JP2007288006A - Electromagnetic wave interference suppression sheet, flat cable for high frequency signal, and flexible printed circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an electromagnetic wave interference suppression sheet, a flat cable for a high frequency signal and a flexible printed circuit board which are suitable for a high density mounting of electronic equipment and are excellent in an electromagnetic wave absorption of a nearby electromagnetic field and fully suppress a reflection and can suppress a degradation of an electromagnetic wave absorption performance caused by a bending or the like. <P>SOLUTION: The resin sheet includes fiber-like conductive carbon and carbonyl iron. It is suitable that a mean particle diameter of the carbonyl iron is 1/3 or less of a sheet thickness. Preferably, it is 1/5 or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention is an electromagnetic interference suppression sheet for suppressing interference of unnecessary electromagnetic waves generated from digital electronic equipment, and uses the electromagnetic interference suppression sheet containing carbonyl iron and fibrous conductive carbon in the resin and the electromagnetic interference suppression sheet The present invention relates to a flat cable for high frequency signals and a flexible printed circuit board.

In recent years, digital electronic devices have made remarkable progress. Especially in mobile electronic devices such as mobile phones, digital cameras, and notebook computers, there are significant demands for higher frequency operation signals and smaller and lighter operating signals. High density mounting of electronic components and wiring boards is one of the biggest technical issues.

Due to the high-density mounting of electronic components and wiring boards for electronic devices and the higher frequency of operation signals, the distance between components that generate noise and other components cannot be secured, and microprocessors and LSIs for electronic devices Electromagnetic interference suppression sheets are used for suppressing unwanted radiation emitted from liquid crystal panels. The absorption and reflection phenomenon of electromagnetic waves in the near electromagnetic field as in this application is difficult to analyze using the transmission line theory as in the far-field electromagnetic field (when the electromagnetic wave is a plane wave) that has been conventionally known (Hashimoto). Osamu, “Trends in radio wave absorbers”, IEICE Journal, Vol. 86
No. 10 pp. 800-803, October 2003), the design of the electromagnetic interference suppression sheet is largely dependent on experience. Recently, an electromagnetic interference suppression sheet of a type in which a flat metal magnetic powder is blended with a resin as a soft magnetic powder for absorbing electromagnetic waves in a near electromagnetic field as in Patent Document 1 and Patent Document 2 has been used.

Up to now, 90% by weight of a flat Fe—Al—Si alloy powder having an average particle diameter of 10 μm as a soft magnetic powder (for compositions 1 and 3, the alloy powder density is 6.9 kg / l, and the resin density is 1). When calculated as 1 kg / l, an electromagnetic wave interference suppressor containing 58.9 vol% is disclosed. The thickness of the electromagnetic wave interference suppressing body is 1.2 mm (Patent Document 1).

In the manufacturing method, “a magnetic coating material in which a flat metal magnetic powder is dispersed in a resin and a solvent is coated on a substrate having a release layer and dried, and then the dried coating film is peeled off to form a magnetic sheet. The manufacturing method of the magnetic sheet | seat characterized by obtaining this is disclosed. Magnetic sheet having a dry film thickness of 120 μm and a sendust powder filling ratio of 80 wt% maximum (56.0 vol% when calculated with a sendust powder density of 6.9 kg / l and a resin content density of 1.1 kg / l) The shield sheet is in the example, and it is shown that a thinner magnetic sheet can be realized as compared with Patent Document 1. A thin magnetic sheet is considered suitable for high-density mounting of electronic components and wiring boards (Patent Document 2).

Japanese Patent Laid-Open No. 7-212079 JP 2000-244171 A

Due to the progress of miniaturization and weight reduction of digital electronic devices, higher density mounting of electronic components and wiring boards is required, and even thinner, excellent electromagnetic wave absorption performance in the nearby electromagnetic field, for electromagnetic wave interference suppression with less electromagnetic wave reflection There is a strong demand for seats. In general, if the electromagnetic interference suppression sheet is made thinner, the electromagnetic wave absorption performance is lowered. To make the sheet even thinner, the content of the magnetic powder is increased, and the practical flexibility and strength of the sheet are secured. It is necessary to suppress deterioration of electromagnetic wave absorption performance due to bending or the like.

  The technical problem can be achieved by the present invention as follows.

That is, the present invention is an electromagnetic interference suppression sheet in which fibrous conductive carbon and carbonyl iron are contained in a resin (Invention 1).

The present invention is an electromagnetic interference suppression sheet that contains fibrous conductive carbon and carbonyl iron in a resin and has little deterioration in electromagnetic wave absorption characteristics due to bending (Invention 2).

The present invention is the electromagnetic interference suppression sheet of the present invention 1 or 2, wherein the form of carbonyl iron is spherical and the fiber length of the fibrous conductive carbon is 10 μm to 20 mm (the present invention). 3).

The present invention is the electromagnetic interference suppression sheet according to any one of the present inventions 1 to 3, wherein the spherical carbonyl iron has an average particle diameter of 1 to 10 μm (Invention 4).

The present invention is the electromagnetic wave interference suppression sheet according to any one of the present inventions 1 to 4 containing 50 to 70 vol% carbonyl iron and 3 to 10 vol% conductive fibers (Invention 5).

The present invention is the electromagnetic interference suppression sheet according to any one of the present inventions 1 to 5, wherein the thickness is 10 to 100 μm (the present invention 6).

Moreover, this invention is a flat cable for high frequency signals using the electromagnetic wave interference suppression sheet in any one of this invention 1-6 (this invention 7).

Moreover, this invention is a flexible printed circuit board using the electromagnetic wave interference suppression sheet in any one of this invention 1-6 (this invention 8).

According to this invention, the electromagnetic wave interference suppression sheet | seat which was excellent in the electromagnetic wave absorption in a near electromagnetic field can be obtained by mix | blending fibrous conductive carbon and carbonyl iron in resin. According to the manufacturing method of the present invention in which the magnetic paint containing the fibrous conductive carbon and carbonyl iron is applied so as to have a dry thickness of 10 to 100 μm and then subjected to heat and pressure molding, electromagnetic wave absorption in the near electromagnetic field An electromagnetic interference suppression sheet that is excellent and suitable for high-density mounting with suppressed reflection can be obtained.

The average particle diameter of the carbonyl iron of the present invention is preferably 1/3 or less of the sheet thickness. Preferably it is 1/5 or less. When the average particle size exceeds 1/3, the surface smoothness of the electromagnetic interference suppression sheet is lowered, so that the adhesion of the sheet to the electromagnetic wave generation source is deteriorated and the electromagnetic wave absorption performance is lowered.

The carbonyl iron of the present invention is spherical in shape and preferably has an average particle size of 1 to 10 μm because it can be highly filled and can be uniformly dispersed in the resin. An average particle size of less than 1 μm is not preferable because the resin mixture has a high viscosity and is difficult to uniformly disperse. If it exceeds 10 μm, it is not preferable because high filling cannot be achieved. The average particle diameter is more preferably 2 to 8 μm.

The carbonyl iron in the present invention is not particularly limited, but surface treatment with a titanate-based or silane-based coupling agent and / or phosphoric acid-based surface treatment may be performed as necessary. Surface treatment is performed with 0.1 to 1.0 wt% coupling agent with respect to carbonyl iron. When the treatment amount of the coupling agent is less than 0.1 wt%, the affinity for the resin cannot be sufficiently increased, so that the oxidation stability cannot be sufficiently maintained. If it exceeds 1.0 wt%, the impedance increases and the electromagnetic wave absorption amount decreases. Preferably it is 0.1-0.5 wt%.
The surface of the particles is surface-treated with 0.1 to 0.5 wt% phosphoric acid based on phosphoric acid with respect to carbonyl iron. When the amount of phosphoric acid is less than 0.1 wt%, the oxidation stability is lowered, the impedance is lowered, and the reflection is increased. When the amount of phosphoric acid exceeds 0.5 wt%, the impedance increases and the absorption decreases. Preferably it is 0.1-0.4 wt%.

Among the coupling agents, titanate coupling agents include isopropyl tristearoyl titanate, isopropyl tris (dioctyl pyrophosphate) titanate, isopropyl tri (N-aminoethyl / aminoethyl) titanate, tetraoctyl bis (ditridecyl phosphate). Examples include titanate, tetra (2-2-diallyloxymethyl-1-butyl) bis (ditridecyl) phosphate titanate, bis (dioctylpyrophosphate) oxyacetate titanate, and bis (dioctylpyrophosphate) ethylene titanate.

As the silane coupling agent, vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-glycidoxypropyl suitable as elastomer coupling agents Trimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldi Ethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropylmethyldimethoxysilane, N-2 (aminoethyl) 3-aminopropyltrimethoxysilane, N-2 (aminoethyl) 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercapto Examples thereof include propyltrimethoxysilane and bis (triethoxysilylpropyl) tetrasulfide.

The fibrous conductive carbon of the present invention is a fibrous carbon obtained by processing a carbon fiber, and a cut fiber having a fiber length of 3 to 24 mm or a milled fiber having a fiber length of 30 to 150 μm is preferable. It is preferable that the fiber length after being processed into the electromagnetic interference suppression sheet is about 10 μm to 10 mm when the sheet surface is observed with a scanning electron microscope. If the thickness is less than 10 μm, the electromagnetic wave absorption performance tends to deteriorate when the sheet is bent. If it exceeds 10 mm, it becomes fluffy and difficult to handle as a sheet. The fiber length after processing is more preferably about 30 μm to 3 mm.

The volume ratio of fibrous conductive carbon and carbonyl iron in the present invention is 3 to 10:50 to 70. Below this range, the electromagnetic wave absorption is low. On the other hand, if the range is exceeded, reflection of electromagnetic waves is increased, and sheet strength and flexibility are also lowered. More preferably, it is 3-10: 53-70, More preferably, it is 4-8: 55-70.

Next, the electromagnetic interference suppression sheet according to the present invention will be described.

The electromagnetic interference suppression sheet according to the present invention preferably contains 3 to 10 vol% of fibrous conductive carbon and 50 to 70 vol% of carbonyl iron, and the thickness of the sheet is preferably 10 to 100 μm. When the amount of carbonyl iron is less than 50 vol%, the electromagnetic wave absorption is low. When carbonyl iron exceeds 70 vol%, reflection of electromagnetic waves is increased, and sheet strength and flexibility are also lowered.
When 3 to 10% by volume of fibrous conductive carbon is blended, it is preferable that the electromagnetic wave absorption characteristics are not deteriorated by bending the sheet. More preferably, it is 4-10 vol%. If the fibrous conductive carbon is less than 3 vol%, the deterioration of the electromagnetic wave absorption characteristics due to the folding of the sheet is not preferable. If the fibrous conductive carbon exceeds 10 vol%, the dispersion becomes poor, a uniform sheet cannot be obtained, and the reflection of electromagnetic waves increases, which is not preferable.
In the present invention, the thickness of the sheet is adjusted according to the state of use, but if it is less than 10 μm, the sheet tends to have insufficient strength. A thickness exceeding 100 μm is too thick for a high-density mounted electronic circuit.
It is preferable that the retention rate of the electromagnetic wave absorption before and after the bending test is 80% or more. More preferably, it is 90% or more.

The electromagnetic interference suppression sheet of the present invention preferably contains 15 to 30% by volume of resin. If it is less than 15 vol%, the flexibility of the sheet is poor. When it exceeds 30 vol%, the electromagnetic wave absorption amount decreases. As the resin, styrene elastomer, olefin elastomer, polyester elastomer, polyamide elastomer, urethane elastomer, silicone elastomer and the like can be used. Examples of the styrene elastomer include SEBS (styrene ethylene butylene styrene block copolymer). An elastomer can be used by mixing an acrylic resin, an epoxy resin, a polyolefin resin, or the like.

The electromagnetic interference suppression sheet according to the present invention preferably contains 5 to 20 vol% of a flame retardant. If it is less than 5 vol%, the flame retardant effect is insufficient. If it exceeds 20 vol%, the amount of absorption decreases, which is not preferable. As the flame retardant, melamine polyphosphate, magnesium hydroxide, hydrotalcite or the like is preferably used. Preferred are magnesium hydroxide and melamine polyphosphate.

The electromagnetic interference suppression sheet according to the present invention preferably contains 0.5 to 3% by volume of an antioxidant. If it is less than 0.5 vol%, the oxidation resistance is low, which is not preferable. Exceeding 3 vol% is not preferable because the amount of absorption decreases. Antioxidants include 2 ′, 3-bis [[3- [3,5-di-tert-butyl-4-hydroxyphenyl] propionyl]] propionohydrazide (Ciba Specialty Chemicals, IRGANOX
MD1024) or the like is preferably used. Antioxidants for resins include tetrakis [methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate], tris- (3,5-di-t-butyl- One that is compatible with the resin is selected from 4-hydroxybenzyl) -isocyanurate, N, N′-hexamethylenebis (3,5-di-tert-butyl-4-hydroxyhydrocinnamide). As an antioxidant for the rubber-based resin, Toray Industries, Inc. CTPI N-cyclohexylthiophthalimide is suitable.

The electromagnetic interference suppression sheet of the present invention is preferably a sheet having a thickness of 100 μm or less, and the electromagnetic wave absorption is preferably 10% or more at 0.5 GHz and 40% or more at 3 GHz. Below that, the amount of electromagnetic wave absorption is insufficient.

The electromagnetic interference suppression sheet of the present invention is preferably a sheet having a thickness of 100 μm or less, and an electromagnetic wave reflection amount is −5 dB or less in a frequency range of 0.1 to 3 GHz. Above that, the electromagnetic wave reflection amount is too large, which is not desirable.

The method for producing an electromagnetic interference suppression sheet according to the present invention is to adjust the thickness of the magnetic sheet after drying by applying a magnetic paint in which the fibrous conductive carbon of the present invention and carbonyl iron powder are dispersed. It is preferable to perform hot pressing. A magnetic coating material is preferable because it can achieve high filling and uniform dispersion.

Next, a high frequency signal flat cable and a flexible printed board according to the present invention will be described.

The flat cable for high-frequency signals and the flexible printed board of the present invention use the electromagnetic interference suppression sheet of the present invention to reduce the size of the board and the noise radiation source of the wiring board itself. As a result, the density of the electronic circuit is increased, the drive voltage can be lowered, the current can be increased, and a substrate having noise resistance can be constructed.

The measuring method of each measured value shown in an Example is described.

[Powder material density]
The density of the powder material was measured as follows. Using a densitometer, a multi-volume density meter 1305 manufactured by Micromeritex Corporation, 28 g (W) of powder was put into a weighing cell, and a helium gas pressure sample volume (V) was obtained to obtain a density.
Density = W / V (g / cm ³ )

[Measurement of electromagnetic wave absorption and reflection]
It is measured with a substrate on which a microstrip line adjusted to a length of 100 mm, a width of 2.3 mm, a thickness of 35 μm, and an impedance of 50Ω is applied. The produced sheet is cut into a width of 40 mm and a length of 50 mm to obtain a test piece.

The microstrip line is connected to a network analyzer 8720D manufactured by Hewlett-Packard Co., and the S parameter of the microstrip line is measured. The length direction of the sheet is aligned with the length direction of the microstrip line, and the centers are mounted so that the respective centers coincide. The S-parameters are measured in a state where a 10 mm thick foamed polystyrene sheet having the same expansion ratio 20 to 30 times as that of the sheet is placed on the sheet and a load of 300 g is placed thereon. The absorption amount (%) and the reflection amount (dB) are calculated from the obtained S parameter.
Absorption amount = (1- | S ₁₁ | ² − | S ₂₁ | ² ) / 1 × 100 (%)
Reflection amount = 20 log | S ₁₁ | (dB)

In the bending test, a test piece cut out to a width of 40 mm and a length of 50 mm was checked for initial characteristics of electromagnetic wave absorption and reflection by a stripline, and then a 3 mm thick plastic plate with a 70-degree sloped edge. The test piece has a slope with the short side (40mm) of the test piece parallel to the side with the slope of the plastic plate, bent along the slope, and the test piece in close contact with the edge and slope. While pulling in the direction perpendicular to the side, slide the plastic plate lightly held in the pulling direction, and fold the entire specimen in order as evenly as possible. Immediately after performing this operation 10 times, the amount of electromagnetic wave absorption and reflection is measured with a strip line, and the change in characteristics is confirmed.

[Example 1]
The volume ratio after removal of the solvent in a solution (TF-4200E, manufactured by Hitachi Chemical Co., Ltd.) in which 20% by weight of a styrene elastomer (density 0.9 g / cm ³ ) is dissolved in cyclohexanone is fibrous conductive carbon (Toray Industries, Inc.) Company cut fiber Trayca TS12 006-C Fiber length 6 mm, fiber diameter 1 μm, density 1.5 g / cm ³ ) is 4 vol%, carbonyl iron (R1470 manufactured by Internal Specialty products, particle size 6.2 μm, density 7.8 g / cm) ³ ) 35 vol%, carbonyl iron (S3000 by International Specialty products, particle size 2 μm, density 7.6 g / cm ³ ) 23 vol%, styrene elastomer 21 vol%, melamine polyphosphate as a flame retardant (Sanwa Chemical Co., Ltd.) Made by M P-A, density 1.8 g / cm ³⁾ magnesium hydroxide and 8 vol% (manufactured by Kyowa Chemical Kisuma 5A, density 2.4 g / cm ³⁾ is metered such that the 8 vol%, mixed, SMT Co. A slurry was obtained by stirring for 60 minutes at 15000 rpm using a power homogenizer. At that time, ethylcyclohexanone having the same volume as the elastomer solution was added to adjust the viscosity. The obtained slurry was subjected to vacuum defoaming treatment, and then applied to a carrier film using a doctor blade. After drying the organic solvent, a sheet having a sheet thickness of 80 μm was produced. Further, the obtained sheet was molded under conditions of a temperature of 130 ° C., a pressure of 90 MPa, and a pressing time of 5 minutes to obtain a sheet having a thickness of 47 μm.
The obtained sheet was a sheet having a smooth surface and excellent flexibility. The S parameter was measured with a network analyzer using a microstrip line with a length of 100 mm, a width of 2.3 mm, a thickness of 35 μm, and an impedance of 50Ω, and the amount of absorption and reflection was calculated. The absorption was 49%, the reflection from 100 MHz to 3 GHz was -14 dB or less, the absorption was high in a wide frequency range, the reflection was low, and the characteristics were excellent in balance.

  Table 1 shows the manufacturing conditions and the initial characteristics of the obtained electromagnetic interference suppression sheet, and Table 2 shows the characteristics after the bending test.

Further, as shown in Table 2, the characteristics of the electromagnetic wave absorption after the bending test were little deteriorated and the excellent characteristics of the electromagnetic interference suppression sheet were maintained.

[Examples 2, 3, 4, 5]
A sheet adjusted to the composition and thickness described in Table 1 in the same manner as in Example 1 was prepared, and the amount of absorption and reflection was measured from the S parameter using a microstrip line. The absorption amount at 500 MHz is 10% or more, the absorption amount at 3 GHz is 40% or more, and the reflections from 100 MHz to 3 GHz are all −5 dB or less, and the absorption is high and the balance is excellent in the low balance. . In addition, carbonyl iron S1641 manufactured by Internal Specialty Products had a particle size of 6.2 μm and a density of 7.6 g / cm ³ .

Further, as shown in Table 2, the electromagnetic wave absorption characteristics after the bending test were hardly deteriorated at a maintenance rate of 85% or more for any of the sheets, and the excellent characteristics of the electromagnetic interference suppression sheet were maintained.

[Comparative Example 1]
In the same manner as in Example 1, the weight ratio of iron, aluminum, and silicon was 85: 6: 9, the aspect ratio was 15 to 20, the density was 6.9 g / cm ³ , and the flat metal powder having an average particle size of 50 μm was 47 vol%. Thus, a sheet having a plate thickness after heat compression molding adjusted to 100 μm was prepared. The absorption amount at 500 MHz is 10%, the absorption amount at 3 GHz is 43%, and the reflection from 100 MHz to 3 GHz is -10 dB or less, and the balance between absorption and reflection is excellent, but the sheet plate thickness is 100 μm, Compared with Example 5, the absorption performance is significantly inferior.

[Comparative Example 2]
Comparative Example 2 produced a sheet with the same composition as Comparative Example 1, adjusted the thickness to 500 μm, and obtained the results shown in Table 1. Absorption and reflection were good characteristics, but it was 500 μm thick and unsuitable for high-density mounting.

[Comparative Examples 3, 4, 5]
In Comparative Examples 3 to 5, in the same manner as in Example 1, sheets adjusted to the composition and thickness of Table 1 were prepared. All the sheets in Comparative Examples 3 to 5 had a reflection of −20 dB or less, but only an electromagnetic wave interference suppressing sheet having a low absorption of less than 4% at 500 MHz and less than 26% at 3 GHz was obtained.

[Comparative Example 6]
Further, in Comparative Example 6, as in Example 1, an attempt was made to prepare a sheet adjusted to the composition and thickness of Table 1. However, since the fibrous conductive carbon does not disperse, the paint can be applied. There wasn't.

[Comparative Examples 7 and 8]
In Comparative Example 7 and Comparative Example 8, in the same manner as in Example 1, sheets adjusted to the composition and thickness of Table 1 were prepared, and the results of Table 1 were obtained. The initial values of electromagnetic wave absorption and reflection were excellent as shown in Table 1, but the characteristics of electromagnetic wave absorption after the bending test were degraded as shown in Table 2. Is less than 80%, and is not suitable for handling as an electromagnetic interference suppression sheet under practical conditions such as bending.

The electromagnetic wave interference suppression sheet according to the present invention has high absorption in a wide frequency range, low reflection, and excellent balance characteristics even when the sheet thickness is thin. It is suitable for an electromagnetic interference suppression sheet having excellent characteristics and low electromagnetic wave reflection.

It is the schematic of a bending test.

Claims (8)

Electromagnetic wave interference suppression sheet containing fibrous conductive carbon and carbonyl iron in resin. An electromagnetic interference suppression sheet that contains fibrous conductive carbon and carbonyl iron in a resin and has little deterioration in electromagnetic wave absorption characteristics due to bending. The electromagnetic interference suppression sheet according to claim 1 or 2, wherein the form of carbonyl iron is spherical, and the fiber length of the fibrous conductive carbon is 10 µm to 10 mm. The average particle diameter of spherical carbonyl iron is 1-10 micrometers, The electromagnetic wave interference suppression sheet in any one of Claims 1-3 characterized by the above-mentioned. The electromagnetic wave interference suppression sheet according to any one of claims 1 to 4, comprising 50 to 70 vol% of carbonyl iron and 3 to 10 vol% of fibrous conductive carbon. The electromagnetic interference suppression sheet according to claim 1, wherein the thickness is 10 to 100 μm. The flat cable for high frequency signals using the electromagnetic wave interference suppression sheet in any one of Claims 1-6. The flexible printed circuit board using the electromagnetic wave interference suppression sheet in any one of Claims 1-6.

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