary 70.

[0055] The fact that the Bi segregation region at grain boundary 70b is segregated as islands rather than films can be confirmed, as described below, based on the Bi elemental mapping data obtained by EDS elemental imaging analysis. First, energy-dispersive X-ray diffraction (EDS) is performed on the STEM image of region 50 to obtain the Bi elemental mapping data. Next, this Bi elemental mapping data is reconstructed along multiple (in this example, 10) scan lines SL1 to SL10 traversing grain boundary 70. Based on the reconstructed elemental mapping data along these scan lines SL1 to SL10, a line profile is obtained for each scan line. The length of the multiple scan lines SL1 to SL10 is, for example, 100 nm, and the interval (scan spacing) between the multiple scan lines SL1 to SL10 is, for example, 20 nm. The multiple scan lines SL1 to SL10 are, for example, set at equal intervals. The number, length, and interval of the scan lines used to obtain the line profile can be appropriately varied.

[0056] The line distribution, as described above, is obtained by reconstructing the elemental surface distribution data of Bi element along scan lines. An example of the line distribution is shown below. Figure 9 and Figure 10 As shown in the figure, the line distribution can be represented as a graph of the count values ​​of Bi at each detection position on the scan line. Figure 9 This represents the line distribution obtained by reconstructing the elemental surface distribution data of Bi elements along scan line SL1. Figure 10 This represents the line distribution obtained by reconstructing the elemental surface distribution data of Bi element along scan line SL2. Figure 9 and Figure 10 In the graph, the horizontal axis represents the detection position on each scan line, and the vertical axis represents the count value of the Bi element at each detection position. The count value of the Bi element represents the detection intensity of Bi, i.e., the Bi detection intensity.

[0057] like Figure 8 As shown, the scan line SL1 is positioned at one of a plurality of Bi segregation regions 90 that are segregated at intervals from each other. Therefore, Figure 9 The line distribution of scan line SL1 shown contains a detection peak of Bi element at the detection position corresponding to grain boundary 70. Scan lines SL3, SL6, SL8, and SL10 are also set at positions passing through Bi segregation region 90, similar to scan line SL1. Therefore, the line distribution of scan lines SL3, SL6, SL8, and SL10 also has a detection peak of Bi element at the detection position corresponding to grain boundary 70, similar to the line distribution of scan line SL1.

[0058] On the other hand, scan line SL2 is set at a position that does not pass through the Bi segregation region 90. Therefore, Figure 10 The line distribution of scan line SL2 shown does not have a detection peak for Bi element at the detection position corresponding to grain boundary 70. Scan lines SL4, SL5, SL7, and SL9 are also set at positions that do not pass through the Bi segregation region 90, similar to scan line SL2. Therefore, the line distribution of scan lines SL4, SL5, SL7, and SL9 also does not have a detection peak for Bi element at the detection position corresponding to grain boundary 70, similar to scan line SL2.

[0059] Most of the Bi element segregates at the grain boundaries, but sometimes trace amounts of Bi can diffuse into the grains. When Bi has diffused into the grains, the elemental plane distribution data of Bi reconstructed along each scan line also shows some degree of count value at the detection positions corresponding to those within the grains. Other Bi elements besides the Bi segregates at the grain boundaries, such as… Figure 9 and Figure 10 As shown, this is reflected as a background detection value in the online distribution. When the scan line passes through the Bi segregation region 90 at the grain boundary, a significantly higher Bi detection intensity than the background Bi detection intensity can be obtained at the detection position corresponding to the grain boundary in the online distribution of this scan line. For a certain online distribution, when the maximum value of the Bi detection intensity at the detection position corresponding to the grain boundary 70 is greater than or equal to the average value of the Bi detection intensity within the grain (i.e., the background detection intensity) by a reference factor, it is determined that the online distribution contains a detection peak of Bi element at the grain boundary. Conversely, for a certain online distribution, when the maximum value of the Bi detection intensity detected at the detection position corresponding to the grain boundary 70 is less than the reference factor of the background Bi detection intensity, it is determined that the online distribution does not contain a detection peak. This reference factor is, for example, 1.2 times. The reference factor can be appropriately changed. The background detection intensity can be the average value of the Bi element count values ​​at multiple detection positions corresponding to the grain within the online distribution. Assuming a scan line length of 100 nm, and defining the region from 40 nm to 60 nm from one end of the scan line as a grain boundary, the average count values ​​of Bi element at six positions (10 nm, 20 nm, 30 nm, 70 nm, 80 nm, and 90 nm) from one end of the scan line are used as the background detection intensity. In this specification, the line distribution containing Bi element detection peaks at the detection positions corresponding to grain boundaries is referred to as the "first line distribution," and the line distribution not containing Bi element detection peaks at the detection positions corresponding to grain boundaries is referred to as the "second line distribution."

[0060] In the case where a foreign object other than Bi segregation in the Bi segregation region 90 exists at the grain boundary 70, the line distribution of the scan line through this foreign object is similar to... Figure 10Similarly, the line distribution shown does not exhibit a detection peak for Bi element at grain boundaries. To prevent false positives caused by foreign matter, the scan line is positioned to avoid locations where foreign matter is not detected. The location of the foreign matter can be determined, for example, based on the elemental plane distribution data of Fe. In the elemental plane distribution data of Fe, if there is a region where the Fe element count value drops sharply compared to the surrounding area, then it is determined that a foreign matter is present at that region.

[0061] exist Figure 8 In the example shown, the line distribution of the 10 scan lines SL1 to SL10 includes multiple first line distributions and multiple second line distributions. The number of first line distributions can be one or more. The number of second line distributions is multiple. There are more than two second line distributions at the grain boundary 70, which confirms that the Bi segregation region 90 is separated from other Bi segregation regions.

[0062] exist Figure 8 In the example shown, the scan line SL6 passing through the Bi segregation region 90 (i.e., the scan line corresponding to the first line distribution) is sandwiched between two scan lines SL5 and SL7 that do not pass through the Bi segregation region 90 (i.e., the two scan lines corresponding to the second line distribution). Since the scan line SL6 passing through the Bi segregation region 90 is positioned between the scan lines SL5 and SL7 that do not pass through the Bi segregation region 90, it can be determined that the Bi segregation region 90 exists at the location where it intersects with the scan line SL6 at the grain boundary 70, but does not exist at the locations where it intersects with the scan lines SL5 and SL7 adjacent to the scan line SL6 at the grain boundary 70. That is, it can be confirmed that there is no Bi segregation region in the area surrounding the Bi segregation region 90 through which the scan line SL6 passes within the grain boundary 70. Similarly, the scan line SL8 passing through the segregation region 90 is sandwiched between scan lines SL7 and SL9 that do not pass through the Bi segregation region 90. Therefore, it can be confirmed that there is no Bi segregation region in the area surrounding the Bi segregation region 90 through which the scan line SL8 passes in the grain boundary 70. As described above, it can be confirmed that the Bi segregation region 90 is separated from other Bi segregation regions 90 in the grain boundary 70.

[0063] The effects of the coil component 1 according to one embodiment of the present invention will now be explained.

[0064] In a drum-shaped magnetic core 10 according to one embodiment of the present invention, a Bi segregation region 90 is present at the grain boundaries 70 of the ferrite grains. This Bi segregation region 90 functions as a stress buffer material against impacts caused by heat, etc., thus suppressing the generation of cracks caused by thermal shock in the drum-shaped magnetic core 10 compared to the absence of the Bi segregation region 90 at the grain boundaries 70. While the Bi segregation region functions to suppress crack generation and propagation, when the Bi segregation region is formed as a layer or film at the grain boundaries 70, it hinders the direct bonding of the grains. Furthermore, the layer or film of Bi segregation is weak and easily peels off / breaks within the layer or film, thus reducing the mechanical strength of the drum-shaped magnetic core 10 relative to external forces. As described above, in conventional ferrite magnetic cores, the stress-relieving layer of Bi oxide or the stress-relieving layer containing Bi oxide is formed at the grain boundaries as a continuous layer or film in which the individual grains do not contact each other. In contrast, in a drum-shaped magnetic core 10 according to one embodiment of the present invention, a plurality of Bi segregation regions 90 are segregated at the grain boundaries 70 in a spaced-apart manner. Because the plurality of Bi segregation regions 90 are spaced apart from each other, in the drum-shaped magnetic core 10, compared with conventional ferrite cores in which layered or film-like stress-relieving layers are formed at the grain boundaries, there is more direct bonding between the particles, and the phenomenon of peeling / fracture within the Bi segregation regions is prevented from propagating and is stopped locally. Therefore, the reduction in mechanical strength relative to external forces can be suppressed. Mechanical strength relative to external forces can be expressed, for example, by bending strength or flexural strength, which can be measured by a standardized method. Whether the Bi segregation regions are spaced apart or form layers or films can be confirmed, as described above, by reconstructing the line distribution obtained by using elemental plane distribution data of Bi element obtained using EDS elemental imaging analysis technology.

[0065] As described above, the drum-shaped magnetic core 10 of one embodiment of the present invention can suppress the generation of cracks caused by thermal shock and can suppress the reduction of mechanical strength relative to external forces.

[0066] The drum-shaped magnetic core 10 of one embodiment of the present invention contains 0.03 wt% to 0.1 wt%, more preferably 0.05 wt% to 0.075 wt% Bi, converted from oxides. Conventional ferrite materials excessively contain Bi and other byproducts; therefore, Bi oxides are considered to form layers or films at grain boundaries. In the above embodiment, the upper limit of the Bi content ratio is set to 0.1 wt% relative to the total amount of the main component, converted from oxides, thereby enabling Bi segregations to form islands rather than layers or films. This suppresses the reduction in mechanical strength caused by the presence of film or layered segregations at grain boundaries.

[0067] In one embodiment of the present invention, a drum-shaped magnetic core 10 is manufactured by adding Bi2O3 powder to a slurry of ferrite powder prepared by wet grinding. The Bi2O3 powder added to the slurry is not ground using a wet grinder. The average particle size of the Bi2O3 powder is, for example, in the range of 1 to 5 μm. The average particle size of the added Bi2O3 powder is set to be the same as or larger than the average particle size of the ground ferrite powder. The average particle size of the ground ferrite powder is, for example, in the range of 1 to 3 μm. The average particle sizes of the Bi2O3 powder and the ground ferrite powder are not limited to the above ranges. For example, the average particle size of the Bi2O3 powder and the average particle size of the ground ferrite powder can be appropriately changed, as long as the condition that the average particle size of the Bi2O3 powder is the same as or larger than the average particle size of the ground ferrite powder is met; for example, they can each be in the range of 0.1 μm to 20 μm. The average particle size of the Bi2O3 powder can be determined by calculating its particle size distribution, using the 50% value (D50) of the calculated distribution. The average particle size of the ferrite powder can be determined similarly. When manufacturing the drum-shaped magnetic core 10, firstly, the average particle size of the Bi2O3 powder is selected, and the ferrite grinding conditions are chosen so that the average particle size of the ground ferrite powder is smaller than the average particle size of the Bi2O3 powder. Therefore, it is possible to make the average particle size of the added Bi2O3 powder the same as or larger than the average particle size of the ground ferrite powder. By making the average particle size of the added Bi2O3 powder the same as or larger than the average particle size of the ground ferrite powder, even with a reduced amount of Bi2O3 powder, it is easy to easily cause multiple Bi segregation regions 90 to segregate at the grain boundaries 70.

[0068] The dimensions, materials, and configurations of the various components described in this specification are not limited to those explicitly described in the embodiments. These components can be modified in any size, material, and configuration that falls within the scope of this invention. Furthermore, components not explicitly described in this specification may be added to the described embodiments, or a portion of the components described in the embodiments may be omitted.

Claims

1. A coil component, characterized in that, include: A magnetic core having multiple ferrite grains and multiple Bi segregation regions present at the grain boundaries of the multiple ferrite grains; and The winding wound on the magnetic core Multiple line distributions obtained by detecting the content of Bi element along multiple scan lines intersecting the grain boundary include: at least one first line distribution containing the detection peak of Bi element at the grain boundary; And multiple second-line distributions that do not include the detection peak, The magnetic core contains more than 0.03 wt% and less than 0.1 wt% Bi in oxide form.

2. The coil component as described in claim 1, characterized in that: The plurality of scan lines includes: at least one first scan line corresponding to the at least one first line distribution; and two second scan lines corresponding to the plurality of second line distributions. At least one of the at least one first scan line is sandwiched between the two second scan lines.

3. The coil component as described in claim 1 or 2, characterized in that: The multiple scan lines are set at equal intervals.

4. The coil component as described in claim 1, characterized in that: The magnetic core contains more than 0.05 wt% and less than 0.075 wt% Bi in oxide form.

5. A coil component, characterized in that, include: A magnetic core having multiple ferrite grains and multiple Bi segregation regions present at the grain boundaries of the multiple ferrite grains; and The winding wound on the magnetic core The multiple Bi segregation regions are spaced apart from each other. The magnetic core contains more than 0.03 wt% and less than 0.1 wt% Bi in oxide form.

6. A circuit board, characterized in that: It includes the coil component as described in any one of claims 1 to 5.

7. An electronic device, characterized in that: Includes the circuit board as described in claim 6.

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