A phosphine ligand synergistic grain refiner and a cyanide-free silver plating solution containing the same and application thereof

Abstract

The application discloses a phosphine ligand synergistic grain refiner, a cyanide-free silver plating solution containing the same and application, and aims to solve the technical problems of the existing cyanide-free silver plating technology, such as various additives, poor plating solution stability and rough and yellow plating layer in a high current density area. The additive is composed of a component A selected from specific phosphine ligands and a component B of a grain refiner such as sodium polyepoxysuccinate, and the mass ratio of the component A to the component B is (5-20):1. The plating solution comprises a silver ion source, the synergistic additive, an electrolyte, a conductive salt and a pH buffer, and the pH is adjusted to 5.0-8.0. The plating solution is prepared by stepwise feeding and standing and ripening, and the plating process parameters are as follows: a current density of 0.5-3.0 A / dm 2 , a temperature of 25-45 DEG C. The formula is simplified, the plating solution has high stability, the obtained silver plating layer is bright and dense, has good adhesion, is cyanide-free and environmentally friendly, and is suitable for high-end fields such as electronic components and semiconductor packaging.

Description

Technical Field

[0001] This invention relates to the field of electroplating technology, specifically to the preparation and application of cyanide-free silver plating additives, cyanide-free silver plating solutions, and especially to a cyanide-free silver plating additive with synergistic effects of phosphine ligands and grain refiners, as well as a cyanide-free silver plating solution containing the additive, a method for preparing the plating solution, and a process method for silver plating using the plating solution. It can be widely used in silver plating of substrates in the fields of electronics, communication equipment, and instruments. Background Technology

[0002] Silver plating, with its excellent electrical and thermal conductivity, solderability, and decorative properties, has irreplaceable application value in the electronics industry, communication equipment, and instrumentation. Traditional silver plating processes often employ cyanide systems. Although this system boasts excellent plating solution stability and superior overall coating performance, cyanide is a highly toxic substance, posing a serious threat to the health of operators and causing irreversible pollution to soil, water, and other ecological environments. Furthermore, the treatment process for cyanide-containing wastewater is complex and costly, failing to meet the requirements of modern industrial green, environmentally friendly, and sustainable development. Therefore, cyanide-free silver plating technology has become an inevitable trend in the industry.

[0003] Currently reported cyanide-free silver plating systems mainly include thiosulfate systems, hydantoin systems, nicotinic acid systems, and sulfonate systems. To obtain a qualified coating, these systems typically require the compounding of multiple functional additives such as brighteners, leveling agents, wetting agents, and complexing agents. This results in complex plating bath formulations, cumbersome preparation operations, and high difficulty in process control. This not only increases the cost and operational threshold of industrial production but also easily leads to fluctuations in coating quality due to imbalances in additive ratios. More importantly, existing cyanide-free silver plating systems suffer from three major targeted technical problems that cannot be effectively solved simultaneously by current technologies: First, the complexing system lacks stability; a single complexing agent is insufficient to stabilize silver ions, leading to silver ion precipitation and degradation of plating bath components with long-term use, resulting in a shortened plating bath life. Second, the coating crystal quality is poor; there are no effective grain refinement methods, and the coating is prone to defects such as coarse grains and rough surfaces, especially in the 0.5-3.0 A / dm² range. 2 In the conventional and high current density range, the coating is prone to yellowing and decreased adhesion, which cannot meet the requirements of high-end electronic components; thirdly, the additives have a single function and cannot achieve the synergistic effect of "complexation stabilization + grain refinement". Multiple components need to be superimposed to barely meet the basic coating requirements, which further exacerbates the complexity of the formula and the difficulty of process control.

[0004] Therefore, how to overcome the shortcomings of the existing technology is the subject of this invention. Summary of the Invention

[0005] The purpose of this invention is to overcome the technical defects of existing cyanide-free silver plating technologies, such as the large variety of additives, poor stability of the plating solution, large fluctuations in plating quality, easy yellowing and insufficient adhesion of the plating in high current density areas, and the inability to achieve the synergistic effect of complexation stability and grain refinement. This invention provides a phosphine ligand synergistic grain refiner and an environmentally friendly and stable cyanide-free silver plating solution containing it. It also provides the preparation method, usage method and application of the plating solution to meet the stringent silver plating requirements of high-end fields such as electronic components and semiconductor packaging.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A phosphine ligand synergistic grain refiner for cyanide-free silver plating, comprising component A and component B: Component A: Phosphine ligand compound selected from one or more of sodium triphenylphosphine tri-m-sulfonate (TPPTS), sodium triphenylphosphine mono-m-sulfonate (TPPMS), bis(diphenylphosphine)ethane, and bis(diphenylphosphine)butane; Component B: Grain refiner, selected from one or more of sodium polyepoxysuccinate (PESA), sodium polyaspartate (PASP), and polyacrylamide morpholine; The mass ratio of component A to component B is (5-20):1.

[0007] A further technical solution is that the mass ratio of component A to component B is (8-15):1. This mass ratio range allows the phosphine ligand and grain refiner to achieve the best synergistic effect, ensuring the stability of the plating solution and effectively controlling the crystallization process of the silver plating layer, resulting in a plating layer with superior performance.

[0008] Furthermore, the present invention also discloses a cyanide-free silver plating solution, comprising components at the following concentrations: Silver ion source 10-50 g / L; The phosphine ligand synergistic grain refiner is 5-30 g / L; Electrolyte 20-100g / L; Conductive salt 10-50 g / L; An appropriate amount of pH buffer is used to adjust the pH of the electroplating solution to 5.0-8.0.

[0009] A further technical solution involves using one or more of silver nitrate, silver methanesulfonate, and silver acetate as the silver ion source. These silver ion sources have good solubility, can rapidly provide a stable concentration of silver ions, and do not introduce harmful impurities, thus helping to ensure the stability of the plating solution and the quality of the plating layer.

[0010] A further technical solution is that the electrolyte is one or more of methanesulfonic acid, aminosulfonic acid, and citric acid, or a salt thereof. This type of electrolyte can improve the conductivity of the plating solution, broaden the current density range, and simultaneously adjust the pH of the plating solution, helping to stabilize silver ions and prevent their precipitation.

[0011] A further technical solution is that the conductive salt is one or more of potassium sulfate, potassium nitrate, and potassium chloride. This type of conductive salt can further improve the conductivity of the plating solution, reduce the tank voltage during electroplating, save energy, and at the same time, will not adversely affect the plating solution system or the performance of the plating layer.

[0012] A further technical solution is that the pH buffer is one of boric acid or a potassium dihydrogen phosphate-dipotassium hydrogen phosphate buffer pair. This type of buffer has excellent buffering performance, stabilizing the pH of the plating solution within the optimal range of 5.0-8.0, ensuring the complexation stability of the phosphine ligands on silver ions and the effectiveness of the grain refiner, thus preventing pH fluctuations from causing a decline in coating quality.

[0013] Furthermore, the present invention also discloses a method for preparing a cyanide-free silver plating solution, characterized in that: the method for preparing the cyanide-free silver plating solution according to any one of claims 3 to 7 includes: Step 1: Dissolve the electrolyte and conductive salt in deionized water and stir until homogeneous to obtain the basic electrolyte solution; Step 2: Add component A of the phosphine ligand synergistic grain refiner to the basic electrolyte obtained in Step 1, and stir until completely dissolved; Step 3: Adjust the pH of the solution obtained in Step 2 to 5.0-8.0 using a pH buffer, and stir well; Step 4: Add the silver ion source to the solution obtained in Step 3, stir to dissolve, and allow the silver ions to fully complex with component A; Step 5: Add component B of the phosphine ligand synergistic grain refiner to the solution obtained in Step 4, and stir until homogeneous; Step 6: Add deionized water to the specified volume, let it stand for 2-4 hours to mature, and then obtain the cyanide-free silver plating solution.

[0014] The above preparation method is simple and easy to operate, requiring no complex equipment. By controlling the order of addition of each component, it can ensure that each component is fully dissolved and works synergistically, effectively avoiding premature precipitation of silver ions and ensuring the stability and consistency of the plating solution.

[0015] Furthermore, the present invention also discloses a method for silver plating, characterized in that: the silver plating is performed using the cyanide-free silver plating solution described in any one of claims 3 to 7, and the method includes: Step a: Pre-treat the substrate, which includes degreasing, pickling, and activation to remove oil, oxide layer, and impurities from the substrate surface; to ensure that the substrate surface is clean and activated, and to improve the adhesion between the coating and the substrate; Step b: Immerse the pretreated substrate in the cyanide-free silver plating solution, using a silver or platinum plate as the anode, at a current density of 0.5-3.0 A / dm³. 2 Electroplating is carried out at a temperature of 25-45℃ under stirring conditions; Step c: After electroplating, the plated parts are sequentially washed with water, passivated, and dried. This removes residual electroplating solution from the surface of the parts, improves the corrosion resistance of the silver plating, and extends the service life of the plating.

[0016] A further technical solution involves using air stirring, mechanical stirring, or cathode movement in step b. This ensures uniform plating solution concentration, sufficient electrode reaction, and the acquisition of a uniform silver plating layer.

[0017] The terms “include,” “including,” and “have” used in this article are all open-ended, meaning they include but are not limited to.

[0018] Unless otherwise specified, the terms used herein generally have their ordinary meaning in the context of the art, the subject matter, and the specific context. Certain terms used to describe this case will be discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in describing this case.

[0019] Compared with the prior art, the present invention has the following significant advantages: 1. Significant synergistic effect: This invention uses a phosphine ligand (component A) and a grain refiner (component B) to form a synergistic system, wherein the phosphine ligand interacts with Ag through the P atom. + The formation of stable complexes effectively prevents silver ions from precipitating under acidic to weakly alkaline conditions, ensuring the long-term stability of the plating solution. The grain refiner adsorbs onto the cathode surface, regulating the nucleation and growth process of silver ions and refining the plating grains. The synergistic effect of these two agents allows for the achievement of finely crystallized, bright, uniform, and dense silver plating without the use of traditional brighteners and leveling agents. This solves the technical problem in existing technologies where single additives have limited functionality and cannot simultaneously achieve plating solution stability and plating grain refinement.

[0020] 2. Simplified additives: Compared with the complex formulations in existing technologies that require the addition of multiple brighteners, leveling agents, and wetting agents, this invention can achieve good coating performance with only two functional components, A and B. This greatly simplifies the plating solution preparation process, reduces the difficulty of plating solution preparation and process control costs, and at the same time reduces mutual interference between additives, improves the stability of plating solution performance, and solves the problems of complex plating solution formulations and high control difficulty in existing technologies.

[0021] 3. Stable coating quality: The silver coating obtained by this invention has dense crystals, a bright surface, and good adhesion to the substrate, with a stability of 0.5-3.0 A / dm². 2 It can obtain a uniform coating over a wide current density range, effectively overcoming the defects of existing cyanide-free silver plating technology, such as yellowing, roughness, and poor adhesion of the coating in the high current density area, and is suitable for the stringent requirements of high-end fields for coating quality.

[0022] 4. Excellent environmental performance: The additives and electroplating solutions of this invention are completely free of cyanide, and the toxicity of the plating solution is extremely low, which meets the requirements of modern industrial green and environmentally friendly development. At the same time, the plating solution has a simple composition, which can simplify the wastewater treatment process, reduce treatment costs, effectively reduce environmental pollution, reduce the environmental burden on enterprises, and solve the problems of serious pollution and difficult wastewater treatment of cyanide-containing plating solutions in the existing technology.

[0023] 5. Wide range of applications: The cyanide-free silver plating solution of the present invention can be adapted to silver plating treatment of various substrates such as copper, nickel, iron, and stainless steel, and the plating performance is stable. It can be applied to multiple fields such as electronic components, semiconductor packaging, precision instruments, and decorations, and has broad industrial application prospects. It solves the problem of limited applicable substrates and narrow application range of existing cyanide-free silver plating systems.

[0024] In summary, unlike conventional cyanide-free silver plating, this invention addresses the specific technical challenges of existing technologies, such as the large variety of additives, poor plating solution stability, poor plating performance in high current density areas, and the inability to achieve synergistic effects of complexation and grain refinement. It designs a two-component synergistic additive system consisting of phosphine ligands (complexation effect) and grain refiners (crystallization regulation effect). This system eliminates the need for multiple functional additives, simultaneously resolving the technical deficiencies of plating solution stability, plating crystal quality, and poor plating performance in high current density areas. It achieves the dual goals of simplifying the plating solution formulation and improving plating performance, thus providing an environmentally friendly, stable, and efficient cyanide-free silver plating solution, filling a gap in existing technologies. Detailed Implementation

[0025] The present case will be clearly described in detail below. Any person skilled in the art who understands the embodiments of the present case can make changes and modifications based on the technology taught in the present case without departing from the spirit and scope of the present case.

[0026] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of this work. Singular forms such as “a,” “this,” “this,” “the,” and “the” as used herein also include plural forms.

[0027] Example 1: This example provides a phosphine ligand synergistic grain refiner for cyanide-free silver plating and its electroplating solution, as detailed below: 1. Phosphine ligand synergistic grain refiner: Component A is sodium triphenylphosphine trimethylsulfonate (TPPTS), and component B is sodium polyepoxysuccinate (PESA). The mass ratio of component A to component B is 10:1.

[0028] When the mass ratio of components A to B is 10:1 (preferred range 8-15:1), the coating gloss and plating solution stability are optimal; when the mass ratio is 5:1 or 20:1, the performance decreases slightly, but still meets the usage requirements.

[0029] 2. Composition (concentration) of cyanide-free silver plating solution: Silver nitrate 30g / L; Phosphine ligand synergistic grain refiner 16.5 g / L (of which TPPTS 15 g / L and PESA 1.5 g / L). Mesylate 40g / L; Potassium sulfate 30 g / L; Add appropriate amount of boric acid (to adjust pH to 6.0).

[0030] 3. Electroplating solution preparation method: Dissolve 40g of methanesulfonic acid and 30g of potassium sulfate in an appropriate amount of deionized water and stir well; add 15g of TPPTS and stir until completely dissolved; adjust the pH of the solution to 6.0 with boric acid and stir well; add 30g of silver nitrate and stir to dissolve; add 1.5g of PESA and stir well; add deionized water to 1L and let stand for 3 hours to obtain a cyanide-free silver plating solution.

[0031] 4. Silver plating method: Using copper sheets as the substrate, the copper sheets are subjected to a series of pretreatments: degreasing (alkaline degreasing agent, 60℃, 10 minutes), pickling (5% dilute sulfuric acid, room temperature, 3 minutes), and activation (1% dilute hydrochloric acid, room temperature, 1 minute). The pretreated copper sheets are then immersed in the prepared electroplating solution, with a silver plate as the anode, at a current density of 1.5 A / dm³. 2 Electroplating was performed at 35℃ with mechanical stirring for 15 minutes. After electroplating, the plated parts were rinsed three times with deionized water, passivated (chromate passivation solution, room temperature, 2 minutes), and dried at 60℃ to obtain the silver-plated product.

[0032] 5. Coating performance test: The resulting silver plating is silvery-white with a bright and uniform surface, free from defects such as yellowing, scratches, and peeling. The adhesion of the plating is grade 0 (qualified) according to the cross-cut test (GB / T9286-1998). The plating is observed to be fine, dense, and free of pores by scanning electron microscopy (SEM). The resistivity of the plating is comparable to that of cyanide silver plating, meeting the requirements for use in the electronic field.

[0033] Example 2: This example provides a phosphine ligand synergistic grain refiner for cyanide-free silver plating and its electroplating solution, as detailed below: 1. Phosphine ligand synergistic grain refiner: Component A is sodium triphenylphosphine monosulfonate (TPPMS), and component B is sodium polyaspartate (PASP). The mass ratio of component A to component B is 10:1.

[0034] When the mass ratio of components A to B is 10:1 (preferred range 8-15:1), the coating gloss and plating solution stability are optimal; when the mass ratio is 5:1 or 20:1, the performance decreases slightly, but still meets the usage requirements.

[0035] 2. Composition (concentration) of cyanide-free silver plating solution: Silver mesylate 25g / L; Phosphine ligand synergistic grain refiner 13.2 g / L (of which TPPMS 12 g / L and PASP 1.2 g / L). 50 g / L of aminosulfonic acid; Potassium nitrate 25g / L; Add an appropriate amount of potassium dihydrogen phosphate-dipoxat phosphate buffer (adjust pH to 6.5).

[0036] 3. The preparation method of the electroplating solution, the silver plating method, and the performance testing method are the same as in Example 1.

[0037] 4. Coating performance test: The resulting silver plating is silvery-white with a bright and uniform surface and no defects; the cross-cut adhesion test shows a grade of 0; SEM observation shows that the plating has fine and dense crystals; the conductivity and corrosion resistance are comparable to the plating obtained in Example 1, and both meet the requirements for use in high-end electronic fields.

[0038] Example 3: Component A was bis(diphenylphosphine)ethane, and component B was polyacrylamide morpholine, with a mass ratio of A to B of 5:1; the electroplating solution contained 10 g / L silver nitrate and 5 g / L synergistic additives; the electroplating conditions included a current density of 0.5 A / dm³. 2 The temperature was 25℃. Electroplating was prepared and tested according to the method in Example 1. The resulting silver plating layer was bright and dense with an adhesion grade of 0. No precipitation occurred after the plating solution was left to stand for 72 hours, and no yellowing occurred in the high current area.

[0039] Example 4: The mass ratio of component A to component B was 20:1; the electroplating solution contained 50 g / L silver methanesulfonate and 30 g / L synergistic additives; the electroplating conditions included a current density of 3.0 A / dm³. 2 The temperature was 45℃. The coating performance was tested according to the method in Example 1, and was comparable to that in Example 1, with no defects.

[0040] Comparative Example 1 (without component B, otherwise the same as Example 1) The difference between this comparative example and Example 1 is that component B (sodium polyepoxysuccinate) is not added, while the composition of the electroplating solution, preparation method, silver plating method and testing method are the same as in Example 1.

[0041] The coating performance test results showed that the obtained silver coating had a rough surface and significantly lower brightness than that of Example 1, especially in the high current density region (>2.0 A / dm²). 2 The coating exhibited slight yellowing; SEM observation revealed coarse grains and a small amount of porosity; the adhesion test result was grade 1, which does not meet the requirements for high-end applications. These results indicate that component B (grain refiner) can effectively refine the coating grains, improve the surface morphology, and prevent yellowing in high current density areas, playing a crucial role in improving coating quality.

[0042] Comparative Example 2 (without component A, otherwise the same as Example 1) The difference between this comparative example and Example 1 is that component A (TPPTS) is not added, while the composition of the electroplating solution, preparation method, silver plating method and testing method are the same as in Example 1.

[0043] Test results: The plating solution became turbid during preparation, and after 24 hours, significant silver salt precipitation (approximately 30%) occurred, making normal electroplating impossible. This result indicates that component A (phosphine ligand) effectively complexes silver ions, preventing precipitation and making it a key component for ensuring the stability of the plating solution.

[0044] Comparative Example 3 (using a conventional brightener, otherwise the same as Example 1) This comparative example refers to the technical solution of the embodiment of Chinese Patent CN201110219268.0. The difference between this example and Example 1 is that: the phosphine ligand synergistic grain refiner of the present invention is not added, and imidazole is used as a brightener (addition amount is 2g / L). The composition of the remaining electroplating solution (silver source, supporting electrolyte, conductive salt, pH buffer), preparation method, silver plating method and testing method are the same as those in Example 1.

[0045] The coating performance test results showed that the obtained silver coating had a bright surface, but its crystal density was slightly poor. The plating solution stability was poor; after one week of storage, the brightener (imidazole) degraded, the plating solution color darkened, and the brightness of the coating obtained by re-electroplating decreased significantly, with the adhesion becoming grade 1. These results indicate that the phosphine ligand synergistic grain refiner of this invention, compared with traditional brighteners, not only achieves superior coating quality but also significantly improves the stability of the plating solution and extends its service life.

[0046] In summary, the test results of the above embodiments and comparative examples show that in the phosphine ligand synergistic grain refiner of the present invention, component A (phosphine ligand) and component B (grain refiner) have a significant synergistic effect, and neither can be dispensed with: component A can stabilize silver ions in the plating solution and ensure the long-term stability of the plating solution; component B can regulate the crystallization process of the silver plating layer, refine the grains, and improve the morphology of the plating layer; the combination of the two can simplify the plating solution formulation and obtain a silver plating layer with excellent performance, which has obvious advantages compared with the prior art.

[0047] All embodiments and comparative examples of this invention were repeated three times in parallel, and the results were consistent. The performance tests were all performed in accordance with the national standards GB / T9286-1998 (cross-cut test) and GB / T10125-2021 (corrosion resistance), and the SEM test acceleration voltage was 20kV.

[0048] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A phosphine ligand synergistic grain refiner for cyanide-free silver plating, characterized in that: Composed of component A and component B: Component A: Phosphine ligand compound selected from one or more of sodium triphenylphosphine tris(m-sulfonate), sodium triphenylphosphine monos(m-sulfonate), bis(diphenylphosphine)ethane, and bis(diphenylphosphine)butane; Component B: Grain refiner, selected from one or more of sodium polyepoxysuccinate, sodium polyaspartate, and polyacrylamide morpholine; The mass ratio of component A to component B is (5-20):

1.

2. The phosphine ligand synergistic grain refiner for cyanide-free silver plating according to claim 1, characterized in that: The mass ratio of component A to component B is (8-15):

1.

3. A cyanide-free silver plating solution, characterized in that: The cyanide-free silver plating solution contains the phosphine ligand synergistic grain refiner as described in claim 1 or 2, and comprises the following components at the following concentrations: Silver ion source 10-50 g / L; The phosphine ligand synergistic grain refiner is 5-30 g / L; Electrolyte 20-100g / L; Conductive salt 10-50 g / L; An appropriate amount of pH buffer is used to adjust the pH of the electroplating solution to 5.0-8.

0.

4. The cyanide-free silver plating solution according to claim 3, characterized in that: The silver ion source is one or more of silver nitrate, silver methanesulfonate, and silver acetate.

5. The cyanide-free silver plating solution according to claim 3, characterized in that: The electrolyte is one or more of methanesulfonic acid, aminosulfonic acid, citric acid, or their salts.

6. The cyanide-free silver plating solution according to claim 3, characterized in that: The conductive salt is one or more of potassium sulfate, potassium nitrate, and potassium chloride.

7. The cyanide-free silver plating solution according to claim 3, characterized in that: The pH buffer is one of boric acid or a potassium dihydrogen phosphate-dipoxat phosphate buffer pair.

8. A method for preparing a cyanide-free silver plating solution, characterized in that: The method for preparing the cyanide-free silver plating solution according to any one of claims 3 to 7 comprises: Step 1: Dissolve the electrolyte and conductive salt in deionized water and stir until homogeneous to obtain the basic electrolyte solution; Step 2: Add component A of the phosphine ligand synergistic grain refiner to the basic electrolyte obtained in Step 1, and stir until completely dissolved; Step 3: Adjust the pH of the solution obtained in Step 2 to 5.0-8.0 using a pH buffer, and stir well; Step 4: Add the silver ion source to the solution obtained in Step 3, stir to dissolve, and allow the silver ions to fully complex with component A; Step 5: Add component B of the phosphine ligand synergistic grain refiner to the solution obtained in Step 4, and stir until homogeneous; Step 6: Add deionized water to the specified volume, let it stand for 2-4 hours to mature, and then obtain the cyanide-free silver plating solution.

9. A method for silver plating, characterized in that: The method comprises using the cyanide-free silver plating solution according to any one of claims 3 to 7, wherein the method includes: Step a: Pre-treat the substrate, including degreasing, pickling, and activation, to remove oil, oxide layer and impurities from the surface of the substrate; Step b: Immerse the pretreated substrate in the cyanide-free silver plating solution, using a silver or platinum plate as the anode, at a current density of 0.5-3.0 A / dm³. 2 Electroplating is carried out at a temperature of 25-45℃ under stirring conditions; Step c: After electroplating is completed, the plated parts are washed with water, passivated, and dried in sequence.

10. The silver plating method according to claim 9, characterized in that: The stirring method in step b is air stirring, mechanical stirring, or cathode movement.