Electroplating method of low-porosity nanoscale bright tin layer

Abstract

The invention discloses an electroplating method of a low-porosity nanoscale bright tin layer, which comprises the following steps: placing a clean metal substrate in an activating solution containing a surface modifier, and applying high pulse current for short-time impact to form a transition layer to obtain a target substrate; a target base material is placed in the nano-composite tin plating solution, electroplating is carried out under the cooperation of a continuous ultrasonic field and target waveform pulse current, and a low-porosity nano-scale bright tin layer is formed; the nanometer composite tin plating solution comprises stannous methanesulfonate, methanesulfonic acid, nanometer silicon carbide, nanometer silicon dioxide, a grain refiner, a dispersing agent, cinnamyl aldehyde, a vinyl pyrrolidone copolymer, ascorbic acid, a wetting agent and the balance deionized water. The binding force of a plating layer without a base coat is improved, the plating layer is strengthened, compact and bright, and the process is environmentally friendly.

Description

Technical Field

[0001] This application relates to the field of electroplating technology, and in particular to an electroplating method for a low-porosity nanoscale bright coating. Background Technology

[0002] Tin plating is widely used in electronic components and other fields due to its excellent solderability, conductivity, and corrosion resistance. With the miniaturization and high reliability of electronic products, there are increasing demands for low porosity, high brightness, and strong adhesion in tin plating. Therefore, traditional processes typically rely on multi-layered base systems such as zinc immersion-copper cyanide-acid copper plating, and add brighteners and nanoparticles (such as...) to the plating bath. , ).

[0003] However, traditional undercoating processes are lengthy and involve highly toxic cyanide, posing significant environmental risks. Conventional brighteners, while pursuing high gloss, often increase internal stress and reduce toughness in the coating, making it more prone to peeling due to stress during direct plating. Furthermore, directly added nanoparticles are highly susceptible to agglomeration and sedimentation in strongly acidic plating solutions, failing to achieve the nanoscale effect and instead exacerbating solution instability and creating defects in the coating, leading to increased porosity and uneven performance. While dispersants can partially alleviate agglomeration, they struggle to maintain long-term uniform dispersion of nanoparticles and effective co-deposition with metal ions during the dynamic electrodeposition process. Therefore, achieving ultra-high adhesion, low porosity, mirror-like gloss, and a green and stable process on the substrate simultaneously without the need for an undercoating remains a pressing technological bottleneck. Summary of the Invention

[0004] This application provides an electroplating method for low-porosity nanoscale bright coatings to solve the technical problems that traditional processes cannot achieve ultra-high adhesion, low porosity, mirror-like brightness, and green and stable processes.

[0005] This application provides a method for electroplating a low-porosity nanoscale bright tin layer, comprising: A clean metal substrate is placed in an activation solution and subjected to a short-term high-pulse current to form a transition layer, thus obtaining the target substrate. The target substrate is placed in a nanocomposite tin plating solution and electroplated under the synergistic effect of a continuous ultrasonic field and a target waveform pulsed current to form a low-porosity nanoscale bright tin layer; wherein each liter of the nanocomposite tin plating solution comprises the following components: Stannous methanesulfonate 60g / L~120g / L, methanesulfonic acid 100mL / L~200mL / L, nano silicon carbide 5g / L~15g / L, nano silica 5g / L~15g / L, grain refiner 0.5g / L~3g / L, dispersant 3g / L~5g / L, cinnamaldehyde 2mL / L~5mL / L, vinylpyrrolidone copolymer 5mL / L~15mL / L, ascorbic acid 0.1g / L~0.5g / L, wetting agent 0.05g / L~0.3g / L, balance deionized water.

[0006] Optionally, the particle size of nano-silicon carbide and nano-silicon dioxide is 10nm~50nm.

[0007] In some of these embodiments, the grain refiner is any one of magnesium sulfate, zinc sulfate, and cobalt chloride; the dispersant is polyethylene glycol; and the wetting agent is a perfluoroalkyl sulfonate.

[0008] In some embodiments, the preparation method of the nanocomposite tin plating solution includes the following steps: Nano-silicon carbide, nano-silica, dispersant and some deionized water are mixed evenly to obtain a nano suspension. Add methanesulfonic acid to another portion of deionized water, stir well, then add stannous methanesulfonate and grain refiner, stir until completely dissolved, and obtain the main base solution; Under stirring conditions, the nano-suspension is slowly added to the main base liquid and mixed evenly. Then, cinnamaldehyde, vinylpyrrolidone copolymer, ascorbic acid and wetting agent are added and stirred evenly. The volume is then adjusted to 3.0~4.5, and the solution is subjected to combined circulation filtration and ultrasonic curing treatment to obtain the nano-composite tin plating solution.

[0009] In some embodiments, the target waveform pulse current is a ramp pulse current, wherein the current density of the ramp pulse current linearly increases from an initial value of 0.5A / dm² to 1A / dm² to a peak value of 2A / dm² to 5A / dm² within one cycle, and then linearly decreases to an end value of 0.8A / dm² to 1.5A / dm², with a single cycle duration of 2s to 5s.

[0010] In some embodiments, the ultrasonic field is co-modulated with the ramp pulse current: when the current density of the ramp pulse current is rising to its peak, the ultrasonic wave operates continuously at a first power; when the current density of the ramp pulse current is decreasing, the ultrasonic wave switches to an intermittent operating mode, the working cycle of which is a first preset duration of activation followed by a second preset duration of deactivation, and the activation power is a second power, which is greater than the first power.

[0011] In some embodiments, the first power is 300W~500W, the second power is 600W~900W, and the ultrasonic frequency mode is a dual-frequency composite mode including a low frequency of 28kHz~40kHz and a high frequency of 80kHz~100kHz.

[0012] In some of these embodiments, each liter of the activation solution comprises the following components: The solution consists of 5 g / L to 20 g / L of divalent tin salt, 0.5 L to 3 g / L of polyethylene glycol octylphenyl ether or fatty alcohol polyoxyethylene, 10 g / L to 30 g / L of complexing agent, and the balance being deionized water; the complexing agent is one or more of tartaric acid, citric acid or gluconic acid; the divalent tin salt is stannous methanesulfonate or stannous sulfate.

[0013] In some embodiments, the method for preparing the activation solution includes the following steps: Dissolve the complexing agent in a portion of deionized water, then add divalent tin salt and stir until completely dissolved to obtain a tin complex solution; add polyethylene glycol octylphenyl ether or fatty alcohol polyoxyethylene to the tin complex solution, stir evenly, add the remaining deionized water to make up the volume, and adjust the pH value to 1.0~3.0 to obtain the activated solution.

[0014] In some embodiments, the positive peak current density of the high pulse current is 10A / dm² to 30A / dm², the pulse width is 0.1ms to 1ms, the frequency is 50Hz to 200Hz, and the impact time is 10s to 60s.

[0015] In some embodiments, the cleaned metal substrate is any one or more of cleaned aluminum alloy, copper alloy, magnesium alloy, stainless steel, and carbon steel.

[0016] Compared with the prior art, this application has the following beneficial effects: By using an activation solution in conjunction with a high-pulse current to impact the substrate, a micro-anchoring structure is constructed on the substrate surface, effectively solving the problem of weak coating adhesion when no underlayer is applied. A dual nanofiller system is used, consisting of nano-silicon carbide as a hard skeleton and nano-silica as a soft filler, along with a brightener system composed of cinnamaldehyde and vinylpyrrolidone copolymer. Combined with a ramp pulse current to simulate ideal deposition kinetics, the ultrasonic cavitation effect is used to clean the surface, enhance mass transfer, and promote the dispersion and co-deposition of nanoparticles, synergistically achieving enhanced, dense, and bright coatings while ensuring environmentally friendly processing. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the electroplated sample shown in Embodiment 1 of this application; Figure 2 This is a schematic diagram of the electroplated sample shown in Comparative Example 2 of this application. Detailed Implementation

[0018] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0019] As used herein, the terms “prepared from” and “comprising” are synonymous. The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0020] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0021] Furthermore, the indefinite articles “a” and “an” preceding the elements or components of this invention do not impose any limitation on the quantity requirement (i.e., the number of times) of the elements or components. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers to the singular form.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0023] Table 1. Component dosage for Activation Solution Preparation Examples 1-3 (per liter).

[0024] The preparation methods of the activation solution preparation examples 1-3 include the following steps: The complexing agent was completely dissolved in a portion of deionized water at 40℃~50℃ under stirring at 300rpm~400rpm. While stirring, divalent tin salt was added and stirred until completely dissolved to obtain a tin complex solution. Polyethylene glycol octylphenyl ether or fatty alcohol polyoxyethylene was pre-diluted in a small amount of deionized water and then added dropwise to the tin complex solution under vigorous stirring. After stirring evenly, the remaining deionized water was added to make up the volume, and the pH was adjusted to 1.0~3.0 to obtain an activation solution.

[0025] Compared with Preparation Example 1 of Activation Solution, Preparation Example 1 of Comparative Solution did not add polyethylene glycol octylphenyl ether, and was otherwise the same as Preparation Example 1; Compared with the preparation example 1 of the activation solution, the comparative preparation example 2 did not add stannous methanesulfonate and tartaric acid, but was otherwise the same as the preparation example 1.

[0026] Table 2. Component dosage for preparation examples 4-6 of nanocomposite tin plating solution (per 1L)

[0027] The preparation methods of the nanocomposite tin plating solution in Examples 4-6 include the following steps: Nano silicon carbide, nano silica, dispersant and some deionized water are mixed and dispersed at 5000rpm~8000rpm for 10min~15min, and then ultrasonically broken up at 300W~500W for 20min~30min to obtain a uniform nano suspension. Add methanesulfonic acid to another portion of deionized water, stir well, then add stannous methanesulfonate and grain refiner, stir until completely dissolved, and obtain the main base solution; Under stirring conditions, the nano-suspension is slowly added to the main base liquid and mixed evenly. Then, cinnamaldehyde, vinylpyrrolidone copolymer, ascorbic acid and wetting agent are added and stirred evenly until the volume is brought to a final consistency. The pH is adjusted to 3.0~4.5. The solution is then circulated and filtered through a 1μm filter bag at a temperature of 20℃~30℃ and subjected to an ultrasonic field of 40 kHz, 100W for 1h~2h to obtain the nano-composite tin plating solution.

[0028] Compared with the preparation example 4 of the nanocomposite tin plating solution, the comparative preparation example 3 used equal amounts of nano titanium dioxide and nano aluminum oxide to replace nano silicon carbide and nano titanium dioxide, and the rest was the same as the preparation example 4. Compared with the preparation example 4 of the nanocomposite tin plating solution, the comparative preparation example 4 used an equal amount of nano silicon carbide instead of nano silicon dioxide, and the rest was the same as the preparation example 4; Compared with Example 4, the comparative preparation example 5 uses an equal amount of silicon dioxide instead of nano silicon carbide, and the rest is the same as in Example 4. Compared with the preparation example 4 of nanocomposite tin plating solution, the comparative preparation example 6 uses an equal amount of cinnamaldehyde instead of vinylpyrrolidone copolymer, and the rest is the same as the preparation example 4; Compared with the preparation example 4 of nanocomposite tin plating solution, the comparative preparation example 7 uses an equal amount of vinylpyrrolidone copolymer instead of cinnamaldehyde, and the rest is the same as the preparation example 4; Compared with the nanocomposite tin plating solution preparation example 4, the comparative preparation example 8 removed ascorbic acid, and the rest was the same as the preparation example 4. Example 1

[0029] An electroplating method for a low-porosity nanoscale bright tin layer includes: Step 1: The clean aluminum alloy is placed in the activation solution of Preparation Example 1, and a high pulse current with a positive peak current density of 30A / dm², a pulse width of 1ms, and a frequency of 50Hz is applied for 10s to form a transition layer and obtain the target substrate. Step 2: The target substrate is placed in the nanocomposite tin plating solution of Preparation Example 3, and electroplating is performed under the synergy of continuous ultrasonic field and ramp pulse current to form a low-porosity nanoscale bright tin layer. The ramp pulse current linearly increases in current density from an initial value of 0.5 A / dm² to a peak value of 2 A / dm² within one cycle, and then linearly decreases to an end value of 0.8 A / dm², with a single cycle duration of 2 s. When the current density of the ramp pulse current is in the rising to peak stage, the ultrasonic wave operates continuously at 500 W. When the current density of the ramp pulse current is in the decreasing stage, the ultrasonic wave switches to an intermittent working mode. The working cycle of the intermittent working mode is 0.5 s on and 0.5 s off, and the on-power is 900 W. The ultrasonic frequency mode is a dual-frequency composite mode including a 28 kHz low frequency and an 80 kHz high frequency. Example 2

[0030] An electroplating method for a low-porosity nanoscale bright tin layer includes: Step 1: The clean copper alloy is placed in the activation solution of Preparation Example 2, and a high pulse current with a positive peak current density of 20 A / dm², a pulse width of 0.5 ms, and a frequency of 120 Hz is applied for 30 s to form a transition layer and obtain the target substrate. Step 2: The target substrate is placed in the nanocomposite tin plating solution of Preparation Example 4, and electroplating is performed under the synergy of continuous ultrasonic field and ramp pulse current to form a low-porosity nanoscale bright tin layer. The ramp pulse current linearly increases in current density from an initial value of 0.8 A / dm² to a peak value of 3.55 A / dm² within one cycle, and then linearly decreases to an ending value of 1.2 A / dm², with a single cycle duration of 3.5 s. When the current density of the ramp pulse current is rising to its peak, the ultrasonic wave operates continuously at 400 W. When the current density of the ramp pulse current is decreasing, the ultrasonic wave switches to an intermittent working mode. The working cycle of the intermittent working mode is a first preset duration followed by a second preset duration, and the power is 750 W. The ultrasonic frequency mode is a dual-frequency composite mode including a 35 kHz low frequency and a 90 kHz high frequency. Example 3

[0031] An electroplating method for a low-porosity nanoscale bright tin layer includes: Step 1: The clean stainless steel is placed in the activation solution of Preparation Example 3, and a high pulse current with a positive peak current density of 10A / dm², a pulse width of 0.1ms, and a frequency of 50Hz is applied for 60s to form a transition layer and obtain the target substrate. Step 2: The target substrate is placed in the nanocomposite tin plating solution of Preparation Example 6, and electroplating is performed under the synergistic effect of continuous ultrasonic field and ramp pulse current to form a low-porosity nanoscale bright tin layer. The ramp pulse current linearly increases in current density from an initial value of 1 A / dm² to a peak value of 5 A / dm² within one cycle, and then linearly decreases to an end value of 1.5 A / dm², with a single cycle duration of 5 s. When the current density of the ramp pulse current is rising to the peak stage, the ultrasonic wave operates continuously at 300 W. When the current density of the ramp pulse current is decreasing, the ultrasonic wave switches to an intermittent working mode, with a working cycle of 0.5 s on and 0.5 s off, and an on power of 600 W. The ultrasonic frequency mode is a dual-frequency composite mode including a 40 kHz low frequency and a 100 kHz high frequency.

[0032] Comparative Example 1 Compared with Example 1, Comparative Example 1 used the activation solution of Comparative Preparation Example 1, and the rest was the same as in Example 1; Comparative Example 2 Compared with Example 1, Comparative Example 2 used the activation solution of Comparative Preparation Example 2, and the rest was the same as in Example 1; Comparative Example 3 Compared with Example 1, Comparative Example 3 used the nanocomposite tin plating solution of Comparative Preparation Example 3, and the rest was the same as in Example 1; Comparative Example 4 Compared with Example 1, Comparative Example 4 used the nanocomposite tin plating solution of Comparative Preparation Example 4, and the rest was the same as in Example 1; Comparative Example 5 Compared with Example 1, Comparative Example 5 used the nanocomposite tin plating solution of Comparative Preparation Example 5, and the rest was the same as in Example 1; Comparative Example 6 Compared with Example 1, Comparative Example 6 used the nanocomposite tin plating solution of Comparative Preparation Example 6, and the rest was the same as in Example 1; Comparative Example 7 Compared with Example 1, Comparative Example 7 used the nanocomposite tin plating solution of Comparative Preparation Example 7, and the rest was the same as in Example 1; Comparative Example 8 Compared with Example 1, Comparative Example 8 used the nanocomposite tin plating solution of Comparative Preparation Example 8, and the rest was the same as in Example 1; Comparative Example 9 Compared with Example 1, Comparative Example 9 omits step one, and is otherwise the same as Example 1; Comparative Example 10 Compared with Example 1, Comparative Example 10 was electroplated only under the action of ramp pulse current, and the rest was the same as Example 1; Comparative Example 11 Compared with Example 1, Comparative Example 11 was electroplated only under the action of an ultrasonic field, and the rest was the same as Example 1.

[0033] Figure 1 The electroplating sample of Example 1, Figure 2 As shown in the comparison of the electroplated samples in Example 1 and Comparison 2, the sample in Example 1 exhibits higher surface gloss and integrity than the sample in Comparison 2. It should be understood that... Figure 1 and 2 The yellowish tint of the sample is due to light reflection; it is actually silvery-white.

[0034] 1. Coating adhesion test: Following the ASTM D3359 grid cutting method, a 6×6 grid (2mm spacing) was fabricated. 3M 610 adhesive tape was applied to the grid area under pressure and then quickly peeled off at a 90° angle. The coating peeling was then examined under a microscope. The test results are shown in Table 4.

[0035] Table 3. Grading Criteria for ASTM D3359 Mesh Cutting Method Results:

[0036] 2. Coating gloss test: Referring to ISO 2813, a calibrated 60° angle gloss meter was used to measure 10 points on the coating surface, and the average value was taken. The test results are shown in Table 4. Evaluation criteria: GU>850 indicates high gloss, 600≤GU≤850 indicates semi-gloss, and GU<600 indicates matte.

[0037] 3. Coating porosity test: Refer to ISO 4524-2 (sticker method), immerse filter paper in the test solution (10 g / L). Add 10g / L NaCl and 5 drops of surfactant, then firmly attach the soaked filter paper to the clean coating surface, ensuring no air bubbles, and allow it to remain in contact for 10 minutes. Remove the filter paper and measure the area per unit area (cm²). 2 The number of blue spots on the coating, with each blue spot corresponding to a pore on the coating, is shown in Table 4.

[0038] Table 4 Test results of sample coating performance

[0039] As shown in Table 4, Examples 1 to 3 used an activation solution to impact the substrate with a high-pulse current, and the nano-composite tin plating solution was electroplated on the substrate under the synergistic effect of ultrasound and ramp pulse current, achieving ultra-high adhesion (all reaching level 5), mirror-like brightness (gloss > 900 GU), and extremely low porosity (1~4 particles / cm). 2 ).

[0040] Compared with Example 1, Comparative Example 1 (the activating solution lacks a surfactant) has insufficient uniformity in its transition layer, resulting in slight edge peeling and increased porosity during the bonding strength test.

[0041] Comparative Example 2 (without activation solution) The complexing agent and Comparative Example 9 (without activation step) resulted in the substrate lacking an effective interfacial transition layer, leading to adhesion failure (level 0) or severe deterioration (level 1), accompanied by a surge in porosity (>35 porosity / cm²); and Comparative Example 2 lacked... The pseudo-activator after the complexing agent damages the substrate surface under high pulse current, resulting in a worse effect than Comparative Example 9.

[0042] Comparative Examples 3-5 replaced the nanofiller with / Alternatively, using a single filler, the porosity will increase to 12-22 porosities / cm², while the brightness will decrease simultaneously, indicating that SiC / The combination offers unique synergistic advantages in achieving low porosity.

[0043] Comparative Examples 6-8 disrupted the brightener system composed of cinnamaldehyde, PVP, and ascorbic acid. Insufficient leveling ability or coarse grain size significantly reduced gloss and affected adhesion. The lack of ascorbic acid further hampered the brightener's effectiveness. The plating solution protection and the positive synergistic effect on the brightener resulted in an increase in porosity to 11 cells / cm².

[0044] Comparative Examples 10-11, lacking either ultrasound or pulsed current physical fields, showed significantly lower porosity (14-16 particles / cm²) and brightness (850 GU-870 GU) compared to Example 1, indicating that multi-physics synergy plays an effective role in optimizing mass transfer and controlling deposition kinetics.

[0045] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0046] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit the scope of protection of this application. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application for those skilled in the art.

Claims

1. A method for electroplating a low-porosity nanoscale bright tin layer, characterized in that, include: A clean metal substrate is placed in an activation solution and subjected to a short-term high-pulse current to form a transition layer, thus obtaining the target substrate. The target substrate is placed in a nanocomposite tin plating solution and electroplated under the synergistic effect of a continuous ultrasonic field and a target waveform pulsed current to form a low-porosity nanoscale bright tin layer; wherein each liter of the nanocomposite tin plating solution comprises the following components: Stannous methanesulfonate 60g / L~120g / L, methanesulfonic acid 100mL / L~200mL / L, nano silicon carbide 5g / L~15g / L, nano silica 5g / L~15g / L, grain refiner 0.5g / L~3g / L, dispersant 3g / L~5g / L, cinnamaldehyde 2mL / L~5mL / L, vinylpyrrolidone copolymer 5mL / L~15mL / L, ascorbic acid 0.1g / L~0.5g / L, wetting agent 0.05g / L~0.3g / L, balance deionized water.

2. The electroplating method for a low-porosity nanoscale bright tin layer as described in claim 1, characterized in that, The grain refiner is any one of magnesium sulfate, zinc sulfate, and cobalt chloride; the dispersant is polyethylene glycol; and the wetting agent is perfluoroalkyl sulfonate.

3. The electroplating method for a low-porosity nanoscale bright tin layer as described in claim 1, characterized in that, The preparation method of the nanocomposite tin plating solution includes the following steps: Nano-silicon carbide, nano-silica, dispersant and some deionized water are mixed evenly to obtain a nano suspension. Add methanesulfonic acid to another portion of deionized water, stir well, then add stannous methanesulfonate and grain refiner, stir until completely dissolved, and obtain the main base solution; Under stirring conditions, the nano-suspension is slowly added to the main base liquid and mixed evenly. Then, cinnamaldehyde, vinylpyrrolidone copolymer, ascorbic acid and wetting agent are added and stirred evenly. The volume is then adjusted to 3.0~4.5, and the solution is subjected to combined circulation filtration and ultrasonic curing treatment to obtain the nano-composite tin plating solution.

4. The electroplating method for a low-porosity nanoscale bright tin layer as described in claim 1, characterized in that, The target waveform pulse current is a ramp pulse current. Within one cycle, the current density of the ramp pulse current linearly increases from the initial value of 0.5A / dm²~1A / dm² to the peak value of 2A / dm²~5A / dm², and then linearly decreases to the end value of 0.8A / dm²~1.5A / dm². The duration of a single cycle is 2s~5s.

5. The electroplating method for a low-porosity nanoscale bright tin layer as described in claim 4, characterized in that, The ultrasonic field is modulated in coordination with the ramp pulse current: when the current density of the ramp pulse current is rising to its peak, the ultrasonic wave operates continuously at a first power; when the current density of the ramp pulse current is decreasing, the ultrasonic wave switches to an intermittent working mode. The working cycle of the intermittent working mode is to be turned on for a first preset duration and then turned off for a second preset duration, and the power is the second power, which is greater than the first power.

6. The electroplating method for a low-porosity nanoscale bright tin layer as described in claim 5, characterized in that, The first power is 300W~500W, the second power is 600W~900W, and the ultrasonic frequency mode is a dual-frequency composite mode including a low frequency of 28kHz~40kHz and a high frequency of 80kHz~100kHz.

7. The electroplating method for a low-porosity nanoscale bright tin layer as described in claim 1, characterized in that, Each liter of the activation solution comprises the following components: The solution consists of 5 g / L to 20 g / L of divalent tin salt, 0.5 L to 3 g / L of polyethylene glycol octylphenyl ether or fatty alcohol polyoxyethylene, 10 g / L to 30 g / L of complexing agent, and the balance being deionized water; the complexing agent is one or more of tartaric acid, citric acid or gluconic acid.

8. The electroplating method for a low-porosity nanoscale bright tin layer as described in claim 1, characterized in that, The preparation method of the activation solution includes the following steps: Dissolve the complexing agent in a portion of deionized water, then add divalent tin salt and stir until completely dissolved to obtain a tin complex solution; add polyethylene glycol octylphenyl ether or fatty alcohol polyoxyethylene to the tin complex solution, stir evenly, add the remaining deionized water to make up the volume, and adjust the pH value to 1.0~3.0 to obtain the activated solution.

9. The electroplating method for a low-porosity nanoscale bright tin layer as described in claim 1, characterized in that, The high-pulse current has a forward peak current density of 10A / dm²~30A / dm², a pulse width of 0.1ms~1ms, a frequency of 50Hz~200Hz, and an impact time of 10s~60s.

10. The electroplating method for a low-porosity nanoscale bright tin layer as described in claim 1, characterized in that, The clean metal substrate is any one or more of aluminum alloy, copper alloy, magnesium alloy, stainless steel and carbon steel after cleaning treatment.

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