JP2000309875A - Substitution type electroless silver plating solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a silver plating film having excellent characteristics with an electroless plating soln. which does not contain cyanogen compds. and has good stability by making an aq. soln. contg. a water soluble silver compd. and a water soluble sulfur-contg. organic compd. having mobosulfide groups in the molecule to be acidic. SOLUTION: In an aq. soln. contg. a water soluble silver compd. and a water soluble sulfur-contg. organic compd. having two monosulfide groups in the molecule, pH is controlled to <=7 with acid to obtain a substitution type electroless silver plating soln. extremely good in bath stability. Preferably, the sulfur-contg. organic compd. has water soluble groups such as hydroxyl group, carboxyl group, sulfonic group, amino group, phosphonic group and mercapto group in the molecules, it is composed of a compd. in which two pieces of 1 to 8C hydrocarbon groups are present between two pieces of monosulfide groups or a salt thereof, and the concn. thereof is preferably controlled to 0.5 to 150 g/l. Moreover, the concn. of the water soluble silver compd. such as silver oxide is controlled to 0.01 to 20 g/l. If required, 1 to 150 g/l thiourea compounds are moreover added as a precipitation improving agent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a substitution type electroless silver plating solution and an electroless silver plating method.

[0002]

2. Description of the Related Art When soldering or bonding to an electronic component, particularly a printed wiring board, usually, after electroless Ni-P plating is applied as a surface treatment of a base, Au is applied.
Plating has been performed. However, this treatment method is complicated because it requires many treatment steps, and has various problems in terms of wastewater treatment and management. Further, there is a problem that the cost is increased because expensive gold is used.

[0003] For this reason, a surface treatment using substitutional electroless silver plating instead of the above-mentioned treatment has been studied. In particular, from the viewpoint of toxicity and wastewater treatment, a cyanide-free substitutional type containing no cyanide is used. There is a need for an electroless silver plating solution. Examples of such a plating solution include, for example, those disclosed in
JP-A-232072 contains a silver ion and a complexing agent such as an amino acid and a polycarboxylic acid, and further contains a surfactant, a wetting agent, a stabilizer, a fine-granulating agent, a discoloration inhibitor and the like. An electrolytic silver plating solution is described. However,
With this electroless silver plating solution, it is possible to form a relatively thin plating film having a thickness of 0.5 μm or less, but the adhesion of the plating film decreases due to an increase in deposition rate and an increase in the film thickness. There are drawbacks. Further, there is a problem that the bath stability is insufficient and silver precipitation easily occurs when left for a long period of time.

Japanese Patent Publication No. 2-50991 discloses that
A method of treating a metal material using a substitutional electroless silver plating solution containing silver sulfate, aminocarboxylic acid, sodium carbonate, or the like and having a pH of 6 or more is described.

However, this electroless silver plating solution also has
Bath stability is not sufficient, and there is a disadvantage that silver precipitates easily occur on standing, which is a great hindrance to practical use. In addition, the obtained film is rough and poor in adhesion, and there is a problem in drainage treatment.

[0006]

SUMMARY OF THE INVENTION The main object of the present invention is to:
It is an object of the present invention to provide a substitution type electroless silver plating solution which is a plating solution containing no cyanide compound, has good bath stability, and can form a silver plating film having excellent characteristics.

[0007]

Means for Solving the Problems The present inventor has made intensive studies in order to solve the problems of the prior art as described above. As a result, the substitution-type electroless silver plating solution comprising a water-soluble silver compound and an aqueous solution containing a water-soluble sulfur-containing organic compound having two monosulfide groups in a molecule and having a pH of 7 or less has extremely high bath stability. It is good and can be used for a long time,
The inventors have found that the formed plating film has excellent film characteristics such as adhesion and appearance, and have completed the present invention.

That is, the present invention provides the following substitution type electroless silver plating solution, an electroless silver plating method, and a silver-plated product. 1. PH 7 containing a water-soluble silver compound and a water-soluble sulfur-containing organic compound having two monosulfide groups in the molecule
A substitution type electroless silver plating solution comprising the following aqueous solution. 2. A water-soluble sulfur-containing organic compound having two monosulfide groups in a molecule has a hydroxyl group, a carboxyl group,
It has at least one water-soluble group selected from a sulfonic acid group, an amino group, a phosphone group and a mercapto group, and has a divalent hydrocarbon group having 1 to 8 carbon atoms between two monosulfide groups. Item 2. The electroless silver plating solution according to the above item 1, wherein the electroless silver plating solution is at least one selected from a compound present and a salt of the compound. 3. The water-soluble silver compound is used in an amount of 0.01 to 20 as a silver metal amount.
3. The electroless silver plating solution according to the above item 1 or 2, comprising an aqueous solution containing 0.5 to 150 g / l of a water-soluble sulfur-containing organic compound having two monosulfide groups in a molecule containing the compound in an amount of 0.5 g / l. 4. The above-mentioned items 1 to 3 containing 5 to 200 g / l of at least one acid selected from borofluoric acid, methanesulfonic acid, p-toluenesulfonic acid, p-phenolsulfonic acid, tartaric acid, gluconic acid and citric acid The electroless silver plating solution according to any one of the above. 5. Item 1 containing 1 to 150 g / l of thioureas
5. The electroless silver plating solution according to any one of 4. 6. 6. An electroless silver plating method, characterized by immersing an object to be plated in the substitutional electroless silver plating solution according to any one of the above items 1 to 5 at a bath temperature of 10 to 80 ° C. 7. Item 7. A silver-plated product on which a silver plating film is formed by the method of the above item 6.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electroless silver plating solution of the present invention is an aqueous solution containing, as essential components, a water-soluble silver compound and a water-soluble sulfur-containing organic compound having two monosulfide groups in a molecule. .

As the water-soluble silver compound, any monovalent silver compound which is adjusted to a predetermined pH range and is soluble in the plating solution of the present invention can be used without particular limitation. For example, in addition to silver oxide,
Silver salts such as various organic acids and inorganic acids can be used.
In particular, silver oxide, silver sulfate, silver chloride, silver nitrate and the like are preferable in that they have good solubility. In addition, when an acid is added for pH adjustment, the use of a silver salt having the same kind of anion as the acid used for pH adjustment can prevent the accumulation of extra anion components. The water-soluble silver compounds can be used alone or in combination of two or more.

The amount of the water-soluble silver compound is preferably about 0.01 to 20 g / l in terms of silver metal.
More preferably, it is 0.05 to 10 g / l. When the amount of silver metal is in the above range, the deposition rate becomes practically sufficient, and the stability of the plating solution becomes good. If the amount of silver metal is too small, the deposition rate is undesirably reduced. Further, even if the amount of the silver compound exceeds the above range, there is no problem in plating performance, but it is not economically preferable because the pumping amount increases.

The water-soluble sulfur-containing organic compound having two monosulfide groups in the molecule includes two monosulfide groups in the molecule and a hydroxyl group, a carboxyl group, a sulfonic acid group, and an amino group in the molecule. Having at least one water-soluble group selected from a phosphonic acid group and a mercapto group, and having 1 to 8 carbon atoms between two monosulfide groups.
Compounds having two divalent hydrocarbon groups, alkali metal salts and ammonium salts of the compounds are preferred. One or more water-soluble groups may be present in the molecule, but preferably two or more. The water-soluble sulfur-containing organic compound includes 1
Species can be used alone or in combination of two or more.

Preferred examples of the water-soluble sulfur-containing compound include compounds represented by the following general formula and salts thereof.

X—R ₁ —S—R ₂ —S—R ₃ —Y (wherein R ₁ , R ₂ and R ₃ are the same or different and each is a straight or branched chain having 1 to 8 carbon atoms) The chain alkylene group, X and Y are the same or different and are a hydroxyl group, a carboxyl group, a sulfonic acid group, an amino group, a phosphonic acid group or a mercapto group.) Specific examples of the water-soluble sulfur-containing organic compound include: 1,2-
Bis (2-hydroxyethylthio) ethane, 2,2′-
(Ethylenedithio) diethanethiol, 1,4-bis (2-hydroxyethylthio) butane, 3,3 ′-(propylenedithio) dipropionic acid, salts of these compounds (alkali metal salts, ammonium salts), etc. Can be mentioned.

The compounding amount of the water-soluble sulfur-containing organic compound is as follows:
It is preferably about 0.5 to 150 g / l,
More preferably, it is about 100 g / l. By blending the water-soluble sulfur-containing organic compound, the plating solution can be stabilized for a long period of time, and a silver film having good adhesion and appearance can be formed. If the amount of the water-soluble sulfur-containing organic compound is insufficient, it is difficult to maintain bath stability for a long time, which is not preferable. On the other hand, if the amount of the sulfur organic compound exceeds the above range, there is no problem in plating performance, but it is economically unfavorable because the removal of the plating solution increases.

The plating solution of the present invention needs to have a pH of 7 or less. If the pH is higher than this, the stability of the plating solution is undesirably reduced. The pH may be adjusted as necessary using an organic acid such as an organic sulfonic acid or a carboxylic acid, or an inorganic acid such as sulfuric acid, nitric acid, or borofluoric acid. Examples of the organic sulfonic acid include methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid, 2-propanesulfonic acid, butanesulfonic acid, 2-butanesulfonic acid,
Pentanesulfonic acid, chloropropanesulfonic acid, 2-
Hydroxyethane-1-sulfonic acid, 2-hydroxypropane-1-sulfonic acid, 2-hydroxybutane-1-
Sulfonic acid, 2-hydroxypentanesulfonic acid, p-
Toluenesulfonic acid, p-phenolsulfonic acid and the like can be used. As organic carboxylic acids, tartaric acid,
Malic acid, citric acid, succinic acid, gluconic acid and the like can be used.

These acids can be used singly or as a mixture of two or more, and the amount of the acid used may be such that the pH of the plating solution becomes 7 or less. The lower limit of the pH is not particularly limited, but an excessive amount of the acid is not economically preferable in terms of taking out the liquid. For this reason, the addition amount of the acid is preferably about 200 g / l or less, and more preferably about 150 g / l or less.

Among the above-mentioned acids, in particular, borofluoric acid, methanesulfonic acid, p-toluenesulfonic acid, p-toluenesulfonic acid
When phenolsulfonic acid, tartaric acid, gluconic acid, citric acid, or the like is added, the stability of the plating solution can be further improved. In order to exert such effects, the amount of these acids is preferably about 5 to 200 g / l, more preferably about 10 to 150 g / l.

In order to raise the pH of the plating solution, alkali hydroxide, aqueous ammonia or the like may be used.

The electroless silver plating solution of the present invention may further contain thioureas, if necessary. By adding thioureas, the deposition rate is improved and the thickness can be increased without impairing the adhesion between the plating film and the material.

As thioureas, in addition to thiourea,
1,3-dimethylthiourea, trimethylthiourea, tetramethylthiourea, diethylthiourea, N, N′-diisopropylthiourea, allylthiourea, acetylthiourea, ethylenethiourea, 1,3-diphenylthiourea,
Thiourea dioxide, thiosemicarbazide and the like can be used.

The thioureas can be used alone or in admixture of two or more, and the amount used is 1 to 150 g / l.
And preferably about 5 to 100 g / l.

The electroless silver plating solution of the present invention may further contain, if necessary, various additives conventionally incorporated in the electroless silver plating solution, for example, a pH buffer, a surfactant,
A silver discoloration inhibitor or the like can be added. Examples of the pH buffer include boric acid, phosphinic acid, phosphonic acid, phosphoric acid, 2-phosphoric acid, tripolyphosphoric acid, acetic acid, citric acid, tartaric acid, and other sodium salts, potassium salts, ammonium salts, and the like, and ammonium chloride and ammonium sulfate. Etc.
One type may be used alone, or two or more types may be used in combination. p
The amount of the H buffer added is not particularly limited, but is usually preferably about 1 to 100 g / l, preferably 10 to 100 g / l.
More preferably, it is set to about 50 g / l.

As the surfactant, any of a nonionic surfactant, an amphoteric surfactant, an anionic surfactant and a cationic surfactant can be used, and a nonionic surfactant is particularly preferable. Specific examples of the nonionic surfactant include nonylphenol polyalkoxylate,
α- (or β-) naphthol polyalkoxylate and the like can be mentioned. Regarding the amount of surfactant added,
Although not particularly limited, it is usually preferably about 0.01 to 40 g / l, more preferably about 0.05 to 10 g / l.

As the silver discoloration inhibitor, a known compound may be used, and for example, a triazole derivative such as benzotriazole can be used. The amount of the discoloration inhibitor is not particularly limited, but is usually 0.01 to 50 g /
1 and more preferably about 0.05 to 10 g / l.

In order to perform plating using the substitutional electroless silver plating solution of the present invention, the object to be plated is immersed in the plating solution adjusted to pH 7 or less while stirring the plating solution as necessary. Good. The temperature of the plating solution is preferably in the range of about 10 to 80 ° C. The plating time is not particularly limited, and the object to be plated may be immersed in a plating solution until a plating film of a required thickness is deposited, and the plating time is usually in a range of about 1 minute to 30 minutes. Good. Also, a plating film can be formed by a method of spraying a plating solution onto an object to be plated.

The material to be plated may be any material capable of replacing and depositing silver in the plating solution of the present invention.
Various types of articles including portions of copper alloy, zinc, iron, nickel and the like can be plated. The shape of the object to be plated is not particularly limited, and for example, plating can be performed on articles having various shapes such as a plate shape and a powder shape.

Using the plating solution of the present invention, copper, copper alloy,
When a plating film is formed on a printed board using nickel, a nickel alloy, or the like, a plating film having excellent pattern deposition properties can be formed without impairing the adhesiveness of the resist.

[0029]

The substitution type electroless silver plating solution of the present invention has good bath stability, has an appropriate deposition rate, can be thickened, and can be easily drained. The silver plating film formed using the plating solution is dense and has excellent pattern deposition properties, and also has good adhesion, corrosion resistance, electrical properties, solderability, and the like.

[0030]

Next, the present invention will be described in detail with reference to examples and comparative examples, but the present invention is not limited to the following examples. (Example 1) One liter of an electroless silver plating solution having the following composition was prepared.

Silver methanesulfonate 10 g / l (as silver) Methanesulfonic acid 100 g / l 1,4-bis (2-hydroxyethylthio) ethane 25 g / l pH 0.5 Bath temperature 40 ° C. Rolled copper plate as plating object (Surface area: 0.5 dm ² ), which was degreased, immersed in the above electroless silver plating solution, and plated for 3 minutes while moving the object to be plated at a speed of 1 m / min using a rocking device. Was.

The appearance of the formed silver plating film,
The adhesion of the plating film and the plating film thickness were evaluated by the following methods. The results are shown in Table 1 below. Plating film evaluation method * Appearance: Evaluated visually. * Adhesiveness of plating film: 1 x 1 cm wide plating surface is cut in 1 mm intervals horizontally and vertically using a cutter knife to make 100 squares. Adhesive tape is stuck on this surface, and momentum is applied. The cells were peeled well and the number of peeled cells was obtained. * Film thickness: The plating film was dissolved with nitric acid and measured using an ICP emission spectrometer (SPS4000 manufactured by Seiko Instruments Inc.). (Example 2) A silver plating film was formed in the same manner as in Example 1 except that an electroless silver plating solution having the following composition was used, and the appearance, adhesion of the plating film, and plating film thickness were evaluated.
The results are shown in Table 1 below.

Silver nitrate 5 g / l (as silver) 1,4-bis (2-hydroxyethylthio) butane 40 g / l 2,2 ′-(ethylenedithio) diethanethiol 90 g / l pH 3.0 (with dilute nitric acid) Adjustment) Bath temperature 25 ° C (Example 3) A silver plating film was formed in the same manner as in Example 1 except that an electroless silver plating solution having the following composition was used, and the appearance, adhesion of the plating film, and plating film thickness were obtained. Was evaluated.
The results are shown in Table 1 below.

Silver oxide 1 g / l (as silver) p-toluenesulfonic acid 30 g / l tartaric acid 50 g / l 2,2 ′-(ethylenedithio) diethanethiol 45 g / l thiourea 20 g / l β-naphthol polyethoxylate (EO15) 5 g / l pH 6.5 (adjusted with NaOH) Bath temperature 70 ° C (Comparative Example 1) Same as Example 1 except that the plating time was 30 minutes using an electroless silver plating solution having the following composition. Then, a silver plating film was formed, and the appearance, adhesion of the plating film, and plating film thickness were evaluated. The results are shown in Table 2 below.

Silver sulfate 3 g / l EDTA-4H 15 g / l Sodium carbonate 10 g / l pH 8.8 (adjusted with sodium carbonate) Bath temperature 25 ° C. (Comparative Example 2) Plating using an electroless silver plating solution having the following composition A silver plating film was formed in the same manner as in Example 1 except that the time was set to 3 minutes, and the appearance, adhesion of the plating film, and plating film thickness were evaluated. The results are shown in Table 2 below.

N, N, N ′, N′-tetrakis- (2-hydroxypropyl) ethylenediamine 50 g / l silver nitrate 1 g / l pH 8.0 (adjusted with NaOH) Bath temperature 20 ° C. (Comparative Example 3) Using an electroless silver plating solution, a plating time was set to 3 minutes, and a silver plating film was formed in the same manner as in Example 1, and the appearance, adhesion of the plating film, and plating film thickness were evaluated. The results are shown in Table 2 below.

Tartaric acid 60 g / l Silver nitrate 1 g / l Benzotriazole 1 g / l pH 4.0 (adjusted with NaOH) Bath temperature 20 ° C. (Comparative Example 4) Using an electroless silver plating solution having the following composition, plating time was 3 minutes In the same manner as in Example 1, a silver plating film was formed, and the appearance, adhesion of the plating film, and plating film thickness were evaluated. The results are shown in Table 2 below.

Diethylenetriaminepentaacetic acid 50 g / l Silver nitrate 15 g / l β-naphthol polyethoxylate (EO15) 5 g / l pH 7.0 (adjusted with NaOH) Bath temperature 45 ° C.

[0039]

[Table 1]

[0040]

[Table 2]

As is clear from the above results, Example 1
By performing displacement plating using the plating solutions of Nos. 1 to 3, a silver plating film having excellent appearance and adhesion was formed.

On the other hand, when the plating solutions of Comparative Examples 1 to 4 were used, the obtained films turned from rough gray to black-gray, and unevenness was observed. Admitted. Storage Test Each plating solution used in Examples 1 to 3 and Comparative Examples 1 to 4 was left at room temperature for 4 weeks, and then subjected to a plating test in the same manner as in each Example and Comparative Example.

As a result, no precipitation was observed in any of the plating solutions of Examples 1 to 3, and the plating test results were equivalent to those at the time of the bathing.

On the other hand, with respect to the plating solutions of Comparative Examples 1 to 4, black precipitates presumed to be oxides or hydroxides of silver were observed. Each plating solution was filtered, and the same plating test was performed. However, the deposition rate was reduced to about 50% of that during bathing. As can be seen from the above results, the substitutional electroless silver plating solution of the present invention has no bathing even when left for a long period of time, has good bath stability, and has excellent appearance, adhesion and the like. A plating film can be formed.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yasuhiro Tanabe 1-10-25 Higashi Higashi, Tsurumi-ku, Osaka City, Osaka Prefecture F-term inside Okuno Pharmaceutical Co., Ltd. 4K022 AA02 AA42 BA01 DA01 DB01 DB02 DB03 DB04 DB07 DB08

Claims (7)

[Claims] A substitution type electroless silver plating solution comprising an aqueous solution having a pH of 7 or less containing a water-soluble silver compound and a water-soluble sulfur-containing organic compound having two monosulfide groups in a molecule. 2. A water-soluble sulfur-containing organic compound having two monosulfide groups in a molecule, wherein at least one selected from a hydroxyl group, a carboxyl group, a sulfonic acid group, an amino group, a phosphone group and a mercapto group in the molecule. Having two or more water-soluble groups and two monosulfide groups having 1 to 8 carbon atoms.
The electroless silver plating solution according to claim 1, wherein the electroless silver plating solution is at least one selected from a compound having a valent hydrocarbon group and a salt of the compound. 3. The method according to claim 1, wherein the water-soluble silver compound is contained in an amount of 0.0
0.5 to 150 g of a water-soluble sulfur-containing organic compound containing 1 to 20 g / l and having two monosulfide groups in a molecule.
The electroless silver plating solution according to claim 1, comprising an aqueous solution containing 1 / l. 4. Borofluoric acid, methanesulfonic acid, p
The electroless silver plating solution according to any one of claims 1 to 3, comprising at least one acid selected from toluene-sulfonic acid, p-phenolsulfonic acid, tartaric acid, gluconic acid, and citric acid in an amount of 5 to 200 g / l. . 5. The electroless silver plating solution according to claim 1, comprising 1 to 150 g / l of a thiourea. 6. An electroless silver plating method comprising immersing an object to be plated in the substitutional electroless silver plating solution according to claim 1 at a bath temperature of 10 to 80 ° C. 7. A silver-plated product on which a silver plating film is formed by the method of claim 6.