Low-temperature curing weldable conductive paste and preparation method and application thereof

Abstract

The invention provides low-temperature curing weldable conductive paste as well as a preparation method and application thereof, and belongs to the technical field of printed electronic materials. The weldable conductive paste comprises the following components by mass: 11-15% of an organic carrier; 70-85% of a conductive component; 0-19% of an organic solvent; the organic carrier comprises a rosin solution, epoxy resin and a latent curing agent; the conductive component is a micron silver sheet loaded with nano silver oxide; the length of the silver sheet is 1-15 [mu] m; the particle size of the nano silver oxide is 200 to 400 nm. According to the low-temperature cured weldable conductive silver paste provided by the invention, the wettability of the solder on the silver ink layer can be improved, so that the welding binding force is improved; and meanwhile, a silver ink layer printed by the paste has relatively high conductivity.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of printed electronic materials, and particularly relates to a low-temperature cured solderable conductive paste as well as a preparation method and application thereof. BACKGROUND

[0002] Surface Mount Technology (SMT) uses solder paste or solder wire as solder to realize the connection between electronic devices and printed circuit boards (PCB) prepared by etching method, and is widely applied in the field of PCB. When SMT is applied to printed silver paste circuit, the rapid connection between electronic devices and silver paste circuit can be realized without changing the existing soldering process, which requires the silver paste to be solderable.

[0003] High-temperature cured silver paste is mainly used in the fields of silicon-based solar cells and ceramic circuits, and during the high-temperature curing process, silver particles are sintered into bulk silver film with high melting point, so that the solderability is good, and the solder tin is easy to wet on the silver film, thereby realizing high soldering tension. Low-temperature cured silver paste is mainly used to prepare conductive circuits on substrates that are not resistant to high temperature (such as nylon cloth, PET, paper, etc.), and has become one of the important applications of flexible printed electronics. After curing, the surface of the silver paste circuit is a mixture layer of conductive particles and organic resin. However, the commonly used organic resin cannot withstand the high temperature of molten solder, causing the silver paste circuit to deform or disappear instantaneously. Therefore, improving the solderability of low-temperature cured silver paste is crucial for its application. Even if a high-temperature resistant organic resin is used, since the silver particles in the low-temperature cured silver paste are not sintered into a silver film, the bonding force between the solder tin and the silver ink layer is weak, which seriously affects the service life.

[0004] The solderability of low-temperature cured silver paste is reflected in two aspects: the circuit formed after the silver paste is cured can withstand the relatively high temperature of molten solder during the soldering process; and a firm physical connection is formed between the solder and the silver ink layer. For the former, a high-temperature resistant resin needs to be used as the connecting material in the silver paste to enable the silver paste circuit to withstand the high temperature of the solder, and a resin with a high Tg after curing needs to be selected. For the latter, since the silver particles in the low-temperature cured silver paste are not sintered into a silver film and there is organic resin on the surface of the ink layer, the bonding force between the solder tin and the silver ink layer is weak. The existing technology discloses a method for improving the soldering bonding force: adding Mxene or silver-indium alloy to silver paste based on micron-level flaky silver powder, spherical silver powder and nano silver powder. This method improves the soldering bonding force by introducing other conductive components. The wettability of molten solder on the surface of the silver ink layer affects the contact area of the two, and directly determines the size of the soldering bonding force. There is no related report on improving the soldering bonding force of the two by changing the composition of the silver ink layer to improve the wettability of the solder on the silver ink layer. SUMMARY

[0005] Therefore, the present application aims to provide a low-temperature cured solderable conductive paste, a preparation method and application thereof.

[0006] In order to achieve the above-mentioned purpose, the present application provides the following solutions.

[0007] The present application provides a low-temperature cured solderable conductive paste, which comprises the following components by mass:

[0008] The organic carrier is 11-15%;

[0009] The conductive component is 70-85%;

[0010] The organic solvent is 0-19%;

[0011] The organic carrier comprises rosin solution, epoxy resin and latent curing agent;

[0012] The conductive component is micron silver flake loaded with nano silver oxide;

[0013] The length of the micron silver flake is 1-15 μm; and the average particle size of the nano silver oxide is 200-400 nm.

[0014] Preferably, the epoxy resin comprises one or more of organosilicon modified epoxy resin, isocyanate modified epoxy resin and multifunctional epoxy resin; and the latent curing agent comprises one or more of dicyandiamide curing agent, microcapsule type curing agent and modified imidazole type curing agent.

[0015] Preferably, the rosin solution is obtained by dissolving rosin in alcohol and / or alcohol ether; the rosin comprises one or more of natural rosin, hydrogenated rosin, polymerized rosin, disproportionated rosin, maleic acid modified rosin, fumaric acid modified rosin and acrylic acid modified rosin; and the mass concentration of the rosin solution is 25%.

[0016] Preferably, the organic solvent comprises one or more of butyl acetate, ethanol, ethyl acetate, diethylene glycol methyl ether, diethylene glycol butyl ether, dibasic acid ester, cyclohexanone, ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, propylene glycol methyl ether acetate and diethylene glycol butyl ether acetate.

[0017] Preferably, the mass ratio of the rosin solution to the total mass of the epoxy resin and the latent curing agent is (3-5):(2-10).

[0018] Preferably, in the conductive component, the mass ratio of the nano silver oxide to the micron silver flake is (5-20):(80-95).

[0019] The application provides a preparation method of the low-temperature cured solderable conductive paste, comprising the following steps:

[0020] The organic carrier, the conductive component and the organic solvent are mixed to obtain the low-temperature cured solderable conductive paste.

[0021] The application provides application of the low-temperature cured solderable conductive paste or the low-temperature cured solderable conductive paste prepared by the preparation method in connection of electronic components.

[0022] Preferably, the application method comprises the following steps:

[0023] The low-temperature cured solderable conductive paste is printed on a substrate, heat curing is performed to obtain the silver ink layer, and electronic components are connected to the surface of the silver ink layer by soldering.

[0024] Preferably, the heat curing temperature is 110-130 DEG C, and the holding time is 40-60 min.

[0025] The application provides a low-temperature cured solderable conductive paste, which comprises the following components in mass content: 11-15% of an organic carrier; 70-85% of a conductive component; and 0-19% of an organic solvent; the organic carrier comprises a rosin solution, an epoxy resin and a latent curing agent; the conductive component is micron silver flake loaded with nano silver oxide; the length of the micron silver flake is 1-15 microns; and the average particle size of the nano silver oxide is 200-400 nanometers. The micron silver flake loaded with nano silver oxide is used as the conductive component, the high-temperature resistant epoxy resin is selected and the rosin solution is added as the organic carrier to prepare the solderable conductive paste without changing the materials and welding process used in the existing welding technology. In the low-temperature curing (120-130 DEG C) process of the printed silver paste, the esterification reaction occurs between the carboxyl group on the rosin and the epoxy group in the epoxy resin, the surface energy of the silver ink layer is improved, the wettability of the solder on the silver ink layer is improved, the contact area between the solder and the silver ink layer is increased, and thus the bonding strength between the solder and the silver ink layer is improved. Meanwhile, the nano silver oxide loaded on the micron silver flake reacts with the rosin in the low-temperature curing process of the printed silver paste to form nano silver particles in situ, the nano silver particles are bridged between the micron silver flakes, the contact resistance between the micron silver flakes is reduced, the electronic transmission path is increased, and thus the conductivity of the silver ink layer is improved. The problem that the silver nano particles cannot be guaranteed to be bridged between the micron silver flakes when the silver nano particles are used as the auxiliary conductive component and are physically mixed into the micron silver flakes is avoided. The silver ink layer formed by the printed conductive paste can meet the solderability requirements of the electric soldering iron, reflow soldering and other processes, the problem of insufficient bonding strength between the solder and the silver ink layer caused by poor tin on the conductive layer in the prior art is solved, and the fast and firm electrical connection between the conductive silver paste and the electronic components is facilitated. Meanwhile, the in-situ formed nano silver particles are used to improve the conductive path between the micron silver flakes, and the printed ink layer has high conductivity.

[0026] The silver paste provided by the application has high conductivity, high solderability, strong interface bonding and environmental friendliness, and meets the high-reliability interconnection requirements of the flexible printed silver paste circuit and external electronic components in wearable electronic devices, medical electronics, laptop keyboards and other devices. The conductive paste provided by the application is suitable for different substrates, and is particularly suitable for high-temperature-resistant fabrics, plastics, paper and other substrates. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0028] Figure 1 Flow chart for preparing the low-temperature cured solderable conductive paste of the present application. DETAILED DESCRIPTION

[0029] The present application provides a low-temperature cured solderable conductive paste, comprising the following components by mass content:

[0030] organic vehicle 11-15%;

[0031] conductive component 70-85%;

[0032] organic solvent 0-19%;

[0033] The organic vehicle comprises rosin solution, epoxy resin and latent curing agent.

[0034] The conductive component is micron silver flake loaded with nano silver oxide.

[0035] The micron silver flake has a length of 1-15 μm; and the nano silver oxide has an average particle size of 200-400 nm.

[0036] Unless otherwise specified, the materials and equipment used in the present application are commercially available.

[0037] The low-temperature cured solderable conductive paste provided by the present application comprises, by mass content, organic vehicle 11-15%, which in the embodiments of the present application can be specifically 11, 12, 13, 14 or 15%. In the present application, the organic vehicle comprises rosin solution, epoxy resin and latent curing agent; the rosin solution is preferably obtained by dissolving rosin in alcohol and / or alcohol ether; the rosin preferably comprises one or more of natural rosin, hydrogenated rosin, polymerized rosin, disproportionated rosin, maleic acid modified rosin, fumaric acid modified rosin and acrylic acid modified rosin; the alcohol preferably comprises preferably glycerol, isopropyl alcohol or ethanol; the alcohol ether preferably comprises diethylene glycol butyl ether or diethylene glycol methyl ether; the mass concentration of the rosin solution is preferably 25%; and the dissolving temperature is preferably 60°C.

[0038] In the present application, the epoxy resin is preferably high-temperature resistant epoxy resin, which can resist the high temperature (200-250°C) of molten solder after crosslinking and curing with the curing agent; the epoxy resin preferably comprises one or more of silicone modified epoxy resin, isocyanate modified epoxy resin and multifunctional epoxy resin; the silicone modified epoxy resin preferably comprises one or more of hydroxyl-terminated polydimethylsiloxane modified epoxy resin, amino-terminated polydimethylsiloxane modified epoxy resin, epoxy-terminated polydimethylsiloxane modified epoxy resin, 3-glycidyloxypropyltrimethoxysilane modified epoxy resin and γ-aminopropyltriethoxysilane modified epoxy resin.

[0039] In the present application, the isocyanate-modified epoxy resin preferably includes a diphenylmethane diisocyanate (MDI)-modified epoxy resin, a hexamethylene diisocyanate (HDI)-modified epoxy resin, a toluene diisocyanate (TDI)-modified epoxy resin, or a 1,5-naphthalene diisocyanate (NDI)-modified epoxy resin.

[0040] In the present application, the multifunctional epoxy resin preferably includes an alicyclic glycidyl ester type epoxy resin, a polyaromatic glycidyl amine type epoxy resin, or a polyphenol glycidyl ether type epoxy resin.

[0041] In the present application, the alicyclic glycidyl ester type multifunctional epoxy resin preferably includes 4,5-epoxycyclohexane-1,2-dicarboxylic acid diglycidyl ester (SWE-90); in the present application, the polyaromatic glycidyl amine type multifunctional epoxy resin preferably includes SW-70 or SW-80. In the present application, the polyphenol glycidyl ether preferably includes resorcinol formaldehyde epoxy, SW-0510, SRN-510, SRN-505, or SRN-8300. In the present application, the phenyl structural unit present in the multifunctional epoxy resin structure and its higher epoxy functionality can make the resin have a high crosslinking density after curing, good thermal stability, and a glass transition temperature of 230-280℃.

[0042] The high-temperature-resistant epoxy resin used in the present application has both high adhesion and resistance to welding temperature impact (200-250℃), and the high-temperature-resistant epoxy resin can still withstand reflow soldering temperature after low-temperature curing, enhancing the anti-aging performance, and is particularly suitable for high-reliability scenarios (such as medical electronics and wearable devices).

[0043] In the present application, the latent curing agent can make the conductive paste have a longer storage and use time; the latent curing agent preferably includes one or more of a dicyandiamide curing agent, a microcapsule type curing agent, and a modified imidazole type curing agent. In the present application, the microcapsule type curing agent preferably includes a liquid microcapsule type latent curing agent; the modified imidazole type curing agent preferably includes a modified imidazole curing agent of the PN series of AJICURE (Japan Ajinomoto).

[0044] In the present application, the preparation method of the organic carrier preferably includes the following steps:

[0045] The rosin solution, the epoxy resin, and the latent curing agent are first mixed to obtain the organic carrier.

[0046] In the present application, the mass ratio of the epoxy resin to the latent curing agent is preferably (12-20):1, and in the embodiments of the present application, it can be specifically 12:1, 12.5:1, 15:1, 15.67:1, 18:1, or 20:1.

[0047] When the epoxy resin is a multi-aromatic ring glycidyl amine type multi-functionality epoxy resin (solid at room temperature), the preparation of the organic carrier also preferably involves the additional addition of a first organic solvent; the first organic solvent preferably includes a dibasic ester (DBE), and the first organic solvent is used to dissolve the solid epoxy resin; the mass ratio of the epoxy resin and the first organic solvent is preferably 1.88:8.

[0048] In the present application, the mass ratio of the rosin solution to the total mass of the epoxy resin and the latent curing agent is preferably (3-5):(2-10), and in the embodiments of the present application, it can be specifically 5:10, 5:2, 3:2, 3:8 or 3:10.

[0049] In the present application, the first mixing is preferably carried out under the condition of planetary mixing homogenization; the rotation speed of the homogenization is 1000 r / min for revolution and 350 r / min for rotation, and the time is 3 min.

[0050] The low-temperature cured solderable conductive paste provided by the present application includes 0-19% of an organic solvent (denoted as a second organic solvent) in terms of mass content, and in the embodiments of the present application, it can be specifically 0%, 3%, 4%, 5%, 8%, 10%, 13%, 15%, 17% or 19%; the second organic solvent preferably does not include the alcohol and / or alcohol ether in the rosin solution. In the present application, the second organic solvent preferably includes butyl acetate, ethanol, ethyl acetate, diethylene glycol methyl ether, diethylene glycol butyl ether, a dibasic ester, cyclohexanone, ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, propylene glycol methyl ether acetate and diethylene glycol butyl ether acetate. The second organic solvent in the present application is used to adjust the viscosity of the conductive paste to meet the printing requirements, and when the viscosity of the conductive paste meets the printing requirements, the second organic solvent can not be added.

[0051] The low-temperature cured solderable conductive paste provided by the present application includes 70-85% of a conductive component in terms of mass content, and in the embodiments of the present application, it can be specifically 70%, 75%, 80%, 82% or 85%; the conductive component is micron silver flake loaded with nano silver oxide; the length of the micron silver flake is 1-15 μm, and in the embodiments of the present application, it can be specifically 1 μm, 5 μm, 10 μm or 15 μm; the average particle size of the nano silver oxide is 200-400 nm.

[0052] In the present application, the preparation method of the conductive component preferably includes the following steps:

[0053] The soluble silver salt, the alcohol solvent, the alkaline solution and the micron silver flake are second mixed to carry out a precipitation reaction to generate a silver hydroxide precipitate, the silver hydroxide precipitate is decomposed to obtain nano silver oxide and is loaded on the micron silver flake to obtain a conductive component; the alkaline solution comprises an alkaline hydroxide solution.

[0054] In the application, the alkaline solution preferably comprises a sodium hydroxide solution or a potassium hydroxide solution; the concentration of the alkaline solution is preferably 0.5 mol / L; the alkaline solution preferably comprises an alcohol solution of alkaline hydroxide.

[0055] In the application, the soluble silver salt preferably comprises silver nitrate; the alcohol solvent preferably comprises ethanol. The application does not have special requirements for the micron silver flake, and the length of the micron silver flake can be 1-15 μm.

[0056] In the application, the mass ratio of the soluble silver salt to the volume of the alcohol solvent is preferably (0.85-3.5) g:1400 mL, and in the embodiments of the application, the mass ratio can be specifically 0.85 g:1400 mL, 1.0 g:1400 mL, 1.698 g:1400 mL or 3.5 g:1400 mL. In the application, the mass ratio of the soluble silver salt to the micron silver flake is preferably (0.85-3.5):10, and in the embodiments of the application, the mass ratio can be specifically 0.5:10, 1.698:10 or 3.5:10.

[0057] In the application, the precipitation reaction is carried out under the condition that the pH is 8-10. The application does not have special requirements for the amount of the alkaline solution, and the pH value of the mixed solution can be adjusted to 8-10 so as to generate the silver hydroxide precipitate.

[0058] In the application, the generation of the nano silver oxide is preferably carried out under the condition of stirring, and the stirring speed is preferably 500 r / min, and the time is preferably 15 h.

[0059] After the micron silver flake loaded with the nano silver oxide is obtained, the application preferably mixes the obtained reaction liquid with ethanol-water, washes and suction filters three times, and vacuum dries the obtained solid.

[0060] In the application, the temperature of the vacuum drying is preferably 60°C, and the time is preferably 12 hours. In the conductive component, the mass ratio of the nano silver oxide to the micron silver flake is preferably (5-20):(80-95), and in the embodiments of the application, the mass ratio can be specifically 10:90, 5:95 or 20:80; the volume ratio of the ethanol to the water is preferably 1:1.

[0061] The application adopts micron silver flake loaded with nano silver oxide as a conductive component, selects high-temperature-resistant epoxy resin and adds rosin solution as an organic carrier to prepare the solderable conductive paste without changing the materials and welding process of the existing welding technology. During the low-temperature curing (120-130 DEG C) of the printed silver paste, the esterification reaction occurs between the carboxyl group on the rosin and the epoxy group in the epoxy resin, the surface energy of the silver ink layer is improved, the wettability of the solder on the silver ink layer is improved, the contact area between the solder and the silver ink layer is increased, and thus the bonding strength between the solder and the silver ink layer is improved. Meanwhile, the nano silver oxide loaded on the micron silver flake reacts with the rosin during the low-temperature curing of the printed silver paste, and the nano silver particles are formed in situ, the nano silver particles are bridged between the micron silver flakes, the contact resistance between the micron silver flakes is reduced, the electronic transmission path is increased, and thus the conductivity of the silver ink layer is improved. The problem that the silver nano particles cannot be guaranteed to be bridged between the micron silver flakes when the silver nano particles are introduced into the micron silver flakes as an auxiliary conductive component (only physical mixing) is avoided. The silver ink layer formed by printing and low-temperature curing of the conductive paste of the application can meet the solderability requirements of the electric soldering iron, reflow soldering and other processes, the problem of insufficient bonding strength between the solder and the silver ink layer caused by poor tin on the conductive layer in the prior art is solved, and the fast and firm electrical connection between the conductive silver paste and the electronic components is facilitated. Meanwhile, the in-situ formed nano silver particles are used to improve the conductive path between the micron silver flakes, and the printed ink layer has high conductivity.

[0062] The silver paste of the conductive paste has high conductivity, high solderability, strong interface bonding and environmental friendliness, and meets the high-reliability interconnection requirements of the flexible printed silver paste circuit and external electronic components in wearable electronic devices, medical electronics, laptop keyboards and other devices. The conductive paste provided by the application is suitable for different substrates, and is particularly suitable for high-temperature-resistant fabrics, plastics, paper and other substrates.

[0063] The application provides a preparation method of the low-temperature cured solderable conductive paste described in the above scheme, including the following steps:

[0064] The organic carrier, the conductive component and the organic solvent are mixed (marked as the third mixing) to obtain the low-temperature cured solderable conductive paste.

[0065] In the application, the third mixing preferably includes adding the conductive component into the organic carrier in batches, and adding the organic solvent (i.e. the second organic solvent) after homogenization and grinding dispersion. In the application, the number of batches is preferably 3-5 times. The application can avoid local agglomeration caused by adding a large amount of conductive components at one time, and is beneficial to the dispersion of the conductive paste. The application can adjust the viscosity of the conductive paste by adding the second organic solvent, and meet the requirements of silk screen printing.

[0066] The application provides application of the low-temperature cured solderable conductive paste described in the above scheme or the low-temperature cured solderable conductive paste prepared by the preparation method described in the above scheme in connection of electronic components.

[0067] In the application, the method for the application preferably comprises the following steps:

[0068] The low-temperature cured solderable conductive paste is printed on a substrate, and is subjected to heat curing to obtain the silver ink layer, and electronic components are connected on the surface of the silver ink layer by soldering.

[0069] In the application, the substrate preferably comprises a polyester fabric, a nylon fabric, a spandex fabric, a polyester plastic film, a polyimide plastic film or an inkjet printing photo paper. In the application, the temperature of the heat curing is preferably 110-130 DEG C, and in the embodiments of the application, can be specifically 110 DEG C, 120 DEG C or 130 DEG C; the holding time is preferably 40-60 min, and in the embodiments of the application, can be specifically 40 min, 50 min or 60 min. In the application, the soldering is well wetted on the silver ink layer and forms a strong binding force.

[0070] In order to further illustrate the application, the low-temperature cured solderable conductive paste, the preparation method and the application thereof provided by the application are described in detail below in combination with the drawings and the embodiments, but they should not be understood as limiting the protection scope of the application.

[0071] Embodiment 1

[0072] Preparation of micron silver flake loaded with nano silver oxide

[0073] 1.698 g of silver nitrate is dissolved in 1400 mL of ethanol, 20 mL of 0.5 mol / L NaOH ethanol solution is added to adjust the pH value of the silver nitrate solution to 9, and then 10 g of micron silver flake (8 μm in length) is added, the obtained mixed solution is stirred at a speed of 500 r / min at room temperature for 15 h, so that the nano silver oxide particles generated in the reaction are loaded on the micron silver flake;

[0074] Finally, the reaction solution is mixed with an ethanol-water (volume ratio 1:1) mixed solvent, washed and suction-filtered three times, and the obtained solid is dried in a vacuum oven at 60 DEG C for 12 h to obtain a composite material powder with a weight ratio of Ag2O / silver flake of 10:90, that is, the conductive component: micron silver flake loaded with nano silver oxide.

[0075] Preparation of an organic carrier

[0076] Glycerol and hydrogenated rosin are weighed and mixed respectively, and are stirred at a high speed (500 r / min) at 60 DEG C until the rosin is dissolved to obtain a rosin solution with a mass concentration of 25%.

[0077] In 5 g of rosin solution, a mixture of hexamethylene diisocyanate (HDI) modified epoxy resin (SQE-1401GT) and modified imidazole curing agent (PN-30) with a total mass of 10 g (mass ratio of epoxy resin and latent curing agent is 100:8) was added, and was pre-dispersed in a planetary homogenizer with a revolution speed of 1000 r / min and a rotation speed of 350 r / min for 3 min to obtain an organic carrier.

[0078] Preparation of low-temperature cured solderable conductive silver paste

[0079] In 1.5 g of the organic carrier, 8.2 g of the conductive component was added in batches, pre-mixed using a planetary homogenizer, and then ground and dispersed using a three-roll mill. Finally, 0.3 g of dibasic acid ester DBE solvent was added to adjust the viscosity to 8300±480 cP to obtain a low-temperature cured solderable conductive silver paste.

[0080] Printing of low-temperature cured solderable conductive silver paste

[0081] The prepared conductive silver paste was printed on a spandex fabric using a 200-mesh screen, and was cured at 130°C for 40 min to obtain a solderable silver ink layer with a film thickness of 30 μm.

[0082] The contact angle of 10 μL of molten lead-free solder tin (SAC305) on the silver ink layer was 25°, the shear strength of the solder tin on the solderable silver ink layer was 27 MPa, and the square resistance of the printed conductive pattern was 9.6 mΩ / □.

[0083] Example 2

[0084] Preparation of micron silver flake loaded with nano silver oxide

[0085] 1.698 g of silver nitrate was dissolved in 1400 mL of ethanol, 20 mL of 0.5 mol / L NaOH ethanol solution was added to adjust the pH of the silver nitrate solution to 9, and then 10 g of micron silver flake (length of 15 μm) was added. The resulting mixed solution was stirred at a speed of 500 r / min at room temperature for 15 h, so that the silver oxide nanoparticles generated in the reaction were loaded on the micron silver flake.

[0086] Finally, the reaction solution was mixed with a mixed solvent of ethanol-water (volume ratio 1:1), washed and filtered three times, and the resulting solid was dried in a vacuum oven at 60°C for 12 h to obtain a composite material powder with a weight ratio of Ag2O / silver flake of 10:90, i.e., a conductive component: micron silver flake loaded with nano silver oxide.

[0087] Preparation of organic carrier

[0088] Weigh out diethylene glycol butyl ether and hydrogenated rosin, mix them, and stir at high speed (500 r / min) at 60℃ until the hydrogenated rosin dissolves to obtain a hydrogenated rosin solution with a mass concentration of 25%.

[0089] Weigh 1.88g of polyaromatic glycidylamine type multifunctional epoxy resin (SW-80) and 8g of diester DBE, heat them to 60℃ and keep the temperature constant until the resin dissolves. After the solution cools, add 0.12g of dicyandiamide curing agent and 5g of hydrogenated rosin solution, and place them in a planetary homogenizer for pre-dispersion at a rotation speed of 1000r / min and a rotation speed of 350r / min for 3min to obtain the organic carrier.

[0090] Preparation of Low-Temperature Curing Solderable Conductive Silver Paste

[0091] 7g of conductive component was added in batches to 1.5g of organic carrier, premixed into a slurry using a planetary homogenizer, then dispersed by grinding using a three-roll mill, and finally 1.5g of diester DBE was added to adjust the viscosity to 7500±350cP. After stirring, a low-temperature curing solderable conductive silver paste was obtained.

[0092] Printing of low-temperature curing solderable conductive silver paste

[0093] Low-temperature curable solderable conductive silver paste was printed onto a polyester plastic film using a 200-mesh screen and cured at 120°C for 60 minutes to obtain a solderable silver ink layer with a film thickness of 25 μm.

[0094] The contact angle of 10 μL of molten lead-free solder (SAC305) on the silver layer is 32°, the shear strength of the solder on the solderable silver layer is 18 MPa, and the sheet resistance of the printed conductive pattern is 20.4 mΩ / □.

[0095] Example 3

[0096] Preparation of micron-sized silver sheets loaded with nano-silver oxide

[0097] 1.698 g of silver nitrate was dissolved in 1400 mL of ethanol. 20 mL of 0.5 mol / L NaOH ethanol solution was added to adjust the pH of the silver nitrate solution to 9. Then, 10 g of micron-sized silver sheet (12 μm in length) was added. The resulting mixture was stirred at 500 r / min for 15 h at room temperature to load the silver oxide nanoparticles generated in the reaction onto the micron-sized silver sheet.

[0098] Finally, the reaction solution was mixed with an ethanol-water (volume ratio 1:1) mixed solvent, washed and filtered three times, and the resulting solid was dried in a vacuum oven at 60°C for 12 hours to obtain a composite material powder with an Ag2O / silver sheet weight ratio of 10:90, namely, the conductive component: micron-sized silver sheets loaded with nano-silver oxide.

[0099] Preparation of organic vehicle

[0100] Isopropanol and polymerized rosin were weighed separately and mixed, and stirred at high speed (500 r / min) at 60°C until the polymerized rosin was dissolved, to obtain a 25% mass concentration of polymerized rosin solution.

[0101] 7.52 g of hydroxyl-terminated polydimethylsiloxane-modified epoxy resin (preparation method reference: Hydroxyl-terminated polydimethylsiloxane-modified epoxy resin resistance performance research, Liaoning Chemical Industry Journal 2024, Vol. 53, 1499-1504), 0.48 g of liquid microcapsule type latent curing agent, and 3 g of polymerized rosin solution were weighed and pre-dispersed in a planetary homogenizer at a revolution speed of 1000 r / min and a rotation speed of 350 r / min for 3 min to obtain the organic vehicle.

[0102] Preparation of low-temperature cured solderable conductive silver paste

[0103] 8.5 g of conductive component was added in batches to 1.1 g of organic vehicle, pre-mixed into a paste using a planetary homogenizer, and then ground and dispersed using a three-roll mill. Finally, 0.4 g of diethylene glycol butyl ether acetate was added to adjust the viscosity to 9800±280 cP, and stirring was performed to obtain the low-temperature cured solderable conductive silver paste.

[0104] Printing of low-temperature cured solderable conductive silver paste

[0105] The low-temperature cured solderable conductive silver paste was printed on an inkjet printing photo paper using a 200-mesh screen, and cured at 120°C for 60 min to obtain a solderable silver ink layer with a film thickness of 35 μm.

[0106] The contact angle of 10 μL of molten lead-free solder (SAC305) on the silver ink layer was 39°, the shear strength of the solder (SAC305) on the solderable silver ink layer was 15 MPa, and the square resistance of the printed conductive pattern was 9.3 mΩ / □.

[0107] Comparative Example 1

[0108] The preparation method was the same as that of Example 1, except that rosin was not added.

[0109] The contact angle of molten lead-free solder (SAC305) on the silver ink layer was 142°, and the shear strength of the solder (SAC305) on the silver ink layer was 3.8 MPa.

[0110] Comparative Example 2

[0111] The preparation method was the same as that of Example 3, except that nano-silver oxide was not loaded on the micron silver flake, and the micron silver flake was directly used as the conductive component.

[0112] The printed conductive pattern has a square resistance of 78.6 mΩ / □.

[0113] Although the above embodiments have been described in detail, they are only some embodiments of the present application, not all embodiments. Other embodiments can be obtained by those skilled in the art without creativity on the basis of the above embodiments, and these embodiments also belong to the protection scope of the present application.

Claims

1. A low-temperature curing, weldable conductive paste, characterized in that, The components include the following mass content: Organic carrier 11-15%; Conductive component 70-85%; Organic solvents 0–19%; The organic carrier includes rosin solution, epoxy resin, and latent curing agent; The conductive component is a micron-sized silver sheet loaded with nano-silver oxide; The length of the micron-sized silver sheet is 1–15 μm; the average particle size of the nano-silver oxide is 200–400 nm.

2. The weldable conductive paste according to claim 1, characterized in that, The epoxy resin includes one or more of silicone-modified epoxy resin, isocyanate-modified epoxy resin, and multifunctional epoxy resin; the latent curing agent includes one or more of dicyandiamide curing agents, microencapsulated curing agents, and modified imidazole curing agents.

3. The weldable conductive paste according to claim 1, characterized in that, The rosin solution is obtained by dissolving rosin in alcohol and / or alcohol ether; the rosin includes one or more of natural rosin, hydrogenated rosin, polymerized rosin, disproportionated rosin, maleic acid modified rosin, fumaric acid modified rosin, and acrylic acid modified rosin; the mass concentration of the rosin solution is 25%.

4. The weldable conductive paste according to claim 1, 2, or 3, characterized in that, The organic solvent includes one or more of butyl acetate, ethanol, ethyl acetate, diethylene glycol methyl ether, diethylene glycol butyl ether, dicarboxylic acid ester, cyclohexanone, ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, propylene glycol methyl ether acetate, and diethylene glycol butyl ether acetate.

5. The weldable conductive paste according to claim 1, 2 or 3, characterized in that, The mass ratio of the rosin solution to the total mass of the epoxy resin and the latent curing agent is (3-5):(2-10).

6. The weldable conductive paste according to claim 1, characterized in that, In the conductive component, the mass ratio of nano-silver oxide to micron-sized silver flakes is (5-20):(80-95).

7. The method for preparing the low-temperature curing solderable conductive paste according to any one of claims 1 to 6, characterized in that, Includes the following steps: The organic carrier, conductive component and organic solvent are mixed to obtain the low-temperature curing weldable conductive paste.

8. The application of the low-temperature curing solderable conductive paste according to any one of claims 1 to 6 or the low-temperature curing solderable conductive paste prepared by the preparation method according to claim 7 in connecting electronic components.

9. The application according to claim 8, characterized in that, The method of application includes the following steps: The low-temperature curable solderable conductive paste is printed on a substrate and then thermally cured to obtain the silver ink layer. Electronic components are then connected to the surface of the silver ink layer using solder.

10. The application according to claim 9, characterized in that, The thermosetting temperature is 110–130°C, and the holding time is 40–60 min.

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