Patent Publication Number: US-2021193370-A1

Title: Coil component and switching regulator

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional of U.S. patent application Ser. No. 15/586,803 filed on May 4, 2017, which claims benefit of priority to Japanese Patent Application 2016-107560 filed May 30, 2016, the entire content of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a coil component and a switching regulator including the coil component. 
     BACKGROUND 
     Conventional coil components include a coil component described in U.S. Pat. No. 6,362,986. This coil component has a plurality of (N) coils, and these coils are negatively magnetically coupled (hereinafter sometimes simply referred to as “negatively coupled”) through a common core, and an excitation inductance is greater than approx. three times a leakage inductance. This indicates that the leakage inductance is small, i.e., the coils are strongly negatively coupled to each other. Additionally, even when Nis larger than three, the coil component has all the coils strongly negatively coupled by winding the coils around the common core. Particularly, the coil component is disclosed in a configuration in which at least two or more coils are most strongly negatively coupled to each of the coils. The coil component is used for an output voltage smoothing circuit of a multi-phase switching regulator (hereinafter referred to as “multi-phase SW regulator”). When a period of a pulse signal input to each of the coils (interval between turn-on transitions) is represented by a phase of 360°, these pulse signals are input to the coils with a phase difference of 360°/N in the multi-phase SW regulator so as to reduce a ripple voltage input to a smoothing capacitor. In a steady state without a load variation, the pulse signals have a constant duty cycle, and the duty cycle is the same between the pulse signals. 
     SUMMARY 
     Problem to be Solved by the Disclosure 
     In the conventional coil component, for example, when N=2, pulse signals having a phase difference of 180° are input to two coils. In this case, if the duty cycle of the pulse signals is 50%, a period of an ON state (an ON period) of the pulse signal input to one coil is a period of an OFF state (an OFF period) of the pulse signal input to the other coil. Although this leads to an increase in current in one coil and a decrease in current in the other coil, since these coils are negatively coupled through the core, changes in magnetic flux in the core due to the current changes are made in the same direction and strengthen each other. Therefore, a change rate of the magnetic flux in the core becomes larger than a change rate of the magnetic flux in the core when the two coils are not magnetically coupled (hereinafter sometimes simply referred to as “non-coupled”) and an effective inductance of each of the coils becomes larger than that in the case of being non-coupled. As a result, a rate of increase in current in one coil decreases while a rate of decrease in current in the other coil decreases, and the ripple current in the coils becomes smaller than that in the case of being non-coupled. Particularly, when the coupling coefficient of the two coils is −1, the ripple current becomes zero, and a direct current flows through the coils. In the present application, the “ripple current” refers to a difference (Ipp) between the maximum value and the minimum value of the electric current (coil current) flowing through the coils. Additionally, if the smoothing capacitor has an extra capacity with respect to the reduced ripple, an improvement in transient response speed can be achieved by reducing the inductance of the coils. 
     However, the inventor of the present application found that the conventional coil component has the following problems. For example, depending on the number (N) of coils and the duty cycle of the pulse signal, two or more coils may have a period in which the input pulse signals are in the ON state at the same time (a simultaneous ON period). In the simultaneous ON period, the current increases in the two or more coils; however, since the two or more coils are negatively coupled in the conventional coil component, the changes in magnetic flux in the core due to the current changes in the two coils are opposite in direction and cancel each other. Additionally, since the two or more coils are strongly negatively coupled and have a large amount of magnetic fluxes canceling each other in the conventional coil component, a rate of change in the magnetic flux in the core in the simultaneous ON period may become smaller than that in the case of being non-coupled. In this state, the effective inductance of the coils becomes smaller as compared to the case of being non-coupled, so that a rate of change in current becomes larger in the coils, which may lead to an increase in the ripple current. The same applies to a simultaneous OFF period, i.e., a period in which two or more coils have the input pulse signals in the OFF state at the same time. Therefore, if all the coils are strongly negatively coupled (at least two or more coils are strongly negatively coupled to each of the coils) as in the conventional coil component, the ripple current may increase. 
     Therefore, a problem to be solved by the present disclosure is to provide a coil component capable of reducing the ripple current of coils when used for a multi-phase SW regulator and a switching regulator including the coil component. 
     Solutions to the Problems 
     An aspect of the present disclosure provides a coil component comprising 
     2N coils, N being an integer of two or more, wherein 
     the 2N coils are configured to form N pairs, and wherein 
     when coils other than a first coil and a second coil forming one of the N pairs are defined as the other coils, a magnetic coupling between the first coil and the second coil is stronger than a magnetic coupling between the first coil and each of the other coils. 
     In this case, coils connected in series within the coil component are regarded as one coil. “A magnetic coupling between the first coil and the second coil is stronger than a magnetic coupling between the first coil and each of the other coils” means that “the absolute value of the coupling coefficient between the first coil and the second coil is larger than the absolute value of the coupling coefficient between the first coil and each of the other coils”. 
     According to the coil component of the aspect, the magnetic coupling between the first coil and the second coil forming a pair is stronger than the magnetic coupling between the first coil and each of the other coils. As a result, when the coil component of the aspect is used for a multi-phase SW regulator, the ripple current of the first coil can be reduced by properly selecting pulse signals input to the coils. 
     In an embodiment of the coil component, the magnetic coupling between the first coil and the second coil is stronger than a magnetic coupling between the second coil and each of the other coils. 
     According to the embodiment, when the coil component is used for a multi-phase SW regulator, the ripple current of the second coil can be reduced by properly selecting the pulse signals input to the coils. 
     In an embodiment of the coil component, the magnetic coupling between the paired coils is stronger than any of the magnetic couplings between the unpaired coils. 
     According to the embodiment, when the coil component is used for a multi-phase SW regulator, the ripple current of the coils can be reduced by properly selecting the pulse signals input to the coils. 
     In an embodiment of the coil component, an electric current is applied to the first coil and the second coil in a direction of negative coupling such that respective magnetic fluxes cancel each other. 
     According to the embodiment, since an electric current is applied to the first coil and the second coil in a direction of negative coupling, the ripple current of the first and second coils can be reduced when signals having a phase difference of 180° is input to the first coil and the second coil. “Respective magnetic fluxes cancel each other” means that the magnetic fluxes cancel each other mainly at a position with a high magnetic flux density such as an inner diameter portion of a coil, for example, and the magnetic flux may strengthen each other at a position with a relatively low magnetic flux density such as a peripheral portion of a coil. 
     In an embodiment of the coil component, 
     the coil component further comprises an element body having a plurality of insulating layers laminated in a first direction, 
     each of the 2N coils is disposed inside the element body and is made up of one or more spiral wiring wound on one of the insulating layers, and 
     when an inside of an innermost circumference of the spiral wiring is defined for each of the 2N coils as an inside diameter portion of the coil, 
     at least a portion of the inner diameter portion of the first coil and at least a portion of the inner diameter portion of the second coil overlap with each other when viewed in the first direction. 
     According to the embodiment, at least a portion of the inner diameter portion of the first coil and at least a portion of the inner diameter portion of the second coil overlap with each other. As a result, when a magnetic flux of the first coil L 1  is generated along the axis of the first coil in the inner diameter portion of the first coil, the magnetic flux passes through the inner diameter portion of the second coil. When a magnetic flux of the second coil is generated along the axis of the second coil in the inner diameter portion of the second coil, the magnetic flux passes through the inner diameter portion of the first coil. Therefore, the first coil and the second coil forming a pair can strongly magnetically be coupled. In the present application, the spiral wirings means curved wirings wound on a plane surface such as an insulating layer and, as shown in an embodiment described later, the spiral wirings include a curved wiring with the number of turns (the number of windings) made less than one. 
     In an embodiment of the coil component, the inner diameter portion of the first coil and the inner diameter portions of the other coils do not overlap with each other. 
     According to the embodiment, the magnetic coupling can be weakened between the first coil and each of the other coils not forming a pair. 
     In an embodiment of the coil component, the first coil and the second coil are wound in different directions. 
     According to the embodiment, the first coil and the second coil can easily negatively be coupled. In the present application, the two coils being wound in different directions means that, for example, if both ends of each of the two coils are led out to one and the other sides when viewed in the first direction, the coils are different in direction of winding from the one side to the other side. Specifically, this means a state in which, for example, one coil is wound clockwise from the one side to the other side while the other coil is wound counterclockwise from the one side to the other side when viewed in the first direction. 
     In an embodiment of the coil component, 
     a plurality of the coils is laminated on the same insulating layer, and wherein 
     the plurality of the coils is wound in the same direction. 
     According to the embodiment, since the plurality of the coils laminated on the same insulating layer is wound in the same direction, a negative coupling can easily be achieved for a set of coils adjacent to each other on the same insulating layer and having a relatively large magnetic coupling out of the sets of the unpaired coils, and the ripple current of the coils can further be suppressed. 
     In an embodiment of the coil component, the 2N coils are all wound in the same direction. 
     According to the embodiment, since the 2N coils are all wound in the same direction, the electric characteristic deviation can be reduced and the manufacturing can be facilitated. Additionally, the paired coils can easily positively be coupled. 
     In an embodiment of the coil component, the insulating layers on both sides in the first direction with respect to the spiral wirings of the 2N coils include magnetic resin layers made of a composite material of a magnetic powder and a resin. 
     According to the embodiment, the insulating layers on both sides in the first direction with respect to the spiral wirings include magnetic resin layers, and this makes it possible to inexpensively provide the coil component capable of ensuring appropriate inductance and coupling coefficient while being small and thin. 
     In an embodiment of the coil component, 
     the magnetic powder has an average particle diameter of 0.5 μm or more and 100 μm or less, and 
     the magnetic powder is contained in an amount of 50 vol. % or more and 85 vol. % or less relative to the resin. 
     According to the embodiment, since the magnetic powder has an average particle diameter of 0.5 μm or more and 100 μm or less, the magnetic resin can be formed into a small core. Additionally, since the magnetic powder is contained in an amount of 50 vol. % or more and 85 vol. % or less relative to the resin, a sufficient magnetic permeability can be acquired, so that the magnetic couplings of the paired coils can be strengthened. 
     In an embodiment of the coil component, 
     the coil component further comprises, for each of the 2N coils, magnetic resin bodies made of a composite material of a magnetic material powder and a resin and provided in the inner diameter portion of the coil and outside the outermost circumference of the spiral wiring of the coil, and 
     the magnetic resin layer and the magnetic resin bodies constitute a closed magnetic circuit. 
     According to the embodiment, the magnetic resin layer and the magnetic resin bodies constitute a closed magnetic circuit. This makes it possible to reduce leakage magnetic fluxes and suppress noises and also makes it possible to strengthen the magnetic coupling between the paired coils while weakening the magnetic couplings between the unpaired coils. 
     In an embodiment of the coil component, 
     the first coil and the second coil are each made up of a plurality of the spiral wirings each wound on one of the insulating layers, and wherein 
     a shortest distance between the first coil and the second coil is longer than a shortest distance between the spiral wirings in each of the first coil and the second coil. 
     According to the embodiment, since the shortest distance between the first coil and the second coil is longer than the shortest distance between the spiral wirings in each of the coils, the insulation can relatively be increased between the first coil and the second coil to which different voltages are applied for a relatively long period, so that the reliability can be improved. 
     In an embodiment of the coil component, 
     the spiral wirings of a plurality of the coils are wound on the same insulating layer, and 
     a shortest distance between the spiral wirings is longer than a wiring interval in the spiral wirings. 
     According to the embodiment, since the shortest distance between the adjacent spiral wirings wound on the same insulating layer is longer than the wiring interval in the spiral wirings, the insulation can relatively be increased between the spiral wirings wound on the same insulating layer in the adjacent coils having a period in which different voltages are applied, so that the reliability can be improved. 
     In an embodiment of the coil component, the insulating layers in contact with the spiral wirings are made of a composite material of an insulator powder and a resin. 
     According to the embodiment, the insulation can further be improved in the spiral wirings and between the spiral wirings. 
     In an embodiment of the coil component, 
     one end of the first coil and one end of the second coil are led out to the same one side with respect to the first coil and the second coil, while the other end of the first coil and the other end of the second coil are led out to the same other side with respect to the first coil and the second coil, and 
     the first coil and the second coil are wound such that respective magnetic fluxes cancel each other when an electric current flows from the one end to the other end. 
     According to the embodiment, when the pulse signals are input such that the first coil and the second coil are negatively coupled, the input ends and the output ends of the first and second coils can be arranged on the same respective sides. As a result, the wiring routing can be facilitated on a board on which the coil component is mounted. 
     In an embodiment of the coil component, the first coil and the second coil are the same as each other in terms of the number of turns, a coil wiring length, and a coil cross-sectional area. 
     According to the embodiment, since the first coil and the second coil are the same as each other in terms of the number of turns, the coil wiring length, and the coil cross-sectional area, deviations of the electrical characteristics of the coils can be reduced. 
     In an embodiment of the coil component, a first external terminal connected to the one end of the first coil and a second external terminal connected to the one end of the second coil are adjacent to each other. 
     According to the embodiment, since the first external terminal and the second external terminal are adjacent to each other, the coil component can be miniaturized 
     In an embodiment of a switching regulator, the switching regulator comprises 
     the coil component; 
     2N switch parts connected to the coils of the coil component; and 
     a smoothing circuit connected to one or the other end side of the coils of the coil component, and 
     one of the 2N switch parts being connected to one end side of one of the coils of the coil component, 
     the switch parts input signals having a phase difference of 180° to the paired coils of the coil component. 
     According to the embodiment, since the coil component is included, the switching regulator can be improved in performance and miniaturized by reducing the ripple current of the coils. 
     Effect of the Disclosure 
     According to the coil component of the present disclosure, the magnetic coupling between the first coil and the second coil forming a pair is stronger than the magnetic coupling between the first coil and each of the other coils and, therefore, when the coil component is used for a multi-phase SW regulator, the ripple current of the first coil can be reduced by properly selecting the pulse signals input to the coils. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified configuration diagram of a coil component  1  according to a first embodiment. 
         FIG. 2  is a perspective view of a coil component  1 A according to a second embodiment. 
         FIG. 3  is an exploded perspective view of the coil component  1 A. 
         FIG. 4  is a cross-sectional view taken along  4 - 4  of  FIG. 2 . 
         FIG. 5A  is an explanatory view for explaining a manufacturing method of the coil component  1 A. 
         FIG. 5B  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5C  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5D  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5E  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5F  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5G  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5H  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5I  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5J  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5K  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5L  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5M  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5N  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5O  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5P  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5Q  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 5R  is an explanatory view for explaining the second embodiment of the manufacturing method of the coil component  1 A. 
         FIG. 6  is a perspective view of a coil component of a comparison example 2. 
         FIG. 7A  is a graph of a relationship between an input voltage and a current of a first coil L 1  in a present example. 
         FIG. 7B  is a graph of a relationship between an input voltage and a current of a second coil L 2  in a present example. 
         FIG. 7C  is a graph of a relationship between an input voltage and a current of a third coil L 3  in a present example. 
         FIG. 7D  is a graph of a relationship between an input voltage and a current of a fourth coil L 4  in a present example. 
         FIG. 8A  is a graph of a relationship between an input voltage and a current of a first coil L 1  in a comparison example 1. 
         FIG. 8B  is a graph of a relationship between an input voltage and a current of a second coil L 2  in a comparison example 1. 
         FIG. 8C  is a graph of a relationship between an input voltage and a current of a third coil L 3  in a comparison example 1. 
         FIG. 8D  is a graph of a relationship between an input voltage and a current of a fourth coil L 4  in a comparison example 1. 
         FIG. 9A  is a graph of a relationship between an input voltage and a current of a first coil L 1  in a comparison example 2. 
         FIG. 9B  is a graph of a relationship between an input voltage and a current of a second coil L 2  in a comparison example 2. 
         FIG. 9C  is a graph of a relationship between an input voltage and a current of a third coil L 3  in a comparison example 2. 
         FIG. 9D  is a graph of a relationship between an input voltage and a current of a fourth coil L 4  in a comparison example 2. 
         FIG. 10A  is an exploded perspective view of a coil component  1 B according to a third embodiment. 
         FIG. 10B  is a cross-sectional view of the coil component  1 B according to the third embodiment. 
         FIG. 11A  is an exploded perspective view of a coil component  1 C according to a fourth embodiment. 
         FIG. 11B  is a cross-sectional view of the coil component  1 C according to the fourth embodiment. 
         FIG. 12A  is a transparent perspective view of a coil component  1 D according to a fifth embodiment. 
         FIG. 12B  is a cross-sectional view taken along  12 - 12  of  FIG. 12A . 
         FIG. 12C  is a transparent top view of the coil component  1 D. 
         FIG. 13A  is a transparent perspective view of a coil component  1 E according to a sixth embodiment. 
         FIG. 13B  is a cross-sectional view taken along  13 - 13  of  FIG. 13A . 
         FIG. 13C  is a transparent top view of the coil component  1 E. 
         FIG. 14A  is a transparent perspective view of a coil component  1 F according to a seventh embodiment. 
         FIG. 14B  is a cross-sectional view taken along  14 - 14  of  FIG. 14A . 
         FIG. 14C  is a transparent top view of the coil component  1 F. 
         FIG. 14D  is a transparent perspective view of a coil component  1 G according to a modification example of the seventh embodiment. 
         FIG. 14E  is a transparent perspective view of a coil component  1 H according to a modification example of the seventh embodiment. 
         FIG. 15  is a schematic diagram of a coil component  1 J according to an eighth embodiment. 
         FIG. 16  is a simplified configuration diagram of a switching regulator  5  according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A form of the present disclosure will now be described in detail with reference to embodiments shown in the drawings. 
     First Embodiment 
       FIG. 1  is a simplified configuration diagram of a coil component  1  according to a first embodiment. As shown in  FIG. 1 , the coil component  1  has 2N (N is an integer of two or more) coils L 1 , L 2 , . . . L(2N). The 2N coils L 1  to L(2N) are configured to form N pairs. Specifically, the first coil L 1  and the second coil L 2  form a pair, the third coil L 3  and the fourth coil L 4  form a pair, and similarly, the (2N−1)-th coil L(2N−1) and the (2N)-th coil L(2N) form a pair. Therefore, in a generalized expression, when M is an integer of one or more and N or less, a (2M−1)-th coil L(2M−1) and a (2M)-th coil L(2M) form a pair. 
     In this case, the 2N coils L 1 , L 2 , . . . L(2N) included in the coil component  1  are magnetically coupled to each other. However, the magnetic coupling between the first coil L 1  and the second coil L 2  forming a pair is stronger than the magnetic coupling between the first coil L 1  and each of the other coils L 3  to L(2N) not forming a pair. In other words, an absolute value of a coupling coefficient between the first coil L 1  and the second coil L 2  is larger than an absolute value of a coupling coefficient between the first coil L 1  and each of the other coils L 3  to L(2N). 
     Specifically, a magnetic coupling K 12  between the first and second coils is stronger than a magnetic coupling K 13  between the first and third coils, and a magnetic coupling K 1 (2N) between the first and (2N)-th coils. In  FIG. 1 , solid arrows indicate strong magnetic couplings and dotted arrows indicate weak magnetic couplings. A current is applied to the first coil L 1  and the second coil L 2  in the direction of negative coupling such that the respective magnetic fluxes cancel each other, specifically, from the input side (e.g., the left side of  FIG. 1 ) to the output side (e.g., the right side of  FIG. 1 ). 
     Similarly, not only when the first coil L 1  is considered as a reference but also when any of the coils L 2  to L(2N) are considered as a reference, the magnetic coupling to the coil paired with the reference coil is stronger than the magnetic coupling to any of the other coils unpaired with the reference coil. For example, when the second coil L 2  is considered as a reference, the magnetic coupling between the first coil L 1  and the second coil L 2  is stronger than the magnetic coupling between the second coil L 2  and each of the other coils L 3  to L(2N). To all the pairs of the coils, a current is applied in the direction of negative coupling such that the respective magnetic fluxes cancel each other. Additionally, in the coil component  1 , the magnetic coupling between the paired coils is stronger than any of the magnetic couplings between the unpaired coils. Specifically, for example, the magnetic coupling between the first coil L 1  and the second coil L 2  forming a pair is stronger than the magnetic coupling between the third coil L 3  and the (2N−1)-th coil L(2N−1) not forming a pair. 
     According to the coil component  1 , the magnetic coupling between the first coil L 1  and the second coil L 2  forming a pair therewith is stronger than the magnetic coupling between the first coil L 1  and each of the other coils L 3  to L(2N) not forming a pair. As a result, when the coil component  1  is used for a multi-phase SW regulator, the ripple current of the first coil L 1  can be reduced by properly selecting pulse signals input to the coils L 1  to L(2N). 
     Specifically, first, when the coil component  1  having the 2N coils L 1  to L(2N) is used for a multi-phase SW regulator, the total number of the pulse signals input to the coil component  1  is 2N and, therefore, the signals are denoted by P 1  to P(2N). In this case, the signals P 1  to P(2N) have the same period and, when the period is represented by a phase of 360°, the signals P 1  to P(2N) are a set of signals having a phase difference of 360°/2N. In a steady state without a load variation, the signals P 1  to P(2N) have the constant same duty cycle. Since 2N is an even number, the 2N signals P 1  to P(2N) include two pulse signals having the phase difference of 180°. 
     Therefore, it is assumed that the signal P 1  input to the first coil L 1  is one of the two pulse signals while the signal P 2  input to the second coil L 2  paired with the first coil L 1  is the other of the two pulse signals. The signal P 2  has the phase difference of 180° from the signal P 1  and is the signal having the largest phase difference with respect to the signal P 1  out of the signals P 2  to P(2N). Therefore, with regard to the intervals of turn-on transitions (or turn-off transitions) of the signals P 2  to P(2N) from the turn-on transition (or the turn-off transition) of the signal P 1 , the signal P 2  is the signal having the largest interval. This means that among the signals P 2  to P(2N), the signal P 2  is a signal having the longest period in which a reduction in the ripple current can be achieved by negative coupling of the coils (period in which one coil is in the ON state and the other coil is in the OFF state) and the shortest period in which the ripple current may possibly increase due to negative coupling of the coils (simultaneous ON period and simultaneous OFF period). Therefore, the signal P 2  is a signal exerting the greatest effect of the ripple current reduction by negative coupling of the coils on the signal P 1 . In the coil component  1 , the ripple current of the first coil L 1  can effectively be reduced by inputting such a signal P 2  to the second coil L 2  relatively strongly negatively-coupled to the first coil L 1  to which the signal P 1  is input. 
     In the case described above, the signals P 3  to P(2N) input to the other coils L 3  to L(2N) unpaired with the first coil L 1  are signals having a phase difference from the signal P 1  smaller than the phase difference between the signal P 1  and the signal P 2 . Therefore, the signals P 3  to P(2N) have a relatively smaller interval between the turn-on transitions or between the turn-off transitions with respect to the signal P 1 . This means that the signals P 3  to P(2N) are signals having a relatively short period in which a reduction in the ripple current can be achieved by negative coupling of the coils and a relatively long period in which the ripple current may possibly increase due to negative coupling of the coils. Therefore, the signals P 3  to P(2N) are signals relatively difficult to exert the effect of the ripple current reduction by negative coupling of the coils on the first pulse signal and possibly causing an increase in the ripple current. In the coil component  1 , an increase in the ripple current of the first coil L 1  can be suppressed by inputting such signals P 3  to P(2N) to the other coils L 3  to L(2N) relatively weakly magnetically-coupled to the first coil L 1  to which the signal P 1  is input. 
     As a result, when the coil component  1  is used for a multi-phase SW regulator, the ripple current of the first coil L 1  can be reduced by properly selecting the pulse signals input to the coils. 
     Particularly, since the current is applied to the first coil L 1  and the second coil L 2  in the direction of negative coupling such that the respective magnetic fluxes cancel each other, the inductor ripple current of the first and second coils L 1 , L 2  can be reduced when the signals P 1  and P 2  having the phase difference of 180° are input to the first coil L 1  and the second coil L 2 . 
     The relative strength relationship of the coupling described above is achieved not only when the first coil L 1  is considered as a reference but also when any of the coils L 2  to L(2N) is used as a reference. Therefore, as is the case with the first coil L 1 , when any of the coils L 2  to L(2N) is considered as a reference, the ripple current of the coils L 2  to L(2N) can be reduced by inputting the pulse signals having the phase difference of 180° to the reference coil and the coil forming a pair therewith. To properly select the pulse signal in this way, for example, after an arbitrary signal is first selected as the signal P 1 , the signal P(2M−1) may be acquired by selecting a signal having a phase difference of (360°/(2N))×(M−1) relative to the signal P 1 , and the signal P(2M) may be acquired by selecting a signal having a phase difference of (360°/(2N))×(M−1)+180° relative to the signal P 1  (M is an integer of one or more and N or less). Specifically, for example, when N=2, the signals P 1  to P 4  may be acquired by first selecting an arbitrary signal as the signal P 1 , selecting a signal having a phase difference of 180° relative to the signal P 1  as the signal P 2 , selecting a signal having a phase difference of 90° relative to the signal P 1  as the signal P 3 , and selecting a signal having a phase difference of 270° relative to the signal P 1  as the signal P 4 . 
     Therefore, when the coil component  1  is used for a multi-phase SW regulator, the ripple current of all the coils L 1  to L(2N) can be reduced by properly selecting the signals P 1  to P(2N) input to the coils L 1  to L(2N) as described above. However, as can be inferred from the above, the coil component  1  may have at least one coil considered as a reference out of the coils L 1  to L(2N) such that the magnetic coupling to a coil paired with this coil becomes stronger than the magnetic coupling to any of the other coils unpaired with this coil. In this state, the ripple current of this coil can be reduced by inputting to the coil paired with this coil the signal having the phase difference of 180° from the signal input to this coil. In this case, any strength relationship of the magnetic coupling may be achieved when a coil other than this coil is considered as a reference. If all the magnetic couplings between the paired coils are stronger than any of the magnetic couplings between the unpaired coils as described above, the ripple current of the coils L 1  to L(2N) can reliably be reduced, which is preferable. As described above, when a certain coil is considered as a reference in the coil component  1 , a coil “paired” with this coil refers to a coil most strongly magnetically-coupled to this coil out of the coils other than this coil. 
     Second Embodiment 
       FIG. 2  is a perspective view of a coil component  1 A according to a second embodiment.  FIG. 3  is an exploded perspective view of the coil component  1 A.  FIG. 4  is a cross-sectional view taken along  4 - 4  of  FIG. 2 . As shown in  FIGS. 2, 3, and 4 , the coil component  1 A has an element body  10 , four (2×2) first to fourth coils L 1  to L 4  provided in the element body  10 , and first to fourth external terminals provided outside the element body  10  and electrically connected to the first to fourth coils L 1  to L 4 . The first to fourth external terminals are made up of external terminals  11   a  to  14   a  provided on the side of a first side surface  10   a  of the element body  10 , and external terminals  11   b  to  14   b  provided on the side of a second side surface  10   b  of the element body  10 . The first side surface  10   a  and the second side surface  10   b  face each other, and the external terminals  11   a  to  14   a  and the external terminals  11   b  to  14   b  are respectively arranged to face each other in this order. The first to fourth external terminals  11   a  to  14   a ,  11   b  to  14   b  are, for example, metal films of Cu, Ni, Sn, etc. formed by plating on the surface of the element body  10  or screen-printed resin films containing a low electric resistance metal such as Cu, Ag, and Au. 
     The coil component  1 A has a mounting surface that is a surface on which both the external terminals  11   a  to  14   a  and the external terminals  11   b  to  14   b  shown in  FIG. 2  are disposed. In the following description, the direction orthogonal to the mounting surface is defined as the up-down direction (corresponding to the up-down direction on the plane of  FIG. 4 ), and the mounting surface side of the coil component  1 A is defined as the lower side, while the opposite surface side thereof is defined as the upper side. 
     The element body  10  has an insulating resin  35  covering each of the first to fourth coils L 1  to L 4  and a magnetic resin  40  covering the insulating resin  35 . The insulating resin  35  is made up of a base insulating resin layer (insulating layer)  30  and first to fourth insulating resin layers (insulating layers)  31  to  34 . The magnetic resin  40  is made up of a first magnetic resin body  41   a  provided in a first hole portion  35   a  of the insulating resin  35 , a second magnetic resin body  41   b  provided in a second hole portion  35   b  of the insulating resin  35 , third magnetic resin bodies  41   c  provided on portions of an outer circumferential surface of the insulating resin  35 , and magnetic resin layers (insulating layers)  42  provided on upper and lower end surfaces of the insulating resin  35 . As a result, the element body  10  has a configuration in which a plurality of the insulating layers  30  to  34 ,  42  is laminated in the up-down direction. Therefore, the up-down direction of this embodiment corresponds to a first direction. In this description, covering an object refers to covering at least a portion of the object, and “covering” refers to not only the case of being disposed above the object but also the case of being disposed on the side or below the object. In  FIG. 3 , the insulating resin  35  is not shown. 
     The first to fourth coils L 1  to L 4  are each disposed inside the element body  10  and are made up of first spiral wirings  21  and second spiral wirings  22  wound on the insulating layers  30  to  33 . For each of the first to fourth coils L 1  to L 4 , the inside of the innermost circumference of the first and second spiral wirings  21 ,  22  is defined as an inner diameter portion. The inner diameter portion includes a winding central axis of each of the coils L 1  to L 4  along the up-down direction (hereinafter sometimes simply referred to as an “axis of the coil”). The second coil L 2  is laminated above the first coil L 1 , and the fourth coil L 4  is laminated on the lateral side of, i.e., on the same insulating layer (the base insulating resin layer  30 ) as, the first coil L 1 . The third coil L 3  is laminated above the fourth coil L 4 , and the third coil L 3  is laminated on the lateral side of, i.e., on the same insulating layer (the second insulating resin layer  32 ) as, the second coil L 2 . 
     It is assumed that the coils arranged in the up-down direction are paired in the coil component  1 A. In this case, the four coils L 1  to L 4  are configured to form two pairs as a set of the first coil L 1  and the second coil L 2  and a set of the third coil L 3  and the fourth coil L 4 . Description will then hereinafter be made of the relationship of the magnetic coupling between paired coils and the magnetic coupling between unpaired coils. 
     The coil component  1 A has the inner diameter portion of the first coil L 1  and the inner diameter portion of the second coil L 2  overlapping with each other when viewed in the up-down direction. As a result, when a magnetic flux of the first coil L 1  is generated along the axis of the first coil L 1  in the inner diameter portion of the first coil L 1 , the magnetic flux passes through the inner diameter portion of the second coil L 2 . When a magnetic flux of the second coil L 2  is generated along the axis of the second coil L 2  in the inner diameter portion of the second coil L 2 , the magnetic flux passes through the inner diameter portion of the first coil L 1 . Therefore, the first coil L 1  and the second coil L 2  forming a pair are strongly magnetically coupled. Although at least a portion of the inner diameter portion of the first coil L 1  and at least a portion of the inner diameter portion of the second coil L 2  may overlap with each other so as to acquire a strong magnetic coupling, a stronger magnetic coupling can be obtained when the axis of the first coil L 1  and the axis of the second coil L 2  are coaxial (the axes are coincident with each other). 
     Similarly, the coil component  1 A has the inner diameter portion of the third coil L 3  and the inner diameter portion of the fourth coil L 4  overlapping with each other when viewed in the up-down direction. Therefore, the third coil L 3  and the fourth coil L 4  forming a pair are strongly magnetically coupled. 
     On the other hand, the axes of the first coil L 1  and the second coil L 2  and the axes of the third coil L 3  and the fourth coil L 4  are arranged in parallel at an interval. In particular, when viewed in the up-down direction, the inner diameter portion of the first coil L 1  and the inner diameter portion of the fourth coil L 4  do not overlap with each other, and the inner diameter portion of the second coil L 2  and the inner diameter portion of the third coil L 3  do not overlap with each other. As a result, as compared to the magnetic coupling between the first coil L 1  and the second coil L 2  and the magnetic coupling between the third coil L 3  and the fourth coil L 4  sharing the inner diameter portions, the magnetic coupling between the first coil L 1  and the fourth coil L 4  and the magnetic coupling between the second coil L 2  and the third coil L 3  are relatively weak. Although the first coil L 1  and the third coil L 3  as well as the second coil L 2  and the fourth coil L 4  are also magnetically coupled, these coils have the inner diameter portions not overlapping with each other and also have the largest inter-coil distance. Therefore, as compared to the magnetic coupling between the first coil L 1  and the fourth coil L 4  and the magnetic coupling between the second coil L 2  and the third coil L 3 , the magnetic coupling between the first coil L 1  and the third coil L 3  and the magnetic coupling between the second coil L 2  and the third coil L 4  are relatively weak and may be at an almost negligible level in terms of coil characteristics, for example. 
     From the above, in the coil component  1 A, when the coils L 3 , L 4  other than the first coil L 1  and the second coil L 2  forming one of the two pairs are defined as the other coils L 3 , L 4 , the magnetic coupling between the first coil L 1  and the second coil L 2  is stronger than the magnetic couplings between the first coil L 1  and each of the other coils L 3 , L 4 . Similarly, the magnetic coupling between the second coil L 2  and the first coil L 1  is stronger than the magnetic couplings between the second coil L 2  and each of the other coils L 3 , L 4 . When the coils L 1 , L 2  other than the third coil L 3  and the fourth coil L 4  forming one of the two pairs are defined as the other coils L 1 , L 2 , the magnetic coupling between the third coil L 3  and the fourth coil L 4  is stronger than the magnetic couplings between the third coil L 3  and each of the other coils L 1 , L 2 . Similarly, the magnetic coupling between the fourth coil L 4  and the third coil L 3  is stronger than the magnetic couplings between the fourth coil L 4  and each of the other coils L 1 , L 2 . 
     Therefore, when any coil is considered as a reference out of the first to fourth coils L 1  to L 4  in the coil component  1 A, the magnetic coupling to a coil paired with this coil is stronger than the magnetic coupling to a coil unpaired with this coil. 
     Additionally, because of the symmetry of the structure of the coil component  1 A, the magnetic coupling between the first coil L 1  and the second coil L 2  has the strength on the same level as the magnetic coupling between the third coil L 3  and the fourth coil L 4 . The magnetic coupling between the first coil L 1  and the fourth coil L 4  has the strength on the same level as the magnetic coupling between the second coil L 2  and the third coil L 3 , and the magnetic coupling between the first coil L 1  and the third coil L 3  has the strength on the same level as the magnetic coupling between the second coil L 2  and the fourth coil L 4 . Therefore, in the coil component  1 A, the magnetic coupling between the paired coils is stronger than any of the magnetic couplings between the unpaired coils. 
     In the coil component  1 A, the first to fourth coils L 1  to L 4  are the same as each other in terms of the number of turns, the coil wiring length, and the coil cross-sectional area. Asa result, deviations of the electrical characteristics (impedance, L-value, etc.) of the coils can be reduced. Additionally, in this case, since the one ends and the other ends of the coils L 1  to L 4  are arranged closely side-by-side, the routing of the coils L 1  to L 4  connected to the external terminals  11   a  to  14   a ,  11   b  to  14   b  can be minimized, so that the coil component  1 A can be miniaturized. This relationship may not necessary be satisfied by all the coils L 1  to L 4  and, if the coils forming at least one pair are the same as each other in terms of the number of turns, the coil wiring length, and the coil cross-sectional area, the effect described above can be produced. The term “the same” allows differences on the level of manufacturing variations or errors in values of the number of turns, the coil wiring length, and the coil cross-sectional area (e.g., several % for the number of turns and the coil wiring length and about 10% for the coil cross-sectional area) and includes the case of being substantially the same. 
     The first coil L 1  is made up of two layers of the first spiral wiring  21  wound on the base insulating resin layer  30  and the second spiral wiring  22  wound on the first insulating resin layer  31 , and a via wiring  25  penetrating the first insulating resin layer  31  in the up-down direction to connect the two layers. The first spiral wiring  21  and the second spiral wiring  22  are arranged in order from the lower layer to the upper layer. The first and second spiral wirings  21 ,  22  are each wound and formed into a planar helical (spiral) shape. In the first coil L 1 , the first spiral wiring  21  is wound counterclockwise from the outer circumference toward the inner circumference, and the second spiral wiring  22  is wound counterclockwise from the inner circumference toward the outer circumference. The first and second spiral wirings  21 ,  22  and the via wiring  25  are made of a low electric resistance metal such as Cu, Ag, and Au, for example. Preferably, the spiral wirings with low electric resistance and narrow pitch can be formed by using Cu plating formed by a semi-additive process. 
     In the first coil L 1 , the second spiral wiring  22  is connected through the via wiring  25  to the first spiral wiring  21 . Specifically, the via wiring  25  connects an inner circumferential end  21   a  of the first spiral wiring  21  and an inner circumferential end  22   a  of the second spiral wiring  22 . An outer circumferential end  21   b  of the first spiral wiring  21  is led out toward the first side surface  10   a  of the element body  10  and connected to the external terminal  11   a . An outer circumferential end  22   b  of the second spiral wiring  22  is led out toward the second side surface  10   b  of the element body  10  and connected to the external terminal lib. As a result, the first coil L 1  has the outer circumferential end  21   b  led out toward the first side surface  10   a  at one end and the outer circumferential end  22   b  led out toward the second side surface  10   b  at the other end and is wound counterclockwise from the one end to the other end. 
     The second to fourth coils L 2  to L 4  are similarly made up of two layers of the first spiral wiring  21  wound on the insulating layer on the lower layer side (the base insulating resin layer  30  or the second insulating resin layer  32 ) and the second spiral wiring  22  wound on the insulating layer on the upper layer side (the first insulating resin layer  31  or the third insulating resin layer  33 ), and the via wiring  25  penetrating the insulating layer on the upper layer side in the up-down direction to connect the two layers. However, in the second coil L 2 , the first spiral wiring  21  is wound clockwise from the outer circumference toward the inner circumference, and the second spiral wiring  22  is wound clockwise from the inner circumference toward the outer circumference. In the second coil L 2 , the via wiring  25  connects the inner circumferential end  21   a  of the first spiral wiring  21  and the inner circumferential end  22   a  of the second spiral wiring  22 . Additionally, in the second coil L 2 , the outer circumferential end  21   b  (one end) of the first spiral wiring  21  is led out toward the first side surface  10   a  of the element body  10  and connected to the external terminal  12   a . The outer circumferential end  22   b  (the other end) of the second spiral wiring  22  is led out toward the second side surface  10   b  of the element body  10  and connected to the external terminal  12   b . As a result, the second coil L 2  is wound clockwise from the one end to the other end. The third coil L 3  has the same configuration as the first coil L 1 , and an outer circumferential end (one end) of the first spiral wiring  21  led out toward the first side surface  10   a  is connected to the external terminal  13   a , while an outer circumferential end (the other end) of the second spiral wiring  22  led out toward the second side surface  10   b  is connected to the external terminal  13   b . As a result, the third coil L 3  is wound counterclockwise from the one end to the other end. The fourth coil L 4  has the same configuration as the second coil L 2 , and an outer circumferential end (one end) of the first spiral wiring  21  led out toward the first side surface  10   a  is connected to the external terminal  14   a , while an outer circumferential end (the other end) of the second spiral wiring  22  led out toward the side surface  10   b  is connected to the external terminal  14   b . As a result, the fourth coil L 4  is wound clockwise from the one end to the other end. 
     As described above, in the coil component  1 A, the one end (the outer circumferential end  21   b ) of the first coil L 1  and the other end (the outer circumferential end  21   b ) of the second coil L 2  forming a pair are led out toward the same first side surface  10   a  (one side) with respect to the first coil L 1  and the second coil L 2 . The other end (the outer circumferential end  22   b ) of the first coil L 1  and the other end (the outer circumferential end  22   b ) of the second coil L 2  are led out toward the same second side surface  10   b  (the other side) with respect to the first coil L 1  and the second coil L 2 . The first coil L 1  and the second coil L 2  are wound counterclockwise and clockwise, respectively, from the one end to the other end, so that the first coil L 1  and the second coil L 2  are wound in different directions. Therefore, the first coil L 1  and the second coil L 2  are wound such that the respective magnetic fluxes cancel each other when a current flows from the one end to the other end. This means that when the first coil L 1  and the second coil L 2  have the one ends both set on the input side of the pulse signals and the other sides both set on the output side of the pulse signals, the first coil L 1  and the second coil L 2  are negatively coupled. 
     Thus, when the coil component  1 A is used for a multi-phase SW regulator, the ripple current of the first coil L 1  and the second coil L 2  can be reduced by inputting the signals having the phase difference of 180° to the one ends of the first coil L 1  and the second coil L 2  on the same side. In other words, when the pulse signals are input such that the first coil L 1  and the second coil L 2  are negatively coupled, the input sides (one ends) and the output sides (the other ends) of the first coil L 1  and the second coil L 2  can be arranged on the same respective sides. As a result, the wiring routing can be facilitated on a board on which the coil component  1 A is mounted. 
     In the coil component  1 A, the third coil L 3  and the fourth coil L 4  forming a pair have the same configuration as the first coil L 1  and the second coil L 2 . Therefore, when the pulse signals are input such that the third coil L 3  and the fourth coil L 4  are negatively coupled in the coil component  1 A, the input sides and the output sides of the third coil L 3  and the fourth coil L 4  can be arranged on the same respective sides. As a result, the wiring routing can be facilitated on the board on which the coil component  1 A is mounted. 
     Additionally, in the coil component  1 A, all the first to fourth coils L 1  to L 4  have the one ends and the other ends led out toward the same sides. As a result, when the pulse signals are input such that all the paired coils are negatively coupled in the coil component  1 A, the input sides and the output sides of the coils L 1  to L 4  can be arranged on the same respective sides. As a result, the wiring routing can further be facilitated on the board on which the coil component  1 A is mounted. 
     In the above description, the outer circumferential end  21   b  and the outer circumferential end  22   b  are described as one end (the input side of the pulse signal) and the other end (the output side of the pulse signal), respectively; however, because of the symmetry of the coil component  1 A, the outer circumferential end  22   b  and the outer circumferential end  21   b  may be defined as one end and the other end, respectively. 
     The base insulating resin layer  30  and the first to fourth insulating resin layers  31  to  34  are arranged in order from the lower layer to the upper layer. The material of the insulating resin layers  30  to  34  is, for example, a single material that is an organic insulating material made of an epoxy resin, bismaleimide, liquid crystal polymer, polyimide, etc., or is an insulating material comprising a combination with an inorganic filler material such as a silica filler and an organic filler made of a rubber material. Preferably, all the insulating resin layers  31  to  34  are made of the same material. In this embodiment, all the insulating resin layers  30  to  34  are made of a composite material of a silica filler (insulator powder) and an epoxy resin. When the insulating layers (the insulating resin layers  30  to  34 ) in contact with the spiral wirings  21 ,  22  are made of the composite material of the insulator powder and the resin in this way, the insulation can further be improved in the spiral wirings  21 ,  22  and between the spiral wirings  21 ,  22 . 
     The first insulating resin layer  31  is laminated on the base insulating resin layer  30  to cover the first spiral wirings  21  of the first and fourth coils L 1 , L 4 . The second insulating resin layer  32  is laminated on the first insulating resin layer  31  to cover the second spiral wirings  22  of the first and fourth coils L 1 , L 4 . 
     The third insulating resin layer  33  is laminated on the second insulating resin layer  32  to cover the first spiral wirings  21  of the second and third coils L 2 , L 3 . The fourth insulating resin layer  34  is laminated on the third insulating resin layer  33  to cover the second spiral wirings  22  of the second and third coils L 2 , L 3 . 
     The via wirings  25  of the coils L 1  to L 4  are arranged so as not to overlap when viewed in the up-down direction. The via wirings  25  are disposed at positions where the thickness of the element body  10  along the up-down direction tends to vary due to variations in amount of filling of the via wirings  25  into the insulating resin layers and, therefore, by arranging such positions so as not to overlap with each other, the variations in the thickness of the element body  10  can be reduced. Additionally, the via wirings  25  of the first coil L 1  and the second coil L 2  are preferably arranged to be line-symmetrical with respect to a straight line passing through the winding center of the first and second coils L 1 , L 2  when viewed in the up-down direction and orthogonal to the first and second side surfaces  10   a ,  10   b . As a result, the shapes of the first and second coils L 1 , L 2  forming a pair can be made symmetrical and the coil component  1 A can be manufactured such that the electrical characteristics of the coils become uniform. The via wirings  25  of the third coil L 3  and the fourth coil L 4  can be arranged in the same positional relationship to acquire the effect described above also from the third and fourth coils L 3 , L 4 . 
     The outer circumferential ends  21   b  of the first spiral wirings  21  of the first to fourth coils L 1  to L 4  are arranged in order along a long-side direction (a direction perpendicular to the up-down direction) of the first side surface  10   a . Therefore, the external terminals  11   a  to  14   a  on the side of the first side surface  10   a  are arranged in order along the long-side direction of the first side surface  10   a.    
     The outer circumferential ends  22   b  of the second spiral wirings  22  of the first to fourth coils L 1  to L 4  are arranged in order along a long-side direction (a direction perpendicular to the up-down direction) of the second side surface  10   b . Therefore, the external terminals  11   b  to  14   b  on the side of the first side surface  10   a  are arranged in order along the long-side direction of the second side surface  10   b.    
     In this way, first external terminals  11  connected to the first coil L 1  and second external terminals  12  connected to the second coil L 2  are arranged adjacent to each other, and the third external terminals  13  connected to the third coil L 3  and the fourth external terminals  14  connected to the fourth coil L 3  are arranged adjacent to each other. In the coil component  1 A, the first coil L 1  and the second coil L 2  forming a pair are arranged in the up-down direction, and the outer circumferential ends  21   b ,  22   b  thereof are located relatively close to each other. Therefore, since the first external terminals  11  and the second external terminals  12  connected to the outer circumferential ends  21   b ,  22   b  are located relatively close to each other, the routing of wirings connected to the external terminals  11 ,  12  of the first coil L 1  and the second coil L 2  can be made shorter. Since the third coil L 3  and the fourth coil L 4  forming a pair have the same configuration, the routing of wirings connected to the respective external terminals  13 ,  14  can also be made shorter. As a result, the outer shape of the coil component  1 A can be miniaturized. In the coil component  1 A, the arrangement order of the external terminals  11   a  to  14   a  on the first side surface  10   a  is identical to the arrangement order of the external terminals  11   b  to  14   b  on the second side surface  10   b . As a result, the arrangement order of wirings on the input side can be made identical to the arrangement order of wirings on the output side on the board on which the coil component  1 A is mounted, so that the mounting is facilitated. Therefore, the small and easily-mountable coil component  1 A can be provided. 
     When the first coil L 1  and the second coil L 2  are each made up of a plurality of the spiral wirings  21  wound on a plurality of the insulating layers (the insulating resin layers  30 ,  31  or the insulating resin layers  32 ,  33 ) as in the case of the coil component  1 A, preferably, the shortest distance between the first coil L 1  and the second coil L 2  is longer than the shortest distance between the spiral wirings  21 ,  22  in each of the first coil L 1  and the second coil L 2 . As a result, in a combination of pulse signals capable of reducing the ripple current of the coils L 1 , L 2 , the insulation can relatively be increased between the first coil L 1  and the second coil L 2  to which different voltages are applied for a relatively long period, so that the reliability of the coil component  1 A can be improved. The same applies to the third coil L 3  and the fourth coil L 4 . 
     Additionally, when the spiral wirings (e.g., the first spiral wirings  21 ) of a plurality of coils (e.g., the first coil L 1  and the fourth coil L 4 ) are wound on the same insulating layer (e.g. the base insulating resin layer  30 ) as in the case of the coil component  1 A, preferably, the wiring interval between the spiral wirings (e.g., the interval between the spiral wirings  21  of the first coil L 1  and the fourth coil L 4 ) is longer than the wiring interval in the spiral wirings. As a result, the insulation can relatively be increased between the spiral wirings wound on the same insulating layer in the adjacent coils having a period in which different voltages are applied, so that the reliability can be improved. 
     The insulating resin  35  has the first hole portion  35   a  around the axes of the first coil L 1  and the second coil L 2  and the second hole portion  35   b  around the axes of the third coil L 3  and the fourth coil L 4 . 
     The magnetic resin  40  is made of a composite material of a magnetic powder and a resin. The magnetic powder is, for example, a metal magnetic material composed of FeSi-, FeCo-, or FeAl-based alloy or amorphous, and the resin is, for example, a resin material such as epoxy. Therefore, in the coil component  1 A, the insulating layers on both sides in the up-down direction with respect to the spiral wirings  21 ,  22  of the first to fourth coils L 1  to L 4  include the magnetic resin layers  42  made of the composite material of the magnetic powder and the resin. As a result, the density of the magnetic fluxes generated by the first to fourth coils L 1  to L 4  is improved by the magnetic resin layers  42 , which makes it possible to inexpensively provide the coil component  1 A capable of ensuring appropriate inductance and coupling coefficient while being small and thin. 
     For all the first to fourth coils L 1  to L 4 , the coil component  1 A further includes the magnetic resin bodies  41   a ,  41   b  provided in the inner diameter portions (the first and second hole portions  35   a ,  35   b ) of the coils L 1  to L 4  and the magnetic resin bodies  41   c  provided outside the outermost circumferences of the spiral wirings  21 ,  22  of the coils L 1  to L 4 . The magnetic resin bodies  41   a ,  41   b ,  41   c  are made of the composite material of the magnetic powder and the resin as described above. The coil component  1 A has respective closed magnetic circuits configured by connecting the magnetic resin layers  42  and the magnetic resin bodies  41   a ,  41   c  for the first and second coils L 1 , L 2  and by connecting the magnetic resin layers  42  and the magnetic resin bodies  41   b ,  41   c  for the third and fourth coils L 3 , L 4 . This makes it possible to reduce leakage magnetic fluxes from the coils L 1  to L 4  and suppress noises and also makes it possible to strengthen the magnetic coupling between the coils L 1 , L 2  and the magnetic coupling between the coils L 3 , L 4  forming a pair while weakening the magnetic couplings between the other unpaired coils. 
     The average particle diameter of the magnetic powder is preferably 0.5 μm or more and 100 μm or less and, as a result, the magnetic resin can be formed into a small core. Additionally, the magnetic powder is preferably contained in an amount of 50 vol. % or more and 85 vol. % or less relative to the resin and, as a result, a sufficient magnetic permeability can be acquired, so that the magnetic couplings of the paired coils can be strengthened. 
     For improvement of the characteristics (inductance value and superposition characteristics) of the coil component  1 A, it is desirable to contain the magnetic powder in an amount of 70 vol. % or more and, for improvement of a filling property of the magnetic resin  40 , it is more desirable to mix two or more types of magnetic powder different in particle size distribution. Additionally, to reliably fill the magnetic powder into the first and second hole portions  35   a ,  35   b  of the insulating resin  35 , the average particle diameter of the magnetic powder is desirably smaller than the first and second hole portions  35   a ,  35   b  and is preferably 40 μm or less. If the use of the coil component  1 A is associated with a high usage frequency, for example, 40 MHz or more, the magnetic powder may be a single magnetic filler having a particle size distribution with an average particle diameter of 1 μm or less. 
     In the coil component  1 A, as shown in  FIG. 3 , preferably, the third magnetic resin body  41   c  is not filled in a portion having the minimum distance between the first coil L 1  and the fourth coil L 4 . As a result, the coupling between the first coil L 1  and the fourth coil L 4  can be made relatively weak. The magnetic resin  40  is made of a resin containing metal and is inferior in voltage endurance as compared to the insulating resin  35  and, therefore, if it is attempted to fill the magnetic resin  40  in the minimum distance between the first coil L 1  and the fourth coil L 4 , the first coil L 1  and the fourth coil L 4  must sufficiently be separated from each other from the viewpoint of reliability, which makes the outer shape size of the coil component  1 A larger. Therefore, the absence of the third magnetic resin body  41   c  filled into the portion having the minimum distance between the first coil L 1  and the fourth coil L 4  can improve the reliability of the coil component  1 A in the same outer shape. The same applies to the portion between the second coil L 2  and the third coil L 3 . 
     In an example of the coil component  1 A, the thickness of the spiral wirings  21 ,  22  is 45 μm; the width of the spiral wirings  21 ,  22  is 60 μm; the wiring interval in the spiral wirings  21 ,  22  is 10 μm; and the thickness of the insulating resin between the spiral wiring  21  and the spiral wiring  22  is 10 μm. The outer shape size of the coil component  1 A is 2.0 mm in width×1.2 mm in depth×0.85 mm in height; the inductance value of the coils L 1  to L 4  of the coil component  1 A is 74 nH; and the coupling coefficient between the paired coils is 0.8. 
     A method of manufacturing the coil component  1 A will be described with reference to  FIGS. 5A to 5R . 
     As shown in  FIG. 5A , a base  50  is prepared. The base  50  has an insulating substrate  51  and base metal layers  52  disposed on both sides of the insulating substrate  51 . In this embodiment, the insulating substrate  51  is a glass epoxy substrate and the base metal layers  52  are Cu foils and have main surfaces that are smooth surfaces. 
     As shown in  FIG. 5B , a dummy metal layer  60  is bonded onto a surface of the base  50 . In this embodiment, the dummy metal layer  60  is a Cu foil. Since the dummy metal layer  60  is bonded to the base metal layer  52  of the base  50 , the dummy metal layer  60  is bonded to the smooth surface of the base metal layer  52 . Therefore, an adhesion force can be made weak between the dummy metal layer  60  and the base metal layer  52  and, at a subsequent step, the base  50  can easily be peeled from the dummy metal layer  60 . Preferably, an adhesive bonding the base  50  and the dummy metal layer  60  is an adhesive with low tackiness. For weakening of the adhesion force between the base  50  and the dummy metal layer  60 , it is desirable that the bonding surfaces of the base  50  and the dummy metal layer  60  are glossy surfaces. 
     Subsequently, the base insulating resin  30  is laminated on the dummy metal layer  60  temporarily bonded to the base  50 . In this case, the base insulating resin  30  is laminated by a vacuum laminator and is then thermally cured. 
     As shown in  FIG. 5C , through-holes  30   a ,  30   d ,  30   e ,  30   f  are formed in portions of the base insulating resin layer  30  to expose the dummy metal layer  60 . The through-holes  30   a ,  30   d ,  30   e ,  30   f  are formed by laser processing and the through-hole  30   a , the through-hole  30   d , and the through-holes  30   e ,  30   f  are formed in places to be filled with the magnetic resin body  41   a , the magnetic resin body  41   b , and the magnetic resin body  41   c , respectively. 
     As shown in  FIG. 5D , a first spiral wiring layer  3   a  and a first spiral wiring layer  3   b  are formed on the base insulating resin layer  30  surrounding the through-holes  30   a ,  30   d . In this case, the first spiral wiring layers  3   a ,  3   b  are formed at the same time by the semi-additive process. The first spiral wiring layer  3   a  constitutes the first spiral wiring  21  of the first coil L 1  and the first spiral wiring layer  3   b  constitutes the first spiral wiring  21  of the fourth coil L 4 . In this process, the wiring layers are also formed in the through-holes  30   a ,  30   d ,  30   e ,  30   f  and on the base insulating resin layer  30  around the through-holes. 
     As shown in  FIG. 5E , the first spiral wiring layers  3   a ,  3   b  are covered with the first insulating resin layer  31 . In this case, the first insulating resin layer  31  is laminated on the base insulating resin layer  30  by a vacuum laminator and is then thermally cured. 
     As shown in  FIG. 5F , through-holes  31   a ,  31   d ,  31   e ,  31   f  and via holes  31   b ,  31   c  are formed in the first insulating resin layer  31  by laser processing. The through-holes  31   a ,  31   d ,  31   e ,  31   f  are formed in the first insulating resin layer  31  above the through-holes  30   a ,  30   d ,  30   e ,  30   f , respectively. 
     The via holes  31   b ,  31   c  are formed at positions where the first spiral wiring layers  3   a ,  3   b  are electrically connected in series to second wiring layers subsequently formed, specifically, in the first insulating resin layer  31  on the portions serving as the inner circumferential ends  21   a  of the first spiral wirings  21 . The through-holes  31   a ,  31   d ,  31   e ,  31   f  and the via holes  31   b ,  31   c  can be processed at the same time to simplify the step. 
     As shown in  FIG. 5G , second spiral wiring layers  5   a ,  5   b  are formed on the first insulating resin layer  31  surrounding the through-holes  31   a ,  31   d  by the same semi-additive process as the first spiral wiring layers  3   a ,  3   b . In this process, a portion of the second spiral wiring layer  5   a  is filled into the via hole  31   b  to form a portion serving as the via wiring  25  to electrically connect the first spiral wiring layer  3   a  and the second spiral wiring layer  5   a . Similarly, the second spiral wiring layer  5   b  forms a portion serving as the via wiring  25  in the via hole  31   c  to electrically connect the first spiral wiring layer  3   b . The second spiral wiring layers  5   a ,  5   b  constitute the second spiral wirings  22  of the first coil L 1  and the fourth coil L 4 , respectively. As a result, the first coil L 1  and the fourth coil L 4  can be formed. In this process, the wiring layers are also formed in the through-holes  31   a ,  31   d ,  31   e ,  31   f  and on the first insulating resin layer  31  around the through-holes. 
     As shown in  FIG. 5H , the second spiral wiring layers  5   a ,  5   b  are covered with the second insulating resin layer  32 . In this case, the second insulating resin layer  32  is laminated on the first insulating resin layer  31  by a vacuum laminator and is then thermally cured. 
     As shown in  FIG. 5I , through-holes  32   a ,  32   d ,  32   e ,  32   f  are formed in the second insulating resin layer  32  by laser processing. The through-holes  32   a ,  32   d ,  32   e ,  32   f  are formed in the second insulating resin layer  32  above the through-holes  31   a ,  31   d ,  31   e ,  31   f , respectively. 
     As shown in  FIG. 5J , a first spiral wiring layer  7   a  and a first spiral wiring layer  7   b  are formed on the second insulating resin layer  32  surrounding the through-holes  32   a ,  32   d  by the same semi-additive process as the first spiral wiring layer  3   a . The first spiral wiring layers  7   a ,  7   b  constitute the first spiral wirings  21  of the second coil L 2  and the third coil L 3 , respectively. In this process, the wiring layers are also formed in the through-holes  32   a ,  32   d ,  32   e ,  32   f  and on the second insulating resin layer  32  around the through-holes. 
     As shown in  FIG. 5K , the first spiral wiring layers  7   a ,  7   b  are covered with the third insulating resin layer  33 . In this case, the third insulating resin layer  33  is laminated on the second insulating resin layer  32  by a vacuum laminator and is then thermally cured. 
     As shown in  FIG. 5L , through-holes  33   a ,  33   d ,  33   e ,  33   f  and via holes  33   b ,  33   c  are formed in the third insulating resin layer  33  by laser processing. The through-holes  33   a ,  33   d ,  33   e ,  33   f  are formed in the third insulating resin layer  33  above the through-holes  32   a ,  32   d ,  32   e ,  32   f , respectively. The via holes  33   b ,  33   c  are formed at positions where the first spiral wiring layers  7   a ,  7   b  are electrically connected in series to wiring layers subsequently formed, specifically, in the third insulating resin layer  33  on the portions serving as the inner circumferential ends  21   a  of the first spiral wirings  21 . 
     As shown in  FIG. 5M , second spiral wiring layers  9   a ,  9   b  are formed on the third insulating resin layer  33  surrounding the through-holes  33   a ,  33   d  by the same semi-additive process as the first spiral wiring layers  7   a ,  7   b . In this process, a portion of the second spiral wiring layer  9   a  is filled into the via hole  33   b  to form a portion serving as the via wiring  25  to electrically connect the first spiral wiring layer  7   a  and the second spiral wiring layer  9   a . Similarly, the second spiral wiring layer  9   b  forms a portion serving as the via wiring  25  in the via hole  33   c  to electrically connect the first spiral wiring layer  7   b . The second spiral wiring layers  9   a ,  9   b  constitute the second spiral wirings  22  of the second coil L 2  and the third coil L 3 , respectively. As a result, the second coil L 2  and the third coil L 3  can be formed. In this process, the wiring layers are also formed in the through-holes  33   a ,  33   d ,  33   e ,  33   f  and on the third insulating resin layer  33  around the through-holes. 
     As shown in  FIG. 5N , the second spiral wiring layers  9   a ,  9   b  are covered with the fourth insulating resin layer  34 . In this case, the fourth insulating resin layer  34  is laminated on the third insulating resin layer  33  by a vacuum laminator and is then thermally cured. 
     As shown in  FIG. 5O , through-holes  34   a ,  34   d ,  34   e ,  34   f  are formed in the fourth insulating resin layer  34  by laser processing. The through-holes  34   a ,  34   d ,  34   e ,  34   f  are formed in the fourth insulating resin layer  34  above the through-holes  33   a ,  33   d ,  33   e ,  33   f , respectively. 
     As shown in  FIG. 5P , the base  50  is peeled off from the dummy metal layer  60  on the bonding plane between one surface of the base  50  (the base metal layer  52 ) and the dummy metal layer  60 . 
     As shown in  FIG. 5Q , the dummy metal layer  60  is removed by etching. In this process, the wiring layers provided in the through-holes  30   a  to  34   a ,  30   d  to  34   d ,  30   e  to  34   e ,  30   f  to  31   f  of the respective insulating resin layers  30  to  34  are etched at the same time, so that spaces forming the inner and outer magnetic paths of the coils are formed. In this way, a coil substrate  2  having the coils L 1  to L 4  is formed. 
     As shown in  FIG. 5R , a plurality of sheets molded from the composite material of the magnetic powder and the resin is disposed on both the upper and lower sides of the coil substrate  2 , heated and press-bonded by a vacuum laminator or a vacuum press machine, and subsequently subjected to a cure treatment. In this process, the composite material is filled into the spaces forming the inner and outer magnetic paths to form the magnetic resin  40  including the magnetic resin bodies  41   a ,  41   b  corresponding to the inner magnetic paths and the magnetic resin layer  42  corresponding to the outer magnetic path. Subsequently, a dicer etc. are used for cutting into individual pieces. In this case, the portions of the first and second spiral wiring layers  3   a ,  3   b ,  5   a ,  5   b ,  7   a ,  7   b ,  9   a ,  9   b  corresponding to the outer circumferential ends  21   b ,  22   b  of the first and second spiral wirings  21  are exposed on cut surfaces. Additionally, by forming the external terminals  11   a  to  14   a ,  11   b  to  14   b  such that the external terminals are connected to the wiring layers exposed on the cut surfaces, the coil component  1 A shown in  FIG. 2  can be acquired. 
     Although the coil substrate  2  is formed on one surface of both sides of the base  50  in the above description, the coil substrate  2  may be formed on each of both sides of the base  50 . Although the one coil substrate  2  is formed on one surface of the base  50  in the above description, a plurality of the coil substrates  2  may be formed in a matrix on one surface of the base  50  and then divided into individual pieces to form a plurality of the coil components  1 A at the same time. With these methods, high productivity can be achieved. The manufacturing methods described above are merely examples of the manufacturing method of the coil component  1 A, and other known methods and techniques may be applied as long as a similar configuration can be acquired. 
     According to the coil component  1 A, the magnetic coupling between the first coil L 1  and the second coil L 2  forming a pair is stronger than the magnetic couplings between the first coil L 1  and each of the third and fourth coils L 3 , L 4  not forming a pair. Therefore, as is the case with the coil component  1  according to the first embodiment, when the coil component  1 A is used for a multi-phase SW regulator, the ripple current of the first coil L 1  can be reduced by properly selecting the pulse signals input to the coils L 1  to L 4 . 
     When any coil is considered as a reference out of the first to fourth coils L 1  to L 4  in the coil component  1 A, the magnetic coupling to a coil pared with this coil is stronger than the magnetic coupling to a coil unpaired with this coil. Therefore, as is the case with the coil component  1  according to the first embodiment, when the coil component  1 A is used for a multi-phase SW regulator, the ripple current of the first to fourth coils L 1  to L 4  can be reduced by properly selecting the pulse signals input to the coils L 1  to L 4 . 
     To properly select the pulse signals so as to reduce the ripple current of the first to fourth coils L 1  to L 4 , for example, a signal having a phase difference of 180° as compared to the signal input to the first coil L 1  may be input to the second coil L 2 ; a signal having a phase difference of 90° as compared to the signal input to the first coil L 1  may be input to the third coil L 3 ; and a signal having a phase difference of 270° as compared to the signal input to the first coil L 1  may be input to the fourth coil L 4 . 
     In the coil component  1 A, the first external terminal  11  connected to the first coil L 1  and the second external terminal  12  connected to the second coil L 2  are adjacent to each other, and the third external terminal  13  connected to the third coil L 3  and the fourth external terminal  14  connected to the fourth coil L 4  are adjacent to each other. In the coil component  1 A, due to the relationship of strength of the magnetic coupling, the interval between the first coil L 1  and the second coil L 2  is shorter than the interval between the first coil L 1  and the other coils L 3 , L 4 , and the first coil L 1  and the second coil L 2  are closely disposed. Therefore, since the first and second external terminals  11 ,  12  connected to the paired coils L 1 , L 2  closely disposed are adjacent to each other, the routing between the coils L 1 , L 2  and the external terminals  11 ,  12  can be reduced in the coil component  1 A. As a result, the coil component  1 A can be miniaturized. Since the third and fourth external terminals  13 ,  14  connected to the third and fourth coils L 3 , L 4  forming the other pair have the same configuration in the coil component  1 A, the coil component  1 A can further be miniaturized. 
     Description will hereinafter be made of the fact that the ripple current of the coils L 1  to L 4  can actually be reduced based on the evaluation conducted by using an example of the coil component  1 A by the present inventors. 
     Table 1 shows configurations, evaluation conditions, and evaluation results of the present example and comparison examples 1, 2. Both the present example and the comparison examples 1, 2 have four coils L 1  to L 4  as a coil component. The coils L 1  to L 4  each have the inductance value of 1 μH. The present example has the configuration of the coil component  1 A shown in  FIGS. 2 to 4 , and the coil L 1  and the coil L 2  as well as the coil L 3  and the coil L 4  are configured to form respective pairs. The comparison example 1 is a coil component in which the four coils L 1  to L 4  are not magnetically coupled to each other. The comparison example 2 has the configuration of the coil component described in U.S. Pat. No. 6,362,986 and, specifically, has a configuration in which four coils L 1  to L 4  are respectively wound around four spokes  101  of a wheel type core  100  as shown in  FIG. 6 . 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                   
                   
                   
                   
                   
                   
                   
                 INPUT 
                 OUTPUT 
               
            
           
           
               
               
               
               
            
               
                   
                 COUPLING COEFFICIENT 
                 VOLTAGE 
                 VOLTAGE 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 L1:L2 
                 L2:L3 
                 L3:L4 
                 L1:L3 
                 L2:L4 
                 L1:L4 
                 [V] 
                 [V] 
               
               
                   
               
               
                 COMPARISON 
                 0 
                 0 
                 0 
                 0 
                 0 
                 0 
                 2 
                 1 
               
               
                 EXAMPLE 1 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 COMPARISON 
                 −0.399 
                 −0.399 
                 −0.399 
                 −0.193 
                 −0.193 
                 −0.399 
                 2 
                 1 
               
               
                 EXAMPLE 2 
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 PRESENT  
                 −0.9 
                 0.1 
                 −0.9 
                 −0.1 
                 −0.1 
                 0.1 
                 2 
                 1 
               
               
                 EXAMPLE 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                   
                   
                 RIPPLE 
               
               
                   
                   
                   
                   
                 INDUCTOR RIPPLE  
                 EFFECTIVE 
               
               
                   
                   
                 FREQUENCY 
                   
                 CURRENT [mA] 
                 VALUE 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 [MHz] 
                 L[μH] 
                 L1 
                 L2 
                 L3 
                 L4 
                 [mA] 
               
               
                   
               
               
                   
                 COMPARISON 
                 4 
                 1 
                 0.124 
                 0.124 
                 0.124 
                 0.124 
                 1.3 
               
               
                   
                 EXAMPLE 1 
                   
                   
                   
                   
                   
                   
                   
               
               
                   
                 COMPARISON 
                 4 
                 1 
                 0.205 
                 0.212 
                 0.196 
                 0.209 
                 1.7 
               
               
                   
                 EXAMPLE 2 
                   
                   
                   
                   
                   
                   
                   
               
               
                   
                 PRESENT  
                 4 
                 1 
                 0.086 
                 0.086 
                 0.087 
                 0.086 
                 0.4 
               
               
                   
                 EXAMPLE 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, in the comparison example 1, the coupling coefficients of the four coils L 1  to L 4  to each other are zero. In the comparison example 2, the four coils L 1  to L 4  are strongly magnetically coupled to each other and, in particular, the magnetic couplings between the coils not arranged on the same straight line in  FIG. 6  (e.g., the magnetic coupling between the coil L 1  and the coil L 2  as well as the magnetic coupling between the coil L 1  and the coil L 4 ) are equal and have the coupling coefficient of −0.399. The coils arranged on the same straight line in  FIG. 6  (e.g., the coil L 1  and the coil L 3  as well as the coil L 2  and the coil L 4 ) have the coupling coefficient of −0.193. The coupling coefficients of the comparison example 2 were calculated from the 3D magnetic field analysis results of the magnetic field analysis software Femtet (manufactured by Murata Software Co., Ltd.). 
     On the other hand, in the present embodiment, the coupling coefficient between the coil L 1  and the coil L 2  forming a pair and the coupling coefficient between the coil L 3  and the coil L 4  forming a pair are −0.9, and the coupling coefficients of the other unpaired coil combinations are −0.1. Therefore, the magnetic couplings between the coil L 1  and the coil L 2  as well as between the coil L 3  and the coil L 4  forming pairs are stronger than the magnetic couplings between the unpaired coils. The comparison examples 1, 2 do not satisfy this relationship of strength of the magnetic coupling. 
     In the present example and the comparison examples 1, 2, the pulse signals input to the coil L 2 , the coil L 3 , and the coil L 4  had the phase differences of 180°, 90°, and 270°, respectively, with respect to the pulse signal input to the coil L 1 .  FIGS. 7A to 7D, 8A to 8D, and 9A to 9D  show a relationship between an input voltages (V) that is a pulse signal input to the coils L 1  to L 4  and a coil current (A) in this case.  FIGS. 7A to 7D, 8A to 8D, and 9A to 9D  correspond to the present example, the comparison example 1, and the comparison example 2, respectively.  FIGS. 7A, 8A, and 9A  correspond to the first coil L 1 ,  FIGS. 7B, 8B, and 9B  correspond to the second coil L 2 ,  FIGS. 7C, 8C, and 9C  correspond to the third coil L 3 , and  FIGS. 7D, 8D, and 9D  correspond to the fourth coil L 4 . In the figures, a rectangular wave represents an input voltage, and a polygonal line indicates a coil current. The coil current was calculated by LTSPICE. The data of the waveforms shown in  FIGS. 7A to 7D, 8A to 8D, and 9A to 9D  are summarized in Table 1. 
     As shown in Table 1, in the present example, the coils L 1  to L 4  have the ripple current reduced by approx. 30% and the ripple effective value reduced by approx. 69% as compared to the comparison example 1 without the coupling. The ripple effective value is a value acquired by subtracting the average value of the coil current from the effective value of the coil current. In the present example, the coils L 1  to L 4  have the ripple current reduced by approx. 58% and the ripple effective value reduced by approx. 76% even as compared with the comparison example 2. Therefore, it can be understood that the ripple current of the coils L 1  to L 4  can be reduced in the present example as compared to the comparison examples 1, 2. In the comparison example 2, the ripple current is increased by approx. 66% and the ripple effective value is increased by approx. 31% as compared to the comparison example 1 without the coupling. Therefore, it was discovered through this evaluation that the ripple current may become larger in the coil component described in U.S. Pat. No. 6,362,986 as compared to the coil component without the coupling in some cases. 
     Third Embodiment 
       FIG. 10A  is an exploded perspective view of a coil component  1 B according to a third embodiment.  FIG. 10B  is a cross-sectional view of the coil component  1 B. The third embodiment is different from the second embodiment in the number of layers of spiral wirings constituting each coil. This different configuration will hereinafter be described. In the third embodiment, the same constituent elements as the second embodiment are denoted by the same reference numerals as the second embodiment and therefore will not be described. 
     As shown in  FIG. 10A  and  FIG. 10B , in the coil component  1 B, the first to fourth coils L 1  to L 4  are each made up of the single-layer spiral wiring  21  and a combination of the via wiring  25  and a lead wiring  75 . The lead wiring  75  has a linear shape and is not a spiral wiring. 
     The insulating resin  35  is made up of the base insulating resin layer  30  and the first, second, and third insulating resin layers  31 ,  32 ,  33 . The spiral wirings  21  of the first and fourth coils L 1 , L 4  are disposed on the base insulating resin layer  30 ; the lead wirings  75  of the first to fourth coils L 1  to L 4  are disposed on the first insulating resin layer  31 ; the spiral wirings  21  of the second and third coils L 2 , L 3  are disposed on the second insulating resin layer  32 ; and these wirings are respectively covered with the first insulating resin layer  31 , the second insulating resin layer  32 , and the third insulating resin layer  33 . 
     The positional relationship of the first to fourth coils L 1  to L 4  in the coil component  1 B is the same as that of the coil component  1 A. Therefore, the magnetic coupling between the first coil L 1  and the second coil L 2  forming a pair is stronger than the magnetic couplings between the first coil L 1  and each of the third and fourth coils L 3 , L 4  as well as between the second coil L 2  and each of the third and fourth coils L 3 , L 4  not forming a pair. Additionally, the magnetic coupling between the third coil L 3  and the fourth coil L 4  forming a pair is stronger than the magnetic couplings between the third coil L 3  and each of the first and second coils L 1 , L 2  as well as between the fourth coil L 4  and each of the first and second coils L 1 , L 2  not forming a pair. 
     In the coil component  1 B, the inner circumferential ends  21   a  of the spiral wirings  21  of the first to fourth coils L 1  to L 4  are connected through the via wirings  25  provided in the first insulating resin layer  31  or the second insulating resin layer  32  to the lead wirings  75  of the coils L 1  to L 4  provided on the insulating resin layer  31 . The lead wirings  75  linearly extend from connection portions with the via wirings  25  toward the side surface of the element body  10  and are connected to the corresponding first to fourth external terminals  11   a  to  14   a ,  11   b  to  14   b . As is the case with the coil component  1 A according to the second embodiment, the outer circumferential ends  21   b  of the spiral wirings  21  of the first coils L 1  to L 4  are led out to the side surface of the element body  10  and connected to the corresponding first to fourth external terminals  11   a  to  14   a ,  11   b  to  14   b.    
     Although the lead wirings  75  are disposed on the first insulating resin layer  31 , i.e., between the layer provided with the spiral wirings  21  of the coils L 1 , L 4  and the layer provided with the spiral wirings  21  of the coils L 2 , L 3  in the above description, the lead wirings  75  are not limited to this configuration. The lead wirings  75  may be disposed in, for example, a layer below the layer provided with the spiral wirings  21  of the coils L 1 , L 4  or a layer above the layer provided with the spiral wirings  21  of the coils L 2 , L 3 . 
     When a first coil is defined as one of the coils L 1  to L 4  and a second coil is defined as the coil forming a pair with the first coil while the coils other than the first coil and the second coil are defined as the other coils in the coil component  1 B, the magnetic coupling between the first coil and the second coil is stronger than the magnetic coupling between the first coil and each of the other coils. Therefore, even when the coil component  1 B is used for a multi-phase SW regulator, the ripple current of the coils L 1  to L 4  can be reduced by properly selecting the pulse signals input to the coils L 1  to L 4 . Additionally, since the coil component  1 B has the coils L 1  to L 4  each made up of the single-layer spiral wiring  21 , the coil component  1 B can be reduced in height. 
     Fourth Embodiment 
       FIG. 11A  is an exploded perspective view of a coil component  1 C according to a fourth embodiment.  FIG. 11B  is a cross-sectional view of the coil component  1 C. The fourth embodiment is different from the third embodiment in the configuration of lead-out portions of the coils L 1  to L 4  to the external terminals. This different configuration will hereinafter be described. In the fourth embodiment, the same constituent elements as the third embodiment are denoted by the same reference numerals as the third embodiment and therefore will not be described. 
     As shown in  FIG. 11A  and  FIG. 11B , in the coil component  1 C, the inner circumferential ends  21   a  of the respective spiral wirings  21  of the first to fourth coils L 1  to L 4  are led through first to fourth columnar electrodes  71  to  74  to the upper surface of the element body  10 . Although not shown, in the coil component  1 C, a portion of the external terminals is provided on the upper surface side of the element body  10 , and the columnar electrodes  71  to  74  of the coils L 1  to L 4  are connected to the corresponding external terminals on the upper surface side. The first to fourth columnar electrodes  71  to  74  are made of a low electric resistance metal such as Cu, Ag, and Au and are formed by a semi-additive process, for example. The outer circumferential ends  21   b  of the respective spiral wirings  21  of the first to fourth coils L 1  to L 4  are led to the side surface of the element body  10  and connected to the corresponding external terminals as in the case with the third embodiment. The internal structure of the coil component  1 C will hereinafter be described in more detail. 
     The inner circumferential ends  21   a  of the spiral wirings  21  of the first and fourth coils L 1 , L 4  are connected through the via wirings  25  provided in the first insulating resin layer  31  to the lead wirings  75  provided on the first insulating resin layer  31 . The lead wirings  75  of the first and fourth coils L 1 , L 4  are connected through the via wirings  25  provided in the second insulating resin layer  32  to the first and fourth columnar electrodes  71 ,  74 , respectively, provided on the first insulating resin layer  32  and in the magnetic resin  40 . 
     The inner circumferential ends  21   a  of the spiral wirings  21  of the second and third coils L 2 , L 3  are connected through the via wirings  25  provided in the second insulating resin layer  32  to the second and third columnar electrodes  72 ,  73  provided on the second insulating resin layer  32  and in the magnetic resin  40 . 
     The positional relationship of the first to fourth coils L 1  to L 4  in the coil component  1 C is the same as that of the coil component  1 A. Therefore, the magnetic coupling between the first coil L 1  and the second coil L 2  forming a pair is stronger than the magnetic couplings between the first coil L 1  and each of the third and fourth coils L 3 , L 4  as well as between the second coil L 2  and each of the third and fourth coils L 3 , L 4  not forming a pair. Additionally, the magnetic coupling between the third coil L 3  and the fourth coil L 4  forming a pair is stronger than the magnetic couplings between the third coil L 3  and each of the first and second coils L 1 , L 2  as well as between the fourth coil L 4  and each of the first and second coils L 1 , L 2  not forming a pair. 
     In particular, when a first coil is defined as one of the coils L 1  to L 4  and a second coil is defined as the coil forming a pair with the first coil while the coils other than the first coil and the second coil are defined as the other coils in the coil component  1 C, the magnetic coupling between the first coil and the second coil is stronger than the magnetic coupling between the first coil and each of the other coils. Therefore, even when the coil component  1 C is used for a multi-phase SW regulator, the ripple current of the coils L 1  to L 4  can be reduced by properly selecting the pulse signals input to the coils L 1  to L 4 . 
     In the coil component  1 C, since one end portion of each of the first to fourth coils L 1  to L 4  is led out to the upper surface of the element body  10  by one of the first to fourth columnar electrodes  71  to  74 , it is not necessary to form a wiring layer other than the spiral wirings  21  as in the coil component  1 B, and the height can further be reduced. Additionally, the coil component  1 C has a portion of the external terminals provided on the upper surface of the element body  10  and, for example, the external terminals can be extended from the upper surface to the side surfaces or the bottom surface, so that surface mounting can be achieved in this case. For example, even when the external terminals are provided only on the upper surface of the element body  10 , the external terminals can directly be connected from the upper surface of the element body  10  to the wiring pattern of a mounting board by adopting three-dimensional mounting such as embedding the coil component  1 C in the mounting board. Moreover, in this case, the wiring pattern of the mounting substrate and the first to fourth columnar electrodes  71  to  74  may directly be connected without providing the external terminals. 
     Fifth Embodiment 
       FIG. 12A  is a transparent perspective view of a coil component  1 D according to a fifth embodiment.  FIG. 12B  is a cross-sectional view taken along  12 - 12  of  FIG. 12A .  FIG. 12C  is a transparent top view of the coil component  1 D. The coil component  1 D is different from the coil component  1 C of the fourth embodiment in the shape of the spiral wirings constituting the coils L 1  to L 4 . This different configuration will hereinafter mainly be described. In the fifth embodiment, the same constituent elements as the first to fourth embodiments are denoted by the same reference numerals as the embodiments and therefore will not be described. 
     As shown in  FIG. 12A , in the coil component  1 D, each of the first to fourth coils L 1  to L 4  is made up of a single-layer spiral wiring  23 D. As shown in  FIG. 12B , the spiral wirings  23 D of the first and fourth coils L 1 , L 4  are provided on the base insulating resin layer  30  and are covered with the first insulating resin layer  31 . The second and third coils L 2 , L 3  are provided on the first insulating resin layer  31  and are covered with the second insulating resin layer  32 . Therefore, the spiral wirings  23 D are disposed inside the element body  10 . As shown in  FIG. 12C , each of the spiral wirings  23 D has a semi-elliptical arc shape when viewed in the up-down direction. Therefore, each of the spiral wirings  23 D is a curved wiring wound around about a half of the circumference on the base insulating resin layer  30  or the first insulating resin layer  31  (on the insulating layer). The number of turns of the spiral wiring  23 D is not limited to about a half of the circumference and may be any number less than one turn. When the number of turns is less than one turn, both ends of the spiral wiring  23 D are located on the outermost circumference (constitute no inner circumferential portion surrounded by itself), so that the need for three-dimensional wiring using a via wiring can be eliminated. 
     The spiral wiring  23 D of the first coil L 1  has both ends  23   a ,  23   b  connected to the first external terminals  11   a ,  11   b  and has a curved shape drawing an arc from the external terminals  11   a ,  11   b  toward the center side of the coil component  1 D. The spiral wiring  23 D of the third coil L 3  has the same shape as the spiral wiring  23 D of the first coil L 1  and has the two ends  23   a ,  23   b  connected to the third external terminals  13   a ,  13   b.    
     The spiral wiring  23 D of the second coil L 2  has the two ends  23   a ,  23   b  connected to the second external terminals  12   a ,  12   b  and has a curved shape drawing an arc from the external terminals  12   a ,  12   b  toward an edge side of the coil component  1 D. The spiral wiring  23 D of the fourth coil L 4  has the same shape as the spiral wiring  23 D of the second coil L 2  and has the two ends  23   a ,  23   b  connected to the fourth external terminals  14   a ,  14   b.    
     It is assumed in the coil component  1 D that an inner diameter portion refers to the inside of the innermost circumference of the spiral wiring  23 D (the area surrounded by the curve of the spiral wiring  23 D and the straight line connecting the ends  23   a ,  23   b  of the spiral wiring  23 D) for each of the coils L 1  to L 4 . In this case, when the coil component  1 D is viewed in the up-down direction, the inner diameter portion of the first coil L 1  and the inner diameter portion of the second coil L 2  overlap each other, and the inner diameter portion of the third coil L 3  and the inner diameter portion of the fourth coil L 4  overlap each other. The inner diameter portion of the first coil L 1  does not overlap with the inner diameter portions of the third and fourth coils L 3 , L 4 , and the inner diameter portion of the second coil L 2  does not overlap with the inner diameter portions of the third and fourth coils L 3 , L 4 . 
     Therefore, as is the case with the coil component  1  of the first embodiment, the coil component  1 D has the first coil L 1  and the second coil L 2  forming a pair and the third coil L 3  and the fourth coil L 4  forming a pair, so that the four coils L 1  to L 4  are configured to form two pairs. Additionally, the magnetic coupling between the first coil L 1  and the second coil L 2  forming a pair is stronger than the magnetic couplings between the first coil L 1  and each of the third and fourth coils L 3 , L 4  as well as between the second coil L 2  and each of the third and fourth coils L 3 , L 4  not forming a pair. The magnetic coupling between the third coil L 3  and the fourth coil L 4  forming a pair is stronger than the magnetic couplings between the third coil L 3  and each of the first and second coils L 1 , L 2  as well as between the fourth coil L 4  and each of the first and second coils L 1 , L 2  not forming a pair. Actually, in the configuration of the coil component  1 D, the 3D magnetic field analysis result was calculated by using the magnetic field analysis software Femtet with the spiral wirings  23 D having the wiring width of 50 μm, the wiring thickness of 45 μm, the wiring minimum interval of 10 μm, and the interlayer minimum interval of 10 μm. As a result, the absolute value of the coupling coefficient between the first coil L 1  and the second coil L 2  forming a pair was 1.5 times or more larger than the absolute value of the coupling coefficient between the first coil L 1  and the fourth coil L 4  adjacent to each other on the base insulating resin layer  30 . The absolute value of the coupling coefficient between the first coil L 1  and the third coil L 3  provided on the different layers and having the large interval between the inner diameter portions was smaller than the absolute values of the coupling coefficients described above. 
     Therefore, when a first coil is defined as one of the coils L 1  to L 4  and a second coil is defined as the coil forming a pair with the first coil while the coils other than the first coil and the second coil are defined as the other coils in the coil component  1 D, the magnetic coupling between the first coil and the second coil is stronger than the magnetic coupling between the first coil and each of the other coils. Therefore, even when the coil component  1 D is used for a multi-phase SW regulator, the ripple current of the coils L 1  to L 4  can be reduced by properly selecting the pulse signals input to the coils L 1  to L 4 . Additionally, since the coil component  1 D has the coils L 1  to L 4  each made up of the single-layer spiral wiring  23 D, the coil component  1 D can be reduced in height. Moreover, since it is not necessary to form a wiring layer other than the spiral wirings  23 D as in the coil component  1 B of the third embodiment, the height can further be reduced. 
     Sixth Embodiment 
       FIG. 13A  is a transparent perspective view of a coil component  1 E according to a sixth embodiment.  FIG. 13B  is a cross-sectional view of the coil component  1 E.  FIG. 13C  is a transparent top view of the coil component  1 E. The coil component  1 E is different from the coil component  1 D of the fifth embodiment in the shape of, and the layers provided with, the coils L 1  to L 4  and is also different in that first to fourth columnar electrodes  71   a  to  74   a ,  71   b  to  74   b  are included. This different configuration will hereinafter mainly be described. In the sixth embodiment, the same constituent elements as the first to fifth embodiments are denoted by the same reference numerals as the embodiments and therefore will not be described. 
     As shown in  FIG. 13A , in the coil component  1 E, the first to fourth coils L 1  to L 4  are each made up of a single-layer spiral wiring  23 E and lead wirings  75 E. As shown in  FIG. 13B , the first to fourth coils L 1  to L 4  are all provided on the base insulating resin layer  30  and are covered with the first insulating resin layer  31 . As shown in  FIG. 13C , both ends of the spiral wiring  23 E are connected to the lead wirings  75 E and led out toward the side surfaces  10   a ,  10   b  of the coil component  1 E. The spiral wiring  23 E has a semi-elliptical arc shape when viewed in the up-down direction. Therefore, the spiral wiring  23 E is a curved wiring wound around about a half of the circumference on the base insulating resin layer  30  (on the insulating layer). The number of turns of the spiral wiring  23 E is not limited to about a half of the circumference and may be any number less than one turn. 
     The lead wirings  75 E of the first coil L 1  each have one end connected to one of the first columnar electrodes  71   a ,  71   b  located on an outer side and have a shape extending from the first columnar electrodes  71   a ,  71   b  to the center side of the coil component  1 E. The lead wirings  75 E of the fourth coil L 4  each have one end connected to one of the fourth columnar electrodes  74   a ,  74   b  located on an outer side and have a shape extending from the fourth columnar electrodes  74   a ,  74   b  to the center side of the coil component  1 E. Each of the spiral wirings  23 E of the first and fourth coils L 1 , L 4  has both ends connected to the other ends of the lead wirings  75 E and has a curved shape drawing an arc from the other ends toward an edge side of the coil component  1 E. 
     The lead wirings  75 E of the second coil L 2  each have one end connected to one of the second columnar electrodes  72   a ,  72   b  located on the inner side and have a shape extending from the second columnar electrodes  72   a ,  72   b  to the edge side of the coil component  1 E. The lead wirings  75 E of the third coil L 3  each have one end connected to one of the third columnar electrodes  73   a ,  73   b  located on the inner side and have a shape extending from the third columnar electrodes  73   a ,  73   b  to the edge side of the coil component  1 E. Each of the spiral wirings  23 E of the second and third coils L 2 , L 3  has both ends connected to the other ends of the lead wirings  75 E and has a curved shape drawing an arc from the other ends toward the center side of the coil component  1 E. 
     It is assumed in the coil component  1 E that an inner diameter portion refers to the inside of the innermost circumference of the spiral wiring  23 E (the area surrounded by the curve of the spiral wiring  23 E and the straight line connecting both ends of the spiral wiring  23 E) for each of the coils L 1  to L 4 . In this case, in the coil component  1 E, the inner diameter portions of any of the coils L 1  to L 4  do not overlap each other when viewed in the up-down direction. 
     On the other hand, in the coil component  1 E, the lead wirings  75 E of the first and second coils L 1 , L 2  come close to each other at the other ends and, therefore, the spiral wirings  23 E of the first and second coils L 1 , L 2  come close to each other at both ends thereof and form curved shapes drawing arcs facing opposite to each other, thereby forming circular arcs of one elliptical shape. The lead wirings  75 E of the third and fourth coils L 3 , L 4  come close to each other at the other ends and, therefore, the spiral wirings  23 E of the third and fourth coils L 3 , L 4  come close to each other at both ends thereof and form curved shapes drawing arcs facing opposite to each other, thereby forming circular arcs of one elliptical shape. Therefore, the spiral wirings  23 E of the first and second coils L 1 , L 2  and the spiral wirings  23 E of the third and fourth coils L 3 , L 4  form the respective elliptical shapes and thereby share the inner diameter portions of the elliptical shapes. In the inner diameter portions of the elliptical shapes, the magnetic fluxes generated by the first and second coils L 1 , L 2  and the magnetic fluxes generated by the third and fourth coils L 3 , L 4  are concentrated, so that the magnetic coupling between the first coil L 1  and the second coil L 1  as well as the magnetic coupling between the third coil L 3  and the fourth coil L 4  become strong. 
     Therefore, as is the case with the coil component  1  of the first embodiment, the coil component  1 E has the first coil L 1  and the second coil L 2  forming a pair and the third coil L 3  and the fourth coil L 4  forming a pair, so that the four coils L 1  to L 4  are configured to form two pairs. Additionally, the magnetic coupling between the first coil L 1  and the second coil L 2  forming a pair is stronger than the magnetic couplings between the first coil L 1  and each of the third and fourth coils L 3 , L 4  as well as between the second coil L 2  and each of the third and fourth coils L 3 , L 4  not forming a pair. The magnetic coupling between the third coil L 3  and the fourth coil L 4  forming a pair is stronger than the magnetic couplings between the third coil L 3  and each of the first and second coils L 1 , L 2  as well as between the fourth coil L 4  and each of the first and second coils L 1 , L 2  not forming a pair. Actually, when the 3D magnetic field analysis result was calculated for the configuration of the coil component  1 E by using the magnetic field analysis software Femtet under the same conditions as the coil component  1 D, the absolute value of the coupling coefficient between the first coil L 1  and the second coil L 2  forming a pair was 1.5 times or more larger than the absolute value of the coupling coefficient between the second coil L 2  and the third coil L 3  adjacent to each other on the base insulating resin layer  30 . The absolute value of the coupling coefficient between the second coil L 2  and the fourth coil L 4  having a large interval between the inner diameter portions was smaller than the absolute value of the coupling coefficient described above. 
     Thus, when a first coil is defined as one of the coils L 1  to L 4  and a second coil is defined as the coil forming a pair with the first coil while the coils other than the first coil and the second coil are defined as the other coils in the coil component  1 E, the magnetic coupling between the first coil and the second coil is stronger than the magnetic coupling between the first coil and each of the other coils. Therefore, even when the coil component  1 E is used for a multi-phase SW regulator, the ripple current of the coils L 1  to L 4  can be reduced by properly selecting the pulse signals input to the coils L 1  to L 4 . Additionally, since the coil component  1 E has the coils L 1  to L 4  each made up of the single-layer spiral wiring  23 E, the coil component  1 E can be reduced in height. Moreover, since it is not necessary to form a wiring layer other than the spiral wirings  23 E as in the coil component  1 B of the third embodiment, the height can further be reduced. Since the coil component  1 E has all the spiral wirings  23 E laminated on the base insulating layer  30  so that the insulating resin  35  can have a two-layer structure, a further reduction in the height can be achieved. External terminals containing metal such as Cu, Ag, Ni, Sn, and Au may be provided on the outer surfaces of the first to fourth columnar electrodes  71   a  to  74   a ,  71   b  to  74   b  and, in this case, the mounting quality can be improved. The outer surfaces of the first to fourth columnar electrodes  71   a  to  74   a ,  71   b  to  74   b  may act as external terminals and, in this case, the coil component  1 E can have a configuration suitable for application in which the coil component is embedded in a mounting board. 
     Seventh Embodiment 
       FIG. 14A  is a transparent perspective view of a coil component  1 F according to a seventh embodiment,  FIG. 14B  is a cross-sectional view of the coil component  1 F, and  FIG. 14C  is a transparent top view of the coil component  1 F. The coil component  1 F is different from the coil component  1 E of the sixth embodiment in the shapes of the coils L 1  to L 4 . This different configuration will hereinafter mainly be described. In the seventh embodiment, the same constituent elements as the first to sixth embodiments are denoted by the same reference numerals as the embodiments and therefore will not be described. 
     As shown in  FIG. 14A , in the coil component  1 F, the first to fourth coils L 1  to L 4  are each made up of a single-layer spiral wiring  23 F. As shown in  FIG. 14B , the first to fourth coils L 1  to L 4  are all provided on the base insulating resin layer  30  and are covered with the first insulating resin layer  31 . As shown in  FIG. 14C , the spiral wiring  23 F has a semi-elliptical arc shape when viewed in the up-down direction. Therefore, the spiral wiring  23 F is a curved wiring wound around about a half of the circumference on the base insulating resin layer  30  (on the insulating layer). 
     The spiral wiring  23 F of the first coil L 1  has both ends connected to the first columnar electrodes  71   a ,  71   b  located on an outer side and has a curved shape drawing an arc from the first columnar electrodes  71   a ,  71   b  toward the center side of the coil component  1 F. The spiral wiring  23 F of the fourth coil L 4  has both ends connected to the fourth columnar electrodes  74   a ,  74   b  located on an outer side and has a curved shape drawing an arc from the fourth columnar electrodes  74   a ,  74   b  toward the center side of the coil component  1 F. 
     The spiral wiring  23 F of the second coil L 2  has both ends connected to the second columnar electrodes  72   a ,  72   b  located on the inner side and has a curved shape drawing an arc from the second columnar electrodes  72   a ,  72   b  toward an edge side of the coil component  1 F. The spiral wiring  23 F of the third coil L 3  has both ends connected to the third columnar electrodes  73   a ,  73   b  located on the inner side and has a curved shape drawing an arc from the third columnar electrodes  73   a ,  73   b  toward an edge side of the coil component  1 F. 
     It is assumed in the coil component  1 F that an inner diameter portion refers to the inside of the innermost circumference of the spiral wiring  23 F (the area surrounded by the curve of the spiral wiring  23 F and the straight line connecting both ends of the spiral wiring  23 F) for each of the coils L 1  to L 4 . In this case, in the coil component  1 F, the inner diameter portions of any of the coils L 1  to L 4  do not overlap each other when viewed in the up-down direction. 
     On the other hand, in the coil component  1 F, the spiral wirings  23 F of the first and second coils L 1 , L 2  come close to each other. Therefore, the magnetic fluxes generated in the spiral wiring  23 F of the first coil L 1  go around the periphery of the spiral wiring  23 F of the second coil L 2  close thereto, and the magnetic fluxes generated in the spiral wiring  23 F of the second coil L 2  go around the periphery of the spiral wiring  23 F of the first coil L 1  close thereto. The same applies to the third and fourth coils L 3 , L 4  having the spiral wirings  23 F coming close to each other. Therefore, the magnetic coupling between the first coil L 1  and the second coil L 1  as well as the magnetic coupling between the third coil L 3  and the fourth coil L 4  become strong. 
     Therefore, as is the case with the coil component  1  of the first embodiment, the coil component  1 F has the first coil L 1  and the second coil L 2  forming a pair and the third coil L 3  and the fourth coil L 4  forming a pair, so that the four coils L 1  to L 4  are configured to form two pairs. Additionally, the magnetic coupling between the first coil L 1  and the second coil L 2  forming a pair is stronger than the magnetic couplings between the first coil L 1  and each of the third and fourth coils L 3 , L 4  as well as between the second coil L 2  and each of the third and fourth coils L 3 , L 4  not forming a pair. The magnetic coupling between the third coil L 3  and the fourth coil L 4  forming a pair is stronger than the magnetic couplings between the third coil L 3  and each of the first and second coils L 1 , L 2  as well as between the fourth coil L 4  and each of the first and second coils L 1 , L 2  not forming a pair. Actually, when the 3D magnetic field analysis result was calculated for the configuration of the coil component  1 F by using the magnetic field analysis software Femtet under the same conditions as the coil component  1 D, the absolute value of the coupling coefficient between the first coil L 1  and the second coil L 2  forming a pair was four times or more larger than the absolute value of the coupling coefficient between the second coil L 2  and the third coil L 3  adjacent to each other on the base insulating resin layer  30 . The absolute value of the coupling coefficient between the second coil L 2  and the fourth coil L 4  having a large interval between the inner diameter portions was smaller than the absolute value of the coupling coefficient described above. 
     Thus, when a first coil is defined as one of the coils L 1  to L 4  and a second coil is defined as the coil forming a pair with the first coil while the coils other than the first coil and the second coil are defined as the other coils in the coil component  1 F, the magnetic coupling between the first coil and the second coil is stronger than the magnetic coupling between the first coil and each of the other coils. Therefore, even when the coil component  1 F is used for a multi-phase SW regulator, the ripple current of the coils L 1  to L 4  can be reduced by properly selecting the pulse signals input to the coils L 1  to L 4 . Additionally, since the coil component  1 F has the coils L 1  to L 4  each made up of the single-layer spiral wiring  23 F, the coil component  1 F can be reduced in height. Moreover, since it is not necessary to form a wiring layer other than the spiral wirings  23 F as in the coil component  1 B of the third embodiment, the height can further be reduced. Since the coil component  1 F has all the spiral wirings  23 F laminated on the base insulating layer  30  so that the insulating resin  35  can have a two-layer structure, a further reduction in the height can be achieved. 
     When currents flow simultaneously through the first and second coils L 1 , L 2  from certain ends on the same side to the other ends on the opposite side in the coil component  1 F, the magnetic fluxes strengthen each other. This means that when the certain ends on the same side of the first coil L 1  and the second coil L 2  are on the input side of the pulse signals and the other ends on the opposite side are on the output side of the pulse signals, the first coil L 1  and the second coil L 2  are positively coupled. However, for example, if one of the first coil L 1  and the second coil L 2  has the one end side used for input and the other end side used for output while the other coil has the one end side used for output and the other end used for input, the first coil L 1  and the second coil L 2  forming a pair can be put into a negatively coupled state. The same applies to the third and fourth coils L 3 , L 4 . 
     In the coil component  1 F, the first and second coils L 1 , L 2  has the portions coming close to each other with an insulating resin layer having the magnetic permeability of one interposed therebetween, for example, and the interval between the spiral wirings  23 F can be narrowed to, for example, 10 μm, while ensuring voltage endurance. In this case, no magnetic resin is present between the portions coming close to each other; however, since the portions are sufficiently close to each other, the magnetic coupling can be ensured as indicated by the calculation result described above. 
       FIG. 14D  is a transparent perspective view of a coil component  1 G according to a modification example of the seventh embodiment. The coil component  1 G is different from the coil component  1 F in arrangement of columnar electrodes. First, it is assumed that an end portion of each of the coils L 1  to L 4  on the side of the first side surface  10   a  of the element body  10  is defined as one end while an end portion of each of the coils L 1  to L 4  on the side of the second side surface  10   b  is defined as the other end. In the coil component  1 G, the first and third columnar electrodes  71   a ,  73   a  connected to the one end side of the first and third coils L 1 , L 3  as well as the second and fourth columnar electrodes  72   b ,  74   b  connected to the other end side of the second and fourth coils L 2 , L 4  are each exposed on the upper side of the element body  10 . The first and third columnar electrodes  71   b ,  73   b  connected to the other end side of the first and third coils L 1 , L 3  as well as the second and fourth columnar electrodes  72   a ,  74   a  connected to the other end side of the second and fourth coils L 2 , L 4  are each exposed on the lower side of the element body  10 . 
     According to this configuration, for example, by embedding the coil component  1 G in the mounting board and arranging input lines of the pulse signals on the upper surface side of the element body  10  while arranging output lines of the pulse signals on the lower surface side of the element body  10 , the sets of the first and second coils L 1 , L 2  and the third and fourth coils L 3 , L 4  forming pairs can more easily negatively be coupled. 
       FIG. 14E  is a transparent perspective view of a coil component  1 H according to a modification example of the seventh embodiment. The coil component  1 H is different from the coil component  1 F in arrangement of columnar electrodes. Specifically, in the coil component  1 H, the first and third columnar electrodes  71   a ,  71   b ,  73   a ,  73   b  connected to the first and third coils L 1 , L 3  are each exposed on the lower side from the element body  10 . The second and fourth columnar electrodes  72   a ,  72   b ,  74   a ,  74   b  connected to the second and fourth coils L 2 , L 4  are exposed on the upper side from the element body  10 . 
     According to this configuration, since the first to fourth external terminals of the coil component  1 H (the first to fourth columnar electrodes) adjacent to each other are exposed on respective different surfaces, the intervals between the terminals can be increased in the coil component  1 H as compared to the coil component  1 F even if the outer shape size is the same, so that it can be made difficult to cause a short circuit between the terminals at the time of connection of wirings to the mounting board. 
     Eighth Embodiment 
     In the second to seventh embodiments, the coil components have a configuration including the element body of laminated insulating layers and the wirings wound on the insulating layers, i.e., a structure of a so-called laminated coil; however, this is not a limitation of the configuration strengthening and weakening the magnetic couplings between paired coils and unpaired coils as in the first embodiment. 
       FIG. 15  is a schematic diagram of a coil component  1 J according to an eighth embodiment. The coil component  1 J is different from the coil component  1 A of the second embodiment in the configuration of the element body  10  and the configuration of the coils L 1  to L 4 . This different configurations will hereinafter mainly be described. In the eighth embodiment, the same constituent elements as the first to seventh embodiments are denoted by the same reference numerals as the embodiments and therefore will not be described. 
     As shown in  FIG. 15 , the coil component  1 J has the element body  10  made up of a first core  40 A, a second core  40 B, and a sealing resin  35 A, and the first to fourth coils L 1  to L 4  are made up of windings respectively wound around the first and second cores  40 A,  40 B. 
     The first and second cores  40 A,  40 B each have a substantially quadrangular frame shape and are made of a magnetic material such as ferrite or iron, for example. The external terminals  11   a  to  14   a ,  11   b  to  14   b  are formed on the sets of opposite sides of the first and second cores  40 A,  40 B. The sealing resin  35 A is a member for sealing both the first and second cores  40 A,  40 B in the one element body  10  and is made of an insulating material such as an epoxy resin, for example. In this configuration, the first core  40 A and the second core  40 B are arranged at an interval. 
     The first to fourth coils L 1  to L 4  are, for example, insulation-coated copper wires and are each wound around one side of the first and second cores  40 A,  40 B and connected at both ends to the first to fourth external terminals  11   a  to  14   a ,  11   b  to  14   b . The first and second coils L 1 , L 2  are wound in the same direction around one side and the other side, respectively, forming a set of sides without the first and second external terminals  11   a ,  11   b ,  12   a ,  12   b  formed thereon out of the sets of the opposite sides of the first core  40 A. The third and fourth coils L 3 , L 4  are wound in the same direction around one side and the other side, respectively, forming a set of sides without the third and fourth external terminals  13   a ,  13   b ,  14   a ,  14   b  formed thereon out of the sets of the opposite sides of the second core  40 B. Therefore, the coil component  1 J has the first coil L 1  and the second coil L 2  wound around the same first core  40 A and the third coil L 3  and the fourth coil L 4  wound around the same second core  40 B. 
     The configuration described above makes the magnetic coupling between the first coil L 1  and the second coil L 2  as well as the magnetic coupling between the third coil L 3  and the fourth coil L 4  stronger in the coil component  1 J. On the other hand, since the first core  40 A and the second core  40 B are arranged at an interval, the magnetic coupling between the first coil L 1  and each of the third and fourth coils L 3 , L 4  becomes weak, and the magnetic coupling between the second coil L 2  and each of the third and the fourth coils L 3 , L 4  becomes weak. 
     Therefore, as is the case with the coil component  1  of the first embodiment, the coil component  1 J has the first coil L 1  and the second coil L 2  forming a pair and the third coil L 3  and the fourth coil L 4  forming a pair, so that the four coils L 1  to L 4  are configured to form two pairs. Additionally, the magnetic coupling between the first coil L 1  and the second coil L 2  forming a pair is stronger than the magnetic couplings between the first coil L 1  and each of the third and fourth coils L 3 , L 4  as well as between the second coil L 2  and each of the third and fourth coils L 3 , L 4  not forming a pair. The magnetic coupling between the third coil L 3  and the fourth coil L 4  forming a pair is stronger than the magnetic couplings between the third coil L 3  and each of the first and second coils L 1 , L 2  as well as between the fourth coil L 4  and each of the first and second coils L 1 , L 2  not forming a pair. 
     Therefore, when a first coil is defined as one of the coils L 1  to L 4  and a second coil is defined as the coil forming a pair with the first coil while the coils other than the first coil and the second coil are defined as the other coils in the coil component  1 J, the magnetic coupling between the first coil and the second coil is stronger than the magnetic coupling between the first coil and each of the other coils. Therefore, even when the coil component  1 J is used for a multi-phase SW regulator, the ripple current of the coils L 1  to L 4  can be reduced by properly selecting the pulse signals input to the coils L 1  to L 4 . 
     In the coil component  1 J, one end of the first coil L 1  and one end of the second coil L 2  are led out to the same one side with respect to the first coil L 1  and the second coil L 2 , and the other end of the first coil L 1  and the other end of the second coil L 2  are led out to the same other side with respect to the first coil L 1  and the second coil L 2 . Additionally, the first coil L 1  and the second coil L 2  are wound in the same direction and therefore are negatively coupled when the one end is on the input side of the pulse signal and the other end is on the output side of the pulse signal. Therefore, the first coil L 1  and the second coil L 2  are wound such that the respective magnetic fluxes cancel each other in the core  40 A when a current flows from the one end to the other end. The same applies to the third coil L 3  and the fourth coil L 4 . 
     Therefore, when the pulse signals are input such that all the paired coils are negatively coupled in the coil component  1 J, the input sides and the output sides of the coils L 1  to L 4  can be arranged on the same respective sides. As a result, the wiring routing can be facilitated on the board on which the coil component  1 J is mounted. 
     Ninth Embodiment 
       FIG. 16  is a simplified configuration diagram of an embodiment of a switching regulator of the present disclosure. As shown in  FIG. 16 , a switching regulator  5  (hereinafter referred to as the “regulator  5 ”) is a step-down type switching regulator and steps down an input voltage Vin to a predetermined output voltage before supplying to a load  7 . The regulator  5  has the coil component  1 , switch parts S 1  to S(2N) respectively connected to the coils L 1  to L(2N) of the coil component  1  on one end portion side thereof, and a capacitor  6  (as an example of a smoothing circuit) connected to the coils L 1  to L(2N) of the coil component  1  on the other end portion side thereof. The regulator  5  is a multi-phase SW regulator, and the sets of the switch parts S 1  to S(2N) and the coils L 1  to L(2N) are connected in parallel between the input voltage Vin and the capacitor  6 . 
     The coil component  1  has the same configuration as the coil component  1  of the first embodiment ( FIG. 1 ). The same constituent elements as the first embodiment are denoted by the same reference numerals as the first embodiment and therefore will not be described. 
     The switch parts S 1  to S(2N) connect either the input voltage Vin or a ground voltage to the coils L 1  to L(2N) connected thereto (corresponding thereto) (a synchronous rectification type). Therefore, a pulse signal input to each of the coils L 1  to L(2N) is a rectangular wave having two values of the input voltage Vin and the ground voltage. It is assumed that the switch parts S 1  to S(2N) are each in an ON state when the input voltage Vin is connected to the coils L 1  to L(2N) corresponding thereto and that the switch parts S 1  to S(2N) are each in an OFF state when the ground voltage is connected to the coils L 1  to L(2N) corresponding thereto. The switching between the ON state and the OFF state is controlled by drive signals P 1  to P(2N) input to the switch parts S 1  to S(2N) from a PWM (Pulse Width Modulation) generator (not shown) included in the regulator  5 . 
     Specifically, a certain oscillation frequency is set to the regulator  5 , and the PWM generator shifts (turns on) the switch parts S 1  to S(2N) to the ON state at this oscillation frequency by the drive signals P 1  to P(2N). Therefore, the interval between turn-ons is the reciprocal of the oscillation frequency. This means that a pulse signal of rectangular waves having the same constant period (reciprocal of the oscillation frequency) is input to each of the coils L 1  to L(2N). 
     The regulator  5  also includes a detection circuit (not shown) detecting the output voltage of the coils L 1  to L(2N) and the current flowing through the coils L 1  to L(2N) and, when the detection circuit detects a voltage or a current equal to or greater than a certain level, the PWM generator shifts (turns off) the switch parts S 1  to S(2N) to the OFF state by the drive signals P 1  to P(2N). In a state (steady state) in which the power consumption of the load  7  does not vary, the interval from turn-on to turn-off is constant. Therefore, the 2N pulse signals input to the coils L 1  to L(2N) in the steady state have the same constant duty cycle (the interval from turn-on to turn-off/the reciprocal of the oscillation frequency) in the same constant period. 
     The regulator  5  is a multi-phase SW regulator and, when the reciprocal of the oscillation frequency is represented by a phase of 360°, the drive signals P 1  to P(2N) are a set of signals having turn-on intervals shifted by 360°/(2N), i.e., signals having a phase difference of 360°/(2N). In this case, the pulse signals input to the coils L 1  to L(2N) are also a set of signals having a phase difference of 360°/(2N). As a result, the peaks of voltages output from the coils L 1  to L(2N) are equally shifted, so that a difference between the minimum value and the maximum value of the composite voltage of the output voltages, i.e., the ripple voltage input to the capacitor  6 , can be reduced. 
     When the pulse signal having the phase difference of 360°/(2N) is input from one end of each of the coils L 1  to L(2N), the rectangular-wave pulse signal is converted into a triangular-wave pulse signal by the inductance of each of the coils L 1  to L(2N), and the triangular wave is output from the other end of each the coils L 1  to L(2N). 
     The output triangular wave is smoothed by the capacitor  6  connected to the other end portion side of the coils L 1  to L(2N) and is supplied to the load  7  on the subsequent stage. In this case, the voltage (output voltage) supplied to the load  7  is the product of the input voltage Vin and the duty cycle. Therefore, by properly setting the constant duty cycle, the regulator  5  steps down the input voltage Vin to a predetermined output voltage before supplying to the load  7 . 
     The regulator  5  has the coil component  1 . Therefore, the ripple current of the coils L 1  to L(2N) can be reduced by properly selecting the pulse signals input to the coils L 1  to L(2N). Specifically, when M is an integer of one or more and N or less, the regulator  5  selects as the signal P(2M−1) a signal having a phase difference of (360°/(2N))×(M−1) relative to the signal P 1  and selects as the signal P(2M) a signal having a phase difference of (360°/(2N))×(M−1)+180° relative to the signal P 1 . In this case, the pulse signals having a phase difference of 180° are input to all the paired coils L(2M−1) and L(2M) of the coil component  1 , so that the ripple current of the coils L 1  to L(2N) can be reduced. 
     Therefore, because of the reduction of the ripple current, the regulator  5  has a reduced loss due to heat generation in the coils L 1  to L(2N) and an improved efficiency. Additionally, because of the reduction of the ripple current, the regulator  5  can reduce the inductance value required for the coils L 1  to L(2N) and the capacitance value required for the capacitor  6  and can achieve an improvement in transient response speed and a miniaturization of a circuit. Therefore, the regulator  5  can be improved in performance and miniaturized. 
     Although the regulator  5  is of the PWM type in the above description, but the regulator may be of a PFM (Pulse Frequency Modulation) type. Even in the case of the PFM type, the 2N pulse signals input to the coils L 1  to L(2N) in the steady state are a set of signals having the same constant duty cycle in the same constant period and having a phase difference of 360°/(2N). Therefore, even in this case, the regulator  5  can be improved in performance and miniaturized by properly selecting the 2N pulse signals. 
     Although the switch parts S 1  to S(2N) are of the synchronous rectification type in the above description, this is not a limitation and, for example, each of the switch parts S 1  to S(2N) may be configured to have one switching element and a diode (a diode rectification type). 
     Although the regulator  5  is of the step-down type in the description, even a multi-phase SW regulator of the step-up type or the step-up/step-down type having the coil component  1  can be improved in performance and miniaturized by reducing the ripple current of the coils L 1  to L(2N). 
     The present disclosure is not limited to the embodiments described above and may be changed in design without departing from the spirit of the present disclosure. For example, respective feature points of the first to ninth embodiments may variously be combined. 
     In the second to eighth embodiments, the coil component has four coils; however, the coil component may have (2N) coils (N is an integer of two or more) and N may be set to N&gt;2. In the second embodiment, each of the coils has two layers of spiral wirings; however, each of the coils may have three or more layers of spiral wirings. 
     In the second embodiment, the coil has a structure in which a plurality of spiral wirings each having the number of turns equal to or greater than one is laminated; however, the coil may have a three-dimensional spiral (helical) structure in which a plurality of spiral wirings each having the number of turns less than one is laminated. 
     In the embodiments described above, the effect in the case of the negatively-coupled paired coils is mainly described; however, the paired coils may magnetically be coupled such that the coupling coefficient of the paired coils becomes positive, i.e., such that respective magnetic fluxes strengthen each other when currents flow through the paired coils at the same time. As a result, the input ripple current to the paired coils can be reduced. To make the coupling coefficient of the paired coils positive, for example, the winding direction of one coil may be reversed in a set of the paired coils, for example, the coils L 1 , L 2 , or the pulse signal may be input/output in the opposite direction for one of the coils L 1 , L 2  in the coil component  1 . Alternatively, for example, the paired coils L 1 , L 2  may be wound in the same direction in the coil component  1 A. 
     In the coil component  1 A, all the coils (spiral wirings) may be wound in the same direction. In this case, since the shapes, arrangement, manufacturing conditions, etc. of the coils can easily be made uniform, the electric characteristic deviation can be reduced and the manufacturing can be facilitated. Additionally, the paired coils can easily positively be coupled. 
     In the coil component  1 A, a plurality of coils (e.g., the coils L 1 , L 4 ) is laminated on the same insulating layer (e.g., the base insulating layer  30 ), and the plurality of coils is wound in different directions; however, this is not a limitation, and the plurality of coils may be wound in the same direction. In this case, since the plurality of coils laminated on the same insulating layer is wound in the same direction, a negative coupling can easily be achieved for a set of coils adjacent to each other on the same insulating layer and having a relatively large magnetic coupling out of the sets of the unpaired coils, and the ripple current of the coils can further be suppressed.