JPH02249290A - Printed wiring board - Google Patents

Abstract

PURPOSE:To sharply decrease interference between the signal lines of a printed wiring board and electrostatic induction and electromagnetic induction noises from the outside and facilitate installation and correction of a wiring by making the printed wiring board and then adhering conductors of copper foil, etc., having potential as low as the grounding or power source potential to the external layers of the printed wiring board. CONSTITUTION:Layer-shaped copper foil pattern layers 2 are formed on prepreg (substrates) 1. the copper foil pattern layers 2 construct circuit patterns including signal lines. A face pattern formed in one of copper foil layers 3 consisting of face patterns is made to be a power source line and the face pattern in the other copper foil layer is made to be a grounding line. After a wiring board is completed, the surfaces of the prepreg 1 are covered by copper foil faces 5 of the power source line and the grounding line.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a printed wiring board, and particularly to a printed wiring board suitable for a high frequency circuit board.

[Prior Art] FIG. 7 shows an example of a conventional multilayer printed wiring board. As shown in the figure, the conventional printed wiring board has
A copper foil pattern layer 2° for signal lines, power lines, ground lines, etc. is formed on the surface of a prepreg (substrate body) 1 serving as an insulating layer.

With this type of printed wiring board, when the operating frequency is low, the electromagnetic coupling between the signal lines due to electromagnetic induction generated from inside the board is relatively small and does not pose a problem, but when the operating frequency is high (
Since the electromagnetic coupling between the signal lines becomes denser as the frequency becomes higher (VHF), there is a problem in that the signals interfere with each other, and this signal interference causes circuit malfunction. Furthermore, if the board does not have a shielding layer, there is a problem in that it is susceptible to external noise such as electromagnetic induction and electrostatic induction, so it is necessary to take measures such as attaching a conductive shielding case or the like. On the other hand, Jikai Showa 5
As shown in Japanese Patent No. 0-11160, many structures in which a shielding layer is provided on a substrate have been proposed, but these have the disadvantage of complicating the structure and increasing costs.

Therefore, Utility Model No. 63-60330 (May 7, 1988)
As Hinode II1), we proposed a printed wiring board in which power lines and ground lines are formed in a planar pattern on the surface of the board.

has a shielding effect, so it is possible to suppress the complexity of the configuration and increase in cost.

[Problem to be solved by the invention]

However, in Utility Model Application Publication No. 63-60330, the power line and ground line are integrated with the board, and the signal line is formed inside the board, which makes it difficult to modify the wiring. was there.

Therefore, it is an object of the present invention to significantly reduce interference between signal lines on a printed wiring board, as well as external electrostatic induction and electromagnetic induction noise, and to facilitate wiring arrangement and modification. An object of the present invention is to provide a printed wiring board.

[Means to solve the problem]

In order to achieve the above-mentioned object, the present invention provides a printed wiring board in which, after the printed wiring board is completed, a conductive material such as copper foil, which has been lowered to the ground potential or power supply potential, is bonded to the outer layer of the printed wiring board. It is something.

That is, the printed wiring board of the present invention lowers the impedance of the signal line by covering the surface of the board with a conductive material such as copper foil connected to the power line, ground line, etc. of the multilayer printed wiring board. This prevents interference due to electromagnetic induction between wires, and uses a foil-like conductor that covers the surface of the board with power supply potential and ground potential to play a shielding role, greatly reducing induced noise. . By making it possible to attach the conductor after the board is completed, it is possible to easily arrange and modify the wiring.

〔Example〕

Embodiments of the present invention will be described based on FIGS. 1 to 6.

FIG. 1 is a sectional view of a main part showing a first embodiment of the present invention. Reference numeral 1 denotes a prepreg (substrate) made of an insulator, and a layered copper foil pattern layer 2 is formed on the prepreg 1. This copper foil pattern layer 2 constitutes a circuit pattern including signal lines. Reference numeral 3 denotes a copper foil layer formed in a plane pattern, for example, the plane pattern formed on one side becomes a power supply line, and the other plane pattern becomes a ground line. Reference numeral 4 is a solder resist that has electrical insulation properties and is intended to prevent solder adhesion during soldering of parts other than soldered parts and through holes. 5 is a conductor (copper foil, etc.) that is attached to the outer surface of the board after the board is completed, and serves as a power supply wire and a ground wire, and serves as the electric wire 3. Ground wire 3
connected to. Therefore, the electric wire 3. The grounding wire 3 has a function of lowering the characteristic impedance, as will be described later, but it does not need to have a function as an external shielding layer, so it can be provided in the inner layer portion as shown. The surface of the prepreg 1 also serves as a component mounting surface and a soldering surface.

According to such a configuration, firstly, the signal line 2 is arranged on the inner layer or outer layer of the prepreg 1, and furthermore, as described later, the characteristic impedance of the signal line is reduced by covering the surface of the prepreg 1 with copper foil or the like. can be made smaller. This will be explained as follows based on FIGS. 2 and 3.

2 and 3 model the signal line 2 of this embodiment as a stripline. FIG. 2 is a model as an unbalanced stripline, and FIG. 3 is a model as a balanced stripline. represents. Generally, in the model shown in Figure 2, the characteristic impedance of the stripline Z0
is expressed by equation (1).

Here, Hr is the effective dielectric constant of the prepreg 1, and W is the conductor width when a signal line etc. is regarded as a strip line.

T is the conductor thickness when a signal line or the like is regarded as a strip line, and H is the thickness of the prepreg 1 of the unbalanced strip line.

On the other hand, in the balanced strip line model shown in Figure 3,
Characteristic impedance Z0 is expressed by equation (2).

Here, L is the thickness of the prepreg 1 of the balanced stripline. From formulas (1) and (2), a circuit pattern 2 including signal lines is formed on the inner and outer layers of the prepreg 1, and a power supply line 3. By arranging the grounding wire 3 and further covering it with the planar copper foil 5, the characteristic impedance can be reduced. the result,
The induced voltage is reduced, and electromagnetic interference between signals can be prevented.

As mentioned above, since the surface of the prepreg l is covered with the copper foil surface 5 for the power supply line, grounding line, etc., this surface plays the role of electrostatic shielding, and has the effect of shielding against external noise and the noise emitted from inside. Improved.

Further, since the copper foil surface 5 is attached to the outside, the thickness (electrical resistance) etc. of the copper foil surface 5 can be changed depending on the desired shielding effect. Therefore, according to this embodiment, it is possible to manufacture a highly reliable printed wiring board.

FIG. 4 shows a second embodiment of the present invention. In this embodiment, in addition to forming a plurality of copper foil pattern layers 2 such as signal lines on the inner layer of the prepreg 1, each copper foil pattern layer 2 is A surface pattern copper foil layer 3 of a power supply line or a ground line is disposed on the top and bottom, and after the board is completed, it is covered with a copper foil surface 5 of a power supply line or a ground line. This embodiment can lower impedance even further than the first embodiment, and can provide a multilayer printed wiring board with higher reliability.

FIG. 5 shows a third embodiment of the present invention, in which the copper foil surface 5 of the power supply line, grounding conductor, etc. is replaced with a laminate tape 6 made by laminating a conductive foil onto a plastic sheet, in contrast to the first embodiment. This can prevent short circuits with signal lines. According to this configuration, the conductive foil to be laminated has a planar shape, but it can also be patterned in accordance with the circuit pattern 2.

In FIG. 6, in contrast to FIG. 5, a laminate tape 6 is attached to cover the components (devices) 7 after the attachment of the components (devices) 7 is completed, so that the influence of external noise on the components can be reduced. In the above embodiments, those using a laminate tape can be easily manufactured by simply spirally winding the laminate tape, vertically winding the tape, and heat-sealing the overlapping surfaces.

〔Effect of the invention〕

As explained above, according to the printed wiring board of the present invention, after the printed wiring board is completed, a conductive material such as copper foil, which has been lowered to the ground potential or power supply potential, is attached to the outer layer of the printed wiring board. Interference between signal lines on printed wiring boards and external electrostatic induction and electromagnetic induction noise have been significantly reduced, and wiring can be easily installed and modified.

[Brief explanation of drawings]

FIG. 1 is a sectional view of essential parts showing a first embodiment of the present invention. Second
The figure is an explanatory diagram in which a multilayer printed wiring board is modeled as an unbalanced strip line in order to explain the present invention in detail. FIG. 3 is an explanatory diagram in which a multilayer printed wiring board is modeled as a balanced strip line for detailed explanation of the present invention. FIG. 4 is a sectional view of a main part showing a second embodiment of the present invention. FIG. 5 is a sectional view of main parts showing a third embodiment of the present invention. FIG. 6 is a sectional view of a main part showing a fourth embodiment of the present invention. FIG. 7 is a sectional view of a main part of an example of a conventional printed wiring board. Explanation of symbols

Claims (1)

[Claims] (1) A printed wiring board characterized in that, after the printed wiring board is completed, a conductor such as copper foil, which is at ground potential or power supply potential, is bonded to the outer layer of the printed wiring board.