Continuous high-phosphorus electroless nickel plating method capable of reducing crystallization of plating solution

Abstract

The present application provides a continuous high-phosphorus electroless nickel plating method capable of reducing the crystallization of the plating solution, comprising the following steps: preparing a plating solution containing nickel sulfate as the main salt, sodium hypophosphite as the reducing agent, sodium citrate as the complexing agent, a buffer, and a crystallization inhibitor according to a predetermined concentration ratio, wherein the crystallization inhibitor is one or more of a composite of an organic polyphosphonate and nano-titanium dioxide, a nitrogen-containing heterocyclic compound, or a polymer having a comb-like structure; controlling the plating temperature, the pH value of the plating solution, and the flow rate of the plating solution within a preset range, and performing continuous plating operations. By adding a crystallization inhibitor to the components of the plating solution, the crystallization inhibitor can form a complex with metal ions such as Ni²⁺ in the plating solution and be uniformly dispersed, regulating the release rate of nickel ions and avoiding local crystallization; these crystallization inhibitors can also provide a three-dimensional barrier effect, reducing the formation of dendrites and abnormal grain growth, thereby achieving the effect of reducing the crystallization of the plating solution and improving the stability and production efficiency of the plating solution.

Description

Technical Field

[0001] This application belongs to the technical field of continuous high-phosphorus electroless nickel plating, and more specifically, relates to a continuous high-phosphorus electroless nickel plating method that can reduce the crystallization of the plating solution. Background Art

[0002] In modern manufacturing, metal surface treatment is a key link to enhance the performance of metal materials and expand their application scope. Continuous electroless nickel plating, as an efficient and widely used surface treatment method, aims to endow metal or non-metal substrates with excellent properties such as corrosion resistance, enhanced hardness, and improved conductivity. However, traditional continuous electroless nickel plating technology faces many challenges in actual operation. In particular, the control of nickel crystallization and the stability of the plating solution are industry problems, which seriously restrict the improvement of coating quality and production efficiency.

[0003] In traditional continuous electroless nickel plating processes, there are many factors leading to the crystallization of the plating solution. The proportion of each component in the plating solution is often not precise enough. For example, when the concentration of the main salt is too high or fluctuates greatly, it is easy to form a supersaturated state in the plating solution, prompting nickel ions to crystallize and precipitate in advance, thereby affecting the electroplating effect and coating quality. At the same time, if the concentration of the reducing agent is not properly controlled, the chemical reactions in the plating solution will be unbalanced, triggering side reactions and generating some insoluble substances, which become the core of the plating solution crystallization and accelerate the crystallization process. In addition, the nickel plating process is a complex chemical reaction process, and there are many other known or unknown factors that can cause the crystallization of the plating solution and further affect the stability of the plating solution, thereby affecting the quality of the final coating and production efficiency. Summary of the Invention

[0004] The purpose of the embodiments of this application is to provide a continuous high-phosphorus electroless nickel plating method that can reduce the crystallization of the plating solution, so as to solve the technical problems of plating solution crystallization in the prior art and further affect the stability of the plating solution.

[0005] To achieve the above purpose, the technical solution adopted in this application is: to provide a continuous high-phosphorus electroless nickel plating method that can reduce the crystallization of the plating solution, including the following steps:

[0006] Prepare a plating solution containing nickel sulfate as the main salt, sodium hypophosphite as the reducing agent, sodium citrate as the complexing agent, a buffer, and a crystallization inhibitor according to a predetermined concentration ratio. The crystallization inhibitor is one or more of a composite of organic polyphosphonate and nano-titanium dioxide, a nitrogen-containing heterocyclic compound, or a polymer with a comb-like structure;

[0007] Control the plating temperature, the pH value of the plating solution, and the flow rate of the plating solution within a preset range, and perform continuous plating operations.

[0008] In one embodiment, the crystallization inhibitor is a complex formed by grafting an organic polyphosphonate ester onto the surface of nano-titanium dioxide through a coupling agent.

[0009] In one embodiment, the crystallization inhibitor is an imidazole compound or a polycarboxylic acid ether polymer.

[0010] In one embodiment, the concentration of the crystallization inhibitor is 0.3 - 0.7 g / L.

[0011] In one embodiment, the buffer is sodium acetate, or the buffer is a composite buffer system of sodium citrate and sodium dihydrogen phosphate.

[0012] In one embodiment, the concentration of nickel sulfate is 28 - 32 g / L, the concentration of sodium hypophosphite is 22 - 26 g / L, the concentration of sodium citrate is 18 - 22 g / L, the buffer is sodium acetate and its concentration is 12 - 18 g / L, and the flow rate of the plating solution is 0.6 - 0.8 m / s.

[0013] In one embodiment, it further includes one or more of the following steps:

[0014] Regularly detect the nickel sulfate concentration in the plating solution through a concentration detector. When the nickel sulfate concentration deviates from the predetermined range, adjust the nickel sulfate concentration in the plating solution by adding nickel sulfate or deionized water;

[0015] Real-time monitor the reduction rate of nickel ions and the change of the plating solution potential in the plating solution, and dynamically adjust the concentration of sodium hypophosphite;

[0016] Adjust the temperature of the plating solution through a heating device and a cooling device so that the fluctuation does not exceed 1 °C based on the set value;

[0017] Use an on-line pH monitor to real-time monitor the pH value of the plating solution. When the pH value of the plating solution deviates from the predetermined range, add sulfuric acid or sodium hydroxide solution to the plating solution through a dosing system to adjust the pH value of the plating solution.

[0018] In one embodiment, it further includes the following steps:

[0019] Regularly filter the solid particles in the plating solution through the filter membrane in the filtering device, wherein the pore size of the filter membrane is 0.2 - 0.5 μm.

[0020] In one embodiment, it further includes the following steps:

[0021] Regularly remove the metal ion impurities in the plating solution through ion exchange resin;

[0022] And / or regularly adsorb the organic pollutants in the plating solution through activated carbon.

[0023] In one embodiment, the method further includes the following steps:

[0024] Periodically change the flow rate and / or flow volume of the plating solution;

[0025] Alternatively, partition the plating bath, such that the plating solutions in different regions have different compositions, pH values, temperatures, and flow rates and are in mutual circulation.

[0026] Compared with the prior art, the continuous high-phosphorus electroless nickel plating method provided by the present application that can reduce plating solution crystallization adds a crystallization inhibitor to the plating solution composition. For example, a composite of organic polyphosphonate and nano-titanium dioxide, a nitrogen-containing heterocyclic compound, or a polymer with a comb-like structure. The crystallization inhibitor can form complexes with metal ions such as Ni²⁺ in the plating solution and be uniformly dispersed, regulating the release rate of nickel ions and avoiding local crystallization; these crystallization inhibitors can also provide a three-dimensional barrier effect, reducing dendrite formation and abnormal grain growth, thereby achieving the effect of reducing plating solution crystallization, improving the stability of the plating solution, and further improving the coating quality and production efficiency. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0028] Figure 1 It is a flowchart of the continuous high-phosphorus electroless nickel plating method provided by the embodiments of the present application that can reduce plating solution crystallization. Detailed Embodiments

[0029] In order to make the technical problems, technical solutions, and beneficial effects to be solved by the present application clearer, the following further details the present application in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0030] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0031] It should be understood that the orientation or positional relationship indicated by terms such as "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present application.

[0032] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, the meaning of "a plurality" is two or more unless otherwise specifically defined.

[0033] A continuous high-phosphorus electroless nickel plating method capable of reducing plating solution crystallization provided by an embodiment of the present application will now be described. The continuous high-phosphorus electroless nickel plating method capable of reducing plating solution crystallization includes the following steps:

[0034] Prepare a plating solution according to a predetermined concentration ratio, which contains nickel sulfate as the main salt, sodium hypophosphite as the reducing agent, sodium citrate as the complexing agent, a buffer, and a crystallization inhibitor. The crystallization inhibitor is one or more of a composite of organic polyphosphonate and nano-titanium dioxide, a nitrogen-containing heterocyclic compound, or a polymer with a comb-like structure;

[0035] Control the plating temperature, the pH value of the plating solution, and the flow rate of the plating solution within a preset range, and perform continuous plating operations.

[0036] Specifically, first prepare the plating solution, which mainly contains nickel sulfate as the main salt, sodium hypophosphite as the reducing agent, sodium citrate as the complexing agent, a buffer, and a crystallization inhibitor. The buffer can be sodium acetate, sodium citrate, sodium dihydrogen phosphate, or other compounds. In addition, the plating solution can also contain other auxiliary components such as a stabilizer, a promoter, a wetting agent, and a brightener.

[0037] The main function of the crystallization inhibitor is to inhibit the premature crystallization and precipitation of nickel ions in the plating solution, or to inhibit the reaction imbalance during the electroplating process, and reduce the phenomenon of generating insoluble substances due to some side reactions and forming crystal nuclei on the surface of the insoluble substances.

[0038] One of the optional crystallization inhibitors is a composite of organic polyphosphonate and nano-titanium dioxide. The organic polyphosphonate is based on polyols or amine compounds and forms a multi-functional group structure through the connection of phosphonate groups (-PO3R). For example, the molecular formula of polyol phosphate (PAPE) is PO4HR1R2. Nano-titanium dioxide has a high specific surface area and many active sites, and can be well dispersed in the plating solution. The organic polyphosphonate can be grafted onto the surface of nano-titanium dioxide through a coupling agent, thereby obtaining organic polyphosphonate-modified nano-titanium dioxide. After being modified by organic polyphosphonate, a hydrophilic and controllable coating layer is formed on the surface of nano-titanium dioxide, improving the dispersion stability in the plating solution and avoiding coating defects caused by particle agglomeration. The organic polyphosphonate forms stable complexes with metal ions (such as Ni²⁺, Cu²⁺) in the plating solution through its phosphonate groups (-PO3R), reducing the concentration of free metal ions and delaying the crystal nucleation rate. Nano-titanium dioxide, relying on its high specific surface area and surface hydroxyl groups, adsorbs metal ions and by-products (such as bubbles), reduces local supersaturation, and inhibits heterogeneous nucleation, thus achieving the effect of inhibiting crystallization.

[0039] Another optional crystallization inhibitor is a nitrogen-containing heterocyclic compound, such as an imidazole compound or a triazole compound. These compounds can form a special coordination structure with nickel ions, preventing the aggregation and crystallization of nickel ions. At the same time, these compounds can adsorb metal ions and by-products (such as bubbles), reduce local supersaturation, and inhibit heterogeneous nucleation, thus achieving the effect of inhibiting crystallization.

[0040] Another optional crystallization inhibitor is a polymer with a comb-like structure, such as carboxymethyl cellulose (CMC). The carboxylic acid groups (-COO⁻) on the molecular chain form dynamic coordination bonds with Ni²⁺, inhibiting the aggregation of crystal nuclei through steric hindrance effects. The main chain of this type of polymer with a comb-like structure can form dynamic complexes with Ni²⁺, while the side chains provide steric barriers, reducing dendrite formation and abnormal grain growth.

[0041] In addition, the crystallization inhibitor can also be a combination of a composite of organic polyphosphonate and nano-titanium dioxide, a nitrogen-containing heterocyclic compound, or a polymer with a comb-like structure. For example, a nitrogen-containing heterocyclic compound and a polymer with a comb-like structure can be added to the plating solution simultaneously. Or, a composite of organic polyphosphonate and nano-titanium dioxide and a nitrogen-containing heterocyclic compound can be added to the plating solution simultaneously. In this way, the organic polyphosphonate can regulate the release rate of nickel ions and avoid local over-deposition; the nitrogen-containing heterocyclic compound, as a secondary reducing agent, can also promote the redox efficiency of sodium hypophosphite, increasing the deposition rate by 10 - 15%.

[0042] After configuring the plating solution composition and concentration, it is necessary to adjust the plating solution temperature, pH value, and plating solution flow rate within a predetermined range. For example, the plating solution temperature range is 88 - 92 °C, the plating solution pH value needs to be maintained within the range of 4.5 - 5.5, and the plating solution flow rate needs to be controlled within 0.6 - 0.8 m / s. Then the substrate to be plated can be placed in the plating solution for continuous plating operation.

[0043] In addition, before continuous plating of the substrate, the substrate can also be pretreated, such as degreasing, rust removal, and surface activation processes. After electroplating, post-treatment can also be carried out, such as cleaning and drying the coating to remove the residual solvent on the coating surface.

[0044] The continuous high-phosphorus electroless nickel plating method provided by this application that can reduce plating solution crystallization adds a crystallization inhibitor to the plating solution composition. For example, a composite of organic polyphosphonate and nano-titanium dioxide, a nitrogen-containing heterocyclic compound, or a polymer with a comb-like structure. The crystallization inhibitor can form complexes with metal ions such as Ni²⁺ in the plating solution and be evenly dispersed, regulating the release rate of nickel ions to avoid local crystallization; these crystallization inhibitors can also provide a three-dimensional barrier effect, reducing dendrite formation and abnormal grain growth, thereby achieving the effect of reducing plating solution crystallization, improving the stability of the plating solution, and further improving the coating quality and production efficiency.

[0045] In one embodiment, the crystallization inhibitor is a composite formed by grafting organic polyphosphonate onto the surface of nano-titanium dioxide through a coupling agent. The specific preparation process is as follows:

[0046] Add nano-titanium dioxide powder to deionized water and stir ultrasonically for 30 minutes to form a uniformly dispersed suspension. Dissolve the silane coupling agent in absolute ethanol, then add the silane coupling agent solution to the nano-titanium dioxide suspension and stir at 60 °C for 3 hours to anchor the silane coupling agent on the surface of nano-titanium dioxide. Finally, dissolve organic polyphosphonate, such as polyol phosphate (PAPE), in a buffer solution and add it to the nano-titanium dioxide suspension modified by the silane coupling agent. Through a condensation reaction, covalent bonding of the phosphonate group and the functional group of the coupling agent is achieved, and the grafting reaction of organic polyol phosphonate is realized.

[0047] The composite of organic polyphosphonate and nano-titanium dioxide prepared by the grafting reaction is an organic-inorganic hybrid. Both organic polyphosphate and nano-titanium dioxide can provide corresponding active sites to complex with metal ions in the plating solution, and the nano-titanium dioxide has good dispersibility, further reducing local supersaturation phenomena and inhibiting heterogeneous nucleation, thereby achieving the effect of inhibiting crystallization.

[0048] In one embodiment, the crystallization inhibitor is an imidazole compound. Due to the strong coordination ability of its nitrogen-containing heterocycle, the imidazole compound can form a special coordination structure with nickel ions, form a stable complex with nickel ions, and prevent the aggregation and crystallization of nickel ions due to local supersaturation. Specifically, one or more of carbonyldiimidazole, benzimidazole, and benzoimidazole can be selected.

[0049] In one embodiment, the crystallization inhibitor is a polycarboxylic acid ether polymer. For example, a polycarboxylate-polyoxyethylene ether graft copolymer (Polycarboxylate Ethers, PCE) can be used. The main chain of PCE is a polycarboxylic acid structure, and the side chain is connected to a polyoxyethylene chain segment (such as APEG, HPEG, TPEG, etc.) through an ether bond (—O—) to form a “comb-like” molecular structure. The polycarboxylic acid ether polymer forms a stable complex with nickel ions (Ni²⁺) through carboxylic acid groups, and at the same time, its side chain prevents the aggregation and growth of nickel salt crystal nuclei through steric hindrance effects, effectively inhibiting the precipitation of crystals such as nickel phosphate in the plating solution and ensuring the long-term stability of the plating solution.

[0050] In one embodiment, the concentration of the crystallization inhibitor is 0.3 - 0.7 g / L. The crystallization inhibitor at this concentration can selectively adsorb on the active sites that may form crystals in the plating solution, interfere with the crystallization process of nickel ions, and make it difficult for nickel ions to aggregate to form large crystal particles, thereby effectively reducing the possibility of plating solution crystallization.

[0051] In one embodiment, the buffer is sodium acetate. Sodium acetate (CH3COONa) is used as a buffer, and its concentration is maintained at 12 - 18 g / L. The buffer can more effectively maintain the stability of the pH value of the plating solution, provide a stable environment for chemical reactions in the plating solution, and reduce the crystallization of the plating solution caused by pH value fluctuations.

[0052] In one embodiment, the buffer is a composite buffer system of sodium citrate and sodium dihydrogen phosphate. A composite buffer system composed of sodium citrate and sodium hydrogen phosphate is used. Sodium citrate can provide additional complexation effects to further stabilize nickel ions, while sodium hydrogen phosphate can play a buffering role in different pH value ranges, enhancing the resistance of the plating solution to pH value changes, so as to maintain the stability of the plating solution during continuous electroless nickel plating with high phosphorus and reduce the possibility of plating solution crystallization.

[0053] In one embodiment, the concentration of nickel sulfate is 28 - 32 g / L, the concentration of sodium hypophosphite is 22 - 26 g / L, the concentration of sodium citrate is 18 - 22 g / L, the buffer is sodium acetate and its concentration is 12 - 18 g / L, and the flow rate of the plating solution is 0.6 - 0.8 m / s.

[0054] Strictly control the concentration of the main salt nickel sulfate (NiSO4·6H2O) within the range of 28 - 32 g / L. This concentration range can not only ensure an adequate supply of nickel ions to meet the electroplating requirements but also avoid supersaturated crystallization caused by too high a concentration. Stabilize the concentration of the reducing agent sodium hypophosphite (NaH2PO2·H2O) at 22 - 26 g / L. An appropriate concentration of the reducing agent can ensure the smooth progress of the reduction reaction of nickel ions in the plating solution and avoid crystallization caused by an overly fast or slow reduction rate leading to imbalance of the plating solution. Use citric acid (C6H8O7·H2O) as a complexing agent, and maintain the concentration range at 18 - 22 g / L. A high-concentration and stable complexing agent can more effectively form stable complexes with nickel ions, reduce the activity of nickel ions, and inhibit their crystallization tendency. Sodium acetate (CH3COONa) is used as a buffer, and its concentration is maintained at 12 - 18 g / L. The buffer can more effectively maintain the stability of the pH value of the plating solution, provide a stable environment for the chemical reactions in the plating solution, and reduce the crystallization of the plating solution caused by pH value fluctuations.

[0055] In addition, the instability of the plating solution flow rate is also an important inducement for the crystallization of the plating solution. If the plating solution flow rate is too slow, the heat and by-products generated in the plating solution cannot be discharged in time and accumulate in local areas, resulting in uneven composition of the plating solution, which also creates conditions for the crystallization of the plating solution. Control the plating solution flow rate at 0.6 - 0.8 m / s with the help of a circulation pump. An appropriate flow rate can ensure the uniform distribution of the plating solution in the plating tank, timely remove the heat and by-products generated by the reaction, avoid abnormal changes in the composition of the plating solution in local areas, and reduce the risk of plating solution crystallization. At the same time, reasonably adjust the power and flow rate of the circulation pump according to the size, shape of the plating tank and the loading amount of the workpieces to ensure the stability of the plating solution flow rate.

[0056] By precisely controlling the concentrations of the main salt nickel sulfate, the reducing agent sodium hypophosphite, the complexing agent sodium citrate, and the buffer sodium acetate within the above ranges, and rationally optimizing the combination of each component ratio, fundamentally adjust the chemical composition and properties of the plating solution, reduce the crystallization tendency of nickel ions, and maintain the chemical balance of the plating solution; at the same time, reasonable control of the plating solution flow rate can avoid problems such as changes in the solubility of substances in the plating solution and chemical reaction imbalance caused by fluctuations in process parameters, thereby effectively inhibiting the crystallization of the plating solution.

[0057] In one embodiment, the following steps are further included: regularly detect the nickel sulfate concentration in the plating solution through a concentration detector, and when the nickel sulfate concentration deviates from the predetermined range, adjust the nickel sulfate concentration in the plating solution by adding nickel sulfate or deionized water.

[0058] In traditional electroplating solutions, the proportions of various components are often not precise enough. For example, as the continuous high-phosphorus electroless nickel plating reaction progresses, the concentration of the main salt nickel sulfate will change. When the concentration of the main salt nickel sulfate is too high or fluctuates greatly, it is easy to form a supersaturated state in the plating solution, which prompts nickel ions to crystallize and precipitate in advance, thereby affecting the electroplating effect and the quality of the coating. Based on this, in this application, a concentration detector is set in the plating solution tank to regularly detect the concentration of the main salt nickel sulfate in the plating solution through the concentration detector, so as to monitor the concentration of the main salt; when the concentration of nickel sulfate is on the high side, deionized water is added to the plating solution to reduce the concentration of nickel sulfate in the plating solution; when the concentration of nickel sulfate is on the low side, nickel sulfate is added to the plating solution to increase the concentration of nickel sulfate in the plating solution. In this way, by regularly detecting the concentration of nickel sulfate in the plating solution and correspondingly adjusting the concentration of nickel sulfate to a predetermined range according to the detection results, it is possible to prevent the large fluctuation of the nickel sulfate concentration from causing the premature crystallization and precipitation of nickel ions in the plating solution.

[0059] In one embodiment, the following steps are further included: real-time monitoring of the nickel ion reduction rate and the change of the plating solution potential in the plating solution, and dynamically adjusting the concentration of sodium hypophosphite.

[0060] If the concentration of the reducing agent sodium hypophosphite is not properly controlled, it will cause the chemical reaction in the plating solution to be out of balance, trigger side reactions, and generate some insoluble substances, which become the nuclei of the plating solution crystallization and accelerate the plating solution crystallization process.

[0061] A cyclic voltage is applied through a three-electrode system (working electrode, reference electrode, counter electrode) to monitor the current peak intensity of the nickel ion reduction reaction, which directly reflects the change of the reduction rate. A platinum electrode and a reference electrode (such as Ag / AgCl) are used to directly measure the ORP value of the plating solution to reflect the activity of sodium hypophosphite (reducing agent) and the nickel ion reduction process in real time. The three-electrode system and the ORP sensor are integrated into a monitoring system. When the potential exceeds the set range (such as greater than 650 mV), an automatic addition of the reducing agent is triggered.

[0062] By real-time monitoring of the reduction of nickel ions in the plating solution and the change of the plating solution potential, the addition amount of sodium hypophosphite is dynamically adjusted to maintain the stability of the reduction reaction in the plating solution.

[0063] In one embodiment, the temperature of the plating solution is adjusted by a heating device and a cooling device so that the fluctuation does not exceed 1°C based on the set value.

[0064] The unstable temperature of the plating solution is also an important inducement for the plating solution crystallization. When the temperature of the plating solution is too high and exceeds the appropriate range, the solubility of various substances in the plating solution changes, and some components may crystallize and precipitate due to the decrease in solubility. Frequent temperature fluctuations will also interfere with the stability of the chemical reaction in the plating solution, resulting in an aggravation of the plating solution crystallization phenomenon.

[0065] By installing a heating device and a cooling device in the plating bath and applying a high-precision temperature control system, the temperature of the plating solution is stably and precisely maintained at 88 - 92 °C, ensuring that the temperature fluctuation of the plating solution does not exceed 1 °C based on the set value. The stable temperature can ensure the stable solubility of various substances in the plating solution, maintain the normal progress of chemical reactions, and greatly reduce the crystallization phenomenon of the plating solution caused by temperature fluctuations.

[0066] In one embodiment, an online pH monitor is used to monitor the pH value of the plating solution in real time. When the pH value of the plating solution deviates from the predetermined range, sulfuric acid or sodium hydroxide solution is added to the plating solution through a dosing system to adjust the pH value of the plating solution.

[0067] The unstable pH value of the plating solution is also an important inducement for the crystallization of the plating solution. If the pH value deviates from the normal range, the functions of components such as complexing agents and buffers in the plating solution are affected, and the stability of nickel ions cannot be effectively maintained, making nickel ions prone to aggregation and crystallization.

[0068] A pH monitor and an automatic dosing system are installed in the plating bath, and an online pH monitor is used to monitor the pH value of the plating solution during the electroplating process in real time. Once the pH value of the plating solution deviates from the range of 4.5 - 5.5, an appropriate amount of sulfuric acid or sodium hydroxide solution is immediately added through the automatic dosing system for adjustment. For example, when the pH value is higher than 5.5, an appropriate amount of sulfuric acid solution is added to lower the pH value; when the pH value is lower than 4.5, sodium hydroxide solution is added to increase the pH value. Through this real-time monitoring and precise adjustment, the stability of the pH value of the plating solution is maintained, and the crystallization of the plating solution caused by abnormal pH value is prevented.

[0069] In one embodiment, the continuous high-phosphorus electroless nickel plating method that can reduce the crystallization of the plating solution further includes the following steps:

[0070] The solid particles in the plating solution are periodically filtered through the filter membrane in the filtering device, and the pore size of the filter membrane is 0.2 - 0.5 μm.

[0071] Due to the solid impurity particles in the plating solution, such as dust, metal debris, and insoluble substances generated by side reactions, if these impurities are not removed in time, they will become the core of the plating solution crystallization and accelerate the crystallization process. Therefore, a high-precision filtering device is installed in the plating bath, and the filtering device is provided with a filter membrane with a pore size of 0.2 - 0.5 μm to filter the plating solution regularly. In the continuous high-phosphorus electroless nickel plating process, the plating solution is filtered through a filter membrane with a pore size of 0.2 - 0.5 μm every 8 - 12 hours to remove the solid impurity particles in the plating solution, thereby reducing the crystallization phenomenon of the plating solution.

[0072] In one embodiment, the continuous high-phosphorus electroless nickel plating method that can reduce the crystallization of the plating solution further includes the following steps:

[0073] Regularly remove metal ion impurities in the plating solution through ion exchange resin;

[0074] And / or, regularly adsorb organic pollutants in the plating solution through activated carbon.

[0075] As the electroplating process continues, impurities in the plating solution gradually increase, such as metal ion impurities, organic pollutants, etc. These impurities will destroy the stability of the plating solution and reduce its ability to inhibit crystallization. Therefore, an ion exchange resin filtration device is installed in the plating tank, and the plating solution is passed through the ion exchange resin filtration device every 3 - 5 days to remove metal ion impurities in the plating solution, such as copper ions, iron ions, etc.

[0076] In addition, the plating solution may also contain organic pollutants, such as unreacted additives, organic by-products, etc., which will also cause the stability of the plating solution to decline. An activated carbon adsorption column can be installed in the plating tank, and the plating solution is regularly passed through the activated carbon adsorption column to remove organic pollutants in the plating solution. By regular purification, the purity of the plating solution is maintained, and the possibility of plating solution crystallization is reduced.

[0077] It should be noted that in the actual production process, an ion exchange resin filtration device and an activated carbon adsorption column can be installed in the plating tank, and a method combining ion exchange and activated carbon adsorption is used to regularly purify the plating solution, maintain the stability of the plating solution, and reduce the possibility of plating solution crystallization.

[0078] In one embodiment, the continuous high-phosphorus electroless plating solution method that can reduce plating solution crystallization further includes the following steps: periodically changing the flow rate and / or flow volume of the plating solution. By periodically changing the flow rate and / or flow volume of the plating solution, that is, the pulsed circulation mode of the plating solution, the local concentration balance in the plating solution is broken, and the accumulation of impurities and heat is reduced, thereby inhibiting the plating solution crystallization phenomenon.

[0079] In one embodiment, the continuous high-phosphorus electroless plating solution method that can reduce plating solution crystallization further includes the following steps: partitioning the plating tank, and the plating solution components, pH value, temperature, and flow rate in different regions are different and achieve mutual circulation.

[0080] According to the reaction characteristics of different regions in the plating tank, the plating tank is managed and circulated in partitions. According to needs, the plating solution components and process parameters such as the pH value, temperature, and flow rate of the plating solution in each region are set differently, and the plating solutions in each region of the plating tank form a mutual circulation system, so as to more accurately meet the electroplating requirements and reduce the risk of plating solution crystallization. Adopting this method of plating solution partition management and circulation requires corresponding modification of the structure of the plating tank and configuration of a corresponding control system to achieve.

[0081] Example 1

[0082] A continuous high-phosphorus electroless nickel plating method that can reduce plating solution crystallization, including:

[0083] Prepare the plating solution by mixing nickel sulfate as the main salt at 30 g / L, sodium hypophosphite at 25 g / L, sodium citrate at 20 g / L, sodium acetate at 20 g / L, and PAPE-modified nano-titanium dioxide at 0.5 g / L;

[0084] Control the plating temperature at 90 °C (±1 °C), the pH value of the plating solution at 5, and the flow rate of the plating solution at 0.8 m / s. Place the substrate in the plating solution for continuous plating operation, and record the time when the plating solution becomes turbid and crystallizes;

[0085] Regularly detect the nickel sulfate concentration in the plating solution through a concentration detector. When the nickel sulfate concentration deviates from 28 - 32 g / L, adjust the nickel sulfate concentration in the plating solution by adding nickel sulfate or deionized water;

[0086] Real-time monitor the reduction rate of nickel ions in the plating solution and the change in the potential of the plating solution, and dynamically adjust the concentration range of sodium hypophosphite to remain between 22 - 26 g / L;

[0087] Adjust the temperature of the plating solution through a heating device and a cooling device so that the fluctuation does not exceed 1 °C based on the set value of 90 °C;

[0088] Use an online pH monitor to real-time monitor the pH value of the plating solution. When the pH value of the plating solution deviates from 4.5 - 5.5, add sulfuric acid or sodium hydroxide solution to the plating solution through a dosing system to adjust the pH value of the plating solution.

[0089] Example 2

[0090] A continuous high-phosphorus electroless nickel plating method for reducing plating solution crystallization, including:

[0091] Prepare the plating solution by mixing nickel sulfate as the main salt at 30 g / L, sodium hypophosphite at 25 g / L, sodium citrate at 20 g / L, sodium acetate at 20 g / L, and carbonyldiimidazole at 0.5 g / L;

[0092] Control the plating temperature at 90 °C (±1 °C), the pH value of the plating solution at 5, and the flow rate of the plating solution at 0.8 m / s. Place the substrate in the plating solution for continuous plating operation, and record the time when the plating solution becomes turbid and crystallizes;

[0093] Regularly detect the nickel sulfate concentration in the plating solution through a concentration detector. When the nickel sulfate concentration deviates from 28 - 32 g / L, adjust the nickel sulfate concentration in the plating solution by adding nickel sulfate or deionized water;

[0094] Real-time monitor the reduction rate of nickel ions in the plating solution and the change in the potential of the plating solution, and dynamically adjust the concentration range of sodium hypophosphite to remain between 22 - 26 g / L;

[0095] Adjust the temperature of the plating solution through a heating device and a cooling device so that the fluctuation does not exceed 1 °C based on the set value of 90 °C;

[0096] The pH value of the plating solution is monitored in real time by an on-line pH monitor. When the pH value of the plating solution deviates from 4.5 - 5.5, sulfuric acid or sodium hydroxide solution is added to the plating solution through a dosing system to adjust the pH value of the plating solution.

[0097] Example 3

[0098] A continuous high-phosphorus electroless nickel plating method that can reduce the crystallization of the plating solution, including:

[0099] Prepare the plating solution according to nickel sulfate as the main salt 30 g / L, sodium hypophosphite 25 g / L, sodium citrate 20 g / L, sodium acetate 20 g / L, and PCE 0.5 g / L;

[0100] Control the plating temperature at 90 °C (±1 °C), the pH value of the plating solution is 5, the flow rate of the plating solution is 0.8 m / s, and place the substrate in the plating solution for continuous plating operation, and record the time when the plating solution becomes turbid and crystallizes;

[0101] Regularly detect the nickel sulfate concentration in the plating solution by a concentration detector. When the nickel sulfate concentration deviates from 28 - 32 g / L, adjust the nickel sulfate concentration in the plating solution by adding nickel sulfate or deionized water;

[0102] Monitor the reduction rate of nickel ions and the change of the plating solution potential in the plating solution in real time, and dynamically adjust the concentration range of sodium hypophosphite to remain at 22 - 26 g / L;

[0103] Adjust the plating solution temperature by a heating device and a cooling device to fluctuate no more than 1 °C based on the set value of 90 °C;

[0104] The pH value of the plating solution is monitored in real time by an on-line pH monitor. When the pH value of the plating solution deviates from 4.5 - 5.5, sulfuric acid or sodium hydroxide solution is added to the plating solution through a dosing system to adjust the pH value of the plating solution.

[0105] Comparative example

[0106] A continuous high-phosphorus electroless nickel plating method that can reduce the crystallization of the plating solution, including:

[0107] Prepare the plating solution according to nickel sulfate as the main salt 30 g / L, sodium hypophosphite 25 g / L, sodium citrate 20 g / L, sodium acetate 20 g / L;

[0108] Control the plating temperature at 90 °C (±1 °C), the pH value of the plating solution is 5, the flow rate of the plating solution is 0.8 m / s, and place the substrate in the plating solution for continuous plating operation, and record the time when the plating solution becomes turbid and crystallizes;

[0109] Regularly detect the nickel sulfate concentration in the plating solution with a concentration detector. When the nickel sulfate concentration deviates from 28 - 32 g / L, adjust the nickel sulfate concentration in the plating solution by adding nickel sulfate or deionized water;

[0110] Real-time monitor the reduction rate of nickel ions and the change of the plating solution potential in the plating solution, and dynamically adjust the concentration range of sodium hypophosphite to be maintained at 22 - 26 g / L;

[0111] Adjust the temperature of the plating solution with a heating device and a cooling device to fluctuate no more than 1°C based on the set value of 90°C;

[0112] Use an online pH monitor to real-time monitor the pH value of the plating solution. When the pH value of the plating solution deviates from 4.5 - 5.5, add sulfuric acid or sodium hydroxide solution to the plating solution through a dosing system to adjust the pH value of the plating solution.

[0113] After continuous plating operations are carried out according to the steps of the above three examples and the comparative example, the recorded times when the plating solution becomes turbid and crystallizes and its stability begins to decline are 80 h, 83 h, 86 h, and 78 h respectively. The results are shown in Table 1:

[0114] Table 1 Experimental data of plating solution stability for three examples and a comparative example

[0115] Serial number Type of crystallization inhibitor Concentration of crystallization inhibitor (g / L) pH value Bath temperature (°C) Crystallization time (h) Example 1 PAPE-modified nano-titanium dioxide 0.5 5 90 80 Example 2 Carbonyldiimidazole 0.5 5 90 83 Example 3 PCE 0.5 5 90 86 Comparative example None None 5 90 78

[0116] From the above data, it can be seen that in the comparative example, since no crystallization inhibitor was added, nickel ions aggregated to form crystal nuclei the fastest, resulting in the plating solution becoming turbid and crystallizing in a short period. In Example 2, carbonyl diimidazole was used as the crystallization inhibitor. Since the molecular weight of carbonyl diimidazole is relatively smaller than that of the crystallization inhibitors in Example 1 and Example 3, the inhibitory effect on the crystallization of the plating solution is slightly weaker. In Example 1, PAPE-modified nano-titanium dioxide was used as the crystallization inhibitor, which delays the growth of crystal nuclei through physical adsorption and steric hindrance, and the nano-structure provides long-term dispersion. In Example 3, PCE was used as the crystallization inhibitor. PCE wraps nickel ions through strong adsorption and forms steric hindrance using polyoxyethylene side chains, significantly inhibiting the formation and growth of crystal nuclei, and the high molecular chain has high stability, is resistant to high temperature and pH fluctuations, and has the best dispersion effect. Therefore, the plating solution has the strongest stability and the longest time to become turbid and crystallize. It can be seen that by adding a crystallization inhibitor to the plating solution in this application, the time for the plating solution to become turbid and crystallize can be significantly extended, and the stability of the plating solution can be improved.

[0117] In summary, the present application provides a plating solution formulation and a supporting process in a brand-new continuous electroless nickel plating process. Through precise formulation, the chemical composition and properties of the plating solution are fundamentally adjusted. By adding a crystallization inhibitor, the crystallization tendency of nickel ions is reduced, and the chemical balance of the plating solution is maintained. Secondly, through a high-precision temperature control system, a pH monitoring and adjustment system, and reasonable control of the plating solution flow rate, it is ensured that the temperature, pH value, and flow rate of the plating solution always remain within a suitable and stable range during the electroplating process, avoiding problems such as changes in the solubility of substances in the plating solution and chemical reaction imbalance caused by fluctuations in process parameters, thereby effectively inhibiting the crystallization of the plating solution. Finally, through continuous impurity removal and plating solution maintenance, regular filtration and purification treatments are carried out to timely remove solid particles, ionic impurities, and organic pollutants in the plating solution, maintain the purity of the plating solution, prevent these substances from becoming the core of the plating solution crystallization, extend the service life of the plating solution, and maintain the stability of the plating solution, reducing the crystallization phenomenon of the plating solution during the continuous electroless high-phosphorus nickel plating process. The technical solution of the present application effectively overcomes the deficiencies of the prior art through precise control of each key element in the electroplating process, achieving the goals of reducing nickel crystallization, improving the coating quality, and the stability of the plating solution, and providing a high-performance and high-stability continuous electroless nickel plating solution for many industries with strict requirements for metal surface performance, such as electronics, mechanical manufacturing, and aerospace.

[0118] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A continuous electroless nickel plating method with high phosphorus content that can reduce the crystallization of plating solution, characterized in that, It includes the following steps: Prepare a plating solution containing nickel sulfate as the main salt, sodium hypophosphite as the reducing agent, sodium citrate as the complexing agent, a buffer, and a crystallization inhibitor according to a predetermined concentration ratio. The crystallization inhibitor is a complex formed by grafting polyol phosphate ester onto the surface of nano-titanium dioxide through a coupling agent; and / or, the crystallization inhibitor is a polycarboxylic acid-polyoxyethylene ether graft copolymer; Control the plating temperature, the pH value of the plating solution, and the flow rate of the plating solution within a preset range, and perform continuous plating operations.

2. The continuous electroless nickel plating method with high phosphorus content capable of reducing crystallization of plating solution according to claim 1, characterized in that, The concentration of the crystallization inhibitor is 0.3 - 0.7 g / L.

3. The continuous electroless nickel plating method with high phosphorus content capable of reducing crystallization of plating solution according to claim 1, characterized in that, The buffer is sodium acetate, or the buffer is a composite buffer system of sodium citrate and sodium dihydrogen phosphate.

4. The continuous electroless nickel plating method with high phosphorus content capable of reducing crystallization of plating solution according to any one of claims 1 to 3, characterized in that, The concentration of nickel sulfate is 28 - 32 g / L, the concentration of sodium hypophosphite is 22 - 26 g / L, the concentration of sodium citrate is 18 - 22 g / L, the buffer is sodium acetate and its concentration is 12 - 18 g / L, and the flow rate of the plating solution is 0.6 - 0.8 m / s.

5. The continuous high-phosphorus electroless nickel plating method capable of reducing the crystallization of plating solution according to any one of claims 1-3, characterized in that, It also includes one or more of the following steps: Regularly detect the concentration of nickel sulfate in the plating solution through a concentration detector. When the concentration of nickel sulfate deviates from the predetermined range, adjust the concentration of nickel sulfate in the plating solution by adding nickel sulfate or deionized water; Real-time monitor the reduction rate of nickel ions and the change of the potential of the plating solution in the plating solution, and dynamically adjust the concentration of sodium hypophosphite; Adjust the temperature of the plating solution through a heating device and a cooling device so that the fluctuation does not exceed 1°C based on the set value; Use an on-line pH monitor to real-time monitor the pH value of the plating solution. When the pH value of the plating solution deviates from the predetermined range, add sulfuric acid or sodium hydroxide solution to the plating solution through a dosing system to adjust the pH value of the plating solution.

6. The continuous high-phosphorus electroless nickel plating method capable of reducing the crystallization of plating solution according to any one of claims 1-3, characterized in that, It also includes the following steps: Regularly filter the solid particles in the plating solution through the filter membrane in the filtering device, where the pore size of the filter membrane is 0.2 - 0.5 μm.

7. The continuous high-phosphorus electroless nickel plating method capable of reducing the crystallization of the plating solution according to any one of claims 1 to 3, characterized in that, It also includes the following steps: Regularly remove the metal ion impurities in the plating solution through ion exchange resin; and / or, regularly adsorb the organic pollutants in the plating solution through activated carbon.

8. The continuous electroless nickel plating method with high phosphorus that can reduce the crystallization of plating solution according to any one of claims 1-3, characterized in that, It also includes the following steps: Periodically change the flow rate and / or the flow volume of the plating solution; Or, partition the plating tank, and the plating solution components, pH value, temperature, and flow rate in different areas are different and achieve mutual circulation.

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