CN110760902B

CN110760902B - Tin electroplating solution and preparation method and application thereof

Info

Publication number: CN110760902B
Application number: CN201911200983.2A
Authority: CN
Inventors: 刘江波; 林章清; 章晓冬; 童茂军; 王亚君
Original assignee: Shanghai Tiancheng Chemical Co ltd
Current assignee: Shanghai Tiancheng Chemical Co.,Ltd.
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2022-01-25
Anticipated expiration: 2039-11-29
Also published as: CN110760902A

Abstract

The invention provides a tin electroplating solution and a preparation method and application thereof. The tin electroplating solution comprises the following components in percentage by mass: 10-50g/L stannous sulfate, 50-200g/L sulfuric acid, 0.05-5g/L wetting agent, 0.01-2g/L antioxidant and 0.01-2g/L grain refiner; the solvent of the tin electroplating solution is water; the crystal refiner is a flavonoid compound. The tin electroplating liquid adopts stannous sulfate as main salt, sulfuric acid as electrolyte to increase conductivity, and wetting agent, antioxidant and grain refiner are added, and all the components are mutually matched to play a synergistic effect, so that the production efficiency is greatly improved and the tin source is saved under the condition of reaching the same coating thickness; meanwhile, the compactness of the tin coating can be improved, so that the tin coating has better alkaline corrosion resistance.

Description

Tin electroplating solution and preparation method and application thereof

Technical Field

The invention belongs to the technical field of electrochemical deposition of metals, and particularly relates to a tin electroplating solution and a preparation method and application thereof.

Background

Tin is a non-toxic white metal, has strong oxidation resistance and sulfide corrosion resistance, has good chemical stability, and has excellent weldability and electrical conductivity. The good corrosion resistance of tin is utilized in the manufacturing process of the printed circuit board, and the tin has the function of protecting the required copper circuit in alkaline copper chloride etching solution. At present, a great deal of electroplating additive research work is mainly carried out on common electroplating, and the electroplating with wide current density is difficult to be sufficient. Particularly, for electroplating pure tin, a large amount of air is involved, so that oxidation of divalent tin is caused under the condition of a large amount of air, and foam of a plating solution is increased easily, so that wettability of a sample and the plating solution is influenced, and the performance of the sample is deteriorated. In addition, the short electroplating time can cause the thickness of the electroplated tin to be too thin in the practical production and application process, if the thickness of the tin is not enough, crystals are not refined enough, the compactness of a plating layer is poor, and etching solution enters the inner layer through a slit to corrode copper.

CN102418123A discloses a high-speed electroplating bright tin plating electroplating solution and a preparation method and application thereof. The raw materials of the material comprise 120-200mL tin methanesulfonate, 100-175mL 70 wt% methanesulfonic acid, 0.03-5g brightener, 30-45g conductive salt, 1-10g grain refiner, 5-20g antioxidant, 0.5-2g wetting agent, 0.0005-0.001g antifoaming agent and the balance of water. The plating layer prepared by the electroplating solution has high organic matter content and high brittleness, can not meet the requirement of an electronic device on the flexibility of the plating layer, has poor displacement effect, and particularly has copper leakage at a low potential in the barrel plating process.

CN104060308A discloses a pure tin electroplating solution for reducing copper exposure and application thereof, wherein the acid electroplating solution adopts a mixed solution of methanesulfonic acid and sulfuric acid, the tin salt adopts a mixed solution of soluble divalent tin salt and hydrogen peroxide, and antioxidant, adjuvant, brightener, wetting agent, surfactant and other components are added.

CN105648483A discloses a high-speed tin plating solution and a preparation method thereof, wherein the tin plating solution mainly comprises methanesulfonic acid, stannous methanesulfonate, an antioxidant, a grain refiner and a surfactant, the tin plating solution can improve the plating speed to a certain extent, but a plating layer prepared from an electroplating solution has high organic matter content, large brittleness and poor compactness, and an etching solution enters an inner layer through a slit to corrode copper.

Therefore, developing a tin electroplating solution with good coating compactness and shorter time consumption under the condition of achieving the same coating thickness in the electroplating process is of great significance.

Disclosure of Invention

In view of the defects of the prior art, the invention aims to provide a tin electroplating solution, a preparation method and application thereof, wherein the tin electroplating solution has excellent dispersing capacity, can improve the compactness of a tin coating and has better alkaline corrosion resistance.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a tin plating solution comprising, by mass concentration:

the solvent of the tin electroplating solution is water;

the crystal refiner is a flavonoid compound.

In the invention, the mass concentration of the stannous sulfate is 10-50g/L, for example, 10g/L, 12g/L, 14g/L, 16g/L, 18g/L, 20g/L, 22g/L, 24g/L, 26g/L, 28g/L, 30g/L, 32g/L, 34g/L, 36g/L, 38g/L, 40g/L, 42g/L, 44g/L, 46g/L, 48g/L and 50 g/L.

In the present invention, the mass concentration of the sulfuric acid is 50-200g/L, for example, 50g/L, 60g/L, 70g/L, 80g/L, 90g/L, 100g/L, 110g/L, 120g/L, 130g/L, 140g/L, 150g/L, 160g/L, 170g/L, 180g/L, 190g/L, 200 g/L.

In the present invention, the wetting agent may be contained at a mass concentration of 0.05 to 5g/L, for example, 0.05g/L, 0.06g/L, 0.07g/L, 0.08g/L, 0.09g/L, 0.1g/L, 0.2g/L, 0.3g/L, 0.4g/L, 0.5g/L, 0.6g/L, 0.7g/L, 0.8g/L, 0.9g/L, 1g/L, 1.2g/L, 1.4g/L, 1.6g/L, 1.8g/L, 2g/L, 2.2g/L, 2.4g/L, 2.6g/L, 2.8g/L, 3g/L, 3.5g/L, 4g/L, 4.5g/L, 5g/L, or the like.

In the present invention, the antioxidant may be present at a mass concentration of 0.01 to 2g/L, for example, 0.01g/L, 0.02g/L, 0.04g/L, 0.06g/L, 0.08g/L, 0.1g/L, 0.2g/L, 0.3g/L, 0.4g/L, 0.5g/L, 0.6g/L, 0.7g/L, 0.8g/L, 0.9g/L, 1.2g/L, 1.4g/L, 1.6g/L, 1.8g/L, or 2 g/L.

In the present invention, the mass concentration of the grain refiner is 0.01 to 2g/L, and may be, for example, 0.01g/L, 0.02g/L, 0.04g/L, 0.06g/L, 0.08g/L, 0.1g/L, 0.2g/L, 0.3g/L, 0.4g/L, 0.5g/L, 0.6g/L, 0.7g/L, 0.8g/L, 0.9g/L, 1.2g/L, 1.4g/L, 1.6g/L, 1.8g/L, or 2 g/L.

In the invention, the tin plating of the stannous sulfate-sulfuric acid system has high current efficiency, high deposition speed and easily obtained raw materials. The grain refiner is a flavonoid compound, can well promote the speed of crystal nucleus formation to be higher than the speed of crystal nucleus growth, has more crystal nuclei and finer tin grains, and can obtain a dense tin layer, small pores and a bright surface, thereby producing a very uniform plating layer with consistent grains. The wetting agent, the antioxidant and the grain refiner are matched with each other to play a synergistic role, and have excellent plating rate, dispersing capacity and anti-foaming capacity. In the electroplating process, additives such as brightener and the like are reduced, the problems of high organic matter content and high coating brittleness in the prepared coating are avoided, and the production cost of electroplating and tinning can be reduced.

Preferably, the tin electroplating solution comprises the following components in percentage by mass:

the solvent of the tin electroplating solution is water;

the crystal refiner is a flavonoid compound.

Preferably, the wetting agent comprises any one of or a combination of at least two of alkylphenol ethoxylates, alkyl ethoxylates or fatty alcohol alkoxy compounds.

As a preferable scheme of the invention, the wetting agent is a combination of alkylphenol ethoxylates, alkyl polyoxyethylene and fatty alcohol alkoxy compounds, and the three wetting agents are matched with each other, so that the synergistic effect can be achieved, the interfacial tension of liquid-gas (plating solution and air) and liquid-solid (plating solution and copper surface) can be further reduced, hydrogen bubbles are more difficult to stay on the surface of a cathode, and dents and pinholes on a plating layer are well avoided, so that the dispersing capacity and the anti-foaming capacity of the plating solution and the displacement performance of the plating solution are further improved.

Preferably, the alkylphenol ethoxylates have an EO number of 5 to 7, which may be, for example, 5, 6 or 7.

Preferably, the alkylphenol ethoxylate comprises any one of nonylphenol ethoxylate, octylphenol ethoxylate, dodecylphenol ethoxylate or dinonylphenol ethoxylate or a combination of at least two thereof.

Preferably, the alkyl polyoxyethylene ether has an EO number of from 2 to 6, and may be, for example, 2, 3, 4, 5 or 6.

Preferably, the alkyl polyoxyethylene ether comprises any one of dodecyl polyoxyethylene ether, hexadecyl polyoxyethylene ether or octadecyl polyoxyethylene ether or a combination of at least two of the dodecyl polyoxyethylene ether, the hexadecyl polyoxyethylene ether and the octadecyl polyoxyethylene ether.

Preferably, the fatty alcohol alkoxy compound has an EO number of 3 to 7, and may be, for example, 3, 4, 5, 6, 7.

Preferably, the fatty alcohol alkoxy compound comprises any one of or a combination of at least two of lauryl alcohol polyoxyethylene ether sulfonate, cetyl alcohol polyoxyethylene ether sulfonate, isomeric lauryl alcohol polyoxyethylene ether, isomeric pentadecyl alcohol polyoxyethylene ether or lauryl alcohol polyoxyethylene ether.

Preferably, the antioxidant comprises any one or a combination of at least two of hydroquinone, catechol, resorcinol, sodium hypophosphite, vitamin C, gluconic acid or citric acid.

Preferably, the flavonoid compound comprises any one or a combination of at least two of ginkgetin, morin, baicalein, baicalin, hesperetin, liquiritin, daidzein, puerarin, snapdragon or 2-phenyl chromone, and is preferably morin and morin.

Preferably, the ginkgetin is ginkgetin.

Preferably, the ginkgetin comprises any one or a combination of at least two of quercetin, kaempferide, isorhamnetin, myricetin, luteolin and tricin.

In a second aspect, the present invention provides a method for preparing the tin plating solution according to the first aspect, the method comprising: weighing sulfuric acid with a formula ratio, adding the sulfuric acid into water, mixing, and adding stannous sulfate, a wetting agent, an antioxidant and a grain refiner to obtain the tin electroplating solution.

In a third aspect, the present invention provides the use of a tin electroplating bath as described in the first aspect for the preparation of a tin coating.

Preferably, the preparation method of the tin plating layer comprises the following steps: and electrifying to carry out electroplating by using a pure tin plate as an anode and a plated piece as a cathode to obtain a tin plating layer.

Preferably, the plated piece is a copper wire or a copper plate.

Preferably, the area ratio of the cathode to the anode is (0.5-2: 1, and may be, for example, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2: 1.

Preferably, the plating temperature is 20-40 ℃, for example, can be 20 ℃, 22 ℃, 24 ℃, 26 ℃, 28 ℃, 30 ℃, 32 ℃, 34 ℃, 36 ℃, 38 ℃, 40 ℃.

Preferably, the time of the electroplating is 1-2min, for example, 1min, 1.1min, 1.2min, 1.3min, 1.4min, 1.5min, 1.6min, 1.7min, 1.8min, 1.9min, 2 min.

Preferably, the current density of the electroplating is 10-30mA/cm²For example, it may be 10mA/cm²、11mA/cm²、12mA/cm²、14mA/cm²、16mA/cm²、18mA/cm²、20mA/cm²、22mA/cm²、24mA/cm²、26mA/cm²、28mA/cm²、30mA/cm²。

The tin plating layer preferably has a thickness of 1 to 5 μm, and may be, for example, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm.

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

(1) the tin electroplating liquid provided by the invention adopts stannous sulfate as a main salt, sulfuric acid as an electrolyte to increase conductivity, and a wetting agent, an antioxidant and a grain refiner are added, so that the components are mutually matched to play a synergistic effect, and the tin electroplating liquid has excellent dispersing capacity, anti-foaming capacity and displacement performance, and thus the production efficiency is greatly improved under the condition of achieving the same plating thickness.

(2) The tin electroplating solution has the advantages of high current efficiency, less hydrogen evolution, high deposition rate and wide working current density in the electroplating process, and the prepared tin plating layer has good corrosion resistance, fine tin grains, compact tin layer, small pores and bright surface.

Drawings

FIG. 1 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by the tin plating solution prepared in example 1.

FIG. 2 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by the tin plating solution prepared in example 2.

FIG. 3 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by the tin plating solution prepared in example 3.

FIG. 4 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by the tin plating solution prepared in example 4.

FIG. 5 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by the tin plating solution prepared in comparative example 1.

FIG. 6 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by the tin plating solution prepared in comparative example 2.

FIG. 7 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by the tin plating solution prepared in comparative example 3.

FIG. 8 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by the tin plating solution prepared in comparative example 4.

Detailed Description

The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

Example 1

The present embodiment provides a tin plating solution, which includes the following components by mass:

the preparation method of the tin electroplating solution described in this example is as follows: weighing sulfuric acid with a formula ratio, adding the sulfuric acid into water, mixing, and adding stannous sulfate, a wetting agent, an antioxidant and a grain refiner to obtain the tin electroplating solution.

Example 2

Example 3

Example 4

Example 5

Example 6

Example 7

Example 8

Example 9

Example 10

Comparative example 1

This comparative example provides a tin electroplating bath, similar to example 1, differing only in that: the stannous sulfate is replaced by stannous methanesulfonate, the sulfuric acid is replaced by methanesulfonic acid, and the content of other components and the preparation method are unchanged.

Comparative example 2

This comparative example provides a tin electroplating bath, similar to example 1, differing only in that: the stannous sulfate is replaced by stannous methanesulfonate, and the content of other components and the preparation method are not changed.

Comparative example 3

This comparative example provides a tin electroplating bath, similar to example 1, differing only in that: the sulfuric acid is replaced by methanesulfonic acid, and the content of other components and the preparation method are not changed.

Comparative example 4

This comparative example provides a tin electroplating bath, similar to example 1, differing only in that: no wetting agent is added, and the contents of other components and the preparation method are not changed.

Comparative example 5

This comparative example provides a tin electroplating bath, similar to example 1, differing only in that: no antioxidant is added, and the contents of other components and the preparation method are unchanged.

Comparative example 6

This comparative example provides a tin electroplating bath, similar to example 1, differing only in that: no crystal refiner is added, and the contents of other components and the preparation method are unchanged.

Comparative example 7

The present comparative example provides a tin electroplating solution, which comprises the following components by mass concentration:

Comparative example 8

Test example 1

Plating solution Performance test

(1) And (4) testing the stability of the plating solution: using the high temperature oxidation resistance test method, 50mL each of the tin plating solutions prepared in examples 1 to 10 and comparative examples 1 to 8 was placed in a 100mL open beaker, and the thermostat water bath was heated from room temperature, and the temperature at which cloudiness began to appear was recorded.

(2) And (3) testing the uniform plating capability: the method is characterized in that a far-near cathode method is adopted for determination, a plating bath is a transparent organic glass rectangular bath (the size of an inner cavity is 150mm multiplied by 50mm multiplied by 70mm), five small baths are uniformly arranged on two sides of the bath for inserting cathodes, the cathodes are red copper sheets with the thickness of 1mm, the size is 50mm multiplied by 80mm, the working surface is smooth and bright, the non-working surface is insulated by insulating paint, and a perforated anode with the same size as the cathodes is used for facilitating the flowing of a plating solution. Placing the anode between two cathode test pieces, and using 20mA/cm²Electroplating for 2min, taking out the cathode, cleaning, weighing the increment of the deposited metal on the far and near cathodes, and calculating the dispersing capacity of the plating solution according to the following formula.

Wherein T represents the dispersibility (%), K represents the far-cathode and near-cathode and anodeDistance ratio, m₁Mass (g) of metal deposited on the near-cathode; m is₂Mass (g) of metal deposited on the remote cathode.

(3) And (3) testing the deposition speed: placing the test piece (50mm × 25mm × 0.4mm copper piece) into a pilot plating tank, and using 20mA/cm under optimum condition²Electroplating for 2min, and measuring the thickness of the deposited coating.

The results of the performance tests of the tin plating solutions prepared in examples 1 to 10 and the tin plating solutions prepared in comparative examples 1 to 8 are shown in Table 1:

TABLE 1

Sample (I)	Temperature at the time of clouding (. degree. C.)	Dispersibility (%)	Coating thickness (μm)
				Example 1	45	97.59	4.5μm
Example 2	43	97.62	4.6μm
				Example 3	44	98.28	4.7μm
Example 4	43	98.23	4.6μm
				Example 5	44	97.88	4.8μm
Example 6	40	95.32	4.2μm
				Example 7	39	96.22	4.0μm
Example 8	39	95.12	3.8μm
				Example 9	40	95.63	3.9μm
Example 10	41	95.21	3.7μm
				Comparative example 1	33	90.14	1.1μm
Comparative example 2	32	87.00	2.2μm
				Comparative example 3	31	89.23	3.1μm
Comparative example 4	33	88.65	1.9μm
				Comparative example 5	35	85.12	1.8μm
Comparative example 6	37	84.23	2.1μm
				Comparative example 7	36	82.56	2.1μm
Comparative example 8	35	85.19	3.2μm

From the above test data, it can be seen that the tin plating solutions prepared in examples 1 to 10 have a temperature of 39 ℃ or higher and a dispersing ability of 95% or higher when turbid, while the tin plating solutions prepared in comparative examples 1 to 8 have a dispersing ability of 90% or lower, which proves that the components of the additive of the present invention cooperate with each other to promote the dispersing ability of the plating solution well, thereby further improving the throwing power.

The plating thickness of the tin plating solutions prepared in examples 1 to 10 reached 3.5 μm or more in a short time (2 min); the plating thicknesses of the tin plating solutions prepared in comparative examples 1 to 8 were not the same as those of the plating solutions provided in this example over the same period of time. This fully explains that the electroplating speed of the tin electroplating solution is greatly improved under the condition of reaching the same plating thickness, so that the tin source can be saved, the production cost is reduced, and the industrialization is facilitated.

Test example 2

Test of plating Properties

The same test pieces (50 mm. times.25 mm. times.0.4 mm red copper pieces) were placed in a pilot plating bath and immersed in the tin plating solutions prepared in examples 1 to 10 and comparative examples 1 to 8, respectively, at 20mA/cm²Electroplating for 2min to obtain a tin coating attached to the surface of the copper sheet.

(1) Test for Corrosion resistance

And soaking the tin-plated test piece in an alkaline etching solution for 2min, soaking the test piece in a tin-stripping solution for 2min, rinsing the test piece with deionized water, drying, and observing whether the obtained copper surface is corroded to generate holes.

(2) Discoloration resistance test

After the plating of the plating layer is finished, trisodium phosphate (50-80g/L) is used for neutralization at the temperature of 50-60 ℃, and then the plating layer is washed clean by hot water and dried. And (3) placing the treated workpiece into a baking oven, baking for 20 hours at 160 ℃, and observing whether the plating layer has a color change phenomenon.

(3) Electron microscope results

The appearance of the tin plating layer on the surface of each sample copper sheet was observed under an SEM scanning electron microscope (Hitachi 3400N). (FIG. 1 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by a tin plating solution prepared in example 1, FIG. 2 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by a tin plating solution prepared in example 2, FIG. 3 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by a tin plating solution prepared in example 3, FIG. 4 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by a tin plating solution prepared in example 4, FIG. 5 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by a tin plating solution prepared in comparative example 1, FIG. 6 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by a tin plating solution prepared in comparative example 2, FIG. 7 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by a tin plating solution prepared in comparative example 3, and FIG. 8 is a scanning electron microscope photograph of a tin plating layer formed on the surface of a copper sheet by a tin plating solution prepared in comparative example 4).

TABLE 2

The test data show that the tin plating layer prepared by using the tin electroplating solution has good corrosion resistance and strong discoloration prevention performance.

In addition, the scanning electron microscope images of the tin plating layers of the examples and the comparative examples show that the tin plating layers prepared by the tin plating solutions of the examples 1 to 4 have fine tin crystal grains, dense tin layers, small pores and bright surfaces; the tin coating prepared by the comparative example has the phenomena of thick tin crystal grains, loose tin layer and large pores in different degrees. Among them, the tin plating layer prepared from the tin plating solution of comparative example 1 and the tin plating layer prepared from the tin plating solution of comparative example 2 showed a columnar tin crystal, and could not completely cover the base copper. The tin plating layer prepared from the tin plating solution of comparative example 3 and the tin plating layer prepared from the tin plating solution of comparative example 4 showed tin crystals in a sheet form, although the base copper was completely covered, the band gap was large, and the etching solution easily permeated into the base copper to corrode it.

The applicant states that the present invention is illustrated by the above examples of the tin plating solution of the present invention, the method of preparing the same and the use thereof, but the present invention is not limited to the above examples, that is, it is not intended that the present invention is necessarily implemented by the above examples. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. The tin electroplating solution is characterized by comprising the following components in percentage by mass:

the solvent of the tin electroplating solution is water;

the wetting agent is the combination of dodecyl phenol polyoxyethylene ether, hexadecyl polyoxyethylene ether and fatty alcohol alkoxy compound; the fatty alcohol alkoxy compound comprises any one or the combination of at least two of isomeric dodecyl alcohol polyoxyethylene ether, isomeric pentadecyl alcohol polyoxyethylene ether or lauryl alcohol polyoxyethylene ether;

the crystal refiner is a flavonoid compound, and the flavonoid compound comprises the combination of at least two of ginkgetin, morin, baicalein, baicalin or 2-phenylchromone.

2. The tin plating solution as recited in claim 1, wherein said dodecylphenol polyoxyethylene ether has an EO number of 5 to 7.

3. The tin plating solution as recited in claim 1, wherein said cetylpolyoxyethylene ether has an EO number of 2 to 6.

4. The tin electroplating solution as set forth in claim 1, wherein the fatty alcohol alkoxy compound has an EO number of 3 to 7.

5. The tin electroplating bath as set forth in claim 1 wherein the antioxidant comprises any one or a combination of at least two of hydroquinone, catechol, resorcinol, sodium hypophosphite, ascorbic acid, gluconic acid, or citric acid.

6. The tin electroplating solution as set forth in claim 1, wherein the ginkgetin comprises any one of quercetin, kaempferide, isorhamnetin, myricetin, luteolin, or tricin, or a combination of at least two thereof.

7. The method for producing a tin plating solution according to any one of claims 1 to 6, characterized by: weighing sulfuric acid with a formula ratio, adding the sulfuric acid into water, mixing, and adding stannous sulfate, a wetting agent, an antioxidant and a grain refiner to obtain the tin electroplating solution.

8. Use of a tin electroplating bath according to any one of claims 1 to 6 for the preparation of tin coatings.

9. The use according to claim 8, wherein the tin coating is prepared by a method comprising: and electrifying to carry out electroplating by using a pure tin plate as an anode and a plated piece as a cathode to obtain a tin plating layer.

10. Use according to claim 9, wherein the plated part is a copper wire or a copper plate.

11. The use according to claim 9, wherein the area ratio of the cathode to the anode is (0.5-2): 1.

12. Use according to claim 9, wherein the temperature of the electroplating is 20-40 ℃.

13. Use according to claim 9, wherein the time of electroplating is 0.5-2 min.

14. Use according to claim 9, wherein the galvanic density of the electroplating is 10-30mA/cm²。

15. Use according to claim 9, characterised in that the tin coating has a thickness of 1-5 μm.