JP3337802B2 - Direct plating method by metallization of copper(I) oxide colloid - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THEINVENTION This invention relates to a direct plating method for producing metallic copper on a non-conductive substrate surface catalyzed by a copper catalyst comprising copper(I) oxide colloid.

[0002]

2. Description of the Prior Art Conventionally, electroless copper plating baths using formaldehyde have been generally used industrially as a method for depositing a copper film on a non-conductive plastic substrate. For example, in the manufacturing process of a printed circuit board, a conductive copper film is formed in a through hole using electroless copper plating, and then electrolytic copper plating is performed using this as a base material. However, this electroless copper plating bath has problems such as the use of formaldehyde, which is carcinogenic, the complexity of analysis management, the need for bail-out (replacement of the working liquid), limitations on bath load (treatment area per unit volume of treatment liquid), the problem of voids (occurrence of non-plated areas) due to the trapping of hydrogen gas in microholes, slow deposition speed, and high cost.

For example, a related prior art method for manufacturing printed circuit boards is disclosed in Japanese Patent Laid-Open Publication No. 60-213085. In this method, after drilling, providing a catalyst, polishing, and imaging using a dry film, a conductive copper film is formed using electroless copper plating, followed by electric copper plating and solder plating. This method involves the use of electroless copper plating, and therefore involves some of the problems mentioned above. In order to solve these problems, several methods that do not use electroless copper plating have been proposed. These methods are commonly known as direct plating methods, and are roughly divided into three types: a Pd-Sn providing method, a carbon black providing method, and an organic conductive film providing method. However, printed wiring boards manufactured by these methods have problems such as adhesion between the copper foil and the plating film, and reliability in heat resistance tests, and therefore their reliability is still not sufficient.

[0004]

[0009] One of the objects of the present invention is to provide a method that can be used as an alternative process to electroless copper plating by solving the problems of conventional electroless copper plating and conventional direct plating methods. Copper catalysts containing copper (I) oxide colloids have the following characteristics, and are therefore currently used as catalysts for electroless copper plating when forming through-hole plating on printed wiring boards. (1) The ζ-potential of copper (I) oxide colloids is positive, so they are easily adsorbed on the surface of a non-conductive substrate that is strongly negative after desmearing (the ζ-potential of palladium catalysts is negative, so they are not easily adsorbed on the surface of a substrate that is strongly negative). (2) The surface tension of the copper (I) oxide colloidal solution is low, so it has good penetration and adsorption into micro-holes. (3) The copper (I) oxide colloidal solution is neutral and does not contain strong acids, so it does not corrode the equipment and does not cause pink rings to grow. In contrast, when palladium colloids or the like are used,
A thick colloidal film is required to ensure electrical conductivity,
Such a thick colloidal film has a problem in terms of adhesion to electrolytic copper plating, which is the biggest drawback of the prior art. Therefore, another object of the present invention is to form a thin film having excellent conductivity that enables subsequent electrolytic copper plating, even if it is an extremely thin film.

[0005] It is yet another object of the present invention to provide a direct plating method which can be applied to the following manufacturing method for printed circuit boards: Substrate (copper-clad laminate) Drilling Through-hole plating Degreasing, rinsing Soft etching, rinsing Copper catalyst containing copper (I) oxide colloid Rinsing Drying Polishing Alkali-soluble dry film imaging (or resist ink printing) Degreasing Rinsing Direct plating according to the present invention Rinsing Acid immersion Rinsing Copper sulfate plating Rinsing Acid immersion Solder plating Rinsing Alkali-soluble dry film peeling Etching Solder peeling Solder mask application HAL (hot air leveler) It is yet another object of the present invention to provide a direct plating method which can also be applied to panel plating.

[0006]

[Means for Solving the Problems] The present inventors have completed the present invention as a result of extensive research in order to solve the problems associated with electroless copper plating and conventional direct plating methods. One embodiment of the direct plating method according to the present invention is a method in which a non-conductive substrate catalyzed with a copper catalyst containing copper oxide (I) colloid is immersed in a solution containing a copper salt, a copper reducing agent for depositing copper, and a copper complexing agent, thereby depositing metallic copper on the surface of the copper oxide (I) colloid to form a conductive copper film. Another embodiment of the direct plating method according to the present invention is a method in which a non-conductive substrate catalyzed with a copper catalyst containing copper oxide (I) colloid is immersed in a solution containing an inorganic acid, thereby forming a conductive copper film by reacting, for example, with copper oxide (I) according to reaction formula 1.
This is a method for forming a conductive copper film on the surface of a non-conductive substrate by a disproportionation reaction such as Cu ₂ O + H ₂ SO ₄ → Cu + CuSO ₄ + H ₂ O Reaction formula 1

In the direct plating method of the present invention, the non-conductive substrate is catalyzed with a copper catalyst containing copper(I) oxide colloids. Catalysis is typically accomplished by rocking the substrate for 7-15 minutes in a copper catalyst solution containing copper(I) oxide colloids having a copper concentration of about 1.3 to about 1.7 g/l, a pH of 7.5 to 8.0, and a temperature of 28 to 32° C. In the present invention, a thin copper film is formed by metallization of the copper(I) oxide colloids, and because copper is about 10 times more conductive than palladium, only a very thin copper film is required for subsequent electrolytic copper plating. In one embodiment of the present invention, the catalyzed non-conductive substrate is immersed in a solution containing a copper salt, a copper reducing agent for depositing copper, and a copper complexing agent.

Copper salts are a source of metallic copper, and any copper salt compound can be added to the plating solution as long as the anions are not harmful to the plating bath. Suitable copper salts include copper sulfate, copper chloride, copper nitrate, copper hydroxide, copper sulfamate, copper carbonate, copper oxide, etc. The copper ion concentration in the plating bath can generally be varied in the range of 0.5 to 5 g/l, but is preferably 1 to 2 g/l. When the concentration of the complexing agent is high, a copper concentration of 2 g/l or more can be used. The type of copper reducing agent is not particularly limited as long as it can reduce copper ions to metallic copper, but from the viewpoint of safety, it is preferable to use a reducing agent other than formalin. The reducing agent used in the present invention is used to effectively deposit copper on a substrate to which a catalyst has been applied by the reduction reaction of copper ions.
The reducing agent added to the bath of the present invention is used at a concentration sufficient to reduce and deposit copper on the surface of the copper(I) oxide colloid adsorbed on the surface of the non-conductive substrate. The most preferred reducing agent is dimethylamine borane. Also preferred are hydrazine and its salts, such as hydrazine hydrate, hydrazine hydrochloride, and hydrazine acetate, hypophosphorous acid and its salts, such as hypophosphorous acid and sodium hypophosphite. The concentration of the reducing agent can generally vary in the range of 0.5 to 20 g/l, but is preferably 1 to 10 g/l.
A concentration of 20 g/l or more is undesirable because it makes the plating bath unstable and also causes rapid consumption of the reducing agent.

As the copper complexing agent, any known complexing agent can be used so long as it is capable of complexing copper ions.
For example, polyamines and their salts, aminocarboxylic acids and their salts, amine alkanol compounds, oxycarboxylic acids and their salts can be used. Examples of polyamines and their salts include ethylenediamine and its sulfate salt,
Examples of suitable polyamines and their salts in the solution of the present invention are diethylenetetramine, diethylenetriamine, and triethylenetetramine. The concentration of polyamines and their salts suitable for the solution of the present invention is generally 1 to 10
The concentration can range from 0 g/l, but is preferably in the range of 5 to 50 g/l.

Examples of aminocarboxylic acids and their salts include iminodiacetic acid and its sodium salt, nitrilotriacetic acid and its sodium salt, hydroxyethylethylenediaminetriacetic acid, tetrahydroxyethylenediamine or dihydroxymethylethylenediaminediacetic acid,
Examples of the aminocarboxylic acid and its salt include ethylenediaminetetraacetic acid and its sodium salt and potassium salt, diethylenetriaminepentaacetic acid and its sodium salt, triethylenetetraminehexaacetic acid, cyclohexane-1,2-diaminetetraacetic acid, ethyleneglycoldiethyletherdiaminetetraacetic acid, ethylenediaminetetrapropionic acid, N,N,N',N'-tetrakis-2(2-hydroxypropyl)ethylenediamine, etc. The concentration of the aminocarboxylic acid and its salt suitable for the solution of the present invention is generally 1 to 100 g.
The range of the amount of the ion exchange resin can be varied within a range of 5/l.
The range is 100-50 g/l.

Preferred amine alkanol compounds are mono-, di- and tri-ethanolamines. The concentration of the amine alkanol compounds suitable for the solution of the present invention can generally vary in the range of 5 to 200 ml/l, but is preferably in the range of 50 to 100 ml/l. Examples of hydroxycarboxylic acids include tartaric acid, citric acid and gluconic acid, and examples of hydroxycarboxylic acid salts include sodium tartrate, potassium tartrate, sodium potassium tartrate, sodium citrate, potassium citrate, ammonium citrate, sodium gluconate and potassium gluconate. The concentration of the hydroxycarboxylic acid suitable for the solution of the present invention can generally vary in the range of 1 to 100 g/l.
The range can be varied within a range of 5 to 5
The above-mentioned complexing agents can be used alone, but by using them in appropriate mixtures,
The stability of the plating bath can be improved and the properties of the deposited film can be improved.In another embodiment of the present invention, the catalyzed non-conductive substrate is immersed in a solution containing an inorganic acid.
The inorganic acid may be any acid that forms copper or a salt of copper with an inorganic acid through the disproportionation reaction of copper(I) oxide, and the precipitated metallic copper is difficult to dissolve. Examples include sulfuric acid, hydrochloric acid, formic acid, sulfamic acid, and acetic acid. The concentration of these acids in the solution can generally be varied in the range of 0.1 to 10 mol/l, but is preferably 1.0 to 2.5 mol/l.
4.0 mol/l range.

Additives commonly used in electroless copper plating in the prior art can be added to the plating bath of the present invention to improve bath properties and film properties of the deposit. These additives include various solution-soluble cyanides, cyanates, sulfides, sulfur-containing compounds such as thio compounds, dipyridyl compounds, and ethylene oxide type surfactants. The pH of the plating solution is:
This is particularly important when plating a substrate coated with a water-soluble resist, and a pH of 5 to 8 is preferred to keep attack of the resist to a minimum.
This is an important factor along with pH to keep plating attack on the resist to a minimum. In the present invention, 15
The plating temperature can be varied in the range of 0° C. to 50° C., but the more preferred temperature range is 20° C. to 30° C. The plating time is sufficient to provide a plating of an appropriate thickness.

[0013]

EXAMPLES

Example 1 A solution having the following composition was prepared: Copper sulfate 2 g/l Hydroxyethylenediaminetetraacetic acid (HEDTA) 10 g/l Triethanolamine 10 ml/l Dimethylamine borane 6 g/l 10% sulfuric acid pH 7.0
A copper-clad epoxy laminate with a hole (3.2 mm) was swung for 10 minutes in a copper catalyst solution containing copper (I) oxide colloids with a copper concentration of 1.5 g/l, pH of 8.0, and temperature of 30° C. to provide a catalyst, and was then imaged using an alkali-soluble dry film.
After the accelerator treatment, the sample was incubated at 25° C. for 1 hour in the solution of the above composition.
After that, copper sulfate plating was performed to a thickness of 25 μm.
After that, the resist was peeled off and etching was performed. The printed wiring board obtained by this method is in no way inferior to the one produced by the conventional method, and meets the standard of MIL-P-55110D.
The heat resistance test results were also good, which was performed according to MIL-P-55110D (288°C/10 seconds, 1 cycle). The same test was also performed on a board printed with an alkali-soluble resist ink instead of the alkali-soluble dry film, and the results were comparable to those produced by the conventional method.
The results of the heat resistance test performed according to the heat cycle were also good.

Example 2 A solution having the following composition was prepared: Copper chloride 2 g/l Disodium ethylenediaminetetraacetate 10 g/l Glycine 10 g/l Dimethylamineborane 6 g/l 10% sulfuric acid pH 7.0
A copper-clad epoxy laminate with holes (3.2 mm) was catalyzed by copper oxide (I) colloid activation treatment in the same manner as in Example 1, and was subjected to imaging treatment using an alkali-soluble dry film. This board was degreased and accelerator-treated, and then copper-plated for 10 minutes at 25°C in a solution of the above composition. Thereafter, copper sulfate plating was applied to a thickness of 25 μm, and solder plating was applied to a thickness of 10 μm, after which the resist was removed and etching was performed. The printed wiring board obtained by this method was in no way inferior to one manufactured by a conventional method using electroless copper plating, and was in accordance with MIL-P-551.
The heat resistance test results in accordance with 10D (288° C./10 seconds, 1 cycle) were also good.

Example 3 A solution having the following composition was prepared: Copper sulfate 2 g/l Triethanolamine 10 g/l Sodium hypophosphite 10 g/l 10% sulfuric acid pH 5.0
A copper-clad epoxy laminate with holes (3.2 mm) was catalyzed by copper oxide (I) colloid activation treatment in the same manner as in Example 1, and was subjected to imaging treatment using an alkali-soluble dry film. This board was degreased and accelerator-treated, and then copper-plated for 10 minutes at 25°C in a solution of the above composition. Thereafter, copper sulfate plating was applied to a thickness of 25 μm, and solder plating was applied to a thickness of 10 μm, after which the resist was removed and etching was performed. The printed wiring board obtained by this method was in no way inferior to one manufactured by a conventional method using electroless copper plating, and was in accordance with MIL-P-551.
The heat resistance test results in accordance with 10D (288° C./10 seconds, 1 cycle) were also good.

Example 4 A solution having the following composition was prepared: Sulfuric acid (36N) 100 ml/l 25 cm x 33 cm (plate thickness 1.6 mm, 2.4 mm,
A copper-clad epoxy laminate with holes (diameter 3.2 mm) was treated with a copper(I) oxide colloid as in Example 1 to provide a catalyst. The board was immersed in the above-mentioned dilute sulfuric acid solution at 25°C for 10 minutes, producing metallic copper. It was then plated with 25 μm of copper sulfate, imaged with a dry film, and etched. The printed wiring board obtained by this method was in no way inferior to those produced by conventional methods, and was found to be in good quality according to MIL-P-55110D (2
The results of the heat resistance test performed according to the method described above (88° C./10 seconds, 1 cycle) were also good.

[0017]

According to the present invention, a highly pure conductive copper film can be formed on a substrate catalyzed with a copper catalyst containing copper oxide (I) colloid by simply immersion at room temperature.Furthermore, according to the present invention, a method of manufacturing a printed wiring board, which was not previously possible for those skilled in the art, is made possible, which comprises the steps of drying and surface polishing after catalyzing with a copper catalyst containing copper oxide (I) colloid, imaging with a dry film soluble in an alkaline aqueous solution (or printing with a resist ink soluble in an alkaline aqueous solution), forming a highly pure copper film only on the pattern and in the through-holes, and then electrolytic copper plating and solder plating.

[0018] By using the direct plating method of the present invention, the following excellent effects can be obtained: (1) Unlike electroless copper plating, no complicated analysis management is required (easy management). (2) No carcinogenic formaldehyde is used (good working environment). (3) Spaces caused by hydrogen gas trapped in minute holes are unlikely to occur. (4) Plating time is shorter than electroless copper plating, and plating coverage is quick. (5) Cost is low (less copper analysis is required). (6) If processed in the above-mentioned PCB manufacturing process, delivery time can be shortened. (7) Pretreatment process can be shortened, and processing time is short. (8) Either the copper(I) oxide colloid processing process or the metallization process is a weakly acidic to neutral solution, so an alkali-soluble resist can be used. As described above, the direct plating method of the present invention is quick and safe, and is extremely excellent in economy and reliability, and will contribute greatly to the printed circuit board industry.

───────────────────────────────────────────────────────── Continued from the front page (56) References JP 62-7687 (JP, A) JP 57-32361 (JP, A) JP 62-30684 (JP, A) JP 1-263278 (JP, A) JP 5-156459 (JP, A) JP 4-74870 (JP, A) JP 5-331660 (JP, A) JP 5-163577 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C23C 18/28 C23C 18/40 H05K 3/18

Claims (1)

(57) [Claims] [Claim 1] A direct plating method in which a non-conductive substrate catalyzed with a copper catalyst containing copper (I) oxide colloid is immersed in a solution containing an inorganic acid, thereby forming a conductive copper film on the surface of the non-conductive substrate through a disproportionation reaction of copper (I) oxide.