JP2000059063A - Shield case with opening - Google Patents

Abstract

PROBLEM TO BE SOLVED: To take a measure for radiating heat and reducing the leakage of radiation interfering waves by locating a conductor larger than an opening of a shield case inside or outside the shield case, in parallel with the opening and bringing the conductor into continuity with the shield case. SOLUTION: A shielding case 101 is provided with an opening 103 at the center of a copper plate. A shielding plate 102 is fixed by a copper plate and is located 8 mm away from one side of the opening face, with short sides connected to the shield case 101 by solder. Thus, the shielding plate 102 overlaps a shield layer by 23 mm on each side, and a single turn loop antenna of 10 mm diameter is installed on the ground face on a side opposide from the opening of the case. By installing the shielding plate in this manner, radiation interfering waves can be suppressed at high frequency range, while efficiently radiating heat and having an opening for extraction of cables.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a shield case for preventing an obstacle caused by an electromagnetic wave radiated from an electronic device.

[0002]

2. Description of the Related Art In recent years, there has been a problem that electromagnetic waves emitted from electronic devices such as computers cause electromagnetic interference or electromagnetic interference in peripheral devices. For this reason, it is obliged to keep the level of the radiated interference wave radiated from the electronic device below the standard value defined by VCCI (Voluntary Council for Radio Interference such as Information Processing Equipment).

[0003] The radiated interference wave exceeding the standard value is usually a harmonic component generated by an electronic circuit having a high clock frequency. Conventionally, as a countermeasure against these radiated interference waves, a method has been adopted in which, for example, an electromagnetic wave shield is provided in a sealed case except for an input / output portion such as a connector in an electronic circuit portion of the device. However, in recent years, the use frequency has been increased, the power consumption has increased, the temperature inside the case has risen, and there is a fear that the operation of the electronic components will be adversely affected. An opening is formed.

On the other hand, in the opening of the connection cable between the boards, a rectangular opening having a large side surface is provided, and no measures are taken against radiated interference by the shield case at present.

[0005]

However, the frequency used in recent computers exceeds 200 MHz, and 60 MHz is used for wiring patterns on electronic circuits. At present, the leakage of radiated emission is large at long side openings.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a shield case capable of reducing the leakage of radiated interference waves while taking measures against heat radiation.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention has been made to solve such a problem, and an opening is provided. A large conductor is arranged inside or outside a shield case, and a shield case with an opening characterized by conduction with the shield case is adopted.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, the leakage of radiated disturbance waves due to the shape of an opening is larger when the length of one side is longer than the area of the opening. Therefore, when drawing out multi-core flat cables,
When an opening is provided in the shield case, the leakage of the radiated interference wave becomes extremely large.

The attenuation of the shield effect by the conventional multiple aperture is expressed by the following equation. S = −18 log N Here, N is a numerical aperture. Increasing the numerical aperture by about 20 to 30 results in an attenuation of 20 dB. Looking at the frequency characteristics, when the diameter of the opening is 5 mm, attenuation starts around 10 Mhz, and when the frequency increases, leakage of the interference wave increases,
A new opening structure is required.

On the other hand, regarding the shielding effect of a metal plate,
If sufficient grounding can be obtained, a shielding effect can be expected, but there is no report on the size covering the source. Therefore, a slit-shaped opening is provided in the conductor, and the Advantest method using a small antenna is used to measure 0, 5,
The shielding effect when the slit position was moved to 10, 15, 35, and 55 mm was evaluated, and the covering range and the shielding effect were obtained.

FIG. 4A is a layout view of an antenna and a slit according to the Advantest method, which is one of the shield effect evaluation devices. The center of the metal casing is separated by a sample, and a magnetic field or electric field antenna of the same type is mounted at a position separated by 20 mm.

FIG. 4 (b) is a block diagram of a system for evaluating the shielding effect in KEC (reported by Kansai Electric Machinery Promotion Association: EMCJ85-52 Hariya). A signal generator is used on the input side, and the power of the attenuated electromagnetic wave is displayed in dBm using a spectrum analyzer on the output side. 4B, reference numeral 2514 denotes a standard signal generator (MG3601A: manufactured by Anritsu);
0 is an amplifier (TR45002: manufactured by Advanced Test), 1217 is an amplifier (8447D: manufactured by HP), and 2518 is a spectrum analyzer (8568B: H).
P).

The sample was made of 100 × 100 mm ABS with a thickness of 3 mm and a slit size of 10 × 50 mm. The slit positions are 0, 5, 15,
There are five points of 35 and 55, and the shield plating is processed on both sides to make the sample conductive.

FIG. 5B is a graph showing the frequency on the horizontal axis and the shielding effect on the vertical axis. From the figure, it can be seen that the shielding effect increases as the position from the center increases. Attenuation of 40 dBm at 100 MHz can be realized at a level of general single-sided plating at a distance of 35 mm. The decrease in the graph above 100 MHz is due to an increase in the ground impedance and a reduction in the shielding effect.

According to the aforementioned EMCJ85-52 Hariya report, the slit position is 0 mm and the slit size is 1 ×.
50mm data is shown, with a similar trend,
Significant attenuation of the shielding effect in horizontal polarization was observed. However, this measurement is slightly higher. This may be due to the thickness of the sample.

From these results, it can be said that, at a frequency of about 100 MHz, a shielding effect substantially the same as that obtained when there is no slit is obtained at a distance of more than 35 mm. In this way, the area around the source of the radiated disturbance is covered with a conductor layer,
It can be said that a sufficient shielding effect can be obtained even if the portion away from the source is replaced with a nonconductor.

Therefore, the specific size of the opening may be smaller than the size of the shielding plate. At the outlet of flat cable etc., protection of plastic etc. is necessary.
An opening of about 0 mm is often used. The distance between the shield plate and the upper surface of the shield case increases as the temperature inside the case increases, and the warmed air inside is released.

Preferably, as shown in FIG. 6B, it is ideal that the overlap of the openings is 50 mm.
Even if it is 0 mm, the shielding effect is slightly reduced, but it can be used as a noise countermeasure.

The shield plate needs to be connected to the ground. When connecting to the shield case, as shown in FIG. 1, if one of the shield plates is long enough to reach the side surface of the shield case and the other is shorter than the shield case, the bending is connected. The structure becomes easy only by the part. At this time, the distance between the shield plate and the shield case is 2 to
It may be about 20 mm.

In the structure according to the second invention, the structure is simplified by separating the shield plate and the shield case. The connection to the shielding plate and the ground affects the shielding effect, but if shared with the ground of the shielding case,
Similar effects can be expected even if they are not integrated.

With this structure, the shield case can be detached while the flat cable or the like is connected to the connector.

The structure according to the third invention is shown in FIG.
As shown in (b), a plurality of openings and conductors corresponding to the positions of the openings are arranged, and the cased case has openings.

When there are a plurality of openings, air convection in the case is improved, and heat dissipation can be expected. Further, in order to increase the heat radiation efficiency, by forming an opening corresponding to the provision of a similar shielding plate on the side surface, the air permeability with the outside of the shielding case is improved, and a higher effect is obtained.

Based on the above configuration, by providing an opening corresponding to the shielding plate, good heat dissipation and wide cable extraction are possible, and an effective shield can be obtained.

[0025]

Embodiments of the present invention will be described below.

(Embodiment 1) FIGS. 1A and 1B are a configuration diagram and a sectional view showing an embodiment 1 of a shield case with an opening according to the present invention.

FIG. 7A shows a configuration of a shield case with an opening according to the present invention, which is evaluated using EMSCAN (here, antenna scan Matsushita Electric Co., Ltd. is used). 101 is a 93 × 93 × 53 mm thick plate 0.075
mm copper plate shield case, 9x80m in the center
m openings are provided. 102 was fixed with a 53 × 93 copper plate having a thickness of 0.075 mm. The position is 8 mm apart from the position of one side of the opening surface, and the short side is connected to the shield case by solder.

Therefore, the distance overlapping the shield layer was set to 23 mm on one side. A one-turn loop antenna with a diameter of 10 mm is attached to the opposite ground surface corresponding to the opening of the case.

In FIG. 7B, the shield case was fixed on the antenna scan with the opening face down. A signal was supplied to the above-mentioned configuration by a signal generator, and the leakage magnetic field strength distribution of the disturbing electromagnetic wave was measured using an antenna scan.

In FIG. 9, a 200 MHz, 400 MHz signal is transmitted from a standard signal generator via a 75 ohm coaxial cable.
z, output at an intensity of 100 dBμV at each frequency of 500 MHz, and supply it to the loop antenna. The antenna scan on the detection side obtains the signal intensity of the frequency of 30 to 1000 MHz as a spare mode, and other frequency components are generated by the aperture. I confirmed that it was low.

FIG. 8 shows that the peak frequency obtained in FIG.
The output of 00 dBμV shows the measurement result of the proximity magnetic field strength distribution by the antenna scan.

The right side shows a configuration in which an opening and a shielding plate are arranged. The left side has a configuration in which only the opening is provided. In the figure, the white inside has a high intensity of 40 dBμV or more, and up to 500 MHz, the magnetic field intensity by the shielding plate is greatly attenuated, and the effect is seen.

When viewed in the 30 to 3540 dBμV range, the portion that looks slightly whitish than black in the background extends to about half of the entire area on the left side of the opening alone, but in the figure on the right side with the shielding plate, At 500 MHz, the effect is reduced as compared with that at 400 MHz, but the signal attenuation is large.

By providing the shielding plate in this way, it is possible to suppress radiated interference waves corresponding to a high frequency range while having an opening for heat radiation and cable drawing.

The same effect can be obtained by arranging the shield plate outside the shield case as shown in FIG. At this time, the shield plate needs to have a structure in which the side surface of the flat plate is bent to connect the case to the ground, or the shield plate is connected to the same ground as the case.

(Embodiment 2) FIG. 3 is a structural view and a sectional view showing Embodiment 2 of a shield case with an opening according to the present invention. FIG. 3A is a perspective view of the shield case, and FIG. 3B is a top view and a side view.

In this configuration, the shield plate and the shield case are separated so that the shield case can be attached and detached without disconnecting the connector even when a flat cable or the like is connected to the outside.

By forming such a shield structure having a shield plate, good heat dissipation and suppression of radiated interference can be achieved.

Comparative Example 1 FIG. 10A is a sectional view, and FIG. 9B is a top view. The opening is 5mm in diameter,
The pitch was 15 mm. At this time, the shielding effect at each frequency when one piece of 5 mm is used is attenuated by the value of −18 logN. When the number of holes is about 30 to 50, the reduction is as large as about 20 dBμV.

In particular, in the 500 MHz class, it is known that a large reduction in radiated interference occurs even with one aperture. In addition, when an opening such as a flat cable is provided, the leakage of interfering electromagnetic waves is greatly increased.

[0041]

As described above, according to the present invention, since the shield structure having such a shield plate is provided, even if there is a cable outlet or a heat radiating port, good heat radiation and effective radiated interference can be obtained. Is obtained.

[Brief description of the drawings]

FIG. 1 is a view for explaining a shield case with an opening according to a first embodiment of the present invention; FIG.
FIG. 1A is a perspective view of a shield case, and FIG.
FIG. 3 is a top view and a cross-sectional view of the shield case.

FIG. 2 is a diagram for explaining a shield case with an opening according to the first embodiment of the present invention.
2A is a front view of the shield case, FIG. 2B is a plan view of the shield case, and FIG. 2C is a side view of the shield case.

FIG. 3 is a view for explaining a shield case with an opening according to a second embodiment of the present invention.
3A is a perspective view of the shield case, and FIG. 3B is a top view and a cross-sectional view of the shield case.

FIG. 4 is a diagram for explaining a shield effect evaluator. FIG. 4A is a layout diagram of an antenna and a slit according to the Advantest method, which is one of the shield effect evaluators. FIG. 4B is a block diagram of a system for evaluating a shielding effect in KEC (reported by Kansai Electric Machinery Promotion Association: EMCJ85-52 Hariya).

FIG. 5 is a diagram for explaining various samples and an attenuation effect, of which FIG. 5A is a diagram for illustrating various slit positions of the sample, and FIG. )
Is a graph showing the amount of attenuation for a sample.

FIG. 6 is a diagram illustrating a result of measuring a proximity magnetic field of a circuit board by EMSCAN.

FIG. 7 is a diagram illustrating a system for evaluating a shielding effect of a near magnetic field in an antenna scan.

FIG. 8 is a diagram showing a result of evaluating a proximity magnetic field distribution in an antenna scan.

FIG. 9 is a graph showing evaluation results of an antenna scan spectro analyzer.

10A and 10B show a configuration of a conventional example, in which FIG. 10A is a cross-sectional view and FIG. 10B is a top view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Shield case 102 Shield plate 103 Opening 202 Shield plate 203 Opening 301 Shield case 302 Shield plate 303 Opening

Claims (4)

[Claims] In a shield case for reducing radiation noise of a circuit board of an electronic device, an opening is provided in a surface of the shield case, and a conductor larger than the opening is arranged inside or outside the shield case in parallel with the opening. And a shield case with an opening, wherein the conductor is connected to the shield case. 2. The shielded case with an opening according to claim 1, wherein said conductor is connected to a common ground with said shielded case. 3. The shield case with openings according to claim 1, wherein a plurality of openings and conductors corresponding to the positions of the openings are arranged. 4. The configuration according to claim 1, wherein the size of the conductor is 1 to 50 mm larger on one side than a position where the opening of the shield case is projected.
Shield case with opening.