JPH07840B2 - Method for controlling electroplating additive and apparatus therefor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for controlling the concentration of a plating additive and an apparatus therefor for obtaining a good plating film.

(Prior Art) In order to obtain a good plating film, a small amount of an organic additive is usually added to a plating bath for the purpose of reducing internal stress of the plating film, imparting flexibility, improving uniform electrodeposition, and imparting gloss.
This additive is consumed by electrolysis, and it is difficult to analyze and control because it is a very small amount when supplemented.

Conventionally, the addition of a plating additive is performed by, for example, adding an amount obtained empirically in proportion to the work amount, or by electrically and mechanically linking the energization amount and the addition operation, By visually observing the state and adjusting the amount added,
I am doing it.

Originally, the additive should be added after measuring the additive concentration in the plating bath.However, since the effective concentration of the additive cannot be easily detected by the above method, avoid excessive addition or insufficient addition. Therefore, it was not possible to obtain a uniform gloss quality, and defective products were often produced.

Recently, an example of using ion chromatography or isotachophoresis for the analysis of additive concentration has been reported, but these devices are expensive, and the analysis value does not reflect the state in the plating bath as it is. Therefore, there is a drawback that the relationship with the surface morphology is not always clear.

As described above, no effective and simple method has been found for optimally controlling the concentration or addition amount of the conventional plating additive and thereby obtaining a good plating film.

In various plating baths, it is already known to use, for example, polymer compounds having surface activity, various organic compounds containing sulfur and nitrogen, etc. as such additives.

As a result of a detailed study on the action of such an additive, the present inventor has found that the polymer compound having surface activity forms an electrodeposition-inhibiting film on the surface to be plated, whereas the sulfur-nitrogen-containing organic compound The compound alone or in the coexistence of the polymer compound or the like has an electrodeposition accelerating property, and the combined use of the electrodeposition-inhibiting additive and the electrodeposition accelerating additive produces a plating film superior to the case of using it alone. Further, each finding that the overvoltage of the plating bath containing both additives is uniquely determined by the concentration of the deposition promoting additive when the deposition inhibiting additive is present at a saturation concentration or higher. The present invention has been obtained.

(Problems to be Solved by the Invention) An object of the present invention is to detect a plating additive consumed through a plating treatment process quantitatively, and to maintain and manage quantitatively an optimum concentration, which is effective and simple. It is to provide a method of adding an additive.

(Means for Solving Problems) One of the present inventions contains an electrodeposition-promoting additive and an electrodeposition-inhibiting additive having a saturation concentration or higher as additives in a plating bath in an electroplating treatment step. At this time, a method of controlling the concentration of the plating additive is characterized by adding and replenishing each additive by controlling so that the overvoltage value peculiar to the plating bath is maintained at the optimum concentration of the electrodeposition accelerating additive. To provide.

Another one is an apparatus for carrying out the method for controlling the additive concentration, which contains both an electrodeposition reaction suppressing additive and an electrodeposition accelerating additive, and is provided with an anode and a cathode. A plating bath and an additive supply device for replenishing both additives consumed as a result of electrolysis are installed in parallel, a constant current power source is connected to the anode and cathode, and the cathode is higher than a set optimum overvoltage value. A plating additive concentration control device is characterized in that an overvoltage control device is connected to open a valve of the additive supply device at an overvoltage and close the valve at an overvoltage lower than a set optimum overvoltage value.

Hereinafter, the method and apparatus of the present invention will be described, but the present invention is based on the following various findings.

The polymer compound having surface activity as a plating additive forms a film that suppresses electrodeposition on the surface to be plated, and its action reaches saturation when added in a certain amount or more. Under sufficiently agitated conditions, when the amount of the polymer compound added is less than the saturated concentration, the overvoltage increases as the amount added increases, but the film formation is insufficient, so that the oscillation phenomenon of the overvoltage is measured. When added in excess of the saturation concentration, a stable and constant overvoltage that is not affected by the amount added is measured over a fairly large concentration range, and this overvoltage is a unique value determined by the bath composition and the type of polymer compound. I found out.

On the other hand, the sulfur-containing / nitrogen-containing organic compound has an action of promoting deposition by itself or in the presence of a surface-active polymer compound and other components. Addition of the sulfur / nitrogen-containing compound alone under sufficiently agitated conditions lowers the overvoltage of the plating bath as compared with that without addition. In this case, it was found that the relationship between the overvoltage and these substances was uniquely determined depending on the type of additive and the composition of the plating bath.

However, the above-mentioned electrodeposition-suppressing additive or electrodeposition-promoting additive rarely achieves the desired effect when added alone, and the desired effect can be obtained only by adding these two components in a well-balanced manner. can get. The plating film having the desired properties is obtained by the synergistic effect of the combination of the electrodeposition-inhibiting additive and the accelerating additive.

Generally, the plated surface is a matte surface when an electrodeposition-suppressing additive is added alone (including the addition of one or more kinds).
It has poor uniformity and is brittle in terms of physical properties, and this tendency does not matter regardless of the bath composition, the type of electrodeposition-inhibiting additive, and the electrodeposited metal.

On the other hand, a plating film obtained by adding an electrodeposition-accelerating additive alone may show luster depending on the type of the additive and the electrodeposited metal, but is generally dull and has good flexibility in terms of physical properties. Indicates.

When the electrodeposition-inhibiting additive is added alone above the saturation concentration, the bath has a certain inherent overvoltage in a fairly wide concentration range above the saturation concentration. At this time, the addition of the deposition promoting additive reduces the overvoltage, and the overvoltage of the plating bath containing both additives shows a unique overvoltage value that is uniquely determined by the concentration of each additive depending on its type. I knew that.

This, of course, does not change depending on the method of adding the deposition promoting additive and the deposition inhibiting additive. For example, at the overvoltage value obtained by simultaneously adding both the electrodeposition-inhibiting and accelerating additives, or by previously adding the electrodeposition-accelerating additive alone, further adding the electrodeposition-inhibiting additive at a saturation concentration or higher. Also, the overvoltage specific to the concentration of the accelerating additive is measured, and sufficient reproducibility is seen.

If the acceleration additive decreases and the initial prescribed concentration decreases due to electrolysis consumption, the overvoltage rises and approaches the overvoltage value obtained when the inhibitor additive is added alone, but the acceleration additive is added and replenished again. Then, when the initial overvoltage value is lowered, the initial concentration is restored and maintained. In this way, the desired concentration of the additive can be achieved by controlling the overvoltage (inherent overvoltage).

In addition, a good correlation is found between the additive concentration-specific overvoltage and the plating film.

In general, good plating is obtained at a certain overvoltage which is greater than the overvoltage without addition of additives, which overvoltage is controlled by controlling the concentration of each additive.

In a certain concentration range of the accelerating additive, the plating itself on the surface of the test electrode shows good gloss, but if it is added in excess, a high-speed electrolytic consumption phenomenon of the accelerating additive can be seen, and at the same time, the test Electrode surface plating may also be dull. Such a phenomenon is in good agreement with the actual state change of the plated product depending on the additive concentration. Therefore, in order to obtain the optimum plating film, the additive concentration is managed by knowing in advance the optimum concentration of the accelerating additive and detecting and controlling the overvoltage of the plating bath to maintain that concentration in the actual plating process. It becomes possible to do it.

In the method of the present invention, a plating treatment is first performed on a trial basis. That is, the electrodeposition-inhibiting additive is added to the plating bath with stirring at a concentration equal to or higher than the saturation concentration, and the inherent overvoltage value is measured. A constant current electrolysis is carried out by further adding an electrodeposition accelerating additive to this solution with stirring under various concentration conditions. At this time, the overvoltage of the entire bath at each concentration is measured, and the state of the plating film obtained at the same time is observed to determine the optimum concentration of the accelerating additive that gives the optimum plating film. Such tests were conducted with various combinations of various plating baths, electrodeposition-suppressing additives, and electrodeposition-accelerating additives, and data on the optimum concentration of accelerator additives and bath overvoltage unique to each combination were obtained. And collect them.

When performing the actual plating treatment, set the overvoltage value at the concentration of the plating bath having the specific concentration containing the specific electrodeposition-suppressing additive and accelerating additive, and set the constant current under the same conditions as the data. Although electrolysis is performed, the amount of each additive that is consumed by electrolysis, that is, the concentration, is controlled by maintaining and controlling the set overvoltage value.

The electrodeposition reaction is carried out in the same manner as the ordinary plating reaction under the current density condition of the ordinary plating reaction due to the polarization of the cathode by the constant current DC power supply.

Thus, it becomes possible to quantitatively add and control the plating additive, and the plating process can be stably performed, so that an excellent plating film can be reliably obtained.

Next, an apparatus for carrying out the method will be specifically described with reference to the accompanying drawings.

The figure shows an example of a control device when a rotating disk electrode is used in the electrolytic plating device and the overvoltage is automatically controlled.

The electroplating equipment consists of a constant current power source (1), a plating bath (1
1), a cathode (5), an anode (7) and a diaphragm (8).

The cathode (5) is connected to a constant current power supply (1), and in the example shown, a rotating disk electrode is used, which is rotated by a motor (10) and vigorously agitates the plating bath solution (9) containing an additive. It is supposed to do. Alternatively, a plate-shaped fixed electrode may be used as long as the stirring conditions allow a uniform electrodeposition-inhibiting film to be formed on the cathode surface, and the stirring of the liquid may be separately performed by a propeller type or air pipe type stirring device.

The anode (7) is connected to the constant current power supply (1).

The additive container (12) is provided close to the plating bath (11), and is added to the plating bath (11) through the additive supply device (13). This may be separately divided into a container for the electrodeposition promoting additive and a container for the electrodeposition suppressing additive, or may be a single container in which both additives are mixed.

An overvoltage control device (2) for the controlled addition of additives is connected to the cathode (5) and comprises a reference electrode (3). In order to detect the deposition potential on the surface of the cathode (5), a Luggin capillary tube (6) is arranged in the vicinity thereof and is connected to the reference electrode (3) by a salt bridge (4). The potential difference between the cathode (5) and the reference electrode (3) is detected by the overvoltage controller (2). The overvoltage control device (2) has a function of controlling to an overvoltage value which gives the optimum concentration of the additive, when the overvoltage value is set.

As the reference electrode (3), any electrode such as a saturated sweet electrode is used. When an electrode composed of an electrolytic solution having the same composition as the plating solution and a plating metal is used as a reference electrode, the measured potential is an immediate overvoltage.

Bridge (4) uses saturated KCl-Kantenbashi. When the reference electrode (3) is made of the above plating solution-plating metal, it may be simply filled with the electrolytic solution.

The additive supply device (13) is interlocked with the overvoltage control device (2), and opens the valve when the voltage is higher than the set overvoltage and closes the valve when the voltage is lower than the set overvoltage.

Although the above example is a device for automatically controlling the overvoltage, it is of course possible to provide a potentiometer instead of the overvoltage control device (2) and manually control the overvoltage to add and manage the additive. It is possible. In this case, the potentiometer will detect the potential difference between the cathode (5) and the reference electrode (3).

(Example) Example 1 (1) CuSO ₄ .5H ₂ O 100 g / l H ₂ SO ₄ 180 g / l Cl ^- ion 65 ppm Temperature 20 ° C. Rotating disk electrode having a surface area of 0.8 cm ² using the above plating bath solution. In a plating apparatus having a (cathode), constant current electrolysis was performed under the conditions of 2.5 A / dm ² while stirring the solution at 600 rpm. Polyethylene glycol (average molecular weight 6000) was added at 300 mg / l as an inhibitory additive to obtain an overvoltage of 308 mV. To this liquid, mercaptobenzothiazole-
Sodium S-propyl sulfonate was added and the overvoltage was measured under the same conditions, and the following results were obtained.

In the above concentration range, there is a generally good linear relationship. Moreover, these values were quite the same between 30 and 1000 mg / l of polyethylene glycol.

It was observed that, of the above concentrations, 2.0 mg / l gave a plating film with the best physical properties and gloss.

(2) Additive Polyethylene glycol 300mg / l Sodium mercaptobenzothiazole sulfonate (S / N compound) A solution having a concentration of 2mg / l is continuously electrolyzed, and the overvoltage increases as the S / N compound is consumed. SN compounds were sequentially added to keep the overvoltage constant within the range of 228 mV ± 3 mV.

As a result, it was concluded that the supplemental amount of 0.4 mg / A · Hr is optimal for maintaining the concentration of 2 mg / l.

Example 2 (1) Polyethylene glycol (average molecular weight 4000) was added to the plating bath solution of Example 1 first as an inhibitory additive.
mg / l was added, and then sodium 3-mercaptopropane-1-sulfonate was added, and constant current electrolysis was performed under the conditions of 700 rpm and 2.5 A / dm ² . As a result, the following overvoltage values were obtained.

In the above concentration range, there is a generally good linear relationship. There was no change in overvoltage in the range of 30 to 1000 mg / l of the above polymer. Also, the best plating film was formed at a concentration of 2.0 mg / l.

(2) Polyethylene glycol 240mg / l 3-Mercaptopropane-1-sulphonic acid sodium salt (SN compound) A plating bath having an additive concentration of 2.0mg / l is electrolyzed continuously and its overvoltage is set to 177mV ± 2mV. The S / N compound was added at any time in order to keep it. For that purpose, it was found that it is optimal to supply 0.45 mg / A · Hr.

Example 3 (1) Using the same plating solution and apparatus as used in Example 1, overvoltage measurement was performed under the conditions of 800 rpm and 2.5 A / dm ² .

An overvoltage of 330 mV was obtained when 200 mg / l of polyoxyethylene (35%) polypropylene glycol (average molecular weight 3000) was added as a suppressive additive. Further, sodium isocyanopropyl sulfonate was added, and the following results were obtained.

Good correlation was obtained although not in a linear relationship. And
It was found that the best plating film was obtained even at a concentration of 2.0 mg / l.

(2) Using the same plating bath as above, under the same conditions, at an additive concentration of polyoxyethylene polypropylene glycol 200 mg / l isocyanopropyl sulfonic acid Na 2.0 mg / l (SN compound), an overvoltage of 169 mV ± 2 mV In order to keep the above value, SN compound was supplemented at a rate of 0.40 mg / A · Hr.

(Effect) Generally, the excessive addition of the electrodeposition-inhibiting additive has little adverse effect on the plating film due to its properties, but the excess or deficiency of the electrodeposition-promoting additive has a great influence on gloss, uniformity, physical properties and the like. Therefore, it is particularly important to control the concentration of the deposition promoting additive,
The present invention can sufficiently meet the demand.

Further, the method of the present invention, in the presence of a certain amount of inhibitor additive, not only measure and control the concentration of the accelerating additive,
By controlling the deposition overvoltage within a certain range, the gloss and physical properties of the plating film can be controlled, which makes a great contribution to the production of the currently required high-performance plating film.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an electroplating additive concentration control device of the present invention. 1 ... Constant current power supply 2 ... Overvoltage control device 3 ... Reference electrode 5 ... Cathode 7 ... Anode 11 ... Plating bath 12 ... Additive container 13 ... Additive supply device

Claims (2)

[Claims] 1. In a plating treatment using an acidic copper sulfate plating bath containing an electrodeposition reaction inhibitory additive and an electrodeposition reaction accelerator additive, the electrodeposition reaction inhibitory additive has a predetermined concentration or more. At this time, by utilizing the fact that a unique overvoltage value uniquely determined by the concentration of the electrodeposition reaction accelerating additive is given, the deposition potential in constant current electrolysis is measured and held at the unique overvoltage value, A method for controlling the concentration of the electrodeposition reaction promoting additive. 2. An apparatus for controlling the concentration of an additive for promoting an electrodeposition reaction in a plating treatment step using an acidic copper sulfate plating bath containing an additive for inhibiting an electrodeposition reaction and an additive for promoting an electrodeposition reaction. A plating bath containing an electrodeposition reaction suppressing additive and an electrodeposition reaction accelerating additive and having an anode and a cathode, and an additive supply device for replenishing both of the additives that are consumed in accordance with electrolysis And are arranged in close proximity to each other, a constant current power source is connected to the anode and the cathode, and an overvoltage controller is connected to the cathode, and the overvoltage controller is the additive at an overvoltage higher than a set overvoltage. A plating additive concentration control device, characterized in that the supply valve of the supply device is opened and closed at an overvoltage lower than a set overvoltage.