WO2017175428A1 - Hard gold plating solution - Google Patents

Abstract

The purpose of the present invention is to provide a hard gold plating solution by which deposition of gold at unwanted locations can be reliably suppressed. Provided is a hard gold plating solution which is for electroplating and which contains a gold ion supply material, an electrically conductive salt, a complexing agent, a metal salt that contains an element that alloys with gold, and a gold deposition-controlling agent. The hard gold plating solution is characterized in that the gold ion supply material is contained at a quantity of 0.5-14 g/L in terms of gold, the specific gravity of the solution is 2-16 ºBe' at a solution temperature of 25ºC, and the electrical conductivity is 10-70 mS/cm at a solution temperature of 25ºC.

Description

Hard gold plating solution

The present invention relates to a hard gold plating solution for electrolysis.

Gold plating films have been widely used as surface treatments for connection terminals of various electronic parts such as connectors, utilizing the excellent electrical properties and corrosion resistance of gold. Since hard gold plating in such applications requires good wear resistance, corrosion resistance, electrical conductivity, etc., it is necessary to control the crystals constituting the gold plating film. Therefore, as shown in Patent Document 1, a cobalt salt, a nickel salt, or the like has been added to a gold plating solution as a crystal adjusting agent for a gold plating film.

Copper materials such as brass and phosphor bronze are generally used as materials for connectors and the like. When gold plating is applied to these, a nickel plating film is formed as a base plating, and gold plating is applied thereon. In plating on electronic components such as connectors, a partial plating process is required in order to prevent the solder from creeping up to unnecessary portions during the soldering process for electrical connection. That is, when hard gold plating is performed on a nickel plating film, selective plating properties are required in which a hard gold plating film is formed at a necessary portion and a gold plating film is not formed at an unnecessary portion. Further, by not performing gold plating on unnecessary portions, money saving and cost reduction can be realized.

On the other hand, as disclosed in Patent Document 2, in a gold-cobalt alloy plating solution containing gold and cobalt, while maintaining a weak acidity, by adding hexamethylenetetramine, a necessary part of an electronic component such as a connector Only a technique for selectively forming a gold-cobalt alloy plating has been proposed. According to Patent Document 2, the technique can form a good plating film in the high current density region, but the plating deposition property is poor in the low current density region. Since plating deposition does not occur, it is said that the plating deposition selectivity is excellent. However, in the technique of Patent Document 2, gold is actually deposited in unnecessary portions, and it is difficult to grasp the consumption amount of the organic compound used, and the plating bath management cannot be performed quickly. There was a problem.

Therefore, the present applicants disclosed “soluble gold salt or gold complex, conductive salt, malic acid, acetic acid, maleic acid, succinic acid, citric acid, glycine, arginine, and salts thereof disclosed in Patent Document 3 as disclosed in Patent Document 3. In a hard gold plating solution containing one or more selected from the group consisting of at least one metal salt selected from a cobalt salt, a nickel salt, and a silver salt, hydrogen peroxide or iodate is included It has been proposed to adopt a hard gold plating solution characterized by

Japanese Patent Laid-Open No. 2004-76026 JP 2008-45194 A Japanese Patent No. 5025815

However, with the invention disclosed in Patent Document 3, there is an inconvenience that even if terminal plating of electronic parts such as connectors is performed, the phenomenon of gold deposition on the above-mentioned unnecessary portions cannot be completely suppressed.

From the above, an object of the present invention is to provide a hard gold plating solution capable of reliably suppressing gold deposition on unnecessary portions.

Therefore, as a result of intensive studies by the inventors of the present application, it was conceived that the above-mentioned problem can be solved by the following method.

The hard gold plating solution according to the present application is a hard gold plating solution for electrolytic plating containing a gold ion supply raw material, a conductive salt, a complexing agent, a metal salt containing an alloy element for gold, and a gold deposition control agent. The gold ion feedstock is contained in an amount of 0.5 g / L to 14 g / L in terms of gold, the solution specific gravity at a solution temperature of 25 ° C. is 2 ° Be ′ to 16 ° Be ′, and the electrical conductivity at a solution temperature of 25 ° C. is 10 mS. / Cm to 70 mS / cm.

The hard gold plating solution according to the present application preferably has a solution specific gravity of 5 ° Be ′ to 10 ° Be ′.

In addition, the hard gold plating solution according to the present application preferably has an electric conductivity of 28 mS / cm to 50 mS / cm.

In the hard gold plating solution according to the present application, the metal salt containing the alloying element for gold is preferably one or more selected from a cobalt salt, a nickel salt, and a silver salt.

When the metal salt is a cobalt salt, it is preferably contained in an amount of 0.025 g / L to 5 g / L in terms of cobalt.

When the metal salt is a nickel salt, it is preferably contained in an amount of 0.025 g / L to 5 g / L in terms of nickel.

When the metal salt is a silver salt, it is preferably contained in an amount of 0.025 g / L to 60 g / L in terms of silver.

In the hard gold plating solution according to the present application, it is preferable that the gold deposition control agent is hydrogen peroxide and has a concentration of 0.05 g / L to 50 g / L.

The hard gold plating solution according to the present application contains a gold ion supply raw material, a conductive salt, a complexing agent, a metal salt containing an alloy element for gold, and a gold precipitation controlling agent, and a solution specific gravity at a solution temperature of 25 ° C. In addition, the electrical conductivity is controlled within a certain range. By using such a hard gold plating solution, it is possible to form a hard gold plating film only at a necessary location and to reliably suppress gold deposition at an unnecessary location. Therefore, by plating the electronic parts such as connectors using this hard gold plating solution, the solder does not crawl up at unnecessary places during the soldering process, thereby suppressing the deterioration of electrical characteristics. In addition, it is possible to reduce the waste of expensive gold and suppress an increase in cost.

4 is a graph showing a Hull cell test result of the hard plating solution of Example 1. 4 is a graph showing a Hull cell test result of the hard plating solution of Example 1. 4 is a graph showing a Hull cell test result of the hard plating solution of Example 1. It is a graph which shows the electroplating process result of the hard plating solution of Example 2.

The hard gold plating solution according to the present application contains a gold ion feedstock, a conductive salt, a complexing agent, a metal salt containing an alloying element for gold, and a gold deposition control agent. Hereinafter, the contents of the invention will be described by explaining the components of the hard gold plating solution according to the present application.

Gold content and gold ion feedstock: The hard gold plating solution according to the present application is intended for a gold ion feedstock containing 0.5 g / L to 14 g / L in terms of gold. By setting the gold content in the above range, it is possible to obtain a deposition rate of gold that satisfies industrial productivity, to obtain a high-quality hard gold plating film, and to prevent waste of expensive gold.

If the gold content is less than 0.5 g / L, the deposition rate of gold decreases and the required industrial productivity cannot be satisfied. In addition, it is necessary to apply a high voltage to ensure a predetermined current density during electrolytic plating. If a high voltage is applied, appearance deterioration such as burns and redness may occur in the obtained hard gold plating film. The gloss of the surface of the hard gold plating film tends to be lost. On the other hand, when the gold content exceeds 14 g / L, the amount of gold remaining in the hard gold plating solution is increased without being used as the deposited gold, so that the economy is impaired.

In the hard gold plating solution according to the present application, the gold content in terms of gold is more preferably in the range of 5 g / L to 12 g / L. By doing this, it is possible to reliably obtain a gold deposition rate that can sufficiently satisfy the required industrial productivity, and to obtain sufficient solution stability as a hard gold plating solution, A high-quality hard gold plating film can be obtained reliably.

As the gold ion supply material in the hard gold plating solution according to the present application, a gold salt (water-soluble gold salt) or a gold complex that is soluble in water can be used. For example, it is possible to use gold gold cyanide, potassium gold cyanide, potassium gold sulfite, sodium gold sulfite, a gold (III) ethylenediamine complex, a gold complex having a hydantoin derivative as a ligand, and the like. Among them, it is preferable to use potassium gold cyanide. This is because it is easily available on the market and the solution stability can be improved.

Solution specific gravity and electric conductivity: The hard gold plating solution according to the present application has a solution specific gravity of 2 ° Be ′ to 16 ° Be ′ at a solution temperature of 25 ° C., and an electric conductivity of 10 mS / cm 2 at a solution temperature of 25 ° C. 70 mS / cm. The specific gravity of the solution in the present application is defined using a heavy Baume degree which is a practical unit, not an absolute unit. Since the specific gravity of the hard gold plating solution according to the present application is a heavy liquid having a specific gravity larger than that of water, pure water is set to 0 ° Be ′, 15% saline solution is set to 15 ° Be ′, and 15 mag in this interval. It is shown as the value when divided and scaled.

Here, in order to facilitate the explanation of the solution specific gravity and the electric conductivity, the correlation between the solution specific gravity and the electric conductivity will be described first. This "solution specific gravity" and "electrical conductivity" contain "gold ion feedstock", "conducting salt", "complexing agent", "alloying element for gold" contained in the hard gold plating solution according to the present application. It is determined by the content of each component of “metal salt” and “gold deposition control agent”. In the case of the hard gold plating solution according to the present application, the content of any of the above components may be adjusted so that the values of “solution specific gravity” and “electric conductivity” are within the above range. However, from the viewpoint of ensuring current-carrying stability during electroplating and suppressing the deposition of gold in unnecessary parts, the "solution specific gravity" and "electrical conductivity" can be changed by changing the content of "conductive salt". Is preferably within the above-mentioned range. When the content of the conductive salt in the hard gold plating solution is increased, the specific gravity of the solution is increased and the amount of ions is increased to increase the electrical conductivity.

The hard gold plating solution according to the present application has a specific gravity of 2 ° Be ′ to 16 ° Be ′ and an electric conductivity of 10 mS / cm to 70 mS / cm, so that a predetermined deposition rate is obtained in a high current density region. The deposition rate can be reduced in the low current density region while ensuring the above. As a result, it is possible to reliably perform gold deposition in places where plating set in the high current density region is necessary, and to suppress gold deposition in places where plating set in the low current density region is unnecessary. it can. For this reason, when performing terminal plating of electronic components such as connectors, it is possible to deposit gold only in necessary places without causing appearance defects, and reliably suppress gold deposition in unnecessary places. Can do.

When the specific gravity of the solution is less than 2 ° Be ′ or the electrical conductivity is less than 10 mS / cm, it is difficult to ensure a predetermined current density in a high current density region during electrolytic plating. Moreover, in order to ensure a predetermined current density in a high current density region, it is necessary to increase the voltage, but when a high voltage is applied, appearance deterioration such as burns or redness occurs in the obtained gold plating film, There is a tendency for the gloss of the surface of the gold plating film to be lost. On the other hand, when the solution specific gravity exceeds 16 ° Be ′ or the electric conductivity exceeds 70 mS / cm, the solution specific gravity is 2 ° Be ′ to 16 ° Be ′ and the electric conductivity is 10 mS / cm to 70 mS. As compared with the case of / cm, the deposition rate decreases in the high current density region, while the deposition rate increases in the low current density region. Therefore, in order to obtain a predetermined film thickness in the high current density region, it is necessary to lengthen the plating process time. However, if the plating time is lengthened, gold deposition further proceeds in the low current density region. Therefore, when the specific gravity of the solution exceeds 16 ° Be ′ or the electrical conductivity exceeds 70 mS / cm, gold deposition occurs not only in the necessary portions but also in unnecessary portions.

The hard gold plating solution according to the present application has a specific gravity of 5 ° Be ′ to 10 ° Be ′ from the viewpoint of preventing appearance defects and reliably preventing gold deposition on unnecessary portions. The electrical conductivity is preferably 28 mS / cm to 50 mS / cm.

Conductive salt: As the conductive salt used in the hard gold plating solution according to the present application, one or more organic acid compounds and inorganic compounds can be used. Examples of the organic acid compound include compounds having one or more carboxyl groups in one molecule, and specific examples include citric acid, tartaric acid, oxalic acid, lactic acid, and salts thereof. Examples of inorganic compounds include phosphoric acid, sulfuric acid, boric acid, and salts thereof. By using these conductive salts, the current-carrying performance as a hard gold plating solution can be stabilized, and the solution specific gravity and electrical conductivity can be easily adjusted.

This conductive salt is preferably contained in the hard gold plating solution at a concentration of 10 g / L to 200 g / L. When the conductive salt concentration is less than 10 g / L, the electrical conductivity may be less than 10 mS / cm. Moreover, the solution stability as a gold plating solution is lowered, and long-term storage becomes difficult. On the other hand, when the conductive salt concentration exceeds 200 g / L, the electrical conductivity may exceed 70 mS / cm.

In the hard gold plating solution according to the present application, the conductive salt concentration is more preferably 20 g / L to 100 g / L. By doing so, a clear difference is caused in the gold deposition efficiency between the region where gold deposition is required (high current density region) and the region where deposition is unnecessary (low current density region), and The gold deposition rate necessary for operation can be obtained stably.

Complexing agent: In the hard gold plating solution according to the present application, the complexing agent forms a metal complex with gold or an alloy element described later in the hard gold plating solution, and stabilizes the metal complex in the solution. Used to improve solution stability. In addition, as described above, when a gold complex is used from the beginning as a gold ion supply material of the hard gold plating solution according to the present application, this complexing agent is mainly used for complex formation of alloy elements. become. As the complexing agent, it is preferable to use one or more selected from formic acid, malic acid, acetic acid, maleic acid, succinic acid, citric acid, glycine, arginine, and salts thereof. These complexing agents can easily form a complex from gold and an alloy element described later. Moreover, since these complexing agents also function as a buffer material for the hard gold plating solution, the pH can be stabilized. The amount of the complexing agent to be added is determined in consideration of the amounts of gold and alloy elements that form a metal complex in the hard gold plating solution.

In the hard gold plating solution according to the present application, the complexing agent concentration is preferably 1.0 g / L to 250 g / L. When the complexing agent concentration is less than 1.0 g / L, it is difficult to complex gold and alloy elements contained in the hard gold plating solution, and the stability of the solution is impaired, and the hard gold plating solution having a short solution life and Therefore, it is not preferable. On the other hand, when the complexing agent concentration exceeds 250 g / L, it exceeds the amount used for complexing, and the effect as a buffering agent is saturated.

Metal salt containing an alloying element for gold: In the hard gold plating solution according to the present application, “metal salt containing an alloying element for gold” includes a metal component that precipitates (eutectoid) in the plating film together with gold. It is a metal salt, and it is preferable to use one or more selected from water-soluble cobalt salts, nickel salts and silver salts. By doing so, it is possible to easily form a hard gold plating film that reliably contains an alloy element, has high hardness and good wear resistance, and can be used as a contact member such as a connector. Specific metal salts are listed below. The metal salts listed here are excellent in water-dissolving performance, have no effect on gold deposition efficiency, and have excellent eutectoid properties with gold.

Cobalt salts include cobalt sulfate, cobalt chloride, cobalt nitrate, cobalt carbonate, phthalocyanine cobalt, cobalt stearate, ethylenediaminetetraacetic acid disodium cobalt, naphthenate cobalt, borate, cobalt thiocyanate, cobalt sulfamate, cobalt acetate, Cobalt citrate, cobalt hydroxide, cobalt oxalate, cobalt phosphate and the like can be used.

Nickel salts include nickel sulfate, nickel acetate, nickel chloride, nickel borate, nickel benzoate, nickel oxalate, nickel naphthenate, nickel oxide, nickel phosphate, nickel stearate, nickel tartrate, nickel thiocyanate, amidosulfuric acid Nickel, nickel carbonate, nickel citrate, nickel formate, nickel cyanide, nickel hydroxide, nickel nitrate, nickel octoate and the like can be used.

As the silver salt, silver chloride, silver hydroxide, silver iodide, silver sulfide, silver phosphate, silver nitrate or the like can be used.

The hard gold plating solution according to the present application has a total metal salt content of 0.025 g / L regardless of whether the cobalt salt, nickel salt and silver salt are used alone or in combination with a plurality of metal salts. It is preferably ˜5 g / L. If the total metal salt content is less than 0.025 g / L, the amount of eutectoid with respect to the gold plating film is lowered, and a gold plating film having sufficient hardness and wear resistance cannot be obtained. On the other hand, if the total content of the metal salt exceeds 5 g / L, the eutectoid amount of the alloy element in the gold plating film becomes excessive, causing an increase in the electrical resistance of the hard gold plating film, and changing the color tone. Since it tends to become remarkable, it is not preferable.

Gold deposition control agent: This gold deposition control agent has an effect of suppressing gold deposition, and lowers gold deposition efficiency in a low current density region. In other words, it is intended to maintain the gold deposition efficiency at the place where gold deposition is necessary (high current density region) and to suppress the gold deposition at the place where gold deposition is unnecessary (low current density region). . Specific gold deposition control agents include hydrogen peroxide, potassium persulfate, sodium persulfate, ammonium persulfate, potassium iodate, potassium hydrogen iodate, sodium iodate, potassium sulfite, potassium hydrogen sulfite, sodium sulfite, hydrogen sulfite. Sodium, ammonium sulfite and ammonium hydrogen sulfite hydrogen peroxide, persulfate, iodate, sulfite and the like can be used. Hydrogen peroxide is more preferable from the viewpoint of the stability of the plating solution.

The content of the gold deposition control agent in the hard gold plating solution according to the present application is preferably in the range of 0.05 g / L to 50 g / L. When the content of the gold deposition control agent is less than 0.05 g / L, it is difficult to obtain the effect of reducing the gold deposition efficiency in the low current density region, which is not preferable. On the other hand, when the content of the gold deposition control agent exceeds 50 g / L, it tends to decrease even the gold deposition efficiency in the high current density region, which is not preferable.

Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples.

1. Evaluation on Solution Specific Gravity and Electrical Conductivity First, hard gold plating solutions 1 to 8 having the following composition were prepared (pH 4.2). Citric acid acts as a complexing agent, conductive salt and buffer, formic acid acts as a complexing agent, conductive salt and buffer, potassium citrate acts as a conductive salt, and hydrogen peroxide is a gold deposition control agent. Acts as The specific gravity of the solution was adjusted by changing the concentration of citric acid in the range of 0 g / L to 90 g / L and changing the concentration of potassium citrate in the range of 0 g / L to 180 g / L.

Specifically, for the hard gold plating solutions 1 to 8, citric acid, potassium citrate and formic acid were first dissolved in pure water, and then cobalt sulfate was added and dissolved. Next, the pH was adjusted to 4.2 using citric acid and potassium hydroxide as a pH adjuster, and potassium gold cyanide was added and dissolved. Finally, hydrogen peroxide was added and dissolved to obtain a hard gold plating solution. Table 1 shows the solution specific gravity (solution temperature 25 ° C.) of the obtained hard gold plating solution during the bathing. The hard gold plating solution 8 is a comparative solution, and the specific gravity of the solution is outside the range of 2 ° Be ′ to 16 ° Be ′.
Potassium cyanide potassium 14.5g / L (10g / L as gold)
Cobalt sulfate 2.5 g / L (0.5 g / L as cobalt)
Citric acid 0g / L ~ 90g / L
Potassium citrate 0g / L ~ 180g / L
Formic acid 5g / L
Hydrogen peroxide 1.5g / L

Also, a hard gold plating solution 9 was prepared as a reference solution, and the solution specific gravity was measured in the same manner. The hard gold plating solution 9 is a solution in which only 14.5 g / L of potassium gold cyanide and 2.5 g / L of cobalt sulfate (0.5 g / L as cobalt) are dissolved in pure water, and citric acid and formic acid. Does not contain potassium citrate and potassium hydroxide.

Next, the electrical conductivity and kinematic viscosity of the obtained hard gold plating solutions 1 to 9 were measured at a bath temperature of 25 ° C. The results are shown in Table 1.

Next, a Hull cell test was performed on the hard gold plating solutions 3, 4, 6, and 8. The hull cell test uses a hull cell (registered trademark) tester (Yamamoto plating tester), and a clean copper plate (length 67 mm x width 100 mm x thickness 0.3 mm) with a nickel plating film of 5 μm as a test piece. The total current was 2 A, the plating time was 1 minute, the stirring speed was 1000 rpm, and the bath temperature was 50 ° C. The results are shown in FIGS.

FIG. 1 is a graph showing the relationship between the distance between the electrodes and the film thickness of the gold plating film formed along with the hull cell test. In FIG. 1, the horizontal axis indicates the distance from the anode to the cathode (clean copper plate), the region where the distance is small corresponds to the high current density region where plating is necessary, and the region where the distance is large is the low current density. This corresponds to a region where plating is unnecessary. Moreover, although the vertical axis | shaft has shown the film thickness of the obtained gold plating film | membrane, it has meant the deposition rate substantially. Moreover, FIG.1 (b) is the graph which expanded partially Fig.1 (a).

FIG. 2 is a graph showing the relationship between the current density and the film thickness of the gold plating film. The current density depends on the distance from the anode to the cathode (clean copper plate). Moreover, FIG.2 (b) is the graph which expanded partially Fig.2 (a).

FIG. 3 is a graph showing the relationship between the distance between the electrodes and the relative film thickness with respect to the maximum film thickness. Here, the maximum film thickness refers to the film thickness at a location where the distance from the anode to the cathode is 1 cm. FIG. 3B is a partially enlarged graph of FIG.

From Table 1, it is clear that the hard gold plating solutions 1 to 9 have higher solution specific gravity as the contents of citric acid, sodium citrate and formic acid are increased. In addition, it is clear that the hard gold plating solutions 1 to 9 increase in electrical conductivity and kinematic viscosity as the solution specific gravity increases. From FIG. 1 and FIG. 2, the lower the solution specific gravity, the higher the precipitation rate in the high current density region and the lower the precipitation rate in the low to medium current density region, while the higher the solution specific gravity, It is clear that the gold deposition rate in the high current density region tends to decrease and the gold deposition rate in the low to medium current density region tends to increase.

As shown in FIGS. 1 and 2, when the hard gold plating solutions 3, 4 and 6 having a solution specific gravity in the range of 2 to 16 ° Be ′ were used, the distance from the anode was 1 cm. Thus, the film thickness at a location where the current density is 10 / dm ² (high current density region) is 1.8 μm or more. On the other hand, when the hard gold plating solution 8 (comparative solution) having a solution specific gravity of 18.4 ° Be ′ and exceeding 16 ° Be ′ is used, the film thickness at the location is about 1.5 μm. . From this result, the hard gold plating solutions 3, 4, and 6 have a high current density region, that is, a high gold deposition rate in a place where plating is required, and can efficiently deposit gold in the place. it is obvious. In addition, since the hard gold plating solution 8 (comparative solution) has a slow deposition rate of gold in the high current density region, in order to make the film thickness of the portion where the distance from the anode is 1 cm is 1.8 μm or more, The plating time needs to be longer than 1 minute. When the plating time is lengthened, it is expected that gold deposition further proceeds at a location where the current density is set low and plating is unnecessary.

Further, when the hard gold plating solutions 3, 4, and 6 are used, the film thickness at a location (low current density region) where the distance from the anode is 9.5 cm and the current density is 0.1 A / dm ^2. Is 0.15 μm or less, when the hard gold plating solution 8 (comparative solution) is used, the film thickness at the above location is 0.2 μm. From this result, it is clear that the hard gold plating solutions 3, 4 and 6 have a lower current density than the hard gold plating solution 8 (comparative solution), and can further suppress gold deposition to places where plating is unnecessary. It is.

Further, as shown in FIG. 3, when the hard gold plating solutions 3, 4 and 6 are used, the current density region is particularly low as compared with the case where the hard gold plating solution 8 (comparative solution) is used. The relative film thickness with respect to the maximum film thickness (high current density region) is small. For example, when the hard gold plating solutions 3, 4 and 6 are used, the relative film thickness at a location where the distance from the anode is 7 cm and the current density is about 1.3 A / dm ² (low current density region). Is 7% or less, when the hard gold plating solution 8 (comparative solution) is used, the relative film thickness at the above-mentioned location is 12%. When the hard gold plating solutions 3, 4 and 6 are used, the relative film at a location (low current density region) where the distance from the anode is 9.5 cm and the current density is 0.1 A / dm ^2. Whereas the thickness is 0.8% or less, when the hard gold plating solution 8 (comparative solution) is used, the relative film thickness at the above location is 1.3%. From these results, the hard gold plating solutions 3, 4 and 6 ensure the film thickness in the places where plating is required and the places where plating is not required compared with the hard gold plating solution 8 (comparative solution). It is clear that gold deposition on the surface can be suppressed.

2. Evaluation on Precipitation Selectivity First, hard gold plating solutions 10 and 11 having the following composition were prepared (pH 4.2). The specific gravity of the solution was adjusted by changing the concentration of citric acid in the range of 40 g / L to 90 g / L and changing the concentration of potassium citrate in the range of 80 g / L to 180 g / L. Table 2 shows the specific gravity of each hard gold plating solution.
Potassium cyanide potassium 14.5g / L (10g / L as gold)
Cobalt sulfate 2.5 g / L (0.5 g / L as cobalt)
Citric acid 40g / L ~ 90g / L
Formic acid 5g / L
Potassium citrate 80g / L-180g / L
Hydrogen peroxide 2g / L

Next, how much gold deposition occurs in unnecessary parts when using a clean copper plate with a nickel plating film of 5 μm as a test piece and performing partial plating using the above hard gold plating solution. Examined.

First, an evaluation mask made of silicone rubber having a thickness of 3 mm and a plating mask made of silicone rubber having a thickness of 1 mm were prepared. The evaluation mask was formed with a first circular hole having a diameter of 10 mm and a square hole communicating with the circular hole. The square hole portion has a length of 20 mm × a width of 5 mm, the length direction thereof coincides with the radial direction of the first circular hole portion, and communicates with the first circular hole portion at one end portion in the length direction. Further, only a second circular hole having a diameter of 10 mm was formed on the plating mask. Subsequently, each mask was brought into close contact with the nickel plating film of the test piece in the order of an evaluation mask and a plating mask. At this time, the 1st circular hole part and the 2nd circular hole part were connected.

Next, the hard gold plating solution was spouted onto the test piece in which the evaluation mask and the plating mask were in close contact with each other by using a pump to form a hard gold plating film on the nickel plating film. The obtained hard gold plating film had a keyhole shape composed of a first circular portion and a rectangular portion communicating with the circular portion, depending on the shape of the evaluation mask. The plating process was performed at a bath temperature of 50 ° C. and a current density of 50 A / dm ² . The plating treatment time was measured in advance until the gold plating film thickness in the region of the first circular portion reached 0.2 μm, and was the same as that time. During the plating process, the region facing the first circular hole portion of the test piece is a high current density region because there is no plating mask on the nickel plating film and the hard gold plating solution is directly jetted. Since the plating mask is present on the nickel plating film, the region facing the square hole portion of the piece is not directly jetted with the hard gold plating solution, and has a lower current than the region facing the first circular hole portion. It becomes a density region. Therefore, when performing such plating, the area facing the first circular hole portion of the test piece is a place where plating is necessary, and the area facing the square hole portion of the test piece is an unnecessary place for plating, Ideally, the hard gold plating film is not formed in the region facing the square hole.

Next, with respect to the obtained keyhole-shaped hard gold plating film, the opposite side of the circular portion where the rectangular portion communicates is the tip of the circular portion, and the film thickness is increased every 2 mm from the tip of the circular portion to the end of the rectangular portion. It was measured. The results are shown in FIG. Further, the deposition rate was calculated based on the average film thickness of the entire circular portion, that is, the average film thickness of the region where the distance from the tip of the circular portion is 10 mm or less. The results are shown in Table 2.

In FIG. 4, the horizontal axis represents the distance from the tip of the circular portion. The region where the horizontal axis is 0 to 10 mm is a place where plating is necessary, and the region where the horizontal axis is 10 mm to 30 mm is a place where plating is not necessary.

As shown in FIG. 4, in both the hard gold plating solutions 10 and 11, a hard gold plating film is formed in a region where the horizontal axis, which is a place where plating is unnecessary, is 10 mm to 30 mm. However, the hard gold plating solution 10 has a smaller overall film thickness in the region where the horizontal axis is 10 mm to 30 mm, compared with the hard gold plating solution 11. In particular, the film thickness is approximately 0 μm in the hard gold plating solution 10 in the region where the horizontal axis exceeds 18 μm, whereas in the hard gold plating solution 11 the region in which the horizontal axis exceeds 24 μm. Therefore, the hard gold plating solution 10 having a solution specific gravity of 10.0 ° Be ′ has a solution specific gravity of 18 °. As compared with the hard gold plating solution 11 which is 4Be ', it is clear that the effect of suppressing the gold deposition to the place where plating is unnecessary is excellent.

Further, as shown in Table 2, it is clear that the hard gold plating solution 10 has a higher deposition rate than the hard gold plating solution 11 having a higher solution specific gravity. From this, it is clear that the hard gold plating solution 10 can obtain a desired film thickness in a short time in a circular portion that is a place where plating is necessary, as compared with the hard gold plating solution 11. Further, the hard gold plating solution 11 needs to have a longer plating time than the hard gold plating solution 10 in order to obtain a desired film thickness in the circular portion. If the plating time is increased, the plating is unnecessary. The film thickness is further increased in the rectangular portion which is a place. That is, gold deposition on a portion that does not require plating further increases.

As described above, according to the hard gold plating solution of the present invention, it is possible to deposit gold only at a necessary location without causing an appearance defect, and reliably suppress gold deposition at an unnecessary location. For this reason, by applying partial plating to the terminals of electronic components such as connectors using the hard gold plating solution of the present invention, it is possible to suppress the creeping of solder to unnecessary portions during soldering processing. Therefore, it is possible to reduce the waste of expensive gold and suppress an increase in cost.

Claims (8)

In a hard gold plating solution for electrolytic plating containing a gold ion feedstock, a conductive salt, a complexing agent, a metal salt containing an alloy element for gold, and a gold deposition control agent,
The gold ion feedstock contains 0.5 g / L to 14 g / L in terms of gold, the solution specific gravity at a solution temperature of 25 ° C. is 2 ° Be ′ to 16 ° Be ′, and the electric conductivity at a solution temperature of 25 ° C. A hard gold plating solution characterized by being 10 mS / cm to 70 mS / cm. 2. The hard gold plating solution according to claim 1, wherein the solution specific gravity is 5 ° Be ′ to 10 ° Be ′. The hard gold plating solution according to claim 1 or 2, wherein the electrical conductivity is 28 mS / cm to 50 mS / cm. The hard gold plating solution according to any one of claims 1 to 3, wherein the metal salt containing an alloying element for gold is one or more selected from a cobalt salt, a nickel salt, and a silver salt. The hard gold plating solution according to claim 4, comprising 0.025 g / L to 5 g / L of the cobalt salt in terms of cobalt. The hard gold plating solution according to claim 4 or 5, which contains 0.025 g / L to 5 g / L of the nickel salt in terms of nickel. The hard gold plating solution according to any one of claims 4 to 6, wherein the silver salt is contained in an amount of 0.025 g / L to 5 g / L in terms of silver. The hard gold plating solution according to any one of claims 1 to 7, wherein the gold deposition control agent is hydrogen peroxide and has a concentration of 0.05 g / L to 50 g / L.

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