Low-temperature lead-free solder paste and preparation method thereof

Abstract

The present application relates to the field of low-temperature lead-free solder paste preparation, and discloses a low-temperature lead-free solder paste and a preparation method thereof, the solder paste protective paste comprises the following components by weight: tin metal alloy 70-80 parts, flux 10-15 parts, organic solvent 1-5 parts, protective agent 3-7 parts, and wetting enhancer 4-9 parts. The present application is composed of tin-nickel alloy, tin-bismuth alloy and tin-silver-copper alloy, compared with single tin alloy, the present application has stable performance, and the tin metal alloy is nanoscale, has good corrosion resistance, especially in high-temperature environment, can effectively resist oxidation and corrosion, has high physical strength and hardness at room temperature, and can reduce the welding temperature. The nanoscale tin metal alloy is used with the flux, can implement coating at a temperature lower than the melting point of the powder, and is widely applicable to the electronic industry.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of low-temperature lead-free solder paste, in particular to a low-temperature lead-free solder paste and a preparation method thereof. BACKGROUND

[0002] With the development of the electronic industry, the amount of solder is increasing, and soldering is one of the most important processes in electronic industry assembly. Solder paste is mainly a stable paste-like mixture composed of solder powder, flux and the like. The flux mainly includes activators, thixotropic agents, solvents and the like. Solder paste plays a role in surface mount technology, such as fixing elements, promoting solder wetting, removing oxides, trace impurities and adsorption layers, protecting the surface from re-oxidation, and forming a firm metallurgical bond. Solder paste is an indispensable processing material in SMT chip production and processing. Solder paste, also known as solder paste, is a new type of welding material mainly used in SMT. It is usually a paste-like mixture of solder powder, flux, other surfactants and thixotropic agents. Different solder pastes are used for different PCBA production and processing requirements.

[0003] The invention patent with publication number CN101244491B provides a welding material, in particular a preparation method of lead-free soldering paste and flux for electronic industry. It is characterized by being composed of 85-90% lead-free solder powder 10-15% and flux. The lead-free solder powder is a 25-45 micron lead-free solder made of tin, copper, silver and titanium. The flux is composed of high-viscosity rosin, organic acid activator, thixotropic agent, wetting agent and solvent. The product combines the advantages of lead-free solder, such as green environmental protection, while improving the shortcomings of high melting point and poor flowability of lead-free solder, with high expansion rate, no halogen, small post-welding residue and corrosion, high insulation resistance, and good protection performance. However, this patent has the following problems: the performance is not stable enough, especially in high-temperature environments, it cannot effectively resist oxidation and corrosion, the solder paste is easily oxidized after long-term use, it cannot better protect the welding products, and the welding temperature needs to be higher. SUMMARY

[0004] The purpose of the present application is to provide a low-temperature lead-free solder paste and a preparation method thereof, which solves the problem of toxic and harmful gas generated during soldering of soldering protection paste, strong odor, and poor corrosion resistance.

[0005] In order to achieve the above-mentioned purpose, the present application is realized by the following technical scheme:

[0006] A low-temperature lead-free solder paste, the weight composition of the soldering protection paste includes: 70-80 parts of tin metal alloy, 10-15 parts of flux, 1-5 parts of organic solvent, 3-7 parts of protective agent, and 4-9 parts of wetting enhancer.

[0007] Preferably, the soldering tin protective paste is composed of 72 parts of tin metal alloy, 11 parts of flux, 3 parts of organic solvent, 5 parts of protective agent and 9 parts of wetting enhancer.

[0008] Preferably, the soldering tin protective paste is composed of 75 parts of tin metal alloy, 13 parts of flux, 5 parts of organic solvent, 3 parts of protective agent and 4 parts of wetting enhancer.

[0009] Preferably, the soldering tin protective paste is composed of 78 parts of tin metal alloy, 10 parts of flux, 2 parts of organic solvent, 4 parts of protective agent and 6 parts of wetting enhancer.

[0010] Preferably, the tin metal alloy is composed of tin-nickel alloy, tin-bismuth alloy and tin-silver-copper alloy, and the preparation method of the tin metal alloy comprises the following steps: a. stirring the metal blocks of tin-nickel alloy, tin-bismuth alloy and tin-silver-copper alloy into powder by a stirring crusher; b. mixing the powders according to a ratio of 2:3:5, and then putting the mixture into a crucible and heating to 350-430 ℃ to melt, and stirring uniformly during the melting process; and c. removing the dross in the alloy melt by a 200-300 mesh hafnium alloy metal filter, and then pouring the uniform alloy melt into a channel steel to cool and solidify, so as to obtain the tin metal alloy.

[0011] Preferably, the tin metal alloy is a nano tin metal alloy, and the nano tin metal alloy is prepared by heating the tin metal alloy to 400-500 ℃ in a copper crucible, adding sodium disulfite and serum protein to decompose the tin metal alloy into granular form, and then synthesizing tin metal nanoparticles with a size of 1-6 nm by a γ-ray method.

[0012] Preferably, the flux is composed of the following raw materials in mass percentage: 28%-50% of rosin resin, 3%-8% of methyl isobutyl ketone, 22%-28% of triethanolamine and 12%-26% of dimethyl succinate.

[0013] Preferably, the organic solvent comprises one or more of styrene, perchloroethylene, ethylene glycol ether and triethanolamine.

[0014] Preferably, the protective agent comprises one or more of urea-formaldehyde resin and polyamide epoxy chloropropane resin.

[0015] A preparation process of low-temperature lead-free soldering tin paste is used to prepare the soldering tin protective paste, and the preparation process of the soldering tin protective paste is as follows:

[0016] (1) 70-80 parts of tin metal alloy, 10-15 parts of flux, 1-5 parts of organic solvent, 3-7 parts of protective agent and 4-9 parts of wetting enhancer;

[0017] (2): Tin metal alloy is poured into a copper crucible and heated, the heating temperature is 330-460 DEG C, and the tin metal liquid is formed by pouring into an organic solvent mixture;

[0018] (3): The tin metal liquid in the above (2) is added into a protective agent, and is stirred uniformly for 8-10 min, and is poured into a closed copper pot and heated at 400-550 DEG C, a wetting enhancer is added, the temperature is lowered to 200-280 DEG C, a flux is added, and cooling is carried out at 20-32 DEG C, and the stirring is continuously carried out for 35-40 min, and then the tin metal liquid is taken out and placed in an enamel container for 3-4 h, and then the tin metal liquid is mixed into a paste, and is divided into containers, and a low-temperature lead-free solder paste is obtained.

[0019] The tin metal alloy has stable performance, low melting point, good fluidity, small shrinkage, fine grain, good toughness, suitable hardness, smooth surface, no sand hole, no defect, no crack, good polishing and electroplating effect, good corrosion resistance, good stability, good heat conductivity, thermal stability, good anti-electromagnetic interference and shielding performance, good noise reduction and vibration reduction function, good casting property of tin bismuth alloy, low reactivity of magnesium and iron, iron crucible can be used during smelting, low heat enthalpy of fusible substances in unit capacity, and good noise reduction and vibration reduction function.

[0020] The flux mainly has the following aspects: assisting heat conduction, removing oxide, reducing surface tension of the welded material, removing oil stains on the surface of the welded material, increasing the welding area, and preventing re-oxidation.

[0021] The organic solvent is difficult to dissolve in water and has good conductivity, and the main function of the organic solvent is to dissolve and disperse organic resin to form an organic carrier for slurry.

[0022] The protective agent is a colorless, odorless, fluorescent transparent oily liquid, does not contain any additive, moisture and mechanical impurities, is dissolved in organic solvents such as diethyl ether, chloroform, gasoline and benzene, is not dissolved in water, has good chemical stability and oxidation resistance, and has good oxidation resistance stability, stability and light stability.

[0023] The tin metal alloy added in the application is composed of tin-nickel alloy, tin-bismuth alloy and tin-silver-copper alloy, and compared with single tin alloy, the tin metal alloy has stable performance, and the tin metal alloy is nano, has good corrosion resistance, can effectively resist oxidation and corrosion in a high-temperature environment, has high physical strength and hardness at room temperature, can reduce the welding temperature, and can be used with the flux to implement coating at a temperature lower than the melting point of the powder, and is widely used in the electronic industry. DETAILED DESCRIPTION

[0024] The specific embodiments of the present application are further described below in conjunction with examples. The following examples are only used to more clearly illustrate the technical solutions of the present application, and cannot be used to limit the protection scope of the present application.

[0025] Example 1

[0026] The specific steps of the preparation method are as follows:

[0027] (1) Tin metal alloy 72 parts, flux 11 parts, organic solvent 3 parts, protective agent 5 parts, wetting enhancer 9 parts;

[0028] (2) Pour the tin metal alloy into a copper crucible and heat, heat to 350°C, pour into the organic solvent to mix into a tin metal liquid;

[0029] (3) Add the tin metal liquid in the above (2) to the protective agent, stand for 8 min, stir evenly, pour into a closed copper pot and heat to 430°C, add the wetting enhancer, cool to 200-280°C, add the flux, cool to room temperature 20°C and continue to stir for 36 min, take out, place in an enamel container and stand for 3 h, mix into a paste, and pack in a container, to obtain the low-temperature lead-free solder paste.

[0030] Example 2

[0031] The specific steps of the preparation method are as follows:

[0032] (1) Tin metal alloy 75 parts, flux 13 parts, organic solvent 5 parts, protective agent 3 parts, wetting enhancer 4 parts;

[0033] (2) Pour the tin metal alloy into a copper crucible and heat, heat to 380°C, pour into the organic solvent to mix into a tin metal liquid;

[0034] (3) Add the tin metal liquid in the above (2) to the protective agent, stand for 9 min, stir evenly, pour into a closed copper pot and heat to 450°C, add the wetting enhancer, cool to 200-280°C, add the flux, cool to room temperature 26°C and continue to stir for 38 min, take out, place in an enamel container and stand for 3.5 h, mix into a paste, and pack in a container, to obtain the low-temperature lead-free solder paste.

[0035] Example 3

[0036] The specific steps of the preparation method are as follows:

[0037] (1) Tin metal alloy 78 parts, flux 10 parts, organic solvent 2 parts, protective agent 4 parts, wetting enhancer 6 parts;

[0038] (2) Pour the tin metal alloy into a copper crucible and heat, heat to 360°C, pour into the organic solvent to mix into a tin metal liquid;

[0039] (3) : tin metal liquid in the above (2) is added into a protective agent, and is left for 10 min, is stirred uniformly, is poured into a closed copper pot, is heated to 490°C, a wetting enhancer is added, is cooled to 200-280°C, a flux is added, is cooled to room temperature 30°C, and is continuously stirred for 40 min, is taken out, is placed in an enamel container, is left for 4 h, is mixed into a paste, is divided into containers, and a low-temperature lead-free soldering tin paste is obtained.

[0040] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A low-temperature lead-free solder paste, characterized in that, The solder paste comprises the following components by weight: 70-80 parts tin alloy, 10-15 parts flux, 1-5 parts organic solvent, 3-7 parts protective agent, and 4-9 parts wetting enhancer. The tin alloy is composed of tin-nickel alloy, tin-bismuth alloy, and tin-silver-copper alloy. The preparation method of the tin alloy is as follows: a) crushing the tin-nickel alloy, tin-bismuth alloy, and tin-silver-copper alloy blocks into powder using a grinder; b) mixing them in a 2:3:5 ratio, placing them in a crucible, and heating to 350°C. The tin alloy is heated to 430℃ and stirred evenly during the melting process. Then, a slag is removed using a 200-300 mesh hafnium alloy metal filter. The molten alloy is then poured into a channel steel to cool and solidify, yielding the tin alloy. The tin alloy is a nano-tin alloy, which is produced by heating the tin alloy in a copper crucible to 400-500℃, adding sodium disulfite and serum protein to decompose it into particles, and then synthesizing tin nanoparticles of 1 to 6 nm size using a gamma-ray method. The flux is composed of the following raw materials in the following mass percentages: rosin resin 28%-50%, toluene isobutyl ketone 3%-8%, triethanolamine 22%-28%, and dimethyl succinate 12%-26%.

2. The low-temperature lead-free solder paste according to claim 1, characterized in that... The solder protective paste consists of the following components by weight: 72 parts tin metal alloy, 11 parts flux, 3 parts organic solvent, 5 parts protective agent, and 9 parts wetting enhancer.

3. The low-temperature lead-free solder paste according to claim 1, characterized in that... The solder protective paste consists of the following components by weight: 75 parts tin metal alloy, 13 parts flux, 5 parts organic solvent, 3 parts protective agent, and 4 parts wetting enhancer.

4. The low-temperature lead-free solder paste according to claim 1, characterized in that... The solder protective paste consists of the following components by weight: 78 parts tin metal alloy, 10 parts flux, 2 parts organic solvent, 4 parts protective agent, and 6 parts wetting enhancer.

5. The low-temperature lead-free solder paste according to claim 1, characterized in that... The organic solvent includes one or more of styrene, perchloroethylene, ethylene glycol ether, and triethanolamine.

6. The low-temperature lead-free solder paste according to claim 1, characterized in that... The protective agent includes one or more combinations of urea-formaldehyde resin and polyamide epichlorohydrin resin.

7. A process for preparing a low-temperature lead-free solder paste, used to prepare the low-temperature lead-free solder paste according to any one of claims 1-6, characterized in that, The preparation process of the solder protective paste is as follows: (1): Prepare 70-80 parts of tin metal alloy, 10-15 parts of flux, 1-5 parts of organic solvent, 3-7 parts of protective agent, and 4-9 parts of wetting enhancer; (2): Pour the tin metal alloy into a copper crucible and heat it to 330-460℃. Then pour in an organic solvent to mix it into a liquid tin metal. (3): Add protective agent to the tin liquid in step (2), let it stand for 8-10 minutes, stir evenly, pour it into a sealed copper pot, heat to 400-550℃, add wetting enhancer, cool to 200-280℃, add flux, cool to 20-32℃ and continue stirring for 35-40 minutes, take it out, place it in an enamel container and let it stand for 3-4 hours, mix it into a paste, and dispense it into containers to obtain low-temperature lead-free solder paste.