JP6544792B2 - Method of selecting a stabilizer for electroless platinum plating solution and electroless platinum plating solution - Google Patents

Description

  The present application relates to a method of selecting a stabilizer for an electroless platinum plating solution and an electroless platinum plating solution.

  Conventionally, platinum plating has excellent corrosion resistance, exhibits good electrical conductivity, and has a beautiful metallic luster, so it is widely used for terminal plating of wiring boards, surface coating of catalysts, surface modification of decorative articles, etc. It has And in performing this platinum plating, the electroless platinum plating method has been used.

  In this electroless platinum plating method, a platinum film is formed on the surface of an object to be plated by utilizing a chemical reduction reaction between a platinum salt and a reducing agent. Hydrazine has been used as a reducing agent to be contained in the electroless platinum plating solution at this time, but hydrazine is said to affect the environment and the human body, and there is a problem that the working environment and waste water treatment load become large.

  Therefore, in order to solve this problem, an electroless platinum plating solution using sodium borohydride as a reducing agent for the electroless platinum plating solution as disclosed in Patent Document 1 and Non-patent Document 1 is studied. ing. And, in such an electroless platinum plating solution, a sulfur compound is used as a stabilizer because the solution lacks long-term stability.

Unexamined-Japanese-Patent No. 9-287078

J. Valsiuniene, J. Vinkevicius and A. Yu. Prokopchik; Liet. TSR Mokslu Akad. Darb. , Ser. B, 5, 25 (1976).

  However, the solution life of electroless platinum plating solutions using sodium borohydride known in the market is said to be still short. In addition, the sulfur compound contained as a stabilizer in the electroless platinum plating solution functions to suppress the oxidation reaction of the reducing agent on the platinum surface, and the deposition rate of platinum on the surface of the object to be plated is reduced. There is.

  As understood from the above, in the market, an electroless platinum plating solution using sodium borohydride having a long solution life and a high deposition rate of platinum on the surface of the object to be plated has been desired.

  Therefore, the inventors of the present application are keenly carrying out research on an optimum sulfur compound to be used as a stabilizer for the electroless platinum plating solution, and the polarization of the electroless platinum plating solution using the sulfur compound as a stabilizer. Focusing on the characteristics, the following invention was conceived.

<Method of selecting a stabilizer for electroless platinum plating solution>
The method of selecting a stabilizer for an electroless platinum plating solution according to the present application is a method of selecting a stabilizer used for an electroless platinum plating solution containing a platinum salt, a reducing agent and a stabilizer, and is stabilized by the following procedure It is characterized by judging the propriety of the sulfur compound as an agent.

Preparation of selected test solution: A basic mixed aqueous solution with a sodium hydroxide concentration of 0.25 mol / dm ³ and a sodium borohydride concentration of 0.1 mol / dm ³ is used, and the sulfur compound to be selected here is 0.005 × 10 ⁻³ It was added at a concentration of ^{mol / dm 3 ~0.050 × 10 -3} mol / dm 3, the solution pH is 13.5, the preparation of a selected test solution having a temperature of 25 ° C..
Polarization potential measurement: A platinum disk as a working electrode, a platinum wire as an auxiliary electrode, and a silver-silver chloride electrode as a reference electrode, which are disposed in the selected test solution to make the potential of the working electrode relative to the reference electrode a natural potential From the potential to 0.002 V / sec. The potential scan is performed at the speed of, the current between the working electrode and the auxiliary electrode at a predetermined measured potential is measured, and a polarization curve (potential-current curve) is obtained.
Judgment of suitability as a stabilizer: In the polarization curve of the selected test solution, it has a polarization characteristic in which the potential at 0.25 A / dm ² falls within the range of −0.7 V to −0.8 V vs Ag / AgCl , and When the electroless platinum plating solution is prepared using the sulfur compound, it is judged that the electroless plating solution can use a sulfur compound which can be stored for 4 weeks or more without deterioration of the solution , as the electroless platinum plating solution.

<Electroless platinum plating solution>
The electroless platinum plating solution according to the present application is an electroless platinum plating solution containing a platinum salt, a reducing agent and a stabilizer, wherein the reducing agent is sodium borohydride, and the stabilizer is the above-mentioned. The sulfur compounds selected by the method of selecting a stabilizer for electroless platinum plating solution of any of thioproine, thiourea and thiosulfuric acid are 0.005 × 10 ⁻³ mol / dm ^{3 to} 0.050 × 10 ⁻³ It is characterized by including polarization characteristics in the concentration range of mol / dm ^{3 and having a} potential at 0.25 A / dm ² in the range of −0.7 V to −0.8 V vs Ag / AgCl in the polarization curve. Do.

  Method of Selecting Stabilizer for Electroless Platinum Plating Solution: Using the method of selecting a stabilizer for electroless platinum plating solution according to the present application, a sulfur compound which functions as a stabilizer used in the electroless platinum plating solution is selected. And, the electroless platinum plating solution using this sulfur compound as a stabilizer has a long solution life and a high deposition rate of platinum on the surface of the object to be plated.

It is the figure which showed the polarization curve for selecting the stabilizer for electroless platinum plating solutions.

  Hereinafter, although an embodiment of the invention is described, evaluation results of examples and comparative examples described later may be used for convenience of explanation.

<Form of selection method of stabilizer for electroless platinum plating solution>
The method of selecting a stabilizer for an electroless platinum plating solution according to the present application is a method of selecting a stabilizer used in an electroless platinum plating solution containing a platinum salt, a reducing agent and a stabilizer. Hereinafter, description will be made according to the procedure for selecting.

Preparation of Selection Test Solution: The stabilizer for an electroless platinum plating solution as referred to herein is a sulfur compound, and the polarization potential measurement described later is used for selection. Therefore, it is necessary to prepare a solution in which the sulfur compound is contained in a predetermined solution. At this time, a basic mixed aqueous solution containing sodium hydroxide at a concentration of 0.25 mol / dm ³ and sodium borohydride at a concentration of 0.1 mol / dm ³ with respect to water is used, and the sulfur compound selected here is 0.005 × 10. was added such that the ^-3 mol ^/ dm 3 ^~0.050 concentration of × ¹⁰ -3 mol / dm ^3, the solution pH is 13.5, the preparation of a selected test solution having a temperature of 25 ° C.. Here, when the concentration of the sulfur compound is less than 0.005 × 10 ⁻³ mol / dm ³ , the amount of the sulfur compound is too small, and the effect of the sulfur compound as a stabilizer can not be expected. On the other hand, there is no particular problem if the concentration of the sulfur compound exceeds 0.050 × 10 ⁻³ mol / dm ³ , but there is no request for the addition of a stabilizer at a concentration higher than this.

Polarization potential measurement: A platinum disk as a working electrode, a platinum wire as an auxiliary electrode, and a silver-silver chloride electrode as a reference electrode, which are disposed in the selected test solution to make the potential of the working electrode relative to the reference electrode a natural potential From the potential to 0.002 V / sec. The potential scan is performed at the speed of, and the current between the working electrode and the auxiliary electrode at a predetermined measurement potential is measured. The polarization curve (potential-current curve) shown in FIG. 1 is obtained.

Judgment of suitability as a stabilizer: In the polarization curve of the selected test solution, the potential at 0.25 A / dm ² (corresponding to about 180 μA in the current axis of FIG. 1) is −0.7 V to −0.8 V vs Ag / It is judged that a sulfur compound having polarization characteristics falling within the range of AgCl can be used for the electroless platinum plating solution. It is possible to enter this range by adjusting the concentration of the additive added to the electroless platinum plating solution. However, simply putting in this range and whether or not the added component is stably present in the electroless platinum plating solution is another problem. This point will be described later.

<Electroless platinum plating solution>
The electroless platinum plating solution according to the present application is an electroless platinum plating solution containing a platinum salt, a reducing agent and a stabilizer, wherein the reducing agent is sodium borohydride, and the above-mentioned as the stabilizer. A sulfur compound selected by the method of selecting a stabilizer for an electroless platinum plating solution is contained in a range of 0.015 × 10 ⁻³ mol / dm ^{3 to} 0.050 × 10 ⁻³ mol / dm ³ concentration. I assume. The electroless platinum plating solution according to the present application is premised on using “sodium borohydride” as the reducing agent.

In the electroless platinum plating solution according to the present application, as a platinum salt, platinum chloride (IV) acid, platinum chloride (II) acid, platinum bromide (IV) acid, platinum bromide (II) acid, hexahydrooxoplatinum (platinum chloride (II) IV) Acid, dinitrodiammine platinum (II) and alkali metal salts thereof (alkali metal salts such as potassium and sodium) or ammonium salts can be used. However, in view of the stability as a solution, it is preferable to use ammonium chloroplatinate (IV). And, in the electroless platinum plating solution according to the present application, it is preferable to contain a platinum salt in the range of 0.001 mol / dm ^{3 to} 0.050 mol / dm ³ concentration. When the concentration of the platinum salt is less than 0.001 mol / dm ³ , the rate of formation of the platinum plating film is low, which makes industrial use difficult. When the concentration of the platinum salt exceeds 0.020 mol / dm ³ , the surface of the platinum plating film to be formed becomes unfavorably roughened.

In the electroless platinum plating solution according to the present application, considering the above range of platinum salt concentration, sodium borohydride which is a reducing agent for reducing platinum ions supplied from the platinum salt is 0.004 mol / dm it is preferably contained in ^{3 ~0.050mol} / dm ³ concentration ranging. If the reducing agent sodium borohydride is less than 0.004 mol / dm ³ , the reduction rate is slow and the platinum ion can not be sufficiently reduced. On the other hand, even if sodium borohydride which is a reducing agent is made to exceed 0.050 mol / dm ³ , the reduction efficiency is saturated, and the formation rate of the platinum plating film is not improved.

And as a sulfur compound chosen by the selection method of the stabilizer for non-electrolytic platinum plating solutions, it is preferable to use either thioproin, thiourea, or sodium thiosulfate. In this study, MPS (sodium 3-mercapto-1-propanesulfonate) and SPS (bis (3-sulfopropyl) disulfide) were stabilized in the electroless platinum plating solution and changed in the plating solution properties, so they were stable. It is considered that the plating performance can not be exhibited, which is not preferable. It is because the electroless platinum plating solution using these exhibits the suitable polarization curve mentioned later. The sulfur compound as a stabilizer for these electroless platinum plating solutions has a concentration of 0.005 × 10 ⁻³ mol / dm ^{3 to} 0.050 × 10 ⁻³ mol / dm ^{3 in the} electroless platinum plating solution. It is preferable to contain. If the concentration of the sulfur compound is less than 0.005 × 10 ⁻³ mol / dm ³ , it does not function as a stabilizer and the solution life is shortened, which is not preferable. On the other hand, when the concentration of the sulfur compound exceeds 0.050 × 10 ⁻³ mol / dm ³ , the solution characteristics of the electroless platinum plating solution are excessively stabilized, and the rate of electroless deposition of platinum is slow, which is preferable. Absent.

In addition, in the case of the electroless platinum plating solution according to the present application, ethylenediamine as a complexing agent, polyoxyethylene alkyl ether as a leveling agent, polyalkylphenyl ether, glycerin ester, polyglycerin ester, sorbitan ester, etc. may also be included. preferable. Concentration as complexing ^{agent, 0.05mol / dm 3 ~0.5mol / dm} 3, the concentration of the leveling agents in the range of 1ppm~100ppm is preferred. Moreover, it is preferable to use sodium hydroxide as a pH adjuster.

  The electroless platinum plating solution described above is preferably used in the range of solution pH = 9 to 13, solution temperature = 40 ° C. to 70 ° C. Sodium hydroxide, potassium hydroxide or the like is preferably used to adjust the solution pH. If the solution pH is less than 8, formation of a platinum plating film is difficult. On the other hand, even if the solution pH exceeds 13, there is no particular problem, but it is uneconomical because the formation rate of the platinum plating film is saturated. When the solution temperature is less than 40 ° C., the formation of the electroless platinum plating film becomes extremely slow, which is not preferable. On the other hand, when the solution temperature exceeds 70 ° C., evaporation of water becomes remarkable, and the solution property fluctuates in a short time, so that solution management becomes complicated, which is not preferable.

In Example 1, chloroplatinic (IV) ammonium (0.005 mol / ^dm 3), sodium borohydride (0.013 mol / ^dm 3), sodium hydroxide (0.25 mol / ^dm 3), ethylenediamine (0. Thiopronin, which is a sulfur compound, is added to a basic mixed aqueous solution of 17 mol / dm ³ ) so as to have a concentration of 0.031 × 10 ⁻³ mol / dm ^3, and the potential at 0.25 A / dm ² is −0.75 V The electroless platinum plating solution which shows the polarization characteristic of vs. Ag / AgCl was prepared. The polarization curve of the electroless platinum plating solution in Example 1 is shown in FIG. 1 by reference numeral 1 (indicated by a circled number in the drawing).

  Then, using a copper plate (10 mm × 10 mm) as an object to be plated, immersion degreasing (50 ° C., 4 minutes), soft etching (30 ° C., 1 minute), acid cleaning (30 ° C., 1 minute), platinum catalyst application ( After pre-treating in the order of 50 ° C., 3 minutes), the substrate was immersed in an electroless platinum plating solution (solution pH = 12.3) at a solution temperature of 60 ° C. for 10 minutes to perform electroless platinum plating. The various evaluations are shown in Table 1 below.

In Example 2, thiourea which is a sulfur compound is added to the basic mixed aqueous solution of Example 1 so as to have a concentration of 0.013 × 10 ⁻³ mol / dm ^3, and the potential at 0.25 A / dm ² is An electroless platinum plating solution having polarization characteristics of -0.75 V vs Ag / AgCl was prepared. The other conditions and the like are the same as in the first embodiment, and duplicate explanations are omitted. The polarization curve is similar to that of Example 1, and the description is omitted. The evaluation is shown in Table 1 below.

In Example 3, thiosulfuric acid which is a sulfur compound is added to the basic mixed aqueous solution of Example 1 so as to have a concentration of 0.0062 × 10 ⁻³ mol / dm ^3, and the potential at 0.25 A / dm ² is An electroless platinum plating solution having polarization characteristics of -0.75 V vs Ag / AgCl was prepared. The other conditions and the like are the same as in the first embodiment, and duplicate explanations are omitted. The polarization curve is similar to that of Example 1, and the description is omitted. The evaluation is shown in Table 1 below.

Comparative example

Comparative Example 1
The sulfur compound of Example 1 was replaced with SPS (bis (3-sulfopropyl) disulfide) to prepare an electroless platinum plating solution exhibiting a polarization characteristic of −0.75 V vs Ag / AgCl at a potential of 0.25 A / dm ² did. The other conditions and the like are the same as in the first embodiment, and duplicate explanations are omitted. The polarization curve of the electroless platinum plating solution in Comparative Example 1 is shown by reference numeral 2 (indicated by a circled number in the drawing) in FIG. The evaluation is shown in Table 1 below.

Comparative Example 2
The sulfur compound of Example 1 is replaced with 2,2′-thiodiacetic acid, and the polarization characteristic is obtained such that the potential at 0.25 A / dm ² falls within the range of −0.7 V to −0.8 V vs Ag / AgCl. An electroless platinum plating solution was prepared. The other conditions and the like are the same as in the first embodiment, and duplicate explanations are omitted. The polarization curve of the electroless platinum plating solution in Comparative Example 2 is shown by symbol a in FIG. The evaluation is shown in Table 1 below.

Comparative Example 3
Electroless platinum plating which does not have polarization characteristics in which the sulfur compound of Example 1 is replaced with sodium thiosulfate and the potential at 0.25 A / dm ² falls within the range of −0.7 V to −0.8 V vs Ag / AgCl. The solution was prepared. The other conditions and the like are the same as in the first embodiment, and duplicate explanations are omitted. The polarization curve of the electroless platinum plating solution in Comparative Example 3 is shown by symbol b in FIG. The evaluation is shown in Table 1 below.

Comparative Example 4
Electroless platinum plating solution having no polarization characteristic in which the sulfur compound of Example 1 is replaced with thiourea and the potential at 0.25 A / dm ² falls within the range of −0.7 V to −0.8 V vs Ag / AgCl Was prepared. The other conditions and the like are the same as in the first embodiment, and duplicate explanations are omitted. The polarization curve of the electroless platinum plating solution in Comparative Example 4 is shown by symbol c in FIG. The evaluation is shown in Table 1 below.

Comparative Example 5
Electroless platinum plating solution having no polarization characteristic in which the sulfur compound of Example 1 is replaced with sodium sulfide and the potential at 0.25 A / dm ² falls within the range of −0.7 V to −0.8 V vs Ag / AgCl Was prepared. The other conditions and the like are the same as in the first embodiment, and duplicate explanations are omitted. The polarization curve of the electroless platinum plating solution in Comparative Example 5 is shown by symbol d in FIG. The evaluation is shown in Table 1 below.

[Blank solution]
This blank solution is a "basic mixed aqueous solution" which does not contain the above-mentioned sulfur compound, and contains only sodium hydroxide and sodium borohydride. The polarization curve of the blank solution is shown by the symbol Bl in FIG. The evaluation is shown in Table 1 below.

<Comparison between Example and Comparative Example>
Table 1 is shown in order to facilitate understanding of the comparison result when performing comparison between the example described below and the comparative example.

  The solution stability evaluation shown in Table 1 was based on putting the electroless platinum plating solution in a polypropylene container and measuring the time until the platinum was reduced and deposited under a room temperature environment. However, during the preparation of the electroless platinum plating solution, it was determined that there was no solution stability if a problem occurred in the process of adjusting the solution temperature. Therefore, looking at the solution stability evaluation in Table 1, the electroless platinum plating solutions of Examples 1 to 3 can be placed in a polypropylene container and stored for at least 4 weeks without reduction precipitation of platinum in a room temperature environment. ing. However, although the electroless platinum plating solution of Comparative Example 1 has no problem immediately after the bath preparation, SPS is decomposed within several days to change the property of the solution. The electroless platinum plating solution and the blank solution of Comparative Example 2 are very unstable solutions, and platinum is reduced and precipitated in the plating tank during heating to perform electroless plating. There is. Moreover, in the case of the electroless platinum plating solutions of Comparative Example 3 to Comparative Example 5, although the problem that platinum is reduced and deposited during heating does not occur, the formation of the electroless platinum plating film is difficult, so the solution stability Not considered for evaluation.

  Next, the formation condition by visual observation of the platinum plating film is observed. Table 1 shows the results as "the state of platinum film formation". As can be seen from Table 1, it is only Examples 1 to 2 and Comparative Example 1 that the electroless platinum plating can be reliably performed. However, with regard to Comparative Example 1, since decomposition of SPS proceeds immediately after construction and the solution properties change, the deposition rate is slow and it can be determined that it is practically difficult to use. Therefore, the polarization curve shown as symbol 2 in FIG. 1 is the one immediately after bathing. In the case of the electroless platinum plating solutions of Comparative Examples 3 to 5, the effect of the used sulfur compound as a stabilizer for an electroless platinum plating solution is excessive, so that formation of an electroless platinum plating film is difficult. It is believed that there is. Therefore, it can be inferred that formation of an electroless platinum plating film can not be performed. In the case of Comparative Example 2 and the blank solution, platinum was reduced and precipitated in the plating tank during heating of the electroless platinum plating solution, so the electroless plating treatment was not performed. And the platinum plating film formed on the copper plate in Example 1- Example 3 measures a film thickness with a fluorescent-X-ray film thickness meter, and has converted the deposition rate from the relationship between a film thickness and immersion time.

Here, referring to FIG. 1, the polarization curves of Example 1 to Example 3 are positioned between the polarization curve group of the blank solution and Comparative Example 2 and the polarization curve group of Comparative Examples 3 to 5. doing. That is, it has a polarization characteristic in which the potential at 0.25 A / dm ² falls within the range of -0.7 V to -0.8 V vs Ag / AgCl.

Furthermore, from the comparison between “Example 2 and Comparative Example 4” and “Example 3 and Comparative Example 3”, the potential at 0.25 A / dm ² is −0.7 V even when the type of sulfur compound to be used is the same. It can be understood that a good electroless platinum plating solution can not be obtained if it does not contain an amount that exhibits polarization characteristics falling within the range of -0.8 V vs Ag / AgCl.

  The method for selecting a stabilizer for an electroless platinum plating solution according to the present application is effective in selecting a stabilizer (sulfur compound) for an electroless platinum plating solution which has a long solution life and a high deposition rate of platinum on the surface of the object to be plated. Demonstrate. The sulfur compound obtained by this selection method is useful for an electroless platinum plating solution which uses sodium borohydride as a reducing agent in place of hydrazine which is a reducing agent that affects the environment and human body. Electroless platinum plating is useful for surface modification of electronic component materials such as printed wiring boards, chip component terminals, etc., decorative articles, and the like.

Claims (2)

A method of selecting a stabilizer used in an electroless platinum plating solution containing a platinum salt, a reducing agent and a stabilizer,
A method of selecting a stabilizer for an electroless platinum plating solution, which comprises determining the suitability of a sulfur compound as a stabilizer according to the following procedure.
Preparation of selected test solution: A basic mixed aqueous solution with a sodium hydroxide concentration of 0.25 mol / dm ³ and a sodium borohydride concentration of 0.1 mol / dm ³ is used, and the sulfur compound to be selected here is 0.005 × 10 ⁻³ It was added at a concentration of ^{mol / dm 3 ~0.050 × 10 -3} mol / dm 3, the solution pH is 13.5, the preparation of a selected test solution having a temperature of 25 ° C..
Polarization potential measurement: A platinum disk as a working electrode, a platinum wire as an auxiliary electrode, and a silver-silver chloride electrode as a reference electrode, which are disposed in the selected test solution to make the potential of the working electrode relative to the reference electrode a natural potential From the potential to 0.002 V / sec. The potential scan is performed at the speed of, the current between the working electrode and the auxiliary electrode at a predetermined measured potential is measured, and a polarization curve (potential-current curve) is obtained.
Judgment of suitability as a stabilizer: In the polarization curve of the selected test solution, it has a polarization characteristic in which the potential at 0.25 A / dm ² falls within the range of −0.7 V to −0.8 V vs Ag / AgCl , and When the electroless platinum plating solution is prepared using the sulfur compound, it is judged that the electroless plating solution can use a sulfur compound which can be stored for 4 weeks or more without deterioration of the solution , as the electroless platinum plating solution. An electroless platinum plating solution comprising a platinum salt, a reducing agent and a stabilizer,
The reducing agent is sodium borohydride,
The stabilizer is any one of thioproine, thiourea and thiosulfuric acid which is a sulfur compound selected by the method of selecting a stabilizer for an electroless platinum plating solution according to claim 1 at 0.005 × 10 ^-3 mol / Containing in the range of dm ^{3 to} 0.050 × 10 ^-3 mol / dm ³ concentration ,
An electroless platinum plating solution having polarization characteristics in which a potential at 0.25 A / dm ² falls within a range of -0.7 V to -0.8 V vs Ag / AgCl in a polarization curve .

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