A neutral bright tin plating solution, its preparation method and application

Abstract

The application discloses a neutral bright tin plating solution and a preparation method and application thereof. The plating solution is composed of tin salt, tin complexing agent, brightener, dispersant and pH buffer. The molar concentration of the tin salt is 0.10-0.40 mol / L. The tin complexing agent is mercaptoacetic acid and its salt. The brightener is flavonol substance. The dispersant is nonylphenol polyoxyethylene ether substance. The pH of the neutral bright tin plating solution is 6.0-8.0. The plating solution has high stability and service life, small hydrogen evolution phenomenon, simple components and easy management. The synergistic effect among the components improves the dispersion capacity and covering capacity of the plating solution, thereby effectively ensuring the performance of the tin-plated parts prepared by plating, and the tin-plated parts have good combination, low porosity, uniformity, compactness and bright appearance, and are beneficial to application in electronic components or mechanical manufacturing technology.

Description

Technical Field

[0001] This invention relates to the field of electroplating technology, and more specifically, to a neutral bright tin plating solution, its preparation method, and its application. Background Technology

[0002] Tin plating is non-toxic, has a low melting point, and possesses excellent stability, aesthetics, ductility, conductivity, corrosion resistance, discoloration resistance, and solderability, making tin-plated parts widely used in electronic components, machinery manufacturing, and other fields.

[0003] Traditional tin plating processes typically employ acidic tin plating systems, which offer advantages such as high cathode current efficiency and fast plating speed. Chinese patents CN117210890A and CN102758228A both disclose an acidic tin plating solution. However, acidic tin plating systems suffer from several problems: First, Sn(II) in the acidic tin plating solution is easily oxidized to Sn(IV). Sn(IV) undergoes hydrolysis to generate stannic acid, which then reacts with other substances in the plating solution to form complex colloidal precipitates, leading to decreased stability, dispersion, and coverage. Second, acidic tin plating solutions exhibit severe hydrogen evolution during electroplating, easily forming bubbles, increasing the porosity of the tin plating layer, reducing its uniformity, and consequently affecting the performance and stability of subsequent tin-plated parts. Furthermore, the additives in acidic tin plating solutions are complex and difficult to manage. They are prone to oxidation and decomposition, generate bubbles that are difficult to eliminate, and have difficulty controlling the internal stress of the plating layer. These problems will further affect the stability, dispersion and coverage of the plating solution, leading to a decline in the performance of tin-plated parts.

[0004] Therefore, given the shortcomings of acidic tin plating systems, such as difficulty in maintaining the stability of the plating solution and inability to electroplat high-performance tin-plated parts, it is urgent to find a neutral bright tin plating solution formulation that can effectively stabilize tin ions, inhibit hydrogen evolution, and has simple and easy-to-manage additive components, in order to prepare tin-plated parts with good bonding, low porosity, uniform density, and bright appearance. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a neutral bright tin plating solution and its application. It utilizes mercaptoacetic acid and its salts as tin complexing agents to prolong the stability of tin ions, flavonols as brighteners to refine grains, and nonylphenol polyoxyethylene ethers as dispersants to increase the solubility of flavonols. Through the synergistic effect between the components, the stability, dispersing ability, covering ability and service life of the neutral bright tin plating solution are improved. The tin-plated parts prepared by electroplating have good bonding, low porosity, uniform density and bright appearance.

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

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

[0008] The present invention also discloses a method for preparing the neutral bright tin plating solution as described above.

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

[0010] The present invention also discloses a neutral bright tin plating solution as described above, or the application of tin-plated parts obtained by the above application in the manufacture of electronic components or machinery.

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

[0012] The mercaptoacetic acid and its salts used in the neutral bright tin plating solution provided by this 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 the addition of stabilizers, the plating solution can remain clear and transparent during long-term storage or long-term plating, resulting in tin-plated parts with uniform performance, stability and high reproducibility.

[0013] The flavonols used in the neutral bright tin plating solution provided by this invention have high stability and are not easily oxidized or decomposed. They can form an adsorption layer on the surface of the workpiece to be plated, increase the overpotential, and hinder the discharge of metal ions. This enables the electroplating of tin-plated parts with fine, uniform, dense grains and a bright appearance.

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

[0015] The neutral bright tin plating solution provided by this invention is a neutral plating solution with minimal hydrogen evolution and low corrosivity.

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

[0017] The neutral bright tin plating solution provided by this invention has a long service life. The tin plating solution after long-term storage or long-term plating has the same plating effect as the freshly prepared tin plating solution. Both can be used to plating tin-plated parts with uniform performance, stability and high reproducibility.

[0018] The neutral bright tin plating solution provided by this invention has a simple composition, is easy to manage, and does not have problems such as the formation of tin-containing precipitates or the oxidative decomposition of additives.

[0019] The neutral bright tin plating solution provided by this invention has excellent electroplating performance, good dispersion and coverage, high cathode current efficiency, and fast electroplating speed. It can electroplat and prepare high-performance tin-plated parts within a wide range of average current densities.

[0020] Tin-plated parts prepared by electroplating using the neutral bright tin plating solution provided by this invention have good bonding properties, low porosity, uniform density, and bright appearance, which is beneficial for their application in electronic components or mechanical manufacturing technology. Attached Figure Description

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

[0022] Figure 2 This is a microstructure image of the tin-plated part prepared with an average current density of 6 ASD in Example 3 of the present invention. Detailed Implementation

[0023] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0024] This invention discloses a neutral bright tin plating solution, which is composed of tin salt, tin complexing agent, brightener, dispersant and pH buffer.

[0025] Furthermore, the pH of neutral bright tin plating solution is 6.0 to 8.0, which is considered a neutral plating solution. It exhibits less hydrogen evolution and lower corrosivity.

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

[0027] In one specific embodiment, the molar concentration of 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 speed 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 over a long period of time, inhibit the oxidation of Sn(II) to Sn(IV), and even without the addition of stabilizers, the plating solution can remain clear and transparent during long-term storage or long-term electroplating, resulting in tin-plated parts with uniform, stable and highly reproducible performance.

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

[0030] In one 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 one specific embodiment, the molar concentration ratio of tin salt to tin complexing agent is 1:(1-5). 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 kept stable during long-term storage or long-term electroplating. If the molar concentration ratio is higher than 1:5, the tin-plated parts prepared by electroplating will have coarse grains.

[0032] Furthermore, the brightener is a flavonol. Specifically, flavonols have high stability, are not easily oxidized or decomposed, and can form an adsorption layer on the surface of the workpiece to be plated, increasing the overpotential and hindering the discharge of metal ions. This enables the electroplating of tin-plated parts with fine, uniform, dense grains and a bright appearance.

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

[0034] In one specific embodiment, the concentration of brightener in the electroplating solution is 0.02 g / L to 0.30 g / L. Specifically, if the concentration is below 0.02 g / L, the tin-plated parts prepared by electroplating will be rough, dull, and have poor solderability. If the concentration is above 0.30 g / L, the tin-plated parts prepared by electroplating will have unstable processes, poor adhesion, and be prone to peeling or flaking.

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

[0036] In one specific embodiment, the degree of polymerization of the nonylphenol polyoxyethylene ether is 20–50. Specifically, if the degree of polymerization is below 20, the flavonols in the electroplating solution cannot be completely dissolved, forming aggregates that affect the quality of the tin-plated parts. If the degree of polymerization is above 50, the electroplating solution will foam severely and be difficult to eliminate, and the tin-plated parts will easily have problems such as incomplete plating, high porosity, and poor uniformity, making the electroplating process impossible.

[0037] In one specific embodiment, the concentration of the dispersant in the electroplating solution is 1.00 g / L to 5.00 g / L. Specifically, if the concentration is below 1.00 g / L, the flavonols in the electroplating solution cannot be completely dissolved, and they are prone to forming aggregates with other components in the electroplating solution, affecting the quality of the tin-plated parts. If the concentration is above 5.00 g / L, the tin-plated parts prepared by electroplating will be uneven, and local thin or thick plating phenomena are likely to occur.

[0038] In one specific embodiment, the pH buffer includes at least one selected from 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, thereby maintaining a stable acidity or alkalinity of the electroplating solution.

[0039] The present invention also discloses a method for preparing a neutral bright tin plating solution as described in any embodiment of the present invention, comprising the following steps:

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

[0041] (2) Mix flavonols and nonylphenol polyoxyethylene ethers to obtain a second reaction solution;

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

[0043] The present invention also discloses the application of a neutral bright tin plating solution as described in any embodiment of the present invention in the preparation of tin-plated parts.

[0044] Specifically, the neutral bright tin plating solution of the present invention has high stability and service life. It maintains clarity and transparency during long-term storage or long-term plating, and produces tin-plated parts with uniform, stable and highly reproducible plating performance.

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

[0046] The workpiece to be plated is immersed in a neutral bright tin plating solution for electroplating to obtain a tin-plated part; wherein the electroplating temperature is 20℃~40℃; the average current density of electroplating is 1ASD~12ASD; and the electroplating method is DC electroplating or periodic square wave pulse electroplating.

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

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

[0049] The present invention also discloses a neutral bright tin plating solution as described in any embodiment of the present invention, or the application of tin-plated parts obtained by applying any embodiment of the present invention in the manufacture of electronic components or machinery.

[0050] The following are specific embodiments.

[0051] Example 1

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

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

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

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

[0056] (2) Mix luteolin and NP-30 to obtain the 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 resulting mixed solution to adjust the pH of the mixed solution to 7.5, so as to obtain a neutral bright tin plating solution.

[0058] The electroplating solution prepared in this embodiment can be stored at room temperature for more than 6 months. Even under conditions of high and low temperature changes, light exposure, long-term storage, or long-term electroplating, it maintains a pale yellow, clear, and transparent state, without the formation of tin-containing precipitates, oxidative decomposition of additives, or discoloration. Figure 1 As shown, Figure 1 The state diagram of the neutral bright tin plating solution prepared for this embodiment after being stored at room temperature for 6 months.

[0059] Electroplating was performed using the neutral bright tin plating solution of this embodiment. The electroplating anode was a platinum-titanium mesh, and the electroplating cathode was a silicon wafer with a Cu seed layer sputtered on its surface. The anode and cathode were immersed in the electroplating solution of this embodiment for electroplating. Direct current electroplating was used, the electroplating temperature was 30°C, and the average current density of electroplating was 4 ASD. The electroplating produced tin-plated parts with good adhesion, a porosity of 4%, uniform density, and a bright appearance.

[0060] Example 2

[0061] The neutral bright tin plating solution of this embodiment includes components of the following concentrations:

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

[0063] The preparation method of the neutral bright tin plating solution in this embodiment includes the following steps:

[0064] (1) Sodium stannate and potassium mercaptoacetate are mixed to obtain the 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 resulting mixed solution to adjust the pH of the mixed solution to 6.2, so as to obtain a neutral bright tin plating solution.

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

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

[0069] Example 3

[0070] The neutral bright tin plating solution of this embodiment includes components of the following concentrations:

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

[0072] The preparation method of the neutral bright tin plating solution in this embodiment includes the following steps:

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

[0074] (2) Mix morin and NP-40 to obtain the 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 resulting mixed solution to adjust the pH of the mixed solution to 7.0, so as to obtain a neutral bright tin plating solution.

[0076] The electroplating solution prepared in this embodiment can be stored at room temperature for more than 6 months. Even under conditions such as high and low temperature changes, light exposure, long-term storage, or long-term electroplating, it still maintains a light yellow, clear, and transparent state, without the formation of tin-containing precipitates, oxidative decomposition of additives, or discoloration.

[0077] Electroplating was performed using the neutral bright tin plating solution of this embodiment. The plating anode was a platinum-titanium mesh, and the plating cathode was a silicon wafer with a Cu seed layer sputtered on its surface. The anode and cathode were immersed in the plating solution of this embodiment for electroplating using a periodic square wave pulse plating method at a temperature of 30°C. The average current density during plating was 6 ASD. The electroplating produced a tin-plated part with good adhesion, a porosity of 2%, uniform density, and a bright appearance. Figure 2 As shown, Figure 2 The image shows the microstructure of a tin-plated part prepared at an average current density of 6 ASD.

[0078] Comparative Example 1

[0079] The electroplating solution used in this comparative example is an acidic tin plating solution. The only difference between this comparative example and Example 1 is that stannous pyrophosphate is replaced with stannous methanesulfonate. The pH of the acidic tin plating solution used in this comparative example is <1.

[0080] Electroplating was performed using the acidic tin plating solution of this comparative example, and the electroplating method was the same as in Example 1. The resulting tin-plated parts had a porosity greater than 30%, a rough appearance, and burnt edges. This was due to the high acidity of the electroplating solution and the severe hydrogen evolution phenomenon.

[0081] Comparative Example 2

[0082] The only difference between this comparative example and Example 1 is that mercaptoacetic acid is replaced with potassium pyrophosphate.

[0083] The neutral tin plating solution prepared in this comparative ratio formed a large amount of white mud-like tin-containing precipitate after being stored at room temperature for one month. This is because the complexation effect of potassium pyrophosphate on Sn(II) is weak and cannot prevent Sn(II) from being oxidized to Sn(IV). Sn(IV) hydrolyzes and forms a complex colloidal structure precipitate, resulting in low stability of the neutral tin plating solution.

[0084] Comparative Example 3

[0085] The only difference between this comparative example and Example 1 is that the molar concentration of thioglycolic acid is changed to 0.10 mol / L.

[0086] The neutral tin plating solution prepared in this comparative ratio formed a large amount of white mud-like tin-containing precipitate after being stored at room temperature for 4 months. This was because the concentration of mercaptoacetic acid was too low, which could not maintain the high stability of the neutral tin plating solution.

[0087] Comparative Example 4

[0088] The only difference between this comparative example and Example 1 is that the molar concentration of thioglycolic acid is changed to 2.5 mol / L.

[0089] Electroplating was performed using the neutral tin plating solution of this comparative example, and the electroplating method was the same as in Example 1. The resulting tin-plated parts had coarse grains in their microstructure.

[0090] Comparative Example 5

[0091] The only difference between this comparative example and Example 1 is that the concentration of luteolin was changed to 0.01 g / L.

[0092] Electroplating was performed using the neutral tin plating solution of this comparative example. The electroplating method was the same as in Example 1. The resulting tin-plated parts had a rough and dark gray appearance and poor solderability.

[0093] Comparative Example 6

[0094] The only difference between this comparative example and Example 1 is that the concentration of NP-30 is changed to 0.1 g / L.

[0095] The neutral tin plating solution prepared in this comparative ratio precipitated a large amount of yellow aggregates during the preparation process. This was due to the low concentration of NP-30, which failed to completely dissolve luteolin.

[0096] Comparative Example 7

[0097] The only difference between this comparative example and Example 1 is that the degree of polymerization of nonylphenol polyoxyethylene ether is changed to 200 (NP-200).

[0098] The neutral tin plating solution prepared in this comparative ratio generates a large number of bubbles during the electroplating process, which are difficult to eliminate, making the electroplating work impossible.

[0099] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by 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 dispersant is a nonylphenol polyoxyethylene ether; The pH of the neutral bright tin plating solution is 6.0~8.0; The tin complexing agent has a molar concentration of 0.10 mol / L to 2.00 mol / L in the electroplating solution; the brightener has a concentration of 0.02 g / L to 0.30 g / L in the electroplating solution; and the dispersant has a concentration of 1.00 g / L to 5.00 g / L in the electroplating solution. The molar concentration ratio of the tin salt to the tin complexing agent is 1:(1~5). The tin salts include Sn(II) salts and / or Sn(IV) salts; The tin complexing agent is at least one selected from mercaptoacetic acid, potassium mercaptoacetate, sodium mercaptoacetate, and ammonium mercaptoacetate. The brightening agent is at least one of morin, quercetin, phytic acid and luteolin; The degree of polymerization of the nonylphenol polyoxyethylene ether is 20-50.

2. A method for preparing the neutral bright tin plating solution as described in claim 1, characterized in that, Includes the following steps: (1) Mix the tin salt and the tin complexing agent to obtain the first reaction solution; (2) Mix the brightener and nonylphenol polyoxyethylene ether to obtain the second reaction solution; (3) Mix the first reaction solution and the second reaction solution, and add a pH buffer to the resulting mixed solution to adjust the pH of the mixed solution to 6.0~8.0, so as to obtain the neutral bright tin plating solution.

3. An application of the neutral bright tin plating solution as described in claim 1 in the preparation of tin-plated parts.

4. The application according to claim 3, characterized in that, The application includes the following steps: The workpiece to be plated is immersed in the neutral bright tin plating solution for electroplating to obtain a tin-plated part. The electroplating temperature is 20 ℃~40 ℃; The average current density of the electroplating is 1 ASD to 12 ASD; The electroplating method is either DC electroplating or periodic square wave pulse electroplating.

5. The application according to claim 4, characterized in that, The porosity of the tin-plated part is less than 5%.

6. The application of a neutral bright tin plating solution as described in claim 1, or the tin-plated parts obtained by the application as described in any one of claims 3-5, in the manufacture of electronic components or machinery.

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