JP3028449B2 - Control method of power supply device for electrodeposition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Industrial applications] plating, dispersion plating, electrolytic coloring,
This is a method for obtaining a stable film, coloration, and anodic oxidation which are not affected by changes in the processing area in a film forming apparatus utilizing electrodeposition or anodic oxidation such as electrodeposition coating or oxide film formation.

[0002]

2. Description of the Related Art Electroplating utilizing electrodeposition of metal ions, dispersion plating in which particles charged with colloids and surfactants are co-deposited with metal ions, and metal is deposited in fine pores of an oxide film. Electroplating for coloring, electrodeposition coating to form a coating film by electrophoretically depositing paint particles charged with colloids and surfactants, electrodeposition and electrodeposition to form an oxide film by anodic oxidation on metal surfaces For many electric depositions such as film formation by anodic oxidation, it is necessary to change the setting of the voltage or current of the power supply or to change the processing time depending on the area to be processed. This setting change can be misleading and erroneous, or if the shape of the part to be processed is complicated, the area calculation is complicated and it is often necessary to generate a stable and high-yield film. With difficulties.

[0003]

SUMMARY OF THE INVENTION The inventor of the present invention has an object to automatically follow a current even when the area of a processing portion changes, and to always generate a stable electrodeposition film or oxide film. This method, which tried to design, detects changes in electrical parameters such as changes in impedance caused by changes in processing area, and calculates appropriate currents and voltages from these changes. Differently, it was very difficult to design a system that could be shared by all devices.

[0004]

As a method of realizing such a problem, a voltage between electrodes when a desired film is generated is digitally recorded as it is, and then reproduced, and a voltage is again generated under this condition to obtain a voltage between electrodes. Even when the deposition area was changed, the current flowed accurately in proportion to the processing area even when the deposition area was changed, and it was invented that the film could be formed stably without being affected by the processing area.

The thickness of the electrodeposited film and the concentration of coloring are determined by the amount of electricity flowing between the electrodes (the difference between the integral of the positive and negative current components flowing between the electrodes when alternating current is superimposed on direct current). There is the strongest correlation. In the state where the electric quantities are different from each other, discrete data of the interelectrode voltage with respect to the electric quantity is taken, and for the intermediate electric quantity, complementary data of the interelectrode voltage when electrodeposition is performed with the electric quantity in the vicinity is obtained by calculation, When electrodeposition is performed based on this result, a film can be formed even for an intermediate amount of electricity that is not actually sampled.

[0006]

[Example] The thickness of the electrodeposited film and the concentration of the color are determined by the amount of electricity flowing between the electrodes (the difference between the integral of the positive and negative current components flowing between the electrodes when alternating current is superimposed on direct current). Has the highest correlation to Even when an alternating current is superimposed on the current to be deposited, a high correlation is often exhibited with respect to the integral value of the current flowing. If the current has a negative period due to the superposition of the alternating current or the inversion of the polarity, the integration is performed such that the integration value in the negative direction is subtracted from the current value in the positive direction. The positive direction current described here is assumed to be positive in the direction in which electrodeposition proceeds. Therefore,
By inserting a current detector between the power supply device and the electrodes and applying this detection signal to an integrator, the amount of electricity during the film formation process can be monitored. On the other hand, a pattern (indicating a temporal change in the integral value of the electrode current) corresponding to a desired film formation speed is generated in an analog or digital manner. In this pattern, the average value of the current flowing between the electrodes is zero in a flat state where there is no change with time, and the density of the current flowing between the electrodes is high if the temporal signal rises steeply, and the gradient of the current is It means the absolute value of the integral, and if it is positive, it indicates the direction in which the film is generated. Therefore, by comparing this signal pattern with the pattern of the integral value of the current flowing through the electrodes and automatically controlling the current or voltage flowing between the electrodes so as to minimize the difference, a film can be formed at a desired speed. This makes it possible to accurately measure the amount of electricity generated in the film. In this case, the power supply may be a constant current power supply or a constant voltage power supply, and may be applied to a case where an alternating waveform of an arbitrary waveform is superimposed on a DC component. This method has already been filed as a method for controlling an electrolytic coloring power supply, and is called the CLCC method.

When the power source for electrodeposition is a constant current power source, a constant current is passed between the electrodes as it is, and when it is desired to change the film formation speed with time, the value of the constant current is changed in proportion to the speed. The same effect can be obtained by the method, and the same operation can be performed even if the current integrator and the correction circuit are omitted.

In this manner, a film is formed while controlling the amount of electricity flowing through the electrodes. The voltage between the electrodes during the formation of this film is taken into the AD converter directly or through a voltage divider. This digital data is directly or subjected to compression processing, and is digitally recorded on a semiconductor memory, a hard disk, a magnetic tape, an optical disk or a digital recording device equivalent thereto. The sample rate of the A / D converter can be relatively low in the case of DC electroplating. However, in a power supply in which an alternating current is superimposed on a direct current, such as electrolytic coloring or special plating, it is necessary to select a sample rate so as to have a band corresponding to the alternating current component. In order to prevent an increase in recording capacity when the sample rate is high, a good result can be obtained by using a data compression method based on the ADPCM technique used for compressing audio signals. This data compression method is a compression method developed so as not to impair the sound perceived by human ears, but also provides good consistency in electrochemical reactions.

[0009] In many cases, the optimal value of the temporal change of the integrated value of the current flowing between both ends of the electrode placed in the electrolytic solution is not simple. In the case of electrolytic coloring, it is necessary to initially make the change negative. To explain with the simplest example of electrolytic coloring, it is necessary to set the integral value of the current flowing between both ends of the electrode to be negative at the beginning of electrolysis, and to set this integral value to be positive after several tens of seconds to several minutes There is. This is a distorted V when plotted on the vertical axis with the integrated value of the current flowing between both ends of the electrode with respect to the time on the horizontal axis.
It becomes a character-like pattern. This pattern has the same meaning as the reference pattern in the claims. This optimal pattern is difficult to calculate by calculation, and usually relies heavily on experience and intuition, and in order to obtain this pattern at first, thought and error may be required. From such a result, a reference pattern considered to be optimal is created, and the temporal change of the integrated value of the current flowing between both ends of the electrode placed in the electrolytic solution so as to satisfy this pattern is made to match this reference pattern. Controls the power source for electrodeposition. That is, the current flowing between both ends of the electrode placed in the electrolytic solution is detected by the current detector, and this value is added to the integrator. The control is performed so that the output of the integrator matches the reference pattern, but the control itself is performed according to the same principle as the feedback control method of a commercially available stabilized power supply. The reference pattern is changed by such a method until a desired electrodeposition is obtained, thereby obtaining an optimum reference pattern. Thereafter, electrodeposition is performed using this reference pattern, and the inter-electrode voltage in the process of performing the electrodeposition is digitally or analogously recorded. When recording is digital data, the data is converted into an analog signal by a DA converter, and this signal is applied to a power supply device as a reference voltage. The power source for electrodeposition applies a voltage equal to the voltage taken in between the electrodes based on the reference voltage. The method of converting the reference voltage into the desired voltage between the electrodes can be easily realized by employing a feedback technology of a commercially available stabilized power supply. An appropriate low-pass filter is inserted in the output circuit of the DA converter to minimize noise generation. In order to prevent the reference signal from deteriorating due to the limitation of the band of the low-pass filter, good results can be obtained by using an oversampling technique and a digital low-pass filter.

In order to widely change the color or thickness of the coloring, in order to obtain data of desired colors,
The operation for obtaining the reference pattern is a time-consuming operation. Therefore, it is necessary to reduce the amount of work required to obtain the reference pattern from actual measured values by collecting data in steps with respect to the total amount of the integrated value of the current flowing between both ends of the electrode. As a result, the data for the total amount of the integrated value of the current flowing between both ends of the electrode becomes discrete. Electrodeposition cannot be performed if this value is not actually tested. Here, for example, the total amount of the integrated value of the current flowing between both ends of the electrode is 1 and the total amount is 2 (this number is for explanation and the actual unit is ampere × time). On the other hand, if a reference pattern is obtained, an actual electrodeposition is performed using each pattern, and the voltage between the electrodes when the electrodeposition is performed at each value is temporally recorded. In order to obtain the case where the total amount of the integrated value of the current is 1.5, the instantaneous value for each time in the case where the total amount of the integrated value of the current is 1 and the case where the total amount of the current is 2 is added and divided by 2. When the total amount of the integral values is 1.5, an approximate temporal interpolation value of the voltage is obtained. By adding the interpolated voltage data between the electrodes, it is possible to perform an approximate electrodeposition without obtaining actual measurement data when the total amount of the integrated value of the current is 1.5. This approximation is effective when the total amount of the integrated value of the current is proportional to the obtained result. However, under actual conditions, the total amount of the integrated value of the current is not always proportional to the obtained result (the degree of coloring or the film pressure). In this case, the total amount of the integrated value of the current and the obtained result are plotted, and the total amount of the integrated value is x, and the obtained result is y, so that the relation between x and y corresponds to a relational expression such as a power, an exponent, and a logarithm. A better approximation is obtained. Which equation corresponds to the relationship between x and y, and what the coefficients are, can be determined by regression calculation. Since the regression calculation is a well-known calculation method, its description is omitted here. It is convenient to calculate the value of the interpolation by digital calculation from the data recorded in the recording device. However, the same purpose can be achieved by converting the digital data back to analog data and then performing the calculation by an analog calculator.

Further, when the oxide film is colored, such as the temperature, concentration, pH, concentration of interfering substances, and electrolytic coloring of the solution, the relationship between the electrodeposition efficiency and the electrode voltage with respect to parameter fluctuations such as the thickness of the oxide film is determined. If available, add the correction value of each parameter to the interpolated data value obtained in [0010]. For example, when the solution temperature rises by 10 ° C., if there is data indicating that the same electrodeposition efficiency as before the temperature rise can be obtained by applying −0.2 V to the electrode voltage, the voltage value obtained by the interpolation data is What is necessary is just to apply -0.2V.
As a specific data collection method when there are many parameters, a method of multivariate analysis may be adopted. This method is described in, for example, Personal Computer Statistical Analysis Handbook II Multivariate Analysis Yutaka Tanaka,
Tatsumi Tarumi, Wakimoto Kazumasa 1884 Kyoritsu Shuppan Co., Ltd. issued a detailed description, but omitted the parameters such as temperature, concentration, pH, concentration of interfering substances, thickness of oxide film, etc. as independent variables. The value of the dependent variable when the independent variable is changed with the efficiency of electrodeposition for this as the dependent variable. The result is expressed as a mathematical expression using a multivariate analysis technique. Next, the inter-electrode voltage and the efficiency data of electrodeposition are also obtained by experiments, and a mathematical expression obtained by multivariate analysis is converted from the data into the inter-electrode voltage. If the converted voltage value is corrected to the interpolation data and the film is generated at this voltage, the yield due to the fluctuation factor can be prevented.

When the alternating current is superimposed on the direct current, it is necessary to accurately synchronize the alternating current signal for obtaining the respective data in order to prevent a failure due to the beat. To satisfy this, the frequency of the AC to be superimposed is synchronized with the sampling frequency of the AD converter. This method requires that the sampling frequency be an integral multiple of the frequency of the superimposed AC component, or that a synchronous circuit using a PLL circuit be used, and that the phases when power is turned on be matched.

[0013]

According to the present invention, not only a process with a small change with respect to a change in the processing area can be performed, but also automation is easy and it is a very effective method for labor saving. In particular, in the case of small-lot production of various kinds in which the shape of the material to be processed is complicated or the area is not constant, an extremely excellent effect can be exhibited.

The effect of the case where the film formation rate can be arbitrarily set will be described by taking, as an example, electrolytic coloring in which a metal is deposited in the fine pores of an oxide film. In electrolytic coloring, a colored solution is provided with an anodized sample and a counter electrode. An electric current is applied between the electrodes to deposit a metal in the fine pores of the oxide film to perform coloring. In this case, immediately after the voltage is applied between the electrodes, the aluminum oxide film side is controlled to averagely anodize in order to improve the throwing power. This corresponds to a pattern having a negative gradient in the pattern indicating the integral value of the electrode current described above. In the constant current power supply, the DC component of the current is superimposed on the AC by the DC constant current component in the direction of making the oxide film side anodically polarized. I do. When such a state is performed at the beginning of coloring, the throwing power can be significantly improved. The reason for this is that if the oxide film side is averagely anodically polarized in the coloring solution, negative ions such as hydroxyl groups and sulfate groups generated by the electrode reaction are generated (when ammonium sulfate is added to the coloring solution, This reacts with the aluminum ions to form a colloid film having a relatively high electric conductivity, and the closer to the electrode, the higher the electric resistance of the surface becomes, and the more difficult it is to color. In such a state, when the oxide film side is formed into a positive gradient pattern (a constant current of a direct current component in a direction in which the oxide film side is converted to the cathode polarization is superimposed on the alternating current, the coloring proceeds) so that the cathode polarization component is increased. I do. If the above treatment is not performed, the direction close to the electrode is strongly colored, and the throwing power is deteriorated. However, due to the above-described treatment, the electric resistance of the surface becomes higher as the electrode is closer to the electrode and coloring is suppressed, and the influence of the portion far from the electrode is reduced and the suppression of coloring is reduced, and the strong coloring near the electrode is reduced. As a result, the throwing power is improved.
In the case where the average current flowing between the electrodes is positive (in the direction in which the oxide film side is cathode-polarized on average), the coloring proceeds, but the transient film whose electric resistance has been increased by the pretreatment also decreases with time. . Considering the case where the substance that increases the electric resistance is aluminum hydroxide, the aluminum hydroxide generated near this electrode acts as a viscous positive colloid, hinders ion conduction, and increases equivalent surface resistance. This positive colloid discharges electric charge when the oxide film side is cathodically polarized and adsorbs on the oxide film, or diffuses into the solution when the polarity is extremely positive.Therefore, immediately after coloring is started after pretreatment is completed The coloring speed also has an effect on the surroundings, and the key to effectively performing the pretreatment is to deposit a metal on the entire surface during the period in which the film having a high resistance exists. Furthermore, in a coloring solution of a strong acid such as a tin bath which reacts faster with aluminum compared to a coloring solution of a neutral or weak acid or a coloring solution containing an amino group, the objective can be achieved even if the treatment time and the polarization level are extremely small. . As described above, in the electrolytic coloring, it is necessary to optimally change the polarity and value of the average value of the current with respect to time, and it takes time and cost to obtain these optimal conditions in a mass production site. However, in the present invention, an optimum value is obtained for a sample having a small area at the laboratory level, this data is accumulated, and in a large-scale mass production, this result is reproduced or colored by supplementary data. It is possible to do.

The present invention was carried out as a test at the industrialization level on March 6, 1993 in the light metal business division of Pilot Co., Ltd. in the presence of Mr. Mizusawa, the same department, after a half-year small-scale test. Has been demonstrated.

Claims (2)

(57) [Claims] 1. Deposition films such as film formation by plating or dispersion plating, coloring by electrolytic coloring, oxide film formation by electrolysis, electrodeposition coating using electrophoresis and electrodeposition (including deposition in micropores). Or a method of obtaining an oxide film, the time change of the integrated value of the current flowing between both ends of the electrode put in the electrolytic solution should be made to match the reference pattern, or the current set value by the programmed constant current power supply By controlling the voltage, a film is generated with the integrated values of the different currents, the voltage between the electrodes during the film formation process is monitored, this monitor signal is converted into a digital signal and recorded, and the total amount of the integrated value of the current flowing through the electrodes is calculated. The voltage data for the integrated value of an arbitrary current is collected from the measured data of the conditions in the vicinity of this by digital or analog calculation. A method of obtaining interpolation data and obtaining a film or coloring by using a voltage obtained from the interpolation data. 2. A correction value is given to the interpolation data according to claim 1 by a parameter that changes the electrodeposition, such as temperature, concentration of a solution, concentration of an interfering substance, pH, or film pressure data of an oxide film. A method for controlling a power source for electrodeposition that generates a film by a voltage.