A conductive copper paste prepared by combining liquid non-ferrous metals with graphene and its preparation method.

Abstract

This invention relates to the field of conductive copper paste technology, specifically to a conductive copper paste prepared using liquid non-ferrous metal combined with graphene and its preparation method. The method includes the following steps: weighing nano-copper-coated graphene composite powder, liquid non-ferrous metal, binder, trifluoropropyltrimethoxysilane, additives, and copper powder; then preparing a dilute solution of trifluoropropyltrimethoxysilane; mixing copper powder and nano-copper-coated graphene composite powder to obtain a composite powder; stirring the liquid non-ferrous metal with the composite powder to obtain a metal paste; adding a resin solution and additives to the metal paste to form a printing paste, and then allowing it to stand for curing. In this invention, by using liquid non-ferrous metal as the main binder phase, the low welding thrust caused by traditional resin systems is avoided. The dispersion and interface compatibility problems are solved synergistically by utilizing nano-copper-coated graphene and silane coupling agent, ultimately obtaining a conductive copper paste with extremely low resistance, high stability, and ultra-high welding thrust.

Description

Technical Field

[0001] This invention relates to the field of conductive copper paste technology, and more specifically, to a conductive copper paste prepared by combining liquid non-ferrous metals with graphene and its preparation method. Background Technology

[0002] Conductive copper paste is a composite material composed of copper powder, thermosetting resin, organic solvent and additives. It forms a conductive film layer through techniques such as screen printing and is mainly used in electronic packaging processes to achieve conductive connections.

[0003] Conductive copper paste is a functional material widely used in the electronics field. Its preparation process directly affects the conductivity, stability, and reliability of the final product. For example, CN116013578A discloses a preparation method and application of an antioxidant and corrosion-resistant graphene composite conductive copper paste. Its composition includes: 20-80wt% passivated copper powder, 0.1-10wt% graphene, 1-30wt% polymer resin, 1-15wt% curing agent, 10-60wt% solvent, and 0.1-20wt% functional additives. The preparation method is as follows: weigh out the surface passivated copper powder, polymer resin, graphene powder, high-boiling-point solvent, and functional additives and add them to the slurry tank. Stir with a double-paddle mixer for 1 hour until uniform and the powder is fully wetted. Then, use a three-roll mill to disperse the conductive paste to a fineness of less than 10μm and collect the graphene composite conductive copper paste with good antioxidant properties.

[0004] In the aforementioned graphene-coated conductive copper paste, the passivation layer on the surface of the copper powder hinders the direct wetting of the molten solder, thereby affecting the bonding effect to form a strong metallurgy and resulting in poor formation of the intermetallic compound layer (IMC). As a conductive reinforcing phase, graphene's inert surface also has poor compatibility with the solder and is prone to forming a weak bonding interface. More importantly, the polymer resin system encapsulating the filler faces the risk of thermal decomposition, carbonization, or bubble generation during high-temperature welding, and its coefficient of thermal expansion (CTE), which is significantly different from that of the metal filler, can also induce internal stress during thermal cycling.

[0005] These factors lead to a fragile welding interface, making the solder joint more prone to cracking or failure under mechanical or thermal stress. In other words, the upper limit of the welding thrust value is low (welding thrust refers to the ability of the solder joint (or the joint between the coating and the substrate) to resist external shear or tensile forces, which is a key indicator for measuring the reliability of electronic component connections), and cannot meet the actual component welding requirements. Summary of the Invention

[0006] The purpose of this invention is to solve the problem that the welding thrust value of existing conductive copper paste cannot meet the welding requirements of actual components due to factors such as resin thermal decomposition, mismatch of thermal expansion coefficients, and obstacles to metallurgical bonding.

[0007] The purpose of this invention is to provide a conductive copper paste prepared by combining liquid non-ferrous metals with graphene and its preparation method. By replacing most of the organic resin with liquid non-ferrous metals, the problems of resin thermal decomposition, mismatch of thermal expansion coefficients and obstacles to metallurgical bonding are fundamentally solved, thereby achieving extremely high welding thrust.

[0008] To achieve the above objectives, one objective of this invention is to provide a conductive copper paste prepared by combining liquid non-ferrous metals with graphene, comprising the following raw materials in the indicated mass percentages:

[0009] The composition consists of 3-8% nano-copper-coated graphene composite powder, 15-25% liquid non-ferrous metal, 2-5% binder, 1-3% trifluoropropyltrimethoxysilane, 1-3% additives, and the remainder is copper powder.

[0010] As a further improvement to this technical solution, the copper powder is spherical or flake-shaped.

[0011] As a further improvement to this technical solution, the liquid non-ferrous metal is one of gallium indium tin alloy or bismuth indium tin alloy.

[0012] As a further improvement to this technical solution, the adhesive is epoxy resin.

[0013] As a further improvement to this technical solution, the additives include thixotropic agents and defoamers, and the mass ratio of thixotropic agents to defoamers is 1:1.

[0014] A second objective of this invention is to provide a method for preparing the conductive copper paste described above, which utilizes liquid non-ferrous metals combined with graphene, comprising the following steps:

[0015] Step S1: Weigh the raw materials according to the mass ratio, and then prepare a dilute solution of trifluoropropyltrimethoxysilane;

[0016] Then, copper powder and nano-coated graphene composite powder are mixed, and a dilute solution is sprayed simultaneously during the mixing process to obtain composite powder.

[0017] Step S2: Under an inert atmosphere, liquid non-ferrous metal is placed into a mixing container as a continuous phase. Then, composite powder is added and stirred using a shear emulsifier to obtain a metal paste.

[0018] Step S3: Remove the metal paste from the inert environment and prepare the adhesive into a resin solution;

[0019] Add resin solution and additives to the metal paste, stir for 30-45 minutes until all components are evenly dispersed in the metal paste to form a printing paste;

[0020] Step S4: Grind the printing paste through a three-roll mill 1-2 times, and finally filter it with a screen to remove agglomerates;

[0021] After the printing paste is allowed to stand and mature to stabilize its rheological properties, it is then sealed and packaged in a light-proof container.

[0022] As a further improvement to this technical solution, in step S1, trifluoropropyltrimethoxysilane is dissolved in anhydrous ethanol to prepare a dilute solution.

[0023] Copper powder and nano-copper-coated graphene composite powder are added to a high-speed mixer, and the above dilute solution is sprayed on the mixture while stirring to make it evenly adhere to the powder surface, thus obtaining composite powder.

[0024] As a further improvement to this technical solution, in step S2, the stirring time of the shear emulsifier is 30-60 minutes.

[0025] As a further improvement to this technical solution, in step S3, the adhesive is dissolved in an ether ester solvent to prepare a resin solution.

[0026] As a further improvement to this technical solution, in step S3, the viscosity of the printing paste is 10000-50000 cP.

[0027] In this invention, liquid non-ferrous metal is used as the main binder phase, which fundamentally avoids the defect of low welding thrust caused by traditional resin systems. At the same time, the dispersion and interface compatibility problems are solved by using nano-copper-coated graphene and silane coupling agent. Finally, a conductive copper paste with extremely low resistance, high stability and ultra-high welding thrust is obtained.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] In this conductive copper paste prepared by combining liquid non-ferrous metals with graphene and its preparation method, a continuous metal bridging network is first constructed between copper powder and nano-copper-coated graphene composite powder using liquid non-ferrous metals. The room temperature liquid phase characteristics are used to achieve perfect wetting and metal bonding of the particle interface, fundamentally replacing the traditional resin binder phase and eliminating the problems of thermal decomposition and thermal expansion mismatch of organic materials. Trifluoropropyltrimethoxysilane binds the metal powder and resin system simultaneously through inorganic-organic bifunctional groups at both ends of the molecule, effectively inhibiting phase separation of components and enhancing the adhesion of the paste-substrate interface.

[0030] Furthermore, under an inert atmosphere, the liquid metal is preferentially and completely coated on the active powder, forming a three-dimensional conductive framework dominated by metallic bonds. The subsequently introduced trace amount of epoxy resin only provides temporary rheological properties and decomposes and carbonizes during the high-temperature welding process, completely avoiding the formation of an organic insulating layer. The resulting slurry undergoes metallurgical intersolidation with the solder and substrate during welding, forming a high-strength intermetallic compound interface, which improves the welding thrust value. At the same time, it has excellent oxidation resistance and environmental stability, meeting the stringent requirements of electronic packaging for conductive interconnect materials. Attached Figure Description

[0031] Figure 1 This is a flowchart of the present invention;

[0032] Figure 2 A schematic diagram showing the volume resistivity of conductive copper paste when the mass percentage of nano-coated graphene composite powder is different.

[0033] Figure 3 A schematic diagram showing the maximum welding thrust of conductive copper paste when the mass percentage of nano-coated graphene composite powder is different.

[0034] Figure 4 A schematic diagram showing the volume resistivity of conductive copper paste when the mass percentage of trifluoropropyltrimethoxysilane is different.

[0035] Figure 5 This diagram illustrates the maximum welding thrust of conductive copper paste when the mass percentage of trifluoropropyltrimethoxysilane varies. Detailed Implementation

[0036] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0037] One objective of this invention is to provide a conductive copper paste prepared by combining liquid non-ferrous metals with graphene, comprising the following raw materials in the following mass percentages:

[0038] The composition consists of 3-8% nano-copper-coated graphene composite powder, 15-25% liquid non-ferrous metal, 2-5% binder, 1-3% trifluoropropyltrimethoxysilane, 1-3% additives, and the remainder is copper powder.

[0039] The copper powder is spherical or flake-shaped and has not undergone passivation treatment to maintain its surface activity.

[0040] The nano-copper-coated graphene composite powder has a core-shell structure in which copper powder is coated with graphene. The graphene layer acts as a reinforcing phase, uniformly coating the surface of the copper particles to form a stable interfacial bond. This structure enhances the interaction between copper and graphene through π-d orbital hybridization, significantly improving the mechanical properties and conductivity of the material. In this invention, the nano-copper-coated graphene powder is pre-prepared using chemical plating or ball milling. Specifically, the copper powder is pretreated and then mixed with a graphene precursor solution. The mixture is then granulated and heat-treated to achieve a one-step synthesis of graphene-coated copper powder, thereby ensuring its quality and conductivity.

[0041] Trifluoropropyltrimethoxysilane has one end of its molecule bonded to inorganic materials (copper powder, graphene) and the other end bonded to organic materials (resin, solvent), which significantly improves the compatibility and dispersion stability between the components, prevents solid-liquid separation, and enhances the adhesion between the final coating and the substrate.

[0042] Furthermore, the liquid non-ferrous metal is either a gallium-indium-tin alloy or a bismuth-indium-tin alloy. This liquid non-ferrous metal is in a liquid state at room temperature or lower temperatures, capable of wetting copper powder and copper nanoparticles coated with graphene, forming a highly conductive metallic bonding network. During welding, this liquid phase can form a strong metallurgical bond with the solder and substrate, thereby increasing the welding thrust value.

[0043] Furthermore, the binder is epoxy resin, used for temporary setting and thickening. It provides the viscosity and thixotropy required for printing the paste, ensuring that the printed pattern does not collapse. Its content is strictly controlled, providing initial strength only during curing. It decomposes or carbonizes during subsequent high-temperature welding, giving way to the dominant bonding effect of the liquid metal, thereby avoiding the formation of a weak interface layer.

[0044] Furthermore, the additives include thixotropic agents and defoamers, with a mass ratio of 1:1 between the thixotropic agents and defoamers, to further precisely control printing performance, prevent sagging and bubble formation, and ensure consistent product quality.

[0045] Please see Figure 1 As shown, a second objective of this invention is to provide a method for preparing the conductive copper paste prepared by combining liquid non-ferrous metals with graphene, comprising the following steps:

[0046] Step S1: Weigh the raw materials according to the mass ratio;

[0047] Then, trifluoropropyltrimethoxysilane is prepared into a dilute solution. Specifically, trifluoropropyltrimethoxysilane is dissolved in a small amount of anhydrous ethanol to prepare a dilute solution.

[0048] Next, copper powder and nano-coated graphene composite powder are added to a high-speed mixer, and the above dilute solution is sprayed on while stirring to ensure uniform adhesion to the powder surface, thus obtaining the composite powder. This step can significantly improve the compatibility of the powder with the subsequent organic phase.

[0049] Step S2: The process is carried out in an inert atmosphere to prevent oxygen from corroding the active metal components. Liquid non-ferrous metal is placed in a mixing container as a continuous phase. Then, composite powder is added and stirred for 30-60 minutes using a high-speed shear emulsifier (>1000 rpm) to obtain a metal paste.

[0050] This step utilizes mechanical shearing force to forcibly inject liquid non-ferrous metal into the graphene sheets of the composite powder, achieving perfect encapsulation and forming a uniform conductive paste. Simultaneously, the activated liquid metal phase, through continuous mechanical energy input and surface diffusion, achieves perfect wetting and coverage of the surface of a large number of copper powder particles. Ultimately, a uniform metal-based paste-like composite system is formed, with liquid non-ferrous metal bridging, copper powder as the skeleton, and embedded nano-copper-encapsulated graphene composite powder. This lays the structural foundation for the subsequent construction of a highly reliable, low-resistance conductive network.

[0051] Step S3: Remove the above-mixed metal paste from the inert environment and prepare the binder into a resin solution. Specifically, dissolve the binder in a high-boiling-point ether ester solvent to prepare a resin solution.

[0052] Using a planetary mixer, slowly add the resin solution and additives to the metal paste, and stir at low speed for 30-45 minutes until all components are evenly dispersed in the metal paste, forming a printing paste with a viscosity of 10,000-50,000 cP and suitable viscosity and thixotropy.

[0053] Step S4: Grind the printing paste through a three-roll mill 1-2 times, and finally filter it with a screen to remove larger agglomerates.

[0054] After the printing paste is left to stand and mature for several hours to stabilize its rheological properties, it is then sealed and packaged in a light-proof container.

[0055] The following specific embodiments will further illustrate the conductive copper paste prepared by combining liquid non-ferrous metals with graphene and its preparation method provided by the present invention.

[0056] Example 1

[0057] Step S1: Weigh out 3% of nano-copper-coated graphene composite powder, 25% of liquid non-ferrous metal, 2% of binder, 3% of trifluoropropyltrimethoxysilane, and 1% of additives according to the mass ratio, with the remainder being copper powder;

[0058] The copper powder is spherical; the liquid non-ferrous metal is a gallium indium tin alloy; the binder is epoxy resin; the additives include thixotropic agents and defoamers, and the mass ratio of thixotropic agents to defoamers is 1:1.

[0059] Then, trifluoropropyltrimethoxysilane is prepared into a dilute solution. Specifically, trifluoropropyltrimethoxysilane is dissolved in a small amount of anhydrous ethanol to prepare a dilute solution.

[0060] Then, copper powder and nano-copper coated graphene composite powder are added to a high-speed mixer, and the above dilute solution is sprayed on the mixture while stirring, so that it is evenly adhered to the surface of the powder to obtain composite powder.

[0061] Step S2: Under an inert atmosphere, liquid non-ferrous metal is placed into a mixing container as a continuous phase. Then, composite powder is added and stirred for 60 minutes using a high-speed shear emulsifier (>1000 rpm) to obtain a metal paste.

[0062] Step S3: Remove the above-mixed metal paste from the inert environment and prepare the binder into a resin solution. Specifically, dissolve the binder in a high-boiling-point ether ester solvent to prepare a resin solution.

[0063] Using a planetary mixer, slowly add the resin solution and additives to the metal paste, and stir at low speed for 30 minutes until all components are evenly dispersed in the metal paste to form a printing paste with a viscosity of 50,000 cP.

[0064] Step S4: Grind the printing paste once through a three-roll mill, and finally filter it with a screen to remove agglomerates.

[0065] After the printing paste is left to stand and mature for several hours to stabilize its rheological properties, it is then sealed and packaged in a light-proof container.

[0066] Example 2

[0067] Step S1: Weigh out 5% of nano-copper-coated graphene composite powder, 20% of liquid non-ferrous metal, 3% of binder, 2% of trifluoropropyltrimethoxysilane, and 2% of additives according to the mass ratio, with the remainder being copper powder;

[0068] The copper powder is in flake form; the liquid non-ferrous metal is a gallium indium tin alloy; the binder is epoxy resin; and the additives include thixotropic agents and defoamers, with a mass ratio of 1:1 between the thixotropic agents and the defoamers.

[0069] Then, trifluoropropyltrimethoxysilane is prepared into a dilute solution. Specifically, trifluoropropyltrimethoxysilane is dissolved in a small amount of anhydrous ethanol to prepare a dilute solution.

[0070] Then, copper powder and nano-copper coated graphene composite powder are added to a high-speed mixer, and the above dilute solution is sprayed on the mixture while stirring, so that it is evenly adhered to the surface of the powder to obtain composite powder.

[0071] Step S2: Under an inert atmosphere, liquid non-ferrous metal is placed into a mixing container as a continuous phase. Then, composite powder is added and stirred for 50 minutes using a high-speed shear emulsifier (>1000 rpm) to obtain a metal paste.

[0072] Step S3: Remove the above-mixed metal paste from the inert environment and prepare the binder into a resin solution. Specifically, dissolve the binder in a high-boiling-point ether ester solvent to prepare a resin solution.

[0073] Using a planetary mixer, slowly add the resin solution and additives to the metal paste, and stir at low speed for 40 minutes until all components are evenly dispersed in the metal paste to form a printing paste with a viscosity of 30,000 cP.

[0074] Step S4: Grind the printing paste twice using a three-roll mill, and finally filter it with a screen to remove agglomerates.

[0075] After the printing paste is left to stand and mature for several hours to stabilize its rheological properties, it is then sealed and packaged in a light-proof container.

[0076] Example 3

[0077] Step S1: Weigh out 8% of nano-copper-coated graphene composite powder, 15% of liquid non-ferrous metal, 5% of binder, 1% of trifluoropropyltrimethoxysilane, and 3% of additives according to the mass ratio, with the remainder being copper powder;

[0078] The copper powder is in flake form; the liquid non-ferrous metal is a bismuth-indium-tin alloy; the binder is epoxy resin; and the additives include thixotropic agents and defoamers, with a mass ratio of 1:1 between the thixotropic agents and the defoamers.

[0079] Then, trifluoropropyltrimethoxysilane is prepared into a dilute solution. Specifically, trifluoropropyltrimethoxysilane is dissolved in a small amount of anhydrous ethanol to prepare a dilute solution.

[0080] Then, copper powder and nano-copper coated graphene composite powder are added to a high-speed mixer, and the above dilute solution is sprayed on the mixture while stirring, so that it is evenly adhered to the surface of the powder to obtain composite powder.

[0081] Step S2: Under an inert atmosphere, liquid non-ferrous metal is placed into a mixing container as a continuous phase. Then, composite powder is added and stirred for 30 minutes using a high-speed shear emulsifier (>1000 rpm) to obtain a metal paste.

[0082] Step S3: Remove the above-mixed metal paste from the inert environment and prepare the binder into a resin solution. Specifically, dissolve the binder in a high-boiling-point ether ester solvent to prepare a resin solution.

[0083] Using a planetary mixer, slowly add the resin solution and additives to the metal paste, and stir at low speed for 45 minutes until all components are evenly dispersed in the metal paste to form a printing paste with a viscosity of 10000 cP.

[0084] Step S4: Grind the printing paste twice using a three-roll mill, and finally filter it with a screen to remove agglomerates.

[0085] After the printing paste is left to stand and mature for several hours to stabilize its rheological properties, it is then sealed and packaged in a light-proof container.

[0086] The conductive copper paste was prepared according to the contents provided in Examples 1-3, and samples were prepared. Then, volume resistivity and welding thrust tests were performed.

[0087] The sample preparation process involves using a screen printing machine (mesh count selected based on the target film thickness, such as 200-300 mesh) to print the paste onto a standard FR-4 PCB substrate or alumina ceramic substrate, forming the designed pattern (e.g., a 100mm long × 1mm wide line for sheet resistance testing, or a Φ5mm disc for solderability testing). The printed substrate is then placed in a forced-air drying oven and heat-treated according to a preset curing process to evaporate the solvent and achieve initial curing. After cooling to room temperature in the oven, the sample to be tested is obtained.

[0088] The volume resistivity test method involves using a four-probe tester to measure the resistance of the line pattern and calculating the sheet resistance value according to the formula (sheet resistance = resistance × width / length). Measurements are taken at least five times at different locations, and the average value is calculated. The volume resistivity (volume resistivity = sheet resistance × film thickness) is then further calculated based on the sheet resistance value, and the results are recorded in Table 1.

[0089] The welding thrust test method involves soldering a solder ball of a specific size (e.g., Φ0.6mm) onto a cured solder paste disk using a reflow oven according to the recommended curve of standard SnAgCu solder paste. Then, a push-pull tester (BondTester) is used, employing a specific shearing fixture to push the solder ball at a constant speed until the solder joint breaks. The maximum force at break is recorded as the welding thrust. This test is repeated at least 20 times, and the average value is calculated. The results are also recorded in Table 1.

[0090] Table 1. Volume resistivity and welding thrust of the conductive copper paste samples prepared in Examples 1-3

[0091] Example 1 Example 2 Example 3 <![CDATA[Volume resistivity / (×10 -5 Ω·cm)]]> 4.8 4.6 4.9 Maximum welding thrust / N 10.2 11.0 10.4

[0092] As shown in Table 1, the volume resistivity of the conductive copper paste samples prepared in Examples 1-3 is no higher than 4.9 × 10⁻⁶. -5 The results show that the conductive copper paste prepared by combining liquid non-ferrous metals with graphene and the preparation method thereof, provided by this invention, can produce conductive copper paste with good conductivity and large welding thrust, with a value of Ω·cm and a maximum welding thrust of not less than 10.2N.

[0093] In this invention, a continuous metal bridging network is first constructed between copper powder and copper nano-coated graphene composite powder using liquid non-ferrous metal. This network utilizes the room-temperature liquid phase properties to achieve perfect wetting and metal bonding at the particle interface, fundamentally replacing the traditional resin binder phase and eliminating the problems of thermal decomposition and thermal expansion mismatch in organic materials. The copper nano-coated graphene forms a strongly coupled core-shell structure through π-d orbital hybridization, significantly improving the mechanical strength of the composite system while enhancing carrier migration efficiency. Trifluoropropyltrimethoxysilane simultaneously bonds the metal powder and resin system through inorganic-organic bifunctional groups at both ends of the molecule, effectively inhibiting phase separation of components and enhancing the adhesion between the slurry and substrate.

[0094] Furthermore, under an inert atmosphere, the liquid metal is preferentially and completely coated on the active powder, forming a three-dimensional conductive framework dominated by metallic bonds. The subsequently introduced trace amount of epoxy resin only provides temporary rheological properties and decomposes and carbonizes during the high-temperature welding process, completely avoiding the formation of an organic insulating layer. The resulting slurry undergoes metallurgical intersolidation with the solder and substrate during welding, forming a high-strength intermetallic compound interface, which improves the welding thrust value. At the same time, it has excellent oxidation resistance and environmental stability, meeting the stringent requirements of electronic packaging for conductive interconnect materials.

[0095] Example 4

[0096] In this invention, the mass percentage of the copper-coated graphene composite powder in the conductive copper paste is 3-8%. This composite powder constructs a core-shell structure through chemical bonding, where the copper core (Cu) and graphene (C) form a strongly coupled Cu-C interface through π-d orbital hybridization, significantly enhancing interfacial electron migration and inhibiting the oxidation process on the copper surface. The graphene shell is further enhanced through sp... 2 Hybrid carbon six-membered ring networks provide mechanical support and electrical conductivity enhancement.

[0097] If the proportion of nano-copper-coated graphene composite powder is too low, the distribution density of the graphene reinforcing phase will be insufficient, making it impossible to effectively construct a continuous three-dimensional reinforcing network. Due to the insufficient graphene content, there are not enough fast electron channels between copper powder particles, and carrier transport still mainly relies on the point contact copper powder network, resulting in an increase in overall resistivity. If the proportion of nano-copper-coated graphene composite powder is too high, the excess graphene sheets will agglomerate due to van der Waals forces, destroying the continuous conductive network formed by the liquid metal. Agglomerates act as insulating barriers in the slurry, hindering electron transport, causing the initial conductivity to decrease instead of increase. At the same time, an excessively thick graphene coating layer will inhibit the effective contact between the liquid metal and the copper core, affecting the metallurgical bonding strength and leading to a decrease in welding thrust. In addition, a high graphene content will increase the viscosity of the slurry, affecting printability and easily causing leveling defects.

[0098] To demonstrate that a 3-8% mass percentage of copper-coated graphene composite powder in the conductive copper paste is a crucial factor in the preparation of conductive copper paste with good conductivity and high welding thrust provided by this invention, this embodiment, based on Example 1, modifies the mass percentage of the copper-coated graphene composite powder in the conductive copper paste, setting it to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%. The conductive copper paste is then prepared according to the steps of Example 1, and tested using the aforementioned detection method. The test results are as follows. Figure 2 , Figure 3 As shown.

[0099] according to Figure 2 It can be seen that when the mass percentage of nano-coated graphene composite powder in the conductive copper paste is 1%, 2%, 9%, or 10%, rather than 3-8%, the volume resistivity of the prepared conductive copper paste is significantly higher than that when the mass percentage of nano-coated graphene composite powder is 3%, 4%, 5%, 6%, 7%, or 8%.

[0100] according to Figure 3 It can be seen that when the mass percentage of nano-coated graphene composite powder in the conductive copper paste is 1%, 2%, 9%, or 10%, rather than 3-8%, the maximum welding thrust of the prepared conductive copper paste is significantly lower than that when the mass percentage of nano-coated graphene composite powder is 3%, 4%, 5%, 6%, 7%, or 8%.

[0101] In summary, the 3-8% mass ratio of nano-copper-coated graphene composite powder in conductive copper paste is one of the important factors that enable the preparation of conductive copper paste with good conductivity and large welding thrust provided by the present invention.

[0102] Example 5

[0103] In step S1 of this invention, when trifluoropropyltrimethoxysilane is prepared into a dilute solution and sprayed onto the powder surface, a hydrolysis reaction occurs to generate highly reactive silanol. Then, the silanol condenses with the hydroxyl groups on the powder surface, while the silanol molecules themselves condense with each other. The specific reaction process is as follows:

[0104] CF3(CH2)2Si(OCH3)3+3H2O→CF3(CH2)2Si(OH)3+3CH3OH

[0105] CF3(CH2)2Si(OH)3 + Cu-OH (surface) → CF3(CH2)2Si(OH)3-O-Cu (surface) + H2O

[0106] CF3(CH2)2Si(OH)3 + C-OH (graphene surface) → CF3(CH2)2Si(OH)2-OC (surface) + H2O In this formula, CF3(CH2)2Si(OCH3)3 is trifluoropropyltrimethoxysilane, H2O is water, CF3(CH2)2Si(OH)3 is trifluoropropyltrisilol, and CH3OH is methanol. During the hydrolysis reaction, the methoxy group (-OCH3) in the trifluoropropyltrimethoxysilane molecule undergoes hydrolysis with water (a trace amount of water from the ethanol solvent). In response, highly reactive silanols (-Si-OH) are generated. Copper powder and graphene surfaces typically have a very thin oxide layer or adsorbed hydroxyl groups (-OH). The silanols react with these to form strong Si-OM covalent bonds (M refers to metal Cu or C). At the same time, the silanol molecules condense with each other to form Si-O-Si chains, constructing an organosilicon network film on the powder surface. Through this series of chemical reactions, trifluoropropyltrimethoxysilane establishes a strong "molecular bridge" between copper powder and graphene, greatly improving interfacial bonding and dispersibility.

[0107] In this invention, the mass percentage of trifluoropropyltrimethoxysilane in the conductive copper paste is 1-3%. If the proportion of trifluoropropyltrimethoxysilane is too low, the trifluoropropyltrimethoxysilane molecules will not be able to completely coat the copper powder and the surface of the nano-copper coated graphene composite powder, failing to form an effective monolayer bridging structure. Due to the insufficient condensation reaction points between the silanol groups (Si-OH) and the hydroxyl groups (M-OH) on the powder surface (Si-OH+HO-M→Si-O-M+H2O), the interfacial compatibility between the inorganic powder and the organic resin phase cannot be sufficiently improved, leading to an increased tendency for powder agglomeration.

[0108] If the proportion of trifluoropropyltrimethoxysilane is too high, the excess silane molecules will form multiple layers of physical adsorption rather than chemical bonding on the powder surface. The hydrophobic trifluoropropyl long chains (CF3(CH2)2-) become intertwined, forming an organic insulating barrier on the powder particle surface. This not only hinders the metallic bonding between the liquid non-ferrous metal and the copper powder, leading to increased bulk resistivity, but also inhibits the metallurgical bonding process during welding, causing a decrease in welding thrust.

[0109] To demonstrate that a 1-3% mass percentage of trifluoropropyltrimethoxysilane in the conductive copper paste is one of the key factors enabling the preparation of conductive copper paste with good conductivity and high welding thrust, this embodiment, based on Example 1, modifies the mass percentage of trifluoropropyltrimethoxysilane in the conductive copper paste, setting it to 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, or 5.0%. The conductive copper paste is then prepared according to the steps of Example 1, and tested using the aforementioned detection method. The test results are as follows. Figure 4 , Figure 5 As shown.

[0110] according to Figure 4 It can be seen that when the mass percentage of trifluoropropyltrimethoxysilane in the conductive copper paste is 0.5%, 3.5%, 4.0%, 4.5%, or 5.0%, which is not 1-3%, the volume resistivity of the prepared conductive copper paste is significantly higher than that of the prepared conductive copper paste when the mass percentage of trifluoropropyltrimethoxysilane is 1.0%, 1.5%, 2.0%, 2.5%, or 3.0%.

[0111] according to Figure 5 It can be seen that when the mass percentage of trifluoropropyltrimethoxysilane in the conductive copper paste is 0.5%, 3.5%, 4.0%, 4.5%, or 5.0%, which is not 1-3%, the maximum welding thrust of the prepared conductive copper paste is significantly lower than that of the prepared conductive copper paste when the mass percentage of trifluoropropyltrimethoxysilane is 1.0%, 1.5%, 2.0%, 2.5%, or 3.0%.

[0112] In summary, the 1-3% mass ratio of trifluoropropyltrimethoxysilane in the conductive copper paste is one of the important factors that enable the preparation of conductive copper paste with good conductivity and large welding thrust provided by the present invention.

[0113] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing conductive copper paste using liquid non-ferrous metals combined with graphene, characterized in that, Includes the following steps: Step S1: Weigh out 3-8% of nano-copper-coated graphene composite powder, 15-25% of liquid non-ferrous metal, 2-5% of binder, 1-3% of trifluoropropyltrimethoxysilane, and 1-3% of additives according to the mass ratio, with the remainder being copper powder. Then, prepare a dilute solution of trifluoropropyltrimethoxysilane. Then, copper powder and nano-coated graphene composite powder are mixed, and a dilute solution is sprayed simultaneously during the mixing process to obtain composite powder. Step S2: Under an inert atmosphere, liquid non-ferrous metal is placed into a mixing container as a continuous phase. Then, composite powder is added and stirred using a shear emulsifier to obtain a metal paste. Step S3: Remove the metal paste from the inert environment and prepare the adhesive into a resin solution; Add resin solution and additives to the metal paste, stir for 30-45 minutes until all components are evenly dispersed in the metal paste to form a printing paste; Step S4: Grind the printing paste through a three-roll mill 1-2 times, and finally filter it with a screen to remove agglomerates; After the printing paste is allowed to stand and mature to stabilize its rheological properties, it is then sealed and packaged in a light-proof container.

2. The method for preparing conductive copper paste using liquid non-ferrous metals combined with graphene according to claim 1, characterized in that: In step S1, the copper powder is spherical or flake-shaped.

3. The method for preparing conductive copper paste using liquid non-ferrous metals combined with graphene according to claim 1, characterized in that: In step S1, the liquid non-ferrous metal is either gallium indium tin alloy or bismuth indium tin alloy.

4. The method for preparing conductive copper paste using liquid non-ferrous metals combined with graphene according to claim 1, characterized in that: In step S1, the adhesive is epoxy resin.

5. The method for preparing conductive copper paste using liquid non-ferrous metals combined with graphene according to claim 1, characterized in that: In step S1, the additives include thixotropic agents and defoamers, and the mass ratio of thixotropic agents to defoamers is 1:

1.

6. The method for preparing conductive copper paste using liquid non-ferrous metals combined with graphene according to claim 1, characterized in that: In step S1, trifluoropropyltrimethoxysilane is dissolved in anhydrous ethanol to prepare a dilute solution. Copper powder and nano-copper coated graphene composite powder are added to a high-speed mixer, and a dilute solution is sprayed on the mixture while stirring to make it evenly adhere to the powder surface, thus obtaining the composite powder.

7. The method for preparing conductive copper paste using liquid non-ferrous metals combined with graphene according to claim 1, characterized in that: In step S2, the stirring time of the shear emulsifier is 30-60 minutes.

8. The method for preparing conductive copper paste using liquid non-ferrous metals combined with graphene according to claim 1, characterized in that: In step S3, the adhesive is dissolved in an ether ester solvent to prepare a resin solution.

9. The method for preparing conductive copper paste using liquid non-ferrous metals combined with graphene according to claim 1, characterized in that: In step S3, the viscosity of the printing paste is 10,000-50,000 cP.

10. A conductive copper paste prepared by the preparation method according to any one of claims 1-9, characterized in that, Including the following raw materials: The composition includes nano-copper-coated graphene composite powder, liquid non-ferrous metal, copper powder, binder, trifluoropropyltrimethoxysilane, and additives, wherein: The liquid non-ferrous metal penetrates into the copper powder and nano-copper-coated graphene composite powder through capillary action and mechanical shear force, forming a three-dimensional conductive network with metal bonds. During the welding process, it undergoes metallurgical intersolidation with the solder to construct a high-strength intermetallic compound interface. The copper powder serves as a conductive framework to provide the main conductive pathway, and its unpassivated active surface achieves low-resistance ohmic contact between particles through bridging by the liquid non-ferrous metal. The trifluoropropyltrimethoxysilane effectively inhibits phase separation of components and enhances the adhesion between the slurry and the substrate interface by simultaneously bonding the metal powder and the resin system through inorganic-organic bifunctional groups at both ends of the molecule. The binder provides temporary rheological properties and decomposes and carbonizes during high-temperature welding to avoid the formation of an organic insulating layer; the additives achieve a balance between slurry leveling and anti-settling through thixotropic and defoaming synergistic regulation.

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