JP6715489B2 - Method for forming paste that suppresses electromagnetic noise - Google Patents

Description

The present invention relates to a method of forming a paste that suppresses electromagnetic noise. By applying a paste that suppresses electromagnetic noise to a necessary portion of an electronic device, it becomes a sheet that prevents unnecessary electromagnetic waves emitted from the electronic device from leaking to the outside or from interfering with an internal circuit. Alternatively, it becomes a sheet that prevents unwanted electromagnetic waves from the outside from entering the electronic device and interfering with the internal circuit.

2. Description of the Related Art In recent years, electronic devices such as mobile phones and personal computers that use high-frequency signals have become very popular. For example, some mobile phones and wireless LANs use high frequency signals ranging from several GHz to 10 GHz. Furthermore, in addition to increasing the frequency of signals used by electronic devices, along with the miniaturization, thinning, and higher performance of electronic devices, malfunctions due to electromagnetic interference in electronic devices and interference due to radiation noise to the outside of the device Is a problem. Therefore, the CISPR22 standard of the International Commission on Radio Interference (CISPR) issued in 2005 regulates electromagnetic noise of up to 6 GHz.

The absorbed energy P of electromagnetic noise is given by Equation 1. The first term is the absorption of electromagnetic noise by the soft magnetic material, and a magnetic loss occurs according to the size of the complex part μ″ of the complex magnetic permeability and the frequency, and this magnetic loss replaces heat. This is the absorption of electromagnetic noise due to the dielectric material, and a dielectric loss occurs depending on the size of the complex part ε″ of the complex dielectric constant and the frequency, and this dielectric loss is also replaced by heat. The third term is the absorption of electromagnetic noise due to conductivity, and a conductive current flows on the surface due to the skin effect of a high-frequency electric field to form a resistance film, and this resistance film changes resistance depending on the magnitude of conductivity σ. This causes a loss, and this resistance loss also replaces heat. Therefore, in the frequency band of electromagnetic noise, if the soft magnetic material has a complex part μ” of a complex magnetic permeability of a certain size, or the dielectric material has a complex part ε” of a complex dielectric constant of a certain size. With it, electromagnetic noise that covers a certain frequency band is absorbed. In Formula 1, E is the magnitude of the electric field in the electromagnetic noise, H is the magnitude of the magnetic field in the electromagnetic noise, f is the frequency of the electromagnetic noise, and σ is the conductivity. When a magnetic body (or a dielectric body) receives an alternating magnetic field (or an alternating electric field) due to electromagnetic noise, a change in magnetic flux density (or electric flux density) causes a phase delay, and the magnetic permeability (or dielectric constant) is , Μ′-jμ″ which is the difference between the real part μ′ and the imaginary part μ″ (or the complex permittivity is given by the difference ε′−jε″ between the real part ε′ and the imaginary part ε″) ..

Number 1
P=πfμ″H ² +πfε″E ² +1/ ² ·σE ²

Conventionally, the performance of a base material relating to electromagnetic noise has been mainly based on the magnetic permeability of the base material. That is, for electromagnetic noise up to around 100 MHz, the magnetic flux converging effect by the real part μ′ of the complex magnetic permeability of the soft magnetic material shields the magnetic field and brings about the magnetic shield effect. In addition, the magnetic loss effect due to the imaginary part μ” of the complex magnetic permeability absorbs electromagnetic noise and converts it into heat, resulting in the effect of suppressing electromagnetic noise. However, many soft magnetic materials are complex at frequencies below 100 MHz. The real part μ'of the magnetic permeability decreases, and decreases sharply as the value of μ'increases. On the other hand, the complex part μ'' of the complex magnetic permeability increases sharply from the frequency before the frequency at which μ'shows the peak value. It exhibits a peak value at a constant frequency, decreases as it goes away from the frequency exhibiting the peak value, and does not have a required magnitude in a frequency band exceeding 500 MHz. Further, the radiation source of electromagnetic noise, that is, the distance between the electronic component and the sheet that suppresses electromagnetic noise is the region of the near electromagnetic field that is shorter than the wavelength of electromagnetic noise, which increases the surface resistance of the soft magnetic material and reduces electromagnetic noise. Need not be reflected on the surface of the substrate.

Therefore, if the imaginary part ε″ of the complex permittivity of the dielectric material has a constant value in the frequency band exceeding 500 MHz, the dielectric loss of the dielectric material based on Formula 1 causes electromagnetic noise in the frequency band exceeding 500 MHz. That is, the dipole of the dielectric (which is called orientation polarization) cannot follow the change of the electric field of 500 MHz or more, and the dielectric dispersion in which the dielectric constant of the dielectric is lowered may occur. This is a phenomenon in which a phase delay occurs in the change of the electric flux density in the alternating electric field of the electromagnetic noise described in paragraph 3. However, in the frequency band of 500 MHz or more, the imaginary part ε″ of the complex permittivity of most dielectrics is Is small. This will be explained by the value of ε″ in the microwave of 2.45 GHz used in the microwave oven.
In the sheet for suppressing electromagnetic noise, the imaginary part ε″ of the complex dielectric constant at 2.45 GHz of the polymer material in which the soft magnetic material is dispersed has a phenol resin of 0.2-0.5 and a urea resin of 0.16−. 0.23, vinyl chloride resin 0.08-0.25, nylon resin 0.12-0.28, cellulose resin 0.03-0.42, synthetic rubber 0.027-0.03, polyethylene Resin is 0.0012 and polypropylene resin is 0.0004, and ε″ of any polymer material is small. On the other hand, the imaginary part ε″ of the complex permittivity of water, which is a typical polar molecule, is as large as 22.0. The size of ε″ of water at 2.45 GHz is used for the principle of heating food in the microwave oven. To be done. That is, when a food is irradiated with a microwave of 2.45 GHz, water molecules contained in the food cannot follow the change of the electric field, and the dielectric loss absorbs the microwave to convert it into heat. On the other hand, the imaginary part ε″ of the complex permittivity of ice at 2.45 GHz is as small as 0.00028, and the ice is not melted by irradiation with microwaves. As described above, it is composed of polar molecules such as water, alcohol, and acetone. Excluding the liquid, the value of the imaginary part ε″ of the complex permittivity in the frequency band of 500 MHz or higher is small, and the electromagnetic noise in the frequency band of 500 MHz or higher cannot be absorbed.

On the other hand, soft magnetic materials except ferrite reflect the electromagnetic noise because they are conductive. Further, if a sheet that suppresses electromagnetic noise is formed directly on an electronic circuit, the circuit is short-circuited. Therefore, if the occupancy rate of the soft magnetic material is reduced to reduce the conductivity of the sheet, the electromagnetic noise absorption capability is reduced in accordance with the reduction of the occupancy rate of the soft magnetic material. Therefore, by laminating the insulating sheets above and below the sheet containing the soft magnetic material as a main component, the reflection of electromagnetic waves by the sheet containing the soft magnetic material as a main component can be prevented, and the short circuit of the circuit can be prevented. However, the process of applying two types of paste and performing heat treatment is repeated three times, which increases the cost for countermeasures against electromagnetic noise. Moreover, since there is no extra space in an electronic circuit in which electronic components such as a mobile phone and a digital still camera are mounted at high density, a laminated sheet cannot be formed.

Various proposals have been made for the above-mentioned problems of the base material that suppresses electromagnetic noise. For example, in Patent Document 1, a technique in which graphite is used as a dielectric constant adjusting agent together with a dielectric substance and/or a magnetic substance as an electromagnetic noise absorber, and the electromagnetic noise absorber is dispersed in rubber or synthetic resin Is proposed. That is, focusing on the complex permittivity of the dielectric material contained in the material composition in the high frequency band, the dielectric loss in the electromagnetic wave absorption characteristics was emphasized.
However, since the composite material of Patent Document 1 has a low specific resistance, if it is directly attached to the circuit board of the electronic component, the circuit may short-circuit, and it is necessary to attach an insulating adhesive tape to the outside of the sheet. .. Also, electromagnetic noise is reflected on the surface. Furthermore, in order for the dielectric material, the magnetic material, and the graphite to act as an electromagnetic noise absorber, an insulation treatment is required in advance, and the insulation treatment increases the manufacturing cost of the noise absorber.

As a technique for solving such a problem, in Patent Document 2, a composite sheet in which a soft magnetic material and a carbon material are dispersed in a synthetic resin is used to have an effect of suppressing high frequency noise in the GHz band, and further, electronic As a measure against short circuit when it is directly attached to the circuit board of parts, a magnetic sheet in which a soft magnetic material with a large surface resistance and an effect of suppressing low frequency noise is dispersed in synthetic resin is laminated on one or both sides of the composite sheet. Is proposed.
However, Patent Literature 2 is in the same category as Patent Literature 1 from the viewpoint of securing the insulating property of the noise suppressing sheet, because the insulating magnetic sheets are laminated in order to secure the insulating property of the noise suppressing sheet. It should be noted that Patent Document 2 has no description of why electromagnetic noise in the GHz frequency band can be absorbed simply by combining a conventional soft magnetic material, graphite, and a polymeric material by a conventional method. There is no description of the values of the imaginary part μ″ of the complex permeability and the imaginary part ε″ of the complex permittivity of the composite sheet in the frequency band of GHz. On the other hand, Patent Document 2 describes that the technique of Patent Document 1 cannot absorb high frequency noise in the GHz frequency band.

JP, 2009-278137, A JP, 2013-182931, A

When the frequency of electromagnetic noise exceeds 500 MHz, it is difficult to actually absorb electromagnetic waves. This is because the value of the imaginary part μ” of the complex magnetic permeability of the soft magnetic material described in the fifth paragraph and the value of the imaginary part ε” of the complex dielectric constant of the dielectric material described in the sixth paragraph are frequencies of 500 MHz or more. It depends on not having the required size in the band. Therefore, the electromagnetic noise that covers a frequency band of 500 MHz or more can only be absorbed by the sheet having a new material structure. Therefore, a first object of the present invention is to realize a sheet that forms a new material structure on the sheet and absorbs electromagnetic noise in the frequency band of 500 MHz to 10 GHz. Further, if the sheet for suppressing electromagnetic noise does not short-circuit the electronic circuit and does not reflect the electromagnetic noise on the surface, the sheet can be formed by applying the paste once. Therefore, the second object of the present invention is that the surface of the sheet is insulative. Due to the skin effect, the electromagnetic noise penetrates only into the surface layer of the base material at higher frequencies, and has a surface layer depth of about 1.5 μm at 1 GHz.
On the other hand, if the surface can be formed with a small amount of base material that absorbs electromagnetic noise, a sheet having high electromagnetic noise receiving sensitivity and high electromagnetic noise absorbing performance can be manufactured at low cost. Furthermore, a sheet that suppresses electromagnetic noise can be formed even in an electronic circuit that has no extra space. Therefore, a third object of the present invention is to have a structure in which a base material that absorbs electromagnetic noise forms a surface with a thickness of a micron level. The sheet that suppresses electromagnetic noise is formed in a general-purpose electronic device. Therefore, the fourth object of the present invention is to manufacture a paste at a low cost by using a cheap raw material. The paste for suppressing electromagnetic noise of the present invention is to realize a paste that solves the four problems associated with a sheet that absorbs these electromagnetic noises.

The method of forming a paste for suppressing electromagnetic noise in the present invention is a method of precipitating a collection of fine particles of a metal oxide having both hard magnetic properties and insulating properties in an insulating organic compound composed of a liquid, In the organic compound in which a collection of oxide fine particles is precipitated, a larger amount of alcohol than the organic compound, the frequency at which the imaginary part of the complex magnetic permeability shows a peak value is higher than that of the soft magnetic ferrite powder, and the complex magnetic permeability. A plurality of types having a first characteristic in which the frequency characteristics of the imaginary part are different from each other, a second characteristic in which the peak value of the imaginary part of the complex magnetic permeability is different from each other, and a third characteristic in which the areas of the flat powders are different from each other A mixture of flat-shaped soft magnetic powders consisting of an alloy of the above, whereby a collection of fine particles of the metal oxide in the organic compound diluted with the alcohol, and a flat shape consisting of the plurality of kinds of alloys. Is a method of forming a paste that suppresses electromagnetic noise, in which a paste having a configuration in which a collection of soft magnetic powders is dispersed.

That is, when the paste according to the present forming method is applied to the base material and then the alcohol is vaporized, the volume of the paste is significantly reduced, and the fine particles of the metal oxide dispersed in the paste and the flat soft magnetic properties of a plurality of alloys are dispersed. The distance to the powder becomes shorter. At this time, the fine particles of the metal oxide having a hard magnetic property are magnetically adsorbed to the closest flat soft magnetic powder. This imparts the hard magnetic property to the flat soft magnetic powder, and the flat soft magnetic powder magnetically attracts each other. As a result, a sheet having a new material structure in which a collection of the magnetically adsorbed flat soft magnetic powders of a plurality of kinds of alloys is confined in the liquid organic compound is formed on the base material. Therefore, a collection of flat soft magnetic powders magnetically attracted spreads over the entire sheet to form a surface, and thus the sensitivity of receiving electromagnetic noise increases. Further, since the compositions of the plurality of kinds of alloys are different from each other, the frequency characteristics of the imaginary part μ of the complex magnetic permeability of the flat soft magnetic powder are different from each other, and the imaginary part of the complex magnetic permeability μ of the collection of the magnetically attracted flat soft magnetic powder μ The frequency characteristic of "is the characteristic obtained by adding the frequency characteristic of the imaginary part μ of the complex magnetic permeability of each flat soft magnetic powder. As a result, the imaginary number of the complex magnetic permeability of a set of flat soft magnetic powders The part μ″ has a constant value in a wide frequency band and absorbs electromagnetic noise of 500 MH to 10 GHz, which has been difficult in the past. The thickness of the sheet is determined by the viscosity of the paste, and the sheet is bonded to the base material by the adhesive force based on the viscosity of the organic compound. It is also possible to apply the paste to the surface of the adhesive tape, vaporize the alcohol after that, and attach the adhesive tape to a necessary portion to use it as a sheet for suppressing electromagnetic noise.
That is, when the soft magnetic powder is subjected to a flattening treatment in the surface direction that is the easy axis direction of magnetization, the demagnetizing factor is reduced, and as the flatness, which is the ratio of the long axis to the thickness, increases, the imaginary part μ” of the complex permeability decreases. On the other hand, due to the skin effect of electromagnetic noise, the higher the frequency is, the shallower the electromagnetic noise enters, and the electromagnetic noise of 10 GHz can only enter the soft magnetic powder to a depth of about 1 μm. In the flat soft magnetic powder that has been flattened to a thickness of less than 1 μm, the entire flat soft magnetic powder participates in the absorption of electromagnetic noise, and a thin sheet having high performance of absorbing electromagnetic noise can be formed.
However, the imaginary part μ″ of the complex magnetic permeability of the flat soft magnetic powder rises and increases at the frequency before the peak value, shows the peak value at a constant frequency, and decreases as the distance from the frequency of the peak value increases. , The frequency band in which the imaginary part μ″ of the complex magnetic permeability has a constant size is limited, and thus the frequency band in which electromagnetic noise can be absorbed by one type of flat soft magnetic powder is limited.
On the other hand, since the alloy flat soft magnetic powder has the following three characteristics, by mixing flat alloy soft magnetic powders of multiple types of alloys, electromagnetic noise ranging from 500 MHz to 10 GHz, which was impossible in the past, can be absorbed. it can. First, the frequency at which the imaginary part μ” of the complex magnetic permeability shows a peak value is higher than that of the soft magnetic ferrite powder, and the frequency at which μ” shows a peak value changes depending on the composition of the alloy. Secondly, the hardness of the alloy changes depending on the composition of the alloy, the oblateness in the flattening process changes depending on the hardness of the alloy, and the larger the oblateness, the larger the peak value of the imaginary part μ″ of the complex magnetic permeability. In addition, the elongation rate of the alloy changes depending on the composition of the alloy.The larger the elongation rate of the alloy, the wider the area of the flat powder in flattening treatment.The wider the area of the flat powder, the higher the sensitivity of receiving electromagnetic noise, and the smaller the soft magnetic powder. Therefore, electromagnetic noise can be absorbed.Therefore, for the flat soft magnetic powders of multiple types of alloys, the flat soft magnetic powders of the alloys are combined so that the frequency at which the imaginary part μ” of the complex permeability shows the peak value spans a wide frequency band. When mixed with each other, the collection of magnetically adsorbed flat soft magnetic powders of multiple types of alloys shows μ” characteristics obtained by adding the μ” characteristics of the flat soft magnetic powders of each alloy, resulting in a wide frequency range. Will have a certain size.
Thus, by using the paste according to the present forming method, a sheet composed of a new material structure in which a collection of magnetically adsorbed flat soft magnetic powders of plural kinds of alloys is confined in a liquid organic compound is formed, and electromagnetic noise is generated. As a sheet for suppressing the above, the following five effects are exhibited.
The first effect is due to the hard magnetic property of the metal oxide fine particles. In other words, when the alcohol is vaporized, the volume of the paste is significantly reduced, the distance between the fine particles of the metal oxide dispersed in the organic compound and the flat soft magnetic powder is shortened, and the hard magnetic metal oxide having spontaneous magnetization is reduced. The particles are magnetically adsorbed on the surface of the nearest flat soft magnetic powder. As a result, the flat soft magnetic powder has a hard magnetic property, and the flat soft magnetic powder magnetically attracts each other between the surfaces. In this way, a thin sheet can be formed with a small amount of flat soft magnetic powder, and a sheet can be formed even in an electronic circuit having no extra space. That is, due to the skin effect, the electromagnetic noise penetrates only into the surface layer of the soft magnetic powder as the frequency increases, and has a surface layer depth of about 1.5 μm at 1 GHz. According to the paste forming method, the flat soft magnetic powder having a thickness of submicron forms 4 to 6 layers and magnetically adsorbs between the surfaces, so that a micron-level thin surface is formed on the entire sheet. , Efficiently absorb electromagnetic noise. As a result, a small amount of flat soft magnetic powder particles are magnetically attracted to each other on their surfaces to form a sheet having a large area and a thin thickness, and efficiently absorbs electromagnetic noise with high performance.
That is, the soft magnetic powder is a soft magnetic material having no spontaneous magnetization and does not stick to each other. Therefore, the flat soft magnetic powder cannot be aligned in the surface direction only by mixing the collection of the flat soft magnetic powder with the polymer material. Therefore, due to the skin effect of electromagnetic noise, as the flatness of the flat soft magnetic powder is higher and the frequency of the electromagnetic noise is higher, most of the flat soft magnetic powder does not participate in the absorption of the electromagnetic noise. As a result, the higher the frequency of electromagnetic noise, the lower the reception sensitivity of electromagnetic noise, and the lower the performance of absorbing electromagnetic noise. In addition, since the flat soft magnetic powder is dispersed in the polymer material to form a sheet, there is always a polymer material between adjacent flat soft magnetic powders, which reduces the electromagnetic noise reception sensitivity and reduces the electromagnetic noise. The ability to absorb noise is also reduced. However, according to the paste of the present forming method, the larger the oblateness is, the overwhelmingly more metal oxide fine particles are magnetically adsorbed on the surface than the side surface of the flattened soft magnetic powder, and the flattened soft magnetic powder faces each other. Magnetically attract each other. As a result, a collection of the magnetically attracted flat soft magnetic powder spreads over the entire sheet to form a thin surface, the electromagnetic noise reception sensitivity is increased, and the electromagnetic noise absorption performance is also improved.
The second function and effect depend on the insulating property of the metal oxide fine particles. That is, the flat soft magnetic powder magnetically adsorbs through a collection of insulating metal oxide fine particles, but eddy current loss due to the metal oxide does not occur. Therefore, the magnetic characteristics of the flat soft magnetic powder are not hindered, and the magnetic characteristics of the flat soft magnetic powder form a collection of the flat soft magnetic powder magnetically adsorbed.
The third effect is due to the flat shape of the soft magnetic powder. That is, since the soft magnetic powder is flattened in the surface direction of the easy axis of magnetization, the diamagnetic field coefficient becomes small, and the imaginary part μ” of the complex permeability increases as the flatness increases. Electromagnetic noise is sufficiently absorbed even by a collection of magnetically adsorbed flat soft magnetic powders of different thickness.The flattening of soft magnetic powders does not depend on long-time batch processing by a ball mill, but atomized soft magnetic powders The flat soft magnetic powder is an inexpensive soft magnetic powder because the flat soft magnetic powder can be continuously obtained in a short time because the attritor processing is performed by using the media stirring mill.
The fourth effect is due to the use of flat soft magnetic powder composed of a plurality of alloys having different alloy compositions. In other words, the alloy flat soft magnetic powder has the following three characteristics. By mixing flat alloy soft magnetic powders of a plurality of types of alloys, electromagnetic noise ranging from 500 MHz to 10 GHz, which has been impossible in the past, is generated. Can be absorbed. First, the frequency at which the imaginary part μ” of the complex permeability shows a peak value is higher than that of the soft magnetic ferrite powder, and the frequency characteristic of the value of the imaginary part μ” of the complex permeability changes depending on the composition of the alloy. Secondly, the hardness of the alloy changes depending on the composition of the alloy, the oblateness in the flattening process changes depending on the hardness of the alloy, and the larger the oblateness, the larger the peak value of the imaginary part μ″ of the complex magnetic permeability. In addition, the elongation of the alloy changes depending on the composition of the alloy, the area of the flat powder in the flattening process changes depending on the elongation of the alloy, and the larger the area of the flat powder, the higher the electromagnetic noise reception sensitivity. Regarding the alloy flat soft magnetic powders, the frequency at which the imaginary part μ” of the complex magnetic permeability shows a peak value covers a wide frequency range. A collection of flat soft magnetic powders of multiple types of alloys shows the characteristic of the imaginary part μ” of the complex permeability obtained by adding the characteristics of the imaginary part μ” of the complex permeability of the flat soft magnetic powders of each alloy. As a result, the value of the imaginary part μ” of the complex magnetic permeability has a constant value in a wide frequency range. Also, since a collection of flat soft magnetic powders composed of multiple kinds of alloys is mixed with a liquid organic compound. , When the alcohols are randomly mixed in the organic compound and the alcohol is vaporized, the randomly mixed flat soft magnetic powders are magnetically adsorbed to form an aggregate of the flat soft magnetic powders. The body exhibits the characteristic of the imaginary part μ” of the complex permeability obtained by adding the characteristic of the imaginary part μ” of the complex permeability of the flat soft magnetic powder of each alloy. As a result, the sheet has a frequency band of 500 MHz to 10 GHz. Absorbs electromagnetic noise that extends to.
The fifth effect is that the organic compound that traps the collection of the flat soft magnetic powder has an insulating property. Therefore, the surface of the sheet exhibits an insulating property and brings about the following four effects. First, it is not necessary to overlay the paste that suppresses electromagnetic noise and the insulating paste. Secondly, applying the paste directly to the electronic circuit does not short circuit the circuit. Third, it does not reflect electromagnetic noise on the surface of the sheet. Fourth, even if the flat soft magnetic powder of the alloy is easily oxidized or corroded by water vapor, the coating of the organic compound blocks the external environment, and the organic compound does not have water absorption, so the flat soft alloy No oxidation or corrosion of magnetic powder occurs.
As described above, the paste according to the present forming method exhibits the above-described five operational effects, and thereby the first, second, and third problems described in the eleventh paragraph can be solved.

The method for forming a paste for suppressing electromagnetic noise described in the 12th paragraph, the fine particles of the metal oxide described in the 12th paragraph are fine particles of maghemite which is a gamma phase of ferric oxide, A paste that suppresses electromagnetic noise according to the method of depositing fine particles of maghemite that is a gamma phase in an insulating organic compound composed of a liquid described in paragraph 12 and forming a paste that suppresses electromagnetic noise described in paragraph 12 Is a method of forming the paste for suppressing electromagnetic noise described in the 12th paragraph.

That is, maghemite has the following three properties, and the soft magnetic powders of the alloy magnetically attract each other through the particles of maghemite to bring about an epoch-making effect.
First, it is an insulator having a specific resistance of 10 ⁶ Ωm. Therefore, the eddy current loss due to maghemite becomes extremely small, and the collection of flat soft magnetic powders of multiple types of alloys magnetically adsorbed by fine particles of maghemite does not hinder the magnetic permeability characteristics of flat soft magnetic powders and Form a mass of magnetic powder. As a result, the collection of flat soft magnetic powders of a plurality of types of alloys absorbs electromagnetic noise ranging from 500 MHz to 10 GHz. Incidentally, the specific resistance of the flat soft magnetic powder is 10 ⁻⁶ −10 ⁻⁷ Ωm, and the eddy current loss is inversely proportional to the specific resistance. Therefore, the eddy current loss due to maghemite is extremely small.
Secondly, it has a kind of ferrimagnetism, which is hard magnetic. Therefore, the maghemite particles with spontaneous magnetization are preferentially magnetically adsorbed on the surface of the alloy flat soft magnetic powder, and the maghemite particles are also magnetically adsorbed, and the magnetically adsorbed maghemite particles are the soft magnetic powder of the alloy. Magnetically attracts to the surface. As a result, the flattened soft magnetic powder of the alloy having the hard magnetic property is magnetically attracted between the surfaces to form an aggregate of the soft magnetic powder. Since the maghemite fine particles once magnetically adsorbed have almost no weight, it is difficult to cancel the magnetic adsorption. Therefore, the collection of the soft magnetic powder of the magnetically adsorbed alloy is not released, and the function of suppressing electromagnetic noise continues to be maintained.
Third, it is a stable oxide and is known as a substance that forms a passive film of iron. Therefore, the surface of the alloy flat soft magnetic powder covered with the aggregation of maghemite particles is protected by the aggregation of maghemite particles.

In the method for forming a paste for suppressing electromagnetic noise described in paragraph 12, the fine particles of maghemite, which is the gamma phase of ferric oxide, produce fine particles of ferrous oxide by thermal decomposition of iron naphthenate, and , fine particles of oxide ferrous, by Rukoto is oxidized to maghemite particles with heat treatment in an air atmosphere, are those prepared in a manner forming an electromagnetic noise suppressing paste according to claim 2 is there.

That is, iron naphthenate undergoes thermal decomposition at 340° C. in the atmosphere to become ferrous oxide FeO. Furthermore, when the temperature rising rate is suppressed to 380° C. and the temperature is kept at 380° C. for a certain period of time, the divalent iron ion Fe ²⁺ in ferrous oxide FeO is oxidized to the trivalent iron ion Fe ^3+, and the oxidation value of it is a gamma phase of ferric _Fe 2 _{O 3} maghemite _γ-Fe 2 _{O 3} is generated.
That is, iron naphthenate, the oxygen ions O constituting the carboxyl group of naphthenic acid ^- is turned ligands, complexes coordinated to iron ions Fe ²⁺ approaching iron ion Fe ^2+. That is, since the oxygen ion O ⁻ approaches and coordinates with the iron ion Fe ²⁺ which is the largest ion, the distance between the two becomes short. This maximizes the distance between the oxygen ion O ⁻ that ^forms a coordinate bond with the iron ion Fe ²⁺ and the ion that forms a covalent bond on the opposite side of the iron ion. In iron naphthenate having such a molecular structure characteristic, when the boiling point of the main component of naphthenic acid is exceeded, the oxygen ion O ⁻ forming the carboxyl group in iron naphthenate is covalently bonded on the opposite side of the iron ion Fe ^2+. The bond with the ion is first split and decomposed into ferrous oxide FeO, which is a compound of iron ion Fe ²⁺ and oxygen ion O ⁻ , and naphthenic acid. Further, when the temperature is raised, the naphthenic acid takes heat of vaporization to be vaporized, and when the vaporization of the naphthenic acid is completed, ferrous oxide FeO is precipitated and the thermal decomposition is completed. Note naphthenic acids in a mixture of saturated fatty acids having 5-membered _ring, represented by the general formula consisting of C _{n H} 2n-1 COOH, main component with a boiling point of 268 ° C., the molecular weight is from _C 9 _H 17 COOH in 170 .. The thermal decomposition reaction of iron naphthenate proceeds at a temperature lower by about 40° C. in the air atmosphere than in the nitrogen atmosphere.
Further, when the temperature rising rate is suppressed to 380° C. in the air atmosphere, the oxidation reaction of the divalent iron ion Fe ²⁺ in ferrous oxide FeO to the trivalent iron ion Fe ³⁺ proceeds. In the initial stage of this oxidation reaction, a part of the divalent iron ion Fe ²⁺ forming the ferrous oxide FeO becomes the trivalent iron ion Fe ³⁺ to become Fe ₂ O ₃ , and the composition formula is FeO. It becomes magnetite Fe ₃ O ₄ of Fe ₂ O ₃ . Further, as the oxidation reaction progresses, all of ferrous oxide becomes magnetite Fe ₃ O ₄ . Further, when kept at 380° C. for a certain period of time, all of the divalent iron ions Fe ²⁺ forming the magnetite FeO·Fe ₂ O ₃ become trivalent iron ions Fe ³⁺ and become ferric oxide Fe ₂ O ₃ . Finish the oxidation reaction. This ferric oxide Fe ₂ O ₃ is maghemite γ-Fe ₂ O ₃ which is a gamma phase of ferric oxide Fe ₂ O ₃ which is a cubic system similar to magnetite Fe ₃ O ₄ . The crystal structure of hematite α-Fe ₂ O ₃ is an alpha-phase ferric oxide Fe ₂ O ₃ is a trigonal, the magnetite crystal structures are different.
Iron naphthenate is an inexpensive industrial chemical that can be easily synthesized. That is, when naphthenic acid which is a general-purpose organic acid is reacted with a strong alkali, an alkali metal naphthenate compound is produced, and when an alkali metal naphthenate compound is reacted with an inorganic iron compound, iron naphthenate is synthesized. Therefore, it is one of the cheapest compounds among organic acid iron compounds. In addition, since naphthenic acid as a raw material has a relatively low boiling point among the boiling points of organic acids, ferrous oxide is precipitated by heat treatment at about 340° C. in the air atmosphere. Iron naphthenate with such properties is commonly used as a dryer for paints/printing inks, adhesives for rubber/tires, extreme pressure agents for lubricating oils, curing agents for polyesters, combustion improvers and polymerization catalysts. ing.
As described above, iron naphthenate is an inexpensive raw material for maghemite described in paragraph 15.

The method of forming a paste for suppressing electromagnetic noise described in the 12th paragraph, the organic compound described in the 12th paragraph has a first property of being dissolved or miscible in an alcohol, and a second property having a higher viscosity than the alcohol. An organic compound having these four properties, which is composed of a third property having a boiling point higher than a heat treatment temperature in an air atmosphere for oxidizing ferrous oxide to maghemite and a fourth property which is an insulator, Suppressing electromagnetic noise according to the method of depositing a group of fine particles of a metal oxide having both hard magnetic properties and insulating properties described in paragraph 12 in an organic compound and forming a paste that suppresses electromagnetic noise described in paragraph 12. This is a method of forming a paste that suppresses electromagnetic noise described in the 12th paragraph.

That is, since the organic compound has four properties, the organic compound serves as a raw material for a paste that suppresses electromagnetic noise, and acts as a coating film that traps a collection of flat soft magnetic powders of a magnetically adsorbed alloy in a sheet that absorbs electromagnetic noise. To do. As a result, the surface of the sheet exhibits insulating properties. In addition, since the collection of the flat soft magnetic powder of the alloy is shielded from the outside by the organic compound, no oxidation or corrosion occurs.
That is, since the organic compound has the first property of being dissolved or mixed in alcohol, when the organic compound was mixed with the alcohol dispersion liquid in which iron naphthenate was dispersed in the alcohol, the iron naphthenate and the organic compound were uniformly mixed. It becomes a mixed solution. Furthermore, since the organic compound has the second property that the viscosity is higher than that of alcohol, the viscosity of the paste that suppresses electromagnetic noise increases according to the blending ratio of the organic compound, and the paste can be applied. Further, the paste thickness after application is determined by the compounding ratio of the organic compound.
Furthermore, the organic compound has the third property that the boiling point is higher than the heat treatment temperature for oxidizing ferrous oxide to maghemite. Therefore, when the above-mentioned mixed solution is heat-treated in the atmosphere, alcohol is first vaporized and fine crystals of iron naphthenate are uniformly precipitated during the organic compounding. When the temperature is further raised to 340° C., iron naphthenate is thermally decomposed, and granular fine particles of ferrous oxide FeO having a size of 40-60 nm are uniformly precipitated in the organic compound. When the temperature rising rate is further suppressed to 380° C. and the temperature is kept at 380° C. for a certain period of time, the divalent iron ion Fe ²⁺ in ferrous oxide FeO is oxidized to the trivalent iron ion Fe ^3+, and the second oxide It becomes granular particles of iron-Fe ₂ O ₃ gamma-phase maghemite. As a result, granular fine particles of maghemite having a size of 40-60 nm are uniformly deposited in the liquid organic compound. This organic compound is mixed with an excess of alcohol and a collection of flat soft magnetic powders made of an alloy to form a paste, and when the paste is applied to the base material and the alcohol is vaporized, the flat soft magnetic alloy is softened. A sheet that absorbs electromagnetic noise is formed on the base material, in which a collection of magnetic powder is confined in a liquid organic compound.
Further, the organic compound has the fourth property of being an insulator. As a result, the surface of the sheet that absorbs electromagnetic noise exhibits insulating properties. Therefore, it is not necessary to apply the paste for suppressing electromagnetic noise and the insulating paste in an overlapping manner. Further, the circuit does not short-circuit even if the paste is directly applied to the circuit board of the electronic component. Also, it does not reflect electromagnetic noise on the surface.
As described above, an organic compound having four properties is a raw material for a paste that suppresses electromagnetic noise, and in a sheet that absorbs electromagnetic noise, the surface is insulative and the flattened soft magnetic alloy is magnetically adsorbed. Prevents the oxidation and corrosion of flat soft magnetic powder by confining a collection of magnetic powder.

The method for forming a paste for suppressing electromagnetic noise described in paragraph 12 is the organic compound described in paragraph 18, wherein the organic compound is a carboxylic acid ester, and the organic compound composed of the carboxylic acid ester is A paste for suppressing electromagnetic noise is formed according to the method of depositing a group of fine particles of a metal oxide having both hard magnetic properties and insulating properties described in the paragraph, and forming the paste for suppressing electromagnetic noise described in the 12th paragraph. , The method of forming a paste for suppressing electromagnetic noise described in paragraph 12.

That is, among the carboxylic acid esters, there are organic compounds having the four properties described in the 18th paragraph in the carboxylic acid esters having a relatively high molecular weight. These carboxylic acid esters serve as a raw material for a paste that suppresses electromagnetic noise, and trap a collection of magnetically adsorbed alloy soft magnetic powders in a sheet that absorbs electromagnetic noise. In addition, carboxylic acid esters having the above four properties are general-purpose industrial chemicals.
Therefore, when an organic compound composed of carboxylic acid esters is mixed with an alcohol dispersion liquid in which iron naphthenate is dispersed in alcohol, a mixed liquid in which iron naphthenate and an organic compound are uniformly mixed in alcohol is obtained. This mixed solution is heat-treated in the atmosphere. When the temperature is raised to 340° C. after vaporizing the alcohol, iron naphthenate is thermally decomposed, and fine particles of ferrous oxide FeO are uniformly deposited on the organic compound. Further, when the temperature rising rate is suppressed to 380° C. and the temperature is kept at 380° C. for a certain period of time, the divalent iron ion Fe ²⁺ of ferrous oxide FeO is oxidized to the trivalent iron ion Fe ^3+, and the oxidation value of The granular particles of ferrous FeO become granular particles of maghemite of the gamma phase of ferric oxide Fe ₂ O ₃ . Furthermore, the heat-treated mixed solution is mixed with an excess of alcohol and a collection of flat soft magnetic powders of a plurality of alloys to form a paste, and when the paste is applied to the base material and the alcohol is vaporized, magnetic adsorption is achieved. A sheet that absorbs electromagnetic noise covered with a liquid organic compound is formed on the base material by gathering the soft magnetic powders of the plurality of types of alloys.
As described above, an organic compound composed of carboxylic acid esters having four properties is a raw material for a paste that suppresses electromagnetic noise, and in a sheet that absorbs electromagnetic noise, the soft magnetic properties of the magnetically adsorbed alloy are used. Enclose a collection of powder. As a result, the surface of the sheet exhibits insulating properties. Further, the soft magnetic powder of the alloy is protected by the organic compound.
ADVANTAGE OF THE INVENTION According to this invention, the sheet|seat which suppresses the electromagnetic noise which covers the frequency band of 500 MHz to 10 GHz is formed with one application of paste, and the paste which wipes off the conventional concept can be implement|achieved. Therefore, using the inexpensive flat magnetic powder described in the 13th paragraph, the inexpensive naphthenic acid described in the 17th paragraph, and the inexpensive organic compound consisting of the above-mentioned carboxylic acid ester, an inexpensive raw material is used. A paste that suppresses electromagnetic noise can be manufactured at a low manufacturing cost based on the manufacturing method described. As a result, the fourth problem explained in the eleventh paragraph was solved.

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FIG. 3 is a diagram schematically illustrating a state in which a collection of flat soft magnetic powders of permalloy magnetically adsorbed by maghemite fine particles are confined with butyl oleate.

Embodiment 1
The present embodiment is an organic compound which is firstly dissolved or miscible in alcohol, secondly has a higher viscosity than alcohol, thirdly has a boiling point higher than 380° C., and fourthly is an insulator and has these four properties. It is an embodiment relating to. As such an organic compound, a carboxylic acid ester having a relatively large molecular weight exists.
On the other hand, carboxylic acid esters include a first ester composed of a saturated carboxylic acid, a second ester composed of an unsaturated carboxylic acid, a third ester composed of an aromatic carboxylic acid, and two carboxyl groups. It is divided into four types of esters consisting of a fourth ester consisting of a dicarboxylic acid having

The first esters, which are saturated carboxylic acids, include acetic acid esters, propionic acid esters, butyric acid esters, bivalic acid esters, caproic acid esters, caprylic acid esters, capric acid esters, and lauric acid. It comprises acid esters, myristic acid esters, palmitic acid esters, stearic acid esters, and the like.
Carboxylic acid esters having a boiling point higher than 380° C., which are soluble or miscible in alcohol and have a higher viscosity than alcohol are stearic acid esters having a molecular weight of butyl stearate or higher. By the way, the boiling point of butyl stearate is 389°C, and the boiling point of octyl stearate is 432°C. Butyl stearate is an insulator having a relative permittivity of 3.1, and octyl stearate is an insulator having a relative permittivity of 3.4.

Next, examples of esters composed of unsaturated carboxylic acids include acrylic acid esters, crotonic acid esters, methacrylic acid esters, and oleic acid esters.
Of these, carboxylic acid esters having a boiling point of higher than 380° C., which are soluble or miscible in alcohol and have a higher viscosity than alcohol, are oleic acid esters having a molecular weight of ethyl oleate or higher. By the way, the boiling point of ethyl oleate is 386°C, and the boiling point of butyl oleate is 415°C. In addition, ethyl oleate is an insulator having a relative dielectric constant of 3.2, and butyl oleate is an insulator having a relative dielectric constant of 4.0.

Further, the esters composed of aromatic carboxylic acids include benzoic acid esters and phthalic acid esters.
Carboxylic acid esters having a boiling point higher than 380° C., which are soluble or miscible in alcohol and have a higher viscosity than alcohol are phthalic acid esters having a molecular weight of bis(2-ethylhexyl) phthalate or higher. By the way, the boiling point of bis(2-ethylhexyl) phthalate is 385° C., and the boiling point of diisononyl phthalate is 403° C. Further, bis(2-ethylhexyl) phthalate is an insulator having a relative permittivity of 5.1, and diisononyl phthalate is an insulator having a relative permittivity of 5.0.

Further, the esters composed of dicarboxylic acids include esters with dicarboxylic acids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, speric acid, azelaic acid, sebacic acid, and fumaric acid. ..
Esters having a boiling point higher than 380° C., which are soluble or miscible in alcohol and have a higher viscosity than alcohol are sebacic acid esters having a molecular weight of dioctyl sebacate or higher. By the way, the boiling point of dioctyl sebacate is 435° C., and it is an insulator with a relative dielectric constant of 4.0.
As described above, among the relatively high molecular weight carboxylic acid esters, there are organic compounds having the four properties described in paragraph 25.

Embodiment 2
The present embodiment relates to an alloy flat soft magnetic powder. When the soft magnetic powder is flattened in the surface direction that is the easy axis of magnetization, the diamagnetic field coefficient is reduced, and the imaginary part μ” of the complex permeability increases as the flatness, which is the ratio of the long axis to the thickness, increases. On the other hand, due to the skin effect of electromagnetic noise, the higher the frequency is, the shallower the electromagnetic noise can enter, and the electromagnetic noise of 10 GHz can only enter the soft magnetic powder to a depth of about 1 μm. In the flat soft magnetic powder that has been flattened to a thin thickness, the entire flat soft magnetic powder participates in the absorption of electromagnetic noise, and it is possible to form a sheet that is thin but has a high performance of absorbing electromagnetic noise.
However, the imaginary part μ″ of the complex magnetic permeability of the flat soft magnetic powder rises and increases at the frequency before the peak value, shows the peak value at a constant frequency, and decreases as the distance from the frequency of the peak value increases. , The frequency band in which the imaginary part μ″ of the complex magnetic permeability has a constant size is limited, and thus the frequency band in which electromagnetic noise can be absorbed by one type of flat soft magnetic powder is limited.
On the other hand, the alloy flat soft magnetic powder has the following three characteristics. By mixing flat alloy soft magnetic powders of multiple kinds of alloys, electromagnetic noise ranging from 500MHz to 10GHz, which was impossible in the past, can be absorbed. .. First, the frequency at which the imaginary part μ” of the complex permeability shows a peak value is higher than that of the soft magnetic ferrite powder, and the frequency at which the imaginary part μ” of the complex permeability shows a peak value changes depending on the composition of the alloy. Secondly, the hardness of the alloy changes depending on the composition of the alloy, the oblateness in the flattening process changes depending on the hardness of the alloy, and the larger the oblateness, the larger the peak value of the imaginary part μ″ of the complex magnetic permeability. In addition, the elongation rate of the alloy changes depending on the composition of the alloy.The larger the elongation rate of the alloy, the wider the area of flat powder in flattening treatment.The larger the area of flattened powder, the higher the sensitivity of receiving electromagnetic noise and the less soft Electromagnetic noise can be absorbed even by magnetic powder.Therefore, for the flat soft magnetic powders of multiple types of alloys, the flat soft magnetic powders of alloys should be designed so that the frequency at which the imaginary part μ” of the complex permeability shows the peak value over a wide frequency band. When mixed and mixed, the collection of flat soft magnetic powders of multiple kinds of magnetically adsorbed alloys is the imaginary number of the complex magnetic permeability obtained by adding the characteristics of the imaginary part μ” of the complex magnetic permeability of the flat soft magnetic powders of each alloy. The characteristic is that of the part μ″, and as a result, it has a constant size in a wide frequency range.

On the other hand, alloy soft magnetic materials include silicon steel in which a small amount of silicon is added to iron, permalloy in which nickel is added to iron, sendust in which silicon and aluminum are added to iron, and cobalt in which iron is added. There are mendules and electromagnetic stainless steels made by adding chromium and silicon to iron. Among them, silicon steel becomes brittle when the content of silicon increases, and the flattening process cannot be performed. Therefore, the amount of silicon added needs to be suppressed to 10% or less. Further, the manufacturing cost of permalloy increases as the amount of nickel added increases, and the permeability decreases when the amount of nickel added is small. Therefore, the amount of nickel must be suppressed to about 50%. In addition, sendust is not suitable for flattening because of its high hardness. Further, since permendur is an alloy with cobalt, its manufacturing cost is high and it is not suitable as a raw material for a sheet that suppresses electromagnetic noise. Further, it is preferable to add aluminum in order to facilitate flattening of electromagnetic stainless steel. For this reason, two types of silicon steels containing 3% and 6% of silicon, permalloy containing 50% of nickel, iron with 7% chromium, 1% silicon and 1.6% aluminum. The flat soft magnetic powders of four types of alloys made of electromagnetic stainless steel with the additions of and are described. The flat soft magnetic powder of the alloy is not limited to these four types. In other words, when the addition amount of nickel is changed in Permalloy, when the addition amount of silicon is changed in silicon steel, and when the addition amount of chromium is changed in electromagnetic stainless steel, the frequency at which the imaginary part μ” of the complex permeability shows a peak value The peak value of the imaginary part μ” of the complex magnetic permeability changes, and the production of such an alloy is easy. Therefore, the compositions of the four alloys are merely examples.

In the manufacture of flat soft magnetic powder of an alloy, first, a spherical alloy powder is created by atomizing argon gas. Next, the alloy powder is continuously subjected to an attritor treatment by using a media agitation type pulverizer, and the alloy powder is subjected to a flattening treatment under the condition that the flattening becomes saturated. At this time, flattening progresses according to the hardness of the alloy, and the flatness increases as the hardness decreases. Further, as the elongation of the alloy increases, the area of the flat powder, that is, the particle size increases. Among the four alloys described above, the hardness is lower in the order of permalloy, silicon steel with 3% silicon, electromagnetic stainless steel, and silicon steel with 6% silicon, and the flatness is 38, 34, 29, 23 in this order. The flattened powder of is obtained. Further, in the above-mentioned four kinds of alloys, permalloy, electromagnetic stainless steel, silicon steel having 3% of silicon, and silicon steel having 6% of silicon have a higher elongation rate, and therefore, in this order, the average grain size is Flattened powders of 14 μm, 12 μm, 9 μm and 8.5 μm are obtained. Therefore, the average thickness of the flat soft magnetic powder is 0.37 μm for permalloy, 0.41 μm for electromagnetic stainless steel, 0.26 μm for silicon steel with 3% silicon, and 0.37 μm for silicon steel with 6% silicon. Since any of the flat soft magnetic powders has a thickness sufficiently smaller than 1 μm, even if the electromagnetic noise is 10 GHz, the electromagnetic noise penetrates into the entire flat soft magnetic powder, and the flat soft magnetic powder efficiently absorbs the electromagnetic noise. ..
Next, the frequency and the peak value at which the imaginary part μ” of the complex magnetic permeability shows a peak value were measured by the S parameter method using a network analyzer. The frequency and the peak value at which the imaginary part μ” of the complex magnetic permeability showed a peak value. Is 8.8 at 3.3 GHz permalloy, 8.7 at 5.9 GHz for silicon steel with 3% silicon, 7.5 for electromagnetic stainless steel at 4.8 GHz and 6.5 for silicon steel with 6% silicon. It became 5.7 at 0 GHz. In the present invention, since a collection of flat soft magnetic powders can be formed by randomly magnetically adsorbing the collection of flat soft magnetic powders through the fine particles of maghemite, when the flat soft magnetic powders of these four alloys are mixed. The frequency band and performance of electromagnetic noise that can be absorbed can be changed according to the mixing ratio.
Here, a description will be given of the frequency at which the imaginary part μ” of the complex magnetic permeability of the flat soft magnetic powder of four kinds of alloys shows a peak value and the compounding of the flat soft magnetic powder by the peak value of the imaginary part μ” of the complex magnetic permeability. .. The frequency at which the imaginary part μ″ of the complex permeability of Permalloy has a peak value is the lowest at 3.3 GHz, and the value of the imaginary part μ″ of the complex permeability at 3.3 GHz is the highest at 8.8. The value of the imaginary part μ″ of the complex permeability of Permalloy intersects the value of the imaginary part μ″ of the complex permeability of silicon steel having 3% silicon at 4.7 GHz. Therefore, the value of the imaginary part μ″ of the complex permeability of permalloy is the largest in the frequency band up to 4.7 GHz. Therefore, the electromagnetic noise in the relatively low frequency band is absorbed as the compounding ratio of permalloy is increased. In contrast, the frequency at which the imaginary part μ” of the complex magnetic permeability of silicon steel with 3% silicon has a peak value is as high as 5.9 GHz, and the imaginary part μ” of the complex magnetic permeability at 5.9 GHz is Therefore, the value of the imaginary part μ″ of the complex permeability is the largest in the frequency band of 5.9 GHz or higher in the silicon steel containing 3% of silicon. Therefore, the electromagnetic noise in a relatively high frequency band can be absorbed as the blending ratio of silicon steel containing 3% of silicon is increased. The frequency at which the imaginary part μ” of the complex permeability of electromagnetic stainless steel exhibits a peak value, and the imaginary part μ” of the complex permeability of permalloy and silicon steel containing 3% of silicon is the middle of the frequency at which the peak value appears. 4.8 GHz, and the value of the imaginary part μ” of the complex permeability at 4.8 GHz is not low at 7.5. Therefore, if the compounding ratio of electromagnetic stainless steel is increased, it will reach an intermediate frequency band of 2-8 GHz. In addition, the frequency at which the imaginary part μ” of the complex permeability of silicon steel in which silicon is 6% shows a peak value is 6.0 GHz, which is the highest frequency, but 6.0 GHz. Since the peak value of the imaginary part μ” of the complex permeability in 5.7 is as low as 5.7 and the peak value of the imaginary part μ” of the complex permeability of electromagnetic stainless steel is smaller, the role of absorbing electromagnetic noise in the intermediate frequency band Is inferior to electromagnetic stainless steel. The frequency at which the imaginary part μ″ of the complex magnetic permeability of the silicon steel containing 3% of silicon intersects the value of the imaginary part μ″ of the complex magnetic permeability of the electromagnetic stainless steel is 4.2 GHz. At frequencies below 0.2 GHz, electromagnetic stainless steel has a higher electromagnetic noise absorption performance, and at frequencies above 4.2 GHz, silicon steel with 3% silicon has a higher electromagnetic noise absorption performance.

The first case of using the alloy flat soft magnetic powder is a case of absorbing electromagnetic noise in a relatively low frequency band. Since permalloy has the lowest hardness, it has the highest oblateness, and since it has the highest elongation, it has the highest average particle size. Further, in the frequency band of 4.7 GHz or less, the value of the imaginary part μ″ of the complex permeability is the largest, and the imaginary part μ″ of the complex permeability has a value of 5.6 even at 1 GHz. Therefore, it is desirable to use Permalloy for the sheet that absorbs electromagnetic noise in the frequency band of 4.7 GHz or less.
The second case using the alloy flat soft magnetic powder is a case of absorbing electromagnetic noise in a relatively high frequency band. Silicon steel with 3% silicon has the third smallest average grain size because of its low elongation, but it has a complex magnetic permeability in the frequency band of 4.7 GHz or higher that intersects the value of the imaginary part μ” of the complex magnetic permeability of Permalloy. Has the largest imaginary part μ″ of the complex magnetic permeability even at 10 GHz and has a value of 5.8. Therefore, a sheet that absorbs electromagnetic noise in the frequency band of 4.7 GHz or higher is made of silicon. It is desirable to use 3% silicon steel.
The third case of using the alloy soft magnetic powder is the case of absorbing electromagnetic noise in a wide frequency band. The frequency at which the imaginary part μ” of the complex magnetic permeability indicated by Permalloy intersects with the value of the imaginary part μ” of the complex magnetic permeability indicated by silicon steel containing 3% of silicon is 4.7 GHz, which is less than 4.7 GHz. In the frequency band, the value of the imaginary part μ″ of the complex permeability of permalloy is the largest, and in the frequency band of 4.7 GHz or higher, the value of μ″ of silicon steel with 3% silicon is the largest. On the other hand, electromagnetic stainless steel has an average grain size 1.3 times larger than that of silicon steel containing 3% silicon. The frequency at which the imaginary part μ” of the complex magnetic permeability of electromagnetic stainless steel intersects the value of the imaginary part μ” of the complex magnetic permeability of permalloy is 5.2 GHz, which is a frequency band of 5.2 GHz or more. Then, the value of the imaginary part μ″ of the complex permeability of silicon steel having 3% of silicon is larger than the value of the imaginary part μ″ of the complex permeability of electromagnetic stainless steel. Therefore, if the flat soft magnetic powder made of electromagnetic stainless steel is added to the flat soft magnetic powder of permalloy and the flat soft magnetic powder of silicon steel containing 3% of silicon, the flat soft magnetic powder of three kinds of alloys is mixed to obtain 2 The performance of absorbing electromagnetic noise in the intermediate frequency band up to −8 GHz is improved. In particular, the electromagnetic stainless steel has a peak value of the imaginary part μ” of the complex permeability of permalloy from 3.3 GHz to 4.8 GHz which shows the imaginary part μ” of the complex permeability of the silicon steel containing 3% of silicon. The performance of absorbing electromagnetic noise in the frequency band up to is improved. As a result, electromagnetic noise from 500 MHz to 10 GHz can be absorbed.
Details of three cases using the above-described alloy flat soft magnetic powder will be described in Examples.

Example 1
This example is an example in which a collection of flat soft magnetic powder of permalloy and a collection of fine particles of maghemite are dispersed in butyl oleate diluted with methanol. As the flat soft magnetic powder, a permalloy flat soft magnetic powder (for example, a product developed by Sanyo Special Steel) containing 50% nickel was used. The flat soft magnetic powder has an oblateness of 38 and an average particle diameter of 14 μm. Also, the imaginary part μ″ of the complex magnetic permeability sharply rises from around 10 MHz, shows a peak value of 8.8 at 3.3 GHz, gently decreases from 4 GHz, and has a value of 3.5 at 10 GHz. Iron naphthenate (for example, a product of Toei Kako Co., Ltd.) was used as a raw material for maghemite. Butyl oleate (for example, a product of Junsei Kagaku Co., Ltd.) was mixed with methanol and had a viscosity of 8.6 times that of methanol. It is an insulator having a boiling point of 415° C. and a dielectric constant of 4.0.
First, a mass of maghemite particles is precipitated in butyl oleate. Therefore, 40 grams corresponding to 0.1 mole of iron naphthenate is dispersed in methanol as 10% by weight, and 17 grams corresponding to 0.05 mole of butyl oleate is mixed in the methanol dispersion. This mixed solution is heat-treated in the atmosphere. First, the temperature of the mixed solution is raised to 65° C. to evaporate methanol to uniformly precipitate fine iron naphthenate crystals in butyl oleate. Next, the mixed solution was heated to 340° C. at a heating rate of 40° C./min, and left at 340° C. for 5 minutes to thermally decompose iron naphthenate, and fine particles of ferrous oxide FeO were added to butyl oleate. Precipitate uniformly. Thereafter, the temperature was raised to 380° C. at a temperature rising rate of 1° C./min, and the mixture was allowed to stand at 380° C. for 30 minutes to convert ferrous oxide FeO to maghemite γ- which is a gamma phase of ferric oxide Fe ₂ O _3. Oxidation to Fe ₂ O ₃ and uniform precipitation of 0.1 mol of maghemite fine particles in 0.05 mol of butyl oleate.
Next, 57 grams of permalloy flat powder and 160 grams corresponding to 5 moles of methanol are mixed with the heat-treated mixed solution. Thus, a paste in which a collection of maghemite fine particles and a collection of permalloy flat powders are dispersed in butyl oleate diluted 10.4 times with methanol is prepared.

Next, the above-mentioned paste was printed on the substrate with a thickness of 50 μm, and methanol was vaporized to form a sheet. The surface resistance of this sheet was measured by a surface resistance meter (for example, surface resistance meter ST-4 manufactured by Simco Japan Co., Ltd.). Since the surface resistance value was 1×10 ¹³ Ω/□ or more, the sheet surface has the insulating property of butyl oleate.
Next, the site where the sheet was formed was cut, and the cut surface was observed with an electron microscope to examine the structure of the sheet that suppresses electromagnetic noise. As the electron microscope, an extremely low accelerating voltage SEM manufactured by JFE Techno Research Co., Ltd. was used. This device is capable of observing the surface with an extremely low accelerating voltage from 100 V, and has a feature that the surface of the sample can be directly observed without forming a conductive film on the sample.
From the observation of the cut surface, the thickness of the sheet was 5.8 μm. Next, the secondary electron beam between 900-1000 V of the reflected electron beam was extracted and image processing was performed. A substance having a thickness of 0.37 [mu]m and a length of 14 [mu]m was bonded to four layers through a collection of 40-60 nm-sized granular fine particles.
Further, regarding a substance having a thickness of 0.37 μm and a length of 14 μm and granular fine particles having a size of 40-60 nm, energy between 900-1000 V of the reflected electron beam is extracted and image processing is performed. The material of the fine particles was observed according to the contrast of the image. Since light and shade were observed in both, it was found that both were formed from multiple types of elements.
Next, the energy of the characteristic X-ray and its intensity were image-processed to analyze the elements. A substance having a thickness of 0.37 μm and a length of 14 μm was found to be permalloy because both iron atoms and nickel atoms were present in a uniform ratio of 1:1 and no uneven distribution was observed. It was Further, it was found that the granular fine particles consisted of iron oxide because both iron atoms and oxygen atoms were uniformly present and no uneven distribution was observed. Further, an EBSP analysis function was added to the SEM function to analyze the crystal structure. As a result, it was confirmed that the particulate particles were maghemite γ-Fe ₂ O ₃ .
From these results, the following was found. The flat soft magnetic powder of permalloy is magnetically adsorbed to each other through a collection of granular particles of maghemite to form a collection of flat soft magnetic powder composed of four layers, and the collection of the flat soft magnetic powder has a thickness of about 1.5 μm. Then, a sheet having a thickness of 5.8 μm, which was confined with butyl oleate to suppress electromagnetic noise, was formed. FIG. 1 schematically shows this result. FIG. 1 shows that permalloy flat soft magnetic powder 1 is magnetically adsorbed in four layers by a collection of maghemite fine particles 2, and the magnetically adsorbed permalloy flat soft magnetic powder 1 is collected in butyl oleate 3 It is the figure which expanded and showed the state of being confined typically.

A sheet was formed on the microstrip line using the above-mentioned paste, and the performance of suppressing electromagnetic noise was evaluated. After printing a paste having a width of 50 mm, a length of 25 mm and a thickness of 50 μm on a substrate on which a microstrip line having a length of 140 mm, a width of 30 mm and a characteristic impedance adjusted to 50Ω was printed, methanol was vaporized, The length direction of the noise suppression sheet was aligned with the length direction of the microstrip line, and the sheets were attached so that their centers coincided with each other to obtain a noise suppression sheet. After that, the S parameter was measured using a network analyzer (N5230A, product of Agilent Technologies, Inc.) connected to the microstrip line. Note that the transmission loss in the microstrip line is the amount of electromagnetic noise absorbed from the S parameter S ₁₁ due to reflection and the S parameter S ₁₂ due to transmission according to the following mathematical formula 2.
The measurement results show that the reflection amount is -36 dB and the absorption amount is 15% at 500 MHz, the reflection amount is -34 dB and the absorption amount is 20% at 1 GHz, and the absorption amount is -32 dB and the absorption amount is 28% at 3.3 GHz. At 5 GHz, the reflection amount was −32 dB and the absorption amount was 15%. At 10 GHz, the reflection amount was −30 dB and the absorption amount was 18%. The absorption amount was 15% or more in the frequency band of 500 MHz to 9.5 GHz. Further, since the surface of the sheet is insulating, it absorbs electromagnetic noise without reflecting it.

Number 2
Reflection amount (dB)=20 log|S ₁₁ |
Transmission amount (dB)=20 log|S ₁₂ |
Absorption ^{_{(%) = (1- | S}} 11 | 2 - | S 12 | 2) × 100

Example 2
In this embodiment, flat soft magnetic powder made of silicon steel containing 3% of silicon (for example, a product developed by Sanyo Special Steel Co., Ltd.) is used as the flat soft magnetic powder of the alloy. The flat soft magnetic powder made of silicon steel containing 3% of silicon has an oblateness of 34 and an average particle diameter of 9 μm. Also, the imaginary part μ″ of the complex magnetic permeability has a required size in the high frequency band in contrast to the permalloy of Example 1. It gradually increases from around 10 MHz and has a value of 2.3 at 1 GHz, It crosses the value of the imaginary part μ” of the complex permeability of Permalloy at 4.7 GHz, shows a peak value of 8.7 at 5.9 GHz, decreases gently from around 6.3 GHz, and has a value of 5.9 even at 10 GHz. And has a value of 3.7 at 12 GHz. Above 4.7 GHz, the value of the imaginary part μ″ of the complex magnetic permeability is larger than that of permalloy.
As in Example 1, fine particles of maghemite corresponding to 0.1 mol are precipitated in 0.05 mol of butyl oleate. Next, 57 grams of silicon steel flat soft magnetic powder and 5 moles of methanol are mixed with butyl oleate. The mixed liquid thus prepared is used as a paste.

Next, in the same manner as in Example 1, the paste was printed on the substrate to a thickness of 50 μm, and methanol was vaporized to form a sheet. The surface resistance of this sheet was measured by a surface resistance meter. Since the surface resistance value was 1×10 ¹³ Ω/□ or more as in Example 1, the sheet surface has an insulating property.
Next, in the same manner as in Example 1, the portion where the sheet was formed was cut, and the cut surface was observed with an electron microscope to examine the structure of the sheet that suppresses electromagnetic noise. As a result, the thickness of the sheet was 5.9 μm. Moreover, the flat soft magnetic powder of silicon steel is magnetically adsorbed through a collection of granular particles of maghemite to form a collection of flat soft magnetic powder composed of 6 layers, and the collection of flat soft magnetic powder is about 1.6 μm. And was confined with butyl oleate to form a sheet having a thickness of 5.9 μm for suppressing electromagnetic noise. A diagram of the structure of the cross section of the sheet is omitted because it is similar to FIG.
Further, similarly to Example 1, a sheet was formed on the microstrip line using the paste of this example, and the performance of suppressing electromagnetic noise was evaluated. The measurement result shows that the reflection amount is -36 dB and the absorption amount is 8% at 500 MHz, the reflection amount is -34 dB and the absorption amount is 12% at 1 GHz, the absorption amount is -32 dB and the absorption amount is 21% and 5.9 GHz at 3 GHz. The reflection amount was −30 dB, the absorption amount was 28%, and the reflection amount was −28 dB and the absorption amount was 21% at 10 GHz. As a result, the absorption amount was 15% or more in the frequency band of 1.7-11.6 GHz. Further, since the surface of the sheet is insulating, it absorbs electromagnetic noise without reflecting it.

Example 3
This embodiment is an example in which three types of flat soft magnetic powders of permalloy, silicon steel containing 3% of silicon, and electromagnetic stainless steel are used as the flat soft magnetic powders of the alloy. The flat soft magnetic powder of Permalloy was the one used in Example 1, and the flat soft magnetic powder of silicon steel containing 3% of silicon was the one used in Example 2. In addition, the flattened soft magnetic powder (for example, a product developed by Sanyo Special Steel) made of electromagnetic stainless steel in which 7% chromium, 1% silicon and 1.6% aluminum are added to iron has an oblateness of 29. The average particle size is 12 μm. The imaginary part μ” of the complex magnetic permeability sharply increases from around 10 MHz, has a value of 3.4 at 1 GHz, intersects with μ” of silicon steel at 4.2 GHz, and has a peak value of 7. 5 shows a gradual decrease from around 5.5 GHz, has a value of 4.8 even at 10 GHz, and has a value of 3.1 at 12 GHz. Therefore, when the flat soft magnetic powder made of electromagnetic stainless steel is mixed with the flat soft magnetic powder of permalloy and the flat soft magnetic powder of silicon steel containing 3% of silicon, the flat soft magnetic powder of three kinds of alloys is mixed, The performance of absorbing electromagnetic noise in the intermediate frequency band up to 8 GHz is improved, and especially from 3.3 GHz at which the imaginary part μ” of the complex permeability of permalloy shows a peak value, the complex permeability of silicon steel containing 3% silicon The performance of absorbing electromagnetic noise in the frequency band up to 4.8 GHz where the imaginary part μ” of the magnetic susceptibility shows a peak value is improved.
In the same manner as in Example 1, 0.1 mol of maghemite fine particle aggregates is precipitated in 0.05 mol of butyl oleate. Next, 18 g of the flat soft magnetic powder of permalloy, 18 g of the flat soft magnetic powder of silicon steel, and 21 g of the soft magnetic powder of electromagnetic stainless steel were mixed, and the mixed flat soft magnetic powder was collected. And 5 mol of methanol are mixed with butyl oleate. The mixed liquid thus prepared is used as a paste.

Next, in the same manner as in Example 1, the paste was printed on the substrate to a thickness of 50 μm, and methanol was vaporized to form a sheet. The surface resistance of this sheet was measured by a surface resistance meter. Since the surface resistance value was 1×10 ¹³ Ω/□ or more as in Example 1, the sheet surface has an insulating property.
Further, as in Example 1, the portion where the sheet was formed was cut and the cut surface was observed with an electron microscope to examine the structure of the sheet that suppresses electromagnetic noise. As a result, the thickness of the sheet was 6.0 μm. Further, the three kinds of flat soft magnetic powders are magnetically adsorbed through a collection of granular particles of maghemite to form a collection of flat soft magnetic powders composed of 5 layers, and the collection of the flat soft magnetic powders is about 1.7 μm. And was confined with butyl oleate to form a sheet having a thickness of 6.0 μm for suppressing electromagnetic noise. A diagram of the structure of the cross section of the sheet is omitted because it is similar to FIG.
Next, as in Example 1, the paste of this Example was used to form a sheet on the microstrip line, and the performance of suppressing electromagnetic noise was evaluated. The measurement result shows that the reflection amount is -36 dB and the absorption amount is 18% at 500 MHz, the reflection amount is -34 dB and the absorption amount is 24% at 1 GHz, and the reflection amount is -32 dB and the absorption amount is 36% at 3.3 GHz. At 7 GHz, the reflection amount was −30 dB, the absorption amount was 38%, at 5.9 GHz, the reflection amount was −28 dB, the absorption amount was 37%, and at 10 GHz, the reflection amount was −26 dB and the absorption amount was 28%. As a result, a high absorption amount of 18% or more was obtained in a wide frequency band of 500 MHz to 11.6 GHz, and a high absorption amount of 24% or more was obtained in a wide frequency band of 1-10 GHz. Further, since the surface of the sheet is insulating, it absorbs electromagnetic noise without reflecting it.

In Example 3, flat soft magnetic powders of three types of alloys having different frequencies at which the imaginary part μ” of the complex magnetic permeability shows a peak value are used, and the flat soft magnetic powders are randomly magnetically adsorbed to obtain flat soft magnetic properties. Since the powder aggregate is formed, the frequency range of electromagnetic noise that can be absorbed is significantly widened and noise absorption is greater than in the case of magnetically adsorbing the flat soft magnetic powder of the single alloy of Example 1 and Example 2. As a result, it has become possible to absorb electromagnetic noise in a wide frequency band from 500 MHz to 10 GHz, which was difficult in the past, and the sheet that absorbs electromagnetic noise is magnetically adsorbed. Since the collection of flat soft magnetic powders is confined by an organic compound composed of an insulating liquid, the sheet surface has a high insulating property and has a low reflection amount of electromagnetic noise in a wide frequency band of 500 MHz to more than 10 GHz, and It was possible to realize an epoch-making sheet that absorbs a large amount of electromagnetic noise, and because it was confirmed that the collection of flat soft magnetic powder efficiently absorbs electromagnetic noise even with a thickness of less than 2 μm, It was confirmed that even with the amount of flat soft magnetic powder used, a sheet with epoch-making performance can be realized by magnetically adsorbing it on a surface.In addition, a sheet with a thin insulating film of about 6 μm that absorbs electromagnetic noise Even if it is formed as a sheet, it is possible to realize an epoch-making sheet that has a low reflection amount of electromagnetic noise and a high absorption amount of electromagnetic noise. It was confirmed that the sheet can be formed even in an electronic circuit that does not have a large space.
The example of combining the flat soft magnetisms of a plurality of types of alloys is not limited to the third embodiment. In other words, when flat soft magnetic powders of alloys are combined so that the frequency at which the imaginary part μ” of complex magnetic permeability shows a peak value extends over a wide frequency band, the collection of flat soft magnetic powders magnetically adsorbed is The characteristics of the imaginary part μ” of the complex permeability obtained by adding the characteristics of the imaginary part μ” of the complex permeability of the flat soft magnetic powder are shown. As a result, the imaginary part μ” of the complex permeability is constant over a wide frequency range. It can have a size and can absorb electromagnetic noise in a wide frequency band.

1 Permalloy flat soft magnetic powder 2 Maghemite particles 3 Butyl oleate

Claims (5)

A method of forming a paste that suppresses electromagnetic noise is performed by precipitating a collection of fine particles of a metal oxide having both hard magnetism and insulating properties in an insulating organic compound composed of a liquid, and further An organic compound in which a collection of fine particles is deposited has a larger amount of alcohol than the organic compound, and the frequency at which the imaginary part of the complex magnetic permeability shows a peak value is higher than that of the soft magnetic ferrite powder, and the imaginary part of the complex magnetic permeability. From a plurality of kinds of alloys having both the first characteristics having different frequency characteristics, the second characteristics having different peak values of the imaginary part of the complex magnetic permeability, and the third characteristics having different flat powder areas. A mixture of flat-shaped soft magnetic powders is mixed, whereby in the organic compound diluted with the alcohol, a collection of fine particles of the metal oxide, and a flat-shaped soft magnetic material composed of the plurality of kinds of alloys are mixed. A method of forming a paste that suppresses electromagnetic noise, wherein a paste having a structure in which powder aggregates are dispersed is formed. The method for forming a paste for suppressing electromagnetic noise according to claim 1, wherein the fine particles of the metal oxide according to claim 1 are fine particles of maghemite that is a gamma phase of ferric oxide, According to the method of depositing the fine particles of maghemite, which is a gamma phase of iron, in the insulating organic compound composed of the liquid according to claim 1 to form the paste for suppressing electromagnetic noise according to claim 1, The method for forming a paste for suppressing electromagnetic noise according to claim 1, wherein a paste for suppressing the noise is formed. The method for forming a paste for suppressing electromagnetic noise according to claim 2 , wherein the fine particles of maghemite, which is a gamma phase of ferric oxide, produce fine particles of ferrous oxide by thermal decomposition of iron naphthenate, Furthermore, a method of fine particles of oxide ferrous, by Rukoto is oxidized to maghemite particles with heat treatment in an air atmosphere, are those prepared to form the electromagnetic noise suppressing paste according to claim 2 .. A method of forming a paste for suppressing electromagnetic noise according to claim 1, wherein the organic compound according to claim 1 has a first property of being dissolved or miscible in alcohol and a second property of having a viscosity higher than that of the alcohol. And an organic compound having these four properties, which is composed of a third property having a boiling point higher than the heat treatment temperature in the air atmosphere for oxidizing ferrous oxide to maghemite and a fourth property that is an insulator. According to the method for forming a paste for suppressing electromagnetic noise according to claim 1, by depositing a group of fine particles of a metal oxide having both hard magnetism and insulating property according to claim 1 in the organic compound. The method for forming a paste for suppressing electromagnetic noise according to claim 1, wherein a paste for suppressing electromagnetic noise is formed. The method for forming a paste for suppressing electromagnetic noise according to claim 1, wherein the organic compound according to claim 4 is an organic compound composed of carboxylic acid esters, and Suppressing electromagnetic noise according to the method of claim 1, wherein a group of fine particles of a metal oxide having both hard magnetic properties and insulating properties is deposited and the paste for suppressing electromagnetic noise is formed according to claim 1. The method for forming a paste for suppressing electromagnetic noise according to claim 1, wherein the paste is formed.

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