JP6773079B2 - Non-cyan electrolytic gold plating solution - Google Patents

Description

The present invention relates to a non-cyanide electrolytic gold plating solution containing no cyanide compound, and more particularly to a non-cyanide electrolytic gold plating solution capable of forming a hard gold plating film.

Gold-plated coatings with excellent corrosion resistance and high electrical conductivity are widely used not only in the decorative field but also in the electronic industry field as contact materials and wiring materials for electronic components. Generally, gold-plated coatings are classified into two types, a hard coating with a Vickers hardness (HV) of 130 or more and a soft coating with an HV of about 50 to 100, depending on the hardness of the connector or printed wiring board that requires wear resistance. A hard gold-plated film is used for the contacts and the like.

Conventionally, as the hard gold plating film, a gold-cobalt alloy plating film or a gold-nickel alloy plating film, which is electrolytically plated with a cyan-based gold plating solution containing mainly cobalt or nickel, has been used. However, in these alloy plating films, there is a problem that cobalt and nickel in the alloy plating film are oxidized by heat treatment such as a solder reflow process, resulting in surface discoloration and an increase in contact resistance.

A cyan-based gold plating solution that does not contain a metal other than gold and can form a pure gold plating film having a hardness reaching HV160 by electrolytic plating is also known. If it is a pure gold-plated film, surface discoloration and increase in contact resistance due to oxidation are unlikely to occur. However, the hardness of the pure gold-plated film is usually lowered by heat treatment. It is considered that this is because the gold crystal grains grow large in the pure gold plating film by heat treatment, and it is difficult to obtain a hard pure gold plating film having excellent heat resistance.

On the other hand, in recent years, cyanide-based gold plating solutions contain highly toxic cyanide compounds, which poses problems such as work safety and environmental load. Non-cyanide-based electrolytic gold plating solutions that do not contain cyanide compounds have attracted attention. There is. For example, Patent Document 1 proposes a non-cyan alloy plating solution containing cobalt or nickel, which can form a hard gold plating film by electrolytic plating. However, the currently used non-cyan electrolytic gold plating solution is mainly used for forming a soft film.

JP-A-2009-280867

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a non-cyanic electrolytic gold plating solution which does not contain a cyanide compound and can form a hard gold plating film having excellent heat resistance. ..

(1) The non-cyan electrolytic gold plating solution of the present invention is characterized by containing a gold ion supply source, at least one of an inorganic acid or an inorganic acid salt, a thiourea compound, and an ethyleneamine compound.

(2) In (1), the thiourea-based compound is characterized by containing at least one selected from thiourea, methylthiourea, and ethylenethiourea.

(3) In (1) or (2), the ethyleneamine compound is characterized by containing at least one selected from ethylenediamine, triethylenetetramine, tetraethylenepentamine, and polyethyleneimine.

(4) In any of (1) to (3), the inorganic acid contains at least one selected from sulfuric acid, hydrochloric acid, sulfite, phosphoric acid, and sulfamic acid, and the inorganic acid salt is sodium sulfite. , Sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, ammonium chloride, and ammonium sulfamate.

(5) In any of (1) to (4), the content of the thiourea compound is 1 mg / L or more and 1000 mg / L or less, and the content of the ethyleneamine compound is 0.5 g / L or more. , 200 g / L or less.

(6) In any one of (1) to (5), it is characterized by containing at least one of an organic acid and an organic acid salt.

According to the present invention, it is possible to provide a non-cyanic electrolytic gold plating solution that does not contain a cyanide compound and can form a hard gold plating film having excellent heat resistance.

It is an SEM image of the surface of the gold plating film of Example 1. It is an SEM image of the surface of the gold plating film of Example 1 after the heat treatment at 400 degreeC. It is an SEM image of the surface of the gold alloy film of Comparative Example 1. It is an SEM image of the surface of the gold alloy plating film of Comparative Example 1 after the heat treatment at 400 degreeC.

The present inventors heat-treat by adding a thiourea compound and an ethyleneamine compound to a water-soluble gold salt containing no cyan and a non-cyan electrolytic gold plating solution containing an inorganic acid or an inorganic acid salt. However, it has been found that a hard gold plating film whose hardness does not decrease can be formed, and as a result of further studies, the present invention has been completed. Hereinafter, examples of embodiments of the present invention will be described in detail, but the present invention is not limited thereto.

The non-cyan electrolytic gold plating solution of the embodiment (hereinafter, also referred to as “gold plating solution”) contains gold ions, at least one of an inorganic acid or an inorganic acid salt, and a thiourea-based compound and an ethyleneamine compound. It is a gold plating solution for electrolytic plating. When the gold plating solution contains a thiourea compound and an ethyleneamine compound, a hard gold plating film having an HV of 130 or more that can maintain hardness even after heat treatment can be formed. Further, since the formed hard gold plating film does not contain a metal other than gold, surface discoloration and an increase in contact resistance due to oxidation are unlikely to occur even if heat treatment is performed.

A water-soluble gold salt containing no cyanide can be used as the gold ion supply source for supplying gold ions. For example, sodium gold sulfite, potassium gold sulfite, ammonium gold sulfite, sodium gold chloride, potassium gold chloride, gold chloride. Ammonium and the like can be used. The amount of the gold ion supply source is preferably adjusted so that the gold concentration in the gold plating solution is 0.5 g / L to 40 g / L.

As the thiourea-based compound contained in the gold plating solution, for example, one or more of thiourea, methylthiourea, and ethylenethiourea can be used. The content of the thiourea compound in the gold plating solution is preferably in the range of 1 mg / L or more and 1000 mg / L or less, and more preferably in the range of 3 mg / L or more and 200 mg / L or less. If the content of the thiourea compound is too small, the effect cannot be obtained, and if it is too large, the liquid stability is lowered.

As the ethyleneamine compound, for example, one or more of ethylenediamine, triethylenetetramine, tetraethylenepentamine, and polyethyleneimine can be used. The content of the ethyleneamine compound in the gold plating solution is preferably in the range of 0.5 g / L or more and 200 g / L or less, and more preferably in the range of 5 g / L or more and 100 g / L or less. If the content of the ethyleneamine compound is too small, the effect cannot be obtained, and if it is too large, the liquid stability is lowered.

The inorganic acid or inorganic acid salt is not particularly limited, and known inorganic conductive salts can be used. Such inorganic acids include, for example, sulfuric acid, hydrochloric acid, sulfite, phosphoric acid, sulfamic acid, etc., and inorganic acid salts include, for example, sodium sulfite, potassium sulfite, sodium sulfate, potassium sulfate, sodium chloride, potassium chloride, ammonium chloride. , Ammonium sulfamate and the like. The amount of the inorganic acid and the inorganic acid salt added to the gold plating solution is not particularly limited, but is preferably 1 g / L or more and 200 g / L or less, more preferably 10 g / L or more and 100 g / L or less.

Further, at least one of an organic acid and an organic acid salt may be added. Examples of the organic acid and the organic acid salt to be added include glutamic acid, aspartic acid, arginine and the like and salts thereof. The amount of the organic acid and the organic acid salt added is not particularly limited, but is preferably 1 g / L or more and 200 g / L or less, more preferably 10 g / L or more and 100 g / L or less.

The pH of the gold plating solution can be adjusted by adding sulfuric acid, hydrochloric acid, sodium hydroxide, potassium hydroxide, ammonia and the like, and the pH is preferably 6 to 11. Further, in the non-cyan electrolytic gold plating solution of the present invention, it is possible to add other components as necessary within a range that does not impair the object of the present invention. For example, a chelating agent may be appropriately added as a countermeasure against impurity metal ions in the plating solution. Surfactants, smoothing agents, antioxidants and the like may be added.

Hereinafter, an evaluation test example of a non-cyan electrolytic gold plating solution which is an example of the present invention and a gold plating film formed by electrolytic plating using the example will be described, but the present invention is limited to these examples. It's not a thing.
[Example 1]
Using gold sodium sulfite as a gold ion source, 1-methylthiourea as a thiourea compound, triethylenetetramine as an ethyleneamine compound, sodium sulfite as an inorganic acid salt, and arginine as an organic acid, the non-cyan of Example 1 has the following composition. A system electrolytic gold plating solution was prepared. The pH of the plating solution was adjusted to pH 9 by adding sodium hydroxide and sulfuric acid. In the following Examples and Comparative Examples, the content (g / L) of sodium gold sulfite is shown as a value converted to the concentration of gold in the gold plating solution.
Gold plating solution composition of Example 1-Gold sodium sulfite 10 g / L (concentration of gold in gold plating solution)
1-Methylthiourea 80 mg / L
・ Triethylenetetramine 30 g / L
・ Sodium sulfite 40 g / L
・ Arginine 10g / L

In order to evaluate the gold plating film, the gold plating solution of Example 1 was used on a Ni plate subjected to non-cyan gold strike plating, and the thickness was 10 μm under the conditions of a liquid temperature of 60 ° C. and a cathode current density of 0.3 A / dm2. Gold-plated film was formed. The gold plating solution was agitated using a stirrer, and an iridium oxide-based electrode Anodec 100 (manufactured by Nikkei Seisei Co., Ltd.) was used as the anode.

The obtained gold-plated film had a glossy appearance, and as a result of measuring the Vickers hardness, it was a hard film of HV179. The contact resistance (measured load: 0.25 N) was 1 mΩ or less.

Next, in order to evaluate the heat resistance of the gold-plated film, heat treatments at 250 ° C., 30 minutes, and 400 ° C. for 30 minutes were performed in the atmosphere, respectively, and changes in Vickers hardness and contact resistance were examined. The gold-plated film after the heat treatment at 250 ° C. had a glossy appearance and no change in appearance was observed, and the hardness was HV178, which was the same as that before the heat treatment. The contact resistance was 1 mΩ or less, and no change was observed from before the heat treatment.

Further, the gold-plated film after the heat treatment at 400 ° C. also had a glossy appearance and no change was observed in the appearance, and the hardness was HV172, which was the same as that before the heat treatment. The contact resistance is 1 mΩ or less, and no change is observed from before the heat treatment. The results of observing the surface of the gold plating film before and after the heat treatment at 400 ° C. with a scanning electron microscope (SEM) are shown in FIGS. 1 and 2. FIG. 1 is an SEM image before heat treatment (As-depo), and FIG. 2 is an SEM image after heat treatment at 400 ° C. for 30 minutes in the atmosphere. Comparing FIGS. 1 and 2, no change was observed on the surface of the gold plating film, and it can be seen that the effect of the heat treatment at 400 ° C. was small.

[Example 2]
The organic acid of Example 1 was changed from arginine to aspartic acid, and the non-cyan electrolytic gold plating solution of Example 2 was prepared with the following composition. The pH of the plating solution was adjusted to pH 8 by adding sodium hydroxide and sulfuric acid.
Gold plating solution composition of Example 2-Gold sodium sulfite 10 g / L (concentration of gold in gold plating solution)
1-Methylthiourea 50 mg / L
・ Triethylenetetramine 30g / L
・ Sodium sulfite 40 g / L
・ Asparaginic acid 40g / L

The gold plating solution of Example 2 was used on a Ni plate subjected to non-cyan gold strike plating, and the thickness was 10 μm as in Example 1 under the conditions of a liquid temperature of 60 ° C. and a cathode current density of 0.4 A / dm2. A gold-plated film was formed. The obtained gold-plated film had a glossy appearance, and as a result of measuring the Vickers hardness, it was a hard film of HV170. The contact resistance (measured load: 0.25 N) was 1 mΩ or less.

This gold-plated film was heat-treated at 250 ° C. for 30 minutes in the atmosphere, and changes in Vickers hardness and contact resistance were examined. As a result, the gold-plated film had a glossy appearance even after the heat treatment, and the hardness was HV167, which was the same as that before the heat treatment. The contact resistance was 1 mΩ or less, and no change was observed before the heat treatment.

[Example 3]
A non-cyan electrolytic gold plating solution of Example 3 was prepared by using thiourea as a thiourea compound and tetraethylenepentamine as an ethyleneamine compound and containing sodium sulfite, sodium sulfite and glutamate in the following compositions. The pH of the gold plating solution was adjusted to pH 8 by adding sodium hydroxide and sulfuric acid.
Gold plating solution composition of Example 3 ・ Gold sodium sulfite 10 g / L (concentration of gold in gold plating solution)
・ Thiourea 30mg / L
・ Tetraethylene pentamine 20g / L
・ Sodium sulfite 40 g / L
・ Glutamic acid 20g / L

The gold plating solution of Example 3 was used on a non-cyan gold strike-plated Ni plate, and the thickness was 10 μm as in Example 1 under the conditions of a liquid temperature of 60 ° C. and a cathode current density of 0.3 A / dm2. A gold-plated film was formed. The obtained gold-plated film had a glossy appearance, and as a result of measuring the Vickers hardness, it was a hard film of HV169. The contact resistance (measured load: 0.25 N) was 1 mΩ or less.

This gold-plated film was heat-treated at 400 ° C. for 30 minutes in the atmosphere, and changes in Vickers hardness and contact resistance were examined. As a result, the appearance was glossy even after the heat treatment, and the hardness was HV176, which was the same as that before the heat treatment. The contact resistance was 1 mΩ or less, and no change was observed before the heat treatment.

[Example 4]
A non-cyan electrolytic gold plating solution of Example 4 was prepared by using thiourea as a thiourea compound and ethylenediamine as an ethyleneamine compound and containing sodium sulfite, sodium sulfite and aspartic acid in the following compositions. The pH of the gold plating solution was adjusted to pH 8 by adding sodium hydroxide and sulfuric acid.
Composition of gold plating solution of Example 4 ・ Sodium gold sulfite 10g / L (concentration of gold in gold plating solution)
・ Thiourea 40mg / L
・ Ethylenediamine 50g / L
・ Sodium sulfite 40 g / L
・ Aspartic acid 40g / L

The gold plating solution of Example 4 was used on a Ni plate subjected to non-cyan gold strike plating, and the thickness was 10 μm as in Example 1 under the conditions of a liquid temperature of 55 ° C. and a cathode current density of 0.4 A / dm2. A gold-plated film was formed. The obtained gold-plated film had a glossy appearance, and as a result of measuring the Vickers hardness, it was a hard film of HV161. The contact resistance (measured load: 0.25 N) was 1 mΩ or less.

This gold-plated film was heat-treated at 350 ° C. for 30 minutes in the atmosphere, and changes in Vickers hardness and contact resistance were examined. As a result, the appearance was glossy even after the heat treatment, and the hardness was HV156, which was the same as that before the heat treatment. The contact resistance was 1 mΩ or less, and no change was observed before the heat treatment.

With respect to the non-cyan electrolytic gold plating solutions of Examples 1 to 4, the number of times (MTO: Metal) of precipitating the same amount of gold as the amount of gold contained in the plating solution by plating and replenishing the reduced components assuming continuous use. I checked Turn Over). As a result, in each of Examples 1 to 4, a good gold plating film could be formed for more than 5 turns, and the plating solution did not become turbid.

From the above results, it can be seen that the non-cyan electrolytic gold plating solutions of Examples 1 to 4 can form a hard gold plating film by electrolytic plating. It can be seen that the formed hard gold plating film is a hard gold plating film having excellent heat resistance, which can maintain its hardness even after heat treatment and does not cause discoloration or increase in contact resistance. Further, it can be seen that the non-cyan electrolytic gold plating solutions of Examples 1 to 4 can form a good gold plating film for more than 5 turns and are excellent in stability.

For comparison, a commonly used cyan-based electrolytic gold plating solution containing cobalt and a non-cyan-based electrolytic gold plating solution containing no thiourea-based compound or ethyleneamine compound were prepared, and gold plating obtained by electrolytic plating was performed. The film was evaluated.
[Comparative Example 1]
As Comparative Example 1, cyanide gold containing 8 g / L of gold potassium cyanide (converted to the concentration of gold in the plating solution) and 1 g / L of cobalt sulfate (converted to the concentration of cobalt in the plating solution). A gold-cobalt alloy plating film having a thickness of 10 μm was formed on a Ni plate subjected to gold strike plating using a cobalt alloy plating solution under the conditions of a liquid temperature of 40 ° C. and a cathode current density of 0.5 A / dm2. Electroplating was carried out by stirring with a stirrer and using an iridium oxide-based electrode Anodec 100 as an anode in the same manner as in Example 1. The obtained gold-cobalt alloy plating film had a glossy appearance, and as a result of measuring the Vickers hardness, it was a hard film of HV159. The contact resistance (measured load: 0.25 N) was 1 mΩ or less.

The obtained gold-cobalt alloy plating film was heat-treated in the atmosphere at 250 ° C. for 30 minutes and at 400 ° C. for 30 minutes, respectively, and changes in Vickers hardness and contact resistance were examined. In the gold-cobalt alloy plating film after the heat treatment at 250 ° C., the hardness was HV160, which was the same as that before the heat treatment, and the contact resistance was 1 mΩ or less, which was the same as before the heat treatment. However, the appearance of the film became slightly darker and a decrease in glossiness was observed.

The hardness of the gold-cobalt alloy plating film after the heat treatment at 400 ° C. was HV155, which was the same as that before the heat treatment. However, the appearance of the film became dark and the glossiness was greatly reduced. In addition, the contact resistance also deteriorated to 20 mΩ or more. The results of observing the surface of the gold-cobalt alloy plating film before and after the heat treatment at 400 ° C. by SEM are shown in FIGS. FIG. 3 is an SEM image before heat treatment (As-depo), and FIG. 4 is an SEM image after heat treatment. Comparing FIGS. 3 and 4, it can be seen that white spot-like regions appear on the surface of the gold-cobalt alloy plating film after the heat treatment, and the cobalt is oxidized by the heat treatment and the surface is altered. In Comparative Example 1, the hardness was maintained even after the heat treatment at 400 ° C., but the glossiness of the appearance was decreased by the heat treatment at 250 ° C., and the contact resistance was deteriorated by the oxidation of cobalt in the heat treatment at 400 ° C.

[Comparative Example 2]
A non-cyan electrolytic gold plating solution having the following composition, which does not contain a thiourea compound, was prepared as Comparative Example 2. The pH of the gold plating solution was adjusted to pH 8 by adding sodium hydroxide and sulfuric acid.
Gold plating solution composition of Comparative Example 2-Gold sodium sulfite 10 g / L (amount of gold in gold plating solution)
・ Triethylenetetramine 20 g / L
・ Sodium sulfite 40 g / L
・ Glutamic acid 20g / L

The gold plating solution of Comparative Example 2 was used on a Ni plate subjected to non-cyan gold strike plating, and the thickness was 10 μm as in Example 1 under the conditions of a liquid temperature of 60 ° C. and a cathode current density of 0.3 A / dm2. A gold-plated film was formed. As a result of measuring the Vickers hardness of the obtained gold-plated film, it was HV102 and no hard gold-plated film was obtained.

[Comparative Example 3]
A non-cyan electrolytic gold plating solution having the following composition, which does not contain an ethyleneamine compound, was prepared as Comparative Example 3. The pH of the gold plating solution was adjusted to pH 8 by adding sodium hydroxide and sulfuric acid.
Composition of gold plating solution of Comparative Example 3 ・ Sodium gold sulfite 10 g / L (amount of gold in gold plating solution)
・ Thiourea 60mg / L
・ Sodium sulfite 40 g / L
・ Aspartic acid 20g / L

On a Ni plate subjected to non-cyan gold strike plating, the gold plating solution of Comparative Example 3 was used, and the thickness was 10 μm as in Example 1 under the conditions of a liquid temperature of 60 ° C. and a cathode current density of 0.3 A / dm2. A gold-plated film was formed. The obtained gold-plated film had a glossy appearance, and as a result of hardness measurement, it was HV170, and the contact resistance (measured load: 0.25N) was 1 mΩ or less. However, the gold plating solution of Comparative Example 3 was turbid during electrolytic plating and the solution was decomposed, so that stable electrolytic plating could not be performed.

[Comparative Example 4]
A non-cyan electrolytic gold plating solution having the following composition, which does not contain a thiourea compound and an ethyleneamine compound, was prepared as Comparative Example 4. The pH of the gold plating solution was adjusted to pH 8 by adding sodium hydroxide and sulfuric acid.
Composition of gold plating solution of Comparative Example 4 ・ Sodium gold sulfite 10g / L (amount of gold in gold plating solution)
・ Sodium arsenate 3 mg / L
・ Sodium sulfite 40 g / L
・ Arginine 20g / L

The gold plating solution of Comparative Example 4 was used on a Ni plate subjected to non-cyan gold strike plating, and the thickness was 10 μm as in Example 1 under the conditions of a liquid temperature of 60 ° C. and a cathode current density of 0.3 A / dm2. A gold-plated film was formed. The obtained gold-plated film had a glossy appearance, and as a result of measuring the Vickers hardness, it was a hard film of HV181. The contact resistance (measured load: 0.25 N) was 1 mΩ or less. However, when this gold-plated film was heat-treated at 250 ° C. for 30 minutes in the atmosphere, the hardness after the heat treatment decreased to HV113, and the hardness could not be maintained.

As described above, the non-cyan electrolytic gold plating solution of the present invention can form a hard gold plating film having excellent heat resistance without a large decrease in hardness even when heat-treated, and without discoloration or deterioration of contact resistance. In addition, since it does not contain highly toxic cyanide compounds, it can work safely and has less environmental load than cyanide-based plating solutions. The present invention is not limited to the above-described embodiment, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

Claims (5)

A non-cyan electrolyte gold containing at least one of a gold ion source, an inorganic acid or an inorganic acid salt, a thiourea compound, an ethyleneamine compound, and at least one of an organic acid or an organic acid salt. Plating liquid. The non-cyan electrolytic gold plating solution according to claim 1, wherein the thiourea-based compound contains at least one selected from thiourea, methylthiourea, and ethylenethiourea. The non-cyan electrolytic gold plating solution according to claim 1 or 2, wherein the ethyleneamine compound contains at least one selected from ethylenediamine, triethylenetetramine, tetraethylenepentamine, and polyethyleneimine. The inorganic acid contains at least one selected from sulfuric acid, hydrochloric acid, sulfite, phosphoric acid, and sulfamic acid, and the inorganic acid salt is sodium sulfite, potassium sulfite, sodium sulfate, potassium sulfate, sodium chloride, potassium chloride. The non-cyan electrolytic gold plating solution according to any one of claims 1 to 3, which comprises at least one selected from ammonium chloride and ammonium sulfamate. Claim 1 is characterized in that the content of the thiourea-based compound is 1 mg / L or more and 1000 mg / L or less, and the content of the ethyleneamine compound is 0.5 g / L or more and 200 g / L or less. The non-cyan electrolytic gold plating solution according to any one of 4 to 4.