Conductive composite material, preparation method thereof and interconnection joint

Abstract

The invention relates to the technical field of novel conductive materials, in particular to a conductive composite material, a preparation method thereof and an interconnection joint. The preparation method comprises the following steps: performing hydrophobic modification treatment on metal particles to obtain modified metal particles; dispersing the modified metal particles in an elastic polymer solution, and carrying out evaporation treatment on a solvent to obtain a self-assembly material; and carrying out annealing treatment on the self-assembled material to obtain the conductive composite material. Hydrophobic modification treatment is beneficial to reduction of agglomeration and sedimentation and uniform dispersion of metal particles, a conductive path is formed through self-assembly in a polymer base material in the evaporation treatment process, and the conductivity is greatly improved through final annealing treatment. The prepared conductive composite material can be used for connecting a flexible device and a hard device, and has relatively high stretchability, bonding strength, connection stability and reliability, conductivity and conductive stability.

Description

Technical Field

[0001] The present application relates to the technical field of new conductive materials, and particularly relates to a conductive composite material, a preparation method thereof, and an interconnecting joint. Background Art

[0002] In the field of consumer electronics, such as flexible smart watches, foldable display screens and other intelligent wearable devices, and in the field of medical electronics, such as brain-computer interfaces, implantable medical devices, etc., flexible electronic technology has achieved rapid development. Flexible electronic technology includes various flexible devices and rigid devices. Flexible devices include various flexible sensors, etc., and rigid devices include various electronic components such as chips, capacitors, resistors, etc. Integrating these devices results in a flexible electronic system. However, there is a major problem in the application of flexible electronic technology: how to achieve a stable and reliable connection between flexible devices and rigid components. This is because the interconnection between flexible devices and rigid devices faces a major challenge of mismatched heterogeneous material interfaces. At the contact interface between the two, there are mainly problems such as stress concentration caused by interface structure mismatch, insufficient bonding strength, significantly reduced stretchability, decreased conductivity, large influence of conductivity by stretching, and insufficient accuracy.

[0003] The connection part of the rigid device is mainly its rigid wire. To solve the above interconnection problem, the prior art uses a liquid conductor to connect the flexible device and the rigid wire, such as silver-containing ink, etc. However, this interconnection method has low bonding strength and is prone to short circuits. There is also prior art that uses soft soldering to connect the flexible device and the rigid wire, but because it requires high-temperature treatment, it is easy to damage the circuit, base film, etc. of the flexible device. Therefore, the existing interconnection technologies show obvious limitations in dealing with these challenges. Summary of the Invention

[0004] The purpose of the present application is to provide a conductive composite material, a preparation method thereof, and an interconnecting joint, aiming to solve the problems in the prior art that the interconnection effect between flexible devices and rigid wires is not good, with insufficient bonding strength, insufficient stretchability, insufficient conductivity, and insufficient conductive stability.

[0005] To achieve the above application purpose, the technical solution adopted by the present application is as follows: In the first aspect, the present application provides a preparation method of a conductive composite material, including the following steps: Perform hydrophobic modification treatment on metal particles to obtain modified metal particles; Disperse the modified metal particles in an elastic polymer solution, and perform evaporation treatment on the solvent to obtain a self-assembled material; Perform annealing treatment on the self-assembled material to obtain a conductive composite material.

[0006] In the preparation method of the present application, hydrophobic modified metal particles are first prepared. When they are subsequently dispersed in an elastic polymer solution, there is a repulsive force between the modified metal particles, which are not easily agglomerated or settled, facilitating uniform dispersion. During the solvent evaporation treatment process, as the solvent evaporates, the repulsive force between the particles gradually decreases, and finally they come into contact with each other and self-assemble into a dense conductive path. This step is a process of liquid-phase to solid-phase transformation. The elastic polymer gradually dissolves to form a substrate, and the modified metal particles are dispersed in the elastic polymer substrate to obtain a self-assembled material. Finally, annealing the self-assembled material can significantly improve the electrical conductivity of the conductive composite material, with a high-order-of-magnitude increase in conductivity. The preparation method of the present application has controllable process, and the prepared conductive composite material has stable structure and physical and chemical properties, and can be used to connect flexible devices and rigid devices, with high stretchability, bonding strength, connection stability and reliability, electrical conductivity, and conductive stability.

[0007] In a second aspect, the present application provides a conductive composite material prepared by the above-mentioned preparation method of the present application.

[0008] The conductive composite material of the present application is prepared by the above-mentioned preparation method. The material includes an elastic polymer substrate and also includes modified metal particles uniformly dispersed therein. These particles self-assemble to form a conductive path. Finally, annealing treatment is further carried out to improve the conductivity. The obtained conductive composite material has good stretchability, strong adhesion, good connection stability, high electrical conductivity, and good conductive stability, and can be used for interconnecting flexible devices and rigid devices.

[0009] In a third aspect, the present application provides an interconnecting joint, and the material of the interconnecting joint includes the conductive composite material prepared by the above-mentioned preparation method of the present application.

[0010] Due to the good stretchability, electrical conductivity, and conductive stability of the conductive composite material prepared above, it can be used for the interconnecting joint. The interconnecting joint is used to connect flexible devices and rigid wires, with good connection stability, and can be stretched and bent according to the dynamic use scenarios of the flexible devices without easy detachment. Moreover, it has good electrical conductivity and conductive stability. When the interconnecting joint is deformed, its conductivity still remains relatively stable, with small fluctuations, stable current signal transmission, and high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0012] Figure 1It is a schematic structural diagram of the interconnection head in Embodiment 1 of the present application connecting a flexible sensor and a rigid wire respectively; Figure 2 It is a partial structural schematic diagram of the interconnection head in Embodiment 1 of the present application connecting a flexible sensor and a rigid wire respectively; Figure 3 It is a schematic diagram of the components when the interconnection head in Embodiment 1 of the present application connects a rigid wire; Figure 4 It is a schematic diagram of the steps of the preparation method of the conductive composite material and the interconnection head in Embodiment 1 of the present application; Figure 5 It is a SEM cross-sectional view of the side of the interconnection film in Embodiment 1 of the present application; Figure 6 It is a SEM surface view of the interconnection film in Embodiment 1 of the present application; Figure 7 It is a test chart of the electrical conductivity of the interconnection film in Embodiments 1 to 4 of the present application; Figure 8 It is a test chart of the electrical conductivity of the interconnection film in Embodiments 1 to 4 of the present application during tensile cycling; Figure 9 It is a comparative chart of the electrical conductivity test of the interconnection film in Embodiment 1 and Embodiment 5 of the present application; Figure 10 It is a comparative chart of the influence of whether to perform surface treatment on metal particles on the electrical conductivity of the interconnection film in Embodiment 1 and Comparative Example 1 of the present application; Figure 11 It is a comparative chart of the influence of whether to perform annealing treatment on the electrical conductivity of the interconnection film in Embodiment 1 and Comparative Example 2 of the present application; Figure 12 It is a test chart of the electrical conductivity of the interconnection head in Embodiments 1 to 4 of the present application; Figure 13 It is a test chart of the electrical conductivity of the interconnection head in Embodiments 1 to 4 of the present application during tensile cycling; Figure 14 It is a comparative chart of the bonding force of the interconnection head in Embodiment 1 and the commercial interconnection materials in Comparative Examples 3 to 6 for connecting a flexible sensor and a rigid wire; Figure 15 It is a side optical photograph of the interconnection head in Embodiment 1 connecting a rigid wire; Figure 16 It is a physical diagram of the interconnection head in Embodiment 1 connecting a flexible sensor and a rigid wire to each other. Detailed implementation manners

[0013] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer and more understandable, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0014] In this application, the term "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Here, A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0015] In this application, "at least one" means one or more, and "a plurality" means two or more. "At least one of the following items" or its similar expressions refer to any combination of these items, including any combination of single items or plural items.

[0016] It should be understood that in various embodiments of this application, the magnitudes of the serial numbers of the above processes do not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation to the implementation process of the embodiments of this application.

[0017] In the specification of the embodiments of this application, the weight of the relevant components mentioned not only can refer to the specific content of each component, but also can represent the proportional relationship of the weights between the components. Therefore, as long as the content of the relevant components in the specification of the embodiments of this application is scaled up or down proportionally, it is within the scope disclosed in the specification of the embodiments of this application. Specifically, the mass in the specification of the embodiments of this application can be mass units well-known in the chemical industry such as µg, mg, g, kg, etc.

[0018] The terms "first" and "second" are only used for descriptive purposes to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. For example, without departing from the scope of the embodiments of this application, the first XX can also be referred to as the second XX. Similarly, the second XX can also be referred to as the first XX. Thus, the features defined with "first" and "second" can explicitly or implicitly include one or more of such features.

[0019] Explanation of some terms: Conductive stability: refers to the performance of maintaining a stable resistance when a conductive material undergoes deformations such as stretching and bending. An ideal interconnect material should have good conductive stability, so that the resistance is relatively stable in the dynamic usage scenarios of flexible electronic technologies, and will not affect the stability, accuracy, and reliability of signal transmission. In the prior art, for most conductive materials, their conductivity will significantly decrease after stretching, the conductivity decreases, and the resistance increases. Therefore, if such materials are used for interconnecting flexible devices and rigid devices in flexible electronic technologies, as the flexible usage scenarios change, the resistance of the interconnect material will also change, resulting in the stability, signal value, reliability, and accuracy of the signal not meeting the requirements.

[0020] In the first aspect of the embodiments of the present application, a method for preparing a conductive composite material is provided, including the following steps: S10: Perform hydrophobic modification on metal particles to obtain modified metal particles; S20: Disperse the modified metal particles in an elastic polymer solution, and perform evaporation treatment on the solvent to obtain a self-assembled material; S30: Anneal the self-assembled material to obtain a conductive composite material.

[0021] In the preparation method of the embodiments of the present application, hydrophobic modified metal particles are first prepared. When subsequently dispersed in an elastic polymer solution, there is a repulsive force between the modified metal particles, which are not easy to agglomerate or settle, facilitating uniform dispersion. During the evaporation treatment of the solvent, as the solvent evaporates, the repulsive force between the particles gradually decreases, and finally they come into contact with each other and self-assemble into a dense conductive path. This step is a process of liquid-phase to solid-phase transformation. The elastic polymer gradually dissolves out to form a substrate, and the modified metal particles are dispersed in the elastic polymer substrate to obtain a self-assembled material. Finally, annealing the self-assembled material can significantly improve the electrical conductivity of the conductive composite material, with a high-order-of-magnitude increase in conductivity. The preparation method of the embodiments of the present application has controllable process, and the prepared conductive composite material has stable structure and physical and chemical properties, and can be used to connect flexible devices and rigid devices, having high stretchability, bonding strength, connection stability and reliability, electrical conductivity, and conductive stability.

[0022] Step S10 is the step of performing hydrophobic modification. In the embodiment, the metal particles may include at least one of silver, gold, and copper, which may be a metal single substance or an alloy, and these metals have good electrical conductivity. At the same time, according to the preparation method of the present application, the particle size of the metal particles has a wide selection range, and similar high performance can be obtained by using small particles and large particles in the preparation method, and the preparation method has strong applicability. In the embodiment, the Dv50 particle size of the metal particles may be 0.01 - 1 μm. In the exemplary example, it may include but is not limited to any value of 0.01 μm, 0.08 μm, 0.2 μm, 0.4 μm, 0.6 μm, 1 μm or the range between any two values. In the embodiment, the metal particles can be prepared by chemical reduction method by themselves, or can be existing finished metal particles.

[0023] The hydrophobic modification treatment is mainly to ensure that when the modified metal particles are dispersed in the elastic polymer solution in the subsequent step S20, there is a repulsive force between the modified metal particles, making them less likely to agglomerate or settle. This is beneficial for uniform dispersion, which in turn helps to evenly distribute the components in the final conductive composite material, improving the connection stability, conductive stability, and signal reliability during interconnection. If phenomena such as agglomeration and sedimentation of metal particles occur, there will be local aggregation areas of metal particles in the finally prepared conductive composite material. Although these local aggregation areas have good electrical conductivity, their elastic properties are relatively low, and they are not compatible with the mechanical and electrical properties of other regions in the composite material. Eventually, this leads to low connection strength and poor connection stability between the conductive composite material and hard and flexible devices, large fluctuations in the interconnection resistance, unstable current, affecting signal accuracy, and unsatisfactory interconnection effects.

[0024] In some embodiments, the hydrophobic modification treatment can be carried out by modifying the metal particles with a modifier. The modifier can include at least one of thiol and silane. The metal particles can be dispersed in an ethanol solvent, and then the modifier is added and stirred thoroughly. For example, stir at a stirring speed of 500 r / min for 2 - 4 hours. After the modifier has fully interacted with the surface of the metal particles to complete the modification, centrifuge and wash to remove the ethanol to obtain the modified metal particles. In a demonstration example, when the modifier is thiol, the thiol can include at least one of propanethiol, octanethiol, and dodecanethiol, and propanethiol can be selected. The sulfur atom in the thiol has a strong binding effect with the metal atom and can form a stable metal - sulfur bond, such as an Ag - S bond, forming a hydrophobic coating layer, which greatly improves the dispersibility of the modified metal particles. In addition, thiol modification is not only beneficial for hydrophobic modification but also helps to improve the compatibility between the modified metal particles and the elastic polymer. In some embodiments, the mass ratio of the modifier to the metal particles can be (2 - 3):1 to achieve a higher hydrophobic modification effect.

[0025] Step S20 is a step for self - assembly treatment of metal particles. First, an elastic polymer solution can be prepared. The elastic polymer can include at least one of styrene - ethylene - butene - styrene block copolymer (SEBS), polydimethylsiloxane (PDMS), and polyimide (PU), and has good stretchability. The solvent can be a volatile solvent, which can include at least one of toluene, ethanol, and n - hexane, and toluene can be selected. During preparation, the elastic polymer particles can be added to the solvent and heated and stirred to dissolve at 80 - 100 °C. The concentration of the prepared elastic polymer solution can be 15 wt%.

[0026] Then, the modified metal particles are dispersed in the elastic polymer solution. The dispersion method can be directly adding the modified metal particles to the elastic polymer solution, or the following steps can be adopted: S21: Disperse the modified metal particles in a dispersion liquid to obtain a slurry; S22: Mix the slurry and the elastic polymer solution.

[0027] Since the modified metal particles have been subjected to hydrophobic modification treatment, in step S21, the modified metal particles are first dispersed in the dispersion liquid. Then, the modified particles in the slurry can reduce agglomeration, reduce sedimentation, and improve dispersibility, which is beneficial to the uniform dispersion of the modified metal particles in the elastic polymer solution in step S22. The dispersion liquid can be a volatile dispersion liquid, which can include at least one of toluene, ethanol, and n-hexane, and can be optionally a mixed dispersion liquid of toluene, ethanol, and n-hexane. In the embodiment, the modified metal particles can be added to the dispersion liquid and subjected to ultrasonic dispersion treatment to uniformly disperse the modified metal particles to obtain the slurry. Then, in step S22, the slurry and the elastic polymer solution are further mixed, which is more conducive to the uniform mixing of the two and the uniform dispersion of the modified metal particles.

[0028] In some embodiments, the mass ratio of the elastic polymer to the modified metal particles in step S20 is (2-3):(7-8), which can include but is not limited to any ratio such as 2:8, 3:7 or the range between any two ratios. In the conductive composite material finally prepared from the materials with these mass ratios, the modified metal particles and the elastic polymer can maintain the corresponding ratio, enabling the conductive composite material to take into account stretchability, connection stability, conductivity, conductive stability, etc.

[0029] The evaporation treatment in step S20 gradually evaporates the solvent, and the elastic polymer will also gradually dissolve out to form the substrate. Moreover, as the solvent evaporates, the repulsive force between the modified metal particles that were originally mutually repulsive in the solvent gradually decreases. During the transformation of the system from the liquid phase to the solid phase, the modified metal particles gradually approach and spontaneously self-assemble to form an efficient conductive path and disperse in the substrate. Also, due to the hydrophobic modification treatment of the modified metal particles in the above step S10, the modified metal particles are not easily sedimented and agglomerated during this evaporation treatment process. In the embodiment, the evaporation treatment can include any one of natural evaporation, reduced-pressure evaporation, and heating evaporation. The above solvent can be a volatile solvent that can volatilize under normal temperature and pressure, or a solvent that can volatilize under conditions such as reduced pressure and heating. Among them, natural evaporation can be carried out by standing in a ventilated place for a period of time, such as standing for 1 day; reduced-pressure evaporation can gradually reduce the pressure in the container to accelerate evaporation and remove the vapor, and the pressure can be reduced to a vacuum; heating evaporation can accelerate the evaporation rate, but the temperature needs to be appropriate. If bubbles are generated or the solvent tumbles, it is not conducive to the dispersion and self-assembly of the modified metal particles. The evaporation treatment can be carried out by placing the mixed liquid in a mold, so that the desired shape of the conductive composite material can be obtained after evaporation is completed.

[0030] Step S30 is the step of annealing treatment. If the self-assembled material prepared in step S20 is used to connect flexible devices and rigid devices, it already has a certain bonding strength and stretchability, but its conductivity still cannot meet the requirements. Even if the content of modified metal particles is increased, the improvement of conductivity is limited. Through research, the applicant found that annealing the self-assembled material can significantly improve the conductivity of the prepared conductive composite material. In some embodiments, the self-assembled material will also change color and other phenomena after annealing treatment, and its conductivity can be increased by 7 to 9 orders of magnitude, that is, the conductivity of the conductive composite material obtained after annealing treatment is 10 7 ~10 9 times that of the self-assembled material before annealing treatment, fully meeting the conductivity requirements of the interconnection material. In some embodiments, the annealing temperature can be 100°C to 200°C, which can include but is not limited to any value or the range between any two values of 100°C, 130°C, 170°C, and 200°C. The annealing time can be 20 to 60 minutes, and the annealing treatment can be carried out on a heating table.

[0031] After the conductive composite material is prepared, it can be further processed by molding. The conductive composite material has excellent processing performance and can be processed by processes such as cutting. The cutting edge is neat, without burrs and cracks, further ensuring the stability and reliability of the interconnection. It can achieve high-resolution patterning, meet the micron-level interconnection requirements, and can be used for the interconnection of high-density and miniaturized electronic devices.

[0032] In the second aspect of the embodiments of the present application, a conductive composite material prepared by the preparation method of the above embodiments of the present application is provided.

[0033] The conductive composite material of the embodiments of the present application is prepared by the above preparation method. The material includes an elastic polymer substrate and also includes modified metal particles uniformly dispersed therein. These particles self-assemble to form a conductive path. Finally, annealing treatment is carried out to further improve the conductivity. The obtained conductive composite material has good stretchability, strong adhesion, good connection stability, high conductivity, and good conductive stability, and can be used for the interconnection of flexible devices and rigid devices.

[0034] In the embodiment, the mass percentage content of the modified metal particles in the conductive composite material can be 70% to 80%, and can include but not limited to any value of 70%, 73%, 75%, 77%, 80% or the range between any two values. At such a mass percentage content, the conductive composite material can balance the stretchability, adhesiveness, connection stability, conductivity, and conduction stability. Especially at such a mass percentage content, its conduction stability is very ideal. Even under long-term cyclic stretching and dynamic working environments, the resistance hardly changes. The resistance is also very low, which is beneficial to reducing the energy loss during current transmission, significantly improving the transmission efficiency of the device, and can also improve the stability and integrity of signal transmission, reduce signal delay and distortion, which is beneficial to achieving high-quality connection between flexible devices and rigid devices, and improving the high performance and stable operation of flexible electronic systems.

[0035] In the embodiment, the shape of the conductive composite material can be film-shaped, which is convenient for connecting flexible devices and rigid devices.

[0036] The third aspect of the embodiment of the present application provides an interconnection joint, and the material of the interconnection joint includes the conductive composite material prepared by the preparation method of the above-mentioned embodiment of the present application.

[0037] Due to the good stretchability, conductivity, and conduction stability of the above-prepared conductive composite material, it can be used for the interconnection joint. The interconnection joint is used to connect flexible devices and rigid wires, and has good connection stability. It can be stretched and bent according to the dynamic use scenarios of flexible devices and is not easy to fall off. Moreover, it has good conductivity and conduction stability. When the interconnection joint is deformed, its conductivity still remains relatively stable with small fluctuations, and the current signal transmission is stable and highly reliable.

[0038] The shape of the interconnection joint can include but not limited to block shape, column shape, spherical shape, strip shape, and layer shape. In some embodiments, the interconnection can include a first conductive film and a second conductive film arranged in a stacked manner, and the materials of the first conductive film and the second conductive film include the conductive composite material. The above-mentioned conductive composite material can be made into a film shape to form a conductive film, and then the two conductive films are stacked. The rigid wire can be combined between the two conductive films to further improve the binding stability between the interconnection joint and the rigid wire. Especially when the elastic polymer includes at least one of SEBS, PDMS, and PU, there is a stronger binding force between the two conductive films.

[0039] In some embodiments, the interconnecting joint can be strip-shaped. One end of the interconnecting joint is connected to a rigid wire, and the other end is connected to a flexible device. The connection method between the rigid wire and the interconnecting joint can include the following steps: inserting one end of the rigid wire between a first conductive film and a second conductive film, and performing hot pressing treatment. The temperature of the hot pressing treatment can be 200 - 400 °C, the time can be 0.5 - 6 min, and the pressure can be 100 - 300 kPa. By performing hot pressing treatment on the two conductive films in this way, the two conductive films can be closely adhered together without other components such as adhesive. The rigid wire will be hot pressed between the two conductive films, and the opposite surfaces of the conductive films will also be extruded into a concave shape by the rigid wire. Therefore, the contact between the wire and the conductive film will change from line contact to surface contact and three-dimensional contact, which is beneficial to improving the connection stability and conductivity. Such an interconnecting joint combined with a rigid wire not only has excellent bonding strength, but also has excellent environmental stability, can withstand harsh conditions such as acid-base corrosion and temperature changes, and exhibits extremely high reliability.

[0040] The rigid wire can be a common copper wire. In the embodiment, the surface treatment of the wire can be carried out, which is more beneficial to improving the reliability, stability and durability of the combination between the wire and the interconnecting joint. Surface cleaning can be carried out first and then surface modification. Specifically, after removing the skin at one end of the wire, it can be cleaned with solutions such as deionized water, ethanol, and acetone, and then the wire can be immersed in a silane coupling agent for 10 - 30 minutes, taken out and immersed in ethanol for 1 minute, and then dried for standby. The molecular structure of the silane coupling agent contains organic functional groups (such as amino group, epoxy group, vinyl group, etc.) and hydrolyzable inorganic groups (such as methoxy group, ethoxy group). After binding to the metal surface of the wire, a chemical bond bridge is formed between the wire and the elastic polymer in the interconnecting joint, thereby increasing the binding force between the wire and the interconnecting joint. In the embodiment, the morphology of the rigid wire can also be optimized. The 3D printing technology can be used to design one end of the wire as a paddle-shaped structure, which is beneficial to further enhancing the mechanical strength, reliability and durability of the combination with the interconnecting joint when it is hot pressed in the middle of the conductive film.

[0041] The other end of the interconnecting joint is connected to a flexible device. The flexible substrate of the flexible device can be an elastic polymer (such as materials like SEBS, etc.). The wire or electrode for connection can be a gold wire (or silver wire, etc.) arranged on the elastic polymer. Then, the other end of the interconnecting joint is directly attached to the gold wire and hot pressing treatment is carried out. The hot pressing treatment parameters for hot pressing the rigid wire can be referred to, and only 30 s of hot pressing is required. In this way, the flexible sensor can be adhesively bonded to the other end of the interconnecting joint through a biphasic nano-dispersed interface (BIND) formed by nano materials such as gold (or silver) and the elastic polymer.

[0042] This interconnection head can be used in flexible electronics technology. In an embodiment, it can be used for a flexible display screen, and in consumer electronic products such as smartphones, tablets, and foldable devices, it is used for the connection between the flexible display screen and the rigid circuit board. It improves the connection stability, the reliability of signal transmission, and the durability of the device. In an embodiment, it can also be used for wearable devices: Wearable devices such as smartwatches and smart bracelets usually include a flexible part (such as a wristband) and a rigid component part (such as a chip and a sensor). This interconnect material can effectively connect these parts and improve the stability of the device when working in complex environments such as bending and stretching.

[0043] This interconnection head can also be used for medical wearable detectors. In the medical field, wearable devices are used to monitor patients' physiological signals in real time (such as heart rate, blood pressure, body temperature, etc.). These devices usually need to connect flexible sensors to rigid data processing and display systems. The interconnection head in the embodiment of the present application is beneficial to the efficient transmission of signals while maintaining the comfort and durability of the device.

[0044] This interconnection head can also be used for implantable medical devices. Some implantable medical devices (such as cardiac pacemakers, nerve stimulators, etc.) need to connect flexible electrodes to rigid electronic components. The interconnection head in the embodiment of the present application can provide a stable electrical connection and adapt to the complex environment in the human body at the same time.

[0045] The following is an illustration with specific embodiments.

[0046] Embodiment 1 This embodiment provides a conductive composite material, its preparation method, and an interconnection head. The preparation method is as Figure 4 shown, including the following steps: S1: Preparation of Ag metal nanoparticles: Polyvinylpyrrolidone (PVP) is used as a surfactant, and silver nanoparticles are prepared by reducing silver nitrate with ethylene glycol at 180 °C. After the reaction is completed, ethanol is used as a detergent, and centrifugal washing is performed 4 times at a rotation speed of 13000 r / min to wash away the residual reactants such as ethylene glycol and PVP. Finally, pure silver nanoparticles are obtained. The Dv50 particle size is 80 nm, and the partial ethanol remaining on the surface can reduce the oxidation of silver.

[0047] S2: Surface modification and dispersion of Ag metal nanoparticles: 0.15 g of metal nanoparticles are dispersed in 30 mL of ethanol, and then 400 μL of propanethiol is added dropwise. Stirring is carried out at a stirring speed of 500 r / min for 3 hours to complete the surface modification. After the modification is completed, centrifugal washing is performed 4 times with ethanol to wash away the residual reactants, and the modified silver nanoparticles are obtained.

[0048] After transferring the modified silver nanoparticles to a beaker and drying them, 1 mL of toluene, 1 mL of ethanol, and 1 mL of n - hexane were added as the dispersion liquid. Subsequently, it was ultrasonically dispersed in an ultrasonic cleaner for 10 minutes to uniformly disperse the modified silver nanoparticles and obtain a dispersion liquid.

[0049] S3: Preparation of the polymer solution and mixing with metal nanoparticles: Using toluene as the solvent, an appropriate amount of SEBS polymer particles were added and heated with stirring overnight at 80 - 100 °C to prepare a polymer solution with a mass fraction of 15 wt%. The dispersion liquid of the modified silver metal nanoparticles after dispersion in step S2 was stirred at a speed of 250 r / min. Subsequently, the above 15% wt polymer solution was slowly added dropwise. First, about 2 mL was added, and then the addition amounts of the two were adjusted so that in the final mixed dispersion liquid, the mass ratio of the modified silver nanoparticles to the polymer SEBS was 8:2. After the addition was completed, the cup mouth was sealed, and it was heated and stirred at 60 °C for 15 minutes to ensure uniform mixing.

[0050] S4: Formation of the solid - state interconnect film: After cleaning the mold with solutions such as deionized water, ethanol, and acetone, the above - mentioned mixed dispersion liquid was poured into the mold and placed in a fume hood for natural evaporation for 1 day for self - evaporation treatment of the solvent to form a black self - assembled material.

[0051] S5: Annealing treatment and separation: The mold was placed on a heating platform and heated at 165 °C for 10 minutes. The black self - assembled material gradually turned yellow to obtain a conductive composite material. The conductive composite material includes a SEBS polymer matrix and metal nanoparticles dispersed therein. The mass percentage content of the modified metal nanoparticles is 80%; as Figure 3 shown, the conductive composite material is in the form of a film. It was taken out of the mold by mechanical peeling and called the interconnect film (or interconnect material). Then it was cut to obtain a first interconnect film (first interconnect material) and a second interconnect film (second interconnect material), both with a thickness of 160 μm, one with a length of about 10 mm and the other with a length of about 5 mm, and the same width, both greater than the diameter of the rigid wire.

[0052] S6: Surface cleaning and surface modification of commercial wires: After removing the skin at one end of the commercial rigid wire, it was cleaned with solutions such as deionized water, ethanol, and acetone. Then the wire was immersed in a silane coupling agent for 20 minutes, taken out, immersed in ethanol for 1 minute, and dried for later use.

[0053] S7: Thermocompression of the interconnect film and the wire and addition of the encapsulation layer: One end of the surface - treated rigid wire was clamped between two layers of interconnect films (that is, the first interconnect material and the second interconnect material in step S5), and it was thermocompressed at 400 °C for 4 minutes to achieve the connection between the interconnect film and the rigid wire. As Figure 3 andFigure 2 As shown, two layers of interconnecting films form an interconnecting joint. The two layers of interconnecting films at the end connecting the rigid wire are flush, and the other longer interconnecting film extends beyond a length of 5 mm for connecting the gold wire (gold conductor) of the flexible sensor. For example, Figure 1 , Figure 2 As shown, the flexible sensor includes a polymer substrate (SEBS flexible substrate), and also includes electrode points and gold wires bonded to the polymer substrate. Attach the extended part of the interconnecting film at the other end of the interconnecting joint to the gold wire and perform hot pressing at 400 °C for 30 s. Then, the other end of the interconnecting joint has been tightly bonded to the gold wire of the flexible sensor; For example, Figure 1 As shown, the interconnection between the flexible device and the rigid device is thus achieved. The flexible device includes a polymer substrate, electrode points, and gold wires, and the rigid device includes a rigid chip and a rigid wire. The interconnecting joint (interconnecting material) connects the two. Finally, a layer of ordinary polymer film is encapsulated by simple hot pressing means in the area where the interconnecting joint is located for protection to enhance the reliability and durability of the interconnecting joint. A large piece of epoxy resin can also be encapsulated continuously for enhanced protection. As shown, Figure 16 shown.

[0054] Example 2 This example provides a conductive composite material, its preparation method, and an interconnecting joint. The difference from Example 1 is only that in step S3, the mass ratio of the modified nano silver particles to the polymer SEBS is changed to 7.5:2.5; in the finally prepared conductive composite material, the mass percentage content of the modified metal nano particles is 75%, and the others are the same. The differences from Example 1 are recorded in Table 1 below.

[0055] Example 3 This example provides a conductive composite material, its preparation method, and an interconnecting joint. The difference from Example 1 is only that in step S3, the mass ratio of the modified nano silver particles to the polymer SEBS is changed to 7:3; in the finally prepared conductive composite material, the mass percentage content of the modified metal nano particles is 70%, and the others are the same. The differences from Example 1 are recorded in Table 1 below.

[0056] Example 4 This example provides a conductive composite material, its preparation method, and an interconnecting joint. The difference from Example 1 is only that in step S3, the mass ratio of the modified nano silver particles to the polymer SEBS is changed to 6.5:3.5; in the finally prepared conductive composite material, the mass percentage content of the modified metal nano particles is 65%, and the others are the same. The differences from Example 1 are recorded in Table 1 below.

[0057] Example 5 This embodiment provides a conductive composite material, its preparation method, and an interconnecting joint. The difference from Embodiment 1 is only that: in step S1, the reduction temperature is changed to 220 °C, and the Dv50 particle size of the obtained silver metal nanoparticles becomes 0.2 μm, and the others are the same. The differences from Embodiment 1 are recorded in Table 1 below.

[0058] Example 6 This embodiment provides a conductive composite material, its preparation method, and an interconnecting joint. The difference from Embodiment 1 is only that: in step S3, SEBS is changed to PDMS polymer particles, and the others are the same. The differences from Embodiment 1 are recorded in Table 1 below.

[0059] Example 7 This embodiment provides a conductive composite material, its preparation method, and an interconnecting joint. The difference from Embodiment 1 is only that: in step S3, SEBS is changed to PU polymer particles, and the others are the same. The differences from Embodiment 1 are recorded in Table 1 below.

[0060] Example 8 This embodiment provides a conductive composite material, its preparation method, and an interconnecting joint. The difference from Embodiment 1 is only that step S1 is changed to prepare gold nanoparticles, and silver nitrate in the raw materials is replaced with chloroauric acid, and the others are the same. The differences from Embodiment 1 are recorded in Table 1 below.

[0061] Example 9 This embodiment provides a conductive composite material, its preparation method, and an interconnecting joint. The difference from Embodiment 1 is only that step S1 is changed to prepare copper nanoparticles, and silver nitrate in the raw materials is replaced with copper acetate, and the others are the same. The differences from Embodiment 1 are recorded in Table 1 below.

[0062] Comparative Example 1 This comparative example provides a conductive composite material, its preparation method, and an interconnecting joint. The difference from Embodiment 1 is only that in step S2, the modification treatment with thiol is not carried out, and the metal silver particles are directly dispersed into a slurry for subsequent step S3, and the others are the same. The differences from Embodiment 1 are recorded in Table 1 below.

[0063] Comparative Example 2 This comparative example provides a conductive composite material, its preparation method, and an interconnecting joint. The difference from Embodiment 1 is only that in step S5, the annealing treatment is not carried out, and the black interconnecting material is directly used as the final interconnecting material for subsequent steps, and the others are the same. The differences from Embodiment 1 are recorded in Table 1 below.

[0064] Comparative Example 3 This comparative example provides an interconnecting material, which is an anisotropic conductive adhesive of model 7303 from 3M Company.

[0065] Comparative Example 4 This comparative example provides an interconnection material, which is zebra paper, the 3610*50 mm model of Chuangli Silicone Rubber Company.

[0066] Comparative Example 5 This comparative example provides an interconnection material, which is silver ink, the 3813 model of Ausbond Company.

[0067] Comparative Example 6 This comparative example provides an interconnection material, which is carbon tape, the 731 model of Rixin Company.

[0068] The differences between the above-mentioned various embodiments and comparative examples are shown in Table 1:

[0069] Relevant performance tests and result analysis 1. Related tests on the conductive composite material (interconnection material, one-layer interconnection film) 1.1 SEM test The cross-section and surface of the interconnection film were observed by a scanning electron microscope (SEM) to analyze the distribution of metal nanoparticles in the polymer matrix. From Figure 5 the cross-sectional view of the interconnection film and Figure 6 the result of the surface view, it can be seen that the metal nanoparticles are evenly distributed in the polymer matrix, forming a complete and dense conductive path, thus realizing the high electrical conductivity and stretchability of the film.

[0070] 1.2 Conductive performance test Five samples of the interconnection films of Examples 1 to 4 were taken and tested by a KEITHLEY DMM6500 digital multimeter. The test method was to coat liquid metal on both sides of the 5 mm*5 mm interconnection film to eliminate the contact resistance. The copper wire led out from the multimeter for measuring resistance was connected to the liquid metal. First, the total resistance of the copper wire plus the film was measured, and then the two copper wires were placed at the same liquid metal position to measure the copper wire resistance. The difference between the two was the sheet resistance of the film. The measured sheet resistances were made into a statistical chart as Figure 7 shown, Figure 7 The resistance (Ω) on the vertical axis is the sheet resistance (Ω / sq). It can be seen that as the content of metal nanoparticles gradually increases, the resistance gradually decreases, and the resistance stability of the samples in each example improves. The sheet resistance of the conductive film in Example 1 can reach 0.01 Ω / sq.

[0071] 1.3 Test on the influence of tensile cycle on conductive performance The interconnection films of Examples 1 to 4 were subjected to cyclic tensile recovery, with a uniform tensile deformation rate of 30%. One tensile plus recovery was completed every 15 s, and continuous tensile cycle tests were carried out. The sheet resistance of the interconnection film was continuously observed. The results are asFigure 8 As shown Figure 8 Figure 8 The resistance (Ω) on the vertical axis, i.e., the sheet resistance (Ω / sq), shows that in each stretching and recovery cycle, the resistance change of Example 4 is the largest, while the resistance of Example 1 is very stable. With cyclic stretching, the resistance of Example 4 gradually increases, and that of Example 3 also increases slightly, while those of Example 1 and Example 2 are very stable. The inventors also tested samples with a metal particle mass percentage of 85%. Although the conductivity is further improved, due to the too low content of the elastic polymer, the overall stretchability is reduced. The cycle with a 30% tensile strain can still be tested, but it is easy to break at a 60% tensile strain.

[0072] Therefore, increasing the mass percentage of metal nanoparticles within a certain range is beneficial to reducing the resistance value, improving the conductivity, reducing the energy loss during current transmission, significantly enhancing the transmission efficiency of the device, and maintaining the stretchability. At the same time, it improves the conductivity stability. Even when stretched by 30%, the conductivity changes very little, improving the stability and integrity of signal transmission, reducing signal delay and distortion, and being suitable for the dynamic working environment in flexible electronics. Moreover, after long-term stretching, the conductivity also changes very little, improving the service life.

[0073] 1.4 Influence of the particle size of metal particles on the conductivity Take several samples of the interconnecting films of Example 1 and Example 5 respectively to test the sheet resistance. The statistical results are as Figure 9 shown Figure 9 Figure 9 The resistance (Ω) on the vertical axis is the sheet resistance (Ω / sq). It can be seen that the resistances of the two examples are very small and very close. It can be seen that as long as the above preparation method is followed, even if the particle sizes of the metal particles are different, the conductivity of the finally obtained conductive composite material (interconnecting film) is very high and very close, and the applicability of the preparation method is wide.

[0074] 1.5 Influence of surface treatment and modification of metal particles on the conductivity Cut the interconnecting films of Example 1 and Comparative Example 1 respectively, and take several samples to test the sheet resistance. The statistical results are as Figure 10 shown Figure 10 Figure 10 The resistance (Ω) on the vertical axis is the sheet resistance (Ω / sq). It can be seen that in Comparative Example 1, the metal particles were not surface-treated. Even for samples cut from the same interconnecting film, the resistance distribution is very uneven. Some are only 0.01 Ω / sq, and some are even 3.4 Ω / sq. When such an interconnecting film is used for interconnecting flexible devices and rigid devices, the uneven internal resistance distribution will greatly affect the stability and authenticity of signal transmission and is prone to distortion. For samples cut from the same interconnecting film of Example 1, the resistance is very small and very close, and the resistance distribution has good uniformity.

[0075] 1.6 Influence of Annealing Treatment on Conductivity Three samples each of the annealed interconnecting thin film of Example 1 and the interconnecting thin film before annealing (self-assembled material, i.e., Comparative Example 2) were taken to measure the sheet resistance. The statistical results are as Figure 11 shown Figure 11 The resistance (Ω) on the vertical axis is the sheet resistance (Ω / sq). It can be seen from the figure that the annealing treatment has a very significant effect on the conductivity of the interconnecting thin film. After annealing, it can reach 10 times that before annealing. The annealing treatment can greatly improve the conductivity of the interconnecting thin film. 7 times, and the annealing treatment can greatly improve the conductivity of the interconnecting thin film.

[0076] 2. Related Tests on Interconnection Joints (Thermal Pressing of Two Layers of Conductive Thin Films) 2.1 Conductivity Test Since the interconnection joints have been connected to the rigid wires, different from the method of measuring the sheet resistance of the above interconnecting thin films, the overall resistance of the interconnection joints combined with the rigid wires is directly measured here instead of the sheet resistance to conform to the actual application scenario. During specific testing, two test electrodes are respectively connected to both ends of the interconnection joint. One is connected to the area where the length of the longer interconnecting thin film in the interconnection joint extends beyond, and the other is connected to the rigid wire extending from the interconnection joint to measure the resistance between these two places. Five samples each of the interconnection joints of Examples 1 to 4 were taken to measure their respective resistances. The statistical chart is as Figure 12 shown. It can be seen that as the content of metal nanoparticles gradually increases, the resistance of the interconnection joints gradually decreases, and the resistance stability of the samples in each example improves. The resistance of the interconnection joint of Example 1 can reach 0.1 Ω.

[0077] 2.2 Test on the Influence of Tensile Cycle on Conductivity The interconnection joints of Examples 1 to 4 were subjected to cyclic tensile recovery. The tensile deformation rate was uniformly 30%, and the tensile direction was parallel to the direction of the two-layer bonding surface. One tensile plus recovery was completed every 15 s for continuous tensile cycle testing, and the resistance of the interconnection joints was continuously observed. The results are as Figure 13 shown. It can be seen that in each tensile recovery cycle, the resistance change of Example 4 is the largest, and the resistance of Example 1 is very stable. With cyclic tensile, the resistance of Example 4 gradually increases, and that of Example 3 also increases slightly, while those of Example 1 and Example 2 are very stable.

[0078] Therefore, increasing the mass percentage content of metal nanoparticles within a certain range is beneficial to reducing the resistance value of the finally prepared interconnection joint, improving the electrical conductivity, reducing the energy loss during the current transmission process, and significantly enhancing the transmission efficiency of the device. At the same time, it improves the electrical conductivity stability. Even when stretched by 30%, the electrical conductivity changes very little, improving the stability and integrity of signal transmission, reducing signal delay and distortion, and being applicable to the dynamic working environment in flexible electronic technology. Moreover, after 600 stretches, the electrical conductivity also changes very little, having a high service life.

[0079] 2.3 Comparison of the bonding force between the interconnection joint and commercial interconnection materials Take several samples of the interconnection joint of Example 1 and the commercial interconnection materials of Comparative Examples 3 - 6 respectively, and conduct the bonding force test between the flexible sensor and the rigid wire. The specific steps are as follows: Use each commercial interconnection material to connect the flexible sensor and the rigid wire. For example, for the anisotropic conductive adhesive, first paste the anisotropic conductive adhesive on the flexible substrate of the flexible sensor, and then press the wire on it. Use a mechanical universal tester to conduct stretching, clamp the flexible sensor at one end and the rigid wire at the other end, measure the maximum bonding strength, and record the statistical results in Figure 14 In Figure 14 It can be seen from that the interconnection joint prepared in the embodiment of the present application is significantly higher than the existing commercial interconnection materials, and the bonding force can reach six times or more of it, which can improve the stability and reliability of the connection between the flexible device and the rigid device and is not easy to fall off during long-term use.

[0080] 2.4 Physical diagram of the interconnection joint Figure 15 It is a side optical photograph of the interconnection joint of Example 1 connecting the rigid wire. It can be seen that after the hot pressing treatment, the two layers of interconnection films are tightly bonded together, and the rigid wire is pressed in the two layers and tightly bonded.

[0081] Figure 16 It is a physical diagram of the interconnection joint connecting the flexible sensor and the rigid wire. It can be seen that the interconnection joint firmly bonds the two together.

[0082] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for preparing a conductive composite material, characterized in that, It includes the following steps: Perform hydrophobic modification on metal particles to obtain modified metal particles; Disperse the modified metal particles in an elastic polymer solution and perform evaporation treatment on the solvent to obtain a self-assembled material; Anneal the self-assembled material to obtain a conductive composite material.

2. The preparation method according to claim 1, characterized in that: The metal particles include at least one of silver, gold, and copper; And / or, the Dv50 particle size of the metal particles is 0.01 - 1 μm; And / or, the modifier for the hydrophobic modification treatment includes at least one of thiol and silane.

3. The preparation method according to claim 2, characterized in that: The thiol includes at least one of propanethiol, octanethiol, and dodecanethiol; And / or, the mass ratio of the modifier to the metal particles is (2 - 3):

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The mass ratio of the elastic polymer to the modified metal particles is (2 - 3):(7 - 8); And / or, the elastic polymer includes at least one of styrene-ethylene-butene-styrene block copolymer, polydimethylsiloxane, and polyimide; And / or, the solvent includes at least one of toluene, ethanol, and n-hexane; And / or, the evaporation treatment includes any one of natural evaporation, vacuum evaporation, and heating evaporation; And / or, dispersing the modified metal particles in an elastic polymer solution includes the following steps: Disperse the modified metal particles in a dispersion liquid to obtain a slurry; Mix the slurry and the elastic polymer solution.

5. The preparation method according to any one of claims 1 to 3, characterized in that: The temperature of the annealing treatment is 100°C - 200°C; And / or, the time of the annealing treatment is 20 - 60 min.

6. A conductive composite material, characterized in that: The conductive composite material is the conductive composite material prepared by the preparation method according to any one of claims 1 - 5.

7. An interconnection joint, characterized in that: The material of the interconnecting joint includes the conductive composite material prepared by the preparation method according to any one of claims 1 - 5.

8. The interconnection joint according to claim 7, wherein: It includes a first conductive film and a second conductive film arranged in a stacked manner, and the materials of the first conductive film and the second conductive film include the conductive composite material.

9. The interconnecting joint according to claim 8, wherein: The interconnecting joint is strip-shaped, one end of the interconnecting joint is connected to a rigid wire, and the other end is connected to a flexible device. The connection method of the rigid wire and the interconnecting joint includes the following steps: Connect one end of the rigid wire between the first conductive film and the second conductive film and perform hot pressing treatment.

10. The interconnecting joint according to claim 9, characterized in that: The temperature of the hot pressing treatment is 200 - 400°C; And / or, the time of the hot pressing treatment is 0.5 - 6 min; And / or, the pressure of the hot pressing treatment is 100 - 300 kPa.

Images