JPH06145997A - Electroless gold plating liquid - Google Patents

Abstract

PURPOSE:To greatly improve a plating speed by using the electroless gold plating liquid which is specified in components consisting of chloroauric acid, sulfurous acid, etc. CONSTITUTION:This plating liquid contains 0.001 to 0.10mol/l gold salt, 0.01 to 1.0mol/l Na sulfite, 0.01 to 1.0mol/l Na thiosulfate, 0.01 to 1.0mol/l Na phosphate, 0.001 to 1.0mol/l ascorbic acid or its Na salt and/or 6X10<-7> to 3X10mol/l as 2-mercaptobenzothiazole, 6-ethoxy-2-mercaptobenzothiazole, 2- mercaptobenzimiclazole or 2-mercaptobenzooxazole and 0.0001 to 0.05mol/l alkylamine compd. Its pH of the liquid is preferably 6 to 8 and its operating temp. is 55 to 65 deg.C.

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 an acid or a salt thereof or a gold (I) complex salt of 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, gold (III) chloride is typically used as a gold source.
A gold plating solution using an acid is known (see, for example, U.S. Pat. No. 4,142,902 and 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 The object of the present invention is that it is possible to perform plating at a high speed under moderate operating conditions at pH conditions near neutrality and at relatively low temperatures, and is also excellent in stability. An object is to provide an electroless gold plating solution.

The inventors of the present invention have conducted intensive studies for the purpose of improving the plating rate while ensuring the stability of the electroless gold plating solution. As a result, (a) gold chloride ( III) Acid or salt thereof or gold (I) complex salt of sulfurous acid or thiosulfuric acid, (b) Alkali metal salt or ammonium salt of sulfurous acid or thiosulfuric acid, (c) Ascorbic acid or salt thereof and (d) pH buffering agent In an electroless gold plating solution consisting of an aqueous solution contained as a component, (e) 2
-Mercaptobenzothiazole, 6-ethoxy-2-mercaptobenzothiazole, 2-mercaptobenzimidazole, 2-mercaptobenzoxazole or a compound selected from salts thereof, and (f) alkylamine compounds, sulfates and hydrochlorides thereof It was found that the above object can be achieved by adding a compound selected from 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. In an electroless gold plating solution comprising an aqueous solution containing a salt, (c) ascorbic acid or a salt thereof and (d) a pH buffering agent, (e)
2-mercaptobenzothiazole, 6-ethoxy-2-
A compound selected from mercaptobenzothiazole, 2-mercaptobenzimidazole, 2-mercaptobenzoxazole or a salt thereof and (f) an alkylamine compound, a compound selected from a sulfate salt thereof and a hydrochloride salt thereof. is there.

The present invention will be described in detail below.

Specific examples of the above-mentioned alkylamine compounds and salts thereof include ethylenediamine, ethylenediamine hydrochloride, ethylenediamine sulfate, diethylenetriamine, triethylenetetramine, tetraethylenehexamine, 1,2-propanediamine, 1,3- Examples thereof include propanediamine, ethanolamine, triethanolamine, hexamethylenetetramine and the like.

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

0.001 to 0.10 mol / gold salt
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 / or 2-mercaptobenzothiazole, 6-ethoxy-2-mercaptobenzothiazole, 2-mercaptobenzimidazole or 6 × 10 as 2-mercaptobenzoxazole.
^It contains ^{−7 to} 3 × 10 ⁻³ mol / liter and an alkylamine compound 0.0001 to 0.05 mol / liter.

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 resulting plating rate and plating solution stability, and have obtained the following findings.

(1) Gold chloride used as a gold source (II
The amount of the acid (I) or its salt or the gold (I) complex salt of sulfurous acid or thiosulfate 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. 0.01 mol
If it is less than 1 liter / liter, a practical plating rate cannot be obtained, and if it is more than 0.1 mol / liter, gold precipitation tends to occur, which is also economically disadvantageous.

(2) Regarding the sulfite, for example, sodium salt is preferably 0.01 to 1.0 mol / liter, and particularly preferably 0.04 to 0.5 mol / liter. 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, but 0.04 to 0.5 mo is particularly preferable.
1 / liter. If it is less than 0.01 mol / liter, the plating solution lacks stability and is apt to decompose, and
When it is 0 mol / liter or more, no particular effect is exhibited 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) For ascorbic acid, for example, as a sodium salt, 0.001 to 1.0 mol / liter is preferable, but 0.01 to 0.5 m is particularly preferable.
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) 2-mercaptobenzothiazole, 6-ethoxy-2-mercaptobenzothiazole,
Regarding 2-mercaptobenzimidazole, 2-mercaptobenzoxazole, or a derivative thereof or a salt thereof, 6 × 10 ^{−7 to} 3 × 10 ⁻³ mol / liter is preferable, and 6 × 10 ^{−6 to} 6 × is particularly preferable. 10
^-5 mol / liter. When it is 6 × 10 ⁻⁷ mol / liter or less, the plating solution becomes unstable and decomposition is likely to occur, which is not preferable. Further, when the concentration is 3 × 10 ⁻³ mol / liter or more, the stability of the plating solution increases, but the plating rate becomes slow, which is not preferable.

(7) The alkylamine compounds such as ethylenediamine and diethylenetriamine and the inorganic salts thereof are preferably 0.0001 to 0.05 mol / liter, and particularly preferably 0.0003 mol / liter to 0.03 mol / liter. . 0.0001
When it is less than mol / liter, there is no special rate increasing effect in the plating reaction, and when it is more than 0.05 mol / liter, gold precipitation is likely to occur in the plating solution, which is not preferable.

(8) 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.

(9) 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.

If necessary, a trace amount of metal ions such as thallium, lead, bismuth and the like can be added to the electroless gold plating solution according to the present invention for the purpose of controlling the physical properties of the deposited gold film. The amount added is generally within the concentration range conventionally used in the field of gold plating.

[0025]

EXAMPLES The present invention will be specifically described below with reference to examples of the present invention.

Examples 1 to 4 An electroless gold plating solution (A) having the following composition was prepared, and each solution containing ethylenediamine at various concentrations shown in Table 1 below was used as a plating test piece. 2 cm x
2μm, 0.1mm thick rolled nickel plate 3μm thick
The nickel coating of No. ^{2 and} the gold coating of 3 μm in thickness were respectively applied by ordinary electroplating as a sample, and plating was performed for 6 hours under a bath load of 0.8 dm ² / L, a temperature of 60 ° C. and stirring conditions. It was Plating was performed under the same conditions as in Comparative Example 1 in the case where ethylenediamine was not added, and in Comparative Example 2 in the case where 300 mg / L of ethylenediamine was added from Solution A except for 2-mercaptobenzothiazole.

Further, the stability of the plating solutions added with ethylenediamine at these various concentrations and the plating solutions obtained in Comparative Examples 1 and 2 at room temperature storage were examined.

Electroless Gold Plating Solution (A) Sodium Chloride (III) Chloride 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 Monosodium dihydrogen phosphate 3 g / L 2-mercaptobenzothiazole 1 ppm pH 7.0

The results of plating in each of the above examples are shown in FIG. 1 below. In the cases of Examples 1 to 4 in which ethylenediamine was added, comparison was made with no addition of ethylenediamine. It can be seen that the speed is remarkably increased as compared with Example 1. Further, the increase in speed depends on the concentration of ethylenediamine added, and the addition of 300 mg or more of ethylenediamine shows that the degree of increase in speed is
It was confirmed that there was a tendency to gradually soften. Furthermore,
It is recognized that the deposition rate tends to decrease with the consumption of gold as the plating rate increases, but in Examples 3 and 4, thick plating of 10 μm or more was possible in 6 hours. The precipitate had a bright yellow, semi-glossy, uniform appearance in all of the examples, and a good precipitation state was observed.

Further, in Examples 1 to 4, the formation of gold precipitate was not recognized during the plating for 6 hours and the stability was good, while 300 mg / L of ethylenediamine was added without adding 2-mercaptobenzothiazole. In the added Comparative Example 2, the effect of increasing the speed was recognized as in the case of the Example, but the plating bath was unstable, and a gold precipitate was formed from about 30 minutes, and 1
It was difficult to perform plating for longer than time.

The results of examining storage at room temperature are as shown in Table 1 below. Compared to Comparative Example 1 in which ethylenediamine was not added, the stability tended to decrease as the amount of ethylenediamine added increased, but it was confirmed that the stability was stable for at least one week. In addition, in the case of Comparative Example 2 in which 2-mercaptobenzothiazole was not added, a gold precipitate was formed in only 6 hours.

From these examples, it is recognized that the electroless gold plating solution according to the present invention exhibits not only an effect of increasing the plating rate but also an excellent effect in terms of stability during plating and during storage.

[0033]

[Table 1]

Examples 5 to 10 The electroless gold plating solution (A) described in Examples 1 to 4 above was used with a plating bath prepared by adding 0.01 mol / liter of various alkylamines as shown in Table 2. The plating rate was investigated. The plating method was the same as in Examples 1 to 4 as a plating test piece, and the bath load was 0.8.
Plating was performed for 1 hour under dm ² / L, temperature of 60 ° C. and stirring conditions.

The results are shown in Table 2. When each alkylamine was added, an increase in plating rate was observed in all cases as compared with Comparative Example 3 in which no alkylamine was added. In addition, the deposits had a bright yellow semi-gloss and uniform appearance in all of the Examples, indicating a good deposit state. Further, during the plating operation, no gold precipitate was found in the bath in any of the examples.

From the results of these examples, it is recognized that the plating solution of the present invention has excellent stability and can be effectively used as a bath having an appropriate plating rate.

[0037]

[Table 2]

Example 11 An electroless gold plating solution (B) having the composition shown below was prepared, and this plating solution was used as a plating test piece having a size of 4 cm × 4.
cm, 0.1 mm thick rolled nickel plate, 3 μm thick nickel film, and then 3 μm thick gold film respectively applied by ordinary electroplating, at a temperature of 60 ° C.
Plating was performed for 2 hours under stirring conditions.

The bath load of the plating solution was 0.8, 1.6, 3.
The effect of increasing the speed when the bath load was increased by changing the value to 2,6.4 dm ² / liter was investigated.

Electroless Gold Plating Solution (B) Sodium Chloride (III) Chloride Gold 2 g / L Sodium sulfite 12 g / L Sodium thiosulfate 24 g / L L-Sodium ascorbate 40 g / L Disodium hydrogen phosphate 7 g / L Sodium dihydrogen phosphate 3 g / L 2-Mercaptobenzothiazole sodium 2 ppm Ethylenediamine sulfate 800 mg / L pH 7.0

The plating rate for one hour under each bath load was 2.7 μm / hr and 1.6 at 0.8 dm ² / liter, respectively.
2.1 μm / hr at dm ² / liter, 3.2 dm ² /
It was 2.1 μm / hr at liter, and 1.8 μm / hr at 6.4 dm ² / liter. In addition, it was confirmed that the precipitate had a bright yellow semi-gloss and uniform appearance in any of the Examples and was in a good precipitation state. It was recognized that the plating rate tended to decrease as the bath load increased, but even under the bath load condition of 6.4 dm ² / liter,
In addition, the effect of increasing the plating rate of ethylenediamine was recognized, and it was possible to perform plating treatment on a large amount of objects in a short time.

From these examples, the electroless gold plating solution according to the present invention can perform high-speed plating even under a high bath load condition, can perform plating on a large number of objects in a short time, and improve work efficiency. It turns out that it brings significant advantages to

Example 12 An electroless gold plating solution (C) having the following composition was prepared, and the stability when stored at room temperature, the plating rate, and the stability during plating were examined. The plating method is the same as the conditions described in Examples 1 to 4. As a comparative example, when only ethylenediamine was removed from the following composition (C) (Comparative Example 4), when only 2-mercaptobenzimidazole was removed (Comparative Example 5),
The same stability and plating rate as above were also examined when both were excluded (Comparative Example 6). The results are shown in Table 3.

Electroless Gold Plating Solution (C) 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 2-mercaptobenzimidazole 100 ppm Ethylenediamine 0.3 g / L pH 7.2

[0045]

[Table 3]

As can be seen from Table 3, in the case of using the example bath composition (C), the plating rate was higher than in the cases of Comparative Examples 4 to 6, and the stability during plating and the stability during storage at room temperature were high. The stability was also good. Comparative Example 4 in which ethylenediamine was not added was superior to the Examples in terms of stability, but the plating rate was slow, and in Comparative Example 5 in which 2-mercaptobenzimidazole was not added, the plating rate was increased, but the bath Became unstable and it was difficult to continue the plating work. Furthermore, in the case of Comparative Example 6 in which both ethylenediamine and 2-mercaptobenzimidazole were not added, the plating rate was slow, and insufficient results were seen in terms of stability.

In Examples and Comparative Example 4, a bright yellow semi-glossy appearance was obtained, but in Comparative Example 5, a gold decomposition product was attached and the surface condition was poor. In Comparative Example 6, the precipitation appearance was It was reddish yellow and matte.

Thus, it was confirmed that the electroless gold plating solution according to the present invention has a remarkably high plating rate and is extremely excellent in stability during plating and during storage.

Example 13 An electroless gold plating solution (D) having the following composition was prepared. Using this solution, plating was performed under the conditions described in Examples 1 to 4, and the plating rate and stability during plating were examined. Further, as comparative examples, when ethylenediamine was removed from the following composition (D) (Comparative Example 7), when 6-ethoxy-2-mercaptobenzothiazole was removed (Comparative Example 8), and when both were excluded (Comparative Example 9). ), The plating rate and stability were similarly examined. The results are shown in Table 4.

Electroless Gold Plating Solution (D) Gold (I) Sulfite Sodium 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 Sodium dihydrogen acid 4 g / L 6-ethoxy-2-mercaptobenzothiazole 2.5 ppm diethylenetriamine 0.25 g / L pH 7.2

[0051]

[Table 4]

As shown in Table 4, when the bath composition (D) was used (Example), the plating rate was higher than that in Comparative Examples 7 to 9 and the stability during plating was good. It was In Comparative Example 7 in which diethylenetriamine was not added, the stability was as good as in Example, but the plating rate was significantly slowed, and in Comparative Example 8 in which 6-ethoxy-2-mercaptobenzothiazole was not added, the plating rate was However, the bath became unstable and it was difficult to continue the plating operation. In the case of Comparative Example 9 in which neither diethylenetriamine nor 6-ethoxy-2-mercaptobenzothiazole was added, the plating rate was slow and the bath stability was insufficient. The appearance of the precipitate was reddish yellow and matte in Comparative Example 7, and the gold decomposition products adhered in Comparative Examples 8 and 9 and the surface condition was poor. It was semi-glossy and had the best appearance of precipitation.

As described above, it can be seen that the electroless gold plating solution according to the present invention has a high plating rate and very good stability.

Examples 14 to 16 Plating solutions having various compositions shown in Table 5 were prepared and plated. As a comparative example, a liquid having each composition excluding the alkylamine compound was prepared from these compositions, and the same plating was performed. The plating method is as follows:
3 to 4 at a temperature of 60 ° C. under stirring conditions.
It was performed by a time immersion treatment.

As can be seen from Table 5, the plating rate was found to be remarkably increased by the addition of the alkylamine compound in each of the Examples, and in Examples 14 and 16, it was used as a grain control agent for gold plating deposits. The known thallium salt and lead salt were used in combination, but no effect on the plating rate increasing effect by the addition of alkylamine and the bath stabilizing effect by the addition of the mercapto compound was observed.

[0056]

EFFECT OF THE INVENTION The electroless gold plating solution according to the present invention improves the plating rate, which has been a problem with the conventionally used electroless gold plating solutions, and has a significantly high plating rate and a high bath load. Also has the property that the plating rate does not decrease. Therefore, there is an excellent advantage that a large number of objects can be plated in a short time. Further, since the plating rate is sustained, thick plating can be performed in a relatively short time.

Furthermore, regarding the storage condition and the usage condition after the bath is built, no precipitation is observed in the bath, and it can be used for a long time in a stable condition and can be used repeatedly.
It has an excellent advantage that the restriction on working time, which must be used immediately after the bath is built up like the conventional gold plating bath, is eliminated.

[0058]

[Table 5]

[Brief description of drawings]

FIG. 1 is a diagram showing the results obtained in Examples 1 to 4 and Comparative Examples 1 and 2 in comparison with each other, wherein the vertical axis represents the obtained plating film thickness (μm) and the horizontal axis represents the plating time (μm). hr) is indicated.

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, (e) 2-mercaptobenzothiazole, 6-ethoxy-2-mercaptobenzothiazole, 2- Mercaptobenzimidazole, 2
An electroless gold plating solution comprising a compound selected from mercaptobenzoxazole or a salt thereof and (f) an alkylamine compound, a compound selected from a sulfate and a hydrochloride thereof.