Coil component and method for manufacturing the coil component

Abstract

To improve the bonding strength between a metal layer and a plating layer in an external electrode.SOLUTION: A method of manufacturing a coil component includes the steps of: forming a compact with a pattern of a precursor of a coil conductor 30 formed therein, the compact including metal magnetic particles; performing heat treatment of the compact to obtain a magnetic base substance 10; forming on a surface of the magnetic base substance 10 a metal layer 62 that is composed of sintered metal particles and is electrically connected with the coil conductor 30; impregnating the inside of the magnetic base substance 10 and the metal layer 62 with a resin; performing acidification of the metal layer 62 to remove a part of the resin intruding between the metal particles from a surface to the inside of the metal layer 62; and forming a plating layer 64 between the metal particles on the metal layer 62 and in a part of the metal layer 62 by using the plating method after the acidification of the metal layer 62, and thereby forming an external electrode 60 having the metal layer 62 and the plating layer 64.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a coil component and a method for manufacturing a coil component. [Background technology]

[0002] In a coil component, an external electrode electrically connected to a coil conductor is formed on the surface of a magnetic base. Here, it is known that the surface of the magnetic base is irradiated with a laser to remove the resin, expose the metal magnetic particles, and reduce the electrical resistance of the surface of the magnetic base, and then the external electrode is formed on the surface of the magnetic base by plating (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-106482 A Summary of the Invention [Problem to be solved by the invention]

[0004] When forming an external electrode having a metal layer and a plating layer by using a plating method to form a plating layer on a metal layer formed on the surface of a magnetic base, it is desirable to improve the bonding strength between the metal layer and the plating layer.

[0005] The present invention has been made in consideration of the above-mentioned problems, and has an object to improve the bonding strength between the metal layer and the plating layer in an external electrode. [Means for solving the problem]

[0006] The present invention is a method for manufacturing a coil component, comprising the steps of: forming a molded body containing metal magnetic particles, with a pattern of a coil conductor precursor formed therein; heat-treating the molded body to form a magnetic base; forming a metal layer on the surface of the magnetic base, the metal particles being sintered and electrically connected to the coil conductor; impregnating the magnetic base and the metal layer with resin; treating the metal layer with acid to remove a portion of the resin that has penetrated between the metal particles from the surface to the inside of the metal layer; and, after treating the metal layer with acid, forming a plating layer using a plating method on the metal layer and between the metal particles on some of the metal layers, thereby forming an external electrode having a metal layer and a plating layer.

[0007] The present invention is a method for manufacturing a coil component, comprising the steps of: forming a molded body containing metal magnetic particles; heat-treating the molded body to form a magnetic base; forming a metal layer on the surface of the magnetic base, the metal particles being sintered; impregnating the magnetic base and the interior of the metal layer with a resin; treating the metal layer with an acid to remove a portion of the resin that has penetrated between the metal particles from the surface to the interior of the metal layer; after treating the metal layer with an acid, forming a plating layer on the metal layer and between the metal particles inside a portion of the metal layer using a plating method; winding a coil conductor around the magnetic base; and connecting ends of the coil conductor to the metal layer and the plating layer on the surface of the magnetic base to form an external electrode having a metal layer and a plating layer.

[0008] The above-mentioned configuration may further include a step of subjecting the metal layer to an acid treatment to form a recess in the surface of the metal layer from which the metal particles have been removed.

[0009] In the above configuration, the step of forming the recessed portion may be configured to form the recessed portion in which a surface of the metal particle is exposed.

[0010] In the above configuration, the plating layer may include a copper plating layer or a nickel plating layer.

[0011] In the above configuration, the metal particles may be silver particles or copper particles.

[0012] The present invention is a coil component comprising: a magnetic base; a coil conductor provided on the magnetic base; and an external electrode provided on the surface of the magnetic base and electrically connected to the coil conductor, the external electrode having a metal layer and a plating layer provided on the metal layer, the plating layer having a portion thereof penetrating between metal particles of the metal layer located in the interior away from the surface of the metal layer. Effect of the Invention

[0013] According to the present invention, the bonding strength between the metal layer and the plating layer in the external electrode can be improved. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view of a coil component according to a first embodiment. [Diagram 2] FIG. 2 is a cross-sectional view of the coil component of FIG. [Diagram 3] FIG. 3 is an exploded perspective view of a magnetic base of the coil component of FIG. [Figure 4] FIG. 4 is a flowchart showing an example of a method for manufacturing the coil component according to the first embodiment. [Diagram 5] FIG. 5(a) is a schematic diagram of a scanning electron microscope (SEM) image of a cross section near the external electrode of a coil component according to a comparative embodiment, and FIG. 5(b) is a schematic diagram of an energy dispersive X-ray analysis (EDS) image of the portion of FIG. 5(a). [Figure 6] FIG. 6(a) is a schematic diagram of a scanning electron microscope (SEM) image of a cross section near an external electrode of a coil component according to the first embodiment, and FIGS. 6(b) and 6(c) are schematic diagrams of energy dispersive X-ray analysis (EDS) images of the portion of FIG. 6(a). [Figure 7] FIG. 7 is a side view of the coil device according to the second embodiment. [Figure 8] FIG. 8 is a flowchart showing an example of a method for manufacturing a coil component according to the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings as appropriate. However, the present invention is not limited to the illustrated embodiment. In addition, components common to multiple drawings are given the same reference numerals throughout the multiple drawings. Please note that the drawings are not necessarily drawn to scale for the sake of convenience.

[0016] [First embodiment] FIG. 1 is a perspective view of a coil component 300 according to a first embodiment. FIG. 2 is a cross-sectional view of the coil component 300 of FIG. 1. FIG. 3 is an exploded perspective view of the magnetic base 10 of the coil component 300 of FIG. 1. FIGS. 1, 2, and 3 show a laminated inductor used as a passive element in various circuits. The laminated inductor is an example of a coil component applicable to the present invention. The present invention can be applied to power inductors used in DC-DC converters or various other coil components. In addition, each step shown in the present invention may be performed in any order, and one step may be performed multiple times, except when the respective dependencies are clearly indicated. Any steps not described may be included before, after, or between each step.

[0017] As shown in Figs. 1, 2, and 3, the coil component 300 in the first embodiment includes a magnetic base 10, a coil conductor 30 embedded in the magnetic base 10, and a pair of external electrodes 60 electrically connected to the coil conductor 30. The "length", "width", and "height" directions of the coil component 300 are defined as the "L-axis", "W-axis", and "T-axis" directions, respectively. The L-axis, W-axis, and T-axis are mutually orthogonal. The direction of the coil axis A of the coil conductor 30 is not particularly restricted, but extends, for example, along the T-axis direction. The size of the magnetic base 10 is not particularly limited, but for example, the length dimension (dimension in the L-axis direction) is 0.2 mm to 6.0 mm, the width dimension (dimension in the W-axis direction) is 0.1 mm to 4.5 mm, and the height dimension (dimension in the T-axis direction) is 0.1 mm to 4.0 mm.

[0018] The magnetic base 10 has a generally rectangular parallelepiped shape (approximately rectangular parallelepiped shape). The outer surface of the magnetic base 10 is defined by six faces. Note that the approximately rectangular parallelepiped shape includes cases where each vertex is rounded, each side (boundary between each face) is rounded, or each face has a curved surface.

[0019] In the first embodiment, when referring to the up-down direction of coil device 300, the up-down direction is based on the up-down direction in Figures 1, 2, and 3. That is, the positive direction in the T-axis direction is the upward direction, and the negative direction is the downward direction.

[0020] The magnetic substrate 10 is formed by including a plurality of metal magnetic particles and a thermosetting or thermoplastic resin. In the present first embodiment, the magnetic substrate 10 will be described by taking as an example a case where a plurality of metal magnetic particles are bonded via an oxide film formed on the surface of the metal magnetic particles. The oxide film formed on the surface of the metal magnetic particles is an oxide of the elements constituting the metal magnetic particles. The metal magnetic particles are formed of soft magnetic alloy materials such as iron-silicon-chromium, iron-silicon-aluminum, or iron-silicon-chromium-aluminum, metal magnetic materials such as iron or nickel, amorphous magnetic metal materials, or nanocrystalline magnetic metal materials. In the present first embodiment, the metal magnetic particles will be described by taking as an example a case where the metal magnetic particles are formed of a soft magnetic alloy material mainly composed of iron. The term "mainly composed of iron" refers to a case where the ratio of iron to the total amount of elements constituting the soft magnetic alloy is 50 wt% (weight %) or more, may be 70 wt% or more, may be 80 wt% or more, or may be 90 wt% or more.

[0021] The resin in the magnetic substrate 10, in which a plurality of metal magnetic particles are bonded via an oxide film formed on the surface of the metal magnetic particles, is formed by introducing the resin into the gaps between the metal magnetic particles by impregnation. The magnetic substrate 10 can also be formed by creating a molded body using a mixture of metal magnetic particles and resin, and curing the molded body by heat treatment. The resin in the magnetic substrate 10 is formed from at least one of silicone resin, epoxy resin, acrylic resin, phenol resin, imide resin, amide resin, silicate resin, urethane resin, polyester resin, and polyethylene resin, for example.

[0022] The coil conductor 30 has a winding portion 32. The winding portion 32 has winding patterns C11 to C15 and vias V1 to V4. The winding patterns C11 to C15 extend along a plane (LW plane) perpendicular to the coil axis A, and are separated from each other in the direction of the coil axis A (T-axis direction). Among the winding patterns C11 to C15, adjacent winding patterns in the T-axis direction are electrically connected via the vias V1 to V4. This forms the winding portion 32 that winds around the coil axis A.

[0023] One end of the winding part 32 is electrically connected to one of the external electrodes 60 by a lead-out part 34a formed by vias V5 and V6. The other end of the winding part 32 is electrically connected to the other external electrode 60 by a lead-out part 34b formed by vias V11 to V16.

[0024] The magnetic substrate 10 has a main body 20 made of magnetic layers 11-15 on which a winding portion 32 is provided, an upper cover layer 16 made of one or more layers provided on the main body 20, and a lower cover layer 17 made of one or more layers provided under the main body 20. The winding pattern C11 and vias V1, V11 are formed in the magnetic layer 11, the winding pattern C12 and vias V2, V12 are formed in the magnetic layer 12, the winding pattern C13 and vias V3, V13 are formed in the magnetic layer 13, the winding pattern C14 and vias V4, V14 are formed in the magnetic layer 14, and the winding pattern C15 and vias V5, V15 are formed in the magnetic layer 15. The vias V6, V16 are formed in the lower cover layer 17.

[0025] The circular patterns C11 to C15 and the vias V1 to V6, V11 to V16 are formed from a metal material having excellent conductivity, such as silver, palladium, copper, aluminum, or an alloy of these.

[0026] The pair of external electrodes 60 are provided on the surface of the magnetic base 10. In the present first embodiment, a case will be described in which the pair of external electrodes 60 are provided on the lower surface of the magnetic base 10, separated in the L-axis direction. One of the pair of external electrodes 60 is electrically connected to one end of the winding part 32 via the lead-out portion 34a, and the other is electrically connected to the other end of the winding part 32 via the lead-out portion 34b. The external electrode 60 includes a metal layer 62 and a plating layer 64. The plating layer 64 is, for example, a laminated film of a nickel plating layer and a tin plating layer.

[0027] [Manufacturing method] FIG. 4 is a flowchart showing an example of a method for manufacturing the coil component 300 according to the first embodiment. As shown in FIG. 4, first, a molded body having a pattern of a precursor of the coil conductor 30 therein is formed (step S10). The molded body is formed by the following method. First, an upper laminate that becomes the upper cover layer 16 is formed. The upper laminate is formed by laminating a plurality of magnetic sheets. The magnetic sheet is obtained, for example, by applying a slurry to the surface of a plastic base film, drying it, and cutting the dried slurry to a predetermined size. The slurry is produced by mixing metal magnetic particles made of a soft magnetic alloy mainly composed of iron with an organic binder and a solvent. For example, a resin material having excellent degreasing properties by heat treatment, such as polyvinyl butyral (PVB) resin or epoxy resin, is used as the organic binder. For example, toluene is used as the solvent.

[0028] Next, a lower laminate that becomes the lower cover layer 17 is formed. The lower laminate is formed by stacking the composite sheet having unsintered conductive vias on the above-mentioned magnetic sheet. The composite sheet is obtained by forming through holes at positions corresponding to the vias V6 and V16 of the magnetic sheet, and filling the through holes with a conductive paste by using, for example, screen printing. The conductive vias may be formed by a method other than screen printing.

[0029] Next, an intermediate laminate that becomes the main body 20 is formed. The intermediate laminate is formed by laminating a composite sheet in which unfired conductor patterns that become the round patterns C11 to C15 and unfired conductor vias that become the vias V1 to V5 and V11 to V15 are provided on a magnetic sheet that becomes the magnetic layers 11 to 15 (the conductor patterns and the conductor vias become the precursor patterns of the coil conductor). In order to form this composite sheet, first, through holes are formed in the magnetic sheet at positions corresponding to the vias V1 to V5 and V11 to V15 described above. Next, an unfired conductor pattern is formed on the magnetic sheet by printing a conductive paste on the magnetic sheet, for example, using screen printing. At this time, the conductive paste is filled in the through holes formed in the magnetic sheet. As a result, the unfired conductor patterns that become the round patterns C11 to C15 and the unfired conductor vias that become the vias V1 to V5 and V11 to V15 are formed on the magnetic sheet. The conductor patterns and the conductor vias may be formed by a method other than screen printing.

[0030] Next, the lower laminate, the intermediate laminate, and the upper laminate are stacked in this order from the negative side to the positive side in the T-axis direction. This laminate is thermocompressed by a press or the like to form a main laminate. Then, the main laminate is cut into pieces of a desired size using a cutting machine such as a dicing machine or a laser processing machine to form a molded body having a precursor pattern of the coil conductor 30 inside.

[0031] Next, the compact is subjected to a heat treatment for firing to form the magnetic base 10 (step S12). The heat treatment is performed at a predetermined temperature in an oxygen-containing atmosphere. This heat treatment forms an oxide film made of an oxide of the material components of the metal magnetic particles on the surfaces of the metal magnetic particles contained in the compact, and the multiple metal magnetic particles are bonded to each other via the oxide film. A coil conductor 30 is formed inside the magnetic base 10.

[0032] Instead of the magnetic base 10 in which an oxide film made of an oxide of the material component of the metal magnetic particles is formed on the surface of the metal magnetic particles and a plurality of metal magnetic particles are bonded to each other via the oxide film, a magnetic base 10 in which a resin is provided around the metal magnetic particles may be formed. That is, in the flow chart of FIG. 4, in step S10, a magnetic sheet is formed using a mixture of the metal magnetic particles and the resin, vias are provided at necessary locations on the magnetic sheet, and a conductor pattern made of a conductive paste is formed, and these are laminated to form a molded body in which a precursor of a coil conductor is embedded. The resin used in this case is formed from at least one of silicone resin, epoxy resin, acrylic resin, phenol resin, imide resin, amide resin, silicate resin, urethane resin, polyester resin, and polyethylene resin. Then, in step S12, the molded body may be heat-treated to harden the resin, thereby forming a magnetic base 10 in which the metal magnetic particles are solidified with the resin.

[0033] Next, a metal layer 62 constituting an external electrode 60 electrically connected to the coil conductor 30 is formed on the surface of the magnetic base 10 (step S14). For example, the metal layer 62 is formed by applying and baking a silver paste (conductive paste). As a result, the metal layer 62 in which silver particles (metal particles) are sintered is obtained on the surface of the magnetic base 10. The metal layer 62 may be formed in step S10 by applying a silver paste (conductive paste) to the magnetic sheet of the lower laminate, which is the bottom layer of the magnetic base 10, to form a conductor pattern that becomes the metal layer 62, or by applying a silver paste (conductive paste) to the magnetic sheet of the lower laminate, which is the bottom layer of the magnetic base 10, to form a conductor pattern that becomes the metal layer 62 after the laminate is compressed to form the main laminate or after the main laminate is divided into chips.

[0034] Next, the magnetic substrate 10 and the metal layer 62 are impregnated with resin and cured (step S16). For example, a resin with excellent insulating properties formed from at least one of silicone resin, epoxy resin, acrylic resin, phenol resin, imide resin, amide resin, silicate resin, urethane resin, polyester resin, and polyethylene resin is used. The resin penetrates between the metal magnetic particles from the surface of the magnetic substrate 10 toward the inside of the magnetic substrate 10. As a result, a resin film is formed on the surface of the metal magnetic particles and on some of the gaps between the particles. The magnetic substrate 10 is impregnated with resin in order to prevent the metal magnetic particles from being corroded by the plating solution or moisture described later penetrating into the magnetic substrate 10. In addition, the resin penetrates between the silver particles (metal particles) of the metal layer 62 from the surface of the metal layer 62 toward the inside of the metal layer 62. As a result, a resin film is formed on the surface of the silver particles of the metal layer 62 and on some of the gaps between the particles. Resin impregnation into the magnetic substrate 10 is preferably performed after the metal layer 62 is formed on the surface of the magnetic substrate 10 for reasons such as preventing the infiltration of plating solution and moisture into the product. If heat treatment for sintering is performed when forming the metal layer 62, the resin will decompose due to the high temperature for sintering. In such a case, resin impregnation is performed after the metal layer 62 is formed on the surface of the magnetic substrate 10. For this reason, resin is also impregnated into the metal layer 62. In addition, resin is preferably impregnated into the metal layer 62 for reasons such as preventing the infiltration of plating solution and moisture into the product through the passages between the metal particles (silver particles) of the metal layer 62. Since the resin attached to the surface of the metal layer 62 inhibits the conduction between the metal layer 62 and the plating layer 64, the resin on the surface of the metal layer 62 is removed after the resin is impregnated.

[0035] Next, the metal layer 62 is acid-treated (step S18). The acid treatment is performed using an acid solution such as a phosphoric acid solution, a hydrochloric acid solution, or a sulfuric acid solution. By setting the conditions of this acid treatment (e.g., concentration, temperature, treatment time, pH, etc.) appropriately, the acid solution can penetrate into the gaps between the silver particles (metal particles) of the metal layer 62 where there is no resin film, and dissolve a part of the resin film formed on the surface of the silver particles (metal particles) and a part of the resin film formed in a part of the gaps between the particles. For example, the acid solution penetrates from between the metal particles exposed on the surface of the metal layer 62 to between the metal particles in contact with the magnetic base 10. In addition, by setting the conditions of the acid treatment appropriately, a part of the silver particles (metal particles) exposed on the surface of the metal layer 62 after the resin is removed can be dissolved and removed, forming a recessed portion on the surface of the metal layer 62. In the recesses formed by removing the silver particles (metal particles), the resin film on the surface of the silver particles (metal particles) of the metal layer 62 can be dissolved by acid treatment to expose at least a part of the silver particles (metal particles). Note that, inside the metal layer 62, a part of the resin film close to the upper surface of the metal layer 62 is dissolved by acid treatment, but most of the resin film remains, so that the silver particles (metal particles) located inside the metal layer 62 do not dissolve even when acid treatment is performed because of the resin film around them. Dissolving a part of the resin film formed on the surface of the silver particles (metal particles) inside the metal layer 62 and a part of the resin film formed in a part of the gap between the particles, and forming a recess on the surface of the metal layer 62 may be performed in a single acid treatment or in separate acid treatments.

[0036] Next, a plating layer 64 constituting an external electrode 60 is formed on the metal layer 62 by electrolytic plating (step S20). The acid treatment performed in step S18 dissolves a part of the resin film formed around the silver particles (metal particles) of the metal layer 62 to form a passage, so that the plating solution penetrates into the inside of the metal layer 62 through the passage between the metal particles (silver particles). For example, the acid treatment forms a passage through which the plating solution can penetrate, continuing from the surface of the metal layer 62 to the magnetic substrate 10. Therefore, the plating layer 64 is formed with a part penetrating between the silver particles (metal particles) located inside the metal layer 62 and away from the surface. In addition, the plating solution penetrates into the recesses formed by removing the silver particles (metal particles) on the surface of the metal layer 62 by the acid treatment, so that the plating layer 64 is formed by penetrating into the recesses. As a result, the external electrode 60 is formed, which is electrically connected to the coil conductor 30 and is composed of the metal layer 62 and the plating layer 64. The plating layer 64 may be a laminated film of a nickel plating layer and a tin plating layer.

[0037] [Comparative form] The coil component according to the comparative embodiment is manufactured by the same method as that of the first embodiment, except that the acid treatment of the metal layer is not performed in the manufacturing method shown in FIG.

[0038] FIG. 5(a) is a schematic diagram of a scanning electron microscope (SEM) image of a cross section near an external electrode of a coil component according to a comparative embodiment, and FIG. 5(b) is a schematic diagram of an energy dispersive X-ray analysis (EDS) image of the portion of FIG. 5(a). The coil component observed was formed by applying silver paste to the surface of a magnetic base 110 and firing the metal layer 162 of the external electrode 160. The plating layer 164 was formed by electrolytic plating, and was a laminated film of a nickel plating layer and a tin plating layer on the nickel plating layer. In FIG. 5(b), the nickel L line is mapped. The hatched area is an area containing a large amount of nickel.

[0039] As shown in Fig. 5(a), in the coil component according to the comparative embodiment, a plating layer 164, which is a laminated film of a nickel plating layer and a tin plating layer on the nickel plating layer, is formed on a metal layer 162. As shown in Figs. 5(a) and 5(b), the plating layer 164 is formed on the metal layer 162 with small irregularities. In addition, since no nickel component is found inside the metal layer 162, it is understood that the nickel plating layer contained in the plating layer 164 is formed on the surface of the metal layer 162 without penetrating inside the metal layer 162.

[0040] [Evaluation of the first embodiment] FIG. 6(a) is a schematic diagram of an SEM image of a cross section of the coil component 300 according to the first embodiment near the external electrode 60 observed by a scanning electron microscope (SEM), and FIG. 6(b) and FIG. 6(c) are schematic diagrams of energy dispersive X-ray analysis (EDS) images of the portion of FIG. 6(a). The coil component 300 observed was formed by applying a silver paste to the surface of the magnetic base 10 and firing the metal layer 62 of the external electrode 60. The plating layer 64 was formed by electrolytic plating to form a laminated film of a nickel plating layer and a tin plating layer on the nickel plating layer. The acid treatment described in step S18 of FIG. 4 was performed for 15 minutes using a phosphoric acid solution with a concentration of 10 vol% (volume %) and a temperature of 60°C. For example, in the case of phosphoric acid treatment, the acid treatment condition can be a treatment in which the metal layer 62 is immersed in a phosphoric acid solution with a concentration of 5 to 25 vol% (volume %) and a temperature of 50 to 70°C for 5 to 30 minutes. Figures 6(b) and 6(c) show the L-lines of silver and nickel. The hatched areas are areas with high concentrations of the corresponding elements. In Figure 6(c), the islands surrounded by dashed lines have a lower nickel content than the strips not surrounded by dashed lines.

[0041] As shown in FIG. 6(a), in the coil component 300 according to the first embodiment, a plating layer 64 is formed on a metal layer 62, which is a laminated film of a nickel plating layer and a tin plating layer on the nickel plating layer. As shown in FIG. 6(b) and FIG. 6(c), it can be seen that the nickel component of the nickel plating layer contained in the plating layer 64 penetrates not only on the surface of the metal layer 62 made of silver, but also between the silver particles not exposed on the surface inside the layer away from the surface. The state of the silver particles can be known by comparing FIG. 6(b) with an electron beam image (not shown) of the same field of view. For example, the nickel component penetrates not only between the silver particles on the surface of the metal layer 62, but also into the interior at a distance of three or more silver particle sizes from the surface of the metal layer 62.

[0042] The reason why the nickel plating layer contained in the plating layer 64 penetrated into the inside of the metal layer 62 is believed to be as follows. That is, it is believed that the acid treatment of the metal layer 62 dissolved part of the resin film formed between the silver particles of the metal layer 62, forming a passage through which the plating solution can penetrate. In this state, the nickel plating layer contained in the plating layer 64 was formed by electrolytic plating, and the plating solution penetrated between the silver particles, and as a result, it is believed that part of the nickel plating layer penetrated into the interior of the metal layer 62, away from the surface.

[0043] 6(a) and 6(b), a recess 70 is formed on the surface of the metal layer 62. It is believed that the recess 70 is formed by dissolving and removing silver particles exposed on the surface of the metal layer 62 by treating the metal layer 62 with an acid. Since the recess 70 is formed on the surface of the metal layer 62 from which the silver particles have been removed, a part of the nickel plating layer included in the plating layer 64 is formed by penetrating into the recess 70, as shown in FIGS. 6(a) and 6(c).

[0044] In this way, a part of the plating layer 64 is formed inside the metal layer 62 and penetrates between the silver particles that are not exposed on the surface, thereby improving the bonding strength between the metal layer 62 and the plating layer 64 compared to the comparative example in which the plating layer 164 is formed only on the surface of the metal layer 162. Also, a part of the plating layer 64 is formed penetrating into the recessed portion 70 formed on the surface of the metal layer 62, thereby improving the bonding strength between the metal layer 62 and the plating layer 64 by the anchor effect.

[0045] As described above, according to the first embodiment, as shown in FIG. 4, a molded body containing metal magnetic particles is formed inside the molded body (step S10). The molded body is heat-treated to form a magnetic base 10 (step S12). A metal layer 62 is formed on the surface of the magnetic base 10 by sintering metal particles and is electrically connected to the coil conductor 30 (step S14). Resin is impregnated into the magnetic base 10 and the metal layer 62 (step S16). The metal layer 62 is acid-treated to remove a part of the resin that has entered between the metal particles from the surface to the inside of the metal layer 62 (step S18). After the metal layer 62 is acid-treated, a plating layer 64 is formed on the metal layer 62 and between the metal particles inside a part of the metal layer 62 by plating, thereby forming an external electrode 60 having the metal layer 62 and the plating layer 64 (step S20). By forming plating layer 64 on metal layer 62 using a plating method after acid treatment of metal layer 62, a plating solution permeates into passages formed by removing a portion of the resin that has penetrated between the metal particles from the surface to the inside of metal layer 62, and plating layer 64 is formed by portions of the resin penetrating between the metal particles located inside and away from the surface of metal layer 62. This makes it possible to improve the bonding strength between metal layer 62 and plating layer 64.

[0046] Moreover, in the first embodiment, the metal layer 62 is acid-treated to form the recessed portion 70 in which metal particles are removed from the surface of the metal layer 62. After the metal layer 62 is acid-treated to form the recessed portion 70, the plating layer 64 is formed on the metal layer 62 by plating, so that a part of the plating layer 64 penetrates into the recessed portion 70. This produces an anchor effect, and the bonding strength between the metal layer 62 and the plating layer 64 can be improved.

[0047] Furthermore, in the first embodiment, when forming the recessed portion 70 by treating the metal layer 62 with an acid, the recessed portion 70 is formed in which the surfaces of the metal particles of the metal layer 62 are exposed. If there is resin between the metal particles of the metal layer 62 and the plating layer 64, there is a risk of a decrease in the bonding strength. However, by exposing the surfaces of the metal particles of the metal layer 62 in the recessed portion 70, there is no resin between the plating layer 64 and the exposed surfaces of the metal particles, and therefore the bonding strength between the metal layer 62 and the plating layer 64 can be improved.

[0048] An example of the acid treatment for removing a part of the resin that has entered between the metal particles from the surface to the inside of the metal layer 62 is immersing the metal layer 62 in a phosphoric acid solution with a concentration of 5 to 25 vol% (volume %) and a temperature of 50 to 70°C for 5 to 30 minutes. In addition, by performing the acid treatment under these conditions, a recess 70 is formed on the surface of the metal layer 62 from which the metal particles have been removed, and the surface of the metal particles of the metal layer 62 can be exposed in the recess 70. It is known that phosphoric acid treatment is conventionally performed in order to precipitate phosphates and enhance insulation in areas where the oxide film (insulating film) on the surface of the metal magnetic particles is damaged and becomes defective, exposing the metal magnetic particles. The phosphoric acid treatment is adjusted under conditions that do not dissolve the metal magnetic particles, and for example, a treatment of immersing the metal layer 62 in a phosphoric acid solution with a concentration of 0.1 vol% (volume %) and a temperature of 50°C for 5 minutes is adopted. Under such conditions, it is not possible to remove a part of the resin that has entered between the metal particles from the surface to the inside of the metal layer 62.

[0049] In the first embodiment, the metal particles constituting the metal layer 62 are silver particles (i.e., the metal layer 62 is formed of silver) and the plating layer 64 includes a nickel plating layer, but the plating layer 64 may include a copper plating layer. The metal particles constituting the metal layer 62 may be copper particles (i.e., the metal layer 62 is formed of copper) and the plating layer 64 may include a nickel plating layer. In this way, by forming one of the metal layer 62 and the plating layer 64 containing copper and the other containing silver or nickel, the bonding strength between the metal layer 62 and the plating layer 64 can be improved.

[0050] Furthermore, according to the first embodiment, the external electrode 60 provided on the surface of the magnetic base 10 includes a metal layer 62 and a plating layer 64 provided on the metal layer 62 and partially penetrating between the metal particles of the metal layer 62 located inside and away from the surface of the metal layer 62. This can improve the bonding strength between the metal layer 62 and the plating layer 64.

[0051] In the above first embodiment, the external electrode 60 is provided only on the lower surface of the magnetic base 10, i.e., is a one-surface electrode, but the present invention is not limited to this. The external electrode 60 may be a two-surface electrode extending from the lower surface to the end surface (WT surface) of the magnetic base 10, or a five-surface electrode extending from the lower surface of the magnetic base 10 via the end surface (WT surface) and side surface (LT surface) to the upper surface.

[0052] [Second embodiment] In the first embodiment, a laminated coil component is exemplified, but in the second embodiment, a wound coil component is exemplified. FIG. 7 is a side view of a coil component 400 according to the second embodiment. As shown in FIG. 7, in the coil component 400 according to the second embodiment, the magnetic base 10a has an axis portion 80 and a pair of flange portions 82 provided at both ends of the axis portion 80. The coil conductor 30 is formed by winding a conductive wire 84 with an insulating coating around the axis portion 80. The conductive wire 84 with an insulating coating has a core wire made of, for example, copper, silver, palladium, or a silver-palladium alloy, and the peripheral surface of the core wire is covered with an insulating coating made of a resin material such as polyimide, polyamideimide, polyurethane, or polyester. The cross-sectional shape of the core wire may be circular or rectangular.

[0053] Two external electrodes 60 are provided on a surface of one of the pair of flanges 82. One of the external electrodes 60 is electrically connected to one end of the coil conductor 30, and the other of the external electrodes 60 is electrically connected to the other end of the coil conductor 30.

[0054] In the second embodiment, one external electrode 60 may be provided on each of the pair of flange portions 82. The position of the external electrode 60 is not limited to this example and can be set arbitrarily on the surface of the magnetic base 10a.

[0055] [Manufacturing method] Fig. 8 is a flowchart showing an example of a manufacturing method of the coil component 400 according to the second embodiment. As shown in Fig. 8, first, a green compact for forming the magnetic base 10a is formed (step S30). For example, a magnetic paste containing magnetic metal particles is filled into a cavity of a mold and press-formed to form a green compact having a shaft portion 80 and a pair of flange portions 82.

[0056] Next, the compact is subjected to a heat treatment for firing to form the magnetic base 10a (step S32). The heat treatment is performed at a predetermined temperature in an oxygen-containing atmosphere. This heat treatment forms an oxide film made of an oxide of the material component of the metal magnetic particles on the surface of the metal magnetic particles contained in the compact, and the multiple metal magnetic particles are bonded to each other via the oxide film.

[0057] Next, a metal layer 62 constituting the external electrode 60 is formed on the surface of the flange portion 82 of the magnetic base 10a (step S34). For example, the metal layer 62 is formed by applying a conductive paste and firing it. As a result, the metal layer 62 in which metal particles are sintered is obtained on the surface of the magnetic base 10a.

[0058] Next, the magnetic base 10a and the metal layer 62 are impregnated with resin and cured (step S36). The resin penetrates between the metal magnetic particles from the surface of the magnetic base 10a toward the inside of the magnetic base 10a. As a result, a resin film is formed on the surface of the metal magnetic particles and in some of the gaps between the particles. The resin also penetrates between the metal particles of the metal layer 62 from the surface of the metal layer 62 toward the inside of the metal layer 62. As a result, a resin film is formed on the surface of the metal particles of the metal layer 62 and in some of the gaps between the particles. Since the resin attached to the surface of the metal layer 62 blocks the electrical connection between the metal layer 62 and the plating layer 64, the resin on the surface of the metal layer 62 is removed after the resin is impregnated.

[0059] Next, the metal layer 62 is acid-treated (step S38). The acid treatment is performed using an acid solution such as a phosphoric acid solution, a hydrochloric acid solution, or a sulfuric acid solution. By setting the conditions of this acid treatment appropriately, the acid solution can penetrate into the gaps between the metal particles of the metal layer 62 where there is no resin film, and can dissolve a part of the resin film formed on the surface of the metal particles and a part of the resin film formed in a part of the gaps between the particles. In addition, by setting the conditions of the acid treatment appropriately, a part of the metal particles exposed on the surface of the metal layer 62 after the resin has been removed can be dissolved and removed, forming a recessed portion on the surface of the metal layer 62. In the recessed portion formed after the metal particles have been removed, the resin film on the surface of the metal particles of the metal layer 62 can be dissolved by the acid treatment to expose at least a part of the metal particles. Incidentally, within the metal layer 62, a portion of the resin film close to the upper surface of the metal layer 62 is dissolved by the acid treatment, but most of the resin film remains. Therefore, even when the acid treatment is performed, the metal particles located within the metal layer 62 do not dissolve but remain as they are because of the resin film surrounding them.

[0060] Next, a plating layer 64 constituting the external electrode 60 is formed on the metal layer 62 by electrolytic plating (step S40). The acid treatment performed in step S38 dissolves part of the resin film formed around the metal particles of the metal layer 62 to form passages, so that the plating solution penetrates into the interior of the metal layer 62 through the passages between the metal particles. As a result, the plating layer 64 is formed such that a part of the plating layer penetrates into the spaces between the metal particles located inside and away from the surface of the metal layer 62. The plating solution also penetrates into the depressions formed by removing the metal particles on the surface of the metal layer 62 by the acid treatment, so that the plating layer 64 also penetrates into these depressions.

[0061] Next, a conductive wire 84 with an insulating coating is wound around the shaft portion 80 of the magnetic base 10a to form the coil conductor 30 (step S42).

[0062] Next, an end of the coil conductor 30 is connected to the metal layer 62 and the plating layer 64 to form an external electrode 60 having the metal layer 62 and the plating layer 64 (step S44).

[0063] According to the second embodiment, as shown in FIG. 8, a molded body containing metal magnetic particles is formed (step S30). The molded body is heat-treated to form a magnetic base 10a (step S32). A metal layer 62 is formed on the surface of the magnetic base 10a by sintering metal particles (step S34). Resin is impregnated into the magnetic base 10a and the metal layer 62 (step S36). The metal layer 62 is acid-treated to remove a part of the resin that has entered between the metal particles from the surface to the inside of the metal layer 62 (step S38). After the metal layer 62 is acid-treated, a plating layer 64 is formed on the metal layer 62 and between the metal particles inside a part of the metal layer 62 by plating (step S40). A coil conductor 30 is wound around the magnetic base 10a (step S42). An external electrode 60 having the metal layer 62 and the plating layer 64 is formed by connecting the ends of the coil conductor 30 to the metal layer 62 and the plating layer 64 (step S44). By forming plating layer 64 on metal layer 62 using a plating method after acid treatment of metal layer 62, a plating solution permeates into passages formed by removing a portion of the resin that has penetrated between the metal particles from the surface to the inside of metal layer 62, and plating layer 64 is formed by portions of the resin penetrating between the metal particles located inside and away from the surface of metal layer 62. This makes it possible to improve the bonding strength between metal layer 62 and plating layer 64.

[0064] In the winding-type coil component shown in the second embodiment, similarly to the first embodiment of the laminated coil component, instead of the magnetic base 10a in which an oxide film made of an oxide of the material component of the metal magnetic particles is formed on the surface of the metal magnetic particles and a plurality of metal magnetic particles are bonded to each other via the oxide film, a magnetic base 10a in which a resin is provided around the metal magnetic particles may be formed. That is, in the flow chart of Fig. 8, in step S30, a compact may be formed using a mixture of metal magnetic particles having an oxide film in advance and a resin, and in step S32, the compact may be heat-treated to harden the resin, thereby forming a magnetic base 10a in which the metal magnetic particles are solidified with the resin.

[0065] In the second embodiment, the magnetic base 10a is a drum core, but it may be a T-core or may have another shape.

[0066] Although the embodiment of the present invention has been described in detail above, the present invention is not limited to such specific embodiment, and various modifications and variations are possible within the scope of the gist of the present invention described in the claims. [Explanation of symbols]

[0067] 10, 10a Magnetic substrate 11~15 Magnetic layer 16 Upper Cover Layer 17 Lower Cover Layer 20 Main body 30 Coil conductor 32 Orbital Division 34a, 34b Drawer section 60 External electrode 62 Metal layer 64 Plating layer 70 Recess 80 Shaft 82 Flange 84 Conductor 110 Magnetic substrate 160 External electrode 162 Metal layer 164 Plating layer 300, 400 Coil parts C11~C15 Circuit Pattern V1~V6, V11~V16 vias

Claims

1. forming a compact including metal magnetic particles having a pattern of a coil conductor precursor formed therein; a step of heat-treating the compact to form a magnetic substrate; forming a metal layer on a surface of the magnetic base, the metal layer being made by sintering metal particles and electrically connected to the coil conductor; impregnating the magnetic substrate and the metal layer with a resin; a step of removing a part of the resin that has entered between the metal particles from the surface to the inside of the metal layer by treating the metal layer with an acid; and after treating the metal layer with an acid, forming a plating layer on the metal layer and between the metal particles inside a portion of the metal layer using a plating method, thereby forming an external electrode having a metal layer and a plating layer.

2. forming a compact containing metal magnetic particles; a step of heat-treating the compact to form a magnetic substrate; forming a metal layer on the surface of the magnetic base by sintering metal particles; impregnating the magnetic substrate and the metal layer with a resin; a step of removing a part of the resin that has entered between the metal particles from the surface to the inside of the metal layer by treating the metal layer with an acid; a step of forming a plating layer on the metal layer and between the metal particles in a part of the metal layer by a plating method after the metal layer is subjected to an acid treatment; a step of winding a coil conductor around the magnetic base; and forming an external electrode having a metal layer and a plating layer by connecting an end of the coil conductor to the metal layer and the plating layer on the surface of the magnetic base.

3. The method for manufacturing a coil component according to claim 1 , further comprising the step of: treating the metal layer with an acid to form a recess in a surface of the metal layer from which the metal particles have been removed.

4. The method for manufacturing a coil component according to claim 3 , wherein the step of forming the recessed portion includes forming the recessed portion such that a surface of the metal particle is exposed within the recessed portion.

5. The method for manufacturing a coil component according to claim 1 , wherein the plating layer includes a copper plating layer or a nickel plating layer.

6. The method for manufacturing a coil component according to claim 1 , wherein the metal particles are silver particles or copper particles.

7. A magnetic substrate; A coil conductor provided on the magnetic base; a coil component comprising: an external electrode provided on the surface of the magnetic base and electrically connected to the coil conductor, the external electrode having a metal layer; and a plating layer provided on the metal layer, the plating layer having a portion thereof penetrating between metal particles of the metal layer located inside and away from the surface of the metal layer.

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