A max phase reinforced three-dimensional network tin-based lead-free solder and a preparation method thereof

Abstract

The application discloses a MAX phase reinforced three-dimensional network tin-based lead-free solder and a preparation method thereof, and belongs to the technical field of lead-free solder. The MAX phase reinforced three-dimensional network tin-based lead-free solder is characterized in that the MAX phase reinforcing phase is distributed in the form of a three-dimensional continuous network skeleton at the grain boundary of a tin-based lead-free solder matrix; and the MAX phase reinforcing phase forms a continuous network penetrating through the whole tin-based lead-free solder matrix. The application also discloses an application of the MAX phase reinforced three-dimensional network tin-based lead-free solder in a high-temperature, high-load and high-frequency vibration scene. Through process innovation and performance optimization, the application aims to finally prepare a "high-strength, high-plasticity and high-temperature stability" tin-based three-dimensional network composite solder, solves the problem that a traditional tin-based single-component lead-free solder is prone to deformation and cracking due to thermal stress and mechanical load, improves the reliability of electronic packaging, and expands the application range of the tin-based lead-free solder in high-demand fields.

Description

Technical Field

[0001] This invention relates to a MAX phase-enhanced three-dimensional network tin-based lead-free solder and its preparation method, belonging to the field of lead-free solder technology. Background Technology

[0002] With the arrival of the "post-Moore's Law era," electronic products are developing towards lighter weight, smaller size, and higher performance. The widespread use of high-temperature and high-power devices is constantly increasing the demands on packaging. To meet the ever-growing performance requirements of lead-free solder, tin-lead solder is the most widely used solder in the traditional packaging industry. However, lead, as a heavy metal that is highly harmful to both the environment and humans, not only negatively impacts human health but also causes significant environmental pollution. Due to environmental protection policies and increasing environmental awareness, the replacement of Sn-Pb solder with lead-free solder has become an inevitable trend, making the promotion of lead-free solder imperative. Compared to traditional tin-lead solder, lead-free solder offers many advantages. It is not only environmentally friendly but also possesses excellent mechanical and comprehensive mechanical properties, such as high strength, good tensile strength, and good thermal fatigue resistance. It also has suitable melting point, thermal conductivity, and electrical conductivity. The wettability of materials used in electronic devices is very important, but lead-free solder does not have outstanding wettability. To enhance the wettability of lead-free solder, different reinforcing phases can be added to form composite solder. The resulting composite solder has better wettability, which not only ensures good electrical connection, improves production efficiency and mechanical strength, but also ensures uniform solder joint formation and can adapt to more complex electronic device structures.

[0003] Currently, strengthening methods for tin-based lead-free solders are a research hotspot, aiming to overcome their inherent mechanical property deficiencies. These methods mainly include particle reinforcement, fiber / whisker reinforcement, alloying modification, and microstructure control. Among these, adding MAX phases falls under particle reinforcement methods. MAX phases combine the advantages of both metals and ceramics, exhibiting good interfacial bonding, and represent a current research frontier. Current research trends favor the combined use of multiple methods, such as synergistic reinforcement with "nanoparticles + rare earth elements." "MAX phase + three-dimensional structural design" aims to address the distribution and interfacial challenges of traditional particle reinforcement, and this is one of the most promising directions.

[0004] The inherent drawback of existing tin-based single-component lead-free solders is that their mechanical properties are difficult to meet the requirements of high-reliability scenarios.

[0005] The traditional tin-based composite solder preparation process has several drawbacks: uneven dispersion of the reinforcement, poor interfacial bonding, and large fluctuations in mechanical properties. Furthermore, existing tin-based composite solders often employ a "high-energy powder mixing + melting / hot pressing" process to add reinforcements (such as Al2O3 or SiC particles). However, high-energy powder mixing easily damages the reinforcement structure (e.g., particle breakage), and during melting, the density difference between the reinforcement and the Sn matrix is ​​significant (e.g., SiC density is 3.2 g / cm³). 3 vs Sn density 7.3g / cm³ 3 This can easily lead to sedimentation / floating, resulting in a non-uniform distribution of reinforcement with "agglomerated blocks and local voids". The solder becomes brittle (easily broken) in some areas due to reinforcement agglomeration, while other areas remain low in strength (easily deformed) due to the absence of reinforcement. The overall mechanical properties (such as tensile strength and hardness) fluctuate by more than 20%, which cannot meet the performance stability requirements of electronic packaging. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for preparing a MAX phase-reinforced three-dimensional network tin-based lead-free solder. The unique feature is that a "three-stage pressureless sintering" process is innovatively applied when preparing the MAX-reinforced phase. In addition, a "liquid dispersion + wet ball milling" process is adopted, and a "three-dimensional oscillating powder mixing + cold pressing" process is used when preparing the composite solder powder.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] In this invention, the three-stage pressureless sintering refers to the design of the temperature program, which is mainly divided into three stages (300℃ / 15min→1000℃ / 20min→1330℃ / 2h).

[0009] Traditional pressureless sintering often employs a "single-stage heating" or "two-stage (pre-sintering + high-temperature sintering)" approach, which suffers from common problems such as "insufficient degassing, uncontrolled mesophase, and volatilization of A-site elements." The core innovation of this process lies in constructing a universal temperature control framework based on the "multi-step reaction thermodynamics and kinetic matching" of the MAX phase: First, the low-temperature pre-sintering stage (300℃ / 15min) adopts a universal "degassing and A-site preservation" strategy. 300℃ is the "universal equilibrium temperature" for MAX phase preparation—① efficiently removing adsorbed water and trace amounts of organic binder in a short 15min time, avoiding density reduction caused by gas residue; ② lower than the significant volatilization temperature of most A-site elements (Al>600℃, Sn>500℃, Zn>550℃), maximizing the retention of A-site elements and providing a precise compositional basis for subsequent multi-element synergistic reactions, adapting to the "A-site preservation" requirements of different MAX phases such as Ti2AlC, Ti3SnC2, and Ti2ZnC.

[0010] Secondly, the intermediate temperature transition section (1000℃ / 20min) is the "directed regulation of intermediate phases" across MAX phases. 1000℃ is the general temperature range for "rapid element diffusion + controllable generation of intermediate phases" in MAX phase systems. ① 20min of holding promotes uniform diffusion of M, A, and X elements across particle boundaries, solving the common problem of "uneven diffusion" in multi-component MAX phases. ② It guides different MAX phases to generate "intermediate phases that are easily converted into the target phase" (rather than stable impurity phases). For example, the Ti2AlC system generates TiAl3 (rather than TiC), and the Ti3SnC2 system generates Ti3Sn (rather than SnC), providing "highly active precursors" for high-temperature synthesis, shortening the target phase formation time, and adapting to the differences in reaction pathways of different MAX phases.

[0011] Finally, the high-temperature sintering section (1330℃ / 2h) represents a low-temperature, short-time "universal synthesis and performance synergy." ① The sintering temperature is reduced by 70-270℃ compared to existing technologies. At 1330℃, the vapor pressure of most A-site elements (Al, Sn, Zn) is only 50%-70% of that at traditional high temperatures, and the volatilization loss rate can be controlled within 5%, adapting to the "controlled volatilization" requirements of different MAX phases. ② The holding time is shortened to 2h, avoiding excessive grain growth (expected average grain size <2μm). Mechanical properties such as hardness and fracture toughness are improved through "fine grain strengthening," and the target phase formation reaction (M...) of most MAX phases occurs at 1330℃. x A γ +MC x →M n+1 AX n ① The kinetic rate is optimal, ensuring complete reaction; ② The pressureless mode does not require high-pressure equipment, and can prepare large-size and complex-shaped samples. The three-section frame can be adapted to different MAX phases without major adjustments (only the temperature of the high-temperature section needs to be finely adjusted ±50℃ according to the target phase), and its universality is far superior to traditional processes.

[0012] Liquid dispersion process refers to the process of dispersing powder into a liquid using magnetic stirring and a dispersant.

[0013] Wet ball milling refers to the process of ball milling powder by combining "vibration and rotation" while retaining the liquid after dispersion treatment.

[0014] Three-dimensional oscillating powder mixing specifically refers to the use of an all-round ball mill to carry out "three-dimensional spatial composite motion" and "ball milling media impact grinding". Through a special driving structure, the ball mill jar can simultaneously complete high-frequency oscillation and rotational motion in the X, Y and Z directions. The grinding balls inside the jar generate impact, grinding and shearing forces as the jar body moves, while driving the powder to make three-dimensional complex flow, ultimately achieving the integration of mixing and ultrafine dispersion.

[0015] Cold pressing refers to the process of cold pressing sample powder into a blank, followed by sintering for strengthening. Three-dimensional oscillating powder mixing not only reduces ball milling resistance but also prevents secondary agglomeration, improving mixing efficiency and uniformity, and protecting the integrity of the reinforcement structure. The core function of cold pressing is to achieve "uniform distribution of reinforcement + preliminary densification of the blank," achieving a uniform three-dimensional network distribution of reinforcement while preserving the integrity of the reinforcement structure. This offers significant advantages and is well-suited to the molding requirements of composite powders. Furthermore, through the effect of the three-dimensional network reinforcement, it significantly improves the room-temperature mechanical properties and high-temperature stability of tin-based solders, making them suitable for "high-temperature, high-load, high-frequency vibration" scenarios such as automotive electronics and aerospace. This addresses the issue of easy solder joint failure in single-component tin-based lead-free solders, improving the reliability of electronic packaging.

[0016] Through the above-mentioned process innovations and performance optimizations, this invention ultimately aims to prepare a tin-based three-dimensional mesh composite solder with "high strength, high plasticity, and high temperature stability," solving the problem that traditional tin-based single-component lead-free solder is prone to deformation and cracking due to thermal stress and mechanical loads, improving the reliability of electronic packaging, and expanding the application range of tin-based lead-free solder in high-requirement fields.

[0017] This invention addresses the inherent mechanical defects of traditional tin-based lead-free solders, overcoming the technical difficulty of forming a three-dimensional network structure in existing technologies. It solves problems such as the inability to construct a "preliminary network skeleton" during powder mixing, the destruction of the reinforcing phase continuity during high-temperature sintering, and the hindering of particle bonding due to the lack of reinforcing phase pretreatment. The invention proposes a MAX phase-reinforced three-dimensional network tin-based lead-free solder. The MAX phase reinforcing phase is distributed in the form of a three-dimensional continuous network skeleton at the grain boundaries of the tin-based lead-free solder matrix. The reinforcing phase particles are interconnected to form "network channels" and encapsulate the matrix phase grains. The matrix grains are "wrapped" by the network reinforcing phase, forming a nested structure of "reinforcing phase skeleton - matrix grains." The reinforcing phase forms a "continuous network" that runs through the entire matrix, exhibiting strong structural integrity and no obvious voids. Relying on the synergistic effect of grain boundary strengthening and network support (the continuous network reinforcing phase locks the grain boundaries, limiting matrix grain deformation; the network skeleton directly bears the load, dispersing local stress), the strengthening efficiency is higher and the performance is more stable.

[0018] The aforementioned MAX phase is a type of molecular formula M n+1 AX n Non-van der Waals layered compounds are a novel type of machinable ceramic material, consisting of a hexagonal layered structure composed of a metallic element (M), a main group element (A), and carbon / nitrogen elements (X), with the general chemical formula M. n+1 AX n Where M represents a transition metal, A is a group III / IVA element, and X is C or N. A schematic diagram of the crystal structure of a conventional MAX phase is shown below. Figure 1 As shown.

[0019] The matrix phase in the aforementioned composite solder includes Sn-Cu alloy, Sn-Ag alloy, Sn-In alloy, Sn-Zn alloy, and Sn-Ag-Cu alloy.

[0020] The core of the preparation method for the aforementioned MAX / Sn-based three-dimensional network lead-free composite solder is to prepare the MAX reinforcing phase using pressureless sintering, liquid dispersion, and wet ball milling processes; then, a tin-based lead-free three-dimensional network composite solder is prepared using three-dimensional oscillating powder mixing and cold pressing processes. After adding the MAX phase, the tin-based lead-free solder forms a three-dimensional network structure. The difficulty in forming this network structure lies in achieving uniformity and controlling the particle size of the network structure itself. This invention improves uniformity and controls particle size through pressureless sintering, liquid dispersion, wet ball milling, three-dimensional oscillating powder mixing, and in-situ preparation processes.

[0021] Existing technologies present numerous technical challenges in forming this three-dimensional network structure. To address the difficulty of particle bonding during the powder mixing stage, this invention improves upon traditional processes in preparing the MAX reinforcing phase. Building upon the "three-stage pressureless sintering" method, it applies a "liquid dispersion + wet ball milling" process. Furthermore, the preparation of the composite solder powder utilizes a "three-dimensional oscillating powder mixing + cold pressing" process. Through the improvements of this invention, a preliminary network of "uniform distribution + continuous connection" is formed, without agglomeration / vacuum, laying the foundation for subsequent molding. Addressing the problems of sedimentation and pressure during cold pressing, this invention utilizes the self-lubricating properties of the MAX phase, eliminating the need for a release agent, preventing network damage during demolding, inhibiting reinforcement sedimentation, and ensuring network symmetry. To address the continuity problem in the sintering stage, low-temperature sintering at 200℃ (holding for 3 hours) is adopted, preserving the preliminary network skeleton, ensuring stable reinforcement particle size (no growth), and achieving network continuity of over 90%. To address the problem of interfacial impurities hindering connection, the reinforcement phase pretreatment process of this invention is: acid washing (removing oxides) → centrifugation (separating impurities) → drying (ensuring cleanliness), improving particle surface cleanliness, increasing interparticle bonding strength by over 30%, and reducing network "fragmentation" rate to below 5%.

[0022] Specifically, the raw material powder is first weighed according to the chemical ratio of each element in the MAX phase solid solution; then the weighed powder is mixed. The preparation method of the above-mentioned MAX / Sn-based alloy composite solder includes the following steps:

[0023] S1: Pour the pre-weighed raw material powder into a stainless steel ball mill jar, mix the grinding balls and powder according to the corresponding mass ratio, and use an all-around ball mill to ball mill and mix them.

[0024] S2: The mixed powder was sintered in a tube furnace and then the MAX reinforced phase powder was prepared using a three-stage pressureless sintering process.

[0025] S3: Take out the sintered powder, slowly pour the dispersant into the ethanol solvent under magnetic stirring, then add the powder in batches and continue stirring until the particles are completely dispersed.

[0026] S4: While retaining the liquid after dispersion treatment, ball milling is performed. Grinding balls and powder are prepared according to the corresponding mass ratio, and ball milling is performed using an all-around ball mill to obtain MAX phase micro-nano powder.

[0027] S5: Acid wash and centrifuge the MAX phase micro-nano powder, and then put the deion tube of the centrifuged powder into the drying oven to dry it to obtain dry mixed powder;

[0028] S6: Mix Sn-based alloy powder with the prepared MAX phase powder and put them into an all-round ball mill, and mix the powder according to the corresponding ball-to-powder ratio;

[0029] S7: Take out the uniformly mixed powder and cold press it to obtain a green body;

[0030] S8: The green blank is placed in a tube furnace and sintered under a protective atmosphere, and then cooled with the furnace to obtain MAX / Sn-based alloy composite solder.

[0031] Preferably, in S1, the mass ratio of agate grinding balls to powder to be treated is 10:1, the frequency of the omnidirectional ball mill is 5-40Hz, the ball milling time is 12-48 hours, and the milling is stopped for 10-15 minutes every 1-2 hours.

[0032] Preferably, in step S2, the temperature program for the tubular furnace is set as follows: 300℃ for 15 minutes, 1000℃ for 20 minutes, and 1330℃ for 2 hours, followed by furnace cooling. The specific temperature program is shown in Table 1 below.

[0033] Table 1 Temperature setting procedure for pressureless sintering in a vacuum tube furnace

[0034] step temperature time heating rate 1 RT~300℃ 30min 10℃ / min 2 300℃ 15min 0 3 300~1000℃ 1 hour 10 minutes 10℃ / min 4 1000℃ 20min 0 5 1000~1330℃ 1h6min 5℃ / min 6 1330℃ 2h 0

[0035] Specifically, the low-temperature preheating section (300℃ / 15min): the tube furnace is heated to 300℃ at a rate of 10℃ / min and held for 15min;

[0036] Medium temperature transition section (1000℃ / 20min): The tube furnace is heated from 300℃ to 1000℃ at a rate of 10℃ / min and held for 20min;

[0037] High-temperature sintering section (1330℃ / 2h): The tubular furnace is heated from 1000℃ to 1330℃ at a rate of 5℃ / min and held for 2h.

[0038] Preferably, in S3, the magnetometer speed is 300-500 r / h, ethanol is used as the dispersion medium, wherein the purity of ethanol is ≥99.7%, the dispersant is sodium dodecyl benzoate (addition amount is 0.5-1% of the powder mass), and the amount of powder to be treated is 0.5-2% of the dispersion liquid mass.

[0039] Preferably, in S4, the ratio of agate grinding balls to wet powder balls to be treated is 10:1, the frequency of the omnidirectional ball mill is 5-40Hz, the ball milling is performed for 12-24 hours, and the milling is stopped for 10-15 minutes every 1-2 hours.

[0040] Preferably, in step S5, 1-1.5g of ball-milled MAX phase powder is added to each centrifuge tube, along with 0.5-2mol / L dilute hydrochloric acid, wherein the ratio of acid to MAX phase powder is 30:1~50:1 (mass ratio), and the mixture is allowed to stand for 12-24 hours. When setting the parameters of the centrifuge, the rotation speed is set to 8000-10000rpm and the time is set to 5-10min. The drying oven temperature is 50-60℃ for drying.

[0041] Preferably, in S6, the mass percentage of Sn-based alloy powder is 95-99%, and the mass percentage of the prepared MAX phase powder is 1-5%; preferably, the mass percentage of Sn-based alloy powder is 95%, and the mass percentage of the prepared MAX phase powder is 5%; the ratio of agate grinding balls to powder balls to be treated is 5:1, the frequency of the omnidirectional ball mill is 5-40Hz, the ball milling is performed for 12-24 hours, and the milling is stopped for 10-15 minutes every 1-2 hours.

[0042] Preferably, in S7, the cold pressing process is as follows: at room temperature, the mixed powder is held under pressure of 5-10 MPa for 1-5 minutes to form a blank.

[0043] Preferably, in step S8, the pressed green blank is placed in a small crucible, and the tube furnace is repeatedly evacuated and purged with argon gas 5-7 times. The pressed blank is then kept at 180-230℃ in the vacuum tube furnace for 2-3 hours, with a heating rate of 5-15℃ / min.

[0044] The present invention has the following beneficial effects:

[0045] This invention, through process innovation and performance optimization, ultimately aims to prepare a tin-based three-dimensional mesh composite solder with "high strength, high plasticity, and high temperature stability," solving the problem that traditional tin-based single-component lead-free solder is prone to deformation and cracking due to thermal stress and mechanical load, improving the reliability of electronic packaging, and expanding the application range of tin-based lead-free solder in high-requirement fields.

[0046] In this invention, the MAX phase reinforcing phase is distributed in the form of a three-dimensional continuous network skeleton at the grain boundaries of a tin-based lead-free solder matrix. The reinforcing phase particles are interconnected to form a "network channel" and encapsulate the matrix phase grains. The matrix grains are "wrapped" by the network reinforcing phase, forming a nested structure of "reinforcing phase skeleton - matrix grains". The reinforcing phase forms a "continuous network" that runs through the entire matrix, exhibiting strong structural integrity and no obvious void areas. Relying on the synergistic effect of grain boundary strengthening and network support (the continuous network reinforcing phase locks the grain boundaries, limiting matrix grain deformation; the network skeleton directly bears the load and disperses local stress), the strengthening efficiency is higher and the performance is more stable.

[0047] This invention improves upon traditional processes in preparing the MAX reinforcing phase. Building upon the "three-stage pressureless sintering" method, it employs a "liquid dispersion + wet ball milling" process, and utilizes a "three-dimensional oscillating powder mixing + cold pressing" process in preparing the composite solder powder. These improvements result in a preliminary network characterized by "uniform distribution and continuous connection," free from agglomeration / vacuum, laying the foundation for subsequent molding. Addressing the challenges of sedimentation and pressure during cold pressing, this invention leverages the self-lubricating properties of the MAX phase, eliminating the need for a release agent. This prevents network damage during demolding and inhibits reinforcement sedimentation, ensuring network symmetry.

[0048] The MAX phase-reinforced three-dimensional network tin-based lead-free solder of the present invention has a Vickers hardness of 14.64-22.31 HV and a tensile strength of 40.7-58.3 MPa; preferably, the Vickers hardness is 22.31 HV and the tensile strength is 58.3 MPa. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the crystal structure of the MAX phase;

[0050] Figure 2 The microstructure diagrams are of typical MAX phase Ti2SnC micro / nano powders in Examples 1 and 2 of this invention.

[0051] Figure 3 This is a microstructure diagram of lead-free solder from Example 1 of the present invention (Ti2SnC micro / nano powder content is 5%). Detailed Implementation

[0052] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0053] A method for preparing a MAX phase-enhanced three-dimensional mesh tin-based lead-free solder includes the following steps:

[0054] S1: First, weigh the raw material powder according to the chemical ratio of each element in the MAX phase (including Ti2AlC, Ti3SnC2, Ti2SnC) solid solution; then mix the weighed powder, pour the mixed raw material powder into a stainless steel ball mill jar, the mass ratio of agate grinding balls to powder to be processed is 10:1, the frequency of the all-round ball mill is 5-40Hz, and the ball milling is carried out for 24-48 hours, with a 10-15 minute break every 1-2 hours to obtain the ball-milled mixed powder.

[0055] S2: The well-mixed powder was sintered in a tube furnace, and the MAX reinforcing phase powder was prepared using a three-stage pressureless sintering process. Specifically, the process included: a low-temperature pre-sintering stage (300℃ / 15min): the tube furnace was heated to 300℃ at a rate of 10℃ / min and held for 15min; a medium-temperature transition stage (1000℃ / 20min): the tube furnace was heated from 300℃ to 1000℃ at a rate of 10℃ / min and held for 20min; a high-temperature sintering stage (1330℃ / 2h): the tube furnace was heated from 1000℃ to 1330℃ at a rate of 5℃ / min and held for 2h; and finally, the powder was cooled in the furnace to obtain the sintered powder.

[0056] S3: Take out the sintered powder and slowly pour sodium dodecyl benzoate dispersant into ethanol solvent (purity ≥99.7%) under magnetic stirring (speed 300-500r / h). The amount of sodium dodecyl benzoate added is 0.5%-1% of the powder mass. Then add the powder in batches, with the amount of powder to be treated being 0.5-2% of the dispersion mass. Continue stirring until the particles are completely dispersed.

[0057] S4: Ball milling is performed while retaining the liquid after dispersion treatment. The ratio of agate grinding balls to wet powder balls to be treated is 10:1. The frequency of the omnidirectional ball mill is 5-40Hz, and the ball milling time is 12-24 hours, with a 10-15 minute break every 1-2 hours. MAX phase micro-nano powder is obtained.

[0058] S5: Acid wash and centrifuge the MAX phase micro / nano powder, then place the deionized powder tube into a drying oven to dry it, obtaining a dry mixed powder; add 1-1.5g of ball-milled MAX phase powder to each centrifuge tube, add 0.5-2mol / L dilute hydrochloric acid, wherein the ratio of acid to MAX phase powder is 30:1~50:1 (mass ratio), and let it stand for 12-24h; when setting the parameters of the centrifuge, set the speed to 8000-10000rpm and the time to 5-10min; dry in a constant temperature drying oven at 50-60℃.

[0059] S6: Mix the Sn-based alloy powder with the prepared MAX phase powder in an all-around ball mill, and mix the powder according to the corresponding ball-to-powder ratio; the mass percentage of Sn-based alloy powder is 95-99%, and the mass percentage of prepared MAX phase powder is 1-5%; preferably, the mass percentage of Sn-based alloy powder is 95%, and the mass percentage of prepared MAX phase powder is 5%; the ball-to-powder ratio of agate grinding balls to powder to be treated is 5:1, the frequency of the all-around ball mill is 5-40Hz, and the ball milling is carried out for 12-24 hours, with a 10-15 minute break every 1-2 hours of grinding.

[0060] Sn-based alloy powders include Sn-Cu alloys, Sn-Ag alloys, Sn-In alloys, Sn-Zn alloys, and Sn-Ag-Cu alloys.

[0061] S7: The uniformly mixed powder is taken out and cold-pressed to obtain a green body; the cold-pressing process is as follows:

[0062] At room temperature, the mixed powder is pressed at 5-10 MPa for 1-5 minutes to form a green body.

[0063] S8: The green blank is placed in a tube furnace and sintered under a protective atmosphere, then cooled in the furnace to obtain MAX / Sn-based alloy composite solder. Specifically, the pressed green blank is placed in a small crucible, and the tube furnace is repeatedly evacuated and purged with argon gas 5-7 times. The pressed blank is held at 180-230℃ in the vacuum tube furnace for 2-3 hours, with a heating rate of 5-15℃ / min.

[0064] This embodiment yields a MAX phase-reinforced three-dimensional network tin-based lead-free solder. The MAX phase reinforcement is distributed in the form of a three-dimensional continuous network skeleton at the grain boundaries of the tin-based lead-free solder matrix. The reinforcement phase particles are interconnected to form "network channels" and encapsulate the matrix phase grains. The matrix grains are "wrapped" by the network reinforcement phase, forming a nested structure of "reinforcement phase skeleton - matrix grains". The reinforcement phase forms a "continuous network" that runs through the entire matrix, exhibiting strong structural integrity and no obvious void areas. Relying on the synergistic effect of grain boundary strengthening and network support (the continuous network reinforcement phase locks the grain boundaries, limiting matrix grain deformation; the network skeleton directly bears the load and disperses local stress), the strengthening efficiency is higher and the performance is more stable.

[0065] This embodiment presents an application of a MAX-reinforced three-dimensional mesh tin-based lead-free solder in high-temperature, high-load, and high-frequency vibration environments. Preferably, these high-temperature, high-load, and high-frequency vibration environments include those in the automotive, electronics, and aerospace industries. Example 1

[0066] The only difference between this embodiment and the above technical solution is that:

[0067] The dispersed Ti2SnC was placed in an omnidirectional ball mill and wet-milled at a frequency of 20 Hz for 24 hours, with a 10-minute pause after every 1 hour of milling, to obtain Ti2SnC micro / nano powder. SAC305 powder was then mixed with the prepared Ti2SnC powder, with each batch containing 5 g of SAC305 powder containing 2% and 5% Ti2SnC reinforcing phase, respectively. Three-dimensional oscillating powder mixing was performed using an all-round ball mill. Balls and powder were added at a ball-to-powder ratio of 5:1 (25g agate balls + 5g powder). The mixture was ball-milled at 20Hz for 24 hours, with a 10-minute break after every 1 hour of milling. The composite solders with Ti2SnC contents of 2% and 5% were weighed and then cold-pressed. The pressed sample was placed in a small crucible, and the tube furnace was repeatedly evacuated and purged with argon gas 5 times. The pressed sample was then held at 200℃ for 3 hours in a vacuum tube furnace with a heating rate of 10℃ / min. After coarse and fine grinding with sandpaper until the surface was smooth, flux was applied to both sides. The sample was sandwiched between two polished copper substrates and placed on a heating platform at 240℃ until the pressed sample was soldered to the copper substrate.

[0068] Preferably, in S3, the magnetometer speed is 500 r / h, ethanol is used as the dispersion medium, sodium dodecyl benzoate is used as the dispersant (addition amount is 0.8% of the powder mass), and the amount of powder to be treated is 1% of the dispersion mass.

[0069] Preferably, in S4, the ratio of agate grinding balls to wet powder balls to be treated is 10:1, the frequency of the omnidirectional ball mill is 20Hz, the ball milling is carried out for 24 hours, and the milling is stopped for 10 minutes every 1 hour.

[0070] Preferably, in step S5, 1g of ball-milled MAX phase powder is added to each centrifuge tube, along with 40mL of 1mol / L dilute hydrochloric acid, and the mixture is allowed to stand for 18h. When setting the parameters of the centrifuge, the rotation speed is set to 10000rpm and the time is set to 5min. The drying oven temperature is 60℃.

[0071] Preferably, in S7, the cold pressing process is as follows: at room temperature, the mixed powder is held under a pressure of 5 MPa for 5 minutes to form a blank.

[0072] Preferably, in step S8, the pressed green blank is placed in a small crucible, and the tube furnace is repeatedly evacuated and purged with argon gas 5 times. The pressed blank is then kept at 200°C for 3 hours in the vacuum tube furnace, with a heating rate of 10°C / min. Example 2

[0073] The only difference between this embodiment and Embodiment 1 is that:

[0074] The dispersed Ti2SnC was placed in an omnidirectional ball mill and wet-milled at a frequency of 20 Hz for 24 hours, with a 10-minute break after every 1 hour of milling, to obtain Ti2SnC micro / nano powder. SAC0307 powder was mixed with the prepared Ti2SnC powder, with each batch containing 5g of SAC0307 powder containing 1%, 2%, and 5% Ti2SnC reinforcing phase, respectively. Three-dimensional oscillating powder mixing was performed using an omnidirectional ball mill. Balls and powder were added at a ball-to-powder ratio of 5:1 (25g agate balls + 5g powder). The mixture was ball-milled at a frequency of 20Hz for 24 hours, with a 10-minute break after every 1 hour of milling. The composite solder powders with Ti2SnC contents of 1%, 2%, and 5% were weighed and then cold-pressed. The pressed sample was placed in a small crucible, and the tube furnace was repeatedly evacuated and purged with argon gas 5 times. The pressed sample was then held at 200℃ for 3 hours in a vacuum tube furnace with a heating rate of 10℃ / min. After coarse and fine grinding with sandpaper until the surface was smooth, flux was applied to both sides. The sample was sandwiched between two polished copper substrates and placed on a heating platform at 240℃ until the pressed sample was soldered to the copper substrate. Example 3

[0075] The only difference between this embodiment and Embodiment 1 is that:

[0076] The dispersed Ti3SiC2 was placed in an omnidirectional ball mill and wet-milled at a frequency of 20 Hz for 24 hours, with a 10-minute break after every 1 hour of milling, to obtain Ti3SiC2 micro / nano powder. SAC305 powder was then mixed with the prepared Ti3SiC2 powder, with each batch containing 5 g of SAC305 powder containing 2% and 5% Ti3SiC2 reinforcing phase, respectively. Three-dimensional oscillating powder mixing was performed using an all-round ball mill. Balls and powder were added at a ball-to-powder ratio of 5:1 (25g agate balls + 5g powder). The mixture was ball-milled at a frequency of 20Hz for 24 hours, with a 10-minute break after every 1 hour of milling. The composite solder powder with Ti3SiC2 contents of 2% and 5% was weighed and then cold-pressed. The pressed sample was placed in a small crucible, and the tube furnace was repeatedly evacuated and purged with argon gas 5 times. The pressed sample was then held at 230℃ for 3 hours in a vacuum tube furnace with a heating rate of 5℃ / min. After coarse and fine grinding with sandpaper until the surface was smooth, flux was applied to both sides. The sample was sandwiched between two polished copper substrates and placed on a heating platform at 240℃ until the pressed sample was soldered to the copper substrate.

[0077] Preferably, the dispersant in S3 is sodium dodecyl benzoate (added at 1% of the powder mass), and the amount of powder to be treated is 2% of the dispersion mass.

[0078] Preferably, in S4, the ratio of agate grinding balls to wet powder balls to be treated is 10:1, and the frequency of the omnidirectional ball mill is 40Hz.

[0079] Preferably, in step S5, 1.5g of ball-milled MAX phase powder is added to each centrifuge tube, along with 75mL of 2mol / L dilute hydrochloric acid, and the mixture is allowed to stand for 24 hours. Example 4

[0080] The only difference between this embodiment and Embodiment 1 is that:

[0081] The dispersed Ti2AlC was placed in an omnidirectional ball mill and wet-milled at a frequency of 5 Hz for 12 hours, with a 15-minute pause every 2 hours, to obtain Ti2AlC micro / nano powder. SAC0307 powder was mixed with the prepared Ti2AlC powder, with each batch containing 5g of SAC0307 powder containing 2%, 3%, and 5% Ti2AlC reinforcing phase, respectively. Three-dimensional oscillating powder mixing was performed using an omnidirectional ball mill. Balls and powder were added at a ball-to-powder ratio of 5:1 (25g agate balls + 5g powder). The mixture was ball-milled at a frequency of 5Hz for 12 hours, with a 15-minute break every 2 hours. The composite solder powders with Ti2AlC contents of 2%, 3%, and 5% were weighed and then cold-pressed. The pressed sample was placed in a small crucible, and the tube furnace was repeatedly evacuated and purged with argon gas 7 times. The pressed sample was then held at 180℃ for 2 hours in a vacuum tube furnace with a heating rate of 15℃ / min. After coarse and fine grinding with sandpaper until the surface was smooth, flux was applied to both sides. The sample was sandwiched between two polished copper substrates and placed on a heating platform at 240℃ until the pressed sample was soldered to the copper substrate.

[0082] Preferably, in S3, the magnetometer speed is 300 r / h, ethanol is used as the dispersion medium, sodium dodecyl benzoate is used as the dispersant (addition amount is 0.5% of the powder mass), and the amount of powder to be treated is 0.5% of the dispersion liquid mass.

[0083] Preferably, in S4, the ratio of agate grinding balls to wet powder balls to be treated is 10:1, the frequency of the omnidirectional ball mill is 5Hz, the ball milling is performed for 12 hours, and a 15-minute break is made every 2 hours of grinding.

[0084] Preferably, in step S5, 1.5g of ball-milled MAX phase powder is added to each centrifuge tube, along with 45mL of 0.5mol / L dilute hydrochloric acid, and the mixture is allowed to stand for 12h. When setting the parameters of the centrifuge, the rotation speed is set to 8000rpm and the time is set to 10min. The drying oven temperature is 50℃.

[0085] Preferably, in S7, the cold pressing process is as follows: at room temperature, the mixed powder is held under a pressure of 10 MPa for 1 minute to form a blank.

[0086] Comparative Example 1 (This comparative example does not contain a three-dimensional mesh MAX phase reinforcement phase)

[0087] SAC305 powder was cold-pressed into shape. The pressed sample was placed in a small crucible and the tube furnace was repeatedly evacuated and purged with argon five times. The pressed sample was kept at 200°C for 3 hours in the vacuum tube furnace with a heating rate of 10°C / min. After coarse and fine grinding with sandpaper until the surface was smooth, flux was applied to both sides and sandwiched between two polished copper substrates. The sample was then placed on a heating platform and kept at 240°C until the pressed sample was soldered to the copper substrate.

[0088] Comparative Example 2 (This comparative example does not contain a three-dimensional mesh MAX phase reinforcement phase)

[0089] SAC0307 powder was cold-pressed into shape. The pressed sample was placed in a small crucible and the tube furnace was repeatedly evacuated and purged with argon five times. The pressed sample was kept at 200°C for 3 hours in the vacuum tube furnace with a heating rate of 10°C / min. After coarse and fine grinding with sandpaper until the surface was smooth, flux was applied to both sides and sandwiched between two polished copper substrates. The sample was then placed on a heating platform and kept at 240°C until the pressed sample was soldered to the copper substrate.

[0090] To evaluate the reinforcing effect of the lead-free solder containing a three-dimensional network MAX reinforcing phase prepared using the present invention, Comparative Examples 1 and 2 used SAC305 and SAC0307 solders that were not treated with the above-described improved process as a control group. The improved process was used in the examples, wherein the added MAX reinforcing phases were Ti2SnC, Ti3SiC2, and Ti2AlC. The study found that the SAC305 and SAC0307 matrices without the above-described improved process did not obtain a three-dimensional network structure. Mechanical property tests showed that the mechanical properties of the tin-based lead-free solder without the above-described improved process were significantly worse.

[0091] Taking Examples 1 and 2 as examples, the microstructure of Ti2SnC is shown in the figure below. Figure 2Mechanical property tests revealed that the average hardness values ​​of the SAC305 solders containing 2% Ti2SnC reinforcement and 5% Ti2SnC reinforcement were 18.40 HV and 22.31 HV, respectively, and their tensile strengths were 49 MPa and 58.3 MPa, respectively. Compared to the pure SAC305 solder without reinforcement in Comparative Example 1 (Vickers hardness 15.36 HV, tensile strength 40.5 MPa), the addition of 2% and 5% Ti2SnC reinforcement in Example 1 increased the hardness of the SAC305 solder by 19.79% and 45.24%, respectively, and increased the strength by 20.99% and 43.95%, respectively. Mechanical property tests on the pure SAC0307 solder alloy in Comparative Example 2 showed a tensile strength of 35.1 MPa and a Vickers hardness of 13. In Example 2, the tensile strengths of SAC307 solders with Ti2SnC contents of 1%, 2%, and 5% were 40.7 MPa, 45.2 MPa, and 50.5 MPa, respectively, and the Vickers hardness values ​​were 14.64 HV, 16.19 HV, and 19.98 HV, respectively. The tensile strength was increased by 11.33%, 23.11%, and 51.93% compared with Comparative Example 2, and the hardness was increased by 21.78%, 26.88%, and 51.94%. In Example 3, the composite solder using SAC305 as the base solder and Ti3SiC2 as the reinforcing phase, compared to the pure SAC305 solder without reinforcing phase in Comparative Example 1 (Vickers hardness 15.36 HV, tensile strength 40.5 MPa), showed that when the Ti3SiC2 content was 2%, the Vickers hardness increased to 17.82 HV (an increase of 16.02%), and the tensile strength increased to 47.2 MPa (an increase of 16.54%); when the Ti3SiC2 content increased to 5%, the Vickers hardness further increased to 21.58 HV (an increase of 40.49%), and the tensile strength increased to 56.1 MPa (an increase of 38.52%); in Example 4, using... The composite solder with SAC0307 as the base solder and Ti2AlC as the reinforcing phase, compared to the pure SAC0307 solder without the reinforcing phase in Comparative Example 2 (Vickers hardness 13.15 HV, tensile strength 35.1 MPa), showed a significant increase in Vickers hardness (15.82 HV, 20.31% increase), tensile strength (42.3 MPa, 20.51% increase), tensile strength (46.8 MPa, 33.33% increase), and tensile strength (49.8 MPa, 41.88% increase) as the Ti2AlC content increased from 2% to 3% and then to 5%. These data directly demonstrate that the three-dimensional network distribution of the MAX phase reinforcement significantly improves the mechanical properties of the tin-based lead-free solder.

[0092] Taking the SAC305 lead-free solder with 5% Ti2SnC reinforcing phase added in Example 1 as an example, the microstructure of the obtained lead-free solder is as follows: Figure 3 As shown, Ti2SnC is distributed in a three-dimensional network on the grain boundaries. The reinforcing phase surrounds the matrix phase, which enhances its mechanical properties. The enhancement mechanism is as follows: the addition of Ti2SnC reinforcing phase will increase the hardness and strength of SAC305 and SAC0307 solders because the network distribution of the reinforcing body fits the characteristics of the upper limit microstructure in HS theory, that is, the reinforcing phase surrounds the matrix phase, and the reinforcing phase distributed on the interface phase fully exerts the "grain boundary strengthening" effect.

[0093] Comparative Example 3

[0094] The only difference between this comparative example and Example 1 is that:

[0095] MAX reinforced phase powder was prepared using a four-stage pressureless sintering process.

[0096] Specifically, the low-temperature preheating section (300℃ / 15min): the tube furnace is heated to 300℃ at a rate of 10℃ / min and held for 15min;

[0097] Medium temperature transition section (1000℃ / 20min): The tube furnace is heated from 300℃ to 1000℃ at a rate of 10℃ / min and held for 20min;

[0098] High-temperature sintering section (1330℃ / 2h): The tubular furnace is heated from 1000℃ to 1330℃ at a rate of 5℃ / min and held for 2h.

[0099] The tube furnace was heated from 1330℃ to 1380℃ at a rate of 5℃ / min and held for 10 min. The lead-free solder obtained in this comparative example (with 5% Ti2SnC micro / nano powder added) had a Vickers hardness of 18.30 HV and a tensile strength of 48.5 MPa.

[0100] Comparative Example 4

[0101] The only difference between this comparative example and Example 1 is that:

[0102] MAX reinforced phase powder was prepared using a one-stage pressureless sintering process.

[0103] Specifically, the tube furnace directly heated from room temperature to 1380℃ at a rate of 8℃ / min, held at that temperature for 30 minutes, without an intermediate holding stage. The lead-free solder obtained in this comparative example (with 5% Ti2SnC micro / nano powder added) had a Vickers hardness of 16.75 HV and a tensile strength of 43.2 MPa.

[0104] Comparative Example 5

[0105] The only difference between this comparative example and Example 1 is that:

[0106] MAX reinforced phase powder was prepared using a two-stage (pre-sintering + high-temperature sintering) pressureless sintering process.

[0107] Specifically, the pre-calcination section (500℃ / 25min): the tube furnace heats up to 500℃ at a rate of 10℃ / min and holds for 25min to remove residual impurities and adsorbed moisture from the powder.

[0108] High-temperature sintering section (1380℃ / 90min): The tube furnace was heated from 500℃ to 1380℃ at a rate of 5℃ / min and held for 90min to complete the densification of the MAX phase crystal structure. The lead-free solder obtained in this comparative example (with 5% Ti2SnC micro / nano powder added) had a Vickers hardness of 17.92 HV and a tensile strength of 46.8 MPa.

[0109] It should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the above description of exemplary embodiments of the invention. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all the features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0110] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0111] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a MAX phase-reinforced three-dimensional network tin-based lead-free solder, characterized in that, The MAX phase reinforcing phase is distributed in the form of a three-dimensional continuous network skeleton at the grain boundaries of the tin-based lead-free solder matrix; the MAX phase reinforcing phase forms a continuous network that runs through the entire tin-based lead-free solder matrix; The preparation method includes the following steps: S1. The pre-weighed MAX phase reinforcing phase raw material powder is ball-milled and mixed. The mass ratio of agate grinding balls to the MAX phase reinforcing phase raw material powder to be treated is 10:

1. The frequency of the all-round ball mill is 5-40Hz. The ball milling is carried out for 12-48 hours, with a 10-15 minute break every 1-2 hours to obtain the well-mixed powder. S2, using a tube furnace to sinter the well-mixed powder and a three-stage pressureless sintering process to prepare MAX reinforced phase powder; Low-temperature pre-firing section: The tubular furnace is heated to 300℃ at a rate of 10℃ / min and held for 15min; Medium-temperature transition section: The tubular furnace is heated from 300℃ to 1000℃ at a rate of 10℃ / min and held for 20min; High-temperature sintering section: The tubular furnace is heated from 1000℃ to 1330℃ at a rate of 5℃ / min and held at that temperature for 2 hours; S3, remove the sintered powder, and pour the dispersant into the ethanol solvent while magnetically stirring at 300-500 r / h to obtain a dispersion. Then, add the sintered powder in batches and continue stirring until the particles are completely dispersed. The amount of dispersant added is 0.5-1% of the mass of the sintered powder, and the amount of sintered powder added is 0.5-2% of the mass of the dispersion. S4. Ball milling is performed while retaining the liquid after dispersion treatment. The ratio of agate grinding balls to wet powder balls to be treated is 10:

1. The frequency of the omnidirectional ball mill is 5-40Hz. The ball milling is performed for 12-24 hours, with a 10-15 minute break every 1-2 hours to obtain MAX phase micro-nano powder. S5, the MAX phase micro-nano powder is acid washed and centrifuged, and then the deion tube of the centrifuged powder is placed in a drying oven to dry, so as to obtain a dry mixed powder. S6. The tin-based lead-free solder matrix powder and the dry mixed powder are mixed and placed in an omnidirectional ball mill. The mass percentage of the tin-based lead-free solder matrix powder is 95-99%, and the mass percentage of the dry mixed powder is 1-5%. The ratio of agate grinding balls to powder balls to be processed is 5:

1. The frequency of the omnidirectional ball mill is 5-40Hz. The ball milling is carried out for 12-24 hours, with a 10-15 minute break every 1-2 hours. A uniformly mixed powder is obtained. S7, the uniformly mixed powder is taken out and cold-pressed to obtain a green body; S8, the green billet is placed in a tube furnace and sintered under a protective atmosphere, and then cooled with the furnace to obtain MAX / Sn-based alloy composite solder; In S5, add 1-1.5g of MAX phase micro / nano powder to each centrifuge tube, add 0.5-2mol / L dilute hydrochloric acid, wherein the mass ratio of dilute hydrochloric acid to MAX phase micro / nano powder is 30:1~50:1, let stand for 12-24h; centrifuge speed is 8000-10000rpm, centrifugation time is 5-10min; dry in drying oven at 50-60℃. In S8, the green billet is placed in a crucible, and the tube furnace is repeatedly evacuated and purged with argon gas 5-7 times. The green billet is pressed into sheets and held at 180-230℃ for 2-3 hours in the vacuum tube furnace, with a heating rate of 5-15℃ / min.

2. The preparation method according to claim 1, characterized in that, Tin-based lead-free solder matrix includes Sn-Cu alloy, Sn-Ag alloy, Sn-In alloy, Sn-Zn alloy or Sn-Ag-Cu alloy.

3. The preparation method according to claim 1, characterized in that, The MAX phase-enhanced phases include Ti2AlC, Ti3SnC2, or Ti2SnC.

4. The preparation method according to claim 1, characterized in that, Lead-free solder has a Vickers hardness of 14.64-22.31 HV and a tensile strength of 40.7-58.3 MPa.

5. The preparation method according to claim 1, characterized in that, In S3, the dispersant includes sodium dodecyl benzoate.

6. The preparation method according to claim 1, characterized in that, In S7, the cold pressing process is as follows: at room temperature, the uniformly mixed powder is held under pressure of 5-10MPa for 1-5 minutes to form a blank.

7. The application of a MAX phase-reinforced three-dimensional network tin-based lead-free solder obtained by the preparation method according to any one of claims 1 to 6 in high-temperature, high-load, and high-frequency vibration scenarios, characterized in that, High temperature, high load, and high frequency vibration scenarios include automotive, electronics, and aerospace applications.

Images