Anisotropic conductive elastic material containing liquid metal particles and a method for producing the same

Abstract

The present invention relates to a stretchable anisotropic conductive film containing liquid metal particles and a method for manufacturing the same. The stretchable anisotropic conductive film according to the present invention includes a stretchable substrate and a liquid metal portion formed by being arranged within the stretchable substrate.

Description

Technical Field

[0001] The present invention relates to a stretchable anisotropic conductive film containing liquid metal particles and a method for manufacturing the same.

Background Art

[0002] With the development of materials and process technologies, while the size of electronic elements and circuits and wirings are being miniaturized, highly regular arrays of anisotropic conductive films (ACFs) are essential for electrical connections between the miniaturized electronic elements and circuits. In particular, since the laminated structure of a display performs vertical bonding via an ACF, there are on average 5 - 6 layers of ACF for each display. In an attempt to introduce a three-dimensional structure for stable wiring due to such high integration of displays, or in a situation where there is no ACF that can be vertically bonded while being deformed into a made-to-order type for a three-dimensional structure.

[0003] In the case of conventional ACFs, since the particles responsible for conductivity are hard, there is a limit in compression, and they exhibit low resolution and reliability due to a random conductive particle arrangement. Also, only the portion pressed by the protruding electrode has anisotropic conductivity. When used as a stretchable ACF, only the stretchable polymer stretches during tension, and the conductive particles do not stretch, resulting in problems such as the conductive particles being desorbed from the film or losing electrical connection. Therefore, it is an actual situation that there is a need to develop an ACF that solves such problems and is excellent in all aspects of stretchability and conductivity.

[0004] The background art described above is what the inventor retained or acquired during the process of deriving the disclosure of this specification, and it cannot necessarily be said to be publicly known technology that was publicly disclosed to the general public before this application.

Summary of the Invention

Problems to be Solved by the Invention

[0005] In order to solve the above problems, the present invention provides a stretchable anisotropic conductive film that can be deformed in accordance with the electrode form by including a liquid metal part and has high anisotropic conductivity, and a method for manufacturing the same.

[0006] However, the problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood by those having ordinary knowledge in the technical field from the following description.

Means for Solving the Problems

[0007] The stretchable anisotropic conductive film according to the present invention includes a stretchable base material and a liquid metal part arranged and formed in the stretchable base material.

[0008] The stretchable base material according to one embodiment may include a heat-firable rubber grafted with maleic anhydride containing at least any one heat-firable rubber selected from the group consisting of styrene-ethylene-butylene-styrene (SEBS), styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS), polyurethane (PU)-based rubber, and polyolefin (PO)-based rubber.

[0009] The liquid metal part according to one embodiment may include a gallium liquid metal; or a gallium-based alloy liquid metal containing at least any one metal selected from the group consisting of indium, tin, and zinc and gallium.

[0010] The liquid metal part according to one embodiment may be arranged and formed in a direction perpendicular to the film surface so that both surfaces of the stretch anisotropic conductive film are energized.

[0011] The horizontal size of the liquid metal part according to one embodiment is 5 μm or more, the interval between the liquid metal parts is 5 μm to 100 μm, the pitch is 5 μm to 200 μm, and the horizontal size of the liquid metal part and the interval between the liquid metal parts may be 2:1 to 1:2.

[0012] In one embodiment, the weight ratio of the liquid metal part to the stretchable substrate is 5:1 to 3:1, and the thickness of the stretchable anisotropic conductive film may be 5 μm to 100 μm.

[0013] The liquid metal part according to one embodiment includes a polymer composite containing liquid metal microparticles connected by energization, and the liquid metal microparticles may be droplets dispersed in a stretchable polymer.

[0014] In one embodiment, the size of the dispersed droplets may be 50 nm to 50 μm.

[0015] In one embodiment, the liquid metal microparticles may be 10% to 70% by weight of the polymer composite.

[0016] The method for manufacturing a stretchable anisotropic conductive film according to the present invention includes a step of preparing liquid metal, a step of patterning the liquid metal on a substrate, a step of imparting conductivity to the patterned liquid metal, a step of coating a stretchable substrate on the liquid metal with the imparted conductivity, and a step of removing the substrate.

[0017] The liquid metal according to one embodiment is bulk liquid metal or a polymer composite containing liquid metal microparticles, and the polymer composite containing liquid metal microparticles can be obtained by mixing liquid metal and a stretchable polymer and performing ultrasonic treatment.

[0018] The patterning step according to one embodiment can be performed by a photolithography, nanoimprint, soft lithography, block copolymer lithography, or capillary lithography process.

[0019] The patterning step according to one embodiment may include a step of forming a sacrificial layer on the substrate and patterning a photosensitive agent, a step of coating liquid metal on the patterned substrate, and a step of removing the photosensitive agent.

[0020] The step of imparting the conductivity according to one embodiment is to irradiate microwaves, and the microwaves can be irradiated at a temperature of 180°C to 360°C for 5 seconds or more.

Advantages of the Invention

[0021] The present invention can provide a stretchable anisotropic conductive film having high anisotropic conductivity and a method for manufacturing the same, which can be deformed in accordance with the electrode form by including a liquid metal part.

[0022] Specifically, the stretchable anisotropic conductive film according to the present invention can be deformed in accordance with the concave lower electrode form, uniformly disperse stress throughout the film during stretching, maintain stable contact with the electrode, and be stable against stretching. Therefore, it can be transferred onto the substrate in accordance with bending.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, various changes may be made to the embodiments, and the scope of the patent application is not limited or restricted by such embodiments. It should be understood that all changes, equivalents, or alternatives to the embodiments are included in the scope of the rights.

[0025] The terms used in the embodiments are for illustrative purposes only and are not to be construed as intended to limit. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "including" or "having" indicate the presence of the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0026] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the technical field to which this embodiment belongs. Commonly used pre-defined terms should be construed to have a meaning consistent with their meaning in the context of the related art and should not be construed as having an ideal or overly formal meaning unless clearly defined herein.

[0027] In addition, when explaining with reference to the accompanying drawings, regardless of the reference numerals in the drawings, the same components shall be given the same reference signs, and redundant explanations thereof shall be omitted. In the description of the embodiments, if it is determined that a specific description of related known technologies obscures the gist of the embodiments unnecessarily, the detailed description thereof shall be omitted. Also, when explaining the components of the embodiments, terms such as first, second, A, B, (a), (b), etc. can be used. These terms are for distinguishing the components from other components, and the essence, order, or sequence of the components are not limited by these terms. When it is mentioned that any component is "connected", "coupled", or "joined" to another component, it should be understood that the component is directly connected or joined to the other component, but additional components can be "connected", "coupled", or "joined" between the respective components.

[0028] Components including functions common to the components included in any of the embodiments shall be described using the same names in other embodiments. Unless otherwise stated, the descriptions given in any of the embodiments shall also apply to other embodiments, and specific descriptions within the overlapping scope shall be omitted.

[0029] Hereinafter, the stretchable anisotropic conductive film and its manufacturing method according to the present invention will be specifically described with reference to embodiments and drawings. However, the present invention is not limited to these embodiments and drawings.

[0030] The stretchable anisotropic conductive film according to the present invention includes a stretchable base material; and a liquid metal part arranged and formed within the stretchable base material.

[0031] The stretchable anisotropic conductive film (S-ACF) according to the present invention is excellent in stretchability, that is, elasticity, and is suitable for flexible electronic devices by changing together according to the deformation of the substrate. It has excellent adhesive force and is applied to electronic devices, and can firmly bond the interfaces of different members to each other. By including a liquid metal part having stretchability in a liquid state at room temperature, which is not a conductive particle conventionally used for stretchable anisotropic conductive films, it can cope with the bending of the substrate, allowing high deformation. It can provide a stretchable anisotropic conductive film that can be deformed into an order-made type in a three-dimensional electrode structure not only in terms of the stretchability in the y-axis direction but also when the stretchable anisotropic conductive film is pressure-bonded to a circuit board. The liquid metal of the liquid metal part can be processed and used in a dispersed form as particles, micelles, or a similar form.

[0032] FIG. 1 is a schematic view of a stretchable anisotropic conductive film according to an embodiment of the present invention. Referring to FIG. 1, the liquid metal part 10 is arranged and formed in the stretchable base material 20, and a current flows vertically through the liquid metal part 10, and a stretchable anisotropic conductive film 100 with a vertical conduction path that does not allow current to flow horizontally due to the non-conductive stretchable base material 20 can be provided.

[0033] According to an embodiment, the stretchable base material may include at least one heat-curable rubber grafted with maleic anhydride, which is selected from the group consisting of styrene-ethylene-butylene-styrene (SEBS), styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS), polyurethane (PU)-based rubber, and polyolefin (PO)-based rubber.

[0034] The stretchable base material is excellent in elasticity, has a high elongation rate, and has low conductivity, so that a stretchable anisotropic conductive film can be formed such that electricity flows only at desired positions, and the liquid metal part can be stably supported.

[0035] The heat-firable rubber grafted with maleic anhydride is excellent in flexibility and stretchability and is suitable as a material for the stretchable substrate. The heat-firable rubber grafted with maleic anhydride can form a chemical bond with other members such as a target substrate and form a stable adhesion even at low temperature and low pressure. The heat-firable rubber may preferably be styrene-ethylene-butylene-styrene, but is not limited to those listed above.

[0036] The maleic anhydride may be 1% by weight or more of the heat-firable rubber. When maleic anhydride is contained in the content within the above range, there is an effect of providing a sufficient number of bond-forming sites compared to the adhesion area.

[0037] According to one embodiment, the liquid metal part may include gallium liquid metal; or a gallium-based alloy liquid metal including at least any one metal selected from the group consisting of indium, tin, and zinc and gallium.

[0038] Liquid metal means a metal that is in a liquid state at room temperature and has stretchability and electrical conductivity. The liquid metal part may preferably be a gallium-indium eutectic alloy (EGaIn) liquid metal. The gallium-indium eutectic alloy is formed by gallium and indium in a weight ratio of 3:1 and has physical properties of a liquid at room temperature with a melting point of about 15.5°C. In addition, since it can be easily deformed and recovered in shape by an external physical force, it can be used for flexible electronic elements and the like.

[0039] According to one embodiment, the liquid metal part may be arranged and formed in a direction perpendicular to the film surface so that both surfaces of the stretchable anisotropic conductive film are energized.

[0040] The stretchable anisotropic conductive film can form a vertical conduction path that is energized through the liquid metal portions formed in the vertical direction. In order to allow the current flowing from a member in contact with one surface of the stretchable anisotropic conductive film to flow to another member in contact with the other surface of the stretchable anisotropic conductive film, the liquid metal portions are formed in the vertical direction on the stretchable substrate and the upper and lower portions are exposed to the outside. A stretchable anisotropic conductive film with a vertical conduction path can be provided, in which current flows vertically through the exposed portions of the liquid metal portions and no current flows horizontally due to the non-conductive stretchable substrate.

[0041] Referring to FIG. 1, the liquid metal portions 10 are arranged and formed within the stretchable substrate 20. The arrangement means an arrangement within the vertical direction or that various liquid metal portions 10 are regularly arranged vertically throughout the stretchable anisotropic conductive film 100.

[0042] According to one embodiment, the horizontal size of the liquid metal portions is 5 μm or more, the interval between the liquid metal portions is 5 μm to 100 μm, the pitch is 5 μm to 200 μm, and the horizontal size of the liquid metal portions and the interval between the liquid metal portions may be 2:1 to 1:2.

[0043] The horizontal size of the liquid metal portions indicates the longitudinal length of the liquid metal portions. For example, the horizontal size of the liquid metal portions arranged in a cylinder is the diameter of one surface, the horizontal size of the liquid metal portions arranged in a quadrangular prism is the longest length from one vertex to another vertex of one surface, and the horizontal size of the liquid metal portions arranged in a triangular prism means the longest length from one vertex to one side of one surface.

[0044] When the horizontal size of the liquid metal portions is less than 5 μm, there is a problem that the liquid metal is not filled in the pattern and cannot be patterned.

[0045] The distance between the liquid metal parts indicates the closest distance between the end of one liquid metal part arranged on the stretchable substrate and the end of the other liquid metal part. The distance between the liquid metal parts is preferably 5 μm to 80 μm; 5 μm to 60 μm; 5 μm to 40 μm; 5 μm to 20 μm; 10 μm to 80 μm; 10 μm to 60 μm; 10 μm to 40 μm; 10 μm to 20 μm; 10 μm to 80 μm; 10 μm to 60 μm; 10 μm to 40 μm; or 10 μm to 20 μm.

[0046] The pitch of the liquid metal parts indicates the distance from the center of one liquid metal part arranged on the stretchable substrate to the center of the other liquid metal part. The pitch of the liquid metal parts is preferably 5 μm to 160 μm; 5 μm to 120 μm; 5 μm to 80 μm; 5 μm to 40 μm; 10 μm to 160 μm; 10 μm to 120 μm; 10 μm to 80 μm; 10 μm to 40 μm; 20 μm to 160 μm; 20 μm to 120 μm; 20 μm to 80 μm; or 20 μm to 40 μm, and a stretchable anisotropic conductive film with a fine pitch can be provided.

[0047] When the distance and pitch between the liquid metal parts are outside the above ranges, there will be a problem that the liquid metal straddles between the patterns. When exceeding the above ranges, there is a problem that it is difficult to manufacture a stretchable anisotropic conductive film with a high resolution due to the increase in pitch. The distance and pitch between the liquid metal parts can be adjusted according to the arrangement form, the size of the liquid metal parts, and the application field of the stretchable anisotropic conductive film.

[0048] The horizontal size of the liquid metal part and the distance between the liquid metal parts are preferably 2:1 to 2:3; 2:1 to 1:1; 2:1 to 3:2; 3:2 to 1:1; 3:2 to 2:3; 3:2 to 1:2; 1:1 to 2:3; 1:1 to 1:2; or 2:3 to 1:2.

[0049] According to one embodiment, the weight ratio of the liquid metal part and the stretchable substrate may be 5:1 to 3:1, and the thickness of the stretchable anisotropic conductive film may be 5 μm to 100 μm.

[0050] When the weight ratio of the liquid metal part and the stretchable base material exceeds the above range, there is a problem that the interval between patterns decreases and the shape of the liquid metal part collapses.

[0051] The thickness of the stretchable anisotropic conductive film is preferably 5 μm to 80 μm; 5 μm to 60 μm; 5 μm to 40 μm; 5 μm to 20 μm; 10 μm to 100 μm; 10 μm to 80 μm; 10 μm to 60 μm; 10 μm to 40 μm; 10 μm to 20 μm; 20 μm to 100 μm; 20 μm to 80 μm; 20 μm to 60 μm; or 20 μm to 40 μm. When the thickness is less than 5 μm, there is a problem that it cannot be patterned, and when it exceeds 100 μm, there is an economic problem due to an increase in the filling amount of the liquid metal.

[0052] According to one embodiment, the liquid metal part includes a polymer composite including electrically connected liquid metal fine particles, and the liquid metal fine particles may be droplets dispersed in a stretchable polymer.

[0053] The stretchable polymer may include at least one heat-firable rubber selected from the group consisting of styrene-ethylene-butylene-styrene (SEBS), styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS), polyurethane (PU)-based rubber, and polyolefin (PO)-based rubber, and a heat-firable rubber grafted with maleic anhydride.

[0054] The liquid metal fine particles (particles) are droplets dispersed in a stretchable polymer, and the polymer composite is an aggregate of the droplets. When the liquid metal part includes liquid metal fine particles that are not bulk liquid metal, a stretchable anisotropic conductive film with a fine pitch can be efficiently manufactured.

[0055] Figure 2 is a schematic diagram of a stretchable anisotropic conductive film according to an embodiment of the present invention. Referring to Figure 2, the stretchable anisotropic conductive film 100 can form a liquid metal part as a polymer composite 30 including liquid metal fine particles, that is, an aggregate of droplets dispersed in a stretchable polymer, and be arranged on the stretchable base material 20.

[0056] According to one embodiment, the size of the dispersed droplets may be 50 nm to 50 μm.

[0057] The size of the droplets is preferably 50 nm to 25 μm; 50 nm to 10 μm; 50 nm to 5 μm; 500 nm to 50 μm; 500 nm to 25 μm; 500 nm to 10 μm; 500 nm to 5 μm; 1 μm to 50 μm; 1 μm to 25 μm; 1 μm to 10 μm; or 1 μm to 5 μm. When the size of the droplets is less than 50 nm, there is a problem that the liquid metal fine particles are not dispersed. When it exceeds 50 μm, there are problems that the liquid metal fine particles sink without being dispersed and are formed into an elliptical shape instead of a spherical shape, making patterning difficult. When droplets are formed with a size within the above range, a fine pitch can be formed while maintaining the structure in the stretchable anisotropic conductive film.

[0058] According to one embodiment, the liquid metal fine particles may be 10% to 70% by weight of the polymer composite.

[0059] Preferably, the liquid metal fine particles may be 10% to 50% by weight; 10% to 30% by weight; 20% to 70% by weight; 20% to 50% by weight; or 20% to 30% by weight of the polymer composite. When the content of the liquid metal fine particles is less than 10% by weight, there is a problem that it is difficult to form a uniform film when making a film with a small amount of dispersed liquid metal fine particles. When it exceeds 70% by weight, there is a problem in making it into a fine particle state by ultrasonic pulverization as the volume of the liquid metal increases compared to the solvent. When the content of the liquid metal fine particles is within the above range, sufficient liquid metal fine particles can be formed while maintaining the conductivity of the liquid metal.

[0060] The manufacturing method of the stretchable anisotropic conductive film according to the present invention includes the steps of preparing liquid metal; patterning the liquid metal on a substrate; imparting conductivity to the patterned liquid metal; coating a stretchable substrate on the liquid metal with the imparted conductivity; and removing the substrate.

[0061] The manufacturing method of the stretchable anisotropic conductive film according to the present invention can form a morphological deformation according to the electrode form by including liquid metal, and can manufacture a stretchable anisotropic conductive film having high anisotropic conductivity, solving the disadvantage that it is difficult to pattern and fix due to the high surface tension of the conventional liquid metal, having free form and height adjustment, and can manufacture a stretchable anisotropic conductive film including liquid metal having uniform conductivity that does not deform the form of the structure.

[0062] The step of removing the substrate includes transferring the stretchable anisotropic conductive film.

[0063] Here, since the characteristics of the liquid metal and the stretchable substrate are the same as those of the liquid metal part and the stretchable substrate described above, the following description is omitted.

[0064] According to one embodiment, the liquid metal is a bulk liquid metal or a polymer composite containing liquid metal fine particles, and the polymer composite containing the liquid metal fine particles can be obtained by mixing the liquid metal and the stretchable polymer and performing ultrasonic treatment.

[0065] The step of preparing the liquid metal can prepare a bulk liquid metal or manufacture a polymer composite containing liquid metal fine particles.

[0066] The mixing of the liquid metal and the stretchable polymer may be performed by mixing the liquid metal and the stretchable polymer at a weight ratio of 20:1 to 1:2. When the weight ratio is less than 20:1, it is difficult to disperse the liquid metal into liquid metal fine particles in the solution, and when it exceeds 1:2, when a film is formed, the contact between the liquid metal fine particles decreases and it is difficult to impart conductivity.

[0067] The ultrasonic treatment may be performed at a temperature of 16°C to 100°C for 5 minutes to 1 hour. When performing ultrasonic treatment within the above range, the liquid metal can be sufficiently atomized to form liquid metal microparticles.

[0068] In the case of conventional liquid metal patterning, it is difficult to pattern due to the high surface tension of the liquid metal. There are problems that not only is it difficult to adjust the height of the pattern, but it is also difficult to fix the bulk liquid metal having fluidity in the liquid state. The method for manufacturing a stretchable anisotropic conductive film according to the present invention uses a polymer composite containing liquid metal microparticles by mixing a composite of liquid metal and a stretchable polymer, so that regardless of the wettability and surface tension of the liquid metal compared to bulk liquid metal, the morphology and height can be freely adjusted, and a fine pitch liquid metal structure having a high resolution with uniform size and spacing can be patterned.

[0069] According to one embodiment, the patterning step can be performed in a photolithography, nanoimprint, soft lithography, block copolymer lithography, or capillary lithography process.

[0070] The process in which the patterning step is performed is not particularly limited, but preferably, it may be performed in a photolithography process, and a liquid metal having a high resolution with uniform size and spacing can be patterned.

[0071] According to one embodiment, the patterning step includes: forming a sacrificial layer on the substrate and patterning a photosensitive agent; coating the liquid metal on the patterned substrate; and removing the photosensitive agent.

[0072] FIG. 3 is a schematic diagram of the step of patterning liquid metal in the method for manufacturing a stretchable anisotropic conductive film according to an embodiment of the present invention. Referring to FIG. 3, a sacrificial layer 50 is formed on a substrate 40, and a photosensitive agent 60 is patterned thereon. If a liquid metal 70 is coated on the patterned photosensitive agent 60 and the photosensitive agent 60 is removed, the patterned liquid metal 70 can be obtained.

[0073] The substrate is not particularly limited, and one selected from among silicon, glass, and a metal substrate may be used. Preferably, it may be a silicon substrate.

[0074] Due to the bonding force between the substrate and the liquid metal, a sacrificial layer having a weak adhesive force with the substrate is required. The sacrificial layer means a layer that is removed during transfer to form a stretchable anisotropic conductive film. The sacrificial layer may be formed by coating a polymer on the substrate and performing microwave treatment, and may be a thin film of amorphous carbon. The polymer coated on the substrate may be PEI (Polyethylenimine) or PAA (Polyacrylic acid).

[0075] The photosensitive agent (PR, Photoresist) may be patterned by a photomask. The patterning may be variously aligned in any one of the arrangement forms of a lattice type, a honeycomb type, a linear type, and a square type, but is not limited thereto, and may be arranged in various forms as required. The photosensitive agent can be patterned to arrange a pattern in a desired shape in which the liquid metal is finally arranged.

[0076] The step of coating the liquid metal is to coat the liquid metal on the patterned photosensitive agent to fill the empty space of the pattern. The coating includes at least any one selected from the group consisting of spray coating, spin coating, dip coating, screen coating, knife coating, kiss coating, gravure coating, bar coating, screen printing, and spray-mist spray coating, and preferably, it may be spin coating.

[0077] The step of removing the photosensitive agent may be removed through a solvent, and preferably, it may be removed with acetone. After the photosensitive agent is removed, the liquid metal is patterned by the patterning of the photosensitive agent, enabling the formation of a liquid metal pattern having a regular array of uniform size, spacing, and high resolution.

[0078] Figure 4 is an image of (a) a substrate with a patterned photosensitive agent, (b) a substrate coated with liquid metal, and (c) a substrate with a patterned liquid metal according to an embodiment of the present invention. Referring to Figure 4, a substrate with a patterned photosensitive agent by the step of patterning the photosensitive agent, a substrate coated with liquid metal by the step of coating the liquid metal on the patterned substrate, and a substrate with a patterned liquid metal by the step of removing the photosensitive agent are confirmed. Referring to Figure 4(a), the empty portion other than the patterned photosensitive agent PR can be confirmed. Referring to Figure 4(b), it is confirmed that all the patterns are filled by the liquid metal coating. Referring to Figure 4(c), it is confirmed that, contrary to the patterning of the photosensitive agent, the liquid metal is patterned by removing the photosensitive agent.

[0079] According to an embodiment, the step of imparting conductivity irradiates microwaves, and the microwaves are irradiated at a temperature of 180°C to 360°C for 5 seconds or more.

[0080] The surface of the patterned liquid metal may be in an insulating state. In particular, when in the form of a polymer composite containing liquid metal particles, it is in an insulating state due to the oxide film formed on the surface of the particles. Conventionally, a method of using mechanical force to break the oxide film of liquid metal to form conductivity between particles has been used, but in this case, there are problems such as the shape of the entire structure being damaged or a non-uniform conductivity distribution occurring. Also, a method of growing and breaking the oxide film through heat treatment at a high temperature of 600 °C or higher can be used, but in this case, there is a problem that the initial shape is lost due to non-uniform growth of the oxide film, and transfer using a sacrificial layer cannot be performed due to thermal decomposition of the sacrificial layer. On the other hand, the method of imparting conductivity using microwaves can rapidly impart conductivity at a low temperature, and since the particulate state of the liquid metal does not change, the shape of the entire structure does not change, and conductivity can be uniformly imparted, which is advantageous for patterning.

[0081] FIG. 5 is an image of (a) liquid metal before microwave irradiation and (b) liquid metal after microwave irradiation according to an embodiment of the present invention. Referring to FIG. 5, it is confirmed that the form of the liquid metal particles does not change even after microwave irradiation, and only conductivity is imparted.

[0082] The microwave can preferably be irradiated at a temperature of 180 °C to 350 °C; 180 °C to 300 °C; 180 °C to 250 °C; 250 °C to 360 °C; 250 °C to 350 °C; or 250 °C to 300 °C for 30 seconds or more. When the microwave is irradiated at a temperature lower than 180 °C, there is a problem that conductivity does not occur in the liquid metal part, and when irradiated at a temperature exceeding 360 °C, there is a problem that a crystalline oxide film grows on the surface of the liquid metal and the form of the liquid metal collapses. When the microwave is irradiated for 5 seconds or more, conductivity is ensured, and preferably, when irradiated for 30 seconds or more, overall uniform conductivity can be ensured.

[0083] The step of coating the stretchable substrate includes at least any one selected from the group consisting of spray coating, spin coating, dip coating, screen coating, knife coating, kiss coating, gravure coating, bar coating, screen printing, and spray-mist spray coating, and preferably, it may be spin coating. The stretchable substrate can be coated with a thickness lower than the height of the patterned liquid metal. A stretchable anisotropic conductive film including liquid metal arranged in the stretchable substrate can be formed by coating the stretchable substrate.

[0084] The method further includes the step of coating the stretchable substrate; and the step of subsequently performing oxygen plasma treatment. The coated stretchable substrate is also coated on the patterned liquid metal, and the liquid metal is not exposed on the surface. Since problems occur in energization when the liquid metal is not exposed on the surface, the stretchable substrate coated on the liquid metal can be etched and removed through oxygen plasma treatment.

[0085] The step of removing the substrate includes the steps of attaching a thermal release tape on the coated stretchable substrate; separating the substrate and the sacrificial layer; removing the sacrificial layer; and removing the thermal release tape. The step of removing the substrate includes transferring the stretchable anisotropic conductive film.

[0086] FIG. 6 is a schematic diagram of the step of removing the substrate in the method for manufacturing a stretchable anisotropic conductive film according to an embodiment of the present invention. Referring to FIG. 6, a thermal release tape 80 is attached on a stretchable substrate 20 including liquid metal 70, and the substrate 40 and the sacrificial layer 50 are separated by putting them in water. The sacrificial layer 50 is removed by performing oxygen plasma treatment on the surface of the separated sacrificial layer 50, and the stretchable anisotropic conductive film is transferred to the target substrate while peeling the thermal release tape 80 by heat treatment.

[0087] Conventionally, in order to transfer a film onto a substrate, a method was mainly used in which a polymer dissolved in a solvent was thinly coated on the substrate, then the desired film was placed on it, and the polymer was dissolved by putting it in the solvent. However, in the case of many polymers, since they are carbonized and thermally decomposed at 300°C or higher, there is a problem that it is difficult to use them for transferring a film onto a substrate heat-treated by microwave irradiation. On the other hand, since the sacrificial layer is stable at 300°C or lower, it can be used for a substrate heat-treated by microwave irradiation, and since it has a weak adhesive force with the substrate, it can be easily separated from the substrate and removed.

[0088] The step of separating the substrate and the sacrificial layer may be performed by using water. Since the sacrificial layer has a weak adhesive force with the substrate, it can be easily separated from the substrate by putting it in water.

[0089] The step of removing the sacrificial layer can be performed by etching the sacrificial layer separated from the substrate by oxygen plasma treatment. Even if the sacrificial layer is not removed, a stretchable anisotropic conductive film can be manufactured, but the film may not be transparent and may have a color.

[0090] The step of removing the thermal release tape transfers the stretchable anisotropic conductive film to the desired target substrate or member while peeling the thermal release tape through heat treatment. Since the stretchable anisotropic conductive film contains liquid metal, not only the stretchable base material but also the liquid metal has stretchability, so it can cope with the bending of the target substrate. The heat treatment may be performed at 100°C to 150°C.

[0091] The step of removing the substrate is an effective method that can be used when trying to transfer a target object heat-treated at 300°C or lower from the substrate to another substrate.

[0092] Conventional stretchable anisotropic conductive films use hard conductive particles, making it difficult to form delicate structures such as fine pitches. Since the particles are hard, there are limitations to morphological deformation by thermocompression bonding. Therefore, only the stretchable polymer stretches during tension, and the conductive particles do not stretch, resulting in problems such as the conductive particles being desorbed from the film or losing electrical connection. In the case of a concave lower electrode, it is difficult to energize because the electrode morphology cannot be contacted. On the other hand, the stretchable anisotropic conductive film according to the present invention uses a stretchable, conductive liquid metal that is in a liquid state at room temperature instead of hard conductive particles, efficiently forming a film with a fine pitch, being able to deform morphologically according to the morphology of the concave lower electrode, and imparting high anisotropic conductivity with a metal level (>10 6 S / m) in the vertical direction of the film.

[0093] FIG. 7 is a diagram for explaining the energization of the stretchable anisotropic conductive film according to an embodiment of the present invention. Referring to FIG. 7, by using a stretchable, conductive liquid metal that is in a liquid state at room temperature instead of hard conductive particles during energization with a member having a concave lower electrode, it can be confirmed that morphological deformation can be performed according to the morphology of the concave lower electrode, and thus high anisotropic conductivity can be imparted.

[0094] The stretchable anisotropic conductive film according to the present invention uses a stretchable liquid metal, dispersing stress uniformly throughout the film during stretching, maintaining stable contact with the electrode, and being stable against stretching, so it can be transferred according to the bending of the substrate. Therefore, it can be used for connecting circuits with uneven surface heights and high integration, and is likely to be applied in fields where several anisotropic conductive films are used, such as packaging and displays. In particular, it is used in robotics and electronic devices such as wearable sensors, flexible displays, and electronic textiles that require flexibility and stretchability, and can provide essential elements for miniaturizing equipment.

[0095] Hereinafter, the present invention will be described in more detail by way of embodiments.

[0096] However, the following embodiments are for illustrating the present invention, and the content of the present invention is not limited to the following embodiments.

[0097] Embodiment

[0098] Manufacture of Stretchable Anisotropic Conductive Film

[0099] After dissolving SEBS-g-ma in toluene with a stretchable polymer, 20% by weight of liquid metal (EGaln) was added and ultrasonic treatment (20 minutes) was performed to produce a polymer composite containing liquid metal microparticles.

[0100] To transfer the stretchable anisotropic conductive film, Polyacrylic acid (PAA) polymer was spin-coated (3000 rpm, 30 seconds) on a silicon substrate to form a thin film. Then, the polymer thin film was converted into an amorphous carbon thin film through microwave irradiation at 300 °C for 1 minute to form a sacrificial layer. A photosensitive agent (AZ2070) was patterned on the silicon substrate with the amorphous carbon thin film deposited thereon to have a certain size and interval (5 - 20 μm). A polymer composite containing liquid metal microparticles in the form of ink was spin-coated (2000 rpm, 30 seconds) on the patterned photosensitive agent. The substrate coated with liquid metal was placed in acetone to remove the remaining photosensitive agent and pattern the liquid metal microparticle structure.

[0101] Conductivity was imparted to the patterned liquid metal microparticles through microwave irradiation at 340 °C for 1 minute. SEBS-g-ma was used as a stretchable base material on the substrate with the patterned conductive liquid metal, and it was spin-coated (1000 rpm, 60 seconds) thinner than the height of the liquid metal microparticle structure to produce an 8-μm-thick stretchable anisotropic conductive film containing liquid metal.

[0102] After attaching a thermal release tape to transfer the stretchable anisotropic conductive film, it was placed in water to separate the substrate and the amorphous carbon thin film, and the amorphous carbon thin film was removed by oxygen plasma treatment at an intensity of 200 W for 5 minutes. The stretchable anisotropic conductive film was placed on the target substrate to be transferred, and the film was transferred while peeling the thermal release tape by heat treatment at 120°C.

[0103] Although the embodiments have been described as above, those having ordinary knowledge in the art can apply various technical modifications and deformations based on the above. For example, the described technology may be executed in an order different from the described method, and / or the components such as the described system, structure, device, circuit, etc. may be combined or assembled in a form different from the described method, or replaced or substituted by other components or equivalents, and appropriate results can still be achieved.

[0104] Therefore, other realizations, other embodiments, and those equivalent to the claims, etc. also fall within the scope of the claims described below.

Claims

1. A stretchable base material, and a liquid metal part arranged and formed within the stretchable base material, A stretchable anisotropic conductive film comprising the same.

2. The stretchable base material comprises a heat-firable rubber grafted with maleic anhydride and containing at least any one heat-firable rubber selected from the group consisting of styrene-ethylene-butylene-styrene (SEBS), styrene-isoprene-styrene (SIS), styrene-butadiene-styrene (SBS), polyurethane (PU)-based rubber, and polyolefin (PO)-based rubber. The stretchable anisotropic conductive film according to claim 1.

3. The liquid metal part comprises gallium liquid metal; or a gallium-based alloy liquid metal containing at least any one metal selected from the group consisting of indium, tin, and zinc and gallium. The stretchable anisotropic conductive film according to claim 1.

4. The liquid metal part is arranged and formed in a direction perpendicular to the film surface so that both sides of the stretch anisotropic conductive film are energized. The stretchable anisotropic conductive film according to claim 1.

5. The horizontal size of the liquid metal part is 5 μm or more, The interval between the liquid metal parts is 5 μm to 100 μm, The pitch is 5 μm to 200 μm, The horizontal size of the liquid metal part and the interval between the liquid metal parts are 2:1 to 1:

2. The stretchable anisotropic conductive film according to claim 1.

6. The weight ratio of the liquid metal part and the stretchable base material is 5:1 to 3:1, The thickness of the stretchable anisotropic conductive film is 5 μm to 100 μm. The stretchable anisotropic conductive film according to claim 1.

7. The liquid metal part comprises a polymer composite containing electrically connected liquid metal fine particles, The stretchable anisotropic conductive film according to claim 1, wherein the liquid metal microparticles are droplets dispersed in a stretchable polymer.

8. The stretchable anisotropic conductive film according to claim 7, wherein the size of the dispersed droplets is 50 nm to 50 μm.

9. The stretchable anisotropic conductive film according to claim 7, wherein the liquid metal microparticles are 10% to 70% by weight of the polymer composite.

10. A step of preparing liquid metal; A step of patterning the liquid metal on a substrate; A step of imparting conductivity to the patterned liquid metal; A step of coating the stretchable substrate on the liquid metal with conductivity imparted thereto; A step of removing the substrate; A method for manufacturing a stretchable anisotropic conductive film, comprising:

11. The liquid metal is bulk liquid metal or a polymer composite containing liquid metal microparticles, The method for manufacturing a stretchable anisotropic conductive film according to claim 10, wherein the polymer composite containing liquid metal microparticles is obtained by mixing liquid metal and a stretchable polymer and performing ultrasonic treatment.

12. The method for manufacturing a stretchable anisotropic conductive film according to claim 10, wherein the patterning step is performed by a photolithography, nanoimprint, soft lithography, block copolymer lithography, or capillary lithography process.

13. The patterning step includes: A step of forming a sacrificial layer on the substrate and patterning a photosensitizer; A step of coating liquid metal on the patterned substrate; A step of removing the photosensitizer; The method for manufacturing a stretchable anisotropic conductive film according to claim 10, comprising:

14. The step of imparting the conductivity includes irradiating with microwaves, The microwaves are irradiated at a temperature of 180°C to 360°C for 5 seconds or more. The method for manufacturing a stretchable anisotropic conductive film according to claim 10.

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