A preparation method and application of direct writing printed flexible circuit

Abstract

The application relates to a preparation method and application of a direct writing printed flexible circuit, and belongs to the field of flexible circuits. The application aims to solve the problem of failure of an existing wind power blade heating circuit during high-frequency deformation of the blade. The method comprises the following steps: 1, preparing liquid metal particles; 2, preparing liquid metal slurry for direct writing 3D printing; 3, printing the circuit by using a direct writing 3D printing method; 4, mechanical sintering and transfer of the circuit structure; and 5, interface leading-out and packaging of the flexible circuit. The application is used for the preparation and application of the direct writing printed flexible circuit.

Description

Technical Field

[0001] This invention belongs to the field of flexible circuits. Background Technology

[0002] With the gradual depletion of global fossil fuels and the series of environmental problems caused by their use, the development of clean energy has been included in the strategic development of the world, aiming to achieve a low-carbon economy and the transformation of old and new growth drivers. Wind energy, as one of the clean and renewable energy sources, demonstrates great potential for environmental friendliness and significant economic benefits. However, for wind power generation technology, climate conditions largely limit the stability of wind power generation, thus limiting its application in the power grid. Reducing the randomness in wind energy utilization and increasing its operational stability is a pressing technical challenge for wind power generation. Wind turbine blades are the core component of the wind turbine system. Based on their need to capture wind energy, they must be designed with specific aerodynamic shapes. When they come into contact with excessively cold air, frost may adhere to their surface, damaging their aerodynamic shape and significantly affecting the efficiency of wind power generation. According to statistics, the annual loss of wind power generation due to frost can reach 5%-30%. Furthermore, the rotational imbalance caused by the additional blade load can lead to excessive vibration, and may even cause irreversible damage to the turbine due to excessive load. Traditional blade heating circuits are made of intrinsically non-stretchable conductors, which makes them prone to open circuits under high-frequency strain, thus losing their defrosting effect. Therefore, there is an urgent need for a flexible wind turbine blade heating and defrosting technology suitable for high-frequency strain to solve this technical problem. Summary of the Invention

[0003] This invention aims to solve the problem of failure of existing wind turbine blade heating circuits during high-frequency deformation of the blades, and further provides a method for fabricating and applying a direct-write printed flexible circuit.

[0004] A method for fabricating a direct-write printed flexible circuit, comprising the following steps:

[0005] I. Preparation of liquid metal particles:

[0006] The oxide layer on the surface of the liquid metal droplets is removed, and then the liquid metal droplets are broken into liquid metal particles by ultrasonic crushing.

[0007] II. Preparation of liquid metal paste for direct-write 3D printing:

[0008] A flexible material is added to liquid metal particles and mixed evenly to obtain a liquid metal slurry for direct-write 3D printing;

[0009] The liquid metal particles in the liquid metal slurry for direct-write 3D printing comprise 30% to 90% by mass.

[0010] III. Circuit printing using the direct-write 3D printing method:

[0011] A 3D printed circuit structure was directly written onto an initial substrate using liquid metal paste for direct writing 3D printing, and then dried and cured to obtain an initial substrate with the printed circuit structure.

[0012] IV. Mechanical Sintering and Transfer of Circuit Structure:

[0013] A flexible substrate material is placed on one side of the initial substrate where the circuit structure is printed and cured to form a flexible substrate. The flexible substrate is then peeled off from the initial substrate, and the circuit structure is transferred to the flexible substrate to achieve the connection of the conductive path, resulting in a flexible substrate with the circuit structure attached.

[0014] V. Interface Outlets and Packaging of Flexible Circuits:

[0015] The method for fabricating a direct-write printed flexible circuit involves leading wires from the circuit ports of a flexible substrate with an attached circuit structure and encapsulating them with a flexible material.

[0016] An application of a direct-write printed flexible circuit for flexible heating and defrosting of wind turbine blades.

[0017] The beneficial effects of this invention are:

[0018] 1. This invention proposes a method for activating the conductive pathway of liquid metal particles in liquid metal / polymer composite slurry DIW molding and printing circuits. The conductivity of the printed circuits can reach 10. 5 The S / m order of magnitude, along with the DIW molding method, greatly achieves the principle of allocating materials on demand, saving costs. Furthermore, the availability of flexible materials further expands the applicability of this invention, allowing the fabrication of flexible circuits with various flexible materials as the covering layer.

[0019] 2. The circuit structure of this invention uses liquid metal as the conductive material. Due to the presence of the flexible material matrix, there is no obvious leakage of liquid metal during mechanical sintering (peeling and transfer process), and the internal liquid metal still exists in particle form. After the circuit is formed, it is covered with a flexible material, which has relatively stable conductivity. It has broad application potential in flexible circuits, electronic communications, soft robotics, and other fields. In other words, the addition of flexible material gives the paste better printability, economy, and stability.

[0020] 3. In this specific embodiment, the circuit structure is transferred to a flexible material by stripping and the conductive pathways of the liquid metal particles inside the circuit are activated and connected. That is, the wire circuit prepared by this method of forming conductive pathways with liquid metal is connected by forming an internal permeation network structure.

[0021] 4. By combining the properties of liquid metal that simultaneously satisfy deformation and conductivity, the fabricated flexible circuit can maintain conductivity continuity and relative stability of resistance under 100% strain. Furthermore, it exhibits minimal conductivity decay under high-frequency strain service environments (resistance shows no significant decay after 1000 cycles of 100% strain, with resistance fluctuations of only 0.1Ω during the cycles). In other words, the flexible circuit fabricated using this method can maintain continuity and normal operation under significant tensile conditions, possessing good electromechanical coupling performance and tensile resistance stability. It can maintain stable operation under high-frequency, high-strain service environments, solving the technical problem of failure of wind turbine blade heating circuits during high-frequency blade deformation. This can, to a certain extent, improve the wind turbine's tolerance to climate, thereby increasing the wind turbine's power generation efficiency.

[0022] Instruction manual illustrations

[0023] Figure 1 SEM image of the liquid metal particles prepared in step one of Example 1;

[0024] Figure 2 An optical micrograph of the liquid metal paste for direct-write 3D printing prepared in step two of Example 1;

[0025] Figure 3 The rheological property curve of the liquid metal slurry for direct writing 3D printing prepared in step two of Example 1;

[0026] Figure 4 The microstructure of the flexible substrate with circuit structure prepared in step four of Example 1;

[0027] Figure 5 This is a schematic diagram of the polytetrafluoroethylene mold described in step four of Example 1;

[0028] Figure 6 This is a schematic diagram of the initial substrate with printed circuit structure prepared in step three of Example 1;

[0029] Figure 7 This is a schematic diagram of steps three to four in Example 1;

[0030] Figure 8 The change in tensile resistance of the direct-write printed flexible circuit prepared in step five of Example 1 under 100% strain (stretch rate 10 mm / s);

[0031] Figure 9 This is a flexible LED lamp circuit fabricated using the direct-write printing flexible circuit prepared in step five of Example 1;

[0032] Figure 10This is to characterize the resistivity and uniformity of conductivity at different sites of the test samples prepared by the liquid metal slurry for direct writing 3D printing in steps two of Examples 1, 3 and 4. Detailed Implementation

[0033] Specific Implementation Method 1: This implementation method is a method for fabricating a direct-write printed flexible circuit, which is carried out according to the following steps:

[0034] I. Preparation of liquid metal particles:

[0035] The oxide layer on the surface of the liquid metal droplets is removed, and then the liquid metal droplets are broken into liquid metal particles by ultrasonic crushing.

[0036] II. Preparation of liquid metal paste for direct-write 3D printing:

[0037] A flexible material is added to liquid metal particles and mixed evenly to obtain a liquid metal slurry for direct-write 3D printing;

[0038] The liquid metal particles in the liquid metal slurry for direct-write 3D printing comprise 30% to 90% by mass.

[0039] III. Circuit printing using the direct-write 3D printing method:

[0040] A 3D printed circuit structure was directly written onto an initial substrate using liquid metal paste for direct writing 3D printing, and then dried and cured to obtain an initial substrate with the printed circuit structure.

[0041] IV. Mechanical Sintering and Transfer of Circuit Structure:

[0042] A flexible substrate material is placed on one side of the initial substrate where the circuit structure is printed and cured to form a flexible substrate. The flexible substrate is then peeled off from the initial substrate, and the circuit structure is transferred to the flexible substrate to achieve the connection of the conductive path, resulting in a flexible substrate with the circuit structure attached.

[0043] V. Interface Outlets and Packaging of Flexible Circuits:

[0044] The method for fabricating a direct-write printed flexible circuit involves leading wires from the circuit ports of a flexible substrate with an attached circuit structure and encapsulating them with a flexible material.

[0045] In this specific implementation method, step one achieves the conversion of liquid metal from droplets to micro / nano particles.

[0046] In this specific implementation, the adhesion force of the initial substrate selected in step three to the printed pattern should be much smaller than that of the flexible substrate in step four, so as to facilitate the transfer of the printed circuit.

[0047] The encapsulation material used in step five of this specific embodiment is the same as that used in the flexible substrate in step four, or has a similar elastic modulus; the thickness of the encapsulation layer is preferably 0.5 mm.

[0048] The mechanical sintering described in step four of this specific embodiment refers to the transfer of the circuit structure onto the flexible substrate during the peeling process between the flexible substrate and the initial substrate. At this time, the peeling process allows the liquid metal particles to come into contact with each other, thereby achieving the connection of the conductive path.

[0049] The beneficial effects of this embodiment are:

[0050] 1. This embodiment proposes a method for activating the conductive pathway of liquid metal particles in liquid metal / polymer composite slurry DIW molding and printing circuits. The conductivity of the printed circuit can reach 10. 5 The S / m order of magnitude, along with the DIW molding method, greatly achieves the principle of allocating materials on demand, saving costs. Furthermore, the availability of flexible materials expands the applicability of this embodiment, allowing the fabrication of flexible circuits with various flexible materials as the covering layer.

[0051] 2. In this embodiment, the circuit structure uses liquid metal as the conductive material. Due to the presence of the flexible material matrix, there is no significant liquid metal leakage during mechanical sintering (peeling and transfer process), and the internal liquid metal remains in particle form. After the circuit is formed, it is covered with a flexible material, exhibiting relatively stable conductivity. This makes it a promising candidate for applications in flexible circuits, electronic communications, and soft robotics. Specifically, the addition of the flexible material imparts better printability, economy, and stability to the slurry.

[0052] 3. In this specific embodiment, the circuit structure is transferred to a flexible material by stripping and the conductive pathways of the liquid metal particles inside the circuit are activated and connected. That is, the wire circuit prepared by this method of forming conductive pathways with liquid metal is connected by forming an internal permeation network structure.

[0053] 4. By combining the properties of liquid metal that simultaneously satisfy deformation and conductivity, the fabricated flexible circuit can maintain conductivity continuity and relative stability of resistance under 100% strain. Furthermore, it exhibits minimal conductivity decay under high-frequency strain service environments (resistance shows no significant decay after 1000 cycles of 100% strain, with resistance fluctuations of only 0.1Ω during the cycles). In other words, the flexible circuit fabricated using this method can maintain continuity and normal operation under significant tensile conditions, possessing good electromechanical coupling performance and tensile resistance stability. It can maintain stable operation under high-frequency, high-strain service environments, solving the technical problem of failure of wind turbine blade heating circuits during high-frequency blade deformation. This can, to a certain extent, improve the wind turbine's tolerance to climate, thereby increasing the wind turbine's power generation efficiency.

[0054] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the liquid metal droplets mentioned in step one are room-temperature liquid metal droplets of gallium or gallium alloy. Everything else is the same as in Specific Implementation Method One.

[0055] The liquid metal droplets mentioned in step one of this specific embodiment are room temperature liquid metals such as gallium indium eutectic (75wt% Ga, 25wt% In) and gallium indium tin eutectic (Ga:In:Sn 68.5wt%:21.5wt%:10wt%).

[0056] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the removal of the oxide layer on the surface of the liquid metal droplets in step one specifically involves mixing NaOH solution or HCl solution with the liquid metal, allowing it to stand for 3 to 5 minutes, and finally aspirating the treated liquid metal. This completes the removal of the oxide layer on the surface of the liquid metal droplets. The concentration of the NaOH solution is 1 mol / L to 2 mol / L, and the concentration of the HCl solution is 1 mol / L to 2 mol / L. The volume ratio of liquid to liquid metal is 10:(1-2). In step one, the liquid metal droplets are broken into liquid metal particles by ultrasonic disruption. Specifically, anhydrous ethanol is used as the ultrasonic medium. The liquid metal droplets are added to ethanol and ultrasonically disrupted for 30-60 seconds under the conditions of an ice-water bath, an ultrasonic cell disruptor with a power of 100W-150W, and a distance of 5mm-10mm between the bottom of the amplitude transformer and the upper surface of the droplets. During the ultrasonic process, the ultrasonication is stopped for 5-7 seconds every 3-5 seconds. Finally, the particles are dried until the ethanol is completely evaporated to obtain liquid metal particles. Other steps are the same as in specific implementation method one or two.

[0057] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step two, a solution containing a flexible material is added to the liquid metal particles and mixed evenly. Specifically, this is done using a vacuum stirrer / deaerator at a mixing speed of 500 r / min to 2400 r / min for 5 to 10 minutes. Everything else is the same as in Specific Implementation Methods One to Three.

[0058] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the flexible material mentioned in step two is an adhesive, flexible prepolymer, resin, hydrogel, or silicone rubber; the liquid metal slurry for direct-write 3D printing mentioned in step two is used at a shear rate of 30s. -1 Under these conditions, the viscosity ranges from 200 mPa·s to 16000 mPa·s. Other aspects are the same as in embodiments one through four.

[0059] When the flexible material described in step two of this specific embodiment is thermoplastic polyurethane (TPU), the concentration is preferably 300 mg / mL, and the solvent is dimethylacetamide (DMAC).

[0060] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: in step three, a 3D printed circuit structure is directly written onto the initial substrate using liquid metal paste for direct-write 3D printing. Specifically, the liquid metal paste for direct-write 3D printing is loaded into a dispensing needle, and the circuit is printed on the initial substrate under the following conditions: the height of the printer nozzle from the surface of the initial substrate is 0.05mm to 0.3mm, the air pressure is 4psi to 40psi, the printing speed is 1mm / s to 20mm / s, and the nozzle diameter is 0.1mm to 0.25mm. Everything else is the same as in Specific Implementation Methods One to Five.

[0061] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the initial substrate in step three is a PET film, alumina ceramic plate, silicon nitride ceramic plate, glass, or PVC film; the flexible substrate material in step four is water-based polyurethane or silicone rubber; and a layer of flexible substrate material with a thickness of 0.5 mm to 1 mm is provided in step four. Everything else is the same as in Specific Implementation Methods One to Six.

[0062] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the drying and curing described in step three is specifically carried out at a temperature of 60℃ to 80℃ for 4 to 10 hours; the curing described in step four is specifically carried out at room temperature for 12 to 24 hours, followed by annealing at a temperature of 80℃ to 150℃ for 4 to 6 hours. The rest is the same as in Specific Implementation Methods One to Seven.

[0063] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that: in step five, a wire is led out from the circuit port of the flexible substrate with the circuit structure. Specifically, this is done as follows: first, a low-temperature conductive silver paste is applied to the circuit port of the flexible substrate with the circuit structure and dried; then, a drop of liquid metal is added to the dried conductive silver paste; finally, a copper foil with a thickness of 0.05mm to 0.1mm is used as the lead wire to lead out from the circuit port of the flexible substrate with the circuit structure. Everything else is the same as in Specific Implementation Methods One to Eight.

[0064] Specific Implementation Method 10: This implementation method is an application of a direct-write printing flexible circuit, characterized in that it is used for flexible heating and defrosting of wind turbine blades.

[0065] The beneficial effects of the present invention are verified using the following embodiments:

[0066] Example 1, combined with Figure 6 and Figure 7 Detailed analysis:

[0067] A method for fabricating a direct-write printed flexible circuit, comprising the following steps:

[0068] I. Preparation of liquid metal particles:

[0069] Remove the oxide layer on the surface of the liquid metal droplets, and then use anhydrous ethanol as the ultrasonic medium. Add the liquid metal droplets to the ethanol and sonicate for 30 seconds under the conditions of an ice-water bath, an ultrasonic cell disruptor with a power of 100W and a distance of 5mm between the bottom of the amplitude rod and the upper surface of the droplets. During the sonication process, stop sonicating for 7 seconds every 3 seconds. Finally, dry until the ethanol has completely evaporated to obtain liquid metal particles.

[0070] II. Preparation of liquid metal paste for direct-write 3D printing:

[0071] A thermoplastic polyurethane solution was added to liquid metal particles, and the mixture was stirred for 5 minutes using a vacuum stirrer at a mixing speed of 2400 r / min to obtain a liquid metal slurry (EGaIn / TPU) for direct writing 3D printing.

[0072] The liquid metal slurry for direct-write 3D printing contains 70% liquid metal particles by mass; the thermoplastic polyurethane solution has a concentration of 300 mg / mL and is specifically prepared using dimethylacetamide as a solvent via a water bath method controlled at 80°C; the liquid metal slurry for direct-write 3D printing has a shear rate of 30 s. -1 The viscosity under these conditions is 8500 mPa·s;

[0073] III. Circuit printing using the direct-write 3D printing method:

[0074] Liquid metal paste for direct-write 3D printing was loaded into a dispensing needle. Circuits were printed on the PET film under the following conditions: the height of the printer nozzle from the PET film surface was 0.25 mm, the air pressure was 25 psi, the printing speed was 15 mm / s, and the nozzle diameter was 0.25 mm. Finally, the film was dried at 80°C for 4 hours to obtain an initial substrate with printed circuit structure.

[0075] IV. Mechanical Sintering and Transfer of Circuit Structure:

[0076] The initial substrate with the printed circuit structure is placed in a polytetrafluoroethylene mold. A layer of flexible substrate material with a thickness of 0.5 mm is poured on one side of the initial substrate with the printed circuit structure. The substrate is cured at room temperature for 24 hours and then annealed at 80°C for 6 hours to form a flexible substrate. The flexible substrate is peeled off from the initial substrate, and the circuit structure is transferred to the flexible substrate to achieve the connection of the conductive path, thus obtaining a flexible substrate with the attached circuit structure.

[0077] V. Interface Outlets and Packaging of Flexible Circuits:

[0078] First, low-temperature conductive silver paste is applied to the circuit port of the flexible substrate with the circuit structure and dried at 80°C for 4 hours. Then, a drop of liquid metal is added to the dried conductive silver paste. Finally, a copper foil with a thickness of 0.1 mm is used as a lead wire to lead out from the circuit port of the flexible substrate with the circuit structure, resulting in a flexible circuit with interface lead wires. The flexible circuit with interface lead wires is placed in a polytetrafluoroethylene mold, and a layer of flexible substrate material with a thickness of 0.5 mm is poured on the side with the printed circuit structure. It is cured at room temperature for 24 hours and then annealed at 100°C for 4 hours to complete the encapsulation process and obtain the direct-write printed flexible circuit.

[0079] The liquid metal droplets mentioned in steps one and five are room temperature liquid metal droplets of gallium indium eutectic (EGaIn; 75wt%Ga, 25wt%In);

[0080] The removal of the oxide layer on the surface of the liquid metal droplets described in step one specifically involves mixing 30 mL of NaOH solution with 5 mL of liquid metal, letting it stand for 3 minutes, and finally aspirating the treated liquid metal to complete the removal of the oxide layer on the surface of the liquid metal droplets. The concentration of the NaOH solution is 1 mol / L.

[0081] The thermoplastic polyurethane solution mentioned in step two is BASF's 1190A model.

[0082] The flexible substrate material mentioned in steps four and five is Dongguan Guanzhi PU-6011 waterborne polyurethane emulsion;

[0083] The low-temperature conductive silver paste mentioned in step five is Ketterson low-temperature conductive silver paste.

[0084] Example 2: This example differs from Example 1 in that a silicone rubber mixture is added to the liquid metal particles in step 2. The silicone rubber mixture is Dow Corning 184, manufactured by Dow Corning, and is prepared according to the following steps: Silicone rubber A and B (curing agent) are mixed at a mass ratio of 10:1, and then mixed for 3 minutes using a vacuum degassing machine at a rotation speed of 2500 rpm and a vacuum degree of 50 kPa; the liquid metal slurry for direct-write 3D printing mentioned in step 2 is subjected to a shear rate of 30 s... -1 The viscosity under the given conditions was 14000 mPa·s; Step 3: Liquid metal paste for direct-write 3D printing was loaded into a dispensing needle. Circuit printing was performed on the Al2O3 initial substrate under the conditions of a printer nozzle height of 0.3 mm from the initial substrate, an air pressure of 25 psi, a printing speed of 15 mm / s, and a nozzle diameter of 0.25 mm. The substrate was then dried at 80°C for 4 hours to obtain an initial substrate with printed circuit structures; Step 4: Under the conditions of a printer nozzle height of 0.4 mm from the initial substrate, an air pressure of 25 psi, a printing speed of 50 mm / s, and a nozzle diameter of 0.4 mm, electrical circuits were printed on the initial substrate. A 0.5mm thick flexible substrate material is printed on one side of the circuit structure, cured at room temperature for 12 hours, and then annealed at 80°C for 6 hours to form the flexible substrate. In step five, under conditions of a printer nozzle height of 0.4mm above the flexible substrate, an air pressure of 25psi, a printing speed of 50mm / s, and a nozzle diameter of 0.4mm, a 0.5mm thick flexible substrate material is printed on the side with the circuit structure. It is cured at room temperature for 12 hours, and then annealed at 80°C for 6 hours to complete the encapsulation process. The flexible substrate material mentioned in steps four and five is Dow Corning 184 silicone rubber. Other procedures are the same as in Example 1.

[0085] Example 3: This example differs from Example 1 in that the mass percentage of liquid metal particles in the liquid metal slurry for direct-write 3D printing described in step 2 is 60%. Everything else is the same as in Example 1.

[0086] Example 4: This example differs from Example 1 in that the mass percentage of liquid metal particles in the liquid metal slurry for direct-write 3D printing described in step 2 is 50%. Everything else is the same as in Example 1.

[0087] Examples 1 and 2 utilize Dow Corning 184 silicone rubber and Guanzhi PU-6011 waterborne polyurethane as flexible encapsulation materials to fabricate flexible circuits on two substrates. This process offers advantages such as simple operation, stable conductivity, low liquid metal leakage, high damage repair capability, high economic efficiency, and high printing flexibility. Modularly embedding these materials as overlays within wind turbine blades as heating circuits enables stable defrosting under high-frequency deformation conditions, thereby improving the power generation efficiency of wind turbines.

[0088] Figure 1 The image shows an SEM image of the liquid metal particles prepared in step one of Example 1. As can be seen from the image, the liquid metal can be broken into particles with relatively regular shapes.

[0089] According to particle size analysis software, the particle size of the liquid metal particles prepared in step one of Example 1 is 20 micrometers to 30 micrometers.

[0090] Figure 2 The image shows an optical micrograph of the liquid metal slurry for direct writing 3D printing prepared in step two of Example 1. As can be seen from the image, the liquid metal exists in the composite slurry in the form of particles rather than in the form of a continuous liquid phase.

[0091] Figure 3 The figure shows the rheological properties of the liquid metal slurry for direct-write 3D printing prepared in step two of Example 1. As can be seen from the figure, the addition of liquid metal particles increases the viscosity of the slurry at a shear rate of 30 s⁻¹. -1 The viscosity under the specified conditions is 8500 mPa·s, and its viscosity range meets the requirements for direct-write printing.

[0092] Figure 4 The image shows the microstructure of the flexible substrate with circuit structure prepared in step four of Example 1. As can be seen from the figure, mechanical peeling did not destroy the liquid metal particle structure. After peeling, the liquid metal particles in the printed structure are in contact with each other, realizing the connection of the conductive path, and still exist in the form of particles.

[0093] Figure 5 This is a schematic diagram of the polytetrafluoroethylene (PTFE) mold described in step four of Example 1. As shown in the diagram, casting requires a rectangular mold with a depth of 1 mm, and the internal groove dimensions of this mold are 200 mm × 200 mm × 1 mm. PTFE is the preferred mold material for easy demolding.

[0094] Figure 8 The figure shows the change in tensile resistance of the direct-write printed flexible circuit prepared in step five of Example 1 under 100% strain (stretching rate 10 mm / s). As can be seen from the figure, the resistance of the circuit fluctuates regularly from 0.4 Ω to 0.5 Ω during the stretching process. That is, the resistance does not decrease significantly after 1000 cycles of 100% strain, and the resistance fluctuates by only 0.1 Ω during the cycle.

[0095] Figure 9 The figure shows a flexible LED lamp circuit fabricated using the direct-write printing flexible circuit prepared in step five of Example 1. As can be seen from the figure, the LED lamp circuit is flexible while meeting normal working conditions.

[0096] The liquid metal paste for direct writing 3D printing prepared in Examples 1, 3 and 4 step 2 was printed into a conductivity test sample (a square, fully filled structure with a length of 10 mm and a width of 10 mm), and the resistivity was tested using a four-probe instrument. Figure 10 The figures characterize the resistivity and conductivity uniformity at different sites of the test samples prepared by the liquid metal slurry for direct-write 3D printing in steps two of Examples 1, 3, and 4. It can be seen from the figures that, after conversion, when the liquid metal mass fraction reaches 70 wt%, the conductivity can reach 10. 5 The conductivity is on the order of S / m and the conductivity distribution is relatively uniform.

Claims

1. A method for fabricating a direct-write printed flexible circuit, characterized in that... It is done in the following steps: I. Preparation of liquid metal particles: Remove the oxide layer on the surface of the liquid metal droplets, and then use anhydrous ethanol as the ultrasonic medium. Add the liquid metal droplets to anhydrous ethanol and sonicate for 30s to 60s under the conditions of an ice-water bath, an ultrasonic cell disruptor with a power of 100W to 150W, and a distance of 5mm to 10mm between the bottom of the amplitude rod and the upper surface of the droplets. During the sonication, stop sonication for 5s to 7s every 3s to 5s. Finally, dry until the anhydrous ethanol has completely evaporated to obtain liquid metal particles. II. Preparation of liquid metal paste for direct-write 3D printing: A flexible material is added to liquid metal particles and mixed evenly to obtain a liquid metal slurry for direct-write 3D printing; The liquid metal slurry for direct-write 3D printing contains 30% to 90% liquid metal particles by mass; the liquid metal slurry for direct-write 3D printing is used at a shear rate of 30s. -1 Under these conditions, the viscosity ranges from 200 mPa·s to 16000 mPa·s. The flexible material is a thermoplastic polyurethane solution; III. Circuit printing using the direct-write 3D printing method: Liquid metal paste for direct-write 3D printing is loaded into a dispensing needle. Under the conditions of a printer nozzle height of 0.05mm~0.3mm from the surface of the initial substrate, an air pressure of 25psi~40psi, a printing speed of 15mm / s~20mm / s, and a nozzle diameter of 0.25mm, circuits are printed on the initial substrate. The substrate is then dried at a temperature of 60℃~80℃ for 4h~10h to obtain an initial substrate with printed circuit structures. The initial substrate is a PET film, an alumina ceramic plate, a silicon nitride ceramic plate, glass, or a PVC film; IV. Mechanical Sintering and Transfer of Circuit Structure: A flexible substrate material is placed on one side of the initial substrate with the printed circuit structure and cured at room temperature for 12h~24h. Then, it is annealed at 80℃~150℃ for 4h~6h to form a flexible substrate. The flexible substrate is peeled off from the initial substrate, the circuit structure is transferred to the flexible substrate and the conductive path is connected to obtain a flexible substrate with the attached circuit structure. The flexible substrate material is waterborne polyurethane; V. Interface Outlets and Packaging of Flexible Circuits: The method for fabricating a direct-write printed flexible circuit involves leading wires from the circuit ports of a flexible substrate with an attached circuit structure and encapsulating them with a flexible material.

2. The method for fabricating a direct-write printed flexible circuit according to claim 1, characterized in that... The liquid metal droplets mentioned in step one are room temperature liquid metal droplets of gallium or gallium alloy.

3. The method for fabricating a direct-write printed flexible circuit according to claim 1, characterized in that... The removal of the oxide layer on the surface of the liquid metal droplets described in step one specifically involves mixing NaOH solution or HCl solution with the liquid metal, allowing it to stand for 3 to 5 minutes, and finally aspirating the treated liquid metal. This completes the removal of the oxide layer on the surface of the liquid metal droplets. The concentration of the NaOH solution is 1 mol / L to 2 mol / L, the concentration of the HCl solution is 1 mol / L to 2 mol / L, and the volume ratio of the NaOH solution or HCl solution to the liquid metal is 10:(1 to 2).

4. The method for fabricating a direct-write printed flexible circuit according to claim 1, characterized in that... In step two, a solution containing flexible material is added to the liquid metal particles and mixed evenly. Specifically, a vacuum stirrer is used to stir for 5 to 10 minutes at a mixing speed of 500 r / min to 2400 r / min.

5. The method for fabricating a direct-write printed flexible circuit according to claim 1, characterized in that... In step four, a flexible substrate material with a thickness of 0.5mm to 1mm is set.

6. The method for fabricating a direct-write printed flexible circuit according to claim 1, characterized in that... Step five involves leading wires from the circuit port of the flexible substrate with the circuit structure. Specifically, the following steps are performed: First, apply low-temperature conductive silver paste to the circuit port of the flexible substrate with the circuit structure and dry it. Then, add a drop of liquid metal to the dried conductive silver paste. Finally, use a copper foil with a thickness of 0.05mm to 0.1mm as the lead wire to lead wires from the circuit port of the flexible substrate with the circuit structure.

7. The application of a direct-write printed flexible circuit prepared according to claim 1, characterized in that... It is used for flexible heating and defrosting of wind turbine blades.

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