JPH0337880B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an electromagnetic shielding material in the form of a casing made of a silicon carbide sintered body having characteristics of absorbing low frequency noise mainly generated from computer equipment.

Noise generated from computer equipment equipped with IC semiconductors such as C-MOS is 1 to 500MHz.
Personal computers are known to generate a lot of noise in the low frequency range of 30 to 200 MHz, but the present invention uses sintered silicon carbide that has the effect of shielding these electronic components. The present invention provides an electromagnetic wave shielding material for a casing made of a body.

[Conventional technology]

Conventionally, as electromagnetic shielding materials, for example, (a) JP-A-58-66399, (b) JP-A-58-66400, (c) JP-A-58-49665, and (d) JP-A-59. -Disclosed in Publication No. 27596.

The above (a) has an intermediate layer mainly composed of carbon silicon or an intermediate layer mainly composed of silicon carbide and carbon,
The present invention relates to a shielding sheet material characterized in that the front layer and the back layer are synthetic resin layers.

The above (b) relates to a casing having a shield layer mainly composed of silicon carbide powder or a shield layer mainly composed of a mixture of silicon carbide powder and carbon powder.

Moreover, the above (c) relates to a dielectric heating ceramic body containing 70% by weight or more of silicon carbide.

The above item (d) relates to a microwave absorber characterized by being made of dense silicon carbide having a resistivity of 1 ohm·cm or more.

[Problem that the invention seeks to solve]

The conventional technologies (a) and (b) above utilize silicon carbide's properties as a semiconductor, mechanically having high strength and hardness, and electrically having electromagnetic wave absorption properties. Since the sheet material or the housing uses a large amount of synthetic resin, it has low thermal conductivity and cannot easily dissipate the heat accumulated in electronic components such as semiconductors, which may cause failure of semiconductors, etc.
Furthermore, it has the disadvantage of poor durability because its wear resistance and mechanical strength are inferior to ceramics and metals.

On the other hand, in the prior art (c) and (d) above, since the dielectric heating ceramic body is made of a silicon carbide sintered body, it has high thermal conductivity and bending strength, and also has a small coefficient of thermal expansion, so it has good thermal shock resistance. It takes advantage of the fact that it has a very large resistance to cracks even when rapidly heated or cooled, but it is used for dielectric heating or as a high-frequency absorber, and is used, for example, in homes. Silicon carbide sintered bodies are mainly used in high-frequency ranges with oscillation frequencies of 2450 MHz or higher in cooking microwave ovens, that is, ceramic sintered bodies whose main component is silicon carbide, with various silicon carbide contents. It is characterized by changing the heat generation efficiency (heat conversion efficiency) when induction heating is performed.

The present invention eliminates the drawbacks of the prior art (a) and (b), and further improves the electromagnetic wave absorption characteristics in the low frequency region that have not been solved by the prior art (c) and (d), and particularly improves the electromagnetic wave absorption characteristics in the low frequency range, The main purpose of the present invention is to improve the shielding effect of noise generated from an IC, and this purpose is achieved by providing the electromagnetic wave shielding material described in the claims.

[Means for solving problems and their effects]

Hereinafter, the electromagnetic shielding material of the present invention will be specifically explained based on the characteristics of the silicon carbide sintered body and graphs showing the characteristics.

FIG. 1 is a graph showing the frequency characteristics of the electromagnetic shielding material A of the present invention made of a silicon carbide sintered body and the frequency characteristics of the electromagnetic shielding material made of a conductive paint A or a plastic molded product C as a comparative example. .
As is clear from Figure 1, the electromagnetic shielding material A of the present invention has particularly good absorption characteristics in the low frequency range of 1 to 500 MHz, and in particular, in the 10 to 100 MHz range, the absorption characteristics are 40 dB.
It can be seen that the above electromagnetic wave absorption characteristics are exhibited.
The reason for this is that the shielding material of the present invention is Si-C
The electromagnetic waves absorbed by the bond are 1 to 500 MHz.
It is thought that the frequency range is from 10 to 100 MHz, and it is mainly composed of β-type crystals, especially since it contains 65% by weight or more of β-type crystals. This is thought to be because, unlike the silicon carbide sintered body (d), the aspect ratio, which is the ratio of the short axis to the long axis of the crystal, can be changed arbitrarily in relation to the bulk density. This means that in the shield of the silicon carbide sintered body of the present invention shown in FIG. This is also related to the fact that the frequency characteristics of the sintered body B are different from those of the sintered body B. This is thought to be because a silicon carbide sintered body containing 65% by weight or more of β-type crystals has a property that the aspect ratio increases as the bulk density decreases.

Therefore, according to the present invention, the silicon carbide sintered body contains at least 65% by weight of β-type crystals.
Particularly preferably, the content is 80% by weight or more. The shielding material of the present invention is a silicon carbide sintered body with a theoretical density of 20 to 95% TD and a wide range of bulk ratios from porous to dense dense. It has high conductivity. This is because the shielding material of the present invention has a housing made of a ceramic sintered body mainly composed of silicon carbide, which has particularly excellent electromagnetic wave absorption characteristics in the low frequency range as shown in FIG. By covering an IC semiconductor such as C-MOS, which is a source of noise, with a housing, the heat generated from the semiconductor can be efficiently dissipated, and the electromagnetic wave shielding effect can be improved by the electromagnetic wave absorption property. This is because it can be made more complete.

In addition, the shielding material of the present invention is particularly suitable for 10 to 100 MHz.
It has excellent electromagnetic wave absorption characteristics in the low frequency range such as, but it has excellent electromagnetic wave absorption characteristics in the low frequency range such as the comparative example shown in Fig. By forming a casing in combination with a shielding material having electromagnetic wave absorption characteristics, the range of application can be expanded as an electromagnetic wave shielding material in a relatively high frequency range. Also,
A combination of an electromagnetic wave shielding material in which silicon carbide fine powder with excellent electromagnetic wave absorption characteristics is mixed as a filler into the conductive paint (B) or conductive plastic molded article (C) and the shielding material of the silicon carbide sintered body of the present invention. It is also possible to form a casing.

Next, the most typical embodiment of the present invention will be described.

Example 1 A formed body containing 94% by weight of silicon carbide fine powder mainly consisting of β-type crystals disclosed in JP-A No. 52-142697 as a starting material was fired to achieve a theoretical density of 97%.
A TD silicon carbide sintered body was obtained. The average aspect ratio of this sintered body was 1 for the minor axis to 11 for the major axis. Then, this sintered body was processed into a plate with a thickness of 4 mm, and a casing was formed using the plates of 150 mm x 45 mm and 45 mm x 60 mm, respectively, and the C-MOS IC
It was used as a shielding material. The result of its frequency characteristics is
It was as shown in A of FIG.

Example 2 A green body containing 85% by weight of silicon carbide fine powder consisting of the same β-type crystal as in Example 1 as a starting material was fired to obtain a silicon carbide sintered body having a theoretical density of 86% TD. The average aspect ratio of this sintered body was 1 for the minor axis and 29 for the major axis.

This sintered body was then processed in the same manner as in Example 1 to form a housing, which was used as a shielding material for a C-MOS IC. The results of the frequency characteristics were as shown in B of FIG.

〔Effect of the invention〕

As described above, according to the present invention, especially 1 to 500M
We can provide a shielding material that has excellent electromagnetic wave absorption characteristics and heat dissipation properties in the low frequency range such as Hz, and also has electromagnetic wave reflection characteristics by making it a silicon carbide sintered body with a certain density range. Furthermore, by impregnating a porous silicon carbide sintered body with conductive plastics or metals that have excellent electromagnetic wave absorption characteristics even in relatively high frequency ranges, it can be applied to a wide range of frequencies without being limited to low frequencies. The noise shielding effect can be improved.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the frequency characteristics of the shielding material A of the present invention and the shielding material of the conductive paint B or plastic molded product C of the comparative example. It is a graph showing frequency characteristics with density silicon carbide sintered compact B.

Claims (1)

[Claims] 1 Contains at least 65% by weight of β-type crystals, has an aspect ratio of 2 to 50, and has a theoretical density of 20 to 50.
An electromagnetic shielding material having excellent electromagnetic wave absorption properties mainly in the low frequency range of 1 to 500 MHz, characterized by being composed of a silicon carbide sintered body having a TD of 95%.