Weldable low-temperature conductive silver paste and preparation method thereof

Abstract

The invention belongs to the technical field of electronic conductive adhesives, and relates to weldable low-temperature conductive silver paste and a preparation method thereof. The conductive silver paste comprises the following raw materials: polymer composite resin, silver powder, an organic solvent, a dispersant, a curing agent, a curing accelerator, an organic tin precursor and a lubricant. A TAIC modified PMMA prepolymer is adopted as a polymer composite resin matrix, flake silver powder is compounded, and pulping is carried out through three-roller grinding and decompression defoaming. The silver paste can be cured at the low temperature of 130-150 DEG C, the volume resistivity after curing is smaller than 3 * 10 <-5 > omega.cm, the welding spot shear force after welding is larger than 150 N / cm < 2 >, the pad wetting area is larger than or equal to 95%, the adhesive force reaches 5B, the silver paste is suitable for glass and flexible substrates, various welding requirements such as wave soldering and reflow soldering are met, the shear force retention rate after 500 times of cold and hot circulation is larger than or equal to 80%, and the unification of low-temperature curing and high-temperature welding performance is achieved.

Description

Technical Field

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

[0002] The explosive growth of 5G communications, wearable devices, and foldable screen phones is driving the rapid evolution of electronic assembly towards "thin, flexible, and high-density" designs. While traditional high-temperature sintering silver paste can provide low resistance and strong soldering strength, it requires the substrate to withstand instantaneous thermal shock of nearly 600°C, which clearly contradicts the temperature-limited properties of materials such as glass covers, stainless steel foils, and PET films. Therefore, the market is turning its attention to low-temperature curing systems, hoping to complete conductive wiring at ≤150°C for ≤30 minutes, while retaining a subsequent soldering process window of 180–220°C, forming an inverse temperature span of "low-temperature curing—high-temperature soldering," posing new challenges to material design.

[0003] Currently, commercially available low-temperature curing silver pastes generally use a simple "epoxy-silver powder-solvent" formula, which has four fatal shortcomings: 1. Insufficient soldering heat resistance: The epoxy crosslinking density is low, with a Tg of only 90~110℃. Under the peak reflow soldering temperature of 220℃, the pad blistering rate is >30%; 2. Low interfacial bonding strength: The surface energy difference with glass, aluminum, and stainless steel is large, with a cross-cut adhesion test ≤3B, and conductive breakage occurs after 20 bends; 3. Poor solder wettability: The oxide layer (Ag2O / Ag2CO3) on the surface of the silver powder is not effectively reduced, the solder spreading area is <75%, and the solder joint shear force is <100 N / cm. 2 4. Low conductivity: After curing, the volume resistivity is generally >5×10⁻⁶. -5 The adhesion strength is Ω·cm, which cannot meet the low-loss requirements of high-power devices. Although researchers have tried to improve adhesion by adding silane coupling agents or simple epoxy modification, the inherent performance conflict between low-temperature curing and high-temperature welding remains unresolved.

[0004] Patent CN109887639A discloses a solderable, low-temperature curable functional silver paste and its preparation method. This invention prepares a functional silver paste by using silver powder, modified polymethyl methacrylate (PMMA) resin, organic solvent, crosslinking agent, and additives. After low-temperature curing, the prepared functional silver paste meets the solderability requirements for wave soldering, reflow soldering, gold-tin soldering, and indium tin soldering. However, the long-term thermal reliability of the silver paste described in this patent is insufficient. Its PMMA matrix is ​​prone to aging and embrittlement after repeated high-temperature soldering processes, leading to a decrease in the conductivity of the silver paste or failure of adhesion to the substrate.

[0005] In summary, the industry urgently needs a new type of silver paste material that can complete cross-linking and curing at 130~150℃ and maintain structural integrity, strong interface, and excellent solder wetting at welding peaks of 180~220℃ to fill the gap in existing technology. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art and provide a solderable low-temperature conductive silver paste and its preparation method.

[0007] The objective of this invention can be achieved through the following technical solutions: A solderable low-temperature conductive silver paste, comprising the following components and their weight percentages: 22-28% high molecular composite resin; Silver powder 35-45%; Organic solvents 30-41%; Dispersant 0.4~1.0%; Hardener 0.5~1.0%; Curing accelerator 0.1~0.5%; Organotin precursor 0.1~0.5%; Lubricant 0.05~0.5%.

[0008] Furthermore, the polymeric composite resin is a triallyl isocyanurate (TAIC) modified thermosetting polymethyl methacrylate (T-PMMA) prepolymer with a solid content of 45-55% and a weight-average molecular weight (Mw) of 6-9 × 10⁻⁶. 4 It has a molecular weight distribution (PDI) ≤ 2.0, a glass transition temperature ≥ 135℃ (significantly higher than the 95℃ of ordinary PMMA), and a thermal decomposition temperature higher than 250℃.

[0009] The core crosslinking framework of this polymer composite resin plays a crucial role in the following ways: during the 130℃ low-temperature curing stage, it provides sufficient crosslinkable sites to quickly form a preliminary crosslinking network structure; after entering the welding stage, the residual triallyl functional groups in the resin can further participate in the free radical post-curing reaction to form a denser three-dimensional network, thereby effectively suppressing blistering and cracking caused by solder thermal shock.

[0010] Furthermore, the silver powder is flake-shaped silver powder with a D50 particle size of 3~11 μm and a tap density of 3.0~6.0 g / cm³. 3 The loose bulk density is 1.5~3.5 g / cm³. 3 Its specific surface area is 0.5~2.0 m². 2 / g, burn loss rate <0.7%.

[0011] The silver powder is composed of two or more flake-shaped silver powders with different particle sizes.

[0012] Preferably, the mass ratio of the two flake silver powders with different particle sizes is 4:1 to 1:1.

[0013] Furthermore, the organic solvent is selected from two or more of diethyl succinate, diisobutyl adipate, diethylene glycol methyl ether acetate, divalent ester (DBE), ethylene glycol diacetate, ethylene glycol propyl ether acetate, and diethyl glutarate. The solvent is a low-toxicity, high-boiling-point solvent with an initial boiling point ≥180℃ and a vapor pressure ≤0.2 kPa at 25℃.

[0014] Furthermore, the dispersant is a high molecular block copolymer containing acidic anchoring groups, specifically a polyphosphate solution; the dispersant has an amine value ≤15 mg KOH / g, an acid value of 30~60 mg KOH / g, and a weight-average molecular weight (Mw) of 5000~8000 g / mol.

[0015] Furthermore, the curing agent is a blocked isocyanate with a deblocking temperature of 120~160℃ and an NCO mass fraction of 8~12%; The curing accelerator is a compound of 2-ethyl-4-methylimidazole and 1-methylimidazole, wherein the mass ratio of 2-ethyl-4-methylimidazole to 1-methylimidazole is 1:1 to 1:3.

[0016] Furthermore, the organotin precursor is selected from one or more of stannous octoate, butylstannic acid, and dibutyltin dilaurate. It is used to promote cross-linking reactions, lower curing temperatures, and improve solder wettability. At soldering temperatures (150~220℃), it decomposes and releases reducing tin elements, which in situ promote the formation of an Ag3Sn interfacial alloy layer with silver.

[0017] Furthermore, the lubricant is a siloxane polyether with a dynamic viscosity of 50~200 mPa·s at 25°C.

[0018] The present invention also provides a method for preparing a solderable low-temperature conductive silver paste as described in any of the preceding claims, comprising the following steps: S1. Preparation of organic carrier: Dissolve the polymer composite resin in an organic solvent, then add dispersant, curing agent, curing accelerator, organotin precursor and lubricant, and disperse evenly to obtain organic carrier; In step S1, the dissolution temperature is 70~75℃; the dispersion conditions are high-speed dispersion at 1800~2200rpm for 30~40min.

[0019] S2. Silver paste preparation: Silver powder is added to the organic carrier obtained in step S1, and after premixing, grinding and degassing under reduced pressure, a solderable low-temperature conductive silver paste is obtained.

[0020] In step S2, the grinding is carried out using a three-roll mill with a roll temperature of 15~25℃ and roll gaps of 80 μm, 40 μm and 20 μm respectively, with each roll being circulated 3~5 times; the vacuum degree of the degassing is ≤-0.09 MPa and the degassing time is 10~20 min. Furthermore, the polymeric composite resin is prepared by polymerization reaction of methyl methacrylate, triallyl isocyanurate (TAIC), methacrylic acid, initiator azobisisobutyronitrile (AIBN), and solvent butyl acetate.

[0021] Specifically, methyl methacrylate (MMA), triallyl isocyanurate (TAIC), and methacrylic acid (MAA) are used as monomers, azobisisobutyronitrile (AIBN) is used as an initiator, and butyl acetate is used as a solvent. The above raw materials are mixed and placed in a reactor. Under a nitrogen protective atmosphere, the mixture is stirred and reacted at a temperature of 75~85℃ for 4~6 hours to obtain a high molecular composite resin, namely TAIC-modified T-PMMA prepolymer.

[0022] The synthetic route is as follows: First, methyl methacrylate (MMA) and methacrylic acid (MAA) are polymerized in solution to generate a linear polymer chain; then, the linear polymer chain is subjected to a post-crosslinking reaction with triallyl isocyanurate (TAIC) to obtain a prepolymer containing triallyl active side groups.

[0023] The role of introducing methacrylic acid (MAA) is to introduce carboxyl functional groups into the polymer chain. On the one hand, these functional groups can react with the curing agent (blocked isocyanate) to participate in the construction of the resin crosslinking network; on the other hand, they can significantly enhance the adhesion between the resin and the metal substrate.

[0024] Compared with the prior art, the present invention has the following beneficial effects: This invention proposes a dual-mechanism synergistic strategy of "low-temperature crosslinking" and "in-situ alloying of the welding interface". This strategy is achieved through the following three key designs: (1) Introducing the TAIC triallyl functional group: using triallyl isocyanurate (TAIC) to modify polymethyl methacrylate (PMMA) to give the resin thermosetting characteristics, while significantly improving its crosslinking density and heat resistance; (2) Selecting a blocked isocyanate curing agent: the curing agent can be unblocked and initiate a crosslinking reaction at about 130°C, thereby achieving low-temperature curing of the system; (3) Introducing an organotin precursor: in the subsequent welding stage at 180~220°C, the precursor decomposes and releases tin elements with reducing activity; the tin elements reduce the oxides on the surface of the silver powder on the one hand, and react with silver in situ to generate an Ag3Sn interface alloy layer on the other hand, thereby significantly improving the bonding strength and long-term reliability of the solder joint.

[0025] The conductive silver paste of the present invention can be completely cured at 130~150℃ / 15~30min, which is much lower than the curing temperature of traditional high-temperature curing silver paste (usually ≥200℃). At the same time, the silver paste can maintain structural integrity, interface firmness and excellent solder wetting performance at a welding peak of 180~220℃ / 10~30s. It can not only meet the heat resistance requirements of flexible substrates such as PET, but also reduce production energy consumption, shorten process cycle and meet the efficiency requirements of mass industrial production assembly.

[0026] The conductive silver paste of the present invention can firmly adhere to substrates that are difficult to adhere to, such as glass, aluminum, stainless steel and flexible substrates (such as PET). After curing, the adhesion is >4B (100-cross test), which breaks through the limitations of traditional silver paste on substrate types and provides an adaptable solution for diverse substrate application scenarios in the field of information electronics.

[0027] The conductive silver paste of this invention, after curing, is compatible with various soldering processes such as wave soldering, reflow soldering, gold-tin soldering, and indium-tin soldering, with a pad wetting area ≥95%. Through the decomposition of the organotin precursor during the soldering stage, an Ag3Sn interface alloy layer is formed, resulting in a solder joint shear strength >150 N / cm. 2 Furthermore, after 500 cycles of thermal cycling from -55 to 125°C, the shear force retention rate is ≥80%, effectively suppressing blistering and cracking caused by solder thermal shock, and significantly improving the bonding strength and long-term reliability of the solder joint.

[0028] The conductive silver paste of this invention has a volume resistivity of <3×10⁻⁶ after curing. -5 With a strength of Ω·cm, it possesses excellent electrical conductivity. Furthermore, combined with the dense cross-linked network structure of TAIC-modified PMMA resin, the silver paste maintains a stable conductive path after curing and soldering (silver layer thickness 8~15μm), while also exhibiting good environmental durability, meeting the performance requirements for long-term service of electronic products.

[0029] In summary, this invention fully realizes the unification of the four properties of conductive silver paste: "low-temperature curing, high-temperature welding, wide-area adhesion, and high conductivity." It effectively solves the technical problems of poor adhesion, insufficient welding reliability, and narrow substrate compatibility of traditional low-temperature silver paste, providing key material support for the assembly of high-density and high-reliability electronic products in the field of information electronics, and has broad application prospects and market value. Detailed Implementation

[0030] 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.

[0031] Unless otherwise specified, all raw materials used in this invention are commercially available products.

[0032] Example 1 A solderable low-temperature conductive silver paste is prepared using the following steps: S1, Prepolymer Preparation 120 g of methyl methacrylate (MMA), 15 g of triallyl isocyanurate (TAIC), 8 g of methacrylic acid (MAA), 0.8 g of azobisisobutyronitrile (AIBN), and 150 g of butyl acetate were added to a 1000 mL three-necked flask. Under nitrogen protection, the mixture was reacted at 80 °C for 5 hours to obtain a TAIC-modified thermosetting polymethyl methacrylate (T-PMMA) prepolymer. The prepolymer had a solid content of 52% and a weight-average molecular weight of approximately 7.2 × 10⁻⁶. 4 The molecular weight distribution is 1.8.

[0033] S2, Organic Carrier Preparation Weigh 24g of the T-PMMA prepolymer obtained in step S1 and mix it with 38g of mixed solvent (diethyl succinate:DBE:cyclopentanone = 5:3:2). After stirring and dissolving evenly at 75℃, cool to 25℃ and add 0.8g of blocked isocyanate (NCO content 10%, unblocking temperature 135℃), 0.3g of curing accelerator (2-ethyl-4-methylimidazolium:1-methylimidazolium = 1:2), 0.25g of stannous octoate, 0.5g of dispersant (amine value 12 mg KOH / g, acid value 45 mg KOH / g, weight average molecular weight 6000) and 0.15g of lubricant (siloxane polyether, viscosity 120 mPa·s). Disperse at 2000 rpm for 40 minutes to obtain a uniform and stable organic carrier.

[0034] S3, Silver Paste Preparation Add 36g of flake silver powder (a mixture of flake silver powder with D50=4 μm and D50=9 μm in a mass ratio of 3:2) to the organic carrier obtained in step S2. Premix the mixture in a planetary mixer for 20 minutes, then place it in a three-roll mill for grinding (roll temperature 20℃, roll gaps set sequentially to 80 μm, 40 μm, and 20 μm, with each roll gap being cyclically ground 4 times). Finally, degas the mixture under a vacuum of -0.095MPa for 20 minutes to obtain a solderable low-temperature conductive silver paste.

[0035] Example 2 A solderable low-temperature conductive silver paste is prepared using the following steps: S1, Prepolymer Preparation 100 g of methyl methacrylate (MMA), 12 g of triallyl isocyanurate (TAIC), 6 g of methacrylic acid (MAA), 0.6 g of azobisisobutyronitrile (AIBN), and 120 g of butyl acetate were added to a 500 mL three-necked flask. Under nitrogen protection, the mixture was reacted at 78 °C for 4.5 hours to obtain a TAIC-modified thermosetting polymethyl methacrylate (T-PMMA) prepolymer. The prepolymer had a solid content of 48% and a weight-average molecular weight of approximately 6.8 × 10⁻⁶. 4 The molecular weight distribution is 1.9.

[0036] S2, Organic Carrier Preparation Weigh 22.3g of the T-PMMA prepolymer obtained in step S1 and mix it with 40g of mixed solvent (diisobutyl adipate: propylene glycol methyl ether acetate = 7:3). After stirring and dissolving evenly at 70℃, cool to 25℃ and add 0.7g of blocked isocyanate (NCO content 10%, unblocking temperature 135℃), 0.25g of curing accelerator (2-ethyl-4-methylimidazolium: 1-methylimidazolium = 1:1.5), 0.2g of butylstannic acid, 0.45g of dispersant (amine value 12 mg KOH / g, acid value 45 mg KOH / g, weight average molecular weight 6000) and 0.1g of lubricant (siloxane polyether, viscosity 80 mPa·s). Disperse at 2000 rpm for 30 minutes to obtain a uniform and stable organic carrier.

[0037] S3, Silver Paste Preparation Add 36g of flake silver powder (a mixture of flake silver powder with D50=4 μm and D50=10 μm in a mass ratio of 7:3) to the organic carrier obtained in step S2, premix in a planetary mixer for 15 minutes, then place in a three-roll mill for grinding (roll temperature 18℃, roll gaps set sequentially to 80 μm, 40 μm, and 20 μm, with each roll gap being cyclically ground 3 times), and finally degas under a vacuum of -0.09 MPa for 15 minutes to obtain solderable low-temperature conductive silver paste.

[0038] Example 3 A solderable low-temperature conductive silver paste is prepared using the following steps: S1, Prepolymer Preparation 150 g of methyl methacrylate (MMA), 18 g of triallyl isocyanurate (TAIC), 9 g of methacrylic acid (MAA), 1.0 g of azobisisobutyronitrile (AIBN), and 180 g of butyl acetate were added to a 1000 mL three-necked flask. Under nitrogen protection, the mixture was reacted at 82 °C for 5 hours to obtain a TAIC-modified thermosetting polymethyl methacrylate (T-PMMA) prepolymer. The prepolymer had a solid content of 50% and a weight-average molecular weight of approximately 7.5 × 10⁻⁶. 4 The molecular weight distribution is 1.7.

[0039] S2, Organic Carrier Preparation Weigh 26g of the T-PMMA prepolymer obtained in step S1 and mix it with 36g of mixed solvent (DBE:cyclopentanone = 1:1). After stirring and dissolving evenly at 72℃, cool to 25℃ and add 0.9g of blocked isocyanate (NCO content 10%, unblocking temperature 135℃), 0.35g of curing accelerator (2-ethyl-4-methylimidazolium:1-methylimidazolium = 1:2.5), 0.3g of dibutyltin dilaurate, 0.55g of dispersant (amine value 12 mg KOH / g, acid value 45 mg KOH / g, weight average molecular weight 6000) and 0.18g of lubricant (siloxane polyether, viscosity 150 mPa·s). Disperse at 2000 rpm for 35 minutes to obtain a uniform and stable organic carrier.

[0040] S3, Silver Paste Preparation Add 36g of flake silver powder (a 1:1 mass ratio of flake silver powder with D50=3 μm and D50=8 μm) to the organic carrier obtained in step S2, premix in a planetary mixer for 18 minutes, then place in a three-roll mill for grinding (roll temperature 22℃, roll gaps set sequentially to 80 μm, 40 μm, and 20 μm, with 5 cycles of grinding at each roll gap), and finally degas under a vacuum of -0.10 MPa for 18 minutes to obtain solderable low-temperature conductive silver paste.

[0041] Example 4 A solderable low-temperature conductive silver paste is prepared using the following steps: S1, Prepolymer Preparation 130 g of methyl methacrylate (MMA), 16 g of triallyl isocyanurate (TAIC), 7 g of methacrylic acid (MAA), 0.9 g of azobisisobutyronitrile (AIBN), and 160 g of butyl acetate were added to a 1000 mL three-necked flask. Under nitrogen protection, the mixture was reacted at 80 °C for 4.5 hours to obtain a TAIC-modified thermosetting polymethyl methacrylate (T-PMMA) prepolymer. The prepolymer had a solid content of 51% and a weight-average molecular weight of approximately 7.0 × 10⁻⁶. 4 The molecular weight distribution is 1.8.

[0042] S2, Organic Carrier Preparation Weigh 27.2g of the T-PMMA prepolymer obtained in step S1 and mix it with 35g of mixed solvent (diethyl glutarate: ethylene glycol propyl ether acetate = 6:4). After stirring and dissolving evenly at 70℃, cool to 25℃ and add 0.75g of blocked isocyanate (NCO content 10%, unblocking temperature 135℃), 0.28g of curing accelerator (2-ethyl-4-methylimidazolium: 1-methylimidazolium = 1:1), 0.22g of stannous octoate, 0.48g of dispersant (amine value 12 mg KOH / g, acid value 45 mg KOH / g, weight average molecular weight 6000) and 0.14g of lubricant (siloxane polyether, viscosity 100 mPa·s). Disperse at 2000 rpm for 32 minutes to obtain a uniform and stable organic carrier.

[0043] S3, Silver Paste Preparation Add 36g of flake silver powder (a mixture of flake silver powder with D50=6 μm and D50=11 μm in a mass ratio of 4:1) to the organic carrier obtained in step S2. Premix the mixture in a planetary mixer for 16 minutes, then place it in a three-roll mill for grinding (roll temperature 16℃, roll gaps set sequentially to 80 μm, 40 μm, and 20 μm, with each roll gap being cyclically ground 4 times). Finally, degas the mixture under a vacuum of -0.092MPa for 16 minutes to obtain a solderable low-temperature conductive silver paste.

[0044] Comparative Example 1 A conductive silver paste, the preparation method of which is basically the same as that in Example 1, the only difference being: In step S1, the TAIC-modified T-PMMA prepolymer is replaced with commercially available ordinary linear PMMA resin (solid content 50%, Mw≈8×10). 4 (Tg≈95℃), the dosage remains 24g; The types, proportions, and process parameters of the remaining components (silver powder, solvent, curing agent, accelerator, stannous octoate, dispersant, lubricant) remain unchanged.

[0045] Comparative Example 2 A conductive silver paste, the preparation method of which is basically the same as that in Example 1, the only difference being: In step S2, stannous octoate is completely omitted (i.e., the amount of organotin precursor added is 0). All other raw material types, proportions, and preparation processes are the same as in Example 1.

[0046] To strongly support the beneficial effects of the technical solutions in the embodiments of this application, the following performance tests were conducted on the above-mentioned conductive silver paste samples: 1. Sample preparation The obtained conductive silver paste was screen-printed onto the surface of a PET flexible substrate (75 μm thick, with plasma-treated surface) and the glass tin surface (float glass tin surface) using a 400-mesh screen. The printed pattern was a comb-shaped electrode with a line width / line spacing of 100 μm. After printing, the substrate was placed in an oven and cured at 140℃ for 25 minutes. Then, a reflow soldering process with a peak temperature of 190℃ and a holding time of 20 s was used to obtain the test sample.

[0047] 2. Performance Testing Volume resistivity: A four-probe resistivity meter was used to select five different test points in the effective area (area 1 cm × 1 cm) of the printed pattern. After applying a constant current, the voltage drop was measured. The volume resistivity was calculated using the formula ρ = RS / L (where R is the measured resistance, S is the cross-sectional area of ​​the silver layer, and L is the test spacing). The average value of the five tests was taken.

[0048] Adhesion (Cross-cut Test): Following ASTM D3359-2017, "Cross-cut test method for adhesion of coatings," a cross-cut tester was used to create a 1 mm × 1 mm grid on the cured silver layer surface, penetrating the silver layer to the substrate. After removing debris with a dust brush, 3M 610 tape (25 mm wide) was applied and rolled three times with a 2 kg rubber roller to ensure good contact. After 60 seconds of rest, the tape was quickly peeled off at an angle close to 180°. The extent of silver layer peeling off the grid areas was observed and rated from 0B to 5B, with 5B indicating no peeling.

[0049] Shear strength of weld joints: Referring to IPC-TM-650 2.4.13 "Test method for shear strength of weld joints", a universal testing machine was used to conduct shear tests on the weld joints (weld joint size 2 mm × 2 mm × 0.1 mm) after reflow soldering at a shear rate of 1 mm / min. The maximum shear force value was recorded, and the shear strength per unit area was calculated by dividing the shear force by the weld joint area. The average value of 3 parallel samples was taken.

[0050] Solder wetting area (SAC305): Referring to JIS Z3198-5-2018 "Test methods for lead-free solder - Part 5: Wetting equilibrium method", the cured silver layer sample was immersed in molten SAC305 solder (temperature 250℃, flux is no-clean type), held at this temperature for 20 s, and then removed and cooled to room temperature. The actual wetting area of ​​the solder on the silver layer surface was measured using image analysis method, and the percentage of the wetting area to the total area of ​​the silver layer was calculated.

[0051] Thermal shock resistance: In accordance with IEC 60068-2-14:2009 "Environmental testing - Part 2-14: Test methods - Test N: Temperature change", the test sample was placed in a thermal shock test chamber and subjected to 500 cycles at -55℃ (holding temperature for 30 min) and 125℃ (holding temperature for 30 min), with a cycle transition time ≤ 5 min. After the test, the shear strength of the weld joint was tested on the sample, and the shear strength retention rate was calculated as (shear strength after cycle / shear strength before cycle × 100%).

[0052] Table 1. Performance Test Comparison of Examples 1-4 and Comparative Examples 1-2 (PET Flexible Substrate) Table 2 Comparison of Test Results of Examples 1-4 and Comparative Examples 1-2 (Glass Substrate) The results of the above embodiments show that the low-temperature conductive silver paste prepared by the present invention exhibits excellent conductivity, adhesion, welding reliability and environmental durability on different substrates (PET, glass), and fully realizes the unity of the four properties of "low-temperature curing - high-temperature welding - wide-area adhesion - high conductivity", effectively solving the technical problems mentioned in the background art.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A solderable low-temperature conductive silver paste, characterized in that, The raw materials include the following components and their weight percentage content: 22-28% high molecular composite resin; Silver powder 35-45%; Organic solvents 30-41%; Dispersant 0.4~1.0%; Hardener 0.5~1.0%; Curing accelerator 0.1~0.5%; Organotin precursor 0.1~0.5%; Lubricant 0.05~0.5%.

2. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The polymer composite resin is a thermosetting polymethyl methacrylate prepolymer modified with triallyl isocyanurate.

3. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The silver powder is in flake form, with a D50 particle size of 3-11 μm and a tap density of 3.0-6.0 g / cm³. 3 The loose bulk density is 1.5~3.5 g / cm³. 3 Its specific surface area is 0.5~2.0 m². 2 / g, burn loss rate <0.7%.

4. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The organic solvent is selected from two or more of diethyl succinate, diisobutyl adipate, diethylene glycol methyl ether acetate, divalent esters, ethylene glycol diacetate, ethylene glycol propyl ether acetate, and diethyl glutarate.

5. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The dispersant is a high molecular block copolymer containing acidic anchoring groups, with an amine value ≤15 mg KOH / g, an acid value of 30~60 mg KOH / g, and a weight-average molecular weight of 5000~8000 g / mol.

6. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The curing agent is a blocked isocyanate with a deblocking temperature of 120~160℃ and an NCO mass fraction of 8~12%. The curing accelerator is a compound of 2-ethyl-4-methylimidazole and 1-methylimidazole.

7. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The organotin precursor is selected from one or more of stannous octoate, butylstannic acid, and dibutyltin dilaurate.

8. The solderable low-temperature conductive silver paste according to claim 1, characterized in that, The lubricant is a siloxane polyether with a dynamic viscosity of 50~200 mPa·s at 25°C.

9. A method for preparing a solderable low-temperature conductive silver paste as described in any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Preparation of organic carrier: Dissolve the polymer composite resin in an organic solvent, then add dispersant, curing agent, curing accelerator, organotin precursor and lubricant, and disperse evenly to obtain organic carrier; S2. Silver paste preparation: Silver powder is added to the organic carrier obtained in step S1, and after premixing, grinding and degassing under reduced pressure, a solderable low-temperature conductive silver paste is obtained.

10. The method for preparing solderable low-temperature conductive silver paste according to claim 9, characterized in that, The polymer composite resin is prepared by polymerization reaction of methyl methacrylate, triallyl isocyanurate, methacrylic acid, initiator azobisisobutyronitrile and solvent butyl acetate.

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