Inductor and manufacturing method for the inductor

Abstract

To improve a magnetic saturation allowable current by suppressing the generation of a local magnetic saturation in an element body in an inductor in which a coil conductor is contained in an element body made of a metal magnetic particle and a resin.SOLUTION: An inductor includes an element body having a core including first and second metal magnetic particles having different average particle diameters and a resin, and a coil conductor having a winding part embedded in the core. The element body has two main surfaces that intersect a central axis of the winding part and face each other. In a cross-section of the element body parallel to the central axis of the winding part, a first number density, which is the number per unit length of the first metal magnetic particles along a conductor boundary line, which is a boundary line between the core and the winding portion, of which the distance from the conductor boundary line is equal to or less than a predetermined distance, is lower than the second number density, which is the number per unit length of the first metal magnetic particles along the surface boundary line, which is a boundary line indicating the position of at least one main surface of the element body, of which the distance from the surface boundary line is equal to or less than the predetermined distance.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an inductor and a method for manufacturing an inductor. [Background technology]

[0002] Patent Document 1 discloses composite magnetic particles for use in electronic components such as inductors. The composite magnetic particles include first metal magnetic particles coated with a first resin portion made of a first resin material, and second metal magnetic particles having a smaller diameter than the first metal magnetic particles and bound to the first metal magnetic particles via a second resin portion made of a second resin material having a larger molecular weight than the first resin material. Patent Document 1 states that the composite magnetic particles configured as described above are suppressed from agglomerating when mixed with a resin composition. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-161753 Summary of the Invention [Problem to be solved by the invention]

[0004] In an inductor that contains a coil conductor in a magnetic core body made of metal magnetic particles and resin, the non-uniformity of the magnetic properties within the body can be reduced by suppressing the aggregation of the metal magnetic particles when they are mixed into the resin. However, even if the magnetic properties within the body are uniform, if there is a bias in the magnetic field distribution generated within the body when current is passed through the coil conductor, localized magnetic saturation can occur within the body, reducing the magnetic saturation allowable current of the inductor.

[0005] An object of the present invention is to suppress the occurrence of local magnetic saturation within an element body and improve the magnetic saturation allowable current in an inductor having a coil conductor embedded in an element body made of metal magnetic particles and resin. [Means for solving the problem]

[0006] One aspect of the present invention is an inductor comprising an element body having a core including first metal magnetic particles having an insulating coating, second metal magnetic particles having an insulating coating and an average particle size smaller than that of the first metal magnetic particles, and a resin, and a coil conductor having a winding portion that is a conductor that constitutes a coil embedded in the core, wherein the element body has two main surfaces that face each other and intersect with the central axis of the winding portion, and in a cross section of the element body parallel to the central axis of the winding portion, a first number density, which is the number per unit length along the conductor boundary line of the first metal magnetic particles that are a predetermined distance or less from the conductor boundary line that is the boundary line between the core and the winding portion, is lower than a second number density, which is the number per unit length along the surface boundary line of the first metal magnetic particles that are a predetermined distance or less from the surface boundary line that is the boundary line that indicates the position of at least one of the main surfaces of the element body.

[0007] Another aspect of the present invention is a method for manufacturing an inductor, comprising: a coil conductor forming process for producing a coil conductor having a winding portion; a base body molding process for forming an element body by embedding the coil conductor in a core containing first metal magnetic particles having an insulating coating, second metal magnetic particles having an insulating coating and having an average particle size smaller than the first metal magnetic particles, and resin; and a plating layer forming process for forming external electrodes connected to the coil conductor by plating at planned electrode locations on the element body, wherein in the base body molding process, the element body is formed by heating and pressurizing a mixed powder containing the first metal magnetic particles, the second metal magnetic particles, and the resin that constitute the core, and a portion of at least one main surface of the element body that is the outer surface of the element body and intersects the central axis of the winding portion is formed from the mixed powder having a higher content of first metal magnetic particles than the mixed powder that forms other parts of the element body.

[0008] Yet another aspect of the present invention is a method for manufacturing an inductor, comprising: a coil conductor forming step for producing a coil conductor; a base body molding step for forming an element body by embedding the coil conductor in a core containing first metal magnetic particles having an insulating coating, second metal magnetic particles having an insulating coating and having an average particle size smaller than the first metal magnetic particles, and a resin; and a plating layer forming step for forming external electrodes connected to the coil conductor by plating at planned electrode locations on the element body, wherein in the base body molding step, the element body is formed by heating and pressurizing a mixed powder containing the first metal magnetic particles, the second metal magnetic particles, and the resin that constitute the core, and the coil conductor is embedded in the core with the mixed powder adhered to it, the mixed powder having a lower content of first metal magnetic particles than the mixed powder used to form the element body. [Effects of the Invention]

[0009] According to the present invention, in an inductor having a coil conductor enclosed in an element body made of metal magnetic particles and resin, the occurrence of localized magnetic saturation within the element body can be suppressed, thereby improving the magnetic saturation allowable current. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a perspective view of an inductor according to an embodiment of the present invention, viewed from above; [Figure 2] FIG. 2 is a perspective view of the inductor as viewed from the bottom side. [Figure 3] FIG. 2 is a perspective view showing the internal configuration of an inductor. [Figure 4] 4 is a planar perspective view of the inductor shown in FIG. 3 as viewed from the top surface side. [Figure 5] FIG. 5 is a VV cross-sectional view of the inductor shown in FIG. [Figure 6] FIG. 2 is a partially enlarged view of the vicinity of the conductor boundary line of the element body. [Figure 7] 1A to 1C are diagrams illustrating a manufacturing process of an inductor. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [1. Inductor configuration] First, the configuration of the inductor 1 according to this embodiment will be described. [1.1 Overall structure of inductor] 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-mount 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 4 provided on the surface of the element body 2.

[0012] Hereinafter, in the element body 2, the first main surface that faces the mounting board (not shown) during mounting is defined as the bottom surface 10, the second main surface opposite the bottom surface 10 is called the top surface 12, a pair of third main surfaces that are perpendicular to the bottom surface 10 are called end surfaces 14, and a pair of fourth main surfaces that are perpendicular to the bottom surface 10 and the pair of end surfaces 14 are called side surfaces 16. 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 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. Furthermore, 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 distance is defined as the length direction DL. The inductor 1 has dimensions of, for example, a length L of 2.0 mm, a width W of 1.2 mm, and a thickness T of 0.7 mm.

[0013] 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 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.

[0014] The core 30 is a molded body obtained by compressing and molding a powder mixture of magnetic particles and resin into a substantially hexahedral shape by applying pressure and heat while the coil conductor 20 is enclosed therein.

[0015] In this embodiment, the mixed powder contains two types of magnetic particles, first metal magnetic particles M1 and second metal magnetic particles M2, which are different in average particle size, and a resin Ps. The average particle size of the first metal magnetic particles M1 is larger than that of the second metal magnetic particles M2. This allows the second metal magnetic particles M2, which are small particles, to enter between the first metal magnetic particles M1, which are large particles, together with the resin Ps, during compression molding, thereby increasing the filling rate of the magnetic particles in the core 30 and also increasing the magnetic permeability (see FIG. 6, described below).

[0016] The average particle size (D50) of the first metal magnetic particles M1 is preferably 20 μm or more and 28 μm or less, and more preferably 21.4 μm or more and 27.4 μm or less. The average particle size (D50) of the second metal magnetic particles M2 is preferably 1 μm or more and 6 μm or less, and more preferably 1.5 μm or more and 1.8 μm or less. The mixed powder may contain particles with three or more particle sizes by including particles with an average particle size smaller than the first metal magnetic particles M1 and the second metal magnetic particles M2.

[0017] The shape of the first metal magnetic particles M1 and the second metal magnetic particles M2 is not limited to spherical, but may be any shape such as scale-like, flat, elliptical, wire-like, etc. When the first metal magnetic particles M1 and the second metal magnetic particles M2 are not spherical, the average particle size of the first metal magnetic particles M1 and the second metal magnetic particles M2 can be calculated using the circle-equivalent diameter of the first metal magnetic particles M1 and the second metal magnetic particles M2 as the particle size.

[0018] The first metal magnetic particles M1 and the second metal magnetic particles M2 are both particles that have a metal magnetic particle and an insulating film covering the surface of the particle, the insulating film having a thickness of several to several tens of nanometers. By covering the metal magnetic particle with the insulating film, the insulation resistance and the withstand voltage are increased. The first metal magnetic particles M1 and the second metal magnetic particles M2 may be alloys containing Fe, Ni, and / or Co, or simple metal magnetic particles. In the first metal magnetic particles M1 of this embodiment, for example, Fe-Si-B amorphous alloy powder is used as the metal magnetic particles, and zinc phosphate glass with a thickness of 10 nm to 50 nm is used as the insulating film. In the second metal magnetic particles M2 of this embodiment, for example, carbonyl iron powder is used as the metal magnetic particles, and a sol-gel reaction product containing silica with a thickness of 5 nm to 15 nm is used as the insulating film.

[0019] In the mixed powder of this embodiment, the resin Ps is made of an epoxy resin containing a phenol alkyl type epoxy resin as a main component. The amount of the second metal magnetic particles M2 among the metal magnetic particles contained in the mixed powder is, for example, 15 wt% to 30 wt% and preferably 20 wt% to 30 wt% based on the total weight of the metal magnetic particles. The content of the resin Ps in the mixed powder is 2.0 wt% to 3.5 wt% based on the total weight of the mixed powder.

[0020] In this embodiment, as shown in Fig. 3, the coil conductor 20 has a winding portion 22 formed by winding a conductor wire in a winding method known as "alpha winding," and a pair of lead-out portions 24 drawn out from the winding portion 22. However, the winding portion 22 is not limited to the alpha winding, and may be formed by winding a conductor wire in a spiral shape. Furthermore, the coil conductor 20 may be formed not only by a conductor wire, but also by a conductor pattern formed in a spiral shape on a substrate.

[0021] In this embodiment, the conductor wire forming the coil conductor 20 has a conductor made of copper and an insulating coating formed on the surface of the conductor. The conductor wire is a strip-shaped conductor wire (so-called rectangular conductor wire). The thickness of the conductor wire is 118 μm or less, and preferably 52 μm or more. The width of the conductor wire is 203 μm or less, and preferably 141 μm or more. The aspect ratio of the conductor wire is, for example, 1.3 or more and 3.4 or less. The insulating coating is, for example, polyurethane resin, polyester resin, epoxy resin, or polyimideamide resin, and preferably polyimideamide resin. The thickness of the insulating coating is, for example, 4 μm.

[0022] The conductor wire may have a bonding layer on the insulating coating to bond overlapping conductor wires together in the winding portion 22. For example, the bonding layer is made of polyamide resin, and the thickness is preferably 1 μm or more and 25 μm or less, more preferably 2 μm or more and 25 μm or less, and even more preferably 2 μm or more and 4 μm or less.

[0023] Inside the element body 2, the coil conductor 20 is embedded in the core 30 with the central axis Q of the winding portion 22 aligned along the thickness direction DT of the element body 2. The central axis Q is, for example, the winding axis of the winding portion 22. Here, the bottom surface 10 and the top surface 12 of the element body 2 that intersect with the central axis Q when the coil conductor 20 is embedded in the core 30 correspond to the two main surfaces of the element body 2 that intersect with the central axis Q and face each other in the present disclosure.

[0024] The lead-out portion 24 of the coil conductor 20 is led out from the winding portion 22 to each of the pair of end faces 14, with one main surface of the lead-out portion 24 exposed from the element body 2 and the other main surface embedded in the element body 2. An external electrode 4 is electrically connected to the portion of the lead-out portion 24 that is exposed from the surface of the element body 2.

[0025] 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 the lead-out portion 24 of the coil conductor 20 at the end face 14, and the portion 4A (FIG. 2) extending to the bottom face 10 is electrically connected to wiring on the circuit board by an appropriate mounting means such as solder.

[0026] 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 made of, for example, phenoxy resin and 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, for example, 10 μm or more and 30 μm or less.

[0027] 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.

[0028] [1.2 Distribution of first metallic magnetic particles M1 in the element body] As described above in relation to the background art, even if the distribution of metal magnetic particles in the element body 2 is made uniform to reduce non-uniformity in magnetic properties, if there is a bias in the magnetic field distribution generated inside the element body 2 when current is passed through the coil conductor 20, local magnetic saturation may occur inside the element body 2, and the magnetic saturation allowable current of the inductor 1 may decrease.

[0029] In a configuration like this embodiment in which the coil conductor 20 is embedded in the core 30 with the central axis Q aligned along the thickness direction DT of the substantially rectangular parallelepiped element body 2, the magnetic field generated inside the element body 2 when current is applied to the coil conductor 20 is stronger near the winding portion 22 than on the bottom surface 10 and / or top surface 12 of the element body 2. Therefore, localized magnetic saturation occurs in the portion of the element body 2 near the winding portion 22, and the magnetic saturation in this portion can limit the magnetic saturation allowable current of the inductor 1.

[0030] Therefore, in the inductor 1 of this embodiment, rather than making the distribution of the metal magnetic particles in the element body 2 uniform, the element body 2 is configured so that the number density of the first metal magnetic particles M1 near the winding portion 22 is lower than the number density of the first metal magnetic particles M1 near the bottom surface 10 and / or the top surface 12.

[0031] Specifically, in this embodiment, in a cross section of the element body 2 including a cross section of the winding portion 22 of the coil conductor 20, the number of first metal magnetic particles M1 per unit length along the conductor boundary line that is the boundary line between the element body 2 and the winding portion 22 is defined as a first number density. Also, in the cross section of the element body 2, the number of first metal magnetic particles M1 per unit length along the surface boundary line that is the boundary line that indicates the positions of the bottom surface 10 and the top surface 12 of the element body 2 is defined as a second number density. In the inductor 1 of this embodiment, in the cross section of the element body 2, the first number density is lower than the second number density near the surface boundary line for at least one of the bottom surface 10 and the top surface 12 (or at least one of the second number densities is higher than the first number density).

[0032] Here, a first metal magnetic particle M1 "near" a conductor boundary line or a surface boundary line refers to a first metal magnetic particle M1 that is a predetermined distance or less from the corresponding conductor boundary line or surface boundary line. Preferably, the predetermined distance is 1 / 10 of the circle-equivalent diameter of each first metal magnetic particle M1. In other words, if the distance from the corresponding conductor boundary line or surface boundary line of each first metal magnetic particle M1 is 1 / 10 or less of the circle-equivalent diameter of the first metal magnetic particle M1, the first metal magnetic particle M1 is considered to be in the vicinity of the corresponding conductor boundary line or surface boundary line.

[0033] Furthermore, it is preferable that at least a portion of the first metal magnetic particles M1 located near the surface boundary line, i.e., the first metal magnetic particles M1 located near the surface boundary line at a distance less than the above-mentioned specified distance, are in contact with each other, i.e., two or more first metal magnetic particles M1. This effectively prevents magnetic saturation from occurring on the bottom surface 10 and / or the top surface 12, where local magnetic saturation is likely to occur.

[0034] The first number density and the second number densities do not necessarily have to be lower than the second number density over the entire conductor boundary lines of the two winding parts 22 and over the entire surface boundary lines of the bottom surface 10 and / or top surface 12. The element body 2 only needs to be configured such that, when comparing the first number density over at least a portion of the conductor boundary lines of the two winding parts 22 with the second number density over at least a portion of the surface boundary lines of at least one of the bottom surface 10 and the top surface 12, the first number density is lower than the second number density.

[0035] Fig. 4 is a planar perspective view of the inductor 1 shown in Fig. 1 and Fig. 3 as viewed from the top surface 12. Fig. 5 is a cross-sectional view taken along the arrows VV of the inductor 1 shown in Fig. 4, and is an explanatory diagram for describing the configuration of the element body 2. The cross-sectional view shown in Fig. 5 is an example of a cross-section of the element body 2 including a cross-section of the winding portion 22 of the coil conductor 20, and is, for example, a cross-section of the element body 2 approximately parallel to the central axis Q of the winding portion 22.

[0036] In the cross section shown in Fig. 5, conductor boundary lines 40 (illustrated dashed lines near winding portions 22) are shown near the outlines of the two winding portions 22 on the left and right sides of the figure, which are the boundary lines between each winding portion 22 and the element body 2. Note that in Fig. 5, for ease of viewing, the conductor boundary lines 40 are shown slightly shifted outward from the outlines of each winding portion 22, but it should be understood that in reality, the two conductor boundary lines 40 each coincide with the boundary position between the corresponding winding portion 22 and the element body 2 (for example, the position of the outline of winding portion 22).

[0037] 5, a surface boundary line 42a (shown as a two-dot chain line) indicating the position of the bottom surface 10 is shown near the bottom surface 10 of the element body 2, and a surface boundary line 42b indicating the position of the top surface 12 is shown near the top surface 12 of the element body 2. Note that in FIG. 5, for ease of viewing, the surface boundary lines 42a and 42b are shown slightly offset from the bottom surface 10 and the top surface 12, but it should be understood that in reality, the surface boundary lines 42a and 42b coincide with the positions of the bottom surface 10 and the top surface 12, respectively.

[0038] In this embodiment, as described above, in the cross section of the element body 2, an example of which is shown in Figure 5, the number of first metal magnetic particles M1 per unit length along the conductor boundary line 40 that are a predetermined distance or less from the conductor boundary line 40 is defined as the first number density. In the cross section of the element body 2, for each of surface boundary lines 42a and 42b that indicate the positions of the bottom surface 10 and top surface 12 of the element body 2, the number of first metal magnetic particles M1 per unit length along the corresponding surface boundary line 42a, 42b that are a predetermined distance or less from the corresponding surface boundary line 42a or 42b is defined as the second number density. In the inductor 1 of this embodiment, the element body 2 has a first number density that is lower than the second number density at at least one of the surface boundary lines 42a and 42b.

[0039] 5 , as an example, rectangular areas 44a, 44b, 44c, and 44d are shown as examples of measurement regions for the first number density in the conductor boundary line 40 of the two winding portions 22 on the left and right sides of the figure. Here, rectangular area 44a is a part of the portion of the conductor boundary line 40 that is sandwiched between the bottom surface 10 and the winding portion 22, and rectangular area 44b is a part of the portion of the conductor boundary line 40 that is sandwiched between the top surface 12 and the winding portion 22. The ranges indicated by rectangular areas 44a and 44b correspond to at least a part of the portion of the conductor boundary line 40 in the present disclosure that is sandwiched between the winding portion 22 and at least one of the two main surfaces (i.e., the bottom surface 10 and the top surface 12) of the element body 2 that oppose each other and intersect with the central axis Q of the winding portion 22.

[0040] Furthermore, rectangular area 44c is a part of the conductor boundary line 40 that faces the end face 14 on the left side in the figure, and rectangular area 44d is a part of the conductor boundary line 40 that faces the end face 14 on the right side in the figure. Hereinafter, rectangular areas 44a, 44b, 44c, and 44d will also be collectively referred to as rectangular area 44.

[0041] 5 also shows, as an example, a measurement area for the second number density on the surface boundary line 42a of the bottom surface 10 and a measurement area for the second number density on the surface boundary line 42b of the top surface 12 as rectangular areas 46a and 46b, respectively. Hereinafter, the rectangular areas 46a and 46b will also be collectively referred to as rectangular area 46.

[0042] In the above, the rectangular areas 44 and 46 shown in Figure 5 are examples of areas in which the first number density and second number density are measured in the cross section of the element body 2, and the first number density and second number density can be measured in at least a portion of the conductor boundary line 40 and at least a portion of the surface boundary line 42, respectively, other than the rectangular areas 44 and 46.

[0043] FIG. 6 is a partial enlarged view of the vicinity of the conductor boundary line 40 in the cross section of the element body 2 of FIG. 5. As an example, FIG. 6 shows a partial enlarged view of the portion indicated by the rectangular area 44b of the winding portion 22 on the left side of the illustration in FIG. 5. The hatched area at the bottom of the illustration is the winding portion 22. The thick solid horizontal line corresponding to the surface position of the winding portion 22 is the conductor boundary line 40 between the winding portion 22 and the element body 2 (specifically, the core 30). The element body 2 extending above the conductor boundary line 40 contains first metal magnetic particles M1 (hatched circular portion) and second metal magnetic particles M2 (unhatched circular portion) with different average particle sizes, as well as resin Ps. As described above, the average particle size of the first metal magnetic particles M1 is larger than the average particle size of the second metal magnetic particles M2. Note that although the shapes of the first metal magnetic particles M1 and the second metal magnetic particles M2 are shown as circles in FIG. 6, they may be any shape, such as scale-like, flat, elliptical, or wire-like, as described above.

[0044] 6, the first number density of the first metal magnetic particles M1 is calculated by counting all first metal magnetic particles M1 within rectangular area 44b, as shown in the first metal magnetic particle M1 on the left in the figure, whose distance g from the conductor boundary 40 (specifically, the shortest distance from the conductor boundary 40 to the outer surface of the first metal magnetic particle M1) is 1 / 10 or less of the circle-equivalent diameter of the first metal magnetic particle M1, and dividing the count value by the length of the conductor boundary 40 in rectangular area 44b. The first number density in rectangular areas 44 other than rectangular area 44b at the conductor boundary 40, and the second number density in rectangular areas 46a, 46b of the surface boundary lines 42a, 42b can also be measured in the same manner as above.

[0045] More specifically, the first number density of the first metal magnetic particles M1 near the conductor boundary line 40 and the second number density of the first metal magnetic particles M1 near the surface boundary lines 42a and 42b can be measured as follows.

[0046] First, the side surface 16 of the element body 2 of the inductor 1 is polished in the DW direction (see FIG. 1) to obtain the cross section shown in FIG. 5, i.e., a cross section of the element body 2 that passes through the central axis Q of the winding part 22 and includes a cross section of the winding part 22 and is approximately parallel to the central axis Q. For example, if the central axis Q of the winding part 22 is approximately parallel to the DT and DL directions of the element body 2, the cross section of the element body 2 can be a cross section that includes the DT and DL directions of the element body 2 and is along the center line of the element body 2 in the DW direction. The cross section obtained by the polishing may be subjected to, for example, ion milling.

[0047] Next, in the cross section (hereinafter referred to as the polished surface) of the element body 2 obtained by the above polishing, corresponding to the cross section in Figure 5, the first number density of the first metal magnetic particles M1 is measured, for example, in at least one of the rectangular areas 44 shown on the conductor boundary lines 40 of the two winding portions 22.

[0048] Furthermore, on the polished surface of the element body 2 obtained by the above polishing, corresponding to the cross-sectional view of Figure 5, the second number density of the first metal magnetic particles M1 is measured, for example, in the rectangular area 46a of the surface boundary line 42a of the bottom surface 10 and / or the rectangular area 46b of the surface boundary line 42b of the top surface 12.

[0049] Specifically, the first number density in the rectangular area 44 and the second number density in the rectangular area 46 can be measured as follows. On the polished surface of element body 2, elemental analysis mapping is performed by EDX analysis (energy dispersive analysis) using a FE-SEM (field emission scanning electron microscope) for an area with a field of view of 75 μm × 56 μm to 100 μm × 75 μm, which corresponds to the rectangular areas 44 and 46 to be measured. This obtains an elemental mapping image of element body 2 within the rectangular areas 44 and 46 to be measured.

[0050] Next, in the element mapping image of element body 2 within the rectangular areas 44 and 46 obtained above, the granular portions showing the constituent elements of first metal magnetic particles M1 are identified as first metal magnetic particles M1. In addition, if the composition elements of the first metal magnetic particles M1 are not known, metal magnetic particles of the same composition can be grouped in the elemental analysis mapping image, the particle size distribution of the particle group of the same composition can be determined, and the particle of the particle group with the largest average particle size D50 can be determined as the first metal magnetic particle M1.

[0051] Next, for each of the identified first metal magnetic particles M1, the circle-equivalent diameter of the first metal magnetic particle M1 is measured, and the shortest distance between the contour line of the first metal magnetic particle M1 and the corresponding conductor boundary line 40 or surface boundary line 42 is measured. Subsequently, in each of the rectangular areas 44, 46 to be measured, the number of identified first metal magnetic particles M1 whose shortest distance is equal to or shorter than a predetermined distance is counted, and the length of the conductor boundary line 40 or surface boundary line 42 in each rectangular area 44, 46 is measured. As described above, the predetermined distance may be, for example, 1 / 10 of the circle-equivalent diameter of the corresponding individual first metal magnetic particle M1.

[0052] Then, in each of the rectangular areas 44, 46 to be measured, the value obtained by dividing the number of first metal magnetic particles M1 counted above by the length of the conductor boundary line 40 or surface boundary line 42 measured above is defined as the first number density or the second number density, respectively.

[0053] [2. Inductor manufacturing process] FIG. 7 is a diagram showing a manufacturing process of the inductor 1. As shown in the figure, the manufacturing process of the inductor 1 includes a coil conductor forming step (S1), a preform forming step (S2), an element molding step (S3), a barrel polishing step (S4), and an external electrode forming step (S5).

[0054] The coil conductor forming step (S1) is a step of forming the coil conductor 20 from a conductive wire. In the present embodiment, as an example, the coil conductor 20 is formed into a shape having a winding portion 22 and a pair of lead portions 24 by winding the conductive wire in a winding method called alpha winding.

[0055] The preform forming step (S2) 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) with a groove into which the coil conductor 20 fits, and a second tablet of an appropriate shape (e.g., I-shaped or plate-shaped) that covers the groove of the first tablet.

[0056] In the element molding step (S3), 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 to harden them, integrating the first tablet, the coil conductor, and the second tablet, thereby molding the element 2 in which the coil conductor 20 is enclosed in the core 30.

[0057] In this embodiment, particularly in the element body molding step (S3), element body 2 has at least one of its two main surfaces (i.e., bottom surface 10 and top surface 12) that intersect with central axis Q of winding portion 22 formed from a mixed powder having a higher content of first metal magnetic particles M1 (e.g., the weight percentage of first metal magnetic particles M1 relative to the weight of the mixed powder) than the mixed powder that forms the other parts of element body 2. For example, in the pre-molded body formation step (S2), the part of the first tablet that will become bottom surface 10 of element body 2 and the second tablet that will become top surface 12 of element body 2 are made from a mixed powder with a higher content of first metal magnetic particles M1, and thus in the subsequent element body molding step (S3), element body 2 can be formed to have the above-mentioned configuration.

[0058] Alternatively, the element body 2 having the above-described configuration can be produced, for example, by dipping the coil conductor 20 into a slurry of mixed powder having a lower content of first metal magnetic particles M1 than the mixed powder used for the element body 2 before setting the coil conductor 20 in a molding die for the element body 2. In this way, the coil conductor 20 is embedded in the core 30 with the mixed powder having a lower content of first metal magnetic particles M1 than the mixed powder used to form the element body 2 attached thereto.

[0059] The barrel polishing step (S4) is a step of barrel polishing this molded body, and by this step, the corners of the element body 2 are rounded.

[0060] The external electrode forming step (S5) is a step of forming the external electrodes 4 on the core 30, and includes an element body protective layer forming step (S51), a surface treatment step (S52), and a plating layer forming step (S53).

[0061] The element body protective layer forming step (S51) is a step of coating the entire surface of this molded body with insulating resin. The surface treatment step (S52) is a step 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 lead-out portion 24 is exposed. Specifically, by irradiating the area with laser light, the element body protective layer on the surface of the core 30 and the coating layer on the lead-out portion 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 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.

[0062] In the plating layer forming step (S53), copper is barrel-plated on the surface of the core 30 to form a copper plating layer at the electrode-planed locations irradiated with the laser light, thereby forming the external electrodes 4. The external electrodes 4 may be formed by further providing a Ni plating layer and a Sn plating layer on the copper plating layer.

[0063] 3. Working Example Next, an embodiment of the inductor 1 will be described. Table 1 shows the evaluation results of five examples of the inductor 1 according to this embodiment and a comparative example, which is an inductor of a conventional configuration. Examples 1 to 5 were produced using the manufacturing process shown in FIG. 7 described above, so that the first number density of the first metal magnetic particles M1 in the element body 2 was lower than the second number density. The comparative example was produced using the same manufacturing process as conventional methods, with the entire element body 2 being made using the same mixed powder, so that the distribution of the first metal magnetic particles M1 in the element body 2 was approximately uniform.

[0064] [Table 1]

[0065] In Table 1, column A represents the first number density d1 of the first metal magnetic particles M1 near the conductor boundary line 40 of the winding portion 22. Columns B and C represent the second number density d2 near the surface boundary line 42a of the bottom surface 10 of the element body 2 and the second number density d3 of the first metal magnetic particles M1 near the surface boundary line 42b of the top surface 12, respectively. Columns D and E represent the ratio R1 of the first number density d1 near the winding portion 22 to the second number density d2 near the bottom surface 10, and the ratio R2 of the first number density d1 to the second number density d3 near the top surface 12, respectively. Columns F and G represent the inductance L and the magnetic saturation allowable current Isat, respectively.

[0066] Here, the first number density d1 shown in column A is, more specifically, the first number density in the rectangular area 44b of the conductor boundary line 40 of the left winding portion 22 shown in Figure 5. Furthermore, the second number densities d2 and d3 shown in columns B and C are the second number densities in the rectangular areas 46a and 46b of the surface boundary lines 42a and 42b shown in Figure 5, respectively.

[0067] The method for measuring the first number density and the second number density was as described above, and the predetermined distance was 1 / 10 of the circle-equivalent diameter of each of the first metal magnetic particles M1.

[0068] From Table 1, it can be seen that in Examples 1 to 5 having the configuration of the inductor 1 according to this embodiment, the magnetic saturation allowable current Isat can be improved compared to the comparative example without causing a decrease in inductance L.

[0069] The magnetic saturation allowable current Isat, which had once increased, begins to decrease as R1 and R2 decrease. This is thought to be because an excessive increase in the number of first metal magnetic particles M1 near the bottom surface 10 or the top surface 12 reduces dispersibility with the second metal magnetic particles M2, increasing the frequency of agglomerations when mixed with a resin composition. Table 1 shows that the range of R1 or R2 that can improve the magnetic saturation allowable current Isat without reducing the inductance L is preferably 0.58 or more and 0.89 or less, and more preferably 0.64 or more and 0.80 or less.

[0070] 4. Other Embodiments In the above-described embodiment, the conductor wire constituting the coil conductor 20 is a flat conductor wire having a substantially rectangular cross section, but the conductor wire may have any cross-sectional shape. For example, the conductor wire may have a circular cross section.

[0071] In the above-described embodiment, the external electrode 4 is formed as an L-shaped electrode. However, the external electrode 4 is not limited to an L-shaped electrode, and may be a bottom electrode formed only on the bottom surface 10. The external electrode 4 may also be formed as a so-called five-sided electrode that is provided over the entire end surface 14 and over parts of the bottom surface 10, the top surface 12, and a pair of side surfaces 16 adjacent to the end surface 14. Note that when the five-sided electrode is applied by immersion in a conductive resin, the element protective layer forming step (S51) is not necessarily required.

[0072] All of the above-described embodiments and modifications are merely examples of one aspect of the present invention, and any modifications and applications are possible within the scope of the present invention. Furthermore, unless otherwise specified, the horizontal, 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] 5. Configurations supported by the above embodiments The above-described embodiment supports the following configurations.

[0074] (Configuration 1) An inductor comprising: an element body having a core including first metal magnetic particles having an insulating coating, second metal magnetic particles having an insulating coating and an average particle size smaller than that of the first metal magnetic particles, and a resin; and a coil conductor having a winding portion that is a conductor that constitutes a coil embedded in the core, wherein the element body has two main surfaces that intersect with each other and face each other and intersect with the central axis of the winding portion, and in a cross section of the element body parallel to the central axis of the winding portion, a first number density, which is the number per unit length along the conductor boundary line of the first metal magnetic particles that are a predetermined distance or less from the conductor boundary line that is the boundary line between the core and the winding portion, is lower than a second number density, which is the number per unit length along the surface boundary line of the first metal magnetic particles that are a predetermined distance or less from a surface boundary line that is a boundary line that indicates the position of at least one of the main surfaces of the element body. According to the inductor of Configuration 1, it is possible to suppress the occurrence of local magnetic saturation within the element body and improve the magnetic saturation allowable current.

[0075] (Configuration 2) The inductor according to configuration 1, wherein the predetermined distance is 1 / 10 of the circle-equivalent diameter of each of the first metal magnetic particles. In general, metal magnetic particles with larger circle-equivalent diameters can contribute to increasing or decreasing magnetic saturation near the conductor boundary line or surface boundary line, even if they are farther away from the respective boundary lines than metal magnetic particles with smaller circle-equivalent diameters. According to configuration 2, when calculating the number density, whether or not a first metal magnetic particle is present near the conductor boundary line and whether or not it is present near the surface boundary line is determined based on the distance from the boundary line that corresponds to the circle-equivalent diameter of each first metal magnetic particle. This makes it possible to appropriately grasp and control the number of first metal magnetic particles that can contribute to reducing magnetic saturation near the conductor boundary line and surface boundary line. As a result, it is possible to effectively suppress the occurrence of localized magnetic saturation within the element and improve the magnetic saturation allowable current.

[0076] (Configuration 3) An inductor described in configuration 1 or 2, wherein, in a cross section of the element body parallel to the central axis of the winding portion, at least some of the first metal magnetic particles that are at a distance from the surface boundary line of at least one of the main surfaces of the element body that is less than the specified distance are in contact with each other, with two or more of the first metal magnetic particles being in contact with each other. According to configuration 3, it is possible to effectively suppress the occurrence of magnetic saturation on the main surface of the element body that intersects with the central axis of the winding, where local magnetic saturation is likely to occur.

[0077] (Configuration 4) The inductor according to any one of configurations 1 to 3, wherein the ratio of the first number density to the second number density is equal to or greater than 0.58 and equal to or less than 0.89. According to the inductor of configuration 4, the magnetic saturation allowable current can be more effectively improved without causing a decrease in inductance.

[0078] (Configuration 5) An inductor described in any one of configurations 1 to 4, wherein the first number density is the number of first metal magnetic particles per unit length along the conductor boundary line, the first metal magnetic particles being at a distance from the conductor boundary line that is less than the predetermined distance in at least a portion of the conductor boundary line that is sandwiched between at least one of the main surfaces of the element body and the winding portion. The part of the element body between the bottom or top surface (i.e., two main surfaces) of the element body and the conductor boundary line can be thicker than the part of the element body between the side or end surface of the element body and the conductor boundary line, which can lead to a correspondingly greater bias in the magnetic flux distribution. According to configuration 5, bias in the magnetic flux portion in the part of the element body between at least one main surface of the element body (i.e., the bottom and / or top surface) and the conductor boundary line can be suppressed, thereby more effectively improving the magnetic saturation allowable current.

[0079] (Configuration 6) A method for manufacturing an inductor, comprising: a coil conductor forming process for producing a coil conductor having a winding portion; an element molding process for forming an element body by embedding the coil conductor in a core containing first metal magnetic particles having an insulating coating, second metal magnetic particles having an insulating coating and having an average particle size smaller than the first metal magnetic particles, and a resin; and a plating layer forming process for forming external electrodes to be connected to the coil conductor by plating at planned electrode locations on the element body, wherein in the element molding process, the element body is formed by heating and pressurizing a mixed powder containing the first metal magnetic particles, the second metal magnetic particles, and the resin that constitute the core, and at least one main surface portion of the element body that is the outer surface of the element body and intersects with the central axis of the winding portion is formed from the mixed powder having a higher content of the first metal magnetic particles than the mixed powder that forms other portions of the element body. According to the manufacturing method of configuration 6, it is possible to easily manufacture an inductor that can suppress the occurrence of local magnetic saturation within the element body and improve the magnetic saturation allowable current.

[0080] (Configuration 7) A method for manufacturing an inductor, comprising: a coil conductor forming process for producing a coil conductor; an element molding process for forming an element body by embedding the coil conductor in a core containing first metal magnetic particles having an insulating coating, second metal magnetic particles having an insulating coating and having an average particle size smaller than the first metal magnetic particles, and a resin; and a plating layer forming process for forming external electrodes to be connected to the coil conductor by plating at planned electrode locations on the element body, wherein in the element molding process, the element body is formed by applying pressure while heating a mixed powder containing the first metal magnetic particles, the second metal magnetic particles, and the resin that constitutes the core, and the coil conductor is embedded in the core with the mixed powder adhered to it, the mixed powder having a lower content of first metal magnetic particles than the mixed powder used to form the element body. According to the manufacturing method of configuration 7, it is possible to easily manufacture an inductor that can suppress the occurrence of local magnetic saturation within the element body and improve the magnetic saturation allowable current. [Explanation of symbols]

[0081] 1...inductor, 2...element body, 4...external electrode, 5...element body protective layer, 10...bottom surface, 12...top surface, 14...end surface, 16...side surface, 20...coil conductor, 22...winding portion, 24...drawing portion, 30...core, 40...conductor boundary line, 42, 42a, 42b...surface boundary line, 44, 44a, 44b, 44c, 44d, 46, 46a, 46b...rectangular area, M1...first metal magnetic particle, M2...second metal magnetic particle, Ps...resin.

Claims

1. a core including first metal magnetic particles having an insulating coating, second metal magnetic particles having an insulating coating and an average particle size smaller than that of the first metal magnetic particles, and a resin; a coil conductor having a winding portion that is a conductor constituting a coil and is embedded in the core; an element body having the element body has two main surfaces that intersect with a central axis of the winding portion and face each other, In a cross section of the element body parallel to the central axis of the winding portion, a first number density, which is the number of the first metal magnetic particles per unit length along the conductor boundary line, the first metal magnetic particles being at a distance of a predetermined distance or less from the conductor boundary line, the boundary line between the core and the winding portion, is lower than a second number density, which is the number of the first metal magnetic particles per unit length along the surface boundary line, the first metal magnetic particles being at a distance of the predetermined distance or less from the surface boundary line, the boundary line indicating the position of at least one of the main surfaces of the element body; Inductor.

2. the predetermined distance is 1 / 10 of the circle-equivalent diameter of each of the first metal magnetic particles; 10. The inductor of claim 1.

3. In a cross section of the element body parallel to the central axis of the winding portion, at least some of the first metal magnetic particles that are located at a distance from a surface boundary of at least one of the main surfaces of the element body that is equal to or shorter than the predetermined distance are in contact with each other.

10. The inductor of claim 1.

4. a ratio of the first number density to the second number density is greater than or equal to 0.58 and less than or equal to 0.89; 10. The inductor of claim 1.

5. the first number density is the number of the first metal magnetic particles per unit length along the conductor boundary line, the first metal magnetic particles being at a distance from the conductor boundary line that is equal to or shorter than the predetermined distance in at least a portion of the conductor boundary line that is sandwiched between at least one of the main surfaces of the element body and the winding portion; 10. The inductor of claim 1.

6. a coil conductor forming step of fabricating a coil conductor having a winding portion; an element molding step of forming an element by embedding the coil conductor in a core including first metal magnetic particles having an insulating coating, second metal magnetic particles having an insulating coating and an average particle size smaller than that of the first metal magnetic particles, and a resin; a plating layer forming step of forming external electrodes connected to the coil conductors by plating on predetermined electrode locations of the element body; and In the element molding step, the element body is formed by applying pressure to a mixed powder containing the first metal magnetic particles, the second metal magnetic particles, and the resin that constitutes the core while heating it; a portion of at least one main surface of the element body that is an outer surface of the element body and intersects with the central axis of the winding portion is formed from the mixed powder having a higher content of the first metal magnetic particles than the mixed powder forming the other portions of the element body; How to manufacture an inductor.

7. a coil conductor forming step of fabricating a coil conductor; an element molding step of forming an element by embedding the coil conductor in a core including first metal magnetic particles having an insulating coating, second metal magnetic particles having an insulating coating and an average particle size smaller than that of the first metal magnetic particles, and a resin; a plating layer forming step of forming external electrodes connected to the coil conductors by plating on predetermined electrode locations of the element body; and In the element molding step, the element body is formed by applying pressure to a mixed powder containing the first metal magnetic particles, the second metal magnetic particles, and the resin that constitutes the core while heating it; the coil conductor is embedded in the core with the mixed powder adhered thereto, the mixed powder having a lower content of the first metal magnetic particles than the mixed powder used to form the element body; How to manufacture an inductor.

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