A nano-silica doped multi-component tin-bismuth based lead-free low temperature solder and a method of making the same

Abstract

The application discloses a kind of nano-silica doped multi-component tin bismuth series lead-free low-temperature solder and preparation method thereof, belong to microelectronic packaging technical field.The solder includes the following mass percentage components:In:0.5-5%, nano-SiO2:0.1-1.5%, the rest is Sn58Bi matrix and inevitable small amount of impurities.Preparation method is: after the above raw materials are mixed, heated to melt, constant temperature stirring, casting, nano-silica doped multi-component tin bismuth series lead-free low-temperature solder is obtained.The method process flow is simple, cost is lower, environment friendly, and the low-temperature solder prepared has good wettability, anti-aging and corrosion resistance and other properties, suitable for microelectronic packaging technical field low-temperature welding.

Description

Technical Field

[0001] This invention belongs to the field of microelectronic packaging technology, and particularly relates to a multi-component tin-bismuth-based lead-free low-temperature solder doped with nano-silica and its preparation method. Background Technology

[0002] Solder is one of the most commonly used solders on the market. Lead-containing solder, with its excellent soldering performance and reliability, is widely used in automotive engine control units and sensors, as well as in industrial motors and power modules—fields with stringent requirements for compatibility and temperature characteristics. In recent years, with the rapid development of the electronics industry, lead pollution has become increasingly prominent. Lead toxicity causes serious harm to the environment, specifically polluting water, air, and soil, and its remediation is difficult, time-consuming, and costly. With the promulgation and implementation of relevant laws and regulations in most countries around the world, the use of lead-containing substances is strictly restricted.

[0003] An ideal lead-free solder alternative must possess core characteristics such as low melting point, excellent wettability, superior mechanical properties, and low cost. Existing lead-free solders in the low-temperature soldering field mainly include tin-indium alloys, tin-zinc alloys, and tin-bismuth alloys. Among these, the application of tin-indium alloys is limited due to the scarcity and high price of indium, and the application of tin-zinc alloys is limited due to the easy oxidation of zinc. While tin-bismuth alloy solders have application potential, they suffer from problems such as a large melting range and stress imbalance leading to solder joint peeling, severely affecting solder joint reliability. This defect can be improved by doping with other substances.

[0004] Patent CN116174993A discloses a nano-titanium dioxide-doped Sn-Ag-Cu-X quaternary solder and its preparation method. The formulation includes 0.1-0.3% nano-TiO2, 0.3-0.7% Ag, 0.5-0.9% Cu, and 0.4-0.6% wettability improver X (selected from Nd, Ga, and In). The preparation process employs a ball milling mixing process. However, the nano-TiO2 used in this technology suffers from poor acid resistance and susceptibility to photocatalytic oxidation reactions leading to structural changes, thus limiting its application scenarios.

[0005] In summary, developing a lead-free, environmentally friendly, cost-controllable, and microelectronic packaging-compatible tin-bismuth-based low-temperature lead-free solder has become a pressing technical challenge in this field. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a multi-component tin-bismuth-based lead-free low-temperature solder doped with nano-silica and its preparation method. This method features a simple process flow, low cost, and environmental friendliness. The resulting low-temperature solder exhibits excellent wettability, anti-aging properties, and corrosion resistance, making it suitable for low-temperature soldering in the field of microelectronic packaging technology.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A multi-component tin-bismuth-based lead-free low-temperature solder doped with nano-silica comprises the following components by mass percentage: In (indium): 0.5-5%, nano-SiO2 (diameter 20-100nm): 0.1-1.5%, with the balance being Sn58Bi matrix and unavoidable small amounts of impurities.

[0008] The multi-component tin-bismuth-based lead-free low-temperature solder of this invention achieves comprehensive performance optimization through the synergistic effect of each component. Specifically, using a tin-bismuth alloy as the matrix, the Bi element not only effectively lowers the melting point of the solder, adapting to the requirements of low-temperature welding, but its unique solidification expansion characteristics can also offset the stress generated by thermal expansion and contraction during welding, significantly reducing the risk of solder joint cracking. The In element has a melting point of only 156.51℃ and possesses excellent thermal and electrical conductivity, fluidity, and low expansion and contraction rate. On the one hand, it can further synergize with the Bi element to lower the overall melting point of the solder; on the other hand, its lead-free and non-toxic properties meet environmental protection requirements, while also improving the alloy's ductility and reducing the tendency to crack.

[0009] The addition of nano-SiO2 brings multiple performance benefits to solder: its excellent mechanical strengthening effect and high chemical inertness can significantly improve the compressive strength and corrosion resistance of the solder; through the filling effect, it can reduce the porosity and defects inside the solder, enhance the structural density, and thus improve the reliability of the solder joint (excessive addition of nano-SiO2 will lead to a significant decrease in the plasticity of the solder); as a reinforcing phase, nano-SiO2 further improves the tensile strength and toughness of the solder through grain refinement and dispersion strengthening mechanisms, and its high modulus and low coefficient of thermal expansion (similar to chip materials) can effectively alleviate stress concentration in the solder joint during thermal cycling and extend the product's service life; at the same time, nano-SiO2 particles can form a dense oxide layer in the solder, inhibit oxygen diffusion, reduce the oxidation tendency during the soldering process, and improve the overall oxidation resistance and thermal stability of the solder with its excellent chemical stability.

[0010] Furthermore, the excellent wettability of In reduces the surface tension of the solder, promoting its uniform spread on the substrate surface. Combined with the microscopic control effect of nano-SiO2, the solder can more precisely fill the gaps between tiny solder joints, significantly reducing porosity and cold solder joints, and optimizing soldering reliability. It is worth mentioning that both In and nano-SiO2 are added in minute quantities, fully leveraging the performance advantages of each component while avoiding the high costs caused by excessive use of precious metals and nanomaterials, achieving a balance between performance and economy.

[0011] Furthermore, the nano-silica-doped multi-component tin-bismuth-based lead-free low-temperature solder comprises the following components by mass percentage: In: 0.5%, nano-SiO2: 0.1-0.5%, with the balance being Sn58Bi matrix and unavoidable small amounts of impurities.

[0012] This invention further optimizes each component in the formulation, retaining the core performance advantages while avoiding the problem of reduced solder plasticity caused by excessive nano-SiO2. Precise proportioning achieves a balance between performance and economy, reducing the cost of using precious metals and nanomaterials, while ensuring that the solder has more stable plasticity, wettability, and anti-aging properties in low-temperature welding scenarios, making it suitable for applications with stringent requirements for both cost and performance.

[0013] Furthermore, in the Sn58Bi matrix, the mass ratio of Sn (tin) to Bi (bismuth) is (41.58-41.79):(57.42-57.71).

[0014] This invention ensures that the Sn58Bi matrix possesses stable low-melting-point characteristics and solidification expansion properties by limiting the specific mass ratio of Sn to Bi in the matrix. The precise Bi content effectively offsets the thermal expansion and contraction stress during the welding process, and the balanced Sn to Bi ratio guarantees the stability of the matrix's mechanical properties. This provides a uniform and reliable substrate foundation for subsequent In and nano-SiO2 doping, further reducing the risk of solder joint cracking and improving the overall structural stability and welding reliability of the solder.

[0015] This invention also provides a method for preparing a multi-component tin-bismuth-based lead-free low-temperature solder doped with nano-silica, comprising the following steps: Preparation of Sn58Bi matrix; In, nano-SiO2 and Sn58Bi matrix are weighed in proportion and mixed to obtain a mixture. The mixture is added to a lead-free graphite heating furnace, an antioxidant is added, and the mixture is heated to melt. The mixture is stirred at a constant temperature to ensure that the multiple elements are mixed evenly. Finally, it is cast into a mold to obtain a multi-component tin-bismuth-based lead-free low-temperature solder doped with nano-silica.

[0016] This invention provides a simple and cost-effective preparation method that requires no complex equipment and is easily scalable for industrial production. By adding antioxidants, oxidation loss of raw materials is reduced, and a constant-temperature stirring process ensures uniform mixing of all components, minimizing internal porosity and defects in the solder. The preparation process is environmentally friendly, generating no harmful pollutants, and the resulting solder exhibits stable and excellent properties such as wettability, anti-aging properties, and corrosion resistance, making it suitable for the low-temperature soldering requirements of large-scale microelectronic packaging.

[0017] Furthermore, the specific preparation steps of the Sn58Bi matrix include: adding Sn into a lead-free graphite heating furnace, heating until melting, then adding Bi, continuing to heat until melting, stirring at a constant temperature to obtain the Sn58Bi matrix.

[0018] This invention clarifies the stepwise preparation process of the Sn58Bi matrix. Sn is melted first, then Bi is added and heating continues to ensure full fusion and uniform composition of the two elements. This avoids matrix component segregation caused by improper mixing order, guarantees the stability of core properties such as low melting point and solidification expansion of the matrix, and provides a high-quality substrate for subsequent multi-component mixing, thus preventing the overall performance degradation of the solder due to matrix performance fluctuations from the outset.

[0019] Furthermore, the heating temperature is 250-350℃; the specific operation steps of the constant temperature stirring are: stirring at 250-350℃ for 30 minutes.

[0020] The temperature range defined by this invention ensures complete melting of Sn, Bi, and subsequent multi-component raw materials while avoiding oxidation and performance degradation caused by high temperatures. A fixed stirring time ensures uniform mixing of the raw materials, reducing localized compositional inconsistencies. Simultaneously, reasonable temperature and time settings reduce production energy consumption, improve process stability, and guarantee consistent solder performance in batch production.

[0021] Furthermore, the amount of antioxidant added is 0.1-0.3% of the mass of the mixture; the antioxidant is rosin.

[0022] This invention specifies that the antioxidant is rosin, and its dosage is controlled at 0.1-0.3%. Rosin is environmentally friendly, non-toxic, and widely available. It can effectively isolate the raw materials from air and inhibit oxidation without introducing harmful impurities that would affect the purity of the solder. The precise dosage is tailored to the needs of the mixed materials, avoiding welding defects caused by excessive antioxidant residue. It balances environmental friendliness and welding reliability, reducing environmental risks and costs in the production process.

[0023] Furthermore, the heating temperature is 300-350℃; the specific operation steps of the constant temperature stirring are: stirring at 300-350℃ for 30-60 minutes.

[0024] This invention optimizes the preparation process parameters, increasing the heating temperature to 300-350℃ and extending the stirring time to 30-60 minutes, making it more suitable for the melting and fusion requirements of multi-component mixtures. Higher temperatures promote the uniform dispersion of nano-SiO2 in the solder, while extended stirring time further reduces internal porosity and defects, enhancing the solder's structural density. The optimized process parameters further improve the solder's tensile strength, toughness, and other mechanical properties, making it suitable for microelectronic packaging scenarios with higher solder joint strength requirements.

[0025] Furthermore, the mold is made of graphite.

[0026] This invention features a high-temperature resistant and chemically inert mold made of graphite. Graphite's strong properties prevent chemical reactions between the mold and the molten solder during casting, ensuring solder purity. The graphite mold allows for smooth demolding, accurately replicating solder dimensions, reducing losses and defects during molding, and improving solder yield. Furthermore, graphite's thermal conductivity helps the solder cool evenly, further ensuring stable solder performance.

[0027] This invention also provides the application of a nano-silica-doped multi-component tin-bismuth-based lead-free low-temperature solder in low-temperature soldering for microelectronic packaging.

[0028] This invention clarifies the application scenarios of solder in low-temperature soldering for microelectronic packaging, specifically addressing the field's need for lead-free, low-melting-point, and high-reliability solders. The excellent wettability of the solder reduces cold solder joints and porosity, while its anti-aging and corrosion resistance extends the lifespan of packaged products. It is suitable for demanding applications such as chip-scale packaging and ball grid arrays, promoting the environmentally friendly and high-performance development of microelectronic packaging.

[0029] Compared with the prior art, the present invention has the following advantages and technical effects: In this invention, In and nano-SiO2 form a highly efficient synergistic effect with the matrix elements, which can significantly enhance the mechanical properties, fatigue resistance and environmental durability of the solder joints. This makes the solder not only suitable for high-reliability fields such as automotive electronics and aerospace, but also meet the application scenarios with stringent requirements for solder joint strength, such as chip-level packaging and ball grid arrays.

[0030] This invention can precisely balance the core indicators of solder, such as melting point, hardness, tensile properties, wettability, fluidity, anti-aging properties, corrosion resistance, and environmental safety, by flexibly adjusting the addition ratio of In and nano-SiO2, thereby adapting to diverse welding scenarios and improving the flexibility and adaptability of process applications. Attached Figure Description

[0031] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The hardness test results are for the solders prepared in Examples 1-2 and Comparative Examples 1-4. Figure 2 The tensile strength test results are for the solders prepared in Examples 1-2 and Comparative Examples 1-4. Figure 3 The wettability test results are for the solders prepared in Examples 1-2 and Comparative Examples 1-4. Detailed Implementation

[0032] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0033] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0034] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0035] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0036] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0037] This invention provides a method for preparing a multi-component tin-bismuth-based lead-free low-temperature solder doped with nano-silica, comprising the following steps: I. Preparation of Experimental Materials 1. Prepare the raw materials of each component according to the mass percentage: In (indium) 0.5-5% (for example, In is 0.5%), nano SiO2 (diameter 20-100nm) 0.1-1.5% (for example, SiO2 is 0.1 or 0.5%), the balance being Sn58Bi matrix (where the mass ratio of Sn to Bi is (41.58-41.79): (57.42-57.71)) and unavoidable small amounts of impurities.

[0038] 2. Prepare the antioxidant rosin, the amount of which should be 0.1-0.3% of the total mass of the subsequent mixture.

[0039] 3. Prepare graphite molds and lead-free graphite heating furnace.

[0040] II. Preparation of Sn58Bi matrix 1. Add Sn raw material with the required purity to a lead-free graphite heating furnace and heat it to 250-350℃ (for example, the temperature is 350℃) until Sn is completely melted.

[0041] 2. Add the Bi raw material in a preset ratio to the melted Sn, and continue heating to 250-350℃ (for example, the temperature is 350℃) to ensure that the Bi is completely melted.

[0042] 3. Stir at the above temperature for 30 minutes to mix Sn and Bi evenly, and obtain Sn58Bi matrix for later use.

[0043] III. Preparation of Nano-Silica Doped Multi-Component Tin-Bismuth Based Lead-Free Low-Temperature Solder 1. Weigh out the corresponding amounts of In, nano-SiO2 and the prepared Sn58Bi matrix according to the preset mass percentage, and mix them evenly to obtain a mixture.

[0044] 2. Add the mixture to the lead-free graphite heating furnace, and at the same time add the preset amount of antioxidant rosin to cover the alloy surface.

[0045] 3. Introduce nitrogen into the heating furnace to create a protective atmosphere, and heat to 300-350℃ until the mixture is completely melted.

[0046] 4. Stir at a constant temperature of 300-350℃ (for example, the temperature is 350℃) for 30-60 minutes (for example, the time is 30 minutes) to ensure that all components are fully mixed and to reduce internal defects.

[0047] 5. Quickly pour the stirred molten solder into a pre-prepared graphite mold, and demold it after natural cooling to obtain a multi-component tin-bismuth-based lead-free low-temperature solder doped with nano-silica.

[0048] IV. Application Scenarios The nano-silica-doped multi-component tin-bismuth-based lead-free low-temperature solder prepared by this invention can be directly applied to low-temperature soldering processes in the field of microelectronic packaging.

[0049] As an example, in the following preferred embodiments of the present invention, the nano-silica-doped multi-component tin-bismuth-based lead-free low-temperature solder comprises the following components by mass percentage: In: 0.5%, nano-SiO2: 0.1-0.5% (exemplary, 0.1% or 0.5%), Sn: 41.58-41.79% (exemplary, 41.58% or 41.79%), Bi: 57.42-57.71% (exemplary, 57.42% or 57.71%), and the balance being unavoidable small amounts of impurities.

[0050] Unless otherwise specified, "room temperature" in this invention refers to 25±2℃.

[0051] All raw materials used in this invention were purchased from the market.

[0052] In the “Sn58Bi matrix” mentioned in this invention, “58” refers to the Bi content in the matrix.

[0053] The technical solution of the present invention will be further illustrated by the following embodiments.

[0054] Example 1 A multi-component tin-bismuth-based lead-free low-temperature solder doped with nano-silica comprises the following components by mass percentage: In: 0.5%, nano-SiO2 with a diameter of 20-100nm: 0.1%, Sn: 41.75%, and Bi: 57.65%.

[0055] A method for preparing a multi-component tin-bismuth based lead-free low-temperature solder doped with nano-silica, comprising the following steps: (1) Preparation of Sn58Bi matrix: Sn was added to a lead-free graphite heating furnace and heated to 350°C until it melted. Then Bi was added and heated to 350°C until it melted. After melting, the mixture was stirred and kept at the temperature for 30 minutes to obtain Sn58Bi matrix. (2) Weigh In, nano SiO2 and Sn58Bi matrix in proportion and mix them to obtain a mixture. Add the mixture to a lead-free graphite heating furnace and cover the surface of the mixture with an antioxidant (the antioxidant is rosin, and the amount added is 0.1-0.3% of the mass of the mixture. The specific amount is enough to evenly cover the surface and achieve the effect of isolating air, the same below). Under a nitrogen atmosphere, heat the material to 350°C. After it is completely melted, stir and keep it at this temperature for 30 minutes. Then cast it into a mold to obtain a multi-component lead-free low-temperature tin-bismuth solder doped with nano silica.

[0056] Example 2 A multi-component tin-bismuth-based lead-free low-temperature solder doped with nano-silica comprises the following components by mass percentage: In: 0.5%, nano-SiO2 with a diameter of 20-100nm: 0.5%, Sn: 41.58%, and Bi: 57.42%.

[0057] A method for preparing a multi-component tin-bismuth based lead-free low-temperature solder doped with nano-silica, comprising the following steps: (1) Preparation of Sn58Bi matrix: Sn was added to a lead-free graphite heating furnace and heated to 350°C until it melted. Then Bi was added and heated to 350°C until it melted. After melting, the mixture was stirred and kept at the temperature for 30 minutes to obtain Sn58Bi matrix. (2) Weigh In, nano SiO2 and Sn58Bi matrix in proportion and mix them to obtain a mixture. Add the mixture to a lead-free graphite heating furnace, cover the surface of the mixture with an antioxidant, heat the material to 350°C under a nitrogen atmosphere, and after it is completely melted, stir and keep it at this temperature for 30 minutes. Then cast it into a mold to obtain a multi-component lead-free low-temperature tin-bismuth solder doped with nano silica.

[0058] Comparative Example 1 A multi-component tin-bismuth-based lead-free low-temperature solder comprises the following components by mass percentage: In: 0.5%, Sn: 41.79%, Bi: 57.71%.

[0059] A method for preparing a multi-component tin-bismuth based lead-free low-temperature solder, comprising the following steps: (1) Preparation of Sn58Bi matrix: Sn was added to a lead-free graphite heating furnace and heated to 350°C until it melted. Then Bi was added and heated to 350°C until it melted. After melting, the mixture was stirred and kept at the temperature for 30 minutes to obtain Sn58Bi matrix. (2) Weigh In and Sn58Bi matrix according to proportion and mix them to obtain a mixture. Add the mixture to a lead-free graphite heating furnace, cover the surface of the mixture with an antioxidant, heat the material to 350°C under a nitrogen atmosphere, and after it is completely melted, stir and keep it at this temperature for 30 minutes. Then cast it into a mold to obtain a multi-component lead-free low-temperature tin-bismuth solder.

[0060] Comparative Example 2 A Sn58Bi solder comprises the following components by weight percentage: Sn: 42%, Bi: 58%.

[0061] A method for preparing Sn58Bi solder includes the following steps: Sn is added to a lead-free graphite heating furnace and heated to 350°C until melted. Then Bi is added and heated to 350°C until melted. After melting, the mixture is stirred and kept at this temperature for 30 minutes to obtain the Sn58Bi matrix.

[0062] Comparative Example 3 A multi-component tin-bismuth-based lead-free low-temperature solder doped with nano-silica comprises the following components by mass percentage: In: 0.5%, nano-SiO2 with a diameter of 20-100nm: 2%, Sn: 40.95%, and Bi: 56.55%.

[0063] A method for preparing a multi-component tin-bismuth-based lead-free low-temperature solder doped with nano-silica, comprising the following steps: (1) Preparation of Sn58Bi matrix: Sn was added to a lead-free graphite heating furnace and heated to 350°C until it melted. Then Bi was added and heated to 350°C until it melted. After melting, the mixture was stirred and kept at the temperature for 30 minutes to obtain Sn58Bi matrix. (2) Weigh In, nano SiO2 and Sn58Bi matrix in proportion and mix them to obtain a mixture. Add the mixture to a lead-free graphite heating furnace, cover the surface of the mixture with an antioxidant, heat the material to 350°C under a nitrogen atmosphere, and after it is completely melted, stir and keep it at this temperature for 10 minutes. Then cast it into a mold to obtain a multi-component lead-free low-temperature tin-bismuth solder doped with nano silica.

[0064] Comparative Example 4 Same as Example 1, except that In is replaced with Zn.

[0065] Performance testing: 1. The hardness of the solders prepared in Examples 1-2 and Comparative Examples 1-4 was tested according to GB / T 2411 standard. HD The test was conducted with five parallel groups for each sample. The test results are shown in Table 1 and 2. Figure 1 .

[0066] Table 1. Hardness test results of the solders prepared in Examples 1-2 and Comparative Examples 1-4 from Figure 1As shown in Table 1, the hardness of the alloy solder in Example 1 is 91.62 HD, the hardness of the alloy solder in Example 2 is 92.94 HD, the hardness of the alloy solder in Comparative Example 1 is 90.46 HD, the hardness of the alloy solder in Comparative Example 2 is 87.94 HD, and the hardness of the alloy solder in Comparative Example 3 is 85.18 HD. This indicates that adding In to Sn58Bi significantly improves the hardness of the alloy solder. Further addition of nano-SiO2 further enhances the hardness, but the amount used is outside the limits of this invention and cannot achieve the desired effect. The hardness of the alloy solder in Comparative Example 4 is 87.86 HD.

[0067] 2. The tensile strength of the solders prepared in Examples 1-2 and Comparative Examples 1-4 was tested according to GB / T 228.1 standard. MPa The test was conducted with three parallel groups for each sample. The test results are shown in Table 2 and [Table data missing]. Figure 2 .

[0068] Table 2. Tensile strength test results of the solders prepared in Examples 1-2 and Comparative Examples 1-4 from Figure 2 As shown in Table 2, the tensile strength of the alloy solder in Example 1 is 65.43 MPa, the tensile strength of the alloy solder in Example 2 is 67.62 MPa, the tensile strength of the alloy solder in Comparative Example 1 is 59.61 MPa, the tensile strength of the alloy solder in Comparative Example 2 is 46.26 MPa, and the tensile strength of the alloy solder in Comparative Example 3 is 60.57 MPa. It can be seen that adding In to Sn58Bi significantly improves the tensile strength of the alloy solder. Further addition of nano-SiO2 further enhances the tensile strength. However, the amount of SiO2 and In added is limited; not any arbitrary ratio will achieve the same effect, and the tensile strength may even decrease.

[0069] 3. Wettability test The wettability of the solders prepared in Examples 1-2 and Comparative Examples 1-4 was tested according to GB / T 11364 standard. Five parallel groups were set for each sample. The test results are shown in Table 3.

[0070] Table 3. Wetting test results of the solders prepared in Examples 1-2 and Comparative Examples 1-4 from Figure 3As can be seen from the data in Table 3, the average wettability test value of the alloy solder in Example 1 was 73.11%, and the average wettability test value of the alloy solder in Example 2 was 71.18%, both higher than that of Comparative Example 1 (62.30%), Comparative Example 3 (56.77%), and Comparative Example 4 (60.24%). This indicates that adding In to the Sn58Bi matrix and further incorporating an appropriate amount of nano-SiO2 still allows the solder to maintain good wetting and spreading properties. Comparative Example 1, without the addition of nano-SiO2, exhibited lower wettability than Examples 1-2, indicating that an appropriate amount of nano-SiO2 helps improve the uniformity of the solder structure and maintain its spreading ability. In Comparative Example 3, the excessive addition of nano-SiO2 significantly reduced wettability, suggesting that excessive nano-SiO2 may lead to particle agglomeration and impeded melt flow, thereby reducing the solder's spreading performance on the substrate surface. In Comparative Example 4, replacing In with Zn resulted in lower wettability than Examples 1-2, indicating that In is more beneficial than Zn in improving the wettability of the Sn58Bi-based solder of this invention. Although the average wettability test value of Comparative Example 2 was 81.32%, higher than Examples 1-2, Tables 1 and 2 show that the hardness and tensile strength of Comparative Example 2 were significantly lower than Examples 1-2, indicating that while a single Sn58Bi matrix has a high spreading rate, it is difficult to simultaneously achieve both mechanical strength and solder joint reliability. Based on the combined results of hardness, tensile strength and wettability tests, it can be seen that Embodiments 1-2 of the present invention significantly improve the mechanical properties of the solder while maintaining good wettability, and have better overall welding performance.

[0071] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A multi-component tin-bismuth-based lead-free low-temperature solder doped with nano-silica, characterized in that, The composition includes the following components by mass percentage: In: 0.5-5%, nano-SiO2: 0.1-1.5%, with the balance being the Sn58Bi matrix and unavoidable impurities.

2. The nano-silica-doped multi-component tin-bismuth-based lead-free low-temperature solder according to claim 1, characterized in that, The composition includes the following components by mass percentage: In: 0.5%, nano-SiO2: 0.1-0.5%, with the balance being the Sn58Bi matrix and unavoidable impurities.

3. The nano-silica-doped multi-component tin-bismuth-based lead-free low-temperature solder according to claim 1, characterized in that, In the Sn58Bi matrix, the mass ratio of Sn to Bi is (41.58-41.79):(57.42-57.71).

4. A method for preparing a nano-silica-doped multi-component tin-bismuth-based lead-free low-temperature solder as described in any one of claims 1-3, characterized in that, Includes the following steps: Preparation of Sn58Bi matrix; In, nano-SiO2 and Sn58Bi matrix are weighed in proportion and mixed to obtain a mixture. The mixture is added to a lead-free graphite heating furnace, an antioxidant is added, and the mixture is heated to melt. The mixture is stirred at a constant temperature and finally cast into a mold to obtain a nano-silica-doped multi-component tin-bismuth-based lead-free low-temperature solder.

5. The preparation method according to claim 4, characterized in that, The specific preparation steps of the Sn58Bi matrix include: adding Sn into a lead-free graphite heating furnace, heating until melting, then adding Bi, continuing to heat until melting, stirring under constant temperature conditions to obtain the Sn58Bi matrix.

6. The preparation method according to claim 5, characterized in that, Both heating processes are carried out at temperatures of 250-350℃; and / or, The specific operating steps for stirring under constant temperature conditions are as follows: stir at 250-350℃ for 30 minutes.

7. The preparation method according to claim 4, characterized in that, The amount of antioxidant added is 0.1-0.3% of the mass of the mixture; and / or, The antioxidant is rosin.

8. The preparation method according to claim 4, characterized in that, The heating temperature is 300-350℃; and / or, The specific operating steps for constant temperature stirring are as follows: stir at 300-350℃ for 30-60 minutes.

9. The preparation method according to claim 4, characterized in that, The mold is made of graphite.

10. The application of a nano-silica-doped multi-component tin-bismuth-based lead-free low-temperature solder as described in any one of claims 1-3 in low-temperature soldering of microelectronic packaging.

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