SnCu alloy laser soldering paste and preparation method thereof

Abstract

The present invention discloses a SnCu alloy laser solder paste and a preparation method thereof. The raw materials of the SnCu alloy laser solder paste include solder powder and flux paste, wherein the solder powder includes Cu@Sn metal powder and silver metal powder, and the flux paste includes a modified rosin-based carboxylic acid, a modified rosin-based acrylate polymer, a solvent, a wetting agent, an organic amine, an antioxidant and anti-discoloration agent, and a thixotropic agent. The synergistic combination of the components in the SnCu alloy laser solder paste described in this application can effectively promote the wetting and diffusion of the alloy powder, while reducing oxidation and contamination during the welding process. The paste can be widely used in fields such as precision assembly of consumer electronics, high-reliability welding of automotive electronics, packaging of new energy equipment, medical / aerospace extreme environment devices, optical communication core modules, and industrial precision devices, achieving micron-level precision welding and high-reliability connections.

Description

Technical Field

[0001] The present invention relates to the field of microelectronic packaging technology, specifically to a SnCu alloy solder paste suitable for laser soldering and a preparation method thereof, and in particular provides an innovative solution to the material compatibility problem in the welding of high-precision electronic components. Background Art

[0002] In the existing electronic packaging process, surface mount technology (SMT) generally adopts wave soldering and reflow soldering processes, but these traditional thermal processing methods have significant technical defects: (1) Metal interdiffusion occurs between molten solder and copper-based pads at high temperatures of 240-260°C, forming brittle intermetallic compounds such as Cu6Sn5; (2) During the overall heating process, electronic components will be subjected to severe thermal shock. The difference in thermal expansion coefficient causes residual stress of the order of 50-80MPa inside the components. Finite element simulation confirms that this stress value has exceeded the tolerance limit of the QFN packaging structure; (3) The thermal process lasting 5-10 minutes causes the solder joint grains to grow to 20-50μm. Scanning electron microscopy observations show that the average thickness of the IMC layer exceeds the critical value of 5μm, resulting in a 40% decrease in the fatigue life of the solder joint.

[0003] Although laser welding technology effectively avoids the thermal damage problem of traditional processes through local heating mode (heat-affected zone 0.1-0.3mm), existing SMT solder paste exposes serious process defects under the conditions of laser instantaneous heating: ① Rapid vaporization of organic carriers causes a probability of tin explosion of more than 35%, and X-ray detection shows that the dispersion of solder ball diameter reaches ±25μm; ② Insufficient thermal decomposition of flux causes wetting angle fluctuations of more than 15°, and contact angle tests show that the average wettability is 27% lower than that of traditional processes; ③ The interaction between the laser beam and solder paste produces micron-level spatter, and 3D morphology analysis shows that the density of tin beads around the solder joint is more than 150 / mm 2 These defects seriously restrict the application of laser welding technology in the packaging of micro components below 0402.

[0004] The solder paste formulations currently described in published patent literature are primarily designed for traditional reflow soldering processes, resulting in inherent compatibility issues between their thermal response characteristics and laser processing parameters. In particular, in SnAgCu solders, the abnormal growth of Ag3Sn intermetallic compounds (TEM observations show enrichment at grain boundaries) can exacerbate material spattering under laser action. Existing technologies have yet to effectively address the issue of coordinating material phase transformation control and thermodynamic response in high-energy beam welding, a key bottleneck hindering the development of precision electronic packaging technology. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a preparation method of SnCu alloy laser solder paste, the preparation method and the application of the same in medical packaging.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] On the one hand, the present application provides a SnCu alloy laser solder paste, the raw materials of which include solder powder and flux paste;

[0008] The solder powder includes Cu@Sn metal powder and silver metal powder, and the flux paste includes modified rosin-based carboxylic acid, modified rosin-based acrylate polymer, solvent, wetting agent, thixotropic agent, organic amine, and antioxidant and anti-discoloration agent.

[0009] Furthermore, the average particle size of the Cu@Sn metal powder is 55-80 nm, wherein the average particle size of the Cu core is 50-70 nm, and the average thickness of the Sn shell is 4-8 nm;

[0010] Specifically, the average particle size of the Cu@Sn metal powder can be 55nm, 60nm, 65nm, 70nm, or 80nm; the average particle size of the Cu core can be 50nm, 55nm, 60nm, 65nm, or 70nm; and the average thickness of the Sn shell can be 4nm, 5nm, 6nm, 7nm, or 8nm.

[0011] Furthermore, the average particle size of the silver metal powder is 80-120 nm;

[0012] Furthermore, the structural formula of the modified rosin-based carboxylic acid is ;

[0013] Furthermore, the preparation method of the modified rosin-based acrylate polymer includes: taking rosin and glycidyl methacrylate and placing them in toluene, then adding hydroquinone and triethylamine, and reflux reaction for 6-8 hours. After the reaction is completed, removing the solvent to obtain an intermediate product; taking the intermediate product and polyethylene glycol monomethacrylate and placing them in acetonitrile, then adding an initiator, raising the temperature to 80-90°C, continuing the reaction for 10-14 hours, and distilling off the acetonitrile after the reaction is completed to obtain a modified rosin-based acrylate polymer;

[0014] Furthermore, the mass ratio of the rosin to the glycidyl methacrylate is 1-3:1, specifically, 1:1, 1.5:1.1, 2:1, 2.5:1, 3:1, etc.;

[0015] Furthermore, the amount of the hydroquinone is 0.5%-1.5% of the total mass of the rosin and the glycidyl methacrylate, specifically, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.;

[0016] Furthermore, the amount of triethylamine used is 1wt‰-5wt‰ of the total mass of the rosin and the glycidyl methacrylate;

[0017] Furthermore, the mass ratio of the intermediate product to the polyethylene glycol monomethacrylate is 1:1-1.5, specifically, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, etc.;

[0018] Furthermore, the initiator includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, tert-butyl hydroperoxide, methyl ethyl ketone peroxide, and benzoyl peroxide;

[0019] Furthermore, the amount of the initiator is 1%-4% of the total mass of the intermediate product and the polyethylene glycol monomethacrylate, specifically, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc.;

[0020] Furthermore, the solvent is selected from one or more of diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, glycerol, diethylene glycol monooctyl ether and hexylene glycol;

[0021] Furthermore, the thixotropic agent is selected from one or more of stearic acid amide, modified hydrogenated castor oil, and ethylene acetimide; the organic amine is selected from one or more of n-propanolamine, triethanolamine, and triisopropanolamine;

[0022] Furthermore, the antioxidant and anti-discoloration agent is selected from one or more of benzotriazole, antioxidant 245, N-ethylimidazole, and 2-ethylimidazole;

[0023] Furthermore, the raw materials of the SnCu alloy laser solder paste include 85%-95% solder powder and 5%-15% flux paste, calculated by weight percentage;

[0024] Preferably, the raw materials of the SnCu alloy laser solder paste include 75%-85% Cu@Sn metal powder, 3%-7% silver metal powder and 12%-18% flux paste;

[0025] More preferably, the raw materials of the SnCu alloy laser solder paste include 85% Cu@Sn metal powder, 5% silver metal powder and 15% soldering paste;

[0026] Furthermore, the soldering paste comprises, by weight, 20-30 parts of modified rosin-based carboxylic acid, 20-30 parts of modified rosin-based acrylate polymer, 30-40 parts of solvent, 0.5-1.5 parts of organic amine, 3-5 parts of antioxidant and anti-discoloration agent, and 4-6 parts of thixotropic agent;

[0027] Preferably, the soldering paste comprises 20-30 parts of modified rosin-based carboxylic acid, 20-30 parts of modified rosin-based acrylate polymer, 30-40 parts of solvent, 0.8-1.2 parts of organic amine, 3-5 parts of antioxidant and anti-discoloration agent, and 4-6 parts of thixotropic agent;

[0028] More preferably, the soldering paste comprises 20-30 parts of modified rosin-based carboxylic acid, 20-30 parts of modified rosin-based acrylate polymer, 30-40 parts of solvent, 1 part of organic amine, 4 parts of antioxidant and anti-discoloration agent, and 5 parts of thixotropic agent.

[0029] On the other hand, the present application also provides a method for preparing SnCu alloy laser solder paste, the preparation method comprising the following steps:

[0030] Step 1: Add modified rosin-based carboxylic acid, modified rosin-based acrylate polymer, solvent, wetting agent, thixotropic agent, organic amine, and antioxidant anti-discoloration agent to a reaction kettle, mix and stir evenly, and heat until completely dissolved to prepare a mixed solution. Then, stir thoroughly and cool to room temperature to form a paste. Then, grind with a three-roll mill and refrigerate for 12 hours until the paste fully recovers its thixotropy to obtain a soldering flux paste.

[0031] Step 2: Place the solder powder and the flux paste obtained in step 1 into a solder paste mixing barrel and mix them evenly to prepare SnCu alloy laser solder paste;

[0032] The solder powder comprises Cu@Sn metal powder and silver metal powder, and the solder paste comprises modified rosin-based carboxylic acid, modified rosin-based acrylate polymer, solvent, wetting agent, organic amine, antioxidant and anti-discoloration agent, and thixotropic agent;

[0033] Furthermore, the soldering paste comprises, by weight percentage, 20-30 parts of modified rosin-based carboxylic acid, 20-30 parts of modified rosin-based acrylate polymer, 30-40 parts of solvent, 0.5-1.5 parts of organic amine, 3-5 parts of antioxidant and anti-discoloration agent, and 4-6 parts of thixotropic agent;

[0034] The raw materials of the SnCu alloy laser solder paste include 85%-95% solder powder and 5%-15% flux paste by weight percentage;

[0035] Furthermore, the average particle size of the Cu@Sn metal powder is 55-80 nm, wherein the average particle size of the Cu core is 50-70 nm, and the average thickness of the Sn shell is 4-8 nm;

[0036] The average particle size of the silver metal powder is 80-120 nm;

[0037] The structural formula of the modified rosin-based carboxylic acid is ;

[0038] The solvent is selected from one or more of diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, glycerol, diethylene glycol monooctyl ether and hexylene glycol;

[0039] The thixotropic agent is selected from one or more of stearic acid amide, modified hydrogenated castor oil, and ethylene acetimide;

[0040] The organic amine is selected from one or more of n-propanolamine, triethanolamine and triisopropanolamine;

[0041] The antioxidant and anti-discoloration agent is selected from one or more of benzotriazole, antioxidant 245, N-ethylimidazole, and 2-ethylimidazole;

[0042] Furthermore, the preparation method of the modified rosin-based acrylate polymer includes: taking rosin and glycidyl methacrylate and placing them in toluene, then adding hydroquinone and triethylamine, and reflux reaction for 6-8 hours. After the reaction is completed, removing the solvent to obtain an intermediate product; taking the intermediate product and polyethylene glycol monomethacrylate and placing them in acetonitrile, then adding an initiator, raising the temperature to 80-90°C, continuing the reaction for 10-14 hours, and distilling off the acetonitrile after the reaction is completed to obtain a modified rosin-based acrylate polymer;

[0043] Furthermore, the mass ratio of the rosin to the glycidyl methacrylate is 1-3:1, specifically, 1:1, 1.5:1.1, 2:1, 2.5:1, 3:1, etc.;

[0044] Furthermore, the amount of the hydroquinone is 0.5%-1.5% of the total mass of the rosin and the glycidyl methacrylate, specifically, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, etc.;

[0045] Furthermore, the amount of triethylamine used is 1wt‰-5wt‰ of the total mass of the rosin and the glycidyl methacrylate;

[0046] Furthermore, the mass ratio of the intermediate product to the polyethylene glycol monomethacrylate is 1:1-1.5, specifically, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, etc.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The present invention discloses a SnCu alloy laser solder paste and a preparation method thereof. The raw materials of the SnCu alloy laser solder paste include solder powder and flux paste, wherein the solder powder includes Cu@Sn metal powder and silver metal powder, and the flux paste includes a modified rosin-based carboxylic acid, a modified rosin-based acrylate polymer, a solvent, a wetting agent, a thixotropic agent, an organic amine, and an antioxidant and anti-discoloration agent. The synergistic combination of the components in the SnCu alloy laser solder paste described in this application can effectively promote the wetting and diffusion of the alloy powder, while reducing oxidation and contamination during the welding process. The paste can be widely used in fields such as precision assembly of consumer electronics, high-reliability welding of automotive electronics, packaging of new energy equipment, medical / aerospace extreme environment devices, optical communication core modules, and industrial precision devices, achieving micron-level precision welding and high-reliability connections. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs. The terms used in the present specification are intended solely for the purpose of describing specific embodiments and are not intended to limit the present invention. In the description of this application, it should be understood that "and / or" describes an association relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can mean: A exists alone, A and B exist simultaneously, or B exists alone. A and B can be singular or plural. In this application, "at least one" means one or more, and "plurality" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can each be single or plural.

[0051] The present application will be described in detail below through specific examples. The following examples are only some examples of the present application and cannot be used to limit the present application.

[0052] Preparation Example of Cu@Sn Metal Powder

[0053] This embodiment provides Cu@Sn metal powder and a preparation method thereof, wherein the preparation method comprises the following steps:

[0054] Preparation of nano-copper powder: 1 L of copper sulfate aqueous solution (0.15 mol / L) was slowly added to 10.0 wt% ammonia water under a nitrogen atmosphere. The addition of ammonia water was stopped after the solution became completely clear. 40 g of polyvinyl pyrrolidone and 0.5 g of sodium lauryl sulfonate were then added. The temperature was raised to 80°C. Then, under stirring, a 2.5 wt% hydrazine hydrate aqueous solution at 80°C was added. When the pH value reached 10, the addition of the hydrazine hydrate aqueous solution was stopped. The mixture was stirred for 1 h and centrifuged under a nitrogen atmosphere. The obtained solid was washed three times with distilled water and then with ethanol, and dried to obtain nano-copper powder with an average particle size of 60 nm (measured by field emission scanning electron microscopy (FE-SEM)).

[0055] 180 ml of deionized water was placed in a beaker and heated to 80°C. 18 g of thiourea, 5 g of polyethylene glycol-2000, 0.3 g of EDTA-2Na, and 0.3 g of hydroquinone were then added to the beaker in sequence, with a stirring rate of 80 rpm maintained until the solution became clear and transparent. The solution was cooled to room temperature, and 9.5 g of nano-copper powder was added. After stirring and dispersing evenly, a mixed solution was obtained. Under stirring, 10 ml of a 5 mol / L aqueous solution of stannous chloride was added three times (each time with an interval of 20 min, and each time about 3.3 ml was added). After the addition was complete, the reaction was continued with stirring for 1 h. The mixture was then placed in a funnel and filtered. The obtained solid was washed three times with distilled water and then with ethanol, and dried to obtain Cu@Sn metal powder with an average particle size of 66 nm (measured by field emission scanning electron microscopy (FE-SEM)).

[0056] Preparation Example of Modified Rosin-Based Carboxylic Acid

[0057] This embodiment provides a modified rosin-based carboxylic acid and a preparation method thereof, the preparation method comprising the following steps:

[0058] 0.1 mol of abietic acid, 0.1 mol of propylene-1,2,3-tricarboxylic acid, 0.01 mol of p-toluenesulfonic acid and 30 ml of acetic acid were added to a reactor. After replacing with N2 gas, stirring was started, and the mixture was heated to 180°C and reacted at a constant temperature for 4 hours. After the reaction was completed, 70 ml of acetic acid was added, stirred evenly, and heated to 120°C. The mixture was then allowed to stand to room temperature, and then cooled in an ice-water bath to complete crystallization. The modified rosin-based carboxylic acid was obtained after filtration, washing with water, and drying.

[0059] ;

[0060] Modified rosin-based carboxylic acid

[0061] Preparation Example of Modified Rosin-Based Acrylate Polymer

[0062] This embodiment provides a modified rosin-based acrylate polymer and a preparation method thereof, wherein the preparation method comprises the following steps:

[0063] 18.8 g of rosin and 8.9 g of glycidyl methacrylate were placed in 500 ml of toluene, and then 0.1 g of hydroquinone and 0.3 g of triethylamine were added. The mixture was refluxed for 7 hours. After completion of the reaction, the solvent was removed to obtain an intermediate product. 20 g of the intermediate product and 20 g of polyethylene glycol monomethacrylate (CAS: 25736-86-1) were placed in 200 ml of acetonitrile. After stirring, 1 ml of an acetonitrile solution of AIBN (azobisisobutyronitrile) (0.5 g / ml) was added dropwise. After the addition was complete, the mixture was heated to 80°C and the reaction was continued for 12 hours. After completion of the reaction, the acetonitrile was evaporated to obtain a modified rosin-based acrylate polymer.

[0064] Example 1

[0065] This embodiment provides a SnCu alloy laser solder paste and a preparation method thereof, the preparation method comprising the following steps:

[0066] 30 g of modified rosin-based carboxylic acid, 20 g of modified rosin-based acrylate polymer, 19 g of diethylene glycol monooctyl ether, 15 g of diethylene glycol monoethyl ether, 1 g of triethanolamine, 4 g of benzotriazole, 2 g of stearic acid amide (CAS No.: 124-26-5), and 3 g of modified hydrogenated castor oil (CAS No.: 61788-85-0) were added to a reactor and mixed and stirred uniformly. The mixture was heated until completely dissolved to obtain a mixed solution, which was then thoroughly stirred and cooled to room temperature to form a paste. The mixture was then ground using a three-roll mill and refrigerated for 12 hours to fully restore the thixotropy of the paste to obtain a solder flux paste. 15 g of the solder flux paste, 80 g of Cu@Sn metal powder, and 5 g of silver metal powder (average particle size of 100 nm) were taken and stirred uniformly in a mixing barrel to obtain a SnCu alloy laser solder paste.

[0067] Example 2

[0068] This embodiment provides a SnCu alloy laser solder paste and a preparation method thereof, the preparation method comprising the following steps:

[0069] 25 g of modified rosin-based carboxylic acid, 25 g of modified rosin-based acrylate polymer, 19 g of diethylene glycol monooctyl ether, 15 g of diethylene glycol monoethyl ether, 1 g of triethanolamine, 4 g of benzotriazole, 2 g of stearic acid amide (CAS No.: 124-26-5), and 3 g of modified hydrogenated castor oil (CAS No.: 61788-85-0) were added to a reactor and mixed and stirred uniformly. The mixture was heated until completely dissolved to obtain a mixed solution, which was then thoroughly stirred and cooled to room temperature to form a paste. The mixture was then ground using a three-roll mill and refrigerated for 12 hours until the paste completely regained its thixotropy to obtain a solder flux paste. 15 g of the solder flux paste, 80 g of Cu@Sn metal powder, and 5 g of silver metal powder (average particle size of 100 nm) were taken and stirred uniformly in a mixing barrel to obtain a SnCu alloy laser solder paste.

[0070] Example 3

[0071] This embodiment provides a SnCu alloy laser solder paste and a preparation method thereof, the preparation method comprising the following steps:

[0072] 20 g of modified rosin-based carboxylic acid, 30 g of modified rosin-based acrylate polymer, 19 g of diethylene glycol monooctyl ether, 15 g of diethylene glycol monoethyl ether, 1 g of triethanolamine, 4 g of benzotriazole, 2 g of stearic acid amide (CAS No.: 124-26-5), and 3 g of modified hydrogenated castor oil (CAS No.: 61788-85-0) were added to a reactor and mixed and stirred uniformly. The mixture was heated until completely dissolved to obtain a mixed solution, which was then thoroughly stirred and cooled to room temperature to form a paste. The mixture was then ground using a three-roll mill and refrigerated for 12 hours until the paste completely regained its thixotropy to obtain a solder flux paste. 15 g of the solder flux paste, 80 g of Cu@Sn metal powder, and 5 g of silver metal powder (average particle size of 100 nm) were taken and stirred uniformly in a mixing barrel to obtain a SnCu alloy laser solder paste.

[0073] Comparative Example 1

[0074] Compared with Example 1, the only difference is that modified rosin-based carboxylic acid and modified rosin-based acrylate polymer are not added during the preparation of the soldering solder paste.

[0075] Comparative Example 2

[0076] Compared with Example 1, the only difference is that “30 g of modified rosin-based carboxylic acid and 20 g of modified rosin-based acrylate polymer” are replaced by “50 g of modified rosin-based carboxylic acid”.

[0077] Comparative Example 3

[0078] Compared with Example 1, the only difference is that “30 g of modified rosin-based carboxylic acid and 20 g of modified rosin-based acrylate polymer” are replaced by “50 g of modified rosin-based acrylate polymer”.

[0079] Performance Testing

[0080] 1. Expansion Rate Test The expansion rates of Examples 1-3 and Comparative Examples 1-5 were tested respectively with reference to SJ / T 11390-2019. The test results are shown in Table 1.

[0081] 2. Welding Test: Examples 1-3 and Comparative Examples 1-3 were subjected to welding tests respectively. The welding was performed under the condition of a laser light source power of 12 W, and the occurrence of tin balls was recorded. The test results are shown in Table 1.

[0082] 3. Shear Strength Test The shear strength of the solder joints obtained after welding of Examples 1-3 and Comparative Examples 1-5 was measured with reference to JIS-Z3198. The test board was a copper PCB and the chip component was a 0805 capacitor. The test results are shown in Table 1.

[0083] Table 1 Test results

[0084] Expansion rate (%) Wuxi beads Shear strength (MPa) Example 1 85.8% Wuxi beads 58.5 Example 2 82.5% Wuxi beads 53.4 Example 3 83.9% Wuxi beads 52.6 Comparative Example 1 62.8% There are a lot of solder beads 34.6 Comparative Example 2 72.4% There are trace amounts of tin beads 43.4 Comparative Example 3 75.2% There are a few tin beads 44.6

[0085] It can be seen from the above test results that the laser solder paste prepared in this application changes the rheological properties of the solder paste under the synergistic effect of various components, and can reduce the formation of solder balls and the phenomenon of solder splashing. At the same time, it also forms microstructures during the solder curing process, thereby enhancing the mechanical strength of the solder joints.

[0086] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method of this application and its core ideas. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting this application, and the scope of protection of the present invention should be based on the scope defined by the claims. For those skilled in the art in this field, without departing from the spirit and scope of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the scope of protection of the present invention. Those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A SnCu alloy laser solder paste, characterized in that: The raw materials of the SnCu alloy laser soldering paste include solder powder and flux paste; Wherein, the solder powder includes Cu@Sn metal powder and silver metal powder, and the flux paste includes modified rosin-based carboxylic acid, modified rosin-based acrylate polymer, solvent, wetting agent, organic amine, antioxidant and anti-discoloration agent, and thixotropic agent; The structural formula of the modified rosin-based carboxylic acid is ; The preparation method of the modified rosin-based acrylate polymer comprises: placing rosin and glycidyl methacrylate in toluene, then adding hydroquinone and triethylamine, and performing a reflux reaction for 6-8 hours. After the reaction is completed, removing the solvent to obtain an intermediate product; placing the intermediate product and polyethylene glycol monomethacrylate in acetonitrile, then adding an initiator, heating to 80-90° C., continuing the reaction for 10-14 hours, and distilling off the acetonitrile after the reaction is completed to obtain the modified rosin-based acrylate polymer; Calculated by weight percentage, the raw materials of the SnCu alloy laser solder paste include 85%-95% solder powder and 5%-15% flux paste; calculated by weight, the flux paste includes 20-30 parts of modified rosin-based carboxylic acid, 20-30 parts of modified rosin-based acrylate polymer, 30-40 parts of solvent, 0.5-1.5 parts of organic amine, 3-5 parts of antioxidant and anti-discoloration agent, and 4-6 parts of thixotropic agent.

2. The SnCu alloy laser solder paste according to claim 1, characterized in that The average particle size of the Cu@Sn metal powder is 55-80 nm, wherein the average particle size of the Cu core is 50-70 nm, and the average thickness of the Sn shell is 4-8 nm; The average particle size of the silver metal powder is 80-120 nm.

3. The SnCu alloy laser solder paste according to claim 1, characterized in that The mass ratio of the rosin to the glycidyl methacrylate is 1-3:1; the amount of the hydroquinone is 1wt‰-5wt‰ of the total mass of the rosin and the glycidyl methacrylate; the amount of the triethylamine is 0.5%-1.5% of the total mass of the rosin and the glycidyl methacrylate; the mass ratio of the intermediate product to the polyethylene glycol monomethacrylate is 1:1-1.5; the initiator includes one or more of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, tert-butyl hydroperoxide, methyl ethyl ketone peroxide, and benzoyl peroxide; the amount of the initiator is 1%-4% of the total mass of the intermediate product and the polyethylene glycol monomethacrylate.

4. The SnCu alloy laser solder paste according to claim 1, characterized in that The solvent is selected from one or more of diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, glycerol, diethylene glycol monooctyl ether and hexylene glycol; the thixotropic agent is selected from one or more of stearic acid amide, modified hydrogenated castor oil, and ethylene acetimide; the organic amine is selected from one or more of n-propanolamine, triethanolamine and triisopropanolamine; the antioxidant and anti-discoloration agent is selected from one or more of benzotriazole, antioxidant 245, N-ethylimidazole, and 2-ethylimidazole.

5. A method for preparing SnCu alloy laser solder paste, characterized in that: The preparation method comprises the following steps: Step 1: Add modified rosin-based carboxylic acid, modified rosin-based acrylate polymer, solvent, wetting agent, thixotropic agent, organic amine, and antioxidant anti-discoloration agent to a reaction kettle, mix and stir evenly, and heat until completely dissolved to prepare a mixed solution. Then, stir thoroughly and cool to room temperature to form a paste. Then, grind with a three-roll mill and refrigerate for 12 hours until the paste fully recovers its thixotropy to obtain a soldering flux paste. Step 2: Place the solder powder and the flux paste obtained in step 1 into a solder paste mixing barrel and mix them evenly to prepare SnCu alloy laser solder paste; Wherein, the solder powder includes Cu@Sn metal powder and silver metal powder, and the flux paste includes modified rosin-based carboxylic acid, modified rosin-based acrylate polymer, solvent, wetting agent, organic amine, antioxidant and anti-discoloration agent, and thixotropic agent; The structural formula of the modified rosin-based carboxylic acid is ; The preparation method of the modified rosin-based acrylate polymer comprises: placing rosin and glycidyl methacrylate in toluene, then adding hydroquinone and triethylamine, and performing a reflux reaction for 6-8 hours. After the reaction is completed, removing the solvent to obtain an intermediate product; placing the intermediate product and polyethylene glycol monomethacrylate in acetonitrile, then adding an initiator, heating to 80-90° C., continuing the reaction for 10-14 hours, and distilling off the acetonitrile after the reaction is completed to obtain the modified rosin-based acrylate polymer; The soldering paste comprises, by weight, 20-30 parts of modified rosin-based carboxylic acid, 20-30 parts of modified rosin-based acrylate polymer, 30-40 parts of solvent, 0.5-1.5 parts of organic amine, 3-5 parts of antioxidant and anti-discoloration agent, and 4-6 parts of thixotropic agent; Calculated by weight percentage, the raw materials of the SnCu alloy laser solder paste include 85%-95% solder powder and 5%-15% flux paste.

6. The method for preparing SnCu alloy laser solder paste according to claim 5, characterized in that: The average particle size of the Cu@Sn metal powder is 55-80 nm, wherein the average particle size of the Cu core is 50-70 nm, and the average thickness of the Sn shell is 4-8 nm; The average particle size of the silver metal powder is 80-120 nm; The solvent is selected from one or more of diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, glycerol, diethylene glycol monooctyl ether and hexylene glycol; The thixotropic agent is selected from one or more of stearic acid amide, modified hydrogenated castor oil, and ethylene acetimide; The organic amine is selected from one or more of n-propanolamine, triethanolamine and triisopropanolamine; The antioxidant and anti-discoloration agent is selected from one or more of benzotriazole, antioxidant 245, N-ethylimidazole, and 2-ethylimidazole.

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