High-temperature-resistant flexible circuit and preparation method and application thereof

Abstract

The invention discloses a high-temperature-resistant flexible circuit and a preparation method and application thereof, and belongs to the technical field of flexible electronics. Liquid metal particles and a solution of a high-temperature-resistant polymer are blended, the mixed solution is subjected to blade coating on a glass plate to form a film, then the film is placed in a drying oven to evaporate a solvent and is subjected to high-temperature crosslinking, then an ultraviolet laser imprinting machine is used for conducting circuit imprinting on the surface of the cooled film, and the high-temperature-resistant flexible circuit is obtained. According to the invention, the high-temperature-resistant polymer is used as the flexible circuit substrate, and the laser-activated dispersed liquid metal particles are used as the circuit, so that the high-temperature-resistant performance of the flexible circuit is improved.

Description

Technical Field

[0001] The present invention relates to the field of flexible electronic technology, and in particular to a high-temperature resistant flexible circuit and a preparation method and application thereof. Background Art

[0002] Flexible electronics have found widespread application in biomedical devices, soft robotics, wearable electronics, and other fields. Power supplies, sensors, processors, and other electronic components are integrated onto flexible substrates. Currently, the manufacture of stretchable flexible substrates is one of the main challenges hindering the development of flexible electronics. Liquid metal, with its rheological properties and high conductivity, is an ideal conductive medium for manufacturing flexible electronics. Commonly used liquid metal processing methods include microchannel injection, vacuum filling microchannels, extrusion, hand-drawing, masking, and 3D printing.

[0003] Sintering is an important post-deposition process for treating the surface oxide around each nanoparticle to form a conductive path, thereby realizing the function of printed electronic devices. Sintering methods for ordinary solid metal particles include thermal sintering, microwave sintering, photon sintering, and plasma sintering. Nanoparticles can be mechanically sintered at room temperature. Mechanical pressure is applied to break the oxide shell of the nanoparticles, making them insulating, releasing the liquid metal core, and combining them into an electrical path. For example, in Nat. Mater. 20, 851–858 (2021), liquid metal is applied to the surface of a silicon wafer, then calcined at high temperature to connect the liquid metal to form a liquid metal network, which is then transferred to the surface of a flexible substrate. The steps are numerous, and the transfer process can easily damage the circuit. Combining jet printing with laser direct sintering can simplify the process. For example, in ACS Appl. Mater. Interfaces 2018, 10, 28232-28241, liquid metal ink is sprayed onto a flexible substrate, and then the ink on the substrate is sintered using a laser to form a liquid metal conductive network. There are many methods for preparing flexible conductive networks. However, the flexible conductive networks prepared so far usually use flexible substrates that are not resistant to high temperatures and are difficult to operate in high-temperature environments. Such reports are rare.

[0004] Therefore, how to develop a method that can improve the high temperature resistance of flexible circuits and improve the circuit stability and circuit resolution at high temperatures is a technical problem that those skilled in the art urgently need to solve. Summary of the Invention

[0005] In view of this, the present invention provides a high-temperature resistant flexible circuit and a preparation method and application thereof.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for preparing a high-temperature resistant flexible circuit, characterized by comprising the following steps:

[0008] (1) mixing liquid metal particles with a solution of a high-temperature resistant polymer to obtain a mixed solution;

[0009] (2) applying the mixed solution to a glass plate to form a film, and then placing the glass plate in an oven to heat and evaporate the solvent and perform high-temperature cross-linking to form a film;

[0010] (3) Using an ultraviolet laser engraving machine, a circuit is engraved on the surface of the cooled film to obtain a high-temperature resistant flexible circuit.

[0011] Furthermore, in step (1), the mass ratio of the liquid metal particles to the high temperature resistant polymer is 1:0.5-1.5.

[0012] The beneficial effect of adopting the above further solution is that the above solution of the present invention can effectively improve the electrical properties by adding an appropriate amount of liquid metal particles while ensuring the mechanical properties of the polymer film.

[0013] Furthermore, the preparation method of the liquid metal particles is:

[0014] The liquid metal is added to N,N-dimethylformamide, and then ultrasonicated with an ultrasonic cell crusher. After the ultrasonication is completed, centrifugation is performed to obtain a precipitate, which is the liquid metal particles.

[0015] The liquid metal is gallium-indium alloy liquid metal, and its melting point is 16°C.

[0016] Furthermore, the ratio of the mass of the liquid metal to the volume of N,N-dimethylformamide is 1-3 g:15 ml;

[0017] The ultrasonic power is 350w, and the ultrasonic time is 2-15min.

[0018] The centrifugal speed is 4500 rpm and the centrifugal time is 5 min. The precipitate is dried at room temperature for 24 h to form liquid metal particles.

[0019] Furthermore, the high temperature resistant polymer can continuously work at 200°C for more than 100 hours;

[0020] Preferably, the high temperature resistant polymer is any one of polyimide, polyetheretherketone, and polyaryletherketone;

[0021] The solvent in the high-temperature resistant polymer solution is a mixture of one or more of N,N-dimethylformamide, N,N-dimethylformamide, N-methylpyrrolidone, and tetrahydrofuran.

[0022] Preferably, the solid content of the high temperature resistant polymer solution is 12-35 wt.%.

[0023] The beneficial effect of adopting the above further solution is that the addition of an appropriate solid content in the present invention can ensure the effect and performance of the subsequent film-forming by blade coating of the polymer solution.

[0024] Furthermore, in step (1), the liquid metal and the high-temperature resistant polymer solution are mixed and stirred evenly in a planetary mixer, and then scraped onto a glass plate.

[0025] Furthermore, the planetary mixer was stirred at a speed of 1500 rpm for 10 min, and the mixed solution was degassed in a vacuum oven at 100 Pa for 30 min.

[0026] The beneficial effect of adopting the above further solution is that the sufficient stirring and vacuum degassing process in the present invention can reduce the phenomenon of uniform distribution of liquid metal particles and pinhole defects during the polymer film forming process.

[0027] Furthermore, in step (2), the scraping process is performed using a scraper with a spacing of 500 μm.

[0028] Furthermore, the coating thickness in step (2) is 50-500 μm, the oven heating temperature is 120-220° C., and the heating time is 30-250 min.

[0029] Furthermore, the frequency of the ultraviolet laser in step (3) is 20 kHz, the pulse width is 10-30 μs, and the line spacing is 0.01-0.08 mm.

[0030] Furthermore, the width of the laser-engraved circuit is 0.1-5 mm.

[0031] The beneficial effect of adopting the above further solution is that the wider laser engraving width set by the present invention is conducive to low resistance of the circuit.

[0032] The present invention also provides the use of the high-temperature resistant flexible circuit prepared by the above method in sensor integration.

[0033] The beneficial effects of the present invention are: the present invention solves the problem that flexible circuits cannot operate at high temperatures, greatly improving the potential use of flexible circuits in harsh environments. The flexible circuit is resistant to high temperatures, has stable resistance, strong designability, and high resolution. The preparation process is simple and highly flexible, overcoming the problems of numerous and complex traditional preparation processes. By using a high-temperature resistant polymer as a substrate and liquid metal as a conductor, a flexible circuit at high temperature is realized, which has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a scanning electron microscope image of the polyimide film prepared in Example 1 of the present invention without laser imprinting;

[0035] Figure 2This is a scanning electron microscope image of the laser-engraved polyimide film prepared in Example 1 of the present invention;

[0036] Figure 3 This is the stress-strain curve of the laser-engraved polyimide film prepared in Example 1 of the present invention;

[0037] Figure 4 The linear relationship between distance and resistance at different liquid metal contents in the membrane imprinted circuit according to Example 1 of the present invention;

[0038] Figure 5 This is a graph showing the resistance variation trend of the high-temperature resistant flexible circuit prepared in Example 1 of the present invention at high temperatures. DETAILED DESCRIPTION

[0039] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0040] Example 1

[0041] A method for preparing a high-temperature resistant flexible circuit comprises the following steps:

[0042] (1) 1 g of gallium-indium alloy liquid metal and 15 ml of N,N-dimethylformamide were placed in a glass bottle, and treated in an ultrasonic pulverizer at a power of 350 W for 15 minutes. After the ultrasonication was completed, the precipitate was treated in a centrifuge at a speed of 4500 rpm for 5 minutes. The precipitate was taken and dried at room temperature for 24 hours to obtain the liquid metal particles. An N-methylpyrrolidone solution of polyamic acid with a solid content of 15 wt.% was mixed with the liquid metal particles, with the mass ratio of liquid metal to polyamic acid being 1:1. The mixture was stirred in a planetary mixer at a speed of 1500 rpm for 10 minutes, and then degassed in a vacuum oven at 100 Pa for 30 minutes. The mixture was then scraped on a glass plate using a scraper with a spacing of 500 μm.

[0043] (2) The coated glass plate is placed in an oven and the solvent is evaporated and imidization cross-linked by a programmed temperature increase method; the oven temperature increase program is: 25°C-80°C (30 min)-120°C (30 min)-180°C (30 min)-220°C (30 min)-25°C.

[0044] (3) The film was peeled off from the glass plate and then placed in an ultraviolet laser. The frequency of the ultraviolet laser was set to 20 kHz, the pulse width was set to 30 μs, the line spacing was set to 0.03 mm, and the printed circuit width was set to 0.1 mm to obtain the high-temperature resistant flexible circuit.

[0045] The diameter of the liquid metal particles is 5-20μm. After circuit performance analysis, the square resistance is 0.0012Ω. When the temperature rises to 300℃, the square resistance change rate is less than 40%. Figure 1 and Figure 2 The changes of the membrane before and after laser engraving can be observed by observing the liquid metal. Figure 3 It can be judged that the liquid metal particles have a significant improvement on the tensile properties of the diaphragm. Figure 4 It can be judged that the liquid metal particles are evenly dispersed in the diaphragm and there is no short circuit phenomenon. Figure 5 The high temperature resistant flexible resistor has a small resistance change as the temperature rises.

[0046] Examples 2-4

[0047] Compared with Example 1, Examples 2-4 adjust the distribution density of liquid metal particles in the polyimide film by changing the mass ratio of liquid metal particles to polyamic acid in step (1), thereby producing high-temperature resistant flexible circuits with different liquid metal contents. The other steps are the same as Example 1.

[0048] The experimental conditions and parameters of Examples 2-4 are listed in Table 1. As can be seen from Table 1, when the mass ratio of liquid metal to polyamic acid is between 1:0.5-1.5, the sheet resistance is low and the conductive performance is stable.

[0049] Table 1

[0050]

[0051]

[0052] Examples 5-7

[0053] Compared with Example 1, Examples 5-7 control the circuit density by changing the laser engraved circuit width in step (3), thereby producing circuits of different widths. The other steps are the same as Example 1. As shown in Table 2, the circuit engraving width has little effect on the square resistance, and can be as low as 0.1 mm, and the conductive performance is stable.

[0054] Table 2

[0055] Circuit marking width (mm) Room temperature square resistance (Ω) 300℃ Square resistance (Ω) Example 1 0.1 0.0012 0.0014 Example 5 0.2 0.0012 0.0014 Experimental Example 6 0.5 0.0012 0.0013 Experimental Example 7 1 0.0011 0.0012

[0056] Example 8

[0057] Compared with Example 1, Example 8 changes the composition of the high-temperature resistant polymer solution, dissolving polyetheretherketone in a mixed solvent of tetrahydrofuran and N,N-dimethylacetamide, with a volume ratio of 15 / 85, thereby producing high-temperature resistant flexible circuits with different substrate types. The rest is the same as Example 1.

[0058] The square resistance of Example 8 is 0.0014Ω, and the square resistance at 300°C is 0.0017Ω. The type of high-temperature resistant polymer has little effect on the square resistance of the circuit, and the conductive performance is stable.

[0059] Comparative Example 1

[0060] This comparative example provides a method for preparing a high-temperature resistant flexible circuit. The preparation method is the same as Example 1 except that the mass ratio of liquid metal to polyamic acid in step (1) is 1:0.4.

[0061] The square resistance of Comparative Example 1 is 4.17Ω, and the square resistance is 5.77Ω at 300°C. When the mass fraction of liquid metal particles is low, it is difficult to form a connected conductive network, resulting in a large square resistance. The square resistance increases significantly when the temperature rises, making it difficult to integrate electronic devices into flexible circuits.

[0062] Comparative Example 2

[0063] This comparative example provides a method for preparing a high-temperature resistant flexible circuit. The preparation method is the same as that of Example 1 except that the width of the laser engraved circuit in step (3) is 0.02 mm.

[0064] The sheet resistance of Comparative Example 2 is 2.44Ω, and the sheet resistance is 2.51Ω at 300°C. When the laser-engraved circuit width is narrow, the liquid metal particles are partially disconnected, resulting in a large sheet resistance. When the temperature rises, the sheet resistance increases significantly, making it difficult to integrate electronic devices into flexible circuits.

[0065] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a high temperature resistant flexible circuit, characterized in that: The following steps are involved: (1) mixing liquid metal particles with a solution of a high-temperature resistant polymer to obtain a mixed solution; (2) applying the mixed solution to a glass plate to form a film, and then placing the glass plate in an oven to heat and evaporate the solvent and perform high-temperature cross-linking to form a film; (3) Using an ultraviolet laser engraving machine, a circuit is engraved on the surface of the cooled film to obtain a high-temperature resistant flexible circuit.

2. The method for preparing a high temperature resistant flexible circuit according to claim 1, characterized in that: In step (1), the mass ratio of the liquid metal particles to the high-temperature resistant polymer is 1:0.5-1.

5.

3. The method for preparing a high temperature resistant flexible circuit according to claim 2, characterized in that: The preparation method of the liquid metal particles is: The liquid metal is added to N,N-dimethylformamide, and then ultrasonicated with an ultrasonic cell crusher. After the ultrasonication is completed, centrifugation is performed to obtain a precipitate, which is the liquid metal particles. The liquid metal is a gallium-indium alloy.

4. The method for preparing a high temperature resistant flexible circuit according to claim 3, characterized in that: The ratio of the mass of the liquid metal to the volume of N,N-dimethylformamide is 1-3 g:15 ml; The ultrasonic power is 350w, and the ultrasonic time is 2-15min.

5. The method for preparing a high temperature resistant flexible circuit according to claim 2, wherein: The high temperature resistant polymer is any one of polyimide, polyetheretherketone, and polyaryletherketone; The solvent in the high-temperature resistant polymer solution is a mixture of one or more of N,N-dimethylformamide, N,N-dimethylformamide, N-methylpyrrolidone, and tetrahydrofuran.

6. The method for preparing a high temperature resistant flexible circuit according to claim 1, characterized in that: The scraping thickness in step (2) is 50-500 μm, the oven heating temperature is 120-220° C., and the heating time is 30-250 min.

7. The method for preparing a high temperature resistant flexible circuit according to claim 1, characterized in that: The frequency of the ultraviolet laser in step (3) is 20 kHz, the pulse width is 10-30 μs, and the line spacing is 0.01-0.08 mm.

8. The method for preparing a high temperature resistant flexible circuit according to claim 7, characterized in that: The width of the laser engraved circuit is 0.1-5mm.

9. A high temperature resistant flexible circuit, characterized in that: The method according to any one of claims 1 to 8 is used to prepare the present invention.

10. Use of the high-temperature resistant flexible circuit according to claim 9 in sensor integration.

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