inductor

Abstract

To provide an inductor having a good characteristic.SOLUTION: An inductor includes: an element assembly 2 incorporating a coil 20; and an external terminal formed on a front surface of the element assembly. The element assembly has: a main surface of a rectangular form having a side along first and second directions; a pair of first surfaces 16 along the first direction; a pair of second surfaces 14 along the second direction; first side gap parts 30a and 30b formed between an outer periphery of a winding part of the coil and the pair of first surfaces; and second side gap parts 30c and 30d formed between the outer periphery and the pair of second surfaces. When an area of the main surface is S1, a sum of dimensions in the second direction of the first side gap part is WSG, a sum of dimensions in the first direction of the second side gap part is LSG, an area of an inner side of an inner periphery of the winding part when penetrating it from a direction vertical to the main surface is S3, an area between the outer periphery and an outer edge of the element assembly is S4, and SG is set to a value of a formula (A), K is 70 or more and 110 or less: SG=WSG×LSG...(A), and K=(S1 / SG)×(S4 / S3)...(B).SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a surface mount inductor that includes a molded body having a coil formed by winding a conductive wire and an element body made of a sealing material containing resin and a magnetic material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-245473 Summary of the Invention [Problem to be solved by the invention]

[0004] In this type of inductor, the area inside the inner circumference of the coil in the element body and the area outside the outer circumference of the coil in the element body have traditionally been designed to meet the required DC bias rated current and DC resistance values. However, especially in inductors with small-sized element bodies, it has been difficult to meet the required characteristics even with the conventional optimization of these parameters, and there has been room for improvement in parameter setting. [Means for solving the problem]

[0005] One aspect of the present invention is a coil including a winding portion around which a rectangular conductor wire is wound, and a pair of lead-out portions led out from the winding portion; a first metal magnetic powder and a second metal magnetic powder having an average particle size smaller than that of the first metal magnetic powder; Magnetic powder and 、 Resin and 、 and an element body that houses the coil, and an external terminal that is formed on a surface of the element body and is connected to the lead-out portion, wherein the element body intersects with a winding axis of the coil, The longitudinal direction of the element body and width direction of the element body a main surface having a rectangular shape with sides along the line, and a substrate adjacent to the main surface, The longitudinal direction of the element bodya pair of first surfaces along the line, and adjacent to the main surfaces, width direction of the element body a pair of second surfaces along the line 11a, a first side gap portion formed between an outer periphery of the winding portion and the pair of first surfaces, and a second side gap portion formed between the outer periphery and the pair of second surfaces, the lead-out portion has a surface of the conductor along a longitudinal direction of the conductor exposed to the second surface or the main surface of the element body and connected to the external terminal; The area of ​​the main surface is S1, and the area of ​​each of the first side gap portions is S2. In the width direction of the element body The sum of the dimensions is WSG, and each of the second side gap portions In the longitudinal direction of the element body The inductor has the following dimensions: LSG, the area inside the inner circumference of the winding portion when viewed from a direction perpendicular to the main surface is S3, the area between the outer circumference and the outer edge of the element body is S4, and SG is a value calculated by the following formula (A): K calculated by the following formula (B) is equal to or greater than 70 and equal to or less than 110. SG=WSG×LSG (A) K = (S1 / SG) × (S4 / S3) (B) [Effects of the Invention]

[0006] According to the present invention, an inductor having good characteristics can be provided. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view of an inductor according to a first embodiment of the present invention, viewed from above. [Figure 2] 1 is a perspective view of the inductor according to the first embodiment as viewed from the bottom side. [Figure 3] 1 is a perspective view showing the internal configuration of an inductor according to a first embodiment. [Figure 4] 1A to 1C are schematic diagrams illustrating a manufacturing process for the inductor according to the first embodiment. [Figure 5] FIG. 2 is a schematic view showing the element body according to the first embodiment seen through from a direction perpendicular to the top surface. [Figure 6] 1 is a table showing various parameters and calculated values ​​K in a simulation of an example. [Figure 7]10 is a diagram showing the relationship between the value K and Isat / Rdc in a simulation of an example. [Figure 8] 10 is a graph showing the relationship between the value K and Isat / Rdc in a simulation of an example. [Figure 9] FIG. 10 is a perspective view of an element body according to a second embodiment. [Figure 10] FIG. 10 is a schematic view showing an element body according to embodiment 2 seen through a direction perpendicular to the top surface. [Figure 11] FIG. 11 is a perspective view of an element body according to a third embodiment. [Figure 12] Schematic diagram showing the element body as seen from the bottom side. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Embodiment 1] A method for manufacturing the inductor 1 according to the first embodiment and the inductor 1 will be described below. (Overall inductor configuration) FIG. 1 is a perspective view of an inductor 1 according to this embodiment as viewed from a top surface 12 side, and FIG. 2 is a perspective view of the inductor 1 as viewed from a bottom surface 10 side. The inductor 1 of this embodiment is configured as a surface-mounted electronic component, and includes an element body 2 having an approximately rectangular parallelepiped shape, which is one form of an approximately hexahedral shape, and a pair of external electrodes (external terminals) 4 provided on the surface of the element body 2.

[0009] Hereinafter, in the element body 2, the first main surface that faces a mounting board (not shown) during mounting is defined as the bottom surface (main surface) 10, the second main surface opposite the bottom surface 10 is called the top surface (main surface) 12, a pair of outer surfaces that are perpendicular to the bottom surface 10 are called end surfaces (second surfaces) 14, and a pair of outer surfaces that are perpendicular to the bottom surface 10 and the pair of end surfaces 14 are called side surfaces (first surfaces) 16. The pair of end surfaces 14 are arranged opposite each other. The pair of side surfaces 16 are also arranged opposite each other. The bottom surface 10, top surface 12, end surfaces 14, and side surfaces 16 each have a substantially rectangular shape. As shown in FIG. 1 , the distance from the bottom surface 10 to the top surface 12 of the element body 2 is defined as the thickness T of the element body 2, the distance between a pair of side surfaces 16 is defined as the width W of the element body 2, and the distance between a pair of end surfaces 14 is defined as the length L of the element body 2. The direction of the thickness T is defined as the thickness direction DT, the direction of the width W is defined as the width direction (second direction) DW, and the direction of the length distance is defined as the length direction (first direction) DL. That is, the bottom surface 10 and the top surface 12 are aligned along the width direction DW and the length direction DL, the end surfaces 14 are aligned along the width direction DW and the thickness direction DT, and the side surfaces 16 are aligned along the length direction DL and the thickness direction DT. The end surfaces 14 are adjacent to the bottom surface 10, the top surface 12, and the pair of side surfaces 16. The side surfaces 16 are adjacent to the bottom surface 10, the top surface 12, and the pair of end surfaces 14. The nominal size of the inductor 1 as a finished product is, for example, a length L dimension of 1.4 mm, a width W dimension of 1.2 mm, and a thickness T dimension of 0.65 mm.

[0010] Hereinafter, the plane along the DL direction and DT direction will be referred to as the LT plane, the plane along the DT direction and DW direction will be referred to as the TW plane, and the plane along the DL direction and DW direction will be referred to as the LW plane. Also, the cross sections of the inductor 1 along the LT plane, TW plane, and LW plane will be referred to as the LT cross section, TW cross section, and LW cross section, respectively.

[0011] FIG. 3 is a perspective view showing the internal configuration of the inductor 1. As shown in FIG. The element body 2 includes a coil conductor (coil) 20 and a core 30 having a substantially hexahedral shape in which the coil conductor 20 is embedded, and is configured as a molded inductor in which the coil conductor 20 is sealed in the core 30.

[0012] The core 30 is a molded body obtained by compression molding a powder mixture of magnetic particles (magnetic powder) and resin into a substantially hexahedral shape by applying pressure and heat while the coil conductor 20 is enclosed therein.

[0013] The magnetic particles of this embodiment are made of a soft magnetic material and include particles of two different particle sizes: first magnetic particles that are large particles with a relatively large average particle size, and second magnetic particles that are small particles with a relatively small average particle size. As a result, during compression molding, the second magnetic particles, which are small particles, enter between the first magnetic particles, which are large particles, together with the resin, thereby increasing the filling rate of the magnetic particles in the core 30 and also increasing the magnetic permeability. In this embodiment, the average particle size of the metal particles of the first magnetic particles is 20 μm or more and 28 μm or less, and the average particle size of the metal particles of the second magnetic particles is 1 μm or more and 6 μm or less. The average particle size of the first magnetic particles is preferably 21.4 μm or more and 27.4 μm or less, and the average particle size of the second magnetic particles is preferably 1.5 μm or more and 1.8 μm or less. Furthermore, the magnetic particles may contain particles with different average particle sizes from the first magnetic particles and the second magnetic particles, resulting in particles of three or more different particle sizes.

[0014] The first magnetic particles and the second magnetic particles are both particles having a metal particle, an oxide film covering the surface of the metal particle, and an insulating film covering the surface of the oxide film. By covering the metal particle with the oxide film and the insulating film, the insulation resistance and the withstand voltage are increased. In the first magnetic particles of this embodiment, Fe-Si-B amorphous alloy powder is used as the metal particles. The oxide film of the first magnetic particles is composed of two layers, an SiO layer and an Fe2SiO4 layer, and the total thickness of the oxide film is 20 nm to 155 nm. The insulating film of the first magnetic particles is made of phosphate glass and has a thickness of 10 nm to 50 nm.

[0015] In addition, in the second magnetic particles of this embodiment, carbonyl iron powder is used as the metal particles. The oxide film of the second magnetic particles is iron oxide formed by surface oxidation of carbonyl iron powder, which is a metal particle. Furthermore, the insulating film of the second magnetic particles is a sol-gel reaction product containing silica. This increases the slipperiness of the surface of the second magnetic particles, making it easier for the second magnetic particles to penetrate between the first magnetic particles during the element molding and curing process of the element body 2, which will be described later. As a result, the density of the magnetic material in the core 30 can be further increased, further increasing the relative permeability of the core 30.

[0016] In addition, in the first magnetic particles, the metal particles may be Fe-Si-Cr alloy powder, Fe-Ni-Al alloy powder, Fe-Cr-Al alloy powder, Fe-Si-Al alloy powder, Fe-Ni alloy powder, or Fe-Ni-Mo alloy powder. In the first magnetic particles, the insulating film may be made of phosphoric acid, zinc phosphate, manganese phosphate, glass, or resin.

[0017] The resin material contained in the mixed powder of this embodiment includes bisphenol A epoxy resin and rubber-modified epoxy resin, which allows the inductor 1 to be manufactured with improved element body 2 in both strength and toughness.

[0018] In this embodiment, the magnetic powder contained in the mixed powder is such that the first magnetic particles account for 70 wt% to 85 wt% and the second magnetic particles account for 15 wt% to 30 wt% of the total weight of the magnetic particles contained in the mixed powder. Furthermore, the resin contained in the mixed powder is 2.0 wt% to 3.5 wt% of the total weight of the magnetic powder and resin. The first magnetic particles are preferably 70 wt% to 80 wt%, and the second magnetic particles are preferably 20 wt% to 30 wt%. Furthermore, the resin is preferably 2.7 wt% to 30 wt%.

[0019] As shown in Fig. 3, the coil conductor 20 includes a winding portion 22 in which a conductor wire is wound spirally around a winding axis Q in two upper and lower stages so that both ends are located on the outer periphery and connected to each other on the inner periphery, and a pair of lead-out portions 23 led out from the winding portion 22. Each lead-out portion 23 is formed with a pair of external electrode connection regions 24, which are conductor wire portions for connection to external electrodes described below. The winding portion 22 includes two winding regions 22a and 22b that overlap along the winding axis Q. The conductor wires of the winding regions 22a and 22b are connected to each other at a portion of their inner peripheries.

[0020] Coil conductor 20 is embedded in element body 2 so that winding axis Q extends along thickness direction DT of element body 2. That is, winding axis Q is perpendicular to bottom surface 10 and top surface 12 and extends in a direction along end surfaces 14 and side surfaces 16.

[0021] The conducting wire constituting the coil conductor 20 is composed of a conductor and a coating layer formed on the surface of the conductor. The conducting wire is a flat wire with a rectangular cross section, and the conductor is a strip-shaped conductor made of copper with a rectangular cross section. The conductor has a thickness of 52 μm to 118 μm and a width of 110 μm to 180 μm. The coating layer is composed of an insulating layer formed on the surface of the strip-shaped conducting wire and a fusion layer formed on the surface of the insulating layer for bonding the overlapping strip-shaped conducting wires together in the winding portion 22. The insulating layer is made of, for example, polyimide amide resin and has a thickness of 3 μm. The fusion layer is made of, for example, polyamide resin and has a thickness of 1 μm to 25 μm.

[0022] The lead-out portion 23 is led out from the winding portion 22 and is electrically connected to the external electrode 4 via the external electrode connection regions 24 that are led out to and exposed on each of the pair of end faces 14 . The pair of external electrodes 4 are so-called L-shaped electrodes, consisting of L-shaped members extending from each of the end faces 14 of the element body 2 to the bottom face 10. Each of the external electrodes 4 is connected to an external electrode connection region 24 of the coil conductor 20 at the end face 14, and a portion 4A (FIG. 2) extending to the bottom face 10 is electrically connected to wiring on a circuit board by an appropriate mounting means such as solder.

[0023] An element body protective layer (not shown) is formed on the surface of the element body 2 excluding the area of ​​the external electrodes 4. The element body protective layer is, for example, a resin in which phenoxy resin is added to novolac resin, and contains nanosilica as a filler. The element body protective layer is formed on the surface of the element body 2 to a thickness of 10 μm or more and 30 μm or less. The thickness of the element body protective layer is preferably 10 μm or more and 20 μm or less, and more preferably 15 μm or less.

[0024] Inductor 1 with this configuration can improve DC bias characteristics by using a soft magnetic material for the magnetic particles, and is therefore used as an electronic component in electric circuits through which large currents flow, as a choke coil in DC-DC converter circuits and power supply circuits, and as an electronic component in electronic devices such as personal computers, DVD players, digital cameras, TVs, mobile phones, smartphones, car electronics, medical and industrial machinery, etc. However, the uses of inductor 1 are not limited to these, and it can also be used in, for example, tuning circuits, filter circuits, rectifying and smoothing circuits, etc.

[0025] (Outline of inductor manufacturing process) FIG. 4 is a schematic diagram of the manufacturing process of the inductor 1. As shown in the figure, the manufacturing process of the inductor 1 includes a coil conductor forming step, a preform forming step, an element molding and hardening step, an element polishing step, and an external electrode forming step.

[0026] The coil conductor formation process is a process of forming the coil conductor 20 from a conductive wire. In this process, the coil conductor 20 is formed into a shape having the above-mentioned winding portion 22 and lead-out portion 23 by winding the conductive wire using a winding method called "alpha winding." Alpha winding refers to a state in which the conductive wire, which functions as a conductor, is wound in two stages in a spiral shape so that the lead-out portions 23 at the start and end of the winding are located on the outer periphery. The number of turns of the coil conductor 20 is not particularly limited.

[0027] The preform forming step is a step of forming a preform called a tablet. The preform is formed by pressing the above-mentioned mixed powder, which is the material of the base body 2, into a solid form that is easy to handle.In this embodiment, two types of tablets are formed: a first tablet of an appropriate shape (e.g., E-shaped or T-shaped) in which the coil conductor 20 is arranged, and a second tablet of an appropriate shape (e.g., I-shaped or plate-shaped) in which the coil conductor 20 is sandwiched between the first tablet and the second tablet.

[0028] In the element molding and hardening process, the first tablet, the coil conductor, and the second tablet are set in a molding die, and while applying heat, pressure is applied in the overlapping direction of the first tablet and the second tablet, and they are hardened to integrate the first tablet, the coil conductor, and the second tablet. This forms the element 2 in which the coil conductor 20 is enclosed in the core 30. The element 2 obtained in this process may also be subjected to barrel polishing to remove burrs and the like that have occurred on the element 2 and to chamfer the corners of the element 2.

[0029] The element body polishing process is a process in which the side surface 16 of the element body 2 is polished to adjust the width W of the element body 2. In the element body polishing process, the element body 2 is held by a plate-shaped member called a holding plate and is sandwiched from above and below between the upper and lower grinding wheels of the polishing machine. In this state, the polishing machine is operated to rotate the upper and lower grinding wheels, thereby polishing the side surface of the element body 2. The element body polishing process sets the first side gap WSG, which is the sum of width dimensions WSG1 and WSG2 (described below), to 0.14 mm or less.

[0030] The external electrode forming step is a step of forming the external electrodes 4 on the element body 2, and includes an element body protective layer forming step, a surface treatment step, and a plating layer forming step.

[0031] The element body protective layer forming step is a step of coating the entire surface of the element body 2 with an insulating resin.

[0032] The surface treatment process is a process of modifying the surface of the planned electrode area by irradiating the area with laser light. Here, the planned electrode area refers to the area on the surface of the core 30 where the external electrode 4 is to be formed, including the area where the external electrode connection region 24 is exposed. Specifically, by irradiating the area with laser light, the element body protective layer on the surface of the element body 2 and the coating layer on the external electrode connection region 24 of the coil conductor 20 are removed in the planned electrode area, the resin on the surface of the core 30 is removed, and the insulating film on the surface of the magnetic particles exposed from the core 30 is removed. As a result, the exposed area of ​​the metal of the magnetic particles per unit area of ​​the surface of the core 30 is larger in the planned electrode area of ​​the surface of the core 30 than in other surface areas of the core 30. Note that after the laser light irradiation, a cleaning process (e.g., etching process) may be performed to clean the surface of the planned electrode area.

[0033] In the plating layer forming step, a copper plating layer is formed at the electrode locations irradiated with the laser light by barrel plating copper on the surface of the core 30. In addition, the plating layer may be formed by further providing a Ni plating layer and a Sn plating layer on the copper plating layer.

[0034] The inductor 1 of this embodiment will be described in further detail below. After describing the evaluation indexes for the characteristics of the inductor 1 and various parameters that affect the evaluation indexes, the preferred ranges of the various parameters will be described.

[0035] (Indicator for evaluating inductor characteristics) In addition to inductance, other important performance characteristics of the inductor 1 include the DC bias rated current (hereinafter referred to as Isat) and DC resistance (hereinafter referred to as Rdc). Isat is the current value when the inductance of the inductor 1 drops by a predetermined percentage from its initial value due to magnetic saturation; in this embodiment, it is the current value when the inductance drops by 30% from its initial value. Rdc is the resistance value when a DC current flows through the inductor 1. Generally, the inductor 1 is considered to have better characteristics the larger its Isat and the smaller its Rdc. For this reason, in this embodiment, the inductor 1 is evaluated as having better characteristics the larger its Isat / Rdc, obtained by dividing Isat by Rdc.

[0036] (Parameter description) In the inductor 1, the main parameters that affect Isat / Rdc include the total area S1, the outer peripheral area S4, the inner peripheral area S3, the first side gap WSG, and the second side gap LSG. Each of these parameters will be described below.

[0037] The total area S1 is the area of ​​the main surfaces, that is, either the top surface 12 or the bottom surface 10. Note that the top surface 12 and the bottom surface 10 are substantially rectangular with sides along the DW and DL directions, so the total area S1 may be calculated as the product of the width W of the element body 2 and the length L of the element body 2.

[0038] Fig. 5 is a schematic view showing the element body 2 seen through from a direction perpendicular to the top surface 12. A perspective view corresponding to Fig. 5 can be obtained by, for example, radiography using X-rays. In this embodiment, the element body 2 is a substantially rectangular parallelepiped, and therefore, as shown in Fig. 5, the area inside the outer edge 2a of the element body 2 when viewed from a direction perpendicular to the top surface 12 is substantially the same as the area of ​​the top surface 12 and the bottom surface 10. Therefore, the area inside the outer edge 2a of the element body 2 when viewed from a direction perpendicular to the top surface 12 may be used as the total area S1.

[0039] The outer periphery area S4 is the area of ​​the region between the outer periphery 22c of the winding portion 22 and the outer edge 2a of the element body 2 when the element body 2 is seen through in a direction perpendicular to the top surface 12. The outer periphery 22c of the winding portion 22 refers to the outer edge of the outermost conductor of the winding portion 22, which is the sum of the two winding regions 22a, 22b, when seen through in a direction perpendicular to the top surface 12. In other words, the outer periphery 22c may be made up of both the outer edge of the outermost conductor of the winding region 22a and the outer edge of the outermost conductor of the winding region 22b.

[0040] The inner periphery side area S3 is the area inside the inner periphery 22d of the winding portion 22 when the element body 2 is seen through in a direction perpendicular to the top surface 12. The inner periphery 22d of the winding portion 22 refers to the inner edge of the conductor on the innermost side of the winding portion 22, which is the sum of the two winding regions 22a and 22b, when seen through in a direction perpendicular to the top surface 12. In other words, the inner periphery 22d may be constituted by both the inner edge of the conductor on the innermost side of the winding region 22a and the inner edge of the conductor on the innermost side of the winding region 22b.

[0041] The outer peripheral area S4 and the inner peripheral area S3 can be obtained by, for example, taking an X-ray of the element body 2 from a direction perpendicular to the top surface 12 and measuring the area from the obtained image. Furthermore, as described below, the outer peripheral area S4 and the inner peripheral area S3 are required to determine the value S2 of equation (1) described below. Since the value S2 is obtained by dividing the outer peripheral area S4 by the inner peripheral area S3, it is not necessary to determine the values ​​of the outer peripheral area S4 and the inner peripheral area S3 individually to calculate the value S2. Therefore, the value S2 may be directly determined by calculating the ratio between the area corresponding to the outer peripheral area S4 and the area corresponding to the inner peripheral area S3 from the image obtained by the X-ray photography described above.

[0042] The first side gap WSG is the sum of width dimensions WSG1, WSG2 of two first side gaps 30a, 30b formed between the outer periphery 22c of the winding portion 22 and two side surfaces 16 of the element body 2. The first side gaps 30a, 30b are each part of the core 30. Furthermore, the width dimensions WSG1, WSG2 are both the dimensions of the first side gaps 30a, 30b in the DW direction. Specifically, the width dimension WSG1 of the first side gap 30a is the minimum value of the distance in the DW direction between the outer periphery 22c of the winding portion 22 and one of the side surfaces 16 when the element body 2 is seen through in a direction perpendicular to the top surface 12. Similarly, the width dimension WSG2 of the first side gap portion 30b is specifically the minimum value of the distance in the DW direction between the outer periphery 22c of the winding portion 22 and the other side surface 16 when the element body 2 is viewed from a direction perpendicular to the top surface 12.

[0043] Furthermore, for example, the width dimensions WSG1 and WSG2 may be the measured value of the distance on an imaginary line L1 between the outer periphery 22c of the winding part 22 and the two side surfaces 16 when the element body 2 is viewed from a direction perpendicular to the top surface 12, as shown in FIG. 5 . The imaginary line L1 is an imaginary straight line that passes through the winding axis Q of the winding part 22 and extends in the DW direction when the element body 2 is viewed from a direction perpendicular to the top surface 12. By measuring the width dimensions WSG1 and WSG2 in this manner, it is possible to make the width dimensions WSG1 and WSG2 sufficiently approximate the minimum distance in the DW direction between the outer periphery 22c of the winding part 22 and the side surfaces 16 when the element body 2 is viewed from a direction perpendicular to the top surface 12. Note that the position of the winding axis Q when the element body 2 is viewed from a direction perpendicular to the top surface 12 may be the center of the largest inscribed circle relative to the inner periphery 22d of the winding part 22, for example. The virtual line L1 may also be placed at the center of the element body 2 in the DL direction.

[0044] The second side gap LSG is the sum of length dimensions LSG1, LSG2 of two second side gaps 30c, 30d formed between the outer periphery 22c of the winding portion 22 and the two end faces 14 of the element body 2. The second side gaps 30c, 30d are each part of the core 30. Furthermore, the length dimensions LSG1, LSG2 are both the dimensions of the second side gaps 30c, 30d in the DL direction. Specifically, the length dimension LSG1 of the second side gap 30c is the minimum value of the distance in the DL direction between the outer periphery 22c of the winding portion 22 and one end face 14 when the element body 2 is seen through in a direction perpendicular to the top surface 12. Similarly, the length dimension LSG2 of the second side gap portion 30d is specifically the minimum value of the distance in the DL direction between the outer periphery 22c of the winding portion 22 and the other end face 14 when the element body 2 is seen through in a direction perpendicular to the top surface 12. Note that in FIG. 5, the winding portion 22 has a lead-out portion 23 extending from the outer periphery 22c of the winding portion 22 toward the end face 14 of the element body, but the portion where the lead-out portion 23 and the winding portion 22 connect, i.e., the portion where the surface of the outermost conductor on the winding axis Q side begins to separate from the innermost conductor, is excluded from the outer periphery 22c of the winding portion.

[0045] Furthermore, for example, the length dimensions LSG1 and LSG2 may be measured values ​​of the distance on an imaginary line L2 between the outer periphery 22c of the winding portion 22 and the two end faces 14 when the element body 2 is viewed from a direction perpendicular to the top surface 12, as shown in FIG. 5 . The imaginary line L2 is an imaginary straight line that passes through the winding axis Q of the winding portion 22 and extends in the DL direction when the element body 2 is viewed from a direction perpendicular to the top surface 12. By measuring the length dimensions LSG1 and LSG2 in this manner, the length dimensions LSG1 and LSG2 can be made to sufficiently approximate the minimum distance in the DL direction between the outer periphery 22c of the winding portion 22 and the side surface 16 when the element body 2 is viewed from a direction perpendicular to the top surface 12. Note that the imaginary line L2 may be positioned at the center of the element body 2 in the DW direction.

[0046] (Optimal range of parameters) As a result of the below-described examples carried out by the inventors regarding these parameters, it was found that in order to increase Isat / Rdc, the preferable range of the value K calculated by the following formula (1) is 70 or more and 110 or less. It was also found that the more preferable range of the value K is 80 or more and 100 or less. K = S1 / (WSG × LSG) × (S4 / S3) =(S1 / SG) × (S4 / S3) =B×S2 (1) In this embodiment, the value K is set to be equal to or greater than 70 and equal to or less than 110. Therefore, the Isat / Rdc of the inductor 1 can be increased, and an inductor 1 with good characteristics can be obtained.

[0047] [Example] The inventors conducted experiments to verify the relationship between the various parameters described above and the characteristics of the inductor. In the examples, the inventors created one element body 2 and calculated the value K by changing various parameters in a simulation based on the created element body 2. Furthermore, the inventors calculated Isat / Rdc for each calculated value K to determine a suitable range for the value K. Details of this are described below.

[0048] (Sample preparation) First, the inventors created the element 2 to be used in the simulation. The inventors used a mixed powder for the core 30, which consisted of a metal magnetic powder containing Fe-Si-Cr alloy powder as the first magnetic particles and carbonyl iron powder as the second magnetic particles. Measurements using a particle size distribution analyzer revealed that the metal magnetic powder in the example had an average particle size of 25.3 μm for the first magnetic particles and 1.7 μm for the second magnetic particles. The resin in the example contained bisphenol A epoxy resin and rubber-modified epoxy resin, accounting for 2.7 wt% of the mixed powder. According to measurements by the inventors, the mixed powder had a relative permeability of 34 and a saturation magnetic flux density of 1.36 T. The relative permeability was measured using a BH analyzer and an impedance material analyzer with a high-frequency signal at a frequency of 1 MHz. The saturated magnetic flux density was determined by measuring the inductance change during superposition using an LCR meter and a DC power supply, and then back-calculating the BH data to determine the value at which the magnetic flux became saturated.

[0049] In the example, the inventors used a rectangular conductor having cross-sectional dimensions of 0.128 mm in length and 0.083 mm in width to create a coil conductor 20. As in the first embodiment, the coil conductor 20 was formed into a shape having a winding portion 22 formed by winding in two stages and a lead-out portion 23.

[0050] In the examples, the inventors produced an element body 2 using the above-described core 30 and coil conductor 20. During compression molding, the coil conductor 20 was placed in an E-shaped preform, which was a mixture of metal magnetic powder and resin, similar to the core 30 of the examples. The coil conductor 20 was placed in a mold, sandwiched between the E-shaped preform and an I-shaped preform made of the same material as the E-shaped preform. In this state, the E-shaped preform, the coil conductor 20, and the I-shaped preform were thermally compressed to form the element body 2. At this time, the coil conductor 20 was oriented so that the winding axis Q of the winding portion 22 was approximately perpendicular to the bottom surface 10, which is the mounting surface of the element body 2.

[0051] As a result, an element body 2 was produced having a length L of 1.52 mm along the length direction DL, a width W of 1.35 mm along the width direction DW, and a thickness T of 0.57 mm along the thickness direction DT.

[0052] (simulation) 6 is a table showing various parameters and calculated values ​​K in the simulation. Note that the letters of each parameter in FIG. 6 correspond to the letters of each parameter described in embodiment 1. Also, inner radius R is the value of the radius of curvature of the curved portion of inner circumference 22d of winding portion 22. The inventors performed a simulation based on the shapes of each part of the obtained element body 2, and calculated the value K of the element body 2 when the first side gap WSG was 0.1 mm, the second side gap LSG was 0.2 mm, and the inner diameter R of the coil conductor 20 was 0.25 mm. The calculated value K was 63.4.

[0053] The inventors then performed a simulation in which the cross-sectional dimensions of the rectangular conductor, the inner diameter R, the first side gap WSG, and the second side gap LSG were varied to calculate the value K for each pattern, so that the inductance value was 0.31 μH. The outer dimensions of the element body 2 were fixed at length L of 1.52 mm, width W of 1.35 mm, and thickness T of 0.57 mm. As a result, as shown in Figure 6, values ​​K ranging from 59.8 to 112.5 were obtained for a total of 12 parameter combinations.

[0054] It is possible to adjust the first side gap WSG and the second side gap LSG not only in simulations but also during actual manufacturing by changing the size of the space within the mold. The sizes of the first side gap WSG and the second side gap LSG can also be adjusted by making the size of the space within the mold larger than the final size of the element body 2 and polishing the core 30 after compression molding.

[0055] The inventors further performed a simulation on the change in Isat / Rdc corresponding to the value K in FIG. Fig. 7 is a diagram showing the relationship between the value K and Isat / Rdc in a simulation. Fig. 8 is a graph showing the relationship between the value K and Isat / Rdc in a simulation. The curve in Fig. 8 is an interpolated curve of the simulation results shown in Fig. 7.

[0056] 7 and 8, among the simulated values ​​of K, the largest Isat / Rdc was when the value K was 93.2, and Isat / Rdc at this time was 0.2629 A / mΩ. Also, as shown in Fig. 7, Isat / Rdc had a peak, and as the value K increased or decreased from the peak value, Isat / Rdc tended to decrease.

[0057] 7 and 8, in the second simulation of the example, Isat / Rdc remains at 90% or more of the maximum value of Isat / Rdc when the value K is in the range of 70 or more and 110 or less. Furthermore, Isat / Rdc remains at 95% or more of the maximum value of Isat / Rdc when the value K is in the range of 80 or more and 100 or less.

[0058] Therefore, from the examples, it was found that, taking into account the measurement accuracy of each parameter in the actual product, the preferable range of the value K is not less than 70 and not more than 110. Furthermore, from the examples, it was found that the more preferable range of the value K is not less than 80 and not more than 100.

[0059] The reason for this effect is unclear, but it is thought to be because the element size is larger than the 1412 size (1.4 mm x 1.2 mm), and therefore requires a different design concept from conventional products. In addition, the reason why Isat / Rdc for the value K has a peak as shown in Figure 7 is thought to be because there are suitable ranges for increasing Isat / Rdc for each of the values ​​B and S2 used in the above-mentioned equation (1).

[0060] When the value S2 is large, the outer peripheral area S4 is large and the inner peripheral area S3 is small. In this case, because the outer peripheral area S4 is large, the diameter of the outer periphery 22c is small, the length of the conducting wire forming the coil conductor 20 is likely to be short, and Rdc is likely to be small. On the other hand, because the inner peripheral area S3 is small, magnetic saturation is likely to occur and Isat is likely to be small. When the value S2 is small, the outer peripheral area S4 is small and the inner peripheral area S3 is large. In this case, because the outer peripheral area S4 is small, the diameter of the outer periphery 22c is large, the length of the conducting wire forming the coil conductor 20 tends to be long, and Rdc tends to be large. On the other hand, because the inner peripheral area S3 is large, magnetic saturation is unlikely to occur and Isat tends to be large. In this way, when the value S2 is large, both Rdc and Isat tend to become small, and when the value S2 is small, both Rdc and Isat tend to become large. Therefore, it is thought that there exists a range of the value S2 that is suitable for increasing Isat / Rdc without Isat / Rdc increasing or decreasing monotonically with respect to the value S2.

[0061] If we consider the total area S1 as the product of the width W and the length L, the value B can be transformed into the following equation (2). B=S1 / SG =(W×L) / (WSG×LSG) =(W / WSG)×(L / LSG) (2) That is, the value B can be regarded as the product of the reciprocal of the ratio WSG / W of the first side gap WSG to the width W and the reciprocal of the ratio LSG / L of the second side gap LSG to the length L.

[0062] Therefore, when the value B is large, the ratios WSG / W and LSG / L are small. In this case, when viewed from a direction perpendicular to the top surface 12, the outer periphery 22c of the winding portion 22 is located close to the side surface 16 and end surface 14 of the element body 2. In other words, the length of the conducting wire constituting the coil conductor 20 tends to be long, and Rdc tends to be large. Furthermore, the diameter of the inner periphery 22d of the winding portion 22 tends to be large, making it difficult for magnetic saturation to occur and making Isat large. Furthermore, when the value B is small, the ratios WSG / W and LSG / L are large. This means that, when viewed from a direction perpendicular to the top surface 12, the outer periphery 22c of the winding portion 22 is located far from the side surface 16 and end surface 14 of the element body 2. In other words, the length of the conducting wire constituting the coil conductor 20 is likely to be short, and Rdc is likely to be small. Furthermore, the diameter of the inner periphery 22d of the winding portion 22 is likely to be small, which means that magnetic saturation is likely to occur and Isat is likely to be small. In this way, when the value B is large, both Rdc and Isat tend to become large, and when the value B is small, both Rdc and Isat tend to become small. For this reason, Isat / Rdc does not monotonically increase or decrease with respect to the value B, and it is thought that there exists a range of the value B that is suitable for increasing Isat / Rdc.

[0063] Thus, it is believed that there is a suitable range for each of the values ​​B and S2 in terms of increasing Isat / Rdc. Therefore, it is believed that there is also a suitable range for the value K, which is the product of the values ​​B and S2, in terms of increasing Isat / Rdc.

[0064] [Embodiment 2] Next, a second embodiment will be described with reference to Figures 9 and 10. Note that only the differences from the first embodiment will be described below, and the same description will be omitted.

[0065] Fig. 9 is a perspective view of an element body 102 according to embodiment 2. Fig. 9 is a schematic view showing the element body 102 seen through in a direction perpendicular to the top surface 12. In the element body 102 according to the second embodiment, unlike the element body 2 of the first embodiment, cross sections 123a of the conductor wires constituting the two lead portions 123 of the coil conductor 20 are exposed from the two end faces 14. More specifically, the cross sections 123a of the conductor wires constituting the lead portions 123 are substantially flush with the two end faces 14 of the element body 102. In other words, the cross sections 123a of the conductor wires constituting the lead portions 123 are substantially flush with the end faces 14 of the element body 102. The cross sections 123a of the conductor wires constituting the lead portions 123 are exposed from the end faces 14 of the element body 102 and become substantially flush with the end faces 14, for example, by grinding the two end faces 14 of the element body 102 together with the lead portions 23 in the DL direction in an element body polishing process. The cross section 123a of the conductor constituting the lead portion 123 exposed from the end face 14 of the element body 102 is connected to the external electrode 4 in the external electrode formation step.

[0066] In this way, by removing the end surface 14 of the element body 102 to expose the cross section 123a of the conductor constituting the lead portion 123 from the end surface 14 of the element body 102, the length dimensions LSG1, LSG2 of the second side gap portions 30c, 30d can be easily adjusted. Therefore, the value K calculated by the above formula (1) can be easily adjusted to be equal to or greater than 70 and equal to or less than 110.

[0067] [Embodiment 3] Next, a third embodiment will be described with reference to Figures 11 and 12. Note that only the differences from the first and second embodiments will be described below, and the same description will be omitted.

[0068] Fig. 11 is a perspective view of an element body 202 according to embodiment 3. Fig. 12 is a schematic diagram showing the element body 202 as viewed from the bottom surface 10 side. In the element body 202 according to the third embodiment, unlike the first and second embodiments, the two lead portions 223 of the coil conductor 20 are bent toward the bottom surface 10, and the lead portions 223 are exposed from the bottom surface 10. More specifically, the surfaces 223a of the conductors constituting the lead portions 223 are exposed from the bottom surface 10 of the element body 202. The surfaces 223a of the conductors constituting the lead portions 223 exposed from the bottom surface 10 of the element body 202 are connected to the external electrode 4 in the external electrode formation step.

[0069] In this way, by exposing the surface 223a of the conductive wire constituting the lead portion 223 from the bottom surface 10 of the element body 202, the lead portion 223 can be connected to the external electrode 4 even if the lead portion 223 is not exposed from the end surface 14 of the element body 202. Therefore, it is no longer necessary to expose the lead portion 223 from the end surface 14 of the element body 202, and the degree of freedom in adjusting the length dimensions LSG1, LSG2 of the second side gap portions 30c, 30d can be increased. This makes it easier to adjust the value K calculated by the above formula (1) to be equal to or greater than 70 and equal to or less than 110.

[0070] [Other embodiments] In the above embodiment, the external electrode 4 has been described as an L-shaped electrode formed across the end face 14 and bottom face 10 of the element body 2, 102, 202, but this is just one example. The external electrode 4 is not limited to an L-shaped electrode, and may be configured to be formed across the end face 14 of the element body 2, 102, 202 and the bottom face 10, top face 12, and two side faces 16 adjacent to the end face 14. In this case, the surface 223a of the conductive wire constituting the lead-out portion 223 described in embodiment 3 may be exposed from the top face 12 rather than the bottom face 10 of the element body 202.

[0071] In the above embodiment, two first side gaps 30a, 30b are formed between the winding portion 22 and the two side surfaces 16. However, this is merely an example. For example, the outer periphery 22c of the winding portion 22 may be exposed from one of the side surfaces 16, and only one of the first side gaps 30a, 30b may be formed. In this case, the first side gap WSG coincides with one of the width dimensions WSG1, WSG2. Similarly, the winding portion 22 may be exposed from one of the end surfaces 14, and only one of the second side gaps 30c, 30d may be formed between the winding portion 22 and the two end surfaces 14, and the second side gap LSG may coincide with one of the length dimensions LSG1, LSG2.

[0072] All of the above-described embodiments and modifications are merely examples of aspects of the present invention, and any modifications and applications are possible without departing from the spirit of the present invention. In addition, any elements of the above-described embodiments may be combined to form a new embodiment. Furthermore, unless otherwise specified, the horizontal, perpendicular, vertical, and other directions, various numerical values, shapes, and materials in the above-described embodiments include a range (so-called equivalent range) that produces the same effect as those directions, numerical values, shapes, and materials.

[0073] [Configuration supported by the above embodiment] The above-described embodiment supports the following configurations.

[0074] (Configuration 1) A coil having a winding portion around which a rectangular conductor wire is wound and a pair of lead-out portions led out from the winding portion, an element body containing magnetic powder and resin and incorporating the coil, and external terminals formed on a surface of the element body and connected to the lead-out portions, wherein the element body has a rectangular main surface that intersects with a winding axis of the coil and has sides along a first direction and a second direction, a pair of first surfaces adjacent to the main surface and aligned with the first direction, a pair of second surfaces adjacent to the main surface and aligned with the second direction, first side gap portions formed between the outer periphery of the winding portion and the pair of first surfaces, and a front an inductor having second side gap portions formed between the outer periphery and the pair of second surfaces, wherein when the area of ​​the main surface is S1, the sum of the dimensions of each of the first side gap portions in the second direction is WSG, the sum of the dimensions of each of the second side gap portions in the first direction is LSG, the area inside the inner periphery of the winding portion when viewed from a direction perpendicular to the main surface is S3, and the area between the outer periphery and the outer edge of the element body is S4, and SG is a value calculated by the following formula (A), K calculated by the following formula (B) is equal to or greater than 70 and equal to or less than 110. SG=WSG×LSG (A) K = (S1 / SG) × (S4 / S3) (B) According to the inductor of configuration 1, Isat / Rdc can be increased, and therefore an inductor with good characteristics can be provided.

[0075] (Configuration 2) The inductor according to configuration 1, wherein a cross section of the conductive wire constituting the lead-out portion is exposed on the second surface, and the cross section is flush with the second surface. According to the inductor of configuration 2, it is easy to adjust the dimension of the second side gap portion in the first direction, and it is easy to adjust K to be equal to or greater than 70 and equal to or less than 110. This makes it easy to provide an inductor with good characteristics.

[0076] (Configuration 3) The inductor according to configuration 1 or 2, wherein the surface of the conductive wire that constitutes the lead-out portion is exposed from the main surface. According to the inductor of configuration 3, the degree of freedom in the dimension of the second side gap portion in the first direction is increased, and it is easy to adjust K to be not less than 70 and not more than 110. This makes it easy to provide an inductor with good characteristics. [Explanation of symbols]

[0077] 1...inductor, 2...element body, 2a...outer edge, 4...external electrode (external terminal), 10...bottom surface (main surface), 12...top surface (main surface), 14...end surface (second surface), 16...side surface (first surface), 20...coil conductor (coil), 22...winding portion, 22c...outer circumference, 22d...inner circumference, 23...lead portion, 30...core, 30a...first side gap portion, 30b...first side gap portion, 30c...second side gap portion, 30d...second side gap portion, 102...element body, 123...lead portion, 123a...cross section, 202...element body, 223...lead portion, 223a...surface, Q...winding axis.

Claims

1. a coil having a winding portion around which a rectangular conductor wire is wound and a pair of lead-out portions led out from the winding portion; an element body containing the coil, the element body containing a first metal magnetic powder, a second metal magnetic powder having an average particle size smaller than that of the first metal magnetic powder, and a resin; an external terminal formed on a surface of the element body and connected to the lead-out portion, The element body is a rectangular main surface that intersects with the winding axis of the coil and has sides along the longitudinal direction of the element body and the width direction of the element body; a pair of first surfaces adjacent to the main surfaces and extending along the longitudinal direction of the element body; a pair of second surfaces adjacent to the main surfaces and extending along the width direction of the element body; a first side gap portion formed between an outer periphery of the winding portion and the pair of first surfaces; second side gap portions formed between the outer periphery and the pair of second surfaces, the lead-out portion has a surface of the conductor along a longitudinal direction of the conductor exposed on the second surface of the element body or the main surface of the element body, and connected to the external terminal; The area of ​​the main surface is S1, the sum of the dimensions of the element body in the width direction of each of the first side gap portions is defined as WSG, the sum of the longitudinal dimensions of the element body in each of the second side gap portions is denoted by LSG, When viewed from a direction perpendicular to the main surface, the area inside the inner periphery of the winding portion is defined as S3, and the area between the outer periphery and the outer edge of the element body is defined as S4, When SG is a value calculated by the following formula (A), An inductor in which K calculated by the following formula (B) is equal to or greater than 70 and equal to or less than 110. SG=WSG×LSG (A) K=(S1 / SG)×(S4 / S3) (B)

2. The element body is The magnetic powder contains 70 wt % or more and 85 wt % or less of the first metal magnetic powder and 15 wt % or more and 30 wt % or less of the second metal magnetic powder, based on the total weight of the first metal magnetic powder and the second metal magnetic powder, The resin content is 2.0 wt % or more and 3.5 wt % or less based on the total weight of the first metal magnetic powder, the second metal magnetic powder, and the resin.

10. The inductor of claim 1.

3. The element body has a longitudinal dimension of 1.52 mm, a width dimension of 1.35 mm, and a thickness dimension of 0.57 mm, The WSG is 0.14 mm or less.

3. The inductor according to claim 1 or 2.

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