JPH0250636B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a copper through-hole printed wiring board.

Conventional technology The hole-filling method, tenting method, and solder stripping method have traditionally been used as methods for manufacturing copper through-hole printed wiring boards, but these methods have low productivity and poor reliability of the etching resist film. This method has drawbacks such as easy product defects and high manufacturing costs.

In order to eliminate these drawbacks, the applicant of the present patent has already proposed a method of using a film made of a copper complex of an alkylimidazole compound as an alkaline etching resist. (Japanese Unexamined Patent Application Publication No. 61-90492) This invention involves drilling holes at necessary locations in a double-sided copper-clad laminate, then performing electroless copper plating, and then performing electrolytic copper plating. A negative resist film [A] soluble in an alkaline aqueous solution was formed by a printing method or a photographic method on parts other than the circuit to be removed with an alkaline etching solution, and then treated in this way. The laminate is a salt of an alkylimidazole compound represented by the following general formula. [However, in the formula, R ₂ is a long-chain alkyl group, R ₄ is a hydrogen atom or a lower alkyl group, and HA is an organic or inorganic acid.] After immersing it in an aqueous solution, the through-hole is formed by drying. An etching resist film [B] made of the copper complex of the alkylimidazole compound is formed on the copper surface of the circuit portion including the circuit portion (that is, the portion not covered with the negative resist film [A]), and then immersed in an alkaline aqueous solution. The alkali-soluble resist film [A] is dissolved and removed to expose the copper surface of the negative area, and then treated with an alkaline etching solution (in this case, the area covered with the etching resist film [B] remains unchanged). This is a method for manufacturing the desired copper through-hole printed wiring board.

This method takes advantage of the property that the alkylimidazole compound reacts selectively with the copper surface to form a highly alkali-resistant film made of a copper complex of the alkylimidazole compound, resulting in improved productivity and reliability. It has advantages such as high price and low manufacturing cost.

Problems to be Solved by the Invention However, in the method described in JP-A-61-90492, since the etching resist film [B] made of a copper complex of an alkylimidazole compound is extremely thin, its physical strength is not necessarily sufficient. I can't say that.

That is, in the step of dissolving and removing the resist film [A] soluble in an alkaline aqueous solution or the etching step, this etching resist film [B]
However, if it comes into contact with a solid object or if the spray pressure is too high, a part of this etching resist film [B] may be damaged and a good product may not be obtained.

Therefore, it has been desired to further increase the physical strength of the etching resist film [B] made of the copper complex of this alkylimidazole compound.

Measures to Solve the Problem In view of the above circumstances, the inventors of the present invention have conducted extensive research, and as a result, have drilled holes at the necessary locations in a double-sided copper-clad laminate, performed copper plating treatment, and developed a solution that is soluble in an alkaline aqueous solution. Form a negative resist film using a resist of [However, in the formula, R ₂ is a long-chain alkyl group, R ₄ is a hydrogen atom or a lower alkyl group, and HA is an organic or inorganic acid.] After immersing the copper-clad laminate in an aqueous solution containing copper ions, It has been discovered that the above object can be fully achieved by immersing the laminate in a buffer solution and treating the laminate with an alkaline etching solution, thereby completing the present invention.

The long-chain alkylimidazole used in the method of the present invention bonds with the copper surface with strong force, but does not show bonding force to parts other than copper that constitute the laminate.

Therefore, the formation of the negative resist film [A] required before contacting the double-sided copper-clad laminate with an aqueous solution containing a salt of an alkylimidazole compound can be achieved using the conventionally known heat soluble alkaline aqueous solution. This can be carried out using a dry type or ultraviolet curable resist ink, an alkali-developable photosensitive film, or an alkali-developable liquid resist ink.

The salt of a long-chain alkylimidazole used in the method of the present invention is formed from an imidazole having a long-chain alkyl group and either an organic acid or an inorganic acid. Acid, glycolic acid, paranitrobenzoic acid, paratoluenesulfonic acid, picric acid, oxalic acid, succinic acid, maleic acid, fumaric acid,
Tartaric acid, adipic acid, hydrochloric acid, sulfuric acid, phosphoric acid, lactic acid,
These include oleic acid and phthalic acid.

The step of contacting the double-sided copper-clad laminate, which has been subjected to hole-drilling and copper plating and has formed a negative resist film using a resist soluble in an alkaline aqueous solution, with a long-chain alkylimidazole salt is to ~5%, preferably at a temperature range of 30~60°C for a period of several tens of seconds to several tens of minutes.
Vibrating the copper-clad laminate, stirring the solution containing the long-chain alkylimidazole salt, or applying vibration using ultrasonic waves are effective means to obtain a constant film thickness in a short time. be. In addition to the immersion method, a method of flowing the liquid down along the copper-clad laminate is also possible. A suitable pH of an aqueous solution containing a long chain alkylimidazole salt is between 3.8 and 4.5.

Next, the mode of treatment with a buffer solution containing copper ions in the method of the present invention will be described.

The copper ions constituting the buffer solution in the present invention may be of any material as long as it dissolves to generate copper ions. Typical examples thereof include metallic copper such as copper plates, copper wires, and copper powder, and copper chloride. These are copper compounds such as copper, cupric chloride, copper hydroxide, cuprous oxide, cupric oxide, copper phosphate, copper carbonate, copper sulfate, or copper acetate.

The acid constituting the buffer solution containing copper ions may be any organic acid or inorganic acid, and representative examples thereof include acetic acid, capric acid, glycolic acid, paranitrobenzoic acid, paranitrosulfonic acid, picric acid, These include oxalic acid, succinic acid, maleic acid, fumaric acid, tartaric acid, adipic acid, hydrochloric acid, sulfuric acid, phosphoric acid, lactic acid, oleic acid, and phthalic acid.

Furthermore, the base constituting the buffer solution containing copper ions may be either an organic base or an inorganic base.
Typical of these are ammonia, diethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, dimethylethanolamine, diethylethanolamine, isopropylethanolamine, lithium hydroxide, potassium hydroxide, sodium hydroxide, etc. .

The effect is recognized when the copper ion concentration is several PPm or more, but it is necessary to have a copper ion concentration of 50 PPm or more to obtain a sufficient effect.If the pH of the buffer solution is 7.0 or higher, copper will precipitate, and if the PH is 4.6 or lower, copper will precipitate. Since the film thickness of the etching resist decreases, it is preferable to maintain the pH in the range of 6.0 to 4.8.

The immersion temperature can range from 0 to 100°C, but is preferably 30°C or higher, and the immersion time ranges from several seconds to
A range of several tens of minutes is possible, and at a temperature of about 50℃, 1 to 2
minutes is appropriate.

Note that the method of the present invention can be carried out on both rigid printed wiring boards and flexible printed wiring boards.

Effect When a copper-clad laminate is immersed in an aqueous solution of a salt of an alkylimidazole compound, the alkylimidazole molecules form a copper complex on the copper surface, and further, due to the van der Waals force of the long-chain alkyl group and the hydrogen bonding force of imidazole, the alkylimidazole molecules form a copper complex on the copper surface. As a result, alkylimidazole molecules gather one after another on the etching resist film, and at the same time as the etching resist film grows, copper moves from the copper surface into the film. However, the movement of copper is not sufficient;
Further migration of copper occurs during the subsequent drying, but the etching resist film is completely cured before it becomes a complete copper complex. That is, it is considered that the etching resist film made of the copper complex of the alkylimidazole compound thus produced is in a copper-deficient state and becomes a non-uniform film. On the other hand, if a copper-clad laminate is immersed in an aqueous solution of the salt of the alkylimidazole compound and then further immersed in a buffer solution containing copper ions, the movement of copper from the copper surface into the film will continue. At the same time as the etching progresses, copper moves from the solution into the film, and the etching resist film thus obtained becomes a uniform film consisting of a complete copper complex of an alkylimidazole compound, and its physical strength is remarkable. improves.

Note that if the solution containing copper ions is not a buffer solution, the aqueous solution of the salt of the alkylimidazole compound remaining on the copper-clad laminate and inside the through-holes will be mixed in, resulting in a decrease in pH and the formation of the copper complex of the alkylimidazole compound. The alkylimidazole compound forming the etching resist film is dissolved into the processing solution, and the film thickness of the etching resist is reduced. However, if this solution is a buffer solution, the pH after processing will hardly change, and therefore the film thickness of the etching resist will hardly decrease.

Example 1 By drilling holes in a 1.6 m/m thick FR-4 (trade name "R-1705" manufactured by Matsushita Electric Works, Ltd.) double-sided copper-clad laminate, electroless copper plating, and then electrolytic copper plating. Copper plating with a thickness of 25 to 30 μm was formed inside the hole and on both sides.

Next, a resist ink (trade name "KM-10" manufactured by Taiyo Ink Manufacturing Co., Ltd.) containing acrylic acid/styrene copolymer as the main component is applied by screen printing to create a thickness.
Form a negative resist film of about 20μ and apply on one side at a time.
Dry for 10 minutes at a temperature of 80°C.

Next, the treated copper clad laminate was immersed in an 11% sulfuric acid aqueous solution containing 20% sodium persulfate for 30 seconds to soft-etch the copper surface.
2% aqueous solution of undecylimidazole acetate (PH
4.45) for 3 minutes at a temperature of 50°C.

After that, take out the copper-clad laminate and use cupric chloride.
0.02%, 90% acetic acid 0.1% and 25% ammonia water 0.1
% buffer solution (PH5.38, copper 75PPm) at a temperature of 50°C for 2 minutes. Next, the copper-clad laminate was taken out, washed with water, and dried at 120° C. for 10 minutes to form an etching resist film made of a copper complex of 2-undecylimidazole on the copper surface of the circuit portion including the through holes. The thickness of this film is 2.1μ, and the amount of copper is 96.4% of the theoretical value of the copper complex of 2-undecylimidazole.
The pencil hardness of the film was 3H.

Subsequently, the negative resist film was dissolved and removed using a 2% aqueous sodium hydroxide solution to expose copper in areas that did not need to be left as wiring.

Next, using an alkaline etching agent (trade name "A Process" manufactured by Meltex Co., Ltd.), the temperature was 50°C.
Etching was carried out by passing the treated copper clad laminate for 120 seconds during spraying. The etching spray pressure was 0.8Kg/cm ² and 1.6Kg/cm ² , but the resulting copper through-hole printed wiring board could be etched with any spray pressure of 0.8Kg/cm ² or 1.6Kg/cm ^{2 .} It was good and warm.

Example 2 Assuming the contamination of an aqueous solution of a salt of an alkylimidazole compound, cupric chloride 0.02%, 90
°C A solution containing 0.1% acetic acid and 0.1% 25% ammonia water to which 2% 2-undecylimidazole acetate aqueous solution (PH4.45) was added (PH5.23/copper).
75PPm), the film thickness of the etching resist was 2.0μ, the copper content was 96.7%,
The pencil hardness of the film was 3H, and the resulting copper through-hole printed wiring board was good.

Comparative Example 1 Exactly the same as in Example 1 except for the step of immersing in a buffer solution (PH5.38 copper 75PPm) containing 0.02% cupric chloride, 0.1% 90% acetic acid and 0.1% 25% aqueous ammonia. When the above treatment was carried out, the thickness of the etching resist film was 2.1 μ, the copper content was 66.6%, and the pencil hardness of the film was F. The resulting copper through-hole printed wiring board ^was Although the temperature was good, at 1.6 kg/cm ² part of the copper in the wiring part was missing.

Comparative Example 2 Assuming the contamination of an aqueous solution of a salt of an alkylimidazole compound when the solution containing copper ions is not a buffer solution, 0.02% cupric chloride and 90% acetic acid from Example 1 were used.
0.02 cupric chloride instead of 0.1% and 25% buffer containing 0.1% aqueous ammonia (PH5.38, copper 75PPm)
A similar treatment was carried out using an aqueous solution (PH 4.56, copper 75 PPm) containing 2% aqueous solution of 2% and 2-undecylimidazole acetate. In this case, the film thickness of the etching resist was reduced to 1.3μ, the copper content was 97.4%, the pencil hardness of the film was 3H, and the resulting copper through-hole printed wiring board was sprayed at a spray pressure of 0.8Kg/cm ² and
In both cases of 1.6 kg/cm ² , a portion of the copper in the wiring section was missing.

Effects of the Invention The method of the present invention improves the physical strength of an etching resist film made of a copper complex of an alkylimidazole compound and further increases its reliability, making it possible to manufacture copper through-hole printed wiring boards more efficiently. .

Claims (1)

[Scope of Claims] 1. Holes are drilled at necessary locations in the double-sided copper-clad laminate, copper plating is performed, and a negative resist film is formed using a resist soluble in an alkaline aqueous solution, and the double-sided copper-clad laminate is is a salt of an alkylimidazole compound represented by the following general formula. [However, in the formula, R ₂ is a long-chain alkyl group, R ₄ is a hydrogen atom or a lower alkyl group, and HA is an organic or inorganic acid]. A copper through-hole characterized in that an etching resist film is formed, the double-sided copper-clad laminate subjected to the above treatment is immersed in a buffer solution containing copper ions, and then the laminate is brought into contact with an alkaline etching solution. A method for manufacturing printed wiring boards.