Inductors

Abstract

The present invention provides an inductor capable of suppressing a decrease in DC superposition characteristics even when the filling rate of magnetic powder is increased. The inductor comprises: a coil having a winding portion and a pair of lead portions led out from the winding portion, and a unit body including magnetic powder containing first magnetic powder and second magnetic powder in which the coil is embedded, wherein the average particle size of the first magnetic powder is larger than the average particle size of the second magnetic powder, and when a Voronoi diagram is divided in a cross section of the unit body including a winding axis of the winding portion and extending in the long side direction of the unit body with the center of gravity of each magnetic powder as a parent point, and when a standard deviation of the area of ​​the Voronoi diagram divided region with the magnetic powder having a particle size of 6 μm or more as a base point is calculated, the standard deviation is 300 or less.

Description

Technical Field

[0001] The present invention relates to inductors. Background Art

[0002] Inductors used in electronic devices, especially inductors for power supplies, are required to be small in size and have high performance (high inductance, high DC superposition characteristics, etc.). One such inductor includes an inductor having a coil embedded in a unit body and an external terminal connected to the coil and exposed from the unit body (for example, see Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2007-165779 Summary of the invention

[0006] In order to improve the performance of the inductor described in Patent Document 1, it is conceivable to increase the filling rate of magnetic powder contained in the inductor. However, if the filling rate of magnetic powder is increased, magnetic saturation is likely to occur, and there is a problem that the DC superposition characteristics are degraded.

[0007] An object of one embodiment of the present invention is to provide an inductor capable of suppressing a decrease in DC superposition characteristics even when the filling rate of magnetic powder is increased.

[0008] An inductor according to one embodiment of the present invention is characterized in that it comprises: a coil having a winding portion and a pair of lead portions led out from the winding portion, and a unit body including magnetic powder containing first magnetic powder and second magnetic powder in which the coil is embedded, wherein the average particle size of the first magnetic powder is larger than the average particle size of the second magnetic powder, and when a Voronoi diagram is divided with the center of gravity of each magnetic powder as a base point in a cross section of the unit body including the winding axis of the winding portion and extending in the long side direction of the unit body, and when a standard deviation of the area of ​​the Voronoi diagram divided region with the magnetic powder having a particle size of 6 μm or more as the base point is calculated, the standard deviation is 300 or less.

[0009] An object of one embodiment of the present invention is to provide an inductor capable of suppressing a decrease in DC superposition characteristics even when the filling rate of magnetic powder is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a top perspective view showing the inductor according to the first embodiment of the present invention.

[0011] Figure 2 It is a bottom perspective view showing the inductor according to the first embodiment of the present invention.

[0012] Figure 3 It only means Figure 1A three-dimensional view of the magnetic base of an inductor.

[0013] Figure 4 It only means Figure 1 A three-dimensional diagram of the coil of an inductor.

[0014] Figure 5 yes Figure 1 Cross-sectional view of line A1-A1.

[0015] Figure 6 yes Figure 1 Cross-sectional view of line A2-A2.

[0016] Figure 7 Yes means Figure 1 FIG. 1 is a diagram showing the outline of the winding portion of the inductor shown in the plane including the opening end surface of the upper stage portion.

[0017] Figure 8 Yes means Figure 1 FIG. 1 is a diagram showing the contour of the winding portion of the inductor within a plane including the boundary surface of the lower stage portion.

[0018] Fig. 9 It means that it is configured in Figure 1 Figure 2 shows the conductive resin layer of the inductor.

[0019] Fig.10 is a diagram illustrating Voronoi diagram partitioning.

[0020] Fig.11 (a) is a diagram showing an example of a cross section of a unit cell, (b) is a diagram showing an example of a Voronoi diagram segmentation region of a magnetic substrate region, and (c) is a diagram showing an example of a Voronoi diagram segmentation region of a magnetic exterior casing region.

[0021] Fig.12 (a) is a graph showing the particle size distribution in the cross section of the magnetic substrate, and (b) is a graph showing the particle size distribution in the cross section of the magnetic body casing.

[0022] Fig.13 (a) is a coordinate diagram showing the particle size distribution of large particles and small particles in the cross section of the magnetic substrate, and (b) is a coordinate diagram showing the particle size distribution of large particles and small particles in the cross section of the magnetic body casing.

[0023] Fig.14 (a) is a coordinate diagram showing the particle size distribution of large particles in the cross section of the magnetic matrix and the cumulative frequency distribution of the log-normal distribution of the large particles, and (b) is a coordinate diagram showing the particle size distribution of large particles in the cross section of the magnetic body casing and the cumulative frequency distribution of the log-normal distribution of the large particles.

[0024] Fig.15This is a diagram schematically showing a cross-sectional image of a magnetic substrate. DETAILED DESCRIPTION

[0025] Hereinafter, embodiments and examples for implementing the present invention will be described with reference to the drawings. It should be noted that the inductor described below is for embodying the technical idea of ​​the present invention, and the present invention is not limited to the following description unless otherwise specified.

[0026] In each of the drawings, components with the same function are sometimes given the same symbols. Considering the ease of explanation or understanding of the key points, for convenience, there are cases where they are divided into implementation methods and examples, but the parts of the components shown in different implementation methods and examples can be replaced or combined. In the implementation methods and examples described later, the same matters as those mentioned above are omitted, and only the differences are described. In particular, the same effects obtained by the same structure are not mentioned in sequence in each implementation method and example. In order to make the description clearer, the size, positional relationship, etc. of the components shown in each of the drawings are also exaggerated. In addition, in the following description, terms indicating a certain direction and position (for example, "up", "down", "right", "left" and other terms containing these terms) are used as needed. The use of these terms is to make it easier to understand the invention with reference to the drawings, and the technical scope of the present invention is not limited by the meaning of these terms.

[0027] 1. Implementation Method 1

[0028] Reference from Figures 1 to 9 The inductor according to the first embodiment of the present invention will be described. Figure 1 It is a top perspective view showing the inductor according to the first embodiment of the present invention. Figure 2 It is a bottom perspective view showing the inductor according to the first embodiment of the present invention. Figure 3 It only means Figure 1 A three-dimensional view of the magnetic base of an inductor. Figure 4 It only means Figure 1 A three-dimensional diagram of the coil of an inductor. Figure 5 yes Figure 1 Cross-sectional view of line A1-A1. Figure 6 yes Figure 1 Cross-sectional view of line A2-A2. Figure 7 Yes means Figure 1 FIG. 1 is a diagram showing the outline of the winding portion of the inductor shown in the plane including the opening end surface of the upper stage portion. Figure 8 Yes means Figure 1 FIG. 1 is a diagram showing the contour of the winding portion of the inductor within a plane including the boundary surface of the lower stage portion. Fig. 9 It means that it is configured in Figure 1 Figure 2 shows the conductive resin layer of the inductor.

[0029] 1. Implementation Method 1

[0030] like Figure 1 and Figure 2 As shown, the inductor 1 includes a unit cell 2 and a pair of external terminals 4a and 4b formed on the surface of the unit cell 2. The unit cell 2 includes a magnetic substrate 8, a coil 54, and a magnetic outer package 6.

[0031] The magnetic base 8 includes a base portion 10 and a columnar portion 16 formed on an upper surface 10 a of the base portion 10 .

[0032] The coil 54 has a winding portion 44 wound around the columnar portion 16 and a pair of lead portions 40, 42 led out from the outer periphery of the winding portion 44. The winding portion 44 is composed of a conductive wire having mutually opposed wide widths and a rectangular cross-section. By making one side of the wide width contact the side surface of the columnar portion 16, it is wound in two sections with respect to the columnar portion 16, and the two ends of the winding portion are located at the outer periphery, and it has an upper section 46 and a lower section 48 connected to each other by the conductive wire constituting the inner periphery. The top view shape of the winding portion 44 from the upper surface of the unit body 2 is a circular ring shape having a short side direction and a long side direction. The upper section of the winding portion 44 has a protrusion protruding in the short side direction and a straight section 52 extending in the short side direction and protruding in the long side direction. The pair of lead portions 40 and 42 are led out from the outer periphery of the winding portion 44 toward the side surface of the base portion 10 , respectively, and the front end portions 40 a and 42 a are arranged on the lower surface 10 b of the base portion 10 .

[0033] The magnetic exterior coating 6 covers a portion of the magnetic base 8 , a portion of the lead portions 40 , 42 , and at least a portion of the wound portion 44 .

[0034] The pair of external terminals 4 a and 4 b are arranged to cover the front end portions 40 a and 42 a of the pair of lead portions 40 and 42 and the lower surface 10 b around the front end portions 40 a and 42 a .

[0035] Hereinafter, each component will be described in detail.

[0036] (1) Magnetic substrate

[0037] The magnetic base 8 includes a base portion 10 and a columnar portion 16 .

[0038] <Base part>

[0039] like Figure 3As shown, the base part 10 is a plate-like component with an upper surface 10a and a lower surface 10b having a substantially rectangular shape with a long side direction and a short side direction. The base part 10 has cutouts 14 and 15 at the corner formed by the first side surface 10c extending in the long side direction and the second side surface 10d extending in the short side direction and at the corner formed by the first side surface 10c and the fourth side surface 10f extending in the short side direction. The cutouts 14 and 15 are used to configure the lead-out portions 40 and 42 of the coil 54. Figure 2 As shown, a recess 12 is provided in the central portion of the lower surface 10b of the base portion 10 along the short side direction. As described later, the lower surface 10b of the base portion 10 is provided with external terminals 4a and 4b, and serves as a mounting surface of the inductor 1. The length of the base portion 10 in the long side direction is, for example, about 1.4 mm to 2.2 mm, the length in the short side direction is, for example, 0.6 mm to 1.4 mm, and the thickness (the length between the upper surface 10a and the lower surface 10b) is, for example, 0.1 mm to 0.2 mm.

[0040] <Columnar part>

[0041] The columnar portion 16 is disposed on the upper surface 10 a of the base portion 10 .

[0042] The root portion of the columnar portion 16 on the side of the base 10 in a cross section approximately orthogonal to the reel B1 is in a substantially oblong shape having a short side direction and a long side direction. The reel B1 coincides with the central axis of the root portion of the columnar portion 16 on the side of the base 10. In addition, the short side direction and the long side direction of the columnar portion 16 are approximately consistent with the short side direction and the long side direction of the base 10. The side surface of the columnar portion 16 has two planar regions 28 and 30 extending in the long side direction of the base 10 and two curved surface regions 32 and 34 connecting the two planar regions 28 and 30. The height of the columnar portion 16 is approximately twice the height of the wire forming the coil 54. When the columnar portion 16 is divided into an upper portion 18 and a lower portion 20, the first planar region 28 of the upper portion 18 has a protruding surface 22 protruding in the short side direction. The protruding surface 22 is a curved surface. The protruding degree of the protruding surface 22 increases as the distance from the base 10 increases. Therefore, the upper portion 18 of the columnar portion 16 becomes thicker as the distance from the base portion 10 increases (see Figure 5 ).

[0043] In addition, the first curved surface region 32 of the upper portion 18 of the columnar portion 16 has a flat surface 24 extending in the short side direction. The protrusion of the flat surface 24 increases as the distance from the base portion 10 increases. Therefore, the upper portion 18 of the columnar portion 16 becomes thicker as the distance from the base portion 10 increases (see Figure 6 ).

[0044] The columnar portion 16 is disposed on the upper surface 10 a of the base 10 such that a length D1 between the rolling axis B1 of the columnar portion 16 and the first side surface 10 c of the base 10 is longer than a length D2 between the rolling axis B1 of the columnar portion 16 and the third side surface 10 e of the base 10 .

[0045] Next, the material of the magnetic substrate 8 is described. The magnetic substrate 8 is formed of a composite magnetic body containing magnetic powder and resin. The magnetic powder contains large particles (first magnetic powder) and small particles (second magnetic powder) whose average particle size is smaller than the average particle size of the large particles. The average particle size of the large particles is, for example, 15 μm to 25 μm, and the average particle size of the small particles is, for example, 1.5 μm to 4.0 μm. The filling rate of the magnetic powder of the magnetic substrate 8 is 60 wt% or more, preferably 80 wt% or more. The magnetic powder uses iron-based metal magnetic powders such as Fe, Fe-Si-Cr, Fe-Ni-Al, Fe-Cr-Al, Fe-Si, Fe-Si-Al, Fe-Ni, Fe-Ni-Mo, etc., metal magnetic powders of other composition systems, metal magnetic powders such as amorphous, metal magnetic powders whose surfaces are coated with insulators such as glass, metal magnetic powders whose surfaces are modified, and nano-level tiny metal magnetic powders. As the resin, a thermosetting resin such as an epoxy resin, a polyimide resin, or a phenolic resin or a thermoplastic resin such as a polyethylene resin or a polyamide resin is used.

[0046] (2) Coil

[0047] like Figure 1 and Figure 4 As shown, the coil 54 includes a winding portion 44 wound around the columnar portion 16 and a pair of lead portions 40 and 42 led out from the outer peripheral portion of the winding portion 44 .

[0048] The conductor used to form the coil 54 is a conductor having an insulating coating on the surface of the conductor and a fusion layer on the surface of the coating, and having a rectangular cross-section with wide widths 64 and 66 facing each other (so-called rectangular wire). The conductor is formed of copper, for example, and has a width of 140 μm to 170 μm and a thickness of 67 μm to 85 μm. The coating is formed of an insulating resin such as polyamide-imide, and has a thickness of 1 μm to 7 μm, preferably 6 μm. The fusion layer is formed of a thermoplastic resin or a thermosetting resin containing a self-fusion component and can fix the conductors constituting the winding portion to each other, and has a thickness of 1 μm to 3 μm, preferably 1.5 μm. Therefore, the length of the conductor in the line width direction (the width of the wide widths 64 and 66, the line width) w1 is, for example, 144 μm to 190 μm, and the thickness (the length between the facing wide widths 64 and 66) t1 is, for example, 71 μm to 105 μm.

[0049] <Winding section>

[0050] The winding portion 44 is formed by using one such wire, which is wound in two sections, the upper and lower sections, so that the two ends are located at the outer periphery, forming an upper section 46 and a lower section 48. The upper section 46 and the lower section 48 are connected to each other by the wire constituting the inner periphery. The winding portion 44 is wound on the columnar portion 16 so that the winding axis B2 is roughly consistent with the winding axis B1 of the columnar portion 16 and the wide width of the wire is in contact with the side surface of the columnar portion 16. The winding portion 44 is configured so that the opening end surface H1 of the lower section 48 is roughly consistent with the upper surface 10a of the base portion 10 of the magnetic body base 8. In addition, the opening end surface H2 of the upper section 46 is roughly consistent with the upper surface 16a of the columnar portion 16. The top view shape of the winding portion 44 is an elongated ring shape having a short side direction and a long side direction. The winding portion 44 has a first planar area 56 and a second planar area 58, a first curved area 60 connecting the two planar areas 56 and 58, and a second curved area 62. The first planar region 56 is a region along the first planar region 28 of the columnar portion 16 of the magnetic body base 8, and the second planar region 58 is a region along the second planar region 30 of the columnar portion 16. The first curved region 60 is a region along the first curved surface region 32 of the columnar portion 16, and the second curved region 62 is a region along the second curved surface region 34 of the columnar portion 16. The first planar region 56 of the upper section 46 includes a protruding portion 50 protruding in the short-side direction along the protruding surface 22 of the columnar portion 16. In addition, the first curved region 60 of the upper section 46 includes a straight portion 52 extending in the short-side direction along the plane 24 of the columnar portion 16.

[0051] (Protrusion)

[0052] The protrusion 50 is a region where the wire is bent and protrudes in the short side direction. The wire width direction of the protrusion 50 is inclined relative to the winding axis B2. The wire width direction of the protrusion 50 is inclined away from the winding axis B2 as the distance from the lower stage 48 increases (see Figure 5 ).

[0053] Therefore, the protrusion 50 protrudes in the short-side direction between the boundary surface H3 between the upper stage portion 46 and the lower stage portion 48 and the opening end surface H2 of the upper stage portion 46 , and the degree of protrusion is maximum at the opening end surface H2 .

[0054] Reference Figure 7 and Figure 8 , the maximum size of the protruding portion 50 of the opening end surface H2 with the largest protrusion will be described. Figure 7 and Figure 8 The outline 100 of the winding portion 44 is shown for illustration.

[0055] like Figure 7 As shown, the contour line 100 of the winding portion 44 at the opening end surface H2 of the upper stage portion 46 includes an inner peripheral contour line 102 of the winding portion 44 and an outer peripheral contour line 104 of the winding portion 44 .

[0056] The inner circumference contour line 102 is composed of the inner circumference contour line 106 of the first plane region 56, the inner circumference contour line 108 of the second plane region 58, the inner circumference contour line 110 of the first curved region 60, and the inner circumference contour line 112 of the second curved region 62. In addition, the inner circumference contour line 106 of the first plane region 56 includes the inner circumference contour line 114 of the protruding portion 50, and the inner circumference contour line 110 of the first curved region 60 includes the inner circumference contour line 116 of the straight portion 52. In addition, as indicated by the dotted line, the inner circumference contour line 108 of the second plane region 58 is located inside the inner circumference contour line 108, and includes an inner circumference contour line 108' formed by a conductive line extending from the opening end surface H2 of the upper section 46 to the boundary surface H3 of the lower section 48.

[0057] The outer contour line 104 is composed of an outer contour line 120 of the first planar region 56, an outer contour line 122 of the second planar region 58, an outer contour line 124 of the first curved region 60, and an outer contour line 126 of the second curved region 62. In addition, the outer contour line 120 of the first planar region 56 includes an outer contour line 128 of the protruding portion 50, and the outer contour line 124 of the first curved region 60 includes an outer contour line 130 of the straight portion 52.

[0058] like Figure 8 As shown, a contour line 150 of the winding portion 44 at the boundary surface H3 of the lower stage portion 48 of the winding portion 44 includes an inner peripheral contour line 152 of the winding portion 44 and an outer peripheral contour line 154 of the winding portion 44 .

[0059] The inner peripheral contour line 152 is composed of the inner peripheral contour line 156 of the first plane area 56, the inner peripheral contour line 158 of the second plane area 58, the inner peripheral contour line 160 of the first curved area 60, and the inner peripheral contour line 162 of the second curved area 62. In addition, as indicated by the dotted line, the inner peripheral contour line 158 of the second plane area 58 is located inside the inner peripheral contour line 158, and includes an inner peripheral contour line 158' formed by a conductive line extending from the boundary surface H3 of the lower stage portion 48 to the opening end surface H2 of the upper stage portion 46.

[0060] Outer contour line 154 is formed by an outer contour line 170 of first planar region 56 , an outer contour line 172 of second planar region 58 , an outer contour line 174 of first curved region 60 , and an outer contour line 176 of second curved region 62 .

[0061] The length y3 in the longitudinal direction between the two ends 114a and 114b of the inner peripheral contour line 114 of the protrusion 50 is about 1 / 4 to 3 / 4 of the length y4 between the two ends 106a and 106b of the inner peripheral contour line 106 of the first planar region 56 (see Figure 7 ).

[0062] The maximum length x2 in the short-side direction between the inner circumferential contour line 108′ formed by the wire extending from the opening end surface H2 of the upper section 46 to the boundary surface H3 of the lower section 48, located inside the inner circumferential contour line 108 of the second planar region 58, and the inner circumferential contour line 114 of the protrusion 50 is only about 1 / 6 to 1 / 3 of the length x1 between the inner circumferential contour line 156 of the first planar region 56 of the lower section 48 and the inner circumferential contour line 158′ formed by the wire extending from the boundary surface H3 of the lower section 48 to the opening end surface H2 of the upper section 46, located inside the inner circumferential contour line 158 of the second planar region 58, which is longer than the length x1 (refer to Figure 7 and Figure 8 ). The length x2 corresponds to the width of the inner peripheral contour line 102 in the short side direction.

[0063] Next, the arrangement relationship between the conductive wires of the protruding portion 50 and the conductive wires of the lower stage portion 48 located below the protruding portion 50 will be described. Figure 5 As shown in FIG. 1 , the conductive wires of each circle of the protrusion 50 are not arranged directly above the conductive wires of each circle of the lower section 48. Specifically, the first conductive wire 70a of the first circle starting from the inner side of the protrusion 50 is arranged above the first conductive wire 72a of the first circle and the second conductive wire 72b of the second circle of the lower section 48. That is, the first conductive wire 70a of the protrusion 50 is supported by the first conductive wire 72a and the second conductive wire 72b of the lower section 48. Similarly, the conductive wires of the protrusion 50 after the second circle are also supported by two conductive wires on the continuous circumference of the lower section 48. However, the conductive wire 70c of the outermost circumference of the protrusion 50 is supported only by the conductive wire 72c of the outermost circumference of the lower section 48. Furthermore, the cross section of the boundary surface H3 between the conductive wire of the protrusion 50 and the conductive wire of the lower section 48 located below the protrusion 50 is substantially wavy.

[0064] (Straight line)

[0065] like Figure 6 As shown, the line width direction of the conductor of the straight portion 52 is inclined relative to the winding axis B2.

[0066] The line width direction of the conductor of the straight portion 52 is inclined away from the winding axis B2 as the distance from the lower portion 48 increases. Therefore, the boundary surface H3 between the upper portion 46 and the lower portion 48 of the straight portion 52 protrudes in the long-side direction and the degree of protrusion is the largest at the opening end surface H2.

[0067] Reference Figure 7, the length of the short side direction of the straight portion 52 is described. The length x4 of the inner peripheral contour line 116 of the straight portion 52 (the length between the two ends 116a, 116b) is about 1 / 4 to 3 / 4 of the length x3 between the inner peripheral contour line 106 of the first plane area 56 and the inner peripheral contour line 108' formed by the wire extending from the opening end surface H2 of the upper section 46 to the boundary surface H3 of the lower section 48, which is located inside the inner peripheral contour line 108 of the second plane area 58. And, referring to Figure 7 and Figure 8 , the protrusion degree of the straight portion 52 is described. The maximum length y2 in the long-side direction between the inner peripheral contour line 116 of the straight portion 52 and the inner peripheral contour line 112 of the second curved region 62 is only about 1 / 8 to 1 / 6 of the maximum length y1 in the long-side direction between the inner peripheral contour line 160 of the first curved region 60 of the lower section 48 and the inner peripheral contour line 162 of the second curved region 62, which is longer than the length y1. The length y2 is equivalent to the width of the inner peripheral contour line 102 in the long-side direction.

[0068] In addition, the conductive wires of each circumference of the straight portion 52 are similar to the conductive wires of the protruding portion 50, except that the conductive wires 70c of the outermost circumference are supported by the conductive wires of two adjacent circumferences of the lower section 48 located below the straight portion 52. In addition, the cross section of the boundary surface H3 between the conductive wires of the straight portion 52 and the conductive wires of each circumference of the lower section located below the straight region is also substantially wavy.

[0069] <Leading section>

[0070] Next, refer to Figure 1 and Figure 4 , the lead-out portions 40 and 42 are described.

[0071] The pair of lead portions 40, 42 are respectively continuous with the outermost conductors of the step portions 46, 48 of the winding portion 44. The pair of lead portions 40, 42 are led out from the upper surface 10a side to the lower surface 10b side through the cutouts 14, 15 of the base portion 10 of the magnetic base 8. The wide surfaces 64, 66 of the pair of lead portions 40, 42 are approximately parallel to the upper surface 10a of the base portion 10, and the upper surface 10a side of the base portion 10 is twisted approximately 90 degrees. The front end portions 40a, 42a of the lead portions 40, 42 led out on the lower surface 10b side are arranged so that one wide surface 66 contacts the lower surface 10b. In addition, the wire width of the lead-out portions 40 and 42 closer to the cutouts 14 and 15 is wider than the wire width of the copper wire of the winding portion 44 , and the wire thickness of the lead-out portions 40 and 42 closer to the cutouts 14 and 15 is thinner than the wire thickness of the winding portion 44 .

[0072] (3) Magnetic external mounting

[0073] The magnetic outer casing 6 covers the upper surface 10a of the base portion 10 of the magnetic base 8 and the inner side surfaces of the cutouts 14 and 15, the columnar portion 16 of the magnetic base 8, the winding portion 44 of the coil 54, and the area except the front end portions 40a and 42a of the lead portions 40 and 42 of the coil 54. However, the outer wide surface 64a of the wire at the outermost periphery of the second planar area 58 of the winding portion 44 may be exposed from the magnetic outer casing 6. In this case, it is preferred that the outer wide surface 64a of the wire is arranged on a plane that is substantially the same as the third side surface 10e of the base portion 10 of the magnetic base 8. This can be achieved by appropriately setting the length D1 between the winding axis B1 of the columnar portion 16 and the first side surface 10c of the base portion 10, and the thickness t1 and the number of turns N of the wire forming the coil 54.

[0074] The magnetic body outer coating 6 is formed of a composite magnetic body containing magnetic powder and resin. The magnetic powder contains large particles (first magnetic powder) and small particles (second magnetic powder) having an average particle size larger than that of the large particles and smaller than that of the large particles. The average particle size of the large particles is, for example, 15 μm to 25 μm, and the average particle size of the small particles is, for example, 1.5 μm to 4 μm. The filling rate of the magnetic powder of the magnetic body outer coating 6 is 60 wt% or more, preferably 80 wt% or more. The magnetic powder uses iron-based metal magnetic powders such as Fe, Fe-Si-Cr, Fe-Ni-Al, Fe-Cr-Al, Fe-Si, Fe-Si-Al, Fe-Ni, Fe-Ni-Mo, metal magnetic powders of other composition systems, metal magnetic powders such as amorphous, metal magnetic powders with surfaces coated with insulators such as glass, metal magnetic powders with modified surfaces, and nano-level tiny metal magnetic powders. The resin uses thermosetting resins such as epoxy resins, polyimide resins, and phenolic resins, or thermoplastic resins such as polyethylene resins and polyamide resins.

[0075] It should be noted that the magnetic powder of the magnetic base 8 and the magnetic powder of the magnetic outer casing 6 may be magnetic powders of the same composition, average particle size of the first magnetic powder and the second magnetic powder, density, etc., or they may be different magnetic powders. In addition, the resin of the magnetic base 8 and the resin of the magnetic outer casing 6 may be the same resin or different resins.

[0076] The magnetic substrate 8, the coil 54 and the magnetic outer casing 6 form a unit body 2. The unit body 2 is formed into a substantially rectangular parallelepiped shape having an upper surface and a lower surface and four side surfaces adjacent to the upper surface and the lower surface, and the upper surface and the lower surface have a substantially rectangular shape in the long side direction and the short side direction.

[0077] (4)External terminal

[0078] like Figure 2As shown, a pair of external terminals 4a, 4b are arranged to be separated from the mounting surface of the unit body 2 (i.e., the lower surface 10b of the base portion 10 of the magnetic base 8). The pair of external terminals 4a, 4b are arranged to cover the front end portions 40a, 42a of the lead portions 40, 42 and the lower surface 10b near the front end portions 40a, 42a, respectively. The pair of external terminals 4a, 4b have a conductive resin layer 80 containing silver powder, a nickel layer, and a tin layer in the order of being arranged on the front end portions 40a, 42a and the lower surface 10b side. The thickness of the conductive resin layer 80 is 6μm to 13μm, the thickness of the nickel layer is 3μm to 6μm, the thickness of the tin layer is about 1μm, and the thickness of the external terminals 4a, 4b is 10μm to 20μm.

[0079] An outer coating resin (not shown) is formed on the surface of the unit body 2 outside the region where the pair of external terminals 4a, 4b are arranged. The outer coating resin may contain a thermosetting resin such as epoxy resin, polyimide resin, phenolic resin, or a thermoplastic resin such as polyethylene resin, polyamide resin, and may further contain a filler containing silicon, titanium, or the like.

[0080] It should be explained, such as Fig. 9 As shown, the conductive resin layer 80 may be formed in a shape in which a notch is provided on the lower surface 10b and the two end regions 40c, 42c of the front end portions 40a, 42a so that the central regions 40b, 42b of the front end portions 40a, 42a sandwiched between the two end regions 40c, 42c are exposed. In this case, the nickel layer is disposed on the conductive resin layer 80 and the central regions 40b, 42b of the front end portions 40a, 42a. The tin layer is disposed on the nickel layer. In addition, the notches are disposed so as to face each other.

[0081] The unit cell 2 of the inductor formed in this way, including the exterior resin, has a length in the long-side direction of, for example, 1.4 mm to 2.2 mm, a length in the short-side direction of, for example, 0.6 mm to 1.4 mm, and a height of, for example, 0.6 mm to 1 mm.

[0082] The inventors of the present invention compared the performance of a plurality of inductors constructed in this way and found that even if the filling rate of magnetic powder in the magnetic body and the filling rate of magnetic powder in the magnetic body were the same, the DC superposition characteristics were different. Therefore, the inventors focused on the possibility that the difference in the filling state of magnetic powder particles affects the DC superposition characteristics of the inductor. As a result, the following understanding was obtained: compared with the case where the magnetic powder is partially agglomerated, the concentration of local magnetic flux is alleviated in the inductor where the magnetic powder is not magnetically saturated, and the DC superposition characteristics can be improved.

[0083] Next, the inventors of the present invention came up with the idea of ​​dividing the cross section of the unit cell into Voronoi diagrams with each particle as a base point and calculating the standard deviation of the area of ​​each divided region in order to index the filling state of the magnetic powder.

[0084] Here, Voronoi graph segmentation is described.

[0085] Voronoi diagram segmentation is a method of drawing a perpendicular bisector on a straight line connecting adjacent base points to segment the nearest neighbor region of each base point to form a Voronoi diagram segmentation region.

[0086] The order of forming the Voronoi diagram partitioning region is as follows:

[0087] STEP 1: Prepare 300 base points to be analyzed (refer to Fig.10 (a));

[0088] STEP2: Connect each base point 300 with a line (refer to Fig.10 (b));

[0089] STEP3: Draw the perpendicular bisectors of the sides of the triangle formed in STEP2, and connect the perpendicular bisectors (refer to Fig.10 (c)); The area divided by the vertical bisector 302 is the Voronoi diagram segmentation area 304 (refer to Fig.10 (d)).

[0090] Based on the above findings, the inventors conducted the following:

[0091] (1) Actually manufacturing the inductor 1 according to the first embodiment;

[0092] (2) The Voronoi diagram is divided with the center of gravity of each magnetic powder as the base point in the cross section including the winding axis B2 of the winding portion 44 and extending in the longitudinal direction of the unit cell 2:

[0093] (3) Fig.11 As shown, with respect to the magnetic base region 306 and the magnetic exterior coating region 308, the standard deviation of the area of ​​the Voronoi diagram segmented region with the magnetic powder as the base point of each region is calculated.

[0094] The smaller the value of the standard deviation calculated in this way, the closer the magnetic powders are arranged at equal intervals. In other words, it can be seen that the smaller the value of the standard deviation, the more the magnetic saturation is relaxed, and thus the DC superposition characteristics are good.

[0095] Fig.11 This is an example of the Voronoi diagram division of the magnetic base region 306 and the magnetic exterior region 308 in the cross section extending in the longitudinal direction of the unit cell 2 . Fig.11(a) is a diagram showing an example of a cross section of a unit cell, (b) is a diagram showing an example of a Voronoi diagram segmentation of a magnetic base region 306 , and (c) is a diagram showing an example of a Voronoi diagram segmentation of a magnetic exterior casing region 308 .

[0096] (Example 1)

[0097] In this embodiment, the unit body is formed by using a material of the same material as the material of the large particles of the magnetic powder of the magnetic matrix and the material of the large particles of the magnetic powder of the magnetic body outer casing, using a material of the same material as the material of the small particles of the magnetic powder of the magnetic matrix and the material of the small particles of the magnetic powder of the magnetic body outer casing, and using a material of the same material as the resin of the magnetic matrix and the resin of the magnetic body outer casing. In addition, the magnetic powder of the magnetic matrix uses a magnetic powder having a ratio of the average particle size of the small particles to the average particle size of the large particles of 7.5, and the magnetic powder of the magnetic body outer casing uses a magnetic powder having a ratio of the average particle size of the small particles to the average particle size of the large particles of 6.3.

[0098] The dimensions of the unit body 2 used in this embodiment are 1.6 mm in the long side direction and 0.8 mm in the short side direction. It should be noted that the material, particle size (μm), and ratio (%) of the magnetic powder used in this embodiment to the total volume of large particles and small particles are shown in Table 1.

[0099] [Table 1]

[0100]

[0101] Next, the steps performed in this example are described.

[0102] STEP 1:

[0103] The particle sizes of the magnetic substrate and the magnetic outer shell of the unit body, which are cross-sections including the winding axis of the winding part and extending in the longitudinal direction of the unit body, can be measured by image analysis, and the particle sizes can be expressed as Fig.12 The coordinate diagram of the particle size distribution is shown. Fig.12 (a) is a graph of particle size measured by image analysis of a cross section of a magnetic matrix, and (b) is a graph of particle size measured by image analysis of a cross section of a magnetic body, with the horizontal axis being particle size (μm) and the vertical axis being probability density (normalized). 1 represents the particle size distribution counted by image analysis of a cross section of a magnetic body matrix, and 2 represents the particle size distribution of the result of fitting 1. In addition, 3 represents the particle size distribution counted by image analysis of a cross section of a magnetic body, and 4 represents the particle size distribution of the result of fitting 3.

[0104] STEP 2:

[0105] In order to express the particle size distribution of large particles and the particle size distribution of small particles Fig.122 and 4, such as Fig.13 As shown, a coordinate diagram showing the particle size distribution is prepared for large particles and small particles respectively. Fig.13 (a) is a coordinate diagram showing the particle size distribution of large particles and small particles in the cross section of the magnetic matrix, and (b) is a coordinate diagram showing the particle size distribution of large particles and small particles in the cross section of the magnetic body casing, with the horizontal axis being the particle size (μm) and the vertical axis being the frequency. Fig.13 In (a), 5 represents the log-normal distribution of large particles, and 6 represents the log-normal distribution of small particles. Fig.13 The sum of 5 and 6 in (a) is Fig.12 (a) 2. In addition, Fig.13 In (b), 7 represents the log-normal distribution of large particles, and 8 represents the log-normal distribution of small particles. Fig.13 The sum of 7 and 8 in (b) is Fig.12 (b)4.

[0106] STEP 3:

[0107] Next, based on Fig.13 5 and 7, to represent Fig.14 Shown are plots of the lognormal distribution of large particles and the cumulative frequency distribution of the lognormal distribution of large particles. Fig.14 (a) means Fig.13 The log-normal distribution of 5 large particles and the cumulative frequency distribution of the log-normal distribution of large particles are shown in (b). Fig.13 7 is a graph of the logarithmic normal distribution of large particles and the cumulative frequency distribution of the logarithmic normal distribution of large particles, with the horizontal axis being the particle size (μm), the left vertical axis being the frequency, and the right vertical axis being the cumulative. 9 represents the cumulative frequency distribution of the logarithmic normal distribution of large particles of 5, and 10 represents the cumulative frequency distribution of the logarithmic normal distribution of large particles of 7.

[0108] STEP 4:

[0109] use Fig.13 and Fig.14 The lower limit value of the particle size of the object is determined by performing Voronoi diagram segmentation of the cross section of the magnetic substrate and the magnetic outer casing of the unit body.

[0110] At this time, the lower limit of the particle size of the object of the Voronoi diagram segmentation of the cross section of the magnetic matrix and the magnetic body of the unit body is preferably determined as not to identify small particle sizes as much as possible, and to identify particles on the lower limit side of large particles. The result of the study is that the particle size distribution of large particles rises when the accumulation is 0.01 as the lower limit.

[0111] As a result, the lower limit of the particle size for which the Voronoi diagram of the cross section of the unit magnetic substrate is segmented is 6.5 μm, and the lower limit of the particle size for which the Voronoi diagram of the cross section of the unit magnetic exterior is segmented is 11.5 μm.

[0112] STEP 5:

[0113] Fig.15 The particle having a particle size above the lower limit is extracted using the cross-sectional image of the unit body magnetic matrix. At this time, by extracting the circle equivalent diameter representing the diameter of the true circle equivalent to the area of ​​the figure depicted in the image from the two-dimensional cross-sectional image, which is 6.5 μm, the particle of the object for which the Voronoi diagram of the cross section of the unit body magnetic matrix is ​​segmented can be extracted.

[0114] Next, the method for calculating the particle diameters described in Table 1 will be described.

[0115] In this specification, the average particle size is the median particle size D50, which represents the median particle size based on volume. In addition, D10 and D90 are the particle sizes when the volume is accumulated at 10% and 90%, respectively. The volume ratio and particle size of large particles and small particles can be obtained by analyzing the SEM (scanning electron microscope) image of the cross section.

[0116] First, the cross section of the unit body including the winding part and extending in the long side direction of the unit body is cut out with a wire saw or the like, and is monolithicized. After the cross section is flattened using a milling device or the like, a 300-fold image and a 1000-fold image of reflected electron images of each of 5 fields of view are taken by SEM in a specified area of ​​the magnetic matrix of the unit body and a specified area of ​​the magnetic outer casing of the unit body. It should be noted that the reason for taking the 300-fold image (low-magnification image) and the 1000-fold image (high-magnification image) is to accurately analyze the particle size of large particles and the particle size of small particles.

[0117] Next, the obtained SEM image is binarized using image analysis software, and the equivalent circular diameter of the cross section of the magnetic powder in the specified area of ​​the magnetic matrix and the specified area of ​​the magnetic body outer casing is obtained from the binarized image. The frequency of counting the equivalent circular diameter obtained by image analysis is obtained, and a histogram is obtained. There is a frequency difference caused by the difference in magnification in the 300-fold image and the 1000-fold image. In order to match the frequency of the 1000-fold image with the frequency of the 300-fold image, the frequency of the 1000-fold image is multiplied by the square of (1000 / 300). In addition, the value of the particle size whose deviation of the histogram of the 1000-fold image is greater than the deviation of the histogram of the 300-fold image is obtained, and the value of the 300-fold image is used for the frequency of the particle size above the particle size, and the value of the 1000-fold image is used to make a histogram for the frequency of the particle size less than the particle size.

[0118] In order to use the frequency of the histogram as a distribution based on volume, a calculation is performed based on morphometrics by multiplying the frequency by the volume calculated from the particle size interval and dividing it by the particle size (reference: RT De Hoff, FN Rhines, Kunio Makishima, Yasutada Shinohara, Hisashi Komori, "Morphometrics", Uchida Rokuho Shinsha, 1972, pp. 167-203). The above calculation is based on the study of morphometrics that the smaller the cross-sectional area, the higher the frequency of the particles. Here, the sum of the frequencies is divided by the frequency of each interval to make the sum of the frequencies 1 and normalize.

[0119] By fitting the volume-based histogram obtained in this way with the sum of two lognormal distributions (the sum of the lognormal distribution of large particles and the lognormal distribution of small particles), the average particle size of each of the large particles and the small particles and the volume ratio (matching ratio) of the large particles and the small particles are calculated. The probability density function of the lognormal distribution is given by the following formula 1.

[0120] (Formula 1)

[0121]

[0122] In the above formula, variable x corresponds to the data interval particle size, σ corresponds to the logarithmic dispersion, and μ corresponds to the logarithmic average. This probability density function is respectively expressed for large particles and small particles, so the variables become x1 and x2 given as particle size, and σ1, σ2, μ1, and μ2 given arbitrarily. It should be noted that the 1 at the end of each variable represents large particles, and 2 represents small particles. In addition, in order to represent the probability density function of large particles and the probability density function of small particles as one probability density function, each probability density function is multiplied by a specified ratio (p1, p2) and summed. The probability density function obtained by synthesizing the large particles and small particles thus obtained is normalized in advance so that it can be fitted with the histogram of the volume benchmark.

[0123] Among the variables of the probability density function, the data interval particle diameters x1 and x2 are given by the data interval of the volume-based histogram. Therefore, the synthesized probability density function is used to fit the volume-based histogram, so the dispersion σ1 and σ2, the average φ1 and φ2, and the proportions p1 and p2 are used as variables and optimized using the least squares method to minimize the difference between the two. From the probability density functions of the large particles and small particles given by the optimized variables, the value of the data interval that accumulates the normalized density function to 0.5 is obtained to obtain the average particle diameter of the large particles and small particles. In addition, the volume-based matching ratio (volume ratio) of the large particles and small particles is obtained from the optimized ratio of p1 to p2.

[0124] In addition, based on the image obtained by binarizing the SEM image using the image analysis software, the Voronoi diagram segmentation software "WinROOF2018" (manufactured by Mitani Shoji Co., Ltd.) was used. Fig.11 (b) and (c) are used to perform Voronoi diagram segmentation. Fig.11 As shown in (b), the magnetic substrate region 306 is segmented by a Voronoi diagram with magnetic powder having a circle equivalent diameter of 6.5 μm or more as the base point, as shown in FIG. Fig.11 As shown in (c), the magnetic outer casing region 308 was segmented by a Voronoi diagram using magnetic powder with a circle equivalent diameter of 11.5 μm or more as a base point. The standard deviation of the area of ​​the Voronoi diagram segmented region obtained by the Voronoi diagram segmentation was calculated, and the results are shown in Table 2.

[0125] In addition, the area ratio of the metal particles in the observation field was calculated based on the image subjected to the binary processing of the SEM image, and the filling rate was obtained as shown in Table 2. The interpretation of the area ratio as the filling rate is based on metrological morphology (reference: RT DeHoff, FN Rhines, Kunio Makishima, Yasushi Shinohara, Hisashi Komori, "Metric Morphology", Uchida Rokuho Shinsha, 1972, pp. 52-55).

[0126] [Table 2]

[0127] Magnetic substrate Magnetic external mount Filling rate of magnetic powder (%) 80 77 Standard deviation of the area of ​​the Voronoi diagram segment 298 194

[0128] From the above results, it can be seen that the standard deviation of the area of ​​the Voronoi diagram segmented region of the magnetic outer casing 6 is smaller than the standard deviation of the area of ​​the Voronoi diagram segmented region of the magnetic base 8. In addition, it can be seen that the filling rate of the magnetic powder of the magnetic base is greater than the filling rate of the magnetic powder of the magnetic outer casing. In such an inductor, the magnetic base has a higher magnetic permeability than the magnetic outer casing, so the inductance value can be increased compared with the existing inductor.

[0129] (Example 2)

[0130] In this embodiment, the unit body is formed by using a material different from the material of the large particles of the magnetic powder of the magnetic matrix and the material of the large particles of the magnetic powder of the magnetic body outer casing, using a material that is the same as the material of the small particles of the magnetic powder of the magnetic matrix and the material of the small particles of the magnetic powder of the magnetic body outer casing, and using a material that is the same as the resin of the magnetic matrix and the resin of the magnetic body outer casing. In addition, the magnetic powder of the magnetic matrix uses a material in which the ratio of the average particle size of the small particles to the average particle size of the large particles is 8, and the magnetic powder of the magnetic body outer casing uses a material in which the ratio of the average particle size of the small particles to the average particle size of the large particles is 5.3.

[0131] The dimensions of the unit body 2 used in this embodiment are 2.0 mm in the long side direction and 1.2 mm in the short side direction. In addition, the material, particle size (μm), and ratio (%) of the magnetic powder used in this embodiment to the total volume of large particles and small particles are shown in Table 3.

[0132] [Table 3]

[0133]

[0134] The magnetic body base region 306 and the magnetic body outer casing region 308 were segmented by Voronoi diagram using the same method as in Example 1. At this time, the Voronoi diagram segmentation was performed with the magnetic powder having a circle equivalent diameter of 6 μm or more as the base point, and the standard deviation of the area of ​​the Voronoi diagram segmentation region was calculated. The results are shown in Table 4. In addition, based on the image of the SEM image that was binarized, the area ratio of the metal particles in the observation field was calculated, and the filling rate was obtained. The results are shown in Table 4.

[0135] [Table 4]

[0136] Magnetic substrate Magnetic external mount Filling rate of magnetic powder (%) 82 83 Standard deviation of the area of ​​the Voronoi diagram segment 239 283

[0137] From the above results, it can be seen that the standard deviation of the area of ​​the Voronoi diagram segmented region of the magnetic substrate 8 is smaller than the standard deviation of the area of ​​the Voronoi diagram segmented region of the magnetic outer casing 6. In addition, it can be seen that the filling rate of the magnetic powder of the magnetic outer casing is greater than the filling rate of the magnetic powder of the magnetic substrate. Therefore, in the inductor 1 manufactured in this embodiment, the rated current value determined by the reduction of the inductance value can be increased.

[0138] According to the results of Example 1 and Example 2, it is known that the standard deviation of the area of ​​the Voronoi diagram segmentation region of the magnetic substrate 8 is preferably 230 to 300, and the standard deviation of the area of ​​the Voronoi diagram segmentation region of the magnetic body outer casing 6 is 190 to 290. These standard deviation ranges are also effective in reducing the concentration of magnetic flux between particles that are locally close in the magnetic substrate 8 and the magnetic body outer casing 6, respectively.

[0139] In addition, according to the results of the above-mentioned Examples 1 and 2, it can be seen that the standard deviation of the area of ​​the Voronoi diagram segmented region of the magnetic outer casing 6 is different from the standard deviation of the area of ​​the Voronoi diagram segmented region of the magnetic base 8. Therefore, it can be seen that by adjusting the standard deviation of the area of ​​the Voronoi diagram segmented region of the magnetic base 8 and / or the standard deviation of the area of ​​the Voronoi diagram segmented region of the magnetic outer casing 6, an inductor having a desired inductance value and / or a rated current value can be manufactured.

[0140] In addition, generally, the filling rate of the magnetic powder filled in the inductor contributes to the determination of the magnetic permeability of the inductor, and therefore contributes to the determination of the inductor's inductance value L. In the inductor 1 manufactured in the above-mentioned Examples 1 and 2, the filling rate of the magnetic powder contained in the magnetic base 8 is 80% or more, and the filling rate of the magnetic powder contained in the magnetic body outer casing 6 is 77% or more, and it is a sufficient filling rate. However, it is known that there is a trade-off relationship between the magnetic permeability and the rated current value determined by the reduction of the inductance value. When the magnetic permeability is high, the magnetic body is magnetically saturated under a lower magnetic field. In this way, even if the magnetic field generated by the direct current applied to the inductor is reduced, the magnetic body of the inductor is magnetically saturated. Therefore, even if the direct current value applied to the inductor is small, the inductance value obtained by the alternating current is reduced due to the magnetic saturation of the magnetic body. Therefore, if the magnetic permeability is too large, that is, if the filling rate is too large, the DC superposition characteristics are reduced. Therefore, the inventors of the present invention determined that the upper limit of the filling rate of the magnetic powder contained in the magnetic base 8 and the magnetic body outer casing 6 is preferably set to 85%. In other words, the inventors concluded that the filling rate of the magnetic powder contained in the magnetic base 8 is preferably 80% to 85%, and the filling rate of the magnetic powder contained in the magnetic body outer casing 6 is preferably 77% to 85%.

[0141] Therefore, one embodiment of the present invention involves an inductor comprising: a coil 54 having a winding portion 44 and a pair of lead portions 40 and 42 led out from the winding portion 44, and a unit body 2 containing magnetic powder containing first magnetic powder and second magnetic powder in which the coil 54 is buried, the average particle size of the first magnetic powder is larger than the average particle size of the second magnetic powder, and a Voronoi diagram is divided with the center of gravity of each magnetic powder as the base point in a cross section of the unit body 2 including the winding axis of the winding portion 44 and extending in the long side direction of the unit body 2, and the standard deviation of the area of ​​the Voronoi diagram divided region with the magnetic powder having a particle size of 6 μm or more as the base point is calculated, and the standard deviation is less than 300.

[0142] The inductor configured as described above can suppress a decrease in the rated current value due to a decrease in the inductance value even if the filling rate of the magnetic powder is increased.

[0143] Furthermore, the magnetic powder filled in the inductor configured as described above includes large particles and small particles having different average particle sizes, thereby increasing the filling rate of the magnetic powder efficiently filled in the inductor by filling small particles in the gaps between large particles.

[0144] 6. Manufacturing method

[0145] Next, a method for manufacturing the inductor 1 configured as described above will be described.

[0146] The manufacturing method of the inductor 1 comprises the following steps:

[0147] (1) a step of forming the magnetic substrate 8,

[0148] (2) a step of forming the coil 54,

[0149] (3) Molding and curing process,

[0150] (4) a step of forming an outer coating resin on the unit body,

[0151] (5) a step of removing the outer resin of the unit body, the coating layer of the wire and the fusion layer,

[0152] (6) Step of forming the external terminals 4a and 4b.

[0153] (1) Step of forming magnetic substrate 8

[0154] The mixture of magnetic powder and resin is filled into the cavity of a metal mold capable of forming the columnar portion 16 and the base portion 10. The metal mold has a cavity, which has, for example, a first portion having a depth and for forming the shape of the base portion 10, and a second portion having a depth and for forming the shape of the columnar portion, which is provided on the bottom surface of the first portion. The mixture of magnetic powder and resin is filled into the metal mold at a rate of 1 t / cm 2 ~10t / cm 2 The magnetic matrix 8 is formed by pressing the mixture of magnetic powder and resin for several seconds to several minutes under a certain degree of pressure. At this time, the magnetic matrix 8 can also be formed by heating the mixture of magnetic powder and resin to a temperature higher than the softening temperature of the resin (for example, 60°C to 150°C) and pressing. Then, the mixture is heated to a temperature higher than the curing temperature of the resin (for example, 100°C to 220°C) to cure it, and a magnetic matrix 8 having a matrix 10 and a columnar portion 16 formed on the matrix portion 10 is obtained. In addition, there is also a case of semi-curing, in which the semi-curing is achieved by adjusting the temperature (for example, 100°C to 220°C) and the curing time (1 minute to 60 minutes).

[0155] (2) Step of forming coil 54

[0156] By winding a conductive wire around the columnar portion 16 of the obtained magnetic base 8 , a coil 54 including a winding portion 44 and a pair of lead portions 40 and 42 led out from the winding portion 44 is formed.

[0157] The conductor has a coating layer and uses a rectangular cross-section flat wire. In addition, the winding portion 44 is formed by making one of the wide widths of the conductor contact the side of the columnar portion 16 and winding it in two stages above and below the columnar portion 16, with both ends of the conductor located at the periphery.

[0158] The lead portions 40 and 42 of the coil 54 are formed by pressing the front portions closer to the cutouts 14 and 15 of the base portion 10 of the magnetic base 8 to have the front end portions 40 a and 42 a wider than the conductive wire of the winding portion 44 .

[0159] The pair of lead portions 40, 42 of the coil 54 are led out from one side surface of the base portion 10 of the magnetic base 8. At this time, the pair of lead portions 40, 42 are twisted toward the center of the base portion 10 of the magnetic base 8, and one wide surface 66 is led out from the lower surface 10b side of the base portion 10 to contact the inner side surfaces of the cutouts 14, 15. The front end portions 40a, 42a of the lead portions 40, 42 led out on the lower surface 10b side are bent and arranged on the lower surface 10b of the magnetic base 8.

[0160] (3) Molding and curing process

[0161] The magnetic substrate 8 equipped with the coil 54 obtained by the above process is housed in a cavity of a metal mold having a convex portion on the bottom surface of the cavity, with the lower surface 10b of the substrate 10 facing the bottom surface of the cavity, so that the lower surface 10b of the substrate 10 is in contact with the bottom surface of the cavity of the metal mold. Next, the cavity is filled with a mixture of magnetic powder and resin. In addition, the mixture of magnetic powder and resin is heated to a temperature above the softening temperature of the resin (for example, 60°C to 150°C) in the metal mold at a pressure of 100kg / cm 2 ~500kg / cm 2 The resin is pressed and heated to a temperature higher than the curing temperature of the resin (e.g., 100°C to 220°C) to be molded and cured. Thus, the magnetic outer casing 6, the coil 54, and the magnetic base 8 are integrated to form the unit body 2. It should be noted that curing can be performed after molding.

[0162] By this molding and curing, the magnetic base 8 and the coil 54 wound around the columnar portion 16 of the magnetic base 8 are incorporated, and the recess 12 (seat) is formed on the mounting surface (the lower surface 10 b of the base portion 10 ).

[0163] When the mixture of magnetic powder and resin filled in the metal mold is pressurized, molded, and cured, the mixture of magnetic powder and resin is heated to a temperature higher than the softening temperature of both the resin and the fusion layer of the conductor (for example, 60°C to 150°C) using the metal mold and then heated at 100 kg / cm 2 ~500kg / cm 2By applying pressure to the left and right sides and heating to a temperature higher than the curing temperature of the resin (e.g., 100°C to 220°C) to form and cure it, the conductive wires of the upper section 46 and the conductive wires of the lower section 48 of the winding section 44 of the coil 54 are formed to be nested with each other. The region where the conductive wires of the upper section 46 and the conductive wires of the lower section 48 are nested with each other is not formed on the entire circumference of the winding section 44, but can be formed in a part. At this time, due to the pressure during molding, the conductive wires of the upper section 46 of the winding section 44 form a portion of the conductive wire that is inclined in the direction away from the winding axis B2. As a result, the protrusion 50 and the straight section 52 are formed in a part of the upper section 46. In addition, the columnar section 16 of the magnetic body substrate 8 that contacts the inner circumference of the winding section 44 is thicker at the front end than the root portion, and a protruding surface 22 and a flat surface 24 are formed on the side.

[0164] (4) Step of forming exterior resin on unit body

[0165] In this step, the outer coating resin is formed on the entire surface of the obtained unit body 2. The outer coating resin is formed by applying a thermosetting resin such as epoxy resin, polyimide resin, phenol resin, or a thermoplastic resin such as polyethylene resin, polyamide resin, etc. on the surface and curing it.

[0166] (5) Process of removing the outer resin, the coating layer and the fusion layer of the conductor

[0167] The outer resin, the wire coating layer and the fusion layer are removed from the unit body 2 formed with the outer resin at the positions where the external terminals 4a and 4b are formed. The outer resin, the wire coating layer and the fusion layer are removed by physical means such as laser, sandblasting, and grinding.

[0168] (6) Step of forming external terminals

[0169] A resin containing silver powder is applied to the position where the external terminals 4a and 4b are formed on the mounting surface of the unit body 2 so as to cover the front end portions 40a and 42a of the lead-out portions 40 and 42 of the coil 54. At this time, the resin containing silver powder may be applied to cover the end regions of the front end portions 40a and 42a of the lead-out portions 40 and 42 of the coil 54, leaving the central regions 40b and 42b exposed.

[0170] The unit body 2 is plated to form external terminals 4a and 4b on the portion of the unit body 2 except for the outer resin. The external terminals 4a and 4b are formed by growing plating on the metal magnetic powder exposed on the surface of the unit body 2 and on the resin containing silver powder. In addition, when the resin containing silver powder is applied to cover the both end areas of the front end parts 40a and 42a of the lead-out parts 40 and 42 of the coil 54 and expose the central areas 40b and 42b, the external terminals 4a and 4b are formed by growing plating on the metal magnetic powder exposed on the surface of the unit body 2 and on the resin containing silver powder, and on the central areas 40b and 42b of the front end parts 40a and 42a of the lead-out parts 40 and 42 of the coil 54. The plating growth forms, for example, a nickel layer composed of nickel, and then a tin layer composed of tin is formed on the nickel layer.

[0171] 7. Modifications

[0172] The inductor 1 shown above includes the coil 54, the magnetic substrate 8, the magnetic outer casing 6, and the external terminals 4a, 4b, but is not limited thereto. The inductor according to the present invention may be composed of the coil 54, the magnetic outer casing 6, and the external terminals 4a, 4b without the magnetic substrate 8, for example.

[0173] The coil 54 of the inductor 1 shown above is in the shape of an elongated circular ring in plan view, but the present invention is not limited thereto. The shape of the coil 54 in plan view may be, for example, an elliptical ring, a perfect circular ring, or a substantially rectangular ring with curved corners.

[0174] The above describes the embodiments and examples of the present invention, but the disclosed contents may be changed in the details of the configuration, and the combination and order of the elements of the embodiments and examples may be implemented without departing from the scope and concept of the present invention protected by the patent claims.

[0175] Explanation of symbols

[0176] 1.201 Inductor

[0177] 2-unit body

[0178] 4a, 4b external terminals

[0179] 6. Magnetic external packaging

[0180] 8Magnetic substrate

[0181] 10 Matrix

[0182] 10a Upper surface

[0183] 10b Lower surface

[0184] 10c First side

[0185] 10d Second side

[0186] 10e third side

[0187] 10fFourth side

[0188] 12 recesses

[0189] 14, 15 incision

[0190] 16 Columnar part

[0191] 18 upper part

[0192] 20 lower part

[0193] 22 protruding surface

[0194] 24 planes

[0195] 28, 30 plane area

[0196] 32, 34 curved surface area

[0197] 40, 42, 240, 242 lead-out section

[0198] 40a, 42a front end

[0199] 44 Winding Department

[0200] 46 upper section

[0201] 48 lower section

[0202] 50 protrusion

[0203] 52 Straight Line

[0204] 54, 254 coil

[0205] 56, 58 plane area

[0206] 60, 62 bending area

[0207] 64, 66 wide format

[0208] H1 Open end face

[0209] H2 Open end face

[0210] H3 Boundary Surface

[0211] 70, 72 wire

[0212] 70a, 72a 1st turn conductor

[0213] 72b Wire of the second loop

[0214] 70c, 72c outermost wire

[0215] 100, 150 contour lines

[0216] 102, 152 inner contour line

[0217] 104, 154 outer contour line

[0218] 106, 156 Inner peripheral contour line of the first plane area 56

[0219] 106a, 106b, 114a, 114b ends

[0220] 108, 158 Inner peripheral contour line of the second plane area 58

[0221] 110 , 160 Inner peripheral contour line of the first curved region 60

[0222] 112, 162 Inner peripheral contour line of the second curved area 62

[0223] 114 Inner peripheral contour line of the protrusion 50

[0224] 116 Contour line of the straight line portion 52

[0225] 120 , 170 Outer peripheral contour line of the first plane area 56

[0226] 122, 172 Outer peripheral contour line of the second plane area 58

[0227] 124, 174 Outer peripheral contour line of the first bending area 60

[0228] 126, 176 Outer peripheral contour line of the second curved area 62

[0229] 128 Outer peripheral contour line of the protrusion 50

[0230] 130 Outer peripheral contour line of the straight portion 52

[0231] 132 The outline of unit 2

[0232] 240a, 242a first area

[0233] 240b, 242b Second area

[0234] 240c, 242c Third area

[0235] 300 basis points

[0236] 302 perpendicular bisector

[0237] 304 Voronoi diagram segmentation region

[0238] 306 Magnetic Matrix Area

[0239] 308 Magnetic External Mounting Area

Claims

1. An inductor, It is characterized in that It has a coil and a unit body. The coil includes a winding portion and a pair of lead portions led out from the winding portion; The coil is embedded in the unit body, which contains magnetic powder including first magnetic powder and second magnetic powder; The unit body is composed of a magnetic substrate and a magnetic outer casing, the winding portion is wound on the magnetic substrate and contains the magnetic powder; the magnetic outer casing covers a part of the magnetic substrate, a part of the pair of lead portions and the winding portion, and contains the magnetic powder, The average particle size of the first magnetic powder is greater than the average particle size of the second magnetic powder, the average particle size of the first magnetic powder is 16 μm to 23 μm, and the average particle size of the second magnetic powder is 1.9 μm to 3.5 μm. In the cross section of the unit body including the winding axis of the winding portion and extending in the long side direction of the unit body, the filling rate of the magnetic powder of the magnetic matrix is ​​80% to 85%. When the Voronoi diagram is segmented using the center of gravity of each magnetic powder as the base point, and the standard deviation of the area of ​​the Voronoi diagram segmented area using the magnetic powder with a particle size of 6 μm or more as the base point is calculated, the standard deviation of the area of ​​the Voronoi diagram segmented area of ​​the magnetic matrix is ​​230 to 300. The filling rate of the magnetic powder of the magnetic body outer casing is 77% to 85%. When the Voronoi diagram is segmented using the center of gravity of each magnetic powder as the base point, and the standard deviation of the area of ​​the Voronoi diagram segmented area using the magnetic powder with a particle size of 11.5 μm or more as the base point is calculated, the standard deviation of the area of ​​the Voronoi diagram segmented area of ​​the magnetic body outer casing is 190 to 290.

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