Composite coating structure and preparation method therefor, conductive terminal and connector

Abstract

The present disclosure belongs to the technical field of electrical engineering. Disclosed are a composite coating structure and a preparation method therefor, a conductive terminal and a connector. The composite coating structure comprises a substrate, an intermediate coating stacked on the substrate and a noble metal coating stacked on the intermediate coating, wherein the substrate is a copper substrate or a copper alloy substrate; and the intermediate coating comprises first intermediate coatings and second intermediate coatings which are alternately stacked, each of the first intermediate coatings and the second intermediate coatings is a nickel-tungsten coating or a cobalt-tungsten coating, and the tungsten content of the first intermediate coating is different from that of the second intermediate coating. The composite coating structure can be used for a terminal of a connector, and endows the terminal with good electrical contact performance, good corrosion resistance, good insertion / withdrawal endurance, relatively low internal stress of a coating, and relatively low costs.

Description

Composite coating structure and its preparation method, conductive terminals and connectors

[0001] This application claims priority to Chinese Patent Application No. 202411612056.2, filed on November 12, 2024, entitled "Composite Coating Structure and Preparation Method Thereof, Conductive Terminal and Connector", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to the field of electrical technology, and in particular to composite coating structures and their preparation methods, conductive terminals and connectors. Background Technology

[0003] A terminal refers to the metal contact portion of a connector, used for electrical connection between the connector and other electronic devices. Common terminal types include pins, plugs, slots, and leads. To enhance contact reliability, improve conductivity, and prevent oxidation and corrosion, a metal plating is usually applied to the surface of the terminal.

[0004] Currently, the metal plating applied to the surface of terminals is typically a precious metal plating, such as gold or silver. However, when the precious metal plating comes into contact with the copper substrate of the terminal, it is prone to current corrosion due to potential difference, resulting in pinholes or other surface defects on the precious metal plating surface. Related technologies have attempted to overcome this problem by increasing the thickness of the precious metal plating; however, the increased thickness significantly increases the amount of precious metal used, leading to higher costs.

[0005] Public content

[0006] This disclosure provides a composite coating structure and its preparation method, as well as conductive terminals and connectors, which can solve the technical problems existing in related technologies. Specifically, the technical solutions are as follows.

[0007] On one hand, a composite coating structure is provided, the composite coating structure including a substrate, an intermediate coating layer stacked on the substrate, and a noble metal coating layer stacked on the intermediate coating layer; wherein, the substrate is a copper substrate or a copper alloy substrate; the intermediate coating layer includes a first intermediate coating layer and a second intermediate coating layer stacked alternately, the first intermediate coating layer and the second intermediate coating layer are both nickel-tungsten coating layers or cobalt-tungsten coating layers, and the tungsten content of the first intermediate coating layer is different from that of the second intermediate coating layer.

[0008] The composite coating structure provided in this disclosure, by setting an intermediate coating layer between the substrate and the noble metal coating layer, achieves two objectives: firstly, the noble metal coating layer establishes and maintains a stable resistance in the composite coating structure; secondly, by using a nickel-tungsten or cobalt-tungsten coating layer as the intermediate coating layer, the thickness of the noble metal coating layer is reduced to lower costs while avoiding defects such as pinholes. Furthermore, the excellent corrosion resistance and wear resistance of the intermediate coating layer itself enhance the mechanical properties of the composite coating structure. Specifically, the intermediate coating layer includes alternating layers of a first intermediate coating layer and a second intermediate coating layer, with different tungsten contents in the first and second intermediate coating layers. This difference in tungsten content results in different grain sizes within the coating. Higher tungsten content leads to lower and finer grain sizes, while lower tungsten content results in higher grain sizes. By alternately stacking first and second intermediate coatings with different tungsten contents, the grain orientation and size distribution between the layers of the intermediate coatings can be altered. On one hand, this effectively avoids through-type vacancy defects in the intermediate coatings, which is more beneficial for enhancing the wear resistance and corrosion resistance of the composite coating structure. On the other hand, it can also change the interlayer corrosion direction of the intermediate coatings and slow down the corrosion rate, which is more beneficial for enhancing the corrosion resistance of the composite coating structure. Furthermore, this can reduce the interlayer stress of the intermediate coatings, improve the mechanical properties of the composite coating structure, thereby further optimizing its wear resistance and corrosion resistance and extending its service life. Based on the above, the composite coating structure provided in this embodiment can be used for connector terminals, giving the terminals excellent electrical contact performance, excellent corrosion resistance, excellent insertion and extraction resistance, low coating internal stress, and low cost.

[0009] In some possible implementations, when the difference in tungsten content between the first intermediate coating and the second intermediate coating is greater than a set threshold, both the substrate and the noble metal coating are in contact with the one with the lower tungsten content in the first intermediate coating and the second intermediate coating.

[0010] In some possible implementations, the atomic percentage of tungsten in the first intermediate coating is 1%-10%.

[0011] In some possible implementations, the atomic percentage of tungsten in the second intermediate coating is 2%-40%.

[0012] In some possible implementations, the thickness of the first intermediate coating is 0.05 μm-4 μm, and the thickness of the second intermediate coating is 0.05 μm-4 μm.

[0013] In some possible implementations, the total number of layers of the first intermediate coating and the second intermediate coating is 3-15.

[0014] In some possible implementations, the precious metal coating is made of gold, silver, palladium, or an alloy thereof, and the thickness of the precious metal coating is 0.01 μm to 1.27 μm.

[0015] On the other hand, a method for preparing a composite coating structure is provided, wherein the composite coating structure is as described in any of the above descriptions, and the method for preparing the composite coating includes: forming an alternately arranged first intermediate coating and a second intermediate coating on a substrate by a thin film deposition process to obtain an intermediate coating, and then forming a noble metal coating on the intermediate coating to obtain the composite coating structure.

[0016] In some possible implementations, the thin film deposition process is an electroplating process, and the current density corresponding to forming the first intermediate coating is different from the current density corresponding to forming the second intermediate coating, and the range of the current density is 0.2ASD-4ASD.

[0017] On another front, a conductive terminal is provided, wherein the conductive terminal adopts the above-mentioned composite plating structure, and the substrate of the composite plating structure is the conductive substrate of the conductive terminal.

[0018] In another aspect, a connector is provided, the connector including an insulating terminal block and conductive terminals fixedly connected to the insulating terminal block, the conductive terminals being as described above. Attached Figure Description

[0019] Figure 1 is a schematic diagram of an exemplary composite coating structure provided in an embodiment of this disclosure;

[0020] Figure 2 is a schematic diagram of another exemplary composite coating structure provided in the embodiments of this disclosure.

[0021] The reference numerals in the attached figures represent: 100, substrate; 200, intermediate coating; 201, first intermediate coating; 202, second intermediate coating; 300, precious metal coating. Detailed Implementation

[0022] Terminals, also known as electrical interfaces, are used for electrical connections between connectors and other electronic devices. Terminals require insertion and removal, which introduces friction when they come into contact with the wires of other electronic components. Frequent and prolonged insertion and removal can cause wear on the terminal surface, leading to poor electrical contact. To enhance contact reliability, improve conductivity, and prevent oxidation and corrosion, a metal plating is typically applied to the surface of the terminal.

[0023] Currently, the metal plating on the terminal surface is typically a precious metal plating, such as gold or silver. However, when this precious metal plating comes into contact with the copper substrate of the terminal, it is prone to current corrosion due to potential difference, resulting in pinholes or other surface defects on the precious metal plating surface. During use, corrosive media in the atmosphere can corrode the substrate through these surface defects, causing connector contact failures and poor signal transmission stability. Related technologies have attempted to overcome this problem by increasing the thickness of the precious metal plating; however, increasing the thickness of the precious metal plating significantly increases the amount of precious metal consumed, leading to higher costs.

[0024] To address the technical problems existing in related technologies, this disclosure provides a composite coating structure, as shown in Figure 1. The composite coating structure includes a substrate 100, an intermediate coating 200 stacked on the substrate 100, and a noble metal coating 300 stacked on the intermediate coating 200. The substrate 100 is a copper substrate 100 or a copper alloy substrate 100. The intermediate coating 200 includes alternatingly stacked first intermediate coatings 201 and second intermediate coatings 202. Both the first intermediate coating 201 and the second intermediate coating 202 are nickel-tungsten coatings or cobalt-tungsten coatings, and the tungsten content of the first intermediate coating 201 is different from that of the second intermediate coating 202.

[0025] The substrate 100 is a copper substrate 100 or a copper alloy substrate 100, enabling the composite plating structure to be applied to electrical connectors, such as terminals, to provide excellent mechanical and electrical properties. For example, some suitable copper alloy substrates 100 may be brass, phosphor bronze, silicon bronze, zirconium copper, copper, etc., or the copper alloy substrate 100 may also be a known copper alloy product, such as copper alloy C7025.

[0026] Using a nickel-tungsten plating layer or a cobalt-tungsten plating layer as the intermediate plating layer 200 gives the intermediate plating layer 200 at least the following advantages: dense structure, high wear resistance, strong corrosion resistance, strong oxidation resistance, and strong heat resistance.

[0027] In this embodiment of the present disclosure, along the direction from the substrate 100 to the noble metal plating layer 300, the first intermediate plating layer 201 and the second intermediate plating layer 202 are alternately stacked, and the number of the first intermediate plating layer 201 and the second intermediate plating layer 202 is at least one layer, and further, both can be multiple layers.

[0028] In this embodiment, both the first intermediate coating 201 and the second intermediate coating 202 are nickel-tungsten coatings, or both are cobalt-tungsten coatings. The same material is used for both to ensure that the crystal lattice between the layers is as compatible as possible, reducing interface defects. The tungsten content of the first intermediate coating 201 can be greater than that of the second intermediate coating 202, or the tungsten content of the first intermediate coating 201 can be less than that of the second intermediate coating 202. That is, the alloy compositions of the first intermediate coating 201 and the second intermediate coating 202 are different, so that although their crystal structures are generally compatible, they are not completely identical. This enhances the corrosion resistance and wear resistance of the composite coating structure.

[0029] The following section, in conjunction with the structural arrangement of the intermediate coating 200, briefly explains the mechanism by which the intermediate coating 200 enhances the corrosion resistance and wear resistance of the composite coating structure.

[0030] During the deposition process of a metal coating, metal grains are stacked sequentially along the thickness of the coating. Vacancy defects typically exist during this stacking process. If only the first intermediate coating 201 or only the second intermediate coating 202 is deposited, the vacancy defects will continue as the thickness of the metal coating increases, eventually penetrating the metal coating along its thickness. In this embodiment, the intermediate coating 200 is configured to include alternating layers of the first intermediate coating 201 and the second intermediate coating 202. The tungsten content of the first intermediate coating 201 and the second intermediate coating 202 differs, resulting in different grain arrangements and sizes. When they are alternately stacked, the grain growth trend is interrupted and disrupted between any two adjacent layers. Correspondingly, vacancy defects in the metal coating are also interrupted, preventing the formation of vacancy defects penetrating the top and bottom of the intermediate coating 200. This is clearly advantageous for improving the corrosion resistance and wear resistance of the intermediate coating 200.

[0031] For nickel-tungsten or cobalt-tungsten coatings, higher tungsten content results in lower and finer grain size, and consequently, stronger corrosion resistance, hardness, and heat resistance. Conversely, lower tungsten content leads to higher grain size and lower corrosion resistance. Taking the first intermediate coating 201 as an example where the tungsten content is lower than that of the second intermediate coating 202, the lower tungsten content of the first intermediate coating 201 results in lower corrosion resistance and a faster corrosion rate. The corrosion direction of the low-tungsten intermediate coating 200 tends to be along the coating thickness direction (i.e., the vertical direction in Figure 1). When a corrosion defect extending along the thickness direction appears in the first intermediate coating 201, the corrosion defect in the first intermediate coating 201 is interrupted at the second intermediate coating 202. Furthermore, the second intermediate coating 202 has a higher tungsten content, resulting in stronger corrosion resistance than the first intermediate coating 201, leading to a slower corrosion rate. These factors prevent the corrosion defect extending along the coating thickness direction from continuing from the first intermediate coating 201 to the second intermediate coating 202. Instead, the corrosion direction changes in the second intermediate coating 202, extending along the coating's planar direction (i.e., the horizontal direction in Figure 1). Therefore, in this embodiment, first intermediate coatings 201 and second intermediate coatings 202 with different tungsten contents are alternately stacked, thereby changing the corrosion direction of the intermediate coating 200 at different layer interfaces. For example, the corrosion direction changes from along the coating thickness direction to along the coating's planar direction. The change in corrosion direction represents a change in corrosion path, effectively preventing the corrosion path from directly penetrating the substrate 100 and the precious metal coating 300 along the thickness direction of the coating. This is particularly beneficial for slowing down the corrosion rate of the composite coating structure.

[0032] Moreover, the alternating stacking of the first intermediate plating layer 201 and the second intermediate plating layer 202 allows the grains at the interface between them to fill the gaps between them, resulting in a more compact grain arrangement at the interface. This is also very beneficial for reducing the internal stress at the interface between the first intermediate plating layer 201, the second intermediate plating layer 202, and the interface between them.

[0033] In summary, the composite coating structure provided in this embodiment achieves several advantages. Firstly, by setting an intermediate coating 200 between the substrate 100 and the noble metal coating 300, the noble metal coating 300 establishes and maintains a stable resistance in the composite coating structure. Secondly, by using a nickel-tungsten or cobalt-tungsten coating as the intermediate coating 200, the thickness of the noble metal coating 300 is reduced to lower costs, while preventing defects such as pinholes. Furthermore, the excellent corrosion resistance and wear resistance of the intermediate coating 200 enhance the mechanical properties of the composite coating structure. Specifically, the intermediate coating 200 includes alternating layers of a first intermediate coating 201 and a second intermediate coating 202. The tungsten content of the first intermediate coating 201 differs from that of the second intermediate coating 202. This difference in tungsten content results in different grain sizes within the coating. Higher tungsten content leads to lower and finer grain sizes, while lower tungsten content results in higher grain sizes. By alternately stacking a first intermediate plating layer 201 and a second intermediate plating layer 202 with different tungsten contents, the grain orientation and size distribution between the layers of the intermediate plating layer 200 can be changed. On the one hand, this effectively avoids through-type vacancy defects in the intermediate plating layer 200, which is more beneficial for enhancing the wear resistance and corrosion resistance of the composite plating structure. On the other hand, it can also change the interlayer corrosion direction of the intermediate plating layer 200 and slow down the corrosion rate, which is more beneficial for enhancing the corrosion resistance of the composite plating structure. Furthermore, it can reduce the interlayer stress of the intermediate plating layer 200 to improve the mechanical properties of the composite plating structure, thereby further optimizing its wear resistance and corrosion resistance and extending its service life. Based on the above, the composite plating structure provided by the embodiments of this disclosure can be used for connector terminals and at least gives the terminals the following advantages: excellent electrical contact performance, excellent corrosion resistance, excellent insertion and extraction resistance, low plating internal stress, and low cost.

[0034] In this embodiment, the intermediate plating layers 200 that are in contact with the substrate 100 and the precious metal plating layer 300 can all be the first intermediate plating layer 201, or all be the second intermediate plating layer 202. Alternatively, one of the first intermediate plating layer 201 and the second intermediate plating layer 202 can be in contact with the substrate 100 and the other can be in contact with the precious metal plating layer 300. The appropriate intermediate plating layer can be selected according to actual needs.

[0035] Taking an example where both the substrate 100 and the precious metal plating 300 are in contact with the first intermediate plating layer 201, the first intermediate plating layer 201 can be multi-layered, and the second intermediate plating layer 202 can be at least one layer, as shown in Figure 1. Taking a total of 5 intermediate plating layers 200 as an example, the structural arrangement of the intermediate plating layers 200 along the direction from the substrate 100 to the precious metal plating layer 300 is as follows: First intermediate plating layer 201 - Second intermediate plating layer 202 - First intermediate plating layer 201 - Second intermediate plating layer 202 - First intermediate plating layer 201. The number of the first intermediate plating layer 201 and the second intermediate plating layer 202 can be adaptively adjusted according to the total number of intermediate plating layers 200.

[0036] Taking the example where the substrate 100 is in contact with the first intermediate plating layer 201 and the precious metal plating layer 300 is in contact with the second intermediate plating layer 202, the number of both the first intermediate plating layer 201 and the second intermediate plating layer 202 can be set to multiple layers, as shown in Figure 2. Taking a total of 6 layers for the intermediate plating layer 200, the structural arrangement of the intermediate plating layer 200 along the direction from the substrate 100 to the precious metal plating layer 300 is as follows: first intermediate plating layer 201 - second intermediate plating layer 202 - first intermediate plating layer 201 - second intermediate plating layer 202 - first intermediate plating layer 201 - second intermediate plating layer 202. The number of the first intermediate plating layer 201 and the second intermediate plating layer 202 can be adaptively adjusted according to the total number of intermediate plating layers 200.

[0037] In some examples, when the difference in tungsten content between the first intermediate coating 201 and the second intermediate coating 202 is greater than a set threshold, both the substrate 100 and the noble metal coating 300 are in contact with the phase with the lower tungsten content in the first intermediate coating 201 and the second intermediate coating 202.

[0038] Using the atomic percentage of tungsten as a comparison standard for tungsten content, the threshold value can be any value between 5% and 10%. For example, when the difference in the atomic percentage of tungsten in the first intermediate coating 201 and the second intermediate coating 202 is greater than 5%, 6%, 7%, 8%, 9%, or 10%, the substrate 100 and the noble metal coating 300 can both be in contact with the phase with the lower tungsten content in the first intermediate coating 201 and the second intermediate coating 202. For example, the tungsten content of the first intermediate plating layer 201 can be lower than that of the second intermediate plating layer 202. That is, the copper or copper alloy substrate 100 is in contact with the first intermediate plating layer 201 with a lower tungsten content, and the precious metal plating layer 300 is also in contact with the first intermediate plating layer 201 with a lower tungsten content (see Figure 1). With this plating arrangement, on the one hand, the stress of the first intermediate plating layer 201 with a low tungsten content is smaller, making its interface matching with the substrate 100 and the precious metal plating layer 300 stronger. On the other hand, the internal stress generated by electroplating the first intermediate plating layer 201 with a low tungsten content is also correspondingly smaller, which is beneficial to enhancing the mechanical properties of the composite plating structure.

[0039] When the difference in tungsten content between the first intermediate plating layer 201 and the second intermediate plating layer 202 is less than or equal to a set threshold, both the substrate 100 and the precious metal plating layer 300 can contact either the first intermediate plating layer 201 or the second intermediate plating layer 202. It is not excluded that the substrate 100 and the precious metal plating layer 300 can also contact the one with the higher tungsten content between the first intermediate plating layer 201 and the second intermediate plating layer 202. For example, if the tungsten content of the first intermediate plating layer 201 is greater than that of the second intermediate plating layer 202, the copper or copper alloy substrate 100 can contact the first intermediate plating layer 201 with the higher tungsten content, and the precious metal plating layer 300 can also contact the first intermediate plating layer 201 with the higher tungsten content. In this plating arrangement, the first intermediate plating layer 201 has a higher plating content, a smaller grain size, and higher grain refinement, making it easier to fill pores and other defects on the surfaces of the substrate 100 and the precious metal plating layer 300, thereby facilitating the formation of a plating layer with tightly packed metal particles and a smooth surface.

[0040] When the first intermediate coating 201 is configured as multiple layers, the tungsten content in the multiple layers of the first intermediate coating 201 can be the same, partially the same while another part is different, or even different from each other. Taking a three-layer configuration of the first intermediate coating 201 as an example, along the bottom-up direction, the tungsten content of the three layers of the first intermediate coating 201 can be the same; or the tungsten content of the three layers of the first intermediate coating 201 can be different from each other (for example, gradually increasing, further, the atomic percentage of tungsten increases by 1%-3%; or gradually decreasing, further, the atomic percentage of tungsten decreases by 1%-3%, etc.); or the tungsten content of the first layer of the first intermediate coating 201 and the second layer of the first intermediate coating 201 can be the same, and the tungsten content of the third layer of the first intermediate coating 201 can be further increased or decreased compared to the former two.

[0041] Similarly, when the second intermediate coating 202 is configured as multiple layers, the tungsten content in the multiple layers of the second intermediate coating 202 can be the same, partially the same and partially different, or different from each other. Taking the second intermediate coating 202 as a three-layer example, along the bottom-up direction, the tungsten content of the three first intermediate coatings 201 can be the same; or the tungsten content of the three first intermediate coatings 201 can be different from each other (for example, gradually increasing, further, the atomic percentage of tungsten increases by 5%-10%; or gradually decreasing, further, the atomic percentage of tungsten decreases by 5%-10%, etc.); or the tungsten content of the first second intermediate coating 202 and the second second intermediate coating 202 can be the same, and the tungsten content of the third second intermediate coating 202 can be further increased or decreased compared to the former two.

[0042] In this embodiment of the disclosure, for the coating with lower tungsten content in the first intermediate coating 201 and the second intermediate coating 202, the atomic percentage of tungsten is 1%-10%. Taking the first intermediate coating 201 as an example of a low-tungsten content coating, the atomic percentage of tungsten in each of the multiple first intermediate coatings 201 is independently 1%-10%. For example, some examples of the atomic percentage of tungsten in the first intermediate coating 201 can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, etc.

[0043] This embodiment of the invention achieves the purpose of refining the grains of the intermediate coating 200 by controlling the atomic percentage of tungsten in the low-tungsten content intermediate coating 200 to 1%-10%. At the same time, since the coating has not yet reached the amorphous state, its stress is relatively small, effectively avoiding problems such as cracking of the intermediate coating 200.

[0044] In this embodiment of the disclosure, for the first intermediate coating 201 and the second intermediate coating 202, where the tungsten content is higher, the atomic percentage of tungsten is 2%-40%. For example, the atomic percentage of tungsten in the high-tungsten-content intermediate coating 200 can be 2%-10%, 10%-20%, 10%-30%, 20%-30%, 20%-40%, etc. The tungsten content of the high-tungsten-content intermediate coating 200 can be arbitrarily selected within the above range, as long as its tungsten content is greater than that of the low-tungsten-content intermediate coating 200, thereby creating a difference in the grain arrangement between the two, thus interrupting the trend of vacancy defects inside the coating.

[0045] This embodiment of the invention, by alternately stacking intermediate coatings 200 with 1%-10% tungsten content and intermediate coatings 200 with 2%-40% tungsten content, effectively improves the corrosion resistance and wear resistance of the coatings, while also effectively preventing the intermediate coatings 200 from cracking, collapsing and other adverse problems.

[0046] Taking the second intermediate coating 202 as an example of a high tungsten content coating, the atomic percentage of tungsten in each of the multiple second intermediate coatings 202 is independently 2%-40%.

[0047] Furthermore, the tungsten content of the second intermediate coating 202 can be 20%-30%, 20%-40%, etc. Within these ranges, the high tungsten content intermediate coating 200 exhibits an amorphous state, which is beneficial for improving its corrosion resistance. For example, some examples of the atomic percentage of tungsten in the high tungsten content second intermediate coating 202 can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, etc.

[0048] When the atomic percentage of tungsten in the first intermediate coating 201 is 1%-10% and the atomic percentage of tungsten in the second intermediate coating 202 is 20%-40%, the difference in tungsten content between the two is relatively large. In this case, the first intermediate coating 201 can be configured as multiple layers, and the second intermediate coating 202 can be configured as at least one layer. Both the substrate 100 and the noble metal coating 300 are in contact with the first intermediate coating 201, which has a lower tungsten content. The first intermediate coating 201 with a lower tungsten content has lower stress, resulting in better interfacial compatibility between it and the substrate 100 and the noble metal coating 300.

[0049] When the atomic percentage of tungsten in the first intermediate coating 201 is 1%-10% and the atomic percentage of tungsten in the second intermediate coating 202 is 2%-20% (further 2%-10%), the substrate 100 and the noble metal coating 300 may be in contact with either the first intermediate coating 201 or the second intermediate coating 202. For example, the scheme shown in Figure 1 or the scheme shown in Figure 2 may be used.

[0050] In this embodiment of the present disclosure, the thickness of the first intermediate plating layer 201 is 0.05μm-4μm, and the thickness of the second intermediate plating layer 202 is 0.05μm-4μm, or more specifically, 0.1μm-2μm. When the thicknesses of the first intermediate plating layer 201 and the second intermediate plating layer 202 are each within the above-mentioned ranges, the requirement for alternating stacking can be met.

[0051] For example, some examples of the thickness of the first intermediate coating 201 and the second intermediate coating 202 can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2. 9μm, 3μm, 3.1μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, 4μm, etc.

[0052] In the embodiments disclosed herein, the total number of layers of the first intermediate plating layer 201 and the second intermediate plating layer 202 is 3-15, for example, 3, 5, 7, 9, 11, 13, etc. A higher total number of intermediate plating layers 200 results in a better enhancement of the corrosion resistance and wear resistance of the composite plating structure; however, it may, to some extent, degrade the electrical conductivity and internal stress of the composite plating structure. The total number of intermediate plating layers 200 can be selected according to actual needs.

[0053] In this embodiment of the disclosure, the precious metal plating 300 is made of gold, silver, palladium or their alloys. This type of precious metal plating 300 has low contact resistance, resulting in excellent conductivity. At the same time, it also has excellent weldability.

[0054] In some examples, in the composite coating structure involved in the embodiments of this disclosure, the thickness of the noble metal coating 300 is 0.01 μm-1.27 μm, more specifically 0.01 μm-0.15 μm, and even more specifically 0.1 μm-0.15 μm. Compared with related technologies, the embodiments of this disclosure, while ensuring the excellent effects brought by the noble metal coating 300, can significantly reduce the thickness of the noble metal coating 300, thereby significantly reducing the cost of the composite coating structure.

[0055] In conjunction with any of the above-mentioned embodiments, this disclosure further discloses some examples of composite coating structures, the structures of which can also be seen in Figure 1.

[0056] In some instances, the composite coating structure includes a substrate 100, an intermediate coating 200, and a precious metal coating 300 arranged in sequence. The substrate 100 is made of copper or a copper alloy, and the precious metal coating 300 is made of gold, silver, palladium, or an alloy thereof, with a thickness of 0.01 μm to 0.15 μm.

[0057] The intermediate plating layers 200 are all nickel-tungsten plating layers, which include alternatingly stacked first intermediate plating layers 201 and second intermediate plating layers 202. For example, the number of layers of the first intermediate plating layer 201 is three and the number of layers of the second intermediate plating layer 202 is two. The composite plating structure includes the following layers stacked in sequence: substrate 100, first intermediate plating layer 201, second intermediate plating layer 202, first intermediate plating layer 201, second intermediate plating layer 202, first intermediate plating layer 201, and precious metal plating layer 300.

[0058] The atomic percentage of tungsten in the first intermediate coating 201 is 1%-10%, and the thickness of the first intermediate coating 201 is 0.05μm-4μm. The atomic percentage of tungsten in multiple layers of the first intermediate coating 201 can be the same or different, and the thickness of the multiple layers of the first intermediate coating 201 can be the same or different. The atomic percentage of tungsten in the second intermediate coating 202 is 2%-10%, 10%-20%, 10%-30%, 20%-30%, 20%-40%, etc., and the thickness of the second intermediate coating 202 is 0.05μm-4μm. The atomic percentage of tungsten in multiple layers of the second intermediate coating 202 can be the same or different, and the thickness of the multiple layers of the second intermediate coating 202 can be the same or different.

[0059] In other examples, the composite coating structure includes a substrate 100, an intermediate coating 200 and a precious metal coating 300 arranged in sequence. The substrate 100 is made of copper or a copper alloy, and the precious metal coating 300 is made of gold, silver, palladium or an alloy thereof, and has a thickness of 0.01 μm to 0.15 μm.

[0060] The intermediate coating 200 is a cobalt-tungsten coating, which includes a first intermediate coating 201 and a second intermediate coating 202 arranged alternately. For example, the first intermediate coating 201 has three layers and the second intermediate coating 202 has two layers. The composite coating structure includes the following layers arranged in sequence: substrate 100, first intermediate coating 201, second intermediate coating 202, first intermediate coating 201, second intermediate coating 202, first intermediate coating 201, and precious metal coating 300.

[0061] The atomic percentage of tungsten in the first intermediate coating 201 is 1%-10%, and the thickness of the first intermediate coating 201 is 0.05μm-4μm. The atomic percentage of tungsten in multiple layers of the first intermediate coating 201 can be the same or different, and the thickness of the multiple layers of the first intermediate coating 201 can be the same or different. The atomic percentage of tungsten in the second intermediate coating 202 is 2%-10%, 10%-20%, 10%-30%, 20%-30%, 20%-40%, etc., and the thickness of the second intermediate coating 202 is 0.05μm-4μm. The atomic percentage of tungsten in multiple layers of the second intermediate coating 202 can be the same or different, and the thickness of the multiple layers of the second intermediate coating 202 can be the same or different.

[0062] As mentioned above, the composite plating structure provided in the embodiments of this disclosure can be used for connector terminals. It is not excluded that the composite plating structure provided in the embodiments of this disclosure can also be used for other types of communication equipment, electronic equipment, household appliances, etc.

[0063] In addition to the aforementioned composite coating structure, this disclosure provides a method for preparing a composite coating structure. The method includes: forming multiple layers of first intermediate coating 201 and at least one layer of second intermediate coating 202 sequentially on a substrate 100 by a thin film deposition process to obtain an intermediate coating 200; and then forming a noble metal coating 300 on the intermediate coating 200 to obtain a composite coating structure.

[0064] Taking the first intermediate coating 201 having three layers and the second intermediate coating 202 having two layers as an example, the preparation method of the composite coating structure can be as follows: a first intermediate coating 201 is formed on a substrate 100 by a thin film deposition process, then a second intermediate coating 202 is formed on the first intermediate coating 201, then another first intermediate coating 201 is formed on the second intermediate coating 202, then another second intermediate coating 202 is formed on the first intermediate coating 201, then yet another first intermediate coating 201 is formed on the second intermediate coating 202, and finally a noble metal coating 300 is formed on the first intermediate coating 201, thereby completing the preparation of the composite coating structure.

[0065] Some thin film deposition processes applicable to the embodiments of this disclosure may be electroplating, electroless plating, magnetron sputtering, etc. Among them, electroplating is simple and reliable to operate, and has strong controllability, especially in terms of fine control of tungsten content. In some examples, the thin film deposition process used in the embodiments of this disclosure is electroplating.

[0066] In electroplating, current density has a significant impact on the composition and quality of the coating. For example, current density affects the coating thickness, uniformity, crystallinity, and grain size. Furthermore, changes in current density can influence the reduction rate and deposition rate of metal ions, thereby affecting the coating composition. For instance, during electroplating, a higher current density promotes the rapid reduction and deposition of doped metal ions in the plating bath (such as tungsten ions as described in the embodiments of this disclosure), resulting in an increase in the tungsten content in the coating.

[0067] Based on this, in this embodiment of the disclosure, the current density corresponding to the formation of the first intermediate plating layer 201 is different from the current density corresponding to the formation of the second intermediate plating layer 202. That is, the first intermediate plating layer 201 and the second intermediate plating layer 202 are formed by alternating electroplating with different current densities, so as to more accurately control the tungsten content in the first intermediate plating layer 201 and the second intermediate plating layer 202.

[0068] Furthermore, the current density range for forming the first intermediate plating layer 201 and the second intermediate plating layer 202 is 0.2ASD-4ASD.

[0069] Studies have found that when the current density is too high, the element deposition rate is faster, resulting in uneven and non-dense grain accumulation. Simultaneously, the internal grain sequence is disordered, leading to higher internal stress. For example, in the nickel-tungsten or cobalt-tungsten plating involved in this embodiment, excessively high current density during electroplating causes the tungsten content in the plating to increase too rapidly, resulting in high internal stress and making it prone to cracking. Therefore, in this embodiment, the current density range for electroplating the intermediate plating layer 200 of the nickel-tungsten or cobalt-tungsten plating material is 0.2 ASD-4 ASD, and more specifically 0.5 ASD-4 ASD, where ASD refers to amperes per square decimeter, to ensure a dense structure of the intermediate plating layer 200 and improve its wear resistance and corrosion resistance.

[0070] For example, the atomic percentage of tungsten in the first intermediate plating layer 201 is 1%-10%, and the corresponding current density range when electroplating to form the first intermediate plating layer 201 can be 0.2ASD-2ASD, or more specifically 0.5ASD-1ASD. The atomic percentage of tungsten in the second intermediate plating layer 202 is 20%-40%, and the current density range when electroplating to form the second intermediate plating layer 202 can be 2ASD-4ASD.

[0071] Besides current density, other factors during the electroplating process, such as temperature, stirring speed, and plating solution composition, also affect the quality of the plating layer. Therefore, during the electroplating process, it is necessary to comprehensively consider these factors and take corresponding measures to ensure the quality of each plating layer.

[0072] The following is an exemplary description of the electroplating process for forming an intermediate plating layer 200 of nickel-tungsten or cobalt-tungsten plating material.

[0073] In some examples, before electroplating the intermediate plating layer 200, the substrate 100 can be degreased and activated polished to remove the oxide film on the surface of the substrate 100 and to form a smooth and flat surface on the substrate 100, thereby facilitating the tight deposition of the intermediate plating layer 200 thereon.

[0074] In this embodiment, the intermediate plating layer 200 can be electroplated using a pulse electroplating process. When electroplating the intermediate plating layer 200, the electroplating temperature corresponding to the low tungsten content intermediate plating layer 200 and the electroplating temperature corresponding to the tungsten content intermediate plating layer 200 can both be 50℃-70℃, or more specifically 50℃-65℃, to ensure the smooth progress of the electroplating process and obtain a high-quality plating layer.

[0075] After each layer of the intermediate plating layer 200 is electroplated, the electroplated product can be removed and subjected to cleaning, neutralization, and drying operations to ensure that each layer of the intermediate plating layer 200 is formed with high quality.

[0076] For nickel-tungsten plating, the corresponding electroplating solution can include nickel salts, tungsten salts, acids, and water. Among them, nickel salts can be, for example, nickel sulfate, nickel chloride, etc., and the concentration of nickel salts can be 65g / L-75g / L. Tungsten salts can be, for example, sodium tungstate dihydrate, calcium tungstate, potassium tungstate, borotungstate, phosphotungstate, fluorotungstate, etc., and the concentration of tungsten salts can be 60g / L-70g / L. Acids can be, for example, citric acid, phosphonic acid, boric acid, hydrochloric acid, methanesulfonic acid and their salts, etc., and the concentration of acid should be such that the pH value of the electroplating solution is in the range of 3-5.

[0077] For cobalt-tungsten plating, the corresponding electroplating solution can include cobalt salt, tungsten salt, acid, and water. The cobalt salt can be, for example, cobalt sulfate, cobalt chloride, etc., and the concentration of the cobalt salt can be 65g / L-75g / L. The tungsten salt can be, for example, sodium tungstate dihydrate, calcium tungstate, potassium tungstate, borotungstate, phosphotungstate, fluorotungstate, etc., and the concentration of the tungsten salt can be 90g / L-105g / L. The acid can be, for example, citric acid, phosphonic acid, boric acid, hydrochloric acid, methanesulfonic acid and its salts, etc., and the concentration of the acid should be such that the pH value of the electroplating solution is in the range of 4-6.

[0078] During electroplating, for nickel-tungsten or cobalt-tungsten plating layers with different tungsten contents, the concentration of tungsten salts in the plating solution used for intermediate plating layers with different tungsten contents can be the same. Furthermore, the same plating solution can be used, and the tungsten content in different intermediate plating layers can be changed by altering the current density. Of course, it is not excluded that the concentration of tungsten salts in the plating solution corresponding to a low-tungsten-content nickel-tungsten plating layer can be lower than the concentration of tungsten salts in the plating solution corresponding to a high-tungsten-content nickel-tungsten plating layer.

[0079] In another aspect, the present disclosure also provides a conductive terminal, which adopts any of the composite plating structures mentioned above, and the substrate 100 of the composite plating structure is the conductive substrate of the conductive terminal.

[0080] The conductive terminals provided in this disclosure have all the advantages of the composite plating structure involved in this disclosure, and will not be repeated here.

[0081] In some examples, the types of conductive terminals provided in embodiments of this disclosure may include pins (also known as PIN pins), plugs, slots, leads, etc.

[0082] On the other hand, embodiments of this disclosure also provide a connector including an insulating terminal block and conductive terminals fixedly connected to the insulating terminal block, wherein the conductive terminals are as described in any of the above descriptions.

[0083] Since the connector uses any of the conductive terminals (i.e. composite plating structure) mentioned above as electrical connection terminals, the connector involved in the embodiments of this disclosure has all the advantages of the conductive terminals and composite plating structure involved in the embodiments of this disclosure, which will not be repeated here.

[0084] In some examples, the types of connectors provided in this disclosure include, but are not limited to, the following: board-to-board connectors, board-to-cable connectors, interface connectors, power connectors, RF connectors, IC socket connectors, etc. Some exemplary examples may be as follows: D-type connectors, circular connectors, backplane connectors, flat cable connectors, terminal connectors, etc.

[0085] Exemplary embodiments of this application will now be described in more detail. While exemplary embodiments of this application are described below, it should be understood that this application can be implemented in various forms and should not be limited to the embodiments set forth herein. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with techniques or conditions described in the literature in the art or according to product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0086] Example 1

[0087] Example 1 provides a composite coating structure, which includes a substrate 100, an intermediate coating 200 and a precious metal coating 300 arranged in sequence. The substrate 100 is made of copper alloy C7025, and the precious metal coating 300 is made of gold with a thickness of 0.15μm.

[0088] The intermediate plating layers 200 are all nickel-tungsten plating layers, which include alternatingly stacked first intermediate plating layers 201 and second intermediate plating layers 202. The first intermediate plating layer 201 has four layers, and the second intermediate plating layer 202 has three layers. That is to say, the composite plating structure includes the following layers stacked in sequence: substrate 100, first intermediate plating layer 201, second intermediate plating layer 202, first intermediate plating layer 201, second intermediate plating layer 202, first intermediate plating layer 201, second intermediate plating layer 202, first intermediate plating layer 201, and precious metal plating layer 300.

[0089] All first intermediate coatings 201 contain 8% tungsten and have a thickness of 2 μm, while all second intermediate coatings 202 contain 30% tungsten and have a thickness of 2 μm.

[0090] Both the intermediate plating layer 200 and the precious metal plating layer 300 are prepared by electroplating. The electroplating solution used for the first intermediate plating layer 201 and the second intermediate plating layer 202 has the same formula as shown below: nickel chloride hexahydrate 71.35 g / L, sodium tungstate dihydrate 66.16 g / L, sodium citrate dihydrate 74.5 g / L, hydroxyethylidene diphosphonic acid 40.1 g / L, and the pH value of the electroplating solution is 4.

[0091] During the electroplating process, the electroplating temperature is 60℃, the current density corresponding to the formation of the first intermediate plating layer 201 is 1ASD, and the current density corresponding to the formation of the second intermediate plating layer 202 is 2.5ASD.

[0092] Example 2

[0093] Example 2 provides a composite coating structure, which includes a substrate 100, an intermediate coating 200 and a precious metal coating 300 arranged in sequence. The substrate 100 is made of copper alloy C7025, and the precious metal coating 300 is made of gold with a thickness of 0.15μm.

[0094] The intermediate coating 200 is a cobalt-tungsten coating, which includes a first intermediate coating 201 and a second intermediate coating 202 arranged alternately. The first intermediate coating 201 has three layers and the second intermediate coating 202 has two layers. That is to say, the composite coating structure includes the following layers arranged in sequence: substrate 100, first intermediate coating 201, second intermediate coating 202, first intermediate coating 201, second intermediate coating 202, first intermediate coating 201, and precious metal coating 300.

[0095] All first intermediate coatings 201 contain 5% tungsten and have a thickness of 1 μm, while all second intermediate coatings 202 contain 25% tungsten and have a thickness of 1 μm.

[0096] Both the intermediate plating layer 200 and the precious metal plating layer 300 are prepared by electroplating. The electroplating solution used for the first intermediate plating layer 201 and the second intermediate plating layer 202 has the same formula as shown below: cobalt chloride hexahydrate 71.47 g / L, sodium tungstate dihydrate 98.92 g / L, sodium citrate dihydrate 118.12 g / L, hydroxyethylidene diphosphonic acid 40.23 g / L, and the pH value of the electroplating solution is 5.

[0097] During the electroplating process, the electroplating temperature is 50℃, the current density corresponding to the formation of the first intermediate plating layer 201 is 0.5ASD, and the current density corresponding to the formation of the second intermediate plating layer 202 is 2ASD.

[0098] Test case

[0099] The test samples of the composite coating structures provided in Examples 1 and 2 were tested using test examples, wherein the test samples were 5cm×5cm squares.

[0100] First, X-ray energy dispersive spectroscopy analysis was performed on the test samples of the composite coating structures provided in Examples 1 and 2. The analysis results showed that in the intermediate coating 200, the content of tungsten in the first intermediate coating 201 and the content of tungsten in the second intermediate coating 202 exhibited an alternating gradient distribution, which verified the alternating distribution scheme of tungsten content in the intermediate coating 200.

[0101] Secondly, in accordance with GB64060-86 Accelerated Acetic Acid Spray Test for Copper Coatings with Metallic Coatings, the test samples of the composite coating structures provided in Examples 1 and 2 were subjected to salt spray resistance tests.

[0102] Meanwhile, comparative test sample 1 and comparative test sample 2 of the composite coating structure are provided. Comparative test sample 1 includes a copper alloy C7025 substrate and a gold coating with a thickness of 0.76 μm formed on the copper alloy substrate. Comparative test sample 2 includes a copper alloy C7025 substrate and a gold coating with a thickness of 0.2 μm formed on the copper alloy substrate.

[0103] Test results show that the test samples of the composite coating structures provided in Examples 1 and 2, as well as the first comparative test sample, can withstand 48 hours of salt spray, while the second comparative test sample cannot withstand 24 hours of salt spray.

[0104] Third, according to the EIA-364-09C electrical connector life abrasion resistance test, abrasion resistance tests were conducted on the test samples of the composite plating structure provided in Example 1 and Example 2, as well as the aforementioned comparative test sample one and comparative test sample two.

[0105] Test results show that the wear resistance of the test samples with composite coating structures provided in Examples 1 and 2 is comparable to that of the first comparative test sample, and is superior to that of the second comparative test sample.

[0106] In summary, the composite coating structure provided in this embodiment has corrosion resistance and wear resistance comparable to the composite coating structure containing a 0.76 μm thick gold coating. However, the gold coating of the composite coating structure provided in this embodiment has a thickness of 0.15 μm, which significantly reduces the cost compared to a 0.76 μm thick gold coating.

[0107] The above description is only for the purpose of enabling those skilled in the art to understand the technical solutions disclosed herein, and is not intended to limit the scope of this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A composite coating structure, wherein, The composite coating structure includes a substrate (100), an intermediate coating (200) stacked on the substrate (100), and a noble metal coating (300) stacked on the intermediate coating (200). Wherein, the substrate (100) is a copper substrate or a copper alloy substrate; The intermediate coating (200) includes a first intermediate coating (201) and a second intermediate coating (202) arranged alternately. Both the first intermediate coating (201) and the second intermediate coating (202) are nickel-tungsten coatings or cobalt-tungsten coatings, and the tungsten content of the first intermediate coating (201) is different from that of the second intermediate coating (202).

2. The composite coating structure of claim 1, wherein, When the difference in tungsten content between the first intermediate coating (201) and the second intermediate coating (202) is greater than a set threshold, both the substrate (100) and the noble metal coating (300) come into contact with the phase with the lower tungsten content between the first intermediate coating (201) and the second intermediate coating (202).

3. The composite coating structure of claim 1, wherein, The atomic percentage of tungsten in the first intermediate coating (201) is 1%-10%.

4. The composite coating structure of claim 2, wherein, The atomic percentage of tungsten in the second intermediate coating (202) is 2%-40%.

5. The composite coating structure of claim 1, wherein, The thickness of the first intermediate coating (201) is 0.05μm-4μm, and the thickness of the second intermediate coating (202) is 0.05μm-4μm.

6. The composite coating structure according to any one of claims 1 to 5, wherein, The total number of layers of the first intermediate coating (201) and the second intermediate coating (202) is 3-15.

7. The composite coating structure according to any one of claims 1 to 6, wherein, The precious metal plating (300) is made of gold, silver, palladium or an alloy thereof, and the thickness of the precious metal plating (300) is 0.01μm-1.27μm.

8. A method of producing a composite coating structure, wherein, The composite coating structure is as described in any one of claims 1-7, and the method for preparing the composite coating includes: By means of thin film deposition process, a first intermediate coating layer (201) and a second intermediate coating layer (202) are sequentially formed on a substrate (100) to obtain an intermediate coating layer (200), and a noble metal coating layer (300) is formed on the intermediate coating layer (200) to obtain the composite coating structure.

9. The method of claim 8, wherein the step of applying the second layer of metal is performed after the step of applying the first layer of metal. The thin film deposition process is an electroplating process, and the current density corresponding to the formation of the first intermediate coating (201) is different from the current density corresponding to the formation of the second intermediate coating (202), and the range of the current density is 0.2ASD-4ASD.

10. An electrically conductive terminal, wherein, The conductive terminal adopts the composite plating structure according to any one of claims 1-7, and the substrate (100) of the composite plating structure is the conductive substrate of the conductive terminal.

11. A connector, wherein, The connector includes an insulating terminal block and conductive terminals fixedly connected to the insulating terminal block, as described in claim 10.

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