Patent Publication Number: US-11664150-B2

Title: Coil component and its manufacturing method

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a coil component and its manufacturing method and, more particularly, to a coil component having a structure in which a wire-shaped coil conductor is embedded in a magnetic element body and its manufacturing method. 
     Description of Related Art 
     As a coil component having the structure in which a wire-shaped coil conductor is embedded in a magnetic element body, coil components described in JP 2014-175437A and JP 2013-149814A are known. In the coil components described in JP 2014-175437A and JP 2013-149814A, an end portion of the coil conductor embedded in the magnetic element body is exposed from the magnetic element body, and the surface of the exposed end portion is plated, to thereby form a terminal electrode. 
     However, in the coil component described in JP 2014-175437A, the terminal electrode is directly formed by plating on the end portion of the coil conductor, so that it is difficult to form the terminal electrode on the surface of the magnetic element body from which the coil conductor is not exposed. On the other hand, in the coil component described in JP 2013-149814A, a pasty conductive resin is applied on the surface of the magnetic element body so as to contact the end portion of the coil conductor, followed by curing and then formation of a plating film on the surface of the conductive resin, so that it is possible to easily form the terminal electrode on the surface of the magnetic element body from which the coil conductor is not exposed. 
     To enhance bonding strength between the conductive resin and the plating film, a conductive resin containing large-sized conductive particles is preferably used. However, when the size (diameter) of the conductive particles is large, the specific surface area thereof is small, so that connection reliability with respect to the end portion of the coil conductor may be unsatisfactory. The reason for this is considered as follows: electrical conduction between the conductive resin and the plating film is ensured by metal bonding between the conductive particles and the plating film, while electrical conduction between the conductive resin and the coil conductor is ensured by physical contact between them, so that when the size of the conductive particles is large, physical contact area between the conductive particles and the coil conductor becomes insufficient. 
     SUMMARY 
     It is therefore an object of the present invention to provide a coil component having a structure in which a wire-shaped coil conductor is embedded in a magnetic element body, capable of improving the connection reliability of the conductive resin with respect to the end portion of the coil conductor while ensuring the bonding structure between the conductive resin and the plating film. Another object of the present invention is to provide a manufacturing method for such a coil component. 
     A coil component according to the present invention includes: a magnetic element body; a coil conductor embedded in the magnetic element body and having an end portion exposed from the magnetic element body; and a terminal electrode connected to the end portion of the coil conductor, wherein the terminal electrode includes: a conductive resin contacting the end portion of the coil conductor and containing conductive particles and a resin material; and a metal film covering the conductive resin, the conductive resin including: a first conductive resin contacting the end portion of the coil conductor; and a second conductive resin contacting the metal film without contacting the end portion of the coil conductor, wherein the specific surface area of the conductive particles contained in the first conductive resin is larger than that of the conductive particles contained in the second conductive resin. 
     According to the present invention, two kinds of conductive resins differing in the specific surface area of the conductive particles are used, so that connection reliability with respect to the coil conductor can be improved by the first conductive resin with a large specific surface area, and connection reliability with respect to the metal film can be improved by the second conductive resin with a small specific surface area, i.e., a large particle volume. 
     In the present invention, the end portion of the coil conductor may have an exposed surface exposed from the magnetic element body and contacting the first conductive resin, and a non-exposed surface covered with the magnetic element body. The exposed surface may be larger in surface roughness than the non-exposed surface. This can further improve connection reliability between the end portion of the coil conductor and the conductive resin. In this case, the exposed surface of the coil conductor may have an outer exposed surface positioned outside the magnetic element body and an inner exposed surface embedded in the magnetic element body without contacting the magnetic element body, and the first conductive resin may contact both the outer and inner exposed surfaces. This can further improve connection reliability between the end portion of the coil conductor and the conductive resin. 
     In the present invention, the surface of the magnetic element body may be covered with a resin coating, and the second conductive resin may be formed on the resin coating. With this configuration, even when a conductive magnetic material is exposed to the surface of the magnetic element body, the conductive magnetic material exposed to the surface of the magnetic element body and the second conductive resin are prevented from contacting each other. 
     In the present invention, the conductive particles contained in the conductive resin may be bonded together through sintered metal. This can further reduce a resistance value of the conductive resin. 
     In the present invention, the magnetic element body may include a lower magnetic element body positioned within the inner diameter region of the coil conductor and an upper magnetic element body positioned outside the coil conductor, and the lower magnetic element body may be higher in density than the upper magnetic element body. Such a configuration can be obtained when a pressure for pressing the upper magnetic element body in a state where the coil conductor is mounted on the lower magnetic element body is set lower than a pressure for singly pressing the lower magnetic element body so as to prevent deformation or disconnection of the coil conductor. 
     A coil conductor manufacturing method according to the present invention includes: a first step of embedding a coil conductor in a magnetic element body such that an end portion of the coil conductor is exposed from the magnetic element body; a second step of preparing a first conductive resin containing conductive particles with a comparatively large specific surface area and a second conductive resin containing conductive particles with a comparatively small specific surface area; a third step of forming the first conductive resin on the surface of the magnetic element body so as to contact the end portion of the coil conductor; a fourth step of forming the second conductive resin so as to contact the first conductive resin without contacting the end portion of the coil conductor; and a fifth step of forming a metal film on at least the surface of the second conductive resin. 
     According to the present invention, connection reliability with respect to the coil conductor can be improved by the first conductive resin containing the conductive particles with a large specific surface area, and connection reliability with respect to the metal film can be improved by the second conductive resin containing the conductive particles with a small specific surface area, i.e., a large particle volume. 
     The coil conductor manufacturing method according to the present invention may further include, before the third step, steps of covering the surface of the magnetic element body with a resin coating and partially peeling the resin coating so as to expose the end portion of the coil conductor. With this configuration, even when a conductive magnetic material is exposed to the surface of the magnetic element body, the conductive magnetic material exposed to the surface of the magnetic element body and the second conductive resin are prevented from contacting each other. 
     As described above, according to the present invention, there can be provided a coil component having a structure in which a wire-shaped coil conductor is embedded in a magnetic element body, capable of improving the connection reliability of the conductive resin with respect to the end portion of the coil conductor while ensuring the bonding structure between the conductive resin and the plating film. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic perspective view of a coil component according to a preferred embodiment of the present invention as viewed from the upper surface side; 
         FIG.  2    is a schematic perspective view of the coil component shown in  FIG.  1    as viewed from the mounting surface side; 
         FIG.  3    is an xz cross-sectional view of the coil component shown in  FIG.  1   ; 
         FIG.  4    is a yz cross-sectional view of the coil component shown in  FIG.  1   ; 
         FIG.  5    is a schematic cross-sectional view illustrating, in an enlarged manner, a connection portion between one end of a coil conductor and a terminal electrode; 
         FIG.  6    is a flowchart for explaining manufacturing processes of the coil component shown in  FIG.  1   ; 
         FIG.  7    is a schematic perspective view illustrating the shape of a press-molded lower magnetic element body; 
         FIG.  8    is a schematic perspective view illustrating the shape of the coil conductor; and 
         FIG.  9    is a schematic perspective view illustrating a state where the one and the other ends of the coil conductor are exposed by partial peeling of a resin coating. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
       FIGS.  1  and  2    are schematic perspective views each illustrating the outer appearance of a coil component  1  according a preferred embodiment of the present invention.  FIG.  1    is a perspective view as viewed from the upper surface side, and  FIG.  2    is a perspective view as viewed from the mounting surface side.  FIG.  3    is an xz cross-sectional view of the coil component  1 , and  FIG.  4    is a yz cross-sectional view of the coil component  1 . 
     As illustrated in  FIGS.  1  to  4   , the coil component  1  according to the present embodiment includes a magnetic element body  10  having a substantially rectangular paralleled shape, a coil conductor  30  embedded in the magnetic element body  10 , and two terminal electrodes  21  and  22  each provided so as to extend over a mounting surface and a side surface of the magnetic element body  10  and to be connected to the coil conductor  30 . 
     The magnetic element body  10  is made of a composite magnetic material containing a magnetic material and a binder and includes a lower magnetic element body  11  and an upper magnetic element body  12 . The magnetic material contained in the composite magnetic material is particularly preferably soft magnetic metal powder having high permeability, and examples thereof include: ferrites such as Ni—Zn, Mn—Zn, and Ni—Cu—Zn; permalloy (Fe—Ni alloy); super permalloy (Fe—Ni—Mo alloy); sendust (Fe—Si—Al alloy); Fe—Si alloy; Fe—Co alloy; Fe—Cr alloy; Fe—Cr—Si alloy; Fe; amorphous (Fe group based alloy); and nanocrystal. The binder may be a thermosetting resin material such as epoxy resin, phenol resin, silicon resin, diallyl phthalate resin, polyimide resin, or urethane resin. 
     As illustrated in  FIGS.  3  and  4   , the lower magnetic element body  11  has a flat part  11   a  and a protruding part  11   b , and the coil conductor  30  is placed on the flat part  11   a  such that the protruding part  11   b  is inserted into the inner diameter part of the coil conductor  30 . Accordingly, the lower magnetic element body  11  is positioned in a region below the coil conductor  30  and within the inner diameter region thereof. The upper magnetic element body  12  is a portion where the coil conductor  30  placed on the lower magnetic element body  11  is embedded. Accordingly, the upper magnetic element body  12  is positioned above the coil conductor  30  and outside thereof. Although not particularly limited, in the present embodiment, the protruding part  11   b  has a tapered shape, so that when the lower magnetic element body  11  is molded using a die, the protruding part  11   b  is easily removed from the die. 
     The coil conductor  30  is a wire-shaped coated conducting wire obtained by applying insulating coating on a core material of copper (Cu) or the like. In the present embodiment, one coil conductor  30  is wound by a plurality of turns around the protruding part  11   b . One end  31  and the other end  32  of the coil conductor  30  are exposed from the magnetic element body  10  to be connected respectively to the terminal electrodes  21  and  22 . The coil conductor  30  may be a round wire having a circular cross section or a flat wire having a rectangular cross section. 
       FIG.  5    is a schematic cross-sectional view illustrating, in an enlarged manner, a connection portion between the one end  31  of the coil conductor  30  and the terminal electrode  21 . A connection portion between the other end  32  of the coil conductor  30  and the terminal electrode  22  has a structure similar to that of the forgoing connection portion of  FIG.  5   , so overlapping description will be omitted. 
     As illustrated in  FIG.  5   , the one end  31  of the coil conductor  30  is partially embedded in the magnetic element body  10  and partially exposed. More specifically, the one end  31  of the coil conductor  30  has an exposed surface A having an insulating coating  33  removed therefrom and exposed from the magnetic element body  10  and a non-exposed surface B covered with the magnetic element body  10  through the insulating coating  33 . The exposed surface A has an outer exposed surface A 1  positioned outside the magnetic element body  10  and an inner exposed surface A 2  embedded in the magnetic element body  10  without contacting the magnetic element body  10 . While the inner exposed surface A 2  is embedded in the magnetic element body  10 , the former is separated from the latter by the thickness of the insulating coating  33  due to the absence of the insulating coating  33 . The exposed surface A is larger in surface roughness than the non-exposed surface B, whereby a contact area of the exposed surface A with the terminal electrode  21  is increased. 
     The surface of the magnetic element body  10  is covered with a resin coating  50  excluding an area thereof where the one and the other ends  31  and  32  of the coil conductor  30  are exposed. Although it is not essential to provide such a resin coating  50  in the present invention, the existence of the resin coating  50  allows application of coating even when a conductive magnetic material is exposed to the surface of the magnetic element body  10 . 
     As illustrated in  FIG.  5   , the terminal electrode  21  includes a first conductive resin  41 , a second conductive resin  42 , and a metal film  43 . The first and second conductive resins  41  and  42  both contain conductive particles and a resin material and function as conductive resin layers serving as underlying layers of the metal film  43 . In the present embodiment, the specific surface area of the conductive particles contained in the first conductive resin  41  is larger than that of the conductive particles contained in the second conductive resin  42 . In other words, the average particle volume of the conductive particles contained in the second conductive resin  42  is larger than that of the conductive particles contained in the first conductive resin  41 . 
     The first conductive resin  41  is formed on the surface of the magnetic element body  10  so as to contact the exposed surface A of the magnetic element body  10 . Accordingly, the first conductive resin  41  contacts both the exposed surface A of the coil conductor  30  and a mounting surface  10   a  of the magnetic element body  10 . The first conductive resin  41  may be partially provided on the resin coating  50 . The first conductive resin  41  contacts both the outer and inner exposed surfaces A 1  and A 2  of the exposed surface A of the coil conductor  30 , whereby connection reliability is improved. 
     The second conductive resin  42  covers a side surface  10   b  of the magnetic element body  10  through the resin coating  50  and partially goes around to the mounting surface  10   a  side to contact the first conductive resin  41 . The second conductive resin  42  does not directly contact the exposed surface A of the coil conductor  30  but is electrically connected to the coil conductor  30  through the first conductive resin  41 . Although the second conductive resin  42  covers only a part of the first conductive resin  41  in the example of  FIG.  5   , it may cover the entire surface of the first conductive resin  41 . 
     The metal film  43  is formed by plating on the surfaces of the first and second conductive resins  41  and  42 . The metal film  43  may be a laminated film of nickel (Ni) and tin (Sn). Thus, the metal film  43  is not formed directly on the magnetic element body  10 , but formed thereon through the first conductive resin  41  or second conductive resin  42 . 
     As described above, the coil component  1  according to the present embodiment uses two kinds of conductive resins differing in the specific surface area of the conductive particles. The first conductive resin  41  contains the conductive particles with a large specific surface area (a small particle volume), so that it is possible to ensure a sufficient contact area between the exposed surface A of the coil conductor  30  and the conductive particles. Further, by increasing the content ratio of the magnetic material, adhesion with respect to the exposed surface A of the coil conductor  30  and the surface of the magnetic element body  10  is improved. On the other hand, the second conductive resin  42  contains the conductive particles with a small specific surface area (a large particle volume), so that bonding strength between the conductive particles and the metal film  43  formed by plating is enhanced. 
     The following describes a manufacturing method for the coil component  1  according to the present embodiment. 
       FIG.  6    is a flowchart for explaining manufacturing processes of the coil component  1  according to the present embodiment. 
     First, a first composite magnetic material containing a magnetic material and a binder is prepared and subjected to pressing to thereby mold the lower magnetic element body (step S 1 ). The form of the first composite magnetic material is not particularly limited and may be powdery, liquid, or pasty. The molded lower magnetic element body  11  is shaped as illustrated in  FIG.  7    and has the flat part  11   a  and the protruding part  11   b . The flat part  11   a  has openings  11   c . Although the lower magnetic element body  11  illustrated in  FIG.  7    corresponds to a single coil component  1 , simultaneous molding of a large number of the lower magnetic element bodies  11  arranged in an array allows a plurality of the coil components  1  to be obtained. 
     Then, the coil conductor  30  in an air-core shape wound as illustrated in  FIG.  8    is prepared and is mounted on the lower magnetic element body  11  such that the protruding part  11   b  is inserted into the inner diameter region of the coil conductor  30  (step S 2 ). At this time, the mounting is made such that the one and the other ends  31  and  32  of the coil conductor  30  are positioned on the back surface side of the lower magnetic element body  11  through the openings  11   c.    
     Then, a second composite magnetic material containing a magnetic material and a binder is prepared and subjected to pressing together with the lower magnetic element body  11  on which the coil conductor  30  is mounted to thereby mold the upper magnetic element body  12  (step S 3 ). The form of the second composite magnetic material is not particularly limited and may be powdery, liquid, or pasty. Further, the composition of the second composite magnetic material may be the same as or different from that of the first composite magnetic material. As a result, the coil conductor  30  is embedded in the magnetic element body  10  constituted of the lower and upper magnetic element bodies  11  and  12 , and the one and the other ends  31  and  32  of the coil conductor  30  are exposed from the magnetic element body  10 . 
     A pressure for press-molding the upper magnetic element body  12  may be lower than that for press-molding the lower magnetic element body  11 . This is because that the coil conductor  30  does not exist in the stage of press-molding the lower magnetic element body  11 , so that pressing can be carried out at a high pressure, while the upper magnetic element body  12  is press-molded together with the coil conductor  30 , so that when the pressing is carried out at an excessively high pressure, deformation or disconnection of the coil conductor  30  may occur. Particularly, when a powdery material is used as the composite magnetic material, it is necessary to carry out the pressing at a higher pressure than when a liquid or pasty composite magnetic material is used, so that the coil conductor  30  is more liable to deform or to be disconnected. To prevent such deformation or disconnection, it is preferable to make the pressure for press-molding the upper magnetic element body  12  lower than that for press-molding the lower magnetic element body  11 . In this case, even when the same composite magnetic material is used, the lower magnetic element body  11  becomes higher in density than the upper magnetic element body  12 , allowing a boundary therebetween to be visually confirmed. 
     Then, the resin coating  50  is formed on the entire surface of the magnetic element body  10  (step S 4 ), followed by irradiation of laser beam to peel the resin coating  50  of a portion covering the one and the other end  31  and  32  of the coil conductor  30  (step S 5 ). As a result, as illustrated in  FIG.  9   , the one and the other ends  31  and  32  of the coil conductor  30  are exposed, and the insulating coating  33  at the exposed portions is removed, whereby the coil conductor  30  has the exposed surface A. At this time, a part of the insulating coating  33  that is embedded in the magnetic element body  10  is preferably removed by adjusting the irradiation time or output of the laser beam to form the inner exposed surface A 2 . Further, the exposed surface A of the coil conductor  30  is preferably roughened by adjusting the irradiation time or output of the laser beam. 
     Then, the first conductive resin  41  is formed on the exposed surface of the magnetic element body  10  so as to contact the one and the other ends  31  and  32  of the coil conductor  30  (step S 6 ), and the second conductive resin  42  that covers the first conductive resin  41  and resin coating  50  is formed (step S 7 ). Specifically, the first and second conductive resins  41  and  42  can be formed by application of a pasty conductive resin material, followed by curing thereof. As described above, the specific surface area of the conductive particles contained in the first conductive resin  41  is larger than that of the conductive particles contained in the second conductive resin  42 . Thus, the first conductive resin  41  directly contacting the one and the other ends  31  and  32  of the coil conductor  30  can be improved in terms of connection reliability with respect to the one and the other ends  31  and  32 . On the other hand, the second conductive resin  42  does not directly contact the one and the other ends  31  and  32  of the coil conductor  30 , allowing conductive particles with a small specific surface area and a large particle volume to be used therefor. 
     The first and second conductive resins  41  and  42  each preferably contain sintered metal. The sintered metal may be nanosized silver (Ag). Using the first and second conductive resins  41  and  42  containing the sintered metal, the conductive particles not only contact with each other but also are bonded together through the sintered metal during sintering, thereby allowing resistance values of the first and second conductive resins  41  and  42  to be reduced. Particularly, when the sintered metal is added to the first conductive resin  41 , an alloy layer is formed on the surface of the coil conductor  30 , allowing connection reliability between the coil conductor  30  and the first conductive resin  41  to be further improved. For example, when a core material of the coil conductor  30  is made of copper (Cu), and the sintered metal is nanosized silver (Ag), an alloy layer of copper (Cu) and silver (Ag) is formed on the surfaces of the one and the other ends  31  and  32  of the coil conductor  30 . 
     Then, the metal film  43  is formed by electrolytic plating on the surfaces of the first and second conductive resins  41  and  42 , whereby the coil component  1  according to the present embodiment is completed. When the metal film  43  is formed by electrolytic plating, the conductive particles contained in the first and second conductive resins  41  and  42  and the metal film  43  are metal-bonded. Thus, conductive particles with a higher particle volume can provide a higher bonding strength. Since most of the metal film  43  contacts the second conductive resin  42  in the present embodiment, the bonding strength of the metal film  43  can be enhanced. When a conductive magnetic material is exposed to the surface of the magnetic element body  10 , the metal film  43  may be unintentionally formed also on the surface of the magnetic element body  10  in the stage of formation of the metal film  43  by electrolytic plating. However, by covering the surface of the magnetic element body  10  with the resin coating  50  in advance, it is possible to prevent the metal film  43  from being formed on an unintended portion. 
     It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention.