EP1881091A1 - Process and apparatus for controlling the plating result on a substrate surface - Google Patents

Abstract

The controlling deposition effect of a metal layer/an alloy layer deposited on a substrate surface, comprises determining a free corrosion potential between the substrate surface to be coated and a reference electrode (3) occasionally during coating process, and comparing the determined value with a given value. The given value is selected so that a sufficient deposition effect obtains during the correlation of the determined value with the given value. The free corrosion potential is continuously determined between a measuring electrode and a reference electrode. The controlling deposition effect of a metal layer or an alloy layer deposited on a substrate surface, comprises determining a free corrosion potential between the substrate surface to be coated and a reference electrode (3) occasionally during coating process, and comparing a determined value with a given value. The given value is selected so that a sufficient deposition effect obtains during the correlation of the determined value with the given value. The free corrosion potential during the entire coating process is continuously determined between a measuring electrode consisting of a material identical with respect to its composition to the surface to be coated, and a reference electrode. An independent claim is included for a device for controlling deposition effect of metal-/alloy layer on substrate surface.

Description

The present invention relates to a method and a device for controlling the deposition result of a deposited on a substrate surface metal or metal alloy layer. In particular, the invention relates to a method and a device for determining the deposition result in the treatment of metallic surfaces, in particular aluminum or magnesium surfaces or surfaces of aluminum or magnesium alloys with so-called Zinkatbeizen.

Aluminum and also magnesium substrate surfaces as well as surfaces of their alloys are covered with more or less thick oxide layers. Before further galvanic surface treatment, these oxide layers must be removed. In order to avoid re-formation of oxide layers, the corresponding substrate surfaces are treated in a so-called "Sudabscheidung". These can be electrolytes for the deposition of tin, silver, gold, copper, zinc and zinc alloys. Widely used are the so-called zincate solutions.

Zincate solutions are alkaline or, in the case of magnesium, acidic zincate solutions. When contacting aluminum or magnesium surfaces or corresponding alloy surfaces with a zincate solution, the formula is distinguished

3 Zn (OH) 4 ^2- + 2Al → 3 Zn + 2 Al (OH) ₄ ^- + 4 OH ^-

Zinc on the substrate surface from. It is dissolved alumina (magnesium oxide) and also aluminum (magnesium) on the surface and zinc deposited by charge exchange.

The term zincate layer is to be understood in the sense of the invention a deposited zinc layer.

In order to obtain sufficient adhesion of the deposited zinc to the surface, it is common in the art to remove the deposited zinc layers with a suitable reagent such as nitric acid and repeatedly contact the surface with the zincate solution. The layers thus deposited are referred to as the zincate layer.

In addition to the deposition of pure zincate layers, it is also known from the prior art to deposit zinc alloy layers on aluminum and / or magnesium-containing substrate surfaces. Alloy metals may be, for example, nickel or iron, wherein binary Zn / Ni or Zn / Fe alloys or even ternary Zn / Fe / Ni alloys can be deposited. For the deposition of corresponding zinc alloys, the zincate solutions usually have suitable nickel and / or iron compounds. The zincate solutions known from the prior art can be cyanide-containing or can also be used as a cyanide-free system. The metals contained in the zincate solutions, if they do not form hydroxo complexes, must be complexed with suitable complexing agents.

Acid zincate solutions are based on pyrophosphate.

The formation of a zincate layer depends essentially on the free hydroxide concentration, the pretreatment of the surface, the composition of the surface to be coated, the foreign metal content and the complexing agent content of the zincate pickling. Depending on these parameters, which also change during the coating process, adherent dense or porous to spongy layers can be deposited on the substrate surfaces who have very good to bad or no liability. On the one hand, the coating result depends on the parameters mentioned, but on the other hand also on parameters such as temperature and coating time.

Since the zincate coating of an aluminum- and / or magnesium-containing surface is often the basis for a subsequent electroplating coating, for example with a nickel-containing or copper-containing layer in an electrochemical or autocatalytic coating process, a poorly deposited zincate layer, in particular a poorly adhering zincate layer, can lead to deficient coating results to lead. In many cases, such defects only show up during storage or tempering of the finished coated substrate surface or of the finished coated part, where blistering or chipping may occur. In particular, by the later occurrence of such damage, these lead to large committee and the associated high costs. In the worst case, the damage caused by a bad Zinkatschicht occur only in a final built-up part, which can lead to significant costs in the replacement of such parts.

In addition, other Sudabscheideverfahren known from the prior art.

Chemical tin, better known in English as "immersion tin electrolytes", is deposited as HASL (hot air solder leveling) substitute on tracks. In the same way, silver from sump electrolytes is increasingly used. In the semiconductor industry, gold electrolytes are also based on charge exchange. A classic process of sud deposition is the coppering of wires from hot sulfuric copper sulfate solutions.

Also, deposition of other metal or metal alloy layers such as copper-, nickel-, or chromium-containing layers on substrate surfaces may result in coating defects due to lack of adhesion of the deposited layers.

This also applies mutatis mutandis to all other layer systems following a zincate layer.

In view of the above, it is therefore an object of the present invention to provide a method and a device with which even during the coating process, in particular a sufficient adhesion of the deposited metal or metal alloy layer can be determined in order to control the coating process depending on this.

This object is achieved with respect to the method by a method for controlling the deposition result of a deposited on a substrate surface metal or metal alloy layer, the free corrosion potential between a substrate surface to be coated and a reference electrode at least temporarily determined during the coating process and the particular value with a predetermined value is compared, wherein the predetermined value is selected so that when the predetermined value coincides with the predetermined value, a sufficient deposition result is obtained.

As part of its investigations, the Applicant has found that the deposition result, for example, in the deposition of Zinkatschichten on aluminum or magnesium-containing substrate surfaces not only on the composition of the zincate solution and the set process conditions depends, but also in particular on the composition and nature of the substrate surface on which a corresponding metal or metal alloy layer is to be deposited.

It has been found that the determination of the free corrosion potential between the substrate surface to be coated and the reference electrode is suitable to observe the process of deposition on the substrate surface.

The free corrosion potential is understood to mean the electrode potential of a metal or an alloy in an attack agent without the influence of external currents, measured against a nonpolarizable reference electrode.

It turned out that the free corrosion potential approaches a limit in the course of the coating process. This limit value depends on the one hand on the composition of the coating solution, for example a zincate solution, on the other hand on the composition and / or nature of the substrate surface to be coated.

The investigations have shown that the observed free corrosion potentials correlate with the adhesive strength of the deposited metal or metal alloy layers on the substrate surface.

Without making this theory the basis of the invention, the Applicant believes that the measured free corrosion potential reaches a limit as soon as the deposited layer on the substrate surface is completely closed and concomitantly has good adhesion properties.

It is thus possible, by determining the free corrosion potential between a substrate surface to be coated and a counterelectrode and comparing the determined free corrosion potential with a fixed limit independently of the further coating parameters, to determine the time at which a metal or metal alloy layer on a substrate surface is sufficient Separation result. In this case, the value with which the specific potential value is compared can be selected as a function of the desired deposition result.

The determination of the free corrosion potential thus allows for the first time the direct control of the deposition result already during the coating process. This results in very good options, in particular with regard to quality control, which leads to a significant reduction in rejects and, as a result, to significant cost optimization.

As a reference electrode for the determination of the free corrosion potential, in particular a calomel electrode is suitable. However, all other suitable reference electrodes can also be used as the counterelectrode in the method according to the invention.

Advantageously, the free corrosion potential is determined continuously during the entire coating process and compared with a predetermined value.

Since the direct contacting of substrate surfaces to be coated for determining the free corrosion potential can often be difficult in practice, it is proposed with the invention to determine the free corrosion potential between a measuring electrode and a reference electrode, wherein the measuring electrode with respect to their composition with the material identical to the substrate surface to be coated. This makes it possible to use electrically contactable measuring electrodes, which pass through the coating process together with the substrates to be coated.

With regard to the device, the object underlying the invention is achieved by a device for controlling the deposition result of a deposited on a substrate surface metal or metal alloy layer, which comprises a device for determining the free corrosion potential between a substrate surface to be coated and a counter electrode, and a device for comparison of the determined free corrosion potential having a predetermined value.

The means for comparing the determined free corrosion potential with the predetermined value may output a signal when the predetermined potential matches the predetermined value. Such a signal is advantageously a control signal which controls a device for terminating or interrupting the coating process, so that the coating process is terminated when the predetermined value for the free corrosion potential is reached.

This can be done, for example, by interrupting the power supply to the substrate surfaces to be coated in the case of a galvanic coating process or by terminating the contacting of the substrate surface to be coated with the electrolyte composition used, for example by lifting or extending the to be coated Substrates from the electrolyte bath, which can be used in particular for autocatalytic coating processes.

To determine the free corrosion potential between a substrate surface to be coated and a counterelectrode, which can be, for example, a calomel electrode, the measuring electrode used to determine the free corrosion potential is an electrode which is identical in composition to the material of the substrate surface to be coated.

For example, a piece of a material sample of the substrate surfaces to be coated can be introduced into a suitable carrier device. Such a support means may comprise means for electrically contacting the sample of material to pick up the free corrosion potential flow. A designed carrier device can then serve as a measuring electrode.

To carry out the measurement, a reference electrode is used.

In an advantageous embodiment of the device according to the invention, a corresponding measuring electrode is attached, for example, to a support frame for substrates to be coated, whereby the measuring electrode can also go through the coating process of the substrates. This ensures that the measuring electrode is exposed to the same conditions as the substrate surfaces to be coated.

The carrier device for the measuring electrode can also be designed as an electrode array and also receive the reference electrode in addition to the measuring electrode. Advantageously, such a designed measuring device transmits the determined potential value wirelessly to the device for comparing the determined potential value with a predetermined value.

By means of such an embodiment, the device according to the invention can be easily adapted to the respective substrate surfaces to be coated or their composition and can be used universally.

In particular, the apparatus of the invention can be easily integrated into existing coating systems, whereby the inventive method is also applicable to existing coating equipment.

It is also possible to carry out the measurement of the free corrosion potential in addition to the system in a laboratory. Thus, the control of the zincate solution and the immersion time is almost continuously possible. As a rule, one to two measurements per shift (eight hours) are sufficient. When using new alloys, these must first be checked in the laboratory and the appropriate conditions determined. These are usually: type of zincate solution, concentration of the ingredients in the zincate solution, immersion time, temperature. If necessary, it is possible to work with different coating solutions.

The method according to the invention is also suitable for determining the deposition results of chromating on zinc layers.

1 shows by way of example the experimental setup for Example 1. In a suitable container 1 a Zinkatbeize 5 is presented. The free corrosion potential is determined with a suitable reference electrode 2, such as a saturated calomel electrode, between it and the base material 3 to be coated via a suitable measuring device 4. For this purpose, the reference electrode 2 and the base material 3 are electrically contacted with the measuring device 4 in a suitable manner.

Fig. 2 shows the measured free corrosion potential for different aluminum alloy compositions as a base material. The alloy compositions in region A show a fast approach to a limit, whereas the alloy compositions in region B show a much slower approach to a limit.

The following exemplary embodiments show, by way of example, the determination according to the invention of free corrosion potentials during the coating process, wherein the idea of the invention can not be limited to the alloy compositions and coating methods listed by way of example.

example 1

Samples of base materials to be coated are embedded in a plastic ring with epoxy such that one side remains open. This side is wet sanded, last with 500 grit, rinsed and dried with filter paper. Subsequently, these samples are immersed in a Zinkatbeize type ALUMON EN the company. Enthone and measured with a Lugginkapillare against a saturated calomel electrode (SCE) the potential and the course of the potential 120s at room temperature (23 ° C) followed and recorded electronically, as shown in Fig 1. The solutions are not tempered.

The temporal potential curve in FIG. 2 shows surprisingly clear differences between the individual types of alloy.

Group A shows the desired result. In a short time, about 20 seconds, a dense, firmly adhering zincate layer is formed. The curve swings in the horizontal after just 20 seconds. The parts of group A show after the galvanic layer structure: copper / nickel / chromium during annealing no bubbles. The adhesion of the galvanic layers is excellent. The Group A substrates show dense but thin zincate layers with good adhesion.

Group B includes alloys that take about 40 to 80 seconds to stop the oscillation of the values due to gas evolution, and that the potential remains constant at about 100 s. Overall, the curve shows the surface not yet closed, around 200mV to 300 mV negative potentials. The horizontal curve part is only reached after about 80 s. The zincate layer is also dense after this time, but slightly thicker and more voluminous. The potential then approaches the 1400 to 1450 mV / SCE range again. The adhesion is good and there are no bubbles after annealing. If the parts were to be removed from the bath after about 60 seconds, adhesion problems would be expected since the zincate layer is not yet completely formed.

An alloy (AlSi ₁₁ / Mg) did not form perfect dense zincate layers even after 120 seconds. The oscillation of the measured values will be smaller, but does not disappear completely. The layers can be wiped with pulp and are obviously porous. This also shows the more negative potential of about 1550 mV / SCE after 120 s. Here adhesion problems are to be expected, if one does not carefully control the stripping of the first zincate layer and the formation of the second zincate layer. The size and shape of the silicon crystallites seems to exert a significant influence here.

Example 2

Test pieces with freshly deposited bright copper were clamped in a sample holder and connected to the input for the working electrode of a potentiostat. The calomel reference electrode already dipped into the tin immersion solution STANNOSTAR GEM plus from Enthone, which had a temperature of 68 ° C., before the start of the measurement, and was connected to the corresponding input of the potentiostat. The measuring process of the potentiostat was started and a second later the test specimen in the Zinntauchlösung. The corrosion potential was recorded for 3 min., A plot of the measured free corrosion potential is shown in FIG.

Example 3

Test pieces with freshly deposited bright copper were clamped in a sample holder and connected to the input for the working electrode of a potentiostat. The calomel reference electrode already dipped into the immersion solution ALPHASTAR SILVER from Enthone, which had a temperature of 50 ° C., and was connected to the corresponding input of the potentiostat before the start of the measurement. The measuring process of the potentiostat was started and one second later the specimen in the silver immersion solution. The corrosion potential was recorded for 3 min., A plot of the measured free corrosion potential is shown in FIG.

LIST OF REFERENCE NUMBERS

1

container

2

reference electrode

3

base material

4

measuring device

5

zincate

Claims (11)

A method of controlling the deposition result of a metal or metal alloy layer deposited on a substrate surface, wherein the free corrosion potential between a substrate surface to be coated and a reference electrode is determined at least temporarily during the coating process and the determined value is compared to a predetermined value, the predetermined value being selected is that if the specified value coincides with the predetermined value, a sufficient separation result is obtained. The method of claim 1, wherein the free corrosion potential is determined continuously throughout the coating process. Method according to one of the preceding claims, wherein the free corrosion potential is determined between a measuring electrode consisting of a material identical in composition to the surface to be coated and a reference electrode. Method according to one of the preceding claims, wherein the substrate surface to be coated is formed of an aluminum and / or magnesium-containing material and the metal or metal alloy layer to be deposited is zinc-containing. Method according to one of claims 1 to 3, wherein the surface to be coated consists of steel, copper, brass, bronze or another metallic base material and copper, tin, silver, gold or other metallic layers are deposited on them in a brewing process. Device for controlling the deposition result of a metal or metal alloy layer deposited on a substrate surface, comprising means for determining the free corrosion potential between a substrate surface to be coated and a counter electrode, and means for comparing the determined free corrosion potential with a predetermined value. Apparatus according to claim 6, comprising means for outputting a signal, wherein the means for outputting a signal is connected to the means for comparing the determined free corrosion potential with the predetermined value such that when the determined free corrosion potential value matches the predetermined value, a signal is issued. Apparatus according to claim 7, wherein the means for outputting a signal outputs a control signal to a means for terminating the deposition process. Device according to one or more of claims 6 to 8, comprising a measuring electrode consisting of a material identical in its composition to the surface to be coated. Apparatus according to claim 9, wherein at least the measuring electrode is attachable to a frame for receiving substrates to be coated. Device according to one or more of claims 9 and 10, wherein the measuring electrode transmits the measured value wirelessly to a device for comparing the determined free corrosion potential with a predetermined value.

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