A solderable low temperature conductive silver paste, its preparation method and application

Abstract

This invention relates to a solderable low-temperature conductive silver paste, its preparation method, and its applications. The silver paste comprises, by weight percentage, 60%-80% silver powder, 6%-9% resin, 0.5%-3% soldering aid, 1%-2% dispersant, 0.5%-1% curing agent, 0.1%-1% accelerator, and 10%-40% organic solvent. The preparation method includes steps such as silver powder surface treatment, functional filler preparation, organic carrier formulation, mixing and grinding, and vacuum degassing. Compared with existing technologies, this invention has advantages such as excellent conductivity, good solderability, and adhesion, and is suitable for flexible electronics, membrane switches, RFID tags, and low-temperature electronic packaging. The process is simple and suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of electronic materials technology, and in particular to a solderable low-temperature conductive silver paste, its preparation method, and its application. Background Technology

[0002] Emerging fields such as flexible electronics, membrane switches, radio frequency identification (RFID) tags, and low-temperature electronic packaging have placed comprehensive performance requirements on conductive pastes, demanding "low-temperature sintering, solderability, high conductivity, and high adhesion." Traditional high-temperature sintering silver pastes (≥500 ℃) are no longer sufficient to meet the processing needs of polymer substrates such as PET, PI, and TPU due to limitations in substrate heat resistance. While existing low-temperature curing conductive adhesives can form films at 120℃-160℃, they generally lack solderability, with solder joint strength below 2 N. After reflow soldering or manual soldering, the film layer becomes brittle, warped, or even detached, making it difficult to achieve an integrated process of "paste conduction—component mounting—solder secondary interconnection."

[0003] Chinese patent CN202211287771.4 discloses a low-temperature silver paste for high-tenacity solar cells and its preparation method. It uses 75%-90% silver powder, 1%-5% nano-bismuth powder, 3%-8% resin, 3%-8% organic solvent, 0.1%-1% curing agent, 0.2%-1% dispersant, and 0.5%-2% adhesion promoter. The solder joint tensile strength is 1.6N~2.5N, which is higher than commonly used pastes, but still has some shortcomings. Chinese patent CN202111283955.9 discloses a method for preparing a low-temperature conductive paste and electrode for heterojunction solar cells, which consists of 70-92% Sn-Bi alloy powder, 5-20% flux and the balance binder. Although it has high welding strength and low cost, it is prone to oxidation and can easily lead to functional failure.

[0004] Chinese patent CN117457258B discloses a method for preparing and applying conductive silver paste, which comprises 88-95% silver powder, 0.5-5% adhesive, 0.1-2% thermoplastic resin, 0.1-0.5% latent cationic curing agent, 1-3% organic solvent and 0.1-1% additive components. The preparation process involves the following steps: S1 Raw material preparation; S2 Organic carrier preparation; S3 Addition of curing agent; S4 Addition of silver powder; S5 Three-roll milling; S6 Vacuum degassing. However, the silver powder content in this patented formula is as high as 88-95%, while the resin and solvent content is relatively low. This leads to problems such as excessively rapid drying and poor leveling during the printing process, affecting printing accuracy and film integrity. Secondly, the curing system uses a latent cationic curing agent, which can achieve low-temperature curing, but lacks effective synergistic effects of accelerators, resulting in low curing efficiency. Furthermore, the flexibility and adhesion of the cured film layer need to be improved. In addition, this patent does not involve the addition of soldering aids, and the resulting conductive silver paste does not have solderability, making it difficult to meet the process requirements of subsequent component mounting and secondary solder interconnection. Finally, the silver powder is not surface-treated, resulting in poor dispersion stability in the paste and easy agglomeration during storage, affecting the consistency of conductivity.

[0005] In summary, existing technologies have not yet achieved the desired results in "low silver content, low temperature sintering (≤200 ℃), and high electrical conductivity (≤5×10⁻⁶)". -5 Achieving a balance between high conductivity (Ω·cm), high solder joint strength (≥5 N), and high adhesion (zero-level peeling of 3M tape) is challenging, but issues such as poor storage stability, narrow process window, and unsuitability for continuous printing exist. Therefore, developing a low-temperature conductive silver paste that is based on a single silver powder, requires no alloy fillers or glass phase, yet possesses solderability, high conductivity, high adhesion, and process compatibility has become an urgent need in the fields of flexible electronics and low-temperature packaging. Summary of the Invention

[0006] The purpose of this invention is to solve at least one of the above problems by providing a solderable low-temperature conductive silver paste, its preparation method and application. The conductive silver paste has a low sintering temperature (150-200℃), excellent conductivity, strong adhesion, and can be well soldered with tin-based solders, making it suitable for flexible electronics and low-temperature electronic packaging.

[0007] The objective of this invention can be achieved through the following technical solution: a solderable low-temperature conductive silver paste, comprising the following components by mass percentage: Silver powder 60%–80%; Resin 6%–9%; Welding aid 0.5%–3%; Dispersant 1%–2%; Hardener 0.5%–1%; Accelerator 0.1%–1%; Organic solvents 10%–40%; The silver powder therein is a mixture of flake-shaped silver powder with an average particle size of 0.5 μm–3 μm and spherical silver powder with a particle size of 20 nm–100 nm in a weight ratio of (5–9):1; After the flake-shaped silver powder is surface-treated with a silane coupling agent, the active groups in the silane coupling agent molecules undergo a chemical bonding reaction with the hydroxyl groups on the surface of the silver powder, uniformly coating the silver powder surface with an aminosilane layer of 2 nm–5 nm thickness. The mechanism of action of this aminosilane coating layer is as follows: (1) Mechanism of improving dispersion stability: The aminosilane coating effectively reduces the surface energy of silver powder, inhibits the van der Waals forces between silver powder particles and the tendency to agglomerate, significantly improves the dispersion uniformity of silver powder in the silver paste system, and prevents sedimentation and phase separation.

[0008] (2) Low-temperature sintering promotion mechanism: The amino groups in the coating layer can activate the surface of silver powder particles during the low-temperature sintering process of 150–200℃, promote the diffusion and melting of surface atoms, effectively reduce the activation energy and sintering threshold of silver powder, and help to quickly form a continuous and dense silver conductive film.

[0009] (3) Mechanism of interface compatibility optimization: The organosilane coating layer acts as a bridge, with one end firmly bonded to the surface of silver powder through Si-O bonds, and the organic functional groups at the other end interacting with the organic carriers (such as resins, solvents, etc.) in the silver paste system, which significantly enhances the interface compatibility between silver powder and other components of the system, and further optimizes the conductivity of silver paste, its adhesion to the substrate and its welding compatibility with tin-based solder.

[0010] Furthermore, the resin is a mixed resin composed of bisphenol A type epoxy resin and flexible polyurethane acrylate in a weight ratio of (2–4):1, which has good adhesive properties. The epoxy equivalent of the bisphenol A type epoxy resin is 180 g / eq–220 g / eq; The glass transition temperature of the flexible polyurethane acrylate is ≤-20℃.

[0011] Mechanism analysis: Bisphenol A type epoxy resin (epoxy equivalent 180 g / eq~220 g / eq): As the main adhesive component, its epoxy groups can form strong chemical bonds with the substrate surface during the curing process (such as reacting with polar groups such as hydroxyl and carboxyl groups). At the same time, its rigid molecular skeleton gives the system high cohesive strength and adhesion, which is the basis for achieving good adhesive performance.

[0012] Flexible polyurethane acrylate (glass transition temperature ≤ -20℃): Its low Tg property endows the resin system with excellent flexibility and elasticity. Under stress or temperature changes, this component can effectively absorb and disperse stress, reducing interfacial debonding or cracking caused by internal stress concentration, thereby improving the durability and impact resistance of the adhesive layer.

[0013] During the curing process, the two resins can undergo synergistic cross-linking to form an interpenetrating or semi-interpenetrating network structure that combines rigid support with flexible buffering, thereby significantly improving the overall toughness and adaptability while maintaining high bonding strength.

[0014] Furthermore, the welding aid is one or more of polymerized rosin, hydrogenated rosin, and disproportionated rosin, used to improve the welding performance of silver paste; its acid value is 150 mgKOH / g–180 mgKOH / g; The welding aid also includes 5 wt%–15 wt% of an active amine halide, wherein the active amine halide is one or more of cyclohexylamine hydrochloride and diethylamine hydrobromide. The synergistic effect of the active amine halide with polymerized rosin, hydrogenated rosin, and disproportionated rosin is as follows: Enhanced activation: Hydrogen halides produced by the decomposition of amine salts can form intermediate active species (such as acyl halides or complex acids) with carboxyl groups in rosin, which significantly enhances the chemical erosion ability of oxide films and achieves more thorough surface cleaning.

[0015] Wetting and spreading promotion: Amines can reduce the interfacial tension between solder and substrate, improve the fluidity of molten solder, and work together with rosin to form a uniform flux film, thereby improving welding quality and solder joint reliability.

[0016] Furthermore, the dispersant is a phosphate ester polymeric dispersant, including one or more of polyoxyethylene ether phosphate, alkylphenol polyoxyethylene ether phosphate, and polyether phosphate, used to improve the dispersibility of silver powder in the slurry; the phosphate ester groups in the molecular structure of the phosphate ester polymeric dispersant can form a strong chemical adsorption effect with the surface of silver powder, and at the same time, the molecular chains are arranged in an orderly manner through steric hindrance effect, forming a dense monomolecular adsorption layer with a thickness of 1 nm-3 nm on the surface of silver powder; this monomolecular adsorption layer can effectively prevent the agglomeration of silver powder particles, so that the silver powder is uniformly dispersed in the silver paste system; The dispersant has a number-average molecular weight of Mn 2000–5000 and an acid value of 40 mgKOH / g–80 mgKOH / g; The dispersant forms a monomolecular adsorption layer on the surface of the silver powder, with a thickness of 1 nm–3 nm.

[0017] Furthermore, the curing agent is a blocked isocyanate, including one or more of methyl ethyl ketone oxime blocked isocyanate, caprolactam blocked isocyanate, and phenol blocked isocyanate, used to promote the curing of the resin; The curing agent has a desealing temperature of 140℃–160℃ and an NCO content of 8 wt%–12 wt%.

[0018] Furthermore, the accelerator is composed of 2-ethyl-4-methylimidazole and dimethylaniline in a weight ratio of 1:(0.5–2), used to accelerate the curing reaction. Dimethylaniline, as a tertiary amine accelerator, can rapidly activate the active groups of the curing agent (such as blocked isocyanate) in the silver paste system, reducing the activation energy of the curing reaction and providing efficient catalytic power for reaction initiation. 2-ethyl-4-methylimidazole, as an imidazole accelerator, not only further enhances the catalytic effect but also forms an intermediate transition state with the active groups of the curing agent, promoting the deblocking and cross-linking reaction process of the active groups. Simultaneously, the synergistic ratio of the two accelerators precisely matches the low-temperature sintering requirements of silver paste at 150-200℃, accelerating the curing reaction and shortening the curing time while ensuring the density of the cured silver paste film. This balances the conductivity, adhesion, and welding reliability with tin-based solders, making it suitable for applications in flexible electronics and low-temperature electronic packaging.

[0019] Furthermore, the organic solvent is a mixed solvent composed of divalent ester, propylene glycol monomethyl ether acetate, and isophorone in a weight ratio of (3–5):(2–4):1, used to adjust the viscosity of the slurry; The mixed solvent has an initial boiling point ≥150℃ and an evaporation rate ≤0.3 g / (cm³) at 25℃. 2 ·h).

[0020] In a second aspect, the present invention provides a method for preparing a solderable low-temperature conductive silver paste, comprising the following steps: a) Silver powder surface treatment: Add flake silver powder and spherical silver powder to an ethanol-water solution containing an aminosilane coupling agent, heat to 50℃–60℃, stir, filter, and vacuum dry to obtain surface-modified silver powder. b) Preparation of functional filler: The surface-modified silver powder obtained in step a) is first mixed with the welding aid at a low speed, then heated to 70℃–80℃, sheared at high speed, and cooled to room temperature to obtain a multifunctional silver-based filler; c) Organic carrier preparation: Dissolve resin, dispersant, curing agent and accelerator in organic solvent, heat to 60℃–70℃ and stir, filter through filter cartridge to obtain homogeneous organic carrier; d) Mixing and grinding: Add the multifunctional silver-based filler from step b) and the homogeneous organic carrier from step c) to a double planetary mixer, premix first, and then transfer to a three-roll mill for circulating grinding to obtain a grinding slurry; e) Vacuum degassing: The grinding slurry is placed under vacuum to degas, thereby obtaining the solderable low-temperature conductive silver paste.

[0021] Further, in step (a), the mass percentage of the aminosilane coupling agent in the ethanol-water solution containing the aminosilane coupling agent is 0.5 wt%–2 wt%, and the stirring time is 20–40 min; In step (b), the low-speed mixing speed is 200 rpm–400 rpm and the low-speed mixing time is 1–10 min; the high-speed shearing speed is 800 rpm–1200 rpm and the high-speed shearing time is 5–15 min. The stirring time in step (c) is 40-80 minutes; In step (d), the premixing speed is 10 rpm–20 rpm, the premixing time is 5–15 min, and the roller spacing of the three-roll mill is set to 50 μm, 30 μm, 15 μm, 10 μm and 5 μm respectively. After each grinding, the particle size is measured online with a laser particle size analyzer. Grinding is stopped when D90 ≤ 8 μm. In step (e), the vacuum condition is ≤-0.09 MPa, the degassing time is 5-10 min, and after degassing, the slurry is left to stand at 20-30℃ for 1-3 h without visible bubbles, and the density change rate is ≤0.5%.

[0022] This invention also provides an application of a solderable low-temperature conductive silver paste, characterized in that the conductive silver paste is applied to electronic devices, and the conductive silver paste is sintered at 150℃–200℃ for 10 min–30 min to form a conductive film, the volume resistivity of the conductive film being ≤5×10⁻⁶. -5 Ω·cm, solder joint strength >5 N, and no detachment after passing the 3M 600 tape rapid peel test.

[0023] Furthermore, the conductive lines formed by sintering the conductive silver paste on PET, PI, TPU or paper-based substrates at 150℃-200℃ have a line width / spacing ≥80 μm / 80 μm, and after three reflow soldering cycles at 260℃ for 10 s, the resistance change rate is ≤5%, and the solder joint strength in the pad area is still >5 N.

[0024] Furthermore, the electronic device is a flexible thin-film switch, an RFID antenna, a cryogenic packaged interconnect pad, or a wearable heating film.

[0025] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention effectively improves the conductivity of conductive silver paste by mixing flake silver powder with spherical silver powder and treating it with 0.5-2% KH-550 aminosilane, and the sheet resistance is <10 mΩ / □.

[0026] 2. The conductive silver paste prepared by this invention has a low sintering temperature (150–200°C), making it suitable for flexible substrates; it welds well with tin-based solders, with a solder joint strength >5 N; it has strong adhesion, showing no peeling after a 3M tape test; and the process is simple, making it suitable for large-scale production. Detailed Implementation

[0027] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0028] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, each point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value, or combined with other lower or upper limits, to form a range not explicitly stated. In the description of this application, it should be noted that, unless otherwise stated, "above" includes the stated number, and "multiple" in "one or more" means two or more.

[0029] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0030] Numerous details are explored in the following description to provide a more thorough explanation of embodiments of this application; however, it will be apparent to those skilled in the art that embodiments of this application may be practiced without these specific details.

[0031] To further understand the present invention, the following embodiments are provided. It is worth noting that, unless otherwise specified, all raw materials used in the present invention are commercially available; and all methods and equipment employed are common in the art.

[0032] Example 1: A solderable low-temperature conductive silver paste is prepared according to the following steps: (1) Formula (percentage by mass): Silver powder 70% (63% flake silver powder, d50=1.5 μm; 7% spherical silver powder, d50=50 nm, both treated with 1% KH-550 aminosilane); 7.5% resin (5.5% bisphenol A type epoxy resin, epoxy equivalent 200 g / eq; 2% flexible polyurethane acrylate, Tg=-25 ℃); Welding aid 1.5% (polymerized rosin 1.3%, acid value 165 mgKOH / g; cyclohexylamine hydrochloride 0.2%); Dispersant 1.5% (alkylphenol polyoxyethylene ether phosphate APE-10P, Mn=3500, acid value 60 mgKOH / g); Curing agent 0.8% (caprolactam-blocked isocyanate TS-280, unblocking temperature 150 ℃, NCO=10%); Accelerator 0.3% (2-ethyl-4-methylimidazole 0.2%, dimethylaniline 0.1%); Organic solvents 18.4% (DBE 10%, PMA 6.4%, isophorone 2%).

[0033] (2) Preparation steps: a) Silver powder surface treatment: Add 2g of KH-550 aminosilane coupling agent to 198g of ethanol-water solution (ethanol to water volume ratio 1:1) to make the mass concentration of aminosilane coupling agent in the solution 1%. Add 63g of flake silver powder and 7g of spherical silver powder, stir at 55℃ for 30 min, filter and vacuum dry to obtain surface modified silver powder. b) Preparation of functional filler: 1.3g of polymerized rosin and 0.2g of cyclohexylamine hydrochloride were mixed evenly to obtain a welding aid, which was added to the surface-modified silver powder obtained in step a). The mixture was first mixed at a low speed of 350 rpm for 5 min, then heated to 75℃ and sheared at a high speed of 1000 rpm for 10 min. After cooling to room temperature, a multifunctional silver-based filler was obtained. c) Preparation of organic carrier: Dissolve 7.5g of resin, 1.5g of dispersant, 0.8g of blocked isocyanate curing agent, 0.2g of 2-ethyl-4-methylimidazolium, and 0.1g of dimethylaniline in an organic solvent (a mixed solvent of 10g of DBE, 6.4g of PMA, and 2g of isophorone), stir at 65℃ for 60 min, and filter through a 1 μm filter to obtain a homogeneous organic carrier; d) Mixing and grinding: Add the multifunctional silver-based filler from step b) and the organic carrier from step c) to a double planetary mixer, premix at 20 rpm for 10 min, and then transfer to a three-roll mill for four cycles of grinding. The roller spacing of the three-roll mill is set to 50 μm, 30 μm, 15 μm, 10 μm and 5 μm respectively. After each grinding, the particle size is measured online with a laser particle size analyzer. Grinding is stopped when D90 ≤ 8 μm. The roller temperature is ≤ 25℃ to obtain the grinding slurry. e) Vacuum degassing: The grinding slurry is placed under a vacuum of ≤-0.09 MPa for 8 minutes to degas. After degassing, the slurry is left to stand at 25℃ for 2 hours. No visible bubbles are observed, and the density change rate is ≤0.5%, thus obtaining the solderable low-temperature conductive silver paste.

[0034] (3) Performance testing: 1) Volume resistivity test: The solderable low-temperature conductive silver paste prepared above was screen-printed onto the surface of a 75μm thick PET (polyethylene terephthalate) film. After coating, the film was sintered at 150℃ for 20 minutes to obtain a silver paste film layer with a thickness of 12μm. The volume resistivity of the silver paste film layer was tested using the four-probe method, and its volume resistivity was measured to be 3.2×10⁻⁶. -5 Ω•cm (The test method conforms to the standard four-probe test specifications in this field to ensure the accuracy of the test results).

[0035] 2) Adhesion test: Take the above-mentioned sintered silver paste film sample and use 3M 600 tape to conduct a rapid peel test. After peeling 3 times, the silver paste film did not fall off or peel up, indicating that the silver paste has good adhesion to the PET film.

[0036] 3) Welding reliability test: Sn96.5Ag3Cu0.5 solder balls with a diameter of 0.5mm were spot-coated on the surface of the above silver paste film. The sample after spot-coating the solder balls was placed in an environment of 260℃ for reflow treatment for 10s. After reflow, the bonding strength between the solder balls and the silver paste film was tested by a push-pull force tester. After multiple tests, the average push-pull force was measured to be 6.8N.

[0037] 4) High-temperature reflow stability test: The silver paste to be tested was prepared into a line sample with a line width / spacing of 100μm / 100μm by screen printing. The line sample was subjected to three reflow treatments at 260℃ / 10s (the reflow conditions were the same as those in the above soldering reliability test). The line resistance value was measured before reflow and after three reflows. The resistance change rate of the line after three reflows was calculated to be 2.1%, indicating that the silver paste line has good high-temperature reflow stability.

[0038] 5) Storage stability test: The silver paste to be tested was stored in a sealed environment at 25℃ for 6 months. The viscosity of the silver paste was tested at the beginning of storage and after 6 months of storage. The initial viscosity was 22 Pa•s and the viscosity after 6 months of storage was 23.6 Pa•s. The viscosity change rate was calculated to be 7.3%, indicating that the silver paste has good storage stability under sealed conditions at 25℃.

[0039] Example 2: A solderable low-temperature conductive silver paste is prepared according to the following steps: In Example 1, the proportion of silver powder was increased to 77%, the resin was reduced to 6%, the organic solvent was reduced to 12.9%, and the rest remained unchanged.

[0040] The same performance tests as in Example 1 were performed, and the results are as follows: The resulting silver paste had a viscosity of 28 Pa·s and a volume resistivity of 2.4 × 10⁻⁶ after sintering at 150 ℃ for 15 min. -5 Ω·cm, solder joint strength 7.2 N, bending radius 1 mm, resistance change rate after 1000 cycles 3.5%, meeting the requirements of ultra-high conductivity flexible RFID antenna.

[0041] Example 3: A solderable low-temperature conductive silver paste is prepared according to the following steps: In Example 1, the welding aid was increased to 2.5%, the blocked isocyanate was reduced to 0.5%, the organic solvent was reduced to 17.7%, and the rest remained unchanged.

[0042] The same performance tests as in Example 1 were performed, and the results are as follows: For use on 50 μm PI films, sintering at 180 ℃ / 10 min, solder joint strength 5.6 N, resistivity change rate after three reflows 1.8%, suitable for low-temperature packaged interconnect pads.

[0043] Comparative Example 1: A solderable low-temperature conductive silver paste is prepared according to the following steps: The silver powder was not treated with aminosilane, and the rest was the same as in Example 1.

[0044] The same performance tests as in Example 1 were performed, and the results are as follows: The sintered film has a weld strength of only 3.1 N, 30% of the 3M tape tested detached, and the viscosity increased by 38% after 3 months of storage, showing obvious agglomeration.

[0045] Comparative Example 2: A solderable low-temperature conductive silver paste is prepared according to the following steps: The welding aid does not contain active amine halide salts, and is otherwise the same as in Example 1.

[0046] The same performance tests as in Example 1 were performed, and the results are as follows: The solder wetting angle at 260℃ is 42° and the solder joint strength is 2.8 N, which cannot meet the requirements for secondary reflow.

[0047] Comparative Example 3: A solderable low-temperature conductive silver paste is prepared according to the following steps: Conventional aliphatic amine curing agent (isophorate) was used instead of blocked isocyanate, and the rest was the same as in Example 1.

[0048] The same performance tests as in Example 1 were performed, and the results are as follows: The room temperature working period was shortened to 6 hours, and dry screen and jagged edges appeared 4 hours after printing.

[0049] The test results of Examples 1-3 and Comparative Examples 1-3 are shown in the table below: The table above shows that the type of silver powder treatment, active amine halide, and curing agent plays a crucial role in the soldering strength, adhesion, and storage stability of the silver paste. Example 1 exhibits balanced overall performance and is suitable for general flexible electronics applications. Example 2 has the highest silver powder content (77%) and the best conductivity (2.4 × 10⁻⁶). -5 Example 3 has the highest solder joint strength (7.2N) and is suitable for applications requiring high conductivity. Example 3 has the highest soldering flux content (2.5%), resulting in slightly lower solder joint strength but good reflow stability, making it suitable for applications involving encapsulated pads.

[0050] The foregoing has shown and described the basic process, 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 illustrative of the principles of 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 solderable low-temperature conductive silver paste, characterized in that, Includes the following components by mass percentage: Silver powder 60%–80%; Resin 6%–9%; Welding aid 0.5%–3%; Dispersant 1%–2%; Hardener 0.5%–1%; Accelerator 0.1%–1%; Organic solvents 10%–40%; The silver powder therein is a mixture of flake-shaped silver powder with an average particle size of 0.5 μm–3 μm and spherical silver powder with a particle size of 20 nm–100 nm in a weight ratio of (5–9):1; After the flake silver powder is surface-treated with a silane coupling agent, its surface is coated with an aminosilane layer with a thickness of 2nm–5nm.

2. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The resin is a mixture of bisphenol A type epoxy resin and flexible polyurethane acrylate in a weight ratio of (2–4):

1. The epoxy equivalent of the bisphenol A type epoxy resin is 180 g / eq–220 g / eq; The glass transition temperature of the flexible polyurethane acrylate is ≤-20℃.

3. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The welding aid is one or more of polymerized rosin, hydrogenated rosin, and disproportionated rosin; its acid value is 150 mg KOH / g–180 mg KOH / g. The welding aid also includes 5 wt%–15 wt% of an active amine halide, wherein the active amine halide is one or more of cyclohexylamine hydrochloride and diethylamine hydrobromide.

4. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The dispersant is a phosphate ester polymeric dispersant, including one or more of polyoxyethylene ether phosphate, alkylphenol polyoxyethylene ether phosphate, and polyether phosphate; The dispersant has a number-average molecular weight of Mn2000–5000 and an acid value of 40 mgKOH / g–80 mgKOH / g; The dispersant forms a monomolecular adsorption layer on the surface of the silver powder, with a thickness of 1 nm–3 nm.

5. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The curing agent is a blocked isocyanate, including one or more of methyl ethyl ketone oxime blocked isocyanate, caprolactam blocked isocyanate, and phenol blocked isocyanate; The curing agent has a desealing temperature of 140℃–160℃ and an NCO content of 8wt%–12wt%.

6. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The accelerator is composed of 2-ethyl-4-methylimidazolium and dimethylaniline in a weight ratio of 1:(0.5–2).

7. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The organic solvent is a mixed solvent composed of divalent ester, propylene glycol monomethyl ether acetate, and isophorone in a weight ratio of (3–5):(2–4):1; The mixed solvent has an initial boiling point ≥150℃ and an evaporation rate ≤0.3g / (cm³) at 25℃. 2 ·h).

8. A method for preparing a solderable low-temperature conductive silver paste as described in any one of claims 1-7, characterized in that, Prepare according to the following steps: a) Silver powder surface treatment: Add flake silver powder and spherical silver powder to an ethanol-water solution containing an aminosilane coupling agent, heat to 50℃–60℃, stir, filter, and vacuum dry to obtain surface-modified silver powder. b) Preparation of functional filler: The surface-modified silver powder obtained in step a) is first mixed with the welding aid at a low speed, then heated to 70℃–80℃, sheared at high speed, and cooled to room temperature to obtain a multifunctional silver-based filler; c) Organic carrier preparation: Dissolve resin, dispersant, curing agent and accelerator in organic solvent, heat to 60℃–70℃ and stir, filter through filter cartridge to obtain homogeneous organic carrier; d) Mixing and grinding: Add the multifunctional silver-based filler from step b) and the homogeneous organic carrier from step c) to a double planetary mixer, premix first, and then transfer to a three-roll mill for circulating grinding to obtain a grinding slurry; e) Vacuum degassing: The grinding slurry is placed under vacuum to degas, thereby obtaining the solderable low-temperature conductive silver paste.

9. The method for preparing a solderable low-temperature conductive silver paste according to claim 8, characterized in that: In step (a), the mass percentage of aminosilane coupling agent in the ethanol-water solution containing aminosilane coupling agent is 0.5 wt%–2 wt%, and the stirring time is 20–40 min; In step (b), the low-speed mixing speed is 200 rpm–400 rpm and the low-speed mixing time is 1–10 min; the high-speed shearing speed is 800 rpm–1200 rpm and the high-speed shearing time is 5–15 min. The stirring time in step (c) is 40-80 minutes; In step (d), the premixing speed is 10 rpm–20 rpm, the premixing time is 5–15 min, and the roller spacing of the three-roll mill is set to 50 μm, 30 μm, 15 μm, 10 μm and 5 μm respectively. After each grinding, the particle size is measured online with a laser particle size analyzer. Grinding is stopped when D90 ≤ 8 μm. In step (e), the vacuum condition is ≤-0.09 MPa, the degassing time is 5-10 min, and after degassing, the slurry is left to stand at 20-30℃ for 1-3 h without visible bubbles, and the density change rate is ≤0.5%.

10. An application of the solderable low-temperature conductive silver paste as described in any one of claims 1-7, characterized in that, The conductive silver paste is applied to electronic devices, and after sintering at 150℃–200℃ for 10 min–30 min, a conductive film is formed. The volume resistivity of the conductive film is ≤5×10⁻⁶. -5 Ω·cm, solder joint strength >5 N, and no detachment after passing the 3M 600 tape rapid peel test.

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