JPH11163480A - Circuit substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress electromagnetic waves radiated from the side surface of a circuit substrate. SOLUTION: A power source wiring 21 is formed on the upper surface of a first FRP substrate 11, while a lower layer signal wiring 22a is formed on the lower surface. On the first FRP substrate 11 and the power source wiring 21, a ground pattern 23 and radiating electromagnetic wave preventing wiring 24 are formed via a second FRP substrate 12. The radiation electromagnetic wave preventing wiring 24 for suppressing the radiating electromagnetic waves is formed along the end of the ground pattern 23 of a ground layer, in which a polarity inversion signal in which its polarity is inverted with respect to a clock signal is applied. On the ground pattern 23 and the radiating electromagnetic wave preventing wiring 24, an upper layer signal wiring 22b is formed via a third FRP substrate 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board used for electronic equipment, and more particularly to a circuit board for suppressing unnecessary electromagnetic noise radiated from a circuit board.

[0002]

2. Description of the Related Art In recent years, with the development of multimedia, demands for high-speed data processing and data communication have been increasing. In response to these demands, research and development of hardware and software have been actively conducted, and remarkable performance improvements have been made. In particular, in the field of semiconductor technology, the speed and function of microprocessors, which are the core of computers, and the speed and capacity of memories are increasing, and high-speed data processing and data communication are possible even with inexpensive personal computers.

However, unnecessary electromagnetic waves radiated from electronic devices have become a problem as the speed and function of the system have increased. This electromagnetic wave not only has a bad effect on other electronic devices, but also has a concern about a human body.

Most of unnecessary electromagnetic wave radiation is generated on a circuit board on which an LSI or a passive component is mounted. Noise induced between signal wiring and a power supply layer and a ground layer due to signal reflection, crosstalk between wirings, switching of semiconductor elements, and the like. Responsible. Unnecessary electromagnetic waves are radiated from the circuit board due to this noise, and further radiated outside the device through heat dissipation holes or the like of the housing.

[0005] These unnecessary electromagnetic wave radiations are classified into radiation from a surface on which a circuit pattern through which a high-speed signal propagates is formed, and radiation from the side surface of a substrate due to a resonance phenomenon between a power supply layer and a ground layer. Unwanted electromagnetic wave emission from the surface on which the circuit pattern is formed can be obtained by applying a copper paste to the circuit pattern surface via an insulator as described in, for example, JP-A-8-228055, and applying this copper paste. There is known a method of shielding by dropping to ground.

[0006] The shield method using a steel paste increases the cost because an expensive copper paste film must be formed on a solder resist or the like. In addition, since the adhesion between the copper paste and the solder resist is weak, peeling occurs and there is a problem in reliability.

As another shielding method, Japanese Patent Laid-Open No.
As described in Japanese Patent No. 18099, there is also known a method of forming a ground wiring between branched signal wirings and mutually canceling electromagnetic waves induced from the respective wirings, thereby preventing generation of unnecessary electromagnetic waves. I have.

In this method, a ground wiring must be added to the wiring layer, and the signal wiring must be branched into two, so that the number of layers increases due to a reduction in wiring density, which leads to an increase in price. There was a problem.

Further, with respect to the electromagnetic wave radiation due to the resonance phenomenon between the power supply layer and the ground layer, the collection of proceedings of the 11th Annual Meeting of the Circuit Packaging Society of Japan, "Reduction of unnecessary radiation caused by the power supply / ground layer of the printed wiring board" As described in "Method," a method has been proposed in which a ground layer is formed on both surfaces of a power supply layer via an insulating layer to suppress electromagnetic wave radiation. However, even in this method, an increase in cost is indispensable because one unnecessary ground layer must be added.

[0010]

As described above, the conventional circuit board for preventing electromagnetic wave radiation has a problem that the number of manufacturing steps is increased and the manufacturing cost is increased. In addition, there is a problem that reliability is lacking. An object of the present invention is to provide a circuit board capable of preventing electromagnetic radiation without lowering reliability and increasing costs.

[0011]

Means for Solving the Problems [Configuration] The present invention is configured as follows to achieve the above object. (1) According to the present invention (claim 1), in a circuit board in which a power supply pattern and a ground pattern are formed in a region different from a signal wiring region, at least one of the region in which the power supply wiring pattern or the ground pattern is formed, A radiated electromagnetic wave prevention wiring is formed in which a signal having a reverse polarity or a phase shifted by 180 ± 10 degrees with respect to a signal selected from the signals transmitted through the signal wiring is formed.

A preferred embodiment of the present invention will be described below.
The radiated electromagnetic wave prevention wiring is formed along the periphery of the ground pattern or the power supply pattern.

The signal wiring and the power supply pattern or the ground pattern are formed in different layers. The selected signal is a clock signal.

[Function] The present invention has the following functions and effects by the above configuration. The signal selected from the signals transmitted through the signal wiring has the opposite polarity or phase of 180 ± 1.
By applying a signal shifted by 0 degrees, the two signals cancel each other out, so that radiated electromagnetic waves can be suppressed.

As a selected signal, a signal having a steep rise or fall of a signal and a signal having a long wiring length to be propagated is highly effective. Therefore, in many digital circuits, it is desirable to select a clock signal.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a circuit board according to one embodiment of the present invention. FIG. 1A is a plan view of the circuit board 10, and FIG. 1B is a cross-sectional view of the circuit board 10.

A power supply wiring pattern 21 is formed on the upper surface of the first FRP substrate 11, and a lower signal wiring 22a is formed on the lower surface. On the first FRP board 11 and the power supply wiring pattern 21, a ground pattern 23 and a radiated electromagnetic wave prevention wiring 24 are formed via a second FRP board 12. The upper layer signal wiring 22b is formed on the ground pattern 23 and the radiated electromagnetic wave prevention wiring 24 via the third FRP substrate 13.

The radiated electromagnetic wave preventing wiring 24 for suppressing the radiated electromagnetic wave is formed in the same layer as the ground pattern 23 and along the periphery of the ground pattern 23. The line width of the radiated electromagnetic wave prevention wiring 24 is a characteristic impedance that enables the polarity inversion signal to be transmitted while maintaining a good waveform, for example, 50 to 50.
It is sufficient to select a line width that can provide about 100Ω, and a line width of about 100 microns is appropriate in consideration of the yield.

The radiated electromagnetic wave prevention wiring 24 can be easily realized by a general printed circuit board forming process. In other words, if the pattern of the radiated electromagnetic wave prevention wiring 24 is written on a mask when the ground pattern 23 is formed, the ground pattern 2 can be formed without adding a special process.
A desired pattern can be obtained in the step of forming No. 3. Thus, in the present embodiment, even if a pattern for suppressing radiated electromagnetic waves is inserted, there is no increase in cost.

Next, the polarity inversion signal applied to the radiated electromagnetic wave prevention wiring 24 will be described. FIG. 2 is a diagram showing waveforms of a clock signal of 0 to 5 V and a polarity inversion signal obtained by inverting the polarity of the clock signal. When the clock signal rises from 0V to 5V, the polarity inversion signal is changed from 0V to -5V.
When the clock signal falls from 5V to 0V, the signal rises from -5V to 0V, that is, a signal whose polarity is inverted. Although a 5V system is described as an example, other voltage systems, such as a 3.3V system, can provide the effect of suppressing radiated electromagnetic waves, which will be described later.

Next, the effects of the present invention will be described based on experimental results. The wiring 22 (22a, 22a) of the circuit board shown in FIG.
The electromagnetic wave radiated from the substrate when the 1 MHz clock signal was propagated in b) was measured. FIG.
FIG. 4 is a characteristic diagram showing a radiation electric field spectrum measured in a range of 0 MHz. FIG. 3A is a characteristic diagram showing a result of the substrate having the conventional structure without the radiated electromagnetic wave prevention wiring, and FIG. 3B is a characteristic diagram showing a result of the printed circuit board shown in FIG. In the case of the substrate having the conventional structure, a large peak appears around 35 MHz.
In the substrate of the present embodiment, the peak is very small. From the above experimental results, it is clear that radiated electromagnetic waves can be effectively suppressed by forming the radiated electromagnetic wave prevention wiring.

In addition, as shown in FIG. 4, not only the signal having the opposite polarity but also a signal having a phase shifted by 180 degrees with respect to the clock signal is applied to the radiated electromagnetic wave prevention wiring to prevent the radiated electromagnetic wave. The effect can be obtained. However, as a result of experiments, it has been confirmed that a signal having the opposite polarity is more likely to prevent radiated electromagnetic waves than a signal whose phase is shifted by 180 degrees.

The signal applied to the radiated electromagnetic wave prevention wiring does not need to be shifted by 180 degrees from the clock signal. If the signal is shifted by 180 ± 10 degrees, there is an effect of suppressing the radiated electromagnetic wave. FIGS. 5 and 6 show the results of measuring the reduction rate of the radiated electromagnetic wave when a signal having a phase difference of 160 to 200 degrees is applied to the radiated electromagnetic wave prevention wiring. As shown in FIGS. 5 and 6, it can be seen that if the phase difference is in the range of 180 ± 10 degrees, the radiated electromagnetic wave is suppressed to 50% or less.

Further, as shown in FIG. 7, the radiated electromagnetic wave prevention wiring 24 may be formed on both the power supply layer and the ground layer. Forming both on the power supply layer and the ground layer further increases the effect as compared with the case of one of them.

Further, the radiated electromagnetic wave prevention wiring 24 does not need to cover the entire periphery of the ground pattern. In the case of the substrate 10 having a special shape as shown in FIG. 8, the radiated electromagnetic wave prevention wiring 24 is formed partially. Is also good. Radiated electromagnetic wave prevention wiring 2
Even in a configuration in which 4 is partially formed, a sufficient effect of suppressing radiated electromagnetic waves can be obtained.

Further, as shown in FIG. 9, the radiated electromagnetic wave prevention wiring 24 of the present invention is also applied to the circuit board 10 on which the signal wiring 22, the power supply pattern 21 and the ground pattern 23 are formed in the same layer. Can be applied.

Although the embodiments of the present invention have been described with experimental results, the present invention is not limited to the above-described embodiments. For example, in the above embodiment, a case where the present invention is applied to a general printed wiring board has been described.
The present invention can be applied to all circuits in which a power / ground pattern is formed, such as a thin-film multilayer substrate such as CM), a thick-film hybrid substrate, and an integrated circuit.

The present invention can be applied to not only a solid ground pattern but also a mesh ground pattern. In the case of the stripe ground pattern, the radiated electromagnetic waves can be suppressed by alternately arranging the ground lines and the radiated electromagnetic wave prevention lines. In addition, the present invention does not depart from the gist thereof,
Various modifications are possible.

[0029]

As described above, according to the present invention, the polarity or phase of the signal selected from the signals applied to the signal wiring is shifted by 180 degrees in the formation region of the power supply pattern or the ground pattern. By forming the radiated electromagnetic wave prevention wiring through which the signal propagates, it is possible to provide a measure against electromagnetic wave radiation without increasing the cost and reducing the reliability of the circuit board.

[Brief description of the drawings]

FIG. 1 is a view showing a configuration of a circuit board according to an embodiment of the present invention.

FIG. 2 is a diagram showing waveforms of a clock signal and a polarity inversion signal applied to the circuit board of FIG. 1;

FIG. 3 is a diagram illustrating frequency dependence of radiated electromagnetic waves.

FIG. 4 is a diagram showing a waveform of a polarity inversion signal different from the polarity inversion signal of FIG. 2;

FIG. 5 shows a case where a signal whose phase is shifted from 160 degrees to 200 degrees with respect to a clock signal is applied to a radiated electromagnetic wave prevention wiring.
The figure which shows the peak of radiation electromagnetic wave.

FIG. 6 is a characteristic diagram showing the phase difference dependence of the radiated electromagnetic wave in FIG.

FIG. 7 is a sectional view showing the configuration of a circuit board according to one embodiment of the present invention.

FIG. 8 is a sectional view showing a configuration of a circuit board according to one embodiment of the present invention.

FIG. 9 is a sectional view showing a configuration of a circuit board according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Circuit board 11 ... 1st FRP board 12 ... 2nd FRP board 13 ... 3rd FRP board 21 ... Power supply pattern 22 ... Signal wiring 22a ... Lower signal wiring 22b ... Upper signal wiring 23 ... Ground pattern 24 ... Radiation Electromagnetic wave prevention wiring

Claims (4)

[Claims] 1. A circuit board having a power supply wiring pattern and a ground pattern formed in a region different from a region in which a signal wiring is formed, wherein at least one of the region in which the power supply wiring pattern or the ground pattern is formed is provided. The signal selected from the signals transmitted through the signal wiring has the opposite polarity or phase of 1
A circuit board, wherein a radiation electromagnetic wave prevention wiring through which a signal shifted by 80 ± 10 degrees propagates is formed. 2. The circuit board according to claim 1, wherein the radiated electromagnetic wave prevention wiring is formed along a periphery of the ground pattern or the power supply pattern. 3. The circuit board according to claim 1, wherein said signal wiring and said power supply pattern or ground pattern are formed in different layers. 4. The circuit board according to claim 1, wherein said selected signal is a clock signal.