JPH09246776A - Printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To permit easy fixture and absorb noises generating between a power supply pattern and an earth pattern during the operation of electronic circuit. SOLUTION: A multi-layer printed wiring board 1 is provided with a power supply layer 2 (solid pattern 2) and an earth layer 3 (solid pattern 3) in its internal layer and with a power supply pattern 2a and an earth pattern 3a in its surface layer. The layer 2 and pattern 2a and the layer 3 and pattern 3a are connected with each other through through-holes 6 respectively. A radiation noise absorbing part 4 is provided on the side surface part of the board 1 in such a manner that the board 1 is surrounded therewith along the lengthwise direction of the side surface part. The part 4 is provided with a ferrite 7 and an electrode 8. The electrode 8 is connected electrically with the patterns 2a and 3a through a conductor 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printed wiring board having a power source pattern and an earth pattern.

[0002]

2. Description of the Related Art Generally, a printed wiring board on which a plurality of electronic circuits are mounted to form a predetermined electronic circuit includes a power source pattern for supplying power to each electronic circuit and an earth pattern. In such a printed wiring board, a voltage fluctuation occurs between the power supply pattern and the ground pattern during the operation of each electronic circuit, and this fluctuation becomes a noise source, and the noise is radiated into space. Therefore, conventionally, a capacitor called a bypass capacitor (or decoupling capacitor) that electrically connects a power supply pattern and an earth pattern has been mounted to absorb voltage fluctuations and reduce radiation noise.

[0003]

Generally, a bypass capacitor is provided in the vicinity of, for example, an IC or LSI, and the more bypass capacitors are provided, the more radiation noise can be reduced. The noise radiated due to the voltage fluctuation between the pattern and the ground pattern is radiated from the end of the printed wiring board, so there was a method of providing a bypass capacitor uniformly at the end of the printed wiring board. . However, when the capacitor becomes a chip type, it is much smaller than the printed wiring board (about 1 [mm]), and various patterns are printed on the printed wiring board. Therefore, the bypass capacitor is actually printed. It was difficult to mount on the edge of the wiring board without a gap.

The equivalent circuit of the capacitor has not only the pure capacitance of the capacitor but also the resistance and the inductance. When the frequency becomes high, the inductance becomes effective and the impedance becomes large. Therefore, the conventional radiation noise reduction method using a bypass capacitor has a problem that radiation noise at the resonance frequency caused by the shape and dimensions of the printed wiring board may not be absorbed.

[0005]

[Means for Solving the Problems] A solution means provided by the present invention for solving the above problems is a printed wiring provided with a power source pattern for supplying electric power to a mounted electronic circuit and a ground pattern for grounding. In the board, ferrite is provided along the length direction on the side surface of the printed wiring board, and the ferrite is electrically connected to the power supply pattern and the earth pattern.

According to the above-mentioned solution means, when voltage fluctuation occurs between the power supply pattern and the ground pattern during operation of the electronic circuit to generate noise, the radiation noise is absorbed by the ferrite.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. Elements common to the drawings are denoted by the same reference numerals.

First Embodiment FIG. 1 is an enlarged side sectional view showing a multilayer printed wiring board according to the first embodiment of the present invention, and FIG. 2 is a view from the direction of arrow A of the multilayer printed wiring board shown in FIG. FIG. 3 is a schematic cross-sectional view of the multilayer printed wiring board shown in FIG. 2 taken in the direction of arrow B.

The multi-layer printed wiring board 1 is a four-layer printed wiring board composed of, for example, glass epoxy and copper pattern, and has a power supply layer 2 (solid pattern 2) and a ground layer 3 (solid pattern 3) as inner layers. . On the surface layer (signal layer) of the multilayer printed wiring board 1, there are provided a signal pattern 5, a power source pattern 2a drawn from the power source layer 2, and a ground pattern 3a drawn from the ground layer 3. The power supply layer 2 and the power supply pattern 2a, and the ground layer 3 and the ground pattern 3a are connected by through holes 6 as shown in FIG.

A radiation noise absorbing portion 4 is provided on the side surface of the multilayer printed wiring board 1 so as to surround the multilayer printed wiring board 1 along the lengthwise direction of the side surface. Radiated noise absorber 4
Has a ferrite 7 and electrodes 8 provided on the upper and lower surfaces of the ferrite 7. The ferrite 7 is made of a material such as nickel-zinc ferrite or manganese-zinc ferrite. The electrode 8 is electrically connected to the power source pattern 2a and the ground pattern 3a by a conductor 9.

Next, the relationship between the voltage between the power supply layer 2 and the ground layer 3 and the radiation noise when a signal is externally supplied between the layers 2 and 3 will be described. FIG. 4 is a diagram for explaining the result of measurement of radiation noise with a spectrum analyzer in a multilayer printed wiring board having no radiation noise absorber. In the figure, the horizontal axis represents frequency and the vertical axis represents radiation noise.

Frequency 488 with increasing radiated noise
[MHz] and 677 [MHz] are the long side (297 [mm]) and short side (21 [21 mm]) of the multilayer printed wiring board 1, respectively.
It is a frequency that resonates with a length of 0 [mm]). Details can be confirmed by the calculation shown in the following formula. Where λ is the wavelength [m] of the signal propagating in the air, and Co is the speed of light [m /
s] and fo represent the resonance frequency [Hz].

[0013]

## EQU1 ## λ = Co / fo (1) Further, the resonance signal transmitted to the multilayer printed wiring board 1 is inversely proportional to the square root of the permittivity ε of the multilayer printed wiring board 1 with λo as the wavelength [m]. Because

[0014]

[Equation 2]

## EQU1 ## Therefore, the multilayer printed wiring board 1 made of glass epoxy has fo = 48 with ε = 4.5.
Taking the case of 3 [MHz] as an example and applying it to the equation (2),

[0016]

(Equation 3)

As shown by the equation (3), the calculation result agrees with the long side 297 [mm] of the multilayer printed wiring board.

FIG. 5 is a diagram for explaining the results of measuring the voltage between the power supply layer and the ground layer at the end of the noise-printed printed wiring board shown in FIG. 4 with a spectrum analyzer. As can be seen from the figure, the same frequency (488 [MHz] and 677 [MH] as the radiation noise shown in FIG.
z]), the voltage is high.

By the way, FIG. 6 shows a radiation noise measurement result when, for example, 32 bypass capacitors are mounted on the side surface portion of the multilayer printed wiring board 1 at equal intervals instead of providing the multilayer printed wiring board with the radiation noise absorbing portion. It is a thing. FIG. 7 shows the measurement result of the voltage at the end of the multilayer printed wiring board in this case, that is, when only the bypass capacitor is mounted.

As can be seen by comparing FIGS. 4 and 5 with FIGS. 6 and 7, at the resonance frequency, the radiation noise is not sufficiently reduced only by mounting the bypass capacitor.

FIG. 8 shows the radiation noise measurement result in the first embodiment, and FIG. 9 shows the voltage measurement result at the end portion of the multilayer printed wiring board in the first embodiment.

When an electronic component (not shown) mounted on the multilayer printed wiring board 1 is operated, energy of radiation noise is generated at the end of the multilayer printed wiring board 1 due to the potential difference between the power supply layer 2 and the ground layer 3. However, since the radiation noise absorbing section 4 absorbs the radiation noise energy, it is not radiated into space.

Therefore, as can be seen by comparing FIGS. 4 to 7 with FIGS. 8 and 9, in the first embodiment, 30 [M
The radiation noise energy is absorbed by the ferrite 7 in the range of [Hz] to 1 [GHz], and the radiation noise is reduced.

In the first embodiment, the ferrite 7 may be provided along the side surface portion according to the size of the multilayer printed wiring board 1, and therefore, the mounting is easier than mounting a plurality of bypass capacitors. As an example of how to provide, two copper plates 4a (or phosphor bronze plates or the like) having a substantially L-shaped cross section are fixed to the multilayer printed wiring board 1 with solder 4b as shown in FIG. Spread the space between both copper plates 4a and insert the ferrite 7, and insert the ferrite 7 with both copper plates 4a.
There is a method of sandwiching and holding, but is not limited to this method. FIG. 10 is an explanatory diagram of mounting the radiation noise absorbing unit according to the first embodiment.

11 and 12 are schematic side sectional views showing a modification of the first embodiment, and FIG. 13 is a schematic perspective view showing a modification of the first embodiment. The ferrite 70 of the radiation noise absorber 4 shown in FIG. 13 is electrically connected to the power supply layer 2 and the ground layer 3 by a conductor (not shown).

In the first embodiment, the ferrite 7 has the same thickness as that of the multilayer printed wiring board 1 (thickness parallel to the direction of arrow A) and is integrated with the multilayer printed wiring board 1. As shown in FIG. 11 and FIG. 12, even if the thickness, shape, and dimensions of the ferrites 7a and 7b are changed, the conductors 90a and 90b connect the ferrites 7a and 7b to the power source pattern 2a. Also, the same effect as in the first embodiment can be obtained by electrically connecting to the ground pattern 3a.

Further, the ferrite 7 of the same material is not provided so as to surround the multilayer printed wiring board 1, but as shown in FIG. The ferrites 70b) may be alternately arranged to surround the multilayer printed wiring board 1. In this case, the nickel-zinc ferrite 70a corresponds to a relatively high frequency, and manganese-
The zinc-based ferrite 70b corresponds to a relatively low frequency, so that the corresponding frequency characteristic can be wide band.

Second Embodiment In the second embodiment, a plurality of chip type bypass capacitors are further mounted on the multilayer printed wiring board 1 of the first embodiment. The second embodiment will be described below with reference to FIGS. 14 to 16. 14 is an enlarged side sectional view showing the multilayer printed wiring board according to the second embodiment, FIG. 15 is a plan view of the multilayer printed wiring board shown in FIG. 14 from the direction of arrow A, and FIG. 16 is a multilayer printed board shown in FIG. It is a schematic sectional drawing when a wiring board is cut | disconnected in the arrow B direction.

The signal layer on the power supply layer 2 side of the multilayer printed wiring board 100 is provided with chip type bypass capacitors 101 (hereinafter referred to as decaps 101) uniformly at the ends. The distance between the respective bypass capacitors 101 is about 4 [cm], and they are electrically connected to the power source pattern 2a and the earth pattern 3a. The distance between the decaps 101 is not limited to 4 [cm],
It may be larger than this to reduce the number of decaps 101 attached, or may be smaller between the decaps 101 to increase the number of decaps 101 attached. The multilayer printed wiring board 100 has a QFP type L as an electronic component.
An SI 102, an IC (not shown), and the like are mounted. Further, the multilayer printed wiring board 100 has an interface cable for electrically connecting a device (not shown) incorporating the multilayer printed wiring board 100 to another device or the like. Is connected.

The other structure is the same as that of the first embodiment, and the description is omitted.

Next, the relationship between the voltage between the power supply layer 2 and the ground layer 3 and the radiation noise when a signal is externally supplied between the layers 2 and 3 will be described. FIG. 17 is a multilayer printed wiring board that does not include a radiation noise absorber and a decap, and the radiation noise spectrum is obtained when a conductor of length 1 [m] is drawn from the multilayer printed wiring board instead of the interface cable. The result measured by the analyzer is shown. In the figure, the horizontal axis represents frequency and the vertical axis represents radiation noise.

If fo is the resonance frequency [Hz], Co is the speed of light [m / s], and L is the length [m] of the conducting wire, the following equation is established.

[0033]

## EQU00004 ## fo = Co / L (4) Therefore, the resonance frequency fo [Hz] of the conductor 1 [m] is

[0034]

(5) fo = 3 × 10 ⁸ = 1 = 300 × 10 ⁶ = 300 [MHz] (5) The radiated noise is radiated greatly when the length of the conductive wire corresponds to 1/4 of one wavelength.

[0035]

## EQU00006 ## A large peak of radiation noise occurs at 300 [MHz] / 4 = 75 [MHz] (6).

By the way, FIG. 18 shows the result of measurement of the radiation noise of the multilayer printed wiring board having the radiation noise absorbing section by a spectrum analyzer. By providing the radiation noise absorber 4, the radiation noise is absorbed at 100 [MHz] or higher. However, since the LSI 102 is mounted, this becomes a noise source,
Radiated noise near 0 [MHz] is not absorbed.

FIG. 19 is a diagram showing the radiation noise measurement result of the multilayer printed wiring board according to the second embodiment.

Comparing FIG. 18 and FIG. 19, 70 [M
It is understood that the radiated noise in the vicinity of [Hz] is absorbed by the decap 101, and the radiated noise of a frequency higher than 70 [MHz] is absorbed by the ferrite 7.

In the second embodiment, the multilayer printed wiring board 1 having the radiation noise absorbing section 4 of the first embodiment is further provided with the decap 101, so that the interface extending outside the multilayer printed wiring board 1 can be obtained. The noise radiated from the ground wire of the cable can be reduced, the same effect as that of the first embodiment can be obtained, and the radiated noise can be reduced more than that of the first embodiment.

Further, as described in the modification of the first embodiment, the ferrite 7 may be changed in thickness and shape as shown in FIGS. 11 and 12, and as shown in FIG. The small ferrites 70a and 70b made of different materials may be alternately arranged.

Third Embodiment In the third embodiment, the decapacitor 1 of the second embodiment is used.
Instead of providing 01, the power source pattern connected to the IC or LSI and the surrounding power source pattern are connected as an unnecessary radiation wave absorber via, for example, ferrite beads, an EMI filter including a capacitor, or a resistor having a small resistance value. As a result, the radiation noise from the IC or LSI is reduced. The third embodiment will be described below with reference to FIGS. 20 and 21. 20 is a schematic plan view of the multilayer printed wiring board according to the third embodiment, and FIG. 21 is a schematic cross-sectional view of the multilayer printed wiring board shown in FIG. 20 taken along arrow B. In the present embodiment, ferrite beads will be described as an example of the unnecessary radiation wave absorber.

L mounted on the multilayer printed wiring board 200
As shown in FIG. 21, the power supply layer 20 that supplies power to the SI 102 is provided separately from the other power supply layers 2. The power supply layer 20 is electrically connected to the power supply layer 2 via the chip-type ferrite beads 201, the power supply pattern 2 a, and the through holes 6. Other structures are the same as those of the first embodiment, and the description is omitted.

FIG. 22 shows the radiation noise measurement result of the multilayer printed wiring board according to the third embodiment.

In the third embodiment, the radiation noise near 70 [MHz] generated in the LSI 102 (see FIG. 18) is absorbed by the ferrite bead 201, and 100
Radiation noise above [MHz] is absorbed by the ferrite 7. Therefore, the radiation noise is reduced as in the second embodiment.

In the third embodiment, the ferrite beads 201 electrically connect the power supply layer 2 and the power supply layer 20, but the method is not limited to this method and radiation noise generated in the LSI 102 can be absorbed. If so, for example, ferrite beads may be directly fitted into the terminals of the LSI 201 connected to the power supply pattern. In this case, power supply pattern 2
It is not necessary to separate 0a from the power supply pattern 2a.

Further, as described in the modification of the first embodiment, the ferrite 7 may be changed in thickness and shape as shown in FIGS. 11 and 12, and as shown in FIG. The small ferrites 70a and 70b made of different materials may be alternately arranged.

In the first, second and third embodiments,
The ferrite is provided over the entire four side surface portions of the multilayer printed wiring board, but the present invention is not limited to this, and may be partially provided such as one side surface portion, two side surface portions, or three side surface portions. .

Further, in the first, second, and third embodiments, an example in which the radiation noise absorbing portion is provided on the multilayer printed wiring board has been described, but the invention is not limited to the multilayer printed wiring board, and for example, on the surface. Equipped with a power source pattern and an earth pattern,
The radiation noise absorbing section may be provided on a two-layer printed wiring board on which electronic components such as LSI and IC are mounted on the back surface, or a one-layer printed wiring board. In this case, ferrite may be provided so as to cover the power supply pattern and the ground pattern on the surface of the printed wiring board to absorb the radiation noise.

[0049]

As described in detail above, the present invention provides
By providing ferrite along the length direction on the side surface of the printed wiring board and electrically connecting this ferrite to the power supply pattern and the ground pattern, it is possible to connect the power supply pattern and the ground pattern during the operation of the electronic circuit. When voltage fluctuations occur and noise is generated, this radiation noise is absorbed by the ferrite.

Further, since the ferrite may be provided along the side surface portion according to the size of the printed wiring board, it can be easily provided.

[Brief description of drawings]

FIG. 1 is an enlarged side sectional view showing a multilayer printed wiring board according to a first embodiment of the present invention.

FIG. 2 is a schematic plan view of the multilayer printed wiring board according to the first embodiment.

FIG. 3 is a schematic cross-sectional view of the multilayer printed wiring board according to the first embodiment.

FIG. 4 is an explanatory diagram of a radiation noise measurement result of a multilayer printed wiring board.

FIG. 5 is an explanatory diagram of measurement results of voltage between a power supply layer and a ground layer.

FIG. 6 is an explanatory diagram of a radiation noise measurement result of a multilayer printed wiring board.

FIG. 7 is an explanatory diagram of the measurement result of the voltage at the end of the multilayer printed wiring board.

FIG. 8 is an explanatory diagram of a radiation noise measurement result according to the first embodiment.

FIG. 9 is an explanatory diagram of the measurement result of the voltage at the end portion of the multilayer printed wiring board according to the first embodiment.

FIG. 10 is an explanatory diagram of mounting a radiation noise absorbing unit according to the first embodiment.

FIG. 11 is a schematic side sectional view showing a modified example of the first embodiment.

FIG. 12 is a schematic side sectional view showing a modified example of the first embodiment.

FIG. 13 is a schematic perspective view showing a modified example of the first embodiment.

FIG. 14 is an enlarged side sectional view showing a multilayer printed wiring board according to a second embodiment.

FIG. 15 is a plan view of the multilayer printed wiring board according to the second embodiment.

FIG. 16 is a schematic cross-sectional view of the multilayer printed wiring board according to the second embodiment.

FIG. 17 is an explanatory diagram of a radiation noise measurement result of a multilayer printed wiring board.

FIG. 18 is an explanatory diagram of a radiation noise measurement result of a multilayer printed wiring board.

FIG. 19 is an explanatory diagram of a radiation noise measurement result according to the second embodiment.

FIG. 20 is a schematic plan view of a multilayer printed wiring board according to a third embodiment.

FIG. 21 is a schematic side sectional view of a multilayer printed wiring board according to a third embodiment.

FIG. 22 is an explanatory diagram of a radiation noise measurement result according to the third embodiment.

[Explanation of symbols]

 1, 100, 200 Multilayer printed wiring board 2 Power supply layer 2a Power supply pattern 3 Earth layer 3a Earth pattern 4 Radiated noise absorbing part 7, 70 Ferrite

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Norihiro Morimoto 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (6)

[Claims] 1. A printed wiring board having a power supply pattern for supplying electric power to a mounted electronic circuit and a ground pattern for grounding, wherein ferrite is provided along a length direction on a side surface portion of the printed wiring board. A printed wiring board characterized in that the ferrite is electrically connected to the power source pattern and the ground pattern. 2. The printed wiring board according to claim 1, wherein the ferrite is provided over the entire side surface of the printed wiring board. 3. The printed wiring board according to claim 2, wherein a plurality of bypass capacitors electrically connecting the power supply pattern and the ground pattern are arranged at the end portion of the printed wiring board. 4. The printed wiring board according to claim 2, wherein electric power from the power source pattern is supplied to the electronic circuit via an unnecessary radiation wave absorber. 5. The printed wiring board according to claim 2, wherein the ferrite is formed by alternating nickel-zinc based ferrite and manganese-zinc based ferrite. 6. The printed wiring board according to claim 2, 3 or 4, wherein the ferrite is formed of nickel-zinc based ferrite.