Lead-free solder composition and preparation method thereof

Abstract

The present invention relates to the field of welding technology, and in particular to a lead-free solder composition and a preparation method thereof. The composition includes solder and flux, and the solder includes: 55-65 parts of copper, 30-40 parts of zinc, 0.5-1 parts of silver, 0.1-1 parts of tin, 0.1-0.5 parts of nickel, 0.02-0.15 parts of lanthanum, 0.03-0.15 parts of cerium, and 0.05-0.2 parts of indium; The flux includes: 18-22 parts of borax, 13-17 parts of boric acid, 25-32 parts of potassium fluoride and potassium fluoroborate complex, 3-5 parts of calcium fluoride, 12-16 parts of aluminum oxide, and 8-11 parts of magnesium oxide. The lead-free solder composition does not contain toxic lead elements, and the pollution caused to the environment and ecosystem is less, and its wettability, corrosion resistance, strength and stability, etc. are improved, and the welding quality is comprehensively improved. The preparation method of the invention ensures uniform distribution and precise control of the solder and the flux, ensures the stability and consistency of product quality, is easy to operate, and is suitable for mass production.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to a lead-free solder composition and a preparation method thereof. Background Art

[0002] In the field of modern electronic manufacturing and welding technology, the research and development and application of lead-free solders have always been the focus of much attention. With the increasingly stringent environmental protection requirements, traditional lead-containing solders are gradually being eliminated, and the demand for lead-free solders is growing. At present, the common lead-free solders on the market still have some shortcomings in terms of performance. For example, some lead-free solders have a high melting point, which increases the energy consumption and operation difficulty during the welding process. At the same time, its corrosion resistance, wettability, and strength and stability after welding need to be further improved. In the prior art, in order to improve the performance of lead-free solders, researchers have made many attempts. Common methods include adjusting the composition ratio, adding different alloying elements, etc., but the effect is often limited and may bring new problems, such as increased costs and complex processes. The research on fluxes also faces similar challenges. Existing fluxes still have room for improvement in removing oxides, improving welding quality and stability. In terms of preparation technology, the existing lead-free solder preparation methods may have problems such as complex processes, imprecise parameter control, and difficulty in large-scale production. At the same time, how to effectively combine solder and flux to achieve the best welding effect is also a difficult problem that current technology needs to solve.

[0003] The Chinese patent document with application number CN202410898385.1 discloses a lead-free solder, including, by weight percentage: 5-6% Ag, 0.7-1.3% Cu, 1.5-3.5% Bi, 0.0004-0.001% P, 0.02-2% Ce, 0.02-0.3% Ni, 0.7-1.3% In, more than 0.2% Nd, and the balance is Sn. The lead-free solder is compatible with electronic components and materials currently using Sn-Pb solder due to the low melting point of the solder alloy; the solder has good antioxidant properties, and the welding process does not require the protection of rare gases such as N gas, thereby reducing the loss of tin slag; the amount of Ag used is reduced, which reduces the cost of raw materials, but overall there are still some defects in terms of wettability, mechanical properties, surface quality and environmental adaptability.

[0004] The Chinese invention patent with application number CN202111158543.2 discloses a copper-based solder, its preparation method and application. The copper-based solder includes, by mass percentage: Mn 10%-12%, Ni 3%-4%, Si 0.5%-2%, Cr0.3%-0.9%, B 0.03%-0.5%, Fe 1.5%-3%, Co 0-0.2%, Zn 0-0.5%, and the balance is Cu and unavoidable impurities. The copper-based solder of this invention eliminates the production of low-melting-point copper-aluminum eutectic and aluminum-silicon eutectic compounds, and improves the high-temperature performance of the copper-based solder by regulating the various components within the above range. However, its poor fluidity will make it difficult for the solder to spread evenly during the welding process, affecting the welding quality. It is brittle and prone to cracks during the welding process, affecting the reliability and service life of the solder joint.

[0005] In summary, in order to meet the demand for high-performance, low-cost and easy-to-produce lead-free solder in soldering, it is of great significance to develop a new lead-free solder composition and an optimized preparation method thereof. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a lead-free solder composition and a preparation method thereof, wherein the lead-free solder composition does not contain toxic lead elements, causes less pollution to the environment and ecosystem, and improves its wettability, corrosion resistance, strength and stability, etc., thereby comprehensively improving the welding quality. The preparation method ensures uniform distribution and precise control of the solder and flux, ensures the stability and consistency of product quality, is easy to operate, and is suitable for mass production.

[0007] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0008] A lead-free solder composition comprises a solder and a flux, wherein the solder comprises the following raw materials by weight: 55-65 parts of copper, 30-40 parts of zinc, 0.5-1 parts of silver, 0.1-1 parts of tin, 0.1-0.5 parts of nickel, 0.02-0.15 parts of lanthanum, 0.03-0.15 parts of cerium, and 0.05-0.2 parts of indium;

[0009] The brazing flux comprises the following raw materials by weight: 18-22 parts of borax, 13-17 parts of boric acid, 25-32 parts of potassium fluoride and potassium fluoroborate complex, 3-5 parts of calcium fluoride, 12-16 parts of aluminum oxide, and 8-11 parts of magnesium oxide;

[0010] The preparation method of the potassium fluoride and potassium fluoroborate complex is as follows:

[0011] Step 1, potassium fluoride and potassium fluoroborate are mixed, nano-alumina and nano-magnesium oxide are added, and nano-treatment is performed by ball milling, the ball milling time is 4-5 hours, the ball-to-material ratio is 8-12:1, and the ball mill speed is 500-600 rpm to obtain a composite 1;

[0012] Step 2, using lithium fluoride and sodium fluoride as coating materials to perform surface coating treatment on the composite 1: adding lithium fluoride, sodium fluoride and deionized water to the composite 1 to form a uniform suspension, and then performing microwave hydrothermal reaction for 3-4 hours at a microwave power of 600-800 W and a temperature of 180-220° C., and then cooling, filtering, washing, removing the reactants remaining on the surface, and finally drying the product to obtain a composite 2;

[0013] Step 3, adding multi-walled carbon nanotubes and graphene to the composite 2, and then heat treating for 2-3 hours at a temperature of 400-500° C. under an inert gas protection condition to obtain a composite 3;

[0014] Step 4, cooling, crushing and screening the heat-treated composite 3 to obtain a composite of potassium fluoride and potassium fluoroborate.

[0015] Copper and zinc are the main components of the solder, providing basic welding performance and strength. Silver can improve the conductivity and wettability of the solder, and tin helps to lower the melting point and improve the processability of welding. Nickel can inhibit the intergranular corrosion of copper-zinc alloys, improve the corrosion resistance of solder joints, and enhance the corrosion resistance and high-temperature stability of the solder. At the same time, nickel can also increase the solid solution strengthening effect of the silver-rich phase in the solder seam and improve the shear strength of the brazed joint. Rare earth elements lanthanum and cerium can refine the grains and improve the toughness and oxidation resistance of the solder. Indium can reduce the viscosity of the solder melt, improve the spreading performance of the solder, and further improve the wettability and welding reliability. These components work together to enable the solder to flow better and fill the weld during the welding process, forming a firm and reliable welded joint.

[0016] Among the brazing fluxes, borax and boric acid are commonly used brazing fluxes with good defilming ability, but their melting points are relatively high, so they need to be used in combination with other ingredients to reduce the melting point and enhance activity. Potassium fluoride and potassium fluoroborate can significantly improve the defilming ability of the brazing flux, especially when processing copper and its alloys. Potassium fluoride can effectively remove oxides and accelerate the removal of the oxide layer, thereby improving the wettability and bonding strength of the weld. It can also reduce the melting point of borax, reduce energy consumption and improve welding efficiency. Borax and boric acid in the brazing flux will form a thin liquid film during the heating process, covering the surface of the base material and the brazing material, isolating oxygen and preventing oxidation. Potassium fluoride and potassium fluoroborate also play a protective role. They decompose at high temperatures to form protective gases to prevent the base material and the brazing material from oxidizing during the welding process. They can also reduce the surface tension of the base material, thereby improving the wettability of the liquid brazing material on the base material surface. Potassium fluoride and potassium fluoroborate can also activate the base material surface, promote the metallurgical bonding between the brazing material and the base material, and improve the wettability and welding quality. Calcium fluoride in the flux can improve the ability to remove oxides, reduce defects such as pores in the weld, and thus improve the quality of the welded joint. Alumina and magnesium oxide enhance the activity of the flux by providing an alkaline environment, thereby improving wettability and welding results. The various components in the flux work synergistically to not only effectively remove the oxide film, protect the base material and the brazing material from oxidation, and activate the base material surface to promote metallurgical bonding, but also adjust the melting point, reduce corrosiveness, and improve the corrosion resistance of the weld.

[0017] The potassium fluoride and potassium fluoroborate complex in the flux is subjected to a series of treatments such as nano-treatment and coating. Among them, the nano-treatment can significantly increase the specific surface area of ​​potassium fluoride and potassium fluoroborate, thereby increasing the contact area and reaction efficiency with metal oxides and improving the activity. The nano-sized particles have higher surface energy and can react with metal oxides more effectively to remove the oxide film. Nano-alumina and nano-magnesium oxide have excellent high-temperature stability, which can improve the thermal stability of the complex at high temperatures and prevent its decomposition. Nano-alumina and nano-magnesium oxide have a large specific surface area and surface activity. They can be adsorbed on the surface of fluoride particles to form a steric hindrance effect, preventing direct contact and mutual attraction between particles, thereby avoiding the occurrence of agglomeration and improving its uniform dispersion in the flux. Uniformly dispersed nano-alumina, nano-magnesium oxide and fluoride can improve the deoxidation ability and wettability of the flux, making it easier for the solder to spread on the metal surface.

[0018] The coating layer of lithium fluoride and sodium fluoride can form a protective shell to prevent the nanoparticles from agglomerating or oxidizing at high temperatures, prevent the composite from undergoing unnecessary reactions or deterioration during use, prevent decomposition at high temperatures, and improve the chemical stability and thermal stability of the composite. The coating layer can also play a slow-release role, control the release rate of active ingredients, and extend the effective action time of the flux. The coating layer materials of lithium fluoride and sodium fluoride can improve the compatibility of the composite with the solder and promote the spreading and wetting of the solder.

[0019] Multi-walled carbon nanotubes and graphene have extremely high thermal conductivity, which can significantly improve the thermal conductivity of the flux and improve heat transfer during welding. The addition of multi-walled carbon nanotubes and graphene can also increase the mechanical strength and toughness of the composite, prevent the flux from cracking or deforming at high temperatures, and thus improve the overall performance of the weld.

[0020] High temperature heat treatment makes the crystal structure in the composite more complete and orderly, and improves the stability of its physical and chemical properties. At the same time, it enhances the binding force between components such as multi-walled carbon nanotubes, graphene and fluoride, helps to form a closer bond between the components, and improves the overall strength and stability of the composite.

[0021] The above-mentioned composite modification method significantly improves the specific surface area and reaction activity of the potassium fluoride and potassium fluoroborate complex, enhances the deoxidation ability, reduces the corrosiveness, improves the stability, extends the service life, improves the comprehensive properties such as thermal conductivity and mechanical strength, and improves the overall performance of the flux.

[0022] Preferably, in step 1, the weight proportions of potassium fluoride, potassium fluoroborate, nano-aluminum oxide and nano-magnesium oxide are 12-15 parts, 8-12 parts, 0.4-0.5 parts and 0.2-0.3 parts respectively.

[0023] Preferably, in step 2, the amount of lithium fluoride is 0.4%-0.6% of the weight of the composite 1, the amount of sodium fluoride is 0.2%-0.4% of the weight of the composite 1, and the amount of deionized water is 3-5 times the weight of the composite 1.

[0024] Preferably, in step 3, the amounts of the multi-walled carbon nanotubes and graphene are 0.4%-0.6% and 0.2%-0.4% by weight of the composite 2, respectively.

[0025] Preferably, the particle sizes of the nano-aluminum oxide and nano-magnesium oxide in step 1 are both 10-50 nm.

[0026] Preferably, the coating thickness in step 2 is 20-30 nm.

[0027] Preferably, the particle size of the potassium fluoride and potassium fluoroborate complex is 10-50 μm.

[0028] The preparation method of the lead-free solder composition comprises the following steps:

[0029] S1, melting, casting, hot rolling, cold rolling and cutting the brazing material into strips;

[0030] S2, after uniformly mixing the components of the flux, extruding at 150-200°C to obtain a thin core with a diameter of 0.6-0.8 mm, at an extrusion speed of 10-20 mm / sec;

[0031] S3, placing the flux on the strip solder for wrapping, winding the strip solder at a speed of 50-100 revolutions per minute through a winding device, and then stretching the strip solder to a diameter of 0.3-0.5 mm.

[0032] Preferably, the specific steps of preparing the solder into a strip shape in step S1 are as follows:

[0033] 1) Weigh the solder raw materials according to the above weight proportions, and smelt them at a temperature of 1450-1550°C for 30-60 minutes;

[0034] 2) Casting and cooling the smelted solder alloy;

[0035] 3) hot rolling the cooled slab at a temperature of 800-900°C to form a strip with a thickness of 0.5-2.0 mm;

[0036] 4) Cold rolling the hot-rolled strip to a strip thickness of 0.1-0.5 mm;

[0037] 5) Annealing the cold-rolled strip at a temperature of 400-500°C for 2-3 hours;

[0038] 6) The annealed strip is surface treated by pickling or polishing.

[0039] Preferably, in step 6), the annealed strip is surface treated by polishing, and the specific steps of polishing are: using a polishing cloth impregnated with a polishing agent, polishing at a polishing machine speed of 1500-2000 rpm for 3-6 minutes, and the polishing agent is a cerium oxide polishing liquid with a particle size of 0.5-1 μm.

[0040] The present invention has the following beneficial effects:

[0041] The lead-free solder composition of the present invention does not contain toxic lead elements, causes less pollution to the environment and ecosystem, and improves its wettability, corrosion resistance, strength and stability, etc., thereby improving the overall welding quality. The solder can significantly improve the welding quality through the reasonable proportion of each component, ensure the high strength of the welding joint, reduce the formation of brittle compounds, and improve the oxidation resistance, corrosion resistance and processing performance of the solder. The potassium fluoride and potassium fluoroborate complex in the flux of the present invention is processed by a series of processes such as nano-processing and coating, wherein the nano-processing can significantly increase the specific surface area of ​​potassium fluoride and potassium fluoroborate, improve the activity, and enable it to react with metal oxides more effectively to remove the oxide film. The surface coating treatment of lithium fluoride and sodium fluoride can improve the stability of the complex and prevent decomposition at high temperatures. The addition of multi-walled carbon nanotubes and graphene improves the corrosion resistance and thermal conductivity of the welding joint, helps heat conduction during welding, and improves the welding quality. Nano-aluminum oxide and nano-magnesium oxide have excellent high-temperature stability, which can improve the thermal stability of the complex at high temperatures and prevent it from decomposing. Through the above modification, the performance of the potassium fluoride and potassium fluoroborate composite in high-temperature brazing is significantly improved, ensuring the high quality and high reliability of the welded joint.

[0042] The preparation method of the present invention, the structural design of the solder wrapped with the flux, the wrapping and stretching process ensure the uniform distribution and precise control of the solder and the flux, ensure the uniform release of the flux during the welding process, improve the welding quality, and stretch into a filamentous structure to facilitate welding operation, and can achieve precise welding control. Furthermore, through operations such as hot rolling, cold rolling, extrusion, and stretching, the shape and size of the solder and the flux can be accurately controlled to ensure the consistency and stability of the product. Thermal processing processes such as smelting and rolling help to improve the organizational structure and performance of the solder, while winding and stretching can make the solder and the flux more closely bonded and improve the welding effect. DETAILED DESCRIPTION

[0043] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0044] The raw materials used in the following examples are all common commercial products. Among them, copper, purity 99.97%; zinc, purity 99.9%; silver, purity 99.99%; tin, purity 99.99%; nickel, purity 99.96%; lanthanum, purity 99.9%; cerium, purity 99.9%; indium, purity 99.995%; borax, effective ingredient content 99% in the flux component; aluminum oxide, particle size 3-5mm, Changge Ruiyuan Chemical Co., Ltd.; magnesium oxide, effective ingredient content 99%, density 3.58, Jiangsu Bosite Chemical Technology Co., Ltd.; lithium fluoride used in the potassium fluoride and potassium fluoroborate complex, white powder, purity 99%, sodium fluoride, white crystalline powder, purity 99%, multi-walled carbon nanotubes, diameter 10nm-30nm, length 5-20 microns, Guangzhou Hongwu Material Technology Co., Ltd.; graphene, particle size 3-9nm, Nangong Jiuxin New Material Technology Co., Ltd. Example 1

[0045] A lead-free solder composition comprises a solder and a flux, wherein the solder comprises the following raw materials by weight: 60 parts of copper (Cu), 35 parts of zinc (Zn), 0.8 parts of silver (Ag), 0.3 parts of tin (Sn), 0.3 parts of nickel (Ni), 0.10 parts of lanthanum (La), 0.12 parts of cerium (Ce), and 0.13 parts of indium (In);

[0046] The brazing flux comprises the following raw materials by weight: 20 parts of borax, 15 parts of boric acid, 28 parts of potassium fluoride and potassium fluoroborate complex, 4 parts of calcium fluoride, 14 parts of aluminum oxide, and 10 parts of magnesium oxide;

[0047] The preparation method of the potassium fluoride and potassium fluoroborate complex is as follows:

[0048] Step 1, mixing potassium fluoride and potassium fluoroborate, adding nano-alumina and nano-magnesium oxide, and performing nano-treatment by high-energy ball milling, the ball milling time is 4.5 hours, the ball-to-material ratio is 10:1, and the ball mill speed is 550 rpm to obtain a composite 1, wherein the weight portions of the potassium fluoride, potassium fluoroborate, nano-alumina and nano-magnesium oxide are 14 parts, 9 parts, 0.45 parts, and 0.25 parts, respectively, and the particle sizes of the nano-alumina and nano-magnesium oxide are both 10-50 nm;

[0049] Step 2, using lithium fluoride and sodium fluoride as coating materials to perform surface coating treatment on the composite 1: lithium fluoride, sodium fluoride, and deionized water are added to the composite 1 to form a uniform suspension, and then microwave hydrothermal reaction is performed for 3.5 hours at a microwave power of 700 W and a temperature of 200° C. After the reaction is completed, the reaction container is taken out of the microwave device and naturally cooled to room temperature. The cooled reaction product is poured into a filtration device and filtered using a microporous filter membrane with a pore size of 2-5 μm to remove the liquid part in the reaction medium. The filtered solid product was washed with deionized water for several times, 150 mL of deionized water was used each time, and the solid product was washed 4 times to remove the reactants and impurities remaining on the surface. The washed solid product was placed in a drying oven and dried at 65° C. for 20 hours to obtain a composite 2. In the process of forming the suspension, the amount of lithium fluoride was 0.45% of the weight of the composite 1, the amount of sodium fluoride was 0.3% of the weight of the composite 1, the amount of deionized water was 4 times the weight of the composite 1, and the coating thickness was 25 nm.

[0050] Step 3, adding multi-walled carbon nanotubes and graphene to the composite 2, and then heat treating it at 450° C. in a nitrogen atmosphere for 2.5 h to obtain a composite 3, wherein the amount of the multi-walled carbon nanotubes and graphene is 0.5% and 0.3% of the weight of the composite 2, respectively;

[0051] Step 4, cooling the heat-treated composite 3 to room temperature, crushing it with a jet mill under the conditions of a compressed air pressure of 0.6-MPa and an air flow velocity of 200 m / s, and then sieving to obtain a potassium fluoride and potassium fluoroborate composite, wherein the obtained potassium fluoride and potassium fluoroborate composite has a particle size of 30-40 μm.

[0052] The preparation method of the lead-free solder composition comprises the following steps:

[0053] S1, making the brazing material into a strip, the specific steps are as follows:

[0054] 1) Weigh the solder raw materials according to the above weight proportions and put them into a vacuum induction melting furnace for melting at a temperature of 1500°C for 45 minutes;

[0055] 2) Casting the melted brazing alloy into a slab and cooling it;

[0056] 3) hot rolling the cooled slab at a temperature of 850°C to a strip thickness of 1.2 mm;

[0057] 4) cold rolling the hot-rolled strip to a strip thickness of 0.4 mm;

[0058] 5) The cold-rolled strip is annealed at a temperature of 450°C for 2.5 hours;

[0059] 6) polishing the annealed strip for surface treatment, wherein the specific steps of polishing are: using a polishing cloth impregnated with a fine polishing agent, polishing at a polishing machine speed of 1800 rpm for 4 minutes, and the polishing agent is a cerium oxide polishing liquid with a particle size of 0.5-1 μm;

[0060] S2, after mixing the flux components uniformly, extruding at 180°C into a thin core with a diameter of 0.7 mm, and an extrusion speed of 15 mm / s;

[0061] S3, placing the flux on the strip solder for wrapping, winding the strip solder at a speed of 70 revolutions per minute through a winding device, and stretching the strip solder to a diameter of 0.4 mm at room temperature. Example 2

[0062] A lead-free solder composition comprises a solder and a flux, wherein the solder comprises the following raw materials by weight: 55 parts of copper (Cu), 32 parts of zinc (Zn), 0.5 parts of silver (Ag), 0.5 parts of tin (Sn), 0.5 parts of nickel (Ni), 0.08 parts of lanthanum (La), 0.03 parts of cerium (Ce), and 0.05 parts of indium (In);

[0063] The brazing flux comprises the following raw materials by weight: 22 parts of borax, 17 parts of boric acid, 32 parts of potassium fluoride and potassium fluoroborate complex, 4 parts of calcium fluoride, 16 parts of aluminum oxide, and 8 parts of magnesium oxide;

[0064] The preparation method of the potassium fluoride and potassium fluoroborate complex is as follows:

[0065] Step 1, mixing potassium fluoride and potassium fluoroborate, adding nano-alumina and nano-magnesium oxide, and performing nano-treatment by high-energy ball milling, wherein the ball milling time is 5 hours, the ball-to-material ratio is 12:1, and the ball mill speed is 500 rpm to obtain a composite 1, wherein the weight portions of the potassium fluoride, potassium fluoroborate, nano-alumina and nano-magnesium oxide are 13 parts, 12 parts, 0.4 parts, and 0.28 parts, respectively, and the particle sizes of the nano-alumina and nano-magnesium oxide are both 10-50 nm;

[0066] Step 2, using lithium fluoride and sodium fluoride as coating materials to perform surface coating treatment on the composite 1: lithium fluoride, sodium fluoride and deionized water are added to the composite 1 to form a uniform suspension, and then a microwave hydrothermal reaction is performed for 3 hours at a microwave power of 600 W and a temperature of 190° C. After the reaction is completed, the reaction vessel is taken out from the microwave device and naturally cooled to room temperature. The cooled reaction product is poured into a filter device and filtered using a microporous filter membrane with a pore size of 2-5 microns to remove the liquid part in the reaction medium, and then the filtered solid product is washed with deionized water for multiple times, using 100 mL of deionized water each time, and washed 5 times to remove the reactants and impurities remaining on the surface, and the washed solid product is placed in a drying oven and dried at a temperature of 70° C. for 18 hours to obtain a composite 2; in the process of forming the suspension, the amount of lithium fluoride is 0.5% of the weight of the composite 1, the amount of sodium fluoride is 0.2% of the weight of the composite 1, the amount of deionized water is 3 times the weight of the composite 1, and the coating thickness is 28 nm;

[0067] Step 3, adding multi-walled carbon nanotubes and graphene to the composite 2, and then heat treating the composite 2 at 400° C. in a nitrogen atmosphere for 3 h to obtain a composite 3, wherein the amounts of the multi-walled carbon nanotubes and graphene are 0.4% and 0.4% by weight of the composite 2, respectively;

[0068] Step 4, cooling the heat-treated composite 3 to room temperature, crushing it with a jet mill under the conditions of a compressed air pressure of 0.6-MPa and an air flow velocity of 200 m / s, and then sieving to obtain a potassium fluoride and potassium fluoroborate composite, wherein the obtained potassium fluoride and potassium fluoroborate composite has a particle size of 10-20 μm.

[0069] The preparation method of the lead-free solder composition comprises the following steps:

[0070] S1, making the brazing material into a strip, the specific steps are as follows:

[0071] 1) Weigh the brazing material according to the above weight proportions and put it into a vacuum induction melting furnace for melting at a temperature of 1450°C for 60 minutes;

[0072] 2) Casting the melted brazing alloy into a slab and cooling it;

[0073] 3) hot rolling the cooled slab at a temperature of 850°C to a strip thickness of 1.5 mm;

[0074] 4) cold rolling the hot-rolled strip to a strip thickness of 0.5 mm;

[0075] 5) The cold-rolled strip is annealed at a temperature of 400°C for 3 hours;

[0076] 6) polishing the annealed strip for surface treatment, wherein the specific steps of polishing are: using a polishing cloth impregnated with a fine polishing agent, polishing at a polishing machine speed of 1500 rpm for 6 minutes, and the polishing agent is a cerium oxide polishing liquid with a particle size of 0.5-1 μm;

[0077] S2, after mixing the flux components uniformly, extruding them into a thin core with a diameter of 0.6 mm at 150°C, with an extrusion speed of 10 mm / s;

[0078] S3, placing the flux on the strip solder for wrapping, winding the strip solder at a speed of 100 revolutions per minute through a winding device, and stretching the strip solder to a diameter of 0.3 mm at room temperature. Example 3

[0079] A lead-free solder composition comprises a solder and a flux, wherein the solder comprises the following raw materials by weight: 65 parts of copper (Cu), 30 parts of zinc (Zn), 1 part of silver (Ag), 1 part of tin (Sn), 0.1 part of nickel (Ni), 0.15 parts of lanthanum (La), 0.15 parts of cerium (Ce), and 0.2 parts of indium (In);

[0080] The brazing flux comprises the following raw materials by weight: 18 parts of borax, 14 parts of boric acid, 25 parts of potassium fluoride and potassium fluoroborate complex, 3 parts of calcium fluoride, 12 parts of aluminum oxide, and 11 parts of magnesium oxide;

[0081] The preparation method of the potassium fluoride and potassium fluoroborate complex is as follows:

[0082] Step 1, mixing potassium fluoride and potassium fluoroborate, adding nano-alumina and nano-magnesium oxide, and performing nano-treatment by high-energy ball milling, the ball milling time is 4 hours, the ball-to-material ratio is 8:1, and the ball mill speed is 600 rpm to obtain a composite 1, wherein the weight portions of the potassium fluoride, potassium fluoroborate, nano-alumina and nano-magnesium oxide are 12 parts, 10 parts, 0.5 parts, and 0.3 parts, respectively, and the particle sizes of the nano-alumina and nano-magnesium oxide are both 10-50 nm;

[0083] Step 2, using lithium fluoride and sodium fluoride as coating materials to perform surface coating treatment on the composite 1: lithium fluoride, sodium fluoride and deionized water are added to the composite 1 to form a uniform suspension, and then a microwave hydrothermal reaction is performed for 4 hours at a microwave power of 800 W and a temperature of 180° C. After the reaction is completed, the reaction vessel is taken out from the microwave device and naturally cooled to room temperature. The cooled reaction product is poured into a filter device and filtered using a microporous filter membrane with a pore size of 2-5 microns to remove the liquid part in the reaction medium, and then the filtered solid product is washed with deionized water for multiple times, using 200 mL of deionized water each time, and washed 3 times to remove the reactants and impurities remaining on the surface, and the washed solid product is placed in a drying oven and dried at a temperature of 80° C. for 12 hours to obtain a composite 2; in the process of forming the suspension, the amount of lithium fluoride is 0.6% of the weight of the composite 1, the amount of sodium fluoride is 0.4% of the weight of the composite 1, the amount of deionized water is 5 times the weight of the composite 1, and the coating thickness is 20 nm;

[0084] Step 3, adding multi-walled carbon nanotubes and graphene to the composite 2, and then heat treating it at a temperature of 500° C. in a nitrogen atmosphere for 2 hours to obtain a composite 3, wherein the amount of the multi-walled carbon nanotubes and graphene is 0.6% and 0.2% by weight of the composite 2, respectively;

[0085] Step 4, cooling the heat-treated composite 3 to room temperature, crushing it with a jet mill under the conditions of a compressed air pressure of 0.6-MPa and an air flow velocity of 200 m / s, and then sieving to obtain a potassium fluoride and potassium fluoroborate composite, wherein the obtained potassium fluoride and potassium fluoroborate composite has a particle size of 40-50 μm.

[0086] The preparation method of the lead-free solder composition comprises the following steps:

[0087] S1, making the brazing material into a strip, the specific steps are as follows:

[0088] 1) Weigh the solder raw materials according to the above weight proportions and put them into a vacuum induction melting furnace for melting at a temperature of 1550°C for 30 minutes;

[0089] 2) Casting the melted brazing alloy into a slab and cooling it;

[0090] 3) hot rolling the cooled slab at a temperature of 800°C to a strip thickness of 0.5 mm;

[0091] 4) cold rolling the hot-rolled strip to a strip thickness of 0.1 mm;

[0092] 5) The cold-rolled strip is annealed at a temperature of 500°C for 2 hours;

[0093] 6) The annealed strip is subjected to surface treatment by polishing, wherein the specific steps of the polishing are:

[0094] Use a polishing cloth impregnated with a fine polishing agent, polish at a polishing machine speed of 2000 rpm for 3 minutes, and the polishing agent is a cerium oxide polishing liquid with a particle size of 0.5-1 μm;

[0095] S2, after mixing the flux components uniformly, extruding them into a thin core with a diameter of 0.8 mm at 200°C, with an extrusion speed of 10 mm / s;

[0096] S3, placing the flux on the strip solder for wrapping, winding the strip solder at a speed of 50 revolutions per minute through a winding device, and stretching the strip solder to a diameter of 0.5 mm at room temperature. Example 4

[0097] A lead-free solder composition comprises a solder and a flux, wherein the solder comprises the following raw materials in parts by weight: 62 parts of copper (Cu), 40 parts of zinc (Zn), 0.6 parts of silver (Ag), 0.1 parts of tin (Sn), 0.4 parts of nickel (Ni), 0.02 parts of lanthanum (La), 0.08 parts of cerium (Ce), and 0.15 parts of indium (In);

[0098] The brazing flux comprises the following raw materials by weight: 21 parts of borax, 13 parts of boric acid, 30 parts of potassium fluoride and potassium fluoroborate complex, 5 parts of calcium fluoride, 15 parts of aluminum oxide, and 9 parts of magnesium oxide;

[0099] The preparation method of the potassium fluoride and potassium fluoroborate complex is as follows:

[0100] Step 1, mixing potassium fluoride and potassium fluoroborate, adding nano-alumina and nano-magnesium oxide, and performing nano-treatment by high-energy ball milling, the ball milling time is 5 hours, the ball-to-material ratio is 9:1, and the ball mill speed is 570 rpm to obtain a composite 1, wherein the weight portions of the potassium fluoride, potassium fluoroborate, nano-alumina and nano-magnesium oxide are 15 parts, 8 parts, 0.5 parts, and 0.2 parts, respectively, and the particle sizes of the nano-alumina and nano-magnesium oxide are both 10-50 nm;

[0101] Step 2, using lithium fluoride and sodium fluoride as coating materials to perform surface coating treatment on the composite 1: lithium fluoride, sodium fluoride and deionized water are added to the composite 1 to form a uniform suspension, and then microwave hydrothermal reaction is performed for 4 hours at a microwave power of 670 W and a temperature of 220° C. After the reaction is completed, the reaction container is taken out of the microwave device and naturally cooled to room temperature. The cooled reaction product is poured into a filtration device and filtered using a microporous filter membrane with a pore size of 2-5 microns to remove the liquid portion in the reaction medium. The filtered solid product was then washed with deionized water for multiple times, using 180 mL of deionized water each time, for three times to remove the reactants and impurities remaining on the surface, and the washed solid product was placed in a drying oven and dried at 60° C. for 24 hours to obtain a composite 2; in the process of forming the suspension, the amount of lithium fluoride was 0.4% of the weight of the composite 1, the amount of sodium fluoride was 0.24% of the weight of the composite 1, the amount of deionized water was 3.5 times the weight of the composite 1, and the coating thickness was 30 nm;

[0102] Step 3, adding multi-walled carbon nanotubes and graphene to the composite 2, and then heat treating it at a temperature of 480° C. in a nitrogen atmosphere for 3 hours to obtain a composite 3, wherein the amounts of the multi-walled carbon nanotubes and graphene are 0.46% and 0.24% by weight of the composite 2, respectively;

[0103] Step 4, cooling the heat-treated composite 3 to room temperature, crushing it with a jet mill under the conditions of a compressed air pressure of 0.6-MPa and an air flow velocity of 200 m / s, and then sieving to obtain a potassium fluoride and potassium fluoroborate composite, wherein the obtained potassium fluoride and potassium fluoroborate composite has a particle size of 30-40 μm.

[0104] The preparation method of the lead-free solder composition comprises the following steps:

[0105] S1, making the brazing material into a strip, the specific steps are as follows:

[0106] 1) Weigh the brazing material according to the above weight proportions and put it into a vacuum induction melting furnace for melting at a temperature of 1530°C for 40 minutes;

[0107] 2) Casting the melted brazing alloy into a slab and cooling it;

[0108] 3) hot rolling the cooled slab at a temperature of 900°C to a strip thickness of 2.0 mm;

[0109] 4) cold rolling the hot-rolled strip to a strip thickness of 0.3 mm;

[0110] 5) The cold-rolled strip is annealed at a temperature of 480°C for 2 hours;

[0111] 6) The annealed strip is subjected to surface treatment by polishing, wherein the specific steps of the polishing are:

[0112] Use a polishing cloth impregnated with a fine polishing agent, polish at a polishing machine speed of 1700 rpm for 5 minutes, and the polishing agent is a cerium oxide polishing liquid with a particle size of 0.5-1 μm;

[0113] S2, after mixing the flux components uniformly, extruding them into a thin core with a diameter of 0.6 mm at 170°C, with an extrusion speed of 12 mm / s;

[0114] S3, placing the flux on the strip solder for wrapping, winding the strip solder at a speed of 80 revolutions per minute through a winding device, and stretching the strip solder to a diameter of 0.4 mm at room temperature.

[0115] Comparative Example 1

[0116] A lead-free solder composition comprises a solder and a flux, wherein the solder comprises the following raw materials by weight: 60 parts of copper (Cu), 35 parts of zinc (Zn), 2.8 parts of silver (Ag), 0.3 parts of tin (Sn), 0.3 parts of nickel (Ni), and 0.13 parts of indium (In);

[0117] The brazing flux comprises the following raw materials by weight: 20 parts of borax, 15 parts of boric acid, 28 parts of potassium fluoride, 4 parts of calcium fluoride, 14 parts of aluminum oxide, and 10 parts of magnesium oxide; the rest is the same as in Example 1.

[0118] Comparative Example 2

[0119] A lead-free solder composition comprises a solder and a flux, wherein the solder comprises the following raw materials by weight: 60 parts of copper (Cu), 35 parts of zinc (Zn), 0.8 parts of silver (Ag), 0.3 parts of tin (Sn), 0.3 parts of nickel (Ni), 0.10 parts of lanthanum (La), 0.12 parts of cerium (Ce), and 0.13 parts of indium (In);

[0120] The brazing flux comprises the following raw materials by weight: 20 parts of borax, 15 parts of boric acid, 14 parts of potassium fluoride, 14 parts of potassium fluoroborate, 4 parts of calcium fluoride, 14 parts of aluminum oxide, and 10 parts of magnesium oxide;

[0121] The rest is the same as in Example 1.

[0122] Performance Testing:

[0123] Wettability: The lead-free solder compositions prepared in Examples 1-4 and Comparative Examples 1-2 were subjected to a wetting performance test and a maximum wetting force test using a SWB-2 solderability tester according to the wetting balance method specified in J-STD-002.

[0124] Tensile strength and shear strength: The solder compositions of Examples 1 to 4 and Comparative Examples 1 and 2 were used to connect copper materials, and the tensile strength and shear strength of the welded joints were tested according to GB / T228.1-2010 and GB / T 11363-2008.

[0125] Table 1. Welding performance test results

[0126]

[0127] It can be seen from Table 1 that the lead-free solder compositions of Examples 1-4 of the present invention have better solder wettability and mechanical properties of solder joints than those of Comparative Examples 1 and 2.

[0128] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0129] Although the embodiments of the present application have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present application, and that the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A lead-free solder composition, characterized in that The invention comprises a solder and a solder flux, wherein the solder comprises the following raw materials by weight: 55-65 parts of copper, 30-40 parts of zinc, 0.5-1 parts of silver, 0.1-1 parts of tin, 0.1-0.5 parts of nickel, 0.02-0.15 parts of lanthanum, 0.03-0.15 parts of cerium, and 0.05-0.2 parts of indium; The brazing flux comprises the following raw materials by weight: 18-22 parts of borax, 13-17 parts of boric acid, 25-32 parts of potassium fluoride and potassium fluoroborate complex, 3-5 parts of calcium fluoride, 12-16 parts of aluminum oxide, and 8-11 parts of magnesium oxide; The preparation method of the potassium fluoride and potassium fluoroborate complex is as follows: Step 1, potassium fluoride and potassium fluoroborate are mixed, nano-alumina and nano-magnesium oxide are added, and nano-treatment is performed by ball milling, the ball milling time is 4-5 hours, the ball-to-material ratio is 8-12:1, and the ball mill speed is 500-600 rpm to obtain a composite 1; Step 2, using lithium fluoride and sodium fluoride as coating materials to perform surface coating treatment on the composite 1: adding lithium fluoride, sodium fluoride and deionized water to the composite 1 to form a uniform suspension, and then performing microwave hydrothermal reaction for 3-4 hours at a microwave power of 600-800 W and a temperature of 180-220° C., and then cooling, filtering, washing, removing the reactants remaining on the surface, and finally drying the product to obtain a composite 2; Step 3, adding multi-walled carbon nanotubes and graphene to the composite 2, and then heat treating for 2-3 hours at a temperature of 400-500° C. under an inert gas protection condition to obtain a composite 3; Step 4, cooling, crushing and screening the heat-treated composite 3 to obtain a composite of potassium fluoride and potassium fluoroborate.

2. The lead-free solder composition according to claim 1, characterized in that In step 1, the weight proportions of potassium fluoride, potassium fluoroborate, nano-aluminum oxide and nano-magnesium oxide are 12-15 parts, 8-12 parts, 0.4-0.5 parts and 0.2-0.3 parts respectively.

3. The lead-free solder composition according to claim 1, characterized in that In step 2, the amount of lithium fluoride used is 0.4%-0.6% of the weight of the composite 1, the amount of sodium fluoride used is 0.2%-0.4% of the weight of the composite 1, and the amount of deionized water used is 3-5 times the weight of the composite 1.

4. The lead-free solder composition according to claim 1, characterized in that In step 3, the amounts of the multi-walled carbon nanotubes and graphene are 0.4%-0.6% and 0.2%-0.4% by weight of the composite 2, respectively.

5. The lead-free solder composition according to claim 1, characterized in that The particle sizes of the nano-aluminum oxide and nano-magnesium oxide in step 1 are both 10-50 nm.

6. The lead-free solder composition according to claim 1, characterized in that The coating thickness in step 2 is 20-30 nm.

7. The lead-free solder composition according to claim 1, characterized in that The particle size of the potassium fluoride and potassium fluoroborate complex is 10-50 μm.

8. The method for preparing the lead-free solder composition according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1, melting, casting, hot rolling, cold rolling and cutting the brazing material into strips; S2, after uniformly mixing the components of the flux, extruding at 150-200°C to obtain a thin core with a diameter of 0.6-0.8 mm, at an extrusion speed of 10-20 mm / sec; S3, placing the flux on the strip solder for wrapping, winding the strip solder at a speed of 50-100 revolutions per minute through a winding device, and then stretching the strip solder to a diameter of 0.3-0.5 mm.

9. The method for preparing a lead-free solder composition according to claim 8, characterized in that: The specific steps of preparing the solder into a strip in step S1 are as follows: 1) Weigh the brazing material and melt it at 1450-1550℃ for 30-60 minutes; 2) Casting and cooling the smelted solder alloy; 3) hot rolling the cooled slab at a temperature of 800-900°C to form a strip with a thickness of 0.5-2.0 mm; 4) Cold rolling the hot-rolled strip to a strip thickness of 0.1-0.5 mm; 5) Annealing the cold-rolled strip at a temperature of 400-500°C for 2-3 hours; 6) The annealed strip is surface treated by pickling or polishing.

10. The method for preparing a lead-free solder composition according to claim 9, characterized in that: In step 6), the annealed strip is surface treated by polishing. The specific steps of polishing are: using a polishing cloth impregnated with a polishing agent, polishing is performed at a polishing machine speed of 1500-2000 rpm for 3-6 minutes, and the polishing agent is a cerium oxide polishing liquid with a particle size of 0.5-1 μm.

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