Multilayer stack including gold-based layer and platinum-based layer and related methods

Abstract

A multilayer stack is described comprising a copper-based layer; a nickel-based layer provided on the copper-based layer; a gold-based layer provided on the nickel-based layer; and a platinum-based layer provided on the gold-based layer. The multilayer stack exhibits excellent corrosion resistance, particularly in chlorinated environments and under oxidizing conditions, and improves the catalytic performance, mechanical properties, and / or lifespan of the multilayer stack. A method for manufacturing the aforementioned multilayer stack, the use of the aforementioned multilayer stack as an electrode or electrical conductor in electrical connectors and / or electrical circuits, and a method for improving the corrosion resistance of nickel-plated copper by utilizing the stack configuration are likewise described. Additionally, a biosensor comprising the aforementioned multilayer stack is described.

Description

Technology Field

[0001] The present invention relates to a multilayer stack comprising layers based on copper, nickel, gold, and platinum in a given order, which can be used for manufacturing electrodes or electrical conductors having enhanced corrosion resistance.

[0002] In certain embodiments, the present invention relates to a method for manufacturing the multilayer stack and its use, as well as a method for improving the corrosion resistance of nickel-plated copper. Background Technology

[0003] Platinum (Pt) is a material commonly used in electrical contacts, particularly in wet chemical processes, and functions as a catalyst for many commercial applications, including fuel cells, the petroleum industry, and autocatalytic converters. Platinum electrodes with catalytic activity find widespread applications across all fields of electrochemistry. Particularly for medical applications (e.g., operating or counter electrodes in neurostimulators or biochemical sensors), electrodes containing Pt have gained increased interest due to their biocompatibility and resistance to oxidation (e.g., by blood, sweat, or saline).

[0004] Since Pt is scarce and expensive, cost reduction is typically achieved by forming a stack of multiple metal layers including a Pt layer as the outermost layer.

[0005] For this purpose, it is known to use a copper (Cu) layer, plate it with a nickel (Ni) layer for enhanced mechanical strength and corrosion stability, and form a Pt layer on the Ni layer. By using Ni in the intermediate layer, problems regarding poor adhesion between the Cu and Pt layers due to the relatively large potential difference between the metals can be avoided. For example, CN 113394417 B discloses the aforementioned three-layer structure in a core-shell configuration and reports higher stability of the catalyst compared to pure Pt. CN 217 387 609 U discloses several multilayer structures composed of four metal plating layers. CN 116 165 259 A describes electrodes manufactured by PCB processing technology. C. A. Thomas et al., Experimental Cell Research 1972, 74, 61–66 disclose the use of platinum black layers for the fabrication of biosensors including multilayer structures.

[0006] CN 105154931 A discloses a method for electroplating a base layer made of nickel, titanium, tantalum, copper, or silver with platinum by electrodeposition from an electroplating solution. Another exemplary method for depositing Pt by electroplating is disclosed in JP 2022-107487 A.

[0007] However, the corrosion resistance of the described multilayer stacks tends to be insufficient for many applications. Furthermore, it has been found that copper and / or nickel can diffuse into the platinum layer in corrosive environments (particularly in chlorinated media and under oxidizing conditions, e.g., in the presence of H2O2), which can consequently negatively affect the catalytic performance, mechanical properties, and / or lifespan of the multilayer stack.

[0008] Therefore, it is still desirable to provide a Pt-containing multilayer stack that exhibits enhanced corrosion resistance and enables extended functionality (e.g., as an electrode catalyst or electrical conductor), thereby expanding options for potential applications while still maintaining lower manufacturing costs compared to pure Pt.

[0009] Furthermore, it would be desirable to provide a method to effectively improve the corrosion resistance of nickel-plated copper.

[0010] The present invention solves these objectives as the subject of the claims as defined herein. The advantages of the present invention will be further described in detail in the sections below, and additional advantages will be apparent to a person skilled in the art when considering the disclosure of the invention.

[0011] Generally speaking, in one aspect, the present invention provides a multilayer stack comprising a copper-based layer (Cu-based layer); a nickel-based layer (Ni-based layer) provided on the copper-based layer; a gold-based layer (Au-based layer) provided on the nickel-based layer; and a platinum-based layer (Pt-based layer) provided on the gold-based layer.

[0012] In another aspect, the present invention provides a method for manufacturing the aforementioned multilayer stack, the method comprising the steps of: providing a nickel / copper multilayer film (Ni / Cu-multilayer film) comprising a nickel-based layer and a copper-based layer; depositing a layer of gold on the nickel-based layer to form a gold-based layer; and depositing a layer of platinum on the gold-based layer to form a platinum-based layer.

[0013] In another aspect, the present invention relates to the use of the aforementioned multilayer stack as an electrode or electrical conductor in electrical connectors and / or electrical circuits.

[0014] In another aspect, the present invention provides a method for improving the corrosion resistance of nickel-plated copper (Ni-plated Cu), the method comprising the steps of depositing a layer of gold on the surface of the nickel-plated copper to form a gold-based layer, and depositing a layer of platinum on the gold-based layer to form a platinum-based layer.

[0015] In another aspect, the present invention provides a biosensor or medical device comprising the aforementioned multilayer stack. Brief explanation of the drawing

[0016] FIG. 1 is a schematic diagram of an exemplary embodiment of a multilayer stack of the present invention. FIG. 2a is a schematic diagram of an exemplary embodiment of a multilayer stack of the present invention including a substrate. FIG. 2b is a schematic diagram of an exemplary embodiment of a multilayer stack of the present invention comprising a substrate having a channel / cavity. FIG. 3 is a schematic diagram of an exemplary embodiment of a multilayer stack of the present invention having covered edges and a substrate. FIG. 4a illustrates an exemplary embodiment of a multilayer stack of the present invention having a core-shell structure. FIG. 4b is a schematic diagram of an exemplary embodiment of a multilayer stack of the present invention comprising a substrate having a channel / cavity. Specific details for implementing the invention

[0017] For a more complete understanding of the present invention, the following description of its exemplary embodiments is now referred to:

[0018] Multilayer stack

[0019] In a first embodiment, the present invention relates to a multilayer stack comprising a copper-based layer; a nickel-based layer provided on the copper-based layer; a gold-based layer provided on the nickel-based layer; and a platinum-based layer provided on the gold-based layer.

[0020] Specifically, it has been found that a remarkably high improvement in corrosion resistance can be achieved by utilizing a specific order of layers within the stack. Although copper, nickel, and gold are substantially more susceptible to corrosion than platinum (especially in chlorinated media such as salt spray solutions or phosphate-buffered saline) and are vulnerable in oxidative electrochemical environments (e.g., upon exposure to hydrogen peroxide), providing the three-layer stack under the platinum-based layer improves the properties attributable to the platinum-based layer to an unexpected degree (i.e., synergistic effect).

[0021] Other layers may be inserted between each layer of the stack, but it is preferred that the platinum-based layer be in contact with the gold-based layer. Independently or in combination, it is preferred that the copper-based layer be provided in contact with the nickel-based layer. Independently or in combination, the nickel-based layer be provided in contact with the gold-based layer. In a particularly preferred embodiment, no layers are inserted between the copper-, nickel-, gold-, and platinum-based layers. An exemplary configuration of the above embodiment is illustrated in FIG. 1, where the copper-based layer (1), nickel-based layer (2), gold-based layer (3), and platinum-based layer (4) are provided in contact with each other. In FIG. 1, an optional additional functional layer (5), which will be described in more detail below, is provided on and in contact with the platinum-based layer (4).

[0022] The multilayer stack may further include a substrate on which the stack is disposed, deposited, or attached through chemical adhesives, preferably through a copper-based layer.

[0023] FIGS. 2A and FIGS. 2B show preferred configurations of a multilayer stack on a substrate (17 / 27).

[0024] The substrate (17 / 27) is not particularly limited and may include polymers, silicon, ceramic substrates, glass, fabric, paper, and combinations thereof. Examples of polymers may be mentioned, for instance, polyetheretherketone (PEEK), polyphenylsulfone (PPSU), polyethylene terephthalate (PET), polyimide (PI), polyetherimide (PEI), liquid crystal polymer (LCP), or epoxy glass), ceramics, or paper. Preferred substrate materials for biocompatibility include epoxy glass, polyethylene terephthalate (PET), and polyetherimide (PEI), among which polyetherimide (PEI) is particularly preferred. Typically, the substrate thickness is in the range of 20 to 200 μm, more preferably between 50 and 150 μm.

[0025] The substrate may further comprise one or more channels or cavities (28) that can be punched into the substrate, for example, as illustrated in FIG. 2b. In such a configuration, the copper-based layer (21) may have depositions of additional metal layers (preferably a nickel layer (29a) and a gold layer (29b) in this order, with the nickel layer (29a) in contact with the copper-based layer (21)) that extend into the channel or cavity (28) and cover the copper-based layer (21) from the opposite side of the nickel-based layer (22). Generally, the copper-based layer is composed essentially of copper or an alloy having copper as its main component. Thus, the copper-based layer comprises at least 50 wt.-% copper based on the total weight of the copper-based layer, preferably at least 85 wt.-%, more preferably at least 90 wt.-% copper. In a further preferred embodiment, the copper-based layer is essentially composed of copper. In particular, the expression “essentially composed” as used herein is understood to define that each layer is composed of the said material, except for unavoidable impurities that may be present in an amount of up to 0.5 wt.-% of each layer.

[0026] By analogy, the nickel-based layer is essentially composed of nickel or an alloy having nickel as its main component. Accordingly, the nickel-based layer contains at least 50 wt.-% nickel based on the total weight of the nickel-based layer, preferably at least 85 wt.-%, and more preferably at least 90 wt.-% nickel. The presence of the nickel-based layer provides improved adhesion to subsequent coating layers (e.g., gold-based layers).

[0027] Nickel plating is generally considered to also serve as a barrier preventing the diffusion of copper into the outer layers. However, it has been found that a nickel-based layer cannot prevent copper from diffusing into the platinum layer, thereby degrading the corrosion resistance and ultimately the electrical properties of the platinum layer. To this end, the present invention comprises a gold-based layer as an effective barrier preventing both copper and nickel from diffusing into the platinum-based layer.

[0028] In a preferred embodiment, a layer of Ni-P alloy (see 16 and 26 in FIG. 2a and FIG. 2b, respectively) may be deposited between the nickel-based layer and the gold-based layer to improve mechanical, tribological, and electrochemical properties.

[0029] The gold-based layer is essentially composed of gold or an alloy having gold as its main component. Accordingly, the gold-based layer comprises at least 50 wt.-% gold based on the total weight of the gold-based layer, preferably at least 85 wt.-%, and more preferably at least 90 wt.-% gold. In a further preferred embodiment, the gold-based layer is essentially composed of gold.

[0030] In another preferred embodiment, the gold-based layer comprises a flash-deposited gold sub-layer having higher porosity than the rest of the gold-based layer, with a preferred thickness in the range of 5 to 30 nm, more preferably between 8 and 20 nm. In this configuration, the flash-deposited sub-layer is preferably in contact with a nickel-based layer or, if present, a layer of Ni-P alloy.

[0031] The platinum-based layer is preferably composed of at least 95 wt.-%, more preferably at least 97 wt.-%, and even more preferably at least 99 wt.-% of platinum based on the total weight of the platinum-based layer. In a particularly preferred embodiment, the platinum-based layer is composed essentially of platinum.

[0032] Alternatively, the platinum-based layer is essentially composed of a platinum alloy containing platinum as its main component. Thus, the platinum-based layer contains at least 50 wt.-% platinum, more preferably at least 60 wt.-% platinum, based on the total weight of the platinum-based layer.

[0033] A layer containing one or more platinum group metals other than Pt (i.e., ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os) and / or iridium (Ir)) may be inserted between the gold-based layer and the platinum-based layer. Among these metals, Pd is preferred. Such a layer may essentially be composed of one or more of Ru, Rh, Pd, Os and Ir, or may essentially be composed of an alloy having one of the aforementioned metals as its main component.

[0034] Where copper, nickel, gold, and / or platinum are present as the main components of the alloys in any of the aforementioned layers, such alloys preferably comprise one or more metals selected from transition metals. Among the preferred transition metals, gold, cobalt, copper, nickel, and / or iron may be mentioned.

[0035] In addition, metal oxides (including but not limited to CeO2, WO3, Ta2O5, Nb2O5, and ZrO2) may be present within the platinum-based layer to alter catalytic activity for desired purposes.

[0036] The thickness of each layer is not specifically limited and can be appropriately selected by a skilled technician according to the desired characteristics and purpose of the multilayer stack.

[0037] Although not limited thereto, the copper-based layer typically has a thickness of 1 to 50 μm, 10 to 40 μm in the examples, and more preferably 15 to 30 μm.

[0038] Independently or in combination, the nickel-based layer typically has a thickness of 0.4 to 50 μm, 0.5 to 20 μm in the examples, and more preferably 1 to 5 μm. It may be preferred that the gold-based layer has a minimum thickness of 15 nm, and preferably a thickness of 20 nm to 500 nm.

[0039] In addition, to fully utilize the advantages of the present invention, the platinum-based layer has a thickness of 15 nm or greater, preferably 20 nm to 600 nm, and more preferably 25 nm to 500 nm.

[0040] An additional functional layer (5) may be optionally provided on the platinum-based layer (4), and preferably in contact with it.

[0041] Normally, a platinum-based layer obtained by electroplating through an electroplating solution will be smooth, shiny, and have low porosity. One approach to increasing the surface area of ​​the platinum-based layer without increasing the surface area is to rapidly electroplat platinum, which results in a platinum surface generally known as "platinum black." Platinum black has a porous and rough surface with lower density and lower reflectivity than shiny platinum.

[0042] Accordingly, in the embodiments, it may be preferred that the multilayer stack further comprises a layer of platinum black on the platinum-based layer as an additional functional layer (5), which is more preferably in contact with the platinum-based layer (4). In further preferred embodiments, the layer of platinum black is preferably 2 to 50 m 2 / g range, more preferably 20 to 50 m 2 It has a specific surface area in the range of / g. The thickness of the platinum black layer is not particularly limited and can be appropriately adjusted to balance the desired catalytic activity and structural integrity.

[0043] In an alternative embodiment, as illustrated in FIGS. 2a and 2b, the multilayer stack of the present invention may further include a second gold-based layer (15 / 25) on top of a platinum-based layer (14 / 24) as an additional functional layer, which is more preferably in contact with the platinum-based layer (14 / 24). The second gold-based layer (15 / 25) may partially or wholly cover the platinum-based layer (14 / 24) and may provide an enhanced metallic appearance to the multilayer stack. The second gold-based layer (15 / 25) may be composed of gold or an alloy having gold as its main component. Thus, the gold-based layer (15 / 25) contains at least 50 wt.-% gold. Non-limiting examples of gold-copper alloys deposited on a metal surface to provide electrical contact pads having a rose gold appearance are disclosed in EP 3 892 759 A1.

[0044] In a preferred embodiment also illustrated in FIG. 2a and 2b, the second gold-based layer (15 / 25) may also include a flash-deposited gold sub-layer (15a / 25a) having higher porosity than the remainder of the second gold-based layer (15 / 25), with a preferred thickness in the range of 5 to 30 nm, more preferably between 8 and 20 nm. In this configuration, the flash-deposited sub-layer (15a / 25a) is preferably in contact with a platinum-based layer (14 / 24).

[0045] To provide more effective corrosion protection, it may be preferred that each cover layer of the stack extends over the sides of the layer below. An example of this is illustrated in FIG. 3, where the nickel-based layer (32) extends over the sides of the copper-based layer (31) to cover it, the gold-based layer (33) extends over the sides of the nickel-based layer (32) to cover it, and the platinum-based layer (34) extends over the sides of the gold-based layer (33) to cover it. In such a configuration, an optional functional layer (35) may or may not extend over the sides of the platinum-based layer (34) to cover it. The shape provided for the multilayer stack is not particularly limited and may include cylindrical, bar-shaped, and flat (e.g., rectangular, circular, etc.) geometric structures.

[0046] In the preferred embodiment illustrated in FIG. 4a, the multilayer stack exhibits a core-shell configuration, wherein a copper-based layer (41) represents the core and is surrounded by a shell formed by a nickel-based layer (42), a gold-based layer (43), a platinum-based layer (44), and an optional functional layer (45) in a given order. Such a configuration is particularly preferred for substrate-free stacks.

[0047] However, the above configuration may also be used in combination with a continuous substrate (not shown) or a substrate including a channel or cavity, as exemplified in FIG. 4b.

[0048] Method for manufacturing a multilayer stack

[0049] In a second embodiment, the present invention relates to a method for manufacturing a multilayer stack according to the first embodiment described above, the method comprising the steps of: providing a nickel / copper multilayer film comprising a nickel-based layer and a copper-based layer; depositing a layer of gold on the nickel-based layer to form a gold-based layer; and depositing a layer of platinum on the gold-based layer to form a platinum-based layer.

[0050] The method for providing a nickel / copper multilayer film comprising a nickel-based layer and a copper-based layer is not particularly limited and can be achieved by any method known to a skilled technician. For example, the nickel layer may be deposited on a copper foil or wire (e.g., by electrodeposition from a nickel-salt solution).

[0051] In particular, a nickel / copper multilayer film comprising a nickel-based layer and a copper-based layer can be provided in the form of a conductive layer of an electrical circuit (e.g., a printed circuit board or a printed wiring board).

[0052] A layer of nickel-phosphorus (Ni-P) alloy, where present, can be deposited by methods known in the art. A. Lelevic et al., Surface and Coatings Technology 2019, 369, 198-220 disclose exemplary electrodeposition methods for this purpose.

[0053] The method of depositing a layer of gold on a nickel-based layer to form a gold-based layer is also not particularly limited and may include electroplating methods and electroless plating methods known in the art (e.g., by using electroless nickel immersion gold (ENIG)).

[0054] A flash-deposited gold sublayer may be provided according to methods known in the art, including but not limited to electroless methods such as deposition and chemical reduction.

[0055] Electroless deposition is also possible, but the platinum-based layer is preferably deposited by electrodeposition from a solution containing a platinum precursor. Generally, such a precursor will be selected from Pt(II) and Pt(IV) salts. Examples of Pt(II) precursors include, but are not limited to, PtCl4·5 H2O, H2PtCl6·6 H2O, (NH4)PtCl6, Pt(NH3)2(NO2)2, and dinitrosulfatoplatinites (e.g., based on the complex dihydrogen bis(nitrito-N)[sulphato(2-)-O,O']platinate(2-)(dihydrogen bis(nitrito-N)[sulphato(2-)-O,O']platinate(2-), H2Pt(NO2)2SO4), whereas suitable Pt(IV) precursors include alkali hexahydroxyplatinates (e.g., Na2Pt(OH)6 or K2Pt(OH)6), phosphates (e.g., (NH4)2HPO4, Na2HPO4), but It is not limited to this.

[0056] Preferably, the platinum-based layer is deposited by electrodeposition from a solution containing dihydrogen bis(nitrite-N)[sulfato(2-)-O,O']platinate(2-)(H2Pt(NO2)2SO4), which promotes the deposition of a high-quality platinum-based layer having excellent coverage and low porosity. The electrodeposition solution may further include water-soluble phosphate, sodium dodecyl sulfate, or dodecyl sulfate as additives. Furthermore, pH conditions can be appropriately adjusted according to the selected precursor by the addition of an acid or a base.

[0057] The reduction of platinum precursors by electroless deposition proceeds in almost the same manner as in electrochemical deposition, but differs in that electrons are provided by a reducing agent rather than by an external source.

[0058] The electrodeposition step itself can be performed by galvanostatic, potentiostatic, or potentiocyclic methods, which can be appropriately selected by a skilled technician, for example, depending on the desired surface roughness and layer stability. Pulsed electrodeposition can be adopted to alternate different potentials and the corresponding different processes.

[0059] A platinum-based layer containing a platinum alloy can be fabricated by the co-deposition of two or more metals from their salts.

[0060] In particular, the steps for manufacturing the multilayer stack of the present invention can be carried out efficiently and economically through a reel-to-reel process.

[0061] Uses of multilayer stacks

[0062] Generally, the multilayer stack according to the present invention can be used in any application requiring excellent electrical properties, catalytic activity, biocompatibility, stability, and corrosion resistance.

[0063] Accordingly, in the third embodiment, the present invention relates to the use of the multilayer stack according to the first embodiment described above as an electrode or electrical conductor in electrical connectors and / or electrical circuits, particularly in medical devices and biosensors.

[0064] The types of electrodes are not particularly limited. Non-limiting examples include biosensor electrodes or medical electrodes (e.g., reusable disc-type electrodes). For example, biosensor applications may include using the multilayer stack of the present invention as an electrochemical catalyst (e.g., to accelerate the reaction of enzymes), as a sensor electrode to enhance electron charge transfer, and for enzymatic reactions.

[0065] Non-limiting examples of electrical connectors and electrical circuits each include connector pads and integrated circuits within a smart card (SC) (i.e., chip cards, or integrated circuit cards (ICC or IC cards)). Here, the multilayer stack of the present invention may be used to provide enhanced resistance to corrosion caused by sweat, saltwater, or oxidizing agents.

[0066] Methods to improve corrosion resistance

[0067] As discussed in the description above, a specific multilayer stack arrangement according to the present invention provides improved resistance to corrosion compared to configurations without a gold-based layer and / or without a platinum-based layer.

[0068] Accordingly, the fourth embodiment of the present invention relates to a method for improving the corrosion resistance of nickel-plated copper, the method comprising the steps of: depositing a layer of gold on the surface of the nickel-plated copper to form a gold-based layer; and depositing a layer of platinum on the gold-based layer to form a platinum-based layer.

[0069] The steps of depositing a gold-based layer and a platinum-based layer are described in conjunction with the second embodiment.

[0070] The method according to the fourth embodiment is, in principle, applicable to all types of electrical components and / or circuits including nickel-plated copper-based conductors. Improvement in corrosion resistance may be evaluated, for example, by the neutral salt spray method (5% NaCl) according to ISO 9227 standard tests, though not limited thereto. Other tests include the steps of immersing a specimen in hydrogen peroxide at ambient temperature (23 ± 2 °C) according to ASTM G31-21 (Standard Guide for Laboratory Immersion Corrosion Testing of Metals), removing the specimen from the solution, rinsing with deionized water (DI water), and measuring the loss of corrosion metal according to ASTM G1-03 (Standard Practice for Preparation, Washing and Evaluation of Corrosion Test Specimens) and / or analyzing the surface morphology of the tested specimen by scanning electron microscopy (SEM) and / or X-ray photoelectron spectroscopy (XPS) after a predetermined immersion period.

[0071] Biosensors and medical devices

[0072] In the fifth embodiment, the present invention relates to a biosensor or medical device comprising a multilayer stack according to the first embodiment.

[0073] A biosensor is understood as an analytical device used for the detection of chemical substances by combining biological components with physicochemical detectors. Here, the components comprising the multilayer stack according to the first embodiment may be used as electrochemical catalysts (e.g., to accelerate the reaction of enzymes), as sensor electrodes to enhance electron charge transfer, and as precursor materials for enzyme-modified electrodes, wherein the surface of the multilayer stack is modified with enzymes to fix the substrate and maintain enzyme activity. Although not limited thereto, the biosensor may be adopted for the detection of bioactive substances such as glucose, glutamate, neurotransmitters, or hormones.

[0074] Medical devices may also include, but are not limited to, medical sensors (e.g., medical pumps, minimally invasive equipment, sensors in respiratory care or vital sign monitoring). For example, examples of medical devices may also include surgical instruments (e.g., marker bands and guidewires for catheters, electrodes for catheters), electromedical implants (e.g., pacemakers, hearing aids, heart pumps, defibrillators, neuromodulators), interventional devices (e.g., stents), orthopedic devices (e.g., knee or hip implants, spinal fixation devices), or similar items.

[0075] These embodiments are advantageous in that they fully utilize the excellent biocompatibility, durability, conductivity, and radiopacity of Pt.

[0076] It will be understood that the present invention may adopt any of the preferred features specified above in connection with the description of the first to fifth embodiments, and that the preferred features may be combined in any combination, except for combinations in which at least some of the features are mutually exclusive.

[0077] Once the above disclosure is given, many other features, variations, and improvements will become apparent to a skilled technician. Explanation of the symbols

[0078] 1 / 11 / 21 / 31 / 41 / 51 Copper (Cu)-based layer 2 / 12 / 22 / 32 / 42 / 52 Nickel (Ni)-based layer 3 / 13 / 23 / 33 / 43 / 53 Gold (Au)-Base Layer 13a / 23a Flash Gold (Au) Layer (Optional) 4 / 14 / 24 / 34 / 44 / 54 Platinum (Pt)-Based Layer 5 Additional function layer (optional) 15 / 25 2nd Gold (Au)-Base Layer (Optional) 15a / 25b Flash Gold (Au) Layer (Optional) 16 / 26 Ni-P layer (optional) 17 / 27 / 37 / 57 Substrates (Optional) 28 / 58 channels (optional) 29a Ni layer (optional) 29b Au layer (optional)

Claims

Claim 1 A multilayer stack comprising a copper-based layer; a nickel-based layer provided on the copper-based layer; a gold-based layer provided on the nickel-based layer; and a platinum-based layer provided on the gold-based layer. Claim 2 A multilayer stack according to claim 1, wherein the platinum-based layer is in contact with the gold-based layer. Claim 3 A multilayer stack according to claim 1 or 2, wherein the copper-based layer is provided in contact with the nickel-based layer. Claim 4 A multilayer stack according to any one of claims 1 to 3, wherein the nickel-based layer is provided in contact with the gold-based layer. Claim 5 A multilayer stack according to any one of claims 1 to 4, wherein the copper-based layer comprises at least 85 wt.-% and preferably at least 90 wt.-% of copper based on the total weight of the copper-based layer; and / or the nickel-based layer comprises at least 85 wt.-% and preferably at least 90 wt.-% of nickel based on the total weight of the nickel-based layer; and / or the gold-based layer comprises at least 85 wt.-% and preferably at least 90 wt.-% of gold based on the total weight of the gold-based layer. Claim 6 A multilayer stack according to any one of claims 1 to 5, wherein the gold-based layer has a minimum thickness of 15 nm, preferably a thickness of 20 nm to 500 nm. Claim 7 A multilayer stack according to any one of claims 1 to 6, wherein the platinum-based layer comprises at least 95 wt.-%, preferably at least 97 wt.-%, and more preferably at least 99 wt.-% of platinum based on the total weight of the platinum-based layer. Claim 8 A multilayer stack according to any one of claims 1 to 6, wherein the platinum-based layer is composed of a platinum alloy comprising at least 60 wt.-% platinum based on the total weight of the platinum-based layer, and the platinum alloy preferably further comprises a metal selected from one or more transition metals. Claim 9 A multilayer stack according to any one of claims 1 to 8, wherein the platinum-based layer has a thickness of 15 nm or more, preferably 20 nm to 600 nm, and more preferably 25 nm to 500 nm. Claim 10 In any one of claims 1 to 9, the structure further comprises a layer of platinum black on and in contact with the platinum-based layer, wherein the platinum black layer is preferably 2 to 50 m 2 A multilayer stack having a specific surface area in the range of / g. Claim 11 A multilayer stack according to any one of claims 1 to 9, further comprising a second gold-based layer on and in contact with a platinum-based layer. Claim 12 A multilayer stack according to any one of claims 1 to 11, further comprising a substrate selected from polymers, silicon, ceramic substrates, glass, fabrics, paper, and combinations thereof. Claim 13 A method according to any one of claims 1 to 12, comprising the steps of: providing a nickel / copper multilayer film comprising the nickel-based layer and the copper-based layer; depositing a layer of gold on the nickel-based layer to form the gold-based layer; and depositing a layer of platinum on the gold-based layer to form the platinum-based layer. Claim 14 A method according to claim 13, wherein the platinum-based layer is deposited by electroplating from a solution containing dihydrogen bis(nitrite-N)[sulfato(2-)-O,O']platinate(2-)(H2Pt(NO2)2SO4). Claim 15 Use of a multilayer stack according to any one of claims 1 to 12 as an electrode or electrical conductor in electrical connectors and / or electrical circuits. Claim 16 A method for improving the corrosion resistance of nickel-plated copper, comprising the steps of: depositing a layer of gold on the surface of the nickel-plated copper to form a gold-based layer; and depositing a layer of platinum on the gold-based layer to form a platinum-based layer. Claim 17 A biosensor or medical device comprising a multilayer stack according to any one of claims 1 to 12.

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