JP4475282B2 - Electroless gold plating solution and electroless gold plating method - Google Patents

Description

  The present invention relates to an electroless gold plating solution and an electroless gold plating method.

  In recent years, electroless gold plating solutions that can be used at neutral and low temperatures have been developed in place of conventional high-temperature, highly alkaline electroless gold plating solutions. This electroless gold plating solution was developed for the purpose of expanding the range of use of resists and electronic components that can be plated. However, existing products have insufficient plating solution stability and throwing power. Also inferior.

  There are two reasons for such a decrease in stability: (1) the stability of electroless gold plating itself is insufficient, and (2) the stability is reduced due to impurity metal contamination by the plating process. It is assumed that attempts have been made to improve the plating solution from these viewpoints.

  For example, Patent Document 1 discloses using ascorbic acid as a reducing agent in order to realize electroless gold plating near neutrality without using a cyanide compound.

  In addition, Patent Document 2 and Patent Document 3 disclose that a metal masking agent of a mercaptobenzothiazole-based compound is added for the purpose of suppressing impurity metal contamination by plating and improving liquid stability.

  Furthermore, Patent Document 4 discloses that a hydrazine compound (10 to 30 g / L) is used as a reducing agent in an electroless gold plating solution, and this bath is practically used at a lower concentration than the above ascorbic acid bath. It is said that a typical deposition rate can be obtained.

  In addition, the metal masking agent of the benzotriazole compound has been improved to suppress impurity metal contamination by plating and to improve liquid stability, and the management range of this masking agent is wide (3 to 10 g / L). This is disclosed in Patent Document 5.

On the other hand, Patent Document 6 discloses a method using thiourea or a phenyl compound as a reducing agent, and it is shown that thiourea can reduce gold at a low concentration.
Japanese Patent Laid-Open No. 1-191782 JP-A-4-350172 Japanese Patent Laid-Open No. 6-145997 JP-A-3-215567 Japanese Patent Laid-Open No. 4-314871 Japanese Patent No. 2972209

  However, the following problems existed in the above-described conventional plating solutions. That is, the reduction with ascorbic acid has a low reduction efficiency, and the sodium ascorbate concentration is excessively blended with 60 to 100 g / L in order to secure a practical precipitation rate, so that the stability of the plating solution was lowered.

  In addition, the metal concealing agent of the mercaptobenzothiazole compound has a problem that the use management range is very narrow (0.1 to 5 ppm), the work efficiency is low, and if the addition amount is large, a throwing-out defect occurs. It was.

  On the other hand, when a hydrazine compound is used as the reducing agent, this bath can obtain a practical precipitation rate at a lower concentration than the ascorbic acid bath, but the stability of the hydrazine compound itself is low and the stability of the liquid cannot be ensured. There was a problem. In addition, the metal masking agent of the benzotriazole-based compound has been improved for the purpose of suppressing impurity metal contamination by plating treatment and improving the liquid stability, but the result is that the reducing agent itself has low stability as described above. In particular, the stability improvement is insufficient and practical application is difficult.

  In addition, the electroless gold plating solution containing both the thiourea compound and the phenyl compound reducing agent is obtained by reducing the by-product of thiourea with a phenyl compound reducing agent to improve the liquid stability. However, it is difficult to completely return the thiourea by-product to the original reducing agent, and this residual by-product may cause poor adhesion and instability of the plating and may not maintain sufficient stability. there were. In addition, since the phenyl compound reducing agent has a reducing power at neutrality (pH 7 to 7.5), a practical deposition rate cannot be obtained, and in the weakly alkaline region (around pH 9.0), the appearance of the film However, there was a problem that the solution was decomposed during plating.

  Thus, an electroless gold plating solution containing both thiourea compound and phenyl compound reducing agents has been proposed (JP-A-3-104877). According to this plating solution, a by-product of thiourea is produced. Since it is reduced with a phenyl compound-based reducing agent, the liquid stability can be improved. In addition, it has been proposed to add a metal masking agent of a benzotriazole-based compound to this bath (Japanese Patent Laid-Open No. 9-1557859). According to this plating solution, the suppression of impurity metal contamination and the improvement of the liquid stability are proposed. As a result, the stability can be improved as compared with the conventional bath.

  However, at present, there is a demand for a plating solution that is more stable, neutral, and exhibits a practical deposition rate at low temperatures. Accordingly, an object of the present invention is an electroless gold plating solution that exhibits a sufficient gold deposition rate even at a low temperature of about 60-80 ° C. in a neutral region of about pH 6-8, It is to provide an electroless gold plating solution having particularly excellent properties. Another object of the present invention is to provide an electroless gold plating method using such an electroless gold plating solution.

  As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by an electroless gold plating solution containing a specific reducing agent and a heavy metal salt, and completed the present invention. I let you.

  That is, the electroless gold plating solution of the present invention includes a gold salt, a reducing agent represented by the following general formula (I), and a heavy metal salt.

［式中、Ｒ^１は水酸基又はアミノ基を示し、Ｒ^２、Ｒ^３及びＲ^４はそれぞれ独立に水酸基、アミノ基、水素原子又はアルキル基を示す。］

[Wherein, R ¹ represents a hydroxyl group or an amino group, and R ² , R ³ and R ⁴ each independently represents a hydroxyl group, an amino group, a hydrogen atom or an alkyl group. ]

  The electroless gold plating solution of the present invention uses a reducing agent combined with a gold salt as a compound represented by the above general formula (I) and also uses a heavy metal salt, so that the solution temperature is 60 in a neutral region of about pH 6-8. Even at a low temperature of about ˜80 ° C., not only a sufficient gold deposition rate is exhibited, but also the stability of the plating solution becomes particularly excellent.

  The electroless gold plating solution of the present invention preferably further includes a complexing agent, preferably further includes a pH buffer, and preferably further includes a metal ion concealing agent. That is, it is preferable that the electroless gold plating solution of the present invention further includes at least one of a complexing agent, a pH buffering agent, and a metal ion concealing agent. By containing such a component, the stability of the plating solution is further improved.

  The heavy metal salt is preferably at least one heavy metal salt selected from the group consisting of a thallium salt, a lead salt, an arsenic salt, an antimony salt, a tellurium salt and a bismuth salt, and the heavy metal salt is particularly a thallium salt. preferable. The heavy metal salt is preferably a heavy metal inorganic compound salt or a heavy metal organic complex salt, and the electroless gold plating solution preferably contains a heavy metal salt so that the heavy metal derived from the heavy metal salt is 1 to 100 ppm. When the heavy metal salt is the above compound or at the above concentration, the deposition rate of gold and the stability of the plating solution are further improved.

  In the electroless gold plating solution of the present invention, the reducing agent is preferably a reducing agent represented by the following general formula (II). By using the reducing agent represented by the general formula (II), it is possible to improve the stability of the plating solution and improve the deposition rate of gold.

［式中、Ｒ^２１は水酸基又はアミノ基を示し、Ｒ^２２は水素原子又は炭素数１〜４のアルキル基を示す。］

[Wherein, R ²¹ represents a hydroxyl group or an amino group, and R ²² represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. ]

  The electroless gold plating solution of the present invention preferably has a pH of 5-10. When the pH of the electroless gold plating solution is in the above range, it is possible to perform electroless gold plating on various objects to be plated at neutral and low temperatures. It becomes possible.

In the present invention, the deposition rate of gold at a pH of 6 to 8 and a liquid temperature of 60 to 80 ° C. is 0.2 to 1.0 μm / hour, and plating is performed at 65 ° C. for 1 hour at a plating load of 0.36 dm ² / L. The electroless gold plating solution is characterized in that the abnormal precipitation component is 0% when left at room temperature for 1 day after performing the above.

  The present invention further relates to an electroless gold plating method in which a body to be plated is immersed in an electroless gold plating solution to form a gold film on the surface of the body to be plated. An electroless gold plating method characterized by being a gold plating solution. In such a method, the pH of the electroless gold plating solution is preferably 6 to 8, and the gold film is preferably formed with an electroless plating solution having a liquid temperature of 60 to 80 ° C. By applying this method, it is possible to perform electroless gold plating on various objects to be plated at neutral and low temperatures.

  According to the present invention, an electroless gold plating solution that exhibits a sufficient gold deposition rate even at a low temperature of about 60 to 80 ° C. in a neutral region of about pH 6 to 8, and the stability of the plating solution is high. It becomes possible to provide a particularly excellent electroless gold plating solution. It is also possible to provide an electroless gold plating method using such an electroless gold plating solution.

As described above, the electroless gold plating solution of the present invention contains a gold salt, a reducing agent, and a heavy metal salt as essential components. First, an embodiment of the essential component will be described.

(Gold salt)
Examples of the gold salt that can be used in the electroless gold plating solution of the present invention include cyan gold salts and non-cyan gold salts. Examples of cyanide gold salts include potassium primary cyanide and potassium secondary gold cyanide. Examples of non-cyanide gold salts include chloroaurate, goldsulfite, gold thiosulfate, gold thiomalate. Salts can be exemplified. Only 1 type may be used for gold salt and it may use it in combination of 2 or more type.

  As the gold salt, gold sulfite and gold thiosulfate are preferable, and the content thereof is preferably in the range of 1 to 10 g / L as gold. If the gold content is less than 1 g / L, the gold precipitation reaction decreases, and if it exceeds 10 g / L, the stability of the plating solution decreases and the amount of gold consumed increases due to the removal of the plating solution. Therefore, it is not preferable economically. The content is more preferably in the range of 2 to 5 g / L.

(Reducing agent)
The reducing agent used in the electroless gold plating solution of the present invention is a compound represented by the following general formula (I) (hereinafter referred to as “Compound I”).

In compound I, R ¹ is a hydroxyl group or an amino group, and R ² , R ³ and R ⁴ are each independently a hydroxyl group, an amino group, a hydrogen atom or an alkyl group, and the alkyl group is a linear or branched carbon. A C1-C6 alkyl group is preferable, and a linear or branched C1-C4 alkyl group (a methyl group, an ethyl group, t-butyl group, etc.) is more preferable.

  Specific examples of compound I include, for example, phenol, o-cresol, p-cresol, o-ethylphenol, p-ethylphenol, t-butylphenol, o-aminophenol, p-aminophenol, hydroquinone, catechol, pyrogallol, methyl Hydroquinone, aniline, o-phenylenediamine, p-phenylenediamine, o-toluidine, p-toluidine, o-ethylaniline, p-ethylaniline and the like can be used, and one or more of these can be used.

  From the viewpoint of the stability of the plating solution and the deposition rate of gold, the compound I is preferably a compound represented by the following general formula (II) (hereinafter referred to as “compound II”).

In Compound II, R ²¹ is a hydroxyl group or an amino group, and R ²² is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms (methyl group, ethyl group, t-butyl group, etc.). Specific examples of compound II include p-phenylenediamine, methylhydroquinone, hydroquinone and the like.

  The content of the reducing agent is preferably 0.5 to 50 g / L based on the total capacity of the plating solution. When the content of the reducing agent is less than 0.5 g / L, it is difficult to obtain a practical deposition rate. If it exceeds 50 g / L, the stability of the plating solution tends not to be ensured. The content of the reducing agent is more preferably 2 to 10 g / L.

(Heavy metal salt)
In the present invention, a major feature is that a heavy metal salt is added to the combination of the gold salt and the reducing agent described above. By adding a heavy metal salt, a practically sufficient gold deposition rate (0.2 μm / hour or more) is possible even at a low temperature of about 60 to 80 ° C. in a neutral region of about pH 6 to 8. That is, the heavy metal salt functions as a deposition rate accelerator. In addition, excellent plating solution stability, which was impossible with the prior art, can be obtained.

  From the viewpoint of further promoting the deposition rate, the heavy metal salt is preferably at least one selected from the group consisting of thallium salt, lead salt, arsenic salt, antimony salt, tellurium salt and bismuth salt.

  Examples of the thallium salt include inorganic compound salts such as thallium sulfate salt, thallium chloride salt, thallium oxide salt, and thallium nitrate salt, and organic complex salts such as dithallium malonate salt. Lead salts include lead sulfate salt, nitric acid salt, and the like. Examples include inorganic compound salts such as lead salts and organic complex salts such as lead acetate.

  Arsenic salts include inorganic compound salts such as arsenite, arsenate, and arsenic trioxide, and organic complex salts. Antimony salts include organic complex salts such as antimony tartrate, antimony chloride salts, and antimony oxysulfate. And inorganic compound salts such as salts and antimony trioxide.

  Examples of tellurium salts include inorganic compound salts and organic complex salts such as tellurite and tellurate. Examples of bismuth salts include bismuth sulfate (III), bismuth chloride (III), and bismuth nitrate (III). And an inorganic complex salt such as bismuth (III) oxalate.

  In the present invention, it is particularly preferable to use a thallium salt (preferably a thallium inorganic compound salt or a thallium organic complex salt) as the heavy metal compound salt.

  Although the heavy metal salt mentioned above can use 1 type (s) or 2 or more types, 1-100 ppm is preferable on the basis of the plating solution total capacity, and 1-10 ppm is more preferable. If it is less than 1 ppm, the effect of improving the deposition rate may not be sufficient, and if it exceeds 100 ppm, the stability of the plating solution tends to deteriorate.

  The electroless gold plating solution of the present invention preferably contains at least one of a complexing agent, a pH buffering agent and a metal ion concealing agent in addition to the above-described gold salt, reducing agent and heavy metal salt. It is more preferable to contain. Hereinafter, such components will be described.

(Complexing agent)
The electroless gold plating solution of the present invention preferably contains a complexing agent. By containing the component, gold ions (Au ⁺ ) are stably complexed, and Au ⁺ is disproportionated. The generation of the reaction (3Au ⁺ = Au ³⁺ + 2Au) is reduced, and the effect that the liquid is kept stable is obtained. Only one type of complexing agent may be used, or two or more types may be used in combination, and suitable complexing agents include cyan complexing agents and / or non-cyanide complexing agents.

  Examples of the cyanate complexing agent include cyanate salts such as sodium cyanide and potassium cyanide, and examples of the non-cyanide complexing agent include sulfite, thiosulfate, and thiomalate.

  As the complexing agent, sulfites and thiosulfates are preferable, and the content of the complexing agent is preferably 1 to 200 g / L based on the total capacity of the plating solution. When the content of the complexing agent is less than 1 g / L, the gold complexing power tends to be low and the stability tends to be low. On the other hand, if it exceeds 200 g / L, the stability of the plating solution is improved, but recrystallization occurs in the solution, resulting in an economical burden. The content of the complexing agent is more preferably 20 to 50 g / L.

(PH buffer)
The electroless gold plating solution of the present invention preferably contains a pH buffering agent, and by adding the component, the deposition rate can be adjusted to a desired value, and the pH and the like can be kept constant. it can. Only one type of pH buffer may be used, or two or more types may be used in combination. Suitable pH buffering agents include phosphates, acetates, carbonates, borates, citrates, sulfates, etc. Among these, borates and / or sulfates are particularly preferable.

  The content of the complexing agent is preferably 1 to 100 g / L based on the total capacity of the plating solution. If the content of the complexing agent is less than 1 g / L, there may be no pH buffering effect and the state of the plating bath may change. If it exceeds 100 g / L, recrystallization tends to proceed in the plating solution. It is in. The content of the complexing agent is more preferably in the range of 20 to 50 g / L.

(Metal ion concealing agent)
The electroless gold plating solution of the present invention preferably contains a metal ion concealing agent, and the following effects can be obtained by including the component. That is, impurities such as copper, nickel, iron, etc. due to contamination of the plating equipment during work by bringing in rust, metal fragments, etc. or contamination of the base metal into the plating solution due to insufficient coverage of the object to be plated When the ions are mixed and the abnormal reaction of the plating solution proceeds and the decomposition of the plating solution occurs, such an abnormal reaction can be suppressed.

  As the metal ion masking agent, a benzotriazole-based compound can be used, and examples of such a compound include benzotriazole sodium, benzotriazole potassium, tetrahydrobenzotriazole, methylbenzotriazole, nitrobenzotriazole and the like.

  The content of the metal ion concealing agent is preferably 0.5 to 100 g / L based on the total capacity of the plating solution. When the content of the metal ion concealing agent is less than 0.5 g / L, the effect of concealing impurities is small, and sufficient liquid stability tends not to be ensured. On the other hand, if it exceeds 100 g / L, recrystallization may occur in the plating solution. In consideration of cost and effect, the content of the metal ion concealing agent is more preferably 2 to 10 g / L.

(PH of electroless gold plating solution)
The pH of the electroless gold plating solution of the present invention is preferably 5-10. If the pH of the electroless gold plating solution is less than 5, the sulfite or thiosulfate that is the gold complexing agent of the plating solution may be decomposed to generate toxic sulfite gas. Moreover, when pH exceeds 10, it exists in the tendency for stability of a plating solution to fall. The pH of the electroless gold plating solution is more preferably 6-8, and still more preferably 7-8.

(Electroless gold plating method)
Next, the electroless gold plating method of the present invention will be described. The electroless gold plating method of the present invention is characterized in that a body to be plated is immersed in the electroless gold plating solution of the present invention described above to form a gold film on the surface of the body to be plated.

  In such a method, the pH of the electroless gold plating solution is preferably 5 to 10, more preferably 6 to 8, and still more preferably 7 to 8. Further, the gold film is preferably formed with an electroless plating solution having a solution temperature of 60 to 80 ° C., and the solution temperature is more preferably 65 to 80 ° C.

  Next, although an Example demonstrates this invention concretely, this invention is not restrict | limited by this.

[Sample preparation]
A 3cm x 3cm x 0.3mm rolled copper plate is used for the plating test sample, and Z-200 (trade name, manufactured by World Metal Co., Ltd.), which is acidic degreasing, is used to remove rust and organic matter on the surface. Treated at 45 ° C. for 3 minutes. Furthermore, in order to remove excess surfactant, hot water washing (45 degreeC, pure water) was implemented for 1 minute. Then, the water washing process was performed for 1 minute. Furthermore, in order to make the shape of the surface uniform, a soft etching treatment was performed in which the substrate was immersed in an ammonium persulfate solution (120 g / L) for 3 minutes at room temperature. Then, the water washing process was performed for 1 minute. Next, in order to remove the copper oxide on the surface, it was immersed in sulfuric acid (10%) at room temperature for 1 minute, then washed with water for 1 minute, and then replaced with SA-100 (Hitachi Chemical Co., Ltd.). The company-made product name) was immersed for 5 minutes at room temperature. Then, the water washing process was performed for 1 minute.

  Next, an immersion treatment is performed at 85 ° C. for 25 minutes in NIPS-100 (trade name, manufactured by Hitachi Chemical Co., Ltd.), which is an electroless Ni—P plating solution, and a nickel-phosphorous plating film is formed to about 5 μm. After washing with water for 1 minute, it was immersed in HGS-500 (trade name, manufactured by Hitachi Chemical Co., Ltd.) which is a displacement gold plating solution at 85 ° C. for 10 minutes, and was about 0.05 to 0.1 μm. A gold plating film having a thickness was formed and washed with water for 1 minute, and further evaluated by performing the following electroless gold plating. Moreover, the resin tank made from a polypropylene was used for the plating tank for evaluation of an electroless gold plating solution.

[Gold plating solution stability evaluation method]
(Cleaning method of the experimental tank for gold plating solution stability evaluation)

  In the gold plating solution stability evaluation method, a 1 L beaker made of PP (polypropylene) resin was used as a plating tank. In order to remove impurities adhering to the tank, the inside of the tank was washed with aqua regia (1: 3 = nitric acid: hydrochloric acid, diluted to 50% with pure water) for 6 hours or more at room temperature before the experiment. Thereafter, washing with water and washing with pure water were sufficiently carried out successively, dried at 80 ° C. and used for the experiment.

(Gold plating solution stability evaluation method)
The gold plating solution stability was classified into three conditions and evaluated. First, (1) using the above plating tank, the stability of the gold plating solution was evaluated when the solution temperature was set to 65 ° C. and left for 1 hour before plating. Next, (2) after the temperature rise, plating was performed for 1 hour (65 ° C.) with a plating load of 0.36 dm ² / L. Next, (3) the plating solution is naturally cooled, the gold plating solution is allowed to stand at room temperature for one day, and the ratio of the area where the abnormal deposit covers the bottom of the plating tank (abnormal deposition occurrence area (%) in the tank), that is, abnormal The plating solution stability was evaluated by the precipitation component (%). The evaluation criteria are as shown in Table 1.

[Film appearance and plating failure evaluation method]
As for the plating appearance and plating failure, the appearance close to an electrogold plating film (corresponding to 0.5 μm) was standard. In addition, the plating endurance was evaluated by visually observing the plating end with a microscope (equivalent to 20 to 50 times).

[Production and evaluation of electroless gold plating solution]
(Examples 1-4)
The electroless gold plating solutions of Examples 1 to 4 were prepared so as to have the compositions shown in Table 2, and evaluated based on the evaluation method described above. In Examples 1 to 4, the concentration of hydroquinone, which is a reducing agent, was fixed to 3 g / L, and experiments were conducted. Moreover, it used as thallium nitrate as a heavy metal salt which is a precipitation rate accelerator, and Tl (thallium) ions in the electroless gold plating solutions of Examples 1 to 4 were 1, 3, 5, and 10 ppm, respectively.

  Table 2 summarizes the deposition rate, film appearance, plating failure, and stability of the gold plating solution. The deposition rate increased when the thallium ion concentration was 1 ppm, approximately twice that of the unadded bath. An improvement in deposition rate was confirmed. Further, the appearance of the plating film was uniform lemon yellow, and it was good without occurrence of poor attachment. Also, the stability of the gold plating solution during and after plating was good. Furthermore, as the thallium ion content became 3, 5, and 10 ppm, the deposition rate increased, and the addition rate of 10 ppm showed a deposition rate of 0.36 μm / hour (about three times that when no addition was made). Moreover, the appearance of the plating film was uniform lemon yellow, and it was good without the occurrence of defective plating with the increase in the deposition rate. Also, the liquid stability during and after plating was good.

(Examples 5 to 8)
Electroless gold plating solutions of Examples 5 to 8 were prepared so as to have the compositions shown in Table 3, and evaluated based on the evaluation method described above. In Examples 5 to 8, experiments were conducted with the concentration of hydroquinone as a reducing agent being kept constant at 5 g / L. Moreover, it used as thallium nitrate as a heavy metal salt which is a deposition rate accelerator, and Tl (thallium) ions in the electroless gold plating solutions of Examples 5 to 8 were 1, 3, 5, and 10 ppm, respectively.

  The deposition rate, film appearance, plating failure, and gold plating solution stability are summarized in Table 3. As shown in Table 1, an increase in the deposition rate was observed when the thallium ion concentration was 1 ppm. Compared with Example 4), it was confirmed that the deposition rate was improved about twice. Also, the appearance of the plating film was uniform lemon yellow, and it was good without the occurrence of defects with plating. Also, the stability of the gold plating solution during and after plating was good. Further, as the thallium ion content becomes 3, 5, and 10 ppm, the deposition rate increases, and the deposition rate of 0.56 μm / hr under conditions of hydroquinone 5 g / L, thallium 10 ppm, pH 7.5 (when not added) About 3 to 4 times greater). Moreover, the appearance of the plating film was uniform lemon yellow, and it was good without the occurrence of defective plating with the increase in the deposition rate. Also, the liquid stability during and after plating was good.

(Examples 9 to 12)
The electroless gold plating solutions of Examples 9 to 12 were prepared so as to have the compositions shown in Table 4, and evaluated based on the evaluation method described above. As in Examples 5 to 8, the gold plating solution composition is 5 g / L of hydroquinone as a reducing agent, pH is 7.5 with good liquid stability, and thallium ions are 1, 3, 5 as a deposition rate accelerator. The experiment was conducted at a plating temperature of 80 ° C. under the condition of 10 ppm.

  The deposition rate, film appearance, plating failure, and gold plating solution stability are summarized in Table 4. When the plating temperature is 80 ° C., the deposition rate is further increased, and the addition of 1.0 ppm is about 0.5 μm / The deposition rate at the time was shown. Further, when the addition amount was further increased, a practical precipitation rate of 1.15 μm / hour was exhibited with addition of 10.0 ppm. As for the plating appearance, all of the conditions of Examples 9 to 12 showed a uniform lemon yellow appearance, which was a good result with no defective plating around and no occurrence of precipitation unevenness. Regarding the stability of the gold plating solution, good results were obtained before plating, during plating, after plating, and after plating (1 day or more).

(Comparative Examples 1-4)
The electroless gold plating solutions of Comparative Examples 1 to 4 were prepared so as to have the compositions shown in Table 5, and evaluated based on the evaluation method described above. Comparative Examples 1, 2, 3 and 4 were subjected to gold plating by adding hydroquinone as a reducing agent at 0, 1, 3 and 5 g / L, respectively.

  Table 5 summarizes the deposition rate, film appearance, plating failure, and stability of the gold plating solution. When hydroquinone as a reducing agent is not added, even if immersed in the plating solution for 1 hour, it is almost a gold film. There was no increase in thickness, and precipitation did not proceed. On the other hand, when hydroquinone is added as the reducing agent, the deposited film thickness gradually increases, and a deposited film thickness of 0.152 μm / hour (about 2.5 times that when no additive is added) can be obtained at 5 g / L hydroquinone. It was.

  Moreover, on the conditions of Comparative Examples 2-4, the external appearance of the plating film was uniform lemon yellow, and it was good without the occurrence of a dipping failure. Also, the liquid stability during and after plating was good. However, the deposition rate was slower than that of a practical electroless gold plating solution (about 0.2 to 1.0 μm / hour or more). For this reason, it has been found that wire bonding substrates such as package substrates are problematic because of poor productivity.

(Comparative Examples 5 to 8)
Electroless gold plating solutions of Comparative Examples 5 to 8 were prepared so as to have the compositions shown in Table 6, and evaluated based on the evaluation method described above. Table 6 summarizes the deposition rate, film appearance, plating failure, and gold plating solution stability. When the pH of the gold plating solution is changed to 8, 9, and 10 using 1N NaOH, Under the condition of pH 9, the deposition rate increased remarkably and showed about 0.8 μm / hour. However, under the conditions of pH 9 and 10, the plating solution was very unstable and abnormal precipitation occurred in the plating tank during the temperature rise, resulting in difficulty in normal use. Further, even under the condition of pH 8.0 (Comparative Example 5), abnormal deposition occurred in a part of the plating tank after 1 day from the plating.

  Further, the plating appearance was a uniform surface of lemon yellow under the condition of pH 8, but the results of red and brown appearance were poor at pH 9 and 10. In addition, with regard to the wraparound property with plating, there was no problem under the conditions of Comparative Examples 5, 6, and 7. As for Comparative Example 8, the experiment was conducted at pH 9.0 and the plating temperature of 80 ° C. as in Comparative Example 6, but the plating appearance was poor reddish brown and the liquid stability was further deteriorated compared to 65 ° C. In addition, the consumption of gold ions in the liquid was large, and the deposition rate was the same as that at 65 ° C.

  From the above results, the electroless gold plating solution of the present invention can increase the deposition efficiency of hydroquinone, which is a reducing agent, by adding a heavy metal salt, and also has a practical deposition rate (0.2 to 1.0 μm). It was found that electroless gold plating having a stable and uniform lemon yellow film appearance is possible. Also, since the pH of the solution is near neutral (6-8) and can be used under low temperature conditions (60-80 ° C), the gold plating solution is low in stability and cannot be mass-produced. The neutral electroless gold plating that has not been performed becomes possible, and the range of applicable materials and electronic parts is greatly expanded.

Claims (14)

An electroless gold plating solution comprising a gold salt, a reducing agent represented by the following general formula (I), and a heavy metal salt.

[Wherein, R ¹ represents a hydroxyl group or an amino group, and R ² , R ³ and R ⁴ each independently represents a hydroxyl group, an amino group, a hydrogen atom or an alkyl group. ]   The electroless gold plating solution according to claim 1, further comprising a complexing agent.   The electroless gold plating solution according to claim 1 or 2, further comprising a pH buffer.   The electroless gold plating solution according to any one of claims 1 to 3, further comprising a metal ion concealing agent.   The heavy metal salt is at least one heavy metal salt selected from the group consisting of a thallium salt, a lead salt, an arsenic salt, an antimony salt, a tellurium salt, and a bismuth salt. The electroless gold plating solution described in 1.   The electroless gold plating solution according to any one of claims 1 to 5, wherein the heavy metal salt is a thallium salt.   The electroless gold plating solution according to any one of claims 1 to 6, wherein the heavy metal salt is a heavy metal inorganic compound salt or a heavy metal organic complex salt.   The electroless gold plating solution according to any one of claims 1 to 7, wherein the heavy metal salt is contained so that the heavy metal derived from the heavy metal salt is 1 to 100 ppm. The electroless gold plating according to any one of claims 1 to 8, wherein the reducing agent represented by the general formula (I) is a reducing agent represented by the following general formula (II). liquid.

[Wherein, R ²¹ represents a hydroxyl group or an amino group, and R ²² represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. ]   The electroless gold plating solution according to any one of claims 1 to 9, wherein the pH is 5 to 10. The electroless gold plating solution according to any one of claims 1 to 10, wherein the content of the reducing agent is 2 to 10 g / L based on the total capacity of the electroless gold plating solution. . In the electroless gold plating method of immersing the object to be plated in an electroless gold plating solution to form a gold film on the surface of the object to be plated,
The electroless gold plating solution according to any one of claims 1 to 11, wherein the electroless gold plating solution is an electroless gold plating method.   13. The electroless gold plating method according to claim 12, wherein the electroless gold plating solution has a pH of 6-8.   The electroless gold plating method according to claim 12 or 13, wherein the gold coating is formed with the electroless gold plating solution having a liquid temperature of 60 to 80 ° C.