JPH09268400A - Plating solution component concentration control method - Google Patents

Abstract

(57) Abstract: Even if the total bath volume fluctuates due to water entering and exiting the plating system, abnormal control of pH can be prevented by feedback control of component concentrations. SOLUTION: In a plating facility in which water flows in and out of the system, in a plating solution component concentration control method for controlling a metal concentration of a plating solution when performing electroplating using an insoluble anode, water in the plating system is controlled. When the actual value of the total bath amount, which is the total plating solution present in the plating system, fluctuates from the bath amount target value (A), when the fluctuation occurs,
The feedback control target value of the metal concentration is set to the plating solution p
In order to keep the H value constant (C), the setting target value is changed to the corrected target value calculated based on the predetermined metal concentration target value and the fluctuation amount of the total bath amount (B).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the concentration of a plating solution component, particularly a plating facility in which water flows in and out of the system, and the concentration of the plating solution when electroplating using an insoluble anode. The present invention relates to a plating solution component concentration control method suitable for application to control.

[0002]

2. Description of the Related Art Generally, in electroplating using an insoluble anode, the concentration of plating solution components such as metal ions and free sulfuric acid dissolved in the plating solution is controlled. In order to maintain the concentration (hereinafter, also simply referred to as the metal concentration) at a target value, a predicted metal consumption amount that is predicted to be consumed in the plating from the plating conditions (feed forward: FF) and a concentration actual value are set in advance. The sum of the metal deviation amounts obtained from the deviation from a certain concentration target value is set as the metal input amount during the metal concentration feedback (FB) control.

Regarding such a plating technique, for example, in JP-A-2-217499, as a bath concentration control method for alloy electroplating, a plating energization amount is measured, and metal ions in the plating bath are measured based on the measured value. A technique of calculating the consumption amount and adjusting one or more of metal ions, free acids, and water in a plating bath is disclosed.

Japanese Patent Laid-Open No. 5-320997 discloses a standard supply of a metal salt calculated based on a plating current value and a dragout amount of a plating solution as a method for controlling the metal ion concentration in a zinc alloy electroplating solution. The amount of the metal salt to be supplied is determined by the sum of the amount and the corrected supply amount of the metal salt calculated based on the component concentration in the electroplating liquid and the pH value of the electroplating liquid, and the determined metal salt There is disclosed a technique for controlling the metal ion concentration in the electroplating solution by replenishing the electroplating solution in the electroplating solution.

In each of the concentration control methods for electroplating disclosed in the above publications, the target value for feedback control is set to a fixed value as a predetermined target value.

By the way, in the electroplating of metal strips, since the strips are cleaned, water flows from outside the system into the plating system as cleaning water, and the plating solution is diluted with the inflow of water. Therefore, a water evaporation operation for removing excess water is performed by an evaporator device to balance the inflow amount of water into the system and the evaporation amount of water to the outside of the system.

As described above, even when electroplating is performed while balancing the amount of water flowing into the system and the amount of evaporation to the outside of the system, one of the two becomes excessive and the balance between the two is lost, and the total amount existing in the system is lost. The total bath volume, which is the plating bath volume, may fluctuate. Even in such a case, if the control target value as disclosed in the above publication is set to a constant value and the feedback control for eliminating the difference between the target value and the actual value of the metal concentration is applied, it is as follows. Phenomena occur.

For example, as shown in FIG. 3 (A), when the total bath volume in the plating system increases (between t1 and t2) because the water inflow exceeds the water evaporation amount, the excess water is added. In order to replenish the amount of the metal concentration that has been diluted due to the plating solution being diluted, the metal is fed in by feedback control, and the total molar concentration of the metal is maintained at a constant target value, as shown in FIG. At the same time, since the added metal is consumed in the dissolution reaction with sulfuric acid, H2 SO4 is reduced, so that H2 SO4 is added to maintain the sulfuric acid concentration.

Here, the total molar concentration is used as the metal concentration, for example, when the plating solution contains two or more kinds of metal ions, such as alloy plating of zinc and nickel, the total of these concentrations is used. Means to use the value.

In the above plating, it is possible to discharge the strip cleaning water as it is to the outside of the system to avoid the above problems, but this means discarding some of the plating solution contained in the cleaning water. Therefore, the basic unit of drug is deteriorated. Also, if the washing water is not released outside the system as it is, the plating solution will gradually increase unless only water is released outside the system by the water evaporation operation. There is no choice but to throw it away. Therefore, the above-mentioned method of balancing the amount of water flowing into the system with the amount of water to be evaporated is effective.

[0011]

However, when electroplating is carried out in a facility where water flows in and out of the plating system as described above, it is disclosed in JP-A-2-217499 and JP-A-5-320997. In all cases, the target value for feedback control is set to a predetermined target value, so that the balance between the amount of water inflow from outside the system and the amount of water evaporation to the outside of the system is applied. When is broken, there are the following problems.

To explain this again with reference to FIG. 3, the state of (amount of water inflow from outside the system> amount of water evaporation to the outside of the system) continues during time t1 → t2, and the plating solution is diluted. When a phenomenon occurs, as described above, the metal is excessively added to eliminate the diluted portion in order to keep the metal concentration constant by the feedback control. As a result, according to the following reaction formula, since the charged excess metal is dissolved in sulfuric acid, free sulfuric acid is also consumed and reduced.

Zn + H2SO4 → ZnSO4 + H2 ↑ (A)

When the free sulfuric acid is reduced as described above, H2 SO4 is added in order to maintain the H2 SO4 concentration of the plating solution at the target concentration by feedback control. As a result, the total bath volume of the plating solution was maximized t2
At this point, both the metal concentration (total molar concentration) and the pH are at their target values, even though the plating solution itself has significantly increased.

After that, when the water for the dilution of the plating solution is discharged to the outside of the system by the water evaporation operation between t2 and t3 and the plating is advanced so that the metal concentration maintains the target value, at the time of t3. When the total bath volume of the plating solution has returned to the target value, the H2 SO4 added to dissolve the excessively added metal has no escape area, so that the pH of the plating solution is changed as shown in FIG. 3 (C). Cannot be returned to the original target value, and the pH of the plating solution is lowered (the free H2 SO4 concentration is increased).

This phenomenon will be described in further detail by taking the case where the metal is zinc (Zn) as an example. Originally, in electroplating, the plating reaction (electrodeposition reaction) represented by the following reaction formulas (B) and (C) )
Therefore, the amount of free H2 SO4 is determined by the reaction formula (C).
It is balanced by the increase due to the plating reaction and the decrease due to the reaction with the input metal according to the formula (A).

Zn ²⁺ + 2e ⁻ → Zn ↓ (B) H 2 O + SO 4 ² → → H 2 SO 4 + 1 / 2O 2 ↑ + 2e ⁻ (C)

FIG. 4 conceptually shows this relationship in the case of pure zinc (Zn) plating as an example, in which the vertical axis represents the metal concentration and the horizontal axis represents the free H2 SO4 concentration. Control is performed so that the two balance at the intersection of the target values.

That is, as is clear from the equation (B),
Since the excess metal can be removed by taking it out by plating, even if water is evaporated, the metal concentration can be controlled to a target value as shown in FIG. 3B by advancing the plating at the same time. At the same time, H2 according to equation (C)
As the SO4 increase reaction occurs, the sulfuric acid increased by this reaction has no escape area as described above.
4 An increase in concentration, that is, a decrease in pH will occur,
It has become clear that this causes various adverse effects.

A similar phenomenon occurs in the case of alloy plating. This will be described in detail below, although the contents are partially duplicated.

As described above, generally, in electroplating equipment for plating a steel sheet, sealing water and water used for cleaning the surface of the plated steel sheet (strip) flow into the plating equipment. When water flows in from the outside of the system and the plating solution is diluted in this way, excess water that has flowed into the plating solution is removed by evaporation to the outside of the system by an evaporator device. However, since the evaporator device cannot continuously change the evaporation amount, the actual value of the total bath amount of the plating solution (the total amount of the plating solution present in the plating system) fluctuates by about 5 to 10% with respect to the target amount. It is inevitable to do.

As described above, when the actual total bath volume of the plating solution increases due to the inflow of water from the outside of the system, the measured value of the metal ion concentration ([g / l] or [mol / l]) is Will be reduced to. Therefore, in this case, if the metal ion concentration is controlled to be constant, a metal agent containing the target metal (for example, the metal itself, its salt, its oxide, etc.) is added to the plating solution in order to supplement the shortage. Will be required.

Explaining this in the case of, for example, a sulfuric acid acidic plating solution for Zn (zinc) -Ni (nickel) alloy plating, it is necessary to add Zn and Ni chemicals (metal chemicals). When such chemicals are added, Zn chemicals become Zn
In the case of O and the Ni agent is metallic Ni, the following (D),
Since the reaction of the formula (E) causes a decrease in H2 SO4 (that is, an increase in pH), it is necessary to add H2 SO4 in order to keep the H2 SO4 concentration (or pH) at a constant concentration. .

ZnO + H 2 SO 4 → ZnSO 4 + H 2 O (D) Ni + H 2 SO 4 → NiSO 4 + H 2 ↑ (E)

In the electroplating of Zn-Ni alloy, the following (F), which is the same as the equation (B), is usually used on the cathode (steel plate) surface.
And a metal (Z
(n, Ni) ion consumption and an increase in H2 SO4 represented by the following formula (H), which is the same as the formula (C), occur on the anode surface.
By replenishing the metal ions consumed by the plating reaction of the formula (G) by the formulas (D) and (E), both the metal ion concentration and the H2 SO4 concentration (or pH) are balanced. .

Zn ²⁺ + 2e ⁻ → Zn ↓ (F) Ni ²⁺ + 2e ⁻ → Ni ↓… (G) H 2 O + SO 4 ² → → H 2 SO 4 + 1 / 2O 2 ↑ + 2e ⁻ (H)

Therefore, when the total bath volume of the plating solution is increased by the inflow of water from the outside of the system, if metal chemicals, H2 SO4, are added to keep the component concentration constant, the plating is performed by subsequent water evaporation. When the total bath volume of the liquid returns to the target value, both metal ions and H2 SO4 become excessive, so that the introduction of all the metals and sulfuric acid must be stopped. In this case, the metal ions are steadily reduced because they are consumed by the formulas (F) and (G) by continuing the plating while the supply by the formulas (D) and (E) is stopped. be able to. However, H2 SO4 is
If the plating is continued in order to return the metal ion concentration to an appropriate value as well as the decrease due to the equations (D) and (E) disappears, it will increase unilaterally according to the equation (H), and thus the same. In addition, the H2 SO4 concentration will further increase (pH decrease).

The present invention has been made to solve the above-mentioned conventional problems. When the total bath volume changes due to the inflow and outflow of water into the plating system, and the concentration of the plating solution changes, for example, water is used. Flows into the system, and even when the concentration decreases due to the total bath volume increasing and the plating solution being diluted, feedback control of the metal concentration prevents an abnormal decrease in pH or an abnormal increase in free acid concentration. An object of the present invention is to provide a method for controlling the concentration of a plating solution component that can be performed.

[0029]

The invention according to claim 1 is a plating facility in which water flows into and out of the system, and plating is performed to control the metal concentration of the plating solution when electroplating using an insoluble anode. In the liquid component concentration control method, when water enters and leaves the plating system, the actual value of the total bath amount of all plating solutions present in the plating system changes from the bath amount target value. At the time of the change, the feedback control target value of the component concentration is calculated based on the predetermined component concentration target value and the fluctuation amount of the total bath amount so that the pH value of the plating solution is maintained constant. The above problem is solved by changing the setting to the target value.

A second aspect of the present invention is a method for controlling the concentration of a plating solution component, which comprises controlling the metal concentration of the plating solution when performing electroplating using an insoluble anode in a plating facility in which water flows in and out of the system. If the actual value of the total bath volume that is the total plating solution present in the plating system changes from the bath amount target value due to the inflow and outflow of water into the plating system, the metal concentration will change when the change occurs. Change the feedback control target value to the corrected target value calculated based on the predetermined metal concentration target value and the total bath volume fluctuation so that the free acid concentration of the plating solution is maintained constant. By doing so, the above problems are similarly solved.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor has conducted a detailed study on electroplating using an insoluble anode, which is carried out in a facility where water flows in and out, and as a result, the balance between the inflow amount and the evaporation amount of water is lost. When the plating solution concentration fluctuates, in order to perform plating with high accuracy, the p
It was found that controlling the H value to an appropriate value is extremely important.

The present invention was made on the basis of the above findings, and the actual value of the total bath amount, which is the total plating solution present in the plating system, varies from the target value of the total bath amount, which is the target value. When it occurs, the feedback control target value of the metal concentration is set to a predetermined amount of fluctuation of the metal concentration target value and the total bath amount so that the pH value of the plating solution or the free acid concentration is maintained constant. The setting is changed to the correction target value calculated based on

That is, paying attention to the relationship between the metal concentration and the sulfuric acid concentration shown in FIG. 4, for example, when the total bath volume of the plating solution increases with the inflow of water and the concentration is diluted, Is to increase the amount of free sulfuric acid by advancing the plating reaction of the formula (C) without excessively adding the metal corresponding to the diluted concentration so that the sulfuric acid concentration becomes constant and the pH is kept constant. Try to keep it.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a first embodiment according to the present invention.
1 shows a schematic configuration of an entire plating control device to which the control method of the embodiment is applied.

This control device includes a plating cell 10 for electroplating, a circulation tank 12 for circulating and supplying a plating solution to the cell 10, and an auxiliary facility for supplying metal, sulfuric acid, etc. to the tank 12. And a bath amount calculation unit 1, a control calculation unit 2, and a concentration feedback (FB) for controlling the component concentration of the plating system.
Control unit 3 and concentration feedforward (FF) control unit 4
And a control system having.

A level meter 16 is attached to the circulation tank 12 and the auxiliary equipment 14, and a liquid analyzer 18 is attached to the former.

In the above plating control device, when the total bath volume of the plating system changes, the metal concentration target value when the metal concentration is feedback-controlled in the control calculation unit 2 is set to the correction target value. At that time, this modified target value: CTMC
When the plating solution is a sulfuric acid bath, sp [mol / l] is calculated by the following equation (1).

CTMCsp = CTMsp · (Vrot + Vsp−Vall) / Vrot + (CAsp / Ma) (Vsp−Vall) / Vrot (1) where CTMsp: target total molar concentration target value [mol /
l] Vsp: Bath volume target value [m ³ ] Vall: Total bath volume [m ³ ] Vrot: Circulating bath volume [m ³ ] CAsp: H 2 SO 4 concentration target value [g / l] Ma: H 2 SO 4 molecular weight [g / mol]

In the above equation (1), the total bath amount Vall is the total amount of the plating solution actually present in the plating system, and is the actual calculated value obtained by calculation from the measured value. The difference from the amount target value Vsp corresponds to the bath amount variation.

The circulating bath amount Vrot means a bath amount that actually circulates the plating system during plating. When all of the total bath amount Vall is circulated, Vall = Vrot, which is a part of the plating equipment. Is bypassed and the plating solution existing in that portion is not circulated, the total bath volume Vall is the amount obtained by removing the plating solution in this non-circulation portion.

The total bath amount Vall is basically calculated by the bath amount calculation unit 1 based on the actual value by the level meter 16. However, when the pipe volume other than the circulation tank 12 or the bath volume of the unmeasured portion changes, the level performance of the circulation tank 12 changes. Therefore, the amount of bath in the piping and unmeasured area is
It is calculated as an equipment constant according to the operating state of the pump, etc. or,
The circulating bath amount Vrot is similarly calculated by the bath amount calculating unit 1 by subtracting the bath amount which is not circulating from the total bath amount depending on the operating state of the pump, the state of the bypass valve and the like.

The set total molar concentration target value: CTM
sp is, when the total bath volume Vall is equal to the bath volume target value Vsp,
It is a target value set when feedback control of the component concentration is performed.

For the sake of convenience, the above equation (1) is used to simplify the calculation.
The density of) is derived from the following equation (2) assuming that the predetermined target value remains unchanged.

CTMsp * Vsp + (CAsp / Ma) * Vsp = CTMCsp * Vrot + CTMsp * (Vall-Vrot) + (CAsp / Ma) * Vall (2)

In the above equation (2), when the bath amount is at the target value Vsp, the left side representing the sum of the metal amount and the sulfuric acid amount when both the metal concentration and the sulfuric acid concentration are at the target values, and the bath amount are When the total bath volume Vall fluctuates, the circulating bath volume Vro of the circulating portion of the total bath volume is maintained while maintaining the sulfuric acid concentration at the target value.
It is assumed that the right side representing the sum of the amount of metal and the amount of sulfuric acid when the metal concentration of t is the corrected target value: CTMCsp is equal. This equation presupposes that the sum of the sulfate radicals (SO4 ^2- ) contained in the metal sulfate and the sulfate radicals contained in free sulfuric acid is always kept constant. This equation (2) is
By rearranging CTMCsp, the above equation (1) is obtained.

The corrected target density: CTMCsp calculated by the equation (1) as described above is calculated by the control calculation unit 2 as the density FB.
The actual concentration that is output from the liquid analyzer 18 is output to the control unit 3, and the FB control unit 3 uses it as the target value of the metal concentration feedback control when the total bath amount fluctuates from the target value. The density deviation amount between On the other hand, the concentration FF control unit 4 obtains a predicted metal consumption amount estimated to be consumed in plating based on the prediction calculation information given as the plating condition.

After that, the metal feeding speed obtained based on the sum of the predicted metal consumption amount and the concentration deviation amount is output to the auxiliary equipment 14 and set. At this time, the H2 SO4 concentration is obtained and set by the same method so that the H2 SO4 concentration is always maintained at the target value CAsp.

By doing so, when the plating solution is in a diluted state due to (water inflow from outside system> water evaporation amount to outside system), the metal concentration target value is lowered and In addition, (water inflow from outside the system <water evaporation out of the system)
For this reason, when the plating solution is concentrated,
Perform the operation to increase the metal concentration target value.

By the above operation, the amount of metal charged is adjusted,
By suppressing excessive metal input, the free sulfuric acid concentration (hydrogen ion concentration: H ⁺ ) in the plating solution can be made constant and the pH can be controlled to a constant value against disturbances due to changes in the balance of the water balance. It became so.

A more specific example of this embodiment will be described below.

In the conventional method described with reference to FIG.
When about 5% of the plating solution is diluted by the inflow of water, when the evaporation operation of the water is finally completed and the bath amount target value Vsp is reached, the metal concentration is also controlled to match the target value. Then, at time t1 before the inflow of water, pH = 1.4, but at time t3 after the completion of evaporation, the pH may decrease to 1.0.

The transition of the metal concentration (total molar concentration) and the sulfuric acid concentration (pH), which is the result of applying the embodiment of the present invention to the case where the same bath amount variation as in FIG. 3A occurs, Are shown in FIGS. 2 (B) and 2 (C), respectively. Note that FIG. 2 (A) shows the same total bath amount fluctuation as in FIG. 3 (A).

In this embodiment, as shown in FIG. 2 (A), the total molar concentration of the metal decreases as shown in FIG. 2 (B) caused by the dilution of the plating solution with the inflow of water. On the other hand, while the bath volume is fluctuating, by performing the feedback control of the metal concentration with the correction target value calculated by the formula (3), the excessive metal supply is suppressed, and the metal equivalent to the plating solution dilution is controlled. Even if the concentration is intentionally lowered and the pH is kept constant during the fluctuation of the bath amount, and the plating liquid bath amount returns to the target value at the time t3 by the subsequent water evaporation,
It is possible to prevent abnormal lowering of pH.

As a result of a detailed study by the present inventor, the sulfuric acid concentration (pH) of the plating solution is a variation factor for the plating efficiency, which is the ratio of the actual coating weight to the coating weight based on Faraday's theory. When the alloy plating of zinc (Zn) and nickel (Ni) is performed, it has a great influence on the efficiency, and it is clear that this plating efficiency is a large factor of variation with respect to the Ni content. became.

Therefore, according to the present embodiment, it is possible to stabilize the sulfuric acid concentration (pH) even when the plating bath amount fluctuates due to the inflow of water or the like. It is possible to stabilize the rate.

Also, when the bath volume of the plating solution is changing,
Further, even when the pH value is returned to the target value, it is possible to prevent the pH from abnormally lowering, so that it is possible to reduce the power consumption per unit of plating (to suppress the lowering of the plating efficiency).

Next, a second embodiment according to the present invention will be described.

The present embodiment is a control method in the case of alloy plating in which two or more metal chemicals are charged, and the dosage of each metal chemical is set so that the metal ion concentration ratio becomes a target value. It was done.

That is, in the control of the concentration of the alloy-based electroplating solution, the metal ion concentration ratio and the H2 SO4 concentration (or pH) can be controlled independently, but the above (D) to (H)
As shown in the reaction equation of H2SO4
Concentration (or pH) control increases the basic unit of drug,
Interference occurs unless an alkaline drug is added.

However, as described above, the present inventor
In electroplating, plating efficiency (ratio of actual deposition amount to theoretical deposition amount of metal obtained from Faraday's theoretical formula)
As a result of detailed examination of the influencing factors on the metal ion concentration, the metal ion concentration has little effect on the plating efficiency in the range of ± 10%, while the free acid (eg H2S
It has been found that an increase in O4) concentration (or a decrease in pH) leads to a decrease in plating efficiency, which deteriorates the basic unit of plating power. When we actually analyzed the operation data, when the pH value decreased by 0.1, the plating efficiency was about 2.5%.
It became clear that it would decrease.

Furthermore, as a result of analyzing the actual operation data and examining the influence on the plating efficiency, when the metal ion concentration ratio increases by 4% from the target value, the plating efficiency decreases by about 6%, and the alloy in the plating layer is reduced. It was found that the plating efficiency decreased by about 10% when the ratio increased by 7% from the target value. Therefore, in controlling the concentration of an alloy-based electroplating solution such as Zn-Ni, it is important to control the metal ion concentration ratio prior to the metal ion concentration, like the H2 SO4 concentration (or pH). It became clear.

The second embodiment is based on the above findings. Hereinafter, the second embodiment will be described in detail with reference to FIG. 5 by taking electroplating of a Zn—Ni alloy in a sulfuric acid bath as an example.

In the present embodiment, although illustration of the plating equipment is omitted, Zn-Ni alloy is continuously plated while moving the steel plate in a plating bath using an insoluble anode. At that time, according to the flow of processing shown by the arrow in FIG. 5, the component concentration of the plating solution is appropriate even when the total bath amount varies based on the measured value of the total bath amount which is the total amount of the plating liquid present in the plating system. To control.

That is, the total bath amount calculation unit 20 calculates the total bath amount based on the detected value of the plating solution level by the level meter installed in the plating equipment for each control cycle, and the calculated value is the total bath amount. The measured value is output to the concentration control calculation unit 22. The concentration control calculation unit 22 controls the metal ion concentration to a corrected target value: CTMCsp of the metal ion concentration calculated based on the input measured value and a preset target value of the total bath amount. Amount of the metal chemical is determined as shown in FIG.
Inputting is done by outputting to. Further, in this concentration control calculation unit 22, the result of measuring the H2 SO4 concentration in the plating solution at each control cycle is input from a sulfuric acid concentration meter (not shown), and the H value is calculated based on the measured value.
When the dose of the 2 SO4 chemical is determined, the dose command signal is similarly output to the dosing device 26B of the plating facility. The dose of the H2 SO4 drug may be determined by using the pH value measured by a pH meter.

Further, at this time, the total bath amount measurement value obtained by the total bath amount calculation unit 20 is simultaneously input to the bath amount control unit 14, and here, a control signal based on the deviation from the total bath amount target value is sent. It is output to the evaporation control unit 28 of the evaporator device to evaporate the water in the plating solution to eliminate the deviation of the total bath amount.

Hereinafter, various calculations executed by the concentration control calculation unit 22 up to the calculation of the metal chemical input amount and the sulfuric acid chemical input amount will be described in detail.

In this embodiment, the metal ion concentration is controlled so that the total amount of metal ions existing in the plating system is maintained constant even if the total bath amount fluctuates. Is performed while changing the above-mentioned corrected target value: CTMCsp, which changes according to the actually measured total bath amount. Hereinafter, this will be described in detail.

Metal ion concentration ([g / l] or [mol / l
]) Is the amount of metal ions per unit bath volume [l] of the plating solution. If the total concentration of plating solution increases or decreases and the concentration is the same, the total amount of metal ions increases or decreases. Will be there. Therefore, when the total bath volume fluctuates, the corrected target value of the metal ion concentration: CTMCsp for keeping the total metal ion volume constant can be obtained so that the following equation (3) holds. . In addition,
The meanings of the symbols used in the formula (3) are substantially the same as in the case of the formula (1), but re-posts including new ones are shown again for easy understanding.

CTMsp × Vsp + (CAsp / Ma) × Vsp = CTMCsp × Vall + (CAsp / Ma) × Vall (3) where CTMsp is a predetermined metal ion concentration target value [mol / l] CTMsp = Znsp / Mz + Nisp / Mn Znsp: Predetermined Zn ion concentration target value [g / l] Nisp: Predetermined Ni ion concentration target value [g / l] Mz: Zn atomic weight Mn: Ni atomic weight Vsp: Target Plating solution total bath volume [m ³ ] CAsp: Predetermined H 2 SO 4 concentration target value [g / l] Vall: Plating solution total bath volume measurement value [m ³ ] Ma: H 2 SO 4 molecular weight

Therefore, the corrected target value: CTMCsp can be obtained by the following equation (4). In addition, this equation (4) is an equation in which Vrot = Vall in the above equation (1),
That is, it corresponds to the formula when the total bath volume is circulated.

CTMCsp = (CTMsp + CAsp / Ma) × Vsp / Vall−CAsp / Ma [mol / l] (4)

Corrected target value of metal ion concentration obtained by the above equation (4): By controlling the metal ion concentration in CTMCsp, it is possible to suppress the excessive addition of metal when the total bath volume of the plating solution is increased, By suppressing the reactions of the equations (D) and (E), it is possible to suppress the decrease of H2 SO4, and thus it is possible to suppress the excessive addition of H2 SO4.

In the above equations (3) and (4), H2 SO
4 When pH is used instead of concentration, the target value of pH: pHsp obtained by the conversion formula of the following formula (5) may be used.

PHsp = −a × log {(Mh / Ma) × CAsp} + b (5) Here, Mh: H 2 molecular weight a, b: conversion coefficient (eg: a = 1.37, b = 0.59) )

Next, the calculation of the dose of the metal chemical agent to the plating system necessary for controlling the metal ion concentration to the corrected target value determined according to the actually measured total bath amount Vall will be described.

First, the consumption rate of metal ions consumed by the plating reaction (electrodeposition reaction) of the above formulas (F) and (G),
That is, Zn ion consumption rate: Gz, Ni ion consumption rate:
Gn is calculated by the following equations (6) and (7).

Gz = J × (η / kF) × (1-εN) × (Mz / 2) × 3600 [kg / h] (6) Gn = J × (η / kF) × εN × (Mn / 2) × 3600 [kg / h] (7) where J: plating current [KA] η: plating efficiency kF: Faraday constant εN: Ni content of Zn-Ni alloy plating layer Mz: Zn atomic weight Mn: Ni Atomic weight

Then, Z according to the above equations (6) and (7)
Feed-forward (FF) control input amounts of n and Ni chemicals: FFZ and FFN are calculated by the following equations (8) and (9).

FFZ = Gz / λz [kg / h] (8) FFN = Gn / λn [kg / h] (9) where λz: Zn content of Zn drug λn: Ni content of Ni drug

On the other hand, the actually measured metal ion concentration: CTM and the corrected target value of the metal ion concentration: CT
The metal ion concentration deviation ΔCTM is calculated from MCsp, and the feedback (FB) control input amounts FBZ and FBN of Zn and Ni chemicals necessary to eliminate this deviation are also considered, and the metal ion concentration ratio target value: CMNsp is also taken into consideration. Next (1
It is calculated by the equations 0) and (11).

FBZ = ΔCTM × (1-CMNsp) × Mn × Vall / λz / t _fb [kg / h] (10) FBN = ΔCTM × spCMN × Mz × Vall / λz / t _fb [kg / h] ... (11) Here, ΔCTM = CTMCsp−CTM CTM: metal ion concentration measured value [mol / l] CTM = Zn / Mz + Ni / Mn Zn: Zn ion concentration measured value [g / l] Ni: Ni ion concentration measured value [ g / l] CMNsp: predetermined target value of metal ion concentration ratio CMNsp = Nisp / Mn / CTMsp t _fb : FB control period [h]

Next, the total control input doses of Zn and Ni chemicals: TZ and TN are obtained by the following equations (12) and (13), and a command signal is output from the concentration control calculation unit 22 to the metal feeding device of the plating equipment. Then, the corresponding amount of each metal chemical is added.

TZ = FFZ + g _fbz × _FBZ [kg / h] (12) TN = FFN + g _fbn × FBN [kg / h] (13) Here, g _fbz : _FBZ gain g _fbn : FBN gain (each of these gains) Is adjusted by the accuracy of the measured value and the drug supply capacity)

At the above total control input amount, each metal chemical was added, and the H2SO4 concentration of the plating solution was also measured. Based on the concentration deviation from the target value at that time, H2SO4 concentration was measured.
4 feedback (FB) control input amount: FBHS is calculated by the following equation (14), and the input command is output from the concentration control calculation unit 12 to the plating equipment.

FBHS = g _fbhs × (CAsp−CA) × Vall / γa / λa [m ³ ] (14) Here, g _fbhs : FBHS gain CA: H 2 SO 4 concentration measurement value [g / l] γa: H 2 SO4 drug specific gravity λa: H2 SO4 drug H2 SO4 content rate

In this embodiment, the above (12), (13)
Total control input amount calculated by the formula: By controlling the supply rates of the Zn chemical agent and the Ni chemical agent according to TZ and TN, the total amount of metal ions is controlled to be constant with respect to the fluctuation of the total bath volume of the plating solution. Is possible. Therefore, even if the H2 SO4 concentration (or pH) is subjected to the general feedback control according to the above equation (13), it is possible to prevent excessive H2 SO4 injection.

As described in detail above, according to this embodiment,
For example, if the fluctuation of the total bath volume of the plating solution is within a range of about ± 5%, the metal ion concentration will fluctuate within a range of ± 5% because the total amount of metal ions is controlled to be constant even during the fluctuation. However, this level has almost no effect on the plating efficiency.

Although the metal ion concentration varies as described above, the metal ion concentration ratio and pH can be controlled with high accuracy. Statistical analysis of actual operation data shows that the control accuracy is 2σ of the metal ion concentration ratio when the standard deviation is σ.
≦ 0.5% and pH 2σ ≦ 0.07.

As described above, since the metal ion concentration ratio can be stabilized and the H2SO4 concentration is not increased (or the pH is lowered), the control can be performed with high precision, so that the plating efficiency and the plating efficiency can be improved. By making it possible to stabilize the alloy ratio of the plating layer, it is possible to greatly contribute to stabilizing the quality of alloy plating and reducing the production cost (electric power consumption rate).

Further, as the alloy ratio of the plating layer stabilizes, the plating efficiency also stabilizes, and the amount of plating adhered also stabilizes. Furthermore, the concentration control of the electroplating solution is controlled by the sulfuric acid concentration (or pH).
At the same time, since the metal ion concentration ratio can be controlled under an ideal control configuration in which the metal ion concentration is controlled in preference to the metal ion concentration, it is possible to prevent the use of an excessive amount of chemicals and consequently reduce the cost of chemicals. .

The present invention has been specifically described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention.

For example, in the above-described embodiment, the single metal plating is described as the Zn electroplating solution in the sulfuric acid bath, and the alloy plating is as the Zn-Ni alloy electroplating solution in the sulfuric acid bath. However, the present invention is not limited thereto. However, if the component concentration of the electroplating solution is controlled, the present invention can be applied to other alloy plating as well as other single metal plating.

[0093]

As described above, according to the present invention,
Even if the total bath volume fluctuates due to water flowing in and out of the plating system, the pH of the plating solution or the free acid concentration can be maintained at a constant value by feedback control of the component concentrations, and the abnormal pH drop or It is possible to prevent an abnormal increase in the free acid concentration from occurring. Therefore, electroplating can be performed with high efficiency and high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of plating control equipment applied to a first embodiment.

FIG. 2 is a diagram showing the effect of the first embodiment.

FIG. 3 is a diagram showing the problems of the conventional control method.

FIG. 4 is a diagram showing the relationship between the concentration of components and the concentration of sulfuric acid in a plating system using an insoluble anode.

FIG. 5 is a block diagram showing a schematic configuration of a control device applied to the second embodiment.

[Explanation of symbols]

 1 ... Bath amount calculation unit 2 ... Control calculation unit 3 ... Concentration feedback control unit 4 ... Concentration feedforward control unit 10 ... Plating cell 12 ... Circulation tank 14 ... Auxiliary equipment 16 ... Level meter 18 ... Liquid analyzer 20 ... Total bath amount Calculation unit 22 ... Concentration control calculation unit 24 ... Bath amount control unit 26 ... Dosing device 28 ... Evaporator device evaporation amount control unit

Claims (4)

[Claims] 1. A plating solution component concentration control method for controlling the metal concentration of a plating solution when performing electroplating using an insoluble anode in a plating facility in which water flows in and out of the system. When the actual value of the total bath volume, which is the total plating solution present in the plating system, fluctuates from the bath volume target value due to the inflow and outflow of water, when the fluctuation occurs, the feedback control target value of the metal concentration is set. Is set to a correction target value calculated based on a predetermined metal concentration target value and a variation amount of the total bath amount so that the pH value of the plating solution is maintained constant. Method for controlling concentration of plating solution component. 2. A plating solution component concentration control method for controlling the metal concentration of a plating solution when performing electroplating using an insoluble anode in a plating facility in which water flows in and out of the system. When the actual value of the total bath volume, which is the total plating solution present in the plating system, fluctuates from the bath volume target value due to the inflow and outflow of water, when the fluctuation occurs, the feedback control target value of the metal concentration is set. To keep the free acid concentration of the plating solution constant,
A method for controlling the concentration of a plating solution component, which comprises setting and changing to a correction target value calculated based on a predetermined metal concentration target value and a variation amount of the total bath amount. 3. The modified target value according to claim 1 or 2, when the plating solution is a sulfuric acid bath: CTMCsp
[Mol / l] is expressed by the following equation: CTMCsp = CTMsp. (Vrot + Vsp-Vall) / V
rot + (CAsp / Ma) (Vsp-Vall) / Vrot (CTMsp: set total molar concentration target value [mol / l],
Vsp: bath amount target value [m ³ ], Vall: total bath amount [m ³ ],
Vrot: circulating bath volume [m ³ ], CAsp: H 2 SO 4 concentration target value [g / l], Ma: H 2 SO 4 molecular weight [g / mol]). 4. The alloy plating according to claim 1 or 2, wherein in the case of alloy plating in which two or more kinds of metal chemicals are charged, the amount of each metal chemical added is set so that the metal ion concentration ratio becomes a target value. And a method for controlling the concentration of plating solution components.