Inductor and method for manufacturing inductor

Abstract

Provided are an inductor capable of appropriately generating a magnetic flux by a via conductor electrically connecting a coil and an external electrode, and a method for manufacturing the inductor. An inductor according to the present disclosure comprises: an element body 10 in which a plurality of magnetic layers ML are laminated; a coil C that is disposed in the element body 10 and is configured by laminating coil conductors CD; and via conductors VDa, VDb that electrically connect respective ends of the coil C and external electrodes 20a, 20b and extend in the lamination direction. In a cross-sectional view cut along the lamination direction, the via conductors VDa, VDb have a smaller degree of unevenness on the outer surface on the outer side of the element body 10 than the degree of unevenness on the inner surface on the inner side of the element body 10.

Description

Inductor and Method for Manufacturing Inductor

[0001] The present disclosure relates to an inductor and a method for manufacturing an inductor.

[0002] Patent Document 1 discloses a multilayer coil component including: an element body formed by laminating a plurality of insulating layers in a lamination direction; external electrodes formed on a bottom surface of the element body; a coil section provided in the element body; and a through-hole connecting section provided in the element body and electrically connecting an end of the coil section to the external electrodes, wherein a coil pattern and a through-hole pattern are respectively formed on the plurality of layers, and the through-hole pattern in at least one first layer among the plurality of layers is offset from the through-hole pattern in another second layer when viewed from the lamination direction (see claim 1).

[0003] According to the multilayer coil component of Patent Document 1, by arranging the through-hole patterns in an offset manner, it is possible to suppress the volume of the conductor resulting from joining a plurality of through-hole patterns while ensuring conductivity in the lamination direction (see paragraph

[0007] of Patent Document 1).

[0004] Japanese Unexamined Patent Publication No. 2022-144852

[0005] In the multilayer coil component disclosed in Patent Document 1, no consideration has been given to magnetic flux generated by the through-holes that electrically connect the coil inside the element body to the external electrodes. Specifically, in Patent Document 1, by arranging the through-hole patterns in an offset manner, magnetic flux is generated to circulate in a gap between the through-hole pattern and the element body in a plan view. However, when the offset amount of the through-hole pattern is increased, the gap between the through-hole pattern and the element body becomes narrowed, which poses a problem that magnetic flux is less likely to be generated.

[0006] The present disclosure has been made in view of such a problem. That is, a main object of the present disclosure is to provide an inductor and a method for manufacturing an inductor that can appropriately generate magnetic flux by via conductors electrically connecting a coil to external electrodes.

[0007] The inductor of this disclosure comprises a coil disposed within the element and formed by stacking coil conductors, and via conductors that electrically connect each end of the coil to an external electrode and extend in the stacking direction, wherein, in a cross-sectional view taken along the stacking direction, the degree of unevenness of the outer surface on the outside side of the element is smaller than the degree of unevenness of the inner surface on the inside side of the element.

[0008] The method for manufacturing an inductor according to the present disclosure comprises: a forming step of forming a base material precursor by stacking a magnetic material layer and a coil conductor; a pressing step of pressing the formed base material precursor with a warm hydrostatic press; and a heat treatment step of forming the base material by heat treatment after the pressing step.

[0009] According to this disclosure, it is possible to provide an inductor that can appropriately generate magnetic flux by via conductors that electrically connect a coil and an external electrode, and a method for manufacturing an inductor.

[0010] Figure 1 is a schematic perspective view of an inductor according to the first embodiment. Figure 2 is a schematic exploded plan view of the inductor according to the first embodiment. Figure 3 is a schematic cross-sectional view of the main part of the magnetic layer. Figure 4 is an enlarged plan view of the main part of layer G4 shown in Figure 2. Figure 5 is a schematic cross-sectional view taken along the VV line in Figure 4. Figure 6 is a schematic cross-sectional view of layer G4 in a comparative example. Figure 7 is a schematic exploded plan view of an inductor according to the second embodiment. Figure 8 is a process flow of the manufacturing method of the inductor according to the present disclosure.

[0011] The inductor described herein will be explained in detail below. While the drawings will be referenced as necessary, the illustrations are for illustrative purposes only to aid in understanding this disclosure, and their appearance and dimensional ratios may differ from those of the actual product. The following drawings are schematic, and their dimensions, aspect ratios, etc., may differ from those of the actual product.

[0012] In this specification, terms indicating relationships between elements (e.g., "parallel," "orthogonal," etc.) and terms indicating 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 defined as the "stacking direction." Furthermore, a plan view refers to a plan view of the element seen from above (in the height direction).

[0013] <Inductor of the First Embodiment> The inductor 1 of the first embodiment comprises a base body 10 on which external electrodes 20a and 20b are provided on the mounting surface, a coil C disposed within the base body 10, and via conductors VDa and VDb that electrically connect the coil C and the external electrodes 20a and 20b.

[0014] The base body 10 is, for example, a hexahedron with six faces. As an example, it may be a rectangular prism or a roughly rectangular prism. The base body 10 may have rounded corners and edges. The corners are the parts where three faces of the base body 10 intersect, and the edges are the parts where two faces of the base body 10 intersect.

[0015] Figure 1 shows the long side direction, short side direction, and height direction of the inductor 1 and the element 10 as the L direction, W direction, and T direction, respectively. The long side direction L, the short side direction W, and the height direction T are mutually orthogonal.

[0016] The base body 10 shown in Figure 1 has a first main surface 11 and a second main surface 12 facing the height direction T, a first end surface 13 and a second end surface 14 facing the long side direction L, and a first side surface 15 and a second side surface 16 facing the short side direction W. In the example shown in Figure 1, external electrodes 20a and 20b are formed on the first main surface 11 of the base body 10, and the first main surface 11 of the base body 10 corresponds to the mounting surface (bottom surface of the base body) of the inductor 1.

[0017] Figure 2 is a schematic exploded perspective view showing an example of the internal structure of the inductor 1 of this disclosure. As shown in Figure 2, the base body 10 is constructed by laminating a coil conductor CD, a magnetic material layer ML containing metallic magnetic particles, and via conductors VDa and VDb.

[0018] The base body 10 is made up of stacked layers G1 to G7, with external electrodes 20a and 20b formed on the underside of layer G7. The boundaries between each layer of the stacked structure of the base body 10 may disappear. Each layer G1 to G7 may be made up of multiple layers stacked to achieve a desired thickness.

[0019] (Layer G1) Layer G1 has a magnetic material layer ML and may constitute the second main surface 12 of the base body 10 (see Figure 1).

[0020] (Layer G2) Layer G2 may comprise a coil conductor CD and a magnetic material layer ML arranged around the coil conductor CD.

[0021] The coil conductor CD of layer G2 may be wound along the outer edge of the element 10 from a position corresponding to the external electrode 20a in a plan view to a position corresponding to the interlayer connecting conductor TH of layer G3. In other words, the coil conductor CD of layer G2 may be wound counterclockwise with respect to the winding axis Ax of coil C.

[0022] (Layer G3) Layer G3 may comprise a via conductor VDa, an interlayer connecting conductor TH, and a magnetic layer ML disposed around the via conductor VDa and the interlayer connecting conductor TH.

[0023] The via conductor VDa of layer G3 may electrically connect one end of the coil conductor CD of layer G2 to the via conductor VDa of layer G4. Furthermore, the interlayer connecting conductor TH of layer G3 may electrically connect the other end of the coil conductor CD of layer G2 to one end of the coil conductor CD of layer G4.

[0024] (Layer G4) Layer G4 may comprise a coil conductor CD, a via conductor VDa, and a magnetic layer ML disposed around the coil conductor CD and the via conductor VDa.

[0025] The coil conductor CD of layer G4 may be wound along the outer edge of the element 10 from a position corresponding to the interlayer connecting conductor TH of layer G3 in a plan view to a position corresponding to the interlayer connecting conductor TH of layer G5. In other words, the coil conductor CD of layer G4 may be wound counterclockwise with respect to the winding axis Ax of coil C.

[0026] The coil conductor CD of layer G4 may have a relief portion AP at its corner in a plan view, which is cut out. The via conductor VDa of layer G4 may then be placed in the space created by the relief portion AP. By providing the relief portion AP in this way, contact with the via conductor VDa can be avoided, and the coil diameter and the planar area of ​​the via conductor can be increased.

[0027] The via conductor VDa of layer G4 may be electrically connected to the via conductor VDa of layer G3 and the via conductor VDa of layer G5.

[0028] (Layer G5) Layer G5 may comprise a via conductor VDa, an interlayer connecting conductor TH, and a magnetic layer ML disposed around the via conductor VDa and the interlayer connecting conductor TH.

[0029] The via conductor VDa of layer G5 may electrically connect the via conductor VDa of layer G4 and the via conductor VDa of layer G6. Furthermore, the interlayer connecting conductor TH of layer G5 may electrically connect the other end of the coil conductor CD of layer G4 to one end of the coil conductor CD of layer G6.

[0030] (Layer G6) Layer G6 may comprise a coil conductor CD, a via conductor VDa, and a magnetic layer ML disposed around the coil conductor CD and the via conductor VDa.

[0031] The coil conductor CD of layer G6 may be wound along the outer edge of the element 10 from a position corresponding to the interlayer connecting conductor TH of layer G5 in a plan view to a position corresponding to the via conductor VDb of layer G7. In other words, the coil conductor CD of layer G6 may be wound counterclockwise with respect to the winding axis Ax of coil C.

[0032] The coil conductor CD of layer G6 may have a relief portion AP at its corner in a plan view, which is cut out. The via conductor VDa of layer G4 may then be placed in the space created by the relief portion AP. By providing the relief portion AP in this way, contact with the via conductor VDa can be avoided, and the coil diameter and the planar area of ​​the via conductor can be increased.

[0033] The via conductor VDa of layer G6 may be electrically connected to the via conductor VDa of layer G5 and the via conductor VDa of layer G7.

[0034] (Layer G7) Layer G7 may comprise via conductors VDa and VDb, and a magnetic layer ML arranged around the via conductors VDa and VDb and the interlayer connecting conductor TH. The via conductors VDa and VDb of layer G7 may electrically connect the via conductors VDa and VDb of layer G6 to the external electrodes 20a and 20b.

[0035] As described above, when the base body 10 has a laminated structure comprising layers G1 to G7, irregularities are provided on the sides of the via conductors VDa, VDb and coil conductor CD in the lamination direction. Details of the degree of irregularities will be described later. Furthermore, an inductor 1 with such a laminated structure offers greater design flexibility. For example, when manufacturing an inductor 1 with external electrodes 20a and 20b on the bottom surface (first main surface 11) of the base body 10, it becomes easier to draw out the via conductors VDa and VDb to the bottom surface. The laminated structure comprising layers G1 to G7 may be laminated from the second main surface 12 side or the first main surface 11 side of the base body 10. In addition, the materials constituting the interlayer connecting conductor TH and / or via conductors VDa and VDb may be repeatedly printed sequentially by screen printing or the like until the via conductors reach the desired thickness, or they may be formed by an inkjet method or other known method.

[0036] Next, the magnetic layer ML, coil C, and via conductors VDa and VDb, which are provided inside the base body 10, will be described in detail.

[0037] -Magnetic Layer- The magnetic layer ML may contain metallic magnetic particles MP composed of a metallic magnetic material (see Figure 3). The metallic magnetic particles MP may contain Fe and / or Si. More specifically, they may be Fe particles or Fe alloy particles. Examples of Fe alloys include Fe-Si alloys, Fe-Cr alloys, Fe-Si-Cr alloys, Fe-Si-Al alloys, Fe-Si-B-P-Cu-C alloys, Fe-Si-B-Nb-Cu alloys, etc. The metallic magnetic particles MP may also contain impurities such as Cr, Mn, Cu, Ni, P, S, or Co that are not intended during manufacturing. Furthermore, the metallic magnetic particles MP may be contained in the magnetic paste. Therefore, the metallic magnetic particles MP may contain elements that are more easily oxidized than Fe added during the production of the magnetic paste (e.g., Cr, Al, Li, Zn, Zr).

[0038] The surface of the metal magnetic particle MP described above may be covered with an insulating film IL (see Figure 3). Covering the surface of the metal magnetic particle with an insulating film IL increases the insulation between the metal magnetic particle MPs, improves the dielectric strength of the inductor, and suppresses eddy currents generated in the metal magnetic particle MPs. Methods for forming the insulating film IL on the surface of the metal magnetic particle MPs include the sol-gel method and the mechanochemical method. The materials constituting the insulating film IL may be oxides of P, Si, zinc phosphate, or manganese phosphate. The insulating film IL may also be an oxide film formed by oxidation of the surface of the metal magnetic particle MPs with oxygen in the atmosphere, or an oxide film of an element that oxidizes more easily than Fe. The thickness of the insulating film IL 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 IL can be measured by taking a scan transmission electron microscope (STEM) image of a cross-section obtained by polishing an inductor sample, and then measuring the thickness of the insulating film IL covering the surface of the metal magnetic particle MPs from the resulting STEM image.

[0039] The average particle size of the metallic magnetic particles MP is preferably 2 μm to 50 μm, more preferably 4 μm to 20 μm, and even more preferably 5 μm to 10 μm. This average particle size of metallic magnetic particles MP can be measured by the procedure described below. A sample of the inductor is cut to obtain a sample cross-section. Specifically, a sample cross-section is obtained by cutting through the center of the base body 10 perpendicular to the mounting surface and end face of the coil component. Multiple areas (e.g., 5 areas) other than the insulating film IL (e.g., 130 μm × 100 μm) of the obtained cross-section are photographed with an SEM, and the obtained SEM images are analyzed using image analysis software (e.g., image analysis software WinROOF2021 (manufactured by Mitani Corporation)) to determine the equivalent circle diameter of the metallic magnetic particles. The average value of the obtained equivalent circle diameters is taken as the average particle size of the metallic magnetic particles.

[0040] The element body 10 including the magnetic layer ML may be subjected to the pressing step and heat treatment step described below after being laminated like layers G1 to G7 as described above. In this case, the metal magnetic particles MP included in the magnetic layer ML have an oxide film (insulating film IL) on the surface. This oxide film is derived from the metal magnetic particles MP and is formed by the heat treatment step. In the element body 10, adjacent metal magnetic particles MP may be bonded to each other via the oxide film.

[0041] Further, the element body 10 including the magnetic layer ML may be impregnated with a resin material after firing of the element body 10 in order to further improve the strength of the element body. As an example of the resin that increases the strength of the element body, epoxy resin and / or phenol resin and / or silicone resin may be used.

[0042] -Coil- The coil C includes a plurality of coil conductors CD in the lamination direction (for example, the height direction T). Adjacent coil conductors CD are connected to each other via interlayer connection conductors TH (see FIG. 2). Electric power is inputted and / or outputted to / from the coil conductor CD via via conductors VDa and VDb from external electrodes 20a and 20b.

[0043] The coil C may have a desired number of turns by including coil conductors CD formed in different layers in the lamination direction (see FIG. 2). The "number of turns" in the present specification means that 0.25 turns is added each time the direction of the coil conductor changes by 90° in a plan view, and when the direction of the coil conductor changes by 360° in a plan view, the coil conductor is wound by 1 turn. For an example, the coil C shown in FIG. 2 is wound for 2.5 turns by layers G2 to G6. However, the number of turns of the coil C is not limited to 2.5 turns.

[0044] -Via conductors- Via conductors VDa and VDb, which are one of the features of the present embodiment, as shown in FIG. 2, electrically connect each end of the coil C to the external electrodes 20a and 20b, and extend in the lamination direction. Since via conductors VDa and VDb are repeatedly laminated until a desired thickness is obtained, unevenness (see FIGS. 4 and 5) is formed on the side surfaces (inner side surface IS and outer side surface OS) extending in the lamination direction due to the lamination.

[0045] Via conductors VDa and VDb are, as shown in FIG. 4 and FIG. 5, in a cross-sectional view cut along the layer direction along a line V (see FIG. 4) orthogonal to avoiding portion AP of via conductor Va or Vb and the coil conductor in plan view, the degree of unevenness of outer side surface OS on the outer side of element body 10 is smaller than the degree of unevenness of inner side surface IS on the inner side of element body 10. The "degree of unevenness of the inner side surface" as used in the present specification refers to, as shown in FIG. 5, a length L1a from the most recessed position to the most projected position of inner side surface IS. Similarly, the "degree of unevenness of the outer side surface" as used in the present specification refers to, as shown in FIG. 5, a length L2a from the most recessed position to the most projected position of outer side surface OS.

[0046] The technical significance of reducing the degree of unevenness of outer side surfaces OS of via conductors VDa and VDb compared to the degree of unevenness of inner side surfaces IS of via conductors VDa and VDb in the cross-sectional view as described above will be described with reference to FIG. 4 to FIG. 6.

[0047] FIG. 6 shows an embodiment where the degree of unevenness of inner side surface IS of via conductor VDa and the degree of unevenness of outer side surface OS of the via conductor are approximately equal. In such a case, gap GP between outer side surfaces OS of via conductors VDa and VDb and element body 10 is relatively small. Therefore, magnetic flux circling around via conductors VDa and VDb is unlikely to be generated.

[0048] However, when the degree of unevenness of outer side surfaces OS of via conductors VDa and VDb is smaller than the degree of unevenness of inner side surfaces IS of via conductors VDa and VDb as in the present embodiment, gap GP between outer side surfaces OS of via conductors VDa and VDb and element body 10 can be made wider than that in the embodiment shown in FIG. 6, as shown in FIG. 4 and FIG. 5. Therefore, as shown in FIG. 4, magnetic flux B (see FIG. 4) circling around via conductors VDa and VDb, which is generated when current flows through via conductors VDa and VDb (for example, upward on the paper surface in FIG. 4), can be appropriately generated.

[0049] Furthermore, as an additional effect of the inductor according to the present embodiment, since unevenness is provided on inner side surfaces IS and outer side surfaces OS of via conductors VDa and VDb, the bonding strength between via conductors VDa, VDb and element body 10 can be increased by the anchor effect, and the strength of element body can be improved.

[0050] The via conductors VDa and VDb may be provided at the corners of the element 10 in a plan view. In this specification, "corner of the element" refers to a position close to the intersection formed by the meeting of two outer surfaces of the element. By providing the via conductors VDa and VDb at the corners of the element 10, interference with the winding of the coil C in a plan view can be prevented, and the coil can be appropriately positioned inside the element. Furthermore, a suitable magnetic flux can be generated in the gap GP between the outer surfaces OS of the via conductors VDa and VDb and the element 10.

[0051] Furthermore, regarding the shape of the via conductors VDa and VDb, the outer surface OS of the via conductors VDa and VDb faces the outer surface of the base body 10, and the inner surface IS of the via conductors VDa and VDb may be a curved surface. The curved surface may correspond to the degree of curvature of the avoidance portion AP of the coil conductor described above. With such shapes for the via conductors VDa and VDb, the via conductors VDa and VDb can be appropriately arranged in the space left open by the avoidance portion AP.

[0052] The above-described configuration of the degree of unevenness may also be provided in the coil conductor CD, and in a cross-sectional view cut along the lamination direction, the degree of unevenness of the outer surface OS on the outside side of the base body 10 (for example, length L2b in Figure 5) may be smaller than the degree of unevenness of the inner surface IS on the inside side of the base body 10 (for example, length L2a in Figure 5). The technical significance of this will be explained.

[0053] If the coil conductor CD has the same degree of unevenness as the via conductors VDa and VDb, as can be seen from Figure 4, the coil conductor CD can be positioned as close as possible to the via conductors VDa and VDb, thereby increasing the coil diameter and improving the magnetic properties. As an additional effect of providing unevenness on the side surface of the coil conductor CD, the surface area is increased by the unevenness on the side surface, and copper loss can be reduced by the skin effect.

[0054] <Inductor of the Second Embodiment> Next, the inductor of the second embodiment will be described with reference to Figure 7. In describing the inductor of the second embodiment, configurations common to the inductor of the first embodiment described above will be omitted from the explanation as appropriate.

[0055] In the second embodiment, the inductor has multiple coils C arranged along the stacking direction. As an example, in Figure 7, two coils (first coil C1 and second coil C2) are arranged along the stacking direction.

[0056] In this embodiment, the first coil C1 and the second coil C2 may be negatively coupled magnetically. In other words, the magnetic flux passing through the first coil C1 and the magnetic flux passing through the second coil C2 may be in opposite directions. By negatively coupling the first coil C1 and the second coil C2 magnetically in this way, the load response characteristics of the power supply circuit can be improved, magnetic saturation can be suppressed, and AC losses can be reduced. Alternatively, the first coil C1 and the second coil C2 may be positively coupled instead of negatively coupled.

[0057] Furthermore, in the inductor of the second embodiment, in which multiple coils are arranged in the stacking direction within the base body and the multiple coils are magnetically coupled, the degree of unevenness of the outer surface OS on the outside side of the base body 10 may be smaller than the degree of unevenness of the inner surface IS on the inside side of the base body 10 when viewed in cross-section along the stacking direction of the first coil conductor CD1 and the second coil conductor CD2. In the inductor of the second embodiment, if the degree of unevenness of the first coil conductor CD1 and the second coil conductor CD2 is the same as that of the first via conductors VD1a, VD1b and the second via conductors VD2a, VD2b, the first via conductors VD1a, VD1b which are electrically connected to the first coil conductor CD1 on the upper side in the stacking direction and arranged within the base body 10, and the second coil conductor CD2 on the lower side in the stacking direction can be arranged closer together, and the coil conductor CD can be placed as close as possible to the via conductors VD1a, VD1b to increase the coil diameter and improve the magnetic characteristics.

[0058] <Inductor Manufacturing Method> Next, the inductor manufacturing method will be described with reference to Figure 8. The inductor manufacturing method of this disclosure comprises at least a forming step of forming a primary precursor, a pressing step of pressing the primary precursor, and a heat treatment step of forming the primary body. The inductor manufacturing method of this disclosure will be described in detail below.

[0059] The formation process involves stacking magnetic layers and coil conductors to form a primary precursor. As an example, the primary precursor is formed by stacking layers G1 to G8 as described in Figure 2. Therefore, first, the magnetic material (magnetic paste) that constitutes the magnetic layers ML of layers G1 to G8 and the conductive paste that constitutes the coil conductor CD are prepared.

[0060] As an example of a method for producing a magnetic paste, a metallic magnetic powder containing Fe and Si with a D50 (cumulative 50% particle size by volume) of 2 μm to 20 μm is prepared. A magnetic paste is produced by kneading this metallic magnetic 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).

[0061] As a conductive paste, for example, a paste containing Cu as a conductive material is prepared. Note that the conductive material is not limited to Cu; conductive materials such as Ag, Au, or alloys thereof, in paste form may also be used.

[0062] Using the magnetic paste and conductive paste described above, layers G1 to G8 shown in Figure 2 are prepared and laminated by screen printing or the like.

[0063] -Pressing Process- The pressing process involves pressing the raw material precursor formed in the formation process described above using a warm hydrostatic press (WIP). This warm hydrostatic press is one of the characteristic processes in the inductor manufacturing method of this disclosure. In other words, regarding the degree of unevenness of the inner and outer surfaces of the via conductor, before the warm hydrostatic press, the degree of unevenness of the inner and outer surfaces is about the same, but after the warm hydrostatic press, the degree of unevenness of the outer surface of the via conductor becomes smaller than the degree of unevenness of the inner surface of the via conductor. This can be appropriately adjusted by the warm hydrostatic press profile, as well as by additives to the magnetic paste and conductor paste.

[0064] In the inductor manufacturing method described herein, the degree of unevenness on the outer surface of the via conductor is made smaller than the degree of unevenness on the inner surface of the via conductor by warm hydrostatic pressing. However, the method is not limited to this method, and any pressing method other than warm hydrostatic pressing may be used as long as the degree of unevenness on the outer surface of the via conductor can be made smaller than the degree of unevenness on the inner surface of the via conductor.

[0065] - Degreasing process (optional additional process) - A degreasing process may be included as a manufacturing process for a suitable inductor. The degreasing process is a process for removing the binder contained in the magnetic paste and conductive paste. For example, degreasing is performed at a temperature of about 300°C to 500°C. This removes the binder contained in the magnetic paste and conductive paste.

[0066] - Heat treatment process: After the degreasing process, a heat treatment is performed. The heat treatment temperature is such that the coil conductor sintersects, for example, it may be between 400°C and 1000°C. Furthermore, to achieve both a reduction in coercivity and suppression of heat diffusion of the coil conductor material components into the substrate, it is desirable to set the temperature between 650°C and 900°C. This heat treatment forms an oxide film on the surface of the metal magnetic particles within the substrate, and adjacent metal magnetic particles can be bonded together by the oxide film.

[0067] Furthermore, in order to increase the strength of the base material, resin may be impregnated into the gaps between the oxide films of adjacent metal magnetic particles within the base material and cured. The resin used to impregnate the base material is epoxy resin, but one or more resins selected from the group consisting of phenolic resin, polyester resin, polyimide resin, polyolefin resin, silicone resin, acrylic resin, polyvinyl butyral resin, cellulose resin, and alkyd resin may also be used. By going through the above steps, the base material of the inductor of this disclosure is formed.

[0068] Subsequently, external electrodes electrically connected to the coil conductor are formed on the formed body. The external electrodes are formed by electroplating at positions where via conductors are exposed on the mounting surface (first main surface 11) of the body 10. 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. After forming the external electrodes, the element can be cut into individual components to manufacture the inductor of this embodiment.

[0069] As described above, the method for manufacturing an inductor according to this disclosure makes it possible to manufacture an inductor in which the degree of unevenness of the outer surface OS of via conductors VDa and VDb is smaller than the degree of unevenness of the inner surface IS of via conductors VDa and VDb. Therefore, when current flows through via conductors VDa and VDb, it is possible to appropriately generate magnetic flux circulating around via conductors VDa and VDb.

[0070] The embodiments disclosed herein are illustrative in all respects and do not constitute a limiting interpretation. Therefore, the technical scope of this disclosure is not construed 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 equivalence to the claims.

[0071] The inductor of this disclosure can be suitably used as an electronic device capable of appropriately generating magnetic flux by via conductors that electrically connect the coil and external electrodes.

[0072] 1 Inductor 10 Base 11 First main surface 12 Second main surface 13 First end surface 14 Second end surface 15 First side surface 16 Second side surface G1-G7 Layers CD Coil conductor CD1 First coil conductor CD2 Second coil conductor 20a, 20b External electrodes 21a, 21b First external electrodes 22a, 22b Second external electrodes VDa, VDb Via conductors VD1a, VD1b First via conductors VD2a, VD2b Second via conductors IS Inner surface OS Outer surface TH Interlayer connection conductor Ax Winding shaft AP Avoidance section IL Insulating film B Magnetic flux

Claims

1. An inductor comprising: a base body having multiple stacked magnetic layers; a coil disposed within the base body and composed of stacked coil conductors; and via conductors that electrically connect each end of the coil to an external electrode and extend in the stacking direction, wherein, in a cross-sectional view taken along the stacking direction, the degree of unevenness of the outer surface on the outside of the base body is smaller than the degree of unevenness of the inner surface on the inside of the base body.

2. The inductor according to claim 1, wherein a plurality of coils are provided along the stacking direction.

3. The inductor according to claim 1 or 2, wherein, in a cross-sectional view, the degree of unevenness of the outer surface of the base body is smaller than the degree of unevenness of the inner surface of the base body on the inner side.

4. The inductor according to any one of claims 1 to 3, wherein the via conductor is provided at the corner of the main body in a plan view.

5. The inductor according to any one of claims 1 to 4, wherein the outer surface of the via conductor faces the outer surface of the base body, and the inner surface of the via conductor is a curved surface.

6. A method for manufacturing an inductor according to any one of claims 1 to 5, comprising: a forming step of forming a base material precursor by laminating a magnetic paste and a conductive paste; a pressing step of pressing the formed base material precursor with a warm hydrostatic press; and a heat treatment step of forming the base material by firing after the pressing step.

Images