Ultra-high precision direct writing printing method and its application in OLED display panel repair

Abstract

The application relates to the fields of semiconductor display manufacturing and micro-nano additive manufacturing technology, and discloses an ultrahigh-precision direct writing printing method and application thereof in OLED display panel repair, which comprises the following steps: providing high-viscosity nano-conductive paste; injecting the paste into an ultrahigh-precision direct writing printing system with a precise air pressure control unit and a flexible glass nozzle, adjusting the flexible glass nozzle to make it contact with the surface of a to-be-printed substrate; applying pre-press air pressure and forming a meniscus on the nozzle end face, rising to a target air pressure, starting a motion platform to control the nozzle to move for contact type direct writing printing, continuously keeping the air pressure at the target air pressure during the printing process, and lowering to a preset air pressure after reaching the end point to complete the ink breaking forming direct writing wire; and using 532nm continuous wave laser, hot air or a heating furnace to perform sintering treatment on the direct writing wire to generate a repaired wire. In the contact printing state, the flexible nozzle can absorb stress to avoid scratching the substrate, and the constant pressure printing and pressure reduction ink breaking mechanism are combined to realize efficient and high-yield in-situ repair of extremely fine open circuit defects.

Description

Technical Field

[0001] This invention relates to the fields of semiconductor display manufacturing and micro / nano additive manufacturing technology, specifically to an ultra-high precision direct-write printing method and its application in OLED display panel repair. Background Technology

[0002] As OLED display panels advance towards higher resolutions, the width of the gate and source / drain wires inside the TFT backplane has shrunk to the micrometer level. At the micrometer scale, the randomness of the photolithography and etching processes can lead to open-circuit or short-circuit defects in the circuitry. To restore the continuity of the pixel unit circuitry in the panel, conductive material needs to be deposited at the defect locations to restore circuit conductivity.

[0003] Electrohydrodynamic printing (EHDP) is currently commonly used for repairing micro and nano-wires. EHDP utilizes a high-voltage electric field to create a Taylor cone filament ejection from the nozzle tip. However, in actual industrial production environments, the EHDP filamentation process is easily affected by ambient humidity, temperature, and airflow disturbances, making it difficult to maintain a stable and continuous jet. The viscosity range of the filaments suitable for EHDP is typically between 100 and 500 centipoise, limiting the use of high-solids-content conductive filaments and resulting in higher resistance values ​​for the formed wires. Furthermore, the jet assisted by the high-voltage electric field is prone to lateral deviation, and the minimum stable linewidth is limited by the nozzle inner diameter and the stability of the Taylor cone, making it difficult to print sub-micron-level wires.

[0004] Laser chemical vapor deposition (LCD) is also a method for repairing micro-wires. LCD utilizes a focused laser to decompose precursor gases and deposit metal wires on a substrate surface. However, LCD has a low single-point deposition rate, resulting in long wire repair times. Furthermore, LCD is limited to using vaporizable precursor materials and cannot use conductive pastes containing silver nanoparticles, as the resistivity of the deposited tungsten film is much higher than that of silver. Additionally, LCD systems require a laser system and a high-vacuum chamber, leading to high equipment and maintenance costs.

[0005] Traditional pneumatic printing technology uses compressed gas to drive slurry extrusion from a nozzle. For printing requirements with micron-level linewidths, the minimum adjustment step of conventional pressure regulators cannot meet the resolution requirements for extrusion flow control. As slurry viscosity increases, the required extrusion pressure also increases, leading to a deterioration in flow control linearity. Furthermore, traditional pneumatic printing technology typically uses rigid nozzles, which are prone to scratching the delicate surface of TFT substrates when printing within micron-level working gaps. Existing micro / nano wire repair technologies all have shortcomings in terms of printing accuracy, equipment cost, extrusion flow control, and protection of the substrate being printed. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an ultra-high precision direct-write printing method and its application in OLED display panel repair. It solves the problems of unstable slurry extrusion at the micron scale, easy filament pulling and shrinkage after molding, and uneven conductivity of the formed micro-wires in existing direct-write printing technologies.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides an ultra-high precision direct-write printing method, comprising the following steps: We provide high-viscosity nano-conductive slurry made from a mixture of conductive phase, polymer binder, organic solvent, thixotropic agent and dispersant; High-viscosity nano-conductive slurry is injected into an ultra-high precision direct-write printing system with a precision air pressure control unit and a flexible glass nozzle. The flexible glass nozzle is positioned above the starting point of the substrate to be printed using a vision alignment system. The height of the flexible glass nozzle in the Z-axis direction is adjusted by a distance sensor so that the nozzle end face contacts the surface of the substrate to be printed. Pre-pressurized air pressure is applied by a precision air pressure control unit and a curved liquid surface is formed on the nozzle end face. When the target air pressure is reached, the XYZ precision motion platform is activated to control the flexible glass nozzle to move relative to the substrate to be printed for direct writing printing. When the endpoint is reached, the pressure is reduced to the convergence air pressure and the air pressure output is cut off to maintain a slight positive pressure, so that the high viscosity nano-conductive paste and the substrate to be printed undergo fluid breakage to avoid paste shrinkage and form direct writing wires. The direct-write wires are sintered using a 532nm continuous wave laser sintering device, a hot air sintering device, or a heating furnace sintering device to generate repaired wires. The repaired wires are then subjected to online resistance testing using a resistance testing device.

[0008] By adopting the above technical solution, and utilizing high-viscosity nano-conductive paste combined with multi-stage air pressure control technology, a direct-write conductor with high linewidth consistency and no wire-drawing or current-breaking defects is achieved. The specific mechanism is as follows: The polymeric binder and organic solvent dissolve to form a polymeric network, while the thixotropic agent constructs a hydrogen-bonded network structure within the system, suspending the conductive nanoparticles coated with the dispersant within it. In a static state, the hydrogen-bonded network maintains the system's high viscosity, preventing the metal nanoparticles from settling.

[0009] The distance sensor performs closed-loop adjustment of the height in the Z-axis direction to maintain direct contact between the nozzle end face and the surface of the substrate to be printed. A constant contact pressure is maintained by using a specific flexible glass nozzle deformation buffer, so that the extruded fluid is spread evenly.

[0010] The pre-pressurized air pressure overcomes the viscous resistance and capillary resistance of the fluid inside the nozzle, driving the slurry in the system to converge at the nozzle end face and bulge outward to form a hemispherical meniscus.

[0011] As the gas pressure rises to the target pressure, the thixotropic hydrogen bond network inside the slurry breaks under high shear stress, exhibiting shear thinning. The viscosity decreases by an order of magnitude, allowing the slurry to flow smoothly out of the nozzle opening and adhere to the surface of the substrate to be printed. After the slurry leaves the high-shear region of the nozzle, the intermolecular hydrogen bond network is reconstructed, the viscosity recovers, and it supports and maintains the cross-sectional morphology of the direct-write wires.

[0012] When printing ends, the air pressure drops to the preset pressure, instantly eliminating the system's output kinetic energy and extrusion thrust. The ink, having lost its kinetic energy, undergoes necking and fracture at the contact interface due to the shearing and stretching action of the platform movement, completing physical ink cutoff, blocking capillary backflow in the pipeline, and inhibiting ink retraction or stringing.

[0013] Organic solvents are vaporized and diffused by laser irradiation, hot air blowing, or heating furnace environment heating, while polymer binders, thixotropic agents, and dispersants are pyrolyzed and volatilized under continuous heat input.

[0014] Nanoscale conductive phase particles possess high surface energy, leading to surface melting below the melting point of the bulk metal. Adjacent nanoparticles undergo neck growth through thermal diffusion of surface atoms, triggering the Oswald ripening effect. This results in nanoparticle aggregation, growing into a continuous and dense metallic conductive network, thereby reducing the bulk resistivity of the direct-write wire.

[0015] Preferably, the high-viscosity nano-conductive slurry is made from the following raw materials in parts by weight: 68-85 parts conductive phase, 2-8 parts polymeric binder, 10-20 parts organic solvent, 0.5-3 parts thixotropic agent, and 0.5-2 parts dispersant; the conductive phase is silver nanoparticles or gold nanoparticles, the polymeric binder is ethyl cellulose, the organic solvent is one or a mixture of two of terpineol and ethylene glycol butyl ether acetate, the thixotropic agent is fumed silica or polyamide wax, and the dispersant is a polycarboxylic acid ester polymeric superdispersant.

[0016] By employing the above technical solutions, ethyl cellulose provides skeletal support and a suitable combustion residue rate. Terpineol and ethylene glycol butyl ether acetate, possessing different saturated vapor pressures, construct a gradient volatilization system, preventing cracking of the direct-write conductive surface due to excessively rapid drying. Fumed silica, with its hydroxyl functional groups, rapidly forms a cross-linked network after shear stress relief, enhancing the system's thixotropic recovery response rate. The branched chains of polycarboxylate superdispersants adsorb onto the surface of metal particles, utilizing steric hindrance to isolate high-solids-content silver or gold nanoparticles, inhibiting aggregation.

[0017] Preferably, the preparation method of high-viscosity nano-conductive slurry includes: mixing raw materials and stirring at 60-80℃ for 2-4 hours to generate an initial mixture; placing the mixture in a high-speed disperser and dispersing it at 1500-3000 rpm for 20-40 minutes to generate a high-speed dispersed mixture; transferring the high-speed dispersed mixture to a three-roll mill and adjusting the gap between the milling rollers to 5-20 μm for multiple milling passes to generate a milled mixture; and placing the milled mixture in a vacuum defoamer and defoaming it at a vacuum of 0.1-1.0 kPa for 10-20 minutes.

[0018] By employing the above technical solutions, heating and stirring reduce initial fluid resistance and accelerate the wetting of solid components. The high-speed mechanical shear force output by the high-speed disperser initially breaks down soft aggregates in the conductive phase system. The powerful shear and extrusion forces of the three-roll mill forcefully deagglomerates particles within the gaps between the milling rollers, refining the particle size distribution and ensuring uniform dispersion of the metallic phase within the polymer matrix. The vacuum environment causes tiny bubbles mixed into the slurry system to expand outward and burst, improving fluid continuity and eliminating the risk of gas explosions and flow interruptions during subsequent printing processes.

[0019] Preferably, when the organic solvent is a mixture of terpineol and ethylene glycol butyl ether acetate, the mass ratio of terpineol to ethylene glycol butyl ether acetate is 1:1 or 2:1; the average particle size of the conductive phase is 20-80 nm; and the high-viscosity nano-conductive slurry is tested at 25°C and a shear rate of 1 s. -1 The initial viscosity under the given conditions is 100,000-300,000 cP.

[0020] By adopting the above technical solution, the limited ratio of mixed solvents optimizes the boiling point range of the system, and controls the drying rate of the slurry at the micron-level nozzle to prevent clogging. An average particle size of 20-80 nm increases the specific surface area while maintaining non-agglomeration at room temperature, reducing the sintering activation energy of subsequent heating processes. A high initial viscosity of 100,000-300,000 cP causes the slurry to exhibit solid-like yield stress in a static state, supporting the micron-level straight-line width and resisting gravitational collapse.

[0021] Preferably, the nozzle opening of the flexible glass nozzle is 1.0-2.0 μm, the length of the flexible thinning region is 5-15 mm, the wall thickness of the flexible thinning region of the flexible glass nozzle is 5-20 μm, and the convergence angle of the internal conical convergence channel is 15-30°.

[0022] By employing the above technical solution, the micron-level nozzle opening defines the fluid extrusion boundary and the lower limit of the width of the direct-write conductor. The flexible thinning region reduces the local mechanical stiffness of the nozzle, generating micron-level deformation to absorb stress when the nozzle accidentally contacts the substrate to be printed, thus preventing scratches to the underlying substrate circuitry. The 15-30° tapered convergence angle provides a smooth fluid acceleration channel, eliminates internal fluid dead zones, reduces head loss along the flow path, and maintains laminar flow output of high-viscosity slurry.

[0023] Preferably, the working gap is set to 5-20μm, and the pre-pressure value applied by the precision air pressure control unit is 0.05-3.5bar; wait 0.3-1.0s to form a curved liquid surface on the nozzle end face of the flexible glass nozzle.

[0024] By adopting the above technical solution, the defined working gap matches the substrate wetting force and the platform drag force. Applying a preset pre-pressure and providing a fluid deformation relaxation time of 0.3-1.0s overcomes the increased fluid resistance in the ultra-fine conical convergence channel, ensuring that the fluid overlaps on the substrate the instant the platform starts moving, and preventing material shortage delay at the printing start.

[0025] Preferably, the target air pressure is set to 0.1-5.0 bar; the XYZ precision motion platform is started to control the flexible glass nozzle to move at a speed of 1-20 mm / s relative to the substrate to be printed along the preset path.

[0026] By adopting the above technical solution, the extrusion volume flow rate set by the air pressure thrust is coupled and matched with the feed speed set by the motion platform, so that the output and consumption of fluid reach a state of conservation, maintain the morphological consistency of the wire width and thickness, and prevent wire accumulation expansion or tensile breakage defects caused by flow velocity mismatch.

[0027] Preferably, the reduced convergence pressure is set to 0.03-2.5 bar, and the convergence pressure is maintained for 0.1-0.5 s; the pressure output is cut off and a slight positive pressure of 0.01-0.05 bar is maintained.

[0028] By adopting the above technical solution, the reduced pressure consumes the remaining elastic potential energy accumulated inside the fluid delivery pipeline, thus slowing down the extrusion speed. After the main gas pressure is cut off, a slight positive pressure is maintained to provide a constant reverse compensation thrust to the fluid interface, counteracting the internal volume contraction and vacuum back suction caused by pipeline cut-off, and causing the fluid to break at the interface and detach from the nozzle.

[0029] Preferably, the temperature for hot air sintering using the hot air sintering equipment is 180-250℃; and the time for hot air sintering using the hot air sintering equipment is 10-60 minutes.

[0030] By employing the above technical solution, a temperature window of 180-250℃ provides the nanoparticles with the thermal diffusion kinetic energy required to overcome the potential barrier, without damaging the organic light-emitting substrate material of the bottom OLED display panel. A holding time of 10-60 minutes ensures deep densification of the metallic phase, eliminates insulating organic residues, and enables the direct-write conductors to complete the transition to a low-resistance state.

[0031] Secondly, this invention provides the application of an ultra-high precision direct-write printing method in the repair of defects in the TFT substrate of an OLED display panel. The TFT substrate of the OLED display panel is used as the substrate to be printed. The resistance value of the repaired wires is confirmed to be within the qualified judgment standard range, thereby realizing the repair of open circuit defects in the TFT substrate of the OLED display panel.

[0032] By employing the above technical solution, high-yield in-situ circuit repair is achieved by using fluid printing technology to treat dimensional defects. The specific repair mechanism is as follows: The control circuit traces inside the TFT substrate are distributed at the micrometer or even submicrometer level, and space is limited. This solution utilizes a high-viscosity slurry and a thixotropic rheological control mechanism, combined with multi-stage air pressure and flexible micrometer nozzle output, to directly deposit a metallic phase fluid containing nanoparticles onto the tiny open-circuit defects in a non-contact state. The forming process is not interfered with by surrounding non-destructive circuits. By setting thermal conditions, the nanoparticle surface is stimulated to melt and crystallize interconnect, forming bridging wires with current-carrying capacity. This transforms the local open-circuit state of the substrate into a connected state, thereby restoring the normal charge transport function of the panel pixel unit circuit.

[0033] This invention provides an ultra-high precision direct-write printing method and its application in OLED display panel repair. It offers the following advantages: 1. This invention provides a high-viscosity nano-conductive paste and applies multi-stage air pressure using a precision air pressure control unit. At the start of printing, the precision air pressure control unit applies pre-pressure to cause the high-viscosity nano-conductive paste to form a meniscus on the nozzle end face. During the steady-flow printing stage, the pressure is increased to the target pressure, utilizing shear-thinning properties to extrude the high-viscosity nano-conductive paste. Throughout the printing process, the air pressure remains at the set target pressure, stabilizing the extrusion of the high-viscosity nano-conductive paste using shear-thinning properties. Upon reaching the endpoint, the air pressure is reduced to a preset pressure to complete ink cutoff, eliminating fluid extrusion thrust and forcing the high-viscosity nano-conductive paste to undergo fluid breakage, thus avoiding material shortage delays and stringing phenomena in direct-write leads.

[0034] 2. This invention injects high-viscosity nano-conductive slurry into an ultra-high precision direct-write printing system with a flexible glass nozzle. A ranging sensor controls the flexible glass nozzle to press down in the Z-axis direction so that it is in contact with the surface of the substrate to be printed. A specific flexible thinning area at the end of the flexible glass nozzle undergoes elastic deformation to absorb and buffer stress during the contact printing state, avoiding rigid direct contact that could scratch the surface of the substrate to be printed, and ensuring the integrity of the original undamaged circuit traces inside the TFT substrate of the OLED display panel.

[0035] 3. This invention uses a mixture of conductive phase, polymer binder, organic solvent, thixotropic agent, and dispersant to prepare a high-viscosity nano-conductive slurry. The thixotropic agent constructs a hydrogen bond network structure to support the cross-sectional morphology of the high-viscosity nano-conductive slurry after it leaves the nozzle opening, preventing the high-viscosity nano-conductive slurry from diffusing or collapsing on the surface of the substrate to be printed. It is then used in conjunction with a 532nm continuous wave laser sintering equipment, hot air sintering equipment, or heating furnace sintering equipment to solidify and sinter the direct-write wires, stimulating the conductive phase surface to melt, grow, and coalesce to form a continuous metallic conductive network, generating repaired wires that meet the qualified judgment criteria, thus completing the repair of open circuit defects in the TFT substrate of the OLED display panel. Attached Figure Description

[0036] Figure 1 This is a diagram showing the shear thinning characteristics of the high-viscosity nano-conductive slurry of the present invention. Figure 2 This is a diagram showing the mechanical response of the nozzle under overpressure contact conditions according to the present invention. Figure 3 This is a graph showing the yield variation during the continuous defect repair process of this invention. Figure 4 This is a diagram showing the ink release delay time distribution during the continuous printing process of this invention. Figure 5 This is a graph showing the change in volume resistivity at different sintering times according to the present invention. Figure 6 This is a test graph showing the rate of change of resistance under different bending cycles according to the present invention. Detailed Implementation

[0037] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Examples 1-6: Example 1: This embodiment provides a method for repairing defects in the TFT substrate of an OLED display panel based on high-viscosity nano-silver paste, specifically including the following steps: S1. 72 parts by mass of silver nanoparticles with an average particle size of 50 nm were used as the conductive phase, 5 parts by mass of ethyl cellulose were used as the polymer binder, 15 parts by mass of a mixture of terpineol and ethylene glycol butyl ether acetate in a mass ratio of 2:1 were used as the organic solvent, 2 parts by mass of fumed silica were used as the thixotropic agent, and 1 part by mass of polycarboxylate superdispersant were used as the dispersant. The mixture was stirred at 70 °C for 3 h to generate an initial mixture. The initial mixture was placed in a high-speed disperser and dispersed at 2000 rpm for 30 min to generate a high-speed dispersed mixture. The high-speed dispersed mixture was transferred to a three-roll mill and the gap between the milling rollers was adjusted to 10 μm for multiple milling passes to generate a milled mixture. The milled mixture was placed in a vacuum defoamer and defoamed at a vacuum degree of 0.5 kPa for 15 min to obtain a high-viscosity nano-silver paste. The paste was tested at 25 °C and a shear rate of 1 s⁻¹. -1 The initial viscosity under the given conditions is 150,000 cP; S2. High-viscosity nano-silver paste is injected into an ultra-high precision direct-write printing system with a precision air pressure control unit and a flexible glass nozzle. A flexible glass nozzle with a nozzle opening of 1.5μm, a flexible thinning region length of 10mm, a flexible thinning region wall thickness of 10μm, and an internal conical convergence channel convergence angle of 20° is used. The visual alignment system of the ultra-high precision direct-write printing system is used to precisely position the flexible glass nozzle above the starting point of the defect to be repaired on the TFT substrate. The distance sensor of the ultra-high precision direct-write printing system is used to adjust the height of the flexible glass nozzle in the Z-axis direction, control the nozzle end face of the flexible glass nozzle to contact the surface of the TFT substrate, and set the Z-axis downward displacement to 10μm to maintain stable contact, thereby achieving the positioning of the flexible glass nozzle. S3. Apply pre-pressure air to the flexible glass printhead through the precision air pressure control unit of the ultra-high precision direct writing printing system. Set the pre-pressure air value to 0.5 bar and wait 0.5 s to form a meniscus on the nozzle end face of the flexible glass printhead. Increase the air pressure output by the precision air pressure control unit to the target air pressure of 0.8 bar. At the same time, start the XYZ precision motion platform of the ultra-high precision direct writing printing system to control the flexible glass printhead to move at a speed of 5 mm / s relative to the TFT substrate along the preset path for direct writing printing. Control the flexible glass printhead to reach the endpoint of the defect to be repaired on the TFT substrate. Reduce the air pressure output by the precision air pressure control unit to the preset air pressure of 0.03 bar to complete the ink cut-off. This causes the high viscosity nano silver paste to undergo fluid breakage with the TFT substrate, avoiding paste shrinkage and completing the formation of the direct writing wire on the surface of the TFT substrate. S4. Use a 532nm continuous wave laser sintering equipment, hot air sintering equipment, or heating furnace sintering equipment to sinter the formed direct-write wires. Taking hot air sintering equipment as an example, set the processing temperature to 200℃ and the time to 30 minutes to generate the repaired wires. Use a resistance detection equipment to perform online resistance detection on the repaired wires to confirm that the resistance value of the repaired wires is within the qualified judgment standard range, thereby realizing the repair of open circuit defects in the TFT substrate of the OLED display panel.

[0039] Example 2: This embodiment provides a method for repairing defects in the TFT substrate of an OLED display panel based on high-viscosity nano-silver paste, specifically including the following steps: S1. 80 parts by mass of silver nanoparticles with an average particle size of 80 nm were used as the conductive phase, 8 parts by mass of ethyl cellulose was used as the polymer binder, 20 parts by mass of terpineol was used as the organic solvent, 3 parts by mass of polyamide wax was used as the thixotropic agent, and 2 parts by mass of polycarboxylate polymeric superdispersant was used as the dispersant. The mixture was stirred at 80 °C for 4 h to generate an initial mixture. The initial mixture was placed in a high-speed disperser and dispersed at 3000 rpm for 40 min to generate a high-speed dispersed mixture. The high-speed dispersed mixture was transferred to a three-roll mill and the gap between the milling rollers was adjusted to 5 μm for multiple milling passes to generate a milled mixture. The milled mixture was placed in a vacuum defoamer and defoamed at a vacuum degree of 1.0 kPa for 20 min to obtain a high-viscosity nano-silver paste. The paste was tested at 25 °C and a shear rate of 1 s⁻¹. -1 The initial viscosity under the given conditions is 300,000 cP; S2. High-viscosity nano-silver paste is injected into an ultra-high precision direct-write printing system with a precision air pressure control unit and a flexible glass nozzle. A flexible glass nozzle with a nozzle opening of 2.0 μm, a flexible thinning region length of 15 mm, a flexible thinning region wall thickness of 20 μm, and an internal conical flow channel convergence angle of 30° is used. The visual alignment system of the ultra-high precision direct-write printing system is used to precisely position the flexible glass nozzle above the starting point of the defect to be repaired on the TFT substrate. The distance sensor of the ultra-high precision direct-write printing system is used to adjust the height of the flexible glass nozzle in the Z-axis direction, control the nozzle end face of the flexible glass nozzle to contact the surface of the TFT substrate, and set the Z-axis downward displacement to 20 μm to maintain stable contact, thereby achieving the positioning of the flexible glass nozzle. S3. Apply pre-pressure air to the flexible glass printhead through the precision air pressure control unit of the ultra-high precision direct writing printing system. Set the pre-pressure air value to 3.5 bar and wait 1.0 s to form a meniscus on the nozzle end face of the flexible glass printhead. Increase the air pressure output by the precision air pressure control unit to the target air pressure of 5.0 bar. At the same time, start the XYZ precision motion platform of the ultra-high precision direct writing printing system to control the flexible glass printhead to move along the preset path relative to the TFT substrate at a speed of 20 mm / s for direct writing printing. Control the flexible glass printhead to reach the end point of the defect to be repaired on the TFT substrate. Reduce the air pressure output by the precision air pressure control unit to the preset air pressure of 0.05 bar to complete the ink cut-off. This causes the high viscosity nano silver paste to undergo fluid breakage with the TFT substrate, avoiding paste shrinkage and completing the formation of direct writing wires on the surface of the TFT substrate. S4. Use a 532nm continuous wave laser sintering equipment, hot air sintering equipment, or heating furnace sintering equipment to sinter the formed direct-write wires. Taking the hot air sintering equipment as an example, set the processing temperature to 250℃ and the time to 60min to generate the repaired wires. Use a resistance detection equipment to perform online resistance detection on the repaired wires to confirm that the resistance value of the repaired wires is within the qualified judgment standard range, thereby realizing the repair of open circuit defects in the TFT substrate of the OLED display panel.

[0040] Example 3: This embodiment provides a method for repairing defects in the TFT substrate of an OLED display panel based on high-viscosity nano-silver paste, specifically including the following steps: S1. 70 parts by mass of silver nanoparticles with an average particle size of 20 nm were used as the conductive phase, 2 parts by mass of ethyl cellulose was used as the polymer binder, 10 parts by mass of ethylene glycol butyl ether acetate was used as the organic solvent, 0.5 parts by mass of fumed silica was used as the thixotropic agent, and 0.5 parts by mass of polycarboxylate superdispersant was used as the dispersant. The mixture was stirred at 60 °C for 2 h to generate an initial mixture. The initial mixture was placed in a high-speed disperser and dispersed at 1500 rpm for 20 min to generate a high-speed dispersed mixture. The high-speed dispersed mixture was transferred to a three-roll mill and the gap between the milling rollers was adjusted to 20 μm for multiple milling passes to generate a milled mixture. The milled mixture was placed in a vacuum defoamer and defoamed at 0.1 kPa for 10 min to obtain a high-viscosity nano-silver paste. The paste was tested at 25 °C and a shear rate of 1 s⁻¹. -1 The initial viscosity under the given conditions is 100,000 cP; S2. High-viscosity nano-silver paste is injected into an ultra-high precision direct-write printing system with a precision air pressure control unit and a flexible glass nozzle. A flexible glass nozzle with a nozzle opening of 1.0 μm, a flexible thinning region length of 5 mm, a flexible thinning region wall thickness of 5 μm, and an internal conical convergence channel convergence angle of 15° is used. The visual alignment system of the ultra-high precision direct-write printing system is used to precisely position the flexible glass nozzle above the starting point of the defect to be repaired on the TFT substrate. The distance sensor of the ultra-high precision direct-write printing system is used to adjust the height of the flexible glass nozzle in the Z-axis direction, control the nozzle end face of the flexible glass nozzle to contact the surface of the TFT substrate, and set the Z-axis downward displacement to 5 μm to maintain stable contact, thereby achieving the positioning of the flexible glass nozzle. S3. Apply pre-pressure air to the flexible glass printhead through the precision air pressure control unit of the ultra-high precision direct writing printing system. Set the pre-pressure air value to 0.05 bar and wait 0.3 s to form a meniscus on the nozzle end face of the flexible glass printhead. Increase the air pressure output by the precision air pressure control unit to the target air pressure of 0.1 bar. At the same time, start the XYZ precision motion platform of the ultra-high precision direct writing printing system to control the flexible glass printhead to move at a speed of 1 mm / s relative to the TFT substrate along the preset path for direct writing printing. Control the flexible glass printhead to reach the end point of the defect to be repaired on the TFT substrate. Reduce the air pressure output by the precision air pressure control unit to the preset air pressure of 0.01 bar to complete the ink cut-off. This causes the high viscosity nano silver paste to undergo fluid breakage with the TFT substrate, avoiding paste shrinkage and completing the formation of the direct writing wire on the surface of the TFT substrate. S4. Use a 532nm continuous wave laser sintering equipment, hot air sintering equipment, or heating furnace sintering equipment to sinter the formed direct-write wires. Taking hot air sintering equipment as an example, set the processing temperature to 180℃ and the time to 10 minutes to generate the repaired wires. Use a resistance detection equipment to perform online resistance detection on the repaired wires to confirm that the resistance value of the repaired wires is within the qualified judgment standard range, thereby realizing the repair of open circuit defects in the TFT substrate of the OLED display panel.

[0041] Example 4: This embodiment provides a method for repairing defects in the TFT substrate of an OLED display panel based on high-viscosity nano gold paste, specifically including the following steps: S1. 68 parts by mass of gold nanoparticles with an average particle size of 25 nm were used as the conductive phase; 5 parts by mass of ethyl cellulose was used as the polymer binder; 15 parts by mass of a mixture of terpineol and ethylene glycol butyl ether acetate in a 1:1 mass ratio was used as the organic solvent; 2 parts by mass of fumed silica was used as the thixotropic agent; and 1 part by mass of a polycarboxylate superdispersant was used as the dispersant. The mixture was stirred at 70°C for 3 hours to generate an initial mixture. The initial mixture was then placed in a high-speed disperser and dispersed at 2000 rpm for 30 minutes to generate a high-speed dispersed mixture. The high-speed dispersed mixture was then transferred to a three-roll mill, and the gap between the milling rollers was adjusted to 10 μm for multiple milling passes to generate a milled mixture. The milled mixture was then placed in a vacuum defoamer and defoamed at a vacuum of 0.5 kPa for 15 minutes to obtain a high-viscosity gold nanoparticle paste. Testing showed that this paste exhibited good viscosity at 25°C and a shear rate of 1 s⁻¹. -1 The initial viscosity under the given conditions is 180,000 cP; S2. High-viscosity nano-gold paste is injected into an ultra-high precision direct-write printing system with a precision air pressure control unit and a flexible glass nozzle. A flexible glass nozzle with a nozzle opening of 1.0 μm, a flexible thinning region length of 10 mm, a flexible thinning region wall thickness of 15 μm, and an internal conical convergence channel convergence angle of 25° is used. The visual alignment system of the ultra-high precision direct-write printing system is used to precisely position the flexible glass nozzle above the starting point of the defect to be repaired on the TFT substrate. The distance sensor of the ultra-high precision direct-write printing system is used to adjust the height of the flexible glass nozzle in the Z-axis direction, control the nozzle end face of the flexible glass nozzle to contact the surface of the TFT substrate, and set the Z-axis downward displacement to 10 μm to maintain stable contact, thereby achieving the positioning of the flexible glass nozzle. S3. Apply pre-pressure air to the flexible glass printhead through the precision air pressure control unit of the ultra-high precision direct writing printing system. Set the pre-pressure air value to 0.7 bar and wait 1.0 s to form a meniscus on the nozzle end face of the flexible glass printhead. Increase the air pressure output by the precision air pressure control unit to the target air pressure of 1.0 bar. At the same time, start the XYZ precision motion platform of the ultra-high precision direct writing printing system to control the flexible glass printhead to move at a speed of 3 mm / s relative to the TFT substrate along the preset path for direct writing printing. Control the flexible glass printhead to reach the endpoint of the defect to be repaired on the TFT substrate. Reduce the air pressure output by the precision air pressure control unit to the preset air pressure of 0.03 bar to complete the ink cut-off. This causes the high viscosity nano gold paste to undergo fluid breakage with the TFT substrate, avoiding paste shrinkage and completing the formation of the direct writing wire on the surface of the TFT substrate. S4. Use a 532nm continuous wave laser sintering equipment, hot air sintering equipment, or heating furnace sintering equipment to sinter the formed direct-write wires. Taking hot air sintering equipment as an example, set the processing temperature to 250℃ and the time to 45min to generate the repaired wires. Use a resistance detection equipment to perform online resistance detection on the repaired wires to confirm that the resistance value of the repaired wires is within the qualified judgment standard range, thereby realizing the repair of open circuit defects in the TFT substrate of the OLED display panel.

[0042] Example 5: This embodiment provides a method for repairing defects in the TFT substrate of an OLED display panel based on high-viscosity nano gold paste, specifically including the following steps: S1. 85 parts by mass of gold nanoparticles with an average particle size of 80 nm were used as the conductive phase, 8 parts by mass of ethyl cellulose was used as the polymer binder, 20 parts by mass of terpineol was used as the organic solvent, 3 parts by mass of polyamide wax was used as the thixotropic agent, and 2 parts by mass of polycarboxylate polymeric superdispersant was used as the dispersant. The mixture was stirred at 80 °C for 4 h to generate an initial mixture. The initial mixture was placed in a high-speed disperser and dispersed at 3000 rpm for 40 min to generate a high-speed dispersed mixture. The high-speed dispersed mixture was transferred to a three-roll mill and the gap between the milling rollers was adjusted to 5 μm for multiple milling passes to generate a milled mixture. The milled mixture was placed in a vacuum defoamer and defoamed at a vacuum degree of 1.0 kPa for 20 min to obtain a high-viscosity nano-gold paste. The paste was tested at 25 °C and a shear rate of 1 s⁻¹. -1 The initial viscosity under the given conditions is 300,000 cP; S2. High-viscosity nano-gold paste is injected into an ultra-high precision direct-write printing system with a precision air pressure control unit and a flexible glass nozzle. A flexible glass nozzle with a nozzle opening of 2.0μm, a flexible thinning region length of 15mm, a flexible thinning region wall thickness of 20μm, and an internal conical convergence channel convergence angle of 30° is used. The visual alignment system of the ultra-high precision direct-write printing system is used to precisely position the flexible glass nozzle above the starting point of the defect to be repaired on the TFT substrate. The distance sensor of the ultra-high precision direct-write printing system is used to adjust the height of the flexible glass nozzle in the Z-axis direction, control the nozzle end face of the flexible glass nozzle to contact the surface of the TFT substrate, and set the Z-axis downward displacement to 20μm to maintain stable contact, thereby achieving the positioning of the flexible glass nozzle. S3. Apply pre-pressure air to the flexible glass printhead through the precision air pressure control unit of the ultra-high precision direct writing printing system. Set the pre-pressure air value to 3.5 bar and wait 1.0 s to form a meniscus on the nozzle end face of the flexible glass printhead. Increase the air pressure output by the precision air pressure control unit to the target air pressure of 5.0 bar. At the same time, start the XYZ precision motion platform of the ultra-high precision direct writing printing system to control the flexible glass printhead to move at a speed of 20 mm / s relative to the TFT substrate along the preset path for direct writing printing. Control the flexible glass printhead to reach the end point of the defect to be repaired on the TFT substrate. Reduce the air pressure output by the precision air pressure control unit to the preset air pressure of 0.05 bar to complete the ink cut-off. This causes the high viscosity nano gold paste to undergo fluid breakage with the TFT substrate, avoiding paste shrinkage and completing the formation of direct writing wires on the surface of the TFT substrate. S4. Use a 532nm continuous wave laser sintering equipment, hot air sintering equipment, or heating furnace sintering equipment to sinter the formed direct-write wires. Taking the hot air sintering equipment as an example, set the processing temperature to 250℃ and the time to 60min to generate the repaired wires. Use a resistance detection equipment to perform online resistance detection on the repaired wires to confirm that the resistance value of the repaired wires is within the qualified judgment standard range, thereby realizing the repair of open circuit defects in the TFT substrate of the OLED display panel.

[0043] Example 6: This embodiment provides a method for repairing defects in the TFT substrate of an OLED display panel based on high-viscosity nano gold paste, specifically including the following steps: S1. 70 parts by mass of gold nanoparticles with an average particle size of 20 nm were used as the conductive phase, 2 parts by mass of ethyl cellulose was used as the polymer binder, 10 parts by mass of ethylene glycol butyl ether acetate was used as the organic solvent, 0.5 parts by mass of fumed silica was used as the thixotropic agent, and 0.5 parts by mass of polycarboxylate superdispersant was used as the dispersant. The mixture was stirred at 60 °C for 2 h to generate an initial mixture. The initial mixture was placed in a high-speed disperser and dispersed at 1500 rpm for 20 min to generate a high-speed dispersed mixture. The high-speed dispersed mixture was transferred to a three-roll mill and the gap between the milling rollers was adjusted to 20 μm for multiple milling passes to generate a milled mixture. The milled mixture was placed in a vacuum defoamer and defoamed at 0.1 kPa for 10 min to obtain a high-viscosity gold nanoparticle paste. The paste was tested at 25 °C and a shear rate of 1 s⁻¹. -1 The initial viscosity under the given conditions is 100,000 cP; S2. High-viscosity nano-gold paste is injected into an ultra-high precision direct-write printing system with a precision air pressure control unit and a flexible glass nozzle. A flexible glass nozzle with a nozzle opening of 1.0 μm, a flexible thinning region length of 5 mm, a flexible thinning region wall thickness of 5 μm, and an internal conical convergence channel convergence angle of 15° is used. The visual alignment system of the ultra-high precision direct-write printing system is used to precisely position the flexible glass nozzle above the starting point of the defect to be repaired on the TFT substrate. The distance sensor of the ultra-high precision direct-write printing system is used to adjust the height of the flexible glass nozzle in the Z-axis direction, control the nozzle end face of the flexible glass nozzle to contact the surface of the TFT substrate, and set the Z-axis downward displacement to 5 μm to maintain stable contact, thereby achieving the positioning of the flexible glass nozzle. S3. Apply pre-pressure air to the flexible glass printhead through the precision air pressure control unit of the ultra-high precision direct writing printing system. Set the pre-pressure air value to 0.05 bar and wait 0.3 s to form a meniscus on the nozzle end face of the flexible glass printhead. Increase the air pressure output by the precision air pressure control unit to the target air pressure of 0.1 bar. At the same time, start the XYZ precision motion platform of the ultra-high precision direct writing printing system to control the flexible glass printhead to move at a speed of 1 mm / s relative to the TFT substrate along the preset path for direct writing printing. Control the flexible glass printhead to reach the end point of the defect to be repaired on the TFT substrate. Reduce the air pressure output by the precision air pressure control unit to the preset air pressure of 0.01 bar to complete the ink cut-off. This causes the high viscosity nano gold paste to undergo fluid breakage with the TFT substrate, avoiding paste shrinkage and completing the formation of the direct writing wire on the surface of the TFT substrate. S4. Use a 532nm continuous wave laser sintering equipment, hot air sintering equipment, or heating furnace sintering equipment to sinter the formed direct-write wires. Taking hot air sintering equipment as an example, set the processing temperature to 180℃ and the time to 10 minutes to generate the repaired wires. Use a resistance detection equipment to perform online resistance detection on the repaired wires to confirm that the resistance value of the repaired wires is within the qualified judgment standard range, thereby realizing the repair of open circuit defects in the TFT substrate of the OLED display panel.

[0044] Comparative Examples 1-5: Comparative Example 1: Compared with Example 1, the difference lies in the air pressure control process in step S3. In Comparative Example 1, a target air pressure of 0.8 bar is directly applied to the inside of the flexible glass printhead through a precision air pressure control unit for direct writing printing. After the flexible glass printhead reaches the endpoint of the defect to be repaired on the TFT substrate, the output air pressure is directly reduced to 0 bar. There is no step of applying pre-pressure to form a curved liquid surface, and no step of reducing the air pressure to the preset level to cut off the ink at the endpoint. Everything else is the same.

[0045] Comparative Example 2: The difference between this example and Example 1 lies in the initial mixture formulation in step S1. In Comparative Example 2, 2 parts by mass of fumed silica in the initial mixture formulation were replaced with 2 parts by mass of a mixture of terpineol and ethylene glycol butyl ether acetate in a mass ratio of 2:1. No thixotropic agent was added, and all other aspects remained the same.

[0046] Comparative Example 3: The difference between Comparative Example 1 and Example 2 lies in the nozzle structure in step S2. In Comparative Example 3, a straight glass capillary with an inner diameter of 1.5 μm is used instead of a flexible glass nozzle. The straight glass capillary has no flexible thinning region and no internal conical converging flow channel; all other aspects are the same.

[0047] Comparative Example 4: Compared to Example 1, the difference lies in the working gap parameter in step S2. In Comparative Example 4, the height of the flexible glass nozzle in the Z-axis direction is adjusted using a distance sensor, so that the working gap between the nozzle end face of the flexible glass nozzle and the surface of the TFT substrate is set to 50 μm, and all other parameters are the same.

[0048] Comparative Example 5: Compared with Example 1, the difference lies in the endpoint air pressure cutoff control in step S3. In Comparative Example 5, after the flexible glass printhead reaches the endpoint of the defect to be repaired on the TFT substrate, the air pressure output by the precision air pressure control unit is reduced to -0.1 bar to perform negative pressure back-pulling ink cutoff. There is no endpoint reduction to the preset air pressure ink cutoff step, and the rest are the same.

[0049] Test Examples 1-6: Test Example 1: The high-viscosity nano-silver paste prepared in Example 1, the high-viscosity nano-gold paste prepared in Example 4, the mixture of fumed silica-free material prepared in Comparative Example 2, and the conventional low-viscosity conductive silver paste prepared in Comparative Example 5 were extracted as test samples.

[0050] Each type of test sample was placed in a constant temperature bath and left to stand for later use. The parameters of the constant temperature bath were adjusted to maintain the test environment temperature at 25℃.

[0051] Steady-state shear tests were performed using a rotational rheometer. A cone-plate testing system was selected, and the cone-plate gap was set by adjusting the parameters of the cone-plate testing system. The test sample was then added to the cone-plate testing system.

[0052] The shear rate scan range was set to 0.1 s in the rotational rheometer control software. -1 up to 1000s -1 The rotational rheometer was started to obtain the continuous viscosity values ​​of the test sample at different shear rates. Based on the continuous viscosity values ​​obtained from the test, the shear rate of 1 s was extracted. -1 The initial viscosity value under the given conditions was obtained, and the shear rate was extracted at 100 s.-1 Viscosity values ​​under certain conditions.

[0053] A step shear test was conducted using a rotational rheometer, with the initial shear rate set to 1 s in the control software. -1 The initial test baseline was established and maintained for a preset time. The shear rate was then transitioned to 500 s. -1 The test interval is maintained at a preset time to form a high-shear state. Finally, the shear rate is instantly restored to 1 second. -1 The viscosity recovery curves of the test samples generated by continuous sampling are recorded.

[0054] Based on the viscosity recovery curve, determine the data trend, calculate the time required for the viscosity of the test sample to rise and recover to 90% of the initial viscosity value corresponding to the initial test baseline, and record the calculated value as the recovery time value.

[0055] Table 1. Test data of slurry rheological properties

[0056] Figure 1 This is a graph showing the shear-thinning characteristics of the high-viscosity nano-conductive slurry of this invention. The horizontal axis in the graph represents the shear rate (s). -1 The vertical axis in the figure represents viscosity (cP), and the curves in the figure represent the viscosity changes of Example 1, Example 4, Comparative Example 2, and Comparative Example 5 at different shear rates.

[0057] in conclusion: According to Table 1 and Figure 1 The data shows that at a shear rate of 1 s -1 Under the given conditions, the initial viscosity of the high-viscosity silver nanoparticle paste prepared in Example 1 and the high-viscosity gold nanoparticle paste prepared in Example 4 exceeded 140,000 cP. This high initial viscosity allowed both the high-viscosity silver nanoparticle paste and the high-viscosity gold nanoparticle paste to maintain high structural strength under low shear conditions. At a shear rate of 100 s⁻¹, the initial viscosity remained relatively stable. -1 At that time, the viscosity values ​​of Examples 1 and 4 decreased. The network structure constructed by fumed silica in the initial mixture disintegrated under mechanical shearing, resulting in a reduction in fluid flow resistance and exhibiting shear thinning characteristics, which met the fluid dynamics requirements for fluid extrusion through the opening of the flexible glass nozzle.

[0058] Comparative Example 2 removed the fumed silica thixotropic agent component and changed the amount of the mixture of terpineol and ethylene glycol butyl ether acetate in a mass ratio of 2:1. The sample of Comparative Example 2 was tested at a shear rate of 1 s⁻¹. -1 The initial viscosity decreased under the given conditions, and at a shear rate of 100 s⁻¹ -1The viscosity reduction under the given conditions is limited. The system lacks a supporting network structure and therefore does not exhibit shear-thinning behavior. The recovery time in Comparative Example 2 is increased; after the external shear force is removed, the original structure cannot be quickly restored, resulting in fluid collapse and diffusion phenomena after direct-write printing.

[0059] Comparative Example 5 reduced the mass fraction of silver nanoparticles with an average particle size of 50 nm and increased the mass fraction of a mixture of terpineol and ethylene glycol butyl ether acetate at a mass ratio of 2:1. Test data showed that the initial viscosity of the sample in Comparative Example 5 was too low. The low initial viscosity failed to meet the resistance standard to prevent the slurry from flowing freely inside the flexible glass nozzle, resulting in dripping during the start and stop phases. In Examples 1 and 4, after the shear force was removed, the fumed silica network was reconstructed within a recovery time of 0.5 s to fix the fluid morphology after extrusion and prevent edge diffusion.

[0060] Test Example 2: The flexible glass nozzle used in Example 1, the flexible glass nozzle used in Example 2, and the straight glass capillary used in Comparative Example 3 were extracted as test samples.

[0061] The ranging sensor in the ultra-high precision direct-write printing system is connected to the XYZ precision motion platform and then to the micromechanical testing platform. A TFT substrate is fixed on the support platform of the micromechanical testing platform. Test samples are then loaded into the clamping mechanisms of the XYZ precision motion platform.

[0062] Set the XYZ precision motion platform's movement speed in the Z-axis direction to 1 mm / s. Start the XYZ precision motion platform to drive the test sample toward the TFT substrate surface. Monitor the distance between the end face of the test sample and the TFT substrate surface using a distance sensor.

[0063] After the test sample contacts the TFT substrate surface, the XYZ precision motion platform continues to generate Z-axis downward displacement. The target value for the Z-axis downward displacement is set to 30 μm. The contact force values ​​during the increase of the Z-axis downward displacement are continuously recorded using the mechanical sensors of the micro-mechanical testing platform. The contact force value when the Z-axis downward displacement reaches 30 μm is extracted and recorded as the maximum displacement contact force value.

[0064] The XYZ precision motion platform is controlled to lift upwards, removing the downward displacement along the Z-axis. A high-speed camera records the morphological changes of the test sample, and the time required for the sample to recover to its initial shape is calculated and recorded as the deformation recovery time after unloading. For Comparative Example 3, the test sample fractured during the downward compression process; therefore, the deformation recovery time after unloading was not recorded.

[0065] The XYZ precision motion platform was controlled to repeatedly perform 100 overpressure contact tests at different coordinate positions on the TFT substrate surface, with the Z-axis downward displacement set to 30 μm. After the overpressure contact test was completed, the TFT substrate was placed under an optical microscope to observe the surface condition of the test area. The total number of areas with cracks and plastic indentations on the TFT substrate surface was counted and recorded as the number of damage scratches.

[0066] Table 2. Test Data of Nozzle Mechanical Performance and Substrate Safety Protection

[0067] Figure 2 This is a mechanical response diagram of the nozzle under overpressure contact state according to the present invention. The horizontal axis of the diagram represents the Z-axis downward displacement (μm), and the vertical axis represents the contact force value (mN). The curves in the diagram represent the changes in contact force values ​​under different Z-axis downward displacements for Examples 1, 2, and 3, respectively.

[0068] in conclusion: According to Table 2 and Figure 2 Data shows that within the set Z-axis downward displacement range of 30 μm, the contact force values ​​generated by the flexible glass nozzles used in Example 1 and Example 2 exhibit a gradual upward trend. When the Z-axis downward displacement reaches 30 μm, the maximum displacement contact force value of Example 1 is below 5 mN, and the maximum displacement contact force value of Example 2 is below 10 mN. The wall thickness of the flexible thinning region in Example 1 is 10 μm, and the wall thickness of the flexible thinning region in Example 2 is 20 μm. The wall thickness parameter setting, combined with the length of the flexible thinning region, enables the flexible glass nozzle to possess structural flexibility in the Z-axis direction. The flexible thinning region undergoes elastic bending deformation to absorb the strain energy generated by overpressure contact, preventing local contact stress from exceeding the bearing limit of the TFT substrate surface. The number of damage scratches in 100 overpressure contact tests for Examples 1 and 2 is 0, demonstrating substrate protection capabilities.

[0069] In Examples 1 and 2, after the Z-axis downward displacement was removed, the deformation recovery time after unloading was less than 0.2 seconds. The flexible thinning area has elastic recovery characteristics, supporting the flexible glass printhead to quickly spring back to its original alignment state, meeting the structural stability requirements of continuous ultra-high precision direct-write printing.

[0070] Comparative Example 3 uses a straight glass capillary tube without a flexible thinning region. As the Z-axis downward displacement increases, the contact force in Comparative Example 3 rises. The straight glass capillary tube, being a rigid structure, cannot relieve the mechanical stress generated by the Z-axis downward displacement through its own deformation. The overpressure contact process directly leads to stress concentration and breakage within the straight glass capillary tube itself. Rigid contact completely transfers the mechanical load to the TFT substrate surface, causing damage to the TFT substrate in the test area of ​​Comparative Example 3, with 100 scratches. The nozzle structure of Comparative Example 3 lacks a buffer function, increasing the scrap rate of the TFT substrate under a small working gap setting.

[0071] Test Example 3: The OLED display panel TFT substrates that have undergone repair treatment in Examples 1 to 6 are prepared as test substrates. The test sample size is set so that the test substrates corresponding to each set of examples contain 1000 open circuit defect repair locations.

[0072] The test substrate is fixed on the stage of the optical profilometer. The scanning program of the optical profilometer is started to acquire three-dimensional topographic data of the repaired wire on the surface of the test substrate. The linewidth and height values ​​are extracted from the scan data. The aspect ratio of the repaired wire is obtained by performing a division operation on the extracted height and linewidth values.

[0073] The test substrate, after morphology testing, is transferred to the probe station system. The micromanipulator is used to adjust the coordinates of the two test probes, controlling them to establish contact with the start and end points of the repaired wires, respectively. The resistance detection device is activated, outputting a constant test current of 10mA. The end-to-end resistance value displayed on the screen is read and recorded.

[0074] The high-viscosity nano-silver paste and high-viscosity nano-gold paste from Examples 1 to 6 were respectively loaded into an industrial ultra-high precision direct-write printing system. Under continuous operation, 1000 open-circuit defects were repaired in each system. The morphology of the repaired conductors was compared using optical inspection equipment on the production line, and the electrical continuity was verified using online resistance testing equipment. The number of repaired conductors that simultaneously met the morphology and electrical continuity acceptance criteria was counted. The percentage of the number of acceptable repaired conductors was converted to calculate the first-pass yield for each set of process conditions.

[0075] Table 3. Test data on conductor defect repair yield and electrical performance.

[0076] Figure 3This is a graph showing the yield variation during the continuous defect repair process of the present invention. The horizontal axis represents the number of defects repaired (units), and the vertical axis represents the first-pass yield (%). The curves in the graph represent the first-pass yield variations of Examples 1, 3, 4, and 6 under different defect repair numbers.

[0077] in conclusion: According to Table 3 and Figure 3 The data shows that the end-to-end resistance of the repaired wires prepared in Examples 1 to 6 is all below 50Ω, meeting the qualification criteria for OLED display panel TFT substrates. After hot air sintering in a hot air sintering equipment, the ethyl cellulose polymer binder and organic solvents such as terpineol added to the formula undergo volatilization and decomposition reactions, and the silver nanoparticles and gold nanoparticles fuse together to form a dense conductive structure, ensuring that the repaired wires have low resistance characteristics.

[0078] In Examples 1 and 4, the measured linewidth values ​​remained below 1.6 μm after printing, while the aspect ratio exceeded 0.9. With the accompanying micro-positive pressure maintenance step and pre-pressure setting, the high-viscosity nano-silver paste and high-viscosity nano-gold paste did not overflow laterally onto the TFT substrate surface after extrusion. The fluid morphology was constrained by the fumed silica network structure and fixed within the preset path, maintaining sufficient conductive cross-sectional area at a small size.

[0079] In long-term continuous testing, the first-pass yield curves of Examples 1 and 4 remained stable as the number of defect repairs increased, with the final first-pass yield exceeding 98%. By controlling the nozzle end face of the flexible glass printhead to maintain contact printing with the TFT substrate surface, and using an internal tapered flow channel to control the fluid jet pattern, ink skewing or ink interruption was avoided. The system maintained a uniform conductor deposition state throughout the entire operation cycle, preventing defect repair failures due to missing prints or flow interruptions.

[0080] Examples 3 and 6 employ smaller nozzle opening parameters and lower pre-pressure settings. During continuous direct-write printing, slight ink ejection delays occasionally occur due to increased flow resistance caused by the reduced flow channel size and the lower target air pressure, resulting in a slight decrease in first-pass yield compared to Examples 1 and 4. However, the final first-pass yield values ​​for Examples 3 and 6 remain above 93%, demonstrating that the provided method is feasible under the limiting parameters of a 1.0 μm nozzle opening, supporting ultra-high precision circuit break repair work under industrial conditions.

[0081] Test Example 4: Prepare an ultra-high precision direct-write printing system and a high-speed camera test platform. Set up a macro lens on the high-speed camera test platform and adjust the macro lens's focal plane to the working area of ​​the ultra-high precision direct-write printing system's printhead. Inject the slurries corresponding to Example 1, Comparative Example 1, Comparative Example 3, and Comparative Example 5 into their respective test printheads and install them onto the Z-axis motion platform of the ultra-high precision direct-write printing system.

[0082] Edit a program in the system control software to create a continuous intermittent direct-write printing task containing 50 independent straight line segments. Start the system control software and simultaneously trigger a high-speed camera to record video. Obtain the system timestamp of the air pressure output command issued by the control system, and extract the actual image timestamps of the fluid front contacting the TFT substrate surface frame by frame from the image sequence recorded by the high-speed camera. Calculate the difference between the system timestamp and the actual image timestamp to obtain the ink release delay time for each straight line segment. Statistically analyze the highest and lowest ink release delay times during the 50 operations, and perform a subtraction operation to obtain the ink release delay time range.

[0083] After each straight line is printed to its endpoint and the ink is cut off, the XYZ precision motion platform is raised 100 μm in the Z-axis direction. An optical microscope is used to record the length of the suspended fluid between the end of the residual fluid on the nozzle face and the end of the deposited wire on the TFT substrate surface. The maximum elongation before the suspended fluid breaks is measured and recorded as the fluid wire drawing length.

[0084] A high-magnification transmitted light source, combined with a side-mounted camera, was used to continuously observe the fluid state inside the printhead. The total number of independent air bubbles that accumulated in the inner diameter area of ​​the printhead after completing 50 independent straight-line segment continuous intermittent direct-write printing tasks was counted and recorded as the number of air bubbles entrained.

[0085] Set up a batch continuous defect repair verification task involving 5000 test leads. Start the ultra-high precision direct-write printing system to execute the batch continuous defect repair verification task. After the task is completed, use a resistance testing device to measure each test lead individually. Test leads with resistance values ​​exceeding the acceptance criteria are judged as broken wires. Calculate the breakage rate by counting the percentage of broken wires out of the total number of test leads.

[0086] Table 4. Comparative Test Data of Multi-Stage Pressure Control Mechanisms

[0087] Figure 4 This is a graph showing the distribution of ink delay time during the continuous printing process of the present invention. The horizontal axis represents the number of consecutive prints (times), and the vertical axis represents the ink delay time (ms). The curves in the graph represent the changes in ink delay time for Example 1, Comparative Example 1, Comparative Example 3, and Comparative Example 5 under different consecutive print counts.

[0088] in conclusion: According to Table 4 and Figure 4 Data shows that in Example 1, a pre-pressure of 0.5 bar is applied to the interior of the flexible glass printhead via a precision air pressure control unit. This pre-pressure setting induces the formation of a meniscus in the high-viscosity silver nanoparticles at the nozzle end face. After the meniscus is constructed, the pressure is increased to the target pressure of 0.8 bar. The contact between the high-viscosity silver nanoparticles and the TFT substrate surface is highly consistent, and the corresponding ink release delay time difference remains at a low level of 2.1 ms. In Comparative Example 1, a target air pressure of 0.8 bar is directly applied to the interior of the printhead for direct-write printing. The lack of a pre-adjustment step to form the meniscus results in an inconsistent initial position of the high-viscosity silver nanoparticles at the start of each print. This positional fluctuation alters the air pressure drive distance, causing drastic fluctuations in the ink release delay time.

[0089] Comparative Example 3 uses a straight glass capillary tube without an internal tapered flow channel design. The constant internal fluid channel diameter ensures a uniform pressure drop distribution and eliminates the fluid convergence acceleration effect. The high-viscosity nano-silver paste experiences increased starting friction resistance within the rigid straight tube, resulting in a generally higher ink lag time accompanied by unstable starting behavior.

[0090] Example 1 reduces the air pressure to a preset pressure of 0.03 bar at the printing endpoint to complete ink cutoff. The pressure reduction instantly eliminates the extrusion thrust and suppresses fluid output, causing the slurry to break up under the mechanical stretching action on the TFT substrate surface. In Example 1, the fluid filament length is reduced to 1.2 μm, and the number of air bubbles entangled is zero. Comparative Example 1 directly reduces the output air pressure to 0 bar at the endpoint. The fluid's inertia causes the breakage location to be random, increasing the fluid filament length to 18.5 μm. The slight backflow caused by the pressure cutoff introduces a small number of air bubbles.

[0091] Comparative Example 5 uses negative pressure retraction by reducing the pressure to -0.1 bar after the flexible glass printhead reaches its endpoint. The forced intake of outside air forms a bubble cluster inside the printhead, with up to 87 bubbles entrained. This large number of bubbles entering the fluid system disrupts the continuous phase structure of the high-viscosity nano-silver paste. When subsequent printing commands are issued, the compressed air absorbs external energy, causing the ink release delay time of Comparative Example 5 to increase and fluctuate significantly after multiple intermittent operations. The bubbles, expelled with the paste, cause line breaks, with a breakage rate as high as 24.5%. Example 1 utilizes multi-stage air pressure control to prevent flow interruptions and tailing.

[0092] Test Example 5: Test samples of Examples 1, 4, Comparative Example 2, and Comparative Example 5 were prepared and printed on the surface of a TFT substrate using an ultra-high precision direct-write printing system. It was ensured that the surface of the test samples contained linear conductive patterns with fixed length and width dimensions.

[0093] Place the prepared test samples into the heating chamber of the hot air sintering equipment. Set the heating parameters of the hot air sintering equipment to maintain the ambient temperature inside the heating chamber at 150℃. Turn on the hot air sintering equipment to perform the thermosetting treatment.

[0094] During the thermosetting process, a four-probe resistance meter was used to probe the surface of the test sample at different sintering time points, capturing linear conductive patterns. The surface resistance values ​​of these patterns were measured and read. The volume resistivity values ​​of the test sample at different sintering time points were obtained by multiplying and dividing the extracted surface resistance values ​​with the cross-sectional area and length of the linear conductive patterns. The continuous change in volume resistivity values ​​with increasing sintering time was recorded and exported. The final volume resistivity value generated at a sintering time of 60 minutes was extracted.

[0095] After sintering for 60 minutes, turn off the hot air sintering equipment. Remove the test sample and place it in a 25°C environment to cool. Use a cross-cutting tool to cut 100 individual 1mm × 1mm grids on the surface of the cooled test sample. Cover the grid area with standard adhesion test tape. Apply vertical downward pressure to the standard adhesion test tape to ensure complete adhesion of the bonding surfaces.

[0096] Hold the edge of the standard adhesion test tape and perform a rapid peeling motion at a 60-degree angle. Place the peeled test sample under an optical microscope and observe the residual state of the linear conductive patterns within the grid area. Count the number of grids that did not detach and convert the counted number of detached grids into an adhesion percentage value.

[0097] Table 5. Sintering process and electrical conductivity test data.

[0098] Figure 5 This is a graph showing the change in volume resistivity under different sintering times according to the present invention. The horizontal axis in the graph represents the sintering time (min), and the vertical axis represents the volume resistivity value (μΩ·cm). The curves in the graph represent the changes in volume resistivity values ​​of Examples 1, 4, Comparative Example 2, and Comparative Example 5 under different sintering times.

[0099] in conclusion: According to Table 5 and Figure 5 The data shows that in the initial stage of sintering, the volume resistivity values ​​of Examples 1, 4, Comparative Example 2, and Comparative Example 5 were all at a relatively high level. As the hot air sintering equipment continuously outputs heat, the organic solvents such as terpineol and ethylene glycol butyl ether acetate inside the test samples undergo thermal volatilization.

[0100] In Examples 1 and 4, the volume resistivity decreased rapidly after sintering for 30 minutes. The network structure constructed from fumed silica and ethyl cellulose in the formulation underwent volume shrinkage during solvent removal. This volume shrinkage reduced the distance between silver nanoparticles with an average particle size of 50 nm. The silver nanoparticles underwent surface melting and interconnection at 150°C, forming a dense and continuous electronic conduction network. When the sintering time reached 60 minutes, the final volume resistivity of Example 1 decreased to 4.6 μΩ·cm, and the final volume resistivity of Example 4 decreased to 5.2 μΩ·cm.

[0101] The ethyl cellulose polymer binder transforms into a solid adhesive network after thermosetting. This solid adhesive network anchors downwards to the TFT substrate surface and upwards encapsulates the cured silver nanoparticles. In Examples 1 and 4, after peel testing, the adhesion percentage remained above 98%, meeting the standard requirements for conductor adhesion strength in TFT substrates.

[0102] Comparative Example 2 had its fumed silica component removed. The lack of the network support provided by fumed silica caused structural collapse in the slurry during the initial heating phase. This structural collapse hindered the uniform three-dimensional distribution of silver nanoparticles. Localized pores disrupted electron transport paths. The volume resistivity of Comparative Example 2 decreased gradually, eventually settling at 12.8 μΩ·cm. The internal pores reduced the overall cohesion of the structure, leading to interlayer fracture under external peeling forces, resulting in a decrease in the adhesion percentage of Comparative Example 2 to 85%.

[0103] Comparative Example 5 varied the mass fraction of the mixture of terpineol and ethylene glycol butyl ether acetate. An increase in solvent evaporation rate was observed. Excessive solvent evaporation created gas escape channels within the incompletely cured silver nanoparticle layer. These gas escape channels disrupted the continuous metal network, resulting in an increase in the final volume resistivity of Comparative Example 5 to 18.5 μΩ·cm. Rapid evaporation also prevented the bottom ethyl cellulose from establishing sufficient wetting with the TFT substrate surface, causing the adhesion percentage to drop to 62%.

[0104] Test Example 6: Test samples from Examples 1, 4, 2, and 4 (Comparative Example 2 and Comparative Example 4) were extracted and printed on the surface of a flexible substrate using an ultra-high precision direct-write printing system and then cured and sintered. The test samples had a 10mm long linear conductive pattern attached to their surface.

[0105] Secure the ends of the test specimen within the dynamic and static fixtures of the automatic bending tester. Connect the test probe of the online multi-channel resistance recorder to both ends of the linear conductive pattern. Read and record the initial resistance value on the system interface.

[0106] In the control software of the automatic bending tester, set the bending radius to 2mm and the bending frequency to 60 times / min. Start the automatic bending tester to perform continuous cyclic bending.

[0107] During the operation of the automatic bending tester, a continuous resistance value of the linear conductive pattern is continuously and synchronously acquired using an online multi-channel resistance recorder. The resistance value of the test node corresponding to every 1000 bending actions is extracted. The difference between the extracted resistance value and the initial resistance value is calculated and divided by the initial resistance value to obtain the resistance change rate of each test node. The final data corresponding to 10,000 consecutive bending actions is recorded.

[0108] Stop the automatic bending tester and unload the test sample. Use a scanning electron microscope to collect the morphology of the linear conductive pattern on the surface of the test sample. At a fixed 1mm... 2 The total number of gaps that transversely penetrate the conductive pattern within the field of view is counted, and the statistical results are recorded as microcrack density values.

[0109] Table 6. Data on bending fatigue and morphology tests of flexible conductors

[0110] Figure 6 This is a test graph of the resistance change rate under different bending times of the present invention. The horizontal axis of the graph represents the number of bending times, and the vertical axis represents the resistance change rate (%). The curves in the graph represent the resistance change rate changes of Example 1, Example 4, Comparative Example 2, and Comparative Example 4 under different bending times.

[0111] in conclusion: According to Table 6 and Figure 6 The data shows that in the initial stage when the number of bends was between 0 and 2000, the resistance change rate of the test samples remained in a low range for Examples 1, 4, Comparative Examples 2 and 4. The deformation stress generated by the flexible substrate itself was absorbed by the polyimide matrix and did not cause tensile damage to the internal structure of the linear conductive pattern attached to the surface.

[0112] As the number of bending cycles increased to 10,000, the rate of change in resistance in Examples 1 and 4 remained below 3.5%, and the microcrack density was 15 cracks / mm. 2The following describes the process: After curing and sintering in a hot air sintering device, the ethyl cellulose polymer binder in the formula crosslinks around silver and gold nanoparticles with an average particle size of 50 nm, forming an organic polymer network. This organic polymer network exhibits elastic deformation characteristics. The mechanical stress generated by cyclic bending is dispersed and dissipated within the organic polymer network. The contact positions between the silver and gold nanoparticles remain stable, and the electron transport network maintains continuous conductivity.

[0113] Comparative Example 4 reduced the mass fraction of ethyl cellulose polymer binder. The linear conductive pattern lost the encapsulation and mechanical buffering provided by the organic polymer network. The rigidly connected metal network structure directly experienced mechanical fatigue damage under cyclic mechanical stress. The microcrack density of Comparative Example 4 reached 315 cracks / mm. 2 Numerous microcracks crisscross the electron conduction path, increasing the resistance to electron transport. As a result, the resistance change rate of Comparative Example 4 after 10,000 bends climbs to 92.41%, and the linear conductive pattern essentially loses its current transport capability.

[0114] Comparative Example 2 removed the fumed silica component. During the initial stages of printing and heating, the slurry experienced internal structural collapse, resulting in randomly distributed pores within the metal network. These pores evolved into mechanical crack initiation sites under the stress concentration effect of bending. The cracks propagated outwards from the pore edges, blocking local electron transport, causing the resistivity change rate of Comparative Example 2 to increase to 15.38% after 10,000 bends. Examples 1 and 4, through the combined action of fumed silica and ethyl cellulose polymer binder, exhibited resistance to mechanical fatigue, meeting the operational requirements of flexible display panels in bending environments.

Claims

1. An ultra-high precision direct-write printing method, characterized in that, Includes the following steps: We provide high-viscosity nano-conductive slurry made from a mixture of conductive phase, polymer binder, organic solvent, thixotropic agent and dispersant; The high-viscosity nano-conductive slurry is injected into an ultra-high precision direct-write printing system with a precision air pressure control unit and a flexible glass nozzle. The flexible glass nozzle is positioned above the starting point of the substrate to be printed using a vision alignment system. The height of the flexible glass nozzle in the Z-axis direction is adjusted by a distance sensor, so that the nozzle end face contacts the surface of the substrate to be printed. The precision air pressure control unit applies pre-pressure and forms a curved liquid surface on the nozzle end face. The pressure is raised to the target pressure, and the XYZ precision motion platform is activated to control the flexible glass printhead to move relative to the substrate to be printed for direct writing printing. During the printing process, the air pressure is maintained at the target pressure. After reaching the end point, the pressure is reduced to the preset pressure to complete the ink cut-off. This causes the high-viscosity nano-conductive paste to undergo fluid breakage with the substrate to be printed, preventing the paste from shrinking back and forming a direct writing wire. The direct-write wire is sintered using a 532nm continuous wave laser sintering device, a hot air sintering device, or a heating furnace sintering device to generate a repaired wire, and the repaired wire is then subjected to online resistance testing using a resistance testing device.

2. The ultra-high precision direct-write printing method according to claim 1, characterized in that, The high-viscosity nano-conductive slurry is made from the following raw materials in parts by weight: 68-85 parts conductive phase, 2-8 parts polymer binder, 10-20 parts organic solvent, 0.5-3 parts thixotropic agent, and 0.5-2 parts dispersant. The conductive phase is silver nanoparticles or gold nanoparticles, the polymeric binder is ethyl cellulose, the organic solvent is one or a mixture of two of terpineol and ethylene glycol butyl ether acetate, the thixotropic agent is fumed silica or polyamide wax, and the dispersant is a polycarboxylic acid ester polymeric superdispersant.

3. The ultra-high precision direct-write printing method according to claim 2, characterized in that, The preparation method of the high-viscosity nano-conductive slurry includes: mixing raw materials and stirring at 60-80℃ for 2-4 hours to generate an initial mixture, and then placing it in a high-speed disperser for 20-40 minutes at a speed of 1500-3000 rpm to generate a high-speed dispersed mixture. The high-speed dispersion mixture is transferred to a three-roll mill and the gap between the milling rollers is adjusted to 5-20 μm for multiple milling processes to generate a milled mixture. The milled mixture is then placed in a vacuum defoamer and defoamed for 10-20 min under a vacuum of 0.1-1.0 kPa.

4. The ultra-high precision direct-write printing method according to claim 2, characterized in that, When the organic solvent is a mixture of terpineol and ethylene glycol butyl ether acetate, the mass ratio of terpineol to ethylene glycol butyl ether acetate is 1:1 or 2:

1. The conductive phase has an average particle size of 20-80 nm, and the high-viscosity nano-conductive slurry is subjected to a shear rate of 1 s at 25 °C. -1 The initial viscosity under the given conditions is 100,000-300,000 cP.

5. The ultra-high precision direct-write printing method according to claim 1, characterized in that, The flexible glass nozzle has a nozzle opening of 1.0-2.0 μm and a flexible thinning region length of 5-15 mm. The flexible glass nozzle has a flexible thinning region with a wall thickness of 5-20 μm and an internal conical converging flow channel with a convergence angle of 15-30°.

6. The ultra-high precision direct-write printing method according to claim 1, characterized in that, The Z-axis downward displacement is set to 5-30μm to keep the nozzle end face in contact with the surface of the substrate to be printed, and the pre-pressure value applied by the precision air pressure control unit is 0.05-3.5 bar; Wait 0.3-1.0s for the curved surface to form on the nozzle end face of the flexible glass nozzle.

7. The ultra-high precision direct-write printing method according to claim 1, characterized in that, The target air pressure is set to 0.1-5.0 bar; The XYZ precision motion platform is activated to control the flexible glass printhead to move at a speed of 1-20 mm / s relative to the substrate to be printed along a preset path.

8. The ultra-high precision direct-write printing method according to claim 1, characterized in that, The preset air pressure is set to decrease to 0-0.05 bar after reaching the endpoint, thus completing the ink cut-off and fluid breakage.

9. The ultra-high precision direct-write printing method according to claim 1, characterized in that, When the hot air sintering equipment or the heating furnace sintering equipment is used for sintering, the sintering temperature is set to 180-250℃ and the sintering time is 10-60min. When using the 532nm continuous wave laser sintering equipment for sintering, the matching laser scanning power and speed are set according to the morphology parameters of the direct-write conductor.

10. The application of an ultra-high precision direct-write printing method according to any one of claims 1 to 9 in the repair of defects in TFT substrates of OLED display panels, characterized in that, The TFT substrate of the OLED display panel is used as the substrate to be printed; The resistance value of the repaired wire is confirmed to be within the acceptable range, thus achieving the repair of the open circuit defect in the TFT substrate of the OLED display panel.

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