JP7554078B2 - Inductors - Google Patents

Description

The present invention relates to an inductor.

As disclosed in JP-A-10-144526 (Patent Document 1), a conventional inductor is known that has a magnetic base made of ferrite material, a rectangular parallelepiped internal conductor provided within the magnetic base, and two external electrodes connected to one end and the other end of the internal conductor. When viewed from above, the internal conductor extends linearly from one external electrode to the other external electrode.

Japanese Patent Application Publication No. 10-144526

In recent years, devices and circuits, particularly electrical components, have become larger in current, and soft magnetic metal materials, which are less likely to experience magnetic saturation even when large currents flow through them, are increasingly being used as materials for the magnetic base of inductors. However, magnetic bases made from soft magnetic metal materials are more likely to generate eddy currents than magnetic bases made from ferrite materials, and are more likely to experience temperature increases due to Joule heat generated by eddy currents.

Furthermore, when a large current flows through an inductor, heat is generated from the current path in the inductor. Most of the heat generated in the inductor's current path is dissipated by thermal conduction to the printed circuit board on which the inductor is mounted. However, when a large current flows through an inductor, heat dissipation by thermal conduction to the printed circuit board alone may not be enough to dissipate the heat generated in the inductor.

The object of the present invention is to solve or alleviate at least some of the problems mentioned above. One of the more specific objects of the present invention is to improve the heat dissipation characteristics of an inductor. Other objects of the present invention will become apparent throughout the entire specification.

The inductor according to one aspect of the present invention comprises a base having a mounting surface facing a circuit board, an upper surface facing the mounting surface, and an end surface connecting the mounting surface and the upper surface, a first external electrode attached to the mounting surface of the base, a second external electrode attached to the mounting surface of the base at a distance from the first external electrode in a length direction perpendicular to the end surface, and an internal conductor provided within the base, one end electrically connected to the first external electrode and the other end electrically connected to the second external electrode, and extending linearly from the first external electrode to the second external electrode in a plan view seen from a thickness direction perpendicular to the mounting surface. In one aspect, in a front view seen from a width direction perpendicular to the thickness direction and the length direction, the distance between the mounting surface and the position farthest from the mounting surface on the axis of the internal conductor is smaller than half the distance between the upper surface and the mounting surface.

In one aspect of the present invention, the base is partitioned into an upper region and a lower region between the intermediate surface and the upper surface by an intermediate surface that extends parallel to the mounting surface and the upper surface and is equidistant from the mounting surface and the upper surface.
The entirety is disposed in the lower region.

In one aspect of the present invention, the base is partitioned into a first region surrounded by the internal conductor and the mounting surface in the front view, and a second region other than the first region, and the first region is formed from a material having a higher saturation magnetic flux density than the second region.

In one aspect of the present invention, the first external electrode is attached to the base only on the mounting surface.

In one aspect of the present invention, the second external electrode is attached to the base only on the mounting surface.

In one aspect of the present invention, the internal conductor is formed from a conductive material having a higher electrical conductivity than the material of the first external electrode.

In one embodiment of the present invention, the substrate contains metal magnetic particles.

In one aspect of the present invention, the internal conductor has a first internal conductor pattern and a second internal conductor pattern arranged within the base at a distance from the internal conductor pattern, and each of the first internal conductor pattern and the internal conductor pattern extends linearly from the first external electrode to the second external electrode in a plan view seen from a thickness direction perpendicular to the mounting surface, with one end exposed from the mounting surface and connected to the first external electrode, and the other end exposed from the mounting surface and connected to the second external electrode.

One embodiment of the present invention relates to a circuit board having any of the above inductors.

One embodiment of the present invention relates to an electronic device that includes the above-mentioned circuit board.

The disclosure of this specification makes it possible to improve the heat dissipation characteristics of an inductor.

FIG. 2 is a perspective view of an inductor according to an embodiment of the present invention mounted on a circuit board. FIG. 2 is a front view of the inductor of FIG. 1 . FIG. 2 is a plan view of the inductor of FIG. FIG. 2 is an exploded view of the inductor of FIG. 2 is a cross-sectional view of the inductor shown in FIG. 1 along line XX. 4 is a cross-sectional view of an inductor according to another embodiment of the present invention. 4 is a cross-sectional view of an inductor according to another embodiment of the present invention. 4 is a cross-sectional view of an inductor according to another embodiment of the present invention. 4 is a cross-sectional view of an inductor according to another embodiment of the present invention. 4 is a cross-sectional view of an inductor according to another embodiment of the present invention. 4 is a cross-sectional view of an inductor according to another embodiment of the present invention. 4 is a cross-sectional view of an inductor according to another embodiment of the present invention. 4 is a cross-sectional view of an inductor according to another embodiment of the present invention. FIG. 2 is a front view of an inductor according to another embodiment of the present invention.

Various embodiments of the present invention will be described below with reference to the drawings as appropriate. Note that components common to multiple drawings are given the same reference numerals throughout the multiple drawings. Please note that the drawings are not necessarily drawn to scale for ease of explanation.

An inductor 1 according to one embodiment of the present invention will be described with reference to Figures 1 to 5. First, an overview of the inductor 1 will be described with reference to Figures 1 to 3. Figure 1 is a perspective view of the inductor 1 according to one embodiment of the present invention, Figure 2 is a front view of the inductor 1, and Figure 3 is a plan view of the inductor 1. As shown, the inductor 1 comprises a base 10, an internal conductor 25 provided within the base 10, an external electrode 21 provided on the surface of the base 10, and an external electrode 22 provided on the surface of the base 10 at a position spaced apart from the external electrode 21.

In each figure, an L axis, a W axis, and a T axis that are perpendicular to each other are shown. In this specification, unless otherwise understood in the context, the "length" direction, the "width" direction, and the "thickness" direction of the inductor 1 are respectively defined as the "L" direction, the "W" direction, and the "T" direction in FIG. 1. According to this definition of directions, the external electrode 22 is disposed at a position spaced apart from the external electrode 21 in the length direction (L direction).

Inductor 1 is used, for example, in a high-current circuit through which a large current flows. Inductor 1 may also be used in a signal circuit or a high-frequency circuit. Inductor 1 may also be used as a bead inductor for noise reduction.

The inductor 1 is mounted on a circuit board 2. The mounting board of the circuit board 2 is provided with two lands 3a and 3b. The external electrode 21 is arranged so as to face the land 3a when the inductor 1 is mounted on the circuit board 2, and the external electrode 22 is arranged so as to face the land 3b of the circuit board 2 when the inductor 1 is mounted on the circuit board 2. The inductor 1 may be mounted on the circuit board 2 by soldering the external electrode 21 to the land 3a and the external electrode 22 to the land 3b. In addition to the inductor 1, various electronic components may be mounted on the circuit board 2. The circuit board 2 may be mounted on various electronic devices. Electronic devices in which the circuit board 2 may be mounted include smartphones, tablets, game consoles, automotive electrical equipment, and various other electronic devices. The inductor 1 may be an internal component embedded inside the mounting board of the circuit board 2.

The base 10 is formed from a magnetic material in a rectangular parallelepiped shape. In one embodiment of the present invention, the base 10 is formed so that the length dimension (dimension in the L direction) is 0.4 mm to 10 mm, the width dimension (dimension in the W direction) is 0.2 to 10 mm, and the height dimension (dimension in the T direction) is 0.2 to 10 mm. The present invention can be widely applied to inductors ranging from relatively small to relatively large inductors. The dimensions of the base 10 are not limited to the dimensions specifically described in this specification. In this specification, the term "rectangular parallelepiped" or "rectangular parallelepiped shape" does not only mean "rectangular parallelepiped" in the strict mathematical sense.

The base 10 has a first main surface 10a, a second main surface 10b, a first end surface 10c, a second end surface 10d, a first side surface 10e, and a second side surface 10f. The outer surface of the base 10 is defined by these six surfaces. The first main surface 10a and the second main surface 10b face each other, the first end surface 10c and the second end surface 10d face each other, and the first side surface 10e and the second side surface 10f face each other. Each of the first end surface 10c and the second end surface 10d connects the first main surface 10a and the second main surface 10b, and also connects the first side surface 10e and the second side surface 10f. When the circuit board 2 is used as a reference, the first main surface 10a is on the upper side of the base 10, so the first main surface 10a is sometimes called the "upper surface". Similarly, the second main surface 10b may be referred to as the "lower surface". Since the inductor 1 is disposed so that the second main surface 10b faces the circuit board 2, the second main surface 10b may be referred to as the "mounting surface" or the "mounting surface 10b". When referring to the up-down direction of the inductor 1, the up-down direction in FIG. 1 is used as a reference. The thickness direction of the inductor 1 or the base 10 may be perpendicular to at least one of the upper surface 10a and the mounting surface 10b. The length direction of the inductor 1 or the base 10 may be perpendicular to at least one of the first end surface 10c and the second end surface 10d. The width direction of the inductor 1 or the base 10 may be perpendicular to at least one of the first side surface 10e and the second side surface 10f. The width direction of the inductor 1 or the base 10 may be perpendicular to the thickness direction and the length direction of the inductor 1 or the base 10.

In the illustrated embodiment, the external electrode 21 is provided so as to contact the mounting surface 10b, the first end surface 10c, and the top surface 10a of the base 10. The external electrode 22 is provided so as to contact the mounting surface 10b, the second end surface 10d, and the top surface 10a of the base 10. At least one of the external electrode 21 and the external electrode 22 may be provided on the base 10 so as to contact only the mounting surface 10b. FIG. 15 shows an inductor 1 in which the external electrodes 21 and 22 are both provided so as to contact only the mounting surface 10b. The shapes and arrangements of the external electrodes 21 and 22 are not limited to those explicitly described in this specification.

The base 10 is made of a magnetic material. The magnetic material for the base 10 may include a plurality of metal magnetic particles. The metal magnetic particles included in the magnetic material for the base 10 are, for example, (1) metal particles such as Fe and Ni, (2) crystalline alloy particles such as Fe-Si-Cr alloy, Fe-Si-Al alloy, Fe-Ni alloy, (3) amorphous alloy particles such as Fe-Si-Cr-B-C alloy, Fe-Si-Cr-B alloy, or (4) mixed particles of these. The composition of the metal magnetic particles included in the core 10 is not limited to the above. For example, the metal magnetic particles included in the core 10 may be a Co-Nb-Zr alloy, Fe-Zr-Cu-B alloy, Fe-Si-B alloy, Fe-Co-Zr-Cu-B alloy, Ni-Si-B alloy, or Fe-AL-Cr alloy. The Fe-based metal magnetic particles contained in the substrate 10 may contain 80 wt% or more of Fe. An insulating film may be formed on the surface of each of the metal magnetic particles. This insulating film may be an oxide film formed by oxidizing the above metal or alloy. The insulating film provided on the surface of each of the metal magnetic particles may be, for example, a silicon oxide film coated by a sol-gel method.

In one embodiment, the metal magnetic particles have an average particle size of 1.5 to 20 μm. The average particle size of the metal magnetic particles contained in the base 10 may be smaller than 1.5 μm or larger than 20 μm. The base 10 may contain two or more types of metal magnetic particles having different average particle sizes. For example, the metal magnetic particles for the composite magnetic material may include first metal magnetic particles having a first average particle size and second metal magnetic particles having a second average particle size smaller than the first average particle size.

The substrate 10 may be formed from a composite magnetic material containing metal magnetic particles and a binder. When the substrate 10 is formed from a composite magnetic material, the binder contained in the composite magnetic material is, for example, a thermosetting resin with excellent insulating properties. As the binder, for example, epoxy resin, polyimide resin, polystyrene (PS) resin, high density polyethylene (HDPE) resin, polyoxymethylene (POM) resin, polycarbonate (PC) resin, polyvinylidene fluoride (PVDF) resin, phenolic resin, polytetrafluoroethylene (PTFE) resin, or polybenzoxazole (PBO) resin may be used. In addition, the binder may be an oxide film on the surface of each of the metal magnetic particles, or an oxide other than the oxide film. The metal magnetic particles may be bonded to each other by these oxides.

The internal conductor 25 is provided so as to electrically connect the external electrode 21 and the external electrode 22 within the base 10. The internal conductor 25 may have multiple internal conductor patterns, or may have only a single internal conductor pattern. In the illustrated embodiment, the internal conductor 25 has six internal conductor patterns 25a to 25f. The internal conductor pattern 25a has one end and the other end exposed from the mounting surface 10b toward the outside of the base 10, and is connected to the external electrode 21 at the one end and to the external electrode 22 at the other end. The end face of the internal conductor 25 that contacts the external electrode 21 faces the land 3a when the inductor 1 is mounted on the circuit board 2, and the end face of the internal conductor 25 that contacts the external electrode 22 faces the land 3b when the inductor 1 is mounted on the circuit board 2. The internal conductors 25b to 25f have the same or similar shape as the internal conductor 25a. The internal conductor patterns 25a to 25f are arranged at a distance from each other within the base 10. In this manner, the internal conductors 25a to 25f are arranged in parallel between the external electrode 21 and the external electrode 22 within the base 10. Each of the internal conductor patterns 25a to 25f may be connected to an adjacent internal conductor pattern. For example, a part or the entirety of the internal conductor pattern 25b may be connected to at least one of the internal conductor patterns 25a and 25c within the base 10.

As shown in FIG. 3, the internal conductor pattern 25a extends linearly from the external electrode 21 to the second external electrode 22 in a plan view (from the perspective of the T-axis). In other words, the internal conductor pattern 25a does not have any parts that are arranged opposite each other in the base 10 when viewed in a plan view. In this specification, when the internal conductor pattern 25a does not have any parts that are arranged opposite each other in the base 10 when viewed in a plan view, the internal conductor pattern 25a is said to extend linearly from the external electrode 21 to the external electrode 22. The internal conductor pattern 25a may be arranged on a straight line drawn from the external electrode 21 to the second external electrode 22. The internal conductor patterns 25b to 25f also extend linearly from the external electrode 21 to the second external electrode 22 in a plan view (from the perspective of the T-axis) like the internal conductor pattern 25a.

Next, referring to FIG. 4, the laminated structure of the inductor 1 created by the lamination process will be described. FIG. 4 shows an exploded view of the inductor 1. For convenience of explanation, the external electrodes 21 and 22 are omitted from FIG. 4. As shown in FIG. 4, the base body 10 includes magnetic layers 11a to 11f, a cover layer 12, and a cover layer 13. Each of the magnetic layers 11a to 11f, the cover layer 12, and the cover layer 13 is made of a magnetic material. The base body 10 is laminated in the order of the cover layer 12, the magnetic layers 11a to 11f, and the cover layer 13 from the positive side to the negative side in the W-axis direction. Each of the cover layers 12 and 13 may have multiple magnetic layers. The inductor 1 may be created by a method other than the lamination process. For example, the inductor 1 may be created by a thin film process or a compression molding process.

Internal conductor patterns 25a to 25f are provided on one surface of each of the magnetic layers 11a to 11f. In the illustrated embodiment, the internal conductor patterns 25a to 25f are provided on the surface on the negative side of the W-axis direction of the pair of surfaces of the magnetic layers 11a to 11f that intersect with the W-axis direction. The internal conductor patterns 25a to 25f are formed, for example, by printing a conductive paste made of a metal or alloy with excellent conductivity using a screen printing method. The surface of the magnetic layers 11a to 11f on which the internal conductor patterns 25a to 25f are formed is an example of a coil formation surface. The material of this conductive paste can be Ag, Pd, Cu, Al, or an alloy thereof. The internal conductor patterns 25a to 25f may be formed by a method other than the screen printing method, such as a sputtering method, an inkjet method, or other known method. In one embodiment, the internal conductor patterns 25a to 25f are formed from a material with a higher electrical conductivity than the external electrodes 21 and 22.

Next, the internal conductor pattern 25a will be described with further reference to FIG. 5. FIG. 5 is an X-X line cross-sectional view of the inductor 1. The X-X line cross-section of the inductor 1 shows a cross-section of the base 10 cut along a cutting plane that is parallel to the LT plane and passes through the internal conductor pattern 25a. FIG. 5 may be considered to show a perspective view of the base 10 so that the internal conductor pattern 25a is visible when viewed from the front from the W-axis direction (i.e., from the width direction). The description of the internal conductor pattern 25a also applies to the internal conductor patterns 25b to 25f as far as possible within the context. In other words, the internal conductor patterns 25a to 25f will be described below using the internal conductor pattern 25a as an example.

The base 10 extends parallel to the top surface 10a and the mounting surface 10b, and is divided into an upper region and a lower region by an intermediate surface B that is equidistant from the top surface 10a and the mounting surface 10b. That is, the base 10 is divided by the intermediate surface B into an upper region that is between the intermediate surface B and the top surface 10a, and a lower region that is between the intermediate surface B and the mounting surface 10b. As is clear from this definition, at any position included in the upper region, the distance from the top surface 10a is smaller than the distance from the mounting surface 10b, and at any position included in the lower region, the distance from the top surface 10a is greater than the distance from the mounting surface 10b.

As shown in the figure, the internal conductor pattern 25a extends from the external electrode 21 to the external electrode 22 along the axis A extending from the external electrode 21 to the external electrode 22. The internal conductor pattern 25a has a first portion 25a1, the lower end of which is exposed from the mounting surface 10b and extends from the one end in the positive direction of the T axis and the positive direction of the L axis, a second portion 25a2, the lower end of which is exposed from the mounting surface 10b and extends from the one end in the positive direction of the T axis and the negative direction of the L axis, and a third portion 25a3 that connects the upper end of the first portion 25a1 to the upper end of the second portion 25a2. The lower end of the first portion 25a1 is connected to the external electrode 21, and the lower end of the second portion 25a2 is connected to the external electrode 22. In the illustrated embodiment, the third portion 25a3 extends parallel to the upper surface 10a.

The internal conductor pattern 25a has an inner circumferential surface 25X extending parallel to the axis A from the external electrode 21 to the external electrode 22 between the axis A and the mounting surface 10b, and an outer circumferential surface 25Y extending parallel to the axis A from the external electrode 21 to the external electrode 22 between the axis A and the upper surface 10a. The axis A of the internal conductor pattern 25a may be determined based on the inner circumferential surface 25X. For example, the axis A may be a set of points equidistant from the inner circumferential surface 25X. The axis A may be a set of midpoints of line segments between a point on the inner circumferential surface 25X, a normal to that point, and a point where the normal intersects with the outer circumferential surface 25Y. The axis A generally coincides with the direction in which current flows within the internal conductor pattern 25a.

In one embodiment, the internal conductor pattern 25a is configured and arranged so that the distance between the mounting surface 10b and the position furthest from the mounting surface 10b on the axis A is smaller than half the distance (T1) between the upper surface 10a and the mounting surface 10b. In one embodiment, the internal conductor pattern 25a is configured and arranged so that the first portion 25a1, the second portion 25a2, and the third portion 25a3 are all included in the lower region of the base 10.

In one embodiment, the cross-sectional area of the internal conductor pattern 25a cut along a direction perpendicular to the axis A (internal conductor cross-sectional area) is larger than the cross-sectional area of the external electrode 21 cut along a direction parallel to the mounting surface 10b (external conductor cross-sectional area) of the portion of the external electrode 21 in contact with the first end face 10c. In one embodiment, the cross-sectional area of the internal conductor pattern 25a cut along a direction perpendicular to the axis A is larger than the cross-sectional area of the external electrode 22 cut along a direction parallel to the mounting surface 10b of the portion of the external electrode 22 in contact with the second end face 10d. If the cross-sectional area of the external electrode 21 along the mounting surface 10b is not constant, the average of the cross-sectional areas of the external electrode 21 in each cross section passing through three points arranged at equal intervals in the T-axis direction can be used as the cross-sectional area of the external electrode 21. The same applies to the cross-sectional area of the external electrode 22.

The internal conductor pattern 25a is disposed at a position spaced apart from the top surface 10a by an upper margin D1. More specifically, the internal conductor pattern 25a is disposed so that the distance between the top surface 10a of the base 10 and the outer peripheral surface 25Y of the internal conductor pattern 25a is the upper margin D1. In the illustrated embodiment, the internal conductor pattern 25a is configured and disposed so that the upper margin D1 is greater than half (T1/2) of the height dimension T1 of the base 10.

In one embodiment, the internal conductor pattern 25a is configured and arranged so that the distance T2 between the axis A and the top surface 10a of the base 10 is greater than half the distance between the top surface 10a and the mounting surface 10b in the X-X cross section. In the illustrated embodiment, the distance between the top surface 10a and the mounting surface 10b is equal to the height dimension T1 of the base 10. Therefore, in the illustrated example, the relationship T2>T1/2 holds.

In the X-X cross section (i.e., in the front view seen from the W axis), the base 10 is divided into a first region 10r1 surrounded by the internal conductor pattern 25a and the mounting surface 10b by the internal conductor pattern 25a, and a second region 10r2 other than the first region 10r1. More specifically, the first region 10r1 is a region surrounded by an inner peripheral edge that is the intersection line between the inner peripheral surface 25X and the X-X cross section, and a bottom edge that is the intersection line between the mounting surface 10b and the X-X cross section, in the front view seen from the W axis. The second region 10r2 is a region surrounded by an outer periphery which is an intersection line between the outer periphery surface 25Y and the X-X cross section, an upper edge which is an intersection line between the top surface 10atp and the first end face 10c and the X-X cross section, a right edge which is an intersection line between the first end face 10c and the X-X cross section, and a left edge which is an intersection line between the second end face 10d and the X-X cross section, in a front view seen from the W axis. The area of the first region 10r1 is smaller than that of the second region 10r2. Therefore, if the first region 10r1 and the second region 10r2 are formed from the same magnetic material, magnetic saturation is likely to occur in the first region 10r1, which may cause deterioration of the DC superposition characteristics of the inductor 1. Therefore, in one embodiment, the first region 10r1 may be formed from a magnetic material with a relatively high saturation magnetic flux density, and the second region 10r2 may be formed from a magnetic material with a lower saturation magnetic flux density than the first region 10r1. For example, the saturation magnetic flux of the first region 10r1 can be increased by making the Fe content of the metal magnetic particles contained in the first region 10r1 greater than the Fe content of the metal magnetic particles contained in the second region 10r2.

The shape and arrangement of the internal conductor pattern 25a are not limited to those illustrated in FIG. 5. The internal conductor pattern 25a may have various shapes and arrangements different from those illustrated in FIG. 5. Modified examples of the internal conductor pattern 25a will be described with reference to FIGS. 6 to 13.

In another embodiment of the present invention as a modified example of the internal conductor pattern 25a, as shown in FIG. 6, the internal conductor pattern 25a may have a curved surface. If the outer peripheral surface 25Y has an intersection point where straight lines intersect, magnetic flux may concentrate near the intersection point. According to the internal conductor pattern 25a shown in FIG. 6, since it does not have an intersection point where straight lines intersect, it is possible to prevent magnetic flux from concentrating near the intersection point. This further improves the DC superposition characteristics of the inductor 1.

In another embodiment of the present invention as a modified example of the internal conductor pattern 25a, the internal conductor pattern 25a may have its inner circumferential surface 25X and outer circumferential surface 25Y each formed of only curves in a cross section viewed from the W-axis direction. For example, as shown in FIG. 7, the curves forming the inner circumferential surface 25X and outer circumferential surface 25Y may be partial elliptical arcs of an ellipse whose major axis is parallel to the L axis or whose major axis coincides with the L axis. As shown in FIG. 8, the curves forming the inner circumferential surface 25X and outer circumferential surface 25Y may be partial elliptical arcs of an ellipse whose minor axis is parallel to the L axis or whose minor axis coincides with the L axis. As shown in FIG. 7 and FIG. 8, when the internal conductor pattern 25a does not have a linear portion parallel to the upper surface 10a, the distance between the position of the outer circumferential surface 25Y of the internal conductor pattern 25a closest to the upper surface 10a and the upper surface 10a is set as the upper margin D1. The curves forming the inner circumferential surface 25X and outer circumferential surface 25Y may be partial circular arcs or partial elliptical arcs of an ellipse. By configuring the inner peripheral surface 25X and the outer peripheral surface 25Y only with curves in a cross section seen from the W-axis direction, it is possible to prevent magnetic flux from concentrating in a certain area within the base body 10, thereby improving the DC superposition characteristics of the inductor 1. In particular, by configuring the inner peripheral surface 25X and the outer peripheral surface 25Y with curves that are partial elliptical arcs or partial circular arcs of an ellipse, it is possible to prevent magnetic flux concentration and lower the DC resistance (Rdc) while maintaining the inductance value.

In another embodiment of the present invention as a modified example of the internal conductor pattern 25a, the first portion 25a1 and the second portion 25a2 of the internal conductor pattern 25a may extend in a direction parallel to the T-axis, as shown in Figures 9 and 10. In these embodiments, the side margin D2, which is the distance between the first portion 25a1 and the first end face 10c of the base 10, is smaller than the upper margin D1. In the illustrated embodiment, the distance between the second portion 25a2 and the first end face 10c of the base 10 is equal to the side margin D2. The distance between the second portion 25a2 and the second end face 10d of the base 10 may be larger or smaller than the side margin D2. The internal conductor pattern 25a shown in Figure 9 has a first protruding portion 25a4 protruding from the lower end of the first portion 25a1 toward the first end face 10c, and a second protruding portion 25a5 protruding from the lower end of the third portion 25a3 toward the second end face 10d. Although the area of the region between the first portion 25a1 of the internal conductor pattern 25a and the first end surface 10c is reduced by the first protrusion 25a4 and the second protrusion 25a5, the area of the region is magnetically saturated immediately after the current starts to flow through the internal conductor pattern 25a, so that the effect on the DC superimposition characteristics is small even if the area of the region is reduced. Therefore, the first protrusion 25a4 and the second protrusion 25a5 increase the contact area between the internal conductor pattern 25a and the external electrodes 21, 22, and can reliably connect them electrically without substantially adversely affecting the DC superimposition characteristics. In addition, by increasing the contact area between the internal conductor pattern 25a and the external electrodes 21, 22, the heat in the inductor 1 can be dissipated more efficiently from the external electrodes 21, 22 via the lands 3a, 3b. As shown in FIG. 10, the internal conductor pattern 25a may be configured to be exposed only from the mounting surface 10b without having the first protrusion 25a4 and the second protrusion 25a5. In another embodiment, the side margin D2 may be zero.

In another embodiment of the present invention as a modified example of the internal conductor pattern 25a, further modified examples of the internal conductor pattern 25a are shown in Figs. 11 to 13. In Figs. 11 to 13, the external electrodes 21 and 22 are omitted to simplify the illustration. Fig. 11 shows a modified example of the internal conductor pattern 25a shown in Fig. 8. The internal conductor pattern 25a in Fig. 11 is disposed between the inner imaginary ellipse C1 and the outer imaginary ellipse C2. The imaginary ellipse C1 has a center at the midpoint in the L-axis direction of the side corresponding to the mounting surface 10b in the X-X cross section, and has a minor axis with a length of G4/2 extending in the T-axis direction and a major axis with a length of L1/2 extending in the L-axis direction. L1 is the dimension of the base 10 in the L-axis direction and is smaller than twice the dimension of the base 10 in the height direction. In other words, the relationship L1<2T1 holds. G4 is greater than 0 and preferably smaller than T1/4. This allows the internal conductor pattern 25a to be located near the mounting surface 10b, thereby improving heat dissipation efficiency. G4 is preferably greater than T1/8 in order to obtain inductance and suppress magnetic saturation in the first region 10r1. In addition to this geometric arrangement of the internal conductor pattern 25a, the first region 10r1 is formed from a magnetic material with a relatively high saturation magnetic flux density, and the second region 10r2 is formed from a magnetic material with a lower saturation magnetic flux density than the first region 10r1, thereby further suppressing concentrated magnetic saturation in the first region 10r1. The outer virtual ellipse C2 is concentric with the virtual ellipse C1 and has a minor axis with a length of T1/2 and a major axis with a length of L1 extending in the T-axis direction.

Figure 12 shows a modified example of the internal conductor pattern 25a shown in Figure 11. The internal conductor pattern 25a in Figure 12 is arranged between the virtual circle C11 and the virtual circle C12. The internal conductor pattern 25a shown in Figure 12 has a shape obtained by extending the internal conductor pattern 25a shown in Figure 11 in the L-axis direction. In the embodiment of Figure 12, the virtual ellipse C1 is centered at the midpoint in the L-axis direction and has a minor axis with a length of G4/2 extending in the T-axis direction and a major axis with a length of T1 extending in the L-axis direction. L1 is equal to twice the height dimension of the base 10. In other words, the relationship L1 = 2T1 holds. The virtual ellipse C2 on the outside is concentric with the virtual ellipse C1 and has a minor axis with a length of T1/2 extending in the T-axis direction and a major axis with a length of L1.

Figure 13 shows a modified example of the internal conductor pattern 25a shown in Figure 11. The internal conductor pattern 25a in Figure 13 is disposed between an inner virtual line C21 and an outer virtual line C22. In the embodiment of Figure 13, the virtual lines C21 and C22 are composed of curved lines at both ends and straight line segments connecting the curved lines. One of the curved lines of the virtual lines C21 and C22 extends in the L-axis direction from the position of the first end face 10c by a length of T1 in the L-axis direction, and the other curved line extends in the L-axis direction from the position of the second end face 10d by a length of T1 in the L-axis direction. The straight line segments of the virtual lines C21 and C22 have a length obtained by subtracting 2T1 from L1.

In the embodiment shown in Figures 11 to 13, the curves constituting the inner circumferential surface 25X and the outer circumferential surface 25Y are partial elliptical arcs or partial circular arcs of an ellipse, which not only prevents magnetic flux concentration but also makes it possible to reduce the direct current resistance (Rdc) while maintaining the inductance value.

Next, an exemplary method for manufacturing the inductor 1 according to one embodiment of the present invention will be described. The inductor 1 can be manufactured, for example, by a lamination process. An example of a method for manufacturing the inductor 1 by a lamination process will be described below. For this description, FIG. 4 will be referred to as appropriate.

First, multiple unsintered magnetic sheets made of a magnetic material are created. After firing, these unsintered magnetic sheets become the magnetic layers 11a-11f and the cover layers 12, 13. The unsintered magnetic sheets are formed, for example, from a composite magnetic material containing a binder and multiple metal magnetic particles. Next, a conductive paste is printed on the surface of each of the unsintered magnetic sheets to form unsintered conductor patterns that will become the internal conductor patterns 25a-25f after firing.

Next, the unsintered magnetic sheets on which the unsintered conductor patterns are formed are stacked to obtain an intermediate laminate. A plurality of unsintered magnetic sheets that will become the cover layer 12 are stacked on one end of the intermediate laminate in the stacking direction, and a plurality of unsintered magnetic sheets that will become the cover layer 13 are stacked on the other end to obtain an unsintered laminate.

Next, the unfired stack is divided into individual pieces using a cutting machine such as a dicing machine or a laser processing machine to obtain an unfired chip stack. Next, this unfired chip stack is degreased, and the degreased unfired chip stack is fired to obtain a fired chip stack. Next, a polishing process such as barrel polishing is performed on this fired chip stack.

Next, external electrodes 21 and 22 are formed on the surface of this chip stack. The external electrodes 21 and 22 are formed, for example, by applying a conductive paste to the surface corresponding to the mounting surface 10b of the chip stack to form a base electrode, and then forming a plating layer on the surface of this base electrode. The plating layer has, for example, a two-layer structure of a nickel plating layer containing nickel and a tin plating layer containing tin. At least one of a solder barrier layer and a solder wetting layer may be formed on the external electrodes 21 and 22 as necessary. In this manner, the inductor 1 is obtained.

Some of the steps included in the above manufacturing method may be omitted as appropriate. In the manufacturing method of the inductor 1, steps not explicitly described in this specification may be performed as necessary. Some of the steps included in the manufacturing method of the inductor 1 may be performed in a different order at any time, as long as this does not deviate from the spirit of the present invention. Some of the steps included in the manufacturing method of the inductor 1 may be performed simultaneously or in parallel, if possible.

Next, the effects of the above embodiment will be described. According to the inductor 1 according to the above embodiment, in a front view, the distance between the mounting surface 10b and the position on the axis A of the internal conductor 25 (e.g., the internal conductor pattern 25a) farthest from the mounting surface 10b is smaller than half the distance between the upper surface 10a and the mounting surface 10 (e.g., the height T1 of the base 10), so that the Joule heat generated in the internal conductor 25 can be dissipated more efficiently from the mounting surface 10b of the base 10. When the entire internal conductor is disposed in a lower region below the virtual line B of the base 10, the heat can be dissipated even more efficiently from the mounting surface 10b. Most of the Joule heat generated in the internal conductor 25 moves by thermal conduction from the internal conductor 25 to another member constituting the circuit board 2 via the lands 3a and 3b, but the heat dissipation by this thermal conduction alone may not be enough to dissipate all of the Joule heat generated in the internal conductor 25. Therefore, by positioning the internal conductor 25 so that the distance (T1-T2) between the axis A of the internal conductor 25 and the mounting surface 10b is smaller than half the distance between the upper surface 10a and the mounting surface 10b (e.g., the height T1 of the base 10), the Joule heat generated in the coil conductor 25 can be efficiently conducted from the mounting surface 10b of the base 10 to the circuit board 2.

According to the embodiment described above, the entire internal conductor 25 is disposed in the lower region below the imaginary line B of the base 10, so that the length of the internal conductor within the base 10 can be made shorter than when the internal conductor passes through the upper region of the base 10. This can reduce the DC resistance of the internal conductor, thereby reducing Joule heat generated by the internal conductor 25.

According to the above embodiment, the internal conductor 25, which extends linearly in a plan view, is exposed from the mounting surface 10b to the outside of the base 10 and connected to the external electrodes 21 and 22. Therefore, the current flowing from the land 3a to the internal conductor 25 through the external electrode 21 passes through the internal conductor 25 and flows to the land 3b through the external electrode 22. In this way, the current flowing through the inductor 1 flows through the external electrodes 21 and 22 only for a short distance (a distance equivalent to the thickness of the external electrodes 21 and 22 in the T-axis direction) between the land 3a and one end of the internal conductor 25 and between the land 3b and the other end of the internal conductor 25. In general, the external electrodes of an inductor are made of a material with a lower electrical conductivity than the internal conductor. In addition, the portion of the external electrode that contacts the end face of the base (the face that connects the mounting surface and the top face) has a smaller cross-sectional area than the internal conductor. For this reason, if the internal conductor is exposed from the end face of the base as in a conventional inductor in which the internal conductor extends linearly, the current will pass through the external electrode in the section from the exposed position of the internal conductor to the land. Since the distance from the exposed position of the internal conductor on the end face of the substrate to the land is longer than the distance from the mounting surface of the substrate to the land, the external electrodes intervening in the section from the exposed position of the internal conductor to the land are a factor in increasing the DC resistance of the inductor. In the inductor 1 according to the embodiment of the present invention, the internal conductor 25 is exposed from the mounting surface 10b of the substrate 10, so the current passing through the inductor 1 passes through the external electrodes 21, 22 only for a short distance between the land 3a and one end of the internal conductor 25 and between the land 3b and the internal conductor 25. Thus, according to the inductor 1, the proportion of the external electrodes 21, 22 in the current path is smaller than that of conventional inductors, so that the DC resistance can be reduced more than that of conventional inductors.

If the Fe content in the Fe-based metal magnetic particles contained in the base 10 is 80 wt % or more, the inductor 1 can be used in applications requiring a current value per unit volume of 0.15 A/mm ³ or more. If the Fe content in the metal magnetic particles contained in the base 10 is 85 wt % or more, the inductor 1 can be used in applications requiring a current value per unit volume of 0.2 A/mm ³ or more. If the Fe content in the metal magnetic particles contained in the base 10 is 90 wt % or more, the inductor 1 can be used in applications requiring a current value per unit volume of 0.25 A/mm ³ or more. As described above, magnetic saturation is suppressed in the base 10 of the inductor 1 according to one or more embodiments of the present invention, so that a large current can be passed through the internal conductor 25. For example, when the inductance L of the inductor 1 is made smaller than 300 nH, the current value per unit volume can be made 0.15 A/mm ³ or more. Furthermore, when the inductance L of the inductor 1 is made smaller than 150 nH, the current value per unit volume can be made 0.2 A/mm3 or ^more . When the inductance L of the inductor 1 is made smaller than 75 nH, the current value per unit volume can be made 0.25 A/mm3 or ^more . In the inductor 1 having the base 10 containing metal magnetic particles with an Fe content of 80 wt% or more, heat generation due to application of current is small. Also, it can be used in high frequency applications, for example, frequencies of 5 MHz or more.

When mounting the inductor 1 on the circuit board 2, by arranging the end face of the internal conductor 25 that contacts the external electrode 21 to face the land 3a of the circuit board 2, and arranging the end face of the internal conductor 25 that contacts the external electrode 22 to face the land 3b of the circuit board 2, it is possible to suppress not only heat generation in the inductor 1, but also heat generation in the region between the inductor 1 and the lands 3a and 3b. Even if the external electrodes 21 and 22 between the inductor 1 and the lands 3a and 3b are made of a material with low electrical conductivity, heat generation in the external electrodes 21 and 22 when a current is applied can be suppressed.

According to the above embodiment, at least one of the external electrodes 21 and 22 is provided so as to contact only the mounting surface 10b, so that the external electrodes 21 and 22 do not contact the first end face 10c and the second end face 10d of the base 10. As a result, when the dimension of the inductor 1 in the L-axis direction is fixed, the dimension of the base 10 in the L-axis direction can be increased by the width of the external electrodes 21 and 22.

The dimensions, materials, and arrangement of each component described in this specification are not limited to those explicitly described in the embodiments, and each component can be modified to have any dimensions, materials, and arrangement that can be included in the scope of the present invention. In addition, components not explicitly described in this specification can be added to the described embodiments, and some of the components described in each embodiment can be omitted.

REFERENCE SIGNS LIST 1 inductor 2 circuit board 3a, 3b land 10 base 10a upper surface 10b mounting surface 10r1 first region 10r2 second region 21, 22 external electrode 25 internal conductor 25a to 25f internal conductor pattern

Claims (9)

a base having a mounting surface facing a circuit board, an upper surface facing the mounting surface, and an end surface connecting the mounting surface and the upper surface;
a first external electrode attached to the mounting surface of the base;
a second external electrode attached to the mounting surface of the base body at a distance from the first external electrode in a length direction perpendicular to the end surface;
an internal conductor that is provided within the base, one end of which is electrically connected to the first external electrode and the other end of which is electrically connected to the second external electrode, and that extends linearly from the first external electrode to the second external electrode in a plan view seen in a thickness direction perpendicular to the mounting surface;
Equipped with
when viewed from the front in a width direction perpendicular to the thickness direction and the length direction, a distance between the mounting surface and a position on an axis of the internal conductor farthest from the mounting surface is smaller than half a distance between the upper surface and the mounting surface,
When viewed from the front, the base is partitioned into a first region surrounded by the internal conductor and the mounting surface and a second region other than the first region,
The area of the first region is smaller than the area of the second region,
the first region is formed of a material having a higher saturation magnetic flux density than the second region;
The one end and the other end of the internal conductor are both exposed to the outside of the base from the mounting surface.
Inductor. the base is divided by an intermediate surface extending parallel to the mounting surface and the upper surface and equidistant from the mounting surface and the upper surface into an upper region between the intermediate surface and the upper surface and a lower region between the intermediate surface and the mounting surface;
the inner conductor is entirely disposed in the lower region;
2. The inductor of claim 1. The inductor according to claim 1 , wherein the first external electrode is attached to the base only on the mounting surface. The inductor according to any one of claims 1 to 3, wherein the second external electrode is attached to the base only on the mounting surface. the inner conductor is formed of a conductive material having a higher electrical conductivity than a material of the first outer electrode;
The inductor according to any one of claims 1 to 4 . The substrate includes metal magnetic particles.
The inductor according to any one of claims 1 to 5 . the internal conductor has a first internal conductor pattern and a second internal conductor pattern disposed within the base body and spaced apart from the first internal conductor pattern;
each of the first internal conductor pattern and the second internal conductor pattern extends linearly from the first external electrode to the second external electrode in a plan view seen from a thickness direction perpendicular to the mounting surface, one end of the first internal conductor pattern is exposed from the mounting surface and connected to the first external electrode, and the other end of the second internal conductor pattern is exposed from the mounting surface and connected to the second external electrode;
The inductor according to any one of claims 1 to 6 . A circuit board comprising the inductor according to any one of claims 1 to 7 . An electronic device comprising the circuit board according to claim 8 .