A method for thinning a solder layer of a copper clad ceramic substrate

Abstract

The application discloses a kind of methods for thinning copper-clad ceramic substrate brazing layer, it is related to copper-clad ceramic substrate technical field.Processes include the following: step 1: after ceramic substrate pretreatment, solder paste is printed on its surface using dot matrix screen, and solder paste dot matrix is formed;Ceramic substrate A is obtained;Step 2: copper foil is assembled with ceramic substrate A;Stacked assembly is obtained;Step 3: stacked assembly is heated to above liquidus line of brazing filler metal in solder paste using vacuum brazing furnace, mechanically pressurized, heat preservation pressure, cooling pressure relief, and the brazing layer of thinning copper-clad ceramic substrate is obtained.The brazing layer of thinning copper-clad ceramic substrate prepared by square dot matrix screen printing and vacuum pressurized brazing process in the application, combined with specific solder paste, achieves the purpose of thinning, and meets the needs of the industry.

Description

Technical Field

[0001] This invention relates to the field of copper-clad ceramic substrate technology, specifically a method for thinning the solder layer of a copper-clad ceramic substrate. Background Technology

[0002] With the development of the electronics industry, the market has increasingly stringent requirements for power module packaging. Among them, AMB copper-clad ceramic substrate has high thermal conductivity, electrical insulation performance and reliable interface bonding strength, and has become a popular core material for power module packaging. It is gradually being applied in high-voltage and high-power fields such as new energy vehicles, rail transit and smart grids.

[0003] Active metal brazing (AMB) technology is one of the core processes for preparing copper-clad ceramic substrates. It achieves a reliable connection between ceramic and metal by adding a solder containing active elements such as titanium between the ceramic substrate and the copper foil in a high-temperature vacuum environment, thereby ensuring the stability of the packaging structure.

[0004] However, traditional AMB still has obvious defects at present, especially for the widely used silver-copper-titanium (Ag-Cu-Ti) solder. In order to ensure the formation of a continuous and defect-free connection layer after soldering, a full-board printing method is usually adopted, which prints an excessive amount of continuous solder on the ceramic substrate or copper surface, resulting in serious solder waste and increased production costs.

[0005] More importantly, the AMB copper-clad ceramic substrates prepared by the above method have a high thickness, which seriously affects production and use. When the printing thickness or mesh size is close to or smaller than the metal powder particle size, it is impossible to ensure that the solder paste passes through the mesh smoothly and evenly, which easily leads to defects such as missing prints and uneven thickness, and large voids, affecting the thickness. At the same time, the printing limit thickness is also limited by the wire diameter of the stencil. Too fine a wire diameter will increase the risk of stencil breakage due to insufficient strength, and the thickness will increase.

[0006] In summary, solving the above problems and preparing a thinner copper-clad ceramic substrate brazing layer is of great significance. Summary of the Invention

[0007] The purpose of this invention is to provide a method for thinning the solder layer of a copper-clad ceramic substrate, so as to solve the problems mentioned in the background art.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for thinning the solder layer of a copper-clad ceramic substrate includes the following steps: Step 1: After pre-treating the ceramic substrate, solder paste is printed on its surface using a dot matrix stencil to form a solder paste dot matrix; thus obtaining ceramic substrate A; Step 2: Assemble the copper foil with the ceramic substrate A; to obtain the laminated assembly; Step 3: Heat the stacked assembly to above the liquidus line of the solder paste using a vacuum brazing furnace, apply mechanical pressure, maintain temperature and pressure, and then cool and release pressure to obtain a thinned copper-clad ceramic substrate brazing layer.

[0009] In a more optimized manner, the pattern of the dot matrix stencil in the printed solder paste is a discrete dot matrix, with dot matrix units being square, circular, or irregularly shaped. The square dots have a side length of 0.3~2mm, and the dot spacing is 30%~50% of the side length. The stencil is a 250-mesh steel wire composite mesh with a wire diameter of 22~30μm. This method reduces solder consumption by 45% compared to traditional full-board printing. The above printing operation is repeated to print square solder paste dot matrices of the same specifications on the other side of the Si3N4 ceramic substrate.

[0010] In a more optimized manner, the process parameters in the printed solder paste are: squeegee angle 50~70°, squeegee pressure 0.2~0.4MPa, printing speed 40~60mm / s, and screen distance 1~3mm.

[0011] In a more optimized manner, the liquidus temperature of the solder in the solder paste is 750~800℃; the mechanical pressure is 1~3MPa; the temperature for heat preservation and pressure holding is 800~850℃, and the holding time is 30~50min; the molten solder flows from the center of the lattice to the surrounding area under pressure, completely filling the copper foil / ceramic interface and forming a dense solder layer.

[0012] Ideally, during the heating process in the vacuum brazing furnace, the vacuum level is lower than 5 × 10⁻⁶. -3 Pa, raise the temperature from room temperature to 400-440℃ at a rate of 4-6℃ / min, and hold for 50-70min; continue to raise the temperature to 550-650℃ at a rate of 7-9℃ / min, and hold for 20-40min.

[0013] More preferably, the solder paste in the printed solder paste is Ag-Cu-Ti solder paste; the raw materials of the Ag-Cu-Ti solder paste include the following components: by mass parts, 70-90 parts of solder, 0.1-0.4 parts of dispersant, 0.05-0.1 parts of thixotropic agent, and 15-20 parts of organic solvent.

[0014] In a further embodiment, the dispersant is stearic acid; the thixotropic agent is hydrogenated castor oil; and the organic solvent comprises terpineol and diethylene glycol butyl ether in a mass ratio of 3:(1~2).

[0015] In a more optimized manner, the raw materials of the brazing filler metal include silver-copper-titanium brazing filler metal powder and functional additives in a mass ratio of 100:(3~5); the raw materials of the silver-copper-titanium brazing filler metal powder include silver powder, copper powder and titanium hydride powder in a mass ratio of (79.5~84.5):(13.5~17.5):(2.0~3.0).

[0016] A more optimized method for preparing the functional additive is as follows: Step 1: Titanium nitride and carbon nanotubes are modified with epoxy-based silane coupling agents to obtain epoxy-based composite fillers; Step 2: Under a nitrogen atmosphere, POSS-SH, epoxy-based composite filler, and triethylamine are added to DMF (N,N-dimethylformyl) and reacted at 50~70℃ for 6~8h. After cooling to room temperature, the mixture is washed and dried to obtain the functional additive.

[0017] In a further embodiment, the epoxy-based composite filler is prepared by adding titanium nitride, carbon nanotubes, and epoxy-based silane coupling agent (KH-560) to an ethanol aqueous solution, reacting at 60-80°C for 4-8 hours, cooling, washing, and drying to obtain the epoxy-based composite filler.

[0018] In a further embodiment, the preparation method of POSS-SH is as follows: mercaptopropyltrimethoxysilane and concentrated hydrochloric acid (37%) are added to methanol at a mass ratio of 1:2.3, stirred evenly, reacted at a temperature of 85~95℃ for 1.5~2.5 hours, purified and dried to obtain POSS-SH.

[0019] In a more optimized manner, the raw materials of the epoxy composite filler contain titanium nitride with a particle size of 50-200 nm and carbon nanotubes with an outer diameter of 10-20 nm.

[0020] In a more optimized manner, the mass ratio of titanium nitride, carbon nanotubes, and epoxy silane coupling agent in the raw materials of the epoxy composite filler is (1~3):(0.1~0.3):(0.1~0.2). In the raw materials of the functional additive, the mass ratio of POSS-SH, epoxy-based composite filler, and triethylamine is (0.4~0.7):10:(0.05~0.1).

[0021] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) Compared with traditional full-page printing screens, this application adopts a discontinuous dot matrix screen design, so that the solder paste is distributed in a discrete dot array, rather than a continuous thin film. Since the solder paste is printed in a dot matrix, the thickness of a single dot is higher than the final required solder layer thickness, while full-page printing reaches the printing limit due to the pursuit of thinness. This is different from the limitation of the size of the solder particles on uniform ultra-thin printing; (2) This application utilizes a pressure brazing process with specific process parameters to achieve dense and thin brazing of the solder. Specifically, during vacuum brazing, when the temperature reaches above the liquidus line of the solder, a mechanical pressure of 0.5~3MPa is applied to the stacked assembly of "ceramic substrate-solder lattice-copper foil". The pressure drives the molten solder to flow from the center of the lattice to the surrounding uncovered areas, eventually filling the entire welding interface. Under the action of pressure, the initially thicker solder lattice is flattened and spread out, forming a continuous, uniform, and significantly thinned (target <5μm) brazing layer.

[0022] (3) Dot matrix printing combined with vacuum pressure brazing process can save solder paste. However, the dot matrix printing is in the form of discrete dots. Compared with the full matrix printing in the existing technology, the titanium element in the solder paste reacts in a smaller interface area and is consumed at a faster rate. This will cause an excessively thick TiN reaction layer, which will reduce the strength of the solder layer. At the same time, it will also generate a brittle Ti-Si phase, which will increase the thickness and affect the reliability of the product.

[0023] Therefore, in order to solve the above problems, the solution reduces the content of copper and titanium elements on the basis of the original Ag-Cu-Ti solder paste and introduces functional additives to achieve a balance between the supply and demand of titanium elements and suppress the formation of brittle phases.

[0024] In this composite filler, titanium nitride and carbon nanotubes of specific sizes and mass ratios are used. Titanium nitride particles act as an inert barrier, physically preventing excessive diffusion of titanium elements into the ceramic interface. Simultaneously, the TiN lattice matches the TiN reaction layer generated in situ at the interface, serving as a nucleation substrate to promote uniform growth of the reaction layer and prevent local over-thickness. Carbon nanotubes react in situ with some active titanium at the brazing temperature to generate a TiC reinforcing phase, consuming excess titanium and further balancing the titanium content. Furthermore, the formation of TiC can inhibit the formation of agglomerated TiCu brittle phases, refine the brazing seam structure, improve joint toughness, further balance the titanium content to prevent excessive TiN reaction layer thickness, and inhibit the formation of Ti-Si brittle phases. POSS-SH improves the dispersibility of the composite filler in the solder paste through thiol-epoxy reactions and metal chelation, preventing nanoparticle agglomeration. Its thiol groups preferentially oxidize during the descaling stage, protecting active titanium from oxidation and failure. In addition, POSS-SH can also inhibit the coarsening of intermetallic compounds, alleviate CTE mismatch stress, and suppress stress concentration.

[0025] It is important to note that the amount and size of titanium nitride and carbon nanotubes introduced need to be controlled. If the amount of carbon nanotubes introduced is too large, the agglomeration will be severe, which will coarsen the brazing structure and reduce the joint strength. At the same time, too much titanium will be consumed, which will affect the interfacial reaction. If the particle size of titanium nitride is too large, the specific surface area will be small, and the barrier effect will be reduced. At the same time, it will be mismatched with the TiN lattice at the interface, and the nucleation substrate effect will be weakened.

[0026] The above-mentioned functional additives are indispensable. They work together to balance the titanium content, prevent the reaction layer from becoming too thick and reducing the bonding strength, and at the same time, inhibit the formation of brittle phases and improve product reliability. Attached Figure Description

[0027] Figure 1 This is a process flow diagram from Embodiment 1 of the present invention; Figure 2 This is a design drawing of the dot matrix mesh panel in Embodiment 1 of the present invention; Figure 3 This is a SEM image of the brazing interface in Embodiment 1 of the present invention; Figure 4 This is a SEM image of the brazing interface in Comparative Example 1 of the present invention. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The following examples specifically illustrate the preparation method of POSS-SH: mercaptopropyltrimethoxysilane and 37% concentrated hydrochloric acid were added to methanol at a mass ratio of 1:2.3, stirred evenly, reacted at 90°C for 2 hours, purified and dried to obtain POSS-SH.

[0030] Example 1: A method for thinning the solder layer of a copper-clad ceramic substrate, comprising the following steps: (Specific process follows...) Figure 1 As shown; Pretreatment of ceramic substrate: Place a 0.32mm thick Si3N4 ceramic substrate with dimensions of 138mm×190mm into an ultrasonic cleaning tank, use anhydrous ethanol as the cleaning medium, set the ultrasonic power to 300W and the ultrasonic time to 15min to remove surface oil and dust; after ultrasonic treatment, place the substrate in a forced-air drying oven and dry it at 80℃ for 30min to ensure that there is no residual moisture and ethanol on the surface. Pre-preparation: (1) Add titanium nitride (50nm), carbon nanotubes (15nm), and epoxy silane coupling agent (KH-560) to an 80wt% ethanol aqueous solution at a mass ratio of 2:0.2:0.15. React at 70℃ for 6 hours, cool, wash and dry to obtain epoxy composite filler; (2) Under nitrogen atmosphere, add POSS-SH, epoxy composite filler and triethylamine to DMF at a mass ratio of 0.55:10:0.08. React at 60℃ for 8 hours, cool to room temperature, wash and dry to obtain functional additive; (3) Mix 80 parts of solder, 0.25 parts of dispersant (stearic acid), 0.07 parts of thixotropic agent (hydrogenated castor oil), and 18 parts of organic solvent (terpineol and diethylene glycol butyl ether at a mass ratio of 3:1.5) evenly to obtain Ag-Cu-Ti solder paste; In the above scheme, the raw materials of the brazing filler metal include silver-copper-titanium brazing filler metal powder in a mass ratio of 100:4 (including silver powder, copper powder, and titanium hydride powder in a mass ratio of 82:15.5:2.5) and functional additives. Step 1: After pre-treating the ceramic substrate, solder paste is printed on its surface using a dot-matrix stencil. (After pre-treating the ceramic substrate, it is placed on the screen printing machine table. The stencil position is calibrated so that the dot-matrix pattern is aligned with the center of the substrate. Screen printing parameters are set: squeegee angle 60°, squeegee pressure 0.3MPa, printing speed 50mm / s, and screen spacing 2mm. Ag-Cu-Ti solder paste is evenly applied to the stencil, and the screen printing machine is started to complete the printing. Then, it is transferred to an oven and dried at 100℃ for 15 minutes to form a discrete square solder paste dot matrix on the surface of the ceramic substrate. The stencil is a 250-mesh steel wire composite mesh with a wire diameter of 25μm. A portion of the dot-matrix pattern on the stencil is shown below.) Figure 2 As shown, the square has a side length of 1mm and a dot pitch of 0.3mm. Repeat the above printing operation to print square solder paste dot arrays of the same specifications on the other side of the Si3N4 ceramic substrate to form solder paste dot arrays; thus obtaining ceramic substrate A. Step 2: Assemble the copper foil with the ceramic substrate A (flatly cover the front and back surfaces of the ceramic substrate A with two 134mm×184mm 0.8mm thick oxygen-free copper foils to form a copper foil-soldering paste matrix-ceramic substrate sandwich structure, and press a 140mm×190mm graphite block on top as a pressure transmission medium)); to obtain the laminated assembly; Step 3: Heat the laminated assembly using a vacuum brazing furnace (place the laminated assembly directly below the mechanical pressure head inside the vacuum brazing furnace, close the furnace door, and evacuate to 5×10). -3The furnace temperature was increased from room temperature to 420°C at a rate of 5°C / min and held for 60 minutes to remove the organic carrier of the solder paste. The temperature was then increased to 600°C at a rate of 8°C / min and held for 30 minutes to remove residual carriers and adsorbed gases, preparing for solder melting. The temperature was then increased to above the liquidus line of the solder paste. Mechanical pressure was applied and maintained (the liquidus line temperature of the Ag-Cu-Ti solder paste is approximately 780°C; the furnace temperature was further increased to 830°C (50°C above the liquidus line) at a rate of 5°C / min to ensure complete melting of the solder paste. The mechanical pressure device inside the furnace was activated, applying 2MPa of mechanical pressure to the component through a graphite pressure head and maintaining the pressure for 40 minutes). The pressure was then released by cooling (after the pressure holding period, the temperature was lowered to 750°C at a rate of 10°C / min (when the solder was completely solidified), and then the mechanical pressure was released; the temperature was then slowly lowered to room temperature, and the furnace door was opened to remove the component). This resulted in a thinned solder layer on the copper-clad ceramic substrate.

[0031] Example 2: A method for thinning the solder layer of a copper-clad ceramic substrate, comprising the following steps: Pretreatment of ceramic substrate: Place a 0.32mm thick Si3N4 ceramic substrate with dimensions of 138mm×190mm into an ultrasonic cleaning tank, use anhydrous ethanol as the cleaning medium, set the ultrasonic power to 300W and the ultrasonic time to 15min to remove surface oil and dust; after ultrasonic treatment, place the substrate in a forced-air drying oven and dry it at 80℃ for 30min to ensure that there is no residual moisture and ethanol on the surface. Pre-preparation: (1) Add titanium nitride (50nm), carbon nanotubes (15nm), and epoxy silane coupling agent (KH-560) to 80wt% ethanol aqueous solution at a mass ratio of 1:0.3:0.2. React at 70℃ for 6 hours, cool, wash and dry to obtain epoxy composite filler; (2) Under nitrogen atmosphere, add POSS-SH, epoxy composite filler and triethylamine to DMF at a mass ratio of 0.4:10:0.1. React at 60℃ for 8 hours, cool to room temperature, wash and dry to obtain functional additive; (3) Mix 80 parts of solder, 0.25 parts of dispersant (stearic acid), 0.07 parts of thixotropic agent (hydrogenated castor oil), and 18 parts of organic solvent (terpineol and diethylene glycol butyl ether at a mass ratio of 3:1.5) evenly to obtain Ag-Cu-Ti solder paste; In the above scheme, the raw materials of the brazing filler metal include silver-copper-titanium brazing filler metal powder in a mass ratio of 100:3 (including silver powder, copper powder, and titanium hydride powder in a mass ratio of 79.5:17.5:3.0) and functional additives; Step 1: After pretreatment of the ceramic substrate, solder paste is printed on its surface using a dot matrix stencil (the pretreated ceramic substrate is adsorbed onto the screen printing machine table, and the stencil position is calibrated to align the dot matrix pattern with the center of the substrate; screen printing parameters are set: squeegee angle 60°, squeegee pressure 0.3MPa, printing speed 50mm / s, and screen spacing 2mm; Ag-Cu-Ti solder paste is evenly applied to the stencil, the screen printing machine is started to complete the printing, and then transferred to an oven at 100℃ for 15 minutes to form a discrete square solder paste dot matrix on the surface of the ceramic substrate. The stencil is a 250-mesh steel wire composite mesh with a wire diameter of 25μm. A portion of the squares in the dot matrix pattern on the stencil has a side length of 1mm and a dot spacing of 0.3mm. The above printing operation is repeated to print square solder paste dot matrices of the same specifications on the other side of the Si3N4 ceramic substrate), forming a solder paste dot matrix; ceramic substrate A is obtained. Step 2: Assemble the copper foil with the ceramic substrate A (flatly cover the front and back surfaces of the ceramic substrate A with two 134mm×184mm 0.8mm thick oxygen-free copper foils to form a copper foil-soldering paste matrix-ceramic substrate sandwich structure, and press a 140mm×190mm graphite block on top as a pressure transmission medium)); to obtain the laminated assembly; Step 3: Heat the laminated assembly using a vacuum brazing furnace (place the laminated assembly directly below the mechanical pressure head inside the vacuum brazing furnace, close the furnace door, and evacuate to 5×10). -3 The furnace temperature was increased from room temperature to 420°C at a rate of 5°C / min and held for 60 minutes to remove the organic carrier of the solder paste. The temperature was then increased to 600°C at a rate of 8°C / min and held for 30 minutes to remove residual carriers and adsorbed gases, preparing for solder melting. The temperature was then increased to above the liquidus line of the solder paste. Mechanical pressure was applied and maintained (the liquidus line temperature of the Ag-Cu-Ti solder paste is approximately 780°C; the furnace temperature was further increased to 830°C (50°C above the liquidus line) at a rate of 5°C / min to ensure complete melting of the solder paste. The mechanical pressure device inside the furnace was activated, applying 2MPa of mechanical pressure to the component through a graphite pressure head and maintaining the pressure for 40 minutes). The pressure was then released by cooling (after the pressure holding period, the temperature was lowered to 750°C at a rate of 10°C / min (when the solder was completely solidified), and then the mechanical pressure was released; the temperature was then slowly lowered to room temperature, and the furnace door was opened to remove the component). This resulted in a thinned solder layer on the copper-clad ceramic substrate.

[0032] Example 3: A method for thinning the solder layer of a copper-clad ceramic substrate, comprising the following steps: Pretreatment of ceramic substrate: Place a 0.32mm thick Si3N4 ceramic substrate with dimensions of 138mm×190mm into an ultrasonic cleaning tank, use anhydrous ethanol as the cleaning medium, set the ultrasonic power to 300W and the ultrasonic time to 15min to remove surface oil and dust; after ultrasonic treatment, place the substrate in a forced-air drying oven and dry it at 80℃ for 30min to ensure that there is no residual moisture and ethanol on the surface. Pre-preparation: (1) Add titanium nitride (50nm), carbon nanotubes (15nm), and epoxy silane coupling agent (KH-560) to 80wt% ethanol aqueous solution at a mass ratio of 3:0.1:0.1. React at 70℃ for 6 hours, cool, wash and dry to obtain epoxy composite filler; (2) Under nitrogen atmosphere, add POSS-SH, epoxy composite filler and triethylamine to DMF at a mass ratio of 0.7:10:0.1. React at 60℃ for 8 hours, cool to room temperature, wash and dry to obtain functional additive; (3) Mix 80 parts of solder, 0.25 parts of dispersant (stearic acid), 0.07 parts of thixotropic agent (hydrogenated castor oil), and 18 parts of organic solvent (terpineol and diethylene glycol butyl ether at a mass ratio of 3:1.5) evenly to obtain Ag-Cu-Ti solder paste; In the above scheme, the raw materials of the brazing filler metal include silver-copper-titanium brazing filler metal powder (including silver powder, copper powder, and titanium hydride powder in a mass ratio of 84.5:13.5:2.0) and functional additives in a mass ratio of 100:5; Step 1: After pretreatment of the ceramic substrate, solder paste is printed on its surface using a dot matrix stencil (the pretreated ceramic substrate is adsorbed onto the screen printing machine table, and the stencil position is calibrated to align the dot matrix pattern with the center of the substrate; screen printing parameters are set: squeegee angle 60°, squeegee pressure 0.3MPa, printing speed 50mm / s, and screen spacing 2mm; Ag-Cu-Ti solder paste is evenly applied to the stencil, the screen printing machine is started to complete the printing, and then transferred to an oven at 100℃ for 15 minutes to form a discrete square solder paste dot matrix on the surface of the ceramic substrate. The stencil is a 250-mesh steel wire composite mesh with a wire diameter of 25μm. A portion of the squares in the dot matrix pattern on the stencil has a side length of 1mm and a dot spacing of 0.3mm. The above printing operation is repeated to print square solder paste dot matrices of the same specifications on the other side of the Si3N4 ceramic substrate), forming a solder paste dot matrix; ceramic substrate A is obtained. Step 2: Assemble the copper foil with the ceramic substrate A (flatly cover the front and back surfaces of the ceramic substrate A with two 134mm×184mm 0.8mm thick oxygen-free copper foils to form a copper foil-soldering paste matrix-ceramic substrate sandwich structure, and press a 140mm×190mm graphite block on top as a pressure transmission medium)); to obtain the laminated assembly; Step 3: Heat the laminated assembly using a vacuum brazing furnace (place the laminated assembly directly below the mechanical pressure head inside the vacuum brazing furnace, close the furnace door, and evacuate to 5×10). -3The furnace temperature was increased from room temperature to 420°C at a rate of 5°C / min and held for 60 minutes to remove the organic carrier of the solder paste. The temperature was then increased to 600°C at a rate of 8°C / min and held for 30 minutes to remove residual carriers and adsorbed gases, preparing for solder melting. The temperature was then increased to above the liquidus line of the solder paste. Mechanical pressure was applied and maintained (the liquidus line temperature of the Ag-Cu-Ti solder paste is approximately 780°C; the furnace temperature was further increased to 830°C (50°C above the liquidus line) at a rate of 5°C / min to ensure complete melting of the solder paste. The mechanical pressure device inside the furnace was activated, applying 2MPa of mechanical pressure to the component through a graphite pressure head and maintaining the pressure for 40 minutes). The pressure was then released by cooling (after the pressure holding period, the temperature was lowered to 750°C at a rate of 10°C / min (when the solder was completely solidified), and then the mechanical pressure was released; the temperature was then slowly lowered to room temperature, and the furnace door was opened to remove the component). This resulted in a thinned solder layer on the copper-clad ceramic substrate.

[0033] In Examples 1-3 above, the Si3N4 ceramic substrate has dimensions of 138mm × 190mm and a thickness of 0.32mm; the copper foil has a thickness of 0.8mm and a size of 134mm × 184mm; the titanium nitride has a thickness of 50nm; the carbon nanotubes (multi-walled carbon nanotubes) are MWCNT (-OH, 10-20nm, 98%), product number TNMH3; the silver powder has a thickness of 2μm; the copper powder has a thickness of 5μm; the titanium hydride powder has a thickness of 400 mesh; and the terpineol (CAS number 8000-41-7) is commercially available.

[0034] Comparative Example 1: Based on Example 1, using conventional full-plate printing screen and pressureless vacuum brazing process; otherwise the same as Example 1; the specific difference is: Step 1: After pretreatment of the ceramic substrate, solder paste is printed on its surface using a full-size printing screen (the pretreated ceramic substrate is adsorbed onto the screen printing machine table, and the screen position is calibrated to align the printing area with the center of the substrate; screen printing parameters are set: squeegee angle 60°, squeegee pressure 0.3MPa, printing speed 50mm / s, screen spacing 2mm; Ag-Cu-Ti solder paste is evenly applied to the screen, the screen printing machine is started to complete the printing, and then transferred to an oven at 100℃ for 15 minutes to form a continuous solder paste on the surface of the ceramic substrate. The screen is a 250-mesh steel wire composite mesh with a wire diameter of 25μm. The printing operation is repeated to print the same continuous solder paste on the other side of the ceramic substrate) to form a full-size solder paste array; ceramic substrate A is obtained; Step 2: Assemble the copper foil with the ceramic substrate A (flatly cover the front and back surfaces of the ceramic substrate A with two 134mm×184mm 0.8mm thick oxygen-free copper foils to form a copper foil-soldering paste-ceramic substrate sandwich structure, and press a 140mm×190mm graphite block with a mass of 5kg (corresponding to a natural pressure of about 0.002MPa) on top of it); to obtain the laminated assembly; Step 3: Vacuum brazing of the laminated assembly (place the laminated assembly into a vacuum brazing furnace, close the furnace door, and evacuate to 5×10⁻⁶ ℃). -3 Below Pa, the temperature is increased from room temperature to 420℃ at 5℃ / min and held for 60min to remove the organic carrier of the solder paste; then the temperature is increased to 830℃ at 5℃ / min and held for 40min, cooled to room temperature, and removed to obtain a thinned copper-clad ceramic substrate solder layer.

[0035] Comparative Example 2: Based on Example 1, titanium nitride was not added to the raw materials of the functional additive; the rest was the same as in Example 1.

[0036] Comparative Example 3: Based on Example 1, carbon nanotubes were not added to the raw materials of the functional additive; the rest was the same as in Example 1.

[0037] Comparative Example 4: Based on Example 1, POSS-SH was not added to the raw materials of the functional additive; the rest was the same as in Example 1.

[0038] Comparative Example 5: Based on Example 1, the amount of carbon nanotubes introduced into the raw materials of the functional additive was too large; the rest was the same as in Example 1; the specific difference was that titanium nitride (50nm), carbon nanotubes (15nm), and epoxy silane coupling agent (KH-560) were added to an 80wt% ethanol aqueous solution at a mass ratio of 2:2:0.15, reacted at 70°C for 6 hours, cooled, washed and dried to obtain epoxy composite filler.

[0039] Comparative Example 6: Based on Example 1, the particle size of titanium nitride in the raw materials of the functional additive is too large; the rest is the same as in Example 1; the specific difference is that titanium nitride (titanium nitride: 500nm), carbon nanotubes (15nm), and epoxy silane coupling agent (KH-560) are added to an 80wt% ethanol aqueous solution at a mass ratio of 2:0.2:0.15, reacted at 70°C for 6 hours, cooled, washed and dried to obtain epoxy composite filler.

[0040] Comparative Example 7: Based on Example 1, the amount of copper powder and titanium hydride powder introduced into the silver-copper-titanium solder powder was adjusted in the raw materials of the solder; the rest was the same as in Example 1; the specific difference was that the raw materials of the solder included silver-copper-titanium solder powder (including silver powder, copper powder and titanium hydride powder in a mass ratio of 68.8:26.7:4.5) and functional additives in a mass ratio of 100:4.

[0041] Testing experiments: The products prepared in Examples 1-3 and Comparative Examples 1-7 were sliced; their thickness and shear strength (tested at room temperature using an Instron-5569 electronic universal testing machine) were measured, and the results are shown in Table 1; SEM images of the brazing interface of Example 1 and Comparative Example 1 are shown below. Figure 3 , Figure 4As shown; Table 1

[0042] Conclusion: As shown in Table 1 above, this application combines a dot-matrix stencil design with a pressure brazing process. Firstly, a discontinuous dot-matrix stencil is designed, with the pattern area occupying 40%–60% of the printing area. This allows for the printing of solder paste in a discrete dot-matrix pattern on the ceramic substrate, rather than the traditional full-plate printing. The dot-matrix design uses square, circular, or irregular patterns, preferably square dots with a side length of 0.3–2 mm, a dot spacing of 30%–50% of the side length, and a single dot area of ​​0.05–4 mm². 2 This design significantly reduces the initial amount of solder applied, saving 40% to 60% of the solder usage based on the area of ​​the printed area, and avoids the problem of achieving uniform ultra-thin printing by thinning the stencil due to the limitation of solder metal powder particle size.

[0043] Subsequently, during the vacuum brazing process, when the temperature rises above the solder liquidus line, an auxiliary pressure of 0.5–3 MPa is applied to the "ceramic substrate-solder paste lattice-copper foil" stacked assembly. The pressure varies depending on the solder formulation and printing thickness. Appropriate pressure can flatten the molten lattice solder while preventing edge solder overflow, allowing the molten lattice solder to contact and fuse together, ultimately forming a continuous, uniform, and significantly thinned (target <5 μm) dense solder layer.

[0044] Data from Comparative Example 1 shows that using conventional full-plate printing and pressureless vacuum brazing processes significantly increases product thickness and decreases shear strength. Data from Comparative Example 2 shows that without titanium nitride in the raw materials of the functional additive, the titanium element is unbalanced, there is no TiN barrier, and the overall performance decreases. Data from Comparative Example 3 shows that without carbon nanotubes in the raw materials of the functional additive, there is a lack of a phase to suppress brittleness, resulting in decreased overall performance. Data from Comparative Example 4 shows that without POSS-SH in the raw materials of the functional additive, the dispersibility decreases, there is a lack of chelation with metals, resulting in decreased antioxidant properties and decreased overall performance. Data from Comparative Example 5 shows that the raw materials of the functional additive contain carbon nanotubes... Excessive introduction of titanium nitride leads to severe agglomeration, which coarsens the brazing seam structure and reduces joint strength. Simultaneously, excessive consumption of titanium affects interfacial reactions, resulting in decreased overall performance. Data from Comparative Example 6 shows that in the raw materials of the functional additives, the excessively large particle size of titanium nitride reduces its barrier effect. Furthermore, the mismatch between titanium nitride and the interfacial TiN lattice weakens the nucleation substrate effect, leading to decreased overall performance. Data from Comparative Example 7 shows that adjusting the amount of copper powder and titanium hydride powder introduced into the silver-copper-titanium brazing filler metal powder results in an imbalance of titanium elements. Excessive copper content leads to an increase in the Cu-Ti brittle phase, while simultaneously increasing melt viscosity and decreasing fluidity. Under the same pressure conditions, this increases spreading resistance, increases brazing layer thickness, and reduces overall performance.

[0045] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for thinning the solder layer of a copper-clad ceramic substrate, characterized in that: Includes the following steps: Step 1: After pre-treating the ceramic substrate, use a dot matrix stencil to print solder paste on its surface to form a solder paste dot matrix; Ceramic substrate A is obtained; Step 2: Assemble the copper foil with the ceramic substrate A; to obtain the laminated assembly; Step 3: Heat the stacked assembly to above the liquidus line of the solder paste using a vacuum brazing furnace, apply mechanical pressure, maintain temperature and pressure, and then cool and release pressure to obtain a thinned copper-clad ceramic substrate brazing layer.

2. The method for thinning the solder layer of a copper-clad ceramic substrate according to claim 1, characterized in that: In the printed solder paste, the pattern of the dot matrix stencil is a discrete dot matrix, and the dot matrix unit is square, circular or irregular. The side length of the square dot is 0.3~2mm, and the dot spacing is 30%~50% of the side length.

3. The method for thinning the solder layer of a copper-clad ceramic substrate according to claim 2, characterized in that: The process parameters for the printed solder paste are: squeegee angle 50~70°, squeegee pressure 0.2~0.4MPa, printing speed 40~60mm / s, and screen distance 1~3mm.

4. The method for thinning the solder layer of a copper-clad ceramic substrate according to claim 1, characterized in that: The temperature of the liquidus in the solder paste is 750~800℃; the mechanical pressure is 1~3MPa; the temperature for heat preservation and pressure holding is 800~850℃, and the holding time is 30~50min.

5. The method for thinning the solder layer of a copper-clad ceramic substrate according to claim 1, characterized in that: During the heating process in the vacuum brazing furnace, the vacuum level is lower than 5×10⁻⁶. -3 Pa, raise the temperature from room temperature to 400-440℃ at a rate of 4-6℃ / min, and hold for 50-70min; continue to raise the temperature to 550-650℃ at a rate of 7-9℃ / min, and hold for 20-40min.

6. The method for thinning the solder layer of a copper-clad ceramic substrate according to claim 2, characterized in that: The solder paste is Ag-Cu-Ti solder paste; the raw materials of the Ag-Cu-Ti solder paste include the following components: by mass, 70-90 parts of solder, 0.1-0.4 parts of dispersant, 0.05-0.1 parts of thixotropic agent, and 15-20 parts of organic solvent.

7. The method for thinning the solder layer of a copper-clad ceramic substrate according to claim 6, characterized in that: The raw materials of the brazing filler metal include silver-copper-titanium brazing filler metal powder and functional additives in a mass ratio of 100:(3~5); the raw materials of the silver-copper-titanium brazing filler metal powder include silver powder, copper powder and titanium hydride powder in a mass ratio of (79.5~84.5):(13.5~17.5):(2.0~3.0).

8. The method for thinning the solder layer of a copper-clad ceramic substrate according to claim 7, characterized in that: The preparation method of the functional additive is as follows: Step 1: Titanium nitride and carbon nanotubes are modified with epoxy-based silane coupling agents to obtain epoxy-based composite fillers; Step 2: Under a nitrogen atmosphere, POSS-SH, epoxy-based composite filler, and triethylamine are added to DMF and reacted at 50-70°C for 6-8 hours. After cooling to room temperature, the mixture is washed and dried to obtain the functional additive.

9. A method for thinning the solder layer of a copper-clad ceramic substrate according to claim 8, characterized in that: In the raw materials of the epoxy composite filler, the particle size of titanium nitride is 50~200nm, and the outer diameter of carbon nanotubes is 10~20nm.

10. A method for thinning the solder layer of a copper-clad ceramic substrate according to claim 8, characterized in that: In the raw materials of the epoxy-based composite filler, the mass ratio of titanium nitride, carbon nanotubes, and epoxy-based silane coupling agent is (1~3):(0.1~0.3):(0.1~0.2). In the raw materials of the functional additive, the mass ratio of POSS-SH, epoxy-based composite filler, and triethylamine is (0.4~0.7):10:(0.05~0.1).

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