DE2759952C2 - Process for the operational control of a copper plating bath that works without an external power supply - Google Patents

Description

The invention relates to a method for Operational control of a person working without an external power supply Copper plating bath using the deposition process as a function of oxidation and reduction of forming bath parameters measured as mixed potential.

The automatic control of electroless metallization baths via the redox mixpotentIaI is generally known and indispensable for an economical operation of such baths. For example, for the Durni-Coat process a continuously working system known, which in connection with the currentless Nickel plating of objects is different

ίο measuring probes operated for a plurality of parameters are used, so for temperature measurement, measurement of the pH value, the nickel ion concentrate'Mn, The stabilizer and reducing agent concentration as well as the cloudiness of the bath. The ones from the probes continuously supplied electrical signals are correlated via a process computer and used for control the corresponding operating data is used (electroless thick nickel plating according to the Kanigen-Durnl-Coat and Nibodurverfahren 1971, pp. 9 to 10).

A measuring method and its technical application for continuous, electroless metallization systems has also been described above, in which a special device is used for measuring the pH value, which works in such a way that the circuit, which runs via an heating system to keep the temperature constant, Samples are continuously taken in the bypass circuit. The sample is geleitel respectively before introduction into the measuring chamber via a cooler which lowers the sample temperature of 68 "C to about 20 ^J C, was said to be observed even in a long-term use of the electrodes no copper plating of the diaphragm, so that hereby a Continuous measurement of the pH value of reductive copper plating baths is guaranteed. This measurement is the prerequisite for the continuous regulation of the pH value, whereby the metal ion concentration and the bath density for the automatic operation of the bath are controlled in parallel (Dissert & Uen 1972 by ü. Herrmann, Clausthal University of Technology).

The use of comparison electrodes for measurement of the mixed electrode potential in electroless nickel-plating baths In connection with a process for measuring the mixed potential is also not new (see. US-PS 33 75 178), where the measurement of the However, the mixed potential is used exclusively to determine the point at which the metal deposition occurs Should use in the bathroom.

In the above-mentioned known methods, the means of known control technology are used for the purpose of supplementing individual bath components in the continuous operation of electroless metallization baths, but either the mixed potential for the control process does not play a role or serves the sole purpose mentioned above. Quite generally, in a theoretical work on shelling of copper plating with electroless copper from copper sulfate solutions containing EDTA, it has been said that inexplicable behavior when copper is deposited from copper sulfate solutions and solutions containing EDTA as a complexing agent, the resulting mixed potential can play a role (cf.Plating 55, 1968, pp. 1161 to 1167).
The present invention is now based on the task of developing a method of the type mentioned at the beginning in such a way that the bath activity is detected by measuring the mixed potential and can be used to regulate certain bath components in order to

ΐ Swinging swirls and thus being able to keep the bath activity within M optimal limits.
ti This object is achieved according to

achieved by the features specified in the characterizing part of claim 1.

K Advantageous developments and further developments

y -. [. This task solution results from the sub-ΐ sayings.

V It is essential in the present process that

'' The use of the measured value the present purpose only is the mixed potential for ^ advantageously possible when the mixed potential on a; '' - held certain predetermined constant value { '' ■ is that of the target composition of the bath solution '■: ■■■ depends. The value of the mixed potential is therefore a value that is characteristic of the bath activity, which is by no means to be equated with the bath concentration.
Ψ- Is, for example, kept constant under otherwise

i; Conditions, the mixed potential for measuring the Badak-% tivity of these positive or a negative beeiniS this flow ends Badbestandteils used, the measurement can be:? J signal or the deviation from a target value to i; Returning the activity to the desired value by means of the addition of the relevant ft Badbestandteils DIE f ', NEN. If a divalent sulfur compound is used as Badf. if used as an addition, it causes a decrease in concentration; f an increase in bath activity; too high concen- "tration other hand, leads to a comparison ^{unerwünsch'en;.} ringerung the bath activity, which can lead to a stop of the deposition, the measurement of such Badzu- 'sets of analytical means abuts due to the extremely low concentrations in which those With the present method, the activity of the bath is advantageously determined by means of a mixing poientla! And its deviation from the nominal value is used in order to add enough divalent sulfur compound by means of the usual automatic addition method that the Mlschpotentlal wlecor is returned to the nominal value.

It is also possible to function independently or simultaneously with the measurement of the activity ah an additive that is usually used to stabilize the bath and reduce the activity, a second additive can be added to be controlled by means of mixed potential, which increases the BadaktlvitiU. Here, too, the deviation used by the nominal value to accomplish in additions by means of preferably automatic devices, until the bath activity indicated by the mixed potential has reached the setpoint again. As a case in point for this, the addition of formaldehyde can be mentioned, in which, similar to the example given above, the concentration determination by means of usual analytical methods because of the complexity and Unreliability is unsatisfactory.

Furthermore, is a particular advantage of the present Procedure to indicate that activity variations caused by changes in the concentration of the excipients Within certain limits, as would be permissible per se for bathing, but because of you Uncontrollers have been extremely annoying up to now and have to be automatically compensated. For example the bath activity within certain limits due to temperature or pH fluctuations and the like this fact is increased by the present Method automatically taken into account that the addition of the mlschpo.cntlalabhänglgen component or components is only done in such a way that the specified Mlschpotentlal and thus the specified

Ceases bath activity.

A typical electroless copper-depositing bath consists of a copper salt, a complexing agent, a lye, a component to improve the ductility of the deposited copper layer, a stabilizer and a wetting agent. The composition can be, for example, the following:

(1) 0.02 to 0.08 mol / l CuSO ₄ or CuCl ₂ ;

(2) NaOH or KOH in an amount that the pH value of the solution is between 11 and 14;

(3) 0.01 to 3.0 moles of a reducing agent such as formaldehyde or a hydride such as borohydride or aminoborane;

(4) 0.02 to 0.4 mol of complexing agents, such as Na ₄ EDTA, K- ^{] i} Na tartrate, HPE [tetrak (2-hydroxypropyl) ethylenediamine], a polyalkanolamine or an amino acid;

(5) 10- ^J Ws ΙΟ " ¹ g / l ductility promoter such as NaCN:

(6) 10- 'to 10 " ³ g / i of a stabilizer, as well

(7) up to 5 g / l of a new egg, such as aikyiphenoxy- or polyethoxyphosphate ester.

In addition to the components mentioned above, for example, from which the bath is originally composed, the copper deposition bath still draws during operation a number of by-products generated during bath operation.

The bath parameters, such as pH value, copper ion concentration. Reducing agent concentration.

jo concentration of the complexing agent, temperature. Deposition rate, bath loading, type and intensity of bath movement, rate of removal of the hydrogen formed during the reduction. The concentration of the by-products resulting from the reduction and the amount of poisoning substances are kept as constant as possible through regular analysis of the bath components and the corresponding chemical additives.
In addition to the automatic control methods already described, another control option is specified by determining the "mixed potential", the mixed potential being used to control the bath conditions, in particular as a measured variable for controlling the activity of the bath or the concentration of the bath-stabilizing additives, is used. The control of certain bath stabilizers by chemical analysis is known to be very difficult because of the usually extremely low concentrations, so that previous attempts to use the mixing potential to determine the slabllizer-dependent bath activity have produced unsatisfactory results because too many other components influence the mixing potential.
The present method for operating a currentless copper plating bath overcomes the previous drawbacks and enables a reliable bath belt and the connection of the spontaneous decay of the bath solution.
It is advantageous to use in the present method

so to measure two electrodes, whereby metal is deposited on one electrode, while the other serves as a reference electrode. The mixed potential is kept constant within a certain tolerance range. This tolerance range is determined by factors that wear out, for example the composition of the bath solution or the nature of the reference electrode.
To determine the Mlschpotentlals

Both electrodes are located within the separation bath. However, if the bath operates at high temperatures, so it is appropriate to put the reference electrode in a to accommodate a separate chamber.

The Cu "ion concentration can be colorimetric by measuring the absorption in the red spectral range to be determined. It should be noted that this measurement by the pH value, the temperature and some Complexing agents can be influenced; Corresponding corrections must therefore be made.

The cyanide concentrate can be obtained by means of commercially available Special electrodes are carried out, provided that that the bath level is reduced to such an extent that there is no metal on the measuring or comparison electrode knocks down. Also with this measurement are temperature and pH value to be taken into account.

The formaldehyde concentrate can also be colored • be determined metrically or photometrically by adding a reagent which colored with formaldehyde Forms connections. Another method is to lower the pH of the solution to such an extent that Formaldehyde reacts with an excess of added sodium sulphide. The one caused by the reaction An increase in the pH value is a measure of the formaldehyde concentration, wherein the starting pH is chosen so that the resulting after the reaction pH value is in a favorable measuring range.

The concentration of the reaction by-products can be determined by determining the density of the bath solution will.

The "Mlschpotenlial" of the bath liquid is fundamental the sum of the half-reactions, which essentially result from the oxidation of the reducing agent and the Reduction of the copper ions to metallic copper exist. Running on the same conductive surface several Oxidallon / Redukiions processes at the same time, so each reaction has its own equilibrium and ith own electrode potential. But since there is only one potential on a conductive electrode surface can, a constant potential, dus "mixed potential", develops during the course of the reaction.

The mixed potential of an electroless metal-depositing bath is measured by means of two electrodes, the metal isolation electrode is in the working bath liquid and a comparison electrode trade In their immediate vicinity. The mixed potential arises from the deposition reaction and is measured between the deposition and comparison electrodes.

The deposition electrode consists of a metal, for example platinum, backing with a copper coating, see above because copper is constantly separating out of the bath liquid. Almost every metal electrode is after the When placed in an electroless copper plating bath, immediately coated with a copper layer.

AsI comparison electrode can either be a calomel or a silver / chlorosilver electrode can be used.

The determination of the mixing potential in the active bath liquid presents certain difficulties. For example the temperature of the working bath is between 40 and 95 ° C. Under these conditions the If the comparison electrode is placed next to the deposition electrode, then copper will usually also appear on the Knock down the reference electrode and thereby render it unusable; the comparison electrode will continue If it is located away from the deposition electrode, the measurement conditions are unstable. Satisfactory Results can be achieved if the comparison electrode is placed in a separate chamber at reduced Temperature and bath movement applies, which over a liquid wedge bridge with the active bath liquid and the deposition electrode mounted therein is connected, the liquid bridge as possible should be kept short (S to 10 cm).

The chamber with the comparison electrode can be used against that of the deposition electrode must be thermally insulated. Of the Contact between the comparison electrode and the active bath liquid is preferably via a connection produced, which contains an inert salt solution and which on the one hand with the chamber of the comparison electrode and on the other hand with the active bath liquid through each a porous membrane is in communication. The activity the bath liquid in the comparison electrode chamber is reduced by reducing the bath temperature and movement degraded.

Between the concentration of the individual bath components and the mixed potential there is no simple relationship; so has z. B. a change in concentration of the bath components does not result in a linear increase in the mixed potential. For example, the concentration of formaldehyde is increased to such an extent that there are no longer enough copper ions to increase the rate of reaction are available, the mixed potential does not increase any longer.

This is in accordance with the present procedural system Mixing potential of the bath liquid within certain Maintain tolerance limits. For commercial copper plating the result was a range between -200 mV and -1.5 V, measured against a standard calomel electrode, and -115 mV and 1.455 V, measured against a silver / chlorine-silver electrode, as the most favorable value. Advantageously the mixed potential is set to values between -600 to -850 mV, measured against a calomel electrode, and to -555 to -805 mV, measured against a silver / chlorine silver electrode.

The best results are obtained with values between -630 to -760 mV (standard calomel electrode) and -585 to 715 mV (silver / chlorine silver electrode) achieved. If using a standard calomel electrode, which one the measured values compared to other electrodes, for example silver / chlorine-silver electrodes, by about 45 mV. In practice, there may be a deviation in the mixed potential can be accepted against the specified target value of ± 5 mV to ± 50 mV; preferably However, the value will be within a range of ± 10 to 2.25 mV held. For example, the target value for a specific copper plating bath based on EDTA is -675 mV ± 10 mV or ± 25 mV.

The device used for the present process determines and sets the individual bath parameters adjust these to the desired values. After practically all parameters determine the mixed potential effect, you will practically only determine and set the bath parameters that are greatest Have influence on the mixed pool. These include copper ion concentration, active concentration of the Reducing agent, active concentration of the stabilizer, pH and temperature. Preferably with the device measured the mixed potential and the temperature, the pH value, the copper ion concentration and the stabilizer concentration is determined and kept within predetermined values. The device will designed so that the corresponding addition is a consequence of the measurement, with the temperature also being automatic is set. The device measures the mixed potential and sets the temperature, the copper ion concentration

tion and the pH value and at the same time adapts the active stabilizer and reducing agent concentration accordingly, so that the mixed potential remains within the specified range. In one embodiment the mixed potential is measured and, accordingly, the activity of the reducing agent and / -> ler of the stabilizer set and so the Mlschpoientl.d Maintained within the specified setpoints; the temperature is also determined automatically and regulated and the copper concentration, the pH and the cyanide concentration is always on your target values held.

The parameters influencing the mixed potential are measured with the aid of the device described above, which is to be determined in each case and / or to be controlled bath parameters is adapted and each parameter individually as well as the Mlschpotentlal certainly.

Such a device is shown in Fig. I and consists of a pump 1 for pumping out a control amount of the bath liquid as a Tesiflüsslgkell, which Im Separation tank 2 is removed and passed through a valve 3 into a chamber 4 where the separation electrode is located 5 is located.

Adjacent to the chamber 4 is a chamber 6 with the comparison electrode 7, which together with the shielding electrode 5 for measuring the mixed potential serves. The clamp 4 contains a thermistor 8, which is also in the position 9 or the degasser lOzum Enigr. ~ <En of the liquid can be arranged. Of the Chamber 4 is the test liquid through the heat exchanger U and 12 and then into the Chamber 13, which is used for the colorimetric determination of the copper ion content. From the chamber 13 is the Test liquid passed into the chamber 15, which also a thermistor 16 and a combined pH-value comparison electrode Π. Then the test fiows flow via the first heat exchanger U back into the separation tank 2. The second heat exchanger is cooled with water from outside the system.

Another embodiment of the device is in fl. 2 and is used to measure the temperature, the copper ion concentration, the pH value, the Cyanide and formaldehyde activity as well as the determination of the amount of by-products that are produced in the Badarbelt attack.

The test liquid is by means of a pump 19 of the Bath liquid 18 removed and passed through the valve 20 into the chamber 21, which the Abscheldungseleklode 22 contains which In connection with the Verglelchselek- so Trode 24 in the adjacent chamber 23 is used to measure the mixed potential. The chamber 21 can also contain a thermistor 25, which can also be mounted in position 26 or on the carburetor 27.

The test liquid is transferred from the chamber 21 via the Heat exchangers 28 and 29 passed into chamber 30, soft the copper color meter 31 and the cyan electrode 32 contains. The liquid is then placed in the chamber 33 passed, which contains a second thermistor 34 and a pH value measuring electrode 35. A part of Test liquid is then passed into chamber 36, in which Their density and thus the amount of by-products formed is determined with the device 37. The remaining test liquid is put into the reagent pump 38 geieitet, which pumps it into a device where it is charged with air and treated with sodium sulfite. from there the liquid arrives in a mixing vessel 39 in which there is an acid. The supply of sodium sulfite and acid comes from storage vessels 40 and 41. The liquid enriched with acid and sodium sulphate is from the mash container 39 into the chamber 42 where with the help of the pH value comparison electrode

43 their pH is determined. The increase in pH is proportional to the amount of formaldehyde present.

Normally the test liquid will flow through the pipe

44 discharged as waste liquid. If your composition however that corresponds to the bath composition, it can also be used directly or together with the other part of the test liquid from the chamber 36 In the separation tank 18 can be geled back.

The test liquid from the chamber 36 is via the Heat exchanger 28 and back dropped into separation tank 18; the second heat exchanger 29 becomes cooled with cooling water from outside the system.

The In the Flg. 1 and 2 shown devices also contain control units for the automatic registration and implementation of the by the measuring devices delivered signals. Each test device generates a millivolt signal, which is controlled by a type of potentiometer, such as a digital control potentiometer. The control device enables measurement and triggering corresponding reactions to the measured values by means of electrical signals, preferably in millivolts. Each generated signal is applied to a potentiometer, which is given certain limit values. The potentiometer in turn generates an output signal via a decision gate or the like, if the signals are outside the specified limit values, which means, for example, the addition of a certain Amount of a certain chemical is effected. If the control unit detects a pH value that is too low, it cause the addition of a certain alkaline solution. In another embodiment, that can Control signal trigger the addition of stabilizer liquid when the mixed potential has a value that Too far in the negative realm, or it loosens in the opposite If the addition of formaldehyde as a reducing agent fails, if the value of the Mlschpotentlals is too far in the positive range.

In a further embodiment in which the Formaldehyde content, as shown in Fig. 2, constant is maintained, deviations in the values of the mixed potential can have other causes. A sign there is a negative potential for the addition of stabilizer. When the control signal for the Mlschpotentlal an accelerator or a formaldehyde oxidation catalyst must be used be admitted.

Some examples are shown below: Comparative experiment A

The copper deposition bath used was composed as follows:

Copper sulfate 10 g / l Tetrakis-2-hydroxypropylene ethylene chloride 17 g / l Formaldehyde (37%) i5 ml / l PH value 12.8 temperature 28 ° C Sodium cyanide 25 mg / 1 Potassium sulfide 0.4 g / l 2-mercaptobenzothlazole 0.04 g / l

The copper ion structure of this deposit bath was constantly checked by means of a colorimeter, which at the same time controlled the required addition of Kupfersql fat. The Tetrakjs-2-hydroxypropyläthyIendi-

11 59

ίο

amln was not consumed during the coating process, so that daily or weekly checks and, if necessary, additions are sufficient. Proportional to The addition of copper sulfate became a 37% formaldehyde solution added; In addition, the formaldehyde content was analyzed daily and the appropriate amounts were added. The pH value is constantly monitored, with Using a glass electrode and a calomel electrode as a reference electrode. The resulting from the pH value measurement The control signal simultaneously controlled the addition of NaOH. Sodium cyanide was proportional as an aqueous solution added to the NaOH. The stabilizer additions kallumsulfld and 2-mercaptobenzothlazole were correspondingly the amount of copper plated and the amount of tent that has elapsed.

The Mlschpotentlal was between an im deposition bath located plate and the calomel electrode, which is used as a comparison electrode for the pri-VVeri-Mcssung serves, determined. The Mlschpotentlal pointed in this case very fluctuating values between - 520 mV and - 720 mV.

The deposition bath was difficult to control; either the copper hit the walls of the vessel down and the bathroom tended to decay spontaneously; or, if enough sulfur-containing stabilizer is added the deposited copper turned dark in color, became passive, and the deposition came very soon completely to a standstill.

By increasing the layer of liquid in the overflow vessel, the uptake of oxygen was reduced and the release of hydrogen more difficult, as a result of which the pulp potential changed and now showed a value of -640 mV. The height of the liquid in the overflow was now about V ₄ 'of the height in the separation tank, while it had previously only been about V ₁ . By adjusting this level and by regulating the addition of sulfur-containing stabilizer, it was possible to keep the bath at a Mlschpotentlal of -635 mV ± ! 0 mV; it worked satisfactorily for two consecutive weeks without a break. This experiment shows that the Mlschpotentlal can be used to control and regulate the hydrogen and oxygen content.

Example III

An electroless copper stripping bath was made according to the following composition:

Example I.

30th

The determination of the mixed potential according to Comparative Experiment A was changed in the way that a SlI-ber / Chlorosilber electrode used as a reference electrode and this in close proximity to the shielding electrode was attached. However, it was found that he! the comparative copper was also deposited on the deposition electrode, so that it was used for measurement became unusable. The comparison electrode was therefore placed in a separate, cooled bath solution filled chamber attached, which has a with a Intermediate pain filled with inert saline solution with the active deposition bath and thus with the deposition electrode was connected. Satisfactory results have been obtained with this device. The electrodes were connected to a differential amplifier; the signal sent by this was used to control the Added stabilizer used. An aqueous solution of kallumsulfld and 2-mercaptobenzothlazole served as the stabilizer in a ratio of 10: 1. The target value for the Mlsch potential was -635 mV ± 10 mV. The so controlled Deposition bath worked excellently; the deposited copper was shiny and ductile and the bath sloped neither to spontaneous decay, nor did the copper surface show any signs of passivation.

Example Il

The bath according to A was used in a tank containing a circulation pump. Which was a tank wall lower than the other and served as an overflow. The eo Pump pumped the overflow liquid back into the tank. Through this overflow device was simultaneous an uptake of oxygen and an escape of the hydrogen produced in the reaction enables. The Mlschpotentlal was -600 mV; the deposited copper layer was dark and the The peeling process came to a complete standstill after a few hours.

Copper sulfate 12.5 g / l Tetrakls (2-hydroxypropyl- 15.6 g / l ethylenediamine Formaldehyde (37%) 3.5 ml / l Sodium hydroxide for 12.95 Adjusting the pH to Sodium cyanide 10.0 mg / 1 Potassium sulphide 1.0 mg / 1 2-mercaptobenzothlazole 0.1 mg / 1 Wetting agents 0.14 g / l temperature 53 C Bath loading 2.5 dnV / liter Bath liquid kelt

The copper content of this bath was constantly checked by means of colorimetric measurements and appropriate automatically controlled additions kept constant. The pH value was also increased, as it was before described, continuously measured and added the appropriate amounts of sodium hydroxide. Sodium cyanide was added according to the sodium hydroxide additions and formaldehyde according to the kolorlmetrlscher Measurement of the required amounts of copper sulphate.

The Mlschpotentlal was, as described in Example H, determined by means of a silver / chlorosilver electrode as a reference electrode. The measured values were as also described in Example II, used for the automatic control of the stabilizer content; this consisted of potassium sulphide and 2-mercaptobenzothlazole in a ratio of 10: 1 in aqueous solution. Of the The nominal value of the mixed potential was between -650 and -655 mV.

This type of bath works at an elevated temperature, which means that the formaldehyde concentration is at most 5 to 6 ml / l, otherwise spontaneous decomposition occurs. This means that at the same time all copper ions are reduced to copper, which is easy to do with it it can be seen that the blue copper sulfate solution turned red through finely divided metallic copper Solution transformed in which the finely divided red copper dust gradually sinks and the supernatant liquid is water-clear. At the same time there is a violent evolution of hydrogen, which causes the bath to foam up.

The bathroom described here turned out to be a strange one Phenomenon observed: due to a switching error, the valve for the addition of the formaldehyde

IO

Example V

A current working copper plating bath of the following Composition was made:

Copper sulfate

PH value

HPÄ

temperature formaldehyde Sodium cyanide Wetting agents

0.036 mol / l
12.9

0.08 moles /!
53 = C

0.05 mol / l
30 mg / l
0.1 g / l

Copper sulfate

PH value

HPÄ

formaldehyde Wetting agents temperature

0.036 mol / l

12.9

0.08 mol / l

0.05 mol / l

0.1 g / l

53 ⁰ C

solution and the concentration of formaldehyde rose to 22 rr.l / l. Contrary to expectations, there was no spontaneous one Failure instead, but the bathroom worked normally. The explanation for this was that due to the falling Value for the Mlschpotentlal stabilizer was constantly added. That went well until the supply ran out Stabilizer was exhausted after 16 hours; then the bath decomposed within half an hour.

Example IV

The bath from experiment A was controlled automatically and the one deposited on a platinum electrode after 20 minutes Determined amount of copper, whereby a measure of the Abscheldu.igsgeschwlndlgkelt was obtained. At the same time, the Mlschpotentlal was measured and found that this is exactly proportional to Detachment speed behavior.

Solution was always added when the Mlschpotentlal displayed a value more positive than -640 mV.

The bathroom worked well; the deposited copper was shiny and ductile; a copper deposit on the Tank walls were not observed.

Example VI

This example illustrates the use of the mixing potential also to control the bath ventilation. For this purpose, a bath with the following composition was made:

Kettle ion concentration, pH value and temperature were constantly checked and the necessary additions controlled automatically. Formaldehyde in 37%

Copper sulfate

HPÄ

formaldehyde Sodium hydroxide Sodium cyanide temperature

0.04 mol / l
0.06 mol / l
0.26 mol / l
0.36 mol / l
0.0002 moles / 1
24 ¹ C

When air was bubbled through, the bath showed a mash potential νυη -703 mV; if the air flow was interrupted, the potential slowly sank to -720 mV.

Example VIII

A bathroom that works without electricity, in which a complex blind used and which had the following composition was prepared:

Copper ion content, pH value, temperature and formaldehyde concentration were constantly checked and, if necessary, the corresponding additions were made automatically made. The cyanide ion concentration was measured and measured at -150 mV using a Calomel and one cyanide ion electrode set.

An aqueous solution of potassium polysultide was used as the stabilizer used and always added when this is done with the help of a silver / chloro-silver comparison electrode measured Mlschpotentlal dropped below -670 mV. A 37% formaldehyde solution was always used then added when the Mlschpotentlal rose above -640 mV. The bathroom worked satisfactorily, the secluded one Copper was shiny, ductile, and uniform, and was only found in the desired places.

Continued analyzes during the Badarbelt showed that the formaldehyde concentration was between 0.01 and 0.04 mol / l was kept.

Example VI

To illustrate the effect on the setting the formaldehyde content alone made a bath as follows Composition made:

Copper sulfate Complexing agents formaldehyde Sodium hydroxide temperature Wetting agents

7.5 g / l
22 ml / 1
15 ml / l
6 g / l
27 ³ C
0.1 g / l

Initially the mixed potential was -720 mV (measured against a standard calomel electrode). The copper leather strike was colored dark. Sodium cyanide was added until the potential was at -680 mV was, the copper deposited at this value was shiny and ductile.

Example IX

The mixing potential can also be used to control and regulate the bath movement. W; d that If the bath is vigorously moved, it absorbs oxygen, the action of which increases the mixed potential; becomes the bath movement stopped, the mixed potential sinks again.

The bath used to illustrate this effect was composed as follows:

Copper sulfate 14.6 g / l Na-K tartrate 7.5 g / l Sodium hydroxide 7.5 g / l formaldehyde 38 ml / l temperature 26 ^C C

At the beginning, without bath movement, the wiping potential was -720 mV. After switching on the device for moving the bath, the potential rose. The bath movement was now set so that the mixed potential remained constant between -640 mV and -680 mV. That under Copper deposited under these conditions was bright and ductile.

For this purpose 2 sheets of drawings

Claims (10)

Patent claims: 1. Method for the operational control of a copper plating bath that operates without an external power supply using that formed during the deposition process as a function of oxidation and reduction and bath parameters measured as mixed potential, characterized in that with With the exception of the bath stabilizer, the bath parameters within specified tolerances are known per se Be kept wise; that the value for the mixed potential is determined empirically at which the Badarbelt optimal values with regard to the deposition rate and / or the bath stability and / or the nature of the metal deposit; and that this value of the mixed potential as Setpoint is used and according to the deviation from this setpoint or a specific one Setpoint tolerance range the addition of the bath stabilizer is regulated automatically. 2. The method according to claim 1, characterized in that the mixed potential between the Deposition electrode and a reference electrode is measured. 3. The method according to claim 2, characterized in that a calomel electrode as the reference electrode is used. 4. The method according to claim 3, characterized in that that a silver / Sllberchlorld electrode is used as a reference electrode will. 5. Process according to d * n cracks 3 and 4, characterized in that d * ß the metal separation bath at a higher temperature ^ -trleben and the reference electrode is surrounded by cooled bath liquid. 6. The method according to claim I, characterized in that the deviation from the setpoint of the Mixed potential after setting the conventionally controllable bath parameters no more than =. 5 mV up to * 50 mV, preferably not more than 10 mV, from a setpoint between -0.2 V to -1.5 V. measured against a standard calomel electrode. 7. The method according to claim 1, characterized in that the deviation of the mixed potential at ■ not more than < 25 mV and preferably ± 10 mV from its nominal value between -600 mV to -850 mV, measured against a standard calomel electrode. is echoed. 8. The method according to claim I, characterized in that air or oxygen is used as the stabilizer is passed through the bath. 9. The method according to claim 8, characterized in that air or oxygen by appropriate Movement of the bath is supplied. 10. The method according to claim I, characterized in that as a function of the decrease in the mixed potential compared to a predetermined target value, the amount of stabilizer solution that the target value adjusts again, is added.