JPS605237B2 - How to form printed circuits - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a printed circuit, and more particularly to a method for forming a printed circuit in which a conductive pattern is formed using chemical plating or a combination of chemical plating and flash plating.

In recent years, as the practical use of ICs and BI has progressed, the devices to be mounted are becoming more 4-type, higher in performance, and higher in reliability.

Correspondingly, there is a strong demand for printed circuit boards to be smaller, more reliable, and lower in cost through higher density wiring. Through-hole printed circuit boards are currently being put into practical use to meet these demands, and their manufacturing method uses copper-clad laminates as the starting material, holes for through-holes, and then chemical plating and electroplating. After that, the circuit pattern part and through-hole part are protected with a resist, and unnecessary parts of the copper foil are removed by etching.The manufacturing process is complicated and requires a large amount of material cost.
The drawback is that it cannot meet the demand for lower costs.

By the way, the additive method of selectively forming a circuit pattern on an insulating substrate not only allows through-holes and circuit patterns to be formed simultaneously in a simple manufacturing process, but also has the advantage of reducing material costs, making it economically advantageous. be. However, with the above additive method, the adhesion between the circuit layer (metal layer) formed by plating on the insulating substrate and the board is inferior to that of copper-clad laminates, so the circuit layer tends to peel off, making it difficult to use as a printed circuit. It has the disadvantage of being less reliable.

As a measure to improve the adhesion between the circuit layer and the insulating substrate, an adhesive layer (underlying layer) containing, for example, nitrile rubber as a main component is provided on the surface of the insulating substrate to be plated, and then a hydrophilic treatment is performed using a chromium sulfuric acid solution. A method of chemical plating has been proposed, but
This method also does not provide sufficient performance and is undesirable because it requires waste liquid treatment equipment for using a chromium sulfuric acid solution. As a result of repeated studies in order to eliminate the above-mentioned drawbacks and inconveniences, the inventors of the present invention have integrally molded an anodized aluminum foil surface and a laminate via an adhesive layer mainly composed of Gen-based synthetic rubber. Afterwards, ``If some or all of the aluminum foil and anodized layer are etched away and the exposed adhesive surface is subjected to corona discharge treatment, the resulting adhesive surface has excellent suitability for chemical plating.'' I found out what I was doing.

In other words, the chemically plated layer can be easily obtained, and especially when applied to the manufacture of printed circuit boards, the insulating substrate and the plated layer are tightly adhered, achieving the adhesion strength and soldering heat resistance required for printed circuits. I found out that I was prepared. Based on the above findings, the present invention aims to provide a method for forming a printed circuit which can easily form a circuit with excellent adhesion strength by chemical plating without requiring treatment with a chromium sulfuric acid solution.

To explain the present invention in detail below, the present invention consists of {1) coating an adhesive layer mainly composed of Gen-based synthetic rubber on an aluminum foil that has been made uneven by anodizing treatment, and leaving this in a semi-cured state; Step of laminating the above adhesive coated surface and the insulating substrate or prepreg, and integrally forming it by heating and pressurizing; '3- Etching away the aluminum foil and anodized layer to expose the uneven adhesive surface The process of '
4-A printed circuit comprising the steps of: subjecting the uneven adhesive surface to a corona discharge treatment; and (5) chemically plating the corona discharge-treated uneven surface to form a conductive pattern. This is the formation method.

In general, phosphoric acid method, sulfuric acid method, oxalic acid method, chromic acid method, etc. are known as anodizing methods for aluminum surfaces, but in the present invention, anodizing treatment using phosphoric acid method is particularly preferred, as it improves adhesion. .

Examples of the absolute substrate used in the present invention include plastic plates, glass plates, ceramic plates, laminate plates, and insulating substrates obtained by coating the surface of a metal plate with an insulating resin.

Furthermore, the adhesive used in the present invention is mainly composed of a DEN-based synthetic rubber, and the DEN-based synthetic rubber includes, for example, butadiene polymer, butadiene styrene copolymer, butadiene acrylonitrile copolymer, isoprene rubber, Alternatively, chloroprene rubber and the like may be mentioned.

These polymers or copolymers may be used as they are, but they may also be supplemented with thermosetting resins such as epoxy resins and phenolic resins, and fillers such as silica gel, zirconium silicate, and magnesium silicate, which serve as reinforcing agents. It may be used by adding and blending. Next, in order to apply the above adhesive to the anodized aluminum foil surface, the adhesive is dissolved in a solvent, the adhesive solution is prepared, and then wire percoating, roll coating, curtain coating, bonding, printing, or other methods are used. It is applied to the surface of the anodized layer by heating and dried to a semi-cured state.

The heating conditions required for a semi-cured state cannot be stated in general terms because they depend on the type of solvent used in the adhesive solution and the ease of curing of the adhesive resin used. However, it is necessary to experimentally find conditions in which the amount of solvent remaining in the adhesive is sufficiently small and the aluminum foil and the insulating substrate are in close contact with each other when integrally formed. The heating and pressure conditions during integral molding are as follows: When integrally molding the prepreg and the aluminum foil surface provided with the adhesive layer, it is desirable to match the curing conditions of the adhesive and the prepreg. When using a paper base material impregnated with phenol resin or a glass base material impregnated with epoxy resin as prepreg, the temperature is 140 to 19,000 °C, and the temperature is 50 to 150 k9.
/Earth pressure is normal. Furthermore, when integrally molding the aluminum foil surface provided with the adhesive layer and the insulating substrate, heating and pressurizing conditions are required that do not impair the electrical, mechanical, and chemical properties inherent to the insulating substrate. To expose the uneven adhesive layer by removing the aluminum foil and anodized layer from the aluminum foil-attached insulating substrate (hereinafter referred to as the insulating substrate, including prepreg) that has been integrally formed with the adhesive layer interposed therebetween. The aluminum foil and anodized layer may be removed by etching.

Caustic soda and hydrochloric acid aqueous solutions are commonly used for etching. Next, the corona discharge treatment used in the present invention is direct current. Although either a high-frequency corona or an AC corona can be used, a high-frequency corona is preferable because it can provide a uniform corona over the treated surface. Also, regarding the high frequency corona, a vacuum tube method is used from the circuit,
There are spark gap methods, solid state methods, etc., and although there are differences in frequency and high frequency waveform, any of these methods can be used. The reason why the adhesion between the insulating substrate and the plating metal layer is improved by the corona discharge treatment of the present invention is as follows.
For each large unevenness formed on the adhesive surface by removing the aluminum foil and anodized layer, small unevenness is further formed by corona discharge treatment, and at the same time, the surface is made hydrophilic by this treatment. This is thought to be because chemical plating is formed from a sufficiently deep part of the adhesive layer. In fact, when the adhesive layer is subjected to a corona discharge treatment, the surface tension increases from approximately 3 m2/skin to more than 5 m/skin. In the present invention, after the corona discharge treatment, so-called electroless plating is performed using, for example, chemical steel plating or chemical nickel plating in the same manner as in the prior art to form a desired printed circuit. This printed circuit may be formed by forming a conductive pattern using only the electroless plating process, or by using a combination of electroless plating and draught plating processes. As described above, according to the present invention, it is possible to easily obtain a circuit board in which the metal foil adheres firmly without requiring treatment with a chromium sulfuric acid solution, and which is excellent in terms of soldering heat resistance and the like.

Examples of the present invention are described below.

Examples 1 to 5, Comparative Examples 1 to 5 The following formulations were mixed using a homogenizer, and then mixed sufficiently uniformly using a triple roll.

Thereafter, the adhesive solution was diluted to 25% by weight with a butyl cellosol solution. o Nitrile rubber (manufactured by Nippon Zeon ■,
Product name: Hiker 1072) 2% by weight methyl ethyl ketone solution...
・25 parts by weight o phenolic resin (manufactured by Mitsubishi Gas Chemical ■,
5% by weight methanol solution of Nicanol PR-1440M (trade name: Nicanol PR-1440M)
Methyl ethyl ketone solution of 5 parts by weight of epoxy resin (manufactured by Shell Petrochemical ■, trade name: Epikot 1001) in 8 parts by weight of methyl ethyl ketone 31
Part by weight o 20% by weight solution of acid anhydride resin curing agent (manufactured by Nippon Kayaku ■, trade name: Kayahard CLA) in butyl cellosolve 1 part by Marugame Next 50 mm thick Aluminum foil (material: AIA3 Misaki-1
8) under the following conditions.

Pretreatment liquid 1: Alkaline soak cleaner, Kakufuku; 9 pi 0, time: 5 minutes Pretreatment liquid 2: Ammonium hydrogen fluoride,
Temperature: room temperature, time: 3 minutes Electrolyte: 1 cloud cover% day 3P0
4. Current density: 0.8 A/d〆, temperature: 50 qo, time: 15 minutes The above adhesive solution was applied with a wire bar onto an aluminum foil whose surface had been roughened by anodizing treatment, and 1
It was dried in an oven at 20 qC for 20 minutes to a semi-cured state.

Next, the adhesive-coated aluminum foil was placed on both the front and back sides of a 1.6-thick willow paper epoxy laminate with the adhesive side in contact with the adhesive side, and placed in a multi-stage heat press at 160oo for 60 minutes at a pressure of 20kg/carp. It was integrally molded under the following conditions.

As a result, a laminate was obtained in which the aluminum foil was firmly adhered to the cured paper epoxy resin base material. Furthermore, the aluminum foil and anodized layer were removed by immersion for 5 minutes using an etching solution consisting of an aqueous solution containing 5% by weight of caustic soda and 0.5% by weight of sodium gluconate, which was flooded with 50 qo, resulting in uneven bonding. The drug surface was exposed. Next, the adhesive layer with the uneven surface was subjected to corona discharge treatment using a solid-state corona discharge machine.

The processing conditions are as follows. o Device manufactured by Pillar Co., Ltd.
Model 2.1KVAo applied voltage 8500Vo frequency 9. Substrate with adhesive feeding speed: 15 m/min Input power: 143.5 V, gap between electrodes: 2.4 volts The above corona discharge treated substrate with adhesive was plated in the usual manner to reduce the thickness of the metal layer. Chemical steel plated to approximately 4000A.

For the plating bath and plating pretreatment, 32 Beni Process (trade name) manufactured by Shipley Co., Ltd. was used. Furthermore, electric steel plating was applied, and the thickness of the steel foil was increased to approximately 30 mm. Table 1 shows the appearance after chemical steel plating, the adhesion between the plated copper film and the laminate, and the solder heat resistance, which were examined in accordance with JISC-6481. Table 1 * The numbers in parentheses are the number of passes when the adhesive-coated laminate was continuously passed through the corona discharge machine in Table 1. Examples 1 to 5 had the adhesive layer of the present invention, and It has undergone oxidation treatment and corona discharge treatment, and this result is JB
Standard values based on C-6482 (for paper-epoxy copper clad laminates), adhesion strength: 14k9'cM, solder heat resistance value (2
60±8°C seconds); it exceeds 1 second, which is a practically sufficient value.

On the other hand, in Comparative Examples 1 to 5, either the adhesive layer of the present invention or the corona discharge treatment was missing, or both were missing, and both were significantly inferior in adhesion and soldering heat resistance. Note that the alumite layer is considered to play a complementary role in improving adhesion and soldering heat resistance. Example
6-10 Chemical plating and electroplating were performed under the same conditions as Examples 1-5, except that the following was used as anodizing treatment in the steps used in Examples 1-5, and the thickness of the copper foil was I filled it up to about 30A.

Table 2 shows the appearance after chemical copper plating, the adhesion between the plated copper film and the laminate, and the solder heat resistance determined in accordance with JISC-6481. Pretreatment solution; alkaline soak cleaner, ambient temperature; 4000, time; 1 minute; electrolyte; 3% by weight day 3P04; current density; 0. ship/d
〆, ordinary temperature: 30qo, time: about 1 minute Table 2 The numbers in parentheses indicate the number of passes when the adhesive-coated laminate was passed through the corona discharge machine continuously. Even if the adhesive layer of the present invention is present and corona discharge is performed, the value exceeds the standard value based on JISC-6482, and as in Examples 1 to 5, it is confirmed that the value is sufficient for practical use. I understand.

Examples 11 and 12 Electroplating was performed in the same manner as in Examples 1 to 5, except that a spark gap type corona discharge machine was used instead of the solid state type corona discharge machine used in Examples 1 to 5.

The plating appearance is good, and the adhesion and soldering heat resistance values are as shown in Table 3, which are equivalent to the results of Examples 1 to 5 and exceed the standard values based on JISC-6482, which are sufficient values for practical use. I understand. Table 3 As shown above, according to the printed circuit forming method using the adhesive layer, the replica by removing the aluminum foil layer, and the corona discharge treatment according to the present invention, excellent adhesion and soldering heat resistance can be achieved without using chromic acid or the like. A printed circuit board is obtained.

Claims (1)

[Claims] 1. A step of applying an adhesive mainly composed of diene synthetic rubber onto an aluminum foil that has been made to have an uneven surface by anodizing treatment, and drying it to form a semi-cured adhesive layer, which is insulated from the adhesive layer. A step of laminating substrates or prepregs and integrally molding them when heated and pressurized, a step of etching away the anodized aluminum foil to expose an adhesive layer with an uneven surface, a step of subjecting the uneven surface to a corona discharge treatment, and A method for forming a printed circuit, comprising the step of chemically plating the corona discharge-treated uneven surface to form a conductive pattern.