Inductor

Abstract

The present invention provides an inductor in which magnetic flux concentration is mitigated and variations in magnetic properties due to differences in the arrangement of magnetic powder are suppressed. [Solution] An inductor comprising a coil conductor having a winding portion around which a conductor wire is wound and a pair of lead portions drawn out from the winding portion, a base body containing magnetic powder 32 and resin 31 and enclosing the coil conductor, and external electrodes formed on the surface of the base body and connected to the lead portions, wherein the magnetic powder comprises a first magnetic powder 32a (small particles) and a second magnetic powder 32b (large particles) having a volume-based particle size distribution mode greater than the mode of the volume-based particle size distribution of the first magnetic powder, and the interparticle distance is adjusted.

Description

Technical Field

[0001] The present invention relates to an inductor.

Background Art

[0002] Patent Document 1 describes a technique related to a magnetic core containing metal magnetic powder and resin. In the magnetic core according to Patent Document 1, the metal magnetic powder includes small particles having a small particle size within a predetermined range and large particles having a large particle size within a predetermined range. By adjusting the distance between the small particles and the distance between the small particles and the large particles, the magnetic core is provided with high withstand voltage and excellent DC superposition characteristics. In the magnetic core described in Patent Document 1, only the small particles are added and primary kneading is performed, and then large particles and the like are added for secondary kneading to adjust the distance between the small particles and the distance between the small particles and the large particles.

Prior Art Documents

Patent Documents

[0003]

Patent Document No. 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the magnetic core having the above configuration, the purpose is to improve the withstand voltage and DC superposition characteristics, and since the suppression of variations in magnetic characteristics is not the purpose, the measures regarding magnetic characteristics are not sufficient, and there is a problem that the magnetic characteristics may vary.

Means for Solving the Problems

[0005] One aspect of the present invention is an inductor comprising: a coil conductor having a winding portion around which a conductor wire is wound and a pair of lead portions drawn out from the winding portion; a base body containing magnetic powder and resin and enclosing the coil conductor; and external electrodes formed on the surface of the base body and connected to the lead portions, wherein the magnetic powder comprises a first magnetic powder and a second magnetic powder having a volume-based particle size distribution mode greater than the mode of the volume-based particle size distribution of the first magnetic powder, the particle size of D10 in the volume-based particle size distribution of the magnetic powder being greater than the mode of the volume-based particle size distribution of the first magnetic powder, and the magnetic powder having particle sizes greater than or equal to the particle size of D10 An inductor wherein, in a predetermined magnetic powder, the average interparticle distance obtained by averaging the interparticle distances of combinations of predetermined magnetic powders where the interparticle distance between one predetermined magnetic powder and another predetermined magnetic powder is less than the particle size of D10 is 3.4 μm or more, and in a second predetermined magnetic powder having a particle size greater than or equal to the particle size of the mode of the volume-based particle size distribution of the magnetic powder, the average interparticle distance obtained by averaging the interparticle distances of combinations of second predetermined magnetic powders where the interparticle distance between one second predetermined magnetic powder and another second predetermined magnetic powder is less than the particle size of D50 of the volume-based particle size distribution of the magnetic powder is 8.5 μm or more. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide an inductor in which the concentration of magnetic flux is mitigated and variations in magnetic properties due to differences in the arrangement of magnetic powder are suppressed. [Brief explanation of the drawing]

[0007] [Figure 1] This is a perspective view of the inductor according to this embodiment, viewed from the top side. [Figure 2] This is a perspective view of the inductor according to this embodiment, viewed from the bottom side. [Figure 3] This is a perspective view showing the internal structure of an inductor. [Figure 4] This is a plan view showing the internal structure of an inductor. [Figure 5] Figure 4 is a cross-sectional view along the VV line. [Figure 6]This is a cross-sectional view corresponding to the line VI-VI in Figure 4. [Figure 7] This is an overview diagram of the inductor manufacturing process. [Figure 8] This diagram schematically shows the structure of a magnetic core. [Figure 9] This figure shows an example of the volume-based particle size distribution of metallic magnetic particles in a magnetic core. [Figure 10] This is an explanatory diagram of the interparticle distance of a given magnetic powder. [Figure 11] This figure shows the relationship between the interparticle distance and the coating thickness. [Figure 12] This figure shows the simulation results of the magnetic flux density distribution of the magnetic core, specifically when the thickness of the large-particle coating is set to 1 μm. [Figure 13] This figure shows the simulation results of the magnetic flux density distribution of the magnetic core, specifically when the film thickness of the large particle coating is set to 0.0001 μm. [Figure 14] This figure shows a graph illustrating the relationship between the average interparticle distance and the coefficient of variation for cases where D10 or higher is shown in Table 1. [Figure 15] This figure shows a graph illustrating the relationship between the average interparticle distance and the coefficient of variation for cases where D50 or higher is shown in Table 1. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the drawings.

[0009] [Overall Inductor Configuration] Figure 1 is a perspective view of the inductor 1 according to this embodiment, viewed from the top surface 12. Figure 2 is a perspective view of the inductor 1 according to this embodiment, viewed from the bottom surface 10. The inductor 1 of this embodiment is configured as a surface-mounted electronic component. The inductor 1 of this embodiment includes a substantially rectangular parallelepiped-shaped element body 2 which is a form of a substantially hexahedral shape, a pair of external electrodes 4 provided on the surface of the element body 2, and an element protection layer 6 that covers the outer surface of the element body 2 excluding the range of the external electrodes 4 of the element body 2. Note that the element protection layer 6 may be omitted.

[0010] Hereinafter, in the element body 2, at the time of mounting, the first main surface facing the mounting substrate (not shown) is defined as the bottom surface 10, the second main surface facing the bottom surface 10 is referred to as the top surface 12, a pair of third main surfaces orthogonal to the bottom surface 10 are referred to as end surfaces 14, and a pair of fourth main surfaces orthogonal to the bottom surface 10 and the pair of end surfaces 14 are referred to as side surfaces 16.

[0011] As shown in FIG. 1, the distance from the bottom surface 10 to the top surface 12 is defined as the thickness T of the element body 2, the distance between the pair of side surfaces 16 is defined as the width W of the element body 2, and the distance between the pair of end surfaces 14 is defined as the length L of the element body 2. Also, 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 DW, and the direction of the length L is defined as the length direction DL. The nominal size of the inductor 1 as a finished product is, for example, a length L dimension of 2.0 mm, a width W dimension of 1.2 mm, and a thickness T dimension of 0.7 mm.

[0012] Hereinafter, the surface along the length direction DL and the thickness direction DT (the surface orthogonal to the width direction DW) is referred to as the LT surface, the surface along the thickness direction DT and the width direction DW (the surface orthogonal to the length direction DL) is referred to as the TW surface, and the surface along the length direction DL and the width direction DW (the surface orthogonal to the DT direction) is referred to as the LW surface. Also, the cross-sections of the inductor 1 along the LT surface, the TW surface, and the LW surface are referred to as the LT cross-section, the TW cross-section, and the LW cross-section, respectively.

[0013] FIG. 3 is a perspective view showing the internal structure of the inductor 1. FIG. 4 is a plan view showing the internal structure of the inductor 1. The element body 2 includes a coil conductor 20 and a substantially hexahedral magnetic core 30 in which the coil conductor 20 is embedded. The element body 2 is configured as a molded inductor in which the coil conductor 20 is encapsulated in the magnetic core 30. In this embodiment, the length L dimension of the element body 2 is 1.95 mm, the width W dimension is 1.15 mm, and the thickness T dimension is 0.65 mm. That is, the element body 2 is of a size of an inductor of 1 or less. Also, when viewed from the upper surface of the element body 2 (see FIG. 4), the dimension of the narrowest interval between the coil conductor 20 (that is, the winding portion 22) wound in a substantially rectangular shape and the end face 14 and the side face 16 of the element body 2 is called the side gap of the element body 2.

[0014] FIG. 5 is a cross-sectional view taken along line V-V of FIG. 4. In other words, FIG. 5 shows the TW cross-section of the inductor 1. The magnetic core 30 is a molded body compression-molded into a substantially hexahedral shape by pressurizing and heating a mixed powder obtained by mixing magnetic particles and resin while enclosing the coil conductor 20. In this embodiment, the mixed powder is manufactured by a single kneading in which the steps of adding magnetic particles and resin are each performed once. Here, the ratio of the resin is 2.0 wt% or more and 3.5 wt% or less based on the total weight of the magnetic particles and the resin.

[0015] The magnetic particles of this embodiment are formed of a soft magnetic material. The magnetic particles are 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 particles with the oxide film and the insulating film, the insulation resistance and the withstand voltage are increased. The magnetic particles have two types of particle sizes. However, the magnetic particles may have two or more types of particle sizes.

[0016] In the magnetic particles, as the metal particles, Fe-Si alloy powder, Fe-Si-Cr alloy powder, Fe-Ni-Al alloy powder, Fe-Cr-Al alloy powder, Fe-Si-Al alloy powder, Fe-Ni alloy powder, Fe-Ni-Mo alloy powder, and carbonyl iron powder are used. Also, the insulating film is formed of phosphoric acid, zinc phosphate, manganese phosphate, glass, phosphate glass, or resin. Further, the insulating film may be formed in multiple layers.

[0017] The resin contained in the mixed powder includes materials of multiple types of resins. In this embodiment, the resin contained in the mixed powder includes at least bisphenol A type epoxy resin and rubber-modified epoxy resin. This makes it possible to manufacture an inductor 1 in which both the strength and toughness of the base body 2 are improved. In addition, the resin contained in the mixed powder may also include phenol novolac type epoxy resin in addition to bisphenol A type epoxy resin and rubber-modified epoxy resin.

[0018] In this case, when the resin is composed of bisphenol A type epoxy resin and rubber-modified epoxy resin, the bisphenol A type epoxy resin is 50 wt% to 90 wt% and the rubber-modified epoxy resin is 10 wt% to 50 wt% based on the total weight of the resin contained in the mixed powder. In this case, by setting the ratio of bisphenol A type resin to rubber-modified epoxy resin in the resin contained in the mixed powder and molding a base body 2 with the coil conductor 20 sealed by a base body molding and curing process, an inductor 1 that achieves both strength and toughness can be manufactured.

[0019] On the other hand, when the resin is composed of bisphenol A type epoxy resin, rubber-modified epoxy resin, and phenol novolac type epoxy resin, the total weight of the resins contained in the mixed powder is such that the bisphenol A type epoxy resin is 40 wt% to 80 wt%, the rubber-modified epoxy resin is 10 wt% to 50 wt%, and the phenol novolac type epoxy resin is 1 wt% to 30 wt%. In this case, the phenol novolac type epoxy resin plays a role in the base body molding and curing process by adjusting the viscosity when the mixed powder is flowed to form the base body 2, and by adjusting the glass transition temperature of the base body 2, thereby improving the strength of the base body 2 when it reaches high temperatures. Therefore, by appropriately blending the phenol novolac type epoxy resin, it is possible to manufacture an inductor 1 that achieves both strength and toughness while improving the strength of the base body 2 against heating during molding.

[0020] In addition to epoxy resin, thermosetting resins such as phenolic resin, polyester resin, polyimide resin, and polyolefin resin may also be used as the resin material included in the mixed powder. Furthermore, phenoxy resins of bisphenol A, F, and S types are considered as alternatives to bisphenol A type epoxy resins. Furthermore, resins or rubbers that could be considered as alternatives to rubber-modified epoxy resins include urethane-modified, NBR (Acrylonitrile Butadiene Rubber)-modified, CTBN (Carboxyl Terminated Butadiene Acrylonitrile)-modified, and CTBN rubber.

[0021] Furthermore, resins that could be considered as alternatives to phenol novolac-type epoxy resins include, if limited to novolac-type resins, cresol, dicyclopentadiene, phenol aralkyl, biphenyl, naphthol, xylylene, triphenylmethane, and tetrakisphenolethane; and if not limited to novolac-type resins, naphthalene, biphenyl, and triazine can also be mentioned.

[0022] The coil conductor 20 has a wire 42 wound around it and is brought out to the surface of the base body 2. In this embodiment, the coil conductor 20 is alpha wound. Alpha winding refers to a state in which the coil conductor 20 is wound in a spiral shape in two stages such that the lead-out portions 23 at the beginning and end of the winding are located on the outer circumference. Note that the coil conductor 20 may be edgewise wound instead of alpha wound. In this case, the lead-out portions 23 of the coil conductor 20 are brought out from the winding portion 22 to the end face 14 of the base body 2.

[0023] As shown in Figures 3 and 4, the coil conductor 20 of this embodiment, which is an alpha winding, comprises a winding section 22 in which a conductor 42 is wound in a spiral shape along the winding shaft K in two stages, upper and lower, such that both ends of the conductor 42 are located on the outer circumference and connected to each other on the inner circumference; a pair of lead-out sections 23 drawn out from the winding section 22; and a pair of external electrode connection sections 24 connected to each of the lead-out sections 23, which are conductor sections for connecting to the external electrode 4. The winding section 22 includes two winding regions 22a and 22b (see Figure 3) that overlap along the winding shaft K. The conductors of winding region 22a and winding region 22b are connected to each other in a part of their inner circumference.

[0024] The winding portion 22 is approximately rectangular in plan view (see Figure 4) as viewed from the direction of the winding shaft K. The coil conductor 20 is embedded in the base body 2 such that the winding shaft K is aligned with the thickness direction DT of the base body 2, and that in plan view as viewed from the direction of the winding shaft K, each side of the approximately rectangular winding portion 22 aligns with each side of the approximately rectangular base body 2 (for example, parallel to it). The dimensions of the winding portion 22 are, for example, a thickness T dimension (height dimension) of 0.4 mm, an outer diameter in the width direction DW of 1.17 mm, and an inner diameter of 0.55 mm.

[0025] The lead-out portion 23 is pulled out from the winding portion 22. The lead-out portion 23 is electrically connected to the external electrode 4 via external electrode connection portions 24 that are pulled out and exposed to each of the pair of end faces 14.

[0026] Figure 6 is a cross-sectional view corresponding to the line VI-VI in Figure 4. In Figure 6, a cross-section perpendicular to the extending direction of the external electrode connection portion 24 at the connection portion between the lead portion 23 and the external electrode 4 is shown. The conductor 42 constituting the coil conductor 20 is composed of a conductor 43 and a coating layer 45 formed on the surface of the conductor 43. The conductor 42 is a flat wire with a rectangular cross-section. Using a flat wire makes it easy to wind the conductor 42 without gaps. The conductor 43 is a strip-shaped conductor with a rectangular cross-section. Copper is preferred as the material for the conductor 43, but instead of a copper conductor 43, a copper-clad aluminum conductor 42 or an aluminum conductor 42 with an insulating coating formed on its surface may be used.

[0027] The coating layer 45 is composed of an insulating layer formed on the surface of the conductor 43 and a fusion layer formed on the surface of the insulating layer. The insulating layer ensures the insulation of the conductor 42. The insulating layer is made of, for example, polyimideamide resin. The thickness of the insulating layer is, for example, 4 μm. While polyimideamide resin is preferable for the insulating layer, polyurethane resin, polyester resin, or epoxy resin may be used instead.

[0028] The fusion layer fixes the conductors 42 together. That is, the fusion layer adheres the overlapping conductors 42 in the winding portion 22. The fusion layer is made of, for example, a polyamide resin. The thickness of the fusion layer is preferably 1 μm to 25 μm, more preferably 2 μm to 25 μm, and even more preferably 2 μm to 4 μm.

[0029] The pair of external electrodes 4 are so-called L-shaped electrodes (see Figure 3), consisting of L-shaped members extending from each end face 14 of the base body 2 to the bottom face 10. Each external electrode 4 is connected to the external electrode connection portion 24 of the coil conductor 20 at the end face 14, and the portion 4A extending to the bottom face 10 (see Figure 2) is electrically connected to the wiring of the circuit board by appropriate mounting means such as soldering.

[0030] A pair of external electrodes 4 provided on the surface of the base body 2 are connected to a conductor 43 that is exposed after the coating layer of the external electrode connection portion 24 is removed. The width W dimension at the bottom surface 10 of the base body 2 of the external electrode 4 is between 0.88 mm and 1.12 mm, and the length L dimension is between 0.3 mm and 0.7 mm. The thickness DT dimension at the end surface 14 of the base body 2 of the external electrode 4 is approximately between 0.43 mm and 0.60 mm.

[0031] The thickness of the external electrode 4 was measured as follows: In the inductor 1, the four corners of the top surface 12 were connected by their respective diagonals, and the points where the diagonals intersect were defined as the intersection points. The body 2 was cut parallel to the side surface 16 so as to intersect with these intersection points, and in the cross section LT that intersects with the intersection points, the film thickness at points that divide the length DL of the external electrode 4 formed on the bottom surface 10 of the body 2 into four equal parts was measured using a microscope at 1000x magnification. The average of the film thicknesses measured at the four equally divided points was determined as the measured value. This measured value was then obtained for 10 different inductors 1, and the average of these measured values ​​was taken as the thickness of the external electrode 4. A VHX-7000 microscope manufactured by Keyence Corporation was used.

[0032] As shown in Figure 6, the external electrode 4 has a plated conductor 50. In this embodiment, the plated conductor 50 has a copper plating layer 51 as a plating layer with the same metallic component as the conductor 43. The copper plating layer 51 is a plating layer that plates the surface of the conductor 43. The copper plating layer 51 and the conductor 43 are connected.

[0033] A Ni plating layer 52 is formed on the copper plating layer 51. A Sn plating layer 53 is formed on the Ni plating layer 52. The plated conductor 50 of this embodiment has a copper plating layer 51, a Ni plating layer 52, and a Sn plating layer 53. However, the Sn plating layer 53 may be omitted in the plated conductor 50. Furthermore, the Ni plating layer 52 may also be omitted in the plated conductor 50.

[0034] The copper plating layer 51 may be formed in a portion of the lead portion 23 of the coil conductor 20, spanning both the lead portion 23 of the coil conductor 20 and the base body 2. Instead of the copper plating layer 51, a layer of copper may be formed by sputtering, conductive resin, or metal plate. Alternatively, aluminum, silver, palladium, etc., may be used instead of copper.

[0035] Furthermore, although the external electrode 4 has been described as having an L-shaped electrode configuration, instead of an L-shaped electrode, a total of five electrodes may be made using resin on the end face 14 and the four surrounding faces of the base body 2, namely the end face 14, the bottom face 10, the top face 12, and the pair of side faces 16. Of these, the top face 12, the end face 14, and the pair of side faces 16 may be coated with an insulator to form the bottom electrode. Furthermore, a portion of the lead-out portion 23 of the coil conductor 20 may be covered with resin, and a copper plating layer may be applied on top of it. Also, the external electrode 4 may be a five-sided electrode or a bottom-sided electrode.

[0036] As shown in Figure 5, a protective layer 6 is formed on the surface of the substrate 2. The protective layer 6 covers the outer surface of the substrate, excluding the area of ​​the external electrode 4. The protective layer 6 contains resin and filler. The thickness of the protective layer 6 is 10 μm or more and 30 μm or less, preferably 10 μm or more and 20 μm or less, and more preferably 15 μm. If the thickness of the protective layer 6 is 10 μm or more, even if metal magnetic powder protruding from the substrate 2 is exposed from the protective layer 6, it is possible to prevent plating from forming on the surface of this exposed metal magnetic powder. Also, if the thickness of the protective layer 6 is 30 μm or less, it is possible to prevent the substrate 2 from becoming larger than a predetermined size.

[0037] The resin of the base protective layer 6 contains epoxy resin as the main component. The resin of the base protective layer 6 also contains novolac resin to enhance heat resistance. Furthermore, phenoxy resin is added to the resin of the base protective layer 6 to impart toughness, with a phenoxy resin ratio of 20% or more. Adding carbon black pigment to the resin of the base protective layer 6 improves processability when forming the external electrode formation region. However, the resin of the base protective layer 6 does not necessarily need to contain pigment. A solvent is added to the resin of the base protective layer 6 to adjust its drying properties.

[0038] Inductor 1 with this configuration can improve DC superposition characteristics by using soft magnetic material for the magnetic particles, and is therefore used as an electronic component in electrical circuits where 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, and medical and industrial machinery. However, the applications of inductor 1 are not limited to these, and it can also be used in tuning circuits, filter circuits, and rectifier / smoothing circuits, for example.

[0039] [Overview of the Inductor Manufacturing Process] Figure 7 is a schematic diagram of the manufacturing process for inductor 1. As shown in the figure, the manufacturing process for the inductor 1 includes a coil conductor formation process, a pre-molded body formation process, a base body molding and hardening process, a base body grinding process, and an external electrode formation process.

[0040] The coil conductor formation process is a process of forming a coil conductor 20 from a flat rectangular wire made of copper as the conductor. In this embodiment, in this process, the coil conductor 20 is formed in a shape having the aforementioned winding portion 22, lead portion 23, and external electrode connection portion 24 by winding the conductor using a winding method called "alpha winding". Alpha winding refers to a state in which the conductor, which functions as a conductor, is wound in a spiral shape in two stages such that the lead portions 23 at the beginning and end of the winding are located on the outer circumference. The number of turns of the coil conductor 20 is not particularly limited, but the number of turns is determined so that the desired inductance is obtained.

[0041] The pre-molded body formation process is the process of forming pre-molded bodies, which are called tablets. The pre-molded body is formed by pressurizing the mixed powder material of the base body 2 to create a solid that is easy to handle. In this embodiment, two types of tablets are formed: a first tablet of an appropriate shape (e.g., E-type) having a groove into which the coil conductor 20 fits (i.e., the first core portion 30a of the manufactured product (see Figure 5)), and a second tablet of an appropriate shape (e.g., I-type or plate-shaped) covering the groove of the first tablet (i.e., the second core portion 30b of the manufactured product (see Figure 5)).

[0042] The base body molding and hardening process involves setting the first tablet, the coil conductor 20, and the second tablet in a molding die, applying heat, and pressing them in the overlapping direction of the first and second tablets to harden them, thereby integrating the first tablet, the coil conductor 20, and the second tablet. This forms a base body 2 in which the coil conductor 20 is enclosed within the magnetic core 30.

[0043] In the base material grinding process, abrasive grains are applied to the side surface of the molded body obtained in the base material molding and hardening process, so that the side surface is ground down until the width W reaches a predetermined width.

[0044] This process yields a base body 2 with the width W of the molded body downsized to a predetermined width. This downsizing reduces the distance (also called the side gap) between the coil conductor 20 inside the base body 2 and the side surface of the base body 2, thereby increasing the radial occupancy rate of the coil in the winding portion 22 of the coil conductor 20.

[0045] Furthermore, since the molded body obtained by compression molding is ground to a predetermined size to obtain the base body 2, dimensional variations in the base body 2 can be reduced compared to the case where the base body 2 is controlled to a predetermined size by compression molding alone. In the base body grinding process, polishing (for example, barrel polishing) may be performed to chamfer the corners created by grinding the sides of the base body 2.

[0046] The external electrode formation step is a step of forming an external electrode 4 on the base body 2, and includes a base body protective layer formation step, a surface treatment step, and a plating layer formation step.

[0047] The base body protective layer formation process involves coating the entire surface of the base body 2 with an insulating resin. The base body protective layer 6 is formed by spraying the protective material onto the base body 2 using a rotary spray device. The method for forming the base body protective layer 6 may also be by spraying or immersion.

[0048] The surface treatment process involves modifying the surface of the planned electrode areas on the surface of the magnetic core 30 by irradiating these areas with laser light. Here, the planned electrode areas refer to the areas on the surface of the magnetic core 30 where the external electrodes 4 should be formed, and include the areas where the external electrode connection parts 24 are exposed. Specifically, by irradiating with laser light, the protective layer 6 on the surface of the base body 2 and the coating layer of the external electrode connection parts 24 of the coil conductor 20 are removed in the area of ​​the planned electrode areas, as well as the resin on the surface of the magnetic core 30 and the insulating film on the surface of the magnetic particles exposed from the magnetic core 30. As a result, the area of ​​exposed metal of the magnetic particles per unit area of ​​the surface of the magnetic core 30 is larger in the area of ​​the planned electrode areas compared to other parts of the surface of the magnetic core 30. In addition, the metallic magnetic powder of the base body 2 in the laser-irradiated area comes into contact with adjacent magnetic powders. After irradiation with laser light, a cleaning process (e.g., etching) may be performed to clean the surface of the planned electrode areas.

[0049] In the plating layer formation process, copper is barrel-plated onto the surface of the magnetic core 30 to form a copper plating layer at the electrode location where the laser light is to be irradiated. In addition, in this embodiment, the plating layer is formed by further providing a Ni plating layer and a Sn plating layer on top of the copper plating layer.

[0050] The details of the inductor 1 in this embodiment will be further described below.

[0051] [Inductor detailed configuration] As shown in Figure 5, the magnetic core 30 of the inductor 1 in this embodiment has a first core portion 30a on the bottom surface 10 side and a second core portion 30b on the top surface 12 side. The first core portion 30a has a plate-shaped portion 30a1 that forms one end in the winding axis direction. In other words, the first core portion 30a has a plate-shaped portion 30a1 that forms the bottom surface 10. A central core portion 30a2 is provided in the center of the plate-shaped portion 30a1, protruding toward the upper surface 12. Furthermore, an outer peripheral portion 30a3 is provided on the outer periphery of the plate-shaped portion 30a1, protruding toward the upper surface 12. The outer peripheral portion 30a3 forms the end surface 14 and the side surface 16. A coil conductor 20 is arranged between the central core portion 30a2 and the outer peripheral portion 30a3 of the first core portion 30a.

[0052] The second core portion 30b is formed in a plate shape located at the other end in the winding axis direction. In other words, the second core portion 30b is formed in a plate shape that constitutes the upper surface 12. The second core portion 30b is provided so as to cover the first core portion 30a and the coil conductor 20.

[0053] Figure 8 is a schematic diagram showing the structure of the magnetic core 30. Figure 9 is a diagram showing an example of the volume-based particle size distribution of the metallic magnetic particles 32 in the magnetic core 30. The magnetic core 30 consists of a resin 31 and metallic magnetic particles (magnetic powder, metallic magnetic powder) 32. In Figure 8, the resin 31 is shown with a dot pattern. The filling rate of the metallic magnetic particles 32 in the magnetic core 30, that is, the ratio of the total volume of metallic magnetic particles 32 to the total volume of resin 31 and metallic magnetic particles 32, is 80% or more.

[0054] In this embodiment, the metallic magnetic particles 32 include small particles (first magnetic powder) 32a having a mode of a predetermined volume-based particle size distribution, and large particles (second magnetic powder) 32b having a mode of a volume-based particle size distribution greater than the mode of the volume-based particle size distribution of the small particles 32a. Hereinafter, the mode λ32a of the volume-based particle size distribution of the small particles 32a (see Figure 9) will also be simply referred to as the mode λ32a. Similarly, the mode λ32b of the volume-based particle size distribution of the large particles 32b (see Figure 9) will also be simply referred to as the mode λ32b. The mode λ32a of the volume-based particle size distribution for small particles 32a is between 1 μm and 5 μm. The mode λ32b of the volume-based particle size distribution for large particles 32b is between 18 μm and 28 μm.

[0055] In the metallic magnetic particles 32, small particles 32a and large particles 32b are mixed together, and at least two peaks appear in the volume-based particle size distribution of the metallic magnetic particles 32. Generally, the smallest peak among the multiple peaks corresponds to the mode λ32a of the small particles 32a. Also, the largest peak among the multiple peaks corresponds to the mode λ32b of the large particles 32b.

[0056] Figure 10 is an explanatory diagram of the interparticle distances La and Lb of the predetermined magnetic powder 61. Figure 10 corresponds to the diagram in Figure 8 which shows only the predetermined magnetic powder 61 among the metallic magnetic particles 32. In this embodiment, the particle size λD10 of the volume-based particle size distribution D10 of the metallic magnetic particles 32 is larger than the mode λ32a of the small particles 32a (see Figure 9). Furthermore, in this embodiment, among the metallic magnetic particles 32, in a predetermined magnetic powder 61 having a particle size λD10 or larger, the average interparticle distance AL, which is the average of the interparticle distances La and Lb of combinations of predetermined magnetic powders 61 where the interparticle distances La and Lb between one predetermined magnetic powder 61 and another predetermined magnetic powder 61 are less than the particle size λD10 of D10, is 3.4 μm or larger. Here, the metallic magnetic particles 32 have metal particles 71 (see Figure 10), an oxide film 72 covering the surface of the metal particles 71 (see Figure 10), and an insulating film 73 covering the surface of the oxide film 72 (see Figure 10). The interparticle distances La and Lb of the predetermined magnetic powder 61 refer to the distance between the metal particles 71 of the predetermined magnetic powder 61.

[0057] By calculating the average interparticle distance AL using only metallic magnetic particles 32 with a particle size λD10 or larger, it becomes easier to target only the particles that have a significant impact on magnetic properties. Furthermore, by excluding metallic magnetic particles 32 with a particle size less than λD10, it is possible to reliably capture particles while introducing a concept similar to the nearest neighbor distance into the value of the average interparticle distance AL.

[0058] The average inter-particle distance AL is calculated by analyzing observation images of the cross-section of the inductor 1. Specifically, for example, the inductor 1 is cut at the center of its length DL, passing through the winding axis K of the winding portion 22 of the coil conductor 20, and the WT cross-section is observed at five locations using a Scanning Electron Microscope (SEM). Each of these five SEM observation images is taken with a field of view of 500 μm square and at a magnification of 1000x. These SEM observation images are loaded into a predetermined image software and analyzed to calculate the average inter-particle distance AL. An example of the predetermined image software is WinROOF2021 manufactured by Mitani Corporation.

[0059] Figures 8 and 10 will be used to explain the specific method for calculating the average interparticle distance AL. In Figure 8, metal magnetic particles 32 with a particle size of less than λD10 are shown as black circles. In addition, predetermined magnetic powder 61, which is metal magnetic particles 32 with a particle size of λD10 or more, is shown as white circles.

[0060] As shown in Figure 10, one predetermined magnetic powder 61 is selected from among the predetermined magnetic powders 61. For this predetermined magnetic powder 61, another predetermined magnetic powder 61 is identified that is located at a distance of less than λD10 from the surface of the first predetermined magnetic powder 61. More precisely, for this predetermined magnetic powder 61, another predetermined magnetic powder 61 is identified in which the metal particles 71 are located at a distance of less than λD10 from the surface of the first predetermined magnetic powder 61. The same applies hereafter. In Figure 10, the distance of λD10 from the surface of the first predetermined magnetic powder 61 is shown by the dashed line C61. Therefore, the predetermined magnetic powder 61 that intersects the dashed line C61 is the other predetermined magnetic powder 61 located at a distance of less than λD10 from the surface of the first predetermined magnetic powder 61. Note that the interparticle distance Lb between the predetermined magnetic powder 61 that does not intersect the dashed line C61 and the first predetermined magnetic powder 61 is λD10 or greater.

[0061] The interparticle distance La from one predetermined magnetic powder 61 to all other predetermined magnetic powders 61 that intersect the dashed line C61 is determined. In Figure 10, five other predetermined magnetic powders 61 are identified for one predetermined magnetic powder 61. Therefore, five interparticle distances La are obtained.

[0062] Next, one of the predetermined magnetic powders 61 that has not been selected is selected as a new predetermined magnetic powder 61. That is, one of the predetermined magnetic powders 61 that has not been selected as a new predetermined magnetic powder 61 is selected. Similarly, for this new predetermined magnetic powder 61, other predetermined magnetic powders 61 located at a distance of less than λD10 from the surface of the first predetermined magnetic powder 61 are identified. Then, for the other predetermined magnetic powders 61 located at a distance of less than λD10 from the surface of the new predetermined magnetic powder 61, the interparticle distance La between the first predetermined magnetic powder 61 and the other predetermined magnetic powders 61 is determined.

[0063] In this way, for all predetermined magnetic powders 61 within the SEM's imaging field of view, the interparticle distance La is determined between each predetermined magnetic powder 61 and other predetermined magnetic powders 61 located at a distance of less than λD10 from the surface of that predetermined magnetic powder 61. Assuming that there are N determined interparticle distances La, and by adding a number indicating the order in which they were determined to the interparticle distances La, the average interparticle distance AL is calculated as AL = (La1 + La2 + La3 + ... + LaN) / N. In the magnetic core 30 of this embodiment, this average interparticle distance AL is 3.4 μm or more. Note that the average interparticle distance AL is the value between each predetermined magnetic powder 61 and other predetermined magnetic powders 61 located at a distance of less than λD10 from the surface of one predetermined magnetic powder 61, and is therefore less than or equal to the particle size λD10.

[0064] Furthermore, in this embodiment, in a second predetermined magnetic powder 62 (see Figure 8) having a particle size greater than or equal to the particle size of the mode of the volume-based particle size distribution of the metallic magnetic particles 32, the average interparticle distance obtained by averaging the interparticle distances Lc of combinations of second predetermined magnetic powders 62 such that the interparticle distance Lc (see Figure 11) between one second predetermined magnetic powder 62 and another second predetermined magnetic powder 62 is less than the particle size λD50 (see Figure 9) of D50 in the volume-based particle size distribution of the metallic magnetic particles 32 is 8.5 μm or more.

[0065] In this inductor 1, when the interparticle distances La, Lb, and Lc of the metal magnetic particles 32 are close, the influence of particle arrangement becomes larger, and the coefficient of variation of the magnetic properties increases. In particular, larger particle sizes have a greater influence on the magnetic properties than smaller particle sizes. For example, large particles 32b concentrate the magnetic flux, so their influence is greater. Therefore, in this embodiment, the interparticle distances La and Lc of the predetermined magnetic powder 61 with a particle size λD10 or larger that is not too small, and the second predetermined magnetic powder 62 with a relatively large particle size, are adjusted so that they do not become too close. Therefore, in this embodiment, the concentration of magnetic flux is mitigated, and the inductor 1 can be made in which variations in magnetic properties due to differences in the arrangement of the metal magnetic particles 32 are suppressed.

[0066] Figure 11 shows the relationship between the interparticle distance Lc and the film thickness λc of the coating 74. The inventors of this invention have found that in a two-particle arrangement of metallic magnetic particles 32 containing small particles 32a and large particles 32b, the interparticle distance Lc can be adjusted by adjusting the film thickness λc of the coating 74 covering the metal particle 71 portion of the large particle 32b, thereby suppressing variations in magnetic properties. In other words, the metal particles 71 of the large particle 32b are unlikely to approach each other beyond the film thickness λc of the coating 74 covering the metal particle 71. That is, the metal particles 71 are unlikely to approach each other beyond the film thickness λc of two adjacent particles. Therefore, by adjusting the film thickness λc of the coating 74 covering the large particle 32b, it is possible to suppress the interparticle distance Lc from becoming too small, and to reduce the difference in magnetic properties due to the arrangement of the large particles 32b. The coating 74 in this embodiment is composed of an oxide film 72 covering the surface of the metal particle 71 and an insulating film 73 covering the surface of the oxide film 72.

[0067] Figure 12 shows the simulation results of the magnetic flux density distribution of the magnetic core 30, when the film thickness λc of the coating 74 on the large particle 32b is set to 1 μm. Figure 13 shows the simulation results of the magnetic flux density distribution of the magnetic core 30, when the film thickness λc of the coating 74 on the large particle 32b is set to 0.0001 μm. In Figures 12 and 13, the more densely packed the points are, the greater the magnetic flux density.

[0068] As shown in Figure 13, when the film thickness λc of the coating 74 on the large particle 32b is set to 0.0001 μm, it is confirmed that the magnetic flux density distribution ranges from large to small values. In particular, it was confirmed that the large values ​​extend in streaks vertically, indicating magnetic flux concentration. In contrast, as shown in Figure 12, when the film thickness λc of the coating 74 on the large particle 32b is set to 1 μm, it is confirmed that the magnetic flux density distribution is almost the same value across the entire region. That is, it was confirmed that by setting the film thickness λc of the coating 74 on the large particle 32b to 1 μm, the variation in magnetic properties, specifically magnetic flux density, is suppressed.

[0069] Next, Table 1 shows the average interparticle distances for particles with particle sizes greater than or equal to D10 and D50 in the volume-based particle size distribution when the film thickness of the coating 74 on the large particle 32b is varied.

[0070] [Table 1]

[0071] Figure 14 is a graph showing the relationship between the average interparticle distance and the coefficient of variation for the case of D10 or higher in Table 1. Figure 15 is a graph showing the relationship between the average interparticle distance and the coefficient of variation for the case of D50 or higher in Table 1. In Figures 14 and 15, the horizontal axis represents the average interparticle distance. The vertical axis represents the initial permeability in the upper graph and the DC superposition characteristics in the lower graph. The graphs in Figures 14 and 15 illustrate approximate lines based on the spline method. As shown in Figures 14 and 15, it can be observed that as the average interparticle distance increases, the coefficients of variation for both the initial permeability and the DC superposition characteristics tend to decrease. In particular, Figure 14 shows that each coefficient of variation increases after reaching its minimum value. This is understood to be because an increase in the average interparticle distance means that the film thickness λc of the coating 74 becomes thicker, and the film thickness λc of the coating 74 becomes too thick, making it impossible to obtain sufficient inductance.

[0072] As described above, the inductor 1 comprises a coil conductor 20 having a winding portion 22 around which a conductor 42 is wound and a pair of lead portions 23 drawn out from the winding portion 22, a base body 2 containing metallic magnetic particles 32 and resin 31 and enclosing the coil conductor 20, and external electrodes 4 formed on the surface of the base body 2 and connected to the lead portions 23. In this inductor 1, the metallic magnetic particles 32 include small particles 32a and large particles 32b whose volume-based particle size distribution has a mode λ32b that is larger than the mode λ32a of the volume-based particle size distribution of the small particles 32a. The particle size λD10 of the volume-based particle size distribution D10 of the metallic magnetic particles 32 is larger than the mode λ32a of the volume-based particle size distribution of the small particles 32a. In a predetermined magnetic powder 61 of the metallic magnetic particles 32 having a particle size λD10 or larger, the interparticle distance La, Lc between one predetermined magnetic powder 61 and another predetermined magnetic powder 61 is equal to the particle size λD The average interparticle distance AL, obtained by averaging the interparticle distances La of combinations of predetermined magnetic powders 61 where the interparticle distance is less than 10, is 3.4 μm or more. Among the metallic magnetic particles 32, for the second predetermined magnetic powder 62 having a particle size equal to or greater than the mode of the volume-based particle size distribution of the metallic magnetic particles 32, the interparticle distance Lc between one second predetermined magnetic powder 62 and another second predetermined magnetic powder 62 is 8.5 μm or more. Therefore, in the metallic magnetic particles 32, the average interparticle distance AL between predetermined magnetic powders 61 that are not too small, such as having a particle size of D10 λD10 or larger, is 3.4 μm or more, and the particle size of D10 λD10 or less. In the metallic magnetic particles 32, the average interparticle distance between relatively large second predetermined magnetic powders 62 that are larger than or equal to the particle size of the mode of the volume-based particle size distribution of the metallic magnetic particles 32 is 8.5 μm or more, and the particle size of D50 λD50 or less. Therefore, it is possible to provide an inductor 1 in which the concentration of magnetic flux is mitigated and variations in magnetic properties due to differences in the arrangement of metallic magnetic particles 32 are suppressed.

[0073] Furthermore, in the inductor 1 of this embodiment, the mode λ32a of the volume-based particle size distribution of small particles 32a is 1 μm or more and 5 μm or less, and the mode λ32b of the volume-based particle size distribution of large particles 32b is 18 μm or more and 28 μm or less. With this configuration, by combining large and small metallic magnetic particles 32 whose mode values ​​in the volume-based particle size distribution differ by approximately 13 μm or more, it becomes easier to highly pack the metallic magnetic particles 32 in the base material 2, and the inductor 1 can be made smaller relative to the required characteristics of the inductor 1.

[0074] Furthermore, in the inductor 1 of this embodiment, the filling rate of the metal magnetic particles 32 in the base body 2 is 80% or more. With this configuration, by ensuring a sufficient filling ratio, it is possible to prevent the inductance of inductor 1 from becoming extremely low.

[0075] Furthermore, in the inductor 1 of this embodiment, the magnetic powder is metallic magnetic particles 32. This configuration makes it easier to manufacture an inductor 1 with the desired characteristics compared to the case where the magnetic powder is not metallic magnetic particles 32.

[0076] Furthermore, in the inductor 1 of this embodiment, the interparticle distances La and Lc of the metal magnetic particles 32 are adjusted by adjusting the film thickness λc of the coating 74. With this configuration, by adjusting the film thickness λc of the coating 74, the interparticle distance Lc of the large particles 32b with a high mode λ32b in the volume-based particle size distribution can be adjusted. Therefore, when metallic magnetic particles 32 of different particle sizes are included, variations in magnetic properties can be reduced while suppressing the number of mixing cycles.

[0077] [Other embodiments] In the embodiments described above, a configuration in which the magnetic powder is metallic magnetic particles 32 was described, but the magnetic powder does not have to be metallic magnetic particles.

[0078] All embodiments and modifications described above illustrate one aspect of the present invention and can be arbitrarily modified and applied without departing from the spirit of the invention. Furthermore, unless otherwise specified, the horizontal and vertical directions, various numerical values, shapes, and materials in the embodiments described above include a range that produces the same effects as those directions, numerical values, shapes, and materials (the so-called equivalence range).

[0079] [Configurations supported by the above embodiment] The embodiments described above support the following configurations.

[0080] (Configuration 1) An inductor comprising: a coil conductor having a winding portion around which a conductor wire is wound and a pair of lead portions drawn out from the winding portion; a base body containing magnetic powder and resin and enclosing the coil conductor; and external electrodes formed on the surface of the base body and connected to the lead portions, wherein the magnetic powder comprises a first magnetic powder and a second magnetic powder having a volume-based particle size distribution mode greater than the mode of the volume-based particle size distribution of the first magnetic powder, the particle size of D10 in the volume-based particle size distribution of the magnetic powder being greater than the mode of the volume-based particle size distribution of the first magnetic powder, and the magnetic powder having a particle size greater than or equal to the particle size of D10. An inductor wherein, in a predetermined magnetic powder, the average interparticle distance obtained by averaging the interparticle distances of combinations of predetermined magnetic powders where the interparticle distance between one predetermined magnetic powder and another predetermined magnetic powder is less than the particle size of D10 is 3.4 μm or more, and in a second predetermined magnetic powder having a particle size greater than or equal to the particle size of the mode of the volume-based particle size distribution of the magnetic powder, the average interparticle distance obtained by averaging the interparticle distances of combinations of second predetermined magnetic powders where the interparticle distance between one second predetermined magnetic powder and another second predetermined magnetic powder is less than the particle size of D50 of the volume-based particle size distribution of the magnetic powder is 8.5 μm or more. In the inductor of configuration 1, the average interparticle distance between predetermined magnetic powder particles that are not too small (i.e., larger than or equal to the particle size of D10) is 3.4 μm or more and less than or equal to the particle size of D10. Furthermore, the average interparticle distance between relatively large second predetermined magnetic powder particles that are larger than or equal to the particle size of the mode of the volume-based particle size distribution of the magnetic powder is 8.5 μm or more and less than or equal to the particle size of D50. Therefore, it is possible to provide an inductor in which magnetic flux concentration is mitigated and variations in magnetic properties due to differences in the arrangement of magnetic powder are suppressed.

[0081] (Configuration 2) The inductor according to Configuration 1, wherein the mode of the volume-based particle size distribution of the first magnetic powder is 1 μm or more and 5 μm or less, and the mode of the volume-based particle size distribution of the second magnetic powder is 18 μm or more and 28 μm or less. According to the inductor of configuration 2, by combining large and small magnetic powders whose mode values ​​in the volume-based particle size distribution differ by approximately 13 μm or more, it is possible to easily achieve high density of magnetic powder in the substrate, and the inductor can be made smaller relative to the required inductor characteristics.

[0082] (Configuration 3) The inductor according to Configuration 1 or 2, wherein the filling rate of the magnetic powder in the base material is 80% or more. With the inductor of configuration 3, by ensuring a sufficient filling ratio, it is possible to suppress the inductance of the inductor from becoming extremely low.

[0083] (Configuration 4) The inductor according to any one of Configurations 1 to 3, wherein the magnetic powder is a metallic magnetic powder. With the inductor of configuration 4, it is easier to manufacture an inductor with the desired characteristics compared to the case where the magnetic powder is not metallic magnetic powder. [Explanation of symbols]

[0084] 1...Inductor, 2...Base body, 4...External electrode, 4A...Part, 6...Base body protective layer, 10...Bottom surface, 12...Top surface, 14...End face, 16...Side, 20...Coil conductor, 22...Winding section, 22a...Winding region, 22b...Winding region, 23...Outlet section, 24...External electrode connection section, 25...End, 28...End, 30...Magnetic core, 30a...First core section, 30a1...Plate-shaped section, 30a2...Middle core section, 30a3...Outer periphery section, 30b...Second core section, 31...Resin, 32...Metal magnetic particles (magnetic powder) , metal magnetic powder), 32a... small particles (first magnetic powder), 32b... large particles (second magnetic powder), 42... wire, 43... conductor, 45... coating layer, 50... plated conductor, 51... copper plating layer, 52... Ni plating layer, 53... Sn plating layer, 61... specified magnetic powder, 62... second specified magnetic powder, 71... metal particles, 72... oxide film, 73... insulating film, 74... coating, C61... dashed line, K... winding shaft, La... interparticle distance, Lb... interparticle distance, Lc... interparticle distance, Ni... copper plating layer, λc... film thickness.

Claims

1. An inductor comprising: a coil conductor having a winding portion around which a conductor wire is wound and a pair of lead portions drawn out from the winding portion; a base body containing magnetic powder and resin and enclosing the coil conductor; and external electrodes formed on the surface of the base body and connected to the lead portions, The magnetic powder comprises a first magnetic powder and a second magnetic powder having a volume-based particle size distribution mode greater than the mode of the volume-based particle size distribution of the first magnetic powder. The particle size of D10 in the volume-based particle size distribution of the magnetic powder is greater than the mode of the volume-based particle size distribution of the first magnetic powder. Among the magnetic powders, a predetermined magnetic powder having a particle size equal to or greater than the particle size of D10, wherein the average interparticle distance obtained by averaging the interparticle distances of combinations of predetermined magnetic powders where the interparticle distance between one predetermined magnetic powder and another predetermined magnetic powder is less than the particle size of D10 is 3.4 μm or more. In the magnetic powders, a second predetermined magnetic powder having a particle size equal to or greater than the particle size of the mode of the volume-based particle size distribution of the magnetic powder, wherein the interparticle distance between one second predetermined magnetic powder and another second predetermined magnetic powder is less than the particle size of D50 in the volume-based particle size distribution of the magnetic powder, and the average interparticle distance obtained by averaging the interparticle distances of such combinations of second predetermined magnetic powders is 8.5 μm or more. Inductor.

2. The mode of the volume-based particle size distribution of the first magnetic powder is 1 μm or more and 5 μm or less. The mode of the volume-based particle size distribution of the second magnetic powder is 18 μm or more and 28 μm or less. The inductor according to claim 1.

3. The filling rate of the magnetic powder in the aforementioned substrate is 80% or more. The inductor according to claim 1 or 2.

4. The magnetic powder is a metallic magnetic powder. The inductor according to claim 1 or 2.

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