JP2595835B2 - Measurement method of chelating agent concentration, hydroxide ion concentration and reducing agent concentration in chemical copper plating solution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for measuring the concentration of a chelating agent, the concentration of a hydroxide ion and the concentration of a reducing agent in a chemical copper plating solution.

[0002]

2. Description of the Related Art In recent years, most printed wiring boards have been manufactured by providing circuit conductors on an insulating substrate by chemical copper plating. In this case, the chemical copper plating film as the circuit conductor is required to have good electrical and mechanical properties.

In general, a chemical copper plating solution contains copper ion, a complexing agent such as a chelating agent for copper ions, a reducing agent for copper ions, and a hydroxide of an alkali metal as main components. And
The alkali metal hydroxide and the reducing agent are consumed by the plating reaction and the concentration decreases. Further, a part of the chelating agent forms a chelate with the copper ion due to a change in the concentration of the copper ion or the like, so that the concentration of the chelating agent not forming a chelate with the copper ion changes.

The mechanical properties of a chemical copper plating film are significantly affected by the alkali metal hydroxide concentration and the reducing agent concentration in the plating solution and the concentration of a chelating agent which does not form a chelate with copper ions. For this reason, in order to maintain good properties of the chemical copper plating film, it is necessary to control the concentration of these components. Therefore, conventionally, the chelating agent concentration, the hydroxide concentration, and the reducing agent concentration in the chemical copper plating solution have been separately measured.

A conventional method for measuring the concentration of a chelating agent is to make a copper sulfate aqueous solution of a certain concentration alkaline with ammonium water, add a murexide indicator therein, titrate the solution with a chemical copper plating solution, and turn the solution from blue-green to blue-violet. The end point of the reaction was determined from the change in the color of the solution, and the concentration of the chelating agent that did not form a chelate with copper ions in the chemical copper plating solution was determined from the titration amount at this time. The method of measuring the hydroxide ion concentration was to measure the hydrogen ion concentration in the chemical copper plating solution by the glass electrode method and indirectly determine the hydroxide ion concentration by calculation from the ion product of water. .

Further, conventionally, in order to measure the concentration of formaldehyde as a reducing agent in a chemical copper plating solution, first, the pH of the chemical copper plating solution whose concentration is to be measured and the pH of the sulfite solution mixed with the chemical copper plating solution become equal. And then mix both solutions and after the pH change of this mixed solution is over,
An acid was added to this mixed solution until the pH before mixing was reached, and the concentration of formaldehyde as a reducing agent was determined from the volume of the acid added.

[0007]

However, in the above-mentioned conventional method, the operation of measuring the concentration of the chelating agent, the concentration of the hydroxide, and the concentration of the reducing agent are separate, and are complicated and time-consuming. Also,
There were problems with each method. That is, in the above-described measurement of the chelating agent concentration, skill is required to accurately detect the color change at the end point of the reaction, and the color once changed due to the slow chemical reaction at the end point detection returns after 1-2 minutes. And other problems. Further, since the method for measuring the hydroxide ion concentration is a glass electrode method, there are problems such as a large alkali error at pH 11 or higher, lack of accuracy, and deterioration of the electrode.

Further, the method of measuring the formaldehyde concentration by utilizing the reaction between a chemical copper plating solution and a sulfite as described above and titrating with a hydroxide ionic acid generated by this reaction involves the following steps. Under the influence of a chelating agent that has not formed a chelate with copper ions of
The concentration of formaldehyde as a reducing agent in the chemical copper plating solution could not be accurately measured.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the object has been achieved by titrating a chemical copper plating solution with an aqueous solution of a salt of a heavy metal ion. The present inventors have found that the present invention has been completed based on this finding.

That is, according to the present invention, a certain amount of a chemical copper plating solution containing copper ions, a chelating agent for copper ions, a reducing agent for copper ions, and an alkali metal hydroxide as main components is used to prepare a salt of heavy metal ions. The change in pH of the sample solution is detected by titration with an aqueous solution, and the change is recorded over time.

Next, an alkali metal sulfite is added in excess of the equivalent of the reducing agent to the sample solution after the titration, and titration is performed with an aqueous solution of a salt of a heavy metal ion to detect a change in pH of the sample solution. To record. A method for measuring a concentration of a chelating agent, a concentration of a hydroxide ion, and a concentration of a reducing agent in a chemical copper plating solution, wherein a concentration of a chelating agent, a concentration of a hydroxide ion, and a concentration of a reducing agent are obtained from these two titrations. Is what you do.

The chemical copper plating solution to be used in the present invention contains copper ions, a chelating agent for copper ions, a reducing agent for copper ions, and a hydroxide of an alkali metal as main components.

As a chelating agent for copper ions contained in the chemical copper plating solution, ethylenediaminetetraacetic acid or a salt thereof is preferable from the viewpoint of the stability of the chemical copper plating solution. In addition, the chemical copper plating solution may contain a cyan compound, a surfactant, α, α′-dipyridyl, a metal oxide ion, and the like as additives in addition to the above components.

In the present invention, a fixed amount of the above-mentioned chemical copper plating solution is titrated with an aqueous solution of a salt of a heavy metal ion. As a salt of a heavy metal ion used for titration, a salt of an ion such as an alkaline earth metal, a transition metal, aluminum, tin or lead is preferred from the viewpoint of reactivity with a chelating agent.

When a certain amount of the above-described chemical copper plating solution is titrated with an aqueous solution of a salt of a heavy metal ion, the chelating agent (Y ⁴⁻ ) and the hydroxide ion (OH ⁻ ) in the chemical copper plating solution are titrated.
Reacts sequentially with the heavy metal ion (M ² +) as follows. M ² ++ Y ^4- → MY ^2- [I] ^{M 2 ++ 2OH - → M (} OH) 2 (II)

Here, the reaction of the formula [I] is fast, and the reaction of the formula [II]
More likely to occur than the reaction. Further, there is almost no change in the pH of the sample solution due to this reaction. On the other hand, the reaction of the formula [II] starts at the stage when the reaction of the formula [I] is completed, and the pH of the sample solution is largely changed because OH ^- is reduced by this reaction. Therefore, while measuring and recording the pH with a glass electrode or the like, when an aqueous solution of a heavy metal ion having a known concentration is dropped on the chemical copper plating solution, the changes in the pH of the sample solution are expressed by the formulas (I) and (II). You can know the end point of the reaction.

FIG. 1 is a graph showing an example of a titration curve when a chemical copper plating solution is titrated with an aqueous solution of a salt of a heavy metal ion based on the measuring method of the present invention. The horizontal axis indicates the titer (ml) of the aqueous solution of the heavy metal ion salt, and the vertical axis indicates the pH.

As shown in FIG. 1, the abscissa plots the titration amount of the aqueous solution of the heavy metal ion and the ordinate plots the pH, and the titration curve is plotted between the reaction of formula [I] and the reaction of formula [II]. PH during and after the reaction
, The titration curve is bent. The end point of the reaction of the formula [I] is a point at which the pH that has been gradually decreasing linearly and gradually starts to decrease rapidly (point A in FIG. 1). This point is also the starting point of the reaction of the formula [II]. The end point of the reaction of the formula [II] is an inflection point (point B in FIG. 1) at which the rapid decrease in pH becomes gentle. Therefore, the end points of the reactions of the formulas [I] and [II] can be known from the change in the slope of the titration curve.

From the titration of the aqueous solution of the heavy metal ion salt up to the end of the reaction of the formulas [I] and [II] and the concentration of the aqueous solution of the heavy metal ion salt, the chelate in the chemical copper plating solution was determined. The agent concentration and hydroxide ion concentration can be determined.

Next, when the end point of the reaction [II] is obtained, the titration of the aqueous solution of the salt of the heavy metal ion is stopped. When an alkali metal sulfite is added to this sample solution, the following reaction occurs. _{Na 2 SO 3 + CH 2 O} + H 2 O → CH 3 OSO 3 + NaOH (III) formaldehyde in the titration is a reducing agent that does not react as [III] reacts with sulfite, formaldehyde amount of hydroxide ions And an equivalent amount. Therefore, a second titration is carried out with an aqueous solution of a salt of a heavy metal ion in the same manner as in the reaction formula [II], and a hydroxide ion newly generated by the reaction [III] is determined to determine the concentration of the reducing agent which is formaldehyde.

[0021]

In the present invention, when an aqueous solution of a salt of a heavy metal ion is added to a certain amount of a sample solution of a chemical copper plating solution, first, a reaction between a chelating agent not forming a chelate with the copper ion and the heavy metal ion proceeds. However, at the same time as the completion of this reaction, the reaction between heavy metal ions and hydroxide ions proceeds. The former reaction has a small change in pH, and the latter reaction has p
Since the change in H is large, a certain amount of the chemical copper plating solution is titrated with an aqueous solution of a salt of a heavy metal ion, and at the same time, the end points of both the former reaction and the latter reaction are known by detecting the pH of the mixed solution. Thus, the chelating agent concentration and the hydroxide ion concentration can be measured at once.

Next, since the reducing agent does not react in the above titration, the addition of sulfite generates hydroxide ions equal to the amount of the reducing agent. Therefore, the concentration of the reducing agent can be determined by the same method as in the above titration. In the second titration, there is no problem because the chelating agent has reacted with the heavy metal ions in the first titration.

[0023]

The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples. The chemical copper plating solution having the following composition was used. Copper sulfate _{10 g / l (CuSO 4 ·} 5H 2 O) (0.04 mol / l) of tetrasodium ethylenediamine tetraacetate 54.2g / g (EDTA · 4Na) (0.02 mol / l) formalin 3 ml / l (37% formaldehyde aqueous solution) Sodium hydroxide 2 g / l (NaOH) (0.05 mol / l) Additive small amount

10 ml of the above chemical copper plating solution was placed in a beaker, and pure water was added to make about 50 ml. A glass electrode (composite glass electrode No. 6366 manufactured by Horiba, Ltd.) connected to the pH meter and the recorder was immersed in this beaker. To this, a 0.1 mol / l aqueous solution of copper sulfate was dropped using a burette, and a change in pH at this time was detected and recorded with time. The result is shown in FIG. The horizontal axis indicates the titer (ml) of the aqueous copper sulfate solution, and the vertical axis indicates the pH.

The point A in FIG. 1 is the end point of the reaction between the chelating agent and the copper ion and the start point of the reaction between the hydroxide ion and the copper ion. Point B is the end point of the reaction between the copper ion and the hydroxide ion. From this, the titer of the aqueous solution of copper sulfate at point A was 8.0 ml, and the concentration of the chelating agent not forming a complex with copper ions in the chelating agent of the chemical copper plating solution was 0.08 mol / mol.
1 was obtained. The difference between the titration amounts of the copper sulfate aqueous solution at the points B and A is 2.5 ml, and the reaction ratio between copper ions and hydroxide ions is 1: 2. Mol / l were obtained. In addition. The concentration was calculated according to the following formula [IV] for the chelating agent concentration, and according to the following formula [V] for the hydroxide ion. CV = C′V ′ [IV] C ₁ V = 2C′V ₁ [V] [where C is the concentration of the chelating agent in the chemical copper plating solution,
V is the amount of the chemical copper plating solution collected (10 ml), C 'is the concentration of the copper sulfate aqueous solution used for the titration (0.1 mol / l), V'
Represents the titer of the aqueous copper sulfate solution at point A, C ₁ represents the concentration of hydroxide ion in the chemical copper plating solution, and V ₁ represents the difference between the titer of the aqueous copper sulfate solution at points B and A. ]

The plating solution sample after the use of the above titration was added with 0.1%.
About 50 ml of a 1 mol / l sodium sulfite aqueous solution is added. After stirring for 2 minutes, titration was performed with the aqueous copper sulfate solution (0.1 mol / l) used in the above titration. The change in pH at this time was detected and recorded over time. The result is shown in FIG. The horizontal axis and the vertical axis are the same as in FIG.

The point C in FIG. 2 is the end point of the reaction between the copper ion and the hydroxide ion similarly to the point B, and the concentration of the hydroxide ion is adjusted to 0.04 mol / mol according to the above formula [V].
1 was obtained. This concentration is equal to the formalin concentration. Therefore, when the molar concentration was converted to the ml / l concentration using the following formula [VI], M = 0.75M '[VI] was obtained at 3 ml / l. M is ml / l concentration, M 'is mol / l
Concentration.

[0027]

According to the present invention, the concentration of the chelating agent and the concentration of hydroxide ion in the chemical copper plating solution can be easily and simply determined by simply adding an aqueous solution of a salt of a heavy metal ion to the chemical copper plating solution at once. Can be measured. Further, the concentration of the reducing agent can be measured with the same sample solution and the same titrant.

[Brief description of the drawings]

FIG. 1 (a) is a diagram showing one embodiment of the present invention, and shows a titration curve when a chemical copper plating solution is titrated with an aqueous solution of a salt of a heavy metal ion; The titration amount (ml) of the aqueous solution of the salt of the heavy metal ion, and the vertical axis indicates the pH. (B) is a diagram showing one embodiment of the present invention, and FIG.
Add sodium sulfite to the sample solution after the titration of
It shows a titration curve when titrating with a salt of a heavy metal ion, and the horizontal axis represents the titer of an aqueous solution of a salt of a heavy metal ion (m
l), the vertical axis indicates pH.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiro Okamura 1500 Oji Ogawa, Shimodate City, Ibaraki Pref.Hitachi Kasei Kogyo Co., Ltd. (72) Inventor: Tomoko Watanabe, Shimodate, Ibaraki Prefecture

Claims (3)

(57) [Claims] 1. A method for measuring each component in a chemical copper plating solution containing copper ions, a chelating agent for copper ions, a reducing agent for copper ions, and a hydroxide of an alkali metal as main components, comprising the following steps: A method for measuring a concentration of a chelating agent, a concentration of a hydroxide ion, and a concentration of a reducing agent in a chemical copper plating solution. A. A fixed amount of sample solution from the chemical copper plating solution is titrated with an aqueous solution of a salt of a heavy metal ion to detect a change in pH of the sample solution,
Record over time. Add an alkali metal sulfite salt in excess of the equivalent amount of the reducing agent to the sample solution after titration, titrate with an aqueous solution of heavy metal ion salt, detect the pH change of the sample solution, and record over time. . From the diagram of the appropriate amount and the pH determined in the step A, the chelating agent concentration was determined from the appropriate amount and the concentration of the appropriate solution at the first point where the sign of the slope of the change with respect to the appropriate amount of the pH was replaced. The hydroxide ion concentration was determined from the appropriate amount and the concentration of the appropriate solution at the next point where the sign of the slope of the change with respect to the appropriate amount of pH was changed. Calculate the reducing agent concentration from the appropriate amount and the concentration of the appropriate solution at the first point where the sign of the change slope with respect to the appropriate amount is changed 2. The method for measuring a concentration of a chelating agent, a concentration of a hydroxide ion, and a concentration of a reducing agent in a chemical copper plating solution according to claim 1, wherein the copper ion chelating agent is ethylenediaminetetraacetic acid or a salt thereof. 3. The concentration of a chelating agent in a chemical copper plating solution according to claim 1 or 2, wherein the salt of a heavy metal ion is a salt of an ion of an alkaline earth metal, a transition metal, aluminum, tin or lead. Method for measuring the concentration of substance ions and reducing agent.