Inductor and method for manufacturing inductor

Abstract

The invention provides an inductor and a manufacturing method of the inductor. The adhesion strength between a Cu plating layer and a main body, wherein the Cu plating layer is formed on the surface of the main body containing metal magnetic particles as an external electrode. The inductor is provided with: a main body that contains a metal magnetic particle and a resin and that encloses a coil conductor; and an external electrode that is arranged on the surface of the main body and that contains a copper plating layer and that is connected to the coil conductor, the metal magnetic particle including an iron (Fe)-containing particle. An intermediate layer containing phosphorus (P) and oxygen (O) or sulfur (S) and oxygen (O) is provided between the surface of the main body and the copper plating layer of the external electrode.

Description

Technical Field

[0001] The present invention relates to an inductor and a method for manufacturing an inductor. Background Art

[0002] Patent Document 1 discloses an inductor including: a main body containing metal magnetic particles and resin, a coil conductor disposed within the main body, and an external electrode containing a Cu (copper) plating layer formed on the surface of the main body. The Cu plating layer is formed by electroplating, for example.

[0003] The adhesion strength between the main body and the external electrode can greatly affect the environmental resistance (e.g., resistance to temperature, humidity, vibration, shock, etc.) and long-term reliability of the inductor.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2023-72640 Summary of the Invention

[0007] An object of the present invention is to improve the adhesion strength of an external electrode on the surface of a main body in an inductor including a main body containing metal magnetic particles and resin, a coil conductor disposed within the main body, and an external electrode formed on the surface of the main body.

[0008] One aspect of the present invention is an inductor including: a main body containing metal magnetic particles and resin and enclosing a coil conductor, and an external electrode containing a copper plating layer disposed on the surface of the main body and connected to the coil conductor, wherein the metal magnetic particles include iron (Fe) particles, and an intermediate layer containing phosphorus (P) and oxygen (O) or containing sulfur (S) and oxygen (O) is provided between the surface of the main body and the copper plating layer of the external electrode.

[0009] Another aspect of the present invention is a method for manufacturing an inductor, including: a step of manufacturing a coil having a pair of lead portions, a step of burying the coil in a main body containing metal magnetic particles containing iron (Fe) and resin and exposing the lead portions of the coil from the surface of the main body, a step of forming an intermediate layer containing phosphorus (P) and oxygen (O) or containing sulfur (S) and oxygen (O) at least partially in an external electrode formation region on the surface of the main body including the lead portions exposed from the main body, and a step of forming an external electrode including a copper plating (Cu) layer in the external electrode formation region where the intermediate layer is at least partially formed.

[0010] According to the present invention, in an inductor including a main body containing metal magnetic particles and a resin, a coil conductor disposed within the main body, and an external electrode formed on the surface of the main body, the adhesion strength of the external electrode on the surface of the main body can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 FIG. 6 is a perspective view of an inductor according to an embodiment of the present invention as viewed from the upper surface side.

[0012] Figure 2 FIG. 10 is a perspective view of the inductor as viewed from the bottom surface side.

[0013] Figure 3 FIG. 14 is a perspective view showing the internal structure of the inductor.

[0014] Figure 4 FIG. 18 is a plan perspective view of the inductor shown in Figure 3 FIG. 20 as viewed from the upper surface side.

[0015] Figure 5 FIG. 24 is Figure 4 a V-V cross-sectional view of the inductor shown in

[0016] Figure 6 FIG. 30 is Figure 5 a partial detailed view of part P in the cross-section shown in

[0017] Figure 7 FIG. 36 is a diagram showing the manufacturing process of the inductor.

[0018] Figure 8 FIG. 40 is an example of a cross-sectional SEM image of an inductor for evaluating elements in the film of the intermediate layer.

[0019] Figure 9 FIG. 44 is an example of an EDX analysis image of a cross-section of an inductor for evaluating elements in the film of the intermediate layer.

[0020] SYMBOL DESCRIPTION

[0021] 1... Inductor, 2... Main body, 4... External electrode, 5... Main body protective layer, 6... Intermediate layer, 10... Bottom surface, 12... Upper surface, 14... End face, 16... Side face, 20... Coil conductor, 22... Winding portion, 24... Lead-out portion, 30... Core, 30a... Metal magnetic particle, 30b... Resin, 41... Cu plating layer, 42... Ni plating layer, 43... Sn plating layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] When a Cu plating layer constituting the external electrode is formed on the surface of a main body containing metal magnetic particles and a resin by electroplating, the adhesion strength of the Cu plating layer on the surface of the main body depends on the state of the surface of the main body at the start of the electroplating process.

[0023] The inventors have conducted in-depth research on the adhesion strength of the external electrodes on the surface of the main body, and confirmed that the replacement plating layer of Cu formed on the surface of the main body when the main body is immersed in the Cu electroplating solution is a factor that reduces the adhesion strength between the subsequently formed Cu plating layer by the electroplating process and the surface of the main body.

[0024] Such a Cu replacement plating layer can be generated within a short time (e.g., several seconds) after the main body is immersed in the Cu electroplating solution, and it is difficult to prevent it only through the design of the plating process.

[0025] Based on the above insights, the present invention is completed. From the aspect of the inductor structure, it suppresses the reduction of the adhesion strength of the Cu plating layer caused by the formation of the Cu replacement plating layer, and improves the connection strength of the external electrodes.

[0026] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

[0027] [1. Structure of Inductor]

[0028] First, the structure of the inductor 1 of the present embodiment will be described.

[0029] [1.1 Overall Structure of Inductor]

[0030] Figure 1 , Figure 2 and Figure 3 are diagrams showing the overall structure of the inductor 1.

[0031] Figure 1 is a perspective view of the inductor 1 observed from the upper surface 12 side, Figure 2 is a perspective view of the inductor 1 observed from the bottom surface 10 side.

[0032] The inductor 1 of the present embodiment is configured as a surface-mounted electronic component, and includes a main body 2 having a substantially rectangular parallelepiped shape as a form of a substantially hexahedron shape, and a pair of external electrodes 4 provided on the surface of the main body 2.

[0033] Hereinafter, in the main body 2, the first main surface facing an unillustrated mounting substrate during installation is defined as the bottom surface 10, the second main surface opposite to the bottom surface 10 is called the upper surface 12, the pair of third main surfaces orthogonal to the bottom surface 10 are called the end surfaces 14, and the pair of fourth main surfaces orthogonal to the bottom surface 10 and the pair of end surfaces 14 are called the side surfaces 16.

[0034] As Figure 1As shown, the distance from the bottom surface 10 to the upper surface 12 is defined as the thickness T of the main body 2, the distance between a pair of side surfaces 16 is defined as the width W of the main body 2, and the distance between a pair of end surfaces 14 is defined as the length L of the main body 2. In addition, the direction of the thickness T is defined as the thickness direction DT, the direction of the width W is defined as the width direction DW, and the direction of the length L is defined as the length direction DL.

[0035] The size of the inductor is, for example, the length L dimension is 2.0 mm, the width W dimension is 1.2 mm, and the thickness T dimension is 0.9 mm.

[0036] Figure 3 It is a perspective three-dimensional view showing the internal structure of the inductor.

[0037] The main body 2 includes a coil conductor 20 and a core 30 having a substantially hexahedral shape in which the coil conductor 20 is embedded, and is configured as a molded inductor in which the coil conductor 20 is encapsulated in the core 30.

[0038] The core 30 is a molded body obtained by compressing and heating a mixed powder in which metal magnetic particles 30a and a resin 30b (refer to Figure 6 ) are mixed in a state of enclosing the coil conductor 20 into a substantially hexahedral shape. The mixed powder may contain a solvent and / or a curing agent. The mixed powder may further contain additives such as a lubricant.

[0039] The metal magnetic particles 30a of the present embodiment include first magnetic particles having a relatively large average particle diameter and second magnetic particles having a relatively small average particle diameter. Thus, during compression molding, the second magnetic particles as small particles enter between the first magnetic particles as large particles together with the resin, whereby the filling rate of the metal magnetic particles 30a in the core 30 can be increased, and the magnetic permeability can also be improved.

[0040] In the present embodiment, the D50 particle diameters (median diameters) of the metal particles of the first magnetic particles and the second magnetic particles are 28 μm and 4.0 μm, respectively. It should be noted that the D50 particle diameter of the first magnetic particles is preferably 10 μm to 50 μm, and the D50 particle diameter of the second magnetic particles is preferably 1 μm to 5 μm. In addition, the magnetic particles may include particles having three or more particle sizes by including particles having an average particle diameter different from that of the first magnetic particles and the second magnetic particles.

[0041] Both the first magnetic particles and the second magnetic particles are particles having a metal particle and an insulating film covering its surface. By covering the metal particles with the insulating film, the insulation resistance and the withstand voltage can be improved.

[0042] As the metal particles of the first magnetic particles and the second magnetic particles, for example, Fe-based metal magnetic particles such as Fe (pure iron) or Fe alloys are used. As an example of the Fe alloy, one or more alloys selected from alloys containing Fe and Ni, alloys containing Fe and Co, alloys containing Fe and Si, alloys containing Fe, Si and Cr, alloys containing Fe, Si and Al, alloys containing Fe, Si, B and Cr, and alloys containing Fe, P, Cr, Si, B, Nb and C can be used.

[0043] The compositions of the metal particles of the first magnetic particles and the metal particles of the second magnetic particles may be the same or different.

[0044] The insulating film formed on the surfaces of the metal particles of the first magnetic particles and the second magnetic particles can be, for example, one or more insulating films selected from inorganic glass films, organic-inorganic hybrid films, and inorganic insulating films formed by the reaction of metal alkoxides.

[0045] In the present embodiment, Fe-Si-Cr amorphous alloy powder is used as the metal particles for the first magnetic particles, and Fe-Si-Cr amorphous alloy powder is used as the metal particles for the second magnetic particles.

[0046] In the above-mentioned mixed powder, as the resin material, at least one selected from epoxy resins, phenolic resins, polyester resins, polyimide resins, polyolefin resins, and silicone resins can be used. Among them, when an epoxy resin is used as the resin, a magnetic molded body with high electrical insulation and / or mechanical strength can be obtained. In addition to the above, as the resin material, thermoplastic resins such as polyamideimide, polyphenylene sulfide, and / or liquid crystal polymer can be used. The curing reaction is preferably a reaction caused by heat. That is, the resin is preferably a thermosetting resin. As an example, a thermosetting epoxy resin can be cited. If such a resin is used, the curing reaction can be caused by a simple method.

[0047] A solvent for mixing the metal magnetic particles 30a and the resin 30b to obtain a slurry can be added to the mixed powder. The solvent is preferably an organic solvent. For example, the solvent can be any one of aromatic hydrocarbons such as toluene or xylene; ketones such as acetone, methyl ethyl ketone, or methyl isobutyl ketone; alcohols such as methanol, ethanol, or isopropyl alcohol; and glycol ethers such as propylene glycol monomethyl ether or propylene glycol monomethyl ether acetate.

[0048] A curing agent for curing the resin can be added to the mixed powder. As an example, the curing agent can include any one of imidazole-based curing agents, amine-based curing agents, or guanidine-based curing agents (such as dicyandiamide).

[0049] In order to improve the lubricity of the first magnetic particles and the second magnetic particles and increase the filling rate, a lubricant can be added to the mixed powder. The lubricant can also be added to facilitate demolding from the mold during molding. As the lubricant, for example, any one of nano-silica, barium sulfate, or stearic acid compounds (such as lithium stearate, magnesium stearate, zinc stearate, or potassium stearate) can be included.

[0050] In addition, for the weight ratio of each raw material contained in the mixed powder, the first magnetic particles and the second magnetic particles can be 94% by weight to 98% by weight based on the overall basis, the resin and the curing agent can be 1% by weight to 5% by weight based on the overall basis, and the rest can be the lubricant and the solvent. The ratio of the first magnetic raw material particles to the second magnetic raw material particles is preferably the weight of the first magnetic raw material particles: the weight of the second magnetic raw material particles = 10:90 to 50:50. The ratio of the resin to the curing agent is preferably the weight of the resin: the weight of the curing agent = 95:5 to 98:2.

[0051] As Figure 3 shown, the coil conductor 20 includes a winding portion 22 around which a wire is wound and a pair of lead portions 24 that extend from the winding portion 22 and at least a part of which protrudes from the main body 2.

[0052] The coil conductor 20 is composed of a wire and a coating layer formed on the surface of the wire. The wire is a rectangular cross-sectioned strip-shaped wire made of copper (so-called flat angle wire).

[0053] It should be noted that the coil conductor 20 is not necessarily wound and can also be in a straight shape, a serpentine shape, etc.

[0054] The winding portion 22 of the coil conductor 20 is formed by winding the wire in a spiral shape such that both ends of the strip-shaped wire (hereinafter also simply referred to as the wire) are led out to the outer circumference and connected to each other on the inner circumference. Inside the main body 2, the coil conductor 20 is buried in the core 30 with the central axis of the winding portion 22 along the thickness direction DT of the main body 2. The lead portions 24 are respectively led out from the winding portion 22 to a pair of end faces 14, one main surface of which protrudes from the main body 2 and the other main surface is buried in the main body 2. The above-mentioned one main surface of the lead portion 24 that protrudes from the main body 2 is electrically connected to the external electrode 4.

[0055] The pair of external electrodes 4 are so-called L-shaped electrodes composed of L-shaped members that extend from the end faces 14 of the main body 2 to the bottom face 10 respectively. The external electrodes 4 are respectively connected to the lead portions 24 of the coil conductor 20 on the end faces 14, and in addition, the portions 4A ( Figure 2 ) extending to the bottom face 10 are electrically connected to the wiring of the circuit board by an appropriate mounting means such as solder.

[0056] In addition, a main body protective layer 5 as an insulating film is formed on the surface of the main body 2 outside the range of the external electrode 4 (refer toFigure 5 。 Figures 1 to 4 Although not shown. The main body protective layer 5 is, for example, an epoxy resin, a phenoxy resin, and a phenolic varnish resin, and a material containing metal oxide fine particles can be used as a filler. In the present embodiment, the main body protective layer 5 contains a filler of silica that becomes metal oxide fine particles and an epoxy resin. In addition to the above materials, the main body protective layer 5 may also be a resin such as polyurethane, acrylic, polyimide, polyimide amide, polyamide, or glass or an oxide film.

[0057] An inductor having such a configuration can improve the DC superposition characteristics by using a soft magnetic material as magnetic particles, and is therefore used as an electronic component for a circuit through which a large current flows, a choke coil for a DC-DC converter circuit or a power supply circuit, and also as an electronic component for electronic devices such as personal computers, DVD players, digital cameras, TVs, mobile phones, smartphones, automotive electronics, and medical and industrial machinery. However, the use of the inductor is not limited thereto, and for example, it can also be used for a tuning circuit, a filter circuit, a rectifying and smoothing circuit, etc.

[0058] [1.2 Structure of the boundary portion between the main body surface and the external electrode]

[0059] Next, the structure of the boundary portion between the surface of the main body 2 and the external electrode 4 will be further described.

[0060] Figure 4 is a plan perspective view of the inductor 1 as viewed from the upper surface 12 side Figure 1 and Figure 3 shown. Figure 5 is Figure 4 the V-V sectional view of the inductor 1 shown, Figure 6 is Figure 5 a partial detailed view of the P portion in the cross section shown.

[0061] Referring to Figure 6 , the external electrode 4 includes a Cu (copper) plating layer 41 as the lowermost layer closest to the main body surface. The Cu plating layer 41 is connected to the lead-out portion 24 of the coil conductor 20 exposed on the surface of the main body 2 ( Figure 6 not shown in the figure). In the present embodiment, the Cu plating layer 41 is formed by electroplating.

[0062] The external electrode 4 may further include a Ni (nickel) plating layer 42 formed on the Cu plating layer 41 and a Sn (tin) plating layer 43 formed on the Ni plating layer 42. Due to the Ni plating layer 42 and the Sn plating layer 43, the corrosion resistance and solder wettability of the external electrode 4 are improved. The Ni plating layer 42 and the Sn plating layer 43 can also be formed by electroplating.

[0063] In the present embodiment, particularly in order to prevent the formation of a Cu replacement coating on the surface of the Fe-containing metal magnetic particles exposed from the surface of the main body 2 when the main body 2 is immersed in the electroplating solution during the formation of the Cu coating 41, an intermediate layer 6 is disposed between the surface of the main body 2 and the Cu coating 41.

[0064] As described later, by configuring the intermediate layer 6 to contain phosphorus (P) and oxygen (O) or to contain sulfur (S) and oxygen (O), the formation of the Cu replacement coating can be suppressed, and the adhesion between the Cu coating 41 and the surface of the main body 2 can be improved. As described later, the intermediate layer 6 containing phosphorus (P) and oxygen (O) can be formed using pyrophosphoric acid (chemical formula: H4P2O7) which is generally used for producing a Cu electroplating solution, and the intermediate layer 6 containing sulfur (S) and oxygen (O) can be formed using ammonium sulfate (chemical formula: (NH4)2SO4) which is generally used for producing a Ni electroplating solution. That is, the intermediate layer 6 containing phosphorus (P) and oxygen (O) or containing sulfur (S) and oxygen (O) has the advantage that it can be easily produced using the agents for forming the external electrode 4.

[0065] In addition, the intermediate layer 6 may further contain potassium (K). The intermediate layer 6 containing phosphorus (P), oxygen (O) and potassium (K) can be formed using potassium pyrophosphate (chemical formula: K4O7P2) which is generally used for a Cu electroplating solution, and the intermediate layer 6 containing sulfur (S), oxygen (O) and potassium (K) can be formed using potassium sulfate (chemical formula: K2SO4) which is generally used for a Ni electroplating solution. In particular, since the intermediate layer 6 containing phosphorus (P), oxygen (O) and potassium (K) uses potassium pyrophosphate which is used for a Cu electroplating solution, the cleaning of the main body 2 between the formation process of the intermediate layer 6 and the formation process of the Cu coating 41 can be omitted, and the process can be simplified.

[0066] From the viewpoint of preventing the formation of a Cu replacement coating on the surface of the metal magnetic particles 30a exposed on the surface of the main body 2, it is sufficient that the intermediate layer 6 is disposed at least between the metal magnetic particles 30a and the Cu coating 41, and it is not necessarily required to be formed on the resin 30b of the core 30 constituting the main body 2. By disposing the intermediate layer 6 between the metal magnetic particles 30a and the Cu coating 41, it is possible to more effectively prevent the decrease in the adhesion strength between the Cu coating 41 and the main body 2 caused by the Fe-Cu replacement reaction during the formation process of the Cu coating 41, and to improve the connection strength between the external electrode 4 and the main body 2.

[0067] In addition, no intermediate layer 6 is disposed between the main body 2 and the main body protective layer 5 covering the surface of the main body 2. Thereby, it is possible to prevent an adverse effect on the adhesion strength between the main body 2 and the main body protective layer 5 that may occur when the intermediate layer 6 exists between the surface of the main body 2 and the main body protective layer 5.

[0068] The thickness of the intermediate layer 6 may also be non-uniform along the surface of the main body 2. This is because even if the thickness of the intermediate layer 6 is non-uniform, if it is located on the surface of the metal magnetic particles 30a, it can prevent the formation of a Cu replacement plating layer on this surface. In addition, since it is not necessary to form the intermediate layer 6 to have a uniform thickness along the surface of the main body 2, the intermediate layer 6 can be easily formed.

[0069] In addition, the intermediate layer 6 does not need to be formed continuously along the surface of the main body 2. As Figure 6 shown, it may also be discontinuous along the surface of the main body 2. Even if the intermediate layer 6 is formed discontinuously, it can prevent the formation of a Cu replacement plating layer in the region covering the surface of the metal magnetic particles 30a, and thus can prevent the reduction of the adhesion force of the entire Cu plating layer 41 to the surface of the main body 2. In addition, since it is not necessary to form the intermediate layer 6 continuously along the surface of the main body 2, the intermediate layer 6 can be easily formed.

[0070] The average thickness of the intermediate layer 6 in the region where the Cu plating layer 41 is formed is preferably 0.01 μm to 50 μm, and more preferably 0.5 μm to 20 μm. This is because if the intermediate layer 6 is too thin, the effect of preventing the formation of the Cu replacement plating layer is reduced, and if it is too thick, in order to control the external dimensions of the inductor 1 within the allowable range, it may be necessary to reduce the external dimensions of the main body 2 at the expense of electrical characteristics.

[0071] In addition, the surface roughness represented by the arithmetic mean roughness Ra in the region of the surface of the main body 2 where the Cu plating layer 41 is formed is preferably 1.0 μm to 10 μm. Thus, through the anchoring effect generated by the unevenness of the surface of the main body 2, the adhesion force between the intermediate layer 6 and the surface of the main body 2, or the adhesion force between the intermediate layer 6 and the Cu plating layer 41 and the surface of the main body 2 can be further improved, and the adhesion strength between the external electrode 4 and the surface of the main body 2 can be further improved.

[0072] In addition, the resistivity (e.g., volume resistivity) of the intermediate layer 6 can be within any numerical range of a conductor or an insulator, and does not necessarily need to be constant along the surface of the main body 2.

[0073] [2. Manufacturing process of the inductor]

[0074] The inductor 1 can be manufactured as follows.

[0075] Figure 7 is a diagram showing the manufacturing process of the inductor 1.

[0076] The manufacturing process of the inductor 1 may include a coil conductor forming process (S1), a preform forming process (S2), a main body forming process (S3), a barrel polishing process (S4), a surface treatment process (S5), an intermediate layer forming process (S6), and an external electrode forming process (S7).

[0077] The coil conductor forming step (S1) is a step of forming a coil conductor 20 from a wire. In this step, the coil conductor 20 is formed into a shape having the above-described winding portion 22 and a pair of lead portions 24 by winding the wire by a winding method called "alpha winding". Alpha winding means spiral two-stage winding in such a manner that the lead portions 24 where the winding of the wire that functions as a conductor starts and ends are located on the outer periphery. The number of turns of the coil conductor 20 is not particularly limited.

[0078] The preform forming step (S2) is a step of forming a preform called a flat plate.

[0079] The preform is obtained by pressing the above-described mixed powder that is the material of the main body 2 into an easily handleable solid shape. In the present embodiment, two flat plates are formed, namely, a first flat plate having an appropriate shape (such as an E shape, etc.) of a groove for the coil conductor 20 to enter and a second flat plate having an appropriate shape (such as an I shape, plate shape, etc.) covering the groove of the first flat plate.

[0080] In the main body forming step (S3), the first flat plate, the coil conductor, and the second flat plate are set in a molding die, and while heating, they are pressed in the overlapping direction of the first flat plate and the second flat plate to cure them, thereby integrating the first flat plate, the coil conductor, and the second flat plate. Thus, the main body 2 in which the coil conductor 20 is enclosed in the core 30 is molded.

[0081] In the drum grinding step (S4), a plurality of main bodies 2 are filled in a drum, and the drum is rotated in such a manner that an excessive impact is not applied. In addition, a coating liquid that becomes the main body protective layer 5 is sprayed with a sprayer. Thus, rounding of the corners of the main body 2 and coating of the coating liquid on the main body 2 are performed. In the present embodiment, the coating liquid contains a filler of silica that becomes metal oxide fine particles and an epoxy resin that becomes an organic resin.

[0082] Next, by taking out the main body 2 coated with the coating liquid from the drum and performing heat treatment, the main body protective layer 5 is formed on the surface of the main body 2.

[0083] It should be noted that the formation of the main body protective layer 5 is not limited to the above, and it can be set as a step separate from the drum grinding step (S4), and can be performed by various methods such as spraying the coating liquid onto the main body 2, immersing the main body 2 in the coating liquid, supplying the coating liquid to the surface of the main body 2 through a dispenser, and / or printing a coating material onto the surface of the main body 2 using various printing methods.

[0084] The surface treatment process (S5) is a process of modifying the surface of the predetermined electrode portion of the core 30 by irradiating the laser on the predetermined electrode portion of the surface of the core 30. Here, the predetermined electrode portion refers to the range on the surface of the core 30 where the external electrode 4 is to be formed, including the exposed portion of the lead-out portion 24. Specifically, by irradiating the laser, the main protective layer 5 on the surface of the core 30 and the coating layer of the lead-out portion 24 of the coil conductor 20 are removed within the range of the predetermined electrode portion, and the resin 30b on the surface of the core 30 is removed and the insulating film on the surface of the metal magnetic particles 30a exposed from the core 30 is removed. As a result, compared with other surface portions of the core 30, the exposed area of the metal of the metal magnetic particles 30a per unit area of the surface of the core 30 is increased in the portion of the predetermined electrode portion on the surface of the core 30.

[0085] The wavelength of the laser is, for example, 180 nm to 3000 nm, more preferably 532 nm to 1064 nm. In addition, the irradiation energy of the laser is preferably 1 W / mm 2 ~30 W / mm 2 ,more preferably 5 W / mm 2 ~12 W / mm 2 。

[0086] In the intermediate layer formation process (S6), the main body 2 is immersed in the treatment liquid, and the intermediate layer 6 is formed on the predetermined electrode portion of the core 30 of the main body 2. For example, when forming a layer containing phosphorus (P) and oxygen (O) as the intermediate layer 6, a solution containing polyphosphoric acid can be used as the treatment liquid. In addition, when forming a layer containing sulfur (S) and oxygen (O) as the intermediate layer 6, for example, a solution containing sulfate ions can be used as the treatment liquid.

[0087] More specifically, as the treatment liquid containing polyphosphoric acid, for example, an aqueous solution of pyrophosphoric acid or potassium pyrophosphate can be used. In addition, as the treatment liquid containing sulfate ions, for example, an aqueous solution of ammonium sulfate or potassium sulfate can be used.

[0088] As described above, in the case of using an aqueous solution containing potassium pyrophosphate or potassium sulfate, as the intermediate layer 6, a layer containing potassium (K) can also be formed.

[0089] The thickness of the intermediate layer 6 can be controlled by adjusting the concentration, temperature of the treatment liquid and / or the immersion time of the main body 2 in the treatment liquid.

[0090] In the external electrode formation process (S7), the external electrode 4 is formed on the predetermined electrode portion of the core 30 on which the intermediate layer 6 is formed. Specifically, first, a Cu plating layer 41 is formed on the predetermined electrode portion of the core 30 on which the intermediate layer 6 is formed by electroplating. Then, an Ni plating layer 42 and an Sn plating layer 43 can be formed on the Cu plating layer 41 by electroplating.

[0091] For example, when forming the Cu plating layer 41, copper sulfate plating, pyrophosphate copper plating, or copper cyanide plating can be used as electroplating copper.

[0092] When forming the Ni plating layer 42 and the Sn plating layer 43, additives such as brightening materials can be added to the plating solution.

[0093] [3. Examples]

[0094] Next, examples of the inductor 1 will be described.

[0095] Examples and comparative examples shown in Table 1 were fabricated, and the adhesion strength of the external electrode 4 to the main body 2 was evaluated. Examples 1 to 6 were fabricated under the same fabrication conditions through the Figure 7 manufacturing processes shown above, but the fabrication conditions of the intermediate layer 6 in the intermediate layer formation process (S6) were different from each other. The comparative example is a sample without the intermediate layer 6 and was fabricated under the same fabrication conditions as Examples 1 to 6 except that the intermediate layer formation process was not performed. In Examples 1 to 6 and the comparative example, 30 pieces were fabricated each.

[0096] [Table 1]

[0097]

[0098] [3.1 Fabrication of Examples and Comparative Examples]

[0099] <Fabrication of the Main Body>

[0100] In Examples 1 to 6 and the comparative example, the composition of the mixed powder in the preform formation process (S2) was as follows.

[0101] Metal magnetic particles 30a:

[0102] First magnetic particles: D50 particle size 28 μm

[0103] Fe-6.7Si-2.5Cr amorphous alloy

[0104] (Fe: Si: Cr = 90.8: 6.7: 2.5 (weight ratio))

[0105] Second magnetic particles: D50 particle size 4.0 μm

[0106] Fe-6.7Si-2.5Cr amorphous alloy

[0107] (Fe: Si: Cr = 90.8: 6.7: 2.5 (weight ratio))

[0108] Resin 30b: Thermosetting epoxy resin

[0109] Curing agent: Imidazole

[0110] Lubricant: Nano-silica (diameter 50nmφ), particle shape

[0111] The weight ratio of the first magnetic particles and the second magnetic particles in the mixed powder is 96.0% by weight based on the total amount of the mixed powder, the weight ratio of the resin and the curing agent is 3.6% by weight based on the total amount of the mixed powder, and the lubricant is 0.4% by weight based on the total amount of the mixed powder.

[0112] The compression molding conditions of the main body 2 in the main body molding process (S3) are a temperature of 180°C, a pressure of 20 Mpa, and a compression time of 600 seconds. In the core 30 of the molded main body 2, the weight ratio of the first magnetic particles: the weight ratio of the second magnetic particles = 25:75, and the weight ratio of the resin: the weight ratio of the curing agent = 97.4:2.6.

[0113] After forming the main body protective layer 5 on the surface of the main body 2 through the drum grinding process (S4), in the surface treatment process (S5), laser irradiation is performed on the electrode predetermined part of the exposed part including the lead-out part 24 of the coil conductor 20 on the surface of the main body 2. The irradiation energy of the laser is 12 W / mm 2 。

[0114] <Formation of the intermediate layer>

[0115] In Examples 1 to 6, the intermediate layer 6 is formed through the intermediate layer forming process (S6).

[0116] The types of the treatment liquids, the treatment liquid temperatures, and the immersion times of the main body 2 in the treatment liquids in Examples 1 to 6 are shown in Table 1.

[0117] <Formation of the external electrode>

[0118] For Examples 1 to 6 and the comparative example, the external electrode 4 is formed through the above external electrode forming process (S7). First, the main body 2 is put into a Cu plating bath (pyrophosphate copper plating solution), and a Cu plating layer 41 is formed by electroplating. The average thickness of the Cu plating layer 41 along the surface of the main body 2 is 30 μm. Then, the main body 2 is taken out of the Cu plating bath and washed with water, and then put into a Ni plating bath (Watts bath), and a Ni plating layer 42 is formed by electroplating. The average thickness of the Ni plating layer 42 along the surface of the main body 2 is 5 μm. Then, the main body 2 is taken out of the Ni plating bath and washed with water, and then further put into a Sn plating bath (neutral bath), and a semi-glossy Sn plating layer 43 is formed by electroplating. The average thickness of the Sn plating layer 43 along the surface of the main body 2 is 5 μm.

[0119] [3.2 Evaluation]

[0120] The average film thickness of the formed intermediate layer 6 and the analysis of the elements in the film of the intermediate layer 6 were measured for the fabricated Examples 1 to 6. The adhesion test of the external electrode 4 was performed for Examples 1 to 6 and Comparative Examples.

[0121] [3.2.1 Evaluation Method]

[0122] The evaluation was carried out by the following method.

[0123] <Measurement of Average Film Thickness and Analysis of Elements in the Film>

[0124] First, for Examples 1 to 6, the main body 2 was polished along the DW direction (refer to Figure 1 ) to obtain a cross-section (hereinafter referred to as the LT cross-section) including the DT direction and the DL direction along the center line in the DW direction. Next, the thickness of the intermediate layer 6 was measured at any five points within the range where the intermediate layer 6 was formed in the obtained LT cross-section, and the average value of these measured values was taken as the average film thickness of the intermediate layer 6.

[0125] Then, in the above LT cross-section, SEM-EDX analysis was performed on the region including the boundary portion between the external electrode 4 and the main body 2 to analyze the elements in the film of the intermediate layer 6.

[0126] Figure 8 is an example of an LT cross-section SEM (scanning electron microscope) image of the inductor 1 for evaluating the elements in the film of the intermediate layer 6 of Example 3. Figure 8 The image shows the main body 2 including the coil conductor 20 and the core 30, and the external electrodes 4 formed on the left and right end faces 14 of the main body 2. Figure 9 is an example of an SEM (scanning electron microscope) image and an EDX analysis image of the region including the boundary portion between the external electrode 4 and the main body 2 in the LT cross-section of the main body 2 for evaluating the elements in the film. Specifically, Figure 9 is in Figure 8 an SEM magnified image and an EDX image of the Q portion shown by the dotted rectangle in the SEM image.

[0127] Figure 9 In, (A) is an SEM image of the Q portion. In addition, Figure 9 (B) of is an image of characteristic X-rays indicating the presence of the element Cu (copper) observed during the EDX analysis of the Q portion. The bright spots indicating the presence of the element Cu are concentrated in the region corresponding to the Cu plating 41, and this region is brightly displayed. Figure 9 (C), (D), and (E) of are images of characteristic X-rays indicating the presence of the elements O (oxygen), P (phosphorus), and K (potassium) observed during the EDX analysis of the Q portion. In Figure 9In the images of (C), (D), and (E), bright spots indicating the presence of elements O (oxygen), P (phosphorus), and K (potassium) can be seen at the boundary between the Cu plating layer 41 and the main body 2. From this, it can be known that an intermediate layer 6 containing O (oxygen), P (phosphorus), and K (potassium) as elements in the film is formed at the boundary between the Cu plating layer 41 and the main body 2.

[0128] In addition, the groups of bright spots indicating the presence of elements O (oxygen), P (phosphorus), and K (potassium) are discontinuous along the surface of the main body 2, and the shape formed by the outer edge of the group of bright spots is not rectangular. Therefore, it can be known that the intermediate layer 6 is formed discontinuously along the surface of the main body 2, and its thickness is uneven along the surface of the main body 2.

[0129] It should be noted that the characteristic X-ray image of the elements not included in the intermediate layer 6 shows a black image without bright spots. For example, in the EDX analysis of the intermediate layer 6 in Example 1, the characteristic X-ray image corresponding to Figure 9 K (potassium) of (E) becomes a black image without bright spots.

[0130] <Evaluation of the adhesion force of the external electrode>

[0131] According to the adhesion (shear strength) test described in AEC (Automotive Electronics Council, In-vehicle Electronics Component Council) standard AEC-Q200 Rev E for the reliability of in-vehicle passive components, the adhesion force of the external electrode 4 to the main body 2 was evaluated. Specifically, after soldering the external electrodes 4 of the inductors 1 of Examples 1 to 6 and the comparative example to the test substrate (FR-4) by reflow soldering, a thrust of 17.7 N was applied vertically to the side of each inductor 1 for 60 seconds, and it was evaluated whether the inductor 1 peeled off from the test substrate.

[0132] [3.2.2 Evaluation results]

[0133] The evaluation results are shown in Table 2.

[0134] [Table 2]

[0135]

[0136] As shown in Table 2, in the comparative example without the intermediate layer 6, in the adhesion test, peeling of the external electrode 4 was observed for 5 out of 30 samples. In contrast, in Examples 1 to 6 with the intermediate layer 6, peeling of the external electrode 4 was not observed in all 30 inductors 1. Thus, it was confirmed that the intermediate layer 6 containing phosphorus and oxygen or sulfur and oxygen as elements in the film has the effect of improving the adhesion strength between the Cu plating layer 41 of the external electrode 4 and the main body 2.

[0137] In addition, from the comparison between Examples 3 to 6 and Examples 1 and 2, it can be seen that even when K is also contained as an element in the film in the intermediate layer 6, the effect of improving the adhesion strength of the Cu plating layer 41 to the main body 2 is obtained in the same manner as in the case where K is not contained.

[0138] Furthermore, from the comparison between Examples 3, 5, and 6, it can be seen that the longer the immersion time of the main body 2 in the treatment liquid in the intermediate layer forming step (S6), the thicker the intermediate layer 6 formed, and the intermediate layer 6 can exhibit the effect of improving the adhesion strength of the Cu plating layer 41 at least within the range where the average thickness is 20 μm or less.

[0139] [4. Other Embodiments]

[0140] In the above embodiment, the core 30 contains two kinds of magnetic particles having different average particle diameters as the metal magnetic particles 30a, but it may be composed of one kind of magnetic particle.

[0141] In addition, in the above embodiment, the Cu plating layer 41 is formed by electroplating, but it may also be formed by electroless copper plating.

[0142] It should be noted that all of the above embodiments and examples illustrate one mode of the present invention, and can be arbitrarily deformed and applied within the scope not departing from the gist of the present invention.

[0143] In addition, unless otherwise specified, the horizontal and vertical directions, various numerical values, shapes, and materials in the above embodiments include ranges (so-called equivalent ranges) that have the same effects as these directions, numerical values, shapes, and materials.

[0144] [5. Configurations Supported by the Above Embodiments and Examples]

[0145] The above embodiments and examples support the following configurations.

[0146] (Configuration 1) An inductor, comprising: a main body containing metal magnetic particles and resin and enclosing a coil conductor, and an external electrode disposed on the surface of the main body and connected to the coil conductor and including a Cu plating layer, the metal magnetic particles containing iron (Fe) particles, and having an intermediate layer containing phosphorus (P) and oxygen (O) or containing sulfur (S) and oxygen (O) between the surface of the main body and the Cu plating layer of the external electrode.

[0147] According to the inductor of Configuration 1, it is possible to effectively prevent a decrease in the adhesion strength between the Cu plating layer and the main body caused by a displacement reaction between copper in the plating solution and iron (Fe) of the metal magnetic particles on the surface of the main body when the main body is immersed in the plating solution during the formation process of the Cu plating layer, and improve the connection strength between the external electrode including the Cu plating layer and the main body.

[0148] (Configuration 2) The inductor according to Configuration 1, wherein the intermediate layer is disposed at least between the metal magnetic particles and the copper plating layer.

[0149] The inductor according to Configuration 2 can more effectively prevent the reduction of the adhesion strength between the copper plating layer and the main body caused by the Fe-Cu displacement reaction in the copper plating layer formation process, and improve the connection strength between the external electrode and the main body.

[0150] (Configuration 3) The inductor according to Configuration 1 or 2, wherein a main body protective layer as an insulating film is disposed in a region of the surface of the main body other than the region where the external electrode is formed.

[0151] The inductor according to Configuration 3 can prevent the formation of an unnecessary copper plating layer in the region of the main body surface where the external electrode is not formed.

[0152] (Configuration 4) The inductor according to Configuration 3, wherein the intermediate layer is not disposed between the main body and the main body protective layer.

[0153] The inductor according to Configuration 4 can prevent the adverse effect on the adhesion strength between the main body and the main body protective layer that may occur when an intermediate layer exists between the main body surface and the main body protective layer.

[0154] (Configuration 5) The inductor according to any one of Configurations 1 to 4, wherein the external electrode has a nickel (Ni) plating layer and a tin (Sn) plating layer on the copper plating layer formed on the surface of the main body via the intermediate layer.

[0155] The inductor according to Configuration 5 can form an external electrode with improved adhesion strength between the external electrode and the main body and excellent corrosion resistance and solder wettability.

[0156] (Configuration 6) The inductor according to any one of Configurations 1 to 5, wherein the intermediate layer further contains potassium (K).

[0157] For the inductor according to Configuration 6, a chemical agent containing the same components as the copper plating solution containing potassium that can usually be used in the copper plating layer formation process can be used to form the intermediate layer. Therefore, for the inductor according to Configuration 6, the cleaning process between the intermediate layer formation process (S6) and the subsequent copper plating layer formation process can be omitted (without introducing new chemical agent components), and the external electrode can be easily formed.

[0158] (Configuration 7) The inductor according to any one of Configurations 1 to 6, wherein the thickness of the intermediate layer is non-uniform along the surface of the main body.

[0159] According to the inductor of Configuration 7, it is not necessary to form the intermediate layer to have a uniform thickness along the surface of the main body. Therefore, according to the inductor of Configuration 7, the intermediate layer can be easily formed.

[0160] (Configuration 8) According to the inductor described in any one of Configurations 1 to 7, wherein the intermediate layer is discontinuous along the surface of the main body.

[0161] According to the inductor of Configuration 8, it is not necessary to continuously form the intermediate layer along the surface of the main body. Therefore, according to the inductor of Configuration 8, the intermediate layer can be easily formed.

[0162] (Configuration 9) According to the inductor described in any one of Configurations 1 to 8, wherein the surface roughness represented by the arithmetic mean roughness Ra of the surface of the main body is 1.0 μm to 10 μm.

[0163] According to the inductor of Configuration 9, through the anchoring effect generated by the unevenness of the surface of the main body, the adhesion between the intermediate layer and the surface of the main body, or the adhesion between the intermediate layer and the copper plating layer and the surface of the main body can be further improved, and the connection strength between the external electrode and the surface of the main body can be further improved.

[0164] (Configuration 10) According to the inductor described in any one of Configurations 1 to 9, wherein the average thickness of the intermediate layer is 20 μm or less.

[0165] According to the inductor of Configuration 10, within the allowable range of the overall required external dimensions of the inductor, it is possible to avoid unnecessarily restricting the volume of the main body due to the presence of the intermediate layer (therefore, it is possible to avoid unnecessarily restricting the electrical characteristics of the inductor), and it is possible to improve the connection strength between the external electrode and the surface of the main body.

[0166] (Configuration 11) A method for manufacturing an inductor, comprising: a step of manufacturing a coil having a pair of lead-out portions, a step of embedding the coil in a main body containing iron (Fe) metal magnetic particles and resin such that the lead-out portions of the coil are exposed from the surface of the main body, a step of forming an intermediate layer containing phosphorus (P) and oxygen (O) or containing sulfur (S) and oxygen (O) at least partially in an external electrode formation region on the surface of the main body including the lead-out portions exposed from the main body, and a step of forming an external electrode including a copper plating (Cu) layer in the external electrode formation region where the intermediate layer is at least partially formed.

[0167] According to the method for manufacturing an inductor of Configuration 11, an inductor can be manufactured that can effectively prevent a decrease in the adhesion strength between the copper plating layer and the main body caused by a displacement reaction between copper in the plating solution and iron (Fe) of the metal magnetic particles on the surface of the main body when the main body is immersed in the plating solution during the copper plating layer formation process, and can improve the connection strength between the external electrode including the copper plating layer and the main body.

Claims

1. An inductor includes a main body and external electrodes, wherein the main body contains metal magnetic particles and resin and encloses a coil conductor, the external electrodes are disposed on the surface of the main body and connected to the coil conductor, and include a copper plating layer; Among them, the metal magnetic particles include particles containing iron (Fe), a middle layer is provided between the surface of the main body and the copper plating layer of the external electrode, and the middle layer contains phosphorus (P) and oxygen (O) or contains sulfur (S) and oxygen (O).

2. The inductor according to claim 1, wherein, The middle layer is disposed at least between the metal magnetic particles and the copper plating layer.

3. The inductor according to claim 1, wherein, A main body protective layer serving as an insulating film is disposed in a region of the surface of the main body other than the region where the external electrodes are formed.

4. The inductor according to claim 3, wherein, The middle layer is not disposed between the main body and the main body protective layer.

5. The inductor according to claim 1, wherein, The external electrode has a nickel (Ni) plating layer and a tin (Sn) plating layer on the copper plating layer formed on the surface of the main body via the middle layer.

6. The inductor according to claim 1, wherein, The middle layer further contains potassium (K).

7. The inductor according to claim 1, wherein, The thickness of the middle layer is non-uniform along the surface of the main body.

8. The inductor according to claim 1, wherein, The middle layer is discontinuous along the surface of the main body.

9. The inductor according to claim 1, wherein, The surface roughness of the surface of the main body represented by the arithmetic mean roughness Ra is 1.0 μm to 10 μm.

10. The inductor according to any one of claims 1 to 9, wherein, The average thickness of the middle layer is 20 μm or less.

11. A method for manufacturing an inductor, comprising: a step of fabricating a coil having a pair of lead portions, a step of embedding the coil in a main body containing iron (Fe) metal magnetic particles and resin and exposing the lead portions of the coil from the surface of the main body, a step of at least partially forming a middle layer containing phosphorus (P) and oxygen (O) or containing sulfur (S) and oxygen (O) in an external electrode formation region on the surface of the main body including the lead portions exposed from the main body, and a step of forming an external electrode including a copper (Cu) plating layer in the external electrode formation region where the middle layer is at least partially formed.

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