Low-temperature sintering copper paste, preparation method and application thereof

Abstract

This invention discloses a low-temperature sintering copper paste, its preparation method, and its application, belonging to the field of conductive copper paste. The preparation method includes adding deionized water to a reducing agent, dissolving it, adding copper salt, stirring copper particles evenly, adjusting the pH, reacting to generate a copper particle composite protected by nano-copper(II) hydride, washing the composite until the pH becomes neutral, and drying to obtain a copper particle composite coated with nano-copper(II) hydride. Then, an organic carboxylic acid is added to the obtained copper particle composite for surface modification treatment, and resin and solvent are added to the treated composite to obtain a slurry of nano-copper(II) hydride / copper composite particles. This invention's preparation method can coat the surface of copper particles with a layer of nano-copper(II) hydride, achieving anti-oxidation sintering between particles at low temperatures.

Description

Technical Field

[0001] This invention relates to the field of conductive copper paste technology, and in particular to a low-temperature sintering copper paste comprising nano-hydrogenated cuprous / copper composite particles and its preparation method. Background Technology

[0002] Conductive patterns can be obtained by screen printing conductive paste onto a substrate such as PET / PI or glass. Pastes used for forming conductive lines include silver paste, copper paste, and carbon paste. Silver paste is prone to silver ion migration after the circuit is formed, and it is also very expensive. Carbon paste is less expensive but has poor conductivity, making it suitable only for low-end applications. Due to its high conductivity and relatively low cost, copper has been extensively studied as a potential material for obtaining highly conductive printed patterns.

[0003] One method for obtaining conductive patterns involves printing metals, such as copper nanoparticles or copper organic precursors, onto a substrate, followed by heating to sinter the nanoparticles or decompose the precursors to obtain continuous conductive lines. This sintering / decomposition step is performed by heating the printed paste to a high temperature of >150°C, typically for 10-60 minutes; however, due to the rapid oxidation rate of copper nanoparticles, heating must be carried out in an inert or reducing atmosphere.

[0004] In the invention patent with publication number CN107022772A entitled "A Low-Temperature Sintering Copper Paste and Its Preparation Method", a low-temperature sintering copper paste and its preparation method are disclosed. The advantage of this method is that the nano copper powder is prepared by electrolysis, and the copper powder in the paste is a monodisperse nanoparticle with good dispersion, resulting in good dispersion of the paste. However, the nano copper powder prepared is required to have a particle size of 10-30 nm, and its surface is covered with polyvinylpyrrolidone, sodium dodecyl sulfate and sodium ethylenediaminetetraacetate, which are not easy to remove during the sintering process, affecting the fusion between the nano copper particles.

[0005] In the invention patent with publication number CN106981324A, entitled "A Copper Conductive Paste and Its Preparation Method and Use," a flash lamp sintering electronic paste based on micron-sized copper powder is disclosed, along with its preparation method and use. This method reduces the copper oxide content in the copper wire by adding a stabilizer to the system and reducing copper oxide during sintering, thus obtaining a conductive circuit with low copper oxide content. However, a problem exists: it is difficult to achieve uniform dispersion between nano-copper particles and micron-sized copper particles, and the nano-copper particles are prone to agglomeration. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a low-temperature sintering copper paste comprising nano-hydrogenated cuprous / copper composite particles, its preparation method, and its application.

[0007] To achieve the above-mentioned objectives, the present invention proposes the following technical solution: a method for preparing low-temperature sintering copper paste, comprising the following steps:

[0008] S1. Add deionized water to the reducing agent, dissolve it, then add copper salt and stir until completely dissolved;

[0009] S2. After adding copper particles to the above solution and stirring evenly, adjust the pH. After the reaction, a copper particle composite protected by nano-hydride cuprous oxide is generated.

[0010] S3. Wash with water and acetone or ethanol until the pH becomes neutral, and then air dry to obtain a copper particle composite coated with nano-hydrocubic copper.

[0011] S4. Add small molecule organic carboxylic acids to the prepared copper particle composite coated with nano-hydrocubic copper for surface modification and treatment.

[0012] S5. Add resin, solvent, dispersant and curing agent to the treated composite and mix evenly to obtain a slurry of nano-hydrogenated cuprous / copper composite particles.

[0013] In one or more embodiments of the present invention, the reducing agent in S1 is hypophosphorous acid;

[0014] In one or more embodiments of the present invention, the copper salt in S1 is selected from one or more of basic copper carbonate, copper hydroxide, copper oxide, cuprous oxide, copper chloride, copper formate, and copper acetate.

[0015] In one or more embodiments of the present invention, in step S2, the copper particles have a spherical, flake-like, or rod-like morphology and a particle size of 50 nm-20 μm.

[0016] In one or more embodiments of the present invention, in step S2, the pH is 1-4, the reaction temperature is 20-60°C, and the reaction time is 0.1-12h.

[0017] In one or more embodiments of the present invention, the particle size of the copper hydride nanoparticles in the composite obtained in S3 is 10-100 nm.

[0018] In one or more embodiments of the present invention, in step S4, the small molecule organic carboxylic acid is selected from one or more of formic acid, acetic acid, propionic acid, isobutyric acid, valeric acid, and hexanoic acid, which can provide a certain number of protons and prevent the oxidative decomposition of cuprous hydride particles.

[0019] In one or more embodiments of the present invention, the organic carboxylic acid has a boiling point below 250°C.

[0020] In one or more embodiments of the present invention, the main chain of the organic carboxylic acid comprises 1-10 carbons, preferably 2-8 carbons.

[0021] In one or more embodiments of the present invention, in step S5, the resin is selected from one or more of epoxy resin, polyester resin, polyurethane resin, acrylic resin, phenolic resin, polyoxyethylene ether butyral resin, urea-formaldehyde resin, furan resin, silicone resin, and polyamide resin.

[0022] In one or more embodiments of the present invention, in step S5, the solvent is selected from one or more of the following solvents:

[0023] Alcohol solvents: ethylene glycol, polyethylene glycol, propylene glycol, glycerol, isopropanol;

[0024] Ether solvents: ethylene glycol ethyl ether, ethylene glycol butyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol butyl ether, dipropylene glycol methyl ether;

[0025] Ester solvents: ethylene glycol ethyl ether acetate, diethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate;

[0026] Alkylamine solvents: triethanolamine, diethanolamine, triisopropanolamine.

[0027] The present invention also proposes a low-temperature sintering copper paste, which includes the low-temperature sintering copper paste prepared by the preparation method of the present invention.

[0028] This invention also proposes an application of low-temperature sintering copper paste, in which circuit patterns are printed on a substrate material using screen printing to form conductive circuits.

[0029] In one or more embodiments of the present invention, the printed circuit pattern on the substrate material is heated in an air atmosphere for a certain time to obtain a conductive pattern; the preferred heating temperature is 120-300℃ and the heating time is 1min-60min.

[0030] The preparation method of this invention involves coating the surface of copper particles with a layer of nano-copper hydride. When heated at low temperature, active copper nanoparticles are generated, which promotes the sintering of the copper particles and their interconnection to form a conductive path.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. This invention employs the heterogeneous nucleation theory, promoting rapid deposition of atomic nuclei on particle surfaces through surface catalysis or assisted nucleation processes that lower the nucleation barrier. By adding small-diameter copper particles as nuclei for cuprous hydride growth, the particle size of cuprous hydride generated on the copper particle surface can be effectively controlled.

[0033] 2. In the preparation method of the present invention, the size of the added copper particles can be nanometer-scale or micrometer-scale, making the preparation more convenient and reducing costs.

[0034] 3. The decomposition temperature of cuprous hydride is 60℃. Active copper nanoparticles can be obtained at a relatively low heating temperature. At the same time, due to the size effect of the copper nanoparticles, sintering between particles can be achieved at low temperatures.

[0035] 4. Cuprous hydride generates hydrogen gas, a reducing protective gas, when heated, which can prevent the oxidation of copper nanoparticles during sintering.

[0036] 5. The composite particles are treated with small molecule organic carboxylic acids, making them more stable during storage. They also have a certain antioxidant effect during sintering, resulting in copper paste with antioxidant properties and low-temperature sintering. Attached Figure Description

[0037] Figure 1 This is a scanning electron microscope image of the nano-hydrogenated cuprous / copper composite particle slurry prepared in Example 1;

[0038] Figure 2 This is a scanning electron microscope image of the nano-hydrogenated cuprous / copper composite particle slurry prepared in Example 2;

[0039] Figure 3 These are the XRD diffraction patterns of copper / cuprous hydride composite particles after different surface treatments, both initially and after being placed in air for 7 days. Detailed Implementation

[0040] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0041] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated ingredients or components without excluding other ingredients or other components.

[0042] The present invention will now be described in detail with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection of the present invention.

[0043] This invention proposes a method for preparing low-temperature sintered copper paste, which uses copper particles protected by nano-cuprous hydride, or a composite of copper particles coated with cuprous hydride, or cuprous hydride / copper composite particles, or a copper / cuprous hydride core-shell composite to prepare conductive copper paste. A preferred embodiment of the preparation method includes the following steps:

[0044] S1. Add deionized water to the reducing agent and stir until completely dissolved. Then slowly add copper salt and stir until completely dissolved.

[0045] S2. Slowly add copper particles to the above solution and stir until evenly mixed. Adjust the pH and react for a certain time at a certain temperature and speed to generate a copper particle composite protected by nano-hydride cuprous oxide.

[0046] S3. Wash with water, acetone or ethanol in sequence until the pH becomes neutral, and then dry to obtain a copper particle composite coated with nano-hydrocubic copper.

[0047] S4. Add small molecule organic carboxylic acids to the prepared copper particle composite coated with nano-hydrocubic copper for surface modification and treatment.

[0048] S5. Add resin, solvent, and other additives to the treated composite and mix evenly to obtain a slurry of nano-hydrogenated cuprous / copper composite particles.

[0049] The paste prepared by the method is then screen-printed onto a substrate such as glass to create a circuit pattern. The pattern is then heated in air for a certain time to obtain a conductive pattern. The preferred heating temperature is 120-300℃, and the heating time is 1-60 minutes.

[0050] The reducing agent in S1 is hypophosphorous acid.

[0051] The copper salt is selected from one or more of the following: basic copper carbonate, copper hydroxide, copper oxide, cuprous oxide, copper chloride, copper formate, and copper acetate.

[0052] The copper particles are spherical, flake-shaped, or rod-shaped, with a particle size of 50 nm to 20 μm.

[0053] The composite obtained in S3 has a copper hydride nanoparticle size of 10-100 nm.

[0054] The small molecule organic carboxylic acid is selected from one or more of formic acid, acetic acid, propionic acid, isobutyric acid, valeric acid, and hexanoic acid, and can provide a certain number of protons to prevent the oxidative decomposition of cuprous hydride particles.

[0055] The other additives include dispersants and curing agents.

[0056] The organic carboxylic acid has a boiling point below 250°C, so that it can be removed during subsequent low-temperature sintering.

[0057] The main chain of organic carboxylic acids includes 1-10 carbons, preferably 2-8 carbons. When long-chain carboxylic acids are modified, they cannot effectively prevent the oxidation of cuprous hydride particles, and are not easily removed during subsequent low-temperature sintering, thus hindering the sintering of active copper particles generated during the decomposition of cuprous hydride particles.

[0058] Example 1

[0059] S1. Weigh 50 mL of hypophosphite (50% aqueous solution) and place it in a three-necked flask. Add 350 mL of deionized water and stir until completely dissolved. Weigh 10 g of copper oxide and slowly add it to the above solution, stirring until completely dissolved.

[0060] S2. Weigh 10g of spherical copper powder (average particle size of 500nm) and slowly add it to the above solution. Adjust the pH to 2, the temperature to 45℃, and react for 0.5h. Then, centrifuge to separate the solid particles.

[0061] S3. Wash with deionized water and acetone until the pH becomes neutral. After washing, air dry to obtain nano-sized cuprous hydride / copper composite particles.

[0062] S4. Take 5g of the prepared composite particles, add 0.14g of formic acid and an appropriate amount of solvent, and stir thoroughly. After standing, pour off the upper liquid and let it air dry naturally to obtain surface-treated nano-hydrogenated cuprous / copper composite particles.

[0063] S5. Take 1g of surface-treated composite particles, 0.05g of epoxy resin, and appropriate amount of solvent, and mix them evenly using a gravity mixer to obtain a slurry containing nano-hydrogenated cuprous / copper composite particles. Figure 1 The image shown is a scanning electron microscope (SEM) image of the nano-hydrogenated cuprous / copper composite particle slurry prepared in this embodiment.

[0064] The paste was screen printed onto a substrate such as glass to create circuit patterns. The substrate was then heated at 150°C for 10 minutes in air, and the volume resistivity was measured as shown in Table 1 below.

[0065] Example 2

[0066] The preparation steps of Example 1 were repeated, except that the particle size of the spherical copper particles was changed to 1 μm, the reaction time was changed to 2 h, and the formic acid was replaced with acetic acid in the post-treatment process.

[0067] Take 1g of surface-treated nano-hydrogenated cuprous / copper composite particles and 0.05g of phenolic resin, mix them evenly using a gravity mixer to obtain a slurry containing nano-hydrogenated cuprous / copper composite particles, such as... Figure 2 The image shown is a scanning electron microscope (SEM) image of the nano-hydrogenated cuprous / copper composite particle slurry prepared in this embodiment.

[0068] The paste was screen printed onto a substrate such as glass to create circuit patterns. The substrate was then heated at 150°C for 10 minutes in air, and the volume resistivity was measured as shown in Table 1 below.

[0069] Example 3

[0070] The preparation steps of Example 1 were repeated, except that formic acid was replaced with propionic acid in the post-processing.

[0071] Take 1g of surface-treated nano-hydrogenated cuprous / copper composite particles and 0.05g of epoxy resin, mix them evenly using a gravity mixer to obtain a slurry containing nano-hydrogenated cuprous / copper composite particles.

[0072] The paste was screen printed onto a substrate such as glass to create circuit patterns. The substrate was then heated at 150°C for 10 minutes in air, and the volume resistivity was measured as shown in Table 1 below.

[0073] Example 4

[0074] The preparation steps of Example 1 were repeated, except that the spherical copper particles were replaced with flake copper powder with a length of 1 μm and a width and thickness of 100 nm.

[0075] Take 1g of surface-treated nano-hydrogenated cuprous / copper composite particles and 0.05g of epoxy resin, mix them evenly using a gravity mixer to obtain a slurry containing nano-hydrogenated cuprous / copper composite particles.

[0076] The paste was screen-printed onto a substrate such as glass to create circuit patterns. The substrate was then heated at 150°C for 10 minutes in air, and its volume resistivity was measured as shown in Table 1 below.

[0077] The performance comparison of different embodiments is shown in Table 1 below. Figure 3 As shown in Table 1, the resistivity of each embodiment is low and the change is not significant after 7 days, indicating that the copper paste prepared has relatively stable conductivity. Figure 3 In the diagram, curve 1 shows the initial XRD diffraction pattern of the original copper / cuprous hydride composite particles (without organic acid treatment) after being placed in air; curve 2 shows the XRD diffraction pattern of the untreated copper / cuprous hydride composite particles after 7 days; curve 3 shows the XRD diffraction pattern of the formic acid-treated copper / cuprous hydride composite particles after 7 days; curve 4 shows the XRD diffraction pattern of the acetic acid-treated copper / cuprous hydride composite particles after 7 days; and curve 5 shows the XRD diffraction pattern of the propionic acid-treated copper / cuprous hydride composite particles after 7 days. The diffraction patterns reveal that the untreated composite particles exhibit poor antioxidant properties, with a significant amount of cuprous oxide present.

[0078] According to the XRD detection results, the characteristic peak positions correspond to the typical copper hydride (110), (002), (101), (102), (110), (103), (112), (201) crystal planes and the typical copper (111), (200), (220) crystal planes, indicating that the particles synthesized in step S3 are copper / copper hydride composite particles.

[0079] Furthermore, from Figure 3 The results show that after the original sample was exposed to air for 7 days, the characteristic peaks of cuprous hydride almost disappeared, and a large number of characteristic peaks of cuprous oxide appeared. The copper / cuprous hydride composite particles treated with formic acid, acetic acid, and propionic acid also showed a small number of cuprous oxide characteristic peaks after being exposed to air for 7 days. However, most of the characteristic peaks of cuprous hydride were retained, and the retention of cuprous hydride characteristic peaks was most pronounced in the acetic acid-treated copper / cuprous hydride composite particles. This indicates that the copper / cuprous hydride composite particles treated with organic acids exhibit a certain antioxidant effect in air.

[0080] Table 1. Volume resistivity of different embodiments

[0081]

[0082] The description of specific exemplary embodiments of the present invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for preparing low-temperature sintering copper paste, characterized in that, Includes the following steps: S1. Add deionized water to the reducing agent, dissolve it, and then add copper salt; S2. After adding copper particles to the above solution and stirring evenly, adjust the pH. After the reaction, a copper particle composite protected by nano-hydride cuprous oxide is generated. S3. Wash the composite until the pH becomes neutral, and dry it to obtain a copper particle composite coated with nano-hydrocubic cuprous oxide. S4. Add small molecule organic carboxylic acid to the prepared copper particle composite coated with nano-copper hydride for surface modification treatment, wherein the small molecule organic carboxylic acid is selected from one or more of formic acid, acetic acid, propionic acid, isobutyric acid, valeric acid and hexanoic acid that can provide protons and prevent the oxidative decomposition of copper hydride particles, and the boiling point of the organic carboxylic acid is below 250°C. S5. Add resin, solvent, dispersant and curing agent to the composite and mix evenly to obtain a slurry of nano-hydrogenated cuprous / copper composite particles.

2. The method for preparing low-temperature sintering copper paste according to claim 1, characterized in that, The reducing agent in S1 is hypophosphorous acid, and the copper salt is selected from one or more of basic copper carbonate, copper hydroxide, copper oxide, cuprous oxide, copper chloride, copper formate, and copper acetate.

3. The method for preparing low-temperature sintering copper paste according to claim 1, characterized in that, In S2, the copper particles are spherical, plate-like, or rod-like in shape, with a particle size of 50 nm to 20 μm.

4. The preparation method of low-temperature sintering according to claim 1, characterized in that, In the S2 reaction, the pH is 1-4, the reaction temperature is 20-60℃, and the reaction time is 0.1-12h.

5. The method for preparing low-temperature sintering copper paste according to claim 1, characterized in that, In step S3, the composite is washed with water and acetone or ethanol until the pH becomes neutral, and the particle size of the hydride cuprous nanoparticles in the obtained composite is 10-100 nm.

6. The method for preparing low-temperature sintering copper paste according to claim 1, characterized in that, In step S5, the resin is selected from one or more of epoxy resin, polyester resin, polyurethane resin, acrylic resin, phenolic resin, polyoxyethylene ether butyral resin, urea-formaldehyde resin, furan resin, silicone resin, and polyamide resin.

7. The method for preparing low-temperature sintering copper paste according to claim 1, characterized in that, In step S5, the solvent is selected from one or more of the following solvents: Alcohol solvents: ethylene glycol, polyethylene glycol, propylene glycol, glycerol, isopropanol; Ether solvents: ethylene glycol ethyl ether, ethylene glycol butyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, propylene glycol methyl ether, propylene glycol butyl ether, dipropylene glycol methyl ether; Ester solvents: ethylene glycol ethyl ether acetate, diethylene glycol ethyl ether acetate, propylene glycol methyl ether acetate; Alkylamine solvents: triethanolamine, diethanolamine, triisopropanolamine.

8. A low-temperature sintering copper paste, characterized in that, Including the low-temperature sintered copper paste prepared by any one of the preparation methods of claims 1-7.

9. An application of a low-temperature sintering copper paste, characterized in that, By screen printing, the low-temperature sintered copper paste described in claim 8 is printed onto the substrate material to form a circuit pattern, thereby forming a conductive circuit.

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