JPH01136395A - Manufacture of flexible wiring board integral with reinforcing plate - Google Patents

Abstract

PURPOSE:To form the title wiring board having an arbitrary thickness and shape easily, and to improve a function and reduce cost by sticking an irradiated crosslinking type engineering plastic film at a position required for reinforcing a flexible base board and conducting injection molding onto the film. CONSTITUTION:A conductor circuit 3 is formed onto one surface of a flexible base board 2, and an insulating layer 4 is executed and shaped onto the circuit 3 by a cover-lay material with the exception of a terminal section and a land section. An irradiated crosslinking type engineering plastic film 5 previously coated with adhesives is stuck onto the rear of the flexible base board 2. The formation of the insulating layer 4 and the sticking of the film 5 may be conducted separately, and it is preferable that a cover-lay film is pasted while being contact-bonded by a hot press on processes. Irradiated crosslinking type engineering plastics melted at a high temperature are injection molded onto the engineering plastic film 5, and a reinforcing section 6 is shaped and unified while being thermally welded. Electron rays are applied and plastics are crosslinked for improve solder heat resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a reinforcing plate-integrated flexible wiring board in which a reinforcing portion is formed and integrated on a flexible wiring board.

(Prior art and problems to be solved) With the development of the electronics industry in recent years, the mounting method of industrial and consumer equipment has been simplified, and printed wiring boards are required to be smaller, more reliable, and higher performance. is desired.

In particular, flexible wiring boards based on plastic films that are lightweight and can be mounted three-dimensionally are attracting attention.

However, since flexible wiring boards are wiring boards with a thickness of 50 to 200 μm, they are too flexible to automatically mount components, making it difficult to mount them, and also making it difficult to attach them to equipment. A reinforcing plate of 5 to 2.0 ■■ is partially pasted.

Figure 3 is a cross-sectional view of an example of a conventional reinforced flexible wiring board, in which a conductor circuit (3) is formed on one side of a base substrate (2), and an insulating layer (4) is formed on it using a coverlay material. A reinforcing plate (6') with pre-drilled holes is attached to the flexible wiring board (1) with the adhesive layer (5') interposed therebetween, and the adhesive 1! It was formed by curing l(5').

The flexible base board (2) is often made of a heat-resistant polyimide film, and the reinforcing board (B') is a paper phenol board or glass/epoxy laminate, which may sometimes deform when soldered. A material that does not shrink is used, and the adhesive (5') is an adhesive made of epoxy, urethane, acrylic, phenol, triazine, or the like.

However, the adhesive was applied to the flexible wiring board (1) or the reinforcing board (8'), which was pasted together and then press-bonded at high temperature and pressure to form an integral body. Those reinforcement plates (
6') had to be pre-punched or NC-processed and bonded one by one to one product using an adhesive, and in some cases, as many as 4 to 5 pieces had to be bonded together. This not only requires a lot of effort and expense, but also causes performance problems such as air bubbles entering the adhesive and misalignment. In addition, in order to bond them in the specified positions, make alignment holes in the flexible wiring board (1) and reinforcing plate (8'), and use a pin jig to bond them together, or make sure that the temporarily bonded items do not shift. It took a lot of effort to set it in place and let the adhesive harden.

(Means for Solving the Problems) The present invention provides a method for manufacturing a reinforcing plate-integrated flexible wiring board that solves the above-mentioned problems, and has the following characteristics:
After forming the required conductor circuits on the flexible base board, an insulating layer with soldering heat resistance is applied except for the terminals and lands, and an irradiated cross-linked engineering plastic film is applied to the positions where reinforcement of the flexible base board is required. After that, irradiated cross-linked engineering plastics melted at high temperature are injection molded onto the film, the engineering plastics are heat-fused and integrated, and then electron beams are irradiated to cross-link them. There is a particular thing.

FIG. 1 is a sectional view of an example of a reinforcing plate-integrated flexible wiring board obtained by the manufacturing method of the present invention.

In the drawing, (1) is a flexible wiring board, which has a conductor circuit (3) formed on one side of a flexible base board (2), and is insulated with coverlay material on top of it with the exception of terminals and lands. (4).

The back surface of the flexible base substrate (2) may be irradiated and cross-linked with an adhesive coated in advance, but from the viewpoint of the process, it is preferable to bond the coverlay film simultaneously with a hot press.

Thereafter, irradiation cross-linked engineering plastics melted at high temperature is injection molded onto the engineering plastic film (5) and thermally welded to form the reinforcing portion (6).
form and integrate. Furthermore, in order to improve the soldering heat resistance, the engineering plastic is crosslinked by irradiation with an electron beam.

FIG. 2 is a back view of the flexible distribution board Ii shown in FIG. 1, and a reinforcing portion (6) made of engineering plastics having an arbitrary shape and thickness can be easily formed. In this way, wiring boards, which were conventionally flat, can be easily formed into any thickness and shape depending on the mounting method and location of the wiring board, and the shape and function of the parts. It is possible to improve functionality and reduce costs.

Such a flexible wiring board can be formed not only on one side of the base substrate but also as a double-sided wiring board, and the reinforcing portion can be formed not only on one side but also on both sides at the same time. Further, the number of reinforcing parts can be from 1 to 10, and can be arbitrarily selected according to the shape of the component to be mounted.

Conventionally, the method for integrating the flexible wiring board and the engineering plastics that form the reinforcing part has been to attach an adhesive film in a B-stage state to the flexible base board in advance, thereby making it possible to integrate the injected engineering plastics. It was thought that the material would be melted and hardened by heat to form a single piece. The curing speed has been determined by selecting an adhesive film depending on the injection temperature, or by integrating only by thermal fusion, and then performing after-curing by heating in a thermostatic oven or the like.

However, on the adhesive film in the B-stage state, 40
Engineering plastics at a high temperature of around 0℃
When injection molding was performed at a high pressure of around 1,000 kg/cJ, the adhesive film was washed away, resulting in uneven thickness near the gate and around the mold, entrapment of air bubbles, and uneven adhesive strength. Also, if you perform after-cure in a constant temperature bath,
Warpage of the reinforcing plate increased due to distortion during injection molding and distortion due to curing shrinkage of the resin.

The present invention was developed in view of the above, and solves the above problems by processing radiation-crosslinked engineering plastics similar to the material to be injection molded into a film in advance and pasting this onto the back side of a flexible substrate. did.

The irradiation cross-linked engineering plastics film is coated with the same adhesive as the coverlay film that protects the conductor circuits, and when applying the coverlay insulation layer, the film is punched into a predetermined shape and pressed together face-to-face. It is formed by These temperatures are around 400℃ and I 000℃.
It was confirmed that the film maintained its shape without being washed away or deformed even when injection molding was performed at a high pressure of around kg/cJ5.

Furthermore, the irradiation cross-linked engineering plastics to be injection molded as the reinforcing plate must be compatible with the film and melt at a temperature of around 400°C. Preferably, it is made of the same material as the film.

[J Crosslinked engineering plastics are those containing 1.0 to 20% by weight of one or more types of polyfunctional monomers such as triallyl isocyanate, trimethylolpropane, triallyl acrylate, etc., and are resistant to γ rays, β
Plastics are three-dimensionally cross-linked by irradiation with electron beams such as a few Mrads to several + Mrads, and they must be resistant to soldering heat and meet at least JISK720.
) is required to have a heat distortion temperature of 180°C or higher. Soldering heat resistance here refers to IC,
Electronic components such as resistors and capacitors can be soldered at 190 to 250℃ by hand, solder dip, solder reflow, etc., and the reinforced parts do not shrink or warp significantly. means.

In this way, integrally forming the flexible wiring board and the reinforcing part by injection molding not only has the advantage of automatically pasting together items that were previously pasted together, but also facilitates assembly into electronic devices. In some cases,
It is also possible to integrate it with the case of the equipment, which significantly improves productivity and functionality. Used as wiring material.

(Example) As a base substrate of a flexible wiring board, polyimide film, polyparabanic acid film, polyphenylene sulfide film, polyether film, etc., which are resistant to soldering heat, are used, and epoxy, phenol, acrylic, silicone, and imide films are used. Apply a type of adhesive such as a chloride-based adhesive, laminate electrolytic steel foil and pressure MtR foil, print an etching resist on the copper foil, or laminate a photosensitive film and form a conductor circuit by etching with iron chloride or chloride steel, etc. did.

After the circuit is formed, a coverlay is performed using a solder resist or a heat-resistant film so that the terminal portions and land portions where components are mounted are exposed, and an insulating layer is formed.

At this time, the solder resist is formed before attaching the engineering plastic film on the back side.
An insulating film made of polyimide, polyparabanic acid, or the like is punched out into a predetermined shape, positioned, and temporarily fixed.

After that, polyethylene terephthalate, polybutylene terephthalate, nylon 8, nylon 6-6, nylon 1
2. Polyfunctional monomers such as triallyl isocyanate, trimethylolpropane, triallyl acrylate, etc. are added to engineering plastics such as polyacetal, polyarylate, polycarbonate, styrene/acrylonitrile copolymer, acrylonitrile butadiene/styrene copolymer, etc. 1. Irradiation-crosslinked engineering plastics mixed with 0 to 20% by weight are extruded to a thickness of 10 to 50 μm to form a film cane. A thermosetting adhesive such as epoxy, acrylic, urethane, silicone, imide, etc. is applied to one side to a thickness of 5 to 20 μm, dried to a semi-cured form, and then fixed to the specified area of the flexible wiring board. Temporarily fix it in position.

Then, the engineering plastics film is attached at the same time as the coverlay insulating film is bonded by high-temperature, high-pressure press. Depending on the structure or shape of the flexible wiring board, the coverlay insulating film and the engineering plastics film may be attached through separate processes.

The flexible wiring board is then set in an injection mold. At this time, it is preferable that the engineering plastic film surface of the flexible wiring board faces perpendicularly to the gate to be injected.

The radiation-crosslinked engineering plastics to be injected are the same or equivalent to the resin of the film used as the lining for the reinforcing portion, and are melted by heat and crosslinked by electron beam irradiation. Such plastics are injected into molds at high temperatures of 250-400°C. At this time, it is necessary that the polyfunctional additives do not react with heat and do not thermally decompose.

If the polyfunctional monomer content is less than 1.0% by weight, it will be difficult to raise the heat distortion temperature to 180°C or higher, and soldering heat resistance will not be obtained, and if the content exceeds 20% by weight, the resin and
It is easy to separate, the molded product becomes non-uniform, and it becomes brittle after crosslinking, making it impractical.

In addition to polyfunctional materials, engineering plastics also use elastomers, homopolymers, and resin modifiers.
Those to which inorganic fillers, pigments, etc. are added can be used.

Irradiation-crosslinked engineering plastics are injection molded into a mold at a temperature that is at least slightly lower than the heat-resistant temperature of the flexible base substrate. The pressure must be such that it does not cause deformation of the conductor circuit. Also, engineering plastics can be molded into any shape, but the shape should be designed so that stress does not remain on the wiring board, and molding distortion will remain on the reinforcing board, causing the board to warp or shrink due to the temperature during soldering. It is necessary to avoid this.

The irradiation cross-linked engineering plastics injection molded into the reinforcing part of the base substrate has a temperature of 2 Nrad after being cooled to room temperature.
Crosslinking is carried out by irradiation with an electron beam of ~40 Mrad.

The irradiation amount is determined by selecting the optimum degree of crosslinking depending on the amount of polyfunctional monomer added and the type of engineering plastics. Further, the electron beam irradiation voltage and time are determined depending on the thickness of the reinforcing plate.

The solder heat resistance properties of irradiation crosslinked engineering plastics are determined by the crosslinked gel fraction and heat distortion temperature.

Crosslinking is carried out continuously using an electron beam irradiation machine, and the pre-applied engineering plastic film and the injection molded engineering plastic are chemically integrated, thereby providing the advantages of the present invention.

(Effects of the Invention) As described above, according to the method of manufacturing a reinforcing plate-integrated flexible wiring board of the present invention, the reinforcing portion is integrally formed on the flexible wiring board by injection molding. In addition to significantly reducing the amount of effort and expense,
The performance of the obtained flexible wiring board is also significantly improved.

Therefore, it will be extremely effective in electronic equipment that will be required to be lighter in weight, smaller in size, and more functional in the future.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an example of a reinforcing plate-integrated flexible wiring board obtained by the manufacturing method of the present invention, and FIG. 2 is a back view of the flexible wiring board of FIG. 1. FIG. 3 is a sectional view of an example of a conventional reinforcing plate-integrated flexible wiring board. 1...Flexible wiring board, 2...Base group [,3
... Conductor circuit, 4... Insulating metal, 5... Irradiation cross-linked engineering plastic film, 6... Reinforcement part.

Claims (2)

[Claims] (1) After forming the required conductor circuit on the flexible base board, apply an insulating layer that is resistant to soldering heat, except for terminals and lands, and apply irradiation cross-linked engineering plastics to the positions where reinforcement of the flexible base board is required. Each film is pasted, and then irradiated cross-linked engineering plastics melted at high temperature are injection-molded onto the films, the engineering plastics are thermally welded and integrated, and then electron beams are irradiated to cross-link them. A method for manufacturing a reinforcing plate-integrated flexible wiring board, characterized by: (2) Irradiation-crosslinked engineering plastics include triallyl isocyanurate, trimethylolpropane,
Polyfunctional monomers such as triallyl acrylate from 1.0 to
2. The method for manufacturing a reinforcing plate-integrated flexible wiring board according to claim 1, wherein the reinforcing plate-integrated flexible wiring board is an engineering plastic containing 20% by weight.