Lead-free tin-based brazing filler metal alloy with high entropy phase and preparation method and special smelting equipment of lead-free tin-based brazing filler metal alloy

Abstract

The invention provides a lead-free tin-based solder alloy with a high-entropy phase and a preparation method and special smelting equipment thereof, and belongs to the technical field of welding material preparation. The alloy comprises the following elements in atomic percent: 10%-25% of Zn, 15%-25% of Bi, 5%-20% of In, 5%-15% of Cu and the balance of Sn. The special smelting equipment comprises a smelting container assembly and an auxiliary equipment assembly. The preparation method comprises the steps that all the components are placed in the special smelting equipment, inert gas is injected for induction smelting after vacuumizing, a cast ingot is obtained after cooling, the cast ingot is smelted again under the same condition, and the brazing filler metal alloy is obtained after the obtained melt is rapidly cooled. The brazing filler metal alloy prepared through the method not only has a unique high-entropy phase, but also has the advantages of being low in melting point, obdurability, good in wettability and capable of inhibiting growth of interface intermetallic compounds, and is suitable for welding of heat-sensitive materials and electronic devices.

Description

Technical Field

[0001] This invention belongs to the field of welding material preparation technology, and particularly relates to a lead-free tin-based solder alloy with a high-entropy phase, its preparation method, and a special melting equipment. Background Technology

[0002] As the global electronic packaging industry moves towards greener practices, traditional lead-based solders are being strictly restricted by regulations such as the EU RoHS (Restriction of Hazardous Substances Directive in Electrical and Electronic Equipment) due to their environmental toxicity. While mainstream lead-free solder systems like Sn-Ag-Cu (SAC) alloys can meet conventional packaging requirements, they still face significant technical bottlenecks in the low-temperature micro-connection field. During long-term service, traditional Sn-based alloys are prone to atomic migration due to thermo-electric coupling, leading to abnormal thickening of the intermetallic compound (IMC) layer and whisker growth at the solder joint interface, significantly reducing the mechanical reliability and conductivity stability of devices. In emerging low-temperature packaging scenarios such as flexible electronics and biomedical devices, existing solders, with their high melting points (>180 °C), are prone to damaging heat-sensitive substrates, significantly increasing the risk of electronic device failure.

[0003] Currently, low-temperature solder research and development mainly focuses on binary alloy systems (such as Sn-Bi and Sn-In), improving wettability through trace doping. However, single-principal-element solders cannot simultaneously achieve the desired strength and toughness, hindering breakthroughs in overall performance. In recent years, the design concept of multi-principal-element alloys (including high-entropy alloys and medium-entropy alloys) based on the synergistic effect of multiple principal elements has provided a new direction for solder innovation. The unique lattice distortion effect of multi-principal-element alloys can significantly hinder atomic migration and diffusion, improving the strength and toughness of the solder. Its "cocktail effect" is beneficial for optimizing the morphology control of the interfacial IMC. However, due to the limited solid solubility of most elements in the tin matrix, the phases in existing multi-principal-element tin-based solders (such as InSn4 phase) only contain 2-3 elements, making it impossible to form a high-entropy solid solution phase containing 5 elements in the solder to fully utilize the characteristics of high-entropy alloys. Therefore, developing a multi-principal element lead-free tin-based solder alloy that can achieve excellent welding performance at low temperatures and has a high entropy strengthening effect is of great technical significance and application value for meeting the urgent needs of the electronic packaging industry for high-performance, low-temperature-sensitive soldering materials. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention provides a lead-free tin-based solder alloy with a high-entropy phase, its preparation method, and a dedicated melting equipment. This invention addresses the technical problems of existing low-temperature solders, such as high melting point, insufficient solder joint mechanical properties, difficulty in effectively suppressing interfacial diffusion, and insufficient long-term solder joint stability. It proposes a multi-component low-temperature solder containing a high-entropy phase, achieving a synergistic improvement in solder strength and toughness through the multi-principal component synergistic effect. This suppresses the formation of brittle intermetallic compounds at the welding interface and reduces the interfacial atomic diffusion rate, ensuring the long-term service stability of microelectronic packaging structures under thermo-mechanical coupling loads.

[0005] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of the present invention: This invention provides a lead-free tin-based solder alloy with a high-entropy phase. The lead-free tin-based solder alloy has Sn and any one or a combination of two of Bi or In as the main elements, and the remaining elements include any two or a combination of three of Ni, Mn, Ag, Cu and Zn.

[0006] Furthermore, Sn is an essential element in the lead-free tin-based solder alloy, and the lead-free tin-based solder alloy includes five elements; The mixing entropy of the lead-free tin-based solder alloy is ≥1.4R, where R is the ideal gas constant, with a value of 8.314 J / (mol·K).

[0007] Furthermore, the lead-free tin-based solder alloy is mainly composed of Sn, Bi, and In, with the remaining elements including Cu and Zn.

[0008] Furthermore, the elements of the lead-free tin-based solder alloy, by atomic percentage, are: Zn: 10%-25%, Bi: 15%-25%, In: 5%-20%, Cu: 5%-15%, with the balance being Sn.

[0009] Furthermore, the percentage of Sn atoms is ≥30%; The total atomic percentage of the main element is ≥60%.

[0010] More preferably, the lead-free tin-based solder alloy comprises, by atomic percentage, Zn: 16%, Bi: 24%, In: 10%, Cu: 10%, and Sn: 40%; The lead-free tin-based solder alloy comprises, by atomic percentage, Zn: 18%, Bi: 25%, In: 12%, Cu: 10%, and Sn: 35%. The lead-free tin-based solder alloy comprises, by atomic percentage, Zn: 20%, Bi: 25%, In: 15%, Cu: 10%, and Sn: 30%. The lead-free tin-based solder alloy comprises, by atomic percentage, Zn: 10%, Bi: 25%, In: 15%, Cu: 10%, and Sn: 40%.

[0011] The second technical solution of the present invention: The present invention also provides a special melting equipment for lead-free tin-based solder alloys with a high-entropy phase, the special melting equipment including a melting container assembly and an auxiliary equipment assembly; The melting container assembly includes a special container, the top of which is connected to a sealing device, the top of which is connected to a stirring rod, the stirring rod extending through the sealing device into the interior of the special container, and a micro motor connected to the stirring rod; The auxiliary equipment components include a motor mounting bracket, a quick-lifting device, a vacuum circuit, an exhaust pipe, and an inert gas input circuit. One end of the motor mounting bracket is connected to the quick-lifting device, and the other end is connected to the micro motor. The vacuum circuit, exhaust pipe, and inert gas input circuit are all connected to the sealing device via quick-connect flanges. The other end of the vacuum circuit is connected to an external 20-40 L oil-free negative pressure vacuum pump.

[0012] Furthermore, the rapid lifting device includes a main support, a connecting slide rail, a handwheel operating component, and a test tube holder. The motor holder is connected to the main support, and the handwheel operating component is fixedly connected to the main support. The main support is driven by the connecting slide rail through gear engagement, and the handwheel operating component is driven by the connecting slide rail. The test tube holder is fixedly connected to the connecting slide rail and forms a sliding connection with the main support through the connecting slide rail. By rotating the handwheel operating component, the lead screw inside the connecting slide rail is driven to rotate, thereby driving the test tube holder to move up and down, realizing rapid and precise lifting of the melting container assembly.

[0013] Furthermore, the stirring rod is a specially made ceramic stirring rod.

[0014] Furthermore, the sealing device adopts a double sealing structure: the lower seal is achieved by using a quick-connect flange joint in conjunction with a high-temperature resistant rubber ring, and the upper seal is achieved by using a high-elasticity sealing plug; the sealing plug is provided with a stirring rod insertion hole, an exhaust pipe hole and a vacuum passage hole, and the corresponding pipes and stirring rods are inserted through the corresponding holes. To ensure the reliability of the pipes during the melting process, the pipes are made of flexible hoses with steel wire support. The auxiliary equipment components also include an induction coil, a coolant container, a pressure relief valve, and a switching valve; the induction coil is sleeved around the outer periphery of the special container; the coolant container is placed below the special container and contains an ice-water mixture / liquid nitrogen as a cooling medium; the pressure relief valve is located on the exhaust pipe; and switching valves are provided on the vacuum path, the exhaust pipe, and the inert gas input path.

[0015] Furthermore, the high-temperature resistant rubber ring is resistant to high temperatures of 100-150 ℃; The induction coil is connected to an external medium-frequency induction heater, the power of which is 10-35 kW; The pressure relief valve is preferably a 0.1-0.6 MPa pressure relief valve; The special container is preferably a quartz container.

[0016] Furthermore, the working method of the special melting equipment is as follows: before melting, the switch valve is closed, and the special container is evacuated to 0.03 MPa using an external vacuum pump. The external gas cylinder containing inert gas is opened to inject inert gas into the inert gas inlet gas path, and the exhaust gas path switch valve is opened. The pressure relief valve is used to adjust the cavity of the special container to be filled with inert gas. Heating and melting are carried out using an external medium-frequency induction heating device. When cooling is required, the special container is rapidly lowered using a rapid lifting device. On the one hand, the stirring rod is separated from the alloy solution, and on the other hand, the special container is rapidly immersed in the cooling medium to achieve rapid cooling.

[0017] The third technical solution of the present invention: The present invention also provides a method for preparing a lead-free tin-based solder alloy with a high-entropy phase, comprising the following steps: (1) Place each component in the special melting equipment described in claim 5, evacuate and inject inert gas for induction melting, and then let it stand and cool to obtain an ingot; (2) The ingot is placed in the special melting equipment described in claim 5, and after vacuuming, inert gas is injected for remelting. The resulting melt is then rapidly cooled to obtain the lead-free tin-based solder alloy.

[0018] Furthermore, during the induction melting process described in step (1), it is necessary to maintain a slightly positive pressure environment inside the special container to avoid some of the metal from evaporating rapidly in a vacuum environment due to a significant drop in vapor pressure.

[0019] Furthermore, the induction melting temperature in step (1) is 600-700 ℃, and the time is 6-9 min. Ensure that all metals are completely melted, and obtain an ingot after standing and cooling at room temperature. If the temperature is higher than 700 ℃, it will cause a large amount of Zn element to evaporate and be lost during the melting process.

[0020] Furthermore, the remelting temperature in step (2) is 300-600 ℃ and the time is 8-10 min; the melting point of the alloy during the second remelting is much lower than that of the initial raw material, so it can be melted at a lower temperature. The lower remelting temperature is to avoid some elements from evaporating and being lost during the heating process, thus reducing energy loss.

[0021] The remelting is carried out under high-speed stirring at a speed of 300 rpm. During the heating process, the motor is turned on to stir, so as to achieve a thorough and uniform mixing of the melt in the container. The rapid cooling method involves immersing a special container holding the melt into an ice-water mixture or liquid nitrogen, preferably an ice-water mixture.

[0022] Furthermore, when the ice-water mixture is used for cooling, the temperature of the coolant is 0 ℃. After cooling until the alloy shrinks, it separates from the container, which facilitates the removal of the alloy. This method is preferred. When liquid nitrogen is used for cooling, the temperature of the coolant is -196 ℃. After cooling until the alloy shrinks, it separates from the special container, making it easy to remove the alloy.

[0023] Furthermore, the inert gases are all nitrogen or argon; The vacuum was evacuated to 0.03 MPa; The components mentioned in step (1) are solid particles or solid powders.

[0024] The beneficial effects of this invention compared to the prior art are as follows: This invention provides a lead-free and non-toxic high-entropy solder alloy that meets the soldering needs of everyday electronic products and fully complies with RoHS environmental regulations. This invention achieves a solder alloy with a high-entropy solid solution phase, primarily composed of low-melting-point elements such as Sn, Bi, and In, and supplemented by high-melting-point elements such as Cu, Ni, and Ag, through precise control of the solder composition, combined with uniform stirring and ultra-high-speed cooling processes. Compared to other high-entropy alloy solders, this invention's design strategy uses lead-free and non-toxic elements, complying with RoHS requirements. Furthermore, by precisely controlling the proportions of the main elements and optimizing the preparation method, a specific five-element high-entropy phase is obtained within the solder while maintaining high mixing entropy. This achieves multi-phase coupling of intermetallic compounds, traditional solid solution phases, and high-entropy solid solution phases, improving the solder's strength and toughness. Compared to traditional SnBi or SnAgCu solders, this invention uses low-melting-point elements such as Sn, Bi, and In to form a eutectic structure, effectively lowering the solder's melting point and making it more suitable for low-temperature soldering scenarios. Simultaneously, the synergistic effect of multiple principal elements forms reinforcing phases of different sizes and hardnesses, significantly improving the solder's strength and toughness.

[0025] The brazing alloy of this invention exhibits a significant inhibitory effect on Cu diffusion and interface nucleation during brazing, reducing the rate of interface diffusion, effectively suppressing excessive growth of interfacial IMC, reducing IMC thickness, and ensuring the stability of the high-entropy solid solution phase during use, thereby improving the load-bearing capacity of the brazing alloy. It comprehensively achieves low melting point, high strength, and good interfacial stability of the brazing alloy, significantly improving the high-temperature performance and long-term service reliability of the brazed joint.

[0026] The lead-free tin-based solder alloy with a high-entropy phase of this invention has significant advantages in industrial applications: the selected elements such as Sn, Bi, In, and Zn are all conventional metal raw materials in the electronic packaging field, with a mature, stable supply chain and controllable costs; the designed preparation device is characterized by low cost and rich functionality, avoiding the large-scale equipment investment required for traditional vacuum melting. The prepared solder has a very low melting point and good wetting properties, and can achieve good bonding with the substrate at a relatively low reflow temperature, making it particularly suitable for soldering applications of heat-sensitive materials and electronic devices.

[0027] The specialized smelting equipment of this invention has the advantages of simple structure, convenient operation, and low cost, achieving good smelting results without the need for a complex and expensive vacuum smelting furnace. Through a unique rapid lifting mechanism combined with a precise sealing system, this equipment effectively solves the technical problem of insufficient stirring in ordinary smelting devices, making it particularly suitable for smelting various low-melting-point alloys and exhibiting good versatility. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the overall structure of the special melting equipment for lead-free tin-based solder alloy in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the rapid lifting device of the special melting equipment for lead-free tin-based solder alloy in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the melting container assembly of the special melting equipment for lead-free tin-based solder alloys according to Embodiment 1 of the present invention; Figure 1-3The components are as follows: 1. Motor mounting bracket; 2. Quick lifting device; 3. Coolant container; 4. Exhaust pipe; 5. Pressure relief valve; 6. Switch valve; 7. Vacuum circuit; 8. Inert gas input circuit; 9. Handwheel operating component; 10. Main support; 11. Test tube holder; 12. Connecting slide rail; 13. Micro motor; 14. Induction coil; 15. Special container; 16. Quick-connect flange; 17. High-temperature resistant rubber ring; 18. Sealing plug; 19. Stirring rod. Figure 4 Differential scanning calorimetry (DSC) curve of the lead-free tin-based solder alloy prepared in Example 2 of the present invention; Figure 5 The images show the microstructure of the welding interface of the lead-free tin-based solder alloy solder joint prepared in Example 2 of the present invention. Among them, a is the microstructure of the welding interface after welding at 180 °C for 2 min, and b is the microstructure of the welding interface after welding at 180 °C for 3 min. Figure 6 Microstructure images of the lead-free tin-based solder alloy solder joints prepared in Example 2 of the present invention after thermal aging for 0 h, 50 h and 100 h. Figure 7 The image shows the interface EDS line scan of the lead-free tin-based solder alloy solder joint prepared in Example 2 of the present invention after 100 h of thermal aging. In the image, a is the location of the solder interface where the line scan is located, b is a magnified view of the line scan area, and c is a graph showing the change in element content during the line scan. Figure 8 EDS spot scan image (a) and EDS composition analysis image (b) of the interface structure of the lead-free tin-based solder alloy solder joint prepared in Example 2 of the present invention after 100 h of thermal aging. Figure 9 The image shows the BSE diagram of the lead-free tin-based solder alloy prepared in Example 2 of the present invention, where a is the BSE diagram of the entire alloy and b is an enlarged view of the high-entropy phase position. Figure 10 EDS diagram (a) and composition analysis diagram (b) of the high-entropy phase interior points of the lead-free tin-based solder alloy prepared in Example 2 of the present invention. Figure 11 The XRD pattern of the lead-free tin-based solder alloy prepared in Example 2 of this invention; Figure 12 The tensile properties test diagram of the lead-free tin-based solder alloy prepared in Example 2 of this invention; Figure 13 SEM image of the welded cross section of the lead-free tin-based solder alloy prepared in Example 2 of the present invention, under the conditions of welding temperature of 180℃ and welding time of 150s. Detailed Implementation

[0030] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0031] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0032] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0033] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0034] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0035] The room temperature described in the following embodiments of the present invention is 23±2 ℃.

[0036] Example 1 A specialized melting equipment for lead-free tin-based solder alloys with a high-entropy phase, such as... Figure 1-3 As shown, it includes a melting container assembly and auxiliary equipment assemblies; Among them, the above-mentioned smelting container assembly includes a special container (15), the top of the special container (15) is connected to a sealing device, the top of the sealing device is connected to a stirring rod (19), the stirring rod (19) passes through the sealing device and extends into the interior of the special container (15), and a micro motor (13) is connected to the stirring rod (19). The sealing device adopts a double sealing structure: the lower sealing is achieved by the quick-connect flange (16) and the high-temperature resistant rubber ring (17), and the upper sealing adopts a high-elasticity sealing plug (18). The sealing plug (18) is provided with a stirring rod insertion hole, an exhaust pipe hole, a vacuum hole and an inert gas input hole. The corresponding pipes and stirring rod (19) are inserted through the corresponding holes. The pipes are flexible hoses with steel wire support. The above-mentioned auxiliary equipment components include a motor mounting bracket (1), a rapid lifting device (2), a vacuum circuit (7), an exhaust pipe (4), an inert gas input circuit (8), an induction coil (14), a coolant container (3), a pressure relief valve (5), and a switching valve (6). The rapid lifting device includes a main support (10), a connecting slide rail (12), a handwheel operating component (9), and a test tube holder (11). One end of the motor holder (1) is connected to the main support (10), and the other end is connected to a micro motor (13). The handwheel operating component (9) is fixedly connected to the main support (10). The main support (10) is connected to the connecting slide rail (12) through gear meshing. The handwheel operating component (9) is connected to the connecting slide rail (12) through transmission. The test tube holder (11) is fixedly connected to the connecting slide rail (12) and forms a sliding connection with the main support (10) through the connecting slide rail (12). By rotating the handwheel operating component (9), the screw in the connecting slide rail (12) is driven to rotate, thereby driving the test tube holder (11) to move up and down, so as to realize the rapid and precise lifting of the melting container assembly. One end of the vacuum circuit (7) is connected to the vacuum circuit hole on the sealing plug (18) via a quick-connect flange (16), and the other end is connected to an external 20-40L oil-free negative pressure vacuum pump. A switch valve (6) is also provided on the vacuum circuit (7). The exhaust pipe (4) is also connected to the exhaust pipe hole on the sealing plug (18) via a quick-connect flange (16). A pressure relief valve (5) and a switch valve (6) are also provided on the exhaust pipe (4). The inert gas input gas circuit (8) is also connected to the inert gas input gas hole on the sealing plug (18) via a quick-connect flange (16). A switch valve (6) is also provided on the inert gas input gas circuit (8). The induction coil (14) is sleeved on the outer periphery of the special container (15) and connected to the external medium-frequency induction heater. The coolant container (3) is placed below the special container (15) and contains an ice-water mixture as the cooling medium.

[0037] Example 2 A method for preparing a lead-free tin-based solder alloy with a high-entropy phase includes the following steps: (1) Weigh out the following components with the following atomic percentages: Zn: 10%, Bi: 25%, In: 15%, Cu: 10%, Sn: 40%.

[0038] (2) The solid particles of the above components were placed in the special melting equipment of Example 1. The quartz container was evacuated to 0.03 MPa and nitrogen was injected to maintain a slightly positive pressure environment inside the quartz container. Induction melting was carried out under nitrogen gas protection. The melting temperature was 650 °C and the time was 8 min. After cooling, an ingot was obtained.

[0039] (3) Place the above ingot in the special melting equipment of Example 1, evacuate the quartz container to 0.03 MPa and then inject nitrogen to maintain a slightly positive pressure environment inside the quartz container. Under the protection of nitrogen gas, remelt the quartz container at a temperature of 400°C for 10 min to ensure that it is fully melted. During melting, insert a ceramic stirring rod into the melt and rotate it at a high speed of 300 rpm to achieve a thorough and uniform mixing of the melt inside the quartz container.

[0040] (4) Remove the ceramic stirring rod and immerse the quartz container in the cooling liquid of the ice-water mixture. Rapidly cool the solder alloy at 0 °C. After cooling and shrinking, the solder alloy will partially separate from the container. Once it returns to room temperature, remove the solder alloy from the container to obtain the lead-free tin-based solder alloy. The overall mixing entropy of the alloy is 1.46R. Differential scanning calorimetry (DSC) was used to analyze the thermal effect of the melt with temperature changes during the melting process. The thermal analysis curve is shown below. Figure 4 As shown, through Figure 4 It can be seen that the melting peak temperatures of the components of the brazing alloy in this invention are 81.5 ℃ (main melting peak) and 92.3 ℃, which indicates that the melting point of the brazing alloy in this invention is relatively low.

[0041] Example 3 A method for preparing a lead-free tin-based solder alloy with a high-entropy phase includes the following steps: (1) Weigh the following components with the following atomic percentages: Zn: 16%, Bi: 24%, In: 10%, Cu: 10%, Sn: 40%.

[0042] (2) The solid particles of the above components were placed in the special melting equipment of Example 1. The quartz container was evacuated to 0.03 MPa and nitrogen was injected to maintain a slightly positive pressure environment inside the quartz container. Induction melting was carried out under nitrogen gas protection. The melting temperature was 600 °C and the time was 8 min. After cooling, an ingot was obtained.

[0043] (3) Place the above-mentioned ingot in the special melting equipment of Example 1, evacuate the quartz container to 0.03 MPa and then inject nitrogen to maintain a slightly positive pressure environment inside the quartz container. Under the protection of nitrogen gas, remelt the quartz container at a melting temperature of 500°C for 10 min to ensure that it is fully melted. During melting, insert a ceramic stirring rod into the melt and rotate it at a high speed of 300 rpm to achieve a thorough and uniform mixing of the melt inside the quartz container.

[0044] (4) Remove the ceramic stirring rod and immerse the quartz container in the cooling liquid of the ice-water mixture. Cool the solder alloy rapidly at 0 °C. After the solder alloy cools and shrinks, it will separate from the container. When it returns to room temperature, take the solder alloy out of the container to obtain the lead-free tin-based solder alloy. The overall mixing entropy of the alloy is 1.46R.

[0045] Example 4 A method for preparing a lead-free tin-based solder alloy with a high-entropy phase includes the following steps: (1) Weigh the following components with the following atomic percentages: Zn: 18%, Bi: 25%, In: 12%, Cu: 10%, Sn: 35%.

[0046] (2) The solid powder of the above components is placed in the special melting equipment of Example 1. The quartz container is evacuated to 0.03 MPa and then argon is injected to maintain a slightly positive pressure environment inside the quartz container. Induction melting is carried out under the protection of argon gas. The melting temperature is 700 ℃ and the time is 8 min. After cooling, an ingot is obtained.

[0047] (3) Place the above ingot in the special melting equipment of Example 1, evacuate the quartz container to 0.03 MPa and inject argon gas to maintain a slightly positive pressure environment inside the quartz container. Under the protection of argon gas, remelt the quartz container at a melting temperature of 400℃ for 10 min to fully melt it. During melting, insert the ceramic stirring rod into the melt and rotate it at a high speed of 300 rpm to achieve full and uniform mixing of the melt inside the quartz container.

[0048] (4) Remove the ceramic stirring rod and immerse the quartz container in the cooling liquid of the ice-water mixture. Cool the solder alloy rapidly at 0 °C. After the solder alloy cools and shrinks, it will separate from the container. When it returns to room temperature, take the solder alloy out of the container to obtain the lead-free tin-based solder alloy. The overall mixing entropy of the alloy is 1.51R.

[0049] Example 5 A method for preparing a lead-free tin-based solder alloy with a high-entropy phase includes the following steps: (1) Weigh the following components with the following atomic percentages: Zn: 20%, Bi: 25%, In: 15%, Cu: 10%, Sn: 30%.

[0050] (2) The solid particles of the above components were placed in the special melting equipment of Example 1. The quartz container was evacuated to 0.03 MPa and then argon was injected to maintain a slightly positive pressure environment inside the quartz container. Induction melting was carried out under the protection of argon gas. The melting temperature was 680 °C and the time was 7 min. After cooling, an ingot was obtained.

[0051] (3) Place the above ingot in the special melting equipment of Example 1, evacuate the quartz container to 0.03 MPa and inject argon gas to maintain a slightly positive pressure environment inside the quartz container. Under the protection of argon gas, remelt the quartz container at a melting temperature of 450°C for 10 min to ensure that it is fully melted. During melting, insert a ceramic stirring rod into the melt and rotate it at a high speed of 300 rpm to achieve a thorough and uniform mixing of the melt inside the quartz container.

[0052] (4) Remove the ceramic stirring rod and immerse the quartz container in liquid nitrogen. Cool the solder alloy rapidly at 0 °C. After the solder alloy cools and shrinks, it will separate from the container. When it returns to room temperature, remove the solder alloy from the container to obtain the lead-free tin-based solder alloy. The overall mixing entropy of the alloy is 1.54R and the melting peak temperature is 82.6 °C.

[0053] Comparative Example 1 A method for preparing a lead-free tin-based solder alloy differs from Example 2 in that the atomic percentages of each component are: Zn: 20%, Bi: 25%, In: 20%, Cu: 10%, Sn: 25%; The remaining preparation methods and raw material composition are the same as in Example 2. The melting peak temperature of the prepared brazing alloy is 81.2 ℃, the toughness is 82.6%, and the tensile strength is 42.6 MPa, which is much lower than that in Example 2.

[0054] Comparative Example 2 A method for preparing a lead-free tin-based solder alloy differs from Example 2 in that the atomic percentages of each component are: Zn: 20%, Bi: 20%, In: 7%, Cu: 23%, Sn: 30%; The remaining preparation methods and raw material composition are the same as in Example 2. The melting peak temperature of the prepared brazing alloy is 140.6 °C and the elongation is 18.2%, which is much lower than that in Example 2.

[0055] Performance testing The lead-free tin-based solder alloy prepared in Example 2 was cut into sheets and its surface was polished. A small amount of halogen flux was evenly applied to its surface, sandwiched between polished copper blocks, and placed in a reflow oven. The microstructure obtained by soldering at 180 °C for 2 min is shown below. Figure 5 As shown in Figure a, the microstructure after welding at 180 °C for 3 min is as follows. Figure 5 As shown in Figure b, through Figure 3 It can be seen that the IMC thickness after 3 minutes of welding is 0.76 μm, almost the same as the IMC thickness after 2 minutes of welding, indicating that the diffusion rate of the solder prepared in this invention is relatively slow during welding. Under initial welding conditions of 180 °C, after 5 minutes of welding, the solder was heat-aged at 60 °C. The microstructures after 0 h, 50 h, and 100 h of heat aging are as follows: Figure 6 As shown, from Figure 6 It can be observed that the thickness of the interfacial IMC gradually increases with the extension of thermal aging time; however, its growth kinetics are relatively slower than that of traditional SnBi solder. Interface scanning was performed after 100 h of thermal aging, and the results of the interface line scan and spot scan are as follows: Figure 7 and Figure 8 As shown, through Figure 7 and Figure 8 It can be known that the interfacial IMC is a complex five-element compound. Under the influence of the high entropy effect, the interfacial diffusion and interfacial IMC growth process will be significantly inhibited.

[0056] The lead-free tin-based solder alloy prepared in Example 2 was cut into small pieces and polished sequentially with 600-grit, 1000-grit, 1500-grit, and 2000-grit sandpaper, then polished with 1μm silica polishing slurry. BSE (backscattered electron microscopy) observation was performed, and the BSE image is shown below. Figure 9 As shown, Figure a is the BSE diagram of the entire alloy, with the high-entropy phases marked by red and blue boxes. Figure b is a magnified view of the high-entropy phases marked by the red box. Figure 9 It can be seen that the alloy is composed of five phases, which correspond to different contrasting parts in the image. The gray phase corresponds to the tin-rich phase (tin content exceeds 90%), the white phase is the bismuth-rich phase (bismuth content exceeds 90%), the grayish-white phase is the InBi phase, the dark black phase is the CuZn phase, and the gray phase with black spots is a pentagonal high-entropy phase containing five elements, and the phases are evenly distributed.

[0057] The BSE (backscattered electron) image and EDS (energy dispersive spectroscopy) image of the lead-free tin-based solder alloy prepared in Example 2 are shown below. Figure 10 As shown, through Figure 10It is known that the high-entropy phase is composed of five different elements, with the atomic percentages of Cu, Zn, In, Sn, and Bi in the high-entropy phase being 16.0%, 16.4%, 16.8%, 35.6%, and 15.2%, respectively. The calculated entropy value of the high-entropy phase is 1.54R, which is significantly higher than the entropy of phases in traditional solders and other high-entropy solders (1.0R-1.2R), thus falling into the high-entropy category.

[0058] The phase composition of the lead-free tin-based solder alloy prepared in Example 2 was analyzed by X-ray diffraction (XRD), and its XRD pattern is shown below. Figure 11 As shown, through Figure 11 As can be seen, in the upper figure, the main peak positions of Sn in the alloy are at 31.03 degrees and 32.44 degrees, while in the lower figure, the main peak positions of Sn in the standard PDF card are at 30.631 degrees and 32.014 degrees. By comparing the main peak positions of Sn in the two figures, the peak shift can be seen, indicating that the matrix phase in the lead-free tin-based solder alloy material is a solid solution phase. The solder alloy matrix prepared by this invention exhibits a certain degree of solid solution strengthening, which is beneficial to improving the load-bearing capacity of the solder.

[0059] The tensile properties of the lead-free tin-based solder alloy prepared in Example 2 were tested according to ISO 6892-1 / ASTM E8. The test results are as follows: Figure 12 As shown, through Figure 12 It can be seen that the tensile properties of the brazing alloy prepared by the method of the present invention are relatively superior to those of traditional Sn. 58 Bi low-temperature solders offer superior performance, with tensile strength exceeding 60 MPa and elongation exceeding 40%, far surpassing Sn. 58 Bi brazing filler metal has an elongation of 12%-20%, which helps to improve the welding reliability of the filler metal.

[0060] The wetting angle of Embodiment 2 of the present invention was tested, and the test results are as follows: Figure 13 As shown, the SEM image of the welded section was selected under the conditions of welding temperature of 180 ℃ and welding time of 150 s, and its wetting angle was measured to be 46.9°.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A lead-free tin-based solder alloy with a high-entropy phase, characterized in that, The lead-free tin-based solder alloy uses Sn and any one or a combination of two of Bi or In as the main elements, and the remaining elements include any two or a combination of three of Ni, Mn, Ag, Cu and Zn.

2. The lead-free tin-based solder alloy with a high-entropy phase according to claim 1, characterized in that, Sn is an essential element in the lead-free tin-based solder alloy, and the lead-free tin-based solder alloy includes five elements; The mixing entropy of the lead-free tin-based solder alloy is ≥1.4R.

3. The lead-free tin-based solder alloy with a high-entropy phase according to claim 1, characterized in that, The lead-free tin-based solder alloy is mainly composed of Sn, Bi and In, with the remaining elements including Cu and Zn.

4. The lead-free tin-based solder alloy with a high-entropy phase according to claim 3, characterized in that, The lead-free tin-based solder alloy contains the following elements by atomic percentage: Zn: 10%-25%, Bi: 15%-25%, In: 5%-20%, Cu: 5%-15%, with the balance being Sn.

5. A dedicated melting apparatus for lead-free tin-based solder alloys with a high-entropy phase as described in any one of claims 1-4, characterized in that, The specialized smelting equipment includes a smelting container assembly and auxiliary equipment assemblies; The melting container assembly includes a special container, the top of which is connected to a sealing device, the top of which is connected to a stirring rod, the stirring rod extending through the sealing device into the interior of the special container, and a micro motor connected to the stirring rod; The auxiliary equipment components include a motor mounting bracket, a quick-lifting device, a vacuum passage, an exhaust pipe, and an inert gas input passage. One end of the motor mounting bracket is connected to the quick-lifting device, and the other end is connected to the micro motor. The vacuum passage, the exhaust pipe, and the inert gas input passage are all connected to the sealing device via quick-connect flanges.

6. The special melting equipment for lead-free tin-based solder alloys with a high-entropy phase according to claim 5, characterized in that, The rapid lifting device includes a main support frame, a connecting slide rail, a handwheel operating component, and a test tube holder. The motor holder is connected to the main support frame, and the handwheel operating component is fixedly connected to the main support frame and is kinetically connected to the connecting slide rail. The test tube holder is fixedly connected to the connecting slide rail and forms a sliding connection with the main support frame through the connecting slide rail. By rotating the handwheel operating component, the lead screw inside the connecting slide rail is driven to rotate, thereby driving the test tube holder to move up and down.

7. The special melting equipment for lead-free tin-based solder alloys with a high-entropy phase according to claim 5, characterized in that, The sealing device adopts a dual sealing structure: the lower seal is achieved through a quick-connect flange joint and a high-temperature resistant rubber ring, while the upper seal uses a highly elastic sealing plug.

8. A method for preparing a lead-free tin-based solder alloy with a high-entropy phase as described in any one of claims 1-4, characterized in that, Includes the following steps: (1) Place each component in the special melting equipment described in claim 5, evacuate and inject inert gas for induction melting, and then let it stand and cool to obtain an ingot; (2) The ingot is placed in the special melting equipment described in claim 5, and after vacuuming, inert gas is injected for remelting. After cooling the resulting melt, the lead-free tin-based solder alloy is obtained.

9. The method for preparing the lead-free tin-based solder alloy with a high-entropy phase according to claim 8, characterized in that, The induction melting temperature in step (1) is 600-700 ℃ and the time is 6-9 min.

10. The method for preparing the lead-free tin-based solder alloy with a high-entropy phase according to claim 8, characterized in that, The remelting temperature in step (2) is 300-600 ℃ and the time is 8-10 min; The remelting is carried out under high-speed stirring at a speed of 300 rpm; The cooling method involves immersing the container holding the melt in an ice-water mixture or liquid nitrogen.

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