Composite metal coating without electronic escape interference and method for preparing the same

Abstract

The application discloses a composite metal coating without electronic escape interference and a preparation method thereof, and belongs to the technical field of metal coatings. The composite metal coating comprises, from inside to outside, a base material, a first metal conductive layer, a second metal-nonmetal composite conductive layer, a heterojunction structure layer and a third conductive layer. The preparation method comprises the following steps: pretreating the base material; sequentially electrodepositing the first metal conductive layer and the second metal-nonmetal composite conductive layer; performing phosphorization or nitridation treatment and heat treatment on the second metal-nonmetal composite conductive layer to form the heterojunction structure layer capable of effectively shielding electronic migration; and finally electrodepositing the third conductive layer. The heterojunction structure layer utilizes the hybrid property of inorganic nonmetal and metal ions, forms a structure with high oxidation resistance and stability, effectively shields the electronic active migration of the inner layer copper and nickel, and solves the adverse influence of intermetallic compounds formed due to electronic migration on weldability and corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal coating, in particular to a composite metal coating without electron escape interference and a preparation method thereof. BACKGROUND

[0002] In many industrial applications, metal coatings play a crucial role in improving the corrosion resistance, enhancing the weldability, and improving the electrical conductivity of materials. However, traditional metal coatings have some problems that need to be solved.

[0003] Taking common metal coatings such as copper or nickel as examples, these metals have high electron activity and are prone to electron migration in specific environments (such as electric field and high temperature). Electron migration can form intermetallic compounds (IMC), which can cause irreversible changes in the internal structure of the metal coating, such as the formation of pores or whiskers, which can seriously affect the physical and chemical properties of the coating. For example, in the field of electronic components, electron migration can cause circuit short circuit, signal interference and other failures, which can significantly reduce the reliability and service life of the components; in the fields of aerospace and automobile manufacturing, electron migration can accelerate the electrochemical corrosion of the metal coating, weaken the protection ability of the parts, and bring safety hazards.

[0004] Therefore, there is an urgent need in the art to develop a new type of metal coating that can effectively inhibit the formation of intermetallic compounds caused by electron migration and a preparation method thereof. SUMMARY

[0005] The present application aims to provide a composite metal coating without electron escape interference and a preparation method thereof, to solve the technical problem of performance degradation of metal coatings caused by electron migration forming intermetallic compounds in the prior art.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] The present application provides a composite metal coating without electron escape interference, which comprises from inside to outside:

[0008] a substrate, the material of the substrate is copper alloy, which serves as the bearing basis of the coating;

[0009] a first metal conductive layer, the material of the first metal conductive layer is copper or nickel, which is used to provide a conductive basis for the subsequent coating and enhance the bonding force between the coating and the substrate;

[0010] a second metal-nonmetal composite conductive layer, in the second metal-nonmetal composite conductive layer, the metal component includes nickel, and the nonmetal element includes phosphorus or boron;

[0011] A heterojunction structure layer is formed on the second metal-nonmetal composite conductive layer by phosphating and heat treating the second metal-nonmetal composite conductive layer or by nitriding and heat treating the second metal-nonmetal composite conductive layer, for shielding metal electron active migration.

[0012] A third conductive layer is formed on the heterojunction structure layer, and the material of the third conductive layer is tin, for providing conductive performance.

[0013] The application further provides a preparation method of the composite metal coating without electronic escape interference, which is used for preparing the composite metal coating and comprises the following steps:

[0014] S1, pretreating the substrate to remove impurities on the surface of the substrate;

[0015] S2, electrodepositing a first metal conductive layer on the pretreated substrate;

[0016] S3, electrodepositing a second metal-nonmetal composite conductive layer on the first metal conductive layer;

[0017] S4, phosphating or nitriding the second metal-nonmetal composite conductive layer, and then heat treating to form a heterojunction structure layer;

[0018] S5, electrodepositing a third conductive layer on the heterojunction structure layer.

[0019] In some embodiments, in the step S2, the current density for electrodepositing the first metal conductive layer is 1-5 A / dm2, the temperature is 20-40℃, and the time is 10-60 minutes.

[0020] In some embodiments, in the step S3, the current density for electrodepositing the second metal-nonmetal composite conductive layer is 0.5-3 A / dm2, the temperature is 30-50℃, and the time is 15-90 minutes.

[0021] In some embodiments, in the step S4, the temperature for phosphating is 30-60℃, and the time is 5-30 minutes; the nitriding is performed in a nitrogen atmosphere, the temperature is 400-600℃, the nitrogen flow rate is 0.1-1 L / min, and the time is 1-5 hours.

[0022] In some embodiments, in the step S4, the temperature for heat treating is 200-400℃, and the time is 0.5-3 hours.

[0023] Compared with the prior art, the application has the following beneficial technical effects:

[0024] (1) The application builds a heterojunction structure layer on the second metal-nonmetal composite conductive layer, uses the hybridization of inorganic nonmetal (such as phosphide, nitride) and metal ions to form a dense, stable and high-oxidation-resistant barrier structure on the surface of the copper or nickel metal layer, which can effectively block and shield the electron migration of the inner layer of copper, nickel and other active metals, fundamentally reduce the formation of intermetallic compounds due to electron migration, and further cause the damage of coating structure and performance decline, greatly improving the reliability and service life of the coating in harsh environments.

[0025] (2) The preparation method of the application adopts mature and conventional industrial surface treatment processes such as electrodeposition, phosphating / nitriding treatment and heat treatment, the whole process flow is reasonable in design, the steps are closely connected, the process parameters are easy to control and optimize, the production cost is relatively low, and it is very suitable for large-scale industrial production and popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the specific embodiments of the application or the technical solutions in the prior art, the drawings needed in the specific embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0027] Figure 1 is a structure schematic diagram of a composite metal coating without electronic escape interference in the application;

[0028] Figure 2 is a preparation method flow chart of a composite metal coating without electronic escape interference in the application;

[0029] Figure 3 is an electron microscope scanning diagram of the sample prepared in example 1 and comparative example 1 under 1000 times, wherein, Figure 3 a is an electron microscope scanning diagram of the sample prepared in example 1 under 1000 times, Figure 3 b is an electron microscope scanning diagram of the sample prepared in comparative example 1 under 1000 times;

[0030] Figure 4 is an electron microscope scanning diagram of the sample prepared in example 1 and comparative example 1 under 500 times after baking and folding, wherein, Figure 4 a is an electron microscope scanning diagram of the sample prepared in example 1 under 500 times after baking and folding, Figure 4 b is an electron microscope scanning diagram of the sample prepared in comparative example 1 under 500 times after baking and folding.

[0031] In the figure: 1. Substrate, 2. First metal conductive layer, 3. Second metal-nonmetal composite conductive layer, 4. Heterojunction structure layer, 5. Third conductive layer. Detailed Implementation

[0032] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0033] like Figure 1 As shown, the present invention provides a composite metal coating free from electron emission interference, the composite metal coating comprising, from the inside to the outside:

[0034] Substrate 1, the material of which is copper alloy, serves as the base for the coating. Other suitable materials besides copper alloy can also be selected according to the specific application scenario.

[0035] The first metal conductive layer 2 is made of copper or nickel and is used to provide a conductive base for subsequent coatings and enhance the adhesion between the coating and the substrate 1. Other metals with good conductivity can also be selected.

[0036] The second metal-nonmetal composite conductive layer 3 is composed of metal and nonmetal elements. The metal component includes nickel, and the nonmetal element includes phosphorus or boron. It is formed on the surface of the first metal conductive layer 2 by electrodeposition. This composite conductive layer can form a stable structure with the material being processed later, further improving the performance of the coating.

[0037] The heterojunction structure layer 4 is formed on the second metal-nonmetal composite conductive layer 3 by phosphating and heat treatment, or by nitriding and heat treatment. It utilizes the hybrid properties of inorganic nonmetals and metal ions to form a barrier structure with high oxidation resistance and stability on the surface of copper or nickel metal layer, effectively shielding the electron migration of active metals such as copper and nickel.

[0038] The third conductive layer 5 is made of tin and is used to provide conductivity.

[0039] In the above embodiments, the composite metal coating utilizes the hybrid properties of inorganic non-metals and metal ions to effectively form a highly antioxidant and stable barrier structure on the surface of a copper or nickel metal layer. This shields against electron migration from active metals such as copper and nickel, solving the technical problem of intermetallic compounds formed by electron migration affecting the solderability and corrosion resistance of the metal coating. Therefore, the composite metal coating provided by this invention can effectively shield against active electron migration and has great potential for industrial application.

[0040] like Figure 2As shown, the present application also provides a method for preparing the composite metal coating without electron escape interference, which comprises the following steps:

[0041] S1, pretreating the substrate 1 to remove impurities on the surface of the substrate 1;

[0042] Specifically, the substrate 1 is cleaned, degreased, and derusted to remove impurities such as dirt, grease, and oxides on the surface of the substrate 1, so as to ensure the cleanliness and flatness of the surface of the substrate 1 and provide good conditions for the subsequent deposition of the coating; the cleaning method can be selected according to the material and pollution degree of the substrate 1, such as ultrasonic cleaning with an alkaline cleaning agent.

[0043] S2, electrodepositing a first metal conductive layer 2 on the pretreated substrate 1;

[0044] Specifically, the pretreated substrate 1 is used as a cathode and is placed in an electroplating solution containing copper or nickel ions to be electrodeposited, so as to form the first metal conductive layer 2 on the surface of the substrate 1, wherein the current density is controlled to be 1-5 A / dm 2 , the temperature is 20-40℃, and the electrodeposition time is 10-60 min; in other embodiments, the composition and process parameters of the electroplating solution can be adjusted according to the thickness and performance of the required first metal conductive layer 2. For example, the electroplating solution can be an acidic electroplating solution composed of copper sulfate and sulfuric acid.

[0045] S3, electrodepositing a second metal-nonmetal composite conductive layer 3 on the first metal conductive layer 2;

[0046] Specifically, the substrate 1 with the deposited first metal conductive layer 2 is used as a cathode and is placed in a composite electroplating solution containing metal ions and nonmetal elements to be electrodeposited, so as to form the second metal-nonmetal composite conductive layer 3 on the surface of the first metal conductive layer 2, wherein the current density is controlled to be 0.5-3 A / dm², the temperature is 30-50℃, and the electrodeposition time is 15-90 min; the metal ions in the composite electroplating solution can be selected from metals matching the first metal conductive layer 2, and the nonmetal elements can be selected from phosphorus, boron, etc., for example, a composite electroplating solution containing nickel ions and phosphorus elements can be used.

[0047] S4, phosphating or nitriding the second metal-nonmetal composite conductive layer 3, and then performing heat treatment to form a heterojunction structure layer 4;

[0048] In this step:

[0049] The phosphating treatment is specifically: the substrate 1 on which the second metal-nonmetal composite conductive layer 3 is deposited is immersed in a phosphating solution to perform a phosphating reaction, and then a phosphating film is formed on the surface of the second metal-nonmetal composite conductive layer 3, wherein the temperature is controlled at 30-60°C, the time is 5-30 min, and the phosphating solution can be a conventional phosphating solution such as a zinc series or a manganese series;

[0050] The nitriding treatment is specifically: the substrate 1 on which the second metal-nonmetal composite conductive layer 3 is deposited is placed in a nitriding furnace to perform a nitriding treatment, so that the nonmetal element and the metal ion form a nitride to form a heterojunction structure, wherein the nitriding temperature is controlled at 400-600°C, the nitrogen flow rate is 0.1-1 L / min, and the time is 1-5 h;

[0051] The heat treatment is specifically: the substrate 1 after the phosphating treatment or the nitriding treatment is subjected to a heat treatment to further promote the formation and stability of the heterojunction structure, wherein the heat treatment temperature is controlled at 200-400°C, and the time is 0.5-3 h.

[0052] S5, a third conductive layer 5 is formed on the heterojunction structure layer 4 by electrodeposition.

[0053] This step is specifically: the substrate 1 after the treatment in step S4 is used as a cathode and is placed in an electroplating solution containing conductive metal ions (such as tin, copper, nickel, etc.) to perform electrodeposition, and then a third conductive layer 5 is formed on the surface of the heterojunction structure layer 4, thereby obtaining a final composite metal coating without electron escape interference, wherein the electrodeposition current density in this step is controlled at 0.2-2 A / dm², the temperature is 15-35°C, and the electrodeposition time is 5-60 min.

[0054] Based on the description of the composite metal coating without electron escape interference described above, the composite metal coating without electron escape interference prepared by the preparation method of the composite metal coating without electron escape interference has the same beneficial technical effects, which will not be described here.

[0055] In order to further illustrate the technical principles and technical effects of the present application, a composite metal coating for an electronic component lead frame is taken as an example to be described below.

[0056] Example 1

[0057] The composite metal coating is prepared by the preparation method provided by the present application, and the process steps are as shown in the accompanying drawings: Figure 1

[0058] S1, substrate pretreatment: a copper alloy is used as the substrate 1, which is ultrasonically cleaned in an alkaline cleaning solution for 10 minutes, then rinsed with deionized water, and then immersed in dilute sulfuric acid for acid activation;

[0059] ​S2, forming a first metal conductive layer 2 on the pretreated substrate 1 by electrodeposition: using an acidic copper sulfate plating solution, taking the pretreated substrate 1 as the cathode, electrodeposition at a current density of 1 A / dm2 and a temperature of 20℃ for 60 minutes to form a copper layer with a thickness of 5 μm as the first metal conductive layer 2;

[0060] S3, forming a second metal-nonmetal composite conductive layer 3 on the first metal conductive layer 2 by electrodeposition: using a chemical nickel-phosphorus alloy plating solution mainly containing nickel sulfate and sodium hypophosphite, taking the substrate 1 with the first metal conductive layer 2 deposited thereon as the cathode, electrodeposition at a current density of 0.5 A / dm2 and a temperature of 30℃ for 90 minutes to form a Ni-P alloy layer with a thickness of 3 μm as the second metal-nonmetal composite conductive layer 3;

[0061] S4, performing phosphating or nitriding treatment on the second metal-nonmetal composite conductive layer 3, and then performing heat treatment to form a heterojunction structure layer 4: immersing the substrate 1 with the second metal-nonmetal composite conductive layer 3 deposited thereon into a zinc-based phosphating solution, treating at 30℃ for 30 minutes to form a phosphating film; then performing heat treatment at 200℃ for 3 hours under inert gas protection to promote the Ni-P layer to fully react with the nonmetallic phosphorus element to form a stable Ni-P compound (such as Ni3P) heterojunction structure layer 4;

[0062] S5, forming a third conductive layer 5 on the heterojunction structure layer 4 by electrodeposition: using a stannic methanesulfonic acid plating solution, taking the substrate 1 with the heterojunction structure layer 4 formed thereon as the cathode, electrodeposition at a current density of 0.2 A / dm2 and a temperature of 15℃ for 60 minutes to form a third conductive layer 5 with a thickness of 4 μm, thereby obtaining the target composite metal coating.

[0063] Example 2

[0064] The composite metal coating is prepared by the preparation method provided in the present application, and the process steps are as shown in the accompanying Figure 1

[0065] S1, substrate pretreatment: using copper alloy as the substrate 1, ultrasonic cleaning in an alkaline cleaning solution for 10 minutes, then rinsing with deionized water, and then immersing in dilute sulfuric acid for acid activation;

[0066] S2, forming a first metal conductive layer 2 on the pretreated substrate 1 by electrodeposition: using an acidic copper sulfate plating solution, taking the pretreated substrate 1 as the cathode, electrodeposition at a current density of 3 A / dm2 and a temperature of 30℃ for 30 minutes to form a copper layer with a thickness of 5 μm as the first metal conductive layer 2;

[0067] ​S3, forming a second metal-nonmetal composite conductive layer 3 on the first metal conductive layer 2 by electrodeposition: using a chemical nickel-phosphorus alloy plating solution mainly containing nickel sulfate and sodium hypophosphite, taking the substrate 1 with the first metal conductive layer 2 deposited thereon as a cathode, and electrodeposition is performed at a current density of 2 A / dm2 and a temperature of 40°C for 50 minutes to form a Ni-P alloy layer with a thickness of 3 μm as the second metal-nonmetal composite conductive layer 3;

[0068] S4, performing phosphating or nitriding treatment on the second metal-nonmetal composite conductive layer 3, and then performing heat treatment to form a heterojunction structure layer 4: immersing the substrate 1 with the second metal-nonmetal composite conductive layer 3 deposited thereon into a zinc-based phosphating solution, and performing treatment at 40°C for 15 minutes to form a phosphating film; then performing heat treatment at 300°C for 1.5 hours under inert gas protection to promote the Ni-P layer to fully react with the nonmetallic phosphorus element to form a stable Ni-P compound (such as Ni3P) heterojunction structure layer 4;

[0069] S5, forming a third conductive layer 5 on the heterojunction structure layer 4 by electrodeposition: using a stannic methanesulfonate plating solution, taking the substrate 1 with the heterojunction structure layer 4 formed thereon as a cathode, and electrodeposition is performed at a current density of 1.5 A / dm2 and a temperature of 25°C for 30 minutes to form a third conductive layer 5 with a thickness of 4 μm, thereby obtaining the target composite metal coating.

[0070] Example 3

[0071] The composite metal coating is prepared by the preparation method provided in the present application, and the process steps are as shown in the accompanying drawings: Figure 1

[0072] S1, substrate pretreatment: taking copper alloy as the substrate 1, immersing it in an alkaline cleaning solution for ultrasonic cleaning for 10 minutes, then rinsing it with deionized water, and then immersing it in dilute sulfuric acid for acid activation;

[0073] S2, forming a first metal conductive layer 2 on the pretreated substrate 1 by electrodeposition: using an acidic copper sulfate plating solution, taking the pretreated substrate 1 as a cathode, and electrodeposition is performed at a current density of 5 A / dm2 and a temperature of 40°C for 10 minutes to form a copper layer with a thickness of 5 μm as the first metal conductive layer 2;

[0074] S3, forming a second metal-nonmetal composite conductive layer 3 on the first metal conductive layer 2 by electrodeposition: using a chemical nickel-phosphorus alloy plating solution mainly containing nickel sulfate and sodium hypophosphite, taking the substrate 1 with the first metal conductive layer 2 deposited thereon as a cathode, and electrodeposition is performed at a current density of 3 A / dm2 and a temperature of 50°C for 15 minutes to form a Ni-P alloy layer with a thickness of 3 μm as the second metal-nonmetal composite conductive layer 3;

[0075] ​S4. The second metal-nonmetal composite conductive layer 3 is subjected to phosphating or nitriding treatment, followed by heat treatment to form a heterojunction structure layer 4: The substrate 1 on which the second metal-nonmetal composite conductive layer 3 is deposited is immersed in a zinc-based phosphating solution and treated at 60°C for 5 minutes to form a phosphating film; then, under inert gas protection, it is heat-treated at 400°C for 0.5 hours to promote the full reaction of the Ni-P layer with nonmetallic phosphorus elements to form a stable Ni-P compound (such as Ni3P) heterojunction structure layer 4.

[0076] S5. Electrodeposit a third conductive layer 5 on the heterojunction structure layer 4: Using tin methanesulfonate electroplating solution, with the substrate 1 on which the heterojunction structure layer 4 is formed as the cathode, electrodeposit for 5 minutes at a current density of 2A / dm² and a temperature of 35°C to form a third conductive layer 5 with a thickness of 4μm, thus obtaining the target composite metal coating.

[0077] Comparative Example 1

[0078] The same substrate 1 as in Example 1 was selected and pretreated. Then, a copper layer with a thickness of 5 μm was directly electrodeposited on the selected copper alloy substrate, and a third conductive layer 5 (i.e., tin layer) with a thickness of 4 μm was electrodeposited on the surface of the electrodeposited copper layer.

[0079] Product performance testing

[0080] (1) The samples prepared in Example 1 and Comparative Example 1 were subjected to electron microscopy analysis, such as... Figure 3 As shown, Figure 3 a shows the electron microscopy scanning results of the sample prepared in Example 1 under 1000x magnification. Figure 3 b shows the electron microscopy scanning results of the sample prepared in Comparative Example 1 at 1000x magnification. Figure 3 As can be seen, the sample prepared in Example 1 showed almost no electron migration, while the sample prepared in Comparative Example 1 showed a very obvious electron migration phenomenon.

[0081] (2) The samples prepared in Example 1 and Comparative Example 1 were baked at 300°C for 60 min, then quickly immersed in room temperature water for 5 min, and then repeatedly folded 180 degrees 10 times for scanning electron microscopy analysis. Their surface morphology was then observed using a scanning electron microscope. Figure 4 As shown, Figure 4 a shows the electron microscope scanning results of the sample in Example 1 after baking and folding, under 500x magnification. Figure 4 b shows the electron microscopy scanning results of the sample in Comparative Example 1 after baking and folding, under 500x magnification. Figure 4As can be seen from Table 1, the sample surface in Comparative Example 1 appears serious cracking, while the sample surface in Example 1 only appears creases, because the sample prepared in Comparative Example 1 appears obvious electron migration to form intermetallic compounds, and the existence of the intermetallic compounds increases the brittleness of the coating, thus causing the sample in Example 1 to appear serious cracking phenomenon after being folded and baked.

[0082] (3) The sample composite metal coating prepared in Example 1-3 and Comparative Example 1 is subjected to performance test, and the test results are shown in Table 1.

[0083] Table 1 Performance test results of the sample composite metal coating prepared in Example 1-3 and Comparative Example 1

[0084]

[0085] As can be seen from Table 1, the sample composite metal coating prepared in Example 1-3 has no obvious oxidation or corrosion on the surface after high temperature and high humidity test, and the electrical performance is stable; while the sample composite metal coating prepared in Comparative Example 1 has obvious oxidation spots on the surface after high temperature and high humidity test, and the contact resistance is obviously increased. This shows that, compared with the traditional method, the sample composite metal coating prepared by the preparation method provided in the present application has more excellent corrosion resistance;

[0086] The sample composite metal coating prepared in Example 1-3 has large solder spreading area, thin and continuous IMC layer at the solder joint interface, and high strength after solderability test; while the sample composite metal coating prepared in Comparative Example 1 has thick and uneven Cu-Sn IMC layer at the solder joint interface after high temperature and high humidity test, and has crack risk. This shows that, compared with the traditional method, the composite metal coating prepared by the preparation method provided in the present application has better solderability;

[0087] The sample composite metal coating prepared in Example 1-3 has no obvious structural damage after electromigration test; while the sample composite metal coating prepared in Comparative Example 1 has obvious holes formed by copper atom depletion at the cathode side after electromigration test. This shows that, compared with the traditional method, the sample composite metal coating prepared by the preparation method provided in the present application effectively shields the electron active migration.

[0088] In summary, the composite metal coating prepared by the preparation method provided in the present application has excellent effects in inhibiting electron migration, improving solderability and corrosion resistance.

[0089] The above describes in detail the composite metal coating without electronic escape interference and the preparation method thereof provided by the present application. The principles and implementation manners of the present application are described by using specific examples, and the above description of the examples is only used to help understand the core idea of the present application. It should be pointed out that, for those skilled in the art, some improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A composite metal coating free of electronic escape interference, characterized in that From inside to outside in turn includes: A substrate, the material of which is copper alloy, which serves as the bearing base of the coating; A first metal conductive layer, the material of which is copper or nickel, which is used to provide a conductive base for the subsequent coating and enhance the binding force between the coating and the substrate; A second metal-nonmetal composite conductive layer, in which the metal component includes nickel, and the nonmetal element includes phosphorus or boron; A heterojunction structure layer, which is formed on the second metal-nonmetal composite conductive layer by phosphating and heat treatment of the second metal-nonmetal composite conductive layer or by nitriding and heat treatment of the second metal-nonmetal composite conductive layer, and is used to shield the metal electronic active migration; A third conductive layer, the material of which is tin, which is used to provide conductive performance.

2. A method for producing a composite metal coating without electronic escape interference, characterized by, The method is used for preparing the composite metal coating as claimed in claim 1, which comprises the following steps: S1, pretreating the substrate to remove the impurities on the surface of the substrate; S2, electrodepositing the first metal conductive layer on the pretreated substrate; S3, electrodepositing the second metal-nonmetal composite conductive layer on the first metal conductive layer; S4, phosphating or nitriding the second metal-nonmetal composite conductive layer, and then heat treating to form the heterojunction structure layer; S5, electrodepositing the third conductive layer on the heterojunction structure layer.

3. The preparation method according to claim 2, characterized in that, In the step S2, the current density used for electrodeposition of the first metal conductive layer is 1-5 A / dm², the temperature is 20-40℃, and the time is 10-60 minutes.

4. The preparation method according to claim 2, characterized in that, In the step S3, the current density used for electrodeposition of the second metal-nonmetal composite conductive layer is 0.5-3 A / dm², the temperature is 30-50℃, and the time is 15-90 minutes.

5. The preparation method according to claim 2, characterized in that, In the step S4, the temperature of the phosphating treatment is 30-60℃, and the time is 5-30 minutes; the nitriding treatment is carried out in a nitrogen atmosphere, the temperature is 400-600℃, the nitrogen flow rate is 0.1-1 L / min, and the time is 1-5 hours.

6. The preparation method according to claim 2, characterized in that, In the step S4, the temperature of the heat treatment is 200-400℃, and the time is 0.5-3 hours.

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