TWI626337B - Hard gold plating solution - Google Patents

Abstract

The present invention provides a hard gold plating solution which can surely suppress unwanted gold precipitation. The hard gold plating solution is a hard gold plating solution for electrolysis including a gold ion supply raw material, a conductive salt, a distorer, a metal salt containing a gold alloying element, and a gold precipitation controlling agent, and the gold ion supply raw material is 0.5 in terms of gold. g/L~14g/L, when the solution temperature is 25 °C, the specific gravity of the solution is 2°Be'~16°Be', and when the solution temperature is 25°C, the conductivity is 10mS/cm~70mS/cm.

Description

Hard gold plating solution

This invention relates to hard gold plating solutions.

The gold-plated film has good electrical conductivity and corrosion resistance of gold, and can be widely used as a surface treatment of various electronic product terminals such as connectors. In order to have good wear resistance, corrosion resistance, and electrical conductivity, hard gold plating for such use must control the crystals constituting the gold plating film. Therefore, Patent Document 1 discloses that a cobalt salt, a nickel salt, or the like as a gold plating film crystal modifier is added to a gold plating solution.

For materials such as connectors, a copper alloy such as brass or phosphor bronze is generally used. When gold plating is performed, a nickel film as a plating substrate is first formed, and gold plating is performed thereon. Electroplating of electronic products such as these connectors is carried out, and when soldering is performed for electrical connection, in order to prevent solder from climbing on unnecessary portions, partial plating treatment is necessary. In other words, when hard gold plating is performed on the nickel plating film, a hard gold film is formed where necessary, and a hard gold film is not formed where it is not necessary, and it is necessary to perform selective plating. In addition, gold plating is not required where it is not needed, which saves gold consumption and reduces costs.

Further, Patent Document 2 discloses that a gold-cobalt alloy plating solution containing gold and cobalt is maintained in a weakly acidic state, and by adding cyclohexamethylenetetramine, selectively forms only gold and cobalt for a necessary portion of an electronic product such as a connector. Alloy plating. If the technique of Patent Document 2 is used, it can be formed well in a high current density region on the one hand. The plating film is difficult to be plated and deposited in a low current density region, so plating deposition does not occur in an unnecessary portion, and a good selective plating deposition effect is obtained. However, the technique of Patent Document 2 not only causes gold deposition in an unnecessary place, but also makes it difficult to control the consumption amount of the organic compound, and has a problem that the plating bath cannot be quickly managed.

Therefore, the inventors of the present invention disclosed the "including soluble gold salt or gold complex, conductive salt, malic acid, acetic acid, maleic acid, succinic acid, citric acid, glycine, and refined ammonia as a dismuting agent" disclosed in Patent Document 3. One or more selected from the group consisting of an acid and a salt thereof, and a hard gold plating solution, hydrogen peroxide, and iodate selected from at least one metal salt selected from the group consisting of a cobalt salt, a nickel salt, and a silver salt. Hard gold plating solution, etc.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-76026

Patent Document 2: JP-A-2008-45194

Patent Document 3: Japanese Patent No. 5025815

However, even if the terminal of an electronic product such as a connector is plated by the invention disclosed in Patent Document 3, the phenomenon of gold deposition in an unnecessary portion cannot be completely suppressed.

In view of the above, the present invention provides a hard gold plating solution which can surely suppress unwanted gold precipitation.

As a result of extensive research by the present inventors, it has been found that the above problems can be solved by the following.

The hard gold plating solution of the present invention is a hard gold plating solution for electrolysis including a gold ion supply material, a conductive salt, a distorer, a metal salt containing a gold alloying element, and a gold precipitation control agent, and the gold ion supply material is contained in gold. 0.5g/L~14g/L, when the solution temperature is 25°C, the specific gravity of the solution is 2°Be'~16°Be', and when the solution temperature is 25°C, the conductivity is 10mS/cm~70mS/cm.

In the hard gold plating solution of the present invention, the specific gravity of the solution is preferably 5°Be'~10°Be'.

Further, in the hard gold plating solution of the present invention, the conductivity is preferably from 28 mS/cm to 50 mS/cm.

In the hard gold plating solution of the present invention, the metal salt containing the alloying element of gold is preferably at least one or more selected from the group consisting of a cobalt salt, a nickel salt and a silver salt.

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

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

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

In the hard gold plating solution of the present invention, the gold precipitation controlling agent is preferably hydrogen peroxide having a concentration of 0.05 g/L to 50 g/L.

The invention is a hard gold plating solution, comprising a gold ion supply raw material, a conductive salt, a distorting agent, a metal salt containing an alloying element with respect to gold, and a gold precipitation controlling agent. When the solution temperature is 25 ° C, the specific gravity and conductivity of the solution are controlled. Within a certain range. By using this hard gold plating solution, a hard gold film can be formed only where necessary, and gold precipitation can be surely suppressed in an unnecessary place. Therefore, by using this hard gold plating solution, an electronic product such as a connector is plated, and when soldering is performed, solder climbing does not occur in an unnecessary place, deterioration of conductive characteristics can be suppressed, waste of expensive gold material can be reduced, and cost can be prevented from increasing.

Fig. 1 is a graph showing the results of the Hull cell test of the hard gold plating solution of Example 1.

Fig. 2 is a graph showing the results of the Hull cell test of the hard gold plating solution of Example 1.

Fig. 3 is a graph showing the results of the Hull cell test of the hard gold plating solution of Example 1.

Fig. 4 is a graph showing the results of the hard electrolytic plating test of Example 2.

The hard gold plating solution of the present invention includes a gold ion supply material, a conductive salt, a distorer, a metal salt containing an alloying element with respect to gold, and a gold precipitation controlling agent. Hereinafter, the composition of the hard gold plating solution of the present invention will be described separately to explain the present invention in detail.

Gold content and gold ion supply material: The hard gold plating solution of the present invention contains a gold ion supply material and contains 0.5 g/L to 14 g/L in terms of gold. By The gold content is controlled within the above range, which satisfies the gold deposition rate of industrial production, obtains a good quality hard gold plating film, and prevents waste of expensive gold materials.

When the gold content is less than 0.5 g/L, the gold deposition rate is lowered, and the industrial productivity cannot be satisfied. Further, in order to secure the current density set at the time of electrolysis, it is necessary to apply high-voltage electricity, and if high-voltage electric power is applied, the obtained hard gold plating film is discolored or the appearance of red is deteriorated, and the surface of the hard gold plating film is tarnished. Further, when the gold content exceeds 14 g/L, since the amount of gold which is not used in the hard gold plating solution is increased, there is no economic effect.

Further, in the hard gold plating solution of the present invention, it is preferably contained in an amount of 5 g/L to 12 g/L in terms of gold. In this way, the industrial productivity can be fully satisfied, the precipitation rate of gold can be ensured, and the hard gold plating solution has sufficient stability, and a hard gold plating film of excellent quality can be surely obtained.

In the hard gold plating solution of the present invention, a gold ion-soluble raw material may use a water-soluble gold salt (water-soluble gold salt) or a gold complex. For example, potassium cyanide (I) potassium, potassium cyanide (II) potassium, gold potassium sulfite, gold sodium sulfite, gold (III) ethylene diamine complex, and beta carbamide as a ligand can be used. Gold complexes of derivatives, etc. Among them, potassium cyanide (I) is preferred. It is easily available on the market and can increase the stability of the solution.

Solution Specific Gravity and Conductivity: The hard gold plating solution of the present invention has a specific gravity of 2°Be'~16°Be' at a solution temperature of 25 ° C and a conductivity of 10 mS/cm to 70 mS/cm at a solution temperature of 25 ° C. The specific gravity of the solution of the present invention is not an absolute unit but a practical unit Baumé degree. The solution of the hard gold plating solution of the present invention has a specific gravity larger than that of water, and the pure water is 0°Be', and the 15% concentration of the brine is 15°Be', and the numerical value is divided into 15 equal parts.

In the present invention, in order to easily explain the specific gravity and conductivity of the solution, the relationship between the specific gravity of the solution and the conductivity is described. The "solution specific gravity" and the "conductivity" according to the present invention are "gold ion supply raw material", "conductive salt", "distorting agent", and "metal salt containing an alloying element with respect to gold" contained in the hard gold plating solution of the present invention. And the content of each component of the "gold precipitation control agent". In the hard gold plating solution of the present invention, the content of each of the above components is adjusted, and if the "solution specific gravity" and the "electrical conductivity" are within the above range, there is no problem. However, in order to ensure the stability of the current during plating and to suppress the precipitation of gold at an unnecessary portion, it is preferable to change the "conductive salt" content so that the "solution specific gravity" and the "conductivity" are within the above range. The increase in the content of the conductive salt in the hard gold plating solution causes the specific gravity of the solution to increase and the amount of ions to increase, resulting in an increase in conductivity.

The hard gold plating solution of the present invention utilizes a solution specific gravity of 2°Be'~16°Be' and a conductivity of 10 mS/cm to 70 mS/cm to ensure a deposition rate in a high current density region and reduce precipitation in a low current density region. speed. As a result, the high current density region can be set to the portion to be plated, gold deposition is surely performed, and the low current density region is set to a portion where plating is not required, and gold deposition is suppressed. Therefore, when the terminal of an electronic product such as a connector is subjected to electroplating, appearance defects do not occur, and gold deposition can be performed only in a required portion, and gold deposition can be surely suppressed in an unnecessary portion.

If the specific gravity of the solution is less than 2°Be' or the conductivity is less than 10 mS/cm, it is difficult to ensure the current density set in the high current density region during plating. In addition, in order to ensure the current density set in the high current density region, high-voltage electricity must be used, and high-voltage power is applied, which causes the obtained hard gold-plated film to be discolored or produces a red appearance, which causes the surface of the hard gold-plated film to lose its luster. . On the other hand, if dissolved When the specific gravity of the liquid exceeds 16°Be' or the conductivity exceeds 70mS/cm, the precipitation rate of the high current density region is higher than the solution specific gravity of 2°Be'~16°Be' and the conductivity is 10mS/cm~70mS/cm. The drop rate and the precipitation rate in the low current density region increase. Therefore, it is necessary to increase the processing time to obtain the film thickness set for the high current density region, and the plating time is increased, and the gold deposition is continued in the low current density region. Therefore, when the specific gravity of the solution exceeds 16°Be' or the conductivity exceeds 70 mS/cm, gold precipitation occurs not only in the required portion but also in the unnecessary portion.

In the hard gold plating solution of the present invention, the specific gravity of the solution is preferably 5°Be'~10°Be', and the conductivity is preferably from the viewpoint that the appearance is not bad and the unnecessary portion does prevent the precipitation of gold. 28mS/cm~50mS/cm compared.

Conductive salt: As the conductive salt used in the hard gold plating solution of the present invention, one or two or more organic oxides or inorganic compounds may be used. The organic oxide may be selected from a compound having one or more carboxyl groups in one molecule, and specifically, malic acid, tartaric acid, oxalic acid, lactic acid, and salts thereof. The inorganic compound may be selected from phosphoric acid, sulfuric acid, boric acid, and salts thereof. By using these conductive salts, the conductivity of the hard gold plating solution can be stabilized, and the specific gravity and conductivity of the solution can be easily adjusted.

The conductive salt preferably contains a concentration of 10 g/L to 200 g/L in the hard gold plating solution. When the concentration of the conductive salt is less than 10 g/L, the conductivity is less than 10 mS/cm. In addition, a decrease in the stability of the solution of the gold plating solution makes long-term storage difficult. On the other hand, when the concentration of the conductive salt exceeds 200 g/L, the conductivity exceeds 70 mS/cm.

Further, in the hard gold plating solution of the present invention, the conductive salt concentration is preferably from 20 g/L to 100 g/L. Thereby, the region where gold is precipitated (high current density region) The gold precipitation efficiency of the region (the low current density region) is not significantly different from that of the region to be precipitated, and the gold deposition rate necessary for practical operation can be stably obtained.

Staggering agent: In the hard gold plating solution of the present invention, the staggering agent forms a metal complex with gold or an alloying element described later in the hard gold plating solution, and the metal complex is stabilized in the solution to increase the stability of the solution. Further, as apparent from the above, when the gold ion supply raw material of the hard gold plating solution of the present invention is used as a distorting agent at the beginning, the distorting agent is mainly used to form a composite of alloying elements. The error-promoting agent is preferably selected from one or more of formic acid, malic acid, acetic acid, maleic acid, succinic acid, citric acid, glycine, arginine and salts thereof. These distorting agents tend to form a composite of gold and an alloying element described later. In addition, these distorants stabilize the pH because they act as a buffer for hard gold plating solutions. The amount of the distoring agent added can be determined in consideration of the amount of gold and alloying elements forming the metal composite in the hard gold plating solution.

Further, in the hard gold plating solution of the present invention, the concentration of the distoring agent is preferably from 1.0 g/L to 250 g/L. When the concentration of the distoring agent is less than 1.0 g/L, it is difficult to contain gold and an alloying element complex in the hard gold plating solution, and the solution stability of the hard gold plating solution is deteriorated, and the solution life is shortened. On the one hand, when the concentration of the distoring agent exceeds 250 g/L, the amount of misuse is exceeded, because the effect as a buffer is also saturated, and only resources are wasted.

Metal salt containing an alloying element of gold: In the hard gold plating solution of the present invention, the "metal salt containing an alloying element with respect to gold" is a metal salt containing a precipitated (co-precipitated) with gold in a plating film, preferably water-soluble. One or more of the cobalt salt, the nickel salt and the silver salt are selected. Therefore, it does contain alloying elements, has good abrasion resistance due to high hardness, and can be easily formed as a contact material such as a connector. Hard gold plated film used. Hereinafter, specific metal salts are listed. The metal salt exemplified in the present invention has excellent water solubility, does not affect the precipitation efficiency of gold, and has a property of being favorably precipitated together with gold.

As the cobalt salt, cobalt sulfate, cobalt chloride, cobalt nitrate, cobalt carbonate, cobalt phthalocyanine, cobalt stearate, ethylenediamine cobalt tetraacetate, cobalt naphthenate, cobalt borate, cobalt thiocyanate, sulfamic acid can be used. Cobalt, cobalt acetate, cobalt citrate, cobalt hydroxide, cobalt oxalate, cobalt phosphate, and the like.

As the nickel salt, nickel sulfate, nickel acetate, nickel chloride, nickel borate, nickel benzoate, nickel oxalate, nickel naphthenate, nickel oxide, nickel phosphate, nickel stearate, nickel tartrate, cobalt thiocyanate, aminosulfonate can be used. Nickel acid, nickel carbonate, nickel citrate, nickel formate, nickel cyanide, nickel hydroxide, nickel carbonate, nickel octylate, and the like.

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

In the hard gold plating solution of the present invention, when the cobalt salt, the nickel salt and the silver salt are used alone, or when a plurality of metal salts are combined, the total content of the metal salt is preferably from 0.025 g/L to 5 g/L. When the content of the entire metal salt is less than 0.025 g/L, the amount of precipitation of the gold plating film is lowered, and a gold plating film having sufficient hardness and abrasion resistance cannot be obtained. Further, when the total content of the metal salt exceeds 5 g/L, the amount of precipitation of the gold plating film is excessive, and the electric resistance of the hard gold plating film rises, resulting in a remarkable change in color.

Gold precipitation inhibitor: The gold precipitation inhibitor has an effect of suppressing gold precipitation and lowers the gold deposition efficiency in a low current density region. In other words, the gold deposition efficiency is maintained in the portion where the gold is precipitated (high current density region), and the gold deposition is suppressed in the portion where the gold deposition is not required (low current density region). Specific gold precipitation inhibitors, hydrogen peroxide, potassium persulfate, sodium persulfate, ammonium persulfate, iodic acid can be used. Potassium, potassium hydrogen iodate, sodium iodate, potassium sulfite, potassium hydrogen sulfite, sodium sulfite, sodium hydrogen sulfite, ammonium sulfite and ammonium sulfite hydrogen peroxide, persulfate, iodate, sulfite, etc. . From the viewpoint of the stability of the plating solution, hydrogen peroxide is preferred.

The content of the gold precipitation inhibitor in the hard gold plating solution of the present invention is preferably from 0.05 g/L to 50 g/L. If the content of the gold precipitation inhibitor is less than 0.05 g/L, the gold deposition efficiency in the low current density region is lowered. On the other hand, when the content of the gold precipitation inhibitor exceeds 50 g/L, the gold deposition efficiency in the high current density region is also lowered.

Hereinafter, the present invention will be described by way of examples, but it should not be construed as limiting the invention.

[Examples]

1. Evaluation of solution specific gravity and conductivity

First, prepare the following hard gold plating solutions 1 to 8 (pH 4.2). Citric acid is used as a distoring agent, a conductive salt and a buffering agent, formic acid is used as a conductive salt and a buffering agent, potassium citrate is used as a conductive salt, and a peroxidizing agent is used as a gold precipitation inhibitor. By changing the concentration of citric acid in the range of 0 g/L to 90 g/L, the concentration of potassium citrate is varied from 0 g/L to 180 g/L to adjust the specific gravity of the solution.

Specifically, the hard gold plating solution 1-8 first dissolves citric acid, potassium citrate and formic acid in water, and then adds and dissolves cobalt sulfate. Next, using citric acid and potassium hydroxide as a pH adjuster, the pH was adjusted to pH 4.2, and potassium (I) cyanide was added and dissolved. Finally, hydrogen peroxide is added and dissolved to obtain a hard gold plating solution. The specific gravity of the obtained hard gold plating solution at the time of bathing (solution temperature 25 ° C) is shown in Table 1. In addition, hard gold plating solution 8 For the comparative solution, the specific gravity of the solution is outside the range of 2°Be'~16°Be'.

Further, a hard gold plating solution 9 as a reference solution was prepared, and the specific gravity of the solution was measured in the same manner. The hard gold plating solution 9 only dissolves 14.5 g/L potassium cyanide (I) potassium and 2.5 g/L cobalt sulfate (cobalt 0.5 g/L) in pure water, and does not contain citric acid, formic acid, potassium citrate and hydrogen. Potassium oxide.

Next, the obtained hard gold plating solution 1 to 9 was measured for conductivity and dynamic viscosity at a bath temperature of 25 ° C. The results are shown in Table 1.

Next, the above hard gold plating solution 3, 4, 6, 8 is subjected to Hastelloy Groove test. In the Hastelloy test, a clean copper plate (longitudinal 67 mm x lateral 100 mm x thickness 0.3 mm) having a nickel film of 5 μm was used as a test piece using a Hull cell tester (a test instrument of Yamamoto Gold Co., Ltd.). The test was carried out under the conditions of a current of 2 A, a plating time of 1 minute, a stirring speed of 1000 rpm, and a bath temperature of 50 °C. The results are shown in Figures 1 to 3.

Fig. 1 is a schematic diagram showing the relationship between the distance between the electrodes and the thickness of the gold plating film formed by the Hastelloy test. Figure 1 shows the distance from the anode to the cathode (clean copper plate). The small distance is the high current density region, which is equivalent to the need for plating. The large distance is the low current density region, which is equivalent to the need for plating. Further, although the vertical axis indicates the thickness of the obtained gold film, it substantially represents the deposition rate. Further, Fig. 1(b) is a partially enlarged view of Fig. 1(a).

Figure 2 is a graphical representation of the relationship between current density and thickness of a gold plated film. The current density is dependent on the distance from the anode to the cathode (clean copper plate). Further, the second (b) is a partial enlarged view of the second (a) figure.

Figure 3 is a schematic diagram showing the relationship between the electrodes and the maximum film thickness. Here, the maximum film thickness is a film thickness of a portion from the anode to the cathode of 1 cm. Furthermore, Fig. 3(b) is a partially enlarged view of Fig. 3(a).

As can be seen from Table 1, in the hard gold plating solutions 1 to 9, when the content of citric acid, sodium citrate, and formic acid is high, the solution has a high specific gravity. Further, in the hard gold plating solution 1 to 9, if the specific gravity of the solution is high, the apparent electrical conductivity is increased and the dynamic viscosity is increased. Further, as is apparent from FIGS. 1 and 2, when the specific gravity of the solution is low, the deposition rate in the high current density region is increased, and the deposition rate in the low to medium current density region is lowered. On the other hand, if the solution has a high specific gravity, The precipitation rate of the high current density region is reduced, and the precipitation of the low to medium current density region is observed. The speed increases.

In addition, referring to Fig. 1 and Fig. 2, when a hard gold plating liquid solution 3, 4, and 6 having a solution specific gravity of 2 to 16 ° Be' is used, a current density of 1 cm from the anode is 10 A/dm ² (high) The film thickness of the current density region is 1.8 μm or more. On the other hand, when a hard gold plating solution 8 (comparative solution) having a solution specific gravity of 18.4 ° Be' (more than 16 ° Be') was used, the film thickness of the above portion was 1.5 μm. From this result, it is understood that the hard gold plating solutions 3, 4, and 6 have a high rate of gold deposition in a high current density region, that is, a portion where plating is required, and it is apparent that gold is precipitated with good efficiency in this portion. Further, in the hard gold plating solution 8 (comparative solution), since the gold deposition rate in the high current density region is slow, the plating time must be 1 minute or longer in order to make the film thickness at a position of 1 cm from the anode 1.8 μm or more. When the plating time is increased, it is expected that gold deposition will be further performed in a portion which is set to a low current density and which does not require plating.

Further, when the hard gold plating solutions 3, 4, and 6 were used, the film thickness of the portion (low current density region) having a current density of 0.1 A/dm ² was 0.15 μm or less at a distance of 9.5 cm from the anode, when hard gold plating was used. In the case of the solution 8 (comparative solution), the film thickness of the above portion was 0.2 μm. From this result, it is understood that the hard gold plating liquid liquids 3, 4, and 6 can significantly suppress the gold deposition which is not required to be plated, which is set to a low current density, as compared with the hard gold plating liquid liquid 8 (comparative solution).

Furthermore, as can be seen from Fig. 3, compared with the hard gold plating solution 8 (comparative solution), when the hard gold plating solutions 3, 4, and 6 are used, particularly in the low current density region, the maximum film thickness (high current) The relative film thickness of the density region is small. For example, when the current density of 7 cm from the anode is about 1.3 A/dm ² (low current density region) when using the hard gold plating solution 3, 4, 6, the relative film thickness is 7% or less, and is used. In the case of the hard gold plating solution 8 (comparative solution), the relative film thickness of the above portion is 12% or more. In addition, when the current density of 9.5 cm from the anode is about 0.1 A/dm ² (low current density region) when the hard gold plating liquid liquids 3, 4, and 6 are used, the relative film thickness is 0.8% or less. When the hard gold plating liquid 8 (comparative solution) was used, the relative film thickness of the above portion was 1.3%. From this result, it is understood that the hard gold plating solutions 3, 4, and 6 significantly ensure the film thickness of the plated portion as compared with the hard gold plating solution 8 (comparative solution), and suppress the precipitation of gold which does not require plating.

2. Evaluation of precipitation selectivity

First, the following hard gold plating solutions 10, 11 (pH 4.2) were prepared. By changing the concentration of citric acid in the range of 40 g/L to 90 g/L, the concentration of potassium citrate is varied in the range of 80 g/L to 180 g/L to adjust the specific gravity of the solution. The specific gravity of the solution of each hard gold plating solution is shown in Table 2.

Next, a clean copper plate having a nickel film of 5 μm was used as a test piece, and when partial plating was performed using the above hard gold plating solution, the degree of gold deposition occurring in an unnecessary portion was investigated.

First, an evaluation mask made of a rubber having a thickness of 3 mm and a mask for plating made of a rubber having a thickness of 1 mm were prepared. For evaluation A first circular hole portion having a diameter of 10 mm and a square hole portion communicating with the circular hole portion are formed on the mask. The square hole portion has a length of 20 mm and a width of 5 mm. The longitudinal direction is the same as the radial direction of the first circular hole portion, and one end in the longitudinal direction communicates with the first circular hole portion. Further, only the second circular hole portion having a diameter of 10 mm was formed on the plating mask. Next, the mask for evaluation and the mask for plating were closely attached to the nickel film of the test piece. At this time, the first hole and the second hole are connected to each other.

Next, on the test piece in which the evaluation mask and the plating mask were closely adhered, a hard gold plating solution was used, and plating treatment was performed by spraying to form hard gold plating on the nickel plating film. The obtained hard gold plating film is formed into a keyhole shape by the shape of the evaluation mask, and the rectangular portion that communicates with the first circular portion and the circular portion. In the electroplating treatment, the bath temperature was 50 ° C and the current density was 50 A/dm ² . The time required for the gold plating film thickness of the first circular region to be 0.2 μm was measured in advance, and the same time was used as the plating treatment time. In the plating treatment, in the region facing the first round hole portion of the test piece, there is no plating mask on the nickel plating film, and it is directly sprayed by the hard gold plating solution to become a high current density region, and further, facing the hole portion of the test piece. In the region, since the plating mask is present on the nickel plating film, it is not directly sprayed by the hard gold plating solution, and a low current density region is formed which is lower than the area facing the first circular hole portion. Therefore, when electroplating is performed, the area facing the first circular hole portion of the test piece is a portion to be plated, and the area facing the square hole of the test piece is a portion that does not need plating, and a hard surface is formed on the area facing the square hole. The gold plated film is ideal.

Next, regarding the hard gold plating film having the shape of the keyhole obtained, the front end of the circular portion was on the opposite side to the position where the rectangular portion communicated, and the front end of the circular portion was measured for a film thickness of 2 mm from the tip end of the circular portion to the end of the rectangular portion. The result is shown in Figure 4. In addition, according to the overall average thickness of the circular portion, that is, 10 mm from the front end of the circular portion The average film thickness of the lower region was calculated and the deposition rate was calculated. The results are shown in Table 2.

In Fig. 4, the horizontal axis represents the distance from the front end of the circular portion. The area of 0 to 10 mm on the horizontal axis is the part to be plated, and the area on the horizontal axis of 10 to 30 mm is the part that does not need to be plated.

As can be seen from Fig. 4, the hard gold plating solutions 10 and 11 are formed of hard gold plating in a region of 10 to 30 mm in the horizontal axis where the plating portion is not required. However, the film thickness of the hard gold plating solution 10 in the region of 10 to 30 mm on the horizontal axis is smaller overall than that of the hard gold plating solution 11. In particular, when the film thickness is about 0 μm, the hard gold plating solution 10 corresponds to a region in which the horizontal axis exceeds 18 μm, and the hard gold plating solution 11 corresponds to a region in which the horizontal axis exceeds 24 μm. From this, it is understood that the hard gold plating solution 10 having a solution specific gravity of 10.0°Be' has a good effect of suppressing gold precipitation in the plating portion, as compared with the hard gold plating solution 11 having a specific gravity of 18.4°Be'.

Further, as shown in Table 2, the precipitation rate of the hard gold plating solution 10 was significantly higher than that of the hard gold plating solution 11 having a large specific gravity. Therefore, the hard gold plating solution 10 can obtain a desired thickness in a short portion of the circular portion requiring the plating portion as compared with the hard gold plating solution 11. Further, compared with the hard gold plating solution 10, it is necessary to increase the plating time to form a desired thickness on the circular portion of the hard gold plating solution 11. When the plating time is increased, the film thickness of the rectangular portion which does not require the plating portion is further increased. That is to say, in the case of gold precipitation that does not require plating Further increase.

[Industry Utilization]

As described above, when the hard gold plating solution of the present invention is used, a poor appearance does not occur, and gold deposition is performed only in a required portion, and gold precipitation is surely suppressed in an unnecessary portion. Therefore, by using the hard gold plating solution of the present invention to partially plate the terminals of electronic products such as connectors, it is possible to suppress the occurrence of solder climbing on unnecessary portions during the soldering process, and to reduce waste of expensive gold materials and to suppress an increase in cost.

Claims (8)

A hard gold plating solution for electrolytic plating, comprising a gold ion supply material, a conductive salt, a distorer, a metal salt containing an alloying element with respect to gold, and a gold precipitation control agent, wherein the gold ion supply material is contained in gold conversion 0.5g/L~14g/L, when the solution temperature is 25°C, the specific gravity of the solution is 2°Be'~16°Be', and when the solution temperature is 25°C, the conductivity is 10mS/cm~70mS/cm. The hard gold plating solution according to claim 1, wherein the solution has a specific gravity of 5°Be’~10°Be'. The hard gold plating solution according to claim 1 or 2, wherein the conductivity is from 28 mS/cm to 50 mS/cm. The hard gold plating solution according to claim 1 or 2, wherein the metal salt containing the alloying element of gold is selected from one or two of the group consisting of a cobalt salt, a nickel salt and a silver salt. the above. The hard gold plating solution according to claim 4, wherein the cobalt salt contains 0.025 g/L to 5 g/L in terms of cobalt. The hard gold plating solution according to claim 4, wherein the nickel salt contains 0.025 g/L to 5 g/L in terms of nickel. The hard gold plating solution according to claim 4, wherein the silver salt contains 0.025 g/L to 5 g/L in terms of silver. The hard gold plating solution according to claim 1 or 2, wherein the gold precipitation controlling agent is hydrogen peroxide having a concentration of 0.05 g/L to 50 g/L.