JP5176989B2 - Common mode filter and its mounting structure - Google Patents

Description

  The present invention relates to a common mode filter, and more particularly to a structure of a thin film type common mode filter. The present invention also relates to a mounting structure of such a common mode filter.

  In recent years, standards such as USB 2.0 and HDMI are widely used as high-speed signal transmission interfaces, and are used in many digital devices such as personal computers and digital high-definition televisions. Unlike the single-ended transmission method that has been common for a long time, these interfaces employ a differential signal method that transmits a differential signal (differential mode signal) using a pair of signal lines.

  The differential transmission system has an excellent feature that not only the radiation electromagnetic field generated from the signal line is small compared to the single-end transmission system, but also it is less susceptible to external noise. For this reason, it is easy to reduce the amplitude of the signal, and by shortening the rise time and the fall time due to the small amplitude, it becomes possible to perform signal transmission at a higher speed than the single-ended transmission method.

  FIG. 12 is a circuit diagram of a general differential transmission circuit.

  The differential transmission circuit shown in FIG. 12 includes a pair of signal lines 1 and 2, an output buffer 3 that supplies a differential mode signal to the signal lines 1 and 2, and an input buffer that receives a differential mode signal from the signal lines 1 and 2. 4 is provided. With this configuration, the input signal IN given to the output buffer 3 is transmitted to the input buffer 4 via the pair of signal lines 1 and 2 and reproduced as the output signal OUT. Such a differential transmission circuit has a feature that the radiated electromagnetic field generated from the signal lines 1 and 2 is small as described above, but noise (common mode noise) common to the signal lines 1 and 2 is present. When superposed, a relatively large radiated electromagnetic field is generated. In order to reduce the radiated electromagnetic field generated by the common mode noise, it is effective to insert the common mode filter 5 in the signal lines 1 and 2 as shown in FIG.

  The common mode filter 5 has a characteristic that the impedance to the differential component (differential mode signal) transmitted through the signal lines 1 and 2 is low, and the impedance to the in-phase component (common mode noise) is high. For this reason, by inserting the common mode filter 5 into the signal lines 1 and 2, it is possible to block the common mode noise transmitted through the pair of signal lines 1 and 2 without substantially attenuating the differential mode signal.

  As a conventional common mode filter, for example, as shown in Patent Document 1, first and second coil conductors are provided on both surfaces of a nonmagnetic substrate, and a magnetic layer is provided on both surfaces of the nonmagnetic substrate via spacers. A structure in which the periphery of the coil conductor is hollow is known. According to this common mode filter, it is possible to reduce the insertion loss in the differential mode in the high frequency band due to the stray capacitance in the coil conductor and between the coil conductors, and to reduce the common mode noise in a wide band. Patent Document 2 proposes a common mode filter in which two spiral patterns are connected in series to increase inductance against common mode noise.

JP 2006-196812 A JP 2007-181169 A

  Common mode filters used for the latest high-speed digital interfaces such as HDMI are required to be able to suppress common mode noise of 1 GHz or more. However, the conventional common mode filter is not sufficient for suppressing the common mode noise in the GHz band. For this reason, in the common mode filter described in Patent Document 1, stray capacitance is reduced by exposing a part of the coil conductor to the space portion. And there is a problem of a decrease in mechanical strength.

  Accordingly, an object of the present invention is to provide a common mode filter that has a high effect of suppressing common mode noise in the GHz band and that is excellent in workability and mechanical strength. It is another object of the present invention to provide a mounting structure in which the filter characteristics are good when the common mode filter is mounted on a printed board.

  In order to solve the above-mentioned problem, a common mode filter according to the present invention includes two coil conductors that are magnetically coupled to each other in the stacking direction, and first and second ceramic bases that sandwich the two coil conductors. The ceramic substrate is made of a magnetic material, and the dielectric constant of the second ceramic substrate is lower than that of the first ceramic substrate, and the shortest distance from the second ceramic substrate to the coil conductor is from the first ceramic substrate to the coil conductor. It is characterized by being shorter than the shortest distance.

  According to the present invention, in the structure in which the coil conductor is arranged to be biased toward one ceramic base, the low dielectric constant material is used for the ceramic base close to the coil conductor. The stray capacitance generated between turns can be reduced. As a result, the resonance of the impedance can be sharpened intentionally to partially improve the common mode attenuation characteristics, and the resonance frequency can be increased. Therefore, it is possible to provide a common mode filter having a high effect of suppressing common mode noise in the GHz band.

  In the present invention, each of the two coil conductors preferably includes a series connection of two spiral patterns. When a ceramic substrate having a low dielectric constant is used, the inductance is reduced. However, by connecting two spiral patterns in series, the reduction in the inductance can be compensated, and the capacitance in the line can be further reduced. . Therefore, a high-performance common mode filter having a desired inductance can be provided.

  The common mode filter according to the present invention preferably further includes a magnetic body provided inside the first and second coil conductors. When the second ceramic base is made of a low dielectric constant material, the inductance of the coil conductor is reduced. However, when a magnetic material is provided inside the coil conductor, a reduction in inductance can be suppressed.

  In addition, the above-described problem of the present invention includes a common mode filter and a printed circuit board on which the common mode filter is mounted. The common mode filter includes two coil conductors that are magnetically coupled to each other and stacked in the stacking direction. And a dielectric constant of the second ceramic base is lower than that of the first ceramic base, and the shortest distance from the second ceramic base to the coil conductor is the first ceramic base. The common mode filter is shorter than the shortest distance from the base to the coil conductor, and the common mode filter can be solved by a common mode filter mounting structure in which the second ceramic base is mounted facing the printed circuit board. it can.

  According to the present invention, when the common mode filter is mounted, if there is a ground wiring in the mounting area of the printed circuit board, stray capacitance is generated between the coil pattern and the second ceramic substrate is placed on the printed circuit board side. Since it is arranged, stray capacitance can be kept low.

  As described above, according to the present invention, a stray capacitance generated between coil conductors can be suppressed to a low level, and a common mode filter having a high effect of suppressing a common mode noise in the GHz band can be provided. In addition, since no cavity is provided in the interior, it is possible to provide a common mode filter excellent in workability and mechanical strength without inconvenience such as ingress of a plating solution.

  In addition, according to the present invention, it is possible to provide a mounting structure in which the filter characteristics are good when the common mode filter is mounted on a printed board.

1 is a schematic perspective view showing an external configuration of a common mode filter 100 according to a preferred embodiment of the present invention. 2 is a schematic exploded perspective view showing an example of a layer structure of a common mode filter 100. FIG. 2 is a schematic cross-sectional view of a common mode filter 100. FIG. (A) And (b) is a schematic diagram for demonstrating the relationship between a ceramic base | substrate and a coil conductor. 2 is a schematic cross-sectional view showing a mounting structure of a common mode filter 100. FIG. It is a graph which shows the common mode attenuation characteristic of the common mode filter 100 by this embodiment compared with the conventional common mode filter. It is a substantially exploded perspective view which shows the structure of the common mode filter 200 by the 2nd Embodiment of this invention. It is an equivalent circuit schematic of the common mode filter by 2nd Embodiment. It is a substantially exploded perspective view which shows the structure of the common mode filter 300 by the 3rd Embodiment of this invention. It is a schematic sectional drawing which shows the modification of the structure of the ceramic base | substrate 11b. It is a graph which shows the measurement result of the common mode attenuation | damping property of Example sample A1-A3 and comparative example sample B1. It is a circuit diagram of a general differential transmission circuit.

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

  FIG. 1 is a schematic perspective view showing an external configuration of a common mode filter according to a preferred embodiment of the present invention. FIG. 2 is a schematic exploded perspective view showing an example of the layer structure of the common mode filter 100.

  As shown in FIG. 1, the common mode filter 100 according to the present embodiment is a so-called thin film type, and includes first and second ceramic bases 11a and 11b, first ceramic base 11a and second ceramic base 11b. And a sandwiched functional layer 12. First to fourth terminal electrodes 13a to 13d are formed on the outer peripheral surface of the multilayer body including the first ceramic base 11a, the functional layer 12, and the second ceramic base 11b. Among these, the first and second terminal electrodes 13a and 13b are formed on the first side surface 10a, and the third and fourth terminal electrodes 13c and 13d are formed on the second side surface 10b opposite to the first side surface 10a. Is formed.

  The first ceramic base 11a physically protects the functional layer 12 and serves as a closed magnetic circuit for the common mode filter. As a material of the first ceramic bases 11a and 11b, sintered ferrite, composite ferrite (resin containing powdered ferrite), or the like can be used.

The second ceramic base 11b plays a role of physically protecting the functional layer 12 together with the first ceramic base 11a and reducing stray capacitance between coil conductors in the functional layer 12. As a material of the second ceramic substrate 11b, it is preferable to use alumina (Al ₂ O ₃ ) or the like. Since alumina has a lower dielectric constant than ferrite, stray capacitance due to the coil conductor can be suppressed. The second ceramic substrate 11b only needs to contain alumina as a main component, and may not be formed of only alumina.

  As shown in FIG. 2, the functional layer 12 includes adhesive layers 15a and 15b, insulating layers 16a to 16d, a magnetic layer 27, a first coil conductor 17 formed on the insulating layer 16b, and an insulating layer 16c. A second coil conductor 18 formed above, a first lead conductor 19 formed on the insulating layer 16a, and a second lead conductor 20 formed on the insulating layer 16d are provided.

  The insulating layers 16a to 16d serve to insulate the conductor patterns or between the conductor patterns and the magnetic layer 27 and to ensure the flatness of the base surface on which the conductor patterns are formed. As a material for the insulating layers 16a to 16d, it is preferable to use a resin that is excellent in electrical and magnetic insulation and has good workability, and it is preferable to use a polyimide resin or an epoxy resin. As the conductor pattern, it is preferable to use Cu, Al or the like excellent in conductivity and workability. The conductor pattern can be formed by an etching method using photolithography or an additive method (plating).

  An opening 25 penetrating the insulating layers 16a to 16d is provided in the central region of the insulating layers 16a to 16d and inside the first and second coil conductors 17 and 18, and inside the opening 25, A magnetic body 26 for forming a closed magnetic path with the first ceramic base 11a is filled. Therefore, the common mode filter 100 has a semi-closed magnetic circuit structure. When the second ceramic base is made of a low dielectric constant material such as alumina, the inductance of the coil conductors 17 and 18 is reduced. However, when a magnetic material is provided inside the coil conductors 17 and 18, the reduction of the inductance is suppressed. can do. As the magnetic body 26, composite ferrite or the like is preferably used.

  Further, a magnetic layer 27 is formed on the surface of the insulating layer 16d. The magnetic body 26 in the opening 25 is formed by curing a composite ferrite (magnetic powder-containing resin) paste. However, the resin shrinks during the curing, resulting in unevenness in the opening. In order to reduce the unevenness as much as possible, it is preferable to apply the paste not only to the inside of the opening 25 but also to the entire surface of the insulating layer 16d, and the magnetic layer 27 is formed for the purpose of ensuring such flatness. .

  The adhesive layer 15a is a layer necessary for bonding the ceramic substrate 11a and the magnetic layer 27, and the adhesive layer 15b is a layer necessary for bonding the ceramic substrate 11b and the insulating layer 16a. Also, it serves to alleviate the unevenness of the two bonding surfaces and increase the adhesion. Although not particularly limited, epoxy resin, polyimide resin, polyamide resin, or the like can be used as the material for the adhesive layers 15a and 15b.

  The first coil conductor 17 is formed of a rectangular spiral pattern constituting one coil of the common mode filter, and the inner peripheral end of the first coil conductor 17 has a contact hole conductor 21 and a lead conductor penetrating the insulating layer 16b. 19 is connected to the first terminal electrode 13a. The outer peripheral end of the first coil conductor 17 is connected to the third terminal electrode 13 c through the lead conductor 23.

  The second coil conductor 18 is formed of a rectangular spiral pattern constituting the other coil of the common mode filter, and the inner peripheral end of the second coil conductor 18 has a contact hole conductor 22 and a lead conductor penetrating the insulating layer 16d. 20 is connected to the second terminal electrode 13b. Further, the outer peripheral end of the second coil conductor 18 is connected to the fourth terminal electrode 13 d via the lead conductor 24.

  Both the first and second coil conductors 17 and 18 have the same planar shape, and are provided at the same position in plan view. Since the first and second coil conductors 17 and 18 are completely overlapped, a strong magnetic coupling is generated between them. With the above configuration, the two coil conductors in the functional layer 12 constitute a common mode filter.

  FIG. 3 is a schematic cross-sectional view of the common mode filter 100. 4A and 4B are schematic views for explaining the relationship between the ceramic base and the coil conductor.

  As shown in FIG. 3, the common mode filter 100 according to the present embodiment has a laminated structure in which the coil conductors 17 and 18 are arranged so as to be biased toward the second ceramic base 11b, and the first ceramic base 11a. Is made of a magnetic material such as ferrite, and the ceramic substrate 11b is made of a low dielectric constant material such as alumina. That is, the shortest distance between the first ceramic substrate 11a and the coil conductors 17 and 18 (here, the distance from the bonding surface S1 of the ceramic substrate 11a to one surface S2 of the second coil conductor 18) is D1, When the shortest distance between the second ceramic substrate 11b and the coil conductors 17 and 18 (here, the distance from the bonding surface S3 of the ceramic substrate 11b to one surface S4 of the first coil conductor 17) is D2, D1> The relationship D2 is established. The reason why the coil conductors 17 and 18 are biased toward the ceramic base 11b is that a common mode filter is formed by sequentially laminating an insulating layer and a conductor layer on the ceramic base 11b, patterning the conductor layer, and finally forming a magnetic layer. This is due to manufacturing reasons that 100 is completed.

  As shown in FIG. 4A, if one of the ceramic bases 11b adjacent to the coil conductors 17 and 18 is made of a ferromagnetic material such as ferrite, the adjacent turns of the coil conductors 17 and 18 through the ceramic base 11 are arranged. There is a problem that the stray capacitance C <b> 1 generated in the above is increased. However, as shown in FIG. 4B, when the ceramic base 11b is made of a low dielectric constant material such as alumina, the stray capacitance C2 generated between adjacent turns of the coil conductors 17 and 18 via the ceramic base 11 is reduced. Can be small. As a result, it is possible to intentionally sharpen the resonance of the impedance and partially improve the common mode attenuation characteristic, and to increase the resonance frequency. Therefore, it is possible to provide a common mode filter having a high effect of suppressing common mode noise in the GHz band.

  FIG. 5 is a schematic cross-sectional view showing the mounting structure of the common mode filter 100.

  As shown in FIG. 5, the common mode filter 100 is mounted with the second ceramic base 11b facing the printed circuit board 30 side. When the ground wiring 32 exists in the mounting region 31 of the common mode filter 100 provided on the printed circuit board 30, a stray capacitance C 3 is generated between the coil conductors 17 and 18 and the ground wiring 32. When the ceramic base 11b is mounted toward the printed circuit board 30 side, since the second ceramic base 11b made of a low dielectric constant material is interposed between the coil conductors 17 and 18 and the ground wiring 31, The stray capacitance C3 of the coil conductors 17 and 18 can be reduced as compared with the case where the first ceramic base 11a is interposed.

  FIG. 6 is a graph showing the common mode attenuation characteristics of the common mode filter 100 according to the present embodiment in comparison with a conventional common mode filter.

  As shown in FIG. 6, the resonance frequency of the conventional common mode filter in which the first and second ceramic substrates sandwiching the functional layer 12 are both made of a synchronic material such as ferrite is around 1 GHz, and the peak is relatively It is moderate. On the other hand, the resonance frequency of the common mode filter 100 according to the present embodiment is about 2 GHz, and its peak is steeper than that of the conventional common mode filter. Thus, according to the present embodiment, the resonance frequency can be made higher and steeper, and thus the effect of suppressing the common mode noise in the GHz band can be enhanced.

  FIG. 7 is a schematic exploded perspective view showing the configuration of the common mode filter according to the second embodiment of the present invention. FIG. 8 is an equivalent circuit diagram of the common mode filter shown in FIG.

  As shown in FIG. 7, the common mode filter 200 according to the present embodiment is characterized in that the first and second coil conductors 17 and 18 are both configured by connecting two spiral patterns in series. That is, the first coil conductor 17 is formed of a series connection of first and second spiral patterns 17A and 17B, and the second coil conductor 18 is formed of a series connection of third and fourth spiral patterns 18A and 18B. The first spiral pattern 17A corresponds to the inductance L1 shown in FIG. 8, and the second spiral pattern 17B corresponds to the inductance L2. Further, the third spiral pattern 18A corresponds to the inductance L3, and the fourth spiral pattern 18B corresponds to the inductance L4. Since other main configurations are substantially the same as those of the common mode filter 100 according to the first embodiment, the same components are denoted by the same reference numerals, and detailed description thereof is omitted.

  The inner peripheral end of the first spiral pattern 17A is connected to the first terminal electrode 13a via a contact hole conductor 21A and a lead conductor 19A penetrating the insulating layer 16b. Further, the outer peripheral end of the first spiral pattern 17A is connected to the second spiral pattern 17B via the contact hole conductor 21B that penetrates the insulating layer 16b, the lead conductor 19B, and the contact hole conductor 21C that penetrates the insulating layer 16b. Connected to the inner periphery. Further, the outer peripheral end of the second spiral pattern 17B is connected to the third terminal electrode 13c via the lead conductor 19C.

  The inner peripheral end of the third spiral pattern 18A is connected to the second terminal electrode 13b through a contact hole conductor 22A and a lead conductor 20A that penetrate the insulating layer 16d. Further, the outer peripheral end of the third spiral pattern 18A is connected to the fourth spiral pattern 18B via a contact hole conductor 22B penetrating the insulating layer 16d, a lead conductor 20B, and a contact hole conductor 22C penetrating the insulating layer 16d. Connected to the inner periphery. Furthermore, the outer peripheral end of the fourth spiral pattern 18B is connected to the fourth terminal electrode 13d via the lead conductor 20C.

  An opening 25A is provided in a predetermined region of the insulating layers 16a to 16d corresponding to the inside of the spiral patterns 17A and 18A, and the inside of the opening 25A is filled with a magnetic body 26A. An opening 25B is provided in a predetermined region of the insulating layers 16a to 16d corresponding to the inside of the spiral patterns 17B and 18B, and the inside of the opening 25B is filled with a magnetic body 26B.

  The first coil conductor 17 consisting of a series connection of first and second spiral patterns 17A, 17B and the second coil conductor 18 consisting of a series connection of third and fourth spiral patterns 18A, 18B are the first As in the embodiment, both have the same planar shape, and are provided at the same position in plan view. Since the first spiral pattern 17A and the second spiral pattern 18A are completely overlapped, a strong magnetic coupling is generated between them. In addition, since the third spiral pattern 17B and the fourth spiral pattern 18B are completely overlapped, strong magnetic coupling is generated between them. With the above configuration, the two coil conductors in the functional layer 12 constitute a common mode filter.

  As described above, in the common mode filter 200 according to the present embodiment, both the first and second coil conductors 17 and 18 are formed by connecting two spiral patterns in series, and the inductance is approximately smaller than that of a single spiral pattern. Twice the stray capacitance is about ½. Therefore, not only can a decrease in inductance caused by using a ceramic base having a low dielectric constant be compensated, but also a capacitance in the line can be reduced, and a high-performance common mode filter having a desired inductance is provided. be able to.

  FIG. 9 is a schematic exploded perspective view showing the configuration of the common mode filter according to the third embodiment of the present invention.

  As shown in FIG. 9, the common mode filter 300 according to the present embodiment is characterized in that the shape of the first and second coil conductors 17 and 18 is not a spiral spiral but a curved spiral pattern (circular spiral). It is said. When the shape of the first and second coil conductors 17 and 18 is a circular spiral, the overall length can be made shorter than that of a rectangular spiral. Thereby, the cut-off frequency of the common mode of the common mode filter can be further increased. On the other hand, when the overall length of the coil conductor is shortened, the direct current resistance is lowered. Therefore, in the case of a circular spiral, it is necessary to make the conductor thinner. Since other configurations are the same as those of the common mode filter 100 according to the first embodiment, the same reference numerals are given to the same configurations, and detailed descriptions thereof are omitted.

  As described above, according to the present embodiment, the common-mode cutoff frequency in the common-mode filter can be increased, and a higher-performance common-mode filter can be realized.

  The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention, and it goes without saying that these are also included in the present invention. .

  For example, in each of the above embodiments, the case where the entire second ceramic base 11b is made of a low dielectric constant material such as alumina has been described. However, the present invention is not limited to such a configuration, and for example, as shown in FIG. As described above, it is also possible to use a ceramic substrate in which only the portion located almost immediately below the coil conductors 17 and 18 is made of alumina 11c, and most of the other is made of ferrite 11d.

  For example, although the mounting structure of the common mode filter 100 according to the first embodiment has been described with reference to FIG. 5, the common mode filter 200 according to the second embodiment and the common mode filter 300 according to the third embodiment are mounted as illustrated in FIG. It is good also as a structure, and there can exist an effect similar to the common mode filter 100. FIG.

  Example samples A1 to A3 of the common mode filter having the structure shown in FIGS. 1 to 3 were prepared. Further, a comparative sample B1 having the same configuration as that of the example sample A1 was prepared except that the ceramic base was made of ferrite on both the upper and lower sides. The size of the common mode filter is common to each sample, and was set to 1.2 mm × 1.0 mm × 0.6 mm.

  Here, in Example Sample A1, the number of spiral turns was 4.5 Ts, the conductor width was 23 μm, the conductor thickness was 14 μm, the space width between adjacent turns was 5 μm, and the insulation distance between the upper and lower coil conductors was 20 μm. At this time, the characteristic impedance of sample A1 was 100Ω. In the sample A2, the number of spiral turns was 8.5 Ts, the conductor width was 10 μm, the conductor thickness was 14 μm, the space width between adjacent turns was 4 μm, and the insulation distance between the upper and lower coil conductors was 8 μm. At this time, the characteristic impedance of sample A2 was 120Ω. In Example Sample A3, the number of spiral turns was 6.5 Ts, the conductor width was 14 μm, the conductor thickness was 14 μm, the space width between adjacent turns was 5 μm, and the insulation distance between the upper and lower coil conductors was 8 μm. At this time, the characteristic impedance of sample A3 was 90Ω. The reason why the insulation distance of the sample A1 is 20 μm and the insulation distance of the samples A2 and A3 is 8Ω is that the characteristic impedance of each sample is about 100Ω.

  Next, the common mode attenuation characteristics of these Examples A1 to A3 and Comparative Sample B1 were measured. The result is shown in FIG.

  As is clear from FIG. 11, the resonance frequency of the example sample A1 is 2.1 GHz, the example sample A2 is 1.4 GHz, the example sample A3 is 1.1 GHz, and the resonance frequency is higher than that of the comparative example sample B1. It was. In each of the example samples A1 to A3, the resonance peak was steeper than that of the comparative sample B1. On the other hand, the resonance frequency of the comparative example sample B1 was 1.0 GHz, and the peak of the resonance was gentler than that of each of the example samples A1 to A3.

DESCRIPTION OF SYMBOLS 1, 2 Signal line 3 Output buffer 4 Input buffer 5 Common mode filter 10a 1st side surface 10b 2nd side surface 11a 1st ceramic base body 11b 2nd ceramic base body 11c Alumina part 11d of base body Ferrite part 11a of base body Insulating layer 12 functional layer 13a first terminal electrode 13b second terminal electrode 13c third terminal electrode 13d fourth terminal electrodes 15a, 15b adhesive layers 16a to 16d insulating layer 17 first coil conductor 18 second coil conductor 17A First spiral pattern 17B Second spiral pattern 18A Third spiral pattern 18B Fourth spiral pattern 19, 19A-19C Lead conductor 20, 20A-20C Lead conductor 21, 21, A-21C Contact hole conductor 22, 22A-22C Contact hole conductor 2 3 Leader conductor 24 Leader conductors 25, 25A, 25B Openings 26, 26A, 26B Magnetic body 27 Magnetic layer 30 Printed circuit board 31 Common mode filter mounting area 32 Ground wiring 100 Common mode filter 200 Common mode filter 300 Common mode filter

Claims (5)

Two coil conductors that are magnetically coupled to each other in the stacking direction;
First and second ceramic bases sandwiching the two coil conductors,
The first ceramic substrate is made of a magnetic material;
The dielectric constant of the second ceramic substrate is lower than that of the first ceramic substrate,
The shortest distance from the second ceramic base to the coil conductor is shorter than the shortest distance from the first ceramic base to the coil conductor ;
A dielectric constant of a layer interposed in the range of the shortest distance from the second ceramic base to the coil conductor and at least overlapping with the coil conductor in plan view is the first ceramic. A common mode filter characterized by being lower than the substrate .   The common mode filter according to claim 1, wherein each of the first and second coil conductors includes a series connection of two spiral patterns.   The common mode filter according to claim 1, wherein both the first and second coil conductors include a curved spiral pattern.   The common mode filter according to any one of claims 1 to 3, further comprising a magnetic body provided inside the first and second coil conductors. A common mode filter, and a printed circuit board on which the common mode filter is mounted,
The common mode filter includes two coil conductors that are magnetically coupled to each other in the stacking direction, and first and second ceramic bases sandwiching the two coil conductors, and the dielectric constant of the second ceramic base is Lower than the first ceramic substrate, the shortest distance from the second ceramic substrate to the coil conductor is shorter than the shortest distance from the first ceramic substrate to the coil conductor;
A dielectric constant of a layer interposed in the range of the shortest distance from the second ceramic base to the coil conductor and at least overlapping with the coil conductor in plan view is the first ceramic. Lower than the base,
The common mode filter mounting structure of the common mode filter, wherein the second ceramic base is mounted facing the printed circuit board.

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