Soldering alloy, soldering paste, preparation method of soldering paste, soldering flux and welding structural part

Abstract

The invention relates to the technical field of soldering tin materials, in particular to soldering tin alloy, soldering paste, a preparation method of the soldering paste, soldering flux and a soldering structural part, and aims to solve the problems that low-temperature soldering materials are poor in soldering firmness, fragile in soldering spots, poor in soldering performance compared with high-temperature soldering materials, poor in reliability and the like in the prior art. The soldering tin alloy is a ternary alloy material of In, Sn and Bi, and in the ternary alloy material, the mass ratio of In is 40%-60%, the mass ratio of Sn is 20%-40%, and the balance is Bi.

Description

Technical Field

[0001] This application relates to the field of solder materials technology, and in particular to a solder alloy, solder paste and its preparation method, solder and welded structural components. Background Technology

[0002] With the development of the semiconductor and electronics industries, welding technology has continuously advanced, leading to the emergence of various welding materials (also known as solder). As the precision of electronic components continues to increase, especially for certain heat-sensitive materials such as high-strength aluminum alloys and miniature metal parts in precision electronic components, high-temperature welding can cause significant changes in the microstructure of the heat-affected zone, such as grain growth and segregation of alloying elements, thus affecting the material's performance. Low-temperature welding, on the other hand, can better preserve the original properties of the material. Therefore, low-temperature welding is attracting increasing attention.

[0003] With increasing demands for environmental protection and energy conservation, the use of lead-free solder to replace traditional Sn-Pb solder has become a trend. Sn-Bi solder, as an important component of low-temperature lead-free solder, offers advantages such as low cost, good wettability, high solder joint strength, and good thermal fatigue performance. Furthermore, Sn can be infinitely dissolved in Bi within a certain range without forming new compounds. Therefore, the melting point of the solder can be altered by adjusting the Bi content, thus improving the alloy's brittleness to some extent. For example, the lowest melting point of the SnBi58 eutectic composition is 138℃. Currently, most Sn-Bi alloys on the market have a Bi content between 35% and 58%, meeting the requirements for low-temperature soldering at various temperatures.

[0004] However, Sn-Bi solder still has some drawbacks in the soldering process, mainly including poor weld strength, fragile solder joints, unsuitability for products with strength requirements, inferior soldering performance compared to high-temperature solder materials, dull solder joint gloss, and poor reliability. Summary of the Invention

[0005] Based on this, some embodiments of this application provide a solder alloy to solve the problems of poor welding strength, fragile solder joints, inferior welding performance compared to high-temperature solder materials, and poor reliability in related technologies. At the same time, some embodiments of this application also provide solder paste and its preparation method, as well as solder and welding structural components containing the solder.

[0006] In a first aspect, a solder alloy is provided, wherein the solder alloy is a ternary alloy material of In, Sn and Bi, wherein the mass percentage of In is 40% to 60%, the mass percentage of Sn is 20% to 40%, and the balance is Bi.

[0007] Optionally, in the ternary alloy material, In has a mass percentage of 40% to 49%, Sn has a mass percentage of 23% to 35%, and Bi has a mass percentage of 25% to 28%.

[0008] Optionally, the solder alloy is in powder form;

[0009] Optionally, the D50 particle size of the solder alloy is 8μm to 38μm.

[0010] In a second aspect, a solder is provided, comprising: the solder alloy as described in the first aspect.

[0011] Optionally, the solder alloy is in powder form, and the solder further includes flux, wherein the solder alloy is dispersed in the flux;

[0012] Optionally, in the solder, the solder alloy accounts for 80% to 90% by mass, and the flux accounts for 10% to 20% by mass.

[0013] Optionally, the flux comprises: an activator, a solvent, a rosin compound, and a thixotropic agent in a mass ratio of (0.5~5):(30~70):(20~50):(2~20);

[0014] Optionally, the activator comprises at least one of the following: inorganic acid, organic acid, ammonium salt, amine salt, and organic amine compound; wherein the inorganic acid comprises at least one of hydrochloric acid, orthophosphoric acid, and hydrofluoric acid; the organic acid comprises at least one of aliphatic monocarboxylic acid, aromatic acid, oxalic acid, and succinic acid; the ammonium salt comprises at least one of ammonium chloride, ammonium sulfate, ammonium nitrate, and ammonium carbonate; the amine salt comprises at least one of dimethylamine phosphate and ethylenediamine hydrochloride; and the organic amine compound comprises at least one of alkanolamine compound and amide compound.

[0015] Optionally, the solvent includes at least one of the following: alcohol solvents, ether solvents, ester solvents, aliphatic hydrocarbon solvents, and aromatic hydrocarbon solvents; wherein the alcohol solvent includes at least one of n-butanol and tetrahydrofurfuryl alcohol; the ether solvent includes at least one of ethylene glycol ethyl ether, diethylene glycol dimethyl ether, dipropylene glycol methyl ether, propylene glycol butyl ether, and diethylene glycol methyl ethyl ether; the ester solvent includes at least one of butyl acetate, dimethyl oxalate, and diisononyl phthalate; the aliphatic hydrocarbon solvent includes at least one of nitromethane and nitrobenzene; and the aromatic hydrocarbon solvent includes at least one of benzene, toluene, xylene, and trimethylbenzene.

[0016] Optionally, the rosin compounds include at least one of the following: rosin acid, hydrogenated rosin, disproportionated rosin, polymerized rosin, maleic rosin, rosin glycerol ester, and rosin amine;

[0017] Optionally, the thixotropic agent includes at least one of hydrogenated castor oil and its derivatives, polyamide, and fatty acid amide wax.

[0018] Optionally, when the solder further includes flux, the viscosity of the solder is 120 Pa·s to 195 Pa·s.

[0019] Thirdly, a method for preparing a solder alloy is provided, comprising:

[0020] In, Sn and Bi are mixed in a ratio of 40% to 60% by mass of In, 20% to 40% by mass of Sn, and the balance being Bi. The mixture is then melted to prepare the solder alloy.

[0021] Optionally, the solder alloy is in powder form; the preparation method further includes:

[0022] The molten mixture is spray-granulated to obtain the solder alloy;

[0023] Optionally, the melting temperature is greater than or equal to 160°C, and the melting time is 1 to 5 hours.

[0024] Fourthly, a method for preparing solder paste is provided, comprising:

[0025] Flux and solder alloy powder are prepared separately. The solder alloy powder is prepared by mixing In, Sn and Bi in a ratio of 40% to 60% by mass of In, 20% to 40% by mass of Sn, and the balance being Bi, and then by melting and spray granulation.

[0026] The solder paste is obtained by mixing the solder alloy powder and the flux.

[0027] Optionally, the flux comprises: an activator, a solvent, a rosin-like compound, and a thixotropic agent in a mass ratio of (0.5~5):(30~70):(20~50):(2~20); the preparation of the flux comprises:

[0028] The rosin and solvent are mixed in proportion at a first temperature to obtain a first mixture, which is then cooled to a second temperature.

[0029] The cooled first mixture is mixed with the activator at the second temperature in a certain proportion to obtain a second mixture, which is then cooled to a third temperature.

[0030] The cooled second mixture is mixed with the thixotropic agent at the third temperature to obtain a third mixture, which is then cooled to room temperature to obtain the flux.

[0031] Optionally, in the solder paste, the solder alloy powder accounts for 80% to 90% by mass, and the flux accounts for 10% to 20% by mass.

[0032] Fifthly, a weldable structural component is provided, comprising: a weldable component and a welded portion, wherein the weldable component is welded and fixed by the welded portion, and the welded portion comprises solder as described in the second aspect.

[0033] The beneficial technical effects of the solder alloy, solder paste, preparation method thereof, solder and welded structural components provided in this application are as follows:

[0034] The solder alloy provided in this application can improve residual stress in welded structural components through its own phase transformation, and can reduce melting temperature, increase elongation and wettability. This achieves the technical effect of improving weld strength and solder joint strength while realizing low-temperature welding, and enhancing fatigue resistance. It can solve the problems of poor weld strength, fragile solder joints, inferior welding performance compared to high-temperature solder materials, and poor reliability in related technologies.

[0035] In addition, the solder alloy provided in this application embodiment can improve the residual stress in the welded structural parts by utilizing its own phase transformation. It can improve fatigue resistance without the need for post-weld heat treatment or mechanical treatment such as shot peening or hammering of the weld bead to reduce tensile residual stress or even generate compressive residual stress. It is suitable for welding structural parts of different complexities and is not limited by the size and structure of the structural parts. It can reduce the cost increase caused by post-weld heat treatment or mechanical treatment.

[0036] Furthermore, this phase change ternary alloy material can maintain the excellent performance of low-temperature welding materials, and is particularly suitable for welding temperature-sensitive materials, which can reduce high-temperature damage caused by high-temperature welding. Attached Figure Description

[0037] Figure 1 This is a schematic flowchart illustrating a method for preparing solder paste according to an embodiment of this application. Detailed Implementation

[0038] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0039] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as open-ended and encompassing, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "exemplary," or "some examples," etc., are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this disclosure. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics mentioned may be included in any suitable manner in any one or more embodiments or examples.

[0040] This document describes exemplary embodiments with reference to cross-sectional views and / or plan views, which are idealized exemplary drawings. In the drawings, the thickness of layers and regions is enlarged for clarity. Therefore, variations in shape relative to the drawings are contemplated due to, for example, manufacturing techniques and / or tolerances. Thus, exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing processes. For example, etched regions shown as rectangular would typically have curved features. Therefore, the regions shown in the drawings are schematic in nature, and their shapes are not intended to show the actual shapes of the regions of the device, nor are they intended to limit the scope of the exemplary embodiments.

[0041] "A and / or B" includes the following three combinations: A only, B only, and a combination of A and B.

[0042] In this document, unless otherwise stated, "one or more" means one or more.

[0043] In this document, terms such as "for example," "like," "example," and "exemplary" are used for descriptive purposes to indicate a connection in the coverage of different technical solutions presented earlier and later. However, they should not be construed as limitations on the preceding technical solution or as restrictions on the scope of protection outlined herein. Unless otherwise specified, in this document, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0044] In this article, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "options" in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "option" is independent.

[0045] In this article, descriptions such as "optionally contains" and "optionally includes" indicate whether or not the component X is present. "Optional component X" indicates whether component X is present or absent, or whether or not component X is present.

[0046] In this document, the terms "first aspect," "second aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features.

[0047] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0049] In this article, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions that include the listed features.

[0050] In this document, "at least one" means one or more, such as one, two, or more. "Multiple" or "several" means at least two, such as two, three, etc., and "multi-layered" means at least two layers, such as two layers, three layers, etc., unless otherwise expressly and specifically defined. In the description of this application, "several" means at least one, such as one, two, etc., unless otherwise expressly and specifically defined.

[0051] In this document, when referring to numerical intervals (i.e., numerical ranges), unless otherwise specified, the distribution of selectable values ​​within a numerical interval is considered continuous, and includes the two endpoints (i.e., the minimum and maximum values) of the numerical interval, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all subranges included therein. The "numerical value" in this numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include percentage intervals, ratio intervals, proportion intervals, and other numerical interval types.

[0052] Unless otherwise specified, all percentage concentrations mentioned in this article refer to the final concentration. The final concentration refers to the proportion of the added ingredient in the system after the addition of that ingredient.

[0053] In this document, the terms "room temperature" or "normal temperature" generally refer to 4°C to 35°C, for example, 20°C ± 5°C. In some embodiments of this document, "room temperature" or "normal temperature" refers to 10°C to 30°C. In some embodiments of this document, "room temperature" or "normal temperature" refers to 20°C to 30°C.

[0054] In related technologies, Sn-Bi solders suffer from problems such as poor weld strength, fragile solder joints, unsuitability for products requiring strength, inferior welding performance compared to high-temperature solder materials, dull solder joint gloss, and poor reliability. These issues are mainly related to the composition of the solder alloy and residual stress during the welding process. For example, when using welding materials for welding, the entire stress process of welding is as follows: Welding is characterized by localized rapid heating and cooling. During heating, the material expands due to heat, generating compressive plastic strain and a large temperature gradient in local areas. During cooling, the material's own stiffness hinders contraction, inevitably resulting in residual stress after welding.

[0055] Statistics show that 90% of failures occurring during the service life of welded structural components are fatigue failures, all of which are closely related to welding residual stress. For example, welded structural components often contain welding defects such as microcracks and slag inclusions, or fatigue crack initiation occurs at stress concentration points under load. If compressive residual stress exists at the defect or crack tip, it may delay crack propagation; conversely, if tensile residual stress exists, it will accelerate crack propagation.

[0056] In general, welded structural components subjected to alternating loads exhibit higher fatigue strength when compressive stress is present, while their fatigue strength decreases when tensile stress is present. The greater the residual tensile stress, the worse the fatigue strength. To ensure good fatigue resistance of welded structural components during service, it is necessary to minimize the tensile residual stress caused by welding and even generate compressive residual stress, from the perspective of welding residual stress.

[0057] Based on the above, current research primarily utilizes post-weld treatments to improve the residual stress distribution in welded structures. For example, post-weld heat treatment is commonly used to reduce residual tensile stress, while mechanical treatments such as shot peening and hammering are employed to reduce tensile residual stress and even generate compressive residual stress. However, for some complex welded structures, the application of these methods is limited by product structure and dimensions, and can lead to increased time and economic costs in production.

[0058] Based on this, some embodiments of this application provide a solder alloy. Utilizing the soft nature of In, an appropriate amount of In is mixed with Bi and Sn to prepare a ternary alloy material. On the one hand, In can lower the melting point and improve ductility, resulting in a lower melting temperature, better elongation and wettability of the ternary alloy material, thus maintaining the excellent performance of low-temperature welding materials. On the other hand, in the presence of Bi, the ternary alloy material has a lower phase transition temperature. It can utilize the characteristic of low-temperature phase change materials to store and release heat during the solid-liquid phase transition, using its own heat conduction process and volume change to offset the residual stress generated during welding. This allows control of residual stress at the weld joint, thereby improving weld strength and solder joint strength while achieving low-temperature welding, and enhancing fatigue resistance.

[0059] The technical solutions provided in the embodiments of this application will be described in detail below:

[0060] In a first aspect, some embodiments of this application provide a solder alloy, which is a ternary alloy material of In, Sn and Bi, wherein the mass percentage of In is 40% to 60%, the mass percentage of Sn is 20% to 40%, and the balance is Bi.

[0061] For example, in this ternary alloy material, the mass percentage of In can be 40%, the mass percentage of Sn can be 20%, and the mass percentage of Bi can be 40%; or, the mass percentage of In can be 60%, the mass percentage of Sn can be 20%, and the mass percentage of Bi can be 20%; or, the mass percentage of In can be 40%, the mass percentage of Sn can be 40%, and the mass percentage of Bi can be 20%; or, the mass percentage of In can be 40%, the mass percentage of Sn can be 30%, and the mass percentage of Bi can be 30%; or, the mass percentage of In can be 40%, the mass percentage of Sn can be 25%, and the mass percentage of Bi can be... The mass percentage can be 35%, or In can be 45%, Sn can be 20%, and Bi can be 35%, or In can be 45%, Sn can be 30%, and Bi can be 25%, or In can be 50%, Sn can be 25%, and Bi can be 25%, or In can be 50%, Sn can be 20%, and Bi can be 30%, or In can be 50%, Sn can be 30%, and Bi can be 20%, etc.

[0062] In is soft and is an ideal element for improving brittleness. The inventors have found that adding an appropriate amount of In to tin-bismuth alloys can not only lower the melting temperature, but also improve the elongation and wettability; and tin, indium and bismuth can form a phase transformation ternary alloy material.

[0063] This phase change ternary alloy material has a low phase change temperature. It can utilize the characteristic of low-temperature phase change materials to store and release heat during the solid-liquid phase transition. By using its own heat conduction process and volume change, it can offset the residual stress generated during the welding process, thereby controlling the residual stress at the weld. This can improve the weld strength and weld point strength while achieving low-temperature welding, and also improve fatigue resistance.

[0064] Specifically, when the phase change ternary alloy material transforms from a solid to a liquid state, it absorbs heat. At this time, for a system with residual stress, this phase change heat absorption process is equivalent to introducing a local "softening" effect. The surrounding metal lattice will be affected by a certain "relaxation" due to the heat absorption of the phase change ternary alloy material. The residual stress originally generated during processing and manufacturing is alleviated to a certain extent under the effect of this local "softening" and "relaxation".

[0065] When the phase change ternary alloy material transforms from a liquid to a solid state, it releases heat. In a system with residual stress, this process is equivalent to providing an internal "contraction" force. The released heat affects the thermal state of the surrounding materials. At the same time, the solidification shrinkage of the phase change ternary alloy material itself can redistribute the residual stress in the welded structure to a certain extent, thereby reducing local stress concentration.

[0066] During this process, the heat storage and release of the phase change ternary alloy material during the phase change is accompanied by heat conduction. Through heat conduction, the stress in the welded structure can be adjusted, thereby controlling residual stress. For example, during welding, when the phase change ternary alloy material absorbs or releases heat during the phase change, the heat conduction in the welded structure will change the original temperature distribution of the welded structure. Due to the coefficient of thermal expansion of the material, the temperature change will cause the material to expand or contract, thus interacting with the original residual stress, and making the stress distribution in the welded structure more uniform.

[0067] Meanwhile, the volume change of the phase change ternary alloy material exerts a compressive or tensile effect on the surrounding material. This stress generated by the volume change can be superimposed or canceled out with the residual stress, thus controlling the residual attraction in the welded structure. For example, when the phase change ternary alloy material changes from a liquid to a solid state, its volume shrinks. If there is tensile residual stress in a certain direction in the welded structure, the shrinkage of the phase change ternary alloy material may offset part of the tensile stress, thereby adjusting the magnitude and distribution of the residual stress.

[0068] Based on the above, the solder alloy provided in this application can improve the residual stress in the welded structure by utilizing its own phase transformation, and can reduce the melting temperature, increase elongation and wettability. This achieves the technical effect of improving weld strength and solder joint strength while realizing low-temperature welding, and enhancing fatigue resistance. It can solve the problems of poor weld strength, fragile solder joints, inferior welding performance compared to high-temperature solder materials, and poor reliability in related technologies.

[0069] In addition, the solder alloy provided in this application embodiment can improve the residual stress in the welded structural parts by utilizing its own phase transformation. It can improve fatigue resistance without the need for post-weld heat treatment or mechanical treatment such as shot peening or hammering of the weld bead to reduce tensile residual stress or even generate compressive residual stress. It is suitable for welding structural parts of different complexities and is not limited by the size and structure of the structural parts. It can reduce the cost increase caused by post-weld heat treatment or mechanical treatment.

[0070] Furthermore, this phase change ternary alloy material can maintain the excellent performance of low-temperature welding materials, and is particularly suitable for welding temperature-sensitive materials, which can reduce high-temperature damage caused by high-temperature welding.

[0071] In some embodiments, in this ternary alloy material, the mass percentage of In is 40% to 49%, the mass percentage of Sn is 23% to 35%, and the mass percentage of Bi is 25% to 28%.

[0072] For example, in this ternary alloy material, the mass percentage of In is 40%, the mass percentage of Sn is 32%, and the mass percentage of Bi is 28%; or, the mass percentage of In is 40%, the mass percentage of Sn is 35%, and the mass percentage of Bi is 25%; or, the mass percentage of In is 45%, the mass percentage of Sn is 27%, and the mass percentage of Bi is 28%; or, the mass percentage of In is 45%, the mass percentage of Sn is 30%, and the mass percentage of Bi is 25%; or, the mass percentage of In is 45%, the mass percentage of Sn is 29%, and the mass percentage of Bi is 26%; or, the mass percentage of In is 49%, the mass percentage of Sn is 25%, and the mass percentage of Bi is 26%; or, the mass percentage of In is 49%, the mass percentage of Sn is 23%, and the mass percentage of Bi is 28%; or, the mass percentage of In is 49%, the mass percentage of Sn is 26%, and the mass percentage of Bi is 25%, etc.

[0073] In these embodiments, by controlling the mass ratio of In, Sn and Bi in the ternary alloy material within the above-mentioned range, the weld strength, weld point strength and fatigue resistance of the ternary alloy material can be further improved.

[0074] In some embodiments, the solder alloy is in powder form.

[0075] In these embodiments, the solder alloy can be mixed with flux to prepare solder paste, which facilitates soldering.

[0076] In some embodiments, the D50 particle size of the solder alloy is 8 μm to 38 μm. The D50 particle size represents the particle size corresponding to a cumulative volume distribution percentage of 50% for the lithium supplement, and can be obtained by laser particle size analyzer.

[0077] In these embodiments, the D50 particle size of the solder alloy is controlled within the range of 8μm to 38μm, which can meet the soldering requirements of different sizes.

[0078] Secondly, some embodiments of this application provide a solder comprising: the solder alloy as described in the first aspect.

[0079] In these embodiments, the solder can be any material that has a welding effect and can have any possible form; for example, the solder can be solder balls, solder rods, solder powder, or solder paste, etc.

[0080] In some embodiments, the solder alloy is in powder form, and the solder also includes flux in which the solder alloy is dispersed.

[0081] In these embodiments, the solder is solder paste, which facilitates soldering.

[0082] In some embodiments, the solder alloy accounts for 80% to 90% of the mass of the solder, and the flux accounts for 10% to 20% of the mass of the flux.

[0083] For example, in this solder, the solder alloy may account for 80% of the mass, and the flux accounts for 20% of the mass; or, the solder alloy may account for 82% of the mass, and the flux accounts for 18% of the mass; or, the solder alloy may account for 85% of the mass, and the flux accounts for 15% of the mass; or, the solder alloy may account for 87% of the mass, and the flux accounts for 13% of the mass; or, the solder alloy may account for 90% of the mass, and the flux accounts for 10% of the mass.

[0084] In these embodiments, by controlling the mass ratio of solder alloy powder and flux within the above-mentioned range when mixing, solder paste with good fluidity and excellent overall performance can be prepared.

[0085] In some embodiments, the flux comprises an activator, a solvent, rosin, and a thixotropic agent in a mass ratio of (0.5~5):(30~70):(20~50):(2~20).

[0086] For example, the mass ratio of surfactant, solvent, rosin, and thixotropic agent is 0.5:30:20:2, or 0.5:40:30:2, or 0.5:40:20:2, or 0.5:40:20:2, or 0.5:40:20:10, or 0.5:50:20:2, or 0.5:50:30:2, or 0.5:50:30:10, or... The mass ratio of rosin to thixotropic agent is 0.5:50:30:20, or the mass ratio of surfactant, solvent, rosin and thixotropic agent is 5:30:20:2, or the mass ratio of surfactant, solvent, rosin and thixotropic agent is 3:30:20:2, or the mass ratio of surfactant, solvent, rosin and thixotropic agent is 2:30:20:2, or the mass ratio of surfactant, solvent, rosin and thixotropic agent is 1:30:50:2, or the mass ratio of surfactant, solvent, rosin and thixotropic agent is 3:70:20:2, or the mass ratio of surfactant, solvent, rosin and thixotropic agent is 3:60:50:10, or the mass ratio of surfactant, solvent, rosin and thixotropic agent is 3:60:40:5, etc.

[0087] Among them, the activator is the core component of the flux activity. It can remove oxides on the surface of the alloy and the base material, reduce the surface tension between the liquid solder and the material being welded, and promote the flow of the liquid solder and the wetting of the base material.

[0088] Solvents, as carriers in flux, primarily dissolve all components of the flux, making it a homogeneous fluid that is easy to coat. During reflow soldering, they provide an ionization environment for activators and other components, ensuring the full action of the solder and thus successfully completing the soldering process.

[0089] Rosin is a chemical substance with good flowability and thermal conductivity, and it plays two main roles: First, the resinous acids in rosin can remove metal oxides during the soldering process and promote solder wetting; second, rosin can form a dense organic film during soldering to prevent secondary oxidation of the solder, and this organic film has good electrical insulation, corrosion resistance and moisture resistance.

[0090] Thixotropic agents impart certain thixotropic properties to solder, maintaining its excellent storage stability and printability. For example, a thixotropic agent can give the solder a higher viscosity when standing, reducing sedimentation or deformation during storage, and a lower viscosity during printing, ensuring continuous and smooth printing while minimizing stencil clogging or overflow.

[0091] In these embodiments, by mixing the activator, solvent, rosin and thixotropic agent in the above proportions, a flux with good coating performance, printing performance and stability can be prepared, which promotes solder wetting and enables the solder to have good electrical insulation performance, corrosion resistance and moisture resistance when used, so that the flux has good auxiliary soldering ability.

[0092] In some embodiments, the activator includes at least one of inorganic acids, organic acids, ammonium salts, and organic amine compounds;

[0093] Among them, inorganic acids include at least one of hydrochloric acid, orthophosphoric acid and hydrofluoric acid; organic acids include at least one of aliphatic monocarboxylic acids, aromatic acids, oxalic acid and succinic acid; ammonium salts include at least one of ammonium chloride, ammonium sulfate, ammonium nitrate and ammonium carbonate; amine salts include at least one of dimethylamine phosphate and ethylenediamine hydrochloride; and organic amine compounds include at least one of alkanolamine compounds and amide compounds.

[0094] In some embodiments, the solvents described above include at least one of alcohol solvents, ether solvents, ester solvents, aliphatic hydrocarbon solvents, and aromatic hydrocarbon solvents;

[0095] The solvents include at least one of n-butanol and tetrahydrofurfuryl alcohol; the solvents include at least one of ethylene glycol ethyl ether, diethylene glycol dimethyl ether, dipropylene glycol methyl ether, propylene glycol butyl ether, and diethylene glycol methyl ethyl ether; the solvents include at least one of butyl acetate, dimethyl oxalate, and diisononyl phthalate; the solvents include at least one of nitromethane and nitrobenzene; and the solvents include at least one of benzene, toluene, xylene, and trimethylbenzene.

[0096] In some embodiments, rosin compounds include at least one of: rosin acid, hydrogenated rosin, disproportionated rosin, polymerized rosin, maleic rosin, rosin glycerol ester, and rosin amine.

[0097] In some embodiments, the thixotropic agent includes at least one of hydrogenated castor oil and its derivatives, polyamide, and fatty acid amide wax.

[0098] In some embodiments, when the solder also includes flux, the viscosity of the solder is 120 Pa·s to 195 Pa·s.

[0099] In these embodiments, the solder has high solder joint shear strength, welding tensile strength, and appropriate viscosity.

[0100] Thirdly, some embodiments of this application provide a method for preparing a solder alloy, the method comprising:

[0101] In, Sn and Bi are mixed in a ratio of 40% to 60% by mass of In, 20% to 40% by mass of Sn, and the balance being Bi. The mixture is then melted to prepare a solder alloy.

[0102] In the method for preparing the solder alloy provided in the embodiments of this application, the solder alloy as described in the first aspect can be prepared by mixing In, Sn and Bi in a ratio of 40% to 60% by mass of In, 20% to 40% by mass of Sn, and the balance being Bi, and then melting the mixture. The beneficial technical effects of this solder alloy can be found in the above description and will not be repeated here.

[0103] In some embodiments, the melting temperature is greater than or equal to 160°C, and the melting time is 1 to 5 hours. For example, the melting temperature can be 160°C, 170°C, 180°C, 200°C, etc., and the melting time can be 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours, etc.

[0104] In these embodiments, by controlling the melting temperature and time within the above-mentioned range, In, Sn and Bi can be mixed more uniformly, which facilitates the preparation of ternary alloy materials with uniform properties.

[0105] Optionally, the melting temperature is 180~200℃ and the time is 2~4h. For example, the melting temperature can be 180℃, 190℃ or 200℃, etc., and the time can be 2h, 3h or 4h, etc.

[0106] The aforementioned solder alloy can be in any form, such as solder alloy strip or solder alloy powder, and there are no restrictions on its specific form.

[0107] In some embodiments, the solder alloy is in powder form; the preparation method further includes:

[0108] The smelted mixture is spray-granulated to obtain a solder alloy.

[0109] In these embodiments, powdered solder alloys can be prepared, and spray granulation is simple and easy to implement, facilitating the control of the particle size of the solder alloy.

[0110] Fourthly, some embodiments of this application provide a method for preparing solder paste, such as... Figure 1 As shown, the preparation method includes:

[0111] S11. Prepare flux and solder alloy powder respectively. The solder alloy powder is prepared by mixing In, Sn and Bi in a ratio of In mass 40%~60%, Sn mass 20%~40%, and the balance being Bi, and then by melting and spray granulation.

[0112] S12. Mix the solder alloy powder and flux to obtain solder paste.

[0113] In the solder paste preparation method provided in this application embodiment, solder paste can be prepared by preparing solder alloy powder and mixing the solder alloy powder with flux. The preparation method of the solder alloy powder is the same as the preparation method of the powdered solder alloy described in the second aspect, and has the same technical effect as the preparation method of the solder alloy described in the second aspect, and will not be repeated here.

[0114] In some embodiments, the melting temperature is greater than or equal to 160°C, and the time is 1 to 5 hours.

[0115] In these embodiments, by controlling the melting temperature and time within the above-mentioned range, In, Sn and Bi can be mixed more uniformly, which facilitates the preparation of ternary alloy materials with uniform properties.

[0116] Optionally, the melting temperature is 180~200℃ and the time is 2~4h.

[0117] In some embodiments, the flux comprises: an activator, a solvent, a rosin compound, and a thixotropic agent in a mass ratio of (0.5~5):(30~70):(20~50):(2~20); the preparation of the flux comprises:

[0118] Rosin and solvent are mixed at a first temperature to obtain a first mixture, which is then cooled to a second temperature.

[0119] The cooled first mixture is mixed with the activator at the second temperature to obtain the second mixture, which is then cooled to the third temperature.

[0120] The cooled second mixture is mixed with the thixotropic agent at the third temperature to obtain the third mixture, which is then cooled to room temperature to obtain the flux.

[0121] In these embodiments, by gradually adding the components of the flux at a specific temperature in the manner described above, chemical reactions or dissolution and dispersion can occur between them, thereby obtaining a uniform and stable flux.

[0122] In some embodiments, the first temperature is 90~100℃, the second temperature is 70~80℃, and the third temperature is 30℃~40℃.

[0123] In some embodiments, the solder paste contains 80% to 90% solder alloy powder by mass and 10% to 20% flux by mass.

[0124] In these embodiments, by controlling the mass ratio of solder alloy powder and flux within the above-mentioned range when mixing, solder paste with good fluidity and excellent overall performance can be prepared.

[0125] Fifthly, some embodiments of this application provide a welded structural component, which includes a welded component and a welded portion, wherein the welded component is welded and fixed by the welded portion, and the welded portion includes solder as described in the second aspect.

[0126] The welded structural component can be any structural component connected by welding. For example, the welded structural component can be a semiconductor structure, such as a printed circuit board or a solar cell module. When the welded structural component is a printed circuit board, the welded components can be a chip and a substrate, which are fixed together by the aforementioned solder. When the welded structural component is a solar cell module, the welded components can be a solder strip and a solar panel, which are fixed together by the aforementioned solder.

[0127] In order to objectively evaluate the technical effects of the embodiments of this application, this application will be described in detail by way of example through the following embodiments and comparative examples.

[0128] In the following examples and comparative examples, all raw materials were commercially available, and to maintain the reliability of the experiments, the raw materials used in the following examples and comparative examples had the same physical and chemical parameters or were prepared by the same processing method.

[0129] Example 1

[0130] Example 1 provides a solder paste, the preparation method of which is as follows:

[0131] Step (1) Preparation of solder alloy powder: In, Bi and Sn are mixed in a ratio of 49:28:23 and heated to 160℃ to obtain the solder alloy material. The melting time is 2.5h. After melting, the temperature is reduced to 90℃ and then alloy powder with a D50 particle size of 20μm is prepared by spray granulation equipment as solder alloy powder for later use. Among them, In is 200g, Bi is 114.3g and Sn is 93.87g.

[0132] Step (2): Weigh 45 parts by weight of poly(rosin) and 40 parts by weight of n-butanol, heat to 90°C, stir evenly, cool to 70°C, add 5 parts by weight of oxalic acid, stir, cool to 30°C, add 10 parts by weight of polyamide, emulsify and disperse, stir, cool and grind to obtain flux.

[0133] Step (3): Mix the alloy powder obtained in step (1) and the flux prepared in step (2) at a mass ratio of 90:10, and stir them with a solder paste mixer to obtain solder paste.

[0134] Example 2

[0135] Example 2 provides a solder paste, the preparation method of which is as follows:

[0136] Step (1), Preparation of solder alloy powder: In, Bi and Sn are mixed in a ratio of 49:25:26 and heated to 160℃ to obtain the solder alloy material. The melting time is 2.5h. After melting, the temperature is reduced to 90℃ and then alloy powder with a D50 particle size of 20μm is prepared by spray granulation equipment as solder alloy powder for later use; wherein, In is 200g, Bi is 102g and Sn is 106.1g;

[0137] Step (2): Weigh 45 parts by weight of poly(rosin) and 40 parts by weight of n-butanol, heat to 90°C, stir evenly, cool to 70°C, add 5 parts by weight of oxalic acid, stir, cool to 30°C, add 10 parts by weight of polyamide, emulsify and disperse, stir, cool and grind to obtain flux.

[0138] Step (3): Mix the alloy powder obtained in step (1) and the flux prepared in step (2) at a mass ratio of 90:10, and stir them with a solder paste mixer to obtain solder paste.

[0139] Example 3

[0140] Example 3 provides a solder paste, the preparation method of which is as follows:

[0141] Step (1) Preparation of solder alloy powder: In, Bi and Sn are mixed in a ratio of 45:28:27 and heated to 160℃ to obtain the solder alloy material. The melting time is 3.0h. After melting, the temperature is reduced to 90℃ and then alloy powder with a D50 particle size of 20μm is prepared by spray granulation equipment as solder alloy powder for later use. Among them, In is 183.67g, Bi is 114.28g and Sn is 110.2g.

[0142] Step (2): Weigh 45 parts by weight of polymerized rosin and 40 parts by weight of n-butanol, heat to 90°C, stir evenly, cool to 70°C, add 5 parts by weight of oxalic acid, stir, cool to 30°C, add 10 parts by weight of polyamide, emulsify and disperse, stir, cool and grind to obtain flux.

[0143] Step (3): Mix the alloy powder obtained in step (1) and the flux prepared in step (2) at a mass ratio of 90:10, and stir them with a solder paste mixer to obtain solder paste.

[0144] Example 4

[0145] Example 4 provides a solder paste, the preparation method of which is as follows:

[0146] Step (1) Preparation of solder alloy powder: In, Bi and Sn are mixed in a ratio of 45:25:30 and heated to 160℃ to obtain the solder alloy material. The melting time is 3.0h. After melting, the temperature is reduced to 90℃ and then alloy powder with a D50 particle size of 20μm is prepared by spray granulation equipment as solder alloy powder for later use. Among them, In is 183.67g, Bi is 102g and Sn is 122.45g.

[0147] Step (2): Weigh 45 parts by weight of polymerized rosin and 40 parts by weight of n-butanol, heat to 90°C, stir evenly, cool to 70°C, add 5 parts by weight of oxalic acid, stir, cool to 30°C, add 10 parts by weight of polyamide, emulsify and disperse, stir, cool and grind to obtain flux.

[0148] Step (3): Mix the alloy powder obtained in step (1) and the flux prepared in step (2) at a mass ratio of 90:10, and stir them with a solder paste mixer to obtain solder paste.

[0149] Example 5

[0150] Example 5 provides a solder paste, the preparation method of which is as follows:

[0151] Step (1) Preparation of solder alloy powder: In, Bi and Sn are mixed in a ratio of 40:28:32 and heated to 160℃ to obtain the solder alloy material. The melting time is 2.5h. After melting, the temperature is reduced to 90℃ and then alloy powder with a D50 particle size of 20μm is prepared by spray granulation equipment as solder alloy powder for later use. Among them, In is 163.26g, Bi is 114.28g and Sn is 130.61g.

[0152] Step (2): Weigh 45 parts by weight of polymerized rosin and 40 parts by weight of n-butanol, heat to 90°C, stir evenly, cool to 70°C, add 5 parts by weight of ethylene glycol, stir, cool to 30°C, add 10 parts by weight of polyamide, emulsify and disperse, stir, cool and grind to obtain flux.

[0153] Step (3): Mix the alloy powder obtained in step (1) and the flux prepared in step (2) at a mass ratio of 90:10, and stir them with a solder paste mixer to obtain solder paste.

[0154] Example 6

[0155] Example 6 provides a solder paste, the preparation method of which is as follows:

[0156] Step (1) Preparation of solder alloy powder: In, Bi and Sn are mixed in a ratio of 40:25:35 and heated to 160℃ to obtain the solder alloy material. The melting time is 2.5h. After melting, the temperature is reduced to 90℃ and then alloy powder with a D50 particle size of 20μm is prepared by spray granulation equipment as solder alloy powder for later use. Among them, In is 163.26g, Bi is 102g and Sn is 142.85g.

[0157] Step (2): Weigh 45 parts by weight of polymerized rosin and 40 parts by weight of n-butanol, heat to 90°C, stir evenly, cool to 70°C, add 5 parts by weight of ethylene glycol, stir, cool to 30°C, add 10 parts by weight of polyamide, emulsify and disperse, stir, cool and grind to obtain flux.

[0158] Step (3): Mix the alloy powder obtained in step (1) and the flux prepared in step (2) at a mass ratio of 90:10, and stir them with a solder paste mixer to obtain solder paste.

[0159] Example 7

[0160] Example 7 provides a solder paste, the preparation method of which is as follows:

[0161] Step (1), Preparation of solder alloy powder: In, Bi and Sn are mixed in a ratio of 50:30:20 and heated to 160℃ to obtain the solder alloy material. The melting time is 2.5h. After melting, the temperature is reduced to 90℃ and then alloy powder with a D50 particle size of 20μm is prepared by spray granulation equipment as solder alloy powder for later use; wherein, In is 204.1g, Bi is 122.45g and Sn is 81.6g;

[0162] Step (2): Weigh 45 parts by weight of poly(rosin) and 40 parts by weight of n-butanol, heat to 90°C, stir evenly, cool to 70°C, add 5 parts by weight of oxalic acid, stir, cool to 30°C, add 10 parts by weight of polyamide, emulsify and disperse, stir, cool and grind to obtain flux.

[0163] Step (3): Mix the alloy powder obtained in step (1) and the flux prepared in step (2) at a mass ratio of 90:10, and stir them with a solder paste mixer to obtain solder paste.

[0164] Example 8

[0165] Example 8 provides a solder paste, the preparation method of which is as follows:

[0166] Step (1), Preparation of solder alloy powder: In, Bi and Sn are mixed in a ratio of 55:20:25 and heated to 160℃ to melt and obtain the solder alloy material. The melting time is 2.5h. After melting, the temperature is reduced to 90℃ and then alloy powder with a D50 particle size of 20μm is prepared by spray granulation equipment as solder alloy powder for later use; wherein, In is 224.49g, Bi is 81.63g and Sn is 102g;

[0167] Step (2): Weigh 45 parts by weight of poly(rosin) and 40 parts by weight of n-butanol, heat to 90°C, stir evenly, cool to 70°C, add 5 parts by weight of oxalic acid, stir, cool to 30°C, add 10 parts by weight of polyamide, emulsify and disperse, stir, cool and grind to obtain flux.

[0168] Step (3): Mix the alloy powder obtained in step (1) and the flux prepared in step (2) at a mass ratio of 90:10, and stir them with a solder paste mixer to obtain solder paste.

[0169] Example 9

[0170] Example 9 provides a solder paste, the preparation method of which is as follows:

[0171] Step (1), Preparation of solder alloy powder: In, Bi and Sn are mixed in a ratio of 58:22:20 and heated to 160℃ to obtain the solder alloy material. The melting time is 2.5h. After melting, the temperature is reduced to 90℃ and then alloy powder with a D50 particle size of 20μm is prepared by spray granulation equipment as solder alloy powder for later use; wherein, In is 236.7g, Bi is 89.8g and Sn is 81.6g;

[0172] Step (2): Weigh 45 parts by weight of poly(rosin) and 40 parts by weight of n-butanol, heat to 90°C, stir evenly, cool to 70°C, add 5 parts by weight of oxalic acid, stir, cool to 30°C, add 10 parts by weight of polyamide, emulsify and disperse, stir, cool and grind to obtain flux.

[0173] Step (3): Mix the alloy powder obtained in step (1) and the flux prepared in step (2) at a mass ratio of 90:10, and stir them with a solder paste mixer to obtain solder paste.

[0174] Comparative Example 1

[0175] Comparative Example 1 provides a solder paste, the preparation method of which is as follows:

[0176] Step (1), Preparation of solder alloy powder: Bi and Sn are mixed in a ratio of 58:42 and heated to 160℃ to obtain the solder alloy material. The melting time is 2.5h. After melting, the temperature is reduced to 90℃ and then alloy powder with a D50 particle size of 20μm is prepared by spray granulation equipment as solder alloy powder for later use; wherein, Bi is 236.7g and Sn is 171.4g.

[0177] Step (2): Weigh 45 parts by weight of poly(rosin) and 40 parts by weight of n-butanol, heat to 90°C, stir evenly, cool to 70°C, add 5 parts by weight of oxalic acid, stir, cool to 30°C, add 10 parts by weight of polyamide, emulsify and disperse, stir, cool and grind to obtain flux.

[0178] Step (3): Mix the alloy powder obtained in step (1) and the flux prepared in step (2) at a mass ratio of 90:10, and stir them with a solder paste mixer to obtain solder paste.

[0179] Test case

[0180] The performance of the solder pastes provided in Examples 1-9 and Comparative Example 1 was tested. The test methods and results are as follows:

[0181] 1. The viscosity of the solder paste was measured using a Maxcon PCU280 series viscosity tester. The measurement results are shown in Table 1 below.

[0182] 2. The same amount of solder paste was used to solder the solar panel and the solder strip. After the soldering was completed, the shear strength and welding tensile force at the soldering position of the solar panel and the solder strip were tested using a universal tensile strength tester. The test results are shown in Table 1 below.

[0183] Table 1

[0184]

[0185] The aforementioned welding tensile force is the maximum tensile force at the weld position between the solar cell and the solder strip when fracture occurs. The shear strength is calculated by dividing the welding tensile force by the cross-sectional area of ​​the weld position.

[0186] As shown in Table 1, the solder pastes provided in Examples 1-9 have suitable viscosity, which can improve their printability and facilitate the formation of printed patterns. They are suitable for soldering semiconductor devices. Compared with Comparative Example 1, the solder pastes provided in Examples 1-9 have higher soldering strength and firmness. In particular, when the mass percentage of In is 40%-49%, the mass percentage of Sn is 23%-35%, and the mass percentage of Bi is 25%-28%, the soldering strength and soldering firmness of the solder paste are optimal.

[0187] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0188] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A solder alloy, characterized in that, The solder alloy is a ternary alloy material of In, Sn and Bi, wherein In accounts for 40% to 60% of the mass, Sn accounts for 20% to 40% of the mass, and the balance is Bi.

2. The solder alloy according to claim 1, characterized in that, In the ternary alloy material, In accounts for 40% to 49% by mass, Sn accounts for 23% to 35% by mass, and Bi accounts for 25% to 28% by mass.

3. The solder alloy according to claim 1, characterized in that, The solder alloy is in powder form; Optionally, the D50 particle size of the solder alloy is 8μm to 38μm.

4. A solder, characterized in that, include: The solder alloy as described in any one of claims 1 to 3.

5. The solder according to claim 4, characterized in that, The solder alloy is in powder form, and the solder also includes flux, with the solder alloy dispersed in the flux. Optionally, in the solder, the solder alloy accounts for 80% to 90% by mass, and the flux accounts for 10% to 20% by mass.

6. The solder according to claim 5, characterized in that, The flux comprises: an activator, a solvent, a rosin compound, and a thixotropic agent in a mass ratio of (0.5~5):(30~70):(20~50):(2~20); Optionally, the activator comprises at least one of the following: inorganic acid, organic acid, ammonium salt, amine salt, and organic amine compound; wherein the inorganic acid comprises at least one of hydrochloric acid, orthophosphoric acid, and hydrofluoric acid; the organic acid comprises at least one of aliphatic monocarboxylic acid, aromatic acid, oxalic acid, and succinic acid; the ammonium salt comprises at least one of ammonium chloride, ammonium sulfate, ammonium nitrate, and ammonium carbonate; the amine salt comprises at least one of dimethylamine phosphate and ethylenediamine hydrochloride; and the organic amine compound comprises at least one of alkanolamine compound and amide compound. Optionally, the solvent includes at least one of the following: alcohol solvents, ether solvents, ester solvents, aliphatic hydrocarbon solvents, and aromatic hydrocarbon solvents; wherein the alcohol solvent includes at least one of n-butanol and tetrahydrofurfuryl alcohol; the ether solvent includes at least one of ethylene glycol ethyl ether, diethylene glycol dimethyl ether, dipropylene glycol methyl ether, propylene glycol butyl ether, and diethylene glycol methyl ethyl ether; the ester solvent includes at least one of butyl acetate, dimethyl oxalate, and diisononyl phthalate; the aliphatic hydrocarbon solvent includes at least one of nitromethane and nitrobenzene; and the aromatic hydrocarbon solvent includes at least one of benzene, toluene, xylene, and trimethylbenzene. Optionally, the rosin compounds include at least one of the following: rosin acid, hydrogenated rosin, disproportionated rosin, polymerized rosin, maleic rosin, rosin glycerol ester, and rosin amine; Optionally, the thixotropic agent includes at least one of hydrogenated castor oil and its derivatives, polyamide, and fatty acid amide wax; Optionally, when the solder further includes flux, the viscosity of the solder is 120 Pa·s to 195 Pa·s.

7. A method for preparing a solder alloy, characterized in that, include: In, Sn and Bi are mixed in a ratio of 40% to 60% by mass of In, 20% to 40% by mass of Sn, and the balance being Bi. The mixture is then melted to prepare the solder alloy.

8. The method for preparing the solder alloy according to claim 7, characterized in that, The solder alloy is in powder form; the preparation method further includes: The molten mixture is spray-granulated to obtain the solder alloy; Optionally, the melting temperature is greater than or equal to 160°C, and the melting time is 1 to 5 hours.

9. A method for preparing solder paste, characterized in that, include: Flux and solder alloy powder are prepared separately. The solder alloy powder is prepared by mixing In, Sn and Bi in a ratio of 40% to 60% by mass of In, 20% to 40% by mass of Sn, and the balance being Bi, and then by melting and spray granulation. The solder paste is obtained by mixing the solder alloy powder and the flux.

10. The method for preparing solder paste according to claim 9, characterized in that, The flux comprises: an activator, a solvent, a rosin-like compound, and a thixotropic agent in a mass ratio of (0.5~5):(30~70):(20~50):(2~20); the preparation of the flux includes: The rosin and solvent are mixed in proportion at a first temperature to obtain a first mixture, which is then cooled to a second temperature. The cooled first mixture is mixed with the activator at the second temperature in a certain proportion to obtain a second mixture, which is then cooled to a third temperature. The cooled second mixture is mixed with the thixotropic agent at the third temperature to obtain a third mixture, which is then cooled to room temperature to obtain the flux. Optionally, in the solder paste, the solder alloy powder accounts for 80% to 90% by mass, and the flux accounts for 10% to 20% by mass.

11. A welded structural component, characterized in that, include: A welded component and a welded part, wherein the welded component is welded and fixed by the welded part, and the welded part includes the solder as described in any one of claims 4 to 6.

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