Coil Device

Abstract

To provide a coil device which not only can effectively reduce a magnetic leakage flux especially at a high frequency but also allows a reduction in device size and manufacturing cost.SOLUTION: A coil device 2 has: an element body 4 containing a magnetic material; a coil part 6α disposed in the element body 4; and a terminal electrode 8 connected to a lead portion of the coil part 6α. At least one surface 4a of outer surfaces of the element body 4 is provided with a shield layer 10 containing metal and resin.SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to a coil device used for applications such as an inductor. [Background technology]

[0002] Coil devices such as inductors are widely used in electronic devices. In order to reduce leakage of part of the magnetic flux generated by passing a current through such a coil device to the outside of the product, the coil device of Patent Document 1 has a copper sheet shield formed separately from the coil device element body and attached to the element body to block the leakage magnetic flux.

[0003] However, forming and attaching the shield separately from the element body in this way poses the problem that the coil device becomes larger and the manufacturing costs of the coil device increase. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2019-516246 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above circumstances, and its object is to provide a coil device that can effectively reduce leakage magnetic flux, particularly at high frequencies, and that can also be made smaller and reduce manufacturing costs. [Means for solving the problem]

[0006] The inventors conducted extensive research into coil devices that can effectively reduce leakage magnetic flux and also enable the device to be made smaller and its manufacturing costs reduced. As a result, they discovered that by forming a specific shielding layer on the surface of the element body, leakage magnetic flux from the coil device can be effectively reduced, particularly at high frequencies, even if the shielding layer is formed thin, and thus completed the present invention.

[0007] That is, the coil device according to the present invention is an element body including a magnetic material; a coil portion disposed within the element body; a terminal electrode connected to a lead portion of the coil portion, A shield layer containing metal and resin is formed on at least one of the outer surfaces of the element body.

[0008] This shield layer can be formed simply by applying a paste-like material containing metal and resin, drying it, and hardening it, and the thickness of the shield layer can be easily controlled. This makes it easier to manufacture a coil device than a structure in which a metal sheet shield is attached to the element body. Moreover, compared to a coil device in which a metal sheet is attached to the element body, the adhesion between the shield layer and the element body is improved, and the coil device can be made more compact.

[0009] Preferably, the shielding layer has a metal-rich region in which the metal is observed in greater amounts than the resin. Preferably, the cross section of the metal-rich region contains 50% or more of the metal. More preferably, the cross section of the metal-rich region contains 80% or more of the metal. It is believed that this metal-rich region enhances the blocking effect of leakage magnetic flux.

[0010] Preferably, the shielding layer has a resin-rich region where a large amount of the resin is observed, and the resin-rich region is present at the interface between the element body and the metal-rich region. This resin-rich region is thought to improve adhesion between the shielding layer and the element body.

[0011] The terminal electrode may have a region made of the same material as the metal-rich region of the shield layer. This configuration can effectively reduce leakage flux at specific noise frequencies. This is thought to be because the metal-rich region made of the same material can cover a wider area of ​​the element body surface. Furthermore, since the terminal electrode and the shield layer can be formed simultaneously using the same raw material, manufacturing costs can be reduced.

[0012] Preferably, the shield layer has a coating layer formed by applying a paste containing the metal and the resin to the outer surface of the element body. The coating layer can be easily formed and its thickness can be easily controlled. Therefore, design changes are easier than in coil devices with metal sheet shields, and manufacturing costs can be reduced.

[0013] Preferably, the shield layer contains Ag. It has been confirmed that a shield layer containing Ag can effectively reduce leakage flux, especially at high frequencies, even if it is formed thin.

[0014] The paste preferably contains flat metal powder. The paste may also contain spherical metal powder. The coating layer is preferably formed by heat treating the paste at 170°C to 230°C.

[0015] A shielding layer formed from such a paste is more effective in reducing leakage magnetic flux. It is particularly preferable for the paste to contain small metal powder, preferably with an average particle size of 800 nm or less, more preferably 100 to 500 nm. By including such metal powder, the metal content of the metal-rich region can be increased when the paste-coated film is heat-treated at a temperature (170°C to 230°C) that hardens the resin contained in the paste. It is believed that the fine particles of the metal powder cause a phenomenon similar to metal sintering to occur at a temperature lower than the melting point of the metal itself.

[0016] Preferably, the shield layer is formed on the outer surface opposite to the outer surface of the element body on which the terminal electrodes are formed. In this way, a coil device having a shield layer formed on the non-mounting side can effectively reduce leakage magnetic flux from the non-mounting side. A plating layer may be formed on the surface of the shield. The plating layer can be formed simultaneously with the formation of the plating layer formed on the surface of the terminal electrodes of the coil device.

[0017] The shield layer may have a non-mounting-side shield layer formed on the non-mounting side of the element body, and a ground conduction portion extending from the non-mounting-side shield layer through the side of the element body to near the mounting side of the element body.

[0018] By configuring it in this way, the shield layer can be connected to the ground. Therefore, the shield layer can be set to the same potential as the ground potential. As a result, the shield layer can be more effectively used to block leakage magnetic flux. In addition, the ground conductive portion can also function as a shield for leakage magnetic flux on the side surface of the element body. Furthermore, by connecting the ground conductive portion to the ground, the number of connection points of the coil device can be increased in areas other than the terminal electrodes, thereby improving the mounting strength of the coil device.

[0019] The mounting side of the element body may have a recess formed toward the non-mounting side, and the mounting-side shield layer may be formed in the recess. With this configuration, other electronic components such as a capacitor chip can be placed in the space formed between the recess and the mounting substrate. In addition, the shield layer formed in the recess reduces leakage magnetic flux, thereby preventing adverse effects on the electronic components.

[0020] The shield layer may be formed so as to cover the outer surface of the element body excluding the mounting surface, thereby further reducing leakage magnetic flux.

[0021] The terminal electrode may be formed in an L-shape from the mounting side of the element body toward the side of the element body, which makes it easier to form a solder fillet when mounting the element on a substrate or the like. [Brief explanation of the drawings]

[0022] [Figure 1A] FIG. 1A is a perspective view showing a coil device according to one embodiment of the present invention. [Figure 1B] FIG. 1B is a perspective view showing a coil device according to another embodiment of the present invention. [Figure 1C] FIG. 1C is a perspective view showing a coil device according to still another embodiment of the present invention. [Figure 1D] FIG. 1D is a perspective view showing a coil device according to still another embodiment of the present invention. [Figure 1E] FIG. 1E is a perspective view showing a coil device according to still another embodiment of the present invention. [Figure 2A] FIG. 2A is a perspective view of the coil device shown in FIG. 1A, seen from another angle. [Figure 2B] FIG. 2B is a perspective view of the coil device shown in FIG. 1C, seen from another angle. [Figure 3A] FIG. 3A is a cross-sectional view taken along line IIIA-IIIA when the coil device shown in FIG. 1A is mounted on a substrate. [Figure 3B] FIG. 3B is a cross-sectional view taken along line IIIB-IIIB when the coil device shown in FIG. 1B is mounted on a substrate. [Figure 3C] FIG. 3C is a cross-sectional view taken along line IIIC-IIIC when the coil device shown in FIG. 1D is mounted on a substrate. [Figure 4A] FIG. 4A is a schematic diagram of an enlarged cross-sectional photograph of a coil device according to an embodiment. [Figure 4B] FIG. 4B is a schematic diagram of an enlarged cross-sectional photograph of a coil device according to another embodiment. [Figure 5] FIG. 5 is a schematic diagram of a leakage magnetic flux measuring device. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, the present invention will be described based on the embodiments shown in the drawings.

[0024] First embodiment As shown in FIG. 1A, an inductor 2 serving as a coil device according to a first embodiment of the present invention has an element body 4 formed in the shape of a substantially rectangular parallelepiped (substantially hexahedron).

[0025] The element body 4 has a top surface 4a, a bottom surface 4b located on the opposite side of the top surface 4a in the Z-axis direction, and four side surfaces 4c to 4f. The dimensions of the element body 4 are not particularly limited. For example, the dimension of the element body 4 in the X-axis direction can be 1.2 to 6.5 mm, the dimension in the Y-axis direction can be 0.6 to 6.5 mm, and the dimension in the height (Z-axis) direction can be 0.5 to 5.0 mm.

[0026] 1A, 2A, and 3A, a pair of terminal electrodes 8 are formed on the bottom surface 4b of the element body 4. The pair of terminal electrodes 8 are spaced apart in the X-axis direction and insulated from each other. In the inductor 2 of this embodiment, these terminal electrodes 8 can be connected to an external circuit by connecting them to lands 32 or the like formed on the substrate 30 shown in FIG. 3A.

[0027] That is, the inductor 2 can be mounted on various types of substrates 30, such as a circuit board, using a bonding member such as solder 34 or a conductive adhesive. When mounted on the substrate 30, the bottom surface 4b of the element body 4 becomes the mounting surface, and the terminal electrodes 8 and the substrate 30 are bonded by a bonding member such as solder 34.

[0028] The element body 4 has a coil portion 6α therein. This coil portion 6α is formed by winding a conductor wire 6 into a coil shape. In FIG. 1A of this embodiment, the coil portion 6α is crosswise wound, but it may also be normally wound. Alternatively, the wire 6 may be wound directly around the winding core portion 41b.

[0029] The wire 6 constituting the coil portion 6α is composed of a conductor portion mainly containing copper and an insulating layer covering the outer periphery of the conductor portion. More specifically, the conductor portion is made of pure copper such as oxygen-free copper or tough pitch copper, copper alloys such as phosphor bronze, brass, red brass, beryllium copper, silver-copper alloys, or copper-coated steel wire. On the other hand, the insulating layer is not particularly limited as long as it has electrical insulation properties. For example, epoxy resin, acrylic resin, polyurethane, polyimide, polyamideimide, polyester, Nylon, etc. , or a synthetic resin made by mixing at least two of the above resins. In this embodiment, the wire 6 is a round wire as shown in Figures 1A and 3A, and the cross section of the conductor portion is circular.

[0030] 1A and 3A, the element body 4 in this embodiment has a first core portion 41 and a second core portion 42. Both the first core portion 41 and the second core portion 42 can be made of a compact containing a magnetic material and a resin.

[0031] The magnetic material contained in each of the cores 41 and 42 can be, for example, ferrite powder or metal magnetic powder. Examples of ferrite powder include Ni-Zn ferrite and Mn-Zn ferrite. Examples of the metal magnetic powder include, but are not limited to, other soft magnetic alloys such as Fe-Ni alloys, Fe-Si alloys, Fe-Co alloys, Fe-Si-Cr alloys, Fe-Si-Al alloys, amorphous alloys containing Fe, and nanocrystalline alloys containing Fe.

[0032] The ferrite powder or metal magnetic powder may contain appropriate additives. The first core portion 41 and the second core portion 42 may be made of the same magnetic material, so that the relative permeability μ1 of the first core portion 41 and the relative permeability μ2 of the second core portion 42 are equal. The first core portion 41 and the second core portion 42 may be made of different magnetic materials.

[0033] The magnetic material (i.e., ferrite powder or metal magnetic powder) constituting the first core portion 41 or the second core portion 42 may have a median diameter (D50) of 5 μm to 50 μm. Furthermore, the magnetic material may be formed by mixing a plurality of particle groups with different D50s. For example, a large-diameter powder with a D50 of 8 μm to 30 μm, a medium-diameter powder with a D50 of 1 μm to 5 μm, and a small-diameter powder with a D50 of 0.3 μm to 0.9 μm may be mixed together.

[0034] When mixing multiple particle groups as described above, the ratio of the large-diameter powder, medium-diameter powder, and small-diameter powder is not particularly limited. Furthermore, the large-diameter powder, medium-diameter powder, and small-diameter powder can all be composed of the same material, or they can be composed of different materials. By using multiple particle groups to form the magnetic material in the first core portion 41 or the second core portion 42, the filling rate of the magnetic material in the element body 4 can be increased. As a result, various characteristics of the inductor 2, such as the magnetic permeability, eddy current loss, and DC superposition characteristics, are improved.

[0035] The particle size of the magnetic material can be measured by observing the cross section of the element body 4 with a scanning electron microscope (SEM) or a scanning transmission electron microscope (STEM) and performing image analysis of the obtained cross section photograph using software. In this case, it is preferable to measure the particle size of the magnetic material in terms of the circle-equivalent diameter.

[0036] Furthermore, when the first core portion 41 or the second core portion 42 is made of a metal magnetic powder, it is preferable that the particles constituting the powder are insulated from each other. One example of a method for achieving insulation is to form an insulating coating on the particle surface. Examples of insulating coatings include coatings made of resin or inorganic materials, and oxide coatings formed by oxidizing the particle surface through heat treatment. When the insulating coating is made of a resin or inorganic material, examples of the resin include silicone resin and epoxy resin. Examples of inorganic materials include phosphates such as magnesium phosphate, calcium phosphate, zinc phosphate, and manganese phosphate; silicates (water glass) such as sodium silicate; soda-lime glass; borosilicate glass; lead glass; aluminosilicate glass; borate glass; and sulfate glass. Forming an insulating coating can improve the insulation between particles, thereby improving the withstand voltage of the inductor 2.

[0037] Furthermore, the resin contained in the first core portion 41 and the second core portion 42 is not particularly limited, but may be, for example, a thermosetting resin such as epoxy resin, phenolic resin, melamine resin, urea resin, furan resin, alkyd resin, polyester resin, or diallyl phthalate resin, or a thermoplastic resin such as acrylic resin, polyphenylene sulfide (PPS), polypropylene (PP), or liquid crystal polymer (LCP).

[0038] As shown in FIG. 1A, the first core portion 41 has a flange portion 41a, a winding core portion 41b, and a notch portion 41c. The flange portions 41a protrude toward each of the side surfaces 4c to 4f of the element body 4, and four flange portions 41a are formed corresponding to the side surfaces 4c to 4f. The coil portion 6α is mounted on the upper surface of the flange portions 41a, and the flange portions 41a support the coil portion 6α. Here, the two flange portions 41a protruding along the X-axis direction are referred to as first flange portions 41ax, and the two flange portions 41a protruding along the Y-axis direction are referred to as second flange portions 41ay. The thickness of the first flange portions 41ax is thinner than the thickness of the second flange portions 41ay, and a space for accommodating a portion of the lead portion 6a exists below the first flange portions 41ax.

[0039] The winding core 41b is located above the flange 41a in the Z-axis direction and is formed integrally with the flange 41a. The winding core 41b is formed as a substantially elliptical cylinder that protrudes upward in the Z-axis direction and is inserted inside the coil 6α. The shape of the winding core 41b is as shown in FIG. A 3A, it may have any shape that matches the winding shape of the coil portion 6α, such as a cylindrical or prismatic shape.

[0040] The notches 41c are located between the flanges 41a, and four are formed at the four corners of the XY plane. That is, the notches 41c are formed near the points where the side surfaces 4c to 4f of the element body 4 intersect with each other. The notches 41c are used as passages through which the lead portion 6a drawn out from the coil portion 6α passes. The notches 41c also function as passages through which the molding material constituting the second core portion 42 flows from the front surface side to the back surface side of the first core portion 41 during the manufacturing process. A In the figure, the notch 41c is cut out in a substantially square shape, but the shape is not particularly limited as long as it allows the lead 6a and the molding material to pass through. For example, the notch 41c may be a through-hole that penetrates the front and back surfaces of the flange 41a.

[0041] As shown in Fig. 3A, the second core portion 42 covers the first core portion 41. More specifically, the second core portion covers the coil portion 6α and the winding core portion 41b above the flange portion 41a, and fills the space present below the cutout portion 41c and the first flange portion 41ax. Note that, as shown in Fig. 1A, the lower surface of the second flange portion 41ay forms part of the bottom surface 4b of the element body 4, and the second core portion 42 does not fill the space below this second flange portion 41ay.

[0042] 1A, the pair of lead portions 6a are each drawn out from the coil portion 6α along the Y-axis above the first flange portion 41ax. Each of the pair of lead portions 6a is folded back near the side surface 4c of the element body 4 and extends from the side surface 4c toward the side surface 4d below the first flange portion 41ax.

[0043] Here, the height h in the Z-axis direction from the bottom surface 4b of the element body 4 to the first flange portion 41ax (see FIG. 3A) is smaller than the outer diameter of the lead portion 6a. Therefore, below the first flange portion 41ax, most of the lead portion 6a is housed inside the element body 4 (particularly the second core portion 42), but part of the outer periphery of the lead portion 6a is exposed at the bottom surface 4b of the element body 4. All of the lead portions 6a are made of wire 6, and at the portion exposed at the bottom surface 4b, the insulating layer existing on the outer periphery of the wire 6 is removed, exposing the conductor portion of the wire 6. In this embodiment, as shown in FIG. 2A, the portion at the bottom surface 4b where the conductor portion of the wire 6 is exposed is particularly referred to as the extraction electrode portion 61.

[0044] In this embodiment, as shown in FIG. 2A, a pair of terminal electrodes 8 are formed so as to cover a pair of extraction electrode portions 61, respectively, and the extraction electrode portions 61 and the terminal electrodes 8 are electrically connected.

[0045] The terminal electrode 8 may have a resin electrode layer. Alternatively, the terminal electrode 8 may have a laminated structure having a resin electrode layer and other electrode layers. When the terminal electrode 8 has a laminated structure, the resin electrode layer is located in a portion that contacts the extraction electrode portion 61, and the other electrode layers are laminated outside the resin electrode layer, i.e., on the opposite side of the extraction electrode portion 61.

[0046] The other electrode layer may be a single layer or multiple layers, and its material is not particularly limited. For example, the other electrode layer may be made of a metal such as Sn, Au, Ni, Pt, Ag, or Pd, or an alloy containing at least one of these metal elements, and may be formed by plating or sputtering. The average thickness of the entire terminal electrode 8 is preferably 10 μm to 60 μm, and the average thickness of the resin electrode layer included in the terminal electrode 8 is preferably 10 μm to 50 μm.

[0047] 1A, in this embodiment, a shield layer 10 is formed on the top surface 4a of the element body 4. The shield layer 10 has a non-mounting-side shield layer 10a formed over the entire top surface 4a of the element body 4. The non-mounting-side shield layer 10a is formed so as to cover at least the coil portion 6α in a plan view seen from the Z-axis direction. This non-mounting-side shield layer 10a does not necessarily have to be formed over the entire top surface 4a, but it is preferable that it cover a wide range of the top surface 4a.

[0048] Shield layer 10, which is made up of non-mounting-side shield layer 10a, has metal-rich layer 12 as a metal-rich region and resin-rich layer 14 as a resin-rich region, as shown in Figures 4A and 4B, which are schematic cross-sectional photographs of shield layer 10. A plating layer 15 may be formed on the surface of metal-rich layer 12.

[0049] The plating layer 15 may have, for example, an intermediate layer 16 and an outermost layer 18. This plating layer 15 is preferably formed simultaneously with the plating layer formed on the surface of the terminal electrode 8, and the outermost plating layer 18 preferably contains, for example, tin or a tin alloy, which has excellent wettability with solder. The intermediate layer contains, for example, nickel or a nickel alloy, and may be a single layer or a multi-layer laminate.

[0050] In this embodiment, a resin-rich layer 14 is observed at the interface between the surface of the second core portion 42 of the element body 4 and the metal-rich layer 12. Schematic diagrams of SEM cross-sectional photographs of the coil device are shown in FIGS. 4A and 4B. In the SEM cross-sectional photographs, the resin components and spaces are observed as black, the metal components are observed as white, and the magnetic particles are observed as gray. In FIGS. 4A and 4B, which are schematic diagrams of cross-sectional photographs, the cross-sections of the metal observed as white by SEM are represented by diagonal lines or white, the cross-sections of the magnetic particles of the second core portion observed as gray are represented by diagonally crossed dashed lines, and the cross-sections of the element body 4 observed as black represent the resin. The space outside the shield layer observed as black by SEM is represented by diagonally crossed grid-like hatching. Furthermore, the black portions inside the element body 4 and the shielding layer 10 contain not only resin components but also some gap spaces, but other test methods (such as adhesion tests) have confirmed that the black portions in the resin-rich layer 14 are resin components and not gap spaces.

[0051] The metal-rich layer 12 can be defined as a layer on the surface of the element body 4 containing the magnetic particles 42a, where a region is observed in which the white areas representing the metal component are more in area than the black areas representing the resin, excluding the plating layer 15. The resin-rich layer 14 can be defined as a layer on the interface between the metal-rich layer 12 and the surface of the element body 4, where a layered region is observed in which the black areas representing the resin are more in area than the white areas representing the metal component.

[0052] The proportion of metal in the metal-rich layer 12, in terms of area percentage in the cross section, is preferably 50% or more, more preferably 80% or more, and particularly preferably 90% or more. In the resin-rich layer 14, the proportion of metal, in terms of area percentage in the cross section, is preferably 50% or less, more preferably 20% or less, and particularly preferably 3% or less.

[0053] The area occupied by each component can be measured by observing the cross section with an SEM or STEM and analyzing the resulting cross section image. When using an SEM, it is preferable to observe using a backscattered electron image, and when using an STEM, it is preferable to observe using an HAADF image. In the above observation image, the dark contrast areas (areas close to black) are the resin component, and the bright contrast areas (areas close to black) are the resin component. white The part close to is the metal component.

[0054] The resin-rich layer 14 is preferably formed continuously, although there may be some variation in thickness, at the interface between the metal-rich layer 12 and the surface of the element body 4. However, the resin-rich layer 14 may have discontinuous portions along the longitudinal direction.

[0055] The discontinuous portion is defined as a portion where the distance between the metal component (white particles or clumps) of the metal-rich layer 12 and the magnetic particles (gray particles) with a particle size of 1 μm or more contained inside the element body 4 narrows to 0.1 μm or less. Independent particles observed with a particle size of 0.1 μm or less can be defined as being included in the resin-rich layer 14, regardless of whether they are white or gray.

[0056] The thickness of the resin-rich layer 14 is preferably 0.5 to 5 μm, and more preferably 1 to 3 μm. The thickness of the metal-rich layer 12 is preferably 1 to 50 μm, and more preferably 3 to 15 μm.

[0057] The metal in the metal-rich layer 12 preferably includes Ag, and may also include Cu, Ni, Sn, Au, Pd, etc. The resin component in the resin-rich layer 14 is preferably a thermosetting resin such as an epoxy resin or a phenol resin.

[0058] Next, a method for manufacturing the inductor 2 of this embodiment will be described.

[0059] First, the first core portion 41 is produced by a pressing method such as hot-press molding or an injection molding method. In producing the first core portion 41, raw powder of the magnetic material is kneaded with a binder, a solvent, etc. to form granules, and the granules are used as the raw material for molding. When the magnetic material is composed of multiple particle groups, magnetic powders with different particle size distributions can be prepared and mixed in a predetermined ratio.

[0060] Next, the coil portion 6α is mounted on the obtained first core portion 41. The coil portion 6α may be an air-core coil in which the wire 6 is wound in advance in a predetermined shape, and the winding core portion 41b of the first core portion 41 is inserted into this air-core coil. Alternatively, the wire 6 may be directly wound around the winding core portion 41b of the first core portion 41 to form the coil portion 6α. After combining the first core portion 41 and the coil portion 6α, as shown in FIG. 1A, a pair of lead portions 6a are drawn out from the coil portion 6α and placed below the first flange portion 41ax.

[0061] Next, the second core portion 42 is produced by insert injection molding. In producing the second core portion 42, first, the first core portion 41 on which the coil portion 6α is mounted is placed inside a molding die.

[0062] The raw material for the second core portion 42 is a material that is fluid during molding. Specifically, a composite material is used, which is a mixture of raw magnetic material powder and a binder such as a thermoplastic resin or a thermosetting resin. This composite material may contain a solvent, a dispersant, or the like, as appropriate. In insert injection molding, the composite material is introduced into a molding die in a slurried state. The introduced slurry passes through the cutout portion 41c of the first core portion 41 and fills the area below the first flange portion 41ax. During injection molding, heat is applied appropriately depending on the binder material used. In this way, the element body 4 is obtained, in which the first core portion 41, the second core portion 42, and the coil portion 6α are integrated.

[0063] Next, a laser is irradiated onto a portion of the bottom surface 4b of the element body 4, i.e., the portion where the pair of terminal electrodes 8 will be formed in FIG. 3A, to form a planned electrode portion. This laser irradiation removes the insulating layer of the lead portion 6a exposed on the bottom surface 4b, forming the extraction electrode portion 61. The laser irradiation also removes the resin contained in the core portion 42 (as well as 41) from the outermost surface of the bottom surface 4b. That is, in the planned electrode portion, the magnetic material contained in the core portion 42 (as well as 41) is exposed, and the extraction electrode portion 61 is also exposed. This makes it easier for the terminal electrodes 8 to be tightly attached to the bottom surface 4b of the element body 4.

[0064] Next, the resin electrode paste is applied to the electrode portion by a method such as printing. The resin electrode paste used in this process contains a binder as the resin component and a metal raw material powder as the conductor powder. More specifically, the metal raw material powder preferably contains microparticles with particle sizes on the order of micrometers and nanoparticles with particle sizes on the order of nanometers.

[0065] At the same time, a coating film for forming the shielding layer 10 shown in FIG. 1A is formed on the upper surface of the element body 4 using the same paste as the resin electrode paste for forming the terminal electrode 8. The thickness of the coating film may be approximately the same as the thickness of the resin electrode layer of the terminal electrode 8, but is preferably determined so that the thickness of the metal-rich region 12 after heat treatment shown in FIG. 4A or 4B falls within the preferred range described above. When coating, multiple applications may be repeated, or coating and drying may be repeated, to adjust the thickness.

[0066] After applying the resin electrode paste to the electrode portion where the terminal electrode 8 is to be formed and the shield portion where the shield layer 10 is to be formed, the element body 4 is heat-treated under predetermined conditions to harden the binder (resin component) in the paste. The heat treatment conditions are preferably, for example, a treatment temperature (holding temperature) of 170°C to 230°C and a holding time of 60 to 90 minutes.

[0067] After forming the resin electrode layer that will become the terminal electrode 8, a plating film or a sputtering film may be formed on the outer surface of the resin electrode layer as appropriate. For example, forming a plating film of Ni, Cu, Sn, or the like on the outer surface of the resin electrode layer improves wettability with solder. When forming the plating film, a plating layer 15 is simultaneously formed on the surface of the shield layer 10, as shown in FIGS. 4A and 4B.

[0068] By the manufacturing method described above, an inductor 2 is obtained in which a pair of terminal electrodes 8 is formed on the bottom surface (mounting side) 4b of the element body 4 and a shield layer 10 is formed on the top surface (opposite mounting side) 4a. (Summary of the first embodiment)

[0069] Furthermore, in this embodiment, a shield layer 10 containing metal and resin is formed on the top surface 4a, which is at least one of the outer surfaces of the element body 4. This shield layer 10 can be formed simply by applying a paste-like material containing metal and resin, drying it, and hardening it, and the thickness of the shield layer 10 can be easily controlled. This makes it easier to manufacture the coil device 2 than a structure in which a metal sheet shield is attached to the element body. Moreover, compared to a coil device in which a metal sheet is attached to the element body 4, the adhesion between the shield layer 10 and the element body 4 is improved, and the coil device 2 can also be made more compact.

[0070] As shown in Figures 4A and 4B, the shield layer 10 also has a metal-rich layer 12 in which more metal than resin is observed. In the cross section of the metal-rich layer 12 shown in Figure 4A, the metal content is 50% or more. Furthermore, in the cross section of the metal-rich layer 12 shown in Figure 4B, the metal content is 80% or more. It is believed that this metal-rich layer 12 enhances the blocking effect of leakage magnetic flux.

[0071] The shield layer 10 further has a resin-rich layer 14, which exists at the interface between the element body 4 and the metal-rich layer 12. It is believed that this resin-rich layer 14 improves the adhesion between the shield layer 10 and the element body 4.

[0072] Furthermore, the terminal electrode 8 has a resin electrode layer made of the same material as the metal-rich layer 12 of the shield layer 10. This configuration makes it possible to effectively reduce leakage magnetic flux at specific noise frequencies. This is thought to be because the metal-rich layer 12, made of the same material, can cover a wider area of ​​the surface of the element body 4. Furthermore, since the terminal electrode 8 and the shield layer 10 can be formed simultaneously using the same raw material, manufacturing costs can be reduced.

[0073] The shield layer 10 has a coating layer formed by applying a paste containing metal and resin to the outer surface of the element body. The coating layer is easy to form and its thickness is easy to control. Therefore, design changes are easier than in coil devices with metal sheet shields, and manufacturing costs can be reduced.

[0074] Preferably, the shield layer contains Ag. It has been confirmed that a shield layer containing Ag can effectively reduce leakage flux, especially at high frequencies, even if it is formed thin.

[0075] The paste preferably contains flat metal powder. The paste may also contain approximately spherical metal powder. The coating layer is preferably formed by heat treating the paste at 170°C to 230°C.

[0076] A shielding layer formed from such a paste is more effective in reducing leakage magnetic flux. It is particularly preferable for the paste to contain small metal powder, preferably with an average particle size of less than 800 nm, more preferably 100 to 500 nm. By including such metal powder, the metal content of the metal-rich layer can be improved when the paste-coated film is heat-treated at a temperature (170°C to 230°C) that hardens the resin contained in the paste. It is thought that because the metal powder contains nanoparticles, a phenomenon similar to metal sintering occurs at a temperature lower than the melting point of the metal itself.

[0077] In this embodiment, the shield layer 10 is formed on the top surface 4a of the element body 4, opposite to the bottom surface 4b on which the terminal electrodes 8 are formed. In this way, the coil device 2 in which the shield layer 10 is formed on the top surface 4a, which is the side opposite to the mounting surface, can effectively reduce leakage magnetic flux from the side opposite to the mounting surface.

[0078] Second embodiment As shown in FIGS. 1B and 3B, the coil device 2a of this embodiment is similar to the coil device 2 of the first embodiment except as described below, and a common description will be omitted.

[0079] In the coil device 2a of this embodiment, the shield layer 10 has a non-mounting-side shield layer 10a formed on the top surface 4a of the element body 4, and ground conductive portions 10b extending from the non-mounting-side shield layer 10a through each of the side surfaces 4c and 4d of the element body 4 to the bottom surface 4b of the element body 4. Each ground conductive portion 10b is formed along the Z-axis direction at approximately the center in the X-axis direction of each of the side surfaces 4c and 4d of the element body 4, with a width along the X-axis that does not short-circuit the pair of terminal electrodes 8, 8, and is connected to the ground terminal electrode 8a shown in FIG.

[0080] The ground terminal electrode 8a is connected to a ground land 32a formed on the substrate 30 by a connecting member such as solder 34. The ground terminal electrode 8a is formed in the same manner as the terminal electrode 8. Furthermore, each ground conductive portion 10b is formed in the same manner as the non-mounting-side shield layer 10a.

[0081] In the coil device 2a of this embodiment, the shield layer 10 can be connected to the ground land (ground) 32a of the substrate 30. This allows the shield layer 10 to have the same potential as the ground potential. As a result, the shield layer 10 can be more effectively used to block leakage magnetic flux. The ground conductive portion 10b can also function as a shield for leakage magnetic flux at the side surfaces 4c and 4d of the element body 4. Furthermore, by connecting the ground conductive portion 10b to the ground, the number of connection points of the coil device 2a is increased in areas other than the terminal electrodes 8, 8 that supply power to the coil portion 6α, and the mounting strength of the coil device 2a to the substrate 30 can be improved.

[0082] Third embodiment As shown in FIGS. 1C and 2B, the coil device 2b of this embodiment is similar to the coil device 2 or 2a of the above-described embodiment except as described below, and therefore a duplicated description will be omitted.

[0083] In the coil device 2b of this embodiment, the shield layer 10 has a non-mounting side shield layer 10a formed on the top surface 4a of the element body 4, and a side shield layer 10c extending from the non-mounting side shield layer 10a through each of the four side surfaces of the element body 4 to the bottom surface 4b of the element body 4 or close to the bottom surface 4b.

[0084] The side shield layer 10c is formed so as to be continuous with the shield layer 10a, similar to the non-mounting-side shield layer 10a. The lower end of the side shield layer 10c in the Z-axis direction is formed so as to be insulated from the terminal electrode 8. Alternatively, the terminal electrode 8 is formed on the bottom surface 4b of the element body 4, with an area that ensures insulation from the lower end of the side shield layer 10c in the Z-axis direction.

[0085] In this manner, the shield layer 10 of this embodiment may be formed to cover the outer surface of the element body except for the bottom surface 4b, which is the mounting side surface. This configuration also reduces leakage magnetic flux in the direction of a plane (the plane including the X-axis and Y-axis).

[0086] Fourth embodiment As shown in FIGS. 1D and 3C, the coil device 2c of this embodiment is similar to the coil device 2 or 2a to 2b of the above-described embodiments except as described below, and therefore a duplicated description will be omitted.

[0087] In the coil device 2c of this embodiment, a recess 20 recessed upward along the Z axis is formed on the bottom surface 4b of the element body 4 between the legs 22, 22 arranged at a predetermined interval along the X axis. A terminal electrode 8 is formed on each of the bottom surfaces 4b of the legs 22 of the element body 4.

[0088] A mounting-side shield layer 10d is formed on the ceiling surface of the recess 20 of the element body 4. The mounting-side shield layer 10d is formed in the same manner as the non-mounting-side shield layer 10a, and may be formed separately as shown in the figure, or may be formed continuously with partial side shield layers (not shown) formed on the side surfaces 4c and 4d of the element body 4.

[0089] 3C, in the coil device 2c of this embodiment, other electronic components 36 such as a capacitor chip can be placed in the space formed between the recess 20 and the mounting substrate 30. In addition, the shield layer 10d formed in the recess 20 reduces leakage magnetic flux, thereby preventing adverse effects on the electronic components 36.

[0090] Fifth embodiment As shown in FIG. 1E, the coil device 2d of this embodiment is similar to the coil device 2 or 2a to 2c of the above-described embodiments except as described below, and therefore a duplicated description will be omitted.

[0091] In the coil device 2d of this embodiment, each terminal electrode 8 is formed in an L-shape from the bottom surface 4b of the element body 4 toward each side surface 4e, 4f. In order to ensure insulation with each terminal electrode 8, the shield layer 10a on the non-mounting side of the shield layer 10 does not cover the entire top surface 4a of the element body 4, but is spaced apart from each terminal electrode 8 at a predetermined interval in the X-axis direction. top surface It is formed in 4a.

[0092] In the coil device 2d of this embodiment, when it is mounted on the substrate 30 shown in FIG. 3A, it becomes easy to form solder fillets on the terminal electrodes 8 formed on the side surfaces 4e and 4f of the element body 4.

[0093] Other embodiments The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention.

[0094] For example, in the above-described embodiment, the coil portion 6α is made of a round wire 6, but the type of wire 6 is not limited to this and may be a rectangular wire whose conductor has a substantially rectangular cross section. Alternatively, the coil portion 6α may be a square wire or a Litz wire made by twisting together thin wires. Furthermore, the coil portion 6α may be made by laminating conductive plate materials.

[0095] In addition, in the above-described embodiment, a metal raw material powder containing both microparticles and nanoparticles is used as the paste for forming the terminal electrode 8 and the shield layer 10, but only one of them may be used, or metal particles having a larger specific surface area than the microparticles may be used instead of the microparticles.

[0096] Furthermore, in the above-described embodiment, the resin electrode layer of the terminal electrode 8 and the coating film constituting the shielding layer 10 are formed by heat treating the same paste, but they may be made of different materials. For example, the terminal electrode 8 may be any electrode layer that can be electrically connected to the lead portion 6a of the wire 6, and is not particularly limited.

[0097] Furthermore, the metal-rich layer 12 constituting the shield layer 10 is preferably formed by continuously connecting particles or clumps of the metal component to form a layer, as shown in Figure 4B. The paste for forming the metal-rich layer 12 shown in Figure 4B is prepared by mixing the following metal raw material powder: specified It is preferable that the paste contains the above-mentioned components in a content ratio of 1:1.

[0098] That is, a preferred metal raw material powder contains microparticles with particle sizes on the order of micrometers and nanoparticles with particle sizes on the order of nanometers. The microparticles preferably have an average particle size of 1 μm to 10 μm, more preferably 3 μm to 5 μm. On the other hand, the nanoparticles preferably have an average particle size of less than 800 nm, more preferably 100 nm to 500 nm.

[0099] In addition, it is preferable that both the microparticles and the nanoparticles contain Ag as a main component. When the paste contains metal elements other than Ag, the form of existence of the metal elements is not particularly limited. For example, the metal elements other than Ag may exist as particles other than the microparticles and nanoparticles, or may be solid-dissolved in the microparticles.

[0100] Furthermore, in the above-described embodiment, the shield layer 10 is formed by a coating method on the surface of the element body 4 made of resin containing magnetic powder, but the shield layer 10 may also be formed on the surface of an element body made of a sintered body of magnetic powder that does not contain resin.

[0101] For example, the first core portion 41 constituting the element body 4 can be a sintered body of ferrite powder or metal magnetic powder. Alternatively, the element body 4 itself can be an FT-type, ET-type, EI-type, UU-type, EE-type, EER-type, UI-type, drum-type, pot-type, or cup-type green compact core or a sintered compact core, and an inductor element can be formed by winding a coil around the core. In this case, the lead portion does not need to be embedded inside the element body, but can be drawn out along the outer periphery of the core and connected to the outer surface of the terminal electrode 8.

[0102] Furthermore, the coil device according to the present invention is not limited to an inductor, but may be an electronic component such as a transformer, a choke coil, or a common mode filter. [Example]

[0103] The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

[0104] Example 1 1A was fabricated in Example 1. Specifically, an element body 4 was fabricated by the method described in the embodiment, and a shield layer 10 was formed on an upper surface 4a of the element body 4.

[0105] The shield layer 10 was formed by using the paste shown in the embodiment and by carrying out a heat treatment under the conditions described in the embodiment.

[0106] The obtained inductor sample (coil device 2) was connected to a test substrate 30 as shown in FIG. 5, and the leakage magnetic flux of the coil device 2 sample was measured by an analysis device 52 of a leakage magnetic flux measurement device 50.

[0107] Specifically, a measurement plane 56 was assumed above the sample of coil device 2, parallel to substrate 30 at a predetermined interval (for example, 1 mm), and probe 54 was moved along the measurement plane to measure the leakage flux of the sample of coil device 2. The leakage flux test of coil device 2 was conducted under two conditions: condition 1 at 400 kHz and condition 2 at 2 MHz, and the leakage flux in the vertical direction (Z axis) and horizontal directions (X and Y axes) relative to coil device 2 was measured. The results are shown in Table 1.

[0108] [Table 1]

[0109] A cross section of the coil device obtained in Example 1, including the shield layer 10, was photographed using an SEM. A schematic diagram of the resulting cross-sectional photograph is shown in FIG. 4A. The average thickness of the metal-rich layer 10 was 15 μm, and the average thickness of the resin layer 14 was 2 μm. A nickel-plated intermediate layer 16 and a tin-plated outermost layer 18 were also observed. The metal content in the metal-rich layer 10 measured from the cross-sectional photograph is shown in Table 1.

[0110] Example 2 In Example 2, an inductor sample of the coil device 2 was fabricated in the same manner as in Example 1, except for the following points, and measurements were performed in the same manner as in Example 1. The results are shown in Table 1. Also, a schematic diagram of a cross-sectional photograph including the shield layer 10 is shown in FIG. 4B.

[0111] In Example 2, when forming the sealing layer 10, a paste containing metal powder with an average particle size smaller than that of Example 1 was used, and heat treatment was performed under the conditions described in the embodiment.

[0112] Comparative Example 1 In Comparative Example 1, an inductor sample of the coil device 2 was fabricated in the same manner as in Example 1, except that the shield layer 10 was not formed, and measurements were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0113] evaluation As shown in Table 1, it was confirmed that, compared to Comparative Example 1, Example 1, and preferably Example 2, can effectively reduce leakage magnetic flux, particularly at high frequencies, even if the thickness of the shield layer is relatively thin. Furthermore, it was also confirmed that, in Examples 1 and 2, the shield layer 10 can be formed simultaneously with the formation of the terminal electrodes, making it possible to reduce the size of the coil device and the manufacturing costs.

[0114] Furthermore, a peeling test confirmed that the shield layer 10 has excellent adhesion to the surface of the element body 4, similar to the terminal electrode 8. That is, it was confirmed that the black portion at the interface between the surface of the element body 4 and the metal-rich layer 12 shown in Figures 4A and 4B is not a gap, but rather a resin-rich layer 14 filled with resin. [Explanation of symbols]

[0115] 2, 2a, 2b, 2c, … inductors 4... Element body 4a ... Top surface (opposite side to mounting) 4b ... Bottom (mounting side) 4c~4f ... Side 41 ... First core section 41a … Tsuba 41b … Winding core part 41c ... cutout 42 ... Second core section 42a... Magnetic particles 6α … Coil section 6 … wire 6a ... Lead section 61 … Extracting electrode part 8 … Terminal electrode 8a… Grounding terminal electrode 10... Shield layer 10a... Shield layer on the opposite side to the mounting surface 10b... Ground conduction section 10c... Side shield layer 10d... Mounting side shield layer 12... Metal-rich layer (region) 14... Resin-rich layer (area) 15... Plating layer 16... Middle class 18… Outermost layer 20... Recess 22… Legs 30... Circuit board 32... Land 32a... Grounding land 34... Solder 36...Other electronic components 50... Leakage magnetic flux measuring device 52… Analyzer 54... Probe 56…Measurement plane

Claims

1. an element body including a magnetic material; a coil portion disposed within the element body; a terminal electrode connected to a lead portion of the coil portion, a shield layer containing a metal and a resin is formed on at least one of the outer surfaces of the element body; the shield layer has a metal-rich region in which the metal is observed in a larger amount than the resin, and a resin-rich region in which the resin is observed in a larger amount than the metal and which is present at an interface between the element body and the metal-rich region; The metal is a metal powder having a substantially spherical or flat shape, a plating layer is formed on the surface of the shield layer separately from the shield layer; The coil device has a coating layer formed by applying a paste containing the metal and the resin to the outer surface of the element body.

2. The coil device according to claim 1 , wherein the cross section of the metal-rich region contains 50% or more of the metal.

3. The coil device according to claim 2 , wherein the cross section of the metal-rich region contains 80% or more of the metal.

4. 4. The coil device according to claim 1, wherein the terminal electrode has a region made of the same material as the metal-rich region of the shield layer.

5. 5. The coil device according to claim 1, wherein the shield layer contains Ag.

6. 6. The coil device according to claim 1, wherein the coating layer is formed by heat treating the paste at 170 to 230°C.

7. 7. The coil device according to claim 1, wherein the paste contains substantially spherical metal powder.

8. 8. The coil device according to claim 1, wherein the paste contains flat metal powder.

9. 9. The coil device according to claim 1, wherein the shield layer is formed on an outer surface of the element body opposite to the outer surface on which the terminal electrodes are formed.

10. The coil device according to any one of claims 1 to 9, wherein the shield layer has a non-mounting side shield layer formed on the non-mounting side of the element body, and a ground conduction portion extending from the non-mounting side shield layer through the side of the element body to near the mounting side of the element body.

11. 11. The coil device according to claim 1, wherein a recess is formed on the mounting side of the element body toward the non-mounting side, and a mounting-side shield layer is formed in the recess.

12. 12. The coil device according to claim 1, wherein the shield layer is formed so as to cover the outer surface of the element body except for the mounting side.

13. 13. The coil device according to claim 1, wherein the terminal electrodes are formed in an L-shape from the mounting side of the element body toward the side of the element body.

Images