A Conductive Enhancement Structure for Flexible Stretchable Circuits and a Manufacturing Method Thereof

Abstract

A conductive enhancement structure for a flexible and stretchable circuit and a manufacturing method thereof. A microstructure array is distributed in the elastic substrate of the conductive enhancement structure. By utilizing the Poisson effect characteristic, under the stretching action, the Poisson effect causes the material in the vertical direction of the stretching to be compressed. The compression reduces the distance between the microstructures, generating an extrusion effect on the porous conductive filler filled in the microstructures, thereby making the two-dimensional nano conductive materials in the porous conductive filler more closely connected, overcoming the problem that traditional conductive materials are prone to failure under the stretching action, and being able to achieve excellent performance with better conductivity as it is stretched. In the manufacturing method, a process of first scraping and then sintering is adopted to form the porous conductive filler in the microstructures. Compared with the process of first sintering and then scraping, it reduces the initial deformation of the porous structure, which is beneficial for the subsequent realization of the conductive enhancement effect. The present invention solves the problem of easy shedding of the conductive material, has high cycle stability, and is applicable to the manufacture of flexible and stretchable circuits.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-nano manufacturing flexible sensing technology, and particularly relates to a conductive enhancement structure for a flexible and stretchable circuit and a manufacturing method thereof. Background Art

[0002] As a key structure for interconnecting various circuit elements in flexible electronic devices, flexible and stretchable circuits can be widely applied to engineering applications with large deformations, and have broad application prospects in the fields of wearable devices, medical health, etc. Compared with traditional circuits, flexible and stretchable circuits can measure complex surfaces without wear and damage due to their flexible and deformable advantages.

[0003] Currently, the research on flexible and stretchable circuits mainly focuses on two aspects: materials and structures. Commonly used stretchable materials are mainly divided into two types: one is intrinsically stretchable liquid metal materials, and the other is conductive composite materials prepared by applying an elastic substrate and conductive fillers. Although the modification design of materials can achieve high stretchability of materials from the micro-structure, in actual applications, because the stretching effect provided by large stretching scenarios is limited, it is necessary to design stretchable structures at a larger scale to achieve its high stretchability. By designing the structure of the connecting wires, the electronic device can meet the requirements of large deformations while maintaining good electrical performance. Common structures include serpentine structures, wrinkled structures, Kirigami structures, island-bridge structures, etc. However, due to the uneven surfaces and large contact areas generated by these structures, the area of flexible and stretchable circuits is increased, so they are not suitable for the manufacture of high-density devices.

[0004] Although many studies have achieved the regulation of the stretchability of flexible and stretchable circuits, due to the limited ability of existing manufacturing methods to control structures, there are still technical problems in balancing the conductivity and stretchability of flexible and stretchable circuits.

[0005] The patent application with the publication number CN114567966A discloses a stretchable circuit with a serpentine structure, which adopts a strain relief structure. When the strain exceeds the preset value of the structure, there is a problem that the circuit is easily broken. The patent application with the publication number CN115979032A discloses a flexible and stretchable circuit based on liquid metal encapsulation. Although the intrinsically stretchable liquid metal has good stretchability in nature, the fluidity of the liquid makes it easy to leak, resulting in circuit disconnection. The patent application with the publication number CN115881340A discloses a flexible and stretchable electrode with high conductive stability, but the conductive nanocomposite materials used therein often have a trade-off problem between conductivity and stretchability.

[0006] In summary, traditional circuits cannot avoid the problems of increased resistance and even fracture failure under large stretching. Therefore, there is an urgent need for a conductive enhancement structure that can maintain stable electrical properties in large stretching scenarios for flexible and stretchable circuits. Summary of the Invention

[0007] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a conductive enhancement structure for flexible and stretchable circuits and its manufacturing method. By enhancing the conductivity of conductive materials through the Poisson effect of microstructures, stable conductivity under large stretching is achieved and high cycle stability is possessed; it has the characteristics of simple manufacturing process and high repeatability.

[0008] In order to achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A conductive enhancement structure for flexible and stretchable circuits includes an elastic substrate, on the surface of which a microstructure array is distributed. The microstructure array is filled with porous conductive fillers, and the elastic substrate is encapsulated by an elastic film above the microstructure array.

[0010] The porous conductive filler is a porous stretchable conductor prepared from a stretchable elastic material and a two-dimensional nano-conductive material; under the action of stretching, the Poisson effect causes the material to be compressed in the vertical direction of stretching. The compression reduces the distance between the microstructure arrays, generating an extrusion effect on the porous conductive fillers filled in the microstructure arrays, so that the two-dimensional nano-conductive materials in the porous conductive fillers are connected more closely, realizing the conductive enhancement effect.

[0011] The elastic substrate, the elastic film and the microstructure array are elastic materials that can be molded, including polydimethylsiloxane.

[0012] The Young's modulus of the porous conductive filler is less than that of the elastic substrate and the microstructure array.

[0013] The two-dimensional nano-conductive material includes gold flakes, silver flakes or copper flakes.

[0014] The stretchable elastic material is thermoplastic polyurethane TPU.

[0015] The unit structure form of the microstructure array includes a square column, a cylindrical column or a rhombic column structure.

[0016] The unit size and gap size of the microstructure array need to satisfy that the unit size is greater than the gap size.

[0017] The manufacturing method of a conductive enhancement structure for flexible and stretchable circuits includes the following steps:

[0018] The first step, preparation of the imprinting mold: Spin-coat a photoresist on the mold substrate and form a patterned microstructure through photolithography and development. Then, etch the mold substrate through a dry process to obtain an imprinting mold with a microstructure array;

[0019] The second step, preparation of the elastic substrate with a microstructure array: After stirring the polymer material and the curing agent evenly, evacuate to remove air bubbles; then pour it onto the imprinting mold and remove air bubbles again; subsequently, heat and cure it. After curing is completed, cool it to room temperature and demold to obtain an elastic substrate with a microstructure array (5);

[0020] The third step, preparation of the slurry of the porous conductive filler: Dissolve the stretchable elastic material in N,N-dimethylformamide to obtain a homogeneous solution, and then add the two-dimensional nano-conductive material to the homogeneous solution and mix and oscillate to obtain the slurry of the porous conductive filler;

[0021] The fourth step, preparation of the porous conductive filler: Drop the slurry of the porous conductive filler onto the elastic substrate with a microstructure array, and reciprocally scrape and coat it into the gaps of the microstructure array to form a conductive network; then drop the sintering solution onto the slurry of the porous conductive filler, heat and dry it. The sintering solution replaces N,N-dimethylformamide through phase separation to form the porous conductive filler;

[0022] The fifth step, preparation of the conductive enhancement structure: Stir the polymer material and the curing agent evenly to remove air bubbles therein; then press it into a film and heat and cure it to obtain an elastic film; Connect the wire to the porous conductive filler filled in the microstructure array and lead it out to the source meter to measure the resistance signal; Finally, bond the elastic film and the elastic substrate to complete the encapsulation of the entire conductive enhancement structure, and obtain the conductive enhancement structure for the flexible stretchable circuit.

[0023] The polymer material in the second step is polydimethylsiloxane; the curing agent in the second step is an organic peroxide or a platinum catalyst, including chloroplatinic acid or benzoyl peroxide, and the ratio of the polymer material to the curing agent is (1-10):1.

[0024] The stretchable elastic material in the third step is dissolved in N,N-dimethylformamide, and the mass ratio of the two is less than or equal to 0.1 and greater than 0. The mass ratio of the added two-dimensional nano-conductive material to the homogeneous solution is (1-4):2; the stretchable elastic material is thermoplastic polyurethane TPU; the two-dimensional nano-conductive material includes gold flakes, silver flakes or copper flakes.

[0025] The sintering solution in the fourth step is artificial sweat, and the added amount should be able to completely wrap the slurry of the porous conductive filler.

[0026] The polymer material in Step 5 is polydimethylsiloxane; the curing agent in Step 5 is an organic peroxide or a platinum catalyst, including chloroplatinic acid or benzoyl peroxide, and the ratio of the polymer material to the curing agent is (1 - 10):1.

[0027] A flexible and stretchable circuit uses the above conductive enhancement structure or the conductive enhancement structure obtained by using the above manufacturing method.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] (1) In the present invention, porous conductive fillers are filled in the microstructure array, making them not easy to fall off and the sensing performance more stable.

[0030] (2) Under the tensile drive of the microstructure array in the present invention, due to the Poisson effect, the vertical direction undergoes a contraction deformation, which causes the distance between adjacent microstructures to decrease, squeezing the porous conductive fillers filled therein. The two-dimensional nano-conductive materials in the porous conductive fillers are more closely connected under the squeezing, thus achieving the conductive enhancement effect.

[0031] (3) In terms of the preparation method of the present invention, Step 4 adopts the process of scraping and then sintering, so that the porous conductive fillers are formed in the microstructure. Compared with the process of sintering first and then scraping, the initial deformation of the porous structure is reduced, which is beneficial to the subsequent realization of the conductive enhancement effect.

[0032] In summary, the conductive enhancement structure of the present invention utilizes the Poisson effect characteristic. Under the tensile action, the Poisson effect causes the material to be compressed in the vertical direction of the tension, and the compression reduces the distance between the microstructures, generating a squeezing effect on the porous conductive fillers filled in the microstructures. As a result, the two-dimensional nano-conductive materials in the porous conductive fillers are more closely connected, overcoming the problem that traditional conductive materials are prone to failure under tensile action, and achieving the excellent performance of better conductivity with increasing tension; embedding the porous conductive fillers into the elastic substrate with microstructures solves the problem of easy detachment of the conductive material, the sensing performance is more stable, and it has high cycle stability, suitable for long-term continuous signal detection; the manufacturing process of the conductive enhancement structure of the present invention is simple, the processing efficiency is high, it can be mass-produced, and its sensing characteristics can be customized according to actual needs by changing the morphology of the microstructure unit. Description of the Drawings

[0033] Figure 1 It is the overall structure diagram of the present invention.

[0034] Figure 2 It is the schematic structural diagram of the present invention for squeezing porous conductive fillers based on the Poisson effect under tension.

[0035] Figure 3 It is the schematic structural diagram of the imprinting mold of the present invention.

[0036] Figure 4 This is a process schematic diagram for preparing an elastic substrate with a micro-structure array by molding using an imprint mold in the present invention.

[0037] Figure 5 This is a structural schematic diagram of the elastic substrate with a micro-structure array formed after demolding in the present invention.

[0038] Figure 6 This is a process schematic diagram for scraping and coating porous conductive fillers in the present invention.

[0039] Figure 7 This is a schematic diagram of the conductive network structure formed after scraping and coating and wiping off the residual fillers on the surface in the present invention.

[0040] Figure 8 This is a process schematic diagram for encapsulating with an elastic film in the present invention.

[0041] Figure 9 This is a cross-sectional structural schematic diagram of the present invention when not stretched.

[0042] Figure 10 This is a cross-sectional structural schematic diagram of the present invention when stretched.

[0043] Figure 11 This is a performance comparison diagram of the conductive enhancement structure of the present invention and the unstructured wire prepared by printing.

[0044] In the figure, two-dimensional nano-conductive material 1; stretchable elastic material 2; porous conductive filler 3; elastic substrate 4; micro-structure array 5, elastic film 6; imprint mold 7; scraper 8; wire 9; source meter 10. Detailed implementation mode

[0045] The present invention will be described in detail below with reference to the accompanying drawings.

[0046] As Figure 1 shown, a conductive enhancement structure for a flexible stretchable circuit includes an elastic substrate 4, on the surface of which a micro-structure array 5 is distributed, and a porous conductive filler 3 is filled in the micro-structure array 5, and the elastic substrate 4 is encapsulated by an elastic film 6 above the micro-structure array 5.

[0047] The elastic substrate 4, the elastic film 6 and the micro-structure array 5 are elastic materials that can be molded, including polydimethylsiloxane, and different materials can be selected according to different requirements.

[0048] The porous conductive filler 3 is a porous stretchable conductor prepared by a phase separation process of a stretchable elastic material 2 (such as thermoplastic polyurethane TPU) and a two-dimensional nano-conductive material 1, and the Young's modulus of the porous conductive filler 3 is less than that of the elastic substrate 4 and the micro-structure array 5.

[0049] The two-dimensional nano-conductive material 1 includes gold flakes, silver flakes or copper flakes;

[0050] The unit structure form of the microstructure array 5 includes square columns, cylindrical columns or rhombic column structures. Different unit structure forms have different deformation characteristics under the action of Poisson's effect, thus causing different extrusion effects and generating different electrical signal outputs.

[0051] The unit size and gap size of the microstructure array 5 play an important role in the conductivity performance. The unit size needs to be larger than the gap size, and different microstructure arrays can be selected according to different requirements.

[0052] Such as Figure 2 As shown, when the microstructure array 5 is under tensile drive, its vertical direction will undergo a contraction deformation due to Poisson's effect, thereby causing the distance between adjacent microstructures to decrease, squeezing the porous conductive filler 3 filled therein. The two-dimensional nano-conductive material 1 in the porous conductive filler 3 is connected more closely under the extrusion, thereby realizing the conductive enhancement effect.

[0053] A manufacturing method of a conductive enhancement structure for a flexible stretchable circuit includes the following steps:

[0054] The first step, preparation of the imprinting mold 7: Refer to Figure 3 , the imprinting mold 7 is prepared by lithography and dry etching processes; first, a mask template with a microstructure pattern is prepared. A photoresist is spin-coated on a silicon wafer and patterned microstructure arrays 5 are formed through photolithography and development. The polished surface of the silicon wafer is etched by 50 microns through the dry etching process to obtain a silicon mold with the microstructure array 5 as the imprinting mold 7.

[0055] The second step, preparation of the elastic substrate 4 with a microstructure array: Refer to Figure 4 , after mixing the polymer material polydimethylsiloxane and the curing agent in a mass ratio of 10:1, it is placed in a vacuum drying oven to remove the bubbles therein by vacuum pumping; then it is poured onto the imprinting mold 7; subsequently, it is placed on a baking table and heated for more than 2 hours to complete the curing of the polymer. After curing, it is cooled to room temperature and demolded to obtain Figure 5 the elastic substrate 4 with the microstructure array 5 as shown in

[0056] The third step, preparation of the slurry of the porous conductive filler 3: The stretchable elastic material 2 is dissolved in N,N-dimethylformamide in a mass ratio of 1:5 to obtain a mixed solution. Subsequently, the two-dimensional nano-conductive material 1 is added in a mass ratio of 7:4 of the two-dimensional nano-conductive material 1 to the mixed solution to obtain a mixed liquid. The mixed liquid is added to a centrifuge tube and placed in a planetary stirring mixer to be mixed evenly at a speed of 1500 r / min for ten minutes. Subsequently, the mixed liquid is placed in a vortex mixer and oscillated for 4.5 hours to obtain the slurry of the porous conductive filler 3.

[0057] Step 4. Preparation of porous conductive filler 3: Refer to Figure 6 , Figure 7 , and drop the slurry of the prepared porous conductive filler 3 onto the elastic substrate 4 with the microstructure array 5. Use a scraper 8 to scrape back and forth to evenly fill the pores of the microstructure array 5 with the porous conductive filler 3 to form a conductive network. Subsequently, drop artificial sweat on the porous conductive filler 3 for sintering. The amount of artificial sweat added should be able to completely wrap the slurry of the porous conductive filler 3. Heat and dry. The sintering solution can displace N,N-dimethylformamide through phase separation to form the porous conductive filler 3.

[0058] Step 5. Preparation of the conductive enhancement structure: Refer to Figure 8 , after mixing polydimethylsiloxane and a curing agent in a mass ratio of 10:1, place it in a vacuum drying oven to evacuate the bubbles. Subsequently, sandwich it between two glass plates of 20 cm × 20 cm, apply pressure to press the polymer material into a film, and place it on a drying table to cure at 80 °C for 2 hours to obtain an elastic film 6. Connect the wire 9 (a wire or conductive tape made of copper, gold, silver, or other conductive materials) to the conductive filler filled in the microstructure array 5 and lead it out to a source meter 10 to measure the resistance signal. Bond the elastic film 6 to the elastic substrate 4 with the microstructure array 5 to complete the encapsulation of the conductive enhancement structure, and obtain a conductive enhancement structure for a flexible and stretchable circuit as shown in Figure 9 .

[0059] The working principle of the conductive enhancement structure of the present invention is: Refer to Figure 1 , Figure 9 , in the initial state, the porous conductive filler 3 is evenly filled in the microstructure array 5. Under the stretching action, as shown in Figure 2 , Figure 10 , the Poisson effect causes the material to be compressed in the vertical direction of the stretch. The compression reduces the distance between the microstructure arrays 5, resulting in an extrusion effect on the porous conductive filler 3 filled in the microstructure array 5, thereby making the two-dimensional nano-conductive materials 1 in the porous conductive filler connect more closely, achieving a conductive enhancement effect.

[0060] Refer to Figure 11 , it can be seen from the figure that compared with the wire prepared by printing without the Poisson structure effect, the conductive enhancement structure of the present invention can achieve greater stretchability (the stretchability is increased by nearly 40%), and at the same time has a smaller resistance change rate under the same stretch, reflecting its excellent strain-insensitive performance, and can realize the manufacture and application of flexible and stretchable circuits.

Claims

1. A conductive enhancement structure for a flexible stretchable circuit, characterized in that: It comprises an elastic substrate (4), a microstructure array (5) is distributed on the surface of the elastic substrate (4), a porous conductive filler (3) is filled in the microstructure array (5), and the elastic substrate (4) is encapsulated above the microstructure array (5) via an elastic film (6); The porous conductive filler (3) is a porous stretchable conductor prepared from a stretchable elastic material (2) and a two-dimensional nano-conductive material (1); under the action of stretching, the Poisson effect causes the material to be compressed in a direction perpendicular to the stretching, and the compression reduces the distance between the microstructure arrays (5), thereby producing a squeezing effect on the porous conductive filler (3) filled in the microstructure array (5), thereby making the two-dimensional nano-conductive material (1) in the porous conductive filler (3) more tightly connected, thereby achieving a conductive enhancement effect; The Young's modulus of the porous conductive filler (3) is smaller than the Young's modulus of the elastic substrate (4) and the microstructure array (5).

2. The conductive enhancement structure for a flexible stretchable circuit according to claim 1, characterized in that: The elastic substrate (4), the elastic film (6) and the microstructure array (5) are elastic materials capable of being molded, including polydimethylsiloxane; The two-dimensional nano-conductive material (1) comprises a gold sheet, a silver sheet or a copper sheet; The stretchable elastic material (2) is thermoplastic polyurethane TPU.

3. The conductive enhancement structure for a flexible stretchable circuit according to claim 1, characterized in that: The unit structure of the microstructure array (5) includes a square column, a circular column or a rhombus column structure.

4. The conductive enhancement structure for a flexible stretchable circuit according to claim 1, characterized in that: The unit size and gap size of the microstructure array (5) must satisfy that the unit size is larger than the gap size.

5. The method for manufacturing a conductive enhancement structure for a flexible stretchable circuit according to claim 1, characterized in that: The following steps are involved: The first step is to prepare an imprint mold (7): spin-coat a photoresist on a mold substrate and form a patterned microstructure by photolithography development, and then etch the mold substrate by a dry process to obtain an imprint mold (7) having a microstructure array; The second step is to prepare the elastic substrate (4) containing the microstructure array: after the polymer material and the curing agent are mixed evenly, vacuum is applied to remove bubbles; then the polymer material and the curing agent are poured into the imprinting mold (7), and bubbles are removed again; then the material is heated and cured, and after the curing is completed, the material is cooled to room temperature and demolded to obtain the elastic substrate (4) containing the microstructure array (5); The third step is to prepare a slurry of the porous conductive filler (3): the stretchable elastic material (2) is dissolved in N,N-dimethylformamide to obtain a mixed solution, and then the two-dimensional nano-conductive material (1) is added to the mixed solution and mixed and shaken to obtain a slurry of the porous conductive filler (3); The fourth step is to prepare the porous conductive filler (3): drip the slurry of the porous conductive filler (3) onto the elastic substrate (4) containing the microstructure array (5), and scrape and apply it back and forth to fill the gaps in the microstructure array (5) to form a conductive network; Then, a sintering solution is added dropwise onto the slurry of the porous conductive filler (3), and the mixture is heated and dried. The sintering solution replaces N,N-dimethylformamide through phase separation to form a porous conductive filler (3); Step 5: Preparation of the conductive enhancement structure: Mix the polymer material and the curing agent to remove bubbles; It is then pressed into a film and heated and cured to obtain an elastic film (6); a wire (9) is connected to a porous conductive filler (3) filled in a microstructure array (5) and connected to a source meter (10) to measure a resistance signal; finally, the elastic film (6) is bonded to an elastic substrate (4) to complete the packaging of the entire conductive enhancement structure, thereby obtaining a conductive enhancement structure for a flexible stretchable circuit.

6. The method for manufacturing a conductive enhancement structure for a flexible stretchable circuit according to claim 5, characterized in that: The polymer material of step 2 is polydimethylsiloxane; the curing agent of step 2 is an organic peroxide or a platinum catalyst, including chloroplatinic acid or dibenzoyl peroxide, and the ratio of the polymer material to the curing agent is (1-10):

1.

7. The method for manufacturing a conductive enhancement structure for a flexible stretchable circuit according to claim 5, characterized in that: The stretchable elastic material (2) of step three is dissolved in N,N-dimethylformamide, and the mass ratio of the two is less than or equal to 0.1 and greater than 0. The mass ratio of the added two-dimensional nano-conductive material (1) to the mixed liquid is (1-4):2; the stretchable elastic material (2) is thermoplastic polyurethane TPU; the two-dimensional nano-conductive material (1) includes a gold sheet, a silver sheet or a copper sheet.

8. The method for manufacturing a conductive enhancement structure for a flexible stretchable circuit according to claim 5, characterized in that: The sintering solution in step 4 is artificial sweat, and the amount added is required to be enough to completely wrap the slurry of the porous conductive filler (3).

9. The method for manufacturing a conductive enhancement structure for a flexible stretchable circuit according to claim 5, characterized in that: The polymer material of step five is polydimethylsiloxane; the curing agent of step five is an organic peroxide or a platinum catalyst, including chloroplatinic acid or dibenzoyl peroxide, and the ratio of the polymer material to the curing agent is (1-10):1.

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