A solderable type polymer conductive silver paste and a preparation method thereof

Abstract

This application discloses a solderable polymer conductive silver paste and its preparation method. The silver paste comprises flake conductive silver powder, carboxyl-terminated polyamide-imide modified phenolic epoxy resin, 2-ethyl-4-methylimidazolium, diethylene glycol butyl ether acetate, and lauryl phosphate. This application improves conductivity, solderability, and welding reliability through reactive modification and stepwise paste preparation.

Description

Technical Field

[0001] This invention relates to the field of conductive silver paste technology, and in particular to a solderable polymer conductive silver paste and its preparation method. Background Technology

[0002] Conductive silver paste is widely used in electronic components, circuit interconnects, sensors, photovoltaic cells, and flexible electronics. Based on different film-forming mechanisms, conductive silver paste can generally be divided into high-temperature sintering conductive silver paste and low-temperature curing polymer conductive silver paste. High-temperature sintering conductive silver paste typically requires high-temperature sintering, during which organic components are removed, and a relatively continuous metallic conductive network can be formed between the silver powder particles, thus exhibiting good conductivity and solderability. However, its high sintering temperature makes it unsuitable for plastics, films, ink layers, and other low-temperature resistant substrates. Low-temperature curing polymer conductive silver paste can be cured at lower temperatures, offering advantages such as low application temperature, wide substrate adaptability, and simple processing. However, after curing, a significant amount of organic resin components remain in the silver layer, and the silver powder surface is easily coated or isolated by the resin, making it difficult for solder to fully wet the silver powder in the silver layer. This results in insufficient solderability or low solder strength in the silver layer.

[0003] To address the issue of decreased pull-out strength in polymer conductive silver pastes during soldering due to resin softening under heat, existing technologies typically employ resin systems with high heat resistance or high glass transition temperatures as the polymer binder phase. Examples include high-Tg epoxy resins, phenolic resins, polyimide resins, polyamide-imide resins, or high-Tg acrylic resins, aiming to improve the thermal stability of the silver layer under soldering thermal shock. However, simply selecting resin systems with higher Tg or higher heat resistance is insufficient to fully resolve the soldering reliability issue. On one hand, soldering temperatures are typically significantly higher than the glass transition temperatures of ordinary polymer resins, and the resin may still soften, deform thermally, or experience a decrease in interfacial bond strength under solder thermal shock. On the other hand, high-rigidity heat-resistant resins often reduce film flexibility, increase curing shrinkage stress, and affect the silver powder dispersion and the degree of bare silver on the silver layer surface, making it difficult to simultaneously achieve good conductivity, solderability, adhesion, and soldering pull-out strength. Therefore, how to construct a polymer conductive silver paste system that combines soldering thermal shock resistance, substrate adhesion, and silver layer solderability under low-temperature curing conditions has become a pressing technical problem in this field. Summary of the Invention

[0004] This application provides a solderable polymer conductive silver paste, comprising the following components by mass percentage: 60-80% flake-shaped conductive silver powder; Modified organic polymers 3-15%; 1-2% 2-Ethyl-4-methylimidazolium; Diethylene glycol butyl ether acetate 10-25%; Lauryl phosphate 1-3%; The modified organic polymer is a carboxyl-terminated polyamide-imide modified phenolic epoxy resin, which is obtained by reacting carboxyl-terminated polyamide-imide with phenolic epoxy resin.

[0005] It should be noted that the phenolic epoxy resin is modified by reacting carboxyl-terminated polyamide-imide, which allows the carboxyl groups in the polyamide-imide to react with the epoxy groups in the phenolic epoxy resin, thereby introducing heat-resistant segments and a highly polar structure of amide-imide into the phenolic epoxy resin system. This modified organic polymer can provide high crosslinking density and resistance to welding thermal shock by relying on phenolic epoxy resin, and can also improve the interfacial bonding between the resin phase and the sheet-like conductive silver powder and the substrate through the polyamide-imide segments. This reduces the curing shrinkage stress and interfacial delamination risk that are easily generated by pure high-rigidity heat-resistant resin. At the same time, it forms a surface contact conductive network with the sheet-like conductive silver powder. The addition of 2-ethyl-4-methylimidazolium promotes curing, diethylene glycol butyl ether acetate adjusts the rheology during construction, and lauryl phosphate improves the wetting and dispersion of silver powder and the wettability of solder. As a result, the silver paste has good conductivity, adhesion, solderability, and pull-out strength stability after welding under low-temperature curing conditions.

[0006] As a preferred technical solution for solderable polymer conductive silver paste, the mass ratio of phenolic epoxy resin to carboxyl-terminated polyamide imide is (60-90):(10-40).

[0007] It should be noted that, while ensuring the high crosslinking density and heat resistance of phenolic epoxy resin, an appropriate amount of heat-resistant and flexible polyamide-imide segments can be introduced, thereby taking into account welding thermal stability, adhesion and film toughness.

[0008] As a preferred technical solution for solderable polymer conductive silver paste, the acid value of the terminal carboxyl polyamide imide is 20-80 mg KOH / g.

[0009] It should be noted that this ensures that the system has enough carboxyl groups to react with the epoxy groups in the phenolic epoxy resin, while avoiding excessively high acid values ​​that could lead to rapid curing, decreased storage stability, or poor dispersion of the silver powder.

[0010] As a preferred technical solution for solderable polymer conductive silver paste, the number-average molecular weight of the terminal carboxyl polyamide imide is 5000-30000.

[0011] It should be noted that this allows it to possess good reactivity, solubility, dispersibility, and film-forming enhancement, avoiding insufficient heat resistance enhancement due to excessively low molecular weight or excessive viscosity of the slurry due to excessively high molecular weight.

[0012] As a preferred technical solution for solderable polymer conductive silver paste, the particle size D50 of the flake conductive silver powder is 2-8 μm, and the tap density of the flake conductive silver powder is 3.0-5.5 g / cm³. 3 .

[0013] It should be noted that this allows the silver powder to form a denser surface-contact conductive network in the paste, which is beneficial for improving the conductivity of the silver layer, printing stability, and solder wetting contact area.

[0014] In addition, this application provides a method for preparing a solderable polymer conductive silver paste, comprising the following steps: S1. Phenolic epoxy resin, carboxyl-terminated polyamide-imide and triphenylphosphine are added to a portion of diethylene glycol butyl ether acetate and reacted at 80-140℃ to obtain a carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution. S2. Add the remaining diethylene glycol butyl ether acetate to the carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution, adjust the solid content, and then filter to obtain the modified organic polymer carrier. S3. Add 2-ethyl-4-methylimidazolium and lauryl phosphate to the modified organic polymer carrier and disperse evenly to obtain an organic mixture; S4. Add the flake-shaped conductive silver powder to the organic mixture, stir and disperse for 30-60 minutes, and then perform three-roll milling to obtain conductive silver paste; S5. Filter the conductive silver paste through a 400-1000 mesh sieve to obtain a solderable polymer conductive silver paste.

[0015] It should be noted that in S1, a portion of diethylene glycol butyl ether acetate is used as the reaction medium, and under the action of triphenylphosphine, the carboxyl-terminated polyamide imide reacts with the phenolic epoxy resin, so that the heat-resistant segments of the amide imide are introduced into the phenolic epoxy resin system in a chemically bonded manner, rather than through simple physical blending. In S2, the remaining diethylene glycol butyl ether acetate is added to adjust the solid content and viscosity, which is beneficial to obtaining a modified organic polymer carrier with stable reaction degree and suitable rheological properties. In S3, 2-ethyl-4-methylimidazolium and lauryl phosphate are first dispersed in the resin carrier to avoid local enrichment of curing accelerator and wetting dispersant after the addition of silver powder. In S4 and S5, flake conductive silver powder is added and then subjected to three-roll milling and sieve filtration to ensure that the flake silver powder can be uniformly dispersed and form a surface contact conductive network, thereby improving the printing stability, conductivity, solder wettability, and pull-out strength stability after soldering thermal shock of the obtained silver paste.

[0016] The beneficial effects of this application are as follows: This application uses carboxyl-terminated polyamide-imide to reactively modify phenolic epoxy resin, so that the heat-resistant segments and polar structures of polyamide-imide are introduced into the phenolic epoxy resin system in a chemically bonded manner, thereby improving the welding thermal shock resistance, interfacial bonding ability and film toughness of the modified organic polymer; at the same time, it forms a surface contact conductive network with flake conductive silver powder, promotes the full curing of the resin system with 2-ethyl-4-methylimidazolium, adjusts the rheology and construction stability of the slurry with diethylene glycol butyl ether acetate, and improves the wetting and dispersion of flake silver powder and solder wettability with lauryl phosphate. The resulting conductive silver paste can have low volume resistivity, high welding pull strength and resistance stability after multiple reflow soldering under low temperature curing conditions. This solves the problem that existing polymer conductive silver pastes are prone to poor solderability, low welding strength and decreased conductivity during the welding process due to resin softening, insufficient silver powder wetting or poor interfacial bonding. Attached Figure Description

[0017] Figure 1 The infrared spectrum of the carboxyl-terminated polyamide-imide modified phenolic epoxy resin in Example 1 is shown.

[0018] Figure 2 The images show the SEM morphology and EDS surface distribution of the solderable polymer conductive silver paste obtained in Example 1 after curing and soldering. Figure 2 (a) in the image is a surface SEM image of the conductive silver layer; Figure 2 (b) is a cross-sectional SEM image of the conductive silver paste after curing and welding, showing the layered structure of the solder layer, interface bonding area, conductive silver layer and substrate; Figure 2 (f) in the image is the SEM morphology of the conductive silver layer; Figure 2 (g) in the diagram represents the EDS surface distribution of Ag element; Figure 2 (h) in the diagram represents the EDS surface distribution of element C; Figure 2 In the diagram, (i) represents the EDS surface distribution of element O; Figure 2 In the diagram, (j) represents the EDS surface distribution of element P. Detailed Implementation

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0020] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0021] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0022] Example 1

[0023] This embodiment provides a solderable polymer conductive silver paste, comprising the following components by mass percentage: 60.0% flake conductive silver powder, 15.0% modified organic polymer, 1.0% 2-ethyl-4-methylimidazolium, 22.0% diethylene glycol butyl ether acetate, and 2.0% lauryl phosphate. The modified organic polymer is a carboxyl-terminated polyamide-imide modified phenolic epoxy resin, with a mass ratio of phenolic epoxy resin to carboxyl-terminated polyamide-imide of 60:40. The carboxyl-terminated polyamide-imide has an acid value of 20 mg KOH / g and a number-average molecular weight of 5000. The flake conductive silver powder has a particle size D50 of 2 μm and a tap density of 3.0 g / cm³. 3 .

[0024] The preparation method of the solderable polymer conductive silver paste in this embodiment is as follows: S1. Weigh 90g of phenolic epoxy resin, 60g of carboxyl-terminated polyamide-imide, and 0.75g of triphenylphosphine, add them to 132g of diethylene glycol butyl ether acetate, heat to 80℃ under stirring, and keep the reaction at this temperature for 4h to allow the carboxyl groups in the carboxyl-terminated polyamide-imide to react with the epoxy groups in the phenolic epoxy resin, thereby obtaining a carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution.

[0025] S2. Add the remaining 88g of diethylene glycol butyl ether acetate to the carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution obtained in step S1, and continue stirring for 30 minutes to make the solid content and viscosity of the system uniform and stable. Then filter through a 200-mesh filter to obtain the modified organic polymer carrier.

[0026] S3. Add 10g of 2-ethyl-4-methylimidazolium and 20g of lauryl phosphate to the modified organic polymer carrier obtained in step S2, and stir at 800rpm for 30min at room temperature to uniformly disperse the curing promoting component and the wetting and dispersing component in the modified resin carrier to obtain an organic mixture.

[0027] S4. Slowly add 600g of flake conductive silver powder to the organic mixture obtained in step S3 while stirring. After all the flake conductive silver powder has been added, continue stirring for 30 minutes to initially wet and disperse the flake conductive silver powder. Then, the resulting slurry is subjected to three-roll milling, with the gap between the three rollers adjusted to 50μm, 25μm and 10μm respectively. The milling is performed three times to obtain conductive silver paste.

[0028] S5. Filter the conductive silver paste obtained in step S4 through a 400-mesh sieve to remove coarse particles and insufficiently dispersed agglomerates, thereby obtaining a solderable polymer conductive silver paste.

[0029] Example 2

[0030] This embodiment provides a solderable polymer conductive silver paste, comprising the following components by mass percentage: 80.0% flake conductive silver powder, 3.0% modified organic polymer, 2.0% 2-ethyl-4-methylimidazolium, 14.0% diethylene glycol butyl ether acetate, and 1.0% lauryl phosphate. The modified organic polymer is a carboxyl-terminated polyamide-imide modified phenolic epoxy resin, with a mass ratio of phenolic epoxy resin to carboxyl-terminated polyamide-imide of 90:10. The carboxyl-terminated polyamide-imide has an acid value of 80 mg KOH / g and a number-average molecular weight of 30,000. The flake conductive silver powder has a particle size D50 of 8 μm and a tap density of 5.5 g / cm³. 3 .

[0031] The preparation method of the solderable polymer conductive silver paste in this embodiment is as follows: S1. Weigh 27g of phenolic epoxy resin, 3g of carboxyl-terminated polyamide-imide and 0.15g of triphenylphosphine, add them to 84g of diethylene glycol butyl ether acetate, heat to 140℃ under stirring, and keep the temperature for 2h to allow the carboxyl-terminated polyamide-imide to react with the phenolic epoxy resin to obtain a carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution.

[0032] S2. Add the remaining 56g of diethylene glycol butyl ether acetate to the carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution obtained in step S1, continue stirring for 40min, adjust the solid content and rheological state of the system, and then filter through a 300-mesh filter to obtain the modified organic polymer carrier.

[0033] S3. Add 20g of 2-ethyl-4-methylimidazole and 10g of lauryl phosphate to the modified organic polymer carrier obtained in step S2, and stir at 1000rpm for 40min at room temperature to fully disperse 2-ethyl-4-methylimidazole and lauryl phosphate to obtain an organic mixture.

[0034] S4. Add 800g of flake conductive silver powder to the organic mixture obtained in step S3 in batches, keeping the mixture stirred during the addition process. After all the powder has been added, continue stirring for 60 minutes to ensure that the flake conductive silver powder is fully wetted by the modified organic polymer carrier. Then, perform three-roll milling, adjusting the gap between the three rollers to 60μm, 30μm and 15μm in sequence, and milling 4 times to obtain conductive silver paste.

[0035] S5. Filter the conductive silver paste obtained in step S4 through a 1000-mesh sieve to obtain a solderable polymer conductive silver paste with uniform particle size distribution and no obvious agglomeration particles.

[0036] Example 3

[0037] This embodiment provides a solderable polymer conductive silver paste, comprising the following components by mass percentage: 60.0% flake conductive silver powder, 10.0% modified organic polymer, 2.0% 2-ethyl-4-methylimidazolium, 25.0% diethylene glycol butyl ether acetate, and 3.0% lauryl phosphate. The modified organic polymer is a carboxyl-terminated polyamide-imide modified phenolic epoxy resin, with a mass ratio of phenolic epoxy resin to carboxyl-terminated polyamide-imide of 75:25. The carboxyl-terminated polyamide-imide has an acid value of 50 mg KOH / g and a number-average molecular weight of 15000. The flake conductive silver powder has a particle size D50 of 5 μm and a tap density of 4.2 g / cm³. 3 .

[0038] The preparation method of the solderable polymer conductive silver paste in this embodiment is as follows: S1. Weigh 75g of phenolic epoxy resin, 25g of carboxyl-terminated polyamide-imide and 0.50g of triphenylphosphine, add them to 150g of diethylene glycol butyl ether acetate, heat to 110℃ under stirring, and keep the reaction at this temperature for 3h to obtain a carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution.

[0039] S2. Add the remaining 100g of diethylene glycol butyl ether acetate to the carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution obtained in step S1, and continue stirring for 35 minutes to adjust the solid content and viscosity of the modified resin solution to a state suitable for subsequent silver powder dispersion. Then filter through a 250-mesh filter to obtain the modified organic polymer carrier.

[0040] S3. Add 20g of 2-ethyl-4-methylimidazolium and 30g of lauryl phosphate to the modified organic polymer carrier obtained in step S2, and stir at 900rpm for 35min at room temperature to ensure that the curing accelerator and wetting and dispersing agent are evenly distributed in the resin carrier to obtain an organic mixture.

[0041] S4. Add 600g of flake conductive silver powder to the organic mixture obtained in step S3. Keep stirring continuously during the addition process. After the addition is completed, continue stirring for 45min to fully wet and initially disperse the flake conductive silver powder. Then perform three-roll milling, adjusting the gap between the three rollers to 50μm, 20μm and 10μm in sequence, and mill 3 times to obtain conductive silver paste.

[0042] S5. Filter the conductive silver paste obtained in step S4 through an 800-mesh sieve to obtain a solderable polymer conductive silver paste.

[0043] Example 4

[0044] This embodiment provides a solderable polymer conductive silver paste, comprising the following components by mass percentage: 75.0% flake conductive silver powder, 12.0% modified organic polymer, 1.5% 2-ethyl-4-methylimidazolium, 10.0% diethylene glycol butyl ether acetate, and 1.5% lauryl phosphate. The modified organic polymer is a carboxyl-terminated polyamide-imide modified phenolic epoxy resin, with a mass ratio of phenolic epoxy resin to carboxyl-terminated polyamide-imide of 80:20. The carboxyl-terminated polyamide-imide has an acid value of 65 mg KOH / g and a number-average molecular weight of 22000. The flake conductive silver powder has a particle size D50 of 6 μm and a tap density of 4.8 g / cm³. 3 .

[0045] The preparation method of the solderable polymer conductive silver paste in this embodiment is as follows: S1. Weigh 96g of phenolic epoxy resin, 24g of carboxyl-terminated polyamide-imide and 0.60g of triphenylphosphine, add them to 60g of diethylene glycol butyl ether acetate, heat to 125℃ under stirring, and keep the temperature for 3h to allow the carboxyl-terminated polyamide-imide to react with the phenolic epoxy resin to obtain a carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution.

[0046] S2. Add the remaining 40g of diethylene glycol butyl ether acetate to the carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution obtained in step S1, continue stirring for 30min, adjust the solid content and viscosity of the system, and then filter through a 200-mesh filter to obtain the modified organic polymer carrier.

[0047] S3. Add 15g of 2-ethyl-4-methylimidazole and 15g of lauryl phosphate to the modified organic polymer carrier obtained in step S2, and stir at 900rpm for 30min at room temperature to uniformly disperse 2-ethyl-4-methylimidazole and lauryl phosphate in the modified organic polymer carrier to obtain an organic mixture.

[0048] S4. Slowly add 750g of flake conductive silver powder to the organic mixture obtained in step S3, stirring continuously during the addition process. After the addition is completed, continue stirring for 50 minutes to ensure that the flake conductive silver powder is fully wetted by the organic mixture. Then, perform three-roll milling, adjusting the gap between the three rollers to 45μm, 25μm and 10μm in sequence, and milling 3 times to obtain conductive silver paste.

[0049] S5. Filter the conductive silver paste obtained in step S4 through a 600-mesh sieve to obtain a solderable polymer conductive silver paste.

[0050] Compare with Example 1 Compared with Example 1, the difference is that this comparative example does not use carboxyl-terminated polyamide-imide to modify the phenolic epoxy resin. Instead, all the modified organic polymers in Example 1 are replaced with phenolic epoxy resin, that is, 150g of phenolic epoxy resin is used, without adding carboxyl-terminated polyamide-imide. The dosage of other components and the preparation steps are the same as in Example 1. Specifically, in the preparation process, 150g of phenolic epoxy resin and 0.75g of triphenylphosphine are added to 132g of diethylene glycol butyl ether acetate and stirred at 80°C for 4 hours. Then, the remaining 88g of diethylene glycol butyl ether acetate is added, and the mixture is filtered to obtain the phenolic epoxy resin carrier. Then, 10g of 2-ethyl-4-methylimidazole, 20g of lauryl phosphate and 600g of flake conductive silver powder are added in sequence, and the conductive silver paste is prepared by stirring, three-roll milling and filtration through a 400-mesh sieve in the same manner as in Example 1.

[0051] Compare with Example 2 Compared with Example 1, the difference is that the amounts of phenolic epoxy resin and carboxyl-terminated polyamide-imide in this comparative example are still 90g and 60g, respectively. However, they are not modified by reaction, but are formed by physical blending to form a resin carrier. The amounts of other components and subsequent preparation steps are the same as in Example 1. Specifically, 90g of phenolic epoxy resin and 60g of carboxyl-terminated polyamide-imide are directly added to 132g of diethylene glycol butyl ether acetate without adding triphenylphosphine or performing an 80°C reaction treatment. The mixture is stirred at room temperature for 4 hours to form a physically blended resin solution. Then, the remaining 88g of diethylene glycol butyl ether acetate is added and filtered to obtain the physically blended resin carrier. Then, 10g of 2-ethyl-4-methylimidazole, 20g of lauryl phosphate, and 600g of flake conductive silver powder are added in sequence, and the conductive silver paste is prepared by stirring, three-roll milling, and filtration through a 400-mesh sieve in the same manner as in Example 1.

[0052] Compare with Example 3 Compared with Example 1, the difference is that the mass ratio of phenolic epoxy resin to carboxyl-terminated polyamide imide in this comparative example is adjusted to 95:5, which exceeds the range of (60-90):(10-40) defined in this application. The amounts of other components and the preparation steps are the same as in Example 1. Specifically, 142.5g of phenolic epoxy resin, 7.5g of carboxyl-terminated polyamide imide and 0.75g of triphenylphosphine were weighed and added to 132g of diethylene glycol butyl ether acetate. The mixture was reacted at 80°C for 4 hours to obtain a carboxyl-terminated polyamide imide modified phenolic epoxy resin solution. Then, the remaining 88g of diethylene glycol butyl ether acetate was added, and the mixture was filtered to obtain a modified resin carrier. Then, 10g of 2-ethyl-4-methylimidazole, 20g of lauryl phosphate and 600g of flake conductive silver powder were added in sequence, and the mixture was stirred, three-roll milled and filtered according to the same process as in Example 1 to obtain conductive silver paste.

[0053] Compare with Example 4 Compared with Example 1, the difference is that the mass ratio of phenolic epoxy resin to carboxyl-terminated polyamide imide in this comparative example is adjusted to 50:50, which exceeds the range of (60-90):(10-40) defined in this application. The amounts of other components and the preparation steps are the same as in Example 1. Specifically, 75g of phenolic epoxy resin, 75g of carboxyl-terminated polyamide imide and 0.75g of triphenylphosphine were weighed and added to 132g of diethylene glycol butyl ether acetate. The mixture was reacted at 80°C for 4 hours to obtain a carboxyl-terminated polyamide imide modified phenolic epoxy resin solution. Then, the remaining 88g of diethylene glycol butyl ether acetate was added and filtered to obtain a modified resin carrier. Then, 10g of 2-ethyl-4-methylimidazole, 20g of lauryl phosphate and 600g of flake conductive silver powder were added in sequence, and the mixture was stirred, three-roll milled and filtered according to the same process as in Example 1 to obtain conductive silver paste.

[0054] Compare with Example 5 Compared with Example 1, the difference is that this comparative example does not use the method of adding diethylene glycol butyl ether acetate in two parts, but instead adds all 220g of diethylene glycol butyl ether acetate at once in S1. The dosage of other components and the preparation steps are the same as in Example 1. Specifically, 90g of phenolic epoxy resin, 60g of carboxyl-terminated polyamide imide and 0.75g of triphenylphosphine are added to 220g of diethylene glycol butyl ether acetate at once, and reacted at 80°C for 4h to obtain a modified resin solution. After the reaction, the modified resin carrier is obtained by direct filtration. Then, 10g of 2-ethyl-4-methylimidazole, 20g of lauryl phosphate and 600g of flake conductive silver powder are added in sequence, and conductive silver paste is prepared by stirring, three-roll milling and filtration through a 400-mesh sieve in the same manner as in Example 1. This comparative example illustrates that adding all the solvent at once reduces the effective contact concentration between the phenolic epoxy resin and the carboxyl-terminated polyamide imide in the reaction stage, which may lead to insufficient modification reaction or decreased reaction stability, thereby affecting the subsequent wetting and dispersion of silver powder by the resin carrier and the reliability of welding.

[0055] Compare with Example 6 Compared with Example 1, the difference is that lauryl phosphate is not added in this comparative example, and its amount is made up with an equal amount of diethylene glycol butyl ether acetate, i.e., 600g of flake conductive silver powder, 150g of modified organic polymer, 10g of 2-ethyl-4-methylimidazole, 240g of diethylene glycol butyl ether acetate, and 0g of lauryl phosphate. The remaining preparation steps are the same as in Example 1. Specifically, a carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution is first prepared according to the same method as in Example 1, and the remaining diethylene glycol butyl ether acetate is added to adjust the solid content before filtration to obtain the modified resin carrier; then only 10g of 2-ethyl-4-methylimidazole is added and stirred to disperse, then 600g of flake conductive silver powder is added, and stirring is continued for 30 minutes before three-roll milling and filtration through a 400-mesh sieve to obtain conductive silver paste.

[0056] Performance testing methods 1. Volume resistivity test: The conductive silver paste obtained in the examples and control examples was screen-printed onto the surface of a cleaned PET film, PI film, or ceramic substrate to form test lines with a width of 1 mm and a length of 50 mm. After curing at 120–160 °C for 20–40 min and cooling to room temperature, the resistance at both ends of the conductive line was measured using a four-probe resistance meter or a digital micro-ohmmeter. The volume resistivity was calculated based on the line length, width, and cured film thickness. At least 5 locations were tested for each sample, and the average value was taken.

[0057] 2. Welding pull-out strength test: After printing and curing the silver paste obtained in the examples and control examples onto the substrate surface, tin-plated copper wires, solder pads or standard solder pad terminals are soldered to the silver layer area. After soldering, the substrate is placed at room temperature for 24 hours, and then a universal testing machine is used to perform vertical pull-out or 180° peel test. The tensile speed can be set to 50 mm / min. The maximum load when the solder joint or solder terminal is detached from the silver layer surface is recorded. Each group of samples should test no less than 5 solder joints and take the average value.

[0058] 3. Resistance change rate test after multiple reflow soldering: First, test the initial resistance R0 of the cured conductive circuit sample. Then, perform 1, 3, or 5 reflows according to the lead-free reflow soldering temperature profile. The peak temperature can be set to 245-260℃. After each reflow, cool to room temperature and test the resistance Rn. The resistance is calculated using the formula ΔR / R0 = (R... n Calculate the rate of change of resistance using (-R0) / R0×100%.

[0059] Table 1 shows the performance test results of Examples 1-4 and Comparative Examples 1-6.

[0060] In conjunction with Example 1 and Figure 1 It can be seen that, in Example 1, after the phenolic epoxy resin and carboxyl-terminated polyamide-imide react under the action of triphenylphosphine, the resulting carboxyl-terminated polyamide-imide modified phenolic epoxy resin has a viscosity of approximately 3420 cm⁻¹. -1 A relatively broad hydroxyl absorption peak appears at approximately 1735 cm⁻¹. -1 An absorption peak appears at the C=O group of the ester group, and at approximately 1780 cm⁻¹. -1 1720cm -1 1655cm -1 1540cm -1 and 1375cm -1 The peaks at approximately 915 cm⁻¹ exhibit characteristic absorption peaks for imide C=O, amide I, amide II, and imide CN, respectively. -1The characteristic peaks of the epoxy groups were significantly weakened; this indicates that the carboxyl groups in the carboxyl-terminated polyamide-imide underwent a ring-opening reaction with the epoxy groups in the phenolic epoxy resin, generating hydroxyl and ester structures during the reaction. This allows the heat-resistant polyamide-imide segments to be introduced into the phenolic epoxy resin system through chemical bonding, rather than simple physical blending. Therefore, the modified organic polymer obtained in Example 1 retains the high crosslinking density and heat resistance of phenolic epoxy resin, while also introducing the heat resistance, polar interfacial interaction, and certain toughness brought by the amide-imide structure. This is beneficial for improving the dispersion stability of the sheet-like conductive silver powder in the resin carrier, the cohesive strength of the cured silver layer, and the reliability of the interfacial bonding after welding thermal shock.

[0061] In conjunction with Example 1 and Figure 2 It can be seen that the surface morphology of the cured conductive silver paste shows a relatively uniform distribution of flake-shaped conductive silver powder. The silver powder can form an overlapping and staggered contact structure, and no obvious large-sized agglomerates, resin-rich areas, or through-holes are observed. This indicates that lauryl phosphate has a good wetting and dispersing effect on the flake-shaped silver powder. After three-roll milling, the silver powder can form a relatively continuous conductive network in the modified organic polymer carrier. The cross-sectional morphology shows that the conductive silver layer is tightly bonded to the substrate, and the layers between the solder layer, the interface bonding area, and the conductive silver layer are clear. No obvious delamination or through cracks are observed at the interface, indicating that the carboxyl-terminated polyamide-imide modified phenolic epoxy resin can improve the cohesive strength and interfacial bonding stability of the silver layer. The EDS surface distribution further shows that Ag elements are continuously distributed in the conductive silver layer, C and O elements mainly correspond to the modified resin matrix, and P elements are relatively uniformly distributed. This indicates that lauryl phosphate can be well distributed at the interface between the silver powder and the resin, which is beneficial to improving the dispersion of silver powder and the wettability of solder. This demonstrates that the conductive silver paste obtained in Example 1 can form a uniform, dense, and continuous conductive silver layer structure, providing morphological evidence for its low volume resistivity, high welding pull-out strength, and resistance stability after multiple reflow soldering.

[0062] As can be seen from Examples 1 to 4 and Table 1, the volume resistivity of the solderable polymer conductive silver paste obtained in Examples 1 to 4 is 3.9 × 10⁻⁶. -5 ~6.8×10 -5The resistivity was measured in Ω·cm, with a pull-out strength of 16.8–22.8 N. The resistivity change rate after one reflow soldering was 1.5–2.4%, after three reflow solderings it was 3.8–6.2%, and after five reflow solderings it was 6.2–9.5%. These results indicate that, through the combined action of flake-shaped conductive silver powder, carboxyl-terminated polyamide-imide modified phenolic epoxy resin, 2-ethyl-4-methylimidazolium, diethylene glycol butyl ether acetate, and lauryl phosphate, the resulting conductive silver paste can form a relatively continuous flake-shaped silver powder-overlapping conductive network. Simultaneously, the modified organic polymer can maintain the cohesive strength and interfacial bonding stability of the silver layer after soldering thermal shock, enabling the conductive silver paste to possess both low resistivity, high pull-out strength, and stable resistivity after multiple reflow solderings.

[0063] As can be seen from Example 1, Comparative Examples 1 to 6, and Table 1, the volume resistivity of Example 1 is 6.8 × 10⁻⁶. -5 The weld pull-out strength was 20.6 N, and the resistance change rate after 5 reflow soldering cycles was 7.5%, showing significantly better overall performance than the control examples. Control Example 1, which did not use carboxyl-terminated polyamide-imide modified phenolic epoxy resin, saw its weld pull-out strength decrease to 10.8 N, and its resistance change rate after 5 reflow soldering cycles increased to 29.4%, indicating that pure phenolic epoxy resin is difficult to maintain stable interfacial bonding under welding thermal shock. Control Example 2, using only physical blending, achieved a weld pull-out strength of 13.5 N and a resistance change rate of 22.8% after 5 reflow soldering cycles, indicating that the reactive modification between carboxyl-terminated polyamide-imide and phenolic epoxy resin is key to improving weld reliability. Control Example 3... In Comparative Example 4, adjusting the mass ratio of phenolic epoxy resin to carboxyl-terminated polyamide-imide outside the scope of this application resulted in a decrease in weld pull-out strength or an increase in volume resistivity, indicating that the ratio needs to be controlled within an appropriate range. Comparative Example 5 did not use a stepwise addition method for diethylene glycol butyl ether acetate, and its resistance change rate increased to 20.2% after 5 reflow soldering cycles, indicating that stepwise addition is beneficial for balancing early reaction modification and later slurry rheology control. Comparative Example 6 did not add lauryl phosphate, and its volume resistivity increased to 8.7 × 10⁻⁶. -5 The solder pull-out strength decreased to 12.6 N after 5 reflow soldering cycles, while the resistivity change rate increased to 28.1%, indicating that lauryl phosphate plays an important role in the wetting and dispersion of flake silver powder, solder wetting contact, and the stability of the conductive network. Therefore, the components and preparation processes in this application are not simply parallel entities, but rather form a synergistic effect to improve the conductivity, solderability, and solder thermal stability of the polymer conductive silver paste.

[0064] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A solderable type polymer conductive silver paste, characterized in that, By mass percentage, it includes the following components: 60-80% flake-shaped conductive silver powder; Modified organic polymers 3-15%; 1-2% 2-Ethyl-4-methylimidazolium; Diethylene glycol butyl ether acetate 10-25%; Lauryl phosphate 1-3%; The modified organic polymer is a carboxyl-terminated polyamide-imide modified phenolic epoxy resin, which is obtained by reacting carboxyl-terminated polyamide-imide with phenolic epoxy resin.

2. The solderable type polymer conductive silver paste according to claim 1, characterized in that, The mass ratio of the phenolic epoxy resin to the carboxyl-terminated polyamide imide is (60-90):(10-40).

3. The solderable polymer conductive silver paste according to claim 1, characterized in that, The acid value of the terminal carboxyl polyamide imide is 20–80 mg KOH / g.

4. The solderable polymer conductive silver paste according to claim 1, characterized in that, The number-average molecular weight of the terminal carboxyl polyamide imide is 5000–30000.

5. The solderable polymer conductive silver paste according to claim 1, characterized in that, The particle size D50 of the flaky conductive silver powder is 2 to 8 μm, and the tap density of the flaky conductive silver powder is 3.0 to 5.5 g / cm 3 .

6. A method for preparing the solderable polymer conductive silver paste according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Phenolic epoxy resin, carboxyl-terminated polyamide-imide and triphenylphosphine are added to a portion of diethylene glycol butyl ether acetate and reacted at 80-140℃ to obtain a carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution. S2. Add the remaining diethylene glycol butyl ether acetate to the carboxyl-terminated polyamide-imide modified phenolic epoxy resin solution, adjust the solid content, and then filter to obtain the modified organic polymer carrier. S3. Add 2-ethyl-4-methylimidazolium and lauryl phosphate to the modified organic polymer carrier and disperse evenly to obtain an organic mixture; S4. Add the flake-shaped conductive silver powder to the organic mixture, stir and disperse for 30-60 minutes, and then perform three-roll milling to obtain conductive silver paste; S5. Filter the conductive silver paste through a 400-1000 mesh sieve to obtain a solderable polymer conductive silver paste.

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