Neutral bright tinning electroplating solution and preparation method and application thereof

Abstract

The invention discloses a neutral bright tinning electroplating solution and a preparation method and application thereof. The electroplating solution is composed of tin salt, a tin complexing agent, a brightening agent, a dispersing agent and a pH buffering agent. The molar concentration of the tin salt is 0.10 mol / L to 0.40 mol / L; the tin complexing agent is mercaptoacetic acid and salt thereof; the brightener is a flavonol substance; the dispersing agent is a nonylphenol polyoxyethylene ether substance; and the pH value of the neutral bright tinning electroplating solution is 6.0-8.0. The electroplating solution provided by the invention has the advantages of higher stability, longer service life, smaller hydrogen evolution phenomenon, simple components and easiness in management, and the dispersing capacity and covering capacity of the electroplating solution are improved through the synergistic effect of the components, so that the performance of a tin-plated part prepared by electroplating is effectively ensured, and the tin-plated part is good in associativity, low in porosity, uniform, compact and bright in appearance; and the application in the electronic component or mechanical manufacturing technology is facilitated.

Description

Technical Field

[0001] The present invention relates to the field of electroplating technology, and more specifically, to a neutral bright tin electroplating solution, a preparation method thereof, and an application thereof. Background Art

[0002] Due to its non-toxicity, low melting point, and good stability, aesthetics, ductility, electrical conductivity, corrosion resistance, anti-discoloration property, and solderability, the tin-plated parts have a wide range of applications in the fields of electronic components, mechanical manufacturing, etc.

[0003] Traditional tin plating processes usually adopt acidic tin plating systems, which have advantages such as high cathodic current efficiency and fast electroplating speed. Chinese patents with publication numbers CN117210890A and CN102758228A both disclose an acidic tin electroplating solution. However, the acidic tin plating system has the following problems: First, Sn(II) in the acidic tin electroplating solution is easily oxidized to Sn(IV), and Sn(IV) will undergo a hydrolysis reaction to form stannic acid, which then forms a precipitate with a complex micelle structure with other substances in the electroplating solution, resulting in a decrease in the stability of the electroplating solution, as well as a decrease in the dispersion ability and covering ability. Second, the hydrogen evolution phenomenon is serious during the electroplating process of the acidic tin electroplating solution, and bubbles are easily formed, increasing the porosity of the tin coating and reducing the uniformity of the tin coating, thereby affecting the performance and stability of the subsequent tin-plated parts. Third, the additive components in the acidic tin electroplating solution are complex, making management difficult, and there are problems such as easy oxidation and decomposition of the additives, generation of bubbles that are difficult to eliminate, and difficulty in controlling the internal stress of the coating, which will further affect the stability, dispersion ability, and covering ability of the electroplating solution, and thus lead to a decrease in the performance of the tin-plated parts.

[0004] Therefore, based on the defects of the acidic tin plating system that it is difficult to maintain the stability of the electroplating solution and unable to electroplate and prepare high-performance tin-plated parts, how to provide a neutral bright tin electroplating solution formula that can effectively stabilize tin ions, inhibit hydrogen evolution, and has simple additive components and is easy to manage, and prepare tin-plated parts with good adhesion, low porosity, uniform and dense structure, and bright appearance has become an urgent problem to be solved. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects existing in the prior art, and provide a neutral bright tin electroplating solution and an application thereof. Mercaptoacetic acid and its salts are used as tin complexing agents to extend the stability of tin ions, flavonol substances are used as brighteners to refine crystal grains, and nonylphenol polyoxyethylene ether substances are used as dispersants to increase the solubility of flavonol substances. Through the synergistic effect between the components, the stability, dispersion ability, covering ability, and service life of the neutral bright tin electroplating solution are improved, and the tin-plated parts prepared by electroplating have good adhesion, low porosity, uniform and dense structure, and bright appearance.

[0006] To achieve the above purpose, the technical solution of the present invention is as follows:

[0007] A neutral bright tin plating bath, the plating bath is composed of a tin salt, a tin complexing agent, a brightening agent, a dispersant and a pH buffer; the molar concentration of the tin salt in the plating bath is 0.10 mol / L to 0.40 mol / L; the tin complexing agent is mercaptoacetic acid and its salts; the brightening agent is a flavonol substance; the dispersant is a nonylphenol polyoxyethylene ether substance; the pH of the neutral bright tin plating bath is 6.0 to 8.0.

[0008] The present invention also discloses a preparation method of the neutral bright tin plating bath as described above.

[0009] The present invention also discloses an application of the neutral bright tin plating bath as described above in the preparation of tin-plated parts.

[0010] The present invention also discloses an application of the neutral bright tin plating bath as described above, or a tin-plated part obtained by the application as described above in electronic components or mechanical manufacturing.

[0011] Implementing the embodiments of the present invention will have the following beneficial effects:

[0012] Mercaptoacetic acid and its salts used in the neutral bright tin plating bath provided by the present invention can stabilize tin ions and inhibit the oxidation of Sn(II) to Sn(IV), thereby inhibiting the formation of tin-containing precipitates. Even without adding a stabilizer, the plating bath can remain clear and transparent during long-term storage or long-term electroplating, and tin-plated parts with uniform, stable and high reproducibility can be obtained.

[0013] The flavonol substance used in the neutral bright tin plating bath provided by the present invention has high stability and is not easily oxidized and decomposed. It can form an adsorption layer on the surface of the workpiece to be plated, increase the overpotential, hinder the discharge of metal ions, and can electroplate tin-plated parts with fine, uniform, dense and bright appearance.

[0014] The nonylphenol polyoxyethylene ether substance used in the neutral bright tin plating bath provided by the present invention can not only increase the solubility of the flavonol substance as a carrier, prevent the flavonol substance from forming aggregates with other components in the plating bath, and keep the neutral bright tin plating bath clear and transparent during long-term storage or long-term electroplating, ensuring the stability of the plating bath; but also can act synergistically with mercaptoacetic acid and its salts and flavonol substances to optimize the surface current distribution of the workpiece to be plated, improve the dispersion ability and covering ability of the plating bath, and electroplate tin-plated parts with good adhesion, low porosity, uniform density and bright appearance.

[0015] The neutral bright tin plating bath provided by the present invention belongs to a neutral plating bath, with less hydrogen evolution phenomenon and lower corrosivity.

[0016] The neutral bright tin - plating electroplating solution provided by the present invention has high stability and can be stably stored at room temperature for more than 6 months. Even under conditions such as high - low temperature changes, light, long - term storage, or long - term electroplating, it remains clear and transparent, and there are no phenomena such as the formation of tin - containing precipitates, oxidation and decomposition precipitates of additives, or color change.

[0017] The neutral bright tin - plating electroplating solution provided by the present invention has a long service life. The electroplating effect of the tin - plating solution after long - term storage or long - term electroplating is the same as that of the newly prepared tin - plating solution, and both can electroplate tin - plated parts with uniform, stable, and high - reproducibility performance.

[0018] The neutral bright tin - plating electroplating solution provided by the present invention has simple components, is easy to manage, and there are no problems such as the formation of tin - containing precipitates and oxidation and decomposition of additives.

[0019] The neutral bright tin - plating electroplating solution provided by the present invention has excellent electroplating performance, with good dispersion ability and covering ability, high cathode current efficiency, and fast electroplating speed. It can electroplate high - performance tin - plated parts within a relatively wide range of average current densities.

[0020] The tin - plated parts electroplated using the neutral bright tin - plating electroplating solution provided by the present invention have good adhesion, low porosity, uniform density, and bright appearance, which is beneficial for applications in electronic components or mechanical manufacturing technologies. Brief Description of the Drawings

[0021] Figure 1 It is a state diagram of the neutral bright tin - plating electroplating solution prepared in Example 1 of the present invention after being stored at room temperature for 6 months.

[0022] Figure 2 It is a micro - structure picture of the tin - plated part prepared in Example 3 of the present invention when the average current density is 6 ASD. Detailed Embodiments

[0023] The following further illustrates the present invention with specific embodiments, but does not limit the present invention in any way.

[0024] The present invention discloses a neutral bright tin - plating electroplating solution, which is composed of a tin salt, a tin complexing agent, a brightening agent, a dispersant, and a pH buffer.

[0025] Furthermore, the pH of the neutral bright tin - plating electroplating solution is 6.0 - 8.0, belonging to a neutral electroplating solution, with less hydrogen evolution phenomenon and lower corrosivity.

[0026] In a specific embodiment, the tin salt includes Sn(II) salt and / or Sn(IV) salt. Preferably, the tin salt includes at least one of stannous chloride, stannous sulfate, stannous pyrophosphate, sodium stannate, and potassium stannate.

[0027] In a specific embodiment, the molar concentration of the tin salt in the electroplating solution is 0.10 mol / L to 0.40 mol / L. Specifically, if the molar concentration is lower than 0.10 mol / L, the electroplating rate of the electroplating solution will be slow. If the molar concentration is higher than 0.40 mol / L, the cost of the electroplating solution will increase.

[0028] Furthermore, the tin complexing agent is mercaptoacetic acid and its salts. Specifically, the addition of mercaptoacetic acid and its salts can stabilize tin ions for a long time and inhibit the oxidation of Sn(II) to Sn(IV). Even without adding a stabilizer, the electroplating solution can remain clear and transparent during long-term storage or long-term electroplating, and tin-plated parts with uniform, stable, and highly reproducible performance can be obtained.

[0029] In a specific embodiment, the tin complexing agent includes at least one of mercaptoacetic acid, potassium mercaptoacetate, sodium mercaptoacetate, and ammonium mercaptoacetate.

[0030] In a specific embodiment, the molar concentration of the tin complexing agent in the electroplating solution is 0.10 mol / L to 2.00 mol / L.

[0031] In a specific embodiment, the molar concentration ratio of the tin salt to the tin complexing agent is 1:(1 to 5). Specifically, if the molar concentration ratio is lower than 1:1, the stability of the electroplating solution cannot meet the requirements, and the tin ions cannot be stabilized during long-term storage or long-term electroplating. If the molar concentration ratio is higher than 1:5, the grains of the tin-plated parts prepared by electroplating the electroplating solution will be coarse.

[0032] Furthermore, the brightening agent is a flavonol substance. Specifically, flavonol substances have high stability, are not easily oxidized and decomposed, can form an adsorption layer on the surface of the workpiece to be plated, increase the overpotential, hinder the discharge of metal ions, and can electroplate tin-plated parts with fine grains, uniform density, and bright appearance.

[0033] In a specific embodiment, the brightening agent includes at least one of morin, quercetin, herbacetin, and luteolin.

[0034] In a specific embodiment, the concentration of the brightening agent in the electroplating solution is 0.02 g / L to 0.30 g / L. Specifically, if the concentration is lower than 0.02 g / L, the tin-plated parts prepared by electroplating the electroplating solution will be rough, dark gray, and have poor solderability. If the concentration is higher than 0.30 g / L, the process of the tin-plated parts prepared by electroplating the electroplating solution will be unstable, the adhesion will be poor, and it is easy to peel or fall off.

[0035] Further, the dispersant is a nonylphenol polyoxyethylene ether substance. Specifically, on the one hand, the addition of the nonylphenol polyoxyethylene ether substance can act as a carrier to increase the solubility of the flavonol substance, prevent the flavonol substance from forming aggregates with other components in the electroplating solution, and keep the neutral bright tin electroplating solution clear and transparent during long-term storage or long-term electroplating, ensuring the stability of the electroplating solution; on the other hand, it can synergistically act with mercaptoacetic acid and its salts and the flavonol substance to optimize the surface current distribution of the workpiece to be electroplated, improve the dispersion ability and covering ability of the electroplating solution, and electroplate a tin-plated part with good bonding, low porosity, uniform density, and bright appearance.

[0036] In a specific embodiment, the degree of polymerization in the nonylphenol polyoxyethylene ether substance is 20 - 50. Specifically, if the degree of polymerization is lower than 20, it will cause the flavonol substance in the electroplating solution not to be completely dissolved, forming aggregates and affecting the quality of the tin-plated part. If the degree of polymerization is higher than 50, it will cause the electroplating solution to foam severely and be difficult to eliminate, and problems such as missing plating, high porosity, and poor uniformity are likely to occur in the tin-plated part, and the electroplating work will not be able to proceed.

[0037] In a specific embodiment, the concentration of the dispersant in the electroplating solution is 1.00 g / L - 5.00 g / L. Specifically, if the concentration is lower than 1.00 g / L, it will cause the flavonol substance in the electroplating solution not to be completely dissolved, and it is easy to form aggregates with other components in the electroplating solution, affecting the quality of the tin-plated part. If the concentration is higher than 5.00 g / L, it will cause the tin-plated parts prepared by electroplating the electroplating solution to be uneven, and local thin plating or thick plating phenomena are likely to occur.

[0038] In a specific embodiment, the pH buffer includes at least one of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium hydroxide, and hydrochloric acid. Specifically, the addition of the pH buffer can adjust the electroplating solution to a specified pH, keeping the acidity and alkalinity of the electroplating solution stable.

[0039] The present invention also discloses a preparation method of a neutral bright tin electroplating solution according to any embodiment of the present invention, comprising the following steps:

[0040] (1) Mix the tin salt and mercaptoacetic acid and its salts to obtain a first reaction solution;

[0041] (2) Mix the flavonol substance and the nonylphenol polyoxyethylene ether substance to obtain a second reaction solution;

[0042] (3) Mix the first reaction solution and the second reaction solution, and add a pH buffer to the obtained mixed solution to adjust the pH of the mixed solution to 6.0 - 8.0 to obtain a neutral bright tin electroplating solution.

[0043] The present invention also discloses an application of a neutral bright tin electroplating solution according to any embodiment of the present invention in the preparation of tin-plated parts.

[0044] Specifically, the neutral bright tin - plating electroplating solution of the present invention has high stability and service life, maintaining the electroplating solution clear and transparent during long - term storage or long - term electroplating, and electroplating tin - plated parts with uniform, stable and highly reproducible electroplating preparation performance.

[0045] In a specific embodiment, the application includes the following steps:

[0046] Immerse the workpiece to be plated in the neutral bright tin - plating electroplating solution for electroplating to obtain a tin - plated part; wherein, the electroplating temperature is 20°C to 40°C; the average current density of electroplating is 1 ASD to 12 ASD; the electroplating method is direct - current electroplating or periodic square - wave pulse electroplating.

[0047] In a specific embodiment, the porosity of the tin - plated part is less than 5%.

[0048] Specifically, the neutral bright tin - plating electroplating solution of the present invention has excellent electroplating performance, with good dispersion ability and covering ability, high cathode current efficiency and fast electroplating speed, and can electroplate tin - plated parts with good bonding, low porosity, uniform density and bright appearance within a relatively wide range of average current density.

[0049] The present invention also discloses the application of a neutral bright tin - plating electroplating solution according to any embodiment of the present invention, or a tin - plated part obtained by the application according to any embodiment of the present invention in electronic components or mechanical manufacturing.

[0050] The following are specific embodiments

[0051] Example 1

[0052] The neutral bright tin - plating electroplating solution of this embodiment includes components with the following concentrations:

[0053] 0.20 mol / L of stannous pyrophosphate, 0.25 mol / L of mercaptoacetic acid, 0.05 g / L of luteolin, 2.50 g / L of nonylphenol polyoxyethylene ether (polymerization degree is 30: NP - 30), and appropriate amounts of sodium hydroxide and potassium dihydrogen phosphate. The pH of the neutral bright tin - plating electroplating solution of this embodiment is 7.5.

[0054] The preparation method of the neutral bright tin - plating electroplating solution of this embodiment includes the following steps:

[0055] (1) Mix stannous pyrophosphate and mercaptoacetic acid to obtain a first reaction solution.

[0056] (2) Mix luteolin and NP - 30 to obtain a second reaction solution.

[0057] (3) Mix the first reaction solution and the second reaction solution, and add sodium hydroxide and potassium dihydrogen phosphate to the obtained mixed solution to adjust the pH of the mixed solution to 7.5 to obtain the neutral bright tin - plating electroplating solution.

[0058] The electroplating solution prepared in this example can be stored at room temperature for more than 6 months. Even under conditions such as high and low temperature changes, light, long-term storage, or long-term electroplating, it still remains light yellow, clear and transparent, without the formation of tin-containing precipitates, oxidation and decomposition precipitates of additives, or color changes, as Figure 1 shown. Figure 1 Figure 6 is a state diagram of the neutral bright tin electroplating solution prepared in this example after being stored at room temperature for 6 months.

[0059] When electroplating using the neutral bright tin electroplating solution of this example, the electroplating anode is a platinum-titanium mesh, and the electroplating cathode is a silicon wafer with a sputtered Cu seed layer on its surface. The anode and cathode are immersed in the electroplating solution of this example for electroplating. The direct current electroplating method is adopted, the electroplating temperature is 30 °C, and the average current density of electroplating is 4 ASD. A tin-plated part with good adhesion, a porosity of 4%, uniform density, and a bright appearance is prepared by electroplating.

[0060] Example 2

[0061] The neutral bright tin electroplating solution of this example includes components with the following concentrations:

[0062] Sodium stannate at 0.30 mol / L, potassium mercaptoacetate at 0.50 mol / L, quercetin at 0.10 g / L, nonylphenol polyoxyethylene ether (polymerization degree 40: NP-40) at 3.00 g / L, and appropriate amounts of hydrochloric acid and dipotassium hydrogen phosphate. The pH of the neutral bright tin electroplating solution of this example is 6.2.

[0063] The preparation method of the neutral bright tin electroplating solution of this example includes the following steps:

[0064] (1) Mix sodium stannate and potassium mercaptoacetate to obtain a first reaction solution.

[0065] (2) Mix quercetin and NP-40 to obtain a second reaction solution.

[0066] (3) Mix the first reaction solution and the second reaction solution, and add hydrochloric acid and dipotassium hydrogen phosphate to the obtained mixed solution to adjust the pH of the mixed solution to 6.2 to obtain a neutral bright tin electroplating solution.

[0067] The electroplating solution prepared in this example can be stored at room temperature for more than 6 months. Even under conditions such as high and low temperature changes, light, long-term storage, or long-term electroplating, it still remains clear and transparent, without the formation of tin-containing precipitates, oxidation and decomposition precipitates of additives, or color changes.

[0068] Electroplating is carried out using the neutral bright tin - plating electroplating solution of this embodiment. The electroplating anode is a platinum - titanium mesh, and the electroplating cathode is a silicon wafer sputtered with a Cu seed layer on its surface. The anode and cathode are immersed in the electroplating solution of this embodiment for electroplating. The periodic square - wave pulse electroplating method is adopted, the electroplating temperature is 25°C; the average current density of electroplating is 8 ASD, and a tin - plated part with good adhesion, a porosity of 2%, uniform density, and bright appearance is prepared by electroplating.

[0069] Example 3

[0070] The neutral bright tin - plating electroplating solution of this embodiment comprises components with the following concentrations:

[0071] 0.10 mol / L of stannous sulfate, 0.15 mol / L of sodium stannate, 0.50 mol / L of ammonium thioglycolate, 0.05 g / L of morin, 2.00 g / L of nonylphenol polyoxyethylene ether (polymerization degree is 40: NP - 40), and appropriate amounts of hydrochloric acid and dipotassium hydrogen phosphate. The pH of the neutral bright tin - plating electroplating solution of this embodiment is 7.0.

[0072] The preparation method of the neutral bright tin - plating electroplating solution of this embodiment comprises the following steps:

[0073] (1) Mix stannous sulfate, sodium stannate and ammonium thioglycolate to obtain a first reaction solution.

[0074] (2) Mix morin and NP - 40 to obtain a second reaction solution.

[0075] (3) Mix the first reaction solution and the second reaction solution, and add hydrochloric acid and dipotassium hydrogen phosphate to the obtained mixed solution to adjust the pH of the mixed solution to 7.0, obtaining a neutral bright tin - plating electroplating solution.

[0076] The electroplating solution prepared in this embodiment can be stored at room - temperature environment for more than 6 months. Even under conditions such as high - low temperature changes, light, long - term storage or long - term electroplating, it still maintains a light - yellow clear and transparent state, and there are no phenomena such as the formation of tin - containing precipitates, oxidation and decomposition precipitates of additives, or color change.

[0077] Electroplating is carried out using the neutral bright tin - plating electroplating solution of this embodiment. The electroplating anode is a platinum - titanium mesh, and the electroplating cathode is a silicon wafer sputtered with a Cu seed layer on its surface. The anode and cathode are immersed in the electroplating solution of this embodiment for electroplating. The periodic square - wave pulse electroplating method is adopted, the electroplating temperature is 30°C; the average current density of electroplating is 6 ASD, and a tin - plated part with good adhesion, a porosity of 2%, uniform density, and bright appearance is prepared by electroplating, as Figure 2 shown, Figure 2 is the microscopic structure picture of the tin - plated part prepared when the average current density is 6 ASD.

[0078] Comparative Example 1

[0079] The electroplating solution of this comparative example is an acidic tin electroplating solution. Compared with Example 1, the only difference is that stannous pyrophosphate is changed to stannous methylsulfonate, and the pH of the acidic tin electroplating solution in this comparative example is < 1.

[0080] Electroplating is carried out using the acidic tin electroplating solution of this comparative example. The electroplating method is the same as that of Example 1. The porosity of the obtained tin-plated parts is greater than 30%, the appearance is rough, and the edges are charred. This is due to the large acidity of the electroplating solution and the serious hydrogen evolution phenomenon.

[0081] Comparative Example 2

[0082] Compared with Example 1, the only difference in this comparative example is that thioglycolic acid is changed to potassium pyrophosphate.

[0083] A large amount of white muddy tin-containing precipitate is formed after storing the neutral tin electroplating solution prepared in this comparative example at room temperature for 1 month. This is because the complexing effect of potassium pyrophosphate on Sn(II) is weak, and it cannot prevent Sn(II) from being oxidized to Sn(IV). Sn(IV) hydrolyzes and then forms a complex micelle structure precipitate, resulting in low stability of the neutral tin electroplating solution.

[0084] Comparative Example 3

[0085] Compared with Example 1, the only difference in this comparative example is that the molar concentration of thioglycolic acid is changed to 0.10 mol / L.

[0086] A large amount of white muddy tin-containing precipitate is formed after storing the neutral tin electroplating solution prepared in this comparative example at room temperature for 4 months. This is because the concentration of thioglycolic acid is too low to maintain the high stability of the neutral tin electroplating solution.

[0087] Comparative Example 4

[0088] Compared with Example 1, the only difference in this comparative example is that the molar concentration of thioglycolic acid is changed to 2.5 mol / L.

[0089] Electroplating is carried out using the neutral tin electroplating solution of this comparative example. The electroplating method is the same as that of Example 1. The microstructure grains of the obtained tin-plated parts are coarse.

[0090] Comparative Example 5

[0091] Compared with Example 1, the only difference in this comparative example is that the concentration of luteolin is changed to 0.01 g / L.

[0092] Electroplating is carried out using the neutral tin electroplating solution of this comparative example. The electroplating method is the same as that of Example 1. The appearance of the obtained tin-plated parts is rough, dark gray, and the solderability is poor.

[0093] Comparative Example 6

[0094] This comparative example is different from Example 1 only in that the concentration of NP-30 is changed to 0.1 g / L.

[0095] A large amount of yellow aggregates precipitated during the preparation of the neutral tin plating electrolyte prepared in this comparative example, which was caused by the too low concentration of NP-30 to completely dissolve luteolin.

[0096] Comparative Example 7

[0097] This comparative example is different from Example 1 only in that the degree of polymerization of nonylphenol polyoxyethylene ether is changed to 200 (NP-200).

[0098] A large amount of bubbles were generated and difficult to eliminate during the electroplating process of the neutral tin plating electrolyte prepared in this comparative example, and the electroplating work could not be carried out.

[0099] The above-described embodiments only represent several implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of this invention patent shall be subject to the appended claims.

Claims

1. A neutral bright tin plating solution, characterized in that: The electroplating solution is composed of tin salt, tin complexing agent, brightener, dispersant and pH buffer; The molar concentration of the tin salt in the electroplating solution is 0.10 mol / L to 0.40 mol / L; The tin complexing agent is thioglycolic acid and its salt; The brightener is a flavonol substance; The dispersant is a nonylphenol polyoxyethylene ether substance; The pH value of the neutral bright tin plating solution is 6.0-8.

0.

2. The neutral bright tin plating solution according to claim 1, characterized in that: The molar concentration of the tin complexing agent in the electroplating solution is 0.10 mol / L to 2.00 mol / L; the concentration of the brightener in the electroplating solution is 0.02 g / L to 0.30 g / L; and the concentration of the dispersant in the electroplating solution is 1.00 g / L to 5.00 g / L.

3. The neutral bright tin plating solution according to claim 2, characterized in that: The molar concentration ratio of the tin salt to the tin complexing agent is 1:(1-5).

4. The neutral bright tin plating solution according to claim 1, characterized in that: The tin salt includes Sn(II) salt and / or Sn(IV) salt; The tin complexing agent includes at least one of thioglycolic acid, potassium thioglycolate, sodium thioglycolate and ammonium thioglycolate; The brightener comprises at least one of morin, quercetin, herbicide and luteolin; The degree of polymerization of the nonylphenol polyoxyethylene ether substance is 20 to 50; The pH buffer includes at least one of potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium hydroxide and hydrochloric acid.

5. A method for preparing a neutral bright tin plating solution as claimed in any one of claims 1 to 4, characterized in that: The following steps are involved: (1) mixing a tin salt and thioglycolic acid and a salt thereof to obtain a first reaction solution; (2) mixing the flavonol substance and the nonylphenol polyoxyethylene ether substance to obtain a second reaction solution; (3) The first reaction solution and the second reaction solution are mixed, and a pH buffer is added to the obtained mixed solution to adjust the pH of the mixed solution to 6.0-8.0, thereby obtaining the neutral bright tin plating solution.

6. Use of the neutral bright tin-plating solution as claimed in any one of claims 1 to 5 in the preparation of tin-plated parts.

7. The use according to claim 6, characterized in that: The application comprises the following steps: Immersing the workpiece to be plated in the neutral bright tin plating solution for electroplating to obtain a tinned workpiece; The electroplating temperature is 20°C to 40°C; The average current density of the electroplating is 1ASD to 12ASD; The electroplating method is direct current electroplating or periodic square wave pulse electroplating.

8. The use according to claim 7, characterized in that: The porosity of the tin-plated part is less than 5%.

9. Use of the neutral bright tin-plating solution as claimed in any one of claims 1 to 5, or the tin-plated parts obtained by using the solution as claimed in any one of claims 6 to 8 in electronic components or machinery manufacturing.

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