A low melting point alloy ink and its application

Abstract

The present invention relates to the technical field of electronic ink, and discloses a low-melting-point alloy ink and its application. It is made by mixing 20-50% alloy filler, 30-70% metal elemental filler and 10-30% organic mixed soldering flux by mass percentage; the alloy filler that can be welded at low temperature acts as a metal binder to contact and diffuse with the metal elemental filler with high conductivity, improving the conductivity of the alloy ink; the excellent mechanical strength of the metal elemental filler and the long-range penetrating conductive path with tight connection greatly improve the fracture strength and peel strength of the alloy ink.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic ink, and specifically provides a low-melting-point alloy ink and its application. Background Art

[0002] Flexible printed electronics additive manufacturing technology is a technology that uses electronic ink to continuously produce large-area flexible circuits by printing on the surface of flexible substrates. It has the advantages of being green, energy-saving, efficient, and low-cost, and is conducive to realizing the high-density, miniaturization, and thinness of electronic devices. As a key raw material for flexible printed circuit additive manufacturing, electronic ink is a key link to improve the printing production efficiency and the performance of flexible printed circuits.

[0003] The conductive filler of electronic ink is mainly nano- and micron-scale metal or carbon materials, which can form a continuous path only through high-temperature curing and sintering, so as to obtain high conductivity and mechanical strength. However, flexible substrates are not resistant to high temperatures, and high-temperature sintering will damage the structure of flexible circuits and significantly shorten their service life.

[0004] Alloy materials can be flexibly regulated in terms of composition and properties, and can significantly reduce the melting point, showing great application potential in the field of low-temperature electronic ink. "Science China Materials" (2022, Vol. 65, p. 2072) reported an electronic ink using gallium-based liquid metal as a conductive filler, which has both metallic conductivity and liquid ductility at room temperature and is applied to the preparation of flexible printed electronics. However, due to the high surface tension of liquid metal, it has a tendency to spontaneously form spherical droplets, which hinders its wetting of the substrate surface and the formation of circuit patterns, reducing the mechanical strength and printing performance of the alloy ink.

[0005] Therefore, it is necessary to find a new type of alloy filler as a metal binder to weld conductive fillers to achieve the coordinated improvement of the conductive performance, mechanical strength, and printing performance of alloy ink under the condition of reducing the curing temperature.

[0006] Based on this, we propose a low-melting-point alloy ink, hoping to solve the deficiencies in the existing technology. Summary of the Invention

[0007] (1) Technical Problems to be Solved

[0008] In view of the deficiencies of the existing technology, the present invention provides a low-melting-point alloy ink and its application.

[0009] (2) Technical Solutions

[0010] To achieve the above object, the present invention provides the following technical solutions:

[0011] A low melting point alloy ink is made by mixing 20 - 50% alloy filler, 30 - 70% metal elemental filler and 10 - 30% organic mixed soldering flux by mass percentage.

[0012] As a further technical solution: the metal elemental filler includes one or more of copper, tin, silver, nickel, and aluminum.

[0013] As a further technical solution: the organic mixed soldering flux is obtained by mixing tripropylene glycol monobutyl ether, suberic acid, vinyl laurate, dimethyl cyclohexanone, and citric acid in volume fractions of 10 - 20%, 5 - 12%, 25 - 45%, 20 - 40%, and 5 - 12% in sequence.

[0014] As a further technical solution: the preparation method of the alloy filler is as follows:

[0015] Prepare an amorphous alloy nano - seed mixture by low - temperature co - reduction of a mixed metal salt solution;

[0016] Control the temperature for aging growth of the alloy nano - seed mixture to prepare the alloy filler; the average particle size of the amorphous alloy nano - seeds is 3 - 100 nm; the average particle size of the alloy filler is 1 - 20 μm and the melting point is lower than 180°C.

[0017] As a further technical solution: the metal salts are selected from two or more of copper chloride, copper sulfate, bismuth oxide, bismuth chloride, bismuth nitrate, bismuth citrate, silver nitrate, indium chloride, indium nitrate, tin chloride, tin nitrate, and stannous sulfate, and salts of two or more different metals are required;

[0018] Preferably tin salt and bismuth salt;

[0019] Among them, the mixing mass ratio of the tin salt and the bismuth salt is 3 - 4:6 - 7.

[0020] As a further technical solution: the low - temperature co - reduction means dropping the mixed metal salt solution into a reducing agent solution at 0°C and mechanically stirring for 10 - 90 min under the protection of an N2 atmosphere.

[0021] As a further technical solution: the temperature - controlled aging growth is two - step heat treatment. The temperature of the first - step heat treatment is 100 - 160°C, and the heat treatment time is 10 - 60 min. The second step is to heat to 170 - 190°C at a heating rate of 0.5 - 1°C / min and keep warm for 10 - 60 min.

[0022] Applications of the low melting point alloy ink in the fields of flexible circuit board printing, flexible hybrid electronic device packaging, semiconductor packaging, flexible photovoltaics, flexible displays, and flexible sensors.

[0023] A preparation method of a low melting point alloy ink, comprising the following steps:

[0024] (1) Prepare an amorphous alloy nanoseed mixture by co-reducing a mixed solution of metal salts such as copper salt, bismuth salt, silver salt, indium salt, and tin salt at low temperature;

[0025] (2) Control the temperature and ripen the alloy nanoseed mixture to grow alloy fillers;

[0026] (3) Mix the alloy fillers, metal elemental fillers, and organic mixed soldering fluxes evenly to prepare a low-melting-point alloy ink.

[0027] As a further technical solution: The usage method of the low-melting-point alloy ink is as follows:

[0028] Use the low-melting-point alloy ink as a raw material to prepare a flexible circuit through a direct writing process;

[0029] The direct writing process includes multi-dimensional regulation of direct writing printing parameters such as nozzle size, nozzle height, heating temperature, direct writing speed, and extrusion pressure, realizing temperature-controlled melting and extrusion, directly obtaining a conductive path, and no longer requiring annealing treatment.

[0030] The characteristics of the present invention are that the alloy filler with low-temperature welding characteristics infiltrates into the gaps between the metal elemental fillers as a metal binder in a molten state, contacts and diffuses with the metal elemental fillers; when welded and cooled, the metal binder solidifies and cures, and the alloy filler is connected to the metal elemental fillers to form a continuous long-range through-conductive path; by regulating the ratio of the alloy filler to the metal elemental filler, the welding performance and the intrinsic performance of the filler are optimized, effectively reducing the curing temperature of the alloy ink, and synergistically improving its electrical conductivity, mechanical strength, and printing performance; combined with multi-dimensional regulation of direct writing printing parameters such as nozzle size, heating temperature, and extrusion pressure, realizing temperature-controlled melting and extrusion, directly obtaining a conductive path, and no longer requiring annealing treatment.

[0031] (III) Beneficial effects

[0032] Compared with the prior art, the present invention provides a low-melting-point alloy ink, which has the following beneficial effects:

[0033] (1) The alloy filler that can be welded at low temperature contacts and diffuses with the metal elemental filler with high conductivity as a metal binder, improving the electrical conductivity of the alloy ink;

[0034] (2) The excellent mechanical strength of the metal elemental filler and the closely connected long-range through-conductive path greatly improve the fracture strength and peel strength of the alloy ink;

[0035] (3) The low-melting-point alloy is transformed into a high-melting-point intermetallic compound during the low-temperature heating process, effectively eliminating the low-melting-point alloy and improving the weather resistance and working temperature of the printed circuit;

[0036] (4) A conductive path is obtained by directly extruding through temperature-controlled melting, combined with multi-dimensional regulation of direct writing printing parameters, to achieve the efficient preparation of large-area and high-precision flexible circuits. Description of the Drawings

[0037] Figure 1 Flow chart of the low-melting-point alloy ink prepared in the embodiment of the present invention;

[0038] Figure 2 Schematic diagram of the conductive paths formed by different alloy filler contents of the low-melting-point alloy ink prepared in the embodiment of the present invention. Detailed Embodiments

[0039] The following will describe the technical solutions in the embodiments of the present invention clearly and completely in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work shall fall within the scope of protection of the present invention.

[0040] A low-melting-point alloy ink is made by mixing 20 - 50% alloy filler, 30 - 70% metal elemental filler, and 10 - 30% organic mixed soldering flux by mass percentage.

[0041] The elemental filler includes one or more of copper, tin, silver, nickel, and aluminum.

[0042] The organic mixed soldering flux is obtained by mixing tripropylene glycol monobutyl ether, suberic acid, vinyl laurate, dimethyl cyclohexanone, and citric acid in volume fractions of 10 - 20%, 5 - 12%, 25 - 45%, 20 - 40%, and 5 - 12% in sequence.

[0043] The organic mixed soldering flux is composed of tripropylene glycol monobutyl ether, suberic acid, vinyl laurate, dimethyl cyclohexanone, and citric acid in volume fractions of 15%, 8%, 38%, 31%, and 8% in sequence.

[0044] The preparation method of the alloy filler is as follows:

[0045] A mixed solution of metal salts such as copper salts, bismuth salts, silver salts, indium salts, and tin salts is co-reduced at low temperature to prepare an amorphous alloy nano-seed mixture;

[0046] The alloy nano-seed mixture is subjected to temperature-controlled ripening growth to prepare the alloy filler.

[0047] The metal salts are selected from two or more of copper chloride, copper sulfate, bismuth oxide, bismuth chloride, bismuth nitrate, bismuth citrate, silver nitrate, indium chloride, indium nitrate, tin chloride, tin nitrate, and stannous sulfate, and need to include salts of two or more different metals;

[0048] Preferably, tin salts and bismuth salts;

[0049] Among them, the mass ratio of the mixed tin salt and bismuth salt is 3 - 4:6 - 7.

[0050] Low-temperature co-reduction means dropping a mixed solution of metal salts into a reducing agent solution at 0 °C and mechanically stirring for 10 - 90 min under the protection of a N2 atmosphere.

[0051] At room temperature, 3.43 g of SnCl2, 6.62 g of Bi(NO3)3·5H2O, and 0.65 g of PVP were successively added and dissolved in 64 mL of diethylene glycol solvent, and then 66 mL of 1.2 mol / L NaOH ethanol solution was added dropwise to 30 mL of 2.9 mol / L NaBH4 diethylene glycol solution at 0 °C. Under the protection of a N2 atmosphere, it was mechanically stirred at a speed of 200 rpm for 60 min to obtain an amorphous tin-bismuth nano-seed mixture;

[0052] Temperature-controlled ripening growth is a two-step heat treatment. The temperature of the first heat treatment is 100 - 160 °C, and the heat treatment time is 10 - 60 min. The second step is to heat to 170 - 190 °C at a heating rate of 0.5 - 1 °C / min and keep it warm for 10 - 60 min.

[0053] The average particle size of the amorphous alloy nano-seeds is 3 - 100 nm; the average particle size of the alloy filler is 1 - 20 μm and the melting point is lower than 180 °C.

[0054] Applications of the low-melting-point alloy ink in the fields of flexible circuit board printing, flexible hybrid electronic device packaging, semiconductor packaging, flexible photovoltaics, flexible displays, and flexible sensors.

[0055] A preparation method of a low-melting-point alloy ink, comprising the following steps:

[0056] (1) Preparing an amorphous alloy nano-seed mixture by low-temperature co-reduction of a mixed solution of copper salts, bismuth salts, silver salts, indium salts, and tin salts;

[0057] (2) Preparing an alloy filler by temperature-controlled ripening growth of the alloy nano-seed mixture;

[0058] (3) Mixing the alloy filler, metal single-element filler, and organic mixed soldering flux evenly to prepare a low-melting-point alloy ink;

[0059] (4) Preparing a flexible circuit by a direct writing process using the low-melting-point alloy ink as a raw material.

[0060] Among them, the direct writing process includes multi-dimensional regulation of direct writing printing parameters such as nozzle size, nozzle height, heating temperature, direct writing speed, and extrusion pressure to achieve temperature-controlled melting and extrusion, directly obtaining a conductive path, and no longer requiring annealing treatment.

[0061] Among them, the alloy filler infiltrates into the gaps between the elemental metal fillers as a metal binder in a molten state, contacts and diffuses with the elemental metal fillers; when welded and cooled, the metal binder solidifies and cures, and the alloy filler is connected to the elemental metal fillers to form a continuous long-range through-conductive path.

[0062] The following are specific examples:

[0063] Example 1

[0064] (1) At room temperature, 3.43 g of SnCl2, 6.62 g of Bi(NO3)3·5H2O, and 0.65 g of PVP were successively added and dissolved in 64 mL of diethylene glycol solvent, and then the NaOH ethanol solution (1.2 mol / L, 66 mL) was added dropwise to the NaBH4 diethylene glycol solution (2.9 mol / L, 30 mL) at 0 °C, and mechanically stirred (200 rpm) for 60 min under N2 atmosphere protection to obtain an amorphous tin-bismuth nano-seed mixture.

[0065] (2) First, the prepared tin-bismuth nano-seed mixture was ultrasonically treated at 0 °C for 60 min, then aged at 160 °C (T l ) for 30 min, and then heated to 180 °C at a heating rate of 1 °C min -1 and held for 10 min to obtain tin-bismuth alloy filler with a particle size of 3 μm.

[0066] (3) Using a homogenizer, the tin-bismuth alloy filler, copper and tin elemental metal fillers, and organic mixed soldering flux were mixed evenly in mass fractions of 20 - 50%, 50 - 20%, and 30% in turn to obtain low-melting-point alloy inks with tin-bismuth alloy filler contents of 20%, 30%, 40%, and 50%.

[0067] (4) A flexible circuit was prepared with direct writing printing parameters of a nozzle size of 100 μm, a nozzle height of 100 μm, a heating temperature of 150 °C, and a direct writing speed of 35 mm·s -1 , and an extrusion pressure of 400 KPa.

[0068] (5) The prepared low-melting-point alloy ink was tested for fracture strength, peel strength, and electrical conductivity.

[0069] The performance of the low-melting-point alloy ink is as follows:

[0070] Table 1

[0071]

[0072] Example 2

[0073] (1) At room temperature, 3.43 g of SnCl2, 6.62 g of Bi(NO3)3·5H2O and 0.65 g of PVP were added successively and dissolved in 64 mL of diethylene glycol solvent. Then, the NaOH ethanol solution (1.2 mol / L, 66 mL) was added dropwise to the NaBH4 diethylene glycol solution (2.9 mol / L, 30 mL) at 0 °C, and mechanically stirred (200 rpm) for 60 min under the protection of N2 atmosphere to obtain an amorphous tin-bismuth nano-seed mixture.

[0074] (2) First, the prepared tin-bismuth nano-seed mixture was ultrasonically treated at 0 °C for 60 min, then aged at 160 °C (T l ) for 30 min, and then heated to 180 °C at a heating rate of 1 °C min -1 and held for 10 min to obtain tin-bismuth alloy fillers with a particle size of 3 μm.

[0075] (3) Using a homogenizer, the tin-bismuth alloy fillers, copper and tin metal single fillers, and organic mixed soldering fluxes were mixed evenly in mass fractions of 20 - 50%, 70 - 40%, and 10% successively to obtain low-melting-point alloy inks with tin-bismuth alloy filler contents of 20%, 30%, 40%, and 50%.

[0076] (4) A flexible circuit was prepared with direct writing printing parameters of a nozzle size of 100 μm, a nozzle height of 100 μm, a heating temperature of 150 °C, a direct writing speed of 35 mm·s -1 , and an extrusion pressure of 400 KPa.

[0077] (5) The prepared low-melting-point alloy inks were tested for fracture strength, peel strength, and electrical conductivity.

[0078] The properties of the low-melting-point alloy inks are as follows:

[0079] Table 2

[0080]

[0081] Example 3

[0082] (1) At room temperature, 3.43 g of SnCl2, 6.62 g of Bi(NO3)3·5H2O and 0.65 g of PVP were added successively and dissolved in 64 mL of diethylene glycol solvent. Then, the NaOH ethanol solution (1.2 mol / L, 66 mL) was added dropwise to the NaBH4 diethylene glycol solution (2.9 mol / L, 30 mL) at 0 °C, and mechanically stirred (200 rpm) for 60 min under the protection of N2 atmosphere to obtain an amorphous tin-bismuth nano-seed mixture.

[0083] (2) First, the prepared tin-bismuth nano-seed mixture was ultrasonically treated at 0 °C for 60 min, then aged at 160 °C (T l ) for 30 min, and then heated to 190 °C at a heating rate of 1 °C min -1 . After holding for 10 min, a tin-bismuth alloy filler with a particle size of 8 μm was obtained.

[0084] (3) Using a homogenizer, the tin-bismuth alloy filler, copper and tin metal elemental fillers, and organic mixed soldering flux were mixed evenly in mass fractions of 20 - 50%, 50 - 20%, and 30% in sequence, and then low-melting-point alloy inks with tin-bismuth alloy filler contents of 20%, 30%, 40%, and 50% were obtained.

[0085] (4) A flexible circuit was prepared with direct writing printing parameters of a nozzle size of 100 μm, a nozzle height of 100 μm, a heating temperature of 150 °C, and a direct writing speed of 35 mm·s -1 , and an extrusion pressure of 400 KPa.

[0086] (5) The prepared low-melting-point alloy inks were tested for fracture strength, peel strength, and electrical conductivity.

[0087] The properties of the low-melting-point alloy inks are as follows:

[0088] Table 3

[0089]

[0090] Example 4

[0091] (1) At room temperature, 3.43 g of SnCl2, 6.62 g of Bi(NO3)3·5H2O, and 0.65 g of PVP were added and dissolved in 64 mL of diethylene glycol solvent in sequence. Then, the NaOH ethanol solution (1.2 mol / L, 66 mL) was added dropwise to the NaBH4 diethylene glycol solution (2.9 mol / L, 30 mL) at 0 °C, and mechanically stirred (200 rpm) for 60 min under N2 atmosphere protection to obtain an amorphous tin-bismuth nano-seed mixture.

[0092] (2) First, the prepared tin-bismuth nano-seed mixture was ultrasonically treated at 0 °C for 60 min, then aged at 160 °C (T l ) for 30 min, and then heated to 180 °C at a heating rate of 1 °C min -1 . After holding for 40 min, a tin-bismuth alloy filler with a particle size of 15 μm was obtained.

[0093] (3) Using a homogenizer, the tin-bismuth alloy filler, copper and tin metal elemental fillers, and the organic mixed soldering flux are mixed evenly in mass fractions of 20 - 50%, 50 - 20%, and 30% in sequence to obtain low-melting-point alloy inks with tin-bismuth alloy filler contents of 20%, 30%, 40%, and 50%.

[0094] (4) With a nozzle size of 100 μm, a nozzle height of 100 μm, a heating temperature of 150 °C, and a direct writing speed of 35 mm·s -1 , a flexible circuit is prepared with a direct writing printing parameter of an extrusion pressure of 400 KPa.

[0095] (5) The prepared low-melting-point alloy inks are tested for fracture strength, peel strength, and electrical conductivity.

[0096] The properties of the low-melting-point alloy inks are as follows:

[0097] Table 4

[0098]

[0099] Example 5

[0100] (1) At room temperature, 6.62 g of Bi(NO3)3·5H2O, 2.21 g of InCl2, and 0.65 g of PVP are added and dissolved in 64 mL of diethylene glycol solvent in sequence, and then the NaOH ethanol solution (1.2 mol / L, 66 mL) is added dropwise to the NaBH4 diethylene glycol solution (2.9 mol / L, 30 mL) at 0 °C under the protection of a N2 atmosphere, and mechanically stirred (200 rpm) for 60 min to obtain an amorphous bismuth-indium nanoseed mixture.

[0101] (2) First, the prepared bismuth-indium nanoseed mixture is ultrasonically treated at 0 °C for 60 min, then cured at 160 °C (T l ) for 30 min, and then heated to 180 °C at a heating rate of 1 °C min-1 and held for 10 min to obtain bismuth-indium alloy fillers with a particle size of 3 μm.

[0102] (3) Using a homogenizer, the bismuth-indium alloy filler, copper and tin metal elemental fillers, and the organic mixed soldering flux are mixed evenly in mass fractions of 20 - 50%, 50 - 20%, and 30% in sequence to obtain low-melting-point alloy inks with bismuth-indium alloy filler contents of 20%, 30%, 40%, and 50%.

[0103] (4) With a nozzle size of 100 μm, a nozzle height of 100 μm, a heating temperature of 150 °C, and a direct writing speed of 35 mm·s -1 , a flexible circuit is prepared with a direct writing printing parameter of an extrusion pressure of 400 KPa.

[0104] (5) Test the fracture strength, peel strength, and electrical conductivity of the prepared low-melting-point alloy ink.

[0105] The properties of the low-melting-point alloy ink are as follows:

[0106] Table 5

[0107]

[0108] Example 6

[0109] (1) At room temperature, 3.43 g of SnCl2, 6.62 g of Bi(NO3)3·5H2O, and 0.65 g of PVP were successively added and dissolved in 64 mL of diethylene glycol solvent, and then the NaOH ethanol solution (1.2 mol / L, 66 mL) was gradually added dropwise to the NaBH4 diethylene glycol solution (2.9 mol / L, 30 mL) at 0 °C. Under the protection of N2 atmosphere, mechanical stirring (200 rpm) was carried out for 60 min to obtain an amorphous tin-bismuth nanoseed mixture.

[0110] (2) First, the prepared tin-bismuth nanoseed mixture was ultrasonically treated at 0 °C for 60 min, then cured at 160 °C (T l ) for 30 min, and then heated to 180 °C at a heating rate of 1 °C / min -1 and held for 10 min to obtain tin-bismuth alloy fillers with a particle size of 3 μm.

[0111] (3) Using a homogenizer, the tin-bismuth alloy fillers, silver and indium metal single fillers, and organic mixed soldering fluxes were mixed evenly in mass fractions of 20 - 50%, 50 - 20%, and 30% in turn to obtain low-melting-point alloy inks with tin-bismuth alloy filler contents of 20%, 30%, 40%, and 50%.

[0112] (4) Using the direct writing printing parameters of nozzle size 100 μm, nozzle height 100 μm, heating temperature 150 °C, and direct writing speed 35 mm·s -1 , and extrusion pressure 400 KPa to prepare a flexible circuit.

[0113] (5) Test the fracture strength, peel strength, and electrical conductivity of the prepared low-melting-point alloy ink.

[0114] The properties of the low-melting-point alloy ink are as follows:

[0115] Table 6

[0116]

[0117] Example 7

[0118] (1) At room temperature, 3.43 g of SnCl2, 6.62 g of Bi(NO3)3·5H2O and 0.65 g of PVP were successively added and dissolved in 64 mL of diethylene glycol solvent. Then, the NaOH ethanol solution (1.2 mol / L, 66 mL) was gradually added dropwise to the NaBH4 diethylene glycol solution (2.9 mol / L, 30 mL) at 0 °C. Under the protection of N2 atmosphere, mechanical stirring (200 rpm) was carried out for 60 min to obtain an amorphous tin-bismuth nanoseed mixture.

[0119] (2) First, the prepared tin-bismuth nanoseed mixture was ultrasonically treated at 0 °C for 60 min, then aged at 160 °C (T l ) for 30 min, and then heated to 180 °C at a heating rate of 1 °C min -1 . After holding for 10 min, a tin-bismuth alloy filler with a particle size of 3 μm was obtained.

[0120] (3) Using a homogenizer, the tin-bismuth alloy filler, copper and tin metal elemental fillers, and organic mixed soldering flux were mixed evenly in mass fractions of 20 - 50%, 60 - 30%, and 30% in turn to obtain low-melting-point alloy inks with tin-bismuth alloy filler contents of 20%, 30%, 40%, and 50%.

[0121] (4) Using a direct writing printing parameter with a nozzle size of 200 μm, a nozzle height of 150 μm, a heating temperature of 170 °C, and a direct writing speed of 30 mm·s -1 , and an extrusion pressure of 300 KPa, a flexible circuit was prepared.

[0122] (5) The prepared low-melting-point alloy inks were tested for fracture strength, peel strength, and electrical conductivity.

[0123] The properties of the low-melting-point alloy inks are as follows:

[0124] Table 7

[0125]

[0126] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low melting point alloy ink, characterized in that, It is made by mixing 20 - 50% alloy filler, 30 - 70% metal elemental filler and 10 - 30% organic mixed soldering flux by mass percentage; The metal elemental filler includes one or more of copper, tin, silver, nickel, and aluminum; The organic mixed soldering flux is obtained by mixing tripropylene glycol monobutyl ether, suberic acid, vinyl laurate, dimethyl cyclohexanone, and citric acid in volume fractions of 10 - 20%, 5 - 12%, 25 - 45%, 20 - 40%, and 5 - 12% in sequence; The preparation method of the alloy filler is as follows: Prepare an amorphous alloy nanoseed mixture by low-temperature co-reduction of a mixed metal salt solution; Control the temperature for ripening growth of the alloy nanoseed mixture to prepare the alloy filler; The average particle size of the amorphous alloy nanoseeds is 3 - 100 nm; the average particle size of the alloy filler is 1 - 20 μm and the melting point is lower than 180 °C; The metal salts are selected from tin salts and bismuth salts, and the mixing mass ratio of the tin salt to the bismuth salt is 3 - 4:6 - 7; The tin salt is selected from tin chloride, tin nitrate, stannous sulfate, and the bismuth salt is selected from bismuth chloride, bismuth nitrate, and bismuth citrate.

2. The low-melting-point alloy ink according to claim 1, wherein: The low-temperature co-reduction means dropping the mixed metal salt solution into a reducing agent solution at 0 °C and mechanically stirring for 10 - 90 min under the protection of an N2 atmosphere.

3. The low-melting-point alloy ink according to claim 1, wherein: The temperature-controlled ripening growth is a two-step heat treatment. The temperature of the first heat treatment is 100 - 160 °C, and the heat treatment time is 10 - 60 min. The second step is to heat to 170 - 190 °C at a heating rate of 0.5 - 1 °C / min and hold for 10 - 60 min.

4. The low-melting-point alloy ink according to claim 1, characterized in that: The usage method of the low-melting-point alloy ink is as follows: Prepare a flexible circuit by a direct writing process using the low-melting-point alloy ink as a raw material; The direct writing process includes multi-dimensional regulation of direct writing printing parameters to achieve temperature-controlled melting and extrusion, directly obtaining a conductive path. The direct writing printing parameters include nozzle size, nozzle height, heating temperature, direct writing speed, and extrusion pressure.

5. The application of the low-melting-point alloy ink according to claim 1 in the fields of flexible circuit board printing, flexible hybrid electronic device packaging, semiconductor packaging, flexible photovoltaics, flexible displays, and flexible sensors.

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