Inductor and method for manufacturing the same

Abstract

To improve fixing strength of a Cu plating layer formed as an external electrode on a surface of an element body containing metal magnetic particles relative to the element body.SOLUTION: An inductor includes: an element body containing metal magnetic particles and resin and enclosing a coil conductor; and an external electrode disposed on a surface of the element body, connected to the coil conductor, and including a copper plating layer. The metal magnetic particles include particles containing iron (Fe). An intermediate layer is provided containing phosphorus (P) and oxygen (O) or containing sulfur (S) and oxygen (O) between a surface of the element body and the copper plating layer of the external electrode.SELECTED DRAWING: Figure 6

Description

Technical Field

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

Background Art

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

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to improve the adhesion strength of an external electrode on the surface of a base body in an inductor including a base body containing metal magnetic particles and a resin, a coil conductor disposed in the base body, and an external electrode formed on the surface of the base body.

Means for Solving the Problems

[0006] One aspect of the present invention includes a base body containing metal magnetic particles and a resin and enclosing a coil conductor, and an external electrode including a copper plating layer disposed on the surface of the base body and connected to the coil conductor. The metal magnetic particles include particles containing iron (Fe), and there is an intermediate layer containing phosphorus (P) and oxygen (O) or containing sulfur (S) and oxygen (O) between the surface of the base body and the copper plating layer of the external electrode. It is an inductor. Another aspect of the present invention includes a step of manufacturing a coil having a pair of lead-out portions, a step of embedding the coil in a base body containing metal magnetic particles containing iron (Fe) and a resin so that the lead-out portions of the coil are exposed from the surface of the base body, a step of at least partially forming an intermediate 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 base body including the lead-out portions exposed from the base body, and a step of forming an external electrode including a copper (Cu) plating layer in the external electrode formation region where the intermediate layer is at least partially formed. It is a method for manufacturing an inductor.

Advantages of the Invention

[0007] According to the present invention, in an inductor including a base body containing metal magnetic particles and a resin, a coil conductor disposed in the base body, and an external electrode formed on the surface of the base body, the adhesion strength of the external electrode on the surface of the base body can be improved.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

[0009] When forming a Cu plating layer constituting an external electrode by electroplating on the surface of a base body containing metal magnetic particles and resin, the adhesion strength of the Cu plating layer on the surface of the base body depends on the state of the surface of the base body when the electrolytic plating process is started.

[0010] The inventor has intensively studied the adhesion strength of the external electrode on the surface of the base body, and confirmed that the Cu replacement plating layer formed on the surface of the base body when the base body is immersed in a Cu electrolytic plating solution is one of the factors that reduce the adhesion strength of the Cu plating layer formed by the subsequent electrolytic plating process to the surface of the base body.

[0011] Such a Cu replacement plating layer can occur in a short time (for example, several seconds) after the base body is immersed in a Cu electrolytic plating solution, and it is difficult to prevent it only by devising the plating process. The present invention is made based on the above findings, and suppresses a decrease in the adhesion strength of the Cu electrolytic plating layer associated with the formation of the Cu replacement plating layer from the side of the inductor configuration, and improves the connection strength of the external electrode.

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings. [1. Configuration of Inductor] First, the configuration of the inductor 1 according to the present embodiment will be described. [1.1 Overall Configuration of Inductor] FIG. 1, FIG. 2, and FIG. 3 are diagrams showing the overall configuration of the inductor 1. FIG. 1 is a perspective view of the inductor 1 viewed from the side of the upper surface 12, and FIG. 2 is a perspective view of the inductor 1 viewed from the side of the bottom surface 10. The inductor 1 of the present embodiment is configured as a surface-mount type electronic component, and includes a substantially rectangular parallelepiped-shaped element body 2, which is a form of a substantially hexahedron shape, and a pair of external electrodes 4 provided on the surface of the element body 2.

[0013] Hereinafter, in the element body 2, the first main surface facing the mounting substrate (not shown) during mounting is defined as the bottom surface 10, the second main surface facing the bottom surface 10 is referred to as the upper surface 12, a pair of third main surfaces orthogonal to the bottom surface 10 are referred to as end surfaces 14, and a pair of fourth main surfaces orthogonal to the bottom surface 10 and the pair of end surfaces 14 are referred to as side surfaces 16. As shown in FIG. 1, the distance from the bottom surface 10 to the upper surface 12 is defined as the thickness T of the element body 2, the distance between the pair of side surfaces 16 is defined as the width W of the element body 2, and the distance between the pair of end surfaces 14 is defined as the length L of the element body 2. Also, 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 distance is defined as the length direction DL. The size of the inductor is, for example, a length L dimension of 2.0 mm, a width W dimension of 1.2 mm, and a thickness T dimension of 0.9 mm.

[0014] FIG. 3 is a perspective view showing the internal configuration of the inductor. The element body 2 includes a coil conductor 20 and a substantially hexahedron-shaped core 30 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.

[0015] The core 30 is a molded body obtained by compression molding a mixed powder of metal magnetic particles 30a and resin 30b (see FIG. 6) into a substantially hexahedron shape by pressurizing and heating in a state where the coil conductor 20 is enclosed. The mixed powder may contain a solvent and / or a curing agent. The mixed powder may further contain additives such as a lubricant.

[0016] The metal magnetic particles 30a of the present embodiment include two types of particles: first magnetic particles with relatively large average particle diameters, which are large particles, and second magnetic particles with relatively small average particle diameters, which are small particles. As a result, during compression molding, the second magnetic particles, which are small particles, enter between the first magnetic particles, which are large particles, together with the resin, thereby increasing the filling rate of the metal magnetic particles 30a in the core 30 and also increasing the magnetic permeability.

[0017] 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. Note that the D50 particle diameter of the first magnetic particles is preferably 10 μm or more and 50 μm or less, and the D50 particle diameter of the second magnetic particles is preferably 1 μm or more and 5 μm or less. Further, since the magnetic particles include particles with different average particle diameters from the first magnetic particles and the second magnetic particles, they may include particles of three or more particle sizes.

[0018] Both the first magnetic particles and the second magnetic particles are particles having metal particles and an insulating film covering the surface thereof. By covering the metal particles with the insulating film, the insulation resistance and the withstand voltage are increased.

[0019] For 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 the group consisting of 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.

[0020] The composition of the metal particles of the first magnetic particles and the composition of the metal particles of the second magnetic particles may be the same or different from each other. The insulating film formed on the surface of the metal particles of the first magnetic particles and the second magnetic particles can be one or more insulating films selected from the group consisting of, for example, an inorganic glass film, an organic-inorganic hybrid film, and an inorganic insulating film formed by a sol-gel reaction of a metal alkoxide.

[0021] In this 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.

[0022] In the above mixed powder, at least one selected from the group consisting of an epoxy resin, a phenol resin, a polyester resin, a polyimide resin, a polyolefin resin, and a silicone resin can be used as the resin material. 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, a thermoplastic resin such as a polyamideimide, a polyphenylene sulfide, and / or a liquid crystal polymer may be used as the resin material. The curing reaction is preferably by heat. That is, the resin is preferably a thermosetting resin. As an example, a thermosetting epoxy resin can be mentioned. By using such a resin, the curing reaction can be caused by a simple method.

[0023] 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 may contain any 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.

[0024] A curing agent for curing the resin may be added to the mixed powder. As an example, the curing agent may include any one of an imidazole-based curing agent, an amine-based curing agent, or a guanidine-based curing agent (for example, dicyandiamide).

[0025] A lubricant may be added to the mixed powder to improve the lubricity of the first magnetic particles and the second magnetic particles and to improve the filling rate. The lubricant can also be added for the purpose of facilitating the release from the mold during molding. As the lubricant, for example, it may include any one of nanosilica, barium sulfate, or a stearic acid compound (such as lithium stearate, magnesium stearate, zinc stearate, or potassium stearate).

[0026] Also, the weight ratio of each raw material contained in the mixed powder is as follows: the first magnetic particles and the second magnetic particles are 94% by weight or more and 98% by weight or less based on the total; the resin and the curing agent are 1% by weight or more and 5% by weight or less based on the total, and the balance may be a lubricant and a solvent. The ratio of the first magnetic raw material particles and the second magnetic raw material particles is preferably such that the weight of the first magnetic raw material particles: the weight of the second magnetic raw material particles = 10:90 or more and 50:50 or less. The ratio of the resin to the curing agent is preferably such that the weight of the resin: the weight of the curing agent = 95:5 or more and 98:2 or less.

[0027] As shown in FIG. 3, the coil conductor 20 includes a winding portion 22 around which a conducting wire is wound, and a pair of lead portions 24 drawn out from the winding portion 22 and at least a part of which is exposed from the base body 2. The coil conductor 20 is composed of a conducting wire and a coating layer formed on the surface of the conducting wire. The conducting wire is a strip-shaped conducting wire (so-called flat wire) having a rectangular cross-section made of copper. Note that the coil conductor 20 does not necessarily have to be wound, and may have a linear shape, a meander shape, or the like.

[0028] The winding portion 22 of the coil conductor 20 is formed by winding a strip-shaped conductor (hereinafter also simply referred to as a conductor) in a spiral shape such that both ends of the conductor are drawn out to the outer periphery and are connected to each other at the inner periphery. Inside the base body 2, the coil conductor 20 is embedded in the core 30 in a posture where the central axis of the winding portion 22 is along the thickness direction DT of the base body 2. The lead-out portion 24 is drawn out from the winding portion 22 to each of the pair of end faces 14, one main surface thereof is exposed from the base body 2, and the other main surface is embedded in the base body 2. The one main surface of the lead-out portion 24 that is exposed from the base body 2 is electrically connected to the external electrode 4.

[0029] The pair of external electrodes 4 are so-called L-shaped electrodes each constituted by an L-shaped member extending from each of the end faces 14 of the base body 2 across the bottom face 10. Each of the external electrodes 4 is connected to the lead-out portion 24 of the coil conductor 20 at the end face 14, and the portion 4A (FIG. 2) extending to the bottom face 10 is electrically connected to the wiring of the circuit board by an appropriate mounting means such as soldering.

[0030] Also, a base body protective layer 5 which is an insulating film (see FIG. 5. Not shown in FIGS. 1 to 4) is formed on the surface of the base body 2 excluding the range of the external electrode 4. The base body protective layer 5 is, for example, an epoxy resin, a phenoxy resin, and a novolak resin, and a material containing metal oxide fine particles as a filler can be used. In the present embodiment, the base body protective layer 5 contains a filler of silicon dioxide which becomes metal oxide fine particles and an epoxy resin. In addition to the above materials, the base body protective layer 5 may be a resin such as urethane, acrylic, polyimide, polyimide amide, polyamide, or glass or an oxide film.

[0031] An inductor with such a configuration can improve its DC superposition characteristics by using soft magnetic materials for magnetic particles, and thus is used as an electronic component in an electric circuit where a large current flows, a choke coil in a DC-DC converter circuit or a power supply circuit. It is also used as an electronic component in electronic devices such as personal computers, DVD players, digital cameras, TVs, mobile phones, smartphones, automotive electronics, medical and industrial machinery. However, the uses of the inductor are not limited to this, and it can also be used, for example, in tuning circuits, filter circuits, rectifier smoothing circuits, etc.

[0032] [1.2 Structure of the boundary portion between the element body surface and the external electrode] Next, the structure of the boundary portion between the surface of the element body 2 and the external electrode 4 will be further described. FIG. 4 is a plan perspective view of the inductor 1 shown in FIGS. 1 and 3 viewed from the side of the upper surface 12. FIG. 5 is a cross-sectional view of the inductor 1 shown in FIG. 4 taken along the line V-V, and FIG. 6 is a partial detailed view of the P portion in the cross-section shown in FIG. 5.

[0033] Referring to FIG. 6, the external electrode 4 includes a Cu (copper) plating layer 41 as the lowermost layer closest to the surface of the element body. The Cu plating layer 41 is connected to the lead-out portion 24 (not shown in FIG. 6) of the coil conductor 20 exposed on the surface of the element body 2. In this embodiment, the Cu plating layer 41 is formed by electrolytic plating.

[0034] The external electrode 4 may also 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. The Ni plating layer 42 and the Sn plating layer 43 improve the corrosion resistance and solder wettability of the external electrode 4. The Ni plating layer 42 and the Sn plating layer 43 can also be formed by electrolytic plating.

[0035] In this embodiment, particularly when the element body 2 is immersed in the electrolytic plating solution during the formation of the Cu plating layer 41, an intermediate layer 6 is disposed between the surface of the element body 2 and the Cu plating layer 41 to prevent the formation of Cu replacement plating on the surface of the metal magnetic particles containing Fe exposed from the surface of the element body 2.

[0036] As described later, the intermediate layer 6 can be configured to contain phosphorus (P) and oxygen (O) or sulfur (S) and oxygen (O), thereby suppressing the formation of the Cu substitution plating layer and improving the adhesion between the Cu plating layer 41 and the surface of the base body 2. As described later, the intermediate layer 6 containing phosphorus (P) and oxygen (O) can be formed using pyrophosphoric acid (chemical formula: H4P2O7), which can generally be used in the preparation of a Cu electrolytic plating solution, and the intermediate layer 6 containing sulfur (S) and oxygen (O) can be formed using ammonium sulfate (chemical formula: (NH4)2SO4), which can generally be used in the preparation of a Ni electrolytic plating solution. That is, the intermediate layer 6 containing phosphorus (P) and oxygen (O) or sulfur (S) and oxygen (O) has the advantage that it can be easily produced by diverting the chemicals used in the formation of the external electrode 4.

[0037] Further, 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 can generally be used in a Cu electrolytic plating solution, and the intermediate layer 6 containing sulfur (S), oxygen (O), and potassium (K) can be formed using potassium sulfate (chemical formula: K2SO4), which can generally be used in a Ni electrolytic plating solution. In particular, since the intermediate layer 6 containing phosphorus (P), oxygen (O), and potassium (K) uses potassium pyrophosphate that can be used in a Cu electrolytic plating solution, the cleaning of the base body 2 between the formation process of the intermediate layer 6 and the formation process of the Cu plating layer 41 can be omitted, and the process can be simplified.

[0038] From the viewpoint of preventing the formation of a Cu substitution plating layer on the surface of the metal magnetic particles 30a exposed on the surface of the base body 2, the intermediate layer 6 only needs to be disposed at least between the metal magnetic particles 30a and the Cu plating layer 41, and does not necessarily need to be formed on the resin 30b constituting the core 30 of the base body 2. By disposing the intermediate layer 6 between the metal magnetic particles 30a and the Cu plating layer 41, it is possible to more effectively prevent a decrease in the adhesion strength between the Cu plating layer 41 and the base body 2 caused by the Fe-Cu substitution reaction in the formation process of the Cu plating layer 41, and improve the connection strength between the external electrode 4 and the base body 2.

[0039] Further, the intermediate layer 6 is not disposed between the base body 2 and the base body protective layer 5 covering the surface of the base body 2. Thereby, it is possible to prevent an adverse effect on the adhesion strength between the base body 2 and the base body protective layer 5 that may occur when the intermediate layer 6 exists between the surface of the base body 2 and the base body protective layer 5.

[0040] The thickness of the intermediate layer 6 does not have to be uniform along the surface of the base body 2. This is because even if the thickness is not uniform, as long as it is on the surface of the metal magnetic particles 30a, it can prevent the formation of a Cu substitution plating layer on the surface. Also, since it is not necessary to form the intermediate layer 6 to have a uniform thickness along the surface of the base body 2, the intermediate layer 6 can be easily formed.

[0041] Further, the intermediate layer 6 does not have to be continuously formed along the surface of the base body 2, and may be discontinuous along the surface of the base body 2 as shown in FIG. 6. Even if the intermediate layer 6 is discontinuously formed, in the region covering the surface of the metal magnetic particles 30a, it can prevent the formation of a Cu substitution plating layer, so it is possible to prevent a decrease in the adhesion of the entire Cu plating layer 41 to the surface of the base body 2. Also, the fact that it is not necessary to continuously form the intermediate layer 6 along the surface of the base body 2 makes it easier to form the intermediate layer 6.

[0042] In the region where the Cu plating layer 41 is formed, the average thickness of the intermediate layer 6 is preferably 0.01 μm or more and 50 μm or less, and more preferably 0.5 μm or more and 20 μm or less. If the intermediate layer 6 is too thin, the effect of preventing the formation of the Cu substitution plating layer becomes weak. If it is too thick, it may be necessary to reduce the outer dimensions of the base body 2 to keep the outer dimensions of the inductor 1 within the allowable range, sacrificing the electrical characteristics.

[0043] Also, in the region of the surface of the base body 2 where the Cu plating layer 41 is formed, the surface roughness indicated by the arithmetic mean roughness Ra is preferably 1.0 μm or more and 10 μm or less. Thereby, due to the anchor effect caused by the non - smooth surface of the base body 2, the adhesion between the intermediate layer 6 and the surface of the base body 2, or the adhesion between the intermediate layer 6 and the Cu plating layer 41 and the surface of the base body 2 can be further enhanced, and the adhesion strength between the external electrode 4 and the surface of the base body 2 can be further improved.

[0044] Also, the resistivity (for example, volume resistivity) of the intermediate layer 6 may be in any numerical range of a conductor or an insulator, and does not necessarily have to be constant along the surface of the base body 2.

[0045] [2. Manufacturing process of the inductor] The inductor 1 can be manufactured as follows. FIG. 7 is a diagram showing the manufacturing process of the inductor 1. The manufacturing process of the inductor 1 may include a coil conductor forming step (S1), a pre - formed body forming step (S2), a base body forming step (S3), a barrel polishing step (S4), a surface treatment step (S5), an intermediate layer forming step (S6), and an external electrode forming step (S7).

[0046] The coil conductor forming step (S1) is a step of forming the coil conductor 20 from a conducting 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 conducting wire in a winding manner called "alpha winding". Alpha winding refers to a state in which the lead portions 24 at the start and end of winding of the conducting wire functioning as a conductor are located on the outer periphery and are wound in a spiral shape in two stages. The number of turns of the coil conductor 20 is not particularly limited.

[0047] The preform forming step (S2) is a step of forming a preform called a tablet. The preform is formed by pressing the above-described mixed powder, which is the material of the base body 2, into a solid shape that is easy to handle. In the present embodiment, two types of tablets are formed: a first tablet having a groove into which the coil conductor 20 enters and having an appropriate shape (for example, an E shape), and a second tablet having an appropriate shape (for example, an I shape or a plate shape) that covers the groove of the first tablet.

[0048] In the base body forming step (S3), the first tablet, the coil conductor, and the second tablet are set in a molding die, and while applying heat, pressure is applied in the overlapping direction of the first tablet and the second tablet to cure them, thereby integrating the first tablet, the coil conductor, and the second tablet. Thereby, the base body 2 in which the coil conductor 20 is enclosed in the core 30 is molded.

[0049] In the barrel polishing step (S4), a plurality of base bodies 2 are filled in a drum, and the drum is rotated so that an excessively strong impact is not applied. Further, a coating liquid that becomes the base body protective layer 5 is sprayed by a spray. Thereby, rounding of the corners of the base body 2 and application of the coating liquid to the base body 2 are performed. In the present embodiment, the coating liquid contains a filler of silicon dioxide that becomes metal oxide fine particles and an epoxy resin that becomes an organic resin.

[0050] Next, the base body 2 coated with the coating liquid is taken out of the drum and heat-treated to form the base body protective layer 5 on the surface of the base body 2.

[0051] Note that the formation of the base body protection layer 5 is not limited to the above. A separate process from the barrel polishing process (S4) may be provided, and the coating liquid can be sprayed onto the base body 2, the base body 2 can be dipped into the coating liquid, the coating liquid can be supplied to the surface of the base body 2 through a dispenser, and / or the coating material can be printed on the surface of the base body 2 by various printing methods. It can be carried out by various methods.

[0052] The surface treatment process (S5) is a process of modifying the surface of the planned electrode location on the surface of the core 30 by irradiating the planned electrode location with laser light. Here, the planned electrode location refers to the range on the surface of the core 30 where the external electrode 4 is to be formed, including the portion where the lead-out portion 24 is exposed. Specifically, by irradiating laser light, in the range of the planned electrode location, the base body protection 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, 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, in the portion of the surface of the core 30 where the planned electrode location is located, the exposed area of the metal of the metal magnetic particles 30a per unit area of the surface of the core 30 is larger than that of other surface portions of the core 30.

[0053] The wavelength of the laser light is, for example, 180 nm or more and 3000 nm or less, and more preferably 532 nm or more and 1064 nm or less. Also, the irradiation energy of the laser light is 1 W / mm 2 or more and 30 W / mm 2 or less is preferable, and 5 W / mm 2 or more and 12 W / mm 2 or less is more preferable.

[0054] In the intermediate layer formation process (S6), the base body 2 is immersed in a treatment liquid to form an intermediate layer 6 at the planned electrode location of the core 30 of the base body 2. As the treatment liquid, 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. Also, 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.

[0055] More specifically, as the treatment liquid containing polyphosphoric acid, for example, an aqueous solution of pyrophosphoric acid or potassium pyrophosphate can be used. Also, as the treatment liquid containing sulfate ions, for example, an aqueous solution of ammonium sulfate or potassium sulfate can be used. As described above, when potassium pyrophosphate or potassium sulfate is used, a layer containing potassium (K) can be further formed as the intermediate layer 6.

[0056] 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 base body 2 in the treatment liquid.

[0057] In the external electrode forming step (S7), the external electrode 4 is formed at the electrode planned location on the core 30 on which the intermediate layer 6 is formed. Specifically, first, a Cu plating layer 41 is formed by electrolytic plating at the electrode planned location on the core 30 on which the intermediate layer 6 is formed. Subsequently, an Ni plating layer 42 and an Sn plating layer 43 can be formed by electrolytic plating on the Cu plating layer 41.

[0058] As the forming method of the Cu plating layer 41, as electrolytic copper plating, for example, copper sulfate plating, copper pyrophosphate plating, or copper cyanide plating can be used.

[0059] When forming the Ni plating layer 42 and the Sn plating layer 43, additives such as brighteners may be added to the plating solution.

[0060] [3. Examples] Next, an example of the inductor 1 will be described. Examples and comparative examples shown in Table 1 were prepared, and the adhesion strength of the external electrode 4 to the substrate 2 was evaluated. Examples 1 to 6 were prepared under the same preparation conditions by the manufacturing process shown in FIG. 7 described above, but the preparation conditions of the intermediate layer 6 in the intermediate layer formation step (S6) are different from each other. Comparative Example 1 is a sample without the intermediate layer 6, and is prepared under the same preparation conditions as Examples 1 to 6 except that the intermediate formation step is not executed. The number of samples prepared is 30 each in Examples 1 to 6 and the comparative example.

[0061]

Table 1

[0062] [3.1 Preparation of Examples and Comparative Examples] <Preparation of Substrate> In Examples 1 to 6 and the comparative example, the composition of the mixed powder in the preform formation step (S2) is as follows. Metal magnetic particles 30a: First magnetic particles: D50 particle size 28 μm Fe-6.7Si-2.5Cr amorphous alloy (Fe:Si:Cr = 90.8:6.7:2.5 (weight ratio)) Second magnetic particles: D50 particle size 4.0 μm Fe-6.7Si-2.5Cr amorphous alloy (Fe:Si:Cr = 90.8:6.7:2.5 (weight ratio)) Resin 30b: Thermosetting epoxy resin Hardener: Imidazole Lubricant: Nanoscale silica (50 nmφ in diameter), particle shape

[0063] 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 mixed powder, the weight ratio of the resin and the hardener is 3.6% by weight based on the total mixed powder, and the lubricant is 0.4% by weight based on the total mixed powder.

[0064] The compression molding conditions of the green body 2 in the green body forming step (S3) are a temperature of 180°C, a pressure of 20 Mpa, and a pressure application time of 600 seconds. In the core 30 of the green body 2 after molding, 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.

[0065] After forming the green body protective layer 5 on the surface of the green body 2 by the barrel polishing step (S4), in the surface treatment step (S5), laser light irradiation was performed on the planned electrode locations including the exposed portions of the lead-out portions 24 of the coil conductors 20 on the surface of the green body 2. The irradiation energy of the laser light is 12 W / mm 2 is.

[0066] <Formation of the intermediate layer> In Examples 1 to 6, the intermediate layer 6 was formed by the intermediate layer forming step (S6). For each of Examples 1 to 6, the type of treatment liquid, the treatment liquid temperature, and the immersion time of the green body 2 in the treatment liquid used for forming the intermediate layer 6 are as shown in Table 1.

[0067] <Formation of the external electrode> For Examples 1 to 6 and the comparative example, the external electrode 4 was formed by the above-described external electrode forming step (S7). First, the green body 2 was put into a Cu plating bath (pyrophosphate copper plating solution), and a Cu plating layer 41 was formed by electrolytic plating. The average thickness of the Cu plating layer 41 along the surface of the green body 2 is 30 μm. Then, the green body 2 was lifted 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 was formed by electrolytic plating. The average thickness of the Ni plating layer 42 along the surface of the green body 2 is 5 μm. Then, the green body 2 was lifted 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 was formed by electrolytic plating. The average thickness of the Sn plating layer 43 along the surface of the green body 2 is 5 μm.

[0068] [3.2 Evaluation] For the fabricated Examples 1 to 6, the average film thickness of the formed intermediate layer 6 was measured, and the elements in the film of the intermediate layer 6 were analyzed. For Examples 1 to 7 and Comparative Examples, an adhesion test of the external electrode 4 was conducted. [3.2.1 Evaluation Method] The evaluation was conducted by the following method. <Measurement of Average Film Thickness and Analysis of Elements in the Film> First, for Examples 1 to 6, the base body 2 was polished in the DW direction (see Fig. 1), and 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 was obtained. 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.

[0069] Thereafter, 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 base body 2 to analyze the elements in the film of the intermediate layer 6.

[0070] Fig. 8 is an example of an SEM (scanning electron microscope) image of the LT cross-section of the inductor 1 used for the evaluation of the elements in the film of the intermediate layer 6 in Example 3. The image in Fig. 8 shows the base 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 base body 2. Fig. 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 base body 2 in the LT cross-section of the base body 2 used for the evaluation of the elements in the film. Specifically, Fig. 9 is an SEM enlarged image and an EDX image of the Q portion indicated by the dotted rectangular line in the SEM image of Fig. 8.

[0071] In FIG. 9, (A) is a SEM image of part Q. Further, (B) in FIG. 9 is an image of characteristic X-rays showing the presence of element Cu (copper) observed during EDX analysis of part Q. Bright spots indicating the presence of element Cu are concentrated in the region corresponding to the Cu plating layer 41, and the region is shown brightly. (C), (D), and (E) in FIG. 9 are images of characteristic X-rays showing the presence of elements O (oxygen), P (phosphorus), and K (potassium), respectively, observed during EDX analysis of part Q. In the images of (C), (D), and (E) in FIG. 9, 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 base body 2, respectively. From this, it can be understood 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 base body 2.

[0072] Also, since the groups of bright spots indicating the presence of elements O (oxygen), P (phosphorus), and K (potassium) are discontinuous along the surface of the base body 2, and the shape formed by the outer edges of the groups of bright spots is not rectangular, it can be seen that the intermediate layer 6 is formed discontinuously along the surface of the base body 2 and its thickness is not uniform along the surface of the base body 2. Note that for the characteristic X-ray image of an element not contained in the intermediate layer 6, a black image without bright spots is obtained. For example, in the EDX analysis of the intermediate layer 6 of Example 1, the characteristic X-ray image of K (potassium) corresponding to (E) in FIG. 9 is a black image without bright spots.

[0073] <Evaluation of Adhesion of External Electrode> Based on the adhesion (shear strength) test described in AEC-Q200 Rev E, a standard for the reliability of automotive passive components defined by AEC (Automotive Electronics Council), the adhesion of the external electrode 4 to the element body 2 was evaluated. Specifically, after soldering the external electrodes 4 of each of the inductors 1 in Examples 1 to 6 and the Comparative Example to a test substrate (FR-4) by reflow, a pushing force of 17.7 N was applied perpendicularly to the side surface of each inductor 1 for 60 seconds, and the presence or absence of peeling of the inductor 1 from the test substrate was evaluated.

[0074] [3.2.2 Evaluation Results] The evaluation results are shown in Table 2.

Table 2

[0075] As shown in Table 2, in the Comparative Example without the intermediate layer 6, peeling of the external electrode 4 was observed in 5 out of 30 samples in the adhesion test. On the other hand, in Examples 1 to 6 having the intermediate layer 6, peeling of the external electrode 4 was not observed in all 30 inductors 1, respectively. 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 of the Cu plating layer 41 of the external electrode 4 to the element body 2.

[0076] Also, from the comparison between Examples 3 to 6 and Examples 2 and 3, it was confirmed that even when the intermediate layer 6 further contains K as an element in the film, the effect of improving the adhesion strength of the Cu plating layer 41 to the element body 2 can be obtained in the same manner as when K is not contained.

[0077] Furthermore, from the comparison of Examples 3, 5, and 6, it was confirmed that the longer the immersion time of the element body 2 in the treatment liquid in the intermediate layer formation step (S6), the thicker the intermediate layer 6 is formed, and the intermediate layer 6 can exhibit the effect of improving the adhesion strength of the Cu plating layer 41 at least in the range where the average thickness is 20 μm or less.

[0078] [5. Other Embodiments] In the above-described embodiment, the core 30 includes two types of magnetic particles having different average particle diameters as the metal magnetic particles 30a, but it may be composed of one type of magnetic particle. In the above-described embodiment, the Cu plating layer 41 is formed by electrolytic plating, but it may be formed by electroless copper plating.

[0079] Note that all of the above-described embodiments and examples illustrate one aspect of the present invention, and can be arbitrarily modified and applied without departing from the spirit of the present invention. In addition, the horizontal and vertical directions, various numerical values, shapes, and materials in the above-described embodiments include ranges (so-called equivalent ranges) that exhibit the same effects as those directions, numerical values, shapes, and materials as long as there is no special notice.

[0080] [6. Configurations Supported by the Above Embodiments and Examples] The above-described embodiments and examples support the following configurations.

[0081] (Configuration 1) An inductor including a body containing metal magnetic particles and a resin and enclosing a coil conductor, and an external electrode including a copper plating layer disposed on the surface of the body and connected to the coil conductor, wherein the metal magnetic particles include particles containing iron (Fe), and having an intermediate layer containing phosphorus (P) and oxygen (O) or sulfur (S) and oxygen (O) between the surface of the body and the copper plating layer of the external electrode. According to the inductor of Configuration 1, when the body is immersed in the plating solution in the formation process of the copper plating layer, the adhesion strength between the copper plating layer and the body due to the substitution reaction between copper in the plating solution and iron (Fe) of the metal magnetic particles on the surface of the body can be effectively prevented, and the connection strength between the external electrode including the copper plating layer and the body can be improved.

[0082] (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. According to the inductor of Configuration 2, it is possible to more effectively prevent a decrease in the adhesion strength between the copper plating layer and the base body due to the Fe-Cu substitution reaction in the copper plating layer forming step, and improve the connection strength between the external electrode and the base body.

[0083] (Configuration 3) The inductor according to Configuration 1 or 2, wherein a base body protective layer, which is an insulating film, is disposed in a region other than the region where the external electrode is formed on the surface of the base body. According to the inductor of Configuration 3, it is possible to prevent an unnecessary copper plating layer from being formed in a region on the surface of the base body where the external electrode is not formed.

[0084] (Configuration 4) The inductor according to Configuration 3, wherein the intermediate layer is not disposed between the base body and the base body protective layer. According to the inductor of Configuration 4, it is possible to prevent an adverse effect on the adhesion strength between the base body and the base body protective layer that may occur when an intermediate layer exists between the surface of the base body and the base body protective layer.

[0085] (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 base body via the intermediate layer. According to the inductor of Configuration 5, it is possible to configure an external electrode having excellent corrosion resistance and solder wettability while improving the adhesion strength between the external electrode and the base body.

[0086] (Configuration 6) The inductor according to any one of Configurations 1 to 5, wherein the intermediate layer further contains potassium (K). According to the inductor of Configuration 6, the intermediate layer can be formed using a chemical agent containing components similar to those of a copper plating solution containing potassium that can usually be used in the copper plating layer forming step. Therefore, according to the inductor of Configuration 6, it is possible to easily form the external electrode by omitting the cleaning step between the intermediate layer forming step (S6) and the subsequent copper plating layer step (without introducing new chemical components).

[0087] Inductor according to Configuration 1 to 6, wherein the thickness of the intermediate layer is not uniform along the surface of the element body. 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 element body. Therefore, according to the inductor of Configuration 7, the intermediate layer can be easily formed.

[0088] Inductor according to Configuration 1 to 7, wherein the intermediate layer is discontinuous along the surface of the element body. According to the inductor of Configuration 8, it is not necessary to continuously form the intermediate layer along the surface of the element body. Therefore, according to the inductor of Configuration 8, the intermediate layer can be easily formed.

[0089] Inductor according to Configuration 1 to 8, wherein the surface of the element body has a surface roughness represented by an arithmetic mean roughness Ra of 1.0 μm or more and 10 μm or less. According to the inductor of Configuration 9, due to the anchor effect caused by the non-smooth surface of the element body, the adhesion between the intermediate layer and the surface of the element body, or the adhesion between the intermediate layer and the copper plating layer and the surface of the element body can be further increased, and the connection strength between the external electrode and the surface of the element body can be further improved.

[0090] Inductor according to Configuration 1 to 9, wherein the average thickness of the intermediate layer is 20 μm or less. According to the inductor of Configuration 10, within the allowable range of the outer dimensions required for the entire inductor, while avoiding the unnecessary limitation of the volume of the element body due to the presence of the intermediate layer (therefore, while avoiding the unnecessary limitation of the electrical characteristics as an inductor), the connection strength between the external electrode and the surface of the element body can be improved.

[0091] Step of manufacturing a coil having a pair of lead-out portions, and embedding the coil in a base body containing metal magnetic particles containing iron (Fe) and a resin such that the lead-out portions of the coil are exposed from the surface of the base body; step of at least partially forming an intermediate 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 base body, the external electrode formation region including the lead-out portions exposed from the base body; and step of forming an external electrode including a copper (Cu) plating layer in the external electrode formation region where the intermediate layer is at least partially formed. A method for manufacturing an inductor. According to the method for manufacturing an inductor of Configuration 11, when the base body is immersed in a plating solution in the step of forming the copper plating layer, a decrease in the adhesion strength between the copper plating layer and the base body due to a substitution reaction between copper in the plating solution and iron (Fe) of the metal magnetic particles on the surface of the base body can be effectively prevented, and an inductor capable of improving the connection strength between the external electrode including the copper plating layer and the base body can be manufactured.

Explanation of reference numerals

[0092] 1... Inductor, 2... Base body, 4... External electrode, 5... Base body protective layer, 6... Intermediate layer, 10... Bottom surface, 12... Top surface, 14... End face, 16... Side surface, 20... Coil conductor, 22... Winding portion, 24... Lead-out portion, 30... Core, 30a... Metal magnetic particles, 30b... Resin, 41... Cu plating layer, 42... Ni plating layer, 43... Sn plating layer.

Claims

1. A base body containing metal magnetic particles and a resin, and enclosing a coil conductor, an external electrode disposed on the surface of the base body and connected to the coil conductor, the external electrode including a copper plating layer, characterized in that, the metal magnetic particles include particles containing iron (Fe), an intermediate layer containing phosphorus (P) and oxygen (O) or sulfur (S) and oxygen (O) is provided between the surface of the base body and the copper plating layer of the external electrode, inductor.

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

3. An inductor according to claim 1, wherein a base body protective layer, which is an insulating film, is disposed in a region of the surface of the base body other than a region where the external electrode is formed. inductor according to claim 1.

4. The intermediate layer is not disposed between the base body and the base body protective layer, inductor according to claim 3.

5. 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 base body via the intermediate layer, inductor according to claim 1.

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

7. The thickness of the intermediate layer is not uniform along the surface of the base body, inductor according to claim 1.

8. The intermediate layer is discontinuous along the surface of the base body, inductor according to claim 1.

9. The surface of the base body has a surface roughness represented by an arithmetic mean roughness Ra of 1.0 μm or more and 10 μm or less, inductor according to claim 1.

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

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

Images