Patent Publication Number: US-2022224035-A1

Title: Electric contact element for high operating voltages

Description:
The present invention relates to an electrical contact element for a connector suitable for electrical operating voltages of more than 150 V. 
     PRIOR ART 
     Electrical connectors generally have one or more electrical contact elements and one or more insulating bodies. The contact elements are usually designed as male elements or female elements. These are made of base materials which are not resistant to corrosion. These are often copper alloys. To ensure the function of the contact elements over the service life of the connector, thin layers of other metals are therefore applied to the base material. These can comprise an intermediate layer and a wear layer. 
     The intermediate layer can have various purposes. It can improve the adhesion of the wear layer to the base material, create a mechanical balance between the base material and the wear layer, and prevent diffusion processes from taking place between the wear layer and the base material. The intermediate layer often consists of copper or nickel. 
     The wear layer, which is also referred to as the functional layer, is located on the intermediate layer. The wear layer extends the technically useful life of the contact element, can improve electrical transmission, and protect the underlying layers from corrosion. It can consist of soft, non-inert metals such as tin or silver. In connectors in the automotive sector, for example, silver is widely used as a wear layer. If voltages of more than 150 V occur in an application, the force of the electrical potential between different contact elements can increasingly excite metal ions to move from one physical position to another. This metal migration can cause short circuits and other technical problems in the connector. Silver functional surfaces are prone to this type of metal migration at higher voltages. For this reason, more expensive precious metal functional layers are usually used in applications with operating voltages of more than 150 V. By way of example, gold-cobalt alloys or palladium-nickel alloys are thus used. 
     It is an object of the present invention to provide an electrical contact element suitable for use in an electrical connector and suitable for electrical operating voltages of more than 150 V. However, it should be possible to manufacture it at a lower cost than conventional electrical contact elements and still achieve the reliability and service life of conventional electrical contact elements. 
     DISCLOSURE OF THE INVENTION 
     This object is solved by an electrical contact element for a connector, which has a metallic base body or a wear layer applied to the base body. The wear layer can be applied directly to the metallic base body or one or more further layers can be arranged between the metallic base body and the wear layer. The wear layer consists of the following alloy elements: 82-91% by weight nickel, 9-18% by weight phosphorous and 0 to 1% by weight further alloy elements. Preferably, the layer consists of 82-89% by weight nickel, 11-18% by weight phosphorous and 0 to 1% by weight further alloy elements. The sum of the alloy elements is 100% by weight. A proportion of up to 1% by weight of further alloy elements in the alloy, for example as impurities, is acceptable but is preferably avoided. In accordance with the invention, it has been found that the use of such a wear layer provides similarly good electrical transmission and similarly good corrosion protection as can be achieved, for example, with the wear layer made of a gold-cobalt alloy or a palladium-nickel alloy. However, the use of the nickel-phosphorous alloy makes it possible to manufacture the electrical contact element more cost-effectively in comparison. 
     In a preferred embodiment of the invention, the wear layer is arranged directly on the base body, such that there are no further layers between the wear layer and the base body. To ensure good corrosion protection, it is preferred in this embodiment that the wear layer has a thickness in the range of from 1.00 μm to 2.50 μm. Particularly preferably, the thickness is in the range of from 1.50 μm to 2.00 μm. The wear layer used according to the invention offers such good protection against corrosion and such good electrical transmission that these properties could not be significantly improved by further increasing the layer thickness. On the other hand, when using a conventional wear layer of a gold-cobalt alloy or a palladium-nickel alloy, for example, a layer thickness of at least 3 μm with simultaneous use of a metallic intermediate layer is usually required for the electrical contact element to meet the requirements for corrosion resistance and electrical transmission at all. The invention therefore not only makes it possible to manufacture the electrical contact element using less expensive materials, but also to save on the amount of material by using a particularly thin wear layer. 
     In another preferred embodiment of the invention, a metallic intermediate layer is arranged between the base body and the wear layer. Particularly preferably, the intermediate layer is the only layer arranged between the wear layer and the base body, such that the base body is directly connected to the intermediate layer and the intermediate layer is directly connected to the wear layer. As in the conventional design of the electrical contact element, the intermediate layer improves the adhesion of the wear layer to the base body, ensures mechanical compensation between the base body and the wear layer and prevents diffusion processes between the wear layer and the base body. In addition, the intermediate layer enables the use of a thinner wear layer compared to the embodiment of the invention in which the wear layer is arranged directly on the base body. In this embodiment, the wear layer preferably has a thickness in the range of from 0.15 μm to 1.50 μm. Particularly preferably, the thickness is in the range of from 0.30 μm to 1.00 μm. 
     In one embodiment of the contact element, the intermediate layer contains 99 to 100% by weight copper and 0 to 1% by weight further alloy elements. In another preferred embodiment of the contact element, the intermediate layer contains 99 to 100% by weight nickel and 0 to 1% by weight further alloy elements. The sum of the alloy elements is thus 100% by weight. The proportion of the further alloy elements should preferably be as low as possible, but their presence cannot be completely ruled out due to impurities. 
     The thickness of the intermediate layer is preferably 1.5 μm to 4.0 μm, and particularly preferably 2.0 μm to 3.0 μm. 
     Furthermore, it is preferred that a metallic and/or organic sliding layer is arranged on the wear layer. The sliding layer can improve the sliding properties of electrical contact elements, in particular of female elements and male elements. In this way, it helps the wear layer to remain functional for longer under mechanical frictional stress. On the other hand, it can also optimise electrical transmission between the electrical contact elements. If the sliding layer contains both metallic and organic components, it is preferred that a metallic partial layer is applied directly to the wear layer and an organic partial layer is applied to this metallic partial layer. The metallic partial layer and the organic partial layer then together form the sliding layer. 
     A particularly suitable metallic material for the sliding layer is pure gold or a gold alloy consisting of the following alloy elements: 98.5 to 100.0% by weight gold, 0 to 0.5% cobalt and 0 to 1.0% by weight further alloy elements. The sum of the alloy elements is 100% by weight. 
     Particularly suitable organic materials of the sliding layer are at least one fluoropolymer and/or at least one fatty acid salt. The fluoropolymer can, for example, be a perfluoropolyether (PFPE) or polytetrafluoroethylene (PTFE). The fatty acid salt can be, for example, lithium-12-hydroxystearate. 
     The thickness of the sliding layer is preferably in the range of from 0.05 μm to 0.25 μm. Such sliding layers are already sufficient to give the electrical contact element good sliding properties, such that the application of the sliding layer to the wear layer does not result in any significant increase in the thickness of the entire coating. 
     The wear layer of the electrical contact element according to the invention can be used particularly advantageously if the base body is made of copper, a low-alloyed copper alloy or a brass. In this case, it consists of the following alloy elements: 50 to 100% by weight copper, 0 to 45% by weight zinc and 0 to 5% by weight further alloy elements. The sum of the alloy elements in this case is 100% by weight. Even if the sum of the further alloy elements herein can be up to 5% by weight, it is preferred that each individual further alloy element constitutes no more than 2% by weight of the total alloy. Furthermore, it is preferred that only the other alloy elements beryllium, chromium, iron, cobalt, magnesium, manganese, nickel, phosphorous, sulphur, silver, silicon, tellurium, titanium, tin, and zirconium can each be present in the alloy in an amount of up to 2% by weight, and that all other alloy elements not mentioned in this list are present in an amount of not more than 1% by weight in each case. 
     The electrical contact element according to the invention can be manufactured with good technical properties without having to use large quantities of expensive precious metals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiments of the invention are depicted in the drawings and are explained in more detail in the following description. 
         FIG. 1  shows a schematic longitudinal sectional view of an arrangement of two electrical connectors. 
         FIG. 2  shows a cross-sectional view of a contact region between two electrical contact elements in a comparative example. 
         FIG. 3  shows a cross-sectional view of a contact region of two electrical contact elements according to exemplary embodiments of the invention. 
         FIG. 4  shows a cross-sectional view of a contact region of two electrical contact elements according to other exemplary embodiments of the invention. 
     
    
    
     EXEMPLARY EMBODIMENTS OF THE INVENTION 
       FIG. 1  shows the schematic structure of a pair of connectors. A first connector  10  has an electrical contact element  11  in the form of a male element. This is surrounded by a first insulating body  12  made of a plastic. A second connector  20  has a second electrical contact element  21  in the form of a female element. This is surrounded by a second insulating body  22  made of a plastic. When the two connectors  10 ,  20  are plugged into each other in the manner shown, the second insulating body  22  is pushed into the first insulating body  12 , wherein the first electrical contact element  11  slides into the second electrical contact element  21 . In doing so, it bends the tongues of the second contact element  21  apart, which are then pressed firmly onto the first contact element  11  by their spring force. Electrical transmission is then possible in a contact region  30  where the two contact elements  11 ,  21  make contact. 
     In electrical connectors  10 ,  20  that have contact elements  11 ,  21  according to the prior art, the structure of the contact elements  11 ,  21  depicted in  FIG. 2  is present in the contact region  30 . The first contact element  11  has a base body  111 , an intermediate layer  112  arranged on the base body and a wear layer  113  arranged on the intermediate layer. The second contact element  21  has a base body  211 , an intermediate layer  212  arranged on the base body  211 , and a wear layer  213  arranged on the intermediate layer  212 . The base bodies  111 ,  211 , the intermediate layers  112 ,  212  and the wear layers  113 ,  213  each have the composition in percent by weight shown in Table 1: 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Base body 
                 Intermediate layer 
                 Wear layer 
               
               
                   
                 111, 211 
                 112, 212 
                 113, 213 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Au 
                   
                   
                 99.8 
               
               
                   
                 Co 
                   
                   
                 0.2 
               
               
                   
                 Cu 
                 100 
               
               
                   
                 Ni 
                   
                 100 
               
               
                   
                 Ru 
               
               
                   
                 PTFE 
               
               
                   
                   
               
            
           
         
       
     
     In the present example, the intermediate layers  112 ,  212  each have a thickness d 112 , d 212  of 3 μm, and the wear layers  113 ,  213  each have a thickness d 113 , d 213  of 4 μm. The wear layers  113 ,  213  contact each other in the contact region  30 . The large amount of gold-cobalt alloy, which is necessary for manufacturing the wear layers, results in the manufacture of the electrical contact elements  11 ,  21  being expensive. 
       FIG. 3  shows the structure of the electrical contact elements  11 ,  21  according to several exemplary embodiments of the invention, which can be used in the pair of connectors  10 ,  20  according to  FIG. 1 . In addition to the structure of the electrical contact elements  11 ,  21  already depicted in  FIG. 2 , consisting of base bodies  111 ,  211 , intermediate layers  112 ,  212  and useful layers  113 ,  213 , the contact elements  11 ,  21  according to these exemplary embodiments of the invention also have a sliding layer  114 ,  214  on their wear layers  113 ,  213 . This results in no contacting of the wear layers  113 ,  213  occurring in the contact region  30 , but rather a contacting of the sliding layers  114 ,  214 . While the thickness of the intermediate layers  112 ,  212  in the exemplary embodiments of the invention corresponds to the thickness of the intermediate layers  112 ,  212  in the comparative example, the exemplary embodiments according to the invention make do with substantially thinner wear layers  113 ,  213 , the thickness d 113 , d 213  of which is only 0.65 μm in each case. This results in considerable material savings compared with the comparative example. In the embodiments according to the invention, the sliding layers  114 ,  214  each have a thickness d 114 , d 214  of 0.10 μm. Each wear layer  113 ,  213  is thus thinner even together with its respective sliding layers  114 ,  214  than the wear layer  113 ,  213  in the comparative example. 
     In a first exemplary embodiment of the invention, the components of the contact elements  11 ,  21  have the composition in percent by weight listed in Table 2. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 Base body 
                 Intermediate layer 
                 Wear layer 
                 Sliding layer 
               
               
                   
                 111, 211 
                 112, 212 
                 113, 213 
                 114, 214 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Au 
                   
                   
                   
                 99.8 
               
               
                 Co 
                   
                   
                   
                 0.2 
               
               
                 Cu 
                 100 
               
               
                 Ni 
                   
                 100 
                 89 
               
               
                 P 
                   
                   
                 11 
               
               
                 PTFE 
               
               
                   
               
            
           
         
       
     
     The intermediate layer, which consists of pure silver in the comparative example, thus consists of a nickel-phosphorous alloy in the first exemplary embodiment. This results in a cost saving, not only due to less metal used for the wear layer, but also due to the use of a lower-cost alloy. 
     The sliding layer  114 ,  214  consists of the same gold-cobalt alloy as the wear layer  113 ,  213  of the comparative example. Therefore, the sliding properties of the contact elements  11 ,  21  in the comparative example and in the first exemplary embodiment of the invention are equally good. However, the sliding layer  114 ,  214  is very thin compared to the wear layer  113 ,  213  of the comparative example, such that most of the expensive gold-cobalt alloy can be saved. 
     In a second exemplary embodiment of the electrical contact elements  11 ,  21 , their components have the composition in percent by weight shown in Table 3: 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Base body 
                 Intermediate layer 
                 Wear layer 
                 Sliding layer 
               
               
                   
                 111, 211 
                 112, 212 
                 113, 213 
                 114, 214 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Au 
                   
                   
                   
                   
               
               
                 Co 
               
               
                 Cu 
                 100 
               
               
                 Ni 
                   
                 100 
                 89 
               
               
                 P 
                   
                   
                 11 
               
               
                 PTFE 
                   
                   
                   
                 100 
               
               
                   
               
            
           
         
       
     
     Compared to the first exemplary embodiment, the metallic sliding layers  114 ,  214  have been replaced by organic sliding layers, each consisting of PTFE. It was found that by dispensing with an expensive noble metal in the third exemplary embodiment, excellent sliding properties of the contact elements  11 ,  21  can nevertheless be achieved, wherein the electrical transmission is nevertheless no worse than that of the electrical contact elements  11 ,  21  in the comparative example. 
     In a third exemplary embodiment of the invention, the intermediate layer  112 ,  212  is dispensed with, such that the contact elements  11 ,  21  have the structure depicted in  FIG. 4 , wherein the wear layer  113 ,  213  is arranged directly on the base body  111 ,  211  in each case. In contrast to the previous exemplary embodiments, the thickness d 113 , d 213  of the wear layers  113 ,  213  is 1.50 μm in each case. The components of the contact elements  11 ,  21  have the composition listed in Table 4 in percent by weight. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Base body 
                 Wear layer 
                 Sliding layer 
               
               
                   
                 111, 211 
                 113, 213 
                 114, 214 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Au 
                   
                   
                 99.8 
               
               
                   
                 Co 
                   
                   
                 0.2 
               
               
                   
                 Cu 
                 100 
               
               
                   
                 Ni 
                   
                 89 
               
               
                   
                 P 
                   
                 11 
               
               
                   
                 PTFE 
               
               
                   
                   
               
            
           
         
       
     
     By using a thicker wear layer than in the first and second exemplary embodiments of the invention, the contact elements  11 ,  21  can thus also be manufactured without using intermediate layers  112 ,  212 . Although thicker wear layers  113 ,  213  are used here than in the first two exemplary embodiments, these are still significantly thinner than the wear layers  113 ,  213  of the comparative example. 
     In a fourth exemplary embodiment of the invention, the sliding layers  114 ,  214  of the contact elements  11 ,  21  of the third exemplary embodiment are also replaced by organic sliding layers, each of which consists of PTFE, just as the sliding layers  114 ,  214  of the first exemplary embodiment were also replaced by PTFE in the second exemplary embodiment. The components of the electrical contact elements  11 ,  21  then have the composition in percent by weight shown in Table 5: 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                 Base body 
                 Wear layer 
                 Sliding layer 
               
               
                   
                 111, 211 
                 113, 213 
                 114, 214 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Au 
                   
                   
                   
               
               
                   
                 Co 
               
               
                   
                 Cu 
                 100 
               
               
                   
                 Ni 
                   
                 89 
               
               
                   
                 P 
                   
                 11 
               
               
                   
                 PTFE 
                   
                   
                 100 
               
               
                   
                   
               
            
           
         
       
     
     All five described exemplary embodiments of the electrical contact elements  11 ,  21  according to the invention enable a cost-effective replacement of the electrical contact elements  11 ,  21  according to the comparative example, without this leading to an impairment of the properties relevant for the contact elements  11 ,  21 . They are suitable for electrical operating voltages of more than 150 V.