Patent Publication Number: US-11640867-B2

Title: Multilayer coil component

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of priority to Japanese Patent Application No. 2019-038543, filed Mar. 4, 2019, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a multilayer coil component. 
     Background Art 
     As an example of a multilayer coil component, Japanese Unexamined Patent Application Publication No. 2005-109195 discloses a multilayer coil component that includes a ceramic multilayer body formed by stacking a plurality of ceramic layers and a plurality of inner electrodes on top of one another and a helical coil that is formed by electrically connecting the plurality of inner electrodes to one another. The coil diameter of the helical coil decreases in a stepwise or continuous manner in an axial direction of the helical coil. A wide band multilayer coil component in which a resonant frequency is dispersed can be obtained by making the coil diameter of the helical coil decrease in a stepwise or continuous manner in the axial direction of the helical coil. 
     It is required that a multilayer inductor have satisfactory radio-frequency characteristics in a radio-frequency band (for example, a GHz band extending from around 30 GHz) in response to the increasing communication speed and miniaturization of electronic devices in recent years. However, the radio-frequency characteristics of the multilayer coil component disclosed in Japanese Unexamined Patent Application Publication No. 2005-109195 are not satisfactory when the multilayer coil component is used as a noise absorbing component particularly in a radio-frequency range extending from around 30 GHz. In addition, there is a problem arising from the structure in which the coil diameter decreases in a stepwise or continuous manner in that external electrodes, which cover two lead out electrodes, become larger due to the position of a lead conductor that is led out at one end of the coil and the position of a lead out conductor that is led out at the other end of coil are shifted with respect to each other and consequently stray capacitances are increased and the radio-frequency characteristics are degraded. 
     SUMMARY 
     Accordingly, the present disclosure provides a multilayer coil component that has excellent radio-frequency characteristics. 
     A multilayer coil component according to a preferred embodiment of the present disclosure includes a multilayer body that is formed by stacking a plurality of insulating layers on top of one another and that has a coil built into the inside thereof; and a first outer electrode and a second outer electrode that are electrically connected to the coil. The coil is formed by electrically connecting a plurality of coil conductors, which are stacked together with insulating layers, to one another. The multilayer body has a first end surface and a second end surface, which face each other in a length direction, a first main surface and a second main surface, which face each other in a height direction perpendicular to the length direction, and a first side surface and a second side surface, which face each other in a width direction perpendicular to the length direction and the height direction. The first outer electrode is arranged so as to cover part of the first end surface and so as to extend from the first end surface and cover part of the first main surface. The second outer electrode is arranged so as to cover part of the second end surface and so as to extend from the second end surface and cover part of the first main surface. The first main surface is a mounting surface. A stacking direction of the multilayer body and an axial direction of the coil are parallel to the mounting surface. The coil includes a plurality of different coil conductors having different coil diameters, and shortest distances from the first main surface to the coil conductors are identical for all of the plurality of different coil conductors. 
     According to the preferred embodiment of the present disclosure, a multilayer coil component can be provided that has excellent radio-frequency characteristics. 
     Other features, elements, characteristics and advantages of the present disclosure will become more apparent from the following detailed description of preferred embodiments of the present disclosure with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view schematically illustrating a multilayer coil component according to an embodiment of the present disclosure; 
         FIG.  2 A  is a side view of the multilayer coil component illustrated in  FIG.  1   ,  FIG.  2 B  is a front view of the multilayer coil component illustrated in  FIG.  1   , and  FIG.  2 C  is a bottom view of the multilayer coil component illustrated in  FIG.  1   ; 
         FIG.  3    is a sectional view of the multilayer coil component illustrated in  FIG.  1   ; 
         FIGS.  4 A to  4 E  are diagrams schematically illustrating repeating shapes of coil conductors of a multilayer body illustrated in  FIG.  3   ; and 
         FIGS.  5 A and  5 B  are sectional views schematically illustrating other examples of a multilayer coil component according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereafter, a multilayer coil component according to an embodiment of the present disclosure will be described. However, the present disclosure is not limited to the following embodiment and can be applied with appropriate modifications within a range that does not alter the gist of the present disclosure. Combinations of two or more desired configurations among the configurations described below are also included in the scope of the present disclosure. 
       FIG.  1    is a perspective view schematically illustrating a multilayer coil component according to an embodiment of the present disclosure.  FIG.  2 A  is a side view of the multilayer coil component illustrated in  FIG.  1   ,  FIG.  2 B  is a front view of the multilayer coil component illustrated in  FIG.  1   , and  FIG.  2 C  is a bottom view of the multilayer coil component illustrated in  FIG.  1   . 
     A multilayer coil component  1  illustrated in  FIGS.  1 ,  2 A,  2 B, and  2 C  includes a multilayer body  10 , a first outer electrode  21 , and a second outer electrode  22 . The multilayer body  10  has a substantially rectangular parallelepiped shape having six surfaces. The configuration of the multilayer body  10  will be described later, but the multilayer body  10  is formed by stacking a plurality of insulating layers on top of one another and has a coil built into the inside thereof. The first outer electrode  21  and the second outer electrode  22  are electrically connected to the coil. 
     In the multilayer coil component  1  and the multilayer body  10  of the embodiment of the present disclosure, a length direction, a height direction, and a width direction are an x direction, a y direction, and a z direction, respectively, in  FIG.  1   . Here, the length direction (x direction), the height direction (y direction), and a width direction (z direction) are perpendicular to each other. 
     As illustrated in  FIGS.  1 ,  2 A,  2 B, and  2 C , the multilayer body  10  has a first end surface  11  and a second end surface  12 , which face each other in the length direction (x direction), a first main surface  13  and a second main surface  14 , which face each other in the height direction (y direction) perpendicular to the length direction, and a first side surface  15  and a second side surface  16 , which face each other in the width direction (z direction) perpendicular to the length direction and the height direction. 
     Although not illustrated in  FIG.  1   , corner portions and edge portions of the multilayer body  10  are preferably rounded. The term “corner portion” refers to a part of the multilayer body  10  where three surfaces intersect and the term “edge portion” refers to a part of the multilayer body  10  where two surfaces intersect. 
     The first outer electrode  21  is arranged so as to cover part of the first end surface  11  of the multilayer body  10  as illustrated in  FIGS.  1  and  2 B  and so as to extend from the first end surface  11  and cover part of the first main surface  13  of the multilayer body  10 , as illustrated in  FIGS.  1  and  2 C . As illustrated in  FIG.  2 B , the first outer electrode  21  covers a region of the first end surface  11  that includes the edge portion that intersects the first main surface  13 , but does not cover a region of the first end surface  11  that includes the edge portion that intersects the second main surface  14 . Therefore, the first end surface  11  is exposed in the region including the edge portion that intersects the second main surface  14 . In addition, the first outer electrode  21  does not cover the second main surface  14 . Since part of the first end surface  11  is not covered by the first outer electrode  21 , stray capacitances can be reduced and radio-frequency characteristics can be improved compared with a multilayer coil component in which the entire first end surface is covered by the first outer electrode. 
     In  FIG.  2 B , a height E 2  of the part of the first outer electrode  21  that covers the first end surface  11  of the multilayer body  10  is constant, but the shape of the first outer electrode  21  is not particularly limited so long as the first outer electrode  21  covers part of the first end surface  11  of the multilayer body  10 . For example, the first outer electrode  21  may have an arch-like shape that increases in height from the ends thereof toward the center thereof on the first end surface  11  of the multilayer body  10 . In addition, in  FIG.  2 C , a length E 1  of the part of the first outer electrode  21  that covers the first main surface  13  of the multilayer body  10  is constant, but the shape of the first outer electrode  21  is not particularly limited so long as the first outer electrode  21  covers part of the first main surface  13  of the multilayer body  10 . For example, the first outer electrode  21  may have an arch-like shape that increases in length from the ends thereof toward the center thereof on the first main surface  13  of the multilayer body  10 . 
     As illustrated in  FIGS.  1  and  2 A , the first outer electrode  21  may be additionally arranged so as to extend from the first end surface  11  and the first main surface  13  and cover part of the first side surface  15  and part of the second side surface  16 . In this case, as illustrated in  FIG.  2 A , the parts of the first outer electrode  21  covering the first side surface  15  and the second side surface  16  are preferably formed in a diagonal shape relative to both the edge portion that intersects the first end surface  11  and the edge portion that intersects the first main surface  13 . However, the first outer electrode  21  does not have to be arranged so as to cover part of the first side surface  15  and part of the second side surface  16 . 
     The second outer electrode  22  is arranged so as to cover part of the second end surface  12  of the multilayer body  10  and so as to extend from the second end surface  12  and cover part of the first main surface  13  of the multilayer body  10 . Similarly to the first outer electrode  21 , the second outer electrode  22  covers a region of the second end surface  12  that includes the edge portion that intersects the first main surface  13 , but does not cover a region of the second end surface  12  that includes the edge portion that intersects the second main surface  14 . Therefore, the second end surface  12  is exposed in the region including the edge portion that intersects the second main surface  14 . In addition, the second outer electrode  22  does not cover the second main surface  14 . Since part of the second end surface  12  is not covered by the second outer electrode  22 , stray capacitances can be reduced and radio-frequency characteristics can be improved compared with a multilayer coil component in which the entire second end surface is covered by the second outer electrode. 
     Similarly to the first outer electrode  21 , the shape of the second outer electrode  22  is not particularly limited so long as the second outer electrode  22  covers part of the second end surface  12  of the multilayer body  10 . For example, the second outer electrode  22  may have an arch-like shape that increases in height from the ends thereof toward the center thereof on the second end surface  12  of the multilayer body  10 . Furthermore, the shape of the second outer electrode  22  is not particularly limited so long as the second outer electrode  22  covers part of the first main surface  13  of the multilayer body  10 . For example, the second outer electrode  22  may have an arch-like shape that increases in length from the ends thereof toward the center thereof on the first main surface  13  of the multilayer body  10 . 
     Similarly to the first outer electrode  21 , the second outer electrode  22  may be additionally arranged so as to extend from the second end surface  12  and the first main surface  13  and cover part of the first side surface  15  and part of the second side surface  16 . In this case, the parts of the second outer electrode  22  covering the first side surface  15  and the second side surface  16  are preferably formed in a diagonal shape relative to both the edge portion that intersects the second end surface  12  and the edge portion that intersects the first main surface  13 . However, the second outer electrode  22  does not have to be arranged so as to cover part of the first side surface  15  and part of the second side surface  16 . 
     The first outer electrode  21  and the second outer electrode  22  are arranged in the manner described above, and therefore the first main surface  13  of the multilayer body  10  serves as a mounting surface when the multilayer coil component  1  is mounted on a substrate. 
     Although the size of the multilayer coil component  1  according to the embodiment of the present disclosure is not particularly limited, the multilayer coil component  1  is preferably the 0603 size, the 0402 size, or the 1005 size. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0603 size, the length of the multilayer body  10  (length indicated by double-headed arrow L 1  in  FIG.  2 A ) preferably lies in a range of around 0.57 mm to 0.63 mm. In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0603 size, the width of the multilayer body  10  (length indicated by double-headed arrow W 1  in  FIG.  2 C ) preferably lies in a range of around 0.27 mm to 0.33 mm. In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0603 size, the height of the multilayer body  10  (length indicated by double-headed arrow T 1  in  FIG.  2 B ) preferably lies in a range of around 0.27 mm to 0.33 mm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0603 size, the length of the multilayer coil component  1  (length indicated by double arrow L 2  in  FIG.  2 A ) preferably lies in a range of around 0.57 mm to 0.63 mm. In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0603 size, the width of the multilayer coil component  1  (length indicated by double-headed arrow W 2  in  FIG.  2 C ) preferably lies in a range of around 0.27 mm to 0.33 mm. In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0603 size, the height of the multilayer coil component  1  (length indicated by double-headed arrow T 2  in  FIG.  2 B ) preferably lies in a range of around 0.27 mm to 0.33 mm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0603 size, the length of the part of the first outer electrode  21  that covers the first main surface  13  of the multilayer body  10  (length indicated by double-headed arrow E 1  in  FIG.  2 C ) preferably lies in a range of around 0.12 mm to 0.22 mm. Similarly, the length of the part of the second outer electrode  22  that covers the first main surface  13  of the multilayer body  10  preferably lies in a range of around 0.12 mm to 0.22 mm. Additionally, in the case where the length of the part of the first outer electrode  21  that covers the first main surface  13  of the multilayer body  10  and the length of the part of the second outer electrode  22  that covers the first main surface  13  of the multilayer body  10  are not constant, it is preferable that the lengths of the longest parts thereof lie within the above-described range. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0603 size, the height of the part of the first outer electrode  21  that covers the first end surface  11  of the multilayer body  10  (length indicated by double-headed arrow E 2  in  FIG.  2 B ) preferably lies in a range of around 0.10 mm to 0.20 mm. Similarly, the height of the part of the second outer electrode  22  that covers the second end surface  12  of the multilayer body  10  preferably lies in a range of around 0.10 mm to 0.20 mm. In this case, stray capacitances arising from the outer electrodes  21  and  22  can be reduced. In the case where the height of the part of the first outer electrode  21  that covers the first end surface  11  of the multilayer body  10  and the height of the part of the second outer electrode  22  that covers the second end surface  12  of the multilayer body  10  are not constant, it is preferable that the heights of the highest parts thereof lie within the above-described range. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0402 size, the length of the multilayer body  10  preferably lies in a range of around 0.38 mm to 0.42 mm and the width of the multilayer body  10  preferably lies in a range of around 0.18 mm to 0.22 mm. In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0402 size, the height of the multilayer body  10  preferably lies in a range of around 0.18 mm to 0.22 mm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0402 size, the length of the multilayer coil component  1  preferably lies in a range of around 0.38 mm to 0.42 mm. In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0402 size, the width of the multilayer coil component  1  preferably lies in a range of around 0.18 mm to 0.22 mm. In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0402 size, the height of the multilayer coil component  1  preferably lies in a range of around 0.18 mm to 0.22 mm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0402 size, the length of the part of the first outer electrode  21  that covers the first main surface  13  of the multilayer body  10  preferably lies in a range of around 0.08 mm to 0.15 mm. Similarly, the length of the part of the second outer electrode  22  that covers the first main surface  13  of the multilayer body  10  preferably lies in a range of around 0.08 mm to 0.15 mm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0402 size, the height of the part of the first outer electrode  21  that covers the first end surface  11  of the multilayer body  10  preferably lies in a range of around 0.06 mm to 0.13 mm. Similarly, the height of the part of the second outer electrode  22  that covers the second end surface  12  of the multilayer body  10  preferably lies in a range of around 0.06 mm to 0.13 mm. In this case, stray capacitances arising from the outer electrodes  21  and  22  can be reduced. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 1005 size, the length of the multilayer body  10  preferably lies in a range of around 0.95 mm to 1.05 mm and the width of the multilayer body  10  preferably lies in a range of around 0.45 mm to 0.55 mm. In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 1005 size, the height of the multilayer body  10  preferably lies in a range of around 0.45 mm to 0.55 mm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 1005 size, the length of the multilayer coil component  1  preferably lies in a range of around 0.95 mm to 1.05 mm. In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 1005 size, the width of the multilayer coil component  1  preferably lies in a range of around 0.45 mm to 0.55 mm. In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 1005 size, the height of the multilayer coil component  1  preferably lies in a range of around 0.45 mm to 0.55 mm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 1005 size, the length of the part of the first outer electrode  21  that covers the first main surface  13  of the multilayer body  10  preferably lies in a range of around 0.20 mm to 0.38 mm. Similarly, the length of the part of the second outer electrode  22  that covers the first main surface  13  of the multilayer body  10  preferably lies in a range of around 0.20 mm to 0.38 mm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 1005 size, the height of the part of the first outer electrode  21  that covers the first end surface  11  of the multilayer body  10  preferably lies in a range of around 0.15 mm to 0.33 mm. Similarly, the height of the part of the second outer electrode  22  that covers the second end surface  12  of the multilayer body  10  preferably lies in a range of around 0.15 mm to 0.33 mm. In this case, stray capacitances arising from the outer electrodes  21  and  22  can be reduced. 
     The coil that is built into the multilayer body  10  of the multilayer coil component  1  according to the embodiment of the present disclosure will be described next. The coil is formed by electrically connecting a plurality of coil conductors, which are stacked together with insulating layers, to one another. 
       FIG.  3    is a sectional view of the multilayer coil component  1  illustrated in  FIG.  1   . As illustrated in  FIG.  3   , in the multilayer body  10  of the multilayer coil component  1 , the coil includes a plurality of coil conductor groups having different coil diameters from each other. The coil conductor groups consist of a first coil conductor group  30   a , a second coil conductor group  30   b , a third coil conductor group  30   c , a fourth coil conductor group  30   d , and a fifth coil conductor group  30   e . The coil conductor groups  30   a ,  30   b ,  30   c ,  30   d , and  30   e  are respectively formed of a plurality of coil conductors  31   a , a plurality of coil conductors  31   b , a plurality of coil conductors  31   c , a plurality of coil conductors  31   d , and a plurality of coil conductors  31   e , the coil conductors constituting each group having the same coil diameter. In the multilayer body  10 , the coil diameters of the coil conductor groups decrease from the first end surface  11  toward the second end surface  12 . A stacking direction of the multilayer body  10  is a direction from the first end surface  11  toward the second end surface  12  and an axial direction of the coil is the direction in which the coil conductors are stacked and therefore the stacking direction and the axial direction of the coil are parallel to the first main surface  13 , which is the mounting surface. The shortest distances from the first main surface  13 , which is the mounting surface, to the coil conductors  31   a ,  31   b ,  31   c ,  31   d , and  31   e  of the coil conductor groups  30   a ,  30   b ,  30   c ,  30   d , and  30   e , i.e., the distances from the first main surface  13  to the bottom edges of the coil conductors (positions represented by two-dot chain line  20 ) are identical for all the coil conductors. 
     In addition, in the multilayer coil component  1  illustrated in  FIG.  3   , the first outer electrode  21  and the coil conductor that faces the first outer electrode  21  are connected to each other in a straight line by a first connection conductor  41  and the second outer electrode  22  and the coil conductor that faces the second outer electrode  22  are connected to each other in a straight line by a second connection conductor  42 . The first connection conductor  41  and the second connection conductor  42  are connected to the respective coil conductors at the parts of the coil conductors that are closest to the first main surface  13 , which is the mounting surface. The first connection conductor  41  and the second connection conductor  42  overlap the coil conductors in a plan view from the stacking direction and are positioned closer to the first main surface  13 , which is the mounting surface, than all the center axes of the coil conductors. Since the first connection conductor  41  and the second connection conductor  42  are both connected to the coil conductors at the parts of the coil conductors that are closest to the mounting surface, the outer electrodes can be reduced in size and the radio-frequency characteristics can be improved. 
     Next, the shapes of the coil conductors of the coil conductor groups will be described while referring to  FIGS.  4 A to  4 E .  FIGS.  4 A to  4 E  are diagrams schematically illustrating repeating shapes of the coil conductors of the multilayer body  10  illustrated in  FIG.  3   . The multilayer body  10  illustrated in  FIG.  3    includes the first coil conductors  31   a , the second coil conductors  31   b , the third coil conductors  31   c , the fourth coil conductors  31   d , and the fifth coil conductors  31   e  illustrated in  FIGS.  4 A to  4 E . In addition,  FIGS.  4 A to  4 E  schematically illustrate the repeating shapes formed by the plurality of coil conductors, but this does not mean that the coil conductors have circular shapes in the same plane. 
     The plurality of first coil conductors  31   a  illustrated in  FIG.  4 A  collectively form the first coil conductor group  30   a  illustrated in  FIG.  3   . The plurality of second coil conductors  31   b  illustrated in  FIG.  4 B  collectively form the second coil conductor group  30   b  illustrated in  FIG.  3   . The plurality of third coil conductors  31   c  illustrated in  FIG.  4 C  collectively form the third coil conductor group  30   c  illustrated in  FIG.  3   . The plurality of fourth coil conductors  31   d  illustrated in  FIG.  4 D  collectively form the fourth coil conductor group  30   d  illustrated in  FIG.  3   . The plurality of fifth coil conductors  31   e  illustrated in  FIG.  4 E  collectively form the fifth coil conductor group  30   e  illustrated in  FIG.  3   . As illustrated in  FIGS.  4 A to  4 E , the repeating shapes of the coil conductors  31   a  to  31   e  are substantially circular shapes. A repeating shape formed by a plurality of coil conductors having two or more turns is referred to as coil conductor group. 
     The coil conductors  31   a ,  31   b ,  31   c ,  31   d , and  31   e  have different coil diameters d a , d b , d e , d d , and d e  from each other and the size relationship therebetween is d a &gt;d b &gt;d e &gt;d a &gt;d e . The shortest distances from the first main surface  13 , which is the mounting surface, to the coil conductors, i.e., the lengths from the first main surface  13  to the bottom edges of the coil conductors (positions represented by two-dot chain line  20 ) are identical for all the coil conductors. Therefore, a center Ca of the first coil conductors  31   a , a center Cb of the second coil conductors  31   b , a center Cc of the third coil conductors  31   c , a center Cd of the fourth coil conductors  31   d , and a center Ce of the fifth coil conductors  31   e  are shifted from each other and do not overlap in a plan view. Since the overlapping areas of the coil conductors  31   a ,  31   b ,  31   c ,  31   d , and  31   e  are small, the generation of stray capacitances arising from overlapping of the coil conductors can be suppressed and the radio-frequency characteristics can be improved. Furthermore, since the centers of the coil conductors are shifted relative to each other, the coupling coefficients between the coil conductors are changed and the radio-frequency characteristics can be improved. 
     The number of different coil conductors forming the coil is not particularly limited provided that there are at least two different coil conductors, but there are preferably three or more different coil conductors, more preferably four or more different coil conductors, and still more preferably five or more different coil conductors. In this specification, coil conductors having different coil diameters are referred to as different coil conductors. The multilayer coil component  1  illustrated in  FIGS.  3  and  4    is formed of five different coil conductors and the coil conductors form coil conductor groups. When a coil conductor includes a land, the shape of the coil conductor is the shape obtained by removing the land. 
     The coil conductors of the multilayer body  10  of the multilayer coil component  1  according to the embodiment of the present disclosure may form coil conductor groups or may not form coil conductor groups. 
     Examples in which adjacent coil conductors all have different coil diameters will be described while referring to  FIGS.  5 A and  5 B .  FIGS.  5 A and  5 B  are sectional views schematically illustrating other examples of a multilayer coil component according to an embodiment of the present disclosure. In a multilayer coil component  2  illustrated in  FIG.  5 A , a first coil conductor  31   a , a second coil conductor  31   b , a third coil conductor  31   c , a fourth coil conductor  31   d , a fifth coil conductor  31   e , a fourth coil conductor  31   d , a third coil conductor  31   c , a second coil conductor  31   b , and a first coil conductor  31   a  are repeatedly arranged in this order from the first end surface  11  to the second end surface  12 . The shortest distances from the first main surface  13 , which is the mounting surface, to the coil conductors, i.e., the distances from the first main surface  13  to the bottom edges of the coil conductors (positions represented by two-dot chain line  20 ) are identical for all the coil conductors. However, the shortest distance from the main surface on the opposite side from the mounting surface to the coil conductors varies in a regular manner in which the shortest distance first increases and then decreases and returns to its original position in a direction from the first end surface to the second end surface. Adjacent coil conductors do not overlap each other in a region close to the second main surface on the opposite side from the first main surface  13 , which is the mounting surface, in a plan view from the stacking direction. Therefore, generation of stray capacitances can be suppressed and the radio-frequency characteristics can be improved. 
     In a multilayer coil component  3  illustrated in  FIG.  5 B , a first coil conductor  31   a , a second coil conductor  31   b , a third coil conductor  31   c , a fourth coil conductor  31   d , a fifth coil conductor  31   e  are repeatedly arranged in this order from the first end surface  11  to the second end surface  12 . The shortest distances from the first main surface  13 , which is the mounting surface, to the coil conductors, i.e., the distances from the first main surface  13  to the bottom edges of the coil conductors (positions represented by two-dot chain line  20 ) are identical for all the coil conductors. However, the shortest distance from the main surface on the opposite side from the mounting surface to the coil conductors varies in a regular manner in which the shortest distance increases and then returns to its original position in a direction from the first end surface to the second end surface. Adjacent coil conductors do not overlap each other in a region close to the second main surface on the opposite side from the first main surface  13 , which is the mounting surface. Therefore, generation of stray capacitances can be suppressed and the radio-frequency characteristics can be improved. 
     In a multilayer coil component according to an embodiment of the present disclosure, the order in which the coil conductors are arranged is not particularly limited, and the coil conductors may be randomly arranged, coil conductor groups may be regularly arranged as illustrated in  FIG.  3   , or the coil conductors may be regularly arranged as illustrated in  FIGS.  5 A and  5 B . Furthermore, coil conductor groups may be randomly arranged. 
     The repeating shape of the coil conductors is not particularly limited and may be a substantially circular shape or may be a substantially polygonal shape. In the case where the repeating shape of the coil conductors is a substantially polygonal shape, the coil diameter is the diameter of an area-equivalent circle of the polygonal shape and the coil axis is an axis that passes through the center of the polygonal shape and is parallel to the length direction. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0603 size, the inner diameter of the coil conductors preferably lies in a range of around 50 μm to 100 μm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0402 size, the inner diameter of the coil conductors preferably lies in a range of around 30 μm to 70 μm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 1005 size, the inner diameter of the coil conductors preferably lies in a range of around 80 μm to 170 μm. 
     The line width of the coil conductors in a plan view from the stacking direction is not particularly limited but is preferably in a range of around 10% to 30% of the width of the multilayer body  10 . When the line width of the coil conductors is less than around 10% of the width of the multilayer body  10 , a direct-current resistance Rdc may become large. On the other hand, when the line width of the coil conductors exceeds around 30% of the width of the multilayer body  10 , the electrostatic capacitance of the coil may become large and the radio-frequency characteristics may be degraded. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0603 size, the line width of the coil conductors preferably lies in a range of around 30 μm to 90 μm and more preferably lies in a range of around 30 μm to 70 μm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0402 size, the line width of the coil conductors preferably lies in a range of around 20 μm to 60 μm and more preferably lies in a range of around 20 μm to 50 μm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 1005 size, the line width of the coil conductors preferably lies in a range of around 50 μm to 150 μm and more preferably lies in a range of around 50 μm to 120 μm. 
     The inner diameter of the coil conductors in a plan view from the stacking direction is preferably in a range of around 15% to 40% of the width of the multilayer body  10 . 
     The inter coil conductor distance in the stacking direction preferably lies in a range of around 3 μm to 7 μm in the multilayer coil component  1  according to the embodiment of the present disclosure. As a result of making the inter coil conductor distance in the stacking direction lie in a range of around 3 μm to 7 μm, the number of turns of the coil can be increased and therefore the impedance can be increased. Furthermore, a transmission coefficient S 21  in a radio-frequency band can also be increased as described later. 
     It is preferable that a first connection conductor and a second connection conductor be provided inside the multilayer body  10  of the multilayer coil component  1 . The shapes of the first connection conductor and the second connection conductor are not especially restricted, but it is preferable that the first connection conductor and the second connection conductor be each connected in a straight line between an outer electrode and a coil conductor. By connecting the first connection conductor and the second connection conductor from the coil conductors to the outer electrodes in straight lines, lead out parts can be simplified and the radio-frequency characteristics can be improved. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0603 size, the lengths of the first connection conductor and the second connection conductor preferably lie in a range of around 15 μm to 45 μm and more preferably lie in a range of around 15 μm to 30 μm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0402 size, the lengths of the first connection conductor and the second connection conductor preferably lie in a range of around 10 μm to 30 μm and more preferably lie in a range of around 10 μm to 25 μm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 1005 size, the lengths of the first connection conductor and the second connection conductor preferably lie in a range of around 25 μm to 75 μm and more preferably lie in a range of around 25 μm to 50 μm. 
     It is preferable that the first connection conductor and the second connection conductor overlap the coil conductors in a plan view from the stacking direction and be positioned closer to the mounting surface than all the center axes of the coil conductors. Here, the center axis of a coil conductor is an axis that passes through the center of the repeating shape formed by the coil conductor and is parallel to the length direction. For example, in the multilayer coil component  1  illustrated in  FIG.  3   , the first connection conductor  41  and the second connection conductor  42  are connected to the parts of the respective coil conductors that are closest to the mounting surface and therefore the first connection conductor  41  and the second connection conductor  42  are located closer to the mounting surface than the center axes of the coil conductors. 
     Provided that via conductors forming a connection conductor overlap in a plan view from the stacking direction, the via conductors forming the connection conductor do not have to be precisely aligned in a straight line. 
     The width of the first connection conductor and the width of the second connection conductor preferably each lie in a range of around 8% to 20% of the width of the multilayer body  10 . The “width of the connection conductor” refers to the width of the narrowest part of the connection conductor. That is, when a connection conductor includes a land, the shape of the connection conductor is the shape obtained by removing the land. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0603 size, the widths of the connection conductors preferably lie in a range of around 30 μm to 60 μm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 0402 size, the widths of the connection conductors preferably lie in a range of around 20 μm to 40 μm. 
     In the case where the multilayer coil component  1  according to the embodiment of the present disclosure is the 1005 size, the widths of the connection conductors preferably lie in a range of around 40 μm to 100 μm. 
     In the multilayer coil component  1  according to the embodiment of the present disclosure, the lengths of the first connection conductor and the second connection conductor preferably lie in a range of around 2.5% to 7.5% of the length of the multilayer body  10  and more preferably lie in a range of around 2.5% to 5.0% of the length of the multilayer body  10 . 
     In the multilayer coil component  1  according to the embodiment of the present disclosure, there may be two or more of the first connection conductor and the second connection conductor. A case where there are two or more connection conductors indicates a state where a part of an outer electrode covering an end surface and the coil conductor facing that outer electrode are connected to each other in at least two places by the connection conductors. 
     The multilayer coil component  1  according to the embodiment of the present disclosure has excellent radio-frequency characteristics in a radio-frequency band (in particular, in a range of around 30 GHz to 80 GHz). Specifically, the transmission coefficient S 21  at around 40 GHz preferably lies in a range of around −1 dB to 0 dB and the transmission coefficient S 21  at around 50 GHz preferably lies in a range of around −2 dB to 0 dB. The transmission coefficient S 21  is obtained from a ratio of the power of a transmitted signal to the power of an input signal. The transmission coefficient S 21  is basically a dimensionless quantity, but is usually expressed in dB using the common logarithm. When the above conditions are satisfied, for example, the multilayer coil component  1  can be suitably used in a bias tee circuit or the like inside an optical communication circuit. 
     Hereafter, an example of a method of manufacturing the multilayer coil component  1  according to the embodiment of the present disclosure will be described. 
     First, ceramic green sheets, which are insulating layers, are manufactured. For example, an organic binder such as a polyvinyl butyral resin, an organic solvent such as ethanol or toluene, and a dispersant are added to a ferrite raw material and kneaded to form a slurry. After that, magnetic sheets having a thickness of around 12 μm are obtained using a method such as a doctor blade technique. 
     As a ferrite raw material, for example, iron, nickel, zinc and copper oxide raw materials are mixed together and calcined at around 800° C. for around one hour, pulverized using a ball mill, and dried, and a Ni—Zn—Cu ferrite raw material (oxide mixed powder) having an average particle diameter of around 2 μm can be obtained. 
     As a ceramic green sheet material, which forms the insulating layers, for example, a magnetic material such as a ferrite material, a nonmagnetic material such as a glass ceramic material, or a mixed material obtained by mixing a magnetic material and a nonmagnetic material can be used. When manufacturing ceramic green sheets using a ferrite material, in order to obtain a high L value (inductance), it is preferable to use a ferrite material having a composition consisting of Fe 2 O 3  at around 40 mol % to 49.5 mol %, ZnO at around 5 mol % to 35 mol %, CuO at around 4 mol % to 12 mol %, and the remainder consisting of NiO and trace amounts of additives (including inevitable impurities). 
     Via holes having a diameter of around 20 μm to 30 μm are formed by subjecting the manufactured ceramic green sheets to prescribed laser processing. Using a Ag paste on specific sheets having via holes, the coil sheets are formed by filling the via holes and screen-printing prescribed coil-looping conductor patterns (coil conductors) having a thickness of around 11 μm and drying. 
     A plurality of coil sheets are prepared in accordance with the types and arrangements of coil conductors that are to be formed. 
     The coil sheets are stacked in a prescribed order so that a coil having a looping axis in a direction parallel to the mounting surface is formed in the multilayer body after division into individual components. In addition, via sheets, in which via conductors serving as connection conductors are formed, are stacked above and below the coil sheets. At this time, the quantities and thicknesses of the coil sheets and via sheets are preferably adjusted so that the lengths of the connection conductors both lie in a range of around 2.5% to 7.5% of the length of the multilayer body  10 . 
     The multilayer body is subjected to thermal pressure bonding in order to obtain a pressure-bonded body, and then the pressure-bonded body is cut into pieces of a predetermined chip size to obtain individual chips. The divided chips may be processed using a rotary barrel in order to round the corner portions and edge portions thereof. 
     Binder removal and firing is performed at a predetermined temperature and for a predetermined period of time, and fired bodies (multilayer bodies) having a built-in coil are obtained. 
     The chips are dipped at an angle in a layer obtained by spreading a Ag paste to a predetermined thickness and baked to form a base electrode for an outer electrode on four surfaces (a main surface, an end surface, and both side surfaces) of the multilayer body. In the above-described method, the base electrode can be formed in one go in contrast to the case where the base electrode is formed separately on the main surface and the end surface of the multilayer body in two steps. 
     Formation of the outer electrodes is completed by sequentially forming a Ni film and a Sn film having predetermined thicknesses on the base electrodes by performing plating. The multilayer coil component  1  according to the embodiment of the present disclosure can be manufactured as described above. 
     While preferred embodiments of the disclosure have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the disclosure. The scope of the disclosure, therefore, is to be determined solely by the following claims.