JPS61279686A - Electroless silver plating solution - Google Patents

Abstract

PURPOSE:To obtain an electroless Ag plating soln. having superior stability and depositing Ag at a high rate by dissolving specified amounts of NaAg(CN)2 as an Ag ion source, NaCN, NaOH and KBH4 in water. CONSTITUTION:A soln. having a composition contg. 0.01-0.20mol NaAg(CN)2, 0.05-0.4mol NaCN, 0.05-0.5mol NaOH and 0.03-0.20mol KBH4 is used as an electroless Ag plating soln. A body to be plated is hung on a soluble base metal and immersed in the electroless Ag plating soln. at >=50 deg.C, and Ag plating is formed by electroless plating at a high deposition rate of >=15mum/hr.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to an electroless silver plating solution and a method of using this plating bath. Moreover, it is particularly relevant to electroless silver plating solutions that provide fast deposition rates and thick coatings even when obtained using known electroless silver plating baths.

[Conventional technology]

As is well known, silver has a beautiful white luster and is used in Western tableware, ornaments, and arts and crafts.It also has the highest conductivity among metals and is relatively inexpensive, so it is used in electrical components such as contacts. Plating is performed on metal surfaces such as aircraft parts.

There are three main methods of silver plating that are widely practiced today.

Namely, examples include (1) electrolytic plating method, (a) vapor deposition method, and (1) electroless method.

In method (1) above, metal is deposited by electrolysis from a solution containing metal ions. That is, the metallic article to be plated is electrically connected to the cathode K, and the metal serving as the electrode plate is electrically connected to the anode.

A cathode and an anode are placed opposite each other in an electrolytic solution containing the metal salt to be deposited. Then, a DC voltage is applied between the cathode and anode, and the metal ions move to the cathode.

There, the metal ions lose their charge and are deposited as a metal coating layer on the article to be plated.

However, according to this method, it is difficult to uniformly electroplate articles with complex shapes. 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 method 0) above, the article to be plated is placed in a reduced pressure container at the top of the container, and the metal pellet or powder to be deposited is placed at the bottom of the container and these are directly or indirectly placed. Heating the metal pellet or powder deposits a metal layer on the article.

Therefore, according to this method, it is difficult to obtain a thick plating layer, the adhesion to reeds and articles is weak, blind holes with high aspect ratios cannot be plated, and 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 coating of noble metal 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 seed layer.

The displacement plating described above utilizes the potential difference between different metals, and there are many examples, but the deposited metal film is thin.

Even if a thick film is obtained, the surface of the film is rough and a good quality film cannot be obtained. Moreover, the plating solution is difficult to manage because it generates explosive lightning (for example, a mixture of AgNH2, N!, 5N, etc.).

In the above chemical reduction plating, 1, for example, Patent Publication No. 5
As shown in No. 2-28729, chemical reduction baths (or electroless plating baths) using amine borane or borohydride as soluble reducing agents are known, but the plating deposition rate is as slow as 92 μm per hour or less. According to the applicant's confirmation experiment, the stability of the plating bath was poor and it could not be put to practical use.

Therefore, increasing the plating deposition rate and improving the stability of the plating bath will open up many 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 silver plating bath composition and method of using this plating bath. An object of the present invention is to provide an electroless silver plating bath composition that allows plating and has good plating bath stability, and a method of using this plating bath.

[Means for solving problems]

The electroless silver 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 precipitation rate of the plating metal, increase the temperature of the plating bath or adjust the pH to an appropriate level.
Alternatively, they found that the above object can be achieved by finding the amount of reducing agent and keeping the plated article at a negative potential at all times, thus completing the present invention.6.

That is, the electroless silver plating solution of the present invention is soluble in the article to be plated in an aqueous solution containing sodium silver cyanide, sodium hydroxide, and sodium cyanide as a reducing agent such as potassium borohydride. The method is characterized in that plating is carried out by immersing a base metal in the above plating solution while contacting it.

The present invention will be explained in more detail below.

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

That is, FIG. 1 shows how the thickness of the deposited silver film changes as the concentration of silver sodium cyanide changes.

At the same time, the concentration of sodium hydroxide and potassium borohydride will affect the precipitation rate.
i'r:, i! -rfc dE, '/afy, no)
! J ') J, -1) z □ As i increases, the deposited film thickness tends to decrease. The maximum thickness of silver deposited film at (
15 μm/Hour) was obtained. To elaborate further,
At a silver sodium cyanide concentration Q of 01 mol, the precipitate is powdery, and at a concentration of α03 mol, a silver precipitate is obtained as a matte film. It showed the highest precipitation rate (9 μm/Hour) at a potassium concentration of 05 mol, and at a sodium hydroxide concentration of α
15 moles.

A powdery precipitate was formed at a potassium borohydride concentration of 0.05 mol.

At a silver sodium cyanide concentration of 0.05 mol, the silver precipitate appeared as a matte film, and at a sodium hydroxide concentration of 0.05 mol.
1 fi mole to 0.20 mole, potassium borohydride concentration 1 [
Highest precipitation rate at 0.05-0.10 mol (131)w
'aour) and the sodium hydroxide concentration vO mole.

At a potassium borohydride concentration of 0.15 mol, the silver precipitate became rough, and addition of a potassium borohydride concentration of n or more was at the limit.

At a silver sodium cyanide concentration of 0.08 mol, the highest precipitation rate (1
6 μm/Hour), and the sodium hydroxide concentration was 0.
At a potassium borohydride concentration of 0.20 mol and a potassium borohydride concentration of 0.20 mol, roughness and discoloration occurred in the precipitate.

Sodium cyanide concentration is 0.10 mol, sodium hydroxide concentration is 1) 20 mol, potassium borohydride concentration is 0.
At 15 mol, the highest precipitation rate (4 μvi) was observed, and at a sodium hydroxide concentration of 0.20 mol and a potassium borohydride concentration of 120 mol, the precipitate became rough and discolored.

Sodium cyanide concentration a is 15 mol, sodium hydroxide concentration a is 20 mol, and potassium borohydride concentration is 0.1.
At 5 mol, the highest precipitation rate (9 μm/Hour) was shown, and at a sodium hydroxide concentration of 020 mol and a potassium borohydride concentration of 0.20 mol, the precipitate became rough and discolored.

Therefore, it is possible to quickly and thickly deposit silver at a silver sodium cyanide concentration of 0.05 to vO mol.

FIG. 2 shows how the thickness of the deposited silver film changes as the sodium hydroxide concentration changes. When the concentration of sodium hydroxide is in the range of 0.03 to 0.20 mol, the thickness of the deposited silver film tends to increase as the concentration increases, and the maximum thickness of the deposited film (15
μmAour), and shows a tendency to change in the range of α20 to α50 mol. Therefore, the optimum concentration of sodium hydroxide was set at 03 to 50 moles.

FIG. 3 shows how the thickness of the deposited silver film changes as the concentration of potassium borohydride changes. The thickness of silver deposited film tends to increase as the potassium borohydride concentration increases, but at 0.2
Since 0 mole tends to cause roughness and discoloration of the precipitate, the limit was set at cuO mole.

FIG. 4 shows how the thickness of the deposited silver film changes as the sodium cyanide concentration changes. Since the thickness of the deposited silver film decreases as the sodium cyanide concentration increases, the upper limit was set at 0.4 mol.

[Effect]

In this invention, the plating deposition rate is 15 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〕
: In the following, this invention will be explained in further detail by giving examples.
) Explain in detail.

Example A bath with the following composition was prepared.

ゞaAg(C9″°“M !M
aON 0.05M NaOHO, 15
M NBH40,10M While stirring the solution with the above composition using a magnetic stirrer, the plated specimen was hooked onto a soluble base metal, immersed in the above solution, and plated by changing the temperature of the solution. Two fc.

FIG. 5 shows the change in the thickness of the deposited silver film.

The 51st figure shows how the thickness of the deposited silver film changes as the temperature of the plating solution changes. As the temperature of the plating solution increased, the thickness of the deposited silver film increased.

Silver precipitation begins when the temperature of the plating solution reaches 50°C and reaches 70'C.
When the temperature is K, a large amount of hydrogen gas is generated due to the hydrolysis of potassium borohydride, and the thickness of the deposited silver film increases rapidly. Even when the plating solution of the present invention was raised to a temperature of 90° C. or higher, no decomposition of the plating solution was observed.

〔Effect of the invention〕

As explained above, this invention has a high deposition rate of 15 μm per hour to obtain a thick plating layer, and the plating bath is stable without decomposition even when the temperature is raised to 90°C or higher, making it economical. It is a great contribution to the

Due to the above-mentioned effects, it can be expected that it will be widely used in plating articles with complex structures that require improved electrical conductivity, opening up applications that have been limited until now.

[Brief explanation of drawings]

Figure 1 shows the relationship between sodium silver cyanide concentration and silver precipitation rate, Figure 2 shows the relationship between sodium hydroxide concentration and silver precipitation rate, and Figure 3 shows the potassium borohydride concentration. Figure 4 is a diagram showing the relationship between sodium cyanide concentration and silver precipitation rate. Figure 5 is a diagram showing the relationship between plating bath temperature and silver deposition rate. It is.

Claims (2)

[Claims] (1) 0.01 to 0.20 mol of sodium silver cyanide, 0.05 to 0.4 mol of sodium cyanide, and 0.01 to 0.20 mol of sodium cyanide;
0 to a solution containing 0.05 to 0.5 mol of sodium hydroxide.
．． An electroless silver plating solution characterized by using 0.3 to 0.20 mol of potassium borohydride as a reducing agent to cause a reduction reaction and deposit silver. (2) The method according to claim (1), characterized in that plating is carried out by contacting or while contacting a soluble base metal with the article to be plated in the electroless silver plating solution. Electrolytic silver plating solution.