Water-washing type tin-bismuth low-temperature solder paste for aluminum welding and preparation method thereof

Abstract

A water-washable tin-bismuth low-temperature solder paste for aluminum soldering and its preparation method are disclosed. The solder paste comprises 80-85 wt.% tin-based solder powder and 15-20 wt.% flux; the tin-based solder powder is a SnBi alloy; the flux includes 50-65 wt.% activator, 2-3 wt.% thickener, 15-25 wt.% film-forming coating agent, and 15-25 wt.% organic solvent. The solder paste of this invention exhibits good wettability on aluminum soldering surfaces, and post-soldering residues can be cleaned with warm water, resulting in reliable solder joints. The film-forming coating agent effectively coats the activator and other components, preventing the solder paste from drying out. This invention is applicable to the soldering of various aluminum pad components, particularly effective for soldering aluminum pad light source boards and aluminum fin heat sinks.

Description

Technical Field

[0001] This invention relates to the technical field of solder paste for aluminum welding and its preparation method, specifically to a water-washable tin-bismuth low-temperature solder paste for aluminum welding and its preparation method. Background Technology

[0002] Solder paste plays a crucial role in the soldering of electronic products, serving both electrical and physical bonding functions. In the home appliance industry, many structural components utilize materials such as copper and aluminum plates, particularly in electronic products like heat sinks and LED light source boards. Aluminum not only possesses excellent electrical and thermal conductivity but also offers suitable strength, good corrosion resistance, low density, and lower cost, making it a perfect substitute for copper plates in most industries where heat dissipation requirements are not particularly stringent. Copper plates have good solderability, and the copper oxide film on their surface is easily removed by the active substances in solder paste. However, aluminum has a dense and robust oxide film on its surface, and the degree of surface oxidation varies greatly among different aluminum plates. Ordinary solder paste's active substances struggle to remove the metal oxides on its surface, hindering low-temperature soldering and resulting in poor soldering results. To ensure sufficient activity during soldering, current solder pastes for aluminum plate soldering generally suffer from high residue and corrosion rates, which also affects product reliability. For example, Chinese patent application CN104625483A discloses a low-residue, low-corrosion aluminum solder paste and its preparation method. It uses a large amount of tetrahydroxypropyl ethylenediamine hydrofluoric acid. Although the solder paste has good wettability on the aluminum surface, its storage stability cannot be well resolved, and the presence of residue still affects the reliability of the solder joints. Chinese patent application CN103317260A discloses a solder paste for soft soldering of aluminum and aluminum alloys and its preparation method. This solder paste consists of 80-90% solder alloy powder and 10-20% flux. The flux composition includes: 5-15% heavy metal fluoride activator, 65-75% polyhydroxyamine hydrofluoric acid, and 10-25% ethylene glycol. This solder paste has strong activity and can obtain solder joints with strong adhesion. However, this solder paste generates a large number of bubbles and irritating gases during soldering, leaving significant residue after soldering. This residue easily corrodes the solder joints, affecting their service life. Furthermore, the solder paste dries out easily, impacting its printability. Chinese patent CN102922162A discloses an aluminum solder paste and its preparation method. This solder paste consists of 5-30% flux and 70-95% tin powder. The flux composition includes 80% fluorinated hydroxylamine, 15% active metal salt, 2% activator, and 3% corrosion inhibitor. This solder paste also suffers from problems such as significant residue after soldering and severe solder joint corrosion.

[0003] There are many publicly available documents on solder paste for aluminum welding, but they generally suffer from problems such as excessive residue, significant residual corrosion, or insufficient storage stability. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide a water-washable tin-bismuth low-temperature solder paste for aluminum welding that can significantly improve the solder paste's ability to remove oxide film on the surface of aluminum plates, has excellent wettability on aluminum plates, and whose post-soldering residue can be cleaned with warm water and has reliable solder joints. This invention also provides a method for preparing such solder paste.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A water-washable tin-bismuth low-temperature solder paste for aluminum soldering, the solder paste being composed of 80-85 wt.% tin-based solder powder and 15-20 wt.% flux; the tin-based solder powder is a SnBi alloy; the flux comprises 50-65 wt.% compound activator, 2-3 wt.% thickener, 15-25 wt.% compound film-forming coating agent, and 15-25 wt.% organic solvent.

[0007] Furthermore, the compound activator is composed of three materials: D-glucosamine hydrochloride, 2-amino-2',4'-difluoroacetophenone, and tetramethyldisyltriamine hydrofluoride.

[0008] Furthermore, in the compound activator, the mass ratio of D-glucosamine hydrochloride: 2-amino-2',4'-difluoroacetophenone: tetramethyldipropylenetriamine hydrofluoride is 1:(2-3):(4-5).

[0009] Furthermore, the thickener is sodium carboxymethyl cellulose.

[0010] Furthermore, the compounded film-forming coating agent is composed of four water-soluble polymer materials: polymaleic anhydride, polyvinylpyrrolidone, PPG400, and polyacrylamide.

[0011] Furthermore, in the compounded film-forming coating agent, the mass ratio of polymaleic anhydride: polyvinylpyrrolidone: PPG400: polyacrylamide is (2-3):(1-2):(4-5):1.

[0012] Furthermore, the organic solvent is a mixture of two or more of 1,2-propanediol, dipropylene glycol, and polyethylene glycol 200.

[0013] The preparation method of the water-washable tin-bismuth low-temperature solder paste for aluminum welding according to the present invention comprises the following steps:

[0014] (1) Add the compound activator and the compound film-forming agent to the reaction vessel, use the compound film-forming agent to coat the compound activator, then add thickener and organic solvent until it becomes a homogeneous emulsion, pour it into a container, and place it at room temperature to cool to obtain flux paste.

[0015] (2) Grind the flux paste until the grain size is less than 100 μm;

[0016] (3) The milled flux is mixed with tin-based solder powder to obtain the water-washable tin-bismuth low-temperature solder paste for aluminum welding.

[0017] Further, the raw materials for preparing the compound surfactant are added to a container and heated to 120-130℃ to prepare the compound surfactant, which is then cooled and set aside for later use.

[0018] Further, the raw materials for preparing the composite film-forming coating agent are added to a container and heated to 80-100℃ to prepare the composite film-forming coating agent.

[0019] This invention addresses the problems of excessive residue, significant residual corrosion, and insufficient storage stability in existing solder pastes for aluminum plates. It employs a combination of compound activators and compound film-forming coating agents. The compound activator significantly improves the solder paste's ability to remove oxide films from aluminum plate surfaces, resulting in excellent wettability. This is because the compound activator, containing D-glucosamine hydrochloride, 2-amino-2',4'-difluoroacetophenone, and tetramethyldisyltriamine hydrofluoride, releases sufficient amino / hydrofluoric acid / hydrochloric acid / fluoride ions during high-temperature soldering to remove the aluminum surface oxide film. The film-forming coating agent effectively encapsulates the activator and other components, preventing the solder paste from drying out. The compounded film-forming coating agent can also slow down the chemical reaction between the activator in the flux and the solder powder, giving the solder paste good storage performance. This is because the polymaleic anhydride, polyvinylpyrrolidone, PPG400, and polyacrylamide in the compounded film-forming coating agent can form a low-surface-tension polymeric film-forming agent after heating, exhibiting excellent coating effect. The activator, thickener, film-forming coating agent, and organic solvent used in this invention all have good water solubility, allowing soldering residues to be cleaned with warm water, resulting in solder joints with good reliability after cleaning.

[0020] The solder paste of this invention is suitable for soldering various aluminum pad components. It provides strong and reliable soldering of aluminum plate devices or structural parts, which can significantly improve product performance and extend its service life. It is particularly effective for soldering aluminum pad light source boards and aluminum fin heat sinks.

[0021] The solder paste preparation method of the present invention is simple, the process is easy to control, and the prepared product has stable performance. Detailed Implementation

[0022] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the embodiments.

[0023] Example 1

[0024] A water-washable tin-bismuth low-temperature solder paste for aluminum soldering comprises 85 wt.% SnBi58 powder and 15 wt.% flux. The flux ingredients are: 7 g D-glucosamine hydrochloride, 14 g 2-amino-2',4'-difluoroacetophenone, 30 g tetramethyldisyltriamine hydrofluoric acid, 2 g sodium carboxymethyl cellulose, 6 g polymaleic anhydride, 4 g polyvinylpyrrolidone, 10 g PPG400, 2 g polyacrylamide, 15 g 1,2-propanediol, and 10 g dipropylene glycol.

[0025] Solder paste preparation method:

[0026] (1) D-glucosamine hydrochloride, 2-amino-2',4'-difluoroacetophenone, and tetramethyldipropylenetriamine hydrofluoride were added to a beaker and heated to about 125°C to prepare a compound activator. After cooling, it was set aside for later use. Then, polymaleic anhydride, polyvinylpyrrolidone, PPG400, and polyacrylamide were added to a reaction vessel and heated to about 90°C to prepare a compound film-forming coating agent. After that, the prepared compound activator was added to the reaction vessel and the compound activator was coated by the compound film-forming agent. Then, sodium carboxymethyl cellulose, 1,2-propanediol, and dipropylene glycol were added until a homogeneous emulsion was formed. The emulsion was poured into a container and cooled at room temperature to obtain solder paste.

[0027] (2) Grind the flux until the grain size is less than 100 μm;

[0028] (3) Take 75g of the milled flux and mix it with 425g of SnBi58 powder to obtain the water-washable tin-bismuth low-temperature solder paste for aluminum welding.

[0029] Example 2

[0030] A water-washable tin-bismuth low-temperature solder paste for aluminum soldering comprises 82 wt.% SnBi58 powder and 18 wt.% flux. The flux ingredients are: 80 g D-glucosamine hydrochloride, 160 g 2-amino-2',4'-difluoroacetophenone, 320 g tetramethyldisyltriamine hydrofluoric acid, 20 g sodium carboxymethyl cellulose, 60 g polymaleic anhydride, 40 g polyvinylpyrrolidone, 100 g PPG400, 20 g polyacrylamide, 100 g 1,2-propanediol, and 100 g polyethylene glycol 200.

[0031] Solder paste preparation method:

[0032] (1) D-glucosamine hydrochloride, 2-amino-2',4'-difluoroacetophenone, and tetramethyldipropylenetriamine hydrofluoride were added to a beaker and heated to 125-130℃ to prepare a compound activator. After cooling, the compound activator was set aside. Then, polymaleic anhydride, polyvinylpyrrolidone, PPG400, and polyacrylamide were added to a reaction vessel and heated to 80-85℃ to prepare a compound film-forming coating agent. The prepared compound activator was then added to the reaction vessel and coated with the compound film-forming agent. Sodium carboxymethyl cellulose, 1,2-propanediol, and polyethylene glycol 200 were added until a homogeneous emulsion was formed. The emulsion was poured into a container and cooled at room temperature to obtain flux.

[0033] (2) Grind the flux until the grain size is less than 100 μm;

[0034] (3) Take 180g of the milled flux and mix it with 820g of SnBi58 powder to obtain the water-washable tin-bismuth low-temperature solder paste for aluminum welding.

[0035] Example 3

[0036] A water-washable tin-bismuth low-temperature solder paste for aluminum soldering comprises 80 wt.% SnBi35 powder and 20 wt.% flux. The flux ingredients are: 80 g D-glucosamine hydrochloride, 200 g 2-amino-2',4'-difluoroacetophenone, 370 g tetramethyldisyltriamine hydrofluoric acid, 30 g sodium carboxymethyl cellulose, 40 g polymaleic anhydride, 20 g polyvinylpyrrolidone, 90 g PPG400, 20 g polyacrylamide, 100 g 1,2-propanediol, and 50 g polyethylene glycol 200.

[0037] Solder paste preparation method:

[0038] (1) Add 370g of D-glucosamine hydrochloride, 2-amino-2',4'-difluoroacetophenone, and tetramethyldipropylenetriamine hydrofluoric acid to a beaker and heat to 120-122℃ to prepare a compound activator. After cooling, set aside. Then add polymaleic anhydride, polyvinylpyrrolidone, PPG400, and polyacrylamide to a reaction vessel and heat to 95-100℃ to prepare a compound film-forming coating agent. Then add the prepared compound activator to the reaction vessel and use the compound film-forming agent to coat the compound activator. Then add sodium carboxymethyl cellulose, 1,2-propanediol, and polyethylene glycol 200 until it becomes a homogeneous emulsion. Pour it into a container and place it at room temperature to cool to obtain flux.

[0039] (2) Grind the flux until the grain size is less than 100 μm;

[0040] (3) Take 200g of the milled flux and mix it with 800g of SnBi58 powder to obtain the water-washable tin-bismuth low-temperature solder paste for aluminum welding.

[0041] Example 4

[0042] A water-washable tin-bismuth low-temperature solder paste for aluminum soldering comprises 82 wt.% SnBi35 powder and 18 wt.% flux. The flux ingredients are: 60 g D-glucosamine hydrochloride, 180 g 2-amino-2',4'-difluoroacetophenone, 290 g tetramethyldisyltriamine hydrofluoric acid, 20 g sodium carboxymethyl cellulose, 60 g polymaleic anhydride, 40 g polyvinylpyrrolidone, 120 g PPG400, 30 g polyacrylamide, 50 g 1,2-propanediol, 50 g dipropylene glycol, and 100 g polyethylene glycol 200.

[0043] Solder paste preparation method:

[0044] (1) D-glucosamine hydrochloride, 2-amino-2',4'-difluoroacetophenone, and tetramethyldipropylenetriamine hydrofluoride were added to a beaker and heated to about 128°C to prepare a compound activator. After cooling, the compound activator was set aside. Then, polymaleic anhydride, polyvinylpyrrolidone, PPG400, and polyacrylamide were added to a reaction vessel and heated to about 98°C to prepare a compound film-forming coating agent. The prepared compound activator was then added to the reaction vessel and coated with the compound film-forming agent. Sodium carboxymethyl cellulose, dipropylene glycol, and polyethylene glycol 200 were added until a homogeneous emulsion was formed. The emulsion was poured into a container and cooled at room temperature to obtain flux.

[0045] (2) Grind the flux until the grain size is less than 100 μm;

[0046] (3) Take 900g of the milled flux and mix it with 4100g of SnBi58 powder to obtain the water-washable tin-bismuth low-temperature solder paste for aluminum welding.

[0047] The solder pastes prepared in the above four embodiments were tested, and the results are shown in Table 1.

[0048] Table 1. Solder paste performance test table for each embodiment

[0049]

[0050] As can be seen from Table 1, the solder paste of the present invention has good wettability, easy residue removal, good solder joint reliability, and good storage stability.

[0051] The above embodiments are only some embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All embodiments obtained by data modifications and equivalent technical substitutions based on the scope of the claims of the present invention are within the scope of protection of the present invention.

Claims

1. A water-washable tin-bismuth low-temperature solder paste for aluminum soldering, characterized in that, The solder paste is composed of 80-85 wt.% tin-based solder powder and 15-20 wt.% flux; the tin-based solder powder is a SnBi alloy; the flux includes 50-65 wt.% compound activator, 2-3 wt.% thickener, 15-25 wt.% compound film-forming coating agent, and 15-25 wt.% organic solvent; the compound activator is composed of D-glucosamine hydrochloride, 2-amino-2',4'-difluoroacetophenone, and tetramethyldisyltriamine hydrofluoride; the compound film-forming coating agent is composed of four water-soluble polymers: polymaleic anhydride, polyvinylpyrrolidone, PPG400, and polyacrylamide. In the compound activator, the mass ratio of D-glucosamine hydrochloride: 2-amino-2',4'-difluoroacetophenone: tetramethyldipropylenetriamine hydrofluoride is 1:(2-3):(4-5). In the aforementioned compound film-forming coating agent, the mass ratio of polymaleic anhydride: polyvinylpyrrolidone: PPG400: polyacrylamide is (2-3):(1-2):(4-5):

1.

2. The water-washable bismuth-tin low-temperature solder paste for aluminum welding according to claim 1, characterized in that, The thickener is sodium carboxymethyl cellulose.

3. The water-washable tin-bismuth low-temperature solder paste for aluminum welding according to claim 1 or 2, characterized in that, The organic solvent is a mixture of two or more of 1,2-propanediol, dipropylene glycol, and polyethylene glycol 200.

4. A method for preparing a water-washable tin-bismuth low-temperature solder paste for aluminum welding as described in any one of claims 1 to 3, characterized in that, The steps are as follows: (1) Add the compound activator and the compound film-forming agent to the reaction vessel, use the compound film-forming agent to coat the compound activator, then add thickener and organic solvent until it becomes a homogeneous emulsion, pour it into a container, and place it at room temperature to cool to obtain flux paste. (2) Grind the flux paste until the grain size is less than 100 μm; (3) The milled flux is mixed with tin-based solder powder to obtain the water-washable tin-bismuth low-temperature solder paste for aluminum welding.

5. The method for preparing a water-washable tin-bismuth low-temperature solder paste for aluminum welding as described in claim 4, characterized in that, Add all the raw materials for preparing the compound surfactant into a container, heat to 120-130℃ to prepare the compound surfactant, and then cool it for later use.

6. The method for preparing a water-washable tin-bismuth low-temperature solder paste for aluminum welding as described in claim 4, characterized in that, The raw materials for preparing the composite film-forming coating agent are added into a container and heated to 80-100℃ to obtain the composite film-forming coating agent.

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