JPH0143475B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a printed wiring board, particularly a printed wiring board in which a conductive composition is printed on the surface of an insulating substrate to form a circuit base, and metal electroplating is performed on the circuit base to form a desired circuit. The present invention relates to a manufacturing method. Printed wiring boards have recently become widely used in various electronic and electrical devices because they can make wiring layouts smaller, lighter, simpler, and improve circuit characteristics and reliability. . Conventionally, as a method for forming conductive circuits on printed wiring boards, it has been widely used to partially etch the copper layer of a copper composite board consisting of copper and an insulating substrate to form the required circuit. Ta. but,
This method involves many steps, including the step of bonding the copper foil and the insulating substrate together, the step of applying etching resist to cover the required wiring pattern, the step of etching, and the step of removing the etching resist, making the production process complicated and cumbersome. Furthermore, there were various problems such as the need for a special process to treat the etching waste liquid. Recently, with the aim of simplifying the circuit formation process and reducing formation costs, a method has been developed in which the required circuit is directly formed by electroplating metal on the surface of the insulating substrate, without using the method of etching the copper composite substrate. is being attempted. This method applies plating only to the parts necessary for the circuit, so compared to the conventional method,
It is possible to save resources and energy. In this method, in order to perform metal electroplating on the required circuits, it is necessary to form a conductive circuit base at the required positions on the insulating substrate so that metal electroplating can be performed. As a method of forming a conductive circuit base, in the conventionally disclosed technology, chemical plating is applied to the entire surface of an insulating substrate, and a plating resist is provided in areas where metal electroplating is unnecessary. There is. However, since this method uses a pretreatment liquid, an electroless plating liquid, etc., handling and waste liquid treatment are troublesome, and the productivity is not so good, so a simple method for forming the circuit base has been desired. As another method for forming the circuit base,
A method of printing a conductive composition on the surface of an insulating substrate has also been attempted. In this method, the necessary circuit base can be formed by simply printing and solidifying the required circuit base, so the process is simpler and it is effective as a circuit base forming method. However, this method also has the following problems. That is,
In this method, a conductive composition prepared by adding conductive particles such as silver powder to a resin serving as a base material is used as a conductive composition, printed in a desired wiring pattern, and dried or hardened at room temperature or under heat. However, in order to obtain a composition with the conductivity necessary for electroplating, it was necessary to add about 400 to 500 parts by weight of silver powder to 100 parts by weight of the base resin. The value of the conductive composition became relatively expensive, and the printing workability of the circuit base was lowered, so that the finished condition of the circuit base tended to be somewhat worse than that of a plating base. In addition, especially in the case of flexible printed wiring boards, as the amount of silver powder added increases, the flexibility becomes extremely poor, and when the amount of silver powder reaches 400 to 500 parts by weight, the flexibility of the wiring board decreases. Even if the circuit base was electroplated, the circuit part would break and break when the wiring board was bent, making it impossible to create the desired flexible printed wiring board. The present invention solves the above-mentioned problems in a method of manufacturing a printed wiring board in which a conductive composition is printed on the surface of an insulating substrate to form a circuit base, and a circuit is formed by electroplating metal on the circuit base. This has been achieved as a result of further studies on these points, and the various problems mentioned above have been solved without sacrificing the simplicity of the process, which is the advantage of the method of printing a conductive composition in circuit substrate formation. The present invention provides a new manufacturing method that solves these problems. That is, in the present invention, a circuit base is printed on the surface of an insulating substrate using a composition made by adding 80 to 300 parts by weight of silver powder to 100 parts by weight of an electron beam curable resin, and the circuit base is irradiated with an electron beam. The present invention relates to a method for manufacturing a printed wiring board, which comprises curing the circuit board, followed by heat treatment, and performing metal electroplating on the circuit substrate. In particular, in the present invention, 80 to 300 parts by weight, more preferably 100 to 250 parts by weight of silver powder is added to 100 parts by weight of electron beam curable resin as a base material for circuit underprint printing. using a composition. As mentioned above, in the conventionally disclosed technology, it was necessary to add about 400 to 500 parts by weight of silver powder in order to obtain a composition having sufficient conductivity. However, although the reason is not clear, the present inventors used a composition made by adding 80 to 300 parts by weight of silver powder to 100 parts by weight of electron beam curable resin.
By printing a circuit base on the surface of an insulating substrate, curing the circuit base by irradiating it with electron beams, and then performing heat treatment, the amount of silver powder added was mysteriously reduced to 80 to 300 parts by weight. Despite the small number of
Although metal electroplating is performed, it has been discovered that a conductive circuit base having practically sufficient conductivity can be formed, and the present invention has been completed. The silver powder used in the present invention is mainly composed of metallic silver, has a flake-like or lump-like shape, and has an average particle size of 0.1.
They are fine particles of ~10 μm. The shape and particle size of the silver powder are not particularly limited, but considering conductivity, printing workability, economic efficiency, etc., it is preferable that the shape is flaky.
It is better to use particles with a large specific surface area, and in order to perform screen printing, it is desirable to select particles with a small particle size. In the present invention, 80 to 300 parts by weight of silver powder is added to 100 parts by weight of the electron beam curable resin serving as the base material. If the amount added is less than 80 parts by weight, it will not be possible to obtain a circuit base with sufficient conductivity, and if the amount added exceeds 300 parts by weight, the conductivity will be relatively good, but the As mentioned above, the price of conductive compositions has increased, printing workability has decreased, and the finished state of circuit bases has tended to deteriorate somewhat as a plating base. However, flexibility is impaired and even if the circuit base is electroplated, the problem arises that the wiring board will break when bent. Particularly preferably, the amount added is 100 to 250 parts by weight, and a circuit base having sufficient conductivity can be formed without causing the above-mentioned problems. The electron beam curable resin used as the base material used in the present invention refers to a resin having functionality that causes a curing reaction when irradiated with an electron beam, such as epoxy resin, polyurethane resin, silicone resin, etc. A functional resin is used, such as a polymer obtained by modifying the polymer with a functional group to give it functionality, or a polymer having functionality in the molecule, such as an unsaturated polyester resin, a polybutadiene resin, or a spiroacetal resin. These functional resins may be used alone or in combination as required, and functional monomers, oligomers, etc. may also be added. In particular, in order to add the required amount of silver powder and achieve appropriate printing workability, it is effective to use a functional monomer or oligomer with relatively low viscosity. In addition, it is also possible to add viscosity adjusting materials, colorants, etc. to adjust the paint form. In order to make a composition by adding silver powder to a resin that is a base material having these functionalities, it is possible to obtain it by a method of preparing a paint, for example, by uniformly and thoroughly kneading it by roll mixing. can. The method of printing the circuit base on the surface of the insulating substrate is not particularly limited, but a commonly used screen printing method is preferable. In particular, in the present invention, since the amount of silver powder added is smaller than in the conventionally disclosed technology, printing workability is good and it is suitable for use in screen printing. The circuit base formed on the surface of the insulating substrate is hardened by irradiating it with an electron beam. The electron beam irradiation conditions are determined appropriately depending on the resin used, but are usually 5~
A dose of around 30 Mrad is preferred. In the present invention, heat treatment is performed after the circuit base is cured by electron beam irradiation. In the present invention, since the circuit base is printed with a composition made by adding 80 to 300 parts by weight of silver powder to 100 parts by weight of the electron beam curable resin that serves as the base material, the circuit base is printed by electron beam irradiation. When the circuit substrate is cured, the conductivity of the circuit base is not sufficient. However, by heating the circuit base after curing by electron beam irradiation,
The circuit base becomes sufficiently conductive for practical use. The heat treatment conditions range from 80 to 200°C.
If the heat treatment temperature is below 80°C, sufficient conductivity will not be achieved, and if it exceeds 200°C, problems such as distortion of the wiring board due to the effects of heat will occur. Desirably, a range of 100 to 150°C is good. or,
The best heating time is between 5 and 60 minutes. Next, metal electroplating is performed on the circuit substrate to produce a printed wiring board having the required circuit. Hereinafter, the method for manufacturing a printed wiring board based on the present invention will be specifically explained with reference to Examples. Example 1 Aronix oligomer (Toagosei Chemical Industry Co., Ltd.)
A functional resin base consisting of 80 parts by weight of oligoester acrylate (trade name) and 20 parts by weight of lipoxy resin (epoxy acrylate resin trade name, manufactured by Showa Kobunshi Co., Ltd.) was added as shown in Tables 1(a) to (f). Similarly, 80 to 300 parts by weight of metallic silver is added to make a paint, which is screen printed on a glass cloth-epoxy resin laminate board to a thickness of 30 μm, and then an electron beam is applied to it at 15 Mrad.
It was irradiated and hardened. Table 1 shows the results of measuring the conductivity of the paint after curing with electron beam irradiation. No conductivity was observed in cases (a) to (c) where the amount of silver powder added was small, and when the amount of silver powder added was slightly Variations in conductivity were observed in cases (d) to (f) where the number of samples was high. Furthermore, the results of heating these materials at 150° C. for 15 minutes and measuring their conductivity are also shown in Table 1. As seen in Table 1, for those subjected to heat treatment, (a) is 10 ³ Ω or less;
It was found that (b) to (f) all exhibited resistance values of 10Ω or less. Furthermore, using a bright copper sulfate bath on the circuit base made in (a) to (f), copper plating was performed for 4 to 20 minutes with air stirring at a cathode current density of 4A/ ^dm2 .

[Table] As a result of aging, a good circuit with a plating thickness of 3.5 to 18 μm was obtained. Comparative Example 1 Paints were prepared by adding 50 to 70 parts by weight and 400 to 500 parts by weight of metallic silver to the same resin base as in Example 1, as shown in Tables 1(g) to (j). The conductivity of the circuit base was examined by printing under the same conditions as in the case of , and performing electron beam irradiation curing and heat treatment. The results are shown in Table 1. With (g) and (h), which have a small amount of silver added, no conductivity was observed after electron beam irradiation curing and heat treatment, and with (i) and (j), which had a large amount of silver added, there was no practical conductivity during electron beam irradiation curing. In addition, sufficient conductivity was obtained, and no significant change in properties was observed even when these were heated. However, (i) and (j) had poor printability and the finish of the circuit base was poor. Example 2 In (c) of Example 1, a paint containing 150 parts by weight of silver was screen printed on the surface of a 50 μm polyimide film to a thickness of 20 μm, and was cured by electron beam irradiation and heated under the same conditions as Example 1. Although the treatment was carried out, the conductivity of the circuit base was examined and a value of less than 10Ω was obtained. Furthermore, the thickness of this circuit base was increased under the same conditions as in Example 1.
A good circuit was obtained by performing 15μm copper plating. Furthermore, when this printed wiring board was bent, no abnormalities such as circuit bending occurred, and a good flexible printed wiring board could be produced. Comparative Example 2 Using (i) of Comparative Example 1, that is, a paint containing 400 parts by weight of silver, a circuit base was printed under the same conditions as in Example 1, and cured by electron beam irradiation. The conductivity of the circuit base was good, and plating was performed on this circuit base under the same conditions as in Example 1. However, when the printed wiring board was bent, the circuits were bent and cut, making it impossible to produce a good flexible printed wiring board. As mentioned above, in the method for manufacturing a printed wiring board according to the present invention, the circuit base is formed on an insulating substrate using a composition containing 80 to 300 parts by weight of silver powder per 100 parts by weight of electron beam curable resin. is formed, so
The price of the circuit base composition is relatively low, the printing workability is good, and the circuit base is produced in good condition, and it is also possible to apply metal electroplating on the circuit base, especially in flexible printed wiring boards. Good flexibility can be obtained after doing this. In addition, by printing the conductive composition by a commonly used method such as screen printing, curing it by electron beam irradiation, and heat-treating it, a desired circuit base can be easily obtained. It has high industrial value because a metal circuit can be easily formed on the ground by metal electroplating using a conventional method.

Claims (1)

[Claims] 1. 80 to 300 parts of silver powder to 100 parts by weight of electron beam curable resin.
A circuit base is printed on the surface of an insulating substrate using a composition containing parts by weight, and the circuit base is cured by irradiation with an electron beam, followed by heat treatment, and metal electroplating is performed on the circuit base. A method for manufacturing a printed wiring board, characterized by: 2. The method for manufacturing a printed wiring board according to claim 1, wherein the insulating substrate is made of a flexible material.