JPH07162181A - Method for preventing electromagnetic wave of electronic module from leaking - Google Patents

Abstract

PURPOSE:To reduce the possibility of the leaking of the electromagnetic waves to the outside of a metallic case which are radiated from high-frequency circuits provided on printed boards. CONSTITUTION:In a method for preventing the electromagnetic wave of an electronic module from leaking, printed boards 1 are stored in a metallic case 20 whose upper part is opened, and the opening of the metallic case 20 is covered by its cap member or by the bottom plate of another metallic case put in a superimposing way on the upper stage of the metallic case 20. In this method, through holes 50 connected with a ground layer 2 of the printed board 1 are provided respectively in the peripheral parts of the printed board 1, and printed-board fastening screws 45 are inserted into the respective through holes 50, and further, the screws 45 are driven respectively in a fastening way into the female screws of bosses 25 arranged on a bottom plate 21 of the metallic case 20, and thereby, the ground layer 2 is connected with the metallic case 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave leakage prevention method for electronic modules. An electronic module that has a high-frequency circuit formed by mounting semiconductor components on a printed circuit board has the following characteristics: When electromagnetic waves emitted from the high-frequency circuit leak into the surrounding space,
Electronic devices installed nearby may malfunction.

Therefore, in order to prevent such a situation, it is required that the printed board on which the high-frequency circuit is formed is sealed and housed in a metal case.

[0003]

2. Description of the Related Art FIG. 6 is a diagram of a conventional example, (A) is a sectional view, and (B) is a sectional view.
Is a plan view. In the figure, reference numeral 1 denotes a printed board on which semiconductor parts and the like are mounted and a high-frequency circuit is provided, and has a ground layer 2 as an inner layer.

The ground lead of the semiconductor component surface-mounted on the printed board 1 is connected to the ground layer 2 through the ground pattern 3 and the via 4. Reference numeral 20 denotes a shallow box-shaped metal case that is made of aluminum or the like and that accommodates the printed board 1 and has an open top. It is often the case that a plurality of metal cases 20 are stacked and fixed to each other.

Each metal case 20 has a case bottom plate 21.
A boss 25 that supports the back surface of the printed board 1 is provided near the four corners of the upper surface of the above, and a screw hole into which a printed board fixing screw 45 is screwed is provided at the axial center of the boss 25.

Further, bosses 26 (four in the figure) are arranged at desired positions on the upper surface of the case bottom plate 21. A screw hole into which the case connecting screw 46 is screwed is provided in the shaft center of the boss 26 of the lower metal case 20, and a hole through which the case connecting screw 46 penetrates is provided in the shaft center of the boss 26 of the upper metal case 20. It is provided.

Reference numeral 28 denotes a lid member that closes the upper opening of the uppermost metal case 20 and is made of, for example, aluminum, and has a hole for inserting the neck portion of the case connecting screw 46 at a position corresponding to the case connecting screw 46. It is provided.

On the other hand, the printed board 1 is provided with a hole into which the printed board fixing screw 45 is inserted at a position corresponding to the boss 25, and the case connecting screw 46 is provided at a position corresponding to the boss 26.
Is provided with a hole.

The printed board 1 is horizontally accommodated in the metal case 20 and placed on the boss 25, and the printed board fixing screw 45 is attached to the boss 25.
The printed board 1 is fixed by being screwed into 25 screw holes.
Further, each pin of the connector 10 mounted so as to penetrate the selected case side plate 22 of the metal case 20 is connected to the corresponding pad formed on the surface of the printed board 1 via a wire.

The ground pin 11 of the connector 10 is connected to the ground pad 5 via a wire. The ground pad 5 is connected to the ground layer 2 via a ground pattern and a via 6.

On the other hand, the ground pad 5 and the case side plate 22 are connected by soldering wires to ground the ground layer 2 and the ground pin 11 to the metal case 20. Then, the other metal case 20 is stacked on the upper side of one metal case 20, the upper metal case 20 is covered with the lid member 28, and the upper and lower metal cases 20 are fixed by the case connecting screws 46.

The opening of the lower metal case 20 is closed by the case bottom plate 21 of the upper metal case 20, and the upper metal case 20 is closed.
Since the opening is closed by the lid member 28, each printed board 1 is electromagnetically sealed.

In this way, the electromagnetic waves emitted from the printed board 1 are prevented from leaking out of the metal case 20.

[0014]

However, since it is difficult to completely eliminate the gap between the metal case and the lid member and between the metal case and the case bottom plate of the upper metal case, it is difficult to eliminate these gaps. There is a problem that electromagnetic waves leak to the outside of the metal case.

The housing of the connector is molded from resin. Therefore, electromagnetic waves may leak from the connector to the outside of the metal case.
The present invention has been made in view of the above circumstances, and an electromagnetic wave leakage prevention method for an electronic module in which electromagnetic waves emitted from a high frequency circuit provided on a printed board are less likely to leak to the outside of a metal case. Is intended to provide.

[0016]

In order to achieve the above object, the present invention, as illustrated in FIG. 1, accommodates a printed board in a metal case having an opening at the upper side and covers the opening of the metal case with a lid member or In the method of preventing electromagnetic wave leakage of an electronic module that is covered with a case bottom plate of a metal case that is placed on top of one another, a through hole 50 that connects to the ground layer 2 of the printed board 1 is provided in the peripheral portion of the printed board 1 and each through hole is provided. The printed board fixing screw 45 is inserted into the hole 50, and the printed board fixing screw 45 is screwed into the screw hole of the boss 25 arranged on the case bottom plate 21 to connect the ground layer 2 and the metal case 20. .

Further, as illustrated in FIG. 3, through holes
A tube 55 made of a conductive rubber is inserted in 50. Further, as illustrated in FIG. 4, it is assumed that the electromagnetic wave absorbing substance 60 is adhered to the inner surface of the lid member 28 of the metal case 20 or the back surface of the case bottom plate 21 of the metal case 20 that is placed on the upper stage.

Alternatively, as illustrated in FIG. 5, the surface of the electromagnetic wave absorbing material 60 facing the printed board 1 is corrugated.

[0019]

According to the present invention, since the ground layer formed on the printed board is grounded to the metal case through a large number of through holes arranged in the peripheral portion, the potential difference between the ground layer and the metal case is small. Therefore, there is almost no impedance in the ground line of the ground signal.

As a result, the latent antenna is hardly formed in the high frequency circuit, and the electromagnetic waves (noise) emitted from the printed board and the electronic parts mounted on the printed board are suppressed. Therefore, electromagnetic waves leaking out of the metal case are reduced.

If a tube made of conductive rubber is inserted into the through hole, the neck of the printed board fixing screw is inserted into the hollow portion of the tube, and the printed board fixing screw is screwed into the screw hole of the boss, the tube The height is compressed, and the outer peripheral surface of the tube is brought into close contact with the inner wall of the through hole, and the inner wall of the tube is brought into close contact with the outer peripheral surface of the neck portion of the printed board fixing screw.

Therefore, since the potential difference between the ground layer and the metal case is almost eliminated, electromagnetic waves (noise) emitted from the printed board and the electronic parts mounted on the printed board are further suppressed.

On the other hand, by depositing an electromagnetic wave absorbing substance on the inner surface of the lid member of the metal case or the back surface of the case bottom plate of the metal case which is placed on the upper stage, the electromagnetic wave absorbing substance is released from the printed board and the electronic parts mounted on the printed board. Electromagnetic waves (noise) are absorbed. Therefore, electromagnetic waves leaking out of the metal case are reduced.

[0024]

The present invention will be described in detail with reference to the drawings. The same reference numerals denote the same objects throughout the drawings.

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is a plan view of an embodiment of the present invention, FIG. 3 is a sectional view of essential points of another embodiment of the present invention, and FIG. FIG. 5 is a sectional view of the invention, and FIG. 5 is a sectional view of the invention of claim 4.

In the figure, a printed board 1 on which a semiconductor component or the like is mounted and which is provided with a high-frequency circuit is provided with a ground layer 2 as a selected inner layer. 50 is arranged on the peripheral portion of the printed board 1 so as to be connected to the ground layer 2 (9 in FIG. 2).
Through hole).

The ground lead of the semiconductor component surface-mounted on the printed board 1 is connected to the ground layer 2 via the ground pattern 3 and the via 4. A shallow box-shaped metal case 20 made of aluminum or the like having an upper opening is used for accommodating and fixing the printed board 1 in parallel with the case bottom plate 21.
A boss that supports the back surface of the printed board 1 at a position corresponding to 50
25 are arranged, and the printed board fixing screw 45 is attached to the axis of the boss 25.
Is provided with a screw hole for screwing.

Further, bosses 26 (four in the figure) are arranged at desired positions on the upper surface of the case bottom plate 21. The metal case 20 described above is often used by stacking several metal cases.

Therefore, the boss 26 of the lower metal case 20
A screw hole into which the case connecting screw 46 is screwed is provided in the shaft center, and a hole through which the case connecting screw 46 penetrates is provided in the shaft center of the boss 26 of the upper metal case 20.

The lid member 28 made of, for example, aluminum for closing the upper opening of the uppermost metal case 20 is
At the position corresponding to the case connecting screw 46,
There is a hole for inserting the neck portion.

The lower surface of the lid member 28 is a stepped surface so that it fits into the opening of the metal case 20 and comes into close contact therewith, and the back surface of the case bottom plate 21 of the metal case 20 mounted on the upper step is also made.
The stepped surface is formed so as to be fitted into the opening of the metal case 20 in the lower step and closely adhere to it.

The printed board 1 is horizontally housed in the metal case 20 and placed on the boss 25. The printed board fixing screw 45 is inserted into the through hole 50 and screwed into the screw hole of the boss 25 to print. The plate 1 is fixed.

Also, the case side plate selected for the metal case 20.
Each pin of the connector 10 mounted so as to penetrate through 22 is connected to a corresponding pad formed on the surface of the printed board 1 through a wire, and the ground pin 11 of the connector 10 is connected.
Is connected to the ground pad 5 via a wire.

The ground pad 5 is connected to the ground layer 2 via a ground pattern and a via 6. On the other hand, the ground pad 5 and the case side plate 22 are connected by soldering a wire to ground the ground layer 2 and the ground pin 11 to the metal case 20.

Then, the other metal case 20 is placed on the upper stage of one metal case 20, the upper metal case 20 is covered with the lid member 28, and the upper and lower metal cases 20 are fixed by the case connecting screws 46.

Therefore, since the opening of the lower metal case 20 is closed by the case bottom plate 21 of the upper metal case 20, and the opening of the upper metal case 20 is closed by the lid member 28, the respective prints are printed. The plate 1 is electromagnetically sealed.

As described above, a large number of through holes 50 are arranged in the peripheral edge of the printed board 1, and the printed board fixing screws 45 are inserted into the through holes 50 to attach the printed board 1 to a metal case.
Since it is fixed to 20, ground layer 2-through hole 50
-The upper land of the through hole-The printed board fixing screw 45-A large number of ground paths of the metal case 20 are formed.

The ground layer 2-through hole 50-lower land of the through hole-ground path of the metal case 20 is formed. Therefore, the potential difference between the ground layer and the metal case becomes small, and the impedance of the earth line of the earth signal is almost zero. Therefore, the high frequency circuit has almost no latent antenna, and electromagnetic waves emitted from the printed board and the electronic components mounted on the printed board are suppressed. As a result, electromagnetic waves leaking out of the metal case 20 are reduced.

In FIG. 3, reference numeral 55 denotes a through hole having an outer diameter.
It is almost equal to the inner diameter of 50, the inner diameter is slightly larger than the outer diameter of the neck portion of the printed board fixing screw 45, and the length is the printed board 1
It is a tube made of conductive rubber that is slightly thicker than the plate thickness.

The above-mentioned tubes 55 are fitted into the respective through holes 50, the neck portion of the printed board fixing screw 45 is inserted into the hollow portion of the tube 55, and the printed board fixing screw 45 is attached to the boss 25.
The printed board 1 is fixed to the case bottom plate 21 by being screwed into the screw holes.

Therefore, the height of the tube 55 is compressed, and the outer peripheral surface of the tube 55 comes into close contact with the inner wall of the through hole 50, and the inner wall of the tube 55 comes into close contact with the outer peripheral surface of the neck portion of the printed board fixing screw 45.

Therefore, the potential difference between the ground layer 2 and the metal case 20 is almost eliminated. Therefore, the electromagnetic waves emitted from the printed board and the electronic components mounted on the printed board are further suppressed.

In FIGS. 4 and 5, reference numeral 60 is an electromagnetic wave absorbing substance such as soft ferrite. As shown in FIG. 4, the electromagnetic wave absorbing substance 60 is adhered to the inner surface of the lid member 28 and the back surface of the case bottom plate 21 of the upper metal case 20.

As a result, the electromagnetic waves (noise) emitted from the printed board 1 and the electronic parts are absorbed by the electromagnetic wave absorbing material 60.
Electromagnetic waves leaking out of the metal case 20 are reduced because they are absorbed by.

In FIG. 5, reference numeral 61 denotes a corrugated member 61 obtained by bending a corrugated aluminum plate, for example. The electromagnetic wave absorbing substance 60 is adhered to one surface of the corrugated member 61, and the back surface side of the corrugated member 61 covers the inner surface of the lid member 28 and the case bottom plate of the upper metal case 20.
It is adhered to the back surface of 21 using an adhesive or the like.

When the surface of the corrugated member 61 is coated with the electromagnetic wave absorbing material 60 as described above, the electromagnetic wave (noise) absorption area increases. Therefore, the electromagnetic waves leaking out of the metal case 20 are further reduced.

[0047]

As described above, according to the present invention, a large number of through holes for connecting to the ground layer are provided in the peripheral portion of the printed board, and the printed board fixing screws are inserted into the through holes to put the printed board in the metal case. By fixing and grounding the ground layer to the metal case, electromagnetic waves (noise) emitted from the printed board and electronic components mounted on the printed board are suppressed, and electromagnetic waves leaking out of the metal case are reduced. Have an effect. .

The electromagnetic wave absorbing substance is deposited on the inner surface of the lid member of the metal case or the back surface of the case bottom plate of the metal case which is placed on the upper stage, so that the electromagnetic wave absorbing substance is released from the printed board and the electronic parts mounted on the printed board. Electromagnetic waves (noise)
Is absorbed, and the electromagnetic wave leaking to the outside of the metal case is further reduced.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention.

FIG. 2 is a plan view of an embodiment of the present invention.

FIG. 3 is a cross-sectional view of essential parts of another embodiment of the present invention.

FIG. 4 is a sectional view of the invention of claim 3;

FIG. 5 is a sectional view of the invention of claim 4;

FIG. 6 is a view of a conventional example, (A) is a sectional view, and (B) is a plan view.

[Explanation of symbols]

1 printed board 2 ground layer 3 earth pattern 10 connector 11 earth pin 20 metal case 21 case bottom plate 25,26 boss 5 28 lid member 45 printed board fixing screw 46 case connecting screw 50 through hole 55 tube 60 electromagnetic wave absorbing substance 61 corrugated member

Claims (4)

[Claims] 1. A method of preventing electromagnetic wave leakage of an electronic module, wherein a printed board is housed in a metal case having an upper opening, and the opening of the metal case is closed by a lid member or a case bottom plate of the metal case that is placed above the metal case. A through hole (50) that connects to the ground layer (2) of the printed board (1) is provided on the peripheral edge of the printed board (1), and the printed board fixing screw (4) is attached to each of the through holes (50).
5) and insert the printed board fixing screw (45) into the case bottom plate.
(21) A method for preventing electromagnetic wave leakage of an electronic module, characterized in that the ground layer (2) and the metal case (20) are connected to each other by being screwed into the screw holes of the bosses (25) arranged above. 2. A method of preventing electromagnetic wave leakage of an electronic module, characterized in that a tube (55) made of conductive rubber is inserted into the through hole (50) according to claim 1. 3. An electromagnetic wave absorbing substance (60) is applied to the inner surface of the lid member (28) of the metal case (20) or the back surface of the case bottom plate (21) of the metal case (20) which is placed on the upper stage. The method for preventing electromagnetic wave leakage of an electronic module according to claim 1 or 2, characterized in that: 4. The electromagnetic wave absorbing substance (60) according to claim 3,
A method for preventing electromagnetic wave leakage of an electronic module, characterized in that the surface facing the printed board (1) is corrugated.