JPS5915994B2 - silver plating solution - Google Patents

Description

Detailed Description of the Invention 5 The present invention relates to a plating solution for electroplating silver onto a substrate made of copper, nickel, iron, or an alloy thereof, and particularly relates to a plating solution for electroplating silver onto these substrates. This invention relates to a silver plating solution that prevents sticking.

Conventionally, silver plating on the above-mentioned substrates in fields where adhesion and heat resistance are required has been carried out by first applying a thin silver plating using a plating solution with a low silver concentration called strike plating. ,
This was done by plating to the desired thickness using a conventional plating solution with a high silver concentration. The main reason for this is that when silver plating is directly performed on the above substrate from a conventional silver plating solution with a high silver concentration, silver displacement plating occurs on the above substrate in the early stage of plating, which causes This is because it inhibits the adhesion and heat resistance of silver plating. In addition, the strike plating solution itself produces a considerable amount of silver displacement plating j0 on the above-mentioned substrate, and it is necessary to immerse the substrate in the plating solution with a voltage applied in advance. Because silver displacement plating occurs even if liquid or ordinary plating liquid is attached, problems such as contamination and loss of silver in areas other than those that require plating cannot be avoided.
The present invention was developed as a result of various studies to solve the above-mentioned problems, and it is possible to perform strike plating on base materials made of copper, nickel, iron, or alloys thereof, with almost no displacement plating. It is an object of the present invention to provide a silver plating solution that can provide silver plating with excellent heat resistance and adhesion even when not used.

The present invention provides a cyan bath silver plating solution for electroplating silver on a substrate made of copper, nickel, iron or an alloy thereof, in which the amount of free cyanide is 0.5 to 301/l,
and a silver plating solution characterized by adding dithiocarbamic acid or a salt thereof and/or thiosemicarbazide or a salt thereof, thereby preventing displacement plating of silver onto the above-mentioned substrate. . It is particularly effective for copper or copper alloy substrates that undergo silver displacement plating so severe that they turn completely white in ordinary silver plating solutions. For the same purpose as the silver plating solution of the present invention, a silver plating solution containing a free cyanide compound of 10 g/l or less and a mercaptan compound has also been proposed (Japanese Unexamined Patent Application Publication No. 55-34699).

However, even with this liquid, the effect of preventing displacement is not necessarily sufficient. As shown in the below-mentioned comparative example, the silver plating solution of the present invention has a remarkable effect of preventing substitution even when compared with a silver plating solution containing mercaptan. Dithiocarbamic acid or its salt (hereinafter simply referred to as dithiocarpamic acid) or thiosemicarbazide or its salt (hereinafter simply referred to as thiosemicarbazide) is adsorbed on the surface of the substrate or forms a film. shows a strong anti-displacement effect.

When dithiocarbamic acid or thiosemicarbazide is used in combination with a cyanogen-alkaline silver plating solution containing silver as a cyanide complex, it is said that smooth plating with fewer pinholes can be obtained at high current density. A silver plating solution that takes advantage of the excellent features of conventional cyan bath silver plating solutions and hardly causes displacement plating.

However, even the excellent anti-displacement effect of the above compounds rapidly loses its effect when the free cyanide compound exceeds 60 θ/l in a cyan alkaline silver plating solution.

In the present invention, free cyanide is added from 0 to 309/
It is particularly preferred to use a bath in which dithiocarbamic acid and/or thiosemicarpazide is added as a displacement inhibitor to a cyan alkaline silver plating solution.
Dithiocarbamic acid is a compound represented by the general formula (R is hydrogen or a hydrocarbon group), and thiosemicarbazide is a compound represented by the general formula (R is hydrogen or a hydrocarbon group). Dithiocarbamic acid is usually unstable and , in the form of stable salts such as sodium, potassium or ammonium salts.

When contained in the form of these salts, it also has the same anti-replacement effect. Examples of dithiocarbamic acids used in the present invention include diethyldithiocarbamic acid, dimethyldithiocarbamic acid, N-methyldithiocarbamic acid, ethylene-bisthiocarbamic acid, dithiocarbamic acid, dibutyldithiocarbamic acid, etc., and salts thereof, particularly the former Four parties are valid.

In addition, the thiosemicarbazide used in the present invention includes:
4-ethyl-3-thiosemicarbazide, 4-naphthyl-3-thiosemicarbazide, 1,4-diphenyl-3
-thiosemicarbazide, 1-methyl-4-phenyl-3-carbazide, 1-methyl-4-ethyl-3-thiosemicarbazide, etc., or salts thereof, and the effect of preventing substitution between them. The difference is small. A cyan alkaline silver plating solution is usually prepared by dissolving alkali cyanide and silver cyanide, but it is also possible to dissolve alkali silver cyanide and alkali cyanide.

As the alkali metal for these compounds, potassium is excellent because of its smooth plating at high current densities. The concentration of silver is determined by the desired plating current density, and is not particularly specified, but is usually 10 to 651/l. Dithiocarbamic acid and/or thiosemicarbazide are used in such cyan alkaline silver plating solution.
If H is 10 or less, free cyanide is 309
Displacement plating can be prevented even when the pH exceeds 609/l and below 609/l, but when the pH exceeds 10, free cyanide is
If it exceeds 0 g/l and below 60 g/l, kana D substitution plating will occur. If the free cyanide exceeds 30 g/l at PHLO or less, the volatilization of hydrogen cyanide is large, which not only impairs the working environment but also increases the amount of alkali cyanide added. From this point of view,
The required free cyanide concentration in the present invention for cyan alkaline silver plating is 0 to 309/l. However, below 30θ/l of free cyanide,
In addition to the low conductivity of the bath and poor uniform electrodeposition, the pH near the anode decreases during electrolysis, making it easy for insoluble silver cyanide to precipitate. In order to avoid this problem, it is preferable to add a conductive salt having a buffering effect, such as potassium phosphate or potassium pyrophosphate. For example, a bath containing 60 to 1001/l of dipotassium phosphate and adjusted to below PHLO contains 301/l of free potassium cyanide.
Using a silver anode, it is possible to obtain a current density of 1 to 2 A/d, and it can be operated with almost no pH change during electrolysis. If the free cyanide content is less than 201/l, it is essential to use an insoluble anode such as platinum-plated tantalum.
The amount of dithiocarbamic acid or thiosemicarbazide added varies depending on the type, base material, free cyanide concentration in the bath, pH of the bath, etc., but for example, for sodium diethyldithiocarbamate, it is 0.1 to 19%. 114
-0.3 to 39 for ethyl-3-thiosemicarbazide
/l, a sufficient substitution prevention effect can be obtained. It is possible to use a mixture of these anti-displacement agents, or with a substance that has an anti-displacement effect such as another mercaptan, but since this makes management difficult, usually only one type of compound is used for substitution. Prevention can be carried out and sufficient effects can be obtained. However, when dithiocarbamic acid and/or thiosemicarbazide are added, the silver plating may be colored or uneven color may occur.

This tendency is particularly evident when dithiocarbamic acid is added. In that case, additives such as potassium antimonyl citrate, potassium selenium cyanide, or carbon disulfide may be added. Examples of the present invention will be described below.

Example 1: A copper plate was subjected to alkaline electrolytic degreasing and pickling in the usual manner, a platinum-plated titanium plate was used as an anode, and a solution consisting of a silver plating solution was used, and the pH was 8. O, current density 6.5A/DTr
Silver plating with a thickness of 5 μm was carried out at room temperature.

The plated product was heated in the atmosphere at 300°C for 5 minutes, but no heating blisters were observed. Example 2: A phosphor bronze plate was subjected to alkaline electrolysis, degreasing, and pickling in the usual manner, a platinum-plated tantalum plate was used as an anode, a silver plating solution was adjusted to pH 7.6, and the solution was heated at 50°C. Soaked for 1 minute.

This treatment caused almost no change in the color of the phosphor bronze plate surface. Next, silver plating with a thickness of 3 μm was performed using this solution at a current density of 10 A/d.

Adhesion was good, and no heating blisters were observed even after heating at 270°C for 2 minutes. Example 3 Oxygen-free copper foil with a thickness of 35 μm was subjected to acetone degreasing and nitric acid pickling, and then immersed in various silver plating solutions having the compositions shown below to which various additives shown in Table 1 were added.

The pH of the liquid was adjusted to 9.2, and the sample was immersed in a bath at a temperature of 60° C. for 1 minute.

These samples were bath-dissolved in nitric acid, and silver was analyzed by atomic absorption spectrometry to determine the amount of silver displacement plating. The results are shown in Table 1. From Table 1, dithiocarbamic acid according to the present invention,
Silver plating liquid blacks 11 to 15 containing thiosemicarbazide or their salts all had a very small amount of silver displacement plating, whereas comparative examples FL1 to 10 all had a very large amount. I understood.

As described above, the present invention provides a silver plating solution for electroplating silver on a substrate made of copper, nickel, iron, or an alloy thereof, particularly copper or a copper alloy. Since the amount is O~309/l and dithiocarbamic acid or its salt and/or thiosemicarbazide or its salt is added, the above chemicals are adsorbed on the surface of the substrate or form a film. It has the effect of preventing displacement plating of silver onto the base material, so there is very little displacement plating, so silver plating with excellent adhesion and heat resistance can be easily obtained without striking. There are advantages.

Claims (1)

[Claims] 1. In a cyan bath silver plating solution for electroplating silver on a substrate made of copper, nickel, iron or an alloy thereof, the amount of free cyanide is 0 to 30 g/l, and 1. A silver plating solution, which is characterized by containing dithiocarbamic acid or a salt thereof and/or thiosemicarbazide or a salt thereof, thereby preventing substitutional plating of silver onto the substrate. 2 Dithiocarbamic acid or its salt is diethyldithiocarbamic acid, dimethyldithiocarbamic acid, N-
Methylthiocarbamic acid or ethylene-bisdithiocarbamic acid, or a salt thereof, and thiosemicarbazide or a salt thereof is 4-ethyl-3-thiosemicarbazide, 4-naphthyl-3-thiosemicarbazide , 1,4-diphenyl-3-thiosemicarbazide, 1
-Methyl-4-phenyl-3-thiosemicarbazide, 1-methyl-4-ethyl-3-thiosemicarbazide, or a salt thereof, the silver plating solution according to claim 1. .