JP2002121693A - Free cyan electroplating bath and silver plating method - Google Patents

Abstract

(57) Abstract: A silver ion concentration of 0.02 to 55 g / L,
A halide ion concentration of 1 to 550 g / L, p
A free cyanide electroplating bath for stainless steel, tin or tin alloy, wherein H is adjusted to -1.0 to 2.0. According to the present invention, the electrical contact can be improved by using a stainless steel, tin and tin alloy having a high contact resistance as a substrate and forming a silver plating film on the substrate. Further, by adding the crystal modifier, the uniformity of the film thickness is improved and the silver plating film having high adhesion is formed directly on the base material, so that the plating step can be simplified. Furthermore, even if the acidic solution permeates through the pinholes of the silver plating film in an acidic atmosphere, the adhesion of the silver plating film is not impaired due to the corrosion of the substrate due to the corrosion resistance of the substrate itself, and the contact resistance is increased. Can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment for improving electrical contact and corrosion resistance of a stainless steel, tin or tin alloy substrate.

[0002]

2. Description of the Related Art Silver plating films have excellent conductivity and are relatively inexpensive, and thus are widely used as surface treatment films for general-purpose contacts and functional parts for various electronic industries. . Conventionally, silver plating base plating,
Iron, copper, nickel, etc. are used as the base material, but it is easy to cause poor adhesion due to the substitution reaction between the metal and silver of the base material, so the silver plating film is usually used after strike plating in a silver cyanide bath. Is formed.

In recent years, with the diversification of the use environment of the silver plating film, there are long-term corrosion resistance in an acidic atmosphere having a pH of about 2 to 4 in addition to the properties required for the substrate, such as tensile strength and spring property. In other words, under an acidic atmosphere, the corrosion reaction of the underlying metal proceeds through the pinholes of the silver plating film, which may reduce the adhesion between the base material and the silver plating film, thereby improving the corrosion resistance of the silver plating film under the acidic atmosphere. It has been demanded. Therefore,
It has been studied to use stainless steel having good corrosion resistance because of having a passivation film as a base material, and to form a silver plating film on the stainless steel.

However, when silver plating is performed on stainless steel, a nickel strike film is usually formed using a known wood strike bath in order to secure adhesion,
A silver plating film is formed by performing silver cyanide strike plating and silver cyanide plating, so that the number of plating steps increases and the process management becomes complicated.

On the other hand, tin and tin alloy in an oxidized state as a substrate have good corrosion resistance, but it is difficult to perform silver plating directly on the tin and tin alloy substrate like stainless steel, and the nickel strike film , A silver plating film must be formed.

Even if a silver plating film is formed to a thickness of about 10 μm by such a method, the underlying nickel film is particularly corroded through a pinhole or the like of the silver plating film during operation, and the adhesion of the silver plating film to the substrate is reduced. Stable electrical contact cannot be ensured.

The present invention has been made in order to improve the above circumstances. By directly plating silver on a stainless steel, tin or tin alloy substrate, the plating process can be simplified, and electrical contact and corrosion resistance can be improved. An object of the present invention is to provide an electric silver plating bath and a silver plating method that can be improved.

[0008]

Means for Solving the Problems and Embodiments of the Invention The present inventors have made intensive studies to achieve the above object, and as a result, have reached the present invention. In other words, the present inventors degrease stainless steel, tin and tin alloy base materials according to a well-known method, pretreat with a hydrochloric acid (1: 1) solution, and prepare a known silver cyanide solution in order to compensate for the disadvantages of the prior art. Silver plating was performed using a plating bath. However, sufficient adhesion could not be obtained, and there was a problem in producing a highly reliable silver plating film. Further, as a plating bath for forming a silver plating film on stainless steel, tin or a tin alloy, in addition to a silver cyanide plating bath, ammonium ions, thiocyanate ions, and ferrocyanide ions, which readily dissolve silver ions in a silver plating bath. Various studies were conducted on baths containing thiosulfate ion, ethylenediamine, pyrophosphate ion, thiourea and the like as main components. However, there is a problem that any of these does not have mechanical strength of the plating film itself, or that sufficient adhesion cannot be obtained, if any.

As a result of further studies, the present inventors have found that a stainless steel, tin or tin alloy is prepared using an acidic electro-silver plating bath containing a complexing agent containing a halide ion as a main component and having a pH of 2 or less. It has been found that a silver-plated film having high adhesion, excellent electrical contact properties and excellent corrosion resistance can be obtained when directly plated with silver, thereby forming the present invention.

That is, the present invention provides (1) a silver ion concentration of 0.02 to 55 g / L and a halide ion concentration of 1 to
550 g / L, pH adjusted to -1.0 to 2.0, stainless steel, free cyanide silver electroplating bath for tin or tin alloy, and (2) stainless steel, tin or tin Using the alloy as the object to be plated,
A silver ion concentration of 0.02 to 55 g /
L, a cathode current density of 0.01 to 5 A / dm in a free cyanide electroplating bath having a halide ion concentration of 1 to 550 g / L and a pH adjusted to -1.0 to 2.0.
² , plating on the object to be plated with a thickness of 0.01 to
Provided is an electric silver plating method, which comprises forming a 10-μm silver-plated film. In this case, the silver plating bath contains potassium selenite, potassium selenocyanate, potassium selenate, potassium thiocyanate, ammonium sulfamate, sodium thiosulfate, gelatin, triethanolamine, and thiourea as crystal modifiers for the silver plating film. And at least one kind of gum arabic.

According to the present invention, when a silver plating film is formed directly on a stainless steel, tin or tin alloy substrate, halide ions, particularly chloride ions, bromide ions, and iodides are used as main complexing agents for silver ions. By using a solution containing one or more of the ions and having a pH of the solution that is acidified, the oxide film on the surface of the substrate comes into contact with halide ions under acidity during plating, and the oxidation of the surface of the substrate is performed. The film is dissolved, a silver plating film is formed directly on the base metal, and a silver plating film is formed on stainless steel, tin and a tin alloy with high adhesion.

Hereinafter, the present invention will be described in more detail.
The free cyan electroplating bath of the present invention uses stainless steel, tin or a tin alloy as the base material, enhances the electrical contact of the base material, and directly forms an electrosilver plating film having excellent adhesion on the base material. For this purpose, a bath with a halide ion as the main complexing agent is used as the silver plating bath, and a plating bath in which the solution is acidified is used. This provides excellent film thickness uniformity and low internal stress. A silver plating film can be formed.

In this case, as the stainless steel material, a material known as stainless steel can be used.
In the present invention, the stainless material includes inconel and incoloy.

Examples of the tin and tin alloy include tin and tin alloy materials, as well as tin or tin alloy plating films formed by plating materials such as steel and copper. The tin alloy may be any alloy containing 50% by weight or more of tin, and examples thereof include Sn-Pd, Sn-Ag, and Sn-Cu.

The electroplating bath contains silver ions and halide ions (halogen ions).

Here, as the silver ion supply source, one or more of silver nitrate, silver sulfate, silver oxide, silver thiocyanate, silver chloride, silver bromide, silver iodide and the like can be used. The compounding amount is 0.02 to 55 g / L, preferably 0.1 to 15 g / L, more preferably 1 to 5 g / L as silver ions.
L. If the silver ion concentration is too low, the adhesion is poor, and if it is too high, the corrosion resistance is poor.

On the other hand, examples of the halide ion include chloride ion (Cl ⁻ ), bromide ion (Br ⁻ ), and iodide ion (I ⁻ ). Examples of the counter cation of these halide ions include alkali metal ions such as sodium and potassium, alkaline earth metal ions such as magnesium and calcium, and ammonium ions. A water-soluble compound is used. The halide ion content is 1 to 550 g / L, preferably 50 to 400 g / L, and more preferably 150 to 200 g.
/ L. If the amount is too small, the adhesion is poor, and if it is too large, the corrosion resistance is inferior. The halide ions are silver ions 1
10 to 23,000 moles, more preferably 5 to 5 moles per mole.
It is preferably from 0 to 1,000 mol, more preferably from 100 to 150 mol.

Preferably, the silver plating bath contains a crystal modifier for the silver plating film.
One or two of potassium selenite, potassium selenocyanate, potassium selenate, potassium thiocyanate, ammonium sulfamate, sodium thiosulfate, gelatin, triethanolamine, thiourea, gum arabic, etc.
More than one species can be used. The compounding amount is 0.0
5 to 30 g / L is preferable, and more preferably 0.5 to 1 g / L.
0 g / L, more preferably 1-3 g / L.

The pH of the silver plating bath is -1.0 or more,
2.0 or less, 0.0 to 1.5, more preferably 0.5 to
Adjust to 1.0. If the pH is too low, the contact resistance is poor,
If it is too high, the adhesion will be poor. In addition, sulfuric acid, hydrochloric acid, phosphoric acid, etc. can be mentioned for adjustment of pH. Also, pH
In raising the value, caustic alkali or the like can be used.

When plating is performed using the silver plating bath, the cathode current density (D _k ) is 0.01 to 5 A / dm ² , preferably 0.1 to 3 A / dm ² , and more preferably 0.5 to 3 A / dm ² .
Plating is performed at ２2 A / dm ² . If _Dk is too low or too high, the adhesion is poor. The plating temperature is 5 to 90 ° C.
In particular, it can be 30 to 60 ° C. Stirring is not necessarily required, but stirring by cathode locking, a stirrer, or a pump jet may be performed. In addition, although a silver anode can be used as the anode, the present invention is not limited thereto, and an insoluble anode may be used.

The thickness of the silver plating film formed on the substrate is 0.01 to 10 μm, preferably 0.1 to 5 μm.
μm, and more preferably 1-3 μm. If the film thickness is too thin or too thick, the adhesion is poor. That is, if the thickness of the silver plating film is too large, the silver plating film itself may be partially peeled off with the lapse of time due to the internal stress of the silver plating film itself, and the electrical contact property may decrease. Also, if it is too thin, the adhesiveness is low, and there is a possibility that a problem may occur in securing electrical contact.

When the above-mentioned base material is subjected to silver plating, the pre-treatment method can be carried out according to a conventional method. In particular, in the case of a stainless steel material, the concentration is preferably 1 to 30% by weight after degreasing. More preferably, it is immersed in a hydrochloric acid solution having a concentration of 12 to 18% by weight at 5 to 60 ° C., particularly 10 to 30 ° C. for 0.5 to 5 minutes, particularly 1 to 3 minutes. A method of performing can be adopted.

[0023]

EXAMPLES The present invention will be described below in detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Examples and Comparative Examples] 0.15 mm × 50 m
Fluorine resin heat-resistant tape (around the edge portion of the silver plating film) so that the silver plating film is formed in the range of 40 mm x 70 mm on both sides of the base material shown in Tables 1 to 3 of mx 80 mm, respectively ( With a mask made by Chuko Kasei)
A portion of the heat-resistant tape that was not immersed in the silver plating solution was removed to form a lead portion for connecting the substrate to a lead wire during plating. The stainless steel substrate thus treated is degreased, and is immersed in 2N hydrochloric acid at a liquid temperature of 20 ° C.
After immersion for 5 minutes and washing with water, plating was performed on a stainless steel substrate with silver plating solutions and plating conditions shown in Tables 1 to 3.

The samples thus formed were tested for electrical contact, adhesion between the substrate and the silver plating film, and corrosion resistance by the following methods, and further evaluated comprehensively. The results are shown in Tables 4 to 6.

Evaluation of Contact Resistance The electrical resistance of the silver plating films 2 and 2 ′ on the stainless steel plate (base material) 1 was measured by using the apparatus shown in FIG.
evaluated. To measure the contact resistance, cut the carbon meshes 3 and 3 'into a size of 40 mm x 70 mm, adjust the positions so that the carbon meshes 3 and 3' face each other via the silver plating films 2 and 2 ', and mount them. did. Silver plating film 2,
A direct current was passed between 2 ′ and the voltage (V) between the carbon meshes 3 and 3 ′ was read to determine the contact resistance. With respect to the contact resistance, a resistance value between the fired carbon plate and the carbon mesh obtained under a predetermined load was set as a reference (1). FIG.
In the figures, 4, 4 'are mask tapes, 5, 5' are fastening load cells, 6, 6 'are fastening copper plates, 7 is a voltmeter, and 8 is a constant current DC power supply.

Evaluation of Corrosion Resistance The corrosion resistance of the silver plating films 2 and 2 ′ on the stainless steel plate (base material) 1 was evaluated by using a polypropylene jig 9 as shown in FIG.
It was set to 9 ', put in a corrosion test solution, and after the corrosion test, the contact resistance was determined and evaluated by the apparatus shown in FIG. The corrosion test was carried out using a solution adjusted to pH 2 with sulfuric acid as a corrosion test solution and immersing at 80 ° C. for 100 hours. The silver plating films 2 and 2 ′ for corrosion test evaluation and the stainless steel plate 1 had the same shapes as those used for the contact resistance measurement. In addition, during the corrosion test, a part of the mask at the edge of the stainless steel plate 1 was removed in order to connect with the lead wire during electroplating, but the part was also masked so as not to come into contact with the corrosive liquid. Next, the silver plating films 2, 2 'are brought into contact with the carbon plates 10, 10' via carbon meshes 3, 3 ', and jigs 9, 9' made of polypropylene as shown in FIG.
And immersed in a corrosion liquid. When fixed with the jigs 9 and 9 ′ made of polypropylene, the corrosive liquid seeps into the carbon meshes 3 and 3 ′, but the contact positions of the silver plating films 2 and 2 ′ and the carbon meshes 3 and 3 ′ do not shift. The jigs 9 and 9 ′ made of polypropylene were interposed and fixed. After the corrosion test, the sample was taken out of the liquid, the jigs 9 and 9 ′ made of polypropylene were removed, and the silver plating film 2 on the stainless steel plate 1 was removed.
2 ′ was sufficiently washed with water, dried quickly, and measured again by the contact resistance measurement test. Regarding the contact resistance after the corrosion test, the resistance value between the fired carbon plate and the carbon mesh was set as a reference (1), and twice or less thereof was determined to be good, and 1 or less was determined to be excellent. In addition, when it exceeded twice, it was determined to be defective. After the corrosion test, when the sample was removed from the jigs 9, 9 'made of polypropylene, the adhesion of the silver plating films 2, 2' was reduced, and the silver plating films 2, 2 'were peeled off the stainless steel plate 1. Was determined to be defective at that time.

Evaluation of Adhesion The adhesion evaluation test was performed by a cross cut test. In the cross-cut test, the silver plating film on the stainless steel substrate was cut into 16 cells at equal intervals of 2 mm in width and length with a sharp knife, and a polyester adhesive tape was applied to the cut cells, followed by a momentum. Performed by peeling well. At this time, it is good that the silver plating film does not peel off from the stainless steel substrate together with the tape at any one of 16 locations.
A case where it was peeled off at any point was determined to be defective. In addition, the silver plating film determined to be defective in the adhesion evaluation was not evaluated for both contact resistance and corrosion resistance.

Comprehensive evaluation: Comprehensive evaluation means that all of contact resistance, adhesion and corrosion resistance are judged to be good, and that the contact resistance and adhesion are good.
Those whose corrosion resistance was judged to be excellent were judged to be excellent.

[0030]

[Table 1] Note: SUS austenitic stainless steel plate
Same)

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

[Table 5]

[0035]

[Table 6]

[0036]

According to the present invention, electrical contact can be improved by using a stainless steel, tin and tin alloy having a high contact resistance as a substrate and forming a silver plating film on the substrate. . Further, by adding the crystal modifier, the uniformity of the film thickness is improved and the silver plating film having high adhesion is formed directly on the base material, so that the plating step can be simplified. Furthermore, even if the acidic solution permeates through the pinholes of the silver plating film in an acidic atmosphere, the adhesion of the silver plating film is not impaired due to the corrosion of the substrate due to the corrosion resistance of the substrate itself, and the contact resistance is increased. Can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a method for measuring a contact resistance between a silver plating film and a carbon mesh.

FIG. 2 is a cross-sectional view of a sample composition for evaluating corrosion resistance of a silver plating film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stainless steel plate 2, 2 'Silver plating film 3, 3' Carbon mesh 4, 4 'Mask tape 5, 5' Tightening load cell 6, 6 'Tightening copper plate 7 Voltmeter 8 Constant current DC power supply 9, 9' Polypropylene jig 10,10 'carbon plate

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Katsuhisa Tanabe, Inventor 1-5-1, Hirakata-shi, Osaka F-term in the Central Research Laboratory, Uemura Corporation 4K023 AA24 BA07 BA08 BA09 CA01 CA02 CA06 CA09 CB11 CB32 DA02 DA06 DA07 4K024 AA10 AB01 BA01 BA04 CA02 CA03 CA06 CA16 GA01 GA02 GA04

Claims (4)

[Claims] 1. A silver ion concentration of 0.02 to 55 g / L,
A halide ion concentration of 1 to 550 g / L, p
A free cyanide electroplating bath for stainless steel, tin or tin alloy, wherein H is adjusted to -1.0 to 2.0. 2. As a crystal modifier for a silver plating film, potassium selenite, potassium selenocyanate, potassium selenate, potassium thiocyanate, ammonium sulfamate, sodium thiosulfate, gelatin, triethanolamine, thiourea, gum arabic At least one of
The electroplating bath according to claim 1, wherein the bath contains at least one species. 3. A plate to be plated with stainless steel, tin or a tin alloy, the surface of which has a silver ion concentration of 0.02 to 55 g / L and a halide ion concentration of 1 to 1 g / L.
The cathode current density was 550 g / L in a free cyanide electroplating bath whose pH was adjusted to -1.0 to 2.0.
Plated in 01~5A / dm ^2, an electric silver plating method and forming a silver plating film having a thickness of 0.01~10μm above object for plating. 4. The method according to claim 1, wherein the electroplating bath contains potassium selenite, potassium selenocyanate, potassium selenate, potassium thiocyanate, ammonium sulfamate, sodium thiosulfate, gelatin, triethanolamine as a crystal modifier for the silver plating film. 4. The method according to claim 3, wherein at least one of thiourea and gum arabic is contained.