Low-melting point in-bi-sn-ag alloy brazing filler metal, preparation method and application thereof

Abstract

The application discloses a low-melting-point In-Bi-Sn-Ag alloy solder and a preparation method and application thereof, the In-Bi-Sn-Ag alloy solder comprises the following components in percentage by mass: 15-25% of Sn, 10-30% of In, 1-12% of Ag and 40-60% of Bi; the sum of the atomic percentage of In and Ag and the atomic percentage of Bi and Sn are 35.7:39.3:25. Based on a "(cluster) connecting atom" theoretical model, combined with a phase diagram, a mixing enthalpy and a strong interaction principle, Ag and In elements are jointly added on the basis of Sn-Bi, and the component proportion of each alloy element is strictly controlled, so that the alloy solder has the advantages of low melting point, good Cu and Ni substrate wettability, high welding strength, moderate cost, lead-free and environmental protection, and the like, is especially suitable for flexible substrate interconnection, and can also be applied to 3D IC multi-layer packaging.

Description

Technical Field

[0001] This invention relates to the field of alloy brazing technology, and more specifically, to a low-melting-point In-Bi-Sn-Ag alloy brazing alloy, its preparation method, and its application. Background Technology

[0002] Due to its excellent soldering and service performance, lead-tin solder plays a vital role in the electronics industry and is widely used in electronic packaging. However, because lead poses a significant threat to human health and the environment, banning lead has become a global consensus, and international measures have been implemented to prohibit its use. To replace lead-tin solder, researchers have developed lead-free solder. As electronic products become more integrated, high-performance, and multifunctional, warping, pillowing, bridging, and non-wetting defects easily occur when using current lead-free solder for packaging. Research has found that lowering the soldering temperature can effectively solve these problems. Therefore, using low-temperature solder for low-temperature soldering has become a solution. Thus, the successful design and development of low-temperature lead-free alloy solders for flexible substrate interconnects has a very broad application prospect.

[0003] Currently, Sn-Bi-based alloys (eutectic composition Sn-58Bi) are widely used, but the melting point of Sn-Bi-based alloy solder is still too high for flexible substrate interconnects, with brazing process temperatures reaching 170℃~200℃. Furthermore, Sn-Bi-based alloys are brittle and have low toughness, making them unsuitable for current flexible substrate interconnects. To address the issues of high melting point, high cost, and insufficient mechanical properties of binary alloys, Sn-Bi-In ternary alloys have become a highly competitive alternative for flexible substrate interconnects. ML Huang et al. from Dalian University of Technology studied the interfacial microstructure and mechanical properties of a 22.15Sn-18.75Bi-59.1Inat% near-ternary eutectic alloy solder, investigating its tensile properties, elongation, and wettability on Cu substrates. EEMNoor et al. investigated the wetting properties and microstructure of a 19.6Sn-31.6Bi-48.8In wt% ternary eutectic (melting point 61.33℃), calculated the surface tension and contact angle of Sn-Bi-In solder on a Cu substrate at different reflow temperatures, and studied the characteristics of intermetallic compounds (IMCs) and the shear strength of the Cu / solder / Cu joint. However, the presence of the low-melting-point phase InBi (melting point 110℃) in the Sn-Bi-In ternary alloy leads to insufficient solder joint strength, low reliability, and a narrow service temperature range after soldering. Furthermore, the high In content in current alloys results in high costs for the alloy solder, limiting its large-scale application. Therefore, appropriately adding a fourth component to the alloy to improve the strength of the solder and the brazed joint has become a focus of current research.

[0004] Currently, the main patents related to Sn-Bi-In-X are: Patent CN113084391A discloses a low-melting-point green flexible 3D alloy, which uses an alloying method to prepare a Sn-In-Zn-Bi quaternary alloy solder with the composition 88Sn-(10-x)In-2Zn-xBi, where 1≤x≤5. However, its melting point is between 162.5℃ and 179℃, which is too high for existing flexible substrate interconnection and gradient welding. Patent CN103231180A discloses a method for preparing low-temperature aluminum alloy brazing solder. The composition of this alloy is as follows: tin 25%-29%, gallium 12%-17%, indium 22%-26%, with the balance being bismuth. The alloy contains low-melting-point liquid gallium, which cannot meet the requirements for commercial environmental testing. The solder alloy and solder disclosed in patent CN108941968A contain the following composition by mass percentage: indium 18%-28%, bismuth 44.5%-54.5%, zirconium 0.01%-1.45%, with the balance being tin. The solder joints generate a large amount of IMC phase and continuous Bi-rich phase, and the plasticity is insufficient to meet the requirements for flexible substrate interconnection. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned defects in the prior art and provide a low-melting-point In-Bi-Sn-Ag alloy solder with advantages such as low melting point, good wettability on Cu and Ni substrates, high welding strength, moderate cost, and lead-free and more environmentally friendly properties, as well as its preparation method and application.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A low-melting-point In-Bi-Sn-Ag alloy solder, wherein the In-Bi-Sn-Ag alloy solder comprises the following components in mass percentage: 15%–25% Sn, 10%–30% In, 1%–12% Ag, and 40%–60% Bi; the sum of the atomic percentages of In and Ag and the atomic percentages of Bi and Sn is 35.7:39.3:25.

[0008] This invention also discloses a method for preparing the low-melting-point In-Bi-Sn-Ag alloy solder as described above, comprising the following steps:

[0009] Sn, In, Bi and Ag are loaded into a quartz tube and vacuum sealed.

[0010] After sealing, the quartz tube is placed in an electric resistance furnace for melting.

[0011] After the Sn, In, Bi and Ag raw materials are completely melted, they are kept at a constant temperature. The quartz tube is then removed and cooled to room temperature to obtain the In-Bi-Sn-Ag alloy brazing filler metal.

[0012] The present invention also discloses the application of the low-melting-point In-Bi-Sn-Ag alloy solder as described above or the low-melting-point In-Bi-Sn-Ag alloy solder prepared by the above preparation method in the field of electronic packaging.

[0013] Implementing the embodiments of the present invention will have the following beneficial effects:

[0014] This invention addresses the characteristics of Sn-Bi alloy solders. Based on the theoretical model of "(cluster)-connected atoms" and combined with phase diagrams, mixing enthalpy, and strong interaction principles, it incorporates the composite addition of Ag and In elements to the Sn-Bi base solder, while strictly controlling the composition ratio of each alloying element. Specifically, this invention controls the added In element within a specific ratio range with the Sn-Bi base solder. The addition of In causes the eutectic alloy to form a Cu6(Sn,In)5 intermetallic compound phase after reflow, improving the alloy's wettability and interfacial bonding strength. It also lowers the melting point of the alloy solder and effectively controls solder costs. The addition of Ag further optimizes the composition of the In-Bi-Sn based solder, with In and Bi... The enthalpy of mixing (-1 kJ / mol) is higher than that of In and Ag (-2 kJ / mol). During solidification, it tends to generate phases with lower enthalpy of mixing. By reducing the content of the low-melting-point phase InBi and increasing the proportion of γ-Sn and Bi-rich phases, the generation of the low-temperature phase InBi after reflow is reduced. At the same time, Ag2In with a higher melting point and better mechanical properties is introduced into the brazed joint, with a strength of 91.2 MPa. This can improve the alloy strength, inhibit the growth of interfacial IMC, improve the reliability of the brazed joint, and increase the service temperature range without affecting the melting range. It also ensures wetting ability, refines the grains, inhibits grain growth, and makes the distribution of each phase more uniform.

[0015] In summary, the In-Bi-Sn-Ag alloy solder of this invention is based on Sn-Bi solder with compositional adjustments, adding Ag and In elements for compounding, and reducing the amount of In added to allow for the addition of Ag. Through the synergistic effect of In, Bi, Sn, and Ag elements, the overall performance of the alloy, especially its reliability, is significantly improved. The liquidus temperature is controlled between 80℃ and 105℃, and brazing can be performed at a low-temperature brazing process temperature of 110℃ to 130℃. This avoids the warping problem caused by high temperature in the traditional reflow process. It has advantages such as low melting point, good wettability of Cu and Ni substrates, high welding strength, moderate cost, and lead-free and more environmentally friendly properties. It is especially suitable for flexible substrate interconnection and can also be applied to 3D IC multilayer packaging. Attached Figure Description

[0016] Figure 1 These are microstructure diagrams of the bulk solder in Embodiment 1 and Comparative Example 1 of the present invention.

[0017] Figure 2 These are microstructure diagrams of the solder / Cu interface in Embodiment 1 and Comparative Example 1 of the present invention.

[0018] Figure 3 This is a schematic diagram of the lap joint structure of the brazed joint of the present invention.

[0019] Figure 4 This is a schematic diagram of the shear test of the brazed joint of the present invention. Detailed Implementation

[0020] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0021] The inventors conducted an in-depth study on Sn-Bi alloy solders in lead-free alloy solders. First, they investigated the alloy composition by lowering the liquidus temperature. By adding In to Sn-Bi alloy solders, the inventors found that the melting point of Sn-52In eutectic solder was 118°C, which was not much different from that of Sn-Bi eutectic alloys, and it also had the problem of a relatively high melting point. In-Bi alloys have three eutectic points: In-67Bi eutectic alloy (110°C), In-50Bi (88.7°C), and In-32Bi (72°C). At the same time, they found that the presence of the low-melting-point phase InBi led to insufficient solder joint strength, low reliability, and a small service temperature range after soldering. Furthermore, the In content added in the prior art is generally high, resulting in high cost of alloy solders.

[0022] Therefore, considering the overall balance, the inventors added a fourth component to the alloy solder system and further investigated the content of each constituent element in detail.

[0023] The present invention derived from these insights is as follows.

[0024] This invention discloses a low-melting-point In-Bi-Sn-Ag alloy solder, which comprises the following components by mass percentage: 15% to 25% Sn, 10% to 30% In, 1% to 12% Ag and 40% to 60% Bi.

[0025] The principle of this invention is as follows: Sn-Bi alloy solder is selected as the matrix. Based on the theoretical model of "(cluster) connected atoms" and combined with the principles of phase diagram, mixing enthalpy and strong interaction, Ag and In are added in combination on the basis of Sn-Bi alloy solder, and the composition ratio of each alloying element is strictly controlled. The resulting In-Bi-Sn-Ag alloy solder has the advantages of low melting point, good wettability of Cu and Ni substrates, high welding strength, moderate cost, and lead-free and more environmentally friendly properties.

[0026] Specifically, by adding Sn and Bi within the specified range to the lead-free alloy solder, Bi can be dissolved in the Sn matrix, which can further strengthen the lead-free alloy solder. However, if the Sn content is too high, it will lead to the formation of an excessively thick interfacial IMC, reducing the reliability of the joint. If the Sn content is too low, the above effect cannot be achieved. If the Bi content is too low, the above effect cannot be achieved. If the Bi content is too high, the solidification segregation becomes more obvious due to the increase in the solid-liquid coexistence area, and the frequency of warping increases.

[0027] Furthermore, based on the above, the inventors determined the alloy solder composition ratio with excellent performance through a large number of composition optimization experiments: the sum of the atomic percentages of In and Ag and the atomic percentages of Bi and Sn are 35.7:39.3:25. By controlling the added In and Sn-Bi base solder within a specific ratio range, that is, under the synergistic effect of In, Bi and Sn, the eutectic alloy generates Cu6(Sn,In)5 intermetallic compound phase after reflow, which improves the alloy wettability and interfacial bonding force, and can also reduce the melting point of the alloy solder and effectively control the cost of solder. Furthermore, based on the above, in order to further enhance the bonding strength of the brazed joint, a portion of In was replaced with Ag. Through numerous composition optimization experiments, the inventors further optimized the alloy brazing filler metal composition and determined an alloy brazing filler metal composition ratio with excellent performance: the sum of the atomic percentages of In and Ag is 35.7%. This is because the enthalpy of mixing of In and Bi (-1 kJ / mol) is higher than that of In and Ag (-2 kJ / mol), and during solidification, it tends to generate a phase with a lower enthalpy of mixing. This is achieved by reducing the low-melting-point phase In. Increasing the Bi content increases the proportion of γ-Sn and Bi-rich phases, reducing the formation of the low-temperature InBi phase after reflow. Simultaneously, it introduces Ag2In, a high-melting-point and mechanically strong phase with a strength of 91.2 MPa, into the brazed joint. This improves alloy strength, inhibits interfacial IMC growth, enhances brazed joint reliability, and expands the service temperature range without affecting the melting range. It also ensures wetting ability and refines the grains, inhibiting grain growth and resulting in a more uniform phase distribution. However, excessive Ag content may lead to the formation of large Ag3Sn deposits after reflow, resulting in insufficient joint strength. Conversely, insufficient Ag content fails to adequately inhibit interfacial IMC growth, resulting in poor joint strength improvement.

[0028] In one specific embodiment, the inventors first focused on suppressing warping. Since the alloy is a material composed of all constituent elements, these elements influence each other. By achieving a balance between the Sn, Bi, and In contents, the In content is adjusted to a specified range. Furthermore, the total Ag and In contents are limited. Thus, the alloy brazing filler metal of this embodiment can achieve good mechanical strength. The liquidus temperature of the In-Bi-Sn-Ag alloy brazing filler metal is between 80°C and 105°C, and the solidus temperature is between 80°C and 85°C. Brazing can be performed at a low-temperature brazing process temperature of 110°C to 130°C, which avoids the warping problem caused by high temperatures in traditional reflow processes.

[0029] In one specific embodiment, the mass percentage of Ag is preferably 1% to 11%.

[0030] In one specific embodiment, the raw material form of Bi is Bi block with a purity of 99.99%; the raw material form of In is In block with a purity of 99.99%; the raw material form of Ag is Ag block with a purity of 99.99%; and the raw material form of Sn is Sn block with a purity of 99.99%.

[0031] This invention also discloses a method for preparing a low-melting-point In-Bi-Sn-Ag alloy solder as described in any embodiment of this invention, comprising the following steps:

[0032] 1) Fill Sn, In, Bi and Ag into a quartz tube and vacuum seal it.

[0033] 2) After sealing, the quartz tube is placed into the resistance furnace for melting.

[0034] 3) After the Sn, In, Bi and Ag raw materials are completely melted, keep them at a constant temperature, remove the quartz tube and cool it to room temperature to obtain the In-Bi-Sn-Ag alloy brazing filler metal.

[0035] In one specific embodiment, the preparation method of low-melting-point In-Bi-Sn-Ag alloy solder specifically includes the following steps:

[0036] (1) Weigh 100g of Sn (99.99% purity), In (99.99% purity), Bi (99.99% purity), and Ag (99.99% purity) according to the proportions of any embodiment of the present invention, and place them in a quartz tube.

[0037] (2) Use a hydrogen flame to melt and seal one end of the quartz tube, melt the other end to form a narrow opening, and use a vacuum pump to evacuate the tube to a vacuum level of 1×10⁻⁶. -3 Pa ~ 1×10 -4Pa, after purging the air from the tube, melt and seal the narrow opening.

[0038] (3) Place the quartz tube from step 2) in a resistance furnace and heat it to 700℃~1000℃ for melting. After all components have melted, keep it at 700℃~1000℃ for 3h~4h to homogenize the alloy. Rotate the quartz tube every 30min to ensure that the liquid alloy in the quartz tube is more uniform.

[0039] (4) After the melting is completed, the quartz tube is removed and cooled to room temperature to obtain low melting point In-Bi-Sn-Ag alloy brazing filler metal.

[0040] Specifically, the preparation method of the present invention can ensure that trace alloying elements are uniformly added to the alloy solder by adjusting process parameters such as melting temperature, melting time, and cooling method. At the same time, it can more accurately control the alloying element composition, obtain a good microstructure, and finally obtain a low melting point In-Bi-Sn-Ag alloy solder with good solder joint bonding and high reliability.

[0041] The following are specific embodiments.

[0042] Example 1

[0043] The In-Bi-Sn-Ag alloy solder of this embodiment comprises the following components by mass percentage: Sn 19.44%, Bi 53.78%, Ag 1.26%, with the balance being In.

[0044] The liquidus temperature of the In-Bi-Sn-Ag alloy brazing filler metal in this embodiment is 80℃~105℃; the solidus temperature of the In-Bi-Sn-Ag alloy brazing filler metal is 80℃~85℃.

[0045] The preparation method of the low-melting-point In-Bi-Sn-Ag alloy solder in this embodiment includes the following steps:

[0046] (1) Weigh 100g of Sn (99.99% purity), In (99.99% purity), Bi (99.99% purity), and Ag (99.99% purity) according to the proportions of any embodiment of the present invention, and place them in a quartz tube.

[0047] (2) Use a hydrogen flame to melt and seal one end of the quartz tube, melt the other end to form a narrow opening, and use a vacuum pump to evacuate the tube to a vacuum level of 1×10⁻⁶. -3 Pa, after purging the air from the tube, melt and seal the narrow opening.

[0048] (3) Place the quartz tube from step 2) in a resistance furnace and heat it to 700℃~1000℃ for melting. After all components have melted, keep it at 700℃~1000℃ for 3 hours to homogenize the alloy. Rotate the quartz tube every 30 minutes to ensure that the liquid alloy in the quartz tube is more uniform.

[0049] (4) After the melting is completed, the quartz tube is removed and cooled to room temperature to obtain low melting point In-Bi-Sn-Ag alloy brazing filler metal.

[0050] Example 2

[0051] The In-Bi-Sn-Ag alloy solder of this embodiment comprises the following components by mass percentage: Sn 19.46%, Bi 53.83%, Ag 2.52%, with the balance being In.

[0052] The preparation method in this embodiment is the same as that in Example 1.

[0053] Example 3

[0054] The In-Bi-Sn-Ag alloy solder of this embodiment comprises the following components by mass percentage: Sn 19.47%, Bi 53.87%, Ag 3.79%, with the balance being In.

[0055] The preparation method in this embodiment is the same as that in Example 1.

[0056] Example 4

[0057] The In-Bi-Sn-Ag alloy solder of this embodiment comprises the following components by mass percentage: Sn 19.49%, Bi 53.91%, Ag 5.06%, with the balance being In.

[0058] The preparation method in this embodiment is the same as that in Example 1.

[0059] Example 5

[0060] The In-Bi-Sn-Ag alloy solder of this embodiment comprises the following components by mass percentage: Sn 19.50%, Bi 53.96%, Ag 6.33%, with the balance being In.

[0061] The preparation method in this embodiment is the same as that in Example 1.

[0062] Example 6

[0063] The In-Bi-Sn-Ag alloy solder of this embodiment comprises the following components by mass percentage: Sn 19.57%, Bi 54.13%, Ag 11.43%, with the balance being In.

[0064] The preparation method in this embodiment is the same as that in Example 1.

[0065] Comparative Example 1

[0066] The alloy brazing filler metal in this comparative example comprises the following components by mass percentage: Sn 19.43%, Bi 53.74%, with the balance being In.

[0067] The preparation method of this comparative example is the same as that of Example 1.

[0068] Comparative Example 2

[0069] The alloy brazing filler metal in this comparative example comprises the following components by mass percentage: Sn 48%, with the balance being In.

[0070] The preparation method of this comparative example is the same as that of Example 1.

[0071] Comparative Example 3

[0072] The alloy brazing filler metal in this comparative example comprises the following components by mass percentage: Sn 51.6%, Bi 47.7%, with the balance being Ag.

[0073] The preparation method of this comparative example is the same as that of Example 1.

[0074] Comparative Example 4

[0075] The alloy brazing filler metal in this comparative example comprises the following components by mass percentage: Bi 67%, with the balance being In.

[0076] The preparation method of this comparative example is the same as that of Example 1.

[0077] Comparative Example 5

[0078] The alloy brazing filler metal in this comparative example comprises the following components by mass percentage: Sn 42%, with the balance being Bi.

[0079] The preparation method of this comparative example is the same as that of Example 1.

[0080] Comparative Example 6

[0081] The alloy brazing filler metal in this comparative example comprises the following components by mass percentage: Sn 25.53%, Bi 49.94%, Ag 2.58%, with the balance being In.

[0082] The preparation method of this comparative example is the same as that of Example 1.

[0083] Comparative Example 7

[0084] The alloy brazing filler metal in this comparative example comprises the following components by mass percentage: Sn 13.62%, Bi 57.55%, Ag 2.48%, with the balance being In.

[0085] The preparation method of this comparative example is the same as that of Example 1.

[0086] Comparative Example 8

[0087] The alloy brazing filler metal in this comparative example comprises the following components by mass percentage: Sn 19.99%, Bi 55.31%, Ag 2.60%, with the balance being In.

[0088] The preparation method of this comparative example is the same as that of Example 1.

[0089] Comparative Example 9

[0090] The alloy brazing filler metal in this comparative example comprises the following components by mass percentage: Sn 18.98%, Bi 52.49%, Ag 4.93%, with the balance being In.

[0091] The preparation method of this comparative example is the same as that of Example 1.

[0092] Comparative Example 10

[0093] The alloy brazing filler metal in this comparative example comprises the following components by mass percentage: Sn 13.29%, Bi 56.16%, Ag 4.84%, with the balance being In.

[0094] The preparation method of this comparative example is the same as that of Example 1.

[0095] Comparative Example 11

[0096] The alloy brazing filler metal in this comparative example comprises the following components by mass percentage: Sn 42%, Bi 50%, with the balance being In.

[0097] The preparation method of this comparative example is the same as that of Example 1.

[0098] Test case

[0099] 1. Metallographic microstructure tests were performed on Example 1 and Comparative Example 1, such as... Figure 1 and Figure 2 As shown, Cu6(Sn,In)5 and Ag2In were found in the alloy brazing filler metal prepared in Example 1.

[0100] 2. The alloy brazing filler metals of Examples 1-6 and Comparative Examples 1-11 were subjected to wettability tests on copper substrates and shear performance tests on brazed joints. The brazed joints adopted lap joints, and the lap structure was as follows: Figure 3 As shown, Figure 3This is a schematic diagram of the lap joint structure of the brazed joint of the present invention. The experimental conditions are as follows: (1) The alloy brazing filler metals of Examples 1-6 and Comparative Examples 1-11 were made into brazing filler metal balls with a diameter of 1.5 mm. The brazing filler metal balls were placed on copper substrates and nickel substrates coated with 12 mg of commercially available flux. A 300 μm spacer was placed between the copper substrate and the nickel substrate to control the spacing. The lap joint was placed in a reflow oven for heating. The spreading area of ​​the alloy brazing filler metal on the copper substrate and the nickel substrate after reflow soldering was measured using graphic software. (2) After the joint was assembled, it was placed in a reflow oven and heated according to the set reflow curve. After reflow, the brazed joint was taken out and then the shear strength of the brazed joint was tested using a universal tensile testing machine. The schematic diagram of the shear strength tensile test is shown below. Figure 4 As shown, Figure 4 This is a schematic diagram of the shear test of the brazed joint of the present invention. (3) Melting point test: The heating rate was 10℃ / min and the test was conducted using a differential scanning calorimeter (DSC). The sample mass was 30mg. The numerical processing was automatically calculated by the software, and the peak temperature of the DSC curve was recorded as the melting point value of the alloy brazing filler. The test results are shown in Table 1.

[0101] Table 1 Performance test results of Examples 1-6 and Comparative Examples 1-11

[0102]

[0103] According to the test results in Table 1, Examples 1-6 exhibit superior wetting ability and shear strength compared to Comparative Examples 1-11. This indicates that the In-Bi-Sn-Ag alloy solders of Examples 1-6 are based on Sn-Bi solders with adjusted composition, adding Ag and In for compounding. Through numerous composition optimization experiments, an alloy solder composition ratio with excellent performance was determined. By reducing the amount of In added, more space was created for the addition of Ag. When all constituent elements fall within the specified range and meet the specific composition ratio, the synergistic effect of In, Bi, Sn, and Ag significantly improves the overall performance of the alloy, especially its reliability. With the liquidus temperature controlled between 80℃ and 105℃, brazing can be performed at a low-temperature brazing process temperature of 110℃ to 130℃. This avoids the warping problem caused by high temperatures in traditional reflow processes. It has advantages such as low melting point, good wettability on Cu and Ni substrates, high welding strength, moderate cost, and lead-free environmental friendliness. It is particularly suitable for flexible substrate interconnection and can also be applied to 3D IC multilayer packaging.

[0104] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are 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 the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A low-melting-point In-Bi-Sn-Ag alloy solder, characterized in that, The In-Bi-Sn-Ag alloy solder comprises the following components by mass percentage: 15%–25% Sn, 10%–30% In, 1%–12% Ag and 40%–60% Bi; The sum of the atomic percentages of In and Ag is 35.7:39.3:25 compared to the atomic percentages of Bi and Sn.

2. The low-melting-point In-Bi-Sn-Ag alloy solder according to claim 1, characterized in that, The mass percentage of Ag is 1% to 11%.

3. The low-melting-point In-Bi-Sn-Ag alloy solder according to claim 1, characterized in that, The liquidus temperature of the In-Bi-Sn-Ag alloy solder is between 80℃ and 105℃. The solidus temperature of the In-Bi-Sn-Ag alloy solder is 80℃~85℃.

4. The low-melting-point In-Bi-Sn-Ag alloy solder according to claim 1, characterized in that, The raw material form of Bi is Bi lumps with a purity of 99.99%; The raw material form of In is In lumps with a purity of 99.99%; The raw material form of Ag is Ag lumps with a purity of 99.99%; The raw material form of Sn is Sn block with a purity of 99.99%.

5. A method for preparing a low-melting-point In-Bi-Sn-Ag alloy solder as described in any one of claims 1-4, characterized in that, Includes the following steps: Sn, In, Bi and Ag are loaded into a quartz tube and vacuum sealed. After sealing, the quartz tube is placed in an electric resistance furnace for melting. After the Sn, In, Bi and Ag raw materials are completely melted, they are kept at a constant temperature. The quartz tube is then removed and cooled to room temperature to obtain the In-Bi-Sn-Ag alloy brazing filler metal.

6. The method for preparing the low-melting-point In-Bi-Sn-Ag alloy solder according to claim 5, characterized in that, The melting temperature is 700℃~1000℃; The vacuum level inside the tube during vacuum sealing is 1×10⁻⁶. -3 Pa ~ 1×10 -4 Pa.

7. The method for preparing the low-melting-point In-Bi-Sn-Ag alloy solder according to claim 6, characterized in that, The insulation temperature is 700℃~1000℃; The heat preservation time is 3 to 4 hours.

8. The method for preparing low-melting-point In-Bi-Sn-Ag alloy solder according to claim 7, characterized in that, Also includes: The quartz tube is rotated once every 30 minutes during the heat preservation process.

9. The method for preparing low-melting-point In-Bi-Sn-Ag alloy solder according to claim 5, characterized in that, The purity of Sn, In, Bi, and Ag is all 99.99%.

10. The application of a low-melting-point In-Bi-Sn-Ag alloy solder as described in any one of claims 1-4 or a low-melting-point In-Bi-Sn-Ag alloy solder prepared by the preparation method described in any one of claims 5-9 in the field of electronic packaging.

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