阅读说明：本技术 一种降低镀层杂质含量的镀锡电镀液及其制备方法 (Tinning electroplating liquid capable of reducing impurity content of plating layer and preparation method of tinning electroplating liquid ) 是由 蔡国隆 于 2020-12-30 设计创作，主要内容包括：本发明属于电镀技术领域,具体涉及一种降低镀层杂质含量的镀锡电镀液及其制备方法,以去离子水为溶剂,其包含以下浓度的组分：甲基磺酸亚锡0.1～0.5mol/L；甲基磺酸0.3～1mol/L；苯甲酸10～50g/L；季铵化多羟基Gemini表面活性剂1～5g/L；抗氧化剂1～6g/L；光亮剂1～5g/L；络合剂1～10g/L。本发明提供的镀锡电镀液添加了季铵化多羟基Gemini表面活性剂协同苯甲酸,能够在阴极表面形成紧密的覆盖膜层,从而有效抑制了杂质金属离子在阴极表面的还原和沉积,显著降低了锡镀层的杂质含量,使镀层更加均匀致密、细致,厚度更加均匀,可焊性提高。(The invention belongs to the technical field of electroplating, and particularly relates to a tin plating electroplating solution for reducing impurity content of a plating layer and a preparation method thereof, wherein deionized water is used as a solvent, and the tin plating electroplating solution comprises the following components in concentration: 0.1-0.5 mol/L of stannous methanesulfonate; 0.3-1 mol/L of methanesulfonic acid; 10-50 g/L of benzoic acid; 1-5 g/L of quaternized polyhydroxy Gemini surfactant; 1-6 g/L of antioxidant; 1-5 g/L of brightener; 1-10 g/L of complexing agent. The quaternary ammonium polyhydroxy Gemini surfactant and benzoic acid are added into the tin plating solution provided by the invention, and a compact covering film layer can be formed on the surface of the cathode, so that the reduction and deposition of impurity metal ions on the surface of the cathode are effectively inhibited, the impurity content of a tin plating layer is obviously reduced, the plating layer is more uniform, compact and fine, the thickness is more uniform, and the weldability is improved.)

1. A tin plating bath for reducing the impurity content of a plating layer, characterized in that deionized water is used as a solvent, and the tin plating bath comprises the following components in concentration:

2. the tin plating bath according to claim 1, wherein deionized water is used as a solvent and comprises the following components in the following concentrations:

3. the tin plating bath according to claim 1 or 2, wherein the weight ratio of the quaternized polyhydroxy Gemini surfactant to benzoic acid is 1: 10 to 16.

4. The tin plating bath of claim 3, wherein the weight ratio of quaternized polyhydroxy Gemini surfactant to benzoic acid is 1: 16.

5. the tin plating bath according to claim 1 or 2, wherein the quaternized polyhydroxy Gemini surfactant is prepared by:

adding 1, 3-dibromopropane and absolute ethyl alcohol into N, N-dimethyldodecyl tertiary amine, performing reflux reaction for 36-72 hours under stirring, performing rotary evaporation to remove the solvent, washing with diethyl ether for 1-3 times to remove excessive N, N-dimethyldodecyl tertiary amine, filtering, and recrystallizing a filter cake with an ethanol/ethyl acetate mixture to obtain the N, N-dimethyldodecyl tertiary amine.

6. The tin plating bath according to claim 5, wherein the washing with diethyl ether is performed 3 times; in the ethanol/ethyl acetate mixture, the volume ratio of ethanol to ethyl acetate is 0.1-0.5: 2.

7. The tin plating bath according to claim 1 or 2, wherein the brightener is one or a mixture of one or more selected from the group consisting of aldehydes, ketones, organic acids and organic acid derivatives.

8. The tin plating bath according to claim 1 or 2, wherein the antioxidant is resorcinol, cresol, naphthol, or ascorbic acid.

9. The tin plating bath according to claim 1 or 2, wherein the complexing agent is one selected from the group consisting of gluconolactone, gluconic acid, and sulfamic acid.

10. A method for producing the tin plating bath according to claim 1 to 9, comprising the steps of:

adding deionized water into the electroplating bath, adding methanesulfonic acid while stirring, continuously adding stannous methanesulfonate under the stirring state, uniformly stirring, sequentially adding benzoic acid, a quaternized polyhydroxy Gemini surfactant, an antioxidant, a brightener and a complexing agent, and uniformly stirring to obtain the electroplating solution.

Technical Field

The invention belongs to the technical field of electroplating. And more particularly to a tin plating bath for reducing the impurity content of a plating layer and a preparation method thereof.

Background

Aluminum alloys are the most widely used class of non-ferrous structural materials in industry and have found a number of applications in the aerospace, automotive, mechanical manufacturing, marine and chemical industries. The rapid development of industrial economy has increased the demand for aluminum alloy welded structural members, and the research on the weldability of aluminum alloys is also deepened. The tin plating on the aluminum and the aluminum alloy can improve the weldability of the aluminum and the aluminum alloy, but the tin plating on the surface of the aluminum cannot be directly carried out, and a series of pretreatments such as chemical nickel plating, hard chromium plating and other metal coatings are needed, so that the surface hardness, the wear resistance and the corrosion resistance of the aluminum and the aluminum alloy can be obviously improved through the pretreatments, and the application range of the aluminum and the aluminum alloy is expanded. However, these pretreatment methods result in elution of impurities such as nickel ions and chromium ions and deposition on the surface of the cathode during the plating process. The deposition of these impurities on the cathode surface causes inclusions in the coating, which may change the oxidation state of the surface due to the inclusions, resulting in a more easily oxidized surface, or change the size and orientation of the crystalline particles of the deposited layer, ultimately affecting the quality of the coating.

Disclosure of Invention

The invention aims to overcome the defects and shortcomings of the existing tin plating solution and provide the tin plating solution, which can effectively prevent the deposition of impurity metal ions on the surface of a cathode, and has the advantages of more uniform and fine coating surface, more uniform thickness, improved weldability, strong coating bonding force and tight bonding.

The above purpose of the invention is realized by the following technical scheme: a tin plating electroplating solution for reducing impurity content of a plating layer takes deionized water as a solvent, and comprises the following components in concentration:

preferably, deionized water is used as a solvent, and the deionized water comprises the following components in concentration:

preferably, the weight ratio of the quaternized polyhydroxy Gemini surfactant to benzoic acid is 1: 10 to 16.

Preferably, the weight ratio of the quaternized polyhydroxy Gemini surfactant to benzoic acid is 1: 16.

the Gemini surfactant is a double-ended double-tail surfactant formed by connecting two amphiphilic components together through a connecting group on a hydrophilic head group or an alkyl chain close to the hydrophilic head group. Compared with the traditional surfactant, the Gemini surfactant has lower critical micelle concentration, higher surface activity, better wettability and solubility.

The 'quaternized polyhydroxy Gemini surfactant' is obtained by modifying a head group of a Gemini surfactant and introducing a plurality of hydroxyl groups, and preferably, the quaternized polyhydroxy Gemini surfactant is prepared by the following steps:

adding 1, 3-dibromopropane and absolute ethyl alcohol into N, N-dimethyldodecyl tertiary amine, performing reflux reaction for 36-72 hours under stirring, performing rotary evaporation to remove the solvent, washing with diethyl ether for 1-3 times to remove excessive N, N-dimethyldodecyl tertiary amine, filtering, and recrystallizing a filter cake with an ethanol/ethyl acetate mixture to obtain the N, N-dimethyldodecyl tertiary amine.

The benzoic acid can be adsorbed on the surface of the cathode through hydrophobic interaction and pi-pi interaction, meanwhile, molecules of the benzoic acid and molecules can be automatically arranged on the surface of the cathode through hydrogen bonds to form a layer of protective film, so that the surface of the cathode is covered, and dissolved impurity ions are prevented from being reduced and deposited on the surface of the cathode, and the problem of coating quality reduction caused by deposition of impurity metal ions on the surface of the cathode is solved. However, the blocking effect is not stable, and the inventor further introduces a quaternary ammonium polyhydroxy Gemini surfactant, which can enhance the blocking effect of benzoic acid on impurity ions, so that the formed protective film is more stable, wherein the quaternary ammonium polyhydroxy Gemini surfactant has a polyhydroxy structure, molecules and molecules can be self-assembled through hydrogen bond effect in a connecting group, and meanwhile, the quaternary ammonium polyhydroxy Gemini surfactant is connected with benzoic acid through intermolecular force, so that the surface of the quaternary ammonium polyhydroxy Gemini surfactant is covered with a new protective film while the benzoic acid self-assembly film is enhanced, and the effect of benzoic acid on blocking the deposition of impurity metal ions on the surface of a cathode is enhanced.

Preferably, the washing with diethyl ether is performed 3 times; in the ethanol/ethyl acetate mixture, the volume ratio of ethanol to ethyl acetate is 0.5: 2.

Preferably, the brightening agent is selected from one or more of aldehydes, ketones, organic acids and organic acid derivatives. The brightener is used for increasing cathode polarization through coordination of the brightener and metal ions or adsorption of the brightener on a cathode, so that tin deposition potential is shifted negatively, the temperature current density range is expanded, a high-end region and a low-end region are bright as well, and a coating which is fine in crystallization, bright, good in weldability and difficult to fall off is obtained.

PreferablyThe antioxidant is resorcinol, cresol, naphthol or ascorbic acid. The antioxidant is added to improve the stability of the plating solution and inhibit Sn in the plating solution²⁺Oxidizing and improving the polarization capability of the electroplating solution.

Preferably, the complexing agent is selected from one of gluconolactone, gluconic acid and sulfamic acid.

It is another object of the present invention to provide a method for preparing the tin electroplating solution, comprising the steps of:

adding deionized water into the electroplating bath, adding methanesulfonic acid while stirring, continuously adding stannous methanesulfonate under the stirring state, uniformly stirring, sequentially adding benzoic acid, a quaternized polyhydroxy Gemini surfactant, an antioxidant, a brightener and a complexing agent, and uniformly stirring to obtain the electroplating solution.

The invention has the following beneficial effects:

(1) in the tin plating solution provided by the invention, the quaternary ammonium polyhydroxy Gemini surfactant is added to cooperate with benzoic acid, so that a compact covering film layer can be formed on the surface of the cathode, the reduction and deposition of impurity metal ions on the surface of the cathode are effectively inhibited, the content of inorganic impurities in a tin plating layer is obviously reduced, the plating layer is more uniform and fine, the thickness is more uniform, and the weldability is improved.

(2) The brightener is added into the electroplating solution, so that the brightness and the binding force of the plating layer are further improved, and the plating layer is smoother and is not easy to fall off; by adding the antioxidant, the stability of the plating solution is improved.

(3) The electroplating solution provided by the invention is not only suitable for the tin plating of aluminum alloy, but also suitable for the tin plating of electronic equipment, and has wide applicability.

Detailed Description

The present invention is further illustrated by the following specific examples, which are not intended to limit the invention in any way. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.

Unless otherwise indicated, reagents and materials used in the following examples are commercially available.

Example 1 preparation of quaternized polyhydroxy Gemini surfactant

Taking 0.22mol of N, N-dimethyl dodecyl tertiary amine, adding 0.1mol of 1, 3-dibromopropane and 20ml of absolute ethyl alcohol, refluxing and reacting for 72 hours under stirring, removing the solvent by rotary evaporation, washing with diethyl ether for 3 times to remove the excessive N, N-dimethyl dodecyl tertiary amine, filtering, and recrystallizing a filter cake with an ethanol/ethyl acetate mixture to obtain the N, N-dimethyl dodecyl tertiary amine; wherein the volume ratio of ethanol to ethyl acetate in the ethanol/ethyl acetate mixture is 0.5: 2.

Examples 2 to 4 tin plating solutions (1L of deionized water)

The preparation method comprises the following steps:

adding deionized water into the electroplating bath, adding methanesulfonic acid while stirring, continuously adding stannous methanesulfonate under the stirring state, uniformly stirring, sequentially adding benzoic acid, a quaternized polyhydroxy Gemini surfactant, resorcinol, glutaraldehyde and gluconolactone, and uniformly stirring to obtain the electroplating solution.

Application example 1 electroplating Process

S1, pretreatment: carrying out chemical degreasing, alkaline etching, water washing, acid etching, water washing, conditioning pretreatment, nickel pre-dipping, chemical nickel plating and water washing on a workpiece to be plated;

s2, tinning: adding the tin plating electroplating solution of any one of the embodiments 2 to 4 into a plating tank, using the workpiece to be plated obtained by the treatment of the step S1 as a cathode, using a pure tin bar as an anode, switching on the current, controlling the electroplating temperature to be 25 ℃ and the current density to be 1A/dm²The electroplating time is 15 min;

and S3, recycling, washing, warm washing and drying the workpiece obtained by the processing of the step S2 to respectively obtain the workpieces (i) - (iii).

Wherein, the chemical degreasing step is as follows: the workpiece to be plated is placed in a bath containing 20g/L, Na NaOH₂CO₃ 30g/L、Na₃PO₄30g/L, OP-10 g/L emulsifier in 0.5ml/L water at 75 deg.CSoaking for 60S.

The alkaline etching step is specifically operated as follows: the workpiece to be plated after chemical oil removal is placed in a bath containing 50g/L, Na NaOH₂CO₃30g/L、Na₃PO₄30g/L of sodium silicate and 5g/L of sodium silicate, and treating the mixture at 80 ℃ for 50S.

The pickling step is specifically operated as follows: and (3) putting the workpiece to be plated after the alkaline etching into water containing 400g/L of nitric acid and 250g/L of hydrofluoric acid, soaking for 30S at 25 ℃, and repeatedly washing with flowing water.

The conditioning pretreatment is specifically operated as follows: and (3) placing the workpiece to be plated after being washed in deionized water containing 200ml/L of 1.5 wt% ammonia water and 5g/L of trisodium citrate, and treating for 30 seconds at room temperature.

The nickel pre-soaking step is specifically operated as follows: placing the workpiece to be plated after the conditioning pretreatment in a nickel pre-soaking solution, and treating for 40S at room temperature; the nickel pre-impregnation solution takes deionized water as a solvent, and contains 3g/L of nickel acetate, 6g/L of trisodium citrate, 200ml/L of 1.5 wt% ammonia water, 10ml/L of triethanolamine and 10ml/L of lactic acid, and the pH value is 10-11.

The chemical nickel plating step is specifically operated as follows: placing the workpiece to be plated after nickel preplating in a chemical nickel plating solution, and treating for 30min at 65 ℃; the chemical nickel plating solution takes deionized water as a solvent, and comprises 30g/L of nickel sulfate, 30g/L of sodium hypophosphite, 8g/L of trisodium citrate, 20g/L of ammonium sulfate and 30ml/L of lactic acid, and the pH value is 4-6.

Comparative example 1 differs from example 2 in that no quaternized polyhydroxy Gemini surfactant was added, the remaining parameters were the same, and workpiece (iv) was obtained according to the electroplating process of application example 1.

Comparative example 2 is different from example 2 in that benzoic acid was not added and the parameters were the same, and a workpiece was obtained by the plating process according to application example 1.

A comparative example 3 is different from the example 2 in that alkyl glycoside is adopted to replace the quaternary polyhydroxy Gemini surfactant, the other parameters are the same, and a workpiece is obtained by the electroplating process according to the application example 1.

Test example I, plating appearance test

The appearance of the obtained workpiece is observed by combining a visual method and an SEM electron microscope, the indexes of uniformity, roughness, continuity and the like of the appearance of the coating are comprehensively judged, and the observation result is shown in the following table 1.

TABLE 1 test results of appearance quality of coating of samples

As can be seen from the above Table 1, the plating layer of the plated article obtained from the plating solution containing the plating additive of the invention has uniform color and thickness, smooth and compact plating layer, and good brightness, and the grain size and shape of the plating layer are uniform and compact through SEM observation, and the plating layer has excellent appearance performance. If benzoic acid is omitted, the appearance quality of the plating layer is obviously reduced, the plating layer is rough and uneven, the whole plating layer is dark, and the benzoic acid plays a main role in improving the quality of the plating layer; if the non-ionic surfactant alkyl glycoside is adopted to replace the quaternized polyhydroxy Gemini surfactant or the quaternized polyhydroxy Gemini surfactant is omitted, the prepared coating has uniform color and thickness, but large crystal grains and is not uniform enough.

Test example two, adhesion test

Cutting and penetrating a workpiece by adopting a hundred-grid cutter to form a grid pattern on a plating layer, and then slightly brushing the test piece backwards 5 times and forwards 5 times by using a soft brush along two diagonal lines of the grid pattern; finally, a semitransparent adhesive tape with the width of 25mm is attached to the whole scribing grid, the scribing grid is torn off at the minimum angle, the area ratio of the available plating layer to the falling plating layer is counted under a magnifier, each sample is subjected to parallel repeated tests for 3 times, and the test results are shown in the following table 2.

Table 2 adhesion test results

Index (I)

①

②

③

④

⑤

⑥

The size of the coating area occupied by the dropped coating

Without falling off

Without falling off

Without falling off

7.5％

18.3％

5.6％

As shown in the table 2, the coating obtained by using the benzoic acid in cooperation with the quaternized polyhydroxy Gemini surfactant as the additive has better binding force, and the coating is firmly bound with the substrate.

Test example three, solderability test

The workpieces are welded by 75W electric soldering irons, and the results show that the workpieces are firmly welded in the processes of 3S, welding spots are smooth, and a plating layer at the welding position does not bubble and fall off, so that the tin-plated layer is proved to be good in weldability.

Test example four, detection of carbon content in plating layer

The impurity contents in the first to sixth coatings of the workpiece were measured by X-ray photoelectron spectroscopy, and the measurement results are shown in table 3 below.

TABLE 3 determination of impurity content in coating of each workpiece

From the above table, the coating obtained by using benzoic acid in combination with quaternized polyhydroxy Gemini surfactant as additive has lower impurity metal ion content, while the coating with low impurity content is not easy to obtain if only benzoic acid or quaternized polyhydroxy Gemini surfactant is added.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.