JPH09181480A - Method for forming coaxial wiring pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-density circuit and conductor, by using a circuital with a minute width in a coaxial wiring pattern. SOLUTION: A groove 3 is formed on a board 1 using a photosensitive resin 4, and a first conductor 5 is formed thereon. After an epoxy resin 6 is applied, a second conductor is formed thereon. A grinding step is carried out, the second conductor 7 and the epoxy resin 6 are removed to form a circuit 8 on a bottom of the groove 3. In addition, a second photosensitive resin 9 is applied, and a third conductor 10 is formed to obtain a coaxial wiring pattern.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a method for forming a coaxial wiring pattern, and more particularly to a method for forming a coaxial pattern suitable for high-frequency signal transmission.

[0002]

2. Description of the Related Art As electronic equipment has been mounted at higher density and the signal speed of electronic equipment has been increased, it is important to take measures against noise in signal transmission. As one of measures against noise, a coaxial circuit is formed on a multilayer printed wiring board.

As a conventional technique of forming a coaxial circuit pattern, a method of forming a coaxial circuit pattern on a thick film multilayer printing plate is disclosed in Japanese Patent Application Laid-Open No. 267586. In this method, a lower conductor circuit is formed on the surface of a base substrate such as alumina ceramics by a thick film printing method or the like, and then a photosensitive insulating film is formed thereon. After drying this insulating film,
Via holes are formed in the insulating film by photolithography, and the via holes are filled with a conductor paste to form side conductors and signal wiring patterns on the insulating film. Thereafter, sintering is performed, and in the same process, an insulating film is formed, a via hole is formed, and a conductive paste is filled in the via hole to form a side conductor. Then, an upper conductor circuit is formed and a coaxial wiring pattern is formed.

[0004]

However, the above-mentioned conventional method of forming a coaxial wiring pattern has the following drawbacks.

In the method disclosed in Japanese Patent Laid-Open No. 4-267586, the sense of a circuit formed by a thick film printing method and a via hole formed by a photolithography technique is set to about 100 μm in consideration of relative displacement. I was designing. This is because a positional shift occurs when aligning the film of the via hole with an already formed circuit, and the cause of the positional shift is a film alignment error, a dimensional change of the substrate, a dimensional change of the film, and the like.

As described above, when the distance between the circuit and the via hole is designed to be 100 μm, the circuit pitch is 500 μm.
m was the limit.

An object of the present invention is to provide a method of forming a coaxial wiring pattern having a high-density circuit and a conductor which can be designed to have a small space between the circuit and the conductor without the necessity of alignment between the circuit and the conductor. is there.

[0008]

A method of forming a coaxial wiring pattern according to the present invention comprises a step of applying a photosensitive resin to a substrate on which a ground layer is formed and forming a groove in the photosensitive resin, and the step of forming the groove and the groove. A step of forming a first conductor layer on the surface of the photosensitive resin, a step of applying an epoxy resin to the surface of the first conductor and forming a second conductor on the surface of the epoxy resin, and mechanical polishing Removing the epoxy resin and the second conductor to expose the first conductor, forming a circuit at the bottom of the groove, and forming a second photosensitive resin on the circuit. The method is characterized by including the step of forming a third conductor on the surface of the second photosensitive resin and the first conductor.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings.

FIGS. 1A to 1H are sectional views showing the order of steps for explaining an example of a method of forming a coaxial wiring pattern according to an embodiment of the present invention. In an example of the method of manufacturing the coaxial wiring pattern according to the embodiment of the present invention, first, the substrate 1 is manufactured as shown in FIG. At this time, as the substrate 1, a printed wiring board having a ground layer 2 formed by etching a 1.2 mm-thick glass epoxy plate having a 18 μm-thick copper foil laminated on both sides by a subtraction method was used. Next, a photosensitive resin having a thickness of about 100 μm is applied to the substrate 1. As the photosensitive resin, a mixture of a photosensitive epoxy resin obtained by introducing a photosensitive group into an epoxy resin as a main material, a curing agent and a solvent for adjusting the viscosity was used. As a coating method, there are a screen printing method, a spray method, a curtain coating method, a roll coating method, a dipping method and the like. In this embodiment, the curtain coating method was used. Then, after performing leveling for 15 minutes, it is dried by touching at 80 ° C. for 1 hour. Thereafter, the mask film is overlaid and exposed to 4 J / cm ^{2 using} a metal halide lamp. At this time, a masking pattern having a width of 200 μm is formed on the mask film. Next, the unexposed portion is dissolved and removed with an organic solvent containing gamma-butyl lactan. Thereafter, the photosensitive resin 4 is cured by heating at 135 ° C. for 2 hours, and the depth is about 100 μm and the width is about 2 as shown in FIG.
A groove 3 of 00 μm is formed. Next, the surface of the photosensitive resin 4 to be buffed is flattened. At this time Buffalo is 4
No. 00, the rotation speed is 500 to 3000 rpm, and the direction of the substrate 1 with respect to the buff roll is 90 ° at least twice.
By changing and polishing, a flat surface having irregularities of 5 μm or less was obtained, and the thickness of the photosensitive resin 4 was about 80 μm.

Next, the substrate 1 is treated with a permanganic acid solution to roughen the surface of the photosensitive resin 4, and then subjected to a catalytic treatment, electroless copper plating, and electrolytic copper plating to obtain a structure shown in FIG. As described above, the first conductor 5 having a thickness of about 20 μm is formed on the surface of the photosensitive resin 4.
Was formed. Next, as shown in FIG. 1D, the surface of the first conductor 5 was blackened, and then an epoxy resin 6 was applied to about 40 μm. Here, the same material as the photosensitive resin 4 was used for the epoxy resin 6. However, any resin that is roughened by permanganic acid does not need to have photosensitivity, and a normal thermosetting epoxy resin can be used. . Next, after the epoxy resin 6 is cured, the surface of the epoxy resin 6 is roughened by performing a chemical treatment such as a permanganic acid treatment, and the second conductor 7 is formed to a thickness of 20 μm on the surface including the groove 3 by panel plating. Formed. Next, mechanical polishing is performed as shown in FIG. 1E to remove 60 μm, which is the thickness of the second conductor 7 and the epoxy resin 6 adhered to the surface of the substrate 1, thereby exposing the first conductor 5. Let it. In this embodiment, belt sander polishing is used for the mechanical polishing. Belt sander polishing is performed at least twice with a sander belt of 600 to 800.
This was carried out by changing and polishing. After the polishing, the second conductor 7 at the bottom of the groove 3 is not removed and is formed according to the shape of the groove 3 to form a circuit 8. Next, as shown in FIG. 1 (f), the surfaces of the first conductor 5 and the circuit 8 are roughened by performing a blackening process, and then a second photosensitive resin 9 is applied to a thickness of about 100 μm. The second photosensitive resin 9 was made of the same material as the photosensitive resin 4, and the coating method was the curtain coating method. Next, after performing leveling for 15 minutes, touch drying is performed at 80 ° C. for 1 hour. Thereafter, the mask film is overlaid and exposed to 4 J / cm ^{2 using} a metal halide lamp. At this time, exposure is performed at 4 J / cm ^{2 using} a metal halide lamp with the mask film superimposed. At this time, a light-transmitting portion having a width of 300 μm was formed at the position of the groove 3 in the mask film.
Next, the unexposed portion is dissolved and removed with an organic solvent containing gamma-butyl lactan. Thereafter, it is cured by heating at 135 ° C. for 2 hours, and a 300 μm width is placed on the circuit 8 as shown in FIG.
m of the second photosensitive resin 9 is formed. Next, the surface of the second photosensitive resin 9 is flattened by buffing, and then treated with a permanganic acid solution to roughen the surface of the second photosensitive resin 9. Electrolytic copper plating and electrolytic copper plating were performed to form a third conductor 10 having a thickness of about 20 μm on the surface of the second photosensitive resin 9 as shown in FIG. A coaxial pattern having a width of about 300 μm was formed by covering the periphery of a circuit having a width of about 80 μm and a thickness of about 20 μm with a first conductor 5 and a third conductor 10 having a thickness of 20 μm.

In order to connect a coaxial circuit to another layer circuit, via holes and through holes are used. FIG. 2A is a schematic diagram of a substrate when the coaxial wiring portion is connected to another layer circuit by a via hole. In this case, a circular mask pattern is formed on a mask film for exposing the second photosensitive resin. Exposure and development are performed with this mask film, and via holes 12 are formed in unexposed portions corresponding to the mask pattern. After that, through the step of forming the conductor, as shown in FIG. 2A, it is possible to connect to the upper layer through the via hole 12.

FIG. 2B is a schematic diagram of a substrate when the coaxial wiring portion is connected to another layer circuit through a through hole. After the second photosensitive resin is formed, the through hole 13 is formed by drilling. Thereafter, a conductor is attached to the inner wall of the hole through a conductor forming step to form a through-hole 13, thereby making it possible to connect to another layer via the through-hole as shown in FIG. 2B. A coaxial wiring pattern was formed as described above to produce a multilayer printed wiring board.

[0014]

According to the method of forming a coaxial wiring pattern of the present invention, as shown in FIG. 3, the shape of the coaxial circuit is determined by the width W1 of the groove and the thickness T of the resin applied in the groove, and is theoretically the width of the circuit. W2 is W1-2 × T, and the interval W3 between the circuit and the side conductor is T
Becomes equal to Therefore, since the distance between the circuit and the side conductor is formed to be equal, the alignment between the coaxial circuit and the side conductor, which is required in the conventional manufacturing method, becomes unnecessary. For this reason, in the conventional method of forming a coaxial wiring pattern, the circuit width of the coaxial circuit is limited to 500 μm, whereas in the present invention, the circuit width of the coaxial circuit can be formed as thin as 300 μm.

[Brief description of the drawings]

FIGS. 1A to 1H are cross-sectional views shown in the order of steps for explaining an example of a method of forming a coaxial wiring pattern according to an embodiment of the present invention.

2 (a) and 2 (b) are schematic diagrams showing a via-hole connection portion and a through-hole connection portion of the coaxial wiring pattern shown in FIG.

FIG. 3 is a sectional view showing dimensions of each part of the coaxial wiring pattern according to FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Ground layer 3 Groove 4 Photosensitive resin 5 First conductor 6 Epoxy resin 7 Second conductor 8 Circuit 9 Second photosensitive resin 10 Third conductor 11 Coaxial wiring section 12 Via hole 13 Through hole

Claims (1)

[Claims] 1. A step of applying a photosensitive resin to a substrate having a ground layer formed thereon to form a groove in the photosensitive resin, and a step of forming a first conductor on the groove and the surface of the photosensitive resin. ,
A step of applying an epoxy resin to the surface of the first conductor to form a second conductor on the surface of the epoxy resin; and removing the epoxy resin and the second conductor by mechanical polishing to remove the first conductor. A step of forming a circuit on the bottom of the groove while exposing, a step of forming a second photosensitive resin on the circuit, and a step of forming a third photosensitive resin on the surface of the second photosensitive resin and the first conductor. A method of forming a coaxial wiring pattern, comprising the step of forming a conductor.