Electrolytic hard gold plating solution substitution inhibitor and electrolytic hard gold plating solution including same

Abstract

Electrolytic hard gold plating solution substitution inhibitors containing at least one compound selected from the group consisting of an imidazole compound having a mercapto group, a triazole compound having a mercapto group, and an aliphatic compound having a sulfonic acid group and a mercapto group are provided. Electrolytic hard gold plating solutions containing at least one electrolytic hard gold plating solution substitution inhibitor, a gold salt, a soluble cobalt salt and/or a soluble nickel salt, an organic acid conducting salt, and a chelating agent are also provided.

Claims

1. An electrolytic hard gold plating solution comprising: 0.1 to 20 g/L of a gold cyanide salt; 0.01 to 10 g/L of a soluble cobalt salt and/or a soluble nickel salt; 10 to 200 g/L of an organic acid conductive salt; 1 to 50 g/L of a chelating agent; and 0.01 to 5 g/L of a displacement inhibitor for electrolytic hard gold plating solution comprising at least one compound selected from the group consisting of an imidazole compound having a mercapto group, 2-mercapto-1-propanesulfonic acid, and 2-hydroxy-3-mercapto-1-propanesulfonic acid.

2. The electrolytic hard gold plating solution according to claim 1, wherein the chelating agent is at least one selected from the group consisting of a carboxylic acid, an oxycarboxylic acid, and salts thereof.

3. The electrolytic hard gold plating solution according to claim 1 whose pH at 25 C. is in a range of 3 to 7.

Description

DESCRIPTION OF EMBODIMENTS

(1) Hereinbelow, a displacement inhibitor for electrolytic hard gold plating solution according to the present invention and an electrolytic hard gold plating solution containing the same will be described in detail.

(2) The displacement inhibitor for electrolytic hard gold plating solution according to the present invention comprises at least one compound selected from the group consisting of an imidazole compound having a mercapto group, a triazole compound having a mercapto group, and an aliphatic compound having a sulfonate group and a mercapto group.

(3) Examples of the imidazole compound having a mercapto group include 2-mercaptobenzimidazole, 2-mercapto-1-methylimidazole, 5-amino-2-mercaptobenzimidazole, 2-mercapto-5-methylbenzimidazole, 5-chloro-2-mercaptobenzimidazole, 2-mercapto-5-benzimidazolecarboxylic acid, 5-ethoxy-2-mercaptobenzimidazole, 2-mercapto-5-methoxybenzimidazole, 2-mercapto-5-benzimidazolesulfonic acid, 2-mercapto-5-nitrobenzimidazole, and salts thereof.

(4) Examples of the triazole compound having a mercapto group include 3-mercapto-1,2,4-triazole, 3-amino-5-mercapto-1,2,4-triazole, and salts thereof.

(5) Examples of the aliphatic compound having a sulfonate group and a mercapto group include 3-mercapto-1-propanesulfonic acid, 2-hydroxy-3-mercapto-1-propanesulfonic acid, and salts thereof.

(6) The amount of such a displacement inhibitor to be added to an electrolytic hard gold plating solution is usually 0.01 to 5 g/L, preferably 0.05 to 2 g/L. If the amount of the displacement inhibitor to be added is less than 0.01 g/L, the effect of inhibiting displacement cannot sufficiently be obtained, and a large amount of gold is deposited by displacement on a nickel base coat in a portion other than a portion to be plated. Even if the amount of the displacement inhibitor to be added exceeds 5 g/L, an effect obtained by adding the displacement inhibitor does not increase in proportion to the amount of the displacement inhibitor added, which is not economical.

(7) The electrolytic hard gold plating solution according to the present invention comprises a gold salt, a soluble cobalt salt and/or a soluble nickel salt, an organic acid conductive salt, a chelating agent, and the above-described displacement inhibitor for electrolytic hard gold plating solution.

(8) The electrolytic hard gold plating solution according to the present invention contains, as an organic displacement inhibitor, at least one compound selected from the group consisting of an imidazole compound having a mercapto group, a triazole compound having a mercapto group, and an aliphatic compound having a sulfonate group and a mercapto group. This organic displacement inhibitor forms a thin protective film on a nickel base coat before and after electrolytic plating processing (i.e., in a state where no electric current is applied to the gold plating solution) to inhibit a gold displacement reaction. Further, this protective film is easily removed during electrolytic plating processing (i.e., in a state where an electric current is applied to the gold plating solution). Therefore, a normal gold plating film can be obtained without adverse effects on the appearance of gold plating, deposition rate, etc. Such an action allows the electrolytic hard gold plating solution according to the present invention containing an organic displacement inhibitor to inhibit a gold displacement reaction with a nickel base coat in a portion other than a portion to be plated.

(9) As the gold salt, a gold cyanide compound is used.

(10) Examples of the gold cyanide compound include gold potassium cyanide, gold sodium cyanide, and gold ammonium cyanide. The gold ion concentration of the electrolytic hard gold plating solution according to the present invention is 0.1 to 20 g/L, preferably 2 to 15 g/L. If the gold ion concentration is less than 0.1 g/L, cathode current efficiency is too low to achieve a predetermined gold film thickness. If the gold ion concentration exceeds 20 g/L, cathode current efficiency does not increase in proportion to the gold ion concentration. Further, the amount of gold metal to be lost by taking out of the plating solution is large, which is not economical.

(11) The electrolytic hard gold plating solution according to the present invention contains a soluble cobalt salt and/or a soluble nickel salt. Examples of the cobalt salt include cobalt sulfate, cobalt nitrate, cobalt chloride, and basic cobalt carbonate. Examples of the nickel salt include general nickel sulfate, nickel sulfamate, nickel sulfite, and nickel chloride. These salts may be added singly or in combination of two or more of them. The concentration of the cobalt salt and the nickel salt in the electrolytic hard gold plating solution according to the present invention is 0.01 to 10 g/L, preferably 0.1 to 1.0 g/L. If the concentration is less than 0.01 g/L, film hardness is not increased, and therefore a resulting hard gold film cannot have desired properties. Even if the concentration exceeds 10 g/L, an effect obtained by adding the cobalt salt and the nickel salt does not increase in proportion to the concentration, which is not economical. It is to be noted that the term soluble in the soluble cobalt salt and the soluble nickel salt contained in the electrolytic hard gold plating solution according to the present invention means that the gold plating solution can contain them at the above concentration.

(12) The electrolytic hard gold plating solution according to the present invention contains an organic acid conductive salt. Examples of the organic acid conductive salt include potassium citrate, potassium phosphate, potassium nitrate, potassium succinate. These organic acid conductive salts may be added singly or in combination of two or more of them. The concentration of the organic acid conductive salt in the electrolytic hard gold plating solution according to the present invention is 10 to 200 g/L, preferably 50 to 100 g/L. If the concentration is less than 10 g/L, a normal gold film cannot be obtained due to the deterioration of appearance. Even if the concentration exceeds 200 g/L, an effect obtained by adding the organic acid conductive salt does not increase in proportion to the concentration, which is not economical.

(13) As the chelating agent, a carboxylic acid or a salt thereof or an oxycarboxylic acid or a salt thereof is used. Examples of the chelating agent include formic acid, glycolic acid, lactic acid, oxybenzoic acid, oxalic acid, malonic acid, succinic acid, malic acid, tartaric acid, phthalic acid, diglycolic acid, citric acid, and salts thereof. The concentration of the chelating agent in the electrolytic hard gold plating solution according to the present invention is 1 to 50 g/L, preferably 5 to 20 g/L. If the concentration is less than 1 g/L, inorganic impurities are incorporated into a resulting gold film, which deteriorates the appearance and properties of the gold film. Even if the concentration exceeds 50 g/L, an effect obtained by adding the chelating agent does not increase in proportion to the concentration, which is not economical.

(14) The electrolytic hard gold plating solution according to the present invention can be used at a pH (25 C.) of 3.0 to 7.0, but is preferably used at a pH of 4.0 to 5.0. If the pH is lower than 3.0, cathode current efficiency is too low to achieve a predetermined gold film thickness. If the pH is higher than 7.0, a gold film having a reddish appearance is obtained, which is not a normal gold film. It is to be noted that as a pH adjusting agent, sodium hydroxide, potassium hydroxide, ammonium hydroxide, diluted sulfuric acid water, or the like is used.

(15) The electrolytic hard gold plating solution according to the present invention can be used at a liquid temperature of 20 to 90 C., but is preferably used at 40 to 70 C. If the liquid temperature of the plating solution is lower than 20 C., cathode current efficiency is too low to achieve a predetermined gold film thickness. Even if the liquid temperature of the plating solution is higher than 90 C., an effect obtained by increasing the liquid temperature does not increase in proportion to the temperature, which is not economical.

EXAMPLES

(16) Hereinbelow, the present invention will be described in more detail with reference to examples, but is not limited to these examples. The configuration of a device used for a test and the method of evaluation are as follows.

(17) The effect of inhibiting displacement was evaluated using, as a sample, a substrate obtained by coating a copper plate with a nickel sulfamate film having a film thickness of 2 m.

(18) A silicon sheet having an opening of 10 mm10 mm was attached to an acrylic mask plate having an opening of 10 mm10 mm, and the sample was placed on the silicon sheet. The sample was fixed by holding down the sample from above with a hold block covered with a silicon sheet. A gold plating solution was circulated with a pump and sprayed onto the sample from the bottom for 10 minutes through a platinum nozzle having a diameter of 5 mm. In order to evaluate the film thickness of a gold film formed on the nickel base coat by a gold displacement reaction, no electric current was applied to the plating solution. A gold film was formed by displacement on the surface of the sample in the form of the 10 mm10 mm opening of the mask, and the film thickness of the gold film was measured in five positions on the diagonal line of the gold film with the use of a fluorescent X-ray film thickness meter SEA5120 manufactured by SII.

(19) The effect of inhibiting the deposition of gold in a plating bath was evaluated using, as a sample, a 3 cm1 cm piece cut out from a silicon wafer subjected to gold sputtering.

(20) A glass container with lid having a capacity of 20 ml was filled with a plating solution, the sample was immersed in the plating solution, and the glass container was placed in a drier with the lid being closed and allowed to stand at 70 C. for 36 hours. The deposition of gold in a bath is electroless deposition on gold particles, and therefore the effect of inhibiting the deposition of gold can be evaluated by measuring a gold film thickness before and after immersion of the sample subjected to gold sputtering. The gold film thickness was measured in five positions in the center of the sample with the use of a fluorescent X-ray film thickness meter SEA5120 manufactured by SII in the same manner as in the evaluation of effect of inhibiting displacement.

Comparative Example 1

(21) Potassium gold cyanide: 5 g/L (as Au)

(22) Potassium citrate: 120 g/L

(23) Potassium formate: 20 g/L

(24) Cobalt sulfate: 0.96 g/L

(25) A plating solution containing the above components was adjusted to pH 4.2, and sprayed onto a sample at a liquid temperature of 55 C. for 10 minutes. A gold film formed by displacement deposition had a film thickness of 0.100 m.

(26) A sample was immersed in the same plating solution as described above at 70 C. for 36 hours. A gold film formed by electroless deposition had a film thickness of 0.270 m.

(27) Further, a normal gold plating film was obtained at a current density of 10 to 60 A/dm.sup.2.

Comparative Example 2

(28) Potassium gold cyanide: 5 g/L (as Au)

(29) Potassium citrate: 120 g/L

(30) Potassium formate: 20 g/L

(31) Cobalt sulfate: 0.96 g/L

(32) 2-Aminobenzimidazole: 0.1 g/L

(33) A plating solution containing the above components was adjusted to pH 4.2, and sprayed onto a sample at a liquid temperature of 55 C. for 10 minutes. A gold film formed by displacement deposition had a film thickness of 0.950 m.

(34) A sample was immersed in the same plating solution as described above at 70 C. for 36 hours. A gold film formed by electroless deposition had a film thickness of 0.230 m.

(35) Further, a normal gold plating film was obtained at a current density of 10 to 60 A/dm.sup.2.

Comparative Example 3

(36) Potassium gold cyanide: 5 g/L (as Au)

(37) Potassium citrate: 120 g/L

(38) Potassium formate: 20 g/L

(39) Cobalt sulfate: 0.96 g/L

(40) 1,2,3-Benzotriazole: 0.1 g/L

(41) A plating solution containing the above components was adjusted to pH 4.2, and sprayed onto a sample at a liquid temperature of 55 C. for 10 minutes. A gold film formed by displacement deposition had a film thickness of 0.965 m.

(42) A sample was immersed in the same plating solution as described above at 70 C. for 36 hours. A gold film formed by electroless deposition had a film thickness of 0.251 m.

(43) Further, a normal gold plating film was obtained at a current density of 10 to 60 A/dm.sup.2.

Example 1

(44) Potassium gold cyanide: 5 g/L (as Au)

(45) Potassium citrate: 120 g/L

(46) Potassium formate: 20 g/L

(47) Cobalt sulfate: 0.96 g/L

(48) 2-Mercaptobenzimidazole: 0.1 g/L

(49) A plating solution containing the above components was adjusted to pH 4.2, and sprayed onto a sample at a liquid temperature of 55 C. for 10 minutes. A gold film formed by displacement deposition had a film thickness of 0.001 m, and therefore a gold displacement reaction could be significantly inhibited.

(50) A sample was immersed in the same plating solution as described above at 70 C. for 36 hours. A gold film formed by electroless deposition had a film thickness of 0.049 m, and therefore deposition could be inhibited.

(51) Further, a normal gold plating film was obtained at a current density of 10 to 60 A/dm.sup.2.

Example 2

(52) Potassium gold cyanide: 5 g/L (as Au)

(53) Potassium citrate: 120 g/L

(54) Potassium formate: 20 g/L

(55) Cobalt sulfate: 0.96 g/L

(56) 2-Mercapto-1-methylimidazole: 0.1 g/L

(57) A plating solution containing the above components was adjusted to pH 4.2, and sprayed onto a sample at a liquid temperature of 55 C. for 10 minutes. A gold film formed by displacement deposition had a film thickness of 0.001 m, and therefore a gold displacement reaction could be significantly inhibited.

(58) A sample was immersed in the same plating solution as described above at 70 C. for 36 hours. A gold film formed by electroless deposition had a film thickness of 0.051 m, and therefore deposition could be inhibited.

(59) Further, a normal gold plating film was obtained at a current density of 10 to 60 A/dm.sup.2.

Example 3

(60) Potassium gold cyanide: 5 g/L (as Au)

(61) Potassium citrate: 120 g/L

(62) Potassium formate: 20 g/L

(63) Cobalt sulfate: 0.96 g/L

(64) 3-Mercapto-1,2,4-triazole: 0.1 g/L

(65) A plating solution containing the above components was adjusted to pH 4.2, and sprayed onto a sample at a liquid temperature of 55 C. for 10 minutes. A gold film formed by displacement deposition had a film thickness of 0.001 m, and therefore a gold displacement reaction could be significantly inhibited.

(66) A sample was immersed in the same plating solution as described above at 70 C. for 36 hours. A gold film formed by electroless deposition had a film thickness of 0.051 m, and therefore deposition could be inhibited.

(67) Further, a normal gold plating film was obtained at a current density of 10 to 60 A/dm.sup.2.

Example 4

(68) Potassium gold cyanide: 5 g/L (as Au)

(69) Potassium citrate: 120 g/L

(70) Potassium formate: 20 g/L

(71) Cobalt sulfate: 0.96 g/L

(72) 2-Mercapto-1-propanesulfonic acid: 0.1 g/L

(73) A plating solution containing the above components was adjusted to pH 4.2, and sprayed onto a sample at a liquid temperature of 55 C. for 10 minutes. A gold film formed by displacement deposition had a film thickness of 0.001 m, and therefore a gold displacement reaction could be significantly inhibited.

(74) A sample was immersed in the same plating solution as described above at 70 C. for 36 hours. A gold film formed by electroless deposition had a film thickness of 0.059 m, and therefore deposition could be inhibited.

(75) Further, a normal gold plating film was obtained at a current density of 10 to 60 A/dm.sup.2.

Example 5

(76) Potassium gold cyanide: 5 g/L (as Au)

(77) Potassium citrate: 120 g/L

(78) Potassium formate: 20 g/L

(79) Cobalt sulfate: 0.96 g/L

(80) 2-Hydroxy-3-mercapto-1-propanesulfonic acid: 0.1 g/L

(81) A plating solution containing the above components was adjusted to pH 4.2, and sprayed onto a sample at a liquid temperature of 55 C. for 10 minutes. A gold film formed by displacement deposition had a film thickness of 0.001 m, and therefore a gold displacement reaction could be significantly inhibited.

(82) A sample was immersed in the same plating solution as described above at 70 C. for 36 hours. A gold film formed by electroless deposition had a film thickness of 0.060 m, and therefore deposition could be inhibited.

(83) Further, a normal gold plating film was obtained at a current density of 10 to 60 A/dm.sup.2.