JP2020105543A - Immersion gold plating solution and immersion gold plating method - Google Patents

Abstract

To provide immersion gold plating solution with high deposition rate and less variation of a film thickness of a deposition film, and an immersion gold plating solution method, and especially in an ENEPIG method, to provide the immersion gold plating solution and the immersion gold plating method in which corrosion of a lower side nickel intermediate layer in a laminated structure of a palladium intermediate layer/nickel intermediate layer is small.SOLUTION: In a cyan system immersion gold plating solution including a gold cyanide compound and a thallium compound, pH is 2.0 to 4.4 and aminocarboxylic system chelate agent having a hydroxyl group is included. By using the cyanide system gold plating solution including the cyanide gold compound and thallium compound including the aminocarboxylic chelate agent acid having a hydroxyl group of pH of 2.0 to 4.4, a gold surface layer is formed on an intermediate layer of any of copper, nickel or palladium, or on a laminated structure comprising their intermediate layers.SELECTED DRAWING: None

Description

The present invention relates to a displacement gold plating solution and a displacement gold plating method using a gold cyanide compound.

A gold plating layer is usually formed on a bonding pad of a mounting board used for an electronic component of an electronic device. Gold has the second highest electrical conductivity after silver and copper, and is excellent in physical properties such as bondability by thermocompression bonding, as well as in chemical properties such as oxidation resistance and chemical resistance. Therefore, even though gold is expensive, it continues to be used as a bonding pad of a mounting substrate. Since the pattern of such a mounting substrate has restrictions on the power supply lead and there is an independent pattern in which formation of a plating film is difficult, the electroless gold plating method is often adopted.

Displacement gold plating has long been known as a part of electroless gold plating, and when a metal having a less ionizing tendency than gold exists in a solution of gold ions, the surface of the base metal dissolves in the solution. This is a technique that utilizes the principle that gold ions in a solution are deposited as gold metal.

However, displacement gold plating is difficult to thicken because of the reaction mechanism in which gold ions substitute for the base metal and gold metal is deposited. The disadvantage was that the corrosion of some nickel intermediate layers was extended. Therefore, in the electroless gold plating treatment method, a two-step treatment of a substitution type and an autocatalytic type (reduction type) is used. It was necessary to perform one-step processing.

In recent years, electronic devices have become more sophisticated and multifunctional, and mounting boards used for electronic components have become higher in density, and it has become more difficult to form power supply leads due to the miniaturization of bonding pads. The need for plating is increasing. However, as described above, the displacement gold plating is difficult to thicken, and has been replaced by the two-step treatment of the substitution type and the autocatalytic type, or the one-step treatment of the substitution/autocatalyst combined type. However, with the shift of production bases from Japan to emerging countries in Asia, running costs have been required to be reduced, workability has also been emphasized, and the replacement gold plating process has been reviewed again.

The following three types of methods are known for the displacement gold plating process used for the bonding pad of the mounting substrate. That is, (1) Direct Immersion Gold (DIG) method for directly forming a displacement gold plating film on copper, (2) Electroless nickel for forming a displacement gold plating film on a base electroless nickel plating film /Electroless Nickel Immersion Gold (ENIG) method, and (3) Electroless nickel/electroless palladium/Substitution gold (Electroless) in which an electroless palladium plating film is provided between the electroless nickel plating film as the base and the substitution gold plating film. Nickel Electroless Palladium Immersion Gold (ENEPIG) method.

Among them, in the ENEPIG method, the nickel plating film is used as a barrier film for preventing the copper circuit from being corroded by solder, and the palladium plating film is used as a barrier film for preventing diffusion of the nickel plating film into the gold plating film. It Then, a gold plating film having low electric resistance and good solder wettability is applied to the final finish. Therefore, there is an advantage that a joint portion having excellent joint characteristics such as soldering and wire bonding can be formed by the plating film of the base metal made of nickel and palladium and the gold plating film.

For example, in Patent Document 1 (JP 2012-46792 A), "a replacement gold for forming a joint portion in which a nickel layer, a palladium layer, and a gold layer are sequentially laminated on a conductor layer made of a conductive metal is formed. A plating solution, wherein the displacement gold plating solution contains a gold cyanide salt, a complexing agent and a copper compound, and the molar ratio of the complexing agent to the copper compound in the displacement gold plating solution is a complexing agent. /Copper ion=1.0 to 500, and the stability constant at pH 4 to 6 of the compound formed from the complexing agent and the copper compound is 8.5 or more. (Claims, Claim 1) is disclosed. This displacement gold plating is capable of suppressing variations in the gold layer thickness of the bonding part formed on each pad even if the part forming the bonding part has pads of various sizes, and a uniform thickness. We provide a displacement gold plating technology that can realize a gold plating film" (paragraph 0009).

In this ENEPIG method, it is required to increase the gold film thickness in order to apply it to various film thickness specifications of displacement gold plating. However, when the treatment time was extended or the liquid temperature was raised in order to increase the deposited gold film thickness, a new defect that the variation in the gold film thickness became large was revealed. This is because the noble palladium metal is in the upper layer and the base nickel metal is in the lower layer, so that corrosion tends to be unstable. Further, it has been found that the finer the bonding pad, the more the abnormal corrosion of the lower nickel intermediate layer progresses, leading to a serious problem of lowering solder bonding or wire bonding bonding.

JP 2012-46792 A

The present invention has been made in view of the above problems in displacement gold plating, and a displacement gold plating solution and a displacement gold plating solution having a high deposition rate and a small film thickness variation due to the difference in the area of the bonding pad of the mounting substrate. An object is to provide a plating method. In particular, in the conventional ENEPIG method, it is improved that the corrosion ratio of the lower nickel intermediate layer is higher than the corrosion ratio of the upper palladium intermediate layer of the palladium intermediate layer/nickel intermediate layer laminated structure. It is an object of the present invention to provide a substitutional gold plating solution and a substitutional gold plating method with less corrosion.

It is known that the local battery action in the cyan-based displacement gold plating solution is generally a noble metal in the order of gold>palladium>nickel. Studies conducted by the present inventors have revealed that the corrosion of the intermediate plating layer, which is a base metal, greatly depends on the pH of the solution. Then, the present inventors suppress the corrosion of the intermediate plating layer of the base metal by making the gold cyanide compound stable in the neutral to alkaline solution into a compound that is unstable on the acidic side, and increase the deposition rate. We have succeeded in improving and reducing the variation in film thickness due to the difference in the area of the bonding pad of the mounting board.

In particular, when the intermediate plating layer on the copper or copper alloy pad has a laminated structure of a palladium layer and a nickel layer, the local cell action in the cyan-based displacement gold plating solution is such that gold ≈ palladium> nickel tends to occur in the neutral pH range. However, on the other hand, it was found that there is a tendency of gold>palladium>nickel in the weakly acidic region of pH. Therefore, the corrosion rate of the upper palladium intermediate layer can be increased by setting the cyan-based displacement gold plating solution to a weakly acidic region, thereby suppressing the corrosion of the nickel intermediate layer, improving the deposition rate, and increasing the area difference. It is possible to reduce the variation in film thickness due to.

The displacement gold plating solution of the present invention has a pH of 2.0 to 4.4 in a cyan displacement gold plating solution containing a gold cyanide compound and a thallium compound, and an aminocarboxylic acid type chelating agent having a hydroxyl group. It is characterized by containing.

The displacement gold plating method of the present invention is a displacement gold plating solution containing a gold cyanide compound and a thallium compound, having a pH of 2.0 to 4.4 and containing an aminocarboxylic acid type chelating agent having a hydroxyl group. It is characterized in that a gold surface layer is formed on an intermediate layer of any one of copper, nickel, and palladium, or a laminated structure composed of these intermediate layers, using a cyan-based displacement gold plating solution. In particular, the displacement gold plating method of the present invention is a laminated structure comprising an intermediate layer in which an electroless nickel plating film is formed on a copper metal using the cyan-based displacement gold plating solution, and an electroless palladium plating film is further formed. It is characterized in that a gold surface layer is formed thereon.

In the cyan substitution gold plating solution or substitution gold plating method containing a gold cyanide compound and a thallium compound according to the present invention, the pH of the plating solution is set to 2.0 to 4.4, and an aminocarboxylic acid type chelating agent having a hydroxyl group is used. The inclusion is to weaken the binding force of the cyanide and gold ion complex of the cyanide gold compound and to deposit a uniform gold metal film on the entire surface by the mechanism of the chelating agent having a mild reducing action. This is because.

In the cyan-based displacement gold plating solution or the displacement gold plating method of the present invention, generally 0.1 to 10 g/L of gold ion can be used. The practical upper limit is 5 g/L. This is to avoid the retention of gold bullion. If the gold ion concentration is less than the lower limit value, the substitution rate becomes slow and it becomes difficult to form a sufficient substitution plating layer. Further, the upper limit of 10 g/L is to save wasteful cost such as expensive gold metal adhering to the object to be plated and being pumped out to the washing tank (dragout). From a practical point of view, the upper limit of the concentration of gold ions is preferably 5 g/L, particularly preferably 3 g/L. Further, the lower limit value is preferably 0.5 g/L, and particularly preferably 0.8 g/L in order to accelerate the substitution rate of the deposited film.

In the cyan-based displacement gold plating solution or the displacement gold plating method of the present invention, a thallium compound is contained. It is known that in the presence of thallium ions, an underpotential deposition phenomenon occurs in which gold ions are deposited on the underlying metal in a potential region nobler than the equilibrium potential where gold ions are deposited as gold metal, which promotes the substitution reaction of the gold plating solution. However, the present invention also works effectively in the pH range of 2.0 to 4.4 according to the present invention. The thallium ion can be used in the concentration range of 0.1 to 100 mg/L, which is the concentration range of the thallium compound used in a general cyan-based displacement gold plating solution.

In the cyan-based displacement gold plating solution or the displacement gold plating method of the present invention, the substantial upper limit of the thallium compound is 80 mg/L as thallium ion. A small amount of a thallium compound can accelerate the substitution reaction of the gold plating solution, but even if the thallium compound is added as thallium ion in an amount of 5 mg/L or more, the effect of accelerating the substitution reaction is improved in proportion to the concentration of the thallium ion. is not. The thallium compound can be added as various compounds, but water-soluble thallium salts such as thallium sulfate, thallium acetate, thallium nitrate, and thallium formate are preferable.

In the cyan substitutional gold plating solution or the substitutional gold plating method of the present invention, the lower limit of pH is set to 2.0 because when it is less than 2.0, the binding force of the cyanide-gold complex cyanide-gold ion complex. Is too weak, and gold metal is deposited in the displacement gold plating solution, resulting in high loss of expensive gold metal. In addition, the upper limit of pH is set to 4.4, because at 4.4 or more, the binding force of the complex of the cyanide and the gold ion of the cyanide compound is too strong, and it becomes difficult for gold metal to precipitate. This is because the corrosion of nickel metal, which is baser than that of palladium metal, becomes unstable, and the thickness of the gold film varies depending on the area of the bonding pad of the mounting substrate. The preferable upper limit value is 4.0, more preferably 3.8, and most preferably 3.6. The lower limit is preferably 2.2, more preferably 2.4, and most preferably 2.6.

In the cyan substituted gold plating solution or the substituted gold plating method of the present invention, an aminocarboxylic acid type chelating agent having a hydroxyl group is contained in order to moderate the deposition action of gold metal. The content of the aminocarboxylic acid type chelating agent having a hydroxyl group is 0.1 to 100 g/L. By making a predetermined amount of the aminocarboxylic acid type chelating agent having a hydroxyl group coexist with the gold ion, it is possible to suppress the film thickness variation due to the difference in the area of the bonding pad of the mounting substrate. If it is less than the lower limit, thallium ions cannot be complex-formed and the film thickness varies greatly. On the other hand, if the upper limit is exceeded, the effect of variation in film thickness will reach a ceiling.

Examples of the aminocarboxylic acid-based chelating agent having a hydroxyl group include DHEG (Dihydroxyethyl Glycine), HIDA (Hydroxyethyl Imino Diacetic Acid), HEDTA (Hydroxydiptyclic Acrylonitrile-Adicarboxylic Acid). ) And the like. The most effective of these is HEDTA.

In the cyan-based displacement gold plating solution or the displacement gold plating method of the present invention, a pH buffering agent can be further added. By adding a pH buffer, the range of pH 2.0 to 4.4 during the displacement gold plating operation can be maintained more stably, and the range of pH is stable between 2.0 to 4.4. By maintaining it for a long time, the corrosion of the palladium metal is promoted even by the ENEPIG method, and as a result, the corrosion of the base nickel metal can be suppressed.

Specific pH buffering agents include at least one of phosphoric acid, glycine, cyanoacetic acid, malonic acid, phthalic acid, citric acid, formic acid, glycolic acid, lactic acid, succinic acid, acetic acid, butyric acid, propionic acid, and salts thereof. There are more than one species. Of these, acetic acid, acetate, formic acid or formate is preferable, and the most effective one is acetic acid or acetate. It is preferable that the total amount of at least one selected from these groups is 0.1 to 100 g/L.

In the cyan-based displacement gold plating solution or the displacement gold plating method of the present invention, a corrosion inhibitor can be further added. The reason for adding the corrosion inhibitor is to further suppress the corrosion of the base copper metal or nickel metal during the displacement gold plating operation, similarly to the pH buffering agent. As the corrosion inhibitor, polyethylene glycol (average molecular weight 200 to 20000) is preferable. This is because the pH of 2.0 to 4.4 during the displacement gold plating operation is stably maintained. It was also found that amide sulfate or amide sulfate also exhibits the same effect. These compounds may be preferably used alone or in a total amount of 0.1 to 100 g/L.

In the cyan substitutional gold plating solution or the substitutional gold plating method of the present invention, an inorganic acid such as dilute sulfuric acid, an organic acid such as acetic acid, or an alkali hydroxide can be used to adjust the pH of the plating solution. Further, as the liquid temperature becomes higher, the gold deposition rate becomes faster, but the evaporation loss becomes more severe. Generally, the plating operation is performed in the range of 60 to 90°C.

According to the cyan-based displacement gold plating solution of the present invention, the deposition rate of gold metal becomes faster than ever, and moreover, a deposited film with less variation in film thickness due to the difference in the area of the bonding pad of the mounting substrate is formed. effective. Further, the present invention has an effect of forming a deposited film of displacement gold plating which causes less corrosion of the lower nickel intermediate layer in the laminated structure of the palladium intermediate layer/nickel intermediate layer.

Further, according to the cyan displacement gold plating method of the present invention, it is possible to suppress the corrosion of the intermediate layer and to form a displacement gold plating layer having a high deposition rate of displacement gold plating. Furthermore, according to the cyan-based displacement gold plating method of the present invention, there is an effect of reducing the film thickness variation due to the difference in the area of the bonding pad of the mounting substrate. In particular, according to the cyan displacement gold plating method of the present invention, when the gold surface layer is formed on the laminated structure of the palladium intermediate layer/nickel intermediate layer, it is effective in reducing the corrosion of the nickel intermediate layer as the lower layer.

FIG. 1 is a scanning electron micrograph of the surface of a palladium plating film according to an example of the present invention. FIG. 2 is a scanning electron micrograph of the surface of the palladium plating film according to the conventional example.

Hereinafter, embodiments of the cyan-based displacement gold plating solution and the displacement gold plating method according to the present invention will be described in more detail. The object to be plated of the present invention is not particularly limited as in the conventional displacement gold plating method. That is, it can be used on the surface of various metal materials, or a metal film of copper or the like (including electrically independent circuits) formed on an insulating substrate such as plastic or ceramic.

Prior to performing the displacement gold plating of the present invention, a well-known pretreatment step can be performed as in the conventional displacement gold plating method. For example, degreasing of the substrate, soft etching, sulfuric acid activity, addition of a palladium catalyst, etc. can be performed. In addition, if necessary, various metal materials that have been subjected to pretreatment, or an intermediate layer such as a nickel plating film or palladium plating film on the surface of the bonding pad such as copper formed on an insulating base material such as plastic or ceramic Can be formed. In the displacement gold plating method of the present invention, the gold surface layer can be formed on the intermediate layer made of copper, nickel or palladium.

The conditions for cyan-based displacement gold plating according to the present invention are not so different from the conventional conditions. The liquid temperature is preferably as high as possible from the viewpoint of improving the plating rate. It is preferably 80° C. or higher, and more preferably 85° C. or higher. The plating time is generally about 5 to 30 minutes. Further, in the usual ENEPIG method, the nickel intermediate layer is formed with a film thickness of 0.08 to 8 μm, and the palladium intermediate layer is formed with a film thickness of 0.03 to 0.3 μm. The preferable thickness of the displacement gold plating film is 0.03 to 0.3 μm.

After forming a gold film with the displacement gold plating solution of the present invention, heat treatment can be performed. The heat treatment can be performed in a post-treatment step of a known displacement gold plating method. For example, a batch heat treatment furnace, an open tunnel furnace, an autoclave furnace whose atmosphere can be controlled, or the like can be used. When the heat treatment is performed, a swelling-free displacement gold plating film can be stably obtained.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but it goes without saying that the present invention is not limited to the following Examples.
(Examples 1 to 15)
The test piece was performed as follows using a mounting substrate (30 mm×20 mm×thickness 1 mm) made of epoxy resin reinforced with glass fiber. In addition, on the surface of this mounting board, an independent copper pad (0.4 mm × 0.4 mm□, 0.8 mm × 0.8 mm□, 3.0 mm × 3.0 mm□) and a copper circuit (100 μm width) were formed. Connected copper pads (0.4 mm×0.4 mm□, 0.8 mm×0.8 mm□, 3.0 mm×3.0 mm□) are formed.

Acid degreasing (manufactured by Japan Electroplating Engineering Co., Ltd. (hereinafter abbreviated as "EEJA"), Eatrex 15, 45°C, 5 minutes), soft etching (Mitsubishi Gas Chemical Co., Ltd., NPE-300, 25°C, 1 minute), sulfuric acid activity (10% sulfuric acid, 25° C., 1 minute), palladium catalyst application (EEJA, Lectroless AC2, 25° C., 1 minute), electroless nickel plating (EEJA, Lectroless NP7600, 85° C., 27) Min, Ni 5 μm), and electroless palladium plating (EEJA, Lectroless Pd2000S, 52° C., 10 minutes, Pd 0.1 μm).

Next, substitutional gold plating was performed on the laminated structure of the palladium intermediate layer/nickel intermediate layer of this mounting substrate under the composition and conditions of the cyan type substitutional gold plating solutions of Examples 1 to 15 shown in Table 1.

The film thicknesses of the displacement gold plating films of Examples 1 to 15 formed on these six types of copper pads were measured by a fluorescent X-ray film thickness meter (SFT-9550 manufactured by SII Nanotechnology Inc.). From the measurement results, the average film thickness and film thickness variation of Examples 1 to 15 were calculated. Results of the calculated average film thickness and film thickness variation are shown in Examples 1 to 15 of Table 2.
Regarding "liquid stability", the substitution gold plating solution after the completion of the substitution gold plating was visually observed, and the gold precipitate and those without gold deposition on the inner wall of the container were circled (○) to indicate the gold precipitation. What was observed to deposit gold on the inner wall of the container was evaluated by a cross mark (x).

Next, the displacement gold-plated mounting boards of Examples 1 to 15 were stripped off only the displacement gold-plated layer using a gold stripping agent (made by EEJA, Gold Stripper Concentrate N, 25° C., 30 seconds). Then, using a scanning electron microscope (Hitachi High-Technologies Corporation, S-4700, 20 kV, ×10000), the corrosion conditions of the underlying metals (palladium intermediate layer/nickel intermediate layer laminated structure) of Examples 1 to 15 were used. It was confirmed.

1 and 2 are shown as a specific example.
In FIG. 1, only the displacement gold plating layer of Example 2 was peeled off to expose the surface of the base metal. Fine grain boundaries (0.5 μm×0.5 μm) formed on the palladium plating film and large quadrangular grain boundaries (5 μm×5 μm) formed on the lower nickel plating film are observed. Since the displacement gold plating proceeds due to the potential difference between the gold ions in the solution and the base metal that is less base than gold, these grain boundary patterns show traces of corrosion of the base metal by the substitution reaction. Since a fine corrosion pattern is also observed in the palladium plating film, it is suggested that the displacement gold plating solution of Example 2 replaced the palladium plating film relatively uniformly over the entire surface. Corrosion of the nickel plating film is reduced as much as the palladium plating film is corroded. Therefore, the large quadrangular grain boundaries formed in the nickel plating film are larger than those obtained from the conventional substitutional gold plating solutions. , Was unclear and thin.

FIG. 2 shows the surface of the underlying metal exposed by peeling off only the displacement gold plating layer of Comparative Example 2. Only large quadrangular grain boundaries (5 μm×5 μm) formed in the nickel plating film are observed. Fine grain boundaries as shown in FIG. 1 are not observed in the palladium plating film, which suggests that the substitution reaction between the gold ion in the liquid and the palladium plating film does not occur. When the palladium plating film was pierced with tweezers, the palladium plating film was broken and the lower nickel plating film was exposed. In the exposed nickel plating film, large quadrangular grain boundaries were severely corroded, and large cavities were formed. That is, it is suggested that in the displacement gold plating solution of Comparative Example 2, the displacement reaction occurred only in a part of the nickel plating film, that is, a large grain boundary of a substantially square shape.

In the displacement gold plating films of Examples 1 to 15, no remarkable nickel preferential corrosion in which the nickel intermediate layer was preferentially corroded over the palladium intermediate layer was not observed. This is indicated by a circle (◯) in Table 2 as “Ni corrosiveness”. In Table 4, which will be described later, cross marks (x) indicate that nickel preferential corrosion was observed.

As is clear from Table 2, according to the cyan-based displacement gold plating solutions of Examples 1 to 15 of the present invention, the deposition rate is high, and the film thickness variation occurs even if there is a difference in the bonding pad area of the mounting substrate. It can be seen that a deposited film having a small value was obtained. Further, according to the cyan-based displacement gold plating solutions of Examples 1 to 15 of the present invention, a displacement gold plating deposition film in which corrosion of the lower nickel intermediate layer in the laminated structure of the palladium intermediate layer/nickel intermediate layer is extremely small is formed. I can see that I was able to do it.

(Comparative Examples 1-5)
In the same manner as in Example 1, the displacement gold plating of Comparative Examples 1 to 5 was performed under the liquid composition and conditions shown in Table 3. That is, after performing the pretreatment using the same test piece as in Example 1 to form a laminated structure of the palladium intermediate layer/nickel intermediate layer, the cyan-based displacement gold plating solutions of Comparative Examples 1 to 5 shown in Table 3 were obtained. Substitution gold plating was performed according to the composition and conditions.

Here, the displacement gold plating solution of Comparative Example 1 does not contain a thallium compound. Further, the substituted gold plating solution of Comparative Example 2 does not contain an aminocarboxylic acid type chelating agent having a hydroxyl group. Further, the substituted gold plating solution of Comparative Example 3 uses ascorbic acid as a reducing agent instead of the aminocarboxylic acid type chelating agent having a hydroxyl group. The pH of the displacement gold plating solution of Comparative Example 4 is below the lower limit of 2.0. Further, the displacement gold plating solution of Comparative Example 5 has a pH higher than the upper limit value of 4.4.

Then, in the same manner as in Example 1, the average film thickness and the film thickness variation of the displacement gold plating of Comparative Examples 1 to 5 were calculated. The results are shown in Table 4. At the same time, "liquid stability" and "Ni corrosiveness" were measured, and as a result, good ones are indicated by circles (◯) and defective ones are indicated by crosses (x).

As is clear from Table 4, in the cyan-based displacement gold plating solutions of Comparative Examples 1 to 5, when the plating solution is not stable, the deposition rate is slow, and there is a difference in the area of the bonding pad of the mounting board, the film thickness varies. Is large, or the lower nickel intermediate layer in the laminated structure of the palladium intermediate layer/nickel intermediate layer has large corrosion. That is, in the displacement gold plating of Comparative Example 1 containing no thallium compound, the average film thickness was 0.06 μm, which was very thin even when the immersion time was 60 minutes. Moreover, since the film thickness has a large variation of 22.6 and an extremely thin film exists, it is not suitable for a mounting substrate/bonding pad.

Further, in the displacement gold plating solution of Comparative Example 2 containing no aminocarboxylic acid type chelating agent having a hydroxyl group, gold metal was deposited on the wall surface of the container after the plating was completed, and the container was discolored. Further, in the laminated structure of the palladium intermediate layer/nickel intermediate layer, the lower nickel intermediate layer was severely corroded, and the palladium intermediate layer on the independent copper pad was partly peeled off.

Further, the substitutional gold plating solution of Comparative Example 3 containing ascorbic acid had remarkably poor liquid stability.

Further, the substitution gold plating solution of Comparative Example 4 having a pH lower than the lower limit also has poor solution stability. Furthermore, the corrosion of the lower nickel intermediate layer was expanded due to the addition of no polyethylene glycol.

Further, in the displacement gold plating solution of Comparative Example 5 having a pH exceeding the upper limit value, the variation in film thickness was extremely large. Further, in the laminated structure of the palladium intermediate layer/nickel intermediate layer, the lower nickel intermediate layer was severely corroded, and the palladium intermediate layer on the independent copper pad was partly peeled off.

As is clear from the above Examples and Comparative Examples, when the cyan-based displacement gold plating solution of the present invention is used, there is no gold precipitate after the completion of plating and gold deposition on the inner wall of the container, and the plating solution is stable. Further, the deposition rate of gold metal is high, and it is possible to reduce the film thickness variation due to the difference in the area of the bonding pad of the mounting substrate in the ENEPIG method or the like. In particular, according to the cyan displacement gold plating method of the present invention, the gold surface layer can be formed on the laminated structure of the palladium intermediate layer/nickel intermediate layer without violently corroding the lower nickel intermediate layer.

The cyan-based displacement gold plating solution produced by the production method of the present invention can perform displacement gold plating such as spot plating or whole surface plating on an object to be plated such as metal, plastic and ceramic. As a result, it can be used for applications such as electrodes, electric/electronic members, and semiconductor members.

Claims (8)

A substituted gold plating solution containing a cyanide gold compound and a thallium compound, having a pH of 2.0 to 4.4 and containing an aminocarboxylic acid type chelating agent having a hydroxyl group. Plating solution. 2. The substituted gold according to claim 1, wherein the thallium compound is 0.1 to 100 mg/L as thallium ion, and the aminocarboxylic acid type chelating agent having a hydroxyl group is 0.1 to 100 g/L. Plating solution. The displacement gold plating solution according to claim 1 or 2, wherein the aminocarboxylic acid-based chelating agent having a hydroxyl group is HEDTA. The displacement gold plating solution according to claim 1, wherein the pH is 2.2 to 4.0. The corrosion inhibitor further comprises at least one or more of polyethylene glycol (average molecular weight 200 to 20000), amide sulfate or amide sulfate, and the concentration thereof is 0.1 to 100 g/L, respectively. The displacement gold plating solution according to any one of 1 to 4. As a pH buffer, at least one or more of phosphoric acid, glycine, cyanoacetic acid, malonic acid, phthalic acid, citric acid, formic acid, glycolic acid, lactic acid, succinic acid, acetic acid, butyric acid, propionic acid, and salts thereof is further added. The displacement gold plating solution according to any one of claims 1 to 5, comprising: Using the displacement gold plating solution according to any one of claims 1 to 6, a gold surface layer is formed on an intermediate layer of any of copper, nickel, and palladium, or on a laminated structure composed of these intermediate layers. A displacement gold plating method characterized by the above. 8. The displacement gold plating method according to claim 7, wherein the laminated structure is a laminated structure of an intermediate layer in which an electroless nickel plating film is formed on copper metal, and an electroless palladium plating film is further formed.