A silver-copper welding material for ceramic sidewall metal shells and its preparation method

Abstract

This invention belongs to the field of brazing materials and provides a silver-copper welding material for ceramic sidewall metal shells and its preparation method. The invention employs a core-shell composite structure design, with a silver-copper matrix core as the core and a titanium-copper intermetallic compound shell coating on the surface. The shell is formed by the diffusion reaction of titanium and copper in the silver-copper matrix core, connected through a metallurgical interface. The silver content is 53.4 to 74.9 parts, the copper content is 22.1 to 46.4 parts, and the titanium content is 0.2 to 3.0 parts. The core is formed by mixing, pressing, sintering, annealing, and rolling silver-copper powders; the titanium layer is deposited by magnetron sputtering; and the shell is converted into an intermetallic compound through diffusion annealing. This significantly improves active wettability, metallurgical bonding strength, thermal cycling reliability, and storage stability. It also resolves the contradiction between enhanced active wettability and interfacial brittleness in ceramic-metal brazing, as well as the contradiction between high shell coverage and controllable phase structure and storage stability. This invention has broad application value in electronic packaging.

Description

Technical Field

[0001] This invention relates to the field of brazing materials, specifically to a silver-copper brazing material for ceramic sidewall metal shells and its preparation method. Background Technology

[0002] Ceramic-metal packaging structures have irreplaceable application value in electronic devices, vacuum switches, high-power semiconductor devices, and aerospace electronic components. The reliable connection between the ceramic sidewalls and the metal casing is crucial for ensuring the device's hermeticity, thermal conductivity, and long-term reliability. As electronic devices evolve towards higher power density, higher frequency, and higher reliability, ceramic-metal packaging structures face increasingly stringent thermal cycling, mechanical stress, and harsh environmental conditions, placing higher performance demands on brazing materials. While traditional silver-copper brazing fillers possess good electrical and thermal conductivity and suitable brazing temperatures, their wettability on ceramics is poor, requiring pre-metallization on the ceramic surface, a complex and costly process. To improve the brazing filler's wettability and interfacial bonding strength, active elements such as titanium, zirconium, and hafnium are typically added to the silver-copper brazing filler. These active elements react chemically with the ceramic surface to form an intermediate reaction layer, achieving a metallurgical bond between the ceramic and the metal. However, the amount and distribution of active elements have a decisive impact on the performance of brazed joints. Excessive or uneven distribution can lead to thickening of the brittle phase at the interface, which can easily generate and propagate microcracks during thermal cycling, resulting in decreased joint reliability. Therefore, how to effectively control the thickness and distribution of the brittle phase at the interface while achieving active wetting and metallurgical bonding, and improve the thermal cycling reliability of brazed joints, has become an important direction for the development of ceramic-metal brazing technology.

[0003] Current research on active brazing alloys mainly focuses on the selection of active elements, optimization of addition amounts, and improvement of distribution methods, but many shortcomings remain. For example, Chinese patent CN102699567A discloses a zirconium-containing copper-silver-titanium brazing alloy, which adds active elements by adding zirconium powder to silver-copper alloy powder. However, this simple powder mixing method leads to uneven distribution of zirconium, easily forming local zirconium-rich and zirconium-poor regions during brazing. The brittle intermetallic compound layer formed in the titanium-rich region is too thick, becoming a crack source and reducing the thermal cycling resistance of the joint. Another example is Chinese patent CN114193019B, which discloses a composite brazing alloy and its preparation method, including an inner core and an outer sheath, with the outer sheath covering the inner core. The outer sheath is mainly composed of copper and silver; the inner core includes alloy powder, which includes copper and phosphorus. However, the thickness of the coating layer is difficult to control precisely, and the active metal is easily oxidized during storage, leading to a decrease in brazing performance. Furthermore, the preparation process of existing active brazing filler metals is complex, requiring strict control of oxygen content and surface treatment; otherwise, the activity of the active elements will be inhibited, affecting the brazing effect. Simultaneously, the storage stability of active brazing filler metals is also a significant issue. Active elements are prone to react with oxygen and nitrogen during storage, leading to reduced activity and decreased brazing performance. Therefore, there is an urgent need to develop a novel silver-copper brazing material and its preparation method that features uniform distribution of active elements, controllable shell thickness, good storage stability, and high reliability of the brazed joint during thermal cycling. Summary of the Invention

[0004] The purpose of this invention is to provide a silver-copper welding material for ceramic sidewall metal shells and its preparation method, which solves the contradiction between the enhanced active wetting / metallurgical bonding and the decreased thermal cycling reliability caused by interface brittleness in existing ceramic-metal brazing, the contradiction between high shell coverage and controllable shell thickness / phase structure and long-term storage stability, and the coupling contradiction between achieving the functional requirements of active shell and optional Sn / In multi-element control while meeting the requirements of low oxygen and low inclusion and good rolling / powdering processing window.

[0005] This invention achieves uniform distribution of the active element titanium and precise control of the shell thickness by constructing a nanoscale titanium-copper intermetallic compound shell on the surface of a silver-copper matrix core. The metallurgical bonding interface formed by the diffusion reaction between the titanium-copper intermetallic compound shell and the silver-copper matrix core ensures the high bonding strength and stability of the shell. During the brazing process, the titanium in the shell can be quantitatively released and react with the ceramic surface to form an intermediate reaction layer of appropriate thickness, which not only ensures active wetting and metallurgical bonding, but also avoids excessive growth of brittle phase. At the same time, the titanium-copper intermetallic compound shell plays an oxidation barrier role for the internal silver-copper matrix core, which significantly improves the storage stability of the material and the thermal cycling reliability of the brazed joint.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A silver-copper welding material for the metal shell of ceramic sidewalls, wherein the silver-copper welding material is a core-shell composite structure powder or a core-shell composite structure foil.

[0008] The core-shell composite structure includes a silver-copper matrix core and a titanium-copper intermetallic compound shell layer located on the surface of the silver-copper matrix core. The titanium-copper intermetallic compound shell layer is formed by the diffusion reaction of titanium and copper in the silver-copper matrix core, and is connected to the silver-copper matrix core through a metallurgical bonding interface formed by the diffusion reaction.

[0009] Based on a total of 100 parts, the sum of the weight parts of silver, copper, and titanium in the core-shell composite structure is 100 parts; wherein the weight parts of silver are 53.4–74.9 parts, the weight parts of copper are 22.1–46.4 parts, and the weight parts of titanium are 0.2–3.0 parts; wherein the sum of the weight parts of silver and copper is 97.0–99.7 parts, and silver accounts for 55–75% of the sum of the weight parts of silver and copper, and copper accounts for 25–43% of the sum of the weight parts of silver and copper;

[0010] The thickness of the titanium-copper intermetallic compound shell is 50–300 nm.

[0011] Furthermore, the preparation steps of the silver-copper matrix core include:

[0012] A1. Using silver powder and copper powder as raw materials, wherein the purity of the silver powder is 98-99.99 wt%, the purity of the copper powder is 98-99.99 wt%, the particle size D50 of the silver powder is 1-20 µm, and the particle size D50 of the copper powder is 1-20 µm; weighing and dry mixing at a ratio of 55-75 wt% of silver and copper and 25-45 wt% of copper, and mixing for 10-60 min; the dry mixing is carried out using a V-type mixer or a ball mill. If a V-type mixer is used, the speed is 20-60 rpm; if a ball mill is used, the speed is 100-300 rpm, and the material-to-ball ratio is 1:2-1:5.

[0013] A2. Fill the mold with the mixed powder, press it unidirectionally at 100-500 MPa and hold it for 1-5 min to obtain a blank with a diameter of 20-50 mm and a thickness of 5-20 mm;

[0014] A3. Place the pressed billet in a vacuum furnace, first evacuate the furnace to a pressure ≤0.001 Pa, and heat it at a rate of 5-20℃ / min; when the temperature reaches 500-600℃, introduce argon or nitrogen to make the furnace pressure 2.5-3.5 Pa, continue heating to 650-1000℃, and sinter under this protective atmosphere for 0.5-1.5 h;

[0015] A4. After sintering, anneal at 600-700 °C under vacuum (furnace pressure ≤0.001 Pa) or inert gas protective atmosphere (argon or nitrogen, furnace pressure 2.5-3.5 Pa) for 2-10 h;

[0016] A5. Subsequently, hot rolling is performed at 500–700 °C, with a reduction rate of 10–30% per pass. After every 2–4 passes of hot rolling, annealing is performed at 600–700 °C in the atmosphere described in step A4 for 1–3 h. The hot rolling and annealing are repeated alternately until the thickness is reduced to 0.3–1.0 mm. Then, cold rolling is performed at room temperature with a total reduction rate of 60–85% to obtain a silver-copper matrix foil with a thickness of 0.05–0.20 mm, or it can be crushed and sieved through a 120–400 mesh sieve to obtain silver-copper matrix powder.

[0017] The endpoint criterion is that the area fraction of unmelted or unsintered silver or copper elemental inclusions in the silver-copper matrix foil or silver-copper matrix powder is ≤1.0%, and the total oxygen content is ≤0.05 wt%.

[0018] Furthermore, the titanium metal layer serves as a precursor layer for the titanium-copper intermetallic compound shell, and its deposition steps include:

[0019] B1. Place the silver-copper substrate powder or silver-copper substrate foil obtained in step A5 into a magnetron sputtering deposition apparatus, and evacuate to a base vacuum level of 2× Pa~3×10 -3 Pa;

[0020] B2. Introduce argon gas to make the working pressure 0.3–1.2 Pa;

[0021] B3. Using titanium as the sputtering target, with a target-substrate distance of 50–150 mm, pre-sputtering for 5–20 min followed by sputtering deposition, sputtering power of 200–1500 W, substrate temperature controlled at no heating or heated to 50–200 ℃, deposition time of 5–240 min, so that the thickness of the deposited titanium metal layer is 30–200 nm.

[0022] B4. After deposition, the material is cooled and sealed under argon or nitrogen protection to preserve it as a core-shell composite precursor.

[0023] The endpoint criterion is that the coverage of the titanium metal layer on the surface of the silver-copper substrate powder or silver-copper substrate foil is ≥70%.

[0024] Furthermore, the titanium metal layer is transformed into the titanium-copper intermetallic compound shell layer by diffusion annealing, and the diffusion annealing step includes:

[0025] C1. Place the core-shell composite structure obtained in step B4 in a vacuum furnace or an inert atmosphere furnace, heat it to 450-700 ℃ at a heating rate of 5-20 ℃ / min and hold it at that temperature for 0.5-6 h. The atmosphere is a vacuum with a furnace pressure ≤0.001 Pa, or argon or nitrogen at atmospheric pressure.

[0026] C2. Subsequently, cool in the furnace to below 200 ℃ or cool to room temperature at a rate not exceeding 10 ℃ / min;

[0027] The endpoint criterion is that the mass fraction of free titanium in the shell is ≤0.2 wt%, and the thickness of the titanium-copper intermetallic compound shell is 50–300 nm.

[0028] Furthermore, it also satisfies any one or any combination of the following technical features; wherein, when the core-shell composite structure is a powder, feature a applies; when the core-shell composite structure is a foil, feature b applies; and feature a and feature b are not the same when selected:

[0029] a. When the core-shell composite structure is a powder, the particle size D50 of the powder is 10 to 60 µm, and the particle size D90 is not greater than 120 µm;

[0030] b. When the core-shell composite structure is a foil, the thickness of the foil is 0.05–0.20 mm;

[0031] c. The thickness of the titanium-copper intermetallic compound shell is 80–200 nm;

[0032] d. The titanium-copper intermetallic compound shell in the core-shell composite structure is one or more of TiCu, Ti2Cu, TiCu2, and TiCu4;

[0033] e. The silver-copper welding material further comprises tin and / or indium. In a total of 100 parts, the sum of the weight parts of silver, copper, titanium, tin, and / or indium in the core-shell composite structure is 100 parts, and the sum of the weight parts of tin and / or indium is 0.1 to 5.0 parts, wherein the weight parts of silver are 50.7 to 74.7 parts, the weight parts of copper are 21.0 to 46.2 parts, and the weight parts of titanium are 0.2 to 3.0 parts (all of the above ranges should be satisfied simultaneously, and the sum of the weight parts of silver and copper should be 92.0 to 99.7 parts). The sum of the weight parts of silver and copper is 92.0 to 99.7 parts, and silver accounts for 55 to 75% of the sum of the weight parts of silver and copper, while copper accounts for 25 to 43% of the sum of the weight parts of silver and copper.

[0034] f. The total oxygen content of the core-shell composite structure is ≤0.05 wt%; the core-shell composite structure is stored at 25±5 ℃ in an argon or nitrogen atmosphere, and the shell thickness changes from -10% to +10% during storage.

[0035] As a concept of this invention, a core-shell composite structure design employing a silver-copper substrate core with a titanium-copper intermetallic compound shell is primarily used to enhance the active wetting performance of silver-copper brazing filler metal on ceramics and the thermal cycling reliability of brazed joints. The silver-copper substrate core is fully alloyed with silver and copper powder using powder metallurgy, forming a uniformly distributed silver-copper alloy microstructure. This eliminates unmelted or unsintered silver or copper inclusions, ensuring the uniformity of the matrix microstructure and the consistency of its mechanical properties. Simultaneously, strict control of the sintering and annealing processes reduces the total oxygen content to below 0.05 wt%, providing a clean interface for subsequent titanium layer deposition and diffusion reactions. Magnetron sputtering deposition technology is used to deposit a nanoscale titanium metal layer on the silver-copper substrate core surface. This method allows for precise control of the titanium layer thickness and uniformity. By adjusting the sputtering power and deposition time, the titanium layer thickness is controlled within the range of 30–200 nm, achieving a coverage of over 70%, ensuring the uniform distribution of the active element titanium. During diffusion annealing, titanium undergoes a solid-state diffusion reaction with copper in the silver-copper matrix core, forming a titanium-copper intermetallic compound shell within a temperature range of 450–700 °C. This shell includes phases such as TiCu, Ti₂Cu, TiCu₂, and TiCu₄. These intermetallic compounds exhibit moderate brittleness and good thermal stability. The shell thickness is controlled within the range of 50–300 nm, providing sufficient active titanium for reaction with the ceramic surface to form intermediate reaction layers such as TiO and TiN for metallurgical bonding, while avoiding excessive growth of brittle phases that could lead to joint embrittlement. A metallurgical interface is formed between the titanium-copper intermetallic compound shell and the silver-copper matrix core through diffusion reaction. This interface exhibits high bonding strength and is not prone to cracking during thermal cycling, significantly improving the thermal fatigue resistance of the brazed joint. Furthermore, the titanium-copper intermetallic compound shell acts as an oxidation barrier for the internal silver-copper matrix core. During storage, the shell thickness variation is controlled within ±10%, ensuring the long-term storage stability of the material.

[0036] This invention also discloses a method for preparing a silver-copper welding material for ceramic sidewall metal shells, comprising the following steps:

[0037] S1. Preparation of silver-copper matrix core: Using silver powder and copper powder as raw materials, wherein the purity of the silver powder is 98-99.99 wt%, the purity of the copper powder is 98-99.99 wt%, the particle size D50 of the silver powder is 1-20 µm, and the particle size D50 of the copper powder is 1-20 µm; weighing silver at 55-75 wt% of the total mass of silver and copper and copper at 25-45 wt% of the total mass of silver and copper, and dry mixing for 10-60 min; pressing the mixed powder into a blank under 100-500 MPa; placing the pressed blank in a vacuum furnace for sintering and annealing; and then hot rolling and annealing alternately, followed by cold rolling to obtain a silver-copper matrix foil with a thickness of 0.05-0.20 mm, or crushing and sieving to obtain silver-copper matrix powder;

[0038] S2. Depositing a titanium metal layer: The silver-copper substrate foil or the silver-copper substrate powder is placed in a magnetron sputtering deposition apparatus, and a titanium metal layer is deposited on its surface by magnetron sputtering;

[0039] S3. Diffusion annealing to form a shell: The core-shell composite structure obtained in step S2 is placed in a vacuum furnace or an inert atmosphere furnace for diffusion annealing to allow titanium and copper to react and form a titanium-copper intermetallic compound shell.

[0040] Further, in step S1, the furnace pressure is evacuated to ≤0.001 Pa, and the temperature is increased at a rate of 5-20 °C / min. When the temperature reaches 500-600 °C, argon or nitrogen is introduced to make the furnace pressure 2.5-3.5 Pa. Under this protective atmosphere, sintering is carried out at 650-1000 °C for 0.5-1.5 h. After sintering, the furnace is cooled to 600-700 °C, and annealed under vacuum (furnace pressure ≤0.001 Pa) or inert gas protective atmosphere (argon or nitrogen, furnace pressure 2.5-3.5 Pa) for 2-10 h. The endpoint is determined by the area fraction of unmelted or unsintered silver or copper elemental inclusions in the silver-copper substrate foil or silver-copper substrate powder being ≤1.0%, and the total oxygen content being ≤0.05 wt%.

[0041] Furthermore, in step S2, the vacuum is evacuated to a background vacuum level of 2× At a working pressure of 0.3–1.2 Pa, argon gas is introduced to achieve a working pressure of 0.3–1.2 Pa. Titanium target is used for sputtering deposition with a target-substrate distance of 50–150 mm. The substrate temperature is controlled at no heating or heated to 50–200 °C. The sputtering power is 200–1500 W, and the deposition time is 5–240 min, resulting in a titanium metal layer thickness of 30–200 nm. The endpoint criterion is that the coverage of the titanium metal layer on the surface of the silver-copper substrate powder or silver-copper substrate foil is ≥70%.

[0042] Further, in step S3, the temperature is increased to 450–700 °C at a heating rate of 5–20 °C / min and held for 0.5–6 h, with an atmosphere where the furnace pressure is ≤0.001. The furnace is then subjected to a vacuum of Pa, or protected by argon or nitrogen at atmospheric pressure, and subsequently cooled with the furnace to below 200 °C or to room temperature at a rate not exceeding 10 °C / min. The endpoint criterion is that the mass fraction of free titanium in the shell is ≤0.2 wt%, and the thickness of the titanium-copper intermetallic compound shell is 50–300 nm.

[0043] Furthermore, tin and / or indium are introduced between step S1 and step S2 or between step S2 and step S3 to form a silver-copper solder material containing tin and / or indium. Based on a total of 100 parts, the sum of the weight parts of silver, copper, titanium, tin and / or indium in the core-shell composite structure is 100 parts, and the sum of the weight parts of tin and / or indium is 0.1 to 5.0 parts.

[0044] Furthermore, the free titanium is defined as elemental titanium metal.

[0045] Furthermore, the method for detecting the mass fraction of free titanium is XRD quantitative analysis or chemical analysis.

[0046] Furthermore, the method for determining the coverage of the titanium metal layer is to observe the sample surface using a scanning electron microscope and calculate it using energy dispersive spectroscopy combined with image analysis.

[0047] Furthermore, the method for determining the area fraction of silver or copper elemental inclusions is to observe the polished cross-section of the sample under a metallographic microscope and calculate it using image analysis.

[0048] Furthermore, the total oxygen content is determined by inert gas melting-infrared absorption method.

[0049] Furthermore, the shell thickness is measured by cross-sectional SEM or TEM and statistically analyzed at multiple measurement points.

[0050] Furthermore, the target-substrate distance in the magnetron sputtering deposition is 50–150 mm.

[0051] Furthermore, the magnetron sputtering deposition is either DC magnetron sputtering or radio frequency magnetron sputtering.

[0052] Furthermore, the substrate temperature during the deposition process is either not heated, heated to a set temperature, or controlled by water cooling.

[0053] Furthermore, the deposition rate is 0.5–2.0 nm / min.

[0054] As another aspect of this invention, a composite preparation method combining powder metallurgy with magnetron sputtering deposition and diffusion annealing is employed to enhance the microstructure uniformity, shell thickness controllability, and process stability of the core-shell composite structure. The powder metallurgy process, through mixing, pressing, sintering, and annealing of silver and copper powders, achieves full alloying of silver and copper at the micrometer scale, eliminating the compositional inhomogeneity and macroscopic segregation problems caused by simple powder mixing. The sintering process is carried out under strictly controlled vacuum or inert atmosphere, with the furnace pressure controlled below 0.001 Pa or the argon / nitrogen gas pressure controlled between 2.5 and 3.5 Pa. The combination of a sintering temperature of 650–1000 °C and an annealing temperature of 600–700 °C ensures sufficient diffusion and alloying of silver and copper while avoiding grain coarsening and oxidation caused by excessively high temperatures, reducing the total oxygen content to below 0.05 wt%, thus providing a clean interface for subsequent titanium layer deposition. Magnetron sputtering deposition technology has significant advantages over traditional coating and powder mixing methods. The sputtering process is carried out under a high vacuum or low-pressure argon atmosphere, with a base vacuum of 2× The pressure of ~3×10-3 Pa ensures a high level of cleanliness in the deposition environment. The combined control of working pressure of 0.3 to 1.2 Pa and sputtering power of 200 to 1500 W allows titanium atoms to be deposited onto the surface of the silver-copper substrate with appropriate energy. The deposition time of 5 to 240 min can be precisely controlled within the range of 30 to 200 nm, with a coverage of over 70%, achieving uniform distribution of titanium and precise control over its thickness. The diffusion annealing process is a key step in the transformation of the titanium metal layer into a titanium-copper intermetallic compound shell. The combination of process parameters, namely a heating rate of 5–20 °C / min, a holding temperature of 450–700 °C, and a holding time of 0.5–6 h, controls the diffusion kinetics of titanium and copper, enabling titanium to undergo a solid-state diffusion reaction with copper to form intermetallic compound phases such as TiCu, Ti2Cu, TiCu2, and TiCu4. The free titanium mass fraction is reduced to below 0.2 wt%, and the shell thickness is controlled within the range of 50–300 nm. This ensures the full conversion of active elements while avoiding excessive diffusion that could lead to an excessively thick shell or an uncontrollable phase structure. The cooling rate is controlled to be no more than 10 °C / min or furnace cooling is used to avoid thermal stress cracking caused by rapid cooling.

[0055] In this invention, the silver-copper matrix core and the titanium-copper intermetallic compound shell each play different roles and form a synergistic effect. The silver-copper matrix core, as the main component of the solder, with a silver content of 55-75% and a copper content of 25-43%, balances melting point, wettability, electrical and thermal conductivity, and mechanical properties. Silver provides excellent electrical and thermal conductivity and wettability to the metal substrate, while copper reduces solder cost and improves strength. The eutectic or near-eutectic composition of silver and copper gives the solder a suitable melting point (780-850 °C) and good fluidity, meeting the temperature window requirements for ceramic-metal brazing. The titanium-copper intermetallic compound shell, as the active component, is key to achieving active wetting and controlling interfacial brittleness through precise control of titanium content (0.2–3.0 parts) and nanoscale shell thickness (50–300 nm). During brazing, titanium can undergo reduction reactions with oxides on the ceramic surface or form an intermediate reaction layer with ceramic matrix elements, achieving metallurgical bonding between the ceramic and the brazing filler metal. Compared to pure titanium, the titanium-copper intermetallic compound has moderate brittleness and better thermal stability, avoiding the problems of uncontrollable interfacial reactions and excessive growth of brittle phases caused by the excessive reactivity of pure titanium. The synergistic effect of the two is reflected in the following aspects: the silver-copper matrix core melts and wets the metal substrate during the brazing process, providing a liquid phase for the flow of brazing filler metal and filling gaps; the titanium-copper intermetallic compound shell partially decomposes and releases active titanium at the brazing temperature; the titanium diffuses to the ceramic surface and reacts with the ceramic to form an intermediate reaction layer; the precise control of the shell thickness ensures that the amount of titanium released is moderate, and the thickness of the intermediate reaction layer is in the micrometer or submicrometer range, which not only ensures the metallurgical bonding strength but also avoids thermal cycling failure caused by an excessively thick brittle layer; the metallurgical bonding interface between the titanium-copper intermetallic compound shell and the silver-copper matrix core ensures that the shell will not peel off or agglomerate during the brazing process; and the release of active titanium is uniform and controllable, ultimately achieving synergistic optimization of active wetting, metallurgical bonding strength, and thermal cycling reliability.

[0056] Beneficial technical effects

[0057] 1. Significantly improves the metallurgical bonding strength and active wetting performance of ceramic-metal brazed joints: By constructing a core-shell composite structure with a titanium-copper intermetallic compound shell on the surface of a silver-copper matrix, the titanium content is precisely controlled at 0.2-3.0 parts and uniformly distributed in the form of nanoscale shells. During the brazing process, the active element titanium can be quantitatively released and react with the ceramic surface to form intermediate reaction layers such as TiO and TiN, achieving metallurgical bonding between the ceramic and the brazing filler metal. Compared with the traditional method of adding titanium powder to brazing filler metal, the present invention improves the uniformity of titanium distribution, avoids the formation of excessively thick brittle phases in local titanium-rich areas, increases the shear strength of the brazed joint by more than 30%, and reduces the wetting angle to below 30°, significantly improving the wettability of the brazing filler metal to the ceramic and the interfacial bonding strength.

[0058] 2. Significantly improves the thermal cycling reliability and thermal fatigue resistance of brazed joints: The thickness of the titanium-copper intermetallic compound shell is controlled within the range of 50–300 nm. The free titanium content is reduced to below 0.2 wt% through diffusion annealing. The intermetallic compound phases such as TiCu, Ti2Cu, TiCu2, and TiCu4 in the shell have moderate brittleness and good thermal stability. The intermediate reaction layer formed during brazing has a moderate thickness, avoiding excessively thick brittle phases from becoming crack sources during thermal cycling. The metallurgical bonding interface between the titanium-copper intermetallic compound shell and the silver-copper matrix core is not prone to cracking during thermal cycling. This allows the brazed joint to maintain a shear strength retention rate of over 90% after 1000 thermal cycles within the range of -55 to 150 ℃, which is more than 50% higher than the thermal cycling reliability of traditional active brazing filler metals.

[0059] 3. Achieving high coverage and precise control of the thickness of the active shell: A titanium metal layer is deposited on the surface of a silver-copper substrate using magnetron sputtering deposition technology, while strictly controlling the background vacuum level to 2× Process parameters such as ~3×10-3 Pa, working gas pressure 0.3~1.2 Pa, sputtering power 200~1500 W, and deposition time 5~240 min enable precise control of titanium layer thickness within the range of 30~200 nm, achieving a coverage of over 70%. The thickness of the titanium-copper intermetallic compound shell formed after diffusion annealing is controlled within the range of 50~300 nm. Compared with the traditional coating method, the thickness control accuracy is improved by more than 3 times, and the shell uniformity and repeatability are significantly improved, ensuring the consistency of brazing performance between batches.

[0060] 4. Significantly improves the storage stability and long-term reliability of the material: The titanium-copper intermetallic compound shell acts as an oxidation barrier for the internal silver-copper matrix core. The chemical stability of the shell is superior to that of a pure titanium metal layer. Under the protective atmosphere of argon or nitrogen at 25±5 ℃, the shell thickness change is controlled within ±10% after 6 months of storage, the total oxygen content remains below 0.05 wt%, and the active titanium content retention rate reaches over 95%. Compared with traditional active brazing filler metals, the problem of activity decay during storage is fundamentally improved, and the shelf life of the material is extended to more than 2 years, ensuring the long-term storage stability and consistency of brazing performance of the material.

[0061] 5. Achieving a harmonious balance between low oxygen and low inclusions and excellent processing performance: Through sintering and annealing processes in powder metallurgy under strictly controlled vacuum or inert atmospheres, the area fraction of unmelted or unsintered silver or copper elemental inclusions in the silver-copper matrix is ​​reduced to below 1.0%, and the total oxygen content is controlled to below 0.05 wt%. This eliminates the adverse effects of inclusions and oxides on subsequent titanium layer deposition and brazing performance. Simultaneously, through alternating hot rolling and annealing processes and cold rolling, silver-copper matrix foils with a thickness of 0.05–0.20 mm or powders with a particle size D50 of 10–60 µm can be produced. The material morphology can be flexibly adjusted according to different brazing application requirements, taking into account both material purity and processing performance, thus expanding the application range of the material. Attached Figure Description

[0062] Figure 1 The images show the XRD phase analysis diagrams of Example 1, Comparative Example 5, and Comparative Example 8.

[0063] Figure 2 The graphs show the elemental distribution and peak binding energy variations with depth in XPS depth profiling for Examples 1 and 3.

[0064] Figure 3 The following is a DSC melting temperature range diagram for Example 1, Example 3, and Comparative Example 1.

[0065] Figure 4 The high-temperature contact angle wetting angle temperature curves and 850°C holding time curves are for Examples 1, 5, and 7. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0067] Example 1

[0068] A core-shell composite structure powder is provided as a silver-copper welding material for the metal shell of ceramic sidewalls. The core-shell composite structure of this embodiment includes a silver-copper matrix core and a titanium-copper intermetallic compound shell layer located on the surface of the silver-copper matrix core. The titanium-copper intermetallic compound shell layer is formed by the diffusion reaction of titanium and copper in the silver-copper matrix core, and is connected to the silver-copper matrix core through a metallurgical bonding interface formed by the diffusion reaction.

[0069] Based on a total of 100 parts, the sum of the weight parts of silver, copper, and titanium in the core-shell composite structure of this embodiment is 100 parts; wherein the weight parts of silver are 64.0 parts, the weight parts of copper are 34.4 parts, and the weight parts of titanium are 1.6 parts; wherein the sum of the weight parts of silver and copper is 98.4 parts, and silver accounts for 65.0% of the sum of the weight parts of silver and copper, and copper accounts for 35.0% of the sum of the weight parts of silver and copper. The thickness of the titanium-copper intermetallic compound shell in this embodiment is 140 nm.

[0070] The preparation steps of the silver-copper matrix core in this embodiment include: using silver powder and copper powder as raw materials, the purity of the silver powder in this embodiment is 99.5 wt%, the purity of the copper powder in this embodiment is 99.5 wt%, the particle size D50 of the silver powder in this embodiment is 10 µm, and the particle size D50 of the copper powder in this embodiment is 10 µm; weighing silver at 65.0 wt% of the total mass of silver and copper and copper at 35.0 wt% of the total mass of silver and copper, and dry mixing for 30 min. Filling the mixed powder into a mold with a diameter of 30 mm and a thickness of 10 mm, unidirectionally pressing at 300 MPa and holding the pressure for 3 min to obtain a blank. Placing the blank in this embodiment in a vacuum furnace, first evacuating the furnace to a pressure of 0.0008 Pa, heating at a heating rate of 10 °C / min, when the temperature reaches 550 °C, argon gas is introduced to make the furnace pressure 3.0 Pa, and the temperature is continued to rise to 800 °C and sintered for 1.0 h under this protective atmosphere. After sintering, the powder was cooled in the furnace to 650 °C and annealed for 5 h under an argon protective atmosphere (furnace pressure 3.0 Pa). Subsequently, it was hot-rolled at 600 °C with a reduction rate of 20% per pass. After every three passes of hot rolling, it was annealed for 2 h at 650 °C under an argon protective atmosphere (furnace pressure 3.0 Pa). This alternating hot rolling and annealing process was repeated until the thickness was reduced to 0.6 mm. The powder was then crushed and sieved through a 200-mesh sieve to obtain silver-copper matrix powder. In this embodiment, the area fraction of unmelted or unsintered silver or copper elemental inclusions in the silver-copper matrix powder was 0.3%, and the total oxygen content was 0.02 wt%.

[0071] The titanium metal layer in this embodiment serves as the precursor layer for the titanium-copper intermetallic compound shell layer. Its deposition steps include: uniformly spreading the obtained silver-copper substrate powder onto a rotatable powder stage with a spreading thickness of 3 mm; the stage rotation speed is 15 rpm; the target-substrate distance is 100 mm; the substrate temperature is not heated and controlled below 50 °C; and the substrate is placed in a magnetron sputtering deposition apparatus using DC magnetron sputtering, with the vacuum level evacuated to a background vacuum of 0.0001 Pa. Argon gas is introduced to bring the working pressure to 0.7 Pa. Using a titanium target as the sputtering target, pre-sputtering is performed for 10 min, followed by sputtering deposition at a sputtering power of 800 W for 120 min, resulting in a titanium metal layer thickness of 100 nm. After deposition, the layer is cooled under argon protection and sealed for preservation as a core-shell composite structure precursor. The titanium metal layer in this embodiment has a coverage rate of 88% on the surface of the silver-copper substrate powder.

[0072] In this embodiment, the titanium metal layer is transformed into a titanium-copper intermetallic compound shell layer through diffusion annealing. The diffusion annealing step includes: placing the obtained core-shell composite structure in a vacuum furnace, heating it to 575 °C at a heating rate of 10 °C / min and holding it at that temperature for 3 h, under a vacuum atmosphere of 0.0008 Pa. Subsequently, it is cooled to room temperature at a rate of 8 °C / min. In this embodiment, the free titanium mass fraction in the shell layer is 0.05 wt%, and the thickness of the titanium-copper intermetallic compound shell layer is 140 nm.

[0073] The powder in this embodiment has a particle size D50 of 35 µm and a particle size D90 of 80 µm. The thickness of the titanium-copper intermetallic compound shell in this embodiment is 140 nm, which is within the preferred range of 80–200 nm. The titanium-copper intermetallic compound shell in the core-shell composite structure of this embodiment is a mixture of TiCu and Ti₂Cu. The total oxygen content of the core-shell composite structure in this embodiment is 0.02 wt%. The core-shell composite structure of this embodiment, stored at 25 ± 5 °C in an argon atmosphere, showed a shell thickness change of +3% after 90 days of storage.

[0074] Features of this embodiment: This embodiment uses medium-parameter configurations, with a silver content of 64.0 parts, a copper content of 34.4 parts, and a titanium content of 1.6 parts, a silver-copper ratio of 65:35, and a titanium-copper intermetallic compound shell thickness of 140 nm. This embodiment selects medium-sized silver and copper powders (D50 of 10 µm each), employs a medium sintering temperature of 800 °C and a medium sputtering power of 800 W, ensuring stable and controllable process parameters and balanced component proportions, suitable for large-scale stable production. The powder obtained in this embodiment has a D50 of 35 µm, a shell coverage of up to 88%, a total oxygen content as low as 0.02 wt%, high material purity, and excellent storage stability. This embodiment is suitable for conventional brazing applications of ceramic sidewall metal shells where high component stability and process controllability are required, and is particularly suitable for mass production and electronic packaging fields with strict quality consistency requirements.

[0075] Example 2

[0076] A core-shell composite foil is provided as a silver-copper welding material for the metal shell of ceramic sidewalls. The core-shell composite structure of this embodiment includes a silver-copper matrix core and a titanium-copper intermetallic compound shell layer located on the surface of the silver-copper matrix core. The titanium-copper intermetallic compound shell layer is formed by the diffusion reaction of titanium and copper in the silver-copper matrix core, and is connected to the silver-copper matrix core through a metallurgical bonding interface formed by the diffusion reaction.

[0077] Based on a total of 100 parts, the sum of the weight parts of silver, copper, and titanium in the core-shell composite structure of this embodiment is 100 parts; wherein the weight parts of silver are 69.2 parts, the weight parts of copper are 29.6 parts, and the weight parts of titanium are 1.2 parts; wherein the sum of the weight parts of silver and copper is 98.8 parts, and silver accounts for 70.0% of the sum of the weight parts of silver and copper, and copper accounts for 30.0% of the sum of the weight parts of silver and copper. The thickness of the titanium-copper intermetallic compound shell in this embodiment is 90 nm.

[0078] The preparation steps of the silver-copper matrix core in this embodiment include: using silver powder and copper powder as raw materials, the purity of the silver powder in this embodiment is 99.9 wt%, the purity of the copper powder in this embodiment is 99.9 wt%, the particle size D50 of the silver powder in this embodiment is 5 µm, and the particle size D50 of the copper powder in this embodiment is 5 µm; weighing silver at 70.0 wt% of the total mass of silver and copper and copper at 30.0 wt% of the total mass of silver and copper, and placing them in a V-type mixer for dry mixing at 40 rpm for 45 min. Filling the mixed powder into a mold with a diameter of 40 mm and a thickness of 12 mm, and unidirectionally pressing and holding the pressure at 400 MPa for 3 min to obtain a blank. The billet of this embodiment was placed in a vacuum furnace. The furnace was first evacuated to a pressure of 0.0006 Pa, and then heated at a rate of 12 °C / min. When the temperature reached 550 °C, nitrogen gas was introduced to bring the furnace pressure to 2.8 Pa. The temperature was then further increased to 900 °C, and sintered for 1.2 h under this protective atmosphere. After sintering, the billet was cooled to 680 °C in the furnace and annealed for 8 h under a nitrogen protective atmosphere (furnace pressure 2.8 Pa). Subsequently, it was hot-rolled at 650 °C with a reduction rate of 20% per pass. After every three passes of hot rolling, it was annealed for 2 h at 680 °C under a nitrogen protective atmosphere (furnace pressure 2.8 Pa). This alternating hot rolling and annealing process was repeated until the thickness was reduced to 0.8 mm. Finally, it was cold-rolled, resulting in a total reduction rate of 87.5% and a silver-copper substrate foil with a thickness of 0.10 mm. In this embodiment, the area fraction of unmelted or unsintered silver or copper elemental inclusions in the silver-copper substrate foil is 0.2%, and the total oxygen content is 0.01 wt%.

[0079] The titanium metal layer in this embodiment serves as the precursor layer for the titanium-copper intermetallic compound shell layer. Its deposition steps include: placing the obtained silver-copper substrate foil in a magnetron sputtering deposition apparatus and evacuating to a base vacuum level of 5× Argon gas was introduced to bring the working pressure to 0.5 Pa. A titanium target was used as the sputtering target, with a target-substrate distance of 100 mm. The substrate temperature was not heated and controlled below 50 °C. DC magnetron sputtering was employed, with pre-sputtering for 8 min followed by sputtering deposition at a power of 600 W for 60 min, resulting in a titanium metal layer thickness of 60 nm. After deposition, the layer was cooled under nitrogen protection and sealed for storage as a core-shell composite structure precursor. In this embodiment, the titanium metal layer achieved a 93% coverage of the silver-copper substrate foil surface.

[0080] In this embodiment, the titanium metal layer is transformed into a titanium-copper intermetallic compound shell layer through diffusion annealing. The diffusion annealing step includes: placing the obtained core-shell composite structure in a nitrogen atmosphere furnace, heating it to 520 °C at a heating rate of 12 °C / min, and holding it at that temperature for 4 h. It is then cooled to 180 °C in the furnace. In this embodiment, the free titanium mass fraction in the shell layer is 0.08 wt%, and the thickness of the titanium-copper intermetallic compound shell layer is 90 nm.

[0081] The foil thickness in this embodiment is 0.10 mm. The thickness of the titanium-copper intermetallic compound shell in this embodiment is 90 nm, which is within the preferred range of 80–200 nm. The titanium-copper intermetallic compound shell in the core-shell composite structure of this embodiment is a mixture of TiCu2 and TiCu4. The total oxygen content of the core-shell composite structure of this embodiment is 0.01 wt%. The core-shell composite structure of this embodiment, stored at 25 ± 5 °C in a nitrogen atmosphere, showed a shell thickness change of +2% after 120 days of storage.

[0082] Features of this embodiment: This embodiment uses a high silver content configuration, with 69.2 parts silver, 29.6 parts copper, and 1.2 parts titanium, resulting in a silver-copper ratio of 70:30 and a titanium-copper intermetallic compound shell thickness of 90 nm. This embodiment uses fine-grained, high-purity silver and copper powders (D50 of 5 µm and purity of 99.9%), employing a high sintering temperature of 900 °C and a long annealing time of 8 h to obtain a foil material with a thickness of 0.10 mm. This embodiment uses a low sputtering power of 600 W and a short deposition time of 60 min to form a thin shell structure with a shell coverage of up to 93% and an extremely low total oxygen content of 0.01 wt%. This embodiment is suitable for precision brazing applications requiring high conductivity of ceramic sidewall metal shells, and is particularly suitable for high-frequency electronic device packaging, high-reliability aerospace electronic components, and power device packaging requiring low-resistance contacts.

[0083] Example 3

[0084] A core-shell composite structure powder is provided as a silver-copper welding material for the metal shell of ceramic sidewalls. The core-shell composite structure of this embodiment includes a silver-copper matrix core and a titanium-copper intermetallic compound shell layer located on the surface of the silver-copper matrix core. The titanium-copper intermetallic compound shell layer is formed by the diffusion reaction of titanium and copper in the silver-copper matrix core, and is connected to the silver-copper matrix core through a metallurgical bonding interface formed by the diffusion reaction.

[0085] The silver-copper welding material of this embodiment also includes tin. Based on a total of 100 parts, the sum of the weight parts of silver, copper, titanium, and tin in the core-shell composite structure of this embodiment is 100 parts, with tin comprising 2.5 parts by weight. Specifically, silver comprises 55.1 parts by weight, copper 39.9 parts by weight, and titanium 2.5 parts by weight. The sum of the weight parts of silver and copper is 95.0 parts, with silver accounting for 58.0% of the sum of the weight parts of silver and copper, and copper accounting for 42.0% of the sum of the weight parts of silver and copper. The thickness of the titanium-copper intermetallic compound shell layer in this embodiment is 240 nm.

[0086] The preparation steps of the silver-copper matrix core in this embodiment include: using silver powder and copper powder as raw materials, the purity of the silver powder in this embodiment is 99.0 wt%, the purity of the copper powder in this embodiment is 99.0 wt%, the particle size D50 of the silver powder in this embodiment is 15 µm, and the particle size D50 of the copper powder in this embodiment is 15 µm; weighing silver at 58.0 wt% of the total mass of silver and copper and copper at 42.0 wt% of the total mass of silver and copper, and placing them in a V-type mixer for dry mixing at 30 rpm for 20 min. Filling the mixed powder into a mold with a diameter of 30 mm and a thickness of 10 mm, and unidirectionally pressing and holding the pressure at 200 MPa for 3 min to obtain a blank. The billet of this embodiment was placed in a vacuum furnace. The furnace pressure was first evacuated to 0.0005 Pa, and the temperature was increased at a rate of 10 °C / min. When the temperature reached 550 °C, argon gas was introduced to reduce the furnace pressure to 2.6 Pa. The temperature was then increased to 720 °C and sintered for 0.8 h under this protective atmosphere. After sintering, it was annealed at 620 °C for 3 h. Subsequently, it was hot rolled at 600 °C with a reduction rate of 20% per pass. After every three passes of hot rolling, it was annealed for 2 h at 620 °C under an argon protective atmosphere (furnace pressure 2.6 Pa). This alternating hot rolling and annealing process was repeated until the thickness was reduced to 0.7 mm. The powder was then crushed and sieved through a 200-mesh sieve to obtain silver-copper matrix powder. In this embodiment, the area fraction of unmelted or unsintered silver or copper elemental inclusions in the silver-copper matrix powder was 0.6%, and the total oxygen content was 0.03 wt%.

[0087] After the silver-copper matrix powder was prepared, tin powder and silver-copper matrix powder were mixed at a mass ratio of 2.5:97.5. The mixing method was mechanical mixing for 15 min to ensure that the tin powder was evenly dispersed on the surface and in the gaps of the silver-copper matrix powder.

[0088] The titanium metal layer in this embodiment serves as the precursor layer for the titanium-copper intermetallic compound shell layer. Its deposition steps include: uniformly spreading silver-copper matrix powder mixed with tin powder onto a rotatable powder stage with a spreading thickness of 3 mm; the stage rotation speed is 15 rpm; the target-substrate distance is 100 mm; the matrix temperature is not heated and controlled below 50 °C; and the substrate is placed in a magnetron sputtering deposition apparatus using DC magnetron sputtering, with the vacuum level evacuated to a background vacuum of 0.002 Pa. Argon gas is introduced to achieve a working pressure of 1.0 Pa. Using a titanium target as the sputtering target, pre-sputtering is performed for 15 min, followed by sputtering deposition at a sputtering power of 1200 W for 180 min, resulting in a titanium metal layer thickness of 160 nm. After deposition, the layer is cooled under argon protection and sealed for preservation as a core-shell composite structure precursor. The titanium metal layer in this embodiment has a coverage of 82% on the surface of the silver-copper matrix powder.

[0089] In this embodiment, the titanium metal layer is transformed into a titanium-copper intermetallic compound shell layer through diffusion annealing. The diffusion annealing step includes: placing the obtained core-shell composite structure in a vacuum furnace, heating it to 650 °C at a heating rate of 8 °C / min and holding it at that temperature for 2 h, under a vacuum atmosphere of 0.0006 Pa. Subsequently, it is cooled to room temperature at a rate of 6 °C / min. In this embodiment, the free titanium mass fraction in the shell layer is 0.12 wt%, and the thickness of the titanium-copper intermetallic compound shell layer is 240 nm.

[0090] The powder in this embodiment has a particle size D50 of 50 µm and a particle size D90 of 110 µm. The thickness of the titanium-copper intermetallic compound shell in this embodiment is 240 nm. The titanium-copper intermetallic compound shell in the core-shell composite structure of this embodiment is a mixture of TiCu, Ti₂Cu, and TiCu₂. The total oxygen content of the core-shell composite structure of this embodiment is 0.03 wt%. The core-shell composite structure of this embodiment, stored at 25 ± 5 °C in an argon atmosphere, showed a shell thickness change of +5% after 60 days of storage.

[0091] Features of this embodiment: This embodiment uses a high copper content configuration with added tin. The silver content is 55.1 parts, the copper content is 39.9 parts, the titanium content is 2.5 parts, and the tin content is 2.5 parts, with a silver-copper ratio of 58:42. The thickness of the titanium-copper intermetallic compound shell is 240 nm. This embodiment uses larger particle size silver and copper powders (D50 of 15 µm for both), employs a lower sintering temperature of 720℃ and a lower pressing pressure of 200 MPa, resulting in a larger powder particle size of 50 µm. This embodiment uses a higher titanium content and a thicker shell design, with a sputtering power of 1200 W, a deposition time of 180 min, a shell thickness of 240 nm, and a base vacuum of 0.002 Pa. This embodiment lowers the brazing temperature and improves wetting performance by adding tin, making it suitable for brazing applications of ceramic sidewall metal shells that require high mechanical strength and cost control while also needing lower brazing temperatures. It is particularly suitable for automotive electronic packaging, mass production of consumer electronics, and temperature-sensitive sensor packaging.

[0092] Example 4

[0093] A core-shell composite foil is provided as a silver-copper welding material for the metal shell of ceramic sidewalls. The core-shell composite structure of this embodiment includes a silver-copper matrix core and a titanium-copper intermetallic compound shell layer located on the surface of the silver-copper matrix core. The titanium-copper intermetallic compound shell layer is formed by the diffusion reaction of titanium and copper in the silver-copper matrix core, and is connected to the silver-copper matrix core through a metallurgical bonding interface formed by the diffusion reaction.

[0094] The silver-copper welding material of this embodiment also includes indium. Based on a total of 100 parts, the sum of the weight parts of silver, copper, titanium, and indium in the core-shell composite structure of this embodiment is 100 parts, with indium comprising 0.5 parts by weight. Specifically, silver comprises 70.6 parts by weight, copper 26.1 parts by weight, and titanium 2.8 parts by weight. The sum of the weight parts of silver and copper is 96.7 parts, with silver accounting for 73.0% of the sum of the weight parts of silver and copper, and copper accounting for 27.0% of the sum of the weight parts of silver and copper. The thickness of the titanium-copper intermetallic compound shell layer in this embodiment is 260 nm.

[0095] The preparation steps of the silver-copper matrix core in this embodiment include: using silver powder and copper powder as raw materials, the purity of the silver powder in this embodiment is 99.99 wt%, the purity of the copper powder in this embodiment is 99.99 wt%, the particle size D50 of the silver powder in this embodiment is 2 µm, and the particle size D50 of the copper powder in this embodiment is 18 µm; weighing silver at 73.0 wt% of the total mass of silver and copper and copper at 27.0 wt% of the total mass of silver and copper, and placing them in a V-type mixer for dry mixing at 40 rpm for 55 min. Filling the mixed powder into a mold with a diameter of 40 mm and a thickness of 12 mm, and unidirectionally pressing and holding the pressure at 450 MPa for 3 min to obtain a blank. The billet of this embodiment was placed in a vacuum furnace. The furnace was first evacuated to a pressure of 0.0004 Pa, and then heated at a rate of 12 °C / min. When the temperature reached 550 °C, nitrogen gas was introduced to bring the furnace pressure to 3.2 Pa. The temperature was then increased to 950 °C, and sintered for 0.6 h under this protective atmosphere. After sintering, the billet was cooled to 690 °C in the furnace and annealed for 9 h under a nitrogen protective atmosphere (furnace pressure 3.2 Pa). Subsequently, hot rolling was performed at 650 °C with a reduction rate of 20% per pass. After every three passes of hot rolling, annealing was performed at 690 °C under a nitrogen protective atmosphere (furnace pressure 3.2 Pa) for 2 h. This alternating hot rolling and annealing process was repeated until the thickness was reduced to 0.6 mm. Finally, cold rolling was performed, resulting in a total reduction rate of 90.0% and a silver-copper substrate foil with a thickness of 0.06 mm. In this embodiment, the area fraction of unmelted or unsintered silver or copper elemental inclusions in the silver-copper substrate foil is 0.4%, and the total oxygen content is 0.02 wt%.

[0096] After the silver-copper substrate foil was prepared, an indium layer was deposited on the foil surface by electroplating. The thickness of the indium layer was 0.8 µm, so that indium accounted for 0.5% of the total mass of the final core-shell composite structure.

[0097] The titanium metal layer in this embodiment serves as the precursor layer for the titanium-copper intermetallic compound shell layer. Its deposition steps include: placing an indium-plated silver-copper substrate foil in a magnetron sputtering deposition apparatus and evacuating to a base vacuum level of 3× Argon gas was introduced to bring the working pressure to 0.4 Pa. A titanium target was used as the sputtering target, with a target-substrate distance of 100 mm. The substrate temperature was not heated and controlled below 50 °C. DC magnetron sputtering was employed, with pre-sputtering for 18 min followed by sputtering deposition at a power of 1400 W for 200 min, resulting in a titanium metal layer thickness of 180 nm. After deposition, the layer was cooled under nitrogen protection and sealed for storage as a core-shell composite structure precursor. In this embodiment, the titanium metal layer achieved a 91% coverage of the silver-copper substrate foil surface.

[0098] In this embodiment, the titanium metal layer is transformed into a titanium-copper intermetallic compound shell layer through diffusion annealing. The diffusion annealing step includes: placing the obtained core-shell composite structure in an argon-atmospheric atmosphere furnace, heating it to 670 °C at a heating rate of 18 °C / min and holding it at that temperature for 1.0 h. Subsequently, it is cooled to room temperature at a rate of 9 °C / min. In this embodiment, the free titanium mass fraction in the shell layer is 0.15 wt%, and the thickness of the titanium-copper intermetallic compound shell layer is 260 nm.

[0099] The foil thickness in this embodiment is 0.06 mm. The titanium-copper intermetallic compound shell thickness in this embodiment is 260 nm. The titanium-copper intermetallic compound shell in the core-shell composite structure of this embodiment is a mixture of TiCu and TiCu4. The total oxygen content of the core-shell composite structure in this embodiment is 0.02 wt%. The core-shell composite structure of this embodiment, stored at 25±5 °C in a nitrogen atmosphere, showed a shell thickness change of -3% after 90 days of storage.

[0100] Features of this embodiment: This embodiment uses parameter configurations close to the range boundary and adds indium. The silver content is 70.6 parts, close to the upper limit; the copper content is 26.1 parts, close to the lower limit; the titanium content is 2.8 parts, close to the upper limit; and the indium content is 0.5 parts, close to the lower limit. The silver-copper ratio is 73:27, close to the high silver limit, and the thickness of the titanium-copper intermetallic compound shell is 260 nm, close to the upper limit. This embodiment uses a differentiated particle size combination of ultrafine silver powder (D50 of 2 µm) and coarser copper powder (D50 of 18 µm), employing a high sintering temperature of 950 ℃, a high pressing pressure of 450 MPa, and a long annealing time of 9 h to obtain an ultrathin foil material with a thickness of 0.06 mm. This embodiment uses a high sputtering power of 1400 W and a long deposition time of 200 min to form a thick shell structure, with a base vacuum of 3× The Pa, diffusion annealing temperature of 670 °C, and heating rate of 18 °C / min are all at relatively high levels. This embodiment further improves wettability and reduces brazing temperature by adding indium, making it suitable for high-end brazing applications of ceramic sidewall metal shells where performance requirements are extremely high and the feasibility of material formulations and process parameters needs to be verified. It is particularly suitable for military-grade high-reliability packaging, electronic devices operating in extreme environments, and ultra-precision microelectronic packaging.

[0101] Comparative Example 1: Basically the same as Example 1, except that the weight parts of silver are 50.0 parts, the weight parts of copper are 48.4 parts, the weight parts of titanium are 1.6 parts, the silver-copper ratio is 50.8:49.2, and the amounts of other components and preparation conditions remain unchanged.

[0102] Comparative Example 2: It is basically the same as Example 1, except that the weight parts of silver are 76.0 parts, the weight parts of copper are 22.4 parts, the weight parts of titanium are 1.6 parts, the silver-copper ratio is 77.2:22.8, and the amount of other components and preparation conditions remain unchanged.

[0103] Comparative Example 3: It is basically the same as Example 1, except that the weight parts of titanium are 0.08 parts, the weight parts of silver are 64.7 parts, and the weight parts of copper are 35.2 parts. The silver-copper ratio remains unchanged at 65:35, and the amounts of other components and preparation conditions remain unchanged.

[0104] Comparative Example 4: Basically the same as Example 1, except that the weight parts of titanium are 3.5 parts, the weight parts of silver are 62.7 parts, and the weight parts of copper are 33.8 parts. The silver-copper ratio remains unchanged at 65:35, and the amounts of other components and preparation conditions remain unchanged.

[0105] Comparative Example 5: It is basically the same as Example 1, except that a titanium metal layer is not deposited on the surface of the silver-copper matrix powder, that is, the titanium content is 0 parts, and the silver-copper matrix powder is used directly as the brazing material. Other preparation conditions remain unchanged.

[0106] Comparative Example 6: It is basically the same as Example 1, except that the sputtering deposition time is 300 min, so that the thickness of the deposited titanium metal layer is 250 nm, and the thickness of the titanium-copper intermetallic compound shell after diffusion annealing is 350 nm. The amount of other components and preparation conditions remain unchanged.

[0107] Comparative Example 7: It is basically the same as Example 1, except that the sputtering deposition time is 20 min, so that the thickness of the deposited titanium metal layer is 15 nm, and the thickness of the titanium-copper intermetallic compound shell after diffusion annealing is 25 nm. The amount of other components and preparation conditions remain unchanged.

[0108] Comparative Example 8: It is basically the same as Example 1, except that the diffusion annealing temperature is 400 °C and the holding time is 3 h, which leads to insufficient diffusion reaction between titanium and copper. The mass fraction of free titanium in the shell is 5.2 wt%, and the thickness of the titanium-copper intermetallic compound shell is only 45 nm. The amount of other components and the preparation conditions remain unchanged.

[0109] Performance testing:

[0110] Test Object: Ceramic-metal brazed joints prepared with brazing material for core-shell composite structures. Test Objective: To evaluate the shear strength of brazed joints and verify the effect of the core-shell structure on improving interfacial bonding strength. Test Principle: By applying a shear load parallel to the brazed interface, the maximum stress at joint failure is measured, reflecting the bonding strength between the brazed layer and the ceramic and metal substrates, and the interfacial metallurgical quality. Experimental Method: The ceramic sidewalls and metal shell are assembled with the designed gap. After filling with brazing material, the joint is heated in a vacuum or inert atmosphere furnace to the brazing temperature (set to 800-850 ℃ according to the material melting point) and held for 10-20 min. After cooling, standard shear specimens (GB / T 11363-2008) are prepared. Shear tests are performed using a universal testing machine at a loading rate of 0.5-1.0 mm / min. The maximum load is recorded, and the shear strength is calculated. Key parameters: Sample size 10×10 mm, brazing gap 0.05-0.15 mm, brazing temperature 800-850 ℃, test temperature 25±2 ℃, loading rate 0.5-1.0 mm / min. Data processing: Shear strength = maximum load / brazing area, take the average ± standard deviation of n≥5 samples, the evaluation criterion is shear strength ≥80 MPa is qualified.

[0111] Test Object: Wetting angle of core-shell composite brazing material on alumina ceramic. Test Objective: To evaluate the wetting performance of brazing material on the ceramic matrix and verify the improving effect of the titanium-copper intermetallic compound shell on interfacial activity. Test Principle: Based on the seated drop method, the contact angle of molten brazing material on the ceramic surface is measured. A smaller contact angle indicates better wettability and lower interfacial tension, which is conducive to forming a good metallurgical bond. Experimental Method: Core-shell composite brazing material was prepared into droplet samples: when in foil form, it was cut into sheet-like samples of 3–5 mm × 3–5 mm; when in powder form, it was pressed into cylindrical samples with a diameter of 3–5 mm at 200 MPa. The droplet samples were placed on an alumina ceramic substrate polished to Ra ≤ 0.4 µm and placed in a high-temperature contact angle measuring instrument. Under a vacuum ≤ 0.001 Pa or an argon protective atmosphere, the temperature was increased to 850 °C at a rate of 10 °C / min and held. The droplet profile was recorded in real-time using a CCD camera, and the contact angle variation with time and temperature was determined using image analysis software. Key parameters: ceramic substrate surface roughness Ra ≤ 0.4 µm, test temperature 800–900 °C, vacuum ≤ 0.001 Pa, heating rate 10 °C / min, holding time 10–30 min. Data processing: Record the equilibrium contact angle θ and its change curve over time, and take the average value ± standard deviation of n≥3 samples. The evaluation criterion is that θ≤20° is excellent wettability.

[0112] Test Object: Phase composition of the titanium-copper intermetallic compound shell in a core-shell composite structure. Test Objective: To identify the types and crystal structures of the titanium-copper intermetallic compounds in the shell and verify the diffusion reaction products and their correlation with process parameters. Test Principle: X-ray diffraction (XRD) is used to analyze the phase composition of the sample. Based on the position and intensity of characteristic diffraction peaks, intermetallic compound phases such as TiCu, Ti₂Cu, TiCu₂, and TiCu₄ are identified. The content of each phase is then quantitatively analyzed using Rietveld refinement. Experimental Method: Core-shell composite structure powder or foil samples are scanned using an XRD instrument with Cu Kα radiation (λ=0.15406 nm). The scanning range is 20-80° (2θ), the step size is 0.02°, the scanning rate is 2° / min, the operating voltage is 40 kV, and the operating current is 40 mA. The diffraction pattern is compared with a PDF standard card to determine the phase types. Rietveld refinement is then performed using Jade or HighScore Plus software. Key parameters: Cu Kα radiation, scan range 20-80°, step size 0.02°, scan rate 2° / min, voltage 40 kV, current 40 mA. Data processing: Diffraction peak positions and intensities were exported as CSV format, crystal plane indices corresponding to the main characteristic peaks were labeled, and the mass fraction of each phase was quantitatively analyzed (accuracy ±2%).

[0113] Test Object: Chemical state and elemental distribution of the titanium-copper intermetallic compound shell in a core-shell composite structure. Test Objective: To analyze the chemical valence state and bonding state of Ti and Cu in the shell, and to verify the formation and interfacial diffusion mechanism of the titanium-copper intermetallic compound. Test Principle: X-ray photoelectron spectroscopy (XPS) is used to determine the binding energy of Ti 2p and Cu 2p electrons. The Ti-Cu bonding state is analyzed by peak shift and peak fitting, and the elemental concentration distribution curve is obtained by depth profiling. Experimental Method: The core-shell composite structure powder or foil sample is placed in an XPS instrument using an Al Kα ray source (hν = 1486.6 eV) under ultra-high vacuum (≤5× The tests were conducted under the following conditions: First, a full-spectrum scan (0-1200 eV) was performed to determine the elemental composition. Then, high-resolution scans (energy resolution ≤0.5 eV) were performed on Ti 2p, Cu 2p, and O 1s. Depth profiling was performed by sputtering (sputtering rate approximately 2-5 nm / min) to obtain elemental concentration variation curves over sputtering time. Key parameters: Al Kα-ray source, vacuum level ≤ 5× Pa, energy resolution ≤0.5 eV, Sputtering rate: 2-5 nm / min; depth profile interval: 10-30 nm. Data processing: Ti 2p and Cu 2p binding energy spectra and elemental concentration-depth curves were exported in CSV format. The chemical state proportions of Ti-Cu intermetallic compounds were determined by peak fitting.

[0114] Test Object: Microstructure and interface structure of brazed joints. Test Objective: To observe the microstructure and elemental distribution of the ceramic-brazed layer-metal interface, and to verify the thickness of the interfacial reaction layer and the quality of the metallurgical bond. Test Principle: The cross-section of the brazed joint is observed and elemental analyzed using scanning electron microscopy (SEM) combined with energy dispersive spectroscopy (EDS) to identify interfacial reaction products and diffusion layer structure. Experimental Method: The brazed joint is cut, mounted, and polished along a direction perpendicular to the interface until the surface roughness Ra ≤ 0.1 µm. The interface morphology is observed using field emission scanning electron microscopy (accelerating voltage 15-20 kV) at a magnification of 500-10000x. Point, line, and area scans are performed using EDS to determine the concentration distribution of elements such as Ti, Cu, Ag, Al, and O near the interface, and backscattered electron (BSE) imaging is used to identify different phase regions. Key parameters: accelerating voltage 15-20 kV, working distance 8-12 mm, magnification 500-10000x, EDS acquisition time 60-120 s / point, polished surface roughness Ra≤0.1 µm. Data processing: export EDS line scan and area scan elemental concentration data to CSV format, measure the thickness of the interface reaction layer (statistically count n≥10 locations), and analyze the elemental diffusion curve gradient.

[0115] Test Object: Melting temperature range of brazing materials for core-shell composite structures. Test Objective: To determine the solidus and liquidus temperatures of brazing materials, providing a basis for the brazing process temperature window and verifying the rationality of the composition design. Test Principle: Differential scanning calorimetry (DSC) is used to measure the endothermic peak of the sample during the heating process. The solidus temperature Ts is determined based on the peak onset temperature, and the liquidus temperature Tl is determined based on the peak end temperature. The melting temperature range ΔT = Tl - Ts reflects the width of the brazing process window. Experimental Method: Weigh 5-10 mg of core-shell composite structure powder or foil sample and place it in an alumina crucible. Heat from room temperature to 1000 ℃ in a DSC instrument at a heating rate of 10℃ / min, under a high-purity argon atmosphere (purity ≥99.999%) and a flow rate of 50-100 mL / min. Record the heat flow-temperature curve and determine the solidus and liquidus temperatures based on the endothermic peak. Repeat the test with n ≥ 3 samples to verify reproducibility. Key parameters: heating rate 10 ℃ / min, temperature range 25-1000 ℃, argon flow rate 50-100 mL / min, argon purity ≥99.999%, sample mass 5-10 mg. Data processing: Export DSC curve heat flow-temperature data to CSV format, determine Ts and Tl using the tangent method (accuracy ±2 ℃), and calculate the melting temperature range ΔT.

[0116] Figure 1 The XRD patterns for XRD phase analysis are shown. The sample names are Example 1, Comparative Example 5, and Comparative Example 8. The characterization method is XRD phase analysis. Fixed parameters are: scan range 2θ from 20° to 80°, step size 0.02°, relative intensity normalized to 0 to 1000 a.u., and the same coordinate axes and plotting line types. Changing parameters are: switching the sample type from Example 1 to Comparative Example 5 and Comparative Example 8, and the resulting differences in phase composition. Example 1 shows additional diffraction peaks compared to Comparative Example 5 and weakens the characteristic Ti peaks compared to Comparative Example 8, indicating that Example 1 formed a stable shell-related intermetallic compound phase with lower free Ti residue, supporting the rationality of the interfacial reaction pathway and structural design at the phase level.

[0117] Figure 2This is a graph showing the elemental distribution and peak binding energy variation with depth obtained from XPS depth profiling. The sample names are Example 1 and Comparative Example 3, and the characterization method is XPS depth profiling. Fixed parameters were: sputtering depth range of 0 to 300 nm, step size of 5 nm; detected elements were Ti and Cu, expressed as atomic fractions (at.%); and the binding energies of Ti 2p and Cu 2p were simultaneously tracked in eV using the same coordinate axes and plotting line type. Changing parameters involved switching the sample type from Example 1 to Comparative Example 3 and the resulting differences in elemental gradient and chemical state stability. Example 1 showed Ti enrichment on the surface layer, which decreased with depth, while Cu increased with depth, forming a significant gradient. Simultaneously, the peak positions of Ti 2p and Cu 2p showed relatively small changes with depth. Comparative Example 3 showed a generally lower Ti concentration and a weaker gradient, with more pronounced peak position drift. This indicates that Example 1 more easily formed a continuous shell and stable diffusion layer, and the chemical state transition at the interface was more continuous. Both the composition and chemical bonding state demonstrate that the interface design can achieve the expected layered and gradient structure.

[0118] Figure 3 The DSC plots for the melting temperature range are shown below. The sample names are Example 1, Example 3, and Comparative Example 1, and the characterization method is DSC. The fixed parameters are a temperature range of 720°C to 880°C. Heat flow curves are recorded during the heating process, using the same coordinate axes and plotting line types, with endothermic peaks characterizing the melting process. The varying parameters are the sample type switching from Example 1 to Example 3 and Comparative Example 1, and the resulting difference between the solidus temperature Ts and the liquidus temperature Tl. Example 1 corresponds to Ts of approximately 782°C and Tl of approximately 825°C, Example 3 corresponds to Ts of approximately 758°C and Tl of approximately 798°C, while Comparative Example 1 falls between the two. This demonstrates that the melting range can be adjusted and a stable melting window maintained through formulation and microstructure control. From a thermal analysis perspective, this proves that material design can achieve targeted control of melting behavior according to objectives.

[0119] Figure 4The wetting angle temperature curve and the holding time curve at 850°C are shown for high-temperature contact angle. The sample names are Example 1, Comparative Example 5, and Comparative Example 7. The characterization method is high-temperature contact angle testing. The fixed parameters are: temperature curve range of 700°C to 900°C in 2°C increments, using the same coordinate axis and plotting line type, and expressing the wetting state in contact angles; and time curve at a fixed temperature of 850°C for 0 to 30 min in 0.5 min increments, using the same coordinate axis and plotting line type. The variable parameters are: switching the sample type from Example 1 to Comparative Example 5 and Comparative Example 7, and the resulting difference in the rate of contact angle decrease with temperature and the kinetics of decay with time. In Example 1, the contact angle during the heating process was significantly lower than that of Comparative Examples 5 and 7, and it approached the low-angle stable range more quickly. When the temperature was maintained at 850°C, the contact angle decreased rapidly over time and reached a low equilibrium angle of about 15°. In contrast, the equilibrium angles of Comparative Examples 5 and 7 were about 68° and 58°, respectively, and the decay was slower. This indicates that the interface of Example 1 can match better and the wetting kinetics are faster. From both the wetting thermal process and kinetics, it is demonstrated that the constructed interface structure can significantly improve the high-temperature wetting behavior and support the effectiveness of the solution.

[0120] As can be seen from the performance of the embodiments and comparative examples in Table 1, the shear strength of the four embodiments is between 118-135 MPa, which is significantly better than all the comparative examples (55-92 MPa), proving the effectiveness of the core-shell composite structure design. The wetting angle of the embodiments is in the range of 12-18°, which is much smaller than the 28-68° of the comparative examples, indicating that the titanium-copper intermetallic compound shell significantly improves the wetting performance of the brazing material on the ceramic. In Comparative Examples 1 and 2, due to the deviation of the silver-copper ratio from the preferred range, the eutectic temperature range changed and the interfacial activity decreased, resulting in a decrease in shear strength of about 28-32%. In Comparative Examples 3, 4, and 5, due to insufficient titanium content or the absence of a titanium shell, the materials could not fully react with the oxides on the ceramic surface during the brazing process, resulting in an increase in the wetting angle to 45-68° and a decrease in shear strength of 41-57%. Comparative Example 6 showed an excessively thick shell layer, leading to an increase in brittle phases; Comparative Example 7 showed an excessively thin shell layer, failing to provide sufficient interfacial activity; and Comparative Example 8 showed inadequate diffusion reaction, resulting in a large amount of residual free titanium. The shear strength of these three examples decreased by 36%, 52%, and 55%, respectively. Examples 2 and 4, due to their use of foil and high silver content, achieved the highest shear strength (132-135 MPa) while maintaining wettability. Example 3, by adding tin, effectively reduced the soldering temperature (Ts=758℃), providing a solution for temperature-sensitive device packaging. The interfacial reaction layer thickness data showed that the interfacial reaction in the examples was moderate (2.2-3.5 µm), while the comparative examples, due to poor wetting or compositional imbalance, resulted in reaction layers that were either too thin (1.8 µm) or too thick (4.2-7.2 µm), affecting the stability of the joint's mechanical properties.

[0121] Table 1 Performance Comparison Summary Table

[0122]

[0123] 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 them. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A silver-copper welding material for ceramic sidewall metal casing, characterized in that, The silver-copper welding material is a core-shell composite structure powder or a core-shell composite structure foil. The core-shell composite structure includes a silver-copper matrix core and a titanium-copper intermetallic compound shell layer located on the surface of the silver-copper matrix core. The titanium-copper intermetallic compound shell layer is formed by the diffusion reaction of titanium and copper in the silver-copper matrix core, and is connected to the silver-copper matrix core through a metallurgical bonding interface formed by the diffusion reaction. Based on a total of 100 parts, the sum of the weight parts of silver, copper, and titanium in the core-shell composite structure is 100 parts; wherein the weight parts of silver are 53.4–74.9 parts, the weight parts of copper are 22.1–46.4 parts, and the weight parts of titanium are 0.2–3.0 parts; wherein the sum of the weight parts of silver and copper is 97.0–99.8 parts, and silver accounts for 55–75% of the sum of the weight parts of silver and copper, and copper accounts for 25–45% of the sum of the weight parts of silver and copper. The thickness of the titanium-copper intermetallic compound shell is 50–300 nm; The preparation steps of the silver-copper matrix core include: A1. Using silver powder and copper powder as raw materials, wherein the purity of the silver powder is 98-99.99 wt%, the purity of the copper powder is 98-99.99 wt%, the particle size D50 of the silver powder is 1-20 µm, and the particle size D50 of the copper powder is 1-20 µm; weigh out silver at 55-75 wt% of the total mass of silver and copper and copper at 25-45 wt% of the total mass of silver and copper, and dry mix for 10-60 min; A2. Press the mixed powder into a blank at 100–500 MPa; A3. Place the pressed billet in a vacuum furnace, first evacuate the furnace to a pressure ≤0.001 Pa, then introduce argon or nitrogen to make the furnace pressure 2.5-3.5 Pa, and sinter at 650-1000 ℃ for 0.5-1.5 h under a protective atmosphere; A4. After sintering, anneal at 600–700 °C for 2–10 h; A5. Subsequently, hot rolling and annealing are repeated alternately until the thickness is reduced, and then cold rolling is performed to obtain silver-copper matrix foil with a thickness of 0.05 to 0.20 mm, or it is crushed and sieved to obtain silver-copper matrix powder; The titanium metal layer serves as a precursor layer for the titanium-copper intermetallic compound shell, and its deposition steps include: B1. Place the silver-copper substrate powder or silver-copper substrate foil obtained in step A5 into a magnetron sputtering deposition apparatus, and evacuate to a base vacuum level of 2× Pa~3× Pa; B2. Introduce argon gas to make the working pressure 0.3–1.2 Pa; B3. Using a titanium target as the sputtering target, perform sputtering deposition after pre-sputtering for 5 to 20 minutes. The sputtering power is 200 to 1500 W, and the deposition time is 5 to 240 minutes, so that the thickness of the deposited titanium metal layer is 30 to 200 nm. B4. After deposition, the material is cooled and sealed under argon or nitrogen protection to preserve it as a core-shell composite precursor. The titanium metal layer is transformed into the titanium-copper intermetallic compound shell layer by diffusion annealing, and the diffusion annealing step includes: C1. Place the core-shell composite structure obtained in step B4 in a vacuum furnace or an inert atmosphere furnace, heat it to 450-700 ℃ at a heating rate of 5-20 ℃ / min and hold it at that temperature for 0.5-6 h. The atmosphere is a vacuum with a furnace pressure ≤0.001 Pa, or argon or nitrogen at atmospheric pressure. C2. Then cool with the furnace to below 200 ℃ or cool to room temperature at a rate not exceeding 10 ℃ / min.

2. The silver-copper welding material for ceramic sidewall metal shells according to claim 1, characterized in that, It also satisfies any one or any combination of the following technical features; wherein, when the core-shell composite structure is a powder, option a applies; when the core-shell composite structure is a foil, option b applies; and option a and option b are different. a. When the core-shell composite structure is a powder, the particle size D50 of the powder is 10 to 60 µm, and the particle size D90 is not greater than 120 µm; b. When the core-shell composite structure is a foil, the thickness of the foil is 0.05–0.20 mm; c. The thickness of the titanium-copper intermetallic compound shell is 80–200 nm; d. The titanium-copper intermetallic compound shell in the core-shell composite structure is one or more of TiCu, Ti2Cu, TiCu2, and TiCu4; e. The silver-copper welding material further comprises tin and / or indium. In a total of 100 parts, the sum of the weight parts of silver, copper, titanium, tin, and / or indium in the core-shell composite structure is 100 parts, and the sum of the weight parts of tin and / or indium is 0.1 to 5.0 parts, wherein the weight parts of silver are 50.7 to 74.7 parts, the weight parts of copper are 21.0 to 46.2 parts, the weight parts of titanium are 0.2 to 3.0 parts, and the sum of the weight parts of silver and copper is 92.0 to 99.7 parts. Silver accounts for 55 to 75% of the sum of the weight parts of silver and copper, and copper accounts for 25 to 43% of the sum of the weight parts of silver and copper. f. The total oxygen content of the core-shell composite structure is ≤0.05 wt%; the core-shell composite structure is stored at 25±5 ℃ in an argon or nitrogen atmosphere, and the shell thickness changes from -10% to +10% during storage.

3. A method for preparing a silver-copper welding material for ceramic sidewall metal shells as described in any one of claims 1-2, characterized in that, Includes the following steps: S1. Preparation of silver-copper matrix core: using silver powder and copper powder as raw materials, wherein the purity of the silver powder is 98-99.99 wt%, the purity of the copper powder is 98-99.99 wt%, the particle size D50 of the silver powder is 1-20 µm, and the particle size D50 of the copper powder is 1-20 µm; weighing silver at 55-75 wt% of the total mass of silver and copper and copper at 25-45 wt% of the total mass of silver and copper, and dry mixing for 10-60 min; pressing the mixed powder into a blank under 100-500 MPa; placing the pressed blank in a vacuum furnace for sintering and annealing; and then hot rolling and annealing alternately, followed by cold rolling to obtain a silver-copper matrix foil with a thickness of 0.05-0.20 mm, or crushing and sieving to obtain silver-copper matrix powder; S2. Depositing a titanium metal layer: The silver-copper substrate foil or the silver-copper substrate powder is placed in a magnetron sputtering deposition apparatus, and a titanium metal layer is deposited on its surface by magnetron sputtering; S3. Diffusion annealing to form a shell: The core-shell composite structure obtained in step S2 is placed in a vacuum furnace or an inert atmosphere furnace for diffusion annealing to allow titanium and copper to react and form a titanium-copper intermetallic compound shell.

4. The preparation method according to claim 3, characterized in that, In step S1, the furnace pressure is evacuated to ≤0.001Pa, and argon or nitrogen is introduced to make the furnace pressure 2.5-3.5 Pa. Sintering is carried out at 650-1000 ℃ for 0.5-1.5 h under a protective atmosphere. After sintering, annealing is carried out at 600-700 ℃ for 2-10 h. The endpoint is determined by the area fraction of unmelted or unsintered silver or copper elemental inclusions in the silver-copper substrate foil or silver-copper substrate powder being ≤1.0%, and the total oxygen content being ≤0.05wt%.

5. The preparation method according to claim 3, characterized in that, In step S2, the vacuum is evacuated to a background vacuum level of 2× Pa~3×10 -3 Argon gas is introduced to make the working pressure 0.3-1.2 Pa. Titanium target is used for sputtering deposition with a sputtering power of 200-1500 W and a deposition time of 5-240 min to obtain a titanium metal layer with a thickness of 30-200 nm. The endpoint criterion is that the coverage of the titanium metal layer on the surface of the silver-copper substrate powder or silver-copper substrate foil is ≥70%.

6. The preparation method according to claim 3, characterized in that, In step S3, the temperature is increased to 450–700 °C at a heating rate of 5–20 °C / min and held for 0.5–6 h. The atmosphere is a vacuum with a furnace pressure ≤0.001 Pa, or atmospheric pressure protection with argon or nitrogen. Then, the furnace is cooled to below 200 °C or cooled to room temperature at a rate not greater than 10 °C / min. The endpoint criterion is that the mass fraction of free titanium in the shell is ≤0.2 wt%, and the thickness of the titanium-copper intermetallic compound shell is 50–300 nm.

7. The preparation method according to claim 3, characterized in that, Tin and / or indium are introduced between step S1 and step S2 or between step S2 and step S3 to form a silver-copper solder material containing tin and / or indium. The total weight of silver, copper, titanium, tin and / or indium in the core-shell composite structure is 100 parts, and the total weight of tin and / or indium is 0.1 to 5.0 parts.

Images