Low-temperature sintering type porous copper-silver composite conductive paste and preparation method thereof

Abstract

The invention discloses low-temperature sintering type porous copper-silver composite conductive paste and a preparation method, and belongs to the technical field of electronic materials. The low-temperature sintering type porous copper-silver composite conductive paste is composed of solid powder and an organic carrier, and the organic carrier accounts for 10-21% of the total mass; the solid powder is composed of a conductive functional phase and an inorganic binding phase; the conductive functional phase is composite metal powder of a porous copper framework, a silver pinning layer and an Ag-Pd alloy shell; the inorganic binding phase is composed of metal bismuth powder and lead-free glass powder. The preparation method comprises the following steps: preparing the composite powder, mixing and rolling the binding phase and the carrier, and sintering the slurry at low temperature. Through the synergistic effect of the porous composite powder and the bismuth-glass composite binding phase, the unification of low sheet resistance and high adhesive force of the conductive film layer is realized at low temperature, and meanwhile, the conductive film layer has the advantages of low cost and high reliability, and is suitable for the fields of flexible electronics and low-temperature co-fired ceramics.

Description

Technical Field

[0001] This invention relates to a low-temperature sintering porous copper-silver composite conductive paste and its preparation method, which is applicable to the manufacture of heat-sensitive conductive circuits and electrodes in flexible electronics, low-temperature co-fired ceramics (LTCC), and heterojunction solar cells, and belongs to the field of electronic materials technology. Background Technology

[0002] Conductive paste, as a key electronic functional material, is widely used in the manufacture of electrodes and wiring in fields such as solar cells, thick film circuits, printed electronics, and electronic packaging.

[0003] Currently, silver paste remains the mainstream conductive paste on the market. However, the high cost of silver raw materials severely restricts its application in large-scale, low-cost electronic devices. To reduce costs, the industry commonly uses copper powder or silver-coated copper powder as substitutes. However, pure copper powder is chemically reactive and easily oxidizes during paste preparation and sintering, leading to a sharp increase in resistivity and even failure. While silver-coated copper powder alleviates the oxidation problem to some extent, it requires high sintering temperatures (>500℃) to achieve good conductive network connections. This high-temperature process is not only energy-intensive but also unsuitable for heat-sensitive flexible polymer substrates (such as PI and PET) or applications requiring integration with low-temperature co-fired ceramic (LTCC) technology.

[0004] To lower the sintering temperature, several solutions have been proposed in existing technologies. One is to use ultrafine (nanoscale) silver or copper powder, leveraging their high surface energy to achieve low-temperature sintering. However, nanoparticles are expensive, prone to agglomeration, and have poor stability and are easily oxidized. Another approach is to add low-melting-point metals or alloys as sintering aids, such as indium (In), tin (Sn), or their alloys. However, indium is extremely expensive, significantly offsetting the cost advantage of silver-plated copper; while tin-based aids are easily oxidized, and the brittle intermetallic compounds formed with silver / copper can lead to increased resistivity and decreased connection reliability. A third approach is to develop ultra-low melting-point glass powder, but this often comes at the cost of sacrificing chemical stability and mechanical strength.

[0005] Furthermore, a single low-temperature sintering strategy often fails to achieve multiple performance goals simultaneously. For example, while relying solely on metal additives (such as bismuth) can reduce electrical resistance, the mechanical adhesion and durability of the sintered body are poor; and relying solely on low-melting-point glass powder often results in poor electrical conductivity.

[0006] Therefore, a key challenge in this field has long been how to design a novel conductive paste system that can achieve efficient sintering within a true low-temperature window (≤400℃) while significantly reducing reliance on precious metals and raw material costs, and ensuring that the final film simultaneously possesses low resistance, high adhesion strength, and long-term environmental stability comparable to silver paste. Developing an integrated technical solution that synergistically addresses these multiple challenges has significant industrial value. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-temperature sintering porous copper-silver composite conductive paste. This paste has a significantly lower cost than pure silver paste, can be sintered at low temperatures (≤400℃), and forms a conductive film layer with low sheet resistance, strong adhesion, high reliability, and high density.

[0008] Another objective of this invention is to provide a method for preparing the above-mentioned conductive paste, which is complete and controllable from core powder synthesis to paste preparation. The method is simple and suitable for large-scale production.

[0009] Another object of the present invention is to provide applications of the above-mentioned conductive paste.

[0010] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A low-temperature sintering porous copper-silver composite conductive paste is composed of solid powder and an organic carrier, wherein the organic carrier accounts for 10-21% of the total mass, and the solid powder consists of a conductive functional phase and an inorganic binder phase. The conductive functional phase is a composite metal powder of a porous copper skeleton-silver stud layer-Ag-Pd alloy shell; the inorganic binder phase consists of metallic bismuth powder and lead-free glass powder; the metallic bismuth powder accounts for 2-4% of the total mass of the solid powder, and the particle size of the metallic bismuth powder is less than 1 μm; the lead-free glass powder has a softening point of 300-400℃, accounts for 12-25% of the total mass of the solid powder, and the particle size of the lead-free glass powder is less than 10 μm; the conductive functional phase accounts for 71-86% of the total mass of the solid powder.

[0011] Specifically, a low-temperature sintering porous copper-silver composite conductive paste is composed of the following components: a conductive functional phase, an inorganic binder phase, and an organic carrier; The conductive functional phase uses Cu-Zn microalloyed porous copper powder as the skeleton, with silver nailing layers deposited in situ in the pores, and the outer shell is an Ag-Pd alloy thin layer. The inorganic binder phase is composed of metallic Bi powder and Bi2O3-ZnO-B2O3-SiO2 lead-free glass powder. The particle size of the metallic Bi powder is <1 µm, the particle size of the lead-free glass powder is <10 μm, and the softening point is 300-400 ℃. The metallic Bi powder melts at 271 ℃ to form a transient liquid phase, which synergistically promotes the sintering of the neck of the conductive particles with the glass powder.

[0012] Preferably, the pore wall thickness of the Cu-Zn porous copper powder skeleton is 20-80 nm, the grain size of the silver nailing layer inside the pore is 10-50 nm, and the Pd content in the Ag-Pd alloy thin layer is 1-5 wt%.

[0013] Preferably, the mass ratio of the bismuth powder to the lead-free glass powder is (1:10) to (10:1).

[0014] The conductive functional phase is a composite metal powder with an integrated core-porous-shell three-phase structure. This powder uses Cu-Zn microalloyed porous copper powder as a framework, with silver stud layers deposited in situ on the inner walls and outer surface of the porous framework's pores, and an outermost Ag-Pd alloy thin layer. This specific structural design aims to enhance sintering activity by utilizing the high specific surface area of ​​the porous framework, to achieve a strong bond with the copper core using the inner silver stud layer and provide initial conductive channels, and to achieve surface stabilization and optimize sintering interface behavior using the outer Ag-Pd alloy layer.

[0015] The inorganic binder phase consists of bismuth powder and specific lead-free glass powder. The bismuth powder accounts for 2-4% of the total mass of the solid powder and has a particle size of less than 1 μm. The lead-free glass powder is a bismuth-based lead-free glass powder with a softening point of 300-400℃, accounting for 12-25% of the total mass of the solid powder and having a particle size of less than 10 μm. The composition of the lead-free glass powder, by weight percentage, includes: Bi₂O₃ 65-78%, B₂O₃ 15-25%, ZnO 5-10%, and SiO₂ 2-5%. The design principle of this composite binder phase is to utilize the low melting point of bismuth to achieve low-temperature liquid-phase sintering, promoting the connection between conductive particles; simultaneously, it utilizes the flow and wetting of the lead-free glass powder at slightly higher temperatures to achieve final densification of the film, mechanical anchoring, and encapsulation protection of the copper core.

[0016] The organic carrier comprises, by weight percentage: 77-93.5% solvent, 5-15% resin, 0.5-3% dispersant, and 1-5% thixotropic agent. The solvent is one or more of terpineol, diethylene glycol butyl ether acetate, or terpineol; the resin is ethyl cellulose; the dispersant is a phosphate ester or a BYK series dispersant; and the thixotropic agent is hydrogenated castor oil or fumed silica. This organic carrier formulation provides suitable rheological properties to the slurry, ensuring good printability and storage stability.

[0017] The present invention also provides a method for preparing the conductive paste, comprising the following steps: Step 1, Preparation of conductive functional phase powder: a) Preparation of porous copper framework: Cu-Zn pre-alloyed powder (Cu-Zn9010 alloy powder purchased from Ruili Alloy Powder Materials Co., Ltd.) was subjected to selective chemical dealloying treatment to obtain micro-alloyed porous copper powder with a three-dimensional interconnected nanopore structure.

[0018] Specifically, 5-10g of Cu-Zn alloy powder with a particle size of 30-50μm is dispersed in 50-100ml of deionized water to obtain a mixture. The mixture is then poured into 200-500ml of 0.1-0.5mol / L HCl solution and magnetically stirred at 300-500r / min for 5-7 hours. After the reaction is complete, the mixture is immediately washed repeatedly with deionized water through vacuum filtration until the filtrate is neutral. The filter cake is then dried in a vacuum drying oven at 40-60℃ under flowing argon protection for 3-5 hours to obtain microalloyed porous copper powder with a three-dimensional interconnected nanoporous structure.

[0019] b) Silver nailing deposition: A layer of silver is uniformly deposited on the inner and outer surfaces of the pores of the porous copper skeleton by chemical plating or electrochemical displacement.

[0020] Specifically, the porous copper framework is placed in Ag(NH3)2 + Chemical plating is performed in the solution to form a silver stud layer inside the hole.

[0021] More specifically, the silver-studded layer deposition: 2-5g of the porous copper powder was immersed in 200-500mL of a 0.02-0.05 mol / L silver nitrate solution adjusted to pH 9-11 with ammonia water. 0.05-0.1mol / L ascorbic acid was slowly added dropwise for reduction. The mixture was stirred at 300-500 rpm for 30-50 minutes at 20-40℃, resulting in the in-situ deposition of a silver layer on the inner walls and outer surface of the porous framework through a chemical displacement reaction. After the reaction was complete, the mixture was filtered, washed three to four times each with deionized water and anhydrous ethanol, and then vacuum-dried at 40-60℃ to obtain the silver-studded porous copper powder.

[0022] c) Ag-Pd alloy layer coating: An Ag-Pd alloy layer is co-deposited on the surface of the powder with an already deposited silver layer by chemical plating, and finally a composite metal powder is obtained.

[0023] Specifically, the Ag-Pd alloy shell is formed by treating the AgNO3-PdCl2 displacement solution at 40-60 °C for 10-30 min, thus obtaining the conductive functional phase.

[0024] More specifically, the Ag-Pd alloy layer coating: 2.0-4.0g of powder with a silver stud layer deposited (i.e., porous copper powder with silver studs) is dispersed in 100-200ml of deionized water to obtain a powder suspension. The suspension is added dropwise to a chemical plating solution with a pH of 11-12, containing 200-400mL of 0.01-0.02mol / L silver nitrate-palladium chloride (with the Ag:Pd mass ratio controlled at 95:5), 5-10g / L potassium sodium tartrate, and 5-10mL / L formaldehyde (37% concentration). The mixture is stirred at 300-500r / min for 10-30 minutes at 40-60℃ to coat the outermost layer of the powder with a thin Ag-5Pd alloy layer. After undergoing the same washing and drying process (washing three to four times each with deionized water and anhydrous ethanol, and then vacuum drying at 40-60℃), the final "core-porous-shell" three-phase integrated composite conductive powder is obtained.

[0025] Step 2, slurry rolling: The conductive functional phase powder, bismuth metal powder and lead-free glass powder are uniformly mixed in a predetermined ratio (specifically, the solid powder is placed in a ball mill jar and mixed at a speed of 300-500 rpm for 30-60 minutes to obtain a uniform mixed powder), and then rolled with an organic carrier through a three-roll mill 5-10 times until the slurry fineness is ≤15μm.

[0026] Step 3, Coating and Drying: Apply the paste to the substrate by screen printing or scraping, and dry at 80-150℃ for 5-15 minutes.

[0027] Step 4, low-temperature sintering: In a protective atmosphere or vacuum, the temperature is programmed to rise to 250-400℃ at a rate of 2-10℃ / min, and held for 10-30 minutes to complete the sintering.

[0028] Application of a low-temperature sintering porous copper-silver composite conductive paste in conductive components.

[0029] Conductive components include conductive lines or electrodes, which include heat-sensitive conductive lines or electrodes such as flexible electronics, low-temperature co-fired ceramics (LTCC), and heterojunction solar cells.

[0030] A conductive element includes a substrate and a conductive film layer formed on the substrate, the conductive film layer being formed by sintering the conductive paste of this embodiment.

[0031] The sheet resistance of the conductive film layer described in this invention is 0.085-0.103 mΩ, and the adhesion is 4B-5B.

[0032] The binder of this invention differs from existing single-component binders for "Bi-B-Zn glass." This binder is a synergistic blend of two materials with different physicochemical properties (metal and non-metal), different melting / softening temperatures, and different functions (conductivity and adhesion). Bismuth powder, as a low-melting-point metal, melts in the early stages of sintering (approximately 271°C) to form a conductive liquid phase. Its core function is to promote metallic bonding between conductive particles, which is crucial for reducing sheet resistance and establishing a conductive network. Lead-free glass powder, as an inorganic non-metallic binder, softens and flows at slightly higher temperatures (approximately 300-400°C). Its core function is to provide strong mechanical adhesion and dense physical encapsulation.

[0033] The preparation principle of this invention is based on the design concept of "multi-level structural synergy" and "time-sequential functional coupling". By constructing a material system composed of gradient composite conductive powder and functionally complementary binder phase, efficient sintering and performance optimization at low temperature are achieved. Specifically, firstly, a conductive functional phase with a three-phase integrated structure of "porous copper skeleton - silver nail layer - Ag-Pd alloy shell" is prepared through selective dealloying, chemical deposition and controllable coating processes. The porous skeleton provides a highly active surface and driving force, the inner silver nail layer ensures ohmic contact, and the outer alloy shell optimizes interface stability. On this basis, a composite binder phase is innovatively constructed using bismuth powder and lead-free glass powder. The two work synergistically in stages according to their melting point differences during sintering: bismuth melts into a liquid phase first at a lower temperature (about 271°C), promoting the formation of sintering necks between conductive particles through capillary penetration and dissolution-precipitation mechanisms, thus constructing a conductive network; subsequently, the lead-free glass softens and flows at a slightly higher temperature, completing pore filling, providing mechanical anchoring and forming a dense glass encapsulation of the conductive network. The gradient spatial structure of this conductive phase, precisely coupled with the functional relay of the binder phase on the sintering time axis, produces a significant synergistic effect, thereby achieving high conductivity, high adhesion and excellent long-term reliability at a low temperature of ≤400℃.

[0034] Compared with the prior art, the beneficial effects of the present invention are: This invention creatively employs a composite binder phase composed of metallic bismuth powder and lead-free glass powder, which produce a synergistic effect during sintering. The metallic bismuth powder melts at a relatively low temperature (approximately 271°C) to form a liquid phase, which greatly promotes the formation of sintering necks between silver-coated copper particles, ensuring extremely low sheet resistance. Subsequently, the lead-free glass powder softens and flows at a slightly higher temperature, filling pores and forming a strong chemical bond with the substrate, providing excellent adhesion and a dense microstructure, thus solving the problem of performance imbalance in single-agent systems.

[0035] This invention replaces most of the pure silver powder with silver-coated copper powder, significantly reducing the cost of the core conductive phase; it uses inexpensive bismuth powder instead of expensive indium (In) and other additives; and the low-temperature sintering window of 250-400℃ (≤400℃) greatly reduces production energy consumption. This invention has a very strong market competitiveness in terms of cost.

[0036] The core breakthrough of this invention lies in abandoning the traditional approach of relying on the physical mixing of silver / copper powders in slurries, and instead designing based on the intrinsic structure of the material. By designing a unique gradient composite powder of a "porous copper framework-silver anchor layer-Ag-Pd alloy shell," inexpensive copper is used to form the powder body, while trace amounts of silver and palladium are precisely used to achieve key interface functions. This structure significantly reduces material costs. More importantly, the high specific surface area and surface energy provided by the porous framework, combined with the optimized surface sintering activity of the outer alloy shell, produce a synergistic effect, enabling the slurry to achieve a low-temperature sintering driving force far exceeding that of traditional dense powders.

[0037] This invention abandons the simple addition of single-function additives and innovatively adopts a composite bonding system of "phased synergistic action of metallic bismuth and lead-free glass powder". During sintering, low-melting-point metallic bismuth first forms a liquid phase, which promotes interparticle atomic diffusion and neck growth, and dominates the construction of a highly conductive metal network. Subsequently, the softened lead-free glass phase flows, completing the filling of pores, providing strong mechanical anchoring force, and finally forming a dense glass encapsulation layer. This sequential functional division of labor ensures that the sintered film layer has both low resistance and high adhesion. Crucially, the final glass encapsulation layer can effectively isolate water and oxygen, providing intrinsic antioxidant protection for the internal copper-based composite powder, thereby achieving long-term environmental stability that is difficult to achieve with traditional copper-based slurries.

[0038] This invention relates to the field of electronic materials technology, specifically disclosing a low-temperature sintering porous copper-silver composite conductive paste and its preparation method. The conductive paste consists of a composite conductive powder with a specific structure, an inorganic binder phase, and an organic carrier. The composite conductive powder uses microalloyed porous copper obtained through selective dealloying as a framework, and forms a "core-porous-shell" three-phase integrated structure through in-situ deposition of a silver stud layer and an Ag-Pd alloy coating layer. The inorganic binder phase is composed of bismuth powder and Bi2O3-based lead-free glass powder in a specific ratio. The preparation method includes: preparation of the composite powder, mixing and rolling with the binder phase and carrier, and low-temperature sintering of the paste. This invention achieves a balance between low sheet resistance and high adhesion of the conductive film at low temperatures through the synergistic effect of the porous composite powder and the bismuth-glass composite binder phase, while also possessing the advantages of low cost and high reliability, making it suitable for flexible electronics and low-temperature co-fired ceramics. Attached Figure Description

[0039] Figure 1These are SEM images of the conductive functional phase powder of this invention; Figure 2 These are metallographic microstructure images of sintered samples of the low-temperature sintering porous copper-silver composite conductive paste of the present invention, wherein (a) is the sintering image of Comparative Example 4, (b) is the sintering image of Example 1, and (c) is the sintering image of Comparative Example 3. Detailed Implementation

[0040] The following description, in conjunction with the accompanying drawings and embodiments of the present invention, will further clarify the objectives, technical solutions, and advantages of the present invention. The specific embodiments described are merely illustrative and are not intended to limit the scope of the invention.

[0041] A low-temperature sintering porous copper-silver composite conductive paste is composed of solid powder and an organic carrier. The solid powder consists of a conductive functional phase and an inorganic binder phase. The conductive functional phase is a composite metal powder consisting of a porous copper skeleton, a silver bracing layer, and an Ag-Pd alloy shell. The inorganic binder phase consists of metallic bismuth powder and lead-free glass powder. The metallic bismuth powder has a particle size of less than 1 μm. The lead-free glass powder has a softening point of 300-400℃ and a particle size of less than 10 μm.

[0042] A method for preparing a low-temperature sintering porous copper-silver composite conductive paste includes the following steps: 1. Preparation of porous copper framework: 10g of Cu-10Zn alloy powder with a particle size of about 30μm was dispersed in 50ml of deionized water to obtain a mixture. Under ice-water bath conditions, the mixture was slowly poured into 200ml of 0.25mol / L HCl solution and magnetically stirred at 400r / min for 7 hours. After the reaction was completed, the mixture was immediately washed repeatedly with deionized water through vacuum filtration until the filtrate was neutral. The filter cake was then dried in a vacuum drying oven at 60℃ under flowing argon protection for 3 hours to obtain microalloyed porous copper powder with a three-dimensional interconnected nanoporous structure.

[0043] 2. Silver-studded layer deposition: 5.0 g of the porous copper powder was dispersed in 500 mL of a 0.05 mol / L silver nitrate solution adjusted to pH 11.0 with ammonia. 0.05 mol / L ascorbic acid was added dropwise until the reaction was complete. The mixture was stirred at 400 rpm for 30 minutes at 40°C, resulting in in-situ deposition of a silver layer on the inner walls and outer surface of the porous framework via a chemical displacement reaction. After the reaction was complete, the mixture was filtered, washed three times each with deionized water and anhydrous ethanol, and then vacuum-dried at 60°C to obtain the silver-studded porous copper powder.

[0044] 3. Ag-Pd alloy coating: 4.0 g of powder with a silver naphtha layer was dispersed in 100 ml of deionized water to obtain a powder suspension. 400 mL of a chemical plating solution containing 0.02 mol / L silver nitrate-palladium chloride (Ag:Pd mass ratio controlled at 95:5), 10 g / L potassium sodium tartrate, and 10 mL / L formaldehyde was added to the solution with 2 mol / L NaOH to adjust the pH to 12. The suspension was then added dropwise to the plating solution, and the mixture was stirred at 50°C and 400 rpm for 20 minutes to coat the powder with a thin Ag-5Pd alloy layer. After the same washing and drying process, the final product was obtained as shown below. Figure 1 The "core-porous-shell" three-phase integrated composite conductive powder shown is denoted as powder P.

[0045] The technical solution of the present invention will be further described and illustrated below through specific embodiments. It should be understood that the specific embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the present invention. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commonly used raw materials in the art, and the methods used in the embodiments are all conventional methods in the art. Example 1

[0046] A method for preparing a low-temperature sintering porous copper-silver composite conductive paste includes the following steps: Step 1: Weigh 1.52g of powder P, 0.076g of metallic bismuth powder with a particle size of 0.5-1.0μm, and 0.304g of Bi2O3-B2O3-ZnO-SiO2 series lead-free glass powder (Bi2O3 75%, B2O3 15%, ZnO 5%, SiO2 5%) with a softening point of 380℃. The lead-free glass powder has a particle size of less than 10μm. Place the solid powders in a ball mill jar and mix at 300 rpm for 30 minutes to obtain a uniform mixed powder. Step 2: Weigh 0.5g of organic carrier (composition: 85wt% terpineol, 10wt% ethyl cellulose, 2wt% dispersant BYK-180, 3wt% hydrogenated castor oil), drop it into solid powder and roll it 8 times with a three-roll mill until the fineness is <15μm; Step 3: Apply the conductive paste to the alumina substrate and dry it in a drying oven at 80°C for 15 minutes. Step 4: Place the dried conductive paste into a vacuum sintering furnace, heat it to 350°C at 10°C / min, hold it at that temperature for 30 minutes, cool it to room temperature, and then take it out. Use the four-probe method to measure the sheet resistance at three locations and take the average value.

[0047] Application of a low-temperature sintering porous copper-silver composite conductive paste in conductive components.

[0048] Conductive components include conductive lines or electrodes, which include heat-sensitive conductive lines or electrodes such as flexible electronics, low-temperature co-fired ceramics (LTCC), and heterojunction solar cells.

[0049] A conductive element includes a substrate and a conductive film layer formed on the substrate, the conductive film layer being formed by sintering the conductive paste of this embodiment. Example 2

[0050] The difference between this embodiment and Embodiment 1 is that the peak sintering temperature is adjusted to 300℃, while all other conditions are exactly the same. Example 3

[0051] The only difference between this embodiment and Example 1 is the adjustment of the bismuth powder content. Specifically, 1.52g of powder P, 0.038g of bismuth powder, 0.342g of lead-free glass powder, and 0.5g of organic carrier are weighed. The preparation and sintering processes are the same as in Example 1.

[0052] Comparative Example 1

[0053] The preparation methods for this comparative example are the same as those in Example 1, except that: it does not contain bismuth powder and lead-free glass powder, and 1.9g of powder P and 0.5g of organic carrier are weighed.

[0054] Comparative Example 2

[0055] The preparation methods for this comparative example are the same as those in Example 1, except that: it does not contain bismuth powder, and 1.52g of powder P, 0.38g of lead-free glass powder, and 0.5g of organic carrier are weighed.

[0056] Comparative Example 3

[0057] The preparation methods for this comparative example are the same as those in Example 1, except that: no lead-free glass powder is used, and 1.52g of powder P, 0.38g of metallic bismuth powder, and 0.5g of organic carrier are weighed.

[0058] Comparative Example 4

[0059] The preparation methods for this comparative example are the same as those in Example 1, except that commercially available silver-coated copper powder (silver-coated copper powder (S-U05#) was purchased from Zhuoyue Alloy Powder) was used instead of powder P. The types, amounts, and preparation processes of metallic bismuth powder, lead-free glass powder, and organic carrier are exactly the same as those in Example 2.

[0060] like Figure 2 As shown in (a), in Comparative Example 4, the conductive paste prepared using traditional silver-coated copper powder exhibits numerous pores on the film surface after sintering, resulting in insufficient bonding of conductive particles. Figure 2 As shown in (b), the sintered film layer in the preferred embodiment of the present invention has a dense surface, low porosity, and is fully filled with the glass phase. Figure 2As shown in (c), Comparative Example 3 uses only powder P and bismuth powder as the binder phase, resulting in a loose and porous film. These differences in microstructure demonstrate the effectiveness of the conductive paste formulation proposed in this invention. At a lower sintering temperature, the synergistic effect of bismuth powder and lead-free glass powder achieves high conductivity and high reliability during sintering, which is significantly different from the prior art and demonstrates the innovation and practical value of this invention. Example 4

[0061] A method for preparing a low-temperature sintering porous copper-silver composite conductive paste includes the following steps: 1. Preparation of porous copper framework: 5g of Cu-10Zn alloy powder with a particle size of about 50μm was dispersed in 100ml of deionized water to obtain a mixture. Under ice-water bath conditions, the mixture was slowly poured into 500ml of 0.1mol / L HCl solution and magnetically stirred at 300r / min for 5 hours. After the reaction was completed, the mixture was immediately washed repeatedly with deionized water through vacuum filtration until the filtrate was neutral. Then the filter cake was dried in a vacuum drying oven at 40℃ under flowing argon protection for 5 hours to obtain microalloyed porous copper powder with a three-dimensional interconnected nanoporous structure.

[0062] 2. Silver-studded layer deposition: 2.0 g of the porous copper powder was dispersed in 200 mL of a 0.02 mol / L silver nitrate solution adjusted to pH 9.0 with ammonia. 0.1 mol / L ascorbic acid was added dropwise until the reaction was complete. The mixture was stirred at 300 rpm for 50 minutes at 20 °C, resulting in in-situ deposition of a silver layer on the inner walls and outer surface of the porous framework via a chemical displacement reaction. After the reaction was complete, the mixture was filtered, washed four times each with deionized water and anhydrous ethanol, and then vacuum-dried at 40 °C to obtain the silver-studded porous copper powder.

[0063] 3. Ag-Pd alloy coating: 2.0 g of powder with a silver nail layer was dispersed in 200 ml of deionized water to obtain a powder suspension. 200 mL of a chemical plating solution containing 0.01 mol / L silver nitrate-palladium chloride (Ag:Pd mass ratio controlled at 95:5), 5 g / L potassium sodium tartrate, and 5 mL / L formaldehyde was added to the solution with 1 mol / L NaOH to adjust the pH to 11. The suspension was then added dropwise to the plating solution, and the mixture was stirred at 300 r / min for 10 minutes at 40℃, resulting in a thin Ag-5Pd alloy layer coating on the outermost layer of the powder. After undergoing the same washing and drying process (washing four times each with deionized water and anhydrous ethanol, followed by vacuum drying at 40℃), the final "core-porous-shell" three-phase integrated composite conductive powder was obtained, denoted as powder P.

[0064] A method for preparing a low-temperature sintering porous copper-silver composite conductive paste includes the following steps: Step 1: Weigh 1.678g of powder P based on a total mass of 2.0g, 0.064g of metallic bismuth powder with a particle size less than 1μm, and 0.258g of Bi2O3-B2O3-ZnO-SiO2 series lead-free glass powder (Bi2O3 65%, B2O3 20%, ZnO 10%, SiO2 5%) with a softening point of 300℃. The lead-free glass powder has a particle size of less than 10μm. Place the solid powders in a ball mill jar and mix at 500 rpm for 60 minutes to obtain a uniform mixed powder. Step 2: Weigh 0.22g of organic carrier (composition: 77wt% diethylene glycol butyl ether acetate, 15wt% ethyl cellulose, 3wt% dispersant BYK-180, 5wt% fumed silica), drop it into solid powder and roll it 5 times with a three-roll mill until the fineness is <15μm; Step 3: Apply the conductive paste to the alumina substrate and dry it in a drying oven at 150°C for 5 minutes. Step 4: Place the dried conductive paste into a vacuum sintering furnace, heat it to 250°C at 2°C / min, hold it at that temperature for 10 minutes, cool it to room temperature, and then take it out. Use the four-probe method to measure the sheet resistance at three locations and take the average value.

[0065] Application of a low-temperature sintering porous copper-silver composite conductive paste in conductive components.

[0066] Conductive components include conductive lines or electrodes, which include heat-sensitive conductive lines or electrodes such as flexible electronics, low-temperature co-fired ceramics (LTCC), and heterojunction solar cells.

[0067] A conductive element includes a substrate and a conductive film layer formed on the substrate, the conductive film layer being formed by sintering the conductive paste of this embodiment. Example 5

[0068] A method for preparing a low-temperature sintering porous copper-silver composite conductive paste includes the following steps: 1. Preparation of porous copper framework: 8g of Cu-10Zn alloy powder with a particle size of approximately 40μm was dispersed in 70ml of deionized water to obtain a mixture. Under ice-water bath conditions, the mixture was slowly poured into 300ml of 0.5mol / L HCl solution and magnetically stirred at 500r / min for 6 hours. After the reaction was completed, the mixture was immediately washed repeatedly with deionized water through vacuum filtration until the filtrate was neutral. The filter cake was then dried in a vacuum drying oven at 50℃ under flowing argon protection for 4 hours to obtain microalloyed porous copper powder with a three-dimensional interconnected nanoporous structure.

[0069] 2. Silver-studded layer deposition: 3.0 g of the porous copper powder was dispersed in 300 mL of a 0.03 mol / L silver nitrate solution adjusted to pH 10.0 with ammonia. 0.07 mol / L ascorbic acid was added dropwise until the reaction was complete. The mixture was stirred at 500 rpm for 40 minutes at 30 °C, resulting in in-situ deposition of a silver layer on the inner walls and outer surface of the porous framework via a chemical displacement reaction. After the reaction was complete, the mixture was filtered, washed four times each with deionized water and anhydrous ethanol, and then vacuum-dried at 50 °C to obtain the silver-studded porous copper powder.

[0070] 3. Ag-Pd alloy coating: 3.0 g of powder with a silver nail layer was dispersed in 150 ml of deionized water to obtain a powder suspension. 300 mL of a chemical plating solution containing 0.015 mol / L silver nitrate-palladium chloride (Ag:Pd mass ratio controlled at 95:5), 7 g / L potassium sodium tartrate, and 8 mL / L formaldehyde was added to the solution with 1 mol / L NaOH to adjust the pH to 11. The suspension was then added dropwise to the plating solution, and the mixture was stirred at 500 r / min for 30 minutes at 60℃, resulting in a thin Ag-5Pd alloy layer coating on the outermost layer of the powder. After undergoing the same washing and drying process (washing four times each with deionized water and anhydrous ethanol, followed by vacuum drying at 50℃), the final "core-porous-shell" three-phase integrated composite conductive powder was obtained, denoted as powder P.

[0071] A method for preparing a low-temperature sintering porous copper-silver composite conductive paste includes the following steps: Step 1: Weigh 1.44g of powder P based on a total mass of 2.0g, 0.056g of metallic bismuth powder with a particle size less than 1μm, and 0.504g of Bi2O3-B2O3-ZnO-SiO2 series lead-free glass powder (Bi2O3 65%, B2O3 25%, ZnO 7%, SiO2 3%) with a softening point of 400℃ and a particle size less than 10μm. Place the solid powders in a ball mill jar and mix at 400 rpm for 45 minutes to obtain a uniform mixed powder. Step 2: Weigh 0.35g of organic carrier (composition: 93.5wt% terpineol, 5wt% ethyl cellulose, 0.5wt% dispersant BYK-180, 1wt% fumed silica), drop it into solid powder and roll it 10 times with a three-roll mill until the fineness is <15μm; Step 3: Apply the conductive paste to the alumina substrate and dry it in a drying oven at 100°C for 10 minutes. Step 4: Place the dried conductive paste into a vacuum sintering furnace, heat it to 400°C at 5°C / min, hold it at that temperature for 15 minutes, cool it to room temperature, and then take it out. Use the four-probe method to measure the sheet resistance at three locations and take the average value.

[0072] Application of a low-temperature sintering porous copper-silver composite conductive paste in conductive components.

[0073] Conductive components include conductive lines or electrodes, which include heat-sensitive conductive lines or electrodes such as flexible electronics, low-temperature co-fired ceramics (LTCC), and heterojunction solar cells.

[0074] A conductive element includes a substrate and a conductive film layer formed on the substrate, the conductive film layer being formed by sintering the conductive paste of this embodiment. Example 6

[0075] The only difference between this embodiment and Embodiment 1 is that: Based on a total mass of 2.0g, weigh out 1.7g of powder P, 0.045g of metallic bismuth powder with a particle size less than 1μm, and 0.255g of Bi2O3-B2O3-ZnO-SiO2 series lead-free glass powder (Bi2O3 78%, B2O3 15%, ZnO 5%, SiO2 2%) with a softening point of 350℃ and a particle size less than 10μm. Place the solid powders in a ball mill jar and mix at a speed of 400 rpm for 45 minutes to obtain a uniform mixed powder.

[0076] Specifically, the performance of the embodiments and comparative examples is shown in Table 1.

[0077] Table 1 Performance of samples obtained in Examples 1-6 and Comparative Examples 1-4

[0078] It should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the above description of exemplary embodiments of the invention. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all the features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0079] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low-temperature sintering porous copper-silver composite conductive paste, characterized in that: It consists of solid powder and organic carrier, wherein the organic carrier accounts for 10-21% of the total mass; The solid powder consists of a conductive functional phase and an inorganic binder phase; The conductive functional phase is a composite metal powder with a porous copper skeleton, silver nail layer, and Ag-Pd alloy shell. The inorganic binder phase consists of metallic bismuth powder and lead-free glass powder; metallic bismuth powder accounts for 2-4% of the total mass of the solid powder, and the particle size of metallic bismuth powder is less than 1 μm; the softening point of lead-free glass powder is 300-400℃, and the lead-free glass powder accounts for 12-25% of the total mass of the solid powder, and the particle size of lead-free glass powder is less than 10 μm; the conductive functional phase accounts for 71-86% of the total mass of the solid powder.

2. The low-temperature sintering porous copper-silver composite conductive paste according to claim 1, characterized in that: The composition of lead-free glass powder by weight percentage includes: Bi2O3 65-78%, B2O3 15-25%, ZnO 5-10% and SiO2 2-5%.

3. The low-temperature sintering porous copper-silver composite conductive paste according to claim 1, characterized in that: The organic carrier contains, by weight percentage: 77-93.5% solvent, 5-15% resin, 0.5-3% dispersant, and 1-5% thixotropic agent.

4. The low-temperature sintering porous copper-silver composite conductive paste according to claim 3, characterized in that: The solvent is one or more of terpineol, diethylene glycol butyl ether acetate, or terpineol; the resin is ethyl cellulose; the dispersant is a phosphate ester or a BYK series dispersant; and the thixotropic agent is hydrogenated castor oil or fumed silica.

5. The low-temperature sintering porous copper-silver composite conductive paste according to claim 1, characterized in that: The conductive functional phase uses Cu-Zn microalloyed porous copper powder as the framework, with silver nailing layers deposited in situ within the pores, and an Ag-Pd alloy layer as the outer shell.

6. A method for preparing a low-temperature sintering porous copper-silver composite conductive paste according to any one of claims 1 to 5, characterized in that: Includes the following steps: Step 1, Preparation of conductive functional phase powder: Disperse 5-10g of Cu-Zn alloy powder with a particle size of 30-50μm in 50-100ml of deionized water to obtain a mixed solution. Pour the mixed solution into 200-500ml of 0.1-0.5mol / L HCl solution and stir magnetically at 300-500r / min for 5-7 hours. After the reaction is completed, immediately wash the filter cake repeatedly with deionized water through vacuum filtration until the filtrate is neutral. Then dry the filter cake in a vacuum drying oven at 40-60℃ under flowing argon protection for 3-5 hours to obtain microalloyed porous copper powder with a three-dimensional interconnected nanoporous structure. Silver-studded layer deposition: 2.0-5.0 g of microalloyed porous copper powder with a three-dimensional interconnected nanoporous structure is immersed in 200-500 mL of 0.02-0.05 mol / L silver nitrate solution adjusted to pH=9.0-11.0 with ammonia water. 0.05-0.1 mol / L ascorbic acid is added dropwise for reduction. The mixture is stirred at 300-500 r / min at 20-40℃ for 30-50 minutes. A silver layer is deposited in situ on the inner wall and outer surface of the porous framework through a chemical displacement reaction. After the reaction is completed, the mixture is filtered, washed multiple times with deionized water and anhydrous ethanol, and vacuum dried at 40-60℃ to obtain silver-studded porous copper powder. Ag-Pd alloy layer coating: 2.0-4.0g of porous copper powder with silver studs is dispersed in 100-200ml of deionized water to obtain a powder suspension. The suspension is added dropwise to a chemical plating solution with a pH of 11-12 and containing 0.01-0.02mol / L silver nitrate-palladium chloride, 5-10g / L potassium sodium tartrate, and 5-10mL / L formaldehyde. The mixture is stirred at 300-500r / min for 10-30 minutes at 40-60℃ to coat the outermost layer of the powder with an Ag-5Pd alloy layer. The powder is washed multiple times with deionized water and anhydrous ethanol, and then vacuum dried at 40-60℃ to obtain the final core-porous-shell three-phase integrated composite conductive powder, i.e., conductive functional phase powder. Step 2, slurry rolling: After uniformly mixing the conductive functional phase powder, metallic bismuth powder and lead-free glass powder, the mixture is rolled with the organic carrier through a three-roll mill 5-10 times until the slurry fineness is ≤15μm; Step 3, Coating and Drying: Apply the paste to the substrate by screen printing or scraping, and dry at 80-150℃ for 5-15 minutes; Step 4, low-temperature sintering: In a protective atmosphere or vacuum, the temperature is programmed to rise to 250-400℃ at a rate of 2-10℃ / min, and held for 10-30 minutes to complete the sintering process.

7. The preparation method according to claim 6, characterized in that: In step one, the mass ratio of Ag:Pd in ​​silver nitrate-palladium chloride is controlled to be 95:

5.

8. The preparation method according to claim 6, characterized in that: In step two, the mixing method is as follows: place the solid powder in a ball mill jar and mix at a speed of 300-500 rpm for 30-60 minutes to obtain a uniform mixed powder.

9. The application of a low-temperature sintering porous copper-silver composite conductive paste according to any one of claims 1 to 5 in conductive components, characterized in that: Conductive elements include conductive lines or electrodes, which include flexible electronics, low-temperature co-fired ceramic (LTCC), and heterojunction solar cells.

10. A conductive element, characterized in that: The invention includes a substrate and a conductive film layer formed on the substrate. The substrate includes an alumina substrate. The conductive film layer is prepared by a low-temperature sintering porous copper-silver composite conductive paste according to any one of claims 1 to 5. The sheet resistance of the conductive film layer is 0.085-0.103mΩ and the adhesion is 4B-5B.

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