Environment-friendly lead-free chemical nickel plating solution for circuit board and preparation method of environment-friendly lead-free chemical nickel plating solution

Abstract

The invention relates to the technical field of chemical nickel plating solutions, in particular to an environment-friendly lead-free chemical nickel plating solution for a circuit board and a preparation method of the environment-friendly lead-free chemical nickel plating solution. An environment-friendly lead-free chemical nickel plating solution for a circuit board comprises, by mass concentration, 18-25 g / L of nickel sulfate hexahydrate, 20-25 g / L of a reducing agent, 20-25 g / L of a composite complexing agent, 20-25 g / L of a buffering agent, 0.15-0.35 g / L of a composite stabilizer, 2-3 g / L of a composite leveling agent, 0.02-0.03 g / L of an accelerator and 0.06-0.1 g / L of a surfactant, and the reducing agent is composed of sodium hypophosphite and hydrazine according to the mass ratio of 3: 3-4. The chemical nickel plating solution shows excellent comprehensive performance in the aspects of deposition rate, stability, corrosion resistance, environmental protection property, adhesive force and the like, and is suitable for various occasions needing high-quality plating layers, especially circuit board manufacturing in the electronic industry.

Description

Technical Field

[0001] The present application relates to the technical field of electroless nickel plating solutions, and particularly to an environment-friendly lead-free electroless nickel plating solution for circuit boards and a preparation method thereof. Background Art

[0002] The electroless nickel plating solution is a coating applied in the packaging process. In the PCB industry, as electronic products are gradually developing towards high performance, multi-function, high reliability, thin, light, small, portable and low cost, in order to meet the market and technical requirements, the surface treatment process of electroless nickel palladium gold with the reputation of an all-round coating is mostly adopted. Although this coating can meet the requirements of various packaging processes, due to the relatively thick nickel layer, it will affect the signal transmission characteristics of high-frequency or high-speed digitalization. With the continuous development of technology, people's requirements for the manufacturing process of electroless nickel plating solutions are also getting higher and higher.

[0003] The existing electroless nickel plating solutions have certain drawbacks when in use. The conventional nickel layer thickness is 3 - 5 μm. Since the hardness of nickel is greater than that of copper, in the FPC board, it is easy to cause fracture during flexure; since the resistance value of nickel is more than four times that of copper, for occasions with characteristic impedance, the thick nickel layer will generate a large impedance value, and when the signal passes through, large changes (such as loss or distortion, etc.) will occur at the welding point, affecting the signal transmission characteristics; although in the ENIPIG process, adding a thin layer of palladium on the surface of the nickel layer can prevent the nickel layer from corroding, but after the nickel layer becomes thinner, ordinary electroless nickel coatings will have problems such as black spots or black holes, and the uniformity decreases. For this reason, we propose an environment-friendly lead-free electroless nickel plating solution for circuit boards. Summary of the Invention

[0004] The purpose of the present application is to provide an environment-friendly lead-free electroless nickel plating solution for circuit boards and a preparation method thereof in view of the deficiencies of the current technology. The environment-friendly lead-free electroless nickel plating solution of the present application has excellent stability while having a high deposition rate, and the obtained uniform and dense nickel layer has good corrosion resistance.

[0005] In the first aspect, the present application provides an environment-friendly lead-free electroless nickel plating solution for circuit boards, adopting the following technical solution: An environment-friendly lead-free electroless nickel plating solution for circuit boards, calculated by mass concentration, includes the following preparation raw materials: nickel sulfate hexahydrate 18 - 25 g / L, reducing agent 20 - 25 g / L, composite complexing agent 20 - 25 g / L, buffer 20 - 25 g / L, composite stabilizer 0.15 - 0.35 g / L, composite leveling agent 2 - 3 g / L, accelerator 0.02 - 0.03 g / L, surfactant 0.06 - 0.1 g / L, wherein the reducing agent is composed of sodium hypophosphite and hydrazine in a mass ratio of 3:3 - 4.

[0006] By adopting the above technical solutions, the electroless nickel plating solution in this application is an environmentally friendly lead-free formulation designed for circuit boards. It aims to achieve a high deposition rate while ensuring the uniformity of the coating and good corrosion resistance. Nickel sulfate hexahydrate: As the nickel source, it provides the main component of the coating. Reducing agents (sodium hypophosphite and hydrazine): Responsible for reducing nickel ions to metallic nickel and promoting the formation of the coating. Composite complexing agent: By forming complexes with nickel ions, it controls the release rate of nickel ions, thereby regulating the deposition rate and helping hydrogen gas escape from the workpiece surface, reducing the porosity of the coating. Buffer: Maintains the stability of the solution pH value and ensures the consistency of chemical reaction conditions. Composite stabilizer (modified binaphthyl thiourea, chromium chloride, and thiodipropionic acid): Modified binaphthyl thiourea enhances the stability of the plating solution through its structural characteristics and simultaneously introduces hyperbranched polyamide to improve the corrosion resistance of the coating; chromium chloride adsorbs on the electrode surface, increases the oxidation current density, and increases the activation energy of the plating solution, thereby improving the uniformity and fineness of the coating; thiodipropionic acid further strengthens these effects through its coordination. Composite leveling agent: Improves the surface flatness of the coating, making it smoother. Accelerator: Accelerates the reduction rate of nickel ions and improves the deposition efficiency. Surfactant: Reduces the surface tension of the solution, helps gas escape, and further reduces the porosity of the coating. These components work together to ensure a uniform, dense, and efficient deposition process of the coating, while enhancing the corrosion resistance of the coating.

[0007] Preferably, the composite stabilizer is composed of modified binaphthyl thiourea, chromium chloride, and thiodipropionic acid in a mass ratio of 5:1:2 - 4.

[0008] By adopting the above technical solutions, first, the addition of chromium chloride improves the corrosion resistance and deposition rate of the nickel plating layer. Chromium chloride can adsorb on the electrode surface, and its promoting effect on the oxidation of hypophosphite ions is manifested in increasing the oxidation current density, thereby increasing the activation energy of the electroless nickel plating reaction and improving the stability of the plating solution. Second, after blending modified binaphthyl thiourea with chromium chloride and thiodipropionic acid, due to the two hydroxyl groups on the coordinating group of thiodipropionic acid, the combined stabilizer has a strong coordinating effect. This strong coordinating effect makes the coating uniform and fine, tightly combined with the substrate, and enhances the corrosion resistance of the nickel plating layer. Finally, modified binaphthyl thiourea is prepared from methanol, diethylenetriamine, and methyl acrylate as raw materials. First, it reacts to form a terminal amino hyperbranched polyamide, and then reacts with biphenyl isothiocyanate. The modified binaphthyl thiourea with hyperbranched polyamide is generated, which further enhances the stability of the electroless nickel plating solution and can also introduce a small amount of hyperbranched polyamide on the coating to enhance the corrosion resistance of the coating. In summary, the composite stabilizer in this application realizes excellent stability while having a high deposition rate through the combined action of modified binaphthyl thiourea, chromium chloride, and thiodipropionic acid. The obtained uniform and dense nickel layer has good corrosion resistance.

[0009] Preferably, the preparation method of the amino-terminated hyperbranched polyamide is as follows: by mass fraction, under a nitrogen atmosphere, 3 parts of methanol and 1 - 1.2 parts of diethylenetriamine are mixed, stirred evenly under an ice bath, then 0.6 part of methyl acrylate is added, and the reaction continues for 6 - 8 h. The temperature is raised to 110 °C, and the reaction continues for 4 h. Then the temperature is raised to 135 °C again, and the reaction continues for 4 h. Finally, it is dissolved in methanol, precipitated with ether, and dried under vacuum to obtain the amino-terminated hyperbranched polyamide.

[0010] Preferably, the preparation method of the modified binaphthylthiourea is as follows: by mass fraction, under a nitrogen atmosphere, 2 parts of biphenyl isothiocyanate and 18 - 20 parts of tetrahydrofuran are mixed evenly, then 2 parts of the amino-terminated hyperbranched polyamide is added, and the mixture is transferred to an ice bath for reaction for 18 - 20 h. After removing tetrahydrofuran by rotary evaporation, it is purified by column chromatography to obtain the modified binaphthylthiourea.

[0011] By adopting the above technical solution, the amino-terminated hyperbranched polyamide is prepared from methanol, diethylenetriamine and methyl acrylate. First, the amino-terminated hyperbranched polyamide is generated, and then it reacts with biphenyl isothiocyanate to obtain the modified binaphthylthiourea with hyperbranched polyamide, which further enhances the stability of the electroless nickel plating solution and can also introduce a small amount of hyperbranched polyamide on the coating to enhance the corrosion resistance of the coating.

[0012] Preferably, the composite leveling agent is composed of pyridinium hydroxylated propane sulfonate and sulfanilamide ethoxypyridazine in a mass ratio of 6:5 - 6.

[0013] By adopting the above technical solution, the use of the composite leveling agent significantly improves the surface quality of the nickel plating layer. The mixed use of pyridinium hydroxylated propane sulfonate and sulfanilamide ethoxypyridazine reduces surface defects of the nickel plating layer, such as pinholes and pits, and improves the glossiness and smoothness of the coating.

[0014] Preferably, the composite complexing agent is composed of aspartic acid and glycine in a mass ratio of 3:1 - 3.

[0015] By adopting the above technical solutions, first, the ratio of aspartic acid and glycine can effectively control the metal ion concentration in the plating solution, preventing problems such as uneven plating or holes caused by excessive metal ion concentration. At the same time, these two amino acids can also form stable complexes with nickel ions, improving the stability of the plating solution. Secondly, the addition of surfactants can reduce the surface tension of the plating solution, which is beneficial to the escape of hydrogen gas, thereby reducing the pore tension and porosity of the plating layer. In addition, surfactants can also improve the wettability of the plating layer, making the plating layer more uniform and dense. Finally, the combined action of aspartic acid, glycine and surfactants endows the electroless nickel plating solution with excellent stability and corrosion resistance. Under the action of this composite complexing agent, the obtained nickel layer has good compactness, low porosity and strong corrosion resistance. This is very important for electronic products such as circuit boards, because good corrosion resistance can ensure the service life and reliability of the products.

[0016] Preferably, the accelerator is composed of p-hydroxybenzenesulfonate and guanidine hydrochloride in a mass ratio of 2:1-3.

[0017] By adopting the above technical solutions, first, p-hydroxybenzenesulfonate is an effective reducing agent, which can improve the reducing ability in the plating solution, thereby accelerating the reduction rate of nickel ions and increasing the deposition rate. In addition, p-hydroxybenzenesulfonate can also form stable complexes with nickel ions, helping to maintain the stability of the plating solution. Secondly, guanidine hydrochloride, as a strong alkaline substance, can neutralize the acidic substances in the plating solution and maintain the pH value of the plating solution within an appropriate range. This is crucial for ensuring the smooth progress of the electroless nickel plating reaction, because inappropriate pH values may lead to a decrease in the quality of the plating layer or a slowdown in the reaction rate. Finally, the combined action of p-hydroxybenzenesulfonate and guanidine hydrochloride enables the accelerator to not only increase the deposition rate but also maintain the stability of the plating solution, ensuring the acquisition of high-quality plating layers. Under the action of this accelerator, the electroless nickel plating solution can maintain excellent stability while having a high deposition rate, thereby obtaining a uniform, dense nickel layer with good corrosion resistance. This is very important for electronic products such as circuit boards, because good corrosion resistance can ensure the service life and reliability of the products.

[0018] Preferably, the surfactant is fatty acid polyoxyethylene ester.

[0019] Preferably, the buffer is lactic acid.

[0020] In a second aspect, the present application provides a preparation method for an environmentally friendly lead-free electroless nickel plating solution for circuit boards, adopting the following technical solutions: As a general technical concept, the present application also provides the above preparation method for an environmentally friendly lead-free electroless nickel plating solution for circuit boards, including the following steps: Add 18 - 25 g of nickel sulfate hexahydrate, 20 - 25 g of reducing agent, 20 - 25 g of composite complexing agent, 20 - 25 g of buffering agent, 0.15 - 0.35 g of composite stabilizer, 2 - 3 g of composite leveling agent, 0.02 - 0.03 g of accelerating agent, and 0.06 - 0.1 g of surfactant into an appropriate amount of deionized water in sequence and mix evenly. Then, make the volume of the evenly - mixed solution constant to 1 L to obtain an environmentally - friendly lead - free electroless nickel plating solution for circuit boards.

[0021] In summary, the beneficial technical effects of this application are as follows: 1. High deposition rate and stability: The electroless nickel plating solution of the present invention can ensure a high deposition rate while having excellent stability. This means that in practical applications, the required coating thickness can be obtained quickly, while maintaining the stability of the entire plating solution system and reducing quality problems caused by unstable plating solutions.

[0022] 2. Excellent corrosion resistance: Through the combined action of specific composite complexing agents, surfactants, and composite stabilizers, the obtained nickel layer is uniform, dense, has a low porosity, and has good corrosion resistance. This is crucial for electronic products such as circuit boards because good corrosion resistance can significantly improve the service life and reliability of products.

[0023] 3. Environmentally friendly and lead - free: The present invention adopts an environmentally - friendly lead - free formulation, which meets the requirements of current environmental protection regulations and reduces potential hazards to the environment and human health.

[0024] 4. Enhanced adhesion: The combination of chromium chloride and thiodipropionic acid modified binaphthylthiourea and stabilizers can make the coating tightly bond with the substrate, enhancing the adhesion of the coating and further improving the durability and reliability of the coating.

[0025] 5. Introduction of hyperbranched polyamide: The introduction of amino - terminated hyperbranched polyamide not only further enhances the stability of the electroless nickel plating solution but also can form a protective film on the coating, improving the corrosion resistance and mechanical strength of the coating. Detailed implementation manners

[0026] The following will describe the implementation schemes of this application in detail in combination with examples. However, those skilled in the art will understand that the following examples are only used to illustrate this application and should not be regarded as limiting the scope of this application. For those not specified in the examples, the operations are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified for the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0027] In the following preparation examples, 1 part represents 100 g.

[0028] Preparation example 1: Preparation of modified binaphthylthiourea The preparation method of the amino-terminated hyperbranched polyamide is as follows. By mass fraction, under a nitrogen atmosphere, 3 parts of methanol and 1.2 parts of diethylenetriamine are mixed. After stirring evenly under an ice bath, 0.6 part of methyl acrylate is added, and the reaction continues for 8 h. Then the temperature is raised to 110 °C and the reaction continues for 4 h. After that, the temperature is raised to 135 °C again and the reaction continues for 4 h. Finally, it is dissolved with methanol, precipitated with ether, and dried under vacuum to obtain the amino-terminated hyperbranched polyamide; The preparation method of the modified binaphthylthiourea is as follows: By mass fraction, under a nitrogen atmosphere, 2 parts of biphenyl isothiocyanate and 19 parts of tetrahydrofuran are mixed evenly. Then 2 parts of the amino-terminated hyperbranched polyamide are added, and the mixture is transferred to an ice bath for reaction for 19 h. After rotary evaporation to remove tetrahydrofuran, it is purified by column chromatography to obtain the modified binaphthylthiourea.

[0029] Example 1 An environment-friendly lead-free electroless nickel plating solution for circuit boards, by mass concentration, comprises the following preparation raw materials: nickel sulfate hexahydrate 18 g / L, reducing agent 20 g / L, composite complexing agent 20 g / L, lactic acid 20 g / L, composite stabilizer 0.15 g / L, composite leveling agent 2 g / L, accelerator 0.02 g / L, fatty acid polyoxyethylene ester 0.06 g / L. Among them, the reducing agent is composed of sodium hypophosphite and hydrazine in a mass ratio of 3:4; the composite stabilizer is composed of modified binaphthylthiourea, chromium chloride and thiodipropionic acid in a mass ratio of 5:1:2; the composite leveling agent is composed of hydroxylated propane sulfonic acid pyridinium salt and sulfanil ethoxypyridazine in a mass ratio of 6:5; the composite complexing agent is composed of aspartic acid and glycine in a mass ratio of 3:1; the accelerator is composed of p-hydroxybenzenesulfonate and guanidine hydrochloride in a mass ratio of 2:1; The preparation method of the above environment-friendly lead-free electroless nickel plating solution for circuit boards comprises the following steps: 18 g of nickel sulfate hexahydrate, 20 g of reducing agent, 20 g of composite complexing agent, 20 g of lactic acid, 0.15 g of composite stabilizer, 2 g of composite leveling agent, 0.02 g of accelerator, and 0.06 g of fatty acid polyoxyethylene ester are sequentially added to an appropriate amount of deionized water and mixed evenly, and then the mixed solution is made up to 1 L to obtain the environment-friendly lead-free electroless nickel plating solution for circuit boards.

[0030] Example 2 An environmentally friendly lead-free electroless nickel plating solution for circuit boards, by mass concentration, includes the following preparation raw materials: nickel sulfate hexahydrate 25 g / L, reducing agent 25 g / L, composite complexing agent 25 g / L, lactic acid 25 g / L, composite stabilizer 0.35 g / L, composite leveling agent 3 g / L, accelerator 0.03 g / L, fatty acid polyoxyethylene ester 0.1 g / L. Among them, the reducing agent consists of sodium hypophosphite and hydrazine in a mass ratio of 3:3, the composite stabilizer consists of modified binaphthyl thiourea, chromium chloride and thiodipropionic acid in a mass ratio of 5:1:4, the composite leveling agent consists of hydroxylated propane sulfonic acid pyridinium salt and sulfanilamide ethoxypyridazine in a mass ratio of 6:6, the composite complexing agent consists of aspartic acid and glycine in a mass ratio of 3:3, and the accelerator consists of p-hydroxybenzenesulfonate and guanidine hydrochloride in a mass ratio of 2:3; The preparation method of the above-mentioned environmentally friendly lead-free electroless nickel plating solution for circuit boards includes the following steps: Add 25 g of nickel sulfate hexahydrate, 25 g of reducing agent, 25 g of composite complexing agent, 25 g of lactic acid, 0.35 g of composite stabilizer, 3 g of composite leveling agent, 0.03 g of accelerator, and 0.1 g of fatty acid polyoxyethylene ester into an appropriate amount of deionized water in sequence and mix evenly, and then make the volume of the mixed solution constant to 1 L to obtain the environmentally friendly lead-free electroless nickel plating solution for circuit boards.

[0031] Example 3 An environmentally friendly lead-free electroless nickel plating solution for circuit boards, by mass concentration, includes the following preparation raw materials: nickel sulfate hexahydrate 22 g / L, reducing agent 23 g / L, composite complexing agent 23 g / L, lactic acid 22 g / L, composite stabilizer 0.25 g / L, composite leveling agent 2.3 g / L, accelerator 0.025 g / L, fatty acid polyoxyethylene ester 0.08 g / L. Among them, the reducing agent consists of sodium hypophosphite and hydrazine in a mass ratio of 3:3.4, the composite stabilizer consists of modified binaphthyl thiourea, chromium chloride and thiodipropionic acid in a mass ratio of 5:1:3, the composite leveling agent consists of hydroxylated propane sulfonic acid pyridinium salt and sulfanilamide ethoxypyridazine in a mass ratio of 6:5.6, the composite complexing agent consists of aspartic acid and glycine in a mass ratio of 3:2, and the accelerator consists of p-hydroxybenzenesulfonate and guanidine hydrochloride in a mass ratio of 2:2; The preparation method of the above-mentioned environmentally friendly lead-free electroless nickel plating solution for circuit boards includes the following steps: Add 22 g of nickel sulfate hexahydrate, 23 g of reducing agent, 23 g of composite complexing agent, 22 g of lactic acid, 0.25 g of composite stabilizer, 2.3 g of composite leveling agent, 0.025 g of accelerator, and 0.08 g of fatty acid polyoxyethylene ester into an appropriate amount of deionized water in sequence and mix evenly, and then make the volume of the mixed solution constant to 1 L to obtain the environmentally friendly lead-free electroless nickel plating solution for circuit boards.

[0032] Comparative Example 1 Same as Example 3, except that the composite stabilizer is composed of modified binaphthyl thiourea and chromium chloride in a mass ratio of 5:1.

[0033] Comparative Example 2 Same as Example 3, except that the composite stabilizer is composed of chromium chloride and thiodipropionic acid in a mass ratio of 1:3.

[0034] Comparative Example 3 Same as Example 3, except that the composite complexing agent is aspartic acid.

[0035] Comparative Example 4 Same as Example 3, except that the composite complexing agent is glycine.

[0036] Comparative Example 5 Same as Example 3, except that the accelerator is p-hydroxybenzenesulfonate.

[0037] Comparative Example 6 Same as Example 3, except that the accelerator is guanidine hydrochloride.

[0038] Performance Test The environment-friendly lead-free electroless nickel plating solutions for circuit boards prepared in Examples 1 - 3 and Comparative Examples 1 - 6 were respectively used for electroless nickel plating. The process conditions were as follows: temperature 45°C, time 50 minutes. The workpiece to be plated was a PCB resin board, and after undergoing the conventional processes of electroless copper plating, i.e., surface palladium activation treatment, reduction treatment, and electroless copper plating, it could directly enter the electroless nickel plating process for the above-mentioned electroless nickel plating; and the following tests were carried out. The test results are shown in Table 1.

[0039] 1. Plating rate: The coating thickness at 5 - 8 points was measured using an X-ray fluorescence spectrometer (XRF), and the average value was taken, with the unit of μm / h; 2. Plating solution stability test: Since the time required for the plating solution to decompose naturally is relatively long, in order to shorten the experimental time, an accelerated method was adopted. In this application, the palladium chloride acceleration test was used to test the stability of the plating solution: 1 mL of PdCl2 (0.10 g / L) was added to 50 mL of the plating solution, and the temperature was 60°C. The decomposition time of the plating solution was recorded, which was the time elapsed until the tested electroless nickel plating solution started to turn black. The longer the time, the better the stability of the tested electroless nickel plating solution; 3. Neutral salt spray test: The neutral salt spray corrosion test of the coating was carried out according to the method specified in GB / T 2423.18 - 2000, and a salt spray machine FR-1202-90 was used for the salt spray resistance test; 4. Appearance inspection: Observe whether the appearance of the magnesium alloy substrate after electroless nickel plating has a uniform coating, and whether there are phenomena such as pinholes and non-plating.

[0040] Table 1 Performance Test Project Deposition rate (μm / h) Neutral salt spray test / h Stability test / min Appearance Example 1 24.8 24 32.5 Uniform Example 2 25.5 24 32.1 Uniform Example 3 25.3 24 32.9 Uniform Comparative Example 1 23.2 20 28.7 Uniform Comparative Example 2 22.4 14 21.5 Non-uniform Comparative Example 3 25.7 13 24.5 Non-uniform Comparative Example 4 25.2 14 25.3 Non-uniform Comparative Example 5 21.2 17 23.1 Uniform Comparative Example 6 20.4 15 22.7 Uniform Analyzing the data in Table 1, it can be seen that: 1) The environment-friendly lead-free electroless nickel plating solution for circuit boards prepared in Examples 1 - 3 has excellent stability while having a high deposition rate, and the obtained uniform and dense nickel layer has good corrosion resistance.

[0041] 2) Combining the performance comparative analysis of the environment-friendly lead-free electroless nickel plating solutions for circuit boards prepared in Example 3 and Comparative Examples 1 - 2 shows that the composite stabilizer is composed of modified binaphthylthiourea, chromium chloride, and thiodipropionic acid in a mass ratio of 5:1:3. First, the addition of chromium chloride improves the corrosion resistance and deposition rate of the nickel plating layer. Chromium chloride can adsorb on the electrode surface, and its promoting effect on the oxidation of hypophosphite ions is manifested in increasing the oxidation current density, thereby increasing the activation energy of the electroless nickel plating reaction and improving the stability of the plating solution. Secondly, after mixing modified binaphthylthiourea with chromium chloride and thiodipropionic acid, with the help of the two hydroxyl groups on the ligand of thiodipropionic acid, the combined stabilizer has a strong coordination effect. This strong coordination effect enables the coating to be uniform and delicate, tightly combined with the substrate, and enhances the corrosion resistance effect of the nickel plating layer. Finally, modified binaphthylthiourea is prepared from methanol, diethylenetriamine, and methyl acrylate as raw materials. First, it reacts to form a terminal amino hyperbranched polyamide, and then reacts with biphenyl isothiocyanate. The resulting modified binaphthylthiourea with hyperbranched polyamide further enhances the stability of the electroless nickel plating solution and can also introduce a small amount of hyperbranched polyamide on the coating to enhance the corrosion resistance of the coating. In summary, through the combined action of modified binaphthylthiourea, chromium chloride, and thiodipropionic acid, the composite stabilizer in this application achieves excellent stability while having a high deposition rate, and the obtained uniform and dense nickel layer has good corrosion resistance.

[0042] 3) Comparative analysis of the performance of the environmentally friendly lead-free electroless nickel plating solution for circuit boards prepared by combining Example 3 and Comparative Examples 3 - 4 shows that the composite complexing agent is composed of aspartic acid and glycine in a mass ratio of 3:2. First of all, the ratio of aspartic acid and glycine can effectively control the metal ion concentration in the plating solution, preventing problems such as uneven plating or holes caused by excessive metal ion concentration. At the same time, these two amino acids can also form stable complexes with nickel ions, improving the stability of the plating solution. Secondly, the addition of the surfactant can reduce the surface of the plating solution, which is beneficial to the escape of hydrogen, thereby reducing the pore tension and porosity of the plating layer. In addition, the surfactant can also improve the wettability of the plating layer, making the plating layer more uniform and dense. Finally, the combined action of aspartic acid, glycine and the surfactant makes the electroless nickel plating solution have excellent stability and corrosion resistance. Under the action of this composite complexing agent, the obtained nickel layer has good compactness, low porosity and strong corrosion resistance. This is very important for electronic products such as circuit boards, because good corrosion resistance can ensure the service life and reliability of the products.

[0043] 4) Comparative analysis of the performance of the environmentally friendly lead-free electroless nickel plating solution for circuit boards prepared by combining Example 3 and Comparative Examples 5 - 6 shows that the accelerator is composed of p-hydroxybenzenesulfonate and guanidine hydrochloride in a mass ratio of 2:2. The combined action between p-hydroxybenzenesulfonate and guanidine hydrochloride enables the accelerator to not only increase the deposition rate but also maintain the stability of the plating solution, ensuring the acquisition of a high-quality plating layer. Under the action of this accelerator, the electroless nickel plating solution can maintain excellent stability while having a high deposition rate, thereby obtaining a nickel layer that is uniform, dense and has good corrosion resistance.

[0044] The above embodiments are only used to explain and illustrate the technical solutions of the present application rather than to limit them. Although the above embodiments have specifically described the present application, those skilled in the art should understand that modifications or equivalent replacements can still be made to the specific implementation manners of the present invention. Any modification and equivalent replacement that do not depart from the spirit and scope of the present application shall be covered by the protection scope of the present application.

Claims

1. An environmentally friendly lead-free electroless nickel plating solution for circuit boards, characterized in that, By mass concentration, it includes the following preparation raw materials: nickel sulfate hexahydrate 18 - 25 g / L, reducing agent 20 - 25 g / L, composite complexing agent 20 - 25 g / L, buffer 20 - 25 g / L, composite stabilizer 0.15 - 0.35 g / L, composite leveling agent 2 - 3 g / L, accelerator 0.02 - 0.03 g / L, surfactant 0.06 - 0.1 g / L. Among them, the reducing agent is composed of sodium hypophosphite and hydrazine in a mass ratio of 3:3 - 4.

2. The environmentally friendly lead-free electroless nickel plating solution for circuit boards according to claim 1, wherein, The composite stabilizer is composed of modified binaphthyl thiourea, chromium chloride and thiodipropionic acid in a mass ratio of 5:1:2 - 4.

3. The environmentally friendly lead-free electroless nickel plating solution for a circuit board according to claim 2, characterized in that, The preparation method of the modified binaphthyl thiourea is as follows: by mass fraction, in a nitrogen atmosphere, 2 parts of biphenyl isothiocyanate are mixed evenly with 18 - 20 parts of tetrahydrofuran, then 2 parts of terminal amino hyperbranched polyamide are added, and the mixture is transferred to an ice bath for reaction for 18 - 20 h. After removing tetrahydrofuran by rotary evaporation, it is purified by column chromatography to obtain the modified binaphthyl thiourea.

4. The electroless nickel plating solution for circuit boards according to claim 3, wherein The preparation method of the terminal amino hyperbranched polyamide is as follows: by mass fraction, in a nitrogen atmosphere, 3 parts of methanol are mixed with 1 - 1.2 parts of diethylenetriamine, stirred evenly in an ice bath, then 0.6 part of methyl acrylate is added, and the reaction continues for 6 - 8 h. The temperature is raised to 110 °C and the reaction continues for 4 h, then the temperature is raised to 135 °C again and the reaction continues for 4 h. Finally, it is dissolved in methanol, precipitated with ether, and dried in vacuum to obtain the terminal amino hyperbranched polyamide.

5. The electroless nickel plating solution for circuit boards according to claim 1, characterized in that, The composite leveling agent is composed of hydroxylated propane sulfonic acid pyridinium salt and sulfanilamide ethoxypyridazine in a mass ratio of 6:5 - 6.

6. The electroless nickel plating solution without lead and environmentally friendly for circuit boards according to claim 1, characterized in that, The composite complexing agent is composed of aspartic acid and glycine in a mass ratio of 3:1 - 3.

7. The electroless nickel plating solution for circuit boards as claimed in claim 1, wherein, The accelerator is composed of p - hydroxybenzenesulfonate and guanidine hydrochloride in a mass ratio of 2:1 - 3.

8. The environmentally friendly lead-free electroless nickel plating solution for a circuit board according to claim 1, characterized in that, The surfactant is fatty acid polyoxyethylene ester.

9. The electroless nickel plating solution for circuit boards according to claim 1, characterized in that, The buffer is lactic acid.

10. A preparation method of an environmentally friendly lead-free electroless nickel plating solution for a circuit board according to any one of claims 1-9, characterized in that, It includes: 18 - 25 g of nickel sulfate hexahydrate, 20 - 25 g of reducing agent, 20 - 25 g of composite complexing agent, 20 - 25 g of buffer, 0.15 - 0.35 g of composite stabilizer, 2 - 3 g of composite leveling agent, 0.02 - 0.03 g of accelerator, and 0.06 - 0.1 g of surfactant are sequentially added to an appropriate amount of deionized water and mixed evenly, and then the mixed solution is fixed - volume to 1 L to obtain an environmentally friendly lead - free electroless nickel plating solution for circuit boards.