Electroless copper-plating solution

The present invention relates to an electroless copper plating solution and a stabilizer for an electroless copper plating solution.

The electroless copper plating solution is a plating solution widely used for the purpose of imparting conductivity to non-conductor parts in the production of printed circuit boards, formation of metal films on plastics, etc. In the solution, the following 1) to 4 ) Has been reported to occur (see Non-Patent Document 1 below). Cu²⁺ + 2HCHO + 4OH^- Cu + H₂ + 2HCOO^- + 2H₂O 1) 2HCHO + OH^- + CH₃OH + HCOO^- 2) 2Cu²⁺ + HCHO + 5OH^- Cu₂O + HCOO^- + 3H₂O 3) Cu₂O + H₂O Cu + Cu²⁺ + 2OH^- 4) Of the above reactions, the reaction 1) is a copper precipitation reaction due to the oxidation reaction of formaldehyde, which is a reducing agent, and is electroless copper plating. It is the core of the reaction in the liquid. The reaction 2) is called the Cannizzaro reaction, which always occurs in electroless copper plating using formaldehyde.

The reactions 3) and 4) cause so-called natural decomposition reactions, which are very unfavorable reactions for electroless copper plating. Copper metal is generated in the plating solution by these reactions, and the decomposition of the plating solution proceeds at an accelerating rate as the reaction 1) proceeds with the generated copper as a nucleus.

As described above, in the electroless copper plating solution, it is easy to cause a reaction that impairs the stability, so that it is an important issue to maintain the stability. In particular, various additives have been studied in order to suppress the reactions of 3) and 4) above and improve the stability of the electroless copper plating solution. For example, Non-Patent Document 2 below reports the results of a study on a plating bath in which a cyanide compound, a nitrogen-containing organic compound, a sulfur-containing organic compound, or the like is added as an additive. As a result, it is said that the characteristics of the plating film are the best when the cyanide compound is used, and the ductility is lowered and the bending strength is lowered when the nitrogen-containing compound, the sulfur-containing compound and the like are added. Further, Patent Document 1 below describes that the stability of the electroless copper plating solution is improved by using beryllium in combination with arsenic, antimony, bismuth and the like.

However, cyanide and metal compounds such as arsenic, antimony, bismuth, and beryllium are extremely harmful, and their effects on the human body and the environment cannot be ignored. Further, when a nitrogen-containing organic compound, a sulfur-containing organic compound, or the like is added, the bending strength of the formed copper plating film is lowered, which causes circuit breakage or deterioration of adhesion in, for example, a flexible printed substrate. Become.

The following Non-Patent Document 3 describes a method of improving the stability by oxidizing the cuprous ions generated by the reaction of 3) above by air-stirring the electroless copper plating solution. However, when air agitation is performed, oxidation of the reducing agent is promoted, and further, carbon dioxide gas in the air dissolves in the electroless copper plating solution, so that the pH fluctuates drastically and bath management becomes difficult.<nplcit num="1"><text>RM Lukes, Plating, 51, 1066, 1964</text></nplcit><nplcit num="2"><text>Hirohata, Metal Surface Technology, Vol.24, No.6, 1973</text></nplcit><nplcit num="3"><text>Matsuoka et al., Abstracts of the 68th Academic Lecture Meeting of the Metal Surface Technology Association</text></nplcit><patcit num="1"><text>Japanese Unexamined Patent Publication No. 2000-345358</text></patcit>

<p> The present invention has been made in view of the current state of the prior art described above, and its main purpose is good stability in an electroless copper plating solution without deteriorating the characteristics of the electroless copper plating film to be formed. It is an object of the present invention to provide a stabilizer for electroless copper plating made of a highly safe substance capable of imparting.</p>

<p> As a result of intensive studies to achieve the above object, the present inventor has found that a phosphine compound represented by a specific general formula has excellent performance as a stabilizer for an electroless copper plating solution. The present invention has been completed.</p><p> That is, the present invention provides the following electroless copper plating solution and stabilizer for electroless copper plating solution. 1. The following general formula:</p><p><chemistry num="1"><img file="JP2005290415A_D0001.tif" /></chemistry>(In the formula, R₁, R₂And R₃Is the same or different, a monovalent aliphatic hydrocarbon group that may have a substituent, an aryl group that may have a substituent, or a heterocyclic group that may have a substituent). A non-electrolytic copper plating solution containing the phosphine compound to be used as a stabilizer. 2. The electroless copper plating solution according to Item 1 above, wherein the electroless copper plating solution is an aqueous solution containing a water-soluble copper compound, a complexing agent and a reducing agent in addition to the phosphine compound. 3. The following general formula:</p><p><chemistry num="2"><img file="JP2005290415A_D0002.tif" /></chemistry>(In the formula, R₁, R₂And R₃Is the same or different, a monovalent aliphatic hydrocarbon group that may have a substituent, an aryl group that may have a substituent, or a heterocyclic group that may have a substituent). Stabilizer for electroless copper plating solution, which is composed of a phosphine compound. The stabilizer for electroless copper plating solution of the present invention has the following general formula.</p><p><chemistry num="3"><img file="JP2005290415A_D0003.tif" /></chemistry>It is a phosphine compound represented by.</p><p> In the above general formula, R₁, R₂And R₃Is the same or different monovalent aliphatic hydrocarbon group that may have a substituent, an aryl group that may have a substituent, or a heterocyclic group that may have a substituent.</p><p> Examples of the monovalent aliphatic hydrocarbon group include a linear or branched aliphatic hydrocarbon group having about 1 to 8 carbon atoms and an alicyclic group having about 4 to 10 carbon atoms. Both of these aliphatic hydrocarbon groups and alicyclic groups may contain one or two or more unsaturated bonds such as double bonds and triple bonds.</p><p> Among these monovalent aliphatic hydrocarbon groups, specific examples of the linear or branched aliphatic hydrocarbon group include methyl group, ethyl group, n-propyl group, isopropyl group and n-butyl. Alkyl groups such as groups, sec.-butyl groups, tert.-butyl groups, pentyl groups, hexyl groups, heptyl groups, octyl groups; vinyl groups, propenyl groups, propazienyl groups, butenyl groups, butazienyl groups, pentenyl groups, pentadienyl groups. , Hexenyl group, hexadienyl group, hexatrienyl and other hydrocarbon groups containing one or more double bonds; ethynyl group, propynyl group, propadinyl group, butynyl group, butadynyl group, pentynyl group, pentadiynyl group, hexynyl group. , A hydrocarbon group containing one or more triple bonds such as a hexadiynyl group and a hexatrienyl group can be exemplified. Examples of the alicyclic group include a cyclopentyl group, a cyclohexyl group, a cyclooctyl group, and perhydronaphthalene.</p><p> Examples of the aryl group include a phenyl group and a naphthyl group.</p><p> Examples of the heterocyclic group include a sulfur-containing heterocyclic group such as a thienyl group and a benzothienyl group; an oxygen-containing heterocyclic group such as a frill group, a benzofuranyl group, a pyranyl group, a benzopyranyl group and a chromenyl group; a pyrrolyl group and an imidazolyl group. , Pyrazolyl group, pyridyl group, pyrazinyl group, pyrimidyl group, pyridadinyl group, indridinyl group, indolyl group, indazolyl group, prynyl group, quinolyl group, quinolidienyl group, quinolyl group, phthalazienyl group, naphthidinyl group, quinoxanyl group, quinazolinyl group, cinnolinyl group. A nitrogen-containing heterocyclic group such as a group or a pteridinyl group; a heterocyclic group containing a plurality of heteroatoms such as a thiazolyl group and a benzothiazole group can be exemplified.</p><p> The above-mentioned aliphatic hydrocarbon group, aryl group and heterocyclic group may all contain one or more substituents. Examples of such a substituent include an alkyl group, a phenyl group, a hydroxyl group, a nitro group, a thiol group, a carbonyl group, a carboxyl group, an amino group, a nitrile, a nitro group, a sulfone group, a methoxy group and an ethoxy group.</p><p> Specific examples of the phosphine compound represented by the above general formula include trimethylphosphine, triethylphosphine, tri-n-butylphosphine, tri-tert-butylphosphine, tricyclohexylphosphine, tris (p-methoxyphenyl) phosphine, and tri-. O-trilphosphine, tri-2,4-kisilylphosphine, tribenzylphosphine, triphenylphosphine, diphenylphosphinestyrene, diphenyl-2-pyridylphosphine, tris (3-sulfonatophenyl) phosphine, bis (m-sulfo) Natophenyl) phenylphosphine, 3-sulfotriphenylphosphine, diphenylcyclohexylphosphine, tri (1-naphthyl) phosphine, tris (2-cyanoethyl) phosphine, tris (4,6-dimethyl-3-sulfanatophenyl) phosphine, Examples thereof include methyldiphenylphosphine and diethylphenylphosphine.</p><p> In the present invention, the phosphine compound can be used alone or in combination of two or more.</p><p> The electroless copper plating solution of the present invention may have the same composition as the known electroless copper plating solution except that the above-mentioned phosphine compound is contained as a stabilizer.</p><p> Specifically, the electroless copper plating solution composed of an aqueous solution containing a water-soluble copper compound, a complexing agent and a reducing agent may be used as a basic bath, and the above-mentioned phosphine compound may be added thereto.</p><p> The concentration of the phosphine compound in the plating solution is preferably about 0.01 mg / l to 100 g / l, and more preferably about 0.02 mg / l to 10 g / l. If the concentration of the phosphine compound is too low, sufficient stability cannot be imparted and the plating solution is easily decomposed, which is not preferable. On the other hand, if the concentration is too high, the precipitation rate of the plating film is lowered and the precipitation reaction may not occur, which is not preferable.</p><p> The water-soluble copper compound is not particularly limited, but for example, a water-soluble inorganic copper salt such as copper sulfate or copper chloride, a water-soluble organic copper salt such as copper acetate, copper tartrate, or ethylenediamine tetraacetate may be used. Can be done. These copper compounds can be used alone or in admixture of two or more.</p><p> The concentration of the water-soluble copper compound is preferably about 0.001 to 1 mol / l, more preferably about 0.01 to 0.3 mol / l. If the concentration of the water-soluble copper compound is too low, the deposition rate of the film becomes very slow and it takes a long time to form the film, which is not preferable. On the other hand, if the concentration of the water-soluble copper compound is too high, the viscosity of the plating solution becomes high, the fluidity of the solution decreases, the uniform precipitation property is adversely affected, and the cost increases, which is not preferable.</p><p> The complexing agent is an effective component for preventing the precipitation of the copper compound and further suppressing the decomposition at an appropriate rate of the copper precipitation reaction, and is used in various known electroless copper plating solutions. A complexing agent can be used.</p><p> Specific examples of such complexing agents include oxycarboxylic acids such as tartaric acid and malic acid, soluble salts thereof; amino compounds such as ethylenediamine and triethanolamine; ethylenediaminetetraacetic acid and versenol (N-hydroxyethylethylenediamine N, Ethylenediamine derivatives such as N', N'-triacetic acid), quadrol (N, N, N', N'-tetrahydroxyethylethylenediamine), soluble salts thereof; 1-hydroxyethane-1,1-diphosphonic acid, ethylenediamine Examples thereof include phosphonic acids such as tetramethylenephosphonic acid and soluble salts thereof. These complexing agents can be used alone or in admixture of two or more.</p><p> The concentration of the complexing agent varies depending on the type and is not particularly limited, but is usually preferably about 0.001 to 2 mol / l, and more preferably about 0.002 to 1 mol / l. If the concentration of the complexing agent is too low, precipitation of copper hydroxide is likely to occur, and further, the redox reaction is too fast, so that the plating solution is easily decomposed, which is not preferable. On the other hand, if the concentration of the complexing agent is too high, the precipitation rate of the plating film becomes very slow, and the viscosity of the plating solution becomes high, so that the uniform precipitation property is lowered, which is not preferable.</p><p> As the reducing agent, various reducing agents used in known electroless copper plating solutions can be used. Specific examples thereof include aldehyde compounds such as formaldehyde and glyoxylic acid; sodium borohydride compounds such as sodium borohydride, potassium borohydride and dimethylamine borane; and hydrazines.</p><p> The concentration of the reducing agent varies depending on the type and is not particularly limited, but is usually preferably about 0.001 to 1 mol / l, and more preferably about 0.002 to 0.5 mol / l. If the concentration of the reducing agent is too low, the reduction rate of copper ions in the plating solution becomes slow and it takes time to form a film, which is not preferable. On the other hand, if the concentration of the reducing agent is too high, the plating solution is likely to be decomposed, which is not preferable.</p><p> Further, various known additives contained in the electroless copper plating solution can be added to the electroless copper plating solution of the present invention, if necessary. Further, if necessary, the electroless copper plating solution may be stirred.</p><p> The electroless copper plating solution of the present invention preferably has a pH of about 3 to 14, and more preferably about pH 4 to 13. If the pH is too low, the smooth progress of the reduction reaction is hindered, the reducing agent is decomposed, the precipitation property of the plating is lowered, and the plating solution may be decomposed, which is not preferable. On the other hand, if the pH is too high, the stability of the plating solution tends to decrease, which is not preferable.</p><p> The liquid temperature for electroless copper plating varies depending on the specific composition of the plating solution, but is usually preferably about 0 ° C or higher, more preferably about 20 to 80 ° C. .. If the temperature of the plating solution is too low, the plating precipitation reaction becomes slow and the copper plating film is likely to be unprecipitated or have a poor appearance. On the other hand, if the temperature of the plating solution is too high, the plating solution evaporates violently, making it difficult to maintain the plating solution composition within a predetermined range, and further, decomposition of the plating solution is likely to occur, which is not preferable.</p><p> The type of the object to be plated is not particularly limited, and the same object as the object of ordinary electroless copper plating can be used as the object to be plated. Further, for an object to be plated having no catalytic activity such as plastics, electroless copper plating may be performed after applying a catalyst such as palladium according to a conventional method.</p>

<p> The stabilizer for electroless copper plating solution of the present invention contains a substance having higher safety as an active ingredient than cyanide compounds, metal compounds and the like used as conventional stabilizers for electroless copper plating. It is very useful because it has little adverse effect on the human body and the environment.</p><p> The electroless copper plating solution of the present invention containing such a stabilizer is unlikely to cause decomposition or abnormal precipitation of the plating solution, and does not significantly reduce the precipitation rate, and can be used stably for a long period of time. Further, the electroless copper plating film formed is a good film having almost no deterioration in physical properties such as ductility as in the case of adding a nitrogen-containing organic compound, a sulfur-containing organic compound, or the like, and has a good appearance.</p>

Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 An electroless copper plating solution was prepared by using two types of electroless copper plating solutions having the following compositions as a basic bath and adding the additives shown in Table 1 below.

Basic bath composition (formalin bath) Copper sulphate 0.04 mol / l EDTA 0.25 mol / l Formalin 0.13 mol / l Basic bath composition (glyoxylic acid bath) Copper sulphate 0.04 mol / l EDTA 0.25 mol / l Glyoxylic acid 0.20 mol / l

<tables num="1"><img file="JP2005290415A_D0004.tif" /></tables> Using each electroless copper plating solution containing the additives shown in Table 1, using a 5 x 5 cm 96% alumina ceramic plate as the object to be plated, pH 12.5, bath temperature 60 ° C, 1 hour without stirring. Electroless copper plating was performed to form a copper plating film.

The pretreatment process and chemicals used are as follows. (1) Solvent degreasing (brand name: OPC-370 Condiclean M, manufactured by Okuno Pharmaceutical Co., Ltd.) (2) Catalysis addition (brand name: OPC-80 catalyst, manufactured by Okuno Pharmaceutical Co., Ltd.) (3) Activity Chemicals (trade name: OPC-505 Accelerator, manufactured by Okuno Pharmaceutical Co., Ltd.) The characteristics of each electrolytic copper plating film formed by the above method were evaluated by the following method. The results are shown in Table 2 below. 1. Plating deposition rate Measured using a fluorescent X-ray film thickness meter. 2. Bending test Using a 5 x 5 mm stainless steel plate as the object to be plated, an electroless copper plating film is formed in the same manner as above, then the plating film is peeled off from the stainless steel plate, and a 180 ° bending test is performed. The number of times until it broke was calculated. 3. Appearance of the film The plating test piece was visually observed. 4. Bath stability After the plating treatment was completed, the plating solution was kept at the same temperature as the plating treatment temperature for 3 hours, and then the state of the plating solution was observed.

<tables num="2"><img file="JP2005290415A_D0005.tif" /></tables> As is clear from the above results, the plating solutions 1 to 7 of the present invention containing the phosphine compound did not significantly reduce the precipitation rate and had good bath stability. Further, the formed copper plating film had a good appearance, and the result of the bending test was also good and had excellent physical properties.

On the other hand, the comparative plating solution 1 containing no stabilizer could not form a plating film by decomposing during the temperature rise. The comparative plating solution 2 was excellent in bath stability and the deterioration of the physical properties of the plating film was small, but KCN used as a stabilizer is a highly toxic substance.

In the comparative plating bath 3, the physical properties and appearance of the formed plating film were inferior, and the bath stability was also insufficient. In the comparative plating bath 4, the precipitation rate was slow, and the physical properties and appearance of the formed plating film were inferior. Regarding the comparative plating bath 5 using 2-mercaptobenzothiazole as an additive, the formalin bath has no plating, and the glyoxyl bath can form a copper plating film, but the precipitation rate, the physical properties and appearance of the plating film will be different. Was also inferior.