Welding material for substrate packaging welding and welding method

Abstract

The invention discloses a welding material and a welding method for packaging and welding a substrate. The welding material is used for packaging and welding a silicon carbide or aluminum nitride substrate. The welding material is composed of Cu powder and an active metal component, and the active metal component is at least one of Ni powder and Co powder. And according to the mass percent, the adding amount of the active metal component is greater than or equal to 10%, and the balance is Cu powder.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically to a welding material and welding method for substrate packaging welding. Background Technology

[0002] Currently, electronic products and packaged devices are continuously developing towards miniaturization, high integration, and high power. Chip power density is gradually increasing, and solder joint service temperatures are constantly rising, posing new challenges to device reliability. The fabrication of fully integrated circuit (IMC) solder joints can effectively reduce stress concentration issues, resulting in more stable solder joint performance with higher melting points, lower coefficients of thermal expansion, and better thermal performance. Rapidly forming stable, high-temperature resistant solder joints at low temperatures can improve solder joint reliability, thereby ensuring the quality of electronic products, which is a pressing need in the electronic packaging industry.

[0003] However, the existing technologies for high-temperature solders still have many drawbacks: (1) After thermal shock cycling or thermal aging, the shear strength of high-temperature high-lead solders will gradually decrease, and the fracture mechanism will change from ductile fracture to a mixed ductile-brittle fracture; (2) Au-based solders are expensive, and given their brittleness and processing difficulties, their shear strength will decrease after temperature cycling or aging treatment, and the fracture mode will change to brittle. Furthermore, the increase in oxygen content will cause a sharp decrease in wettability and spreadability, resulting in a smaller spread area. Solder joints are prone to porosity and microcracks, and the interfacial reaction products at high temperatures will also hinder solder spread; (3) The preparation of full IMC solder often takes a long time. Some joints will form voids during high-temperature aging, the interface phase structure will change, and the initial shear strength may decrease. In addition, there is the brittleness problem of IMC. (4) The nanoparticles of sintered nano solder are prone to aggregation and oxidation. After aging in the air environment, the shear strength of the joint will decrease significantly, and oxide growth and porous filamentous structure will appear on the surface. When pressure sintering, some parts need to rely on pressure and specific atmosphere assistance. When pressureless sintering, the sintering time is as long as 60 mins or more. After the paste is sintered, the formation of pores or holes will affect the joint strength and thermal and electrical conductivity. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a soldering material and welding method for substrate packaging soldering, thereby solving problems such as the easy decrease in strength of lead-containing solders in high-temperature environments, the high cost and brittleness of Au-based solders, the long preparation time and the formation of pores during high-temperature aging of full IMC solders, the easy aggregation and oxidation of nano-solders, the need for pressure and specific atmosphere assistance in pressure sintering, the long sintering time of 60 minutes or more in pressureless sintering, and the formation of pores or voids after paste sintering affecting the thermal conductivity, electrical conductivity and reliability of the joint.

[0005] To address the aforementioned technical problems, in a first aspect, the present invention provides a welding material for substrate encapsulation welding, the welding material being used for encapsulation welding of silicon carbide or aluminum nitride substrates; the welding material is composed of Cu powder and an active metal component, the active metal component being at least one of Ni powder and Co powder; calculated by mass percentage, the amount of active metal component added is ≥10%, with the remainder being Cu powder.

[0006] Preferably, the amount of Ni powder used is 10%-50% by mass percentage.

[0007] Preferably, the amount of Co powder used is 10%-30% by mass percentage.

[0008] Preferably, the average particle size of the welding material is 1μm-15μm.

[0009] Secondly, the present invention provides a welding method for substrate packaging welding, which uses the above-mentioned welding material for welding, and the specific steps are as follows:

[0010] The soldering material is placed on the substrate at the location where welding is required, and the substrate is encapsulated and welded while undergoing ultrasonic treatment until welding is completed; during the welding process, vertical downward pressure is applied to the substrate.

[0011] Preferably, the process parameters during welding are as follows:

[0012] The ultrasonic generator has an ultrasonic frequency of 20kHz, a power of 300W~2kW, a welding temperature of 200℃~300℃, and a pressure of 2MPa~12MPa applied to the substrate. The substrate is ultrasonically assisted in welding for 5s~15s, and the welding time is 300s~600s.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] 1. The welding material of this invention is based on Cu powder, combined with at least one active metal component from Ni and Co. The core advantage of this welding material stems from the efficient diffusion and solid solution formation between particles and between particles and the base material. During the welding process, Cu powder and active metal particles can form a stable metal solid solution through atomic-level interdiffusion. This solid solution structure is not a simple particle stacking, but a tight bond at the atomic level, which can significantly enhance the bonding strength and structural stability of the weld joint, avoiding the joint fragility problem caused by component separation or phase transformation in traditional welding materials. At the same time, the addition of active metal components can also optimize the contact state between particles, reduce the particle gaps that occur when welding with single Cu powder, and improve the weld density by filling micropores, laying the foundation for subsequent high-temperature stable service.

[0015] 2. The welding material described in this invention, because it does not contain low-melting-point components, exhibits excellent resistance to degradation in high-temperature environments. All metal components are high-melting-point particles, and there is no melting or loss of low-melting-point phases during welding. Instead, a solid solution is formed through solid-state diffusion. Just as high-melting-point particles in Cu-Ni and Cu-Co systems maintain structural integrity at high temperatures, the high-melting-point characteristics of different active metals in the multi-component combination can also synergistically maintain the weld joint morphology. The Cu-Ni, Cu-Co, and Cu-Ni-Co systems are selected because of their low solid solubility and the high service temperature of the solid solution formed by ultrasonic forcing, avoiding phase transformation during high-temperature service. This high-temperature stability at the microscopic level ensures that the weld joint will not soften, deform, or separate even when exposed to high-temperature environments for a long time, effectively solving the reliability problem of traditional low-melting-point solders in high-temperature scenarios. In addition, the solid solution itself has a high melting temperature, further ensuring the structural rigidity of the weld joint at high temperatures and avoiding the generation of microscopic defects (such as microcracks and voids) caused by temperature fluctuations.

[0016] 3. The welding material described in this invention does not require the addition of flux during use and allows for welding in air without a protective atmosphere. This design directly eliminates a series of problems (such as voids and slag) that may be caused by flux residue at the microscopic level. Traditional flux residue easily forms defects such as inclusions and bubbles inside the solder joint, hindering atomic diffusion and solid solution formation. In contrast, the solder particles in this invention can directly contact the surface of the base material. Under ultrasonic assistance, the oxide film between the particles and the base material is effectively broken down, allowing Cu and active metal atoms to directly diffuse and react, forming a pure interface bond. The residue-free microenvironment also reduces the risk of chemical corrosion at the interface, avoids damage to the solid solution structure by oxides or impurities, and ensures that the solder joint interface always maintains a good atomic bonding state, improving long-term service reliability.

[0017] 4. In the welding method described in this invention, the synergistic effect of ultrasonic assistance and pressure application is particularly significant. Ultrasonic vibration can not only break the oxide film on the surface of the base material and particles, but also promote microscopic collision, compression, and rearrangement of solder particles, reducing loose accumulation between particles and improving contact tightness. At the same time, the application of vertical pressure can further increase the contact area between particles and between particles and the base material, shorten the atomic diffusion path, accelerate the solid solution formation process, and reduce microscopic voids and gaps generated during welding. This process combination does not rely on excessively high welding temperatures. Through microscopic interface optimization and diffusion promotion, efficient welding can be achieved, which reduces energy consumption and avoids thermal damage to the substrate (such as silicon carbide and aluminum nitride) caused by high temperatures, ensuring the overall structural integrity of the substrate and the solder joint.

[0018] 5. This invention regulates the particle size of the welding material. A suitable particle size ensures that Cu powder and active metal particles are mixed evenly, avoiding particle agglomeration or increased gaps caused by excessive particle size differences. For example, particles with similar particle sizes in Cu-Ni and Cu-Co systems can form a denser packing structure. In multi-component combinations, matching the particle size of different active metal particles can also achieve a similar uniform distribution effect, providing sufficient contact interfaces for atomic diffusion and solid solution formation, and further improving the microscopic uniformity and macroscopic reliability of the solder joint.

[0019] 6. The raw materials for the welding material described in this invention are readily available. The high-temperature weld joints are prepared at low temperatures by controlling the particle type, size, and ratio during the welding material preparation process. Therefore, this invention does not have overly strict requirements on weld thickness, making the process for preparing high-temperature weld joints simpler. Simultaneously, the welding method described in this invention uses simple equipment, requiring only a standard heating table and an ultrasonic loading device. Low-temperature interconnection is achieved by breaking the oxide film on the base material through the oscillation of the ultrasonic generator. The welding temperature can be lower than that of ordinary reflow soldering, and the welding time is much shorter than the sintering time of nano-sintered solder, saving heating energy. Therefore, the welding material and welding method described in this invention have excellent prospects for industrial application. Attached Figure Description

[0020] Figure 1 A schematic diagram showing the shear strength of the weld joint with different Cu-Co composition ratios.

[0021] Figure 2 This diagram illustrates the shear strength of the solder joints for different Cu-Ni composition ratios.

[0022] Figure 3 The figure shows the change of shear force after aging treatment at 500℃ for different durations in Example 8.

[0023] Figure 4 The figure shows the change of shear force after aging treatment at 500℃ for different durations in Example 16. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the present invention are within the scope of protection of the present invention.

[0025] 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.

[0026] I. A soldering material for substrate packaging welding

[0027] The welding material described in this invention is used for the encapsulation and welding of circuit boards, specifically for the encapsulation and welding of silicon carbide or aluminum nitride substrates. The welding material is composed of Cu powder and an active metal component, wherein the active metal component is at least one of Ni powder or Co powder; the amount of the active metal component added is ≥10% by mass percentage, with the remainder being Cu powder.

[0028] In the research of this invention, many technical problems existing in the welding material level of the prior art were considered: (1) After thermal shock cycling or thermal aging, the shear strength of high temperature high lead solder will gradually decrease, and the fracture mechanism will change from ductile fracture to ductile-brittle mixed fracture; (2) Au-based solder has a high cost, and in addition to the brittleness and processing difficulty of Au-based solder itself, the shear strength will decrease after temperature cycling or aging treatment, the fracture mode will change to brittle, and the increase in oxygen content will lead to a sharp decrease in its wettability and spreadability, the spread area will shrink, the solder joint is prone to porosity and microcracks, and the interface reaction products at high temperature will also hinder the spread of solder; 3) The preparation of full IMC solder often takes a long time. Some joints will form voids during high-temperature aging, the interface phase structure will change, and the initial shear strength may decrease. In addition, IMC has the problem of brittleness. (4) The nanoparticles of sintered nano solder are prone to aggregation and oxidation. After aging in an air environment, the joint shear strength will decrease significantly, and oxide growth and porous filamentous structures will appear on the surface. During pressure sintering, some parts need to rely on pressure and a specific atmosphere. During pressureless sintering, the sintering time is as long as 60 minutes or more. After the paste is sintered, pores or voids will form, which will affect the joint strength and thermal and electrical conductivity. These technical problems make it difficult for existing solders to meet the packaging and service requirements of different substrates such as silicon carbide and aluminum nitride.

[0029] To address this issue, this invention proposes a solution from three dimensions: fundamental component optimization, enhanced synergistic effects, and expanded adaptability. Firstly, it abandons traditional low-melting-point components, selecting high-melting-point Cu powder as the base, combined with at least one active metal component from Ni and Co. Utilizing the strong diffusion and solid-solution capabilities between Cu and these active metals, a high-temperature stable microstructure is constructed from the root. Secondly, by controlling the proportion of active metal components and the average particle size of the solder, agglomeration problems caused by single-component accumulation are avoided, ensuring close contact between particles and providing sufficient pathways for atomic diffusion. Finally, a multi-component combination is designed, leveraging the synergistic effects of different active metals to balance high-temperature stability, interfacial bonding, and other properties, overcoming the performance limitations of single components. This invention uses Cu powder as the main component, limiting the minimum addition ratio of the active metal component to ensure sufficient diffusion reaction with Cu to form a solid solution. It optimizes the proportion range of different active metals to match their diffusion rate with Cu, and controls the average particle size of the solder within a suitable range to ensure uniform mixing of Cu powder and active metal particles, avoiding microscopic gaps caused by excessive particle size differences. It supports binary and multi-element active metal combinations, flexibly adapting to the soldering requirements of different substrates. Based on this, this invention discovers that through the synergistic diffusion and solid solution of Cu and active metals, a stable metal solid solution can be formed under relatively mild temperature conditions. The tightly bonded structure observed in Cu-Ni and Cu-Co systems, combined with multi-element combinations, forms a multi-element synergistic solid solution network. Its high-temperature stability far exceeds that of single metals or traditional low-melting-point solders, and it does not undergo microstructural degradation even under long-term high-temperature environments. Moreover, by abandoning the use of flux, this invention unexpectedly achieves high purity of the solder joint interface through direct diffusion between components and ultrasonic-assisted oxide film removal, completely eliminating microscopic defects caused by flux residue and significantly improving interfacial bonding strength. Meanwhile, the multi-component combination constructed in this invention does not increase the complexity of the process. On the contrary, through the complementarity of different active metals, the solder material can not only meet the high-temperature requirements of silicon carbide but also satisfy the interface bonding requirements of aluminum nitride substrates. Furthermore, it effectively reduces particle agglomeration and porosity at the microscopic level, forming a dense and uniform solder joint structure. More surprisingly, the appropriate addition of active metals not only does not weaken the intrinsic properties of Cu but also further enhances the mechanical strength and fatigue resistance of the solder joints through the solid solution strengthening effect, achieving multiple breakthroughs in high-temperature stability, interface purity, mechanical properties, and compatibility.

[0030] In some embodiments of the present invention, the active metal component is Ni, and the amount of Ni powder used is 10%-50% by mass percentage. In this embodiment, Cu and Ni combine to form a Cu-Ni system. In the Cu-Ni system, when the Ni content is low, the weld is mainly composed of white Cu particles, with Ni particles dispersed in the gaps between Cu particles. At this time, the Cu particles are mostly mechanically interlocked, and there are many gaps at the microscopic level. Some Cu particles are prone to forming oxide films on their surfaces, resulting in insufficient weld bonding and limited mechanical strength and high-temperature stability. As the Ni content gradually increases, the contact area between Cu and Ni particles increases, the atomic diffusion probability increases significantly, the number of gray Cu-Ni solid solutions in the weld increases, the gaps between particles are gradually filled, the microstructure becomes more compact, the shear strength of the weld increases accordingly, and the structural stability at high temperatures is also enhanced simultaneously. When the Ni content reaches a suitable range, Cu particles uniformly coat Ni particles, forming a continuous and dense Cu-Ni solid solution network with almost no obvious gaps or agglomerations at the microscopic level. At this point, the mechanical strength of the weld joint reaches its peak, and its resistance to high-temperature degradation is optimal. If the Ni content is further too high, gray Ni particles in the weld will agglomerate over a large area, reducing the proportion of Cu particles and preventing them from fully contacting and diffusing with Ni particles. This leads to a decrease in the formation of Cu-Ni solid solution, an increase in microscopic gaps, and stress concentration easily occurring in the agglomerated areas of Ni particles. At the same time, the oxidation of the Cu particles is exacerbated, ultimately resulting in a significant reduction in the mechanical properties and structural stability of the weld joint. The change in Cu content indirectly dominates the microstructure and technical effect by affecting the dispersion state of Ni particles and the efficiency of solid solution formation. When the Cu content is high (i.e., the Ni content is low), Cu particles aggregate in large quantities in the weld, forming an irregular blocky structure with obvious gaps between particles and insufficient Ni particles to participate in diffusion. The weld relies solely on the mechanical interlocking between Cu particles and a small amount of oxide film for connection, resulting in a loose microstructure, low weld strength, and susceptibility to failure at high temperatures. As the Cu content decreases moderately (Ni content increases), Cu particles can better encapsulate Ni particles, providing sufficient contact interfaces for atomic diffusion and promoting the formation of a large amount of Cu-Ni solid solution. Microscopically, the particles are tightly bonded, gaps and oxidation defects are reduced, and the mechanical strength and high-temperature stability of the weld gradually improve. When the Cu content is too low (Ni content is too high), the number of Cu particles is insufficient to fully fill the gaps between Ni particles or to make full contact with the agglomerated Ni particles. This leads to Ni particle agglomeration and uneven distribution of Cu-Ni solid solution at the microscopic level, increasing porosity and oxide areas in the weld. Consequently, the weld density and mechanical properties decrease, and interface separation easily occurs at high temperatures due to structural inhomogeneity.Therefore, in this system, the amount of Cu added is 10%-90%, preferably 60%-80%, and can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc., and all ranges and sub-ranges therein; the amount of Ni added is 10%-90%, preferably 10%-50%, preferably 20%-40%, and can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc., and all ranges and sub-ranges therein; it is sufficient to ensure that the sum of the amounts of the two is 100%.

[0031] In some embodiments of the present invention, the active metal component is Co powder, and the amount of Co powder added is 10%-30% by mass percentage. In the Cu-Co system, the change in Co content directly dominates the microstructure reconstruction and technical effect fluctuations: when the Co content is low, the weld is dominated by whitish Cu particles, and Co particles are dispersed in the gaps between Cu particles and surrounded by a large number of Cu particles. At this time, because the Cu particles cannot fully melt and fill the weld, there are many microscopic gaps. The weld joint mainly relies on the diffusion of Cu atoms to achieve mechanical interlocking, and the bonding is not tight enough, resulting in limited mechanical strength and structural stability. As the Co content gradually increases, the proportion of black Co particles in the weld increases, gradually filling the gaps between Cu particles. The contact area between Cu and Co atoms increases, the diffusion probability increases, the number of gray Cu-Co solid solutions increases, and the microstructure improves. As the Co content becomes denser, the shear strength and high-temperature stability of the weld joint improve simultaneously. When the Co content is within a suitable range, Cu particles can uniformly coat Co particles, forming a continuous and dense Cu-Co solid solution network with no obvious gaps or agglomerations at the microscopic level, resulting in optimal overall weld joint performance. However, if the Co content is too high, large-scale Co particle agglomeration will occur in the weld, presenting as elliptical or elongated aggregates. This leads to uneven solder mixing, insufficient Cu particle proportion, and inability to fully contact and diffuse with Co particles, resulting in a decrease in Cu-Co solid solution formation and an increase in microscopic gaps. At the same time, the agglomeration area of ​​Co particles is prone to stress concentration, ultimately significantly reducing the mechanical properties and structural stability of the weld joint. Changes in Cu content indirectly regulate the microstructure and technical performance by affecting the dispersion state of Co particles and the efficiency of solid solution formation. When the Cu content is high (i.e., the Co content is low), the Cu particles in the weld are small in size, with many gaps between them. There is a lack of sufficient Co particles to fill and diffuse the gaps, and the weld relies only on the mechanical interlocking between Cu particles and a small amount of oxide film for connection. The microstructure is loose, the weld joint has low bonding strength, and it is prone to failure at high temperatures. As the Cu content decreases moderately (Co content increases), Cu particles can better encapsulate Co particles, providing sufficient contact interfaces for atomic diffusion and promoting the formation of a large amount of Cu-Co solid solution. Microscopically, the particles are tightly bonded, gaps and oxidation defects are reduced, and the mechanical strength and high-temperature stability of the weld joint gradually improve. When the Cu content is too low (Co content is too high), there are not enough Cu particles to fully fill the gaps between Co particles or to fully contact the agglomerated Co particles. This leads to the phenomenon of Co particle agglomeration and uneven distribution of Cu-Co solid solution at the microscopic level. The porosity and oxidation area in the weld increase, and the density and mechanical properties of the weld joint decrease accordingly. Under high-temperature conditions, the weld joint is prone to interface separation due to structural inhomogeneity.Therefore, the amount of Co added is 10%-90%, preferably 10%-30%, and can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc. and all ranges and sub-ranges therein; the corresponding amount of Cu added is 10%-90%, preferably 70%-90%, and can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc. and all ranges and sub-ranges therein; just ensure that the sum of the amounts of the two is 100%.

[0032] In some embodiments of the present invention, the active metal components are Co powder and Ni powder, forming a Cu-Co-Ni system. In this system, when the amount of Cu powder added is 30%-75%, the amount of Co added is 10%-30%, and the amount of Ni powder added is 10%-50%, the Cu particles uniformly coat the Co and Ni particles at the microscopic level, with sufficient contact area and sufficient atomic diffusion, forming a continuous and dense Cu-Co-Ni multi-component solid solution network. The Co particles fill the micropores and inhibit Ni agglomeration, while the Ni particles enhance the high-temperature stability of the solid solution and promote diffusion. The synergistic effect of the two not only compensates for the performance shortcomings of a single active metal but also strengthens the bonding ability of the Cu substrate, with no obvious particle agglomeration or oxidation defects. At this time, the shear strength, toughness, and high-temperature resistance to degradation of the solder joint are all optimal. The formation of the multi-component solid solution allows the solder joint to combine the high creep resistance of Co, the high stability of Ni, and the high conductivity of Cu, perfectly meeting the high-temperature and high-reliability soldering requirements of the packaging substrate. If any element exceeds the above range, it will disrupt the synergistic diffusion relationship among the three components, leading to microstructural imbalance and ultimately affecting the overall performance of the solder joint. Therefore, it is further preferred that the addition amount of Cu powder is 55%-75%, Co powder is 10%-25%, and Ni powder is 15%-30%; Cu powder can be 30%, 40%, 50%, 60%, 70%, 75%, etc., and all ranges and sub-ranges therein; Co powder can be 10%, 15%, 20%, 25%, 30%, etc., and all ranges and sub-ranges therein; Ni powder can be 10%, 20%, 30%, 40%, 50%, etc., and all ranges and sub-ranges therein; ensuring that the sum of the three components is 100% is sufficient.

[0033] In some embodiments of the present invention, the average particle size of the welding material is 1 μm-15 μm. Controlling the particle size of each component in the welding material within a suitable range, and minimizing the difference in particle size between components, ensures uniform particle dispersion, sufficient contact area, and adequate atomic diffusion, thereby forming a dense solid solution network.

[0034] In the Cu-Ni system, when the Cu particle size is less than 1 μm, the Cu particles are too small at the microscopic level, exhibiting a nanoscale state (nano-copper). This makes the Cu particles easily oxidized and prone to burn-off, especially during pressure sintering, which requires pressure and a specific atmosphere. Pressureless sintering takes 60 minutes or more, and the resulting pores or voids affect the joint strength and thermal and electrical conductivity. When the Cu particle size is smaller (1 μm), the Cu particles are numerous and uniformly dispersed at the microscopic level, tightly encapsulating Ni particles (regardless of whether the Ni particle size matches). The sufficient contact area and short atomic diffusion paths facilitate the formation of a continuous and dense Cu-Ni solid solution network, resulting in no obvious gaps or agglomeration in the weld. Technically, this leads to high weld shear strength, structural stability at high temperatures, and strong resistance to degradation. As the Cu particle size increases, when the Cu particle size reaches 10 μm, the Cu particles can still effectively encapsulate the Ni particles at the microscopic level, but localized small-scale aggregation occurs, and the interparticle gaps increase slightly. The Cu-Ni solid solution distribution remains relatively continuous; the technical effect is slightly inferior to that of small-particle-size Cu, but it still meets basic performance requirements. When the Cu particle size reaches 15 μm, the Cu particles tend to form irregular blocky aggregations at the microscopic level, failing to fully encapsulate the Ni particles. This results in sparsely dispersed or locally accumulated Ni particles, leading to numerous micro-gaps in the weld. The amount of Cu-Ni solid solution formed is sharply reduced, and an oxide film easily forms around the aggregated Cu particles, ultimately causing a significant decrease in the shear strength of the weld joint. At high temperatures, interfacial separation easily occurs due to structural inhomogeneity. Therefore, in the Cu-Ni system, the average Cu particle size is preferably 1 μm-10 μm. Regarding the average particle size of Ni, when the average particle size of Ni is in the range of 1-10 μm, the Ni particles are uniformly dispersed among the Cu particles, with sufficient contact area and adequate atomic diffusion. The Cu-Ni solid solution exhibits a continuous network distribution, with no obvious gaps in the weld, resulting in high shear strength, good stability of the solid solution at high temperatures, and strong resistance to degradation. However, as the Ni particle size increases (reaching 25 μm), the Ni particles begin to agglomerate, forming local particle clusters. This compresses the diffusion space of Cu particles, leading to uneven distribution of the Cu-Ni solid solution, the appearance of micropores around the agglomerated areas, decreased weld density, reduced shear strength, and a tendency for stress concentration in the agglomerated areas at high temperatures. Therefore, in the Cu-Ni system, the preferred average particle size of Ni is 1 μm-10 μm. The Cu-Co system is similar to the Cu-Ni system, with the preferred average particle sizes of both Cu and Co being 1 μm-10 μm.

[0035] In the Cu-Ni-Co system, Cu is the main material, and at the microscopic level, Cu particles act as a substrate, uniformly encapsulating Ni and Co particles. These three materials interpenetrate and disperse, forming a continuous multi-element solid solution network. Co particles inhibit Ni agglomeration, resulting in solder joints that exhibit high strength, high toughness, and high-temperature stability, achieving optimal overall performance. If the particle size is too large or too small, it will affect the diffusion space of Ni and Co, leading to uneven dispersion of the three active metal particles and ultimately causing performance imbalance. Therefore, the preferred average particle size of Cu is 1μm-10μm, and the preferred average particle size of the active metal particles is also 1μm-10μm.

[0036] II. A welding method for substrate packaging welding

[0037] The welding process using the welding material described in this invention involves the following specific steps:

[0038] The soldering material is placed on the substrate at the location where welding is required, and the substrate is encapsulated and welded while undergoing ultrasonic treatment until welding is completed; during the welding process, vertical downward pressure is applied to the substrate.

[0039] In terms of welding process, this invention introduces a synergistic approach of ultrasonic assistance and pressure application. Ultrasonic vibration breaks down the oxide film on the surface of the base material and particles, promoting particle collision and densification. Combined with a gentle welding temperature, this reduces energy consumption and substrate thermal damage, shortens atomic diffusion paths, and improves microscopic contact conditions. This allows stable interconnects, which previously required high-temperature welding, to be achieved at a gentler temperature. Furthermore, the resulting solder joints, due to their atomic-level diffusion solid solution structure, exhibit significantly higher high-temperature resistance to degradation than traditional solders. The flux-free design is not only environmentally friendly but also unexpectedly achieves high purity and density at the solder joint interface, effectively avoiding defects such as microscopic inclusions and bubbles. Even in aging tests, the solder joint microstructure forms a continuous network solid solution, significantly reducing particle agglomeration and gaps, resulting in a substantial improvement in mechanical properties and long-term reliability. The welding method is compatible with various solder combinations such as Cu-Ni, Cu-Co, and Cu-Ni-Co, meeting the welding requirements of different packaging substrates without complex adjustments. This breaks the limitations of traditional solders that are only suitable for a single system and single application scenario, achieving a dual breakthrough in process simplification and performance upgrade.

[0040] In some embodiments of the present invention, the process parameters during welding are as follows:

[0041] The ultrasonic generator has an ultrasonic frequency of 20kHz, a power of 300W~2kW, a welding temperature of 200℃~300℃, and a pressure of 2MPa~12MPa applied to the substrate. The substrate is ultrasonically assisted in welding for 5s~15s, and the welding time is 300s~600s.

[0042] In some embodiments of the present invention, the solder joints are subjected to the following aging treatment:

[0043] Aging treatment at 450℃-550℃ for 24h-168h.

[0044] III. Examples and Comparative Examples

[0045] Example 1

[0046] 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 solder evenly on the metallization layer of the substrate, with the thickness controlled between 0.1mm and 0.3mm.

[0047] 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;

[0048] 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.

[0049] Step 4: After welding is completed, turn off the heating table and allow it to cool naturally to room temperature.

[0050] The welding method of Example 1 was used, and welding was performed according to the welding material composition in Tables 1-3 to obtain the comparative example and the example. The difference between the comparative example and the example is only the difference in welding material composition.

[0051] Table 1 Cu-Co system

[0052]

[0053] Table 2 Cu-Ni system

[0054]

[0055] Table 3 Cu-Co-Ni system

[0056]

[0057] IV. Performance Analysis

[0058] 1. Weld joint shear force test

[0059] 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.

[0060] 2. High-temperature performance test

[0061] 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.

[0062] 3. Test Results

[0063] (1) Cu-Co system

[0064] Figure 1 This diagram illustrates the shear strength of weld joints with different Cu-Co composition ratios. Figure 1As shown in Table 1, the data trend indicates that when the Co content is 20% (Cu content 80%), the weld joint shear strength reaches a peak of 29.76 MPa, significantly higher than the comparison between pure Cu (23.77 MPa) and pure Co (14.89 MPa), and far superior to cases with excessively high Co content (e.g., 90%) or excessively low Co content (e.g., 10%). Behind this result is the synergistic effect mechanism formed by Cu and Co at an appropriate ratio: when the Co content is controlled at around 20%, Co particles can fully fill the tiny pores between Cu particles without agglomerating due to excessive content. Microscopically, Co, as an active metal, has low diffusion resistance between its atoms and the Cu substrate, allowing it to form a continuous and dense Cu-Co solid solution network. Furthermore, the presence of Co can inhibit local aggregation of Cu particles, reducing porosity and oxidation defects in the weld, thereby significantly improving interfacial bonding. This filling-diffusion-synergistic solid solution effect is a direct manifestation of the microstructure optimization achieved by controlling the active metal (Co) content in this invention. Comparing the extreme proportions reveals that pure Cu solder joints, lacking the pore-filling and diffusion-promoting effects of Co, tend to exhibit microscopically bulky aggregates of Cu particles with numerous inter-particle gaps, achieving bonding only through mechanical interlocking, thus limiting shear strength. In contrast, pure Co solder joints, due to the strong agglomeration tendency of Co particles, easily form coarse particle clusters and exhibit poor wettability with the metallization layer of the silicon carbide substrate, resulting in numerous stress concentration zones in the weld due to agglomeration, ultimately leading to extremely low shear strength. This further demonstrates that the ≥10% active metal component addition limit specified in this invention is not a simple proportional range, but a scientific design based on the synergistic effect of the Cu substrate and the active metal. When the Co content is between 10% and 30% (especially around 20%), it can both leverage the diffusion-promoting and pore-filling effects of the active metal and avoid the agglomeration defects caused by excessive amounts, perfectly balancing solid solution formation efficiency and particle dispersibility. Meanwhile, this fully verifies the targeted nature of the present invention for the packaging requirements of silicon carbide substrates: as a carrier of high-power devices, the packaging solder joints of silicon carbide substrates need to withstand long-term thermal cycling and mechanical stress, and the shear strength of 29.76MPa is not only much higher than that of pure metal solder joints, but also meets the high-strength connection requirements between the substrate and copper components.

[0065] Taking Example 8, which has the best performance, as an example, we investigated the changes in shear force at different durations in a high-temperature environment, such as... Figure 3As shown in the figure. The results show that the shear strength of the weld joint exhibits a trend of first significantly increasing and then slowly decreasing with aging time: the initial (0h) shear strength is 29.76MPa, and the strength continues to increase with the extension of aging time, reaching a peak of 56.06MPa at 96h, and still maintaining 45.18MPa at 168h, which is much higher than the initial strength level. This result verifies the effectiveness of the aging treatment process of the present invention from the microscopic mechanism level: in a high temperature environment of 500℃, Cu and active metal atoms obtain sufficient diffusion kinetic energy, accelerating the formation of a continuous and dense solid solution network, while filling the microscopic pores remaining during the welding process and eliminating internal stress, thereby significantly improving the shear strength; when the aging time exceeds 96h, the slight decrease in strength is due to excessive growth of solid solution grains or the appearance of trace brittle phases in some areas caused by excessive aging, but the overall strength is still maintained at a level much higher than the initial strength. Furthermore, this invention demonstrates that the aging process employed in this invention effectively optimizes the microstructure of the solder joints, significantly improving their mechanical stability and long-term service reliability under high-temperature conditions. Even without aging treatment, the shear force of the solder joints obtained using the technical solution described in this invention continues to develop in high-temperature working environments, which is completely different from the expectations of this invention. This is because the strength of existing metallic materials often decreases after high-temperature aging treatment, especially under high-temperature and long-term conditions, which is quite common. However, this invention found in experiments that, especially at an aging time of around 96 hours, the shear strength of the solder joints nearly doubled. This verifies the core technical mechanism of aging promoting atomic diffusion and strengthening solid solution bonding, and also demonstrates the excellent adaptability of this invention in high-temperature application scenarios such as silicon carbide / aluminum nitride substrate packaging, strongly proving the significant advantages of the technical solution in improving the high-temperature mechanical properties and reliability of solder joints.

[0066] (2) Cu-Ni system

[0067] Figure 2 This diagram illustrates the shear strength of weld joints with different Cu-Ni composition ratios. Figure 2 As can be seen from Table 2: Figure 2The variation of shear strength of solder joints in the Cu-Ni system with different Ni contents is shown. When the Ni content is 30% (corresponding to 70% Cu content), the shear strength of the solder joint reaches a peak of 28.01 MPa. As the Ni content deviates from this ratio, whether it increases or decreases, the shear strength shows a decreasing trend. For example, the shear strength is 23.77 MPa when the Ni content is 0% (pure Cu), and only 13.84 MPa when the Ni content is 100% (pure Ni). This shows that when the Ni content is controlled at around 30%, Ni particles can be uniformly dispersed in the Cu substrate, and the atoms of both can diffuse sufficiently to form a continuous and dense Cu-Ni solid solution network. This network not only fills the micropores between Cu particles but also inhibits particle agglomeration and oxidation defects, thereby significantly improving the interfacial bonding force. A comparison of pure Cu and pure Ni proportions reveals that pure Cu solder joints, lacking the diffusion-promoting and structural refinement effects of Ni, are prone to microscopic particle aggregation and gaps, resulting in limited shear strength. Pure Ni solder joints, on the other hand, exhibit strong agglomeration and insufficient wettability with the silicon carbide substrate metallization layer, leading to numerous stress concentration zones and significantly reduced shear strength. This fully verifies that the present invention optimizes the microstructure of the Cu-Ni system by controlling the content of the active metal (Ni) (especially within the range of 10%-50%, with an optimal content of around 30%), utilizing the high diffusion activity of Ni and the substrate support of Cu to form a high-strength solid solution structure.

[0068] Taking the best-performing Example 16 as an example, the variation of shear force under different durations in a high-temperature environment was investigated, such as... Figure 4As shown in the figure. The results show that the shear strength of the weld joint continuously increases with the extension of aging time: the initial (0h) shear strength is 28.01MPa, and the strength gradually increases with the increase of aging time, reaching a peak of 59.54MPa at 168h. Moreover, the strength does not decrease significantly throughout the aging process and always maintains an upward trend. This process is unexpected by the present invention, because in the traditional welding field, the strength decreases after high-temperature aging, which is essentially due to the deterioration of the microstructure caused by excessive aging. However, in the Cu-Ni system of Example 16 of the present invention, the shear strength continuously climbs from the initial 28.01MPa to 59.54MPa at 168h under aging at 500℃, and there is no downward trend. After observing the changes in the micromorphology of the weld joint during this process, it was found that the atomic radii of Cu and Ni (Cu: 0.128nm, Ni: 0.125nm) are very small, and the two can form an infinitely miscible α-single-phase solid solution. This characteristic is the core material basis for the continuous increase in strength. When the Ni content is controlled at 30% (Cu content 70%), this ratio precisely balances the structural support of the Cu substrate with the diffusion-driven nature of Ni active atoms. Cu, as the substrate, provides a stable lattice space for Ni atoms due to its face-centered cubic structure, preventing Ni from agglomerating into a brittle phase due to excess. Meanwhile, Ni's high diffusion activity (its diffusion coefficient in Cu is much higher than its own grain diffusion) becomes the driving force for atomic movement during aging, providing kinetic energy for continuous solid solution optimization. Simultaneously, this invention also observes that the cavitation and acoustic flow effects of ultrasound can break down the oxide film on the surfaces of Cu and Ni particles, allowing for full contact between fresh metal surfaces. Furthermore, ultrasonic vibration introduces a large number of dislocations and microscopic plastic deformation between particles, forming an initial structure in a high-energy storage state, providing more channels for atomic diffusion and defect repair during aging. Under the synergistic effect of preload pressure and ultrasonic vibration, Cu and Ni particles achieve a tight bond through mechanical interlocking and initial diffusion at low temperatures, initially compressing micropores and gaps in the weld, reserving optimization space for subsequent secondary densification during aging. At 500℃, Cu and Ni atoms acquire sufficient diffusion kinetic energy. Ni atoms continuously undergo long-range diffusion across particles and grain boundaries in the Cu lattice, gradually making the initially locally segregated solid solution more uniform. At the same time, Cu atoms also diffuse into Ni particles. The interdiffusion of the two eventually forms a continuous and homogeneous Cu-Ni solid solution network, significantly improving the overall integrity of the interface bonding. Furthermore, defects such as micropores and dislocation entanglements left by welding are continuously filled and eliminated during high-temperature aging. Atomic diffusion not only fills the pores but also, through the synergistic effect of dislocation slip and recrystallization, transforms the dislocation density from a high-energy storage state to a low-energy stable state. This eliminates stress concentration and strengthens grain boundary bonding, ultimately achieving a strengthening effect far exceeding that of conventional aging treatments.This achieves low-temperature, high-efficiency interconnection of solder joints (protecting the substrate from high-temperature damage) and endows the solder joints with excellent high-temperature service capability through aging treatment, perfectly meeting the stringent requirements of high-power device packaging for low-temperature packaging and high-temperature reliability, fully demonstrating the technical value and practicality of this invention in the field of high-temperature packaging.

[0069] (3) Ternary system

[0070] For Examples 19-25, the joint shear strength reached a maximum of 24.15 MPa or more. When the welds of Examples 19-25 were aged at 400℃ and 500℃ for 24h, 48h and 96h respectively, the joint shear strength could still be maintained at 27.35MPa~33.6MPa.

[0071] 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 soldering material for substrate encapsulation welding, characterized in that, The welding material is used for encapsulation welding of silicon carbide or aluminum nitride substrates; the welding material is composed of Cu powder and an active metal component, wherein the active metal component is at least one of Ni powder and Co powder; the amount of active metal component added is ≥10% by mass percentage, and the remainder is Cu powder.

2. The welding material according to claim 1, characterized in that, The amount of Ni powder used is 10%-50% by mass percentage.

3. The welding material according to claim 2, characterized in that, The amount of Co powder used is 10%-30% by weight.

4. The welding material according to claim 1, characterized in that, The average particle size of the welding material is 1μm-15μm.

5. A welding method for substrate packaging welding, characterized in that, Welding is performed using the welding material described in any one of claims 1-4, and the specific steps are as follows: The solder is placed on the substrate at the location where it needs to be soldered. While the substrate is being encapsulated and soldered, ultrasonic treatment is performed simultaneously until the soldering is completed. During the soldering process, vertical downward pressure is applied to the substrate.

6. 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 300W~2kW, a welding temperature of 200℃~300℃, and a pressure of 2MPa~12MPa applied to the substrate. The substrate is ultrasonically assisted in welding for 5s~15s, and the welding time is 300s~600s.

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