JPH07235770A - Multilayer printed wiring board - Google Patents

Abstract

PURPOSE:To provide a multilayer printed wiring board capable of reducing EMI caused by radiation of electromagnetic waves from side faces of the board. CONSTITUTION:Circuit patterns 3a and 3b are formed on a multilayer printed wiring board 5A. A power source layer 1a set to a source potential and ground layer 2 are oppositely on both sides of a dielectric layer 6. An end dielectric layer 10 having a less dielectric const. than that of the layer 6 is formed at the fringe of the layer 6. Electromagnetic waves induced over the layers 1a and 2 at the fringe of the board 5A are attenuated by the layer 10 disposed at the fringe of the dielectric disposed between the layers 1a and 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer printed wiring board used in electronic equipment.

[0002]

2. Description of the Related Art With the recent rapid development of electronic devices,
Circuits formed on a printed wiring board mounted on an electronic device have a high density and its operation speeds up, and electromagnetic waves emitted from the printed wiring board adversely affect the operation of surrounding electronic devices. ) Is a problem.

Generally, in a printed wiring board, a power supply layer set to a power supply potential and a ground layer set to a ground potential are independently provided to stabilize the power supply voltage and malfunction due to fluctuations in the power supply voltage of a circuit pattern. Is being prevented. By doing so, the loop of the current flowing through the circuit pattern becomes small, and the impedance of the power supply layer and the ground layer decreases, so that the electromagnetic waves emitted from the printed wiring board can be suppressed.

However, since the power consumption increases in proportion to the speeding up of the operation in the circuit pattern and the noise current in the power supply layer and the ground layer increases, a means for separately reducing the emission of electromagnetic waves to the printed wiring board. Need to be applied.

In response to this, in Japanese Utility Model Laid-Open No. 3-6859, an insulating layer is formed on a printed wiring board on which a circuit pattern is formed so as to cover the circuit pattern except at least a part of the power supply layer, There is disclosed a printed wiring board that suppresses the emission of electromagnetic waves from the printed wiring board by forming a conductive layer connected to the non-insulated portion of the power supply layer on the insulating layer.

According to the method of this disclosure, the distributed electrostatic capacitance between the circuit pattern and the ground layer becomes large with respect to the conductive layer connected to the power supply layer, and the circuit impedance becomes small. Radiation noise is suppressed by grounding the layer in a high frequency manner. In addition, the conductive layer shields the circuit pattern and the ground layer, so that the circuit impedance is made uniform and high frequency components due to impedance mismatch are prevented.

[0007]

In the printed wiring board according to the above disclosure, no consideration is given to the emission of electromagnetic waves from the peripheral edge portion of the board, which is a problem particularly when the board has a multilayer structure. FIG. 3 is a cross-sectional explanatory view showing a configuration of a conventional multilayer printed wiring board, and FIG. 4 is an explanatory view of electromagnetic wave emission in the conventional multilayer printed wiring board. As shown in FIG. 3, the multilayer printed wiring board 5 is formed by stacking a plurality of boards made of an insulating material such as epoxy resin. On these substrates, circuit patterns 3a, 3b, power supply layers 1a, 1b set to a power supply potential,
The ground layer 2 set to the ground potential is formed by a known photolithography technique.

In the printed wiring board 5 having a multilayer structure, the power supply layer 1a formed on one surface side of one board.
And the ground layer 2 formed on the one surface side of the other substrate,
The dielectric layers 6 made of a resin material or the like are arranged so as to face each other.

In the conventional multi-layered printed wiring board 5 having such a structure, as shown in FIG. 4, at the end positions of the power supply layer 1a and the ground layer 2, electromagnetic waves are spread across the power supply layer 1a and the ground layer 2. 7 is induced and this electromagnetic wave 7
May be emitted from the peripheral edge of the printed wiring board 5, and the emitted electromagnetic waves may adversely affect the operation of electronic devices in the vicinity.

The present invention has been made in view of the present situation of EMI prevention in a printed wiring board as described above,
The purpose is to emit E from the side edge of the substrate.
An object of the present invention is to provide a multilayer printed wiring board capable of reducing MI.

[0011]

According to a first aspect of the present invention, there is provided a multilayer printed wiring board having a circuit pattern, a power source layer set to a power source potential, and a ground set to a ground potential. The layers are opposed to each other with the dielectric layer sandwiched therebetween, and an end dielectric layer having a dielectric constant lower than that of the dielectric layer is provided at a peripheral end of the dielectric layer. Characterize.

In the multilayer printed wiring board according to the present invention, the peripheral ends of the power supply layer and the ground layer are arranged so as to protrude from the peripheral end parts of the dielectric layer, and the power supply layer and the ground layer. The end dielectric layer is disposed between the peripheral end of the dielectric layer and the peripheral end of the dielectric layer.

[0013]

According to this structure, the electromagnetic wave induced across the power supply layer and the ground layer at the peripheral edge of the multilayer printed wiring board is higher than the dielectric constant of the dielectric layer disposed between the power supply layer and the ground layer. Electromagnetic waves that have a low dielectric constant and are attenuated by the end dielectric layers disposed at the peripheral edges of the dielectrics disposed between the power supply layer and the ground layer and emitted from the peripheral edges of the multilayer printed wiring board. The strength of is reduced.

[0014]

EXAMPLE 1 An example of the present invention will be described below with reference to FIGS. 1 is a cross-sectional explanatory view showing the configuration of the same embodiment, and FIG. 2 is an explanatory view of electromagnetic wave suppression of the same embodiment. As shown in FIG. 1, in the present embodiment, the cutout portion 8 is formed in the dielectric layer 6 at the peripheral end portion of the printed wiring board 5A, as compared with the conventional printed wiring board having the multilayer structure described with reference to FIG. Is formed, and the notch 8 is filled with air as the end dielectric layer 10. The configuration of the other parts of the present embodiment is the same as that of the conventional printed wiring board of the conventional multilayer structure already described with reference to FIG.

Next, the operation of suppressing the electromagnetic wave emission of this embodiment having such a configuration will be described. As shown in FIG. 2, in the present embodiment, a cutout 8 is formed in the dielectric layer 6 disposed between the power supply layer 1a and the ground layer 2 at the peripheral end of the printed wiring board 5A. Air having a relative dielectric constant of about 1 is filled in the portion 8 as the end dielectric layer 10.

Generally, when the dielectric constant of the notch 8 is ε and the potential difference between the power supply layer 1a and the ground layer 2 is E, the power supply layer 1a set to the power supply potential and the ground layer 2 set to the ground potential are set. At the end dielectric layer 10 in the cutout 8
The density i of the displacement current flowing in is given by [Equation 1].

[0017]

[Equation 1] i = ε (∂E / ∂t)

Electromagnetic waves are induced between the power supply layer 1 and the ground layer 2 based on the displacement current density i given by [Equation 1], and emitted from the peripheral end portion of the printed wiring board 5A.

In this embodiment, the notch 8 is filled with air, and its dielectric constant ε is significantly smaller than the dielectric constant of the dielectric layer 6, so that the notch 8 is discharged from the peripheral edge of the printed wiring board 5A. The intensity of the electromagnetic wave is greatly reduced, and the electromagnetic wave E emitted from the peripheral edge of the printed wiring board 5A
It becomes possible to prevent MI.

In the embodiment, the case where air is used as the end dielectric layer has been described, but the present invention is not limited to this embodiment, and the end dielectric layer is provided between the power supply layer and the ground layer. Various materials having a dielectric constant smaller than that of the dielectric layer can be used.

[0021]

According to the present invention, the electromagnetic wave induced across the power supply layer and the ground layer at the peripheral edge of the multilayer printed wiring board is more than the dielectric constant of the dielectric layer disposed between the power supply layer and the ground layer. Also has a low dielectric constant, and is attenuated by the end dielectric layers arranged at the peripheral ends of the dielectric layers arranged between the power supply layer and the ground layer. For this reason, the intensity of electromagnetic waves emitted from the peripheral end portion of the multilayer printed wiring board is reduced, and electromagnetic interference (EMI) due to the multilayer printed wiring board is reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing the configuration of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of electromagnetic wave suppression of the example.

FIG. 3 is an explanatory sectional view showing the structure of a conventional multilayer printed wiring board.

FIG. 4 is an explanatory diagram of electromagnetic wave emission of a conventional multilayer printed wiring board.

[Explanation of symbols]

 1a, 1b Power layer 2 Ground layer 3a, 3b Circuit pattern 6 Dielectric layer 8 Notch 10 Edge dielectric layer

Claims (2)

[Claims] 1. A multilayer printed wiring board on which a circuit pattern is formed, a power supply layer set to a power supply potential and a ground layer set to a ground potential are arranged to face each other with a dielectric layer interposed therebetween, A multilayer printed wiring board, characterized in that an end dielectric layer having a dielectric constant lower than that of the layer is disposed at a peripheral end of the dielectric layer. 2. The peripheral edges of the power supply layer and the ground layer are arranged so as to project from the peripheral edges of the dielectric layer, and the peripheral edges of the power supply layer and the ground layer and the dielectric layer are arranged. The multilayer printed wiring board according to claim 1, wherein the end dielectric layer is disposed between the peripheral ends.