Pulsed anodic etching method for producing toothing structures on surfaces of copper and / or copper alloys, and copper and / or copper alloys

Abstract

The invention relates to a pulsed anodic etching method for producing toothing structures in the micrometer and / or nanometer range on surfaces of copper and / or copper alloys, to copper and / or copper alloys having toothing structures on the surface thereof, to a composite system comprising copper and / or copper alloys, and to an associated use. The pulsed anodic etching method for production purposes involves the process of stripping an electrochemical cell comprising a copper and / or copper alloy component as an anode in pulses using an aqueous low-concentration chlorine-containing electrolyte. Copper oxide is formed on the copper and / or copper alloy component surface in phases with a current flow. The copper oxide located on the copper and / or copper alloy component surface is converted into copper chloride in phases with no current flows, and in phases with a current flow, the copper and / or copper alloy component surface together with the formed copper chloride as a dielectric is subjected to the anodic etching process, which leads to the formation of a surface-structured copper and / or copper alloy component having toothing structures in the micro- and / or nanometer range.

Description

[0001] Pulsed anodic etching process for producing gear structures on surfaces of copper and / or copper alloys, copper and / or copper alloys

[0002] The invention relates to a pulsed anodic etching production method of toothed structures in the micrometer and / or nanometer range on surfaces of copper and / or copper alloys, copper and / or copper alloys having toothed structures on the surface, a composite system with copper and / or copper alloys and an associated use.

[0003] The European Union's Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) regulation regulates the handling of "...substances of very high concern (SVHC) due to their potential adverse effects on human health or the environment..." A growing number of chemicals are being classified as harmful. This has a significant impact on today's widely used electrical and mechanical connections and creates a need for alternatives. In particular, chemical interactions occurring in connections should be replaced, at least partially, by mechanical interactions where possible.

[0004] While copper is a readily solderable metal, this is only partially true for copper alloys such as brass, which has a high zinc content. Polymer films are often applied to both classes of materials, particularly for corrosion protection. However, these polymer films do not adhere particularly well and can therefore only be used with chemically aggressive adhesion promoters, many of which will likely be banned in the future under REACH regulations.

[0005] In the area of ​​metal bonding, it is now possible to solve some of the problems encountered for some materials, such as titanium or aluminum, by modeling metal surfaces at the nanoscale using environmentally friendly electrochemical etching. To date, it has not been possible to transfer the knowledge gained from these materials to copper or copper alloys because the dielectric required for the structuring process, copper oxide, is not chemically stable enough.

[0006] State-of-the-art electrochemical etching processes exist for modeling metal surfaces at the nanoscale for various metals.

[0007] The document DE 102021 111 147 A1 discloses a composite structure comprising at least a first partial surface of a structure and / or a workpiece and / or a layer comprising titanium and / or a titanium alloy and / or NiTi, a polymer arranged at least partially or in sections on the first partial surface of the first structure and / or the workpiece and / or the layer, wherein the polymer is connected to the titanium and / or the titanium alloy and / or NiTi at least partially or in sections in the contact region or completely or entirely in the region of the first partial surface via a common anchoring layer. Furthermore, the invention relates to an electrochemical etching production method of undercut structures on surfaces of titanium and / or titanium alloys and / or NiTi for the mechanical coupling of a polymer to produce a composite structure.

[0008] In addition, the document DE 10 2021 111 149 A1 discloses a steel-polymer composite structure having an aluminum-polymer anchoring layer and a method for etching the surface of aluminum-coated metals, and / or in particular of aluminized steels.

[0009] Document DE 102 35 020 B4 discloses a device for etching large-area semiconductor wafers in a trough-shaped holder containing a liquid electrolyte, with a test head provided with a movable etching trough. The test head is provided with a device for holding at least one wafer. Furthermore, a method for etching with electrolytes in the above device is disclosed.

[0010] According to the state of the art, the surfaces of copper and / or copper alloys are not modeled electrochemically, but by means of other processes such as grinding or brushing or even lasers.

[0011] Electrochemical dealloying can be used to produce copper components with pores in the dealloyed areas.

[0012] In the publication "Nanostructuring of copper surfaces by oxygen-induced reconstructions," Materials Science and Engineering Technology 2000, 31(9), 845-849, S. Vollmer et al. disclose a method for structuring the topography of vicinal surfaces of metal single crystals by means of oxygen adsorption, using copper surfaces as an example.

[0013] Furthermore, in their publication "Time Dependence of Wetting Behavior Upon Applying Hierarchic Nano-Micro Periodic Surface Structures on Brass Using Ultra Short Laser Pulses," Appl. Sc. 2018, 8(5), 700, S. Rung et al. disclose a comprehensive experimental study on laser-induced hierarchical nano-micro-periodic surface structures on brass that influence wetting behavior. Using ultrashort laser pulses with a wavelength of 1030 nm, large areas are created that are completely covered by laser-induced periodic surface structures (LIPSS), with these areas overlaid by ablation grooves and U-ribs.

[0014] A. Amanov et al., in their publication "Microstructural evolution and surface properties of nanostructured Cu-based alloy by ultrasonic nanocrystalline surface modification technique," Applied Surface Science 2016, 388(A), 185-195, also disclose a nanostructured surface layer with a thickness of approximately 180 pm in a Cu-based alloy produced using ultrasonic nanocrystalline surface modification (UNSM). The Cu-based alloy is sintered onto low-carbon steel using a powder metallurgy process.

[0015] US 2020 / 0 002 833 A1 discloses a method for chemically modifying a surface of a metallic substrate material made of a first metallic material, comprising the following steps: a) bonding an alloy material made of the first metallic material and a second metallic material to the substrate material; and b) etching away at least a portion of the first metallic material from the bonded substrate material to obtain a modified substrate material, wherein the modified substrate material has an increased specific surface area. A substrate for surface-enhanced Raman spectroscopy (SERS) comprises a modified substrate material.

[0016] US 2005 / 0 145 506 A1 describes a method for electrochemically etching a metal layer deposited on a dielectric with an etch resist layer pattern to form circuits for high-density interconnection electronic modules using a non-active electrolyte solution. The method is particularly useful for printed circuit boards, chip-scale packages, wafer-level packages, and the like. The conductive paths are generally between 50 and 125 micrometers for printed circuit boards, between 5 and 50 micrometers for chip-scale packages, and between 0.1 and 5 micrometers for wafer-level packages. In one embodiment of the invention, the metal layer is copper and the non-active electrolyte solution is a mixture of sodium nitrate and sodium chloride, and a pulsed electric current is used to perform the electrochemical etching.

[0017] Furthermore, DE 101 54 886 A1 describes a method for treating circuit boards, printed circuit boards, and the like. In this method, a metal, particularly copper, is removed first by pulsed electrochemical etching and then by chemical etching. This allows for largely anisotropic metal removal, resulting in structures that are deeper than they are wide.

[0018] The document DE 102014 106276 A1 discloses a galvanized workpiece comprising polycrystalline zinc with grain sizes greater than 20 micrometers on at least parts of the workpiece surface, characterized by irregularly distributed, conical pores of various diameters penetrating the zinc grain walls. Furthermore, the invention relates to a method for producing a workpiece galvanized according to the invention, characterized by electrochemically etching the galvanized workpiece surface in an aqueous electrolyte containing potassium chloride at a predetermined temperature while applying a periodic rectangular voltage.

[0019] Furthermore, the document DE 102006 004653 A1 discloses a method for producing a metal body, which leads to the simple and reliable formation of a defined surface topography, optionally combined in the range from 10 nm to 500 pm, on a metal base body or blank, which should in particular have nanoscopic pores. For this purpose, a metal base body is subjected to a pulsating current in an electrolysis bath, wherein the electrolysis bath is mixed with salt-forming ions tailored to the material of the metal base body. Furthermore, a dental implant with particularly advantageous surface properties is to be presented, in which a nanostructure is superimposed on a superficial microstructure, and wherein nitrogen atoms and / or nitrogen compounds are deposited and / or enclosed in the surface region.

[0020] The problems with the prior art are essentially that the dielectric required for the electrochemical structuring process of copper and / or copper alloys, copper oxide or, in the case of brass, zinc oxide, is not chemically stable enough for the etching process. However, without a chemically stable dielectric, it is not possible to achieve the selectivity required for etching pores as the starting point for the surface structures to be formed via the passivation kinetics of surfaces and pore walls.

[0021] In addition, with copper alloys such as brass, corrosion presents the additional problem that the alloy partner is initially dissolved, while the copper remains.

[0022] One object of the invention disclosed here is to provide an etching manufacturing process that makes it possible to produce copper and / or copper alloys with interlocking structures on the surface. In particular, one object is to provide an environmentally friendly etching manufacturing process for this purpose.

[0023] A further objective is to provide copper and / or copper alloys with interlocking structures on the surface. Furthermore, the objective is to provide copper and / or copper alloys with interlocking structures on the surface and simultaneously improved wettability with aqueous media.

[0024] In addition, a further object is to provide a composite system comprising copper and / or copper alloys with toothed structures on the surface, which can be produced cost-effectively, simply and in an environmentally friendly manner.

[0025] It is also an object to produce such a composite system with improved adhesive properties compared to a prior art system. This object is achieved by a pulsed anodic etching process for producing toothed structures on surfaces of copper and / or copper alloys according to the main claim and copper and / or copper alloys with toothed structures on the surface, and a composite system comprising copper and / or copper alloys according to the independent claims.

[0026] The pulsed anodic etching manufacturing process of toothed structures in the micro- and / or nanometer range on surfaces of copper and / or copper alloys is characterized in that an electrochemical cell with a copper and / or copper alloy component as an anode is pulsed with an aqueous low-concentration chlorine-containing electrolyte, wherein

[0027] - copper oxide is formed on the copper and / or copper alloy component surface in phases with current flow,

[0028] - the copper oxide on the copper and / or copper alloy component surface is converted to copper chloride in phases without current flow and

[0029] - the copper and / or copper alloy component surface is subjected to the anodic etching process in phases with current flow, using the resulting copper chloride as a dielectric, resulting in the formation of a surface-structured copper and / or copper alloy component with interlocking structures in the micrometer and / or nanometer range. During the etching, a chloride-salt layer is formed, which is subsequently mechanically removed, beneath which the interlocking structures are or have been formed.

[0030] The chloride-salt layer formed during the etching process can or will be removed after completion of the etching process, at least before the use of the anchoring structures formed, in particular mechanically, so that after their removal the etched toothing structures are completely exposed.

[0031] In addition, the individual pulse duration can be 0.1 to 5 seconds or preferably 0.3 to 3 seconds and the time between the individual pulses can be 0.5 to 2.5 seconds or preferably 1 second and the electrochemical cell can be switched with a number of 2 to 5 pulses or preferably 3 pulses and the electrochemical cell can be switched with a voltage of 5 V to 50 V, in particular 10 V to 50 V, or preferably 20 V to 30 V.

[0032] The aqueous electrolyte can in particular have an HCl concentration of 0.5 to 1.5 wt.% and / or 0.75 wt.% or an equivalent concentration of chlorine ions in water. In a preferred embodiment, the current source can be in the current density range of 1 to 6 A / cm 2 or 2 to 4 A / cm 2 constant or decreasing to 0.1 to 1 A / cm 2 or 0.2 A / cm 2 be driven.

[0033] The copper chloride formed when carrying out the etching production process according to the invention can in particular be formed as copper(I) chloride.

[0034] The etching production process can also be carried out with an electrolyte temperature of 5°C to 50°C, preferably around room temperature and / or following the etching process, the copper chloride formed can be mechanically removed from the copper and / or copper alloy component and / or following the etching process, the copper and / or copper alloy component can be rinsed with, in particular, distilled water and subsequently dried and / or an active electrolyte circulation can take place during the structuring.

[0035] The copper and / or copper alloys having toothing structures on the surface produced by the pulsed anodic etching production process of toothing structures on surfaces of copper and / or copper alloys is / are characterized in that the toothing structures comprise structures in the micro- and / or nanometer range and undercuts.

[0036] It should be noted again here that during the etching process, a chloride-salt layer is formed that is subsequently mechanically removed. The structures, i.e., the interlocking structures, have formed beneath this chloride-salt layer. This chloride-salt layer formed during etching must be removed, particularly mechanically, before the anchoring structures formed can be used further, for example, by airjetting, lifting with adhesive film, brushing, etc.

[0037] The surface of the copper and / or copper alloys can, in particular, exhibit good wettability with a solder, whether formed with or without flux. For lead-containing solders with flux, the contact angle is less than 10°, for lead-free solders with flux, it is less than 45°, and for lead-free solders without flux, it is 70-90°. For every solder / flux combination tested, the contact angle on the structured surface is significantly smaller than on the conventionally mechanically prepared surface.

[0038] Surfaces structured with undercuts are significantly better protected against crevice corrosion, as the complex three-dimensional structure prevents the formation and propagation of a crevice, thus counteracting the typical mechanism whereby corrosion at the tip of the crevice leads to further widening of the crevice and thus to a self-reinforcing corrosion process.

[0039] The copper alloys may include brass and / or bronze.

[0040] The composite system with copper and / or copper alloys comprising

[0041] - at least two copper and / or copper alloy components or

[0042] - at least one copper and / or copper alloy component and at least one further electrically conductive component and an electrically non-conductive adhesive as a connecting component, characterized in that the composite system is designed to be electrically contacting.

[0043] Copper and / or copper alloys having toothed structures on the surface can be used, for example

[0044] - as part of a metal / metal or metal / polymer composite system with an adhesive or a solder as a joining component and / or

[0045] - as a conductive metal / metal composite system with a conductive or non-conductive adhesive as the connecting component.

[0046] The invention is described below with reference to the accompanying figures in the description of the figures, which are intended to illustrate the invention and are not to be considered limiting. They show:

[0047] Fig. 1 SEM images of an exemplary embodiment of a copper alloy according to the invention in the form of brass having toothed structures on the surface;

[0048] Fig. 2 SEM images of an exemplary embodiment of copper according to the invention having toothed structures on the surface;

[0049] Fig. 3 Photographs of the results of an exemplary test to demonstrate the improved wettability of a copper alloy according to the invention compared to a prior art copper alloy in the form of brass;

[0050] Fig. 4 SEM images of an exemplary partially removed copper chloride layer on a copper alloy according to the invention;

[0051] Fig. 5 SEM-EDX analysis of a partially removed copper chloride layer, exemplified on a copper alloy according to the invention in the form of brass;

[0052] Fig. 6 SEM-EDX analysis of a partially removed copper chloride layer on copper according to the invention; Fig. 7 Photographs of the results of an exemplary bonding test to illustrate the bond strength of bonded conventional brass strips compared to bonded brass strips according to the invention and

[0053] Fig. 8 shows an exemplary schematic representation of a conductive metal / metal composite system with a non-conductive adhesive as a connecting component.

[0054] Figures 1 and 2 show SEM images of two exemplary embodiments of copper according to the invention and / or copper alloys according to the invention having toothed structures on the surface.

[0055] Fig. 1 shows SEM images of the copper alloy brass at various magnifications (Fig. 1 ac) and Fig. 2 shows SEM images of copper at various magnifications (Fig. 2 a, b). Electrochemical pulsing in the pulsed anodic etching manufacturing process according to the invention creates micro- and nanostructures on the surface of the copper and / or copper alloys. The micro- and nanostructures are formed by differences in passivability and, in the case of copper alloys, also by selective leaching phenomena. When using brass, for example, zinc-rich structural components are etched more intensively than copper-rich structural components. Both images clearly show both a strong surface enlargement and the resulting undercuts.Crystal anisotropies and / or alloy variations create pores, and crystal facets create undercuts in the submicrometer range, which provide the basis for potential mechanical interlocking with another component. This effect is further enhanced by a micrometer-scale roughening of the copper and / or copper alloy surface.

[0056] Fig. 3 shows photographs of the results of an exemplary test to demonstrate the improved wettability of a copper alloy according to the invention compared to a prior art copper alloy in the form of brass. Half of a sample piece was etched using the etching production process according to the invention. The piece of brass was then placed on a hot plate and an equal-sized piece of solder (SnPb with flux) was placed on each of the etched and conventionally roughened surfaces (Fig. 3a left and right). Heat was then evenly applied via the hot plate until the solder melted completely. A wait of approximately one minute was made to allow the system time to flow. The sheet was then placed on a steel base to cool. The result, shown in Fig. 3a on the left, shows the significantly larger extent of the soldering point on the surface etched according to the invention. In Figs.In Figures 3b and 3c, the approximate size of each soldering point can be seen by applying a scale. While the contact angle on the mechanically cleaned surface is approximately 90°, it is almost 0° on the etched surface. This impressively demonstrates the significantly increased wettability.

[0057] The copper and / or copper alloy components according to the invention with interlocking structures on the surface are unusually easily wettable with various solders, including lead-containing and lead-free solders, with and almost without flux. This makes it possible to work with very thin solder films, and the solder joints exhibit extreme mechanical strength.

[0058] Fig. 4 shows SEM images of an exemplary partially removed copper chloride layer on a copper alloy according to the invention in the form of brass at different magnifications (Fig. 4a and b).

[0059] A thin, whitish, opaque layer is visible on the copper alloy of the invention immediately after the etching process. This layer cannot be rinsed off with water, isopropanol, ethanol, or acetone, but can only be removed mechanically (e.g., by airjet, removal using adhesive film, or brushing).

[0060] The SEM images of the only partially removed copper chloride layer show that the layer consists of small grains and has a layer thickness of approximately 1 pm.

[0061] In Fig. 5, the SEM-EDX analysis of a partially removed copper chloride layer is shown as an example on a copper alloy according to the invention in the form of brass.

[0062] Fig. 6 shows SEM-EDX analysis of a partially removed copper chloride layer as an example on copper according to the invention.

[0063] SEM-EDX analysis clearly shows that the partially removed layer is copper chloride. Combining color perception with the insolubility in common solvents, the copper chloride can be specified as copper I chloride.

[0064] In addition, Fig. 7 shows photographs of the results of an exemplary bonding test to illustrate the bonding strength of bonded conventional brass strips in comparison to bonded brass strips according to the invention.

[0065] Four identical brass strips (dimensions: 65 mm x 15 mm x 1 mm) were used. Two of the brass strips were conventionally ground using a Dremel tool and finished with a 220-grit sanding brush. The other two brass strips were treated using the inventive etching manufacturing process (parameters: 3 x 1 s pulse, 30 V) so that toothed structures in the micro- and / or nanometer range were present on the surface (Fig. 7a). Subsequently, an area of ​​1.5 cm 2 An adhesive, in this case Pattex Classic superglue, was applied to one side, and the two identical brass strips were joined together. After joining, the strips were clamped together for a curing time of 1.5 hours.

[0066] For the subsequent bending test in the vice, the connected brass strips were each clamped approximately 3 mm below the bond and then pressed horizontally at the upper end until the bond failed (Fig. 7b and c).

[0067] Figures 7c and d clearly show that the sample structured according to the invention can be bent significantly further until the bond fails.

[0068] This effect is essentially explained by the combination of good wettability and mechanical interlocking, and has already been observed, for example, on similarly structured aluminum and steel surfaces. A close examination of the bonded surface of the structured sample shows that at the time of bond failure, it is already plastically deformed. The resulting peeling effect leads to a significantly higher "effective" load on the bond than the mere mechanical deflection of the area outside the bond indicates. This is a further indication of the significantly improved bonding properties of the inventive copper alloy having interlocking structures on the surface.

[0069] Fig. 8 shows an example schematic representation of an electrically conductive metal / metal bonding system with an electrically non-conductive adhesive as the bonding component. On the left, the bonding system with a continuous adhesive film is shown. On the right, there is no gap in many protruding areas, so that electrical contact is possible. Nevertheless, the gap size is sufficient in the deeply etched regions for the adhesive to work. The etched surface structure acts as its own conductive filler and enables flow paths for the adhesive, so that locations with zero gap are possible and a conductive bonding system is formed despite the use of a non-conductive adhesive.

[0070] Such an adhesive bond of an electrically conductive composite system can be used in the future, for example, as a replacement for chemically aggressive components that are no longer permitted under REACH regulations, particularly for soldered joints in corrosive environments.

[0071] According to the etching production method according to the invention, copper chloride, in particular copper(I) chloride, is used as a substitute for a chemically stable oxide required for the electrochemical structuring of the surface of copper and / or copper alloys.

[0072] If such surface-structured copper and / or copper alloy components are used, it will be possible to replace state-of-the-art chemical bonds with mechanical interlocks. This will make it possible to replace harmful, possibly soon-to-be-banned, chemicals with the use of environmentally friendly electrochemistry.

[0073] In the composite system, the chemical properties of solder or adhesive are less relevant due to the interlocking structures present in the components, which results in increased optimization potential in terms of electrical and mechanical properties.

Claims

CLAIMS 1. Pulsed anodic etching manufacturing process of toothed structures in the micro- and / or nanometer range on surfaces of copper and / or copper alloys, characterized in that an electrochemical cell with a copper and / or copper alloy component as an anode is pulsed with an aqueous low-concentration chlorine-containing electrolyte, wherein - copper oxide is formed on the copper and / or copper alloy component surface in phases with current flow; - the copper oxide on the copper and / or copper alloy component surface is converted to copper chloride in phases without current flow and - the copper and / or copper alloy component surface is subjected to the anodic etching process in phases with current flow with the formed copper chloride as a dielectric; which leads to the formation of a surface-structured copper and / or Copper alloy component having toothing structures in the micro- and / or nanometer range, wherein during etching a chloride-salt layer is formed which is subsequently mechanically removed and beneath which the toothing structures are formed.

2. Etching manufacturing method according to claim 1, characterized in that - the individual pulse duration is 0.3 to 3 seconds and - the time between the individual pulses is 0.5 to 2.5 seconds or 1 second and - the electrochemical cell is contacted with a number of 2 to 5 pulses or 3 pulses and - the electrochemical cell is connected to a voltage of 10 V to 50 V or 20 V to 30 V.

3. Etching production method according to claim 1 or 2, characterized in that the aqueous electrolyte has an HCI concentration of 0.5 to 1.5 wt.% and / or 0.75 wt.% or an equivalent concentration of chlorine ions in water.

4. Etching production method according to one of the preceding claims, characterized in that the current source in the current density range of 1 to 6 A / cm 2 or 2 to 4 A / cm 2 constant or decreasing to 0.1 to 1 A / cm 2 or 0.2 A / cm 2 is driven.

5. Etching production method according to one of the preceding claims, characterized in that the copper chloride formed is in the form of copper(I) chloride.

6. Etching manufacturing method according to one of the preceding claims, characterized in that - the etching production process is carried out with an electrolyte temperature of 5 to 50°C or room temperature and / or - following the etching process, the copper chloride formed is mechanically removed from the copper and / or copper alloy component and / or - following the etching process, the copper and / or copper alloy component is rinsed and subsequently dried and / or - active electrolyte circulation takes place during structuring.

7. Copper and / or copper alloys having toothing structures on the surface produced by the pulsed anodic etching production method of toothing structures on surfaces of copper and / or copper alloys according to one of claims 1 to 6, characterized in that the toothing structures comprise structures in the micrometer and / or nanometer range and undercuts.

8. Copper and / or copper alloys according to the preceding claim, characterized in that the surface of the copper and / or copper alloys has good wettability with a solder, formed with or without flux, where - for lead-containing solders with flux the contact angle is less than 10°, for lead-free solders with flux less than 45° and for lead-free solders without flux 70-90° and / or - for each solder / flux combination examined, the contact angle on the structured surface is significantly smaller than on the classically mechanically prepared one.

9. Copper and / or copper alloys according to one of the two preceding claims, characterized in that the copper alloys comprise brass and / or bronze.

10. Composite system with copper and / or copper alloys according to one of claims 7 to 9 comprising - at least two copper and / or copper alloy components or - at least one copper and / or copper alloy component and at least one further electrically conductive component and an electrically non-conductive adhesive as a connecting component, characterized in that the composite system is designed to be electrically contacting.

11. Use of copper and / or copper alloys having toothed structures on the surface according to one of claims 7 to 9 - as part of a metal / metal or metal / polymer composite system with an adhesive or a solder as a joining component and / or - as a conductive metal / metal composite system with a conductive or non-conductive adhesive as the connecting component.

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