JPH06145996A - Electroless gold plating liquid - Google Patents

Abstract

PURPOSE:To improve cost effectiveness and workability by preparing the electroless gold plating liquid which is specified in components consisting of chloroauric acid, sulfurous acid, etc., thereby making a plating bath usable in a stable state over a long period of time. CONSTITUTION:The formation of the precipitate of gold when 2g/l Na chloroaurate as gold, 10g/l Na sulfite, 20g/l Na thiosulfate, 40g/l Na L- ascorbate, 9g/l hydrogen phosphate=Na, 3g/l dihydrogen phosphate-Na, and 7.0 pH are used as the electroless gold plating liquid A and 6-ethoxy-2- mercaptobenzothiazole is added to the soln. in assessed. Consequently, there is no formationof the gold precipitate for two days without addition there of after prepn. of the liquid A, for 6 days with addition of 0.5ppm and 30 days with a bath added with its 5.0ppm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to gold chloride (I
II) An electroless gold plating solution using a gold (I) complex salt of acid or sulfurous acid or thiosulfate.

[0002]

BACKGROUND ART The electroless gold plating method is widely used in the electronic industry field where plating is required for complicated fine circuits and isolated parts where leads are difficult to take due to its excellent functional characteristics. Conventionally, as an electroless gold plating solution which is generally used, a solution containing a highly toxic cyanide compound as a complexing agent for gold (I) ions is used.
It was customary to use this under high temperature and strong alkaline conditions. Therefore, when it is used in the above-mentioned applications, there is a problem that the resist used for masking the circuit is peeled off, or the base of the ceramic substrate is eroded by an alkali, and electroless gold containing a cyanide compound. The plating bath is very toxic, and there are problems in handling, storage and management, and there are problems in safety of the actual working environment and economical aspects of waste liquid treatment.

On the other hand, as a gold plating solution which does not use a cyanide compound, a gold plating solution using gold (IH) chloride as a gold source is known as a typical one (for example, US Pat. No. 4,142,902, British Patent). 2114159). The gold plating solution using this chloroauric acid (III) salt is said to form a gold complex salt thereof with the chloroauric acid (III) salt and the salt of sulfurous acid or thiosulfuric acid as a constituent component. It has been put to practical use as a plating solution that does not use.

The present inventors have previously reported that the above-mentioned gold chloride (II
I) As an improvement of an electroless gold plating solution using an acid as a gold source, a gold plating solution using ascorbic acid as a reducing component was provided (see JP-A-1-191782). This electroless gold plating solution is composed of gold (III) chloride acid or its salt, sulfurous acid or thiosulfuric acid alkali metal salt or ammonium salt,
Ascorbic acid or its salt is used as a composition component, a practical plating rate can be obtained at low temperature and near neutral pH conditions, and the masked resist can be peeled off without attacking the ceramic substrate. It is an excellent material that can be used as a gold plating solution for fine circuits and leads of printed circuit boards and the like.

However, even with this electroless gold plating solution, there are problems to be solved in terms of stability, such as the formation of a small amount of precipitate during use and the precipitation of fine gold particles during storage after the bath is made. However, it is not satisfactory. In this case, a gold plating bath using a gold (I) sulfite complex salt or a gold (I) thiosulfate complex salt as a gold source, or gold capable of internally forming a gold complex from a gold (III) chloride salt and sulfurous acid or thiosulfate. The reason why the stability of the plating bath is not maintained has not been empirically revealed, but the following reasons are considered.

Sulfite ion during storage or during plating,
The natural oxidation of oxidative components such as thiosulfate ion and the decrease in concentration change the equilibrium in the solution, destabilize the gold complex, increase the gold activity and facilitate bath decomposition, and increase the oxidation activity of ascorbic acid in trace amounts. Contamination by metal ions of
For example, the generation of fine gold particles occurs by using these as nuclei to accelerate the decomposition.

[0007]

DISCLOSURE OF THE INVENTION As a result of intensive studies aimed at improving the stability of an electroless gold plating solution, the present inventors have found that (a) gold (III) chloride acid or its salt or sulfurous acid as a gold source, or Electroless consisting of an aqueous solution containing a gold (I) complex salt of thiosulfate, (b) an alkali metal salt or ammonium salt of sulfite or thiosulfate, (c) ascorbic acid or a salt thereof, and (d) a pH buffering agent as constituent components. 6-ethoxy-2-mercaptobenzothiazole,
By containing a compound selected from 2-mercaptobenzimidazole, 2-mercaptobenzoxazole and salts thereof, it is possible to remarkably improve the stability of the plating solution during storage and during plating, and long-term use and long-term use. It was found that the stability of the plating solution during storage can be improved. The present invention has been made based on such findings.

That is, the present invention provides (a) gold (III) chloride or a salt thereof as a gold source or a gold (I) complex salt of sulfurous acid or thiosulfuric acid, (b) an alkali metal salt of sulfurous acid or thiosulfuric acid, or ammonium. Salt, (c) ascorbic acid or salt thereof, (d) pH buffer and (e) selected from 6-ethoxy-2-mercaptobenzothiazole, 2-mercaptobenzimidazole, 2-mercaptobenzoxazole and salts thereof. An electroless gold plating solution containing a compound is provided.

The present invention will be described in detail below.

A preferred embodiment of the electroless gold plating solution according to the present invention is explained as follows.

As a gold salt, 0.001 to 0.10 mol /
Liter, sodium sulfite 0.01-1.0 mol /
Liter, sodium thiosulfate 0.01-1.0 mol
/ Liter, sodium phosphate 0.01-1.0 mol
/ Liter, ascorbic acid or its sodium salt
001 to 1.0 mol / liter and 6-ethoxy-2
-Containing 6 × 10 ^{−7 to} 3 × 10 ⁻³ mol / liter as mercaptobenzothiazole, 2-mercaptobenzimidazole or 2-mercaptobenzoxazole.

The present inventors have made various studies on the relationship between the composition of the electroless gold plating solution according to the present invention and the obtained plating rate and stability of the plating solution, and have obtained the following findings.

(1) Gold chloride (I
The amount of the acid (II) or its salt or the gold (I) complex salt of sulfurous acid or thiosulfuric acid is 0.001 to 0.1 m.
ol / liter is preferable, but 0.00 is particularly preferable.
It is 5 to 0.05 mol / liter. 0.001mo
If it is less than 1 / liter, a practical plating rate cannot be obtained,
Further, if it is 0.1 mol / liter or more, precipitation of gold is likely to occur and it is economically disadvantageous.

(2) Regarding the sulfite salt, for example, as a sodium salt, 0.01 to 1.0 mol / liter is preferable, and 0.04 to 0.5 mol / liter is particularly preferable. If it is 0.01 mol / liter or less, the solution is unstable and easily decomposes, and if it is 1.0 mol / liter or more, the plating rate remarkably decreases, which is not preferable in practice.

(3) Regarding the thiosulfate, for example, as a sodium salt, 0.01 to 1.0 mol / liter is preferable, and 0.04 to 0.5 mol is particularly preferable.
/ Liter. If the amount is less than 0.01 mol / liter, the plating solution lacks stability and easily decomposes.
If it is more than mol / liter, no particular effect is shown in the plating reaction.

(4) As the pH buffering agent, for example, a buffer solution prepared with sodium hydrogen phosphate is suitable, and its content is preferably 0.01 to 1.0 mol / liter, particularly preferably 0. .05 to 0.5 mol
/ Liter. If the amount is 0.01 mol / liter or less, the plated surface tends to be rough. At 1.0 mol / liter or more, no particular effect is expected.

(5) Ascorbic acid, for example, as a sodium salt is preferably 0.001 to 1.0 mol / liter, and particularly preferably 0.01 to 0.5 m.
ol / liter. If it is 0.001 mol / liter or less, the plating rate is slow, and if it is 1.0 mol / liter or more, the plating solution becomes unstable and decomposition is likely to occur.

(6) 6-ethoxy-2-mercaptobenzothiazole, 2-mercaptobenzimidazole,
Regarding 2-mercaptobenzoxazole, its derivative or its salt, 6 × 10 ^{−7 to} 3 × 10 ⁻³
mol / liter is preferable, and 6 × 1 is particularly preferable.
It is 0 ^{−6 to} 6 × 10 ⁻⁵ mol / liter. 6x1
If it is ^0-7 mol / liter or less, the plating solution becomes unstable and decomposition is likely to occur, which is not preferable. Also, 3 × 10
^{If it is -3} mol / liter or more, the stability of the plating solution increases, but the plating rate becomes slow, which is not preferable.

(7) pH of plating solution during use
Is adjusted appropriately with sulfuric acid or caustic soda solution within the range in which the components of the plating solution are not decomposed. A preferred pH range is 5 to 9, particularly pH 6 to 8.

(8) The operating temperature of the plating solution is 50-80.
The temperature can be selected in the range of 50 ° C, preferably 50 to 70 ° C, more preferably 55 to 65 ° C. Being able to plate at such low temperatures is particularly advantageous when the object to be plated is a non-temperature resistant object, which further saves energy and is safe for the operator. Also brings excellent advantages over conventional electroless gold plating solutions.

[0021]

EXAMPLES Next, the present invention will be specifically described with reference to examples of the present invention.

Example 1 An electroless gold plating solution (A) having the following composition was used, and 0.5 ppm, 1.0 ppm and 2.5 ppm shown in Table 1 were used.
Each liquid containing 6-ethoxy-2-mercaptobenzothiazole at various concentrations of ppm and 5.0 ppm was prepared. The stability of each of these solutions when stored at room temperature was investigated. The results are shown in Table 1 below.

Electroless Gold Plating Solution (A) Sodium Chloride (III) Chloride As Gold 2 g / L Sodium Sulfite 10 g / L Sodium Thiosulfate 20 g / L L-Sodium Ascorbate 40 g / L Disodium Hydrogen Phosphate 9 g / L Sodium dihydrogen phosphate 3 g / L pH 7.0

As seen in Table 1, 6-ethoxy-2
-In the bath containing no mercaptobenzothiazole (Comparative Example 1), a gold precipitate was already formed on the second day after the bath, which was unstable and difficult to use for a long time and to store for several days after the bath. is there.

On the other hand, 6-ethoxy-2-mercaptobenzothiazole 0.5 ppm, 1.0 ppm, 2.
In each addition bath (Example) of 5 ppm and 5.0 ppm,
1.0ppm and 2.5 for 6 days with 0.5ppm addition
No precipitation of gold was generated during each period of 15 days in each ppm bath and 30 days in 5.0 ppm addition bath, and the stability was significantly improved compared to the case of no addition, long-term room temperature It was possible to store in. It was also found that the higher the concentration of 6-ethoxy-2-mercaptobenzothiazole added, the better the stability. From these examples, the electroless gold plating solution according to the present invention is
It is recognized that it exerts a remarkable effect in improving the stability of the bath.

[0026]

[Table 1]

Example 2 An electroless gold plating solution (B) having the following composition was used, and 50 ppm, 100 ppm, 250 ppm shown in Table 2 were added thereto.
Each liquid containing 2-mercaptobenzoxazole at various concentrations of 500 ppm was prepared. The stability of each of these solutions when stored at room temperature was investigated. The results are shown in Table 2 below.

Electroless Gold Plating Solution (B) Gold (I) Sodium Sulfite 2 g / L Sodium sulfite 10 g / L Sodium thiosulfate 25 g / L L-Sodium ascorbate 40 g / L Disodium hydrogen phosphate 9 g / L Phosphorus Sodium dihydrogen acid 3 g / L pH 7.0

As can be seen from Table 2, in the bath containing no 2-mercaptobenzoxazole (Comparative Example 2), a gold precipitate was already formed on the third day after the bath was built, which was unstable for a long time. It is also difficult to use, and it is also difficult to store for several days after building the bath.

On the other hand, 2-mercaptobenzoxazole 50 ppm, 100 ppm, 250 ppm, 50
In each addition bath of 0 ppm (Example), 100 ppm, 250 ppm, 50
At 0 ppm, no gold precipitate was formed in the period of 30 days, the stability was significantly improved as compared with the case of no addition, and it was possible to store at room temperature for a long time. Also,
It was also found that the higher the concentration of 2-mercaptobenzoxazole added, the better the stability. From these examples, it is recognized that the electroless gold plating solution according to the present invention has a remarkable effect in terms of bath stability.

[0031]

[Table 2]

Example 3 An electroless gold plating solution (C) having the following composition was prepared, and 6-methoxy-2-mercaptobenzothiazole was added thereto.
Using a solution containing each of the concentrations of 5 ppm, 1 ppm, 2 ppm, and 2.5 ppm, as a plating test piece, a rolled nickel plate having a size of 2 cm × 2 cm and a thickness of 0.1 mm was coated with a nickel film having a thickness of 3 μm. , Next, thickness 3μ
Using the electroplated gold film of m, each was plated for 6 hours under a bath load of 1.2 dm ² / L, a temperature of 60 ° C., and stirring conditions. The results are shown in Table 3 below.

Electroless Gold Plating Solution (C) Sodium Gold (I) Sulfite 2 g / L Sodium sulfite 15 g / L Sodium thiosulfate 30 g / L L-Sodium ascorbate 40 g / L Disodium hydrogen phosphate 12 g / L Phosphorus Monosodium dihydrogen acid 4 g / L pH 7.0

[0034]

[Table 3]

As seen in Table 3, 6-ethoxy-2
-In the bath containing no mercaptobenzothiazole (Comparative Example 3), formation of a trace amount of gold precipitate started in about 3 hours, and it was difficult to use for 6 hours or more.

On the other hand, in the 6-ethoxy-2-mercaptobenzothiazole addition bath (Example), no gold precipitate was observed during the plating for 6 hours, and the bath stability was remarkably improved. It was recognized that Regarding the deposition rate of gold, the plating rate was almost the same as that of the additive-free bath (Comparative Example) when the amount of 6-ethoxy-2-mercaptobenzothiazole added was 2 ppm or less, and there was no decrease in the rate with the improvement in stability. I was not able to admit. However, 6-
Ethoxy-2-mercaptobenzothiazole 2.5pp
It was confirmed that the deposition rate slightly decreased when m was added.

The appearance of the precipitate was reddish yellow matte in the additive-free comparative example, whereas it was a bright yellow semi-gloss in the examples, showing a good appearance.

From these examples, it is recognized that the electroless gold plating solution according to the present invention has an excellent effect on the stability of the bath, does not adversely affect the deposition rate, and has a good deposition appearance. .

Example 4 An electroless gold plating solution (D) having the following composition was prepared, and 50 ppm of 2-mercaptobenzoxazole was added thereto.
Using solutions containing the respective concentrations of 0 ppm, 250 ppm, and 500 ppm, and using the same treatment as that used in Example 3 as a plating test piece, a bath load of 0.8
Plating was performed for 6 hours under a stirring condition of dm ² / L, temperature of 60 ° C. The results are shown in Table 4 below.

Electroless Gold Plating Solution (D) Gold (I) Sulfite Sodium 2 g / L Sodium Sulfite 12.5 g / L
L sodium thiosulfate 25 g / L L-sodium ascorbate 40 g / L disodium hydrogen phosphate 9 g / L monosodium dihydrogen phosphate 3 g / L pH 7.0

[0041]

[Table 4]

As can be seen from Table 4, in the bath containing no 2-mercaptobenzoxazole (Comparative Example 4), a trace amount of gold precipitate started to form in the bath in about 2 hours, and the bath was used for 6 hours or more. It was difficult to do.

On the other hand, in the 2-mercaptobenzoxazole-added bath (Example), no gold precipitate was formed during the plating for 6 hours, and the bath stability was remarkably improved. Admitted. Regarding the deposition rate of gold, the plating rate of the 2-mercaptobenzoxazole-added bath was almost the same as that of the additive-free bath (Comparative Example 4) at any addition concentration, and the rate associated with improvement in stability was No decrease was observed.

The appearance of the precipitate was reddish yellow matte in the case of the non-added comparative example, whereas that of the example was good in light yellow semigloss.

From these examples, the electroless gold plating solution according to the present invention has an excellent effect on the stability of the bath, and has a good deposition appearance without adversely affecting the deposition rate. Is recognized.

Example 5 A gold plating bath in which 25 ppm of 2-mercaptobenzimidazole was added to the electroless gold plating solution (A) was prepared, and the same plating sample as in Example 3 was used under the same plating conditions. After 6 hours of plating under room temperature, the plate was left overnight at room temperature, and then the following day, the plating was repeated under the same conditions every day for 5 consecutive days. 2 as a comparative example
-Plating was performed under the same conditions even when mercaptobenzimidazole was not added.

As a result, in the case of the 2-mercaptobenzimidazole-free bath, it was possible to plate at an average plating rate of 0.85 μm / hr for 6 hours on the first day, but about 3 hours on the first day. Precipitation of fine gold particles was generated in the plating solution at the time of plating, and further, the precipitation of gold was gradually increased during standing overnight at room temperature, and generation of a large amount of precipitation was observed on the next day. Therefore, plating could not be performed after the second day. On the other hand, in the 2-mercaptobenzimidazole 25 ppm addition bath, no decomposition product was found in the bath such as gold precipitate during the plating period of 5 days, and about 10% a day was observed due to the repeated work every day. It was possible to carry out the plating operation for 5 days, although the speed was reduced to some extent. The average plating rate for 6 hours was 0.85 μm / hr on the first day, the second day,
0.77 μm / hr, 3rd day, 0.72 μm / hr, 4
Day 6, 0.66 μm / hr, Day 5, 0.60 μm / h
It was r. From the results of these examples, it is recognized that the inclusion of 2-mercaptobenzimidazole has an excellent effect on the stability of the plating bath, and the generation of decomposed products in the storage state of the solution once heated is also prevented. Therefore, it was confirmed that repeated use over a long period of time was possible.

Example 6 An electroless gold plating solution (E) having the following composition and a solution containing 2 ppm of 6-ethoxy-2-mercaptobenzothiazole were prepared, and each plating bath was used in an unused state. It was stored at room temperature for each storage period shown in Table 5 below.

Using a portion of the plating solution for each of these storage periods, a plating test piece treated in the same manner as in Example 3 was used, and a bath load of 0.8 dm ² / L, a temperature of 60 ° C., and stirring conditions of 6 were used. Time plating was performed, and the speed and finish appearance of each plating solution stored in each storage period were compared. The results are shown in Table 5 below.

Electroless Gold Plating Solution (E) Sodium Chloride (III) Chloride As Gold 2 g / L Sodium Sulfite 12.5 g / L Sodium Thiosulfate 25 g / L L-Sodium Ascorbate 40 g / L Disodium Hydrogen Phosphate 9 g / L monosodium dihydrogen phosphate 3g / L pH 7.0

[0051]

[Table 5]

As seen in Table 5, 6-ethoxy-2
In the bath containing no mercaptobenzothiazole (comparative example), a large amount of gold precipitate was already formed in the bath after a storage period of 1 week, and plating could not be performed. On the other hand, in the 2 ppm addition bath of 6-ethoxy-2-mercaptobenzothiazole (Example), formation of a precipitate was not observed in the liquid until the 28th day. In plating with these storage baths, the plating speed slightly decreased from immediately after the construction bath, but no difference in plating speed due to the number of storage days was observed.
It was possible to plate up to a storage bath of up to 28 days. In the 35-day storage bath, a gold precipitate was formed, and it was impossible to normally perform plating.

In plating with 6 ppm of 6-ethoxy-2-mercaptobenzothiazole added at 2 ppm, a bright yellow matte or semi-gloss uniform deposition film was obtained regardless of the storage period of the plating bath.

As described above, 6-ethoxy-2-mercaptobenzothiazole has a remarkable effect in preventing decomposition of the plating solution, and as a result, the usable period of the plating bath is extended and the plating activity is not lowered. It became possible to store the bath at room temperature for a long time.

[0055]

INDUSTRIAL APPLICABILITY The electroless gold plating solution according to the present invention can prevent the formation of precipitates in the bath in a storage state and a use state after the construction bath, and can use the plating bath in a stable state for a long period of time. , It is possible to perform plating repeatedly using this bath, and while the conventional gold plating bath has the drawback of having to be used immediately after the bath is built, it has the excellent advantage of not being restricted in working time. Have. Therefore, the present invention brings about a significant improvement in the economical efficiency and workability of gold plating.

Claims (1)

[Claims] 1. A (a) gold (III) chloride or a salt thereof as a gold source or a gold (I) complex salt of sulfurous acid or thiosulfuric acid, (b) an alkali metal salt or ammonium salt of sulfurous acid or thiosulfuric acid, (c) ) In an electroless gold plating solution comprising an aqueous solution containing ascorbic acid or a salt thereof and (d) a pH buffering agent as composition components, 6-ethoxy-2-mercaptobenzothiazole, 2-mercaptobenzimidazole, 2-mercaptobenzoxazole And an electroless gold plating solution containing a compound selected from these salts.