Welding material for preparing high-temperature-resistant welding spots and welding method of welding material

Abstract

The invention discloses a welding material for preparing a high-temperature-resistant welding spot. The welding material is used for packaging and welding a silicon carbide or aluminum nitride substrate. The welding material comprises mixed powder of Cu powder and Mo powder, and at least one layer of copper foil is arranged in the mixed powder; according to the mass percentage, the adding amount of the Cu powder is 70%-95%, and the adding amount of the Mo powder is 5%-30%.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically to a welding material for preparing high-temperature resistant weld joints and a welding method thereof. Background Technology

[0002] In the field of electronic packaging, especially in soldering applications on high-performance substrates such as silicon carbide or aluminum nitride, existing soldering technologies face numerous challenges. Traditional solders exhibit insufficient heat resistance under high-temperature operating conditions, easily degrading in performance during thermal cycling, leading to a significant decrease in the reliability of solder joints. Simultaneously, intermetallic compound (IMC)-based solder systems generally carry the risk of brittle fracture; under the combined effects of thermal and mechanical stress, solder joints are prone to cracking or even complete failure. Furthermore, the thermal conductivity of existing high-temperature solders and IMC solder systems often fails to meet the heat dissipation requirements of high-power devices, causing increased device operating temperatures and further exacerbating reliability issues. While advanced solders such as sintered silver have high melting points, they are prone to porosity defects and electromigration in practical applications. These microscopic defects not only reduce the mechanical strength of the solder joints but also severely affect their long-term service stability. These technical problems seriously restrict the development of high-power, high-reliability electronic packaging devices. Summary of the Invention

[0003] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a welding material and welding method for preparing high-temperature resistant solder joints, thereby solving the problems of insufficient heat resistance of traditional solders in high-temperature environments, easy brittle fracture of intermetallic compound (IMC) solders, inability of existing high-temperature solders to meet heat dissipation requirements, porosity defects and electromigration risks in sintered silver solder joints, and interfacial stress problems caused by mismatch in thermal expansion coefficients between different materials.

[0004] To solve the above-mentioned technical problems, in a first aspect, the present invention provides a welding material for preparing high-temperature resistant solder joints, the welding material being used for encapsulation welding of silicon carbide or aluminum nitride substrates;

[0005] The welding material includes a mixture of Cu powder and Mo powder, with the Cu powder content being 70% to 95% and the Mo powder content being 5% to 30% by mass percentage. The welding material also includes an upper copper foil and a lower copper foil, with the mixed powder evenly spread between the upper and lower copper foils.

[0006] Preferably, at least one middle layer of copper foil is laid in the middle of the mixed powder, and the thickness of the upper copper foil, the lower copper foil and the middle copper foil are all 10μm~50μm.

[0007] Preferably, the mixed powder forms a mixed powder layer, and the middle copper foil is evenly spaced along the thickness direction of the mixed powder layer.

[0008] Preferably, the number of layers of the intermediate copper foil is at least one or more.

[0009] Preferably, the average particle size of the Cu powder is 1 μm to 45 μm, and the average particle size of the Mo powder is 0.5 to 10 μm.

[0010] Secondly, the present invention provides a welding method for substrate packaging welding, which uses the above-mentioned welding materials for welding, and the specific steps are as follows:

[0011] The welding material is placed on the substrate at the location where welding is required. While the substrate is being encapsulated and welded, ultrasonic treatment is performed simultaneously until welding is completed. During the welding process, vertical downward pressure is applied to the substrate.

[0012] Preferably, the process parameters during welding are as follows:

[0013] The ultrasonic generator has an ultrasonic frequency of 20kHz, a power of 400w-2000w, and a welding temperature of 240℃-300℃. Ultrasonic assisted welding is performed on the test piece to be welded, with an ultrasonic assisted welding time of 3s-15s and a welding time of 240s-360s.

[0014] Preferably, the pressure applied to the substrate is 2MPa-12MPa.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. This invention unexpectedly discovered a composite structure of copper foil encapsulating Cu-Mo micro / nanoparticles. This design cleverly mimics the layered microstructure characteristics of high-performance heat sink material CPC (copper foil / metal composite / copper foil). CPC materials have attracted much attention in the field of thermal management due to their excellent thermal conductivity and tunable coefficient of thermal expansion. This invention achieves the integrated construction of CPC composite material and welded joint by placing a mixture of high-melting-point Mo particles and Cu particles between copper foil. Mo, with its extremely high melting point, coefficient of thermal expansion close to that of silicon, and excellent intrinsic thermal conductivity, forms a synergistic effect with Cu, generating a supersaturated solid solution under the action of a thermo-acoustic-mechanical field. This CPC-like weld joint not only inherits the advantages of high thermal conductivity and low expansion of traditional CPC materials, but also forms a continuous solid solution network through interfacial atomic interdiffusion, completely eliminating the brittle nature of traditional IMC weld joints. Microstructural characterization confirmed that a Mo-Cu-Mo bridging structure and a stable solid solution interface were formed inside the solder joint. This enabled the solder joint to not only maintain its structural integrity under extreme high-temperature conditions, but also significantly improve its mechanical properties, exhibiting a unique anomalous strengthening behavior. This fundamentally solved the technical problem of high-temperature solder joint failure in high-power electronic packaging.

[0017] 2. This invention discovers that ultrasonic-assisted welding technology, combined with the welding material designed in this invention, can successfully achieve low-temperature in-situ preparation of CPC-like structural weld joints through a multi-field synergistic mechanism of heat, sound, and pressure. This innovative process breaks the technical constraint that traditional high-melting-point metal joining must rely on high-temperature melting. Ultrasonic vibration induces significant local temperature rise and dynamic softening effect at the welding interface. Simultaneously, cavitation and high-frequency friction destroy the interface oxide layer, activating atomic diffusion channels on the surface of micro- and nano-particles. Particularly noteworthy is that this process precisely controls the spatial distribution of the copper foil layer number and Cu-Mo particle ratio, enabling the Cu-Mo system, which originally had extremely low miscibility under thermodynamic equilibrium conditions, to rapidly form a supersaturated solid solution under kinetic drive. This unique preparation process not only retains the layered structural advantages of CPC materials but also achieves atomic-level metallurgical bonding between the copper foil and the intermediate particle layer through an in-situ reaction mechanism, forming a continuous heat conduction pathway and stress buffer gradient. Experimental results show that the microstructure of the solder joints prepared by this method does not degrade after extreme high-temperature aging. Instead, the performance is further improved through solid solution strengthening and phase transformation toughening mechanisms, completely avoiding the risks of void defects and electromigration failure of traditional sintered silver solder joints. Detailed Implementation

[0018] This invention will describe the technical solutions of the embodiments of the invention clearly and completely. Obviously, the described embodiments are only some embodiments of the invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on this invention are within the scope of protection of this invention.

[0019] Unless otherwise specified in the specific circumstances, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within that range, but are not limited to the specific values ​​listed when the range is defined.

[0020] I. A welding material for preparing high-temperature resistant weld joints

[0021] The welding material of the present invention is used for encapsulation welding of silicon carbide or aluminum nitride substrates; the welding material includes a mixed powder composed of Cu powder and Mo powder, and at least one layer of copper foil is disposed in the mixed powder; the amount of Cu powder added is 70%~95% and the amount of Mo powder added is 5%~30% by mass percentage.

[0022] In conducting in-depth research on existing technologies, this invention addresses key issues commonly found in traditional electronic packaging soldering techniques, such as insufficient high-temperature stability of solder joints, high risk of brittle fracture, limited thermal conductivity, and porosity and electromigration in sintered silver solder joints. Therefore, this invention systematically studies these issues from three dimensions: material system, microstructure design, and synergistic fabrication process. In analyzing the packaging requirements of high-power devices, this invention discovered that achieving a balance between low-temperature fabrication and high-temperature service performance requires overcoming the material limitations of traditional solders. To this end, it has conducted in-depth research on the physicochemical properties of high-melting-point metal systems, paying particular attention to the unique advantages of molybdenum due to its extremely high melting point, thermal expansion coefficient close to that of semiconductor materials, and excellent intrinsic thermal conductivity. At the same time, it fully recognizes the superior performance of copper in terms of electrical and thermal conductivity and plastic deformation. Based on this, the present invention discovered that by constructing a layered composite structure using high-melting-point Cu and Mo particles at the micro-nano scale and copper foil, and through a multi-field coupling mechanism of heat, sound and pressure, the Cu-Mo system, which originally had extremely low miscibility in the thermodynamic equilibrium state, was forced to break through the solubility limit under relatively mild process conditions. Surprisingly, a structure similar to the heat sink material CPC (copper foil / metal composite material / copper foil) was formed, ultimately forming a supersaturated solid solution solder joint with excellent comprehensive performance, which was very unexpected.

[0023] In practical applications, this invention has surprisingly demonstrated that after prolonged exposure to extreme high-temperature environments, the solder joints not only did not exhibit the performance degradation common in traditional solders, but also displayed an anomalous strengthening behavior with a significant increase in mechanical strength. This strength gain far exceeded expectations, revolutionizing the reliability of the solder joints under high-temperature service conditions. Even more surprisingly, the fracture mode of the solder joints completely transformed from the initial intergranular brittle fracture to a solid solution fracture mode with obvious plastic deformation characteristics. This fundamentally solves the technical problem of brittle fracture failure of solder joints in high-power devices during thermal cycling. Regarding thermal conductivity, this invention has observed that the solder joints exhibit excellent temperature stability in their thermal conductivity, maintaining a high level of thermal conductivity even at high temperatures. Its thermal conductivity not only far exceeds that of traditional IMC solder joints but also reaches more than half the thermal conductivity of highly conductive metal materials. This thermal advantage provides a completely new solution for heat dissipation management of high-power-density devices. Furthermore, by precisely controlling the number and distribution of copper foil layers in the CPC microstructure, the present invention unexpectedly discovered in practical applications that the thermal expansion coefficient of the solder joint can be precisely matched, which significantly alleviates the problem of interface stress concentration caused by the mismatch of the thermal expansion coefficients of materials during thermal cycling, and enables the welded joint to maintain structural integrity under extreme temperature change conditions.

[0024] In some embodiments of the present invention, the solder material comprises two layers of copper foil, which are located on the upper and lower sides of the mixed powder, respectively. The present invention has discovered that this structural mode can successfully construct a CPC composite microstructure similar to high-performance heat sink materials. The copper foil serves as an outer protective layer and a heat conduction channel, while the mixed powder in the middle forms a high thermal conductivity, low expansion solid solution core under the synergistic effect of a thermo-acoustic-mechanical field. Microstructural analysis shows that this structure not only achieves atomic-level metallurgical bonding between the copper foil and the intermediate solid solution layer, forming a continuous heat conduction pathway, but also significantly improves the overall mechanical properties of the solder joint through the constraint effect of the copper foil. Experimental data shows that after high-temperature aging treatment, the solder joint with this double-layer copper foil structure not only does not exhibit the strength decay common in traditional solder joints, but also shows a significant increase in strength and improved plasticity. Its fracture mode completely transforms from the initial intergranular brittle fracture to a solid solution fracture mode with obvious plastic deformation characteristics. More importantly, by precisely controlling the number of copper foil layers and the thickness distribution, this structure can effectively adjust the overall thermal expansion coefficient of the solder joint, enabling it to achieve a good match with the semiconductor substrate material. This significantly reduces the accumulation of interfacial stress during thermal cycling and significantly improves the long-term reliability and service life of high-power electronic devices under extreme temperature environments.

[0025] In some embodiments of the present invention, the welding material comprises a layer of copper foil located within the mixed powder. During the adjustment of the position and number of copper foil layers, the present invention unexpectedly discovered that this single-layer copper foil embedded structure design cleverly utilizes the spatial distribution characteristics of the copper foil within the mixed powder, forming a unique gradient transition microstructure. Microscopic characterization results show that the copper foil located in the middle of the mixed powder not only serves as a rapid channel for heat and electricity conduction during welding but also plays a crucial role as a stress gradient transition layer, effectively alleviating the interfacial stress concentration caused by the difference in thermal expansion coefficients between the outer and inner layers. Under the synergistic effect of ultrasonic vibration and pressure, this structural design promotes atomic interdiffusion between the copper foil and surrounding micro / nano particles, forming a more uniform and stable solid solution network. Notably, the single-layer copper foil embedded structure also exhibits excellent microstructural stability under high-temperature service conditions. Its microstructure not only did not undergo significant degradation during long-term high-temperature aging but also further improved its mechanical properties through solid solution strengthening and phase transformation toughening mechanisms. This structure is also particularly suitable for applications with extremely high requirements for thermal expansion matching. By precisely controlling the position of the copper foil in the intermediate layer, it achieves precise regulation of the thermal expansion behavior of the solder joints, providing more flexible design space and higher reliability for complex packaging structures.

[0026] In some embodiments of the present invention, the average particle size of the Cu powder is 1 μm to 45 μm, and the average particle size of the Mo powder is 500 nm to 10 μm. Micron-sized Cu powder, with its excellent plasticity and electrical and thermal conductivity, provides superior matrix properties for the solder joints, while nano- to micron-sized Mo powder exhibits extremely high surface activity and diffusion capacity under ultrasonic activation. Microscopic analysis confirms that ultrafine Mo particles, during ultrasonic vibration, can effectively acquire surrounding Cu atoms through a high-frequency collision and friction mechanism, forming a stable Mo-Cu-Mo bridging structure, thereby achieving rapid metallurgical bonding of metal systems with extremely low miscibility under low-temperature conditions. This particle size gradient design not only significantly reduces the process difficulty of ultrasonic-assisted welding but also promotes the formation kinetics of solid solutions through the high surface energy effect of nanoparticles. Experimental observations show that solder joints with this particle size ratio exhibit unique anomalous strengthening behavior during high-temperature aging; their strength not only does not decrease with increasing temperature but also significantly increases, while maintaining good plastic deformation capacity. This superior high-temperature performance is closely related to the particle size distribution design. In particular, when Mo particles reach an ultrafine scale, their solid solubility in the Cu matrix far exceeds the theoretical limit under thermodynamic equilibrium conditions, forming a supersaturated solid solution structure with excellent comprehensive properties. This fundamentally solves the risk of brittle fracture of traditional solder joints under high-temperature environments. Therefore, the average particle size of Cu powder can be 1μm, 5μm, 10μm, 25μm, 45μm, etc., and all ranges and sub-ranges therein; the average particle size of Mo powder can be 500nm, 1μm, 10μm, etc., and all ranges and sub-ranges therein. It should be understood that, in the implementation scheme, any of the above ranges can be combined with any other range.

[0027] II. A welding method for substrate packaging welding

[0028] The welding process using the welding material described in this invention involves the following specific steps:

[0029] The welding material is placed on the substrate at the location where welding is required. While the substrate is being encapsulated and welded, ultrasonic treatment is performed simultaneously until welding is completed. During the welding process, vertical downward pressure is applied to the substrate.

[0030] In some embodiments of the present invention, the process parameters during welding are as follows:

[0031] The ultrasonic generator operates at a frequency of 22 kHz and a power of 400 W-2000 W, with a welding temperature of 200℃-300℃. Ultrasonic-assisted welding is performed on the test pieces for 3-15 seconds, with the actual welding time ranging from 240 to 360 seconds. This optimized combination of process parameters successfully achieves precise control of the thermo-acoustic synergistic effect, providing crucial process assurance for the low-temperature metallurgical joining of high-melting-point metal systems. Ultrasonic vibration at the welding interface not only generates a significant local temperature rise and material softening effect, but more importantly, it destroys the interface oxide layer through high-frequency vibration, activating atomic diffusion channels on the metal surface. This allows the Cu-Mo system, which is inherently difficult to mix under thermodynamic equilibrium conditions, to rapidly form a supersaturated solid solution under kinetic drive. Experimental data fully demonstrate that this ultrasonic treatment within a specific frequency and power range can achieve atomic-level connections between micro- and nano-particles in a very short time under mild temperature conditions, forming solid solution welds with excellent microstructures. Of particular note is that precise control of the ultrasonic treatment time is crucial to avoiding structural damage caused by excessive vibration, while a reasonable setting of the total welding time ensures the sufficiency and uniformity of solid solution formation. This optimized combination of process parameters not only significantly reduces the welding process temperature, avoiding thermal damage to the substrate material from high temperatures, but also significantly improves welding efficiency and joint quality through the ultrasonic activation mechanism, enabling the weld joint to exhibit excellent structural stability and mechanical properties during subsequent high-temperature service.

[0032] In some embodiments of this invention, a pressure of 2 MPa-12 MPa is applied to the substrate. This pressure control, together with the thermal and acoustic fields, constitutes a multi-physics synergistic welding mechanism, providing indispensable mechanical conditions for the formation of high-quality solid solution weld joints. Microscopic analysis reveals that an appropriate vertical pressure not only ensures close contact between the welding material and the substrate, eliminating interfacial gaps, but more importantly, promotes the plastic deformation and interlocking of micro / nano particles under ultrasonic vibration, accelerating the interatomic diffusion process. Research data clearly show that when the pressure parameters are controlled within a specific range, the relationship between material deformation and structural integrity can be effectively balanced: too low a pressure cannot guarantee sufficient interfacial contact and particle deformation, while too high a pressure may lead to substrate damage or excessive particle breakage. This optimized pressure condition, combined with ultrasonic vibration, significantly enhances the fluidity and force transmission effect of the particle medium, enabling Cu-Mo micro / nano particles to rapidly form a dense solid solution network structure under relatively low temperature conditions. Practical application results show that the precise control of this pressure parameter plays a decisive role in achieving the uniformity of the microstructure and the stability of the mechanical properties of the weld joint. In particular, during the high-temperature aging process, the weld joint formed under appropriate pressure exhibits excellent structural stability and anomalous strengthening behavior. Its strength not only does not decrease with increasing temperature, but is significantly improved, completely avoiding the performance degradation problem of traditional weld joints in high-temperature environments.

[0033] In some embodiments of the present invention, the solder joints are subjected to the following aging treatment:

[0034] Aging treatment at 450℃-550℃ for 24h-168h.

[0035] III. Examples and Comparative Examples

[0036] Example 1

[0037] Step 1: Use a commercially available silicon carbide substrate and ultrasonically clean it with anhydrous ethanol to remove surface oil and dust. The silicon carbide substrate has a metallization layer on its surface. Place the silicon carbide substrate flat on the heating stage with the metallization layer facing upwards; spread the soldering material evenly on the metallization layer of the substrate, with the thickness controlled between 0.1mm and 0.3mm.

[0038] Step 2: Press the T2 copper block on top of the welding material and fix it flexibly with a clamp, with a pressure preload of 2MPa;

[0039] Step 3: Heat the heating table to 280℃, start the ultrasonic generator, the ultrasonic frequency is 20kHz, the power is 300w~2kw, the ultrasonic-assisted welding time is 5s~15s, and the total welding time is 300s~600s; maintain pressure until welding is completed.

[0040] Step 4: After welding is completed, turn off the heating table and allow it to cool naturally to room temperature.

[0041] The welding method of Example 1 was used, and welding was performed according to the welding material composition in Table 1 to obtain the comparative example and the examples. The differences between the comparative example and the examples are limited to: Examples 1-3 have an upper copper foil and a lower copper foil, but no middle copper foil, and Cu-Co powder is uniformly spread between the two copper foils; Examples 4-6 have one middle copper foil, and Cu-Co powder is uniformly spread between the upper copper foil and the middle copper foil, and between the middle copper foil and the lower copper foil; Examples 7-9 have two middle copper foils, which are evenly distributed along the thickness direction of the Cu-Co powder layer, and the Cu-Co powder is uniformly spread between the upper copper foil and the middle copper foil, between two adjacent middle copper foils, and between the middle copper foil and the lower copper foil; Examples 10-13 have one middle copper foil with copper foil thicknesses of 10μm, 20μm, 30μm, 40μm, and 50μm, respectively; the comparative example does not have a middle copper foil. For specific differences, please refer to Tables 1-3.

[0042] Table 1

[0043]

[0044] Table 2

[0045]

[0046] Table 3

[0047]

[0048] IV. Performance Analysis

[0049] 1. Weld joint shear force test

[0050] After the sample is placed in the shearing fixture, the compression mode of the CMT-2503 microcomputer-controlled electronic universal testing machine is used for testing. The universal testing machine is controlled online by the computer. The pressure sensor descent rate is 1 mm / min, and the shear force of the weld joint is tested.

[0051] 2. High-temperature performance test

[0052] To test the performance of the solder joints in a high-temperature environment, the examples and comparative examples were subjected to aging treatment. The samples were placed in a protective gas atmosphere and slowly heated to 500°C (≤5°C / min) and held for different times (0-168h) to test the shear force of the solder joints on the samples.

[0053] 3. Test Results

[0054] Table 4

[0055]

[0056] Table 5

[0057]

[0058] Table 6

[0059]

[0060] Table 7

[0061]

[0062] Analysis of Tables 1-7 shows that:

[0063] (1) The number and distribution of copper foil layers affect the solder joint performance. Experimental data demonstrate the crucial role of copper foil in the welded structure. Table 4 shows that at a welding temperature of 280℃, the solder joint strength of Examples 1-3 (containing Co powder and double-layer copper foil) (28.07-33.56 MPa) is significantly better than that of the comparative examples without Co powder (28.56-32.35 MPa). More importantly, the aging results in Tables 5 and 6 reveal the decisive influence of copper foil distribution on long-term reliability: Examples 4-6, containing one layer of intermediate copper foil, reached a peak strength of 64.32 MPa after aging at 500°C for 2 days, while Comparative Examples 5-8, which also contain copper foil but no Co powder, only reached a maximum of 58.75 MPa; Examples 7-9, containing two layers of intermediate copper foil, also showed a similar trend, with a peak strength of 49.57 MPa, far exceeding the 44.41 MPa of the comparative examples; after aging for 7 days, the strength of Examples 4-6 remained at or above 50 MPa, while the strength of Comparative Examples 5-8 was only around 30 MPa. This proves that the introduction of the copper foil layer in this invention not only improves the initial strength, but more importantly, forms a composite microstructure similar to the high-performance heat sink material CPC, significantly improving the mechanical stability of the solder joint under high-temperature service conditions and solving the technical problem of the rapid strength decay of traditional solder joints at high temperatures.

[0064] (2) The addition of Co powder enhances the high-temperature performance of solder joints. Comparing the data of the examples and comparative examples in Tables 5 and 6, the examples with 20% Co powder (Examples 4-6 and 7-9) reached their peak strength after aging at 500℃ for 2-3 days, and the peak strength was 10-20% higher than that of the comparative examples without Co powder. It is particularly noteworthy that Example 4 achieved a strength of 64.32 MPa after 2 days of aging, while Comparative Example 5 only achieved 54.87 MPa. Microscopic mechanism analysis shows that the addition of Co powder promotes the formation of a stable Cu-Co solid solution structure, which produces an anomalous strengthening effect during high-temperature aging. This result proves that the Cu-Co system in this invention can achieve welding at relatively low temperatures (260-280℃), and at the same time obtains excellent high-temperature service performance through aging treatment, successfully achieving the technical goal of "low-temperature interconnection-high-temperature service" and overcoming the defect of insufficient high-temperature stability of traditional solders.

[0065] (3) Optimizing the copper foil thickness can improve the overall performance of the solder joint. Table 7 shows the precise control effect of copper foil thickness on solder joint performance: when the intermediate copper foil thickness is 10-20 μm, the shear strength of the solder joint reaches the optimal value (33.19-33.80 MPa), and the strength decreases significantly after exceeding 30 μm. This finding proves that the mechanical properties of the solder joint can be optimized by precisely controlling the copper foil thickness in this invention. Microstructure analysis shows that a copper foil thickness of 10 μm-20 μm can provide sufficient thermal and electrical conduction channels without excessively weakening the continuity of the Cu-Co solid solution network, forming an ideal gradient transition structure. This structural design not only improves the initial strength of the solder joint, but more importantly, it significantly improves the interface stress distribution through the constraint effect of the copper foil, greatly improves the thermal cycling reliability, and solves the interface failure problem caused by the mismatch of thermal expansion coefficients in high-power device packaging.

[0066] (4) Aging treatment optimizes solder joint performance. Experimental data fully demonstrate the key role of aging treatment in improving solder joint performance. As shown in Table 5, Example 4 achieved a peak strength of 64.32 MPa after aging at 500℃ for 2 days, which is about 90% higher than the unaged state; while Comparative Example 5, even after the same treatment, only achieved a maximum strength of 54.87 MPa. This indicates that the Cu-Co system in this invention forms a more complete solid solution structure during the aging process, and the presence of copper foil further promotes this strengthening mechanism. Particularly important is that the example with optimized aging treatment exhibits excellent stability under long-term high-temperature service conditions, maintaining a high strength of 57.67 MPa after 7 days, while the comparative example has decreased to 38.79 MPa. This result proves that the technology of this invention can construct a solder joint structure with excellent comprehensive performance at the microscopic level through precise process control, fundamentally solving the problem of performance degradation of traditional solder joints under high-temperature environments.

[0067] (5) The multi-field coupling welding process plays a synergistic role in this invention. Experimental data show that under relatively low temperature conditions of 260-280℃, the multi-field coupling process combining ultrasonic assistance (20kHz, 300W-2kW) and pressure loading (2MPa preload) can produce high-strength solder joints. In particular, the solder joint obtained in Example 4 at 280℃ achieved a strength of 64.32 MPa after aging at 500℃ for 2 days, which far exceeds that of traditional solders (usually <30 MPa). Microscopic analysis shows that ultrasonic vibration produces a significant local temperature rise effect and material softening effect at the welding interface, effectively destroying the interface oxide layer, activating atomic diffusion channels, and enabling the Cu-Co system, which originally had very low miscibility, to rapidly form a supersaturated solid solution under kinetic drive. This result proves the welding mechanism of multi-physics field synergy in this invention, successfully realizing the metallurgical connection of high-melting-point metal systems under low temperature conditions, avoiding thermal damage to the substrate material at high temperatures, and providing an innovative solution for the reliable packaging of high-power electronic devices.

[0068] In summary, the examples and comparative examples fully demonstrate that the present invention, through the synergistic effect of material system innovation (Cu-Co mixed powder), microstructure design (multi-layer copper foil distribution), and fabrication process optimization (thermal-acoustic-pressure multi-field coupling), successfully solves the key problems commonly found in traditional electronic packaging welding technology, such as insufficient high-temperature stability of solder joints, high risk of brittle fracture, and limited thermal conductivity, providing a revolutionary technical solution for the reliable packaging of high power density electronic devices.

[0069] 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 the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A welding material for preparing high-temperature resistant solder joints, characterized in that, The welding material is used for encapsulation welding of silicon carbide or aluminum nitride substrates; The welding material comprises a mixed powder composed of Cu powder and Mo powder, wherein the amount of Cu powder added is 70% to 95% and the amount of Mo powder added is 5% to 30% by mass percentage; the welding material also includes an upper copper foil and a lower copper foil, and the mixed powder is uniformly spread between the upper copper foil and the lower copper foil.

2. The welding material according to claim 1, characterized in that, At least one middle layer of copper foil is laid in the middle of the mixed powder, and the thickness of the upper copper foil, the lower copper foil and the middle copper foil are all 10μm~50μm.

3. The welding material according to claim 2, characterized in that, The mixed powder forms a mixed powder layer, and the middle layer of copper foil is evenly spaced along the thickness direction of the mixed powder layer.

4. The welding material according to claim 2, characterized in that, The number of layers of the intermediate copper foil is at least one or more.

5. The welding material according to claim 1, characterized in that, The average particle size of the Cu powder is 1 μm to 45 μm, and the average particle size of the Mo powder is 0.5 μm to 10 μm.

6. A welding method for substrate packaging welding, characterized in that, Welding is performed using the welding material described in any one of claims 1-5, and the specific steps are as follows: The welding material is placed on the substrate at the location where welding is required. While the substrate is being encapsulated and welded, ultrasonic treatment is performed simultaneously until welding is completed. During the welding process, vertical downward pressure is applied to the substrate.

7. The welding method according to claim 5, characterized in that, The process parameters during welding are as follows: The ultrasonic generator has an ultrasonic frequency of 20kHz, a power of 400w-2000w, and a welding temperature of 240℃-300℃. Ultrasonic assisted welding is performed on the test piece to be welded, with an ultrasonic assisted welding time of 3s-15s and a welding time of 240s-360s.

8. The welding method according to claim 5, characterized in that, The pressure applied to the substrate is 2MPa-12MPa.

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