JPS6111184A - Manufacturing method of flexible printed wiring board - 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 [Technical Field of the Invention] The present invention particularly relates to a method for manufacturing a flexible printed wiring board with excellent flexibility.

[Background of the invention]

Flexible printed wiring boards are smaller and lighter than regular electric wire wiring or rigid water boards, and have simpler wiring layouts.
Since it simplifies wiring work and improves circuit characteristics and reliability, it has recently come to be widely used for internal wiring of electronic office equipment, telephones, cameras, and automobile wiring panels.

Flexible printed wiring boards are made by pasting copper foil on one or both sides of a flexible insulating base film with an adhesive, and then reproducing the wiring diagram based on the circuit design as a copper foil electric circuit by etching or other methods. It is manufactured by providing a film overlay or overcoat at necessary locations on the film. Film overlay is made by pasting together an overlay film such as a polyester film or polyimide film and a base film on which a circuit is formed using an adhesive such as polyimide, epoxy, polyester, or phenol/butyranyl.
It is then formed by curing the adhesive. In addition, as a method of providing an overcoat, a method of applying a thermosetting paint made of a liquid resin such as an epoxy type or a urethane type and curing it by heating has been adopted.

Recently, it has become common practice to apply a paint made of a radiation-curable resin and continuously form an overcoat by curing the coating with radiation. According to this method, the coating film can be cured quickly, so that the manufacturing process can be rationalized. Flexible printed wiring boards are often dipped in solder during the parts mounting process, so the overcoat must have heat resistance and flexibility to withstand solder immersion, but conventional technology uses radiation-curable resin. When an overcoat is formed using the above method, it is extremely difficult to achieve a balance between solder resistance and flexibility. That is,
A composition that can withstand being immersed in solder will only yield a hard, brittle product that will break easily when folded, and a composition that will not break when bent will foam or shatter when immersed in a solder bath. All I could get was a combination that made me tingle. In the process of continuing various studies on radiation-curable overcoats, the present inventors have learned that it is extremely difficult to satisfy both solder resistance and flexibility at the same time.

In order to solve the above-mentioned problems, the present inventors have continued to work diligently to create a method for forming an overcoat that is particularly flexible and has satisfactory solder resistance. I proceeded with my research.

As a result, among the many radiation-reactive compounds,
In particular, a coating composition containing a radiation-reactive polybutadiene resin as a paint resin paste and a reactive diluent, a non-reactive diluent, and a phosphoric acid ester compound having an acryloyl group or a methacryloyl group as components. We have discovered that if used, it is possible to form an overcoat that has both excellent flexibility that will not be damaged even when bent 180 degrees and heat resistance that can withstand soldering. In particular, according to conventional general thinking, it was believed that the use of non-reactive diluents as components of paint compositions would significantly reduce the properties of the paint film, such as hardenability and solder resistance. First, it has been found that the coating composition according to the present invention exhibits an unexpected behavior in that the addition of a non-reactive diluent improves the flexibility and solder resistance of the coating film.

[Summary of the invention]

The present invention was made based on the above findings, and the gist of the present invention is to apply radiation-reactive polybutadiene resin, reactive diluent, and A method for producing a flexible printed wiring board, which comprises overcoating a coating composition containing a reactive diluent and an acryloyl group or a methacryloyl group as components, and then curing the overcoat by irradiating with radiation.

[Detailed description of the invention]

The radiation-reactive polybutadiene resin referred to in the present invention has a functional group such as an acryloyl group or a methacryloyl group at the end of the molecule or in the main chain, and has an average molecular weight of 1,000 to 1,000.
4000 polybutadiene prepolymer.

Further, the reactive diluent referred to in the present invention is a low-viscosity compound having one or more functional groups such as acryloyl group or methacryloyl group in the molecule.

Furthermore, the non-reactive diluent referred to in the present invention is a compound that has no reactivity to radiation. Examples of non-reactive diluents include ester plasticizers such as di(2-ethylhexyl) phthalate and di(2-ethylhexyl) heptabacate.

Among the polybutadiene resin, the reactive diluent, and the non-reactive diluent, the total amount of the reactive diluent and the non-reactive diluent accounts for 25 to 55% by weight.

If the blending amount is less than 25%, the printability of the paint will be poor;
Moreover, if it exceeds 55%, the tolerance will decrease.

In addition, the proportion of non-reactive diluent among polybutadiene resin, reactive diluent, and non-reactive diluent is 10 to 30.
%. If the amount of the non-reactive diluent is less than 10% or more than 30%, the heat resistance of the coating film will decrease.

The phosphoric acid ester compound having an acryloyl group or a methacryloyl group referred to in the present invention is an ester compound of a compound having an acryloyl group or a methacryloyl group and phosphoric acid, such as 2-methacryloyloxyethyl phosphate or 2-acryloyl group. There are compounds such as roxyethyl phosphate.

The amount of the phosphoric acid ester compound having an acryloyl group or a methacryloyl group added is 0.8 parts by weight or more based on 100 parts by weight of the total amount of the polybutadiene resin, reactive diluent, and non-reactive diluent. If the amount added is less than 0.8 parts by weight, the solder resistance of the coating film will be poor. Furthermore, if the amount added is too large, the solder resistance tends to decrease.

Particularly preferably, the amount is in the range of 0.5 to 3 parts by weight.

The coating composition according to the present invention may optionally contain sensitizers, colorants such as pigments and dyes, surface treatment agents such as alkyl titanates and silane coupling agents, viscosity modifiers such as ultrafine silica, silicone compounds, etc. leveling agent, organic and
Add auxiliary materials such as inorganic fillers.

The coating composition according to the invention is prepared by kneading with a conventional stirrer or roll.

Methods for applying this paint to an insulating base film having a circuit include brush coating, roller coating, flow coating, and a method called a silk screen method.

In the present invention, the coating composition is applied to a substrate and then cured by irradiation with radiation. As the radiation, electron beams or ultraviolet rays can be used.

The irradiation dose of the electron beam may be 0.5 to 30 Megaland.

Compounds such as compounds and azo compounds are used. Among these compounds, those using sperones, tipxanthones, and phenylketone compounds had better coating film properties. Irradiation with ultraviolet light is preferably carried out for about 5 to 60 seconds using one to several ultraviolet lamps of 1 to 10 KW.

Example 1 Polybutadiene Po1y bd (radiation-reactive polybutadiene resin, trade name manufactured by Idemitsu Petrochemical Co., Ltd.) Acrylic derivative of dipentaerythritol...55 parts by weight (reactive diluent, product made by Nippon Kagaku Co., Ltd.)...30 parts by weight Parts: Di(2-ethylhexyl) phthalate... 15 parts by weight (non-reactive diluent) 2-Acryloyloxyethyl phosphate... 1 part by weight Phthalocysnin Green (coloring agent) 1 part by weight Erosil (ultrafine silica) ) 5 parts by weight of a silicone leveling agent 1 part by weight was kneaded using three rolls to prepare a coating composition.

This coating composition was applied to the surface of a polyimide film having a circuit made of copper foil using a silk screen method.
It was applied to a thickness of m. This was irradiated with an electron beam of 10 Megaland to harden it, thereby producing a flexible printed wiring board. The thus obtained printed wiring board was bent 1,800 degrees with the coating surface facing either outside or inside. As a result, there was no damage to the coating and it was found to have sufficient flexibility and adhesion. Admitted. Furthermore, this printed wiring board is
A solder resistance test was conducted by immersing the sample in a solder tank at ℃ for 10 seconds. As a result, no line abnormalities were observed in the paint film even after immersion in solder.

Example 2 In Example 1, 5 parts by weight of benzyl dimethyl ketal was added as a sensitizer to the coating composition, and the coating was carried out in the same manner as in Example 1, but ultraviolet light was applied using a 2KW ultraviolet lamp instead of electron beam. It was cured by irradiation for 80 seconds. As a result of examining the properties, it was confirmed that the properties were comparable to those of Example 1.

Example 8 A printed wiring board was prepared under the same conditions as in Example 1 except that the proportions of polybutadiene, reactive diluent, and non-reactive diluent were changed. The characteristics were as shown in Table 1.

Table 1゜Comparative Example 1゜In Example 1, printed wiring boards were prepared under the same conditions as in Example 1, except that the blending amounts of polybutadiene, reactive species diluent, and non-reactive diluent were changed. Created. The characteristics were as shown in Table 2.

Comparative Example 2 A printed wiring board was prepared under the same conditions as in Example 1 except that 2-acryloyloxyethyl phosphate was not added. However, it was not possible to satisfy solder resistance.

According to the present invention, it has become possible to easily form a flexible printed wiring board overcoat with extremely excellent solder resistance and bendability using a radiation-curable coating material.

Claims (1)

[Claims] (1) A radiation-reactive polybutadiene resin, a reactive diluent, a non-reactive diluent, and a phosphoric acid ester compound having an acryloyl group or a methacryloyl group are added to the surface of an insulating base film having a circuit formed of copper foil. 1. A method for producing a flexible printed wiring board, which comprises overcoating a coating composition containing as a component, and then curing the overcoat by irradiating with radiation.