Coil parts, circuit boards and electronic devices

Abstract

To provide a coil component having a ferrite core capable of suppressing the occurrence of cracks due to thermal shock and having improved mechanical strength against external force.SOLUTION: A coil component includes a core having at least a portion arranged inside a coil conductor and having a plurality of Bi segregates 90 present at grain boundaries 70 between a plurality of ferrite crystal grains 60 and a plurality of ferrite crystal grains, and a winding wound around the core. A plurality of line profiles obtained by detecting the content of Bi element along the plurality of scanning lines intersecting the grain boundaries includes at least one first line profile including a detection peak of the Bi element at the grain boundary and a plurality of second line profiles that do not include detection peaks.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The disclosure of the present specification relates to a coil component, a circuit board, and an electronic device. [Background technology]

[0002] Various coil components are used in electronic devices. Examples of coil components include inductors and transformers that are used to remove noise from signals. A known example of a coil component is a wire-wound coil component. A wire-wound coil component includes a core that is a sintered body of a ferrite material, a winding wound around the core of the core, and a plurality of external electrodes electrically connected to the ends of the winding. In a reflow process when mounting such a coil component on a circuit board, a crack may occur in the core due to thermal shock.

[0003] In order to suppress the occurrence of cracks in a ferrite core due to thermal shock, it has been proposed to add a subcomponent containing Bi. For example, Japanese Patent Laid-Open Publication No. 4-325458 (Patent Document 1) discloses a ferrite material containing 0.03 mol% to 2 wt% Bi2O3 as a subcomponent relative to the main component. In a ferrite sintered body formed from the ferrite material of Patent Document 1, an amorphous layer consisting of subcomponents and impurities is formed at the grain boundaries of ferrite crystals with a thickness of 2 to 50 nm. According to Patent Document 1, it is said that by providing an amorphous layer at the grain boundaries, a sintered ferrite with excellent thermal shock resistance can be obtained.

[0004] Japanese Patent Laid-Open Publication No. 11-35369 (Patent Document 2) discloses a ferrite material containing 0.05 wt% to 2.0 wt% of bismuth oxide (Bi2O3), 0.05 wt% to 1.0 wt% of silicon dioxide (SiO2), and 0.05 wt% to 1.5 wt% of chromium oxide (Cr2O3) relative to the main components. According to Patent Document 2, a glassy stress relaxation layer containing these minor components is formed at the grain boundaries of ferrite particles, and this stress relaxation layer can stop the progression of cracks, resulting in a sintered ferrite with excellent thermal shock resistance.

[0005] Japanese Patent Laid-Open Publication No. 1-228108 (Patent Document 3) discloses a Ni-Cu-Zn 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 minor components. The sintered body of the ferrite material in Patent Document 3 has a stress relaxation layer made of minor components at the grain boundaries of the crystal grains. In Patent Document 3, it is said that this stress relaxation layer relieves stress when it is applied to the sintered ferrite from the outside, thereby contributing to improving the material strength of the sintered ferrite.

[0006] As described above, it has been known that by adding an oxide of Bi as a secondary component to a ferrite material, a film containing Bi is formed between crystal grains in a sintered body of the ferrite material, and this film suppresses the occurrence and expansion of cracks caused by thermal shock or external stress. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 4-325458 [Patent Document 2] Japanese Patent Application Publication No. 11-35369 [Patent Document 3] Japanese Patent Application Publication No. 1-228108 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in a ferrite core in which a stress relaxation layer containing Bi oxide is formed on the grain boundaries, the crystals are bonded to each other via the soft stress relaxation layer, and therefore the mechanical strength against external forces of the ferrite core in which a stress relaxation layer containing Bi oxide is formed on the grain boundaries is lower than that of a ferrite core that does not have such a stress relaxation layer.

[0009] The object of the present invention is to solve or mitigate the above-mentioned problems. A more specific object of the present invention is to provide a coil component having a ferrite core capable of suppressing the occurrence of cracks due to thermal shock and having improved mechanical strength against external forces. Other objects of the present invention will become apparent throughout the entire specification. [Means for solving the problem]

[0010] A coil component according to an aspect of the present invention includes a core, at least a portion of which is disposed inside the coil conductor, having a plurality of ferrite grains and a plurality of Bi segregates present at grain boundaries of the plurality of ferrite grains, and a winding wound around the core. In one embodiment, a plurality of line profiles obtained by detecting the content of Bi element along a plurality of scanning lines intersecting the grain boundaries include at least one first line profile including a detection peak of Bi element at the grain boundaries and a plurality of second line profiles not including the detection peak.

[0011] In one embodiment, the plurality of scan lines includes at least one first scan line corresponding to the at least one first line profile and two second scan lines corresponding to the plurality of second line profiles, and at least one of the at least one first scan line is sandwiched between the two second scan lines.

[0012] In one embodiment, the plurality of scanning lines are set at equal intervals.

[0013] In one embodiment, the core contains 0.03 wt % or more and 0.1 wt % or less of Bi calculated as an oxide.

[0014] In one embodiment, the core contains 0.05 wt % or more and 0.075 wt % or less of Bi calculated as an oxide.

[0015] A coil component according to one aspect of the present invention includes a core, at least a portion of which is disposed inside the coil conductor, having a plurality of ferrite grains and a plurality of Bi segregates present at grain boundaries of the plurality of ferrite grains, and a winding wound around the core, wherein the plurality of Bi segregates are spaced apart from one another.

[0016] A circuit board according to an aspect of the present invention includes the coil component described above.

[0017] An electronic device according to an aspect of the present invention includes the circuit board. Effect of the Invention

[0018] Various embodiments of the invention disclosed in this specification provide coil components having a ferrite core that can suppress the occurrence of cracks due to thermal shock and has improved mechanical strength against external forces. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a perspective view showing a coil component according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a front view of the coil device shown in FIG. [Diagram 3] FIG. 2 is a right side view of the coil device shown in FIG. [Figure 4] FIG. 2 is a bottom view of the coil device shown in FIG. [Diagram 5] 5 is a cross-sectional view of the coil device shown in FIG. 4 taken along a plane passing through line II. [Figure 6] FIG. 2 is a perspective view of the drum core shown in FIG. [Figure 7] 1 is a schematic diagram of an image of a cross section of a magnetic substrate according to one embodiment of the present invention observed using a scanning transmission electron microscope. [Figure 8] FIG. 8 is a schematic diagram for explaining a method of EDS mapping for the image in FIG. 7. [Figure 9] 1 is an example of a first line profile obtained by the method of EDS mapping. [Figure 10]1 is an example of a second line profile obtained by the method of EDS mapping. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, various embodiments of the present invention will be described with reference to the drawings as appropriate. Components common to multiple drawings are given the same reference numerals throughout the multiple drawings. Please note that the drawings are not necessarily drawn to scale for the sake of convenience of explanation.

[0021] FIG. 1 is a perspective view showing a coil device 1 according to one embodiment of the present invention, FIG. 2 is a front view of the coil device 1, FIG. 3 is a right side view of the coil device 1, FIG. 4 is a bottom view of the coil device 1, FIG. 5 is a cross-sectional view of the coil device 1 taken along line II, and FIG. 6 is a perspective view of a core of the coil device 1.

[0022] The coil component 1 of the illustrated embodiment is mounted on a circuit board 2 via a first land portion 3a and a second land portion 3b. The coil component 1 is, for example, an inductor used to remove noise in an electronic circuit. The coil component 1 may be a power inductor incorporated in a power supply line, or an inductor used in a signal line.

[0023] In Fig. 1, an X direction, a Y direction, and a Z direction that are perpendicular to each other are shown. In this specification, the orientation and arrangement of components of the coil component 1 may be described based on the X direction, the Y direction, and the Z direction shown in Fig. 1. Specifically, the direction in which the axis A of the winding core 11 extends is defined as the X direction, and the direction perpendicular to the axis A of the winding core 11 and parallel to the mounting surface of the circuit board 2 is defined as the Y direction. The direction perpendicular to the X direction and the Y direction is defined as the Z direction. In this specification, the X direction may be referred to as the width direction of the coil component 1, the Y direction as the length direction of the coil component 1, and the Z direction as the height direction of the coil component 1.

[0024] The coil component 1 according to an embodiment of the present invention is formed in a rectangular parallelepiped shape. The coil component 1 has a first end face 1a, a second end face 1b, a first main face 1c (top face 1c), a second main face 1d (bottom face 1d), a first side face 1e, and a second side face 1f. More specifically, the first end face 1a is an end face of the coil component 1 in the negative X-axis direction, the second end face 1b is an end face of the coil component 1 in the positive X-axis direction, the first main face 1c is an end face of the coil component 1 in the positive Z-axis direction, the second main face 1d is an end face of the coil component 1 in the negative Z-axis direction, the first side face 1e is an end face of the coil component 1 in the positive Y-axis direction, and the second side face 1f is an end face of the coil component 1 in the negative Y-axis direction.

[0025] As shown in the figure, the coil component 1 includes a drum core 10 made of a ferrite material, a winding 20, a first external electrode 30a, a second external electrode 30b, and a resin portion 40.

[0026] The drum core 10 has a winding core 11 extending in a direction parallel to the mounting surface of the circuit board 2, a rectangular parallelepiped flange 12a provided at one end of the winding core 11, and a rectangular parallelepiped flange 12b provided at the other end of the winding core 11. The winding core 11 connects the flange 12a and the flange 12b. The flanges 12a and 12b are arranged so that their inner surfaces face each other.

[0027] The drum core 10 has a first end face 10a, a second end face 10b, a first main face 10c (top face 10c), a second main face 10d (bottom face 10d), a first side face 10e, and a second side face 10f.

[0028] In the illustrated embodiment, the winding core 11 has a substantially rectangular prism shape. The winding core 11 may have any shape suitable for winding the winding 20. For example, the winding core 11 may have a polygonal prism shape such as a triangular prism shape, a pentagonal prism shape, or a hexagonal prism shape, a cylindrical shape, an elliptical cylindrical shape, or a truncated cone shape.

[0029] The drum core 10 is a ferrite sintered body obtained by sintering a ferrite material. The ferrite material for the drum core 10 includes oxides, for example, whose main components are Fe2O3, ZnO, CuO, and NiO, and whose subcomponent is Bi2O3. More specifically, the ferrite material for the drum core 10 contains 49.3 mol% Fe2O3, 23.1 mol% ZnO, 6.6 mol% CuO, and 21 mol% NiO2 as main components, and 0.03 wt% to 0.1 wt% Bi2O3 as a subcomponent. The content ratio of each component can be changed. For example, the content ratio of Bi2O3 can be 0.05 wt% to 0.075 wt%.

[0030] The drum core 10 is manufactured according to a conventional method based on the above ferrite material. An example of a method for manufacturing the drum core will be described. First, the powders of the main components Fe2O3, ZnO, CuO, and NiO are mixed, and the mixed powder is calcined at about 850°C. Next, the calcined mixed powder is crushed by a wet crusher to obtain ferrite powder with an average particle size of 2 μm. Next, 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 to which the Bi2O3 powder has been added is stirred by a disperser at a rotation speed of 500 rpm to 1000 rpm for 5 minutes or more. A binder is added to the stirred slurry to form a granulated material. Next, the granulated material is compression molded to obtain a molded body having the shape of the drum core 10. Next, the compact is sintered at about 1050°C in air to produce the drum core 10. The main components of the ferrite material for the drum core 10 are not limited to those described above. The content ratio of the oxides contained as the main components may be changed as appropriate. In addition, various parameters in the manufacturing process may be changed as appropriate.

[0031] A winding 20 is wound around the winding core 11. The winding 20 is formed by coating a conductor made of a metal material with excellent electrical conductivity with an insulating coating. As the metal material for the winding 20, 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, can be used.

[0032] An external electrode 30a is provided on the flange 12a, and an external electrode 30b is provided on the flange 12b. The shapes and arrangements of the external electrodes 30a and 30b shown in the figures are merely examples, and the external electrodes 30a and 30b can have various shapes and arrangements.

[0033] One end of the winding 20 is electrically connected to an external electrode 30a, and the other end of the winding 20 is electrically connected to an external electrode 30b.

[0034] The resin part 40 is formed by filling the gap between the flange 12a and the flange 12b with resin. The resin part 40 covers at least a part of the winding 20. For example, the resin part 40 can cover only the upper surface of the winding 20, thereby ensuring or improving the adhesiveness during mounting. The resin part 40 is made of, for example, a resin or a resin containing a filler. Any resin material used to cover a winding in a wound coil component can be used as the material of the resin part 40. A magnetic material or a non-magnetic material can be used as the filler. By using ferrite powder, metal magnetic particles, alumina particles, or silica particles as the filler, the linear expansion coefficient of the resin part 40 can be reduced and the mechanical strength can be increased.

[0035] Next, the crystal structure contained in the drum core 10 will be described with reference to FIG. 7. FIG. 7 shows a schematic diagram of a STEM image of a cross section of the drum core 10 of one embodiment of the present invention observed by a STEM (scanning transmission electron microscope). FIG. 7 shows a STEM image of a 1.3 μm×1.3 μm region 50 on the cut surface of the drum core 10. For the analysis by EDS mapping described later, the region 50 is selected so that the grain boundary is included within the field of view. The region 50 is selected so that, for example, the triple point of the crystal grains is included. As shown in the figure, the region 50 includes three ferrite crystal grains 60 and a grain boundary 70 between these crystals 60.

[0036] As shown in FIG. 7, a plurality of compositions containing Bi as a main component are segregated at the grain boundaries 70 of the ferrite crystal grains 60. The composition containing Bi as a main component segregated at the grain boundaries 70 of the ferrite crystal grains 60 is referred to as a "Bi segregate" in this specification. In FIG. 7, the Bi segregate 90 is indicated by reference numeral 90. The Bi segregate 90 is segregated in the grain boundaries 70 in the form of islands, not in the form of a film. In other words, a plurality of Bi segregates 90 are present at the grain boundaries 70, spaced apart from one another. FIG. 7 is an example of an image of a cross section of the drum core 10 observed by STEM, but even when other cross sections of the drum core 10 are observed, the grain boundaries 70 contain a plurality of Bi segregates 90 spaced apart from one another.

[0037] The fact that the Bi segregation contained in the grain boundary 70b is segregated in an island shape rather than a film shape can be confirmed based on mapping data of the Bi element obtained by EDS mapping, as follows. First, energy dispersive X-ray analysis (EDS) is performed on the STEM image of the region 50 to obtain mapping data of the Bi element. Next, this mapping data of the Bi element is reconstructed along a plurality of (10 in this example) scanning lines SL1 to SL10 crossing the grain boundary 70. From the mapping data reconstructed along the scanning lines SL1 to SL10, a line profile is obtained for each of the scanning lines SL1 to SL10. The length of the scanning lines SL1 to SL10 is, for example, 100 nm, and the interval (scanning pitch) between the scanning lines SL1 to SL10 is, for example, 20 nm. The scanning lines SL1 to SL10 are set at equal intervals, for example. The number, length, and interval of the scanning lines for obtaining the line profile can be appropriately changed.

[0038] As described above, the line profile is obtained by reconstructing the mapping data of Bi element along the scan line. Examples of the line profile are shown in Figs. 9 and 10. As shown in the figures, the line profile is expressed as a graph of the count value of Bi at each detection position on the scan line. Fig. 9 shows a line profile obtained by reconstructing the mapping data of Bi element along the scan line SL1, and Fig. 10 shows a line profile obtained by reconstructing the mapping data of Bi element along the scan line SL2. In the graphs of Figs. 9 and 10, the horizontal axis indicates the detection position on each scan line, and the vertical axis indicates the count number of Bi element at each detection position. The count number of Bi element indicates the Bi detection intensity, which is the detection intensity of Bi.

[0039] As shown in Fig. 8, the scan line SL1 is set at a position passing through one of the multiple Bi segregates 90 that are separated from one another and segregated. Therefore, the line profile of the scan line SL1 shown in Fig. 9 includes a detection peak of the Bi element at a detection position corresponding to the grain boundary 70. The scan lines SL3, SL6, SL8, and SL10 are also set at positions passing through the Bi segregates 90 like the scan line SL1, so that the line profiles of the scan lines SL3, SL6, SL8, and SL10 also have detection peaks of the Bi element at detection positions corresponding to the grain boundary 70 like the line profile of SL1.

[0040] On the other hand, the scan line SL2 is set at a position that does not pass through the Bi segregates 90. For this reason, the line profile of the scan line SL2 shown in Fig. 10 does not have a detection peak of the Bi element at the detection position corresponding to the grain boundary 70. The scan lines SL4, SL5, SL7, and SL9 are also set at positions that do not pass through the Bi segregates 90 like the scan line SL2, so the line profiles of the scan lines SL4, SL5, SL7, and SL9 also do not have a detection peak of the Bi element at the detection position corresponding to the grain boundary 70 like the line profile of SL2.

[0041] Most of the Bi element segregates at the grain boundaries, but a small amount of Bi element may diffuse into the grains. When the Bi element diffuses into the grains, the mapping data of the Bi element reconstructed along each scan line has a certain number of counts even at the detection position corresponding to the grain interior. Bi elements other than the Bi segregates segregated at the grain boundaries are reflected as background detection values ​​in the line profile as shown in Figs. 9 and 10. When the scan line passes through the Bi segregates 90 segregated at the grain boundaries, a Bi detection intensity significantly higher than the background Bi detection intensity is obtained at the detection position corresponding to the grain boundaries in the line profile of the scan line. When the maximum value of the Bi detection intensity at the detection position corresponding to the grain boundaries 70 is equal to or greater than a reference magnification with respect to the background detection intensity, which is the average of the Bi detection intensity within the grains, for a certain line profile, it is determined that the line profile includes a detection peak of the Bi element at the grain boundaries. On the other hand, when the maximum value of the Bi detection intensity detected at the detection position corresponding to the grain boundaries 70 is less than a reference magnification with respect to the Bi detection intensity in the background, it is determined that the line profile does not include a detection peak. The reference magnification is, for example, 1.2 times. The reference magnification can be changed as appropriate. The background detection intensity can be the average value of the count values ​​of the Bi element at a plurality of detection positions corresponding to the grain interior of the line profile. Assuming that the scan line is 100 nm and the region between 40 nm and 60 nm from one end of the scan line is the grain boundary, the average of the count values ​​of the Bi element at six positions of 10 nm, 20 nm, 30 nm, 70 nm, 80 nm, and 90 nm from one end of the scan line can be the background detection intensity. In this specification, a line profile including a detection peak of the Bi element at a detection position corresponding to the grain boundary is sometimes called a "first line profile", and a line profile not including a detection peak of the Bi element at a detection position corresponding to the grain boundary is sometimes called a "second line profile".

[0042] When a foreign substance other than the Bi segregation 90 is present at the grain boundary 70, the line profile of the scanning line passing through the foreign substance does not have a detection peak of the Bi element at the grain boundary, similar to the line profile shown in FIG. 10. In order to prevent erroneous determination due to such a foreign substance, the scanning line is set at a position that does not pass through the foreign substance. The position of the foreign substance can be identified, for example, based on mapping data for the Fe element. If there is a location in the mapping data for the Fe element where the count value of the Fe element is suddenly lower than the surrounding areas, it is determined that a foreign substance exists at that location.

[0043] 8, the line profiles of the ten scan lines SL1 to SL10 include a plurality of first line profiles and a plurality of second line profiles. The number of the first line profiles may be one or more. The number of the second line profiles is more than one. By the presence of two or more second line profiles at the grain boundary 70, it can be confirmed that the Bi segregates 90 are separated from the other Bi segregates.

[0044] In the example shown in Fig. 8, the scan line SL6 passing through the Bi segregate 90 (i.e., the scan line corresponding to the first line profile) is sandwiched between two scan lines SL5 and SL7 not passing through the segregate (i.e., two scan lines corresponding to the second line profile). By disposing the scan line SL6 passing through the Bi segregate 90 between the scan lines SL5 and SL7 not passing through the Bi segregate 90, it is understood that the Bi segregate 90 is present at the position of the grain boundary 70 intersecting with the scan line SL6, and the Bi segregate 90 is not present at the position of the grain boundary 70 intersecting with the scan lines SL5 and SL7 adjacent to the scan line SL6. In other words, it can be confirmed that the Bi segregate is not present in the region of the grain boundary 70 around the Bi segregate 90 through which the scan line SL6 passes. Similarly, the scan line SL8 that passes through the segregation 90 is sandwiched between the scan lines SL7 and SL9 that do not pass through the Bi segregation 90, so it can be confirmed that no Bi segregation is present in the region of the grain boundary 70 around the Bi segregation 90 through which the scan line SL8 passes. In this way, it can be confirmed that the Bi segregation 90 is separated from other Bi segregations 90 at the grain boundary 70.

[0045] Next, the effects achieved by the coil component 1 according to one embodiment of the present invention will be described.

[0046] In the drum core 10 according to one embodiment of the present invention, the Bi segregation 90 is present at the grain boundary 70 of the ferrite crystal grains. Since the Bi segregation 90 functions as a stress buffer against shocks caused by heat or the like, the occurrence of cracks due to thermal shock in the drum core 10 can be suppressed compared to the case where the Bi segregation 90 is not present at the grain boundary 70. The Bi segregation serves to suppress the occurrence and expansion of cracks, but when formed in a layer or film at the grain boundary 70, it inhibits direct bonding between the crystal grains. In addition, the layer or film of the Bi segregation has a low strength and is easily peeled off / broken within the layer or film, which causes a decrease in the mechanical strength of the drum core 10 against external forces. As described above, in the conventional ferrite core, the stress relaxation layer of the Bi oxide or the stress relaxation layer containing the Bi oxide is formed as a continuous layer or film at the grain boundary of the crystal grains where the crystal grains are not in contact with each other. In contrast, in the drum core 10 according to one embodiment of the present invention, a plurality of Bi segregation 90 are segregated at the grain boundary 70 so as to be separated from each other. The fact that the multiple Bi segregates 90 are spaced apart from each other means that in the drum core 10, there is more direct bonding between particles than in conventional ferrite cores in which stress relief layers are formed in layers or films at the grain boundaries, and peeling / fracture within the Bi segregates is limited to a local phenomenon without being propagated, so that a decrease in mechanical strength against external forces can be suppressed. The mechanical strength against external forces is expressed, for example, by flexural strength or bending strength that can be measured by a standardized method. Whether the Bi segregates are spaced apart or in layers or films can be confirmed by a line profile obtained by reconstructing the mapping data of the Bi element obtained by EDS mapping as described above.

[0047] As described above, the drum core 10 according to one embodiment of the present invention can suppress the occurrence of cracks due to thermal shock, and can also suppress the decrease in mechanical strength against external forces.

[0048] The drum core 10 of one embodiment of the present invention contains 0.03wt% to 0.1wt% Bi in terms of oxide, more preferably 0.05wt% to 0.075wt% Bi. Conventional ferrite materials contain an excessive amount of Bi element and other subcomponents, so it is considered that Bi oxides are formed in layers or films at grain boundaries. In the above embodiment, the upper limit of the Bi content is set to 0.1wt% in terms of oxide with respect to the total amount of the main components, so that Bi segregation is segregated in islands rather than in layers or films. This suppresses the decrease in mechanical strength caused by the presence of film-like or layer-like segregation at grain boundaries.

[0049] In the manufacturing process of the drum core 10 according to an embodiment of the present invention, Bi2O3 powder is added to a slurry of ferrite powder prepared by crushing the ferrite powder with a wet crusher. The Bi2O3 powder added to the slurry is not crushed with a wet crusher. 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 determined to be equal to or larger than the average particle size of the crushed ferrite powder. The average particle size of the crushed ferrite powder is, for example, in the range of 1 to 3 μm. The average particle sizes of the Bi2O3 powder and the crushed 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 crushed ferrite powder can be appropriately changed as long as the condition that the average particle size of the Bi2O3 powder is equal to or larger than the average particle size of the crushed ferrite powder is satisfied, and may be, for example, in the range of 0.1 μm to 20 μm, respectively. The particle size distribution of the Bi2O3 powder can be obtained and the 50% value (D50) of the obtained particle size distribution can be used as the average particle size of the Bi2O3 powder. The average particle size of the ferrite powder is determined in the same manner. When manufacturing the drum core 10, the average particle size of the Bi2O3 powder is first selected, and the crushing conditions of the ferrite are selected so that the average particle size of the crushed ferrite powder is smaller than the average particle size of the Bi2O3 powder. This makes it possible to make the average particle size of the added Bi2O3 powder equal to or larger than the average particle size of the crushed ferrite powder. By making the average particle size of the added Bi2O3 powder equal to or larger than the average particle size of the crushed ferrite powder, multiple Bi segregates 90 can be easily segregated at the grain boundary 70 even if the amount of added Bi2O3 powder is reduced.

[0050] The dimensions, materials, and arrangement of each component described in this specification are not limited to those explicitly described in the embodiments, and each component can be modified to have any dimensions, materials, and arrangement that can be included in the scope of the present invention. Also, components not explicitly described in this specification can be added to the described embodiments, and some of the components described in each embodiment can be omitted. [Explanation of symbols]

[0051] 1 Coil parts 10. Drum Core 11 Roll core 12a, 12b flange 20 Windings 40 Covering part

Claims

1. a core, at least a portion of which is disposed inside the coil conductor, the core having a plurality of ferrite grains and a plurality of Bi segregates present at grain boundaries of the plurality of ferrite grains; A winding wound around the core; Equipped with A plurality of line profiles obtained by detecting the content of Bi element along a plurality of scanning lines intersecting the grain boundary include at least one first line profile including a detection peak of Bi element at the grain boundary, and a plurality of second line profiles not including the detection peak, The core contains 0.03 wt % or more and 0.1 wt % or less of Bi in terms of oxide. Coil parts.

2. the plurality of scan lines includes at least one first scan line corresponding to the at least one first line profile and two second scan lines corresponding to the plurality of second line profiles; At least one of the at least one first scan line is sandwiched between two of the second scan lines. The coil component according to claim 1 .

3. The plurality of scanning lines are set at equal intervals. The coil component according to claim 1 or 2.

4. The core contains 0.05 wt % or more and 0.075 wt % or less of Bi in terms of oxide. The coil component according to claim 3 .

5. a core, at least a portion of which is disposed inside the coil conductor, the core having a plurality of ferrite grains and a plurality of Bi segregates present at grain boundaries of the plurality of ferrite grains; A winding wound around the core; Equipped with The plurality of Bi segregations are spaced apart from one another, The core contains 0.03 wt % or more and 0.1 wt % or less of Bi in terms of oxide. Coil parts.

6. A circuit board comprising the coil component according to any one of claims 1 to 5.

7. An electronic device comprising the circuit board according to claim 6.

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