Patent Publication Number: US-2013248229-A1

Title: Electrical conductors and methods of manufacturing electrical conductors

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/613,650 tiled Mar. 21, 2012, the subject matter of which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The subject matter herein relates generally to electrical conductors and methods of manufacturing electrical conductors. 
     Electrical conductors have many forms, such as a contact, a terminal, a spring contact, a pin, a socket, an eye-of-needle pin, a micro-action pin, a compliant pin, a wire, a cable braid, a trace, a pad and the like. Such electrical conductors are used in many different types of products or devices, including electrical connectors, cables, printed circuit boards, and the like. The metals used in the electrical conductors are susceptible to corrosion, diffusion or other reactions, limiting their use or requiring protective coatings. For example, when copper or copper alloy electrical conductors are used, such conductors are susceptible to corrosion. A gold layer is typically applied to the copper as a corrosion inhibitor. However, the gold and copper materials suffer from diffusion and typically a diffusion barrier, such as nickel is deposited between the copper and gold layers. 
     Corrosion of base metals is detrimental to the conductor interface and signal integrity. Current plating methods used to mitigate corrosion often leave a porous surface, resulting in oxidation and corrosion of the underlying surface. Additionally, some layered structures suffer from problems associated with friction, stiction and other contact forces, limiting application of the conductors. 
     Some known conductors use graphene or other carbon based structures as barriers for the conductors. However, application of the graphene to the conductors is problematic. One known method of applying graphene to the conductor includes depositing the graphene in a chemical vapor deposition (CVD) process. However, such processes use very high temperatures. Subjecting the conductor to such high temperatures may be damaging to the conductor. For example, typical conductors use copper alloys having melting point temperatures that are below the temperatures desired for the CVD process. Subjecting such conductors to the CVD process will cause grain boundaries, triple points and other problems with the conductors. 
     A need remains for an electrical conductor that addresses the aforementioned problems and other shortcomings associated with traditional electrical conductors. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment, a method of manufacturing an electrical conductor is provided including providing a base substrate, providing a foil, depositing a graphene layer on the foil to define a layered structure, and depositing the layered structure on the base substrate. 
     Optionally, the graphene layer may be deposited directly on the foil. The foil may be deposited directly on the base substrate. Depositing the layered structure may include cladding the foil to the base substrate. Depositing the layered structure may include at least one of pressure bonding, rolling, cold welding, laser bonding, or soldering the foil to the base substrate. 
     Optionally, the method may include plating the graphene layer with a surface layer. The base substrate may include a base and a barrier deposited on the base. The layered structure may be deposited on the barrier. The graphene layer may be deposited on the foil prior to the foil being deposited on the base substrate. 
     Optionally, depositing the graphene layer may include depositing graphene on one or more surfaces of the foil by processing the electrical conductor using a chemical vapor deposition process using an organic compound precursor and heat of sufficient temperature to facilitate graphene growth on the metal compound comprising the foil. Optionally, the base substrate is not subjected to the heat of the chemical vapor deposition process. The graphene layer may be deposited by the chemical vapor deposition process prior to the foil being deposited on the base substrate. 
     In another embodiment, an electrical conductor is provided having a base substrate of at least one of copper, copper alloy, nickel or nickel alloy and a layered structure applied to the base substrate. The layered structure includes a foil and a graphene layer deposited on the foil. The layered structure is applied to the base substrate after the graphene layer is deposited on the foil. 
     Optionally, the graphene layer may be deposited directly on the foil. The foil may be deposited directly on the base substrate. The foil may be clad to the base substrate. The foil may be at least one of pressure bonded, pressure rolled, cold welded, laser bonded, and soldered to the base substrate. 
     Optionally, the electrical conductor may include a surface layer on the graphene layer opposite the foil. The surface layer may be plated on the graphene layer opposite the foil. The base substrate and layered structure may be stamped and formed after the layered structure is deposited on the base substrate. The base substrate may include a base and a barrier with the layered structure being deposited on the barrier. 
     Optionally, the graphene layer may be CVD deposited on one or more surfaces of the foil using an organic compound precursor and heat of sufficient temperature to facilitate graphene growth on the metal compound comprising the foil. The graphene layer may be deposited prior to the foil being deposited on the base substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross sectional view of a portion of an electrical conductor formed in accordance with an exemplary embodiment. 
         FIG. 2  illustrates a conductor formation system used to form electrical conductors, such as the electrical conductor shown in  FIG. 1 . 
         FIG. 3  is a flow chart showing an exemplary method of manufacture of an electrical conductor, such as the electrical conductor shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a cross sectional view of a portion of an electrical conductor  100  formed in accordance with an exemplary embodiment. The electrical conductor  100  may be any type of electrical conductor, such as a contact, a terminal, a spring contact, a pin, a socket, an eye-of-the-needle pin, a micro-action pin, a compliant pin, a wire, a cable braid, a trace, a pad and the like. The electrical conductor  100  may form part of an electrical connector, a cable, a printed circuit board and the like. 
     In an exemplary embodiment, the electrical conductor  100  is a multi-layered structure having a base substrate  102  and a layered structure  104  that together define a workpiece  105 . Optionally, layered structures  104  may be applied to both sides of the base substrate  102  to from a workpiece. The workpiece  105  is processed to form the conductor  100 . For example, the workpiece  105  may be plated, stamped, formed, and the like. The layered structure(s)  104  may be a surface layered structure  104  at an outer surface of the electrical conductor  100 . 
     The layered structure  104  provides a corrosion-resistant electrically conductive layer on the base substrate  102 . In an exemplary embodiment, the layered structure  104  includes a conductive foil layer  110  (may be referred to hereinafter as conductive foil  110  or just foil  110 ), a graphene layer  112  and a conductive surface layer  114 . The layered structure  104  may just include the foil  110  and the graphene layer without the surface layer  114  in some embodiments. The foil  110  may be a strip or other stock metal component. The foil  110  may be a copper or copper alloy, a nickel or nickel alloy or another suitable metal. The foil  110  is used to support the graphene layer  112 , such as for application to the base substrate  102  during a later process. The graphene layer  112  includes a graphene deposit or other carbon based barrier to inhibit corrosion and/or enhance other characteristics of the electrical conductor  100 , such as the friction coefficient, conductivity and the like. The surface layer  114  is a non-carbon based layer(s), such as metal plating such as gold, silver, tin, palladium, nickel, palladium-nickel, platinum and the like. The surface layer  114  may be used to inhibit corrosion or enhance other characteristics of the electrical conductor  100 , such as wear resistance, coefficient of friction and the like. 
     The layered structure  104  is generally a thin layer as compared to the base substrate  102 . The layered structure  104  may be deposited on the base substrate  102  by any known process, such as cladding, laminating, adhering, bonding or other suitable process. Optionally, the layered structure  104  may be deposited directly on the underlying base substrate  102 . Alternatively, one or more other layers may be provided between the layered structure  104  and the base substrate  102 . In an exemplary embodiment, the graphene layer  112  is deposited on the foil  110  to define the layered structure  104 , which is applied to the base substrate  102  during a different process. The surface layer  114  may be applied to the layered structure  104  after the layered structure  104  is applied to the base substrate  102 . 
     The base substrate  102  may be a multi-layered structure. In the illustrated embodiment, the base substrate  102  includes a base  106  and a barrier  108  deposited on the base  106 . Optionally, the base  106  and/or the barrier  108  may be a multi-layered structure. The layered structure  104  and the base substrates  102  together define a stackup of layers. The base substrate  102  may only include the base  106  without the barrier  108 , with the layered structure  104  applied directly to the base  106  as opposed to the barrier  108 . 
     In an exemplary embodiment, the base  106  is electrically conductive and includes a metal compound, such as a copper or a copper alloy. Other metal compounds for the base  106  may include nickel, nickel alloy, steel, steel alloy, aluminum, aluminum alloy, palladium-nickel, tin, tin alloy, cobalt, carbon, graphite, graphene, carbon-based fabric, or any other conductive material. The barrier  108  is electrically conductive and includes a metal compound, such as nickel or a nickel alloy. Other metal compounds for the barrier  108  include other metal or conductive material such as copper, gold, silver, cobalt, tungsten, platinum, palladium, or alloys of such. The barrier  108  may provide a diffusion barrier between the base  106  and the layered structure  104 , such as when copper and gold or other metal compounds that have diffusion problems are used. The barrier  108  provides a mechanical backing for application of the layered structure  104 , which may be relatively thin, improving its wear resistance. The barrier  108  may reduce the impact of pores and corrosion problems if present in the layered structure  104 . The barrier  108  may be deposited on the base  106  by any known process, such as plating. Optionally, the barrier  108  may be deposited directly on the underlying base  106 . Alternatively, one or more other layers may be provided between the barrier  108  and the base  106 , such as a graphene layer. 
     In an exemplary embodiment, the graphene layer  112  is used to inhibit corrosion. The graphene layer  112  may be electrically conductive. The graphene layer  112  is deposited on the foil  110 . In an exemplary embodiment, the graphene layer  112  is grown on the exposed portion of the foil  110 . For example, the foil  110  is processed to grow the graphene layer  112  on one or more surfaces of the foil  110  (or in select locations on the foil  110 ). The graphene layer  112  may cover the entire upper surface of the foil  110 . 
     In an exemplary embodiment, the graphene layer  112  may be formed during a chemical vapor deposition (CVD) process in the presence of an organic compound, such as gaseous methane, at a high temperature, such as approximately 800° C. or higher. Deposition mechanisms may also include electron beam, microwave or other process within the vaporous atmosphere. Other processes may be used to deposit the graphene layer  112 , such as laser deposition, plasma deposition or other techniques or processes. Optionally, the graphene layer  112  may be 1 atomic layer thick on the foil  110 . Alternatively, the graphene layer  112  may be thicker. The graphene layer  112  provides corrosion resistance. 
     The graphene layer  112  may be deposited only on the exposed portions of the foil  110 . For example, the metal compound of the foil  110  may be used as a catalyst during the CVD process (or other process) to promote graphene growth at the interface with the foil  110 . Optionally, the CVD process may be controlled to promote graphene growth at such interface, such as by using a suitable organic precursor and processing at a suitable temperature to enhance graphene growth depending on the chemical composition (e.g. metal or metal alloy) of the foil  110 . For example, the type of organic compound or gas precursor used, the pressure of the gas precursor used, the flow rate of the gas precursor, the temperature of the process, or other factors may promote graphene growth on one metal as compared to other metals. 
     The graphene layer  112  operates as a corrosion barrier for the electrical conductor  100  by providing a barrier between the base  106  and the environment to inhibit oxygen atoms from interacting with the metal compounds of the base  106 . The graphene layer  112  may operate as a diffusion barrier to inhibit diffusion between the base  106  and the surface layer  114 . Optionally, the graphene layer  112  may replace the barrier  108 , acting as the diffusion barrier between the base  106  and the surface layer  114 . 
     Optionally, the graphene layer  112  may be the outermost layer of the electrical conductor  100 . The graphene layer  112  may reduce friction on the outermost surface of the electrical conductor  100 , which may make mating of the electrical conductor  100  easier. The graphene layer  112  may reduce stiction of the layered structure  104 . The reduction in stiction may allow use of the electrical conductor  100  in fields or devices that previously were unsuitable for electrical conductors  100  having problems with stiction and/or cold welds, such as electrical conductors having the outermost layer being a gold layer. For example, in microelectromechanical systems (MEMS) switches, stiction is a problem when a gold layer is the outermost layer of the electrical conductor. 
     Having the graphene layer already deposited on the foil in a prior process allows the electrical conductor to be manufactured without having to subject the base substrate to the high temperatures associated with depositing the graphene layer on the foil. For example, the base substrate may be made from a copper alloy having a melting temperature similar to or lower than the temperature needed to effectively promote graphene growth on the foil. Having only the foil, as opposed to the base substrate, transferred through the coating station or other station that deposits the graphene, benefits the electrical conductor  100 , such as by reducing the risk of forming grain boundaries, triple points or pores in the base substrate. Additionally, by not having to process the base substrate through the coating station, the coating station may be operated at a higher temperature than if the base substrate were to be passed through the coating station. 
     In an exemplary embodiment, the foil is made from a material having a higher melting temperature than the base substrate. The foil can withstand higher temperatures than the base substrate without damaging the structure thereof. The foil may be made from a material having a higher melting temperature than the temperature desired for graphene growth and/or deposition. The base substrate may have different characteristics from the foil other than a different melting point temperature, making use of such base substrate desirable to use as opposed to a base substrate of the same material as the foil or of a material having a high enough melting point temperature to withstand the coating station and graphene growth. For example, the base substrate may have better spring characteristics than the material of the foil. The base substrate may be stronger or tougher than the material of the foil. The base substrate may have a finer grain than the material of the foil. The base substrate may have a lower cost than the material of the foil. The base substrate may be more ductile or have better forming characteristics than the material of the foil. The base substrate may have better electrical conductivity than the material of the foil. Other characteristics may be important to the selection of the particular base substrate having the lower melting point temperature. Separating the graphene growth onto a foil separate from the base substrate allows the graphene deposition and/or growth to be tailored to the application. 
       FIG. 2  illustrates a conductor formation system  150  used to form electrical conductors, such as the electrical conductor  100 . The system  150  includes a plurality of stations that perform operations or functions on materials to form the electrical conductor  100 . In the illustrated embodiment, the system  150  is an in-line system that progressively feeds product, such as strips or reels of material, through the stations to process the materials to form the electrical conductor  100 . For example, the product may be continuously feed to stations for processing. In an exemplary embodiment, the system  150  is a reel system that winds and/or unwinds material from reels to progressively process the electrical conductor  100  through the system  150 . 
     The system  150  includes a strip reel  154 , on which the foil  110  is wound in strip form. The foil  110  is continuously unwound and pulled through the system  150  from the strip reel  154 . The conductive foil  110  is used to form the foil  110  (shown in  FIG. 1 ). The width of the copper foil may be dependent on the width and shape for the electrical conductor  100 , which may be stamped, bent or formed to form the final product. 
     The system  150  includes a coating station  156 . The coating station  156  applies the graphene layer  112  to the conductive foil  110 . The product exiting the coating station  156  defines the layered structure  104 . The graphene layer  112  may be applied in a suitable manner, such as by a CVD process. The graphene layer  112  may be grown on the foil  110  as the foil  110  passes through the coating station  156 . The graphene layer  112  may be applied by other coating processes or processes other than coating. 
     A transfer device  158  is used to advance the layered structure  104  through the system  150 . Optionally, the transfer device  158  may be one or more reels upon which the layered structure  104  is wound and/or unwound. The transfer device  158  may be a conveyor, such as a conveyor belt or roll. The foil  110  is used to support the graphene layer  112  for advancing the graphene layer  112  through the system  150 . The graphene layer  112  remains applied to the foil  110  and the foil  110  is attached to the substrate  102  and forms part of the final product. Alternatively, the foil  110  may be later removed from the layered structure  104  to allow the graphene layer  112  to be attached directly to the substrate  102 . 
     The layered structure  104  is progressively transferred through a substrate application station  170 . The substrate  102  is provided on a substrate reel  171 . The substrate  102  is unwound from the reel and progressively presented to the substrate application station  170  for attaching the substrate  102  to the layered structure  104 . The substrate  102  may be advanced by a device other than a reel in alternative embodiments. Once the layered structure  104  is attached to the substrate  102 , the layered structure  104  may be advanced through the system  150  on the substrate  102 . 
     At the substrate application station  170 , the layered structure  104  is applied to the substrate  102 . The layered structure  104  may be applied to the substrate  102  by cladding the foil  110  and the substrate  102 . The layered structure  104  may be applied to the substrate  102  by other processes, such as pressure bonding, rolling, cold welding, laser bonding, soldering or other processes. 
     The product is passed to a processing station  172  where the electrical conductor  100  may be processed, such as to enhance certain characteristics of the electrical conductor  100 . For example, the processing station  172  may include a plating sub-station where the layered structure  104  is plated with the surface layer  114 . The processing station  172  may include a stamping sub-station where the electrical conductors  100  are shaped and/or singulated. The processing station  172  may include a forming sub-station where the electrical conductors  100  are bent and formed into a final shape. 
       FIG. 3  is a flow chart showing an exemplary method of manufacture of an electrical conductor, such as the electrical conductor  100 . The method includes providing  200  a foil, such as the foil  110 . The foil may be a copper or copper alloy layer. 
     The method includes forming  202  a graphene layer, such as the graphene layer  112 , on the foil to form a layered structure. The graphene layer may be formed by a CVD process or another process. The graphene layer may completely cover the foil or may selectively cover portions of the foil. The graphene layer may be formed by growing or depositing one or more graphene layers on the foil. The metal of the foil may act as a catalyst to promote selective growth of the graphene thereon. 
     The method includes providing  204  a base substrate, such as the base substrate  102 . The base substrate may be a layered structure. The base substrate may include a base and a barrier deposited on the base, such as by plating. 
     The method includes depositing  206  the layered structure, such as the layered structure  104 , on the base substrate. The layered structure may be directly deposited on the base substrate. For example, the foil may be clad or otherwise joined to the base substrate. Having the graphene layer already deposited on the foil in a prior process allows the electrical conductor to be manufactured without having to subject the base substrate to the high temperatures associated with depositing the graphene layer on the foil. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Dimensions, types of materials, orientations of the various components, and the number and positions of the various components described herein are intended to define parameters of certain embodiments, and are by no means limiting and are merely exemplary embodiments. Many other embodiments and modifications within the spirit and scope of the claims will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means plus-function format and are not intended to be interpreted based on 35 U.S.C. §112, sixth paragraph, unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure.