CN116497411A - A kind of cyanide-free alkaline silver-plating electroplating solution and its preparation and application - Google Patents

Abstract

The invention relates to the technical field of electro-silvering, in particular to cyanide-free alkaline silver plating electroplating solution, and preparation and application thereof. The cyanide-free alkaline silver plating electroplating solution consists of silver salt, a main complexing agent, an auxiliary complexing agent, conductive salt, an anode depolarizer, a composite additive, a pH value regulator and deionized water; the invention improves the stability, the dispersion capability and the running performance of the electroplating solution by adopting the synergistic effect of a plurality of complexing agents and the composite additive containing aldehyde groups, carboxyl groups and hydroxyl groups, so that the current density interval is widened, the anode is not easy to passivate and is strong in replacement resistance, the obtained plating layer is bright and smooth, is not easy to change color, has good bonding force with a substrate, has high purity and high hardness, and can meet the application of decorative and engineering silver plating.

Description

A kind of cyanide-free alkaline silver-plating electroplating solution and its preparation and application

technical field

The invention relates to the technical field of electroplating, in particular to a cyanide-free alkaline silver plating solution and its preparation and application.

Background technique

Metal silver is a silvery white, ductile, and easy-to-form precious metal material. Because of its reflective properties, antibacterial properties, excellent electrical conductivity, weldability, and chemical stability, it is relatively cheap compared to other precious metals. Therefore, it has been widely used in the fields of tableware, medical treatment, jewelry and musical instruments as a decorative coating and in the fields of electrical appliances, electronics, communication equipment and instruments as a functional coating. Especially in the field of aerospace and aviation, it is widely used. Some structural parts in aerospace products, such as outer conductors, inner conductors, connecting plates, connectors, and welding parts in various antennas, need to be silver-plated to ensure good electrical conductivity and soldering. welding performance. Because the cyanide silver plating process is stable and reliable, the current efficiency is high, and the dispersion and coverage of the plating solution are good, so far, both decorative silver plating and functional silver plating have basically adopted the cyanide silver plating process. However, the electroplating solution of cyanide silver plating adopts sodium cyanide or potassium cyanide as a complexing agent of silver salt, and cyanide is a highly toxic chemical, which will It causes serious pollution to the environment and endangers human health. Therefore, the development of a cyanide-free silver plating process to replace the traditional cyanide silver plating process has become a demand for the development of the industrial field.

The cyanide-free silver plating technology has been studied since the 1960s. The typical cyanide-free silver plating systems reported so far include thiosulfate silver plating, succinimide silver plating, sulfide silver plating, imino di Sulfonate silver plating, ammonium iminodisulfate silver plating, sulfosalicylic acid silver plating, hydantoin silver plating, sulfite silver plating and other cyanide-free silver plating processes. However, the currently reported cyanide-free silver plating systems still have some defects in solution stability, process and coating performance. For example, the components of many cyanide-free silver plating systems are unstable and easy to volatilize and change color, which shortens the service life of the plating solution, requires regular replacement and maintenance, and increases the application cost. These problems have brought many problems to the management and operation of the actual electroplating process. inconvenient. The process performance cannot meet the requirements of actual electroplating processing. For example, the current density range of the non-cyanide silver plating solution reported at present is too narrow, the cathode current density is not high, the solution dispersibility is poor, the anode solubility is not good, and it is easy to passivate, etc. . In addition, the overall performance index of the silver plating layer cannot meet the requirements, especially in the aspect of engineering application silver plating, which puts forward higher requirements on the performance of the silver plating layer than the general decorative silver plating. For example, it is currently reported that the cyanide-free system coating is not bright enough, easy to change color, poor in bonding with the substrate, easy to fall off, low in purity of the coating, and low in hardness. The existence of these problems has seriously limited the practical application and popularization of existing cyanide-free silver plating process.

Contents of the invention

In order to solve the above problems, the object of the invention is to provide a cyanide-free alkaline silver plating solution and its preparation and application. The cyanide-free silver plating solution improves the stability, dispersing ability and moving ability of the plating solution through the synergistic effect of various complexing agents and compound additives containing aldehyde groups, carboxyl groups and hydroxyl groups. The current density range is wide and the anode is not easy to blunt. Moreover, the obtained coating is bright and smooth, not easy to change color, has good bonding force with the substrate, high purity and high hardness of the coating, which can meet the application of decorative and engineering silver plating.

The purpose of the present invention can be achieved through the following technical solutions:

The first object of the present invention is to provide a kind of cyanide-free alkaline silver-plating electroplating solution, by silver salt, main complexing agent, auxiliary complexing agent, conductive salt, anode depolarizer, composite additive, pH value adjusting agent and deionized water;

In the cyanide-free alkaline silver plating solution, the concentration of silver salt is 5~50g/L, the concentration of main complexing agent is 30~150g/L, the concentration of auxiliary complexing agent is 15~90g/L, and the concentration of conductive salt is 30~ 100g/L, the concentration of the anode depolarizer is 8-25g/L, the concentration of the composite additive is 5-10g/L, and the concentration of the pH regulator is 3-10g/L.

In one embodiment of the present invention, the silver salt is selected from one of silver chloride, silver nitrate, silver sulfate or silver carbonate.

In one embodiment of the present invention, the main complexing agent is selected from 1-methylhydantoin, pseudothiohydantoin, 5-phenylhydantoin, 2-thiohydantoin One or more of urea, 5,5-diphenylhydantoin, 5,5-dimethylhydantoin, 1-allylhydantoin or hydantoin-5-acetic acid kind.

In one embodiment of the present invention, the auxiliary complexing agent is selected from succinimide, N-hydroxysuccinimide, ethylenediamine, disodium edetate, trisodium citrate, potassium pyrophosphate , sodium pyrophosphate, ammonium citrate, potassium citrate, sodium metapolyphosphate and sodium polyphosphate, cycloheximide, 4-bromobenzamide or urea.

In one embodiment of the present invention, the conductive salt is selected from one or more of potassium chloride, sodium chloride, potassium carbonate, sodium carbonate, potassium sulfate, sodium sulfate, ammonium chloride or ammonium sulfate.

In one embodiment of the present invention, the anode depolarizer is selected from potassium nitrate, sodium nitrate, ammonium nitrate, potassium sodium tartrate, potassium thiocyanate, sodium thiocyanate, sodium thiosulfate, potassium thiosulfate , ammonium thiosulfate, aminotrimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, hydroxyethylidene diphosphoric acid, dipotassium hydrogen phosphate or disodium hydrogen phosphate.

In one embodiment of the present invention, the composite additive is composed of a surfactant, a primary brightener and a secondary brightener in a mass ratio of 2:5:1,

Wherein, the surfactant is selected from sodium dodecylsulfonate, sodium dodecylbenzenesulfonate, sodium dodecylsulfate, potassium fatty alcohol sulfate, potassium polyether carboxylate, potassium N-acylaminocarboxylate OP, One or more of nonylphenol polyoxyethylene lauryl ether or 2-naphthalenesulfonic acid formaldehyde polymer sodium salt;

The primary brightener is selected from methionine, β-indolyl alanine, α-aminoglutaric acid, phenylalanine, pyridine-3-carboxylic acid, polyethylene glycol, alkylphenol polyoxyethylene ether, fatty amine polyoxyethylene Oxyethylene ether, L-methionine, β-hydroxyalanine, pyridine-4-carboxylic acid, polypropylene imine, α-aminoindole propionic acid, polyethanolamine, α-amino-β-imidazolyl propionate Acid, polyvinyl alcohol, lysine, γ-methyl-α-aminovaleric acid, β-phenyl-α-alanine, polyethyleneimine, α-aminoacetic acid, α-aminovaleramic acid, 1 -pyridine-4-piperidine-4-carboxylic acid, α-amino-β-hydroxybutyric acid, α-tetrahydropyrrolelic acid, α-alanine, 4-(4-piperidine)benzoic acid, 2-pyridyl One or more of acetic acid, 2,6-pyridinedicarboxylic acid or 3,4-pyridinedicarboxylic acid;

The secondary brightener is selected from naphthol, sodium polydithiodipropane sulfonate, thiourea, selenous acid, thiosemicarbazide, D-lyxosylamine, 2-mercaptobenzimidazole, methiouracil, Propylthiouracil, 3-ethoxy-4-hydroxybenzaldehyde, 1,4-butynediol, 4-formyl-2-methoxyphenyl acetate, 4-hydroxy-3-methoxy -5-nitrobenzaldehyde, 3-methoxy-4-hydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 3-hydroxycoumarin, 2-(2-pyridyl)benzimidazole , benzotriazole imidazole, 2-hydroxypyridine, 2,2-bipyridine, 4,4-diamino-2,2-bipyridine, bis(1-benzyl-3-carboxydihydropyridyl) ether One or more of sodium salt, methylbenzotriazole, 4-imidazole formaldehyde, benzimidazole, isothiazole, and 2-piperidone.

In one embodiment of the present invention, the pH adjusting agent is selected from one or more of potassium hydroxide, sodium hydroxide or ammonia water.

Second object of the present invention is to provide a kind of preparation method of cyanide-free alkaline silver plating electroplating solution, comprises the following steps:

(S1) Dissolving the main complexing agent, auxiliary complexing agent and anode depolarizer in deionized water, and mixing (continuously stirring for 3 to 5 minutes at a speed of 300 to 500 rpm) to obtain the first mixed solution;

(S2) adding the silver salt to the first mixed solution prepared in step (S1), and mixing (continuously stirring for 3 to 10 minutes at a speed of 300 to 500 rpm) to obtain a second mixed solution;

(S3) Dissolve the conductive salt in deionized water and add it to the second mixed solution prepared in step (S2), and mix (continuously stir for 2 to 5 minutes at a speed of 300-500 rpm) to obtain the third mixed solution ;

(S4) Dissolving the surfactant, the primary brightener and the secondary brightener in deionized water, and mixing (continuously stirring for 2 to 5 minutes at a speed of 800 to 1200 rpm) to obtain a composite additive solution;

(S5) Add the composite additive solution prepared in step (S4) to the third mixed solution prepared in step (S3), and adjust the pH value of the solution to 9-11 through a pH value regulator, at 800-1200 rpm Stir continuously for 2 to 5 minutes at a constant speed to obtain a cyanide-free alkaline silver plating solution.

The third object of the present invention is to provide a kind of application of cyanide-free alkaline silver plating electroplating solution in the silver plating process, specifically comprising the following steps:

(A1) Pre-treatment: the cathode and the anode are sequentially degreased with alkaline solvent, rinsed with deionized water, ultrasonically degreased with alcohol, rinsed with deionized water, activated by pickling, and rinsed with deionized water for later use;

(A2) Silver electroplating: immerse the pretreated cathode and anode in the cyanide-free alkaline silver plating solution, control the area ratio of the anode and the cathode to be 2 to 5, in the temperature range of 10 to 50°C and the current density of Under the condition of 0.05～9A/dm ² , cyanide-free silver plating is carried out by means of mechanical stirring, cathode reciprocating or continuous movement;

(A3) Post-treatment: Rinse the surface of the part with deionized water to remove the residual silver plating solution, then put it in an oven for drying treatment or take it out and dry it naturally;

Wherein, the cathode is copper, copper alloy or stainless steel substrate;

The anode is a pure silver plate or a pure silver ball;

The alkaline solvent is composed of sodium hydroxide, sodium carbonate, sodium phosphate, sodium silicate and alkylphenol polyoxyethylene ether. Among them, the concentration of alkaline solvent sodium hydroxide is 5g/L, the concentration of sodium carbonate is 15g/L, phosphoric acid The sodium concentration was 10 g/L, the sodium silicate concentration was 2 g/L and the alkylphenol ethoxylate concentration was 0.2 g/L.

Compared with the prior art, the present invention has the following beneficial effects:

The cyanide-free alkaline silver plating solution provided by the present invention uses various organic and inorganic complexing agents to coordinate and complex silver salt ions to improve the stability of the silver plating solution, and the silver plating solution does not appear after one year of storage Precipitation, turbidity and discoloration and other phenomena; at the same time, the use of various organic and inorganic complexing agents in the plating solution also greatly reduces the precipitation potential of silver salts, making the plating solution have good anti-displacement ability, placed in the plating solution for 1 hour There is also no obvious replacement, and silver plating can be directly performed on copper and copper alloy parts without additional flash silver pretreatment during electroplating. In addition, adopting the electroplating silver solution and implementation process provided by the present invention can greatly improve the dispersibility of the solution, avoid anode passivation, have a wide range of current density for plating, have a stable process and strong operability. The obtained coating is flat and bright, has strong discoloration resistance, fine crystallization, excellent mechanical properties, and good bonding force with the substrate. Even if the coating is bent repeatedly, there will be no embrittlement, peeling and fracture. It shows that the coating prepared by the plating solution and process provided by the present invention has excellent mechanical properties and good bonding force, and can meet the requirements of decoration and engineering. permanent silver plating applications.

Description of drawings

Fig. 1 is that the cyanide-free alkaline silver-plating electroplating solution that embodiment 1～6 prepares carries out the test piece macrophotograph schematic diagram that Hall cell experiment obtains;

Fig. 2 is the solution state diagram after the cyanide-free alkaline silver-plating electroplating solution that embodiment 1～6 prepares places 1 year;

3 is a schematic diagram of a macrophotograph of the electroplated anode plate obtained in Example 1.

Fig. 4 is the optical microscopic appearance schematic diagram of the silver coating that embodiment 1～6 obtains;

Detailed ways

The invention provides a cyanide-free alkaline silver plating solution, which is composed of a silver salt, a main complexing agent, an auxiliary complexing agent, a conductive salt, an anode depolarizer, a composite additive, a pH regulator and deionized water;

In the cyanide-free alkaline silver plating solution, the concentration of silver salt is 5~50g/L, the concentration of main complexing agent is 30~150g/L, the concentration of auxiliary complexing agent is 15~90g/L, and the concentration of conductive salt is 30~ 100g/L, the concentration of the anode depolarizer is 8-25g/L, the concentration of the composite additive is 5-10g/L, and the concentration of the pH regulator is 3-10g/L.

In one embodiment of the present invention, the silver salt is selected from one of silver chloride, silver nitrate, silver sulfate or silver carbonate.

In one embodiment of the present invention, the main complexing agent is selected from 1-methylhydantoin, pseudothiohydantoin, 5-phenylhydantoin, 2-thiohydantoin One or more of urea, 5,5-diphenylhydantoin, 5,5-dimethylhydantoin, 1-allylhydantoin or hydantoin-5-acetic acid kind.

In one embodiment of the present invention, the auxiliary complexing agent is selected from succinimide, N-hydroxysuccinimide, ethylenediamine, disodium edetate, trisodium citrate, potassium pyrophosphate , sodium pyrophosphate, ammonium citrate, potassium citrate, sodium metapolyphosphate and sodium polyphosphate, cycloheximide, 4-bromobenzamide or urea.

In one embodiment of the present invention, the conductive salt is selected from one or more of potassium chloride, sodium chloride, potassium carbonate, sodium carbonate, potassium sulfate, sodium sulfate, ammonium chloride or ammonium sulfate.

In one embodiment of the present invention, the anode depolarizer is selected from potassium nitrate, sodium nitrate, ammonium nitrate, potassium sodium tartrate, potassium thiocyanate, sodium thiocyanate, sodium thiosulfate, potassium thiosulfate , ammonium thiosulfate, aminotrimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, hydroxyethylidene diphosphoric acid, dipotassium hydrogen phosphate or disodium hydrogen phosphate.

In one embodiment of the present invention, the composite additive is composed of a surfactant, a primary brightener and a secondary brightener in a mass ratio of 2:5:1,

Wherein, the surfactant is selected from sodium dodecylsulfonate, sodium dodecylbenzenesulfonate, sodium dodecylsulfate, potassium fatty alcohol sulfate, potassium polyether carboxylate, potassium N-acylaminocarboxylate OP, One or more of nonylphenol polyoxyethylene lauryl ether or 2-naphthalenesulfonic acid formaldehyde polymer sodium salt;

The primary brightener is selected from methionine, β-indolyl alanine, α-aminoglutaric acid, phenylalanine, pyridine-3-carboxylic acid, polyethylene glycol, alkylphenol polyoxyethylene ether, fatty amine polyoxyethylene Oxyethylene ether, L-methionine, β-hydroxyalanine, pyridine-4-carboxylic acid, polypropylene imine, α-aminoindole propionic acid, polyethanolamine, α-amino-β-imidazolyl propionate Acid, polyvinyl alcohol, lysine, γ-methyl-α-aminovaleric acid, β-phenyl-α-alanine, polyethyleneimine, α-aminoacetic acid, α-aminovaleramic acid, 1 -pyridine-4-piperidine-4-carboxylic acid, α-amino-β-hydroxybutyric acid, α-tetrahydropyrrolelic acid, α-alanine, 4-(4-piperidine)benzoic acid, 2-pyridyl One or more of acetic acid, 2,6-pyridinedicarboxylic acid or 3,4-pyridinedicarboxylic acid;

The secondary brightener is selected from naphthol, sodium polydithiodipropane sulfonate, thiourea, selenous acid, thiosemicarbazide, D-lyxosylamine, 2-mercaptobenzimidazole, methiouracil, Propylthiouracil, 3-ethoxy-4-hydroxybenzaldehyde, 1,4-butynediol, 4-formyl-2-methoxyphenyl acetate, 4-hydroxy-3-methoxy -5-nitrobenzaldehyde, 3-methoxy-4-hydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 3-hydroxycoumarin, 2-(2-pyridyl)benzimidazole , benzotriazole imidazole, 2-hydroxypyridine, 2,2-bipyridine, 4,4-diamino-2,2-bipyridine, bis(1-benzyl-3-carboxydihydropyridyl) ether One or more of sodium salt, methylbenzotriazole, 4-imidazole formaldehyde, benzimidazole, isothiazole, and 2-piperidone.

In one embodiment of the present invention, the pH adjusting agent is selected from one or more of potassium hydroxide, sodium hydroxide or ammonia water.

The invention provides a kind of preparation method of cyanide-free alkaline silver plating electroplating solution, comprises the following steps:

(S1) Dissolving the main complexing agent, auxiliary complexing agent and anode depolarizer in deionized water, and mixing (continuously stirring for 3 to 5 minutes at a speed of 300 to 500 rpm) to obtain the first mixed solution;

(S2) adding the silver salt to the first mixed solution prepared in step (S1), and mixing (continuously stirring for 3 to 10 minutes at a speed of 300 to 500 rpm) to obtain a second mixed solution;

(S3) Dissolve the conductive salt in deionized water and add it to the second mixed solution prepared in step (S2), and mix (continuously stir for 2 to 5 minutes at a speed of 300-500 rpm) to obtain the third mixed solution ;

(S4) Dissolving the surfactant, the primary brightener and the secondary brightener in deionized water, and mixing (continuously stirring for 2 to 5 minutes at a speed of 800 to 1200 rpm) to obtain a composite additive solution;

(S5) Add the composite additive solution prepared in step (S4) to the third mixed solution prepared in step (S3), and adjust the pH value of the solution to 9-11 through a pH value regulator, at 800-1200 rpm Stir continuously for 2 to 5 minutes at a constant speed to obtain a cyanide-free alkaline silver plating solution.

The invention provides the application of a kind of cyanide-free alkaline silver plating electroplating solution in the silver plating process, specifically comprises the following steps:

(A1) Pre-treatment: the cathode and the anode are sequentially degreased with alkaline solvent, rinsed with deionized water, ultrasonically degreased with alcohol, rinsed with deionized water, activated by pickling, and rinsed with deionized water for later use;

(A2) Silver electroplating: immerse the pretreated cathode and anode in the cyanide-free alkaline silver plating solution, control the area ratio of the anode and the cathode to be 2 to 5, in the temperature range of 10 to 50°C and the current density of Under the condition of 0.05～9A/dm ² , cyanide-free silver plating is carried out by means of mechanical stirring, cathode reciprocating or continuous movement;

(A3) Post-treatment: Rinse the surface of the part with deionized water to remove the residual silver plating solution, then put it in an oven for drying treatment or take it out and dry it naturally;

Wherein, the cathode is copper, copper alloy or stainless steel substrate;

The anode is a pure silver plate or a pure silver ball;

The alkaline solvent is composed of sodium hydroxide, sodium carbonate, sodium phosphate, sodium silicate and alkylphenol polyoxyethylene ether. Among them, the concentration of alkaline solvent sodium hydroxide is 5g/L, the concentration of sodium carbonate is 15g/L, phosphoric acid The sodium concentration was 10 g/L, the sodium silicate concentration was 2 g/L and the alkylphenol ethoxylate concentration was 0.2 g/L.

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments.

In the following examples, unless otherwise specified, the reagents used are all commercially available reagents, and the detection means and methods used are all conventional detection means and methods in the art.

Example 1

This embodiment provides a cyanide-free alkaline silver-plating electroplating solution and its preparation method, as well as its further application in the silver-plating process.

The cyanide-free alkaline silver plating solution of the present embodiment consists of silver nitrate, 5,5-diphenylhydantoin, 1-methylhydantoin, ammonium citrate, sodium pyrophosphate, potassium sodium tartrate, carbonic acid Sodium, ammonium sulfate, sodium dodecylbenzenesulfonate, pyridine-3-carboxylic acid, 2-hydroxy-3-methoxybenzaldehyde, sodium hydroxide and deionized water;

Among them, in the cyanide-free alkaline silver plating solution, the concentration of silver nitrate is 20g/L, the concentration of 5,5-diphenylhydantoin is 40g/L, and the concentration of 1-methylhydantoin is 30g/L , the concentration of ammonium citrate is 15g/L, the concentration of sodium pyrophosphate is 30g/L, the concentration of sodium potassium tartrate is 20g/L, the concentration of sodium carbonate is 15g/L, the concentration of ammonium sulfate is 25g/L, dodecylbenzenesulfonate The sodium hydroxide concentration is 2g/L, the pyridine-3-carboxylic acid concentration is 5g/L, the 2-hydroxy-3-methoxybenzaldehyde concentration is 1g/L, and the sodium hydroxide concentration is 5g/L.

The preparation method specifically comprises the following steps:

(S1) Combine primary complexing agent (5,5-diphenylhydantoin and 1-methylhydantoin), secondary complexing agent (ammonium citrate and sodium pyrophosphate) and anodic depolarizer (potassium sodium tartrate) was dissolved in deionized water, and stirred continuously for 5 minutes at a speed of 400 rpm to obtain the first mixed solution;

(S2) adding silver salt (silver nitrate) to the first mixed solution prepared in step (S1), stirring continuously for 3 minutes at a speed of 400 rpm to obtain a second mixed solution;

(S3) dissolving the conductive salt (sodium carbonate and ammonium sulfate) in deionized water and adding it to the second mixed solution prepared in step (S2), stirring continuously for 3 minutes at a speed of 400 rpm to obtain a third mixed solution ;

(S4) Dissolve surfactant (sodium dodecylbenzenesulfonate), primary brightener (pyridine-3-carboxylic acid) and secondary brightener (2-hydroxy-3-methoxybenzaldehyde) in deionized In water, continuously stirred for 5 minutes at a speed of 800 rev/min) to obtain a composite additive solution;

(S5) Add the composite additive solution prepared in step (S4) to the third mixed solution prepared in step (S3), add deionized water to constant volume, and pass the pH adjusting agent (sodium hydroxide lye) Adjust the pH value of the solution to 9.5, and continuously stir for 2 minutes at a speed of 800 rpm to obtain a cyanide-free alkaline silver plating solution.

Performance testing:

(1) The electroplating solution prepared in the present embodiment was subjected to a Hall cell test at a current density of 2A/dm ² , and the macrophotograph of the obtained Hall cell test piece is shown in Figure 1. As can be seen from Figure 1, the electroplating solution prepared in this example is subjected to the Hall cell experiment, and the test pieces obtained from the low current density range to the high current density range are smooth and bright, and the current density range that can be plated is very wide. According to Compared with the Hall cell current density scale, the maximum current density that can be plated in the electroplating solution of this embodiment can reach 9A/dm ² , and the coating is smooth and bright in the entire range of electroplating, and there is no missing plating phenomenon, indicating that the electroplating solution The dispersing ability and moving ability are good; there is no bending and warping phenomenon on the test piece, indicating that the coating has no stress.

(2) Soak the copper sheet in the electroplating solution to analyze the anti-displacement ability of the electroplating solution; the silver plating solution prepared in this example has good anti-displacement ability. It can be seen from Table 1 that when the pure copper test piece is placed in the electroplating solution of this embodiment, the serious replacement reaction of the test piece does not occur immediately, but a slight silver replacement reaction begins to occur after the soaking time reaches 635 seconds ; And the anti-displacement time of the brass test piece in the electroplating solution of embodiment is about 315 seconds. This shows that the electroplating solution in Example 1 can effectively improve the anti-displacement ability under the synergistic effect of the complexing agent, and can meet the operability and production requirements of silver plating of electronic products.

(3) Place the electroplating solution for 1 year for a long time to investigate the stability of the electroplating solution; the electroplating solution of the present embodiment is placed for 1 year (as shown in Figure 2), and the solution still remains clear and transparent without turbidity and precipitation. The appearance of the plating layer after electroplating is basically the same as that of the new silver plating, which shows that the plating solution has good stability.

The electroplating solution of the present embodiment is carried out the method for silver-plating on pure copper substrate, specifically comprises the following steps:

(A1) Pass the pure copper matrix test piece through 5g/L sodium hydroxide, 15g/L sodium carbonate, 10g/L sodium phosphate, 2g/L sodium silicate and 0.2g/L alkylphenol polyoxyethylene ether successively Alkaline solution for degreasing treatment, deionized water rinse, and then immersed in alcohol solution for 2 minutes of ultrasonic further degreasing, then rinsed with deionized water, and then immersed in a 10% sulfuric acid solution by mass ratio for pickling activation for 60 seconds, Finally rinsed with deionized water;

Immerse the pure silver plate in a nitric acid solution with a mass ratio of 10% for pickling and activation for 30 seconds, and then rinse it with deionized water;

(A2) The pure copper substrate test piece and the pure silver plate after the step (A1) are processed are directly immersed in the electroplating solution, with the pure silver plate anode, the pure copper substrate test piece is the cathode, and the pure silver plate and the pure copper substrate test piece The area ratio is 3, the temperature is 25°C and the current density is 1A/dm ² , and the cathode is reciprocatingly moved for 30 minutes to obtain a macroscopically bright and smooth silver coating with a thickness of about 15 microns. After electroplating, use deionized water to remove the residual electroplating solution on the surface of the component, and dry the silver coating. As shown in Figure 3, the surface of the anode pure silver plate does not appear blackened and discolored and covered by by-products after plating, but presents a silver-white bright surface feature with a typical honeycomb electrolytic microporous structure, indicating that the anode plate has no Passivation occurs.

Performance testing:

(1) Utilize the Olympus optical microscope (OP) to analyze the microscopic morphology and surface smoothness of the silver coating:

Observation by an optical microscope shows that the microscopic surface of the silver coating obtained in this embodiment (as shown in FIG. 4 ) is very flat, the crystals are dense, and the approximately spherical silver grains with a size of about 1-2 microns grow closely with each other.

(2) Utilize EDS energy spectrum analysis to analyze the composition and impurity content of silver coating:

From the energy spectrum analysis (as shown in Table 2), it can be seen that the silver coating obtained by the present embodiment has high purity, except that three trace impurity elements of C, N and O with a total content of no more than 0.16% are detected, other common Impurity elements such as S and P and other metal impurity elements have not been detected, and the mass percentage of the silver coating is as high as 99.84%, which shows that the silver coating obtained in this embodiment has a high purity, which can meet the requirements of electronic products for the purity of the silver coating. Require.

(3) Utilize the Vickers microhardness tester to test the hardness of the silver coating;

By micro-Vickers hardness test results (as shown in table 3), it can be seen that the hardness of the silver coating prepared by the electroplating solution of the present embodiment reaches 116Hv, which is obviously higher than the hardness of the cyanide silver plating reported recently (existing The hardness of cyanide silver plating is in the range of 85-100Hv). This shows that under the coordination of various additives, the crystal grains can be effectively refined to improve the hardness of the silver coating, which can meet the high requirements of electrical components on the mechanical properties of the silver coating.

(4) investigate the binding force of the silver coating by bending the coating test piece experiment;

By repeated bending tests on the pure silver sheet after plating, embrittlement and peeling phenomenon did not occur in the silver coating, which shows that the silver coating obtained by electroplating with the electroplating solution of this embodiment under the coordination of various additives has good toughness and cohesion.

(5) investigate the anti-oxidation ability of silver coating by high temperature baking experiment;

Baking at 250 degrees centigrade for 2 hours in an atmospheric environment, the silver coating did not undergo oxidation and discoloration, indicating that the silver coating obtained in this embodiment has good anti-discoloration ability in an atmospheric environment.

Example 2

This embodiment provides a cyanide-free alkaline silver-plating electroplating solution and its preparation method, as well as its further application in the silver-plating process.

The cyanide-free alkaline silver plating electroplating solution of the present embodiment is made of silver nitrate, 5,5-diphenylhydantoin, 1-methylhydantoin, potassium pyrophosphate, sodium thiosulfate, aminotrimethylene phosphine acid, potassium sulfate, nonylphenol polyoxyethylene lauryl ether, pyridine-3-carboxylic acid, 2-hydroxy-3-methoxybenzaldehyde, sodium hydroxide and deionized water;

Among them, in the cyanide-free alkaline silver plating solution, the concentration of silver nitrate is 30g/L, the concentration of 5,5-diphenylhydantoin is 45g/L, and the concentration of 1-methylhydantoin is 35g/L , The concentration of potassium pyrophosphate is 35g/L, the concentration of sodium thiosulfate is 15g/L, the concentration of aminotrimethylene phosphonic acid is 10g/L, the concentration of potassium sulfate is 50g/L, and the concentration of nonylphenol polyoxyethylene lauryl ether is 3g /L, the concentration of pyridine-3-carboxylic acid was 7.5g/L, the concentration of 2-hydroxy-3-methoxybenzaldehyde was 1.5g/L, and the concentration of sodium hydroxide was 9g/L.

The preparation method specifically comprises the following steps:

(S1) Combine the main complexing agent (5,5-diphenylhydantoin and 1-methylhydantoin), the auxiliary complexing agent (potassium pyrophosphate) and the anodic depolarizer (thiosulfuric acid Sodium and aminotrimethylene phosphonic acid) were dissolved in deionized water, and stirred continuously for 5 minutes at a speed of 400 rpm to obtain the first mixed solution;

(S2) adding silver salt (silver nitrate) to the first mixed solution prepared in step (S1), stirring continuously for 3 minutes at a speed of 400 rpm to obtain a second mixed solution;

(S3) dissolving the conductive salt (potassium sulfate) in deionized water and adding it to the second mixed solution prepared in step (S2), stirring continuously for 3 minutes at a speed of 400 rpm to obtain a third mixed solution;

(S4) Dissolve surfactant (nonylphenol polyoxyethylene lauryl ether), primary brightener (pyridine-3-carboxylic acid) and secondary brightener (2-hydroxy-3-methoxybenzaldehyde) in deionized In water, continuously stirred for 5 minutes at a speed of 800 rev/min) to obtain a composite additive solution;

(S5) Add the composite additive solution prepared in step (S4) to the third mixed solution prepared in step (S3), add deionized water to constant volume, and pass the pH adjusting agent (sodium hydroxide lye) Adjust the pH value of the solution to 9.5, and continuously stir for 2 minutes at a speed of 800 rpm to obtain a cyanide-free alkaline silver plating solution.

Performance testing:

(1) The Hall cell test was carried out at a current density of 2 A/dm ² using the electroplating solution configured in Example 2. The macrophotograph of the obtained Hall cell test piece is shown in Fig. 1 . As can be seen from Figure 1, the Hall cell test piece using the cyanide-free silver plating solution configured in Example 2 is smooth and bright from the low current density range to the high current density range, and there is no missing plating in the low area, indicating the dispersion ability of the electroplating solution And good positioning ability. According to the comparison of the Hall cell current density scale, the maximum current density of the electroplating solution configured in Example 2 can reach 8.5A/dm ² . The Hall cell test piece has no warpage in either the high current density area or the low current density area, which shows that the coating obtained in Example 2 has no internal stress.

(2) The electroplating solution prepared in Example 2 has good resistance to displacement. It can be seen from Table 3 that when the pure copper test piece was placed in the electroplating solution of Example 2, the test piece did not undergo a serious replacement reaction immediately, but a slight silver replacement reaction began to occur after the soaking time reached 672 seconds ; And the anti-displacement time of the brass test piece in the electroplating solution of embodiment 2 is 350 seconds. This shows that the electroplating solution in Example 2 can effectively improve the anti-displacement ability under the synergistic effect of the complexing agent, and can meet the operability and production requirements of silver plating of electronic products.

(3) place the electroplating solution configured in Example 2 for 1 year (as shown in Figure 2), the solution still remains clear and transparent, and the coating appearance after electroplating is basically consistent with the new configuration of silver plating, which shows that the electroplating solution has good stability.

The electroplating solution of the present embodiment is carried out the method for silver-plating on pure copper substrate, specifically comprises the following steps:

(A1) Pass the pure copper matrix test piece through 5g/L sodium hydroxide, 15g/L sodium carbonate, 10g/L sodium phosphate, 2g/L sodium silicate and 0.2g/L alkylphenol polyoxyethylene ether successively Alkaline solution for degreasing treatment, deionized water rinse, and then immersed in alcohol solution for 2 minutes of ultrasonic further degreasing, then rinsed with deionized water, and then immersed in a 10% sulfuric acid solution by mass ratio for pickling activation for 60 seconds, Finally rinsed with deionized water;

Immerse the pure silver plate in a nitric acid solution with a mass ratio of 10% for pickling and activation for 30 seconds, and then rinse it with deionized water;

(A2) The pure copper substrate test piece and the pure silver plate after the step (A1) are processed are directly immersed in the electroplating solution, with the pure silver plate anode, the pure copper substrate test piece is the cathode, and the pure silver plate and the pure copper substrate test piece The area ratio is 3, and the temperature is 25°C and the current density is 2A/dm ² , and electroplating in the way of cathode reciprocating movement for 20 minutes, that is, a macroscopically bright and smooth silver coating with a thickness of about 15 microns is obtained. After electroplating, use deionized water to remove the residual electroplating solution on the surface of the component, and dry the silver coating. After plating, the surface of the anodic pure silver plate does not appear blackening and discoloration and by-product coverage, but presents a silver-white bright surface with a typical honeycomb electrolytic microporous structure, indicating that the anode plate has not been passivated.

Performance testing:

(1) Utilize the Olympus optical microscope (OP) to analyze the microscopic morphology and surface smoothness of the silver coating:

Observation by an optical microscope shows that the microscopic surface of the silver coating obtained in this embodiment (as shown in FIG. 4 ) is very flat, the crystals are dense, and the approximately spherical silver grains with a size of about 1-2 microns grow closely with each other.

(2) Utilize EDS energy spectrum analysis to analyze the composition and impurity content of silver coating:

From the energy spectrum analysis (as shown in Table 2), it can be seen that the silver coating obtained by the present embodiment has high purity, except that three trace impurity elements of C, N and O with a total content of no more than 0.17% are detected, other common Impurity elements such as S and P and other metal impurity elements have not been detected, and the mass percentage of the silver coating reaches 99.83%, which shows that the silver coating obtained in this embodiment has a high purity, which can meet the requirements of electronic products for the purity of the silver coating. Require.

(3) Utilize the Vickers microhardness tester to test the hardness of the silver coating;

By micro-Vickers hardness test results (as shown in table 3), it can be seen that the hardness of the silver coating prepared by the electroplating solution of the present embodiment reaches 113Hv, which is obviously higher than the hardness of the cyanide silver plating reported recently (existing The hardness of cyanide silver plating is in the range of 85-100Hv). This shows that under the coordination of various additives, the crystal grains can be effectively refined to improve the hardness of the silver coating, which can meet the high requirements of electrical components on the mechanical properties of the silver coating.

(4) investigate the binding force of the silver coating by bending the coating test piece experiment;

By repeated bending tests on the pure silver sheet after plating, embrittlement and peeling phenomenon did not occur in the silver coating, which shows that the silver coating obtained by electroplating with the electroplating solution of this embodiment under the coordination of various additives has good toughness and cohesion.

(5) investigate the anti-oxidation ability of silver coating by high temperature baking experiment;

Baking at 250 degrees centigrade for 2 hours in an atmospheric environment, the silver coating did not undergo oxidation and discoloration, indicating that the silver coating obtained in this embodiment has good anti-discoloration ability in an atmospheric environment.

Example 3

This embodiment provides a cyanide-free alkaline silver-plating electroplating solution and its preparation method, as well as its further application in the silver-plating process.

The cyanide-free alkaline silver plating solution of the present embodiment is composed of silver nitrate, 5,5-diphenylhydantoin, 1-methylhydantoin, succinimide, sodium pyrophosphate, hydroxyethylidene di Phosphoric acid, potassium carbonate, potassium sulfate, sodium dodecylbenzenesulfonate, pyridine-3-carboxylic acid, 2-hydroxy-3-methoxybenzaldehyde, sodium hydroxide and deionized water;

Among them, in the cyanide-free alkaline silver plating solution, the concentration of silver nitrate is 35g/L, the concentration of 5,5-diphenylhydantoin is 80g/L, and the concentration of 1-methylhydantoin is 20g/L , The concentration of succinimide is 10g/L, the concentration of sodium pyrophosphate is 30g/L, the concentration of hydroxyethylidene diphosphate is 10g/L, the concentration of potassium carbonate is 45g/L, the concentration of potassium sulfate is 15g/L, dodecane The concentration of sodium phenylsulfonate was 2 g/L, the concentration of pyridine-3-carboxylic acid was 5 g/L, the concentration of 2-hydroxy-3-methoxybenzaldehyde was 1 g/L, and the concentration of sodium hydroxide was 5 g/L.

The preparation method specifically comprises the following steps:

(S1) Depolarize the primary complexing agent (5,5-diphenylhydantoin and 1-methylhydantoin), the secondary complexing agent (succinimide and sodium pyrophosphate) and the anode Agent (hydroxyethylidene diphosphoric acid) was dissolved in deionized water, and stirred continuously for 5 minutes at a speed of 400 rpm to obtain the first mixed solution;

(S2) adding silver salt (silver nitrate) to the first mixed solution prepared in step (S1), stirring continuously for 3 minutes at a speed of 400 rpm to obtain a second mixed solution;

(S3) dissolving the conductive salt (potassium carbonate and potassium sulfate) in deionized water and adding it to the second mixed solution prepared in step (S2), stirring continuously for 3 minutes at a speed of 400 rpm to obtain a third mixed solution ;

(S4) Dissolve surfactant (sodium dodecylbenzenesulfonate), primary brightener (pyridine-3-carboxylic acid) and secondary brightener (2-hydroxy-3-methoxybenzaldehyde) in deionized In water, continuously stirred for 5 minutes at a speed of 800 rev/min) to obtain a composite additive solution;

(S5) Add the composite additive solution prepared in step (S4) to the third mixed solution prepared in step (S3), add deionized water to constant volume, and pass the pH adjusting agent (sodium hydroxide lye) Adjust the pH value of the solution to 9.5, and continuously stir for 2 minutes at a speed of 800 rpm to obtain a cyanide-free alkaline silver plating solution.

Performance testing:

(1) The electroplating solution configured in Example 3 was used to conduct a Hall cell test at a current density of 2A/dm ² . The macrophotograph of the obtained Hall cell test piece is shown in Fig. 1 . As can be seen from Fig. 1, the Hall cell test piece using the electroplating solution configured in Example 3 is smooth and bright from the low current density range to the high current density range, and there is no missing plating in the area, which shows that the electroplating solution has good dispersion ability and the implementation of current The density interval is wide. According to the comparison of the Hall cell current density scale, the maximum current density of the electroplating solution configured in Example 3 can reach the range interval of 8A/dm ² . The coating warpage of the Hall cell test piece shows that the coating obtained in Example 3 has no internal stress.

(2) The electroplating solution prepared in Example 3 has good resistance to displacement. It can be seen from Table 3 that when the pure copper test piece is placed in the electroplating solution of Example 3, the copper test piece does not undergo a serious replacement reaction immediately, but a slight silver replacement begins to occur after the soaking time reaches 665 seconds Reaction; And the anti-displacement time of the brass test piece in the electroplating solution of embodiment 3 is 345 seconds. This shows that the electroplating solution in Example 3 can effectively improve the anti-displacement ability under the synergistic effect of the complexing agent, and can meet the operability and production requirements of silver plating of electronic products.

(3) the electroplating solution configured in Example 3 is placed for 1 year (as shown in Figure 2), the solution still remains clear and transparent, and the coating appearance after electroplating is basically consistent with the new configuration of silver plating, which shows that the electroplating solution has good stability.

The electroplating solution of the present embodiment is carried out the method for silver-plating on pure copper substrate, specifically comprises the following steps:

(A1) Pass the pure copper matrix test piece through 5g/L sodium hydroxide, 15g/L sodium carbonate, 10g/L sodium phosphate, 2g/L sodium silicate and 0.2g/L alkylphenol polyoxyethylene ether successively Alkaline solution for degreasing treatment, deionized water rinse, and then immersed in alcohol solution for 2 minutes of ultrasonic further degreasing, then rinsed with deionized water, and then immersed in a 10% sulfuric acid solution by mass ratio for pickling activation for 60 seconds, Finally rinsed with deionized water;

Immerse the pure silver plate in a nitric acid solution with a mass ratio of 10% for pickling and activation for 30 seconds, and then rinse it with deionized water;

(A2) The pure copper substrate test piece and the pure silver plate after the step (A1) are processed are directly immersed in the electroplating solution, with the pure silver plate anode, the pure copper substrate test piece is the cathode, and the pure silver plate and the pure copper substrate test piece The area ratio is 3, and the temperature is 25°C and the current density is 3A/dm ² , and the cathode is reciprocatingly moved for 10 minutes to obtain a macroscopically bright and smooth silver coating with a thickness of about 15 microns. After electroplating, use deionized water to remove the residual electroplating solution on the surface of the component, and dry the silver coating. After plating, the surface of the anodic pure silver plate does not appear blackening and discoloration and by-product coverage, but presents a silver-white bright surface with a typical honeycomb electrolytic microporous structure, indicating that the anode plate has not been passivated.

Performance testing:

(1) Utilize the Olympus optical microscope (OP) to analyze the microscopic morphology and surface smoothness of the silver coating:

Observation by an optical microscope shows that the microscopic surface of the silver coating obtained in this embodiment (as shown in FIG. 4 ) is very flat, the crystals are dense, and the approximately spherical silver grains with a size of about 1-2 microns grow closely with each other.

(2) Utilize EDS energy spectrum analysis to analyze the composition and impurity content of silver coating:

From the energy spectrum analysis (as shown in Table 2), it can be seen that the silver coating obtained by the present embodiment has high purity, except that three trace impurity elements of C, N and O with a total content of no more than 0.12% are detected, other common Impurity elements such as S and P and other metal impurity elements have not been detected, and the mass percentage of the silver coating is as high as 99.88%, which shows that the silver coating obtained in this embodiment has a high purity, which can meet the requirements of electronic products for the purity of the silver coating. Require.

(3) Utilize the Vickers microhardness tester to test the hardness of the silver coating;

By micro-Vickers hardness test results (as shown in table 3), it can be seen that the hardness of the silver coating prepared by the electroplating solution of the present embodiment reaches 117Hv, which is obviously higher than the hardness of the cyanide silver plating reported recently (existing The hardness of cyanide silver plating is in the range of 85-100Hv). This shows that under the coordination of various additives, the crystal grains can be effectively refined to improve the hardness of the silver coating, which can meet the high requirements of electrical components on the mechanical properties of the silver coating.

(4) investigate the binding force of the silver coating by bending the coating test piece experiment;

By repeated bending tests on the pure silver sheet after plating, embrittlement and peeling phenomenon did not occur in the silver coating, which shows that the silver coating obtained by electroplating with the electroplating solution of this embodiment under the coordination of various additives has good toughness and cohesion.

(5) investigate the anti-oxidation ability of silver coating by high temperature baking experiment;

Baking at 250 degrees centigrade for 2 hours in an atmospheric environment, the silver coating did not undergo oxidation and discoloration, indicating that the silver coating obtained in this embodiment has good anti-discoloration ability in an atmospheric environment.

Example 4

This embodiment provides a cyanide-free alkaline silver-plating electroplating solution and its preparation method, as well as its further application in the silver-plating process.

The cyanide-free alkaline silver plating solution of the present embodiment is composed of silver nitrate, 5,5-diphenylhydantoin, 1-allylhydantoin, cycloheximide, ethylenediaminetetraacetic acid di Sodium, ammonium citrate, ethylenediaminetetramethylenephosphonic acid, potassium carbonate, sodium dodecylbenzenesulfonate, pyridine-3-carboxylic acid 2-hydroxy-3-methoxybenzaldehyde, sodium hydroxide and deionized water composition;

Among them, in the cyanide-free alkaline silver plating solution, the concentration of silver nitrate is 35g/L, the concentration of 5,5-diphenylhydantoin is 50g/L, and the concentration of 1-allylhydantoin is 60g/L. L. The concentration of cycloheximide is 10g/L, the concentration of disodium edetate is 25g/L, the concentration of ammonium citrate is 15g/L, the concentration of ethylenediamine tetramethylene phosphonic acid is 8g/L, carbonic acid The concentration of potassium is 40g/L, the concentration of sodium dodecylbenzenesulfonate is 2g/L, the concentration of pyridine-3-carboxylic acid is 5g/L, the concentration of 2-hydroxy-3-methoxybenzaldehyde is 1g/L, hydrogen Sodium oxide concentration is 5g/L.

The preparation method specifically comprises the following steps:

(S1) The main complexing agent (5,5-diphenylhydantoin and 1-allylhydantoin), auxiliary complexing agent (cycloheximide, disodium edetate and ammonium citrate) and anode depolarizer (ethylenediamine tetramethylene phosphonic acid) were dissolved in deionized water, and stirred continuously for 5 minutes at a speed of 400 rpm to obtain the first mixed solution;

(S2) adding silver salt (silver nitrate) to the first mixed solution prepared in step (S1), stirring continuously for 3 minutes at a speed of 400 rpm to obtain a second mixed solution;

(S3) dissolving the conductive salt (potassium carbonate) in deionized water and adding it to the second mixed solution prepared in step (S2), stirring continuously for 3 minutes at a speed of 400 rpm to obtain a third mixed solution;

(S4) Dissolve surfactant (sodium dodecylbenzenesulfonate), primary brightener (pyridine-3-carboxylic acid) and secondary brightener (2-hydroxy-3-methoxybenzaldehyde) in deionized In water, continuously stirred for 5 minutes at a speed of 800 rev/min) to obtain a composite additive solution;

(S5) Add the composite additive solution prepared in step (S4) to the third mixed solution prepared in step (S3), add deionized water to constant volume, and pass the pH adjusting agent (sodium hydroxide lye) Adjust the pH value of the solution to 9.5, and continuously stir for 2 minutes at a speed of 800 rpm to obtain a cyanide-free alkaline silver plating solution.

Performance testing:

(1) The Hall cell test was carried out at a current density of 2 A/dm ² using the electroplating solution configured in Example 4. The macrophotograph of the obtained Hall cell test piece is shown in Fig. 1 . It can be seen from Figure 1 that the Hall cell test piece using the plating solution configured in Example 4 is smooth and bright from the low current density range to the high current density range, and there is no missing plating in the low area, which shows that the plating solution has the ability to disperse and move. Well, the implementation current density range is wide, and according to the comparison of the Hall cell current density scale, the maximum current density that can be applied to the plating solution configured in Example 4 can reach 9A/dm ² ; the Hall cell test piece does not appear to be warped, Illustrate adopting the coating that embodiment 4 obtains to have no internal stress.

(2) The electroplating solution prepared in Example 4 has good resistance to displacement. It can be seen from Table 3 that when the pure copper test piece is placed in the plating solution of Example 4, the copper test piece does not undergo a serious replacement reaction immediately, but a slight silver replacement begins to occur after the soaking time reaches 680 seconds Reaction; And the anti-displacement time of the brass test piece in the plating solution of embodiment 4 is about 355 seconds. This shows that the electroplating solution of Example 4 can effectively improve the anti-displacement ability under the synergistic effect of the complexing agent, and can meet the operability and production requirements of silver plating of electronic products.

(3) Place the electroplating solution configured in Example 4 for 1 year (as shown in Figure 2), the solution still remains clear and transparent, and no precipitation turbidity occurs, and the appearance of the coating after electroplating is basically consistent with the new configuration of silver plating. It shows that the electroplating solution has good stability.

The electroplating solution of the present embodiment is carried out the method for silver-plating on pure copper substrate, specifically comprises the following steps:

(A1) Pass the pure copper matrix test piece through 5g/L sodium hydroxide, 15g/L sodium carbonate, 10g/L sodium phosphate, 2g/L sodium silicate and 0.2g/L alkylphenol polyoxyethylene ether successively Alkaline solution for degreasing treatment, deionized water rinse, and then immersed in alcohol solution for 2 minutes of ultrasonic further degreasing, then rinsed with deionized water, and then immersed in a 10% sulfuric acid solution by mass ratio for pickling activation for 60 seconds, Finally rinsed with deionized water;

Immerse the pure silver plate in a nitric acid solution with a mass ratio of 10% for pickling and activation for 30 seconds, and then rinse it with deionized water;

(A2) The pure copper substrate test piece and the pure silver plate after the step (A1) are processed are directly immersed in the electroplating solution, with the pure silver plate anode, the pure copper substrate test piece is the cathode, and the pure silver plate and the pure copper substrate test piece The area ratio is 3, and the temperature is 25°C and the current density is 4A/dm ² , and the cathode is reciprocatingly moved for 8 minutes to obtain a macroscopically bright and smooth silver coating with a thickness of about 15 microns. After electroplating, use deionized water to remove the residual electroplating solution on the surface of the component, and dry the silver coating. After plating, the surface of the anodic pure silver plate does not appear blackening and discoloration and by-product coverage, but presents a silver-white bright surface with a typical honeycomb electrolytic microporous structure, indicating that the anode plate has not been passivated.

Performance testing:

(1) Utilize the Olympus optical microscope (OP) to analyze the microscopic morphology and surface smoothness of the silver coating:

Observation by an optical microscope shows that the microscopic surface of the silver coating obtained in this embodiment (as shown in FIG. 4 ) is very flat, the crystals are dense, and the approximately spherical silver grains with a size of about 1-2 microns grow closely with each other.

(2) Utilize EDS energy spectrum analysis to analyze the composition and impurity content of silver coating:

From the energy spectrum analysis (as shown in Table 2), it can be seen that the silver coating obtained by the present embodiment has high purity, except that three trace impurity elements of C, N and O with a total content of no more than 0.12% are detected, other common Impurity elements such as S and P and other metal impurity elements have not been detected, and the mass percentage of the silver coating is as high as 99.88%, which shows that the silver coating obtained in this embodiment has a high purity, which can meet the requirements of electronic products for the purity of the silver coating. Require.

(3) Utilize the Vickers microhardness tester to test the hardness of the silver coating;

By micro-Vickers hardness test results (as shown in table 3), it can be seen that the hardness of the silver coating prepared by the electroplating solution of the present embodiment reaches 120Hv, which is obviously higher than the hardness of the cyanide silver plating reported recently (existing The hardness of cyanide silver plating is in the range of 85-100Hv). This shows that under the coordination of various additives, the crystal grains can be effectively refined to improve the hardness of the silver coating, which can meet the high requirements of electrical components on the mechanical properties of the silver coating.

(4) investigate the binding force of the silver coating by bending the coating test piece experiment;

By repeated bending tests on the pure silver sheet after plating, embrittlement and peeling phenomenon did not occur in the silver coating, which shows that the silver coating obtained by electroplating with the electroplating solution of this embodiment under the coordination of various additives has good toughness and cohesion.

(5) investigate the anti-oxidation ability of silver coating by high temperature baking experiment;

Baking at 250 degrees centigrade for 2 hours in an atmospheric environment, the silver coating did not undergo oxidation and discoloration, indicating that the silver coating obtained in this embodiment has good anti-discoloration ability in an atmospheric environment.

Example 5

This embodiment provides a cyanide-free alkaline silver-plating electroplating solution and its preparation method, as well as its further application in the silver-plating process.

The cyanide-free alkaline silver plating electroplating solution of the present embodiment is made of silver nitrate, 5-phenylhydantoin, thiohydantoin, hydantoin-5-acetic acid, ammonium citrate, potassium pyrophosphate, sulfur Ammonium sulfosulfate, potassium chloride, sodium dodecylbenzenesulfonate, pyridine-3-carboxylic acid, 2-hydroxy-3-methoxybenzaldehyde, sodium hydroxide and deionized water;

Among them, in the cyanide-free alkaline silver plating solution, the concentration of silver nitrate is 40g/L, the concentration of 5-phenylhydantoin is 70g/L, the concentration of thiohydantoin is 40g/L, and the concentration of hydantoin is 40g/L. -5-The concentration of acetic acid is 10g/L, the concentration of ammonium citrate is 15g/L, the concentration of potassium pyrophosphate is 30g/L, the concentration of ammonium thiosulfate is 12g/L, the concentration of potassium chloride is 40g/L, dodecane The concentration of sodium phenylsulfonate was 2 g/L, the concentration of pyridine-3-carboxylic acid was 5 g/L, the concentration of 2-hydroxy-3-methoxybenzaldehyde was 1 g/L, and the concentration of sodium hydroxide was 5 g/L.

The preparation method specifically comprises the following steps:

(S1) The main complexing agent (5-phenylhydantoin, thiohydantoin and hydantoin-5-acetic acid), the auxiliary complexing agent (ammonium citrate and potassium pyrophosphate) and the anode The depolarizing agent (ammonium thiosulfate) was dissolved in deionized water, and stirred continuously for 5 minutes at a speed of 400 rpm to obtain the first mixed solution;

(S2) adding silver salt (silver nitrate) to the first mixed solution prepared in step (S1), stirring continuously for 3 minutes at a speed of 400 rpm to obtain a second mixed solution;

(S3) dissolving the conductive salt (potassium chloride) in deionized water and adding it to the second mixed solution prepared in step (S2), stirring continuously for 3 minutes at a speed of 400 rpm to obtain a third mixed solution;

(S4) Dissolve surfactant (sodium dodecylbenzenesulfonate), primary brightener (pyridine-3-carboxylic acid) and secondary brightener (2-hydroxy-3-methoxybenzaldehyde) in deionized In water, continuously stirred for 5 minutes at a speed of 800 rev/min) to obtain a composite additive solution;

(S5) Add the composite additive solution prepared in step (S4) to the third mixed solution prepared in step (S3), add deionized water to constant volume, and pass the pH adjusting agent (sodium hydroxide lye) Adjust the pH value of the solution to 9.5, and continuously stir for 2 minutes at a speed of 800 rpm to obtain a cyanide-free alkaline silver plating solution.

Performance testing:

(1) The Hall cell test was carried out at a current density of 2 A/dm ² using the electroplating solution configured in Example 5. The macrophotograph of the obtained Hall cell test piece is shown in Fig. 1 . It can be seen from Figure 1 that the Hall cell test piece using the plating solution configured in Example 5 is smooth and bright from the low current density range to the high current density range, and there is no missing plating in the low area, which shows that the plating solution has the ability to disperse and move. Well, the current density range is wide. According to the Hall cell current density scale comparison, the plating solution configured in Example 5 can have a maximum plating current density of 8.5A/dm ² . The Hall cell test piece has no warping phenomenon, indicating that the coating obtained in Example 5 has no internal stress.

(2) The electroplating solution prepared in Example 5 has good resistance to displacement. It can be seen from Table 3 that when the pure copper test piece was placed in the electroplating solution of Example 5, the copper test piece did not undergo a serious substitution reaction immediately, but a slight silver substitution began to occur after the soaking time reached 645 seconds Reaction; And the anti-displacement time of the brass test piece in the electroplating solution of embodiment 5 is 325 seconds. This shows that the electroplating solution in Example 5 can effectively improve the anti-displacement ability under the synergistic effect of the complexing agent, and can meet the operability and production requirements of silver plating of electronic products.

(3) the electroplating solution configured in Example 5 is placed for 1 year (as shown in Figure 2), the solution still remains clear and transparent, and the coating appearance after electroplating is basically consistent with the new configuration of silver plating, which shows that the electroplating solution has good stability.

The electroplating solution of the present embodiment is carried out the method for silver-plating on pure copper substrate, specifically comprises the following steps:

(A1) Pass the pure copper matrix test piece through 5g/L sodium hydroxide, 15g/L sodium carbonate, 10g/L sodium phosphate, 2g/L sodium silicate and 0.2g/L alkylphenol polyoxyethylene ether successively Alkaline solution for degreasing treatment, deionized water rinse, and then immersed in alcohol solution for 2 minutes of ultrasonic further degreasing, then rinsed with deionized water, and then immersed in a 10% sulfuric acid solution by mass ratio for pickling activation for 60 seconds, Finally rinsed with deionized water;

Immerse the pure silver plate in a nitric acid solution with a mass ratio of 10% for pickling and activation for 30 seconds, and then rinse it with deionized water;

(A2) The pure copper substrate test piece and the pure silver plate after the step (A1) are processed are directly immersed in the electroplating solution, with the pure silver plate anode, the pure copper substrate test piece is the cathode, and the pure silver plate and the pure copper substrate test piece The area ratio is 3, and the temperature is 25°C and the current density is 5A/dm ² , and the cathode is reciprocatingly moved for 5 minutes to obtain a macroscopically bright and smooth silver coating with a thickness of about 18 microns. After electroplating, use deionized water to remove the residual electroplating solution on the surface of the component, and dry the silver coating. After plating, the surface of the anodic pure silver plate does not appear blackening and discoloration and by-product coverage, but presents a silver-white bright surface with a typical honeycomb electrolytic microporous structure, indicating that the anode plate has not been passivated.

Performance testing:

(1) Utilize the Olympus optical microscope (OP) to analyze the microscopic morphology and surface smoothness of the silver coating:

Observation by an optical microscope shows that the microscopic surface of the silver coating obtained in this embodiment (as shown in FIG. 4 ) is very flat, the crystals are dense, and the approximately spherical silver grains with a size of about 1-2 microns grow closely with each other.

(2) Utilize EDS energy spectrum analysis to analyze the composition and impurity content of silver coating:

From the energy spectrum analysis (as shown in Table 2), it can be seen that the silver coating obtained by the present embodiment has high purity, except that three trace impurity elements of C, N and O with a total content of no more than 0.12% are detected, other common Impurity elements such as S and P and other metal impurity elements have not been detected, and the mass percentage of the silver coating is as high as 99.88%, which shows that the silver coating obtained in this embodiment has a high purity, which can meet the requirements of electronic products for the purity of the silver coating. Require.

(3) Utilize the Vickers microhardness tester to test the hardness of the silver coating;

By micro-Vickers hardness test result (as shown in table 3), it can be seen that the hardness of the silver coating prepared by the electroplating solution of the present embodiment reaches 115Hv, which is obviously higher than the hardness of the cyanide silver plating reported recently (existing The hardness of cyanide silver plating is in the range of 85-100Hv). This shows that under the coordination of various additives, the crystal grains can be effectively refined to improve the hardness of the silver coating, which can meet the high requirements of electrical components on the mechanical properties of the silver coating.

(4) investigate the binding force of the silver coating by bending the coating test piece experiment;

By repeated bending tests on the pure silver sheet after plating, embrittlement and peeling phenomenon did not occur in the silver coating, which shows that the silver coating obtained by electroplating with the electroplating solution of this embodiment under the coordination of various additives has good toughness and cohesion.

(5) investigate the anti-oxidation ability of silver coating by high temperature baking experiment;

Baking at 250 degrees centigrade for 2 hours in an atmospheric environment, the silver coating did not undergo oxidation and discoloration, indicating that the silver coating obtained in this embodiment has good anti-discoloration ability in an atmospheric environment.

Example 6

This embodiment provides a cyanide-free alkaline silver-plating electroplating solution and its preparation method, as well as its further application in the silver-plating process.

The cyanide-free alkaline silver plating electroplating solution of the present embodiment is made of silver nitrate, 5,5-diphenylhydantoin, 1-methylhydantoin, ammonium citrate, sodium pyrophosphate, ammonium nitrate, thiocyanate Potassium acid potassium, sodium carbonate, ammonium sulfate, sodium dodecylbenzenesulfonate, pyridine-3-carboxylic acid, 2-hydroxy-3-methoxybenzaldehyde, sodium hydroxide and deionized water;

Among them, in the cyanide-free alkaline silver plating solution, the concentration of silver nitrate is 20g/L, the concentration of 5,5-diphenylhydantoin is 40g/L, and the concentration of 1-methylhydantoin is 30g/L , The concentration of ammonium citrate is 15g/L, the concentration of sodium pyrophosphate is 30g/L, the concentration of ammonium nitrate is 5g/L, the concentration of potassium thiocyanate is 8g/L, the concentration of sodium carbonate is 15g/L, and the concentration of ammonium sulfate is 25g /L, the concentration of sodium dodecylbenzenesulfonate is 2g/L, the concentration of pyridine-3-formic acid is 5g/L, the concentration of 2-hydroxy-3-methoxybenzaldehyde is 1g/L, and the concentration of sodium hydroxide is 5g/L.

The preparation method specifically comprises the following steps:

(S1) Combine primary complexing agent (5,5-diphenylhydantoin and 1-methylhydantoin), secondary complexing agent (ammonium citrate and sodium pyrophosphate) and anodic depolarizer (ammonium nitrate and potassium thiocyanate) were dissolved in deionized water, and stirred continuously for 5 minutes at a speed of 400 rpm to obtain the first mixed solution;

(S2) adding silver salt (silver nitrate) to the first mixed solution prepared in step (S1), stirring continuously for 3 minutes at a speed of 400 rpm to obtain a second mixed solution;

(S3) dissolving the conductive salt (sodium carbonate and ammonium sulfate) in deionized water and adding it to the second mixed solution prepared in step (S2), stirring continuously for 3 minutes at a speed of 400 rpm to obtain a third mixed solution ;

(S4) Dissolve surfactant (sodium dodecylbenzenesulfonate), primary brightener (pyridine-3-carboxylic acid) and secondary brightener (2-hydroxy-3-methoxybenzaldehyde) in deionized In water, continuously stirred for 5 minutes at a speed of 800 rev/min) to obtain a composite additive solution;

(S5) Add the composite additive solution prepared in step (S4) to the third mixed solution prepared in step (S3), add deionized water to constant volume, and pass the pH adjusting agent (sodium hydroxide lye) Adjust the pH value of the solution to 9.5, and continuously stir for 2 minutes at a speed of 800 rpm to obtain a cyanide-free alkaline silver plating solution.

Performance testing:

(1) The Hall cell test was carried out at a current density of 2 A/dm ² using the electroplating solution configured in Example 6. The macrophotograph of the obtained Hall cell test piece is shown in Fig. 1 . It can be seen from Figure 1 that the Hall cell test piece using the plating solution configured in Example 6 is smooth and bright from the low current density range to the high current density range, and there is no missing plating in the low area, which shows that the plating solution has the ability to disperse and move. Well, the implementation current density range is wide, and according to the comparison of the Hall cell current density scale, the maximum current density that can be applied to the electroplating solution configured in Example 6 can reach 9A/dm ² ; the Hall cell test piece does not appear to be warped, Illustrate adopting the coating that embodiment 6 obtains to have no internal stress.

(2) The electroplating solution prepared in Example 6 has good resistance to displacement. It can be seen from Table 3 that when the pure copper test piece was placed in the plating solution of Example 6, the test piece did not undergo a serious replacement reaction immediately, but a slight silver replacement reaction began to occur after the soaking time reached 678 seconds ; And the anti-displacement time of the brass test piece in the electroplating solution of embodiment 6 is 340 seconds. This shows that the electroplating solution in Example 6 can effectively improve the anti-displacement ability under the synergistic effect of the complexing agent, and can meet the operability and production requirements of silver plating of electronic products.

(3) the electroplating solution configured in Example 6 is placed for 1 year (as shown in Figure 2), the solution still remains clear and transparent, and the coating appearance after electroplating is basically consistent with the new configuration of silver plating, which shows that the electroplating solution has good stability.

The electroplating solution of the present embodiment is carried out the method for silver-plating on pure copper substrate, specifically comprises the following steps:

(A1) Pass the pure copper matrix test piece through 5g/L sodium hydroxide, 15g/L sodium carbonate, 10g/L sodium phosphate, 2g/L sodium silicate and 0.2g/L alkylphenol polyoxyethylene ether successively Alkaline solution for degreasing treatment, deionized water rinse, and then immersed in alcohol solution for 2 minutes of ultrasonic further degreasing, then rinsed with deionized water, and then immersed in a 10% sulfuric acid solution by mass ratio for pickling activation for 60 seconds, Finally rinsed with deionized water;

Immerse the pure silver plate in a nitric acid solution with a mass ratio of 10% for pickling and activation for 30 seconds, and then rinse it with deionized water;

(A2) The pure copper substrate test piece and the pure silver plate after the step (A1) are processed are directly immersed in the electroplating solution, with the pure silver plate anode, the pure copper substrate test piece is the cathode, and the pure silver plate and the pure copper substrate test piece The area ratio is 3, the temperature is 25°C and the current density is 0.8A/dm ² , and the cathode is reciprocatingly moved for 40 minutes to obtain a macroscopically bright and smooth silver coating with a thickness of about 16 microns. After electroplating, use deionized water to remove the residual electroplating solution on the surface of the component, and dry the silver coating. After plating, the surface of the anodic pure silver plate does not appear blackening and discoloration and by-product coverage, but presents a silver-white bright surface with a typical honeycomb electrolytic microporous structure, indicating that the anode plate has not been passivated.

Performance testing:

(1) Utilize the Olympus optical microscope (OP) to analyze the microscopic morphology and surface smoothness of the silver coating:

Observation by an optical microscope shows that the microscopic surface of the silver coating obtained in this embodiment (as shown in FIG. 4 ) is very flat, the crystals are dense, and the approximately spherical silver grains with a size of about 1-2 microns grow closely with each other.

(2) Utilize EDS energy spectrum analysis to analyze the composition and impurity content of silver coating:

From the energy spectrum analysis (as shown in Table 2), it can be seen that the silver coating obtained by the present embodiment has high purity, except that three trace impurity elements of C, N and O with a total content of no more than 0.12% are detected, other common Impurity elements such as S and P and other metal impurity elements have not been detected, and the mass percentage of the silver coating is as high as 99.88%, which shows that the silver coating obtained in this embodiment has a high purity, which can meet the requirements of electronic products for the purity of the silver coating. Require.

(3) Utilize the Vickers microhardness tester to test the hardness of the silver coating;

By micro-Vickers hardness test result (as shown in table 3), it can be seen that the hardness of the silver coating prepared by the electroplating solution of the present embodiment reaches 119Hv, which is obviously higher than the hardness of the cyanide silver plating reported recently (existing The hardness of cyanide silver plating is in the range of 85-100Hv). This shows that under the coordination of various additives, the crystal grains can be effectively refined to improve the hardness of the silver coating, which can meet the high requirements of electrical components on the mechanical properties of the silver coating.

(4) investigate the binding force of the silver coating by bending the coating test piece experiment;

By repeated bending tests on the pure silver sheet after plating, embrittlement and peeling phenomenon did not occur in the silver coating, which shows that the silver coating obtained by electroplating with the electroplating solution of this embodiment under the coordination of various additives has good toughness and cohesion.

(5) investigate the anti-oxidation ability of silver coating by high temperature baking experiment;

Baking at 250 degrees centigrade for 2 hours in an atmospheric environment, the silver coating did not undergo oxidation and discoloration, indicating that the silver coating obtained in this embodiment has good anti-discoloration ability in an atmospheric environment.

The time when the displacement reaction occurs in the cyanide-free alkaline silver-plating electroplating solution prepared by each embodiment of table 1

The Vickers hardness value (Hv) of the silver coating that each embodiment of table 2 prepares

The composition mass percent of the silver coating that each embodiment of table 3 prepares

The above descriptions of the embodiments are for those of ordinary skill in the art to understand and use the invention. It is obvious that those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described here to other embodiments without creative effort. Therefore, the present invention is not limited to the above-mentioned embodiments. Improvements and modifications made by those skilled in the art according to the explanations of the present invention without departing from the scope of the present invention should fall within the protection scope of the present invention.

Claims (10)

1. The cyanide-free alkaline silver plating electroplating solution is characterized by comprising silver salt, a main complexing agent, an auxiliary complexing agent, conductive salt, an anode depolarizer, a composite additive, a pH value regulator and deionized water;

In the cyanide-free alkaline silver plating solution, the concentration of silver salt is 5-50 g/L, the concentration of main complexing agent is 30-150 g/L, the concentration of auxiliary complexing agent is 15-90 g/L, the concentration of conductive salt is 30-100 g/L, the concentration of anode depolarizer is 8-25 g/L, the concentration of composite additive is 5-10 g/L, pH, and the concentration of regulator is 3-10 g/L.

2. A cyanide-free alkaline silver plating bath according to claim 1, wherein the silver salt is selected from one of silver chloride, silver nitrate, silver sulfate or silver carbonate.

3. A cyanide-free alkaline silver plating bath according to claim 1, wherein the main complexing agent is selected from one or more of 1-methylhydantoin, pseudothiohydantoin, 5-phenylhydantoin, 2-thiohydantoin, 5-diphenylhydantoin, 5-dimethylhydantoin, 1-allylhydantoin or hydantoin-5-acetic acid.

4. The cyanide-free alkaline silver plating bath according to claim 1, wherein the auxiliary complexing agent is selected from one or more of succinimide, N-hydroxysuccinimide, ethylenediamine, disodium edetate, trisodium citrate, potassium pyrophosphate, sodium pyrophosphate, ammonium citrate, potassium citrate, sodium metaphosphate and sodium polyphosphate, cycloheximide, 4-bromobenzamide or urea.

5. The cyanide-free alkaline silver plating bath according to claim 1, wherein the conductive salt is one or more selected from the group consisting of potassium chloride, sodium chloride, potassium carbonate, sodium carbonate, potassium sulfate, sodium sulfate, ammonium chloride and ammonium sulfate.

6. The cyanide-free alkaline silver plating bath according to claim 1, wherein the anode depolarizer is selected from one or more of potassium nitrate, sodium nitrate, ammonium nitrate, potassium sodium tartrate, potassium thiocyanate, sodium thiosulfate, potassium thiosulfate, ammonium thiosulfate, aminotrimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, hydroxyethylidene diphosphate, dipotassium hydrogen phosphate, and disodium hydrogen phosphate.

7. The cyanide-free alkaline silver plating bath according to claim 1, wherein the composite additive comprises a surfactant, a primary brightening agent and a secondary brightening agent according to a mass ratio of 2:5:1 a composition of the composite material,

wherein, the surfactant is selected from one or more of sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, fatty alcohol potassium sulfate, polyether carboxylic acid potassium, N-acyl amino carboxylic acid potassium OP, polyoxyethylene lauryl ether of nonylphenol or formaldehyde polymer sodium salt of 2-naphthalene sulfonic acid;

The primary brightening agent is selected from one or more of methionine, beta-indolylalanine, alpha-aminopentanedioic acid, phenylalanine, pyridine-3-formic acid, polyethylene glycol, alkylphenol ethoxylates, fatty amine ethoxylates, L-methionine, beta-hydroxyalanine, pyridine-4-formic acid, polypropylene imine, alpha-aminoindolylpropionic acid, polyethanolamine, alpha-amino-beta-imidazolylpropionic acid, polyvinyl alcohol, lysine, gamma-methyl-alpha-aminopentanoic acid, beta-phenyl-alpha-aminopropionic acid, polyethylene imine, alpha-aminoacetic acid, alpha-aminopentanamic acid, 1-pyridine-4-piperidine-4-carboxylic acid, alpha-amino-beta-hydroxybutyric acid, alpha-tetrahydropyrroloic acid, alpha-aminopropionic acid, 4- (4-piperidine) benzoic acid, 2-pyridylacetic acid, 2, 6-pyridinedicarboxylic acid or 3, 4-pyridinedicarboxylic acid;

the secondary brightening agent is selected from one or more of naphthol, sodium polydithio-dipropyl sulfonate, thiourea, selenious acid, thiosemicarbazide, D-lyxolylamine, 2-mercaptobenzimidazole, thiouracil, propylthiouracil, 3-ethoxy-4-hydroxybenzaldehyde, 1, 4-butynediol, 4-formyl-2-methoxyphenyl acetate, 4-hydroxy-3-methoxy-5-nitrobenzaldehyde, 3-methoxy-4-hydroxybenzaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 3-hydroxycoumarin, 2- (2-pyridyl) benzimidazole, benzotriazole imidazole, 2-hydroxypyridine, 2-bipyridine, 4-diamino-2, 2-bipyridine, bis (1-benzyl-3-carboxydihydropyridyl) ether sodium salt, methylbenzotriazole, 4-imidazole formaldehyde, benzimidazole, isothiazole and 2-piperidone.

8. The cyanide-free alkaline silver plating bath according to claim 1, wherein the pH adjustor is one or more selected from potassium hydroxide, sodium hydroxide and aqueous ammonia.

9. A method for preparing a cyanide-free alkaline silver plating bath according to any one of claims 1 to 8, comprising the steps of:

(S1) dissolving a main complexing agent, an auxiliary complexing agent and an anode depolarizer in deionized water, and uniformly mixing to obtain a first mixed solution;

(S2) adding silver salt into the first mixed solution prepared in the step (S1), and uniformly mixing to obtain a second mixed solution;

(S3) dissolving conductive salt in deionized water, adding the solution into the second mixed solution prepared in the step (2), and uniformly mixing to obtain a third mixed solution;

(S4) dissolving a surfactant, a primary brightening agent and a secondary brightening agent in deionized water, and uniformly mixing to obtain a composite additive solution;

and (S5) adding the composite additive solution prepared in the step (S4) into the third mixed solution prepared in the step (S3), and regulating the pH value of the solution to 9-11 by a pH value regulator to obtain the high-reliability cyanide-free alkaline silver plating electroplating solution.

10. Use of a cyanide-free alkaline silver plating bath according to any of claims 1 to 8 in a silver plating process, characterized in that the area ratio of anode to cathode is 2 to 5 during silver plating.