Method for producing a nickel-free plating layer and nickel-free plating layer

Abstract

The present application belongs to the technical field of spring needle contact pad plating layer, and particularly relates to a preparation method of nickel-free plating layer and the nickel-free plating layer, comprising the following steps: (S1) electroplating pretreatment; (S2) electroplating bottom layer; (S3) electroplating conductive layer; (S4) electroplating intermediate layer; (S5) electroplating surface layer; (S6) electroplating post-treatment. The copper-tin-zinc alloy bottom layer is used as the bottom layer of the plating layer, the copper-tin-zinc alloy plating layer has excellent toughness and uniform stress, and can deform slightly with the base material, thereby solving the problems of cracks and peeling caused by friction with the spring needle. The silver-antimony alloy conductive layer is used as the conductive layer, the high potential of the palladium intermediate layer and the platinum surface layer is balanced with the low potential of the copper-tin-zinc alloy bottom layer, and the strong electrolytic corrosion caused by the large potential difference is inhibited. The palladium layer is used as the intermediate layer, preventing the upward diffusion and migration of the silver-antimony alloy conductive layer, the contact failure and discoloration caused by the silver sulfide climbing to the surface layer, and blocking the downward penetration of external corrosive media.

Description

Technical Field

[0001] This invention belongs to the technical field of spring pin contact pad coating, and particularly relates to a method for preparing a nickel-free coating and a nickel-free coating. Background Technology

[0002] A Pogo Pad is a stationary metal contact base that presses against a Pogo Pin spring. In the prior art, the Pogo Pad is made of copper and is electroplated on the surface of the copper by electroplating a nickel underlayer and a precious metal surface layer. However, this electroplating process has the following shortcomings: (1) The nickel layer has high internal stress and high brittleness. Under the working conditions of pressing and friction with the spring pin, micro-cracks and peeling are likely to occur, and the coating has poor fatigue resistance; (2) Nickel is the most common sensitizing metal. When in contact with the human body, nickel ions can penetrate into the skin through pores and sebaceous glands, thereby causing skin allergies and inflammation. Summary of the Invention

[0003] The first objective of this invention is to provide a method for preparing a nickel-free coating, which aims to solve the technical problems of poor fatigue resistance and easy skin allergies and inflammation caused by contact with the coating in the prior art.

[0004] To achieve the above objectives, the present invention provides a method for preparing a nickel-free plating layer, comprising the following steps:

[0005] (S1) Electroplating pretreatment: A copper rod is provided, and the copper rod is cut into a blank in the shape of a contact pad by turning. Then the blank is surface treated to obtain a contact pad substrate.

[0006] (S2) Electroplating underlayer: A copper-tin-zinc electroplating main tank is provided, and the contact pad substrate is placed in the copper-tin-zinc electroplating main tank to form a copper-tin-zinc alloy underlayer on the surface of the contact pad substrate.

[0007] (S3) Electroplating conductive layer: A silver-antimony alloy electroplating main tank is provided, and the contact pad substrate is placed in the silver-antimony alloy electroplating main tank, thereby forming a silver-antimony alloy conductive layer on the surface of the copper-tin-zinc alloy bottom layer.

[0008] (S4) Electroplating intermediate layer: A palladium electroplating main tank is provided, and the contact pad substrate is placed in the palladium electroplating main tank to form a palladium intermediate layer on the surface of the silver-antimony alloy conductive layer.

[0009] (S5) Electroplating surface layer: A platinum electroplating main tank is provided, the contact pad substrate is placed in the platinum electroplating main tank, and a platinum surface layer is formed on the surface of the palladium intermediate layer to obtain a nickel-free plating layer on the surface of the contact pad substrate.

[0010] (S6) Post-electroplation treatment: A pure water cleaning tank and a hot air drying oven are provided. First, the contact pad substrate with a nickel-free plating is placed in the pure water cleaning tank for washing. Then, the contact pad substrate is placed in the hot air drying oven for drying.

[0011] Optionally, the method further includes step (S30) of electroplating a buffer layer: providing a pre-plating silver bath, placing the contact pad substrate in the pre-plating silver bath, and thereby forming a silver buffer layer on the surface of the copper-tin-zinc alloy bottom layer. Step (S30) is located between step (S2) and step (S3), and the silver-antimony alloy conductive layer of step (S3) is formed on the surface of the silver buffer layer.

[0012] Optionally, the method further includes step (S300) silver plating pre-immersion: providing a first pre-immersion tank with a volume of 100L, the first pre-immersion solution being 70~80L of pure water, and adding 60~80g / L of potassium pyrophosphate and 5~10g / L of potassium hydroxide to the pure water; step (S300) is located between step (S2) and step (S30).

[0013] Optionally, the method further includes step (S31) silver-antimony pre-immersion: providing a second pre-immersion tank with a volume of 100L, the second pre-immersion solution being 70~80L of pure water, and adding 12~20g / L of free potassium cyanide and 8~12g / L of potassium carbonate to the pure water. Step (S31) is located between step (S30) and step (S3).

[0014] Optionally, the method further includes step (S20) copper-tin-zinc pre-immersion: providing a third pre-immersion tank with a volume of 100L, the third pre-immersion solution being 70~80L of pure water, and adding 80~100g / L of potassium thiocyanate, 40~60g / L of potassium pyrophosphate, and 2~6g / L of potassium hydroxide to the pure water; step (S20) is located between step (S1) and step (S2).

[0015] Optionally, the process further includes step (S40) of palladium pre-immersion: providing a fourth pre-immersion tank with a volume of 100L, the fourth pre-immersion solution being 70~80L of pure water, and adding 15~25g / L of aminosulfonic acid, 8~11g / L of potassium aminosulfonate, and 2~4g / L of potassium hydroxide to the pure water; step (S40) is located between step (S3) and step (S4).

[0016] Optionally, the method further includes step (S50) of platinum pre-impregnation: providing a fifth pre-impregnation tank with a volume of 100L, the fifth pre-impregnation solution being 70~80L of pure water, and adding 8~15g / L of aminosulfonic acid and 12~16g / L of dilute hydrochloric acid to the pure water; step (S50) is located between step (S4) and step (S5).

[0017] The second objective of this invention is to provide a nickel-free plating layer, which is prepared by the method described above and comprises a copper-tin-zinc alloy bottom layer, a silver-antimony alloy conductive layer, a palladium intermediate layer, and a platinum surface layer stacked sequentially from bottom to top, wherein the copper-tin-zinc alloy bottom layer is disposed on the top surface of the contact pad.

[0018] Optionally, the thickness of the copper-tin-zinc alloy bottom layer is 2.5 to 5 μm, the thickness of the silver-antimony alloy conductive layer is greater than or equal to 5 μm, the thickness of the palladium intermediate layer is greater than or equal to 0.5 μm, and the thickness of the platinum surface layer is greater than or equal to 0.625 μm.

[0019] Optionally, the silver-antimony alloy conductor comprises 0.3% to 5% antimony by mass, with the balance being silver.

[0020] The preparation method of the nickel-free coating and one or more of the above-mentioned technical solutions in the nickel-free coating provided in the embodiments of the present invention have at least one of the following technical effects: (1) Using a copper-tin-zinc alloy underlayer as the underlayer of the coating increases the surface adhesion between the underlayer and the contact pad substrate, which is beneficial to improving the overall bonding force of the coating. On the other hand, the copper-tin-zinc alloy coating has excellent toughness and uniform stress, and can deform slightly with the substrate, thereby solving the problem of cracks and peeling caused by pressure friction with the spring pin, and thus improving the service life of the product; (2) Using a copper-tin-zinc alloy underlayer to replace the nickel underlayer meets the nickel release standards of EN1811:2023 and EN12472:2020, thereby avoiding discomfort caused by wearing contact; (3) Using a silver-antimony alloy to conduct electricity As a conductive layer, the hardness of the conductive layer is increased to 90HV~160HV to avoid scratches on the surface during electroplating. On the other hand, it balances the high potential of the palladium intermediate layer and the platinum surface layer with the low potential of the copper-tin-zinc alloy bottom layer, suppressing strong electrolytic corrosion caused by large potential difference. (4) Using the palladium layer as an intermediate layer, it prevents the silver-antimony alloy conductive layer from diffusing upwards and causing poor contact and discoloration due to silver sulfides climbing to the surface. At the same time, it blocks external corrosive media from penetrating downwards. (5) Using the platinum layer as the surface layer, the platinum layer has a very high potential and is very difficult to dissolve anoly. It is not easily electrolyzed, does not turn white, does not turn black, and does not corrode. It achieves the sealing of pinholes, and the surface sweat and electrolyte seep down to the inner plating layer, thus protecting the inner plating layer. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1This is a flowchart illustrating the method for preparing a nickel-free plating layer according to an embodiment of the present invention.

[0023] Figure 2 This is a schematic diagram of the structure of the nickel-free plating provided in an embodiment of the present invention.

[0024] The following are the labeling elements in the figure:

[0025] 1—Contact pad substrate; 2—Copper-tin-zinc alloy bottom layer; 3—Silver-antimony alloy conductive layer

[0026] 31—Silver buffer layer; 4—Palladium intermediate layer; 5—Platinum surface layer. Detailed Implementation

[0027] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain embodiments of the present invention, and should not be construed as limiting the present invention.

[0028] In the description of the embodiments of the present invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0029] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0030] In the embodiments of the present invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention according to the specific circumstances.

[0031] In one embodiment of the present invention, such as Figure 1 As shown, a method for preparing a nickel-free plating layer is provided, comprising the following steps:

[0032] (S1) Electroplating pretreatment: A copper rod is provided, and the copper rod is cut into a blank in the shape of a contact pad by turning. Then the blank is surface treated to obtain the contact pad substrate 1.

[0033] (S2) Electroplating underlayer: A copper-tin-zinc electroplating main tank is provided, and the contact pad substrate 1 is placed in the copper-tin-zinc electroplating main tank, thereby forming a copper-tin-zinc alloy underlayer 2 on the surface of the contact pad substrate 1.

[0034] (S3) Electroplating conductive layer: A silver-antimony alloy electroplating main tank is provided, and the contact pad substrate 1 is placed in the silver-antimony alloy electroplating main tank, thereby forming a silver-antimony alloy conductive layer 3 on the surface of the copper-tin-zinc alloy bottom layer 2.

[0035] (S4) Electroplating intermediate layer: A palladium electroplating main tank is provided, and the contact pad substrate 1 is placed in the palladium electroplating main tank, thereby forming a palladium intermediate layer 4 on the surface of the silver-antimony alloy conductive layer 3.

[0036] (S5) Electroplating surface layer: A platinum electroplating main tank is provided, the contact pad substrate 1 is placed in the platinum electroplating main tank, and then a platinum surface layer 5 is formed on the surface of the palladium intermediate layer 4 to obtain a nickel-free plating layer on the surface of the contact pad substrate 1.

[0037] (S6) Post-plating treatment: A pure water cleaning tank and a hot air drying oven are provided. First, the contact pad substrate 1 with a nickel-free plating is placed in the pure water cleaning tank for washing. Then, the contact pad substrate is placed in the hot air drying oven for drying. The beneficial effects of this embodiment include: (1) Using the copper-tin-zinc alloy bottom layer 2 as the bottom layer of the plating increases the surface adhesion between the bottom layer and the contact pad substrate 1, which is conducive to improving the overall bonding force of the plating. On the other hand, the copper-tin-zinc alloy plating has excellent toughness and uniform stress, and can deform slightly with the substrate, thereby solving the problem of cracks and peeling caused by the pressure and friction with the spring needle, and thus improving the service life of the product; (2) Using the copper-tin-zinc alloy bottom layer 2 to replace the nickel bottom layer meets the nickel release standards of EN1811:2023 and EN12472:2020, thereby avoiding discomfort caused by wearing contact; (3) Using the silver-antimony alloy conductive layer 3 as the conductive layer increases the hardness of the conductive layer. High potential of 90HV to 160HV, avoiding scratches on the surface during electroplating. On the other hand, it balances the high potential of the palladium intermediate layer 4 and the platinum surface layer 5 with the low potential of the copper-tin-zinc alloy bottom layer 2, suppressing strong electrolytic corrosion caused by large potential difference; (4) Using the palladium layer as the intermediate layer, it prevents the silver-antimony alloy conductive layer 3 from diffusing upwards and causing poor contact and discoloration due to silver sulfides climbing to the surface, while blocking external corrosive media from penetrating downwards; (5) Using the platinum layer as the surface layer, the platinum layer has a very high potential and is very difficult to dissolve anoly, is not easily electrolyzed, does not turn white, does not turn black, and does not corrode; it achieves the sealing of pinholes, and the surface sweat and electrolyte seep down to the inner plating layer, thus protecting the inner plating layer. Specifically, in step (S1) pre-plating treatment, the surface treatment includes: (S11) grinding and polishing, using a white alumina grinding wheel (grit size 100~120#) to act on the surface of the contact pad substrate 1 to remove cutting tool marks and burrs; (S12) cleaning, providing an ultrasonic alkaline degreasing tank, placing the ground and polished contact pad substrate 1 into the ultrasonic alkaline degreasing tank, the ultrasonic alkaline degreasing tank has a volume of 100L, the degreasing volume is 75L of pure water, the pure water contains 50 g / L of composite alkaline degreasing agent and 8 g / L of trisodium phosphate, working temperature: 65℃, soaking time: 5 min, thereby removing the powder adhering to the ground and polished surface and removing the processing oil remaining on the surface during turning, avoiding the aforementioned impurities from contaminating the sand particles during subsequent sandblasting; (S13) sandblasting, using sandblasting equipment to form a uniform micro-uneven structure on the surface of the contact pad substrate 1, wherein the surface roughness is Ra0.65, improving the uniformity of the thickness of the subsequent electroplating layer.

[0038] In one embodiment of the present invention, such as Figure 1As shown, the process also includes step (S30) of electroplating a buffer layer: a pre-plating silver bath is provided, and the contact pad substrate 1 is placed in the pre-plating silver bath, thereby forming a silver buffer layer 31 on the surface of the copper-tin-zinc alloy bottom layer 2. Step (S30) is located between steps (S2) and (S3), and the silver-antimony alloy conductive layer 3 of step (S3) is formed on the surface of the silver buffer layer 31. Specifically, the silver-antimony alloy conductive layer 3 is in indirect contact with the copper-tin-zinc alloy bottom layer 2 through the silver buffer layer 31, completely sealing the exposed copper-tin-zinc alloy surface, thoroughly isolating the zinc, tin, and copper bottom layer from contact with the subsequent silver-antimony plating solution, and avoiding the occurrence of replacement black film and loose interlayer layers during the electroplating of the conductive layer.

[0039] In one embodiment of the present invention, such as Figure 1 As shown, it also includes step (S300) silver plating pre-immersion: providing a first pre-immersion tank with a volume of 100L, the first pre-immersion solution being 70~80L of pure water, and adding 60~80g / L of potassium pyrophosphate and 5~10g / L of potassium hydroxide to the pure water; step (S300) is located between step (S2) and step (S30). In this embodiment, the volume of the first pre-impregnation tank is 100L, the first pre-impregnation solution is 75L of pure water, and 70g / L of potassium pyrophosphate and 8g / L of potassium hydroxide are added to the pure water. The pre-impregnation time is 15~20s. Potassium hydroxide is used to maintain the high alkalinity in the first pre-impregnation tank, pH 10.5~11.5, to avoid chemical corrosion and dissolution of Zn and Sn in the copper-tin-zinc alloy in acidic or weakly acidic environments. Potassium pyrophosphate is used as a complexing agent to form a liquid phase complexing buffer layer on the surface of the copper-tin-zinc alloy bottom layer 2, inhibiting the dissolution of alloy metal into the solution. When the contact pad enters the pre-plating silver tank, the liquid phase complexing buffer layer on the surface will complex with some of the silver ions in the pre-plating silver tank to reduce the activity of free Ag⁺ at the interface, reduce the electrochemical driving force of the redox reaction when no current is applied, and reduce the risk of black silver forming on the surface.

[0040] In one embodiment of the present invention, such as Figure 1 As shown, the process also includes step (S31) of silver-antimony pre-immersion: providing a second pre-immersion tank with a volume of 100L, and a second pre-immersion solution of 70-80L pure water, with 12-20g / L of free potassium cyanide and 8-12g / L of potassium carbonate added to the pure water. Step (S31) is located between steps (S30) and (S3). In this embodiment, the second pre-immersion tank has a volume of 100L, the second pre-immersion solution is 75L of pure water, and 16g / L of free potassium cyanide and 10g / L of potassium carbonate are added to the pure water to stabilize the surface complexation state of the contact pad, ensuring uniform silver-antimony alloy deposition and stable antimony content, and avoiding color difference and uneven hardness of the coating.

[0041] In one embodiment of the present invention, such as Figure 1As shown, the process also includes step (S20) of copper-tin-zinc pre-immersion plating: providing a third pre-immersion tank with a volume of 100L, and a third pre-immersion solution of 70-80L pure water, with potassium thiocyanate at 80-100g / L, potassium pyrophosphate at 40-60g / L, and potassium hydroxide at 2-6g / L added to the pure water; step (S20) is located between step (S1) and step (S2). In this embodiment, the third pre-immersion solution is 75L pure water, with potassium thiocyanate at 90g / L, potassium pyrophosphate at 50g / L, and potassium hydroxide at 4g / L added to the pure water, to eliminate plating defects such as mottled spots and pitting, and to improve the uniformity and adhesion of the copper-tin-zinc plating layer.

[0042] In one embodiment of the present invention, such as Figure 1 As shown, the process also includes step (S40) of palladium pre-immersion: providing a fourth pre-immersion tank with a volume of 100L, and a fourth pre-immersion solution of 70-80L pure water, with 15-25g / L of aminosulfonic acid, 8-11g / L of potassium aminosulfonate, and 2-4g / L of potassium hydroxide added to the pure water; step (S40) is located between step (S3) and step (S4). In this embodiment, the fourth pre-immersion tank has a volume of 100L, the fourth pre-immersion solution is 75L of pure water, and 20g / L of aminosulfonic acid, 9g / L of potassium aminosulfonate, and 3g / L of potassium hydroxide are added to the pure water to maintain the micro-activated state of the workpiece surface and prevent the palladium plating surface from being oxidized and passivated again.

[0043] In one embodiment of the present invention, such as Figure 1 As shown, the process also includes step (S50) of platinum pre-impregnation: providing a fifth pre-impregnation tank with a volume of 100L, and the fifth pre-impregnation solution being 70-80L of pure water, with 8-15g / L of aminosulfonic acid and 12-16g / L of dilute hydrochloric acid added to the pure water; step (S50) is located between steps (S4) and (S5). In this embodiment, the fifth pre-impregnation solution is 75L of pure water, with 13g / L of aminosulfonic acid and 15g / L of dilute hydrochloric acid added to the pure water, preheating the contact pad and activating the surface of the palladium intermediate layer 4 to ensure the platinum surface layer 5 is covered and free of pinholes.

[0044] In one embodiment of the present invention, such as Figure 2 As shown, a nickel-free plating layer is also provided, prepared by the method described above. This layer comprises, from bottom to top, a copper-tin-zinc alloy base layer 2, a silver-antimony alloy conductive layer 3, a palladium intermediate layer 4, and a platinum surface layer 5, stacked sequentially. The copper-tin-zinc alloy base layer 2 is disposed on the top surface of the contact pad. Specifically, the copper-tin-zinc alloy base layer 2 is used to fill and smooth out the fine textures and burrs on the surface of the contact pad substrate 1, providing a smooth substrate for the upper silver-antimony alloy conductive layer.

[0045] In one embodiment of the present invention, the thickness of the copper-tin-zinc alloy bottom layer 2 is 2.5–5 μm, the thickness of the silver-antimony alloy conductive layer 3 is greater than or equal to 5 μm, the thickness of the palladium intermediate layer 4 is greater than or equal to 0.5 μm, and the thickness of the platinum surface layer 5 is greater than or equal to 0.625 μm. Specifically, the copper-tin-zinc alloy bottom layer 2 has a thickness of 5 μm, is sufficiently flat, seals pores, and has a moderate thickness that does not generate excessive internal stress; the silver-antimony alloy conductive layer 3 has a thickness of 5 μm, is sufficiently thick, has dense grains, and forms a thick barrier to prevent sweat from completely penetrating to the copper-tin-zinc alloy bottom layer 2; the palladium intermediate layer 4 has a thickness of 0.5 μm, acts as a dense barrier layer, and ensures no pinholes; the platinum surface layer 5 has a thickness of 0.625 μm, ensures that micropores are sealed, and prevents corrosive media from penetrating downwards.

[0046] In one embodiment of the present invention, the silver-antimony alloy conductor comprises 0.3% to 5% antimony by mass, with the balance being silver. In this embodiment, the silver-antimony alloy conductor comprises 2.5% antimony by mass, with the balance being silver, increasing the hardness to 120HV. Compared with pure silver, this significantly improves wear resistance, anti-adhesion, and resistance to fretting wear, thereby extending service life.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a nickel-free plating layer, characterized in that, The steps include the following: (S1) Electroplating pretreatment: A copper rod is provided, and the copper rod is cut into a blank in the shape of a contact pad by turning. Then the blank is surface treated to obtain a contact pad substrate. (S2) Electroplating underlayer: A copper-tin-zinc electroplating main tank is provided, and the contact pad substrate is placed in the copper-tin-zinc electroplating main tank to form a copper-tin-zinc alloy underlayer on the surface of the contact pad substrate. (S3) Electroplating conductive layer: A silver-antimony alloy electroplating main tank is provided, and the contact pad substrate is placed in the silver-antimony alloy electroplating main tank, thereby forming a silver-antimony alloy conductive layer on the surface of the copper-tin-zinc alloy bottom layer. (S4) Electroplating intermediate layer: A palladium electroplating main tank is provided, and the contact pad substrate is placed in the palladium electroplating main tank to form a palladium intermediate layer on the surface of the silver-antimony alloy conductive layer. (S5) Electroplating surface layer: A platinum electroplating main tank is provided, the contact pad substrate is placed in the platinum electroplating main tank, and a platinum surface layer is formed on the surface of the palladium intermediate layer to obtain a nickel-free plating layer on the surface of the contact pad substrate. (S6) Post-electroplation treatment: A pure water cleaning tank and a hot air drying oven are provided. First, the contact pad substrate with a nickel-free plating is placed in the pure water cleaning tank for washing. Then, the contact pad substrate is placed in the hot air drying oven for drying.

2. The method for preparing a nickel-free plating layer according to claim 1, characterized in that, It also includes step (S30) electroplating a buffer layer: providing a pre-plating silver bath, placing the contact pad substrate in the pre-plating silver bath, and then forming a silver buffer layer on the surface of the copper-tin-zinc alloy bottom layer. Step (S30) is located between step (S2) and step (S3), and the silver-antimony alloy conductive layer of step (S3) is formed on the surface of the silver buffer layer.

3. The method for preparing a nickel-free plating layer according to claim 2, characterized in that, It also includes step (S300) silver plating pre-immersion: providing a first pre-immersion tank with a volume of 100L, the first pre-immersion solution being 70~80L of pure water, and adding 60~80g / L of potassium pyrophosphate and 5~10g / L of potassium hydroxide to the pure water; step (S300) is located between step (S2) and step (S30).

4. The method for preparing a nickel-free plating layer according to claim 3, characterized in that, It also includes step (S31) silver-antimony pre-immersion: providing a second pre-immersion tank with a volume of 100L, the second pre-immersion solution being 70~80L of pure water, and adding 12~20g / L of free potassium cyanide and 8~12g / L of potassium carbonate to the pure water. Step (S31) is located between step (S30) and step (S3).

5. The method for preparing a nickel-free plating layer according to claim 1, characterized in that, The method also includes step (S20) copper-tin-zinc pre-immersion: providing a third pre-immersion tank with a volume of 100L, the third pre-immersion solution being 70~80L of pure water, and adding 80~100g / L of potassium thiocyanate, 40~60g / L of potassium pyrophosphate, and 2~6g / L of potassium hydroxide to the pure water; step (S20) is located between step (S1) and step (S2).

6. The method for preparing a nickel-free plating layer according to claim 1, characterized in that, The process also includes step (S40) palladium pre-immersion: providing a fourth pre-immersion tank with a volume of 100L, the fourth pre-immersion solution being 70~80L of pure water, and adding 15~25g / L of aminosulfonic acid, 8~11g / L of potassium aminosulfonate, and 2~4g / L of potassium hydroxide to the pure water; step (S40) is located between step (S3) and step (S4).

7. The method for preparing a nickel-free plating layer according to claim 1, characterized in that, It also includes step (S50) platinum pre-impregnation: providing a fifth pre-impregnation tank with a volume of 100L, the fifth pre-impregnation solution being 70~80L of pure water, with 8~15g / L of aminosulfonic acid and 12~16g / L of dilute hydrochloric acid added to the pure water; step (S50) is located between step (S4) and step (S5).

8. A nickel-free plating, characterized in that, The contact pad is prepared by the preparation method according to any one of claims 1 to 7, comprising a copper-tin-zinc alloy bottom layer, a silver-antimony alloy conductive layer, a palladium intermediate layer, and a platinum surface layer stacked sequentially from bottom to top, wherein the copper-tin-zinc alloy bottom layer is disposed on the top surface of the contact pad.

9. The nickel-free plating according to claim 8, characterized in that, The thickness of the copper-tin-zinc alloy bottom layer is 2.5–5 μm, the thickness of the silver-antimony alloy conductive layer is greater than or equal to 5 μm, the thickness of the palladium intermediate layer is greater than or equal to 0.5 μm, and the thickness of the platinum surface layer is greater than or equal to 0.625 μm.

10. The nickel-free plating according to claim 8, characterized in that, The silver-antimony alloy conductor comprises 0.3% to 5% antimony by mass, with the balance being silver.

Images