JPH0625027Y2 - Printed board for high frequency noise prevention - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] This invention can prevent the generation of high-frequency noise from a high-frequency noise prevention printed board, especially from the high-frequency current source mounted on itself and the reception of high-frequency noise from the outside. And a printed circuit 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 switching signals of clock pulses and power transistors are induced and radiated from electronic device casings and wire harnesses.
Other electronic devices and wireless devices, such as FM radios, radios,
There are problems that TVs, car phones, etc. are adversely affected, radio noise is generated, the device malfunctions, or the function stops.

Conventionally, as a countermeasure against clock noise from such a microcomputer, a method of preventing noise generation by using an element filter by a capacitor or a resistor or by making a clock pulse rise or fall has been used.

In addition, as a measure for suppressing high-frequency noise superimposed on a vehicle wire harness, the Japanese Patent Publication No.
The techniques described in JP-A-595962 and JP-A-52-147622 have been proposed.

That is, a noise trap wire of λ / 4 (where λ is the propagation wavelength of the noise current) is provided along the noise wire of the vehicle defogger heat wire or wire harness, and the high frequency noise current is controlled to an extremely small value in the middle of the noise wire. This reduces the influence of noise on other wires.

Among the conventional techniques, for example, according to Japanese Patent Publication No. 57-59962, a noise wire 32 for connecting a vehicle-mounted battery and a defogger heating wire 30 as shown in FIG.
A noise current i is generated over the entire length, and the first low impedance branch path 34 is connected to the noise wire 32 on which the noise current i is superposed to forcibly form a standing wave by the high frequency noise current, The second low-impedance branch 36 is connected to the position corresponding to the node of the standing wave so that the high-frequency noise current, which is a noise source, does not propagate to other wires extending near the electronic device. Then, these noise trap wires 34, 36
Are taped along the noise wire 32, and the noise current intensity can be reduced to such an extent that other wires are not affected.

[Problems to be Solved by the Invention] Conventional Problems However, all of the above-described measures against clock noise by element filters have limitations in terms of mounting and control, and noise trap wires provide wire harnesses. There is also a problem that taping the noise trap wire for each of these wires increases the number of man-hours.

For the above reasons, today, there is an increasing need to prevent electronic circuits such as microcomputers provided in in-vehicle electronic devices from being affected by strong electromagnetic fields from the outside due to broadcasting stations and high-power radios. For this reason, there has been an increasing demand for realizing a compact noise prevention device on a printed board of an on-vehicle electric device.

However, at the present time, a technique concerning high frequency noise prevention focusing on the circuit wiring pattern of the printed board has not been proposed yet.

The purpose of the present invention is to solve the above problems, and to prevent the influence of high frequency noise by forming a low impedance noise trap pattern near the circuit wiring pattern to prevent the influence of high frequency noise. The purpose is to provide printed boards.

[Means and Actions for Solving Problems] In order to achieve the above object, the present invention provides a print in which a low impedance noise trap pattern is provided in the vicinity of a circuit wiring pattern of a printed circuit board on which various electronic components are mounted. The plate, wherein the noise trap pattern is composed of a conductive pattern provided on both sides of the printed circuit board, and a through hole connecting portion which penetrates the printed circuit board and connects the conductive patterns provided on the both sides. In addition, one end thereof is connected to the circuit side terminal and the other end is opened, and the total length of the noise trap patterns and the through holes provided on the both surfaces is λ / 4 + (λ
/ 2) × n (λ is the propagation wavelength of the noise current, n = 0, 1,
2, ...) is set.

With the above configuration, the high frequency component included in the clock pulse generated from the microcomputer or the like is induced and radiated from the electronic device casing or the wire harness, and the FM radio,
Although it may interfere with radios such as TVs and car phones, it resonates at a wavelength of λ / 4 due to the high-frequency noise trap pattern formed on both sides of the circuit wiring pattern by using through holes. It is possible to suppress the noise by selectively pulling in the frequency region to be changed to the noise trap pattern side.

In this case, the thickness of the noise trap pattern is
Since it has the property of being easily concentrated on the pattern surface due to the skin effect of the high-frequency current, the thickness of the circuit wiring pattern that is generally used is sufficient, and the width of the noise trap pattern is about the width that is generally used as the circuit wiring pattern. Is enough.

In the present invention, the length of the noise trap pattern is the sum of the length of the pattern portion and the length of the through hole formed on both the front and back surfaces of the printed circuit board, so that high frequency noise can be prevented at any position on the printed circuit board. It has the advantage that parts can be provided.

[Embodiment] A preferred embodiment of the present invention will be described below with reference to the drawings.

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

Here, a feature of the present invention is that the noise trap patterns provided on both surfaces of the printed circuit board in the vicinity of the circuit wiring pattern of the printed circuit board on which various electronic parts are mounted, and the noise trap pattern provided on the surface are It is connected by a through hole connecting portion that connects the noise trap patterns provided on both sides of the printed circuit board,
One end of the noise trap pattern is connected to the circuit side terminal and the other end is open, and the total length of the noise trap pattern and the through hole provided on both surfaces is λ / 4 + λ / 2 × n ( λ is the formation of a low impedance noise trap pattern in which the propagation wavelength of the noise current is n = 0, 1, 2, ...

That is, in this embodiment, the printed circuit board 14 is provided with the through hole 24, and the through hole 24 and the microcomputer 1 are provided on the component mounting side.
No. 0 clock terminal 10-5 is connected by a noise trap pattern 22-1, and a noise trap pattern 22-2 having one end connected to the through hole 24 and the other end opened is formed on the solder surface side. ing.

The noise trap pattern 22 and the through hole 24 are formed of copper foil or the like similar to the normal circuit wiring pattern 20. The length l ₁ of the noise trap pattern 22-1 and the noise trap pattern 22-2
Length l _3, and the pattern length l ₂ and a full length plus the through hole 24 portion of the is in the λ / 4 + λ / 2 × n.

The length of the noise trap pattern 22 is n = 0.
At that time, the length of λ / 4 is practical.

When the noise trap pattern 22 is formed in this way, the impedance on the noise trap pattern side and the impedance on the wireness side connected to the external device from the microcomputer 10 via the connector at the extraction portion of the noise trap pattern 22 from the microcomputer 10. Comparing with, the impedance on the wireness side is extremely high, while the impedance on the noise trap pattern 22 side is extremely low. Therefore, the high frequency current mostly flows to the noise trap pattern side and hardly flows to the wire harness side. For example, the high-frequency clock noise contained in the clock pulse signal of the microcomputer mounted in itself is prevented from being generated outside.

The length of the noise trap pattern 22 is, for example, 75 cm in the FM band of 76 to 90 MHz, 30 cm in the TV band of 200 MHz, 15 cm in the amateur radio band of 43 MHz, and 800 MHz for the mobile phone, if n = 0 in the above formula. In case of, it will be about 7.5 cm.

Then, by bringing the noise trap pattern 22-1 as close as possible to a noise source, for example, a clock generation source of the microcomputer 10, an effective filter can be configured and back induction to other mounting patterns can be prevented. .

The horizontal width of the noise pattern 22 is sufficient to be 0.5 to 10 mm, which is a practical width of the normal circuit wiring pattern 20, and the wider the width, the wider the noise prevention frequency body. Further, since the film thickness also flows concentratedly on the surface due to the skin effect of the high frequency current, the usual copper foil thickness of the circuit wiring pattern 20 (for example, 25 μm) is sufficient.

As described above, the high frequency component due to the clock pulse generated from the microcomputer is transmitted through the wire harness through the circuit wiring pattern and the connector and goes out to give an interference to radio equipment such as FM radio, TV and car telephone. However, according to the present embodiment, the noise trap pattern 22 can selectively draw the frequency region resonating at λ / 4 to the noise trap pattern 22 side to prevent noise.

That is, according to the embodiment of the present invention, as shown in FIG. 2, the filter effect is increased by 5 to 5 dB as compared with the conventional printed board, and the noise level can be further reduced. In addition, the printed circuit board 1 using the through holes 24
4, noise trap patterns can be formed at arbitrary positions on both front and back surfaces, and the pattern design becomes easy.

Therefore, the ECU (Electron
By providing a through hole near the high-frequency current generation source such as an ic control unit) and filtering, it is possible not only to effectively prevent the generation of high-frequency noise to the outside, but also to external EMI (Electro Magnetic I nte
It also includes vehicle noise, which is the abbreviation of rference, and external noise caused by broadcast waves.)

Further, according to the embodiment of the present invention, a noise trap pattern can be formed arbitrarily in the process of manufacturing a double-sided through-hole printed circuit board in the same manner as a normal circuit wiring pattern. It is possible to prevent high-frequency noise practically at low cost by eliminating the need for the like.

FIG. 3 shows an embodiment in which two noise trap patterns 122-1 and 122-2 are formed from the terminals of the microcomputer 100 through the through holes 124.

According to this embodiment, for example, respectively lambda ₁ noise propagation wavelength of FM band and TV _band, when the lambda _2, by the length of the noise trap pattern lambda _1/4, and lambda _2/2, FM It is possible to simultaneously prevent the noise of the two suppression frequency bodies of the band and the TV band.

Further, FIG. 4 shows an embodiment in which a filter frequency band can be arbitrarily selected by extending and forming a noise trap wire from each of a plurality of through holes.

That is, the terminal 200- of the microcomputer 200
5 includes through holes 224-1, 224-2, 224.
-3 are respectively connected, and noise trap patterns 222-1, 222-2, 2 having different lengths from these through holes 224-1, 224-2, 224-3.
22-3 is extended.

At this time, FM waves, amateur radio waves, TV
By determining the pattern length according to the noise propagation length of each frequency band such as waves, as shown in Fig. 5, it is very easy to improve the filter effect in the multi-frequency band by 5 to 12 dB compared to the conventional one. You can

[Effect of the Invention] As described above, the present invention uses the element filter for noise prevention by forming the low impedance noise trap pattern near the circuit wiring pattern of the printed circuit board by using the through hole connecting portion. It is possible to effectively prevent high frequency noise. Further, since the conductive patterns on both sides of the printed circuit board can be used by the through holes, the degree of freedom in arranging the electronic component and the circuit wiring pattern can be increased.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment of a printed board for preventing high frequency noise according to the present invention, FIG. 2 is a view showing a filter effect according to the embodiment of the present invention, and FIG. 3 is an embodiment in which two kinds of noise trap wires are formed. FIG. 4 is a view showing an embodiment in which a noise trap wire is formed by extension from each of a plurality of through holes, and a suppression frequency can be selected, and FIG. 5 is a view showing a filter effect according to FIG. FIG. 6 is a diagram showing a conventional example for preventing high frequency noise superimposed on the vehicle wireness. 10, 100, 200 ... Microcomputer 12 ... Connector 14 ... Printed board 16 ... Conductive case 20 ... Circuit wiring pattern 22, 122, 222 ... Noise trap pattern 24, 124, 224 ... Through hole

Claims (1)

[Scope of utility model registration request] 1. A printed board having a low impedance noise trap pattern provided in the vicinity of a circuit wiring pattern of a printed board on which various electronic components are mounted, wherein the noise trap pattern is provided on both surfaces of the printed board. Conductive pattern,
A through-hole connecting portion that penetrates the printed circuit board and connects the conductive patterns provided on the both surfaces, one end of which is connected to a circuit side terminal and the other end is open; The sum of the length of the noise trap pattern and the length of the through hole is set to λ / 4 + (λ / 2) × n (λ is the propagation wavelength of the noise current, n = 0, 1, 2, ...). A printed circuit board for preventing high frequency noise, which is characterized in that