JPH07193386A - Shield case of electronic circuit - Google Patents

Abstract

PURPOSE:To provide a compact, light and inexpensive shield case of an electronic circuit which can strictly shield a required part of a circuit substrate electrostatically and magnetically. CONSTITUTION:A plating metal film 2 is formed approximately all over at least either of an inner surface and an outer surface of a ferrite shield case 1 attached to a circuit substrate and formed to cover a required part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shield case of an electronic circuit mounted on a circuit board of various electronic circuit devices for the purpose of preventing electromagnetic interference between circuit blocks, and more particularly to a shield case made of ferrite. Regarding things using cases.

[0002]

2. Description of the Related Art In recent years, logic integrated circuits used in digital equipment have a small logic amplitude and a high switching speed, which makes sensitivity to noise even more critical. Therefore, when designing an electronic device, it is necessary to minimize the occurrence of noise and to design itself to be resistant to noise. This applies not only to the relationship with other electronic devices but also between circuit blocks in the same device. As is well known, various measures are taken to construct an electronic circuit having high noise resistance against electrostatic induction noise and electromagnetic induction noise. Parts (circuit blocks) on the printed wiring board where electrostatic noise is easily applied
For this, it is effective to cover this with a shield case made of a metal plate having good conductivity, and to make a surface connection of the shield case to the chassis ground. In addition, it is effective to cover a part that needs to be protected from magnetic noise with a shield case made of ferrite. For a portion that needs to be magnetically and electrostatically shielded, a metal plate shield case and a ferrite shield case may be used in duplicate.

[0003]

Conventionally, when the electrostatic shield case made of a metal plate and the magnetic shield case made of ferrite are used in duplicate, the occupied space for double installation of both cases becomes large. , It was a big obstacle to downsizing electronic devices. The double shield case is also heavy, which has been an obstacle to reducing the weight of the device. Further, the mounting work for installing the two shield cases on the circuit board is troublesome, which also causes a cost increase.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is a small, lightweight and inexpensive electronic device capable of strictly shielding electrostatically and magnetically a required portion of a circuit board. It is to provide a shield case for a circuit.

[0005]

In view of the above, according to the present invention, a ferrite shield case attached to a circuit board and formed to cover a required portion is plated almost entirely on at least one of its inner surface and outer surface. A metal film was formed.

[0006]

[Function] The ferrite shield case is effective in shielding electromagnetic induction noise, and the plated metal film formed on the surface of this case is effective in shielding electrostatic induction noise as in the conventional metal plate shield case. Target.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A basic embodiment of the shield case of the present invention is shown in FIG. Ferrite shield case 1
Is preformed in a box shape that matches the electronic circuit to which it is applied, its lower surface side is open so that it can be mounted on a printed wiring board, and it is attached to a predetermined position on the wiring board This covers the required circuit components (circuit blocks) mounted on the board. A plated metal film 2 is formed on almost the entire inner surface of the ferrite shield case 1. The plated metal film 2 serves as a shield having good electrostatic induction noise as in the conventional shield case made of a metal plate. The shield case 1 is attached to the circuit board, and the plated metal film 2 is connected to the chassis ground.

The plated metal film 2 is formed by electroless plating as follows. First, ferrite shield case 1
An aqueous solution of sodium hydroxide is applied to the inner surface of the and then heated to etch the ferrite surface. This etching process activates that portion. In this way, the ferrite shield case 1 in which only the inside of the case is activated is electrolessly nickel-plated using a boron-based reducing agent to form a nickel film 2 having a thickness of about 1 μm.
The nickel crystals deposited on the ferrite surface by electroless nickel plating are sufficiently small, and the adhesion strength with ferrite is very high.

Although the plated metal film 2 is formed only on the inner surface of the case 1 in the above-described embodiment, the present invention is not limited to this embodiment, but only on the outer surface of the case 1. Those having a plated metal film and those having a plated metal film formed on both the outer surface and the inner surface of the case 1 can be manufactured in the same manner as described above, if necessary, and the same operation as the above embodiment Produce an effect. Further, in the above-described embodiment, the ferrite surface is activated by etching during electroless nickel plating, but the present invention is not limited to this embodiment, and the ferrite surface may be activated by sputtering gold or the like. good. Further, in the above-mentioned embodiment, the nickel film is formed on the surface of the ferrite by electroless nickel plating, but the present invention is not limited to this embodiment, and other metals may be plated, for example, on the above nickel plating. Further, electroless copper plating may be further applied to form a plated metal film having a two-layer structure of nickel and copper.
When the surface layer is a copper film, it is preferable to perform surface oxidation prevention treatment.

[0010]

As described in detail above, according to the present invention, a ferrite shield case attached to a circuit board and formed to cover a required portion has substantially the entire inner surface and / or outer surface. Since the plated metal film is formed on the surface, the ferrite shield case effectively shields the electromagnetic induction noise, and the plated metal film formed on the surface of this case is the same as the conventional metal plate shield case. Effectively shields electric noise. Therefore, the required circuit portion can be shielded strictly electrostatically and magnetically. Moreover, the shield case of the present invention is small in size, occupies a small space at the time of installation, and is light in weight, as compared with the conventional shield case having a double structure made of ferrite and metal plate, which has almost the same effect.
Further, since the metal film formed by plating has high suitability for mass production, it can be manufactured at a lower cost than the conventional double-structured shield case.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a shield case according to an embodiment of the present invention.

[Explanation of symbols]

 1 Shield case made of ferrite 2 Plated metal film

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Takeo Maeda 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd.

Claims (1)

[Claims] 1. A ferrite shield case attached to a circuit board and formed to cover a required portion, wherein a plated metal film is formed almost entirely on at least one of an inner surface and an outer surface of the shield case. A shield case for electronic circuits.