Method and contact element for surface treatment of an electrical contact element

Abstract

To provide a cost-effective and reliable process for treating a contact surface of an electrical connector such that the initial mating force can be reduced when mating with a mating connector and such that the surface treatment does not lose its effect even under adverse environmental conditions.SOLUTION: A method for surface treatment of an electrically conductive contact element 100 for an electrical connector 300 with plasma comprises: applying a lubricant 106 to at least a partial region of a contact surface 102; and changing the contact surface of the electrically conductive contact element by plasma treatment to thereby at least partially form a coating of a solid lubricant on the at least partial region of the contact surface of the electrically conductive contact element.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method for surface treating a conductive contact element of an electrical connector. Further, the present invention relates to a conductive contact element whose surface has been treated by such a method.

Background Art

[0002] Electrical connectors and their contact elements are known in many designs. Electrical connectors are intended to be mated with a suitable mating connector to establish an electrical connection. Electrical connectors are generally used for signal transmission or power transmission. For this purpose, electrical connectors generally have conductive contact elements that contact the contact elements of the mating connector when the connectors are mated. The contact elements of one connector element are often designed as contact pins, and the contact elements of the mating connector are often designed as contact springs. When the connector and the mating connector are mated, the contact spring applies an elastic spring force to the contact pin to ensure a reliable conductive connection.

[0003] Electrical connectors are used, for example, in motor vehicles to transmit power and network-connect an electrical system and an electronic system. In motor vehicles, connectors are exposed to extreme temperature variations, vibrations, moisture, and corrosive media. As the operating temperature rises, wear increases, especially in the case of widely used tin-plated copper-based contact elements.

[0004] In particular, base metal contact surfaces containing, for example, tin, nickel, or their alloys tend to exhibit fretting corrosion ("fretting" or "scuffing") when the relative movement is small. Further, in the case of multi-pole connectors, especially during initial mating, the mating force often exceeds the required force, and it is a known problem that, for example, in the case of noble metal-based noble contact surfaces, there is a tendency for cold welding.

[0005] Therefore, in addition to high wear resistance, a small fitting force and a withdrawal force are required to facilitate the assembly and maintenance of the connector. To improve labor safety, a specific fitting force must not exceed a certain limit, especially during initial fitting.

[0006] In addition, during the fitting of the connector with the mating connector, partial abrasion occurs on the contact surface of the contact element. The wear caused by this abrasion shortens the operating time of the connector because it limits the fitting frequency of the connector.

[0007] German Patent Specification DE1020.16214693B4 describes an electrical contact element of a connector in which cavities filled with auxiliary material are arranged under the contact surface. The contact surface is pre-textured by laser irradiation. After the connector is first fitted to the mating connector, the cavities break open to allow the auxiliary material to leak out and cover the contact surface with a lubricating film. This lubricating film reduces the fitting force when the connector is fitted again. The surface treatment using an interference pattern by laser radiation, in which a dimple structure is exemplarily formed, is hereinafter referred to as the textured surface.

[0008] However, the assembly boundary conditions also define the criterion for the fitting force when the connector is first fitted to the mating connector. This initial fitting force is particularly important when assembling a connector that includes a large number of contacts. Since the connector may be further processed in a warm area, it is further necessary for the contact surface of the connector to have heat resistance. Therefore, applying a lubricating film to the contact surface of the connector is not an appropriate solution because the lubricating film evaporates at warm temperatures. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] Therefore, there is a need for a cost - effective and reliable process for treating the contact surface of an electrical connector so as to reduce the initial fitting force when fitting with a mating connector and ensure that the surface treatment does not lose its effect even under adverse environmental conditions.

Means for Solving the Problem

[0010] This problem is solved by the subject matter of the independent claims. Advantageous embodiments of the invention are the subject matter of the dependent claims.

[0011] In this context, the present invention is based on the idea of improving the surface properties of the contact surface of an electrical connector by means of plasma treatment. For this purpose, a lubricant is first applied to the contact surface so that a coating of solid lubricant is formed on the contact surface by plasma treatment.

[0012] In particular, the present invention includes a method for surface - treating a conductive contact element of an electrical connector, the conductive contact element having a metallic contact surface. In addition, a lubricant is applied to at least a partial region of the contact surface of the conductive contact element. Further, the contact surface of the conductive contact element is changed by plasma treatment, whereby a coating of solid lubricant is at least partially formed on at least a partial region of the contact surface of the conductive contact element.

[0013] The coating of solid lubricant may be, for example, carbon - based, carbonaceous, or sulfide - based. The carbon layer is understood to be a thin layer mainly composed of the chemical element carbon. This includes, for example, a graphite layer or a diamond - like carbon layer. The applied lubricant layer, which functions as an initial lubricant layer, may be, for example, an oil, grease, paste, or another solid lubricant such as graphite, carbon nanotubes, MoS2, or a mixture thereof, which is modified by plasma treatment.

[0014] Surface treatment can reduce the roughness of the contact surface of the electrical connector and achieve higher uniformity. In addition, for example, by selectively forming an intermetallic phase IMP or a nanocrystalline microstructure, the hardness of the contact surface can be increased. Each of these improved properties, which are independent of each other, reduces the initial mating force when the connector is mated with the mating connector. In addition, the change in the coefficient of friction across the entire contact surface can be reduced.

[0015] According to a further advantageous development of the invention, the contact surface of the conductive contact element has a surface texture consisting of protrusions and recesses, and the lubricant applied to the contact surface adheres particularly well.

[0016] The plasma is excited in a pressure range of 1 mbar to 8 bar, which means that a vacuum chamber is not required for plasma treatment and instead atmospheric pressure plasma can be used for plasma treatment, which is advantageous. This has the advantage that liquid chemicals may not be required at all. For this purpose, harmless gases such as nitrogen or compressed air can be used for plasma generation. Alternatively, the plasma can be excited under low vacuum or slight overpressure.

[0017] Hereinafter, the plasma is understood to be a partially or fully ionized gas. A cold plasma or a hot plasma is generated and spreads by a plasma nozzle directed at the material. Inside the nozzle, the plasma is generated by a high voltage between the stator and the rotor. By means of an arc-shaped high voltage discharge, the ionized gas is directed at the surface to be treated. For example, hydrogen, argon, nitrogen, or compressed air can be used as the gas to be ionized.

[0018] In order to form the coating of the above solid lubricant from the applied lubricant layer, it is advantageous for the power of the plasma to be in the range of 50 W to 5 kW.

[0019] According to a further advantageous development of the invention, cavities filled with auxiliary material are encapsulated under the contact surface of the conductive contact element. These filled cavities can rupture while the connector first mates with the mating connector, allowing the auxiliary material to leak out and produce its effect. Thereby, the mating force can be reduced in the first mating process, and the mating force can also be reduced for all subsequent mating processes.

[0020] The auxiliary material, also called an additive, is a substance added in a relatively small amount to achieve or improve certain properties.

[0021] The cavity is understood to be an artificially formed cavity below the surface. The arrangement of the cavity below the contact surface means that the cavity has at most a narrow-dimensioned outlet such that the cavity has no outlet to the contact surface or does not form a through-hole from the contact surface to the cavity so that the auxiliary material filled in the cavity cannot be reached.

[0022] According to another advantageous embodiment of the invention, the auxiliary material is selected from the group consisting of antioxidants, corrosion inhibitors, lubricants, other solid lubricants, and acids. By this group of substances, after leakage to the contact surface of the connector, the mating of this connector with the mating connector is facilitated.

[0023] According to a further advantageous development of the invention, the plasma treatment of the conductive contact element is part of a continuous process. This has the advantage that the edges of the contact surface are also uniformly treated. As a result, a uniformly thin layer of solid lubricant can be advantageously obtained, so that the contact surface has high uniformity.

[0024] According to a further advantageous development of the invention, the plasma treatment includes irradiation with a plasma flame, and the dwell time of the conductive contact element in the plasma flame is 5 ms to 500 ms. After this short dwell time, the above-mentioned favorable effects already occur, whereby a large number of components can be processed in a short time.

[0025] According to a further advantageous development of the invention, the plasma frame jets out from the plasma nozzle, and the distance from the contact surface to the plasma nozzle is 5 mm to 100 mm. By this targeted plasma treatment, it can be easily integrated into existing manufacturing equipment without the need for additional shielding precautions and compliance with safety regulations becomes possible.

[0026] According to a further advantageous development of the invention, the coating of the solid lubricant formed by plasma treatment has a thickness of 1 nm to 300 nm. This thin coating enables the use of plasma treatment for a wide variety of connector types and allows such connectors to be fitted to mating connectors without the need to adjust the dimensions.

[0027] According to a further advantageous development of the invention, the thickness of the lubricant applied to the contact surface of the conductive contact element is 0.1 μm to 5 μm. The thinly applied layer adheres particularly well to rough metal contact surfaces.

[0028] The invention further relates to a related conductive contact element of an electrical connector having a metal contact surface. In addition, the contact surface has a coating of a solid lubricant formed from a lubricant layer by treatment with plasma at least partially. This conductive contact element has the advantage of having a lower initial mating force from the start than conventional contact elements. In addition, the standard deviation of the coefficient of friction is reduced, which is particularly important for connectors containing a large number of contacts.

[0029] Also, it is advantageous if a cavity filled with an auxiliary material is encapsulated under the contact surface of the conductive contact element. When the contact element first contacts the mating contact, the cavity breaks open, the auxiliary material leaks out, and the fitting force can be reduced during the first fitting process and for all subsequent fitting processes. By having the filled cavity located under the contact surface, adverse effects such as rubberification can be avoided. In addition, unwanted loss of the auxiliary material due to solid embedding is eliminated.

[0030] According to another advantageous embodiment of the conductive contact element, the auxiliary material is selected from the group consisting of antioxidants, corrosion inhibitors, lubricants, another solid lubricant, and acids. These substances can reduce wear caused by abrasion and increase the fitting frequency of the connector.

[0031] According to a further advantageous embodiment of the conductive contact element, the metal contact surface comprises tin, and / or nickel, and / or silver, and / or copper, and / or an alloy of tin, nickel, silver, and copper. These materials have rust resistance and heat resistance, thereby guaranteeing the life of the connector.

[0032] According to a further advantageous development of the invention, the square roughness of the surface in the fitting direction is less than 0.3 μm. This value is smaller than the value measured for a surface that has not been modified by the plasma treatment according to the invention. Thus, a small roughness can be achieved, whereby the surface becomes more uniform, and thus the fitting of the connector with the mating connector is enhanced, which is advantageous.

[0033] Surface roughness is the degree of unevenness of a solid surface that is smaller than the shape or undulation of the solid surface but larger than the roughness of the crystal lattice structure. Roughness can affect material properties such as friction. One of the roughness characteristics is the root mean square roughness. This can be detected by optical measurement methods. The evaluation of the measurement is based on the standards of the DIN EN ISO 4287 and DIN EN ISO 11562 series. For fitting a connector to a mating connector, the roughness in the fitting direction is particularly important. Therefore, in this case, the measurement is aligned in the fitting direction. In one embodiment, this alignment can be performed along the surface texture. As in the above embodiment, when the surface texture has ridges and recesses, the alignment of the measurement is performed along the ridges and recesses.

[0034] To understand the present invention more fully, the present invention will be described in more detail with reference to the examples of embodiments shown in the following drawings. In this context, the same parts are denoted by the same reference numerals and the same part designations. Furthermore, some features or combinations of features of different embodiments illustrated and described may also represent independent solutions of the present invention or solutions according to the present invention.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0036] Figure 1 shows a first process step of the method according to the invention by means of a cross-sectional view of a first embodiment of the contact surface of a conductive contact element.

[0037] The method is for surface-treating a conductive contact element 100. The contact element 100 of the electrical connector 300 is conductive and includes a base material 104. The base material 104 can include, for example, tin, nickel, silver, copper, or an alloy of tin, nickel, silver, copper, and / or other elements. One side of the contact element 100 forms a metal contact surface 102. When the connector 300 is mated with a mating connector, the contact surface 102 contacts the contact surface of the mating connector (not shown).

[0038] A lubricant 106 is applied to at least a partial region of the contact surface 102. For example, the lubricant 106 can include oil, grease, paste, acid, or another solid lubricant such as graphite, carbon nanotubes, MoS2, or a mixture thereof. The thickness of the applied lubricant can have a value of 0.1 μm to 5 μm.

[0039] In an advantageous embodiment, the contact surface 102 of the contact element 100 can have a surface texture 112 of protrusions 124 and recesses 122. These protrusions 124 and recesses 122 can be formed at least partially periodically and alternately. In this regard, the recesses 122 form grooves and the protrusions 124 form the walls between the grooves. The protrusions can be, by way of example, about 0.1 μm to 2 μm. However, it should be understood that it is by no means necessary for the surface texture 112 of the contact surface 102 to include protrusions 124 and recesses 122. The contact surface 102 can have any surface texture 112, for example, smooth or having another roughness.

[0040] Figure 2 shows another embodiment of the contact surface 102 of the conductive contact element 200 in a first process step of the method according to the invention.

[0041] The contact element 200 of the electrical connector 400 is conductive and includes a base material 204. The base material 204 can include, for example, tin, nickel, silver, copper, or an alloy of tin, nickel, silver, copper, and / or other elements. One side of the contact element 200 forms a metal contact surface 202, and when the connector 400 is mated with a mating connector, the contact surface 202 contacts the contact surface of the mating connector.

[0042] In the illustrated embodiment, a cavity 208 is encapsulated under the contact surface 202, and the cavity 208 is filled with an auxiliary material 210. In the illustrated embodiment, the cavities 208 are equally spaced from each other under the contact surface 202. In this embodiment, the surface texture 212 has exemplary ridges 224 and recesses 222. These ridges 224 and recesses 222 can be formed at least partially alternately in a periodic manner. In this regard, the recesses 222 form grooves, and the ridges 224 form the walls between the grooves. The ridges can be, for example, about 0.1 μm to 2 μm.

[0043] It should be understood that the cavities 208 may be irregularly spaced from each other at various depths under the contact surface 202. Further, when the contact surface 202 does not have ridges 224 and recesses 222, the cavity 208 may be encapsulated under the contact surface 202. For the method according to the present invention, it is not necessary for the surface texture 212 to include ridges 224 and recesses 222. It should be understood that the contact surface 202 may have any surface texture 212, for example, smooth or having other roughnesses.

[0044] The auxiliary material 210 encapsulated in the cavity 208 can include, for example, oil, grease, paste, or another solid lubricant such as graphite, carbon nanotubes, MoS2, or a mixture thereof. The lubricant 206 is applied to at least a partial region of the contact surface 202. For example, the lubricant 206 can include oil, grease, paste, acid, or another solid lubricant such as graphite, carbon nanotubes, MoS2, or a mixture thereof. The thickness of the applied lubricant can have a value of 0.1 μm to 5 μm.

[0045] FIG. 3 shows the contact element 100 according to the first embodiment in a further process step of the method according to the invention.

[0046] FIG. 3 is a schematic view of the surface treatment of the contact element 100 using plasma. In one possible embodiment, a plasma generator 118 for controlling and monitoring the plasma system is schematically shown, and the plasma nozzle 114 is directed towards the material to be processed. The directed plasma nozzle 114 is used to generate and propagate the plasma. Various nozzle systems such as a single nozzle or a rotating nozzle can be used as the plasma source. The contact surface 102 is processed using the plasma frame 116 from the plasma nozzle 114. The distance from the plasma nozzle 114 to the contact surface 102 ranges from 5 mm to 100 mm.

[0047] In this process, a plasma frame 116 in a pressure range of 1 mbar to 8 bar can be generated, and thus, for example, the surface treatment can also be performed at atmospheric pressure. The power of the plasma frame 116 ranges from 50 W to 5 kW. In this case, the treatment of the contact surface 102 is part of a continuous process in which the contact element 100 passes through the plasma frame 116 at a speed of, for example, 100 mm / s or 200 mm / s. Thereby, the residence time of the contact surface 102 under the plasma frame 116 is 5 ms to 500 ms.

[0048] However, it is clear that the values shown are for illustrative purposes only and are not intended to limit the present invention in any way. The passing speed, distance, and residence time can all be adjusted as desired and adapted to different values of the power of the plasma frame.

[0049] FIG. 4 shows an exemplary first embodiment of the contact surface 102 of the conductive contact element 100 after surface treatment by plasma. By plasma treatment, a coating 120 of a solid lubricant, preferably carbon, is formed on at least a partial region of the contact surface 102. This coating 120 of the solid lubricant can have a thickness of 1 nm to 300 nm and can be transparent. Thus, at least a part of the lubricant applied in the previous process step has been at least partially changed to a coating of a solid lubricant, preferably consisting of carbon.

[0050] In a second embodiment (not shown), when cavities filled with auxiliary material are encapsulated under the contact surface 102 as in the above-described second embodiment of the previous process step, it is fully possible to form a coating 120 of a solid lubricant on the contact surface 202 in the same manner. The cavities remain unchanged by the plasma treatment.

[0051] Advantageously, in addition to preferably a carbon or carbon-containing coating, the surface properties of the contact element can be improved by plasma treatment. Thus, the unevenness of the contact surface is reduced by the treatment, resulting in a smaller root mean square roughness.

[0052] Experimental studies have shown that the root mean square roughness of the surface after treatment by plasma is less than 0.3 μm. This value is 0.1 μm smaller than the value of the root mean square roughness of the surface not treated by the process according to the present invention.

[0053] It is advantageous that a higher hardness of the coating surface can be further achieved. The hardness of the connector surface can be determined by nanoindentation. An indenter with a known geometry is pressed into the surface to be tested with a defined force curve. When a specific maximum force is reached, the indenter is released again in a controlled manner. The indentation depth is recorded both while the load is being applied and while the load is being removed. Various parameters can be calculated from the applied force, the shape of the indenter, and the indentation depth. To measure the surface hardness, approach at least two measurement points at a predetermined distance. The average value of all measurement points on the surface can be used as a comparison reference for the surface hardness. The measurement is first performed on the untreated surface and then a second time after plasma treatment. In an exemplary measurement with 51 measurement points spaced 100 μm apart, an exemplary average hardness value of 450 N / mm 2 can be determined for the untreated surface. However, for the textured and plasma-treated surfaces, an exemplary average value of 750 N / mm 2 can be determined.

[0054] Thus, the surface exhibits a higher hardness after plasma treatment. Comparing the average values, a hardness increase of 40% - 80% is seen, especially for the contact surface that was textured before plasma treatment compared to the untreated surface.

[0055] Finally, the spatially resolved properties of the plasma-treated surface with respect to roughness, hardness, and chemical composition can advantageously show a much more uniform image than, for example, punched or electroplated contacts.

[0056] These advantageous properties occur independently of each other and make the change in the coefficient of friction smaller independently of each other. Thus, by the method according to the invention, a narrower distribution of the standard deviation of the coefficient of friction can be demonstrated within the surface.

[0057] It should be noted that it is quite possible to achieve the same advantageous properties using different plasma generation methods. For example, a plasma frame can be generated in a low-pressure plasma chamber under vacuum.

Explanation of symbols

[0058] 100, 200 contact elements 102, 202 contact surfaces 104, 204 substrates 106, 206 lubricants 208 cavity 210 auxiliary material 112, 212 surface texture 114 plasma nozzle 116 plasma frame 118 plasma generator 120 coating of solid lubricant 122, 222 recesses 124, 224 protrusions d distance from the plasma nozzle to the contact surface 300, 400 connectors

Claims

1. A method for surface treating the conductive contact elements (100, 200) of an electrical connector (300, 400), wherein the conductive contact elements (100, 200) include metal contact surfaces (102, 202), the method comprising: applying a lubricant (106, 206) to at least a partial region of the metal contact surfaces (102, 202) of the conductive contact elements (100, 200); then changing the metal contact surfaces (102, 202) of the conductive contact elements (100, 200) having the at least partial region coated with the lubricant (106, 206) by plasma treatment, thereby at least partially forming a coating (120) of a changed solid lubricant from the applied lubricant (106, 206) on the at least partial region of the metal contact surfaces (102, 202) of the conductive contact elements (100, 200); in the plasma treatment, the plasma frame (116) ejected from the plasma nozzle (114) is irradiated; the thickness of the lubricant (106, 206) applied to the metal contact surfaces (102, 202) of the conductive contact elements (100, 200) is 0.1 μm to 5 μm; the coating (120) of the solid lubricant formed by the plasma treatment has a thickness of 1 nm to 300 nm.

2. The method according to claim 1, wherein the metal contact surfaces (102, 202) of the conductive contact elements (100, 200) have a surface texture of protrusions (124, 224) and recesses (122, 222).

3. The method according to claim 1, wherein the plasma is excited in a pressure range of 1 mbar to 8 bar.

4. The method according to claim 1, wherein the power of the plasma is in the range of 50 W to 5 kW.

5. The method according to claim 1, wherein a cavity (208) filled with an auxiliary material (210) is encapsulated under the metal contact surfaces (102, 202) of the conductive contact elements (100, 200). **Claim 6** The method according to claim 5, wherein the auxiliary material (210) is selected from the group consisting of antioxidants, corrosion inhibitors, lubricants, other solid lubricants, and acids. **Claim 7** The method according to claim 1, wherein the treatment of the conductive contact elements (100, 200) by the plasma is part of a continuous process. **Claim 8** The method according to claim 1, wherein the residence time of the conductive contact elements (100, 200) in the plasma frame (116) is from 5 ms to 500 ms. **Claim 9** The method according to claim 1, wherein the distance from the metal contact surface to the plasma nozzle (114) is from 5 mm to 100 mm. **Claim 10** The method according to claim 1, wherein the plasma is an ionized gas and is generated within the plasma nozzle.

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