Composite active brazing filler metal for aluminum nitride ceramic connection and brazing method of composite active brazing filler metal

Abstract

The invention discloses composite active brazing filler metal for aluminum nitride ceramic connection and a brazing method of the composite active brazing filler metal, and belongs to the technical field of brazing methods.The composite active brazing filler metal comprises basic brazing filler metal, the basic brazing filler metal adopts Ag-Cu-Ti active brazing filler metal alloy powder, and the Ti element is responsible for reacting with aluminum nitride; in the reinforcement phase, a few-layer or few-layer stacked MXene two-dimensional material is introduced, the adding amount of the MXene two-dimensional material is 1.0-5.0 wt.% of the total mass of the brazing filler metal, if the content is too low, the reinforcement and stress buffering effects are not obvious, and if the content is too high, agglomeration is easily caused, and the fluidity and formability of the brazing filler metal are deteriorated. Wherein MXene is of a graphene-like two-dimensional layered structure, the interlayer binding force is relatively weak, and in the brazing process, when molten brazing filler metal is solidified and shrunk and stress is generated through subsequent cooling, an MXene sheet layer can effectively absorb and dissipate strain energy through interlayer slippage, bending and even corrugation microcosmic deformation.

Description

Technical Field

[0001] This invention relates to the field of brazing methods, and in particular to a composite active brazing filler metal for joining aluminum nitride ceramics and its brazing method. Background Technology

[0002] AlN ceramics possess excellent properties such as high strength, high temperature resistance, and corrosion resistance. In particular, their high thermal conductivity, good insulation properties, and dielectric properties make them widely used in semiconductor substrates, electronic device packaging, and impact-resistant materials. However, the difficulty in processing AlN ceramics makes it challenging to fabricate large-sized and complex-shaped AlN ceramic components.

[0003] Choosing a suitable joining technology is one of the important methods to expand the application fields of AlN ceramics. Active metal brazing (AMB) is currently one of the mainstream technologies for joining AlN ceramics, with Ag-Cu-Ti alloy brazing filler metal being the most widely used. This technology relies on the interfacial reaction between the active element (Ti) in the brazing filler metal and the ceramic to form a chemical metallurgical bond. However, this technology faces two core challenges: First, there is a significant mismatch in the coefficient of thermal expansion between the Ag-Cu-Ti brazing filler metal and the AlN ceramic. During the cooling process after brazing, the huge shrinkage difference will generate extremely high residual tensile stress in the joint area, especially in the brittle AlN ceramic near the weld, which can easily induce microcracks and become the root cause of premature joint failure. Second, the strength and creep resistance of a single Ag-Cu-Ti brazing seam are limited at high temperatures, and the distribution and reaction of the active element Ti are not easy to control precisely, which may lead to an uneven interfacial reaction layer.

[0004] In existing technologies, stress relief is often achieved by adding low-expansion particles (such as SiC and Mo) or designing multi-layer gradient intermediate layers. However, this often leads to increased process complexity, deterioration of interfacial wettability, or the introduction of new brittle phases. Therefore, there is a need to develop a novel composite brazing filler metal that can actively and efficiently relieve residual stress at the joint while maintaining excellent wettability and interfacial bonding, and can also strengthen the brazing seam in situ. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a composite active brazing filler metal for joining aluminum nitride ceramics and a brazing method thereof, which reduces the residual stress present when joining aluminum nitride ceramics with composite active brazing filler metal and improves the joint strength and toughness.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] This invention discloses a composite active solder for connecting aluminum nitride ceramics, the composite active solder comprising:

[0008] Basic solder: The basic solder uses Ag-Cu-Ti active solder alloy powder, with Ti element responsible for reacting with aluminum nitride;

[0009] Reinforcing phase: Introduce a few layers or a few stacked layers of MXene two-dimensional material. The amount of MXene two-dimensional material added is 1.0 to 5.0 wt.% of the total mass of the composite active solder. If the content is too low, the strengthening and stress buffering effects will not be obvious. If the content is too high, it will easily lead to agglomeration and deteriorate the fluidity and formability of the solder.

[0010] Preferably, the method for preparing the composite active solder includes:

[0011] Precisely weigh Ag-Cu-Ti active solder alloy powder and MXene two-dimensional material powder according to the design ratio, and then mix them to form a mixed powder;

[0012] The mixed powder and grinding balls are placed together in a vacuum ball mill jar, with a ball-to-powder mass ratio of 8:1 to 12:1.

[0013] Ball milling is carried out under argon protection or vacuum environment, with a ball milling speed of 150-250 r / min and a ball milling time of 8-15 hours;

[0014] After ball milling, a composite brazing filler metal powder with uniform composition and MXene flakes uniformly dispersed or embedded on the surface of alloy particles is obtained. The powder can be mixed with an appropriate amount of organic binder to form a paste, thus forming a paste-like composite active brazing filler metal.

[0015] Preferably, the commercial Ag-Cu-Ti active solder alloy powder is Ag-26.7Cu-4.5Ti.

[0016] Preferably, the MXene two-dimensional material is Ti3C2T. X MXene.

[0017] Preferably, the amount of MXene two-dimensional material added is 2.0 to 4.0 wt.% of the total mass of the solder.

[0018] Another aspect of the present invention discloses a brazing method for connecting aluminum nitride ceramics using the aforementioned composite active solder, the brazing method comprising:

[0019] Surface pretreatment:

[0020] Polish the aluminum nitride ceramic surface to be welded to a surface roughness Ra less than or equal to 0.1 μm, then perform ultrasonic cleaning in acetone and anhydrous ethanol for 15 minutes each, and dry for later use.

[0021] Brazing filler metal application and assembly:

[0022] A paste-like composite active solder is evenly applied to the surface of an aluminum nitride ceramic to be soldered, with a thickness of 80-150 μm. Then, another aluminum nitride ceramic is placed on top of the composite active solder to form an assembly.

[0023] Vacuum brazing:

[0024] The assembly is placed in a vacuum brazing furnace and evacuated to a minimum ultimate vacuum of 5.0 × 10⁻⁶. -3 Pa, heat to 600-650℃ at a rate of 8-12℃ / min, hold for 10-20 minutes, continue to heat to brazing temperature of 820-880℃ at a rate of 5-10℃ / min, hold at brazing temperature for 5-15 minutes, after holding, cool to 400℃ at a controlled rate of 3-8℃ / min, and then cool to room temperature with the furnace, which helps to further release thermal stress.

[0025] Preferably, the brazing temperature is 840–860°C, and the holding time at the brazing temperature is 8–12 minutes.

[0026] The above technical solution has the following beneficial effects:

[0027] MXene has a graphene-like two-dimensional layered structure with relatively weak interlayer bonding. During the brazing process, when the molten brazing filler metal solidifies and shrinks and subsequent cooling generates stress, the MXene sheets can effectively absorb and dissipate strain energy through interlayer slippage, bending, or even wrinkling micro-deformation.

[0028] The uniformly dispersed MXene sheets and the Ti-Cu compounds formed by their reaction with the matrix have significantly lower coefficients of thermal expansion (CTE) than the Ag-Cu eutectic matrix. As low-expansion reinforcing phases, they can reduce the overall effective coefficient of thermal expansion of the brazing seam from a microscopic perspective, narrow the CTE gap with AlN ceramics, and reduce thermal mismatch strain from the source.

[0029] MXene itself is rich in Ti elements, and can partially decompose or participate in the reaction at the brazing temperature. This is equivalent to providing a dispersed and controllable secondary active Ti source in the brazing seam, which helps to react with AlN in a wider area, promotes the formation of a more continuous and uniform interface reaction layer, and improves the interface bonding strength and consistency.

[0030] Ti in MXene reacts with Cu in the brazing filler metal at the interface and inside the brazing seam to generate fine Ti-Cu intermetallic compound particles. These hard particles, together with the unreacted MXene sheets, act as a dispersed strengthening phase, pinning the grain boundaries of the brazing seam matrix and hindering dislocation movement, significantly improving the strength, hardness and creep resistance of the brazing seam at room temperature and high temperature.

[0031] Compared with using a single Ag-Cu-Ti solder, the composite solder of this invention can increase the room temperature shear strength of aluminum nitride joints by more than 35%; the thermal shock resistance of the joints is greatly improved, and the strength retention rate is high after multiple high and low temperature cycles; Detailed Implementation

[0032] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] This invention relates to a highly active, low-stress composite brazing alloy for homogeneous or heterogeneous bonding of aluminum nitride (AlN) ceramics and its vacuum brazing method. By introducing a two-dimensional layered material MXene into a traditional Ag-Cu-Ti active brazing alloy, a composite brazing alloy system with unique interface enhancement and stress buffering functions is constructed, aiming to significantly improve the connection strength and reliability of aluminum nitride ceramic joints.

[0034] This invention aims to overcome the shortcomings of existing Ag-Cu-Ti solders in bonding AlN ceramics, such as high residual stress and insufficient joint strength and toughness. By introducing the two-dimensional layered material MXene into the Ag-Cu-Ti solder, a novel composite solder is constructed. This solder utilizes the multiple functions of MXene:

[0035] (1) Provides a dispersed active Ti source to promote and optimize interfacial reactions;

[0036] (2) Its unique two-dimensional layered structure can absorb strain energy through slip and deformation;

[0037] (3) It reacts with the matrix to generate fine intermetallic compounds, thereby achieving dispersion strengthening of the brazing seam;

[0038] This allows for a synergistic improvement in the strength and reliability of aluminum nitride ceramic joints while simplifying the process.

[0039] Example 1

[0040] Composite active solders include:

[0041] Base solder: Commercial Ag-Cu-Ti active solder alloy powder is used, such as Ag-26.7Cu-4.5Ti, with a melting point of about 780℃. The Ti element is responsible for reacting with aluminum nitride.

[0042] Reinforcing phase: Introducing a few-layer or few-layer stacked MXene two-dimensional material, specifically Ti3C2T. X MXene, Ti3C2T XT in X Representing the surface functional groups -OH, -O, and -F, the amount of MXene two-dimensional material added is 1.0 to 5.0 wt.% of the total mass of the composite active solder. Specifically, the amount of MXene two-dimensional material added can be 1.0 wt.% or 5.0 wt.% of the total mass of the composite active solder. In some embodiments, the amount of MXene two-dimensional material added is 2.0 to 4.0 wt.% of the total mass of the composite active solder. Specifically, the amount of MXene two-dimensional material added can be 2.0 wt.% or 4.0 wt.% of the total mass of the composite active solder, or it can be 3.0 wt.%. If the content is too low, the strengthening and stress buffering effects will not be obvious, and if the content is too high, it will easily lead to agglomeration and deteriorate the fluidity and formability of the solder.

[0043] MXene two-dimensional materials have a graphene-like two-dimensional layered structure with relatively weak interlayer bonding. During the brazing process, when the molten brazing filler metal solidifies and shrinks and generates stress during subsequent cooling, the MXene sheets can effectively absorb and dissipate strain energy through micro-deformations such as interlayer slippage, bending, and even wrinkling, just like having countless tiny "springs" and "shock absorbers" built into the brazing seam.

[0044] The uniformly dispersed MXene sheets and the Ti-Cu compounds (such as TiCu4 and Ti2Cu3) formed by their reaction with the matrix have significantly lower coefficients of thermal expansion than the Ag-Cu eutectic matrix. As low-expansion reinforcing phases, they can reduce the overall effective coefficient of thermal expansion of the brazing seam at the microscopic level, narrowing the gap between its coefficient of thermal expansion and that of aluminum nitride ceramics, thereby reducing thermal mismatch strain at the source.

[0045] MXene (such as Ti3C2T) X TiN itself is rich in Ti and can partially decompose or participate in the reaction at the brazing temperature. This is equivalent to providing a dispersed and controllable secondary active Ti source in the brazing seam, which helps to react with AlN in a wider area, promotes the formation of a more continuous and uniform interface reaction layer (mainly TiN and complex compounds containing Al and Ti), and improves the interface bonding strength and consistency.

[0046] Ti in MXene reacts with Cu in the brazing filler metal at the interface and inside the brazing seam to generate fine Ti-Cu intermetallic compound particles. These hard particles, together with the unreacted MXene sheets, act as a dispersed strengthening phase, pinning the grain boundaries of the brazing seam matrix and hindering dislocation movement, thus significantly improving the strength, hardness and creep resistance of the brazing seam at room temperature and high temperature.

[0047] Compared with using a single Ag-Cu-Ti solder, the AgCuTi and MXene composite solder of the present invention can increase the room temperature shear strength of aluminum nitride joints by more than 35%, for example, from 120 MPa of the single solder to 160 MPa or higher of the composite solder.

[0048] Example 2

[0049] Preparation method of composite active solder:

[0050] Mechanical alloying mixing was performed using high-energy ball milling.

[0051] Accurately weigh Ag-Cu-Ti alloy powder and MXene two-dimensional material powder according to the design ratio;

[0052] The mixed powder and grinding balls are placed together in a vacuum ball mill jar, with a ball-to-powder mass ratio of 8:1 to 12:1. Specifically, the ball-to-powder mass ratio can be 8:1 or 12:1. In some embodiments, the ball-to-powder mass ratio can be 10:1.

[0053] Ball milling is carried out under argon protection or vacuum environment, with a ball milling speed of 150-250 r / min and a ball milling time of 8-15 hours. Specifically, the ball milling speed is 150 r / min or 250 r / min and the ball milling time is 8 hours or 15 hours.

[0054] After ball milling, a composite active brazing filler metal powder with uniform composition and MXene flakes uniformly dispersed or embedded on the surface of alloy particles is obtained. The powder can be mixed with an organic binder to form a paste for easy application, thus forming a paste-like composite active brazing filler metal. Specifically, the organic binder can be acrylic resin.

[0055] Example 3

[0056] The method for connecting aluminum nitride ceramics using the above-mentioned composite brazing filler metal includes the following steps:

[0057] Surface pretreatment:

[0058] Polish the aluminum nitride ceramic surface to be welded with a diamond grinding wheel until the surface roughness Ra is less than or equal to 0.1 μm. Specifically, the surface roughness Ra can be 0.1 μm. Then, perform ultrasonic cleaning in acetone and anhydrous ethanol for 15 minutes each, and dry for later use.

[0059] Brazing filler metal application and assembly:

[0060] A paste-like composite active solder is evenly applied to the surface of an aluminum nitride ceramic to be soldered. The thickness of the paste-like composite active solder is controlled between 80 and 150 μm. Specifically, the paste-like composite active solder can be 80 μm or 150 μm. Then, another aluminum nitride ceramic is aligned and stacked to form a three-layer assembly structure. A slight pressure of 4.5 to 5.5 kPa can be applied to ensure initial contact.

[0061] Vacuum brazing:

[0062] The assembly is placed in a vacuum brazing furnace and evacuated to a minimum ultimate vacuum of 5.0 × 10⁻⁶. -3 Pa, heating to 600–650°C at a rate of 8–12°C / min, and holding at that temperature for 10–20 minutes to completely remove the organic binder; specifically, heating at 8°C / min... Alternatively, the temperature can be increased to 600°C or 650°C at a rate of 12°C / min, held for 10 or 20 minutes, and then increased to a brazing temperature of 820-880°C at a rate of 5-10°C / min. Specifically, the temperature can be increased to 820°C or 880°C at a rate of 5°C / min or 10°C / min. In some embodiments, the brazing temperature is 840-860°C. Specifically, the brazing temperature can be 840°C or 860°C. The temperature is held at the brazing temperature for 5-15 minutes. Specifically, the holding time at the brazing temperature is 8-12 minutes. Specifically, the holding time can be 8 minutes or 12 minutes. After the holding time, the temperature is controlled to cool to 400°C at a rate of 3-8°C / min, and then cooled to room temperature in the furnace. Specifically, after the holding time, the temperature is controlled to cool to 400°C at a rate of 3°C / min or 8°C / min. This slow cooling regime helps to further release thermal stress.

[0063] The joint's thermal shock resistance is significantly improved, and its strength retention rate is high after multiple high and low temperature cycles. Fracture analysis shows that the fracture path is more likely to occur in the AlN base material or inside the brazing seam, rather than at the brittle ceramic / reactive layer interface, proving that the interface bonding is strengthened and stress concentration is effectively alleviated.

[0064] The process is compatible with basic Ag-Cu-Ti brazing, requires no complex pretreatment or multi-layer structure, and is easy to implement.

[0065] Example 4

[0066] The raw material for preparing the composite active solder is Ag-26.7Cu-4.5Ti alloy powder. The chemical composition of Ag-26.7Cu-4.5Ti, by mass fraction, is 68.8% silver, 26.7% copper, and 4.5% titanium, with a particle size of 40–50 μm and a few-layer Ti3C2T alloy. X MXene powder, with a flake diameter of 1–5 μm;

[0067] Composite brazing filler metal preparation: Weigh 97g of Ag-Cu-Ti alloy powder and 3g of MXene powder, place them in a vacuum planetary ball mill jar, add cemented carbide grinding balls, the ball-to-material ratio is 10:1, fill with argon gas for protection, and ball mill at 200r / min for 12 hours to obtain composite active brazing filler metal powder.

[0068] The ball-milled composite active brazing filler powder was mixed with 5 wt.% acrylic resin binder to form a paste;

[0069] The coating is applied to the surface of a pretreated aluminum nitride ceramic sheet (10×10×3 mm). After coating, another piece of aluminum nitride ceramic is assembled. The assembly is then placed in a vacuum brazing furnace and evacuated to a vacuum level of 2×10 mm. -3 Pa; heat to 620℃ at 10℃ / min and hold for 15min to remove glue; heat to 850℃ at 8℃ / min and hold for 10min to weld; cool to 400℃ at 5℃ / min and then cool with the furnace.

[0070] Performance testing: The obtained joint surface has good formation, and the average room temperature shear strength is 158 MPa. SEM observation shows that fine flaky MXene residues and nanoscale Ti-Cu compound particles are uniformly distributed in the brazing matrix. The aluminum nitride / brazing filler metal interface reaction layer is continuous and uniform in thickness. No radial cracks were observed in the aluminum nitride ceramic near the joint.

[0071] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A composite active solder for joining aluminum nitride ceramics, characterized in that, The composite active solder includes: Basic solder: The basic solder uses Ag-Cu-Ti active solder alloy powder, with Ti element responsible for reacting with aluminum nitride; Reinforcing phase: Introduce a few layers or a few stacked layers of MXene two-dimensional material. The amount of MXene two-dimensional material added is 1.0 to 5.0 wt.% of the total mass of the composite active solder. If the content is too low, the strengthening and stress buffering effects will not be obvious. If the content is too high, it will easily lead to agglomeration and deteriorate the fluidity and formability of the solder.

2. The composite active solder for aluminum nitride ceramic bonding according to claim 1, characterized in that, The method for preparing the composite active solder includes: Precisely weigh Ag-Cu-Ti active solder alloy powder and MXene two-dimensional material powder according to the design ratio, and then mix them to form a mixed powder; The mixed powder and grinding balls are placed together in a vacuum ball mill jar, with a ball-to-powder mass ratio of 8:1 to 12:

1. Ball milling is carried out under argon protection or vacuum environment, with a ball milling speed of 150-250 r / min and a ball milling time of 8-15 hours; After ball milling, a composite brazing filler metal powder with uniform composition and MXene flakes uniformly dispersed or embedded on the surface of alloy particles is obtained. The powder can be mixed with an appropriate amount of organic binder to form a paste, thus forming a paste-like composite active brazing filler metal.

3. The composite active solder for aluminum nitride ceramic bonding according to claim 1, characterized in that, The commercial Ag-Cu-Ti active solder alloy powder is Ag-26.7Cu-4.5Ti.

4. The composite active solder for aluminum nitride ceramic bonding according to claim 1, characterized in that, The MXene two-dimensional material is Ti3C2T. X MXene.

5. The composite active solder for aluminum nitride ceramic bonding according to claim 1, characterized in that, The amount of MXene two-dimensional material added is 2.0 to 4.0 wt.% of the total solder mass.

6. A brazing method for joining aluminum nitride ceramics with a composite active solder as described in any one of claims 1-5, characterized in that, The brazing method includes: Surface pretreatment: Polish the aluminum nitride ceramic surface to be welded to a surface roughness Ra less than or equal to 0.1 μm, then perform ultrasonic cleaning in acetone and anhydrous ethanol for 15 minutes each, and dry for later use. Brazing filler metal application and assembly: A paste-like composite active solder is evenly applied to the surface of an aluminum nitride ceramic to be soldered, with a thickness of 80-150 μm. Then, another aluminum nitride ceramic is placed on top of the composite active solder to form an assembly. Vacuum brazing: The assembly is placed in a vacuum brazing furnace and evacuated to a minimum ultimate vacuum of 5.0 × 10⁻⁶. -3 Pa, heat to 600-650℃ at a rate of 8-12℃ / min, hold for 10-20 minutes, continue to heat to brazing temperature of 820-880℃ at a rate of 5-10℃ / min, hold at brazing temperature for 5-15 minutes, after holding, cool to 400℃ at a controlled rate of 3-8℃ / min, and then cool to room temperature with the furnace, which helps to further release thermal stress.

7. The brazing method according to claim 6, characterized in that, The brazing temperature is 840–860°C, and the holding time at the brazing temperature is 8–12 minutes.