Weldable low-temperature sintered silver paste

Abstract

The invention discloses weldable low-temperature sintered silver paste which is prepared by mixing 65-90 parts of micro-nano silver powder, 10-20 parts of metal salt additive, 1-5 parts of polymer additive, 15-19 parts of organic solvent and 1-5 parts of organic additive, the micro-nano silver powder is obtained by mixing nano silver powder with the particle size of 10-50nm and micron silver powder with the particle size of 1-10mu m, and a preparation method comprises the following steps: step 1, preparing a first-stage polymer carrier; the preparation method comprises the following steps: 1, preparing a first-stage polymer carrier, 2, preparing a second-stage polymer carrier, 3, pretreating micro-nano silver powder, and 4, preparing conductive silver paste. Through micro-nano silver powder grading, nano-particles are filled in gaps of micro-particles, the stacking density is improved, the sheet resistance is reduced, an oxidation film is formed on the surface of the passivated micro-nano silver powder, the interface bonding strength can be effectively improved, the sintering activation energy of silver is reduced by the metal salt additive, and by combining the'etching-remelting 'effect of the oxidation film on the surface of the silver powder, the bonding strength of the surface of the silver powder is improved. The sintering temperature is effectively reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of conductive silver paste, and particularly relates to a weldable low-temperature sintering silver paste. BACKGROUND

[0002] At present, micron silver powder or single particle size nanometer silver powder is used for low-temperature sintering. The micron silver powder has low bulk density and is easy to agglomerate, resulting in poor conductivity of the conductive network. In addition, the silver particle diffusion rate is slow during low-temperature sintering, and the decomposition of the high polymer carrier is required to provide pores, resulting in a high sintering temperature, which limits the application. In addition, the interface bonding force after sintering is weak, and the interface is easy to fall off. Therefore, the present application provides a weldable low-temperature sintering silver paste to solve the problems in the prior art. SUMMARY

[0003] In view of the above problems, the present application aims to provide a weldable low-temperature sintering silver paste. The weldable low-temperature sintering silver paste is prepared by using the innovative technologies of micro-nano silver powder grading design, metal salt surface functional modification, double-curing high polymer additive system and silver powder plasma passivation, so as to realize the unity of high conductivity, strong adhesion and good process stability under low-temperature sintering.

[0004] To achieve the purpose of the present application, the present application is realized by the following technical scheme: a weldable low-temperature sintering silver paste is prepared by mixing 65-90 parts of micro-nano silver powder, 10-20 parts of metal salt additives, 1-5 parts of high polymer additives, 15-19 parts of organic solvents and 1-5 parts of organic additives. The micro-nano silver powder is obtained by mixing nanometer silver powder with a particle size of 10-50 nm and micron silver powder with a particle size of 1-10 microns. The high polymer additive includes modified polyethylene terephthalate resin, isocyanate curing agent and photoinitiator. The organic solvent is prepared by compounding dimethyl glutarate and propylene glycol methyl ether acetate at a mass ratio of 3:1.

[0005] Further improvement lies in that: the mass ratio of the nanometer silver powder and the micron silver powder is 8-12:1; the metal salt additive is one or more of alumina, zinc oxide, nickel oxide, silicon oxide, bismuth oxide and copper oxide which are surface modified by a silane coupling agent; the mass percentage of the modified polyethylene terephthalate resin, the isocyanate curing agent and the photoinitiator is 80-90%:5-10%:1-5%; and the organic additive is a thixotropic agent, a leveling agent and a coupling agent.

[0006] Further improvement lies in that: the silane coupling agent is gamma-aminopropyl triethoxysilane or N-(beta-aminoethyl)-gamma-aminopropyl methyl dimethoxysilane, and the modification of the metal salt additive has a coating rate of 80-95%.

[0007] Further improvement lies in that: the mass ratio of the thixotropic agent, the leveling agent and the coupling agent is 2:1:1, the specific surface area of the thixotropic agent is 200-300 m2 / g of fumed silica, the leveling agent is a polyether modified polysiloxane with a viscosity of 500-1000 mPa·s, and the coupling agent is gamma-aminopropyl triethoxysilane.

[0008] Further improvement lies in that the modified polyethylene terephthalate resin has a molecular weight of 10000-20000, and the photoinitiator is 1-hydroxycyclohexyl phenyl ketone or 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0009] A preparation method of a weldable low-temperature sintering silver paste, comprising the following steps:

[0010] Step one, preparation of a primary high molecular carrier, a high molecular additive and an organic solvent are added into a mixer for mixing and stirring, and after stirring, the primary high molecular carrier is obtained by filtration;

[0011] Step two, preparation of a secondary high molecular carrier, a surface modified metal salt additive, a thixotropic agent of an organic additive and a leveling agent are added into a ball mill for ball milling and dispersion, and the secondary high molecular carrier is obtained;

[0012] Step three, pretreatment of micro-nano silver powder, the silver powder is subjected to cold drying treatment, then transferred to a plasma treatment cavity for plasma passivation treatment, and after the plasma passivated micro-nano silver powder is further treated by high-temperature passivation, it is cooled to room temperature;

[0013] Step four, preparation of a conductive silver paste, the secondary high molecular carrier, a coupling agent of an organic additive and the passivated micro-nano silver powder are mixed and ball milled at a weight ratio of 23-30:1-1.5:70-85, and after ball milling, the weldable conductive silver paste is obtained by sieving.

[0014] Further improvement lies in that in step one, the mixing and stirring condition is that the mixing and stirring is carried out at a temperature of 90-100 DEG C and a rotating speed of 300-500 rpm for 3-6 h, and a gradient rotating speed control of 300 rpm→

[0015] 400 rpm→500 rpm is adopted, and after mixing, the mixture is sieved through a 100-mesh filter.

[0016] Further improvement lies in that in step two, the ball milling condition is that the grinding and dispersion is carried out at a temperature of 80-120 DEG C and a rotating speed of 500-800 rpm for 2-4 h, the ball milling medium is a zirconia ball with a diameter of 0.5-1 mm, and the ball-to-material ratio is 5:1.

[0017] Further improvement lies in that step three is specifically:

[0018] S1, first, the micro-nano silver powder is subjected to cold drying treatment at-5 DEG C and a vacuum degree of-0.08 MPa for 2 h to remove surface adsorbed water;

[0019] S2, the cold-dried micro-nano silver powder is transferred to a plasma processing chamber, and is processed under the condition that argon and oxygen are mixed at a gas volume flow ratio of 50:5 and the power is 80-120 W for 8-12 min, so as to form an oxide film with a thickness of 5-20 nm on the surface of the micro-nano silver powder;

[0020] S3, finally, the micro-nano silver powder after plasma processing is kept at a temperature of 120-150 DEG C and a vacuum of-0.09 MPa for 2 h, high-purity helium gas is injected at a rate of 100 sccm, and the pressure is kept at 0.1-0.2 MPa for 20-40 min, and then cooled to room temperature, to obtain passivated micro-nano silver powder.

[0021] Further improvement lies in that the step four adopts a planetary ball mill, and the ball milling condition is that the speed is 200-300 rpm and the grinding time is 4 h, and the ball-milled product is sieved through a 80-100 mesh sieve.

[0022] The beneficial effects of the present application are: the present application fills the gap between microparticles by grading micro-nano silver powder, so that the bulk density is improved and the square resistance is reduced, the compatibility of the surface modified metal salt additive and the polymer carrier is improved, the binding force is improved, the surface of the passivated micro-nano silver powder forms an oxide film, which can effectively improve the interface bonding strength, the double-cured polymer additive system improves the storage stability after curing, the metal salt additive reduces the sintering activation energy of silver, and the sintering temperature is effectively reduced by the combination of the "etching-resmelting" effect of the silver powder surface oxide film, which is suitable for PI / CPI and other ultra-thin flexible substrates. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The present application is illustrated by the accompanying drawings. DETAILED DESCRIPTION

[0024] In order to deepen the understanding of the present application, the present application will be further described in combination with examples, and the present examples are only used to explain the present application and do not constitute a limitation on the protection scope of the present application.

[0025] Flexible circuit board (FPC) is widely used in consumer electronics, 5G communication and automotive electronics due to its lightness, thinness and bendability. As the core material of FPC conductive circuit, silver paste needs to meet the requirements of low temperature sintering, i.e. sintering temperature ≤200 DEG C, to avoid thermal damage to flexible substrates, while having high conductivity (low square resistance), strong adhesion (firmly combined with PI / CPI film and other substrates) and good printing suitability (adapted to silk screen printing, inkjet and other processes).

[0026] However, the existing low temperature sintering silver paste mostly uses micron silver powder or single particle size nano silver powder, which has the following defects:

[0027] The bulk density of micron silver powder is low, and the nano silver powder is easy to agglomerate, resulting in poor connectivity of the conductive network and high square resistance.

[0028] Metal salt additives such as oxides, organic acid salts are not compatible with the polymer carrier, and are not uniformly dispersed, and the interface bonding force is weak after sintering, and is easy to fall off;

[0029] The silver particle diffusion rate is slow during low-temperature sintering, and needs to rely on the decomposition of the polymer carrier to provide pores, resulting in a sintering temperature of ≥180℃, which limits the application of ultra-thin flexible substrates due to the high sintering temperature;

[0030] The initial adhesion after printing is insufficient, and is easy to flow and sag, and the viscosity fluctuates during storage due to solvent evaporation, affecting the process stability.

[0031] Based on the above problems, according to Figure 1 The embodiment provides a weldable low-temperature sintering silver paste, which is prepared by mixing 65-90 parts of micro-nano silver powder, 10-20 parts of metal salt additives, 1-5 parts of a polymer additive, 15-19 parts of an organic solvent and 1-5 parts of an organic additive, wherein the micro-nano silver powder is obtained by mixing nano silver powder with a particle size of 10-50 nm and micron silver powder with a particle size of 1-10 microns, the polymer additive includes modified polyethylene terephthalate resin, isocyanate curing agent and photoinitiator, the double-curing system is printed and then rapidly shaped by photocuring, and the crosslinking density is improved by thermal curing, the organic solvent is prepared by compounding dimethyl glutarate and propylene glycol methyl ether acetate at a mass ratio of 3:1, the solvent is compounded, the viscosity gradient is adjusted, and different printing processes are adapted.

[0032] The specific modification method of the modified polyethylene terephthalate resin is as follows:

[0033] 1. Dissolve PET chips in a dimethyl sulfoxide (DMSO) polar solvent, add concentrated sulfuric acid or p-toluenesulfonic acid as a catalyst, stir at 80-100℃ for 2-4h, activate the hydroxyl (-OH) and carboxyl (-COOH) at the end of the PET molecular chain, and expose more reaction sites;

[0034] 2. Introduce polyethylene glycol (PEG) as a flexible segment: mix the activated PET solution with PEG at a mass ratio of 1:0.5-1, add dicyclohexyl carbodiimide (DCC) condensing agent, and react at 60-80℃ for 4-6h, and graft PEG to the PET main chain through an ester bond (-COO-);

[0035] 3. Introduce γ-aminopropyl triethoxysilane (KH550) silane coupling agent containing carboxyl (-COOH) or amino (-NH2): mix the PEG-grafted PET solution with the silane coupling agent at a mass ratio of 100:1-3, and react at 120-150℃ for 2-3h, and introduce -COOH or -NH2 groups on the PET main chain through hydrolysis-condensation reaction;

[0036] 4. Selecting low crystallinity, high flexibility high polymer (such as polybutylene terephthalate PBT) or elastomer (such as polyolefin elastomer POE), blending according to mass ratio PET:PBT=9:1 or PET:POE=8:2;

[0037] 5. After drying PET, PBT or POE respectively at 80℃ temperature condition for 4h, adding into twin-screw extruder, melt blending for 5-8min at temperature 220-240℃ and rotation speed 100-150rpm, and then extruding and granulating to obtain blended modified PET.

[0038] The mass ratio of nano-silver powder and micro-silver powder is 8-12:1, and the bulk density is optimized; the metal salt additive is one or more of alumina, zinc oxide, nickel oxide, silicon oxide, bismuth oxide and copper oxide which are surface modified by silane coupling agent; the mass percentage of modified polyethylene terephthalate resin, isocyanate curing agent and photoinitiator is 80-90%:5-10%:1-5%; the organic auxiliary agent is thixotropic agent, leveling agent and coupling agent.

[0039] The silane coupling agent is γ-aminopropyl triethoxysilane or N-(β-aminoethyl)-γ-aminopropyl methyl dimethoxysilane, the modification of the metal salt additive is 80-95%, and the functional modification enhances the compatibility with the polymer carrier.

[0040] The mass ratio of thixotropic agent, leveling agent and coupling agent is 2:1:1, the thixotropic agent is fumed silica with specific surface area 200-300m 2 / g, the leveling agent is polyether modified polysiloxane with viscosity 500-1000mPa·s, and the coupling agent is γ-aminopropyl triethoxysilane.

[0041] The molecular weight of the modified polyethylene terephthalate resin is 10000-20000, and the photoinitiator is 1-hydroxycyclohexyl phenyl ketone or 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0042] A preparation method of a weldable low-temperature sintering silver paste, comprising the following steps:

[0043] Step one, preparation of primary polymer carrier, adding polymer auxiliary agent and organic solvent into a mixer, mixing and stirring at temperature 90-100℃ and rotation speed 300-500rpm for 3-6h, and then passing through 100 mesh filter screen to obtain the primary polymer carrier, wherein the stirring is controlled by gradient rotation speed 300rpm(1h)→400rpm(1h)→500rpm(2h).

[0044] Step two, preparation of secondary high molecular carrier, add surface modified metal salt additive, thixotropic agent and leveling agent of organic auxiliary agent to the primary high molecular carrier into the ball mill, grind and disperse at the temperature of 80-120℃ and the rotating speed of 500-800rpm for 2-4h, to obtain the secondary high molecular carrier, wherein the ball milling medium is zirconia ball with the diameter of 0.5-1mm, and the ball to material ratio is 5:1.

[0045] Step three, pretreatment of micro-nano silver powder, transfer the silver powder after cold drying treatment to the plasma treatment chamber for plasma passivation treatment, and further treat the micro-nano silver powder after plasma passivation treatment by high temperature passivation, and then cool to room temperature;

[0046] Specifically,

[0047] S1, first, the micro-nano silver powder is placed in an environment of-5℃ and a vacuum degree of-0.08MPa for cold drying treatment for 2h to remove surface adsorbed water;

[0048] S2, then transfer the cold dried micro-nano silver powder to the plasma treatment chamber, treat under the condition that the argon and oxygen are mixed gas with the gas volume flow ratio of 50:5 and the power is 80-120W for 8-12min, form 5-20nm oxide film on the surface of the micro-nano silver powder, inhibit agglomeration, and enhance the reaction activity with metal salt;

[0049] S3, finally, the micro-nano silver powder after plasma treatment is treated at the temperature of 120-150℃ and the vacuum degree of-0.09MPa for 2h, then inject high-purity helium gas at the rate of 100sccm and keep the pressure at 0.1-0.2MPa for 20-40min, and then cool to room temperature to obtain passivated micro-nano silver powder.

[0050] Step four, preparation of conductive silver paste, mix the primary high molecular carrier, the secondary high molecular carrier, the coupling agent of organic auxiliary agent and the passivated micro-nano silver powder by weight ratio of 20-30:2-3:1-1.5:70-85, sieve after ball milling to obtain the solderable conductive silver paste;

[0051] The ball milling adopts planetary ball mill, and the ball milling condition is 200-300rpm rotating speed for 4h, and sieve after ball milling through 80-100mesh sieve.

[0052] Example 1

[0053] The present embodiment provides a solderable low temperature sintering silver paste, and the raw materials are weighed as follows:

[0054] Micro-nano silver powder: 70 parts, the mass ratio of nano silver powder and micro silver powder is 9:1 (nano silver powder 10nm, 63 parts; micro silver powder 5μm, 7 parts);

[0055] Metal salt additive: 10 parts (silane modified alumina, modified by KH550, particle size 5 μm);

[0056] Polymer additive: 2 parts (modified PET 85wt%, isocyanate 8wt%, 1-hydroxycyclohexyl phenyl ketone 7wt%);

[0057] Organic solvent: 16 parts (dimethyl glutarate 12 parts, propylene glycol methyl ether acetate 4 parts);

[0058] Organic additive: 2 parts (fumed silica 0.8 parts, polyether modified polysiloxane 0.7 parts, gamma-aminopropyl triethoxysilane 0.5 parts).

[0059] Preparation steps:

[0060] First, mix the polymer additive and the organic solvent at 95°C for 4h, using gradient stirring (300rpm / 1h→400rpm / 1h→500rpm / 2h gradient speed control), then pass through a 100 mesh sieve to obtain a primary polymer carrier;

[0061] Then mix the modified metal salt, thixotropic agent, and leveling agent with the primary polymer carrier, and grind at 800rpm for 3h at 100°C to obtain a secondary polymer carrier;

[0062] Subsequently, after cold drying treatment, the micro-nano silver powder is transferred to the plasma treatment chamber for plasma passivation treatment, and after further treatment of the plasma passivation treated micro-nano silver powder by high temperature passivation, it is cooled to room temperature to obtain passivated micro-nano silver powder;

[0063] The specific steps are:

[0064] S1, first, the micro-nano silver powder is placed in an environment of -5°C and a vacuum degree of -0.08MPa for cold drying treatment for 2h to remove surface adsorbed water;

[0065] S2, then the cold-dried micro-nano silver powder is transferred to the plasma treatment chamber, and is treated under the condition of a mixed gas of argon and oxygen in a gas volume flow ratio of 50:5 and a power of 100W for 12min, forming an oxide film of 5-20nm on the surface of the micro-nano silver powder, inhibiting agglomeration and enhancing the reactivity with the metal salt;

[0066] S3, finally, the plasma treated micro-nano silver powder is heated at a temperature of 130°C and vacuumed to a vacuum degree of -0.09MPa for 2h, then high-purity helium gas is injected at a rate of 100sccm and pressurized at a pressure of 0.2MPa for 40min, and then cooled to room temperature to obtain passivated micro-silver powder.

[0067] Finally, the secondary polymer carrier, coupling agent and passivated micro-nano silver powder were mixed in a mass ratio of 27:1:72, ball-milled for 4 h under the condition of 200 rpm, and then sieved through an 80-mesh screen to obtain the solderable low-temperature sintering silver paste.

[0068] Performance test: After sintering the silver paste film, a four-probe tester and an electronic tensile testing machine were used to test it, and the sheet resistance was 9 mΩ / □, the PI film peel strength was 7.2 N / cm, the bending radius after sintering at 150°C was 1 mm, there was no cracking after 1000 times of bending, and the viscosity change after 30 days of storage at 50°C was 7%.

[0069] Example 2

[0070] The present embodiment provides a solderable low-temperature sintering silver paste, and the raw materials are weighed as follows:

[0071] Micro-nano silver powder: 66 parts of nano silver powder and micron silver powder in a mass ratio of 11:1 (nano silver powder 10 nm, 60.5 parts; micron silver powder 5 μm, 5.5 parts);

[0072] Metal salt additive: 15 parts (silane modified zinc oxide, modified by KH550, particle size 5 μm);

[0073] Polymer additive: 2 parts (modified PET 85wt%, isocyanate 8wt%, 1-hydroxycyclohexyl phenyl ketone 7wt%);

[0074] Organic solvent: 15 parts (dimethyl glutarate 12 parts, propylene glycol methyl ether acetate 3 parts);

[0075] Organic additive: 2 parts (fumed silica 0.8 parts, polyether modified polysiloxane 0.7 parts, γ-aminopropyl triethoxysilane 0.5 parts).

[0076] Preparation steps:

[0077] First, the polymer additive and the organic solvent were mixed at 95°C for 4 h, and then sieved through a 100-mesh screen to obtain a primary polymer carrier;

[0078] Then, the modified metal salt, thixotropic agent and leveling agent were mixed with the primary polymer carrier and ground at 100°C for 3 h to obtain a secondary polymer carrier;

[0079] Subsequently, the micro-nano silver powder was subjected to cold drying treatment and then transferred to a plasma treatment chamber for plasma passivation treatment. After further treatment of the plasma passivated micro-nano silver powder by high-temperature passivation, it was cooled to room temperature to obtain the passivated micro-nano silver powder (the specific steps are the same as in Example 1);

[0080] Finally, the primary polymer carrier, the secondary polymer carrier, the coupling agent and the passivated micro-nano silver powder are mixed in a mass ratio of 27:1:72, ball-milled at 200 rpm for 4 h, and then screened through an 80-mesh screen to obtain the weldable low-temperature sintering silver paste.

[0081] Performance test: after sintering the silver paste film, a four-probe tester and an electronic tensile testing machine are used to test the film, and the sheet resistance is 11 mΩ / □, the peel strength with the PI film is 8.1 N / cm, the bending radius after sintering at 160°C is 0.8 mm, the film does not crack after 1000 times of bending, and the viscosity change after storage at 50°C for 30 days is 6%.

[0082] The above shows and describes the basic principles, main features and advantages of the present application. It should be understood by those skilled in the art that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A solderable low-temperature sintering silver paste, characterized by: The invention is prepared by mixing 65 to 90 parts of micro-nano silver powder, 10 to 20 parts of metal salt additives, 1 to 5 parts of polymer additives, 15 to 19 parts of organic solvents and 1 to 5 parts of organic additives. The micro-nano silver powder is obtained by mixing nano silver powder with a particle size of 10 to 50 nm and micro silver powder with a particle size of 1 to 10 μm. The polymer additives include modified polyethylene terephthalate resin, isocyanate curing agent and photoinitiator. The organic solvent is prepared by compounding dimethyl glutarate and propylene glycol methyl ether acetate in a mass ratio of 3:

1.

2. The solderable low-temperature sintering silver paste according to claim 1, characterized in that: The mass ratio of the nano silver powder to the micron silver powder is 8-12:1; the metal salt additive is one or more of aluminum oxide, zinc oxide, nickel oxide, silicon oxide, bismuth oxide and copper oxide surface-modified by a silane coupling agent; the mass percentages of the modified polyethylene terephthalate resin, isocyanate curing agent and photoinitiator are 80-90%:5-10%:1-5%; and the organic additives are a thixotropic agent, a leveling agent and a coupling agent.

3. The solderable low-temperature sintering silver paste according to claim 2, characterized in that: The silane coupling agent is gamma-aminopropyltriethoxysilane or N-(beta-aminoethyl)-gamma-aminopropylmethyldimethoxysilane, and the modified metal salt additive has a coverage rate of 80-95%.

4. The solderable low-temperature sintering silver paste according to claim 2, characterized in that: The mass ratio of the thixotropic agent, leveling agent and coupling agent is 2:1:1, and the thixotropic agent has a specific surface area of ​​200 to 300 m 2 / g of fumed silica, the leveling agent is polyether-modified polysiloxane with a viscosity of 500 to 1000 mPa·s, and the coupling agent is γ-aminopropyltriethoxysilane.

5. The solderable low-temperature sintering silver paste according to claim 1, characterized in that: The molecular weight of the modified polyethylene terephthalate resin is 10,000-20,000, and the photoinitiator is 1-hydroxycyclohexyl phenyl ketone or 2-hydroxy-2-methyl-1-phenyl-1-propanone.

6. The method for preparing a solderable low-temperature sintering silver paste according to any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1, preparation of a primary polymer carrier, adding a polymer auxiliary agent and an organic solvent into a mixer, mixing and stirring, and filtering after stirring to obtain a primary polymer carrier; Step 2: Preparation of a secondary polymer carrier: adding the surface-modified metal salt additive, the thixotropic agent and the leveling agent of the organic additive and the primary polymer carrier to a ball mill for dispersion to obtain a secondary polymer carrier; Step 3: Pretreatment of the micro-nano silver powder: cold-drying the silver powder and transferring it to a plasma treatment chamber for plasma passivation treatment. The plasma-passivated micro-nano silver powder is then further treated by high-temperature passivation and then cooled to room temperature. Step 4: Preparation of conductive silver paste: The secondary polymer carrier, the coupling agent of the organic additive and the passivated micro-nano silver powder are mixed and ball-milled in a weight ratio of 23-30:1-1.5:70-85, and the mixture is sieved after ball milling to obtain a weldable conductive silver paste.

7. The method for preparing a solderable low-temperature sintering silver paste according to claim 6, wherein: The mixing and stirring conditions in step 1 are as follows: mixing and stirring at a temperature of 90-100° C. and a rotation speed of 300-500 rpm for 3-6 hours, and the mixing and stirring speed is 300 rpm→400 rpm→ The speed was controlled at 500 rpm and the mixture was filtered through a 100-mesh filter.

8. The method for preparing a solderable low-temperature sintering silver paste according to claim 6, wherein: The ball milling conditions in the step 2 are grinding and dispersing at a temperature of 80 to 120° C. and a rotation speed of 500 to 800 rpm for 2 to 4 hours, the ball milling medium is zirconia balls with a diameter of 0.5 to 1 mm, and the ball-to-material ratio is 5:

1.

9. The method for preparing a solderable low-temperature sintering silver paste according to claim 6, wherein: The step three is specifically as follows: S1. First, place the nano silver powder in a -5°C and vacuum environment of -0.08 MPa for 2 hours to remove surface adsorbed water; S2, transferring the cold-dried micro-nano silver powder to a plasma treatment chamber, treating for 8-12 minutes under the conditions of argon and oxygen mixed gas with a gas volume flow ratio of 50:5 and a power of 80-120 W, to form a 5-20 nm oxide film on the surface of the micro-nano silver powder; S3. Finally, the plasma-treated micro-nano silver powder is kept at a temperature of 120-150° C. and evacuated to -0.09 MPa for 2 hours, and then high-purity helium is injected at a rate of 100 sccm and maintained at a pressure of 0.1-0.2 MPa for 20-40 minutes, and then cooled to room temperature to obtain passivated micro-nano silver powder.

10. The method for preparing a solderable low-temperature sintering silver paste according to claim 6, wherein: In the step 4, a planetary ball mill is used for ball milling, and the ball milling conditions are grinding at a speed of 200-300 rpm for 4 hours, and after ball milling, the product is passed through an 80-100 mesh sieve.

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