Patent Publication Number: US-2020303110-A1

Title: Multilayer coil component

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a multilayer coil component. 
     2. Description of Related Art 
     Known multilayer coil components include an element body including a plurality of metal magnetic particles and a plurality of coil conductors (see, for example, Japanese Unexamined Patent Publication No. 2013-055316). The plurality of coil conductors is disposed in the element body, the plurality of coil conductors being separated from each other in a predetermined direction and electrically connected to each other. 
     SUMMARY OF THE INVENTION 
     An object of one aspect of the present invention is to provide a multilayer coil component that controls a decrease in Q characteristics in a high-frequency range. 
     A multilayer coil component according to one aspect of the present invention includes an element body including a plurality of metal magnetic particles, a plurality of coil conductors disposed in the element body, the plurality of coil conductors being separated from each other in a predetermined direction and electrically connected to each other. The plurality of coil conductors includes one pair of side surfaces opposing each other in the predetermined direction. Surface roughness of the one pair of side surfaces is less than 40% of an average particle size of the plurality of metal magnetic particles. 
     Q characteristics of the multilayer coil component depend on a resistance of the coil conductors. In a high-frequency range, a current (signal) tends to flow near surfaces of the coil conductors due to the skin effect. Therefore, as the resistance at and near the surfaces of the coil conductors increases, the Q characteristics of the multilayer coil component decreases. Hereinafter, the resistance component at and near the surfaces of the coil conductors is referred to as “surface resistance”. A configuration in which the surfaces of the coil conductors have irregularities substantially increases a length of current flow, and thus increases the surface resistance, as compared with a configuration in which the surfaces of the coil conductors have no irregularities. 
     A configuration in which the surface roughness of the pair of side surfaces opposing each other in the predetermined direction is less than 40% of the average particle size of the plurality of metal magnetic particles controls an increase in surface resistance and controls a decrease in Q characteristics in a high-frequency range, as compared with a configuration in which the surface roughness of the pair of side surfaces is equal to or larger than 40% of the average particle size of the plurality of metal magnetic particles. Therefore, the one aspect controls the increase in the surface resistance and controls the decrease in the Q characteristics in the high-frequency range. 
     In the one aspect, the plurality of coil conductors may include another pair of side surfaces extending to couple the one pair of side surfaces. Surface roughness of the other pair of side surfaces may be smaller than the surface roughness of the one pair of side surfaces. This configuration has low surface resistance, as compared with a configuration in which the surface roughness of the other pair of side surfaces is equal to or greater than the surface roughness of the one pair of side surfaces. Therefore, this configuration further controls the increase in the surface resistance and further controls the decrease in the Q characteristics in the high-frequency range. 
     In the one aspect, the plurality of coil conductors may be plating conductors. 
     In a case in which the coil conductors are sintered metal conductors, the coil conductors are each formed by sintering a metal component (metal powder) contained in a conductive paste. In this case, the metal magnetic particles bite into the conductive paste before the metal component is sintered. Irregularities due to the shape of the metal magnetic particles are formed on a surface of the conductive paste. The formed coil conductors are deformed so that the metal magnetic particles bite into the coil conductors. Therefore, a configuration in which the coil conductors are the sintered metal conductors significantly increases the surface roughness of the coil conductors. 
     In a case in which the coil conductors are the plating conductors, the metal magnetic particles tend not to bite into the coil conductors. In this case, deformation of the coil conductors is reduced. Therefore, the configuration in which the coil conductors are the plating conductors controls an increase in the surface roughness of the coil conductors and controls an increase in the surface resistance. 
     The present invention will become more fully understood from the detailed description given hereinafter and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention. 
     Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a multilayer coil component according to an embodiment; 
         FIG. 2  is an exploded perspective view of the multilayer coil component according to the embodiment; 
         FIG. 3  is a schematic diagram illustrating a cross-sectional configuration of the multilayer coil component according to the embodiment; 
         FIG. 4  is a view illustrating a cross-sectional configuration of a coil conductor; and 
         FIG. 5  is a view illustrating a cross-sectional configuration of a coil conductor in a case in which the coil conductor is a sintered metal conductor. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same elements or elements having the same functions are denoted with the same reference numerals and overlapped explanation is omitted. 
     A configuration of a multilayer coil component  1  according to an embodiment will be described with reference to  FIGS. 1 to 3 .  FIG. 1  is a perspective view illustrating the multilayer coil component according to the embodiment.  FIG. 2  is an exploded perspective view of the multilayer coil component according to the embodiment.  FIG. 3  is a schematic diagram illustrating a cross-sectional configuration of the multilayer coil component according to the embodiment. 
     As illustrated in  FIGS. 1 to 3 , the multilayer coil component  1  includes an element body  2  and a pair of external electrodes  4 ,  5 . The pair of external electrodes  4 ,  5  is disposed at both ends of the element body  2 . The multilayer coil component  1  is applicable to, for example, a bead inductor or a power inductor. 
     The element body  2  has a rectangular parallelepiped shape. The rectangular parallelepiped shape includes a rectangular parallelepiped shape in which corners and ridges are chamfered, and a rectangular parallelepiped shape in which the corners and ridges are rounded. The element body  2  includes a pair of end surfaces  2   a ,  2   b  opposing each other and includes four side surfaces  2   c ,  2   d ,  2   e ,  2   f . The four side surfaces  2   c ,  2   d ,  2   e ,  2   f  extend in a direction in which the pair of end surfaces  2   a ,  2   b  opposes each other to connect to the pair of end surfaces  2   a ,  2   b.    
     The end surfaces  2   a  and the end surface  2   b  oppose each other in a first direction D 1 . The side surface  2   c  and the side surface  2   d  oppose each other in a second direction D 2 . The side surface  2   e  and the side surface  2   f  oppose each other in a third direction D 3 . The first direction D 1 , the second direction D 2 , and the third direction D 3  are approximately orthogonal to each other. The side surface  2   d  includes a surface that opposes an electronic device (not illustrated) when the multilayer coil component  1  is mounted on the electronic device, for example. Examples of the electronic device include a circuit board and an electronic component. In the present embodiment, the side surface  2   d  is arranged to constitute a mounting surface. The side surface  2   d  includes the mounting surface. 
     The element body  2  is configured by laminating a plurality of magnetic layers  7 . The magnetic layers  7  are laminated in the third direction D 3 . The element body  2  includes the plurality of laminated magnetic layers  7 . In an actual element body  2 , the plurality of magnetic layers  7  is integrated in such a way that boundaries between the magnetic layers cannot be visually recognized. 
     Each of the magnetic layers  7  includes a plurality of metal magnetic particles. The metal magnetic particles are made of, for example, a soft magnetic alloy. The soft magnetic alloy is, for example, an Fe—Si alloy. In a case in which the soft magnetic alloy is an Fe—Si alloy, the soft magnetic alloy may contain P. The soft magnetic alloy may be, for example, an Fe—Ni—Si-M alloy. “M” includes at least one element selected from Co, Cr, Mn, P, Ti, Zr, Hf, Nb, Ta, Mo, Mg, Ca, Sr, Ba, Zn, B, Al, and rare earth elements. In the magnetic layers  7 , the metal magnetic particles are bonded to each other. The metal magnetic particles are bonded to each other through, for example, bonding of oxide films formed on surfaces of the metal magnetic particles. The element body  2  includes resin. The resin exists between the plurality of metal magnetic particles. The resin is a resin having an electrical insulation, that is, insulating resin. Examples of the insulating resin include a silicone resin, a phenol resin, an acrylic resin, and an epoxy resin. 
     An average particle size of the metal magnetic particles is in a range of from 0.5 μm to 15 μm. In the present embodiment, the average particle size of the metal magnetic particles is 5 μm. In the present embodiment, the “average particle size” corresponds to a particle size at an integrated value of 50% in a particle size distribution obtained by a laser diffraction/scattering method. 
     The external electrode  4  is disposed on the end surface  2   a  of the element body  2 , and the external electrode  5  is disposed on the end surface  2   b  of the element body  2 . The external electrode  4  and the external electrode  5  are separated from each other in the first direction D 1 . The external electrodes  4 ,  5  have an approximately rectangular shape in plan view, and corners of the external electrodes  4 ,  5  are rounded. The external electrodes  4 ,  5  include an electrically-conductive material. The electrically-conductive material is, for example, Ag or Pd. The external electrodes  4 ,  5  are each configured as a sintered body of a conductive paste. The conductive paste contains a conductive metal powder and glass frit. The conductive metal powder is, for example, an Ag powder or a Pd powder. On surfaces of the external electrodes  4 ,  5 , plating layers are formed. The plating layers are formed by, for example, electroplating. The electroplating is, for example, Ni electroplating or Sn electroplating. 
     The external electrode  4  includes five electrode portions. The external electrode  4  includes an electrode portion  4   a  located on the end surface  2   a , an electrode portion  4   b  located on the side surface  2   d , an electrode portion  4   c  located on the side surface  2   c , an electrode portion  4   d  located on the side surface  2   e , and an electrode portion  4   e  located on the side surface  2   f . The electrode portion  4   a  covers a whole of the end surface  2   a . The electrode portion  4   b  covers a part of the side surface  2   d . The electrode portion  4   c  covers a part of the side surface  2   c . The electrode portion  4   d  covers a part of the side surface  2   e . The electrode portion  4   e  covers a part of the side surface  2   f . The five electrode portions  4   a ,  4   b ,  4   c ,  4   d ,  4   e  are formed integrally. 
     The external electrode  5  includes five electrode portions. The external electrode  5  includes an electrode portion  5   a  located on the end surface  2   b , an electrode portion  5   b  located on the side surface  2   d , an electrode portion  5   c  located on the side surface  2   c , an electrode portion  5   d  located on the side surface  2   e , and an electrode portion  5   e  located on the side surface  2   f . The electrode portion  5   a  covers a whole of the end surface  2   b . The electrode portion  5   b  covers a part of the side surface  2   d . The electrode portion  5   c  covers a part of the side surface  2   c . The electrode portion  5   d  covers a part of the side surface  2   e . The electrode portion  5   e  covers a part of the side surface  2   f . The five electrode portions  5   a ,  5   b ,  5   c ,  5   d ,  5   e  are integrally formed. 
     The multilayer coil component  1  includes a coil  20  and a pair of connection conductors  13 ,  14 . The coil  20  is disposed in the element body  2 . The coil  20  includes a plurality of coil conductors CC. In the present embodiment, the plurality of coil conductors CC includes six coil conductors  21  to  26 . The coil  20  includes a through-hole conductor  17 . The pair of connection conductors  13 ,  14  is also disposed in the element body  2 . 
     The coil conductors CC (coil conductors  21  to  26 ) are disposed in the element body  2 . The coil conductors  21  to  26  are separated from each other in the third direction D 3 . Distances Dc between the coil conductors  21  to  26  adjacent to each other in the third direction D 3  are equivalent to each other. The distances Dc may be different from each other. A coil axis of the coil  20  extends along the third direction D 3 . A thickness of the coil conductors  21  to  26  is, for example, about 40 μm. A width of the coil conductors  21  to  26  is, for example, about 150 μm. 
     The distances Dc are, for example, in a range of from 5 μm to 30 μm. In the present embodiment, the distances Dc are 15 μm. A surface of each of the coil conductors  21  to  26  has roughness as described later, and thus, the distances Dc vary in response to a surface shape of each of the coil conductors  21  to  26 . Therefore, the distances Dc are obtained, for example, as follows. 
     A cross-sectional photograph of the multilayer coil component  1  including each of the coil conductors CC (each of the coil conductors  21  to  26 ) is acquired. The cross-sectional photograph is obtained, for example, by capturing a cross-section of the multilayer coil component  1  when cut along a plane that is parallel to the pair of end surfaces  2   a ,  2   b  and is separated from the end surface  2   a  by a predetermined distance. The plane may be located equidistant from the pair of end surfaces  2   a ,  2   b . The cross-sectional photograph may be obtained by capturing a cross-section of the multilayer coil component  1  when cut along a plane that is parallel to the pair of side surfaces  2   e ,  2   f  and is separated from the side surface  2   e  by a predetermined distance. 
     A distance between the coil conductors CC adjacent to each other in the third direction D 3  on the acquired cross-sectional photograph is measured at a plurality of given positions. The number of measurement positions is, for example, “50”. An average of the measured distances is calculated. The calculated average value is the distance Dc. 
     One end and another end of each of the coil conductors  21 ,  23 ,  25 ,  26  are separated from each other in the third direction D 3 . One end and another end of each of the coil conductors  22 ,  24  are separated from each other in the second direction D 2 . Each of the coil conductors  21  to  26  adjacent to each other in the third direction D 3  includes a first conductor portion and a second conductor portion. The first conductor portions overlap each other when viewed from the third direction D 3 . The second conductor portions do not overlap each other when viewed from the third direction D 3 . 
     The through-hole conductor  17  is located between ends of the coil conductors  21  to  26  adjacent to each other in the third direction D 3 . The through-hole conductor  17  connects the ends of the coil conductors  21  to  26  adjacent to each other in the third direction D 3 . The plurality of coil conductors  21  to  26  is electrically connected to each other through the through-hole conductor  17 . An end of the coil conductor  21  constitutes one end of the coil  20 . An end of the coil conductor  26  constitutes another end of the coil  20 . An axis direction of the coil  20  extends along the third direction D 3 . 
     The connection conductor  13  is connected to the coil conductor  21 . The connection conductor  13  is contiguous with the coil conductor  21 . The connection conductor  13  is formed integrally with the coil conductor  21 . The connection conductor  13  couples an end  21   a  of the coil conductor  21  and the external electrode  4  and is exposed at the end surface  2   a  of the element body  2 . The connection conductor  13  is connected to the electrode portion  4   a  of the external electrode  4 . The connection conductor  13  electrically connects the one end of the coil  20  and the external electrode  4 . 
     The connection conductor  14  is connected to the coil conductor  26 . The connection conductor  14  is contiguous with the coil conductor  26 . The connection conductor  14  is formed integrally with the coil conductor  26 . The connection conductor  14  couples an end  26   b  of the coil conductor  26  and the external electrode  5  and is exposed at the end surface  2   b  of the element body  2 . The connection conductor  14  is connected to the electrode portion  5   a  of the external electrode  5 . The connection conductor  14  electrically connects the other end of the coil  20  and the external electrode  5 . 
     The coil conductors CC (coil conductors  21  to  26 ) and the connection conductors  13 ,  14  are plating conductors. The coil conductors CC and the connection conductors  13 ,  14  include an electrically-conductive material. The electrically-conductive material is, for example, Ag, Pd, Cu, Al, or Ni. The through-hole conductor  17  includes an electrically-conductive material. The an electrically-conductive material is, for example, Ag, Pd, Cu, Al, or Ni. The through-hole conductor  17  is constituted as a sintered body of a conductive paste. The conductive paste contains a conductive metal powder. The conductive metal powder is, for example, an Ag powder, a Pd powder, a Cu powder, an Al powder, or an Ni powder. The through-hole conductor  17  may be a plating conductor. 
     Each of the coil conductors CC (each of the coil conductors  21  to  26 ) includes a pair of side surfaces SF 1 , as illustrated in  FIGS. 3 and 4 . The pair of side surfaces SF 1  is opposes each other in the third direction D 3 . Each of the coil conductors CC includes a pair of side surfaces SF 2  different from the pair of side surfaces SF 1 . The pair of side surfaces SF 2  extends to couple the pair of side surfaces SF 1 . Each of the coil conductors CC has an approximately square shape in cross-section. Each of the coil conductors CC has, for example, an approximately rectangular or trapezoidal shape in cross-section.  FIG. 4  is a schematic diagram illustrating a cross-sectional configuration of the coil conductor. In  FIG. 4 , hatching representing the cross-section is omitted. 
     Surface roughness of each of the side surfaces SF 1  is less than 40% of an average particle size of metal magnetic particles MM. In the present embodiment, the surface roughness of each of the side surfaces SF 1  is less than 2 μm. The surface roughness of each of the side surfaces SF 1  is, for example, in a range of from 1.0 μm to 1.8 μm. In this case, the surface roughness of each of the side surfaces SF 1  is in a range of from 20% to 36% of the average particle size of the metal magnetic particles MM. The surface roughness of each of the side surfaces SF 1  may be approximately 0 μm. As illustrating in  FIG. 4 , resin RE exists between the metal magnetic particles MM. As described above, examples of the resin RE include a silicone resin, a phenol resin, an acrylic resin, and an epoxy resin. 
     The surface roughness of each of the side surfaces SF 1  of the coil conductors CC is obtained, for example, as follows. 
     A cross-sectional photograph of the multilayer coil component  1  including each of the coil conductors CC (each of the coil conductors  21  to  26 ) is acquired. As described above, the cross-sectional photograph is obtained, for example, by capturing the cross-section of the multilayer coil component  1  when cut along the plane that is parallel to the pair of end surfaces  2   a ,  2   b  and is separated from the end surface  2   a  by the predetermined distance. In this case, the plane may be located equidistant from the pair of end surfaces  2   a ,  2   b . As described above, the cross-sectional photograph may be obtained by capturing the cross-section of the multilayer coil component  1  when cut along the plane that is parallel to the pair of side surfaces  2   e ,  2   f  and that is separated from the side surface  2   e  by the predetermined distance. 
     A curve corresponding to each of the side surfaces SF 1  on the acquired cross-sectional photograph is represented by a roughness profile. A portion of the side surface SF 1  (roughness profile) on the cross-sectional photograph is sampled only by a sampling length, and a peak line at the highest peak in the sampled portion is obtained. The sampling length is, for example, 100 μm. The peak line is orthogonal to the third direction D 3  and serves as a reference line. The sampled portion is equally divided into a predetermined number of sections. The predetermined number is, for example, “10”. A valley line at the lowest bottom is obtained for each of the equally divided sections. The valley line is also orthogonal to the third direction D 3 . A distance between the peak line and the valley line in the third direction D 3  is measured for each of the equally divided sections. An average of the measured distances is calculated. The calculated average is the surface roughness. The surface roughness is obtained for each of the side surfaces SF 1  by the above-described procedure. 
     A plurality of cross-sectional photographs is acquired at different positions, and the surface roughness may be obtained for each of the cross-sectional photographs. In this case, the average value of the plurality of degrees of obtained surface roughness may be the surface roughness. 
     Q characteristics of the multilayer coil component  1  depend on a resistance of the coil conductors CC (coil conductors  21  to  26 ). In a high-frequency range, a current (signal) tends to flow near the surfaces of the coil conductors CC due to the skin effect. Therefore, as the surface resistance of the coil conductors CC increases, the Q characteristics of the multilayer coil component  1  decreases. A configuration in which the surfaces of the coil conductors CC have irregularities substantially increases a length of current flow, and thus increases the surface resistance, as compared with a configuration in which the surfaces of the coil conductors CC have no irregularities. 
     A configuration in which the surface roughness of each of the side surfaces SF 1  is less than 40% of the average particle size of the metal magnetic particles MM controls an increase in surface resistance and controls a decrease in Q characteristics in a high-frequency range, as compared with a configuration in which the surface roughness of each of the side surfaces SF 1  is equal to or greater than 40% of the average particle size of the metal magnetic particles MM. Therefore, the multilayer coil component  1  controls the increase in the surface resistance and controls the decrease in the Q characteristics in the high-frequency range. 
     In the multilayer coil component  1 , the surface roughness of the pair of side surfaces SF 2  is smaller than the surface roughness of the pair of side surfaces SF 1 . The multilayer coil component  1  has low surface resistance of the coil conductors CC (coil conductors  21  to  26 ), as compared with a configuration in which the surface roughness of the pair of side surfaces SF 2  is equal to or greater than the surface roughness of the pair of side surfaces SF 1 . Therefore, the multilayer coil component  1  further controls the increase in the surface resistance and further controls the decrease in the Q characteristics in the high-frequency range. 
     In the multilayer coil component  1 , the coil conductors CC (coil conductors  21  to  26 ) are plating conductors. 
     In a case in which the coil conductors are sintered metal conductors, the coil conductors are each formed by sintering a metal component (metal powder) contained in the conductive paste. In this case, the metal magnetic particles bite into the conductive paste before the metal component is sintered. Irregularities due to the shape of the metal magnetic particles are formed on a surface of the conductive paste. As illustrated in  FIG. 5 , in a case in which a coil conductor  31  is a sintered metal conductor, the coil conductor  31  is deformed so that the metal magnetic particles  33  bite into the coil conductor  31 . Therefore, the configuration in which the coil conductor  31  is the sintered metal conductor significantly increases surface roughness of the coil conductor  31 . Resin  35  exists between the metal magnetic particles  33 .  FIG. 5  is a schematic diagram illustrating a cross-sectional configuration of the coil conductor in a case in which the coil conductor is the sintered metal conductor. In  FIG. 5 , hatching representing the cross-section is omitted. 
     In a case in which the coil conductors CC are the plating conductors, as illustrated in  FIG. 4 , the metal magnetic particles MM tend not to bite into the coil conductors CC, and deformation of the coil conductor CC is reduced. Therefore, the configuration in which the coil conductors CC are the plating conductors controls an increase in the surface roughness of the coil conductors CC and controls an increase in the surface resistance. 
     Although the embodiments and modifications of the present invention have been described above, the present invention is not necessarily limited to the embodiments and modifications, and the embodiment can be variously changed without departing from the scope of the invention. 
     The number of coil conductors CC (coil conductors  21  to  26 ) is not limited to the above-descried number. 
     The coil axis of the coil  20  may extend along the first direction D 1 . In this case, the magnetic layers  7  are laminated in the first direction D 1 , and the coil conductors CC (coil conductors  21  to  26 ) are separated from each other in the first direction D 1 . 
     The external electrode  4  may include only one of the electrode portions  4   a ,  4   b . The external electrode  5  may also include only one of the electrode portions  5   a ,  5   b.