High-performance alloyed silver amalgam low-temperature high-strength brazing filler metal and preparation and brazing method thereof

Abstract

The application discloses a kind of high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal and its preparation and brazing method, belong to brazing technical field;The brazing filler metal is paste composition made by amalgamation reaction, and the composition includes silver powder 5-20wt%, mercury balance and alloy strengthening component by total mass;The application triggers solid solution strengthening, precipitation strengthening and fine-grain strengthening multi-mechanism synergistic effect in brazing process by accurately controlling the type and ratio of alloy component, forms complex microstructure with toughness silver-based solid solution as base, embedded dispersed nanoscale strengthening phase in weld. The brazing method includes: cleaning silver-plated surface, applying brazing filler metal, assembling workpiece, connecting at 150-290 DEG C, 0.1-1.5MPa for 10-60 minutes. The application overcomes the defects of insufficient strength of pure silver amalgam and high brittleness of gold-silver brazing filler metal, realizes high-strength, high-toughness, high-heat-resistant connection under low-temperature conditions, and is suitable for high-end electronic packaging.

Description

Technical Field

[0001] This invention belongs to the field of brazing technology, specifically relating to a high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal and its preparation and brazing method. Background Technology

[0002] With the rapid development of the electronics and information industry, the application of high-power-density, high-heat-generating electronic devices (such as IGBTs, power MOSFETs, lasers, and aerospace electronic equipment) is becoming increasingly widespread, and their service environments are becoming increasingly harsh (such as high temperature, high humidity, strong vibration, and thermal cycling). This places unprecedentedly high demands on electronic packaging technology, especially on the reliability of interconnections between dissimilar materials (such as metal substrates and semiconductor chips). As a key process for achieving this hermetically tight and high-strength interconnection, the performance of the core material—the solder—directly determines the performance, lifespan, and cost of the final product.

[0003] Currently, in the field of high-end electronic packaging, gold-based solders, especially Au-Sn eutectic solders (typically 80wt% Au and 20wt% Sn, with a eutectic point of approximately 278℃), are considered the industry standard due to their excellent wettability, superior corrosion resistance, high strength, and reliable long-term service performance. Their solder joints can withstand severe thermomechanical fatigue, ensuring the functional integrity of devices throughout their lifespan. However, the gold-tin solder system has inherent drawbacks such as extremely high cost, high intrinsic brittleness (a large amount of brittle intermetallic compounds in the solder joint can easily lead to reliability issues), microstructure deterioration, and high soldering temperatures (≥300℃ poses a risk of damage to heat-sensitive devices). The industry has been seeking alternative solutions.

[0004] Amalgam brazing filler metals have attracted widespread attention in recent years as a potential low-temperature bonding material. Their core advantages lie in their ability to achieve bonding in the low-temperature range of 120–350°C, significantly reducing thermal damage; their raw material cost is far lower than that of gold-based brazing filler metals; and their simple preparation process (physical mixing) facilitates industrial application. However, their basic system still has shortcomings in terms of joint strength, high-temperature stability, and creep resistance, making it difficult to fully meet the extreme reliability requirements of high-end packaging. This is mainly due to their single bonding mechanism and lack of systematic application of various strengthening mechanisms in materials science.

[0005] Therefore, this invention provides a high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal and its preparation and brazing method. Summary of the Invention

[0006] The technical problem to be solved: To overcome the shortcomings of existing technologies, this invention provides a high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal and its preparation and brazing method. The core of this invention lies in introducing specific alloying strengthening components into the silver amalgam system, systematically utilizing and synergistically employing material strengthening mechanisms such as solid solution strengthening, precipitation strengthening (through in-situ generation of high-melting-point intermetallic compounds), and grain refinement strengthening to fundamentally reconstruct and optimize the microstructure and properties of the brazed joint. This solves the defects of existing technologies, such as high cost of gold-tin brazing fillers, high solder joint brittleness, potential long-term reliability issues, and insufficient strength and heat resistance of basic silver amalgam brazing fillers.

[0007] The technical solution of this invention is: a high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal, wherein the filler metal is a paste-like composition prepared by amalgamation reaction, and its composition, based on its total mass, includes: Silver powder: 5-20 wt% Mercury: Balance; The alloy strengthening components include Cu, Ni, Sn, and In, with the contents of each element controlled as follows: Cu 1–8 wt%, Ni 1–3 wt%, Sn 1–5 wt%, and In <3 wt%. After low-temperature brazing, the brazing filler metal forms a complex microstructure in the brazing seam, with a tough silver-based solid solution as the matrix and embedded, dispersed nanoscale reinforcing phases. During the brazing process, the alloy reinforcing components selectively react with Ag and / or Hg, achieving a simultaneous improvement in the mechanical properties and high-temperature stability of the joint through the synergistic effect of multiple mechanisms, including solid solution strengthening, precipitation strengthening, and grain refinement strengthening.

[0008] A further technical solution of the present invention is: in the alloy strengthening component, Cu undergoes a selective reaction with Ag and / or Hg during brazing, nucleating and growing in situ in the Ag-Hg liquid phase to generate a dispersed high-melting-point Cu-Ag intermetallic compound strengthening phase, which dominates precipitation strengthening and improves the softening temperature and high-temperature creep resistance of the brazed joint.

[0009] A further technical solution of the present invention is: Ni in the alloy strengthening component is dispersed in the Ag-Hg liquid phase in the form of tiny particles during the brazing process, serving as heterogeneous nucleation points and pinning Ag grain boundaries, inhibiting grain coarsening, and mainly achieving fine grain strengthening, thereby improving the joint strength and thermal fatigue resistance.

[0010] A further technical solution of the present invention is: Sn in the alloy strengthening component dissolves in the Ag matrix during the brazing process to form a substitutional solid solution, which induces lattice distortion and dominates solid solution strengthening, thereby improving the strength and toughness of the silver matrix.

[0011] A further technical solution of the present invention is: In the alloy strengthening component, In dissolves in the Ag matrix during the brazing process to form a substitutional solid solution, which induces lattice distortion and improves the wettability of the brazing filler metal to the base material, so that the brazing filler metal can wet the surface of the aluminum alloy. A further technical solution of the present invention is: the content of the silver powder is 10-20 wt%, which is suitable for low-temperature brazing of electronic devices; or the content of the silver powder is 5-10 wt%, which is suitable for low-stress connection of consumer electronics.

[0012] A method for preparing the solder includes the following steps: Step 1: Accurately weigh the silver powder, alloy strengthening component powder, and mercury according to the specified ratio; Step 2: Mechanically mix the silver powder with the alloy reinforcing component powder to obtain a uniform mixed powder; Step 3: Add mercury to the mixed powder, shake and mix to trigger the amalgamation reaction, and obtain a paste-like solder with uniform composition and stable performance.

[0013] A method for low-temperature brazing of the aforementioned filler metal includes the following steps: Step 1: Clean the silver-plated surface to be soldered; Step 2: Apply the paste-like solder evenly to the surface to be soldered; Step 3: Assemble the workpieces to be welded to form the assembly to be welded; Step 4: Place the component to be brazed in a vacuum, protective atmosphere or atmospheric environment, heat it to 150-290°C and hold it for 10-60 minutes. At the same time, apply a welding pressure of 0.1-1.5 MPa during the holding stage to promote interfacial reaction and interdiffusion of elements between the brazing filler metal and the base material, and complete the brazing connection.

[0014] A further technical solution of the present invention is: in step 4, by coordinating and limiting the temperature, pressure, and time within a window of 150–290°C, 0.1–1.5 MPa, and 10–60 min, the following is achieved: To ensure that Sn and In are fully dissolved in the Ag matrix to form a substitutional solid solution, while avoiding a decrease in solid solubility or the formation of excessive low-melting-point phases due to excessively high temperature or time; To ensure that Cu reacts selectively with Ag and Hg, and to generate in situ a dispersed high-melting-point Cu-Ag intermetallic compound strengthening phase, while avoiding the formation of a continuous brittle compound layer; To ensure that Ni is stably dispersed in the form of tiny particles, so as to exert the heterogeneous nucleation particles and grain boundary pinning effect, while avoiding Ni particle agglomeration or excessive dissolution that would lead to loss of fine grain effect; Ensure that the amalgamation reaction proceeds fully and that the brazing filler metal wets the base metal evenly, while avoiding residual welding stress.

[0015] A further technical solution of the present invention is: the composition of the brazing filler metal by mass percentage is: 10% silver powder, 3% copper powder, 3% tin powder, 2.5% nickel powder, 1% indium powder, and the balance being mercury.

[0016] Beneficial effects The beneficial effects of this invention are as follows: 1. Method-Driven Performance Breakthrough: This invention does not stop at the level of material substitution, but actively constructs an ideal microstructure based on a tough silver-based solid solution containing dispersed high-melting-point reinforcing phases through a method chain of "alloying design - strengthening mechanism activation - microstructure regulation". This method enables the joint to maintain the advantages of low-temperature connection while its strength, hardness, and high-temperature stability can be comparable to or even surpass those of traditional gold-tin brazing joints, achieving a leapfrog improvement in performance.

[0017] 2. Synergistic Solution of Intrinsic Challenges Through Multiple Mechanisms: By synergistically utilizing multiple strengthening mechanisms, the method of this invention effectively solves the problem of insufficient strength of the basic silver amalgam, while simultaneously overcoming the reliability risks caused by the intrinsic brittleness of intermetallic compounds in gold-tin solder. The induced high-melting-point intermetallic compounds are "fixed" in the tough matrix as beneficial strengthening phases, rather than forming a continuous brittle layer, thereby ensuring excellent toughness while improving strength.

[0018] 3. Enhanced Reliability Design and Controllability: The method provided by this invention offers high design flexibility. By adjusting the type and ratio of alloy reinforcing components, the contribution of different strengthening mechanisms can be precisely controlled, achieving "on-demand customization" of the final solder joint performance to meet various reliability requirements, from consumer electronics to aerospace. The joints prepared by this method exhibit significantly optimized thermal fatigue resistance and long-term microstructural stability.

[0019] 4. Excellent process and economic advantages: This method inherits the advantages of silver amalgam system, such as low raw material cost, simple preparation process (physical mixing), and low temperature connection with little thermal damage. On this basis, through significant performance improvement, it further enhances the technical and economic feasibility of replacing gold-tin brazing filler metal in high-end fields, making it very suitable for industrial mass production. Attached Figure Description

[0020] Figure 1 Rod-shaped specimens welded with alloyed silver amalgam brazing filler and macroscopic morphology of fracture surfaces. Figure 2 Microstructure of the welded joint after tension and local magnification; Figure 3 Microstructure of the brazed joint fracture surface at 290℃-60min-3MPa; Figure 4 Room temperature tensile properties of low-temperature brazed joints at 290℃-60min-3MPa. Detailed Implementation The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0021] Existing technology CN121289851A discloses a pure silver amalgam brazing filler metal and its low-temperature brazing method. This method utilizes isothermal solidification to form a tough solder joint dominated by a silver-based solid solution, effectively avoiding the formation of large amounts of brittle intermetallic compounds. It shows potential to replace gold-tin brazing filler metals in terms of cost and processing temperature. However, pure silver amalgam brazing filler metals still face fundamental challenges in practical applications: their microstructure is a single silver-mercury solid solution, lacking an effective reinforcing phase. Although the solid solution matrix imparts good intrinsic toughness to the joint, under high-temperature service or long-term thermal cycling conditions, this structure struggles to provide sufficient creep resistance and high-temperature strength. The joint is prone to softening or fatigue failure, making it difficult to fully meet the extreme requirements of "high strength and high heat resistance" in high-reliability fields such as aerospace.

[0022] Based on the problems existing in the prior art, this invention proposes a high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal. The filler metal is a paste-like composition prepared through an amalgamation reaction, and its composition, based on its total mass, includes: Silver powder: 5-20 wt% Mercury: Balance; The alloy strengthening components include Cu, Ni, Sn, and In, with the contents of each element controlled as follows: Cu 1–8 wt%, Ni 1–3 wt%, Sn 1–5 wt%, and In <3 wt%. After low-temperature brazing, the brazing filler metal forms a complex microstructure in the brazing seam, with a tough silver-based solid solution as the matrix and embedded, dispersed nanoscale reinforcing phases. During the brazing process, the alloy reinforcing components selectively react with Ag and / or Hg, achieving a simultaneous improvement in the mechanical properties and high-temperature stability of the joint through the synergistic effect of multiple mechanisms, including solid solution strengthening, precipitation strengthening, and grain refinement strengthening.

[0023] The present invention also proposes a method for preparing the solder, comprising the following steps: Step 1: Accurately weigh the silver powder, alloy strengthening component powder, and mercury according to the specified ratio; Step 2: Mechanically mix the silver powder with the alloy reinforcing component powder to obtain a uniform mixed powder; Step 3: Add mercury to the mixed powder, shake and mix to trigger the amalgamation reaction, and obtain a paste-like solder with uniform composition and stable performance.

[0024] The present invention also proposes a method for low-temperature brazing of the aforementioned brazing filler metal, comprising the following steps: Step 1: Clean the silver-plated surface to be soldered; Step 2: Apply the paste-like solder evenly to the surface to be soldered; Step 3: Assemble the workpieces to be welded to form the assembly to be welded; Step 4: Place the component to be brazed in a vacuum, protective atmosphere or atmospheric environment, heat it to 150-290°C and hold it for 10-60 minutes. At the same time, apply a welding pressure of 0.1-1.5 MPa during the holding stage to promote interfacial reaction and interdiffusion of elements between the brazing filler metal and the base material, and complete the brazing connection.

[0025] This invention synergistically limits temperature, pressure, and time within a critical window of 150–290℃, 0.1–1.5MPa, and 10–60min, with the aim of: To ensure that tin and indium are fully dissolved in the Ag matrix to form a substitutional solid solution, while avoiding a decrease in solid solubility or the formation of excessive low-melting-point phases due to excessively high temperature or time; This ensures that copper reacts selectively with silver and mercury, generating in situ a dispersed high-melting-point Cu-Ag intermetallic compound strengthening phase, while avoiding the formation of a continuous brittle compound layer. This ensures that nickel is stably dispersed in the form of tiny particles, giving full play to the heterogeneous nucleation particles and grain boundary pinning effect, while avoiding nickel particle agglomeration or excessive dissolution that would lead to the loss of fine grain effect; Ensure that the amalgamation reaction proceeds fully and that the brazing filler metal wets the base metal evenly, while avoiding residual welding stress.

[0026] The above technical solution will be further analyzed below with reference to the accompanying drawings and examples: Example 1: I. Solder Preparation This embodiment provides a high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal, the composition of which by mass percentage is: 10% silver powder, 3% copper powder, 3% tin powder, 2.5% nickel powder, 1% indium powder, and the balance being mercury.

[0027] The silver powder is high-purity silver powder with a purity ≥99.9% and a particle size distribution range of 50–300 nm; the copper powder, nickel powder, tin powder, and indium powder are all high-purity metal powders with a purity ≥99.5% and a particle size distribution range of 50–300 nm; the mercury is high-purity mercury with a purity ≥99.99%.

[0028] The preparation steps for the solder are as follows: Step 1: According to the above proportions, use a high-precision electronic balance to accurately weigh the silver powder, copper powder, nickel powder, tin powder, indium powder, and mercury; Step 2: Place the weighed silver powder, copper powder, nickel powder, tin powder, and indium powder into a mixing container and mechanically mix for 10 minutes to obtain a uniform mixed powder. Step 3: Add the weighed mercury to the mixed powder, seal the container and place it in a vibrating mixer, vibrate for 20 seconds to trigger the amalgamation reaction, and obtain a paste-like solder with uniform composition and stable performance.

[0029] II. Principles of Component Design This invention precisely limits the amount of each component added to the brazing filler metal to ensure that the filler metal possesses good wettability, formability, and overall mechanical properties of the joint. The working principle of each component and the basis for limiting its amount are as follows: 1. Silver powder (5-20 wt%) Silver powder is the main component forming the solder matrix. After undergoing an amalgamation reaction with mercury, it forms a silver-based solid solution. The silver powder content is limited to 5–20 wt% because: when the silver powder content is <5 wt%, a sufficient silver matrix cannot be formed, resulting in poor solder wettability and difficulty in forming a continuous and reliable weld; when the silver powder content is >15 wt%, the amalgamation reaction is incomplete, and the solder remains solid and cannot be properly coated and formed. Depending on the application scenario, the silver powder content can be further optimized: 10–20 wt% is suitable for low-temperature brazing with high reliability requirements, such as in aerospace electronic devices; less than 10 wt% is suitable for low-stress connections in consumer electronics.

[0030] 2. Copper powder (1-8 wt%) Copper is the core component for precipitation strengthening in this invention. During brazing, copper selectively reacts with silver and mercury, nucleating and growing in situ in the Ag-Hg liquid phase to generate a dispersed, high-melting-point Cu-Ag intermetallic compound strengthening phase. These nanoscale strengthening phases effectively hinder dislocation movement through the Orowan bypass mechanism, significantly improving the softening temperature and high-temperature creep resistance of the brazed joint. The copper powder addition is limited to 1–8 wt% because: when the addition is less than 1 wt%, the amount of precipitated strengthening phase is insufficient, making it difficult to form effective dispersed strengthening, and the improvement in high-temperature performance of the joint is not significant; when the addition is greater than 8 wt%, continuous, coarse, and brittle Cu-based intermetallic compounds are easily generated, disrupting the continuity of the joint matrix, leading to joint embrittlement, a significant decrease in mechanical properties, and a reduction in the wettability and fluidity of the brazing filler metal.

[0031] 3. Nickel powder (1-3 wt%) Nickel is the core component for achieving grain refinement strengthening in this invention. During brazing, nickel has low solubility in the Ag-Hg liquid phase and is uniformly dispersed in the liquid phase as tiny particles. It acts as heterogeneous nucleation sites to increase the nucleation rate of the brazed joint structure, while simultaneously pinning Ag grain boundaries, effectively inhibiting Ag grain coarsening during the welding thermal cycle, refining the brazed joint microstructure, and thus improving the joint strength and thermal fatigue resistance. The basis for limiting the nickel powder addition to 1-3 wt% is that: when the addition is <1 wt%, the number of heterogeneous nucleation sites is insufficient, the grain refinement effect is limited, and it cannot significantly improve the structure and properties; when the addition is >3 wt%, excessive Ni particles are prone to agglomeration and uneven distribution, forming local hard agglomeration areas, increasing the internal stress of the joint, reducing the toughness and reliability of the joint, and inhibiting the amalgamation reaction and brazing filler metal wetting and spreading.

[0032] 4. Tin powder (1-5 wt%) Tin is one of the core components for solid solution strengthening in this invention. During brazing, tin dissolves in the Ag matrix to form a substitutional solid solution, inducing Ag lattice distortion, hindering dislocation movement, and effectively improving the strength and toughness of the silver matrix. The basis for limiting the amount of tin powder added to 1-5 wt% is that: when the amount added is <1 wt%, the degree of solid solution is low, the lattice distortion effect is weak, and the solid solution strengthening effect is not significant; when the amount added is >5 wt%, over-solution or formation of continuous brittle Ag-Sn intermetallic compounds is likely to occur, resulting in a significant decrease in the plasticity and toughness of the joint, while also reducing the low-temperature stability of the brazing filler metal and the interfacial bonding strength.

[0033] 5. Indium powder (<3wt%) Indium is another core component in this invention for achieving solid solution strengthening, and it also has the unique function of improving wettability. During the brazing process, indium dissolves in the Ag matrix to form a substitutional solid solution, inducing lattice distortion and improving the strength and toughness of the matrix. More importantly, pure amalgam brazing filler metal cannot wet aluminum alloy surfaces, which greatly limits its application range. The addition of indium powder can significantly improve the wettability of amalgam brazing filler metal on difficult-to-wet materials such as aluminum alloys. The basis for limiting the amount of indium powder added to less than 3 wt% is that experiments have shown that adding 3 wt% indium powder can further increase the bonding strength of the joint on the basis of improving wettability. When the amount of indium powder added exceeds 3 wt%, it is easy to form an excessive amount of low-melting-point phase or brittle intermetallic compounds, resulting in a sharp decrease in joint strength.

[0034] III. Brazing Methods This embodiment uses the brazing filler metal prepared above for low-temperature brazing. The specific steps are as follows: Step 1: Preparation before welding; Pure silver rods were selected as the base material and completely immersed in anhydrous ethanol solution. They were then treated with ultrasonic cleaning for 5 minutes. After ultrasonic cleaning, the sample was removed, the surface was wiped clean with degreased cotton, and then dried with a hot air dryer for later use.

[0035] Step 2: Apply solder; Use a non-metallic scraper to take an appropriate amount of the prepared paste-like brazing filler metal and apply it evenly to the surface to be soldered, controlling the coating thickness to be about 15μm.

[0036] Step 3: Assembly; Align and fit the two workpieces coated with brazing filler metal together, apply a slight preload to ensure good initial contact, and then place the assembled assembly into the welding fixture.

[0037] Step 4: Brazing connection; The assembled components are placed in a vacuum brazing furnace. The temperature is raised to 290°C and held for 60 minutes, while a welding pressure of 3 MPa is applied during the holding period. After the holding period, the components are cooled to room temperature and then removed.

[0038] IV. Performance Testing and Microstructure Characterization The brazed joints prepared in this embodiment were subjected to performance testing and microstructure characterization. The results are as follows: 1. Macroscopic morphology Figure 1 This image shows the macroscopic morphology of the rod-shaped specimen and fracture surface welded using alloyed silver amalgam brazing filler metal in this embodiment. From... Figure 1 It can be seen that the surface of the welded sample is smooth and flat, the weld is well formed, and there are no obvious defects such as cracks or holes.

[0039] 2. Microstructure analysis Figure 2 This is a magnified view of the cross-sectional structure of the brazed joint after stretching in this embodiment. Figure 2 In (a), the area covered by the red dashed line is the weld area. It can be observed that the fracture location includes part of the base material, indicating that the joint has good mechanical properties and is as strong as the base material. From the magnified view (b), it can be seen that the brazed seam structure is uniform and dense, with good interface bonding and no defects such as slag inclusions or cracks.

[0040] 3. Fracture morphology analysis Figure 3 The fracture surface morphology of the brazed joint in this embodiment is shown. The joint fracture exhibits typical ductile fracture characteristics, with numerous dimples present. The dimple morphology shows no obvious cleavage planes, river patterns, or other brittle fracture features, indicating that the welding process did not cause embrittlement due to heat input, and the joint possesses good plasticity and toughness.

[0041] 4. Mechanical property testing Figure 4 The results show the room temperature tensile properties of the low-temperature brazed joints in this embodiment. The average tensile strength of the brazed joints using AuSn20 brazing filler metal was 50–60 MPa, while the average tensile strength of the joints using pure silver amalgam brazing filler metal in the control group was approximately 70 MPa. In contrast, the average tensile strength of the joints using alloyed silver amalgam brazing filler metal in this embodiment reached 95 MPa. The test results indicate that through alloying design and multi-mechanism synergistic strengthening, the brazing filler metal of this invention can effectively improve the joint bonding strength, increasing it by approximately 35% compared to pure silver amalgam brazing filler metal and by approximately 60%–90% compared to gold-tin brazing filler metal.

[0042] V. Mechanism Analysis The core technical idea of ​​this invention lies not in simply introducing alloying elements into the amalgam, but in actively controlling the isothermal solidification path and phase transformation thermodynamics during the welding process. Extensive experiments have revealed that specific alloying elements (Cu, Ni, In, Sn) preferentially react with Ag or Hg during the welding heating process. The reaction products are not simple intermetallic compound frameworks, but rather high-melting-point nanoparticles that nucleate, grow, and disperse in situ within the Ag-Hg liquid phase.

[0043] The "in-situ precipitation" process of this invention involves the synergistic effect of three enhancement mechanisms: 1. Solid Solution Strengthening: In and Sn elements can form substitutional solid solutions with Ag, inducing Ag lattice distortion, hindering dislocation movement, and effectively improving the strength and toughness of the silver-based matrix. Simultaneously, they can improve the wettability of the solder, enhancing the interfacial bonding between the solder and the base material. Furthermore, since pure amalgam solder cannot wet aluminum alloy surfaces, its application is significantly limited. The addition of In powder greatly improves the wettability of amalgam solder, enabling it to wet aluminum alloy surfaces. Experiments have shown that when the In addition exceeds 3 wt%, excessive low-melting-point phases or brittle intermetallic compounds are easily formed, leading to a sharp decrease in joint strength; therefore, the addition amount should be controlled to <3 wt%.

[0044] 2. Precipitation strengthening: During the brazing process, Cu reacts selectively with Ag and Hg, nucleating and growing in situ in the Ag-Hg liquid phase to generate a dispersed high-melting-point Cu-Ag intermetallic compound strengthening phase. This phase hinders dislocation movement through the Orowan bypass mechanism, significantly improving the softening temperature and high-temperature creep resistance of the brazed joint.

[0045] 3. Refining grain strengthening: Ni can act as a heterogeneous nucleation point to improve the nucleation rate of the brazed joint structure. At the same time, it can pin the grain boundaries of Ag grains, effectively inhibit the coarsening of Ag grains during the welding thermal cycle, refine the microstructure of the brazed joint, and thus improve the strength and thermal fatigue resistance of the joint.

[0046] These three mechanisms occur synergistically and promote each other during the welding process, ultimately forming an "endogenous composite material" structure based on a tough Ag-based solid solution and containing a dispersed nano-reinforcing phase. This is the essential difference between this invention and existing technologies (such as pure silver amalgam single-phase solid solution structures).

[0047] Example 2: I. Solder Preparation This embodiment provides a high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal, the composition of which by mass percentage is: 15% silver powder, 4% copper powder, 3% tin powder, 2% nickel powder, 0.8% indium powder, and the balance being mercury.

[0048] The silver powder is high-purity silver powder with a purity ≥99.9% and a particle size distribution range of 50–300 nm; the copper powder, nickel powder, tin powder, and indium powder are all high-purity metal powders with a purity ≥99.5% and a particle size distribution range of 50–300 nm; the mercury is high-purity mercury with a purity ≥99.99%.

[0049] The preparation steps for the solder are as follows: Step 1: According to the above proportions, use a high-precision electronic balance to accurately weigh the silver powder, copper powder, nickel powder, tin powder, indium powder, and mercury; Step 2: Place the weighed silver powder, copper powder, nickel powder, tin powder, and indium powder into a mixing container and mechanically mix for 10 minutes to obtain a uniform mixed powder. Step 3: Add the weighed mercury to the mixed powder, seal the container and place it in a vibrating mixer, vibrate for 20 seconds to trigger the amalgamation reaction, and obtain a paste-like solder with uniform composition and stable performance.

[0050] II. Brazing Method This embodiment uses the brazing filler metal prepared above for low-temperature brazing. The specific steps are as follows: Step 1: Preparation before welding; Pure silver rods were selected as the base material and completely immersed in anhydrous ethanol solution. They were then treated with ultrasonic cleaning for 5 minutes. After ultrasonic cleaning, the sample was removed, the surface was wiped clean with degreased cotton, and then dried with a hot air dryer for later use.

[0051] Step 2: Apply solder; Use a non-metallic scraper to take an appropriate amount of the prepared paste-like brazing filler metal and apply it evenly to the surface to be soldered, controlling the coating thickness to be about 15μm.

[0052] Step 3: Assembly; Align and fit the two workpieces coated with brazing filler metal together, apply a slight preload to ensure good initial contact, and then place the assembled assembly into the welding fixture.

[0053] Step 4: Brazing connection; The assembled components are placed in a vacuum brazing furnace. The temperature is raised to 290°C and held for 60 minutes, while a welding pressure of 3 MPa is applied during the holding period. After the holding period, the components are cooled to room temperature and then removed.

[0054] Example 3: I. Solder Preparation This embodiment provides a high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal, the composition of which by mass percentage is: 8.5% silver powder, 2% copper powder, 2% tin powder, 0% nickel powder, 1% indium powder, and the balance being mercury.

[0055] The silver powder is high-purity silver powder with a purity ≥99.9% and a particle size distribution range of 50–300 nm; the copper powder, nickel powder, tin powder, and indium powder are all high-purity metal powders with a purity ≥99.5% and a particle size distribution range of 50–300 nm; the mercury is high-purity mercury with a purity ≥99.99%.

[0056] The preparation steps for the solder are as follows: Step 1: According to the above proportions, use a high-precision electronic balance to accurately weigh the silver powder, copper powder, nickel powder, tin powder, indium powder, and mercury; Step 2: Place the weighed silver powder, copper powder, nickel powder, tin powder, and indium powder into a mixing container and mechanically mix for 10 minutes to obtain a uniform mixed powder. Step 3: Add the weighed mercury to the mixed powder, seal the container and place it in a vibrating mixer, vibrate for 20 seconds to trigger the amalgamation reaction, and obtain a paste-like solder with uniform composition and stable performance.

[0057] II. Brazing Method This embodiment uses the brazing filler metal prepared above for low-temperature brazing. The specific steps are as follows: Step 1: Preparation before welding; Pure silver rods were selected as the base material and completely immersed in anhydrous ethanol solution. They were then treated with ultrasonic cleaning for 5 minutes. After ultrasonic cleaning, the sample was removed, the surface was wiped clean with degreased cotton, and then dried with a hot air dryer for later use.

[0058] Step 2: Apply solder; Use a non-metallic scraper to take an appropriate amount of the prepared paste-like brazing filler metal and apply it evenly to the surface to be soldered, controlling the coating thickness to be about 15μm.

[0059] Step 3: Assembly; Align and fit the two workpieces coated with brazing filler metal together, apply a slight preload to ensure good initial contact, and then place the assembled assembly into the welding fixture.

[0060] Step 4: Brazing connection; The assembled components are placed in a vacuum brazing furnace. The temperature is raised to 290°C and held for 60 minutes, while a welding pressure of 3 MPa is applied during the holding period. After the holding period, the components are cooled to room temperature and then removed.

[0061] Examples 2 and 3 use the same preparation and brazing methods as Example 1, only adjusting the types and proportions of alloy reinforcing components to verify the synergistic effect of different compounding schemes.

[0062] Comparative Example 1 (Pure Silver Mercury Brazing Filler) Following the formula and process disclosed in CN121289851A, a pure silver amalgam brazing alloy (15% silver powder, 85% mercury) was prepared and brazed using the same base material and process conditions (290℃, 60 min, 3 MPa) as in Example 1. Test results showed that the average tensile strength of the joint was approximately 70 MPa, and the microstructure was a single silver amalgam solid solution without dispersed reinforcing phases. Compared to Example 1 (95 MPa), the strength of the alloyed silver amalgam brazing alloy of this invention is increased by approximately 35%, fully demonstrating the significant effect of alloying design and multi-mechanism synergistic strengthening.

[0063] Table 1. Comparison of performance of the embodiments of the present invention with existing brazing filler metals

[0064] In summary, this invention, through a method chain of alloying design, strengthening mechanism activation, and microstructure control, actively constructs an ideal microstructure based on a tough silver-based solid solution, containing dispersed high-melting-point reinforcing phases. This method enables the joint to maintain the advantages of low-temperature connection (150–290°C) while achieving strength, hardness, and high-temperature stability comparable to or even surpassing traditional gold-tin solder joints, realizing a significant performance improvement and making it highly suitable for the industrial mass production of high-end electronic packaging.

[0065] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal, characterized in that, The solder is a paste-like composition prepared by amalgamation reaction, and its composition, based on its total mass, includes: Silver powder: 5-20 wt% Mercury: Balance; The alloy strengthening components include Cu, Ni, Sn, and In, with the contents of each element controlled as follows: Cu 1–8 wt%, Ni 1–3 wt%, Sn 1–5 wt%, and In <3 wt%. After low-temperature brazing, the brazing filler metal forms a complex microstructure in the brazing seam, with a tough silver-based solid solution as the matrix and embedded, dispersed nanoscale reinforcing phases. During the brazing process, the alloy reinforcing components selectively react with Ag and / or Hg, achieving a simultaneous improvement in the mechanical properties and high-temperature stability of the joint through the synergistic effect of multiple mechanisms, including solid solution strengthening, precipitation strengthening, and grain refinement strengthening.

2. The high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal according to claim 1, characterized in that: In the alloy strengthening component, Cu undergoes a selective reaction with Ag and / or Hg during brazing, nucleating and growing in situ in the Ag-Hg liquid phase to generate a dispersed high-melting-point Cu-Ag intermetallic compound strengthening phase, which dominates precipitation strengthening and improves the softening temperature and high-temperature creep resistance of the brazed joint.

3. The high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal according to claim 1, characterized in that: In the alloy strengthening component, Ni is dispersed in the Ag-Hg liquid phase in the form of tiny particles during the brazing process. It acts as heterogeneous nucleation points and pins the grain boundaries of Ag grains, inhibiting grain coarsening, and mainly achieving fine grain strengthening, thereby improving the joint strength and thermal fatigue resistance.

4. The high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal according to claim 1, characterized in that: In the alloy strengthening component, Sn dissolves in the Ag matrix during brazing to form a substitutional solid solution, which induces lattice distortion and dominates solid solution strengthening, thereby improving the strength and toughness of the silver matrix.

5. The high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal according to claim 1, characterized in that: In the alloy strengthening component, In dissolves in the Ag matrix during brazing to form a substitutional solid solution, which induces lattice distortion and improves the wettability of the brazing filler metal to the base material, enabling the brazing filler metal to wet the aluminum alloy surface.

6. The high-performance alloyed silver amalgam low-temperature high-strength brazing filler metal according to claim 1, characterized in that: The silver powder content is 10-20 wt%, suitable for low-temperature brazing of electronic devices; or the silver powder content is 5-10 wt%, suitable for low-stress connection of consumer electronics.

7. A method for preparing the solder according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Accurately weigh the silver powder, alloy strengthening component powder, and mercury according to the specified ratio; Step 2: Mechanically mix the silver powder with the alloy reinforcing component powder to obtain a uniform mixed powder; Step 3: Add mercury to the mixed powder, shake and mix to trigger the amalgamation reaction, and obtain a paste-like solder with uniform composition and stable performance.

8. A method for low-temperature brazing using the filler metal described in any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Clean the silver-plated surface to be soldered; Step 2: Apply the paste-like solder evenly to the surface to be soldered; Step 3: Assemble the workpieces to be welded to form the assembly to be welded; Step 4: Place the component to be brazed in a vacuum, protective atmosphere or atmospheric environment, heat it to 150-290°C and hold it for 10-60 minutes. At the same time, apply a welding pressure of 0.1-1.5 MPa during the holding stage to promote interfacial reaction and interdiffusion of elements between the brazing filler metal and the base material, and complete the brazing connection.

9. The low-temperature brazing method according to claim 8, characterized in that: In step 4, by coordinating and limiting temperature, pressure, and time within a window of 150–290℃, 0.1–1.5MPa, and 10–60min, the following is achieved: To ensure that Sn and In are fully dissolved in the Ag matrix to form a substitutional solid solution, while avoiding a decrease in solid solubility or the formation of excessive low-melting-point phases due to excessively high temperature or time; To ensure that Cu reacts selectively with Ag and Hg, and to generate in situ a dispersed high-melting-point Cu-Ag intermetallic compound strengthening phase, while avoiding the formation of a continuous brittle compound layer; To ensure that Ni is stably dispersed in the form of tiny particles, so as to exert the heterogeneous nucleation particles and grain boundary pinning effect, while avoiding Ni particle agglomeration or excessive dissolution that would lead to loss of fine grain effect; Ensure that the amalgamation reaction proceeds fully and that the brazing filler metal wets the base metal evenly, while avoiding residual welding stress.

10. The low-temperature brazing method according to claim 8, characterized in that: The composition of the brazing filler metal by mass percentage is: 10% silver powder, 3% copper powder, 3% tin powder, 2.5% nickel powder, 1% indium powder, and the balance being mercury.

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