Inductor

Abstract

In an inductor composed of a coil sandwiched between two magnetic cores, the generation of cracks in the magnetic cores caused by stress from the mounting substrate is suppressed. [Solution] The inductor comprises a coil conductor having an air core portion around which a conductor wire is wound, a first core and a second core that sandwich the coil conductor, each having a protrusion inserted into the air core portion of the coil conductor and a wall portion surrounding the outer circumference of the coil conductor on one main surface, and a pair of external electrodes provided on the bottom surface, which is the other main surface opposite one main surface of the first core, to which the lead-out portion of the coil conductor is connected. The pair of external electrodes each extend along two opposing sides of the bottom surface and face each other in a direction perpendicular to the direction of extension, and each external electrode is partially separated from the bottom surface and has an air gap between it and the bottom surface in at least a portion of each of the two opposing sides of the bottom surface.

Description

[Technical Field]

[0001] The present invention relates to an inductor. [Background Art]

[0002] Patent Document 1 discloses a surface-mount ferrite inductor that uses a coil formed by alpha-winding a rectangular flat conductor with a rectangular cross-section and two cores each having an E-shaped cross-section with a protrusion at the center of each main surface. The protrusions of the two cores are inserted into the air core of the coil and bonded to each other, whereby the coil is held between the two cores. The winding terminal of the coil is drawn out from the inside of the core and connected to a metal external terminal provided on the exterior of the core. A gap is provided in the outer peripheral portion between the two cores, thereby suppressing magnetic saturation in the core. [Prior Art Literature] [Patent Literature]

[0003] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2005-142459 [Summary of the Invention] [Problem to be Solved by the Invention]

[0004] In the surface-mount ferrite inductor having the above configuration, if the circuit board (hereinafter referred to as a mounting board) deflects after being mounted on the circuit board, the stress caused by the deflection is transmitted from the external terminals to the core, and stress concentrates at the base of the protrusion inside the core, which may cause cracks in the core. The occurrence of cracks resulting from such deflection of the mounting board can be suppressed by increasing the thickness of the core walls and bottom plate, but this may lead to an increase in the outer dimensions of the inductor. Furthermore, when attempting to increase the thickness of the core walls and bottom plate while avoiding an increase in outer dimensions, the cross-sectional area and number of turns of the coil that can be accommodated inside the core are limited, which may limit electrical characteristics.

[0005] The objective of the present invention is to suppress the occurrence of cracks in the magnetic cores caused by stress from the mounting substrate in an inductor composed of a coil sandwiched between two magnetic cores. [Means for solving the problem]

[0006] One aspect of the present invention is an inductor comprising: a coil conductor having an air core portion around which a conductor wire is wound; a first core and a second core sandwiching the coil conductor, each having a protrusion inserted into the air core portion of the coil conductor and a wall portion surrounding the outer circumference of the coil conductor on one main surface; and a pair of external electrodes provided on the bottom surface, which is the other main surface of the first core opposite the first main surface, to which the lead-out portion of the coil conductor is connected, wherein the pair of external electrodes each extend along two opposing sides of the bottom surface and face each other in a direction perpendicular to the direction of extension, and each of the external electrodes is partially separated from the bottom surface and has an air gap between it and the bottom surface in at least a portion of each of the two opposing sides of the bottom surface. [Effects of the Invention]

[0007] According to the present invention, in an inductor composed of a coil sandwiched between two magnetic cores, it is possible to suppress the occurrence of cracks in the magnetic core caused by stress from the mounting substrate. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a view of an inductor according to one embodiment of the present invention, seen from the top. [Figure 2] Figure 2 is a quadrature view of the inductor, adding the bottom view to the three views showing the front, top, and side. [Figure 3] Figure 3 is a perspective view of the top surface of the inductor. [Figure 4] Figure 4 is a three-view drawing showing the configuration of the first core. [Figure 5] Figure 5 is a cross-sectional view of the first core shown in Figure 4, taken along the VV line. [Figure 6]Figure 6 shows the state in which the coil conductor is attached to the first core. [Figure 7] Figure 7 shows the bottom surface of the inductor. [Figure 8] Figure 8 is a cross-sectional view of the inductor shown in Figure 7, taken along the line VIII-VIII. [Figure 9] Figure 9 shows the inductor mounted on the circuit board. [Figure 10] Figure 10 is a schematic diagram showing a cross-section of a conventional inductor. [Modes for carrying out the invention]

[0009] [1. Embodiments] Embodiments of the present invention will be described below with reference to the drawings. Figures 1, 2, and 3 show the configuration of an inductor 1 according to one embodiment of the present invention. Figure 1 is a perspective view of the inductor 1 as seen from the top surface 12, and Figure 2 is a quadrature view of the inductor 1, which includes the front 14a, top surface 12, side surface 16, and bottom surface 10. Figure 3 is a perspective view of the top surface 12 of the inductor 1.

[0010] In this embodiment, in the inductor 1, the first main surface that faces the mounting substrate (e.g., a circuit board) not shown during mounting is defined as the bottom surface 10, and the second main surface opposite the bottom surface 10 is called the top surface 12. Of the two pairs of main surfaces that are perpendicular to the bottom surface 10 and face each other, the main surface on which the lead-out window 5 from which the lead-out portion 24 of the coil conductor 20 is led out to the outside is called the front surface 14a, and the main surface opposite the front surface 14a is called the back surface 14b. Furthermore, the pair of main surfaces perpendicular to the bottom surface 10, the front surface 14a, and the back surface 14b are called the side surfaces 16.

[0011] The two ridges where the front surface 14a and the pair of side surfaces 16 intersect have chamfered corners in a plan view from the top surface 12, forming a pair of electrode holding surfaces 18, 18. Similarly, the two portions where each of the back surfaces 14b and the pair of side surfaces 16 intersect have chamfered corners in a plan view. As a result, the inductor 1 has a roughly octagonal shape in a plan view.

[0012] As shown in Figure 1, the distance from the bottom surface 10 to the top surface 12 is defined as the height H of the inductor 1, the distance between the front surface 14a and the back surface 14b is defined as the length L of the inductor 1, and the distance between the pair of side surfaces 16 is defined as the width W of the inductor 1. Furthermore, the direction of height H is defined as the height direction DH, the direction of length L is defined as the length direction DL, and the direction of width W is defined as the width direction DW.

[0013] The inductor 1 has a first core 30a and a second core 30b made of a magnetic material, and a coil conductor 20 sandwiched between the first core 30a and the second core 30b. The first core 30a and the second core 30b are combined so as to sandwich the coil conductor 20, forming a roughly octagonal prism-shaped magnetic core 50.

[0014] The magnetic material constituting the first core 30a and the second core 30b is, for example, ferrite. The ferrite may be, for example, Ni-Zn ferrite or Mn-Zn ferrite. Instead of ferrite, the first core 30a and the second core 30b may be made of a magnetic material obtained by compression molding a mixed powder of magnetic powder such as a metallic magnetic material and a resin.

[0015] The coil conductor 20 includes a wound portion 22 around which a conductor wire having an insulating coating and a fusion-bonding layer on the insulating coating is wound, and a pair of lead-out portions 24 led out from the wound portion 22 (Fig. 3). The coil conductor 20 is, for example, a coil having an air-core portion formed by alpha-winding a conductor wire. The wound portion 22 is formed by spirally winding the conductor wire in two stages such that the two lead-out portions 24, which are the winding start and winding end of the conductor wire, are located on the outer circumference, and then fusion-bonded, and has an air-core portion. The conductor wire is, for example, a rectangular wire with a rectangular cross-section. Note that the coil conductor 20 is not necessarily configured by alpha winding, and may be, for example, a non-orderly wound conductor wire with a circular cross-section, or an edgewise wound conductor wire with a rectangular cross-section.

[0016] The inductor 1 includes a pair of external electrodes 4, 4 extending and provided on the bottom surface 10 (Fig. 3(d)). Each of the external electrodes 4 is a metal fitting formed by processing a metal (e.g., copper) plate extending from the bottom surface 10 to the electrode holding surface 18, and is adhesively fixed to the bottom surface 10.

[0017] The tip ends of the pair of lead-out portions 24, 24 of the coil conductor 20 are pre-soldered in advance, led out from the lead-out window 5 of the magnetic core 50, and connected to the pair of external electrodes 4, 4 respectively. The pair of external electrodes 4, 4 are provided with clamps that clamp and fix the conductor wires of the pair of lead-out portions 24, 24, and the coil conductor and the external electrodes are heated and pressurized by a heater chip or the like to be electrically connected (Fig. 1, Fig. 2(a)).

[0018] Fig. 4 is three views showing the configuration of the first core 30a. Fig. 4(a) shows a plan view of the first core 30a, Fig. 4(b) shows a front view of the first core 30a, and Fig. 4(c) shows a side view of the first core 30a. Fig. 5 is a cross-sectional view taken along line V-V of the first core 30a shown in Fig. 4. In the present embodiment, the second core 30b has the same configuration as the first core 30a shown in Fig. 4.

[0019] The first core 30a has a roughly octagonal shape in plan view, with the four corners of a square being chamfered (Figure 4(a)). On one main surface (the surface shown in Figure 4(a)), the first core 30a has a convex portion 31 in the central part of the roughly octagonal outer shape in plan view, and a wall portion 32 along the outer circumference of the roughly octagon (Figure 4(a)). As a result, the VV cross section of the first core 30a has an E-shape (Figure 5).

[0020] The wall portion 32 has a notch portion 33 in which a part along the front surface 14a is cut out. The notch portion 33 of the first core 30a and the notch portion 33 of the second core 30b constitute a pull-out window 5 that pulls out the lead portion 24 of the coil conductor 20 to the outside of the magnetic core 50 when the coil conductor 20 is sandwiched between the first core 30a and the second core 30b. The surface opposite the surface on which the protrusion 31 is formed corresponds to the bottom surface 10 of the first core 30a, and to the top surface 12 of the second core 30b, which has the same configuration as the first core 30a.

[0021] The first core 30a and the second core 30b are placed facing each other, and their respective protrusions 31 are inserted into the air core of the coil conductor 20. By adhesively fixing the opposing surfaces of the protrusions 31 of the first core 30a and the protrusions of the second core 30b, the coil conductor 20 is held within the magnetic core 50 composed of the first core 30a and the second core 30b. In this state, the opposing surfaces of the wall portion 32 of the first core 30a and the wall portion 32 of the second core 30b are spaced apart, and magnetic saturation in the magnetic core 50 is suppressed (Figures 1 and 2(d)).

[0022] In this embodiment, the notch 33 is positioned so that its center is offset from the center line Cw of the width W of the first core 30a (in the example of Figure 4, it is offset to the right in the illustration). Since the first core 30a and the second core 30b are configured identically, when the coil conductor 20 is sandwiched between the first core 30a and the second core 30b, the notch 33 of the first core 30a and the notch 33 of the second core 30b that constitute the drawer window 5 are positioned so that they are offset from each other in a direction perpendicular to the center line Cw in the width direction of the drawer window 5 (see Figure 2(b)).

[0023] Figure 6 shows the state in which the coil conductor 20 is attached to the first core 30a. As described above, the coil conductor 20 is alpha wound, and the winding portion 22 is wound in two stages, upper and lower, along the winding shaft. As shown in Figure 6, when the coil conductor 20 is attached to the first core 30a, the pair of lead-out portions 24 of the coil conductor 20 intersect near the notch 33 and are pulled out in the left and right directions shown in the figure. In the example of Figure 6, of the two stages of winding portion 22, one lead-out portion 24 (hereinafter referred to as lead-out portion 24a) is pulled out from the stage closer to the first core 30a (hereinafter referred to as the lower stage) toward the right side shown in the figure from the notch 33.

[0024] Furthermore, since the notch 33 of the first core 30a is shifted to the right in the diagram with respect to the center line Cw of the width W, as described above, the lead-out portion 24a drawn out from the lower part of the winding portion 22 can reach the position of one of the external electrodes 4 (hereinafter referred to as external electrode 4a) on the right side of the diagram by drawing a natural curve without bending. This prevents the generation of long-term stress in the lead-out portion 24a.

[0025] Furthermore, as can be easily inferred from the description in Figure 6, when a second core 30b having the same configuration as the first core 30a is placed over the first core 30a on which the coil conductor 20 is attached, one of the two winding sections 22, the section furthest from the first core 30a and therefore closer to the second core 30b (hereinafter referred to as the upper section), will be pulled out from the notch 33 toward the left in the figure.

[0026] Furthermore, since the notch 33 of the second core 30b, which has the same configuration as the first core 30a, is positioned to the left of the center line Cw of the width W in Figure 6, the lead-out portion 24b drawn out from the upper part of the winding portion 22 can reach the position of the other external electrode 4 (hereinafter referred to as external electrode 4b) to the left of the figure by drawing a natural curve without bending. This prevents the generation of long-term stress in the lead-out portion 24b.

[0027] In conventional inductors, which have a coil sandwiched between two cores with an E-shaped cross-section and external terminals on the bottom surface of one of the cores, mechanical damage to the core can occur if the circuit board (hereinafter referred to as the mounting board) flexes after mounting to the circuit board. Figure 10 is an explanatory diagram for illustrating core damage caused by the flexing of the mounting board in a conventional inductor. Figure 10 schematically shows the cross-section of a conventional inductor 80. Similar to inductor 1, inductor 80 is composed of two cores 81a and 81b, each having a convex portion 82a and 82b and an E-shaped cross-section, and a coil conductor 83 having an air core.

[0028] The coil conductor 83 is formed by spirally winding a wire, and is held between cores 81a and 81b with protrusions 82a and 82b inserted into its air core. The cores 81a and 81b are fixed together by an adhesive layer ap8 between the protrusions 82a and 82b. In addition, a pair of external electrodes 84 are provided on the bottom surface of core 81a at opposing positions on the left and right sides as shown in the figure. The external electrodes 84 are fixed to the mounting substrate WB with solder or the like.

[0029] In this state, when forces indicated by arrows on the left and right sides of the mounted substrate WB are applied to the mounted substrate WB, the mounted substrate WB bends toward the dotted line position, and this bending causes stress to be applied to the core 81a. This stress concentrates at the roots bp8 on the left and right sides of the convex portion 82a, and cracks cr may be generated from the roots bp8 toward the interior of the core 81a.

[0030] Therefore, in the inductor 1 of this embodiment, the above problem is solved by making the configuration of the external electrode 4 on the bottom surface 10 of the first core 30a different from the conventional configuration.

[0031] Figures 7 and 8 are explanatory diagrams illustrating the configuration of the external electrodes 4 of the inductor 1. Figure 7 shows the bottom surface 10 of the inductor 1, and Figure 8 is a cross-sectional view of the inductor 1 shown in Figure 7, taken along the line VIII-VIII. Referring to Figure 8, in the inductor 1, the opposing surfaces of the protrusion 31a of the first core 30a and the protrusion 31b of the second core 30b are fixed by an adhesive layer ap3, and the opposing surfaces of the wall portion 32a of the first core 30a and the wall portion 32b of the second core 30b are spaced apart.

[0032] Referring to Figure 7, a pair of external electrodes 4, 4 are provided on the bottom surface 10 of the first core 30a at the positions shown on the left and right. The pair of external electrodes 4, 4 each extend along two opposing sides Lb, Lb of the bottom surface 10 and face each other on the bottom surface 10. In this embodiment, the two sides Lb are two sides parallel to the opposing sides 16, 16.

[0033] In particular, in this embodiment, each of the external electrodes 4, 4 is partially separated from the bottom surface 10 and has a gap a between it and the bottom surface 10 at least a portion of each of the two opposing sides Lb, Lb of the bottom surface 10, and does not come into contact with the two opposing sides Lb of the bottom surface 10 (Figure 8). For example, the height h1 from the bottom surface 10 of the portion of each external electrode 4 that has a gap a between it and the bottom surface 10 is higher than the height h2 of the portion that does not have a gap a (Figure 8).

[0034] Figure 9 shows the inductor 1 mounted on a mounting substrate, and is a cross-sectional view of Figure 8 with the mounting substrate WB added. In Figure 9, the external electrodes 4 of the inductor 1 are fixed to the mounting substrate WB with solder or the like. As shown in Figure 9, in the inductor 1, because the external electrodes 4, 4 have the above configuration, when the mounting substrate WB is deflected due to forces indicated by arrows on the left and right sides of the mounting substrate WB, the external electrodes 4 can elastically deform so that the portion with the air gap a is aligned with the mounting substrate WB. As a result, the stress from the deflected mounting substrate WB is distributed to the external electrodes 4, and the stress transmitted to the first core 30a is reduced. As a result, the stress concentrated at the root portions bp3, bp3 on the left and right sides of the convex portion 31a of the first core 30a is reduced, and the occurrence of mechanical damage such as cracks in the first core 30a can be suppressed.

[0035] Here, from the viewpoint of reducing the stress concentrated at the root portion bp3 of the first core 30a via the external electrodes 4 from the mounting substrate WB, it is preferable that each external electrode 4 extends to a range including the position closest to the portion of the external electrode 4 having a gap a on the outer circumference (dotted line in the figure) of the region of the bottom surface 10 corresponding to the protrusion 31a of the first core 30a (i.e., the position of the root portion bp3 shown in Figure 7), as shown in Figure 7. As a result, the position of the bottom surface 10 corresponding to the root portion bp3, where stress tends to concentrate, is reinforced by the external electrodes 4, and the occurrence of cracks in the first core 30a caused by stress from the mounting substrate WB can be further suppressed.

[0036] It should be noted that the present invention is not limited to the configuration of the embodiments described above, and can be implemented in various forms without departing from the spirit of the invention.

[0037] [2. Configurations supported by the above embodiment] The embodiments described above support the following configurations.

[0038] (Configuration 1) An inductor comprising: a coil conductor having an air core portion around which a conductor wire is wound; a first core and a second core sandwiching the coil conductor, each having a protrusion inserted into the air core portion of the coil conductor and a wall portion surrounding the outer circumference of the coil conductor on one main surface; and a pair of external electrodes provided on the bottom surface, which is the other main surface of the first core opposite the one main surface, to which the lead portion of the coil conductor is connected, wherein the pair of external electrodes each extend along two opposing sides of the bottom surface and face each other in a direction perpendicular to the direction of extension, and each of the external electrodes is partially separated from the bottom surface and has an air gap between it and the bottom surface in at least a portion of each of the two opposing sides of the bottom surface. In the inductor of configuration 1, when the mounting substrate to which the external electrodes are fixed with solder or the like flexes, the external electrodes can elastically deform so that the portion with air gaps conforms to the mounting substrate. As a result, the stress from the mounting substrate is distributed to the external electrodes, and the stress transmitted from the mounting substrate to the first core is reduced. Consequently, in the inductor of configuration 1, the occurrence of cracks in the first core caused by stress from the mounting substrate can be suppressed.

[0039] (Configuration 2) The inductor according to Configuration 1, wherein the protrusions of the first core and the protrusions of the second core, which face each other, are bonded and fixed together, and the walls of the first core and the walls of the second core, which face each other, are spaced apart. With the inductor of configuration 2, even in a configuration where a gap is provided between the wall of the first core and the wall of the second core to suppress magnetic saturation, the occurrence of cracks in the first core caused by stress from the mounting substrate can be suppressed.

[0040] (Configuration 3) The inductor according to Configuration 1 or 2, wherein each of the external electrodes extends over the outer circumference of the region of the bottom surface corresponding to the protrusion of the first core, and includes the position closest to the gap portion of the external electrode. In the inductor of configuration 3, the position of the bottom surface corresponding to the outer peripheral position of the protrusion where stress tends to concentrate is reinforced by the external electrode, so that the occurrence of cracks in the first core caused by stress from the mounting substrate can be further suppressed.

[0041] (Configuration 4) The inductor according to any one of Configurations 1 to 3, wherein the external electrode is made of metal. In the inductor of configuration 4, by making the external electrodes out of metal, the elastic deformation of the external electrodes becomes easier, so the occurrence of cracks in the first core caused by stress from the mounting substrate can be effectively suppressed. [Explanation of symbols]

[0042] 1, 80...Inductor, 4, 4a, 4b, 84...External electrode, 5...Drawer window, 10...Bottom surface, 12...Top surface, 14a...Front, 14b...Back, 16...Side, 18...Electrode holding surface, 20, 83...Coil conductor, 22...Winding section, 24, 24a, 24b...Drawer section, 30a...First core, 30b...Second core, 50...Magnetic core, 31, 31a, 31b, 82a, 82b...Convex section, 32...Wall section, 33...Notch section, 81a, 81b...Core, ag...Gap, ap3, ap8...Adhesive layer, bp3, bp8...Root section, cr...Crack, Cw...Width-direction centerline, Lb...Edge, WB...Mounting substrate.

Claims

1. A coil conductor having an air core around which a wire is wound, A first core and a second core that sandwich the coil conductor, each having a protrusion inserted into the air core portion of the coil conductor and a wall surrounding the outer circumference of the coil conductor on one main surface, A pair of external electrodes are provided on the bottom surface, which is another main surface of the first core opposite to the first main surface, to which the lead-out portion of the coil conductor is connected, It has, The pair of external electrodes each extend along two opposing sides of the bottom surface and face each other in a direction perpendicular to the direction of extension. Each of the external electrodes has a gap between it and the bottom surface, with at least a portion of each of the two opposing sides of the bottom surface, and is partially separated from the bottom surface. Inductor.

2. The protrusions of the first core and the protrusions of the second core, which face each other, are bonded and fixed together. The wall portion of the first core and the wall portion of the second core, which face each other, are spaced apart. The inductor according to claim 1.

3. Each of the external electrodes extends to the outer circumference of the region of the bottom surface corresponding to the protrusion of the first core, and includes the position closest to the gap portion of the external electrode. The inductor according to claim 1.

4. The external electrode is made of metal. The inductor according to any one of claims 1 to 3.

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