JPH01183889A - Printed wiring board manufacturing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a printed wiring board having an electromagnetic shielding function.

(Prior Art) In general, a printed wiring board is a board that reproduces an electrical wiring pattern that connects circuit components based on a circuit design as an electrical conductor on an insulating substrate. With computerization, it is being expanded to all industrial fields.

Conventionally, this printed wiring board has been manufactured by using a steel-clad laminate for printing, forming a resist pattern on it, performing an etching process, and then performing the above process to remove any distortion or turns as desired. The printed wiring board has an electrical circuit.

However, in this method, the manufacturing process of the printed wiring board and the process of forming the electric circuit are performed as separate processes, and after the electric circuit is formed, large openings, chamfering, punching, or punching are required to mount the circuit components. This required complicated mechanical processing such as external processing.

On the other hand, thermoplastic resins with excellent heat resistance and dielectric properties have been developed to replace conventional printed wiring boards, and there is a method of manufacturing printed wiring boards by injection molding the resin. According to this method, the printed wiring board can be formed into a desired shape in advance, so complicated mechanical processing such as 6-cutting, chamfering 9, or punching after forming the electric circuit is almost unnecessary. Even complex shapes can be easily and inexpensively manufactured.

However, even with the above method, a step of forming an electric circuit is required after the printed wiring board is molded.

However, since it is impossible to perform copper cladding on this electric circuit, it is not possible to clad it with steel, and the process of forming the electric circuit using a full additive plating method, that is, the process of forming an electric circuit using an ultraviolet curing type on the substrate. A catalyst layer is applied, and then ultraviolet rays are irradiated through a mask to leave only the wiring portions of the catalyst layer with four turns, and then electroless plating is performed to form an electric circuit. Therefore, the process is complicated, and
In particular, it is technically extremely difficult to form an electric circuit on a substrate having a three-dimensional shape.

As an improvement method for matatare, electrical circuits and patterns are formed on a removable base sheet, and the transfer sheet is placed in an injection molding mold, and then thermoplastic resin is injected into the entire interior to print wiring. There is a method in which a printed wiring board is obtained by simultaneously forming a substrate and forming the above-mentioned electric circuit/stone on the surface of the substrate, and then peeling off the base sheet.

However, the printed wiring board obtained by this method does not have an electromagnetic wave shielding function, and even if a process such as applying a conductive paint to the board is performed, the electromagnetic noise emitted by the board is sufficiently shielded. It was impossible.

(Problems to be Solved by the Invention) As a result of intensive research in view of the current situation, the present invention was developed by molding a printed wiring board having an electromagnetic wave shielding function by injection molding, and simultaneously forming an electric circuit on the surface of the board. A method for manufacturing a printed wiring board with excellent 'flLa wave shielding function has been developed.

(Means for Solving the Problems) The method of the present invention involves installing a transfer sheet in which an electric circuit/mother turn is formed on the surface of a removable base sheet in a metal molding machine, and then After molding a printed wiring board by injecting a thermoplastic resin mixture into which a conductive filler is mixed into each turn surface via an adhesive, and at the same time forming the four turns of the electric circuit on the board surface, It is characterized by peeling off the one-piece sheet.

A feature of the method of the invention is the use of a thermoplastic resin admixture in which a conductive filler is incorporated into the thermoplastic resin to obtain a printed circuit board.

As the conductive filler, for example, stainless steel fibers, glass fibers coated with metals such as nickel, Kagen fibers coated with metals such as nickel, copper or copper alloy fibers, iron or iron alloy fibers, etc. are used.

In addition, the thermoplastic resin must be able to withstand high temperatures of 170 to 180°C in order to solder and process printed wiring boards prepared by the method of the present invention, such as polysulfone having heat resistance and dielectric properties.

/riethersulfone, polyetherimide, precargonate, polyethylene terephthalate, etc. are used.

By mixing a conductive filler into the thermoplastic resin, the resin becomes mesh-like and the probability of electricity flow is increased.

Therefore, the conductive filler preferably has a large aspect ratio and preferably has a long length and a rope diameter. For example, it is desirable to have a length of 15 to 20 Am and a thickness of 3 to 6 μm.

Further, although the blending ratio of the thermoplastic resin and the conductive filler is not particularly limited, the conductive filler is usually mixed in an amount of 10 to 20 vt%. The reason for this is that if it is less than 10wt%, it is difficult to pass through the printed wiring board that has an electromagnetic wave shielding function, and if it exceeds 20w*chi, the KFi
It reduces the mechanical properties of thermoplastic resins such as tensile strength and inhibits the flow of resin during injection molding.

Next, the transfer sheet will be explained.

The transfer sheet used in the present invention is formed by forming an electric circuit mother turn on a removable base sheet. As the base sheet for this transfer sheet, heat-resistant glass films such as polyester films, polyethylene films, Although polypropylene film, nylon film, etc. are used, polyester film is particularly preferred because of its excellent heat resistance, moldability, and one-dimensional stability.

A desired electric circuit is formed on this base sheet after a peeling process is performed according to an appropriate procedure.

The electric circuit pattern is prepared using a conductive paste of silver, copper, carmen, etc., and subjected to equal pressure printing using a screen printing method or a Clavia printing method, and then an insulating layer is printed thereon to obtain a transfer sheet.

After placing this transfer sheet at a predetermined position in an injection mold and closing the mold, the thermoplastic resin mixture is melted and injected into the mold, and the printed wiring board is brought into close contact with the electric circuit surface. get it.

Next, the substrate is removed from the mold and the base seal is peeled off from the surface of the substrate, thereby obtaining the printed wiring board of the present invention in which the electric circuit is closely attached to the surface of the substrate.

(Example) A conductive paste mainly composed of silver was applied onto a 25 μm thick polyethylene terephthalate film that had been subjected to mold release treatment using melamine resin, a desired electric circuit was screen printed, and an adhesive was applied on top of the conductive paste. 3μm by gravure printing method
After applying a thick overcoat and obtaining a transfer sheet, this transfer sheet was placed in a predetermined position in an injection mold for printing printed wiring boards, and the metal was opened. A polysulfone mixture mixed with 10 wt % of stainless steel fibers (length: 3 to 6 cm, diameter: 8 μm) was heated and melted and injection molded to obtain a printed wiring board.

Next, the printed wiring board was taken out from the metal interior, and the base sheet for the transfer sheet was peeled off, thereby obtaining a printed wiring board of the present invention on which a desired electric circuit could be printed on the armpit plate surface.

In addition, in order to compare with the printed wiring board of the present invention, the above-mentioned ? A printed wiring board was obtained in the same manner as in Example except that only polysulfone was used instead of the risulfone mixture.

In order to test the electromagnetic shielding function of the thus obtained printed wiring board of the present invention and the printed wiring board of the comparative example, the leaking electric field strength was measured. The results are shown in Table 1.

Table 1 (Effects) As detailed above, according to the method of manufacturing a printed wiring board of the present invention, the printed wiring board can be molded, and secondary machining processes such as drilling, chamfering, punching, etc. after molding can be performed. Since the process and the desired electric circuit formation process can be carried out at the same time, the workability is extremely simple and it is extremely useful industrially, such as producing a printed wiring board having an excellent electromagnetic shielding function.

Claims (1)

[Claims] A transfer sheet with an electrical circuit pattern formed on the surface of a releasable base sheet is placed in an injection mold, and then a conductive filler is mixed into the electrical circuit pattern surface of the transfer sheet via an adhesive using heat. A method for manufacturing a printed wiring board, which comprises injecting a plastic resin mixture to mold a wiring board, simultaneously transferring and forming the electric circuit pattern on the surface of the board, and then peeling off the base sheet.