JPH1126977A - Sheet for absorbing electromagnetic wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sheet with shielding and absorption effects of an electromagnetic wave even in a high frequency range, and high insulation performance which can be deformed into an arbitrary shape. SOLUTION: Soft magnetic metallic flake powder whose particle diameter is 0.01-10 μm, and whose aspect ratio (long diameter or short diameter/thickness) is more than 2 is distributed in a matrix 3 made of rubber or soft synthetic resin so as to be arrayed in parallel to the facial direction of the sheet and formed like a sheet. Thus, a powder distribution sheet 1 in which the soft magnetic metallic flake powder being more than 30% by volume of the sheet exist, and more than 10<11> Ω.cm of a specific resistance is ensured can be formed. This power distribution sheet 1 and a soft magnetic foil 2 are laminated. The soft magnetic metal is preferably selected from permalloy, Sendust, permendule (Fe-Co system alloy), Fe-Al-Cr alloy, and electromagnetic stainless steel. Both faces of the soft magnetic metallic foil are interposed by the power distribution sheet in a preferred structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave,
The present invention relates to a flexible sheet for shielding and absorbing electromagnetic waves up to a high frequency range of Hz or higher.

[0002]

2. Description of the Related Art In order to cope with the tendency that the operating frequency of various electronic devices shifts to a higher frequency region and to meet the demand for further miniaturization, electromagnetic waves are effectively shielded in a high frequency region. It is necessary that the device does not emit extraneous electromagnetic waves and that the electronic device does not receive external electromagnetic waves. In addition to the shield, it is necessary to absorb electromagnetic waves generated inside the electronic device and prevent interference caused by scattering of the electromagnetic waves inside.

[0003] As an electromagnetic wave interference suppressor meeting such demands, an insulating soft magnetic layer made of a soft magnetic powder and an organic binder is provided on one or both surfaces of a conductive support such as a metal net. The provided one has been proposed (Japanese Patent Laid-Open No. 7-212079). This electromagnetic interference suppressor,
Due to the presence of the conductive support, a shielding effect equivalent to that of the conductive shield material is obtained against the transmission of electromagnetic waves, and the reflection that may be caused by the conductive support is suppressed by the insulating soft magnetic layer. Things. However, this type of shielding material has a reduced shielding performance in a frequency region of 200 MHz or higher.

As a material having a high shielding performance in a high frequency region, a material obtained by laminating an insulating soft magnetic layer and a copper foil may be considered. When the characteristics of such a shielding material are measured, the performance of shielding electromagnetic waves passing through the sheet is good, but the rate of reflection of the electromagnetic waves at the sheet is high, and the electromagnetic waves are not scattered inside the electronic device. The desire to do so cannot be fully met.

[0005] The inventors worked on the development of an electromagnetic wave shielding material capable of maintaining the shielding performance even in a high frequency region, and made use of flaky powder of soft magnetic metal selected from permalloy, sendust, Fe-Al-Cr alloy and electromagnetic stainless steel. The flake-like powder having a particle diameter of 0.01 to 10 μm and an aspect ratio (major axis / minor axis / thickness) of 2 or more is placed in a matrix sheet made of rubber or a soft synthetic resin. The sheet is dispersed and formed so as to be arranged in parallel to the surface direction of the sheet, and a flake-like powder of soft magnetic metal is present in 30% by volume or more of the sheet, provided that the specific resistance is secured to 10 ¹¹ Ω · cm or more. Have found that it meets this purpose and have already proposed it (Japanese Patent Application No. 9-6135).
No. 2).

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a device which has a high capability of shielding and absorbing electromagnetic waves in a high frequency range, and which can be easily cut into arbitrary shapes, is flexible, and is used in electronic devices and the like. An object of the present invention is to provide an electromagnetic wave shielding sheet that can be deformed according to the shape of a component, has high insulation properties, and can be used by being attached to an IC substrate or the like.

[0007]

As shown in FIG. 1, the electromagnetic wave absorbing sheet of the present invention is a flaky powder (4) of a soft magnetic metal, having a particle size of 0.01 to 10 μm and an aspect ratio. The particles having a (major axis / minor axis / thickness) of 2 or more are dispersed in a matrix (3) made of rubber or a soft synthetic resin such that the flake-like powder is arranged in parallel to the surface direction of the sheet. The flake powder of the soft magnetic metal is present in 30% by volume or more of the sheet, provided that the powder dispersion sheet (1) having a specific resistance of 10 ¹¹ Ω · cm or more, and the soft magnetic metal It is formed by laminating a foil (2).

The soft magnetic metal flake powder includes permalloy, sendust, permendur (Fe-Co).
Flake-like powders of those selected from the group consisting of a Fe-Al-Cr alloy and an electromagnetic stainless steel.
It is also useful to quench these alloys to make them amorphous or near amorphous. Similarly, as the soft magnetic metal foil, foils of permalloy, sendust, permendur (Fe—Co alloy), Fe—Al—Cr alloy, and electromagnetic stainless steel are preferable.

As the material of the matrix, various rubbers and soft synthetic resins such as synthetic rubber such as chloroprene rubber, chlorinated polyethylene and soft polyvinyl chloride can be used. Chlorinated polyethylene is optimal.

In order to disperse the soft magnetic metal flake-like powder in the matrix in a state of being arranged parallel to the surface of the sheet, a mixture of the matrix material and the powder is extruded from a T-die to form a sheet, Alternatively, a method of gradually thinning the sheet by a calendering operation may be adopted.

When the metal powder having a high aspect ratio is dispersed in this way, the individual powders are present in the matrix with little contact, while a large number of powders are present in the direction across the sheet. Therefore, the shielding performance can be exhibited while keeping the electric conductivity low as a whole.

[0012] The particle size of the soft magnetic metal powder in the sheet is set at 0.1.
The range of 1 to 10 μm is a condition for ensuring high shielding performance even in a high frequency region of 1 GHz or more. The presence of 30% by volume or more is necessary for obtaining the shielding performance to a desired level in ordinary applications. It is necessary to ensure that the specific resistance is 10 ¹¹ Ω · cm or more in order to obtain an insulation performance that does not cause any trouble even if the sheet comes into contact with the circuit by directly attaching this sheet to the back surface of the IC substrate. When the same metal powder is used, if the content in the sheet increases, the shielding performance is ensured, but the specific resistance is inevitably reduced. In order not to exceed the above limits, mixing of the metal powder should usually be stopped within 70% by volume. The specific resistance is preferably at a level of 10 ¹² Ω · cm.

The thickness of the sheet can be arbitrarily selected as long as it can be processed. Thicker is, of course, more effective in shielding, but for normal use a thickness of 1 mm or less will withstand use. Practically, 0.3 ~
2.0 mm, typically 0.5 mm, is a suitable range of thickness.

The sheet for absorbing electromagnetic waves of the present invention can be made to have characteristics according to the intended use by selecting a material, particularly a matrix material. For example, when the sheet is forced to bend due to the space of the application portion, the matrix material is selected to be thin and highly flexible. Conversely, if it is desired that the sheet be self-supporting, use a rigid material. Where the temperature is relatively high, engineering plastics with a high softening temperature may be used. Due to the relatively high thermal conductivity of this sheet due to the incorporation of a large amount of metal powder,
And the like, it does not hinder heat radiation.

The soft magnetic metal foil to be laminated with the above-mentioned sheet is usually sufficient if it has a thickness of at least 1 μm for absorbing electromagnetic waves. In general, it is difficult to form a thin foil because a soft magnetic metal has low workability. Rather, it is easier to use a thick foil for the structure of the sheet of the present invention. However, recent advances in processing technology have made it possible to obtain, for example, PC Permalloy having a thickness of several μm.

The sheet for electromagnetic wave absorption of the present invention comprises the above-mentioned powder dispersion sheet (1) and foil (2) as shown in FIG.
The basic configuration is a stack of sheets one by one. The soft magnetic metal powder dispersed and arranged in the sheet absorbs the electromagnetic wave from the side of the powder dispersion sheet, as viewed in the figure. The electromagnetic wave reaching the foil is reflected there, but is absorbed while returning in the sheet, so that the electromagnetic wave reflected from the sheet is substantially weak. Here, the electric resistance value of the sheet is important, and the conventional one has only a specific resistance of, for example, about 10 ⁸ Ω · cm. As a result, an eddy current is generated there and a new electromagnetic wave is induced. Reflection increases. If the powder-dispersed sheet according to the invention has a resistivity of at least 10 ¹¹ Ω · cm, preferably of the order of 10 ¹² Ω · cm, the eddy currents generated in the sheet are extremely weak and the electromagnetic waves induced there are problematic. Therefore, the electromagnetic wave apparently reflected by the electromagnetic wave absorbing sheet is also insignificant.

As is apparent from the above mechanism, in the basic configuration of FIG. 1, the electromagnetic wave is not absorbed from the foil side, and the performance of the absorbing sheet is directional. In order to eliminate this directionality and absorb and not reflect electromagnetic waves from either side, according to a preferred embodiment of the present invention, FIG.
A sandwich structure as shown in FIG. That is, it has a layer configuration in which a foil is sandwiched between two powder dispersion sheets. As will be easily understood, if layers are further laminated to form a laminate of three powder dispersion sheets and two foils, the electromagnetic wave absorbing performance is further improved.

[0018]

【Example】

[Examples and Comparative Examples] Fe-
Using powder of 13Cr-3Al alloy or Fe-9Al-7Cr alloy, powder as a raw material was pulverized by an attritor into flakes. The particle size of both powders is 0.01 μm minimum to 10 μm maximum and 1 μm on average, and the aspect ratio is about 10. On the other hand, chlorinated polyethylene rubber was used as a matrix material, and 95 parts by weight of any of the above metal powders and 5 parts by weight of rubber were kneaded and extruded, and were further calendered to a thickness of 0.5%.
It was molded into a sheet of mm. In both sheets, the volume occupied by the metal powder in the sheet reached 60%, but the specific resistance of the sheet surface was 10 ¹² Ω · cm.

Separately, a foil having a thickness of 5 μm was prepared by rolling PC permalloy.

Each of the above-mentioned powder dispersion sheet and foil is used alone as a shielding material, and is used at a frequency of 30 MHz to 1 GHz.
In the frequency range of z, the shielding performance of electric and magnetic fields was examined. The shielding performance measured as the signal attenuation rate is shown in FIGS. 3 and 4 for the electric field wave and FIG. 6 for the magnetic field wave.
And FIG. Next, the same measurement was carried out using a laminate of the powder dispersion sheet and the foil as a shielding material.
FIG. 5 shows the shielding performance for the electric field wave, and FIG. 8 shows the shielding performance for the magnetic field wave.

FIGS. 3 and 4 are compared with FIG. 5, and FIG.
7 and FIG. 8 show that when the powder dispersion sheet and the foil are laminated according to the present invention, a higher shielding performance is obtained than when the powder dispersion sheet is used alone.
It can be seen that it is remarkable in a high frequency region of GHz. These data also show that the electromagnetic wave shielding and absorption is highly enhanced when the layer structure sandwiching the soft magnetic metal foil by the two powder dispersion sheets according to the preferred embodiment of the present invention.

In the above test, the transmitting antenna and the receiving antenna were placed with a square plate-like test object sheet 150 mm in length and horizontal, and the extent to which the signal from the transmitting antenna reached the receiving antenna was measured over each frequency. It records and measures the attenuation of electromagnetic waves passing through the sheet. On the other hand, in order to measure the absorption at the time of reflection, the transmitting antenna was directed at an inclination of 45 ° with respect to the test object sheet, and the receiving antenna was placed on the path where the electromagnetic wave was reflected, and the same measurement was performed. The sheet for absorbing electromagnetic waves of the present invention,
Those that gave -28 dB attenuation for pass at z showed -5 dB absorption for reflection.

[0023]

The electromagnetic wave absorbing sheet of the present invention has a high performance of absorbing and absorbing electromagnetic waves, and can be used in any part of electronic equipment to block the influence of external electromagnetic waves. The electromagnetic waves can be prevented from being scattered inside without emitting the electromagnetic waves.

In particular, the three-layer structure of the preferred embodiment has no directivity in this performance, and thus shields and absorbs electromagnetic waves from any direction of the sheet. This sheet can be of any thickness and can be provided depending on the application, from flexible to those with some rigidity. It goes without saying that various processes such as cutting and bending can be performed. Since it is an insulator having a high specific resistance, it can be used by directly attaching it to an IC circuit board or the like.
Since the shielding and absorption performance does not decrease even in a high frequency region exceeding 1 GHz, it is possible to cope with an increase in the operating frequency and miniaturization of the electronic device.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a sheet showing a basic configuration of an electromagnetic wave absorbing sheet of the present invention.

FIG. 2 is a cross-sectional view of a sheet showing a configuration of a preferred embodiment of the electromagnetic wave absorbing sheet of the present invention.

FIG. 3 is a graph showing performance of a powder dispersion sheet constituting an electromagnetic wave absorbing sheet according to an example of the present invention, and showing a relationship between an electric field wave attenuation rate and a frequency.

FIG. 4 is a graph showing the performance of the foil constituting the electromagnetic wave absorbing sheet of the embodiment of the present invention, and is a graph showing the relationship between the electric field wave attenuation rate and the frequency.

5 is data showing the performance of the electromagnetic wave absorbing sheet of the present invention, which is formed by laminating the powder dispersion sheet of FIG. 3 and the foil of FIG. 4, and shows the relationship between the electric field wave attenuation rate and the frequency. Graph.

FIG. 6 is a graph corresponding to FIG. 3, showing data indicating the performance of the powder dispersion sheet of FIG. 3 and showing the relationship between the magnetic field wave attenuation rate and the frequency.

FIG. 7 is a graph corresponding to FIG. 4, showing data indicating the performance of the foil of FIG. 4 and showing the relationship between the magnetic field wave attenuation rate and the frequency.

8 is a graph corresponding to FIG. 5, showing data indicating the performance of the electromagnetic wave absorbing sheet of the present invention shown in FIG. 5 and showing the relationship between the magnetic field wave attenuation rate and the frequency.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 powder dispersion sheet 2 soft magnetic metal foil 3 rubber or synthetic resin matrix 4 rubber or synthetic resin matrix powder

Claims (5)

[Claims] 1. A flake powder of a soft magnetic metal,
The particles having a particle diameter of 0.01 to 10 μm and an aspect ratio (major axis or minor axis / thickness) of 2 or more are mixed in a matrix made of rubber or a soft synthetic resin, and the flaky powder is applied in the sheet surface direction. It is dispersed so as to be arranged in parallel and formed into a sheet, and the flake powder of the soft magnetic metal is present in 30% by volume or more of the sheet, provided that the specific resistance is 10 ¹¹ Ω ·
An electromagnetic wave absorbing sheet obtained by laminating a powder dispersion sheet secured to at least cm and a soft magnetic metal foil. 2. The flaky powder of a soft magnetic metal is a flaky powder selected from permalloy, sendust, permendur (Fe—Co alloy), Fe—Al—Cr alloy, and electromagnetic stainless steel. 1. An electromagnetic wave absorbing sheet. 3. The soft magnetic metal foil may be made of permalloy, sendust, permendur (Fe—Co alloy), Fe—
The electromagnetic wave absorbing sheet according to claim 1, wherein the sheet is a foil of a material selected from an Al-Cr alloy and an electromagnetic stainless steel. 4. The electromagnetic wave absorbing sheet according to claim 1, wherein a chlorinated polyethylene rubber is used as a matrix. 5. A laminate comprising a soft magnetic metal foil sandwiched between two powder dispersion sheets in which flaky powder of a soft magnetic metal is dispersed in a matrix of rubber or a soft synthetic resin. The electromagnetic wave absorbing sheet of any of the above.