JPS5913585B2 - Automatic management method and device for main components of chemical copper plating solution - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for automatically controlling the concentration of main components in a chemical copper plating solution and the plating speed.

Conventionally, controlling the concentration of the main components of chemical copper plating solutions has been a process of trial and error.

That is, the total surface area of the body to be plated to be plated is roughly estimated, the consumption of the main component is calculated from the plating speed and the plating time based on the factor created by the manufacturer 15-, and a predetermined amount is replenished. However, a more accurate concentration control method has been to perform intermittent chemical analysis to adjust the concentration. When insulating materials such as inorganic and organic materials are coated with metal to make composite materials, chemical 20 copper plating is a pre-treatment method that uses the electrical conductivity of metallic copper to impart conductivity to the insulating material. It was something. In this case, there is no need to place importance on the mechanical properties of the copper plating film, and although the accuracy is low as with the above control method, the time was 25+ minutes using a method that was easy for the customer to control. However, recently there has been an increase in the use of copper metal to form conductors on insulating materials by chemical copper plating, such as in printed wiring boards. In such a case, it is necessary to have not only electrical properties as a conductor but also mechanical properties as a metal to a certain extent. However, since the properties of the plating film are significantly affected by the concentration of the main components of the plating solution, it is natural that plating with good reproducibility and reliability cannot be achieved using the trial-and-error management method described above. It is. Therefore, in order to eliminate the drawbacks of the above methods35, it was considered to perform continuous automatic analysis and control the concentration. When concentration management is automated, concentration changes must be input as changes in current or voltage (potential).

For this purpose, instrumental analyzers are used, but they are generally expensive and complicated, and the coexistence of compounds, ions, etc. other than the target components will cause damage and reduce accuracy. For example, the absorbance measurement method used to control the copper ion concentration of chemical copper plating solutions not only requires expensive equipment, but also allows for the concentration of compounds and ions other than copper ions to be detected due to changes in the pH of the plating solution.
The error was large due to the strong influence of hydrogen gas bubbles present in the plating solution. In a chemical copper plating solution, the main components whose concentrations must be controlled are the pH of the plating solution, copper ions, plating speed, or reducing agent concentration. For pH management, hydrogen ion concentration is generally detected as a potential through a glass electrode and a sweet ice electrode, and a P with high input impedance is used.
Stabilized through H meter. When the detected potential is lower than the potential set by the potentiometer, a solenoid valve or a replenishment pump is operated to replenish the highly alkaline aqueous solution for pH adjustment. When the detected potential becomes higher than the set potential, the solenoid valve or replenishment pump is closed, and replenishment of the highly alkaline aqueous solution is stopped. The above-mentioned absorbance measurement method is used to control the copper ion concentration.

The liquid during the plating reaction is sampled with a micropump, cooled to room temperature, hydrogen gas bubbles in the plating liquid are removed, and then an absorbance meter or colorimeter is used.
It is guided to the measuring cell of the spectrophotometer, and the amount of visible light absorbed is obtained as a change in potential through a photomultiplier tube. Hereinafter, the principle of copper ion replenishment is the same as the above-mentioned pH control. Plating rate is significantly controlled by reducing agent concentration. Therefore, the plating method is sampled from the plating tank using a micropump and introduced into a small volume plating reaction tank. In this reaction tank, metals such as copper, platinum, gold, palladium, etc., each having a certain surface area, are plated and reacted sufficiently on these surfaces for a certain period of time. As a result, the copper ion concentration of the plating solution decreases. If copper ions are detected by the absorbance measurement method described above so that this amount of decrease is constant, the plating rate can be maintained constant by adjusting the reducing agent concentration. Alternatively, hydrogen gas is generated in an equivalent amount to the amount of metallic copper deposited by the reaction. There is also a method of detecting the amount of hydrogen gas. That is, when gas exists as bubbles in the liquid, a method is used in which the amount of light transmitted differs. This method is considered to be cheaper than the above-mentioned method using the spectrophotometric method, but it is important to note that the amount of bubbles is not in an equivalent relationship with the amount of light transmitted, and the size of the bubbles
The accuracy is extremely low because it is affected by the concentration of various compounds in the plating solution. As mentioned above, with the conventional technology,
In order to automatically control the main components of a chemical copper plating solution, one multiple micropump and two expensive absorbance measurement devices were required, and the precision was poor. Furthermore, the concentrations of complexing agents and chelating agents, which are other components of the chemical copper plating solution, were not automatically controlled. The present invention was made in order to solve the above-mentioned drawbacks of controlling copper ions, chelating agent concentration, and plating speed in conventional chemical copper plating solutions. The present invention provides a method for automatically controlling the main components of a chemical copper plating solution with good quality.

The present invention provides a chemical copper plating solution containing an alkali metal hydroxide as a main component as a copper ion, a chelating agent for copper ions, a reducing agent, and a PH adjusting agent.・A chelating agent for copper ions and copper ions in a chemical copper plating solution is detected by detecting the equilibrium potential that occurs when a solution of copper ions, acid, and trivalent titanium ions are mixed at a constant concentration and volume. The concentration, pH, and plating speed are automatically managed.

A detailed explanation will be given below based on a specific experimental example.

first.

A method for automatically managing the main components of a chemical copper plating solution according to the present invention will be explained. The main components of chemical copper plating solution are copper ions,
It consists of an alkali metal hydroxide as a copper ion chelating agent, reducing agent and PH adjusting agent. Therefore, the above 4
It is necessary to control the concentration of ingredients. First, a method for controlling this copper ion concentration will be described. In the plating solution, copper ions form a chelate compound using a chelating agent, and the amount of free copper ions that are not chelated is extremely small. On the other hand, a metal and a metal ion have a chemical equilibrium peculiar to the metal, and this equilibrium is electrochemically expressed as an equilibrium potential. That is, when the equilibrium potential between metallic copper and copper ions is chelated, it is detected as a more base potential according to the Nernst equation, compared to the case where copper ions are not chelated.
Voltage titration is a method of concentration analysis that utilizes changes in potential. In chemical copper plating, compared to the concentration of copper ions,
．． A 5 to 5 times higher concentration of chelating agent is added. Therefore, if a certain amount of a copper ion solution with a predetermined concentration adjusted to contain a small amount of copper ions that do not chelate from the outside is added to a certain volume of such a chemical copper plating solution in a mixing tank, detection can be performed. The potential shown represents the equilibrium potential of unchelated copper ions and metallic copper. The chelating agent is not consumed by the plating reaction, but is only reduced by being attached to the body to be plated and taken out of the plating bath. Therefore, the chelating agent concentration can be considered constant during the plating reaction. Therefore, when the copper ions are consumed by the plating reaction, all of the copper ions are chelated in the mixing tank, and a more base potential is obtained as the potential detected at this time. That is, it is sufficient to replenish copper ions into the plating tank so that the copper ions always exhibit a non-chelated potential in the mixing tank. Since this method detects only the equilibrium reaction between copper ions and the chelating agent, a small amount (1/5 of the copper ions) other than PHL copper ions is detected.
It is not affected by the presence of impure metal ions (about 0 or less), changes in the concentration of chemical copper plating composition other than copper ions and chelating agents, the presence of hydrogen gas and its bubbles generated during the plating reaction, and temperature. Moreover, since the analytical solution discharged from the mixing tank can be circulated to the copper ion supply tank and reused, no waste occurs. From the above, it can be said that this analysis method is significantly more effective and reliable than the above-mentioned absorbance measurement method. In order to make the above method applicable, it is necessary to control the concentration of the chelating agent at a constant level.

Generally, when a chelating agent and a metal ion coexist, it is difficult to analyze both simultaneously, and after determining the absolute concentration of either one, the concentration of the other is determined by substitution, back titration, or the like. In the case of chemical copper plating, the absolute concentration of the chelating agent cannot be determined because the copper ions are removed by creating a stable chelate compound. Therefore, it is necessary to determine the absolute concentration of copper ions. When the pH of the chelating agent is in a strongly acidic region of 1 to 0.5 or less, it becomes unable to dissociate and does not form a chelate compound with the metal ion. Therefore, free metal ions, that is, metal ions that can undergo redox reactions with copper ions, such as S2+)
Titrated with N, Ti needle, 21 etc.

This reaction is shown in equation (1). First, a predetermined concentration of C2 for chemical copper plating is added to a certain volume of chemical copper plating solution from the outside.
To reduce + to C+, there is a slight shortage of strong acid T3.
+ A fixed amount of solution is added and mixed in a mixing tank.

For a given concentration of C2u+, the potential detected by an insoluble electrode such as platinum, gold, rhodium, carbon, palladium, etc. is the equilibrium potential between C2+/Uc+.

When the chelating agent adheres to the plated body and is taken out of the plating bath, and the concentration of the chelating agent decreases, according to the copper ion concentration control method, copper ions are removed in response to the change in the chelating agent concentration. Since the concentration is controlled, the copper ion concentration is controlled to be lower than the predetermined concentration in proportion to the amount of decrease in the chelating agent concentration.

Therefore, C2u+ is below the predetermined concentration, and in this device, T4l7T3. + C27C+ is detected as a more base potential than 1UU.

That is, before charging the body to be plated into the plating tank, an additional C2+ source is supplied until the potential of C2u+/C+u can be constantly detected by this device, and the copper ions in the plating tank are heated to a specified level. Let it be the concentration.

Next, the above-mentioned copper ion concentration control device constantly supplies additional chelating agent until the equilibrium potential between metal/copper ions is reached. As described above, the concentrations of copper ions and chelating agent are simultaneously controlled by the operations of both devices. Furthermore, the plating speed can be controlled by applying the above device.

That is, a part of the plating tank is heated at a constant flow rate, for example, with a volume of 10
It is sent to a reaction tank consisting of about 0 ml. A metal plate having a constant surface area, such as Au, Pt, Pd, Cu, etc., which can be fitted, is immersed in the reaction tank. The plating speed can be controlled from the flow rate of the plating solution, which is the amount u of decrease in C2+ concentration of the discharged solution after the plating reaction.

Detection of the C2+ concentration is performed by the same procedure as in the copper ion concentration control device u.

The plating speed is adjusted by adjusting the concentration of the copper ion solution mixed externally, and the reducing agent is replenished so that the equilibrium potential between metal copper and copper ions is always detected. It is circulated to the supply tank and reused. Further, PH control is performed by detecting the potentials awaited by the glass electrode and the saturated sweet water electrode, as in the prior art. The above description will be specifically explained with reference to the attached drawings.

The figure is a configuration diagram of an automatic control device for the main components of a chemical copper plating solution according to the present invention. In the figure, 1 is a plating tank, and the plating liquid contained therein is sent by a multiple tube pump 2 to each analyzer described later. 3 is a heat exchanger that cools the plating solution to about room temperature, 4 is a PH measurement tank with two glass electrodes, 5 is a PH meter, and 6 is a built-in relay that is activated by the indicated value of PH meter 5. A control device controls the replenishment of alkaline aqueous solution from the replenishment tank 7 to the plating tank 1 by opening the solenoid valve 8 with a switch. 9 is a control device that controls the replenishment of the alkaline aqueous solution from the replenishment tank 7 to the plating tank 1; reference numeral 9 denotes the sucked plating solution and the copper ions sucked in from the copper ion solution tank 10 by the tube pump 11; A mixing tank 12 is used to mix solutions, and 12 is a potential measuring tank that has a spiral metal copper wire connected to a control device 13 and a saturated sweet water electrode, and detects the equilibrium potential of the inhaled mixed solution. is lower than the set potential, the control device 13
A solenoid valve 15 is opened by a built-in relay switch, and the plating tank 1 is supplied with a concentrated copper ion solution from a supply tank 14.

16 is a plating reaction tank, which is installed in the plating tank 1, and plating is performed on metal plates such as copper, platinum, gold, palladium, etc., and the copper ion concentration is reduced by the plating reaction. There is.
17 is a heat exchanger for cooling the plating liquid whose concentration has been reduced in the plating reaction tank 16 to about room temperature; The mixing tank 21 is a potential measuring tank that has a spiral metal copper wire connected to the control device 22 and a saturated Kanaga electrode, and detects the equilibrium potential of the mixed liquid passing through the mixing tank 18. When the potential is higher than the set potential, a relay switch built in the control device 22 causes the solenoid valve 2 to
4 is opened, and the reducing agent solution is supplied from the supply tank 23 to the plating tank 1.

Reference numeral 25 denotes a pot, and by closing the pot 25, the flocculation liquid sucked by the multiple tube pump 2 is sent to the mixing tank 26.

This mixing tank 26 contains the sucked matting liquid and the titanium solution tank 2.
The titanium solution sucked in from the tube pump 28 from the mixing tank 26 is mixed with an insoluble electrode such as a spiral Pt or Au wire connected to the control device 30 and a saturated Kanaga electrode. The voltage is sent to the potential measurement tank 29. A relay switch built in the control device 30 is connected to the solenoid valve 1 of the replenishment tank 14 containing the aforementioned concentrated copper ion solution.
It also performs opening/closing control of 5. Reference numeral 31 denotes a chelating agent supply tank, and the stored chelating agent is controlled by a solenoid valve 32 by a relay switch built into the control device 13 described above. 33 is a waste liquid tank for the analysis liquid containing impure metal ions discharged from the potential measuring tank 29.

Next, the operation of this device will be explained.

First, plating liquid is sent from the plating tank 1 to each analyzer at a constant flow rate by the multiple tube pump 2. In controlling the copper ion concentration, the plating liquid is cooled to about room temperature in the heat exchanger 3. Next, in the PH measuring tank 4, the PH is detected as a potential using a glass electrode and a saturated Kanaga electrode, stabilized through a PH meter 5, and passed through a control device 6, where a relay switch (not shown) is opened and closed based on the set potential. . If the potential is lower than the set potential, the relay switch in the control device 6 is closed, the electromagnetic valve 8 is opened, and the plating tank 1 is supplied with liquid from the concentrated alkaline aqueous solution supply tank 7. The plating liquid coming out of the pH measurement tank 4 enters a mixing tank 9, where it is mixed with the plating liquid and copper ion solution from a copper ion solution tank 10 for titration by a tube pump at a constant flow rate. Next, an equilibrium potential is detected in the potential measuring tank 12 using a spiral metal copper wire and a saturated sweetened water electrode, and a relay switch is opened and closed through the control device 13 based on the set potential. If the potential is lower than the set potential, the concentrated copper ion solution passes through the replenishment tank 14, the relay switch in the control device 13 is closed, the solenoid valve 15 is opened, and the solution is replenished into the plating tank 1. The analytical solution that has left the potential measurement tank 12 is put into the copper ion supply tank 14 and reused. The plating rate is controlled by sufficiently plating a metal plate made of copper, platinum, gold, palladium, etc. with a constant surface area in the reaction tank 16.

In the reaction tank 16, the copper ion concentration is reduced by the plating reaction. This liquid passes through the multiple tube pump 2, enters the heat exchanger 17, and is cooled to about room temperature. Next, mixing tank 1
In order to detect the plating rate, that is, the copper ion concentration decreased in the reaction tank 16, the copper ion solution tank 19 for titration, which is adjusted to a predetermined concentration, passes through the tube pump 20 to the mixing tank 18 at a constant flow rate. sent and mixed. Thereafter, an equilibrium potential is detected in the potential measurement tank 21 by a spiral metal copper wire and a saturated sweet water electrode, and a built-in relay switch is opened and closed by the control device 22 based on the set potential. If the detected potential is higher than the set potential, the relay switch in the control device 22 is closed, the solenoid valve 24 below the reducing agent supply tank 23 is opened, and the reducing agent solution is supplied to the medium tank 1.

Note that the analysis liquid that has left the potential measurement tank 21 is sent to the copper ion replenishment tank 14 and reused. Next, chelating agent supply control will be explained.

First, before charging the body to be plated into the plating tank 1, it is necessary to check or correct the concentration of the chelating agent. In this case, the standing liquid discharged from the multiple tube pump 2 is sent to the mixing tank 26 by closing the pot 25, and the C2+
A strongly acidic titanium solution is sent from the titanium solution tank 27 through the tube pump 28 at a constant flow rate and mixed in the mixing tank 26.

Next, in the potential measurement tank 29, the oxidation-reduction potential is detected through an insoluble electrode such as a Pt or Au wire and a saturated Kanaga electrode, and the control device 30 opens and closes a relay switch based on the set potential. If the detected potential is lower than the set potential, the relay switch in the control device 30 is closed, the solenoid valve 15 below the copper ion supply tank 14 is opened, and the copper ion solution is supplied to the plating tank 1. The copper ions are replenished until the concentration of copper ions inside reaches a predetermined concentration. At the same time, the control device 13
until the detected potential of the controller 13 becomes lower than the set potential.
The relay switch inside is closed, the electromagnetic valve 32 below the chelating agent supply tank 31 is opened, and the chelating agent is replenished into the plating tank 1. The analysis liquid leaving the potential measurement tank 29 is discharged to the waste liquid tank 33 because it contains impure metal ions such as titanium. In this case, each of the above-mentioned mixing tank and potential measuring tank may have a volume of about 257 n1, and the whole is extremely compact.
Therefore, each part can be manufactured by glass work. In FIG. 1, tube pumps 2, 11, 2
0,28 can be operated with one 6-tube pump. The control devices 6, 13, 22, and 30 consist of a control circuit and a relay switch, and are not special.
This is the same principle used in automatic control. These devices are not incidental to the invention, but are necessary for any automatic control, and can be fabricated using potentiometers and integrated circuits. For example, when applying a commercially available product, “Kuwano Electric Digital Comparator EC”
-411" can also be used, but it is preferable to make one suitable only for control according to the present invention, which will be cheaper. Next, we will give specific numerical values and explain in detail. (1)
Composition and conditions of chemical copper plating solution with automatic concentration control (2) Alkaline solution for pH adjustment (3) Replenishment solution for copper ion concentration adjustment and control titrant control conditions (4) Set potential -0.164V (S. S.C.E.)-0.
Replenish the replenishment liquid when it is more negative than 164V - Replenishment liquid for speed adjustment and control titration liquid (5) with replenishment stop when it is more positive than 164V Control condition setting potential -0.164 (Vs.S.C.EOO.l6
If more positive than 4, replenish the replenishment liquid -0.164 V or more negative, stop replenishment Replenishment liquid for chelating agent concentration adjustment and control titrant control condition setting potential +0.080 (Vs.S.E.C) +0.0
If it is more negative than 80, replenish the replenishment liquid in term 3) + If it is more positive than 0.080, stop replenishing the replenishment liquid in term 3) Then in term 3), -
If it is positive than 0.164V, replenish the replenishment liquid in step 5), -0.1
When an attempt was made to automatically control the concentration of a plating solution having a composition and conditions of 64 V or higher under the above control conditions, the results shown in Table 1 were obtained.

These automatic concentration controls were performed for a total of 100 to 200 hours, and when we checked the concentration controls separately by chemical analysis and spectrophotometry, they actually matched the control conditions and were within ±5 The concentration was controlled with an accuracy of 1.5%.

This management requires two tube pumps (Micro Pump RP- manufactured by Furue Science), four solenoid valves (SV-05 manufactured by Daiichi Rika Shokai), and four control devices (digital comparator EC-411 manufactured by Kuwano Electric). This was done using a glass-worked grating device, which proved to be an inexpensive and highly accurate automatic control device. Note that the above automatic control method and apparatus are not limited to the chemical copper plating described in the examples, and may also be used as metal ions, complexing agents or chelating agents for metal ions, and alkali metal hydroxides as PH adjusting agents.
It also applies to the automatic management of gold, silver, copper, nickel, and other chemical plating consisting of reducing agents. As described above in the embodiments, according to the present invention, a control device for controlling the concentration of each main component in a chemical copper plating solution and the plating speed can be constructed easily and inexpensively, and the PH of chemical copper plating can also be controlled easily. This has the advantage that highly accurate management can be automatically performed without being affected by compositions other than the main components of hydrogen gas.

[Brief explanation of the drawing]

The attached figure is a configuration diagram of an automatic control device for the main components of a chemical copper plating solution, showing an embodiment of the present invention. 1...Plating tank, 2, 11, 20, 28...
...Tube pump, 3,17...Heat exchanger, 4...PH measurement tank, 5...PH meter, 6,13,22,30... ...control device, 7
...Alkaline aqueous solution supply tank, 8, 15, 24
, 32... Solenoid valve, 9, 18, 26...
・Mixing tank, 10, 19...Copper ion solution tank, 1
2, 21, 29...Potential measurement tank, 14...
...Copper ion supply tank, 16...Reaction tank, 23.
...Reducing agent supply tank, 25 ... Kotoku, 2
7... Titanium solution tank, 31... Chelating agent supply tank, 33... Waste liquid tank.

Claims (1)

[Claims] 1. Copper ion, copper ion chelating agent, reducing agent, and P
In a method for detecting and managing the main component concentration and plating speed in a chemical copper plating solution containing an alkali metal hydroxide as a main component as an H adjuster, a constant concentration, By detecting the equilibrium potential that occurs when a fixed volume of copper ions, acid, and trivalent titanium ion solution are mixed, the copper ions in the chemical copper plating solution, the copper ion chelating agent concentration, PH, and plating speed can be automatically determined. how to manage it. 2. A means for measuring the pH of the plating solution sucked from the plating tank and replenishing the alkaline aqueous solution to the plating tank when the measured value matches a preset value; and a copper ion solution prepared in advance, and means for replenishing the concentrated copper ion solution to the plating tank when the equilibrium potential of the mixed solution is lower than a set value, and plating the plating tank in the plating tank. A reaction tank is provided, and a plating solution whose concentration is reduced with a metal plate is mixed with a copper ion solution for titration prepared in advance, and when the equilibrium potential of the mixed solution is higher than a set value, the reaction is returned to the plating tank. a means for replenishing the plating agent; and a means for replenishing the plating tank with a concentrated ionic solution for mixing the inhaled plating liquid with a titanium solution prepared in advance and replenishing the concentrated ionic solution to the plating tank when the redox potential of the mixed liquid is lower than a set value. , an automatic main component management device for a chemical copper plating solution comprising a means for replenishing a copper ion chelating agent.