JPH02249291A - Printed wiring board - Google Patents

Abstract

PURPOSE:To sharply decrease interference between the signal lines of a 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, forming insulating films of insulating varnish on the external layers thereof, applying conductive paste into face form on said insulat ing films, and forming shielding layers by heat treatment. CONSTITUTION:Layer-shaped copper foil pattern layers 2 are formed on prepreg (substrates) 1. The copper foil pattern layers 2 construct circuit patterns includ ing 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 printed wiring board is completed, insulating varnish is applied on to the copper foil pattern layers 2 formed on the surfaces of the prepreg 1, conductive paste is applied on to the insulating varnish 5, and face-shaped conductive films 6 are formed by heat treatment.

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. 6 shows an example of a conventional multilayer printed wiring board. As shown in the figure, the conventional printed wiring board is
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 Application 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)
The company proposed a printed wiring board with power supply lines and ground lines formed in a planar pattern on the surface of the board.

According to this printed wiring board, since the power supply line and the ground line have a shielding effect, it is possible to suppress the complexity of the configuration and increase in cost.

[Problems to be Solved by the Invention] However, in Utility Model Application Publication No. 63-60330, the power supply line and the ground line are integrated with the board, and the signal line is formed inside the board, so wiring is difficult. There were problems such as making corrections difficult.

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 forms an insulating film on the outer layer of the printed wiring board using an insulating paint after the printed wiring board is completed, and then applies a conductive paste on the insulating film in a planar manner, and then heat-treats it to form a shielding layer. The present invention provides a printed wiring board formed with the following.

That is, the printed wiring board of the present invention has an insulating film.

Then, by covering the surface of the board with a conductive material made of heat-treated conductive paste, and connecting the conductive material to the power supply line, grounding line, etc. of the multilayer printed wiring board, the impedance of the signal line is lowered and the signal 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, wiring arrangement and
Corrections etc. can be easily made.

〔Example〕

Embodiments of the present invention will be described based on FIGS. 1 to 5.

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 copper foil pattern layer 2 formed on the surface of the prepreg 1 after the board is completed.
This is an insulating paint applied on top. 6 is a planar conductive film created by applying a conductive paste on the insulating paint 5 and subjecting it to heat treatment.

The conductive film 6 is on the prepreg l and the copper foil pattern 1!
It may be provided on 2 with an insulating paint interposed therebetween. Further, 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 Z of the strip line.

is expressed by equation (1).

Here, Er is the effective permittivity of the prepreg 1, 2W is the conductor width when the signal line, etc. is considered as a strip line, T is the conductor thickness when the signal line, etc. is considered as a strip line, and H is the prepreg of the unbalanced strip line. The thickness is 1.

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. The characteristic impedance can be reduced by arranging the ground line 3 and further covering it with the conductive film 6. the result,
The induced voltage is reduced, and electromagnetic interference between signals can be prevented.

As mentioned above, since the surface of the prepreg 1 is covered with the conductive film 6 such as the power line and the ground line, this surface plays the role of electrostatic shielding, and has the effect of shielding against external noise and noise emitted from inside. Improved.

Further, since the conductive film 6 is applied externally, the thickness (electrical resistance) etc. of the conductive film 6 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 multiple layers of copper foil patterns N2 such as signal lines on the inner layer of the prepreg 1, A surface pattern copper foil N3 for the power supply line or ground line is arranged on the surface, and after the board is completed, a conductive film 6 for the power supply line or the ground line is arranged.
It is covered with 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 contrast to the first embodiment, a conductive film made of an insulating paint 5 and a conductive paste is formed to cover the parts (devices) 7 after installation is completed. 6, which can reduce the effects of external noise on the components.

〔Effect of the invention〕

As explained above, according to the printed wiring board of the present invention, after the printed wiring board is completed, an insulating film is formed on the outer layer of the printed wiring board using an insulating paint, and then a conductive paste is applied in a planar manner on the insulating film. By forming a shielding layer through heat treatment, interference between signal lines on the printed wiring board and external electrostatic induction and electromagnetic induction noise can be significantly reduced, and wiring can be easily arranged and modified. was completed.

[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 of an example of a conventional printed wiring board. Explanation of symbols■−・−1−−−・−Prepreg (substrate) 2−・−・−
・-Circuit pattern layer including signal lines 2°-1111・・Circuit pattern layer 3 including signal lines・−−−−−・−Plane pattern layer 4 of power supply line or ground line−−−−−・−・−Solder resist 5・−・−−−−−1−−Insulating paint 6−・・−−1−−−Conductive film

Claims (1)

[Claims] (1) After the printed wiring board is completed, an insulating film is formed on the outer layer of the printed wiring board using an insulating paint, a conductive paste is applied in a planar manner on the insulating film, and a shielding layer is formed by heat treatment. printed wiring board.