JPH0333780B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a method for electrolytically oxidizing formic acid contained together with a complexing agent in an electroless copper plating solution using formaldehyde as a reducing agent and removing it as carbon dioxide gas. be.

[Prior art]

BACKGROUND OF THE INVENTION In recent years, electroless plating, which is a field of surface treatment technology, has made remarkable progress with the development of the electronic equipment industry, the automobile industry, etc. As such an electroless plating solution, an electroless plating solution containing a complexing agent such as EDTA, alkanolamine, or Rothsiel's salt is known. In addition, this plating solution contains formalin as a reducing agent, and if it is used continuously for a long time, a large amount of formic acid, which is an oxide of formalin, will accumulate in the solution, and this accumulated amount will be added to the plating solution. When the amount is 0.8 mol/or more, abnormal copper plating precipitation occurs. Therefore, in order to extend the life of the plating solution, it is necessary to continuously remove formic acid from the plating solution, and for this purpose, a method for removing formic acid by electrolytic oxidation has been proposed. However, the oxidation efficiency of formic acid or current efficiency was not yet satisfactory. For example, if a plating solution containing a complexing agent and formic acid is electrolyzed at a constant potential, the current density will decrease over time, reducing workability.On the other hand, if a plating solution containing a complexing agent and formic acid is electrolyzed at a constant current,
With the passage of time, the anode potential increases, decomposition of the complexing agent and water occurs, and especially when a platinum-based electrode is used, there is a problem that the current efficiency of formic acid oxidation becomes zero.

〔the purpose〕

The present invention aims to solve the above-mentioned problems that occur when formic acid contained in an electroless copper plating solution containing a complexing agent is removed by electrolytic oxidation.

[Structure] According to the present invention, when formic acid contained together with a complexing agent in an electroless copper plating solution using formaldehyde as a reducing agent is electrolytically oxidized and removed as carbon dioxide gas, the anode potential is changed to silver/chloride. Intermediate potential range of +0.5V to +1.2V, +1.3V to +0.5V with respect to silver reference electrode
Complexing agent and water decomposition potential range of +1.8V, +0.5V to +
A method for removing formic acid in an electroless copper plating solution using a multi-stage potential method, which is characterized by performing electrolysis while sequentially varying the intermediate potential range of 1.2V and the formic acid oxidation potential range of -0.25V to +0.4V. is provided.

The plating solution in the present invention is an electroless copper plating solution that contains formalin as a reducing agent and a complexing agent as an auxiliary agent. Here, the complexing agent is used to stabilize copper ions in the plating solution. For example, for high temperature plating solutions, EDTA (ethylenediaminetetraacetic acid or its salt), alkanolamine, etc. is used, and Rothsiel salt etc. are used in the low temperature plating method.

In such a plating solution containing formaldehyde, as plating progresses, formic acid, which is an oxidation product of formalin, accumulates in the plating solution, inhibiting the formation of a high-quality plating film.

The present invention aims to remove formic acid from the formic acid accumulated in the matting solution as carbon dioxide gas by electrolytic oxidation and reuse it. The potential is defined as an intermediate potential range between the formic acid oxidation potential and the decomposition potential of the complexing agent and water, a decomposition potential range of the complexing agent and water, and a range between the formic acid oxidation potential range and the decomposition potential range of the complexing agent and water. The present inventors have discovered that electrolytic oxidation of formic acid can be carried out efficiently over a long period of time when electrolysis is carried out while sequentially varying the intermediate potential range and the formic acid oxidation potential range in that order, leading to the completion of the present invention. .

The formic acid oxidation potential range is the potential in the range where formic acid is efficiently electrolytically oxidized and removed as carbon dioxide gas, relative to the silver/silver chloride electrode (all potentials shown below are based on this electrode). Typically 0.25V
The potential is ~+0.4V. The time to maintain this potential range is usually 3 to 15 seconds, preferably 5 to 12 seconds.

The decomposition potential range of the complexing agent and water is the potential in the region where electrolysis of the complexing agent and water occurs, and is usually in a higher potential range than the formic acid oxidation potential range, and is generally +
The range is 1.3V to +1.8V. The time to maintain this potential range is 0.5 to 5 seconds, preferably 1 to 2 seconds. When using a gold or palladium electrode as an anode, even if a complexing agent is present in the plating solution, the current efficiency of formic acid oxidation in the decomposition potential range of the complexing agent and water is approximately 20 to 45%. However, in the case of platinum electrodes, the current efficiency is zero.

In the intermediate potential range between the formic acid oxidation potential and the decomposition potential of the complexing agent and water, decomposition of formic acid, the complexing agent, and water does not occur, but in order to perform good oxidation removal of formic acid, the anode potential It is important to maintain the voltage in this intermediate potential range for a certain period of time. In the case of the present invention, +0.5V
It is held in the intermediate potential range of ~+1.2V for 0.5 to 5 seconds, preferably 1 to 2 seconds. When the anode potential is not maintained in this intermediate potential range and is directly varied between the formic acid oxidation potential range and the complexing agent and water decomposition potential range, disadvantages such as a decrease in the formic acid oxidation current occur.

As the anode used in the present invention, materials other than platinum-based electrodes such as gold or palladium-based electrodes can be used, but platinum-based electrodes such as ordinary platinum electrodes, platinum-plated titanium electrodes, etc. are preferably used. Ru. The pH of the plating solution is usually in the range of 4 to 12, preferably 4 to 6.

〔effect〕

According to the formic acid electrolytic oxidation method of the present invention, since the anode potential is varied in multiple stages as described above,
The anode is constantly activated and can oxidize and decompose formic acid with high current efficiency.

〔Example〕

Next, the present invention will be explained in more detail with reference to Examples.

Example 1 A model plating solution containing 0.8 mol/mol of sodium formate and 0.05 mol/ EDTA as a complexing agent.
An aqueous solution with a pH of 4.5 was used.

These aqueous solutions were electrolytically treated using a platinum electrode as an anode. In this case, the electrolytic treatment changes the anode potential from the starting point (-0.4V, 1 second) to the intermediate potential (+0.5V, 1 second) to the oxygen evolution potential (1.6V,
This was carried out by repeatedly changing the potential (1 second) → intermediate potential (+0.5 V, 1 second) → formic acid oxidation potential (0 V, 10 seconds) → starting point (−0.4 V, 1 second). As a result of carrying out the electrolytic treatment as described above for a period of time, formic acid was decomposed and removed with a current efficiency of 90%.

In the above description, the reason why the anode potential is returned to the starting point is for convenience in controlling the potential and has no particular meaning.

Comparative example 1 In Example 1, 20A/dm ² (+1.6 volts)
Although electrolytic treatment was carried out at a constant current of 1, the current efficiency of formic acid oxidation was 0%.

Comparative Example 2 In Example 1, electrolytic treatment at intermediate potential (+
When electrolytic treatment was carried out in the same manner except that the voltage (0.5 V, 1 second) was not carried out, the formic acid oxidation current efficiency was 90.
%, but the time required was more than twice that of Example 1.

Example 2 In Example 1, sodium formate 0.8 mol/, EDTA 0.05 mol/
An experiment was conducted in the same manner as in Example 1, except that an aqueous solution of pH 4.5 containing 0.04 mole of copper sulfate was used. In this case, copper was deposited on the cathode electrode, but the platinum electrode (anode electrode) was not affected by this, and as in Example 1, its surface state was always kept active and efficient. It was confirmed that electrolytic oxidation of formic acid was carried out well.

Claims (1)

[Claims] 1. When formic acid contained together with a complexing agent in an electroless copper plating solution using formaldehyde as a reducing agent is electrolytically oxidized and removed as carbon dioxide gas, the anode potential is set to +0.0 with respect to the silver/silver chloride reference electrode. 5V
~ +1.2V intermediate potential range, +1.3V ~ +1.8V complexing agent and water decomposition potential range, +0.5V ~ +1.2V intermediate potential range, and -0.25V ~ +0.4V formic acid oxidation potential. A method for removing formic acid in an electroless copper plating solution using a multi-stage potential method, which is characterized in that electrolysis is performed while sequentially changing the range.