Multilayer inductor and manufacturing method of the same

Abstract

To provide a multilayer inductor in which a connection strength between an external electrode and a through hole is improved, and provide a manufacturing method of the same.SOLUTION: A multilayer inductor comprises: an element body having a coil to which a coil conductor is wound and a through hole that is electrically connected to the coil conductor, and is exposed from a bottom surface of a magnetic body in an inner part of the magnetic body where a magnetic layer containing an iron powder is laminated; an external electrode that is arranged onto the through hole, and is electrically connected to the through hole; and an external resin layer that is arranged on a bottom surface of the magnetic body of the element body. An external electrode E includes projection parts 13a and 13b that are projected in a direction vertical to a lamination direction in an upper end part 11a that is distal to a through hole TH in the lamination direction of the magnetic layer and a lower end part 11b that is proximal to the through hole TH. The external resin layer is arranged over projection parts 10 and 20 of the upper end part 1 and the lower end part 11b.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to a laminated inductor and a method for manufacturing the same. [Background technology]

[0002] In recent years, as equipment becomes more sophisticated, the DC-DC converters in voltage conversion circuits are becoming larger in current and more efficient, and the rated current of the power inductors used in these devices is also increasing.

[0003] Patent Document 1, which shows an example of the above-mentioned inductor, discloses a passive component including a base portion; an internal conductor built into the base portion; a lead conductor electrically connected to the internal conductor and extending toward the bottom surface of the base portion; and an external electrode electrically connected to the lead conductor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-141079 A Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional passive components, as shown in FIG. 8, for example, an external electrode 100 is simply formed on the underside of a base portion 110 and connected to an extraction conductor 105 extending toward the underside, which poses a problem with the connection strength between the external electrode and the extraction conductor.

[0006] A primary object of the present disclosure is to provide a multilayer inductor having improved connection strength between external electrodes and lead conductors, and a method for manufacturing the same. [Means for solving the problem]

[0007] The present disclosure relates to an element body having a coil formed by winding a coil conductor inside a magnetic body formed by laminating magnetic layers containing iron powder, and a through hole electrically connected to the coil conductor and extending toward a bottom surface of the magnetic body; an external electrode disposed on the through hole and electrically connected to the through hole; an exterior resin layer disposed on a bottom surface of the magnetic body of the base body; the external electrode has a protrusion protruding in a direction perpendicular to the lamination direction at an upper end portion distal to the through hole in the lamination direction of the magnetic layers and a lower end portion proximal to the through hole, The present invention relates to a laminated inductor, wherein the exterior resin layer is disposed across the protrusions at the upper end and the lower end. Effect of the Invention

[0008] According to the present disclosure, it is possible to provide a laminated inductor having improved connection strength between the external electrodes and the through holes, and a manufacturing method thereof. Specifically, in the laminated inductor, the external electrodes have protrusions at the upper and lower ends, and the exterior resin layer is disposed between the protrusions at the upper and lower ends, thereby increasing the connection strength between the external electrodes and the lead conductors. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view illustrating an example of the laminated inductor according to the first embodiment. [Diagram 2] FIG. 2 is an exploded perspective view for explaining the laminated structure of the laminated inductor of the first embodiment. [Diagram 3] FIG. 3 is a cross-sectional view of the laminated inductor of the first embodiment, and is an enlarged cross-sectional view of the vicinity of an external electrode. [Figure 4] FIG. 4 is a partially enlarged cross-sectional view of a portion Z in FIG. [Diagram 5] FIG. 5 is a perspective view illustrating an example of the laminated inductor according to the second embodiment. [Figure 6]FIG. 6 is a perspective view illustrating a schematic example of a laminated inductor array according to the present disclosure. [Figure 7A] FIG. 7A is a flow diagram showing a method for manufacturing a laminated inductor according to the present disclosure. [Figure 7B] FIG. 7B is a cross-sectional view showing in detail the exterior resin layer forming step in the manufacturing method for the laminated inductor of the present disclosure. [Figure 8] FIG. 8 is a cross-sectional view of a conventional multilayer inductor, and is an enlarged cross-sectional view of the vicinity of an external electrode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The laminated inductor of the present disclosure will be described below. Note that the present disclosure is not limited to the following configurations, and may be modified as appropriate without departing from the gist of the present disclosure. In addition, a combination of multiple individual preferred configurations described below also constitutes the present disclosure.

[0011] The laminated inductor according to the present disclosure is used, for example, in a choke coil of a DC-DC converter, but can also be used for purposes other than DC-DC converters.

[0012] In this specification, terms indicating the relationship between elements (e.g., "parallel," "orthogonal," "perpendicular," etc.) and terms indicating the shape of elements do not only mean the strict literal form, but also mean a range that is substantially equivalent, for example, a range that includes 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" (e.g., direction T in Figure 1).

[0013] In this specification, the term "plan view" refers to the state when the object is viewed from above or below along the thickness direction based on the stacking direction (top view or bottom view). In addition, the term "cross-sectional view" refers to the cross-sectional state (cross-sectional view) when the object is viewed from a direction approximately perpendicular to the stacking direction T (for example, direction L or W in FIG. 1). The "upper-lower direction" and "left-right direction" used directly or indirectly in this specification correspond to the upper-lower direction and left-right direction in the figure, respectively. Unless otherwise specified, the same reference numerals or symbols indicate the same members / parts or the same meanings. In a preferred embodiment, the vertical downward direction (i.e., the direction in which gravity acts) corresponds to the "downward direction", and the opposite direction corresponds to the "upward direction".

[0014] The drawings shown below are schematic diagrams, and the dimensions, aspect ratio, and scale may differ from those of the actual product.

[0015] <First embodiment of multilayer inductor> First, a first embodiment of the laminated inductor of the present disclosure will be described with reference to Figures 1 to 6 and Figures 7A and 7B. Note that the shapes and arrangements of the laminated inductor and its components are not limited to the examples shown in the drawings.

[0016] Fig. 1 shows a perspective view of a laminated inductor 1A of the present disclosure. As shown in Fig. 1, the laminated inductor 1A includes a coil C formed by winding a coil conductor inside a magnetic body M formed by laminating magnetic layers containing iron powder, an element body B having a through hole TH electrically connected to the coil conductor and extending toward the bottom surface of the magnetic body, an exterior resin having an opening and disposed on the bottom surface of the magnetic body, and an external electrode E disposed in the opening of the outer resin layer and electrically connected to the through hole. The number of turns of the coil C is 2.5. Each component will be described in detail below.

[0017] -Base body- The element body B has, for example, a rectangular parallelepiped shape or a substantially rectangular parallelepiped shape having six sides. The vertices and edges of the element body B may be rounded. The vertices are the parts where three faces of the element body B intersect, and the edges are the parts where two faces of the element body B intersect.

[0018] 1, the length direction, width direction, and height direction of the laminated inductor 1A and the element body B are shown as L direction, W direction, and T direction, respectively. The length direction L, width direction W, and height direction T are perpendicular to each other. The mounting surface of the laminated inductor 1A is, for example, a surface (LW surface) parallel to the length direction L and width direction W.

[0019] 1 has a first main surface B1 and a second main surface B2 facing in a height direction T, a first end surface B3 and a second end surface B4 perpendicular to the height direction T and facing in a length direction L, and a first side surface B5 and a second side surface B6 facing in a width direction W perpendicular to the length direction L and the height direction T. In the example shown in FIG. 1, the first main surface B1 of the element body B corresponds to the mounting surface (bottom surface) of the element body B. It is to be noted that the second main surface B2 may be the mounting surface of the element body B.

[0020] The element body B includes a magnetic body M formed by stacking magnetic layers ML, a coil C formed by winding a coil conductor CM, and a through hole TH electrically connected to the coil conductor and extending toward the bottom surface of the element body B. Specifically, the element body B may include a plurality of magnetic layers ML and coil conductors CM in the stacking direction (e.g., the height direction T).

[0021] 2 is an exploded perspective view for explaining the laminated structure of the laminated inductor 1A according to the present disclosure. In this embodiment, as shown in FIG. 2, the laminated inductor 1A is configured by laminating laminated groups G1 to G7, each including a magnetic layer ML, a coil conductor CM, and a through hole TH. The boundaries between layers in the layered structure of element body B may disappear. Furthermore, each layered group may be configured by laminating a plurality of identical patterns.

[0022] The laminated inductor 1A may be constructed by stacking laminated groups G1 to G7, producing an element body B by firing, and then further stacking laminated group G8 including an exterior resin layer SR having openings EH (e.g., EH1, EH2) for external electrodes E (e.g., E1, E2), and forming the external electrodes E (e.g., E1, E2) by a method described below.

[0023] The lamination group G1 includes a magnetic layer ML and constitutes the second main surface B2 of the element body B.

[0024] The multilayer group G2 includes a magnetic layer ML and a coil conductor CM. The coil conductor CM of the multilayer group G2 constitutes approximately one turn of the coil C. More specifically, the coil conductor CM is disposed substantially along the outer periphery of the magnetic layer ML.

[0025] The multilayer group G3 includes a magnetic layer ML, a second through hole TH2 that electrically connects the coil conductors CM of the multilayer group G2 to the second external electrode E2, and a via hole conductor V for connecting adjacent coil conductors CM in the stacking direction. The second through hole TH2 is disposed near a corner of the magnetic layer ML. The via hole conductor V is disposed adjacent to the second through hole TH2. Note that the term "via hole" is used to refer to a connection path for electrically connecting the coils C (CM) to each other, and the term "through hole" is used to refer to a connection path for electrically connecting the coils C (CM) to the external electrode E.

[0026] The multilayer group G4 includes a magnetic layer ML, a second through hole TH2 that electrically connects the second through hole TH2 of the multilayer group G3 to the second external electrode E2, and a coil conductor CM. The coil conductor CM of the multilayer group G4 constitutes approximately one turn of the coil C. More specifically, the coil conductor CM is arranged along the outer periphery of the magnetic layer ML while avoiding the second through hole TH2 with an avoidance portion Z, and the ends of the coil conductor CM are spaced apart to form a wound structure. To describe the avoidance portion Z in more detail, the avoidance portion Z provided in the multilayer group G4 may be provided on the inside compared to the coil conductor CM arranged along the outer periphery of the multilayer group G2, and avoid the second through hole TH2.

[0027] The multilayer group G5 includes a magnetic layer ML, a second through hole TH2 that electrically connects the second through hole TH2 of the multilayer group G4 and the second external electrode E2, and a via hole conductor V for connecting adjacent coil conductors CM in the stacking direction. The via hole conductor V is located adjacent to the second through hole TH2 at a position where it can be electrically connected to an end of the coil conductor CM of the multilayer group G4.

[0028] The multilayer group G6 includes a magnetic layer ML, a second through hole TH2 that electrically connects the second through hole TH2 of the multilayer group G5 to the second external electrode E2, and a coil conductor CM. The coil conductor CM of the multilayer group G6 constitutes about 0.5 turns of the coil C. More specifically, the coil conductor CM is arranged along the outer periphery of the magnetic layer ML while avoiding the second through hole TH2 with an avoidance portion Z, and the ends of the coil conductor CM are spaced apart to form a winding structure. To describe the avoidance portion Z in more detail, the avoidance portion Z provided in the multilayer group G6 may be provided on the inside compared to the coil conductor CM arranged along the outer periphery of the multilayer group G2, and avoid the second through hole TH2.

[0029] The multilayer group G7 includes a magnetic layer ML, a second through hole TH2 electrically connecting the second through hole TH2 of the multilayer group G6 to the second external electrode E2, and a first through hole TH1 electrically connecting the coil conductor CM of the multilayer group G6 to the first external electrode E1. The first through hole TH1 is disposed near a corner of the magnetic layer ML.

[0030] A multilayer group G8 is further provided on the sintered element body B. The multilayer group G8 includes an exterior resin layer SR provided with a first opening EH1 for a first external electrode E1 electrically connected to the first through hole TH1 of the multilayer group G7 and a second opening EH2 for a second external electrode E2 electrically connected to the second through hole TH2 of the multilayer group G7, and an external electrode E arranged in the first opening EH1 and the second opening EH2. The first opening EH1 and the second opening EH2 are each arranged near a corner of the exterior resin layer SR.

[0031] As described above, when the element body B has a multilayer structure including the multilayer groups G1 to G7, the degree of freedom in designing the multilayer inductor 1A is increased. For example, since the multilayer inductor 1A including the first external electrode E1 and the second external electrode E2 is manufactured on the bottom surface (first main surface B1) of the element body B, it is easy to draw out the coil C to the bottom surface side. The multilayer structure including the multilayer groups G1 to G7 may be formed by stacking a plurality of the above-mentioned groups by sequentially printing (for example, screen printing, etc.) the material constituting the magnetic layer ML, the material constituting the coil conductor CM, and the material constituting the through-hole and via-hole conductors from the second main surface B2 side or the first main surface B1 side of the element body B. In this case, each of the multilayer groups G1 to G7 may be repeatedly printed until the magnetic layer ML, the coil conductor CM, the through-hole and the via-hole conductor reach a desired thickness.

[0032] After manufacturing the element body B, the lamination group G8 forms an exterior resin layer SR having a first opening EH1 and a second opening EH2 on the first main surface B1 side. The exterior resin layer SR may be formed by photolithography, which prints (e.g., screen printing) a photosensitive resin material, exposes it, and develops it. External electrodes E1 and E2 are formed in the first opening EH1 and the second opening EH2 by Cu plating or the like.

[0033] (magnetic material) The magnetic body M (see FIG. 1 and FIG. 2) formed by stacking the magnetic layers ML includes iron powder MP made of a magnetic material. In this specification, "iron powder" is not limited to being strictly powdery, but also includes powdery substances bonded together by heat treatment (sintering) described later. The iron powder MP may contain Fe and / or Si. More specifically, it may be Fe particles or Fe alloy particles. The Fe alloy may be an Fe-Si alloy, an Fe-Si-Cr alloy, an Fe-Si-Al alloy, an Fe-Si-BP-Cu-C alloy, and / or an Fe-Si-B-Nb-Cu alloy. The iron powder MP may also contain impurities such as Cr, Mn, Cu, Ni, P, S, and / or Co that are not intended in the manufacturing process. The iron powder MP may also be contained in the magnetic paste, as will be described in detail in the explanation of the manufacturing method. Therefore, the iron powder may contain elements (e.g., Cr, Al, Li, Zn) that are more easily oxidized than the Fe added when the magnetic paste is prepared.

[0034] The surface of the iron powder MP may be covered with an insulating film (not shown). When the surface of the iron powder MP is covered with an insulating film, the insulation between the iron powder MP can be improved. The insulating film can be formed on the surface of the iron powder MP by a sol-gel method, a mechanochemical method, or the like. The material constituting the insulating film may be an oxide of P and / or Si. The insulating film may also be an oxide film formed by oxidizing the surface of the iron powder MP. The thickness of the insulating film is 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, the cross section obtained by polishing the center of the inductor sample is photographed with a scanning electron microscope (SEM), and the thickness of the insulating film covering the surface of the iron powder MP can be measured from the obtained SEM photograph.

[0035] The average particle size of the iron powder MP in the magnetic body M is preferably 1 μm or more and 30 μm or less, more preferably 1 μm or more and 20 μm or less, and further preferably 1 μm or more and 10 μm or less. The average particle size of the iron powder MP in the magnetic body M can be measured by the procedure described below. A sample of a laminated inductor is cut to obtain a sample cross section. Specifically, a cross section (for example, a sample cross section passing through the center of the first through hole of the element body and perpendicular to the mounting surface B1 of the element body) is obtained. For the obtained cross section, a region (for example, 130 μm × 100 μm) at multiple locations (for example, 5 locations) is photographed by SEM, and the obtained SEM image is analyzed using image analysis software (for example, image analysis software WinROOF2021 (manufactured by Mitani Shoji Co., Ltd.)) to obtain the circle equivalent diameter of the iron powder MP. The average value of the obtained circle equivalent diameters is taken as the average particle size of the metal magnetic particles. Note that when the shape of the through hole is polygonal, the cut is perpendicular to the sides, and when it is circular or elliptical, the cut is perpendicular to the long axis direction.

[0036] Here, even if the iron powder MP contained in the magnetic layer ML is bonded by sintering, voids are generated between the iron powder MP, and the presence of the voids reduces the strength of the element body. The term "voids" as used herein refers to the space between adjacent powder bodies. In other words, it refers to the space determined by the positional relationship between adjacent powder bodies. As described above, the voids can be observed from an SEM image of a cross section of the sample obtained by cutting the sample of the multilayer inductor 1A. As a specific method of identifying the voids, when an observation area of ​​the cross section of the sample is set to 130 μm×100 μm and an SEM image is obtained, and the voids and non-voids in the magnetic body M are image-analyzed using image analysis software, the area ratio of the voids to the entire observation area may be 10% or more and 40% or less.

[0037] In the laminated inductor 1A of this embodiment, in order to reduce a decrease in the strength of the element body due to the presence of voids in the magnetic body, the element body B may be impregnated with a resin material after firing to place resin in the voids. By placing resin in the voids in the magnetic body M, the strength of the element body can be further improved.

[0038] The resin provided in the gaps may contain epoxy resin, silicone resin, or phenol resin. If the resin that fills the gaps in the magnetic body M is epoxy resin or phenol resin, the strength of the body B can be further increased.

[0039] In this embodiment, the surface roughness of the bottom surface B1 (first main surface B1) of the magnetic body in element body B is rougher than the surface roughness of the surface B2 (second main surface B2) opposite to the bottom surface B1 of the magnetic body in element body B. Such surface roughness of the bottom surface B1 of the magnetic body of element body B is caused by the grinding process described below. This can increase the adhesion strength between the bottom surface B1 of the magnetic body of element body B and the exterior resin layer SR.

[0040] The surface roughness of the bottom surface B1 of the magnetic body in the element body B is not particularly limited, and may be, for example, 0.3 μm or more and 1.0 μm or less, and particularly 0.5 μm or more and 1.0 μm or less. The surface roughness of a surface B2 of the magnetic body in element body B opposite to bottom surface B1 is not particularly limited, and may be, for example, 0.1 μm or more and 0.6 μm or less. The difference in surface roughness between the bottom surface B1 of the magnetic body in element body B and the surface roughness of the surface B2 opposite to the bottom surface B1 of the magnetic body in element body B may usually be 0.1 μm or more and 0.9 μm or less.

[0041] In this specification, the surface roughness of the element body B (particularly the magnetic body M) is a surface roughness based on the so-called arithmetic mean roughness Ra, and is the average value of values ​​measured at any 20 points in the central part of the bottom surface of the element body B.

[0042] (coil) The coil includes a plurality of coil conductors CM in a lamination direction (for example, a height direction T). The coil of this embodiment may have about 2.5 turns of lamination groups G2, G4, and G6, as shown in FIG.

[0043] The thickness of the coil conductor CM in each lamination group may be the same. The coil conductor CM may be a metal conductor such as Ag, Cu, and / or Pd, for example. The coil conductor CM may be formed by printing a conductive paste on the magnetic layer ML.

[0044] (Through-hole and via-hole conductors) The coil C may include a through hole TH and a via hole conductor V. The through hole TH may include a first through hole TH1 and a second through hole TH2. The first through hole TH1 and the second through hole TH2 may be provided inside the element body B.

[0045] The first through hole TH1 may connect the first external electrode E1 to an end of the coil conductor CM that is closest to the bottom surface (first main surface B1) of the element body B among the ends of the coil C. The first through hole TH1 may extend along the lamination direction (e.g., the height direction T). The first through hole TH1 may have a laminated structure.

[0046] The second through hole TH2 may connect the other end of the coil C and the second external electrode E2. The second through hole TH2 may extend along the lamination direction (e.g., the height direction T). The second through hole TH2 may have a laminated structure.

[0047] In this manner, the through hole TH is disposed inside the element body B (particularly the magnetic body M), and electrically connects the coil C and the external electrode E.

[0048] The via hole conductor V may electrically connect the coil conductors CM provided in the stacking groups adjacent to each other in the stacking direction. The length of the via hole conductor V in the stacking direction may be shorter than the length of the first through hole TH1, the length of the second through hole TH2, or the length of the via hole. The via hole conductor V may have a stacked structure.

[0049] An example of the material of the through hole TH and the via hole conductor V may be a metal conductor such as Ag, Cu and / or Pd (preferably Ag). The material of the through hole and the via hole conductor may be the same as or different from the coil conductor CM. The through hole and the via hole conductor may be formed, for example, by forming a through hole in the above-mentioned magnetic layer ML and printing a conductive paste in the through hole. The through hole and the via hole conductor may usually be a sintered body.

[0050] The surface roughness of the through-hole end face th1 is rougher than the surface roughness of the exterior resin layer forming region on the bottom face B1 of the magnetic body of the element body B. Such surface roughness of the through-hole end face th1 is due to the second etching process described below. This further increases the connection strength between the external electrode and the lead conductor.

[0051] The surface roughness of the through-hole end surface th1 is not particularly limited, and may be, for example, 0.1 μm or more and 0.2 μm or less. The surface roughness of the bottom surface B1 of the magnetic body in element body B in the region where the exterior resin layer is formed may be similar to the surface roughness of the bottom surface B1 of the magnetic body in element body B described above. The difference in surface roughness between the end face th1 of the through hole and the surface roughness of the bottom face B1 of the magnetic body of the element body B where the exterior resin layer is formed may usually be 0.3 μm or more and 0.9 μm or less.

[0052] In this specification, the surface roughness of the through-hole end surface th1 is a surface roughness based on the so-called arithmetic mean roughness Ra, and is the average value of values ​​measured at any 20 points using a laser microscope (VK-X1000 manufactured by Keyence Corporation).

[0053] -External electrode- 1, the external electrode E may include a first external electrode E1 and a second external electrode E2. The first external electrode E1 and the second external electrode E2 may be provided on a first main surface B1 (bottom surface) of the element body B and electrically connected to the coil C. Providing the external electrodes on the first main surface B1 of the element body B makes it possible to properly mount the laminated inductor 1A on a mounting board or the like.

[0054] The first external electrode E1 may act as an input electrode and / or an output electrode for the coil C. The first external electrode E1 is provided in a square shape in a plan view in Fig. 1 and Fig. 2, but is not particularly limited thereto and may have, for example, a rectangular shape or a circular shape.

[0055] The second external electrode E2 may act as an input electrode and / or an output electrode for the coil C. The second external electrode E2 is provided in a square shape in a plan view in Fig. 1 and Fig. 2, but is not particularly limited thereto and may have, for example, a rectangular shape or a circular shape.

[0056] The external electrodes E (E1 and E2) are usually disposed on the through holes TH (particularly on their end faces) and are electrically connected to the through holes TH.

[0057] 3 is an enlarged cross-sectional view of the vicinity of the external electrode in the laminated inductor of the first embodiment, and is an enlarged cross-sectional view of the vicinity of the external electrode when the laminated inductor of FIG. 1 is placed upside down. As shown in FIG. 3, the external electrode E has an upper end 11a and a lower end 11b in the lamination direction T in a cross-sectional view, and each of the upper end 11a and the lower end 11b has a flange-like protrusion 13a, 13b protruding in a direction perpendicular to the lamination direction T. The upper end 11a is an end that is more distal to the through hole TH in the lamination direction T. The lower end 11b is an end that is more proximal to the through hole TH in the lamination direction T. In detail, the upper end 11a and the lower end 11b of the external electrode E are the upper end and the lower end, respectively, when the element body B is placed with the bottom surface B1 of the magnetic body of the element body B on the upper side and the surface B2 opposite to the bottom surface B1 of the magnetic body of the element body B on the lower side.

[0058] The widths (r1 and r2, respectively) of the upper end 11a and the lower end 11b of the external electrode E are usually larger than the opening width r3 of the exterior resin layer SR in a cross-sectional view (see FIG. 3). In particular, the width r2 of the lower end 11b of the external electrode E being larger than the opening width r3 of the exterior resin layer SR makes the anchor effect of the protrusion 13b of the lower end 11b even more effective. The opening width r3 of the exterior resin layer SR is the minimum width in the direction perpendicular to the stacking direction T when viewing the external electrode E through the cross-sectional view.

[0059] The values ​​of the widths (r1 and r2, respectively) of the upper end 11a and the lower end 11b of the external electrode E are not particularly limited, and may be, for example, each independently, for example, not less than 150 μm and not more than 400 μm.

[0060] The value of the opening width r3 of the exterior resin layer SR is not particularly limited, and may be, for example, 1 μm or more and 10 μm or less, particularly 5 μm or more and 10 μm or less. The opening width r3 of the exterior resin layer SR is the minimum opening width in a cross-sectional view. As described above, the opening width r3 of the exterior resin layer SR corresponds to the minimum width of the external electrode E.

[0061] The protrusions (13a, 13b, respectively) of the upper end 11a and the lower end 11b have a protrusion length that can be confirmed, for example, in a cross-sectional view at a magnification of 5000 times. FIG. 4 is a partially enlarged cross-sectional view of the Z portion of FIG. 3. As shown in FIG. 4, for example, the protrusions (13a, 13b, respectively) (p1, p2 in FIG. 4) of the upper end 11a and the lower end 11b each independently protrude with a protrusion length of 1 μm to 10 μm, particularly 5 μm to 10 μm, and preferably 2 μm to 10 μm, more preferably 4 μm to 10 μm, in terms of further improving the connection strength between the external electrode and the lead conductor. The protrusions do not necessarily have to protrude strictly in a direction perpendicular to the stacking direction, and may protrude in a direction intersecting the stacking direction as long as they protrude in the perpendicular direction as a whole.

[0062] The protrusion lengths of the protrusions 13a, 13b are based on the minimum width of the external electrode E, and more specifically, for example, as shown in Fig. 4, they are protrusion lengths p1 and p2 in the direction perpendicular to the stacking direction T based on the minimum width. The minimum width of the external electrode E is a dimension corresponding to an opening width r3 of the exterior resin layer SR, which will be described later.

[0063] The thickness of the exterior resin layer SR is not particularly limited and may be, for example, from 0.5 μm to 20 μm, particularly from 4 μm to 10 μm. The thickness of the exterior resin layer SR is the average value of values ​​measured at any 20 points.

[0064] The exterior resin constituting the exterior resin layer SR is not particularly limited as long as it is a resin that can withstand etching in the second etching step described below, and may be, for example, an epoxy resin, an acrylic resin, or the like.

[0065] The widths (r1 and r2, respectively) of the upper end 11a and the lower end 11b of the external electrode E are usually smaller than the width R of the through hole TH in a cross-sectional view (see FIG. 3). This makes it possible to suppress an increase in DC resistance and to reduce the plane area of ​​the external electrode E as viewed from the mounting surface B1 side of the element body B. For this reason, the present disclosure is particularly effective for laminated inductors of a multi-phase DC-DC converter. Multi-phase means integrating multiple coils in one element body, as in the second and third embodiments described later. The through hole TH, particularly in the case of a laminated body, has unevenness on its side as shown in FIG. 3. Therefore, the width R of the through hole TH is the average value of the minimum width and the maximum width in the direction perpendicular to the lamination direction T in a cross-sectional view.

[0066] The width R of the through hole TH is not particularly limited and may be 250 μm or more and 400 μm or less.

[0067] The difference between the width R of the through hole TH and the width r1 of the upper end 11a and the difference between the width R of the through hole TH and the width r2 of the lower end 11b are not particularly limited, and may be, for example, independently 0 μm or more and 50 μm or less.

[0068] In this embodiment, the external electrode E is embedded in the exterior resin layer SR between the protruding parts of the upper end 11a and the lower end 11b. "Embedded" means to install while being embedded. In this embodiment, in detail, the entire external electrode E is not embedded in the exterior resin layer, but only the part between the protruding part 13a of the upper end 11a and the protruding part 13b of the lower end 11b is embedded in the exterior resin layer SR, while the upper surface 11a1 of the upper end 11a and the lower surface 11b1 of the lower end 11b are not in direct contact with the exterior resin layer SR. The exterior resin layer SR is disposed (or filled) between the protruding parts (13a and 13b, respectively) of the upper end 11a and the lower end 11b of the external electrode E in the stacking direction T.

[0069] In this way, the external electrode E has protrusions 13a, 13b at its upper end 11a and lower end 11b, and is embedded between them in the exterior resin layer SR, improving the connection strength of the external electrode E from the element body B (particularly the through hole TH). When viewed in a plane from the stacking direction T, for example, only the upper end 11a of the external electrode E is visible, and the lower end 11b is not visible. When viewed in a plane from the stacking direction T of the external electrode E, the upper end 11a exists as an "island" in the exterior resin layer SR as an "ocean".

[0070] From another viewpoint of this embodiment, in a cross-sectional view, the external electrode E holds the exterior resin layer SR between the protrusion 13a at the upper end 11a and the protrusion 13b at the lower end 11b. In particular, the protrusion 13b at the lower end 11b not only exerts an anchor effect, but also holds the exterior resin layer SR together with the protrusion 13a at the upper end 11a, thereby more sufficiently improving the connection strength of the external electrode E from the element B (particularly the through hole TH).

[0071] From the viewpoint of further improving the connection strength between the external electrodes and the lead conductors, the thickness of the exterior resin layer SR between the protrusions is preferably thicker than the thickness of the exterior resin layer SR outside the protrusions. Such a thickness gradient of the exterior resin layer is due to the first and second etching steps (particularly the first etching step) described below.

[0072] The thickness of the exterior resin layer SR between the protrusions is a1 on a reference line P in the stacking direction T that passes through the apex of the protrusion with the longer protrusion length, between the protrusion 13a at the upper end 11a and the protrusion 13b at the lower end 11b, as shown in Fig. 4. The thickness a1 is not particularly limited and may be, for example, 5 µm or more and 12 µm or less.

[0073] The thickness of the exterior resin layer SR outside the protrusions refers to the thickness of the exterior resin layer SR in areas on the bottom surface B1 of the element body B where no external electrodes are formed, and is the average value of thicknesses at any 20 points in the exterior resin layer SR on the magnetic body M. The thickness of the exterior resin layer SR outside the protrusions is not particularly limited, and may be, for example, 4 μm or more and 10 μm or less.

[0074] In Fig. 3, the external electrode E has protrusions 13a, 13b on both the left and right sides at each of the upper end 11a and the lower end 11b, but it is not necessary to have protrusions on both the left and right sides, and it is sufficient that at least the lower end has a protrusion on one of the left and right sides (preferably both sides). From the viewpoint of further improving the connection strength between the external electrode and the lead conductor, it is preferable that the external electrode has protrusions on both the left and right sides at each of the upper end and the lower end. The protrusions at the lower end of the external electrode are due to the external electrode formation step being performed after the second etching step described below.

[0075] The external electrodes may be made of various materials such as Cu, Ni and / or Sn, for example, and are preferably made of Cu. The external electrodes may be formed by any method, but as an example, they may be plated electrodes formed by plating (e.g., electroless plating) directly on the through-holes. When forming the external electrodes by plating, it is necessary to immerse the element body B in a plating solution, but as described above, since a resin is disposed in the voids of the element body B (magnetic body M), it is possible to reduce the infiltration of the plating solution into the voids in the magnetic body.

[0076] <Modification 1 of the First Embodiment of the Multilayer Inductor> In the laminated inductor according to the first embodiment, the external electrode E has protrusions 13a, 13b at the upper end 11a and lower end 11b, which are continuous over the entire circumference of the external electrode E when viewed from above in the lamination direction. However, the external electrode E does not necessarily have to have the protrusions continuously over its entire circumference, and may have the protrusions discontinuously or intermittently over the entire circumference of the external electrode E when viewed from above in the lamination direction. For example, the external electrode E may have the protrusions in any one cross-sectional view.

[0077] <Modification 2 of the First Embodiment of the Multilayer Inductor> In the laminated inductor according to the first embodiment, the external electrodes E are formed in islands (e.g., spots) in a plan view from the lamination direction, but may be formed continuously in the depth direction in Fig. 3. In other words, the external electrodes E may extend in a wall shape in the W direction of the element body. The upper end 11a and the lower end 11b may have protrusions 13a, 13b continuously in the extension direction, or discontinuously or intermittently.

[0078] <Second embodiment of multilayer inductor> Next, the laminated inductor 1B of the second embodiment will be described with reference to FIG. 5. The laminated inductor 1B of the second embodiment differs from the laminated inductor 1A of the first embodiment in terms of the coil configuration. Specifically, the number of coils, the number of turns of the coil, and the positions of the external electrodes are different. In the following description, differences from the laminated inductor described in the above embodiment will be mainly described. The structure of each of the external electrodes E1 to E4 in the laminated inductor 1B of the second embodiment corresponds to the structure of each of the external electrodes E1 to E2 in the laminated inductor 1A of the first embodiment. Therefore, in the second embodiment, as in the first embodiment, the plane area of ​​the external electrodes E (E1 to E4) as viewed from the mounting surface B1 side of the element body B can be made smaller. Therefore, the laminated inductor 1B of the second embodiment can more effectively utilize the bottom surface (mounting surface) B1 of the element body B based on the reduction in the area of ​​the external electrodes E. The structure of the external electrodes includes not only the structure of the external electrodes themselves, but also the relationship between the external electrodes, the through-holes, and the exterior resin layer, and the relationship between the through-holes and the exterior resin layer.

[0079] The coils of the laminated inductor 1B of this embodiment may be arranged so that two or more are overlapped when viewed from the lamination direction. In other words, a first coil C1 and a second coil C2 may be provided inside the element body B. The first coil C1 and the second coil C2 may be magnetically coupled. For example, the coupling coefficient between the first coil C1 and the second coil C2 is 0.1 or more and 0.8 or less. Note that, two coils including only the first coil C1 and the second coil C2 may be provided inside the element body B, or three or more coils including the first coil C1 and the second coil C2 may be provided.

[0080] -First coil- The first coil C1 includes a plurality of first coil conductors CM1 constituting the first coil C1 in the stacking direction (e.g., height direction T). Adjacent first coil conductors CM1 are connected to each other via via hole conductors V. The first coil C1 may have a number of turns of 1.75 by including first coil conductors CM1 formed in two different stacking groups in the stacking direction. The number of turns is not limited to 1.75, and may be, for example, 2 or more, by stacking the first coil conductors CM1 in the stacking direction.

[0081] -Second coil- The second coil C2 is disposed above the first coil C1 in the height direction T, and includes a plurality of second coil conductors CM2 constituting the second coil in the stacking direction (for example, in the height direction T). Adjacent second coil conductors CM2 are connected to each other via via hole conductors V. The second coil C2 may have a number of turns of 1.75 by including second coil conductors CM2 formed in two different stacking groups in the stacking direction. The number of turns is not limited to 1.75 as shown in the figure, and may be, for example, 2 or more by stacking the first coil conductor CM1 in the stacking direction. The number of stacked layers of the second coil conductor CM2 may be the same as or different from the number of stacked layers of the first coil conductor 51.

[0082] -Through holes and external electrodes- The through holes include a first through hole TH1, a second through hole TH2, a third through hole TH3, and a fourth through hole TH4. The first through hole TH1, the second through hole TH2, the third through hole TH3, and the fourth through hole TH4 are provided inside the element body B. The first through hole TH1, the second through hole TH2, the third through hole TH3, and the fourth through hole TH4 are exposed from the mounting surface (first main surface B1) of the element body B.

[0083] The first through hole TH1 connects the end of the first coil C1 of the first coil conductor CM1 that is closest to the bottom surface of the element body B to the first external electrode E1. The first through hole TH1 may extend along the lamination direction (e.g., the height direction T). The first through hole TH1 may have a laminated structure.

[0084] The second through hole TH2 connects the other end of the first coil C1 and the second external electrode E2. The second through hole TH2 may extend along the lamination direction (for example, the height direction T). The second through hole TH2 may have a laminated structure.

[0085] The third through hole TH3 connects the end of the second coil C2 of the second coil conductor CM2 that is closest to the bottom surface of the element body B to the third external electrode E3. The third through hole TH3 may extend along the stacking direction (e.g., the height direction T). The third through hole TH3 may have a stacked structure.

[0086] The fourth through hole TH4 connects the other end of the second coil C2 and the fourth external electrode E4. The fourth through hole TH4 may extend along the stacking direction (for example, the height direction T). The fourth through hole TH4 may have a stacked structure.

[0087] 5, 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 provided on the first main surface B1 of the element body B, and are electrically connected to the first coil C1. The third external electrode E3 and the fourth external electrode E4 are provided on the first main surface B1 of the element body B, and are electrically connected to the second coil C2. In the laminated inductor 1B, the first main surface B1 of the element body B can be used as a mounting surface.

[0088] Even in the laminated inductor 1B of the second embodiment, resin is provided in at least some of the gaps in the magnetic body M and the coil conductor. Therefore, by reducing the gaps, the strength of the element can be increased.

[0089] <Modification of the Second Embodiment of the Multilayer Inductor> In the multilayer inductor according to the second embodiment (FIG. 5), all of the external electrodes E are formed in an island shape (for example, a spot shape) in a plan view from the lamination direction. However, the island-shaped external electrodes may be used as abutments to provide an electrode connection structure in which a bridge portion is joined thereon. In more detail, for example, in the case where the external electrodes E2 and E3 have the same polarity in FIG. 5, an electrode connection structure may be provided that has the external electrodes E2 and E3 as abutments and further has a bridge portion bridging the external electrodes E2 and E3. In such an electrode connection structure, the external electrodes as abutments and the through holes have a sufficient connection strength, so that the electrode connection structure also has a sufficient connection strength. The bridge portion of the electrode connection structure may be made of the same material as the external electrodes E.

[0090] <Multilayer inductor array> Next, the laminated inductor array of the present disclosure will be described with reference to FIG. 6. The laminated inductor array 1C of the present disclosure has two or more coils arranged overlapping each other in a plan view from the lamination direction, and arranged side by side in a direction intersecting the lamination direction (for example, a direction perpendicular to the lamination direction) to form a coil array. Specifically, in addition to the first coil C1 and the second coil C2, the array may include a third coil C3 and a fourth coil C4, as well as a fifth coil C5 and a sixth coil C6. The third coil C3 and the fifth coil C5 have substantially the same structure as the first coil C1, and the fourth coil C4 and the sixth coil C6 have substantially the same structure as the second coil C2.

[0091] The third coil C3 may be electrically connected to the fifth external electrode E5 and the sixth external electrode E6. The end of the third coil C3, that of the third coil conductor layer closest to the bottom surface, may be connected to the fifth external electrode E5 by a fifth through hole TH5. The other end of the third coil conductor layer may be connected to the sixth external electrode E6 by a sixth through hole TH6.

[0092] The fourth coil C4 may be electrically connected to a seventh external electrode (not shown) and an eighth external electrode (not shown). Of the ends of the fourth coil C4, an end of the fourth coil conductor layer closest to the bottom surface may be connected to the seventh external electrode by a seventh through hole. Also, the other end of the fourth coil conductor layer may be connected to the eighth external electrode by an eighth through hole.

[0093] The fifth coil C5 may be electrically connected to the ninth external electrode E9 and the tenth external electrode E10. The end of the fifth coil C5, the end of the fifth coil conductor layer closest to the bottom surface, may be connected to the ninth external electrode E9 by a ninth through hole TH9. The other end of the fifth coil conductor layer may be connected to the tenth external electrode E10 by a tenth through hole TH10.

[0094] The sixth coil C6 may be electrically connected to the eleventh external electrode E11 and the twelfth external electrode E12. Of the ends of the sixth coil C6, the end of the sixth coil conductor layer closest to the bottom surface may be connected to the eleventh external electrode E11 by an eleventh through hole TH11. In addition, the other end of the sixth coil conductor layer may be connected to the twelfth external electrode (not shown) by a twelfth through hole TH12.

[0095] In the multilayer inductor array 1C of the present disclosure, the structure of each of the external electrodes E1 to E12 corresponds to the structure of each of the external electrodes E1 to E2 in the multilayer inductor 1A of the first embodiment. Therefore, in the multilayer inductor array 1C of the present disclosure, as in the first embodiment, the planar area of ​​the external electrodes E (E1 to E12) as viewed from the mounting surface B1 side of the element body B can be made smaller. Therefore, the multilayer inductor array 1C of the present disclosure can make more effective use of the bottom surface (mounting surface) B1 of the element body B by reducing the area of ​​the external electrodes E.

[0096] <Manufacturing method for multilayer inductors> Next, the method for manufacturing a laminated inductor according to the present disclosure will be described with reference to FIG. 7A. FIG. 7A is a flow diagram showing the method for manufacturing a laminated inductor according to the present disclosure. The method for manufacturing a laminated inductor according to the present disclosure may include a body precursor preparation step, a resin impregnation preparation step, a resin impregnation step, a grinding step, a first etching step, an exterior resin layer formation step, a second etching step, and an external electrode formation step. In the method for manufacturing a laminated inductor according to the present disclosure, cross-sectional views showing the resin impregnation step, the grinding step, the first etching step, the exterior resin layer formation step, the second etching step, and the external electrode formation step are more characteristic. The steps will be described in detail below.

[0097] [Element body precursor preparation process] In this process, a base body precursor is prepared, which has a coil with a coil conductor wound inside a magnetic body formed by stacking magnetic layers containing iron powder, and a through hole electrically connected to the coil conductor and exposed from the bottom surface of the magnetic body. In detail, first, a magnetic paste for forming the magnetic layers ML of the multilayer groups described in FIG. 2, a conductor paste for forming the coil conductors CM, and a non-magnetic paste for forming the non-magnetic layers between the coil conductors CM are prepared.

[0098] As an example of a method for producing a magnetic paste, an iron powder such as an Fe-Si alloy or an Fe-Si-Cr alloy with a cumulative 50% particle diameter D50 on a volume basis of 2 μm or more and 20 μm or less is prepared. This iron powder is mixed with a binder such as cellulose or polyvinyl butyral (PVB) and a solvent such as a mixture of terpineol and butyl diglycol acetate (BCA), and then kneaded to produce a magnetic paste.

[0099] When an Fe-Si alloy is used as the iron powder, the Si content is preferably 2.0 at% or more and 8.0 at% or less. When an Fe-Si-Cr alloy is used as the iron powder, the Si content is preferably 2.0 at% or more and 8.0 at% or less. When an Fe-Si-Cr alloy is used as the iron powder, the Cr content is preferably 0.2 at% or more and 6.0 at% or less.

[0100] An insulating coating may be provided on the surface of the iron powder. The insulating coating is preferably a coating containing a metal oxide, more preferably an oxide of Si. The method for forming the insulating coating is preferably a sol-gel method. As an example of forming an insulating coating by the sol-gel method, a sol-gel coating agent containing Si alkoxide and an organic chain-containing silane coupling agent are mixed to form a mixed liquid. After this mixed liquid is attached to the surface of the metal magnetic powder, it is dehydrated and bonded by applying a heat treatment. Then, the insulating coating can be formed by drying at a predetermined temperature.

[0101] As an example of a method for producing a non-magnetic paste, Fe2O3, ZnO, CuO, and additional components as necessary are weighed out to obtain a predetermined composition. The weighed items are placed in a ball mill together with pure water, dispersant, and PSZ media, and mixed and pulverized to obtain a slurry. The obtained slurry is dried, and then calcined at a temperature of 700°C or higher and 800°C or lower for 2 hours or more and 3 hours or less to obtain a non-magnetic material (calcined powder). A predetermined amount of solvent (ketone-based solvent, etc.), resin (polyvinyl acetal, etc.), and plasticizer (alkyd-based plasticizer, etc.) are added to the non-magnetic material (calcined powder), kneaded with a planetary mixer, and then further dispersed with a three-roll mill to produce a non-magnetic paste.

[0102] The non-magnetic paste preferably contains Fe in an amount of 40 mol% or more and 49.5 mol% or less calculated as Fe2O3, Cu in an amount of 4 mol% or more and 12 mol% or less calculated as CuO, and the remainder being ZnO as the main component. The non-magnetic paste is more preferably one in which Mn, Bi, Co, Si, Sn, etc. are added as additives to the above main components as necessary. The non-magnetic paste may contain inevitable impurities.

[0103] As the conductive paste, for example, a paste containing Ag as a conductive material is prepared.

[0104] Using the above-mentioned magnetic paste, non-magnetic paste, and conductor paste, the laminate groups G1 to G7 shown in FIG. 2 are prepared by screen printing or the like. Then, the unsintered element precursor is pressurized by a press process such as warm isostatic pressing (WIP) to form a laminate. After the pressurization process, the laminate is placed in a firing furnace, degreased, and then fired in the air. The firing temperature is, for example, 600° C. or higher and 800° C. or lower. The firing time is, for example, 30 minutes or higher and 90 minutes or lower. An element is prepared by this firing.

[0105] [Resin impregnation preparation process] (Optional additional process) The resin impregnation preparation step is a step that is optionally performed before the resin impregnation step described below. Specifically, the resin impregnation preparation step is a step of reducing gas or moisture in the element body or lowering the viscosity of the resin.

[0106] One example of the resin impregnation preparation step is to degas the fired body to reduce the amount of gas in the body and make it easier to impregnate the body with resin. Degassing and resin impregnation may be repeated. Another method of the resin impregnation preparation step is to heat the fired body to reduce the amount of moisture in the body and make it easier to impregnate the body with resin. Yet another method of the resin impregnation preparation step is to heat the resin to reduce the viscosity of the resin and make it easier to impregnate the body with resin. By going through these steps, the body can be effectively impregnated with resin.

[0107] [Resin impregnation process] (Optional process) In this step, the fired element body precursor is impregnated with resin. This step may be an optional step. When this step is performed, the resin may contain, for example, epoxy resin, silicone resin, or phenol resin. By impregnating the element body with resin, the resin is provided in at least a portion of the voids in the magnetic body and the coil conductor. This makes it possible to reduce the voids and increase the element body strength. It also makes it possible to reduce the infiltration of plating solution, moisture, etc. into the element body. In this step, impregnation resin residue RE remains on the bottom surface B1 (first main surface B1) side of the magnetic body in the element body precursor (FIG. 7A(1)).

[0108] [Grinding process] In this step, the impregnated resin residue RE on the bottom surface B1 side of the resin-impregnated element body precursor is removed by grinding to expose at least the end faces of the through-holes TH, thereby obtaining an element body (FIG. 7A(2)). Grinding can impart the above-mentioned surface roughness to the bottom surface B1 of the magnetic body, and can also adjust the thickness of the element body to a predetermined thickness. This step may also be performed on an element body precursor that is not impregnated with resin.

[0109] [First Etching Step] (Optional Step) This step is an optional step performed before the exterior resin layer forming step described later. Specifically, at least the end face of the through hole is etched on the bottom surface of the magnetic body of the element obtained in the grinding step to obtain a new through hole end face th0 (FIG. 7A(3)). As described above, this step provides a thickness gradient on the bottom surface B1 side of the magnetic body in which the thickness of the exterior resin layer SR between the protrusions is thicker than the thickness of the exterior resin layer SR outside the protrusions, further improving the connection strength between the external electrode and the through hole. The etchant used is a liquid capable of dissolving the through hole and the magnetic body M. Examples of such an etchant may include potassium nitrate-ammonia water, sodium cyanide, and phosphoric acid / hydrogen peroxide. If the magnetic body M is impregnated with resin in this step, the magnetic body is hardly etched.

[0110] [Exterior resin layer formation process] In this step, an exterior resin layer SR is formed on the bottom surface of the magnetic body of the element body in areas other than the through-hole end faces (FIG. 7A(4)). The exterior resin layer SR is a protective layer for the second etching step described below, and may be, for example, a solder resist layer. The method for forming the exterior resin layer SR is not particularly limited as long as it is possible to selectively form the exterior resin layer SR in areas other than the through-hole end faces, and for example, a screen printing method may be adopted. In the screen printing method, a solution of the above-mentioned resin that constitutes the exterior resin layer SR may be used as ink.

[0111] In this step, the exterior resin layer SR is formed on the bottom surface of the magnetic body of the element body so that an area roughly corresponding to the end face of the through hole is opened. More specifically, the area of ​​the opening of the exterior resin layer SR is smaller than the area of ​​the end face of the through hole TH. Because the area of ​​the opening of the exterior resin layer SR is smaller than the area of ​​the end face of the through hole TH, an overlapping portion is obtained between the exterior resin layer SR and the through hole TH (particularly its end face) in a plan view. As a result, in the second etching step described below, a gap is formed between the end face of the through hole and the exterior resin layer, and in the external electrode formation step described below, a protrusion 13b is formed at the lower end of the external electrode.

[0112] 7B is a cross-sectional view showing in detail the exterior resin layer forming step in the manufacturing method of the laminated inductor of the present disclosure. The opening of the exterior resin layer refers to an opening seen through the external electrode in a plan view from the stacking direction T, and is shown in FIG. 7B as the region between two reference lines m4. The reference line m4 is a reference line parallel to the stacking direction T that defines the opening of the exterior resin layer SR.

[0113] The end face of the through hole TH is shown, for example, as the region between two reference lines m3 in Fig. 7B. In a cross-sectional view, the reference line m3 is the center line between a reference line m1 parallel to the lamination direction T that defines the maximum diameter of the through hole TH, and a reference line m2 parallel to the lamination direction T that defines the minimum diameter of the through hole TH. The diameter D of the through hole TH is the maximum diameter defined by the reference line m1, and can be measured from an image of the laminated inductor viewed with an X-ray from the bottom side or from a side in a direction approximately perpendicular to the lamination direction T.

[0114] In this step, more specifically, in a plan view from the stacking direction of the element body on which the exterior resin layer SR is formed, the exterior resin layer SR is formed so as to overlap the periphery of the end face of the through hole TH. The dimension n of the overlapping portion at the periphery of the end face of the through hole TH may be a dimension such that a gap corresponding to the protrusion 13b is formed between the end face of the through hole and the exterior resin layer in the second etching step described later. The dimension n of the overlapping portion at the periphery of the end face of the through hole TH is expressed by the distance between the reference lines m3 and m4 described above, and may be, for example, 2 μm or more, particularly 50 μm or more. The dimension n is preferably as large as possible within the range in which the opening of the exterior resin layer SR is formed, so the upper limit of the dimension n is not particularly limited, and may be, for example, 70 μm or less, particularly 20 μm or less.

[0115] [Second etching process] In this step, the through-hole end face is etched at the bottom surface of the magnetic body of the element body on which the exterior resin layer is formed, to obtain a new through-hole end face th1 (FIG. 7A(5)). After this step is performed, the external electrode formation step described below is performed to form protrusion 13b at the lower end of the external electrode. More specifically, in this step, the through-hole end face is etched, lowering the surface of the through-hole end face, to obtain through-hole end face th1. As a result, a gap corresponding to protrusion 13b is formed between the through-hole end face and the exterior resin layer, and protrusion 13b at the lower end of the external electrode is formed by the external electrode formation step described below.

[0116] In this step, an etching solution is used that dissolves the through-holes but does not dissolve the exterior resin layer SR. For example, a solution containing potassium cyanide, phosphoric acid, nitric acid, acetic acid, or thiourea may be used as such an etching solution. The etching time is not particularly limited, and may be, for example, 30 seconds or more and 900 seconds or less, preferably 500 seconds or more and 700 seconds or less (particularly 600 seconds).

[0117] [External electrode formation process] The external electrode formation process is a process for forming an external electrode E electrically connected to the coil conductor (FIG. 7A(6)). The external electrode is formed by electroless plating in the opening of the exterior resin layer SR (the position where the through hole is exposed on the mounting surface (first main surface B1) of the element body B). The plating material may be Cu plating. Other examples include, but are not limited to, Ni-Sn, Ni-Au, Ni-Cu and / or Cu-Ni-Au.

[0118] In the second etching step, a gap corresponding to the protrusion 13b is formed between the end face of the through hole and the exterior resin layer, so that in the external electrode formation step, simply by forming the external electrode, the protrusion 13b is formed at its lower end.

[0119] In the external electrode formation step, it is important to form the external electrodes higher than the surface of the exterior resin layer SR, so that protrusions 13a are formed at the upper ends of the external electrodes.

[0120] When a plurality of laminated inductors are obtained in series by the exterior resin layer forming step, the laminated inductor of this embodiment can be manufactured by cutting into individual elements after the external electrodes are formed (dicing step).

[0121] The above-mentioned element precursor preparation step, resin impregnation preparation step, resin impregnation step, grinding step, first etching step, exterior resin layer formation step, second etching step, and external electrode formation step are usually performed sequentially in the order described. Note that the resin impregnation preparation step and the first etching step may be omitted or performed independently. For example, when the first etching step is omitted, specifically, the exterior resin layer formation step, the second etching step, and the external electrode formation step may be performed sequentially on the element obtained in the grinding step.

[0122] The technical scope of the present disclosure is not interpreted only by the above-described embodiments, but is defined based on the claims. The technical scope of the present disclosure includes all modifications within the scope and meaning equivalent to the claims.

[0123] The laminated inductor and the manufacturing method thereof according to the present disclosure include the following aspects. <1> an element body having a coil formed by winding a coil conductor inside a magnetic body formed by laminating magnetic layers containing iron powder, and a through hole electrically connected to the coil conductor and extending toward a bottom surface of the magnetic body; an external electrode disposed on the through hole and electrically connected to the through hole; an exterior resin layer disposed on a bottom surface of the magnetic body of the base body; the external electrode has a protrusion protruding in a direction perpendicular to the lamination direction at an upper end portion distal to the through hole in the lamination direction of the magnetic layers and a lower end portion proximal to the through hole, The exterior resin layer is disposed across the protrusions at the upper end and the lower end of the laminated inductor. <2> a width of the upper end portion and the lower end portion of the external electrode is larger than a width of an opening of the exterior resin layer in the cross-sectional view; <1> The laminated inductor according to claim 1. <3> a width of the upper end portion and the lower end portion of the external electrode is smaller than a diameter of the through hole in the cross-sectional view; <1> or <2> The laminated inductor according to claim 1. <4> the thickness of the exterior resin layer on the through hole is greater than the thickness of the exterior resin layer outside the through hole; <1> ~ <3> 2. The laminated inductor according to claim 1 . <5> The external electrodes are plating electrodes formed directly on the through holes. <1> ~ <4> 2. The laminated inductor according to claim 1 . <6> the external electrodes are copper-plated electrodes; The through hole is a silver sintered body. <1> ~ <5> 2. The laminated inductor according to claim 1 . <7> a surface roughness of a bottom surface of the magnetic body in the element body is greater than a surface roughness of a surface of the magnetic body opposite to the bottom surface of the element body; <1> ~ <6> 2. The laminated inductor according to claim 1 . <8> the surface roughness of the end face of the through hole is greater than the surface roughness of an exterior resin layer forming region on the bottom surface of the magnetic body of the element body; <1> ~ <7> 2. The laminated inductor according to claim 1 . <9> The element further includes a resin disposed in a gap in the magnetic body. <1> ~ <8> 2. The laminated inductor according to claim 1 . <10> The coils are arranged in a stacked manner in two or more layers when viewed from the stacking direction. <1> ~ <9> 2. The laminated inductor according to claim 1 . <11> The coils are arranged in a stacked manner in two or more layers when viewed from the stacking direction, and are arranged in parallel in a direction intersecting the stacking direction to form a coil array. <1> ~ <10> 2. The laminated inductor according to claim 1 . <12> an element precursor preparation step of preparing an element precursor having a coil formed by winding a coil conductor inside a magnetic body formed by laminating magnetic layers containing iron powder, and a through hole electrically connected to the coil conductor and exposed from a bottom surface of the magnetic body; a grinding step of removing impregnated resin residue on a bottom surface side of the magnetic body in the element precursor by grinding to expose end surfaces of the through holes, thereby obtaining an element; an exterior resin layer forming step of forming an exterior resin layer on a bottom surface of the magnetic body of the element body so as to overlap a peripheral portion of an end surface of a through hole when viewed in a plan view from the stacking direction; an etching step of etching an end face of the through hole on a surface of the element body on which an exterior resin layer is formed; and forming an external electrode on an end face of the through hole, the external electrode being electrically connected to the coil conductor. <13> a resin impregnation step of impregnating the precursor body with a resin is further provided between the precursor body preparation step and the grinding step. <12> A method for manufacturing the laminated inductor according to claim 1. <14> a step of etching an end face of the through hole in the bottom surface of the magnetic body of the element body, the step being performed between the grinding step and the exterior resin layer forming step; <12> or <13> A method for manufacturing the laminated inductor according to claim 1. <15> <1> ~ <11> The laminated inductor according to any one of the above items is manufactured. <12> ~ <14> 2. A method for producing the laminated inductor according to claim 1 , [Industrial Applicability]

[0124] The present disclosure can be used for a multilayer inductor with improved connection strength between external electrodes and through holes. [Explanation of symbols]

[0125] 1A, 1B multilayer inductors 1C Multilayer Inductor Array B Base C coil CM Coil Conductor E External electrode E1 1st external electrode E2 2nd external electrode M Magnetic material MP Iron Powder ML magnetic layer SR exterior resin layer TH1 First through hole TH2 Second through hole

Claims

1. an element body having a coil formed by winding a coil conductor inside a magnetic body formed by laminating magnetic layers containing iron powder, and a through hole electrically connected to the coil conductor and extending toward a bottom surface of the magnetic body; an external electrode disposed on the through hole and electrically connected to the through hole; an exterior resin layer disposed on a bottom surface of the magnetic body of the base body; the external electrode has a protrusion protruding in a direction perpendicular to the lamination direction at an upper end portion distal to the through hole in the lamination direction of the magnetic layers and a lower end portion proximal to the through hole, The external electrodes are disposed across the projections at the upper end and the lower end.

2. The multilayer inductor according to claim 1 , wherein a width of the upper end portion and the lower end portion of the external electrodes is larger than a width of an opening of the exterior resin layer in the cross-sectional view.

3. The multilayer inductor according to claim 1 , wherein a width of the upper end and the lower end of the external electrode is smaller than a diameter of the through hole in the cross-sectional view.

4. The multilayer inductor according to claim 1 , wherein a thickness of said exterior resin layer on said through hole is greater than a thickness of said exterior resin layer outside said through hole.

5. 2. The multilayer inductor according to claim 1, wherein the external electrodes are plated electrodes formed directly on the through holes.

6. the external electrodes are copper-plated electrodes; The laminated inductor according to claim 1 , wherein the through-hole is made of sintered silver.

7. 2. The multilayer inductor according to claim 1, wherein a surface roughness of a bottom surface of said magnetic body in said element body is greater than a surface roughness of said magnetic body on the opposite side to said bottom surface.

8. 2. The multilayer inductor according to claim 1, wherein the surface roughness of the end face of the through hole is greater than the surface roughness of an exterior resin layer-forming region on the bottom surface of the magnetic body of the element body.

9. The laminated inductor according to claim 1 , wherein the element further comprises a resin disposed in voids within the magnetic body.

10. The laminated inductor according to claim 1 , wherein two or more of the coils are arranged overlapping each other when viewed from above in the lamination direction.

11. The laminated inductor according to claim 1 , wherein the coils are arranged in a stacked manner in a plan view from the stacking direction, and are arranged in parallel in a direction intersecting the stacking direction to form a coil array.

12. an element precursor preparation step of preparing an element precursor having a coil formed by winding a coil conductor inside a magnetic body formed by laminating magnetic layers containing iron powder, and a through hole electrically connected to the coil conductor and exposed from a bottom surface of the magnetic body; a grinding step of removing impregnated resin residue on a bottom surface side of the magnetic body in the element precursor by grinding to expose end surfaces of the through holes, thereby obtaining an element; an exterior resin layer forming step of forming an exterior resin layer on a bottom surface of the magnetic body of the element body so as to overlap a peripheral portion of an end surface of a through hole when viewed in a plan view from the stacking direction; an etching step of etching an end face of the through hole on a surface of the element body on which an exterior resin layer is formed; and forming an external electrode on an end face of the through hole, the external electrode being electrically connected to the coil conductor.

13. The method for producing a laminated inductor according to claim 12, further comprising a resin impregnation step of impregnating the precursor body with a resin, between the precursor body preparation step and the grinding step.

14. The method for manufacturing a laminated inductor according to claim 12, further comprising an etching step of etching an end face of the through hole in the bottom surface of the magnetic material of the element body, between the grinding step and the exterior resin layer forming step.

15. The method for producing a laminated inductor according to claim 12, which produces the laminated inductor according to any one of claims 1 to 11.

Images