Anisotropically conductive stretchable electronic solder and methods of making and using the same

Abstract

The application discloses anisotropic conductive stretchable electronic solder as well as a preparation method and application thereof, the stretchable electronic solder comprises a polymer binder and silver nanosheets, and the mass ratio of the polymer binder to the silver nanosheets is (5-20):1; the polymer binder is obtained by heating reaction of bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether and furfurylamine at 40-60 DEG C, and then heating reaction of N,N'-(4,4'-methylene diphenyl) bismaleimide at 60-80 DEG C. The anisotropic conductive stretchable electronic solder provided by the application can effectively offset the stress concentration problem caused by the difference in physical and chemical properties of soft / hard substrates, and ensure that the electrical interface always maintains stable connection in the stretching deformation process, and successfully realizes the universal welding of flexible, stretchable and rigid materials and devices.

Description

Technical Field

[0001] This invention relates to the field of flexible electronic materials technology, specifically to anisotropic conductive stretchable electronic solder, its preparation method, and its application. Background Technology

[0002] Flexible and stretchable electronic components, as core components of wearable devices, stretchable displays, electronic skin, and other flexible or stretchable devices, can perfectly conform to substrates or biological surfaces of various shapes and maintain stable performance during deformation due to their unique flexibility or stretchability. Among them, stretchable electronic components, compared to electronic components that can only bend, can withstand a wider range of deformation types, making them more practical in wearable devices and other applications. However, due to the significant differences in the physicochemical properties of stretchable electronic components compared to traditional electronic device materials and flexible circuit board materials, key technical bottlenecks are encountered during device integration: insufficient bonding strength at the integration interface, and the tendency for stress-strain concentration during deformation, leading to easy failure of electrical interfaces during deformation, severely limiting the overall tensile strength and lifespan of the device.

[0003] In recent years, existing technologies have disclosed some flexible conductive adhesives and related connection methods suitable for soft-hard interface connections, but there are still many shortcomings that need to be addressed: First, the interface connection lacks reversibility, making it impossible to achieve the core function of replacing electronic components on demand as in traditional soldering technology; second, the connection methods are complex, cumbersome, and time-consuming, which is not conducive to efficient production; third, the connection materials are generally expensive and have complex preparation processes, making it difficult to achieve industrial-scale promotion. In addition, although the design of anisotropic conductive films can significantly reduce the amount of conductive filler incorporated, the formed anisotropic conductive films are difficult to adapt to the connection requirements of materials of different shapes and different sites, which greatly hinders their large-scale application in the fabrication of flexible devices. While dynamic chemical polymer adhesives have shown potential in the field of self-healing, they have not yet formed a mature solution for the synergistic optimization of adhesive strength, flexibility, and temperature response to adapt to flexible electronic connections, making it difficult to meet the comprehensive performance requirements of stretchable electrical connections. Summary of the Invention

[0004] The purpose of this invention is to solve the technical problems in existing flexible connection technologies, such as the difficulty in stretching and easy failure of electrical interfaces due to the difference in physicochemical properties between soft and hard materials, the lack of reversibility in the connection which prevents the replacement of electronic components on demand, the complexity and time-consuming operation of the connection method, the high price of the connection material, the complexity of the preparation process and the difficulty in industrialization, as well as the poor compatibility of anisotropic conductive films and the insufficient comprehensive performance of dynamic chemical polymer adhesives. The invention provides anisotropic conductive stretchable electronic solder, its preparation method and application, which provides a convenient, universal, stable and reversible stretchable connection for various flexible, stretchable and rigid materials and devices, realizes the process of replacing electronic components on demand in traditional soldering technology, and thus provides a new integration method for flexible or stretchable devices.

[0005] The above-mentioned objective of the present invention is achieved through the following technical solution:

[0006] The first aspect of the present invention provides an anisotropic conductive stretchable electronic solder, the anisotropic conductive stretchable electronic solder comprising a polymer binder and silver nanosheets, wherein the mass ratio of the polymer binder to the silver nanosheets is (5-20):1.

[0007] The polymeric adhesive is obtained by reacting bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, and furfurylamine at 40-60°C, followed by reacting them with N,N'-(4,4'-methylenediphenyl)bismaleimide at 60-80°C.

[0008] This invention introduces the Diels-Alder reaction, commonly used in the self-healing field, into a polymer adhesive system, constructing a cross-linked network structure with dynamic covalent bonds. Based on this, by controlling the ratio of hard and soft segments of the polymer monomers (the molar ratio of bisphenol A diglycidyl ether to polyethylene glycol diglycidyl ether) and the ratio of the cross-linking agent (N,N'-(4,4'-methylenediphenyl)bismaleimide), synergistic optimization of adhesive strength, flexibility, and temperature responsiveness is achieved. The hard segments provide structural support and adhesive strength, the soft segments impart flexibility and stretchability to the material, and the cross-linking agent regulates the network density to balance viscosity and dynamic responsiveness, ultimately preparing a dynamic chemical polymer adhesive that combines high viscosity with excellent temperature responsiveness. The dynamic covalent bonds in this polymer adhesive can undergo reversible dissociation at 80-100 ℃. This characteristic not only meets the requirements for solder use but also avoids damage to flexible / stretchable materials caused by high temperatures: when heated, the dynamic covalent bonds break, which temporarily destroys the cross-linking network, and the material changes from a solid state to a state with good fluidity, making it easy to fill the tiny gaps at the substrate interface; after cooling, the dynamic covalent bonds spontaneously recombine under the drive of intermolecular forces, the cross-linking network is quickly restored, and the solder regains stable adhesive strength.

[0009] Furthermore, the number-average molecular weight of the polyethylene glycol diglycidyl ether is 400-600. As a soft segment, the number-average molecular weight of polyethylene glycol diglycidyl ether directly affects the flexibility and stretchability of the solder.

[0010] Furthermore, the diameter of the silver nanosheets is 1-5 μm. As a conductive filler, the diameter of the silver nanosheets determines the efficiency of conductive pathway formation.

[0011] Furthermore, the molar ratio of bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, and furfurylamine is 1:(1-2):(2-3).

[0012] Further, the molar ratio of furfurylamine to N,N'-(4,4'-methylenediphenyl)bismaleimide is (20-100):1, preferably (40-60):1. N,N'-(4,4'-methylenediphenyl)bismaleimide acts as a crosslinking agent, forming a crosslinked network through reaction with the furan groups in furfurylamine.

[0013] A second aspect of the present invention provides a method for preparing the anisotropic conductive stretchable electronic solder described in the first aspect, comprising the following steps:

[0014] (1) Bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether and furfurylamine are dissolved in a solvent and heated at 40-60℃ to obtain a reaction solution;

[0015] (2) Remove the solvent from the reaction solution, mix it with N,N'-(4,4'-methylenediphenyl)bismaleimide, and then heat it at 60-80 °C to obtain a polymer adhesive;

[0016] (3) The polymer adhesive is mixed with silver nanosheets and dried to obtain the anisotropic conductive stretchable electronic solder.

[0017] Further, in step (1), the solvent is methanol.

[0018] Further, in step (1), the mass ratio of the solvent to bisphenol A diglycidyl ether is (6-8):1.

[0019] Furthermore, in step (1), the heating reaction time is 36-48 h.

[0020] Furthermore, step (1) includes a step of purifying bisphenol A diglycidyl ether before dissolution.

[0021] Furthermore, the purification process specifically involves drying bisphenol A diglycidyl ether at 40-50 °C for 2-4 h.

[0022] Further, in step (1), the dissolution temperature is 20-30 ℃, and the method is stirring.

[0023] In a specific embodiment, in step (1), purified bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether and furfurylamine are dissolved in a solvent at 20-30 ℃ and heated at 40-60 ℃ for 36-48 h to obtain a reaction solution.

[0024] Further, in step (1), the mixing temperature is 20-30 ℃, and the method is stirring.

[0025] Furthermore, in step (2), the heating reaction time is 0.5-1 h.

[0026] In a specific embodiment, in step (2), the solvent of the reaction solution is evaporated, mixed with N,N'-(4,4'-methylenediphenyl)bismaleimide at 20-30 °C, and then heated at 60-80 °C to obtain a polymer adhesive.

[0027] In a specific embodiment, in step (3), the polymer adhesive is mixed with silver nanosheets for 160-200 s to obtain a mixture; the mixture is dried at 60-80 ℃ to obtain the anisotropic conductive stretchable electronic solder.

[0028] A third aspect of the present invention provides an application of the anisotropic conductive stretchable electronic solder described in the first aspect for welding flexible, stretchable, and rigid materials and devices.

[0029] This invention develops an anisotropic conductive stretchable electronic solder by mixing a polymer binder with silver nanosheets, and provides a flexible soldering technology based on this solder. This stretchable electronic solder is highly versatile and can be easily applied to the welding of various flexible, stretchable, and rigid materials and devices, enabling reversible and stretchable electrical connections that are both universal and robust.

[0030] In a specific implementation, the chip is placed on a printed circuit board (PCB) and heated to 80-100°C using a hot plate or hot air gun. The anisotropic conductive stretchable electronic solder provided by this invention is then taken out and uniformly coated onto the target area. The chip is then placed and a brief light pressure is applied. After cooling, a stable electrical connection can be achieved. The entire operation is as convenient as traditional soldering technology and can achieve the same stable electrical connection effect.

[0031] Furthermore, the anisotropic conductive stretchable electronic solder can be processed into a general-purpose washable anisotropic conductive stretchable electronic solder bar or solder paste.

[0032] This invention utilizes the excellent temperature response characteristics of stretchable electronic solder, employing an application method that forms an anisotropic conductive film during the soldering process, allowing it to adapt to substrate surfaces of any shape. After heating and pressing, the solder is pressed into an extremely thin state, achieving stable anisotropic conductivity even with very low silver nanosheet doping, while preserving to the greatest extent the original high viscosity, flexibility, and reversible bonding properties of the polymer adhesive.

[0033] Furthermore, with the continuous trend of miniaturization in flexible devices, the anisotropic conductive stretchable electronic solder provided by this invention has significant advantages for the integrated application of miniaturized devices due to its excellent longitudinal conductivity and anisotropic transverse insulation. Its excellent longitudinal conductivity and transverse insulation anisotropic characteristics can effectively avoid the circuit short circuit problem that is prone to occur during the integration of miniaturized devices, and ultimately realize convenient, stable and reversible stretchable electrical connection between devices.

[0034] Compared with the prior art, the above-described technical solution of the present invention has the following advantages:

[0035] 1. This invention combines the design concepts of dynamic chemical polymer adhesives and anisotropic conductive films. Dynamic chemical polymer adhesives are constructed through cycloaddition reactions. With the help of their dynamic covalent bonds that can be dissociated at 80-100 °C, the solder has high viscosity, excellent flexibility and stretchability, and also has faster and milder temperature response characteristics. The design of anisotropic conductive films, while ensuring a stable conductive path, significantly reduces the amount of conductive filler incorporated, thus preserving the excellent performance of dynamic chemical polymer adhesives to the greatest extent, thereby forming anisotropic conductive stretchable electronic solder.

[0036] 2. The anisotropic conductive stretchable electronic solder provided by this invention, with its excellent flexibility and stretchability imparted by the dynamic chemical polymer adhesive, can effectively offset the stress concentration problem caused by the difference in physicochemical properties between soft and hard substrates, ensuring that the electrical interface maintains a stable connection during stretching deformation. This successfully achieves universal welding of flexible, stretchable, and rigid materials and devices. Based on this, this invention further develops a novel flexible connection method—flexible soldering technology. This not only expands the application scenarios of the solder but also achieves universal, stable, and reversible stretchable electrical connections. It overcomes many technical problems in existing flexible connection technologies, such as the difficulty in stretching and reversibly connecting electrical interfaces due to the difference in properties between soft and hard substrates, as well as the complexity, cumbersome steps, and long time consumption of connection methods, and the high cost, complex preparation, and difficulty in industrialization of connection materials. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the process for preparing anisotropic conductive stretchable electronic solder according to the present invention.

[0038] Figure 2 The 1H NMR spectra of bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, furfurylamine, and furanyl polymer in Example 1 are shown.

[0039] Figure 3 Scanning electron microscope image of the anisotropic conductive stretchable electronic solder prepared in Example 1.

[0040] Figure 4 The image shows a physical sample of the anisotropic conductive stretchable electronic solder prepared in Example 1, processed into a solder bar.

[0041] Figure 5 The resistance data are plotted for the anisotropic conductive stretchable electronic solders prepared in Examples 1, 6 and 7.

[0042] Figure 6 The viscosity-temperature curve of the anisotropic conductive stretchable electronic solder prepared in Example 1.

[0043] Figure 7 This is a schematic diagram of the overlapping structure used in Test Example 2 to test the anisotropic conductivity of the stretchable electronic solder prepared in Example 1, which is an anisotropic conductive material.

[0044] Figure 8 The figure shows the test results of the anisotropic conductivity of the stretchable electronic solder prepared in Example 1, which is an anisotropic conductive material.

[0045] Figure 9 The test curve shows the lap shear strength of the anisotropic conductive stretchable electronic solder prepared in Example 1 against copper-polyethylene terephthalate (Cu-PET).

[0046] Figure 10 The figure shows the test results of the lap shear strength of the anisotropic conductive stretchable electronic solder prepared in Example 1 to connect Cu-PET, in order to reuse the solder.

[0047] Figure 11 The cyclic electrical tensile test curves of the anisotropic conductive stretchable electronic solder prepared in Example 1 on gallium indium alloy@polydimethylsiloxane (EGaIn@PDMS).

[0048] Figure 12 Cyclic electrical tensile test curves of the anisotropic conductive stretchable electronic solder prepared in Example 1 on gallium indium alloy@styrene-ethylene-butene-styrene block copolymer (EGaIn@SEBS).

[0049] Figure 13This is a physical image of a stretchable device using the anisotropic conductive stretchable electronic solder of the present invention to integrate pressure and temperature sensing functions. Detailed Implementation

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0051] The present invention provides an anisotropic conductive stretchable electronic solder, wherein the anisotropic conductive stretchable electronic solder comprises a polymer binder and silver nanosheets, and the mass ratio of the polymer binder to the silver nanosheets is (5-20):1.

[0052] The polymeric adhesive is obtained by reacting bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, and furfurylamine at 40-60°C, followed by reacting them with N,N'-(4,4'-methylenediphenyl)bismaleimide at 60-80°C.

[0053] This invention provides a method for preparing anisotropic conductive stretchable electronic solder, comprising the following steps:

[0054] (1) Bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether and furfurylamine are dissolved in a solvent and heated at 40-60℃ to obtain a reaction solution;

[0055] (2) Remove the solvent from the reaction solution, mix it with N,N'-(4,4'-methylenediphenyl)bismaleimide, and then heat it at 60-80 °C to obtain a polymer adhesive;

[0056] (3) The polymer adhesive is mixed with silver nanosheets and dried to obtain the anisotropic conductive stretchable electronic solder.

[0057] In a specific embodiment, the process diagram for preparing anisotropic conductive stretchable electronic solder according to the present invention is as follows: Figure 1 As shown, the preparation method includes the following steps:

[0058] (1) The purified bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether and furfurylamine were added to methanol and mixed evenly, and then a furanyl polymer solution was obtained by polymerization reaction;

[0059] (2) The solvent in the furan-based polymer solution is evaporated, and the furan-based polymer is mixed with N,N'-(4,4'-methylenediphenyl)bismaleimide and a cycloaddition reaction is carried out to obtain a polymeric adhesive;

[0060] (3) The polymer adhesive and silver nanosheets are mixed evenly by a planetary mixer, and after being loaded into a suitable mold, excess solvent is evaporated to obtain the anisotropic conductive stretchable electronic solder.

[0061] In a specific embodiment, the method for preparing the anisotropic conductive stretchable electronic solder includes the following steps:

[0062] (1) Dry bisphenol A diglycidyl ether at 40-50 °C for 2-4 h to complete the purification process and obtain purified bisphenol A diglycidyl ether; dissolve the purified bisphenol A diglycidyl ether in a solvent, the mass ratio of solvent to bisphenol A diglycidyl ether is (6-8):1, stir evenly, add polyethylene glycol diglycidyl ether and furfurylamine with a number average molecular weight of 400-600 at room temperature (20-30 °C) (the molar ratio of bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether and furfurylamine is 1:(1-2):(2-3)), continue stirring and heat to 40-60 °C for 36-48 h, cool after the reaction to obtain the reaction solution;

[0063] (2) The solvent of the reaction solution was evaporated by rotary evaporator. The obtained product was mixed with N,N'-(4,4'-methylenediphenyl)bismaleimide at room temperature (20-30 °C) (the molar ratio of furfurylamine to N,N'-(4,4'-methylenediphenyl)bismaleimide was (20-100):1). After stirring evenly, the mixture was heated to 60-80 °C and reacted for 0.5-1 h. After cooling, a polymer adhesive was obtained.

[0064] (3) Add the polymer adhesive to a 30 mL PE mixing tank, then add silver nanosheets. The mass ratio of the polymer adhesive to the silver nanosheets with a diameter of 1-5 μm is 19:1. After sealing the mixing tank, put it into a planetary mixer and stir for 160-200 s. Put the well mixed material into a suitable mold, place it in a vacuum oven, heat it to 60-80 ℃ and dry it for 4-6 h to obtain the anisotropic conductive stretchable electronic solder.

[0065] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0066] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used are commercially available.

[0067] The bisphenol A diglycidyl ether used in the following examples was purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd., item number D3415-250G; polyethylene glycol diglycidyl ether was purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd., item number 475696; furfurylamine was purchased from Tokyo Chemical Industry Co., Ltd., item number F0091; N,N'-(4,4'-methylenediphenyl)bismaleimide was purchased from Sigma-Aldrich (Shanghai) Trading Co., Ltd., item number 227463-100G.

[0068] Example 1

[0069] A method for preparing anisotropic conductive stretchable electronic solder includes the following steps:

[0070] (1) The bisphenol A diglycidyl ether was dried at 45 °C for 2 h to complete the purification process and obtain purified bisphenol A diglycidyl ether; the purified bisphenol A diglycidyl ether was dissolved in methanol, the mass ratio of methanol to bisphenol A diglycidyl ether was 7:1, and after stirring evenly, polyethylene glycol diglycidyl ether with a number average molecular weight of 500 and furfurylamine (the molar ratio of bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether and furfurylamine was 1:1:2) were added at room temperature (25 °C), the mixture was stirred continuously and heated to 50 °C for 42 h, and the reaction solution was cooled after the reaction was completed.

[0071] (2) The solvent of the reaction solution was evaporated by rotary evaporator. The obtained furanyl polymer and N,N'-(4,4'-methylenediphenyl)bismaleimide were mixed at room temperature (25 °C) (the molar ratio of furfurylamine to N,N'-(4,4'-methylenediphenyl)bismaleimide was 50:1). After stirring evenly, the mixture was heated to 70 °C and reacted for 0.75 h. After cooling, a polymer adhesive was obtained.

[0072] (3) Add 9.5 g of polymer adhesive to a 30 mL PE mixing tank, then add 0.5 g of silver nanosheets with a diameter of 1-5 μm. After sealing the mixing tank, place it in a planetary mixer and stir for 180 s. The total mass of the counterweight system of the mixer is 500 g, the revolution speed of the mixer is 1500 r / min, and the rotation speed of the mixer is 1000 r / min. The uniformly mixed material is loaded into a suitable mold, placed in a vacuum oven, heated to 70 ℃ and dried for 4 h to obtain anisotropic conductive stretchable electronic solder.

[0073] Figure 2The 1H NMR spectra of bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, furfurylamine, and furanyl polymer in Example 1 are shown below. Figure 2 As can be seen, the characteristic peaks of the furan-based polymer spectrum are significantly different from those of the raw materials bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, and furfurylamine. The characteristic peaks of the epoxy groups, furan rings, and other characteristic structures in the raw material spectra are significantly weakened or disappeared in the furan-based polymer spectrum, while new characteristic peaks appear. This indicates that bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, and furfurylamine have undergone ring-opening polymerization to generate the target furan-based polymer intermediate.

[0074] Figure 3 Scanning electron microscope image of the anisotropic conductive stretchable electronic solder prepared in Example 1, from Figure 3 As can be seen, silver nanosheets, as conductive fillers, exhibit a uniformly dispersed state in the solder without obvious agglomeration. Furthermore, the particle size and distribution density remain consistent. This dispersed state lays the structural foundation for the solder to construct continuous longitudinal conductive pathways under pressure, while also avoiding stress concentration problems caused by local agglomeration and preserving the flexibility and stretchability of the polymer adhesive to the greatest extent.

[0075] The anisotropic conductive stretchable electronic solder prepared in Example 1 was processed into solder rods with regular shapes, as shown in the figure below. Figure 4 As shown, the solder surface is smooth and free of obvious impurities or delamination, exhibiting good formability and structural uniformity. This indicates that the solder has good processing performance and can be processed into rod-shaped forms that are easy to apply manually or perform spot welding, adapting to different welding scenario requirements.

[0076] Example 2

[0077] A method for preparing anisotropic conductive stretchable electronic solder is basically the same as that in Example 1, except that in step (2), the molar ratio of furfurylamine to N,N'-(4,4'-methylenediphenyl)bismaleimide is 100:1.

[0078] Example 3

[0079] A method for preparing anisotropic conductive stretchable electronic solder is basically the same as that in Example 1, except that in step (2), the molar ratio of furfurylamine to N,N'-(4,4'-methylenediphenyl)bismaleimide is 100:3.

[0080] Example 4

[0081] A method for preparing anisotropic conductive stretchable electronic solder is basically the same as that in Example 1, except that in step (2), the molar ratio of furfurylamine to N,N'-(4,4'-methylenediphenyl)bismaleimide is 100:4.

[0082] Example 5

[0083] A method for preparing anisotropic conductive stretchable electronic solder is basically the same as that in Example 1, except that in step (2), the molar ratio of furfurylamine to N,N'-(4,4'-methylenediphenyl)bismaleimide is 100:5.

[0084] Example 6

[0085] A method for preparing anisotropic conductive stretchable electronic solder is basically the same as in Example 1, except that in step (3), 9.0 g of polymer adhesive is added to a 30 mL PE mixing tank, and then 1.0 g of silver nanosheets are added. After sealing the mixing tank, it is placed in a planetary mixer and stirred for 180 s.

[0086] Example 7

[0087] A method for preparing anisotropic conductive stretchable electronic solder is basically the same as in Example 1, except that in step (3), 8.5 g of polymer adhesive is added to a 30 mL PE mixing tank, and then 1.5 g of silver nanosheets are added. After sealing the mixing tank, it is placed in a planetary mixer and stirred for 180 s.

[0088] Example 8

[0089] A method for preparing anisotropic conductive stretchable electronic solder includes the following steps:

[0090] (1) The bisphenol A diglycidyl ether was dried at 50 °C for 2 h to complete the purification process and obtain purified bisphenol A diglycidyl ether; the purified bisphenol A diglycidyl ether was dissolved in methanol, the mass ratio of methanol to bisphenol A diglycidyl ether was 6:1, and after stirring evenly, polyethylene glycol diglycidyl ether with a number average molecular weight of 500 and furfurylamine (the molar ratio of bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether and furfurylamine was 1:2:3) were added at room temperature (25 °C), and the mixture was stirred continuously and heated to 50 °C for 37.5 h. After the reaction was completed, the mixture was cooled to obtain the reaction solution;

[0091] (2) The solvent of the reaction solution was evaporated by rotary evaporator. The obtained product was mixed with N,N'-(4,4'-methylenediphenyl)bismaleimide at room temperature (25 °C) (the molar ratio of furfurylamine to N,N'-(4,4'-methylenediphenyl)bismaleimide was 100:1). After stirring evenly, the mixture was heated to 60 °C and reacted for 0.5 h. After cooling, a polymer adhesive was obtained.

[0092] (3) Add 9.5 g of polymer adhesive to a 30 mL PE mixing tank, then add 0.5 g of silver nanosheets with a diameter of 1-5 μm. After sealing the mixing tank, place it in a planetary mixer and stir for 180 s. The total mass of the counterweight system of the mixer is 500 g, the revolution speed of the mixer is 1500 r / min, and the rotation speed of the mixer is 1000 r / min. The uniformly mixed material is loaded into a suitable mold, placed in a vacuum oven, heated to 60 ℃ and dried for 4 h to obtain anisotropic conductive stretchable electronic solder.

[0093] Example 9

[0094] A method for preparing anisotropic conductive stretchable electronic solder includes the following steps:

[0095] (1) The bisphenol A diglycidyl ether was dried at 40 °C for 4 h to complete the purification process and obtain purified bisphenol A diglycidyl ether; the purified bisphenol A diglycidyl ether was dissolved in methanol, the mass ratio of methanol to bisphenol A diglycidyl ether was 8:1, and after stirring evenly, polyethylene glycol diglycidyl ether with a number average molecular weight of 500 and furfurylamine (the molar ratio of bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether and furfurylamine was 2:3:5) were added at room temperature (25 °C), the mixture was stirred continuously and heated to 40 °C for 48 h, and the reaction solution was cooled after the reaction was completed.

[0096] (2) The solvent of the reaction solution was evaporated by rotary evaporator. The obtained product was mixed with N,N'-(4,4'-methylenediphenyl)bismaleimide at room temperature (25 °C) (the molar ratio of furfurylamine to N,N'-(4,4'-methylenediphenyl)bismaleimide was 25:1). After stirring evenly, the mixture was heated to 80 °C and reacted for 1 h. After cooling, a polymer adhesive was obtained.

[0097] (3) Add 9.0 g of polymer adhesive to a 30 mL PE mixing tank, then add 1.0 g of silver nanosheets with a diameter of 1-5 μm. After sealing the mixing tank, place it in a planetary mixer and stir for 200 s. The total mass of the counterweight system of the mixer is 500 g, the revolution speed of the mixer is 1500 r / min, and the rotation speed of the mixer is 1000 r / min. The uniformly mixed material is loaded into a suitable mold, placed in a vacuum oven, heated to 70 ℃ and dried for 6 h to obtain anisotropic conductive stretchable electronic solder.

[0098] Comparative Example 1

[0099] A method for preparing anisotropic conductive stretchable electronic solder includes the following steps:

[0100] (1) Bisphenol A diglycidyl ether was dried at 45 °C for 2 h to complete the purification process and obtain purified bisphenol A diglycidyl ether; the purified bisphenol A diglycidyl ether was dissolved in methanol, the mass ratio of methanol to bisphenol A diglycidyl ether was 7:1, and after stirring evenly, polyethylene glycol diglycidyl ether with a number average molecular weight of 500 and furfurylamine (the molar ratio of bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether and furfurylamine was 1:1:2) were added at room temperature (25 °C), and the mixture was stirred continuously and heated to 50 °C for 42 h. After the reaction was completed, the mixture was cooled to obtain the reaction solution. The solvent of the reaction solution was evaporated by rotary evaporator to obtain furanyl polymer;

[0101] (2) Add 9.5 g of furanyl polymer to a 30 mL PE mixing tank, then add 0.5 g of silver nanosheets with a diameter of 1-5 μm. After sealing the mixing tank, place it in a planetary mixer and stir for 180 s. The total mass of the counterweight system of the mixer is 500 g, the revolution speed of the mixer is 1500 r / min, and the rotation speed of the mixer is 1000 r / min. The uniformly mixed material is loaded into a suitable mold, placed in a vacuum oven, heated to 70 ℃ and dried for 4 h to obtain anisotropic conductive stretchable electronic solder.

[0102] Test Example 1

[0103] The resistance properties of the anisotropic conductive stretchable electronic solders prepared in Examples 1, 6, and 7 were tested. The test method was as follows: A copper sheet was overlapped with a copper (Cu)@polyimide (PI) strip (a flexible conductive strip with 9 parallel Cu conductive lines 1 mm wide integrated on the surface of PI as a substrate). Under the heating conditions of a hot air gun (100 ℃), solder (coating area of ​​1 mm × 5 mm, thickness of 20 µm) was applied to the interface between the two. Test points were set at 1 cm on each end of the interface for resistance testing. The test results are as follows: Figure 5 As shown, solders with different silver nanosheet contents all exhibit excellent and similar conductivity and electrical stability. Taking all factors into consideration, the preferred technical solution is a polymer binder to silver nanosheet mass ratio of 19:1.

[0104] Test Example 2

[0105] The anisotropic conductive stretchable electronic solders prepared in Examples 1-5 and Comparative Example 1 were subjected to rheological property testing. The testing method was as follows: the solder was uniformly coated onto the test stage of a rotational rheometer with a coating thickness of 1 mm and a shear frequency of 0.1 s. -1 The viscosity of the solder was characterized dynamically with temperature within the range of 30-100 ℃. The test results are as follows: Figure 6 As shown in Table 1:

[0106] Table 1

[0107]

[0108] The viscosity-temperature curves of the anisotropic conductive stretchable electronic solder prepared in Example 1 show that the solder viscosity decreases significantly with increasing temperature, exhibiting typical thermal response characteristics. Comparative data with different contents of N,N'-(4,4'-methylenediphenyl)bismaleimide crosslinking agent further indicate that the anisotropic conductive stretchable electronic solder prepared in Example 1 has a viscosity of 604 kPa·s at room temperature (30 ℃), maintaining good structural hardness. At 80 ℃ and 100 ℃, the viscosities are 5.40 kPa·s and 1.06 kPa·s, respectively, demonstrating excellent melt flowability and the ability to fully fill interfacial gaps under light finger pressure to achieve stable electrical connections. The solder in Example 2 has lower viscosity at room temperature and relatively insufficient structural hardness; the solders in Examples 3-5 have higher viscosity at 80-100 ℃, making it difficult to achieve effective electrical connections by finger pressure, but reliable electrical connections can still be achieved under further heating or assisted pressure.

[0109] Test Example 3

[0110] The anisotropic conductive stretchable electronic solder prepared in Example 1 was subjected to anisotropic conductivity testing. The testing method was as follows: a gold (Au)@polyethylene terephthalate (PET) strip (with PET as the substrate and 10 parallel Au conductive lines integrated on the surface) with a size of 60 mm × 20 mm and a 1 mm wide fracture in the middle was selected as the lower layer. Another Au@PET strip with a size of 10 mm × 20 mm was selected as the upper layer. The upper strip was overlapped over the fracture area of ​​the lower strip, so that the Au conductive lines of the upper and lower layers were in face-to-face contact. The schematic diagram of the overlap structure is shown in Figure 1. Figure 7As shown. Under hot air gun heating conditions (100 ℃), solder was evenly applied to the overlap area, ensuring that the solder completely covered the lower fracture point and the upper strip, with no gaps or residue. A Tektronix DMM6500 6.5-digit multimeter was used to measure the resistance between different test points: The two test points of R1 are located on both sides of the solder overlap area and on the same Au conductive line, used to detect the resistance of the longitudinal conductive path formed after the solder is compressed. The two test points of R2 are located on both sides of the solder overlap area and on different Au conductive lines, used to detect the interlayer (lateral) resistance between the upper and lower Au@PET strips. The two test points of R3 are located on the same side of the solder overlap area and on two adjacent Au conductive lines, used to detect the resistance between adjacent Au conductive lines.

[0111] Test results are as follows Figure 8 As shown, the R1 values ​​of the 10 Au conductive lines remained stable within the range of 12.6-20.4 Ω, proving that the solder successfully constructed a continuous conductive path in the longitudinal direction, effectively achieving electrical connection of the lower broken strips, and demonstrating good longitudinal conductivity. In contrast, no effective conductive signal was detected in R2 and R3, indicating that the solder did not form a conductive path between adjacent conductive lines in the lateral direction, thus eliminating the risk of short circuits. This result fully verifies that the solder possesses stable anisotropic conductivity characteristics, achieving conductivity only in the longitudinal direction under pressure and compaction, while maintaining insulation in the lateral direction, fully meeting the dual requirements of conductivity and insulation for precision electronic connections.

[0112] Test Example 4

[0113] A flexible, bendable PET sheet with dimensions of 1 cm × 3 cm was selected and connected to a copper sheet. Under the heating conditions (100 °C) of a hot table, the anisotropic conductive stretchable electronic solder prepared in Examples 1-5 was uniformly coated on the surface of the PET substrate to be connected, with a coating area of ​​1 cm × 1 cm. Then, the copper sheet was attached to the welding point and a brief light pressure was applied to make the final solder thickness 20 µm. After cooling, the Cu-PET overlap shear strength was tested using a universal testing machine.

[0114] Figure 9 The test curves for the anisotropic conductive stretchable electronic solder prepared in Example 1 and its lap shear strength against copper-polyethylene terephthalate (Cu-PET) are shown below. Figure 9 As can be seen, the shear strength of the solder can be stably raised to a peak level of about 1200 kPa, and it can still maintain a high strength when the displacement reaches about 5 mm. This indicates that the solder can achieve a stable electrical connection while also having excellent mechanical load-bearing capacity. It can adapt to the mechanical deformation requirements of flexible materials during bending and stretching, and ensure the reliability of the connection structure.

[0115] Without adding additional solder, the anisotropic conductive stretchable electronic solder prepared in Example 1 was repeatedly used to connect Cu-PET. The lap shear strength test results are as follows: Figure 10 As shown, during 10 reuse cycles, the shear strength of the solder remained stable at a high level of 900-1200 kPa without a significant downward trend. This result indicates that the solder has excellent reusability. The reversible dissociation characteristics of its dynamic covalent bonds allow the solder to achieve multiple melting flows and cooling solidifications under mild heating conditions, maintaining stable mechanical connection strength without the need for additional solder. This provides reliable technical support for the rework and reassembly of flexible electronic devices.

[0116] Test Example 5

[0117] The long-term electrical tensile stability of the anisotropic conductive stretchable electronic solder prepared in Example 1 was tested. Stretchable conductive materials gallium indium alloy@polydimethylsiloxane (EGaIn@PDMS) and gallium indium alloy@styrene-ethylene-butene-styrene block copolymer (EGaIn@SEBS) with dimensions of 1 cm × 3 cm were selected. Under hot-stage heating conditions (80 ℃), the anisotropic conductive stretchable electronic solder prepared in Example 1 was uniformly coated onto the surfaces of EGaIn@PDMS and EGaIn@SEBS, respectively, with a coating area of ​​1 cm × 1 cm. After bonding, a brief light pressure was applied to achieve a final solder thickness of 30 µm. After cooling, a stable electrical connection was achieved. The resistance was measured using a KEITHLEY DMM6500 6.5-digit multimeter, and liquid metal lines were drawn on the sample surface to optimize the contact performance with the multimeter leads. Mechanical strain was applied using a mechanical tensile stage to achieve simultaneous characterization of electrical and mechanical properties.

[0118] Figure 11 The cyclic electrical tensile test curves of the anisotropic conductive stretchable electronic solder prepared in Example 1 on EGaIn@PDMS are shown below. Figure 11 As can be seen, in the EGaIn@PDMS sample, after the solder underwent more than 10,000 cycles of stretching at 60% stretching rate, the resistance remained stable at a low level of about 1.8 Ω without significant fluctuations. Figure 12 The cyclic electrical tensile test curves of the anisotropic conductive stretchable electronic solder prepared in Example 1 on EGaIn@SEBS are shown below. Figure 12As can be seen, in the EGaIn@SEBS sample, after the solder underwent more than 30,000 cycles of tensile testing at 100% tensile strength, the resistance only increased slightly and remained within a stable range below 2 Ω. This result fully verifies that the solder possesses excellent long-term electrical tensile stability, maintaining stable electrical connections even under harsh conditions of large strain and high cycle count, fully meeting the reliability requirements of flexible devices such as wearables in dynamic usage scenarios.

[0119] Application Example 1

[0120] The anisotropic conductive stretchable electronic solder of this invention is used to integrate a stretchable device. Specifically, a stretchable pressure sensor, a stretchable temperature sensor, and a conventional signal processing device are selected. Under heating conditions such as a hot plate or hot air gun, the anisotropic conductive stretchable electronic solder of this invention is uniformly coated onto the interface surface of the conventional signal processing device. Then, the stretchable pressure sensor and the stretchable temperature sensor are connected, and a brief light pressure is applied to the solder joint. After cooling, a stable electrical connection is completed, resulting in a stretchable device integrating pressure and temperature sensing functions. A physical image is shown below. Figure 13 As shown, the area marked in red is the electrical connection interface implemented using the anisotropic conductive stretchable electronic solder of this invention. At this interface, the solder stably connects the stretchable pressure sensor, the stretchable temperature sensor, and the traditional signal processing device. Its combined anisotropic conductivity and stretchability ensure the reliability of the electrical connection of the device under dynamic deformation.

[0121] The flexible and stretchable functional parts of flexible / stretchable devices are more susceptible to damage from external forces than rigid components and circuit boards, which is a key factor limiting the overall service life of flexible / stretchable devices. Based on the anisotropic conductive stretchable electronic solder of this invention, which possesses excellent reversible connection, versatility, and easy removal, the overall lifespan of the device can be effectively extended by replacing sensing components as needed, and the components can also be recycled. After using this solder to fabricate a stretchable device integrating pressure and temperature sensors, if the sensing components need to be replaced, the welding interfaces can be separated under heating conditions on a hot plate or hot air gun. New stretchable pressure and temperature sensors can be directly connected without adding new solder, quickly producing a new integrated sensing stretchable device. When the device enters the recycling stage, the welding interfaces are separated using the same heating method, and the interfaces are wiped with ethanol to thoroughly remove the solder, resulting in recyclable device components and achieving efficient resource reuse.

[0122] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art should understand that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A stretchable electronic solder with anisotropic conductivity, characterized in that, The anisotropic conductive stretchable electronic solder comprises a polymer binder and silver nanosheets, wherein the mass ratio of the polymer binder to the silver nanosheets is (5-20):

1. The polymeric adhesive is obtained by reacting bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, and furfurylamine at 40-60 °C, followed by reacting them with N,N'-(4,4'-methylenediphenyl)bismaleimide at 60-80 °C.

2. The anisotropic conductive stretchable electronic solder according to claim 1, characterized in that, The number-average molecular weight of the polyethylene glycol diglycidyl ether is 400-600; the diameter of the silver nanosheets is 1-5 μm.

3. The anisotropic conductive stretchable electronic solder according to claim 1, characterized in that, The molar ratio of bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether, and furfurylamine is 1:(1-2):(2-3).

4. The anisotropic conductive stretchable electronic solder according to claim 1, characterized in that, The molar ratio of furfurylamine to N,N'-(4,4'-methylenediphenyl)bismaleimide is (20-100):

1.

5. A method for preparing anisotropic conductive stretchable electronic solder according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Bisphenol A diglycidyl ether, polyethylene glycol diglycidyl ether and furfurylamine are dissolved in a solvent and heated at 40-60 °C to obtain a reaction solution; (2) Remove the solvent from the reaction solution, mix it with N,N'-(4,4'-methylenediphenyl)bismaleimide, and then heat it at 60-80 °C to obtain a polymer adhesive; (3) The polymer adhesive is mixed with silver nanosheets and dried to obtain the anisotropic conductive stretchable electronic solder.

6. The preparation method according to claim 5, characterized in that, In step (1), the mass ratio of the solvent to bisphenol A diglycidyl ether is (6-8):1; the heating reaction time is 36-48 h.

7. The preparation method according to claim 5, characterized in that, In step (1), the process of purifying bisphenol A diglycidyl ether is included before dissolution.

8. The preparation method according to claim 7, characterized in that, The purification process specifically involves drying bisphenol A diglycidyl ether at 40-50 °C for 2-4 h.

9. The preparation method according to claim 5, characterized in that, In step (2), the heating reaction takes 0.5-1 h.

10. The application of an anisotropic conductive stretchable electronic solder according to any one of claims 1-4, characterized in that, Used for welding flexible, stretchable and rigid materials and devices.

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