Patent Publication Number: US-10319506-B2

Title: Coil component

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a coil component and, more particularly, to a coil component obtained by embedding a coil conductor in an element body made of a magnetic material. 
     Description of Related Art 
     There is widely known a coil component obtained by embedding a coil conductor in an element body made of a magnetic material. In a coil component of this type, an element body is made of a magnetic material, so that most of the magnetic flux generated by making current flow in a coil conductor can be confined inside the element body. However, a part of the magnetic flux leaks outside the element body, which may degrade magnetic characteristics or may adversely affect other electronic components adjacent to the coil component. 
     To cope with such a problem, Japanese Patent Application Laid-open No. 2013-045848 and Japanese Utility Model Application Laid-open No. H02-067609 disclose a coil component in which a magnetic film is formed on the surface of the element body. In the coil component described in the above publications, a magnetic film is formed on the upper and lower surfaces perpendicular to the coil axis. 
     However, in the coil component described in the above publications, a large eddy current is generated in the magnetic film with a change in the magnetic flux, resulting in a large eddy current loss. Further, in this coil component, each of the upper and lower surfaces having a high magnetic flux density is covered with a single magnetic film, so that the magnetic film is easily magnetically saturated. Furthermore, in this coil component, spread of the magnetic flux in the side surface direction of the coil component is not sufficiently suppressed, so that when the coil component is mounted on a printed circuit board in a high density, other electronic components adjacent thereto may be affected by leakage magnetic flux. 
     SUMMARY 
     It is therefore an object of the present invention to provide a coil component suitable for high density mounting by reducing leakage magnetic flux while suppressing an eddy current loss and magnetic saturation and by suppressing the spread of magnetic flux in the side surface direction. 
     A coil component according to the present invention includes an element body made of a first magnetic material, a coil conductor embedded in the element body, and first and second magnetic films each made of a second magnetic material having higher permeability than that of the first magnetic material. The element body has an upper surface crossing the coil axis of the coil conductor and first and second side surfaces extending parallel to the coil axis. The first magnetic film is formed on the upper surface and first side surface of the element body, and the second magnetic film is formed on the upper surface and second side surface of the element body. 
     According to the present invention, the magnetic film formed on the upper surface having a high magnetic flux density is divided into a plurality of parts, so that an eddy current generated with a change in magnetic flux can be reduced, and magnetic saturation is made difficult to occur. In addition, each magnetic film covers the side surface of the element body, so that most of leakage magnetic flux circulates while passing through the magnetic film. As a result, spread of magnetic flux in the side surface direction is suppressed, enabling higher density mounting as compared with a conventional coil component. 
     In the present invention, the element body preferably further has a mounting surface positioned on the side opposite the upper surface, and the first and second magnetic films are preferably formed on the mounting surface of the element body as well. With this configuration, leakage magnetic flux can further be reduced, and the vertical directionality of the coil component can be eliminated. 
     The coil component according to the present invention preferably further includes a first terminal electrode connected to one end of the coil conductor and a second terminal electrode connected to the other end of the coil conductor. The element body preferably further has third and fourth side surfaces extending parallel to the coil axis and crossing at right angles the first and second side surfaces. The first terminal electrode is preferably formed on at least the third side surface, and the second terminal electrode is preferably formed on at least the fourth side surface. With the above configuration, the magnetic film can be formed without interference with the terminal electrode. 
     In the present invention, a part of the first magnetic film that is formed on the first side surface may be separated by a slit, and similarly, a part of the second magnetic film that is formed on the second side surface may be separated by a slit. This configuration makes the magnetic film more difficult to magnetically saturate, reducing an eddy current loss. In this case, the slit is preferably extended in the direction perpendicular to the coil axis and is more preferably offset to the mounting surface of the element body positioned on the side opposite the upper surface. 
     The coil component according to the present invention may further include a third magnetic film formed on the upper surface of the element body independent of the first and third magnetic films. This configuration further reduces leakage magnetic flux, making magnetic saturation less likely to occur. 
     As described above, according to the present invention, leakage magnetic flux can be reduced by the magnetic film. In addition, an eddy current loss and magnetic saturation can be suppressed by division of the magnetic film into a plurality of parts. Further, spread of magnetic flux in the side surface direction is suppressed, so that adverse effect on electronic components adjacent to the coil component can be reduced. This enables achievement of high density mounting on the printed circuit board. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of this invention will become more apparent by reference to the following detailed description of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a schematic perspective view illustrating the outer appearance of a coil component according to a first embodiment of the present invention; 
         FIG. 2  is a development view for explaining the surface structure of the coil component shown in  FIG. 1 ; 
         FIG. 3  is an exploded perspective view for explaining the internal structure of the coil component shown in  FIG. 1 ; 
         FIG. 4  is a schematic perspective view illustrating the outer appearance of a coil component according to a second embodiment of the present invention; 
         FIG. 5  is a development view for explaining the surface structure of the coil component shown in  FIG. 4 ; 
         FIG. 6  is a schematic perspective view illustrating the outer appearance of a coil component according to a third embodiment of the present invention; 
         FIG. 7  is a development view for explaining the surface structure of the coil component shown in  FIG. 6 ; 
         FIG. 8  is a schematic perspective view illustrating the outer appearance of a coil component according to a fourth embodiment of the present invention; and 
         FIG. 9  is a development view for explaining the surface structure of the coil component shown in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Preferred embodiments of the present invention will now be explained in detail with reference to the drawings. 
     &lt;First Embodiment&gt; 
       FIG. 1  is a schematic perspective view illustrating the outer appearance of a coil component  10 A according to the first embodiment of the present invention.  FIG. 2  is a development view for explaining the surface structure of the coil component  10 A.  FIG. 3  is an exploded perspective view for explaining the internal structure of the coil component  10 A. 
     As illustrated in  FIGS. 1 and 2 , the coil component  10 A according to the present embodiment includes an element body  20  having a substantially rectangular parallelepiped shape, first and second terminal electrodes  31  and  32  formed on the surface of the element body  20 , and first and second magnetic films  41  and  42  formed on the surface of the element body  20 . Although not particularly limited, the coil component  10 A according to the present embodiment is suitably used as a power supply inductor, in which a larger current than that in a coil component used as a signal inductor flows, so that a large number of magnetic fluxes is generated. Thus, the coil component  10 A is a product particularly requiring reduction in leakage magnetic flux. 
     The element body  20  is a laminated sintered body of ceramic green sheets including a magnetic material such as ferrite (Ni—Cu—Zn-based ferrite, Ni—Cu—Zn—Mg-based ferrite, Cu—Zn-based ferrite, or Ni—Cu-based ferrite). The permeability of the element body  20  is about 20 to about 200. 
     As illustrated in  FIG. 3 , in the present embodiment, the element body  20  is constituted of a plurality of insulating layers  20 A to  20 J each having the xy plane. The insulating layers  20 A to  20 J have the same planar shape. Of the insulating layers  20 A to  20 J, the insulating layers  20 A to  20 H have loop-shaped conductor patterns  50 A to  50 H constituting a coil conductor  50 , respectively, on their surfaces. The conductor patterns  50 A to  50 H are each a sintered body of a conductive paste including a conductive material (e.g., Ag powder or Pd powder). A plurality of insulating layers  20 I each having no conductor pattern are disposed above the insulating layer  20 A, and a plurality of insulating layers  20 J each having no conductor pattern are disposed below the insulating layer  20 H. 
     The conductor patterns  50 A to  50 H are connected to each other through a through hole conductor penetrating the insulating layers  20 A to  20 G to thereby form one coil conductor  50 . One end  51  of the coil conductor  50  is formed by the conductor pattern  50 A and drawn out to one side of the element body  20  in the x-direction to be connected to the first terminal electrode  31 . The other end  52  of the coil conductor  50  is formed by the conductor pattern  50 H and drawn out to the other side of the element body  20  in the x-direction to be connected to the second terminal electrode  32 . The coil axis of the coil conductor  50  extends in the z-direction. 
     The number of insulating layers  20 A to  20 J and the shape of the conductor pattern  50 A shown in  FIG. 3  are for illustrative purposes only, and the present invention is not limited to these examples. For example, although the number of turns of the coil conductor  50  is 6.5 in the present embodiment, the number is not limited thereto, but may be designed appropriately depending on characteristics required. Further, in the present invention, the element body  20  need not necessarily be the laminated sintered body of ferrite, and may be made of a composite magnetic material obtained by mixing magnetic powder and binder resin. Further, the coil conductor  50  need not necessarily be formed of a combination of conductor patterns, and may be formed by winding a coated conducting wire. 
     As illustrated in  FIGS. 1 and 2 , the element body  20  has first to fourth side surfaces  21  to  24  extending parallel to the coil axis (z-direction), an upper surface  25 , and a mounting surface  26 . The upper surface  25  and mounting surface  26  extends perpendicular to the coil axis (z-direction). The first and second side surfaces  21  and  22  each constitute the xz plane and are positioned on the sides opposite each other. The third and fourth side surfaces  23  and  24  each constitute the yz plane and are positioned on the sides opposite each other. The upper surface  25  and mounting surface  26  each constitute the xy plane and are positioned on the sides opposite each other. The mounting surface  26  is the surface that faces a printed circuit board when the coil component  10 A is mounted on the printed circuit board; however, the coil component  10 A according to the present embodiment has no directionality in the vertical direction (z-direction), so that the coil component  10 A may be mounted with the upper surface  25  and mounting surface  26  reversed, that is, with the upper surface  25  facing the printed circuit board. 
     The third side surface  23  is entirely covered with the first terminal electrode  31 . A part of the first terminal electrode  31  is also formed on the first and second side surfaces  21  and  22 , upper surface  25 , and mounting surface  26 . The fourth side surface  24  is entirely covered with the second terminal electrode  32 . A part of the second terminal electrode  32  is also formed on the first and second side surfaces  21  and  22 , upper surface  25 , and mounting surface  26 . However, the coil component  10 A according to the present embodiment has no directionality in the left-right direction (x-direction), so that the first terminal electrode  31  and the second terminal electrode  32  may be reversed. 
     The coil component  10 A according to the present embodiment further includes the first and second magnetic films  41  and  42 . The first and second magnetic films  41  and  42  are each made of a magnetic material having permeability higher than that of the magnetic material constituting the element body  20 . The permeability of the first and second magnetic films  41  and  42  is preferably 10 times or more, e.g., about 50 times as high as the permeability of the element body  20 . Specifically, the permeability is preferably about 1000 to 10000. Examples of the material of the first and second magnetic films  41  and  42  include 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, and Fe. 
     The film thickness of the first and second magnetic films  41  and  42  is set as small as possible in a range capable of ensuring sufficient magnetic characteristics. For example, the film thickness is preferably set to about 0.5 μm to about 5 μm. As a method of forming the first and second magnetic films  41  and  42 , a thin-film formation such as a sputtering method or a vapor deposition method is preferably used. 
     As illustrated in  FIGS. 1 and 2 , the first magnetic film  41  includes a part  41   a  covering the upper surface  25 , a part  41   b  covering the first side surface  21 , and a part  41   c  covering the mounting surface  26  which are continuously formed. Similarly, the second magnetic film  42  includes a part  42   a  covering the upper surface  25 , a part  42   b  covering the second side surface  22 , and a part  42   c  covering the mounting surface  26  which are continuously formed. 
     The first magnetic film  41  and the second magnetic film  42  are not in contact with each other and therefore separated from each other on the upper surface  25  and mounting surface  26 . That is, on the upper surface  25 , a gap G 1  is provided between the first and second magnetic films  41  and  42 , whereby the first and second magnetic films  41  and  42  are separated from each other without any contact with each other. Similarly, on the mounting surface  26 , a gap G 2  is provided between the first and second magnetic films  41  and  42 , whereby the first and second magnetic films  41  and  42  are separated from each other without any contact with each other. Needless to say, the first and second magnetic films  41  and  42  and the first and second terminal electrodes  31  and  32  are separated from each other without any contact being made among them. 
     The first and second magnetic films  41  and  42  each function as a magnetic path of magnetic flux generated when current is made to flow in the coil conductor  50  and, particularly, play a role of confining leakage magnetic flux to be radiated outside within the element body  20 . The leakage magnetic flux circulates mainly from the upper surface  25  toward the mounting surface  26  (or vice versa) and, in the present embodiment, most of the leakage magnetic flux passes through the first and second magnetic films  41  and  42 . This allows spread of the leakage magnetic flux particularly in the side surface direction (y-direction) to be significantly suppressed. Thus, when the coil component  10 A is mounted on the printed circuit board, adverse effect of the leakage magnetic flux on electronic components adjacent to the coil component  10 A can be reduced, so that it is possible to reduce the distance from the adjacent electronic components in the y-direction as compared with conventional approaches. Therefore, it is possible to achieve higher density mounting. 
     Further, in the present embodiment, the first and second magnetic films  41  and  42  are separated from each other on the upper surface  25  and the mounting surface  26  each of which has a high magnetic flux density, so that generation of an eddy current can be suppressed more than a case where a single magnetic film is formed on the upper surface  25  and mounting surface  26 . In addition, the configuration in which the first and second magnetic films  41  and  42  are separated from each other on the upper surface  25  and mounting surface  26  makes it difficult for the first and second magnetic films  41  and  42  to be magnetically saturated, so that even when the coil component  10 A is used as a power inductor in which a large current flows, magnetic saturation does not occur, and the spreading of the leakage magnetic flux can be suppressed effectively. 
     &lt;Second Embodiment&gt; 
       FIG. 4  is a schematic perspective view illustrating the outer appearance of a coil component  10 B according to the second embodiment of the present invention.  FIG. 5  is a development view for explaining the surface structure of the coil component  10 B. 
     As illustrated in  FIGS. 4 and 5 , the coil component  10 B according to the present embodiment differs from the coil component  10 A according to the first embodiment in that slits G 3  and G 4  are formed in the first and second magnetic films  41  and  42 , respectively. Other configurations are the same as those of the coil component  10 A according to the first embodiment, so the same reference numerals are given to the same elements, and overlapping description will be omitted. 
     The slit G 3  is formed in the part  41   b  of the first magnetic film  41  that covers the first side surface  21  and extends in the x-direction so as to separate the part  41   b  in the z-direction. Similarly, the slit G 4  is formed in the part  42   b  of the second magnetic film  42  that covers the second side surface  22  and extends in the x-direction so as to separate the part  42   b  in the z-direction. As a result, the slits G 3  and G 4  each function as a magnetic gap, making it more difficult for the first and second magnetic films  41  and  42  to be saturated and allowing an eddy current loss to be reduced. 
     Further, in the present embodiment, the slits G 3  and G 4  are offset to the mounting surface  26  side, so that the magnetic flux leaking from the slits G 3  and G 4  is positioned in the vicinity of the surface of the printed circuit board. As a result, adverse effect of the leakage magnetic flux on electronic components adjacent to the coil component  10 B can be minimized. 
     &lt;Third Embodiment&gt; 
       FIG. 6  is a schematic perspective view illustrating the outer appearance of a coil component  10 C according to the third embodiment of the present invention.  FIG. 7  is a development view for explaining the surface structure of the coil component  10 C. 
     As illustrated in  FIGS. 6 and 7 , the coil component  10 C according to the present embodiment differs from the coil component  10 A according to the first embodiment in that third and fourth magnetic films  43  and  44  are additionally formed. Other configurations are the same as those of the coil component  10 A according to the first embodiment, so the same reference numerals are given to the same elements, and overlapping description will be omitted. 
     The third magnetic film  43  is formed on the upper surface  25  of the element body  20  independent of the first and second magnetic films  41  and  42 . Similarly, the fourth magnetic film  44  is formed on the mounting surface  26  of the element body  20  independent of the first and second magnetic films  41  and  42 . The third and fourth magnetic films  43  and  44  are located at the same positions in terms of the xy direction and are each disposed in a substantially center portion of the upper surface  25  or mounting surface  26  so as to cover at least a part of the inner diameter portion of the coil conductor  50  in a plan view (as viewed in the z-direction). 
     The coil component  10 C according to the present embodiment further includes the third and fourth magnetic films  43  and  44  and thus can shield the leakage magnetic flux more effectively. In addition, the magnetic film is divided into three parts on the upper surface  25  and mounting surface  26  of the element body  20 , allowing an eddy current to be further reduced and making magnetic saturation difficult to occur. 
     &lt;Fourth Embodiment&gt; 
       FIG. 8  is a schematic perspective view illustrating the outer appearance of a coil component  10 D according to the fourth embodiment of the present invention.  FIG. 9  is a development view for explaining the surface structure of the coil component  10 D. 
     As illustrated in  FIGS. 8 and 9 , the coil component  10 D according to the present embodiment differs from the coil component  10 A according to the first embodiment in that slits G 5  and G 6  are formed in the first and second magnetic films  41  and  42 , respectively. Other configurations are the same as those of the coil component  10 A according to the first embodiment, so the same reference numerals are given to the same elements, and overlapping description will be omitted. 
     The slit G 5  is formed over the parts  41   a  to  41   c  so as to divide the first magnetic film  41  in the x-direction. Similarly, the slit G 6  is formed over the parts  42   a  to  42   c  so as to divide the second magnetic film  42  in the x-direction. It follows that the slits G 5  and G 6  extend in the z-direction on the respective first and second side surfaces  21  and  22  and extend in the y-direction on the upper surface  25  and mounting surface  26 . 
     In the present embodiment, the magnetic film is divided into four parts on the upper surface  25  and mounting surface  26  of the element body  20 , allowing an eddy current to be further reduced and making magnetic saturation difficult to occur. 
     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. 
     For example, although the first and second magnetic films  41  and  42  are formed on the mounting surface  26  in the above embodiments, the magnetic film need not necessarily be formed on the mounting surface  26  and may be omitted.