Conductivity enhancing structure for flexible stretchable circuit and manufacturing method thereof

Abstract

The invention discloses a conductivity enhancing structure for a flexible stretchable circuit and a manufacturing method thereof. A microstructure array is distributed in an elastic substrate of the conductivity enhancing structure; by applying the Poisson effect characteristic, under the stretching effect, the Poisson effect causes the material to be compressed in the vertical direction of stretching, the distance between the microstructures is reduced through compression, and an extrusion effect is generated on the porous conductive filler filled in the microstructures, so that the connection of the two-dimensional nano conductive material in the porous conductive filler is tighter; the problem that a traditional conductive material is prone to failure under the stretching effect is solved, and the excellent performance that the conductivity is better when the material is pulled can be achieved; according to the manufacturing method, the process of firstly blade coating and then sintering is adopted, so that the porous conductive filler is formed in the microstructure, and compared with the process of firstly sintering and then blade coating, the initial deformation of the porous structure is reduced, and the subsequent implementation of the conductive enhancement effect is facilitated; the invention solves the problem that the conductive material is easy to fall off, has high cycle stability, and is suitable for manufacturing a flexible stretchable circuit.

Description

Technical Field

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

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

[0003] At present, the research on flexible and stretchable circuits mainly focuses on materials and structures. Commonly used stretchable materials are mainly divided into two types: one is an intrinsically stretchable liquid metal material, and the other is a conductive composite material prepared by using an elastic substrate and a conductive filler. Although the modified design of the material can achieve high stretchability of the material from the microstructure, in practical applications, because the stretching effect provided by the large stretching scenario is limited, it is necessary to design a stretchable structure on a larger scale to achieve its high stretchability. Through the structural design of the connecting wires, electronic devices can meet large deformation requirements while maintaining good electrical properties. Common structures include serpentine structures, wrinkled structures, Kirigami structures, island bridge structures, etc. However, due to the uneven surface and large contact area generated by these structures, the area of ​​the flexible and stretchable circuit is increased, so it is not suitable for the manufacture of high-density devices.

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

[0005] The patent application with publication number CN114567966A discloses a stretchable circuit with a serpentine structure, which adopts a strain release structure. When the strain exceeds the preset value of the structure, there is a problem that the circuit is easy to break. The patent application with publication number CN115979032A discloses a flexible stretchable circuit based on liquid metal packaging. Although the 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 publication number CN115881340A discloses a flexible stretchable electrode with high conductive stability, but the conductive nanocomposite material used therein often has a trade-off problem between conductivity and stretchability.

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

[0007] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a conductive enhancement structure for a flexible stretchable circuit and a manufacturing method thereof, which enhances the conductive properties of the conductive material through the Poisson effect of the microstructure, achieves stable conductivity under large stretching and has high cycle stability; and has the characteristics of simple manufacturing process and high repeatability.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is: A conductive enhancement structure for a flexible stretchable circuit comprises an elastic substrate, a microstructure array is distributed on the surface of the elastic substrate, the microstructure array is filled with porous conductive fillers, and the elastic substrate is encapsulated by an elastic film above the microstructure array; The porous conductive filler is a porous stretchable conductor prepared from stretchable elastic material and two-dimensional nano-conductive material; under stretching, the Poisson effect causes the material to be compressed in the direction perpendicular to the stretching, and the compression reduces the distance between the microstructure arrays, producing an extrusion effect on the porous conductive filler filled in the microstructure array, thereby making the two-dimensional nano-conductive material in the porous conductive filler more tightly connected, thereby achieving a conductivity enhancement effect.

[0009] The elastic substrate, the elastic film and the microstructure array are elastic materials capable of compression molding, including polydimethylsiloxane.

[0010] The Young's modulus of the porous conductive filler is smaller than that of the elastic substrate and the microstructure array.

[0011] The two-dimensional nano conductive material includes a gold sheet, a silver sheet or a copper sheet.

[0012] The stretchable elastic material is thermoplastic polyurethane TPU.

[0013] The unit structure of the microstructure array includes a square column, a circular column or a rhombus column structure.

[0014] The unit size and gap size of the microstructure array must satisfy that the unit size is larger than the gap size.

[0015] The method for manufacturing a conductive enhancement structure for a flexible stretchable circuit comprises the following steps: The first step is to prepare an imprint mold: spin-coat a photoresist on the 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 with a microstructure array; The second step is to prepare the elastic substrate 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, 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 containing the microstructure array (5); The third step is to prepare a slurry of a porous conductive filler: dissolving a stretchable elastic material in N,N-dimethylformamide to obtain a mixed solution, and then adding a two-dimensional nano-conductive material to the mixed solution, mixing and oscillating to obtain a slurry of a porous conductive filler; The fourth step is to prepare a porous conductive filler: drip the slurry of the porous conductive filler onto the elastic substrate containing the microstructure array, and fill the gaps in the microstructure array by scraping back and forth to form a conductive network; then drip a sintering solution onto the slurry of the porous conductive filler, heat and dry it, and the sintering solution replaces N,N-dimethylformamide through phase separation to form a porous conductive filler; The fifth step is the preparation of the conductive enhancement structure: the polymer material and the curing agent are mixed and evenly mixed to remove the bubbles; then they are pressed into a film and heated and cured to obtain an elastic film; the wires are connected to the porous conductive fillers filled in the microstructure array and connected to the source meter to measure the resistance signal; finally, the elastic film is bonded to the elastic substrate to complete the packaging of the entire conductive enhancement structure, and a conductive enhancement structure for flexible and stretchable circuits is obtained.

[0016] 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.

[0017] The stretchable elastic material in 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 to the mixed liquid is (1-4):2; the stretchable elastic material is thermoplastic polyurethane TPU; the two-dimensional nano-conductive material includes gold sheets, silver sheets or copper sheets.

[0018] The sintering solution in step 4 is artificial sweat, and the amount added needs to be able to completely wrap the slurry of the porous conductive filler.

[0019] 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.

[0020] A flexible and stretchable circuit adopts the above-mentioned conductive enhancement structure or the conductive enhancement structure obtained by the above-mentioned manufacturing method.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention fills the microstructure array with porous conductive fillers, making it difficult to fall off and making the sensing performance more stable.

[0022] (2) When the microstructure array of the present invention is driven by tension, it will shrink and deform in the vertical direction due to the Poisson effect, thereby causing the distance between adjacent microstructures to decrease, squeezing the porous conductive filler filled therein. The two-dimensional nano-conductive material in the porous conductive filler is more tightly connected under squeezing, thereby achieving a conductive enhancement effect.

[0023] (3) In the preparation method of the present invention, step 4 adopts a process of first scraping and then sintering to form a porous conductive filler in the microstructure. Compared with the process of first sintering and then scraping, the initial deformation of the porous structure is reduced, which is beneficial to the subsequent realization of the conductive enhancement effect.

[0024] To sum up, the conductive enhancement structure of the present invention utilizes the characteristics of the Poisson effect. Under the action of stretching, the Poisson effect causes the material to be compressed in the direction perpendicular to the stretching. The compression reduces the distance between the microstructures, and produces an extrusion effect on the porous conductive filler filled in the microstructure, so that the two-dimensional nano-conductive material in the porous conductive filler is more tightly connected, overcoming the problem that traditional conductive materials are prone to failure under stretching, and can achieve excellent performance of better conductivity as they are stretched; the porous conductive filler is embedded in an elastic substrate with a microstructure, which solves the problem that the conductive material is easy to fall off, and the sensing performance is more stable, with high cycle stability, which is suitable for long-term continuous signal detection; the conductive enhancement structure of the present invention has a simple manufacturing process and high processing efficiency, can be produced on a large scale, and its sensing characteristics can be customized according to actual needs by changing the morphology of the microstructure unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is the overall structure diagram of the present invention.

[0026] Figure 2 It is a schematic diagram of the structure of the present invention of extruding porous conductive filler under tension based on Poisson effect.

[0027] Figure 3 It is a schematic structural diagram of the imprinting mold of the present invention.

[0028] Figure 4 This is a schematic diagram of the process of preparing an elastic substrate containing a microstructure array by compression molding using an imprint mold according to the present invention.

[0029] Figure 5 It is a schematic structural diagram of the elastic substrate containing the microstructure array formed after demoulding of the present invention.

[0030] Figure 6 It is a schematic diagram of the process of scraping porous conductive filler according to the present invention.

[0031] Figure 7 This is a schematic diagram of the conductive network structure formed after wiping off the residual filler on the surface after scraping in the present invention.

[0032] Figure 8 This is a schematic diagram of the process of using elastic film packaging in the present invention.

[0033] Fig. 9 It is a schematic diagram of the cross-sectional structure of the present invention when it is not stretched.

[0034] Fig.10 It is a schematic diagram of the cross-sectional structure of the present invention during stretching.

[0035] Fig.11 This is a performance comparison diagram of the conductive enhancement structure of the present invention and the unstructured conductive line prepared by printing.

[0036] In the figure, there are two-dimensional nanoconductive material 1; stretchable elastic material 2; porous conductive filler 3; elastic substrate 4; microstructure array 5, elastic film 6; imprinting mold 7; scraper 8; wire 9; source surface 10. DETAILED DESCRIPTION

[0037] The present invention will be described in detail below with reference to the accompanying drawings.

[0038] like Figure 1 As shown, a conductive enhancement structure for a flexible stretchable circuit includes an elastic substrate 4, a microstructure array 5 is distributed on the surface of the elastic substrate 4, the microstructure array 5 is filled with porous conductive fillers 3, and the elastic substrate 4 is encapsulated by an elastic film 6 above the microstructure array 5.

[0039] The elastic substrate 4, the elastic film 6 and the microstructure array 5 are elastic materials that can be molded, including polydimethylsiloxane. Different materials can be selected according to different requirements.

[0040] 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 smaller than that of the elastic substrate 4 and the microstructure array 5.

[0041] The two-dimensional nano-conductive material 1 comprises a gold sheet, a silver sheet or a copper sheet; The unit structure of the microstructure array 5 includes a square column, a round column or a rhombus structure. Different unit structure forms have different deformation characteristics under the Poisson effect, thereby causing different squeezing effects and generating different electrical signal outputs.

[0042] The unit size and gap size of the microstructure array 5 play an important role in the conductive performance. The unit size needs to be larger than the gap size. Different microstructure arrays can be selected according to different requirements.

[0043] like Figure 2 As shown, under tensile drive, the microstructure array 5 will shrink and deform in the vertical direction due to the Poisson 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 more tightly connected under squeezing, thereby achieving a conductive enhancement effect.

[0044] The method for manufacturing a conductive enhancement structure for a flexible stretchable circuit comprises the following steps: The first step is to prepare the imprint mold 7: Figure 3 The imprinting mold 7 is prepared by photolithography and dry etching processes; first, a mask having a microstructure pattern is prepared, photoresist is spin-coated on a silicon wafer and a patterned microstructure array 5 is formed by photolithography development, and the polished surface of the silicon wafer is etched by 50 microns by a dry etching process to obtain a silicon mold having a microstructure array 5 as the imprinting mold 7.

[0045] Step 2: Preparation of the elastic substrate 4 containing the microstructure array: Figure 4 , the polymer material polydimethylsiloxane and the curing agent are mixed in a mass ratio of 10:1, and then placed in a vacuum drying oven to remove air bubbles; then poured on the imprinting mold 7; then placed on a drying table and heated for more than 2 hours to complete the curing of the polymer, and after the curing is completed, cooled to room temperature and demolded to obtain Figure 5 An elastic substrate 4 is shown containing an array 5 of microstructures.

[0046] 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 at a mass ratio of 1:5 to obtain a mixed solution, and then the two-dimensional nanoconductive material 1 is added at a mass ratio of 7:4 to the mixed solution to obtain a mixed solution, the mixed solution is added to a centrifuge tube and placed in a planetary stirring mixer and mixed at a speed of 1500 r / min for ten minutes, and then the mixed liquid is placed in a vortex mixer and oscillated for 4.5 hours to obtain a slurry of the porous conductive filler 3.

[0047] Step 4: Preparation of porous conductive filler 3: Figure 6 , Figure 7, drip the prepared slurry of porous conductive filler 3 onto the elastic substrate 4 containing the microstructure array 5, and use a scraper 8 to scrape back and forth to make the porous conductive filler 3 evenly fill the gaps in the microstructure array 5 to form a conductive network; then drip artificial sweat on the porous conductive filler 3 for sintering, and the amount of artificial sweat added must be able to completely wrap the slurry of the porous conductive filler 3; heat and dry, the sintering solution can replace N,N-dimethylformamide through phase separation to form a porous conductive filler 3.

[0048] Step 5: Preparation of conductive enhancement structure: refer to Figure 8 , polydimethylsiloxane and curing agent are mixed in a mass ratio of 10:1, and then placed in a vacuum drying oven to remove air bubbles; then it is sandwiched between two 20 cm×20 cm glass plates, pressure is applied to press the polymer material into a film, and it is placed on a drying table and heated at 80°C for 2 hours to solidify to obtain an elastic film 6; a wire 9 (made of copper, gold, silver or other conductive material wire or conductive tape) is connected to the conductive filler filled in the microstructure array 5, and connected to a source meter 10 to measure the resistance signal; the elastic film 6 is bonded to the elastic substrate 4 containing the microstructure array 5 to complete the packaging of the conductive enhancement structure, and the following is obtained: Fig. 9 Conductive enhancement structures for flexible and stretchable circuits are shown.

[0049] The working principle of the conductive enhancement structure of the present invention is: Figure 1 , Fig. 9 In the initial state, the porous conductive filler 3 is uniformly filled in the microstructure array 5; under the stretching action, as shown in FIG. Figure 2 , Fig.10 As shown, the Poisson effect causes the material to be compressed in the direction perpendicular to the stretching. The compression reduces the distance between the microstructure arrays 5, and produces 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 more tightly connected, thereby achieving a conductive enhancement effect.

[0050] Reference Fig.11 As can be seen from the figure, the conductive enhancement structure of the present invention can achieve greater stretchability (stretchability is improved by nearly 40%) compared to the printed conductor without Poisson's structural effect, and at the same time has a smaller resistance change rate under the same stretching, reflecting its excellent strain-insensitive performance, which can realize the manufacture and application of flexible 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.

2. The conductive enhancement structure for a flexible stretchable circuit according to claim 1, characterized in that: 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).

3. 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.

4. 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.

5. 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.

6. 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 the 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 air bubbles; then the polymer material and the curing agent are poured into the imprinting mold (7), and air 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); Step 4: preparing the porous conductive filler (3): dripping the slurry of the porous conductive filler (3) onto the elastic substrate (4) containing the microstructure array (5), and reciprocatingly scraping and coating to fill the gaps in the microstructure array (5) to form a conductive network; Subsequently, 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 and remove the bubbles therein; It is then pressed into a film and heated and cured to obtain an elastic film (6); the wire (9) is connected to the porous conductive filler (3) filled in the microstructure array (5) and connected to a source meter (10) to measure the resistance signal; finally, the elastic film (6) is bonded to the elastic substrate (4) to complete the packaging of the entire conductive enhancement structure, thereby obtaining a conductive enhancement structure for a flexible stretchable circuit.

7. The method for manufacturing a conductive enhancement structure for a flexible stretchable circuit according to claim 6, 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.

8. The method for manufacturing a conductive enhancement structure for a flexible stretchable circuit according to claim 6, characterized in that: The stretchable elastic material (2) of step 3 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; and the two-dimensional nano-conductive material (1) includes a gold sheet, a silver sheet or a copper sheet.

9. The method for manufacturing a conductive enhancement structure for a flexible stretchable circuit according to claim 6, characterized in that: The sintering solution in step 4 is artificial sweat, and the amount added is required to be enough to completely cover the porous conductive filler (3).

10. The method for manufacturing a conductive enhancement structure for a flexible stretchable circuit according to claim 6, 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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