JPH10330998A - Electroplating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel electroplating method excellent in corrosion resistance and durability, with the decomposition of sulfamic acid reduced even when operated at a high current density and capable of being stably operated over a long period. SOLUTION: When nickel electroplating is conducted by using a plating bath contg. sulfamic acid, an insoluble metallic electrode having an electrode catalyst layer consisting essentially of iridium oxide and the balance tantalum oxide or tin oxide is used as an anode. A plating bath contg. nickel chloride is also effective. Meanwhile, an insoluble metallic electrode obtained by forming an electrode catalyst layer coated with the oxide consisting or 60-90 mol.% iridium oxide and the balance tantalum oxide or tin oxide on a titanium substrate is preferably used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plating method in which a so-called sulfamate plating bath is used for electroplating nickel mainly on electronic parts and steel sheets, and more particularly, has a capability of suppressing the decomposition of sulfamic acid. The present invention relates to a plating method using an anode made of an insoluble metal electrode.

[0002]

2. Description of the Related Art A plating solution containing sulfamic acid is usually used for nickel plating of components requiring particularly high precision such as electronic components. This is because the use of this plating solution not only has good throwing power of the plating and is suitable for precision plating, but also has such properties that highly corrosive chlorine ions and the like do not remain in the plating film.

In nickel plating using a plating solution containing sulfamic acid, nickel metal is usually used as an anode. Nickel metal is a so-called soluble metal in which nickel gradually dissolves in the solution as plating progresses. An anode is formed. Since such an anode is used at the dissolution potential of nickel, there is no decomposition of other components in the plating solution,
Nickel ions in the plating solution are reduced by plating on the surface of the cathode material, but the reduced amount of nickel ions is said to be replenished from the anode. Had been considered the most desirable.

[0004]

However, such a soluble anode actually has the following problems. That is, when the current density increases, passivation occurs on the surface of the nickel anode, and it is not possible to expect smooth dissolution of nickel in the plating solution. In addition, current flows through the passivation layer, thus increasing the overvoltage at the anode. That is, various problems occur because the resistance loss increases.

That is, in this case, the plating voltage (bath voltage) increases. There was a problem that the decomposition of the sulfamic acid in the plating solution became remarkable due to the increase of the plating voltage accompanying the increase of the overvoltage, and it was difficult to perform a normal plating operation. Furthermore, since the generation rate of passive bodies is not constant,
There is also a problem that the amount of nickel eluted from the anode changes, and it is difficult to control the components of the plating solution. Furthermore, if the passivation film falls off in the plating solution, slime is generated, and the slime is codeposited on the nickel electrodeposition film, which causes a problem that the product is defective. In order to avoid eutectoid deposition of slime on the nickel electrodeposition film, it is often used to use an anode bag, in which case nickel is dissolved from the nickel anode and supplied to the plating solution. It becomes difficult. Eventually, there was a problem that the plating operation had to be stopped periodically and a complicated operation of replenishing the nickel anode had to be performed.

In order to solve these problems, attempts have been made to use a platinum-plated titanium electrode, which is an insoluble electrode, as the anode. Platinum-plated titanium electrodes are insoluble and do not cause the problem of slime formation or the increase in interelectrode distance due to dissolution of the electrodes themselves. However, since the anodic reaction in the case of performing nickel plating using an insoluble electrode is an oxygen generating reaction, the anodic potential increases. In addition, when a platinum-plated titanium electrode is used, the oxygen overvoltage is as high as 600 to 800 mV, so that the added anode potential is further increased.

Therefore, in this case, there is a problem that not only the electrolytic voltage rises, but also the decomposition of organic substances such as sulfamic acid in the plating solution is accelerated. Since the potential is further higher, when nickel chloride is contained in this type of plating solution, chlorine ions are dissociated, and a part of the ions is discharged as chlorine gas. When the chlorine gas is discharged, the strong oxidizing action accelerates the decomposition of organic substances in the plating solution, which causes a problem such as causing corrosion of the plating tank. Further, in a plating solution containing an organic substance and chlorine ions, there is a problem that the platinum plating electrode is greatly consumed and its life is short.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is particularly excellent in corrosion resistance and durability in a nickel plating solution containing sulfamic acid. It is an object of the present invention to provide an electroplating method using an anode which can be operated stably for a long period of time with little decomposition.

[0009]

The present invention has solved the problem by the following means. (1) In performing nickel electroplating using a plating bath containing sulfamic acid, an insoluble metal electrode having an electrode catalyst layer mainly composed of iridium oxide and the remainder composed of tantalum oxide or tin oxide is used as an anode. Electroplating method. (2) The insoluble metal electrode is formed by forming an oxide-coated electrode catalyst layer composed of 60 to 90 mol% of iridium oxide and the remainder of tantalum or tin oxide on a titanium substrate. The electroplating method according to (1) above.

(3) The insoluble metal electrode is characterized in that the oxide-coated electrode catalyst layer is prepared by a thermal decomposition method from a solution containing an iridium salt and a tantalum salt or a tin salt. The electroplating method according to (1) or (2). (4) The electricity according to any one of (1) to (3), wherein a contact between the anode and the plating solution is suppressed by providing a porous diaphragm on the surface of the insoluble metal electrode. Plating method. (5) The electroplating method according to (4), wherein the porous diaphragm is made of an insulating material containing silica.

[0011]

Next, an embodiment of the present invention will be described. In the present invention, the base material of the anode provided in the plating solution is preferably titanium in principle. The shape of the titanium substrate is plate-like,
It can take a shape such as a rod shape, an expanded shape, or a perforated plate shape.
It is desirable that the surface of the base material is subjected to grid blasting or shot blasting treatment to increase the actual surface area as much as possible.

The substrate surface is coated with an electrode material constituting an insoluble anode catalyst layer, and is formed by, for example, coating and thermal decomposition. The following composite oxide is used as the insoluble anode material. Specifically, a composite oxide of iridium oxide and tantalum oxide or a composite oxide of iridium oxide and tin oxide is used. The composition ratio of iridium oxide is 50 mol% or more in the whole composite oxide, preferably 60 to 90%.
It is good to be mol%. If the composition ratio of iridium oxide is less than 50 mol%, the reaction point as an electrode may decrease or the oxygen generation overpotential may increase, which may promote the decomposition of organic substances, which is not preferable. .

In addition, when nickel chloride is contained in the plating solution, even if the ratio of iridium oxide is small, the catalytic action on the chlorine generation reaction is not significantly impaired.
However, since the oxygen generation overpotential rises, the chlorine generation reaction may be relatively accelerated, which is not so preferable. Further, when the composition ratio of iridium oxide is larger than 90 mol%, the overvoltage of oxygen generation also increases in this case, and when nickel chloride is contained, the chlorine generation reaction is accelerated, which is not preferable.

The most suitable method for producing such an insoluble metal electrode is a thermal decomposition method. The pyrolysis method is to apply a solution containing a metal salt that constitutes the present electrode substance onto a base metal,
This is a method of thermally decomposing at 450 to 650 ° C. in air. In addition to the thermal decomposition method, for example, a method in which an oxide or a hydroxide is previously supported on an electrode substrate using a binder or the like, such as a sol-gel method, or a reactive PVD method.
(Vacuum deposition) and CVD (chemical vapor deposition). Although there is no particular problem with these other than the pyrolysis method,
Except for the thermal decomposition method, in general, the crystallinity of the coating is improved and it is chemically stabilized.Insoluble metal electrodes using manufacturing methods other than the thermal decomposition method generate oxygen when used as an anode in the plating solution. Tend to increase overvoltage. Therefore, there is a tendency to accelerate the decomposition of organic substances, and it is desirable that they be formed by a thermal decomposition method if possible.

It is preferable to attach a porous diaphragm to the surface of the insoluble metal electrode in order to prevent diffusion of organic substances and chloride ions. The membrane to be attached to the surface of the insoluble metal electrode may be a membrane such as a so-called filter cloth, or a porous insulating layer or the like may be provided by a method such as thermal decomposition. For example, using water glass or silica, etc., providing a porous thin coating film having insulation and corrosion resistance,
It is preferable to suppress contact between the anode and the plating solution.

In order to prevent slime in the plating solution due to elution or collapse of the electrode material, the electrode in the plating solution needs to have sufficiently high corrosion resistance. An electrode in which an electrode material containing a platinum group metal oxide called DSE is coated on all metal surfaces has extremely high durability and is optimal for achieving the object of the present invention. The present invention solves the conventional problems by using an electrode whose characteristics, particularly electrochemical characteristics, are adapted to the purpose.

In the present invention, a sufficient durability as an insoluble metal electrode is given to the anode by using, as the main electrode catalyst material, stable iridium oxide which is not affected by the oxygen generation reaction among the DSE type electrodes. Furthermore, to minimize the decomposition of organic substances such as sulfamic acid in the plating solution, the anode potential should be as low as possible, and if possible, the chance of contact of these organic substances with the anode surface should be minimized. is required. Also, when chlorine ions are contained in the plating solution, it is necessary that the oxygen generation potential is low and the chlorine generation overpotential is as large as possible in order not to generate chlorine by oxidizing it. The present invention, as a result of intensive studies mainly on the iridium oxide electrode catalyst material, it was found that a composite oxide of iridium oxide and tantalum oxide, and a composite oxide coating of iridium oxide and tin oxide are most suitable, furthermore It has been found that the desired characteristics can be obtained by specifying the composition, and the present invention has been completed.

A porous diaphragm may be attached to the surface of the insoluble metal electrode for the purpose of preventing diffusion of organic substances and chloride ions. When a corrosion-resistant coating such as an insulating thin layer of water glass or porous silica is provided on the electrode surface, decomposition of sulfamic acid, which is diffusion-controlled, generation of chlorine gas, and the like can be further suppressed.

[0019]

The present invention will be described below by way of examples, but it is needless to say that the present invention is not limited thereto. (Examples 1 to 10) The surface of a titanium substrate (50 x 50 mm) was subjected to grid blast treatment, and was pickled with hot oxalic acid. After that, iridium chloride and tantalum chloride, and iridium chloride and tin chloride were each dissolved in each hydrochloric acid solvent,
A metal salt solution having a concentration of 100 g / liter in terms of metal was obtained. The thus obtained metal salt solution is applied to the surface of the titanium base material, and then is applied at 100 ° C. for 10 minutes.
After drying for 20 minutes, heat treatment is performed in an electric furnace at 500 ° C. for 20 minutes to obtain iridium oxide (60 to 90 mol%).
And tantalum oxide (40 to 10 mol%) and tin oxide (4
(0 to 10 mol%) of a mixed oxide was obtained on the surface of the titanium substrate.

The application of the metal salt solution, drying and heat treatment were repeated to produce the following insoluble metal electrodes. That is, the ratio of iridium oxide is 60, 70,
Insoluble metal electrodes having an electrode material layer in which the proportion of tantalum oxide is 40, 30, 20, 10 mol%, or the proportion of tin oxide is 40, 30 instead of tantalum oxide. , 20, 10 mol%
Insoluble metal electrodes each having an electrode material layer were prepared. The amount of iridium oxide only is 15 g / m
^{And 2} .

The prepared insoluble metal electrodes were used as anode materials for electroplating in Examples 1 to 8, respectively. Separately, an insoluble metal electrode having an electrode catalyst layer in which the ratio of iridium oxide was 70 mol% was prepared as follows. That is, about 10 g / m ² of silica was applied to the surface of the electrode catalyst layer for those containing tantalum oxide or tin oxide as the balance. The silica was applied by applying water-soluble colloidal silica on the surface in advance and drying in an oven at 150 ° C. for 20 minutes. Those coated with silica were used in Examples 9 and 10 as anode materials for electroplating.

On the other hand, an electrode was formed by forming an electrode catalyst layer having a iridium oxide ratio of 100% on a titanium base material in the same manner as in the above embodiment, and an electrode was prepared. The wood was served. In addition, iridium oxide 30 mol
%, And an electrode having an electrode catalyst layer composed of each mixed oxide containing 70% by mole of tantalum oxide or tin oxide was prepared and used as an anode material for electroplating in Comparative Examples 2 and 3. The amount of iridium oxide alone was 15 g / m2.
^{And 2} . Further, a commercially available platinum titanium electrode having a platinum coating thickness of about 3 μm was prepared and used as an anode material for electroplating in Comparative Example 4.

Each electrode prepared as described above was used as an anode for electroplating as follows. That is, 30 minutes from the cathode of the copper plate (50 × 50 mm) in the electroplating tank.
It was mounted as an anode at a position separated by mm. Nickel sulfamate 300g / L, Nickel chloride 30g /
Liter, a synthetic nickel plating solution containing 30 g / l of boric acid was placed in an electroplating tank, and the anode current density was 20
Electroplating was performed at A / dm ^{2 at} a liquid temperature of 50 ° C. for 1000 hours. The cathode was replaced periodically, and nickel ions consumed in the plating solution were replenished by charging nickel hydroxide salt.

Electroplating was carried out for each anode material for 1000 hours. After completion, the concentration of sulfate ions in the plating solution was analyzed by barium sulfate gravimetric method, and the result was converted into the decomposition rate (%) of sulfamic acid. In addition, the consumption rate (%) of the electrode catalyst was measured using a fluorescent X-ray analyzer (Rigaku Denki Co., Ltd./3511-S).
Determined by the calibration curve method. Table 1 shows the results of the plating treatment for each electrode as the decomposition rate of sulfamic acid and the consumption rate of the electrode catalyst.
It was shown to.

[0025]

[Table 1]

From Table 1, it was found that Examples 1 to 8 had a decomposition rate of sulfamic acid of 16 to 22% and a consumption rate of the catalyst of 3 to 7%. Further, in Examples 9 and 10, it was found that both the decomposition rate of sulfamic acid and the consumption rate of the catalyst were further drastically reduced to 2%. On the other hand, the comparative example shows the decomposition rate,
Both the consumption rate and the consumption rate were large, and particularly in the comparative example using the platinum-plated titanium electrode, both the decomposition rate and the consumption rate were extremely large.

When each electrode used in this example was used as an anode of a nickel plating solution containing nickel sulfamate as an electrolyte, the oxygen generation potential was reduced by about 300 mV as compared with a platinum plating electrode, and the decomposition rate of sulfamic acid was reduced. (%) Could be reduced to 1/3 or less. Furthermore, the consumption rate (%) of the catalyst can be reduced to 1/8 or less of that of the platinum-plated electrode, and a stable plating operation can be performed for a long time.

[0028]

The electroplating method of the present invention uses an electrode catalyst layer, that is, an insoluble metal electrode covered with an electrode catalyst layer mainly containing iridium oxide and also containing tantalum oxide or tin oxide on the surface of the anode material. A stable plating operation over a long period of time becomes possible. In particular, organic substances such as sulfamic acid are hardly decomposed, and substantially no chlorine is generated even when the plating solution contains nickel chloride. It has excellent corrosion resistance and durability, and substantially no slime is generated even when operated at a high current density. The plating solution is extremely low in contamination, and is most suitable for applications requiring precision, such as plating of electronic parts.

Claims (5)

[Claims] In the electroplating of nickel using a plating bath containing sulfamic acid, an insoluble metal electrode having an electrode catalyst layer composed mainly of iridium oxide and the remainder composed of tantalum oxide or tin oxide is used as an anode. An electroplating method comprising: 2. The method according to claim 1, wherein the insoluble metal electrode is formed by forming an oxide-coated electrode catalyst layer comprising 60 to 90 mol% of iridium oxide and a balance of tantalum oxide or tin oxide on a titanium substrate. The electroplating method according to claim 1, wherein: 3. The insoluble metal electrode, wherein the oxide-coated electrode catalyst layer is produced by a thermal decomposition method from a solution containing an iridium salt and a tantalum salt or a tin salt. The electroplating method according to claim 1 or 2. 4. The electroplating according to claim 1, wherein a contact between the anode and the plating solution is suppressed by providing a porous diaphragm on the surface of the insoluble metal electrode. Method. 5. The electroplating method according to claim 4, wherein said porous diaphragm is made of an insulating material containing silica.