Cu-sn-ti sintering paste for active metal brazing ceramic copper clad substrate and preparation method thereof

Abstract

This invention discloses a Cu-Sn-Ti sintering solder paste for active metal brazing ceramic copper-clad substrates and its preparation method, belonging to the field of electronic packaging materials technology. The Cu-Sn-Ti sintering solder paste for active metal brazing (AMB) ceramic copper-clad substrates of this invention comprises the following components: 80-92 wt% alloy powder and 8-20 wt% organic carrier. The preparation method of the sintering solder paste is as follows: (1) preparing alloy powder; (2) preparing organic carrier; (3) preparing sintering solder paste. The preparation method of the active metal brazing ceramic copper-clad substrate is as follows: (1) substrate pretreatment; (2) sintering solder paste printing; (3) mounting sintering solder paste; (4) vacuum sintering; (5) post-treatment. The Cu-Sn-Ti sintering solder paste for active metal brazing ceramic copper-clad substrates provided by this invention significantly reduces costs compared to traditional silver-based materials, eliminates the risk of silver migration, and greatly improves overall performance.

Description

Technical Field

[0001] This invention belongs to the field of electronic packaging materials technology, and in particular relates to the preparation technology of active metal brazing (AMB) ceramic copper-clad substrate for third-generation semiconductor power module packaging and a silver-free Cu-Sn-Ti active sintering solder paste and its preparation method. Background Technology

[0002] With the rapid development of third-generation semiconductor devices such as silicon carbide (SiC) and gallium nitride (GaN), their power density has increased to 3-5 times that of traditional silicon-based devices, and their operating temperature can reach over 200℃. The supporting packaging substrates must meet the following stringent performance and reliability requirements: thermal conductivity of the silicon nitride (Si3N4) substrate ≥80 W / (m·K), tested according to GB / T 10294 standard; coefficient of thermal expansion of 2.5-3.1 ppm / K within the temperature range of 40-400℃ to match the thermal expansion characteristics of SiC chips; bending strength ≥700 MPa, tested according to GB / T 4741 standard; copper foil peel strength ≥17 N / mm, tested according to T / BMCA standard; insulation withstand voltage ≥3.5 kV under AC 60Hz, 1min conditions, tested according to GB / T 507 standard; thermal shock reliability under temperature cycling of -55℃ to 150℃ ≥5000 cycles, tested according to GJB standard. 548B-2005 standard.

[0003] Active Metal Brazing (AMB) ceramic copper-clad substrates have become a core substrate material for third-generation semiconductor power module packaging due to their excellent thermal conductivity, matched coefficient of thermal expansion, and high bonding strength. AMB technology introduces the active element Ti (2%~5% by mass) into the solder, allowing it to react with the ceramic surface under high-temperature vacuum conditions to form intermetallic compound reaction layers such as titanium nitride (TiN) and pentatidium trisilide (Ti5Si3), which can be wetted by liquid solder, thus achieving a metallurgical bond between the ceramic and oxygen-free copper foil. Compared to traditional direct copper cladding (DBC) technology, AMB technology has significant advantages: (1) Void rate: The interface void rate can be controlled below 0.5%, which is significantly better than the traditional DBC process of more than 3%; (2) Thermal shock life: Si3N4-AMB substrate can reach more than 5000 times (-55℃~150℃, high and low temperature stay for 15min each, conversion time <30s), while aluminum nitride (AlN) substrate can only reach 1500 times and Al2O3 substrate can only reach 500 times. (3) Copper layer thickness: It can achieve the brazing of copper layers with a thickness of more than 0.8mm, and the current carrying capacity is increased by 40% compared with the DBC substrate.

[0004] Currently, the solders widely used in AMB processes are mainly Ag-Cu-Ti based solders. For example, patent CN120533356A proposes a low-silver lead-free tin-based solder paste, which reduces the silver content to 0.35~0.6wt% by adding Bi and Ni elements, but still does not completely eliminate the dependence on silver. Patent CN121423910A develops a silver-copper-titanium active solder paste with a high recovery coefficient, which improves the printability of the solder paste by compounding thixotropic agents, and has a silver content as high as 60%.

[0005] Silver-based solders have mature performance, but they have inherent defects that are difficult to overcome: the silver content in traditional Ag-Cu-Ti solders (typical composition is 68.8Ag-26.7Cu-4.5Ti) is as high as 60%~70%, and its raw material cost accounts for more than 90% of the total cost of AMB substrates. Moreover, the price of silver, as a precious metal, fluctuates greatly, which seriously restricts the industrialization and promotion of AMB substrates. Under high temperature, high humidity and DC bias coupling, silver ions are prone to electrochemical migration and the formation of conductive dendrites, which leads to substrate insulation breakdown and significantly reduces the long-term reliability of power modules.

[0006] To address the aforementioned issues, silver-free active solders have become a research hotspot in this field. Cu-Sn-Ti solders, due to their low cost and high performance tunability, have become the main development direction for silver-free AMB solders. For example, patent CN121776731A proposes a MAB phase-reinforced Cu-Sn-Ti active solder, which achieves matrix dispersion strengthening while forming a strong and tough gradient interface by introducing layered ternary boride ceramics. However, this solder is mainly used for the preparation of diamond composite wear-resistant coatings and is not suitable for AMB soldering of ceramics and copper. Patent CN120516266A discloses a Cu-Ti-Ni-CeO2 solder, which reduces the void ratio by adding nano-CeO2. However, the Ti content is as high as 15~30wt%, which can easily lead to an excessively thick interfacial reaction layer, reducing the temperature cycling reliability of the substrate.

[0007] In addition to the aforementioned existing technological achievements, the Cu-Sn-Ti system also faces the following technological bottlenecks: (1) Insufficient wettability: Excessive Sn content (>25%) will reduce the surface tension of the solder, but excessive Sn will form a coarsened CuSnTi3 intermetallic compound (IMC) phase and a brittle eutectic structure, resulting in a decrease in shear strength. Insufficient Sn content will result in insufficient wettability of the solder, making it impossible to achieve effective bonding between ceramic and metal. (2) Excessive thickness of the interface reaction layer: When the thickness of the reaction layer is >100μm, it will lead to the deterioration of the substrate surface flatness, resulting in a substrate height fluctuation of about 15μm, and the temperature cycling index will be significantly reduced. (3) Oxygen sensitivity: Ti is easily oxidized and deactivated at high temperatures. Current technology requires a vacuum level better than 10 during the brazing process. -3 The oxygen content of the solder powder must be controlled below 500 ppm, which places stringent requirements on production equipment and process control.

[0008] Therefore, developing a low-cost Cu-Sn-Ti sintering solder paste with optimized wettability and mechanical properties, controllable interface reaction, and strong process adaptability is of great significance for promoting the low-cost and high-reliability development of third-generation semiconductor power modules. Summary of the Invention

[0009] The purpose of this invention is to address the core technical bottlenecks in existing technologies, such as the high cost of silver-based AMB solders, the potential for silver migration failure, and the difficulty in synergistically controlling wettability and mechanical properties, uncontrollable interfacial reaction layer thickness, and stringent process requirements due to the high oxygen sensitivity of Ti. This invention also aims to overcome the shortcomings of existing patented technologies, including reliance on rare metals, brittleness caused by excessive Ti content, insufficient bonding strength, and inability to meet the requirements of high-end third-generation semiconductor packaging. This invention provides a Cu-Sn-Ti sintering solder paste for AMB copper-clad substrates and its preparation method. Based on thermodynamic calculations of the Cu-Sn-Ti ternary phase diagram and interfacial reaction kinetics analysis, the optimal synergistic range of Sn (18%~25%) and Ti (2%~5%) is identified. The system achieves synergistic optimization of solder wettability, joint mechanical strength, and interfacial reaction layer thickness; it also features a customized organic carrier compatible with the Cu-Sn-Ti alloy system, which forms an in-situ oxygen barrier layer during heating through the gradient decomposition characteristics of the thickener, effectively inhibiting Ti oxidation and deactivation. This reduces the stringent requirements for vacuum levels in production equipment while ensuring performance, thus improving process stability. Furthermore, it employs a completely silver-free copper-based alloy system, eliminating the constraints of silver price fluctuations and significantly reducing raw material costs. This also fundamentally eliminates the risk of insulation failure caused by silver migration, enhancing the long-term reliability of power modules under complex conditions of high temperature, high humidity, and DC bias. Finally, it optimizes the rheological properties and sintering process window of the solder paste, enabling direct compatibility with existing AMB ceramic copper-clad substrate production lines for screen printing and vacuum sintering without requiring large-scale equipment modifications, facilitating rapid industrialization.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a Cu-Sn-Ti sintering solder paste for active metal brazing of ceramic copper-clad substrates, characterized in that it comprises the following components by mass fraction: alloy powder 80~92 wt%, organic carrier 8~20 wt%; Furthermore, the alloy powder composition is: Cu 70~78 wt%, Sn 18~25 wt%, Ti 2~5 wt%; powder particle size D 50 =15~30 μm, oxygen content ≤500 ppm; Furthermore, the organic carrier composition is as follows: 50-70 wt% organic solvent, 10-25 wt% thickener, 3-8 wt% thixotropic agent, 1-3 wt% activator, 0.5-1.5 wt% corrosion inhibitor, and 0.3-1 wt% antioxidant.

[0011] Furthermore, the organic solvent is one or more of terpineol, diethylene glycol butyl ether, and butyl carbitol acetate; Furthermore, the thickener is one or more of ethyl cellulose and hydroxypropyl cellulose, with a molecular weight of 50,000 to 100,000; Furthermore, the thixotropic agent is a polyamide wax with a specific surface area of ​​200±25 m². 2 One or more of the following: / g of fumed silica.

[0012] Furthermore, the active agent is one or more of glutaric acid, salicylic acid, and citric acid; Furthermore, the corrosion inhibitor is benzotriazole (BTA) and its derivatives; Furthermore, the antioxidant is one or more of vitamin E or 2,6-di-tert-butyl-p-cresol (BHT).

[0013] This invention also provides a method for preparing the Cu-Sn-Ti sintering solder paste, comprising the following steps: (1) Cu-Sn-Ti alloy powder was prepared by gas atomization or mechanical alloying, and the oxygen content was controlled to be ≤500ppm; (2) Heat the organic solvent to 50~70℃, add thickener and stir to dissolve for 2~4h, add thixotropic agent and disperse for 1~2h, grind in a three-roll mill with a roller gap of 5μm three times until the fineness is ≤10μm, degas under a vacuum of ≤100Pa for 30min, and filter with a 400 mesh filter. (3) Mix the alloy powder with the organic carrier at a mass ratio of (80~92): (8~20), stir under vacuum to remove bubbles, and grind with three rollers at 25℃ and 10rpm until the viscosity is 80~120 Pa·s.

[0014] Furthermore, when the alloy powder in step (1) is prepared by gas atomization, the steps are as follows: melting metal raw materials Cu, Sn, and Ti, and controlling the melting vacuum degree to ≤10. -2The melting temperature is 1200~1300℃. After the alloy melt temperature stabilizes, it is atomized using high-pressure argon gas, with the argon pressure controlled at 3.5~5.0 MPa and the gas-metal mass ratio at 4:1~6:1, to obtain alloy powder with a sphericity ≥90%. The atomized powder is then sieved using air classifiers to remove excessively large or small particles and satellite particles, yielding D... 50 The target powder has a particle size distribution of 15~30μm; high-purity argon gas is used for protection throughout the process, and the powder is finally sealed in a vacuum aluminum foil bag to strictly control the oxygen content of the powder to ≤500ppm.

[0015] Furthermore, when the alloy powder in step (1) is prepared by mechanical alloying, the steps are as follows: Cu, Sn, and Ti metal powders are placed in a ball milling jar, stainless steel grinding balls with a diameter of 5-10 mm are added, the ball-to-material ratio is controlled at 10:1, and 1-2 wt% stearic acid is added as a process control agent; the ball milling jar is sealed, vacuumed, and filled with high-purity argon gas, repeated 3 times, and ball milled for 20-40 hours at a speed of 300-400 rpm; after ball milling, the powder is taken out and placed in a vacuum annealing furnace for annealing treatment, and the vacuum degree is controlled at ≤10. -3 Pa, annealing temperature 300~400℃, hold for 2~4 hours.

[0016] This invention also provides a method for preparing the active metal brazing ceramic copper-clad substrate, comprising the following steps: (1) Degreasing and deoxidation treatment of silicon nitride (Si3N4) or aluminum nitride (AlN) ceramic copper-clad substrates; (2) The sintered solder paste is screen-printed onto the surface of the ceramic substrate to a thickness of 80~120μm; (3) Apply oxygen-free copper foil to the surface of the printed solder paste, and apply a printing pressure of 0.1~0.5MPa; (4) When the vacuum degree is ≤10 -3 Sintering for 10-30 minutes under the conditions of Pa, temperature 820-880℃, and pressure 1-5MPa; (5) Ultrasonic cleaning removes residues and tests void ratio and bonding strength.

[0017] Furthermore, in step (4), the heating rate is 5~10℃ / min, and the vacuum degree is maintained at ≤10 during the heat preservation stage. - 3 Pa, cooling rate after sintering ≤5℃ / min.

[0018] Furthermore, in step (1), the thermal conductivity of the silicon nitride ceramic substrate is ≥80 W / (m·K), and the bending strength is ≥700 MPa.

[0019] Furthermore, in step (3), the oxygen-free copper foil has a purity of ≥99.95% and a thickness of 0.3~0.8mm.

[0020] Furthermore, the active metal brazed ceramic copper-clad substrate has a void ratio of ≤0.5%, a shear strength of ≥80 MPa, a copper foil peel strength of ≥17 N / mm, and a thermal shock cycle count of ≥5000 cycles under temperature cycling from -55℃ to 150℃.

[0021] A Cu-Sn-Ti sintering solder paste for active metal brazing of ceramic copper-clad substrates is prepared by the above-mentioned method.

[0022] A Cu-Sn-Ti sintered solder paste for active metal brazing ceramic copper-clad substrates has comprehensive performance advantages such as low cost, high reliability, high thermal conductivity, high current carrying capacity and no silver migration risk. It can be widely used in the packaging field of third-generation semiconductor power devices represented by SiC and GaN. It is a key basic material for core power modules of high-end equipment such as new energy vehicles, photovoltaic inverters, energy storage power stations, industrial transmission, rail transit, and aerospace.

[0023] The technical principle of this invention is based on the thermodynamics of the Cu-Sn-Ti ternary phase diagram and the kinetics of interfacial reactions. It is achieved through the synergistic effects of precise alloy composition design, powder structure control, functional matching of organic carriers, and vacuum pressure sintering. 1. In terms of alloy composition design, based on the phase equilibrium and interfacial reaction thermodynamics calculations of the Cu-Sn-Ti system, the Ti content is controlled at 2%~5%. This ensures that Ti reacts in situ with the ceramic surface under high temperature and vacuum, generating continuous and dense active transition layers such as TiN and Ti5Si3, realizing the transformation of the ceramic surface from non-wetting to wettable. It also avoids excessive growth of the interfacial reaction layer and joint embrittlement failure caused by excessive Ti. The Sn content is controlled at 18%~25%, which can effectively reduce the liquidus temperature of the solder, improve melt flowability and spreading wettability, and avoid the formation of coarse Cu4Sn phase and SnTi3 brittle phase. This balances wettability, sintering activity and joint mechanical properties, and makes the shear strength stably higher than 80MPa.

[0024] 2. In the preparation of alloy powders, the gas atomization method is suitable for vacuum degrees ≤10. -2 Vacuum melting at 1200~1300℃ and Pa can achieve uniform solid solution of Ti without segregation. Crushing and solidification under 3.5~5.0 MPa argon gas and a gas-metal mass ratio of 4:1~6:1 yields alloy powder with ≥90% sphericity and excellent flowability. D is obtained through gas flow classification. 50Narrowly distributed particles of 15~30μm are vacuum-packed and kept inert throughout the process to ensure an oxygen content of ≤500ppm, thus preventing Ti oxidation and deactivation. The mechanical alloying method involves spheroidizing under high-purity argon protection, supplemented with 1~2 wt% stearic acid to inhibit cold welding agglomeration, and then vacuum annealing at 300~400℃ to eliminate internal stress, stabilize the microstructure, and ensure the sintering activity of the powder.

[0025] 3. Regarding the organic carrier system, organic solvents with moderate boiling points, uniform volatility, and low residual carbon content (<0.1%), such as terpineol (boiling point 217℃) and diethylene glycol butyl ether (boiling point 230℃), are used to adjust the viscosity. These solvents can completely evaporate during sintering, preventing residual carbon from affecting the joint's density and thermal conductivity. Ethyl cellulose (N50 type) and hydroxypropyl cellulose are used as thickeners. During heating, they adhere to the alloy powder surface to form a protective film, isolating oxygen and effectively inhibiting the oxidation and deactivation of Ti, thus preventing oxidation and sedimentation. The thickeners gradually decompose thermally at around 200℃, without hindering the formation of the liquid phase and its contact diffusion with Cu. Fumed silica (specific surface area 200±25 m²) is used. 2 Thixotropic agents such as polyamide wax impart suitable thixotropic properties to the solder paste, improving printability and ensuring that the print form does not collapse; organic acid activators such as glutaric acid, salicylic acid, and citric acid can remove the oxide film on the surface of metal powder and copper foil, promoting wetting; benzotriazole (BTA) and its derivatives are used as corrosion inhibitors, and antioxidants such as vitamin E and 2,6-di-tert-butyl-p-cresol (BHT) are used to prevent copper foil corrosion and oxidation deterioration during the storage of solder paste, achieving a balance between printability, protection, and clean sintering.

[0026] 4. In the preparation of AMB ceramic copper-clad substrates, high-cleanliness activation of the ceramic and copper foil surfaces is achieved through multi-stage ultrasonic cleaning; a uniform solder paste layer of 80~120μm is formed by screen printing, followed by substrate mounting; and the process is carried out under a vacuum degree ≤10 -3 Sintering at 820~880℃ under pressure of 1~5MPa for 10~30min, on the one hand, high vacuum inhibits Ti oxidation, and on the other hand, external pressure can effectively squeeze out residual pores in the liquid phase solder, reducing the interface void ratio to below 0.5%; the heating rate is controlled at 5~10℃ / min to avoid the rapid decomposition of organic carrier and the generation of gas defects, and finally achieves reliable metallurgical bonding between Cu-Sn-Ti solder and ceramic and copper foil, obtaining AMB copper-clad substrate with high thermal conductivity, high current carrying capacity and long life.

[0027] In summary, the innovative points of this invention are: 1. Precise optimization of alloy composition: Based on the Cu-Sn-Ti ternary phase diagram and interfacial reaction thermodynamic calculations, the optimal ratio of Cu (70%~78%)-Sn (18%~25%)-Ti (2%~5%) is determined to balance the wettability of the solder, the joint strength and the thickness of the interfacial reaction layer, and to avoid the brittleness caused by excessive Sn and the bonding defects caused by improper Ti content; 2. Dedicated organic carrier design: It is equipped with a customized organic carrier (containing organic solvents, thickeners, thixotropic agents and other components) to solve the problems of solder paste printability and oxidation resistance. It can also form a protective film through thickener to prevent Ti element oxidation and deactivation, while ensuring no residue after sintering.

[0028] 3. Process optimization and adaptation: The gas atomization method is preferred for preparing alloy powder and solder paste preparation process. The oxygen content of the powder is controlled to be ≤500ppm, and the sintering temperature is reduced to 820~880℃. Pressure is the most important factor affecting the void ratio. The key parameters such as vacuum degree, brazing pressure and heating rate of AMB substrate preparation are clearly defined to strictly control the void ratio to ≤0.5%, thereby reducing energy consumption and equipment requirements.

[0029] Compared with the prior art, the present invention has at least the following advantages: Compared to traditional silver-based solders (Ag-Cu-Ti): (1) Costs are reduced by at least 65%, freeing us from the constraints of silver price fluctuations and making us more suitable for large-scale production; (2) No silver migration risk, significantly improved insulation reliability under high temperature and high humidity conditions; (3) Sintering energy consumption is reduced by 15-20%, shear strength is increased by 15-20%, and overall performance is better.

[0030] Compared to existing Cu-Sn-Ti solders: (1) Excellent wettability and strength, shear strength ≥80MPa, avoiding embrittlement and over-wetting caused by excessive Sn; (2) The thickness of the interface reaction layer is controllable (8~12μm), eliminating substrate undulation and thermal shock failure caused by excessive thickness; (3) Oxygen sensitivity is significantly reduced, process controllability is improved, and production equipment requirements and costs are reduced; (4) The void ratio is ≤0.5%, which is far superior to the existing silver-free solder paste (1%~5%) and meets the high-end packaging standards. Attached Figure Description

[0031] Figure 1 This is a flow chart of the Cu-Sn-Ti solder paste preparation process.

[0032] Figure 2 Flowchart of the process for preparing active metal brazing ceramic copper-clad substrates.

[0033] Figure 3 This is a schematic diagram of an active metal brazing ceramic copper-clad substrate structure. Detailed Implementation

[0034] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0035] It should be noted that, in all aspects of the present invention, the same components or terms in each aspect are described only once in one aspect and not repeatedly, and those skilled in the art should not understand this as a limitation of the present invention.

[0036] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0037] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0038] In this invention, the D 50 Both refer to the diameter of the particles.

[0039] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this invention.

[0040] Example 1 Fabrication of Si3N4 ceramic copper-clad substrate: Si3N4 ceramic with a thermal conductivity of 90 W / (m·K) and a thickness of 0.32 mm was selected as the substrate to ensure that the substrate has good thermal conductivity and structural stability; oxygen-free copper foil with a thickness of 0.3 mm and a purity of ≥99.95% was selected as the copper cladding layer.

[0041] The solder used is a Cu-20Sn-3Ti (mass fraction) solder paste, which is composed of alloy powder and organic carrier mixed at a mass ratio of 85:15. The alloy powder is prepared using a gas atomization method, with a particle size D... 50 The size is 22μm, and the oxygen content is controlled at 380ppm; The viscosity of the solder paste was measured by a rotational viscometer and was 95 Pa·s at 25℃ and 10 rpm, which meets the requirements of the screen printing process.

[0042] The Si3N4 ceramic copper-clad substrate was prepared according to the following steps: (1) The Si3N4 ceramic substrate and oxygen-free copper foil were subjected to standard degreasing, pickling and activation treatment to remove the surface oxide film and impurities; (2) Use a 250 mesh screen to print solder paste on the surface of the ceramic substrate, strictly control the printing thickness to 100μm, and ensure that the solder paste layer is continuous, uniform and without obvious defects; (3) The ceramic substrate after solder paste printing is bonded to the treated copper foil to ensure close adhesion between the copper foil and the solder paste layer; (4) The assembled green body is sent into a vacuum sintering furnace and vacuum pressure sintering process is performed: the vacuum degree is set to ≤5×10 -3 Pa, heating rate 8℃ / min, sintering temperature 850℃, holding temperature for 20 min, and simultaneously applying 3 MPa sintering pressure to form a stable metallurgical bond structure between the brazing filler metal and the ceramic and copper foil. (5) After sintering, the product is ultrasonically cleaned, dried and surface residues are detected to finally obtain Si3N4 ceramic copper-clad substrate.

[0043] Example 2 Fabrication of AlN ceramic copper-clad substrates: AlN ceramic with a thermal conductivity of 230 W / (m·K) and a thickness of 0.635 mm was selected as the substrate to fully utilize the advantages of AlN ceramic in terms of high thermal conductivity and high insulation; oxygen-free copper foil with a thickness of 0.5 mm and a purity of ≥99.95% was selected as the copper cladding layer.

[0044] The solder used is a Cu-22Sn-4Ti (mass fraction) based solder paste, which is composed of alloy powder and organic carrier mixed at a mass ratio of 87:13; the alloy powder is prepared by gas atomization, and the particle size D is... 50 The solder paste has a viscosity of 25μm and an oxygen content of 420ppm, which meets the requirement of high-end applications for an oxygen content of ≤500ppm. The viscosity of the solder paste at 25℃ and 10 rpm is 102 Pa·s, which meets the requirements of screen printing process.

[0045] Prepare an AlN ceramic copper-clad substrate according to the following steps: (1) Standard degreasing, pickling and activation treatments were performed on AlN ceramic substrate and oxygen-free copper foil to remove surface oxide film and impurities; (2) Use a 200-mesh screen for solder paste printing and control the printing thickness to be 110 μm; (3) The AlN substrate after the solder paste is printed is attached to the copper foil to make the copper foil and the solder paste layer in close contact; (4) The billet is placed in a vacuum sintering furnace for vacuum pressure sintering. The process parameters are: vacuum degree ≤ 8 × 10 -3 Pa, heating rate 7℃ / min, sintering temperature 860℃, holding temperature for 15 min, and simultaneously applying 4 MPa sintering pressure; (5) After sintering, ultrasonic cleaning and drying are performed to obtain AlN ceramic copper-clad substrate.

[0046] Example 3 Fabrication of thick copper Si3N4 ceramic copper-clad substrate: Si3N4 ceramic with a thickness of 0.5 mm was selected as the substrate, and oxygen-free copper foil with a thickness of 0.8 mm (double-sided) and a purity of ≥99.95% was selected as the copper cladding layer.

[0047] The solder used is Cu-18Sn-5Ti (mass fraction) based solder paste, which is composed of alloy powder and organic carrier mixed at a mass ratio of 90:10; the alloy powder particle size D 50 The solder paste has a thickness of 18 μm and an oxygen content of 350 ppm. The viscosity of the solder paste at 25℃ and 10 rpm is 110 Pa·s, which meets the printing and sintering requirements of thick copper substrates.

[0048] Thick copper Si3N4 ceramic copper-clad substrates were prepared according to the following steps: (1) The Si3N4 ceramic substrate and oxygen-free copper foil were degreased, acid-washed and activated. (2) Use a 300-mesh screen for solder paste printing and control the printing thickness to be 120μm; (3) The processed copper foil is attached to the solder paste layer on both sides of the ceramic substrate to ensure that the copper foil and the solder paste layer are tightly bonded.

[0049] (4) The green body is sent into a vacuum sintering furnace and vacuum pressure sintering process is performed: vacuum degree ≤ 3×10 -3 Pa, heating rate 10℃ / min, sintering temperature 870℃, holding time 25 min, and sintering pressure of 5 MPa applied simultaneously.

[0050] (5) After sintering, ultrasonic cleaning and drying are performed to finally obtain a double-sided thick copper Si3N4 ceramic copper-clad substrate.

[0051] The products prepared in Examples 1-3 were subjected to performance testing, and the results are shown in Table 1.

[0052] Table 1 Performance Test Table for Ceramic Copper-Clad Substrates

[0053] In Table 1, "-" indicates that the item was not tested in this embodiment, and does not mean that the item is not up to standard; all test items were performed in accordance with the corresponding standards and conventional test methods, and the test results all meet the technical requirements of this invention and related application needs; the test standards refer to the relevant specifications of GJB 548B series and GB / T series, and the test instruments all meet the requirements of the corresponding test standards.

[0054] The Si3N4 ceramic copper-clad substrate prepared in Example 1 has excellent structural reliability and mechanical properties, making it suitable for medium-power electronic device scenarios. It can be applied to automotive electronic modules, industrial control power supplies, intermediate frequency power amplifiers, and other fields, which can reduce production costs and ensure long-term stable operation of devices. The AlN ceramic copper-clad substrate of Example 2 has both high thermal conductivity and high insulation properties, making it suitable for electronic devices with high power and high insulation requirements. It can be applied to high-end fields such as power semiconductor modules, high-frequency communication equipment, and medical electronic equipment, helping to promote the miniaturization and high efficiency of equipment. The double-sided thick copper Si3N4 ceramic copper-clad substrate of Example 3 has the advantages of high current carrying capacity, high strength and high reliability, and is suitable for high-power and high-current electronic device scenarios. It can be applied to fields such as power modules for new energy vehicles, traction converters for rail transit, and high-power energy storage equipment, solving the problems of insufficient current carrying capacity and easy failure after long-term use of traditional substrates.

[0055] Comparative Example 1 Si3N4 ceramic copper-clad substrates were prepared using conventional Ag-Cu-Ti solder paste (68.8-26.7-4.5) following the steps in Example 1. The performance of Comparative Example 1 was compared with that of Examples 1-3, and the results are shown in Table 2.

[0056] Table 2 Performance Comparison of Ceramic Copper-Clad Substrates

[0057] As can be seen from the comparison results in Table 2, the present invention uses a silver-free Cu-Sn-Ti solder paste, which does not contain the precious metal silver in its raw materials. Compared with the traditional Ag-Cu-Ti solder with a silver content as high as 68.8%, it can significantly reduce the raw material cost by about 65%. At the same time, the sintering temperature of the solder paste of the present invention is lower than that of the traditional solder, which can effectively reduce the energy consumption of the sintering process by 15-20%. Moreover, the present invention has better mechanical bonding performance and can meet the same reliability requirements. In addition, the solder paste system of the present invention does not contain silver, which fundamentally eliminates the failure risks such as leakage and short circuit caused by silver migration. Its reliability under long-term high voltage and high humidity and heat conditions is significantly better than that of the traditional Ag-Cu-Ti solder system, which represents a significant improvement over current technology.

[0058] Comparative Example 2 A comparative experiment was conducted using Cu-28Sn-3Ti solder paste with a composition exceeding the scope of this invention to study the effect of excessive Sn on soldering performance. The results are shown in Table 3.

[0059] Table 3. Test results on the effect of excessive Sn content on brazing interface performance.

[0060] As can be seen from Table 3, when the Sn content exceeds the limit of this invention, although the wetting angle is reduced, problems such as excessive solder flow and increased interfacial porosity are likely to occur. At the same time, a large number of brittle intermetallic compounds are generated, resulting in a significant decrease in the joint shear strength, which cannot meet the mechanical properties and reliability requirements of ceramic copper-clad substrates.

[0061] Comparative Example 3 A comparative experiment was conducted using Cu-20Sn-1.5Ti solder paste with a Ti content lower than that of this invention to study the effect of insufficient Ti active elements on ceramic wetting and interfacial bonding. The results are shown in Table 4.

[0062] Table 4. Test results on the effect of low Ti content on brazing interface performance.

[0063] As shown in Table 4, when the Ti content is lower than the range specified in this invention, the wettability of the solder paste to the ceramic substrate deteriorates significantly, making it difficult to form a continuous and dense active reaction layer at the interface. Effective metallurgical bonding cannot be achieved between the ceramic and the copper foil, ultimately resulting in a significant reduction in the joint shear strength, which fails to meet the requirements for use of ceramic copper-clad substrates.

[0064] The embodiments described above are merely preferred embodiments of the present invention, but the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A Cu-Sn-Ti sintered solder paste for active metal brazing of ceramic copper-clad substrates, characterized in that, The composition comprises the following components by mass fraction: alloy powder 80-92 wt%, organic carrier 8-20 wt%; The alloy powder composition is: Cu 70~78 wt%, Sn 18~25 wt%, Ti 2~5 wt%; The particle size of the alloy powder is: D 50 =15~30 μm, oxygen content ≤500 ppm; The organic carrier consists of: 50-70 wt% organic solvent, 10-25 wt% thickener, 3-8 wt% thixotropic agent, 1-3 wt% activator, 0.5-1.5 wt% corrosion inhibitor, and 0.3-1 wt% antioxidant.

2. The Cu-Sn-Ti sintering solder paste for active metal brazing of copper-clad ceramic substrates according to claim 1, characterized in that, The organic solvent is one or more of terpineol, diethylene glycol butyl ether, and butyl carbitol acetate; The thickener is one or more of ethyl cellulose and hydroxypropyl cellulose, with a molecular weight of 50,000 to 100,000. The thixotropic agent is a polyamide wax with a specific surface area of ​​200±25 m². 2 One or more of the following: / g of fumed silica.

3. The Cu-Sn-Ti sintering solder paste for active metal brazing of copper-clad ceramic substrates according to claim 1, characterized in that, The active agent is one or more of glutaric acid, salicylic acid, and citric acid; The corrosion inhibitor is benzotriazole and its derivatives; The antioxidant is one or more of vitamin E or 2,6-di-tert-butyl-p-cresol.

4. A method for preparing Cu-Sn-Ti sintering solder paste as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Cu-Sn-Ti alloy powder was prepared by gas atomization or mechanical alloying, and the oxygen content was controlled to be ≤500ppm; (2) Heat the organic solvent to 50~70℃, add thickener and stir to dissolve for 2~4h, add thixotropic agent and disperse for 1~2h, grind with three rollers to fineness ≤10μm, degas under vacuum and filter; (3) Mix the alloy powder with the organic carrier at a mass ratio of (80~92): (8~20), stir under vacuum to remove bubbles, and grind with three rollers at 25℃ and 10rpm until the viscosity is 80~120 Pa·s.

5. The Cu-Sn-Ti sintering solder paste for active metal brazing of copper-clad ceramic substrates according to claims 1-4, characterized in that, The alloy powder in step (1) is prepared by gas atomization, with the following process parameters: melting temperature 1200~1300℃, vacuum degree ≤10 -2 Pa, argon pressure 3.5~5.0 MPa, gas-metal mass ratio 4:1~6:1, after atomization, alloy powder is obtained by airflow classification to obtain D 50 =15~30 μm powder.

6. A method for preparing an active metal brazing ceramic copper-clad substrate as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Degreasing and deoxidation treatment of silicon nitride or aluminum nitride ceramic copper-clad substrate; (2) The sintered solder paste is screen-printed onto the surface of the ceramic substrate to a thickness of 80~120μm; (3) Apply oxygen-free copper foil to the surface of the printed solder paste, and apply a printing pressure of 0.1~0.5MPa; (4) When the vacuum degree is ≤10 -3 Sintering for 10-30 minutes under the conditions of Pa, temperature 820-880℃, and pressure 1-5MPa; (5) Ultrasonic cleaning removes residues and tests void ratio and bonding strength.

7. The preparation method according to claim 6, characterized in that, In step (4), the heating rate is 5~10℃ / min, and the vacuum level is maintained at ≤10 during the heat preservation stage. -3 Pa, cooling rate after sintering ≤5℃ / min.

8. The preparation method according to claim 6, characterized in that, The thermal conductivity of the silicon nitride ceramic substrate in step (1) is ≥80 W / (m·K), and the bending strength is ≥700 MPa; the oxygen-free copper foil in step (3) has a purity of ≥99.95% and a thickness of 0.3~0.8 mm.

9. The active metal brazing ceramic copper-clad substrate prepared according to any one of claims 6-8, characterized in that, The active metal brazed ceramic copper-clad substrate has a void ratio of ≤0.5%, a shear strength of ≥80 MPa, a copper foil peel strength of ≥17 N / mm, and a thermal shock cycle count of ≥5000 cycles under temperature cycling from -55℃ to 150℃.

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