Lead-free and halogen-free no-clean copper paste, preparation method and application thereof

Abstract

This invention relates to the field of high-performance device packaging technology, and in particular to a lead-free, halogen-free, no-clean copper paste, its preparation method, and its application. The no-clean copper paste provided by this invention is lead-free and halogen-free, leaves no residue after soldering, requires no cleaning, and exhibits good stability. The no-clean copper paste provided by this invention has good oxidation resistance and can be heat-applied after drying, effectively avoiding chip displacement problems during chip mounting, transfer, and sintering. Furthermore, the internal structure of the sintered copper paste is uniform, with no cracks or voids after ultra-scanning, effectively preventing defects and exhibiting high strength. In addition, the dried structure has a uniform structure after sintering, without obvious defects, and can well meet actual production requirements.

Description

Technical Field

[0001] This invention relates to the field of high-performance device packaging technology, and in particular to a lead-free, halogen-free, no-clean copper paste, its preparation method, and its application. Background Technology

[0002] With the rapid development of third-generation wide-bandgap semiconductors and surface-mount electronic component soldering technology, the industry's requirements for reliability are becoming increasingly stringent. Simultaneously, with the development of the semiconductor industry, the performance and quality requirements for solder paste used in low-temperature interconnects and high-temperature operations are also rising. Compared to solder paste, copper paste has a higher melting point after sintering and maintains good reliability above 350°C, eliminating the risk of chip detachment from the substrate. To extend the lifespan of electronic products, cleaning agents based on fluorinated and chlorinated solvents are typically used. However, currently used cleaning agents are difficult to completely remove all residues, leading to suboptimal electrical performance and affecting product reliability. Furthermore, the use of cleaning agents pollutes the environment and increases production costs.

[0003] Existing soldering materials mostly use wet bonding processes for reflow soldering, which inevitably leaves residual organic matter spilling onto the substrate after soldering. While this method has high production efficiency for chip or pin soldering, it makes it difficult for organic matter to volatilize in system-level chip packaging, resulting in gas escape channels in the sintered body, which has an adverse effect on product quality and reliability.

[0004] There is an urgent need to invent a no-clean copper paste and develop a surface mount technology (SMT) process to improve product reliability, reduce costs, and increase production efficiency. Therefore, this invention is proposed. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a lead-free, halogen-free, no-clean copper solder paste, its preparation method and application. The solder paste leaves no residue after soldering and has good surface mount performance.

[0006] Specifically, the technical solution of the present invention is as follows: In a first aspect, the present invention provides a copper solder paste comprising 75-80 parts by weight of modified copper powder and 20-25 parts by weight of organic components; wherein, calculated on a total basis of 100%, the organic components comprise 1%-3% thixotropic agent, 0.5%-2% dispersant, 0.1%-0.5% antioxidant, 0.3%-0.8% binder, 0.5%-2% leveling agent, 0.5%-1% adhesion promoter, and 90.7%-97.1% solvent.

[0007] Preferably, the modified copper powder is obtained by treating copper powder with a surface modifier; the particle size of the copper powder is 2-10 μm; the surface modifier is a compound containing functional groups that form coordination bonds with copper ions.

[0008] Preferably, the surface modifier is phthalic acid or its salt, oleic acid or its salt, or folic acid or its salt; the surface modification method is as follows: the surface modifier is prepared into a 0.1%-1% surface modification solution, and then copper powder is placed in the surface modification solution for full contact; the mass ratio of copper powder to surface modification solution is 1:2~10; the full contact time is 0.5~2h.

[0009] Preferably, the thixotropic agent is selected from at least one of modified castor oil, polyamide wax, fumed silica, and organobentonite, and more preferably modified castor oil and / or polyamide wax.

[0010] Preferably, the dispersant is selected from at least one of ethanol, ethylene glycol, diethylene glycol, cyclohexanol, isopropanol, glycerol and n-butanol, and is more preferably diethylene glycol or glycerol.

[0011] Preferably, the antioxidant is selected from at least one of 2-mercaptobenzothiazole, N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexamethylenediamine, 2,6-di-tert-butyl-p-cresol, 4,4'-methylenebis(2,6-di-tert-butylphenol), and 1,3,5-tris(phenylamino)benzene, and is optimized to be 2-mercaptobenzothiazole or 2,6-di-tert-butyl-p-cresol.

[0012] Preferably, the binder is selected from at least one of cellulose acetate, sodium carboxymethyl cellulose, carboxymethyl cellulose, polyvinyl carbonate, and polypropylene carbonate, and is more preferably carboxymethyl cellulose and / or polypropylene carbonate.

[0013] Preferably, the leveling agent is selected from at least one of polydimethylsiloxane, polymethylalkylsiloxane, organic modified polysiloxane, polyether modified polysiloxane, acrylate copolymer, and fluorinated acrylate copolymer, and is preferably polyether modified polysiloxane or acrylate copolymer.

[0014] Preferably, the adhesion promoter is selected from at least one of titanate, aminosilane, and phosphate, with titanate being the most preferred.

[0015] Preferably, the solvent is selected from at least one of N-methylpyrrolidone, diethylene glycol monoethyl ether acetate, propylene carbonate, 1,4-dioxane, N,N-dimethylformamide, caprolactone, ethyl acetate, ethylene glycol ether, a mixture of dimethyl glutarate and dimethyl adipate, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and ethylene glycol phenyl ether, and more preferably diethylene glycol dimethyl ether, ethylene glycol phenyl ether, and N-methylpyrrolidone.

[0016] Secondly, the present invention provides a method for preparing the copper solder paste, comprising the following steps: mixing a dispersant, an antioxidant, a binder, and a solvent at a temperature of 50°C to 80°C; cooling the mixture to 40°C to 50°C and then mixing it with a thixotropic agent; further cooling the mixture to 20°C to 30°C and then mixing it with a leveling agent and an adhesion promoter; and finally mixing the mixture with modified copper powder.

[0017] Preferably, the preparation method of modified copper powder includes: mixing copper powder and surface modification solution at a mass ratio of 1:2~10, stirring and reacting for 30-60 min; centrifuging at 4500-6000 r / min for 5-10 min to remove surface modification solution; and vacuum drying at 50-80℃ for 5-8 h.

[0018] Preferably, when mixing the mixture with the modified copper powder, the mixing speed is 1000-1200 r / min and the mixing time is 10-15 min.

[0019] Thirdly, the present invention provides the application of the copper solder paste or the copper solder paste prepared by the preparation method in the packaging of power devices.

[0020] As one more specific embodiment, the present invention provides a method for mounting lead-free, halogen-free, no-clean copper paste for power device packaging, comprising the following steps: a) By printing, the copper solder paste or the copper solder paste prepared by the preparation method is uniformly coated on the front side of the substrate to obtain a stacked structure of solder paste and substrate.

[0021] b) Place the printed copper paste substrate in a drying oven to dry it, and obtain a pre-dried copper paste substrate.

[0022] c) Chips are mounted on a pre-dried copper paste substrate using a heat-mounting machine to obtain a pre-sintered module.

[0023] d) The pre-sintered module is placed in a vacuum or inert atmosphere for sintering to obtain the power device packaging structure.

[0024] Preferably, in step a), the printing thickness is 50-150 μm.

[0025] Preferably, in step b), the drying oven uses air, vacuum or inert gas atmosphere for drying, the drying temperature is 90-110℃, and the drying time is 10-20min.

[0026] Preferably, in step c), the chip size is 1×1~5×5mm, the substrate temperature of the heat-applied machine is 70-90℃, the upper pressure head temperature is 130℃-150℃, and the application pressure is 5-8kg.

[0027] Preferably, in step d), the sintering conditions are: sintering temperature 180℃-280℃, sintering pressure 2-20MPa, and sintering time 3-5min.

[0028] Beneficial effects: This invention provides a lead-free, halogen-free, no-clean copper paste, its preparation method, and its application. The copper paste comprises 75-80 parts by weight of modified copper powder and 20-25 parts by weight of organic components; wherein, calculated based on 100% of the total organic components, it includes 1%-3% thixotropic agent, 0.5%-2% dispersant, 0.1%-0.5% antioxidant, 0.3%-0.8% binder, 0.5%-2% leveling agent, 0.5%-1% adhesion promoter, and 90.7%-97.1% solvent. The no-clean copper paste provided by this invention is lead-free, halogen-free, leaves no residue after soldering, requires no cleaning, and exhibits good stability. The no-clean copper paste provided by this invention has good oxidation resistance and can be heat-applied after drying, effectively avoiding chip displacement problems during chip mounting, transportation, and sintering. Moreover, the internal structure of the copper paste after sintering is uniform, with no cracks or holes after ultra-scanning, effectively avoiding defects and exhibiting high strength. Furthermore, the dried structure has a uniform structure after sintering with no obvious defects, which can well meet the actual production requirements. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in this invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be described below.

[0030] Figure 1 A schematic diagram of the process flow for using lead-free, halogen-free, no-clean copper paste for power device packaging.

[0031] Figure 2 The image shows a white light interference pattern after printing of the lead-free, halogen-free, no-clean copper paste provided in Embodiment 1 of the present invention.

[0032] Figure 3 This is a schematic diagram of chip packaging.

[0033] Figure 4 The image shows an ultrasonic scan of a module after chip mounting and sintering, using the lead-free, halogen-free, no-clean copper paste provided in Embodiment 1 of the present invention. Detailed Implementation

[0034] This invention provides a lead-free, halogen-free, no-clean copper paste for power device packaging. It requires no cleaning after soldering, exhibits good storage stability, excellent printability, and superior sintering performance. Being lead-free, it meets the environmentally friendly halogen-free standards of the EU RoHS directive. This invention also provides a method for applying the copper paste to power device packaging, effectively preventing chip displacement and crushing during the sintering process.

[0035] The technical solution provided by this invention specifically includes the following contents: First, this invention provides a lead-free, halogen-free, no-clean copper paste, comprising the following raw materials in weight percentages: 75-80% surface-modified copper particles and 20-25% organic solvent system. The organic solvent system comprises the following components in weight percentages: 1%-3% thixotropic agent, 0.5%-2% dispersant, 0.1%-0.5% antioxidant, 0.3%-0.8% binder, 0.5%-2% leveling agent, 0.5%-1% adhesion promoter, and 90.7%-97.1% solvent.

[0036] In this invention, copper particles are treated with a compound on their surface; specifically, the morphology of the copper particles is one or more of spherical, near-spherical, or plate-like shapes; the particle size of the copper particles is 2-10 μm, preferably 2-5 μm, more preferably 2-4 μm, for example 2 μm, 3 μm, or 4 μm.

[0037] In this invention, the surface modifier is selected from compounds containing functional groups that can form coordination bonds with copper ions; including: carboxyl, hydroxyl, amino, aldehyde, nitro, thiol, sulfonic acid, phosphate, cyano, chloro, bromine, and iodo groups, etc., one or more of the above can be selected. Among them, carboxyl is particularly preferred. In addition, the number of functional groups constituting the polar compound that can form coordination bonds with copper ions can be more than one. In particular, having one or two functional groups that can form coordination bonds with copper ions is most ideal.

[0038] In this invention, the surface modifier is selected from at least one compound containing a carboxyl group, preferably phthalic acid, 1,2-cyclohexanediol, 4-cyclohexene-1,2-diol, 1,1-cyclohexanediol, 2,2'-biphenyldicarboxylic acid, octanoic acid, decanoic acid, oleic acid, and folic acid. It is preferable to select one or more from this group, with phthalic acid, oleic acid, and folic acid being more preferred. Salts of these compounds (such as sodium or potassium salts) can also be used, such as disodium phthalate, sodium octanoate, sodium decanoate, and sodium oleate.

[0039] In this invention, the surface modification treatment method for copper powder can be selected from solid phase surface modification treatment, liquid phase surface modification treatment, gas phase surface modification treatment, and preferably liquid phase surface modifier treatment.

[0040] In this invention, the surface modification solution is prepared by mixing a surface modifier and a solvent (such as ethanol, ethylene glycol, propylene glycol, 1,3-propanediol, etc., preferably at least one of ethanol and ethylene glycol) at a mass ratio of surface modifier to solvent of (0.1-1):(99-99.9), preferably 0.3:99.7.

[0041] Copper powder surface modification treatment can be performed using homogenizing equipment such as centrifuges, shakers, and magnetic stirrers. The surface modification solution and copper particles are mixed at a mass ratio of 1:2, 1:5, or 1:10, with a preferred ratio of 1:5. The treatment time is 0.5-2 hours.

[0042] The thixotropic agent is selected from modified castor oil, polyamide wax, fumed silica, organobentonite, etc., preferably one or both of modified castor oil and polyamide wax.

[0043] The dispersant is selected from at least one of ethanol, ethylene glycol, diethylene glycol, cyclohexanol, isopropanol, glycerol, and n-butanol, preferably diethylene glycol or glycerol.

[0044] The antioxidant is selected from one or more of the following: 2-mercaptobenzothiazole, N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexamethylenediamine, 2,6-di-tert-butyl-p-cresol, 4,4'-methylenebis(2,6-di-tert-butylphenol), 1,3,5-tris(phenylamino)benzene, and is optimized to 2-mercaptobenzothiazole and 2,6-di-tert-butyl-p-cresol.

[0045] The binder is selected from at least one of cellulose acetate, sodium carboxymethyl cellulose, carboxymethyl cellulose, polyvinyl carbonate, and polypropylene carbonate, preferably carboxymethyl cellulose or polypropylene carbonate.

[0046] The leveling agent is selected from at least one of polydimethylsiloxane, polymethylalkylsiloxane, organic modified polysiloxane, polyether modified polysiloxane, acrylate copolymer, and fluorinated acrylate copolymer, preferably polyether modified polysiloxane or acrylate copolymer.

[0047] The adhesion promoter is selected from at least one of titanate, aminosilane, and phosphate, preferably titanate.

[0048] The solvent is preferably selected from one or more of N-methylpyrrolidone, diethylene glycol monoethyl ether acetate, propylene carbonate, 1,4-dioxane, N,N-dimethylformamide, caprolactone, ethyl acetate, ethylene glycol ether, a mixture of dimethyl glutarate and dimethyl adipate, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and ethylene glycol phenyl ether, and is more preferably diethylene glycol dimethyl ether, ethylene glycol phenyl ether, or N-methylpyrrolidone.

[0049] The present invention does not impose any particular limitation on the source of the above components; any commercially available raw materials in the art are acceptable.

[0050] Furthermore, the preparation method of the lead-free, halogen-free, no-clean copper paste includes the following steps: S1. The copper powder is subjected to surface modification treatment and dried to obtain surface-modified copper powder.

[0051] S2. Add dispersant, antioxidant, binder and solvent to the reaction vessel, heat to 50℃~80℃ and stir.

[0052] S3. Cool down to 40℃~50℃, add thixotropic agent to the reactor and stir evenly to fully activate it.

[0053] S4. Continue cooling to 20℃~30℃, add leveling agent and adhesion promoter to the reactor and stir evenly to obtain an organic solvent system.

[0054] S5. The copper powder treated in S1 is mixed, stirred, dispersed, and packaged with the mixed organic solution in S4 to obtain the lead-free, halogen-free, and no-clean copper paste.

[0055] Specifically and preferably, step S1 includes: S11. Mix copper powder and surface modification solution at a mass ratio of 1:5, stir thoroughly with a stirrer, and react for 30-60 minutes.

[0056] S12. After surface modification, the copper powder is centrifuged at 4500-6000 r / min for 5-10 min to remove the surface modification solution. The centrifuged copper powder is then dried by vacuum drying.

[0057] In step S12, vacuum drying is performed. After vacuum drying, uniformly dispersed copper powder is obtained.

[0058] In step S5, a mixer is used at 1000-1200 rpm for 10-15 minutes to obtain a mixed copper paste, which is then further packaged using a filling machine.

[0059] The present invention also provides the application of the above-mentioned lead-free, halogen-free, no-clean copper paste in high-power devices.

[0060] The present invention also provides a method for mounting lead-free, halogen-free, no-clean copper paste for power device packaging, comprising the following steps: a) By printing, the above-mentioned lead-free, halogen-free, no-clean copper paste is evenly coated on the front side of the substrate to obtain a stacked structure of solder paste and substrate.

[0061] b) Place the printed copper paste substrate in a drying oven to dry it, and obtain a pre-dried copper paste substrate.

[0062] c) Chips are mounted on a pre-dried copper paste substrate using a heat-mounting machine to obtain a pre-sintered module.

[0063] d) The pre-sintered module is placed in a vacuum or inert atmosphere for sintering to obtain the power device packaging structure.

[0064] Specifically and preferably, in step a), the printing thickness is 50-150 μm. In step b), the drying oven uses air, vacuum, or an inert gas atmosphere for drying, with a drying temperature of 90-110℃ and a drying time of 10-20 min. In step c), the chip size is 1*1~5*5 mm, the substrate temperature in the heat mounter is 70-90℃, the upper pressure head temperature is 130℃-150℃, and the mounting pressure is 5-8 kg. In step d), the sintering conditions are: sintering temperature 180℃-280℃, sintering pressure 2-20 MPa, and sintering time 3-5 min.

[0065] This invention uses polypropylene carbonate or carboxymethyl cellulose to replace the large amount of rosin or acrylic resin in traditional solders. While ensuring adhesion, it prevents binder overflow during sintering, improves sintering stability, and mitigates the overscan defects caused by uneven binder distribution due to solvent evaporation during soldering. The invention uses titanate as an adhesion promoter, effectively addressing the risk of poor chip mounting performance during thermal bonding and chip breakage due to chip displacement during sintering. Furthermore, the invention uses carboxyl organic acids to modify the surface of copper powder, improving sintering activity and reducing sintering porosity. The antioxidant 2-mercaptobenzothiazole is used to improve storage stability. Modified castor oil and polyamide wax are used as thixotropic agents to prevent solder paste settling. Additionally, the solvent used in this invention is a compound of at least one of diethylene glycol dimethyl ether, ethylene glycol phenyl ether, or N-methylpyrrolidone in a specific weight ratio, effectively controlling the solvent evaporation rate, improving sintering quality, and reducing sintering defects.

[0066] The no-clean copper paste of this invention is lead-free, halogen-free, leaves very little residue after soldering, requires no cleaning, is non-corrosive, and has good stability.

[0067] The present invention also proposes a chip mounting method that can prevent chip displacement during sintering, and at the same time prevent contamination of the sintering cavity and the creation of gas escape channels in the sintered body due to the volatilization of a large amount of organic matter during the sintering process.

[0068] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0069] The endpoints and any values ​​of the ranges disclosed in this specification 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.

[0070] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "specific implementation," or "some specific implementations," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0071] In the embodiments provided in this specification, unless specific techniques or conditions are specified, the techniques or conditions described in the literature in this field, or the product instructions, shall be followed. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased from legitimate channels.

[0072] In the following examples and comparative examples: the lead-free, halogen-free, no-clean copper paste comprises the following components by weight percentage: 75% copper powder and 25% organic components. The copper powder used in the examples and comparative examples is phthalic acid surface modifier-treated copper powder with a D50 of 2 μm.

[0073] Examples 1-5 Examples 1-5 provide lead-free, halogen-free, no-clean copper pastes, and the specific formulations and dosages (unit: %) of their respective organic components are shown in Table 1 below.

[0074] The preparation method of the above-mentioned lead-free, halogen-free, no-clean copper paste includes the following steps: S1. Surface-modify copper powder and dry it to obtain surface-modified copper powder.

[0075] S2. Add dispersant, antioxidant, binder and solvent to the reaction vessel, heat to 50℃~80℃ and stir.

[0076] S3. Cool down to 40℃~50℃, add thixotropic agent to the reactor and stir evenly to fully activate it.

[0077] S4. Continue cooling to 20℃~30℃, add leveling agent and adhesion promoter to the reactor and stir evenly to obtain an organic solvent system.

[0078] S5. The copper powder treated in S1 is mixed, stirred, dispersed, and packaged with the mixed organic solution in S4 to obtain the lead-free, halogen-free, and no-clean copper paste.

[0079] Specifically, step S1 includes: S11. Mix copper powder and surface modification solution at a mass ratio of 1:5, stir thoroughly with a stirrer, and react for 30-60 minutes.

[0080] S12. After surface modification, the copper powder is centrifuged at 4500-6000 r / min for 5-10 min to remove the surface modification solution. The centrifuged copper powder is then dried by vacuum drying.

[0081] In step S12, vacuum drying is performed. After vacuum drying, uniformly dispersed copper powder is obtained.

[0082] In step S5, a mixer is used at 1000-1200 rpm for 10-15 minutes to obtain a mixed copper paste, which is then further packaged using a filling machine.

[0083] Comparative Examples 1-5 Comparative Examples 1-5 each provide a lead-free, halogen-free, no-clean copper paste. The specific formulations and dosages (unit: %) of their respective organic components are shown in Table 2 below.

[0084] The preparation method of the above-mentioned lead-free, halogen-free, no-clean copper paste is the same as that in the aforementioned embodiments.

[0085] Experimental Example 1 The copper pastes prepared in Examples 1-5 and Comparative Examples 1-5 were tested under standard test conditions. The test results are shown in Table 3.

[0086] As shown in Table 3, the lead-free and halogen-free no-clean copper pastes provided in the embodiments of the present invention exhibit good performance in terms of solder paste stability, surface mount performance, and printing smoothness, and are generally superior to the comparative examples. Among the embodiments, Examples 1 and 3 perform best, as they are lead-free and halogen-free, leave no residue after soldering, require no cleaning, are stable in storage, have excellent surface mount performance, good printing smoothness, and possess excellent reliability and stability.

[0087] Through testing, this invention uses polypropylene carbonate or carboxymethyl cellulose to replace the large amount of rosin or acrylic resin in traditional solders. This ensures adhesion while preventing binder overflow during sintering, improving sintering stability and mitigating overscan defects caused by uneven binder distribution due to solvent evaporation during soldering. The invention uses titanate as an adhesion promoter, effectively addressing the risk of poor chip mounting performance during thermal bonding and chip breakage due to chip displacement during sintering. Furthermore, this invention uses carboxyl organic acids to modify the surface of copper powder, improving sintering activity and reducing sintering porosity. The antioxidant 2-mercaptobenzothiazole improves storage stability. Modified castor oil and polyamide wax are used as thixotropic agents to prevent solder paste settling. Additionally, the solvent in this invention is a compound of at least one of diethylene glycol dimethyl ether, ethylene glycol phenyl ether, or N-methylpyrrolidone in a specific weight ratio, effectively controlling the solvent evaporation rate, improving sintering quality, and reducing sintering defects.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A copper solder paste, characterized in that, The product comprises 75-80 parts by weight of modified copper powder and 20-25 parts by weight of organic components; wherein, based on the total amount of organic components being 100%, it consists of 1%-3% thixotropic agent, 0.5%-2% dispersant, 0.1%-0.5% antioxidant, 0.3%-0.8% binder, 0.5%-2% leveling agent, 0.5%-1% adhesion promoter, and 90.7%-97.1% solvent; the modified copper powder is obtained by treating copper powder with a surface modifier, and the particle size of the copper powder is 2-10 μm; the adhesion promoter is titanate; and the binder is selected from polypropylene carbonate. The dispersant is selected from at least one of ethanol, ethylene glycol, diethylene glycol, cyclohexanol, isopropanol, glycerol, and n-butanol; The solvent is selected from at least one of N-methylpyrrolidone, diethylene glycol monoethyl ether acetate, propylene carbonate, 1,4-dioxane, N,N-dimethylformamide, caprolactone, ethyl acetate, ethylene glycol ether, a mixture of dimethyl glutarate and dimethyl adipate, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and ethylene glycol phenyl ether.

2. The copper solder paste according to claim 1, characterized in that, The surface modifier is a compound containing functional groups that form coordination bonds with copper ions.

3. The copper solder paste according to claim 2, characterized in that, The surface modification method is as follows: prepare a surface modifier solution of 0.1%-1%, and then place copper powder in the surface modification solution for full contact; the mass ratio of copper powder to surface modification solution is 1:2~10; the full contact time is 0.5~2h.

4. The copper solder paste according to any one of claims 1-3, characterized in that, The thixotropic agent is selected from at least one of modified castor oil, polyamide wax, fumed silica, and organobentonite; And / or, the dispersant is diethylene glycol or glycerol; And / or, the antioxidant is selected from at least one of 2-mercaptobenzothiazole, N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexamethylenediamine, 2,6-di-tert-butyl-p-cresol, 4,4'-methylenebis(2,6-di-tert-butylphenol), and 1,3,5-tris(phenylamino)benzene; And / or, the leveling agent is selected from at least one of polydimethylsiloxane, polymethylalkylsiloxane, organic modified polysiloxane, polyether modified polysiloxane, acrylate copolymer, and fluorinated acrylate copolymer; And / or, the solvent is diethylene glycol dimethyl ether, ethylene glycol phenyl ether, and N-methylpyrrolidone.

5. The copper solder paste according to claim 4, characterized in that, The thixotropic agent is modified castor oil and / or polyamide wax; And / or, the antioxidant is 2-mercaptobenzothiazole or 2,6-di-tert-butyl-p-cresol; And / or, the leveling agent is a polyether-modified polysiloxane or an acrylate copolymer.

6. The method for preparing the copper solder paste according to any one of claims 1-5, characterized in that, The process includes the following steps: mixing the dispersant, antioxidant, binder and solvent at a temperature of 50℃~80℃; cooling the mixture to 40℃~50℃ and then mixing it with the thixotropic agent; further cooling the mixture to 20℃~30℃ and then mixing it with the leveling agent and adhesion promoter; and finally mixing the mixture with modified copper powder.

7. The preparation method according to claim 6, characterized in that, The preparation method of modified copper powder includes: mixing copper powder and surface modification solution at a mass ratio of 1:2~10, stirring and reacting for 30-60 min; centrifuging at 4500-6000 r / min for 5-10 min to remove surface modification solution; and vacuum drying at 50-80℃ for 5-8 h.

8. The preparation method according to claim 6 or 7, characterized in that, When mixing the mixture with the modified copper powder, the mixing speed is 1000-1200 r / min and the mixing time is 10-15 min.

9. The application of the copper solder paste according to any one of claims 1-5 or the copper solder paste prepared by the preparation method according to any one of claims 6-7 in the packaging of power devices.

10. A method for mounting lead-free, halogen-free, no-clean copper paste for power device packaging, characterized in that, Includes the following steps: a) By printing, the copper solder paste according to any one of claims 1-5 or the copper solder paste prepared by any one of claims 6-8 is uniformly coated on the front side of the substrate to obtain a stacked structure of solder paste and substrate. b) Place the printed copper paste substrate in a drying oven to dry it, and obtain a pre-dried copper paste substrate; c) Use a heat-mounting machine to mount chips onto a pre-dried copper paste substrate to obtain a pre-sintered module; d) The pre-sintered module is placed in a vacuum or inert atmosphere for sintering to obtain the power device packaging structure.

11. The patching method according to claim 10, characterized in that, In step a), the printing thickness is 50-150 μm; And / or, in step b), the drying oven uses air, vacuum or inert gas atmosphere for drying, the drying temperature is 90-110℃, and the drying time is 10-20min; And / or, in step c), the chip size is 1×1~5×5mm, the substrate temperature of the heat-mounting machine is 70-90℃, and the upper pressure head temperature is 130℃-150℃; And / or, in step d), the sintering conditions are: sintering temperature 180℃-280℃, sintering pressure 2-20MPa, and sintering time 3-5min.

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