Inductor and method for manufacturing inductor

Abstract

To achieve good electrical characteristics while improving environmental resistance, in an inductor.SOLUTION: An inductor includes a coil conductor having a pair of lead-out portions, an element body containing magnetic particles and a first resin and enclosing the coil conductor, an external electrode connected to each lead-out portion exposed from the surface of the element body, and an element body protective film having an opening at least in a portion where each lead-out portion is exposed from the surface of the element body and covering the surface of the element body. The external electrode includes a first plating layer formed on each lead-out portion and a second plating layer formed on the first plating layer. The first plating layer and the second plating layer extend while covering an edge of the opening of the element body protective film. An edge of each of the first plating layer and the second plating layer is in contact with the element body protective film. In the element body protective film, an average film thickness in a range where the edge of the first plating layer contacts is thinner than an average film thickness in a range where the edge of the second plating layer contacts.SELECTED DRAWING: Figure 6

Description

[Technical Field]

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

[0002] Patent Document 1 describes an inductor having a coil conductor with a pair of lead-out portions, an element body containing metal magnetic particles and resin and enclosing the coil conductor, an element body protective film covering the surface of the element body, and a pair of external electrodes electrically connected to the lead-out portions exposed from the element body protective film. In this inductor, the external electrodes can be formed so as to ride on part of the element body protective film.

[0003] If an external electrode is provided so that it overlaps part of the element protection film, the portion of the external electrode that overlaps the element protection film will rise, increasing the external dimensions of the inductor. As a result, the element dimensions must be reduced to fit the inductor within the external dimension constraints, which degrades the inductor's electrical characteristics. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2017 / 135058 Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to improve environmental resistance in an inductor by forming external electrodes that extend over the edges of an element protective film, while preventing the external electrodes from protruding due to this extension and placing restrictions on the external dimensions of the element, thereby achieving good electrical characteristics. [Means for solving the problem]

[0006] One aspect of the present invention is an inductor comprising: a coil conductor having a pair of lead portions; an element body containing metal magnetic particles and a first resin and encapsulating the coil conductor; an external electrode connected to the lead portions exposed from the surface of the element body; and an element body protective film covering the surface of the element body and having an opening at least in the portion where the lead portions are exposed from the surface of the element body, wherein the external electrode includes a first plating layer formed on the lead portions and a second plating layer formed on the first plating layer, and the first plating layer and the second plating layer extend to cover the edges of the opening in the element body protective film, with each end of the first plating layer and the second plating layer contacting the element body protective film, and the element body protective film has an average thickness in the area where the end of the first plating layer contacts that is thinner than the average thickness in the area where the end of the second plating layer contacts. 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 pair of lead portions; an element molding process for embedding the coil conductor in an element body containing metal magnetic particles and a first resin so that the lead portions of the coil conductor are exposed from the surface of the element body; an element protective film forming process for forming an element protective film on the surface of the element body so that the lead portions cover the surface of the element body; a surface treatment process for removing the element protective film from planned electrode locations on the surface of the element body, including exposed portions of the lead portions exposed from the element body; and an external electrode forming process for forming external electrodes by plating on the exposed portions of the lead portions at the planned electrode locations and on the surface of the element body, wherein in the surface treatment process, the element protective film is removed so that the thickness of the edge of the removed element protective film gradually becomes thinner toward the inside of the planned electrode locations, and in the external electrode forming process, a copper plating layer is formed to an extent that covers the edge portions of the element protective film, which has been formed to have a gradually thinner thickness, and a nickel plating layer is formed on the copper plating layer. [Effects of the Invention]

[0007] According to the present invention, in an inductor, the external electrodes are formed so as to ride over the edges of the element protective film, thereby improving environmental resistance, while preventing the external electrodes from rising up due to this riding over and causing restrictions on the external dimensions of the element, thereby achieving good electrical characteristics. [Brief explanation of the drawings]

[0008] [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. 6 is a partial detailed view of part A in the cross section shown in FIG. 5. [Figure 7] FIG. 7 is a diagram showing an example of an element mapping image in EDX analysis of part B shown in FIG. 6. [Figure 8] 1A to 1C are diagrams illustrating a manufacturing process of an inductor. [Figure 9] FIG. 10 is a diagram for explaining element molding. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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] 1, 2, and 3 are diagrams showing the overall configuration of the inductor 1. FIG. FIG. 1 is a perspective view of the inductor 1 as viewed from the top surface 12 side, and FIG. 2 is a perspective view of the inductor 1 as viewed from the 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.

[0010] 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 has a length L of 2.0 mm, a width W of 1.2 mm, and a thickness T of 0.9 mm, for example.

[0011] FIG. 3 is a perspective view showing the internal configuration of the inductor. 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.

[0012] The core 30 is a molded body obtained by pressurizing and heating a mixed powder of metal magnetic particles 30a and a first resin 30b while the mixed powder contains the coil conductor 20, thereby molding the mixed powder into a substantially hexahedral shape. The mixed powder may contain a solvent and / or a hardener. The mixed powder may further contain additives such as a lubricant.

[0013] The metal magnetic particles 30a of this embodiment include particles of two particle sizes: first magnetic particles that are large particles with a relatively large average particle size, and second magnetic particles that are small particles with a relatively small average particle size. As a result, during pressure molding, the second magnetic particles, which are small particles, enter between the first magnetic particles, which are large particles, together with the resin, thereby increasing the filling rate of the metal magnetic particles 30a in the core 30 and also increasing the magnetic permeability.

[0014] In this embodiment, the D50 particle diameters (median diameters) of the first and second magnetic metal particles are 28 μm and 4.0 μm, respectively. The D50 particle diameter of the first magnetic particles is preferably 10 μm or more and 50 μm or less, and the D50 particle diameter of the second magnetic particles is preferably 1 μm or more and 5 μm or less. Furthermore, the magnetic particles may contain particles with different average particle diameters from the first and second magnetic particles, resulting in particles of three or more different particle sizes.

[0015] The first magnetic particles and the second magnetic particles are both particles having a metal particle and an insulating film covering the surface thereof. By covering the metal particle with the insulating film, the insulation resistance and the withstand voltage are increased.

[0016] The first and second magnetic particles may be made of Fe (pure iron) or Fe alloys, etc. Examples of Fe alloys include one or more alloys selected from the group consisting of alloys containing Fe and Ni, alloys containing Fe and Co, alloys containing Fe and Si, alloys containing Fe, Si and Cr, alloys containing Fe, Si and Al, alloys containing Fe, Si, B and Cr, and alloys containing Fe, P, Cr, Si, B, Nb and C.

[0017] The composition of the metal particles of the first magnetic particles and the composition of the metal particles of the second magnetic particles may be the same or different from each other. The insulating film formed on the surface of the metal particles of the first magnetic particles and the second magnetic particles may be, for example, one or more insulating films selected from the group consisting of inorganic glass films, organic-inorganic hybrid films, and inorganic insulating films formed by the sol-gel reaction of metal alkoxides.

[0018] In this embodiment, the first magnetic particles are made of Fe-Si-Cr amorphous alloy powder as metal particles, and the second magnetic particles are made of Fe-Si-Cr amorphous alloy powder as metal particles.

[0019] In the mixed powder, the material of the first resin 30b can be at least one selected from the group consisting of epoxy resin, phenolic resin, polyester resin, polyimide resin, polyolefin resin, and silicone resin. In particular, when epoxy resin is used as the resin, a magnetic molding with high electrical insulation and / or mechanical strength can be obtained. In addition to the above, thermoplastic resins such as polyamide-imide, polyphenylene sulfide, and / or liquid crystal polymer may also be used as the resin material. The curing reaction is preferably thermal. In other words, the resin is preferably a thermosetting resin. One example is a thermosetting epoxy resin. Using such a resin allows the curing reaction to occur using a simple method.

[0020] A solvent can be added to the mixed powder to mix the metal magnetic particles 30a and the first resin 30b to obtain a slurry. The solvent is preferably an organic solvent. For example, the solvent may include any of aromatic hydrocarbons such as toluene or xylene; ketones such as acetone, methyl ethyl ketone, or methyl isobutyl ketone; alcohols such as methanol, ethanol, or isopropyl alcohol; and glycol ethers such as propylene glycol monomethyl ether or propylene glycol monomethyl ether acetate.

[0021] A curing agent for curing the first resin 30b may be added to the mixed powder. For example, the curing agent may include an imidazole-based curing agent, an amine-based curing agent, or a guanidine-based curing agent (e.g., dicyandiamide).

[0022] A lubricant may be added to the mixed powder to improve the lubricity of the first and second magnetic particles and increase the packing ratio. The lubricant may also be added to facilitate release from the mold during molding. The lubricant may include, for example, nanosilica, barium sulfate, or a stearic acid compound (lithium stearate, magnesium stearate, zinc stearate, potassium stearate, etc.).

[0023] The weight ratio of each raw material contained in the mixed powder may be such that the first magnetic particles and second magnetic particles are 94% to 98% by weight of the total, the first resin 30b and hardener are 1% to 5% by weight of the total, and the remainder is lubricant and solvent. The ratio of the first magnetic raw particles to the second magnetic raw particles is preferably 10:90 to 50:50 (weight of first magnetic raw particles:weight of second magnetic raw particles). The ratio of the first resin 30b to the hardener is preferably 95:5 to 98:2 (weight of first resin 30b:weight of hardener).

[0024] As shown in FIG. 3, the coil conductor 20 includes a winding portion 22 around which a conducting wire is wound, and a pair of lead-out portions 24 that are led out from the winding portion 22 and at least partially exposed from the element body 2. The coil conductor 20 is composed of a conductive wire and a coating layer formed on the surface of the conductive wire. The conductive wire is a strip-shaped conductive wire made of copper and having a rectangular cross section (so-called rectangular conductive wire). The coil conductor 20 does not necessarily have to be wound, but may be linear or meandering.

[0025] The winding portion 22 of the coil conductor 20 is formed, for example, by winding a strip-shaped conductor wire (hereinafter simply referred to as a conductor wire) in a spiral shape so that both ends are drawn out to the outer periphery and connected to each other at the inner periphery. Inside the element body 2, the coil conductor 20 is embedded in the core 30 with the central axis of the winding portion 22 oriented along the thickness direction DT of the element body 2. The drawn-out portions 24 are drawn out from the winding portion 22 to each of the pair of end faces 14, with one main surface exposed from the element body 2 and the other main surface embedded in the element body 2.

[0026] An element protective film 5, which is an insulating film that covers the surface of the element body 2, is formed on the surface of the element body 2. The element protective film 5 includes a second resin 51 and an inorganic filler 52. For example, the second resin 51 may be epoxy, urethane, acrylic, polyimide, polyimide amide, or polyamide. The material of the inorganic filler 52 may be, for example, titanium oxide, silicon dioxide, alumina, or calcium carbonate. The shape of the inorganic filler may be any shape, such as flaky, flat, spherical, elliptical, or wire-like.

[0027] 2, the element body protective film 5 (the hatched portion in the figure) has an opening at least in the portion where the lead portion 24 is exposed. In this embodiment, the opening in the element body protective film 5 extends from each end surface 14 of the element body 2 to the bottom surface 10 in accordance with the shape of the external electrode 4 described below.

[0028] 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.

[0029] In this embodiment, the external electrode 4 is formed to cover the edge of the opening in the element body protective film 5 and ride up on the element body protective film 5. By having the external electrode 4 cover and ride up on the edge of the element body protective film 5, the length of the interface between the external electrode 4 and the element body protective film 5 is increased, which, for example, can prevent moisture from penetrating from the interface to the surface of the element body 2, thereby improving the environmental resistance of the inductor 1.

[0030] Inductors with such a configuration can improve DC bias characteristics by using a soft magnetic material for the magnetic particles, and are therefore used as electronic components in electric circuits through which large currents flow, as choke coils in DC-DC converter circuits and power supply circuits, and as electronic components 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 inductors are not limited to these, and they can also be used in tuning circuits, filter circuits, rectifying and smoothing circuits, etc.

[0031] [1.2 Configuration of the opening edge of the element protection film] Next, a further description will be given of the configuration of the edge of the opening in the element body protective film 5. As described above, the external electrode 4 is formed so as to extend over the edge of the opening in the element body protective film 5. 4 is a planar perspective view of the inductor 1 shown in FIGS. 1 and 3 as viewed from the top surface 12 side, and FIG. 5 is a cross-sectional view of the inductor 1 shown in FIG. 4 taken along the line VV.

[0032] As shown in Figure 5, the two lead portions 24 of the coil conductor 20 are exposed from the left and right end faces 14, respectively. The element body protective film 5 (hatched areas in the figure) covering the surface of the element body 2 has openings in the portions of the lead portions 24 exposed from the left and right end faces 14, and each opening (the hatched areas of the surface of the element body 2 where the element body protective film 5 is not present) extends from the left and right end faces 14 to the bottom surface 10. The left and right external electrodes 4 in the figure cover the edges of the openings in the element body protective film 5 and ride up on top of the element body protective film 5.

[0033] Fig. 6 is a partial detailed view of part A shown in Fig. 5. Part A shown in Fig. 5 is the part where the external electrode 4 on the left side of the figure covers the edge of the opening in the element protective film 5 on the bottom surface 10 and rides up onto the element protective film 5.

[0034] 6, the external electrode 4 includes a first plating layer 41 formed on the surface of the element body 2 and a second plating layer 42 formed on the first plating layer 41. As described above, the external electrode 4 extends from the end surface 14 to the bottom surface 10, and therefore the first plating layer 41 is formed on the lead portion 24 at the end surface 14.

[0035] The external electrode 4 may also include a third plating layer 43 formed on the second plating layer 42. In this embodiment, the first plating layer 41 and the second plating layer 42 are a copper plating layer and a nickel plating layer, respectively. The third plating layer 43 may be, for example, a tin plating layer.

[0036] The first plating layer 41, the second plating layer 42, and the third plating layer 43 that constitute the external electrode 4 cover the edges of the element body protective film 5 and extend over the element body protective film 5, and the ends of each of the first plating layer 41, the second plating layer 42, and the third plating layer 43 contact the element body protective film 5 at the right side as shown in the figure. The average thickness tc1 of the element protective film 5 in the area a1 where the end of the first plating layer 41 contacts is smaller than the average thickness tc2 in the area a2 where the end of the second plating layer 42 contacts.

[0037] As a result, the thickness of the element body protective film 5 is made thinner at the edge of the opening in the element body protective film 5, and this reduces the height of the external electrodes 4 that rise up onto the edge of the opening in the element body protective film 5. As a result, while the external electrodes 4 are formed so as to rise up onto the edge of the element body protective film 5 to improve environmental resistance, restrictions on the external dimensions of the element body 2 due to the external electrodes 4 rising up as described above are prevented, and good electrical characteristics can be achieved.

[0038] In the case where the external electrode 4 includes a third plating layer 43 formed on the second plating layer 42, as in this embodiment, the element protective film 5 may further be formed so that the average thickness tc2 of the area a2 where the end of the second plating layer 42 contacts is thinner than the average thickness tc3 of the area a3 where the end of the third plating layer 43 contacts. This improves environmental resistance even when the external electrode 4 has a three-layer structure, preventing the external electrode 4 from protruding above the edge of the element body protective film 5 and restricting the external dimensions of the element body 2, thereby achieving good electrical characteristics.

[0039] 6, in this embodiment, the thickness of element protective film 5 at the edge is gradually reduced toward the opening (i.e., gradually reduced from right to left in the figure). As a result, inductor 1 is configured such that the average film thicknesses tc3, tc2, and tc1 of element protective film 5 at the contact points of third plating layer 43, second plating layer 42, and first plating layer 41 decrease in this order. This effectively prevents the external electrodes 4 from rising up onto the edges of the openings in the element protective film 5 .

[0040] In the example of Figure 6, the edge of the element protective film 5 is formed so that its thickness changes linearly, but it may also be formed so that it changes non-linearly, such as by having a curved portion or a step.

[0041] As an example, the average thickness of the first plating layer 41 is 3 μm or more and 30 μm or less, and the average thicknesses of the second plating layer 42 and the third plating layer are each 3 μm. In addition, in Fig. 6, the ride-over length Lc, which is the length by which the external electrode 4 rides over the edge of the element body protective film 5, is, for example, 10 μm or more and 100 μm or less. Note that when the first plating layer 41 and the second plating layer 42 are respectively formed of a copper plating layer and a nickel plating layer, the adhesion of the external electrode 4 to the element body 2 can be improved by making the average thickness of the nickel plating layer, in which tensile stress is likely to accumulate, thinner than the average thickness of the copper plating layer.

[0042] <Method for evaluating average film thickness tc1, tc2, and tc3> The average film thicknesses tc1, tc2, and tc3 of element protective film 5 in areas a1, a2, and a3 where first plating layer 41, second plating layer 42, and third plating layer 43 are in contact with each other can be measured as follows. First, the side surface 16 of the element body 2 of the fabricated inductor 1 is polished in the DW direction (see FIG. 1 ) to obtain a cross section (hereinafter referred to as the LT cross section) along the center line of the DW direction, including the DT and DL directions. The LT cross section in the center of the DW direction of the inductor 1 obtained by the above polishing may be subjected to, for example, ion milling. Next, in the obtained LT cross section, a portion corresponding to portion A in FIG. 5 is subjected to elemental analysis mapping by EDX (energy dispersive electron spectroscopy) analysis using a field emission scanning electron microscope (FE-SEM) over an area with a field of view of 75 μm × 56 μm to 100 μm × 75 μm, which corresponds to the range shown in FIG. 6 . This results in an elemental mapping image of the area corresponding to portion A near the edge of the opening in the element body protective film 5.

[0043] FIG. 7 shows an example of an element mapping image obtained as described above near the edge of the opening in element protective film 5, in a portion corresponding to portion B in FIG. 6. The element mapping image shown in FIG. 7 includes element body 2, element protective film 5, first plating layer 41 which is a copper plating layer, and second plating layer 42 which is a nickel plating layer. In FIG. 7, the large and small spheres inside element body 2 are metal magnetic particles 30a, and the portion filling the spaces between the spheres is first resin 30b. Inside element protective film 5, inorganic filler 52 and second resin 51 filling the spaces between inorganic filler 52 can be seen.

[0044] Next, using the element mapping image obtained as described above, the thickness of the element body protective film 5 within the range of overhang length Lc shown in Figure 6 is measured at 1 µm intervals along the direction of the boundary line between the element body 2 and the element body protective film 5 (the DL direction shown in Figure 6). Then, for each of the range a1 where the first plating layer 41 overhangs the element body 2, the range a2 where the end of the second plating layer 42 contacts the element body protective film 5, and the range a3 where the end of the third plating layer 43 contacts the element body protective film 5, the average value of the thickness measurements of the element body protective film 5 measured at 1 µm intervals is calculated, and these are defined as the average film thicknesses tc1, tc2, tc3 of the element body protective film 5 in the ranges a1, a2, and a3 where the first plating layer 41, the second plating layer 42, and the third plating layer 43 contact, respectively.

[0045] The above average film thicknesses tc1, tc2, and tc3 are not limited to the LT cross section along the center line in the DW direction, but may be measured for the LT cross section at any one or more positions in the DW direction from any side surface 16 (for example, three positions (three cross sections) at W / 4, W / 2, and 3W / 4 from the side surface). The average film thicknesses tc1, tc2, and tc3 are determined for each of these cross sections, and it is confirmed that the conditions set forth in the claims are satisfied for each cross section.

[0046] [1.3 Preferred configurations of element body protective film and element body] Next, a preferred configuration of the element body protective film 5 and the element body 2 will be described. [1.3.1 Film composition of element protective film] As described above, it is preferable that the element protective film 5 contains the second resin 51. This improves the flexibility of the element protective film 5 due to the flexibility that resins generally have, and therefore damage such as cracking in the element protective film 5 can be suppressed even when stress is applied to the inductor 1. Furthermore, by including the second resin in the element protective film 5, it is possible to achieve an element protective film 5 that is less likely to dissolve in a copper plating solution when a copper plating layer is formed as part of the external electrode 4.

[0047] Furthermore, the average particle size of inorganic filler 52 contained in element protective film 5, measured in terms of the circle-equivalent diameter, is preferably 10 μm or less. As a result, when stress is applied to the inductor 1, microcracks occur around the inorganic filler 52 having a small average particle size, which suppresses the application of stress to the element body 2, effectively preventing the occurrence of fatal defects such as cracks in the element body 2. The average particle size of the inorganic filler 52 is preferably 1 nm or more.

[0048] The average particle size of each of the metal magnetic particles 30a and the inorganic filler 52 does not necessarily have to be the average particle size for the entire element body 2 and the entire element body protective film 5, but may be the average particle size for each portion of the element body 2 and the element body protective film 5. In particular, from the viewpoint of the stress relaxation described above, it is preferable that the average particle size of the inorganic filler 52 at the edge portion of the element body protective film 5 on which the external electrode 4 rests is smaller than the average particle size of the metal magnetic particles 30a in the portion of the element body 2 that contacts the edge portion of the element body protective film 5.

[0049] Furthermore, the comparison of the average particle size of the metal magnetic particles 30a and the inorganic filler 52 can be performed, for example, by using the average value of the circle equivalent diameters in the images of the metal magnetic particles 30a and the inorganic filler 52 as the average particle size.

[0050] <Method for comparing and evaluating the sizes of metal magnetic particles and inorganic fillers> Specifically, the sizes of the metal magnetic particles and the inorganic filler can be compared as follows. First, for each of multiple inductors 1 (e.g., three inductors) manufactured in the same production lot, the side surface 16 of the element body 2 is polished in the DW direction (see FIG. 1 ) to obtain an LT cross section, for example, along the center line in the DW direction. The LT cross section in the center of the inductor 1 in the DW direction obtained by the above polishing may be subjected to, for example, ion milling. Next, elemental analysis mapping is performed on an area with a field of view of 75 μm × 56 μm to 100 μm × 75 μm inclusive for any portion of the obtained LT cross section, including the boundary between the element body 2 and the element body protective film 5. In the obtained mapping image, the circle-equivalent diameters of each of the metal magnetic particles 30 a and inorganic filler 52 shown in the mapping image are determined. At this time, for each of the metal magnetic particles 30 a and inorganic filler 52 shown in the obtained mapping image, if only a portion of the metal magnetic particles 30 a and inorganic filler 52 is shown at the edge of the mapping image, a supplementary mapping image with a shifted field of view may be obtained to determine the circle-equivalent diameter.

[0051] The overall average value of the individual circular equivalent diameters of the metal magnetic particles 30a obtained for each of the above multiple inductors 1 is taken as the average particle size of the metal magnetic particles 30a, and the overall average value of the individual circular equivalent diameters of the inorganic filler 52 obtained above is taken as the average particle size of the inorganic filler 52. Then, the average particle size of metal magnetic particles 30a determined as above is compared with the average particle size of inorganic filler 52.

[0052] As an example, in this embodiment, the average particle size of the first magnetic particles is in the range of 20 μm to 60 μm, and the average particle size of the inorganic filler 52 at the edge of the element protective film 5 is in the range of 0.01 μm to 10 μm.

[0053] [1.3.2 Arrangement of element protective film on element surface] As shown in Figure 6, it is preferable that the element protective film 5 is not disposed between the surface of the element 2 and the first plating layer 41, except for the portion where the first plating layer 41 of the external electrode 4 covers the edge of the element protective film 5 (i.e., the edge of the element protective film 5 on which the external electrode 4 rides). This prevents the formation of the element body protective film 5 on unnecessary parts of the surface of the element body 2, which would otherwise cause bulges on the surfaces of the external electrodes 4, and prevents restrictions on the external dimensions of the element body 2.

[0054] [1.3.3 Composition of the element field] The content of the first resin 30b in the surface layer portion of the element body 2 (hereinafter referred to as the surface layer portion) is preferably greater than the content of the first resin 30b in the portion other than the surface layer (hereinafter referred to as the non-surface layer portion). As a result, in the inductor 1, the density of the metal magnetic particles 30a is maintained high in the outer surface portion of the element body 2, thereby maintaining good inductance characteristics, while the resistivity of the outer surface portion of the element body 2 where the external electrode 4 is formed is made higher than that of the outer surface portion, thereby improving the voltage resistance performance of the inductor 1.

[0055] Here, the surface layer of the element body 2 refers to a layered range extending from the surface of the element body 2 to a depth of a predetermined distance toward the interior of the element body 2, and the predetermined distance is, for example, 25 μm.

[0056] As described below, the content ratio of the first resin 30b in the surface layer portion of the element body 2 can be adjusted in the element body molding process (S2) in the manufacturing process of the inductor 1, for example, by adjusting the clearance between the opening of the cavity 65 used for hot molding and the outer shape of the punch 66.

[0057] <Method for comparatively evaluating the first resin content in the surface layer portion and the non-surface layer portion of the element body> A comparative evaluation of the content ratio of the first resin 30b in the surface layer portion of the element body 2 and the content ratio of the first resin 30b in the portion other than the surface layer can be performed as follows. First, the side surface 16 of the element body 2 of the fabricated inductor 1 is polished in the DW direction (see FIG. 1) to obtain an LT cross section at a position W / 4 from the side surface 16. The LT cross section obtained by the above polishing may be subjected to, for example, ion milling. Next, elemental analysis mapping is performed on the obtained LT cross section over an area with a field of view of 75 μm × 56 μm to 100 μm × 75 μm.

[0058] The surface of the element body 2 is defined as a depth of 0 μm, and the depth range from 0 μm to less than 25 μm toward the interior of the element body 2 is defined as the surface layer range. Elemental quantitative analysis is performed on the surface layer range across the entire width of the field of view of the EDX image. The carbon content ratio (unit: atom %) in the range obtained as a result of this analysis is defined as an evaluation quantity indicating the content ratio of the first resin 30b in the surface layer portion of the element body 2.

[0059] Furthermore, the surface of the element body 2 is defined as a depth of 0 μm, and the depth range from 25 μm to 50 μm toward the interior of the element body 2 is defined as the non-surface range. Elemental quantitative analysis is performed on the non-surface range across the entire field of view of the EDX image. The carbon content ratio in the range obtained as a result of this analysis is defined as an evaluation quantity indicating the content ratio of the first resin 30b in the non-surface portion of the element body 2.

[0060] The LT cross section of the element body 2 that has been subjected to the above analysis is further polished in the DW direction (see FIG. 1) to obtain an LT cross section at a position W / 2 from the side surface 16. For the LT cross section at the position W / 2 obtained above, an evaluation amount of the content ratio of the first resin 30b in the surface layer portion and an evaluation amount of the content ratio of the first resin 30b in the portion outside the surface layer are obtained in the same manner as above.

[0061] Similarly, for the LT cross section at the position 3W / 4 from the side surface 16, the evaluated amount of the content ratio of the first resin 30b in the surface layer portion and the evaluated amount of the content ratio of the first resin 30b in the non-surface layer portion are obtained.

[0062] Then, for each of the three LT cross sections at positions W / 4, W / 2, and 3W / 4 from the side surface 16, it is confirmed that the evaluated content ratio of the first resin 30b in the surface layer portion is greater than the evaluated content ratio of the first resin 30b in the portion outside the surface layer. From the viewpoint of the withstand voltage performance of the inductor 1, it is preferable that the evaluated content ratio of the first resin 30b in the surface layer portion is greater than the evaluated content ratio of the first resin 30b in the portion outside the surface layer by 5 atoms / % or more (i.e., it is preferable that the carbon content ratio of the surface layer portion is greater than the carbon content ratio of the portion outside the surface layer by 5 atoms / % or more).

[0063] [2. Inductor manufacturing process] The inductor 1 can be fabricated as follows. FIG. 8 is a diagram showing a manufacturing process of the inductor 1. The manufacturing process of the inductor 1 may include a coil conductor forming step (S1), an element molding step (S2), a barrel polishing step (S3), a surface treatment step (S4), and an external electrode forming step (S5).

[0064] The coil conductor formation step (S1) is a step of forming a coil conductor 20 from a conductive wire. In this step, the coil conductor 20 is formed into a shape having the above-mentioned winding portion 22 and a pair of lead-out portions 24 by winding the conductive wire using a winding method known as "alpha winding." Alpha winding refers to a state in which the conductive wire, which functions as a conductor, is wound in two stages in a spiral shape so that the lead-out portions 24 at the beginning and end of the winding are located on the outer periphery. The number of turns of the coil conductor 20 is not particularly limited. As mentioned above, the coil conductor 20 does not necessarily have to be wound, and may be linear, meandering, or the like.

[0065] In the element molding step (S2), the mixed powder is preformed to form a tablet (a solid object of a predetermined shape), and the tablet and the coil conductor 20 are placed in the cavity of a molding die. Next, the tablet and the coil conductor 20 are pressed together using a punch while the cavity is heated, and the tablet is pressure-molded to produce the element 2.

[0066] As shown in FIG. 9, two types of tablets are used for the preformed tablets: a first tablet 60 having an appropriate shape (e.g., E-shaped) with a groove 61 into which the coil conductor 20 fits, and a second tablet 62 having an appropriate shape (e.g., I-shaped or plate-shaped) that covers the groove 61 of the first tablet 60. During pressure molding, the first tablet 60 with the coil conductor 20 fitted in the groove 61 and the second tablet 62 are placed one on top of the other in a cavity 65 of a molding die 64. Then, while applying heat to the first tablet 60 and the second tablet 62, pressure is applied in the overlapping direction using a punch 66 from the side of the first tablet 60 and / or the second tablet 62 (the side of the second tablet 62 in the example of FIG. 9), thereby integrating the first tablet 60, the coil conductor 20, and the second tablet 62. The pressure molding is performed under conditions such as a temperature of 180°C in the cavity 65, a pressure of 20 MPa by the punch 66, and a pressure time of 600 seconds.

[0067] Here, by adjusting the clearance between the opening of cavity 65 of molding die 64 used in the pressure molding and the outer shape of punch 66 to a value larger than the value at which the two fit together, it becomes possible to move first resin 30b inside element 2 toward the surface layer of element 2 during the heat molding. This makes it possible to make the content ratio of first resin 30b in the surface layer portion of element 2 after heat molding larger than the content ratio of first resin 30b in the portion outside the surface layer.

[0068] In the barrel polishing step (S3), a plurality of element bodies 2 are loaded into a drum, and the drum is rotated so as not to apply excessively strong impacts. A coating liquid that will become the element body protective film 5 is sprayed using a sprayer. This rounds the corners of the element bodies 2 and applies the coating liquid to the element bodies 2. In this embodiment, the coating liquid contains a silicon dioxide filler that will become the inorganic filler 52, and an epoxy resin that will become the second resin 51.

[0069] Next, the element body 2 coated with the coating liquid is taken out of the drum and heat treated, whereby an element body protective film 5 is formed on the surface of the element body 2 .

[0070] The formation of the element body protective film 5 is not limited to the above, but can be carried out by various methods, such as by providing a separate process from the barrel polishing process (S3) and spraying a coating liquid onto the element body 2, dipping the element body 2 into the coating liquid, supplying the coating liquid onto the surface of the element body 2 via a dispenser, and / or printing a coating material onto the surface of the element body 2 using various printing methods.

[0071] The surface treatment step (S4) is a step of modifying the surface of the planned electrode locations on the surface of the core 30 by irradiating the locations with laser light. Here, the planned electrode locations refer to areas on the surface of the core 30 where the external electrodes 4 are to be formed, including the areas where the lead-out portions 24 are exposed. Specifically, by scanning the laser light within the planned electrode locations, the element protective film 5 on the surface of the core 30 and the coating layer on the lead-out portions 24 of the coil conductor 20 are removed, the first resin 30b on the surface of the core 30 is removed, and the insulating film on the surfaces of the metal magnetic particles 30a exposed from the core 30 is removed. As a result, the exposed area of ​​the metal of the metal magnetic particles 30a per unit area on the surface of the core 30 is larger in the planned electrode locations on the surface of the core 30 than in other surface areas of the core 30. Furthermore, by removing the element protective film 5 from the planned electrode locations on the surface of the element body 2, the element protective film 5 has openings on the surface of the element body 2 at the planned electrode locations.

[0072] The wavelength of the laser light is, for example, 180 nm or more and 3000 nm or less, more preferably 532 nm or more and 1064 nm or less. The irradiation energy of the laser light is 1 W / mm 2 More than 30W / mm 2 Less than 5W / mm is preferable. 2 More than 12W / mm 2 The following is more preferred:

[0073] In this embodiment, particularly in the above-mentioned planned electrode locations, the element body protective film 5 is removed so that the thickness of the removed edge of the element body protective film 5 gradually decreases toward the inside of the planned electrode location. Such thickness changes at the edge of the element body protective film 5 can be adjusted, for example, by modulating the irradiation intensity of the laser light when scanning the planned electrode location with the laser light. Specifically, at the outer edge of the planned electrode location (a position corresponding to the edge of the opening in the element body protective film 5), the intensity of the laser light spot moving toward the outside of the planned electrode location can be gradually reduced, thereby gradually decreasing the thickness of the element body protective film 5 at the edge toward the planned electrode location.

[0074] The thickness change at the edge of the element body protective film 5 can be adjusted by any method, not limited to modulating the irradiation intensity of the laser light. For example, if the element body protective film 5 at the planned electrode locations is removed by blasting, the element body protective film 5 may be shaped so that the thickness at the edge of the element body protective film 5 gradually decreases toward the planned electrode locations by adjusting the blast pressure at the outer edge of the planned electrode locations.

[0075] In the external electrode formation step (S5), the external electrodes 4 are formed at predetermined electrode locations on the core 30. Specifically, first, a copper (Cu) plating layer is formed as the first plating layer 41 by electrolytic plating at the predetermined electrode locations on the core 30. Subsequently, a nickel (Ni) plating layer and a tin (Sn) plating layer can be formed as the second plating layer 42 and the third plating layer 43 on the first plating layer 41 by electrolytic plating.

[0076] The copper plating layer can be formed by, for example, copper sulfate plating, copper pyrophosphate plating, or copper cyanide plating.

[0077] When forming the Ni plating layer and the Sn plating layer, additives such as a brightener may be added to the plating solution.

[0078] In this embodiment, particularly in the external electrode formation process (S5), a copper plating layer that will become the first plating layer 41 is formed to cover the edge of the element body protective film 5, which is formed so as to gradually thin, and a nickel plating layer that will become the second plating layer 42 is formed on the copper plating layer. The copper plating layer that covers the edge of the element body protective film 5 can be formed, for example, by adjusting the plating process time to be long when forming the copper plating layer described above, thereby causing the copper plating layer formed in the intended electrode location to grow toward the surface of the edge of the element body protective film 5.

[0079] 5. Other Embodiments The first plating layer 41 of the external electrode 4 may be formed so as to be in direct contact with the lead portion 24, or another layer having conductivity may be included between the first plating layer 41 and the lead portion 24. By including another layer, for example, the adhesive strength between the lead portion 24 and the external electrode 4 can be improved. For example, a single or multiple conductive layers formed by applying resin silver and / or resin copper, and / or a single or multiple metal layers formed by sputtering or the like may be provided between the first plating layer 41 and the lead portion 24. The material of the metal layer may be, for example, an elemental metal such as platinum (Pt), gold (Au), aluminum (Al), copper (Cu), nickel (Ni), lead (Pd), or chromium (Cr), and / or an alloy of multiple metals selected from these.

[0080] Furthermore, except for the portion where the external electrode 4 covers the edge of the element body protective film 5 and extends above the element body protective film 5, the first plating layer 41 of the external electrode 4 may be in direct contact with the surface of the element body 2, or another layer similar to the above may be present between the first plating layer 41 and the surface of the element body 2.

[0081] Furthermore, in the above-described embodiment, the ends of the first plating layer 41, the second plating layer 42, and the third plating layer 43 are in direct contact with the element body protective film 5, but they may also be in indirect contact with the element body protective film 5 via another layer formed on the element body protective film 5. In this case, the above-described average film thicknesses tc1, tc2, and tc3 of the element body protective film 5 can be defined as the average film thicknesses in the ranges a1, a2, and a3, respectively, of the element body protective film 5 to which the first plating layer 41, the second plating layer 42, and the third plating layer 43 are in indirect contact via the other layer.

[0082] In the above-described embodiment, the metal magnetic particles 30a contained in the base body 2 are composed of two types of magnetic particles with different average particle sizes, but they may also be composed of one type of magnetic particles or three or more types of magnetic particles with different average particle sizes.

[0083] All of the above-described embodiments and examples 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.

[0084] [6. Configurations supported by the above embodiments and examples] The above-described embodiments and examples support the following configurations.

[0085] (Configuration 1) An inductor comprising: a coil conductor having a pair of lead portions; an element body containing metal magnetic particles and a first resin and encapsulating the coil conductor; an external electrode connected to the lead portions exposed from the surface of the element body; and an element body protective film covering the surface of the element body and having an opening at least in the portion where the lead portions are exposed from the surface of the element body, wherein the external electrode includes a first plating layer formed on the lead portions and a second plating layer formed on the first plating layer, and the first plating layer and the second plating layer extend to cover the edge of the opening in the element body protective film, with each end of the first plating layer and the second plating layer contacting the element body protective film, and the element body protective film has an average thickness in the area where the end of the first plating layer contacts that is thinner than the average thickness in the area where the end of the second plating layer contacts. According to the inductor of configuration 1, the thickness of the element protective film at the edge of the opening in the element protective film is made thinner the closer to the opening, so the height of the external electrodes that climb up onto the edge of the opening in the element protective film is kept low. As a result, while the external electrodes are formed to climb up onto the edge of the element protective film, improving environmental resistance, restrictions on the external dimensions of the element due to the external electrodes climbing up are prevented, and good electrical characteristics can be achieved.

[0086] (Configuration 2) The inductor according to configuration 1, wherein the first plating layer is a copper plating layer and the second plating layer is a nickel plating layer. According to the inductor of configuration 2, the first plating layer closest to the lead-out portion of the coil conductor is made of copper, a metal with high conductivity similar to the copper wire commonly used as a coil conductor, and the second plating layer is made of nickel, which has high corrosion resistance.This makes it possible to achieve good DC resistance characteristics and environmental resistance while ensuring good adhesion of the external electrode to the element body.

[0087] (Configuration 3) An inductor described in configuration 1 or 2, wherein the external electrode further includes a third plating layer formed on the second plating layer, the third plating layer, together with the first plating layer and the second plating layer, covers the edge of the element protective film, the end of the third plating layer contacts the element protective film, and the element protective film has an average thickness in the area where the end of the second plating layer contacts that is thinner than the average thickness in the area where the end of the third plating layer contacts. According to the inductor of configuration 3, even when a three-layer external electrode is used, it is possible to improve environmental resistance while preventing the external electrode from protruding above the edge of the element protective film, which would restrict the external dimensions of the element, thereby achieving good electrical characteristics.

[0088] (Configuration 4) The inductor according to configuration 3, wherein the third plating layer is a tin plating layer. According to the inductor of configuration 4, the third plating layer is made of tin, which has high solder wettability, making it easy to mount the inductor on a mounting board.

[0089] (Configuration 5) The inductor according to any one of configurations 1 to 4, wherein the element body protective film includes a second resin. According to the inductor of configuration 5, the flexibility of the element protection film is improved due to the flexibility that resin generally has, so that even when stress is applied to the inductor, damage such as cracking in the element protection film can be suppressed, and when a copper plating layer is formed as part of the external electrode, an element protection film that is less likely to dissolve in a copper plating solution can be achieved.

[0090] (Configuration 6) An inductor described in any one of configurations 1 to 5, wherein the element protective film contains inorganic filler having an average particle size measured in equivalent circle diameter of 10 μm or less, and an average particle size smaller than that of the metal magnetic particles. According to the inductor of configuration 6, when stress is applied to the inductor, microcracks occur around the inorganic filler with a small average particle size, thereby suppressing the application of stress to the element body 2, thereby effectively preventing the occurrence of fatal defects such as cracks in the element body 2.

[0091] (Configuration 7) The inductor according to any one of configurations 1 to 6, wherein the element body protection film is formed so that the thickness at the edge portion gradually decreases toward the opening. According to the inductor of Configuration 7, it is possible to effectively prevent the external electrodes from rising up onto the edges of the openings in the element protective film.

[0092] (Configuration 8) An inductor described in any of configurations 1 to 7, wherein the content ratio of the first resin in the surface layer of the base body containing the metal magnetic particles and the first resin is greater than the content ratio of the first resin in parts other than the surface layer of the base body. Furthermore, according to the inductor of configuration 8, the density of metal magnetic particles is maintained high in the outer surface portion of the element body, thereby maintaining good inductance characteristics, while the content ratio of the first resin is increased in the outer surface portion of the element body where the external electrodes are formed, thereby increasing the resistivity of the outer surface portion and improving the voltage resistance performance of the inductor.

[0093] (Configuration 9) An inductor described in any one of configurations 1 to 8, in which the element protective film is not disposed between the surface of the element and the first plating layer, except for the portion where the first plating layer covers the edge portion of the element protective film. According to the inductor of configuration 9, it is possible to prevent the formation of an element protective film on unnecessary parts of the element surface, which would cause protrusions on the surfaces of the external electrodes, thereby preventing restrictions on the external dimensions of the element body.

[0094] (Configuration 10) A method for manufacturing an inductor, comprising: a coil conductor forming process for producing a coil conductor having a pair of lead portions; an element molding process for embedding the coil conductor in an element containing metal magnetic particles and a first resin so that the lead portions of the coil conductor are exposed from the surface of the element; an element protective film forming process for forming an element protective film on the surface of the element body so that the lead portions cover the surface of the element body; a surface treatment process for removing the element protective film from planned electrode locations on the surface of the element body, including exposed portions of the lead portions exposed from the element body; and an external electrode forming process for forming external electrodes by plating on the exposed portions of the lead portions at the planned electrode locations and on the surface of the element body, wherein in the surface treatment process, the element protective film is removed so that the thickness of the edge portions of the removed element protective film gradually becomes thinner toward the inside of the planned electrode locations, and in the external electrode forming process, a copper plating layer is formed to an extent that covers the edge portions of the element protective film, which has been formed to have a gradually thinner thickness, and a nickel plating layer is formed on the copper plating layer. According to the inductor manufacturing method of configuration 10, the external electrodes are formed so as to extend over the edges of the element protective film, thereby improving environmental resistance, while preventing the external electrodes from rising up due to the extension and causing restrictions on the external dimensions of the element, thereby making it possible to manufacture an inductor that can achieve good electrical characteristics. [Explanation of symbols]

[0095] 1...inductor, 2...element body, 4...external electrode, 5...element body protective film, 10...bottom surface, 12...top surface, 14...end surface, 16...side surface, 20...coil conductor, 22...winding portion, 24...drawing portion, 30...core, 30a...metal magnetic particles, 30b...first resin, 41...first plating layer, 42...second plating layer, 43...third plating layer, 51...second resin, 52...inorganic filler, 60...first tablet, 62...second tablet, 64...molding die, 65...cavity, 66...punch.

Claims

1. a coil conductor having a pair of lead portions; an element body containing metal magnetic particles and a first resin and enclosing the coil conductor; an external electrode connected to the lead portion exposed from the surface of the element body; an element body protective film that covers the surface of the element body and has an opening at least in a portion where the lead portion is exposed from the surface of the element body; and The external electrode is a first plating layer formed on the lead portion; and a second plating layer formed on the first plating layer; and the first plating layer and the second plating layer extend to cover an edge of the opening in the element protective film, and ends of the first plating layer and the second plating layer contact the element protective film; The element protective film is the average film thickness of the area where the end of the first plating layer contacts is smaller than the average film thickness of the area where the end of the second plating layer contacts; Inductor.

2. The inductor according to claim 1 , wherein the first plating layer is a copper plating layer and the second plating layer is a nickel plating layer.

3. the external electrode further includes a third plating layer formed on the second plating layer, the third plating layer, together with the first plating layer and the second plating layer, covers the edge of the element protective film, and an end of the third plating layer contacts the element protective film; the element protective film has an average thickness smaller in a region where an end portion of the second plating layer contacts than in a region where an end portion of the third plating layer contacts; 10. The inductor of claim 1.

4. The inductor according to claim 3 , wherein the third plating layer is a tin plating layer.

5. the element protective film includes a second resin; 10. The inductor of claim 1.

6. the element protective film contains an inorganic filler having an average particle size, measured in terms of a circle equivalent diameter, of 10 μm or less; 10. The inductor of claim 1.

7. the element body protective film is formed so that the thickness at the edge portion gradually decreases toward the opening; 10. The inductor of claim 1.

8. a content ratio of the first resin in a surface layer of the element body containing the metal magnetic particles and the first resin being greater than a content ratio of the first resin in a portion other than the surface layer of the element body; 10. The inductor of claim 1.

9. the element protective film is not disposed between the surface of the element and the first plating layer except for a portion where the first plating layer covers the edge portion of the element protective film; 9. An inductor according to any one of claims 1 to 8.

10. a coil conductor forming step of fabricating a coil conductor having a pair of lead portions; an element molding step of embedding the coil conductor in an element containing metal magnetic particles and a first resin so that the lead portion of the coil conductor is exposed from a surface of the element; an element body protective film forming step of forming an element body protective film on a surface of the element body so as to cover the surface of the element body; a surface treatment step of removing the element body protective film from a portion of the surface of the element body where an electrode is to be formed, the portion including an exposed portion of the lead portion exposed from the element body; an external electrode forming step of forming external electrodes by plating on the exposed portions of the lead portions and the surface of the element body at the intended electrode locations; and In the surface treatment step, the element body protective film is removed so that the thickness of the edge of the removed element body protective film gradually decreases toward the inside of the electrode-planed portion; In the external electrode forming step, a copper plating layer is formed to cover an edge portion of the element body protective film, which is formed so as to have a gradually thinner thickness, and a nickel plating layer is formed on the copper plating layer. How to manufacture an inductor.

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