JP3792981B2 - Chlorine concentration measuring device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a chlorine concentration measuring apparatus for measuring the concentration of free chlorine contained in a plating solution such as an electrolytic plating solution.
[0002]
[Prior art]
Conventionally, as a chlorine concentration measuring device for measuring the concentration of chlorine in a plating solution, one described in Japanese Patent Application Laid-Open No. 8-313481 is known.
[0003]
FIG. 8 is a schematic view showing a conventional chlorine concentration measuring apparatus. This chlorine concentration measuring device is a two-electrode type measuring device that measures the concentration of chlorine in the plating solution.
[0004]
In this chlorine concentration measuring apparatus, reference numeral 102 denotes a flow cell. A plating solution inlet 104 is formed on the lower side of the flow cell 102, and a plating solution outlet 106 is formed on the lateral side. A plating solution 108 is introduced into the flow cell 102, and a cylindrical detection electrode support 110 is immersed in the plating solution 108, and a circular detection electrode (platinum) is formed on the outer peripheral surface of the detection electrode support 110. Electrode) 112 is attached. Further, a cylindrical counter electrode support 114 is immersed in the plating solution 108, and a circular counter electrode (silver / silver chloride electrode) 116 is attached to the outer peripheral surface of the detection electrode support 114. Reference numeral 118 denotes a detection pole rotating motor, reference numeral 120 denotes an applied voltage circuit, and reference numeral 122 denotes an ammeter.
[0005]
The flow cell 102 is partitioned into a detection electrode chamber 126 and the counter electrode chamber 128 by a partition 124, beads for detecting electrode cleaning in the plating solution in the detection electrode chamber 126 (not shown) is turned .
[0006]
When the chlorine concentration is measured using a conventional chlorine concentration measuring device, the detection electrode support 110 is rotated by the operation of the motor 118, thereby rotating the detection electrode 112. Then, a measurement voltage is applied between the detection electrode 112 and the counter electrode 116 by the applied voltage circuit 120, and at this time, a measurement current i flowing between the detection electrode 112 and the counter electrode 116 is detected by the ammeter 122.
[0007]
[Problems to be solved by the invention]
However, in the conventional chlorine concentration measurement device, the counter electrode (silver / silver chloride electrode) 116 also serves as a reference (reference) electrode that provides a reference for the potential. It is difficult to apply a potential accurately.
[0008]
Further, in the conventional chlorine concentration measuring apparatus, this error is reduced by limiting the measurement current to 0.2 μA or less, but the measurement method itself is limited such that only a small current can flow. . Furthermore, even if a weak current flows repeatedly, the counter electrode (silver / silver chloride electrode) 116 deteriorates, and the silver / silver chloride electrode deteriorates.
[0009]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a chlorine concentration measuring device that can accurately measure the chlorine concentration by eliminating measurement errors due to deterioration of the silver / silver chloride electrode. And
[0011]
[Means for Solving the Problems]
In order to solve the above-described problem, a chlorine concentration measuring device according to claim 1 is a chlorine concentration measuring device that measures the concentration of chlorine contained in a plating solution. A counter electrode disposed in the container, a working electrode disposed in the container, a reference electrode disposed in the container, and a potential of the working electrode with respect to the reference electrode being a predetermined potential. A power source for passing a current between the working electrode and the counter electrode, and a control means for obtaining a chlorine concentration of the plating solution based on a current value flowing between the working electrode and the counter electrode, The control means controls the power supply to sweep the voltage of the working electrode with respect to the reference electrode; and a recording means for recording a current value flowing between the working electrode and the counter electrode when the voltage is swept. The chlorine concentration is different Correlation recording means for recording the correlation between the current value and chlorine concentration recorded by the recording means for a plurality of calibration plating solutions, and a calibration curve created based on the correlation recorded by the correlation recording means are stored. And means for determining the chlorine concentration of the plating solution based on the current value recorded by the recording unit and the calibration curve for the plating solution of unknown chlorine concentration.
A chlorine concentration measuring device according to claim 2 is the chlorine concentration measuring device according to claim 1, further comprising drive means for rotating the working electrode.
[0012]
Furthermore, the chlorine concentration measuring apparatus according to claim 3 is the chlorine concentration measuring apparatus according to claim 1 or 2 , wherein the working electrode has a smooth electrode surface.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of a chlorine concentration measuring method according to the present invention will be described below with reference to the drawings.
[0014]
FIG. 1 is a schematic configuration diagram of a chlorine concentration measuring apparatus according to an embodiment of the present invention. The chlorine concentration measuring device includes a measuring cell 1, and the measuring cell 1 is filled with a copper sulfate plating solution (hereinafter simply referred to as a plating solution). In the measurement cell 1, a counter electrode 2, a working electrode 3, and a reference electrode 4 are provided. The counter electrode 2 is made of a copper electrode (Cu), a platinum electrode (Pt), stainless steel (SUS) or the like, and the working electrode 3 is made of any conductive material that is inactive in the plating solution to be measured, For example, a platinum electrode (Pt) or a gold electrode (Au) is used, and a silver / silver chloride electrode or a saturated calomel electrode is used as the reference electrode 4.
[0015]
The working electrode 3 is connected and connected to the motor 8 via the rotary shaft 31, and the working electrode 3 is rotated at a predetermined rotational speed (for example, 2500 rpm) in the plating solution as the motor 8 is driven. Let The working electrode 3 has a smooth electrode surface with a diameter of about 5 mm. Since the working electrode 3 has this smooth electrode surface, current can be easily passed between the working electrode 3 and the counter electrode 2.
[0016]
The counter electrode 2 is connected to the potentiostat 5 via the wiring 20, the working electrode 3 is connected to the potentiostat 5 via the wiring 30, and the reference electrode 4 is connected to the potentiostat 5 via the wiring 40. Connected with. The potentiostat 5 is a kind of constant voltage power source, and allows a necessary current to flow between the working electrode 3 and the counter electrode 2 so that the potential of the working electrode 3 with respect to the reference electrode 4 becomes a predetermined potential. .
[0017]
The potentiostat 5 is further connected to the control unit 6. A computer or the like is used for the control unit 6, a function for measuring and recording the current output from the potentiostat 5 (function as a recording means) , and a function for recording the correlation between the measured current value and the chlorine concentration ( A function as a correlation recording means) , a function for calculating the chlorine concentration by comparing the current value with the above correlation ( a function as a means for obtaining the chlorine concentration of the plating solution) , and a function for indicating the potential applied to the potentiostat 5 (Function as means for controlling the power supply) .
[0018]
A setting means 7 is further connected to the control unit 6. The setting means 7 sets the chlorine concentration of the plating solution or sets an arbitrary potential.
[0019]
In addition to chlorine, the plating solution contains a plurality of organic substances such as dipropyl disulfide-3,3′-sulfonic acid, polyethylene glycol (PEG), and the like in the concentration measurement of such organic substances. Also, this chlorine concentration measuring device (a conventionally used additive measuring device) is used. Any one of the organic substance concentration measurement and the chlorine concentration measurement may be performed first.
[0020]
Next, the chlorine concentration measuring method according to the present invention will be described.
This chlorine concentration measuring method is roughly provided with two stages of “creating a calibration curve” and “measuring the chlorine concentration of the plating solution”. “Creation of calibration curve” is to obtain a correlation between the obtained current value and chlorine concentration by using a plating solution prepared in advance and having a plurality of known chlorine concentrations. “Measurement of chlorine concentration in plating solution” is the same as “Creation of calibration curve” for plating solution with unknown chlorine concentration, and measures the chlorine concentration of plating solution based on the above correlation. It is. In the following, description will be given in the order of “creation of calibration curve” and “measurement of chlorine concentration in plating solution”.
[0021]
A Creation of Calibration Curve First, the calibration curve creation process will be described. In this embodiment, a case where four types of calibration plating solutions are used will be described.
[0022]
In preparing the calibration curve, first, a calibration plating solution is put in a separate beaker or the like outside the measurement cell 1, and a predetermined amount of hydrochloric acid is added to the calibration plating solution, followed by thorough stirring. Thereby, the Nth calibration plating solution having a predetermined chlorine concentration is prepared (step A-1). The chlorine concentration of the Nth calibration plating solution is set in the setting means 7 (step A-2). The chlorine concentration of the Nth calibration plating solution set by the setting means 7 is stored in the control unit 6.
[0023]
The amount of the Nth calibration plating solution prepared in step A-1 is such that the counter electrode 2, the working electrode 3 and the reference electrode 4 are sufficiently immersed in the measurement cell 1 (for example, 100 ml). Then, transfer from the beaker into the measurement cell 1 (step A-3). Since the measured current value directly reflects the chlorine concentration, not the amount of chlorine ions, the amount of plating solution does not affect the measurement accuracy at all.
[0024]
Next, the motor 8 is driven to rotate the working electrode 3 in the plating solution (step A-4). The purpose of the rotation of the working electrode 3 is to keep the flow of the plating solution on the surface of the working electrode 3 during concentration measurement constant. For that purpose, it is necessary to rotate at a high speed of 1000 rpm or more. In the present embodiment, the rotational speed is set to 2500 rpm. Further, if the working electrode 3 is rotated, the working electrode 3 can be easily moved as compared with other methods such as vertical movement and vibration.
[0025]
Next, with the working electrode 3 rotated, the voltage of the working electrode 3 with respect to the reference electrode 4 is swept (step A-5). Note that the voltage to be swept is set in advance from the setting means 7, and the voltage is stored in the control unit 6. The measurement conditions of the voltage sweep at this time are sweep start voltage +500 mV, upper limit voltage +1575 mV, lower limit voltage -225 mV, and voltage sweep speed 100 mV / sec. Then, as shown in FIG. 3, (1) first forward sweep, (2) reverse sweep, and (3) second forward sweep and voltage change pattern are triangular waves. Specifically, the potentiostat 5 is connected between the counter electrode 2 and the working electrode 3 in accordance with an instruction from the control unit 6 so that the voltage is swept according to the voltage change pattern of (1), (2), and (3). Current flows between them. The relationship between the current value (mA) and the voltage value (mV) at this time is as shown in FIG.
[0026]
As shown in FIG. 4, in one cycle from the start of the sweep to the end of the sweep, one waveform related to the current value (mA) and the voltage value (mV), that is, a cyclic voltammogram (CV, hereinafter simply referred to as CV). Is obtained (step A-6).
[0027]
From the measured CV, the current (I _ch ) resulting from the electrode reaction of chlorine represented by the following formula (1) and the current (I _con ) in the portion not including the chlorine current are read (step A-7).
Formula (1)
2Cl ⁻ → Cl ₂ + 2e ⁻
[0028]
Specifically, as shown in FIG. 5, from the measured CV, the current during the forward sweep at two specific potentials, that is, the current during the first forward sweep, is the current (I _ch : It reads as current (I _con : Contamination current) in a portion not including Chloride Current) and chlorine current. Here, the “current due to the electrode reaction of chlorine (I _ch )” means the limiting diffusion current of the oxidation reaction of chlorine, and the “current in a portion not including the current of chlorine (I _con )” The current value at a voltage at which the reaction between copper and chlorine does not occur, which means the background current due to the formation of an oxide film on the electrode, the reaction of impurities in the plating solution, and the like. The specific voltage at this time is set to +1075 mV and +1425 mV.
[0029]
Next, the control unit 6 obtains a difference between the read current (I _con ) and the current (I _ch ) as a measured current value (I _diff ) (step A-8). The obtained measured current value (I _diff ) is set in the setting means 7 in step A-2 described above, and corresponds to the chlorine concentration (μl / L) of the Nth calibration plating solution stored in the control unit 6. And stored in the control unit 6 (step A-9). Since the measured current value (I _diff ) is the difference between the read current (I _con ) and the current (I _ch ), the chlorine concentration (μl / L) of the calibration plating solution in step A-14 described later L) and the accuracy of the result of the correlation between the measured current value (I _diff ) are increased.
[0030]
When the current measurement process from step A-5 to step A-9 is completed, the drive of the motor 7 is stopped and the rotation of the working electrode 3 in the plating solution is stopped (step A-10). Then, the Nth calibration plating solution is discharged from the measurement cell 1 (step A-11). Thereby, a series of processes of the Nth calibration plating solution is completed.
[0031]
When a series of processes of the Nth calibration plating solution is completed, it is determined whether N has reached the number of calibration plating solutions. In the present embodiment, N <4 is determined as an example in which four types of calibration plating solutions are used (step A-12). If it is determined in step A-12 that N <4, the process proceeds to step A-13, where “N ← N + 1” is performed, and the above-described steps A-1 to A-11 are performed again. If it is determined in step A-12 that N <4 is not satisfied, the control unit 6 obtains a correlation result between the chlorine concentration (μl / L) of the calibration plating solution and the measured current value (I _diff ). It is created (step A-14).
[0032]
The results of correlation between the chlorine concentration (μl / L) of the calibration plating solution and the measured current value (I _diff ) are as follows.
When N = 1 100 μl / L 347.5 / μA
When N = 2 150 μl / L 375.2 / μA
When N = 3 200 μl / L 410.3 / μA
When N = 4 250 μl / L 453.1 / μA
[0033]
Next, based on the result of this correlation, a calibration curve as shown in FIG. 6 is obtained (step A-15). This calibration curve may be a linear function as in the following equation (2) or a quadratic function as in the following equation (3).
Linear function: Formula (2)
C = 1.421 * I-388.406
Quadratic function: Formula (3)
C = −0.0043 * I2 + 4.8725 * I-107.1
(C: HCl concentration (μl / L), I: I _diff / μA)
Note that there is an advantage that the error is smaller in the case of the calibration curve of the quadratic function than in the case of the calibration curve of the linear function.
[0034]
When this calibration curve is obtained, it is stored in the control unit 6 (step A-16. Function of the control unit 6 as a means for storing the calibration curve) . Thus, a series of calibration curve creation steps is completed.
[0035]
Chlorine concentration measurement of B plating solution will now be described with the chlorine concentration measurement step of the plating solution. In the measurement of the chlorine concentration of a plating solution whose chlorine concentration is unknown, first, an amount sufficient to immerse the counter electrode 2, the working electrode 3, and the reference electrode 4 in the measuring cell 1 (for example, , 100 ml) into the measuring cell 1 (step B-1). Note that the measurement current value, which will be described later, reflects the chlorine concentration, not the amount of chlorine ions, so the amount of plating solution does not affect the measurement accuracy at all.
[0036]
Next, the motor 8 is driven to rotate the working electrode 3 in the plating solution (step B-2). The rotation of the working electrode 3 is intended to keep the flow of the plating solution on the electrode surface during concentration measurement constant as in the case of the calibration plating solution. For this purpose, the working electrode 3 is rotated at a high speed of 1000 rpm or more. There is a need to. In the present embodiment, the rotational speed is set to 2500 rpm. Further, if the working electrode 3 is rotated, the working electrode 3 can be easily moved as compared with other methods such as vertical movement and vibration.
[0037]
Next, with the working electrode 3 rotated, the voltage of the working electrode 3 with respect to the reference electrode 4 is swept (step B-3). Note that the voltage to be swept is set in advance from the setting means 7, and the voltage is stored in the control unit 6. The measurement conditions of the voltage sweep at this time are the sweep start voltage +500 mV, the upper limit voltage +1575 mV, the lower limit voltage -225 mV, and the voltage sweep rate 100 mV / sec, as in the case of obtaining the calibration curve of the calibration plating solution. Then, as shown in FIG. 3, (1) first forward sweep, (2) reverse sweep, and (3) second forward sweep and voltage change pattern are triangular waves. Specifically, the potentiostat 5 is placed between the counter electrode 2 and the working electrode 3 under the control of the control unit 6 so that the voltage is swept in the voltage change pattern of (1), (2), and (3). Current is passed through. The relationship between the current value (mA) and the voltage value (mV) at this time is as shown in FIG.
[0038]
As shown in FIG. 4, in one cycle from the start of the sweep to the end of the sweep, one waveform related to the current value (mA) and the voltage value (mV), that is, a cyclic voltammogram (CV, hereinafter simply referred to as CV). Is obtained (step B-4).
[0039]
From the measured CV, the current (I _ch ) resulting from the electrode reaction of chlorine represented by the following formula (4) and the current (I _con ) in the portion not containing the chlorine current are read (step B-7).
Formula (4)
2Cl ⁻ → Cl ₂ + 2e ⁻
[0040]
Specifically, as shown in FIG. 5, from the measured CV, the current during the forward sweep at two specific potentials, that is, the current during the first forward sweep, is the current (I _ch : It reads as current (I _con : Contamination current) in a portion not including Chloride Current) and chlorine current. Here, the “current due to the electrode reaction of chlorine (I _ch )” means the limiting diffusion current of the oxidation reaction of chlorine, and the “current in a portion not including the current of chlorine (I _con )” The current value at a voltage at which the reaction between copper and chlorine does not occur, which means the background current due to the formation of an oxide film on the electrode, the reaction of impurities in the plating solution, and the like. The specific voltage at this time is set to +1075 mV and +1425 mV.
[0041]
In the control unit 6, a difference between the read current (I _con ) and the current (I _ch ) is obtained as a measured current value (I _diff ) (step B-6). The obtained measured current value (I _diff ) is substituted into the linear function I or the quadratic function I stored in step A-16, and the chlorine concentration of the plating solution is obtained (step B). -7).
[0042]
When the current measurement process from step B-3 to step B-7 is completed, the motor 8 is stopped to stop the rotation of the working electrode 3 in the plating solution (step B-8). Then, the plating solution is discharged from the measurement cell 1 (step A-9). Thereby, a series of processes in the plating solution concentration measurement process is completed.
[0043]
In the embodiment of the present invention, the case where four types of calibration plating solutions are used has been described as an example, but at least two types of calibration plating solutions may be used.
[0044]
【The invention's effect】
As described above in detail, according to the chlorine concentration measuring apparatus according to the present invention, the power source passes a current between the working electrode and the counter electrode so that the potential of the working electrode with respect to the reference electrode becomes a predetermined potential, Since the chlorine concentration of the plating solution is obtained based on the current value flowing between the working electrode and the counter electrode, the measurement error due to the deterioration of the silver / silver chloride electrode is eliminated and the chlorine concentration is accurately measured. it can.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a chlorine concentration measuring apparatus according to an embodiment of the present invention.
FIG. 2 is a flowchart showing processing steps for creating a calibration curve.
FIG. 3 is a diagram illustrating a voltage sweep method.
4 is a diagram showing a cyclic voltammogram based on the voltage sweep method shown in FIG. 3. FIG.
FIG. 5 is a diagram showing a part of the cyclic voltammogram shown in FIG. 4;
FIG. 6 is a diagram showing a linear function and a quadratic function showing a correlation between a chlorine concentration and a measured current value.
FIG. 7 is a flowchart showing processing steps for measuring the chlorine concentration of a plating solution.
FIG. 8 is a schematic view of a conventional chlorine concentration measuring apparatus .
[Explanation of symbols]
1 Measurement Cell 2 Counter Electrode 3 Working Electrode 4 Reference Electrode 5 Potentiostat 6 Control Unit 7 Setting Means

Claims (3)

In a chlorine concentration measuring device that measures the concentration of chlorine contained in the plating solution,
A container for containing a plating solution;
A counter electrode disposed in the container;
A working electrode disposed in the container;
A reference electrode disposed in the container;
A power source for passing a current between the working electrode and the counter electrode so that the potential of the working electrode with respect to the reference electrode becomes a predetermined potential;
Control means for determining the chlorine concentration of the plating solution based on the current value flowing between the working electrode and the counter electrode;
With
The control means controls the power supply to sweep the voltage of the working electrode with respect to the reference electrode; and a recording means for recording a current value flowing between the working electrode and the counter electrode when the voltage is swept. A correlation recording unit that records a correlation between the current value recorded by the recording unit and the chlorine concentration for a plurality of calibration plating solutions having different chlorine concentrations, and a correlation recording unit that is created based on the correlation recorded by the correlation recording unit; Chlorine comprising means for storing a calibration curve, and means for determining the chlorine concentration of the plating solution based on the current value recorded by the recording unit and the calibration curve for a plating solution with an unknown chlorine concentration Concentration measuring device. In the chlorine concentration measuring apparatus according to claim 1 ,
A chlorine concentration measuring device further comprising a driving means for rotating the working electrode. In the chlorine concentration measuring apparatus according to claim 1 or 2 ,
The said working electrode has a smooth electrode surface, The chlorine concentration measuring apparatus characterized by the above-mentioned.

Images