Method for producing a multilayer structure, multilayer structure and use of a multilayer structure

Abstract

The invention relates to a method for producing a multi-layer structure (10) comprising the following method steps: a) providing a flexible carrier layer (2) made of at least one polymer material, b) providing and / or producing at least one electrically conductive layer (1) made of at least one metallic material, c) applying a connecting layer (3) made of a metallic material to a surface of the electrically conductive layer (1), wherein the connecting layer (3) forms or has a very thin oxide layer on its surface, in particular wherein the oxide layer is formed on the surface of the connecting layer (3) with a layer thickness of less than 200 nm, d) positioning the composite of the at least one electrically conductive layer (1) and the connecting layer (3) with respect to the flexible carrier layer (2) such that a surface of the very thin oxide layer of the connecting layer (3) and a surface of the flexible carrier layer (2) face each other and at least partially abut each other, e) bonding the composite and the flexible carrier layer (2) under pressure and at a temperature (T) which is greater than the glass transition temperature (T G ) of the polymer material. Furthermore, the invention relates to a multilayer structure (10) and the use of a multilayer structure (10).

Description

[0001] The invention relates to a method for producing a multilayer structure, a multilayer structure and the use of a multilayer structure.

[0002] Multilayer structures are used in many biomedical products, such as active or passive implants, catheters, or sensor components. Such multilayer structures typically comprise a carrier substrate onto which one or more electrically conductive layers or an electrically conductive structure are applied.

[0003] Many biomedical products utilize a polymer support substrate because it is a highly flexible material that is biocompatible, cost-effective, and easy to manufacture. There are many proven and approved thermoplastic and thermosetting polymers for use in biomedical engineering, such as PU, TPU, TPFE, PC, TPE, PET, PDMC, PI, or silicone. These polymers offer material properties that are advantageous in contact with the human body. The polymer substrate can serve as a support for additional metal components in the biomedical product to form so-called "stacks," e.g., for bioelectronic systems or for gas-tight encapsulation of active implants.

[0004] In general, it is not easy to create a bond between a polymer and a metallic material or metal layer. However, for use in a biomedical product, it is necessary to transfer and bond the metal layer to the polymer substrate reliably and with very strong, homogeneous adhesion. Furthermore, it is essential that the material properties of the various materials remain unchanged during the transfer and bonding process itself, and that long-term biocompatibility is maintained.

[0005] Any technical process that transfers and bonds substrates for biomedical applications must function over the long term without changing the material properties. Such a technical process is usually very demanding, especially when the materials to be bonded have different chemical, physical, mechanical, and material properties. Today, it is very difficult to create a strong bond between metals and polymers using simple technical processes while maintaining flexible, robust, deformable, and implantable properties during material transfer and bonding. One possibility, for example, is for a bond to be formed by van der Waals forces. However, this bond only exhibits good adhesion properties when the materials to be bonded are at an atomic distance from each other.To meet these requirements, a surface must have (in addition to optimal surface and interface properties) a very low surface roughness and a small oxide layer in the nanometer range.

[0006] Thermal lamination is generally a typical process for transferring and bonding polymers. However, thermal lamination generally only works well between similar material groups, e.g. between certain polymers, or requires additional chemical or surface treatments before the actual lamination process. Alternatively, additional polymer, silicon or aluminum interlayers can be applied to the surface of the polymer to achieve a sufficient adhesive bond. However, these additional processes or interlayers can change the material and component properties and / or the materials used are often not biocompatible. In particular, joining metallic materials with low surface roughness (Ra < 1 µm) and polarities is almost impossible using thermal lamination alone. The surface and interface properties must therefore be determined before thermal lamination, e.g. using a thermal analyzer.They can be modified, for example, using adhesion promoters, plasma, or sandblasting processes to achieve improved surface and interface properties with altered and rough surface conditions and polarities. Since rough surfaces also exhibit a shorter fatigue life, it is therefore desirable to develop a new thermal lamination process with which biocompatible metals or metallic layer systems (so-called "metal stacks") can be transferred and bonded to polymer substrates, avoiding the aforementioned disadvantages.

[0007] It is therefore an object of the present invention to provide a method for producing a multilayer structure, with which at least one electrically conductive layer made of a metallic material or a layer system made of several different materials, with at least the layer to be bonded being metallic, can be applied to a flexible carrier layer made of a polymer material. The invention is further based on the object of providing a multilayer structure and the use of such a multilayer structure.

[0008] According to the invention, the object is achieved with regard to the method by the subject matter of claim 1. With regard to the multi-layer structure, the object is achieved by the subject matter of claim 10 and with regard to the use by the subject matter of claim 15.

[0009] The method for producing a multilayer structure, in particular a multilayer structure for a medical device or a multilayer structure which is a medical device, comprises the following method steps: a) providing a flexible carrier layer made of at least one polymer material (or: polymer substrate), b) providing and / or producing at least one electrically conductive layer made of at least one metallic material (or: metal layer), c) applying a connecting layer made of a metallic material (or: metal connecting layer) to a surface of the electrically conductive layer, wherein the connecting layer forms or has a very thin oxide layer on its surface, in particular wherein the oxide layer is formed on the surface of the connecting layer with a layer thickness of less than 200 nm, d) positioning the composite of the at least one electrically conductive layer and the connecting layer with respect to the flexible carrier layer such that a surface of the oxide layer of the connecting layer and a surface of the flexible carrier layer face each other and at least partially abut each other, e) bonding the composite of the at least one electrically conductive layer and the connecting layer and the flexible carrier layer under pressure and at a temperature which is greater than the glass transition temperature of the polymer material.

[0010] By applying a bonding layer made of a metallic material, which forms a very thin oxide layer on its surface, to the at least one electrically conductive layer, the invention enables the production of a multilayer structure consisting of a polymer and a metal layer by thermal lamination without the need for further preparatory steps for surface treatment. The comparatively thin oxide layer has a surface roughness that ensures long-lasting adhesion of the electrically conductive layer to the polymer substrate.

[0011] According to the invention, the metal layer that is transferred to and bonded to the polymer substrate can be both structured and unstructured. Furthermore, both a single metal layer and multilayer metal layers with intermediate insulating layers ("material stacks"), which can be used, for example, as electrodes, can be transferred to and bonded to the polymer substrate. The phrase "at least one electrically conductive layer made of at least one metallic material" or "metal layer" thus also encompasses layer systems with at least one electrically conductive layer made of at least one metallic material.

[0012] The metal layer(s) can also be a continuous, closed metal layer (also: metal film). However, a metal layer within the meaning of the invention also includes peeled and transferred metallic connecting layers (also as microflakes, through microcracks) which are transferred to the polymer substrate and connected to it in the same way, but are created by peeling off the upper metal layer. The connecting layer can thus be in the form of closed metal films or microflakes and used as a conductive layer, conductor track or for other connecting processes. The aforementioned possibilities can also be combined; for example, one of the metal layers of a multilayer metal layer can be continuously connected, e.g. unstructured and designed as a metal film, i.e. completely and strongly connected to the polymer.Another metal layer of the multilayer metal coating is structured or connected only by bonded microflakes without adhesion to the polymer substrate. In all cases, however, it has been shown that the finished and targeted single- or multilayer metal coatings adhere very strongly to the polymer substrate without altering the physical, chemical, or mechanical properties of the individual materials.

[0013] In the process according to the invention, the metal layer is transferred to the polymer substrate with biocompatible and strong long-term adhesion. This is achieved by the low surface roughness of the bonding layer or its oxide layer and its thickness. Depending on the polymer substrate used, the bonding process takes between minutes and hours. After the process time has elapsed and the thermal lamination process is complete, the metallic bonding layer or its oxide layer exhibits very strong adhesion to the flexible polymer substrate. The bonding layer also adheres very strongly to the metal layer.

[0014] The method according to the invention thus provides a biomedical bond between metals and polymers, with the bond being flexible and elastic, allowing it to adapt to biological structures without causing harmful stresses. The multilayer structure is mechanically stable and does not tear when used in medical products or systems. Furthermore, the bond is preferably continuous, i.e., has no holes or gaps, thus reliably preventing the penetration of body fluids or moisture.

[0015] The at least one electrically conductive layer and / or the bonding layer are preferably produced by deposition. In particular, the production is carried out by physical vapor deposition (PVD), preferably sputter deposition, e.g., magnetron sputtering, chemical vapor deposition (CVD), such as atomic layer deposition (ALD) or plasma-enhanced chemical vapor deposition (PECVD), or by thermal deposition. The bonding layer can, in particular, be deposited directly onto the metal layer.

[0016] According to an advantageous embodiment, the at least one electrically conductive layer is produced or provided with a layer thickness between 1 and 500 µm, preferably with a layer thickness between 1 and 250 µm, particularly preferably with a layer thickness between 1 and 25 µm, and / or a surface roughness Ra < 1 µm. This can be achieved in particular by deposition using sputter deposition.

[0017] Preferably, the at least one electrically conductive layer is made or provided from a biocompatible metallic material, in particular from titanium, nitinol, stainless steel, tantalum, cobalt-containing alloys, magnesium, platinum, gold and / or tungsten, in order to avoid rejection reactions or incompatibilities.

[0018] In a preferred embodiment, the bonding layer is applied to the electrically conductive layer with a layer thickness between 1 nm and 2 µm, preferably with a layer thickness between 250 nm and 1 µm. A bonding layer thickness between 1 nm and 2 µm prevents the material properties of the metal layer from being altered by the bonding layer. Furthermore, by depositing the bonding layer by sputter deposition, the surface of the bonding layer has a very low surface roughness Ra of less than 1 µm, thereby improving adhesion to the polymer substrate.

[0019] In particular, a bonding layer made of platinum, gold, or indium is applied or manufactured from platinum, gold, or indium. These materials form only very small oxide layers with a thickness of less than 200 nm on the surface of the bonding layer. For bioelectronic components, platinum or gold are preferably used as a bonding layer on the metal layer, as these materials can be used as contact electrodes and conductors.

[0020] According to a preferred embodiment, the composite comprising the at least one electrically conductive layer and the connecting layer and the carrier layer are pressed together during thermal lamination by means of clamping means, for example, two plates clamping the composite and the carrier layer between them. In particular, a clamping pressure greater than 0.01 MPa is applied or generated with the clamping means. The clamping means are preferably made of a non-adhesive material, for example, Teflon or PEEK, or coated with such a non-adhesive material to prevent the composite or the polymer substrate from adhering to the clamping means.

[0021] According to a further advantageous embodiment, the bonding of the composite comprising the at least one electrically conductive layer and the connecting layer and the carrier layer takes place in a vacuum chamber in which, in particular, a relative vacuum pressure of less than -100 mbar is generated.

[0022] Furthermore, it can be provided that the at least one electrically conductive layer is removed after the connection layer has been connected to the carrier layer in order to produce a polymer substrate with a thin metallic layer.

[0023] The multilayer structure according to the invention, in particular a multilayer structure for a medical device or a multilayer structure which is a medical device, comprises a flexible carrier layer made of at least one polymer material, at least one electrically conductive layer made of at least one metallic material (or: metal layer) and at least one electrically conductive connecting layer which is arranged between the flexible carrier layer and the at least one electrically conductive layer or the electrically conductive structure and is connected to each of these.

[0024] According to an advantageous embodiment, the at least one electrically conductive layer has a layer thickness between 1 and 500 µm, preferably a layer thickness between 1 and 250 µm, particularly preferably a layer thickness between 1 and 25 µm, and / or a surface roughness Ra < 1 µm. This can be achieved by producing the metal layer by deposition, in particular by physical vapor deposition (PVD), preferably sputtering (magnetron sputtering), chemical vapor deposition (CVD) (atomic layer deposition, PECVD), or thermal deposition.

[0025] Furthermore, the at least one electrically conductive layer consists of a biocompatible metallic material, in particular titanium, nitinol, stainless steel, tantalum, cobalt-containing alloys, magnesium, platinum, gold and / or tungsten, or comprises a biocompatible metallic material, in particular titanium, nitinol, stainless steel, tantalum, cobalt-containing alloys, magnesium, platinum, gold and / or tungsten.

[0026] In a preferred development, the connecting layer has a layer thickness between 1 nm and 2 µm, preferably a layer thickness between 250 nm and 1 µm, and / or an oxide layer on the surface of the connecting layer has a layer thickness of less than 200 nm.

[0027] Furthermore, in advantageous embodiments, it can be provided that the connecting layer consists of platinum, gold or indium or comprises platinum, gold or indium.

[0028] A preferred material for the flexible carrier layer is selected from PU, TPU, PC, TPE or PET or other thermoplastics.

[0029] The materials used make the multilayer structure biocompatible and hemocompatible, preventing the formation of thrombi and embolism. Furthermore, the multilayer structure is chemically inert to body tissue and fluids.

[0030] The use of multilayer construction is not limited to medical applications, although this is a very important use case. In principle, multilayer construction can be used in one of the following technical areas: - in medical, bioelectrical, active or passive implants, in particular for the detection and stimulation of biological tissue, - in and / or as catheter components, - in and / or as sensor components, - in the integration of MEMS technology, - in the hermetic sealing and encapsulation of medical components, short- and long-term implants, - in conjunction with highly flexible bioelectronic circuits, - Connections with medical balloon systems, - for metal coating of polymeric substrates (e.g. hydraulic or fluid components or assemblies).

[0031] The invention is described in more detail below using exemplary embodiments and with reference to the attached schematic drawings.

[0032] In these show Fig. 1 a schematic representation of a cross-section through a metal layer with a connecting layer applied thereon and a carrier layer before they are joined together (steps a) to c)), Fig. 2 a schematic representation of a cross-section during the bonding of the metal layer with the bonding layer applied thereon to the carrier layer (steps e) and d)), Fig. 3a a schematic representation of a cross-section through the multi-layer structure in a side view, Fig. 3b a schematic representation of the multilayer structure in a plan view, Fig. 4a a schematic representation of a cross-section through the multilayer structure during the removal of the metal layer from the connecting layer in a side view, Fig. 4b a schematic representation of the removal of the metal layer from the connection layer in a plan view.

[0033] Fig. 1 shows an electrically conductive layer 1 made of a metallic material, onto which a connecting layer 3 made of a metallic material is applied. The material for the electrically conductive layer 1 can, for example, be selected from the group consisting of titanium, nitinol, stainless steel, tantalum, cobalt-containing alloys, magnesium, platinum, gold, and / or tungsten. In the exemplary embodiment shown, the electrically conductive layer 1 is produced by sputter deposition and has a surface roughness Ra < 1 µm. The layer thickness of the electrically conductive layer 1 can be between 1 and 500 µm. In the exemplary embodiment, the electrically conductive layer 1 has, for example, a layer thickness of 20 µm.

[0034] The electrically conductive layer 1 can be a single metal layer or a single metal film. Likewise, the electrically conductive layer 1 can comprise multiple metal layers, i.e., be a multilayer metal layer.

[0035] The material for the connection layer 3 can, for example, be selected from the group consisting of platinum, gold, and / or indium. In the exemplary embodiment shown, the connection layer 3 is also produced by sputter deposition and has a surface roughness Ra of less than 1 µm. The layer thickness of the connection layer 3 is preferably many times smaller than the layer thickness of the electrically conductive layer 1 and can be between 1 nm and 2 µm. In the exemplary embodiment, the connection layer 3 has, for example, a layer thickness of 500 nm. An oxide layer formed on the surface of the connection layer 3 (not explicitly shown) has a layer thickness of less than 200 nm, for example a layer thickness of 100 nm, or is formed with a layer thickness of less than 200 nm.

[0036] Furthermore, Fig. 1 a carrier layer 2 made of a polymer material. The carrier layer is flexible. The material for the carrier layer 2 can be, for example, PU, ​​TPU, PC, TPE or PET. As can be seen from Fig. As can be seen from Figure 1, the carrier layer 2 and the electrically conductive layer 1 have a similar layer thickness. Other ratios are possible.

[0037] Fig. 2 schematically shows the thermal lamination or the bonding of the composite of the at least one electrically conductive layer 1 and the connecting layer 3 with the flexible carrier layer 2.

[0038] First, the composite of the at least one electrically conductive layer 1 and the connecting layer 3 is positioned with respect to the flexible carrier layer 2 such that a surface of the oxide layer of the connecting layer 3 and a surface of the flexible carrier layer 2 face each other and at least partially abut each other. Clamping means 4 are used to press the composite of the at least one electrically conductive layer 1 and the connecting layer 3 and the carrier layer 2 together for bonding and to hold them during the thermal lamination process.

[0039] According to the exemplary embodiment, the clamping means are designed as two clamping plates 4, which are made of a non-adhesive material such as Teflon or Peek or are coated with such a material. A clamping pressure of greater than 0.01 MPa is applied by means of the clamping means 4.

[0040] The bonding of the composite and the flexible carrier layer 3 takes place in a vacuum chamber 5, in which a relative vacuum pressure of less than -100 mbar is generated. Furthermore, the thermal lamination takes place at an elevated temperature. A process temperature T is set that is at least greater than the glass transition temperature T G of the polymer material used to enable a connection of the polymer substrate with the oxide layer or the metal layer.

[0041] In the embodiment shown, the metal layer 1 is applied on one side (in Fig. 3 above) is applied to the polymer substrate 2 and bonded to it. It is also possible to apply the metal layer 1 on the opposite side (in Fig. 3 below) onto the polymer substrate 2 and bonding it thereto. It is also conceivable to apply a metal layer 1 to both sides of the polymer substrate 2.

[0042] Fig. 4a shows a cross-section through a multi-layer structure 10 in a side view, Fig. 4b shows a plan view of the multilayer structure 10. The multilayer structure 10 comprises the flexible carrier layer 2 made of polymer material, at least one electrically conductive layer 1 made of a metallic material, and an electrically conductive connecting layer 3 made of a metallic material. The connecting layer 3 is arranged between the flexible carrier layer 2 and the electrically conductive layer 1 and is connected to each of them. The electrically conductive layer 1 has a layer thickness between 1 and 500 µm. The material for the electrically conductive layer 1 is selected from the group consisting of titanium, nitinol, stainless steel, tantalum, cobalt-containing alloys, magnesium, platinum, gold, and / or tungsten.

[0043] The connecting layer 3 has a layer thickness between 1 nm and 2 µm and can consist of platinum, gold or indium or comprise platinum, gold or indium.

[0044] Fig.5a shows an optional further process step in which the electrically conductive layer 1 is removed, for example peeled off, from the connecting layer 3 after the connecting layer 3 has been connected to the carrier layer 2. Thus, only the connecting layer 3, in particular in the form of flakes (metal film with microcracks), is transferred to the carrier layer 2. This is possible provided that the connecting layer 3 adheres more strongly to the carrier layer 2 than to the electrically conductive layer 1, which can be influenced by the duration of the process or other process parameters such as pressure or temperature. During the thermal lamination process, therefore, only the metal connecting layer is transferred and bonded to the polymer substrate due to controlled adhesion between the metal connecting layer and the metal layer.It is therefore possible to transfer only the metal compound layer, either completely or partially, onto the polymer substrate, so that a targeted and / or fragmented transfer of only the metal compound layer onto the polymer substrate occurs.

[0045] The multilayer structure 10 described according to the embodiment can preferably be used in the medical field, for example in medical, bioelectrical, active or passive implants, in / as catheter or sensor components, in the integration of MEMS technology, in the hermetic sealing and encapsulation of medical components, short- and long-term implants, in connection with highly flexible bioelectronic circuits, in connection with medical balloon systems or for the metal coating of polymeric substrates (e.g. hydraulic or fluid components or assemblies).

Claims

[1] Method for producing a multilayer structure (10) comprising the following process steps: a) Providing a flexible support layer (2) made of at least one polymer material, b) Providing and / or manufacturing at least one electrically conductive layer (1) made of at least one metallic material, c) Applying a compound layer (3) of a metallic material to a surface of the electrically conductive layer (1), wherein the compound layer (3) forms or has a very thin oxide layer on its surface, in particular wherein the oxide layer on the surface of the compound layer (3) is formed with a layer thickness of less than 200 nm, d) Positioning the composite of the at least one electrically conductive layer (1) and the compound layer (3) in relation to the flexible support layer (2) such that a surface of the very thin oxide layer of the compound layer (3) and a surface of the flexible support layer (2) are facing each other and are at least partially in contact with each other, e) Joining the composite and the flexible support layer (2) under pressure and at a temperature (T) greater than the glass transition temperature (T G ) of the polymer material. [2] Method for producing a multilayer structure (10) according to claim 1 characterized by , that the at least one electrically conductive layer (1) and / or the compound layer (3) are produced by deposition, in particular by physical vapor deposition (PVD), preferably chemical vapor deposition (CVD) or thermal deposition. [3] Method for producing a multilayer structure (10) according to claim 1 or 2 characterized by , that at least one electrically conductive layer (1) with a layer thickness between 1 and 500 µm and / or a surface roughness Ra < 1 µm is produced or provided. [4] Method for producing a multilayer structure (10) according to any one of the preceding claims characterized by , that at least one electrically conductive layer (1) is made of a biocompatible metallic material, in particular titanium, nitinol, stainless steel, tantalum, cobalt-containing alloys, magnesium, platinum, gold and / or tungsten, is manufactured or provided. [5] Method for producing a multilayer structure (10) according to any one of the preceding claims characterized by , that the compound layer (3) is applied with a layer thickness between 1 nm and 2 µm and / or a surface roughness Ra < 1 µm. [6] Method for producing a multilayer structure (10) according to any one of the preceding claims characterized by , that a compound layer (3) of platinum, gold or indium is applied. [7] Method for producing a multilayer structure (10) according to any one of the preceding claims characterized by , that the composite consisting of the at least one electrically conductive layer (1) and the connecting layer (3) and the carrier layer (2) are pressed together by means of clamping means (4), wherein a clamping pressure greater than 0.01 MPa is applied by means of the clamping means (4). [8] Method for producing a multilayer structure (10) according to any one of the preceding claims characterized by, that the joining of the composite consisting of the at least one electrically conductive layer (1) and the connecting layer and the support layer (2) takes place in a vacuum chamber (5) in which, in particular, a relative vacuum pressure of less than -100mbar is generated. [9] Method for producing a multilayer structure (10) according to any one of the preceding claims characterized by , that at least one electrically conductive layer (1) is removed after joining the connecting layer (3) with the support layer (2). [10] Multilayer structure (10) comprising a flexible support layer (2) of at least one polymer material, at least one electrically conductive layer (1) of at least one metallic material and at least one connecting layer (3) of a metallic material, which is arranged between the flexible support layer (2) and the at least one electrically conductive layer (1) and is connected to each of them. [11] Multilayer structure (10) according to claim 10 characterized by , that the at least one electrically conductive layer (1) has a layer thickness between 1 and 500 µm and / or a surface roughness Ra < 1 µm. [12] Multilayer structure (10) according to one of claims 10 or 11 characterized by , that the at least one electrically conductive layer (1) consists of or comprises a biocompatible metallic material, in particular titanium, nitinol, stainless steel, tantalum, cobalt-containing alloys, magnesium, platinum, gold and / or tungsten. [13] Multilayer structure (10) according to one of claims 10 to 12 characterized by , that the compound layer (3) has a layer thickness between 1 nm and 2 µm and / or the oxide layer on the surface of the compound layer (3) has a layer thickness of less than 200 nm. [14] Multilayer structure (10) according to one of claims 10 to 13 characterized by , that the compound layer (3) consists of or comprises platinum, gold or indium. [15] Use of the multilayer structure (10) according to any one of claims 10 to 14 - in medical, bioelectrical, active or passive implants, especially for the detection and stimulation of biological tissue, - in and / or as catheter components, - in and / or as sensor components, - in the integration of MEMS technology, - in the hermetic sealing and encapsulation of medical components, short- and long-term implants, - in conjunction with highly flexible bioelectronic circuits, - in conjunction with medical balloon systems, - for metal coating of polymer substrates.

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