Method and apparatus for the automated determination of the stabilizer content in a chemical nickel bath

Abstract

Method for the automated determination of the content of a stabilizer reacting with a palladium(II) salt in a chemical nickel bath, the method comprising: the extraction of a sample of the chemical nickel bath, the volume of which is measured, and the transfer of the sample into a vessel whose wall is transparent to light at least at two opposite points, the connecting line between the two points passing through the sample, the portionwise addition of measured volumes of an aqueous solution of the palladium(II) salt to the sample, wherein the solution has a known concentration of palladium(II) salt, wherein the sample is stirred, and wherein the addition is continued until a discoloration of the sample due to precipitation of nickel is observed, and the calculation of the stabilizer content based on the total volume of solution added to the sample up to the point of discoloration, characterized by the fact that The solution is added by a dosing device which is controlled by a control device. The detection of discoloration is carried out using an optical sensor that is located outside the vessel and measures the transmittance of the sample to light along the aforementioned connecting line. the control device is connected to the optical sensor and stops adding the solution when the optical sensor detects the discoloration of the sample, and The light is infrared light.

Description

Field of the InventionThe present invention relates to a method and an apparatus for automatically determining the stabilizer content in a chemical nickel bath.BACKGROUND OF THE INVENTIONChemical nickel baths are used in coating processes for the electroless formation of nickel coatings on substrates. They contain a stabilizer which prevents the premature (spontaneous) precipitation of nickel. Chemical nickel baths are used over a longer period of time and are used repeatedly for individual coating processes. The stabilizer is gradually consumed, but at a speed not known exactly. In order that the coating process can be carried out with constant results, the content of the stabilizer in the chemical nickel bath must be determined at regular intervals and, if appropriate, adjusted to a desired value by subsequent metering of the stabilizer.Prior ArtThe determination of the content of a particular stabilizer (sold under the trade designation "SLOTONIP 36") in a nickel chemical bath (such as the bath sold under the trade designation "SLOTONIP 30-3") is described in an analytical protocol of Dr. Ing. Max Schlotter GmbH & Co. KG, Volume 14.08.2013 (title "Analysis of Stabilizer SLOTONIP 36"), which distributes, among other things, said chemical nickel bath and said stabilizer.According to the analytical instructions mentioned, the content (i.e. the concentration) of the stabilizer in the chemical nickel bath is determined by adding, to a sample of the nickel bath of known volume, in portions measured volumes of a palladium(II) nitrate solution of known palladium(II) nitrate concentration until the decomposition of the bath is detected.The palladium(II) nitrate first reacts with the stabilizer (still) present in the nickel bath and consumes this. When the stabilizer is completely consumed, the further addition of the palladium(II) nitrate causes precipitation of metallic nickel, which is accompanied by a marked black coloration of the sample and a evolution of gas.In the method described, the palladium(II) nitrate solution is added manually (by means of an Eppendorf pipette or burette) and the black coloration is determined visually (with the naked eye).From the amount (i.e., volume) of the palladium(II) nitrate solution added until this end point is reached and the concentration of the palladium(II) nitrate in the solution as well as the volume of the bath sample, the concentration of the stabilizer in the nickel bath can be calculated.US 3,723,062 A describes a method for photoelectric endpoint detection in colorimetric titrations. US 5,618,495 A describes a colorimetric titration method and apparatus therefor. However, these publications contain no information regarding the determination of the stabilizer content in a chemical nickel bath.The METROHM AG, Herisau (Switzerland) sells an optical sensor for photometric titrations under the name OPTRODE, which however has proved unsuitable in the hands of the inventors for determining the stabilizer content in a chemical nickel bath.US 2010 / 035356 A1 describes a method and an apparatus for determining the stability of an electroless coating bath. Thereafter, the stability of an electroless plating bath for depositing a metal (e.g., nickel) is determined by titrating a sample of the plating bath with a titrating agent containing ions of a catalytic metal (e.g., palladium) and detecting the hydrogen released at the titration endpoint. The amount of titrant required to reach the endpoint is a measure of the stability of the electroless plating bath.US 5 618 495 A relates to a method and apparatus for colorimetric titration. The document describes in particular a colorimetric titration method, a titrator and a colorimeter apparatus. The titrator comprises radiant energy means for generating radiant energy. The apparatus comprises means for modulating an amplitude of an intensity of the radiation energy at a modulation frequency. The radiant energy is partially absorbed by an adjacent solution in a sample cup having a color indicator dissolved therein. Means for focusing the radiant energy focuses the modulated radiant energy transmitted through the sample and the cup onto means for detecting the radiant energy. The radiant energy detection means generates a transmitted signal, the intensity of the transmitted signal being directly proportional to the intensity of the transmitted energy. A filter device filters the transmitted signal such that a center frequency of the filter device matches the modulation frequency of the radiant energy device. The filter means generates a filtered transmitted energy signal representative only of the amount of radiant energy transmitted from the radiant energy source through the solution free of other sources of radiant energy. The colorimetric titrator also includes means for creating a titration curve, means for calculating the first derivative of the titration curve, means for calculating the second derivative of the titration curve, control means for controlling the addition of titrator in dependence on the first derivative of the titration curve, and means for invoking the endpoint of the titration using the second derivative of the titration curve.K. Wang et al. (AIChE Journal, 2009, Vol. 55, No. 4, pp. 1046-1055) describe the role of the Bi 3+- complex ion as stabilizer in the electroless nickel plating process.Mallory, G.O. and Hajdu, J.B. (Electroless Plating: Fundamentals and Applications [Chapter 1], 1990, Ukraine) describe basic aspects of nickel chemical plating.DESCRIPTION OF THE INVENTIONThe method described in the abovementioned analytical specification for determining the content of the stabilizer in a chemical nickel bath is time-consuming and labor-intensive. In particular, the person making the determination cannot do other tasks for a longer time.Moreover, the results are dependent on the subjective assessment of the colour of the sample by the person carrying out the method and are therefore poorly accurate and poorly reproducible. Since various influencing variables have effects on the result of the determination of the content of the stabilizer, the test conditions must be exactly complied with in order to achieve comparable results. Finally, the results of the determination cannot be automatically documented and further processed in the known method.The object of the present invention is to provide a method for determining the content of the stabilizer in a chemical nickel bath and an apparatus therefor which enable the determination of the stabilizer content to be carried out quickly, with little work and easily, the results being accurate and reproducible regardless of which person carries out the determination.This object is achieved by a method for automatically determining the content of the stabilizer which is reacted with a palladium(II) salt in a nickel chemical bath, the method comprising: (i) taking a sample of the nickel chemical bath, wherein the volume of the sample is measured, and transferring the sample into a vessel whose wall is transparent to light at least at two opposite points, wherein the connecting line between the two points runs through the sample, (ii) adding in portions measured volumes of an aqueous solution of a palladium(II) salt to the sample, wherein the solution has a known concentration of palladium(II) salt, wherein the sample is stirred, and wherein the addition is continued for as long as, until discoloration of the sample is detected by precipitation of nickel, and (iii) the stabilizer content is calculated from the volume of the solution added to the sample until discoloration is detected overall, characterized in that (a) the solution is added by a metering device controlled by a control device, (b) the discoloration is detected by an optical sensor which is arranged outside the vessel and measures the transmittance of the sample for light along said connecting line, and (c) the control device is connected to the optical sensor and stops the addition of the solution when the optical sensor detects discoloration of the sample and the light is infrared light.To achieve the above object, there is also provided an apparatus for automatically determining the content of the stabilizer which is reacted with a palladium(II) salt in a nickel chemical bath, the apparatus comprising: (i) a vessel for receiving a sample of the nickel chemical bath, the wall of which is transparent to light at least at two opposite sites, the line of connection between the two sites passing through the sample, (ii) a device for stirring the sample, (iii) a control device, (iv) a dosing device for adding a solution of a palladium(II) salt to the sample, which is controlled by the control device, (v) an optical sensor which is arranged outside the vessel and measures the transparency of the sample to light along said line of connection, wherein the control device is connected to the optical sensor and is configured to control the dosing device such that the addition of the solution is ended when the optical sensor determines that the transmittance of the sample for light has fallen below a predetermined value, and wherein the optical sensor comprises a light source that emits infrared light and a light receiver that is sensitive to infrared light.The term "nickel chemical bath" as used herein means an electrolytic bath for electrolessly depositing nickel coatings on substrates (nickel chemical plating). Such nickel baths are known to the skilled person and are commercially available. For example, Dr. Ing sells. Max Schlotter GmbH & Co. KG such baths under the trade mark "SLOTONIP"; a chemical nickel bath to which the method according to the invention can be applied is, for example, that from Dr. Ing. Max Schlotter GmbH & Co. KG under the designation "SLOTONIP 30-3".Nickel chemical baths contain stabilizers to keep the discharge of nickel ions stably at the deposition level during metal deposition and to counteract spontaneous bath decomposition. The mode of action of stabilizers is complex, but the compounds used follow certain laws. A particular task is associated with the respective stabilizer system in chemical nickel baths because it primarily interferes with the catalytic process in a reaction-determining and corrective manner.The content (i.e. the concentration) of the stabilizer in the chemical nickel bath must therefore be kept constant within certain limits. Since the stabilizer is consumed during use of the bath, the content of the stabilizer in the chemical nickel bath must be determined at regular intervals and, if appropriate, adjusted to a desired value by subsequent metering of the stabilizer.The stabilizer content is determined by adding a solution of a palladium(II) salt with a known concentration of palladium(II) salt. From the volume of the solution which must be added until the stabilizer is consumed and then decomposition of the bath occurs, the content (i.e. concentration) of the stabilizer in the nickel bath can be calculated. The decomposition of the bath is accompanied by discoloration (black coloration) of the bath sample by precipitation of metallic nickel and by evolution of gas.The palladium(II) salt is preferably palladium(II) nitrate. The concentration of the palladium(II) salt in the solution is preferably 10 to 100 mg / L, given as palladium. The solution may additionally contain an inorganic acid such as hydrochloric acid.A suitable palladium(II) salt solution is obtained by mixing 125 mg of palladium(II) nitrate dihydrate (Pd(NO 3)2 · 2 H 2 O) with 20 ml of conc. Hydrochloric acid and make-up with distilled water to 1000 ml. The solution thus obtained contains 50 mg / L palladium.In order to enable automatic detection of the decomposition of the bath sample, an optical sensor is used according to the invention for detecting the discoloration (black coloration) of the sample. When the palladium(II) salt solution is added, the sample is located in a vessel whose wall is transparent to infrared light at least at two opposite points, the connecting line between the two points running through the sample. The optical sensor is arranged outside the vessel in which the bath sample is located and measures the light transmittance of the sample along said connecting line. The optical sensor is connected to a control device which stops the addition of the solution when the sensor detects the discoloration of the sample.The vessel is preferably made of glass. It may be, for example, a conventional laboratory beaker.The optical sensor acts like a light barrier. It comprises a light source emitting infrared light and a light receiver sensitive to infrared light. The light source and the light receiver are preferably arranged at the opposite ends of a U-shaped component, so that the vessel in which the bath sample is located can be arranged between the two limbs of the U-shaped component.The light source emits light in the infrared wavelength range, in particular light having a wavelength in the range from 790 to 810 nm, preferably light having a wavelength of approximately 800 nm. The light receiver has sensitivity to the light emitted from the light source and generates a signal depending on whether or not such light impinges thereon.As long as the bath sample has not yet decomposed, i.e., discoloration (black coloration) has not yet occurred, the light emitted from the light source passes through the vessel and the sample, and is detected by the light receiver. After the stabilizer is consumed by the addition of the palladium(II) salt solution and discoloration of the sample has occurred, the transmission of the light is no longer possible and the light receiver no longer records the light emitted from the light source. This detects the discoloration of the sample. The optical sensor outputs a corresponding signal which is recorded and processed by the control device.A preferred circuit diagram for the optical sensor used in accordance with the invention is shown in Fig. 1. The circuit consists of a light source V1 and a light receiver V2. When light is incident on the receiver, transistors V2 and V3 become conductive and transistor V5 becomes non-conductive. The switching behavior of the transistors V 3 and V 5 is accelerated via the feedback resistor R 4 and the switching threshold is set. V 4 acts as a freewheeling diode for protection against overvoltage of the transistor V 5.The light source and the light receiver are selected and tuned in such a way that the detection is insensitive to daylight, which has a wavelength of approximately 555 nm.Preferably, the light source V1 is an infrared diode. The light receiver V 2 is preferably a phototransistor.The voltage supply of 5 V (direct voltage) for the circuit is preferably effected via a USB connection.During the addition of the palladium(II) salt solution, the pH of the sample is preferably maintained in the range of 4.3 to 4.5.During the addition of the palladium(II) salt solution, the temperature of the sample is preferably maintained in the range of 75 to 85°C.BRIEF DESCRIPTION OF THE DRAWINGFIG. 1 shows the circuit diagram of an optical sensor used according to the invention.Example:The invention is explained in more detail below with reference to an example:An apparatus for carrying out the process according to the invention was constructed from the following components: 1 automatic programmable titrator (manufacturer: Metrohm AG, Herisau (Switzerland), commercial name: "907 Titrando") 2 magnetic heat-stirring plate 3 metering apparatus (manufacturer: Metrohm AG, Herisau (Switzerland), commercial name: "800 Dosino", volume: 20 ml) 4 brown glass bottle with palladium(II) salt solution (volume: 1 L) 5 lid 6 pH electrode 7 burette with tube 8 contact thermometer 9 optical sensor 10 beaker (for receiving the bath sample, volume: 600 ml) with magnetic stirring fishThe lid was placed above the beaker and serves to reduce heat loss to save time in the heating phase. It has holes as a holder for the burette, the contact thermometer and the pH electrode.The optical sensor was designed in the form of a U-shaped component. Two boards of the phototransistor circuit shown in FIG. 1 are integrated therein, which detect the discoloration (discoloration) of the sample. It also serves as a mechanical stop for the beaker so that the measurement always takes place at the same point.The cover and the optical sensor were attached to a telescopic arm.To automatically determine the stabilizer content in a sample of a nickel chemical bath, the titrator was programmed using the manufacturer's software (program "tiamo 2.3") as follows:Since the pH value is decisive for the rate of decomposition of the bath, this is measured via a pH electrode. The pH should be between 4.3 and 4.5. To adjust the pH, the titrator was programmed so that the addition of the palladium(II) salt solution only begins when the pH is within the desired range, so that an accurate determination of the stabilizer becomes possible. The optical sensor measures the resistance during the addition of the palladium(II) salt solution and simultaneously controls the dosing device with the palladium(II) salt solution. If the resistance drops from about 1 V DC to 20 mV DC, the passage of light was interrupted since the bath breaks down with a clear black coloration, and thus reaches the end of the addition of the palladium(II) salt solution.The titrator calculates the content of the stabilizer from the amount of palladium(II) salt solution added up to this point. The calculated result is transferred via a report into a database and can be exported from there into an Excel document.Specifically, determination was made as follows:500 mL of a nickel chemical bath was placed in the 600 mL beaker, after which a magnetic stirring bar was placed. The beaker with sample contents was then placed on the magnetic hot stirring plate and the contact thermometer was conductively connected. The thermometer was passed through the opening provided for this purpose in the cover, dipped approximately 2 cm deep into the sample and fixed with a clamp. The stirring speed was set to 650 U / min - the stirring vortex should reach the 200 ml mark of the beaker - and the sample was heated to 80°C. After this temperature had been reached, the pH electrode was pushed through the opening provided for this purpose in the cover as far as the stop. The burette was also mounted on the dosing device in the opening provided for this purpose in the cover. Thereafter, adjustment of the pH was started through the software for controlling the titrator. On its display, the pH measurement was followed. After completion, the pH electrode was pulled out of the opening and inserted back into the holder to prevent nickel plating.The palladium(II) nitrate solution (concentration: 50 mg Pd / ml) was then automatically metered in using the metering device and titrated to the end point. After titration, the thermometer was taken out of the sample and briefly immersed in nitric acid to dissolve any nickel platings formed. The sample was disposed of in the art, the beaker and the magnetic stirring fish were freed of nickel without any residues with nitric acid, since these nickels are crystallisation nuclei and can thus interfere with the next determination. The pH determined and the stabilizer content were then read off in the database.

Claims

A method for automatically determining the content of a stabilizer that reacts with a palladium(II) salt in a nickel chemical bath, the method comprising: taking a sample of the nickel chemical bath, wherein the volume of the sample is measured, and transferring the sample into a vessel whose wall is transparent to light at least at two opposing sites, wherein the connecting line between the two sites runs through the sample, adding in portions measured volumes of an aqueous solution of the palladium(II) salt to the sample, wherein the solution has a known concentration of palladium(II) salt, wherein the sample is stirred, and wherein the addition is continued until discoloration of the sample is detected by precipitation of nickel, A stabilizer content calculation based on the total solution volume added to the sample until the discoloration is detected, characterized in that the solution is added by a dosing device controlled by a control device, the discoloration is detected by an optical sensor disposed outside the vessel and measuring the transmittance of the sample for light along said connecting line, the control device is connected to the optical sensor and stops the addition of the solution when the optical sensor detects the discoloration of the sample and the light is infrared light.The method of claim 1, wherein the light has a wavelength of about 800 nm.The method of any preceding claim, wherein the palladium(II) salt is palladium(II) nitrate.A method according to any preceding claim wherein the pH of the sample is maintained in the range of 4.3 to 4.5 during the addition of the palladium(II) salt solution.The method of any preceding claim, wherein the temperature of the sample during addition of the palladium(II) salt solution is maintained in the range of 75 to 85°C.An apparatus for automatically determining the content of a stabilizer that reacts with a palladium(II) salt in a nickel chemical bath, the apparatus comprising: a vessel for receiving a sample of the nickel chemical bath, the wall of which is transparent to light at least at two opposite locations, wherein the connecting line between the two locations runs through the sample, an apparatus for stirring the sample, a control apparatus, a dosing apparatus for adding a solution of the palladium(II) salt to the sample, which is controlled by the control apparatus, an optical sensor which is arranged outside the vessel and measures the transparency of the sample to light along said connecting line, wherein the control apparatus is connected to the optical sensor and is configured to control the dosing apparatus in such a way, terminating the addition of the solution when the optical sensor detects that the transmittance of the sample for light has fallen below a predetermined value, and wherein the optical sensor comprises a light source emitting infrared light and a light receiver sensitive to infrared light.The apparatus of claim 6, wherein the infrared light has a wavelength of about 800 nm.Device according to one of claims 6 or 7, wherein the optical sensor has the form of a U-shaped component, wherein a light source or a light receiver is located at the opposite ends of the legs of the component.

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