TW201631222A - Cyanogen-free gold electroplating liquid and gold electroplating method - Google Patents

Abstract

Provided is a cyanogen-free gold electroplating liquid with which conventional gold electroplating liquids comprising cyanogen-based compounds can be replaced, the cyanogen-free gold electroplating liquid being characterized by containing components (a) through (c): (a) is a monovalent metal complex represented by general formula (I) (where in general formula (I), R1 is hydrogen or an optionally branched C1-4 alkyl group optionally having mercapto groups, R2 is hydrogen or an optionally branched C1-4 alkyl group, R3 is hydrogen, an optionally branched C1-4 alkyl group, a hydroxyalkyl group, or an optionally branched C1-4 carboxyalkyl group optionally having mercapto groups, and n is an integer of 1 to 10); (b) is an electrolyte; and (c) is a crystal modifier selected from metals.

Description

Cyanide-free electrolytic gold plating solution and gold plating method

The invention relates to a cyanide-free electrolytic gold plating solution and a gold plating method.

Gold-plated films have not only been used in decorative or food utensils since ancient times, because of their excellent chemical stability or electrical conductivity, and low mechanical hardness, for example, even in bump electrode formation or wire bonding, solder ball solder pads. The surface of the (Bonding pad), etc., is also widely used in the electronics industry.

The gold plating solutions used in the past are almost all cyanide solutions containing toxic gold cyanide, but recently the problem of safe operation or drainage treatment, attack on the corrosion of semiconductor parts, etc., has been improved to non-cyanide. For the requirements of the gold plating solution, various cyanide-free gold plating is proposed. As such a gold plating solution, for example, it has been reported that sodium gold (I) sulfite is used as a gold salt user (for example, Patent Documents 1 and 2).

However, in the case of a gold plating solution using gold (I) sodium sulfite, the sulfite ions in the solution are naturally reduced in concentration by oxidizing oxygen generated from the anode or oxygen in the atmosphere. As a result, reducing the gold complex in the gold plating solution The stability results in a problem of a change in the physical properties of the electromorph or a decomposition of the plating solution.

Further, as another gold plating solution, for example, a gold plating solution using a Hydantoin derivative as a crosslinking agent has been reported (Patent Document 3). However, since the plating solution has low stability and high cost, the performance of the film is not as good as that of the cyanide solution, and the practical use is limited. Accordingly, development of a cyanide-free gold plating solution which is excellent in solution stability and has a plating film property similar to that of a cyanide solution is desired.

Recently, it has been reported that 6-aminopenicillanic acid, tiopronin or the like is used as a coupling agent to obtain a monovalent gold complex, and a gold plating solution is used (Patent Document 4). However, the electrolytic plating solution disclosed herein contains sodium chloroaurate, 6-aminopenicillanic acid, citric acid, bipyridine, or PEG 200. Although it can be plated with gold, the current efficiency and the hardness of the gold film are precipitated. It is not practical in terms of purity, precipitation state, and the like.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 11-61480

[Patent Document 2] Japanese Laid-Open Patent Publication No. 2011-184734

[Patent Document 3] US Patent Application Publication No. 2003/111353

[Patent Document 4] International Publication No. 2014/10301

Therefore, the present inventors have provided a cyanide-free electrolytic gold plating solution which can be used in place of the electrolytic gold plating solution containing the cyanide compound used so far.

As a result of intensive studies to solve the above problems, the inventors of the present invention have found that a practical cyanide-free electrolytic gold plating solution can be obtained by combining a monovalent gold complex of a specific structure with an electrolyte and a metal crystal modifier. invention.

That is, the present invention is a cyanide-free electrolytic gold plating solution characterized by containing the following components (a) to (c),

(a) a monovalent gold complex represented by the following general formula (I)

(In the formula (I), R ₁ represents hydrogen or an alkyl group having 1 to 4 carbon atoms which may have a mercapto group, and R ₂ represents hydrogen or a branched alkyl group having 1 to 4 carbon atoms, R ₃ is a carboxyalkyl group having 1 to 4 carbon atoms which may have hydrogen, may also be branched, or a hydroxyalkyl group, or a carboxyalkyl group having 1 to 4 carbon atoms which may have a mercapto group, and n represents an integer of 1 to 10. ),

(b) electrolyte

(c) a metal crystal modifier selected from metals.

Further, the present invention is a cyanide-free electrolytic gold plating method for a member to be plated, which is to perform electrolytic plating on a plated member in the cyanide-free electrolytic gold plating solution.

The cyanide-free electrolytic gold plating solution of the present invention is extremely excellent in stability, and does not change in one year after preparation, and it is difficult to cause a change in precipitation gold property or decomposition of a gold plating solution in a gold plating operation.

Further, the gold plating film obtained by the gold plating method using the cyanide-free electrolytic gold plating solution of the present invention has a beautiful appearance, a dense crystal structure, and excellent solder joint properties and wire bonding properties. Further, since the current efficiency of the present invention is 90% or more, it is a practical person. Further, according to the cyanide-free electrolytic gold plating method of the present invention, it is also possible to control the hardness, purity, crystal state, and the like of the obtained gold plating.

Fig. 1 is a view showing a polarization curve measured in Test Example 1.

Fig. 2 is a SEM photograph of a gold plating film deposited in Example 2.

Fig. 3 is a SEM photograph of a gold plating film deposited in Example 3.

Fig. 4 is a SEM photograph of a gold plating film deposited in Example 4.

Fig. 5 is a SEM photograph of a gold bump formed in Example 5.

Fig. 6 is a graph showing the results of the welding ball joint shear strength and the fracture mode of Test Example 2.

Fig. 7 is a view showing a fracture mode in the measurement of wire bonding tensile strength.

Fig. 8 is a graph showing the results of the wire bonding strength of Test Example 2.

Fig. 9 is a SEM photograph of a gold plating film deposited in Example 7.

In the present specification, the cyanide-free electrolytic gold plating solution refers to a cyano compound such as potassium cyanide which is not used in the conventional gold plating solution.

The following general formula (I) of the component (a) used in the cyanide-free electrolytic gold plating solution of the present invention

The monovalent gold complex represented by R ₁ represents hydrogen or an alkyl group having 1 to 4 carbon atoms which may have a mercapto group, preferably hydrogen, methyl, ethyl, propyl, isopropyl or butyl. Base, isobutyl, decylmethyl (-CH ₂ -SH), more preferably hydrogen, methyl. Further, R ₂ represents hydrogen or a branched alkyl group having 1 to 4 carbon atoms, preferably hydrogen, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, more preferably hydrogen, methyl. Further, R ₃ represents hydrogen, a branched alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group, or a carboxyalkyl group having 1 to 4 carbon atoms which may have a mercapto group, and is preferably hydrogen or methyl. Carboxymethyl, carboxyethyl, hydroxyethyl, isocarboxyethyl (-CH(CH ₃ )-COOH), mercaptocarboxymethyl (-CH(SH)-COOH), 2-mercapto-isocarboxyethyl ( -CH(CH ₂ SH)-COOH), more preferably carboxymethyl or hydrogen. Further, n is an integer of 1 to 10, preferably an integer of 3 to 6, more preferably 4. Here, n indicates that the monovalent gold complex is formed by a polymer.

The monovalent gold complex represented by the above general formula (I), for example, a trivalent gold aqueous solution containing gold (III) tetrachloride acid ions or a gold salt aqueous solution of sodium sulfite, and the following general formula (II) It is added in such a manner that 1 to 5 times the molar amount of the gold salt is preferably 3 to 3.5 times the molar amount, and if necessary, an acidic substance is added, and after adjusting the pH to 3 or less, it can be prepared by sufficiently stirring.

The compound represented (except that X represents hydrogen, ammonium ion, metal, preferably alkali metal such as sodium or potassium, alkaline earth metal such as calcium or magnesium, ammonium ion, silver, tin, antimony, bismuth, lead, antimony. , cobalt, indium, mercury, nickel, zinc, more preferably hydrogen, sodium, potassium. and, R ₁ ~ R ₂ represents a system the same as those described above, R ₃ 'represents the above-described system are the same as R _3, or R ₃ above The hydrogen of the alkyl, hydroxyalkyl or carboxyalkyl group is replaced by the above X (except hydrogen).

Examples of the compound represented by the above general formula (II) include tiopronin, 2-mercaptoacetamide, N-(2-mercaptoethanol) glycine, and N-(2-mercaptoethyl)glycine. And N-(2-hydroxyethyl)-2-mercaptoacetamide or N-(2-mercapto-1-oxypropyl)glycine and such sodium salts, potassium salts, tin salts and the like.

The trivalent gold aqueous solution containing the above-described gold (III) chloride tetrachloride acid can be prepared, for example, by dissolving gold in aqua regia or dissolving sodium chloroaurate in pure water. Further, the monovalent gold salt aqueous solution of sodium sulfite sulfate can be prepared, for example, by dissolving gold in aqua regia and setting the pH to 8 or more, and reacting the separated gold hydroxide with sodium sulfite.

In addition, the acidic substance to be used for the adjustment of the pH is not particularly limited, and examples thereof include a carboxylic acid such as acetic acid, citric acid, lactic acid or tartaric acid, carbonic acid, phosphoric acid or the like.

The monovalent gold complex prepared as described above is prepared by a pH of 3 or less, and cannot be dissolved to form a precipitate. Therefore, the monovalent gold complex can be purified by a known purification means such as filtration or centrifugation using a membrane filter or the like. Moreover, the purification means can be improved by performing the purification means twice or more.

In order to increase the degree of purification of the monovalent gold complex, for example, a monovalent gold complex obtained by filtration and centrifugation is introduced into water, and an alkaline substance such as potassium hydroxide or sodium hydroxide is added to the aqueous solution. The pH was adjusted to about 5 to dissolve the monovalent gold complex. Next, the acidic substance was added to the aqueous solution, and the pH was adjusted to 3 or less to reprecipitate the monovalent gold complex. By repeating this one time or more, the monovalent gold complex can be increased. The degree of purification.

The monovalent gold complex prepared as described above may be directly subjected to, for example, the purified monovalent gold complex is added to water in an amount of 50 to 100 g/L of gold ions, and potassium hydroxide and sodium hydroxide are added. The basic substance such as the alkaline substance adjusts the pH of the aqueous solution to a pH of about 5, and is used as a slurry for dissolving the monovalent gold complex.

In the cyanide-free electrolytic gold plating solution of the present invention, the content of the monovalent gold complex of the component (a) is not particularly limited, but is, for example, 2 to 30 g/L, preferably 4 to 16 g/L, as the gold ion. range. When the amount of gold is less than 2 g/L, the precipitation rate of gold may be unsuitable for actual operation, and when it exceeds 30 g/L, the cost is increased, and industrial applicability may be lost.

Further, the electrolyte of the component (b) used in the cyanide-free electrolytic gold plating solution of the present invention is not particularly limited, and examples thereof include a potassium salt, a sodium salt, and an ammonium salt of an inorganic acid or an organic acid. Examples of the inorganic acid or organic acid include sulfuric acid, formic acid, carbonic acid, nitric acid, phosphoric acid, citric acid, acetic acid, lactic acid, succinic acid, glycolic acid, tartaric acid, and the like, and sulfuric acid or formic acid is preferred. These electrolytes may be used alone or in combination of two or more.

In the cyanide-free electrolytic gold plating solution of the present invention, the content of the electrolyte of the component (b) is not particularly limited, but is, for example, 0.01 to 10 mol/L, preferably 0.1 to 1 mol/L. When the electrolyte is less than 0.01 mol/L, it may be difficult to ensure sufficient conductivity as a plating solution. When it exceeds 10 mol/L, the effect as an electrolyte may not increase.

Further, the component (c) used in the cyanide-free electrolytic gold plating solution of the present invention is selected from the group consisting of metal crystal modifiers having crystal adjustment The metal to be used is not particularly limited, and examples thereof include metals such as ruthenium, osmium, arsenic, antimony, tin, lead, indium, antimony, bismuth, selenium, cobalt, and nickel. Among these, ruthenium, osmium, iridium and tin are preferred. These metal crystallization modifiers may be used alone or in combination of two or more. Further, a metal crystal modifier selected from the group consisting of a metal salt such as formic acid, sulfuric acid, tartaric acid or methanesulfonic acid is preferably added to the cyanide-free electrolytic gold plating solution of the present invention.

In the cyanide-free electrolytic gold plating solution of the present invention, the content of the metal crystal modifier selected from the component (c) is not particularly limited, but is, for example, 1 to 1000 ppm, preferably 5 ppm to 100 ppm.

In addition to the above components (a) to (c), the cyanide-free electrolytic gold plating solution of the present invention preferably further contains one or two selected from the group consisting of the components (d) and (e).

(d) pH buffer

(e) a crystal modifier selected from the group consisting of sulfur-containing compounds.

The pH buffering agent of the component (d) is not particularly limited as long as it has a pH buffering action, and examples thereof include inorganic acids, organic carboxylic acids, organic phosphoric acid, pyridinesulfonic acid, and the like. Sodium salt, ammonium salt, and the like. Examples of the pH buffering agent include inorganic acids such as phosphoric acid, carbonic acid, and boric acid, organic carboxylic acids such as ethylenediaminetetraacetic acid (EDTA), nitrosotriacetic acid (NTA), citric acid, and tartaric acid, and 1- Organic phosphoric acid such as hydroxyethane-1,1-diphosphonic acid (HEDP), 1,1,1-nitrosole (methylphosphonic acid) (ATMP), ethylenediaminetetramethylenephosphonic acid (EDTMP) , 3-pyridine sulfonic acid, 2-pyridine sulfonic acid, 5-methyl-3-pyridine sulfonic acid, 4-hydroxypyridine-3-sulfonic acid, etc., and the like, potassium salt, sodium salt, ammonium salt Etc., preferably EDTA. These pH buffering agents can be used alone or in combination of two or more.

In the cyanide-free electrolytic gold plating solution of the present invention, the content of the pH buffer of the component (d) is not particularly limited, but is, for example, 0.5 to 10 mol, preferably 1 to 2 mmol, per mol of the gold ion in the gold plating solution. Further, by adding the pH buffer of the component (d), since the pH of the solution becomes stable, the gold complex is stabilized and the precipitation uniformity of the plating is improved. Moreover, the obtained gold plating has a brighter appearance and a uniform precipitation. Further, even in the case of performing plating for a long period of time, the stability of the solution can be ensured.

The crystal modifier of the component (e) selected from the group consisting of sulfur-containing compounds is not particularly limited as long as it is a sulfur-containing compound having a crystal-adjusting action, and examples thereof include thiosulfuric acid, thiophosphoric acid, and the like. A sodium salt, an ammonium salt, an organic compound having both a thiol group and a carboxyl group, and the like. Among these crystal modifiers selected from sulfur-containing compounds, preferred are thiosulfuric acid, thiosalicylic acid, Thioglycolic acid, 4-mercaptobenzoic acid, 3-mercaptopropionic acid, preferably thio. Sulfuric acid, thiosalicylic acid. These crystal modifiers selected from the group consisting of sulfur-containing compounds may be used alone or in combination of two or more.

In the cyanide-free electrolytic gold plating solution of the present invention, the content of the crystal modifier of the component (e) selected from the sulfur-containing compound is not particularly limited, but is, for example, 0.0001 to 0.025 mol/L, preferably 0.001 to 0.01 mol. /L. Further, by adding the crystal modifier of the component (e) selected from the sulfur-containing compound, the nanopore cannot be confirmed even by SEM observation of gold plating.

Further, in the cyanide-free electrolytic gold plating solution of the present invention, components such as a surfactant, a glossing agent, and other additives may be added without impairing the effects of the present invention.

Further, the cyanide-free electrolytic gold plating solution of the present invention can be adjusted by adjusting the type or amount of the metal added as the crystal modifier of the component (c) and the pH of the cyanide-free electrolytic gold plating solution. Cyanide-free electrolytic gold plating solution.

Specifically, in the cyanide-free electrolytic gold plating solution of the present invention, for example, when cerium is added as the component (c), it becomes a soft gold which is almost pure gold. On the other hand, when ruthenium is added as the component (c), pure gold is easily formed at 10 ppm and a pH of 7 or less, and soft gold is formed, and a gold/rhodium alloy is easily formed at 20 ppm and a pH of 7 or more, and the hardness is also improved. When tin is added, it becomes a gold/tin alloy.

The pH of the cyanide-free electrolytic gold plating solution of the present invention described above is not particularly limited, but is, for example, 3 to 14, preferably 5 to 8. In the adjustment of the pH value, an acidic substance such as potassium hydroxide, sodium hydroxide or ammonia, or an acidic substance such as sulfuric acid, citric acid or acetic acid may be suitably used.

The cyanide-free electrolytic gold plating solution of the present invention can be produced by adding the above components to water and stirring, and if necessary, adjusting the pH.

The cyanide-free electrolytic gold plating solution of the present invention described above can be used for electrolytic gold plating. Specifically, electrolytic gold plating can be performed by electrolyzing a member to be plated in the cyanide-free electrolytic gold plating solution of the present invention. The plated member used for the electrolytic gold plating is not particularly limited, and is, for example, a wafer, a printed circuit board, a connector for an electronic component device, a lead frame, or the like. Such The material of the member to be plated is not particularly limited, and examples thereof include nickel, copper, gold, and the like.

Further, the conditions for electrolytic gold plating using the cyanide-free electrolytic gold plating solution of the present invention are not particularly limited, and for example, the liquid temperature is 20 to 80 ° C, and the current density is 0.1 to 6 A/dm ² .

The plated member subjected to electrolytic gold plating as described above is excellent in appearance, improves corrosion resistance, and is excellent in solder jointability and wire bonding property. Further, since the gold purity of the film can be adjusted by the composition of the gold plating solution or the plating conditions, the regulation of softness, hardness, and the like is also possible.

Hereinafter, the present invention will be described in detail by way of examples, but the invention is not limited thereto.

Reference example 1

Modulation of monovalent gold complex slurry:

An aqueous solution containing tiopronin 0.15 M, acetic acid 0.50 M, and sodium chloroaurate 0.05 M was stirred at 20 ° C for 10 hours to form a monovalent gold complex. Further, since the pH of the aqueous solution is 3 or less, the formed monovalent gold complex is not dissolved and becomes fine particles. Next, the aqueous solution was separated by a membrane filter of 0.4 μm to separate the monovalent gold complex. The recovery of gold in this operation was 99.9%. Further, the structure of the monovalent gold complex is as known as the tetramer structure of the following formula (III) (Carrie A. Simpson et al., Inorganic Chemistry 2010, 49 (23), 10858-10866).

The monovalent gold complex was obtained by adding the above-obtained monovalent gold complex to water, adding potassium hydroxide, and adjusting to a pH of 5. Next, the precipitate was again formed by adjusting the pH to 3 or less by the above operation, and further purified by filtration. This operation was repeated twice, and finally, a monovalent gold complex which was purified to a purity of 98% or more (confirmed by NMR) was obtained.

The monovalent gold complex purified as described above was placed in water, and adjusted to pH 5 with potassium hydroxide to prepare a monovalent gold complex slurry containing 100 g/L of gold ions.

Reference example 2

Modulation of a monovalent gold complex:

An aqueous solution containing 0.05 mg of tiopronin and 0.05 M of sodium sulfite was stirred at 20 ° C for 10 hours to form a monovalent gold complex. By setting the pH of the aqueous solution to 3 or less with acetic acid, a monovalent gold complex precipitate is formed. Next, the aqueous solution was separated by a membrane filter of 0.4 μm to separate the monovalent gold complex. The recovery rate of gold in this operation 99.9%.

Reference example 3

Modulation of electrolytic gold plating solution:

An aqueous solution containing 50 ml/L of a monovalent gold complex slurry prepared in Reference Example 1 (5 g/L as a gold ion) and 35 g/L of tripotassium citrate monohydrate was prepared, and the pH of the aqueous solution was oxidized. Potassium was adjusted to 7.2 as an electrolytic gold plating solution.

Reference example 4

Electrolytic gold plating:

The copper test piece is subjected to electrolytic nickel plating by performing a known treatment such as electrolytic degreasing, soft etching, and acid treatment. Immediately thereafter, the electrolytic gold plating solution prepared in Reference Example 3 was used, and gold plating was performed on the copper-nickel-plated test piece. The size of the plated portion of the test piece was 2 cm × 2 cm, and the area of the anode was 1.5 to 2.0 times the plated area. The anode was an insoluble anode of titanium which used ruthenium oxide as a coating layer, and the distance from the test piece (as a cathode) was about 6 cm. The plating bath made of a heat-resistant vinyl chloride having a capacity of 100 ml was subjected to electrolytic gold plating for 2 minutes while maintaining a liquid temperature of 60 ° C and stirring at a current density of 0.4 A/dm ² .

The gold-plated appearance is gold. Further, after SEM observation of gold plating, it was a smooth surface having a regular shape. However, when the cathode current efficiency (hereinafter referred to as current efficiency) of electrolytic gold plating is calculated from "actual precipitation amount / theoretical precipitation amount × 100%", it is 30%. Again, for a long time In the case of plating, it is understood that the appearance is liable to become red, and the pH of the plating solution is gradually lowered.

Example 1

Electrolytic gold plating:

An aqueous solution containing 40 ml/L of a monovalent gold complex slurry prepared in Reference Example 1 (4 g/L as a gold ion), 44 g/L of potassium sulfate, and 24.4 ppm of cesium formate (20 ppm as a cerium ion) was prepared. The pH of the aqueous solution was adjusted to 6.2 with potassium hydroxide as an electrolytic gold plating solution.

When the electrolytic gold plating solution was subjected to electrolytic gold plating under the same plating conditions as in Reference Example 4, the appearance after gold plating was gold. When the current efficiency in electrolytic gold plating was calculated in the same manner as in Reference Example 4, it was 90% or more. However, in the case of performing long-time plating, although it is not as in Reference Example 4, it is understood that the appearance is liable to become red, and the pH of the plating solution is gradually lowered.

Test example 1

Electrochemical determination:

The polarization curve obtained by electrochemical measurement of the electrolytic gold plating solution obtained in Example 1 (20 ppm added) and the electrolytic gold plating solution prepared in Reference Example 3 (without adding ruthenium) is shown in Fig. 1. It is understood that as a crystal modifier, the polarization curve is shifted to the right side by the addition of a metal, that is, bismuth, and the polarization becomes very easy. Further, the current efficiency of the electrolytic gold plating solution to which ruthenium was added was about twice as high as that of the electrolytic gold plating solution to which no ruthenium was added, and was almost 100%.

Example 2

Electrolytic gold plating:

The monovalent gold complex slurry prepared in Reference Example 1 was prepared in an amount of 50 ml/L (as a gold ion of 5 g/L), potassium formate 42 g/L, cesium formate 24.4 ppm (as a cesium ion of 20 ppm), and EDTA 7.31 g/ An aqueous solution of L is used as an electrolytic gold plating solution in which the pH of the aqueous solution is adjusted to 7.4 with potassium hydroxide.

When the electrolytic gold plating solution was subjected to electrolytic gold plating in the same manner as in Reference Example 4, the appearance after gold plating was brighter than that obtained in Reference Example 4 and Example 1. When the current efficiency in electrolytic gold plating was calculated in the same manner as in Reference Example 4, it was 90% or more. Further, even if plating is performed for a long period of time, the pH of the plating solution is stabilized. However, when the gold plating film was observed by SEM, although it was not as in Reference Example 4, some micronanopores were observed (Fig. 2).

Example 3

Electrolytic gold plating:

The monovalent gold complex slurry prepared in Reference Example 1 was prepared in an amount of 50 ml/L (as a gold ion of 5 g/L), potassium formate 42 g/L, cesium formate 24.4 ppm (as a cesium ion of 20 ppm), and EDTA 7.31 g/ L. An aqueous solution of 1.54 g/L of thiosalicylic acid, and the pH of the aqueous solution was adjusted to 7.4 with potassium hydroxide as an electrolytic gold plating solution.

For this electrolytic gold plating solution, the same as in Reference Example 4 When electrolytic gold plating is performed, the appearance after gold plating is brighter than that obtained in Reference Example 4 and Example 2. When the current efficiency in electrolytic gold plating was calculated in the same manner as in Reference Example 4, it was 95% or more. Further, when the gold plating film was observed by SEM, the nanopore found in the gold plating film obtained in Example 2 was not observed (Fig. 3).

The gold plating film was dissolved in a gold stripping agent, and the purity of the gold plating film obtained in Examples 1, 2, and 3 was confirmed by ICP analysis, and any of them was 99.9% or more. Therefore, it was found that the gold plating films obtained in Examples 1, 2, and 3 were pure gold. Further, when the hardness of the gold film was confirmed, the hardness of the gold plating film was measured using a MVK-G3 Vickers hardness tester (manufactured by AKASHI) at a load of 5 g. The gold plating films obtained in Examples 1, 2, and 3 all had a Vickers hardness of 110 HV or less, and were annealed at 300 ° C for 30 minutes to become 60 to 70 HV, showing good performance required for a pure gold plating film of an electronic product.

Example 4

Electrolytic gold plating:

The preparation of the monovalent gold complex slurry prepared in Reference Example 1 was 40 ml/L (4 g/L as gold ion), 44 g/L potassium sulfate, potassium bismuth tartrate (10 ppm as cerium ion), and EDTA 7.31 g/L. An aqueous solution of trisodium citrate 10 g/L and thiosalicylic acid 0.77 g/L, and the pH of the aqueous solution was adjusted to 6.2 with potassium hydroxide as an electrolytic gold plating solution.

When the electrolytic gold plating solution was subjected to electrolytic gold plating in the same manner as in Reference Example 4, the appearance of the gold plating film was more than that obtained in Reference Example 4. Bright gold, a more lustrous appearance than the gold-plated film obtained in Example 3. When the current efficiency in electrolytic gold plating was calculated in the same manner as in Reference Example 4, it was 95% or more. Further, when the gold plating film was observed by SEM, the crystal was dense and had a smooth surface (Fig. 4). Moreover, although the purity of gold is slightly reduced, the Vickers hardness is increased to 170 HV, and it is 80 to 90 HV after annealing at 300 ° C for 30 minutes.

Example 5

Formation of microbumps:

The bump plating of the semiconductor wafer was performed using the electrolytic gold plating solution prepared in Example 4. Gold plating was performed on a wafer patterned by resist patterning (plating of the underlying material was sputtered gold) at a current density of 0.4 A/dm ² , a liquid temperature of 60 ° C, and 40 minutes. After the plating, the resist was peeled off, and when the surface was observed, fine gold bumps (width: 10 μm, height: about 10 μm) as shown in Fig. 5 were formed. After learning that the gold bumps were straight up, the electrolytic gold plating solution did not attack the resist.

Comparative example 1

Electrolytic gold plating:

SKYGOLD S-10 (manufactured by JCU), an electrolytic pure gold plating solution, was used as a commercially available product of cyanide gold plating, and electrolytic gold plating was performed for 2 minutes (film thickness: 0.35 μm) while stirring at a liquid temperature of 60 ° C and a current density of 0.3 A/dm ² .

Comparative example 2

Electrolytic gold plating:

Preparation of sodium gold sulfite (10g/L as gold ion), 80g/L of sodium sulfite, barium sulfate (20ppm as barium ion), 10g/L of ethylenediamine, 4g/L of EDTA, 20g/L of sodium hydrogen phosphate An aqueous solution of 1 g/L of 3,5-dinitrobenzoic acid was used as an electrolytic gold plating solution by adjusting the pH of the aqueous solution to 8.0 with potassium hydroxide. Using this solution, electrolytic gold plating was performed for 70 seconds (film thickness: 0.35 μm) with stirring at a liquid temperature of 60 ° C and a current density of 0.5 A/dm ² .

Test example 2

Physical property determination:

(1) Welding ball joint shear strength and fracture mode

The welded ball joint shear strength and fracture mode of the gold-plated film obtained in the solutions of Examples 3 and 4 and Comparative Examples 1 and 2 were compared (Fig. 6).

The evaluation of solder ball bonding is performed using 0.75 mm of M705 (Sn-3.0 Ag-0.5Cu). Welded ball (made by Senju Metal Industry Co., Ltd.), flux used 529D (paste: manufactured by Senju Metal Industry Co., Ltd.), reflow soldering system using RF-430-M2 (made of Pulse), with top temperature of 260 ° C, retention time above melting point After about 32 seconds of solder mounting, a shear test was performed using a Bond Tester 4000HS (manufactured by ARCTEK) at a shear rate of 40 mm/s. Further, the film thickness of the gold plating evaluated was all (Ni 5.0 μm/Au 0.35 μm).

The rupture mode is evaluated on the failure surface by the ratio of the remaining area of the welded ball. In the case where there is no interface damage and the residual amount of the solder ball remains, the jointability is evaluated to be strong, and no solder ball remains, and in the case where the interface is broken, the joint evaluation is performed. Weak. As shown in Fig. 6, the number of samples was 20, and the welding joint strengths of Example 3 and Example 4 of the present invention were the same as Comparative Example 1 and Comparative Example 2, and there was almost no interface failure in the fracture mode. On the other hand, in the case of the cyanide gold plating solution of Comparative Example 1 and the sulfite gold plating solution of Comparative Example 2, there were a few cases in which the welding residue was small, and there was also a case of interface destruction, and sometimes it was not as in Example 3 and Example 4. Excellent.

(2) Wire bonding strength

The wire bonding strength of the gold plating film obtained in the solutions of Examples 3 and 4 and Comparative Examples 1 and 2 was compared.

Wire bonding strength is measured using gold wire 18 μm (manufactured by GMH), which was mounted by hitting a lead HW27U-HF (manufactured by Panasonic), and tensile strength was measured using a tensile tester BT-14 (manufactured by DAGE) (breaking mode measured in tensile strength (A) The 5 stages of ~E are shown in Figure 7. A and E are unqualified). Further, the film thickness of the gold plating evaluated was all (Ni 5.0 μm/Au 0.35 μm). The measurement results of Examples 3 and 4 and Comparative Examples 1 and 2 were all B (passed). As the wire bonding strength, as shown in FIG. 8, the gold plating solutions of Example 3 and Example 4 of the present invention were not significantly different from the gold plating gold plating solution of Comparative Example 1 and the sulfurous acid gold plating solution of Comparative Example 2, and the same. Excellent.

From the above measurement results, the gold plating film obtained by the gold plating solutions of Examples 3 and 4 had the same degree or more as the gold plating film obtained by the conventionally used cyanide bath of Comparative Example 1 and the sulfurous acid bath of Comparative Example 2. The characteristics required for the part. Therefore, it is understood that the present invention can be used to take An electrolytic gold plating solution containing a cyanide compound.

Example 6

Electrolytic gold plating:

The preparation of the monovalent gold complex slurry prepared in Reference Example 1 was 50 ml/L (5 g/L as gold ion), potassium formate 42 g/L, cesium methanesulfonate (20 ppm as hydrazine), and EDTA 7.31 g/L. An aqueous solution of 0.46 g/L of Thioglycolic acid was used, and the pH of the aqueous solution was adjusted to 7.4 with potassium hydroxide as an electrolytic gold plating solution.

When the electrolytic gold plating solution was subjected to electrolytic gold plating in the same manner as in Reference Example 4, the appearance after gold plating was a brighter gold than that of Reference Example 4. When the current efficiency in electrolytic gold plating was calculated in the same manner as in Reference Example 4, it was 90% or more.

Example 7

Electrolytic gold plating:

An aqueous solution containing 50 ml/L of a monovalent gold complex slurry prepared in Reference Example 1 (5 g/L as a gold ion), 42 g/L of potassium formate, tin sulfate (100 ppm as tin), and EDTA 5.8 g/L was prepared. The pH of the aqueous solution was adjusted to 7.4 with potassium hydroxide as an electrolytic gold plating solution.

The electrolytic gold plating solution was placed in a test piece coated with nickel on copper, and gently stirred at a liquid temperature of 60 ° C and a current density of 1 A/dm ^{2 to} carry out electrolytic gold plating for 3 minutes. The appearance after plating becomes a shiny, bright gold. When observed by SEM, the surface morphology was smooth, and compared with Examples 3 and 4, the interface of the crystal particles was completely invisible (Fig. 9). When the current efficiency of electrolytic gold plating was calculated in the same manner as in Reference Example 4, it was 40%. When the purity of the gold of the film was confirmed, the composition was a gold alloy of 99.4% gold and 0.6% tin.

Example 8

Electrolytic gold plating:

The preparation of the monovalent gold complex slurry prepared in Reference Example 1 was 80 ml/L (8 g/L as gold ion), 44 g/L potassium sulfate, tin sulfate (100 ppm as tin), EDTA 7.31 g/L, sulfur An aqueous solution of 1.54 g/L of salicylic acid was used, and the pH of the aqueous solution was adjusted to 7.4 with potassium hydroxide as an electrolytic gold plating solution.

When the electrolytic gold plating solution was subjected to electrolytic gold plating in the same manner as in Reference Example 4, the appearance after gold plating was brighter than that obtained in Reference Example 4 and Example 1. The current efficiency in electrolytic gold plating was 90% as calculated in the same manner as in Reference Example 4. When the purity of the gold of the film was confirmed, the composition was a gold alloy having a gold content of 99.2% and a tin content of 0.8%.

Example 9

Modulation of electrolytic gold plating solution:

An aqueous solution containing 2-mercaptoacetamide 0.15 M and chloroauric acid 0.05 M formed by hydrolysis of 2,4-thiazolidinedione was stirred at 20 ° C for 10 hours to form a monovalent gold complex. . Further, since the pH of the aqueous solution is 3 or less, the formed monovalent gold complex is not dissolved and becomes a precipitate. Second, by filtering the aqueous solution with a membrane of 0.4 μm The filter was filtered to separate the monovalent gold complex. The recovery of gold in this operation was 99.9%. Further, the structure of the monovalent gold complex was confirmed by NMR as the structure of the formula (IV) (n is 1 to 10). This monovalent gold complex can be used in the electrolytic gold plating solution in the same manner as in the above examples.

Example 10

Electrolytic gold plating:

An aqueous solution containing 0.15 M of N-(2-mercaptoethanolyl)glycine and 0.05 M of chloroauric acid formed by hydrolysis of Rhodanine-3-acetic acid was stirred at 20 ° C for 10 hours to make a monovalent gold The complex is formed. Further, since the pH of the aqueous solution is 3 or less, the formed monovalent gold complex is not dissolved and becomes a precipitate. Next, the aqueous solution was separated by a membrane filter of 0.4 μm to separate the monovalent gold complex. The recovery of gold in this operation was 99.9%. Further, the structure of the monovalent gold complex was confirmed by NMR as the structure of the formula (V) (n is 1 to 10).

The monovalent gold complex of the above formula (V) was used as a slurry in the same manner as in Reference Example 1, and the electrolytic gold plating solution was prepared by substituting the monovalent gold complex slurry used in Example 1. When the electrolytic gold plating solution was subjected to electrolytic gold plating, the same gold plating film was obtained.

Example 11

Modulation of electrolytic gold plating solution:

An aqueous solution containing N-(2-hydroxyethyl)-2-mercaptoacetamide 0.15M and chloroauric acid 0.05M formed by hydrolysis of 2,4-thiazolidinedione and 2-aminoethanol at 20 ° C Stir for 10 hours to form a monovalent gold complex. Further, since the pH of the aqueous solution is 3 or less, the formed monovalent gold complex is not dissolved and becomes a precipitate. Next, the aqueous solution was separated by a membrane filter of 0.4 μm to separate the monovalent gold complex. The recovery of gold in this operation was 99.9%. Further, the structure of the monovalent gold complex was confirmed by NMR as in the structure of the formula (VI) (n is 1 to 10). This monovalent gold complex can be used in the electrolytic gold plating solution in the same manner as in the above examples.

[Industrial availability]

The cyanide-free electrolytic gold plating solution of the present invention is useful for replacing an electrolytic gold plating solution containing a cyanide compound used so far.

Claims (11)

A cyanide-free electrolytic gold plating solution characterized by containing the following components (a) to (c): (a) a monovalent gold complex represented by the following general formula (I) (In the formula (I), R ₁ represents hydrogen or an alkyl group having 1 to 4 carbon atoms which may have a mercapto group, and R ₂ represents hydrogen or a branched alkyl group having 1 to 4 carbon atoms, R ₃ is a hydrogen, a branched alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group, or a carboxyalkyl group having a carbon number of 1 to 4 which may have a mercapto group, and n is an integer of 1 to 10; b) The electrolyte (c) is selected from the group consisting of metal crystal modifiers. The cyanide-free electrolytic gold plating solution according to claim 1, wherein the monovalent gold complex represented by the general formula (I) of the component (a) is that R ₁ in the formula (I) represents hydrogen, and R ₂ represents a methyl group. R ₃ represents a carboxymethyl group and n is 4. The cyanide-free electrolytic gold plating solution according to claim 1, wherein the electrolyte of the component (b) is one or more selected from the group consisting of a potassium salt, a sodium salt and an ammonium salt of an inorganic acid or an organic acid. The cyanide-free electrolytic gold plating solution of claim 1, wherein the metal of the component (c) selected from the metal crystal modifier is selected from the group consisting of ruthenium, osmium, One or more of the group consisting of arsenic, antimony, tin, lead, indium, antimony, gallium, antimony, bismuth, selenium, cobalt, and nickel. The cyanide-free electrolytic gold plating solution according to any one of claims 1 to 4, further comprising one or two selected from the group consisting of the components (d) and (e); (d) pH buffering The agent (e) is selected from a crystal modifier of a sulfur-containing compound. The cyanide-free electrolytic gold plating solution according to claim 5, wherein the pH buffer of the component (d) is selected from the group consisting of inorganic acids, organic carboxylic acids, organic phosphoric acid, pyridine sulfonic acid, and the like, potassium salts, sodium salts and ammonium salts. One or more of the group consisting of. The cyanide-free electrolytic gold plating solution of claim 5, wherein the sulfur-containing compound of the component (e) selected from the crystal modifier of the sulfur-containing compound is selected from the group consisting of thiosulfuric acid and thiophosphoric acid, and the potassium salt and sodium thereof. One or two or more selected from the group consisting of a salt, an ammonium salt, and an organic compound having both a thiol group and a carboxyl group. The cyanide-free electrolytic gold plating solution according to any one of claims 1 to 7, wherein the pH is 3 to 14. A cyanide-free electrolytic gold plating method for a member to be plated, characterized in that the plated member is subjected to electrolytic plating in a cyanide-free electrolytic gold plating solution according to any one of claims 1 to 8. The cyanide-free electrolytic gold plating method of the member to be plated according to claim 9, wherein the liquid temperature in the electrolytic plating is 20 to 80 ° C, and the current density is 0.1 to 6 A/dm ² . A gold-plated member obtained by a cyanide-free electrolytic gold plating method of a member to be plated as claimed in claim 9 or 10.