Tin-lead conductive paste based on bimodal particle size distribution and preparation method thereof

Abstract

The invention relates to the technical field of photovoltaic cell materials, and particularly discloses tin-lead conductive paste based on bimodal particle size distribution and a preparation method thereof, and the tin-lead conductive paste is composed of 40%-70% of T5 tin-lead alloy powder, 1%-30% of T6 tin-lead alloy powder and 5%-15% of an organic carrier. The core of the invention lies in that a tin-lead alloy system with the best comprehensive performance is preferably selected as a conductive phase, and on the basis, the defects of the existing low-temperature tin-lead paste in microstructure are fundamentally overcome by introducing a double-peak particle size distribution design; therefore, the electrode paste which is low in cost, low in process temperature, high in conductivity, strong in adhesion and low in contact resistance and is excellent in comprehensiveness is provided. Tin-lead alloy powder with bimodal particle size distribution is adopted as a conductive phase, and particularly, the tin-lead alloy powder is a compound system of T5 (15 microns to 25 microns) and T6 (5 microns to 15 microns) tin-lead alloy powder. Compared with the prior art, the method has the effects of remarkably improving the printing quality and precision, remarkably improving the conductivity and quality, optimizing the cost and improving the material stability.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic cell materials technology, and in particular to a tin-lead conductive paste based on a bimodal particle size distribution and its preparation method. Background Technology

[0002] Crystalline silicon solar cells are the core components for photoelectric conversion, with their electrodes playing a crucial role in collecting and transmitting photocurrent. The performance of the electrodes directly determines the cell's series resistance, fill factor, and ultimately, the photoelectric conversion efficiency. Currently, the electrodes of commercially available crystalline silicon solar cells are primarily fabricated using conductive pastes through screen printing and high-temperature sintering. In this technological approach, silver paste has long held a dominant position due to its excellent conductivity and ability to form good ohmic contact with the antireflective coating on the silicon wafer at high temperatures. The basic principle is as follows: a paste composed of micron- or submicron-sized silver powder, glass powder, and an organic carrier is precisely screen-printed onto the silicon wafer surface to form a grid pattern, followed by rapid heat treatment in a belt sintering furnace exceeding 700°C. During this process, the organic carrier is volatilized and burned, the glass powder melts and slightly erodes the antireflective layer, promoting a strong, low-contact-resistance ohmic contact between the silver conductor and the silicon substrate. Simultaneously, the silver particles themselves sinter into a continuous three-dimensional conductive network.

[0003] However, this existing technology, which relies primarily on high-temperature sintering of silver paste, suffers from several inherent drawbacks that are difficult to overcome. First, high cost is a major bottleneck. Silver is a precious metal, and its price is expensive and highly volatile, directly increasing the manufacturing cost of solar cells and becoming a key factor restricting further cost reduction and efficiency improvement in the photovoltaic industry. Second, the process is energy-intensive and unfriendly to the substrate. The high-temperature sintering process, exceeding 700°C, consumes a large amount of energy. Simultaneously, the high-temperature thermal stress on silicon wafers, especially increasingly thinner high-efficiency wafers (such as N-type and PERC cells), can lead to increased breakage rates, cell warping, and a decrease in minority carrier lifetime, thus affecting cell performance and yield. Furthermore, while the glass powder in the silver paste forms ohmic contacts by etching the antireflection layer, it may also form an excessive glass layer at the interface or undergo an excessive "silver-glass eutectic" reaction, damaging the passivation layer on the silicon wafer surface and leading to increased recombination.

[0004] To address the cost issues of silver paste, the industry has explored alternatives using base metals such as copper, aluminum, and tin. Among these, solder paste systems have attracted attention due to their good conductivity, solderability, and relatively mature process foundation. However, these low-temperature curing solder pastes have significant technical drawbacks. The primary problem lies in the difficulty of simultaneously achieving good conductivity and adhesion at their electrodes, and they are generally inferior to high-temperature silver pastes.

[0005] Structurally, the reasons are as follows: First, existing solder pastes mostly use tin powder with a single particle size or normal distribution. After curing, the packing density between the tin powder particles is low, resulting in more pores. This leads to greater scattering and tunneling resistance during electron transport, manifesting as a higher bulk resistivity. Second, its conductivity and mechanical strength are highly dependent on the cured film formed by the organic resin binder. The resin itself is non-conductive; excessive addition will coat the surface of conductive particles, hindering direct contact between metal particles and significantly increasing contact resistance. Conversely, insufficient resin will result in insufficient adhesion between the paste and the silicon substrate, poor electrode mechanical strength, and easy detachment during subsequent soldering or transportation. Third, due to the lack of an "anchoring" mechanism similar to that of glass powder in silver paste, the solder paste and the silicon wafer surface are mainly bonded by physical adsorption and weak van der Waals forces, resulting in typically high contact resistance and weak adhesion.

[0006] Therefore, developing an electrode material that can take into account the advantages of low-temperature processing and match or approach the performance of traditional silver paste in key properties such as conductivity, adhesion and contact resistance has become an urgent technical need in the photovoltaic field. Summary of the Invention

[0007] The purpose of this invention is to provide a tin-lead conductive paste based on a bimodal particle size distribution and its preparation method. By introducing a bimodal particle size distribution design, the defects in the microstructure of existing low-temperature tin-lead pastes are fundamentally solved, thereby providing a comprehensive electrode paste with advantages of low cost, low-temperature processing, high conductivity, strong adhesion and low contact resistance, thus solving the problems encountered in the above-mentioned background art.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] A tin-lead conductive paste based on bimodal particle size distribution and its preparation method are disclosed, comprising 40%-70% T5 tin-lead alloy powder, 1%-30% T6 tin-lead alloy powder, and 5%-15% organic carrier.

[0010] In the above scheme, the average particle size of the T5 tin-lead alloy powder is 15-25 μm, and the T5 tin-lead alloy powder is composed of 50-70% Sn and 30-45% Pb. The particles of the T5 tin-lead alloy powder are in contact with each other in the slurry, forming a stable three-dimensional spatial network, which constitutes the main pathway of the conductive network, and provides a framework for filling and adhering to the particles of the T6 tin-lead alloy powder during the curing process.

[0011] The T5 particles contact each other in the slurry, forming a stable three-dimensional network. This rigid framework structure greatly enhances the anti-collapse ability of the wet slurry after screen printing, effectively preventing the finely printed electrode grid lines from flowing, spreading, or deforming before subsequent curing, thus ensuring the high precision and high resolution of the final electrode pattern. Secondly, due to the lower specific surface area of ​​the large-diameter particles, the introduction of T5 powder relatively reduces the total amount of organic binder required to completely encapsulate the conductive particles. This makes it possible to achieve a higher metal content in the formulation, laying the material foundation for obtaining a low-resistance electrode. Therefore, the core role of T5 tin-lead alloy powder is to form the main pathway of the conductive network and provide a framework for filling and adhering to the finer T6 particles during the curing process.

[0012] In the above scheme, the T6 tin-lead alloy powder has an average particle size of 5-15 μm and is composed of 50-70% Sn and 30-45% Pb. The T6 tin-lead alloy powder acts as a highly efficient interstitial filler in the preparation of the slurry, filling the macroscopic voids formed by the particle accumulation of the T5 tin-lead alloy powder.

[0013] Due to its relatively finer particle size, T6 powder primarily functions as a highly efficient interstitial filler. When mixed with larger-sized T5 powder, it precisely fills the macroscopic voids formed by the accumulation of T5 particles. This close packing effect of coarse-fine particles significantly increases the packing density of the conductive film layer formed after curing. This densified microstructure directly translates into two core advantages: firstly, it greatly increases the contact points and contact area between conductive metal particles, forming a more developed and interconnected three-dimensional conductive network during curing, thereby significantly reducing the bulk resistivity of the electrode and improving charge transfer efficiency; secondly, the dense structure reduces porosity, enhancing the mechanical strength of the electrode.

[0014] In the above scheme, the organic carrier includes 10wt% to 20wt% organic solvent, 5wt% to 15wt% rosin, 0.5wt% to 2.5wt% curing agent, 1wt% to 3wt% organic acid, 0.5wt% to 1.5wt% thixotropic agent, and 1.5wt% to 2.5wt% defoamer.

[0015] Organic solvents play a crucial role in the slurry system by dissolving organic binders (such as epoxy resin and acrylic resin) and dispersing functional components (such as conductive fillers and additives) to form a uniform and stable processing system. By adjusting the type and ratio of solvents, the viscosity, evaporation rate, and rheological properties of the slurry can be precisely controlled, directly determining the slurry's screen printing suitability and spreading effect, and ultimately affecting the density, defect level, and electrical properties of the cured film. The organic solvents are one or more of diethylene glycol butyl ether, diethyl carbonate, cyclohexanone, dodecyl glycidyl ether, and terpineol, with a content of 10wt% to 20wt%. The organic solvents improve the viscosity and rheological properties of T6 tin-lead alloy powder within the voids of T5 tin-lead alloy powder, resulting in greater uniformity and density.

[0016] Rosin, containing rosin acid, effectively removes the oxide film on the surface of metal fillers, significantly improves the wettability of liquid solder to metals, and promotes reliable ohmic contact at the welding interface. Simultaneously, it melts and flows upon heating, and forms a dense protective film upon cooling, which helps fix the conductive network, enhances adhesion, and isolates air to prevent secondary oxidation, thereby improving the overall solderability of the slurry and the long-term reliability of the solder joint. The rosin includes, but is not limited to, one or more of modified epoxy resin and polymerized rosin, with a content of 5wt%~15wt%. Rosin here improves the adhesion of T6 tin-lead alloy powder to the voids in T5 tin-lead alloy powder, facilitating subsequent welding and enhancing post-weld reliability.

[0017] The curing agent's core function is to cross-link with the resin matrix in the slurry system, transforming it from a liquid to a solid state by forming a stable three-dimensional network structure. This curing agent includes, but is not limited to, one or more of triethanolamine, ethylenediamine, diethylenetriamine, and triethylenetetramine, with a content ranging from 0.5wt% to 2.5wt%. The curing agent enhances the three-dimensional network structure of T6 tin-lead alloy powder within the voids of T5 tin-lead alloy powder.

[0018] Among them, organic acids: The carboxyl groups and other functional groups in organic acid molecules can be firmly adsorbed on the surface of conductive powders (such as metal particles). By forming a strong electric double layer or providing steric hindrance, they effectively overcome the interparticle attraction caused by van der Waals forces, thereby preventing particle aggregation and sedimentation, and ensuring that the slurry obtains excellent consistency and long-term storage stability. These include, but are not limited to, one or more of anhydrous oxalic acid, formic acid, malonic acid, and adipic acid, with a content of 1wt% to 3wt%. Organic acids can also improve the consistency and stability of T6 tin-lead alloy powder in the voids of T5 tin-lead alloy powder.

[0019] Thixotropic agents are used to impart good thixotropic properties to the slurry, ensuring that the printed grid lines have clear outlines and high resolution. They include, but are not limited to, one or more combinations of hydrogenated castor oil, polyethylene wax, and inorganic gelling agents, with a content of 0.5wt% to 1.5wt%.

[0020] Among them, defoamers: The core function of defoamers is to puncture existing bubbles by rapidly spreading and reducing local surface tension, thereby eliminating foam in the system. Simultaneously, they inhibit foam regeneration, preventing defects such as pinholes and fisheyes caused by bubbles during production and film formation, ensuring the density and integrity of the final product. Defoamers include, but are not limited to, one or more combinations of tributyl phosphate, acetylacetonate tributyl citrate (ATBC), and dipropylene glycol butyl ether acetate, at a content of 1.5wt% to 2.5wt%. The defoamer here improves the density of T6 tin-lead alloy powder within the voids of T5 tin-lead alloy powder, eliminating foam within the voids.

[0021] A method for preparing a tin-lead conductive paste based on a bimodal particle size distribution is characterized by: firstly, preparing a carrier; then mixing in T5 and T6 tin-lead alloy powders; and finally, fine rolling and dispersing the mixed paste.

[0022] First, accurately weigh each component required for the organic carrier according to the design ratio. Under continuous stirring and moderate heating, add the organic solvent, rosin, curing agent, organic acid, thixotropic agent and defoamer to the reaction vessel in sequence. Stir thoroughly to completely dissolve and mix them evenly, and finally form a uniform and stable organic carrier system.

[0023] Subsequently, a specific ratio of T5 and T6 tin-lead alloy powders was slowly added to the prepared organic carrier, and a planetary mixer was used to perform preliminary mixing at a low speed to ensure that the powder was fully wetted.

[0024] Finally, the pre-mixed slurry is transferred to a three-roll mill for multiple rolling and dispersion passes. The strong shearing force generated between the rollers further breaks up the powder agglomerates, promoting a highly uniform distribution of the metal powder in the organic system.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] This invention employs a bimodal particle size distribution tin-lead alloy powder as the conductive phase, specifically a compound system of T5 (15μm-25μm) and T6 (5μm-15μm) tin-lead alloy powders. Compared to existing technologies, this invention significantly improves printing quality and precision, significantly enhances conductivity and quality, optimizes costs, and improves material stability.

[0027] Specifically, in terms of structural features: by introducing T6 small-particle-size tin-lead alloy powder, its fine particles can pass through the screen mesh more smoothly. Compared with existing technologies, this effectively eliminates printing defects such as jagged edges and loose connections that occur when using T5 alloy powder alone, making the edges of printed graphics clearer and the lines more complete, greatly improving printing quality and product appearance precision.

[0028] Specifically, in terms of structural characteristics: the bimodal particle size distribution generates a dense packing effect, enabling the construction of a more complete and dense conductive network during slurry curing. Compared to existing technologies, this fundamentally improves the void problem caused by poor conductive phase structure, significantly enhancing the conductivity of the slurry and thus improving the performance and reliability of the final product.

[0029] Specifically, in terms of structural characteristics: by optimizing the ratio of T5 and T6 tin-lead alloy powders, the amount of expensive T6 small-particle-size alloy powder used is reduced while ensuring performance. Compared with existing technologies, this avoids the use of high-cost T6 tin-lead alloy powder throughout, achieving cost minimization while maintaining or improving performance. Simultaneously, it improves stability and reduces oxidation risk. Because T6 powder has a large specific surface area and is more easily oxidized, reducing its usage lowers the overall oxidation tendency of the slurry, which helps maintain long-term stability of conductivity and indirectly reduces losses caused by poor performance. Attached Figure Description

[0030] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts. Wherein:

[0031] Figure 1 This is a process and technical route diagram of the present invention;

[0032] Figure 2 This is a schematic diagram of the resistivity of Comparative Example 1 in this invention;

[0033] Figure 3 This is a resistivity diagram of Embodiment 1 in this invention;

[0034] Figure 4 This is a resistivity diagram of Embodiment 2 in this invention;

[0035] Figure 5 This is a resistivity diagram of Embodiment 3 in this invention;

[0036] Figure 6 This is a resistivity diagram of Embodiment 4 in this invention. Detailed Implementation

[0037] To make the technical means, creative features, objectives, and effects of this invention readily understandable, the invention will now be described in further detail with reference to the accompanying drawings. These drawings are simplified schematic diagrams, illustrating only the basic structure of the invention, and therefore only show the relevant components of the invention.

[0038] According to the technical solution of the present invention, without changing the essential spirit of the present invention, those skilled in the art can propose various interchangeable structural methods and implementations. Therefore, the following detailed embodiments and accompanying drawings are merely exemplary descriptions of the technical solution of the present invention, and should not be regarded as the entirety of the present invention or as a limitation or restriction of the technical solution of the present invention.

[0039] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0040] A tin-lead conductive paste based on bimodal particle size distribution, please refer to [link / reference]. Figure 1 It consists of 40%-70% T5 tin-lead alloy powder, 1%-30% T6 tin-lead alloy powder, and 5%-15% organic carrier.

[0041] In the above scheme, the average particle size of the T5 tin-lead alloy powder is 15-25 μm, and the T5 tin-lead alloy powder is composed of 50-70% Sn and 30-45% Pb. The particles of the T5 tin-lead alloy powder are in contact with each other in the slurry, forming a stable three-dimensional spatial network, which constitutes the main pathway of the conductive network, and provides a framework for filling and adhering to the particles of the T6 tin-lead alloy powder during the curing process.

[0042] In the above scheme, the T6 tin-lead alloy powder has an average particle size of 5-15 μm and is composed of 50-70% Sn and 30-45% Pb. The T6 tin-lead alloy powder acts as a highly efficient interstitial filler in the preparation of the slurry, filling the macroscopic voids formed by the particle accumulation of the T5 tin-lead alloy powder.

[0043] In the above scheme, the organic carrier includes 10wt% to 20wt% organic solvent, 5wt% to 15wt% rosin, 0.5wt% to 2.5wt% curing agent, 1wt% to 3wt% organic acid, 0.5wt% to 1.5wt% thixotropic agent, and 1.5wt% to 2.5wt% defoamer.

[0044] A method for preparing a tin-lead conductive paste based on a bimodal particle size distribution involves first preparing a carrier; then mixing in T5 and T6 tin-lead alloy powders; and finally, fine rolling and dispersing the mixed paste.

[0045] Specifically, first, the components required for the organic carrier are precisely weighed according to the design ratio. Under continuous stirring and moderate heating, the organic solvent, rosin, curing agent, organic acid, thixotropic agent and defoamer are added to the reaction vessel in sequence. The mixture is thoroughly stirred to completely dissolve and mix evenly, thus forming a uniform and stable organic carrier system.

[0046] Subsequently, a specific ratio of T5 and T6 tin-lead alloy powders was slowly added to the prepared organic carrier, and a planetary mixer was used to perform preliminary mixing at a low speed to ensure that the powder was fully wetted.

[0047] Finally, the pre-mixed slurry is transferred to a three-roll mill for multiple rolling and dispersion passes. The strong shearing force generated between the rollers further breaks up the powder agglomerates, promoting a highly uniform distribution of the metal powder in the organic system.

[0048] This invention aims to address the core problems of high-temperature silver paste, which relies on high-temperature sintering and the use of precious metal silver, resulting in high cost, high energy consumption, and significant thermal damage to the silicon substrate. Therefore, this invention seeks to utilize a base metal system capable of low-temperature curing for electrode fabrication. Among numerous candidate materials, tin-based alloys, particularly tin-lead alloys, exhibit comprehensive advantages.

[0049] While ensuring good conductivity, it has a suitable melting point, excellent oxidation resistance and weldability. Its process maturity and comprehensive performance are the most outstanding among various tin-based alloys, making it an ideal choice for low-temperature, low-cost electrode manufacturing.

[0050] However, directly applying existing low-temperature curing tin-lead pastes still faces inherent drawbacks. Therefore, the specific problems that this invention further aims to solve include:

[0051] 1. Solve the printing defects caused by existing pastes in screen printing. Due to the relatively large particle size of T5 tin-lead alloy powder, serrated or loosely connected screen printing defects may occur. After adding T6 tin-lead alloy powder, the smaller particles can pass through the screen better, effectively solving the defects left by screen printing.

[0052] 2. This invention addresses the void problem that occurs during low-temperature curing of existing low-temperature tin-lead pastes due to poor conductive phase structure. The invention aims to utilize tin-lead alloy powder with a bimodal particle size distribution and its close packing effect to construct a more complete conductive network during paste curing, reducing voids and significantly improving conductivity.

[0053] 3. This invention addresses the issues of high cost and easy oxidation of existing slurries. Because T6 tin-lead alloy powder consists of small particles, it is more expensive than T5 tin-lead alloy powder. Furthermore, due to its smaller particle size and larger specific surface area, T6 alloy powder is more prone to oxidation during production and application, thus affecting conductivity. This slurry utilizes a bimodal particle size distribution, effectively improving conductivity while minimizing cost.

[0054] In summary, the core of this invention lies in selecting the tin-lead alloy system with the best overall performance as the conductive phase, and on this basis, by introducing a bimodal particle size distribution design, fundamentally solving the defects in the microstructure of existing low-temperature tin-lead pastes, thereby providing a comprehensive electrode paste that combines low cost, low-temperature processing, high conductivity, strong adhesion and low contact resistance.

[0055] The following examples illustrate this in detail, using a comparative example that provides only one type of T5 tin-lead alloy powder, and four examples that include both T5 and T6 tin-lead alloy powders.

[0056] Comparative Example 1

[0057] Step (1): Place 15wt% cyclohexanone and 10wt% polymerized rosin into a constant temperature magnetic stirrer oil bath and heat for 35-45 minutes. The oil bath temperature is 120-140℃ and the stirrer speed is 100 rpm. Place 20g of modified epoxy resin into a constant temperature magnetic stirrer oil bath and heat for 40 minutes. The oil bath temperature is 120-140℃ and the stirrer speed is 100 rpm.

[0058] Step (2): Mix 1.5wt% ethylenediamine, 0.8wt% polyethylene wax, 1wt% anhydrous oxalic acid and 1.7wt% dipropylene glycol butyl ether acetate, heat in an oil bath for 5 hours, the oil bath temperature is 90-110℃, and the stirrer speed is 250rpm.

[0059] Step (3): Grind using a three-roll mill with a front roller gap of 20 micrometers and a rear roller gap of 10 micrometers, for 7 grinding cycles;

[0060] Step (4): Add 70wt% T5 tin-lead alloy powder to the ground carrier. Add the corresponding amount of metal powder and carrier together to a double planetary stirrer for stirring. Stir for 5-10 minutes under standard atmospheric pressure, and then stir for 5-10 minutes under vacuum. The stirrer speed is 300 rpm.

[0061] Step (5): Print graphics of different widths onto a substrate using screen printing technology;

[0062] Step (6): Place the substrate in a tunnel furnace for curing and sintering;

[0063] Step (7): Finally, the resistivity at gate linewidths of 500 μm and 200 μm was measured using the four-probe method. Figure 2 As shown.

[0064] Example 1

[0065] Step (1): Place 15wt% cyclohexanone and 10wt% polymerized rosin into a constant temperature magnetic stirrer oil bath and heat for 35-45 minutes. The oil bath temperature is 120-140℃ and the stirrer speed is 100 rpm. Place 20g of modified epoxy resin into a constant temperature magnetic stirrer oil bath and heat for 40 minutes. The oil bath temperature is 120-140℃ and the stirrer speed is 100 rpm.

[0066] Step (2): Mix 1.5wt% ethylenediamine, 0.8wt% polyethylene wax, 1wt% anhydrous oxalic acid and 1.7wt% dipropylene glycol butyl ether acetate, heat in an oil bath for 5 hours, the oil bath temperature is 90-110℃, and the stirrer speed is 250rpm.

[0067] Step (3): Grind using a three-roll mill with a front roller gap of 20 micrometers and a rear roller gap of 10 micrometers, for 7 grinding cycles;

[0068] Step (4): Add 63wt% T5 tin-lead alloy powder and 7wt% T6 tin-lead alloy powder to the ground carrier. Add the corresponding amounts of metal powder and carrier to a double planetary stirrer for stirring. Stir for 5-10 minutes under standard atmospheric pressure, and then stir for 5-10 minutes under vacuum. The stirrer speed is 300 rpm.

[0069] Step (5): Print the prepared paste into graphics of different widths on the substrate using screen printing technology;

[0070] Step (6): Place the substrate in a tunnel furnace for curing and sintering;

[0071] Step (7): Finally, the resistivity at gate linewidths of 500 μm and 200 μm was measured using the four-probe method. Figure 3 As shown.

[0072] Example 2

[0073] Step (1): Place 15wt% cyclohexanone and 10wt% polymerized rosin into a constant temperature magnetic stirrer oil bath and heat for 35-45 minutes. The oil bath temperature is 120-140℃ and the stirrer speed is 100 rpm. Place 20g of modified epoxy resin into a constant temperature magnetic stirrer oil bath and heat for 40 minutes. The oil bath temperature is 120-140℃ and the stirrer speed is 100 rpm.

[0074] Step (2): Mix 1.5wt% ethylenediamine, 0.8wt% polyethylene wax, 1wt% anhydrous oxalic acid and 1.7wt% dipropylene glycol butyl ether acetate, heat in an oil bath for 5 hours, the oil bath temperature is 90-110℃, and the stirrer speed is 250rpm.

[0075] Step (3): Grind using a three-roll mill with a front roller gap of 20 micrometers and a rear roller gap of 10 micrometers, for 7 grinding cycles;

[0076] Step (4): Add 56wt% T5 tin-lead alloy powder and 14wt% T6 tin-lead alloy powder to the ground carrier. Add the corresponding amounts of metal powder and carrier to a double planetary stirrer for stirring. Stir for 5-10 minutes under standard atmospheric pressure, and then stir for 5-10 minutes under vacuum. The stirrer speed is 300 rpm.

[0077] Step (5): Print graphics of different widths onto a substrate using screen printing technology;

[0078] Step (6): Place the substrate in a tunnel furnace for curing and sintering;

[0079] Step (7): Finally, the resistivity at gate linewidths of 500 μm and 200 μm was measured using the four-probe method. Figure 4 As shown.

[0080] Example 3

[0081] Step (1): Place 15wt% cyclohexanone and 10wt% polymerized rosin into a constant temperature magnetic stirrer oil bath and heat for 35-45 minutes. The oil bath temperature is 120-140℃ and the stirrer speed is 100 rpm. Place 20g of modified epoxy resin into a constant temperature magnetic stirrer oil bath and heat for 40 minutes. The oil bath temperature is 120-140℃ and the stirrer speed is 100 rpm.

[0082] Step (2): Mix 1.5wt% ethylenediamine, 0.8wt% polyethylene wax, 1wt% anhydrous oxalic acid and 1.7wt% dipropylene glycol butyl ether acetate, heat in an oil bath for 5 hours, the oil bath temperature is 90-110℃, and the stirrer speed is 250rpm.

[0083] Step (3): Grind using a three-roll mill with a front roller gap of 20 micrometers and a rear roller gap of 10 micrometers, for 7 grinding cycles;

[0084] Step (4): Add 49wt% T5 tin-lead alloy powder and 21wt% T6 tin-lead alloy powder to the ground carrier. Add the corresponding amounts of metal powder and carrier to a double planetary stirrer for stirring. Stir for 5-10 minutes under standard atmospheric pressure, and then stir for 5-10 minutes under vacuum. The stirrer speed is 300 rpm.

[0085] Step (5): Print graphics of different widths onto a substrate using screen printing technology;

[0086] Step (6): Place the substrate in a tunnel furnace for curing and sintering;

[0087] Step (7): Finally, the resistivity at gate linewidths of 500 μm and 200 μm was measured using the four-probe method. Figure 5 As shown.

[0088] Example 4

[0089] Step (1): Place 15wt% cyclohexanone and 10wt% polymerized rosin into a constant temperature magnetic stirrer oil bath and heat for 35-45 minutes. The oil bath temperature is 120-140℃ and the stirrer speed is 100 rpm. Place 20g of modified epoxy resin into a constant temperature magnetic stirrer oil bath and heat for 40 minutes. The oil bath temperature is 120-140℃ and the stirrer speed is 100 rpm.

[0090] Step (2): Mix 1.5wt% ethylenediamine, 0.8wt% polyethylene wax, 1wt% anhydrous oxalic acid and 1.7wt% dipropylene glycol butyl ether acetate, heat in an oil bath for 5 hours, the oil bath temperature is 90-110℃, and the stirrer speed is 250rpm.

[0091] Step (3): Grind using a three-roll mill with a front roller gap of 20 micrometers and a rear roller gap of 10 micrometers, for 7 grinding cycles;

[0092] Step (4): Add 42wt% T5 tin-lead alloy powder and 28wt% T6 tin-lead alloy powder to the ground carrier. Add the corresponding amounts of metal powder and carrier to a double planetary stirrer for stirring. Stir for 5-10 minutes under standard atmospheric pressure, and then stir for 5-10 minutes under vacuum. The stirrer speed is 300 rpm.

[0093] Step (5): Print graphics of different widths onto a substrate using screen printing technology;

[0094] Step (6): Place the substrate in a tunnel furnace for curing and sintering;

[0095] Step (7): Finally, the resistivity at gate linewidths of 500 μm and 200 μm was measured using the four-probe method. Figure 6As shown.

[0096] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. 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 tin-lead conductive paste based on a bimodal particle size distribution, characterized in that: It consists of 40%-70% T5 tin-lead alloy powder, 1%-30% T6 tin-lead alloy powder, and 5%-15% organic carrier.

2. The tin-lead conductive paste based on bimodal particle size distribution according to claim 1, characterized in that: The average particle size of the T5 tin-lead alloy powder is 15-25 μm, and the T5 tin-lead alloy powder is composed of 50-70% Sn and 30-45% Pb.

3. The tin-lead conductive paste based on bimodal particle size distribution according to claim 2, characterized in that: The T5 tin-lead alloy powder is composed of 63% Sn and 37% Pb.

4. A tin-lead conductive paste based on a bimodal particle size distribution according to claim 2 or 3, characterized in that: The particles of the T5 tin-lead alloy powder come into contact with each other in the slurry, forming a stable three-dimensional spatial network, which constitutes the main path of the conductive network, and provides a framework for filling and adhering to the particles of the T6 tin-lead alloy powder during the curing process.

5. The tin-lead conductive paste based on bimodal particle size distribution according to claim 1, characterized in that: The T6 tin-lead alloy powder has an average particle size of 5-15 μm and is composed of 50-70% Sn and 30-45% Pb.

6. A tin-lead conductive paste based on a bimodal particle size distribution according to claim 5, characterized in that: The T6 tin-lead alloy powder is composed of 63% Sn and 37% Pb.

7. A tin-lead conductive paste based on a bimodal particle size distribution according to claim 5 or 6, characterized in that: The T6 tin-lead alloy powder acts as a highly efficient gap filler when making slurry, filling the macroscopic voids formed by the particle accumulation of the T5 tin-lead alloy powder.

8. A tin-lead conductive paste based on a bimodal particle size distribution according to claim 1, characterized in that: The organic carrier comprises 10wt% to 20wt% organic solvent, 5wt% to 15wt% rosin, 0.5wt% to 2.5wt% curing agent, 1wt% to 3wt% organic acid, 0.5wt% to 1.5wt% thixotropic agent, and 1.5wt% to 2.5wt% defoamer. The organic solvent is one or more of diethylene glycol butyl ether, diethyl carbonate, cyclohexanone, dodecyl glycidyl ether, and terpineol; the rosin is one or more of modified epoxy resin and polymerized rosin; the curing agent is one or more of triethanolamine, ethylenediamine, diethylenetriamine, and triethylenetetramine; the organic acid is one or more of anhydrous oxalic acid, formic acid, malonic acid, and adipic acid; the thixotropic agent is one or more of hydrogenated castor oil, polyethylene wax, and inorganic gelling agents; and the defoamer is one or more of tributyl phosphate, acetylacetonate tributyl citrate (ATBC), and dipropylene glycol butyl ether acetate.

9. A method for preparing a tin-lead conductive paste based on a bimodal particle size distribution according to any one of claims 1-8, characterized in that: First, the carrier material is prepared; then T5 and T6 tin-lead alloy powders are mixed in, and finally the mixed slurry is finely rolled and dispersed.

10. The method for preparing a tin-lead conductive paste based on a bimodal particle size distribution according to claim 9, characterized in that: First, accurately weigh each component required for the organic carrier according to the design ratio. Under continuous stirring and moderate heating, add the organic solvent, rosin, curing agent, organic acid, thixotropic agent and defoamer to the reaction vessel in sequence. Stir thoroughly to completely dissolve and mix them evenly, and finally form a uniform and stable organic carrier system. Subsequently, a specific ratio of T5 and T6 tin-lead alloy powders was slowly added to the prepared organic carrier, and a planetary mixer was used to perform preliminary mixing at a low speed to ensure that the powder was fully wetted. Finally, the pre-mixed slurry is transferred to a three-roll mill for multiple rolling and dispersion passes. The strong shearing force generated between the rollers further breaks up the powder agglomerates, promoting a highly uniform distribution of the metal powder in the organic system.

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