Circuit board provided with coil component

The present invention relates to a circuit board provided with a coil component, more particularly, to a circuit board provided with a coil component having a drum-shaped core wound with a wire.

As a coil component having a drum-shaped core wound with wire, one described in JP 2011-82463A is known. In the coil component described in JP 2011-82463A, a wire is wound around a winding core part in three layers, and the self-resonant frequency of the coil component is adjusted by the number of turns in each winding layer.

However, the method described in JP 2011-82463A has difficulty in increasing the self-resonant frequency although being successful in reduction thereof. Further, this method cannot obtain sufficient effect in a frequency band exceeding 1 GHz.

It is therefore an object of the present invention to provide a circuit board provided with a coil component having an increased self-resonant frequency in a wide frequency band.

A circuit board according to an aspect of the present invention includes a substrate and a coil component mounted on the substrate, wherein the coil component includes a core and a wire wound around the core, and the substrate includes a dielectric and a capacitive electrode capacitively coupled to the wire through the dielectric and supplied with a ground potential.

According to the present invention, a capacitive component is added between the wire and the capacitive electrode, so that a capacitive component between turns of the wire (i.e., inter-wire capacitance) is apparently reduced. This can increase the self-resonant frequency of the coil component in a wide frequency band. In addition, the dielectric is provided between the wire and the capacitive electrode, allowing an increase in the capacitive component between the wire and the capacitive electrode.

In the present invention, the core may include a winding core part wound with the wire, a first flange part positioned at one axial end of the winding core part, and a second flange part positioned at the other axial end of the winding core part. The coil component may further include a first terminal electrode provided on the first flange part and connected to one end of the wire and a second terminal electrode provided on the second flange part and connected to the other end of the wire. The substrate may further include a first land pattern connected to the first terminal electrode and a second land pattern connected to the second terminal electrode. The height of the capacitive electrode may be greater than the height of the first and second land patterns, bringing the wire and capacitive electrode close to each other, which allows a larger capacitive component to be added.

In the present invention, the capacitive electrode may include a first capacitive electrode covering the wire in a first direction and a second capacitive electrode covering the wire in a second direction different from the first direction. Thus, the wire is covered with the capacitive electrode in a plurality of directions, allowing a larger capacitance to be added.

A circuit board according to another aspect of the present invention includes a substrate and a coil component mounted on the substrate, wherein the coil component includes a core and a wire wound around the core, the substrate includes a capacitive electrode capacitively coupled to the wire and supplied with a ground potential, and the capacitive electrode includes a first capacitive electrode covering the wire in a first direction and a second capacitive electrode covering the wire in a second direction different from the first direction.

According to the present invention, a capacitive component is added between the wire and the capacitive electrode, so that a capacitive component between turns of the wire (i.e., inter-wire capacitance) is apparently reduced. This can increase the self-resonant frequency of the coil component in a wide frequency band. In addition, the wire is covered with the capacitive electrode in a plurality of directions, allowing a large capacitance to be added.

In the present invention, the capacitive electrode may be a case member mounted on the surface of the substrate, and the coil component may be accommodated in the case member. Thus, it is possible to add a larger capacitance without applying complicated processing to the substrata.

In the present invention, the substrate may have a cavity accommodating at least a part of the coil component, and the capacitive electrode may be provided on the inner wall of the cavity. Thus, it is possible to add a larger capacitive component without using an additional member such as a case member.

According to the present invention, there can be provided a circuit board provided with a coil component having an increased self-resonant frequency in a wide frequency band.

The above features and advantages of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic perspective view illustrating the outer appearance of a circuit board 3 according to a first embodiment;

FIG. 2 is a schematic perspective view illustrating the outer appearance of a coil component 1 ;

FIG. 3 is a schematic perspective view of the substrate 2 on which the coil component 1 is mounted;

FIG. 4 is a schematic sectional view of the circuit board 3 ;

FIG. 5 is an equivalent circuit diagram of the circuit board 3 ;

FIG. 6 is a schematic cross-sectional view for explaining the structure of a circuit board 3 A according to a first modification;

FIG. 7 is a schematic perspective view illustrating the outer appearance of a circuit board 3 B according to a second modification;

FIGS. 8 and 9 are respectively a schematic perspective view and a schematic plan view illustrating the circuit board 3 B from which the coil component 1 has been removed;

FIG. 10 is a schematic transparent perspective view illustrating the outer appearance of a circuit board 3 C according to a third modification;

FIG. 11 is a schematic perspective view illustrating the outer appearance of a circuit board 3 D according to a fourth embodiment;

FIG. 12 is a schematic perspective view illustrating the outer appearance of a circuit board 4 according to a second embodiment of the present invention;

FIG. 13 is a schematic plan view illustrating the circuit board 4 from which the coil component 1 has been removed;

FIG. 14 is a schematic perspective view illustrating an example in which capacitive electrodes 25 to 27 are provided inside a cavity 2 c ; and

FIG. 15 is a schematic perspective view illustrating an example in which capacitive electrodes 26 and 27 are provided inside the cavity 2 c.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a schematic perspective view illustrating the outer appearance of a circuit board 3 according to a first embodiment.

As illustrated in FIG. 1 , the circuit board 3 according to the first embodiment includes a substrate 2 having a surface 2 a and a coil component 1 mounted on the surface 2 a . The coil component 1 has a structure illustrated in FIG. 2 . As shown in FIG. 2 , the coil component 1 includes a drum-shaped core 10 , terminal electrodes E 1 to E 4 , and a wire W. The drum-shaped core 10 includes a winding core part 13 whose axis extends in the x-direction, a flange part 11 provided at one end of the winding core part 13 in the x-direction, and a flange part 12 provided at the other end of the winding core part 13 in the x-direction. The drum-shaped core 10 is preferably made of a high permeability material having a permeability μ of 10 H/m to 400 H/m, such as ferrite.

The terminal electrodes E 1 and E 3 are provided on the flange part 11 , and the terminal electrodes E 2 and E 4 are provided on the flange part 12 . The terminal electrodes E 1 to E 4 may each be a terminal fitting or a conductive paste applied onto the surfaces of the flange parts 11 and 12 . The wire W is wound around the winding core part 13 so as to be connected at one end to the terminal electrode E 1 and at the other end to the terminal electrode E 2 . The terminal electrodes E 3 and E 4 may be omitted or may be used as a dummy terminal for enhancing mounting strength. The terminal electrodes E 1 and E 3 may be integrally formed; similarly, the terminal electrodes E 2 and E 4 may be integrally formed.

FIG. 3 is a schematic perspective view of the substrate 2 on which the coil component 1 is mounted.

As illustrated in FIG. 3 , the substrate 2 has, on the surface 2 a , a mounting area 2 b in which the coil component 1 is mounted. Land patterns P 1 and P 2 are provided within the mounting area 2 b . When the coil component 1 is mounted in the mounting area 2 b , the terminal electrodes E 1 and E 3 are connected to the land pattern P 1 , and the terminal electrodes E 2 and E 4 are connected to the land pattern P 2 . Further, a capacitive electrode 20 is provided within the mounting area 2 b . The surface of the capacitive electrode 20 is covered with a dielectric 30 . Thus, as illustrated in a cross-sectional view of FIG. 4 , when the coil component 1 is mounted in the mounting area 2 b , the capacitive electrode 20 overlaps the wire W through the dielectric 30 to be capacitively coupled to the wire W. The connection between the land pattern P 1 and the terminal electrodes E 1 , E 3 and the connection between the land pattern P 2 and the terminal electrodes E 2 , E 4 are made through a solder 40 . A space S is provided between the wire W and the dielectric 30 so as to prevent interference therebetween.

The land patterns P 1 and P 2 are connected to wiring patterns L 1 and L 2 , respectively. The wiring patterns L 1 and L 2 constitute a pair of input/output lines and connected to the coil component 1 through the wire W of the coil component 1 . The capacitive electrode 20 is connected to a wiring pattern L 3 . The wiring pattern L 3 is a ground pattern supplied with a ground potential GND.

FIG. 5 is an equivalent circuit diagram of the circuit board 3 according to the present embodiment.

As illustrated in FIG. 5 , in the circuit board 3 according to the present embodiment, the wire W functioning as a coil is connected between the wiring patterns L 1 and L 2 , and a capacitive component is added between the wire W and the capacitive electrode 20 . The amount of capacitive component to be added can be adjusted depending on a condition such as the area of the capacitive electrode 20 , the thickness and dielectric constant of the dielectric 30 , or the size of the space S. Adding such a capacitive component reduces the influence that a capacitive component generated between adjacent turns of the wire W (i.e., inter-wire capacitance) has on the self-resonant frequency, with the result that the self-resonant frequency increases. This means an apparent reduction in the inter-wire capacitance. Such an effect can be obtained even in a frequency band exceeding 1 GHz.

As described above, in the circuit board 3 according to the present embodiment, the capacitive electrode 20 supplied with the ground potential GND is provided in the mounting area 2 b of the substrate 2 , so that when the coil component 1 is mounted on the substrate 2 , a capacitive component is added between the wire W and the capacitive electrode 20 . Thus, it is possible to make the self-resonant frequency higher than that calculated from an actual inter-wire capacitance without involving a design change of the coil component 1 . In addition, since the capacitive electrode 20 is covered with the dielectric 30 , it is possible to add a larger capacitive component and to prevent a short failure between the wire W and the capacitive electrode 20 .

FIG. 6 is a schematic cross-sectional view for explaining the structure of a circuit board 3 A according to a first modification.

The circuit board 3 A according to the first modification illustrated in FIG. 6 differs from the circuit board 3 according to the first embodiment in that a height T 2 of the capacitive electrode 20 with respect to the surface 2 a of the substrate 2 is greater than a height T 1 of the land patterns P 1 and P 2 with respect to the surface 2 a of the substrate 2 . The back surface of the substrate 2 is covered with a ground pattern G, and the capacitive electrode 20 is constituted by a post conductor penetrating the substrate 2 to be connected to the ground pattern G. Other basic configurations are the same as those of the circuit board 3 according to the first embodiment, so the same reference numerals are given to the same elements, and overlapping description will be omitted.

In the first modification, the height T 2 of the capacitive electrode 20 is greater than the height T 1 of the land patterns P 1 and P 2 , so that the capacitive electrode 20 can be brought closer to the wire W, which means a reduction in the size of the space S. This allows a larger capacitive component to be added. However, when the height T 2 of the capacitive electrode 20 is excessively great, the wire W and the capacitive electrode 20 are brought too close to each other, which may cause a high-frequency short circuit depending on a frequency band to be used. Thus, considering a frequency band to be used, the distance between the wire W and the capacitive electrode 20 is preferably designed so as not to cause the high-frequency short circuit.

FIG. 7 is a schematic perspective view illustrating the outer appearance of a circuit board 3 B according to a second modification. FIGS. 8 and 9 are respectively a schematic perspective view and a schematic plan view illustrating the circuit board 3 B from which the coil component 1 has been removed.

The circuit board 3 B according to the second modification illustrated in FIGS. 7 to 9 differs from the circuit board 3 according to the first embodiment in that the capacitive electrode 20 is constituted of three capacitive electrodes 21 to 23 . Other basic configurations are the same as those of the circuit board 3 according to the first embodiment, so the same reference numerals are given to the same elements, and overlapping description will be omitted.

The capacitive electrode 21 constitutes the xy plane and overlaps the wire W in the z-direction, once the coil component 1 is mounted. The capacitive electrodes 22 and 23 constitute the xz plane and overlap the wire W in the y-direction, once the coil component 1 is mounted. Thus, the wire W and the capacitive electrode 20 overlap each other in three directions, allowing a larger capacitive component to be added. In particular, when the planar size of the coil component 1 is small, it is difficult to add a sufficient capacitive component only with the capacitive electrode 21 constituting the xy plane; however, according to the present modification, a sufficient capacitive component can be added even when the planar size of the coil component 1 is small.

FIG. 10 is a schematic transparent perspective view illustrating the outer appearance of a circuit board 3 C according to a third modification.

The circuit board 3 C according to the third modification illustrated in FIG. 10 differs from the circuit board 3 according to the first embodiment in that it has a capacitive electrode 24 formed of a case member. Other basic configurations are the same as those of the circuit board 3 according to the first embodiment, so the same reference numerals are given to the same elements, and overlapping description will be omitted. The capacitive electrode 24 is a metal case member and accommodates therein the coil component 1 . The capacitive electrode 24 is supplied with the ground potential GND. Thus, the capacitive electrode 24 and the wire W are capacitively coupled to each other even when a metal case member is used as the capacitive electrode 24 , allowing the self-resonant frequency to be adjusted.

However, when the case-shaped capacitive electrode 24 is connected to the ground pattern at a plurality of points, the ground pattern including the capacitive electrode 24 forms a loop. In this case, the capacitive electrode 24 and ground pattern function as a coil, significantly reducing the inductance. To prevent this, the capacitive electrode 24 and ground pattern are preferably connected at one point. Further, the capacitive electrode 24 itself is preferably designed so as not to form a loop. For example, an opening is formed in a part of the capacitive electrode 24 , or a part of the capacitive electrode 24 is made of a non-conductive material.

FIG. 11 is a schematic perspective view illustrating the outer appearance of a circuit board 3 D according to a fourth embodiment.

The circuit board 3 D according to the fourth modification illustrated in FIG. 11 differs from the circuit board 3 according to the first embodiment in that a plate-like core 14 is additionally provided in the coil component 1 . Other basic configurations are the same as those of the circuit board 3 according to the first embodiment, so the same reference numerals are given to the same elements, and overlapping description will be omitted.

The plate-like core 14 is fixed to the flange parts 11 and 12 and functions as a magnetic path connecting the flange parts 11 and 12 . The material of the plate-like core 14 and the high permeability material of the drum-shaped core 10 are preferably the same. By thus additionally providing the plate-like core 14 , a closed magnetic path is formed by the drum-shaped core 10 and plate-like core 14 , making it possible to increase the inductance.

Second Embodiment

FIG. 12 is a schematic perspective view illustrating the outer appearance of a circuit board 4 according to a second embodiment of the present invention. FIG. 13 is a schematic plan view illustrating the circuit board 4 from which the coil component 1 has been removed.

As illustrated in FIGS. 12 and 13 , the circuit board 4 according to the second embodiment differs from the circuit board 3 according to the first embodiment in that the substrate 2 has a cavity 2 c , in which the coil component 1 is accommodated. The cavity 2 c has land patterns P 1 and P 2 on its bottom surface and has capacitive electrodes 25 and 26 on its inner wall (xz plane). Other basic configurations are the same as those of the circuit board 3 according to the first embodiment, so the same reference numerals are given to the same elements, and overlapping description will be omitted.

In the present embodiment, when the coil component 1 is mounted in the cavity 2 c , the capacitive electrodes 25 , 26 are capacitively coupled to the wire W. This allows adjustment of the self-resonant frequency as in the first embodiment. In addition, since the capacitive electrodes 25 and 26 are provided on the inner wall of the cavity 2 c , it is possible to add a larger capacitive component than that in the first embodiment and to eliminate the need to provide a member for supporting the capacitive electrodes 25 and 26 . Further, since the coil component 1 is accommodated in the cavity 2 c , the height of the circuit board 4 can be reduced. In this case, the entire coil component 1 need not be accommodated in the cavity 2 c , and only a part thereof may be accommodated in the cavity 2 c.

In the substrate 2 illustrated in FIG. 13 , the capacitive electrodes 25 and 26 are formed also on the surface 2 a of the substrate 2 ; however, this is not essential in the present invention. Further, in the substrate 2 illustrated in FIG. 13 , the capacitive electrodes 25 and 26 are provided on the inner wall (xz plane) of the cavity 2 c ; however, the position of the capacitive electrode is not particularly limited. For example, in addition to the capacitive electrodes 25 and 26 , a capacitive electrode 27 may be provided on the bottom surface of the cavity 2 c as in the example illustrated in FIG. 14 , or the capacitive electrode 27 may be provided on the bottom surface of the cavity 2 c in place, while omitting the capacitive electrode 25 , as in the example illustrated in FIG. 15 . Thus, the self-resonant frequency can be adjusted depending on the position or area of the capacitive electrode.

It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention.