Ultra-flexible electronic circuit and manufacturing method thereof

Abstract

The present invention discloses an ultra-flexible electronic circuit and a method for making the same, and relates to the technical field of ultra-flexible electronic circuits. The method for making the ultra-flexible electronic circuit comprises: step 1, printing a first electronic paste on a flexible substrate according to a target circuit pattern to form an inner electronic circuit; step 2, printing a second electronic paste on the inner electronic circuit according to a target circuit pattern to form a surface electronic circuit covering the inner electronic circuit; the flexibility of the inner electronic circuit is better than that of the surface electronic circuit, and the mechanical strength of the surface electronic circuit is better than that of the inner electronic circuit; step 3, after the surface electronic circuit is dried and solidified, an ultra-flexible circuit is obtained. The ultra-flexible electronic circuit in the present invention is provided with an inner and outer two-layer electronic circuit, the inner electronic circuit is a liquid metal ultra-flexible structure, and the outer electronic circuit is formed by an electronic paste with good conductivity to restrain and protect the inner electronic circuit, thereby ensuring the flexibility and conductivity of the ultra-flexible electronic circuit.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-flexible electronic circuits, and in particular relates to an ultra-flexible electronic circuit and a manufacturing method thereof. Background Art

[0002] Flexible Printed Circuit Board (FPC) is a printed circuit made of a flexible substrate that can be bent and folded freely to achieve the integration of component assembly and wire connection.

[0003] There are three main types of traditional flexible circuit board processes. The first is to directly use copper foil, aluminum foil, etc. to form electronic circuits. This method is currently relatively mature in industrialization, but its bending performance is poor and it is easy to break, so it cannot be used in ultra-flexible electronic circuits. The second is to use traditional electronic silver paste to form electronic circuits. The bending performance of this method is only slightly better than the copper foil and aluminum foil in the first method. Its bending performance is still insufficient, and the adhesion of the sintered electronic silver paste on the substrate is poor. After the substrate is repeatedly bent, it is easy to break and fall off at the bend, and it cannot be used in ultra-flexible circuits either. The third method is to use liquid metal as conductive ink to form electronic circuits through printing and other methods. Liquid metal refers to a low-melting-point metal that is in liquid state under appropriate low-temperature conditions. Due to its liquid properties, it can meet the needs of ultra-flexibility and can be bent and curved. However, it is still immature in industrial applications. Compared with electronic circuits formed by traditional copper foil, aluminum foil, and electronic silver paste, due to the existence of liquid metal phase, there is a risk of small droplets of liquid metal escaping, which can easily lead to cross-contamination of electronic circuits and cause the electronic circuits to fail.

[0004] Therefore, the prior art lacks an ultra-flexible circuit board that meets the requirements of being ultra-flexible, bendable, and foldable without the risk of escape causing cross-contamination of electronic circuits. Summary of the invention

[0005] In view of this, an object of the present invention is to provide a method for manufacturing an ultra-flexible electronic circuit to solve the problem that the flexible electronic circuits in the prior art have poor flexibility and bendability and are prone to escape risks leading to cross-contamination of the electronic circuits.

[0006] In some illustrative embodiments, the method for making the ultra-flexible electronic circuit includes: step 1, printing a first electronic paste on a flexible substrate according to a target circuit pattern to form an inner electronic circuit; the inner electronic circuit contains liquid metal, a first conductive metal powder and a resin; step 2, printing a second electronic paste on the inner electronic circuit according to a target circuit pattern to form a surface electronic circuit covering the inner electronic circuit; the surface electronic circuit contains a second conductive metal powder and a resin; wherein the inner electronic circuit has better flexibility than the surface electronic circuit, and the surface electronic circuit has better mechanical strength than the inner electronic circuit; step 3, after the surface electronic circuit is dried and cured, an ultra-flexible circuit is obtained.

[0007] In some optional embodiments, the first electronic paste composition includes, by weight: 25%-40% liquid metal, 15%-30% first conductive metal powder, 7%-15% high-toughness resin, 20%-50% organic solvent, 0.2%-2% thickener, 1%-2% toughening agent, 0.5%-2% curing agent and 1%-3% adhesion promoter.

[0008] In some optional embodiments, the method for preparing the first electronic paste includes: mixing, stirring and dispersing a high-toughness resin, a thickener, a toughening agent, a curing agent, and an organic solvent to obtain a first organic carrier; then adding the first conductive metal powder to the first organic carrier, and sequentially subjecting the mixture to mechanical stirring and grinding to obtain a first premixed slurry; then adding the liquid metal to the first premixed slurry, and subjecting the mixture to centrifugation to obtain the first electronic paste.

[0009] In some optional embodiments, the first conductive metal powder is spherical particles of 0.1-20 μm.

[0010] In some optional embodiments, the second electronic paste composition includes, by weight: 40%-70% of a second conductive metal powder, 7%-15% of a high-toughness resin, 20%-50% of an organic solvent, 0.2%-2% of a thickener, 1%-2% of a toughening agent and 0.5%-2% of a curing agent.

[0011] In some optional embodiments, the method for preparing the second electronic paste includes: mixing, stirring and dispersing a high-toughness resin, a thickener, a toughening agent, a curing agent, and an organic solvent to obtain a second organic carrier; then adding the second conductive metal powder to the second organic carrier, and sequentially subjecting the mixture to mechanical stirring and grinding to obtain a second electronic paste.

[0012] In some optional embodiments, the second conductive metal powder is selected from flaky particles of 0.1-20 μm.

[0013] In some optional embodiments, the first electronic paste and / or the second electronic paste is formed by screen printing; wherein the lines in the screen circuit pattern used in the screen printing are 0-10 μm smaller than the line width of the target circuit pattern.

[0014] Another object of the present invention is to provide an ultra-flexible electronic circuit to solve the problems existing in the prior art.

[0015] In some illustrative embodiments, the ultra-flexible electronic circuit includes: a flexible substrate, an inner layer electronic circuit attached to the flexible substrate and containing liquid metal, and a surface layer electronic circuit covering the inner layer electronic circuit; wherein the inner layer electronic circuit has better flexibility than the surface layer electronic circuit, and the surface layer electronic circuit has better mechanical strength than the inner layer electronic circuit.

[0016] In some optional embodiments, the film thickness of the inner electronic circuit is 5-30 μm; and / or the film thickness of the outer electronic circuit is 5-30 μm.

[0017] Compared with the prior art, the present invention has the following technical advantages:

[0018] The ultra-flexible electronic circuit in the present invention is formed by setting up an inner and outer layer of electronic circuits. The inner layer of the electronic circuit is a liquid metal ultra-flexible structure, and the outer layer of the electronic circuit is formed by an electronic slurry with good conductivity to restrain and protect the inner layer of the electronic circuit, thereby ensuring the flexibility and conductivity of the ultra-flexible electronic circuit; and, since the outer layer of the electronic circuit covers the inner layer of the electronic circuit, the inner and outer layers of the electronic circuit can infiltrate each other, thereby further improving the adhesion of the outer layer of the electronic circuit on the flexible substrate, making it not easy to break or fall off, thereby ensuring the structural stability of the ultra-flexible electronic circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a method for manufacturing an ultra-flexible electronic circuit in an embodiment of the present invention;

[0020] Figure 2 Schematic diagram of the line width of the image and the actual line width in the screen printing plate in an embodiment of the present invention;

[0021] Figure 3 Schematic diagram of the structure of the ultra-flexible electronic circuit in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The following description and the accompanying drawings fully illustrate specific embodiments of the present invention so that those skilled in the art can practice them. Other embodiments may include structural, logical, electrical, process and other changes. The examples represent possible variations only. Unless explicitly required, separate components and functions are optional, and the order of operation may vary. Parts and features of some embodiments may be included in or replace parts and features of other embodiments. The scope of the embodiments of the present invention includes the entire scope of the claims, and all available equivalents of the claims. In this article, these embodiments of the present invention may be represented individually or collectively by the term "invention", which is merely for convenience, and if more than one invention is disclosed in fact, it is not intended to automatically limit the scope of the application to any single invention or inventive concept.

[0023] It should be noted that the various technical features in the embodiments of the present invention can be combined with each other without conflict.

[0024] The present invention discloses a method for manufacturing an ultra-flexible electronic circuit. Specifically, Figure 1 As shown, Figure 1 The manufacturing flow chart of the ultra-flexible electronic circuit in the embodiment of the present invention includes:

[0025] Step S1, printing a first electronic paste on a flexible substrate according to a target circuit pattern to form an inner electronic circuit; the inner electronic circuit comprises liquid metal, a first conductive metal powder and a resin;

[0026] Step S2, printing a second electronic paste on the inner electronic circuit according to a target circuit pattern to form a surface electronic circuit covering the inner electronic circuit; the surface electronic circuit comprises a second conductive metal powder and a resin;

[0027] Wherein, the flexibility of the inner layer electronic circuit is better than that of the surface layer electronic circuit, and the mechanical strength of the surface layer electronic circuit is better than that of the inner layer electronic circuit;

[0028] Step S3: After the surface electronic circuit is dried and solidified, an ultra-flexible circuit is obtained.

[0029] The ultra-flexible electronic circuit in the present invention is formed by setting up an inner and outer layer of electronic circuits. The inner layer of the electronic circuit is a liquid metal ultra-flexible structure, and the outer layer of the electronic circuit is formed by an electronic slurry with good conductivity to restrain and protect the inner layer of the electronic circuit, thereby ensuring the flexibility and conductivity of the ultra-flexible electronic circuit; and, since the outer layer of the electronic circuit covers the inner layer of the electronic circuit, the inner and outer layers of the electronic circuit can infiltrate each other, thereby further improving the adhesion of the outer layer of the electronic circuit on the flexible substrate, making it not easy to break or fall off, thereby ensuring the structural stability of the ultra-flexible electronic circuit.

[0030] The ultra-flexibility of the ultra-flexible electronic circuit in the embodiment of the present invention may refer to its flexible and bendable performance being better than that of traditional copper foil, aluminum foil, conductive silver paste, and the like.

[0031] The first electronic paste in the embodiment of the present invention includes at least liquid metal, first conductive metal powder, high-toughness resin and organic solvent; in other embodiments, the first electronic paste may also include one or more functional additives; functional additives such as thickeners, toughening agents, curing agents, adhesion promoters, etc.

[0032] Preferably, an embodiment of the present invention proposes a preferred formula of the first electronic paste, and the first electronic paste, by weight, is composed of: 25%-40% liquid metal, 15%-30% first conductive metal powder, 7%-15% high-toughness resin, 20%-50% organic solvent, 0.2%-2% thickener, 1%-2% toughening agent, 0.5%-2% curing agent and 1%-3% adhesion promoter.

[0033] Among them, the liquid metal can be selected from low-melting-point metal elements or alloys that are molten at the application environment temperature of ultra-flexible electronic circuits, and the melting point range is below 300°C, for example, low-melting-point metal elements or alloys with a melting point below 300 degrees Celsius, low-melting-point metal elements such as mercury, gallium, cesium, indium, tin, and potassium, and low-melting-point metal alloys such as gallium-based alloys, indium-based alloys, bismuth-based alloys, and tin-based alloys, specifically such as gallium-indium alloys, gallium-indium-tin alloys, gallium-tin alloys, gallium-zinc alloys, gallium-indium-zinc alloys, gallium-tin-zinc alloys, gallium-indium-tin-zinc alloys, gallium-tin-cadmium alloys, gallium-zinc-cadmium alloys, bismuth-indium alloys, bismuth-tin alloys, bismuth-indium-tin alloys, bismuth-indium-zinc alloys, bismuth-tin-zinc alloys, bismuth-indium-tin alloys, tin-lead alloys, tin-copper alloys, tin-zinc-copper alloys, tin-silver-copper alloys, and bismuth-lead-tin alloys. Preferably, the melting point range of the liquid metal is selected below 100°C, such as one or more of gallium-based alloys, indium-based alloys, bismuth-based alloys, tin-based alloys, etc.; preferably, the liquid metal is selected from gallium-based alloys, which have the advantage of being molten at room temperature, thereby satisfying the requirement that ultra-flexible electronic circuits can exhibit good flexibility in a wide range of application environments, and compared to mercury, it is non-toxic, and its preparation, storage, and use can all be guaranteed to be safe. On the other hand, the liquid metal in the first electronic paste can fully fill the gaps between the first conductive metal powders, so that the series connection density between the conductive phases is high, significantly improving the conductivity of the first electronic paste; and, the liquid metal exists as a flexible connection between the conductive phases, so there is no problem of mechanical fracture in the inner electronic circuit, and even when mechanical fracture occurs, the liquid metal therein can quickly repair the fracture to ensure the stability and reliability of the inner electronic circuit.

[0034] Specifically, by weight, the above-mentioned proportion of liquid metal may be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34.5%, 35%, 35%, 36%, 37.8%, 38%, 39%, and 40%.

[0035] Among them, the first conductive metal powder can be selected from solid metal particles with better conductivity than liquid metal, such as one or more of silver powder, copper powder, aluminum powder, silver-coated copper powder, etc. Preferably, the first conductive metal powder is silver powder, which can greatly improve the conductivity of the first electronic slurry. In addition, the first conductive metal powder can be selected from one or more of spherical powder, flaky powder, dendritic powder, etc. Preferably, the first conductive metal powder is spherical powder. Compared with other powder structures, the use of spherical powder can further improve the bendability of the inner electronic circuit, and liquid metal is easier to fill into the gap of the spherical powder, further increasing the series density between the conductive phases and ensuring the conductivity of the inner electronic circuit.

[0036] Specifically, the particle size of the first conductive metal powder is in the range of 0.1-20 μm; preferably, the particle size of the first conductive metal powder is in the range of 0.5-6 μm, which can be more easily tightly connected with the liquid metal and has a relatively lower production cost.

[0037] Specifically, by weight, the proportion of the first conductive metal powder may be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%.

[0038] Among them, the high-toughness resin in the embodiment of the present invention refers to a tough polymer resin. In the art, it is believed that a resin with an elongation greater than 200% can be called a high-toughness resin; preferably, the glass transition temperature of the high-toughness resin in the embodiment of the present invention is 0-50°C; more preferably, the glass transition temperature of the high-toughness resin is in the range of 0-40°C, which helps the inner electronic circuit to quickly transform in a lower temperature environment, reduce preparation requirements, and improve preparation efficiency. On the other hand, the high-toughness resin can be selected from a resin with a reactive corona functional group, and the reactive functional group is selected from a hydroxyl group, a carboxyl group, an epoxy group, or an isocyanate group, which can improve the conductivity of the electronic paste while ensuring that the coating has good adhesion; preferably, the reactive functional group is selected from a hydroxyl group, which can improve the adhesion of the first electronic paste on most substrates, thereby increasing the selection range of the first electronic paste for the substrate.

[0039] Specifically, by weight, the above-mentioned proportion of high-toughness resin may be 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15%.

[0040] The organic solvent may be selected from solvents with a boiling point between 100-250°C and a volatility of less than 0.1, preferably, a solvent with a boiling point between 180-210°C and a volatility of less than 0.05, such as lipid and ketone solvents.

[0041] Specifically, the above-mentioned proportion of organic solvent may be 20%, 21%, 22%, 23%, 24%, 30%, 31%, 36%, 38%, 40%, 41%, 44%, 48%, or 50% by weight.

[0042] The thickener is selected from one or more of hydroxyethyl cellulose, modified bentonite or fumed silica. By adding the thickener, the system viscosity of the first electronic paste can be adjusted, the coating and printing performance of the first electronic paste can be improved, which is beneficial to the processing and production of the electronic paste. On the other hand, it can also improve the binding ability of the electronic paste to the liquid metal and prevent the liquid metal from escaping from the system.

[0043] Specifically, by weight, the above proportion of the thickener may be 0.2%, 0.5%, 0.9%, 1.5%, or 2%.

[0044] Among them, the toughening agent can be selected from the toughening agents commonly used in the art; preferably, in the embodiment of the present invention, the toughening agent can be selected from liquid nitrile rubber.

[0045] Specifically, by weight, the above-mentioned proportion of the toughening agent may be 1%, 1.1%, 1.3%, 1.5%, 1.8%, or 2%.

[0046] The curing agent may be a curing agent commonly used in the art; preferably, the curing agent in the embodiment of the present invention may be a blocked isocyanate having a deblocking temperature lower than 150°C.

[0047] Specifically, by weight, the above proportion of the curing agent may be 0.5%, 1%, 1.3%, 1.5%, 1.8%, or 2%.

[0048] The adhesion promoter may be one or more of silane type, titanate type, zirconate type, zirconium aluminate type, and alkyl phosphate type; preferably, a silane type adhesion promoter is selected.

[0049] Specifically, by weight, the above-mentioned proportions of the adhesion promoter are 1%, 1.5%, 2%, and 3%.

[0050] The preparation of the first electronic paste in the embodiment of the present invention can be obtained by mixing liquid metal, first conductive metal powder, high-toughness resin, organic solvent, thickener, toughening agent, curing agent and adhesion promoter together, or they can be mixed step by step in sequence or selectively; the mixing method is not limited to one or more of manual stirring, mechanical stirring, grinding, ball milling, centrifugation and the like, and the above mixing methods can be selected from one of them, or can be carried out in sequence or selectively.

[0051] Preferably, the preferred preparation method of the first electronic paste in the embodiment of the present invention is as follows:

[0052] When there is no need to improve the adhesion of the first electronic paste, first, the materials except the liquid metal and the first conductive metal powder are mixed, stirred and dispersed to obtain a first organic carrier; then, the first conductive metal powder is added to the obtained first organic carrier and mixed to obtain a first premixed slurry; finally, the liquid metal is added to the obtained first premixed slurry and mixed to obtain the first electronic paste.

[0053] When it is necessary to improve the adhesion of the first electronic paste, first, the materials other than the liquid metal, the first conductive metal powder and the adhesion promoter are mixed, stirred and dispersed to obtain a first organic carrier; then, the first conductive metal powder is added to the obtained first organic carrier and mixed to obtain a first premixed slurry; finally, the liquid metal and the adhesion promoter are added to the obtained first premixed slurry and mixed to obtain the first electronic paste.

[0054] For example, a high-toughness resin, a thickener, a toughening agent, a curing agent, and an organic solvent are mixed, stirred, and dispersed at one time; then conductive metal silver powder is added in sequence, and stirred at a speed of 1200 rpm for 15 minutes to obtain a premixed slurry; the obtained premixed slurry is ground into a fineness of 5 to 10 μm using a three-roll grinder; liquid metal and an adhesion promoter are added, and a centrifugal degasser is used to centrifuge at 2000 rpm for 5 minutes to obtain a first electronic slurry.

[0055] The first electronic paste prepared in the above manner has good adhesion, conductivity and bending resistance.

[0056] The second electronic paste in the embodiment of the present invention comprises at least: a second conductive metal powder, a high-toughness resin and an organic solvent; in other embodiments, the second electronic paste may further comprise one or more functional additives; functional additives such as thickeners, toughening agents, curing agents, adhesion promoters, etc.

[0057] Preferably, an embodiment of the present invention proposes a preferred formula of the second electronic paste. The second electronic paste, by weight, is composed of: 40%-70% of a second conductive metal powder, 7%-15% of a high-toughness resin, 20%-50% of an organic solvent, 0.2%-2% of a thickener, 1%-2% of a toughening agent, and 0.5%-2% of a curing agent.

[0058] Among them, the second conductive metal powder can be selected from solid metal particles with better conductivity than liquid metal, such as one or more of silver powder, copper powder, aluminum powder, silver-coated copper powder, etc. Preferably, the second conductive metal powder is selected from silver powder, which can greatly improve the conductive performance of the second electronic paste. In addition, the second conductive metal powder can be selected from one or more of spherical powder, flaky powder, dendritic powder, etc. Preferably, the second conductive metal powder is selected from flaky powder. Compared with other powder structures, the coverage of flaky powder is better than other types of powders, which can improve the mechanical strength of the surface electronic circuit formed after the curing of the second electronic paste, and can ensure the covering and packaging protection of the inner electronic circuit. Furthermore, the second conductive metal powder is selected from a combination of flaky powder and spherical powder, which can further improve the conductivity of the second electronic paste.

[0059] Specifically, the particle size range of the second conductive metal powder is 0.1-20 μm; preferably, the particle size range of the second conductive metal powder is 1-10 μm. Compared with small particle sizes, this particle size range can improve the mechanical strength of the surface electronic circuit without affecting the flexibility of the ultra-flexible electronic circuit.

[0060] Specifically, by weight, the proportion of the second conductive metal powder may be 40%, 43%, 45%, 48%, 50%, 55%, 57%, 58%, 60%, 62%, 65%, 67%, 68%, 69%, or 70%.

[0061] Among them, the high-toughness resin in the embodiment of the present invention refers to a tough polymer resin. In the art, it is believed that a resin with an elongation greater than 200% can be called a high-toughness resin; preferably, the glass transition temperature of the high-toughness resin in the embodiment of the present invention is 0-50°C; more preferably, the glass transition temperature of the high-toughness resin is in the range of 0-40°C, which helps the inner electronic circuit to quickly transform in a lower temperature environment, reduce preparation requirements, and improve preparation efficiency. On the other hand, the high-toughness resin can be selected from a resin with a reactive corona functional group, and the reactive functional group is selected from a hydroxyl group, a carboxyl group, an epoxy group, or an isocyanate group, which can improve the conductivity of the electronic paste while ensuring that the coating has good adhesion; preferably, the reactive functional group is selected from a hydroxyl group, which can improve the adhesion of the second electronic paste on most substrates, thereby increasing the selection range of the second electronic paste for the substrate.

[0062] Specifically, by weight, the above-mentioned proportion of high-toughness resin may be 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15%.

[0063] The organic solvent may be selected from solvents with a boiling point between 100-250°C and a volatility of less than 0.1, preferably, a solvent with a boiling point between 180-210°C and a volatility of less than 0.05, such as lipid and ketone solvents.

[0064] Specifically, the above-mentioned proportion of organic solvent may be 20%, 21%, 22%, 23%, 24%, 30%, 31%, 36%, 38%, 40%, 41%, 44%, 48%, or 50% by weight.

[0065] The thickener is selected from one or more of hydroxyethyl cellulose, modified bentonite or fumed silica. By adding the thickener, the system viscosity of the second electronic paste can be adjusted, the coating and printing performance of the second electronic paste can be improved, which is beneficial to the processing and production of the electronic paste. At the same time, the thickener has good wettability with the resin, and its surface dipole effect can produce an interface effect with the resin, improve the performance of the resin after curing, increase the wear resistance and hardness of the system, and improve the mechanical strength of the surface electronic circuit.

[0066] Specifically, by weight, the above proportion of the thickener may be 0.2%, 0.5%, 0.9%, 1.5%, or 2%.

[0067] The toughening agent may be any toughening agent commonly used in the art; preferably, in the embodiment of the present invention, liquid nitrile rubber may be used as the toughening agent.

[0068] Specifically, by weight, the above-mentioned proportion of the toughening agent may be 1%, 1.1%, 1.3%, 1.5%, 1.8%, or 2%.

[0069] The curing agent may be a curing agent commonly used in the art; preferably, the curing agent in the embodiment of the present invention may be a blocked isocyanate having a deblocking temperature lower than 150°C.

[0070] Specifically, by weight, the above proportion of the curing agent may be 0.5%, 1%, 1.3%, 1.5%, 1.8%, or 2%.

[0071] Preferably, the preferred preparation method of the second electronic paste in the embodiment of the present invention is as follows:

[0072] First, materials other than the second conductive metal powder are mixed, stirred and dispersed to obtain a second organic vehicle; then, the second conductive metal powder is added to the obtained second organic vehicle and mixed to obtain a second electronic paste.

[0073] For example, a high-toughness resin, a thickener, a toughening agent, a curing agent, and an organic solvent are mixed, stirred, and dispersed at one time; then conductive metal silver powder is added in sequence, and stirred at a speed of 1200 rpm for 15 minutes to obtain a premixed slurry; the obtained premixed slurry is ground into a fineness of 5 to 10 μm using a three-roll grinder; and the second electronic slurry is obtained.

[0074] The second electronic paste prepared in the above manner has good adhesion, conductivity, mechanical strength, wear resistance, and good bending performance.

[0075] The first electronic paste and / or the second electronic paste in the embodiment of the present invention can be formed by printing, spraying, relief printing, gravure printing, flexographic printing, screen printing, steel screen printing, coating, pad printing, overprinting, etc. Preferably, the first electronic paste and the second electronic paste in the embodiment of the present invention can be formed by screen printing. Compared with other printing methods, the screen printing industry is mature at this stage, and it is also relatively easy to prepare the first electronic paste and the second electronic paste that meet the requirements of screen printing, and the cost is low.

[0076] Specifically, the screen printing screen with screen specifications of SUS325 / 23, SUS400 / 18, SUS360 / 16, and SUS380 / 14 is suitable for printing the first electronic paste and / or the second electronic paste in the embodiment of the present invention. Among them, the film thickness specification of the screen printing screen is 5-30μm. (That is, it can meet the printing of 5-30μm thin films)

[0077] Preferably, the first electronic paste and the second electronic paste in the embodiment of the present invention are printed using a SUS380 / 14 screen printing plate with a film thickness of 8-15 μm.

[0078] In the embodiment of the present invention, the first electronic paste / second electronic paste printed will diffuse a small amount based on the original line position, and the diffusion range is 0-5μm. Therefore, when selecting a silk screen, the line width in the silk screen can be selected to be 0-10μm less than the target line width, thereby reducing the impact on the printing accuracy of the first electronic paste / second electronic paste.

[0079] Specifically, Figure 2 As shown, the line in the screen printing screen 200 is symmetrical with the line center as the axis of symmetry, and the left and right sides are 0-5(a) less than the target line width, so as to achieve overflow uniformity of the line 100 during screen printing and ensure the consistency of the printed line pattern with the target line pattern.

[0080] Preferably, the pattern line in the screen printing plate for printing the first electronic paste is 1-10 μm shorter than the target electronic circuit pattern; further, the line width difference a can be designed to be 1-3 μm.

[0081] Preferably, the pattern line in the screen printing plate for printing the second electronic paste is 0-10 μm shorter than the target electronic circuit pattern; further, the line width difference a can be designed to be 1-2 μm.

[0082] Preferably, in the embodiment of the present invention, when the first electronic paste and the second electronic paste are printed in sequence, the first electronic paste is printed first to form an inner electronic circuit; then when the inner electronic circuit is completely dry or surface dry, the second electronic paste can be printed on the inner electronic circuit in a similar overprinting manner to form a surface electronic circuit, and an ultra-flexible electronic circuit is obtained after the surface electronic circuit is dried and cured.

[0083] The drying / curing of the inner layer electronic circuit and the surface layer electronic circuit in the embodiment of the present invention can be carried out by natural drying and curing, or by air drying, heat baking, sintering, high temperature, light irradiation, etc., which can be selected according to actual conditions.

[0084] Preferably, the inner electronic circuit surface can be dried for a certain period of time at a temperature of 25°C to 200°C; the time can be 0.5-120 minutes; preferably, the temperature environment can be set to 80°C-180°C, which can achieve a quick surface drying effect, and can also adapt to most flexible substrates to avoid damage and deformation of the flexible substrate due to high temperature.

[0085] Preferably, the surface electronic circuit can be dried and cured under a temperature environment of 100°C to 200°C for a certain period of time, and the time can be 0.5-120 minutes; preferably, the temperature environment can be set to 150°C-200°C, which can achieve the effect of rapid drying and curing, and can also adapt to most flexible substrates to avoid damage and deformation of the flexible substrate due to high temperature.

[0086] The flexible substrate in the embodiment of the present invention can be a heat-resistant flexible substrate on the market; preferably, PI polyimide film, PET high-temperature resistant polyester film, PEN polynaphthalene film can be selected.

[0087] In order for those skilled in the art to quickly understand the main ideas and effects of the present invention, the experimental data are explained here:

[0088] Table 1: Composition of the first electronic paste (DP1)

[0089]

[0090] According to the formula in Table 1, high-toughness resin, thickener, toughening agent, curing agent and organic solvent are mixed, stirred and dispersed at once; then conductive metal silver powder is added in sequence, and stirred at 1200 rpm for 15 minutes to obtain a premixed slurry; the obtained premixed slurry is ground into a fineness of 5 to 10 μm using a three-roll grinder; liquid metal and adhesion promoter are added, and centrifuged at 2000 rpm for 5 minutes using a centrifugal degassing machine to obtain the first electronic slurry DP1;

[0091] The first electronic paste DP1 is evenly printed on PI by screen printing. The PI film is baked in a blast oven at 150°C for 50 minutes, then taken out, cooled, and the line thickness (film thickness is 8-10μm), line resistance, adhesion, bending and other performance results are measured. According to the film thickness, line resistance, line width, and line length, the square resistance of the first electronic paste after baking is calculated using the square resistance calculation formula. The corresponding performance test results are shown in Table 2. It can be seen from the data in Table 2 that the first electronic paste prepared by the present invention has the advantages of high conductivity, excellent bending resistance, good adhesion, and solves the problem of liquid metal escape. It can be seen from the results of the comparative examples that the bending resistance and conductivity of the electronic paste are significantly improved after the introduction of liquid metal. By adding an appropriate amount of thickener, the problem of liquid metal escape can be effectively controlled.

[0092] Table 2: Properties of the first electronic paste DP1 after curing

[0093]

[0094] Table 3: Composition of the second electronic paste DP2

[0095]

[0096] According to the formula in Table 3, high-toughness resin, thickener, toughening agent, curing agent and organic solvent are mixed and stirred and dispersed at once; then conductive metal silver powder is added in sequence and stirred at 1200 rpm for 15 min to obtain a premixed slurry; the obtained premixed slurry is ground into a fineness of 5 to 10 μm using a three-roll grinder to obtain conductive silver paste DP2;

[0097] The second electronic paste DP2 is evenly printed on PI by screen printing. The PI film is baked in a blast oven at 150°C for 50 minutes, then taken out and cooled. The line thickness (film thickness is 8-10μm), line resistance, adhesion, bending, hardness and other performance results are measured. According to the film thickness, line resistance, line width and line length, the square resistance of the second electronic paste after baking is calculated using the square resistance calculation formula. The corresponding performance test results are shown in Table 4. It can be seen from the data in Table 4 that the second electronic paste prepared by the present invention has the advantages of high conductivity and high hardness. By comparing the results of the examples, it can be seen that after the thickener is introduced, the hardness of the electronic paste after baking is significantly improved; the method of combining flaky silver powder and spherical silver powder can effectively improve the resistance.

[0098] Table 4: Properties of the second electronic paste DP2 after curing

[0099]

[0100] Use the DP1-2 electronic paste in the specific embodiment, the DP2-1 and DP2-3 electronic pastes in the specific embodiment, and in accordance with the ultra-flexible electronic circuit printing and manufacturing method in this patent, adopt a secondary precision overprinting printing method, and first print the first electronic paste DP1 according to the electronic circuit pattern, and perform surface drying and curing; then overprint the second electronic paste DP2, and dry and cure. Measure the line thickness (film thickness is 8 to 10 μm), line resistance, adhesion, bending, hardness and other performance results. According to the film thickness, line resistance, line width, and line length, the square resistance of the conductive silver paste after baking is calculated using the square resistance calculation formula. The corresponding performance test results are shown in Table 5. From the data in Table 5, it can be seen that:

[0101] After overprinting DP2-1 and DP2-3 electronic paste on DP1-2 electronic paste, the circuit has excellent bending resistance.

[0102] DP2-1 was overprinted on DP1-2 electronic paste. After baking, the surface of the electronic paste was wiped and slight black scratches were found on the surface, indicating that the covering ability of DP2-1 was slightly poor.

[0103] DP2-3 is overprinted on DP1-2 electronic paste. After baking, the surface of the electronic paste is wiped and there is no change on the surface. The hardness reaches 5H and the adhesion reaches 5B. It is an ultra-flexible electronic circuit.

[0104] The hiding ability of DP2-3 for liquid metal is better than that of DP2-1, which shows that the silver powder combination of DP2-3 can improve the hiding ability of liquid metal.

[0105] Table 5: Performance of electronic paste DP1 overprint DP2 after curing

[0106]

[0107] An embodiment of the present invention also discloses an ultra-flexible electronic circuit, which can be obtained by the above-mentioned preparation method. Specifically, the ultra-flexible electronic circuit includes: a flexible substrate 1, an inner layer electronic circuit 2 attached to the flexible substrate 1 and containing liquid metal, and a surface layer electronic circuit 3 covering the inner layer electronic circuit 2; wherein the flexibility of the inner layer electronic circuit 2 is better than that of the surface layer electronic circuit 3, and the mechanical strength of the surface layer electronic circuit 3 is better than that of the inner layer electronic circuit 2.

[0108] Among them, the flexible substrate in the embodiment of the present invention can be selected from the temperature-resistant flexible substrate on the market; preferably, PI polyimide film, PET high-temperature resistant polyester film, PEN polynaphthalene film can be selected.

[0109] The inner electronic circuit may include liquid metal, a first conductive metal powder and a resin; preferably, the inner electronic circuit may be formed by printing a first electronic paste; the first electronic paste in the embodiment of the present invention includes at least liquid metal, a first conductive metal powder, a high-toughness resin and an organic solvent; in other embodiments, the first electronic paste may also include one or more functional additives; functional additives such as thickeners, toughening agents, curing agents, adhesion promoters, etc.

[0110] Preferably, an embodiment of the present invention proposes a preferred formula of the first electronic paste. The first electronic paste, in parts by weight, is composed of: 30%-40% liquid metal, 20%-30% first conductive metal powder, 7%-15% high-toughness resin, 20%-50% organic solvent, 0.2%-2% thickener, 1%-2% toughening agent, 0.5%-2% curing agent and 1%-3% adhesion promoter.

[0111] The surface electronic circuit may include a second conductive metal powder and a resin; preferably, the surface electronic circuit may be formed by printing the second electronic paste; the second electronic paste in the embodiment of the present invention includes at least: a second conductive metal powder, a high-toughness resin and an organic solvent; in other embodiments, the second electronic paste may also include one or more functional additives; functional additives such as thickeners, toughening agents, curing agents, adhesion promoters, etc.

[0112] Preferably, an embodiment of the present invention proposes a preferred formula of the second electronic paste. The second electronic paste, by weight, is composed of: 50%-70% of a second conductive metal powder, 7%-15% of a high-toughness resin, 20%-50% of an organic solvent, 0.2%-2% of a thickener, 1%-2% of a toughening agent, and 0.5%-2% of a curing agent.

[0113] Those skilled in the art will also appreciate that the various illustrative logic blocks, modules, circuits, and algorithmic steps described in conjunction with the embodiments herein can all be implemented as electronic hardware, computer software, or a combination thereof. In order to clearly illustrate the interchangeability between hardware and software, various illustrative components, blocks, modules, circuits, and steps are generally described above around their functions. Whether such functions are implemented as hardware or software depends on specific applications and the design constraints imposed on the entire system. A skilled person can implement the described functions in an alternative manner for each specific application, but such implementation decisions should not be interpreted as departing from the scope of protection of the present disclosure.

Claims

1. A method for manufacturing an ultra-flexible electronic circuit, characterized in that: include: Step 1, printing a first electronic paste on a flexible substrate according to a target circuit pattern to form an inner layer electronic circuit; The inner electronic circuit comprises liquid metal, first conductive metal powder and resin; Step 2, printing a second electronic paste on the inner electronic circuit according to a target circuit pattern to form a surface electronic circuit covering the inner electronic circuit; The surface electronic circuit comprises a second conductive metal powder and a resin; Wherein, the flexibility of the inner layer electronic circuit is better than that of the surface layer electronic circuit, and the mechanical strength of the surface layer electronic circuit is better than that of the inner layer electronic circuit; Step 3, after the surface electronic circuit is dried and solidified, an ultra-flexible circuit is obtained; The first electronic paste comprises, by weight: 25%-40% of liquid metal, 15%-30% of first conductive metal powder, 7%-15% of high-toughness resin, 20%-50% of organic solvent, 0.2%-2% of thickener, 1%-2% of toughening agent, 0.5%-2% of curing agent and 1%-3% of adhesion promoter; By weight, the second electronic paste comprises: 40%-70% of a second conductive metal powder, 7%-15% of a high-toughness resin, 20%-50% of an organic solvent, 0.2%-2% of a thickener, 1%-2% of a toughening agent and 0.5%-2% of a curing agent.

2. The method for manufacturing an ultra-flexible electronic circuit according to claim 1, characterized in that: The method for preparing the first electronic paste comprises: Mixing and dispersing a high-toughness resin, a thickener, a toughening agent, a curing agent, and an organic solvent to obtain a first organic carrier; Then, the first conductive metal powder is added to the first organic carrier, and mechanically stirred and ground in sequence to obtain a first premixed slurry; The liquid metal is then added to the first premixed slurry, and the first electronic slurry is obtained after centrifugation.

3. The method for manufacturing an ultra-flexible electronic circuit according to any one of claims 1 or 2, characterized in that: The first conductive metal powder is selected from spherical particles of 0.1-20 μm.

4. The method for manufacturing an ultra-flexible electronic circuit according to claim 1, characterized in that: The method for preparing the second electronic paste comprises: Mixing and dispersing a high-toughness resin, a thickener, a toughening agent, a curing agent, and an organic solvent to obtain a second organic carrier; Then, the second conductive metal powder is added into the second organic carrier, and mechanically stirred and ground in sequence to obtain a second electronic paste.

5. The method for manufacturing an ultra-flexible electronic circuit according to claim 1 or 4, characterized in that: The second conductive metal powder is selected from flake particles of 0.1-20 μm.

6. The method for manufacturing an ultra-flexible electronic circuit according to claim 1, characterized in that: The first electronic paste and / or the second electronic paste is formed by screen printing; wherein the line in the screen circuit pattern used in the screen printing is 0-10 μm smaller than the line width of the target circuit pattern.

7. An ultra-flexible electronic circuit, characterized in that: include: A flexible substrate, an inner layer electronic circuit attached to the flexible substrate and containing liquid metal, and a surface layer electronic circuit covering the inner layer electronic circuit; wherein the inner layer electronic circuit has better flexibility than the surface layer electronic circuit, and the surface layer electronic circuit has better mechanical strength than the inner layer electronic circuit; wherein the inner layer electronic circuit is formed by a first electronic paste, and the surface layer electronic circuit is formed by a second electronic paste; The first electronic paste comprises, by weight: 25%-40% of liquid metal, 15%-30% of first conductive metal powder, 7%-15% of high-toughness resin, 20%-50% of organic solvent, 0.2%-2% of thickener, 1%-2% of toughening agent, 0.5%-2% of curing agent and 1%-3% of adhesion promoter; By weight, the second electronic paste comprises: 40%-70% of a second conductive metal powder, 7%-15% of a high-toughness resin, 20%-50% of an organic solvent, 0.2%-2% of a thickener, 1%-2% of a toughening agent and 0.5%-2% of a curing agent.

8. The ultra-flexible electronic circuit according to claim 7, characterized in that: The film thickness of the inner layer electronic circuit is 5-30 μm; and / or the film thickness of the surface layer electronic circuit is 5-30 μm.

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