JPS61279685A - Electroless gold plating solution - Google Patents

Abstract

PURPOSE:To obtain an electroless Au plating soln. having a high plating rate and superior stability by dissolving KAu(CN)2 as an Au ion source and specified amounts of KOH, KCN and KBH4 in water. CONSTITUTION:A soln. contg. KAu(CN)2 as an Au ion source, 0.1-0.4mol KOH, 0.05-0.15mol KCN and 0.1-0.2mol KBH4 as a pH adjusting agent, a reducing agent, etc. is used as an electroless Au plating soln. A body to be plated is hung on a soluble base metal and immersed in the electroless Au plating soln. at 70 deg.C, and thick Au plating is formed by electroless plating at >=10mum/hr rate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field] This invention relates to electroless gold plating bath compositions and methods of using this plating bath.

[Conventional technology]

As is well known, gold plating has been applied to ornaments such as beads and bracelets, and jewelry since ancient times.

Recently, in various applications of two types of industrial products, gold plating has been carried out on the surface of metal objects in order to obtain a better appearance, a corrosion-resistant coating, and an electrically conductive coating with good spread. (As for gold plating, which is widely practiced in Imada), there are three main methods. 1
Namely, examples include (7) electrolytic plating method, (a) vapor deposition method, and (y) electroless method.

In method (7) above, from a solution containing metal ions,
,,)' The metal is deposited by electrolysis. That is, the metallic article to be plated is electrically connected to the cathode.

and a metal serving as an electrode plate is electrically connected to the anode; b.
@asf<@*pt4*t@tr*W4Mmltc@
＆＞z ,・Place the anode opposite・”・Between the cathode, the anode, and 0.

A DC voltage is applied to the metal ions, which transfer metal ions to the cathode.
), where the metal ions lose their charge and are deposited as a metal coating layer on the article to be plated.
・,,1 However, according to this method, it is difficult to uniformly electroplate an article having a complicated shape. Also, it is usually impossible to plate high aspect ratio blind holes, resulting in a thick layer of plating on the tips or edges of the article to be plated, and a thin layer on the recessed surfaces.

Moreover, it requires an external power source.

In the method (a) above, the article to be plated is placed in a reduced-pressure container at the top of the container, the metal pellets or powder to be vapor-deposited are placed at the bottom of the container, and
Alternatively, heating these metal pellets or powders indirectly results in the deposition of a metal layer on the article.

Therefore, according to this method, it is difficult to obtain a thick plating layer, the adhesion to the article is weak, and blind holes with a high 7 aspect ratio cannot be plated. Moreover, the equipment is very expensive.

In method (1) above, displacement plating utilizes the potential difference between different metals in a solution. Electrons released by dissolution are transferred to noble metal ions in the solution, forming a noble metal coating on the surface of the base metal.

On the other hand, in chemical reduction plating, that is, when the article to be plated is immersed in a solution in which a metal salt and a soluble reducing agent coexist, the electrons released by the oxidation of the reducing agent are transferred to the metal ions in the solution, causing plating to occur on the article. Some may precipitate as a metal coating layer.

The above displacement plating uses the potential difference between different metals, and the deposited metal is thin (for example, about 0.5 μF or less).
There are many pinholes.

Furthermore, the adhesion to articles is weak and cannot be put to practical use.

In the above chemical reduction plating, Patent Publication No. 49-4
3173. Various chemical reduction baths (or electroless plating baths) using aliphatic amine poranes or borohydrides as soluble reducing agents have been known, as seen in 1983-3743.

The plating deposition rate is slow, less than 2 μm per hour, and the applicant's confirmation experiments show that the plating bath is too unstable to be put to practical use.

Therefore, creating a plating bath with a fast plating deposition rate and good stability (at least 8 hours) will open up restricted applications and contribute to technological development.

[Problem that the invention seeks to solve]

This invention was made for the purpose of improving the technical problems associated with the above-mentioned electroless gold plating bath composition and method of using this plating bath. It is an object of the present invention to provide an electroless gold plating bath composition that allows fast plating as thick as 10 μm and has good plating bath stability, and a method for using this plating bath.

[Means for solving problems]

The electroless gold plating bath composition and method of using this plating bath according to this invention are the result of extensive research.

To maintain the stability of the plating bath and increase the rate of precipitation of the plating metal, increase the temperature of the plating bath or add an appropriate amount of P.
The present inventors have found that the above object can be achieved by determining the amount of hydrogen or reducing agent and by keeping the plated article at a base potential at all times, and have completed the present invention.

Namely, the electroless gold plating solution of the present invention is an aqueous solution containing potassium gold cyanide, potassium hydroxide, and potassium cyanide, and potassium borohydride as a reducing agent. Plating is carried out by immersing the plate in the plating solution while contacting the plate.

The invention will be explained in more detail below.

The composition of the electroless gold plating bath of the present invention and the method of using this plating bath were determined by the applicant as a result of extensive experiments.

That is, when the temperature of the plating solution is set to 70'C, gold precipitation becomes active, and when it is raised to 80°C or higher, the plating solution becomes easily decomposed, so care must be taken.

Potassium hydroxide is used to adjust the pH of the plating solution and to control the rate of gold precipitation. FIG. 1 shows how the thickness of the deposited gold film changes as the concentration of potassium hydroxide changes.

Potassium hydroxide! Gold precipitation increased to 190.2 mol,
When the amount exceeds 0.3 mol, the rate of gold precipitation decreases.

The deposition rate was 4 μm per hour.

Based on this result, the potassium hydroxide concentration is 0.1 to 0.4
Mole is optimal.

FIG. 2 shows how the thickness of the deposited gold film changes as the concentration of potassium borohydride as a reducing agent changes. The thickness of the deposited gold film increases as the potassium borohydride concentration increases, but if more than 0.3 mol is added, the plating solution will easily decompose, so the potassium borohydride concentration should be set at 0.1 to 0.2 mol. did.

[Effect]

In this invention, the plating deposition rate is 10 per hour.
It is possible to obtain a thick plating layer as fast as μm, and the stability of the plating bath is good.

〔Example〕

The present invention will be explained in more detail below with reference to Examples.

Example 1 A bath with the following composition was prepared.

KAu (CN)2 1 Q, OI/IKCN
6.511/I KOH11, O11 // KBH45,0171 Bath temperature T5 ± 2°C While stirring the solution with the above composition using magnetics and a roller, hook the coated specimen on the soluble base metal,
Plating was performed by immersing it in the above solution. .

The results of an impurity analysis and a pinhole test performed on the gold-plated film after plating are shown in FIGS. 3 and 4, respectively.

Figure 3 shows impurities in the deposited gold plating film.
1 analysis results are shown.

This is the result of Auger electron spectroscopy analysis of a gold-plated film of approximately 10 μm, and was carried out while electron etching was performed from the surface of the gold-plated film toward the substrate. The detected elements were sulfur, gold, boron, carbon, etc. Among the impurities except gold, boron was below the detection limit.

FIG. 4 shows the results of a pinhole test on the deposited gold plating film.

For comparison, we conducted a pinhole test on the electroless gold plating film, and found that when the gold plating thickness is 1.5 μm or less, the electroless gold plating film has more pinholes, but when the gold plating thickness is 1.5 μm or more, the electroless gold plating film has more pinholes. The gold plating film and the electroless gold plating film are now equivalent.

Example 2 A copper plate was hooked onto a soluble base metal in solutions having various liquid compositions as shown in FIG. 5, and immersed in the solution for 1 m to perform gold plating. After gold plating, the copper plate was melted, thoroughly washed and dried, and the resistance of the gold plated film was measured.

The specific resistance was calculated.

For comparison, electrolytic gold plating film (Tempslex 4 (
The resistance of N ) was measured and the specific resistance was calculated.

As a result, the specific resistance of the electrolytic gold plating film was 2.22X10
-6QrcrrL, the specific resistance of the electroless gold plating film is 2.
It was 50x10 Ω-.

This value does not pose any problem in practice.

〔Effect of the invention〕

As explained above, this invention has a deposition rate as high as 10 μm per hour to obtain a thick plating layer, and the resulting impurity coating has less eutectoid impurities, and compared to electrolytic gold plating coating, there are no pinholes. The number, specific resistance value, etc. are almost the same. In addition, the plating bath has good stability and contributes greatly economically.

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It can be expected that it will be widely used for attaching objects with rough structures, opening up many uses that have been restricted until now.

゛・'5

[Brief explanation of drawings]

: Figure 1 of the jar shows the relationship between potassium hydroxide concentration and gold precipitation rate.
:. Figure 2 shows the relationship between potassium borohydride and
[i,; Figure 3 shows the relationship between degree and gold precipitation rate.
. The gold film that was put out. Oak. Electron spectroscopy results
Figure 5 shows the pinhole test results of the deposited gold plating film, and Figure 5 shows the results of various compositions.
Pa)′□′1 Measurement results of the specific resistance value of the gold-plated film obtained
41,...; It is a figure showing the result.
``:・; [;□ Agent Masuo Oiwa ・1.! Figure 1 Figure 2! II Messy time 1lJ5 (min) Kasoten M-(μ-

Claims (2)

[Claims] (1) A predetermined amount of potassium gold cyanide and 0.1 to 0.
0.1 to 0.2 mol of potassium borohydride is added as a reducing agent to an aqueous solution containing 4 mol of potassium hydroxide and 0.05 to 0.15 mol of potassium cyanide, and the reduction reaction produces gold. An electroless gold plating solution characterized by depositing 5 μm or more. (2) The invention as set forth in claim (1), characterized in that plating is carried out by bringing a soluble base metal into contact with the object to be plated in the electroless gold plating solution, or by contacting the object with a soluble base metal. Electrolytic gold plating solution.