Patent Publication Number: US-2020303108-A1

Title: Common mode noise filter

Description:
TECHNICAL FIELD 
     The present invention relates to common mode noise filters for use in a wide range of electronic equipment that includes digital equipment, audiovisual (AV) equipment, and information communication terminals. 
     BACKGROUND ART 
       FIG. 9  is a cross-sectional view of conventional common mode noise filter  500 . Common mode noise filter  500  includes laminated body  1 , two coil conductors  2  and  3  formed inside laminated body  1  and facing each other, and lead conductors  2   a  and  3   a  connected to coil conductors  2  and  3 , respectively. Coil conductors  2  and  3  and lead conductors  2   a  and  3   a  are buried in non-magnetic body  4  of laminated body  1 . 
       FIG. 10  is an enlarged cross-sectional view of common mode noise filter  500  for illustrating cross sections of coil conductors  2  and  3 . The cross sections of coil conductors  2  and  3  have rectangular shapes. Common mode noise filter  500  may greatly attenuate differential signals in high frequencies. 
     A conventional common mode noise filter similar to common mode noise filter  500  is disclosed in, e.g. PTL 1. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Patent Laid-Open Publication No. 2012-89543 
     SUMMARY 
     A common mode noise filter includes an insulating layer, a first coil conductor disposed on a first surface of the insulating layer and extending slenderly, and a second coil conductor disposed on a second surface of the insulating layer and extending slenderly. The second coil conductor faces the first coil conductor across the insulating layer. A portion of the second coil conductor has a cross section crossing a direction in which the portion of the second coil conductor extends slenderly. The cross section includes an apex portion facing the first coil conductor across the insulating layer and a base side portion opposite to the apex portion. A width of the apex portion is smaller than a width of the base-side portion. 
     The common mode noise filter reduces attenuation of differential signals in high frequencies. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of a common mode noise filter according to an exemplary embodiment. 
         FIG. 2  is an exploded perspective view of the common mode noise filter according to the embodiment. 
         FIG. 3  is a perspective view of the common mode noise filter according to the embodiment. 
         FIG. 4  is an enlarged cross-sectional view of a main part of the common mode noise filter according to the embodiment. 
         FIG. 5  is a cross-sectional view of the common mode noise filter according to the embodiment for illustrating a method of manufacturing the common mode noise filter. 
         FIG. 6  is a cross-sectional view of the common mode noise filter according to the embodiment for illustrating a method of manufacturing the common mode noise filter. 
         FIG. 7  is a cross-sectional view of a coil conductor of the common mode noise filter according to the embodiment. 
         FIG. 8  is an enlarged cross-sectional view of another common mode noise filter according to the embodiment. 
         FIG. 9  is a cross-sectional view of a conventional common mode noise filter. 
         FIG. 10  is an enlarged cross-sectional view of the common mode noise filter shown in  FIG. 9 . 
     
    
    
     DETAIL DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  is a cross-sectional view of common mode noise filter  1000  according to an exemplary embodiment.  FIG. 2  is an exploded perspective view of common mode noise filter  1000 .  FIG. 3  is a perspective view of common mode noise filter  1000 .  FIG. 1  is the cross-sectional view of common mode noise filter  1000  along line I-I shown in  FIG. 3 . 
     Common mode noise filter  1000  shown in  FIG. 1  includes laminated body  11  and coil conductors  12  and  13  that are formed inside laminated body  11  and that face each other in lamination direction DX, i.e. an up-down direction. 
     Each of cross sections of coil conductors  12  and  13  perpendicular to directions in which currents flow has an apex portion and a base side portion. The apex portion of coil conductor  12  faces the base side portion of coil conductor  13 . 
     As shown in  FIG. 2 , laminated body  11  includes insulating layers  11   a  to  11   g , coil conductor  12  formed on upper surface  111   c  of insulating layer  11   c , lead conductor  114  formed on upper surface  111   c  of insulating layer  11   c , coil conductor  13  formed on upper surface  111   d  of insulating layer  11   d , lead conductor  115  formed on upper surface  111   d  of insulating layer  11   d , lead conductor  14  formed on upper surface  111   b  of insulating layer lib, and lead conductor  15  formed on upper surface  111   e  of insulating layer  11   e . Lead conductor  14  is connected to coil conductor  12 . Lead conductor  15  is connected to coil conductor  13 . Coil conductor  12  and lead conductor  114  are connected to each other, and are made of a single conductor in accordance with the embodiment. Coil conductor  13  and lead conductor  115  are connected to each other, and made of a single conductor in accordance with the embodiment. Insulating layers  11   a  to  11   g  are laminated in lamination direction DX. This configuration causes coil conductor  12  to be disposed on lower surface  211   d  of insulating layer  11   d.    
     As shown in  FIG. 3 , external electrodes  16   a  to  16   d  are provided on both ends of laminated body  11 . Lead conductors  114 ,  115 ,  14 , and  15  are connected to external electrodes  16   a ,  16   b ,  16   c , and  16   d , respectively. Coil conductor  12  is coupled to external electrode  16   a  via lead conductor  114 . Coil conductor  13  is coupled to external electrode  16   b  via lead conductor  115 . Currents flow from external electrodes  16   a  and  16   c  through lead conductors  114 , coil conductor  12 , and lead conductor  14 . Currents flow from external electrodes  16   b  and  16   d  through lead conductor  115 , coil conductor  13 , and lead conductor  15 . 
     Coil conductor  12  is coupled to lead conductor  14  via via-electrode  17   a  that passes through insulating layer  11   c  so as to constitute one coil. Coil conductor  13  is coupled to lead conductor  15  via via-electrode  17   b  that passes through insulating layer  11   e  so as to constitute another coil. 
     Lead conductors  14  and  15  linearly extend in accordance with the embodiment; however, the conductors may extend spirally. Both lead conductors  14  and  15  may be formed on one insulating layer among insulating layers  11   a  to  11   f , and the locations of lead conductors  14  and  15  shown in  FIG. 1  may be reversed to each other. 
     Coil conductor  12  and lead conductor  14  may be located between coil conductor  13  and lead conductor  15 . 
     Insulating layers  11   a  to  11   g  are laminated in this order from below. Insulating layers  11   b  to  11   f  are made of non-magnetic material, such as glass ceramic, that contains glass, and have sheet shapes. Insulating layers  11   a  and  11   g  are made of magnetic material, such as Cu—Ni—Zn ferrite, and have sheet shapes. 
     Coil conductors  12  and  13  are disposed inside non-magnetic part  18  constituted by insulating layers  11   b  to  11   f . Insulating layer  11   a  made of the magnetic material constitutes magnetic part  19   a  that is disposed below non-magnetic part  18 . Insulating layer  11   g  constitutes magnetic part  19   b  that is disposed above non-magnetic part  18 . 
     The number of the insulating layers, i.e. insulating layers  11   a  to  11   g  is not limited to the number shown in  FIG. 2 . 
     Coil conductors  12  and  13  has spiral shapes, and are formed by plating or printing conductive material, such as silver. Coil conductor  12  faces coil conductor  13  across insulating layer  11   d . In accordance with the embodiment, coil conductor  12  entirely faces coil conductor  13  across insulating layer  11   d . That is, coil conductors  12  and  13  except both ends of the conductors are disposed substantially at the same position and wound in the same direction when viewed from above, i.e. when viewed in lamination direction DX. This configuration the coil conductors to be magnetically coupled to each other. 
     Coil conductors  12  and  13  may not necessarily have the spiral shapes, and may have other shapes, such as helical shapes. 
       FIG. 4  is an enlarged cross-sectional view of common mode noise filter  1000  shown in  FIG. 1  for illustrating cross sections of portions  112  and  113  of coil conductors  12  and  13  shown in  FIG. 2 . The cross sections, shown in  FIG. 4 , of portions  112  and  113  of coil conductors  12  and  13  are perpendicular to, i.e. cross direction D  11  in which portions  112  and  113  extend slenderly. That is, the cross sections, shown in  FIG. 4 , of coil conductors  12  and  13  are perpendicular to, i.e. cross lamination direction DX in which coil conductors  12  and  13  are laminated. Each of the cross sections, as a whole, substantially has a triangular shape having an apex portion and a base side portion opposite to the apex portion. Specifically, the cross section of portion  112  of coil conductor  12  has apex portion  12   a  and base side portion  12   b  opposite to apex portion  12   a . The cross section of portion  113  of coil conductor  13  has apex portion  13   a  and base side portion  13   b  opposite to apex portion  13   a . Apex portion  12   a  of coil conductor  12  faces base side portion  13   b  of coil conductor  13  across insulating layer  11   d  in lamination direction DX. 
     Base side portions  12   b  and  13   b  of coil conductors  12  and  13  include protrusion portions  12   c  and  13   c  protruding arcuately, respectively. The cross section, shown in  FIG. 4 , of portion  112  of coil conductor  12  further has leg side portions  12   d  connected to both apex portion  12   a  and base side portion  12   b . The cross section, shown in  FIG. 4 , of portion  113  of coil conductor  13  further has leg side portions  13   d  connected to both apex portion  13   a  and base side portion  13   b . Leg side portions  12   d  and  13   d  of coil conductors  12  and  13  have protrusion portions  12   e  and  13   e  protruding arcuately. Apex portions  12   a  and  13   a  of coil conductors  12  and  13  have arcuate shapes. 
     The cross sections of portions  112  and  113  of coil conductors  12  and  13  thus substantially have triangular shapes as a whole. Three apex portions including apex portion  12   a  ( 13   a ) of each triangular shape have arcuate shapes. The triangular shape has three sides, i.e. leg side portions  12   d  ( 13   d ) and base side portion  12   b  ( 13   b ) which protrude arcuately. 
     In the cross section of coil conductor  12  shown in  FIG. 4 , portion  12   p  which has the largest width when viewed from above deviates from the center of coil conductor  12  in lamination direction DX toward base side portion  12   b . Similarly, in the cross section of coil conductor  13  shown in  FIG. 4 , portion  13   p  which has the largest width when viewed from above deviates from the center of coil conductor  13  in lamination direction DX toward base side portion  13   b.    
     Each of base side portions  12   b  and  13   b  is a side positioned on the lower side of the corresponding cross section in lamination direction DX. Each of apex portions  12   a  and  13   a  is a point that is positioned on the upper side of the corresponding cross section in lamination direction DX. Each of leg side portions  12   d  corresponds to a line that connects between apex portion  12   a  and corresponding one of both ends of base side portion  12   b . Each of leg side portions  13   d  corresponds to a line that connects between apex portion  13   a  and corresponding one of both ends of base side portion  13   b.    
     In coil conductors  12  and  13 , portions  112  and  113  having cross sections having triangular shapes as a whole may be respective effective portions of the respective coil conductors excluding lead conductors  14 ,  15 ,  114 , and  115 . The effective portions of coil conductors  12  and  13  faces each other across insulating layer  11   d  in lamination direction DX. That is, portion  112  of coil conductor  12  may be any portion of coil conductor  12 , and portion  113  of coil conductor  13  may be any portion of coil conductor  13 . As shown in  FIG. 4 , heights of the cross sections of coil conductors  12  and  13  in lamination direction DX is larger than widths of the cross sections in a direction perpendicular to lamination direction DX. However, the widths may be larger than the heights. 
     Portions  112  and  113  of coil conductors  12  and  13  having the cross sections with the triangular shapes when viewed as a whole and having apex portion  12   a  of coil conductor  12  and base side portion  13   b  of coil conductor  13  facing each other may be not the entire of the effective portions of coil conductors  12  and  13  but respective parts of the effective portions. 
     Portions  112  and  113  in which apex portion  12   a  of coil conductor  12  faces base side portion  13   b  of coil conductor  13  may be, e.g. respective halves of the effective portions. 
     A method of manufacturing common mode noise filter  1000  in accordance with the embodiment will be described below.  FIGS. 5 and 6  are cross-sectional views of common mode noise filter  1000  for illustrating the method of manufacturing the filter. 
     First, laminated body  11  shown in  FIG. 1  including magnetic parts  19   a  and  19   b  and non-magnetic part  18  which contains glass. 
     In this step, coil conductors  12  and  13  and lead conductors  14 ,  15 ,  114 , and  115  made of silver and facing each other in lamination direction DX are formed inside non-magnetic part  18 . 
     Coil conductors  12  and  13  are formed by the following method. First, as shown in  FIG. 5 , resist  21  made of resin is formed on base plate  20  along the shape of coil conductor  12  ( 13 ). Then, base plate  20  is plated with silver to form plated layer  22 . Plated layer  22  is a part constituting coil conductor  12  ( 13 ). 
     After that, as shown in  FIG. 6 , both plated layer  22  and resist  21  which are formed on base plate  20  are transferred to transfer body  23  as they are. Transfer body  23  constitutes each of insulating layers  11   c  ( 11   d ). Then, both base plate  20  and resist  21  are removed, thereby forming only plated layer  22  on transfer body  23 , i.e. insulating layer  11   c  ( 11   d ). Insulating layers  11   a  to  11   g  including insulating layers  11   c  and  11   d  on which plated layers  22  have been transferred are laminated to form laminated body  11 , thereby forming coil conductors  12  and  13  inside non-magnetic part  18 . 
     Then, laminated body  11  is fired at a temperature of, e.g. about 940° C. The temperature is higher than the glass-transition temperature (e.g. about 800° C.). 
     Finally, external electrodes  16   a  to  16   d  are formed on the both ends of laminated body  11 . 
     In this method, the firing is executed at a temperature higher than the glass-transition temperature which increases the liquidity of glass, thereby easily changing the shapes of coil conductors  12  and  13  inside non-magnetic part  18 . In addition, the firing causes coil conductors  12  and  13  made of silver to change the shapes thereof to reduce the surface areas thereof and allowing the cross sections of coil conductors  12  and  13  to have triangular shapes when viewed as a whole. 
     In this case, as shown in  FIG. 5 , plated layer  22  is slightly higher than resist  21 . In addition, a portion of plated layer  22  which contacting base plate  20  and which constitutes portion  12   a  ( 13   a ) has a small area. Moreover, adjusting the firing temperature and plating conditions provides coil conductors  12  and  13  with the cross sections having the triangular shapes as a whole. 
     This method does not require the previous preparation for causing coil conductors  12  and  13  to have the cross sections with triangular shapes as a whole. Thus, the lamination and firing provides the cross sections with the triangular shapes. 
     The above method of forming coil conductors  12  and  13  is just an example; therefore, another method may be employed for forming them. 
     The shapes of coil conductors  12  and  13  may not necessarily be the triangular shapes shown in  FIG. 4  as a whole. The same effect is obtained in the case that the cross section of coil conductor  12  ( 13 ) includes apex portion  12   a  ( 13   a ) and base side portion  12   b  ( 13   b ) having a larger width than apex portion  12   a  ( 13   a ) when viewed from above, i.e. in a direction parallel to upper surface  111   c  and lower surface  211   c  of insulating layer  11   c , and the width decreases monotonously as a whole as being distanced away from base side portion  12   b  ( 13   b ) toward apex portion  12   a  ( 13   a ) while apex portion  12   a  ( 13   a ) has an arcuate shape. 
       FIG. 7  is a cross-sectional view of coil conductors  12  and  13  for illustrating cross sections of coil conductors  12  and  13  having other shapes. As shown in  FIG. 7 , parts of the cross sections of the coil conductors may protrude outward, or may slant as a whole. Variations in the firing temperature and/or plating conditions may result in these other shapes. 
     In common mode noise filter  1000  according to the embodiment, leg side portion  12   d  of each of coil conductor  12  faces base side portion  13   b  of corresponding coil conductor  13  and the distance between leg side portion  12   d  and base side portion  13   b  is long, accordingly decreasing a capacitance between coil conductors  12  and  13 . Such a decreased capacitance between coil conductors  12  and  13  increases in a cut-off frequency at which differential signals drop by 3 dB, thus reducing attenuation of differential signals at high frequencies. 
     In conventional common mode noise filter  500  shown in  FIGS. 9 and 10 , in case that the filter has a low profile, the distance between coil conductors  2  and  3  facing each other decreases, accordingly increasing a capacitance between coil conductors  2  and  3 . This may cause a large drop in differential signals in high frequencies. 
     In conventional common mode noise filter  500  shown in  FIG. 10 , coil conductors  2  and  3  have rectangular cross sections. Distance t 4  between coil conductors  2  and  3  is constant over portions  2   b  and  3   b  facing each other, preventing the capacitance between coil conductors  2  and  3  from decreasing. 
     In contrast, in common mode noise filter  1000  according to the embodiment, even if distance t 1  between apex portion  12   a  of coil conductor  12  and base side portion  13   b  of coil conductor  13  in lamination direction DX in which coil conductors  12  and  13  and the insulating layers are laminated, as shown in  FIG. 4 , is equivalent to the distance between the rectangular cross sections of the coils having being rectangular, a distance between leg side portion  12   d  of coil conductor  12  and base side portion  13   b  of coil conductor  13  in lamination direction DX increases at a position farther away from apex portion  12   a . Accordingly, at such a farther position, the distance between coil conductor  12  and coil conductor  13  is longer. 
     The above configuration reduces the capacitance at the positions where leg side portion  12   d  of coil conductor  12  face base side portion  13   b  of coil conductor  13 . Moreover, distance t 2  between leg side portion  12   d  of coil conductor  12  and base side portion  13   b  of coil conductor  13  is longest at ends  24  of coil conductors  12  and  13  when viewed in lamination direction DX. In cases where the common mode noise filter has a low profile to have a thickness of insulating layer  11   d , i.e. a distance between coil conductors  12  and  13  ranging, e.g. from 1 μm to 10 μm, and yet where coil conductors  12  and  13  have rectangular cross sections as shown in  FIG. 10 , such a distance between coil conductors  12  and  13  is so short that the capacitance between coil conductors  12  and  13  is large. For this reason, a cut-off frequency may become low. 
     In common mode noise filter  1000  according to the embodiment, the cross sections of coil conductors  12  and  13  have the triangular shapes as a whole allow the distance between coil conductors  12  and  13  to be long. This configuration decreases the capacitance between coil conductors  12  and  13  even in cases where the triangular cross sections have the same area as the rectangular cross sections. 
     Moreover, such a decrease in the capacitance between coil conductors  12  and  13  causes a peak of common mode impedance of common mode noise filter  1000  to shift to higher frequency, facilitating to remove common mode noises in frequencies of gigahertz. 
     The decrease in the capacitance between coil conductors  12  and  13  increases the characteristic impedance of common mode noise filter  1000  up to a predetermined characteristic impedance that complies with various communications standards. This configuration prevents degradation, such as decay, of differential signals. 
     In common mode noise filter  1000 , base side portions  12   b  and  13   b  of coil conductors  12  and  13  include protrusion portions  12   c  and  13   c , respectively, each of which protrudes arcuately. This configuration allows the distance between leg side portions  12   d  of coil conductor  12  and base side portion  13   b  of coil conductor  13  to be long, accordingly further decreasing the capacitance between coil conductors  12  and  13 . 
     Moreover, protrusion portions  12   c  and  13   c  of base side portions  12   b  and  13   b  and protrusion portions  12   e  and  13   e  of leg side portions  12   d  and  13   d  of coil conductors  12  and  13  protrude arcuately. The protrusion portions provide coil conductors  12  and  13  with large cross-sectional areas, accordingly reducing an increase of direct-current resistance of the conductors. 
     The increase of the direct current resistance may can be reduces even with only one of protrusion portion  12   c  ( 13   c ) of base side portion  12   b  ( 13   b ) and protrusion portion  12   e  ( 13   e ) of leg side portion  12   d  ( 13   d ). 
     Apex portions  12   a  and  13   a  of coil conductors  12  and  13  have arcuate shapes. Arcuate portions of the apex portions relieve stresses to be received by coil conductors  12  and  13  when laminating the conductors. Therefore, even in cases where coil conductors  12  and  13  are thick, this configuration reduces degradation in adhesion between the insulating layers and coil conductors  12  and  13 , thereby preventing coil conductors  12  and  13  from being delaminated from the insulating layers. Thus, even in cases where coil conductors  12  and  13  are close to each other, this configuration reduces the occurrence of the delamination and short circuits between them. 
     In conductors among coil conductors  12  and  13  adjacent to each other in a lateral direction perpendicular to lamination direction DX, points on leg side portions  12   d  ( 13   d ) are located away from each other in the lateral direction in which the lateral distance between the leg side portions increases as the points are located away from the widest portion of the conductor when viewed from above. Thus, the distance between the positions of the conductors adjacent to each other in the lateral direction becomes long. This configuration reduces possibility of accidental short circuit between the conductors adjacent to each other in the lateral direction, accordingly allows the distance between the conductors adjacent to each other in the lateral direction to be short, that is, allows the space between the conductors to be narrow. This allows an increase in the number of turns of each of coil conductors  12  and  13 , accordingly increasing common mode impedance of common mode noise filter  1000 . 
       FIG. 8  is an enlarged cross-sectional view of another common mode noise filter  1001  according to the embodiment. In  FIG. 8 , components identical to those of common mode noise filter  1000  shown in  FIG. 4  are denoted by the same numerals. In common mode noise filter  1001  shown in  FIG. 8 , apex portions  12   a  of coil conductor  12  face apex portions  13   a  of coil conductor  13  across insulating layer  11   d  in lamination direction DX. 
     In common mode noise filter  1001 , apex portions  13   a  and base side portions  13   b  of coil conductor  13  are reversed in lamination direction DX with respect to common mode noise filter  1000  shown in  FIG. 4 . 
     This configuration increases the distance between leg side portion  12   d  of coil conductor  12  and leg side portion  13   d  of coil conductor  13  in lamination direction DX at a farther distance away from apex portions  12   a  and  13   a , respectively. Thus, at such a farther distance, the distance between coil conductor  12  and coil conductor  13  is longer, accordingly further reducing the capacitance between coil conductor  12  and coil conductor  13 . 
     In particular, in common mode noise filter  1001  shown in  FIG. 8 , distance t 3  between leg side portion  12   d  of coil conductor  12  and base side portion  13   b  of coil conductor  13  is much longer at ends  24  of coil conductors  12  and  13  when viewed in lamination direction DX than common mode noise filter  1000  shown in  FIG. 4 . 
     In common mode noise filters  1000  and  1001  described above in accordance with the embodiment, coil conductors  12  and  13  face each other across insulating layer  11   d  in lamination direction DX and are magnetically coupled to each other. Each common mode noise filter according to the embodiment may include plural pairs of coil conductors, each of the pairs includes coil conductors that face each other across an insulating layer in lamination direction DX and that are magnetically coupled to each other. Moreover, such plural pairs may be disposed in an array type. 
     In the embodiments, terms, such as “upper surface”, “lower surface”, and “up-down direction”, indicating directions indicate relative directions determined only by the relative positional relationship of constituent components, such as the insulating layers and the coil conductors, of the common mode noise filter, and do not indicate absolute directions, such as a vertical direction. 
     INDUSTRIAL APPLICABILITY 
     A common mode noise filter in accordance with the present invention prevents degradation of differential signals. The filter is useful particularly in applications common mode noise filters that are used, as countermeasures against noise, in a wide range of electronic equipment including digital equipment, audiovisual (AV) equipment, and information communication terminals. 
     REFERENCE MARKS IN THE DRAWINGS 
     
         
           11  laminated body 
           11   a - 11   g  insulating layer 
           12  coil conductor (first coil conductor) 
           12   a  apex portion 
           12   b  base side portion 
           13  coil conductor (second coil conductor) 
           13   a  apex portion 
           13   b  base side portion