Coil element and method for manufacturing same

Abstract

A coil element according to the present invention comprises an element body and an external electrode disposed on the element body. The element body has: a magnetic body in which metal magnetic body layers containing metal magnetic particles are laminated; and an internal electrode that is disposed inside the magnetic body and around which an internal conductor is wound. The magnetic body includes: a peroxide region that contains first metal magnetic particles which serve as the metal magnetic particles, and that contacts the internal electrode; and a non-peroxide region that is disposed between the internal conductors adjacent to each other in the lamination direction, contains second metal magnetic particles as the metal magnetic particles, and contacts the peroxide region. A first metal element constituting the first metal magnetic particles has a higher ionization tendency than a third metal element constituting the internal conductor. The amount of oxygen in the peroxide region is higher than the amount of oxygen in the non-peroxide region.

Description

Coil element and manufacturing method thereof

[0001] The present disclosure relates to a coil element and a method for manufacturing the same.

[0002] Patent Document 1 discloses a coil-type electronic component having a coil inside or on the surface of an element body. In this electronic component, the element body is composed of a group of particles of a soft magnetic alloy containing iron, silicon, and elements that are more easily oxidized than iron, and an oxide layer is formed on the surface of each soft magnetic alloy particle by oxidizing the particle. The oxide layer contains a larger amount of elements that are more easily oxidized than iron compared to the alloy particles, and the particles are bonded to each other via the oxide layer.

[0003] JP 2011-249774 A

[0004] However, as a result of thorough investigation by the inventors of the coil component of Patent Document 1, it was found that structural defects (cracks) occur between the coil (internal conductor) and the element body, and that there is room for improvement in the adhesive strength between the internal conductor and the element body.

[0005] The present disclosure has been made in view of the above-mentioned problems. That is, a primary object of the present disclosure is to provide a coil element that improves the bonding strength between the internal conductor and the element body (magnetic body) and suppresses the occurrence of structural defects (cracks). Another object of the present disclosure is to provide a method for manufacturing such a coil element.

[0006] A coil element according to one embodiment of the present disclosure comprises a base body and an external electrode disposed on the base body, wherein the base body has a magnetic body formed by stacking metal magnetic layers containing metal magnetic particles, and an internal electrode disposed inside the magnetic body and wound around an internal conductor, wherein the magnetic body has an overoxidized region containing first metal magnetic particles as the metal magnetic particles and in contact with the internal electrode, and a non-peroxidized region disposed between the internal conductors adjacent in the stacking direction and containing second metal magnetic particles as the metal magnetic particles and in contact with the peroxidized region, wherein a first metal element constituting the first metal magnetic particles has a greater ionization tendency than a third metal element constituting the internal conductor, and the amount of oxygen in the peroxidized region is greater than the amount of oxygen in the non-peroxidized region.

[0007] A method for manufacturing a coil element according to another embodiment of the present disclosure includes: forming a body precursor having a magnetic body precursor in which metal magnetic body layer precursors containing metal magnetic particles are stacked; and an internal electrode precursor disposed inside the magnetic body precursor and wound with an internal conductor precursor; and firing the body precursor under a low-oxygen atmosphere or a reducing atmosphere to form a body, wherein the magnetic body precursor has a first region containing first metal magnetic particles as metal magnetic particles and in contact with the internal electrode precursor, and a second region disposed between adjacent internal conductor precursors in the stacking direction and containing second metal magnetic particles as metal magnetic particles and in contact with the first region, and wherein the first metal element constituting the first metal magnetic particles has a greater ionization tendency than the third metal element constituting the internal conductor.

[0008] According to the coil component according to one aspect of the present disclosure, the occurrence of structural defects (cracks) can be suppressed.

[0009] Fig. 1 is a perspective view of a coil element according to a first embodiment of the present disclosure. Fig. 2 is an exploded perspective view of the coil element according to the first embodiment of the present disclosure. Fig. 3 is a cross-sectional view taken along the arrow III-III in Fig. 1. Fig. 4 is a cross-sectional view of a coil element according to a second embodiment of the present disclosure. Fig. 5 is a cross-sectional view of a coil element according to a third embodiment of the present disclosure.

[0010] The following describes a coil element and a manufacturing method thereof according to the present disclosure. Note that the present disclosure is not limited to the following configurations and may be modified as appropriate within the scope of the present disclosure. In addition, a combination of multiple individual preferred configurations described below also constitutes the present disclosure.

[0011] In this specification, terms indicating the relationship between elements (e.g., "parallel," "orthogonal," etc.) and terms indicating the shape of elements do not only mean the strict literal form, but also mean a range of substantial equivalence, for example, a range including a difference of about a few percent. Note that in this specification, the direction in which the magnetic layers and coil conductors that make up the element body are stacked is referred to as the "stacking direction."

[0012] Furthermore, in the description of this specification, references to directions or orientations are made merely for the convenience of explanation and are not intended to limit the scope of the present disclosure unless otherwise explicitly stated. For example, relative terms such as "outside (or outer, external, or outer circumference)" and "inside (or inner, internal, or inner circumference)" and their derivatives should be understood to refer to the direction as described or illustrated. In other words, unless otherwise explicitly stated, the invention is not necessarily limited to a specific direction, orientation, or form. Similarly, terms such as "provided," "disposed," and "connected" and their derivatives may refer to a configuration in which other elements, such as intervening elements, are present, rather than being limited to a direct configuration, unless otherwise explicitly stated.

[0013] The drawings shown below are schematic diagrams, and the dimensions, aspect ratio, scale, etc. may differ from those of the actual product.

[0014] Various numerical ranges mentioned in this specification are intended to include the lower and upper limit values ​​themselves, unless otherwise specified, such as "less than." That is, for example, a numerical range such as 2 to 15 μm is interpreted as including the lower limit of 2 μm and the upper limit of 15 μm.

[0015] <First embodiment: coil element> The first embodiment relates to a coil element. The coil element according to the first embodiment includes an element body and an external electrode disposed on the element body, the element body having a magnetic body formed by laminating metal magnetic body layers containing metal magnetic particles, and an internal electrode disposed inside the magnetic body and winding an internal conductor, the magnetic body having an overoxidized region containing first metal magnetic particles as the metal magnetic particles and in contact with the internal electrode, and a non-peroxidized region disposed between adjacent internal conductors in the lamination direction and containing second metal magnetic particles as the metal magnetic particles and in contact with the overoxidized region, the first metal element constituting the first metal magnetic particles has a greater ionization tendency than the third metal element constituting the internal conductor, and the amount of oxygen in the overoxidized region is greater than the amount of oxygen in the non-peroxidized region.

[0016] [Mechanism of Action] The coil element according to the first embodiment can suppress the occurrence of structural defects (cracks). Without being bound by any particular theory, the reason for this is presumed to be as follows. In the coil element according to the first embodiment, the magnetic body has an over-oxidized region in contact with the internal electrode and a non-per-oxidized region in contact with the over-oxidized region, and the amount of oxygen in the over-oxidized region is greater than the amount of oxygen in the non-per-oxidized region. When the over-oxidized region with a relatively high amount of oxygen is positioned so as to be in contact with the internal electrode, the magnetic body is firmly bonded to the internal electrode. This makes it possible to effectively suppress structural defects (cracks) at the interface between the magnetic body and the internal electrode. Therefore, it is believed that the coil element according to the first embodiment can suppress the occurrence of structural defects (cracks).

[0017] [Motivation for Proposing the Present Disclosure] The present inventors have thoroughly investigated the reasons why structural defects occur in conventional coil elements, and have come to the technical knowledge that shrinkage occurs during the firing process in the manufacture of coil elements, accompanied by the formation of internal electrodes, and that internal stress caused by the shrinkage acts locally, particularly at the interface between the magnetic body and the internal electrode, causing structural defects (cracks). Based on this technical knowledge, the present inventors have focused on the generation of "internal stress caused by shrinkage" and discovered that by simultaneously generating internal stress caused by expansion during the manufacture of coil elements, the internal stress caused by the shrinkage can be offset, thereby suppressing the internal stress caused by shrinkage. The inventors have then come up with the idea of ​​arranging a peroxide layer as a specific means for generating internal stress caused by expansion, and have invented the coil element according to the present disclosure.

[0018] The coil element (or laminated inductor) according to the first embodiment will be described in more detail mainly with reference to Figures 1 to 3. Figure 1 is a perspective view of the coil element according to the first embodiment of the present disclosure, Figure 2 is an exploded perspective view of the coil element according to the first embodiment, and Figure 3 is a cross-sectional view taken along the line III-III in Figure 1. Note that the shape and arrangement of the coil element and its components are not limited to the examples shown in the figures.

[0019] The coil element 1 according to the first embodiment includes an element body 10 and external electrodes E1, E2, E3, and E4. The element body 10 has a magnetic body M formed by laminating metal magnetic layers ML containing metal magnetic particles, and internal electrodes (coils) C1 and C2 disposed inside the magnetic body M and wound around internal conductors (coil conductors) CD1 and CD2. The magnetic body M has an overoxidized region P containing first metal magnetic particles as metal magnetic particles and in contact with the internal electrode C, and a non-peroxidized region NP disposed between the internal conductors CD1 and CD2 adjacent in the stacking direction, containing second metal magnetic particles as metal magnetic particles, and in contact with the overoxidized region P.

[0020] [Large Amount of Oxygen] The amount of oxygen in the peroxidized region P is greater than the amount of oxygen in the non-peroxidized region NP. In other words, the peroxidized region P has a greater amount of oxygen than the non-peroxidized region NP. The oxygen atomic ratio of the peroxidized region P is 15 to 35% by volume. The oxygen atomic ratio of the non-peroxidized region NP is 10% by volume or less. The method for determining these oxygen atomic ratios will be described later.

[0021] In this specification, the amount of oxygen refers to the volume of oxygen atoms present at a specific location.

[0022] (Method for Determining the Amount of Oxygen) The fact that the amount of oxygen in the peroxidized region P is greater than the amount of oxygen in the non-peroxidized region NP can be determined by the following method. First, a cross section of the coil element 1 is formed, and an SEM image of the cross section is taken. This cross section includes the winding axis of the internal electrode (coil) C and is parallel to the winding axis and the long axis direction (L direction) of the coil element 1. Here, the magnification of the SEM image is, for example, 1,000 times, and the adjacent internal conductor CD is set within the field of view of the SEM image.

[0023] Next, EDX mapping is performed on the SEM image of the cross section, and the areas where oxygen atoms are present are colored. From the binarized SEM image of the cross section, the area ratios where oxygen atoms are present in the peroxidized region P and the non-peroxidized region NP (oxygen atom ratio: volume %) are calculated. Based on the relative size of the area ratios where oxygen atoms are present in the peroxidized region P and the non-peroxidized region NP, it is determined whether the amount of oxygen in the peroxidized region P is greater than the amount of oxygen in the non-peroxidized region NP. Note that the oxygen atom ratio in the peroxidized region P is the above-mentioned "area ratio where oxygen atoms are present in the peroxidized region P," and the oxygen atom ratio in the non-peroxidized region NP is the above-mentioned "area ratio where oxygen atoms are present in the non-peroxidized region NP."

[0024] At this time, the distinction between the peroxidized region P and the non-peroxidized region NP is determined by the color tone in EDX mapping of oxygen. Also, if the second magnetic particles and the first metal magnetic particles have different compositions (for example, different constituent atoms), the SEM image can be subjected to EDX mapping processing to distinguish the first metal magnetic particles and the second magnetic particles based on the material of the metal magnetic particles, thereby distinguishing the peroxidized region P and the non-peroxidized region NP. Alternatively, if the average particle size of the first metal magnetic particles and the average particle size of the second metal magnetic particles are different, the peroxidized region P and the non-peroxidized region NP can also be distinguished by distinguishing the first metal magnetic particles and the second magnetic particles based on their average particle size using SEM images and image analysis software.

[0025] Specifically, the coil element 1 is cut along a TL cross section (a cross section taken along the arrow direction of line III-III in FIG. 3 ) passing through the intersection of the diagonals of the second main surface (top surface, upper surface) 12 of the approximately rectangular coil element 1 shown in FIG. 1 . Using a scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDX), signals derived from the material (oxygen atoms) that constitutes the peroxidized region P are measured for the cross section thus formed. Based on the measurement results, a mapping process is performed on the cross-sectional image, and an analysis image showing the distribution of the material is created. As a result, areas where oxygen atoms are present and areas where metal magnetic particles (first metal magnetic particles) are present are colored in the analysis image. The peroxidized region P contains first metal magnetic particles.

[0026] The total area of ​​the locations where oxygen atoms are present and the locations where the first metal magnetic particles are present per unit area in the analysis image corresponding to the peroxidized region P (containing the first metal magnetic particles) and the area of ​​the locations where oxygen atoms are present per unit area are calculated. From the obtained total area and area, the area ratio of oxygen atoms per unit area in the peroxidized region P is calculated. Similarly, the area ratio of oxygen atoms per unit area in the non-peroxidized region NP is calculated. From the magnitude relationship of the obtained area ratios, it is determined whether the amount of oxygen in the peroxidized region P is greater than the amount of oxygen in the non-peroxidized region NP.

[0027] To quantitatively express that the amount of oxygen in the peroxidized region P is greater than the amount of oxygen in the non-peroxidized region NP, for example, the amount of oxygen in the peroxidized region P is more than twice the amount of oxygen in the non-peroxidized region NP, and the cross-sectional area of ​​the peroxidized region P is 0.2 to 10 times the cross-sectional area of ​​the non-peroxidized region NP.

[0028] The ratio of the amount of oxygen in the peroxidized region P to the amount of oxygen in the non-peroxidized region NP is calculated as follows to determine the magnitude relationship. Spectra are measured using EDX at multiple locations corresponding to the peroxidized region P and multiple locations corresponding to the non-peroxidized region NP. The average values ​​of the intensity of the spectra obtained for the locations corresponding to the peroxidized region P and the non-peroxidized region NP are calculated. The two average values ​​based on the spectral intensities are compared to determine the ratio. The ratio of the cross-sectional area of ​​the peroxidized region P to the cross-sectional area of ​​the non-peroxidized region NP is determined by calculating the area ratio of the area where oxygen atoms exist in the peroxidized region P (oxygen atomic ratio: volume %) relative to the area ratio of the area where oxygen atoms exist in the non-peroxidized region NP (oxygen atomic ratio: volume %).

[0029] (Means for increasing the amount of oxygen) Specific means for realizing that the amount of oxygen in the peroxidized region P is greater than the amount of oxygen in the non-peroxidized region NP include, for example, (1) contacting or bringing the first metal element constituting the first metal magnetic particle into close proximity with the third metal element constituting the internal conductor, (2) having a greater ionization tendency than the third metal element constituting the internal conductor, (3) having an average particle size smaller than that of the second metal magnetic particle, and (4) having the first metal magnetic particle contain at least one atom (additive atom) selected from the group consisting of Bi, Cl, Na, and K. Other specific means include (5) contacting or bringing the first metal element constituting the first metal magnetic particle into close proximity with the second metal element constituting the second metal magnetic particle, and (6) having a greater ionization tendency than the second metal element constituting the first metal magnetic particle.

[0030] In detail, in the state of the raw materials in the manufacturing method of the coil element 1, the average particle size of the first metal magnetic particles as described above, the composition of the first metal magnetic particles (inclusion of added atoms), the relative positioning of the internal conductor, the first metal element, and the second metal element, and the magnitude relationship of the ionization tendencies of the internal conductor and the first metal element are adjusted, so that the first metal magnetic particles in contact with the internal conductor are more susceptible to oxidation than the surrounding materials, resulting in a greater amount of oxidation.

[0031] In (1) and (2), corrosion between dissimilar metals (galvanic corrosion) is utilized. When the first metal element that mainly constitutes the first metal magnetic particles is brought into contact with or close to the third metal element that constitutes the internal conductor, and the first metal element that constitutes the first metal magnetic particles has a greater ionization tendency than the third metal element that constitutes the internal conductor, when the first metal element and the third metal element come into contact with each other through moisture in the presence of moisture to form a battery system, the first metal atom that has a relatively greater ionization tendency is preferentially (or selectively) oxidized.

[0032] In (3), when the first metal magnetic particles have a smaller average particle size than the second metal magnetic particles, the surface area per unit volume of the first metal magnetic particles is larger than the surface area per unit volume of the second metal magnetic particles. As a result, when the first metal magnetic particles come into contact with the internal conductor, the surface area per unit volume of the metal magnetic particles is larger than when the second metal magnetic particles come into contact with the internal conductor. Therefore, the surface of the first metal magnetic particles may be oxidized in the coil element manufacturing method. As a result, the amount of oxygen in the peroxidized region P increases.

[0033] In (4), when the first metal magnetic particles contain additive atoms, oxidation is promoted. Therefore, in the manufacturing method of the coil element 1, the first metal magnetic particles are oxidized, and the amount of oxygen in the peroxidized region P increases.

[0034] In (5) and (6), corrosion between dissimilar metals (galvanic corrosion) is utilized. When a first metal element that mainly constitutes a first metal magnetic particle is brought into contact with or close to a second metal element that constitutes a second metal magnetic particle, and the first metal element that constitutes the first metal magnetic particle has a greater ionization tendency than the second metal element that mainly constitutes the second metal magnetic particle, when the first metal element and the second metal element come into contact with each other through moisture in the presence of moisture to form a battery system, the first metal atom with the relatively greater ionization tendency is preferentially (or selectively) oxidized.

[0035] Each component will be described in detail below. [Element Body] The element body 10 has, for example, a rectangular or approximately rectangular parallelepiped shape having six sides. The corners and ridges of the element body 10 may be rounded. A corner is a portion where three sides of the element body 10 intersect, and a ridge is a portion where two sides of the element body 10 intersect.

[0036] 1, the length direction, width direction, and height direction of the coil element 1 and the base body 10 are shown as the L direction, the W direction, and the T direction, respectively. The length direction (long axis direction) L, the width direction (short axis direction) W, and the height direction (stacking direction of the internal conductors) T are perpendicular to each other. The mounting surface of the coil element 1 is, for example, a plane (LW plane) parallel to the length direction L and the width direction W.

[0037] 1 has a first main surface 11 and a second main surface 12 that face each other in the height direction T, a first end surface 13 and a second end surface 14 that are perpendicular to the height direction T and face each other in the length direction L, and a first side surface 15 and a second side surface 16 that face each other in the width direction W that is perpendicular to the length direction L and the height direction T. In the example shown in FIG. 1 , the first main surface 11 of the element body 10 corresponds to the mounting surface (bottom surface) of the element body 10. Note that the second main surface 12 may also be the mounting surface of the element body 10.

[0038] The element body 10 has a magnetic body M and an internal electrode (coil) C, and the coil C is arranged within the element body 10. The element body 10 is formed by stacking multiple metal magnetic layers ML in which coil conductors CD can be formed. In the first embodiment, as shown in FIG. 2 , the element body 10 is a laminate in which multilayer groups G1 to G10, each including a metal magnetic layer ML or at least one metal magnetic layer ML and a coil conductor CD, are stacked in the stacking direction (height direction T). Note that the boundaries between each layer in the laminate structure of the element body 10 (particularly, the boundaries between metal magnetic layers ML made of the same material) have disappeared. Each multilayer group layer may be formed by stacking multiple identical patterns.

[0039] (Stacking Groups) The element body 10 will be described using stacking groups G1 to G10 shown in Fig. 2. Note that in Fig. 2, the thicknesses of the stacking groups G1 to G10 are omitted.

[0040] -Layer group G1- The layer group G1 has a metal magnetic layer ML including an overoxidized region P, and constitutes the second main surface 12 of the element body 10. The overoxidized region P is located in a recess formed in the lower surface of the metal magnetic layer ML. Here, the recess has a shape when viewed from a cut surface (cross-sectional view) perpendicular to the extension direction of the overoxidized region P. The pattern of the overoxidized region P is provided to correspond to the winding shape of the second coil conductor CD2 of the layer group G2, which will be described later, and has a pattern slightly larger than the pattern of the second coil conductor CD2 of the layer group G2. Therefore, in the element body 10, the upper surface CD-1 of the second coil conductor CD2 is covered with the overoxidized region P.

[0041] -Lamination Group G2- The lamination group G2 has a metal magnetic layer ML and a second coil conductor CD2 that forms part of the second coil C2.

[0042] The second coil conductor CD2 of the multilayer group G2 forms one winding of the second coil C2. More specifically, one end of the second coil conductor CD2 is connected to a via conductor (not shown) for connection to the second coil conductor CD2 of the multilayer group G4, and the other end of the second coil conductor CD2 is connected to a fourth through-hole conductor (not shown) for electrical connection to the fourth external electrode E4.

[0043] The second coil conductor CD2 is disposed in a recess formed in the upper surface of the metal magnetic layer ML via an over-oxidized region P. In other words, the side surfaces (inner surface CD-3 and outer surface CD-4) and the lower surface CD-2 of the second coil conductor CD2 are disposed so as to be surrounded by the over-oxidized region P (note that the lower surface coating is not shown in FIG. 2).

[0044] -Multilayer Group G3- The multilayer group G3 has a metal magnetic layer ML, a via conductor V provided in the metal magnetic layer ML, and a fourth through-hole conductor T4 provided in the metal magnetic layer ML.

[0045] The metal magnetic layer ML has a peroxidized region P disposed in a recess formed on its underside. Here, the recess has a shape when viewed from a cut surface (cross-sectional view) perpendicular to the direction in which the peroxidized region P extends. The pattern of the peroxidized region P is provided to correspond to the winding shape of the second coil conductor CD2 of the multilayer group G4 (described below), and has a pattern slightly larger than the pattern of the second coil conductor CD2 of the multilayer group G2. Therefore, in the element body 10, the upper surface CD-1 of the second coil conductor CD2 is covered with the peroxidized region P.

[0046] The via conductor V of the multilayer group G3 is disposed at a position where it is connected to one end of the second coil conductor CD2 of the multilayer group G2.

[0047] The fourth through-hole conductor T4 of the multilayer group G3 connects the fourth through-hole conductors T4 of the multilayer groups G2 and G4 adjacent to each other in the stacking direction, and is electrically connected to the fourth external electrode E4. Therefore, the fourth through-hole conductor T4 is disposed above the fourth external electrode E4 in a planar perspective view.

[0048] -Lamination Group G4- The lamination group G4 includes a metal magnetic layer ML, a second coil conductor CD2 that forms part of the second coil C2, and a fourth through-hole conductor T4 provided in the metal magnetic layer ML.

[0049] The second coil conductor CD2 of the multilayer group G4 forms another winding of the second coil C2. More specifically, the metal magnetic layers ML have holes penetrating surfaces facing each other in the stacking direction, and the second coil conductor CD2 is disposed in the holes. One end of the second coil conductor CD2 is connected to the second coil conductor CD2 of the multilayer group G2, and the other end of the second coil conductor CD2 is connected to a third through-hole conductor (not shown) for electrical connection to the third external electrode E3.

[0050] The fourth through-hole conductor T4 of the multilayer group G4 connects the fourth through-hole conductors T4 of the multilayer groups G3 and G5 adjacent to each other in the stacking direction, and is electrically connected to the fourth external electrode E4. Therefore, the fourth through-hole conductor T4 may be disposed at a corner of the metal magnetic layer ML located on the fourth external electrode E4.

[0051] The second coil conductor CD2 is disposed in a recess formed in the upper surface of the metal magnetic layer ML via an overoxidized region P. In other words, the side surfaces (inner surface CD-3 and outer surface CD-4) and the lower surface CD-2 (not shown) of the second coil conductor CD2 are disposed so as to be surrounded by the overoxidized region P.

[0052] -Lamination Group G5- The lamination group G5 includes a metal magnetic layer ML, an overoxidized region P, and a third through-hole conductor T3 and a fourth through-hole conductor T4 provided in the metal magnetic layer ML.

[0053] The peroxide region P of the multilayer group G5 electrically insulates the first coil C1 and the second coil C2. The peroxide region P is disposed in a recess formed in the lower surface of the metal magnetic layer ML. Here, the recess has a shape when viewed from a cut surface (cross-sectional view) perpendicular to the extending direction of the peroxide region P. The pattern of the peroxide region P is provided to correspond to the winding shape of the first coil conductor CD1 of the multilayer group G6 (described below), and has a pattern slightly larger than the pattern of the first coil conductor CD1 of the multilayer group G6. Therefore, in the element body 10, the upper surface CD-1 of the second coil conductor CD2 is covered with the peroxide region P.

[0054] The third through-hole conductor T3 of the multilayer group G5 connects the third through-hole conductors T3 of the multilayer groups G4 and G6 adjacent to each other in the stacking direction, and is electrically connected to the third external electrode E3. Therefore, the third through-hole conductor T3 is disposed on the third external electrode E3 in a planar perspective view.

[0055] The fourth through-hole conductor T4 of the multilayer group G5 connects the fourth through-hole conductors T4 of the multilayer groups G4 and G6 adjacent to each other in the stacking direction, and is electrically connected to the fourth external electrode E4. Therefore, the fourth through-hole conductor T4 is disposed above the fourth external electrode E4 in a planar perspective view.

[0056] -Lamination group G6- The laminated group G6 has a metal magnetic layer ML, a first coil conductor CD1 that forms part of the first coil C1, and a third through-hole conductor T3 and a fourth through-hole conductor T4 provided in the metal magnetic layer ML.

[0057] The first coil conductor CD1 of the multilayer group G6 constitutes one winding of the first coil C1. More specifically, the metal magnetic layers ML have holes penetrating surfaces facing each other in the stacking direction, and the first coil conductor CD1 is disposed in the holes. One end of the first coil conductor CD1 is provided with a via conductor (not shown) for connection to the first coil conductor CD1 provided in the multilayer group G8, and the other end of the first coil conductor CD1 is provided with a second through-hole conductor (not shown) for electrical connection to the second external electrode E2.

[0058] The third through-hole conductors T3 of the multilayer group G6 connect the third through-hole conductors T3 of the multilayer groups G5 and G7 adjacent to each other in the stacking direction, and are electrically connected to the third external electrode E3. Therefore, the third through-hole conductors T3 may be disposed at the corners of the metal magnetic layers ML located on the third external electrode E3.

[0059] The fourth through-hole conductor T4 of the multilayer group G6 connects the fourth through-hole conductors T4 of the multilayer groups G5 and G7 adjacent to each other in the stacking direction, and is electrically connected to the fourth external electrode E4. Therefore, the fourth through-hole conductor T4 may be disposed at a corner of the metal magnetic layer ML located on the fourth external electrode E4.

[0060] The first coil conductor CD1 is disposed in a recess formed in the upper surface of the metal magnetic layer ML via an overoxidized region P. In other words, the side surfaces (inner surface CD-3 and outer surface CD-4) and the bottom surface CD-2 (not shown) of the first coil conductor CD1 are disposed so as to be surrounded by the overoxidized region P.

[0061] -Lamination group G7- The laminated group G7 has a metal magnetic layer ML, an overoxidized region P, a via conductor V provided in the overoxidized region P, and a second through-hole conductor T2, a third through-hole conductor T3 and a fourth through-hole conductor T4 provided in the metal magnetic layer ML.

[0062] The peroxidized region P of the multilayer group G7 is disposed in a recess formed in the lower surface of the metal magnetic layer ML. Here, the recess has a shape when viewed from a cut surface (cross-sectional view) perpendicular to the extension direction of the peroxidized region P. The pattern of the peroxidized region P is provided to correspond to the winding shape of the first coil conductor CD1 of the multilayer group G8 (described below), and has a pattern slightly larger than the pattern of the first coil conductor CD1 of the multilayer group G8. Therefore, in the element body 10, the upper surface CD-1 of the first coil conductor CD1 is covered with the peroxidized region P.

[0063] The via conductor V of the multilayer group G7 is disposed at a position where it is connected to one end of the first coil conductor CD1 of the multilayer group G6.

[0064] The second through-hole conductor T2 of the multilayer group G7 connects the second through-hole conductors T2 of the multilayer groups G6 and G8 adjacent to each other in the stacking direction, and is electrically connected to the second external electrode E2. Therefore, the second through-hole conductor T2 is disposed on the second external electrode E2 in a planar perspective view.

[0065] The third through-hole conductor T3 of the multilayer group G7 connects the third through-hole conductors T3 of the multilayer groups G6 and G8 adjacent to each other in the stacking direction, and is electrically connected to the third external electrode E3. Therefore, the third through-hole conductor T3 is disposed on the third external electrode E3 in a planar perspective view.

[0066] The fourth through-hole conductor T4 of the multilayer group G7 connects the fourth through-hole conductors T4 of the multilayer groups G6 and G8 adjacent to each other in the stacking direction, and is electrically connected to the fourth external electrode E4. Therefore, the fourth through-hole conductor T4 is disposed above the fourth external electrode E4 in a planar perspective view.

[0067] -Lamination group G8- The laminated group G8 has a metal magnetic layer ML, a first coil conductor CD1 that forms part of the first coil C1, and a second through-hole conductor T2, a third through-hole conductor T3, and a fourth through-hole conductor T4 provided in the metal magnetic layer ML.

[0068] The first coil conductor CD1 of the multilayer group G8 constitutes another winding of the first coil C1. More specifically, the first coil conductor CD1 is wound approximately along the outer periphery of the metal magnetic layer ML. One end of the first coil conductor CD1 is connected to the first coil conductor CD1 of the metal magnetic layer ML of the multilayer group G6, and the other end of the first coil conductor CD1 is provided with a first through-hole conductor (not shown) for electrical connection to the first external electrode E1.

[0069] The second through-hole conductors T2 of the multilayer group G8 connect the second through-hole conductors T2 of the multilayer groups G7 and G9 adjacent to each other in the stacking direction, and are electrically connected to the second external electrode E2. The second through-hole conductors T2 may also be disposed at corners of the metal magnetic layers ML located on the second external electrode E2.

[0070] The third through-hole conductors T3 of the multilayer group G8 connect the third through-hole conductors T3 of the multilayer groups G7 and G9 adjacent to each other in the stacking direction, and are electrically connected to the third external electrode E3. The third through-hole conductors T3 may also be disposed at corners of the metal magnetic layers ML located on the third external electrode E3.

[0071] The fourth through-hole conductor T4 of the multilayer group G8 connects the fourth through-hole conductors T4 of the multilayer groups G7 and G9 adjacent to each other in the stacking direction, and is electrically connected to the fourth external electrode E4. The fourth through-hole conductor T4 may also be disposed at a corner of the metal magnetic layer ML located on the fourth external electrode E4.

[0072] The first coil conductor CD1 is disposed in a recess formed in the upper surface of the metal magnetic layer ML via an overoxidized region P. In other words, the side surfaces (inner surface CD-3 and outer surface CD-4) and the bottom surface CD-2 (not shown) of the first coil conductor CD1 are disposed so as to be surrounded by the overoxidized region P.

[0073] - Multilayer group G9 - In the multilayer group G9, a first through-hole conductor T1, a second through-hole conductor T2, a third through-hole conductor T3, and a fourth through-hole conductor T4 are provided at the corners of the metal magnetic layers ML. The areas of the first through-hole conductors T1 to the fourth through-hole conductors T4 of the multilayer groups G1 to G9 in a plan view from the stacking direction are substantially the same.

[0074] - Multilayer group G10 - The multilayer group G10 has first to fourth through-hole conductors T1 to T4 at the corners of the metal magnetic layers ML, which have larger planar areas than the first to fourth through-hole conductors of the multilayer group G9. The first to fourth through-hole conductors T1 to T4 are used as base electrodes for the external electrodes E1 to E4. By making the planar areas of the first to fourth through-hole conductors of the multilayer group G10 larger than the planar areas of the first to fourth through-hole conductors of the multilayer group G9, strength during mounting can be improved.

[0075] The thickness of the first coil conductor CD1 and the second coil conductor CD2 in each stacking group may be the same. Peroxidized regions P are arranged between all of the coil conductors CD in the stacking direction. Specifically, peroxidized regions P may be arranged in stacking groups G2 to G7 (see FIG. 2).

[0076] (Magnetic body) The magnetic body M is formed by laminating metal magnetic body layers containing metal magnetic particles. The magnetic body M has peroxidized regions P that contain first metal magnetic particles as the metal magnetic particles and are in contact with the internal electrodes C, and non-peroxidized regions NP that are arranged between the internal conductors C adjacent in the stacking direction, contain second metal magnetic particles as the metal magnetic particles, and are in contact with the peroxidized regions P.

[0077] -Peroxidized region- As shown in Fig. 3, the peroxidized region P contacts the surfaces (upper surface CD-1 and lower surface CD-2) that intersect with the stacking direction of the internal conductor CD in a cross-sectional view, as well as the surfaces (inner surface CD-3 and outer surface CD-4) that do not intersect. When the internal conductor CD is arranged so that the entire surface is surrounded by the peroxidized region P in this way, the internal conductor CD and the magnetic material M are firmly bonded, thereby suppressing the occurrence of structural defects (cracks) at the interface between the internal conductor CD and the magnetic material M. All of the eight internal conductors CD in Fig. 3 are surrounded by the peroxidized region P.

[0078] 3 (from a macroscopic viewpoint), the peroxidized region P is in contact with the internal conductor CD, but from a microscopic viewpoint (i.e., from a molecular-level viewpoint), it does not have to be in contact with the molecules and atoms that make up the internal conductor CD. This is because, in the laminate firing step of the manufacturing method described below, when a dew point temperature dp of 0 to 30° C. is adopted as a firing condition, if the molecules and atoms that make up the internal conductor precursor and the first metal element that makes up the peroxidized region precursor can come into contact with each other via water to form a battery system, the peroxidized region precursor can be sufficiently oxidized, and the peroxidized region P can be formed.

[0079] The peroxidized regions P arranged on the opposing surfaces of the internal conductors CD adjacent to each other in the stacking direction are spaced apart from each other and are not joined together. That is, the non-peroxidized regions NP of the magnetic material M are present between the peroxidized regions P arranged on the opposing surfaces of the internal conductors CD adjacent to each other in the stacking direction.

[0080] The average thickness of the peroxidized region P in the stacking direction is, for example, 2 to 50 μm, preferably 2 to 15 μm. In the cross-sectional image mapped in the method for determining the amount of oxygen described above, the peroxidized region P, the non-peroxidized region NP, and the internal conductor CD are each identified, and the length of the peroxidized region P in the stacking direction is measured multiple times (number of measurements n=5). The measurement points are the peroxidized regions P between adjacent internal conductors CD, and are the length in the stacking direction from the interface between the peroxidized region P and the internal conductor CD to the interface between the peroxidized region P and the non-peroxidized region NP. The average of these measured values ​​is calculated, and the obtained average value is taken as the thickness of the peroxidized region P in the stacking direction.

[0081] The peroxide region P contains first metal magnetic particles. The first metal magnetic particles preferably have an average particle size of more than 1 μm and not more than 29 μm, more preferably more than 1 μm and not more than 19 μm, and even more preferably more than 1 μm and not more than 9 μm. From the viewpoint of realizing that the first metal magnetic particles have a larger amount of oxygen than the second metal magnetic particles, the first metal magnetic particles can have an average particle size smaller than that of the second metal magnetic particles.

[0082] The average particle size of the first metal magnetic particles in the overoxidized region P can be measured using the procedure described below. The coil element 1 is cut to obtain a cross section. Specifically, the cross section is obtained by cutting the coil element 1 through the center thereof perpendicular to the mounting surface and end surface of the element body 10. Multiple regions (e.g., 130 μm × 100 μm) of the obtained cross section (e.g., five regions in the overoxidized region P arranged between adjacent internal conductors CD in FIG. 3 ) are photographed using an SEM. The obtained SEM images are analyzed using image analysis software (e.g., image analysis software "Win R00F" (manufactured by Mitani Corporation)) to determine the circle-equivalent diameters of the first metal magnetic particles. The average value of the obtained circle-equivalent diameters is defined as the average particle size of the first metal magnetic particles. Note that the term "average particle size" used in this specification refers to the average particle size D50 (particle size equivalent to a cumulative percentage of 50% on a volume basis).

[0083] The first metal magnetic particles may contain Fe as a magnetic material. More specifically, the first metal magnetic particles may be Fe particles or Fe alloy particles. Elements other than Fe contained in the Fe alloy include Cr (chromium), Ni, Al (aluminum), B (boron), P (phosphorus), Cu (copper), C (carbon), and Nb (niobium). Examples of Fe alloys include Fe-Si-Cr (chromium)-based alloys, Fe-Si-Al (aluminum)-based alloys, Fe-Si-B (boron)-P (phosphorus)-Cu (copper)-C (carbon)-based alloys, Fe-Si-B-Nb (niobium)-Cu-based alloys, and Fe-Ni-based alloys. Among these Fe and Fe-based alloys, Fe and Fe-Ni-based alloys are preferred from the viewpoint of appropriately forming the peroxidized region P in the manufacture of the coil element 1. The first metallic magnetic particles may also contain impurities such as Cr, Mn (manganese), Cu, Ni (nickel), P, S (sulfur), or Co (cobalt) that are not intentionally present during manufacturing.

[0084] In order to ensure that the first metal magnetic particles have a greater amount of oxygen than the second metal magnetic particles, the first metal magnetic particles may contain at least one atom (additive atom) selected from the group consisting of Bi, Cl, Na, and K.

[0085] In manufacturing the coil element 1, from the viewpoint of appropriately forming the peroxidized region P, the first metal element constituting the first metal magnetic particles has a greater ionization tendency than the third metal element constituting the internal conductor CD. When the first metal element constituting the first metal magnetic particles has a greater ionization tendency than the third metal element constituting the internal conductor CD, the peroxidized region P is more likely to be formed in manufacturing the coil element 1. When the first metal element is in proximity to or contact with the third metal element and water is interposed between the first and third metal elements, a battery system is formed. At this time, the first metal element with a greater ionization tendency is preferentially oxidized. In this way, the peroxidized region P is formed. In such a case, in the manufacturing method of the coil element 1, the first metal element is in proximity to or contact with the third metal element and water is interposed between the first and third metal elements to form a battery system. Therefore, in the resulting coil element 1, the first metal element is in proximity to or contact with the third metal element. In other words, the peroxide region P and the internal conductor are in contact with each other from a macroscopic perspective (e.g., to the human eye), but from a microscopic perspective (e.g., under the magnification of an electron microscope), they may be in contact with each other or may be close to each other (without touching).

[0086] In one embodiment, the second metal magnetic particles contain a second metal element composed of a metal element other than Fe, and the first metal element has a greater ionization tendency than the second metal element. When the first metal element constituting the first metal magnetic particles has a greater ionization tendency than the second metal element constituting the second metal magnetic particles, peroxidized regions P are more likely to be formed during the production of the coil element 1. When the first metal element is in proximity to or contact with the second metal element and water is interposed between the first and second metal elements, a battery system is formed. At this time, the first metal element with a greater ionization tendency is preferentially oxidized. In this way, the peroxidized regions P are formed. In this case, the method for producing the coil element 1 simply requires that the first metal element be in proximity to or contact with the second metal element, and water be interposed between the first and second metal elements to form a battery system. Therefore, in the resulting coil element 1, the first metal element is in proximity to or contact with the second metal element. In other words, the peroxidized region P and the non-peroxidized region NP are in contact with each other from a macroscopic perspective (e.g., to the human eye), but from a microscopic perspective (e.g., at the magnification of an electron microscope), they may be in contact with each other or may be close to each other (without touching).

[0087] The first metal element constitutes the first metal magnetic particle. In one embodiment, the first metal element mainly constitutes the first metal magnetic particle. Here, the first metal element in "the first metal element mainly constitutes the first metal magnetic particle" refers to the metal element contained in the first metal magnetic particle in the largest amount. The first metal magnetic particle contains, for example, 60 mol% or more, 70 mol% or more, or 80 mol% or more of the first metal element.

[0088] The second metal element can constitute the second metal magnetic particles. In one embodiment, the second metal element mainly constitutes the second metal magnetic particles. Here, the second metal element in "the second metal magnetic particles mainly constituted by the second metal element" refers to the metal element contained in the second metal magnetic particles in the largest amount, other than the metal element (Fe) that contributes to the magnetism. The second metal magnetic particles contain, for example, 60 mol% or more, 70 mol% or more, or 80 mol% or more of the second metal element.

[0089] The third metal element constitutes the internal conductor. In one embodiment, the third metal element constitutes the main component of the internal conductor. Here, the third metal element in "the main component of the internal conductor" refers to the metal element that is contained in the largest amount among the metal elements contained in the internal conductor. The internal conductor contains, for example, 60 mol % or more, 70 mol % or more, or 80 mol % or more of the third metal element.

[0090] In a preferred embodiment, the first metal element is at least one metal element selected from the group consisting of Fe and Ni. In a preferred embodiment, the absolute value of the difference in standard electrode potential between the first metal element and the second metal element is 0.5 V or more. In such a preferred embodiment, for example, the first metal element and the second metal element are Fe and Cu, Fe and Ag, Ni and Cu, and Ni and Ag, respectively.

[0091] -Non-peroxide region- The non-peroxide region NP occupies, for example, the region of the magnetic material M other than the peroxide region P. The non-peroxide region NP contains second metal magnetic particles. The second metal magnetic particles may contain Fe as a magnetic material. More specifically, the second metal magnetic particles may be Fe particles or Fe alloy particles. Elements other than Fe contained in the Fe alloy include Cr (chromium), Ni, Al (aluminum), B (boron), P (phosphorus), Cu (copper), C (carbon), and Nb (niobium). Examples of the Fe alloy include Fe-Si-Cr (chromium)-based alloys, Fe-Si-Al (aluminum)-based alloys, Fe-Si-B (boron)-P (phosphorus)-Cu (copper)-C (carbon)-based alloys, Fe-Si-B-Nb (niobium)-Cu-based alloys, and Fe-Ni-based alloys. Among these Fe and Fe-based alloys, Fe and Fe-Ni-based alloys are preferred from the viewpoint of appropriately forming the peroxide region P in the manufacture of the coil element 1. Furthermore, the first metal magnetic particles may contain impurities such as Cr, Mn (manganese), Cu, Ni (nickel), P, S (sulfur), or Co (cobalt) that are not intended in the manufacture.

[0092] The surfaces of the second metal magnetic particles may be covered with an insulating coating (not shown). As used herein, "insulating" refers to a volume resistivity of 1 MΩcm or greater. Covering the surfaces of the first metal magnetic particles with an insulating coating can enhance the insulation between the first metal magnetic particles. Examples of methods for forming an insulating coating on the surfaces of the first metal magnetic particles include the sol-gel method and the mechanochemical method. The insulating coating may be made of an oxide of P, Si, or the like. The insulating coating may also be an oxide film formed by oxidizing the surfaces of the first metal magnetic particles. The thickness of the insulating coating may be preferably 1 nm or more and 50 nm or less, more preferably 1 nm or more and 30 nm or less, and even more preferably 1 nm or more and 20 nm or less. For example, a cross section obtained by polishing a sample of the coil element 1 can be photographed using a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and the thickness of the insulating coating covering the surfaces of the metal magnetic particles can be measured from the obtained SEM image.

[0093] The second metal magnetic particles may have an oxide film on their surfaces. This oxide film originates from the second metal magnetic particles and may be formed by heat treatment (oxidation treatment). In the element body 10, adjacent first metal magnetic particles may be bonded to each other via the oxide film.

[0094] The average particle size of the second metallic magnetic particles is preferably greater than 2 μm and not greater than 30 μm, more preferably greater than 2 μm and not greater than 20 μm, and even more preferably greater than 2 μm and not greater than 10 μm.

[0095] The average particle size of the second metal magnetic particles can be measured using the same procedure as for the first metal magnetic particles. Specifically, the coil element 1 is cut to obtain a cross section. The cross section is obtained by cutting the coil element 1 through the center thereof so as to intersect perpendicularly with the mounting surface and end surface of the element body 10. For the obtained cross section, multiple regions (e.g., 130 μm × 100 μm) are photographed using an SEM (e.g., in FIG. 3, five regions in the magnetic material M between the outer surface of the peroxide region P located on the outer surface CD-4 of the internal conductor CD and the outer surface of the element body 10). The obtained SEM images are analyzed using image analysis software (e.g., image analysis software "Win R00F" (manufactured by Mitani Corporation)) to determine the circle-equivalent diameter of the second metal magnetic particles. The average value of the obtained circle-equivalent diameters is defined as the average particle size of the second metal magnetic particles. Note that the average particle size in this specification refers to the average particle size D50 (particle size equivalent to a cumulative percentage of 50% on a volume basis).

[0096] The surfaces of the second metal magnetic particles may be covered with an oxide film, that is, the second metal magnetic particles may have an oxide film on their surfaces.

[0097] The second metal magnetic particles may contain at least one additive metal element selected from the group consisting of Al, B, Nb, Cu, C, Co, P, and S. Examples of Fe—Si alloys containing such additive metal elements include Fe—Si—Cr (chromium)-based alloys, Fe—Si—Al (aluminum)-based alloys, Fe—Si—B (boron)-P (phosphorus)-Cu (copper)-C (carbon)-based alloys, and Fe—Si—B—Nb (niobium)-Cu-based alloys. Furthermore, the first metal magnetic particles may contain impurities such as Cr, Mn (manganese), Cu, Ni (nickel), P, S (sulfur), or Co (cobalt) that are not intended during manufacturing.

[0098] (Internal Electrode) The internal electrode C is disposed inside the magnetic body M. The internal electrode C is configured by connecting multiple internal conductors CD wound on a plane inside the magnetic body via via conductors V. The internal electrode C has a first coil C1 and a second coil C2 disposed above the first coil C1 in the height direction T. The first coil C1 is wound inside the element body 10 by stacking the above-mentioned lamination groups G6 to G8 (see FIG. 2 ) and connecting the first coil conductors CD1 between the layers in a spiral shape via via conductors V. The second coil C2 is wound inside the element body 10 by stacking the later-described lamination groups G2 to G4 (see FIG. 2 ) and connecting the second coil conductors CD2 between the layers in a spiral shape via via conductors (not shown).

[0099] The average thickness of the internal electrode CD in the stacking direction is, for example, 2 to 100 μm. In the cross-sectional image mapped in the method for determining the oxygen content described above, the peroxidized region P, the non-peroxidized region NP, and the internal conductor CD are each identified, and the length of the internal electrode CD in the stacking direction is measured multiple times (number of measurements n=5). The measurement points are the thickness of the internal conductor CD, that is, the length in the stacking direction from the top surface to the bottom surface of the internal conductor CD. The average of these measured values ​​is calculated, and the obtained average value is used as the thickness of the peroxidized region P in the stacking direction.

[0100] The coil provided inside the element body 10 is not limited to the above-described configuration, and may be a configuration including one coil or two or more coils.

[0101] -First Coil- The first coil C1 has a plurality of first coil conductors CD1 connected to each other by via conductors V, a first through-hole conductor T1, and a second through-hole conductor T2.

[0102] As described above, the multiple first coil conductors CD1 are arranged in two stacking groups (stack groups G6 and G8 (see FIG. 2)). This gives the first coil C1 a spiral structure within the base body 10. Furthermore, the length in the stacking direction of the via conductors V connecting the multiple first coil conductors CD1 together may be shorter than the length of the first through-hole conductors T1 or the length of the second through-hole conductors T2.

[0103] The first through-hole conductor T1 electrically connects the first external electrode E1 to the end of the first coil conductor CD1 of the first coil C1 that is closest to the bottom surface (first main surface 11) of the element body 10. The first through-hole conductor T1 extends along the stacking direction of the metal magnetic layers (e.g., the height direction T of the element body). The first through-hole conductor T1 may have a stacked structure.

[0104] The second through-hole conductor T2 electrically connects the other end of the first coil C1 and the second external electrode E2. The second through-hole conductor T2 extends along the stacking direction of the metal magnetic layers (e.g., the height direction T of the element body). The second through-hole conductor T2 may have a stacked structure.

[0105] - Second Coil - The second coil C2 may be provided above the first coil C1 in the stacking direction inside the element body 10. The second coil C2 may include a plurality of second coil conductors CD2 connected to each other by via conductors (not shown), a third through-hole conductor T3, and a fourth through-hole conductor T4.

[0106] As described above, the multiple second coil conductors CD2 may be arranged in two stacking groups (stack groups G2 and G4 (see FIG. 2)). This allows the second coil C2 to have a spiral structure within the base body 10. Furthermore, the length in the stacking direction of the via conductors (not shown) connecting the multiple second coil conductors CD2 together may be shorter than the length of the third through-hole conductor T3 or the length of the fourth through-hole conductor T4.

[0107] The third through-hole conductor T3 may electrically connect the end of the second winding portion of the second coil C2 that is closest to the bottom surface (first main surface 11) of the element body 10 to the third external electrode E3. The third through-hole conductor T3 may extend along the stacking direction of the metal magnetic layers (e.g., the height direction T of the element body). The third through-hole conductor T3 may have a stacked structure.

[0108] The fourth through-hole conductor T4 may connect the other end of the second coil C2 and the fourth external electrode E4. The fourth through-hole conductor T4 may extend along the stacking direction of the metal magnetic layers (e.g., the height direction T of the element body). The fourth through-hole conductor T4 may have a stacked structure.

[0109] In a preferred embodiment, the internal conductor CD contains a third metal element, and the first metal element has a greater ionization tendency than the third metal element constituting the internal conductor CD. In this case, when the third metal atom and the first metal particle are in contact or proximity with each other and moisture is present between the third metal atom and the first metal particle during the manufacture of the coil element 1, a battery system is formed. The first metal element is selectively (or preferentially) oxidized, and peroxidized regions P are likely to be formed. In a preferred embodiment, the third metal element constituting the internal conductor CD is at least one metal element selected from the group consisting of Ag and Cu.

[0110] [External Electrodes] The external electrodes are provided on the bottom surface of the element body 10. The external electrodes include a first external electrode E1, a second external electrode E2, a third external electrode E3, and a fourth external electrode E4. The first external electrode E1 and the second external electrode E2 are electrically connected to the first coil C1. The third external electrode E3 and the fourth external electrode E4 are electrically connected to the second coil C2. Providing external electrodes on the bottom surface (first main surface 11) of the element body 10 allows the coil element 1 to be properly mounted on a mounting board or the like.

[0111] The external electrodes may be made of various materials such as Cu or Ni, for example. The external electrodes may be formed of a single layer or may have a laminated structure of two or more layers. The external electrodes may be formed by any method, but may be plated electrodes formed by plating (e.g., electroless plating), for example.

[0112] [Method for manufacturing coil element] A method for manufacturing a coil element according to the first embodiment comprises: forming a body precursor having a magnetic body precursor in which metal magnetic body layer precursors containing metal magnetic particles are stacked; and an internal electrode precursor which is disposed inside the magnetic body precursor and around which an internal conductor precursor is wound; and firing the body precursor under a low-oxygen atmosphere or a reducing atmosphere to form a body, wherein the magnetic body precursor contains first metal magnetic particles as metal magnetic particles and has a first region in contact with the internal electrode precursor, and a second region which is disposed between adjacent internal conductor precursors in the stacking direction and contains second metal magnetic particles as metal magnetic particles and in contact with the first region, and wherein the first metal element constituting the first metal magnetic particles has a greater ionization tendency than the third metal element constituting the internal conductor.

[0113] An example of a method for manufacturing the coil element according to the first embodiment will be described below. The method for manufacturing the coil element according to the first embodiment includes forming a body precursor having a magnetic body precursor in which metal magnetic body layer precursors containing metal magnetic particles are laminated, and an internal electrode precursor disposed inside the magnetic body precursor and wound with an internal conductor precursor (body precursor forming step), and firing the body precursor in a low-oxygen atmosphere or a reducing atmosphere to form an body (body precursor firing step).

[0114] (Element precursor forming process) In the element precursor forming process, an element precursor is formed, which includes a magnetic precursor formed by laminating metal magnetic layer precursors containing metal magnetic particles, and an internal electrode precursor disposed inside the magnetic precursor and wound with an internal conductor precursor. Specifically, a first metal magnetic paste, a second metal magnetic paste, and a conductive paste are first prepared. The first metal magnetic paste is prepared by dispersing the first metal magnetic particles in a solvent. The second metal magnetic paste is prepared by dispersing the second metal magnetic particles in a solvent. The conductive paste is prepared by dispersing a conductive powder, such as copper powder, silver powder, or gold powder, in a solvent. These pastes may further contain a dispersant.

[0115] Next, the prepared paste is printed in a desired pattern to form precursors for each of the lamination groups G1 to G10. The first metal magnetic paste forms a first region (precursor of the overoxidized region of the magnetic material precursor). The first region contains first metal magnetic particles as metal magnetic particles and is formed so as to be in contact with the internal electrode precursor. The second metal magnetic paste forms a second region (precursor of the non-peroxidized region of the magnetic material precursor). The second region is disposed between the internal conductor precursors adjacent in the lamination direction, contains second metal magnetic particles as metal magnetic particles, and is formed so as to be in contact with the first region. The conductive paste forms the internal electrode precursor, the through-hole conductor precursor, and the via conductor precursor. In this manner, the precursors for the lamination groups G1 to G10 are stacked to form an element precursor.

[0116] The element precursor may be formed by laminating the precursors of the lamination groups G1 to G10 after forming each of them, or by sequentially laminating the precursors of the lamination groups G1 to G10. The precursors of the lamination groups G1 to G10 may be formed by repeatedly printing the metal magnetic layers ML, overoxidized regions P, coil conductors, through-hole conductors, and via conductors until they reach the desired thickness.

[0117] In the method for manufacturing the coil element 1, the first metal element has a greater ionization tendency than the third metal element constituting the internal conductor, from the viewpoint of appropriately forming the peroxidized region P. For example, the internal conductor precursor may contain third metal particles, and the first metal element may have a greater ionization tendency than the third metal element constituting the third metal particles.

[0118] Furthermore, the second metal magnetic particles may contain a second metal element composed of a metal element other than Fe, and the first metal element may have a greater ionization tendency than the second metal element constituting the second metal magnetic particles. Other preferred embodiments include the following from the viewpoint of properly forming the peroxidized regions P. In one preferred embodiment, the second metal magnetic particles have an average particle size smaller than that of the first metal magnetic particles. In another preferred embodiment, the second metal magnetic particles contain at least one atom selected from the group consisting of Bi, Cl, Na, and K.

[0119] (Element precursor firing process) In the element precursor firing process, the element precursor is fired in a low-oxygen atmosphere or a reducing atmosphere. By firing the element precursor, the peroxidized region precursor made of the first metal magnetic paste becomes the peroxidized region P, the non-peroxidized region precursor made of the second metal magnetic paste becomes the non-peroxidized region NP, and the internal electrode precursor, through-hole conductor precursor, and via conductor precursor made of the conductive paste become the internal electrode, through-hole conductor, and via conductor, respectively.

[0120] Furthermore, in the element precursor firing process, the internal electrode precursor, the through-hole conductor precursor, and the via conductor precursor shrink and become denser through firing, resulting in lower resistance. Furthermore, in the element precursor firing process, the internal electrode precursor, the through-hole conductor precursor, and the via conductor precursor (particularly the internal electrode precursor) shrink through firing, while the peroxide region precursor expands as it is oxidized through firing. Therefore, in firing the element precursor, the contraction of the internal electrode precursor, the through-hole conductor precursor, and the via conductor precursor is offset (or partially offset) by the expansion of the peroxide region precursor, thereby alleviating internal stress that occurs during firing. Therefore, compared to a coil element that does not form peroxide regions, the occurrence of cracks (particularly near the surface of the internal conductor perpendicular to the stacking direction) is suppressed.

[0121] The firing conditions in the element precursor firing step are as follows: the firing atmosphere is a low-oxygen atmosphere (oxygen concentration is, for example, 1×10 －６ ~1 x 10 －３ The firing atmosphere is a low-oxygen atmosphere (for example, a mixed gas atmosphere of nitrogen and argon with an oxygen concentration of, for example, 1×10 －６ ~1 x 10 －３ The firing temperature is, for example, 500°C to 900°C, and the firing time is, for example, 1 to 6 hours. The dew point temperature is 0 to 30°C dp, preferably 20 to 30°C dp (the dew point temperature can be adjusted by controlling the amount of humidified water using bubbler water temperature management).

[0122] By setting such firing conditions, the peroxide region P can be formed in the element precursor firing step.

[0123] <Second embodiment: coil element> The coil element according to the second embodiment differs from the coil element 1 according to the first embodiment in the arrangement of the peroxide region. This different configuration will be mainly described below. In the second embodiment, the same reference numerals as those in the first embodiment represent the same configuration as in the first embodiment, and therefore, in principle, description thereof will be omitted.

[0124] [Configuration of Coil Element] The arrangement of the over-oxidized region will be described with reference to Fig. 4. Fig. 4 is a cross-sectional view showing a schematic configuration of the coil element according to the second embodiment. As shown in Fig. 4, in the coil element 1A according to the second embodiment, the over-oxidized region P Ａ In cross section, the peroxide region P contacts the surfaces (upper surface CD-1 and lower surface CD-2) that intersect with the lamination direction of the internal conductor CD, but does not contact the surfaces (inner surface CD-3 and outer surface CD-4) that do not intersect with the lamination direction of the internal conductor CD. Ａ are disposed only on the upper surface CD-1 and the lower surface CD-2 of the internal conductor CD, and are not disposed on the inner surface CD-3 and the outer surface CD-4.

[0125] In addition, the peroxide region P Ａ In a plan view seen from the top surface 12 of the element body 10, the peroxide region P extends toward the winding axis of the internal electrode CD relative to the inner surface CD-3 of the internal conductor CD, and extends toward the outer surface of the element body 10 relative to the outer surface CD-4 of the internal conductor CD. In this case, in a plan view, the peroxide region P Ａ extends, and further, an overoxidized region P Ａ Since the extension of the inner surface CD-3 and the inner surface CD-1 extends in this manner, it is possible to prevent stress from concentrating on the corners of the internal electrode CD (for example, the corners formed at the intersections of the inner surface CD-3 and the upper surface CD-1 in the cross section of FIG. 4), and it is possible to prevent cracks from occurring near the corners of the internal electrode CD.

[0126] [Method for Manufacturing Coil Element] The coil element 1A according to the second embodiment can be manufactured in the same manner as in the first embodiment except for the element precursor formation step.

[0127] (Element precursor forming step) In the element precursor forming step, an element precursor is formed in the same manner as the laminate forming step in the manufacturing method of the coil element 1 according to the first embodiment, except for the following points. However, the peroxidized region precursor is not disposed on the side surfaces (inner surface and outer surface) of the internal conductor precursor, but is disposed only on the upper and lower surfaces of the internal conductor precursor. Furthermore, the peroxidized region P Ａ is disposed so as to extend toward the winding axis of the internal electrode CD with respect to the inner surface CD-3 of the internal conductor CD, and to extend toward the outer surface of the element body 10 with respect to the outer surface CD-4 of the internal conductor CD, in plan view.

[0128] <Third embodiment: Coil element> The coil element according to the third embodiment differs from the coil element 1 according to the first embodiment in the arrangement of the over-oxidized region and the cross-sectional shape of the internal conductor. The following mainly describes these different configurations. In the third embodiment, the same reference numerals as those in the first embodiment represent the same configuration as in the first embodiment, and therefore, in principle, their description will be omitted.

[0129] [Configuration of Coil Element] The arrangement of the over-oxidized region will be described with reference to Fig. 5. Fig. 5 is a cross-sectional view showing a schematic configuration of the coil element according to the third embodiment. As shown in Fig. 5, in the coil element 1B according to the third embodiment, unevenness is formed on the side surface of the internal conductor CD. Then, the over-oxidized region P Ｂ is the plane (top CD) that intersects with the lamination direction of the internal conductor CD in a cross-sectional view. Ｂ -1 and bottom CD Ｂ -2) and does not intersect with the lamination direction of the internal conductor CD (inner surface CD Ｂ -3 and outer CD Ｂ -4) does not come into contact with the unevenness of the peroxide region P Ｂ is the top surface CD of the internal conductor CD Ｂ -1 and bottom CD Ｂ -2 only, and is located on the inner surface CD Ｂ -3 irregularities and outer surface CD ＢIt is not placed on the unevenness of -4.

[0130] Peroxide area P Ｂ is the inner conductor CD in cross section. Ｂ The surface that intersects with the stacking direction (top CD Ｂ -1 and bottom CD Ｂ -2) and the inner conductor CD Ｂ The depression on the surface that does not intersect with the lamination direction (inner surface CD Ｂ -3 and outer CD Ｂ -4) Peroxide region P Ｂ However, when viewed in cross section of the internal conductor CD, there is a bending point on the side surface of the internal conductor CD. Ｂ Inner surface CD Ｂ -3 and outer CD Ｂ The inner conductor CD-4 is not a straight line but is formed by a straight line having a bending point (i.e., it is a straight line having a bending point). Ｂ When the plane that does not intersect with the lamination direction has a bending point in a cross-sectional view, internal stress due to shrinkage of the internal conductor precursor is unlikely to occur in the element precursor firing step of manufacturing the coil element 1B, and the internal conductor CD Ｂ Side CD Ｂ -3, CD Ｂ In this case, the internal conductor CD is not easily affected locally at the interface between the internal conductor CD and the magnetic material M (non-peroxide region NP). Ｂ Side CD Ｂ -3, CD Ｂ The contact area between the magnetic material M (non-peroxide region NP) and the internal conductor CD-4 increases, and the anchor effect is exerted. Ｂ Side CD Ｂ -3, CD Ｂ -4 is firmly bonded to the magnetic material M (non-peroxide region NP), and the internal conductor CD Ｂ Side CD Ｂ -3, CD Ｂ This suppresses the occurrence of structural defects (cracks) at the interface between -4 and the magnetic material M (non-peroxide region NP).

[0131] [Method for Manufacturing Coil Element] The coil element 1B according to the second embodiment can be manufactured in the same manner as in the first embodiment except for the element precursor formation step.

[0132] (Element precursor forming process) In the element precursor forming process, an element precursor is formed in the same manner as the element precursor forming process in the manufacturing method of the coil element 1 according to the first embodiment, except for the following points: The peroxidized region precursor is not disposed on the side surfaces (inner and outer surfaces) of the internal conductor precursor, but is disposed only on the top and bottom surfaces of the internal conductor precursor. Furthermore, the side surfaces of the internal conductor precursor have a bending point in cross section.

[0133] Other Embodiments The present disclosure is not limited to the above-described embodiments, and design changes are possible without departing from the gist of the present disclosure.

[0134] In the second embodiment, the peroxide region P Ａ In plan view, the peroxide region P extends toward the winding axis of the internal electrode CD with respect to the inner surface CD-3 of the internal conductor CD, and extends toward the outer surface of the element body 10 with respect to the outer surface CD-4 of the internal conductor CD, but is not limited to this. For example, Ａ In plan view, it may be one of extending toward the winding axis of the internal electrode CD with respect to the inner surface CD-3 of the internal conductor CD, and extending toward the outer surface of the element body 10 with respect to the outer surface CD-4 of the internal conductor CD.

[0135] In addition, the first to third embodiments may be combined. For example, in the second and third embodiments, as shown in FIGS. 3 and 4, all of the eight internal conductors have the shapes of the internal conductors of the second and third embodiments, respectively, and the peroxide region P Ａ , P Ｂ For example, among the eight adjacent internal conductors, at least one internal conductor may have the shape of the internal conductor of the second embodiment or the third embodiment, and / or the overoxidized region P Ａ , P Ｂ The eight internal conductors may have the shape of the internal conductors in the second and third embodiments, and / or the peroxide region P Ａ , P Ｂ may be arranged in combination.

[0136] The present disclosure includes the following aspects: <1> A coil element including an element body and external electrodes arranged on the element body, wherein the element body has a magnetic body formed by stacking metal magnetic body layers containing metal magnetic particles, and an internal electrode arranged inside the magnetic body and winding an internal conductor, wherein the magnetic body has an overoxidized region containing first metal magnetic particles as the metal magnetic particles and in contact with the internal electrode, and a non-peroxidized region arranged between the internal conductors adjacent in the stacking direction and containing second metal magnetic particles as the metal magnetic particles and in contact with the overoxidized region, wherein a first metal element mainly constituting the first metal magnetic particles has a greater ionization tendency than a third metal element constituting the internal conductor, and an amount of oxygen in the overoxidized region is greater than the amount of oxygen in the non-peroxidized region. <2> The coil element according to <1>, wherein the second metal magnetic particles contain a second metal element composed of a metal element other than Fe, and wherein the first metal element has a greater ionization tendency than the second metal element. <3> The coil element according to <1> or <2>, wherein the peroxidized region is in contact with a surface that intersects with the lamination direction of the internal conductor in a cross-sectional view. <4> The coil element according to any one of <1> to <3>, wherein the thickness of the peroxidized region in the lamination direction is 2 to 50 μm. <5> The coil element according to any one of <1> to <4>, wherein the peroxidized region extends toward the winding axis of the internal electrode with respect to the inner surface of the internal conductor and / or extends toward the outer surface of the element body with respect to the outer surface of the internal conductor in a plan view seen from the top surface of the element body. <6> The coil element according to any one of <1> to <5>, wherein the amount of oxygen in the peroxidized region is at least twice the amount of oxygen in the non-peroxidized region, and wherein the cross-sectional area of ​​the peroxidized region is 0.2 to 10 times the cross-sectional area of ​​the non-peroxidized region. <7> The coil element according to any one of <1> to <6>, wherein the second metal magnetic particles contain a second metal element composed of a metal element other than Fe, and the absolute value of the difference in standard electrode potential between the first metal element and the second metal element is 0.5 V or more.<8> The coil element according to any one of <1> to <7>, wherein the first metal element is at least one metal element selected from the group consisting of Fe and Ni, and the third metal element constituting the internal conductor is at least one metal element selected from the group consisting of Ag and Cu. <9> The coil element according to any one of <1> to <8>, wherein the peroxidized region is in contact with a surface that intersects with the stacking direction of the internal conductor in a cross-sectional view, and a surface that does not intersect with the stacking direction of the internal conductor is not in contact with the peroxidized region, and has an inflection point in a cross-sectional view. <10> The coil element according to any one of <1> to <9>, wherein the peroxidized region is in contact with a surface that intersects with the stacking direction of the internal conductor and a surface that does not intersect with the stacking direction of the internal conductor in a cross-sectional view. <11> A method for producing the coil element according to any one of <1> to <10>, comprising: forming a body precursor having a magnetic body precursor in which metal magnetic body layer precursors containing metal magnetic particles are laminated, and an internal electrode precursor which is disposed inside the magnetic body precursor and around which an internal conductor precursor is wound; and firing the body precursor under a low-oxygen atmosphere or a reducing atmosphere to form an element, wherein the magnetic body precursor contains first metal magnetic particles as the metal magnetic particles and has a first region in contact with the internal electrode precursor, and a second region which is disposed between the internal conductor precursors adjacent in the lamination direction and contains second metal magnetic particles as the metal magnetic particles and in contact with the first region, and wherein a first metal element which mainly constitutes the first metal magnetic particles has a greater ionization tendency than a third metal element which constitutes the internal conductor. <12> The method for manufacturing a coil element according to <11>, wherein the second metal magnetic particles contain a second metal element composed of a metal element other than Fe, and the first metal element has a greater ionization tendency than the second metal element. <13> The method for manufacturing a coil element according to <11> or <12>, wherein sintering the element precursor to form the element is performed under sintering conditions of a dew point of 0 to 30°C dp, a sintering temperature of 500 to 900°C, and a sintering time of 1 to 6 hours.<14> The method for manufacturing a coil element according to any one of <11> to <13>, wherein the internal conductor precursor contains a third metal element, and the first metal element has a greater ionization tendency than the third metal element constituting the internal conductor.

[0137] The coil element according to the present disclosure is used in, for example, a DC-DC converter, and can also be used for purposes other than DC-DC converters.

[0138] 1, 1A, 1B Coil element 10 Body C, C Ｂ Internal electrode (coil) C1 First internal electrode (first coil) C2 Second internal electrode (second coil) CD, CD Ｂ Internal conductor (coil conductor) CD1 First internal conductor (first coil conductor) CD2 Second internal conductor (second coil conductor) CD-1, CD Ｂ -1 Top surface (top surface) of internal electrode (coil) CD-2, CD Ｂ -2 Underside (bottom) of internal electrode (coil) CD-3, CD Ｂ -3 Inner surface of internal electrode (coil) CD-4, CD Ｂ -4 Outer surface of internal electrode (coil) E1 First external electrode E2 Second external electrode E3 Third external electrode E4 Fourth external electrode G1 to G10 Stacking groups P, P Ａ , P Ｂ Peroxide region M Magnetic material ML Metallic magnetic material layer T1 First through-hole conductor T2 Second through-hole conductor T3 Third through-hole conductor T4 Fourth through-hole conductor V Via conductor

Claims

1. A coil element comprising an element body and an external electrode disposed on the element body, wherein the element body has a magnetic body formed by laminating metal magnetic layers containing metal magnetic particles, and an internal electrode disposed inside the magnetic body and wound around an internal conductor, wherein the magnetic body has an overoxidized region containing first metal magnetic particles as the metal magnetic particles and in contact with the internal electrode, and a non-peroxidized region disposed between adjacent internal conductors in the lamination direction and containing second metal magnetic particles as the metal magnetic particles and in contact with the overoxidized region, wherein a first metal element constituting the first metal magnetic particles has a greater ionization tendency than a third metal element constituting the internal conductor, and the amount of oxygen in the peroxidized region is greater than the amount of oxygen in the non-peroxidized region.

2. A coil element as described in claim 1, wherein the second metal magnetic particles contain a second metal element composed of a metal element other than Fe, and the first metal element has a greater ionization tendency than the second metal element.

3. A coil element according to claim 1 or 2, wherein the peroxidized region is in contact with a plane that intersects with the lamination direction of the internal conductor in a cross-sectional view.

4. A coil element according to any one of claims 1 to 3, wherein the average thickness of the peroxide region in the stacking direction is 2 to 50 μm.

5. A coil element according to any one of claims 1 to 4, wherein the peroxidized region, in a plan view seen from above the top surface of the element body, extends toward the winding axis of the internal electrode relative to the inner surface of the internal conductor, and / or extends toward the outer surface of the element body relative to the outer surface of the internal conductor.

6. A coil element according to any one of claims 1 to 5, wherein the amount of oxygen in the peroxidized region is at least twice the amount of oxygen in the non-peroxidized region, and the cross-sectional area of ​​the peroxidized region is 0.2 to 10 times the cross-sectional area of ​​the non-peroxidized region.

7. A coil element according to any one of claims 1 to 6, wherein the second metal magnetic particles contain a second metal element composed of a metal element other than Fe, and the absolute value of the difference in standard electrode potential between the first metal element and the second metal element is 0.5 V or more.

8. A coil element according to any one of claims 1 to 7, wherein the first metal element is at least one metal element selected from the group consisting of Fe and Ni, and the third metal element constituting the internal conductor is at least one metal element selected from the group consisting of Ag and Cu.

9. A coil element according to any one of claims 1 to 8, wherein the overoxidized region is in contact with a surface that intersects with the stacking direction of the internal conductor in a cross-sectional view, and a surface that does not intersect with the stacking direction of the internal conductor is not in contact with the overoxidized region and has a bending point in a cross-sectional view.

10. A coil element according to any one of claims 1 to 9, wherein the peroxidized region contacts a surface that intersects with the lamination direction of the internal conductor and a surface that does not intersect with the lamination direction in a cross-sectional view.

11. A method for producing a coil element according to any one of claims 1 to 10, comprising: forming a body precursor having a magnetic body precursor in which metal magnetic body layer precursors containing metal magnetic particles are laminated, and an internal electrode precursor disposed inside the magnetic body precursor and wound with an internal conductor precursor; and firing the body precursor in a low-oxygen atmosphere or a reducing atmosphere to form an element, wherein the magnetic body precursor contains first metal magnetic particles as the metal magnetic particles and has a first region in contact with the internal electrode precursor, and a second region disposed between the internal conductor precursors adjacent in the lamination direction and containing second metal magnetic particles as the metal magnetic particles and in contact with the first region, and wherein a first metal element constituting the first metal magnetic particles has a greater ionization tendency than a third metal element constituting the internal conductor.

12. A method for manufacturing a coil element as described in claim 11, wherein the second metal magnetic particles contain a second metal element composed of a metal element other than Fe, and the first metal element has a greater ionization tendency than the second metal element.

13. A method for manufacturing a coil element according to claim 11 or 12, wherein the firing of the element precursor to form the element is carried out under firing conditions of a dew point of 0 to 30°C dp, a firing temperature of 500 to 900°C, and a firing time of 1 to 6 hours.

14. A method for manufacturing a coil element according to any one of claims 11 to 13, wherein the internal conductor precursor contains third metal particles, and the first metal element has a greater ionization tendency than the third metal element that mainly constitutes the third metal particles.

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