WO2009046427A1

WO2009046427A1 - Method for galvanotechnical coating of substrate surfaces

Info

Publication number: WO2009046427A1
Application number: PCT/US2008/078958
Authority: WO
Inventors: Dr. Christoph Werner; Dr. Andreas KÖNIGSHOFEN
Original assignee: Enthone Inc.
Priority date: 2007-10-05
Filing date: 2008-10-06
Publication date: 2009-04-09
Also published as: DE102007048142A1

Abstract

The present invention relates to a method for the galvanotechnical treatment of substrate surfaces with a process solution or a cleaning solution. In accordance with the invention it is provided that the dynamic surface tension of the solution is adjusted by the addition of surface active compounds, providing that an optimum wetting result is achieved for the respective substrate surface to be treated.

Description

METHOD FOR GALVANOTECHNICAL COATING OF SUBSTRATE SURFACES

FIELD OF THE INVENTION

[0001 ] The present invention relates to a method for the galvanotechnical coating of substrate surfaces. The invention also relates to compositions of process solutions and cleaning solutions for use in galvano technology for coating substrate surfaces.

BACKGROUND OF THE INVENTION

[0002 ] From prior art there have been known different methods for coating substrate surfaces by means of galvanotechnical processes. In this connection it is not only known to deposit metal layers on corresponding conducting or non-conducting substrate surfaces, and also to alter the substrate surfaces by means of appropriate treatment solutions. Examples for such treatments include the etching of surfaces or the formation of conversion layers on surfaces.

[0003 ] For the deposition of metals on substrate surfaces both galvanic processes and autocatalytic processes are known. In the case of the galvanic deposition of metal layers on substrates, the reduction of the deposition metal present in the process solution in the form of metal cations to form the elementary metal on the substrate surface is effected by applying an external voltage. In the autocatalytic deposition of a metal layer on a substrate surface, this reduction is accomplished not by applying an external voltage, but by application of reducing agents in process solutions.

[0004 ] Besides the described process solutions for metal deposition or etching solutions, a great number of different treatment solutions are employed in the galvano technology for preparing substrate surfaces to be coated for a coating process. Such treatment solutions can serve to clean the substrate surfaces to be coated in one aspect, such as for instance washing solutions and degreasing solutions, and to the chemical preparation of the substrate surfaces in other aspects.

[0005 ] All the process solutions or washing solutions used in galvano technology have in common that the solutions impart a surface tension between the substrate surface and the solution.

[0006] This surface tension or interfacial tension describes the force which is effective in a line lying in a boundary between two phases. Here, the surface tension which is expressed by mN/m can have a negative or a positive sign. In the case of the negative sign, the surface tension tends to increase the boundaries between two phases; while in the case of the positive sign, the surface tension tends to reduce this boundary. The process solutions or washing solutions employed in galvano technology normally have positive values for the surface tension. Now, if the substrate surfaces to be coated or to be treated are contacted with or immersed in corresponding process solutions or washing solutions, a corresponding phase boundary will be formed between the substrate surface and the treatment solution or the washing solution, where the above-described surface tension takes effect.

[0007 ] Here, the case may occur that a strongly positive surface tension prevents complete wetting of the substrate surface with the treatment solution, so that not all areas of the substrate surface are in direct contact with the treatment solution. This is especially the case where the substrates to be coated include cavities which cannot be penetrated by the treatment solutions or the cleaning solutions due to the positive surface tension thereof.

[ 0008 ] To overcome this problem it is known from prior art to add wetting agents to the process solutions or the cleaning solutions, for reducing the surface tension. Here, the addition of the wetting agents or surface active compound (SAC) is performed essentially on the basis of empirical experiences. Accordingly, the result which is obtained is dependent on the particular wetting agent or surface active compound (SAC) that is used, and on the concentration of the wetting agent or surface active compound (SAC) that is used. For obtaining optimum deposition or treatment results, the surface tension must be suited to the surface structure of the substrate to be coated or to be treated, so that the process solution or the treatment solution which is used will achieve an optimum wetting of the substrate surface. But in this case it is decisive that the surface tension of the process solution or the treatment solution is not reduced to an extent such that cracks are caused in the liquid films formed on the substrate surfaces or in the boundaries between substrate and process solution or cleaning solution.

[0009 ] From prior art it is known to determine the surface tension of electrolytes by means of so-called ring balance meters. Here, a ring of a defined size is immersed in the surface of a liquid of which the surface tension is to be determined and is then slowly removed until the tearoff of the liquid film between the ring and the liquid surface. The maximum force which is required for this is determined and constitutes the value for the surface tension.

[0010 ] However, with conventional surface tension measuring methods only the static surface tension is obtained. Two typical methods to described here are "Wilhelmy plate" and the ring method based on Lecomte du Nouy. The Wilhelmy plate method uses a standardized plate with a ring/plate tensiometer to measure the surface tension. The plate is moved towards the surface until the meniscus connects with it. The surface tension is calculated from the resulting force. The Lecomte du Nouy uses a ring which is dipped into a solution and pulled back. The maximum pull back force is determined which is proportional to the surface tension: the higher the force, the higher is the surface tension, All these methods describe here determine the static surface tension. This means there are no results if there is a kinetic impact on surface tension.

[0011 ] But in prior art the problem occurs that process solutions or washing solutions lead to different coating results, despite identically determined surface tensions.

SUMMARY OF THE INVENTION

[0012 ] In view of the above, the invention is based on one object of providing a method for the treatment or coating of substrate surfaces which can overcome the above- mentioned problems.

[0013 ] Briefly, therefore, the invention is directed to a method for the galvanotechnical treatment of a substrate surface with a solution selected from the group consisting of process solutions and cleaning solutions, the method comprising measuring a dynamic surface tension of the solution; and adding a surface active compound to the solution to adjust the dynamic surface tension to improve wetting of the solution to the substrate.

[0014 ] Other objects and features will be in part apparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE FIGURES

[0015 ] Figures 1 and 2 are graphs of data generated according to the working examples herein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0016] This application claims priority from German patent application 10 2007

048 142.1 filed October 5, 2007, the entire disclosure of which is incorporated by reference.

[0017 ] This invention involves a method for the galvanotechnical treatment of substrate surfaces with a process solution or a cleaning solution, in which method the dynamic surface tension of the process solution or the cleaning solution is adjusted by the addition of a surface active compound (SAC), providing that an optimum wetting result for the substrate surfaces to be treated is achieved.

[0018 ] Surprisingly it has been found that statistical methods for the determination of the surface tension are not suitable for adjusting process solutions or cleaning solutions for the galvanotechnical treatment of substrate surfaces in such a way that reproducible results are obtained.

[0019 ] It has been discovered that consideration of the dynamic surface tension in galvanotechnical process solutions or cleaning solutions offers the possibility to adjust these solutions in a reproducible fashion for the substrate surfaces to be treated, concerning their wetting ability.

[0020 ] A suitable method for the determination of the dynamic surface tension is the so-called bubble pressure tensiometry. In the bubble pressure tensiometry, the surface tension is determined as the dynamic surface tension in dependence of age of the bubble surface. For this purpose, a stream of gas is introduced in the liquid through a capillary immersed in a liquid. The bubble surface which is formed at the capillary exit curves while continuously reducing the bubble diameter, until the bubble tears off from the capillary. The maximum pressure inside the bubble prior to its tearoff is used for determining the surface tension.

[0021 ] Dynamic surface tension measurements based on the principle that the time of the surface tension formation are determined. This means that the user gets information about the age of a bubble surface and the formed surface tension. A dynamic method is the bubble pressure tensiometry. The bubble pressure tensiometry determines the surface tension at various bubble life times. At short bubble life times (e.g. 100 ms), the measurement reflects kinetic information about the surfactant penetration process. This answers the question whether there are surface active compounds available for fast wetting. If yes, the surface tension drops quite fast even at low bubble lifetimes.

[0022 ] Longer bubble lifetimes lead to results according the balance properties. Even surfactant molecules with a low mobility have the chance to penetrate the gas bubble.

[0023 ] By the determination of the dynamic surface tension, the dynamic processes in the process solutions or in the treatment solutions are taken into account. Accordingly, a certain time is required for the SAC to become correspondingly collected or oriented at the boundaries between two phases.

[0024 ] For electroplating application, the velocity of surfactant penetration of interfaces is of major interest. During plating processes gas bubbles maybe formed which can inhibit the plating. These inhibiting gas bubbles (or other inhibiting agents) must be removed by agitation or / and lowering the surface tension. The rate of removing unwanted compounds from the surface without having negative impacts by overdosing of surface active additives itself has been discovered to be a key issue for successful plating chemistry application. [0025 ] A suitable device for the determination of the dynamic surface tension by means of bubble pressure tensiometry is the tensiometer of the type "Science Line T60" by Sita Messtechnik GmbH.

[0026] The determination of the dynamic surface tension is also advantageous for electrolytes for the deposition of copper, zinc, noble metal or alloys of these metals as well as for the pre-treatment of substrates. By the determination and control of the wetting rates, for example wafer (bumping) platings can be optimized as well as decorative platings or pre- treatment processes. The inventive method supports the process reproducibility and the certainty since an optimum surface tension value can be adjusted, which value keeps the process in an optimal range.

[0027 ] In the following the present invention is described in more detail by way of examples. It should be noted, however, that the invention is not limited to the described embodiments.

Example 1

Plating on Magnesium

[0028 ] Plating on magnesium is a very difficult process. Magnesium is extremely sensitive. Before building up layers the magnesium (or magnesium alloy) has to be protected. One possibility to protect Mg intermediately is to apply a zinc layer by immersion plating. This protection layer has to be impervious. Otherwise pitting corrosion can occur which leads to adhesion problems and blistering after plating. Therefore, there is a strong need for the immersion zinc protection layer to cover all defects that occur due to the casting / grinding / polishing processes.

[0029 ] By testing surfactants it turned out that only some perform well while others lead to plating defects. Using bubble pressure tensiometry, surfactants having a dynamic surface tension between 48 and 60 dyn/cm at a bubble lifetime of 100 ms lead to good coverage of the zinc. Exceeding this physical limitation will result in plating defects. The dynamic surface tensiometer therefore can be applied to maintain the immersion zinc plating solution.

[0030 ] Between 0.5 ml/1 and 3 ml/1 of a surface active compound of the type

Nonpitter 62A were added to a zincate etching solution for the treatment of magnesium or magnesium alloy surfaces which included 100 g/1 to 250 g/1, preferably 200 g/1 sodium phyrophosphate * 10H₂O, 25 g/1 to 60 g/1, preferably 50 g/1 zinc sulfate *7H₂O, up to 6 g/1, preferably 4.5 g/1 sodium carbonate and 2-4 g/1 sodium fluoride, for the adjustment of the surface tension. By means of the above-described method of determination of the dynamic surface tension under the use of the bubble pressure tensiometry, the values given in Fig. 1 were obtained. The upper curve is of zincate with no surface active compound. Then below that is zincate with 0.5 ml/L of the surface active compound, then 1 ml/L, then 1.54 ml/L, then 2 ml/L and 3 ml/L are the two lowest lines which closely track each other. It turned out, that at a dynamic surface tension of < 60 mN/mm, preferably between 48 mN/mm and 60 mN/mm for a lifetime of the bubbles < 500 ms, preferably about 100 ms, treatment results are obtainable which are good enough for being reproduced.

[0031 ] By a purposeful selection of the bubble lifetime, i.e. the time until tearoff, the measuring of the dynamic surface tension by means of bubble pressure tensiometry allows the determination of the mobility of the SAC that is used in the process solutions or in the cleaning solutions for the adjustment of the surface tension. Apparently, this is decisive for the coating result or for the treatment result.

[0032 ] If little surface active compound is present, the resulting surface tension will be high for short lifetimes of the bubbles. The same result will be obtained by slow surface active compounds, hence such SAC which are less mobile than other SAC in the corresponding process solutions or cleaning solutions. If sufficient SAC is present or if sufficiently fast SAC are present in the solutions, this will result in a lower dynamic surface tension.

[0033 ] It is the consideration of these dynamic effects which makes the use of the dynamic surface tension advantageously suited as a parameter for the adjustment of process solutions or cleaning solutions regarding their wetting abilities.

[0034 ] Accordingly, by measuring the surface tension at different bubble lifetimes by means of the bubble pressure tensiometry, the effective SAC concentration can be freely determined.

Example 2

Matt Nickel Plating

[0035 ] Matt nickel plating electrolytes offer a broad range of different surface finishes. But for maintaining such a system a lot of parameters have to be considered. Therefore, the dynamic surface tension measurement was applied to a matt nickel process known as the Enthone Pearlbrite process.

[0036] It was discovered that only a specific dynamic surface tension allows one to plate with an effective balance between matt-effect and the absence of defects. If the surfactant concentration exceeds a certain value, only a bright surface can be achieved. When the surfactant concentration is too low, plating defects like bright spots occur. The reason for this is that gas bubbles have to be removed from the surface. On one hand, if the dynamic surface tension is too high, the bubbles cannot be removed by agitation. On the other hand, if the surface tension is too low, the matt effect cannot be established.

[0037 ] Therefore, the dynamic tensiometer turns out to be the perfect tool to maintain matt nickel electrolytes and to ensure the desired effects. [0038 ] Here, it is remarkable that the overall concentration of the added surfactant and determined by analytical methods cannot be used to maintain this type of electrolyte. Both the survey of the concentration of surfactant added as well as the analytical methods do not lead to reproducible results. Only the measurement of the dynamic surface tension allow to find out if the electrolyte is in the parameter range to achieve the right plating conditions.

• measured at 50 ⁰C

[0039 ] Figure 2 shows the dynamic surface tensions in dependence of the addition of SAC determined for a semi-gloss nickel electrolyte. Here, Nonpitter 62A was added as a SAC at different concentrations. The surface tensions were determined for newly prepared electrolyte baths (referred to as "Neuansatz" or "N" in Fig. 2) with 0, 1, 2, 5, 8, and 11 ml/L added SAC on the one hand, and on the other hand for electrolyte baths which were already in use with these same concentrations SAC. The electrolytes which are already in use are denoted "Kunde B" or "K B."

[0040 ] In a further electrolyte already in use, which is denoted "Kunde A 0823

Relief or "K A 0823 Relief," coating defects occurred during the deposition.

[0041 ] For all electrolytes that showed a dynamic surface tension smaller than that of the curve denoted "Kunde A 0823", deposition results free from defects were obtained.

Example 3

Nickel Plating

[0042 ] Bright or semi bright nickel electrolytes have broader operation ranges like the matt nickel electrolytes mentioned before. But still, the optimum dynamic surface tension is an important issue. The determination of the SAC concentration in plating electrolyte is difficult and sometimes does not lead to reproducible results. The use of titration methods on a used electrolyte results in values which are too high. The use of static surface tension methods is not appropriate to differ between good and bad electrolyte conditions since the values resulting are too low. Therefore the dynamic surface tension method has also been applied to bright and semi bright electrolyte system. It turned out that if the following parameters lead to results free of defects:

Example 4

Deposition of a Chromium Layer from a Trivalent Chromium Electrolyte

[0043 ] In general, the deposition of a chromium layer from a trivalent chromium electrolyte is difficult. Surface active compounds have a detrimental effect on the plating result. At high current density as well as low current density ranges, failures occur. At the same time, due to the low current efficiency, hydrogen gas is produced at the cathode, which disappears from the bath in form of atomized spray which negatively impacts the environment. Therefore, an exactly dosaged amount of foaming surface active substances is added to the electrolyte, which foaming additives are on one hand intended to avoid the formation of atomized spray, and on the other hand do not influence the deposition in a negative way.

[0044 ] Surprisingly it was found that at a dynamic surface tension in the range between 69 and 73 dyn/cm at 100 ms bubble life time and 63 to 67 dyn/cm at 2.5 s bubble life time a good plating result is achieved while avoiding the formation of atomized spray. The preferred dynamic surface tension is about 71 dyn/cm at 100 ms bubble life time and 65 dyn/cm at 2.5 s bubble life time. In this example, dynamic surface tension was determined at a temperature of 30° C. The trivalent chromium electrolyte used comprised 1 to 9 g/1 (Cr3+), 50 to 200 g/1 potassiumsulphate, and 50 to 120 g/1 boric acid.

[0045 ] When introducing elements of the present invention or the preferred embodiments(s) thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0046] In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

[0047 ] As various changes could be made in the above products and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Claims

1. A method for the galvanotechnical treatment of a substrate surface with a solution selected from the group consisting of process solutions and cleaning solutions, the method comprising: measuring a dynamic surface tension of the solution; and adding a surface active compound to the solution to adjust the dynamic surface tension to improve wetting of the solution to the substrate.

2. The method of claim 1 wherein the dynamic surface tension of the solution is measured by bubble pressure tensiometry.

3. The method of claim 1 or 2 wherein the galvanotechnical treatment is the deposition of a zinc-based layer onto a magnesium-based surface by immersion plating.

4. The method according to claim 3 wherein the adding the surface active compound adjusts the dynamic surface tension to a value <60 mN/mm at a bubble lifetime <500 ms.

5. The method according to claim 1 or 2 wherein the galvanotechnical treatment is the deposition of a matt nickel or nickel alloy layer on a surface.

6. The method according to claim 1 wherein the adding the surface active compound adjusts the dynamic surface tension to a value in the range of between 45 mN/mm and 55 mN/mm at a bubble lifetime of 110 ms.

7. The method according to claim 1 or 2 wherein the galvanotechnical treatment is the deposition of a microporous, semibright, or bright nickel or nickel alloy layer.

8. The method according to claim 7, wherein the adding the surface active compound adjusts the at a bubble lifetime of 100 ms to an upper limit of 40 mN/mm for the deposition of a mircoporous layer, an upper limit of 38mN/mm for the deposition of a semibright layer, and an upper limit of 35 mN/mm for the deposition of a bright layer.