Wire-wound coil component and method for manufacturing a wire-wound coil component

Abstract

Wire-wound coil component (3) having the following features: a core (50; 60; 70) comprising a coil former (53; 63, 71) and a flange (51, 52; 61, 62; 72, 73) connected to an end section of the coil former (53; 63; 71); a wire (57) wound around the coil former (53; 63; 71); and an outer electrode (54, 55; 64, 65; 74-77) with which an end section (57a, 57b) of the wire (57) is electrically coupled, wherein: the flange (51, 52; 61, 62; 72, 73) has a side surface (51a, 52a; 72b, 73b) and a bottom surface (51b, 52b; 72a, 73a) and the outer electrode (54, 55; 64, 65; 74-77) has a metal thin-film segment (55a) that touches the lateral surface (51a, 52a; 72b, 73b) and a thick-film electrode segment (55b) that is a metal composite film that touches the lower surface (51b, 52b; 72a, 73a); wherein a part of the lateral surface (51a, 52a; 72b, 73b) that touches the metal thin film segment (55a) has a low-resistance region (43); wherein the flange (51, 52; 61, 62; 72, 73) consists of a ceramic material containing a metal oxide; and the low-resistance region (43) contains a metal resulting from the reduction of part of the metal oxide; and wherein one surface side of the low-resistance region (43) is a reoxidized coating (43b) and the reoxidized coating (43b) contains a metal oxide resulting from a reoxidation of the metal.

Description

[0001] The present disclosure relates to a wire-wound coil component and a method for manufacturing a wire-wound coil component. In particular, the present disclosure relates to the structure of an outer electrode of a wire-wound coil component.

[0002] Wire-wound coil components typically have outer electrodes, and these outer electrodes are usually formed by coating flanges of a core with a conductive paste containing metal and glass, firing the coatings into base electrodes, and plating the base electrodes to form upper electrodes (e.g., see Japanese unexamined patent publications No. JP 2008 - 210 978 A and JP 2011 - 109 020 A).

[0003] A proposed alternative to these existing methods is to form the outer electrodes solely by plating (Japanese unexamined patent publication no. JP 2004-040084A). This method for manufacturing a multilayer coil component, which, for example, has a ceramic body and inner electrodes within it, comprises exposing several end sections of the inner electrodes along an edge of the ceramic body, with the exposed end sections being close to one another; exposing blind terminals, referred to as armature tabs, along the same edge of the ceramic body as the end sections of the inner electrodes, with the exposed sections of the blind terminals being close to one another; and electroless plating of the ceramic body. Layers of the plating metal grow from the exposed end sections of the inner electrodes and armature tabs, forming outer electrodes.

[0004] WO 2016 / 032 005 A1 describes an electronic component with a body part and electrodes arranged within it. The structure of the electrodes is described.

[0005] US 2009 / 0 058 591 A1 describes a wire-wound component with a ferrite core.

[0006] US 2017 / 0287634A1 describes an electronic component consisting of a housing and an electrode mounted on the housing. The electrode comprises a first metal layer, a second metal layer, and a third metal layer.

[0007] The object of the present invention is to provide a wire-wound coil component that combines a reduced space requirement or reduced footprint and an enhanced bond connection with a substrate, and a method for producing a wire-wound coil component with improved characteristics.

[0008] This problem is solved by a wire-wound coil component according to claim 1 and a method for manufacturing a wire-wound coil component according to claim 7 or 8.

[0009] Methods in which base electrodes are formed by applying conductive paste, such as the one published in the Japanese unexamined patent publication No. JP 2008-210978A, offer limited options for the shape of the resulting outer electrodes. For example, if the base electrodes are formed by dipping a lateral surface of rectangular flanges into conductive paste, the conductive paste not only covers the lateral surface of each flange but also extends to the four adjacent surfaces. The resulting outer electrodes therefore extend over five surfaces. A particularly important factor is that the base electrodes are thick films. They are thicker than thin metal films, are produced by a process such as plating, atomization, or vapor deposition, and therefore have a significant impact on the component's external dimensions.

[0010] One solution is to form outer electrodes with base electrodes only on the lower side of the flanges, i.e., on the side facing the substrate to which the component is attached, as described in Japanese unexamined patent publication No. JP 2011-109 020 A. This reduces the thickness of the outer electrode sections that protrude and extend to the four surfaces adjacent to the lower surface of the flanges, including the side surfaces of the flanges, thereby reducing the area occupied by the wire-wound coil component on the main surface of the substrate (space requirement). However, the use of wire-wound coil components may change. They may become smaller, and their future applications may include use under extreme conditions, such as in automotive equipment.In such situations, simply soldering the underside of the flanges may be insufficient to provide a secure bond between the wire-wound coil component and the substrate on which it is mounted.

[0011] In the process described in the Japanese unexamined patent publication No. JP 2004-040084A, the resulting outer electrodes are thin metal films formed by plating. However, this technology requires that the components inside the body (core) have electrodes including armature tabs and is therefore difficult to apply to wire-wound coil components, which have a wire spiral around a core instead of electrodes inside the core.

[0012] According to an embodiment of the present disclosure, a wire-wound coil component comprises a core having a coil former and a flange connected to an end section of the coil former, a wire wound around the coil former, and an outer electrode with which an end section of the wire is electrically coupled. The flange has a side surface and a bottom surface. The outer electrode has a thin-film metal segment contacting the side surface and a thick-film electrode segment, which is a metal composite film, contacting the bottom surface. A portion of the side surface contacting the thin-film metal segment has a low-resistance region.The flange consists of a ceramic material containing a metal oxide, and the low-resistance region contains a metal resulting from the reduction of a portion of the metal oxide. One surface of the low-resistance region is a reoxidized coating, and this reoxidized coating contains a metal oxide resulting from the reoxidation of the metal.

[0013] The term "metal thin-film segment" refers to an electrode segment formed, for example, by plating, atomization, or vapor deposition. The term "metal composite film" refers to a film obtained by applying a conductive paste and curing it by baking, heat curing, drying, or any other method. Some types of conductive pastes contain metal particles and glass, others contain metal particles and thermosetting resin, and still other types are available. Therefore, metal thin-film and thick-film electrode segments can be distinguished not only by their formation process but also by their composition.The former is a film made of a conductor, for example metal, an alloy or an intermetallic compound, while the latter is a film made of a mixture of a conductor, for example metal, and a binder, for example glass or resin.

[0014] In this design, the thick-film electrode segment does not extend to the side of the flange's lateral surface, resulting in a smaller footprint for the wire-wound coil component on the substrate to which it is mounted. However, the entire outer electrode extends not only to the side of the lower surface but also to the side of the flange's lateral surface. This facilitates the formation of a solder fillet along the flange's lateral surface when the coil component is soldered to a substrate, strengthening the bond between the wire-wound coil component and the substrate. Consequently, the wire-wound coil component combines a reduced footprint with a reinforced bond to the substrate.

[0015] In the structure described above, a portion of the lateral surface contacting the metal thin-film segment exhibits a low-resistance region. This low-resistance region provides a starting point for the metal thin film to grow, thus enabling efficient metal thin-film formation. The term "low-resistance region," as used here, refers to a region of the core where the electrical resistance is lower than in the rest of the structure, such as the flange or coil former.

[0016] In the structure described above, the flange is made of a ceramic metal containing a metal oxide, and the low-resistance region contains a metal resulting from the reduction of a portion of the metal oxide. In this case, the low-resistance region is a modified form of the flange material and therefore does not require a complex formation process. The reduced metal can be a simple metal, a component of an alloy or intermetallic compound, or a component of a metal oxide in which the metal has a lower valence than in the original metal oxide.

[0017] In the structure described above, the surface of the low-resistance region is a reoxidized coating, and this coating contains a metal oxide resulting from the reoxidation of the metal. The reoxidized coating controls the reoxidation of the reduced metal in the low-resistance region, thus preventing the flange material from undergoing more than necessary changes.

[0018] In the structure described above, the flange is made of a ceramic metal containing a metal oxide, and a portion of the lateral surface contacting the metal thin-film segment may exhibit a reduced layer. This reduced layer contains a metal resulting from the reduction of a portion of the metal oxide. The reduced layer, formed by the modification of the flange material, enables the selective and efficient formation of the metal thin-film segment.

[0019] In the above structure, the wire end can be connected to the outer electrode above the lower surface. Thus, during the connection of the wire end to the outer electrode, for example by thermocompression bonding, the amount of heat or external force transferred to the flange is reduced by being absorbed by the thick-film electrode segment.

[0020] In the above structure, the thick-film electrode segment can be covered by the thin-film metal segment. This facilitates the formation of an outer electrode that extends from the side surface to the bottom surface of the flange.

[0021] In the structure described above, the bottom surface can be a surface facing a substrate, and the side surface can be a surface perpendicular to the substrate when the coil component is mounted on the substrate. This results in a smaller footprint for the wire-wound coil component on the substrate to which it is mounted. When it is stated herein that a surface is facing a substrate or perpendicular to it, this means that the surface is facing or perpendicular to the main surface of the substrate.

[0022] In the above structure, the side surface can be opposite a connection surface where the flange is connected to the coil former, and the bottom surface can be positioned between the side surface and the connection surface. This results in a smaller footprint for the wire-wound coil component if the coil component is of the horizontal type.

[0023] In the above structure, the flange can be made of a ferrite material. In this case, the core does not need to have a complex structure so that the outer electrode can be thin.

[0024] According to another embodiment of the present disclosure, a method for producing a wire-wound coil component comprises: A, producing a core having a coil former and a flange connected to an end section of the coil former; B, forming a thick-film electrode segment, which is a metal composite film, on a lower surface by applying a conductive paste to the lower surface and by firing or heat-curing the paste; and C, forming a thin-film metal segment on a lateral surface.The process is carried out such that a portion of the lateral surface contacting the metal thin-film segment has a low-resistance region; such that the flange is made of a ceramic material containing a metal oxide; and the low-resistance region contains a metal resulting from a reduction of a portion of the metal oxide; and such that a surface side of the low-resistance region is a reoxidized coating and the reoxidized coating contains a metal oxide resulting from a reoxidation of the metal.

[0025] In this process, the thick-film electrode segment is not formed on the side of the flange's lateral surface, resulting in a smaller footprint for the wire-wound coil component. However, the entire outer electrode is formed not only on the bottom surface but also on the side of the flange's lateral surface. This facilitates the formation of a solder fillet along the flange's lateral surface when the wire-wound coil component is soldered to a substrate, thereby strengthening the bond between the coil component and the substrate. This process therefore yields a wire-wound coil component that combines a reduced footprint with a reinforced bond to the substrate.

[0026] According to further embodiments of the present disclosure, a method for producing a wire-wound coil component comprises: A, producing a core made of a ceramic material containing a metal oxide and comprising a coil former and a flange connected to an end section of the coil former; B, forming a thick-film electrode segment, which is a metal composite film, on a lower surface by applying a conductive paste to the lower surface and by firing the paste; C, forming a low-resistance region by locally heating a lateral surface; and D, forming a thin-film metal segment covering the thick-film electrode segment and the low-resistance region by plating.

[0027] This method, in addition to being advantageous in the same way as the one described above, requires no pretreatment on the lower surface of the flange for the formation of the outer electrode. The manufacturer can form the outer electrode without compromising its strength, reliability, or adhesion to the lower surface of the flange. Furthermore, the low-resistance region provides a starting point from which the thin-film metal segment can grow, thus making its formation efficient. It should be noted that the low-resistance region is formed after the thick-film electrode segment. Otherwise, the firing process for the formation of the thick-film electrode segment would further oxidize the low-resistance region, increasing its electrical resistance and hindering the subsequent formation of the thin-film metal segment.Furthermore, the simultaneous formation of the metal thin-film segment, an electrode formed by plating, on the thick-film electrode segment and on the low-resistance region simplifies the formation of the outer electrode.

[0028] The above method can further include: E, winding a wire around the coil former, and F, joining an end section of the wire to the thick-film electrode segment by thermocompression bonding of the lower surface. In this arrangement, the heat and external force applied during thermocompression bonding of the wire end section to the thin-film metal segment are absorbed by the thick-film electrode segment, and little is transferred to the flange. The effect on the strength, reliability, and adhesion of the outer electrode relative to the lower surface is therefore further reduced.

[0029] Other features, elements, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of some embodiments of the present disclosure with reference to the attached drawings.

[0030] Preferred embodiments of the present invention are explained in more detail below with reference to the accompanying drawings. These show: Fig. 1 a front view of a first example of a wire-wound coil component according to an embodiment of the present disclosure; Fig. 2 a perspective view of the wire-wound coil component in Fig. 1, which is positioned upside down; Fig. 3 an enlarged partial cross-sectional view of the wire-wound coil component in Fig. 1; Fig. 4 a front view of the wire-wound coil component in Fig.1, which is attached to a substrate; Fig. 5A Side views of a flange which is irradiated on its lateral surface with a laser up to 5C; Fig. 6A Cross-sectional diagrams illustrating a process of the formation of an external electrochemical potential; 6D Trode Fig. 7 an enlarged cross-sectional view of an example of a low-resistance region; Fig. 8A Cross-sectional diagrams illustrating another example of a process from 8D formation of an external electrode; Fig. 9 a vertical coil component as a second example of a wire-wound coil component according to an embodiment of the present disclosure and Fig. 10 a vertical coil component as a third example of an embodiment of the present disclosure.

[0031] Fig. 1 and Fig.Figure 2 shows a front view and a perspective view, respectively, of a surface-mounted inductor 1 as a first example of a wire-wound coil component according to an embodiment of the present disclosure. Fig. Inductor 1 is upside down. As in Fig. 1 and Fig. As illustrated in Figure 2, the inductor 1 has a core 50, a wire 57, and outer electrodes 54 and 55. The core 50 has a coil former 53 and two flanges 51 and 52, which are connected to the two end sections of the coil former 53. The wire 57 is wound around the coil former 53. The end sections of the wire 57 are electrically coupled to the outer electrodes 54 and 55. All drawings, including Fig. 1. These are schematic representations. In actual products, the size of each element, such as dimensions and aspect ratios, may vary.

[0032] The core 50 is made of a ceramic material containing a metal oxide, such as Ni-Zn ferrite or Ni-Cu-Zn ferrite. Fig. Figure 3 is an enlarged partial cross-sectional view of the wire-wound coil component in Fig. Figure 1 illustrates the flange 52 of the core 50 and its surroundings. The flange 51 of the core 50 and its surroundings have the same structure as in Figure 1. Fig. 3, although this is neither illustrated nor described. As in Fig.As illustrated in Figure 3, the flange 52 has a side surface 52a and a bottom surface 52b. When the coil component is mounted on a substrate (not illustrated), the bottom surface 52b faces the substrate, and the side surface 52a is perpendicular to the substrate. Furthermore, the side surface 52a is opposite a connection surface of the flange 52, the surface where the flange 52 is connected to the coil former 53, and the bottom surface 52b is positioned between the side surface 52a and the connection surface. That is, the inductor 1 is what is referred to as a horizontal inductor, with the coil former 53 extending parallel to the substrate on which the inductor 1 is mounted.

[0033] The wire 57 is a metal wire, such as a copper, silver, or gold wire, and is coated with a resin, such as polyurethane, polyesterimide, or polyamideimide, for insulating purposes. When the inductor 1 is mounted on a substrate, the winding axis of the wire 57 is parallel to the substrate. As shown in Fig. As illustrated in Figure 3, one end section 57a ​​of the wire 57 is electrically coupled to the outer electrode 55 by thermocompression bonding on the side where the lower surface 52b of the flange 52 is located. The other end section 57b of the wire 57 is similarly electrically coupled to the outer electrode 54 on the side where the lower surface 51b of the flange 51 is located (see Figure 3). Fig. 2).

[0034] The outer electrodes 54 and 55 are, as in Fig.Figure 1 illustrates essentially L-shaped electrodes which, when viewed from the front, cover the sides of the lateral and lower surfaces of flanges 51 and 52. As shown in Fig.Figure 3 shows that the outer electrode 55 has a metal thin-film segment 55a contacting the lateral surface 52a, a base electrode segment (thick-film electrode segment) 55b contacting the lower surface 52b, and a first and a second coating 55c and 55d covering the metal thin-film segment 55a and the base electrode segment 55b, respectively. The metal thin-film segment 55a is a thin film of metal formed by a plating process, as described below, in which low-resistance regions 43 provide starting points for growth, and is made of a metallic material with low electrical resistance, such as Cu, Au, or Ag. The base electrode segment 55b is a thick film containing a metal with low electrical resistance, such as Ag, Cu, or Au, and glass, such as silica.The first and second coatings 55c and 55d, for example, are thin films of Ni and Sn respectively, produced separately by plating, and improve the corrosion resistance and wettability of the outer electrode 55. Ni and Sn are not the only possible materials for the first and second coatings 55c and 55d. Each of these coatings can contain Cu, Au, and / or Ag in addition to Ni or Sn, and can even be made from an alloy, an intermetallic compound, or any similar material containing these metals.

[0035] As can be seen from the above, the outer electrode 55 of the inductor 1 is thinner on the side of the lateral surface 52a than on the side of the lower surface 52b, where the base electrode segment 55b is located, because the thin-film metal segment 55a of the flange 52 is located on the lateral surface 52a, and the base electrode segment 55b does not extend to this area. Therefore, the inductor 1 requires less space on the substrate to which it is mounted compared to existing substrates, provided it is mounted in a suitable orientation with the lower surface 52b facing the substrate and the lateral surface 52a perpendicular to the substrate.

[0036] Furthermore, the outer electrodes 54 and 55 of the inductor 1 are located not only on the side of the lower surface 51b, 52b, but also on the side of the lateral surface 51a, 52a of the flanges 51 and 52. As shown in Fig. As illustrated in Figure 4, when the inductor 1 is attached to a substrate 10 by soldering to connection areas 11 and 12, this supports the formation of solder fillets 13 and 14 along the side surfaces 51a and 52a. Consequently, the inductor 1 is more securely bonded to the substrate 10 than it would be if it were merely soldered to the side of the lower surface 51b, 52b.

[0037] It can be observed that the lateral surface 52a of the inductor 1, which contacts the metal thin-film segment 55a, has a reduced layer 52c. The reduced layer 52c comprises low-resistance regions 43 (not shown in Fig.Figure 3 illustrates the formation of a reduced metal oxide. The low-resistance regions 43 exhibit a lower electrical resistance than the rest of the flange 52 and the coil former 53 (core 50). The thin-film metal segment 55a of the inductor 1, which contacts the lateral surface 52a, is formed using these low-resistance regions 43. One formation method is as follows.

[0038] Fig. Figures 5A to 5C illustrate the irradiation of the lateral surface 52a of the flange 52 with a laser L as preparation for the formation of the metal thin-film segment 55a on the lateral surface 52a. Fig.In the drawing, laser L scans the lateral surface 52a in the horizontal direction and continuously emits a beam (or the core 50 moves in the horizontal direction in the drawing). The scanning direction is not critical and can be vertical in the drawing, and the laser can even move in zigzag or circular motions. Irradiation with laser L produces many linear markings 40 on the lateral surface 52a. Although the linear markings 40 in Fig. Since the 5A in the drawing are vertically spaced, the linear markings 40 can alternatively be created close together, overlapping each other. Fig. 5B The laser L is irradiated in a dot pattern. This produces many distributed dot markings 41 on the lateral surface 52a. Fig.Figure 5C illustrates irradiation with the laser L in a dashed-line pattern, which generates numerous line segment markings 42 on the lateral surface 52a. In all these cases, it is intended that the section of the lateral surface 52a in which the metal thin-film segment 55a is to be formed is irradiated uniformly with the laser L.

[0039] Fig. Figures 6A to 6D schematically illustrate an example of a process for the formation of the metal thin film segment 55a, in particular one in which the lateral surface 52a of the flange 52 is irradiated with a laser L in a pattern of evenly spaced lines.

[0040] First, as in Fig.6A The lateral surface 52a of the flange 52 is irradiated with a laser within the section where the outer electrode is to be formed. This creates a laser marking 40 on the lateral surface 52a of the flange 52, which has a substantially V- or U-shaped cross-section. Although the laser L in Fig.When the laser 6A is focused on a specific point, the laser L can strike a surface. The laser melts and solidifies the surface of the flange 52, leaving the laser mark 40 as a scar. The extent of the change is greatest at the center of the point where the laser energy reaches its peak value, hence the essentially V- or U-shaped cross-section of the laser mark 40. Surrounding the laser mark 40 is a low-resistance region 43, which comprises the inner walls of the mark. The low-resistance region 43 is a modified form of the ceramic material from which the flange 52 is made (ferrite) and exhibits a lower electrical resistance than the ceramic material.In particular, if the flange 52 (core 50) is made of Ni-Zn ferrite containing an oxide of Fe, Ni, and Zn, the low-resistance region 43 contains a reduced form of the metal oxide (more precisely, a portion of the Fe from the ferrite) resulting from laser irradiation, possibly together with reduced Ni and / or Zn. If the flange 52 (core 50) is a piece of Ni-Cu-Zn ferrite containing an oxide of Fe, Ni, Cu, and Zn, the low-resistance region 43 contains a reduced form of the metal oxide (more precisely, Fe and / or Cu from the ferrite) resulting from laser irradiation, possibly together with reduced Ni and / or Zn. A metal or metals of this type, reduced from a metal oxide, exist in the low-resistance region 43, for example, in the form of a simple metal, a component of an alloy or intermetallic compound, or a component a metal oxide in which the metal orThe metals have a lower valence than in the original metal oxide, resulting in the low-resistance region 43 having an electrical resistance lower than in the rest of the core 50, where the metal(s) are generally in oxide form. The dimensions of the low-resistance region 43, such as depth and width, can be modified by adjusting the laser processing parameters, such as energy and exposure area.

[0041] Then, as in Fig.6B The laser irradiation is repeated to generate several laser marks 40 with a distance D between them on the lateral surface 52a of the flange 52. In the illustrated process, the center-to-center distance D between the projected points of two laser light pulses is longer than the width W of the low-resistance regions 43 (e.g., the mean of the diameters of the laser marks 40 or the lengths of the marks 40 as measured in the direction in which they are repeated). Thus, insulating regions 44 are present between the laser marks 40 and the low-resistance regions 43. In the insulating sections 44, the ceramic material from which the flange 52 is made is exposed.The reduced layer 52c is a region comprising several low-resistance regions 43 formed in this way and may include insulating regions 44 (regions where the electrical resistance is not lower than in the rest of the core 50) adjacent to the low-resistance regions 43.

[0042] Then, as in Fig. 6C, the core 50, including the flange 52, is immersed in an electroplating bath in view of the laser-formed low-resistance regions 43. An early stage of the plating process is illustrated. In the low-resistance regions 43, where the electrical resistance is lower than in the rest (insulating regions 44), the current density is also lower. The metal deposits 45a are therefore only present on the surfaces of the low-resistance regions 43, not yet on the insulating regions 44. Therefore, at this stage, the continuous thin-film metal segment 55a still needs to be completed.

[0043] Fig.Figure 6D illustrates a completed electroplating process. As the plating process continues, a layer of plating metal grows around the metal deposits 45a on the low-resistance regions 43, extending to reach the insulating regions 44 adjacent to the low-resistance regions 43. Plating continues until the adjacent metal deposits 45a merge, forming a continuous thin-film metal segment 55a on the lateral surface 52a. Because the plating metal accumulates more rapidly on the reduced layer 52c formed by laser irradiation than on the rest of the flange 52, it selectively forms a layer on the reduced layer 52c without strict control of the plating duration. The completion time and the thickness of the thin-film metal segment 55a can be adjusted by setting the plating duration or the voltage or current used for plating.

[0044] Including this process of forming the metal thin film segment 55a, the procedure for manufacturing the inductor 1 is as follows.

[0045] First, a core 50 is manufactured. The core 50 is made of a ceramic material containing a metal oxide and has a coil former 53 and two flanges 51 and 52 which are connected to the two end sections of the coil former 53.

[0046] A conductive paste containing metal and glass is then applied to the section of the flange 52 that is to provide the lower surface 52b, and the resulting coating is fired to form a base electrode segment 55b. The application and firing of the conductive paste can be carried out by a known method. For example, a resin containing an silver powder and a glass frit are applied to the lower surface 52b of the flange 52 by screen printing, dipping, inkjet printing, or any other method, and the resulting coating is fired. If the conductive paste contains metal and a thermosetting resin, the base electrode segment 55b can be formed by heating the applied coating of the conductive paste to a temperature at which the thermosetting resin cures.

[0047] Subsequently, a reduced layer 52c including low-resistance regions 43 is formed by locally limited heating of the section of the flange 52 that is to provide the lateral surface 52a, for example using the laser irradiation described above.

[0048] Then, for example by means of the plating process described above, a metal thin film segment 55a is formed to cover the base electrode segment 55b and the low-resistance regions 43 (reduced layer 52c).

[0049] In this way, an outer electrode 55 is formed on the core 50. With this method, the base electrode segment 55b is not formed on the side of the lateral surface 52a of the flange 52, thus reducing the space required for the inductor 1. However, the entire outer electrode 55 is formed not only on the side of the lower surface 52b but also on the side of the lateral surface 52a of the flange 52. This facilitates the formation of a solder joint along the lateral surface 52a when the inductor 1 is soldered to a substrate, thereby strengthening the bond between the inductor 1 and the substrate. Furthermore, no pretreatment is required on the side of the lower surface 52b of the flange 52 for the formation of the outer electrode 55.This means that the manufacturer can form the outer electrode 55 without affecting the strength, reliability, or adhesion of the outer electrode 55 to the lower surface 52b. Furthermore, the low-resistance regions 43 provide starting points for the growth of the metal thin-film segment 55a, thus making its formation efficient. It should be noted that the low-resistance regions 43 are formed after the base electrode segment 55b. Otherwise, the firing process for the formation of the base electrode segment 55b would further oxidize the low-resistance regions 43, thereby increasing the electrical resistance there, which would impair the subsequent formation of the metal thin-film segment 55a.

[0050] In this process, the base electrode segment 55b is also covered with the metal thin-film segment 55a, which supports the formation of an outer electrode 55 that extends continuously from the lateral surface 52a to the lower surface 52b of the flange 52. The metal thin-film segment 55a can optionally be covered with a first and a second coating 55c and 55d for improved corrosion resistance and wettability of the outer electrode 55.

[0051] A wire 57 is then wound around the coil former 53, and an end section 57a ​​of the wire 57 is connected by thermocompression bonding to the second coating 55d on the side where the section of the flange 52 is located that is to provide the lower surface 52b, thus completing the inductor 1. The connected end section 57a ​​of the wire 57 can penetrate the second coating 55d, the first coating 55c, and the metal thin-film segment 55a, reaching the base electrode segment 55b. This connects the end section 57a ​​of the wire 57 to the outer electrode 55 on the side of the lower surface 52b where the base electrode segment 55b is located.In this type of connection, the heat and external force applied during the thermocompression bond between the end section 57a ​​of the wire 57 and the thin-film metal segment 55a are absorbed by the base electrode segment 55b, and little is transferred to the flange 52. The effect on the strength, reliability, and adhesion at the outer electrode 55 relative to the lower surface 52b is therefore further reduced. experiment

[0052] The following describes an experiment in which the outer electrodes 54 and 55 of an inductor 1 were actually formed. (1) A Ni-Cu-Zn ferrite core 50 was irradiated with a forward- and backward-moving laser, forming a reduced layer 52c including low-resistance regions 43. The processing parameters were as shown in the table below. According to the inventor's research, the wavelength of the laser is not critical, as long as it is approximately in the range of, for example, 532 nm to 10,620 nm. The distance represents the center-to-center distance between the projected points of outgoing and reflected pulses of laser light. Table 1 [Laser processing parameters] wavelength 1064 nm (YVO4) Output power 14 A Sampling speed 200 mm / s Q-switch frequency 20 kHz Distance 30 µm Point diameter 70 µm Energy density 1 J / sec

[0053] (2) The laser-irradiated core 50 was electroplated by barrel plating under the conditions listed in the table below. Table 2 [Plating Conditions] Electroplating bath copper pyrophosphate bath Rotational speed [rpm] 24 rpm Current [A] 12 A Temperature [°C] 55 °C Length of time 8 min

[0054] Plating under the above-mentioned conditions yielded a good thin-film metal segment 55a of Cu with an average thickness of approximately 2 µm on the lateral surface 52a of the flange 52. A Ni-Zn ferrite core 50 gave similar results. Solution baths other than a copper pyrophosphate bath, for example a copper sulfate bath and a copper cyanate bath, can also be used. Evaluation

[0055] The state of the laser-formed reduced layer 52c (low-resistance regions 43) was then evaluated by determining the Fe, Cu, and Zn valence on the surface of a laser-irradiated Ni-Cu-Zn ferrite sample and an unirradiated sample using XPS (x-ray photoelectron spectroscopy) and conversion sectorron yield-K-edge-XAFS (x-ray absorption fine structure) of Fe, Cu, and Zn. XPS revealed that the laser-irradiated sample was free of metal in the surface layer but contained metal in the lower layer. XAFS revealed that the laser-irradiated sample contained metallic Cu in the surface layer. The surface layer of the laser-irradiated sample was also free of metallic Fe but contained semiconducting and insulating Fe components. In the lower layer, the ratio of Fe 2+ to Fe 3+higher than that in the entire sample. When ferrite is irradiated with a laser, the metal oxide in the ferrite is thermally decomposed, and the metals in the exposed sections are reduced. However, in this experiment, it appears that in the surface layer of the exposed sections, some of the metals were reoxidized by residual heat (not to the extent that the metals were sintered), while in the lower layer, the metals remained reduced.

[0056] Fig.Figure 7 illustrates an example of a cross-sectional structure of a low-resistance region 43 prepared in this manner. The lower layer of the low-resistance region 43 is a reduced region 43a, in which the metals reduced by the metal oxide in the ferrite remain reduced, and the surface side of the low-resistance region 43 is a reoxidized coating 43b containing semiconducting and / or insulating components that are metal oxides resulting from reoxidation of the metals. The reduced region 43a and the reoxidized coating 43b constitute the low-resistance region 43. The reoxidized coating 43b is not essential for the low-resistance region 43, and it is possible to control the formation of the reoxidized coating 43b by performing the laser irradiation in a vacuum or an N2 atmosphere, not in air.

[0057] If formed, the reoxidized coating 43b can have the following advantages: Fe3O4 in the reoxidized coating 43b is not simply reoxidized further at room temperature. It therefore slows down the reoxidation of the underlying reduced region 43a, preventing the material from changing more than necessary and limiting the change in the quality of the reoxidized coating 43b over time. The reoxidized coating 43b is a type of semiconductor, and its electrical resistance is lower than that of ferrite, which is an insulator. Therefore, if the flange is electroplated, the reoxidized coating 43b can be used as a starting point for the growth of a layer of the plating metal.However, it can be observed that the formation of the metal thin film segment 55a with low-resistance regions 43, which have a reduced region 43a under the reoxidized coating 43b, is more efficient, which is due to an improved current density in such low-resistance regions 43 during electroplating.

[0058] Fig. Figures 8A to 8D illustrate another example of an outer electrode formation process 55, in particular one in which the lateral surface 52a of the flange 52 is densely irradiated with a laser L. The term "densely irradiated" means that the center-to-center distance D between the projected points of laser light is essentially equal to or less than the previously mentioned width W of the low-resistance regions 43. Therefore, the low-resistance regions 43 are interconnected under adjacent laser markings 40 (see Figure 8A to 8D). Fig.8B). Not all low-resistance regions 43 need to be connected. Due to dense irradiation, almost the entire reduced layer 52c on the lateral surface 52a of the flange 52 is covered by low-resistance regions 43.

[0059] In this case, it becomes apparent how in Fig. Figure 8C illustrates that shortly after the start of plating, metal deposits 45a form on the surfaces of the low-resistance regions 43. The metal deposits 45a are very close to each other, and therefore adjacent metal deposits 45a bond rapidly. Consequently, a continuous thin-film metal segment 55a forms faster than in the Fig. 6A to 6D illustrate the process.

[0060] If the side surface 52a as in Fig.When 8A to 8D are densely irradiated with a laser L, the laser markings 40 are also densely generated. The section of the lateral surface 52a in which the reduced layer 52c was formed is therefore recessed. Since the metal thin-film segment 55a is formed in this recess in the lateral surface 52a, the surface of the metal thin-film segment 55a can be essentially flush with or lower than the rest of the lateral surface 52a. Together with the thinness of the metal thin-film segment 55a itself, this limits the thickness of the protruding section of the outer electrode 55, further reducing the space requirement.

[0061] Although the outer electrode 55 of the inductor 1 is located only on the sides of the lateral surface 52a and the lower surface 52b of the flange 52, the outer electrode 55 can also be formed on any other surface of the flange 52 (e.g., on the surfaces that are in Fig.1 on the front and back sides). This has a minor effect on the space requirement, as it is possible to omit the base electrode segment on this surface or these surfaces by forming a thin metal film 55a there in the same way as on the side surface 52a.

[0062] Although the inductor 1 has an outer electrode on each flange, outer electrode 54 on flange 51 and outer electrode 55 on flange 52, any number of outer electrodes can be present on flanges 51 and 52; for example, two can be present on each flange. That is to say, a wire-wound coil component according to an embodiment of the present disclosure can be a common-mode choke, a transducer, or any other coil component having multiple wires 57.

[0063] Fig.Figure 9 illustrates a vertical surface-mounted inductor 2 as a second example of a wire-wound coil component according to an embodiment. The inductor 2 has a core 60 and outer electrodes 64 and 65. The core 60 has a coil former 63 and two flanges 61 and 62, which are connected to the two end sections of the coil former 63. The outer electrodes 64 and 65 have the same structure as the outer electrodes 54 and 55 of the inductor 1, but both extend from the top surface to a lateral surface of a flange of the core 60, the flange 61. A wire (not shown) is wound around the coil former 63, the two end sections of which are connected one-to-one to the outer electrodes 64 and 65.When inductor 2 is mounted on a substrate, the upper surface of flange 61 in this drawing can become the lower surface facing the substrate, and the side surfaces of flange 61 become perpendicular to the substrate. That is, inductor 2 differs from inductor 1 in that the lower surface of flange 61 faces the connection surface where flange 61 is connected to coil former 63, and the side surfaces are located between the lower surface and the connection surface. Inductor 2 also combines a reduced footprint with a reinforced bond to a substrate, similar to inductor 1.

[0064] Although the inductor in Fig. 9 has two external electrodes 64 and 65, four or more external electrodes may be present on the flange 61 if two or more wires are used.

[0065] Fig. Figure 10 illustrates an example of a common-mode choke coil with two conductors as an application of a coil component according to an embodiment of the present disclosure. Fig. In Figure 10, the coil component 3 is inverted. The core 70 of the coil component 3 has a coil former 71 in its center along its length and a pair of flanges 72 and 73 at the ends of the coil former 71. Two parallel wires are wound around the coil former 71 (not shown). Each of the flanges 72 and 73 has two projections on the side of its lower surface, and on these projections are two external electrodes 74 and 75 or 76 and 77 (four in total). The two wires are connected and attached at one end to the external electrodes 74 and 75 on the flange 72 and at the other end to the external electrodes 76 and 77 on the flange 73.

[0066] In this drawing, the upper surfaces of the projections of flanges 72 and 73 are the lower surfaces (mounting surfaces) 72a and 73a of the coil component 3, and the outer lateral surfaces of flanges 72 and 73 are the lateral surfaces 72b and 73b of component 3, perpendicular to the mounting surfaces. Each of the outer electrodes 74 to 77 consists of a stack of a thick-film electrode segment and a thin-film metal segment located on the side of the mounting surface 74a to 77a, and a thin-film metal segment located on the side of the lateral surface 74b to 77b. Because of this structure, the connection between the wire ends and the side of the connection surface 74a to 77a of the outer electrodes 74 to 77 is extremely resilient, and when the coil component 3 is mounted on a substrate, the bond between them is strong.The flanges 72 and 73 are thinner on the side of the lateral surface 74b to 77b than on the side of the mounting surface 74a to 77a, thus requiring less space. In this arrangement as well, the heat and external force applied during the connection of the wire ends to the outer electrodes, for example by thermocompression bonding, are absorbed by the base electrode segments, with little being transferred to the flanges, since the wire ends are connected to the mounting surface 74a to 77a of the outer electrodes 74 to 77.

[0067] Although the ceramic material for the core in the examples above is ferrite, ferrite is not the only ceramic material that can be used. Aluminum, for example, can be used instead. As long as the side of the flange's lateral surface—the side where the thin-film metal segment is formed—is made of a ceramic material containing a metal oxide, the coil former and the other sides of the flanges can be made of a different material.

[0068] Although electroplating is used in the examples above, electroless plating can also be employed. With electroless plating, it is also possible to selectively form the metal thin-film segment on the reduced layer through a substitution reaction between the metals reduced by the metal oxide in the ceramic material and the metal in the plating bath. If electroless plating is used, the surface of the reduced layer can be treated with a catalyst to accelerate the substitution reaction.

[0069] Although the examples above achieve localized heating through laser irradiation, other heating methods, such as electron beam irradiation and the use of an image oven, can also be employed. All these alternatives are capable of focusing energy from a heat source and heating a specific area of ​​the flange's lateral surface, thus not affecting the characteristics of the rest of the flange.

[0070] In another variation, unlike the examples above, the laser light can be split to hit different points simultaneously.

[0071] Furthermore, the laser can be defocused, so that the light hits a larger area than if the laser were focused.

[0072] Although in the examples above the metal thin-film segment covers the base electrode segment, the metal thin-film segment only needs to lie on at least part of the reduced layer. Even in such a case, covering the metal thin-film and base electrode segments with any other element, for example, a first and a second coating, results in an outer electrode in which the metal thin-film and base electrode segments are combined. Alternatively, the metal thin-film and base electrode segments can form separate electrodes instead of being combined. In such a case, the metal thin-film segment acts as a dummy electrode, reinforcing the bond between the coil component and a substrate by facilitating the formation of a solder fillet.

[0073] Although the metal thin-film segment in the examples above is formed by plating, other thin-film formation methods, such as atomization and vapor deposition, can also be used. If one of these alternatives is used, the lateral surface of the flanges does not need to have the low-resistance regions and the reduced layer. However, it is preferred to first form a reduced layer, including low-resistance regions, and then a metal thin-film segment by plating. This would be more practical, for example, in terms of the availability of production equipment and the ease of carrying out the process.

[0074] Although in the examples above the side of the lower surface of the flanges does not have low-resistance regions or a reduced layer, low-resistance regions and a reduced layer can be formed on the side of the lower surface prior to the formation of the base electrode segment.

Claims

[1] Wire-wound coil component (3) having the following features: a core (50; 60; 70) comprising a coil former (53; 63, 71) and a flange (51, 52; 61, 62; 72, 73) connected to an end section of the coil former (53; 63; 71); a wire (57) wound around the coil former (53; 63; 71); and an outer electrode (54, 55; 64, 65; 74-77) with which an end section (57a, 57b) of the wire (57) is electrically coupled, wherein: the flange (51, 52; 61, 62; 72, 73) has a side surface (51a, 52a; 72b, 73b) and a bottom surface (51b, 52b; 72a, 73a) and the outer electrode (54, 55; 64, 65; 74-77) has a metal thin-film segment (55a) that touches the lateral surface (51a, 52a; 72b, 73b) and a thick-film electrode segment (55b) that is a metal composite film that touches the lower surface (51b, 52b; 72a, 73a); wherein a part of the lateral surface (51a, 52a; 72b, 73b) that touches the metal thin film segment (55a) has a low-resistance region (43); wherein the flange (51, 52; 61, 62; 72, 73) consists of a ceramic material containing a metal oxide; and the low-resistance region (43) contains a metal resulting from the reduction of part of the metal oxide; and wherein one surface side of the low-resistance region (43) is a reoxidized coating (43b) and the reoxidized coating (43b) contains a metal oxide resulting from a reoxidation of the metal. [2] Wire-wound coil component (3) according to claim 1, wherein the end section (57a, 57b) of the wire (57) is connected to the outer electrode (54, 55; 64, 65; 74-77) above the lower surface. [3] Wire-wound coil component (3) according to claim 1 or 2, wherein the thick-film electrode segment (55b) is covered with the metal thin-film segment (55a). [4] Wire-wound coil component (3) according to any one of claims 1 to 3, wherein the lower surface (51b, 52b; 72a, 73a) is a surface facing a substrate (10) and the side surface (51a, 52a; 72b, 73b) is a surface perpendicular to the substrate (10) when the coil component (3) is attached to the substrate (10). [5] Wire-wound coil component (3) according to any one of claims 1 to 4, wherein the lateral surface (51a, 52a; 72b, 73b) is opposite a connecting surface to which the flange (51, 52; 61, 62; 72, 73) is connected to the coil body (53; 63; 71) and the lower surface (51b, 52b; 72a, 73a) is positioned between the lateral surface (51a, 52a; 72b, 73b) and the connecting surface. [6] Wire-wound coil component (3) according to any one of claims 1 to 5, wherein the flange (51, 52; 61, 62; 72, 73) is made of a ferrite material. [7] Method for manufacturing a wire-wound coil component (3) wherein the method comprises the following steps: A, Manufacturing a core (50; 60; 70) comprising a coil former (53; 63; 71) and a flange (51, 52; 61, 62; 72, 73) connected to an end section of the coil former (53; 63; 71); B, Forming a thick-film electrode segment (55b) which is a metal composite film, on a lower surface (51b, 52b; 72a, 73a) by applying a conductive paste to the lower surface (51b, 52b; 72a, 73a) and by firing or heat-curing the paste and C, Forming a metal thin film segment (55a) on a lateral surface (51a, 52a; 72b, 73b); so that a part of the lateral surface (51a, 52a; 72b, 73b) that touches the metal thin film segment (55a) has a low-resistance region (43); such that the flange (51, 52; 61, 62; 72, 73) consists of a ceramic material containing a metal oxide; and the low-resistance region (43) contains a metal resulting from the reduction of a portion of the metal oxide; and such that one surface side of the low-resistance region (43) is a reoxidized coating (43b) and the reoxidized coating (43b) contains a metal oxide resulting from a reoxidation of the metal. [8] Method for manufacturing a wire-wound coil component (3) wherein the method comprises the following steps: A, Manufacturing a core (50; 60; 70) made of a ceramic material containing a metal oxide and comprising a coil former (53; 63; 71) and a flange (51, 52; 61, 62; 72, 73) connected to an end section of the coil former (53; 63; 71); B, Forming a thick-film electrode segment (55b) which is a metal composite film on a lower surface (51b, 52b; 72a, 73a) by applying a conductive paste to the lower surface (51b, 52b; 72a, 73a) and by firing or heat-curing the paste; C, Formation of a low-resistance region (43) by locally heating a lateral surface (51a, 52a; 72b, 73b) and D, Forming a metal thin-film segment (55a) covering the thick-film electrode segment (55b) and the low-resistance region (43) by plating. [9] Method according to claim 8 for producing a wire-wound coil component (3), wherein the method further comprises the following steps: E, winding a wire (57) around the coil body (53; 63; 71) and F, Connecting an end section (57a, 57b) of the wire (57) to the thick-film electrode segment (55b) by thermocompression bonding above the lower surface (51b, 52b; 72a, 73a).

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