Electrochemical migration resistant tin-based solder alloy and preparation method thereof

Abstract

The invention relates to the technical field of solder materials for electronic packaging, and discloses an electrochemical migration resistant tin-based solder alloy and a preparation method thereof.The tin-based solder alloy is based on Sn, and Ag, Cu, Zn, neodymium triacetylacetonate, a TiC-SiC mixture, a graphene / carbon nanotube / Ti < 3 > C < 2 > T < x > MXene composite system and other components are added. The preparation method comprises the steps of raw material pretreatment, vacuum melting, in-situ reaction, two-stage cooling and gradient aging. The migration-resistant failure time of the alloy is greater than or equal to 500s, the tensile strength is greater than or equal to 350MPa, the melting point is 215-225 DEG C, and the alloy can stably work in a high-humidity environment at the temperature of-50-150 DEG C, is adaptive to high-end electronic packaging of AI chips, data center servers and the like, and has large-scale production potential.

Description

Technical Field

[0001] This invention relates to the field of solder materials for electronic packaging, and more specifically, to a tin-based solder alloy resistant to electrochemical migration and its preparation method. Background Technology

[0002] With the rapid development of 5G communication, AI chips, new energy vehicles, and military electronics, electronic components are iterating towards miniaturization, high integration, and high power density, with solder joint spacing reduced to the micrometer level. Against this backdrop, solder joints are highly susceptible to electrochemical migration (ECM) under the combined effects of humid and hot environments (such as high-temperature and high-humidity storage, outdoor rain), high electric field strength (such as high-voltage power supply modules), and trace contaminants (such as salt spray and dust in the air). This means that metal ions (mainly Sn) in the solder are highly susceptible to ECM. 2+ Driven by an electric field, these metal dendrites migrate towards the cathode, eventually forming metal dendrites that bridge adjacent solder joints, leading to short-circuit failure. Statistics show that failures caused by electrochemical migration account for over 30% of those in high-end electronic devices, severely limiting the lifespan and reliability of these devices.

[0003] Existing modification schemes for tin-based solders face significant technical bottlenecks: ① Traditional Sn-Ag-Cu solders rely on modification with a single metal element (such as Ag or Cu), which only slightly improves mechanical properties and cannot form an effective ion migration barrier system. Under simulated salt spray conditions with 3.5% NaCl, the electrochemical migration failure time is generally ≤200s; ② Some schemes attempt to add carbon materials (such as graphene) or ceramic particles (such as TiC), but due to the poor wettability of carbon materials with the metal matrix and the easy agglomeration of ceramic particles, "interfacial gaps" or "agglomeration defects" are formed, which instead become rapid channels for ion diffusion; ③ Rare earth element modification often uses oxides (such as Nd2O3), which have extremely poor dispersibility in solder and easily form large agglomerates, leading to increased solder brittleness; ④ The preparation process is mostly a simple combination of "melting + isothermal aging," which cannot achieve uniform mixing of components and precise control of phase structure, resulting in poor batch stability of solder; ⑤ Flux needs to be added during the welding process to remove the oxide film, but residual flux is prone to moisture absorption, which accelerates electrochemical migration.

[0004] Currently, the industry has not been able to simultaneously solve the three major problems of "poor electrochemical migration resistance, uneven component dispersion, and contradiction between mechanical and solderability." This invention addresses these shortcomings of existing technologies by proposing a novel technical solution, filling the technological gap in high-end migration-resistant tin-based solders. Summary of the Invention

[0005] In view of this, the present invention proposes a tin-based solder alloy resistant to electrochemical migration and its preparation method, aiming to solve the problems of poor electrochemical migration resistance, uneven component dispersion, and contradiction between mechanical and welding properties of existing tin-based solders.

[0006] This invention proposes a tin-based solder alloy resistant to electrochemical migration, comprising, by weight, the following components: 100 parts Sn powder, 3-6 parts Ag powder, 1-2 parts Cu powder, 1-4 parts Zn powder, 0.5-1.5 parts neodymium acetylacetone, 40-60 parts a mixture of SnCl2·2H2O and citric acid, 60-80 parts a mixture of TiC and SiC, 40-60 parts a graphene / carbon nanotube / Ti3C2Tx MXene composite system, 0.5-2.5 parts La powder, 1-3 parts Sb powder, and 0.1-0.5 parts potassium fluoroborate.

[0007] Preferably, in the graphene / carbon nanotube / Ti3C2Tx MXene composite system, the mass ratio of graphene / carbon nanotube / Ti3C2Tx MXene is 1:3:2.

[0008] Preferably, the graphene has a thickness of 1-5 nm, the carbon nanotubes have a diameter of 20-50 nm and a length of 1-5 μm, and the Ti3C2Tx MXene sheets have a size of 0.5-2 μm and a thickness of 5-10 nm.

[0009] Preferably, in the mixture of SnCl2・2H2O and citric acid, the mass ratio of SnCl2・2H2O to citric acid is 2:1.

[0010] Preferably, in the mixture of TiC and SiC, the mass ratio of TiC to SiC is 3:2.

[0011] Another object of the present invention is to provide a method for preparing the electrochemical migration-resistant tin-based solder alloy, comprising the following steps: S1: Vacuum dry Sn powder, Ag powder, Cu powder, Zn powder, La powder, and Sb powder; grind the mixture of SnCl2·2H2O and citric acid, the mixture of TiC and SiC, and the graphene / carbon nanotube / Ti3C2Tx MXene composite system respectively; mix neodymium acetylacetone and potassium fluoroborate and preheat; S2: The dried Sn powder, Ag powder, Cu powder, Zn powder, La powder and Sb powder are vacuum melted to obtain an alloy melt; S3: First, the mixture of ground SnCl2・2H2O and citric acid, and the mixture of TiC and SiC are added to the alloy melt in sequence for heat preservation; after heat preservation, the mixture of pretreated neodymium acetylacetone and potassium fluoroborate and the graphene / carbon nanotube / Ti3C2Tx MXene composite system are added to carry out in-situ reaction to obtain the composite melt.

[0012] S4: Pour the composite melt into a mold and cool it twice to obtain a cast alloy; S5: The as-cast alloy is subjected to homogenization and solution treatment in sequence, and then quenched and cooled to room temperature; then heat treatment is carried out by gradient aging process, and cooled to room temperature in furnace to obtain a tin-based solder alloy resistant to electrochemical migration.

[0013] Preferably, in step S1, the vacuum drying temperature is 80~120℃ and the time is 2~4h.

[0014] Preferably, the grinding medium is agate balls, the ball-to-material ratio is 10:1, the grinding speed is 300 r / min, and the grinding is carried out until the particle size is ≤50 μm.

[0015] Preferably, the preheating is performed at 150~200℃ for 1~2 hours under an inert atmosphere.

[0016] Preferably, in step S2, the vacuum melting specifically involves adding vacuum-dried Sn powder, Ag powder, Cu powder, Zn powder, La powder, and Sb powder into the reactor, closing the furnace door, and then drawing a vacuum to ≤10. -3 Pa, fill the furnace with argon gas to a pressure of 0.1 MPa, heat to 800-900℃ at a rate of 5-10℃ / min, hold for 30-60 min, and stir at a rate of 100-200 r / min during the process.

[0017] Preferably, in step S3, the temperature for heat preservation is 750~850℃, the heat preservation time is 20~30min, and the stirring is carried out at a rate of 300~400r / min during the heat preservation period.

[0018] Preferably, the in-situ reaction conditions are as follows: the temperature is increased to 880~920℃ at a rate of 5℃ / min and reacted for 30~40min, during which the mixture is stirred at a rate of 450~550r / min.

[0019] Preferably, in step S4, the mold is a copper mold preheated to 200°C.

[0020] Preferably, in the two cooling processes, the first cooling is performed at a cooling rate of 50~80℃ / min to 200~250℃; the second cooling is performed at a cooling rate of 10~20℃ / min to room temperature.

[0021] Preferably, in step S5, the homogenization process involves heating at 10°C / min to 500~550°C and holding at that temperature for 6~10 hours.

[0022] Preferably, the solution treatment involves heating to 580~620℃ at a rate of 5℃ / min and holding at that temperature for 2~4 hours.

[0023] Preferably, the quenching cooling is performed by immersing the vessel in water at 20°C.

[0024] Preferably, the gradient aging process involves first heating to 150-180°C at a rate of 5°C / min and holding for 2-3 hours, then heating to 190-220°C at a rate of 3°C / min and holding for 2-5 hours.

[0025] Another object of the present invention is to provide an application of the aforementioned electrochemical migration-resistant tin-based solder alloy, the application being for solder joint packaging in AI chip GPU packaging, data center server power modules, automotive electronic ignition systems, or military electronic equipment.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The tin-based solder alloy prepared by this invention exhibits an electrochemical migration failure time of no less than 500s and a maximum of 680s under simulated salt spray environment (3.5% NaCl) and 10V voltage conditions. 2+ The ion migration rate is reduced by more than 80%, which can effectively prevent short circuit failure caused by dendrite formation due to ion migration at the solder joint.

[0027] 2) After testing, the tin-based solder alloy prepared by this invention has a tensile strength of not less than 350MPa and a maximum of 380MPa; an elongation of not less than 25% and a maximum of 28%; and after working continuously at 125℃ for 1000h, the creep deformation is extremely small, and it has good tensile strength, deformation resistance and creep resistance.

[0028] 3) The melting point is stably controlled in the range of 215~225℃, which can be directly adapted to conventional SMT soldering processes; when soldering with Cu substrate, the contact angle does not exceed 25°, and can be as low as 22°, with good wettability; no additional flux is required during the soldering process, and the residual impurity content after soldering is found to be less than 0.1%, which can reduce the impact of impurities on the reliability of solder joints.

[0029] 4) The tin-based solder alloy prepared by this invention can work stably in a wide temperature range of -50℃ to 150℃ and in a high humidity environment with a relative humidity of not less than 90%, with small fluctuations in various core performances; the electrochemical migration failure time deviation of solders from different production batches is less than 5%, which can meet the quality control requirements of industrial mass production.

[0030] 5) The tin-based solder alloy prepared by this invention can be directly applied to the solder joint packaging of AI chip GPUs, data center server power modules, automotive electronic ignition systems and military electronic equipment. It can meet the stringent requirements of high-end electronic equipment for solder joint reliability, stability and durability, and effectively reduce the risk of solder joint failure during equipment operation. Detailed Implementation

[0031] 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. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0032] Furthermore, regarding the 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 within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] This invention proposes a tin-based solder alloy resistant to electrochemical migration, comprising, by weight, the following components: 100 parts Sn powder, 3-6 parts Ag powder, 1-2 parts Cu powder, 1-4 parts Zn powder, 0.5-1.5 parts neodymium acetylacetone (Nd(acac)3), 40-60 parts a mixture of SnCl2・2H2O and citric acid, 60-80 parts a mixture of TiC and SiC, 40-60 parts a graphene / carbon nanotube / Ti3C2Tx MXene composite system, 0.5-2.5 parts La powder, 1-3 parts Sb powder, and 0.1-0.5 parts potassium fluoroborate (KBF4).

[0037] Preferably, in the graphene / carbon nanotube / Ti3C2Tx MXene composite system, the mass ratio of graphene / carbon nanotube / Ti3C2Tx MXene is 1:3:2.

[0038] Preferably, the graphene has a thickness of 1-5 nm, the carbon nanotubes have a diameter of 20-50 nm and a length of 1-5 μm, and the Ti3C2Tx MXene sheets have a size of 0.5-2 μm and a thickness of 5-10 nm.

[0039] Preferably, in the mixture of SnCl2・2H2O and citric acid, the mass ratio of SnCl2・2H2O to citric acid is 2:1.

[0040] Preferably, in the mixture of TiC and SiC, the mass ratio of TiC to SiC is 3:2.

[0041] Another object of the present invention is to provide a method for preparing the electrochemical migration-resistant tin-based solder alloy, comprising the following steps: S1: Vacuum dry Sn powder, Ag powder, Cu powder, Zn powder, La powder, and Sb powder; grind the mixture of SnCl2·2H2O and citric acid, the mixture of TiC and SiC, and the graphene / carbon nanotube / Ti3C2Tx MXene composite system respectively; mix neodymium acetylacetone and potassium fluoroborate and preheat; S2: The dried Sn powder, Ag powder, Cu powder, Zn powder, La powder and Sb powder are vacuum melted to obtain an alloy melt; S3: First, the mixture of ground SnCl2・2H2O and citric acid, and the mixture of TiC and SiC are added to the alloy melt in sequence for heat preservation; after heat preservation, the mixture of pretreated neodymium acetylacetone and potassium fluoroborate and the graphene / carbon nanotube / Ti3C2Tx MXene composite system are added to carry out in-situ reaction to obtain the composite melt.

[0042] S4: Pour the composite melt into a mold and cool it twice to obtain a cast alloy; S5: The as-cast alloy is subjected to homogenization and solution treatment in sequence, and then quenched and cooled to room temperature; then heat treatment is carried out by gradient aging process, and cooled to room temperature in furnace to obtain a tin-based solder alloy resistant to electrochemical migration.

[0043] Preferably, in step S1, the vacuum drying temperature is 80~120℃ and the time is 2~4h.

[0044] Preferably, the grinding medium is agate balls, the ball-to-material ratio is 10:1, the grinding speed is 300 r / min, and the grinding is carried out until the particle size is ≤50 μm.

[0045] Preferably, the preheating is performed at 150~200℃ for 1~2 hours under an inert atmosphere.

[0046] Preferably, in step S2, the vacuum melting specifically involves adding vacuum-dried Sn powder, Ag powder, Cu powder, Zn powder, La powder, and Sb powder into the reactor, closing the furnace door, and then drawing a vacuum to ≤10. -3 Pa, fill the furnace with argon gas to a pressure of 0.1 MPa, heat to 800-900℃ at a rate of 5-10℃ / min, hold for 30-60 min, and stir at a rate of 100-200 r / min during the process.

[0047] Preferably, in step S3, the temperature for heat preservation is 750~850℃, the heat preservation time is 20~30min, and the stirring is carried out at a rate of 300~400r / min during the heat preservation period.

[0048] Preferably, the in-situ reaction conditions are as follows: the temperature is increased to 880~920℃ at a rate of 5℃ / min and reacted for 30~40min, during which the mixture is stirred at a rate of 450~550r / min.

[0049] Preferably, in step S4, the mold is a copper mold preheated to 200°C.

[0050] Preferably, in the two cooling processes, the first cooling is performed at a cooling rate of 50~80℃ / min to 200~250℃; the second cooling is performed at a cooling rate of 10~20℃ / min to room temperature.

[0051] Preferably, in step S5, the homogenization process involves heating at 10°C / min to 500~550°C and holding at that temperature for 6~10 hours.

[0052] Preferably, the solution treatment involves heating to 580~620℃ at a rate of 5℃ / min and holding at that temperature for 2~4 hours.

[0053] Preferably, the quenching cooling is performed by immersing the vessel in water at 20°C.

[0054] Preferably, the gradient aging process involves first heating to 150-180°C at a rate of 5°C / min and holding for 2-3 hours, then heating to 190-220°C at a rate of 3°C / min and holding for 2-5 hours.

[0055] Another object of the present invention is to provide an application of the aforementioned electrochemical migration-resistant tin-based solder alloy, the application being for solder joint packaging in AI chip GPU packaging, data center server power modules, automotive electronic ignition systems, or military electronic equipment.

[0056] In this invention, Sn powder serves as the solder matrix, providing basic soldering fluidity and conductivity. Its crystal structure is body-centered cubic, exhibiting good plasticity. The introduction of Ag powder and Cu powder is not simply to enhance strength, but rather to form a precisely proportioned Sn-Ag-Cu ternary eutectic phase (Sn6Ag4Cu1) with Sn. The melting point of this eutectic phase (217℃) is much lower than that of pure Sn (232℃), making it suitable for conventional SMT soldering processes (soldering temperature 240~260℃). More importantly, the atomic radii of Ag and Cu are 0.144nm and 0.128nm, respectively, both close to that of Sn (0.151nm), allowing them to dissolve into the Sn matrix to form a substitutional solid solution, resulting in a solid solution strengthening effect. Simultaneously, Cu can form a stable Cu6Sn5 intermetallic compound (IMC) with Sn, inhibiting excessive growth of IMC at the interface between the solder joint and the Cu substrate. This invention limits the amount of Ag powder to 3-6 parts and Cu powder to 1-2 parts. The core reason is that when Ag < 3 parts, the proportion of eutectic phase is insufficient, the melting point rises above 225℃, and components are easily damaged during soldering; when Ag > 6 parts, coarse Ag3Sn phases are formed, causing the solder joint elongation to drop below 20%; when Cu < 1 part, interfacial IMC growth is out of control, and the bonding strength decreases; when Cu > 2 parts, brittle Cu3Sn phases precipitate, significantly reducing impact resistance. The "eutectic phase + solid solution + fine-grained IMC" structure formed by the two provides a stable mechanical and welding basis for the solder.

[0057] In this invention, Zn powder serves as the active antioxidant component. Its standard electrode potential (-0.76V) is lower than that of Sn (-0.14V). In an electrochemical environment, Zn powder preferentially oxidizes over Sn, forming a dense ZnO passivation film (50-80nm thick). This film has a dense structure and strong adhesion, and can physically block Sn. 2+ The anodic dissolution and migration of Sn. Simultaneously, Zn can form a Sn-Zn solid solution with Sn, further enhancing the corrosion resistance of the matrix. A mixture of SnCl2・2H2O and citric acid (mass ratio 2:1) is a unique component of this invention, and its mechanism of action is "ion capture + composite passivation": SnCl2・2H2O releases Sn during the smelting process. 2+It reacts with ZnO to form a SnO2-ZnO composite passivation layer, further enhancing the membrane's impermeability; citric acid acts as a chelating agent, and its carboxyl group (-COOH) can react with free Sn... 2+ Ag + Formation of stable chelates (stability constant K > 10) 15 This prevents rapid migration of metal ions in an electric field. The mechanism for limiting Zn powder to 1-4 parts and composite salt to 40-60 parts is as follows: When Zn < 1 part, the passivation film is discontinuous and porous, failing to effectively block ions; when Zn > 4 parts, a Sn-Zn binary eutectic phase forms, leading to decreased high-temperature stability of the solder and easy softening at 150℃; when composite salt < 40 parts, the chelating ability is insufficient, with only a 30% decrease in ion migration rate; when composite salt > 60 parts, residual Cl... - It will react with Sn to form SnCl2, a readily soluble compound, which will actually accelerate corrosion.

[0058] In this invention, Nd(acac)3, a rare earth organometallic complex, is used for the first time. Its core advantages lie in its "dispersion + multifunctionality": ① The organic ligand acetylacetone group (acac) - ① It possesses oleophilic properties, and its wettability with the Sn matrix is ​​far superior to that of Nd₂O₃, which can prevent the agglomeration of rare earth elements; ② At high temperatures (880~920℃), acac - The ligand decomposes into CO2 and CH4 gases, releasing Nd2+. 3+ It can be dissolved into the Sn matrix or form the NdSn2 reinforcing phase with Sn, producing a dispersion strengthening effect; ③ The carbon free radicals (・C) generated by decomposition can repair microcracks in the matrix and improve the integrity of the solder joint. Synergistic effect of La powder and Nd(acac)3: La has a very low standard electrode potential and preferentially forms stable compounds with impurities (S, P, O) in the solder, purifying the matrix; at the same time, La can enhance the adhesion between the ZnO passivation film and the matrix, preventing the film from peeling off. The composition of Nd(acac)3 is limited to 0.5-1.5 parts, La powder to 0.5-2.5 parts, and the mass ratio of Zn to Nd(acac)3 is 2-3:1. The reasons are as follows: when Nd(acac)3 is less than 0.5 parts, the dispersion strengthening and crack repair effects are not obvious; when it is greater than 1.5 parts, residual carbon impurities will reduce the conductivity of the solder; when La is less than 0.5 parts, the impurity purification is incomplete; when it is greater than 2.5 parts, a brittle LaSn3 phase will be formed, causing the tensile strength of the solder joint to drop below 300 MPa; an imbalance in the ratio of the two will cause the passivation film and the strengthening phase to fail synergistically, and the migration resistance will decrease by 50%.

[0059] In this invention, Ti3C2Tx MXene is introduced into tin-based solder to construct a one-dimensional-two-dimensional multi-level barrier network with graphene and carbon nanotubes. The mechanism is as follows: ① Graphene (two-dimensional sheet) and Ti3C2Tx MXene (two-dimensional conductive sheet) are superimposed to form a "double-layer physical barrier," Sn 2+ ① A bypass diffusion path is required, extending the diffusion path by more than 80%; ② Carbon nanotubes (one-dimensional fibers) bridge the gaps between graphene and Ti3C2Tx MXene, avoiding the formation of "diffusion channels" and improving the mechanical stability of the network; ③ Ti3C2Tx MXene has high conductivity, which can balance the potential distribution on the solder joint surface, avoid local electric field concentration, and reduce the driving force for ion migration from the root; ④ The hydroxyl groups (-OH) on the surface of Ti3C2Tx MXene form hydrogen bonds with the Sn matrix, significantly improving the bonding force compared to graphene, solving the industry problem of poor bonding force between carbon materials and metal matrices. The composite system is limited to 40-60 parts, with a mass ratio of 1:3:2, because: <40 parts cannot form a complete barrier network; >60 parts cause carbon material agglomeration, destroying the continuity of the matrix and leading to a decrease in wettability during welding; an imbalance in the ratio will lead to an increase in network gaps and failure of the barrier effect.

[0060] In this invention, the traditional welding flux component KBF4 is introduced into the solder body to achieve integrated interface control of "melting-welding," with a unique mechanism: ① During the melting stage, KBF4 decomposes into BF3 gas above 800℃. BF3 has strong reducing properties and can remove the oxide film on the surface of the metal raw material, preventing oxidative impurities from affecting component mixing; ② During solidification, residual F... - It adsorbs onto the surfaces of IMCs such as Cu6Sn5 and Ag3Sn, inhibiting their excessive growth; ③ During the welding stage, the incompletely decomposed KBF4 acts as a flux, reducing the contact angle between the solder and the substrate, eliminating the need for additional flux and avoiding residual flux absorbing moisture and accelerating migration. The amount of KBF4 is limited to 0.1~0.5 parts because: <0.1 parts result in incomplete oxide film removal and uneven component mixing; >0.5 parts result in the corrosive nature of the decomposed KF, which can form SnF2 soluble compounds with Sn, compromising the reliability of the solder joint.

[0061] In this invention, Sb powder and Sn form a Sn-Sb solid solution. After Sb atoms dissolve into the Sn matrix, they hinder the diffusion of Sn atoms, thereby improving the high-temperature stability and creep resistance of the solder. Simultaneously, Sb refines the size of the Ag3Sn phase, preventing increased brittleness caused by its coarsening. The amount of Sb powder is limited to 1-3 parts because: less than 1 part results in only a slight improvement in creep resistance; more than 3 parts cause the solder melting point to rise above 230°C, and the Sn3Sb brittle phase to form, with elongation decreasing to below 18%.

[0062] In this invention, step S1 involves vacuum drying of the metal raw material (80~120℃ / 2~4h) to remove surface-adsorbed moisture (moisture content <0.01%), preventing bubble defects during smelting; grinding the composite component to ≤50μm increases the specific surface area and enhances its reactivity with the matrix; pretreatment with Nd(acac)3 and KBF4 (150~200℃ / 1~2h) induces partial coordination bond breakage, preparing Nd for subsequent in-situ reactions. 3+ This lays the groundwork for release and avoids incomplete ligand decomposition leaving impurities.

[0063] In this invention, the high vacuum and argon protection in step S2 can prevent the oxidation of metal raw materials; the precise heating rate (5~10℃ / min) can prevent local overheating and Sn volatilization; and the moderate stirring (100~200r / min) can ensure that the metal components are uniformly mixed and the eutectic phase ratio has a low deviation.

[0064] In this invention, step S3 is the core of the process, which involves adding components in stages: first, adding composite salt and ceramic particles, and holding at 750~850℃ to ensure uniform dispersion; then adding rare earth complexes and carbon-based composite systems, and heating to 880~920℃ for in-situ reaction to ensure complete decomposition of Nd(acac)3 and stable bonding between Ti3C2Tx MXene and the matrix; high stirring rate (450~550r / min) can break the agglomeration of carbon materials and ceramic particles; the synergistic structure of "reinforcing phase-barrier network-passivation film" formed by the in-situ reaction is the key to excellent migration resistance.

[0065] In this invention, step S4 defines a two-stage rapid cooling: the first stage of rapid cooling (50~80℃ / min) can suppress grain growth, increase the number of grain boundaries, and hinder ion diffusion; the second stage of slow cooling (10~20℃ / min) can release internal stress and prevent alloy cracking.

[0066] In this invention, step S5 employs a gradient aging process for heat treatment: low-temperature pre-aging (150~180℃ / 2~3h) promotes the precipitation of fine Ag3Sn phases, resulting in dispersion strengthening; high-temperature final aging (190~220℃ / 2~5h) ensures uniform distribution of the NdSn2 phase and repairs microcracks generated during cooling; gradient heating avoids phase aggregation and ensures uniform distribution of the strengthening phase.

[0067] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0068] The important raw material information used in the embodiments and comparative examples of this invention is as follows: Neodymium acetylacetonate, CAS: 14589-38-9, purchased from Shanghai Myriel Biochemical Technology Co., Ltd. Graphene, CAS: 1034343-98-0, purchased from Zhejiang Yamei Nanotechnology Co., Ltd. Carbon nanotubes, CAS: 308068-56-6, purchased from Anhui Kerun Nanotechnology Co., Ltd. Ti3C2T x MXene, CAS: 12363-89-2, purchased from Beijing Huawirui Chemical Technology Co., Ltd. Potassium fluoroborate, CAS: 14075-53-7, Nanjing Chemical Reagent Co., Ltd.; TiC (nano titanium carbide), CAS: 12070-08-5, purchased from Beijing Huawirui Chemical Technology Co., Ltd. SiC (nano silicon carbide), CAS: 409-21-2, purchased from Zhejiang Yamei Nanotechnology Co., Ltd.

[0069] Example 1 1) Alloy composition (parts by mass): 100 parts Sn powder, 3 parts Ag powder, 1 part Cu powder, 1 part Zn powder, 0.5 parts Nd(acac)3 (Zn:Nd(acac)3=2:1), 40 parts of a mixture of SnCl2・2H2O and citric acid (2:1), 60 parts of a mixture of TiC and SiC (3:2), 40 parts of a graphene / carbon nanotube / Ti3C2Tx MXene composite system (1:3:2, graphene thickness 1~5nm, carbon nanotube diameter 20~50nm, length 1~5μm, Ti3C2Tx sheet 0.5~2μm, thickness 5~10nm), 0.5 parts La powder, 1 part Sb powder, 0.1 parts KBF4.

[0070] 2) Preparation process S1: Raw material pretreatment: Metal raw materials (Sn, Ag, Cu, Zn, La, Sb) were placed in a vacuum drying oven and dried at 80℃ for 2 hours; Composite components (SnCl2・2H2O-citric acid, TiC-SiC, graphene / carbon nanotubes / Ti3C2Tx MXene) were ground using a planetary ball mill with an agate ball-to-material ratio of 10:1 and a rotation speed of 300 r / min until the particle size was ≤50μm; Nd(acac)3 and KBF4 were mixed and placed in an inert atmosphere furnace (argon flow rate 5L / min) for pretreatment at 150℃ for 1 hour; S2: Vacuum melting: The metal raw material is added to an alumina crucible, and a vacuum of 10 is applied. -3Pa, purged with argon to 0.1 MPa, heated to 800℃ at 5℃ / min, held at that temperature for 30 min, and stirred at 100 r / min to obtain an alloy melt; S3: Composite Modification and In-situ Reaction: Under argon protection, SnCl2・2H2O-citric acid and TiC-SiC were added first, and the mixture was kept at 800℃ for 20 min with a stirring rate of 300 r / min; then Nd(acac)3-KBF4 and a carbon-based composite system were added, and the temperature was increased to 880℃ at 5℃ / min, and the mixture was reacted in-situ for 30 min with a stirring rate of 450 r / min to obtain a composite melt; S4: Rapid cooling: The molten metal is poured into a 200°C copper mold and cooled to 200°C at 50°C / min, then cooled to room temperature at 10°C / min to obtain a cast alloy; S5: Gradient aging heat treatment: The as-cast alloy is placed in a tube furnace, argon gas is introduced (5L / min), the temperature is increased to 500℃ at 10℃ / min, and held for 6 hours to homogenize; the temperature is increased to 580℃ at 5℃ / min, and held for 2 hours to solidify, and then quenched to 20℃; the temperature is then increased to 150℃ at 5℃ / min, held for 2 hours, and then increased to 180℃ at 3℃ / min, held for 2 hours, and then cooled to room temperature with the furnace.

[0071] Example 2 1) Alloy composition (parts by mass): 100 parts Sn powder, 4.5 parts Ag powder, 1.5 parts Cu powder, 2.5 parts Zn powder, 1.0 parts Nd(acac)3 (Zn:Nd(acac)3=2.5:1), 50 parts of a mixture of SnCl2・2H2O and citric acid (2:1), 70 parts of a mixture of TiC and SiC (3:2), 50 parts of a graphene / carbon nanotube / Ti3C2Tx MXene composite system (1:3:2), 1.5 parts La powder, 2 parts Sb powder, and 0.3 parts KBF4.

[0072] 2) Preparation process S1: Raw material pretreatment: The metal raw materials (Sn powder, Ag powder, Cu powder, Zn powder, La powder, Sb powder) were placed in a vacuum drying oven and dried at 100℃ for 3h; the composite components (SnCl2・2H2O-citric acid mixture, TiC-SiC mixture, graphene / carbon nanotube / Ti3C2Tx MXene composite system) were ground using a planetary ball mill with an agate ball-to-material ratio of 10:1 and a grinding speed of 300r / min until the particle size was ≤30μm; Nd(acac)3 and KBF4 were mixed in proportion and placed in an inert atmosphere furnace (argon flow rate 5L / min) for pretreatment at 180℃ for 1.5h to induce partial coordination bond breakage.

[0073] S2: Vacuum Melting: Add the pretreated metal raw material to the alumina crucible of the vacuum induction melting furnace, close the furnace door, and evacuate to 5×10⁻⁶. -4 Pa, fill the furnace with argon gas of ≥99.99% purity until the pressure inside the furnace is 0.1MPa; heat to 850℃ at a heating rate of 7℃ / min, hold for 45min, and mechanically stir at a stirring rate of 150r / min during the process to obtain a uniform alloy melt.

[0074] S3: Composite Modification and In-situ Reaction: Under argon protection, the pretreated SnCl2・2H2O-citric acid mixture and TiC-SiC mixture were added to the alloy melt in sequence, and the temperature was maintained at 800℃. The mixture was kept at a stirring rate of 350r / min for 25min. Then, the pretreated Nd(acac)3 and KBF4 mixture and graphene / carbon nanotube / Ti3C2Tx MXene composite system were added. The temperature was increased to 900℃ at a heating rate of 5℃ / min, and the in-situ reaction was carried out for 35min. During this period, the stirring rate was increased to 500r / min. The total holding time (including in-situ reaction) was 60min, and the composite melt was obtained.

[0075] S4: Rapid cooling: Open the discharge valve of the smelting furnace, pour the composite molten metal into a copper mold preheated to 200°C, cool it to 230°C at a cooling rate of 65°C / min, and then transfer it to an air cooling device to cool it to room temperature at a cooling rate of 15°C / min to obtain the cast alloy.

[0076] S5: Gradient aging heat treatment: The as-cast alloy is placed in a tubular heat treatment furnace. Argon gas (flow rate 5L / min) is first introduced to remove air from the furnace. The temperature is increased to 530℃ at 10℃ / min and held for 8 hours for homogenization treatment. Then, the temperature is increased to 600℃ at 5℃ / min and held for 3 hours for solution treatment. After treatment, the alloy is quickly placed in 20℃ cold water for quenching and cooling to room temperature. Finally, a gradient aging process is adopted: the temperature is increased to 170℃ at 5℃ / min and held for 2.5 hours. Then, the temperature is increased to 200℃ at 3℃ / min and held for 3.5 hours. The alloy is then cooled to room temperature in the furnace.

[0077] Example 3 1) Alloy composition (parts by mass): 100 parts Sn powder, 6 parts Ag powder, 2 parts Cu powder, 4 parts Zn powder, 1.5 parts Nd(acac)3 (Zn:Nd(acac)3=2.7:1), 60 parts of a mixture of SnCl2・2H2O and citric acid (2:1), 80 parts of a mixture of TiC and SiC (3:2), 60 parts of a graphene / carbon nanotube / Ti3C2Tx MXene composite system (1:3:2), 2.5 parts La powder, 3 parts Sb powder, and 0.5 parts KBF4.

[0078] 2) Preparation process S1: Raw material pretreatment: Metal raw materials (Sn powder, Ag powder, Cu powder, Zn powder, La powder, Sb powder) were placed in a vacuum drying oven and dried at 120℃ for 4 hours; Composite components (SnCl2・2H2O-citric acid mixture, TiC-SiC mixture, graphene / carbon nanotube / Ti3C2Tx MXene composite system) were ground using a planetary ball mill with an agate ball-to-material ratio of 10:1 and a grinding speed of 300 r / min until the particle size was ≤50μm; Nd(acac)3 and KBF4 were mixed in proportion and placed in an inert atmosphere furnace (argon flow rate 5L / min) for pretreatment at 200℃ for 2 hours to induce partial coordination bond breakage.

[0079] S2: Vacuum Melting: The pretreated metal raw material is added to the alumina crucible of the vacuum induction melting furnace, and the furnace door is closed before evacuating to 10°C. -4 Pa, fill the furnace with argon gas of ≥99.99% purity until the pressure inside the furnace is 0.1MPa; heat to 900℃ at a heating rate of 10℃ / min, hold for 60min, and mechanically stir at a stirring rate of 200r / min during the process to obtain a uniform alloy melt.

[0080] S3: Composite Modification and In-situ Reaction: Under argon protection, the pretreated SnCl2・2H2O-citric acid mixture and TiC-SiC mixture were added to the alloy melt in sequence, and the temperature was maintained at 850℃. The mixture was held at a stirring rate of 400r / min for 30min. Then, the pretreated Nd(acac)3 and KBF4 mixture and graphene / carbon nanotube / Ti3C2Tx MXene composite system were added. The temperature was increased to 920℃ at a heating rate of 5℃ / min, and the in-situ reaction was carried out for 40min. During this period, the stirring rate was increased to 550r / min. The total holding time (including in-situ reaction) was 70min, and the composite melt was obtained.

[0081] S4: Rapid cooling: Open the discharge valve of the smelting furnace, pour the composite melt into a copper mold preheated to 200°C, cool it to 250°C at a cooling rate of 80°C / min, and then transfer it to an air cooling device to cool it to room temperature at a cooling rate of 20°C / min to obtain the cast alloy.

[0082] S5: Gradient aging heat treatment: The as-cast alloy is placed in a tubular heat treatment furnace. Argon gas (flow rate 5L / min) is first introduced to purge the air in the furnace. The temperature is increased to 550℃ at 10℃ / min and held for 10h for homogenization treatment. Then, the temperature is increased to 620℃ at 5℃ / min and held for 4h for solution treatment. After the treatment, the alloy is quickly placed in 20℃ cold water for quenching and cooling to room temperature. Finally, a gradient aging process is adopted: the temperature is increased to 180℃ at 5℃ / min and held for 3h. Then, the temperature is increased to 220℃ at 3℃ / min and held for 5h. The alloy is then cooled to room temperature in the furnace.

[0083] Comparative Example 1 Except for replacing 50 parts of the graphene / carbon nanotube / Ti3C2Tx MXene composite system with 50 parts of single graphene, the other component types, component mass parts, process flow and process parameters are completely consistent with Example 2.

[0084] Comparative Example 2 Except for replacing Nd(acac)3 with 1.0 part Nd2O3, the other component types, component mass parts, process flow and process parameters are completely consistent with those in Example 2.

[0085] Comparative Example 3 Except for changing step S3 to "add all composite components at once, keep warm at 800℃ for 60 min, and stir at 350 r / min", and canceling the in-situ reaction heating (not heating to 900℃), the other component types, component mass fractions, process flow and process parameters are completely consistent with Example 2.

[0086] Comparative Example 4 Except for changing step S5 to "homogenization at 530℃ for 8 hours, solution treatment at 600℃ for 3 hours, and aging at 200℃ for 6 hours after quenching", the other component types, component mass fractions, process flow and process parameters are completely consistent with those in Example 2.

[0087] Comparative Example 5 Except for replacing the mixture of TiC and SiC (3:2) with 70 parts of single TiC, the other component types, component mass parts, process flow and process parameters are completely consistent with Example 2.

[0088] Comparative Example 6 Except for the absence of KBF4, the types of other components, component mass fractions, process flow and process parameters are completely consistent with those in Example 2.

[0089] Performance test results: The performance test results for the embodiments and comparative examples are shown in Table 1 below.

[0090] Table 1. Performance Test Table for Examples and Comparative Examples

[0091] After the technical solutions were changed, the performance of the tin-based solder alloys in Comparative Examples 1 to 7 was significantly reduced. In particular, the electrochemical migration failure time was generally less than 350s, which was far lower than that of the tin-based solder alloys prepared in the examples.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A tin-based solder alloy resistant to electrochemical migration, characterized in that, By weight, it includes the following components: 100 parts Sn powder, 3-6 parts Ag powder, 1-2 parts Cu powder, 1-4 parts Zn powder, 0.5-1.5 parts neodymium acetylacetone, 40-60 parts of a mixture of SnCl2·2H2O and citric acid, 60-80 parts of a mixture of TiC and SiC, 40-60 parts of a graphene / carbon nanotube / Ti3C2Tx MXene composite system, 0.5-2.5 parts La powder, 1-3 parts Sb powder, and 0.1-0.5 parts potassium fluoroborate.

2. The tin-based solder alloy resistant to electrochemical migration according to claim 1, characterized in that, In the graphene / carbon nanotube / Ti3C2Tx MXene composite system, the mass ratio of graphene / carbon nanotube / Ti3C2Tx MXene is 1:3:2; The graphene has a thickness of 1-5 nm, the carbon nanotubes have a diameter of 20-50 nm and a length of 1-5 μm, and the Ti3C2Tx MXene sheets have a size of 0.5-2 μm and a thickness of 5-10 nm.

3. The tin-based solder alloy resistant to electrochemical migration according to claim 1, characterized in that, In the mixture of SnCl2・2H2O and citric acid, the mass ratio of SnCl2・2H2O to citric acid is 2:1; In the mixture of TiC and SiC, the mass ratio of TiC to SiC is 3:

2.

4. A method for preparing an electrochemically migratable tin-based solder alloy as described in any one of claims 1 to 3, characterized in that, Includes the following steps: S1: Vacuum dry Sn powder, Ag powder, Cu powder, Zn powder, La powder, and Sb powder; grind the mixture of SnCl2·2H2O and citric acid, the mixture of TiC and SiC, and the graphene / carbon nanotube / Ti3C2Tx MXene composite system respectively; mix neodymium acetylacetone and potassium fluoroborate and preheat; S2: The dried Sn powder, Ag powder, Cu powder, Zn powder, La powder and Sb powder are vacuum melted to obtain an alloy melt; S3: First, the mixture of ground SnCl2・2H2O and citric acid, and the mixture of TiC and SiC are added to the alloy melt in sequence for heat preservation; after heat preservation, the mixture of pretreated neodymium acetylacetone and potassium fluoroborate and the graphene / carbon nanotube / Ti3C2Tx MXene composite system are added to carry out in-situ reaction to obtain the composite melt. S4: Pour the composite melt into a mold and cool it twice to obtain a cast alloy; S5: The as-cast alloy is subjected to homogenization and solution treatment in sequence, and then quenched and cooled to room temperature; then heat treatment is carried out by gradient aging process, and cooled to room temperature in furnace to obtain a tin-based solder alloy resistant to electrochemical migration.

5. The method for preparing the electrochemically migratable tin-based solder alloy according to claim 4, characterized in that, In step S1, the vacuum drying temperature is 80~120℃ and the time is 2~4h; The grinding medium is agate balls, with a ball-to-material ratio of 10:1, a grinding speed of 300 r / min, and grinding until the particle size is ≤50μm; The preheating is performed at 150~200℃ for 1~2 hours under an inert atmosphere.

6. The method for preparing the electrochemically migratable tin-based solder alloy according to claim 4 or 5, characterized in that, In step S2, the vacuum melting specifically involves adding vacuum-dried Sn powder, Ag powder, Cu powder, Zn powder, La powder, and Sb powder into the reactor, closing the furnace door, and then drawing a vacuum to ≤10. -3 Pa, fill the furnace with argon gas to a pressure of 0.1 MPa, heat to 800-900℃ at a rate of 5-10℃ / min, hold for 30-60 min, and stir at a rate of 100-200 r / min during the process.

7. The method for preparing the electrochemically migratable tin-based solder alloy according to claim 6, characterized in that, In step S3, the temperature for heat preservation is 750~850℃, the heat preservation time is 20~30min, and the stirring is carried out at a rate of 300~400r / min during the heat preservation period; The conditions for the in-situ reaction are as follows: the temperature is increased to 880~920℃ at a rate of 5℃ / min and the reaction is carried out for 30~40min, during which the mixture is stirred at a rate of 450~550r / min.

8. The method for preparing the electrochemically migrating tin-based solder alloy according to claim 4, 5, or 7, characterized in that, In step S4, the mold is a copper mold preheated to 200°C; The first cooling process involves cooling to 200-250°C at a rate of 50-80°C / min; the second cooling process involves cooling to room temperature at a rate of 10-20°C / min.

9. The method for preparing the electrochemically migratable tin-based solder alloy according to claim 8, characterized in that, In step S5, the homogenization process involves heating at 10℃ / min to 500~550℃ and holding at that temperature for 6~10h. The solution treatment involves heating to 580~620℃ at a rate of 5℃ / min and holding at that temperature for 2~4 hours. The quenching and cooling process involves immersing the equipment in water at 20°C. The gradient aging process involves first heating to 150-180℃ at a rate of 5℃ / min and holding for 2-3 hours, then heating to 190-220℃ at a rate of 3℃ / min and holding for 2-5 hours.

10. The application of a tin-based solder alloy resistant to electrochemical migration as described in any one of claims 1 to 3, characterized in that, The applications are for solder joint packaging in AI chip GPUs, data center server power modules, automotive electronic ignition systems, or military electronic equipment.

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