JP2001203434A - Printed wiring board and electrical apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrict an unwanted electromagnetic radiation which arises from each pattern of a power source layer and a ground layer. SOLUTION: A bypass capacitor 18 has substantially the same resonant frequency as a resonant frequency f of a printed wiring board 10 itself on which electronic components are not mounted, and is mounted between a power source layer 11 and a ground layer 12 of the printed wiring board 10.

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 on which, for example, an IC chip, a transistor, a resistor, a capacitor and the like are mounted, and a high-frequency signal of several tens of MHz or more propagates, and an electric apparatus provided with the printed board.

[0002]

2. Description of the Related Art In digital devices equipped with a microprocessor, the operating speed of the microprocessor has been increased and the signal transmission speed between the microprocessor and another IC chip has also been increased. For example, in the case of a personal computer, the operating frequency of a microprocessor exceeds 600 MHz.

In a printed wiring board equipped with such a microprocessor, a direct RAMBUS memory is planned to be used between the microprocessor and the memory. If this is used, a signal propagating on the printed circuit board is used. 400 between memory and memory
The momentum reaches a high frequency of MHz. However, at present S
DRAM is the mainstream, and the frequency ranges from 100 MHz to 13
Attempting to increase to 3MHz.

A clock signal that propagates on such a printed wiring board has a harmonic component because it is a digital signal, and the frequency of the signal that actually propagates on the printed wiring board is higher than the clock frequency. High frequency signals will propagate. When such a high-frequency signal propagates, noise countermeasures, particularly power supply system noise, are important for printed wiring boards.

[0005] This noise countermeasure will be described with reference to a circuit diagram on a printed wiring board shown in FIG. A plurality of circuit blocks 100, 101, 10
3 are formed, and these circuit blocks 100, 101, 1
03 is supplied from the power supply circuit 104. In an ordinary electronic device, power is supplied to each circuit on a printed wiring board from a power supply circuit or a battery inside the device via a conductor. For example, in a personal computer, a power supply circuit is connected to a power supply layer and a ground layer of a printed wiring board, and supplies power to each circuit block and electronic components mounted on the printed wiring board.

[0006] From the power supply circuit 104 to each circuit block 10
The distances to 0, 101, and 103 are different depending on the individual circuit blocks 100, 101, and 103. Among them, the circuit blocks 100, 1, and
01 or 103 is very long. This power supply circuit 10
An increase in the distance from 4 to each circuit block 100, 101 or 103 means that a huge current loop flowing from the power supply circuit 104 through the ground layer is formed.

Considering a printed wiring board used for a personal computer, the current loop length is
The size is not negligible with respect to the wavelength of the signal propagating on the printed wiring board. In this case, sufficient current cannot be supplied to each of the circuit blocks 100, 101, and 103, and normal operation cannot be expected.

As a countermeasure against this, each circuit block 100,
A capacitor (decoupling capacitor to be described later) 10
5 is connected, and the capacitor 105 is operated as a power supply source. Thereby, each circuit block 100,
This is equivalent to installing a power supply for each of the power supply 101 and the power supply 103, thereby reducing the current loop of the power supply and enabling high-speed operation. The capacitor 105 is called a decoupling capacitor because it functions to equivalently separate the power supplies of the circuit blocks 100, 101, and 103.

At high frequencies, the effect of ground bounce caused by the inductance components of the power supply layer and the ground layer becomes serious, so that the function of the decoupling capacitor 105 becomes important. This decoupling capacitor 105
Is intended to supply power to an IC chip, a capacitor having a large capacity such as 0.1 μF or 0.01 μF is generally selected.

On the other hand, electromagnetic interference (EMI: Electro-Magnetic-I) generated by current flowing through the power supply layer and the ground layer.
The problem is that countermeasures are difficult, the frequency is close to the operating frequency of the electronic device, and the level is large.

The frequency of the electromagnetic waves radiated from the power supply layer and the ground layer is determined by the shapes of the metal patterns of the power supply layer and the ground layer. For example, as shown in FIGS. 12A and 12B, in a printed wiring board 108 including a power supply layer 106 and a ground layer 107, the lengths of the sides of the power supply layer 106 and the ground layer 107 are rectangles of a and b, and The resonance frequency f when the power layer 106 and the ground layer 107 face each other is f = {c / 2π · (ε _f ) ^1/2 } · k (1) k ² = (mπ / a) ² + (nπ / b) ² .

Here, m = 0, 1, 2,... N =
0, 1, 2, ... c: speed of light in vacuum 2.998 × 10 ⁸ m / s ε _f : relative permittivity of dielectric

[0013]

At the resonance frequency f, the intensity of the radiated electromagnetic wave increases, so that it is necessary to take some measures against EMI caused by the radiated electromagnetic wave. Although the above-described decoupling capacitor 4 has an effect of shifting the resonance frequency of the printed wiring board to a higher frequency,
It is not enough from the viewpoint of EMI measures.

As an effective measure against EMI, for example, there is a method of adding a loss between a power supply layer and a ground layer. As this method, for example, JP-A-6-132668 describes a method in which a damping element is connected between a power supply layer and a ground layer to suppress emission of unnecessary electromagnetic waves. Japanese Patent Application Laid-Open No. 10-190237 describes a method in which a resistor is inserted between a power supply layer and a ground layer, and unnecessary electromagnetic waves are absorbed by the resistor.

However, these countermeasures have problems that the number of components mounted on the printed wiring board increases, the structure of the printed wiring board becomes complicated, and the cost of the printed wiring board increases.

Accordingly, an object of the present invention is to provide a printed wiring board which can suppress unnecessary electromagnetic radiation generated from resonance between respective patterns of a power supply layer and a ground layer.

Another object of the present invention is to provide an electric device capable of performing a stable operation by suppressing unnecessary electromagnetic waves.

[0018]

According to a first aspect of the present invention, there is provided a printed wiring board on which at least one IC chip is mounted and at least one power supply layer and one ground layer are formed. A printed wiring board including at least one bypass capacitor connected to a ground layer.

According to a second aspect of the present invention, there is provided the printed wiring board according to the first aspect, wherein the bypass capacitor has an impedance value composed of a capacitor component and an inductance component with respect to frequency substantially matching the resonance frequency of the printed wiring board itself. It is.

According to a third aspect of the present invention, there is provided a printed wiring board according to the first aspect, wherein the bypass capacitor is represented by an equivalent circuit composed of a capacitor component and an inductance component. Also, at least one of the resonance frequencies between the power supply layer and the ground layer determined by the pattern shape of the power supply layer and the ground layer falls within a frequency range in which the impedance of the equivalent circuit in which the capacitor component and the inductance component are connected in series is reduced. The printed circuit board and the bypass capacitor are combined so as to be included.

According to a fourth aspect of the present invention, in the printed wiring board according to the third aspect, the impedance of an equivalent circuit in which the capacitor component and the inductance component are connected in series is smaller than the impedance of the single capacitor component and the single inductance component. The resonance frequency between the power supply layer and the ground layer, which is determined by the pattern shape of the power supply layer and the ground layer included in the given frequency range, is the fundamental frequency.

According to a fifth aspect of the present invention, in the printed wiring board of the third aspect, the impedance of an equivalent circuit in which the capacitor component and the inductance component are connected in series is smaller than the impedance of the single capacitor component and the single inductance component. The bypass capacitors are selected or combined so that a certain frequency range includes different resonance frequencies among the resonance frequencies between the power supply and the ground layer determined by the pattern shapes of the power supply layer and the ground layer.

According to a sixth aspect of the present invention, in the printed wiring board of the first aspect, the bypass capacitor is an IC.
A plurality are arranged so as to surround the chip.

The present invention according to claim 7 provides the invention according to claims 1 to 6
An electric device comprising the printed wiring board according to any one of the above.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a configuration diagram of a printed wiring board. The printed wiring board 10 has at least electronic components such as an IC chip Q, a transistor, a resistor, and a capacitor mounted thereon. Normally, the printed wiring board 10 used for an electronic device has a plurality of conductor layers. In the printed wiring board 10 that handles high-frequency signals, in particular, the power supply layer 11 and the ground layer 11 are provided with dedicated layers. I have. The actual printed wiring board 10 has a signal wiring layer (not shown) for transmitting signals.

Hereinafter, the printed wiring board 10 having only the power supply layer 11 and the ground layer 12 will be described. When considering the resonance phenomenon between the power supply layer 11 and the ground layer 12,
Since the influence of the signal wiring layer is small, other parts are not considered.

FIGS. 2A and 2B show the power supply layer 11 and the ground layer 1.
FIG. 2 is a configuration diagram of a printed wiring board 10 having only two. The printed wiring board 10 includes a power supply layer 11, a ground layer 12, a pad layer 13, a through-hole land layer 14 as described above.
This is a substrate having four conductor layers. These layers 11 to 14
Is made of copper, and the insulator 15 is a general printed wiring board made of glass epoxy. Pads 16 to which chip components for personal computers are connected are formed on the pad layer 13, and elements such as resistors and capacitors can be connected between the power supply layer 11 and the ground layer 12.

The printed wiring board 10 is provided with a power supply coaxial connector pad 17 for mounting a coaxial connector so that S-parameter measurement can be performed.

The power supply layer 11 and the ground layer 12 are each formed in a square of, for example, 182 mm × 182 mm. The distance between the power supply layer 11 and the ground layer 12 is 0.3 mm, and the thickness of the printed wiring board 10 is 0.7 mm.

The resonance frequency f when the parallel flat metal conductors of the power supply layer 11 and the ground layer 12 are arranged to face each other is expressed by the above equation (1). Table 1 shows the resonance frequency f calculated from the above equation (1) for the printed wiring board 10 shown in FIG.

[0032]

[Table 1]

The lowest resonance frequency f is, for example, about the same as the operating frequency of an MPU (Microprocessing Unit) of a personal computer, and may cause some interference.

At the resonance frequency f of the printed wiring board 10 shown in Table 1 above, the efficiency of the printed wiring board 10 as an antenna for radiating electromagnetic waves becomes higher than other frequencies, which may cause EMI problems. . As a method of evaluating the EMI of the printed wiring board, for example, there is a method using S parameters.

This S-parameter represents the concept of the reflection coefficient as 2
This is an extension to a terminal pair network, and is a concept generally used in high frequency measurement. The S parameter does not directly measure the electromagnetic wave radiated from the printed wiring board 10, but it is reported that there is a correlation between the S parameter and the radiated electromagnetic wave. In the case of the printed wiring board 10 shown in FIG. 2, the smaller the level of the S parameter at the resonance point, the larger the radiated electromagnetic wave.

FIG. 3 shows the printed wiring board 10 shown in FIG.
To the printed wiring board 10
Each bypass capacitor 18 having a different capacity in the corner,
For example, no bypass capacitor, capacity 0.01μF ×
4 shows the measurement results of the S parameter (Sll) when each bypass capacitor having a capacitance of 47 pF × 4 and a capacitance of 10 pF × 4 is mounted. FIG. 4 shows the peak value of the S parameter shown in FIG. 3 at the resonance frequency.

When the bypass capacitor 18 is not provided, the S parameter sharply decreases at the resonance frequency f shown in Table 1 above. By mounting the bypass capacitor 18 on the printed wiring board 10, the impedance of the entire printed wiring board 10 including the bypass capacitor 18 changes, and the resonance frequency f and the S at this resonance frequency f
The size of the parameter has changed.

When a capacitor having a capacitance of 0.01 μF, which is generally used as a decoupling capacitor, is mounted, the absolute value of the resonance peak (hereinafter simply referred to as the peak value means the absolute value) is small. But
A new resonance occurs near the frequency of 150 MHz. When the capacitance is 10 pF, there is almost no difference from the case where the bypass capacitor 18 is not provided.

When the capacitance is 47 pF, almost all peak values other than the fundamental frequency decrease. That is, when the capacitance is 47 pF, it is reduced by approximately 1 dB as compared with the case where the bypass capacitor 18 is not provided.

Such a change in the S parameter is considered as follows. Bypass capacitor 18 connected between power supply layer 11 and ground layer 12 of printed wiring board 10
Connects the power supply layer 11 and the ground layer 12 with a specific impedance. If the impedance is sufficiently small, the position at which the bypass capacitor 18 is mounted is hard to vibrate, so that the peak value of the resonance becomes small, and the value of the resonance frequency f changes.

5 and 6 show impedance frequency characteristics. FIG. 5 corresponds to a capacitor having a capacitance of 0.01 μF, and FIG. 6 corresponds to a capacitor having a capacitance of 10 pF and 47 pF. As can be seen from FIG. 5, a large-capacity capacitor usually used as a decoupling capacitor has a low impedance at low frequencies, but has a large impedance in the region of the resonance frequency f shown in Table 1 above.

On the contrary, a capacitor having a small capacity shown in FIG. 6 has a smaller impedance.
Since the capacitor is represented by a series circuit of the inductance and the capacitance of the electrode, the impedance becomes the smallest at the resonance frequency of the capacitor itself.

Therefore, it is possible to mount the bypass capacitor 18 having a resonance frequency substantially equal to the resonance frequency f of the printed wiring board 10 on which no electronic components are mounted.
It can be seen that it is effective for suppressing the resonance between the power supply layer 11 and the ground layer 12.

A 47 pF bypass capacitor 18
Is smaller in impedance in the frequency band of 500 MHz to 1 GHz than other capacitors, and is considered to have been effective in suppressing resonance between the power supply layer 11 and the ground layer 12.

Since the frequency range in which the impedance of the bypass capacitor 18 is small is a frequency band near the resonance frequency, it is not possible to cope with all the resonance frequencies f shown in Table 1 with only one type of capacitor. Therefore, it is conceivable to mount a plurality of capacitors having different characteristics.

FIG. 7 shows the S parameters when the bypass capacitors 18 having different characteristics are mounted. In the figure,
When the bypass capacitor 18 having a capacitance of 47 pF and a capacitance of 0.01 μF is combined, all peak values become 0.01 μF.
It is smaller than the capacitor of F alone.

Accordingly, it can be seen that the combination of the printed wiring board 10 and the bypass capacitor 18 can reduce electromagnetic radiation in all frequency ranges.

As described above, the printed wiring board 10 of the present invention
Has at least one IC chip Q mounted thereon and has a power supply layer 1
A printed wiring board 10 including at least one layer 1 and at least one ground layer 12 includes at least one bypass capacitor 18 connected to the patterns of the power layer 11 and the ground layer 12.

It is preferable that the impedance value of the bypass capacitor 18 composed of the capacitor component and the inductance component with respect to the frequency substantially coincides with the resonance frequency f of the printed wiring board 10 itself.

In this case, if the bypass capacitor 18 is represented by an equivalent circuit composed of a capacitor component and an inductance component, the capacitor component and the inductance component are connected in series rather than the respective impedances of the capacitor component and the inductance component alone. Within a frequency range in which the impedance of the equivalent circuit at the time becomes small, a range including at least one of the resonance frequencies between the power supply layer 11 and the ground layer 12 determined by the pattern shapes of the power supply layer 11 and the ground layer 12 is included. The printed wiring board 10 and the bypass capacitor 18 are combined.

Generally, the bypass capacitor 18 is composed of a conductor of an electrode and a dielectric formed between the electrodes. When represented by an equivalent circuit, as shown in FIG. 8, an inductance component (capacitor electrode inductance) 20 and a capacitor component (capacitor electrode inductance) are formed. (Capacitor capacitance) 21 in series.

The frequency characteristics of the capacitor 21 are shown in FIG.
As shown in (2), the impedance becomes minimum at the resonance frequency f. As shown in the figure, the bypass capacitor 1 connected between the power supply layer 11 and the ground layer 12 of the printed wiring board 10
8 is best when the minimum value of the impedance composed of the capacitor component and the inductance component with respect to the frequency matches the resonance frequency f of the printed wiring board 10 itself.

When such a bypass capacitor 18 is connected between the power supply layer 11 and the ground layer 12 of the printed wiring board 10, the resonance frequency f is equivalent to a short circuit between the power supply layer 11 and the ground layer 12. .

Accordingly, the printed wiring board 1 shown in FIG.
When a bypass capacitor 18 that resonates in the vicinity of the resonance frequency f of the printed wiring board 10 is mounted on the circuit board 0, the vibration areas of the power supply layer 11 and the ground layer 12 are effectively reduced. Radiation can be reduced.

The resonance frequency of the entire structure in which the bypass capacitor 18 is mounted on the printed wiring board 10 moves to a higher frequency side, but at a high frequency, the radiation level of the unnecessary electromagnetic wave is significantly reduced due to the loss of the dielectric material of the printed wiring board 10 and the like. Does not grow. However, only by appropriately selecting the bypass capacitor 18, the power supply layer 1 of the printed wiring board 10 can be used.
1 and the unnecessary electromagnetic wave radiated from the ground layer 12 can be reduced.

Here, various arrangements of the bypass capacitor 18 are used as shown in FIGS. 10 (a) to 10 (d). FIG. 1A shows a configuration in which a bypass capacitor 18 is arranged so as to surround a power supply coaxial connector pad 17, and this arrangement reduces the effective size of the power supply layer 11 and the ground layer 12 of the printed wiring board 10. This is equivalent to the above, and the radiated electromagnetic wave can be further reduced.

FIG. 4B shows a plurality of bypass capacitors 18 arranged at predetermined intervals in the vertical and horizontal directions of the printed wiring board 10. FIG. 4C shows the bypass capacitor 18 shown in FIG. Are arranged at the center of the printed wiring board 10 and the center of each side of the printed wiring board 10. FIG. 5D shows a case where the bypass capacitor 18 is arranged at an arbitrary position on the printed wiring board 10. FIG.
The feeding points in (a) to (d) correspond to the actual printed wiring board 10
Corresponds to the IC chip Q.

As described above, according to the above-described embodiment, the radiation is caused by the resonance phenomenon of the power supply layer 11 and the ground layer 12 of the printed wiring board 10 without mounting a special EMI countermeasure component on the printed wiring board 10. Unwanted electromagnetic waves can be suppressed.

When the printed wiring board 10 is used for various electric devices, it is possible to suppress unnecessary electromagnetic waves in the electric devices and perform a stable operation.

The present invention is not limited to the above embodiment, but may be modified as follows.

For example, the printed wiring board 10 is not limited to a square shape, but may be an irregular shape. Even in the bypass capacitor connected to the irregular-shaped printed wiring board, the minimum value of the impedance composed of the capacitor component and the inductance component with respect to the frequency matches the resonance frequency of the printed wiring board itself as in the first embodiment. is there. The resonance frequency of a printed wiring board having an irregular shape can be obtained by using an electromagnetic field simulation.

[0062]

As described above in detail, according to the present invention, it is possible to provide a printed wiring board capable of suppressing unnecessary electromagnetic radiation generated from each pattern of the power supply layer and the ground layer.

Further, according to the present invention, it is possible to provide an electric device capable of performing a stable operation by suppressing unnecessary electromagnetic waves.

[Brief description of the drawings]

FIG. 1 is an external view showing an embodiment of a printed wiring board according to the present invention.

FIG. 2 is a configuration diagram showing an embodiment of a printed wiring board having only a power supply layer and a ground layer according to the present invention.

FIG. 3 is a diagram showing a measurement result of an S parameter when a bypass capacitor is mounted in one embodiment of the printed wiring board according to the present invention.

FIG. 4 is a diagram showing a peak value of an S parameter at a resonance frequency in one embodiment of the printed wiring board according to the present invention.

FIG. 5 is a diagram showing impedance-frequency characteristics in one embodiment of the printed wiring board according to the present invention.

FIG. 6 is a diagram showing impedance-frequency characteristics in one embodiment of the printed wiring board according to the present invention.

FIG. 7 is a diagram showing S parameters when each bypass capacitor having different characteristics is mounted in the printed wiring board according to the embodiment of the present invention.

FIG. 8 is a series connection circuit in which a bypass capacitor in an embodiment of a printed wiring board according to the present invention is equivalently represented by an inductance component and a capacitor component.

FIG. 9 is a diagram showing frequency characteristics of capacitor capacitance in one embodiment of the printed wiring board according to the present invention.

FIG. 10 is a view showing an example of arrangement of bypass capacitors in a printed wiring board according to an embodiment of the present invention;

FIG. 11 is a circuit diagram on a printed wiring board for describing a conventional noise measure.

FIG. 12 is a configuration diagram of a printed wiring board for explaining electromagnetic waves radiated from a power supply layer and a ground layer in the related art.

[Explanation of symbols]

 10: Printed wiring board 11: Power supply layer 12: Ground layer 13: Pad layer 14: Through hole land layer 15: Insulator 16: Pad 17: Coaxial connector pad for power supply 18: Bypass capacitor Q: IC chip

Claims (7)

[Claims] 1. A printed wiring board on which at least one IC chip is mounted and at least one power supply layer and one ground layer are formed, wherein at least one bypass connected to the power supply layer and the ground layer A printed wiring board comprising a capacitor. 2. The printed wiring board according to claim 1, wherein the bypass capacitor has an impedance value comprising a capacitor component and an inductance component with respect to frequency substantially equal to a resonance frequency of the printed wiring board itself. 3. The capacitor component and the inductance component are connected in series, compared to the impedance of the capacitor component alone and the inductance component alone when the bypass capacitor is represented by an equivalent circuit including a capacitor component and an inductance component. The power supply layer, in a frequency range where the impedance of the equivalent circuit is reduced,
The printed circuit board and the bypass capacitor are combined so as to include at least one of resonance frequencies between the power supply layer and the ground layer determined by a pattern shape of the ground layer. Item 2. The printed wiring board according to Item 1. 4. The power supply layer and the ground layer included in a frequency range in which the impedance of an equivalent circuit in which the capacitor component and the inductance component are connected in series is smaller than the impedance of the capacitor component alone and the inductance component alone. The printed wiring board according to claim 2, wherein the resonance frequency between the power supply layer and the ground layer determined by the pattern shape is a fundamental frequency. 5. A frequency range in which the impedance of an equivalent circuit in which the capacitor component and the inductance component are connected in series is smaller than the impedance of the capacitor component alone and the inductance component alone, is in the power supply layer and the ground layer. 4. The printed wiring board according to claim 3, wherein the bypass capacitor is selected or combined so as to include different ones of resonance frequencies between the power supply and the ground layer determined by a pattern shape. 6. The printed wiring board according to claim 1, wherein a plurality of said bypass capacitors are arranged so as to surround said IC chip. 7. An electric device comprising the printed wiring board according to claim 1. Description: