JPH058693Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention is a printed board for preventing high frequency noise, especially preventing the generation of high frequency noise from the high frequency current generation source mounted on the board and preventing the reception of high frequency noise from the outside. This invention relates to a printed board for preventing high frequency noise.

[Prior Art] In recent years, with the increase in electronic devices equipped with microcomputers in automobiles, high-frequency noise current components generated from clock pulses and power transistor switching signals are induced and radiated from electronic device housings and wire harnesses, adversely affecting other electronic devices and wireless devices, such as FM radios, walkie-talkies, TVs, and car phones, generating radio noise and causing equipment to malfunction or stop functioning.

Conventionally, as a countermeasure against clock noise from such microcomputers, methods have been used to prevent the generation of noise by using element filters using capacitors and resistors, or by smoothing the rising and falling edges of clock pulses.

In addition, as a measure to suppress high-frequency noise superimposed on vehicle wiring harnesses, Japanese Patent Publication No. 57-59962 and Japanese Patent Application Laid-Open No. 52-147622 filed by the present applicant have also been proposed.
The technology described in the publication has been proposed.

In other words, a noise trap wire of λ/4 (λ is the propagation wavelength of the noise current) is installed along the noise wire such as the vehicle defogger heating wire or wire harness, and the high-frequency noise current is suppressed to an extremely small value in the middle of the noise wire. By doing so, the influence of noise on other wires is reduced.

Among these conventional techniques, for example,
According to the publication, as shown in FIG. 5, a noise current i is generated over the entire length of the noise wire 32 that connects the in-vehicle battery and the defogger hot wire 30, and the noise current i is superimposed. A first low-impedance branch 34 is connected to the noise wire 32 that is running, to forcibly form a standing wave due to high-frequency noise current, and a second low-impedance branch is connected to the node of this standing wave. The wire 36 is connected to prevent high-frequency noise current, which is a noise source, from propagating to other wires extending near the electronic device. These noise trap wires 34 and 36 are taped along the noise wire 32, so that the noise current intensity can be reduced to a level that does not affect other wires.

[Problems to be solved by the invention] Conventional problems However, the above-mentioned clock noise countermeasures using element filters, etc. have limitations in terms of implementation and control. Since there are a large number of noise trap wires, there is a problem in that the number of steps required to tape a noise trap wire for each wire increases.

For the above reasons, there is a growing need today to ensure that electronic circuits such as microcomputers installed in in-vehicle electronic devices are not affected by strong electromagnetic fields from outside such as broadcast stations and high-power radio equipment. Therefore, there has been an increasing desire to realize a compact noise prevention device on the printed circuit board of in-vehicle electrical equipment.

However, to date, no technology regarding high frequency noise prevention that focuses on the circuit wiring pattern of a printed board has yet been proposed.

Purpose of the invention This invention was made to solve the above problem, and it forms an impedance noise trap pattern near the circuit wiring pattern of the printed circuit board, and also forms an impedance noise trap pattern on this noise trap pattern with an insulating layer interposed therebetween. The purpose of this paper is to propose a printed board that prevents the effects of high frequency noise by forming a ground pattern.

[Means and effects for solving the problem] In order to achieve the above object, the present invention provides a circuit wiring pattern of a printed circuit board on which various electronic components are mounted, one end of which is connected to a circuit side terminal and the other end of which is connected to a circuit wiring pattern. When opened, its length is λ/4+λ/2×n (λ is the propagation wavelength of the noise current, n=0, 1,
The present invention is characterized in that a low impedance noise trap pattern is formed, and a ground pattern is formed on the noise trap pattern with an insulating layer interposed therebetween.

With the above configuration, high frequency components contained in clock pulses etc. emitted from the microcomputer are induced and radiated from the electronic device housing and wire harness, and there is a risk of interfering with radio equipment such as FM radios, TVs, and car phones. By using the high frequency noise trap pattern formed near the circuit wiring pattern, it is possible to selectively draw a frequency region that resonates at a wavelength of λ/4 to the noise trap pattern side, thereby trapping high frequency noise.

The noise trap pattern is electrostatically coupled to a ground pattern placed close to it via an insulating layer to prevent high frequency noise.

Since the noise trap pattern tends to concentrate on the surface, a commonly used pattern thickness is sufficient, and the width of the noise trap pattern generally used as a circuit wiring pattern is sufficient.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIGS. 1a and 1b show an embodiment of a printed board for preventing high frequency noise according to the present invention. In the figure, a printed circuit board 14 on which a connector 12 for connecting electronic components such as a microcomputer 10 and the outside is mounted is housed in a conductive case 16, and this case 16 is connected to ground 18. .

Here, the characteristic feature of the present invention is that one end is connected to the circuit side terminal and the other end is open near the circuit wiring pattern of the printed circuit board on which various electronic components are mounted, and its length is λ/4 + λ/2. ×n (λ is the propagation wavelength of the noise current, n=0, 1,
2, . . . ), and a ground pattern is formed on the noise trap pattern with an insulating layer interposed therebetween.

That is, in this embodiment, the clock terminal 10-1 of the microcomputer 10 and the connector 1
2 is connected to the terminal 12-1 of the circuit wiring pattern 20, and a low impedance noise trap pattern 2 is connected to the terminal 12-1 of the circuit wiring pattern 20.
2 is formed. This noise trap pattern 22 is formed of copper foil or the like similar to the circuit pattern 20, and has one end connected to the connector terminal 12-1 and the other end open, and its length is set to accommodate the noise current. If the propagation wavelength is λ, then λ/4+λ/2×n (n=0, 1, 2,...).

When the noise trap pattern 22 is formed in this way, comparing the impedance of the noise trap pattern side and the wire harness side including the connector at the lead-out part of the noise trap pattern 22, the impedance of the wire harness side is is extremely large, but the impedance on the noise trap pattern 22 side is extremely small, so
Most of the high-frequency current flows to the noise trap pattern side, with almost no flow to the wire harness side, thereby preventing the high-frequency clock noise contained in the clock pulse signal of the microcomputer mounted on the device from being generated to the outside.

For example, if n=0 in the above equation, the length of this noise trap pattern 22 is 76~
75cm on the 90MHz FM band, 30cm on the 200MHz TV band,
The length is 15cm for the 430MHz amateur radio band, and about 7.5cm for the 800MHz car phone.

Further, the width of the noise trap pattern 22 is sufficient to be about 0.5 to 10 mm, which is the practical width of the ordinary circuit wiring pattern 20, and the wider the width, the higher the noise prevention frequency band becomes. Furthermore, the thickness of the copper foil is 25 .mu.m, which is the usual thickness of the circuit wiring pattern 20, because the high-frequency current is concentrated on the surface due to the skin effect of the high-frequency current.

Next, the present invention is characterized in that a ground pattern 24 is formed on the noise trap pattern 22 with an insulating layer 26 interposed therebetween.

For example, a green mask is used for the insulating layer 26, and the ground pattern 24 is formed by metal plating or screen printing using a conductive material.

This earth pattern 24 is at least longer than the noise trap pattern 22 and has a thickness of several micrometers or more, and in the case of a horizontal pattern, it can be formed to be 2 to 3 times as thick as the noise trap pattern 22 to reduce noise. The electrical coupling is ensured and the noise prevention effect is improved.

That is, an antinode of a standing wave of high-frequency current is formed at the extraction point of the noise trap pattern 22, and noise is generated by electrostatic coupling with the ground pattern 24 disposed close to the noise trap pattern 22 via the insulating layer 26. is reliably absorbed, and high frequency noise can be suppressed.

As explained above, high-frequency components such as clock pulses emitted from a microcomputer are normally transmitted from the connector to the wire harness through the circuit wiring pattern and exit to the outside, and are transmitted to the FM radio, etc.
Although there is a risk of interference with radio equipment such as TVs and car phones, according to this embodiment, the connector terminal 1
Noise trap pattern 22 connected to 2-1
As a result, the frequency region resonating at λ/4 is selectively drawn into the noise trap pattern, and high frequency noise can be prevented by electrostatic coupling with the ground pattern 26 disposed in close proximity via the insulating layer.
In particular, the present invention functions extremely effectively when the case 16 is made of a non-conductive material such as plastic.

That is, according to the embodiment of the present invention, as shown in FIG.
The filter effect increases by about 15 dB, making it possible to further reduce the noise level.

In addition, the ECU mounted on the printed board himself
This function not only prevents high-frequency noise from being generated externally from high-frequency current sources such as electronic control units (electronic control units), but also prevents EMI from external sources.
It is also effective against electromagnetic interference (which is an abbreviation for Eletro Magnetic Interference, which includes vehicle noise and external noise from broadcast waves).

Furthermore, according to the embodiment of the present invention, a noise trap pattern can be formed arbitrarily in the same way as a normal circuit wiring pattern in the printed circuit board manufacturing process, and noise can be prevented by conventionally used circuit element filters. High frequency noise can be effectively prevented at low cost without the need for a filter or the like.

FIGS. 3a and 3b show an embodiment effective for multi-frequency noise prevention.

That is, in this embodiment, the through hole 28
Noise trap pattern 122-1,
122-2, a ground pattern 124 is formed via the insulating layer 126, and the length of the noise trap pattern 122 is set to λ ₁ /
4. By forming the length to be different from λ ₂ /4,
For example, pattern 122-1 corresponds to noise prevention in the FM band, and pattern 122-2 corresponds to noise prevention in the TV band.

As a result, as shown in FIG. 4, it is understood that the filter effect is improved by 10 to 18 dB compared to the conventional printed board.

[Effects of the invention] As explained above, this invention forms a low-impedance noise trap pattern near the circuit wiring pattern of a printed circuit board, and forms a ground pattern on the noise trap pattern via an insulating layer. By doing so, high frequency noise can be effectively prevented without using a noise prevention filter or the like.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of a printed board for high frequency noise prevention according to the present invention, Fig. 2 is a diagram showing a filter effect according to an embodiment of the present invention, and Fig. 3 is an implementation effective for multi-frequency noise prevention. Figure 4 showing an example
The figures show the filter effect according to the embodiment of Fig. 3, and Fig. 5 shows a conventional example for preventing high frequency noise superimposed on a vehicle wire harness. 10... Microcomputer, 12... Connector, 14... Printed circuit board, 16... Case,
20...Circuit wiring pattern, 22,122...Noise trap pattern, 24,124...Earth pattern, 26,126...Insulating layer.

Claims (1)

[Claim for Utility Model Registration] Near the circuit wiring pattern of a printed circuit board on which various electronic components are mounted, one end is connected to a circuit side terminal, the other end is open, and the length thereof is λ/4 + λ/2 × n ( λ is the propagation wavelength of the noise current, n=0, 1,
2. A printed board for high frequency noise prevention, characterized in that a low impedance noise trap pattern is formed, and a ground pattern is formed on the noise trap pattern via an insulating layer.