Coil component

Abstract

To suppress the thickness of an insulating layer.SOLUTION: A coil component according to an embodiment includes a magnetic base formed by bonding together a plurality of metal magnetic particles and having a first surface and a second surface, a conductor provided inside the magnetic base, an insulating layer provided on the first surface having a smaller surface roughness than the second surface, and an external electrode provided on the second surface and electrically connected to the conductor.SELECTED DRAWING: Figure 6

Description

Technical Field

[0001] The present invention relates to coil components.

Background Art

[0002] With the improvement in performance of electronic devices, the quantity of electronic components used in electronic devices has been increasing, and higher performance and miniaturization of electronic components have been demanded. Further, electronic components mounted on a substrate are used in a high-density state with a small component pitch. The same applies to coil components in terms of higher performance, miniaturization, and high-density mounting, and the adoption of metal magnetic materials is progressing for some types of coil components.

[0003] On the other hand, in coil components that employ metal magnetic particles, it is important to ensure insulation. For example, in Patent Document 1, insulation is ensured by providing a surface insulating layer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, forming a thick insulating layer hinders miniaturization of the coil component. Therefore, on the premise that insulation is ensured, it is preferable that the thickness of the insulating layer is thin. In view of the above circumstances, an object of the present invention is to suppress the thickness of the insulating layer.

Means for Solving the Problems

[0006] In order to solve the above problems, a coil component according to one aspect of the present invention includes a magnetic substrate in which a plurality of metal magnetic particles are bonded and which has a first surface and a second surface, a conductor provided inside the magnetic substrate, an insulating layer provided on the first surface having a smaller surface roughness than the second surface, and an external electrode provided on the second surface and electrically connected to the conductor.

[0007] Further, according to the coil component of one aspect of the present invention, the insulating layer is provided adjacent to the first surface and spaced apart from the third surface and the fourth surface of the magnetic substrate different from the second surface. Further, according to the coil component of one aspect of the present invention, the insulating layer is provided at a distance greater than the maximum size of the metal magnetic particles from the third surface and the fourth surface when viewed toward the first surface.

[0008] Further, according to the coil component of one aspect of the present invention, the insulating layer is provided spaced apart from the other four surfaces adjacent to the first surface. Further, according to the coil component of one aspect of the present invention, the magnetic substrate is chamfered or has an R surface at the ridge line portion between the first surface and the surface adjacent to the first surface, and the insulating layer is provided away from the chamfering or R surface.

[0009] Further, according to the coil component of one aspect of the present invention, the first surface has a line roughness of 10 μm or less represented by the line roughness of the surface roughness. Further, according to the coil component of one aspect of the present invention, the insulating layer has a surface with a smaller surface roughness than the first surface.

[0010] Further, according to the coil component of one aspect of the present invention, the insulating layer contains a thermosetting resin. Further, according to the coil component of one aspect of the present invention, the external electrode is provided spaced apart from the other four surfaces adjacent to the second surface.

Advantages of the Invention

[0011] According to the present invention, the thickness of the insulating layer can be suppressed.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the present invention, and not all combinations of the features described in the embodiments are essential to the configuration of the present invention. The configuration of the embodiments can be appropriately modified or changed according to the specifications of the apparatus to which the present invention is applied and various conditions (usage conditions, usage environment, etc.).

[0014] The technical scope of the present invention is defined by the claims and is not limited by the following individual embodiments. The drawings used in the following description may differ from the actual structure, scale, shape, etc. in order to make each component easier to understand. Regarding the components shown in the previously described drawings, reference may be made as appropriate in the description of subsequent drawings.

[0015] <One Embodiment of Coil Component> FIG. 1 is a perspective view showing a coil component according to a first embodiment of the present invention. The coil component 100 is mounted on a substrate 200. For example, two land portions 201 are provided on the substrate 200. The coil component 100 has, for example, two external electrodes 12. The coil component 100 is mounted on the substrate 200 by joining each external electrode 12 and the land portion 201 with solder, for example.

[0016] The circuit board 10 includes a coil component 100 and a substrate 200 on which the coil component 100 is mounted. The circuit board 10 is provided in various electronic devices. Examples of electronic devices including the circuit board 10 include automotive electrical components, servers, board computers, and various other electronic devices.

[0017] In this specification, unless otherwise interpreted in the context, the description of directions is based on the "L-axis" direction, "W-axis" direction, and "H-axis" direction in FIG. 1, and is referred to as the "length" direction, "width" direction, and "height" direction, respectively. The "height" direction may also be referred to as the "thickness" direction.

[0018] The coil component 100 has a rectangular parallelepiped outer shape. That is, the coil component 100 has outer surfaces at both ends in the length direction L, both ends in the height direction H, and both ends in the width direction W, respectively. In the rectangular parallelepiped-shaped coil component 100, the dimensions of each side are such that the dimension in the length direction L is in the range of, for example, 1.0 to 4.5 mm, the dimension in the width direction W is in the range of, for example, 0.5 to 3.2 mm, and the dimension in the height direction H is in the range of, for example, 0.5 to 1.0 mm. Also, the dimension in the height direction H is smaller than the dimension in the length direction L, and furthermore, the dimension in the height direction H is smaller than the dimension in the width direction W.

[0019] All outer surfaces of the coil component 100 may be flat planes or curved curved surfaces. Also, the eight corner portions and the twelve edge portions of the coil component 100 may have rounded corners. In this specification, even when a part of the outer surface of the coil component 100 is curved, or when the corner portions or edge portions of the coil component 100 have rounded corners, such a shape may be referred to as a "rectangular parallelepiped shape". That is, when the term "rectangular parallelepiped" or "rectangular parallelepiped shape" is used in this specification, it does not mean a "rectangular parallelepiped" in a strictly mathematical sense.

[0020] <Structure of Coil Component> FIG. 2 is a cross-sectional view of the coil component 100 shown in FIG. 1. FIG. 2 shows a cross-section along the line A-A shown in FIG. 1. Hereinafter, description will be made with reference to FIGS. 1 and 2. The coil component 100 in the first embodiment of the present invention has a magnetic substrate 11, an external electrode 12, and an insulating layer 13, and has a conductor 14 inside the magnetic substrate 11. The magnetic substrate 11 corresponds to an example of the magnetic substrate referred to in the present invention, and the external electrode 12 corresponds to an example of the external electrode referred to in the present invention. Also, the insulating layer 13 corresponds to an example of the insulating layer referred to in the present invention, and the conductor 14 corresponds to an example of the conductor referred to in the present invention.

[0021] The magnetic substrate 11 in the present embodiment is a magnetic body formed from a metal magnetic material and a binder. The binder binds the metal magnetic materials to each other and is also highly insulating in order to prevent electrical conduction. The binder is such that the resistivity of the magnetic substrate 11 is 10 6 Ωcm or more. For example, a binder having a resistivity of 10 8Those with a resistivity of 10 Ωcm or more are selected. Also, for the purpose of enhancing mechanical strength, as the binder, resin, glass, or metal oxide can be selected.

[0022] The magnetic substrate 11 has a hexahedral shape and is, for example, in the shape of a rectangular parallelepiped. That is, the magnetic substrate 11 has an upper surface 101 at one end in the height direction H and a bottom surface 102 at the other end in the height direction H. Also, the magnetic substrate 11 has a front surface 103 at one end in the width direction W and a rear surface 104 at the other end in the width direction W. Further, the magnetic substrate 11 has side surfaces 105, 106 at both ends in the length direction L.

[0023] The upper surface 101 corresponds to an example of the "first surface" in the present invention, and the bottom surface 102 and the side surfaces 105, 106 correspond to examples of the "second surface" in the present invention. The upper surface 101 is located at a position facing away from the bottom surface 102. Facing away means a positional relationship in which the surfaces face outward in opposite directions. Also, the upper surface 101 is located adjacent to the front surface 103, the rear surface 104, and the side surfaces 105, 106. Adjacent means a positional relationship in which no other surface intervenes between the surfaces and only a ridge line intervenes. In the example shown here, the adjacent surfaces are in an orthogonal positional relationship.

[0024] The magnetic substrate 11 in the present embodiment is a magnetic body formed from a metal magnetic material and a binder. The binder binds the metal magnetic materials to each other and is also highly insulating to prevent electrical conduction. The binder is such that the surface resistance of the magnetic substrate 11 is 10 5 Ω / sq. or more. Since the metal magnetic material mainly composed of Fe itself has a low resistance, it is desirable to adjust the components and compounding ratios of the binder according to the metal magnetic material. As the binder, for example, those with a specific resistance of 10 8 Ωcm or more are selected. Also, for the purpose of enhancing insulation, the binder contains resin, and glass and metal oxide can be selected as components other than resin.

[0025] The magnetic substrate 11 has a very high specific resistance inside and also on the surface, and there is also a binder on the surface. The metal magnetic material is metal magnetic particles containing one or more components of Fe, Ni, and Co. Further, in addition to the metal magnetic particles, the metal magnetic material may contain magnetic particles of one or more of Mg, Mn, and Ni among ceramics or non-magnetic particles such as silica. As the metal magnetic particles, in addition to the components of Fe, Ni, and Co, they may contain one or more components of Si, Cr, Al, B, and P, or a combination of multiple types of metal magnetic particles may be used.

[0026] The metal magnetic material has a particle size of 1 μm or more and 60 μm or less. Further, when the metal magnetic material further contains other materials such as metal fine particles, metal oxides, and ceramic materials in addition to the metal magnetic particles, the average particle size of the other materials is 0.01 to 1 μm, which is smaller than the particle size of the metal magnetic particles. When including materials other than metal magnetic particles, it is possible to reduce voids or supplement mechanical strength rather than enhancing the magnetic function.

[0027] The magnetic substrate 11 has a filling rate of the metal magnetic material of 80 vol% or more and 88 vol% or less, and the balance is other than the metal magnetic material, including an insulator or voids. The conductor 14 is made of a metal material with excellent conductivity. As the metal material for the conductor 14, for example, one or more metals of Cu, Al, Ni, or Ag, or an alloy containing any of these metals can be used. The conductor 14 may be a wound metal wire provided with an insulating film on the surface, or may be formed on the surface of a substrate, sheet, etc. by plating, printing, etc.

[0028] The conductor 14 of this embodiment has a winding portion 402 that winds one or more turns. The number of turns of the winding portion 402 is, for example, 1.5 turns or more and 10.5 turns or less. The shape of the winding portion 402 may be planar or spiral. The winding portion 402 may, for example, have two windings facing each other on the upper and lower sides and form one aggregate.

[0029] The conductor 14 has a lead-out portion 401 for making electrical connection with the outside. The lead-out portion 401 is provided at both ends of the winding portion 402 and connects the external electrode 12 to the conductor 14. For the production of the conductor 14, any of the processes of winding, thin film, and lamination can be used, and there is no particular limitation.

[0030] FIG. 2 illustrates a so-called horizontally wound winding portion 402 in which the conducting wire winds along the bottom surface 102 and the top surface 101 of the magnetic substrate 11. The conductor 14 may have a so-called vertically wound winding portion in which the conducting wire winds along the end surface 103 of the magnetic substrate 11. The coil component 100 includes two external electrodes 12 as an example. The external electrodes 12 shown in FIGS. 1 and 2 are electrodes of a type called two-sided electrodes, and are provided, for example, from the bottom surface 102 to the side surfaces 105 and 106 of the magnetic substrate 11. The external electrode 12 has, for example, a metal layer with a thickness of 1 to 5 μm. The external electrode 12 may be a combination of a plurality of metal layers, and the total thickness is, for example, 5 to 10 μm. Also, the external electrode 12 may be a combination of a metal layer containing resin in part, and the total thickness is, for example, 10 to 20 μm.

[0031] The external electrode 12 is composed of one or both of a layer of the same component as the conductor 14 and a layer of a component with higher resistance than the conductor 14. Also, the external electrode 12 is composed of one or both of a layer with the same filling rate as the conductor 14 and a layer with a lower filling rate than the conductor 14.

[0032] In the case of the example shown in FIG. 2, the external electrode 12 has an underlayer 21 and a metal layer 22. For the underlayer 21, metal materials such as Ag, Cu, Ti, and Ni are used. The underlayer 21 is provided on the surface of the magnetic substrate 11 by plating, coating of a metal material, sputtering method, or vapor deposition method. Also, the underlayer 21 has a thickness of 1 μm or less and may be partially separated from other parts. The underlayer 21 is in close contact with the surface of the magnetic substrate 11 and the lead-out portion 401 of the conductor 14, thereby integrating the external electrode 12 with the magnetic substrate 11 and obtaining electrical connection between the external electrode 12 and the conductor 14.

[0033] The metal layer 22 is made of a metal material with excellent conductivity. As the metal material, for example, Cu and Ag are used, and as another option, Ni, Pd, and Sn can be used. The metal layer 22 is formed in a layered structure where layers mainly composed of respective metal materials or layers alloyed in part overlap each other.

[0034] In the examples shown in FIGS. 1 and 2, the insulating layer 13 is provided over the entire upper surface 101 of the magnetic substrate 11. <Structure of the insulating layer>

[0035] FIG. 3 is an enlarged view conceptually showing the microscopic structure in the insulating layer 13. The insulating layer 13 includes a resin component 301, an aggregate 302 of carbon particles, a first filler 303, and a second filler 304, and is provided on the upper surface 101 of the magnetic substrate 11. On the upper surface 101, there is an uneven structure caused by metal magnetic particles as a microscopic structure, and the insulating layer 13 is provided on the uneven structure. The relationship between the uneven structure of the upper surface 101 and the insulating layer 13 will be described in detail later. In FIG. 3, mainly to show the structure inside the insulating layer 13, it is illustrated thicker than actual, and the surface of the insulating layer 13 is also illustrated as a simple plane.

[0036] The insulating layer 13 has an average thickness of 10 μm or less. As the resin component 301 of the insulating layer 13, for example, a thermosetting resin is used, and it is preferably Tg is higher than 150°C. As the resin component 301, in addition to heat resistance, a resin with high moisture resistance, corrosion resistance, and impact resistance is selected. Considering these, as the resin component 301, for example, acrylic-based, epoxy-based, and phenolic-based resins are preferred. Preferred examples of the resin component 301 include diallyl phthalate resin, bisphenol A type epoxy resin, and trifunctional or higher polyfunctional epoxy resins.

[0037] The resin component 301 is more than 30 vol% of all the elements constituting the insulating layer 13. Also, by combining two or more resins as the resin component 301, it is possible to meet different requirements such as mechanical strength and heat resistance. The insulating layer 13 contains aggregates 302 of carbon particles in the resin component 301.

[0038] As the carbon particles forming the aggregates 302, for example, carbon black, graphite, etc. are used. As the carbon particles, furnace black, acetylene black may be used. Since the carbon particles have conductivity and exist as aggregates 302, a portion having lower electrical resistance than the resin component 301 is formed in the insulating layer 13.

[0039] Also, even if the insulating layer 13 contains aggregates 302 of carbon particles in the resin component 301, the insulating property is ensured by the presence of a resin component 301 having higher insulating property than the low-conductivity carbon particles, and it is an insulator in the normal state. Therefore, the insulating property of the coil component 1 is ensured by the presence of the insulating layer 13. On the other hand, when static electricity or the like occurs, the charging is suppressed by the conductivity of the carbon particles.

[0040] As shown in FIGS. 1 and 2, when the insulating layer 13 covers the upper surface 101 of the base 11, the surface of the base 11 is protected, and the electricity charged in the coil component 100 is easily discharged from the upper surface 101, and the electrical influence on the base 11 of the coil component 100 is alleviated. For example, when a metal or the like other than the coil component 100 comes into contact with the insulating layer 13, the electric charge accumulated in the coil component 100 is discharged from the insulating layer 13 to the metal other than the coil component 100, and in particular, the voltage applied to the magnetic base 11 is suppressed. Therefore, the dielectric breakdown, which is an electrical defect caused by current passing between the metal magnetic particles contained in the magnetic base 11, is suppressed. As those that come into contact with the coil component 100 and accumulate electric charge, those having low electrical resistance such as metal and human fingers are assumed.

[0041] In the coil component 100 using metal magnetic particles, special attention is required for static electricity. This is because static electricity is invisible and is one of the causes of defects that occur without being noticed as an abnormality. Since the influence of static electricity is suppressed by providing the insulating layer 13, the safety of the coil component 100 is enhanced.

[0042] Due to the presence of the insulating layer 13, the coil component 100 can be conveyed with the insulating layer 13 as the contact surface. That is, damage caused by friction or vibration during conveyance is reduced, and even if static electricity is generated by contact friction, the influence on the magnetic substrate 11 is alleviated. In particular, since the insulating layer 13 covers the entire upper surface 101 of the magnetic substrate 11, the entire upper surface 101 of the magnetic substrate 11 is protected, the generation of defects in the insulating layer 13 is prevented, and discharge from parts other than the insulating layer 13 is prevented.

[0043] Since the reflectivity of the insulating layer 13 is small, it becomes easy to distinguish from the magnetic substrate 11 and from the external electrode 12, and it can be used for direction identification using the insulating layer 13. Since the reflectivity of the insulating layer 13 is small, it also becomes easy to visually identify the coil component 100.

[0044] As shown in FIG. 3, in the present embodiment, the insulating layer 13 includes a first filler 303 and a second filler 304 that are inorganic fillers. The first filler 303 contains one or more insulating compounds of magnesium, calcium, titanium, and zirconium. Examples of the insulating compound of the first filler 303 include magnesium silicate, calcium carbonate, titanium oxide, zirconia, and the like. Further, the first filler 303 has a major axis and a minor axis as its outer shape. Specific outer shapes of the first filler 303 include shapes that appear to be flat, elliptical, plate-like, needle-like, and the like.

[0045] The second filler 304 contains one or more insulating compounds of silicon, aluminum, and magnesium. Examples of the insulating compound of the second filler 304 include silicon dioxide, aluminum oxide, magnesium oxide, and the like. Further, the outer shape of the second filler 304 is spherical.

[0046] The first filler 303 is larger than the second filler 304. For example, the major axis of the first filler 303 is larger than the particle size of the second filler 304, and the minor axis of the first filler 303 is larger than the particle size of the second filler 304. The first filler 303 has a major axis of 1 to 10 μm and a minor axis of 100 nm to 1 μm. The second filler 304 has a major axis of 50 to 500 nm, and the minor axis is larger than 80% of the major axis. The proportion of the first filler 303 and the second filler 304 is such that the second filler 304 is contained more than the first filler 303, and the combined proportion of the first filler 303 and the second filler 304 is 30 to 50 vol% of the insulating layer 13. For example, the combined proportion of the first filler 303 and the second filler 304 is in a range less than the resin component 301. By adjusting the combination of the sizes of the inorganic fillers 303 and 304, the target function is ensured and the thickness of the insulating layer 13 is reduced. Also, due to the presence of the first filler 303, shape stability such as at the edge portion of the insulating layer 13 is obtained, and due to the presence of the second filler 304, the dispersion state in the insulating layer 13 is improved and the thickness of the insulating layer 13 is reduced.

[0047] Also, when the inorganic fillers 303 and 304 are light-transmissive such as silica, the sizes of the inorganic fillers 303 and 304 as viewed in the thickness direction of the insulating layer are 100 to 300 nm. These inorganic fillers 303 and 304 can give the insulating layer 13 light shielding properties and can suppress light transmission and reflection. Therefore, even if the thickness of the insulating layer 13 is thin, the magnetic substrate 11 will not be visible.

[0048] Since the insulating layer 13 contains the inorganic fillers 303 and 304, the insulation is enhanced in a normal state without static electricity or the like. That is, the insulating layer 13 can obtain high insulation in the normal use of the coil component 1. For example, in the range where the voltage is lower than 100 V, it means that the insulating layer 13 is an insulator. Represented by the magnitude of the resistance values of each element, when the voltage is lower than 100 V, conductor < substrate ≤ insulating layer, and when the voltage is higher than 100,000 V, conductor < insulating layer < substrate.

[0049] The presence of the inorganic fillers 303 and 304 in the insulating layer 13 contributes to reducing the coefficient of linear expansion. Further, the inclusion of two types of inorganic fillers, the first filler 303 and the second filler 304, enhances the uniformity of the inorganic fillers due to the dispersibility, thereby increasing the mechanical strength. In particular, the inclusion of the first filler 303 reduces the coefficient of linear expansion in the direction parallel to the surface of the insulating layer 13.

[0050] Regarding each element included in the insulating layer 13, it can be confirmed by observing the cross-section of the insulating layer 13 with, for example, a TEM (transmission electron microscope), SEM (scanning electron microscope), or optical microscope. The carbon particles 305, inorganic fillers 303 and 304, and voids are judged to exist from the difference in contrast in the optical observation of the cross-section of the insulating layer 13. Similarly, the presence and size of the fillers can also be judged from the cross-section. The resin component 301 is the other part excluding the aggregates 302 of carbon particles, inorganic fillers 303 and 304, and voids, and the proportion of the resin component 301 is determined.

[0051] <Manufacturing method of coil component> Next, the manufacturing method of the coil component 100 will be described. FIG. 4 is a flowchart showing an example of the manufacturing method of the coil component 100. In step S101, raw material particles for forming a metal magnetic material are mixed with a binder to prepare a composite material which is a composite material. Further, in step S102, a conductor member that becomes the conductor 14 is formed. The conductor member may be formed by, for example, a conducting wire, or may be formed by printing or plating of a conductor material. In the formation of the conductor member, processes such as winding, lamination, and thin film are used, for example.

[0052] Step S103 is a molding process. A conductor member is placed in a mold. For example, by mold molding in which a heated composite material is filled into the mold, compressed, and cooled, a molded body integrated with the conductor member is obtained. The mold may have a resin component on a part of its surface at the molding stage. This resin component is preferably a resin that does not soften at the heating temperature during molding. For example, a thermosetting resin is selected as the resin component. The molded body obtained in step S103 corresponds to the combined body of the magnetic substrate 11 and the conductor 14 in one coil component 100, and the molded body is, for example, a hexahedron.

[0053] In the molding process of step S103, when the composite material is filled into the mold and compressed, it is compressed at a pressure lower than, for example, 10 MPa. Thereby, the deformation of the raw material particles is suppressed, and the aspect ratio of the metal magnetic particles obtained from the raw material particles is within a change range less than 10% with respect to the aspect ratio of the raw material particles.

[0054] Also, during filling, the composite material is heated to a temperature higher than the softening temperature of the binder, so that the binder is in a state where it is easy to move. After compression, it is cooled to a temperature lower than the softening temperature of the binder, so that the binder is in a state where it does not move and a molded body is obtained. That is, in the molding process, by combining heating and cooling without relying on pressure more than the conventional method, a molded body in which the binder exists on the surface of the raw material particles is obtained.

[0055] Step S104 is a processing process. Surface processing is performed on the surface of the molded body where the external electrode 12 is provided. That is, if the external electrode 12 is a one-sided electrode, surface processing is performed on the bottom surface 102. If the external electrode 12 is a two-sided electrode, surface processing is performed on the bottom surface 102 and the side surfaces 105, 106. By this surface treatment, in the example shown in FIG. 2, the lead-out portion 401 of the conductor 14 is exposed on the bottom surface 102, and the surface roughness increases on the bottom surface 102 and the side surfaces 105 and 106. Since the upper surface 101 remains the formed surface obtained in step S103, as a result of the processing step in step S104, the upper surface 101 becomes a surface having a surface roughness smaller than that of the bottom surface 102 and the side surfaces 105 and 106.

[0056] In step S104, the surface treatment may be performed by a method of removing the binder from the surface of the formed body, or may be performed by a method of removing the metal magnetic particles. As the surface treatment of the method of removing the binder, a method may be used in which a laser, sandblasting, etc. are used to damage the binder, and the binder is removed first to also remove the metal magnetic particles. As the surface treatment of the method of removing the metal magnetic particles, a method may be used in which polishing is used to apply a load to the metal magnetic particles, and the metal magnetic particles are removed first to also remove the binder.

[0057] On the surface where the surface treatment is performed, some of the metal magnetic particles are removed, or the binder that fills the gaps between the metal magnetic particles is removed. Therefore, the processed surface after processing has a larger surface roughness than the formed surface before processing. In step S105, the underlayer 21 is formed on the processed surface by sputtering or vapor deposition. The underlayer 21 is formed in the formation range of the external electrode 12, and in the examples shown in FIGS. 1 and 2, it is formed on the bottom surface 102 and the end surfaces 105 and 106. However, the underlayer 21 is not formed on the portion of the bottom surface 102 between the two external electrodes 12.

[0058] In step S106, an insulating layer 13 is formed on, for example, the upper surface 101, which has a smaller surface roughness than the bottom surface 102 and the end surfaces 105 and 106 on which the external electrodes 12 are formed. For this reason, the thickness of the insulating layer 13 is suppressed, contributing to the miniaturization of the coil component 100. Further, since the insulating layer 13 is not provided on the front surface 103 and the rear surface 104, the insulating layer 13 does not affect the outer dimensions of the coil component 100 in the width direction W.

[0059] The insulating layer 13 is formed by spraying, transferring, printing, or the like an insulating material onto the surface of the magnetic substrate 11 in a film shape and then solidifying it by heat. When printing is used, the insulating material adheres to the upper surface 101 so as to flatten the unevenness of the upper surface 101, and thus the surface roughness on the surface of the insulating layer 13 becomes smaller than the surface roughness of the upper surface 101. The insulating layer 13 contains a thermosetting resin. Since the glass transition point of the resin contained in the insulating layer 13 is higher than, for example, 150°C, changes in the insulating layer 13 due to the environmental temperature are suppressed.

[0060] The insulating layer 13 is most easily formed by a method in which an insulating material mainly composed of a resin is used and the resin component is solidified by heat. Here, the point that the thickness of the insulating layer 13 in the present embodiment is suppressed will be described in detail while comparing with a comparative example.

[0061] FIG. 5 is an enlarged cross-sectional view conceptually showing the structure of the insulating layer in the comparative example. In the comparative example shown in FIG. 5, raw material particles serving as metal magnetic particles 501 and a raw material resin of a binder 502 are filled into a mold at a high pressure without going through heating and cooling. As a result, on the surface of the magnetic substrate 500, the binder 502 covers the metal magnetic particles 501 with a substantially uniform thickness and the surface roughness is large.

[0062] And, since deep recesses 504 are formed between the metal magnetic particles 501, the insulating layer 503 formed on the surface of the magnetic substrate 500 becomes a thick layer as a whole so that sufficient insulation can be obtained in the recesses 504. Therefore, the thickness D1 of the insulating layer 503 at the apex portions of the metal magnetic particles 501 is large, and the outer dimensions of the coil component tend to be large, thus hindering miniaturization.

[0063] FIG. 6 is an enlarged cross-sectional view conceptually showing the structure of the insulating layer in the present embodiment. In the case of the present embodiment, among the surfaces of the magnetic substrate 11, for example, the upper surface 101 that has not undergone the processing step in step S104 of FIG. 4 remains as the formed surface obtained in the forming step of step S103. And, on the formed surface, since the binder 120 exists on the surface so as to fill the gaps between the metal magnetic particles 110, the surface roughness of the magnetic substrate 11 is small.

[0064] Specifically, when the surface roughness is represented by the line roughness, the line roughness on the formed surface is 10 μm or less. As a result, the thickness D2 of the insulating layer 13 is 15 μm or less, and sufficient insulation can be obtained over the entire insulating layer 13. As the surface roughness of the formed surface, it is more desirable that it is 5 μm or less when represented by the line roughness, and even more desirable that it is 2 μm or less. As a result, the thickness D2 of the insulating layer 13 becomes 10 μm or less, 5 μm or less, and it becomes possible to make the thickness D2 of the insulating layer 13 smaller. Since the thickness D2 of the insulating layer 13 is small, the influence of the insulating layer 13 on the outer dimensions of the coil component 100 is small, which contributes to the miniaturization of the coil component 100. Note that, for sufficient adhesion of the insulating layer 13, the surface roughness on the formed surface is desirably 2 μm or more, and may be 1 μm or more when represented by the line roughness.

[0065] Also, the surface of the insulating layer 13 has a smaller surface roughness than the surface of the magnetic substrate 11 on which the insulating layer 13 is provided, for example, the upper surface 101. The surface roughness of the surface of the insulating layer 13 is, for example, half or less when represented by the line roughness with respect to the surface roughness of the surface of the magnetic substrate 11 on which the insulating layer 13 is provided. Since the surface roughness of the insulating layer 13 is small, when the surface of the insulating layer 13 is used to convey the coil component 100, friction is suppressed and conveyance becomes easy. Further, since the insulating layer 13 suppresses charging, adsorption between the coil components 100 due to static electricity is suppressed, and even if the coil component 100 is small, conveyance becomes easy.

[0066] After the insulating layer 13 is formed in step S106 of FIG. 4, in step S107, a metal layer 22 is provided on the outside of the base layer 21 by electrolytic plating to form the external electrode 12. An intermediate layer made of a conductive resin material may be provided between the base layer 21 and the metal layer 22 by printing or coating. The metal layer 22 is formed within the range of the base layer 21, and in the examples shown in FIGS. 1 and 2, it is formed on the bottom surface 102 and the end surfaces 105 and 106. With the formation of the external electrode 12, the coil component 100 is completed.

[0067] FIG. 7 is an enlarged cross-sectional view conceptually showing the structure of the external electrode 12. Of the outer surface of the magnetic substrate 11, the surface on which the external electrode 12 is formed has been surface-treated in the processing step of step S104 in FIG. 4, so that the binder 120 is almost absent and the metal magnetic particles 110 are exposed. In addition, since there are also recesses 130 where some of the raw material particles have fallen off, the surface on which the external electrode 12 is formed has a large surface roughness. As a result, the adhesion between the external electrode 12 and the magnetic substrate 11 is high, and the durability against stress from the substrate 200 and the like is high.

[0068] <Modification Example> Next, a modification example for the above-described embodiment will be described. Hereinafter, the description will focus on the differences from the above-described embodiment, and redundant descriptions of the same components as those in the above-described embodiment will be omitted.

[0069] FIG. 8 is a top view showing a first modification example, and FIG. 9 is a cross-sectional view showing the first modification example. FIG. 9 shows a cross-section taken along line B-B in FIG. 8. In the above-described embodiment, the insulating layer 13 is formed on the entire upper surface 101 of the magnetic substrate 11. In the first modification, the insulating layer 13 is formed at a location on the upper surface 101 of the magnetic substrate 11 that avoids the ridge line portions 31 and 41 with respect to the front surface 103 and the rear surface 104, respectively. This is because at the ridge line portions 31 and 41, the surface roughness increases due to, for example, the shedding of raw material particles, and the thickness of the insulating layer 13 may vary between components or within a component.

[0070] In other words, the insulating layer 13 is provided adjacent to the upper surface 101 and spaced apart from the front surface 103 and the rear surface 104 of the magnetic substrate 11, which are different from the bottom surface 102. In the first modification, the front surface 103 corresponds to an example of the "third surface" in the present invention, and the rear surface 104 corresponds to an example of the "fourth surface" in the present invention. It is desirable that the insulating layer 13 be spaced apart from the front surface 103 and the rear surface 104 by a distance greater than the maximum size of the metal magnetic particles 110 when viewed toward the upper surface 101. Chamfering or R-surfacing may be applied to the ridge line portions 31 and 41.

[0071] In the first modification, when forming the insulating layer 13, the insulating material is provided at a location that avoids chamfering or R-surfacing of the ridge line portions 31 and 41. Thereby, when a liquid insulating material is particularly used, the overflow to portions other than the upper surface 101 is suppressed.

[0072] FIG. 10 is a cross-sectional view showing a second modification. In the second modification, similar to the first modification, the insulating layer 13 is provided adjacent to the upper surface 101 and spaced apart from the front surface 103 and the rear surface 104 of the magnetic substrate 11, which are different from the bottom surface 102. In the second modification, the method of forming the insulating layer 13 is different from that in the first modification.

[0073] That is, in the second modification, when forming the insulating layer 13, the insulating material is once provided to overlap even with the ridge line portions 31 and 41, and then the insulating material is removed from the ridge line portions 31 and 41. By using a liquid insulating material in particular in such a forming method, in the second modification, the thickness of the insulating layer 13 on the upper surface 101 is made uniform, and the smoothness of the surface of the insulating layer 13 is enhanced.

[0074] FIG. 11 is a top view showing a third modification, and FIG. 12 is a cross-sectional view showing the third modification. FIG. 12 shows a cross-section along the line C-C in FIG. 11. In the third modification, the external electrode 12 is an electrode of a type called a one-sided electrode, and is provided on the bottom surface 102 as an example. Further, the external electrode 12 is provided so as to be separated from the other four surfaces adjacent to the bottom surface 102, that is, the front surface 103, the rear surface 104, and the side surfaces 105 and 106. Thereby, the influence of the external electrode 12 on the outer dimensions of the coil component can be suppressed, contributing to the miniaturization of the coil component. In the third modification, only the bottom surface 102 corresponds to an example of the second "second surface" in the present invention. Further, the front surface 103 corresponds to an example of the "third surface" in the present invention, and the rear surface 104 corresponds to an example of the "fourth surface" in the present invention. Furthermore, the side surfaces 105 and 106 correspond to examples of the "fifth surface" and the "sixth surface" in the present invention.

[0075] In the third modification, the insulating layer 13 is provided so as to be separated from the other four surfaces adjacent to the upper surface 101, that is, the front surface 103, the rear surface 104, and the side surfaces 105 and 106. Chamfering or R-surfacing may be performed on the ridge line portions 31, 41, 51, and 61 between the upper surface 101 and the front surface 103, the rear surface 104, and the side surfaces 105 and 106, respectively. The insulating layer 13 is provided avoiding each of the four ridge line portions 31, 41, 51, and 61. Thereby, the thickness of the insulating layer 13 becomes uniform.

[0076] In the above description, an example in which the insulating layer 13 and the external electrode 12 do not coexist on any of the six surfaces of the magnetic substrate 11 is shown. However, in the coil component of the present invention, the insulating layer 13 and the external electrode 12 may coexist on any of the six surfaces.

Explanation of Reference Numerals

[0077] 10-circuit board 11-magnetic substrate 12-external electrode 13-insulating layer 14-conductor 21-underlayer 22-metal layer 31, 41, 51, 61-edge line parts 100-coil component 101-top surface 102-bottom surface 103-front surface 104-rear surface 105, 106-side surfaces 110-metal magnetic particles 120-binder 200-substrate 201-land part 301-resin component 302-aggregate of carbon particles 303-first filler 304-second filler 401-lead-out part 402-circumferential part

Claims

1. A magnetic substrate formed by bonding a plurality of metal magnetic particles and having a first surface and a second surface; A conductor provided inside the magnetic substrate; An insulating layer provided on the first surface having a smaller surface roughness than the second surface; An external electrode provided on the second surface and electrically connected to the conductor; A coil component characterized by comprising the above.

2. The coil component according to claim 1, wherein the insulating layer is provided adjacent to the first surface and separated from the third and fourth surfaces of the magnetic substrate different from the second surface.

3. The coil component according to claim 2, wherein the insulating layer is provided at a distance greater than the maximum size of the metal magnetic particles from the third and fourth surfaces when viewed towards the first surface.

4. The coil component according to claim 1, wherein the insulating layer is provided separated from the other four surfaces adjacent to the first surface.

5. The magnetic substrate is chamfered or has an R surface at the ridge line portion between the first surface and the surface adjacent to the first surface, The coil component according to claim 1, wherein the insulating layer is provided away from the chamfering or R surface.

6. The coil component according to claim 1, wherein the first surface has a line roughness of 10 μm or less when the surface roughness is represented by the line roughness.

7. The coil component according to claim 1, wherein the insulating layer has a surface with a smaller surface roughness than the first surface.

8. The coil component according to claim 1, wherein the insulating layer contains a thermosetting resin.

9. The coil component according to claim 1, wherein the external electrode is provided separated from the other four surfaces adjacent to the second surface.

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