Title:
METHOD FOR ELECTROLYTIC SURFACE MODIFICATION OF FLAT METAL WORKPIECES IN COPPER-SULFATE TREATMENT LIQUID CONTAINING SULFATE-METALLATES
Kind Code:
A1


Abstract:
The invention relates to a method for the electrolytic surface modification of a flat workpiece by the deposition of copper aggregates. The invention also relates to flat metal workpieces that can be produced using this method and to the use of said metal workpieces as substrates for the formation of secure adhesive bonds comprising a plurality of materials.



Inventors:
Distelrath, Fabian (Roth, DE)
Booz, Thomas (Roth, DE)
Seidel, Andreas (Altenberg, DE)
Application Number:
15/105824
Publication Date:
11/03/2016
Filing Date:
12/18/2014
Assignee:
SCHLENK METALLFOLIEN GMBH & CO. KG (Roth, DE)
Primary Class:
International Classes:
C25D3/38; C25D7/06
View Patent Images:
Related US Applications:



Primary Examiner:
LA VILLA, MICHAEL EUGENE
Attorney, Agent or Firm:
SCULLY, SCOTT, MURPHY & PRESSER, P.C. (GARDEN CITY, NY, US)
Claims:
1. 1-13. (canceled)

14. A method for the electrolytic surface modification of a flat metal workpiece, comprising; (a) anodically polarizing at least one surface of the flat metal workpiece with a treatment liquid, whereby an anodic dissolving process is induced, and then (b) cathodically polarizing said at least one surface of the flat metal workpiece with the treatment liquid, thereby inducing a cathodic deposition for the deposition of one or more metals on the at least one surface of the flat metal workpiece, wherein said treatment liquid is comprised of a conductive liquid based on sulphuric acid/sulphate solutions of copper and one or more members selected from the group consisting of yttrium, lanthanum and lanthanoids, wherein the ratio between (i) the sum of the amount-of-substance fractions of yttrium, lanthanum and/or the lanthanoids, where contained, and (ii) the amount-of-substance fraction of copper is at least 0.0182.

15. The method according to claim 14 wherein the amount-of-substance fraction of copper is 0.0182 to 0.127.

16. The method according to claim 14, wherein the flat metal workpiece is anodically polarized by at least one cathode without direct contacting for the induction of the dissolving process, and the flat metal workpiece is cathodically polarized by at least one anode without direct contacting for the induction of the deposition process, and the cathode and the anode are arranged in such a way that treatment liquid is located between anode and metal workpiece and between cathode and metal workpiece.

17. The method according to claim 14, wherein the concentration of the sum of yttrium, lanthanum and lanthanoids, where present, in the treatment liquid is at least 0.01 mol/l.

18. The method according to claim 17 wherein the concentration of the sum of yttrium, lanthanum and lanthanoids, where present, in the treatment liquid is in the range from 0.014 mol/l to 0.35 mol/l.

19. The method according to claim 14 wherein the treatment liquid comprises a conductive liquid based on sulphuric acid/sulphate solutions of copper and lanthanum.

20. The method according to claim 14 wherein the lanthanum is present as lanthanum oxide

21. The method according to claim 14, wherein the treatment liquid additionally comprises an additive of the general formula (I):
HO—CHR8—CHR9—Z—(CHR4—CHR5—Z)n—CHR6—CHR7—OH (I) in which: n=an integer from 1 to 11, Z═S or O, R4═H, C1-4-alkyl or phenyl, R5═H, C1-4-alkyl or phenyl, R6═H, C1-4-alkyl or phenyl, R7═H, C1-4-alkyl or phenyl, R8═H, C1-4-alkyl or phenyl, and R9═H, C1-4-alkyl or phenyl.

22. The method according to claim 21, wherein the additive is 1,8-dihydroxy-3,6-dithiaoctane.

23. The method according to claim 14, wherein a metal strip or a metal foil is used as flat metal workpiece.

24. A flat metal workpiece upon which is deposited on the surface thereof metal aggregates in the form of balls covered with vertical lamellae, said surface having average roughness values Ra and Rz values, as determined in accordance with DIN EN ISO 4288:1998, ranging from 0.22 to 0.32 μm and 1.4 to 2.1 μm, respectively.

25. The flat metal workpiece according to claim 24, wherein the average roughness values Ra and Rz range from 0.24 to 0.28 μm and 1.6 to 1.9 μm, respectively.

26. The flat metal workpiece according to claim 24, wherein the metal surface has an adhesive strength, as determined by the 180° peel test using an FR-4 epoxy resin and expressed as peel strength in N/mm, of 1.5 N/mm or greater.

27. The flat metal workpiece according to claim 24 comprised of a metal consisting of copper, tin, silver and iron or a metal alloy comprised of copper, iron, silver or tin.

28. The flat metal workpiece according to claim 24 comprised of copper.

29. The flat metal workpiece according to claim 24, where the metal balls deposited on the flat metal workpiece are comprised of copper balls.

30. The flat metal workpiece according to claim 29, which is a copper foil or a copper strip, the surface of which having the peel strength of 1.5 to 3.0 N/mm.

31. The flat metal workpiece according to claim 27 wherein the metal aggregates located on the surface of said metal workpiece are additionally comprised of lanthanoid.

32. Flat metal workpiece produced by the method according to claim 14.

33. A composition of matter comprised of the flat metal workpiece of claim 27.

34. A composition of matter comprised of the flat metal workpiece of claim 32.

35. The composition of matter according to claim 33 which comprises the flat metal workpiece bonded to a material selected from thermoplastics, synthetic resins, adhesives, lacquers and pastes.

36. The composition of matter according to claim 34 which comprises the flat metal workpiece bonded to a material selected from thermoplastics, synthetic resins, adhesives, lacquers and pastes.

Description:

The present invention relates to a method for the electrolytic surface modification of a flat metal workpiece by deposition of copper aggregates. The invention further relates to the flat metal workpieces produced with this method and to the use of the metal workpieces as substrate for the formation of strong adhesive bonds with a plurality of materials.

The production of a large and rough surface is regarded as a prerequisite for a binder-free pressing of surfaces made of different materials. Depending on the combination of materials, the surfaces are first of all cleaned and then structured. Structuring is effected in the case of metal-metal bonds by dry brushing or grinding. In the case of metal-plastic bonds, which are generally produced by extruding a plastic onto a metal surface, the metal surface is pre-treated, e.g. by conversion, such as phosphating, chromating among other things, or the metal surface is modified by deposition of a deeply structured (“rough”) surface of a metal (treatment). In addition to these developments, in the case of plastics, in particular bio-adapted developments are of interest which lead to surfaces which are covered with micro-dimensioned adhesion islands (e.g. suction feet).

In electrically particularly sensitive and chemically extremely challenging bond systems, the use of as few components as possible in the bonding zone is advantageous because here the release of disruptive substances is less likely and because the failure of the bond can be kept to a minimum.

For this reason, in the above-named areas of application, the bonds are preferably produced from a brushed metal surface or one modified by treatment and the desired material to be rolled, pressed or drawn on.

The production of flat continuous material (strips, foils) with such a treatment is usually effected according to the conventional method of strip electroplating. The technical difficulties of the methods used—degreasing, electrolytic cleaning, pickling, coating—consist in the insufficiently uniform edging of the surface of foils and strips. The achievable “usual” cleanness of the surface and the locally different roughness of the material only permit a locally preferred growth of aggregates of the treatment on the surface.

The electrolytic coating of a metal surface with a metal or a metal alloy represents a known method for the surface treatment of a metal workpiece, such as for example a metal strip or a sheet. For example, in the case of electrolytic strip coating, the strip is guided through one or more electrolytic cells. In each electrolytic cell, the strip is usually brought into a solid-solid connection with the negative terminal of a rectifier via so-called current rolls. The strip consequently serves as negative electrode, i.e. as cathode. As a rule, the positive electrode, i.e. the anode, is formed as a pair of electrodes, wherein the strip runs through between the two electrodes.

Through the electrolytic coating, the metal workpiece to be coated is provided with a substantially level metal coating uniformly on all sides. Even if metal workpieces having a relatively rough surface nature are used, the surface is leveled. However, for applications in which good adhesion to another material is required, a smooth surface may be undesirable. Good adhesion between two materials is achieved when there is a chemical interaction and/or a mechanical engagement in topographical features of the adhesion partners. If this is not or is not sufficiently the case, the adhesion deteriorates. Thus, poor adhesion between a metal surface and the same or a different material, for example a lacquer layer, a paint layer or an adhesive can lead to products which are of inferior quality or even unusable.

Various technical solutions have been developed to improve the adhesion to metal surfaces. Anodizing is known as an electrolytic process for improving the adhesion to metal surfaces. In the case of anodizing, a regularly structured, porous oxide layer is formed on the surface of a metal workpiece connected as anode using an acidic electrolyte, such as e.g. sulphuric, phosphoric or chromic acid. The pores enable the mechanical engagement of the anodized metal workpiece with another material, such as a paint, lacquer or adhesive layer. However, anodizing is limited to a few metal materials, such as for example aluminium, titanium and alloys thereof. Above all, anodizing aluminium is industrially significant (Eloxal process; electrolytic oxidation of aluminium). Here, an aluminium oxide layer with a porous structure forms on the surface of the aluminium material.

An improvement in the adhesion can also be achieved by inserting an earlier step for the electrolytic pre-treatment of the surface to be coated. For example, before the actual cathodic deposition process, the metal workpiece can be subjected to an anodic treatment in which an erosion process is induced in which tiny particles and residues or impurities located on the surface of the metal foil are removed and a bright surface is obtained. In the subsequent cathodic treatment, a deposition/coating process is induced, in which a metal is deposited out of the treatment liquid onto the cleaned and bright surface, usually in the form of aggregates. The anodic and cathodic polarization can be effected in a similar way to the conventional galvanic coating through solid-solid contact or, in a further developed process according to the neutral conductor principle, be a contactless polarization.

In the case of all of the surface modification processes mentioned above, the columnar shape of the deposited aggregates limits the adhesion in the bond. The adhesion in the bond improves with the number of aggregates per unit of area. It always strives towards a threshold value which consists in the tear resistance/breaking strength of the aggregates themselves. For example, through the length of the aggregates, the adhesive bond is substantially dependent on the flow behaviour of the plastics to be pressed on, in particular when the flow behaviour is so poor that the plastic does not reach the base of the treatment and only undercuts form on the tips of the aggregates. The bond can then be compared to a plastic plateau on metal stakes. Even if such an adhesive bond is sufficiently good, there remain cavities in the bond at the base of the conventional aggregates of the treatment, into which aggressive chemicals can penetrate and can damage or destroy the adhesive bond through corrosion.

There is therefore a need for a method for improving the adhesion to metal surfaces. It is thus the object of the present invention to provide a simple and efficient method for increasing the adhesive strength of flat metal workpieces. A further object of the invention is the provision of a method for modifying/converting the surface of a flat metal workpiece by deposition of a copper layer doped with rare earth elements.

BRIEF DESCRIPTION OF THE INVENTION

To achieve this object, a method for the electrolytic surface modification of a flat metal workpiece is provided according to the invention, in which

    • at least one surface of the flat metal workpiece is anodically poled in a treatment liquid and an anodic dissolving process is thereby induced, and then
    • the at least one surface of the flat metal workpiece is cathodically poled in the treatment liquid and a cathodic deposition process is thereby induced for the deposition of one or more metals on the at least one surface of the flat metal workpiece,
    • characterized in that a conductive liquid based on sulphuric acid/sulphate solutions of copper is used as treatment liquid (electrolyte) and the treatment liquid further contains one or more members selected from the group consisting of yttrium, lanthanum and lanthanoids. The ratio between (i) the sum of the amount-of-substance fractions (in mol/l) of yttrium, lanthanum and/or the lanthanoids, where contained, and (ii) the amount-of-substance fractions (in mol/l) of copper is 0.0182 or more, preferably 0.0182 to 0.127.

The method according to the invention provides a simple and efficient method for increasing the adhesive strength of flat metal workpieces.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method for the electrolytic surface modification of a flat metal workpiece, in which at least one surface of the flat metal workpiece is anodically poled in a treatment liquid and an anodic dissolving process is thereby induced, and then the at least one surface of the flat metal workpiece is cathodically poled in the treatment liquid and a cathodic deposition process is thereby induced for the deposition of one or more metals on the at least one surface of the flat metal workpiece.

The treatment liquids used in the method according to the invention are conductive liquids based on sulphuric acid/sulphate solutions of copper. They are produced simply by dissolving suitable salts or oxides of copper in aqueous sulphuric acid. The quantity of sulphuric acid used is preferably chosen such that a residual concentration of free sulphuric acid remains after the dissolving. This residual concentration of free sulphuric acid is preferably at least 0.664 mol/l.

The molar ratio (i.e. the ratio of the amount-of-substance fractions) between copper ions and free sulphuric acid is preferably in the range of from 1.05 to 1.25, more preferably 1.10 to 1.20, in particular in the range of from 1.15 to 1.17. In a specific embodiment, the ratio is approximately 1.16. Among other things, copper(II) sulphate pentahydrate, copper(II) oxide, copper(II) carbonate or basic copper(II) carbonate are suitable as copper source.

Furthermore, one or more conducting salts are added to the treatment liquid. In the case of the present invention, salts of the rare earth elements (REE) yttrium, lanthanum and the lanthanoids (Ln), which convert into readily soluble sulphatometallates of the general formula Cu3[REE(SO4)3]2 (REE=rare earth elements) in the acidic treatment liquid are suitable as conducting salts. The element(III) oxides and the element(III) carbonates are suitable, among other things, as source for yttrium, lanthanum and the lanthanoids. Lanthanum oxide is particularly preferred. The yttrium, lanthanum or lanthanoid salts are added to the treatment liquid in a quantity such that the molar ratio between (i) the sum of the amount-of-substance fractions of Y, La and/or Ln, where contained, and (ii) the amount-of-substance fractions of copper is 0.0182 or more, preferably 0.0182 to 0.127. The concentration of the sum of yttrium, lanthanum or lanthanoid ions is preferably 0.014 mol/l or more, it is preferably in the range of from 0.014 mol/l to 0.35 mol/l, and in particular in the range of from 0.024 to 0.098 mol/l.

In particular, in the case of high ratios between yttrium, lanthanum and/or lanthanoids and copper (>0.024), the sequence of solution of the components is decisive for the rapid preparation of the electrolyte: first of all, the aqueous sulphuric acid is put in, then the copper(II) compound is dissolved and optionally insoluble constituents are separated off in the case that oxides/carbonates of the copper are used. Then, the compound(s) of Y, La and/or Ln used are dissolved. The carbonates and the lanthanum oxides/lanthanoid oxides must always be added with thorough stirring and in partial portions appropriate to the batch size in order to rule out excessive foaming or spattering of the forming electrolyte solution through the carbon dioxide released or otherwise occurring local overheating [La(III) and Ln(III) oxides react highly exothermically with acids].

Examples of suitable acidic treatment liquids (electrolytes) based on copper sulphate are shown in the following Table 1.

TABLE 1
Aqueous sulphuric acid copper REE electrolytes which were produced from the
corresponding oxides of the conductive ions (LaO, YO, NdO, GdO or DyO).
Conc., freeConc.Counterions for
ConductiveConc. Cu ionssulphuric acidconductiveCu and
Electrolyte nameionin mol/lin mol/lions in mol/lconductive ions
Electrolyte 1La0.770.6640.0245Sulphate
Electrolyte 2La0.770.6640.0490Sulphate
Electrolyte 3La0.770.6640.098Sulphate
Electrolyte 4Y0.770.6640.0245Sulphate
Electrolyte 5Nd0.770.6640.0245Sulphate
Electrolyte 6Gd0.770.6640.0245Sulphate
Electrolyte 7Dy0.770.6640.0245Sulphate

The addition of yttrium, lanthanum and/or lanthanoid ions to the treatment liquid in the method according to the invention for surface modification results not in the typical columnar aggregates (also called “dendrites” below) being deposited on the surface to be modified of the flat metal workpiece but rather balls covered with vertical lamellae. The adhesive bond (adhesive force per unit of area) of these aggregates compared with for example plastic increases depending on the specific ratios to twice to almost three times the adhesive bond of the conventionally produced treatment.

The incorporation of the rare earth elements (Y, La and/or Ln) added as conducting salts into the copper layer was found as an additional effect in the deposition from the acidic copper(II) REE sulphate treatment liquids. While the diamagnetic REE(III) ions of the yttrium and the lanthanum are incorporated only loosely bound, the paramagnetic Ln(III) ions of neodymium, gadolinium or dysprosium for example are incorporated firmly anchored into the copper layer at the same concentration in the treatment liquid. This is shown in Table 2.

TABLE 2
Incorporation of rare earth elements (REE) from acidic copper(II) REE
sulphate treatment liquids in the copper layer deposited on the surface
of the flat metal workpiece
Conc. in theEffective
treatmentmagnetic momentMolar ratio in the
REE(III) ionliquid (mol/l)REE(III) (μb)layer n(REE)/n(Cu)
Yttrium0.024600.0036
Lanthanum0.024600.0006
Lanthanum0.049200.0013
Neodymium0.02463.60.0058
Gadolinium0.02467.80.0024
Dysprosium0.024610.80.0021

The structuring of the deposited layer and the incorporation of the REE metals in the copper layer not only depend in a causal way on the magnetic properties of the REE(III) ions but the solubility gradient of the sulphatometallates Cu3[REE(SO4)3]2 has a significant influence in the transition from the comparatively readily soluble copper salts to the less soluble acids H3[REE(SO4)3] (cathodic process). Since the solubility of the sulphates increases significantly after neodymium, the effect of the heavy REE ions on the deposition process decreases. This decisive equilibrium for the deposition of the structured copper layer forces high mass transfer in the area of the electrolytic processes in order, in particular in the case of large molar REE-Cu ratios, to be able to rule out stationary, macroscopic precipitations of REE(III) sulphates (salt spots).

Moreover, the treatment liquid can contain further control additives and additives which influence the viscosity, thermal conductivity, electrical conductivity and/or the deposition of the metal aggregates. For example, the treatment liquid can comprise an additive of the general formula (I):


HO—CHR8—CHR9—Z—(CHR4—CHR5—Z)n—CHR6—CHR7—OH (I)

in which:

    • n=an integer from 1 to 11, in particular an integer from 1 to 3,
    • Z═S or O, in particular S,
    • R4═H, C1-4-alkyl or phenyl,
    • R5═H, C1-4-alkyl or phenyl,
    • R6═H, C1-4-alkyl or phenyl,
    • R7═H, C1-4-alkyl or phenyl,
    • R8═H, C1-4-alkyl or phenyl, and
    • R9═H, C1-4-alkyl or phenyl.

When the compound of formula (I) comprises enantiomers or diastereomers, both pure enantiomers or diastereomers and corresponding mixtures can be used.

In particular, within the framework of the present invention, C1-4-alkyl is methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl or sec-butyl, preferably methyl, ethyl, n-propyl, or n-butyl.

Preferably in the case of the additive of formula (I):

    • n=an integer from 1 to 3,
    • Z═S,
    • R4═H, methyl, ethyl, n-propyl, or n-butyl,
    • R5═H, methyl, ethyl, n-propyl, or n-butyl,
    • R6═H, methyl, ethyl, n-propyl, or n-butyl,
    • R7═H, methyl, ethyl, n-propyl, or n-butyl,
    • R8═H, methyl, ethyl, n-propyl, or n-butyl, and
    • R9═H, methyl, ethyl, n-propyl, or n-butyl.

Alternatively, the additive of formula (I) is a compound of formula (II):


HO—(CHR6—CHR7—Z)n—CHR6—CHR7—OH (II)

in which:

    • n=an integer from 1 to 11,
    • Z═S or O,
    • R6═H, methyl or phenyl, and
    • R7═H, methyl or phenyl,
      wherein preferably n=1-3 and Z═S.

Particularly preferably, the additive is a compound of formula (I), in which:

    • n=1 or 2, in particular 1,
    • Z═S,
    • R4═R5═H or methyl,
    • R6═R9═H or methyl, and
    • R7═R8═H or methyl.

Even more preferably, the additive is a compound of formula (III):


HO—CHR8—CHR9—S—CH2—CH2—S—CHR6—CHR7—OH (III)

in which

    • R6═R9═H or methyl, and
    • R7═R5═H or methyl.

A particularly preferred additive of the general formula (I) which can be used in the treatment liquid in the method according to the invention is 1,8-dihydroxy-3,6-dithiaoctane (DTO).

The additives of formula (I) are commercially available or can be obtained through known chemical synthesis methods or analogously to the latter.

In addition, the following additives can be used to influence the surface tension and the dissolution rate of the finest gas bubbles:

Surface-active substances of the general formula:


CnH2n+1(OC2H4)x—O—(H,CmH2m+1) with n=8 to 18, and x=3 to 9, m=1 to 4


CnH2n+1(OC3H6)y—OH with n=8 to 16 and y=1 to 3.


CnH2n+1(OC2H4)v—(OC3H6)w—OH with n=10 to 16 and v=4 to 5, w=2 to 4, from w=½v to w+1=v

The possible surface-active substances are added individually or as a mixture, wherein the total concentration in the electrolyte must always lie below the saturation limit, as a rule below 0.05 wt.-%. The use of the terminally-etherified polyethoxylates which are less sensitive to oxidation on the anode is advantageous.

In an embodiment of the invention, the method according to the invention is carried out according to the neutral conductor principle, i.e. the flat metal workpiece is contacted neither cathodically nor anodically but is polarized anodically (positively) by at least one cathode and is then polarized cathodically (negatively) by at least one anode. The current is transferred to the flat metal workpiece not by direct contacting of the flat metal workpiece via a contact element (e.g. a current roll) connected to a current source, but through the treatment liquid. During the anodic polarization, an anodic dissolving or erosion process is induced on a surface of the flat metal workpiece in which tiny particles and residues or impurities located on the surface of the metal foil are removed, whereby a clean surface is obtained. Furthermore, the topographical features of the metal surface, in particular the roughness peaks, are leveled.

Furthermore, the anodic polarization or the anodic dissolving process induced thereby leads to an activated surface for the subsequent metal deposition. In particular, the surface obtained with the method according to the invention exhibits structural similarity or structural identity with the metal aggregates deposited on the surface of the flat metal workpiece in the subsequent deposition process (epitaxy or syntaxy). Furthermore, because of the fact that the flat metal workpiece is completely covered by the treatment liquid during the entire electrolytic treatment, it can largely be avoided that the defined activation state of the surface is lost due to contact with the surrounding atmosphere. Through the cathodic polarization which follows, a cathodic deposition process is induced, in which a metal or a metal alloy (i.e. several different metals) is deposited on the surface of the flat metal workpiece.

The flat metal workpiece used within the framework of the present invention is preferably a metal workpiece with a thickness which is at least 100 times, preferably at least 1,000 times and particularly preferably at least 10,000 times smaller than the length and/or width of the metal workpiece. Consequently, as a rule, the term “surface of the flat metal workpiece” means the area defined by the length and width, not the area defined by the thickness and width or thickness and length. The flat metal workpiece is preferably a metal strip or a metal foil. The term “metal strip” herein refers to a flat metal workpiece with a given width and a thickness of from 100 μm to 1 mm. The term “metal foil” refers to a flat metal workpiece with a given width and a thickness of 100 μm or less, preferably with a thickness in the range of from 10 μm to less than 100 μm.

As a rule, the flat metal workpiece consists entirely of a single metal, in particular of copper, tin, silver or iron. However, it can also consist of a metal alloy, for example of at least two of the named metals, preferably of a copper wrought alloy, iron alloy, silver alloy and tin alloy. A flat metal workpiece made of steel can also be used. Particularly preferably, the flat metal workpiece is a copper foil, a copper strip, a silver foil, a silver strip, a tin-plated foil or a tin-plated strip, in particular a tin-plated copper foil or a tin-plated copper strip.

Furthermore, the flat metal workpiece can also consist of two or more layers of a metal or a metal alloy, wherein the layers can be the same or different. Furthermore, the flat metal workpiece can be formed in such a way that at least one and preferably both surfaces of the flat metal workpiece consist of a metal or a metal alloy and the remaining part of the flat metal workpiece can be made of any material, as long as this is suitable for use in the method according to the invention.

Before use in the method according to the invention, the flat metal workpiece is usually pre-treated. Appropriate pre-treatment methods are known in the state of the art and comprise, for example, degreasing, rinsing with water, aqueous surfactant solutions or solvents, and pickling with sulphuric acid.

During the electrolysis, the flat metal workpiece is preferably guided through the treatment liquid and past the at least one cathode and the at least one anode. This is carried out in such a way that the described anodic polarization and cathodic polarization and the anodic dissolving process and cathodic deposition process thereby induced take place. In the case of continuous metal foils or strips, these are usually guided through the treatment liquid using guiding elements (e.g. guide rollers). If a continuous foil installation is used to carry out the method according to the invention, several electrolysis baths (electrolytic cells) can also be connected in series.

Within the framework of the present invention, a variety of arrangements of the at least one cathode and the at least one anode are conceivable. For example, 1, 2, 3, 4 or more cathodes and 1, 2, 3, 4 or more anodes can be used per electrolytic cell or electrolyte bath. These can be arranged differently (e.g. alternately cathode and anode, first all cathodes and then all anodes, several cathodes alternating with several anodes, cathodes and anodes arranged only on one side of the flat metal workpiece or on both sides, etc.).

According to a preferred embodiment, at least one cathode pair and at least one anode pair are preferably used. The two cathodes of the cathode pair and the two anodes of the anode pair are arranged on opposite sides of the flat metal workpiece such that the flat metal workpiece is located between the two anodes and between the two cathodes. Anodic or cathodic polarization consequently occurs on both sides of the flat metal workpiece. Such a configuration permits the two-sided modification of the flat metal workpiece with deposited metal aggregates. According to another preferred embodiment, the flat metal workpiece is first of all anodically polarized by two cathodes which are arranged on the same side of the flat metal workpiece and then cathodically polarized by two anodes which are both arranged on the same side of the flat metal workpiece as the cathodes. A separate rectifier is necessary for each side of the substrate (electrode pair).

Usually, the at least one surface of the flat metal workpiece is first anodically polarized by the at least one cathode and then cathodically polarized by the at least one anode. However, it is also provided that the cycle “anodic polarization/cathodic polarization” is run through several times. Furthermore, the flat metal workpiece can be polarized one or more times anodically and one or more times cathodically in any sequence, wherein typically the anodic dissolving process predominates first and then the cathodic deposition process predominates. A phase with a dominating dissolving process can be interrupted by a short phase with the deposition process (dominating dissolving process, interrupted by deposition process) and vice versa (dominating deposition process, interrupted by dissolving process). The one or more anodic polarizations and the one or more cathodic polarizations can, as already mentioned above, be achieved using a corresponding number of spatially separated anodes and cathodes. However, it is also possible to use electrodes which are connected (contacted) optionally positively or negatively and consequently function both as cathode and as anode.

The cathodes and anodes are operated with direct current or a pulsed current, usually a pulsed direct current. Rectifiers can be used for this. If the number of electrodes exceeds two (i.e. more than one cathode and/or more than one anode), the additional electrodes are preferably operated through an additional rectifier. Within the framework of the present invention it is also possible for each electrode to be supplied by another rectifier in at least one operating region (cathodic, anodic), while in another operating region several rectifiers can be connected to one electrode.

Insoluble or soluble anodes can be used as anodes in the method according to the invention. The insoluble anodes typically consist of an inert material (or oxides thereof), such as, for example, lead, graphite, titanium, platinum and/or iridium (and/or oxides thereof). Preferred insoluble anodes are made of titanium coated with platinum or iridium and/or ruthenium (and/or oxides thereof). A titanium anode coated with iridium or iridium oxide is particularly preferred. On the other hand, the soluble anodes consist of the metal to be coated or the metal alloys to be coated. Examples of suitable soluble anodes are anodes made of copper or tin.

Suitable cathodes can consist of the same material as the material of the anodes. A copper cathode can be used, for example, as cathode. In a preferred embodiment, copper electrodes are used both as anode and as cathode.

The working temperature of the treatment liquid, also called electrolyte in the following, is preferably between 10° C. and 60° C., particularly preferably between 20° C. and 50° C. In order to keep the treatment liquid in this temperature range, it can be continuously cooled or heated.

The necessary recirculation of the treatment liquid depends on the current density used in the electrolytic deposition. The recirculation is necessary in order to reduce to a sufficient minimum the thickness of the electric double layer. The recirculation in the electrode chamber can be ensured, for example, by installing one or more pumps. The recirculation serves above all to preserve the functional efficiency of the electrodes and to avoid salt spots on the foil to be treated. The stacking effects occurring already in the currentless state through the sulphatometallates lead to an extreme primary voltage in order even to set the electrolytic process in motion. This primary voltage can be reduced so much by targeted increase in the recirculation at the electrode surfaces and at the material to be treated in conjunction with a well-chosen time gradient of the current density increase that these electrolytes are available for technical use. The necessary recirculation and the current density gradient depend directly on the REE/Cu ratio used and on the actual REE ion in the sulphate electrolyte. Lanthanum(III) ions provide the greatest sensitivity and thus the best possible process adjustment.

The following data for the recirculation given in Table 3 relate to an electrolyte volume in the treatment chamber of 50 litres, an electrode-foil distance of 20-30 mm and a width and height of the polarization chamber of 240 mm (H) and 300 mm (W). In addition to the targeted recirculation, the circulation delivers 1.2 l/min. over the filtration bypass.

TABLE 3
Dependency of the recirculation and of the current density gradient on
the La/Cu weight ratio and on the current density gradient
Current
Currentdensity
Recircu-densityin the
La—Culationgradient A/Pulseprocess
Electrolytewt. ratioin l/min.dm2sformb)A/dm2
Electrolyte 10.032 1.20.66100013.3
Electrolyte 10.03240a)2.251099722.5
Electrolyte 20.064401.131099722.5
Electrolyte 30.127400.381099722.5
a)40 l/min. corresponds to a flow on the surfaces of the electrode chamber of approx. 2.65 l/(min * dm2)
b)the pulse forms/rates 10001 = 50 mS 1, 50 mS = 0; leff = ½ l(1) 10997 = 50 ms 1, 50 ms 5, 50 ms 1, 50 ms 7 = 1 cycle; leff = 3.5 l(1)

Preferably at least one cathode and/or at least one anode of the device is designed as flow electrode which comprises an electrode housing with a metal mesh through which the treatment liquid can enter the housing. The electrode housing is at least partially filled with metal balls which are in contact with each other and with the metal mesh. The electrode housing further comprises an electrolyte feed for introducing an electrolyte and a flow opening out of which the electrolyte which has flowed through from the electrolyte feed between the metal balls to the flow opening exits. The flow opening is arranged such that a sufficient flow takes place through the operating zone, i.e. the space between electrode and flat metal workpiece. For this, the flow opening is usually arranged so that the exiting electrolyte flows past the metal mesh. The flowing past preferably takes place substantially parallel to the metal mesh.

The flat metal workpiece treated with the method according to the invention is usually subjected to an after-treatment. Such after-treatment methods are known in the state of the art and comprise, for example, rinsing with water or solvents, passivation, for example with a chromium(VI)-containing solution, and drying.

As an example of a device for carrying out the method according to the invention, a device is named which comprises at least one container for receiving a treatment liquid, at least one cathode arranged in the container and at least one anode arranged in the container, wherein the at least one cathode and the at least one anode are connected to a current source and wherein the flat metal workpiece is not connected to a current source.

In addition, the electrode housing usually comprises a cover, in order to prevent the metal balls from falling out and to ensure a defined flow of electrolyte through the flow electrode. The cover can be connected detachably, for example with knurled screws, to the electrode housing and furthermore comprise contacts for connecting to a current source. During operation, the flow electrode is connected anodically or cathodically to a current source, wherein the metal mesh is usually contacted anodically or cathodically.

The electrolyte which has flowed through the metal balls is preferably collected in an electrolyte channel and then supplied to the flow opening. The electrolyte channel and the flow opening are preferably located in the base of the electrode housing. The flow opening is preferably designed as a flow lip which preferably extends over the entire length of the metal mesh in the base of the electrode housing. If a filter nonwoven arranged in front of the metal mesh is used as anode bag, the flow opening is arranged such that the electrolyte exits in front of the filter nonwoven and flows along the latter substantially laminar.

The electrode housing can, for example, consist of a plastic, such as polypropylene. The metal balls can consist of the metals named above for the anode and cathode. Preferably, at least one anode is designed in the form of the flow electrode described above. In the case of the anode, the metal balls preferably consist of the metal or the metals which are to be deposited on the flat metal workpiece. The metal balls are preferably copper balls. The metal mesh is preferably an expanded metal mesh (expanded metal screen area), in particular a titanium expanded metal.

FIG. 1 shows schematically an embodiment of a dissolving/deposition cell 30 for carrying out the method according to the invention for surface treatment of a flat metal workpiece 32, in this case a metal foil. The dissolving/deposition cell 30 has a trough-like container 31, open at the top, in which a treatment liquid 36 is located. The dissolving/deposition cell 30 further has a first, second and third guide roller 34a, 34b and 34c and a first working electrode, which consists of two cathodes 40a and 40b arranged parallel, and a second working electrode, which consists of two anodes 44a and 44b arranged parallel. The cathodes 40a and 40b and the anodes 44a and 44b are connected to a current source 45. The first and third guide rollers 34a, 34c are arranged above the container 31 outside the treatment liquid 36 and above the first and second working electrodes, while the second guide roller is located on the base of the container 31 within the treatment liquid and below the working electrodes. Furthermore, the dissolving/deposition cell 30 has a separating element 48 for reducing blind currents.

The flat metal workpiece 32 runs into the treatment liquid 36 via the first guide roller 34a and through between the two cathodes 40a, 40b, with the result that the latter are located in each case on one of the two sides of the flat metal workpiece 32 passing through. Neither the flat metal workpiece 32 nor the first guide roller 34a is connected to a current source. The region 38a of the flat metal workpiece 32 located between the two cathodes 40a, 40b is positively (anodically) polarized by the two cathodes 40a, 40b. The two cathodes 40a, 40b define a dissolving region 42. In the enlarged and schematically represented section of the dissolving region 42, impurities and possibly occurring foreign metals and/or particular (e.g. uneven) metal structures present on the surface of the flat metal workpiece 32 are largely eliminated. As a result, an impurity-free, homogeneous and defined surface of the flat metal workpiece 32 is obtained which is suitable for achieving defined metal structures in the subsequent deposition step.

After passing through the cathodes 40a, 40b, i.e. the dissolving region 42, the flat metal workpiece 32 is guided via the second guide roller 34b, which likewise is not connected to a current source, between the two anodes 44a, 44b, which are located in each case on one of the two sides of the flat metal workpiece 32 and form the second working electrode. A region 38b of the flat metal workpiece 32 is polarized negatively (cathodically) by the two anodes 44a, 44b. The two anodes define a deposition region 46. In the enlarged and schematically represented section of the deposition region 46, the positively charged metal ions of the treatment liquid 36 migrate to the negatively polarized surface of the flat metal workpiece 32 and are deposited in a defined manner on the surface of the flat metal workpiece 32. After passing through the deposition region 46, the flat metal workpiece 32 runs out of the treatment liquid 36 and over the third guide roller 34c which is not connected to a current source.

A further subject-matter of the present invention is a flat metal workpiece which was produced with the method according to the invention. It was surprisingly found that the method according to the invention leads to the formation of metal aggregates on the surface of the flat metal workpiece, wherein these metal aggregates have the shape of balls covered with vertical lamellae. They differ thereby from the columnar dendrites as are obtained with the usual methods of the state of the art.

FIG. 2 shows a dark field picture (Nikon Eclipse ME600 reflected-light microscope with dark-field unit, camera Leica DFC290, lenses 100×; 50×; 20×; 10×; 5×; software Leica Application Suite 2.6.0 R1; magnification 500 times) of a copper foil surface which was modified according to the method of the invention by deposition of La/Cu from sulphuric acid electrolyte with an La concentration of 14.0 g/l, a Cu concentration of 50.3 g/l and an [La]:[Cu] weight ratio of 0.127 (electrolyte 3) in the continuous foil installation described below. At this magnification, the spherical metal aggregates on the copper foil surface are clearly recognizable.

FIG. 3 shows an SEM photograph of a copper foil surface treated electrolytically according to the method according to the invention with sulphuric acid neodymium-copper electrolyte with an Nd:Cu weight ratio of 0.032 at a magnification of 10,000 times. The photograph reproduces a section of a spherical metal aggregate on the copper foil surface and makes the lamella structure thereof visible.

FIG. 4 shows a dark field picture (Nikon Eclipse ME600 reflected-light microscope with dark-field unit, camera Leica DFC290, lenses 100×; 50×; 20×; 10×; 5×; software Leica Application Suite 2.6.0 R1; magnification 500 times) of a copper foil surface which was modified according to the method of the invention but by deposition of Cu from sulphuric acid electrolyte with a Cu concentration of 7.0 g/l (electrolyte) in the continuous foil installation described below. At this magnification, the columnar metal aggregates on the copper foil surface are clearly recognizable.

The roughness of the metal surface increases to a small extent through the deposition of the metal aggregates. For example, after the deposition of the metal aggregates on a copper foil, the average roughness values Ra and Rz, determined in accordance with DIN EN ISO 4288:1998, are preferably in the range of from 0.22 to 0.32 μm and in particular in the range of from 0.24 to 0.28 μm for Ra, and preferably in the range of from 1.4 to 2.1 μm and in particular in the range of from 1.6 to 1.9 μm for Rz. In contrast, before the deposition, a copper foil has, for example, roughness values of approximately 0.20 μm for Ra and 1.3 μm for Rz.

It was surprisingly established that the adhesive strength of the metal surface which is obtained through the deposition of aggregates in the form of balls covered with vertical lamellae on a surface of a flat metal workpiece according to the method according to the invention is surprisingly high. The adhesive strength, determined in accordance with the 180° peel test described below using an FR-4 epoxy resin and expressed as peel strength in N/mm, preferably lies at or over 1.5 N/mm. In the case of a copper foil or a copper strip, the peel strengths are preferably 1.5 to 3.0 N/mm, in particular 1.8 to 3.0 N/mm.

Because of their excellent adhesive strength, the flat metal workpieces according to the invention can be used as substrate for the formation of strong adhesive bonds with a plurality of materials. In particular, the metal aggregates on the surface of the flat metal workpiece lead to a strong adhesive bond on pressing or rolling (roll cladding) with the same or another material, on lacquering with or without subsequent curing/crosslinking or on gluing. A plurality of materials come into consideration as adhesion partner for the metal workpiece according to the invention, for example thermoplastics such as PA 66, PI and PET, synthetic resins (epoxides), adhesives, lacquers and pastes, such as graphite pastes.

The present invention therefore also relates to the use of the metal workpieces produced according to the method according to the invention as substrate for the formation of strong adhesive bonds. The flat metal workpieces according to the invention can be used for a plurality of applications. Laminates of copper with PET for the shielding of cables and plug and appliance housings from electromagnetic interferences, in particular in signal transmission, can be named by way of example. Furthermore, the use as electrical conductor in the production of MID (moulded interconnect devices) circuits is to be mentioned. These are circuits which are based on hot stamping of metallic foils on thermoplastic substrates. A further application is as substrate for electrode material in battery technology. In particular, the flat metal workpieces according to the invention can also be used in the production of stable connections required in circuit-board technology for the production of copper laminates. Specifically in the production of circuit boards, the adhesive strength of the metallic conductor on the substrate (e.g. FR-4) is of central importance. This is due on the one hand to the process steps necessary in the production (etching, drilling, pressing) and on the other hand to the load on the circuit board in the end product itself.

EXAMPLES

Materials

Various sulphuric acid sulphate electrolytes of copper with or without the addition of lanthanum conducting salt were used as electrolytes for use in the following examples. The composition of these electrolytes is shown in Table 4.

TABLE 4
Properties and composition of the electrolytes used in the examples
Electrolyte 0a)Electrolyte 1Electrolyte 2Electrolyte 3
Density1.071.19 ± 0.021.21 ± 0.021.24 ± 0.02
(g/cm3)
pH valueb)1.9 ± 0.31.9 ± 0.31.9 ± 0.31.9 ± 0.3
Copper7.048.949.550.3
content (g/l)
Lanthanum03.416.914.0
content (g/l)
Sulphate69.477.580.794.2
content (g/l)
Sulphuric60.061.562.363.3
acid (g/l)
[La]:[Cu]00.0320.0640.127
(wt./wt.)
a)Electrolyte 0: for comparison
b)pH value determined for a concentration of the electrolyte of 10 g/l
All La—Cu electrolytes (Electrolyte 1, 2 and 3) contain traces of in total less than 0.2 g/l heavy lanthanoids, such as praseodymium, neodymium and samarium.

Electrolysis Devices

In the examples described herein, on the one hand a continuous foil installation was used and on the other hand a static electrolysis arrangement.

Continuous Foil Installation

The continuous foil installation used is designed for foils and strips up to a width of 330 mm. The machine has a pay-off reel and a pay-on reel with electronic tension control. The control possibilities comprise current strength of the individual electrode segments, strip tension, strip speed and temperature of the electrolyte. The rectifiers used originate from the company plating electronic, pe86CW-6-424-960-4 type with 4 outputs. The maximum pulse current is 960 A, the maximum constant current is 424 A. The course of the current with respect to time can be defined as the pulse sequence via the associated software.

The electrolytic cell of the continuous foil installation used comprises a cathode and an anode for one-sided electrolytic deposition. The cathode and the anode are positioned parallel to the foil run and arranged such that, when the foil passes through, the same side or surface of the metal foil is opposite first the cathode and then the anode. Furthermore, the cathode and the anode are completely surrounded by electrolyte. Although in the tests described herein only one cathode and one anode is used, a plurality of different configurations can be used, for example a double cathode and a double anode for electrolytic deposition on both sides or two cathodes and anodes arranged one after the other.

In the tests described in the following, either a three-part convection electrode or a flow electrode are used as electrodes (anode and cathode). These are connected to rectifiers (pe86CW-6-424-960-4 type with 4 outputs from the company plating electronic, maximum pulse current 960 A, maximum constant current 424 A). The course of the current with respect to time can be defined as the pulse sequence via appropriate software. Furthermore, the current strengths of the individual electrodes, the strip speed and tension as well as the electrolyte temperature are controllable.

The three-part convection electrode used has three electrode segments consisting of a copper sheet. Although the individual electrode segments can be controlled separately via a rectifier, in the following tests all of the electrode segments were connected with the same polarity. The electrode is located in an anode bag made of polypropylene fabric. The necessary flow is produced by means of a B2 rod pump from Lutz (in total 40 l/min. distributed over 2 electrodes).

The flow electrode used comprises an electrode housing made of polypropylene and a high-current titanium contact frame with a screen surface made of titanium expanded metal which is packed behind with copper balls. The electrode is located in an anode bag made of PP fabric. The possible flow rate is up to 20 l/min. The electrolyte is introduced into the flow electrode via an electrolyte feed, flows past the metal balls in the direction of the base of the housing of the electrode housing and is received by an electrolyte channel in the base of the electrode housing. The electrolyte then exits the electrolyte channel via a flow opening in the form of a flow lip and flows upwards past the metal mesh. In the continuous foil installation used, after passing through the flow electrode, the electrolyte reaches the electrolysis bath and from there via an overflow a reservoir, from which the electrolyte is then pumped again into the flow electrode.

The flow electrode described above and used in the following examples represents only one example of a flow electrode which can be used according to the invention. It is clear to a person skilled in the art that numerous embodiments, modifications and/or amendments are conceivable.

Static Electrolysis Arrangement

This electrolysis arrangement was used in order to simulate the change in polarization of the same surface of the flat metal workpiece using little material which is typical for the method according to the invention.

The static electrolytic cell comprises a 1,000 ml glass beaker filled with an electrolyte (900 ml). The glass beaker stands on a heated stirrer. The heated stirrer is used to heat the electrolyte, wherein the temperature is constantly checked by a thermal element with a stainless steel sheath and is kept constant to within +/−2° C. The stirring speed is kept at 1,000 rpm and the stirring is transferred to the electrolyte solution by a round magnetic stir bar (PTFE) with dimensions of 40×d6.

Over the glass beaker there is a cover plate of PP, which is laid over the glass beaker and has an electrode on both sides at a distance in each case of 30 mm. These electrodes can consist of an inert material or be made of the material of the foil to be treated. Exchange is possible within a few minutes without problems. These electrodes are flat sheets which are immersed parallel to each other and in each case perpendicularly into the electrolyte solution. The one-side, immersed surface area is between 60 mm×80 mm and 60 mm×100 mm per electrode. In the centre, the plastic plate was provided with an opening of 20 mm×80 mm parallel to the inert electrodes, through which opening the flexible foil holder can be introduced into the cell. This foil holder was therefore formed flexible so that the foil, once inserted, can then pass through the entire process, including the pre-treatment and after-treatment steps (e.g. cleaning/rinse/rinse, etching/pickling/rinse/rinse, electrolysis/rinse/rinse, passivation/rinse/DI rinse) in the same holder and only needs to be taken out of the holder after the last rinse for drying. The foil holder consists of two PP frames with a window of 80 mm×60 mm, into which the foil is clamped. The clamping screws are manufactured from PA6 plastic. The lower clamping screws serve only to clamp the foil, the upper clamping screws serve in addition to produce a releasable press contact with a TiPt expanded metal mesh. This contact point is immersed in the solution, with the result that the foil is completely immersed in the electrolyte and the contact point is blanked off from the field of the cell by the frame of the foil holder. The expanded metal used for the contacting projects upwards out of the cell and is supplied with current via a crocodile clip. For the current supply, a power unit of the Statron type with pre-selectable current strength and display of the corresponding voltage is used. A pole-inverter switch is located between the power unit and the electrolytic cell, whereby the polarity of the foil and of the electrodes can be reversed (switched) in any sequence and at any time during the test.

Test Methods

Test Method 1—Adhesion Test

An adhesive strip (Tesafilm® Transparent 57404-00002) was placed over the electrolytically treated, dry, cold metal foil surface which had been stored for at least 15 min. and pressed firmly onto the surface with a soft roller. Care was taken that no air bubbles formed between the adhesive tape and the foil surface. After a period of 30 seconds after the adhesive strip had been pressed on, it was gripped at its projection and pulled off from the firmly held metal foil. A pulling speed of 2 to 3 seconds for a length of 8 cm was maintained.

The pulled off adhesive strip was then stuck to a white sheet of paper and the colour change caused by metal aggregates which are torn off from the foil surface and remain on the adhesive strip was assessed. Furthermore, it was assessed whether the adhesive layer of the Tesafilm remained either totally or partially on the surface of the metal foil after the pulling off.

Test Method 2—Peel Strength Test

The peel strength was determined in accordance with DIN EN 60249 on a Zwick BZ2/TN1S model peel device with an Xforce HP 500 N load cell and testXpert 12.3 software. For this, the samples were cut out of a pressed composite sheet and the foil was pulled off or peeled off at an angle of 180°. The pressed composite sheet was produced by pressing the foil with a plastic substrate at a temperature of 160±10° C. under a pressing pressure of 120±5 bar over a period of 60±5 min. The results of the peel test are given in N/mm.

Example 1

Copper Deposition on Copper Foil by Means of a Continuous Foil Installation Using Different Sulphuric Acid Copper Electrolytes with or without Addition of La Conducting Salt

A copper foil with a thickness of 0.035 mm and a width of 300 mm in the hard-as-rolled structural state was first subjected to a pre-treatment which comprised the following steps in the stated sequence:

    • Degreasing: Immersion pass with electrolytic support, 45° C., alkaline cleaning agent
    • Rinse: Water, immersion pass, 45° C.
    • Pickling: Sulphuric acid 4% in water, immersion pass, 30-35° C.
    • Rinse: Water, immersion pass, room temperature
    • Rinse: Water, immersion pass, room temperature

The copper foil pre-treated in this way was then surface-modified in the described continuous foil installation using the electrolytes of Table 4 (Electrolyte 0, Electrolyte 1, Electrolyte 2, Electrolyte 3) and with the following method parameters:

Strip speed: 1 m/min.,

Average current strength: 100 A,

Pulse sequence: 10 ms at 200 A, 10 ms rest,

Electrolyte temperature: 50±2° C.,

Recirculation by means of rod pump at 40 l/min.

After passing through the electrolysis apparatus, the surface-modified copper foil was subjected to an after-treatment which comprised the following steps in the stated sequence:

    • Rinse: Water, immersion pass, room temperature
    • Rinse: Water, immersion pass, room temperature
    • Passivation: Chromium(VI)-containing solution, immersion pass, room temperature
    • Rinse: Water, immersion pass, room temperature
    • Rinse: De-ionized water, misting, room temperature
    • Drying with hot air 90° C.

The surface-modified foils obtained with Electrolytes 1, 2 and 3 exhibited a uniform distribution of deposited spherical copper aggregates on the foil surface. FIG. 2 shows this on the example of a surface obtained with Electrolyte 3. In FIG. 4, the surface with columnar buildups obtained with Electrolyte 0 is shown for comparison.

The foil surfaces with lamellae-covered spherical aggregates obtained with Electrolytes 1, 2 and 3, moreover, had excellent adhesive strengths of adhesives in the adhesion test using Tesafilm. The adhesion between the modified metal foil surface and the adhesive on the adhesive strip is so high that, on pulling the adhesive strip off, the bond between adhesive and plastic carrier breaks and the adhesive layer of the Tesafilm remains on the foil surface. In contrast, in the case of the metal foil modified with Electrolyte 0 (Cu electrolyte without La) with columnar treatment, the debonding of the treatment is observed on pulling off the adhesive strip.

Excellent adhesive strengths between 1.7 and 2.8 N/mm were also obtained in the peel test. The peel strengths determined correlated with increasing surface density of the deposited metal aggregates. The results of the peel test are summarized in Table 5 below.

TABLE 5
Peel strengths of copper surfaces pressed with FR-4 (V = foil speed,
I = average current strength, J = current density, Q = charge density)
Peel
VIJQstrength
Electrolyte(m/min.)(A)(A/dm2)(C/dm2)Pulse form(N/mm)
Electrolyte2.510013.98010997*2.8 ± 0.2
2
Electrolyte115020.830010997*2.8 ± 0.2
2
Electrolyte110013.920010997*1.7 ± 0.2
2
Electrolyte110013.920010001**2.0 ± 0.2
2
Electrolyte219026.419010997*2.0 ± 0.2
2
Electrolyte110013.920010997*2.4 ± 0.2
3
Electrolyte1451.526010001*1.2 ± 0.2
0
*Pulse form 10997 means: Rest for 50 ms; current of strength A (namely 166 A, 250 A, 166 A, 317 A or 166 A) for 50 ms; rest for 50 ms; and current of strength B (greater than A) (namely 233 A, 350 A, 233 A, 443 A or 233 A) for 50 ms (this gives an average current (based on 50 ms) of I = 100 A, 150 A, 100 A, 190 A or 100 A).
**Pulse form 10001 means: Current of strength C (here 200 A) for 50 ms; rest for 10 ms.

Example 2

Incorporation of Rare Earth Elements (REE) into the Aggregates on the Surface of Copper Foil Modified with REE-Cu Electrolytes

A copper foil with a thickness of 0.035 mm and a width of 300 mm in the hard-as-rolled structural state was first of all subjected to a pre-treatment which comprised the following steps in the stated sequence:

    • Pre-cleaning: Purax 6029PUS, 40 g/l, 60° C., currentless, 10 s.
    • Rinse: Water
    • Precision cleaning: Velocit 1127M, 25 g/l, 60° C., currentless, 10 s.
    • Rinse: Water
    • Etching/pickling: Sulphuric acid (7% in water), 25° C.-35° C.
    • Rinse: Water

The copper foil pre-treated in this way was then surface-modified in the described static electrolysis arrangement using Electrolyte 1 and Electrolyte 2 at room temperature with a charge density of 541 C/dm2:

After passing through the electrolysis apparatus, the surface-modified copper foil was subjected to an after-treatment which comprised the following steps in the stated sequence:

    • Rinse: Water
    • Passivation: Solution of 6 g potassium dichromate in water at room temperature.
    • Rinse: Water
    • Drying with hot air between 90° C. and 120° C.

In the case of further experiments within the framework of this example, the lanthanum in the treatment electrolyte Electrolyte 1 was replaced by equimolar quantities of yttrium, neodymium, gadolinium or dysprosium and the surface modification was repeated with otherwise identical parameters.

The layers deposited using the different electrolytes were analysed by means of ICP-OES from nitric acid solution (Argon-Plasma; Perkin Elmer, Optima 3000DV, axial registration emission; as standards in each case the concentrations of 0.1 mg/l, 1 mg/l and 10 mg/l of the respective RE metal were used). The results are shown in Table 6.

TABLE 6
Concentration of the inert ions found in the deposited layer, relative to
the treated surface in μmol/m2 (from acidic REE-Cu electrolytes).
Inert ionConcentration in the aggregates
Lanthanum (Electrolyte 1)0
Lanthanum (Electrolyte 2)0
Yttrium0
Neodymium42.0
Gadolinium13.3
Dysprosium13.5

This example shows that lanthanum and yttrium are not incorporated into the deposited aggregates after the electrolytic surface modification of a copper foil with La—Cu or Y—Cu electrolytes. In contrast, with neodymium, gadolinium and dysprosium, these were recovered as paramagnetic inert ions after the decomposition by nitric acid of the deposited aggregates.