Selective etching solutions for improving adhesion to nickel substrates and their application methods

Abstract

This application provides a selective etching solution for improving the adhesion of nickel substrate surfaces and its application method. The selective etching solution comprises: organic acid, oxidizing agent, corrosion inhibitor, wetting agent, and the balance being deionized water; its pH value is 3.5-4.5. The application method includes: adding 10% ammonia water to the selective etching solution to adjust the pH value; adjusting the operating temperature of the selective etching solution to the range of 20-50°C; and completely immersing the nickel substrate in the selective etching solution for 5-10 minutes to remove nickel oxide from the surface of the nickel substrate. The selective etching solution provided by this application can efficiently and selectively remove the oxide film on the surface of the nickel substrate, while significantly inhibiting excessive corrosion of the nickel metal, improving the adhesion of the nickel substrate surface, thereby stably obtaining a high-bonding subsequent plating layer / nickel substrate interface.

Description

Technical Field

[0001] This application belongs to the field of metal surface treatment technology, and specifically relates to a selective etching solution for improving the adhesion of nickel substrates and its application method. Background Technology

[0002] Nickel and its alloys are widely used as intermediate or bottom layers in multilayer electroplating structures due to their excellent corrosion resistance, electrical conductivity, and solderability. However, nickel readily forms a dense nickel oxide (NiO) passivation film in air. When other metals (such as gold, silver, copper, chromium, etc.) need to be electroplated on the nickel surface, if this oxide film is not effectively removed, it will lead to extremely poor adhesion between the subsequent plating layer and the nickel substrate, resulting in peeling, blistering, or delamination.

[0003] Some existing activation methods (such as strong acid immersion or cathodic activation) often have the drawback of excessive corrosion of the nickel substrate. Common inorganic strong acids (such as hydrochloric acid) can significantly dissolve nickel, leading to changes in workpiece dimensions or excessive surface roughness, and easily causing pitting and grain boundary corrosion on the nickel surface, which in turn damages the interfacial bonding quality. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of the prior art and provide a selective etching solution that can efficiently remove nickel oxide but has almost no corrosion to the nickel metal substrate, thereby improving the surface adhesion of the nickel substrate and its application method.

[0005] To achieve the above objectives, in a first aspect, this application provides: a selective etching solution for improving the adhesion of nickel substrate surfaces, comprising: organic acid, oxidizing agent, corrosion inhibitor, wetting agent, with the balance being deionized water; the pH value of the selective etching solution is 3.5 to 4.5.

[0006] In one feasible embodiment, the organic acid is one or more of citric acid and glycolic acid.

[0007] In one feasible embodiment, the concentration of citric acid is 10–30 g / L.

[0008] In one feasible embodiment, the concentration of the glycolic acid is 5–15 g / L.

[0009] In one feasible embodiment, the oxidizing agent is ammonium persulfate or 30% hydrogen peroxide.

[0010] In one feasible embodiment, the concentration of ammonium persulfate is 0.5–2 g / L.

[0011] In one feasible embodiment, the concentration of the 30% hydrogen peroxide is 0.1–2 mL / L.

[0012] In one feasible embodiment, the corrosion inhibitor is benzotriazole, and the concentration of benzotriazole is 0.1-0.3 g / L.

[0013] In one feasible embodiment, the wetting agent is sodium dodecyl sulfate, and the concentration of sodium dodecyl sulfate is 0.05-0.2 g / L.

[0014] Secondly, this application provides: a method for improving the adhesion of a nickel substrate surface using the selective etching solution described in the first aspect, comprising the following steps:

[0015] S1, add 10% ammonia to the selective corrosion solution to adjust the pH value;

[0016] S2, adjust the working temperature of the selective etching solution to the range of 20-50℃;

[0017] S3. Immerse the nickel substrate completely in the selective etching solution for 5-10 minutes to remove nickel oxide from the surface of the nickel substrate.

[0018] This application has the following advantages compared with the prior art:

[0019] The selective etching solution provided in this application can efficiently and selectively remove the oxide film on the surface of the nickel substrate, while significantly inhibiting excessive corrosion of the nickel metal body and improving the adhesion of the nickel substrate surface, thereby stably obtaining a high-bonding subsequent coating / nickel substrate interface. Specific Implementation

[0020] To illustrate the technical content, structural features, achieved objectives, and effects of the invention in detail, the technical solutions in the embodiments of this application will be described below. Obviously, the described embodiments are merely a part of the embodiments of this application, and not all of them. In the following description, for illustrative purposes, numerous specific details are set forth to provide a detailed description of various exemplary embodiments or implementations of the invention. However, various exemplary embodiments may also be implemented independently without these specific details or in one or more equivalent arrangements. Furthermore, the various exemplary embodiments may differ, but are not necessarily exclusive. For example, the specific shape, structure, and characteristics of the exemplary embodiments may be used or implemented in another exemplary embodiment without departing from the inventive concept.

[0021] This application provides a selective etching solution to improve the adhesion of nickel substrate surfaces. This selective etching solution only etches nickel oxide on the surface of the nickel substrate, but has almost no corrosion on the nickel substrate itself, thereby improving the adhesion between the nickel substrate and subsequent plating layers.

[0022] This selective etching solution contains organic acid, an oxidizing agent, a corrosion inhibitor, and a wetting agent, with the balance being deionized water. The organic acid provides a weakly acidic environment, maintaining the pH of the selective etching solution between 3.5 and 4.5. This acidic environment has a complexing and dissolving capacity for nickel oxide, thereby removing the oxide film, but its dissolution rate for metallic nickel is extremely low. The oxidizing agent preferentially reacts with nickel oxide to form soluble products and does not attack metallic nickel. The corrosion inhibitor chemically adsorbs onto the surface of metallic nickel, forming a protective film that further inhibits the corrosion of metallic nickel. The wetting agent reduces surface tension, ensuring sufficient contact between the etching solution and the oxide film, avoiding localized differences. The use of deionized water ensures that this selective etching solution is a chloride-free aqueous solution, preventing chloride ions from exacerbating pitting corrosion during etching or subsequent electroplating processes.

[0023] The organic acid is one or more of citric acid and glycolic acid. Both citric acid and glycolic acid contain hydroxyl and carboxyl groups, which can form stable complexes with dissolved nickel ions, preventing secondary deposition of nickel ions on the nickel substrate surface or the formation of insoluble hydroxides, thus maintaining interface cleanliness. As weak acids, citric acid and glycolic acid are milder than strong inorganic acids (such as hydrochloric acid and sulfuric acid), helping to maintain the pH of the etching solution within the range of 3.5–4.5. Combined with corrosion inhibitors, they can achieve highly selective removal, thereby removing nickel oxide while maintaining the basic integrity of the nickel substrate surface. Specifically, the concentration of citric acid in the etching solution of this application is 10–30 g / L, and the concentration of glycolic acid in the etching solution of this application is 5–15 g / L.

[0024] The oxidation aid, in combination with organic acids, forms an "oxidation-dissolution" mechanism, which can quickly and thoroughly remove nickel oxide even at room temperature or low temperature. The oxidation treatment can also form a uniform, slightly rough active layer on the nickel substrate surface, which is beneficial to the nucleation and growth of subsequent plating layers.

[0025] The oxidizing agent is ammonium persulfate or 30% hydrogen peroxide. Ammonium persulfate has stable oxidizing properties, a mild and long-lasting effect, and is suitable for relatively long-term corrosion treatment (5-10 min). Its concentration in the corrosion solution of this application is 0.5-2 g / L. 30% hydrogen peroxide leaves no residue after decomposition, producing only water and oxygen, making it environmentally friendly. However, its stability needs to be considered, and it is suitable for short-term or low-temperature treatment. Its concentration in the corrosion solution of this application is 0.1-2 mL / L.

[0026] The corrosion inhibitor is benzotriazole. Benzotriazole is a highly efficient organic corrosion inhibitor for metals such as copper and nickel. The nitrogen atoms in its molecule preferentially adsorb onto the active surface of metallic nickel, forming a dense, hydrophobic adsorption film. This adsorption film significantly hinders the direct contact between hydrogen ions and oxidants and metallic nickel, thereby greatly slowing down the dissolution rate of metallic nickel in acidic media. However, benzotriazole has a very weak adsorption capacity for nickel oxide, so nickel oxide can still be effectively removed. Benzotriazole prevents pitting corrosion, grain boundary corrosion, and excessive dissolution, ensuring that the original size and microstructure of the nickel matrix are not damaged, thus maintaining good mechanical properties. The concentration of benzotriazole in the etching solution of this application is 0.1–0.3 g / L. Too low a concentration will result in insufficient inhibition, while too high a concentration may hinder the removal of nickel oxide or increase costs.

[0027] The wetting agent is sodium dodecyl sulfate (NDS). NDS is chemically stable within a pH range of 3.5–4.5 and does not undergo hydrolysis or precipitation. NDS exhibits good synergy with benzotriazole; after the etching solution spreads evenly, benzotriazole molecules can also reach the nickel substrate surface uniformly, forming a dense and complete protective film. Furthermore, NDS is easy to clean and inexpensive, making it suitable for the selective etching solution used in this application. The concentration of NDS in the etching solution of this application is 0.05–0.2 g / L.

[0028] The selective etching solution of this application exhibits extremely low corrosion to metallic nickel to maintain its excellent coating morphology, while efficiently removing nickel oxide without pitting or grain boundary corrosion, thereby improving the adhesion between the nickel substrate surface and subsequent coatings.

[0029] This application also provides an application method for improving the surface adhesion of a nickel substrate using the above-mentioned selective etching solution, the application method comprising the following steps:

[0030] S1, add 10% ammonia to the selective corrosion solution to adjust the pH value;

[0031] S2, adjust the working temperature of the selective etching solution to the range of 20-50℃;

[0032] S3. Immerse the nickel substrate completely in the selective etching solution for 5-10 minutes to remove nickel oxide from the surface of the nickel substrate.

[0033] The selective etching solution and its application method of this application are further illustrated below through multiple embodiments and comparative examples.

[0034] Example 1

[0035] 1μm of gold was electroplated onto a 50μm nickel substrate, and the nickel substrate was treated before gold plating.

[0036] A selective etching solution was prepared, consisting of: 20 g / L citric acid, 10 g / L glycolic acid, 1.0 g / L ammonium persulfate, 0.2 g / L benzotriazole, 0.1 g / L sodium dodecyl sulfate, with the balance being deionized water. The pH of the selective etching solution was adjusted to 4.0 using 10% ammonia solution. The temperature of the selective etching solution was adjusted to 40°C. The nickel substrate was completely immersed in the selective etching solution for 5 minutes, with gentle magnetic stirring during the immersion. After immersion, the nickel substrate was rinsed with deionized water and immediately transferred to a gold plating bath for gold plating.

[0037] Example 2

[0038] 1μm of gold was electroplated onto a 50μm nickel substrate, and the nickel substrate was treated before gold plating.

[0039] Prepare a selective etching solution with the following components: 15 g / L citric acid, 0.5 g / L ammonium persulfate, 0.1 g / L benzotriazole, 0.05 g / L sodium dodecyl sulfate, and the balance being deionized water.

[0040] Adjust the pH of the selective etching solution to 4.0 using 10% ammonia. Set the selective etching solution to 25°C. Completely immerse the nickel substrate in the selective etching solution for 10 minutes. After immersion, rinse the nickel substrate with deionized water. Immediately transfer the cleaned nickel substrate to a gold plating bath for gold plating.

[0041] Example 3

[0042] 1μm of gold was electroplated onto a 50μm nickel substrate, and the nickel substrate was treated before gold plating.

[0043] Prepare a selective etching solution with the following components: 15 g / L citric acid, 10 g / L glycolic acid, 0.5 mL / L 30% hydrogen peroxide, 0.2 g / L benzotriazole, 0.1 g / L sodium dodecyl sulfate, and the balance being deionized water.

[0044] Adjust the pH of the selective etching solution to 4.0 using 10% ammonia. Set the selective etching solution to 25°C. Completely immerse the nickel substrate in the selective etching solution for 10 minutes. After immersion, rinse the nickel substrate with deionized water. Immediately transfer the cleaned nickel substrate to a gold plating bath for gold plating.

[0045] Example 4

[0046] 1μm of gold was electroplated onto a 50μm nickel substrate, and the nickel substrate was treated before gold plating.

[0047] Prepare a selective etching solution with the following components: 15 g / L citric acid, 1 mL / L 30% hydrogen peroxide, 0.3 g / L benzotriazole, 0.05 g / L sodium dodecyl sulfate, and the balance being deionized water.

[0048] Adjust the pH of the selective etching solution to 4.0 using 10% ammonia solution. Set the selective etching solution temperature to 35°C. Completely immerse the nickel substrate in the selective etching solution for 10 minutes. After immersion, rinse the nickel substrate with deionized water. Immediately transfer the cleaned nickel substrate to a gold plating bath for gold plating.

[0049] Example 5

[0050] 1μm of gold was electroplated onto a 50μm nickel substrate, and the nickel substrate was treated before gold plating.

[0051] Prepare a selective etching solution with the following components: 10 g / L glycolic acid, 1 mL / L 30% hydrogen peroxide, 0.3 g / L benzotriazole, 0.05 g / L sodium dodecyl sulfate, and the balance being deionized water.

[0052] Adjust the pH of the selective etching solution to 4.0 using 10% ammonia solution. Adjust the temperature of the selective etching solution to 40°C. Completely immerse the nickel substrate in the selective etching solution for 10 minutes. After immersion, rinse the nickel substrate with deionized water. Immediately transfer the cleaned nickel substrate to a gold plating bath for gold plating.

[0053] Example 6

[0054] 1μm of gold was electroplated onto a 50μm nickel substrate, and the nickel substrate was treated before gold plating.

[0055] Prepare a selective etching solution with the following components: 15 g / L glycolic acid, 1 g / L ammonium persulfate, 0.3 g / L benzotriazole, 0.1 g / L sodium dodecyl sulfate, and the balance being deionized water.

[0056] Adjust the pH of the selective etching solution to 4.0 using 10% ammonia solution. Set the selective etching solution to 20°C. Completely immerse the nickel substrate in the selective etching solution for 10 minutes. After immersion, rinse the nickel substrate with deionized water. Immediately transfer the cleaned nickel substrate to a gold plating bath for gold plating.

[0057] Comparative Example

[0058] 1μm of gold was electroplated onto a 50μm nickel substrate, and the nickel substrate was treated before gold plating.

[0059] A 3.5% wt hydrochloric acid solution was used as the etching solution. The temperature of the etching solution was adjusted to 25°C. The nickel substrate was completely immersed in the etching solution for 20 minutes. After immersion, the nickel substrate was rinsed with deionized water and immediately transferred to a gold plating bath for gold plating.

[0060] The samples prepared in Examples 1-6 and the comparative examples were subjected to adhesion and bending tests. The adhesion test employed a thermal shock test: the sample was heated to 300°C and held for 5 minutes, then rapidly immersed in room temperature water for quenching; this cycle was repeated 20 times, and the coating was observed for blistering or delamination. The bending test involved folding the sample 180° and observing whether the coating cracked or separated at the crease. The test results are shown in the table below:

[0061] sample Coating condition after thermal shock test Coating condition after bending test Example 1 No bubbling, no peeling No cracks, no delamination Example 2 No bubbling, no peeling No cracks, no delamination Example 3 No bubbling, no peeling No cracks, no delamination Example 4 No bubbling, no peeling No cracks, no delamination Example 5 No bubbling, no peeling No cracks, no delamination Example 6 No bubbling, no peeling No cracks, no delamination Comparative Example localized mild blistering cracking

[0062] As can be seen from the table above, the nickel substrate pretreated with the selective etching solution provided in this application has strong adhesion to the coating and is not prone to peeling, blistering, or delamination.

[0063] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope. The scope of protection of the present invention is defined by the appended claims, specification, and their equivalents.

Claims

1. A selective etching solution for improving adhesion to nickel substrate surfaces, characterized in that, It contains: organic acid, oxidizing agent, corrosion inhibitor, wetting agent, and the balance is deionized water; the pH value of the selective corrosion solution is 3.5 to 4.

5.

2. The selective corrosion liquid according to claim 1, characterized in that, The organic acid is one or more of citric acid and glycolic acid.

3. The selective corrosion liquid according to claim 2, characterized in that, The concentration of citric acid is 10–30 g / L.

4. The selective corrosion liquid according to claim 2, characterized in that, The concentration of the glycolic acid is 5–15 g / L.

5. The selective corrosion liquid according to claim 1, characterized in that, The oxidizing agent is ammonium persulfate or 30% hydrogen peroxide.

6. The selective corrosion liquid according to claim 5, characterized in that, The concentration of ammonium persulfate is 0.5–2 g / L.

7. The selective corrosion liquid according to claim 5, characterized in that, The concentration of the 30% hydrogen peroxide is 0.1–2 mL / L.

8. The selective corrosion liquid according to claim 1, characterized in that, The corrosion inhibitor is benzotriazole, and the concentration of benzotriazole is 0.1-0.3 g / L.

9. The selective corrosion liquid according to claim 1, characterized in that, The wetting agent is sodium dodecyl sulfate, and the concentration of sodium dodecyl sulfate is 0.05-0.2 g / L.

10. A method for improving the surface adhesion of a nickel substrate using the selective etching solution according to any one of claims 1-9, characterized in that, Includes the following steps: S1, add 10% ammonia to the selective corrosion solution to adjust the pH value; S2, adjust the working temperature of the selective etching solution to the range of 20-50℃; S3, immerse the nickel substrate completely in the selective etching solution for 5-10 minutes to remove nickel oxide from the surface of the nickel substrate.