JP7621838B2 - Electronic nickel plating solution and electronic nickel plating method - Google Patents

Description

This disclosure relates to an electrolytic nickel plating solution and an electrolytic nickel plating method.

Traditionally, nickel electroplating has been used for a wide range of purposes, including decorative plating, functional plating, and electroforming, because it forms a film that adheres directly to the metal base of the object to be plated. Nickel electroplating solutions used to form nickel films include a Watts bath made of nickel sulfate, nickel chloride, and boric acid, and a sulfamate bath made of nickel sulfamate, nickel chloride, and boric acid. The boric acid contained in the plating bath is a pH buffer that keeps the pH of the nickel plating bath constant to ensure stable electrodeposition of nickel.

Modern Plating Textbook (Non-Patent Document 1) discloses standard conditions for nickel plating baths. For example, the standard conditions for a Watts bath include nickel sulfate: 240-300 g/L, nickel chloride: 45-50 g/L, boric acid: 30-40 g/L, pH: 4-4.5, and current density: 2-8 A/ ^dm2 , and the standard conditions for a sulfamate bath include nickel sulfamate: 300-450 g/L, nickel chloride: 0-30 g/L, boric acid: 30-40 g/L, pH: 3.5-4.5, and current density: 2-15 A/ ^dm2 .

In recent years, productivity has improved by shortening plating times, and so there is a demand for high-speed plating. In electrolytic nickel plating, the inclusion of a high concentration of nickel salt allows processing at a high current density, enabling nickel plating to be performed at high speed. High-speed nickel plating can be performed by increasing the nickel sulfate concentration in a Watts bath and the nickel sulfamate concentration in a sulfamic acid bath.

Electroplating Research Society, "Modern Plating Textbook", pp. 204-215

However, the inventors have discovered that when using an electro-nickel plating solution that contains a high concentration of nickel salts and uses boric acid as a pH buffer for high-speed nickel plating, crystals form in the electro-nickel plating solution if it is left stationary for about a week. This causes problems such as crystals accumulating at the bottom of the plating tank and taking time to redissolve, and the resulting crystals clogging the pump for circulating the electro-nickel plating solution.

In addition, when citric acid is used as a substitute for boric acid, crystals do not form at the bottom of the electrolytic nickel plating solution, but the current efficiency of nickel deposition decreases, and the target film thickness cannot be obtained.

Furthermore, when nickel plating is performed at a high current density, nickel plating can be performed at high speed, but there is a problem that plating burns occur on the plated surface, resulting in a poor appearance.

The present disclosure has been made to solve the above problems, and aims to obtain an electric nickel plating solution that does not generate crystals, has excellent current efficiency, and does not cause poor appearance on the plated surface, even when an electric nickel plating solution containing a high concentration of nickel salt is used for high-speed nickel plating.

A nickel electroplating solution containing a nickel salt, boric acid, and citric acid,
The concentration of the nickel salt is 82 g/L or more and 192 g/L or less in terms of nickel ions,
The concentration of the boric acid is 5 g/L or more and less than 20 g/L,
The concentration of the citric acid is 5 g/L or more and less than 25 g/L,
The nickel electroplating solution has a pH of 1.5 or more and 3.5 or less.

According to the present disclosure, even when an electrolytic nickel plating solution containing a high concentration of nickel salt is used for high-speed nickel plating, it is possible to obtain an electrolytic nickel plating solution that does not generate crystals, has excellent current efficiency, and does not cause poor appearance of the plated surface.

FIG. 1 is a schematic diagram of a plating tank used in the first and second embodiments. FIG. 2 is a schematic diagram of a plating tank used in the first and second embodiments. FIG. 3 is a schematic diagram of a plating tank used in the third and fourth embodiments. FIG. 4 is a schematic diagram of a plating tank used in the third and fourth embodiments. FIG. 5 is a photograph showing the appearance of the plating film in the examples and comparative examples of the present disclosure.

The following describes an embodiment of the present disclosure. Note that in the drawings, dimensional relationships such as length, width, thickness, and depth have been changed as appropriate to clarify and simplify the drawings, and do not represent actual dimensional relationships.

Embodiment 1.
The first embodiment relates to an electric nickel plating solution and an electric nickel plating method using the electric nickel plating solution.

<Electronic nickel plating solution>
The electric nickel plating solution of this embodiment (hereinafter, referred to as "nickel plating solution") uses nickel sulfate as the nickel salt, and nickel sulfate hexahydrate can be used as the nickel sulfate. The content of nickel sulfate is 118 g/L or more and 192 g/L or less as nickel ions (400 g/L or more and 650 g/L or less as nickel sulfate hexahydrate), and preferably 133 g/L or more and 177 g/L or less (450 g/L or more and 600 g/L or less as nickel sulfate hexahydrate). When the content of nickel sulfate is less than 118 g/L as nickel ions (400 g/L as nickel sulfate hexahydrate), when plating is performed at a high current density, the supply of nickel ions to the cathode surface cannot keep up, and hydrogen gas is generated by electrolysis of water simultaneously with the nickel deposition reaction, so high-speed plating is not possible. If the content of nickel sulfate exceeds 192 g/L in terms of nickel ions (650 g/L in terms of nickel sulfate hexahydrate), nickel crystals may precipitate in the nickel plating solution.

In the nickel plating solution of this embodiment, nickel chloride is preferably used to promote dissolution of the nickel anode, and nickel chloride hexahydrate can be used as the nickel chloride. The content of nickel chloride is 5 g/L or more and 15 g/L or less as nickel ions (20 g/L or more and 60 g/L or less as nickel chloride hexahydrate), and preferably 9 g/L or more and 12 g/L or less (35 g/L or more and 50 g/L or less as nickel chloride hexahydrate). If the content of nickel chloride is less than 5 g/L as nickel ions (20 g/L as nickel chloride hexahydrate), the dissolution of the nickel anode is not promoted, and the anode current efficiency may decrease. If the content of nickel chloride is more than 15 g/L as nickel ions (60 g/L as nickel chloride hexahydrate), the electrodeposition stress of the plating film becomes large, and deformation of the plated object, peeling of the nickel film, cracks, etc. may occur.

The boric acid content is 5 g/L or more and less than 20 g/L, and preferably 10 g/L or more and 15 g/L or less. If the boric acid content is less than 5 g/L, the limiting current density decreases and rough, brittle plating burn may occur on the plating surface. If the boric acid content is 20 g/L or more, crystals may precipitate in the nickel plating solution.

The citric acid content is 5 g/L or more and less than 25 g/L, and preferably 10 g/L or more and 20 g/L or less. If the citric acid content is less than 5 g/L, the limiting current density may decrease and rough and brittle plating burn may occur on the plating surface. If the citric acid content is 25 g/L or more, the cathode current efficiency may decrease.

The pH of the nickel plating solution is 1.5 or more and 3.5 or less, and preferably 1.8 or more and 3.0 or less. If the pH of the nickel plating solution is less than 1.5, the concentration of hydrogen ions in the nickel plating solution increases, making it easier for hydrogen gas to be generated simultaneously with the nickel deposition reaction, and the limiting current density may decrease. If the pH of the nickel plating solution exceeds 3.5, plating burn may occur on the surface of the plating film.

The pH adjuster for adjusting the pH of the nickel plating solution is not particularly limited, but examples include nickel carbonate, nickel hydroxide, ammonia, etc.

Other additives may be added to the nickel plating solution as long as they do not impair the effects of the present disclosure. Examples of other additives include primary brighteners, secondary brighteners, and conductive aids. Examples of primary brighteners include saccharin, sodium naphthalenesulfonate, sulfonamide, and sulfinic acid. Examples of secondary brighteners include 1-4 butynediol and coumarin. Examples of conductive aids include sodium sulfate and ammonium chloride.

<Electronic nickel plating method>
The electrolytic nickel plating method of the present embodiment is a method for forming a nickel film on an object to be plated using the above-mentioned nickel plating solution.

Each step of the plating method using the above nickel plating solution will be described in detail below. Note that, although the highly versatile electrolytic nickel plating on copper alloys will be described here, the object to be plated using the above nickel plating solution is not limited to copper alloys.

(Degreasing process)
First, a copper alloy object to be plated is prepared with a machined shape. Next, the object is degreased using a degreasing agent. This removes surface contaminants such as organic foreign matter from the surface of the object to be plated, ensuring liquid wettability. As the degreasing agent, for example, a commercially available alkaline degreasing agent based on sodium hydroxide or sodium carbonate can be used. When using an object to be plated other than a copper alloy and it is desired to remove organic foreign matter, a treatment liquid that is easy to remove may be selected and used in combination from degreasing processes such as solvent degreasing, immersion degreasing, and electric field degreasing.

(Acid washing process)
Next, the object to be plated is subjected to an acid cleaning process using an acid cleaning agent. This removes surface contaminants such as inorganic foreign matter and oxide films from the surface of the object to be plated. In the acid cleaning process, the active metal surface is exposed to ensure liquid wettability, and ensures adhesion between the plated film formed in the subsequent plating process and the object to be plated. As the acid cleaning agent, for example, an etching solution containing diluted sulfuric acid, hydrochloric acid, etc., a commercially available acid cleaning agent, etc. can be used. Note that when the acid cleaning process is performed in a heated environment, it is preferable to use sulfuric acid rather than hydrochloric acid, which generates gas.

(Plating process)
Fig. 1 is a schematic diagram of a plating tank used in the embodiment 1. With reference to Fig. 1, an electric nickel plating process using the above-mentioned nickel plating solution will be described. As a result, a nickel plating film is formed on an object 2 to be plated.

A direct current power supply 1 is used for the current supply. The object 2 to be plated is illustrated as a plate, but the shape of the object 2 is not limited to plate material, and any shape can be used. The material of the object 2 to be plated is not limited to copper, and any material that can be nickel plated can be selected as the object 2 to be plated. The shape of the anode 3 is illustrated as a general-purpose plate, but any shape, such as a mesh shape, can be used. It is preferable to use pure nickel with an impurity weight of 1% or less as the material of the anode 3, but insoluble anodes such as carbon, platinum, and titanium, and anodes containing nickel and additives can also be used. The plating tank 4 can be made of a material that does not dissolve, change shape, or undergo chemical reactions in the plating solution used, such as a material mainly composed of vinyl chloride.

In the electrolytic nickel plating conditions, the current density is preferably 8 A/dm ² or more and 150 A/dm ² or less, and more preferably 10 A/dm ² or more and 100 A/dm ² or less. Since the plating film formation rate is proportional to the current density, plating can be performed at a higher speed by performing plating in the range of 8 A/dm ² or more and 150 A/dm ² or less, compared with the plating film formation rate in the range of 2 A/dm ² or more and 8 A/dm ² or less described in Non-Patent Document 1. If the current density exceeds 150 A/dm ² , the supply of nickel ions cannot keep up, and hydrogen gas is generated by electrolysis of water simultaneously with the nickel precipitation reaction, so plating cannot be performed at a high speed, and plating burn may occur on the plated surface.

The bath temperature of the nickel plating solution in the plating tank 4 is preferably 30°C or higher and 80°C or lower, and more preferably 40°C or higher and 60°C or lower.

When performing plating, it is preferable to stir the plating solution using the stirring device 5 shown in Figure 1. This promotes the supply of nickel ions to the object 2 to be plated compared to when the plating solution is stationary, and is effective in preventing plating burn. The stirring mechanism can be any stirring method, such as mechanical stirring such as propeller stirring or air stirring. However, this does not apply if it is difficult to use a stirring device due to the configuration of the plating equipment and plating tank.

Figure 2 is a schematic diagram of a plating tank when an electric field shielding plate 6 is used. The configuration other than the electric field shielding plate 6 is the same as in Figure 1, so a description of parts other than the electric field shielding plate 6 will be omitted. Plating with the electric field shielding plate 6 installed allows for uniform plating and is also effective in preventing plating burns. In Figure 2, the electric field shielding plate 6 is in a plate shape, but the shape may be changed as appropriate depending on the electric field concentration state of the object 2 to be plated.

Embodiment 2.
<Electronic nickel plating solution>
The second embodiment differs from the first embodiment in that nickel sulfamate is used as the nickel salt in the nickel plating solution.

In the nickel plating solution of this embodiment, nickel sulfamate can be, for example, nickel sulfamate tetrahydrate. The content of nickel sulfamate is 82 g/L or more and 182 g/L or less as nickel ions (450 g/L or more and 1000 g/L or less as nickel sulfamate tetrahydrate), and preferably 100 g/L or more and 145 g/L or less (550 g/L or more and 800 g/L or less as nickel sulfamate tetrahydrate). If the content of nickel sulfamate is less than 82 g/L as nickel ions (450 g/L as nickel sulfamate tetrahydrate), hydrogen gas is generated by electrolysis of water simultaneously with the nickel precipitation reaction, so plating cannot be performed at high speed. If the content of nickel sulfamate is more than 182 g/L as nickel ions (1000 g/L as nickel sulfamate tetrahydrate), nickel crystals may precipitate in the nickel plating solution.

In the nickel plating solution of this embodiment, nickel chloride is preferably used to promote dissolution of the nickel anode, and nickel chloride hexahydrate can be used as the nickel chloride. The content of nickel chloride is 0 g/L or more and 12 g/L or less as nickel ions (0 g/L or more and 50 g/L or less as nickel chloride hexahydrate), and preferably 2 g/L or more and 7 g/L or less (10 g/L or more and 30 g/L or less as nickel chloride hexahydrate). If the content of nickel chloride exceeds 12 g/L as nickel ions (50 g/L as nickel chloride hexahydrate), the electrodeposition stress of the plating film becomes large, and deformation of the plated object, peeling of the nickel film, cracks, etc. may occur.

Regarding the nickel plating solution of this embodiment, explanations of boric acid, citric acid, the pH of the nickel plating solution, pH buffers, and other additives that overlap with those of embodiment 1 will be omitted.

<Electronic nickel plating method>
A plating method using the above nickel plating solution will be described below. Note that, here, electrolytic nickel plating on copper alloys, which is highly versatile, will be described, but as in the first embodiment, the object to be plated used in the plating method using the above nickel plating solution is not limited to copper alloys. Also, in the first embodiment, the degreasing step, the acid washing step, and the plating step were described. The degreasing step and the acid washing step in the second embodiment are the same as those in the first embodiment, and the description thereof will be omitted.

(Plating process)
FIG. 1 is a schematic diagram of a plating tank used in the second embodiment, as in the first embodiment. The DC power source 1, the object to be plated 2, and the plating tank 4 in the second embodiment are the same as those in the first embodiment, and their explanations are omitted. The shape of the anode 3 is illustrated as a general-purpose plate shape, but any shape of anode, such as a mesh shape, can be used. As the material of the anode 3, it is preferable to use an SK-nickel anode containing sulfur, but it is also possible to use an insoluble anode such as carbon, platinum, or titanium, pure nickel with an impurity weight of 1% or less, or an anode containing nickel and additives. In addition, when using an SK-nickel anode, a black product called slime is produced, so it is preferable to cover the anode with an anode bag or the like to prevent the slime from spreading in the liquid.

In the electrolytic nickel plating conditions, the current density is preferably 15 A/dm ² or more and 200 A/dm ² or less, and more preferably 15 A/dm ² or more and 150 A/dm ² or less. Since the plating film formation rate is proportional to the current density, plating can be performed at a higher speed by performing plating in the range of 15 A/dm ² or more and 200 A/dm ² or less, compared to plating in the range of 2 A/dm ² or more and 15 A/dm ² or less described in Non-Patent Document 1. In addition, plating can be performed at a higher current density than when nickel sulfate used in the first embodiment is used as the nickel salt. When the current density exceeds 200 A/dm ² , the supply of nickel ions cannot keep up, and hydrogen gas is generated by electrolysis of water simultaneously with the nickel precipitation reaction, so plating cannot be performed at a high speed, and plating burn may occur on the plated surface.

The bath temperature of the nickel plating solution in the plating tank 4 is preferably 30°C or higher and 80°C or lower, and more preferably 40°C or higher and 60°C or lower.

As in the first embodiment, it is preferable to stir the plating solution using a stirrer 5 and to install an electric field shielding plate 6 to perform plating, but as this overlaps with the first embodiment, a description of this will be omitted.

Embodiment 3.
In the third embodiment, a nickel plating solution using nickel sulfate as the nickel salt is used, as in the first embodiment, and therefore a duplicated description will be omitted.

Next, a plating method using the above nickel plating solution will be described. Note that here, electrolytic nickel plating onto copper alloys, which is highly versatile, will be described, but as with embodiment 1, the object to be plated used in the plating method using the above nickel plating solution is not limited to copper alloys. Also, in the previous embodiment 1, the degreasing process, acid washing process, and plating process were described. The degreasing process and acid washing process in embodiment 3 are the same as those in embodiment 1, and their description will be omitted.

Figure 3 is a schematic diagram of a plating tank used in embodiment 3. In Figure 3, parts similar to those in embodiment 1 are given the same reference numerals and will not be described. The basic structure of the plating tank in embodiment 3 is the same as that of the plating tank shown in embodiment 1. The difference between embodiment 3 and embodiment 1 is that it is provided with a jet piping 7, a jet nozzle 8, and a pump 9 instead of the stirring device 5. When the plating solution is stirred using the stirring device 5, there is a possibility that poor appearance will occur due to insufficient supply of nickel ions caused by insufficient stirring. Therefore, as shown in Figure 3, by providing a mechanism for circulating the nickel plating solution via a pump instead of the stirring mechanism, the supply of nickel ions can be promoted and the above problem can be solved.

Also, FIG. 4 is a schematic diagram of a plating tank used in the third embodiment, similar to FIG. 3. The difference between FIG. 3 and FIG. 4 is that a plating solution stock tank 10 is added to the plating equipment shown in FIG. 3, and a mechanism for feeding plating solution from the plating solution stock tank 10 to the plating tank 4 is provided. By providing the plating solution stock tank 10, the total volume of the plating solution increases, so that the frequency of maintenance of the plating solution during long-term use can be reduced. The flow rate at which the plating solution is fed from the plating solution stock tank 10 to the plating tank 4 is preferably 0.5 m/sec or more. There is no particular limit to the maximum flow rate, and it may be set appropriately. From the viewpoint of preventing problems such as deformation of the plated object and scattering of the plating solution outside the plating tank due to a high flow rate, it may be, for example, 20 m/sec or less. Note that, as in the first embodiment, an electric field shielding plate 6 may be used.

The electrolytic nickel plating conditions were the same as those in the first embodiment, and therefore a detailed description thereof will be omitted.
Embodiment 4.
In the fourth embodiment, a nickel plating solution using nickel sulfamate as the nickel salt is used, as in the second embodiment, and therefore a duplicated description will be omitted.

In addition, in the fourth embodiment, plating is performed using the nickel plating solution described above, but the method includes a degreasing process, an acid washing process, and a plating process. The degreasing process and the acid washing process are the same as those in the first embodiment, so a description thereof will be omitted.

Figures 3 and 4 are schematic diagrams of the plating tank used in embodiment 4, as in embodiment 3. The DC power supply 1, the object to be plated 2, and the plating tank 4 in embodiment 4 are the same as in embodiment 1, and the anode 3 is the same as in embodiment 2, so their explanations are omitted. Also, as in embodiment 3, a plating tank equipped with a mechanism for circulating the nickel plating solution via a pump is used, so their explanations are omitted. Note that, as in embodiment 1, an electric field shielding plate 6 may be used.

The electrolytic nickel plating conditions are the same as those in embodiment 2, so a detailed explanation is omitted.

The present invention will be explained in more detail below with examples and comparative examples, but the present invention is not limited to these examples. Examples 1 to 3 are based on the embodiment 2 shown above.

<Preparation of nickel electroplating solution>
Each component was dissolved in distilled water to obtain the concentration shown in Table 1, to prepare nickel plating solutions of Examples 1 to 3 and Comparative Examples 1 to 6. In Examples 1, 2 and Comparative Example 6, nickel carbonate was added as a pH adjuster to adjust the pH.

<Electronic nickel plating treatment>
The object to be plated was a Hull Cell cathode plate (B-60-P05, manufactured by Yamamoto Plating Tester Co., Ltd.). The size of the object to be plated was a square piece of material that was cut from 67 mm x 100 mm x 0.3 mm to 67 mm x 20 mm x 0.3 mm. The part to be plated of the object to be plated was the flat surface of the square piece, measuring 15 mm x 20 mm.

First, a degreasing process was performed. In the degreasing process, a sodium hydroxide aqueous solution (40 g/L) was used as the degreasing agent. After that, the copper material was immersed in pure water and left for 1 minute, and then removed.

Next, an acid cleaning process was performed. In the acid cleaning process, an etching solution made of a 2:8 mixture of 35% hydrochloric acid and distilled water was used. After that, the copper material was immersed in pure water and left for 1 minute, and then removed.

Next, nickel electroplating was performed under the following conditions using each of the above-mentioned nickel plating solutions to obtain copper sheets electroplated with nickel for Examples 1 to 3 and Comparative Examples 1 to 6. A Hull Cell anode plate (B-59-P07, manufactured by Yamamoto Plating Tester Co., Ltd.) was used as the anode. In addition, as shown in FIG. 2, an electric field shielding plate was placed between each anode and the copper material.
[Electronic nickel plating conditions]
Bath temperature: 50°C
Current density: 25A/ ^dm2 , 50A/ ^dm2 , 75A/ ^dm2 , 100A/ ^dm2
Plating time: 60 seconds for 25 A/ ^dm2 , 30 seconds for 50 A/ ^dm2 , 20 seconds for 75 A/ ^dm2 , 15 seconds for 100 A/ ^dm2 Stirring speed: 300 rpm
<Evaluation>
(Crystallization)
Each of the nickel plating solutions described above was left stationary in an environment at 3° C. for one week. After one week had passed, the presence or absence of crystals inside each nickel plating solution was visually confirmed. The results are shown in the "Crystallization" column of Table 2. The case where there were no crystals in the nickel plating solution was indicated as "A," the case where there were crystals floating in the nickel plating solution was indicated as "B," and the case where there were crystals deposited at the bottom of the nickel plating solution was indicated as "C."

(Current efficiency)
The current efficiency during the formation of the nickel plating film in the above-mentioned Examples 1 to 3 and Comparative Examples 1 to 6 was calculated based on the weight difference of the copper sheet before and after the nickel electroplating process. The current efficiency was calculated by the following formula.

Current efficiency (%) = (actual deposition weight (m1)) / (theoretical deposition weight (m2)) x 100
Moreover, the above m1 and m2 are calculated by the following formula.

m1 (g) = (weight of copper plate after electrolytic nickel plating) - (weight of copper plate before electrolytic nickel plating)
m2(g)=(I×t×M)/(F×i)
I: Current (A)
t: plating time (sec)
M: Atomic weight (g/mol)
F: Faraday constant (C/mol)
i: valence The current efficiency was the average value when electrolytic nickel plating was performed at current densities of 25 A/dm ² , 50 A/dm ² , 75 A/dm ² , and 100 A/dm ² . The results are shown in the "current efficiency" column in Table 2. A current efficiency of 90% or more was indicated as "A," a current efficiency of 80% or more but less than 90% was indicated as "B," and a current efficiency of less than 80% was indicated as "C."

(exterior)
The appearance of the copper plates electrolytically nickel plated in the above-mentioned Examples 1 to 3 and Comparative Examples 1 to 6 was visually confirmed. A photograph of the appearance is shown in Fig. 5. The appearance was taken as the appearance of the copper plate when electrolytically nickel plated at a current density of 100 A/ ^dm2 . The results are shown in the "Appearance" column of Table 2. The case where there was no burn on the copper plate surface was indicated as "A", the case where there was partial burn on the copper plate surface was indicated as "B", and the case where there was widespread burn on the copper plate surface was indicated as "C".

<Considerations>
As shown in Table 2, no crystals were formed in the nickel plating solutions of Examples 1 to 3, and the current efficiency during the formation of the nickel plating film was also good in Examples 1 to 3. In addition, as shown in Table 2 and Figure 5, the copper plates electroplated in Examples 1 to 3 had good appearances without any burn marks on their surfaces.

On the other hand, from the results of Comparative Examples 3 and 4, it can be confirmed that when the concentration of boric acid is 20 g/L or more, crystals precipitate in the nickel plating solution. In addition, regardless of whether or not the pH is adjusted, when the concentration of citric acid is 10 g/L or less, the current efficiency is good, but from the results of Comparative Examples 1 and 5, it can be confirmed that when the concentration of citric acid is 20 g/L or more and the pH of the nickel plating solution is 1.5 or less, the current efficiency deteriorates. Furthermore, from the results of Comparative Examples 2, 5, and 6, it can be confirmed that when the pH of the nickel plating solution exceeds 3.5 or the concentration of citric acid is 25 g/L or more, the copper plate surface is burned, resulting in a poor appearance.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope of the claims.

1 DC power supply, 2 workpiece to be plated, 3 anode, 4 plating tank, 5 stirring device, 6 electric field shielding plate, 7 jet piping, 8 jet nozzle, 9 pump, 10 plating solution stock tank.

Claims (6)

A nickel electroplating solution containing a nickel salt, boric acid, and citric acid,
The nickel salt is nickel sulfamate,
The nickel sulfamate has a concentration of 100 g/L or more and 145 g/L or less in terms of nickel ions,
The concentration of the boric acid is 10 g/L or more and 15 g/L or less ,
The concentration of the citric acid is 10 g/L or more and 20 g/L or less ,
The pH of the nickel electroplating solution is 1.5 or more and 3.0 or less,
The nickel electroplating solution further contains nickel chloride,
The nickel electroplating solution has a nickel chloride concentration of 2 g/L or more and 7 g/L or less in terms of nickel ions . An electric nickel plating method for forming a nickel coating on an object to be plated, comprising the steps of:
2. An electrolytic nickel plating method using the electrolytic nickel plating solution according to claim 1, comprising setting a current density to 15 A/dm2 or ^more and 200 A/dm2 or ^less and a bath temperature to 30°C or more and 80°C or less. 3. The electrolytic nickel plating method according to claim 2 , wherein the object to be plated is electrically shielded in the electrolytic nickel plating solution. 4. The method for electrolytic nickel plating according to claim 2 , wherein the electrolytic nickel plating is performed while the object to be plated is stirred in the electrolytic nickel plating solution. 5. The method for electrolytic nickel plating according to claim 2 , wherein electrolytic nickel plating is carried out while feeding the electrolytic nickel plating solution at a flow rate of 0.5 m/sec or more. The electrolytic nickel plating method according to claim 2 , wherein the object to be plated is a copper alloy.

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