EP0045970B1 - Process for measuring the current efficiency of electroplating baths - Google Patents

Process for measuring the current efficiency of electroplating baths Download PDF

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Publication number
EP0045970B1
EP0045970B1 EP81106263A EP81106263A EP0045970B1 EP 0045970 B1 EP0045970 B1 EP 0045970B1 EP 81106263 A EP81106263 A EP 81106263A EP 81106263 A EP81106263 A EP 81106263A EP 0045970 B1 EP0045970 B1 EP 0045970B1
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Prior art keywords
electrode
current
rotating disc
electro
time
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German (de)
French (fr)
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EP0045970A1 (en
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Frank Dr. Vangaever
Jacky Dr. Vanhumbeeck
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Siemens AG
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Siemens AG
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D21/00—Processes for servicing or operating cells for electrolytic coating
    • C25D21/12—Process control or regulation

Definitions

  • the invention relates to a method for determining the current yield and possibly for determining the scatter in galvanic baths, according to the preamble of claim 1.
  • the invention has for its object to provide a method for determining the current efficiency in a galvanic bath.
  • the automatic determination of the current yield in conjunction with a corresponding control enables constant layer thicknesses to be maintained, in particular in the case of continuous galvanic systems.
  • the time for anodic removal of the deposited metal is preferably determined from the potential-time curve.
  • the potential between the rotating disk electrode and a reference electrode is recorded, which has a constant voltage.
  • the time for anodic removal is determined by at least two measurements with different distances between the rotating disk electrode and the counter electrode.
  • control of all components required for the automatic implementation of the method and / or the processing of measured values is preferably carried out by a process control circuit.
  • the method according to the invention is explained in more detail with reference to the drawing.
  • the drawing shows an arrangement for automatically measuring the current yield in principle.
  • I denotes a process part that contains a galvanic bath 1 as the most important part in which the process electrolyte is located. It is assumed that the galvanic bath is a continuous galvanic system.
  • the boxes denoted by 3 and 4 are intended to indicate that a defined current density (or current) and a specific belt speed can be specified in order to achieve a specific layer thickness, as indicated by a dashed arrow 5. Such systems are known per se and do not form the subject of this invention.
  • thermostatted measuring cell 6 which can be supplied with a defined amount of electrolyte solution from the galvanic bath 1 by means of a metering syringe 7 via a valve 8 and a line 9.
  • the measuring cell 7 has a rotating disk electrode 10, a counter electrode 11 opposite it and a reference electrode 12 as the working electrode.
  • the disk electrode 10 carries a metal disk 13 at the lower end, which faces the counter electrode 11.
  • the reference electrode 12 is conventional and can be, for example, a calomel, Ag or AgCL electrode.
  • the counterelectrode 11 can be, for example, a platinized titanium sheet, or it is adapted to the respective measurement problem, as is the metal disk 13 of the disk electrode 10.
  • the electromotive drive of the rotating disk electrode 10 is designated by 14, which is connected via lines 15 and 16 to an electronic part III is related, as will be described in more detail below.
  • a pipe 18 is connected, which leads, for example, to a waste container.
  • Another outlet of the three-way valve 18 is connected to the galvanic bath 1 via a pipeline 19, so that the bath sample located in the measuring cell 6 can be returned to the galvanic bath 1, which is particularly important when using a noble metal electrolyte.
  • a suitable electrolyte solution which can also be supplied to the measuring cell 6 by means of a metering syringe 21 via a pipeline 22. Furthermore, water or another liquid for rinsing and cleaning can be supplied to the measuring cell 6 via a pipe 23 and valve 24.
  • the electronic part III contains a control part 25 for the rotating disk electrode 10, the output Ant of which is connected to the connection of the line 15 which is identified by the same name.
  • the rotational speed of the disk electrode 10 can be specified via the control part 25.
  • a potentiograph is designated, which for recording the potential-time Curve serves.
  • the outputs of the potentiograph 26 labeled AE and BE are connected to the correspondingly labeled connections AE and BE of the working electrode 10 and the reference electrode 12, respectively.
  • the disk electrode 10 and the counter electrode 11 lie in a circuit which can be supplied with constant current by a current source 27.
  • the outputs AE and GE of the current source 27 are connected to the correspondingly designated connections of the disk electrode 10 and the counter electrode 11.
  • the electronics part 111 also contains a process control circuit 28 with a microprocessor 29 and an operating panel 30. Furthermore, the entire system is equipped with a controller 31. For example, the speed of rotation of the disc electrode 10 of the desired current density, i.e. be set and controlled by the microprocessor 29 to be examined electrolyte. Furthermore, the entire sequence of the measuring process and the regulation of the current density and the belt speed of the galvanic bath can be controlled by the same microprocessor 29.
  • the measuring cycle consists of the following steps: With the aid of the metering syringe 7, a defined amount of electrolyte solution is removed from the galvanic bath 1 and this bath sample is introduced into the thermostated measuring cell 6. Here, the temperature in the measuring cell during deposition is kept equal to the temperature in the galvanic bath 1.
  • the rotating working electrode 10 is used to increase and keep the mass transport constant.
  • the setting of the corresponding rotational speed of the disk electrode and the current density i k are controlled by the microprocessor 29.
  • the current is switched off and the bath sample from the measuring cell 6 is returned to the galvanic bath 1 via the three-way valve 17 and line 19.
  • the process control 28 then rinses the measuring cell 6 with water via valve 24 and drains it off via line 18.
  • a defined amount of electrolyte solution is then introduced from the electrolyte container 22 into the measuring cell 6 with the aid of the metering syringe 21.
  • This electrolyte solution is adapted to the metal precipitation; however, it should enable a constant, if possible 100% current yield when removing the metal deposited on the metal disk 13 of the disk electrode 10.
  • the potentials on the disk electrode 10 and on the counter electrode 11 are reversed, with the aid of the microprocessor 29 the anodic current i a and the optimum rotational speed of the disk electrode 10 being adjusted for removal.
  • the temperature is also kept constant during anodic removal. For procedural reasons, it can be kept lower, for example to avoid steam formation.
  • the potential-time data are continuously stored in the microprocessor 29 and the end point is determined therefrom.
  • the potential profile between the disk electrode 10 and the reference electrode 12 can be recorded during the removal.
  • the end point of the metal removal results in the time t a and is indicated in the potential-time curve by a strong change in potential.
  • the power supply to the electrodes is switched off; the measuring cell is then emptied and rinsed and prepared for a new measurement.
  • the disc electrode may need to be cleaned of any remaining deposits. A corresponding other liquid is used for this.
  • the amount of electricity required for removal is equal to i a ⁇ t a ⁇ ⁇ a , where ⁇ a is the anodic current yield.
  • the anodic current efficiency ⁇ a 1 can be kept by a suitable choice of the electrolyte solution.
  • the current yield can now be calculated using the microprocessor 29 in the following way:
  • the current density in the galvanic bath and / or the exposure time is preferably regulated as a function of the current yield (r lk ).
  • the evaluation of the potential-time curve for determining t a can be carried out in a manner known per se, for example by the intersection of straight lines through linear sections of the curve or a turning point in the case of an S-shaped curve.
  • the scattering of an electrolyte can also be determined with the method according to the invention.
  • Scattering means the fluctuating layer thickness that occurs on a part to be electroplated, if the distance between the surface of the part and the part ode is not the same.
  • at least two measurements with different distances between the rotating disk electrode 10 and the counter electrode 11 must be carried out to determine the scatter.
  • two mutually independent measuring cells with different distances between the rotating disk electrode (10) and the counter electrode (11) are used to determine the scatter. Two rik values are calculated from this; the ratio of these two values is a measure of the spread.
  • a rotating disk electrode which carries several suitable metal disks at the lower end, e.g. 2 for the ring-disc electrode and 3 for a split ring-disc electrode (i.e. the so-called split-ring-disc electrode).
  • Two or more llk values are calculated from this; the ratio of these values is a measure of the spread.
  • the measuring principle according to the invention is not limited to the direct voltage method, but can e.g. can also be used for pulse separation.

Description

Die Erfindung bezieht sich auf ein Verfahren zur Bestimmung der Stromausbeute und ggf. zur Ermittlung der Streuung bei galvanischen Bädern, gemäss dem Oberbegriff des Anspruchs 1.The invention relates to a method for determining the current yield and possibly for determining the scatter in galvanic baths, according to the preamble of claim 1.

Bei der Metallabscheidung führen Schwankungen in der Stromausbeute zu Schwankungen in der Schichtdicke, vor allem, wenn beim Abscheidungsprozess lediglich nach Stromdichte und Expositionszeit (Amperestundenzahl) gearbeitet wird. Die Stromausbeute ist nicht nur vom Gehalt der Badkomponenten sondern auch von einer ganzen Reihe von Einflussgrössen abhängig, die nicht mit den üblichen analytischen Verfahren erfassbar sind. Daher sind reine Amperestundenzahlen und die übliche analytische Überwachung des Bades keine ausreichenden Kriterien für die Konstanthaltung der Schichtdicke. Für die Konstanthaltung einer bestimmten Schichtdicke ist vielmehr das Produktη massgebend, wobei i den Strom (bzw. die Stromdichte), t die Expositionszeit und 1] die Stromausbeute bedeuten.With metal deposition, fluctuations in the current yield lead to fluctuations in the layer thickness, especially if the deposition process only works according to the current density and exposure time (number of ampere hours). The current efficiency depends not only on the content of the bath components but also on a whole range of influencing factors that cannot be determined using the usual analytical methods. Therefore, pure ampere-hour numbers and the usual analytical monitoring of the bath are not sufficient criteria for keeping the layer thickness constant. Rather, the product η is decisive for keeping a certain layer thickness constant, where i is the current (or the current density), t is the exposure time and 1] is the current efficiency.

Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren zur Bestimmung der Stromausbeute bei einem galvanischen Bad zu schaffen. Insbesondere die automatische Bestimmung der Stromausbeute in Verbindung mit einer entsprechenden Regelung ermöglicht das Einhalten von konstanten Schichtdicken, insbesondere bei galvanischen Durchlaufanlagen.The invention has for its object to provide a method for determining the current efficiency in a galvanic bath. In particular, the automatic determination of the current yield in conjunction with a corresponding control enables constant layer thicknesses to be maintained, in particular in the case of continuous galvanic systems.

Diese Aufgabe wird bei einem Verfahren der eingangs genannten Art dadurch gelöst, dass die auf der rotierenden Scheibenelektrode abgeschiedene Schicht mit Hilfe einer geeigneten Elektrolytlösung unter Umpolung der Gleichspannung bei konstantem Strom ia und in einer zu ermittelnden Zeit ta anodisch abgetragen wird und dass die Stromausbeute rlk nach der Formel

Figure imgb0001
berechnet wird, worin ηa die Stromausbeute des anodischen Abtragens bedeutet.This object is achieved in a method of the type mentioned in that the deposited on the rotating disk electrode layer by means of a suitable electrolyte solution to pole reversal of the DC voltage at a constant current i a and a to be determined time t is a anodically removed and that the current efficiency r lk according to the formula
Figure imgb0001
 is calculated, wherein η a means the current efficiency of the anodic removal.

Vorzugsweise wird die Zeit zum anodischen Abtragen des abgeschiedenen Metalls aus der Potential-Zeit-Kurve ermittelt. Hierbei wird zur Aufnahme der Potential-Zeit-Kurve das Potential zwischen rotierender Scheibenelektrode und einer Bezugselektrode erfasst, welche eine konstante Spannung aufweist.The time for anodic removal of the deposited metal is preferably determined from the potential-time curve. To record the potential-time curve, the potential between the rotating disk electrode and a reference electrode is recorded, which has a constant voltage.

Zur Ermittlung der Streuung wird die Zeit zum anodischen Abtragen durch mindestens zwei Messungen mit verschiedenen Abständen zwischen der rotierenden Scheibenelektrode und der Gegenelektrode ermittelt.To determine the scatter, the time for anodic removal is determined by at least two measurements with different distances between the rotating disk electrode and the counter electrode.

Vorzugsweise erfolgt die Steuerung sämtlicher für die automatische Durchführung des Verfahrens erforderlichen Bauteile und/oder die Messwertverarbeitung von einer Prozesssteuerschaltung.The control of all components required for the automatic implementation of the method and / or the processing of measured values is preferably carried out by a process control circuit.

Anhand der Zeichnung wird das erfindungsgemässe Verfahren näher erläutert. Die Zeichnung zeigt eine Anordnung zum automatischen Messen der Stromausbeute im Prinzip.The method according to the invention is explained in more detail with reference to the drawing. The drawing shows an arrangement for automatically measuring the current yield in principle.

Mit I ist ein Prozessteil bezeichnet, der ein galvanisches Bad 1 als wesentlichsten Teil enthält, in welchem sich der Prozesselektrolyt befindet. Es ist angenommen, dass es sich bei dem galvanischen Bad um eine galvanische Durchlaufanlage handelt. Durch die mit 3 und 4 bezeichneten Kästchen soll angedeutet werden, dass zur Erzielung einer bestimmten Schichtdicke eine definierte Stromdichte (bzw. Strom) und eine bestimmte Bandgeschwindigkeit vorgebbar sind, wie durch einen gestrichelten Pfeil 5 angedeutet ist. Derartige Anlagen sind an sich bekannt und bilden nicht Gegenstand dieser Erfindung.I denotes a process part that contains a galvanic bath 1 as the most important part in which the process electrolyte is located. It is assumed that the galvanic bath is a continuous galvanic system. The boxes denoted by 3 and 4 are intended to indicate that a defined current density (or current) and a specific belt speed can be specified in order to achieve a specific layer thickness, as indicated by a dashed arrow 5. Such systems are known per se and do not form the subject of this invention.

Mit II ist ein Messteil zur Erfassung der für die Bestimmung der Stromausbeute massgebenden Grössen bezeichnet. Er enthält eine thermostatisierte Messzelle 6, der mit Hilfe einer Dosierspritze 7 über ein Ventil 8 und eine Leitung 9 eine definierte Menge Elektrolytlösung aus dem galvanischen Bad 1 zuführbar ist.II designates a measuring part for recording the parameters that are decisive for determining the current yield. It contains a thermostatted measuring cell 6, which can be supplied with a defined amount of electrolyte solution from the galvanic bath 1 by means of a metering syringe 7 via a valve 8 and a line 9.

Die Messzelle 7 weist als Arbeitselektrode eine rotierende Scheibenelektrode 10, eine dieser gegenüberstehende Gegenelektrode 11 und eine Bezugselektrode 12 auf. Die Scheibenelektrode 10 trägt am unteren Ende eine Metallscheibe 13, die der Gegenelektrode 11 gegenübersteht. Die Bezugselektrode 12 ist herkömmlicher Art und kann beispielsweise eine Kalomel-, Ag- oder AgCL-Elektrode sein. Die Gegenelektrode 11 kann beispielsweise ein platiniertes Titanblech sein, bzw. sie ist dem jeweiligen Messproblem angepasst, wie auch die Metallscheibe 13 der Scheibenelektrode 10. Mit 14 ist der elektromotorische Antrieb der rotierenden Scheibenelektrode 10 bezeichnet, der über Leitungen 15 und 16 mit einem Elektronikteil III in Verbindung steht, wie weiter unten noch näher beschrieben wird.The measuring cell 7 has a rotating disk electrode 10, a counter electrode 11 opposite it and a reference electrode 12 as the working electrode. The disk electrode 10 carries a metal disk 13 at the lower end, which faces the counter electrode 11. The reference electrode 12 is conventional and can be, for example, a calomel, Ag or AgCL electrode. The counterelectrode 11 can be, for example, a platinized titanium sheet, or it is adapted to the respective measurement problem, as is the metal disk 13 of the disk electrode 10. The electromotive drive of the rotating disk electrode 10 is designated by 14, which is connected via lines 15 and 16 to an electronic part III is related, as will be described in more detail below.

Am unteren Ende der Messzelle 6 befindet sich ein vorzugsweise automatisch betätigbarer Dreiwegehahn 17, an dem eine Rohrleitung 18 angeschlossen ist, die beispielsweise zu einem Abfallbehälter führt. Ein weiterer Ausgang des Dreiwegehahns 18 ist über eine Rohrleitung 19 mit dem galvanischen Bad 1 verbunden, damit die in der Messzelle 6 befindliche Badprobe in das galvanische Bad 1 zurückgeführt werden kann, was insbesondere bei Verwendung eines Edelmetall-Elektrolyten von Bedeutung ist.At the lower end of the measuring cell 6 there is a preferably automatically operated three-way valve 17, to which a pipe 18 is connected, which leads, for example, to a waste container. Another outlet of the three-way valve 18 is connected to the galvanic bath 1 via a pipeline 19, so that the bath sample located in the measuring cell 6 can be returned to the galvanic bath 1, which is particularly important when using a noble metal electrolyte.

Mit 20 ist ein Elektrolytbehälter bezeichnet, in dem sich eine geeignete Elektrolytlösung befindet, die mit Hilfe einer Dosierspritze 21 über eine Rohrleitung 22 ebenfalls der Messzelle 6 zugeführt werden kann. Ferner kann über eine Rohrleitung 23 und Ventil 24 der Messzelle 6 Wasser oder eine andere Flüssigkeit zum Spülen und Reinigen zugeführt werden.20 denotes an electrolyte container in which there is a suitable electrolyte solution, which can also be supplied to the measuring cell 6 by means of a metering syringe 21 via a pipeline 22. Furthermore, water or another liquid for rinsing and cleaning can be supplied to the measuring cell 6 via a pipe 23 and valve 24.

Der Elektronikteil III enthält einen Steuerungsteil 25, für die rotierende Scheibenelektrode 10, dessen Ausgang Ant mit dem gleich bezeichneten Anschluss der Leitung 15 in Verbindung steht. Über den Steuerungsteil 25 kann die Drehgeschwindigkeit der Scheibenelektrode 10 vorgegeben werden. Mit 26 ist ein Potentiograph bezeichnet, der zur Aufnahme der Potential-Zeit-Kurve dient. Die mit AE und BE bezeichneten Ausgänge des Potentiographen 26 sind mit den entsprechend bezeichneten Anschlüssen AE und BE der Arbeitselektrode 10 bzw. der Bezugselektrode 12 verbunden.The electronic part III contains a control part 25 for the rotating disk electrode 10, the output Ant of which is connected to the connection of the line 15 which is identified by the same name. The rotational speed of the disk electrode 10 can be specified via the control part 25. With 26 a potentiograph is designated, which for recording the potential-time Curve serves. The outputs of the potentiograph 26 labeled AE and BE are connected to the correspondingly labeled connections AE and BE of the working electrode 10 and the reference electrode 12, respectively.

Die Scheibenelektrode 10 und die Gegenelektrode 11 liegen in einem Stromkreis, der von einer Stromquelle 27 mit konstantem Strom versorgt werden kann. Die Ausgänge AE und GE der Stromquelle 27 sind mit den entsprechend bezeichneten Anschlüssen der Scheibenelektrode 10 bzw. dfer Gegenelektrode 11 verbunden.The disk electrode 10 and the counter electrode 11 lie in a circuit which can be supplied with constant current by a current source 27. The outputs AE and GE of the current source 27 are connected to the correspondingly designated connections of the disk electrode 10 and the counter electrode 11.

Schliesslich enthält der Elektronikteil 111 noch eine Prozesssteuerschaltung 28 mit einem Mikroprozessor 29 sowie einem Bedienfeld 30. Ferner ist die ganze Anlage mit einer Regelung 31 ausgestattet. So kann beispielsweise die Rotationsgeschwindigkeit der Scheibenelektrode 10 der gewünschten Stromdichte, d.h. dem zur untersuchenden Elektrolyten von dem Mikroprozessor 29 eingestellt und gesteuert werden. Ferner kann der ganze Ablauf des Messvorgangs und die Regelung der Stromdichte und der Bandgeschwindigkeit des galvanischen Bades von dem selben Mikroprozessor 29 gesteuert sein.Finally, the electronics part 111 also contains a process control circuit 28 with a microprocessor 29 and an operating panel 30. Furthermore, the entire system is equipped with a controller 31. For example, the speed of rotation of the disc electrode 10 of the desired current density, i.e. be set and controlled by the microprocessor 29 to be examined electrolyte. Furthermore, the entire sequence of the measuring process and the regulation of the current density and the belt speed of the galvanic bath can be controlled by the same microprocessor 29.

Der Messzyklus besteht aus folgenden Schritten: Mit Hilfe der Dosierspritze 7 wird eine definierte Menge Elektrolytlösung dem galvanischen Bad 1 entnommen und diese Badprobe in die thermostatisierte Messzelle 6 eingebracht. Hierbei wird die Temperatur in der Messzelle beim Abscheiden gleich der Temperatur in dem galvanischen Bad 1 gehalten.The measuring cycle consists of the following steps: With the aid of the metering syringe 7, a defined amount of electrolyte solution is removed from the galvanic bath 1 and this bath sample is introduced into the thermostated measuring cell 6. Here, the temperature in the measuring cell during deposition is kept equal to the temperature in the galvanic bath 1.

Mit einem konstanten Strom ik (bzw. Stromdichte jk), der möglichst genau der Stromdichte in dem galvanischen Bad 1 entspricht, wird während einer vorgegebenen Zeit tk Metall abgeschieden. Das Produkt ik x tk entspricht der zugeführten Elektrizitätsmenge (Amperestundenzahl). In der Praxis wird jedoch nur ein Teil ηk von dieser gesamten Elektrizitätsmenge für die eigentliche Metallabscheidung verbraucht; daher ist die Grösse ηk die für den vorliegenden Prozess gesuchte Stromausbeute.With a constant current i k (or current density j k ), which corresponds as closely as possible to the current density in the galvanic bath 1, metal is deposited for a predetermined time t k . The product i k xt k corresponds to the amount of electricity supplied (ampere-hour number). In practice, however, only a part η k of this total amount of electricity is used for the actual metal deposition; Therefore, the size η k is the current efficiency sought for the present process.

Die Aussagekraft der automatischen Bestimmung der Stromausbeute in der Messzelle 6 wird desto grösser sein je genauer der Prozessablauf im galvanischen Bad 1 in der Messzelle 6 simuliert wird.The significance of the automatic determination of the current yield in the measuring cell 6 will be greater the more precisely the process sequence in the galvanic bath 1 in the measuring cell 6 is simulated.

Um grosse Stromdichten in der Messzelle verwenden zu können, wie sie z.B. in Durchlaufanlagen üblich sind, wird zur Steigerung und Konstanthaltung des Stofftransportes die rotierende Arbeitselektrode 10 eingesetzt. Die Einstellung der entsprechenden Drehgeschwindigkeit der Scheibenelektrode und der Stromdichte ik werden von dem Mikroprozessor 29 gesteuert. Sobald die eingestellte Elektrolyse-Zeit tk erreicht ist, wird der Strom abgeschaltet und die Badprobe aus der Messzelle 6 über den Dreiwegehahn 17 und Leitung 19 wieder dem galvansichen Bad 1 zugeführt. Anschliessend wird von der Prozesssteuerung 28 über Ventil 24 die Messzelle 6 mit Wasser gespült und dieses über Leitung 18 abgeleitet.In order to be able to use large current densities in the measuring cell, such as are customary, for example, in continuous systems, the rotating working electrode 10 is used to increase and keep the mass transport constant. The setting of the corresponding rotational speed of the disk electrode and the current density i k are controlled by the microprocessor 29. As soon as the set electrolysis time t k has been reached, the current is switched off and the bath sample from the measuring cell 6 is returned to the galvanic bath 1 via the three-way valve 17 and line 19. The process control 28 then rinses the measuring cell 6 with water via valve 24 and drains it off via line 18.

Danach wird mit Hilfe der Dosierspritze 21 eine definierte Menge Elektrolytlösung aus dem Elektrolytbehälter 22 in die Messzelle 6 eingebracht. Diese Elektrolytlösung wird dem Metallniederschlag angepasst; sie soll jedoch eine konstante, möglichst 100%ige Stromausbeute beim Abtragen des auf der Metallscheibe 13 der Scheibenelektrode 10 abgeschiedenen Metalls ermöglichen. Die Potentiale an der Scheibenelektrode 10 und an der Gegenelektrode 11 werden umgepolt, wobei mit Hilfe des Mikroprozessors 29 der anodische Strom ia und die zum Abtragen optimale Rotationsgeschwindigkeit der Scheibenelektrode 10 eingestellt werden. Während des anodischen Abtragens wird die Temperatur ebenfalls konstant gehalten. Sie kann aus verfahrenstechnischen Gründen niedriger gehalten werden, um z.B. Dampfbildung zu vermeiden.A defined amount of electrolyte solution is then introduced from the electrolyte container 22 into the measuring cell 6 with the aid of the metering syringe 21. This electrolyte solution is adapted to the metal precipitation; however, it should enable a constant, if possible 100% current yield when removing the metal deposited on the metal disk 13 of the disk electrode 10. The potentials on the disk electrode 10 and on the counter electrode 11 are reversed, with the aid of the microprocessor 29 the anodic current i a and the optimum rotational speed of the disk electrode 10 being adjusted for removal. The temperature is also kept constant during anodic removal. For procedural reasons, it can be kept lower, for example to avoid steam formation.

Zur Aufnahme der Potential-Zeit-Kurve werden die Potential-Zeitdaten laufend im Mikroprozessor 29 eingespeichert und daraus der Endpunkt ermittelt. Mit Hilfe des Potentiographen 26 kann der Potentialverlauf zwischen Scheibenelektrode 10 und Bezugselektrode 12 während der Abtragung aufgenommen werden. Der Endpunkt der Metallabtragung ergibt die Zeit ta und wird in der Potential-Zeit-Kurve durch eine starke Potentialänderung angezeigt. Nach Bestimmung des Endpunktes wird veranlasst, dass die Stromzufuhr zu den Elektroden abgeschaltet wird; danach wird die Messzelle entleert und gespült und für eine neue Messung vorbereitet.In order to record the potential-time curve, the potential-time data are continuously stored in the microprocessor 29 and the end point is determined therefrom. With the help of the potentiograph 26, the potential profile between the disk electrode 10 and the reference electrode 12 can be recorded during the removal. The end point of the metal removal results in the time t a and is indicated in the potential-time curve by a strong change in potential. After the end point has been determined, the power supply to the electrodes is switched off; the measuring cell is then emptied and rinsed and prepared for a new measurement.

Unter Umständen muss die Scheibenelektrode von restlichen Abscheidungen gereinigt werden. Hierzu wird eine entsprechende andere Flüssigkeit verwendet.The disc electrode may need to be cleaned of any remaining deposits. A corresponding other liquid is used for this.

Die zum Abtragen benötigte Elektrizitätsmenge ist gleich ia × ta × ηa, wobei ηa die anodische Stromausbeute ist. Durch geeignete Wahl der Elektrolytlösung kann die anodische Stromausbeute ηa = 1 gehalten werden. Die Stromausbeute kann nun mit Hilfe des Mikroprozessors 29 auf folgende Weise berechnet werden:

Figure imgb0002
The amount of electricity required for removal is equal to i a × t a × η a , where η a is the anodic current yield. The anodic current efficiency η a = 1 can be kept by a suitable choice of the electrolyte solution. The current yield can now be calculated using the microprocessor 29 in the following way:
Figure imgb0002

Dieser Wert kann zusammen mit der eingestellten Stromdichte und Rotationsgeschwindigkeit protokolliert werden. Vorzugsweise wird die Stromdichte im galvanischen Bad und/oder die Expositionszeit in Abhängigkeit von der Stromausbeute (rlk) geregelt.This value can be logged together with the set current density and rotation speed. The current density in the galvanic bath and / or the exposure time is preferably regulated as a function of the current yield (r lk ).

Die Auswertung der Potential-Zeit-Kurve zur Bestimmung von ta kann in an sich bekannter Weise vorgenommen werden, beispielsweise durch den Schnittpunkt von Geraden durch lineare Abschnitte der Kurve oder einen Wendepunkt bei S-förmigem Kurvenverlauf.The evaluation of the potential-time curve for determining t a can be carried out in a manner known per se, for example by the intersection of straight lines through linear sections of the curve or a turning point in the case of an S-shaped curve.

Mit dem erfindungsgemässen Verfahren kann auch die Streuung eines Elektrolyten bestimmt werden. Unter der Streuung versteht man die an einem zu galvanisierenden Teil auftretende schwankende Schichtdicke, wenn die Entfernung zwischen der Oberfläche des Teiles und der Anode nicht gleich ist. Zur Ermittlung der Streuung sind gemäss einem weiteren Merkmal mindestens zwei Messungen mit verschiedenen Abständen zwischen der rotierenden Scheibenelektrode 10 und der Gegenelektrode 11 vorzunehmen. Vorzugsweise werden zur Ermittlung der Streuung zwei voneinander unabhängige Messzellen mit unterschiedlichen Abständen zwischen der rotierenden Scheibenelektrode (10) und der Gegenelektrode (11) verwendet. Daraus werden zwei rik-Werte errechnet; das Verhältnis dieser beiden Werte ist ein Mass für die Streuung.The scattering of an electrolyte can also be determined with the method according to the invention. Scattering means the fluctuating layer thickness that occurs on a part to be electroplated, if the distance between the surface of the part and the part ode is not the same. According to a further feature, at least two measurements with different distances between the rotating disk electrode 10 and the counter electrode 11 must be carried out to determine the scatter. Preferably, two mutually independent measuring cells with different distances between the rotating disk electrode (10) and the counter electrode (11) are used to determine the scatter. Two rik values are calculated from this; the ratio of these two values is a measure of the spread.

Vorzugsweise wird zur Ermittlung der Streuung im obengenannten Zweizellensystem oder in einer einzigen Zelle, eine rotierende Scheibenelektrode verwendet, welche am unteren Ende mehrere geeignete Metallscheiben trägt, z.B. 2 für die Ring-Scheibe Elektrode und 3 für eine gespaltete Ring-Scheibe Elektrode (d.h. die sog. Split-ring-disc electrode).Preferably, to determine the scatter in the above-mentioned two-cell system or in a single cell, a rotating disk electrode is used which carries several suitable metal disks at the lower end, e.g. 2 for the ring-disc electrode and 3 for a split ring-disc electrode (i.e. the so-called split-ring-disc electrode).

Daraus werden zwei oder mehrere llk-Werte errechnet; das Verhältnis dieser Werte ist ein Mass für die Streuung.Two or more llk values are calculated from this; the ratio of these values is a measure of the spread.

Das erfindungsgemässe Messprinzip ist nicht beschränkt auf das Gleichspannungsverfahren, sondern kann z.B. auch für die Pulsabscheidung eingesetzt werden.The measuring principle according to the invention is not limited to the direct voltage method, but can e.g. can also be used for pulse separation.

Claims (18)

1. A method of determining the current efficiency, and, if necessary, ascertaining the variation, in electro-plating baths, in which a bath sample is taken from the electro-plating bath (1) and under the influence of a negative direct voltage at constant current (ik) during a predetermined time (tk), metal is deposited from said bath sample on to a rotating disc electrode (10) in a measuring cell (6), characterised in that with the aid of a suitable electrolytic solution whilst reversing the polarity of the direct voltage, the layer deposited on the rotating disc electrode (10), is anodically removed at constant current (ia) and in a time (ta) which is to be determined; and that the current efficiency (Tlk) is calculated in accordance with the formula
Figure imgb0004
where ηa represents the current efficiency of the anodic removal.
2. A method according to Claim 1, characterised in that the time (ta) for the anodic removal of the deposited metal is determined from the potential-time curve.
3. A method according to Claim 2, characterised in that the time (tal of the anodic removal of the deposited metal is determined from the change in potential of the potential-time curve.
4. A method according to one of Claims 1 to 3, characterised in that for the anodic removal, an electrolytic solution is used which results in a constant current efficiency.
5. A method according to Claim 4, characterised in that for the anodic separation, an electrolytic solution is used which results in a constant current efficiency of 100%.
6. A method according to one of Claims 1 to 5, characterised in that the current (ik) is so selected that the current density in the measuring cell (6) corresponds approximately to the current density in the electro-plating bath (1).
7. A method according to one of Claims 1 to 6, characterised in that, during the deposition, the temperature in the measuring cell (6) is held the same as the temperature in the electro-plating bath (1).
8. A method according to one of Claims 1 to 7, characterised in that, during the anodic removal, the temperature in the measuring cell (6) is held constant.
9. A method according to one of Claims 1 to 8, characterised in that the current (ik) and the speed of rotation of the rotating disc electrode (10) are adjusted and/or controlled in dependence upon the electrolytic deposition conditions in the electro-plating bath (1).
10. A method according to one of Claims 1 to 9, characterised in that the current density in the electro-plating bath (1), and/or the exposure time, are regulated in dependence upon the current efficiency (rlk).
11. A method according to one of Claims 1 to 10, characterised in that, after the conclusion of the metal deposition and/or at the end of the measurement, the measuring cell (6) is cleansed with a rinsing liquid.
12. A method according to Claim 11, characterised in that for the chemical cleansing of the rotating disc electrode (10), a suitable rinsing liquid is used.
13. A method according to one of Claims 1 to 12, characterised in that the constant currents (ik) and (ia) are led across the rotating disc electrode (10) and a counter-electrode (11), arranged opposite thereto; and that in order to plot the potential-time curve, the potential between the rotating electrode (10) and a reference electrode (12) at constant voltage, is recorded.
14. A method according to Claim 13, characterised in that a metal disc (13) of the rotating disc electrode (10) and/or the kind of metal of the counter-electrode (11) are adapted to the electro-plating bath (1).
15. A method according to one of Claims 1 to 14, characterised in that in order to determine the variation, the time (ta) for the anodic removal is determined by at least two measurements with different spacings between the rotating disc electrode (10) and the counter-electrode (11).
16. A method according to Claim 15, characterised in that in order to determine the variation, at least two measuring cells with different spacings between the rotating disc electrode (10) and the counter-electrode, are used.
17. A method according to one of Claims 1 to 16, characterised in that the control of all components which are required for the automatic performance of the method, and/or the measured value processing, is effected by a process control circuit (28).
EP81106263A 1980-08-13 1981-08-11 Process for measuring the current efficiency of electroplating baths Expired EP0045970B1 (en)

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DE3030664A DE3030664C2 (en) 1980-08-13 1980-08-13 Method for determining the current yield in electroplating baths
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US4595462A (en) 1986-06-17
DE3030664A1 (en) 1982-03-18
JPS5754849A (en) 1982-04-01
CA1166187A (en) 1984-04-24
DE3030664C2 (en) 1982-10-21
JPH021262B2 (en) 1990-01-10

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