An inductor including an element body containing metal magnetic powder and resin and having a coil conductor that has a winding portion, an extended portion extended from the winding portion, and an outer electrode connection portion leading to the extended portion and connected to an outer electrode and is embedded in the element body; and an element body coat covering a surface of the element body. The outer electrode is formed on a surface of the element body and connected to the outer electrode connection portion, in which the outer electrode connection portion has a region covered with the element body coat and a region connected to the outer electrode on the surface of the element body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority to Japanese Patent Application No. 2022-163192 filed Oct. 11, 2022, Japanese Patent Application No. 2022-163193 filed Oct. 11, 2022, Japanese Patent Application No. 2022-163195 filed Oct. 11, 2022, Japanese Patent Application No. 2022-163196 filed Oct. 11, 2022, Japanese Patent Application No. 2022-163201 filed Oct. 11, 2022 and Japanese Patent Application No. 2022-163202 filed Oct. 11, 2022, the entire content of each are incorporated herein by reference.

BACKGROUND

Technical Field

The present disclosure relates to an inductor.

Background Art

International Publication No. 2017/135058 discloses an inductor in which a coil conductor is embedded in an element body made of a composite material of a resin material and metal powder, and the element body is coated with an insulating film. In this inductor, an outer electrode connected to an end portion of the coil conductor exposed from the element body is formed by plating on a portion in which the insulating film is removed by laser irradiation.

In the inductor described above, the end portion of the coil conductor exposed from the element body may be peeled off from the element body before the outer electrode is formed by plating. For this reason, there is room for improvement in the stability of the connection between the end portion of the coil conductor and the outer electrode.

SUMMARY

An aspect of the present disclosure is an inductor including an element body containing metal magnetic powder and resin and having a coil conductor embedded therein, an element body coat covering a surface of the element body, and an outer electrode formed on the surface of the element body. The coil conductor has a winding portion, an extended portion extended from the winding portion, and an outer electrode connection portion leading to the extended portion and connected to the outer electrode, and the outer electrode connection portion has a region covered with the element body coat and a region connected to the outer electrode on the surface of the element body.

According to the present disclosure, since the element body coat prevents the outer electrode connection portion from being peeled off from the surface of the element body, it is possible to improve the stability of the connection between the coil conductor and the outer electrode.

DETAILED DESCRIPTION

Inductor Overall Configuration

FIG.1is a perspective view of an inductor1according to the present embodiment viewed from an upper surface12side, andFIG.2is a perspective view of the inductor1viewed from a bottom surface10side.

The inductor1of the present embodiment is configured as a surface-mount electronic component, and includes an element body2having a substantially rectangular parallelepiped shape, which is an aspect of a substantially hexahedral shape, and a pair of outer electrodes4provided on a surface of the element body2.

Hereinafter, in the element body2, a first main surface facing a mounting substrate (not illustrated) at the time of mounting is defined as the bottom surface10, a second main surface facing the bottom surface10is referred to as the upper surface12, a pair of third main surfaces orthogonal to the bottom surface10are referred to as end surfaces14, and a pair of fourth main surfaces orthogonal to the bottom surface10and the pair of end surfaces14are referred to as side surfaces16.

As illustrated inFIG.1, a distance from the bottom surface10to the upper surface12is defined as a thickness T of the element body2, a distance between the pair of side surfaces16is defined as a width W of the element body2, and a distance between the pair of end surfaces14is defined as a length L of the element body2. In addition, a direction of the thickness T is defined as a thickness direction DT, a direction of the width W is defined as a width direction DW, and a direction of the length L is defined as a length direction DL.

A nominal size of the finished inductor1is, for example, 1.4 mm in length L dimension, 1.2 mm in width W dimension, and 0.8 mm in thickness T dimension.

Hereinafter, a plane along the DL direction and the DT direction (a plane orthogonal to the DW direction) is referred to as an LT plane, a plane along the DT direction and the DW direction (a plane orthogonal to the DL direction) is referred to as a TW plane, and a plane along the DL direction and the DW direction (a plane orthogonal to the DT direction) is referred to as an LW plane. In addition, cross sections of the inductor1taken along the LT plane, the TW plane, and the LW plane are referred to as an LT cross section, a TW cross section, and an LW cross section, respectively.

FIG.3is a perspective view illustrating an internal configuration of the inductor1.

The element body2includes a coil conductor20and a substantially hexahedral core30in which the coil conductor20is embedded, and is configured as a molded inductor in which the coil conductor20is sealed in the core30.

The core30is a molded body that is compression-molded into a substantially hexahedral shape by pressurizing and heating mixed powder obtained by mixing magnetic particles and resin in a state in which the coil conductor20is included.

In addition, the magnetic particles of the present embodiment are formed of a soft magnetic material and include particles having two types of particle sizes, that is, first magnetic particles that are large particles having a relatively large average particle diameter and second magnetic particles that are small particles having a relatively small average particle diameter. As a result, at the time of compression molding, the second magnetic particles that are small particles enter between the first magnetic particles that are large particles together with the resin, and thus it is possible to increase the filling rate of the magnetic particles in the core30and also to increase the magnetic permeability.

In the present embodiment, the average particle diameter of the metal particles of the first magnetic particles is equal to or more than 20 μm and equal to or less than 28 μm (i.e., from 20 μm to 28 μm), and the average particle diameter of the metal particles of the second magnetic particles is equal to or more than 1 μm and equal to or less than 6 μm (i.e., from 1 μm to 6 μm). Note that the average particle diameter of the first magnetic particles is preferably equal to or more than 20 μm and equal to or less than 22 μm (i.e., from 20 μm to 22 μm), and the average particle diameter of the second magnetic particles is preferably equal to or more than 1.5 μm and equal to or less than 1.8 μm (i.e., from 1.5 μm to 1.8 μm). In addition, the magnetic particles may include particles having three or more particle sizes by including particles having an average particle diameter different from that of the first magnetic particles and the second magnetic particles.

Both of the first magnetic particles and the second magnetic particles are particles including metal particles, an oxide film covering surfaces of the metal particles, and an insulating film covering a surface of the oxide film. When the metal particles are covered with the oxide film and the insulating film, insulation resistance and withstand voltage are increased.

In the first magnetic particles of the present embodiment, an Fe—Si—B amorphous alloy powder is used as the metal particles. The oxide film of the first magnetic particles is composed of two layers of a SiO layer and a Fe2SiO4layer, and the thickness of the entire oxide film is equal to or more than 20 nm and equal to or less than 155 nm (i.e., from 20 nm to 155 nm). In addition, the insulating film of the first magnetic particles is formed of phosphate glass having a thickness of equal to or more than 10 nm and equal to or less than 100 nm (i.e., from 10 nm to 100 nm).

In addition, in the second magnetic particles of the present embodiment, carbonyl iron powder is used as the metal particles. The oxide film of the second magnetic particles is iron oxide formed by surface-oxidizing carbonyl iron powder that is a metal particle. In addition, the insulating film of the second magnetic particles is a sol-gel reaction product containing silica as a component. Accordingly, slipperiness of the surface of the second magnetic particles can be increased, and the second magnetic particles can easily enter between the first magnetic particles in an element body molding and curing process of the element body2described below. As a result, the relative magnetic permeability of the core30can be further increased by further increasing the density of the magnetic material in the core30.

Note that in the first magnetic particles, an Fe—Si—Cr alloy powder, an Fe—Ni—Al alloy powder, an Fe—Cr—Al alloy powder, an Fe—Si—Al alloy powder, an Fe—Ni alloy powder, or an Fe—Ni—Mo alloy powder may be used as the metal particles.

In addition, in the first magnetic particles, phosphoric acid, zinc phosphate, manganese phosphate, glass, or resin may be used for the insulating film.

The resin material contained in the mixed powder of the present embodiment contains a bisphenol A-type epoxy resin and a rubber-modified epoxy resin. Thus, it is possible to manufacture the inductor1in which both the strength and the toughness of the element body2are improved.

In the present embodiment, in the magnetic powder contained in the mixed powder, the first magnetic particles are equal to or more than 70 wt % and equal to or less than 85 wt % (i.e., from 70 wt % to 85 wt %) and the second magnetic particles are equal to or more than 15 wt % and equal to or less than 30 wt % (i.e., from 15 wt % to 30 wt %) based on the total weight of the magnetic particles contained in the mixed powder. In addition, the resin contained in the mixed powder is equal to or more than 2.0 wt % and equal to or less than 3.5 wt % (i.e., from 2.0 wt % to 3.5 wt %) based on the total weight of the magnetic powder and the resin. Note that the first magnetic particles are preferably equal to or more than 70 wt % and equal to or less than 80 wt % (i.e., from 70 wt % to 80 wt %), and the second magnetic particles are preferably equal to or more than 20 wt % and equal to or less than 30 wt % (i.e., from 20 wt % to 30 wt %). In addition, the resin is preferably equal to or more than 2.7 wt % and equal to or less than 30 wt % (i.e., from 2.7 wt % to 30 wt %).

As illustrated inFIG.3, the coil conductor20includes a winding portion22in which a conductive wire is spirally wound around a winding axis K in two upper and lower stages along the winding axis K such that both ends of the conductive wire are located on an outer periphery and are connected to each other on an inner periphery, a pair of extended portions23extended from the winding portion22, and a pair of outer electrode connection portions24that are conductive wire portions leading to the extended portions23, respectively, for connection to an outer electrode described later. The winding portion22includes two winding regions22aand22bthat overlap along the winding axis K. The conductive wires in the winding regions22aand22bare connected to each other at a part of the inner periphery thereof.

The winding portion22has, for example, a substantially rectangular shape in plan view viewed from a direction of the winding axis K. The coil conductor20is embedded in the element body2such that the winding axis K extends along the thickness direction DT of the element body2and such that, in plan view seen from the direction of the winding axis K, each side of the winding portion22having a substantially rectangular shape in plan view extends along (e.g., parallel to) each side of the element body2having a substantially rectangular shape in plan view.

The conductive wire constituting the coil conductor20includes a conductor and a coating layer formed on a surface of the conductor. The conductive wire is a rectangular wire having a rectangular cross section, and the conductor is a belt-like conductor made of copper and having a rectangular cross section. The conductor has a thickness of equal to or more than 60 μm and equal to or less than 100 μm (i.e., from 60 μm to 100 μm), and a width of equal to or more than 160 μm and equal to or less than 200 μm (i.e., from 160 μm to 200 μm). The coating layer includes an insulating layer formed on a surface of the belt-like conductive wire and a fusion layer formed on a surface of the insulating layer for bonding the belt-like conductive wires overlapping each other in the winding portion22. The insulating layer is made of, for example, a polyimide amide resin and has a thickness of 3 μm. In addition, the fusion layer is made of, for example, a polyamide resin and has a thickness of equal to or more than 1 μm and equal to or less than 25 μm (i.e., from 1 μm to 25 μm).

The extended portion23is extended from the winding portion22and is electrically connected to the outer electrode4via the outer electrode connection portion24that is extended and exposed to each of the pair of end surfaces14.

Each of the pair of outer electrodes4is a so-called L-shaped electrode constituted by an L-shaped member extending from each of the end surfaces14of the element body2to the bottom surface10. The outer electrodes4are respectively connected to the outer electrode connection portions24of the coil conductor20on the end surfaces14, and portions4A (FIG.2) extending to the bottom surface10are electrically connected to wiring of a circuit substrate by appropriate mounting means such as solder.

In addition, an element body protective layer (not illustrated) is formed on the surface of the element body2except for a range of the outer electrode4. The element body protective layer is, for example, resin obtained by adding a phenoxy resin to a novolac resin, and contains nano silica as a filler. The element body protective layer is formed on the surface of the element body2with a thickness of equal to or more than 10 μm and equal to or less than 30 μm (i.e., from 10 μm to 30 μm). Note that the thickness of the element body protective layer is preferably equal to or more than 10 μm and equal to or less than 20 μm (i.e., from 10 μm to 20 μm), and more preferably equal to or less than 15 μm.

The inductor1having such a configuration is used as an electronic component of an electric circuit in which a large current flows, a choke coil of a DC-DC converter circuit or a power supply circuit, or an electronic component of an electronic device such as a personal computer, a DVD player, a digital camera, a TV, a cellular phone, a smartphone, car electronics, or a medical/industrial machine because the inductor1can improve DC superposition characteristics by using a soft magnetic material for the magnetic particles. However, the application of the inductor1is not limited thereto, and the inductor1may be used in, for example, a tuning circuit, a filter circuit, a rectifying and smoothing circuit, or the like.

Outline of Inductor Manufacturing Process

FIG.4is a schematic view of a manufacturing process of the inductor1.

As illustrated in the above drawing, the manufacturing process of the inductor1includes a coil conductor forming process, a preliminary molded body forming process, the element body molding and curing process, an element body grinding process, and an outer electrode forming process.

The coil conductor forming process is a process of forming the coil conductor20from a conductive wire. In this process, the coil conductor20is formed into a shape having the winding portion22, the extended portion23, and the outer electrode connection portion24described above by winding the conductive wire in a winding method called “alpha winding”. The alpha winding refers to a state in which a conductive wire functioning as a conductor is spirally wound in two stages such that the extended portions23at the winding start and the winding end are located on the outer periphery. The number of turns of the coil conductor20is not particularly limited.

The preliminary molded body forming process is a process of forming a preliminary molded body called a tablet.

The preliminary molded body is formed into a solid shape that is easy to handle by pressing the mixed powder that is the material of the element body2, and in the present embodiment, two types of tablets are formed: a first tablet having an appropriate shape (for example, an E shape) having a groove into which the coil conductor20is inserted; and a second tablet having an appropriate shape (for example, an I shape or a plate shape) that covers the groove of the first tablet.

In the element body molding and curing process, the first tablet, the coil conductor, and the second tablet are set in a molding die, pressed in the overlapping direction of the first tablet and the second tablet while applying heat, and cured, thereby integrating the first tablet, the coil conductor, and the second tablet. Thus, the element body2in which the coil conductor20is included in the core30is formed.

In the element body grinding process, abrasive grains are caused to act on a side surface of the molded body obtained in the element body molding and curing process, thereby shaving off (i.e., grinding) the side surface until the width W becomes a predetermined width. By this process, the element body2in which the width W of the molded body is downsized to a predetermined width is obtained. Since a distance (also referred to as a side gap) between the coil conductor20in the element body2and the side surface of the element body2is reduced by this downsizing, the occupancy ratio of the coil in a radial direction of the winding portion22of the coil conductor20is increased. In addition, since the element body2is obtained by grinding the molded body obtained by the compression molding to a predetermined size, it is possible to reduce dimensional variation of the element body2as compared with a case where the element body2is controlled to a predetermined size only by the compression molding. In the element body grinding process, polishing (for example, barrel polishing) may be performed to chamfer corners caused by grinding of the side surfaces of the element body2.

The outer electrode forming process is a process of forming the outer electrode4on the element body2, and includes an element body protective layer forming process, a surface treatment process, and a plating layer forming process.

The element body protective layer forming process is a process of coating the entire surface of the element body2with an insulating resin.

The surface treatment process is a process of modifying a surface of a predetermined electrode portion by irradiating the predetermined electrode portion on a surface of the core30with a laser beam. Here, the predetermined electrode portion refers to a range of the surface of the core30where the outer electrode4is to be formed, and includes a portion where the outer electrode connection portion24is exposed. Specifically, the laser beam is applied thereby to remove the element body protective layer on the surface of the element body2and the coating layer of the outer electrode connection portion24of the coil conductor20, remove the resin on the surface of the core30, and remove the insulating film on the surfaces of the magnetic particles exposed from the core30in the range of the predetermined electrode portion. As a result, an exposed area of the metal of the magnetic particles per unit area of the surface of the core30is larger in the predetermined electrode portion of the surface of the core30than in the other surface portions of the core30. Note that after the irradiation of the laser beam, a cleaning treatment (for example, an etching treatment) may be performed to clean the surface of the predetermined electrode portion.

In the plating layer forming process, copper is barrel-plated on the surface of the core30thereby to form a copper plating layer on the predetermined electrode portion irradiated with the laser beam. In addition to this, the plating layer may be formed by further providing a Ni plating layer and a Sn plating layer on the copper plating layer.

Hereinafter, details of the inductor1according to the present embodiment will be further described.

FIG.5is a plan view illustrating the internal configuration of the inductor1.FIG.6is a cross-sectional view taken along line VI-VI ofFIG.5.FIG.6illustrates a TW cross section of the inductor1.

First, the coil conductor20used in the inductor1will be described. As described above, the coil conductor20includes the winding portion22around which the conductive wire is wound, the pair of extended portions23, and the pair of outer electrode connection portions24.

A left end of the winding portion22is extended from the lower stage of the winding portion22wound in two upper and lower stages, and is connected to a left side of the outer electrode connection portion24via the extended portion23on the left side. The left side of the outer electrode connection portion24is bent in the width direction DW at a bent portion48at the tip of the left side of the extended portion23and extends linearly in the width direction DW. A right end of the winding portion22is extended from the upper stage of the winding portion22wound in two upper and lower stages, and is connected to a right side of the outer electrode connection portion24via the extended portion23on the right side. The right side of the outer electrode connection portion24is bent in the width direction DW at the bent portion48at the tip of the right side of the extended portion23and extends linearly in the width direction DW. In other words, each of the left and right extended portions23extends in an extending direction dc that is inclined toward one side in the width direction DW as it extends outward in the length direction DL. In addition, each of the left and right outer electrode connection portions24extends in an extending direction dp extending from the other side in the width direction DW to the one side in the width direction DW. Note that inFIG.5, the portion of the extended portion23that is inclined to the one side in the width direction DW toward the outer side in the length direction DL is linear, but at least a part thereof may be formed in a curved shape. In addition, inFIG.5, the portion of the outer electrode connection portion24extending from the other side in the width direction DW to the one side in the width direction DW is linear, but at least a part thereof may be formed in a curved shape.

As illustrated inFIG.6, a conductive wire42constituting the coil conductor20includes a conductor43that is a wire rod and a coating layer (the coating layer is not illustrated inFIG.6andFIG.7) that covers the conductor43. The coil conductor20is formed by alpha-winding the conductive wire42. The coil conductor20is embedded in the core30containing magnetic particles and resin.

FIG.7is a conductor cross-sectional view of the conductor43constituting the conductive wire42.FIG.7illustrates a cross section orthogonal to the extending direction of the conductor43.

The conductor43is formed to have a rectangular shape with four right-angled corners in the conductor cross section orthogonal to the extending direction. Here, in this specification, the terms “right angle”, “rectangle”, and “the same” do not necessarily mean “right angle”, “rectangle”, and “the same” in a strict sense, respectively, and may be substantially “right angle”, “rectangle”, and “the same”. That is, in this specification, the terms “right angle”, “rectangle”, and “the same” may be used to mean that substantially “right angle”, “rectangle”, and “the same” include “approximately right angle”, “approximately rectangle”, and “approximately the same”, respectively.

The conductor43has a conductor inner peripheral surface43aon the winding axis K side, a conductor outer peripheral surface43bon the side separated from the winding axis K, and a pair of conductor side surfaces43cand43dconnecting both ends of the conductor inner peripheral surface43aand both ends of the conductor outer peripheral surface43b. The conductive wire42is formed by forming a coating layer on a surface of the conductor43.

The maximum length between the conductor side surfaces43cand43din the thickness direction DT of the conductor43is defined as a line width La. In addition, the maximum length between the conductor inner peripheral surface43aand the conductor outer peripheral surface43bof the conductor43in a direction orthogonal to the thickness direction DT is defined as a line thickness Lb.

Specifically, an angle formed by the conductor inner peripheral surface43aand the conductor side surface43cis a right angle. In addition, an angle formed by the conductor inner peripheral surface43aand the conductor side surface43dis a right angle. Further, an angle formed by the conductor outer peripheral surface43band the conductor side surface43cis a right angle. In addition, an angle formed by the conductor outer peripheral surface43band the conductor side surface43dis a right angle. In the present embodiment, the reference of the right angle is that the right-angled corner portion is a corner formed with a roundness having a curvature radius R of equal to or less than 4.5 μm at a portion where the conductor inner peripheral surface43aor the conductor outer peripheral surface43band the conductor side surface43cor43dforming the right angle intersect. It can be confirmed that the four corners of the conductor are right angles by observing the four corner portions in the cross section of the conductor with a digital microscope and measuring the radius of curvature of each corner portion using a measuring function of the digital microscope.

Here, a virtual circumscribed rectangle S1is set so as to circumscribe the conductor43in the conductor cross section. The circumscribed rectangle S1is set so that the ratio of an area occupied by the conductor43to an area of the circumscribed rectangle S1is maximized. The conductor cross section is a cutting plane obtained by vertically cutting the conductive wire42, when remaining as it is, in a direction orthogonal to the length direction DL of the conductive wire42, and in this cutting plane, a boundary between the coating layer and a conductor41is observed to set the circumscribed rectangle S1. That is, in this cutting plane, the circumscribed rectangle S1is set such that the circumscribed rectangle S1has room for the line width La between the conductor side surfaces43cand43dof the conductor43in the thickness direction DT, and the line thickness Lb between the conductor inner peripheral surface43aand the conductor outer peripheral surface43bof the conductor43in a direction orthogonal to the thickness direction DT. In addition, when the determination is made using the inductor1as a product, the circumscribed rectangle S1is set by observing the conductor cross section per turn of the winding portion22in a cutting plane (cutting plane illustrated inFIG.6) vertically cut along a virtual line extending in the width direction DW of the element body2passing through the winding axis K of the winding portion22when the element body2is viewed from the upper surface. In the present embodiment, the average area ratio of the conductor43to the circumscribed rectangle S1per turn of the winding portion22is equal to or more than 95%. The term “per turn” means an average value in one turn, and means an average value of the area ratios in two conductor cross sections in one turn in the element body cross section. Therefore, for example, inFIG.6, the average value of the area ratios at winding positions P1and P2may be taken. In addition, for example, inFIG.6, the average value of the area ratios at winding positions P3and P4may be taken.

Here, as indicated by broken lines inFIG.7, since a normal conductor81is formed by crushing the conductor having a circular cross section, a conductor inner peripheral surface81aand a conductor outer peripheral surface81bare formed in flat shapes, while conductor side surfaces81cand81dare formed in curved shapes and have large curvatures. For this reason, in the normal conductor81, the area ratio with respect to the circumscribed rectangle S1is likely to be small. On the other hand, since the conductor43of the present embodiment is formed by casting so as to intentionally have a rectangular shape with four right angled corners, the curvatures of the curved shapes of the conductor side surfaces43cand43dare small as compared with the normal conductor81, and the conductor43is linearly formed to have a rectangular shape more approximate to the circumscribed rectangle S1.

As illustrated inFIG.6, in the thickness direction DT in the present embodiment, the coil conductor20is embedded inside the core30such that an upper surface thickness T11, which is a length from the upper surface12of the element body2to an upper surface41aof the winding portion22, is equal to a bottom surface thickness T12, which is a length from a bottom surface41bof the winding portion22to the bottom surface10of the element body2.

In the present embodiment, since the conductor43has a rectangular shape, the line width La can be made smaller than that of the normal conductor81by an area of the corner portion of the conductor43when compared at the same DC resistance value (that is, an area of the conductor cross section is the same). As such, since the DC resistance value can be ensured while decreasing a height (thickness) of the coil conductor20in the thickness direction DT, when the sizes of the element body2are substantially the same, the upper surface thickness T11and the bottom surface thickness T12can be easily increased, and the total value T11+T12of the upper surface thickness T11and the bottom surface thickness T12can be increased.

In the present embodiment, in the thickness direction DT as a direction along the winding axis K, a winding portion thickness T10, which is a length from the upper surface41ato the bottom surface41bof the winding portion22, is equal to the total value T11+T12of the upper surface thickness T11and the bottom surface thickness T12. Alternatively, the winding portion thickness T10may be equal to or less than the total value T11+T12. To be specific, the ratio of the winding portion thickness T10with respect to the height of the element body2is equal to or less than 55%.

This makes it easy to increase the total value T11+T12of the upper surface thickness T11and the bottom surface thickness T12with respect to the winding portion thickness T10, therefore, even when the position of the winding portion22is displaced in a vertical direction in manufacturing, a distance between the winding portion22and the upper and lower surfaces of the element body2can be maintained, and variation in a DC superimposed rated current of the inductor1can be suppressed. Here, when a current flows through the inductor, magnetic saturation of the magnetic body occurs and the inductance decreases. The DC superimposed rated current is obtained by defining a lower limit current value that is usable for the inductance with respect to initial characteristics with no current superimposed.

Note that in the present embodiment, the coil conductor20is embedded inside the core30such that the upper surface thickness T11and the bottom surface thickness T12are the same. However, the coil conductor20may be embedded inside the core30such that the upper surface thickness T11is larger than the bottom surface thickness T12. Alternatively, the coil conductor20may be embedded inside the core30such that the bottom surface thickness T12is larger than the upper surface thickness T11. When one of the upper surface thickness T11and the bottom surface thickness T12is larger, the smaller thickness is set so as not to be smaller than ⅙ of the total value T11+T12of the upper surface thickness T11and the bottom surface thickness T12.

A-2-1. Configuration of Winding Portion

As described above, the size of the inductor1is as small as 1.4 mm in the length L dimension, 1.2 mm in the width W dimension, and 0.8 mm in the thickness T dimension. For this reason, the shape of the winding portion22embedded in the core30in the element body2can greatly affect the value of inductance that can be realized in the inductor1.

FIGS.8A-8Cinclude diagrams for explaining a configuration of a winding portion85of a coil conductor84in an inductor83in which the winding portion of the coil conductor is wound in a normal winding manner.FIG.8AandFIG.8Beach are diagrams of two winding regions85aand85bconstituting the winding portion85of the inductor83having the same configuration as that illustrated inFIG.1, in which the winding portion of the coil conductor is wound in a normal winding manner, viewed from a direction corresponding to a −DT direction (direction looking down on the upper surface12) illustrated inFIG.1. In addition,FIG.8Cis a diagram illustrating a cross section of the inductor83corresponding to the LT cross section taken along the center of the width WinFIG.1when viewed from a direction corresponding to the DW direction inFIG.1.

The coil conductor84includes the winding portion85composed of winding regions85aand85b, an extended portion extended from the winding portion85, and an outer electrode connection portion88that is a conductive wire portion leading to the extended portion for connection to an outer electrode, and constitutes an element body87together with a core86including magnetic particles in which the coil conductor84is embedded. InFIG.8A, the conductive wire in the winding region85aconstituting the winding portion85is wound around a winding axis, extended from the outermost periphery of the winding region85ato the right side in the drawing via the extended portion, and leads to the outer electrode connection portion88on the right side in the drawing, and inFIG.8B, the conductive wire in the winding region85bis wound around the winding axis, extended from the outermost periphery of the winding region85bto the left side in the drawing via the extended portion, and leads to the outer electrode connection portion88on the left side in the drawing. In addition, the conductive wire in the winding region85aillustrated inFIG.8Band the conductive wire in the winding region85billustrated inFIG.8Bare connected to each other at a position P80on the inner periphery of the winding portion85.

The total number of turns of the winding portion85is an odd integer, for example, 5, rounded to the nearest whole number, and the winding regions85aand85b, which overlap along the winding axis to form the winding portion85, each have the same number of turns of about 2.5 turns. For this reason, the two winding regions85aand85bhave two ranges R81and R82in which the numbers of cross sections of the conductive wire included in the two winding regions85aand85bin portions adjacent to each other along a direction of a winding axis Kp are different between one winding region85aand the other winding region85bin a cross section along the direction of the winding axis Kp (a normal direction to the paper surface inFIG.8AandFIG.8B) in the portion in which the conductive wire is wound as viewed from an upper surface of the element body87.

FIG.8Cis a cross-sectional view of the element body87taken along a center line CL80in the width direction of the element body87inFIG.8AandFIG.8B, and includes cross sections of the ranges R81and R82. As illustrated inFIG.8C, in the inductor83in which the winding portion of the coil conductor is wound in the normal winding manner, the inner peripheries of the winding region85aand the winding region85bare located at the same positions P82and P83. The two turns on the inner periphery of each of the winding region85aand the winding region85bare vertically overlapped and located at the same position, while the 0.5 turns located on the outermost periphery are arranged at the outer peripheral positions on the left and right in the drawing, respectively. For this reason, the outer periphery of the winding portion85has a step S80between the winding region85aand the winding region85bon each of the left and right sides in the drawing. The depth of the step S80can be equivalent to a thickness T80of the conductive wire measured in a direction orthogonal to the winding axis Kp.

In the core86constituting the element body87, the portion of the step S80is a dead space and can limit an upper limit value of inductance that can be realized by the inductor83.

For this reason, in the inductor1of the present embodiment, in the portions corresponding to the ranges R81and R82illustrated inFIGS.8A-8C, the inner periphery of one winding region in which the number of cross sections of the conductive wire is small is configured to be shifted to the outer peripheral side with respect to the inner periphery of the other winding region in which the number of cross sections of the conductive wire is large.

FIG.9includes diagrams for explaining the configuration of the winding portion22of the coil conductor20in one embodiment of the inductor1, and corresponds toFIGS.8A-8Cillustrating the configuration of the inductor83in which the winding portion of the coil conductor is wound in the normal winding manner. As described above with reference toFIG.3, the coil conductor20includes the winding portion22in which the conductive wire is wound around the winding axis K, the pair of extended portions23extended from the winding portion22, and the pair of outer electrode connection portions24that are conductive wire portions connected to the extended portions23, respectively, for connection to the outer electrodes. In addition, the winding portion22includes the two winding regions22aand22bthat overlap each other along the winding axis K.

In addition, the conductive wire constituting the coil conductor20includes a conductor and a coating layer covering a surface of the conductor. The conductor has a rectangular cross section orthogonal to an extending direction of the conductor, and four apexes of the rectangle are right angles.

FIGS.9A and9Bare diagrams when the two winding regions22aand22bconstituting the winding portion22are each viewed from the −DT direction inFIG.1(the direction looking down on the upper surface12). In addition,FIG.9Cis a diagram when a cross section of the inductor1corresponding to the LT cross section taken along a center line CL20of the width W of the element body2(seeFIG.1) is viewed from the DW direction.

InFIG.9A, the conductive wire in the winding region22ais extended to the right side in the drawing and leads to the outer electrode connection portion24on the right side in the drawing via the extended portion23, and inFIG.9B, the conductive wire in the winding region22bis extended to the left side in the drawing and leads to the outer electrode connection portion24on the left side in the drawing via the extended portion23. In addition, the conductive wire in the winding region22aillustrated inFIG.9Aand the conductive wire in the winding region22billustrated inFIG.9Bare connected to each other at a position P20on the inner periphery of the winding portion22.

The total number of turns of the winding portion22illustrated inFIGS.9A and9Bis an odd integer, for example, 5, rounded to the nearest whole number. However, this total number of turns is an example for explaining a difference from the inductor83illustrated inFIGS.8A-8Cin which the winding portion of the coil conductor is wound in the normal winding manner, and the total number of turns of the winding portion22may be set to an arbitrary odd number in accordance with an inductance value required for the inductor1.

The winding regions22aand22bconstituting the winding portion22are each formed by the same number of turns of about 2.5 turns. For this reason, the two winding regions22aand22bhave two ranges R20and R21in which the numbers of cross sections of the conductive wire included in the two winding regions22aand22badjacent to each other along the direction of the winding axis K in portions adjacent to each other along the direction of the winding axis K are different between one winding region22aand the other winding region22bin the cross section along the direction of the winding axis K (a normal direction to the paper surface inFIG.9AandFIG.9B) in the portion in which the conductive wire is wound as viewed from the upper surface12of the element body2.

In the inductor1, the winding portion22has a substantially rectangular shape in plan view viewed from the direction of the winding axis K, and the ranges R20and R21are located on two opposing sides of the substantially rectangular shape.

FIG.9Cis a diagram illustrating a cross section of the element body2along the center line CL20of the element body2in the width direction inFIGS.9A and9B, and includes cross sections of the ranges R20and R21.

As illustrated inFIG.9C, the one winding region22aincludes a larger number of conductive wires in the one range R20than in the other winding region22b, and includes a smaller number of conductive wires in the other range R21than in the other winding region22b. Similarly, the one winding region22bincludes a larger number of conductive wires in the one range R21than in the other winding region22a, and includes a smaller number of conductive wires in the other range R20than in the other winding region22a.

In the present embodiment, for example, the ranges R20and R21are located on two opposing sides of the winding portion22parallel to the end surface14of the element body2as illustrated inFIG.9AandFIG.9Bso as not to be located in the vicinity of the position P20on the inner periphery of the winding portion22connecting the winding region22aand the winding region22b, and in particular, as illustrated inFIG.9C, in the ranges R20and R21, the inner periphery of one winding region having a smaller number of cross sections of the conductive wire in the cross section along the direction of the winding axis K is shifted to an outer peripheral side of the winding portion22with respect to the inner periphery of the other winding region having a larger number of cross sections of the conductive wire in the cross section along the direction of the winding axis K.

To be specific, in the range R20, the inner periphery of the winding region22bin which the number of cross sections of the conductive wire in the cross section along the direction of the winding axis K is small is shifted by a distance D21toward the outer peripheral side of the winding portion22with respect to the inner periphery of the winding region22ain which the number of cross sections of the conductive wire in the cross section along the direction of the winding axis K is large. In addition, in the range R21, the inner periphery of the winding region22ain which the number of cross sections of the conductive wire in the cross section along the direction of the winding axis K is small is shifted by a distance D20toward the outer peripheral side of the winding portion22with respect to the inner periphery of the winding region22bin which the number of cross sections of the conductive wire in the cross section along the direction of the winding axis K is large.

In the example ofFIG.9C, the distances D20and D21are both equal to a thickness T20of the conductive wire measured in a direction orthogonal to the winding axis K. Thus, in each of the ranges R20and R21, a step is not formed between the outer periphery of the winding region22aand the outer periphery of the winding region22b. That is, in each of the ranges R20and R21, the outer peripheries of the two winding regions22aand22bare formed such that a difference between a distance of one winding region from the winding axis K and a distance of the other winding region from the winding axis K is within ½ of the thickness of the conductive wire, and inFIG.9C, the distances from the winding axis K are substantially equal to each other.

According to the above-described configuration, in the winding portion22of the inductor1, there is no step S80at the outer periphery of the winding portion85formed in the inductor83in which the winding portion of the coil conductor illustrated inFIG.8Cis wound in the normal winding manner. That is, in the inductor1, since the step S80as illustrated inFIG.8Cis not provided, the upper limit value of the inductance that can be realized by the inductor1can be improved as compared with the inductor83in which the winding portion of the coil conductor is wound in the normal winding manner. In addition, in the inductor1illustrated inFIGS.9A-9C, the winding axis having a large magnetic flux density can be formed greatly in each of the winding regions22aand22b.

Note that in the two winding regions22aand22b, the inner periphery of one winding region does not necessarily have to be shifted with respect to the inner periphery of the other winding region in an entire winding direction (the circumferential direction around the winding axis K) of each of the ranges R20and R21. That is, in the two winding regions22aand22b, in at least a part of each of the ranges R20and R21in the winding direction, the inner periphery of one winding region having a smaller number of cross sections of the conductive wire in the cross section along the winding axis K may be shifted toward the outer peripheral side of the winding portion22with respect to the inner periphery of the other winding region having a larger number of cross sections of the conductive wire in the cross section along the direction of the winding axis K.

In addition, the shift amount of the inner periphery of one winding region with respect to the inner periphery of the other winding region in the ranges R20and R21, that is, the distances D20and D21inFIG.9Cmay be equal to or more than ½ of the thickness T20of the conductive wire measured in the direction orthogonal to the winding axis K. Also in this case, the size of step between the winding regions22aand22bin an outer peripheral portion of the winding portion22is made smaller than the step S80in the inductor83illustrated inFIG.8Cin which the winding portion of the coil conductor is wound in the normal winding manner, so that the upper limit value of the inductance that can be realized by the inductor1can be improved as compared with the inductor83in which the winding portion of the coil conductor is wound in the normal winding manner.

A-2-2. Configuration of Extended Portion and Outer Electrode Connection Portion

As described above with reference to the related art, in an inductor such as the inductor1illustrated inFIG.1that includes an element body including a core containing magnetic particles formed of a soft magnetic material and a coil conductor embedded in the core, variations may occur in the position and an exposed area of an extended portion on an end surface of the element body due to the shape of the entire coil conductor, the posture of the coil conductor inside the element body, and the like. Such variations in the position and the exposed area of the extended portion on the end surface of the element body may cause variations in an electrical connection state between the extended portion and the outer electrode and may cause variations in the DC resistance value at a connection portion between the extended portion and the outer electrode.

For this reason, the inductor1of the present embodiment is configured such that the shape of the coil conductor20, in particular, an angle formed by the extended portion23extended from the winding portion22and the outer electrode connection portion24satisfies a predetermined condition in plan view viewed from a normal direction of the upper surface12of the element body2. In addition, the inductor1is configured such that the posture of the coil conductor20inside the element body2, in particular, an angle formed by a normal direction of the end surface14of the element body2on which the outer electrode4is formed and the extending direction of the outer electrode connection portion24satisfies a predetermined condition in plan view viewed from the normal direction of the upper surface12of the element body2.

FIG.10is a diagram of the coil conductor20embedded in the element body2in an example of the inductor1as viewed from above the upper surface12of the element body2along the −DT direction. In the inductor1illustrated inFIG.10, as illustrated on the left side in the drawing in the inductor1, a boundary between the extended portion23and the outer electrode connection portion24is the bent portion48in which the conductive wire is bent, and a first angle θ1formed by the extending direction dp of the outer electrode connection portion24extending from the bent portion48as a starting point and a normal direction do of the end surface14passing through the bent portion48toward the inside of the element body2is greater than 90 degrees. When the first angle θ1is smaller than 90 degrees, the entire outer electrode connection portion24, from the base to the tip of the outer electrode connection portion24, is separated from the end surface14of the element body2toward the inside of the element body, and an exposed area of the outer electrode connection portion24exposed from the end surface14is reduced. In addition, when the first angle θ1is 90 degrees, although the exposed area of the outer electrode connection portion24exposed from the end surface14can be increased, there is a possibility that the outer electrode connection portion24is embedded in the element body2in a case where the bent portion48is displaced in an inward direction of the element body2. On the other hand, when the first angle θ1is greater than 90 degrees, a tip side of the outer electrode connection portion24extends in a direction protruding from the end surface14of the element body2, and the tip of the outer electrode connection portion24extends in a state nearly parallel to the end surface14of the element body2by being in contact with an inner wall of the molding die in the element body molding and curing process described above, whereby the exposed area of the outer electrode connection portion24exposed from the end surface14can be increased. Note that the extended portion23and the outer electrode connection portion24on the right side in the drawing of the inductor1are also configured in the same manner as described above, and the first angle θ1can be defined.

As a result, in the inductor1, it is possible to reduce variation in the exposed area of the outer electrode connection portion24exposed from the end surface14and to reduce variation in the DC resistance at a connection portion between the outer electrode connection portion24and the outer electrode4. Here, when the first angle θ1is greater than 90 degrees on both the left and right sides of the inductor1in the drawing, the variation in the exposed area of the outer electrode connection portion24exposed from each of the left and right end surfaces14in the drawing can be reduced, and the variation in the DC resistance at the connection portion between the outer electrode connection portion24and the outer electrode4can be reduced.

In addition, the inductor1illustrated inFIG.10, a second angle θ2formed by the extending direction dc of the extended portion23starting from the bent portion48and the extending direction dp of the outer electrode connection portion24extending from the bent portion48is equal to or more than 150 degrees and less than 180 degrees (i.e., from 150 degrees to 180 degrees). As a result, it is possible to further reduce the variation in the exposed area of the outer electrode connection portion24exposed from the end surface14.

From the viewpoint of reducing the variation in the exposed area of the outer electrode connection portion24, the first angle θ1is preferably in a range of equal to or less than 100 degrees in addition to being greater than 90 degrees as described above.

Here, inFIG.10, the coil conductor20is embedded in the element body2such that the winding axis K is along the normal direction of the upper surface12(the normal direction to the paper surface). In addition, in an outer shape of the winding portion22in plan view (that is, in plan view illustrated inFIG.10) viewed from the normal direction of the upper surface12, a first length Wc that is the maximum length in a direction (for example, the DW direction) orthogonal to the side surface16is equal to or greater than a second length Lc that is the maximum length measured in a direction (for example, the DL direction) orthogonal to the end surface14. The ratio of the first length Wc to the second length Lc may be in a range of equal to or more than 1 and equal to or less than 1.5 (i.e., from 1 to 1.5).

The relationship between the winding portion22and the element body2is such that the first length Wc of the winding portion22is longer than the second length Lc, and a distance Ld between the pair of end surfaces14of the element body2is longer than a distance Wb between the pair of side surfaces16. Here, the distance Ld is equal to the length obtained by subtracting the thickness of the outer electrode4from the length L of the inductor1, and the distance Wb is substantially equal to the width W of the inductor1.

Further, from the viewpoint of reducing the variation in the exposed area of the outer electrode connection portion24, the bent portion48is preferably within a range R25, which is ½ of the distance Wb between the pair of side surfaces16, of a width in a direction orthogonal to the pair of side surfaces16(e.g., the DW direction) with respect to a line L25as a center that passes through the center of the end surface14and is parallel to the side surfaces16.

The length of the outer electrode connection portion24is preferably equal to or more than 30% and equal to or less than 50% (i.e., from 30% to 50%) of the distance Wb between the pair of side surfaces16of the end surface14.

In the element body2, for example, the distance Wb between the pair of side surfaces16is equal to or more than 1.2 mm and equal to or less than 1.4 mm (i.e., from 1.2 mm to 1.4 mm), and the distance Ld between the pair of end surfaces14is equal to or more than 1.4 mm and equal to or less than 1.6 mm (i.e., from 1.4 mm to 1.6 mm). Here, the actual size of the inductor1may include errors of about several percent with respect to the above-described nominal sizes of the inductor1, i.e., the length L dimension of 1.4 mm, the width W dimension of 1.2 mm, and the thickness T dimension of 0.8 mm. In addition, it should be noted that the above-described size of the inductor1is the size of the entire inductor1including the outer electrode4, the size of the element body2is generally smaller than the size of the inductor1, and the ratio of the distance Wb between the side surfaces16to the distance Ld between the end surfaces14may be different from the ratio of the width W to the length L in an outer shape of the entire inductor1.

Next, a connection configuration between the outer electrode and the outer electrode connection portion24of the coil conductor20and a configuration of the outer electrode on the element body surface will be described.

B-1. Connection Configuration of Outer Electrode and Outer Electrode Connection Portion

FIG.11is a cross-sectional view taken along line XI-XI ofFIG.5.FIG.11illustrates a cross section orthogonal to the extending direction dp of the outer electrode connection portion24in the connection portion between the outer electrode connection portion24and the outer electrode4.

The pair of outer electrodes4are provided on the surface of the element body2. The outer electrode4is connected to the conductor43that is exposed by removing a coating layer45of the outer electrode connection portion24. The outer electrode4has a plated conductor50formed by plating. The plated conductor50of the present embodiment has a copper plating layer51as a plating layer having the same metal component as the conductor43. The copper plating layer51is a plating layer for plating the surface of the conductor43. The copper plating layer51and the conductor43are connected to each other.

A Ni plating layer52is formed on the copper plating layer51. A Sn plating layer53is formed on the Ni plating layer52. The plated conductor50of the present embodiment has the copper plating layer51, the Ni plating layer52, and the Sn plating layer53. The plated conductor50is formed on the conductor outer peripheral surface43bof the outer electrode connection portion24and the conductor side surfaces43cand43dexposed by removing the coating layer45of the conductive wire42of the outer electrode connection portion24. As illustrated inFIG.11, the amounts of exposure of the conductor side surfaces43cand43dare different between the conductor side surfaces43cand43d. That is, inFIG.11, the positions of the ends of the coating layer45on the outer electrode4side are different in the right-left direction between the conductor side surface43cand the conductor side surface43d, and the amount of exposure of the conductor side surface43dis larger than that of the conductor side surface43c.

FIG.12is a cross-sectional view when the normal conductor81corresponding toFIG.11is used.

Since the normal conductor81does not have a rectangular shape with four right-angled corners, the length of the conductor outer peripheral surface81bin the direction of the line width La is shorter than the line width La of the conductor81, and the conductor side surfaces81cand81don both sides of the conductor outer peripheral surface81bin the direction of the line width La are likely to have curved surfaces with large curvatures.

Here, in manufacturing the inductor, in a conductive wire80of the normal conductor81, when the coil conductor20is embedded in the element body2, the thickness of the element body2on the curved surfaces where the conductor outer peripheral surface81band the conductor side surfaces81cand81dare connected to each other (in other words, the length in the length direction DL from the outer surface of the element body2to the above curved surface) is larger than the thickness of the element body2on the conductor outer peripheral surface81b(in other words, the length in the length direction DL from the outer surface of the element body2to the conductor outer peripheral surface81b). Therefore, when the coating layer45on the conductor outer peripheral surface81bside of the conductive wire80embedded in the element body2is peeled off in the surface treatment process, only the coating layer45on the conductor outer peripheral surface81bside is easily peeled off due to the different thicknesses of the element body2, and the coating layer45and the magnetic particles on the curved surfaces connecting the conductor outer peripheral surface81band the conductor side surfaces81cand81dare likely to be left. For this reason, when plating is grown on the conductor outer peripheral surface81b, a constricted shape81eis likely to be formed at a connection portion between the conductive wire80and the plated conductor50. That is, in the normal conductor81, the conductor outer peripheral surface81band the plated conductor50are connected to each other so as to form the constricted shape81e, therefore, a connection area between the conductor81and the plated conductor50is likely to be smaller than the line width La. As such, there is a problem in that the DC resistance of the outer electrode4increases or connection reliability between the outer electrode4and the conductor81of the coil conductor20decreases.

On the other hand, since the conductor43of the present embodiment has a substantially rectangular shape, when the coil conductor20is embedded in the element body2, the thickness of the element body2on the corner portions of the conductor outer peripheral surface43band the conductor side surfaces43cand43dare less likely to be larger than the thickness of the element body2on the conductor outer peripheral surface43b. Therefore, when the coating layer45on the conductor outer peripheral surface43bside of the conductive wire42embedded in the element body2is peeled in the surface treatment process, not only the coating layer45on the conductor outer peripheral surface43bbut also the coating layer45of the conductor side surfaces43cand43don the conductor outer peripheral surface43bside can be peeled.

Note that inFIG.11, the positions of an end of the coating layer45are different in the right-left direction between the conductor side surface43cand the conductor side surface43ddue to a direction of laser irradiation in the surface treatment process. That is, inFIG.11, the laser beam is applied while moving from the bottom to the top (in a direction from the conductor side surface43dtoward the conductor side surface43cwith respect to the conductive wire42) to remove the resin layer. For this reason, in the conductor side surface43d, the coating layer45is easily removed because the laser beam moves closer to each other, whereas in the conductor side surface43c, the coating layer45is hardly removed because the laser beam moves away from each other. Thus, the position of an end of the coating layer45on the conductor side surface43dis cut to the inner side of the element body2relative to the position of an end of the coating layer on the conductor side surface43c.

At this time, when the plating is grown on the conductor outer peripheral surface43b, the plating is likely to be formed not only on the conductor outer peripheral surface43bbut also on the conductor side surfaces43cand43dexposed from the coating layer45at positions adjacent to the conductor outer peripheral surface43b, thus, the plated conductor50protruding outward from the conductor side surfaces43cand43din the thickness direction DT is formed. Therefore, since the shape formed by the conductor outer peripheral surface side of the conductor43and the plated conductor50can be made to spread toward the outer surface of the element body2, it is possible to prevent the occurrence of a constricted shape in the conductor side surfaces43cand43dportions, and to make a connection area between the conductor outer peripheral surface43band the plated conductor50substantially equal to the line width La. To be specific, the plated conductor50is formed on the conductor side surfaces43cand43dsuch that of angles θ3and04formed by a circumscribed line50aof the plated conductor50formed on the conductor outer peripheral surface43band a circumscribed line50bof the plated conductor50formed on the conductor side surfaces43cand43d, the angle θ3on the conductor43side is equal to or less than 90°.

It can also be restated as follows. That is, in the cross section illustrated inFIG.11, a virtual inscribed rectangle S2is set so as to be inscribed in a surface of the copper plating layer51formed on the conductor inner peripheral surface43aand the conductor side surfaces43cand43dand the conductor outer peripheral surface43bof the conductors43. The inscribed rectangle S2is a virtual rectangle set on the conductor43side so as to satisfy the following four conditions. First, the inscribed rectangle S2is set such that a side S2bon the conductor outer peripheral surface43bside is inscribed in the copper plating layer51of the plated conductor50. Second, the inscribed rectangle S2is set such that a side S2a(the side S2aopposite to the side S2b) on the conductor inner peripheral surface43aside is inscribed in the conductor43(including a case where an end of the side S2a, that is, at a corner, is in contact with the conductor43). Thirdly, the inscribed rectangle S2is set such that the area ratio of the area occupied by the conductor43and the copper plating layer51with respect to an area of the inscribed rectangle S2is maximized while satisfying the first condition and the second condition.

In the present embodiment, in the inscribed rectangle S2set as described above, corners S2eand S2fon the conductor inner peripheral surface43aside are likely to be occupied by the right-angled rectangular conductors43, and corners S2gand S2hon the copper plating layer51side are occupied by the copper plating layer51on the conductor outer peripheral surface43b. At this time, the area ratio of the conductor43and the copper plating layer51with respect to the inscribed rectangle S2, i.e., the area ratio of copper, which is a metal for the conductor43, was equal to or more than 99%.

Therefore, since the conductor43of the present embodiment has a rectangular cross-section with four right-angled corners, the conductor43can be easily connected to the coil conductor20with the copper plating layer51having a size equal to or larger than the size of the conductor outer peripheral surface43b, and the conductor43and the plated conductor50are widely connected to each other. Therefore, the DC resistance of the outer electrode4can be reduced, and the connection reliability between the outer electrode4and the coil conductor20can be improved.

Note that as illustrated inFIG.12, when the inscribed rectangle S2is set as described above with respect to the normal conductor81, the constricted shape81eenters the inscribed rectangle S2.

B-2. Configuration of Outer Electrode on Surface of Element Body

Next, the configuration of the outer electrode4on the surface of the element body will be described.

B-2-1. Configuration of Predetermined Electrode Portion and Outer Electrode Connection Portion

FIG.13is a side view of the inductor1viewed from the end surface14side of the element body2. As described above, the outer electrode4is formed by plating so as to cover a predetermined electrode portion R30. The predetermined electrode portion R30is formed by peeling off an element body coat70in the surface treatment process, the element body coat70being insulating resin coated on the surface of the element body in the element body protective layer forming process. The predetermined electrode portion R30is formed in a rectangular shape on each of the end surface14and the bottom surface10of the element body2.

As illustrated inFIG.13, the predetermined electrode portion R30is formed in a region that overlaps the portion of the outer electrode connection portion24exposed from the end surface14of the element body2. On the end surface14of the element body2, the outer electrode connection portion24is exposed along the width direction DW of the element body2over the predetermined electrode portion R30and a coating portion R31that is a region in an outer side portion of the predetermined electrode portion R30. In the outer electrode connection portion24exposed from the end surface14of the element body2, a coated portion64blocated at the coating portion R31is located closer to a tip64cside of the outer electrode connection portion24than a peeled portion64alocated at the predetermined electrode portion R30. That is, the tip64cof the outer electrode connection portion24is located at the coating portion R31. In addition, an area of the peeled portion64ais set to be larger than a cross-sectional area of the conductive wire constituting the coil conductor20.

As described above, the surface protective layer forming process is performed after the element body forming and curing process and the element body grinding process. That is, an entire surface of the outer electrode connection portion24exposed from the end surface14after the surface protective layer forming process is coated with the insulating resin. In addition, in the surface treatment process, a part of the coating is peeled off to form the predetermined electrode portion R30.

At this time, in the outer electrode connection portion24exposed from the end surface14of the element body2, only the coating applied to the peeled portion64ais peeled off, and the peeled portion64ais connected to the outer electrode4in the plating layer forming process. As described above, since the area of the peeled portion64ais set to be larger than the cross-sectional area of the conductive wire constituting the coil conductor20, the resistance is unlikely to increase at a connection portion between the peeled portion64aand the outer electrode4.

On the other hand, even after the surface treatment process, the element body coat70remains in the coating portion R31. As such, the coated portion64bis in a state of being covered with the element body coat70, and the tip64cof the outer electrode connection portion24is covered at least with the element body coat70. Since the coated portion64band the tip64care covered with the element body coat70, the outer electrode connection portion24exposed from the end surface14is fixed to the end surface14by the element body coat70on the tip64cside. For this reason, the outer electrode connection portion24is not easily peeled off from the end surface14until the outer electrode4is formed, and the connection between the outer electrode4and the outer electrode connection portion24is easily stabilized.

As illustrated inFIG.13, the coating portion R31includes a first thickness region70aand a second thickness region70b. The coated portion64bis covered by both the first thickness region70aand the second thickness region70b.

In addition, in the outer electrode connection portion24exposed from the end surface14of the element body2, the coating layer of the conductive wire is removed when the coating is removed at the peeled portion64a, the exposed conductor is connected with the outer electrode4in the plating layer forming process, the coated portion64bis covered with the element body coat70(i.e., both the first thickness region70aand the second thickness region70b) in a state where the coating layer of the conductive wire remains, and the coating layer of the conductive wire is located between the conductor and the element body coat70. Further, an area of a region of the outer electrode connection portion24connected to the outer electrode is equal to or larger than the cross-sectional area of the conductive wire constituting the coil conductor20.

Furthermore, the length of the coated portion64bof the outer electrode connection portion24is equal to or more than 5% of the length of the outer electrode connection portion24. The longer the length of the coated portion64bof the outer electrode connection portion24is, the larger the fixing force on the end surface of the element body2applied by the element body coat70can be, however, when the length of the coated portion64bexceeds 50% of the length of the outer electrode connection portion24, the area for connecting to the outer electrode4decreases. Therefore, the length of the coated portion64bto the outer electrode connection portion24is equal to or more than 5% and equal to or less than 50% (i.e., from 5% to 50%), preferably equal to or more than 10% and equal to or less than 45% (i.e., from 10% to 45%).

Furthermore, the peeled portion64aof the outer electrode connection portion24on the side opposite to the tip64c(i.e., the base of the outer electrode connection portion24) is located at a position within 50% of the length of the end surface of the element body2in the DW direction with respect to the center of the length of the end surface14of the element body2in the DW direction as a center (inFIG.13, 7% of the length of the end surface of the element body2in the DW direction on the left side of the center of the length of the end surface14of the element body2in the DW direction). At this position, the outer electrode connection portion24is extended from the extended portion having the coating layer embedded in the element body2to the end surface of the element body2, the outer electrode connection portion24on the side opposite to the tip64cat the coating layer of the conductive wire is removed, and the conductor of the conductive wire is exposed from the end surface14of the element body2and is also exposed from the element body coat. When the peeled portion64aof the outer electrode connection portion24on the tip64cside is too close to the center of the length of the end surface14of the element body2in the DW direction, an area of the outer electrode cannot be increased, therefore, inFIG.13, the peeled portion64aon the tip64cside is arranged at a position of equal to or more than 14% and equal to or less than 20% (i.e., from 14% to 20%), preferably 17% of the length of the end surface of the element body2in the DW direction from the side surface16side on the left side of the end surface14of the element body2. At this position, the outer electrode connection portion24on the tip64cside is covered with the coating portion R31of the element body coat70and the coating layer of the conductive wire.

In addition, when the tip64cof the outer electrode connection portion24is too close to the center of the length of the end surface14of the element body2in the DW direction, the area of the outer electrode cannot be increased, therefor, inFIG.13, the tip64cof the outer electrode connection portion24is arranged at a position of equal to or more than 6% and equal to or less than 12% (i.e., from 6% to 12%), preferably 9% of the length of the end surface of the element body2in the DW direction from the side surface16side on the left side of the end surface14of the element body2.

B-2-2. Configuration of Outer Electrode and Element Body Coat

As illustrated inFIG.13, when the inductor1is viewed from the one end surface14side, the outer electrode4is arranged so as to be biased toward the bottom surface10side of the end surface14, and the outer electrode4is surrounded by the element body coat70.

The first thickness region70ais formed in a boundary region between the predetermined electrode portion R30and the coating portion R31. The second thickness region70bis located farther away from the predetermined electrode portion R30than the first thickness region70awhen viewed from the predetermined electrode portion R30. The first thickness region70ais provided on the end surface14and the bottom surface10at the position to surround the predetermined electrode portion R30formed on the end surface14and the bottom surface10of the element body2.

FIG.14is a view schematically illustrating a cross section taken along line XIV-XIV inFIG.13. Note that the XIV-XIV cross section is a cross section perpendicular to a boundary between the predetermined electrode portion R30and the coating portion R31in a side view from the end surface14side of the element body2. That is, the XIV-XIV cross section is a cutting plane obtained by cutting the element body2in the length direction DL along a straight line orthogonal to a boundary between the outer electrode4and the element body coat70when viewed from the end surface14. In addition, in the XIV-XIV cross section, the DT direction is a direction away from the predetermined electrode portion R30.

In the surface treatment process, the first thickness region70ais formed by removing a part of the element body coat70by emitting the laser beam while adjusting the irradiation time and the irradiation power such that the irradiation amount of the laser beam is smaller than the irradiation amount of the laser beam with which the predetermined electrode portion R30is irradiated. As such, the thickness of the first thickness region70ais smaller than an average thickness T30of the element body coat70.

The average thickness T30is an average value of the thicknesses of the element body coat70at positions sufficiently away from the predetermined electrode portion R30in the element body coat70covering the entire element body2. The average thickness T30is obtained, for example, as an average value of measured values of the thicknesses of the element body coat70measured at arbitrary three points in a central portion of the upper surface around the winding axis K in a cutting plane vertically cut along a virtual line extending along the length direction DL of the element body2passing through the winding axis K of the coil when the element body2is viewed from the upper surface.

The second thickness region70bis a portion of the element body coat70formed in the surface protective layer forming process that has not received the laser beam in the surface treatment process. The thickness of the second thickness region70bis substantially equal to the average thickness T30and is larger than the thickness of the first thickness region70a.

As illustrated inFIG.14, in the XIV-XIV cross section, a flat portion75and a stepped portion71are provided in the first thickness region70a. The flat portion75is a portion of the first thickness region70awhere the thickness of the element body coat70is approximately constant on average. The stepped portion71is a portion of the first thickness region70athat becomes abruptly thicker in the direction away from the predetermined electrode portion R30. The stepped portion71connects the flat portion75and the second thickness region70bthat have different thicknesses, and the formation of the stepped portion71facilitates the formation of the flat portion75and the second thickness region70b. The stepped portion71is formed to be inclined by, for example, about 17 degrees with respect to the flat portion75.

As illustrated inFIG.14, a peripheral edge65, which is a part of the outer electrode4, is formed on the first thickness region70a. A tip65aof the peripheral edge65of the outer electrode4, which is located farthest away from the predetermined electrode portion R30, is located on the flat portion75of the first thickness region70a. For this reason, the peripheral edge65of the outer electrode4is not formed on the stepped portion71and the second thickness region70b. In other words, the tip65aof the peripheral edge65of the outer electrode4is located closer to the predetermined electrode portion R30side than the stepped portion71and the second thickness region70b. In addition, in the direction away from the predetermined electrode portion R30, the length of the peripheral edge65of the outer electrode4is shorter than the length of the flat portion75of the first thickness region70a. In other words, in the XIV-XIV cross section, the length of the flat portion75in the direction away from the predetermined electrode portion R30is longer than the length of the portion (peripheral edge65) of the outer electrode4formed on the element body coat70. For this reason, the entire peripheral edge65of the outer electrode4is easily formed on the flat portion75of the first thickness region70a.

The outer electrode4has a copper plating layer (first plating layer)51, a Ni plating layer (second plating layer)52, and a Sn plating layer (third plating layer)53. The copper plating layer51is a portion formed first by plating in the plating layer forming process. The copper plating layer51is slightly formed also on the coating portion R31. However, since the element body coat70has insulation properties, the copper plating layer51of the outer electrode4on the coating portion R31, that is, the copper plating layer51of the peripheral edge65of the outer electrode4is thinner than the copper plating layer51formed in contact with the core30constituting the element body2at the predetermined electrode portion R30.

The Ni plating layer52is formed by plating next to the copper plating layer51and is formed on the copper plating layer51. The Sn plating layer53is formed by plating next to the Ni plating layer52, and is formed on the Ni plating layer52. The Ni plating layer52and the Sn plating layer53of the peripheral edge65of the outer electrode4are formed on the copper plating layer51and the Ni plating layer52, respectively, which are conductors. As such, the thicknesses of the Ni plating layer52and the Sn plating layer53at the peripheral edge65of the outer electrode4are substantially equal to the thicknesses of the Ni plating layer52and the Sn plating layer53located at the predetermined electrode portion R30.

Since the copper plating layer51at the peripheral edge65of the outer electrode4is thinner than the copper plating layer51at the other portions, the peripheral edge65is formed to have thickness smaller than an average thickness T33of the outer electrode4.

The average thickness T33of the outer electrode4is larger than the average thickness T30, and the outer electrode4protrudes more outward than the element body coat70from the end surface14and the bottom surface10. In other words, in the XIV-XIV cross section, the thickness of the portion of the outer electrode4formed on the surface of the element body2(the portion formed in the predetermined electrode portion R30) is larger than the thickness of the second thickness region70b. Thus, the outer electrode4can be easily connected to a substrate or the like at the time of mounting. The average thickness T33of the outer electrode4is obtained, for example, as an average value of thicknesses at three or more arbitrary points of the outer electrode4excluding the peripheral edge65and the connection portion with the peeled portion64ain a cutting plane vertically cut along a virtual line extending along the length direction DL of the element body2passing through the winding axis K of the coil when the element body2is viewed from the upper surface.

As described above, the peripheral edge65of the outer electrode4thinner than the average thickness T33is formed on the first thickness region70ahaving the thickness equal to or less than the thickness of the second thickness region70b. As such, the peripheral edge65of the outer electrode4on the first thickness region70ais unlikely to protrude in a direction away from the element body2. That is, the peripheral edge65of the outer electrode4is less likely to protrude to the outer side portion of the end surface14and the bottom surface10of the element body2than the outer electrode4formed at the predetermined electrode portion R30. In addition, the thickness of the tip65aof the outer electrode4is smaller than a difference in thickness between the first and second thickness regions70aand70b, and the tip65aof the outer electrode4is located closer to the element body2and the core30side than a surface of the second thickness region70b. For this reason, the tip65ais unlikely to protrude in the direction away from the element body2.

Furthermore, as described above, since the first thickness region70ais arranged at a position surrounding the predetermined electrode portion R30, the first thickness region70asurrounds the outer electrode4. For this reason, around the outer electrode4, the peripheral edge65is less likely to protrude in the direction away from the element body2and in a direction away from the core30.

FIG.15is a cross-sectional view taken along line XIV-XIV ofFIG.13. As illustrated inFIG.15, in practice, the thickness and shape of the first thickness region70avary depending on the accuracy of laser processing for irradiating the element body coat70with the laser beam. Hereinafter, a specific definition of each element will be described with reference toFIG.15.

In the XIV-XIV cross section, the first thickness region70ais defined as the element body coat70extending from a portion of the element body coat70closest to the predetermined electrode portion R30to the portion of the element body coat70having a maximum thickness T32in the XIV-XIV cross section.

In the XIV-XIV cross section, the second thickness region70bis a portion in which the element body coat70has the maximum thickness T32in the XIV-XIV cross section. More strictly, in the XIV-XIV cross section, the second thickness region70bis defined as the element body coat70located on the side in the direction away from the predetermined electrode portion R30starting from the portion in which the thickness of the element body coat70is the maximum thickness T32in the XIV-XIV cross section.

FIG.16is a cross-sectional view taken along line XVI-XVI ofFIG.13. The XVI-XVI cross section is a cutting plane obtained by cutting the element body2in the length direction DL along a straight line orthogonal to the boundary between the outer electrode4and the element body coat70when viewed from the end surface14. In the XVI-XVI cross section, the DT direction is the direction away from the predetermined electrode portion R30. As illustrated inFIG.16, in the XVI-XVI cross section, in the boundary region between the predetermined electrode portion R30and the coating portion R31, an inclined portion73is formed in the element body coat70so as to become thicker on average in the direction away from the predetermined electrode portion R30. In other words, in the XVI-XVI cross section, the inclined portion73is a portion in which the thickness of the element body coat70is averagely increased toward the second thickness region70b. The inclined portion73is formed in the direction away from the predetermined electrode portion R30from the boundary between the predetermined electrode portion R30and the coating portion R31to a position where the element body coat70has the maximum thickness T32in the XVI-XVI cross section. For this reason, the inclined portion73is formed in the entire first thickness region70ain the XVI-XVI cross section. In addition, in the XVI-XVI cross section, the flat portion75is not formed in the first thickness region70a.

In addition, in the XVI-XVI cross section, the stepped portion71in which the thickness abruptly changes is not formed in the first thickness region70a. That is, the difference in thickness between the first thickness region70aand the second thickness region70bis formed not by the stepped portion71in which the thickness of the element body coat70changes abruptly but by the inclined portion73. In the XVI-XVI cross section, the first thickness region70ais the element body coat70from a portion of the element body coat70closest to the predetermined electrode portion R30to a portion of the element body coat70having the maximum thickness T32in the XVI-XVI cross section. In addition, in the XVI-XVI cross section, the second thickness region70bis the element body coat70located on the side in the direction away from the predetermined electrode portion R30from the portion in which the element body coat70has the maximum thickness T32in the XVI-XVI cross section. The formation of the inclined portion73facilitates the formation of the first thickness region70aand the second thickness region70beven when the stepped portion71is not formed.

As described above, in the element body coat70, the difference in thickness between the first thickness region70aand the second thickness region70bmay be caused by the stepped portion71or by the inclined portion73. As in the present embodiment, in the element body coat70of one inductor1, a portion in which the stepped portion71is formed and a portion in which the inclined portion73is formed may be mixed in each cutting plane. In addition, only one of the stepped portion71and the inclined portion73may be formed in the element body coat70of one inductor1.

Up to this point, in [B-2-2. Configuration of Outer Electrode and Element Body Coat], the description based on the one end surface14illustrated inFIG.13also applies to the other end surface14on the opposite side of the element body2.

In addition, in [B-2-2. Configuration of Outer Electrode and Element Body Coat], the end surface14has been described with reference toFIG.13toFIG.16. When the element body2is viewed from the bottom surface10side, the inductor1also has the outer electrode4located on the one end surface14side, the outer electrode4located on the other end surface14side, and the element body coat70surrounding the two outer electrodes4(seeFIG.2). For this reason, the above description of the end surface14with reference toFIG.13toFIG.16also applies to the bottom surface10. That is, the above description using the cutting planes ofFIG.14toFIG.16also applies to a cutting plane cut in the thickness direction DT of the element body2along a straight line orthogonal to the boundary between arbitrary one of the outer electrodes4and the element body coat70when viewed from the bottom surface10.

Other Embodiments

In the embodiment illustrated in [B-2-1. Configuration of Predetermined Electrode Portion and Outer Electrode Connection Portion] described above, it has been described that the element body coat70has the first thickness region70aand the second thickness region70b, but this is merely an example. The element body coat70need not include the first thickness region70aand the second thickness region70b.

In the embodiment illustrated in [B-2-2. Configuration of Outer Electrode and Element Body Coat] described above, it has been described that the tip65aof the peripheral edge65of the outer electrode4is located on the flat portion75of the first thickness region70a, but this is merely an example. For example, the tip65aof the peripheral edge65may be positioned on the stepped portion71.

In the embodiment illustrated in [B-2-2. Configuration of Outer Electrode and Element Body Coat] described above, it has been described that in the XIV-XIV cross section, the thickness of the portion of the outer electrode4formed on the surface of the element body2is greater than the thickness of the second thickness region70b, but this is merely an example. That is, in a cutting plane obtained by cutting the element body2in the length direction DL along a straight line orthogonal to the boundary between the outer electrode4and the element body coat70when viewed from the end surface14, the thickness of the portion of the outer electrode4formed on the surface of the element body2may be smaller than the thickness of the second thickness region70b.

All the embodiments and modifications described above exemplify one aspect of the present disclosure, and can be arbitrarily modified and applied without departing from the gist of the present disclosure.

In addition, directions such as horizontal, orthogonal, and vertical directions, various numerical values, shapes, and materials in the above-described embodiments include ranges (so-called equivalent ranges) in which the same operational effects as those of the directions, the numerical values, the shapes, and the materials are achieved unless otherwise specified.

Configurations Supported by the Above Embodiments

The above-described embodiment supports the following configurations.

(Configuration 1) An inductor comprising an element body containing metal magnetic powder and resin and having a coil conductor embedded in the element body; an element body coat covering a surface of the element body; and an outer electrode formed on the surface of the element body. The coil conductor has a winding portion, an extended portion extended from the winding portion, and an outer electrode connection portion leading to the extended portion and connected to the outer electrode, and the outer electrode connection portion has a region covered with the element body coat and a region connected to the outer electrode on the surface of the element body.

According to the inductor of Configuration 1, the outer electrode connection portion exposed on the surface of the element body can be fixed to the element body by the element body coat. For this reason, the outer electrode connection portion is less likely to be peeled off from the element body, and the stability of the connection between the coil conductor and the outer electrode is improved.

(Configuration 2) The inductor according to Configuration 1, wherein a tip of the outer electrode connection portion is covered with the element body coat.

According to the inductor of Configuration 2, the element body coat can prevent the tip of the outer electrode connection portion from being peeled off from the element body.

(Configuration 3) The inductor according to Configuration 1 or 2, wherein the element body coat has a first thickness region and a second thickness region thicker than the first thickness region in a portion covering the outer electrode connection portion.

According to the inductor of Configuration 3, while the outer electrode connection portion is fixed to the element body by the element body coat, a portion of the outer electrode formed on the element body coat is less likely to protrude. Therefore, it is easy to increase the size of the external shape of the element body. With this configuration, it is easy to achieve both improvement in the stability of the connection between the coil conductor and the outer electrode and improvement in characteristics of the inductor.

(Configuration 4) The inductor according to any one of Configurations 1 to 3, wherein in the outer electrode connection portion, an area of a region connected to the outer electrode has an area equal to or larger than a cross-sectional area of a conductive wire constituting the coil conductor.

According to the inductor of Configuration 4, the coil conductor and the outer electrode are easily connected to each other in an area equal to or larger than the cross-sectional area of the conductive wire. Therefore, the resistance of the connection portion between the coil conductor and the outer electrode is less likely to be larger than the resistance of the conductive wire, and the resistance of the inductor can be reduced.

(Configuration 5) The inductor according to any one of Configurations 1 to 4, wherein in a region of the outer electrode connection portion covered with the element body coat, a coating layer of the conductive wire is present between the element body coat and a conductor of a conductive wire constituting the coil conductor.

According to the inductor of Configuration 5, the coating layer is present between the conductor of the conductive wire and the element body coat at the outer electrode connection portion in the region covered with the element body coat, thus, even when the element body coat covering the outer electrode connection portion is peeled off due to an impact or the like, the conductor of the conductive wire can be protected by the coating layer.

(Configuration 6) The inductor according to Configuration 5, wherein a coating layer of the conductive wire of the outer electrode connection portion is equal to or more than 5% and equal to or less than 50% (i.e., from 5% to 50%) of a length of the outer electrode connection portion.

According to the inductor of Configuration 6, the connection between the outer electrode connection portion and the outer electrode can be ensured.

(Configuration 7) The inductor according to any one of Configurations 1 to 6, wherein a tip of the outer electrode connection portion is arranged such that a length between an end surface of the element body on a side surface side and a tip of the outer electrode connection portion is in a range of equal to or more than 6% and equal to or less than 12% (i.e., from 6% to 12%) of a length in a width direction of the end surface of the element body.

According to the inductor of Configuration 7, it is possible to increase a connection area between the outer electrode connection portion and the outer electrode.

(Configuration 8) The inductor according to any one of Configurations 1 to 7, wherein a base of the outer electrode connection portion is arranged within a range of 50% of a length of an end surface of the element body in a width direction with a center of the end surface of the element body in a width direction as a center.

According to the inductor of Configuration 8, it is possible to increase the connection area between the outer electrode connection portion and the outer electrode.