Abstract:
An electric contact, in particular an electric contact of a plug-in connector, has a metallic substrate to which a contact layer is applied. The contact layer is arranged as a structured layer.

Description:
FIELD OF THE INVENTION  
       [0001]     The exemplary embodiment of the present invention is directed to an electric contact, in particular an electric contact of a plug-in connector.  
       BACKGROUND INFORMATION  
       [0002]     An electric contact of this type is available and is used, for example, in the automobile industry.  
         [0003]     Such an electric contact includes a metallic substrate, which is normally made of a copper-based alloy such as CuSn 4  bronze, CuNiSi or the like, on which a contact layer made of tin is situated. The contact layer may be a hot-tin-plated or electrolytically deposited layer which has a thickness of a few micrometers. An intermediary layer made of intermetallic compounds such as CuSn 4 , Cu 5 Sn 6  is formed by diffusion on the boundary surface with the substrate when a tin contact layer is used. The intermediary layer is harder than the contact layer and may grow as a function of the temperature.  
         [0004]     Tin or a tin alloy is characterized by high ductility and good electric conductivity. Tin alloys or tin layers, however, have the disadvantage that they tend to wear off due to their low hardness and the resulting low wear resistance upon frequent insertions or vibrations caused by the vehicle or the engine, which results in increased oxidation, known as friction corrosion. Friction wear and/or friction corrosion may in turn result in failure of an electric automobile component associated with the contact in question, in particular a sensor, a control unit, or the like.  
         [0005]     In tin or tin alloy layers of this type it is furthermore disadvantageous that the insertion forces for many applications are excessively high, because these contact layers have a strong tendency toward adhesion and high plastic deformability.  
         [0006]     Furthermore, a tin-based contact layer of an electric contact, known as thermotin, is known in industry, which is made entirely of intermetallic phases and is manufactured by artificial aging. However, it has been found that thermotin has limited applicability, which may be shown in particular on the basis of chemical and abrasion testing.  
         [0007]     Furthermore, Au—Co alloys on a nickel layer, silver plating on a copper or nickel layer, or gold plating were previously often used as contact layers in electric contacts.  
         [0008]     In particular, silver-based, but also tin surfaces or contact layers tend toward cold fusion due to adhesion and are characterized by high friction coefficients in self-mated pairs.  
         [0009]     Even in silver or gold layers previously used in electric contacts, oxidative wear of the substrate or of an intermediary layer used as an adhesion layer, often made of copper or nickel, may occur in the event of friction wear or flaking of the layer.  
       SUMMARY OF THE INVENTION  
       [0010]     The electric contact according to the exemplary embodiment of the present invention, having a metallic substrate to which a structured contact layer is applied, has the advantage of an optimized tribological characteristic, which is adjustable via structuring. In particular, a contact layer of an electric contact having reduced friction coefficients and increased wear resistance may be manufactured via suitable structuring.  
         [0011]     As usual, the contact layer of the electric contact according to the present invention has a layer thickness of between 1 μm and 6 μm. Structuring may be in the range between 1 nm and 1 μm, which qualifies it as nanostructuring.  
         [0012]     The substrate of the electric contact according to the present invention may be a substrate normally used in the automobile industry for plug-in connectors, for example, a copper-based alloy such as CuSn 4  bronze, CuNiSi, or the like. Alternatively, a substrate made of a nickel-based alloy may also be used.  
         [0013]     According to an exemplary embodiment of the electric contact according to the present invention, the structuring features particles between approximately 1 nm and 1 μm distributed, i.e., dispersed, in a matrix of the contact layer. A solid-state dispersion or nanodispersion is thus created. The nanodispersion may be produced by an electrolytic method. The particles may be dispersed in the crystalline or amorphous matrix in a crystalline or amorphous form.  
         [0014]     The particle size of the particles dispersed in the matrix, whose proportion in the matrix may be between 1 vol. % and 50 vol. %, is advantageously in the range of 20 nm to 200 nm. Such particle sizes have been found ideal regarding their electrical and mechanical properties in 1 μm to 6 μm thick contact layers.  
         [0015]     By introducing the nanodispersion into the contact layer matrix, the service life, in particular the number of insertion cycles and/or the friction corrosion resistance of the electric contact, may be increased.  
         [0016]     The strength and hardness of the contact layer may thus be increased by introducing particles whose hardness is greater than that of the matrix. Particles of this type are made, for example, of Al 2 O 3  which are dispersed in a matrix of tin or silver, for example. Alternatively, particles of yttrium oxide, zirconium oxide, titanium aluminide, titanium nitride, ruthenium alloy phases and/or the like may also be used. Introducing electrically conductive phases such as titanium nitride or ruthenium alloy phases as the particles dispersed in the matrix has the advantage that the electrical properties of the contact layer are not affected.  
         [0017]     However, particles dispersed in the matrix, a silver matrix in particular, may also be formed by a solid-state lubricant. A solid-state lubricant of this type may be, for example, graphite or MOS 2 , and results in reduced friction forces and insertion forces which must be applied to connect the electric contact with a mating contact.  
         [0018]     In another exemplary embodiment of the electric contact according to the present invention, the dispersed particles are micro-oil capsules.  
         [0019]     The micro-oil capsules, which represent lubricant capsules of a microscopic size and may be introduced into the matrix using an electrolytic process, may contain a tribologically active lubricant containing antioxidants and/or antiadhesive additives and are wrapped in a polymer skin, for example. The antioxidants and antiadhesive additives are released in the case of such a contact where the highest surface stresses occur on insertion or for micromovements due to vibrations. The polymer skins which wrap the oil capsules melt under the effect of a brief exposure to heat, for example, in the event of an increase in temperature to approximately 100° C. to 200° C., for example.  
         [0020]     Homogeneous distribution of the micro-oil capsules in the matrix may be achieved using ultrasound-generated turbulence or other hydraulic measures.  
         [0021]     Alternatively, oil capsules or oil cavities may be introduced by melting a hot-tin-plated surface in an oil bath or by an electrolytic method. In this case, the oil capsules have no polymer skin.  
         [0022]     The micro-oil capsules introduced into the matrix represent carbon-containing islands in the structure and cause the friction forces and insertion forces to be optimized, increase the service life of the layer and the friction corrosion resistance.  
         [0023]     In an exemplary embodiment of the present invention, tin or silver may be used as a matrix for the micro-oil capsules.  
         [0024]     In another embodiment of the electric contact according to the present invention, structuring is formed by a multilayer system which is made up of successive layers having varying chemical compositions. The friction coefficients of the contact layer may be reduced and its wear resistance increased also by using such a multilayer system.  
         [0025]     For example, the multilayer system may be a contact layer manufactured on the basis of gold or silver, such as a gold/cobalt layer system or a silver/indium layer system. Each of the individual layers of the multilayer system is made of an alloy of these elements, for example, the proportion of the individual elements varying from layer to layer. It is also conceivable to select a gold/silver layer system as the contact layer, the proportion of gold and silver varying from layer to layer. The layer sequence may be ABABA . . . , for example.  
         [0026]     To improve the contact between the electric contact and its mating contact, the contact layer may have a noble metal cover layer, at least in some areas. The noble metal cover layer may have a thickness of between 0.1 μm and 0.3 μm, thus representing a “flash” layer. Ruthenium, gold, platinum, and/or palladium in particular are suitable as noble metals for the flash layer.  
         [0027]     The contact layer of the electric contact according to the present invention may be manufactured using an electrolytic method.  
         [0028]     Further advantages and advantageous refinements of the object according to the present invention are described herein and/or by the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]      FIG. 1  shows a section of a first embodiment of an electric contact.  
         [0030]      FIG. 2  shows a section of a second embodiment of an electric contact.  
         [0031]      FIG. 3  shows a section of a third embodiment of an electric contact.  
         [0032]      FIG. 4  shows a section of a fourth embodiment of an electric contact. 
     
    
     DETAILED DESCRIPTION  
       [0033]      FIG. 1  schematically illustrates a surface of an electric contact  10 , which is a contact of a plug-in connector for use in an automobile.  
         [0034]     Electric contact  10  includes a substrate  11  which is manufactured from a copper-based alloy such as CuSn 4 , CuNi 2 Si or the like. Substrate  11  has a thickness of between 0.1 mm and 0.5 mm.  
         [0035]     A contact layer  12  is applied to substrate  11  by an electrolytic method. Contact layer  12  has a layer thickness of between approximately 1 μm and 3 μm and has a matrix  13  made of tin. Hard particles  14  of aluminum oxide Al 2 O 3  having a particle size of between 20 nm and 200 nm are distributed, i.e., “dispersed,” in matrix  13 . Contact layer  12  thus represents a solid-state nanodispersion.  
         [0036]      FIG. 2  schematically illustrates an electric contact  20 , which is also a contact of a plug-in connector for use in an automobile.  
         [0037]     Similar to the electric contact of  FIG. 1 , electric contact  20  includes a substrate  11  which is made of a copper-based alloy.  
         [0038]     Substrate  11  of electric contact  20  is provided with a contact layer  22 , which has a matrix  23  of silver. Graphite particles  24 , known as graphite flakes, are homogeneously distributed in silver matrix  23 . Graphite flakes  24  are used as a solid-state lubricant and have a particle size of between 1 μm and 1 nm. The graphite flakes may be present in a platelet form and may have a length/thickness ratio of approximately 2 to 50 and/or have any other shape, for example, a spherical shape.  
         [0039]      FIG. 3  illustrates an electric contact  30 , which is also a contact of a plug-in connector for use in an automobile.  
         [0040]     Similar to the electric contact of  FIG. 1 , electric contact  30  includes a substrate  11  which is made of a copper-based alloy. However, substrate  11  of electric contact  30  is provided in this case with a contact layer  32 , which has a matrix  33  of silver, in which oil capsules  34  are distributed, i.e., dispersed. The diameter of oil capsules  34  is less than 1 μm, i.e., it is in the sub-micrometer range. The oil capsules contain a tribologically active lubricant having antioxidants and antiadhesive additives, as well as a polymer skin, which melts even upon brief exposure to heat. Lubricant capsules  34  allow the friction/insertion forces occurring when electric contact  20  is connected to a mating contact to be reduced.  
         [0041]      FIG. 4  illustrates an electric contact  40 , which is also a contact of a plug-in connector for use in an automobile.  
         [0042]     In electric contact  40 , a multilayer system  42  is situated on a substrate  11 , which corresponds to the substrates in the exemplary embodiments according to  FIGS. 1 through 3  and is thus made of a copper-based alloy and is composed of a plurality of layers whose thickness is in the nanometer range. The individual layers differ through their chemical compositions and represent a silver/indium alloy, in which the proportion of silver and indium varies from layer to layer. Layer system  42  has a layer sequence ABAB . . . here, where A and B stand for a silver/indium alloy having a defined composition.  
         [0043]     In this embodiment, a flash layer  43  made of ruthenium or gold, designed as a cover layer, is situated on the top of contact layer  42 . Cover layer  43  may have a thickness of approximately 0.1 μm.