Multilayer inductor and method for manufacturing 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

[0007] , ,

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

Background Art

[0002] In recent years, due to the high functionality of devices, the DC-DC converters of voltage conversion circuits have been evolving towards larger current and higher efficiency, and the rated current of the power inductors used in these devices has also been increasing.

[0003] Patent Document 1, which shows an example of the inductor, discloses a passive component including a substrate portion; an internal conductor built in the substrate portion; a lead-out conductor electrically connected to the internal conductor and extending in the downward direction of the substrate portion; and an external electrode electrically connected to the lead-out conductor.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In conventional passive components, for example, as shown in FIG. 8, since the external electrode 100 is simply formed on the lower surface of the substrate portion 110 and connected to the lead-out conductor 105 extending in the downward direction of the lower surface, there is a problem with the connection strength between the external electrode and the lead-out conductor.

[0006] The main object of the present disclosure is to provide a stacked inductor and a method for manufacturing the same, which improve the connection strength between the external electrode and the lead-out conductor.

Means for Solving the Problems

[0007] The present disclosure is A magnetic material having a laminated magnetic layer containing iron powder, a coil with a coil conductor wound around it, and a substrate electrically connected to the coil conductor and having a through-hole extending in the direction of the bottom surface of the magnetic material, An external electrode positioned on the through-hole and electrically connected to the through-hole, The substrate comprises an outer resin layer disposed on the bottom surface of the magnetic material, The external electrode has a projection that protrudes in a direction perpendicular to the stacking direction at its upper end distal to the through-hole and its lower end proximal to the through-hole in the stacking direction of the magnetic layer. The present invention relates to a laminated inductor in which the outer resin layer is arranged between the protrusions at the upper and lower ends. [Effects of the Invention]

[0008] This disclosure provides a multilayer inductor with improved connection strength between external electrodes and through-holes, and a method for manufacturing the same. Specifically, in the multilayer inductor, the external electrodes have protrusions at the upper and lower ends, and the outer resin layer is arranged between the protrusions at the upper and lower ends, thereby increasing the connection strength between the external electrodes and the lead conductors. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 is a schematic perspective view showing an example of a multilayer inductor according to the first embodiment. [Figure 2] Figure 2 is an exploded perspective view illustrating the stacked structure of the stacked inductor according to the first embodiment. [Figure 3] Figure 3 is a cross-sectional view of a multilayer inductor according to the first embodiment, and is an enlarged cross-sectional view of the vicinity of the external electrodes. [Figure 4] Figure 4 is a partially enlarged cross-sectional view of section Z in Figure 3. [Figure 5] Figure 5 is a schematic perspective view showing an example of a multilayer inductor according to the second embodiment. [Figure 6]Figure 6 is a schematic perspective view showing an example of a multilayer inductor array according to this disclosure. [Figure 7A] Figure 7A is a flowchart illustrating the manufacturing method of the multilayer inductor of this disclosure. [Figure 7B] Figure 7B is a cross-sectional view showing in detail the outer resin layer formation step in the manufacturing method of the laminated inductor of this disclosure. [Figure 8] Figure 8 is a cross-sectional view of a conventional multilayer inductor, specifically an enlarged cross-sectional view near the external electrodes. [Modes for carrying out the invention]

[0010] The multilayer inductor of this disclosure will be described below. However, this disclosure is not limited to the configurations described below and may be modified as appropriate without departing from the gist of this disclosure. Furthermore, combinations of several of the individual preferred configurations described below also constitute this disclosure.

[0011] The multilayer inductor of this disclosure is used, for example, as a choke coil in a DC-DC converter. The multilayer inductor of this disclosure is also applicable to applications other than DC-DC converters.

[0012] In this specification, terms describing relationships between elements (e.g., "parallel," "orthogonal," "perpendicular," etc.) and terms describing the shape of elements mean not only strictly defined aspects but also substantially equivalent ranges, such as ranges with differences of a few percent. In this specification, the direction in which the magnetic layers and coil conductors constituting the element are stacked is referred to as the "stacking direction" (e.g., direction T in Figure 1).

[0013] As used in this specification, "plan view" refers to the state (top view or bottom view) when an object is viewed from above or below along the thickness direction based on the stacking direction. Further, "cross-sectional view" refers to the cross-sectional state (cross-sectional view) when an object is viewed from a direction substantially perpendicular to the stacking direction T (for example, direction L or W in FIG. 1). The "vertical direction" and "horizontal direction" directly or indirectly used in this specification correspond to the vertical direction and horizontal direction in the drawing, respectively. Unless otherwise specified, the same reference numerals or symbols indicate the same members, parts, or the same meaning content. In a certain preferred embodiment, it can be understood that the vertically 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 their dimensions, scales of aspect ratios, etc. may be different from those of actual products.

[0015] <First Embodiment of Stacked Inductor> First, a first embodiment of the stacked inductor of the present disclosure will be described with reference to FIGS. 1 to 6 and FIGS. 7A and 7B. Note that the shapes and arrangements of the stacked inductor and each component are not limited to the illustrated examples.

[0016] FIG. 1 shows a perspective view of a stacked inductor 1A of the present disclosure. As shown in FIG. 1, the stacked inductor 1A includes a coil C in which a coil conductor is wound inside a magnetic body M formed by laminating magnetic layers containing iron powder, a body B having a through hole TH that is electrically connected to the coil conductor and extends in the bottom surface direction of the magnetic body, an exterior resin disposed on the bottom surface of the magnetic body and having an opening, and an external electrode E disposed in the opening of the outer layer resin layer and electrically connected to the through hole. The number of turns of the coil C is 2.5. Hereinafter, each component will be described in detail.

[0017] - Body - The body B has, for example, a rectangular parallelepiped shape or a substantially rectangular parallelepiped shape with six faces. The body B may have rounded vertices and edges. A vertex is a portion where three faces of the body B intersect, and an edge is a portion where two faces of the body B intersect.

[0018] Figure 1 shows the length, width, and height directions of the multilayer inductor 1A and the base body B as the L, W, and T directions, respectively. The length direction L, the width direction W, and the height direction T are orthogonal to each other. The mounting surface of the multilayer inductor 1A is, for example, a surface parallel to the length direction L and the width direction W (LW surface).

[0019] The base body B shown in Figure 1 has a first main surface B1 and a second main surface B2 that are opposite to the height direction T, a first end surface B3 and a second end surface B4 that are perpendicular to the height direction T and opposite to the length direction L, and a first side surface B5 and a second side surface B6 that are perpendicular to the length direction L and the height direction T and opposite to the width direction W. In the example shown in Figure 1, the first main surface B1 of base body B corresponds to the mounting surface (bottom surface) of base body B. The second main surface B2 may also be the mounting surface of base body B.

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

[0021] Figure 2 is an exploded perspective view illustrating the laminated structure of the laminated inductor 1A of this disclosure. In this embodiment, as shown in Figure 2, it is constructed 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 each layer of the layered structure of base body B may disappear. Furthermore, each layered group may be composed of multiple layers of the same pattern.

[0022] The multilayer inductor 1A may be constructed by stacking multilayer groups G1 to G7, manufacturing a base body B by firing, then further stacking a multilayer group G8 which includes an outer resin layer SR having openings EH (e.g., EH1, EH2) for the external electrodes E (e.g., E1, E2), and forming the external electrodes E (e.g., E1, E2) by a method described later.

[0023] The laminated group G1 has a magnetic layer ML and constitutes the second main surface B2 of the base body B.

[0024] The laminated group G2 is provided with a magnetic layer ML and a coil conductor CM. The coil conductor CM of laminated group G2 constitutes approximately one turn of coil C. More specifically, the coil conductor CM is arranged along the approximate outer edge of the magnetic layer ML.

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

[0026] The laminated group G4 includes a magnetic layer ML, a second through-hole TH2 that electrically connects the second through-hole TH2 of the laminated group G3 to the second external electrode E2, and a coil conductor CM. The coil conductor CM of the laminated group G4 constitutes approximately one turn of coil C. More specifically, the coil conductor CM is arranged along the outer edge 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. More specifically regarding the avoidance portion Z, the avoidance portion Z provided in the laminated group G4 may be located inward compared to the coil conductor CM arranged along the outer edge of the laminated group G2, thereby avoiding the second through-hole TH2.

[0027] The laminated group G5 is provided with a magnetic layer ML, a second through-hole TH2 that electrically connects the second through-hole TH2 of the laminated group G4 to the second external electrode E2, and via-hole conductors V for connecting adjacent coil conductors CM in the laminated direction. The via-hole conductors V are positioned adjacent to the second through-hole TH2 so as to be electrically connectable to the ends of the coil conductors CM of the laminated group G4.

[0028] The laminated group G6 includes a magnetic layer ML, a second through-hole TH2 that electrically connects the second through-hole TH2 of the laminated group G5 to the second external electrode E2, and a coil conductor CM. The coil conductor CM of the laminated group G6 constitutes approximately 0.5 turns of the coil C. More specifically, the coil conductor CM is arranged along the outer edge 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. More specifically regarding the avoidance portion Z, the avoidance portion Z provided in the laminated group G6 may be provided further inward compared to the coil conductor CM arranged along the outer edge of the laminated group G2, thereby avoiding the second through-hole TH2.

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

[0030] A laminated group G8 is further provided on top of the fired body B. Laminated group G8 is provided with an outer resin layer SR having a first opening EH1 for a first external electrode E1 electrically connected to a first through-hole TH1 of laminated group G7, and a second opening EH2 for a second external electrode E2 electrically connected to a second through-hole TH2 of laminated group G7, and external electrodes E positioned within the first opening EH1 and the second opening EH2. The first opening EH1 and the second opening EH2 are each located near the corners of the outer resin layer SR.

[0031] As described above, if the base body B has a laminated structure comprising laminated groups G1 to G7, the design freedom of the laminated inductor 1A is increased. For example, since the laminated inductor 1A is manufactured with a first external electrode E1 and a second external electrode E2 on the bottom surface (first main surface B1) of the base body B, it becomes easier to pull out the coil C from the bottom surface side. The laminated structure comprising the above laminated groups G1 to G7 may be formed by stacking multiple layers by sequentially printing (e.g., screen printing) the material constituting the magnetic layer ML, the material constituting the coil conductor CM, and the material constituting the through-holes and via-hole conductors from the second main surface B2 side or the first main surface B1 side of the base body B. In this case, each of the laminated groups G1 to G7 may be repeatedly printed until the magnetic layer ML, coil conductor CM, through-holes and via-hole conductors reach the desired thickness.

[0032] Furthermore, after the manufacturing of the base body B, the laminated group G8 forms an outer resin layer SR having a first opening EH1 and a second opening EH2 on the first main surface B1 side. The outer resin layer SR may be formed by photolithography, which involves printing (e.g., screen printing) a photosensitive resin material, followed by exposure and development. External electrodes E1 and E2 are formed at the first opening EH1 and the second opening EH2 by Cu plating or the like.

[0033] (magnetic material) The magnetic material M (see Figures 1 and 2), constructed by laminating magnetic layers ML, contains iron powder MP composed of magnetic material. In this specification, "iron powder" is not strictly limited to being in powder form, but also includes materials where powdery particles are bonded together by a 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. Examples of Fe alloys include Fe-Si alloys, Fe-Si-Cr alloys, Fe-Si-Al alloys, Fe-Si-BP-Cu-C alloys, and / or Fe-Si-B-Nb-Cu alloys. Furthermore, the iron powder MP may contain impurities such as Cr, Mn, Cu, Ni, P, S, and / or Co, which are unintended during manufacturing. Also, the iron powder MP may be contained in the magnetic paste, as will be detailed in the description of the manufacturing method. Therefore, the iron powder may contain elements that oxidize more easily than Fe added during the production of the magnetic paste (e.g., Cr, Al, Li, Zn).

[0034] The surface of the iron powder MP described above may be covered with an insulating film (not shown). Covering the surface of the iron powder MP with an insulating film can improve the insulation between the iron powder MPs. Methods for forming the insulating film on the surface of the iron powder MP include the sol-gel method and the mechanochemical method. The material constituting the insulating film may be an oxide of P and / or Si. Alternatively, the insulating film may be an oxide film formed by oxidizing the surface of the iron powder MP. The thickness of the insulating film is preferably 1 nm to 50 nm, more preferably 1 nm to 30 nm, and even more preferably 1 nm to 20 nm. For example, the thickness of the insulating film covering the surface of the iron powder MP can be measured from the obtained SEM image of a cross-section obtained by polishing the center of an inductor sample.

[0035] The average particle size of the iron powder MP in the magnetic material M is preferably 1 μm to 30 μm, more preferably 1 μm to 20 μm, and even more preferably 1 μm to 10 μm. The average particle size of the iron powder MP in the magnetic material M can be measured by the procedure described below. A sample of the multilayer 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 base body and perpendicular to the mounting surface B1 of the base body) is obtained. Multiple areas (for example, 5 areas) of the obtained cross-section (for example, 130 μm × 100 μm) are photographed with an SEM, and the obtained SEM images are analyzed using image analysis software (for example, image analysis software WinROOF2021 (manufactured by Mitani Corporation)) to determine the equivalent circle diameter of the iron powder MP. The average value of the obtained equivalent circle diameters is taken as the average particle size of the metallic magnetic particles. Note that if the shape of the through-hole is polygonal, the cut should be made perpendicular to the sides, and if it is circular or elliptical, the cut should be made perpendicular to the long axis.

[0036] Even when the iron powder MP contained in the magnetic layer ML is bonded by firing, voids are created between the iron powder MP, and the presence of these voids reduces the strength of the base material. In this specification, "voids" refers to the space between adjacent powder particles. In other words, it refers to the space determined by the positional relationship between adjacent powder particles. As mentioned above, voids can be observed from the SEM image of the sample cross-section obtained by cutting a sample of the multilayer inductor 1A. As a specific method for identifying voids, an SEM image is obtained by setting the observation area of ​​the sample cross-section to 130 μm × 100 μm, and when the voids and non-void areas within the magnetic material M are analyzed using image analysis software, the area ratio of voids to the entire observation area may be between 10% and 40%.

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

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

[0039] In this embodiment, the surface roughness of the bottom surface B1 (first main surface B1) of the magnetic material in the base 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 material in the base body B. This surface roughness of the bottom surface B1 of the magnetic material in the base body B is due to the grinding process described later. This makes it possible to increase the adhesion strength between the bottom surface B1 of the magnetic material in the base body B and the outer resin layer SR.

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

[0041] In this specification, the surface roughness of element B (especially magnetic material M) is a surface roughness based on the so-called arithmetic mean roughness Ra, and the average value of measurements taken at any 20 points in the central part of the bottom surface of element B is used.

[0042] (coil) The coil includes multiple coil conductors CM in the stacking direction (e.g., the height direction T). In this embodiment, the coil may have approximately 2.5 turns due to the stacking groups G2, G4, and G6, as shown in Figure 2, for example.

[0043] The thickness of the coil conductor CM in each laminated group may be the same. The coil conductor CM may be a metallic conductor such as Ag, Cu, and / or Pd, as an example of its material. The coil conductor CM may be formed, for example, by printing a conductive paste onto the magnetic layer ML described above.

[0044] (Through-hole and via-hole conductors) Coil C may have through-holes TH and via-hole conductors V. Through-holes 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 located inside body B.

[0045] The first through-hole TH1 may connect the end of the coil conductor CM closest to the bottom surface (first main surface B1) of the base body B with the first external electrode E1. The first through-hole TH1 may extend along the stacking direction (e.g., the height direction T). The first through-hole TH1 may have a stacked structure.

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

[0047] Thus, the through-hole TH is positioned inside the base body B (especially the magnetic material M), and electrically connects the coil C to the external electrode E.

[0048] The via-hole conductor V may electrically connect coil conductors CM provided in adjacent stacking groups 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 also have a stacked structure.

[0049] As an example of the material for the through-hole TH and via-hole conductor V, it may be a metal conductor such as Ag, Cu, and / or Pd (preferably Ag). Furthermore, the material for the through-hole and via-hole conductor may be the same as that used for the coil conductor CM, or a different material may be used. The through-hole and via-hole conductor may be formed, for example, by forming through-holes in the magnetic layer ML described above and printing conductive paste into the through-holes. The through-hole and via-hole conductor may also be a sintered body.

[0050] The surface roughness of the through-hole end face th1 is rougher than the surface roughness of the outer resin layer formation region on the bottom surface B1 of the magnetic material of the base body B. This surface roughness of the through-hole end face th1 is due to the second etching process described later. This further enhances the connection strength between the external electrode and the lead conductor.

[0051] The surface roughness of the through-hole end face 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 outer resin layer formation region on the bottom surface B1 of the magnetic material of base body B may be the same as the surface roughness of the bottom surface B1 of the magnetic material of base body B as described above. The difference between the surface roughness of the through-hole end face th1 and the surface roughness of the outer resin layer formation region on the bottom surface B1 of the magnetic material of the base body B is usually 0.3 μm or more and 0.9 μm or less.

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

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

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

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

[0056] External electrodes E (E1 and E2) are typically located on and electrically connected to through-holes TH (particularly their end faces).

[0057] Figure 3 is an enlarged cross-sectional view of the vicinity of the external electrode in a multilayer inductor of the first embodiment, and is an enlarged cross-sectional view of the vicinity of the external electrode when the multilayer inductor of Figure 1 is placed upside down. As shown in Figure 3, in cross-sectional view, the external electrode E has an upper end 11a and a lower end 11b in the stacking direction T, and each of the upper end 11a and lower end 11b has flange-shaped projections 13a, 13b in a direction perpendicular to the stacking direction T. The upper end 11a is the end that is more distal to the through-hole TH in the stacking direction T. The lower end 11b is the end that is more proximal to the through-hole TH in the stacking direction T. In more detail, the upper end 11a and lower end 11b of the external electrode E are the upper end and lower end, respectively, when the element B is positioned with the bottom surface B1 of the magnetic material of the element B facing upwards and the surface B2 opposite to the bottom surface B1 of the magnetic material of the element B facing downwards.

[0058] The widths of the upper end 11a and lower end 11b of the external electrode E (r1 and r2, respectively) are usually larger than the opening width r3 of the outer resin layer SR in a cross-sectional view (see Figure 3). In particular, the fact that the width r2 of the lower end 11b of the external electrode E is larger than the opening width r3 of the outer resin layer SR allows the anchoring effect of the projection 13b of the lower end 11b to be exerted even more effectively. The opening width r3 of the outer resin layer SR is the minimum width in the direction perpendicular to the lamination direction T when the external electrode E is viewed through in a cross-sectional view.

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

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

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

[0062] The protruding lengths of the protrusions 13a and 13b are the protruding lengths relative to the minimum width of the external electrode E. More specifically, as shown in Figure 4, for example, these are the protruding lengths p1 and p2 respectively in the direction perpendicular to the lamination direction T, relative to the said minimum width. The minimum width of the external electrode E is the dimension corresponding to the opening width r3 of the outer resin layer SR, which will be described later.

[0063] The thickness of the outer resin layer SR is not particularly limited and may be, for example, 0.5 μm or more and 20 μm or less, and especially 4 μm or more and 10 μm or less. The thickness of the outer resin layer SR is determined using the average value of measurements taken 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 process described later, and may be, for example, epoxy resin, acrylic resin, etc.

[0065] The widths of the upper end 11a and lower end 11b of the external electrode E (r1 and r2, respectively) are usually smaller than the width R of the through-hole TH in a cross-sectional view (see Figure 3). This suppresses the increase in DC resistance and makes it possible to reduce the planar area of ​​the external electrode E as seen from the mounting surface B1 side of the base body B. For this reason, this disclosure is particularly effective for multilayer inductors of multiphase DC-DC converters. Multiphase refers to integrating multiple coils into a single base body, as in the second and third embodiments described later. The through-hole TH, especially in the case of a laminate, has irregularities on its side surface as shown in Figure 3. Therefore, the width R of the through-hole TH is the average value of the minimum and maximum widths in the direction perpendicular to the stacking direction T in a cross-sectional view.

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

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

[0068] In this embodiment, the external electrode E is embedded in the outer resin layer SR between the projections at its upper end 11a and lower end 11b. "Embedded" means installed while being embedded. More specifically in this embodiment, the entire external electrode E is not embedded in the outer resin layer; only the portion between the projection 13a at the upper end 11a and the projection 13b at the lower end 11b is embedded in the outer 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 outer resin layer SR. The outer resin layer SR is arranged (or filled) across the projections (13a and 13b, respectively) at the upper end 11a and lower end 11b of the external electrode E in the lamination direction T.

[0069] The external electrode E has protrusions 13a and 13b at its upper end 11a and lower end 11b, respectively, and is embedded between them by the outer resin layer SR, thereby improving the connection strength of the external electrode E from the base body B (especially the through-hole TH). In a plan view of the external electrode E from the stacking direction T, for example, only the upper end 11a is visible, and the lower end 11b is not. In a plan view of the external electrode E from the stacking direction T, the upper end 11a exists as an "island" within the outer resin layer SR, which is like a "sea".

[0070] From another perspective of this embodiment, in a cross-sectional view, the external electrode E sandwiches the outer resin layer SR between the projection 13a at the upper end 11a and the projection 13b at the lower end 11b. In particular, the projection 13b at the lower end 11b not only provides an anchoring effect, but together with the projection 13a at the upper end 11a, it sandwiches the outer resin layer SR, thereby significantly improving the connection strength of the external electrode E from the base body B (especially the through-hole TH).

[0071] From the viewpoint of further improving the connection strength between the external electrodes and the lead conductors, it is preferable that the thickness of the outer resin layer SR between the protrusions is greater than the thickness of the outer resin layer SR outside the protrusions. This thickness gradient of the outer resin layer is due to the first and second etching processes (particularly the first etching process) described later.

[0072] The thickness of the outer resin layer SR between the protrusions is, as shown in Figure 4, the thickness a1 on the reference line P in the lamination direction T that passes through the apex of the protrusion 13a at the upper end 11a and the protrusion 13b at the lower end 11b, whichever has the longer protrusion length. This 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 outer resin layer SR outside the protrusions is the thickness of the outer resin layer SR in the region where no external electrodes are formed on the bottom surface B1 of the base body B, and the average value of the thickness of any 20 points on the outer resin layer SR on the magnetic material M is used. The thickness of the outer 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 Figure 3, the external electrode E has protrusions 13a and 13b on both the left and right sides at the upper end 11a and lower end 11b, respectively. However, it is not necessary for the external electrode E to have protrusions on both the left and right sides; it is sufficient for the lower end to have protrusions on at least one side (preferably both sides). From the viewpoint of further improving the connection strength between the external electrode and the lead conductor, it is preferable for the external electrode to have protrusions on both the left and right sides at both the upper and lower ends. The protrusion at the lower end of the external electrode is a result of performing the external electrode formation process after the second etching process, which will be described later.

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

[0076] <Modification 1 of the first embodiment of the multilayer inductor> In the multilayer inductor according to the first embodiment, the external electrode E has projections 13a and 13b at its upper end 11a and lower end 11b, which are continuous around its entire circumference in a plan view from the stacking direction. However, the external electrode E does not necessarily have to have projections continuously around its entire circumference; it may have projections discontinuously or intermittently around its entire circumference in a plan view from the stacking direction. For example, the external electrode E may have projections in any one cross-sectional view.

[0077] <Modification 2 of the first embodiment of the multilayer inductor> In the multilayer inductor according to the first embodiment, the external electrodes E are formed in an island shape (e.g., spot shape) when viewed from the stacking direction, but may be formed continuously in the depth direction, for example, as shown in Figure 3. In other words, the external electrodes E may extend in a wall shape in the W direction of the base body. The upper end 11a and lower end 11b may have projections 13a and 13b continuously in the extension direction, or they may be discontinuous or intermittently present.

[0078] <Second embodiment of a multilayer inductor> Next, the laminated inductor 1B of the second embodiment will be described with reference to Figure 5. The laminated inductor 1B of the second embodiment differs from the laminated inductor 1A of the first embodiment described above in its coil configuration. Specifically, the number of coils, the number of coil turns, and the position of the external electrodes are different. The following description will focus on the differences from the laminated inductor described in the above embodiment. Note that 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 planar area of ​​the external electrodes E (E1 to E4) as seen from the mounting surface B1 side of the base body B can be made smaller. Accordingly, the laminated inductor 1B of the second embodiment can make more effective use of the bottom surface (mounting surface) B1 of the base body B based on the reduction of 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 and the through-holes and the outer resin layer, and the relationship between the through-holes and the outer resin layer.

[0079] The coils of the stacked inductor 1B in this embodiment may be arranged in overlapping pairs when viewed from the stacking direction. In other words, a first coil C1 and a second coil C2 may be provided inside the base 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 the base body B may contain only two coils, including the first coil C1 and the second coil C2, or it may contain three or more coils, including the first coil C1 and the second coil C2.

[0080] -Coil 1- The first coil C1 includes a plurality of first coil conductors CM1 that constitute the first coil C1 in the stacking direction (e.g., the height direction T). Adjacent first coil conductors CM1 are connected via via hole conductors V. The first coil C1 may have 1.75 turns 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 2 or more by stacking the first coil conductors CM1 in the stacking direction.

[0081] -Coil 2- The second coil C2 is positioned above the first coil C1 in the height direction T and includes multiple second coil conductors CM2 in the stacking direction (e.g., in the height direction T). Adjacent second coil conductors CM2 are connected via via hole conductors V. The second coil C2 may have 1.75 turns 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 example, and may be 2 or more by stacking the first coil conductor CM1 in the stacking direction. The number of stacks of the second coil conductor CM2 may be the same as or different from the number of stacks of the first coil conductor 51.

[0082] -Through-hole 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 located inside the base 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 base body B.

[0083] The first through-hole TH1 connects the end of the first coil conductor CM1 closest to the bottom surface of the base body B, which is one of the ends of the first coil C1, to the first external electrode E1. The first through-hole TH1 may extend along the stacking direction (e.g., the height direction T). The first through-hole TH1 may have a stacked structure.

[0084] The second through-hole TH2 connects the other end of the first coil C1 to the second external electrode E2. The second through-hole TH2 may extend along the stacking direction (e.g., the height direction T). The second through-hole TH2 may have a stacked structure.

[0085] The third through-hole TH3 connects the end of the second coil conductor CM2 closest to the bottom surface of the base body B, which is one of the ends of the second coil C2, 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 to the fourth external electrode E4. The fourth through-hole TH4 may extend along the stacking direction (e.g., the height direction T). The fourth through-hole TH4 may have a stacked structure.

[0087] As shown in Figure 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 base 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 base body B and are electrically connected to the second coil C2. In the multilayer inductor 1B, the first main surface B1 of the base body B can be used as the mounting surface.

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

[0089] <Modified example of the second embodiment of the multilayer inductor> In the stacked inductor according to the second embodiment (Figure 5), the external electrodes E are all formed in an island shape (e.g., spot shape) when viewed in a plan view from the stacking direction. However, an electrode connection structure may be provided in which the island-shaped external electrodes are used as abutments and a girder portion is connected on top of them. Specifically, for example, if the external electrodes E2 and E3 in Figure 5 have the same polarity, an electrode connection structure may be provided that has these external electrodes E2 and E3 as abutments and further has a girder portion that bridges the external electrodes E2 and E3. In such an electrode connection structure, the connection strength between the external electrodes as abutments and the through-holes is more sufficient, so the electrode connection structure also has more sufficient connection strength. The girder portion of the electrode connection structure may be made of the same material as the external electrodes E.

[0090] <Multilayer inductor array> Next, the multilayer inductor array of this disclosure will be described with reference to Figure 6. The multilayer inductor array 1C of this disclosure has two or more coils arranged to overlap in a plan view from the stacking direction, and the coils are arranged in parallel in a direction intersecting the stacking direction (for example, a direction perpendicular to the stacking direction) to constitute a coil array. Specifically, in addition to the first coil C1 and the second coil C2, it 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. Of the ends of the third coil C3, the end of the third coil conductor layer closest to the bottom surface may be connected to the fifth external electrode E5 by the fifth through-hole TH5. The other end of the third coil conductor layer may be connected to the sixth external electrode E6 by the sixth through-hole TH6.

[0092] The fourth coil C4 may be electrically connected to the seventh external electrode (not shown) and the eighth external electrode (not shown). Of the ends of the fourth coil C4, the 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. In addition, 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. Of the ends 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 the ninth through-hole TH9. The other end of the fifth coil conductor layer may be connected to the tenth external electrode E10 by the 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 the eleventh through-hole TH11. The other end of the sixth coil conductor layer may be connected to the twelfth external electrode (not shown) by the twelfth through-hole TH12.

[0095] Even in the multilayer inductor array 1C of this 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 this 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 base body B can be made smaller. Accordingly, the multilayer inductor array 1C of this disclosure can make more effective use of the bottom surface (mounting surface) B1 of the base body B based on the reduction of the area of ​​the external electrodes E.

[0096] <Manufacturing method for multilayer inductors> Next, the method for manufacturing a multilayer inductor according to the present disclosure will be described with reference to Figure 7A. Figure 7A is a flowchart showing the method for manufacturing a multilayer inductor according to the present disclosure. The method for manufacturing a multilayer inductor according to the present disclosure may include a substrate precursor preparation step, a resin impregnation preparation step, a resin impregnation step, a grinding step, a first etching step, an outer resin layer formation step, a second etching step, and an external electrode formation step. This is a cross-sectional view showing a more characteristic resin impregnation step, grinding step, first etching step, outer resin layer formation step, second etching step, and external electrode formation step in the method for manufacturing a multilayer inductor according to the present disclosure. The steps will be described in detail below.

[0097] [Element body precursor preparation process] In this process, a coil is prepared in which a coil conductor is wound inside a magnetic material having a laminated magnetic layer containing iron powder, and a precursor body is prepared which is electrically connected to the coil conductor and has a through-hole exposed from the bottom surface of the magnetic material. For more details, first, prepare the magnetic paste that constitutes the magnetic layer ML of the laminated group as explained in Figure 2, the conductive paste that constitutes the coil conductor CM, and the non-magnetic paste that constitutes the non-magnetic layer between the coil conductors CM.

[0098] As an example of a method for producing magnetic paste, iron powder such as Fe-Si alloy or Fe-Si-Cr alloy with a D50 (cumulative 50% particle size by volume) of 2 μm or more and 20 μm or less is prepared. A magnetic paste is produced by kneading this iron powder with a binder such as cellulose or polyvinyl butyral (PVB) and a solvent such as a mixture of terpineol and butyl diglycol acetate (BCA).

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

[0100] An insulating film may be provided on the surface of the iron powder. The insulating film is preferably a film containing a metal oxide, and more preferably a silicon oxide. The sol-gel method is preferred as a method for forming the insulating film. As an example of forming an insulating film by the sol-gel method, a mixture is prepared by mixing a sol-gel coating agent containing a Si alkoxide with an organic chain-containing silane coupling agent. After this mixture is applied to the surface of the metal magnetic powder, dehydration bonding is induced by heat treatment. Subsequently, the insulating film can be formed by drying at a predetermined temperature.

[0101] As an example of a method for preparing a non-magnetic paste, Fe2O3, ZnO, CuO, and any necessary additives are weighed to obtain a predetermined composition. The weighed materials are placed in a ball mill together with pure water, a dispersant, and PSZ media, and mixed and pulverized to obtain a slurry. After drying the obtained slurry, it is 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 (such as a ketone-based solvent), resin (such as polyvinyl acetal), and plasticizer (such as an alkyd-based plasticizer) are added to the non-magnetic material (calcined powder), mixed in a planetary mixer, and then dispersed in 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), with ZnO as the main component for the remainder. More preferably, the non-magnetic paste contains Mn, Bi, Co, Si, Sn, etc., as additives to the above main components, as needed. The non-magnetic paste may contain unavoidable impurities.

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

[0104] Using the magnetic paste, non-magnetic paste, and conductive paste described above, laminate groups G1 to G7 shown in Figure 2 are prepared by screen printing or the like. Then, the unfired raw material precursors are subjected to pressurization, such as warm isostatic pressing (WIP), to form laminates. After pressurization, the laminates are placed in a firing furnace, degreased, and then fired in the atmosphere. 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. The raw material is prepared by this firing process.

[0105] [Preparation process for resin impregnation] (Optional additional process) The resin impregnation preparation step is an optional step performed before the resin impregnation step described later. Specifically, the resin impregnation preparation step is a step to reduce the amount of gas or moisture in the substrate, or to lower the viscosity of the resin.

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

[0107] [Resin impregnation process] (Optional additional process) In this step, the substrate precursor after firing is impregnated with resin. This step may be performed as an optional additional step. When this step is performed, the resin may contain, for example, epoxy resin, silicone resin, or phenolic resin. By impregnating the substrate with resin, resin is provided in at least a portion of the voids in the magnetic body and coil conductor. This reduces the voids and increases the strength of the substrate. It also reduces the penetration of plating solution or moisture into the substrate. In this step, impregnated resin residue RE remains on the bottom surface B1 (first main surface B1) side of the magnetic material in the substrate precursor (Figure 7A(1)).

[0108] [Grinding process] In this process, the resin-impregnated precursor is ground to remove the resin residue RE on the bottom surface B1 side of the magnetic material, exposing at least the end face of the through-hole TH to obtain the base material (Figure 7A(2)). Grinding can impart the above-mentioned surface roughness to the bottom surface B1 of the magnetic material and adjust the thickness of the base material to a predetermined thickness. This process may also be performed on a base material precursor that is not impregnated with resin.

[0109] [First Etching Process] (Optional additional process) This step is an optional additional step performed before the exterior resin layer formation step described later. Specifically, at least the through-hole end faces are etched on the bottom surface of the base magnetic material obtained in the grinding step to obtain new through-hole end faces th0 (Figure 7A(3)). As described above, this step provides a thickness gradient on the bottom surface B1 side of the magnetic material, where the thickness of the exterior resin layer SR between the protrusions is greater 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 etching solution used is one that can dissolve the through-hole and the magnetic material M. For example, potassium nitrate-ammonia water, sodium cyanide, or a phosphate hydrochloride system may be used as such an etching solution. Note that if the magnetic material M is impregnated with resin in this step, the magnetic material will hardly be etched.

[0110] [Exterior resin layer formation process] In this process, an outer resin layer SR is formed on the bottom surface of the magnetic material, in areas other than the through-hole end faces (Figure 7A(4)). The outer resin layer SR is a protective layer for the second etching process described later, and may be, for example, a solder resist layer. The method for forming the outer resin layer SR is not particularly limited as long as the outer resin layer SR can be selectively formed in areas other than the through-hole end faces, and for example, a screen printing method may be employed. In the screen printing method, the resin solution that constitutes the outer resin layer SR may be used as an ink.

[0111] In this process, the outer resin layer SR is formed such that an opening exists at the bottom surface of the magnetic material of the base body, in a region that substantially corresponds to the end face of the through-hole. More specifically, the area of ​​the opening in the outer resin layer SR is smaller than the area of ​​the end face of the through-hole TH. Because the area of ​​the opening in the outer resin layer SR is smaller than the area of ​​the end face of the through-hole TH, an overlapping portion is obtained between the outer resin layer SR and the through-hole TH (especially its end face) in a plan view. As a result, in the second etching process described later, a gap is formed between the end face of the through-hole and the outer resin layer, and in the external electrode formation process described later, the projection 13b at the lower end of the external electrode is formed.

[0112] Figure 7B is a cross-sectional view showing in detail the outer resin layer formation step in the manufacturing method of the laminated inductor of the present disclosure. The opening of the outer resin layer is the opening when the external electrodes are viewed through in a plan view from the lamination direction T, and is shown in Figure 7B as the region between the two reference lines m4. The reference lines m4 are reference lines parallel to the lamination direction T that define the opening of the outer resin layer SR.

[0113] The end face of a through-hole TH is, for example, shown in Figure 7B as the region between the two reference lines m3. Reference line m3 is the midpoint between reference line m1, which is parallel to the stacking direction T and defines the maximum diameter of the through-hole TH in a cross-sectional view, and reference line m2, which is also parallel to the stacking direction T and defines the minimum diameter of the through-hole TH. The diameter D of the through-hole TH is the maximum diameter defined by reference line m1 and can be measured from an image obtained by X-ray transmission of the multilayer inductor from the bottom side or from a direction approximately perpendicular to the stacking direction T.

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

[0115] [Second Etching Process] In this process, the through-hole end face is etched on the bottom surface of the magnetic material of the base body on which the outer resin layer is formed, to obtain a new through-hole end face th1 (Figure 7A(5)). After this process, the projection 13b at the lower end of the external electrode is formed by the external electrode formation process described later. Specifically, in this process, by etching the through-hole end face, the surface of the through-hole end face is lowered, and the through-hole end face th1 is obtained. As a result, a gap corresponding to the projection 13b is formed between the through-hole end face and the outer resin layer, and the projection 13b at the lower end of the external electrode is formed by the external electrode formation process described later.

[0116] In this process, the etching solution used is one that dissolves the through-holes without dissolving the outer resin layer SR. As such an etching solution, for example, a solution containing potassium cyanide, phosphoric acid, nitric acid, acetic acid, or thiourea may be used. 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 the process of forming external electrodes E that are electrically connected to the coil conductor (Figure 7A(6)). External electrodes are formed by electroless plating at the openings in the outer resin layer SR (positions where through-holes are exposed on the mounting surface (first main surface B1) of the base body B). The plating material may be Cu plating. Other materials include, but are not limited to, Ni-Sn, Ni-Au, Ni-Cu and / or Cu-Ni-Au.

[0118] In the second etching process, a gap corresponding to the projection 13b is formed between the through-hole end face and the outer resin layer. Therefore, in the external electrode formation process, the projection 13b is formed at the lower end of the external electrode simply by forming the external electrode.

[0119] In the external electrode formation process, it is important to form the external electrode higher than the surface of the outer resin layer SR. This results in the formation of a projection 13a at the upper end of the external electrode.

[0120] When multiple laminated inductors are obtained in a series through the outer resin layer formation process, the laminated inductor of this embodiment can be manufactured by performing element dicing (dicing process) after the formation of the external electrodes.

[0121] The above-described steps—preparation of the substrate precursor, preparation of the resin impregnation, resin impregnation, grinding, first etching, formation of the outer resin layer, second etching, and formation of the external electrode—are usually carried out sequentially in this order. The resin impregnation preparation and first etching steps may be omitted or performed independently. For example, if the first etching step is omitted, the outer resin layer formation, second etching, and external electrode formation steps may be carried out sequentially on the substrate obtained in the grinding step.

[0122] The technical scope of this disclosure is not to be interpreted solely by the embodiments described above, but is defined based on the claims. Furthermore, the technical scope of this disclosure includes all modifications within the meaning and scope of the claims.

[0123] The multilayer inductor and its manufacturing method described herein encompass the following embodiments. <1> A magnetic material having a laminated magnetic layer containing iron powder, a coil with a coil conductor wound around it, and a substrate electrically connected to the coil conductor and having a through-hole extending in the direction of the bottom surface of the magnetic material, An external electrode positioned on the through-hole and electrically connected to the through-hole, The substrate comprises an outer resin layer disposed on the bottom surface of the magnetic material, The external electrode has a projection that protrudes in a direction perpendicular to the stacking direction at its upper end distal to the through-hole and its lower end proximal to the through-hole in the stacking direction of the magnetic layer. The aforementioned outer resin layer is arranged between the protrusions at its upper and lower ends, thereby forming a laminated inductor. <2> The widths of the upper and lower ends of the external electrode are greater than the opening width of the outer resin layer in the cross-sectional view. <1> The multilayer inductor described above. <3> The widths of the upper and lower ends of the external electrode are smaller than the diameter of the through-hole in the cross-sectional view. <1> or <2> The multilayer inductor described above. <4> The thickness of the outer resin layer on the through-hole is greater than the thickness of the outer resin layer outside the through-hole. <1> ~ <3> A multilayer inductor as described in any of the following. <5> The external electrode is a plated electrode formed directly on the through-hole. <1> ~ <4> A multilayer inductor as described in any of the following. <6> The external electrode is a copper-plated electrode. The aforementioned through-hole is made of a silver sintered body. <1> ~ <5> A multilayer inductor as described in any of the following. <7> The surface roughness of the bottom surface of the magnetic material in the aforementioned body is rougher than the surface roughness of the surface opposite to the bottom surface of the magnetic material in the aforementioned body. <1> ~ <6> A multilayer inductor as described in any of the following. <8> The surface roughness of the through-hole end face is rougher than the surface roughness of the outer resin layer formation region on the bottom surface of the magnetic material of the base body. <1> ~ <7> A multilayer inductor as described in any of the following. <9> The aforementioned body further comprises a resin disposed in the void within the magnetic body. <1> ~ <8> A multilayer inductor as described in any of the following. <10> The aforementioned coils are arranged in such a way that two or more are overlapping when viewed in a plan view from the stacking direction. <1> ~ <9> A multilayer inductor as described in any of the following. <11> The coils are arranged in a plan view from the stacking direction, with two or more overlapping, and are arranged in parallel in a direction intersecting the stacking direction to form a coil array. <1> ~ <10> A multilayer inductor as described in any of the following. <12> A precursor preparation step involves preparing a precursor having a coil with a coil conductor wound inside a magnetic material having a laminated magnetic layer containing iron powder, and a through-hole electrically connected to the coil conductor and exposed from the bottom surface of the magnetic material. A grinding step to remove impregnation resin residue from the bottom side of the magnetic material in the substrate precursor by grinding, exposing the end face of the through hole to obtain the substrate, An outer resin layer forming step is performed on the bottom surface of the magnetic material of the base body, such that the outer resin layer overlaps with the peripheral edge of the through-hole end face when viewed in plan from the lamination direction, The etching process involves etching the through-hole end face on the outer resin layer forming surface of the base body, A method for manufacturing a laminated inductor, comprising: an external electrode forming step of forming an external electrode on the through-hole end face that is electrically connected to the coil conductor. <13> A resin impregnation step of impregnating the aforementioned precursor with resin is further provided between the precursor preparation step and the grinding step. <12> A method for manufacturing a multilayer inductor as described above. <14> The claim further includes an etching step between the grinding step and the exterior resin layer formation step, in which the through-hole end face is etched on the bottom surface of the magnetic material of the base body. <12> or <13> A method for manufacturing a multilayer inductor as described above. <15> <1> ~ <11> A multilayer inductor described in any of the above is manufactured. <12> ~ <14> A method for manufacturing a multilayer inductor as described in any of the following. [Industrial applicability]

[0124] This disclosure can be used in a multilayer inductor that improves the connection strength between the external electrodes and the through-holes. [Explanation of Symbols]

[0125] 1A, 1B multilayer inductors 1C Multilayer Inductor Array B Base Body 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. A magnetic material having a laminated magnetic layer containing iron powder, a coil with a coil conductor wound around it, and a substrate electrically connected to the coil conductor and having a through-hole extending in the direction of the bottom surface of the magnetic material, An external electrode positioned on the through-hole and electrically connected to the through-hole, The substrate comprises an outer resin layer disposed on the bottom surface of the magnetic material, The external electrode has a projection that protrudes in a direction perpendicular to the stacking direction at its upper end distal to the through-hole and its lower end proximal to the through-hole in the stacking direction of the magnetic layer. The external electrode is arranged across the projections at the upper and lower ends of the stacked inductor.

2. The laminated inductor according to claim 1, wherein the widths of the upper and lower ends of the external electrode are greater than the opening width of the outer resin layer in a cross-sectional view.

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

4. The laminated inductor according to claim 1, wherein the thickness of the outer resin layer on the through-hole is greater than the thickness of the outer resin layer outside the through-hole.

5. The multilayer inductor according to claim 1, wherein the external electrode is a plated electrode directly formed on the through-hole.

6. The external electrode is a copper-plated electrode. The multilayer inductor according to claim 1, wherein the through-hole is made of a silver sintered body.

7. The laminated inductor according to claim 1, wherein the surface roughness of the bottom surface of the magnetic material in the substrate is rougher than the surface roughness of the surface opposite to the bottom surface of the magnetic material in the substrate.

8. The laminated inductor according to claim 1, wherein the surface roughness of the through-hole end face is rougher than the surface roughness of the outer resin layer formation region on the bottom surface of the magnetic material of the base body.

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

10. The laminated inductor according to claim 1, wherein two or more coils are arranged to overlap in a plan view from the lamination direction.

11. The laminated inductor according to claim 1, wherein two or more coils are arranged to overlap 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. A precursor preparation step involves preparing a precursor having a coil with a coil conductor wound inside a magnetic material having a laminated magnetic layer containing iron powder, and a through-hole electrically connected to the coil conductor and exposed from the bottom surface of the magnetic material. A grinding step to remove impregnation resin residue from the bottom side of the magnetic material in the substrate precursor by grinding, exposing the end face of the through hole to obtain the substrate, An outer resin layer forming step is performed on the bottom surface of the magnetic material of the base body, such that the outer resin layer overlaps with the peripheral edge of the through-hole end face when viewed in plan from the lamination direction, The etching process involves etching the through-hole end face on the outer resin layer forming surface of the base body, A method for manufacturing a laminated inductor, comprising: an external electrode forming step of forming an external electrode on the through-hole end face that is electrically connected to the coil conductor.

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

14. A method for manufacturing a laminated inductor according to claim 12, further comprising an etching step between the grinding step and the outer resin layer formation step, in which the through-hole end face is etched on the bottom surface of the magnetic material of the base body.

15. A method for manufacturing a multilayer inductor according to claim 12, wherein a multilayer inductor according to any one of claims 1 to 11 is manufactured.

Images