TWI586833B - Electroless platinum plating solution - Google Patents

Description

Electroless platinum plating solution

This invention relates to an electroless platinum plating bath.

Previously, electroless platinum plating solutions were known to contain dinitrodiamine platinum or dinitrotetramine platinum as a platinum salt, ethylenediamine or ammonia as a crosslinking agent, hydrazine monohydrate or hydroxide as a reducing agent. Sodium borate (for example, refer to Patent Documents 1 to 4).

Dinitrodiamine platinum and dinitrotetramine platinum are poorly soluble in water. Therefore, by adding ethylenediamine or ammonia as a crosslinking agent to the electroless platinum plating solution, a platinum complex formed by copolymerizing ethylenediamine or ammonia in platinum is formed and dissolved in water.

Usually, by adding a reducing agent to the electroless platinum plating solution, the metal ion or the metal complex can be reduced to precipitate the metal on the surface of the plating substrate. Since the above-mentioned platinum complex compound in which ethylenediamine or ammonia is coordinated in platinum is not easily reduced, as a reducing agent, a ruthenium monohydrate or a hydroxide having a strong reduction effect is added to the electroless platinum plating solution. Sodium borate. However, since the reducing power of cerium monohydrate and sodium borohydride is too strong, there is a problem that platinum is precipitated in the plating solution due to the reduction of the platinum complex or hydrogen is generated by the reduction reaction.

Therefore, in order to solve the above problem, a heavy metal ion or a thiol compound such as lead or bismuth is added to the above electroless platinum plating solution as a stability. The agent enhances the stability of the solution.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. Hei 5-222543

[Patent Document 2] Japanese Patent Laid-Open No. Hei 9-287078

[Patent Document 3] Japanese International Publication No. 2014/162935

[Patent Document 4] Japanese International Publication No. 2013/094544

However, since the above heavy metal ions or thiol compounds require concentration management, the operation of the plating solution becomes complicated. Further, the above heavy metal ions are harmful to the human body, and the eutectoid precipitation with the precipitated platinum film causes the film to have a low purity. Further, since ammonia gas is generated from the plating solution with use, the working environment is lowered due to the generation of ammonia gas.

Therefore, an object of the present invention is to provide an electroless platinum plating solution which can provide ammonia stability without using heavy metal ions and a thiol compound.

As a result of intensive studies, the inventors of the present invention found that the prior electroless platinum plating solution caused the stability of the solution to be low for the following reasons. That is, the prior electroless platinum plating solution forms a platinum complex by using ethylenediamine or ammonia as a linking agent and coordinating in platinum ions. Because ethylenediamine or ammonia and platinum ions strongly form a complex, in order to return the platinum complex Originally, it is precipitated on the surface of the plated substrate, and a reducing agent having a strong reducing action is required. As a result, the electroless platinum plating solution is reduced and decomposed due to the reducing power of the reducing agent having a strong reducing action.

Therefore, the inventors of the present invention have achieved the above problems by using the following electroless platinum plating solution.

The electroless platinum plating solution of the present invention contains a water-soluble platinum compound and one or more reducing agents selected from the group consisting of formalin, glucose, formic acid, and formate.

In the electroless platinum plating solution of the present invention, the water-soluble platinum compound is selected from the group consisting of platinous chloride (II), platinous chloride (II) acid, and platinic chloride. (II) acid salt, platinic chloride (IV), white gold (IV) chloride, white gold (IV) chloride, hexahydroxyplatinum (IV) acid, hexahydroxyplatinum (IV) acid One or more water-soluble platinum compounds of a group consisting of a salt and a dichlorotetramine platinum (II) are preferred.

In the electroless platinum plating solution of the present invention, it is preferred to contain an organic acid as a crosslinking agent. The organic acid is preferably one or more compounds selected from the group consisting of aliphatic hydroxy acids having a molecular weight of 90 to 500.

In the electroless platinum plating solution of the present invention, since a water-soluble platinum compound is used, the platinum compound forms a platinum complex even if it does not contain a complexing agent such as ethylenediamine or ammonia which strongly forms a complex with platinum ions. And easy to dissolve in water. The platinum complex formed from the water-soluble platinum compound is easily reduced compared to the platinum complex formed by the ethylene diamine or ammonia previously formed in the electroless platinum plating solution. Therefore, as a reducing agent, even It is also possible to reduce the form of the platinum complex by the reduction of the formalin, glucose, and formate having a weak reduction effect.

Further, compared with the hydrazine monohydrate or sodium borohydride, the reducing action of either of the carbaryl, glucose, formic acid or formate as a reducing agent is weak. Therefore, the electroless platinum plating solution is not decomposed by the reducing agent. Therefore, compared with the prior electroless platinum plating solution, the electroless platinum plating solution can obtain excellent solution stability even without using heavy metal ions or thiol compounds. Further, it is also preferable that the amount of hydrogen generated by any of the formalin, glucose, formic acid or formate is less than that of the hydrazine monohydrate or sodium borohydride which has been used as a reducing agent.

Further, since the electroless platinum plating solution does not contain a compound which generates ammonia gas such as ethylenediamine or ammonia, it is possible to prevent generation of ammonia gas.

Fig. 1 is a graph showing the deposition characteristics of the electroless platinum plating solution of the present embodiment.

Fig. 2 is an SEM image of a platinum electroless film obtained by electroless plating treatment using the electroless platinum plating solution of Example 1.

Fig. 3 is an SEM image of a platinum electroless film obtained by electroless plating treatment using the electroless platinum plating solution of Example 2.

Hereinafter, an embodiment of the electroless platinum plating solution of the present invention will be described.

[1. Electroless Platinum Plating Solution]

The electroless platinum plating solution of the present invention contains a water-soluble platinum compound, And an aqueous solution of one or more reducing agents selected from the group consisting of formalin, glucose, formic acid, and formate.

The water-soluble platinum compound may, for example, be selected from the group consisting of white gold (II) chloride, white gold (II) chloride, white gold (II) chloride, white gold (IV) chloride, and white gold (IV) chloride. One or more water-soluble platinum compounds of the group consisting of acid, platinum chloride (IV) acid salt, hexahydroxy platinum (IV) acid, hexahydroxy platinum (IV) acid salt, and dichlorotetrachloroplatinum (II).

The electroless platinum plating solution preferably contains the water-soluble platinum compound in a range of 0.0005 mol/L or more and 0.05 mol/L or less, and is contained in a range of 0.0025 mol/L or more and 0.01 mol/L or less. good. When the content of the water-soluble platinum compound in the electroless platinum plating solution is less than 0.0005 mol/L, the formation of the platinum electroless film becomes difficult, or the plating speed is lowered, and when it is more than 0.05 mol/L, although the plating itself can Good progress, but economic downturn.

Platinum chloride (1V) is easily dissolved in the electroless platinum plating solution and forms a platinum complex represented by the following formula (1).

Dichlorotetramine platinum (II) is easily dissolved in the electroless platinum plating solution and forms a platinum complex represented by the following formula (2).

The platinum complex represented by the above formula (1) and formula (2) is any one of the platinum complexes in which the ethylenediamine formed in the prior electroless platinum plating solution is coordinated to platinum. Both are easier to restore. Therefore, the electroless platinum plating solution does not require the use of a reducing agent having a strong reducing action, and can be a state in which the platinum complex is reduced even if a reducing agent having a weak reducing action is used.

One or more kinds of reducing agents selected from the group consisting of formalin, glucose, formic acid, and formate are preferred because the reduction effect of either one is small, but the above formula (1) and formula (2) can be easily obtained. ) indicates the state of reduction of the platinum complex. Any of the above-mentioned reducing agents produced by the reduction reaction is mainly carbon dioxide and water, and has an advantage that the amount of hydrogen generation is small compared to hydrazine monohydrate or sodium borohydride. Further, the electroless platinum plating solution is adjusted to a range of pH 6.5 to 12.0 as described later, and the reducing agent can be used in the entire pH range.

The electroless platinum plating solution is preferably contained in an amount of 0.1 mol/L or more and 1.0 mol/L or less, and more preferably in a range of 0.2 mol/L or more and 0.8 mol/L or less. When the reducing agent having an electroless platinum plating solution content of less than 0.1/mol L is used, an unprecipitated portion may be generated. When the amount is less than 1.0 mol/L, the reduction action of the reducing agent may become excessive and the stability of the solution may be impaired.

Further, as formate, sodium formate, potassium formate, and A can be used. Ammonium acid. In terms of water solubility and ease of handling, sodium formate is preferred.

In the electroless platinum plating solution, since a water-soluble platinum compound is used, a binder for dissolving the platinum compound in water is not necessarily required. However, the electroless platinum plating solution can be made more stable by adding a miscending agent.

As the binder, it is preferred to use an organic acid. The organic acid is preferably one or more compounds selected from the group consisting of aliphatic hydroxy acids having a molecular weight of 90 to 500, and for example, lactic acid, malic acid, citric acid, trisodium citrate, ammonium citrate, and sweet can be used. One or more compounds of the group consisting of aminic acid, gluconic acid, malonic acid, oxalic acid, succinic acid, acetic acid, maleic acid, and fumaric acid. The complexing agent also functions as a pH buffering material.

The electroless platinum plating solution is preferably contained in an amount of 0.01 mol/L or more and 0.5 mol/L or less, and more preferably in a range of 0.02 mol/L or more and 0.3 mol/L or less. When the content of the above organic acid in the electroless platinum plating solution is less than 0.01 mol/L, there is no effect as a blocking agent. When the amount is more than 0.5 mol/L, although the plating itself can be performed well, the economy is low. .

The electroless platinum plating solution can be configured to further contain various components such as a surfactant, a stress relaxation agent, and a pH adjuster.

As the surfactant, in addition to polyethylene glycol, various conventional surfactants can be used. When polyethylene glycol is used as the surfactant, the surface of the plating substrate can be easily removed from the surface of the plating substrate by increasing the wettability of the surface of the plating substrate while generating bubbles on the surface of the plating substrate.

As a stress relieving agent, in addition to saccharin, 1.4-butynediol, benzenesulfonic acid, naphthalene disulfonic acid, it is also possible to use various previously known stresses. A demulcent.

As the pH adjuster, sodium hydroxide, sulfuric acid or the like can be used. The electroless platinum plating solution is preferably adjusted to a pH of 6.5 to 13.0 by adding a pH adjuster. When the pH of the electroless platinum plating solution is less than 6.5, the reduction action of the above reducing agent is lowered. Even if the pH of the electroless platinum plating solution is 13.0, the problem is not particularly problematic, but the workability such as pH adjustment or the plating bath management is preferably 13.0 or less.

Further, in the electroless platinum plating solution, the appearance of the obtained electroless gold plating film can be changed by adjusting the pH within the above range. For example, when the pH of the electroless platinum plating solution is 7, a gray platinum electroless film can be obtained, and when the pH is 12, a white platinum electroless film can be obtained.

According to the electroless platinum plating solution of the present embodiment, water solubility such as chloroplatinum (II) chloride, platinum (IV) chloride, hexahydroxyplatinum (IV) acid salt or dichlorotetramine platinum (II) is used. Since the platinum compound is not contained, the platinum compound can form a platinum complex and can be easily dissolved in water. Further, the platinum complex formed from the above water-soluble platinum compound is easily reduced as compared with the platinum complex formed by the ethylene diamine or ammonia previously formed in the electroless platinum plating solution. Therefore, even if a formalin, glucose, formic acid or formate having a weak reducing action is used as a reducing agent, it is possible to easily reduce the platinum complex.

Further, compared with the hydrazine monohydrate or sodium borohydride, the reducing action of either of the carbaryl, glucose, formic acid and formate as a reducing agent is weak. Therefore, the electroless platinum plating solution is not decomposed by the reducing agent. Thus, the electroless platinum plating system is compared to the prior electroless platinum plating solution. Even if heavy metal ions and thiol compounds are not used, excellent solution stability can be obtained. Further, it is also preferable that the amount of hydrogen generated by any of the formalin, glucose, formic acid, and formate is less than that of the hydrazine monohydrate or sodium borohydride which has been used as a reducing agent.

Further, since the electroless platinum plating solution does not contain a compound which generates ammonia gas such as ethylenediamine, it is possible to prevent generation of ammonia gas.

[2. Electroless plating treatment using electroless platinum plating solution]

Hereinafter, an example of a plating method of the electroless platinum plating solution of the present embodiment will be described. Here, the case where the plating substrate as the object to be plated is a plating substrate in which a copper film and a nickel film are formed on the surface of the insulating substrate in the following order by electroless plating treatment are used. The electroplated substrate is not limited by the above, and a previously known electroplated substrate can also be used.

First, a platinum film (platinum electrolytic film) is formed on the surface of the nickel film by electroplating the plated substrate.

Next, a plating substrate on which a platinum electrolytic film is formed on the surface of the nickel film is immersed in the electroless platinum plating solution of the present embodiment to perform an electroless plating treatment. The platinum alloy in the electroless platinum plating solution is reduced and precipitated on the surface of the platinum electrolytic film, and a platinum film (platinum electroless film) can be formed on the surface of the platinum electrolytic film.

By using the electroless plating treatment of the electroless platinum plating solution of the present embodiment, the deposition rate is 1 to 2 μm/hour, and an electroless platinum plating solution containing dinitrodiamine platinum or dinitrotetramine platinum can be obtained. The same rate of precipitation.

The use temperature of the electroless platinum plating solution is 40 to 90 ° C The range is good. When the temperature is less than 40 ° C, the plating speed is slow, and when it is more than 90 ° C, there is a case where the amount of water evaporation increases and the composition fluctuates.

The plating time using the electroless platinum plating solution depends on the thickness of the formed platinum electroless plating film. For example, when an electroless platinum plating solution containing 0.005 mol/L of dichlorotetramine platinum (II) (in terms of platinum in an amount of 1.0 g/L) is used as the water-soluble platinum compound, the thickness can be formed by setting the plating time to 30 minutes. 0.5 μm white gold electroless film.

The above reducing agent mainly produces carbon dioxide and water along with the reduction reaction. Since carbon dioxide and water are not accumulated in the electroless platinum plating solution, the electroless platinum plating solution does not deteriorate and can be used for a long period of time.

[3. Use of electroless platinum plating solution]

The electroless platinum plating solution of the present embodiment is suitable for an electronic component made of a metal or the like, an electrode material, a synthetic resin such as an ABS resin, a polyamide resin, or a polycarbonate resin, or an alumina or a zirconia. Electroplating of conductive ceramics and the like. In particular, it can be suitably used for an electrode of an oxygen sensor composed of a ceramic such as zirconia or the like, and various jewels.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by the following examples.

[Example 1]

[Manufacture of electroplated substrate]

First, a nickel film having a thickness of 3 μm was formed by electrolytic plating on a copper plate. Next, a platinum plating film (platinum electrolytic film) having a thickness of 0.1 μm was formed on the surface of the nickel film by electrolytic plating to produce a plating substrate.

[Preparation of electroless platinum plating solution]

In this embodiment, as a water-soluble platinum compound, dichlorotetramine platinum (II) is 0.005 mol/L (in terms of platinum, 1.0 g/L), sodium formate is used as a reducing agent, 0.5 mol/L, and an apple as a wrong agent. The acid 0.1 mol/L was dissolved in water to prepare an electroless platinum plating solution. Next, using sodium hydroxide and sulfuric acid as a pH adjuster, the pH (temperature: 25 ° C) of the electroless platinum plating solution was adjusted to 7.0.

[electroless plating treatment]

The obtained electroless platinum plating solution is heated to a temperature of 70 ° C, and an electroless plating treatment is performed by immersing the plating substrate on which the platinum electrolytic film is formed in the electroless platinum plating solution, thereby forming on the surface of the platinum electrolytic film. Platinum film (Platinum electroless film).

At this time, the thickness of the platinum electroless film was measured every 10 minutes until the immersion time reached 60 minutes. The results are shown in Figure 1. From the first graph, it was confirmed that the deposition rate in the electroless plating treatment was 1.0 μm/hr.

Further, by electroless plating treatment for 60 minutes, a platinum electroless film having a thickness of 0.5 μm was formed. It was confirmed by visual observation that the obtained platinum electroless film system was gray. Further, when the surface of the obtained electroless gold plating film was observed at a magnification of 30,000 times using a scanning electron microscope (SEM), as shown in Fig. 2, the platinum particles had a large particle size and a surface morphology having irregularities.

Next, the temperature of the electroless platinum plating solution was changed to 50 ° C, 60 ° C, 70 ° C, and 80 ° C, and the plating substrate on which the platinum electrolytic film was formed was immersed in the electroless platinum plating solution for 2 hours. Electrolytic plating treatment. At this time, it was judged whether or not the electroless platinum plating solution was decomposed by observing whether or not platinum precipitates were generated in the electroless platinum plating solution. The results are shown in Table 1. The × mark means that the electroless platinum plating solution is decomposed within 1 hour, △ The symbol means decomposition within 2 hours, and the ○ symbol means that it is not completely decomposed even after 2 hours.

Next, the electroless platinum plating solution held at a temperature of 50 to 80 ° C for 2 hours was naturally cooled, and then heated again to the same temperature every other day, and the plated substrate was immersed for 2 hours to carry out an electroless plating treatment. The electroless platinum plating solution is heated to any temperature, and can be subjected to electroless plating treatment normally. From this situation, it is clear that the electroless platinum plating solution can be continuously used.

[Embodiment 2]

In the present example, the electroless platinum plating solution was prepared in the same manner as in Example 1 except that the pH (temperature: 25 ° C) was adjusted to 11.0.

The obtained electroless platinum plating solution was heated to a temperature of 70 ° C, and the electroplated substrate on which the platinum electrolytic film was formed was immersed in the electroless platinum plating solution for 60 minutes to perform electroless plating treatment, and in the platinum electrolytic film. A white gold electroless film having a thickness of 0.5 μm was formed on the surface. The obtained platinum electroless film was visually confirmed to have a white gloss appearance. Further, when the surface of the obtained electroless gold plating film was observed at a magnification of 30,000 times using an SEM. As shown in Fig. 3, the platinum particles are small in particle size and have a smooth surface morphology.

Next, using the obtained electroless platinum plating solution, the same procedure as in Example 1 was carried out to determine whether or not the electroless platinum plating solution was decomposed. The results are shown in Table 1.

Next, the electroless platinum plating solution after the temperature was kept at 50 to 80 ° C for 2 hours was carried out in exactly the same manner as in Example 1, and electroless plating treatment was performed every other day. The electroless platinum plating solution is heated to any temperature, and can be subjected to electroless plating treatment normally. From this situation, clearly understand that there is no Electrolytic platinum plating solution can be used continuously.

[Comparative Example 1]

In this comparative example, an electroless platinum plating solution was prepared in the same manner as in Example 2 except that 0.5 mol/L of hydrazine monohydrate was used instead of sodium formate as a reducing agent, and then the pH (temperature: 25 ° C) was adjusted. Become 11.0. Next, using the obtained electroless platinum plating solution, the same procedure as in Example 1 was carried out, and it was judged whether or not the electroless platinum plating solution was decomposed. The results are shown in Table 1.

[Comparative Example 2]

In this comparative example, an electroless platinum plating solution was prepared in the same manner as in Example 2 except that sodium borohydride 0.5 mol/L was used instead of sodium formate as a reducing agent, and then the pH (temperature: 25 ° C) was adjusted. Become 11.0. Next, using the obtained electroless platinum plating solution, it was carried out in exactly the same manner as in Example 1 to determine whether or not the electroless platinum plating solution was decomposed. The results are shown in Table 1.

[Comparative Example 3]

In this comparative example, except that dinitrodiammine platinum (II) 0.005 mol/L (in terms of platinum, 1.0 g/L) was used instead of dichlorotetramine platinum (II) as a platinum compound, it was completely identical to Comparative Example 1. The electroless platinum plating solution was prepared in the same manner, and then the pH (temperature: 25 ° C) was adjusted to 11.0. Next, using the obtained electroless platinum plating solution, it was carried out in exactly the same manner as in Example 1 to determine whether or not the electroless platinum plating solution was decomposed. The results are shown in Table 1.

[Comparative Example 4]

In this comparative example, except that dinitrodiammine platinum (II) 0.005 mol/L (in terms of platinum, 1.0 g/L) was used instead of dichlorotetramine platinum (II) as a platinum compound, it was completely identical to Comparative Example 2. Equivalent electroless white The gold plating solution was then adjusted to a pH (temperature 25 ° C) of 11.0. Next, using the obtained electroless platinum plating solution, it was carried out in exactly the same manner as in Example 1 to determine whether or not the electroless platinum plating solution was decomposed. The results are shown in Table 1.

As shown in Table 1, it is clear that the platinum compound is dichlorotetramine platinum (II), the reducing agent is sodium formate, and the electroless platinum plating solution of Example 1 and Example 2 is either at a temperature of 50 to 80 ° C. The range does not cause decomposition for 2 hours and has excellent solution stability. On the other hand, it is clear that any of the electroless platinum plating solutions of Comparative Example 1 to Comparative Example 4 in which the reducing agent is hydrazine monohydrate or sodium borohydride is decomposed within 1 hour at a temperature of 70 to 80 ° C, even if In the temperature range of 50 to 60 ° C, decomposition occurs within 2 hours and the solution stability is poor.

Industrial use possibility

As described above, since the electroless platinum plating solution of the present invention has excellent solution stability, it can withstand long-term use. Further, since the electroless platinum plating solution does not contain a compound which generates ammonia gas such as ethylenediamine or ammonia, it is possible to prevent generation of ammonia gas. Therefore, it is possible to prevent the odor caused by the generation of ammonia gas from causing the working environment to be lowered. Moreover, since the electroless platinum plating solution is not used, such as ethylenediamine, ammonia, etc., strongly forms a complex with platinum ions. Since the complexing agent is used, it is possible to use a reducing agent having a weak reducing action such as formalin, glucose, formic acid or formate. Further, these reducing agents can reduce the amount of hydrogen gas generated compared to hydrazine monohydrate or sodium borohydride.

Further, the electroless platinum plating solution of the present embodiment is suitable for electroplating of electronic parts, electrode materials, various synthetic resins, ceramics, and the like which are made of metal or the like. In particular, it can be suitably used for an electrode of an oxygen sensor composed of a ceramic such as zirconia or the like, and various jewels.

Claims (4)

An electroless platinum plating solution, which is an electroless platinum plating solution containing a water-soluble platinum compound and a reducing agent, characterized in that the water-soluble platinum compound is selected from the group consisting of white gold (II) chloride and white gold (II) chloride. One or more groups consisting of acid, platinum chloride (II) acid salt, hexahydroxy platinum (IV) acid, hexahydroxy platinum (IV) acid salt, and dichlorotetrachloroplatinum (II); and the aforementioned reducing agent system One or more selected from the group consisting of glucose, formic acid, and formate are selected. The electroless platinum plating solution according to claim 1, wherein the water-soluble platinum compound is contained in a range of 0.0005 mol/L or more and 0.05 mol/L or less, and is 0.1 mol/L or more and 1.0 mol/ The range below L contains the aforementioned reducing agent. An electroless platinum plating solution as described in claim 1 or 2, which contains an organic acid as a binder. The electroless platinum plating solution according to claim 3, wherein the organic acid is one or more compounds selected from the group consisting of aliphatic hydroxy acids having a molecular weight of 90 to 500.