A high-phosphorus, low-corrosion electroless nickel plating solution for circuit boards, its preparation method, and its application.

Abstract

This application relates to the fields of surface treatment and chemical deposition technology, and in particular to a high-phosphorus, low-corrosion electroless nickel plating solution for circuit boards, its preparation method, and its application. The preparation method includes: S1, preparing component M: adding citric acid to a first portion of deionized water, followed by nickel salt, to form a homogeneous solution; S2, preparing component A: adding succinic acid and / or succinate and a buffer to a second portion of deionized water, and adding a grain refiner to obtain component A; S3, preparing component D: adding a corrosion inhibitor, a wetting and hydrogen-releasing agent, and a stabilizer to a third portion of deionized water to obtain component D; S4, preparing the working solution: sequentially adding component M, component A, and component D to a fourth portion of deionized water; S5, after uniformly mixing component M, component A, and component D, adding hypophosphite to obtain the electroless nickel plating solution. This achieves an electroless nickel plating solution that balances high phosphorus, low corrosion, high deposition rate, excellent solderability, good adhesion, and OSP adaptability.

Description

Technical Field

[0001] This application relates to the fields of surface treatment and chemical deposition technology, and in particular to a high-phosphorus, low-corrosion electroless nickel plating solution for circuit boards, its preparation method, and its application. Background Technology

[0002] Electroless nickel plating, a key surface treatment process in printed circuit board (PCB) manufacturing, is widely used in electronic packaging, communication equipment, and consumer electronics. This technology forms a uniform nickel-phosphorus alloy coating on the substrate surface through an autocatalytic reduction reaction, providing a foundation for subsequent surface treatments such as immersion gold and OSP. Existing electroless nickel plating systems typically consist of nickel salts, reducing agents, complexing agents, buffers, and various additives. Specific coating properties are achieved by controlling reaction conditions. In practical industrial applications, electroless nickel plating processes have formed relatively mature production line configurations, including degreasing, micro-etching, activation, and electroless nickel plating, capable of meeting the surface treatment requirements of conventional PCBs. The plating solution is often prepared using a one-time mixing or batch addition method, with daily maintenance performed by monitoring parameters such as nickel ion concentration and pH value to ensure the continuity of the production process and the stability of the coating quality.

[0003] However, in areas such as fine lines on circuit boards, pad edges, and orifices, plating quality control faces continuous challenges, leading to unstable plating performance in localized areas. Summary of the Invention

[0004] This application provides a high-phosphorus, low-corrosion electroless nickel plating solution for circuit boards, its preparation method, and its application, in order to solve the above-mentioned problems.

[0005] In a first aspect, this application provides a high-phosphorus, low-corrosion electroless nickel plating solution for circuit boards, comprising the following components based on the working solution: Nickel salts, equivalent to Ni² + It is 4.5-5.0 g / L; Hypophosphite 26-34 g / L; Citric acid 20-32 g / L; Succinic acid and / or succinate 8-20 g / L; Buffer 3-12 g / L; Grain refiner 0.05-0.8 g / L; Preservative inhibitor 10-80 mg / L; Wetting and hydrogen-releasing agent 20-150 mg / L; Stabilizer 0.2-5 mg / L; The electroless nickel plating solution has a pH of 4.5-4.8, and the mass ratio of citric acid to succinic acid and / or succinate is 1.5-3.0:1. The electroless nickel plating solution is formulated from component M, component A, component D and hypophosphite. Component M includes at least the nickel salt and citric acid. Component A includes at least the succinic acid and / or succinate, buffer and grain refiner. Component D includes at least the corrosion inhibitor, wetting and hydrogen release agent and stabilizer.

[0006] Beneficial effects: It forms a nickel ion release system that combines the main complexing and secondary complexing regulation functions, reducing the risk of localized corrosion in the edges of fine lines, pads and orifice areas of the circuit board; at the same time, the grouping of components M, A, D and hypophosphite helps to reduce the problems of trace additive failure, uneven local complexing of nickel salts and premature participation of reducing agents in the reaction, thus achieving a balance of high phosphorus coating, low corrosion, high deposition rate, good solderability and adhesion.

[0007] Optionally, the nickel salt is nickel sulfate and / or nickel chloride, and the hypophosphite is sodium hypophosphite.

[0008] Beneficial effects: By selecting nickel sulfate and / or nickel chloride as the nickel source and sodium hypophosphite as the reducing agent, the stability and industrial availability of raw material sources can be improved, and Ni² can be made more readily available. + The release has good compatibility with the hypophosphite reduction reaction, which is beneficial for obtaining a nickel-phosphorus alloy coating with stable phosphorus content. At the same time, it is convenient to control the solution preparation and replenishment on existing circuit board electroless nickel plating production lines.

[0009] Optionally, the citric acid content is 22-30 g / L, the succinic acid and / or succinate content is 10-18 g / L, and the mass ratio of the citric acid to the succinic acid and / or succinate is 1.8-2.6:1.

[0010] Beneficial effects: It can improve deposition kinetics while maintaining the stability of nickel ion complexation, avoid the deposition rate decrease caused by excessive complexation, and avoid local nickel precipitation and edge corrosion caused by insufficient complexation, thereby improving the uniformity of coating thickness in fine line areas and the stability of plating solution operation.

[0011] Optionally, the corrosion inhibitor is one or at least two of benzotriazole, imidazole, and nicotinamide, and the wetting and hydrogen-releasing agent is an acetylenic diol modified polyether nonionic surfactant.

[0012] Beneficial effects: By selecting one or more of benzotriazole, imidazole and nicotinamide as corrosion inhibitors, and combining them with acetylenol-modified polyether nonionic surfactants as wetting and hydrogen release agents, a synergistic effect of interface protection and bubble release can be formed at the copper / nickel interface and easily corroded locations such as circuit board orifices and pad edges. This reduces local defects caused by pinholes, pitting and hydrogen retention, while improving corrosion resistance and solder coverage in subsequent OSP treatment and soldering processes.

[0013] Optionally, the content of the buffer is 5-10 g / L, the content of the grain refiner is 0.1-0.5 g / L, the content of the stabilizer is 0.5-3 mg / L, and the pH of the electroless nickel plating solution is 4.6-4.8.

[0014] Beneficial effects: By further limiting the buffer, grain refiner, stabilizer and pH within the preferred range, the acid-base buffering capacity and micro-stability control of the plating bath can be improved, making the reaction rate more stable during nickel plating; the grain refiner helps to form a dense and uniform nickel-phosphorus coating, while the stabilizer can inhibit the self-decomposition of the bath and abnormal nickel precipitation, thereby improving the life of the plating bath, the density of the coating and the consistency of batch production.

[0015] Secondly, this application provides a method for preparing a high-phosphorus, low-corrosion electroless nickel plating solution for circuit boards, the preparation method comprising: S1. Preparation of component M: Add citric acid to the first portion of deionized water and stir at 40-50℃ until dissolved. Then add nickel salt and continue stirring until a homogeneous solution is formed. S2. Preparation of component A: Add succinic acid and / or succinate and buffer to the second portion of deionized water, stir to dissolve, and then add a grain refiner to obtain component A. S3. Preparation of component D: Add corrosion inhibitor, wetting and hydrogen release agent and stabilizer to the third part of deionized water, stir and mix at a temperature not exceeding 35°C, and filter through 0.2-1μm to obtain component D; S4. Preparation of working solution: Add component M, component A, and component D sequentially to the fourth part of deionized water, wherein the amount of component M added is 14-16% by volume, the amount of component A added is 4-6% by volume, and the amount of component D added is 0.2-0.5% by volume. S5. After thoroughly mixing components M, A, and D, add hypophosphite to adjust the Ni² concentration in the working solution. + The concentration of the electrolyte is 4.5-5.0 g / L, the concentration of hypophosphate is 26-34 g / L, the pH is 4.5-4.8, and the solution is heated to 80-84℃ and aged for 20-40 min to obtain the electroless nickel plating solution.

[0016] Beneficial effects: By dividing the preparation process of electroless nickel plating solution into stepwise preparation of components M, A, and D, and then mixing them sequentially in a specific volume ratio, and adding hypophosphite and aging treatment after uniform mixing, it is possible to avoid uneven reaction or local failure of nickel salt, complexing agent, trace additives, and reducing agent in the initial stage of preparation. At the same time, the process of dissolving component M at 40-50℃, preparing component D at no higher than 35℃, and aging at 80-84℃ for 20-40 minutes is conducive to improving the initial activity and system stability of the working solution, and ensuring the uniformity of subsequent deposition rate, phosphorus content, and low corrosion performance.

[0017] Optionally, in step S1, citric acid is added first and completely dissolved before adding nickel salt; in step S2, succinic acid and / or succinate and buffer are added first and completely dissolved before adding grain refiner.

[0018] Beneficial effects: By completely dissolving citric acid in S1 before adding nickel salt, nickel ions can be uniformly complexed in time after entering the solution, reducing the risk of uneven complexation or precipitation caused by local high concentrations of nickel salt; By completely dissolving succinic acid and / or succinate and buffer in S2 before adding grain refiner, the dispersion uniformity of grain refiner in the system can be improved, thereby improving the grain refinement effect and surface smoothness of the coating.

[0019] Optionally, the preparation temperature of component D in step S3 shall not exceed 35°C, and the filtration accuracy shall be 0.2-1 μm.

[0020] Beneficial effects: By controlling the preparation temperature of component D to no higher than 35℃, the risk of volatilization, decomposition, or adsorption failure of corrosion inhibitors, wetting and hydrogen-releasing agents, and stabilizers during the formulation process can be reduced; at the same time, after filtration through 0.2-1μm, tiny insoluble substances and particulate impurities can be removed, reducing pinholes, pitting, and abnormal deposition defects on circuit board orifices, fine line edges, and pad surfaces, thereby improving the appearance quality and corrosion resistance stability of the coating.

[0021] Optionally, in step S5, after adding hypophosphite, the pH of the working solution is adjusted to 4.5-4.8, and then the temperature is raised to 80-84℃ for aging, with an aging time of 20-40 minutes.

[0022] Beneficial effects: By adjusting the pH of the working solution to 4.5-4.8 after adding hypophosphite, and then heating it to 80-84℃ and aging it for 20-40 minutes, the reducing agent, nickel complex system and auxiliary agent system can complete the reaction activation and balance establishment under suitable acidity, avoiding the sudden reduction reaction or decrease in the stability of the bath caused by direct high temperature rise; this aging step helps to improve the consistency of the initial deposition rate and reduce the problems of rough coating, increased corrosion depth or thickness fluctuation in the early stage of mass production.

[0023] Thirdly, this application provides a method for applying a high-phosphorus, low-corrosion electroless nickel plating solution to circuit boards, the method comprising: During the process of using the electroless nickel plating solution in circuit board production, the Ni²⁺ content in the working solution is detected at intervals of 0.5 MTO. + The concentration and pH were adjusted, and components M, A, D, and hypochlorite were added separately to maintain the Ni² concentration in the working solution during the 0-3.8 MTO production cycle. + The concentration is 4.5-5.0 g / L, and the pH is 4.5-4.8; During the 0-3.8 MTO production cycle, the Ni² content in the working fluid was measured every 0.5 MTO. + The concentration and pH were adjusted, and by adding components M, A, D and hypophosphite, the working temperature of the electroless nickel plating solution was maintained at 80-84℃, and the electroless nickel plating deposition rate on the circuit board surface was maintained at 6.5-9.5 μin / min.

[0024] Beneficial effects: By detecting Ni² at 0.5 MTO intervals during the circuit board manufacturing process. + By adjusting the concentration and pH, and supplementing with components M, A, and D respectively, the nickel ion concentration, pH, operating temperature, and deposition rate can be maintained within a stable range during the 0-3.8 MTO production cycle. This avoids imbalances in the complexation system, corrosion inhibition system, and wetting system caused by simply adding nickel or reducing agent. This application method helps ensure the consistency of plating phosphorus content, deposition rate, solderability, and corrosion resistance after OSP in long-cycle production. It is particularly suitable for bath maintenance and quality stability control in continuous circuit board production. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A flowchart illustrating a method for preparing a high-phosphorus, low-corrosion electroless nickel plating solution for circuit boards, provided in this application; Figure 2 This is a cross-sectional SEM image of the nickel-phosphorus coating obtained in Example 1 of this application; Figure 3 This is a cross-sectional SEM image of the nickel-phosphorus coating obtained in Example 2 of this application; Figure 4 This is a cross-sectional SEM image of the nickel-phosphorus coating obtained in Example 3 of this application near the orifice. Figure 5This is a surface SEM image of the nickel-phosphorus coating obtained in Example 4 of this application in the orifice region; Figure 6 This is a cross-sectional SEM image of the nickel-phosphorus coating obtained in Example 5 of this application; Figure 7 This is a cross-sectional SEM image of the nickel-phosphorus coating obtained in Example 6 of this application. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0028] Furthermore, the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this article, unless otherwise specified, generally indicates that the preceding and following related objects have an "or" relationship.

[0029] The embodiments of this application will now be described in further detail with reference to the accompanying drawings.

[0030] Unless otherwise specified, all materials, reagents and instruments used in the embodiments of this application can be obtained through commercial channels.

[0031] In this application, OSP refers to organic solderability protective film treatment; MTO refers to metal turnover, which indicates the degree of turnover of nickel ions in the electroless nickel plating bath as they are consumed and replenished during production.

[0032] Example 1 This embodiment aims to verify the comprehensive performance of the dual-complex nickel control system and the interface synergistic control system under basic parameters.

[0033] Take approximately 90 mL of the first portion of deionized water, add 22.0 g of citric acid, and stir in a 45°C water bath for 15 minutes until completely dissolved. Then add 21.3 g of nickel sulfate hexahydrate in three portions, with each addition 3 minutes apart and continuous stirring. After complete dissolution, add deionized water to bring the volume to 150 mL to obtain component M. Take approximately 40 mL of the second portion of deionized water, add 12.0 g of sodium succinate, 3.0 g of boric acid, and 2.0 g of sodium acetate, and stir at 35-45°C until completely dissolved. Then add 0.20 g of PEG-4000, and continue stirring until the solution is homogeneous. Add deionized water to bring the volume to 60 mL to obtain component A. Take approximately 80 mL of deionized water and add 0.857 g of benzotriazole, 0.286 g of nicotinamide, 1.714 g of Dynol 960, 0.017 g of thiourea, and 0.034 g of bismuth nitrate to a 30°C constant temperature water bath. Stir for 30 min in the dark, then add deionized water to bring the volume to 100 mL. Filter the solution under vacuum through a 0.45 μm PTFE membrane to obtain component D. Add approximately 720 mL of deionized water to the reaction tank, then add 150 mL of component M, 60 mL of component A, and 3.5 mL of component D sequentially. Stir for 20 min. Add 28.0 g of sodium hypophosphite, adjust the pH to 4.65 with 10% NaOH solution, and then add deionized water to bring the volume to 1 L. Then raise the temperature to 82°C and age at this temperature for 30 min to obtain the working plating solution.

[0034] The resulting plating solution was clear and transparent, with a pH of 4.65 at 25°C. (Ni²) + The concentration was 4.75 g / L, and the hypophosphite concentration was 28.0 g / L. Electroless nickel plating was performed on FR-4 substrate (linewidth / spacing = 30 / 30 μm) under the following conditions: 82℃, pH 4.65, and time 25 min. The deposition rate was 8.3 μin / min; the phosphorus content of the coating was 10.8 wt% (ICP-OES). Figure 2 As shown, the cross-sectional SEM image shows a coating thickness of 5.2 μm, with no pores or cracks; the nickel corrosion depth is 0.32 μm (85℃ / 85%RH / 96h); the solderability tin coverage reaches 98.2%; there is no peeling after cross-cut test combined with ultrasonic peeling; and there is no red rust after 12h salt spray test.

[0035] The results show that the basic formulation achieves a balance between high phosphorus, low corrosion, high deposition rate and excellent process stability under optimized parameters, verifying the effectiveness of dual complexation and interface synergistic design.

[0036] Example 2 This embodiment is intended to verify the feasibility and performance retention capability under the lower limit of the mass ratio of citric acid to succinate (1.5:1) in this application.

[0037] With all other preparation conditions the same as in Example 1, only the amount of sodium succinate in component A was adjusted from 12.0g to 14.7g, so that the mass ratio of citric acid to sodium succinate in the final working solution was about 1.5:1. The other components and process parameters remained unchanged, and the working plating solution was obtained.

[0038] The resulting plating solution Ni² + The concentration was 4.75 g / L, and the pH was 4.63. Deposition was performed on the same FR-4 substrate for 25 min at a deposition rate of 7.1 μin / min; the phosphorus content of the coating was 10.5 wt%. Figure 3 As shown, the cross-sectional SEM image shows a coating thickness of 4.4 μm, with slight thickness fluctuations (±9%) at the edges of fine lines; the nickel corrosion depth is 0.41 μm (accelerated corrosion under the same conditions); the solderability tin coverage is 96.5%; and the remaining performance indicators meet the requirements.

[0039] The results show that the product can still achieve the technical effects of the present invention, thus proving that the technical solution of the present invention has good feasibility and stability within the mass ratio of citric acid to succinate of 1.5–3.0:1.

[0040] Example 3 This embodiment is intended to verify the interface regulation limit performance under the condition of the upper limit of the content of the anticorrosive agent (80 mg / L) in this application.

[0041] With all other preparation conditions the same as in Example 1, only the total concentration of benzotriazole and nicotinamide in component D was increased to make its total content in the final working solution 80 mg / L, wherein the mass ratio of benzotriazole to nicotinamide was kept at 3:1, and the other components and process parameters remained unchanged.

[0042] The resulting plating solution Ni² + The concentration was 4.75 g / L, and the pH was 4.64. Deposition was performed on FR-4 substrate for 25 min at a deposition rate of 7.5 μin / min; the phosphorus content of the coating was 10.7 wt%. Figure 4 As shown, the cross-sectional SEM revealed that the coating thickness was 4.7 μm, with no pitting in the orifice area; the nickel corrosion depth was 0.35 μm; the solderability tin coverage was 97.1%; however, the residual BTA on the coating surface reached 0.18 at%, which led to a 12% decrease in the adhesion of the subsequent immersion gold layer (the cross-cut rating dropped from 5B to 4B).

[0043] The results showed that increasing the total dosage of benzotriazole and nicotinamide to 0.080 g could still maintain low corrosion performance, but attention should be paid to its potential impact on the compatibility of downstream processes. This upper limit is a safety boundary that takes into account the adaptability of multiple processes.

[0044] Example 4 This embodiment aims to verify the effect of the lower limit of the addition amount of component D (0.2 vol%) on the micro-interface regulation function in this application.

[0045] With all other preparation conditions the same as in Example 1, only the amount of component D added was adjusted from 3.5 mL to 2.0 mL, i.e. 0.2 vol%, and the other components and process parameters remained unchanged to obtain the working plating solution.

[0046] The resulting plating solution Ni² + The concentration was 4.75 g / L, and the pH was 4.65. Deposition on FR-4 substrate was performed for 25 min at a deposition rate of 8.2 μin / min; the phosphorus content of the coating was 10.8 wt%. Figure 5 As shown, SEM revealed a small number of pits (density 3.2 per mm²) in the orifice area; the nickel corrosion depth increased to 0.48 μm; and the solderability tin coverage was 95.3%.

[0047] The results showed that when the concentration of component D was reduced to 0.2 vol%, the wetting, hydrogen release, and corrosion inhibition functions remained basically effective, but the local defect rate increased slightly, confirming that this lower limit value is the minimum feasible concentration to ensure the performance of key interfaces.

[0048] Example 5 This embodiment is intended to verify the effect of the lower limit of the aging temperature (80°C) on the activation effect of the plating solution in this application.

[0049] With all other preparation conditions the same as in Example 1, only the aging temperature in step S5 was adjusted from 82°C to 80°C, while the aging time remained at 30 min, to obtain the working plating solution.

[0050] The resulting plating solution Ni² + The concentration was 4.75 g / L, and the pH was 4.65. Deposition was performed on FR-4 substrate for 25 min at a deposition rate of 7.6 μin / min; the phosphorus content of the coating was 10.6 wt%. Figure 6 As shown, the cross-sectional SEM revealed a coating thickness of 4.8 μm, but the surface roughness Ra increased from 0.12 μm to 0.18 μm; the nickel corrosion depth was 0.43 μm.

[0051] The results show that aging at 80℃ can still complete basic activation, but the maturity of the catalytic core is slightly lower, resulting in a slight decrease in deposition kinetics and surface quality. The lower limit of this temperature is a reliable boundary for process robustness.

[0052] Example 6 This embodiment is intended to verify the controllability of the endpoint performance of the MTO replenishment cycle upper limit (3.8MTO) in this application.

[0053] The working plating solution was prepared according to Example 1 and put into continuous production. Ni² was tested every 0.5 MTO.+ Concentration, pH, and sodium hypophosphite concentration, and according to Ni² + Replenish the consumed amount of component M, and simultaneously replenish components A and D according to the proportion of component M replenishment. Also replenish sodium hypophosphite to ensure the Ni²⁺ content in the working solution is within acceptable limits. + The concentration was maintained at 4.5-5.0 g / L, the pH at 4.5-4.8, and the sodium hypophosphite concentration at 26-34 g / L. At the 3.8 MTO endpoint, Ni²... + The concentration was 4.62 g / L, and the pH was 4.63. The final plating solution was applied to an FR-4 substrate for 25 minutes.

[0054] The deposition rate was 7.1 μin / min; the phosphorus content of the coating was 10.4 wt%; such as Figure 7 As shown, the cross-sectional SEM image shows a coating thickness of 4.5 μm, with a thickness fluctuation of ±8% at the edge of the fine lines; a nickel corrosion depth of 0.78 μm; a solderability tin coverage of 95.7%; no peeling after cross-cut test combined with ultrasonic peeling; and no red rust after 12 hours of salt spray testing.

[0055] The results show that the plating solution of the present invention still fully meets the technical requirements at the 3.8MTO endpoint, confirming that the MTO-based linkage replenishment strategy can effectively maintain the stability of performance throughout the entire cycle.

[0056] Example 7 This embodiment verifies the consistency of corrosion resistance of plating solutions prepared according to different implementation methods after OSP.

[0057] The working plating solutions prepared in Examples 1-6 were used to plate FR-4 substrates for 25 min (82℃, pH 4.65). After rinsing and drying, all samples underwent OSP treatment (EntekPlusCu, 50℃, 60 s), followed by a damp heat test at 85℃ / 85%RH / 168 h. The nickel layer corrosion depth of each sample was measured (cross-sectional SEM measurement), and the results are shown in Table 1.

[0058] Table 1 Results of nickel corrosion depth test after OSP

[0059] As shown in Table 1, after OSP treatment, the nickel corrosion depth of the plating solutions prepared in all embodiments was ≤0.36μm, which is far below the industry standard limit of 1.0μm. The difference between the maximum and minimum values ​​was only 0.08μm, and the coefficient of variation was 9.2%. This indicates that the technical solution of the present invention can stably achieve excellent corrosion resistance after OSP within the parameter boundary range, verifying the overall support of the range.

[0060] Example 8 This embodiment provides an application of a high-phosphorus, low-corrosion electroless nickel plating solution for printed circuit boards. Experimental results show that the electroless nickel plating solution prepared by this invention exhibits good deposition uniformity, high phosphorus content, and low corrosion characteristics on FR-4, Rogers RO4350B, and polyimide flexible substrates. Therefore, it can be used to prepare protective coatings for preventing and / or treating nickel layer corrosion of printed circuit boards under soldering, OSP, and high humidity and heat environments.

[0061] Comparative Example 1: Sodium succinate was removed; the remaining components and preparation method were the same as in Example 1. The resulting plating solution showed significant Ni²⁺ after 1.0 MTO. + Concentration decay (Δ[Ni²) + ]= The deposition rate decreased from 8.3 μin / min to 6.2 μin / min (2.0 MTO) with a concentration of 0.31 g / L per MTO. The etching depth at the fine line edges reached 1.2 μm (96 h), and the solder coverage decreased to 89.4%.

[0062] Comparative Example 2: Benzotriazole and nicotinamide were removed, and the remaining components and preparation method were the same as in Example 1. The resulting plating solution had a pit density of 12.5 pits / mm² in the orifice area, and the corrosion depth after OSP was 0.83 μm (168 h). The gold adhesion rating decreased from 5B to 3B.

[0063] Comparative Example 3: Dynol 960 was removed, and the remaining components and preparation method were the same as in Example 1. The resulting plating solution showed dense pinholes (density 28.6 pinholes / mm²) at the edges of fine lines, with a deposition rate fluctuation of ±15.3%, and the final nickel etching depth at 3.8 MTO was 1.05 μm.

[0064] Comparative Example 4: No additional steps were performed; all other steps were the same as in Example 1. The resulting plating solution was subjected to 2.0 MTO before Ni² was deposited. + When the concentration was reduced to 4.21 g / L, the pH was reduced to 4.41, the deposition rate was reduced to 5.1 μin / min, and the corrosion depth after OSP reached 1.32 μm (168 h).

[0065] Table 2 Results of the Effect Test

[0066] As shown in Table 2, the synergistic effect of the various technical features of this invention is significantly better than the case of a single missing feature: the dual complexation system (DP1 vs S1) reduced the nickel corrosion depth by 73.3%, confirming its dominant inhibitory effect on localized corrosion; the combination of corrosion inhibitor and wetting aid (DP2+DP3 vs S1) reduced the corrosion depth after OSP by 66.1%, highlighting the interface synergistic mechanism; and the MTO replenishment logic (DP4 vs S1) reduced the corrosion depth at the 3.8 MTO endpoint by 72.4%, demonstrating the core value of periodic control. All data support that the technical solution defined in this invention possesses outstanding substantive features and significant progress.

[0067] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A high-phosphorus, low-corrosion electroless nickel plating solution for circuit boards, characterized in that, Based on the working fluid, it includes the following components: Nickel salts, equivalent to Ni² + It is 4.5-5.0 g / L; Hypophosphite 26-34 g / L; Citric acid 20-32 g / L; Succinic acid and / or succinate 8-20 g / L; Buffer 3-12 g / L; Grain refiner 0.05-0.8 g / L; Preservative inhibitor 10-80 mg / L; Wetting and hydrogen-releasing agent 20-150 mg / L; Stabilizer 0.2-5 mg / L; The electroless nickel plating solution has a pH of 4.5-4.8, and the mass ratio of citric acid to succinic acid and / or succinate is 1.5-3.0:

1. The electroless nickel plating solution is formulated from component M, component A, component D and hypophosphite. Component M includes at least the nickel salt and citric acid. Component A includes at least the succinic acid and / or succinate, buffer and grain refiner. Component D includes at least the corrosion inhibitor, wetting and hydrogen release agent and stabilizer.

2. The high-phosphorus, low-corrosion electroless nickel plating solution according to claim 1, characterized in that, The nickel salt is nickel sulfate and / or nickel chloride, and the hypophosphite is sodium hypophosphite.

3. The high-phosphorus, low-corrosion electroless nickel plating solution according to claim 1, characterized in that, The citric acid content is 22-30 g / L, the succinic acid and / or succinate content is 10-18 g / L, and the mass ratio of the citric acid to the succinic acid and / or succinate is 1.8-2.6:

1.

4. The high-phosphorus, low-corrosion electroless nickel plating solution according to claim 1, characterized in that, The corrosion inhibitor is one or at least two of benzotriazole, imidazole and nicotinamide, and the wetting and hydrogen-releasing agent is an alkynyldiol-modified polyether nonionic surfactant.

5. The high-phosphorus, low-corrosion electroless nickel plating solution according to claim 1, characterized in that, The buffer content is 5-10 g / L, the grain refiner content is 0.1-0.5 g / L, the stabilizer content is 0.5-3 mg / L, and the pH of the electroless nickel plating solution is 4.6-4.

8.

6. A method for preparing a high-phosphorus, low-corrosion electroless nickel plating solution for circuit boards, used to prepare the high-phosphorus, low-corrosion electroless nickel plating solution as described in any one of claims 1-5, characterized in that, include: S1. Preparation of component M: Add citric acid to the first portion of deionized water and stir at 40-50℃ until dissolved. Then add nickel salt and continue stirring until a homogeneous solution is formed. S2. Preparation of component A: Add succinic acid and / or succinate and buffer to the second part of deionized water, stir to dissolve, and then add grain refiner to obtain component A; S3. Preparation of component D: Add corrosion inhibitor, wetting and hydrogen release agent and stabilizer to the third part of deionized water, stir and mix at a temperature not exceeding 35°C, and filter through 0.2-1μm to obtain component D; S4. Preparation of working solution: Add component M, component A, and component D sequentially to the fourth part of deionized water, wherein the amount of component M added is 14-16% by volume, the amount of component A added is 4-6% by volume, and the amount of component D added is 0.2-0.5% by volume. S5. After thoroughly mixing components M, A, and D, add hypophosphite to adjust the Ni² concentration in the working solution. + The concentration of the electrolyte is 4.5-5.0 g / L, the concentration of hypophosphate is 26-34 g / L, the pH is 4.5-4.8, and the solution is heated to 80-84℃ and aged for 20-40 min to obtain the electroless nickel plating solution.

7. The preparation method according to claim 6, characterized in that, In step S1, citric acid is added first and completely dissolved before nickel salt is added. In step S2, succinic acid and / or succinate and buffer are added first and completely dissolved before grain refiner is added.

8. The preparation method according to claim 6, characterized in that, In step S3, the preparation temperature of component D is no higher than 35℃, and the filtration accuracy is 0.2-1μm.

9. The preparation method according to claim 6, characterized in that, In step S5, after adding hypophosphite, adjust the pH of the working solution to 4.5-4.8, and then heat it to 80-84℃ for aging, with an aging time of 20-40 minutes.

10. A method for applying a high-phosphorus, low-corrosion electroless nickel plating solution for circuit boards, wherein the high-phosphorus, low-corrosion electroless nickel plating solution is prepared by the method described in claim 6, characterized in that... During the process of using the electroless nickel plating solution in circuit board production, the Ni²⁺ content in the working solution is detected at intervals of 0.5 MTO. + The concentration and pH were adjusted, and components M, A, D, and hypochlorite were added separately to maintain the Ni² concentration in the working solution during the 0-3.8 MTO production cycle. + The concentration is 4.5-5.0 g / L, and the pH is 4.5-4.8; During the 0-3.8 MTO production cycle, the Ni² content in the working fluid was measured every 0.5 MTO. + The concentration and pH were adjusted, and by adding components M, A, D and hypophosphite, the working temperature of the electroless nickel plating solution was maintained at 80-84℃, and the electroless nickel plating deposition rate on the circuit board surface was maintained at 6.5-9.5 μin / min.

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