High-toughness sn-bi-based soldering rod and continuous production method thereof

Abstract

The application relates to a high-toughness Sn-Bi-based soldering strip and a continuous preparation method thereof, belongs to the field of low-temperature interconnecting materials for electronic manufacturing and packaging, and is characterized in that Sn-Bi powder, a flux and a solvent are mixed, Sn@NiCoCuAgM composite powder is added, and the soldering strip is formed through mould pressing and extrusion. In soldering, the Sn core phase in the Sn@NiCoCuAgM melts into Sn-Bi, Ni, Co, Cu and Ag form intermetallic compounds with Sn, the nucleation and growth of the Sn phase are promoted, high-density materials participate in organization regulation, the Bi phase is inhibited from being coarsened and continuously segregated, and the mechanical and structural stability of the Sn-Bi-based solder joint, weld or interconnecting structure is improved. The device realizes the continuous preparation of powder feeding, proportioning, mixing, forming, shaping and collecting, is suitable for the soldering connection of metal / metal, metal / ceramic, electronic packaging pads, flexible electronics, temperature-sensitive components and advanced packaging low-temperature interconnecting structures.

Description

Technical Field

[0001] This invention belongs to the technical field of low-temperature interconnect materials for electronic manufacturing and packaging, specifically relating to a high-toughness Sn-Bi-based low-temperature soldering electrode and its continuous preparation method, as well as an integrated device for preparing the low-temperature soldering electrode and its application. The low-temperature soldering electrode is suitable for low-temperature soldering connections in metal / metal, metal / ceramic, and electronic packaging pads, and is particularly suitable for low-temperature micro-interconnect manufacturing in advanced electronic packaging such as flexible electronics, temperature-sensitive components, chiplet packaging, and 3D-IC packaging. Background Technology

[0002] Sn-Bi solders possess advantages such as low melting point, low reflow temperature, low thermal stress, and compliance with lead-free environmental requirements, making them important low-temperature interconnect materials in low-temperature electronic packaging, flexible electronics, temperature-sensitive components, and micro-interconnect manufacturing. Eutectic or near-eutectic Sn-Bi solders, in particular, can achieve brazing connections at lower temperatures, which helps reduce the heat load during packaging and minimizes the risk of thermal damage to temperature-sensitive devices.

[0003] However, existing Sn-Bi-based solders still have certain shortcomings in practical applications. During solidification, this system of solders easily forms a eutectic structure composed of Sn-rich and Bi-rich phases. The Bi phase is hard and brittle, and is prone to coarsening, continuity, or local enrichment, resulting in high brittleness and low plasticity of the solder as a whole. Under external impact, mechanical bending, thermal cycling, or thermo-mechanical coupling loads, the Bi-rich phase enrichment areas and the Sn / Bi phase interface are prone to becoming weak points for crack initiation and propagation, leading to solder joint cracking or even failure. This makes it difficult to meet the mechanical reliability and service stability requirements of high-density packaging and micro-solder joint structures.

[0004] To address the aforementioned issues, existing technologies typically employ alloying modification or particle reinforcement modification to regulate Sn-Bi solders. Alloying modification, such as adding elements like Ag, Ni, and Cu, can improve the solder microstructure or interfacial reactions to some extent, but may lead to problems such as the growth of intermetallic compounds at the interface, changes in solidification microstructure, or a weakening of the advantages of low-temperature welding. Particle reinforcement modification, such as adding metal nanoparticles like Ni and Cu, can have a certain impact on microstructure and properties, but ordinary single-component nanoparticles are prone to agglomeration, uneven dispersion, or insufficient interfacial bonding in the solder system, making it difficult to stably and effectively participate in phase nucleation and microstructure regulation during the Sn-Bi solder solidification process.

[0005] Furthermore, existing processing methods for preparing Sn-Bi-based low-temperature brazing electrodes primarily rely on intermittent mixing and individual molding. The lack of continuous and integrated collaborative control among stages such as powder feeding, proportioning control, mixing and dispersion, electrode molding, secondary shaping, and cooling collection easily leads to problems such as insufficient dispersion of the core-shell composite powder, inconsistency in proportioning, and fluctuations in electrode size and performance, hindering industrial-scale mass production and stable application. Therefore, there is an urgent need to develop a low-temperature brazing electrode preparation method and apparatus that can balance the effects of core-shell composite powder microstructure regulation, continuous Sn-Bi-based electrode preparation capability, and integrated processing stability, thereby improving the microstructure stability, mechanical toughness, and engineering applicability of Sn-Bi-based brazing electrodes. Summary of the Invention

[0006] The purpose of this invention is to address the problems of coarsening and continuous agglomeration of the Bi-rich phase in existing Sn-Bi-based low-temperature brazing fillers, which leads to brittle weld joints and easy cracking under external loads or thermal cycling conditions. This invention provides a high-toughness Sn-Bi-based low-temperature brazing electrode and its continuous preparation method. This invention introduces Sn@NiCoCuAgM core-shell composite powder into the Sn-Bi-based low-temperature brazing filler system, enabling it to participate in Sn phase nucleation, growth, and Sn / Bi phase spatial distribution regulation during brazing. The Sn nucleus phase improves the compatibility of the composite powder with the Sn-Bi-based brazing filler system. One or more elements from Ni, Co, Cu, and Ag can react with Sn to form intermetallic compounds and promote Sn phase nucleation. High-density M particles can participate in melt microstructure regulation, thereby reducing the tendency of Bi-rich phase coarsening and continuous agglomeration, and improving the microstructure uniformity, mechanical toughness, and structural stability of the brazed weld joint, weld seam, or interconnect structure. Meanwhile, this invention achieves stable preparation of Sn-Bi-based low-temperature brazing electrodes through continuous processes such as powder feeding, liquid addition, premixing, vacuum mixing and degassing, continuous conveying, heating and molding, cooling, cutting and collecting, thereby improving the mixing uniformity of the brazing precursor, the dimensional stability of the electrode and batch consistency.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A continuous preparation method for a high-toughness Sn-Bi-based brazing electrode includes the following steps:

[0009] S1) Preparation of Sn-Bi-based solder precursor slurry: Sn-Bi alloy powder, organic flux and solvent are mixed to obtain Sn-Bi-based solder precursor slurry;

[0010] S2) Preparation of Sn@NiCoCuAgM core-shell composite powder: Using spherical or near-spherical Sn atomized powder as the core phase, the Sn atomized powder is surface activated and then added to a Ni-containing compound. 2+ Co2+ Cu 2+ Ag + In a multi-component coating solution containing one or more metal ions and high-density material M nanoparticles, in-situ chemical deposition is used to embed or coat the metal particles and high-density material M nanoparticles onto the surface of the Sn core phase, resulting in Sn@NiCoCuAgM core-shell structured composite powder; the density of the high-density material M is not less than 9.0 g / cm³. 3 It is selected from one of Mo, Ta, W, Au, Pd, and Pt, or one or more of the carbides, nitrides, and oxides of Mo, Ta, W, Au, Pd, and Pt;

[0011] S3) Preparation of solder precursor: Sn@NiCoCuAgM core-shell structured composite powder obtained in S2 is added to Sn-Bi-based solder precursor slurry obtained in S1 at a mass fraction of 0.01wt% to 5wt%. After vacuum stirring, ultrasonic dispersion treatment and degassing treatment, solder precursor is obtained.

[0012] S4) Molding: The brazing precursor obtained in S3 is molded or extruded into Sn-Bi based brazing electrode.

[0013] In S1, the Sn-Bi alloy powder is a eutectic Sn-Bi alloy powder, a near-eutectic Sn-Bi alloy powder, or a Sn-rich hypoeutectic Sn-Bi alloy powder, with a particle size of 1 to 50 μm; the solvent accounts for 0.1 wt% to 10 wt% of the total weight of the Sn-Bi-based solder precursor slurry.

[0014] A high-toughness Sn-Bi-based brazing electrode is prepared using the method described in this invention.

[0015] In S2, the chemical coating process includes: surface-activating spherical or near-spherical Sn atomized powder with a particle size of 1-10 μm, and then adding Ni-containing... 2+ Co 2+ Cu 2+ Ag + In situ chemical deposition is carried out in a multi-component coating solution containing one or more metal ions, high-density material M nanoparticles, complexing agents, and reducing agents, so that the metal particles and high-density material M nanoparticles are embedded or coated on the surface of the Sn core phase. After cleaning and drying, Sn@NiCoCuAgM core-shell structured composite powder is obtained.

[0016] In S4, the forming method is molding or extrusion; the diameter of the resulting Sn-Bi-based brazing electrode is 1.0 to 5.0 mm, and the length is 100 to 500 mm.

[0017] During the brazing process of the Sn-Bi based brazing electrode, the Sn nucleus phase in the Sn@NiCoCuAgM core-shell composite powder melts and enters the Sn-Bi melt. One or more elements among Ni, Co, Cu, and Ag react with Sn to form intermetallic compounds, promoting Sn phase nucleation and growth. Simultaneously, high-density M nanoparticles participate in the microstructure regulation of the Sn-Bi melt, inhibiting Bi phase coarsening and continuous agglomeration. Through the synergistic effect of intermetallic compounds and high-density M nanoparticles, the continuity tendency of the Bi phase is reduced in the brazed joints, welds, or interconnect structures, and the Sn / Bi phase microstructure distribution is more uniform, which is beneficial to improving the tensile strength, elongation, crack resistance, and service stability of the weld joint.

[0018] An integrated apparatus for implementing the above method includes a powder feeding unit (1), a liquid adding unit (2), a premixing unit (3), a vacuum mixing unit (4), a delivery pump (6), a molding and sintering unit (7), and a cooling, cutting, and collecting unit (8) connected in sequence, and includes a vacuum control unit (5) connected to the vacuum mixing unit (4); wherein:

[0019] The powder feeding unit (1) is used to add Sn-Bi alloy powder and Sn@NiCoCuAgM core-shell structure composite powder;

[0020] The liquid addition unit (2) is used to add organic flux and solvent to the premixing unit (3);

[0021] The premixing unit (3) is used to perform preliminary mixing of Sn-Bi alloy powder, Sn@NiCoCuAgM core-shell composite powder, organic flux and solvent to obtain a premix;

[0022] The vacuum mixing unit (4) is connected to the premixing unit (3) and is used to vacuum stir, disperse and degas the premix to obtain the solder precursor;

[0023] The vacuum control unit (5) is connected to the vacuum mixing unit (4) and is used to monitor and adjust the vacuum level in the vacuum mixing unit (4);

[0024] The delivery pump (6) is located between the vacuum mixing unit (4) and the molding and sintering unit (7) for continuously delivering the brazing precursor to the molding and sintering unit (7).

[0025] The forming and sintering unit (7) is used to heat, extrude and form strips of the brazing precursor to obtain continuous Sn-Bi-based low-temperature brazing electrodes;

[0026] The cooling, cutting and collecting unit (8) is located at the rear end of the forming and sintering unit (7) and is used to cool, cut and collect the formed Sn-Bi-based low-temperature brazing electrode.

[0027] The powder feeding unit (1) is a sealed powder feeding structure and is equipped with an anti-bridging device; the liquid adding unit (2) is equipped with a liquid metering structure; the premixing unit (3) is equipped with a mechanical stirring structure; the vacuum mixing unit (4) includes a vacuum stirring structure; the vacuum control unit (5) includes at least one of a vacuum pump, a vacuum gauge, a vacuum valve, and a vacuum pipeline; the delivery pump (6) is one of a screw pump, a gear pump, or a plunger pump; the forming and sintering unit (7) includes a heating structure and a strip forming structure; the cooling, cutting, and collecting unit (8) includes a cooling structure, a cutting structure, and a collecting structure.

[0028] The device of this invention enables continuous feeding, premixing, vacuum dispersion and degassing, continuous conveying, heating and molding, and cooling and collection of Sn-Bi alloy powder, Sn@NiCoCuAgM core-shell composite powder, organic flux and solvent, thereby improving the continuity, mixing uniformity, proportioning consistency and batch stability of the Sn-Bi based low-temperature brazing electrode preparation process.

[0029] The Sn-Bi-based low-temperature brazing electrode can be used for low-temperature brazing connections of metal / metal, metal / ceramic, electronic packaging pads, flexible electronics, temperature-sensitive components, or advanced packaging low-temperature interconnect structures. The brazing is performed at 150–200°C for 0.5–10 min under a protective atmosphere.

[0030] Compared with the prior art, the advantages of the present invention are:

[0031] 1. This invention uses Sn@NiCoCuAgM core-shell structured composite powder to modify Sn-Bi-based low-temperature soldering electrodes, unlike the common method of directly adding single nanoparticles. This core-shell structured composite powder uses Sn powder as the core phase, with one or more metal particles from Ni, Co, Cu, and Ag, as well as high-density material M particles embedded or coated on the surface. This improves the compatibility and dispersion stability between the modified particles and the Sn-Bi-based solder system.

[0032] 2. In this invention, one or more elements selected from Ni, Co, Cu, and Ag can react with Sn during brazing to form intermetallic compounds, promoting the nucleation and growth of the Sn phase; high-density material M particles can participate in the microstructure regulation of the Sn-Bi melt. The synergistic effect of these two elements helps to reduce the coarsening and continuous agglomeration tendency of the Bi phase, thereby improving the microstructure brittleness problem of Sn-Bi-based brazing filler metal.

[0033] 3. The present invention uses vacuum stirring, ultrasonic dispersion and degassing treatment to prepare the brazing precursor, which is beneficial to improve the dispersion uniformity of Sn@NiCoCuAgM core-shell structure composite powder in Sn-Bi based brazing precursor and reduce bubble defects in the precursor, thereby improving the electrode forming quality and the microstructure stability after brazing.

[0034] 4. The integrated device provided by the present invention can realize the continuous connection of processes such as powder feeding, liquid addition, premixing, vacuum mixing and degassing, continuous conveying, molding / reflowing, cooling, cutting and collection, reducing batch fluctuations caused by manual transfer, proportioning error and uneven mixing in traditional intermittent processing, which is conducive to the stabilization and continuous preparation of Sn-Bi based low temperature brazing electrodes.

[0035] 5. The Sn-Bi-based low-temperature brazing electrode prepared by this invention can be used for low-temperature brazing at 150-200°C. It is suitable for brazing connections of metal / metal, metal / ceramic, electronic packaging pads, flexible electronics, temperature-sensitive components, and advanced packaging low-temperature interconnect structures. It is especially suitable for the manufacturing and repair of multi-level micro solder joint interconnects in chiplet packaging, 3D chip packaging, or 3D-IC packaging. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the overall structure of the Sn-Bi-based low-temperature brazing electrode continuous preparation device of the present invention.

[0037] Figure 2 This is a schematic diagram of the Sn@NiCoCuAgM core-shell composite powder of the present invention.

[0038] Figure 3 Comparison of the microstructures of ordinary Sn-Bi brazing electrodes and Sn-Bi brazing electrodes with Sn@NiCoCuAgM core-shell structure composite powder (Sn58Bi-Sn@NiCoCuAgW).

[0039] Figure 4 Comparison of fracture morphology between ordinary Sn-Bi brazing electrode and Sn-Bi brazing electrode with Sn@NiCoCuAgM core-shell structure composite powder (Sn58Bi-Sn@NiCoCuAgW). Detailed Implementation

[0040] To make the technical problems, technical solutions and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0041] Example 1: Continuous preparation apparatus and its working process

[0042] This embodiment is for illustration. Figure 1The structure, connection relationship, and working process of the continuous preparation device shown are described, and it is used for the continuous preparation of Sn-Bi-based low-temperature brazing electrodes.

[0043] like Figure 1 As shown, the continuous preparation apparatus of the present invention includes a powder feeding unit 1, a liquid adding unit 2, a premixing unit 3, a vacuum mixing unit 4, a conveying pump 6, a molding and sintering unit 7, and a cooling, cutting, and collecting unit 8 connected sequentially along the material conveying direction. It also includes a vacuum control unit 5 connected to the vacuum mixing unit 4. Specifically, the powder feeding unit 1 is used to quantitatively add Sn-Bi alloy powder and Sn@NiCoCuAgW core-shell structured composite powder in stages; the liquid adding unit 2 is used to add organic flux and solvent; the premixing unit 3 is used to form Sn-Bi-based solder precursor slurry; and the vacuum mixing unit 4 is used to complete the mixing, ultrasonic dispersion, and vacuum degassing of the core-shell structured composite powder.

[0044] S1) Sn-Bi alloy powder feeding. Sn-Bi alloy powder is added to powder feeding unit 1 and quantitatively conveyed to liquid addition unit 2 through powder feeding unit 1. Powder feeding unit 1 is located at the front end of the device and can adopt a hopper-type feeding structure. It can be combined with screw feeding, vibration feeding or gravity feeding to achieve stable and continuous supply of powder raw materials.

[0045] S2) Liquid Addition and Preliminary Wetting. Organic flux and solvent are quantitatively added to the Sn-Bi alloy powder through liquid addition unit 2, causing the Sn-Bi alloy powder to be preliminarily wetted by the liquid components. The organic flux and solvent are continuously added according to a preset ratio and ensure full contact with the Sn-Bi alloy powder to improve powder wettability and subsequent mixing uniformity. The preliminarily wetted mixture enters the premixing unit 3 along the connecting pipeline.

[0046] S3) Preparation of Sn-Bi-based solder precursor slurry. The pre-wetted mixture obtained in S2 is conveyed to premixing unit 3, where it is mechanically stirred to uniformly mix the Sn-Bi alloy powder, organic flux, and solvent, forming the Sn-Bi-based solder precursor slurry. The premixing unit 3 may be equipped with a mechanical stirring structure to improve the initial mixing uniformity of the powder and liquid components and reduce local agglomeration.

[0047] S4) Staged addition of core-shell composite powder. After the Sn-Bi based solder precursor slurry described in S3 is formed, the powder feeding unit 1 performs the second stage of feeding, quantitatively conveying the Sn@NiCoCuAgW core-shell composite powder to the liquid addition unit 2. In this stage, the liquid addition unit 2 stops adding or no longer adds additional organic flux and solvent. The core-shell composite powder enters the premixing unit 3 along the material conveying channel and is initially mixed with the already formed Sn-Bi based solder precursor slurry. Subsequently, the Sn-Bi based solder precursor slurry containing the Sn@NiCoCuAgW core-shell composite powder is conveyed to the vacuum mixing unit 4 through the connecting pipeline.

[0048] S5) Vacuum mixing, ultrasonic dispersion, and degassing. Vacuum mixing unit 4 is used to stir, ultrasonically disperse, and vacuum degas the Sn-Bi based solder precursor slurry containing Sn@NiCoCuAgW core-shell structured composite powder obtained in S4. Vacuum mixing unit 4 may be equipped with an ultrasonic dispersion component, and vacuum control unit 5 is used to monitor and adjust the vacuum level. The two work together to reduce entrained gas in the slurry, improve the dispersion uniformity of the core-shell structured composite powder, and obtain a solder precursor with low bubble content.

[0049] S6) The brazing precursor, after being stirred, ultrasonically dispersed, and vacuum degassed, is continuously transported to the forming and sintering unit 7 via the delivery pump 6. The delivery pump 6 is located between the vacuum mixing unit 4 and the forming and sintering unit 7, and can be a screw pump, gear pump, or plunger pump to adapt to the slurry characteristics of the brazing precursor with a certain viscosity and to ensure the continuity and stability of the feeding process.

[0050] (S7) After the brazing precursor enters the forming and sintering unit 7, it undergoes extrusion and strip forming under heating conditions. The forming and sintering unit 7 may include a front forming heating zone and a rear heating treatment zone. The temperature of the front forming heating zone is 80–140°C, used to reduce the viscosity of the brazing precursor and promote its continuous extrusion forming. The temperature of the rear heating treatment zone is 150–200°C, used to further improve the internal bonding state and dimensional stability of the welding electrode. After processing by the forming and sintering unit 7, the brazing precursor forms a continuous Sn-Bi-based low-temperature brazing electrode.

[0051] S8) The continuous Sn-Bi-based low-temperature brazing electrode obtained in S7 is fed into the cooling, cutting, and collecting unit 8. The cooling, cutting, and collecting unit 8 is located at the rear end of the forming and sintering unit 7 and is used to cool, cut to a fixed length, and collect the formed Sn-Bi-based low-temperature brazing electrode. After cooling, the electrode size tends to stabilize, and then it is cut to obtain Sn-Bi-based low-temperature brazing electrode finished products of a predetermined length.

[0052] pass Figure 1The continuous preparation apparatus shown in the diagram sequentially conveys materials through a powder feeding unit 1, a liquid addition unit 2, a premixing unit 3, a vacuum mixing unit 4, a conveying pump 6, a molding and sintering unit 7, and a cooling, cutting, and collecting unit 8. During the preparation process, Sn-Bi alloy powder is first fed by the powder feeding unit 1 and mixed with organic flux and solvent to form a Sn-Bi-based solder precursor slurry. Subsequently, the powder feeding unit 1 performs a second-stage feeding, adding Sn@NiCoCuAgW core-shell structured composite powder to the formed slurry along the same material channel. Finally, stirring, ultrasonic dispersion, and vacuum degassing are completed in the vacuum mixing unit 4, followed by continuous conveying, heating and molding, cooling, cutting, and collecting.

[0053] Example 2: Preparation of Sn@NiCoCuAgW core-shell structured composite powder and Sn-Bi-based low-temperature brazing electrode by chemical coating process

[0054] This embodiment illustrates the chemical coating preparation method of Sn@NiCoCuAgW core-shell structured composite powder, and the specific process of preparing Sn-Bi-based low-temperature brazing electrodes using the continuous preparation apparatus described in Example 1.

[0055] This embodiment includes the following steps:

[0056] S1) Preparation of Sn-Bi-based solder precursor slurry. 100g of Sn58Bi alloy powder with an average particle size of 25μm was weighed and fed into the liquid addition unit 2 and the premixing unit 3 sequentially through the powder feeding unit 1. At the same time, 8g of organic flux and 3g of terpineol were added. The mixture was stirred at 1000rpm for 40min in the premixing unit 3 to obtain a uniformly dispersed Sn-Bi-based solder precursor slurry.

[0057] S2) Activation of Sn nucleus phase powder. Spherical Sn atomized powder was selected as the nucleus phase. The Sn atomized powder had a purity of 99.9% and an average particle size of 5 μm. The Sn atomized powder was added to 3% dilute hydrochloric acid and ultrasonically cleaned for 8 min to remove the oxide layer on the surface of the Sn powder. Then, it was rinsed with deionized water until neutral, then cleaned once with ethanol, and dried under vacuum at 60℃ for 2 h to obtain surface-activated Sn nucleus phase powder.

[0058] S3) Preparation of the multi-component coating solution. Weigh out nickel sulfate, cobalt sulfate, copper sulfate, and silver nitrate as Ni... 2+ Co 2+ Cu 2 + and Ag + Source, preparation containing Ni 2+ Co 2+ Cu 2+ and Ag +A mixed aqueous solution containing a total metal ion concentration of 0.1 mol / L, Ni 2+ Co 2+ Cu 2+ and Ag + The molar ratio was 7:1:1:1. W nanoparticles, with an average particle size of 80 nm, were added to the mixed aqueous solution at a concentration of 4 g / L. Trisodium citrate (0.05 mol / L) and sodium hypophosphite (0.15 mol / L) were then added as a complexing agent and a reducing agent, respectively. After stirring for 30 min, a multi-component coated solution was obtained. The pH of the multi-component coated solution was adjusted to 4 using dilute hydrochloric acid or ammonia.

[0059] S4) In-situ coating reaction. The surface-activated Sn core phase powder obtained in S2 is added to the multi-component coating solution obtained in S3, and reacted at 65℃ and 400rpm for 2h to allow Ni, Co, Cu, Ag metal components and W nanoparticles to be deposited or embedded in situ on the Sn core phase surface, forming a Sn@NiCoCuAgW core-shell structure composite powder with Sn as the core phase and Ni / Co / Cu / Ag shell particles and W reinforcing particles as surface components.

[0060] like Figure 2 As shown, the Sn@NiCoCuAgW core-shell composite powder comprises a Sn core phase, Ni / Co / Cu / Ag shell particles, and W reinforcing particles. The Sn core phase is located at the center of the composite powder, the Ni / Co / Cu / Ag shell particles are embedded or coated on the surface of the Sn core phase, and the W reinforcing particles are dispersed and embedded between the Ni / Co / Cu / Ag shell particles. This structure is beneficial for improving the compatibility between the reinforcing particles and the Sn-Bi-based solder system, and allows the Ni / Co / Cu / Ag components and W reinforcing particles to participate in the microstructure control of the Sn-Bi melt during subsequent brazing.

[0061] S5) Purification and Drying. After the reaction was completed, the product was centrifuged at 10,000 rpm for 8 minutes. It was then washed four times with deionized water and ethanol alternately to remove residual coating solution and byproducts. It was then dried under vacuum at 70°C for 3 hours and lightly ground to obtain Sn@NiCoCuAgW core-shell composite powder.

[0062] S6) Addition of core-shell composite powder and preparation of solder precursor. After the Sn-Bi-based solder precursor slurry described in S1 is formed, the second stage of feeding is carried out through the powder feeding unit 1 described in Example 1. The Sn@NiCoCuAgW core-shell composite powder obtained in S5 is added to the device at 0.1 wt% of the mass of the Sn-Bi-based solder precursor slurry. The core-shell composite powder passes through the liquid addition unit 2 and the premixing unit 3 in sequence. Under the condition that the addition of organic flux and terpineol is stopped in the liquid addition unit 2, it is initially mixed with the Sn-Bi-based solder precursor slurry obtained in S1 in the premixing unit 3.

[0063] Subsequently, the Sn-Bi-based solder precursor slurry containing Sn@NiCoCuAgW core-shell structured composite powder was transported to the vacuum mixing unit 4 and stirred under vacuum at 1200 rpm for 20 min. Ultrasonic dispersion was then performed using an ultrasonic dispersion component located in the vacuum mixing unit 4 for 10 min, with an ultrasonic power of 500 W and an ultrasonic frequency of 30 kHz. The vacuum level in the vacuum mixing unit 4 was then adjusted by the vacuum control unit 5, and a vacuum degassing treatment was performed for 10 min to obtain a solder precursor with uniform dispersion of the core-shell structured composite powder and low bubble content.

[0064] S7) Brazing electrode forming. The brazing precursor obtained in S6 is continuously conveyed to the forming and sintering unit 7 via the delivery pump 6, and extruded at 100°C and an extrusion rate of 10 mm / s. The formed continuous brazing electrode enters the cooling, cutting and collecting unit 8, where it is cooled and cut to a fixed length in sequence to obtain a Sn-Bi-based low-temperature brazing electrode with a diameter of 2.0 mm and a length of 200 mm.

[0065] S8) Preparation of brazing and comparative samples. The Sn-Bi-based low-temperature brazing electrode obtained in S7 was kept at 180℃ for 5 min under nitrogen protection and then cooled to room temperature to form Sn-Bi-based solder joints. The resulting modified sample was denoted as Sn58Bi-Sn@NiCoCuAgW.

[0066] In contrast, ordinary Sn58Bi solder joints and tensile specimens were prepared under the same conditions using Sn58Bi solder without Sn@NiCoCuAgW core-shell structure composite powder.

[0067] S9) Microstructure, fracture morphology, and mechanical property characterization. Microstructure observation was performed on the ordinary Sn58Bi solder joint and the Sn58Bi-Sn@NiCoCuAgW solder joint obtained in S8. For example... Figure 3 As shown, after adding Sn@NiCoCuAgW core-shell composite powder, the Sn / Bi phase distribution is more uniform and the trend of Bi-rich phase continuity is reduced, indicating that it is beneficial to improve the uniformity of the weld joint structure.

[0068] The fracture surfaces of two groups of tensile specimens obtained from S7 ordinary Sn58Bi were observed, such as... Figure 4 As shown, where Figure 4 The top left and bottom left images (A) represent Sn58Bi, and the top right and bottom right images (B) represent Sn58Bi-Sn@NiCoCuAgW. The results show that adding the Sn@NiCoCuAgW core-shell composite powder increases the number of pits and ductile deformation features in the fracture surface, and makes the crack propagation path more tortuous, indicating that it is beneficial for improving the fracture toughness of Sn-Bi-based solders.

[0069] The tensile property test results are shown in Table 1. The tensile strength and elongation of the ordinary Sn58Bi sample were 64.5 MPa and 13.5%, respectively; after adding 0.1 wt% Sn@NiCoCuAgW core-shell composite powder, these values ​​increased to 81.2 MPa and 52.8%, respectively. The results indicate that this core-shell composite powder can simultaneously improve the strength and plasticity of Sn-Bi solder.

[0070] Table 1

[0071]

[0072] In summary, this invention prepares Sn@NiCoCuAgW core-shell structured composite powder through a chemical coating process, and combines this with a continuous preparation device to obtain Sn-Bi-based low-temperature soldering electrodes with uniform microstructure and stable performance. The core-shell structured composite powder has a significant synergistic effect on strengthening and toughening Sn-Bi solders. The preparation method and device of this invention have advantages such as high degree of continuity, good batch consistency, and ease of industrialization, which can meet the urgent needs of high-reliability soldering materials in fields such as flexible electronics, temperature-sensitive devices, and advanced packaging low-temperature interconnects.

Claims

1. A continuous preparation method for a high-toughness Sn-Bi-based brazing electrode, characterized in that, Includes the following steps: 1) Preparation of Sn-Bi-based solder precursor slurry: Sn-Bi alloy powder is mixed with additives to obtain Sn-Bi-based solder precursor slurry; the additives include organic flux and / or solvents; 2) Preparation of Sn@NiCoCuAgM core-shell composite powder: Using spherical or near-spherical Sn atomized powder as the core phase, a chemical coating process is used to embed or coat high-density material M nanoparticles onto the surface of the Sn core phase, resulting in Sn@NiCoCuAgM core-shell composite powder; the density of the high-density material M is not less than 9.0 g / cm³. 3 It is selected from one of Mo, Ta, W, Au, Pd, and Pt, or one or more of the carbides, nitrides, and oxides of Mo, Ta, W, Au, Pd, and Pt; 3) Preparation of solder precursor: The Sn@NiCoCuAgM core-shell structure composite powder obtained in step 2) is added to the Sn-Bi-based solder precursor slurry obtained in step 1) at a mass fraction of 0.01wt%~5wt%, and after dispersion and degassing treatment, the solder precursor is obtained. 4) Molding: The brazing precursor obtained in step 3) is molded into Sn-Bi based brazing electrode by molding or extrusion.

2. The continuous preparation method of a high-toughness Sn-Bi-based brazing electrode as described in claim 1, characterized in that: In step 1), the Sn-Bi alloy powder is a eutectic Sn-Bi alloy powder, a near-eutectic Sn-Bi alloy powder, or a Sn-rich hypoeutectic Sn-Bi alloy powder, with a particle size of 1~50μm; the solvent accounts for 0.1wt%~10wt% of the total weight of the Sn-Bi-based solder precursor slurry; the mixing is carried out by mechanical stirring.

3. The continuous preparation method of a high-toughness Sn-Bi-based brazing electrode as described in claim 1, characterized in that, In step 2), the chemical coating process includes: acid washing and activation of spherical or near-spherical Sn atomized powder with a particle size of 1~10μm, followed by the addition of Ni... 2+ Co 2+ Cu 2+ Ag + In a multi-component coating solution containing one or more ions, M-type nanoparticles, a complexing agent, and a reducing agent, the mixture is reacted at 50-80℃ and 300-500rpm for 1-3 hours to embed or coat the metal particles and M-type nanoparticles onto the surface of the Sn core phase. After cleaning and drying, Sn@NiCoCuAgM core-shell structured composite powder is obtained.

4. The continuous preparation method of a high-toughness Sn-Bi-based brazing electrode as described in claim 1, characterized in that: In step 4), the obtained Sn-Bi-based brazing electrode has a diameter of 1.0~5.0 mm and a length of 100~500 mm.

5. A high-toughness Sn-Bi-based brazing electrode, characterized in that: It is prepared by the method described in any one of claims 1 to 4.

6. The Sn-Bi-based brazing electrode as described in claim 5, characterized in that: During the brazing process, the Sn nucleus phase in the Sn@NiCoCuAgM core-shell composite powder melts into the Sn-Bi melt; one or more elements among Ni, Co, Cu, and Ag react with Sn to form intermetallic compounds, promoting the nucleation and growth of the Sn phase; high-density material M nanoparticles participate in the microstructure regulation, inhibiting the coarsening and continuous agglomeration of the Bi phase; in the weld joints, weld seams, or interconnect structures formed after brazing, the Bi phase is diffusely distributed.

7. An integrated apparatus for implementing the method according to any one of claims 1 to 4, characterized in that: The system includes a powder feeding unit (1), a liquid adding unit (2), a premixing unit (3), a vacuum mixing unit (4), a delivery pump (6), a molding and sintering unit (7), and a cooling, cutting, and collecting unit (8) connected in sequence, and includes a vacuum control unit (5) connected to the vacuum mixing unit (4); wherein, the powder feeding unit (1) is used to add Sn-Bi alloy powder and Sn@NiCoCuAgM core-shell structure composite powder, the liquid adding unit (2) is used to add organic flux and solvent, the premixing unit (3) is used to form a premix, the vacuum mixing unit (4) is used to stir, disperse and degas the premix to obtain a solder precursor, the delivery pump (6) is used to transport the solder precursor to the molding and sintering unit (7), the molding and sintering unit (7) is used to heat, extrude and strip-shape the solder precursor, and the cooling, cutting, and collecting unit (8) is used to cool, cut and collect the formed Sn-Bi-based soldering electrode.

8. The integrated device as described in claim 7, characterized in that: The powder feeding unit (1) is a sealed powder feeding structure and is equipped with an anti-bridging device; the liquid adding unit (2) is equipped with a liquid metering structure; the premixing unit (3) is equipped with a mechanical stirring structure; the vacuum mixing unit (4) includes a vacuum stirring structure; the vacuum control unit (5) is connected to the vacuum mixing unit (4) and is used to adjust the vacuum degree in the vacuum mixing unit (4); the delivery pump (6) is used to deliver the brazing precursor to the forming and sintering unit (7); the forming and sintering unit (7) includes a heating structure and a strip forming structure; the cooling, cutting and collecting unit (8) includes a cooling structure, a cutting structure and a collecting structure.

9. The application of the Sn-Bi-based soldering electrode as described in claim 5 or 6 in metal / metal connections, metal / ceramic connections, electronic packaging pad connections, flexible electronic device connections, temperature-sensitive component connections, or advanced packaging low-temperature interconnect structure connections.

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