JPH0598457A - Electroless gold plating solution and gold plating method using same - Google Patents

Abstract

PURPOSE:To provide a stable electroless gold plating soln. not causing the corrosion of a base metal by leaching and a gold plating method using the plating soln. CONSTITUTION:This electroless gold plating soln. contains gold ions, a complexing agent, a reducing agent, a reduction accelerator and a corrosion inhibitor and enables plating at pH 5.5-10.0 and 50-90 deg.C. Since the corrosion inhibitor is added, a passive or slightly soluble salt is formed on the surface of a base metal exposed by pinholes, etc., and the leaching of the base metal can be prevented. Even when a metal having a greater ionization tendency than gold, e.g. Ni, Cu, W or Sn is used as the base metal, corrosion is not caused and various metals can be applied to the base metal.

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 and a gold plating method using the same.

[0002]

2. Description of the Related Art Among the conventional electroless gold plating solutions, electroless gold plating solutions for performing neutral or weakly alkaline plating are disclosed in, for example, JP-A-59-85855 and JP-A-62-86171. The gazette is known.

[0003]

The electroless gold plating solution described above can be plated at a pH of around neutrality. However, for example, when the underlying metal has a greater ionization tendency than gold, such as nickel, pinholes cause If the underlying metal is exposed, a local battery is formed and the underlying metal becomes the negative electrode and elutes. If corrosion occurs, the plating solution may seep into the corroded surface, cause blistering, or reduce adhesion. Furthermore, the eluted base metal ions are reduced by the reducing agent in the plating solution and float in the solution as fine metal particles, and due to the substitution reaction with gold ions, they are ionized again and the solution is rapidly decomposed while repeating a vicious cycle. Then, the gold ion concentration is lowered and the plating cannot be continued, which has a great adverse effect on the stability of the solution.

An object of the present invention is to provide an electroless gold plating solution which is free from corrosion and has excellent solution stability.

[0005]

SUMMARY OF THE INVENTION The above objective is to provide a corrosion inhibitor that contains at least gold ions, a complexing agent, and a reducing agent, and has the ability to form a precipitate film in order to block a corrosive environment. It is achieved by an electroless gold plating solution containing the addition of.

As the corrosion inhibitor, polyphosphate, phosphate, phosphonic acid and the like are desirable. Specific compounds of this type include, for example, diphosphoric acid, glycerophosphoric acid, metaphosphoric acid, polyphosphoric acid, tripolyphosphoric acid, hexametaphosphoric acid, pyrophosphoric acid, phosphonic acid, various ammonium salts of phenylphosphonic acid, sodium salt, or potassium salt. Etc. can be mentioned.

A phenyl compound represented by the following general formula may be added as a reduction accelerator.

General formula,

[0009]

[Chemical 1]

In the formula, R1 is either a hydroxyl group or an amino group, and R2 to R4 are at least one selected from the group consisting of a hydroxyl group, an amino group, a hydrogen atom, a halogen group, a methoxy group and an alkyl group. The alkyl group preferably has a small number of carbon atoms in consideration of water solubility, and specifically, at least one of 1 to 4 methyl groups, ethyl groups and t-butyl groups is desirable.

In the above general formula, when R1 is a hydroxyl group, it becomes a phenol compound. Specific compounds of this kind are as follows:
For example, phenol, o-cresol, p-cresol, o-ethylphenol, p-ethylphenol, t
-Butylphenol, o-aminophenol, p-aminophenol, hydroquinone, catechol, pyrogallol, methylhydroquinone, chlorohydroquinone, methoxyhydroquinone.

When R1 is an amino group, it is an aromatic amine compound, and specific compounds of this kind are, for example, aniline, o-phenylenediamine, p-phenylenediamine, o-toluidine and p-toluidine. , O-ethylaniline, p-ethylaniline.

Among these reduction accelerators, the effects of hydroquinone and pyrogallol are remarkable.

The complexing agent is preferably a water-soluble inorganic salt containing sulfur and oxygen, or a cyanide, and particularly one or two or more selected from thiosulfates, sulfites, potassium cyanide, sodium cyanide and the like. can do.

The reducing agent is selected from a thiourea-based organic compound containing a derivative as a typical example, or a boron-based compound. Further, the thiourea-based organic compound is preferably thiourea, N-methylthiourea, At least one selected from the group of 1-acetylthiourea, 1,3-dimethylthiourea and ethylenethiourea can be selected. Further, the boron compound can be selected from at least one selected from the group consisting of borohydrides, dimethylamine borane, diethylamine borane, trimethylamine borane, triethylamine borane and the like.

As the gold ion, any monovalent or trivalent gold ion can be used, and typical examples thereof include chloroauric acid ion, primary gold cyanide ion, secondary cyanide gold ion, and the like. One or more of these may be used.

[0017]

[Operation] As one of the factors that cause corrosion at pH around neutral,
The elution phenomenon of the base metal may be mentioned.

For example, when the base metal is less base than gold, such as nickel, copper, tungsten, or tin, and the base metal is exposed by the pinhole, a local battery is formed and the base metal is the negative electrode. Elutes and corrodes. Further, the eluted base metal ions are reduced by the substitution reaction with the gold ions in the liquid, suspended in the liquid as metal fine particles, and the plating reaction with these as the nuclei promotes the liquid decomposition, which greatly affects the stability of the liquid. It will have an adverse effect.

As a method for preventing the elution of the base metal, the inventors have tried plating with addition of a corrosion inhibitor that forms a film on the exposed surface of the base metal. As the corrosion inhibitors, we focused on phosphates that passivate by forming a film on the surface of the underlying metal by oxidation, and polyphosphates and phosphonates that form a hardly soluble precipitate film on the surface of the underlying metal. By adding these corrosion inhibitors, the elution of the base metal can be suppressed, and the stability of the liquid is also greatly improved.

[0020]

EXAMPLES Specific examples of electroless gold plating solutions will be described below.

(1) Preparation of sample: size 3.0 cm ×
3.0 cm, 0.3 mm thick stainless steel plate,
First, a nickel film having a thickness of 2 μm was formed using a normal electric nickel plating solution, and then a gold film having a thickness of 0.1 μm was formed using a normal electric gold plating solution to obtain a sample.

(2) Electroless plating treatment on the sample: The sample was washed with a degreasing solution, then with dilute hydrochloric acid and then thoroughly washed with water. The sample was weighed after drying with a nitrogen blow.

This sample was immersed in various plating solution compositions for 3 hours. The results are shown in Tables 1 to 4. Table 1 shows an example of adding sodium hexametaphosphate as a corrosion inhibitor, Table 2 shows sodium polyphosphate, Table 3 shows potassium pyrophosphate, and Table 4 shows phosphonic acid as a corrosion inhibitor. The plating rate when added, the presence or absence of corrosion, and the liquid decomposition time were increased. As a comparative example, Table 5 shows the results when no corrosion inhibitor was added.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

[Table 5]

Here, sodium sulfite was added as a sulfite which is a stabilizer for preventing decomposition of thiosulfate ions.
Borax was also added as a pH adjuster to maintain the pH at the desired value. Then, the gold film thickness after 3 hours was measured by a gravimetric method. Furthermore, the presence or absence of corrosion was confirmed with a metallurgical microscope (one hundred times). In addition, in order to investigate the stability of the plating solution of the present invention, the time until gold precipitation occurred in an unloaded state was measured. In each of these tables, the temperature of the plating solution (solution temperature) and the pH of the solution are also shown. Further, in these tables, as comparative examples, the cases where the reduction accelerator is excluded and where the corrosion inhibitor is excluded are also specified. When any of the plating solutions of Examples 1 to 12 was used, the gold film deposited was a dull bright yellow color, and no precipitation was observed in the solution.

From these tables, by adding the corrosion inhibitor, the corrosion in the neutral region was eliminated and the liquid stability was improved as compared with the conventional example. In addition, in the plating solution components and plating conditions other than the examples, the presence or absence of precipitation in the plating rate plating solution and the presence or absence of elution of the underlying metal were examined, and as a result, the following preferred ranges were obtained for the plating solution components and plating conditions. ..

(1) The concentration of the corrosion inhibitor is 0.00001 to 0.1 m
ol / l is good, preferably 0.0001 to 0.05 mol / l,
Particularly preferably, it is 0.005 to 0.01 mol / l. 0.00001mol
When it is less than / l, there is no corrosion effect, and when it is more than 0.1 mol / l, there is no special effect and it is not economically preferable.

(2) When a mixture of a haloaurate and a thiosulfate such as a chloroaurate is used as a raw material for gold, the concentration of the haloaurate is preferably 0.001 to 0.2 mol / l, Preferably 0.006 to 0.05 mol / l, particularly preferably 0.01 to 0.03 m
ol / l. If it is less than 0.001 mol / l, the plating reaction will be slow, and if it is more than 0.2 mol / l, gold will be likely to precipitate in the plating solution.

(3) The concentration of gold cyanide salt is 0.0035 to 0.0
It is preferably 35 mol / l, preferably 0.0050 to 0.025 mol / l, and particularly preferably 0.0070 to 0.015 mol / l.

(4) The concentration of thiosulfate is 0.001 to 0.9 mol /
1 is good, preferably 0.03 to 0.6 mol / l, and particularly preferably 0.04 to 0.2 mol / l. When it is less than 0.001 mol / l, gold is likely to precipitate in the plating solution, and when it is more than 0.9 mol / l, sulfur is likely to be precipitated.

(5) The concentration of sulfite as a stabilizer is
0.01-0.8 mol / l is preferable, and more preferably 0.08-
It is 0.7 mol / l, particularly preferably 0.15 to 0.6 mol / l.

When the amount is less than 0.01 mol / l, sulfur is likely to precipitate in the plating solution, and when the amount is more than 0.8 mol / l, the plating reaction becomes slow.

(6) The concentration of the reducing agent is 0.00001 to 0.5 mol / l
, Preferably 0.0001 to 0.25 mol / l, and particularly preferably 0.002 to 0.1 mol / l. If it is less than 0.00001 mol / l, the plating reaction becomes slow, and if it is more than 0.5 mol / l, gold precipitation occurs in the plating solution.

(7) The concentration of the reduction accelerator is 0.00001 to 0.5 m
ol / l is good, preferably 0.0001 to 0.25 mol / l,
Particularly preferably, it is 0.002 to 0.1 mol / l. 0.00001mol /
If it is less than 1, the plating reaction will be slow, and if it is more than 0.5 mol / l, gold precipitation will occur in the plating solution.

(8) The concentration of the pH adjusting agent is 0.01 to 1.0 mol
/ l is good, preferably 0.05 to 0.7 mol / l, and particularly preferably 0.08 to 0.2 mol / l. If it is less than 0.01 mol / l, pH change occurs after the start of the plating reaction, and if it is more than 1.0 mol / l, there is no special effect on the plating reaction and it is economically unfavorable.

(9) The liquid temperature is 50 to 90 ° C., preferably 5
5-80 degreeC, Especially preferably, it is 60-75 degreeC. 5
If the temperature is lower than 0 ° C, the plating reaction becomes slow, and if the temperature is higher than 90 ° C, gold precipitates in the plating solution.

[0041]

According to the present invention, by adding the corrosion inhibitor to the plating solution, a film is formed on the exposed surface of the base metal in the pinhole, and the elution of the base metal can be prevented. Therefore, even if a metal such as nickel, copper, tungsten, or tin that has a greater ionization tendency than gold is used as the base metal, there is no risk of corrosion.

Furthermore, the addition of the corrosion inhibitor can prevent the elution of the base metal, so that the decomposition of the plating solution due to the mixing of the base metal can be avoided. Therefore, the stability of the plating solution is improved.

[0043]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Kashimura 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Stocks Institute of Industrial Science, Hitachi, Ltd. (72) Nobuyasu Murayama 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Production Engineering Research Laboratory, Hitachi, Ltd.

Claims (4)

[Claims] 1. An electroless gold plating solution comprising a corrosion inhibitor in a gold plating solution containing at least gold ions, a complexing agent and a reducing agent. 2. The electroless gold plating solution according to claim 1, wherein the corrosion inhibitor is a water-soluble compound containing phosphorus and oxygen. 3. The electroless gold plating solution according to claim 2, wherein the water-soluble compound containing phosphorus and oxygen comprises polyphosphate, phosphate and phosphonate. 4. The electroless gold plating method according to claim 1, 2 or 3, wherein an electroless gold plating is performed by bringing an object to be plated into contact with the electroless gold plating.