DE102024111115A1 - Pulsed anodic etching process for producing gear structures on surfaces of copper and/or copper alloys, copper and/or copper alloys - Google Patents

Abstract

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.
The pulsed anodic etching manufacturing method comprises an electrochemical cell with a copper and/or copper alloy component as the anode which is pulsed with an aqueous, low-concentration chlorine-containing electrolyte, whereby copper oxide is formed on the copper and/or copper alloy component surface in phases with current flow, the copper oxide located 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 interlocking structures in the micrometer and/or nanometer range.

Description

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.

The European Union's Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) regulation regulates the handling of "...substances of very high concern (SVHC) because of 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, where possible, be at least partially replaced by mechanical interactions.

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.

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.

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

The printed matter DE 10 2021 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.

In addition, the publication reveals DE 10 2021 111 149 A1 a steel-polymer composite structure comprising an aluminum-polymer anchoring layer and a method for etching the surface of aluminum-coated metals, and/or in particular of aluminized steels.

In the printed matter DE 102 35 020 B4 A device for etching large-area semiconductor wafers in a trough-shaped holder containing a liquid electrolyte is disclosed, comprising 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.

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.

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

S. Vollmer et al. disclose in the paper “Nanostructuring of copper surfaces by oxygen-induced reconstructions”, Materials Science and Engineering Technology 2000, 31(9), 845-849 a method for structuring the topography of vicinal surfaces of metal single crystals using oxygen adsorption using copper surfaces as an example.

In addition, S. Rung et al. in the 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 a comprehensive experimental study on laser-induced hierarchical nano-micro-periodic surface structures on brass that influence the 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 trenches and U-ribs.

Also, A. Amanov et al. in the 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, a nanostructured surface layer with a thickness of approximately 180 µm was fabricated in a Cu-based alloy using ultrasonic nanocrystal surface modification (UNSM). The Cu-based alloy is sintered onto low-carbon steel using a powder metallurgy process.

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.

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

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.

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.

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.

It is also an object to produce such a composite system with improved adhesive properties compared to a state-of-the-art system.

This object is achieved by a pulsed anodic etching production method of 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 with copper and/or copper alloys according to the independent claims.

• - auf der Kupfer- und/oder Kupferlegierungs-Bauteil-Oberfläche in Phasen mit Stromfluss Kupferoxid gebildet wird,
• - das auf der Kupfer- und/oder Kupferlegierungs-Bauteil-Oberfläche befindliche Kupferoxid in Phasen ohne Stromfluss zu Kupferchlorid umgewandelt wird und
• - die Kupfer- und/oder Kupferlegierungs-Bauteil-Oberfläche in Phasen mit Stromfluss mit dem gebildeten Kupferchlorid als Dielektrikum dem anodischen Ätzprozess unterliegt,

was zur Ausbildung eines oberflächenstrukturierten Kupfer- und/oder Kupferlegierungs-Bauteils aufweisend Verzahnungsstrukturen im Mikro- und/oder Nanometerbereich führt.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,
where

• - 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.

The aqueous electrolyte may 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 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 connected with a number of 2 to 5 pulses or preferably 3 pulses and the electrochemical cell can be connected with a voltage of 5 V to 50 V or preferably 20 V to 30 V.

In a preferred embodiment, the current source can be in the current density range of 1 up 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 .

The copper chloride formed during the etching production process according to the invention can in particular be formed as copper(I) chloride.

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.

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.

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.

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.

The copper alloys may include brass and/or bronze.

• - zumindest zwei Kupfer- und/oder Kupferlegierungs-Bauteile oder
• - zumindest ein Kupfer- und/oder Kupferlegierungs-Bauteil und zumindest ein weiteres elektrisch leitfähiges Bauteil

und einen elektrisch nicht leitfähigen Klebstoff als Verbindungskomponente ist dadurch gekennzeichnet, dass das Verbundsystem elektrisch kontaktierend ausgebildet ist.The composite system with copper and/or copper alloys 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 is characterized in that the composite system is designed to be electrically contacting.

• - als Bestandteil eines Verbundsystems Metall/Metall oder Metall/Polymer mit einem Klebstoff oder einem Lötmittel als Verbindungskomponente und/oder
• - als leitfähiges Verbundsystem Metall/Metall mit einem leitfähigen oder nicht leitfähigen Klebstoff als Verbindungskomponente.

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

• - 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.

• REM-Aufnahmen einer beispielhaften Ausführungsvariante einer erfindungsgemäßen Kupferlegierung in Form von Messing aufweisend Verzahnungsstrukturen auf der Oberfläche;
• REM-Aufnahmen einer beispielhaften Ausführungsvariante von erfindungsgemäßem Kupfer aufweisend Verzahnungsstrukturen auf der Oberfläche;
• Fotographien der Ergebnisse eines beispielhaften Versuches zur Darstellung der verbesserten Benetzbarkeit einer erfindungsgemäßen Kupferlegierung gegenüber einer Kupferlegierung nach dem Stand der Technik in Form von Messing;
• REM-Aufnahmen einer beispielhaft partiell entfernten Kupferchlorid-Schicht auf einer erfindungsgemäßen Kupferlegierung;
• REM-EDX-Analyse einer partiell entfernten Kupferchlorid-Schicht beispielhaft auf einer erfindungsgemäßen Kupferlegierung in Form von Messing;
• REM-EDX-Analyse einer partiell entfernten Kupferchlorid-Schicht beispielhaft auf erfindungsgemäßem Kupfer;
• Fotographien der Ergebnisse eines beispielhaften Klebeversuches zur Darstellung der Klebefestigkeit von verklebten konventionellen Messingstreifen im Vergleich zu verklebten erfindungsgemäßen Messingstreifen und
• eine beispielhafte schematische Darstellung eines leitfähigen Verbundsystems Metall/Metall mit einem nicht leitfähigen Klebstoff als Verbindungskomponente.

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:

• 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;
• SEM images of an exemplary embodiment of copper according to the invention having toothed structures on the surface;
• 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;
• SEM images of an exemplary partially removed copper chloride layer on a copper alloy according to the invention;
• SEM-EDX analysis of a partially removed copper chloride layer, for example on a copper alloy according to the invention in the form of brass;
• SEM-EDX analysis of a partially removed copper chloride layer, for example on copper according to the invention;
• 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 and
• an exemplary schematic representation of a conductive metal/metal composite system with a non-conductive adhesive as a connecting component.

The show SEM images of two exemplary embodiments of copper according to the invention and/or copper alloys according to the invention having toothing structures on the surface.

shows SEM images for the copper alloy brass in different magnifications ( ) and shows SEM images of copper in different magnifications ( ). Through electrochemical pulsing in the pulsed anodic etching manufacturing process according to the invention, micro- and nanostructures are created 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 strongly than copper-rich structural components. Both images clearly show both a strong surface enlargement and the formation of undercuts. Crystal anisotropies and/or alloy variations create pores, and crystal facets produce undercuts in the sub-micrometer range, which allow for possible mechanical interlocking with another component. This effect is further enhanced by an overarching roughening of the copper and/or copper alloy surface in the micrometer range.

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. A piece of measurement was half-etched using the etching manufacturing process according to the invention. Subsequently, the piece of brass was placed on a hot plate, and an equal-sized piece of solder (SnPb with flux) was applied to each of the etched and conventionally roughened surfaces ( left and right). Heat was then evenly applied through the heating 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 can be seen in left, the significantly larger extent of the soldering point on the surface etched according to the invention. The approximate size of each soldering point can be determined 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.

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.

shows SEM images of an exemplary partially removed copper chloride layer on a copper alloy according to the invention in the form of brass in various magnifications ( and b).

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).

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 µm.

In 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.

shows SEM-EDX analysis of a partially removed copper chloride layer, for example on copper according to the invention.

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.

In addition, Photographs of the results of an exemplary bonding test to illustrate the bonding strength of bonded conventional brass strips compared to bonded brass strips according to the invention.

Four identical brass strips (dimensions: 65 mm × 15 mm × 1 mm) were used. Two of the brass strips were sanded conventionally using a Dremel tool and finished with a 220-grit sanding brush. The other two Brass strips were treated using the etching manufacturing process according to the invention (parameters: 3 × 1 s pulse, 30 V) so that toothing structures in the micro- and/or nanometer range were present on the surface ( . An adhesive, in this case Pattex Classic superglue, was then applied to one side of a 1.5 ^cm² area, and the two identical brass strips were then joined together. After joining, the strips were clamped together for a curing time of 1.5 hours.

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 ( ).

The clearly show that the sample structured according to the invention can be bent significantly further until the bond fails.

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 with interlocking structures on the surface.

shows an example schematic representation of an electrically conductive metal/metal bonding system with an electrically non-conductive adhesive as the connecting component. On the left, the bonding system is shown with a continuous adhesive film. 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 areas for the adhesive to work. The etched surface structure acts as its own conductive filler and enables flow paths for the adhesive, so that areas with zero gap are possible and a conductive bonding system is formed despite the use of a non-conductive adhesive.

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.

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.

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.

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.

QUOTES CONTAINED IN THE DESCRIPTION

This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 10 2021 111 147 A1 [0006]
• DE 10 2021 111 149 A1 [0007]
• DE 102 35 020 B4 [0008]

Cited non-patent literature

• S. Vollmer et al. disclose in the publication “Nanostructuring of copper surfaces by oxygen-induced reconstructions”, Materials Science and Engineering Technology 2000, 31(9), 845-849 [0011]
• In addition, S. Rung et al. in the 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 [0012]
• Microstructural evolution and surface properties of nanostructured Cu-based alloy by ultrasonic nanocrystalline surface modification technique", Applied Surface Science 2016 [0013]

Claims (11)

Pulsed anodic etching production method for toothing structures in the micrometer 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 the anode is pulsed with an aqueous, low-concentration chlorine-containing electrolyte, whereby - copper oxide is formed on the copper and/or copper alloy component surface in phases with current flow; - the copper oxide present 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 the dielectric; which leads to the formation of a surface-structured copper and/or copper alloy component having toothing structures in the micrometer and/or nanometer range. Etching manufacturing process according to Claim 1 characterized in that the aqueous electrolyte has an HCl concentration of 0.5 to 1.5 wt.% and/or 0.75 wt.% or an equivalent concentration of chlorine ions in water. Etching manufacturing process according to Claim 1 or 2 characterized in that - the individual pulse duration is 0.1 to 5 seconds or 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 connected with a number of 2 to 5 pulses or 3 pulses and - the electrochemical cell is connected with a voltage of 5 V to 50 V or of 20 V to 30 V. Etching production method according to one of the preceding claims, characterized in that the current source is operated 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 . 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. Etching production method according to one of the preceding claims, characterized in that - the etching production method 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 - an active electrolyte circulation takes place during the structuring. 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 according to one of the Claims 1 until 6 characterized in that the toothing structures comprise structures in the micro- and/or nanometer range and undercuts. Copper and/or copper alloys according to the preceding claim, characterized in that the surface of the copper and/or the copper alloys has good wettability with a solder, formed with or without flux, wherein - in the case of lead-containing solders with flux the contact angle is less than 10°, in the case of lead-free solders with flux it is less than 45° and in the case of lead-free solders without flux it is 70-90° and/or - in the case of each solder/flux combination examined, the contact angle on the structured surface is significantly smaller than on the classically mechanically prepared surface. Copper and/or copper alloys according to one of the two preceding claims, characterized in that the copper alloys comprise brass and/or bronze. Composite system with copper and/or copper alloys according to one of the Claims 7 until 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. Use of copper and/or copper alloys having toothed structures on the surface according to one of the Claims 7 until 9 - as a component of a metal/metal or metal/polymer composite system with an adhesive or a solder as the joining component and/or - as a conductive metal/metal composite system with a conductive or non-conductive adhesive as the joining component.