Patent Application
20200255929
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The invention relates to a method for producing an electrically conductive foil. A foil in the sense of the invention refers to a flat, self-supporting and flexible structure having a maximum thickness of 1.5 mm and made of a material that is homogeneous across its surface and does not lose its essential material properties even after repeated bending or rolling.
A variety of methods for producing electrically conductive foils have been established. For example, electrically conductive foils can be produced by mechanically rolling an electrically conductive starting material. These types of production processes are limited by the minimum achievable thickness of such a foil. Copper foils having a minimum thickness of about 6 μm can be produced using rolling processes, for example, but this is not thin enough for certain applications. Another disadvantage is that the surfaces of the foils are often scored by the rolling process.
For the production of electrically conductive foils having a foil thickness of less than 6 μm, for example, layer systems comprising electrically conductive material are deposited on flexible substrates using vacuum processes and the flexible substrate is subsequently removed. DE 10 2015 003 369 A1 proposes first depositing a sacrificial layer onto a carrier substrate, and then a wear layer of electrically conductive material onto a carrier substrate, using vacuum coating processes. The layer system produced in this way is then exposed to laser beams, for example, which causes cracks to form in the sacrificial layer and allows the wear layer to be separated from the carrier substrate. The disadvantage of this is that, even after the wear layer has separated from the carrier substrate, remnants of the sacrificial layer remain stuck to the wear layer, which necessitates additional cleaning steps for an electrically conductive foil produced in this way.
From WO 2017/054889 A1 it is known, for reasons of stability, to first deposit a layer composite consisting of at least two layers of different materials onto a flexible substrate using vacuum coating processes. Lithium can be deposited as the first layer, for example, and copper as the second layer. The flexible substrate is then removed from the layer composite. However, this procedure can only be used to produce a foil composite consisting of at least two different materials.
The underlying technical problem of the invention is therefore to create a method for producing an electrically conductive foil, by means of which the disadvantages of the state of the art can be overcome. The method according to the invention should in particular also make it possible to produce an electrically conductive foil having with a foil thickness of less than 1 μm. The foil should furthermore consist of only one material when viewed across the thickness of the foil.
In the method according to the invention for producing a foil made of an electrically conductive material, wherein the foil consists of the same material along the extension of the foil thickness, a flexible substrate is first placed into a working chamber. A layer of the electrically conductive material is then deposited onto at least one surface region of the substrate using a vacuum coating process. For this, an electrically conductive material can be used which, for example, comprises at least one of the chemical elements from the group consisting of copper, indium, aluminum, tin, zinc, magnesium, and silver. The method according to the invention is particularly suitable for producing copper foils. Magnetron sputtering and/or evaporation are particularly suitable as the vacuum coating process for depositing the first layer of the electrically conductive material, and metal foils (in particular made of stainless steel), plastic foils, glass or paper are suitable as the flexible substrate.
After the deposition of the first layer of the electrically conductive material, the first layer is peeled off of the flexible substrate using mechanical means. It has been surprisingly been shown that a single layer of an electrically conductive material deposited directly onto a flexible substrate using vacuum coating processes can be mechanically peeled off of the flexible substrate, if the adhesive force between the flexible substrate and the deposited layer is set such that said adhesive force is lower than the binding forces within the deposited layer and lower than the binding forces within the flexible substrate.
According to the invention, an adhesive force between the flexible substrate and the deposited layer required for peeling is set by carrying out an ion etching process on at least the surface region of the flexible substrate on which the layer of electrically conductive material is to be deposited. The ion etching cleans the substrate surface region and also changes the surface structure of the substrate, which then has a beneficial effect on subsequent method steps. The ions used for ion etching can, for example, originate from a hollow cathode plasma or a magnetron plasma.
The ion etching process presumably creates a surface roughness on the substrate, which makes the mechanical peeling of the single layer of electrically conductive material off of the flexible substrate possible.
Additionally or alternatively to the ion etching of the substrate prior to the deposition of the layer, the layer of electrically conductive material can be heated during and/or after deposition of the layer, which reduces the adhesive force between the flexible substrate and the deposited layer and thus makes the peeling of the deposited layer off of the flexible substrate possible. For this purpose, it is also possible to deposit the layer of electrically conductive material in at least two sublayers, for example, whereby a first sublayer of the layer is deposited using a first vacuum coating process and a second sublayer of the layer is deposited using a second vacuum coating process, whereby the second vacuum coating process is associated with a stronger heat development than the first vacuum coating process.
The procedure according to the invention also allows the mechanical peeling of the flexible substrate if, prior to peeling off of the flexible substrate, a second layer of a different material is deposited onto the layer of electrically conductive material or also multiple layers of a different material are deposited onto the layer of electrically conductive material.
The method according to the invention is particularly suitable for producing electrically conductive foils having a foil thickness of less than 3 μm. Using the method according to the invention, it was even possible to produce electrically conductive foils (in particular copper foils) having a foil thickness of less than 1 μm.
The present invention is explained in more detail below using design examples.
The second process station, which follows the first process station when viewed in the direction of movement of the substrate 11, includes a magnetron 14 with a copper target. The magnetron 14 uses known process steps to dust copper particles off of the copper target, which then settle on the flexible substrate 11 as a copper layer. The magnetron 14 can preferably be operated in such a way that a copper layer having a layer thickness from the two-digit nanometer range to the single-digit micrometer range is deposited on the flexible substrate 11. After the copper layer has been deposited, the composite 15, which consists of the flexible substrate 11 and the copper layer, is guided past one or more deflection rollers and then wound onto a winding roller.
After the ribbon-like flexible substrate 11 has been completely coated with a copper layer, the roller with the composite 15 is removed from the working chamber 10 and the copper layer is mechanically peeled off of the flexible substrate 11 which is configured as a plastic foil. For this purpose, the roller on which the composite 15 is wound can, for example, be placed onto a smooth base. The front of the ribbon-like composite 15 is unwound a little from the roller and placed onto the smooth base with the substrate side of the composite facing down. Shortly before the end of the ribbon of composite 15, a sharp cutting tool is used to cut through the copper layer at right angles to the direction of the ribbon without cutting through the substrate 11. If the composite 15 is bent along the cut line in the direction of the side of the substrate 11, a beginning can be found at which the copper layer can be peeled off of the plastic foil by hand. The ends of the thus obtained separated plastic foil and copper layer can subsequently be wound onto separate rollers in a ribbon winding machine and the copper layer can then be peeled off of the flexible substrate 11 along the entire ribbon-like composite 15 by the ribbon winding machine. This results in an electrically conductive foil wound on a roller, which consists of the same material along the extension of the foil thickness; in this design example, copper.
The previously described peeling of the copper layer off of the flexible substrate 11 at the front of the composite 15 by hand is described here merely as an example. There are also devices, with which the copper layer can be peeled off of the flexible substrate 11 from the front of the composite 15 as well.
The second process station, which follows the first process station when viewed in the direction of movement of the substrate 21, includes a magnetron 24 with a copper target. The magnetron 24 uses known process steps to dust copper particles off of the copper target, which then settle on the flexible substrate 21 as a first copper sublayer. The magnetron 24 can preferably be operated in such a way that the first copper sublayer is deposited on the flexible substrate 21 with a layer thickness in the two-digit nanometer range.
After the first copper sublayer has been deposited, the substrate 21 is guided past a third process station. This includes a vessel 25, in which copper is evaporated, which settles on the substrate 24 as a second copper sublayer. In one embodiment, a second copper sublayer is deposited with a layer thickness in the two-digit nanometer range or the single-digit micrometer range. Processes of thermal evaporation, for example, in which all the copper in the vessel 25 is heated, or processes of evaporation using an electron beam, are suitable for the evaporation of the copper in the vessel 25.
It is known that evaporation processes typically involve greater heat development than magnetron sputtering, which heats a substrate to be coated and the layers already on it. In the method according to the invention, the evaporation process causes the flexible substrate 21 and the first copper sublayer to be heated to about 300° C. This leads to a structural change in the first copper sublayer, which is accompanied by a reduction in the adhesive strength of the first copper sublayer on the flexible substrate 21 and has a beneficial effect on subsequent process steps. The procedure described in the second design example is therefore particularly advantageous for producing electrically conductive foils from materials which have a similar or even lower melting point than copper. Therefore, in one embodiment of the invention, an electrically conductive material is used which contains at least one of the chemical elements from the group copper, indium, aluminum, tin, zinc, magnesium, silver.
After the second copper sublayer has been deposited, the composite 26, which consists of the flexible substrate 21 and the first and second copper sublayer, is guided past one or more deflection rollers and then wound onto a winding roller.
After the ribbon-like flexible substrate 21 has been completely coated with the first and second copper sublayer, the roller with the composite 26 is removed from the working chamber 20 and the copper layer, which consists of the first and second copper sublayer, is mechanically peeled off of the flexible substrate 21 which is configured as a stainless steel foil. For this purpose, the roller on which the composite 26 is wound can, for example, be placed onto a smooth base. The front of the ribbon-like composite 26 is unwound a little from the roller and placed onto the smooth base with the stainless steel side of the composite facing down. Shortly before the end of the ribbon of composite 26, a sharp cutting tool is used to cut through the copper layer at right angles to the direction of the ribbon without cutting through the stainless steel foil. If the composite 26 is bent along the cut line in the direction of the side of the stainless steel foil, a beginning can be found at which the copper layer can be peeled off of the stainless steel foil by hand. The ends of the thus obtained separated stainless steel foil and copper layer can subsequently be wound onto separate rollers in a ribbon winding machine and the copper layer can then be peeled off of the flexible substrate 21 along the entire ribbon-like composite 26 by the ribbon winding machine. This results in an electrically conductive foil wound on a roller, which consists of the same material along the extension of the foil thickness; in this design example, copper. In the second design example described above, the second and third process station were components of one and the same system. The method according to the invention according to the second design example can alternatively also be carried out if the second and third process station are components of separate systems.
To clarify the use of and to hereby provide notice to the public, the phrases “at least one of <A>, <B>, . . . and <N>” or “at least one of <A>, <B>, <N>, or combinations thereof” or “<A>, <B>, . . . and/or <N>” are defined by the Applicant in the broadest sense, superseding any other implied definitions hereinbefore or hereinafter unless expressly asserted by the Applicant to the contrary, to mean one or more elements selected from the group comprising A, B, . . . and N. In other words, the phrases mean any combination of one or more of the elements A, B, . . . or N including any one element alone or the one element in combination with one or more of the other elements which may also include, in combination, additional elements not listed. Unless otherwise indicated or the context suggests otherwise, as used herein, “a” or “an” means “at least one” or “one or more.”
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2017 119 308.1 | Aug 2017 | DE | national |
This application is a 371 nationalization of international patent application PCT/EP2018/071564 filed Aug. 8, 2018, which claims priority under 35 USC § 119 to German patent application 10 2017 119 308.1 filed Aug. 23, 2017. The entire contents of each of the above-identified applications are hereby incorporated by reference.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/071564 | 8/8/2018 | WO | 00 |
