JPS6338094B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the pH of an aqueous solution containing copper ions and a reducing agent thereof, such as a chemical copper plating solution, using a copper oxide electrode.

Conventionally, aqueous solutions such as chemical copper plating solutions were used.
The PH was measured using a glass electrode as a main electrode and an aqueous electrode as a reference electrode, and the PH of an aqueous solution as a potential (see, for example, Japanese Patent Laid-Open No. 44434/1983).

However, when continuously measuring the pH of a solution with a pH of 11 or higher, such as a chemical copper plating solution, using the above method, the measurement error is as large as ±10%, and the glass wall of the glass electrode is attacked by alkali. The drawback is that the values change over time, so in order to reduce measurement errors, the glass electrode must be cleaned with a pH standard solution at predetermined intervals, and in order to reduce the change in measured values over time, it is necessary to clean the glass electrode with a pH standard solution. There was the inconvenience of having to take measurements intermittently.

Therefore, as an electrode without the above drawbacks,
Mercury oxide, silver oxide, antimony oxide, zinc oxide,
Cadmium oxide and other materials were considered. However, silver oxide and antimony oxide are attacked by the reducing agent in the chemical copper plating solution, and zinc oxide and cadmium oxide are attacked by the substitution reaction with copper ions, so both of them are affected by the pH of the aqueous solution such as the chemical copper plating solution. It could not be used for measurement.

The object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a PH that can accurately and continuously measure the PH of aqueous solutions such as chemical copper plating solutions.
To provide a measurement method.

In order to achieve this object, the present invention is characterized in that the PH measurement is performed using a copper oxide electrode and after adding a substance that suppresses the sinking reaction accompanying PH measurement to the aqueous solution. .

First, before explaining the present invention in detail with reference to examples, an outline of the present invention will be explained. It is possible to observe the potential based on the reaction of Eq.

Cu ₂ O + H ₂ O → 2CuO + 2H ⁺ + 2e ^- E = 0.669 + 0.0591PH However, E in the above formula is expressed as the potential (V) based on the hydrogen electrode.

Since the reaction in the above equation is related only to pH, even chemical copper plating solutions have the characteristic that they are not affected by the copper ion concentration in the solution. In addition, even if the cupric oxide on the surface is dissolved by the chelating agent of divalent copper ions in the chemical copper plating solution, the cuprous oxide on the electrode surface is oxidized by the oxygen dissolved in the plating solution. It is stable because it is oxidized to cupric oxide, and the cuprous oxide is replenished by the oxidation of the underlying metal copper. Therefore, by detecting the potential using a reference electrode, the pH of the plating solution can be detected.

Next, the method for manufacturing such a copper oxide electrode will be described in detail as follows.

Prepare metal copper to be used as an electrode, and
Etch the surface with 14N acid. The metal copper used at this time should preferably have a purity of 99.9% or higher, and its shape may be either a plate or a wire. The acid used for etching is preferably an inorganic acid such as hydrochloric acid, sulfuric acid or nitric acid, preferably nitric acid.

Next, the etched copper electrode is treated with an alkali metal hydroxide solution to coat the surface of the metallic copper with an oxide film. Practical alkali metal hydroxides used in this case are KOH and NaOH.

By the way, when measuring the pH of a chemical copper plating solution using such a copper oxide electrode, there is a special consideration that must be taken into account because the chemical copper plating solution contains divalent copper ions and reducing agents. The purpose is to prevent plating reactions from occurring on the oxide electrode. When a plating reaction occurs, the copper oxide electrode will show the plating reaction potential, not the potential related to PH as shown above, so the PH
This is because it becomes impossible to measure.

Therefore, in order to solve such problems, in the present invention, a substance that stops the catalytic action of the reducing agent is added to the chemical copper plating solution, and the PH is measured in a state where the plating reaction does not occur. It takes .

Suitable such substances are organic compounds containing nitrogen and sulfur in their molecules, and inorganic compounds containing sulfur. Such a substance stops the reaction of a reducing agent such as formaldehyde by adsorbing on the surface of a copper oxide electrode, and the following substances and concentrations are particularly suitable.

The amount of inorganic sulfur compounds that generate sulfur ions in aqueous solution may be 1 to 50 mg per unit, and nitrogen-containing heteroaromatic compounds such as 2-methylimidazole and 1,2,3-benzotriazole are
0.1-100mg is suitable.

The plating reaction of heterocyclic aromatic compounds containing nitrogen and sulfur, such as 2-mercaptobenzothiazole and 2-benzimidazolethiol, stops at 0.01 to 10 mg.

Heteroaromatic compounds containing sulfur, such as thiophene, and aliphatic compounds, such as thiourea and thioacetamide, each have a dosage of 0.1 to 10 mg.
The reaction stops.

When using a complex containing the above compound such as copper dimethyldithiocarbamate, the plating reaction stops when 1 to 100 mg is added due to its large molecular weight. For active agents, it is necessary to add 0.1 to 10 g.

In addition, the above-mentioned copper oxide electrode can stably detect the potential at a pH of 11 or higher, so when measuring a pH of 11 or lower, add alkali to the chemical copper plating solution.
Just measure the PH. Suitable alkalis for this purpose include alkali metal hydroxides such as NaOH and KOH, and alkali metal salts of weak acids such as sodium carbonate and sodium phosphate.

Next, in order to explain the present invention more specifically, the present invention will be described in detail below using Examples and in comparison with Comparative Examples. However, since the embodiments described below are merely examples of application of the present invention, it goes without saying that the present invention is not limited only to the following embodiments. There is no doubt that the detection method and apparatus relate to the present invention.

First, the PH detection device used in the example will be explained in detail with reference to the drawings. The figure shows a device commonly used in the following examples, in which chemical copper plating solution 1 and mixed solution 2 are sampled at a rate of 30 ml/h using a metering pump 4.
The mixture was thoroughly mixed using mixer 5. Detect this cell 8
was introduced into the PH measurement chamber 10 and brought into contact with the copper oxide electrode 6. A saturated calomel electrode (SCE) 7 was provided in one of the reference electrode chambers 9, and a saturated Kcl solution 3 was constantly supplied by a metering pump 4. 11 is a diaphragm. The copper oxide electrode is a bare copper wire with a diameter of 1 mm (purity of 99.9% or more).
was etched with 0.1-14N nitric acid for 1-10 seconds, then etched in 0.1-1N caustic soda solution for 5 seconds.
It was oxidized for ~30 minutes.

The results of measuring the pH of a chemical copper plating solution using such an electrode and device are shown below.

Comparative Example (1) The pH of the following chemical copper plating solution (1) was detected using the apparatus shown in the figure. In this case, since the PH can be easily detected when the PH is about 11 or higher, the mixed solution 2 shown in the figure was not used, and the chemical copper plating solution was directly brought into contact with the copper oxide electrode to determine the PH.

(a) Chemical copper plating solution CuSO ₄・5H ₂ O EDTA2Na NaOH 37% formalin K ₂ S Ethoxy surfactant water 13g 40g Amount to adjust pH to 11-13.5 3ml 0.1mg 0.1g Amount to make 1 (a) The chemical copper plating solution can be used in the manufacturing process of printed circuit boards, and has a rate of depositing metallic copper at approximately 1 to 3 μm/h when plating is performed at 70°C.

The results of measuring the pH of the plating solution after cooling it to 25°C show that the relationship between the pH of the plating solution and the detected potential is expressed by the following equation (1):
The following relationship was obtained, and the pH of the plating solution could be determined accurately and stably.

^E = -0.0019 The PH of a chemical copper plating solution can be easily measured using copper oxide without stopping and performing any special treatment.

However, the measurement temperature of the chemical copper plating solution (a) was set to 40℃.
In the case of PH measurement using physical electrodes was not possible.

This tendency is particularly noticeable when the measurement temperature is high or the pH of the chemical copper plating solution is high, especially when the pH is 13.
It was most significant when it exceeded .

As mentioned above, in measuring the pH of a chemical copper plating solution using a copper oxide electrode, strict control of the measurement temperature is required.

Comparative Example (2) Comparative Example (1) uses a chemical copper plating solution that operates at a high temperature of 70°C, whereas Comparative Example (2) uses a chemical copper plating solution that reacts at room temperature. It is something.

The chemical copper plating solution having the composition (b) has the ability to deposit metallic copper at a rate of 0.5 to 2 μm/h at room temperature.

This plating solution was applied to a copper oxide electrode under the same conditions as in Comparative Example (1), that is, without using Mixed Solution 2 shown in the figure.
When measuring PH, the detection potential at 25℃ indicates the deposition reaction potential of chemical copper plating, and the PH
It was impossible to detect.

(b) Chemical copper plating solution CuSO ₄・5H ₂ O Lotusel salt glycine NaOH 37% formalin water 10g 50g 8g Amount to adjust pH to 11-13.5 25ml Amount to adjust to 1 Example (1) Comparative example (1), ( The pH of the solution was detected using the same solution and the same equipment as those used in 2) (a) and (b). In this example, by mixing the mixed liquid 2 shown in the figure with the mixer 4, it is possible to stably demonstrate the ability of the copper oxide electrode even when it cannot be detected in comparative examples (1) and (2). be.

The following solution containing a nitrogen-containing heterocyclic aromatic compound was used as a mixed solution mixed with the chemical copper plating solution.

(c) Mixed liquid 1,2,3-benzotriazole water 0.1-100 mg 1 amount After mixing this liquid well with chemical copper plating solution (a),
When the liquid pH was measured using a copper oxide electrode, Comparative Example (1)
Even at a temperature of 40°C, which was impossible to measure due to the deposition reaction potential, the pH of the chemical copper plating solution was
The relationship between the detection potential and the detection potential is as shown in the following equation, and the pH is stabilized.
was able to be detected.

E=-0.00016×PH ^5.82
(mVvsS.CE) ...(2) In addition, for chemical copper plating solution (b), after mixing the mixed solution as in this example, copper does not remain on the copper oxide electrode even at 25℃. There was no precipitation, and the detection potential now had exactly the same relationship as Equation (1), making it possible to stably measure PH.

As described above, according to the method of the present invention, PH can be easily measured using an extremely simple method even under conditions and liquids where it is difficult to detect PH using a copper oxide electrode. I understood.

Furthermore, the pH of nitrogen-containing heteroaromatic compounds other than 1,2,3-benzotriazole was detected using the same method as above. It was found that nitrogen heteroaromatic compounds and their derivatives have exactly the same effect.

Example (2) The pH of a chemical copper plating solution was measured in the same manner as in Example (1) using a mixed solution (d) with the following composition. The relationships shown in equations (1) and (2) are obtained both when measuring and when measuring room temperature reaction type chemical copper plating solution (b), respectively.
It was found that the present invention has the effects.

It has also been found that such an effect is commonly observed in heterocyclic aromatic compounds containing nitrogen and sulfur other than 2-mercaptobenzothiazole and their derivatives.

(d) Mixed liquid 2-mercaptobenzothiazole water 0.01 to 10 mg Amount to be 1 Example (3) Using mixed liquid (e) with the following composition, prepare a chemical copper plating solution in the same manner as in Example (1). When PH was measured, both when measuring the chemical copper plating solution (a) at 40℃ and when measuring the room temperature reaction type chemical copper plating solution (b),
Measurements could be made in exactly the same manner as in Examples (1) and (2).

It was also found that such effects are common to sulfur-containing heteroaromatic compounds such as thiophene and their derivatives.

(e) Mixed liquid Thiophene water 0.1 to 10 mg Amount to be 1 Example (4) Using the mixed liquid (f) with the following composition, the PH of the chemical copper plating solution was measured in the same manner as in Example (1). However, both when measuring the chemical copper plating solution (a) at 40℃ and when measuring the room temperature reaction type chemical copper plating solution (b),
It was possible to measure in exactly the same manner as in Examples (1) to (3).

It has been found that such effects are common not only to thiourea but also to aliphatic compounds containing nitrogen and sulfur, such as thioacetamide, and their derivatives.

(f) Mixed solution Thiourea water 0.1 to 10 mg Amount to be 1 Example (5) The PH of a chemical copper plating solution was measured in the same manner as in Example (1) using a mixed solution (i) with the following composition. However, Examples (1)-(4 ) could be measured in exactly the same way.

The phosphoric ester used in the mixed solution is a phosphoric ester containing an ethoxy group, which is known as a type of surfactant that is extremely stable in alkaline solutions.
Such substances include, for example, ADEKA COL manufactured by Asahi Denka Co., Ltd.
It is commercially available under a name such as PS236.

The effects of phosphoric esters on the present invention were not only possessed by the above-mentioned surfactants, but were common to phosphoric esters having the following structures. Here, R includes an alkyl group or an allyl group, and X includes H, an alkyl group, an aryl group, or the like.

(i) Mixed solution Adecokol PS236 Water 0.1-10g/1 Example (6) Using the mixed solution (g) with the following composition, adjust the pH of the chemical copper plating solution in the same manner as in Example (1). As a result of measurement, Examples (1) to (5) were found to be the same when the chemical copper plating solution (a) was measured at 40℃ and when the room temperature reaction type chemical copper plating solution (b) was measured at 25℃. ) could be measured in exactly the same way.

(g) Mixed solution Copper dimethyldithiocarbamate solution 1 to 100 mg Amount to be 1 Example (7) Using the mixed solution (h) with the following composition, adjust the pH of the chemical copper plating solution in the same manner as in Example (1). As a result of measurements, Examples (1) to ( It turns out that it can be measured in exactly the same way as 6).

It was also found that this effect is not limited to K ₂ S, but is common to compounds that generate sulfur ions in aqueous solution, such as Na ₂ S.

(h) Mixed liquid K ₂ S water 1 to 50 mg 1 Example (8) This example shows that even for solutions with a pH of 11 or less, which is the lower limit of the PH measurement method using a copper oxide electrode, the copper oxide It enables pH detection with an electrode, and uses a mixed solution (j) with the following composition to create a chemical copper plating solution (k) with the following composition.
The PH was measured at 25°C using the same device as in Example (1).

By using this method, even chemical copper plating solutions with a pH of 11 or less can have a pH level within the detection cell that is measured using a copper oxide electrode.
It was found that the pH value was 11 or higher, indicating that there were no problems with PH measurement and that detection was extremely stable. in the mixture
When the NaOH concentration is 3g/, the following formula (3)
It was also found that PH can be measured using the following relationship.

E=-0.0086PH ^5.14 (mVvsS.CE) ...(3) Furthermore, the alkalis that can be used in the mixed solution are:
It has also been found that, without being limited to NaOH, alkali metal hydroxides such as KOH and alkali metal salts of weak acids such as Na ₂ CO ₃ and Na ₃ PO ₄ have exactly the same effect as NaOH.

(j) Mixed liquid NaOH Water 1~10g Amount to make 1 (k) Chemical copper Plating liquid CuSO ₄ 5H ₂ O EDTA ₂ Na NaOH 37% formalin K ₂ S Ethoxy surfactant water 13g 40g PH to 7~13.5 Amount: 3 ml Example (9) In this example, alkali and
By adding both of the compounds that stop the plating reaction at the same time, the conditions are such that the precipitation reaction occurs at the copper oxide electrode, and the pH of the chemical copper plating solution is 11.
This paper shows a method that enables PH measurement also in the following cases.

Using the same equipment as in Example (1), the chemical copper plating solution was
The liquid with the composition (k), that is, the liquid with the liquid composition (a).
PH detection was attempted at 40°C and 25°C for two types, one with a pH of 7 to 13.5 and the other with the liquid composition of (b) with a pH of 7 to 13.5. Mixture
It was found that the effect of (l) was extremely good, and that PH detection under a wide range of conditions as the object of the present invention could be performed extremely stably.

As shown in this example, even if an alkali to raise the pH of the test solution and a compound to stop the reaction of formalin are added to the mixed solution, the effects of the two act completely independently and there is no effect. It has also become clear that they do not interact.

Also, set the pH of the chemical copper plating solution to 7 to 13.5.
Detection was according to formula (4), and on the other hand, the detection potential of the room temperature reaction type chemical copper plating solution (b) with a pH of 7 to 13.5 was exactly the same as formula (3).

E=-0.00072PH ^6.22 (mV vs SCE) ...(4) (l) Mixed liquid 1,2,3-benzotriazole NaOH Water 1-100mg 3g Amount to be 1 As explained above, according to the present invention, Even if the composition of the chemical copper plating solution used as the test solution or the usage conditions vary greatly, PH can always be measured accurately and continuously. Using a copper oxide electrode, it is possible to measure the pH of plating solutions and the associated liquid quality management extremely easily and economically.
A PH measurement method can be provided.

[Brief explanation of the drawing]

The figure is a configuration diagram showing an example of an apparatus for implementing the PH measurement method using a copper oxide electrode according to the present invention. 1...PH test solution (chemical copper plating solution, etc.), 2...
...mixture, 3...reference electrode solution, 4...metering pump, 5...mixer, 6...copper oxide electrode, 7...
... Reference electrode, 8 ... Detection cell, 9 ... Reference electrode chamber, 10 ... PH measurement chamber, 11 ... Diaphragm.

Claims (1)

[Scope of Claims] 1. A method for measuring the pH of an aqueous solution containing divalent copper ions and a reducing agent for divalent copper ions using a copper oxide electrode, in which a sulfur compound of an alkali metal, triazole, imidazole, thiazole is added to the aqueous solution. ,
The method is configured to measure the pH of the aqueous solution after adding at least one selected from the group consisting of thiophene, thiourea, thioacetamide, ethoxy-containing phosphate ester, dithiocarbamate, or their derivatives. A method for measuring PH using a copper oxide electrode. 2. Claim 1 is characterized in that the PH of the aqueous solution is measured by adding a specified amount of alkali to the aqueous solution to change the PH of the aqueous solution by a specified value in advance. PH measurement method using a copper oxide electrode.