JP2007060535A - Noise filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a noise filter with excellent thermal conductivity for radiating heat accumulated in filter promptly and reducing generated noises effectively. <P>SOLUTION: In the noise filter 1, electrode plates 12A, 12B are formed through an insulating layer on both faces of a carbonaceous board 10 functioning as a ground terminal. A through hole 13 is formed in the carbonaceous board 10. A coil member 14 is embedded in the through hole 13 and the electrode plates 12A, 12B of both the faces are connected thereto. The coil member 14 and an inner circumferential face 131 of the through hole are insulated. In parallel with the coil member 14, a capacitor is formed from the electrode plates 12A, 12B and the carbonaceous board 10 and from the coil member 14 and the carbonaceous board 10 so that an equivalent circuit of π type filter is constituted, wherein ferroelectric ceramic material is contained in the insulating layer. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a noise filter. In particular, the present invention belongs to the technical field of noise filters that reduce noise generated from semiconductor components and the like and are excellent in heat dissipation.

  Noise generated from various electronic devices may be adversely affected on the electronic device itself or other electronic devices by being conducted on the circuit or radiated to the outside. For this reason, various measures have been taken in the past so as not to generate noise or to generate a failure even when receiving noise. In particular, in recent years, G (giga) band devices such as mobile phones, PHS, wireless LANs, and satellite broadcasts are generally used in daily life, and in order to prevent their malfunction and the like, Noise countermeasures are required.

  As one countermeasure against noise, a method of connecting a filter including a coil, a capacitor and the like to an electronic circuit is generally performed. Here, the noise filter may generate heat during use, depending on the type of components constituting the noise filter. In particular, when the number of turns of the coil is increased in order to reduce the size of the filter and maintain sufficient inductance, the amount of heat generated from the coil increases. When heat accumulates and the temperature of the filter rises, parts may deteriorate and unexpected failures such as performance degradation may occur, so it is required to dissipate heat quickly. There is also a problem that the impedance of the circuit is reduced by heat, and the effect of the filter is reduced correspondingly.

As a countermeasure against heat of a conventional noise filter, for example, (Patent Document 1) includes a filter body having at least a coil and a capacitor, and a housing that protects the filter body, and forcibly air-cooling the filter body. In addition, a noise filter provided with forced air cooling means such as a fan is disclosed.
This technique has a disadvantage that the apparatus becomes large and the configuration becomes complicated because a fan or the like is provided separately from the filter.

Further, (Patent Document 2) discloses a noise filter in which a coil is arranged in a case, and a heat radiating plate such as aluminum is arranged on at least one surface side of the coil. .
With this technology, the heat generated in the coil is dissipated to the outside through the heat sink, so it is possible to prevent deterioration of the components, but basically a filter such as a common mode choke coil is attached separately from the heat sink It is. Therefore, it has been desired to develop a noise filter that integrates the function of the filter with high heat dissipation and can be made compact as a whole, and that can perform more effective filtering.

JP-A-10-289823 (Claim 1, paragraph 0023) JP-A-7-201581 (Claim 1, paragraph 0010)

Therefore, in view of the above-described conventional situation, the present invention is a novel noise filter that can quickly dissipate heat accumulated in the filter with excellent thermal conductivity, and thereby can sufficiently maintain the performance of the filter. The purpose is to provide.
In addition, the filter circuit is configured using the part responsible for heat dissipation, thereby reducing the noise generated more effectively and reducing the noise in the desired frequency band corresponding to a wide range of frequencies. An object of the present invention is to provide a noise filter which can be easily adjusted in a desired frequency band.

  In order to solve the above-mentioned problems, the present invention provides, as claim 1, a noise filter in which electrode plates are respectively provided on both surfaces of a carbonaceous substrate also serving as a ground terminal via an insulating layer, Has a through hole, a coil member is embedded in the through hole to connect the electrode plates on both sides, the coil member and the inner peripheral surface of the through hole are insulated, and are parallel to the coil member Thus, a capacitor is formed by the electrode plate and the carbonaceous substrate, and the coil member and the carbonaceous substrate to constitute an equivalent circuit of a π-type filter, and the insulating layer contains a ferroelectric ceramic material. It is intended to provide a noise filter.

  According to the said structure, since the heat conductivity of a carbonaceous substrate is high, the heat | fever generated from a coil member etc. and accumulate | stored in a filter is thermally radiated rapidly. In addition, since the carbonaceous substrate has conductivity, when the substrate is a ground terminal, the electrode plates used for input and output are connected in series by a coil member, and further between each electrode plate and the carbonaceous substrate, and the coil A space between the member and the inner peripheral surface of the through hole functions as a capacitor. Thereby, a capacitor input / output type filter circuit is configured as a whole, and filtering is performed at a predetermined frequency, for example, noise conducted on the circuit is reduced. By adding a ferroelectric ceramic material, the dielectric constant of the capacitor can be adjusted in a wide range, and the frequency characteristics of the noise filter can be changed. Here, the π type filter means a capacitor input / output type filter as described above, and therefore includes a circuit configuration such as a so-called double π type.

  A second aspect of the present invention is the noise filter according to the first aspect, wherein the ferroelectric ceramic material contains barium titanate.

  According to the above configuration, an optimum material is selected in terms of dielectric constant, thermal conductivity, cost, and the like.

  According to a third aspect of the present invention, in the noise filter according to the first or second aspect, a total of three lead wires are connected to the electrode plate and the carbonaceous substrate.

  According to the above configuration, the three-terminal type noise filter including the input / output and the ground line is configured.

  According to a fourth aspect of the present invention, in the noise filter according to any one of the first to third aspects, the coil member is provided with an insulating coating so that the coil member and the inner peripheral surface of the through hole are insulated. And

  According to the above configuration, the insulating coating portion functions as a dielectric layer in the capacitor and configures the filter circuit.

  According to a fifth aspect of the present invention, in the noise filter according to any one of the first to fourth aspects, the carbonaceous substrate is a carbon composite material in which carbon fibers are arranged along the thickness direction of the substrate.

  According to the said structure, the heat conductivity in the thickness direction of a carbonaceous board | substrate improves, and heat dissipation improves.

  Moreover, Claim 6 is the noise filter according to any one of Claims 1 to 5, wherein the carbonaceous substrate has micropores, and an inorganic coating agent, a thermosetting resin, or a metal is contained in the micropores. It is impregnated.

  According to the said structure, a carbonaceous board | substrate becomes non-porous by impregnating an inorganic coating agent etc., and thermal conductivity further increases.

According to the present invention, since a carbonaceous substrate having a high thermal conductivity is used, heat can be quickly dissipated to prevent deterioration of components, and impedance can be stabilized and filter performance can be maintained. By adding a ferroelectric ceramic material, it is possible to change the frequency characteristics of the noise filter in accordance with a desired frequency band. In addition, since the dielectric constant can be varied widely depending on the amount of ferroelectric ceramic material added, the frequency characteristics of the noise filter can be adjusted relatively easily according to the desired frequency band where noise is desired to be reduced. Further, since the ferroelectric ceramic material has a higher dielectric constant than alumina or the like, the capacitor capacity can be increased, the insulating layer can be thinned, and the overall thickness of the substrate can be reduced. .
In addition, since the electrode plate is connected through a coil member in the through hole, and a capacitor is formed in parallel with the coil member using a conductive carbonaceous substrate, the entire plate is made of high It can function as a performance filter. Further, since the carbonaceous substrate has a heat dissipation function and becomes a part of the filter circuit as a ground terminal, the whole can be reduced in size.

Hereinafter, the present invention will be described in detail based on embodiments.
One embodiment of the noise filter of the present invention is shown in FIGS. FIG. 1 is a sectional view of a noise filter, and FIG. 2 is an equivalent circuit thereof. In the noise filter 1 of FIG. 1, electrode plates 12A and 12B are provided on both surfaces of a carbonaceous substrate 10 via insulating layers 11A and 11B, respectively. The carbonaceous substrate 10 has conductivity, and is used as a ground terminal by being connected to a frame.

  A through hole 13 is formed in the carbonaceous substrate 10, and a coil member 14 is embedded in the through hole 13. The electrode plate 12 </ b> A and the electrode plate 12 </ b> B are connected in series to the coil member 14 by solder 15. In addition, the coil member 14 is provided with an insulating coating 141, whereby the coil member 14 and the inner peripheral surface 131 of the through hole 13 are insulated. Of course, as shown in FIG. 1, both ends of the coil member 14 are connected to the electrode plates 12A and 12B with the insulating coating 141 peeled off for about one turn and the conductive wires exposed.

At this time, a capacitor (C1 in FIG. 2) having the insulating layer 11A as a dielectric is formed between the electrode plate 12A and the carbonaceous substrate 10, and even between one electrode plate 12B and the carbonaceous substrate 10, A capacitor (C3) using the insulating layer 11B as a dielectric is formed. In addition, a capacitor (C2) having the insulating coating 141 as a dielectric is formed between the coil member 14 and the carbonaceous substrate 10.
That is, a so-called double π-type low-pass filter in which the capacitors C1 to C3 are connected in parallel to the coil member 14 (L1, L2 in FIG. 2) embedded in the through hole 13 is formed. Thereby, the noise contained in the signal etc. which are input from the electrode plate 12A can be effectively reduced. The double π-type low-pass filter configured in FIG. 1 has good matching with a circuit having a relatively high impedance on both the input side and the output side, and exhibits the highest performance in that case.

Subsequently, each element constituting the noise filter 1 will be described in detail.
First, as the carbonaceous substrate 10, a plate-like material such as a carbon composite material using carbon fiber as a reinforcing material and carbon as a matrix, or an isotropic high-density carbon material is used. If the thickness of the carbonaceous substrate 10 is too thin, the impedance increases, which is not preferable as a ground terminal. On the other hand, if the thickness is too large, the thermal conductivity is reduced, leading to an increase in size and cost. Generally, 0.3 to 5 mm is appropriate. In addition, since the carbonaceous substrate 10 constitutes a capacitor relative to the electrode plates 12A and 12B described later, the electric capacity can be controlled by changing the area of the carbonaceous substrate 10. Therefore, an optimum filter according to a desired cutoff wavelength can be configured.

There are several types of carbon composite materials using carbon fibers as reinforcing materials depending on the arrangement of carbon fibers. Specifically, the primary orientation in which carbon fibers are aligned in one direction, the secondary orientation in which carbon fibers are woven fabrics such as plain weave, twill weave, satin weave, etc., and carbon fibers are so-called three-dimensionally woven 3 There are those of the next orientation, those using carbon fibers made of felt or short fibers, and any of them are applicable.
Carbon composite materials as described above are prepared by impregnating carbon fiber composites in various orientation states with a thermosetting synthetic resin such as phenol resin or a matrix material such as petroleum pitch, and the prepreg is necessary. Accordingly, a plurality of layers can be laminated, heated under pressure to cure the matrix material, and then fired at a high temperature in an inert atmosphere to carbonize or graphitize the matrix material. The carbon composite material may be formed into a plate shape so as to have the thickness of the carbonaceous substrate 10 in advance, or a known cutting such as a wire saw, a rotating diamond saw, etc. from the carbon composite material formed into a block shape. You may cut out to predetermined thickness by a means.

  In particular, among various carbon composite materials using carbon fiber as a reinforcing material, a primary-oriented carbon composite material block in which carbon fibers are arranged in one direction in a carbon matrix is cut at right angles to the arrangement direction of the carbon fibers. The plate-like material obtained in this way is preferably used because of its excellent thermal conductivity in the thickness direction.

  In addition, for the above-mentioned isotropic high-density carbon material, the graphite precursor fine particles having sintering properties such as raw coke and mesocarbon microbeads are fired at a high temperature while being pressed, or the graphite fine particles and carbon It can be manufactured by mixing whisker powder or the like with a binder made of a carbon precursor such as pitch or synthetic resin, press-molding, and firing. As in the case of the above-described carbon composite material, the isotropic high-density carbon material may be previously formed into a plate shape so as to have the thickness of the carbonaceous substrate 10, or may be formed into a block shape, etc. A predetermined thickness may be cut out from the isotropic high-density carbon material.

  The carbonaceous substrate 10 as described above is generally porous due to its manufacturing process and has fine pores. Therefore, the carbonaceous substrate 10 can be impregnated with an inorganic coating agent, a thermosetting resin, or a metal in the fine holes as necessary. Thereby, the carbonaceous substrate 10 becomes non-porous, and the thermal conductivity (heat dissipation) of the entire substrate can be further increased. Therefore, the heat accumulated in the noise filter 1 can be quickly removed, the entire impedance is stabilized, and the performance of the filter can be sufficiently extracted.

Specific examples of the inorganic coating agent include silicon-containing polymers that undergo a crosslinking reaction under normal temperature or heating conditions to form a ceramic-like cured product, cements such as alumina cement, and inorganic binders such as water glasses. be able to. These inorganic coating agents may be diluted with an organic solvent in order to improve the impregnation property.
Further, as a method for impregnating the inorganic coating agent, a method of applying the inorganic coating agent to the carbonaceous substrate 10 with a brush or the like, a method of immersing the carbonaceous substrate 10 in the inorganic coating agent, and an inorganic material at high pressure on the carbonaceous substrate 10. A method of press-fitting a coating agent, a method of sucking an inorganic coating agent into the carbonaceous substrate 10 in a high vacuum, and the like can be appropriately employed.

In addition, when impregnating with a thermosetting resin, phenol resin, epoxy resin, polyimide resin or the like is preferably used because of its excellent heat resistance.
The impregnation method can be performed by applying a thermosetting resin having fluidity to the carbonaceous substrate 10 to infiltrate the fine pores, and then heating to cure. Use of a thermosetting resin is advantageous because the thermal conductivity of the carbonaceous substrate 10 can be improved at low cost.

  Furthermore, when impregnating a metal, the kind of the metal is not particularly limited, but aluminum, copper, and the like are preferably used because of their high thermal conductivity. As a method for impregnating a metal, a method of impregnating a molten metal such as aluminum or copper under high temperature and high pressure, a method of impregnating using a vacuum, or the like can be appropriately used. In addition, as a material impregnated with aluminum, CC-MA (trade name; a carbon composite material manufactured by Advanced Materials Co., Ltd. in which carbon fibers are primarily arranged) or the like may be used, and these materials may be used as the carbonaceous substrate 10.

Next, the insulating layers 11A and 11B are applicable as long as they have excellent adhesion to the electrode plates 12A and 12B and the carbonaceous substrate 10 and have electrical insulation. Moreover, in order to make the movement of heat between the electrode plates 12A and 12B and the carbonaceous substrate 10 smooth, it is preferable to have thermal conductivity.
Specific examples include resin materials such as epoxy resins, phenol resins, and polyimide resins. In general, these resin materials can be applied to the carbonaceous substrate 10 by dipping, spraying, electrodeposition or the like and cured to form a layer. In addition, a method of laminating a resin film on the carbonaceous substrate 10 and then heat melting, a method of forming a layer by vapor deposition polymerization on the carbonaceous substrate 10 and the like can be exemplified. In addition to the above resin material, an inorganic paint such as SiO ₂ can be used. The use of an inorganic paint is preferable from the viewpoint of forming a stable filter because a thin and uniform insulating layer can be formed.

The insulating layers 11A and 11B contain a ferroelectric ceramic material. Since the dielectric constant of the insulating layer can be greatly changed by adding a ferroelectric ceramic material, it is formed between the electrode plate 12A (or 12B) and the carbonaceous substrate 10 as shown in (Formula 1). The capacitor capacitance C of the capacitor (C1 (or C3 in FIG. 2)) that uses the insulating layer 11A as a dielectric can be changed. Since the frequency characteristic of the noise filter of the present invention is proportional to C ^−1/2 , the frequency characteristic can be changed according to the blending amount of the ferroelectric ceramic material. Since the dielectric constant can be varied widely depending on the amount of ferroelectric ceramic material added, the frequency characteristics of the noise filter can be adjusted relatively easily according to the desired frequency band where noise is desired to be reduced. Further, since the ferroelectric ceramic material has a higher dielectric constant than alumina or the like, the capacitor capacity can be increased, and the thickness of the insulating layer and the entire substrate can be reduced.

(Formula 1)

Examples of the ferroelectric ceramic material include barium titanate (BaTiO ₃ ), strontium titanate (SrTiO ₃ ), and zirconium oxide (ZrO ₂ ). Various ferroelectric ceramic materials such as barium titanate, strontium titanate, and zirconium oxide include Sn, Ca, Pb, La, Ce, Mg, Bi, Ni, Al, Si, Zn, B, Nb, and W. It is also possible to use those doped with impurities such as Mn, Fe and Cu. Among these, barium titanate is particularly preferable because it can adjust the dielectric constant in a wide numerical range, has a relatively high thermal conductivity, and is commercially available and cost-effective. A high thermal conductivity is preferable because the accumulated heat is quickly dissipated even when the substrate is used for an electronic component that is mounted and generates heat.
Moreover, the shape of the ferroelectric ceramic material to be used may be either spherical or whiskered, but is preferably spherical from the viewpoint of uniform dispersion. If the particle size of the ferroelectric ceramic material used is too large, the film thickness of the insulating layers 11A and 11B may become unnecessarily large and the smoothness of the surface may be impaired. It is preferable to set it as 0.1-50 micrometers inside. In addition, the content ratio of barium titanate in the insulating layers 11A and 11B can generally be set such that the weight ratio of barium titanate to other solids is about 0.5: 5 to 50: 5. preferable.

The thicknesses of the insulating layers 11A and 11B can be set as appropriate on the condition that insulation between the electrode plates 12A and 12B and the carbonaceous substrate 10 is ensured. Note that since the insulating layers 11A and 11B function as a dielectric in the capacitor, the capacitance can be controlled by changing the thickness. Therefore, it is preferable to set the thickness in consideration of a desired cutoff frequency or the like. Specifically, for noise of several hundred MHz to several GHz, a thickness of about 5 to 100 μm, especially about 30 to 100 μm, is appropriate.
Further, the thicknesses of the insulating layer 11A and the insulating layer 11B can be set differently according to the impedances on the input side and the output side.

  Further, if necessary, the insulating layers 11A and 11B can contain a thermally conductive filler. Thereby, heat can be rapidly transferred between the electrode plates 12A and 12B and the carbonaceous substrate 10, and the overall heat dissipation can be further enhanced. Therefore, the impedance of the noise filter is stabilized and the filter performance can be maintained.

As the thermally conductive filler, any material having high thermal conductivity and electrical insulation can be used as appropriate. Among them, alumina (Al ₂ O ₃ ), aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), and boron nitride (BN) are particularly preferable because they have very high electrical insulating properties and are stable up to high temperatures. Used. Any one kind of these heat conductive fillers may be used, or two or more kinds may be used in combination. The shape of the thermally conductive filler can be either spherical or whiskered, but is preferably spherical from the viewpoint of uniform dispersion. If the particle size of the thermally conductive filler is too large, the thickness of the insulating layers 11A and 11B becomes larger than necessary, and the surface smoothness may be impaired, so about 0.5 to 10 μm, especially 0 It is preferable to be 5 to 2 μm. Moreover, although the content rate of the heat conductive filler in insulating layer 11A, 11B changes with kinds etc. of filler, generally weight ratio of heat conductive filler: other solid content is 3: 5-20: It is preferable to set to about 5.

And as electrode plate 12A, 12B, metal foils, such as copper, aluminum, nickel, etc. can be used. The thickness of the metal foil can be appropriately set depending on the application. Specifically, 500 μm or less is preferable.
The metal foil is laminated on the insulating layers 11A and 11B using various adhesives. Or
By using an adhesive having electrical insulation, the insulating layers 11 </ b> A and 11 </ b> B may be bonded to the carbonaceous substrate 10.

The electrode plates 12A and 12B can also be formed on the insulating layers 11A and 11B by electroless plating or the like. In that case, a chemical etching process can be performed in advance in order to impart hydrophilicity to the surfaces of the insulating layers 11A and 11B. Further, in order to efficiently perform initial metal deposition by electroless plating, a catalyst layer of palladium, silver, gold, platinum, or the like may be formed in advance on the surfaces of the insulating layers 11A and 11B.
In addition to the above-described electroless plating method, dry methods such as vacuum deposition, low-temperature sputtering, and ion plating can be applied. The thickness of the input / output terminal by plating or the like is preferably at least 15 μm or more.
In addition, since the electrode plates 12A and 12B constitute a capacitor relative to the carbonaceous substrate 10, the electric capacity can be controlled by changing the area of the electrode plate. Therefore, an optimum filter corresponding to various noises can be configured.

In forming the through hole 13 in the carbonaceous substrate 10, there is a method in which a predetermined position of the electrode plate is removed by etching, followed by irradiation with a CO ₂ laser or the like to form holes in the insulating layer and the carbonaceous substrate. It is preferably used because of its high dimensional accuracy and excellent production efficiency. In addition, you may process mechanically using a drill etc.
In addition, the coil member 14 having an inductance corresponding to a desired filter performance is appropriately selected and used. As a small coil member provided with an insulating coating 141 as shown in FIG. 1, Kyfil (trade name) manufactured by KFM Co., Ltd. may be mentioned.

  In the above-described embodiment, the case where the coil member 14 previously provided with the insulating coating 141 is embedded is described. However, the present invention is not limited to this, and any means that can insulate the coil member 14 from the inner peripheral surface 131 of the through hole. It can be adopted as appropriate. For example, after forming a through hole in a carbonaceous substrate with a laser or the like, masking the part other than the inner peripheral surface of the through hole and forming an insulating layer such as a resin on the inner peripheral surface, or insulating coating the through hole For example, a method may be used in which a coil member that is not used is embedded and a resin is poured into the gap between the inner peripheral surface of the through hole and the coil member to be cured.

The noise filter 1 described above is used by connecting a total of three lead wires to each of the electrode plates 12A and 12B used for input and output and the carbonaceous substrate 10 which is a ground terminal, and mounting them on a printed board or the like. . When connecting the lead wire, it can be performed by a method of soldering the lead wire to the electrode plates 12A, 12B and the carbonaceous substrate 10 or the like. May be provided. In addition, for the carbonaceous substrate 10 also serving as a ground terminal, a lead portion may be formed protrudingly on the substrate itself, and this portion may be directly screwed to the conductive grounding portion, instead of connecting a lead wire separately.
The noise filter 1 shown in FIG. 1 is finally connected to the electrode plate or the like by exposing only a part of the electrode plates 12A and 12B and a part of the carbonaceous substrate 10 by hardening the periphery with resin or the like. A package in which only the lead wires are drawn out may be used. Alternatively, it can be shielded by a magnetic shield case and used as an EMI filter.
1 uses a single carbonaceous substrate 10. However, the present invention is not limited to this. For example, a plurality of dielectric layers are provided inside the carbonaceous substrate 10 to provide a capacitor. A more complicated filter circuit may be formed by forming a stacked structure.

Next, although an Example is shown and this invention is demonstrated further in detail, it is not limited to this.
Example 1
First, a square carbonaceous substrate having a thickness of 1.5 mm and a side of 10 mm (a porous carbon composite material in which carbon fibers are primarily oriented is impregnated with a phenol resin as a thermosetting resin) has a diameter. A 2.0 mm through hole was formed. Subsequently, an insulating layer made of an epoxy resin having a thickness of 120 μm is formed on both surfaces of the carbonaceous substrate and the inner peripheral surface of the through hole, and copper serving as an electrode plate is formed on both surfaces of the carbonaceous substrate through the insulating layer. A foil (thickness 35 μm) was adhered. The insulating layer contains 77% by weight of barium titanate having an average particle size of 30 μm as a ferroelectric ceramic material with respect to the entire insulating layer. Then, a coil member (with a ferrite core) having 14 turns and an outer diameter of 1.15 mm is embedded in the through hole, and both ends of the coil member are soldered to the electrode plates on both sides of the board, respectively, to thereby obtain a target noise filter. Produced.

(Example 2)
The same procedure as in Example 1 was performed except that the content of barium titanate in the insulating layer was 70% by weight with respect to the entire insulating layer.

(Example 3)
The same operation as in Example 1 was performed except that the content of barium titanate in the insulating layer was 60% by weight with respect to the entire insulating layer.

(Comparative Example 1)
The same operation as in Example 1 was performed except that 77% by weight of alumina (Al ₂ O ₃ ) was blended in the insulating layer with respect to the entire insulating layer.

(Comparative Example 2)
The same operation as in Example 1 was performed except that 70% by weight of alumina (Al ₂ O ₃ ) was blended in the insulating layer with respect to the entire insulating layer.

(Comparative Example 3)
The same operation as in Example 1 was performed except that 60% by weight of alumina (Al ₂ O ₃ ) was blended in the insulating layer with respect to the entire insulating layer.

  About the noise filter obtained in each said Example and each comparative example, the dielectric constant in the frequency 0.03-6GHz of each noise filter was measured using the dielectric constant measuring apparatus HP8752C (Hewlett Packard). The measurement results are shown in FIG.

  In addition, a dielectric constant measuring device (network analyzer) HP8752C (Hewlett Packard) is connected to the noise filter obtained in each of the above examples and comparative examples, and the filter characteristics (insertion loss) with respect to transmission noise with a frequency of 0.03 to 1 GHz. ) Was measured. During measurement, a noise measuring filter was attached to the noise filter to shield external noise. The measurement results are shown in FIG.

  As shown in FIG. 3, it can be seen that the dielectric constant of the noise filter is high when barium titanate is added to the insulating layer. Specifically, as shown by arrows (A) and (B) in FIG. 3, when alumina is added, the dielectric constant width is about 1 to 6, whereas barium titanate is insulated. When added to the layer, it can be seen that the dielectric constant width can be as wide as about 1 to 16 by changing the addition amount. From this result, it is easy to control the frequency characteristics of the noise filter, and if the capacitor capacity is the same, the thickness of the insulating layer can be reduced, and the overall thickness of the substrate can be reduced accordingly. I understand.

  And as shown in FIG. 4, the frequency in the attenuation | damping peak of the noise filter obtained in (Examples 1-3) is different, and it turns out that filter characteristics can be adjusted by changing the addition amount of barium titanate. .

It is sectional drawing of the noise filter in embodiment of this invention. It is the equivalent circuit of the noise filter in embodiment of this invention. It is a graph which shows the measurement result in an Example and a comparative example. It is a graph which shows the measurement result in an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Noise filter 10 Carbon substrate 11A, 11B Insulating layer 12A, 12B Electrode board 13 Through hole 131 Inner peripheral surface 14 Coil member 141 Insulation coating 15 Solder

Claims (6)

  A noise filter in which electrode plates are provided on both surfaces of a carbonaceous substrate also serving as a ground terminal via an insulating layer, and a through hole is formed in the carbonaceous substrate, and a coil member is embedded in the through hole. The electrode plates are connected to each other, and the coil member and the inner peripheral surface of the through hole are insulated, and the electrode plate, the carbonaceous substrate, and the coil member are arranged in parallel to the coil member. And a capacitor formed by the carbonaceous substrate to constitute an equivalent circuit of a π-type filter, and the insulating layer contains a ferroelectric ceramic material.   2. The noise filter according to claim 1, wherein the ferroelectric ceramic material contains barium titanate.   3. The noise filter according to claim 1, wherein a total of three lead wires are connected to the electrode plate and the carbonaceous substrate.   The noise filter according to any one of claims 1 to 3, wherein the coil member is provided with an insulating coating so that the coil member and the inner peripheral surface of the through hole are insulated.   5. The noise filter according to claim 1, wherein the carbonaceous substrate is a carbon composite material in which carbon fibers are arranged along a thickness direction of the substrate.   The noise filter according to any one of claims 1 to 5, wherein the carbonaceous substrate has fine holes, and the fine holes are impregnated with an inorganic coating agent, a thermosetting resin, or a metal. And a noise filter.

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