JPH089786B2 - Method of measuring reducing agent concentration in chemical copper plating solution - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for measuring a reducing agent concentration in a chemical copper plating solution used for manufacturing a printed wiring board or the like.

[Conventional technology]

In recent years, many printed wiring boards are manufactured by providing a circuit conductor on an insulating substrate by chemical copper plating. In this case, the chemical copper plating film which is the circuit conductor is required to have good electrical and mechanical properties.

Generally, the chemical copper plating solution contains copper ions, complexing agents such as chelating agents for copper ions, reducing agents for copper ions, and hydroxides of alkali metals. Formaldehyde is usually used as a reducing agent for copper ions. And
This copper ion reducing agent is consumed by the plating reaction,
The concentration decreases.

By the way, the mechanical properties of the chemical copper plating film are significantly affected by the reducing agent concentration of copper ions in the plating solution. Therefore, in order to keep the properties of the chemical copper plating film good, it is necessary to control the concentration of this component. Therefore, in order to measure the formaldehyde concentration, which is the reducing agent in the conventional chemical copper plating solution, first adjust the pH of the chemical copper plating solution whose concentration is to be measured and the pH of the lead sulfite solution mixed with this chemical copper plating solution to be equal. Then, after mixing both solutions and ending the pH change of this mixed solution, add acid to this mixed solution until reaching the pH before mixing, and from the capacity of the added acid, the concentration of formaldehyde, which is the reducing agent, Was seeking.

[Problems to be Solved by the Invention]

However, in the method of measuring the formaldehyde concentration by titrating the hydroxide ion generated by this reaction with an acid by utilizing the reaction between the chemical copper plating solution and the sulfite as described above, Under the influence of a chelating agent that does not form a chelate with copper ions,
The concentration of formaldehyde, which is a reducing agent, in the chemical copper plating solution could not be accurately measured. Therefore, a method of accurately measuring the reducing agent concentration of the chemical copper plating solution has been desired.

The present invention has been made in view of the above problems, and an object thereof is a method utilizing a reaction with a sulfite salt to eliminate the influence of a chelating agent contained in a chemical copper plating solution. It is to provide a method for accurately measuring the concentration of a reducing agent in a plating solution.

[Means for solving the problem]

As a result of intensive studies to solve the above problems, the present inventors have added a heavy metal ion to a chemical copper plating solution to form a chelate with a chelating agent that does not form a chelate with a copper ion and a heavy metal ion, and form a chelate. It was found that the object can be achieved by measuring the reducing agent concentration in the chemical copper plating solution by a method utilizing the reaction with sulfite to eliminate the influence of the agent, and the present invention was completed based on this finding. Came to do.

That is, the present invention adds a heavy metal ion to a chemical copper plating solution containing copper ions, a chelating agent for copper ions, formaldehyde which is a reducing agent for copper ions, and hydroxide of an alkali metal until the precipitation of hydroxide is generated. A supernatant is obtained, and the pH of the supernatant is adjusted to be equal to the pH of the solution of sulfite to be mixed with the supernatant, and then the supernatant and the solution of sulfite are mixed to obtain a mixed solution. After the pH change of the mixed solution is completed, an acid is added to the mixed solution until the pH of the mixed solution reaches the value before mixing, and the formaldehyde concentration is obtained from the volume of the added acid. A method for measuring the concentration of a reducing agent in a medium is provided.

The chemical copper plating solution which is the object of the present invention contains copper ions, a chelating agent for copper ions, formaldehyde which is a reducing agent for copper ions, and hydroxide of an alkali metal. In addition to that, as a additive, cyanide compounds, surfactants,
It may contain α, α′-dipyridyl, metal oxide ions and the like.

In the method for measuring the concentration of a reducing agent of the present invention, first, heavy metal ions are added to the above-mentioned chemical copper plating solution until precipitation of hydroxide is formed.

The heavy metal ions added are preferably those that react with the chelating agent. Specifically, ions of copper, nickel, cobalt, zinc, iron, lead, aluminum, chromium or cadmium are more preferable than the reactivity of the copper ion of the chemical copper plating solution with the chelating agent. The heavy metal ions may be added to the chemical copper plating solution in the form of a solution, or may be added to the chemical copper plating solution in the form of a salt thereof.

When a heavy metal ion is added to the above chemical copper plating solution, as shown in the following formula [I], a chelating agent (Y ^4- ) for copper ions such as ethyne rediamine tetraacetic acid in the chemical copper plating solution and a heavy metal ion (M ²⁺ ) and form a chelate.

M ²⁺ + Y ^4- → MY ^2- [I] A method for measuring the concentration of a reducing agent using the reaction between a conventional chemical copper plating solution and sulfite, that is, a chemical copper plating solution for measuring the concentration. Adjust the pH of the sulfite solution to be mixed with this chemical copper plating solution to be equal, then mix both solutions to end the pH change of this mixed solution, and then add the acid to this mixed solution before adjusting the pH. In addition,
In the method of determining the concentration of formaldehyde, which is a reducing agent in the chemical copper plating solution, from the capacity of the acid required for this, acid-base titration is used. At this time, if a chelating agent (Y ^4- ) that does not chelate copper ions is present in the chemical copper plating solution, the chelating agent has a buffering effect on the acid-base titration, which adversely affects the acid-base titration. And the concentration of the reducing agent cannot be accurately measured. However, MY ²⁻ generated by the reaction of the formula [I] does not affect the measurement of the reducing agent concentration using acid-base titration. Therefore, in the present invention, by adding a heavy metal ion to the chemical copper plating solution in advance, formaldehyde and sulfite in the state where the chelating agent that does not form a chelate with the copper ion that adversely affects the measurement of the concentration of the reducing agent is eliminated Since the concentration of the reducing agent is measured using the reaction, the concentration of the reducing agent can be accurately measured.

Here, heavy metal ions are added to the chemical copper plating solution until hydroxide precipitation occurs. That is, it is preferable to add the heavy metal ions to be added in excess of the amount of the chelating agent. When it becomes excessive, the hydroxide ion and the heavy metal ion in the chemical copper plating solution react with each other to form a precipitate of a heavy metal hydroxide. Therefore, it is preferable to stop adding the heavy metal ion at this time.

Next, a certain amount of the supernatant liquid obtained above is used as a sample solution, and this sample solution is used for reduction according to the conventional method for measuring the concentration of a reducing agent using the reaction between a chemical copper plating solution and sulfite. Measure the agent concentration. That is, this supernatant liquid
The pH is adjusted to be equal to the pH of the sulfite solution to be mixed with the supernatant, and then the supernatant and the sulfite solution are mixed to form a mixed solution, after the pH change of this mixed solution is completed. , Acid is added to the mixed solution until the pH of the mixed solution reaches the value before mixing, and the formaldehyde concentration is determined from the volume of acid required for this.

As the sulfite solution to be mixed with the above-mentioned supernatant liquid, for example, an aqueous solution of sodium sulfite at a concentration of 0.1 mol / about is suitable.

Adjust the pH of the supernatant by adjusting the sulfite solution to be mixed.
The pH is adjusted to be equal to the pH, and the pH can be adjusted by adding an appropriate acid or base to the supernatant while measuring the pH of the supernatant with a pH electrode. The pH value is preferably adjusted to a value between 3 and 11.

When the supernatant and the sulfite solution are mixed to form a mixed solution, the sulfite is excessive with respect to the formaldehyde depending on the formaldehyde concentration and the sodium sulfite concentration in the sample liquid. As appropriate.

In this mixed solution, the reaction represented by the following formula [II] occurs and the pH of the mixed solution changes.

Na ₂ SO ₃ + CH ₂ O + H ₂ O → Na (CH ₃ O) SO ₃ + NaOH [II] The acid is added to the mixed solution after the above pH change is completed. This is because the hydroxide ion derived from NaOH generated in the above formula [II] is titrated with an acid.

Titration with an acid is usually performed using a known concentration of an inorganic acid such as hydrochloric acid, sulfuric acid or nitric acid. At this time, while the pH electrode is put in the mixed solution and the pH of the mixed solution is measured, the acid is added until the pH of the mixed solution reaches the value before mixing.

The amount of hydroxide ion is obtained from the capacity of the acid added by the above operation, and the concentration of formaldehyde, which is the reducing agent in the chemical copper plating solution, can be obtained by using the relation of the formula [II]. At this time, since formaldehyde is usually used as formalin, which is a 37% formaldehyde aqueous solution,
The formaldehyde concentration is obtained as the formalin concentration using the relationship shown in the following formula [III].

Formalin concentration (ml /) = 0.75 × V [III] [where V represents the volume (ml) of the added acid above]. [Operation] According to the present invention, the heavy metal ion added to the chemical copper plating solution forms a chelate with a chelating agent of a copper ion such as ethylenediaminetetraacetic acid in the chemical copper plating solution to form a sulfite. Accurately measure the concentration of formaldehyde, which is the reducing agent in the chemical copper plating solution, as it can be eliminated from the sample solution of the chelating agent that adversely affects the measurement of the hydroxide ion generated by the reaction of bromine with formaldehyde by acid titration. be able to.

[Examples] Hereinafter, the present invention will be described in detail based on Examples,
The present invention is not limited to this.

Example 1 Chemical copper plating was performed under the following plating conditions using a chemical copper plating solution having the following composition.

<Chemical copper plating solution composition> Copper sulfate (CuSO ₄ / 5H ₂ O) 10g / ethylenediaminetetraacetic acid tetrasodium (EDTA / 4Na / 2H ₂ O) 20g / formanline (37% formaldehyde aqueous solution) 3ml / sodium hydroxide (NaOH) 4 g / additive A small amount <Plating conditions> Plating temperature 70 ° C Plating area 1 dm ² / Plating speed 2.5 μm / h While performing the above chemical copper plating, a part of the chemical copper plating solution was sampled and cooled to room temperature. And 10 ml of this
The mixture was dispensed into a beaker, and then copper sulfate powder was added until a copper hydroxide precipitate was formed.

The pH of the supernatant of this chemical copper plating solution was adjusted to 9.0 as measured by a pH electrode, and 10 ml of the supernatant was collected and added to about 75 ml of 0.1 mol / sodium sulfite aqueous solution. Here, the sodium sulfite aqueous solution has a pH of 9.0 in advance.
The one used was. Both solutions were mixed and left for 2-3 minutes.
The pH change of the mixed solution was completed while it was left standing.

Then, a 0.1 N sulfuric acid aqueous solution was added to the mixed solution until the pH of the mixed solution reached 9.0. The volume of the aqueous sulfuric acid solution added was V (ml), the formaldehyde concentration was the formalin concentration, and the value was determined by the above formula [III]. The results are shown in Table 1.

Example 2 In Example 1, the concentration of ethylenediaminetetraacetic acid was set to 30.
The formaldehyde concentration was determined in the same manner as in Example 1 except that g / was set. The results are shown in Table 1.

Example 3 The concentration of ethylenediaminetetraacetic acid in Example 1 was 40 g /
The formaldehyde concentration was determined in the same manner as in Example 1 except that The results are shown in Table 1.

Comparative Example 1 The formaldehyde concentration was determined in the same manner as in Example 1 except that the step of adding the copper sulfate powder was omitted in Example 1. The results are shown in Table 1.

Comparative Example 2 The formaldehyde concentration was determined in the same manner as in Example 2 except that the step of adding the copper sulfate powder was omitted in Example 2. The results are shown in Table 1.

Comparative Example 3 The formaldehyde concentration was determined in the same manner as in Example 3 except that the step of adding the copper sulfate powder was omitted in Example 3. The results are shown in Table 1.

[Effects of the Invention] According to the method for measuring the reducing agent concentration in the chemical copper plating solution of the present invention, the reducing agent concentration in the chemical copper plating solution can be accurately measured without being affected by the chelating agent in the chemical copper plating solution. Can be measured.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Akashi Nakaso 1500 Ogawa, Shimodate, Ibaraki Pref., Shimodate Research Laboratory, Hitachi Chemical Co., Ltd. Shimodate Laboratory Ltd. (56) Reference JP-A-53-149389 (JP, A) JP-A-54-83635 (JP, A) JP-A-63-91549 (JP, A)

Claims (2)

[Claims] 1. A heavy metal ion is added to a chemical copper plating solution containing copper ions, a chelating agent for copper ions, formaldehyde which is a reducing agent for copper ions, and hydroxide of an alkali metal until hydroxide precipitates. A supernatant is obtained, and the pH of the supernatant is adjusted to be equal to the pH of the solution of sulfite to be mixed with the supernatant, and then the supernatant and the solution of sulfite are mixed to obtain a mixed solution. PH of mixed solution
After the change is finished, an acid is added to the mixed solution until the pH of the mixed solution reaches the value before mixing, and the formaldehyde concentration is determined from the volume of the added acid. A reducing agent in a chemical copper plating solution. How to measure concentration. 2. Heavy metal ions are copper, nickel, cobalt,
The method for measuring the concentration of a reducing agent in a chemical copper plating solution according to claim 1, which is an ion of zinc, iron, lead, aluminum, chromium or cadmium.