JPH09287077A - Electroless gold plating solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroless gold plating solution low in toxicity, excellent in the durability of a resist and stable even at the time of letting naturally stand for a long period and even in the case continuously using. SOLUTION: This electroless gold plating solution contains a gold sulfite or a chloroaurate as a gold salt, a thiosalfate or a sulfite as a complexing agent of gold, a borate as a buffer, an urea compound as a reducing agent, a phenyl compound as a reduction accelerating agent, benzotriazol as a stabilizer to the contamination of copper ion and a 4C or 5C aliphatic saturated alcohol as a self-decomposition reaction preventing agent of the reducing agent and is adjusted to pH6.5-8.5 by using hydrochloric acid or sodium hydroxide as a pH adjuster.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electroless gold plating solution used when gold plating is applied to a printed wiring board.

[0002]

2. Description of the Related Art To apply gold plating to a printed wiring board,
The electrolytic gold plating method or the electroless gold plating method is used, but the electrolytic gold plating method is mainly used in terms of cost and liquid stability.

However, the electrolytic gold plating method has problems in designing the leads and plating on an isolated pattern when performing electrolytic plating in response to the recent demand for high-density mounting, and thus the electroless gold plating method is used. Plating methods are needed.

The electroless gold plating method is divided into a substitution type and a reduction type.
There is a passage, among them, the displacement gold plating method, by immersing the base metal conductor in the displacement type gold plating solution, gold in the solution is deposited by substitution on the base metal conductor, but since it is a substitution reaction, gold is The substitution reaction stops when it is deposited on the entire surface of the base metal conductor, making thick gold plating impossible. For it,
In the reduction type gold plating method, gold is deposited by the reduction reaction, so by supplementing each component of the electroless gold plating solution,
Gold plating with a thickness of several μm is possible.

[0005]

As for such a reduction type electroless gold plating solution, many composition components have been reported so far, but most of them contain a cyanide compound. There was a problem that it was highly toxic.

Further, most of the electroless gold plating solutions containing a cyanide compound are used in a highly alkaline solution having a pH of 11 or higher, as described in, for example, Japanese Patent Application Laid-Open No. 57-169077, so that the plating resist is dissolved. However, there is a problem that the pattern plating property is deteriorated (plating does not uniformly deposit).

In order to solve such a problem, research and development have been carried out on a low toxicity electroless gold plating solution containing no cyanide compound, which is disclosed in JP-B-56-20353 and JP-A-3-104877. Has been done.

However, the electroless plating solution containing potassium chloroaurate and amine borane as the main components disclosed in Japanese Examined Patent Publication No. 56-20353 has a low toxicity but a pH of 12 or more, and the durability of the resist is low. There was a problem.

The electroless plating solution containing a chloroauric acid salt as a gold salt, thiourea as a reducing agent, and a phenyl compound as a reduction accelerator as disclosed in JP-A-3-104877 has low toxicity, Moreover, since the pH is close to neutral, the durability of the resist is excellent, but when left alone for several weeks, some gold is reduced in the liquid by the autolysis reaction of the reducing agent thiourea. Therefore, there is a problem that the liquid becomes cloudy yellow and gold is deposited in the tank. In addition, when the liquid was continuously used, the same problem as above occurred when the number of turns of the liquid used was 0.5 or more (1 turn is the time when the same amount of gold for the building bath is replenished). ).

Therefore, the present invention has been made in view of the above problems.
Low toxicity and good durability of resist,
It is an object of the present invention to provide a stable electroless gold plating solution even when left alone for a long period of time or continuously used.

[0011]

In order to achieve the above-mentioned object, the electroless gold plating solution of the present invention comprises a sulfite gold salt or chloroauric acid salt as a source of gold ions and a sulfite salt as a gold complexing agent. And a thiosulfate, a borate as a buffer, a urea compound as a reducing agent, a phenyl compound as a reduction accelerator, a pH adjuster, and an electroless gold plating solution containing benzotriazole as a solution stabilizer against copper ion contamination,
The pH is adjusted to 6.5 to 8.5 with a pH adjuster, and an aliphatic saturated alcohol having 4 or 5 carbon atoms is contained as a reducing agent autolysis reaction inhibitor.

Here, gold sulfite or chloroaurate is used as a source of gold ions. Sodium gold sulfite and potassium gold sulfite are used as the gold sulfite, and sodium chloroaurate and potassium chloroaurate are used as the chloroaurate. And the concentration of gold salt is 1-10 g / l as gold ion.
It is preferable to use. When the concentration of gold ions is less than 1 g / l, the gold deposition rate is extremely slow, and when it exceeds 10 g / l, the plating characteristics do not change, but the effect does not change and it is not economical.

As the gold complexing agent, it is preferable to use thiosulfate and sulfite, and as the thiosulfate,
It is preferable to use sodium thiosulfate or potassium thiosulfate.

The concentration of thiosulfate is 0.02 mol / l to 0.40 mo
It is preferable to use 1 / l, and the concentration of thiosulfate is 0.
If it is less than 02 mol / l or more than 0.40 mol / l, the plating solution becomes unstable and decomposes.

As the sulfite, sodium sulfite or potassium sulfite is preferably used, and the sulfite concentration is preferably 0.08 mol / l to 0.80 mol / l. If the sulfite concentration is less than 0.08 mol / l, the plating solution becomes unstable and decomposes. Further, if it exceeds 0.80 mol / l, it is not completely dissolved and the plating solution becomes cloudy.

As the buffer, borate is preferably used, and as the borate, sodium tetraborate,
There is potassium tetraborate. The concentration of borate is 0.02 mol /
It is preferable to use 1 to 0.20 mol / l. When the borate concentration is less than 0.02 mol / l, the effect of the buffer is weak and the pH of the plating solution tends to fluctuate. It does not dissolve and the plating solution becomes cloudy.

A urea compound is preferably used as the reducing agent. Examples of urea compounds include thiourea, methylthiourea, and dimethylthiourea. The concentration of the urea compound is preferably 2.6 × 10 ⁻³ mol / l to 2.6 × 10 ⁻² mol / l, and the urea compound is preferably used. The concentration is 2.6 × 10 ^-3 mol / l
Below 1, the gold deposition rate is remarkably slow and 2.6 × 10 ^-2 mol / l
If it exceeds, the plating solution becomes unstable and the solution decomposes.

A phenyl compound is preferably used as the reduction accelerator. Examples of the phenyl compound include hydroquinone, methylhydroquinone, catechol, pyrogallol, aminophenol, and phenylenediamine. The concentration of the phenyl compound is 8.1 × 10 ⁻³ mol / l to 2.7.
It is preferably used at × 10 ^-2 mol / l. When the concentration of the phenyl compound is less than 8.1 × 10 ^-3 mol / l, the gold deposition rate is remarkably slow, and when it exceeds 2.7 × 10 ^-2 mol / l, the plating solution becomes unstable and decomposes.

Benzotriazole is preferably used as a liquid stabilizer against copper ion contamination, and the concentration is 4.
It is preferably used at 2 × 10 ⁻³ mol / l to 6.7 × 10 ⁻² mol / l. If the concentration of benzotriazole is less than 4.2 × 10 ^-3 mol / l, the effect of solution stability against copper ion contamination cannot be obtained, and if it exceeds 6.7 × 10 ^-3 mol / l, the temperature of the plating solution is 15
If the temperature drops below ℃, it will recrystallize and it will be difficult to keep the plating solution.

It is preferable to use an aliphatic saturated alcohol having 4 or 5 carbon atoms as the self-decomposition reaction inhibitor of the reducing agent. As the aliphatic saturated alcohol having 4 or 5 carbon atoms, 1-butanol and its structural isomers, 1-butanol
There are pentanol and its structural isomers, and the concentration is 50
It is preferable to use ppm to 1,000 ppm. An aliphatic saturated alcohol with less than 4 carbon atoms has a boiling point of less than 100 ° C and vaporizes immediately when used at high temperatures, so the effect of preventing the autolysis reaction of the reducing agent cannot be obtained, and the liquid remains for several hours. Disassemble with. Since aliphatic saturated alcohols having more than 5 carbon atoms are hardly dissolved in the liquid, the effect of preventing the autolysis reaction of the reducing agent cannot be obtained, and the liquid decomposes in several hours. When the concentration of the saturated aliphatic alcohol having 4 or 5 carbon atoms is less than 50 ppm, the effect of preventing the autolysis reaction of the reducing agent cannot be obtained, and the liquid decomposes within several days. If the concentration exceeds 1,000 ppm, the saturated concentration will be reached in the liquid, and no further effect will be obtained.

As the pH adjuster, it is preferable to use hydrochloric acid for decreasing the pH and sodium hydroxide or potassium hydroxide for increasing the pH.

With such an adjusting agent, the pH is adjusted to 6.5 to 8.
When the pH is less than 6.5, the gold deposition rate is extremely slow, and when it exceeds 8.5, the plating solution becomes unstable and the solution decomposes.

The electroless gold plating solution of the present invention can be manufactured, for example, as follows. When producing 1 liter of electroless gold plating solution, first of all, 1 liter
Add 0.51 liter of pure water to the (liter) container and start stirring with a magnetic stirrer. Next, sodium sulfite 0.08
~ 0.80mol Sodium gold sulfite as gold ion 1-1
0 g, sodium thiosulfate 0.02 mol to 0.40 mol, sodium tetraborate 0.02 mol to 0.20 mol, benzotriazole
4.2 × 10 ^-3 mol to 6.7 × 10 ^-2 mol, thiourea 2.6 × 10 ^-3 m
ol ~ 2.6 × 10 ^-2 mol, hydroquinone 8.1 × 10 ^-3 ~ 2.7
× 10 ^-2 mol, 3-methyl-1-butanol 5.7 × 10 ^-4 mo
l ~ 5.7 x 10 ^-3 mol is dissolved successively and the pH is adjusted to 6.5 ~ 8.5 with a 2 mol / l hydrochloric acid aqueous solution. Finally, the plating solution is filtered with a filter. The filter preferably has a mesh of 1 μm or less.

The electroless gold plating solution thus produced can be used at a liquid temperature of 45 to 80 ° C. If the liquid temperature is lower than 45 ° C, the gold deposition rate is extremely slow, and if it exceeds 80 ° C, the plating solution becomes unstable and the solution decomposes.

The electroless gold plating solution of the present invention does not undergo a self-decomposition reaction of the reducing agent for 1 month or more in a state of being left naturally, and therefore the solution does not become yellow and cloudy and gold does not deposit in the bath.

In the electroless gold plating solution of the present invention, when a material to be plated on which 3 μm of nickel and 0.05 μm of displacement gold is plated on copper is immersed, 0.4 to 1.2 per hour is obtained.
A μm gold plated film is obtained. Furthermore, in an electroless gold plating solution of 25 g / l of gold, when the time of consuming 2.5 g of gold is set as 1 turn, even when 10 turns are continuously plated, the self-decomposition reaction of the reducing agent is prevented, so that the solution is Good results can be obtained without yellow and turbidity and no gold deposition in the tank.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the electroless gold plating solution according to the present invention will be described below based on Examples.

[0028]

【Example】

<Examples 1 to 12> A copper-clad laminate having a size of 5 cm x 5 cm was used as a material to be plated, and the material to be plated was degreased, lift-etched, and pickled, and then substituted palladium catalyst SA-100 for electroless nickel plating (Hitachi Kasei Kogyo) Made in Japan, product name) 2
Immerse for 2 minutes at 5 ℃, wash with water, electroless nickel plating solution
NIPS-10P (trade name, manufactured by Hitachi Chemical Co., Ltd.) at 80 ℃
For 15 minutes to form a nickel coating having a thickness of 3 μm on copper.

Next, a displacement gold plating solution HGS-100 (trade name of Hitachi Chemical Co., Ltd.) was immersed at 80 ° C. for 10 minutes to form a displacement gold coating having a thickness of 0.06 μm on the nickel coating. This material to be plated was immersed in No. 1 to No. 12 electroless gold plating solutions shown in Table 1 and continuously subjected to plating treatment for 10 turns, and the stability of the solution against the number of turns was examined.

At that time, gold and other components were replenished, and gold was added in an electroless gold plating solution having a gold concentration of 2.5 g / l to 2.
When 5g was consumed for one turn, 2.5g of gold was supplied, and 5% of the initial concentration of other components was supplied.

Next, the reducing agent concentration of the treatment solution for 10 turns was set to 100%.
(Thiourea was adjusted to 1.3 g / l), filtration was performed with a mesh of 1 μm, and the filtered solution was allowed to stand naturally, and changes in the reducing agent concentration with respect to the number of days left and stability of the solution were examined.

Table 1 shows the results of the stability of the above-mentioned liquids. As shown in the table, as a reducing agent autolysis reaction inhibitor, an additive of an aliphatic saturated alcohol having 4 or 5 carbon atoms was used. All of the put things did not change the appearance of the liquid after 10 turns, and did not cause any change in the appearance of the liquid even after being left for 30 days.

[0033]

[Table 1]

<Comparative Example> In the same manner as in Examples 1 to 12, No. 1 in Table 2 (Comparative Example 1) was used as a plated material in which a nickel film having a thickness of 3 μm and a displacement gold film having a thickness of 0.05 μm were formed on copper. ), No2 (Comparative Example 2), and No3 (Comparative Example 3) were immersed in the electroless gold plating solutions, and the stability of the solution with respect to the number of turns and the stability of the solution with respect to the number of days left were examined.

Table 2 shows the results of the stability of the liquid described above. As shown in the table, the appearance of the liquid changes when the number of turns is 0 without the additive shown in No. 1. However, when the number of turns was 0.5 or more, the liquid became yellow, and when left for 3 days or more, the liquid became yellow.

When 1-ethanol was used as the additive shown in No. 2, the same result as that of No. 1 in which no additive was added was obtained.

When 1-propanol was used as the additive shown in No. 3, the liquid changed when the number of turns was 1 or more, and when left for 5 days or longer, the liquid turned yellow. It was

[0038]

[Table 2]

[0039]

INDUSTRIAL APPLICABILITY As described above, the electroless gold plating solution of the present invention comprises a sulfite gold salt or chloroauric acid salt as a source of gold ions, a sulfite salt or a thiosulfate salt as a gold complexing agent, and a borate salt as a buffering agent. , An electroless gold plating solution containing a urea compound as a reducing agent, a phenyl compound as a reduction accelerator, a pH adjuster, and benzotriazole as a solution stabilizer against copper ion contamination. It does not contain a cyanide compound, so its toxicity should be low. You can

Furthermore, since the reducing agent self-decomposition reaction inhibitor contains an aliphatic saturated alcohol having 4 or 5 carbon atoms, the self-decomposition reaction of the reducing agent can be prevented and the stability of the liquid can be maintained for a long period of time.

Claims (1)

[Claims] 1. A gold sulfite or chloroaurate as a source of gold ions, a sulfite or a thiosulfate as a gold complexing agent, a borate as a buffer, a urea compound as a reducing agent, and a reduction accelerator. In the electroless gold plating solution containing a phenyl compound, a pH adjuster, and benzotriazole as a solution stabilizer against copper ion contamination, a reducing agent self-decomposition reaction inhibitor having 4 or 5 carbon
An electroless gold plating solution containing the above aliphatic saturated alcohol.