Patent Publication Number: US-2006006971-A1

Title: Laminated coil array

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a laminated coil array including a plurality of coil conductors embedded in a ceramic laminate.  
      2. Description of the Related Art  
      Among laminated coil arrays used for noise elimination in OA equipment, such as computers, there is a laminated coil array described in Japanese Unexamined Patent Application Publication No. 2001-23822. As shown in  FIG. 6 , this laminated coil array  91  includes ceramic layers  33 , on the surface of which internal conductors  34  to  37  are provided. The internal conductors  34  are electrically connected in series through via holes  43  provided in the ceramic sheets  33  to define a spiral coil conductor L 1 . In the same manner, the internal conductors  35 ,  36 , and  37  are also electrically connected in series through via holes  43  to define spiral coil conductors L 2 , L 3 , and L 4 .  
      As shown in  FIG. 6 , the ceramic layers  33  are laminated in order and, after the ceramic layers  32  including via holes  42  are disposed on their top and bottom surfaces, the layers are integrally fired to form a laminate  45  as shown in  FIG. 7 . External electrodes  51  to  54  are disposed on the end surfaces of the laminate  45 . The external electrodes  51  to  54  are electrically connected to the end portions of the coil conductors L 1  to L 4  which are led out to the surface of the laminate  45  through via holes  42 .  
      In the laminated coil array  91  having the structure described above, when the coil conductors L 1  to L 4  are arranged close together in the laminate  45  to reduce the size of the laminated coil array  91 , the inductances of the coil conductors L 1  to L 4  have different values.  
      That is, in the coil conductors L 1  and L 4  located at both end portions in the arrangement direction of the coil conductors L 1  to L 4  in the laminate  45 , the magnetic path is narrowed at the end portions of the laminate  45 . Therefore, the inductance of the coil conductors L 1  and L 4  is less than that of the coil conductors L 2  and L 3  not located at both ends in the arrangement direction of the coil conductors L 1  to L 4 .  
     SUMMARY OF THE INVENTION  
      To overcome the problems described above, preferred embodiments of the present invention provide a laminated coil array in which three or more coil conductors are arranged inside a laminate and variations in the inductance of the coil conductors are reduced.  
      A laminated coil array according to a preferred embodiment of the present invention includes a laminate including a plurality of ceramic layers and a plurality of internal conductors disposed one on top of another, at least three spiral conductors defined by electrically connecting the internal conductors and arranged in line inside the laminate, and external electrodes provided on the surface of the laminate and electrically connected to end portions of the coil conductors. In the laminated coil array, the winding direction of the coil conductors not located at both end portions in the arrangement direction of the coil conductors is partially reversed.  
      In the laminated coil array according to this preferred embodiment of the present invention, the inductance of coil conductors located at both end portions in the arrangement direction of the coil conductors is substantially equal to the inductance of coil conductors not located at both end portions in the arrangement direction of the coil conductors.  
      Since the winding direction of the coil conductors not located at both end portions is partially reversed, the inductance of the coil conductors is reduced. That is, in a portion where the winding direction is reversed in the coil conductor, a magnetic field is generated so as to disturb a magnetic field generated by a normally wound portion. The total inductance of the coil conductor is reduced such that the magnetic field generated in the portion where the winding direction is reversed and the magnetic field generated in the normally wound portion cancel each other. As a result, the partially reversed portion of the coil conductors not located at both end portions in the arrangement direction of the coil conductors suppresses variations in the inductances of each coil conductor arranged inside the laminate.  
      Furthermore, in the laminated coil array according to this preferred embodiment of the present invention, the direct-current resistance of coil conductors located at both end portions in the arrangement direction of the coil conductors is substantially equal to the direct-current resistance of coil conductors not located at both end portions in the arrangement direction of the coil conductors.  
      More specifically, the direct-current resistance is preferably set to be substantially equal to each other such that the line length of coil conductors located at both end portions in the arrangement direction of the coil conductors is substantially equal to the line length of coil conductors not located at both end portions in the arrangement direction of the coil conductors.  
      As the line length of the coil conductors increases, the direct-current resistance increases. To suppress variations in the inductance of each coil conductor and to suppress variations in the direct-current resistance, the line length of each of the coil conductors is preferably substantially equal.  
      However, a method for setting the direct-current resistance to be substantially equal is not limited thereto, and, even if the line lengths are different, the direct-current resistances may be set to be substantially equal by a method for making the line width different.  
      As described above, according to this preferred embodiment of the present invention, a magnetic field generated by partially reversing the winding direction of the coil conductor cancels a magnetic field generated by a normally wound portion to reduce the total inductance of the coil conductor. Thus, a laminated coil array is obtained in which variations in the inductance of each coil conductor are reduced and the reliability is high. Moreover, for example, when the line length of the coil conductors is set to be substantially equal, a laminated coil array in which variations in the inductance of each coil conductor are reduced and variations in direct-current resistance are also reduced is obtained.  
      These and other features, elements, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an exploded perspective view showing a laminated coil array according to a first preferred embodiment of the present invention;  
       FIG. 2  is a perspective view showing the laminated coil array according to the first preferred embodiment of the present invention;  
       FIG. 3  is an exploded perspective view showing a laminated coil array according to a second preferred embodiment of the present invention;  
       FIG. 4  is an exploded perspective view showing a laminated coil array according to a third preferred embodiment of the present invention;  
       FIG. 5  is an exploded perspective view showing a laminated coil array according to a fourth preferred embodiment of the present invention;  
       FIG. 6  is an exploded perspective view showing a related laminated coil array; and  
       FIG. 7  is a perspective view showing the related laminated coil array. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
      Hereinafter, preferred embodiments of the present invention are described with reference to the drawings.  
     First Preferred Embodiment  
       FIG. 1  is an exploded perspective view showing a laminated coil array  11  according to a first preferred embodiment of the present invention, and  FIG. 2  is a perspective illustration of the laminated coil array.  
      As shown in  FIG. 1 , the laminated coil array  11  includes ceramic layers  3  having internal conductors  4 ,  5   a ,  5   b ,  6   a ,  6   b , and  7  and via holes  12  and  13  disposed at fixed locations and ceramic layers  2  having via holes  12 . The internal conductors  4  to  7  are formed on the surface of the ceramic layers  3  by a method of printing, sputtering, evaporation, or other suitable methods. Furthermore, the via holes  12  and  13  are provided by forming through holes and filling the through holes with conductive paste. The internal conductors  4  to  7  and via holes  12  and  13  are made of materials such as Ag, Ag—Pd, Cu, Ni, or other suitable materials. The ceramic layers  2  and  3  are made of magnetic ceramic materials such as an Ni—Cu—Zn system ferrite, or other suitable magnetic ceramic materials.  
      The internal conductors  4  are electrically connected in series through the via holes  13  in the ceramic layers  3  to define a spiral coil conductor L 1 . In the same manner, the internal conductors  5   a ,  5   b ,  6   a ,  6   b , and  7  are also electrically connected in series to define spiral coil conductors L 2 , L 3 , and L 4 .  
      As shown in  FIG. 1 , the internal conductors  5   b  and  6   b  defining the coil conductors L 2  and L 3 , which are not located at both end portions in the arrangement direction of the coil inductors L 1  to L 4 , are provided on the surface of the ceramic layers  3  so as to partially reverse the winding direction of the coil conductors L 2  and L 3 . More specifically, when the laminated coil array  11  is seen from the upper portion of the drawing, although the internal conductors  4 ,  5   a ,  5   b , and  7  are arranged such that the coil conductors L 1  to L 4  are wound counterclockwise, the internal conductors  5   b  and  6   b  are arranged so as to be wound clockwise. Thus, the winding direction of the coil conductors L 2  and L 3  are partially reversed at portions where the internal conductors  5   b  and  6   b  are disposed.  
      Then, as shown in  FIG. 1 , the ceramic layers  3  are laminated in order and the ceramic layers  2  having the via holes  12  are disposed on the top and bottom surfaces of the ceramic layers  3 . After that, the ceramic layers  2  and  3  are pressed and integrally fired to form a laminate  15  as shown in  FIG. 2 . Inside the laminate  15 , the four coil conductors L 1  to L 4  are arranged in line in a direction that is substantially perpendicular to the direction of the coil axis. Furthermore, external electrodes  21  to  24  of the coil conductors L 1  to L 4  are provided on the end surfaces of the laminate  15 . The external electrodes  21  to  24  are electrically connected to the coil conductors L 1  to L 4  that are led out to the surface of the laminate  15  through the via holes  12 . These external electrodes  21  to  24  are formed such that, after the conductive paste of Ag, Ag—Pd, Cu, Ni, or other suitable conductive paste, has been printed, it is baked or further wet plated.  
      In the laminated coil array  11  having the above-described structure, a magnetic field generated in a portion where the winding is reversed from that of the other portions of the coil conductors L 2  and L 3  cancels a magnetic filed generated in a normally wound portion to reduce the total inductance of the coil conductors L 2  and L 3 . As a result, the variations between the inductance of the coil conductors L 1  and L 4  located at both end portions in the arrangement direction of the coil conductors L 1  and L 4  and the inductance of the coil conductors L 2  and L 3  not located at both end portions in the arrangement direction are reduced.  
     Second Preferred Embodiment  
       FIG. 3  is an exploded perspective view showing a laminated coil array  61  according to a second preferred embodiment of the present invention. Moreover, in  FIG. 3 , the portions in common with or corresponding to those in  FIG. 1  are given the same reference numerals, and their description is omitted.  
      In the laminated coil array  61  according to the present preferred embodiment, as shown in  FIG. 3 , the internal conductors  5   b  and  6   b  defining the coil conductors L 2  and L 3  are provided on the surface of the ceramic layers such that the winding direction of the coil conductors L 2  and L 3  is partially reversed. More specifically, when the laminated coil array  61  is seen from the upper portion of the drawing, although the internal conductors  4 ,  5   a ,  6   a , and  7  are arranged such that the coil conductors L 1  and L 4  are wound counterclockwise, the internal conductors  5   b  and  6   b  are wound clockwise. Thus, the winding direction of the coil conductors L 2  and L 3  is partially reversed in the middle portion at which the internal conductors  5   b  and  6   b  are provided.  
      Then, a magnetic field generated in a portion where the winding is reversed from that of the other portion of the coil conductors L 2  and L 3  cancel a magnetic field generated in a normally wound portion to reduce the total inductance of the coil conductors L 2  and L 3 . Thus, variations of the inductance among the coil conductors L 1  to L 4  are reduced.  
     Third Preferred Embodiment  
       FIG. 4  is an exploded perspective view showing a laminated coil array  71  according to a third preferred embodiment of the present invention. Moreover, in  FIG. 4 , the portions in common with or corresponding to those in  FIG. 1  are given the same reference numerals, and their description is omitted.  
      In the laminated coil array  71  according to the present preferred embodiment, as shown in  FIG. 4 , the internal conductors  5   b  and  6   b  defining the coil conductors L 2  and L 1  are provided on the surface of the ceramic layers such that the winding direction of the coil conductors L 2  and L 3  is partially reversed. More specifically, when the laminated coil array  71  is seen from the upper portion of the drawing, although the internal conductors  4 ,  5   a ,  6   a , and  7  are formed such that the coil conductors L 1  and L 4  are wound counterclockwise, the internal conductors  5   b  and  6   b  are wound clockwise. Thus, the winding direction of the coil conductors L 2  and L 3  is partially reversed.  
      Furthermore, in the laminated coil array  71  according to the present preferred embodiment, the number of turns of the internal conductors  5   c  and  6   c  is less than that of the internal conductors  4  and  7  provided on the same ceramic layers  3 . That is, although the number of turns of the internal conductors  5   c  and  6   c  is approximately ¼, the number of turns of the internal conductors  4  and  7  formed on the same ceramic layer is approximately ¾. The line length of the coil conductors L 2  and L 3  is increased by forming the internal conductors  5   b  and  6   b . Then, the line length of the coil conductors L 1  to L 4  is set to be substantially equal such that the number of turns of the internal conductors  5   c  and  6   c  is less than that of the internal conductors  4  and  7  provided on the same ceramic layer  3 .  
      A magnetic field generated in a portion where the winding is reversed from that of the other portion of the coil conductors L 2  and L 3  cancels a magnetic field generated in a normally wound portion to reduce the total inductance of the coil conductors L 2  and L 3 . Thus, variations of the inductance among the coil conductors L 1  to L 4  are reduced. Furthermore, since the line lengths of the coil conductors L 1  to L 4  are substantially equal, variations of the DC resistance of the coil conductors L 1  to L 4  are reduced.  
     Fourth Preferred Embodiment  
       FIG. 5  is an exploded perspective view showing a laminated coil array  81  according to a fourth preferred embodiment of the present invention. Moreover, in  FIG. 5 , the portions in common with or corresponding to those in  FIG. 1  are given the same reference numerals, and their description is omitted.  
      In the laminated coil array  81  of the present preferred embodiment, as shown in  FIG. 5 , the internal conductors  5   b  and  6   b  defining the coil conductors L 2  and L 3  are provided on the surface of the ceramic layers such that the winding direction of the coil conductors L 2  and L 3  are partially reversed. More specifically, when the laminated coil array  81  is seen from the upper portion of the drawing, although the internal conductors  4 ,  5   a ,  6   a , and  7  are arranged such that the coil conductors L 1  and L 4  are wound counterclockwise, the internal conductors  5   b  and  6   b  are wound clockwise. Thus, the winding direction of the coil conductors L 2  and L 3  is partially reversed.  
      Furthermore, in the laminated coil array  81  of the present preferred embodiment, on the ceramic sheet  3  on which the internal conductors  5   b  and  6   b  defining the coil conductors L 2  and L 3  are disposed, the internal conductors  4  and  7  defining the coil conductors L 1  and L 4  are also arranged so as to have substantially the same number of turns. That is, the internal conductors  5   b  and  6   b  and the internal conductors  4  and  7  are provided on the same ceramic sheet such that they have substantially the same number of turns and the coil conductors are wound in opposite directions.  
      A magnetic field generated in a portion where the winding is reversed from that of the other portion of the coil conductors L 2  and L 3  cancels a magnetic field generated in a normally wound portion to reduce the total inductance of the coil conductors L 2  and L 3 . Thus, variations of the inductance among the coil conductors L 1  to L 4  are reduced. Furthermore, since the line length of the coil conductors L 1  to L 4  is substantially equal, variations of the DC resistance of the coil conductors L 1  to L 4  are reduced.  
      Moreover, a laminated coil array according to the present invention is not limited to the above-described preferred embodiments, but it can be variously changed and modified within the scope of the invention. For example, the internal conductor, which arranged such that the winding direction of the coil conductor may be partially reversed, may be continuously or discontinuously arranged over a plurality of ceramic layers. Furthermore, in the above-described preferred embodiments, the surface perpendicular to the direction of the coil axis defines the main surface for forming the external electrodes, however, the surface parallel to the direction of the coil axis may be the main surface for forming the external electrodes. Moreover, in the above-described preferred embodiments, although only the coil conductors are formed inside the laminate, capacitors that are connected in series or in parallel to the coil conductors may be provided. In conclusion, when three or more coil conductors which are electrically separated from each other are arranged inside a laminate, the present invention may be applied.  
      While the present invention has been described with respect to preferred embodiments, it will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than those specifically set out and described above. Accordingly, it is intended by the appended claims to cover all modifications of the present invention that fall within the true spirit and scope of the invention.