JPH09205290A - Circuit substrate with low emi structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the influence of electromagnetic wave radiated from the peripheral part of a circuit substrate. SOLUTION: A power supply layer 1 is provided on one surface of a substrate which is not shown and a ground layer 2 is provided on the other surface. Fine conductor patterns 4 and 5 are alternately arranged at the peripheral part of one surface and fine conductor patterns 3 and 6 are alternately arranged also on the other surface. Then, every other conductor pattern 4 arranged at the peripheral part of one surface is connected to a ground layer 2 and the other every other conductor pattern 5 is connected to the power supply layer 1, every other conductor pattern 3 which opposes the conductor pattern 4 arranged at the peripheral part of one surface is connected to the power supply layer 1 and every other conductor pattern 6 which opposes the conductor pattern 5 is connected to the ground layer 2. As a result, the conductor patterns 3 and 4 form a fine dipole antenna and the conductor pattern 5 and 6 from a fine dipole antenna for radiating an electromagnetic wave in opposite phase.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to EMI, which is becoming more and more important in speeding up and increasing the density of ICs, LSI elements and circuits.
The present invention relates to a method for suppressing unnecessary radiation noise associated with a compatible electronic device and a circuit board using the same.

[0002]

2. Description of the Related Art In a workstation or personal computer, its circuit elements are driven by a power supply layer and a ground layer to which a direct current is supplied. In recent years, due to the increase in speed of these elements, the switching frequency of the elements has increased. When the element is driven to consume power, a current flows in the power supply layer, and as a result, the potential between the power supply layer and the ground layer changes. This potential fluctuation propagates in these layers,
It reflects at the periphery of these layers. By repeating this reflection, the portion composed of the power supply layer and the ground layer functions as a resonator, and electromagnetic waves are radiated from their peripheral portions to the surroundings.

As a countermeasure against such electromagnetic wave radiation,
Conventionally, it is known to provide a shield as shown in Japanese Patent Laid-Open No. 5-136591. In this conventional technique, in order to prevent unnecessary radiation generated from the circuit board from leaking to the outside, it is considered that the radiation surface is covered with a metal plate to provide a shield by attaching a shield cover to the circuit board. There is.

[0004]

By the way, in the above-mentioned prior art, it is said that the shielding effect can be obtained by enclosing the circuit board with the shield cover, but since the elucidation of the mechanism is delayed, it is sufficient in the necessary frequency range. It is difficult to get the effect.

It is an object of the present invention to provide a circuit board having a low EMI structure which solves the above problem and is capable of sufficiently reducing unnecessary radiation of electromagnetic waves in a required frequency range. .

[0006]

In order to achieve the above object, the present invention provides a circuit board in which a power supply layer is provided on one surface of the board and a ground layer is provided on the other surface, and the periphery of the circuit board is provided. The parts are divided into minute parts, and the phases of radiated electromagnetic waves are opposite to each other between adjacent minute parts.

In a circuit board in which a power supply layer is provided on one surface of the board and a ground layer is provided on the other surface, a phenomenon in which electromagnetic waves are radiated from the peripheral portion of the circuit board is modeled as follows. I can think. That is, it is considered that in the peripheral portion of the circuit board, minute dipole antennas each including a minute portion of the power supply layer and a minute portion of the ground layer facing the power source layer are arranged around the circuit board.
The distance between the dipole antennas that are close to each other can be regarded as almost 0 when viewed from a distance. Therefore, when this circuit board is viewed from a distance, it radiates a composite electromagnetic wave of electromagnetic waves from all these minute dipoles. It can be regarded as one dipole antenna.

Therefore, as described above, when the phases of the electromagnetic waves radiated from the adjacent minute dipoles in the peripheral portion of the circuit board are set to be opposite to each other, at a position sufficiently far from the circuit board, The electromagnetic waves from the adjacent small dipole antennas cancel each other sufficiently, and as a result, the electromagnetic waves from this circuit board have almost no influence.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a main part of an embodiment of a circuit board having a low EMI structure according to the present invention.
Is a power layer, 2 is a ground layer, 3 to 6 are conductor patterns, 7
Reference numerals 10 to 10 are connecting lines.

FIG. 2 is a perspective view schematically showing the whole of this embodiment, in which 11 is a peripheral portion, and the portions corresponding to those in FIG. 1 are designated by the same reference numerals.

First, in FIG. 2, in this embodiment, a power supply layer 1 is provided on one surface of a substrate (not shown) on which circuits are formed, and a ground layer 2 is provided on the other surface.
A circuit element (not shown) is provided in this board to form a circuit board. Then, the circuit element is driven by supplying a DC power supply voltage to the power supply layer 1 and grounding the ground layer 2.

In such a circuit board, its peripheral portion 11
Further, an EMI structure is formed to prevent unnecessary radiation of electromagnetic waves.

Next, the EMI structure will be described with reference to FIG.

Conductor patterns 4 and conductor patterns 5 are alternately arranged on the periphery of the power supply layer 1. Every other conductor pattern 4 is connected to the ground layer 2 by a connecting line 10 passing through a through hole (not shown) provided in a substrate (not shown), and every other conductor pattern 5 is the same as this conductor pattern 5 on the substrate. It is connected to the power supply layer 1 by the connection line 8 formed on the surface.

Similarly, the conductor patterns 3 and the conductor patterns 6 are alternately arranged in the peripheral portion of the ground layer 2, and every other conductor pattern 3 is connected through a through hole (not shown) provided on a substrate (not shown). Power layer 1 by line 9
And every other conductor pattern 6 is connected to the ground layer 2 by a connection line 7 formed on the same surface of the substrate as this conductor pattern 6.

The conductor pattern 4 on the side of the power source layer 1 connected to the ground layer 2 and the conductor pattern 3 on the side of the ground layer 2 connected to the power source layer 1 are arranged to face each other, and the power source layer 1 Pattern 5 on the power supply layer 1 side connected to the
And the conductor pattern 6 on the ground layer 2 side connected to the ground layer 2 are arranged to face each other.

In order to connect the conductor patterns 3 to 6 to the power supply layer 1 or the ground layer 2, respectively,
Cuts are provided on the sides of the power supply layer 1 and the ground layer 2 at a predetermined interval offset from each other, and the respective conductor patterns 3 to 6 are formed.
Has a pattern shape such that a part of it enters the cut. The conductor patterns 3 to 6 have the same size and shape, and the conductor patterns 4 and 5 and the conductor patterns 3 and 6 are arranged in an inverted relationship in the drawing.

According to such a structure, the portion of the conductor pattern 3 that has entered the cut portion of the ground layer 2 faces the power supply layer 1, so that the conductor pattern 3 and the power supply layer 1 are connected through the through hole at that portion. Since the connection line 9 can be used for connection, and the part of the conductor pattern 4 that is cut into the power supply layer 1 faces the ground layer 2,
At that portion, the conductor pattern 4 and the ground layer 2 can be connected by the connection line 10 via the through hole.

Since the conductor pattern 5 and the power supply layer 1 and the conductor pattern 6 and the ground layer 2 face each other on the same plane, they may be connected at any position. From this point, It is not necessary to make the above cuts in the power supply layer 1 and the ground layer 2 for these conductor patterns 5 and 6,
As will be described later, in order to prevent the intensity of the generated electromagnetic wave from being affected differently by the difference in shape between the opposing conductor patterns 3 and 4 and the opposing conductor patterns 5 and 6, these conductor patterns 3 ˜6 have the same pattern shape.

In this structure, when a DC power supply voltage is supplied to the power supply layer 1 and the ground layer 2 is grounded, the potentials of the conductor patterns 3 and 5 change in the same phase as the potential change of the power supply layer 1,
The potentials of the conductor patterns 4 and 6 also change in the same phase as the potential change of the ground layer 2.

FIG. 3 is a front view of a part of the peripheral portion of the circuit board shown in FIG.
Is a small dipole antenna, and the portions corresponding to those in FIG. The conductor patterns 4 and 6 connected to the ground layer 2 are hatched.

In the same figure, between the conductor pattern 5 connected to the power source layer 1 (FIG. 1) and the conductor pattern 6 facing the conductor pattern 5 connected to the ground layer 2 (FIG. 2), the direction shown by the arrow is shown. And an electric field + E is generated between the conductor pattern 3 connected to the power supply layer 1 and the conductor pattern 4 facing the ground layer 2 in the direction indicated by the arrow opposite to the electric field + E. . When these electric fields ± E fluctuate, electromagnetic waves are radiated.

Since the conductor patterns 3 to 6 are minute, the conductor patterns 5 and 6 form the minute dipole antenna 12, and the conductor patterns 3 and 4 are also minute dipole antennas 13.
However, the electromagnetic waves radiated from these small dipole antennas 12 and 13 have opposite phases. Then, the electromagnetic waves from these small dipole antennas 12 and 13 spread and propagate in the space. Therefore, in the distance of the circuit board,
Electromagnetic waves having opposite phases cancel each other and become sufficiently small.

Micro dipole antennas are also formed between the conductor patterns (conductor patterns 4 and 5 and conductor patterns 3 and 6) provided on the same surface of the substrate, and electromagnetic waves are radiated from these antennas. In this case, However, since the electromagnetic waves between the adjacent minute dipole antennas have opposite phases to each other, the electromagnetic waves are sufficiently small at a position distant from the circuit board.

To explain the above in terms of the potential distribution of the power supply layer and the ground layer, in the conventional circuit board, the power supply layer,
The potential distribution in the ground layer forms a sin curve as shown in Fig. 5 (a) with the sides of these layers as open ends. These layers form a resonator, and the potential applied from the peripheral portion Radiates electromagnetic waves due to distribution. The resonance frequency of such a resonator is determined by its structure (that is, the lengths of the sides of the power supply layer and the ground layer), and as shown in FIG. 6, a specific frequency f ₁ according to the lengths of the vertical and horizontal sides of these layers. , F ₂ , and the radiation spectrum of the electromagnetic waves in which the energy is concentrated at the specific frequencies f ₁ and f ₂ are observed.

In this embodiment, as described above, minute dipole antennas are formed around the power supply layer 1 and the ground layer 2 so that the phases of electromagnetic waves radiated between adjacent minute dipole antennas are inverted. Therefore, the potential distribution shown in FIG. 5 (a) becomes as shown in FIG. 5 (b), and at a position distant from the circuit board, electromagnetic waves radiated from adjacent micro dipole antennas accompanying this are generated. By canceling each other out, the concentration of energy at the specific frequencies f ₁ and f ₂ shown in FIG. 6 is greatly reduced, and the influence of electromagnetic waves is almost eliminated.

FIG. 4 (a) is a sectional view taken along the section line BB in FIG. 1, and FIG. 4 (b) is a sectional view taken along the section line C-C, which corresponds to the above-mentioned drawing. Are given the same reference numerals.

As shown in FIG. 4A, the power supply layer 1 and the conductor pattern 5 connected thereto are provided on the same surface of the substrate in close proximity to each other, and the ground layer 2 and the ground layer 2 are connected thereto. Since the electric field between the power supply layer 1 and the conductor pattern 5 and the electric field between the ground layer 2 and the conductor pattern 6 are both 0 in a portion where the conductor pattern 6 is provided close to each other on the same surface of the substrate, Between these, no electromagnetic waves are generated,
On the other hand, as shown in FIG. 4B, a portion where the power supply layer 1 and the conductor pattern 5 connected to the ground layer 2 are provided close to each other on the same surface of the substrate, and the ground layer 2 and the power supply In the portion where the conductor pattern 6 connected to the layer 1 is provided close to each other on the same surface of the substrate, the electric field does not become 0, so electromagnetic waves are generated. For this reason, micro dipole antennas are formed in these parts, but the electromagnetic waves radiated from these micro dipole antennas also have opposite phases,
In the distance of the circuit board, these electromagnetic waves are canceled and become sufficiently small.

In this way, in this embodiment, the electromagnetic wave radiated from the peripheral portion of the circuit board can be made sufficiently small, but in order to completely cancel this electromagnetic wave,
In FIG. 1, further, connecting portions 9 and 10 and connecting portions 7 and 8
It is necessary to make the impedances of the two equal.
This not only makes the dimensions of the conductor patterns 3 to 6 equal to each other, but also adjusts the diameters of the connection parts 9 and 10 in the case of the connection parts 9 and 10 according to the difference in the length of these connection parts, or
In the case of the connecting portions 7 and 8, this can be realized by adjusting the widths of them. At high frequencies, the impedance is determined by the surface area of the conductor due to the skin effect. Therefore, the diameter and length of the connecting portions 9 and 10 are determined so that the surface area thereof is equal to the area of the conductor pattern.

Further, in this embodiment, the peripheral portions of the power supply layer 1 and the ground layer 2 are made less likely to reflect potential fluctuations.

That is, the states of the conductor patterns 3 and 4 and the conductor patterns 5 and 6 are different from each other in terms of high frequency. Therefore, the reflection of the potential fluctuation is not uniform in the peripheral portion 11 (FIG. 2) of the circuit board, and the entire layer does not have a resonator structure. Therefore, the electromagnetic wave as indicated by f ₁ and f _{2 in} FIG. Energy is dispersed in a wide frequency range without amplification of the frequency component of. Therefore, the characteristic of the radiation spectrum that the intensity is large at the specific wavelength (resonance frequency determined by the size of the circuit board) that has been conventionally measured does not appear.

As described above, in this embodiment, as compared with the conventional method in which the energy of the electromagnetic wave is concentrated in a specific frequency, this energy is dispersed in a wide frequency range, and as a result, unnecessary radiation is generated. Level is reduced.

Further, in this embodiment, since the peripheral portions of the power supply layer 1 and the ground layer 2 have the above-mentioned structure, the loss resistance as an antenna for radiating electromagnetic waves to the surroundings is increased. And because the loss resistance of the antenna increases, the radiation efficiency decreases, and as a result,
The amount of radiation from the antenna can also be kept small.

FIG. 7 is a perspective view showing a main part of another embodiment of a circuit board having a low EMI structure according to the present invention.
4, 15 are conductor patterns, 16 and 17 are connection parts,
The parts corresponding to those in FIG. 1 are designated by the same reference numerals.

In the figure, a power supply layer 1 is provided on one surface of a substrate (not shown) and a ground layer 2 is provided on the other surface, and minute conductor patterns 14 and conductor patterns 15 are alternately arranged over the entire end face of the substrate. Are arranged in. Then, every other conductor pattern 14 is connected to the power supply layer 1 by the connecting portion 16, and every other conductor pattern 1 is connected.
5 is connected to the ground layer 2 by the connecting portion 17.

The conductor pattern 14 is bent from the power supply layer 1 and fixed to the end surface of the substrate, and the conductor pattern 15 is formed.
May be bent from the ground layer 2 and fixed to the end surface of the substrate.
You are playing 17.

Needless to say, the tip of the conductor pattern 14 is separated from the ground layer 2 by a small distance, and the tip of the conductor pattern 15 is also separated from the power supply layer 1 by a small distance.

The peripheral portion of this circuit board shown in FIG.
8A, an electric field is generated in the direction indicated by the arrow between the tip of the conductor pattern 14 and the portion of the ground layer 2 facing the tip of the conductor pattern 14 as shown in FIG. The antenna 18 is formed. When the peripheral portion of this circuit board is viewed on the side of arrow C, as shown in FIG. 8B, an arrow is drawn between the tip portion of the conductor pattern 15 and the portion of the power supply layer 1 facing the tip portion. An electric field is generated in the direction shown,
These also form the small dipole antenna 19. And
As is clear from comparison between FIGS. 8A and 8B, the electric fields of the small dipole antennas 18 and 19 are opposite to each other, and thus the phases of electromagnetic waves emitted from them are opposite to each other. .

Therefore, in FIG. 7, in the peripheral portion of the circuit board, the small dipole antenna 1 with the conductor pattern 14 is formed.
4 and the small dipole antennas 19 by the conductor pattern 15 are arranged alternately, and the electromagnetic waves from these small dipole antennas 18 and 19 cancel each other out, as in the embodiment shown in FIG. , Will not reach far.

Here, the shapes of the conductor patterns 14 and 15 are
The dimensions are exactly the same, and the power supply layer 1 and the conductor pattern 1 are
If the connecting portion 16 of No. 4 and the connecting portion 17 of the ground layer 2 and the conductor pattern 15 have exactly the same size and shape, the respective micro dipole antennas 1 as viewed from the power supply layer 1 and the ground layer 2 are formed.
Since the impedances on the 8 and 19 sides are also equal, the cancellation of these electromagnetic waves is sufficiently effective, thereby eliminating the influence of electromagnetic waves in the distance.

As described above, in each of the above embodiments,
The electromagnetic waves radiated from the peripheral part of the circuit board are made to cancel each other out to reduce their strength. However, the smaller the number of small dipole antennas, that is, the number of conductor patterns, the smaller the electromagnetic wave. Although the effect becomes large, as shown in FIG. 9, a sufficient effect can be obtained at a certain number, and when it becomes more than a certain amount, the improvement in the effect becomes small. According to the experiment, when the conductor pattern has an area of 1/6 or less of that of the power supply layer 1 and the ground layer 2, a preferable effect of reducing electromagnetic waves was obtained to some extent.

[0042]

As described above, according to the present invention,
Since minute conductor patterns are provided on the periphery of the power supply layer and the ground layer to form an array of minute dipole antennas, the phases of electromagnetic waves emitted from every other minute dipole antenna can be alternately inverted. Therefore, it is possible to sufficiently suppress the emission of unnecessary electromagnetic waves.

[Brief description of drawings]

FIG. 1 is a perspective view showing a main part of an embodiment of a circuit board having a low EMI structure according to the present invention.

FIG. 2 is an overall perspective view of a circuit board having a low EMI structure according to the present invention.

FIG. 3 is a diagram showing a state of an electric field when FIG. 1 is viewed from an arrow A side.

FIG. 4 is a diagram showing an electric field direction in a cross section taken along section lines BB and CC in FIG. 1.

5 is a diagram showing an electromagnetic wave reducing operation of the embodiment shown in FIG.

FIG. 6 is a diagram showing a radiation spectrum of electromagnetic waves in a conventional circuit board.

FIG. 7 is a perspective view showing a main part of another embodiment of a circuit board having a low EMI structure according to the present invention.

FIG. 8 is an operation explanatory diagram in the embodiment shown in FIG. 7.

FIG. 9 is a diagram showing changes in the electromagnetic wave reduction effect with respect to the number of conductor patterns.

[Explanation of symbols]

 1 power supply layer 2 ground layer 3 to 6 conductor pattern 7 to 10 connection line 11 and 12 small dipole antenna

Claims (6)

[Claims] 1. A circuit board in which a power supply layer is provided on one surface of a substrate on which a circuit is formed and a ground layer is provided on the other surface, and the one surface and the other surface of the board are provided. A plurality of conductor patterns sufficiently smaller than the size of the substrate are provided along the periphery of the substrate, and the conductor patterns provided on the one surface of the substrate are spaced apart from each other. Of the conductor patterns are connected to the power supply layer and the other second conductor patterns are connected to the ground layer, respectively, and the first of the conductor patterns provided on the other surface of the substrate Every other third conductor pattern facing the conductor pattern is connected to the ground layer, and every other fourth conductor pattern facing the second conductor pattern is connected to the power supply layer. A circuit board having a low EMI structure. 2. A circuit board in which a power supply layer is provided on one surface of a substrate on which a circuit is formed and a ground layer is provided on the other surface, and the size of the substrate is set along the side surface of the substrate. A plurality of conductor patterns that are sufficiently smaller than each other are provided close to each other, and every other first conductor pattern of the conductor patterns is connected to the power supply layer, and its tip portion is close to the ground layer, 2. A circuit board having a low EMI structure, wherein every second conductive pattern is connected to the ground layer and is adjacent to the power supply layer. 3. The circuit board according to claim 1, wherein all of the conductor patterns have a size equal to or less than ⅙ of a size of the board. 4. The circuit board according to claim 1 or 2, wherein all of the conductor patterns have substantially the same size and shape. 5. The impedance according to claim 1, which is seen from the power supply layer at a connection portion between the power supply layer and the first and fourth conductor patterns, and the ground layer and the second and third conductor patterns. The circuit board having a low EMI structure, wherein the impedances of the connection parts of the above when viewed from the ground layer are substantially equal to each other. 6. The impedance according to claim 2, wherein the impedance of the connection portion between the power supply layer and the first conductor pattern is viewed from the power supply layer, and the ground of the connection portion between the ground layer and the second conductor pattern. A circuit board having a low EMI structure characterized in that the impedances seen from the layers are all substantially equal.