Atmospheric sintering type low temperature copper paste with high adhesion

Abstract

This invention relates to a high-adhesion atmospheric sintering type low-temperature copper paste, comprising the following raw materials by mass percentage: 4.25-10% nano-copper powder, 40-70% micron-sized copper powder, 5-10% flake copper powder, 3-10% binder, 10-30% solvent, 0.2-4% dispersant, and 0.55-3% chemical bonding agent. This invention also discloses a method for preparing the high-adhesion atmospheric sintering type low-temperature copper paste. The beneficial effect of this invention is that the low-temperature copper paste prepared by this invention is suitable for photon sintering methods, with an applicable energy density range of 4.5-9.2 J / cm². 2 This method can achieve low-temperature sintering by adjusting the energy density to form sintering necks between copper powders without damaging the flexible substrate film. It is suitable for circuit printing, terminal electrode and electronic component fabrication in flexible devices.

Description

Technical Field

[0001] This invention belongs to the field of automotive electronics, and particularly relates to an atmospheric sintering type low-temperature copper paste with high adhesion and its preparation method. Background Technology

[0002] Low-temperature electronic pastes are key materials in flexible electronic components, widely used in automotive electronics, high-end displays, heating devices, and other applications. Among these, low-temperature silver paste, as the most mature product in flexible electronic pastes, suffers from drawbacks such as high cost and susceptibility to electromigration. These shortcomings hinder its sustainable development. For example, the high cost of silver limits its adoption in large-area or low-cost flexible electronic products; while electromigration can lead to electrode short circuits or device failure over long-term use, reducing product reliability and lifespan. Therefore, there is an urgent need to develop new conductive pastes with lower costs and stronger electromigration resistance to meet the ever-evolving demands of flexible electronics technology.

[0003] Low-temperature copper paste has advantages such as low cost, abundant copper reserves, and conductivity similar to silver, making it one of the most promising materials to replace low-temperature silver paste. This gives it broad application prospects in automotive electronics, photovoltaics, and radio frequency identification. The invention patent "A Conductive Paste and Its Preparation Method" (CN121483713A) proposes the idea of ​​using a photothermal conversion aid to achieve low-temperature air sintering. However, this scheme relies on the photothermal conversion aid absorbing light energy and converting it into heat energy. In practical applications, flexible substrates are usually heat-sensitive, and photothermal sintering still requires precise control of the temperature window, increasing the process difficulty. The invention patent "Multi-solvent Synergistic Activation of Low-Temperature Semi-Sintered Copper Paste and Its Preparation Method and Application" (CN121748036A) involves the regulation of multi-solvent systems and dispersants, but its scheme focuses on resin curing and pre-connection of copper particles, failing to fundamentally solve the problem of rapid oxidation of nano-copper powder in an atmospheric environment. Furthermore, it lacks sufficient control over the agglomeration of nano-copper powder, easily leading to increased resistivity. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide an atmospheric sintering type low-temperature copper paste with high adhesion and its preparation method.

[0005] The innovation of this invention lies in the low-temperature copper paste prepared by this invention, which is suitable for photon sintering methods and has an applicable energy density range of 4.5 ~ 9.2 J / cm². 2 This method can achieve low-temperature sintering by adjusting the energy density to form sintering necks between copper powders without damaging the flexible substrate film. It is suitable for circuit printing, terminal electrode and electronic component fabrication in flexible devices.

[0006] A high-adhesion atmospheric sintering type low-temperature copper paste, characterized by comprising the following raw materials in weight percentages:

[0007] Nano copper powder 4.25~10%, micron copper powder 40~70%, flake copper powder 5~10%, binder 3~10%, solvent 10~30%, dispersant 0.2~4%, chemical bonding agent 0.55~3%;

[0008] The adhesive is selected from at least one of ethyl cellulose, polyimide, polyvinyl butyral, benzoxazine resin, hydroxychloroacetic acid resin, and cyanate ester resin;

[0009] The solvent is selected from at least one of ethylene glycol, diester, tripropylene glycol butyl ether, diethylene glycol butyl ether acetate, dimethyl sulfoxide, and dipropylene glycol methyl ester;

[0010] The dispersant is selected from at least one of benzotriazole, polyvinylpyrrolidone, citric acid, silane coupling agent, and ammonium formate;

[0011] The chemical bonding agent is selected from at least one of octyl thiosulfate, hydroxythiophenol, thioglycerol, and allyl mercaptan.

[0012] Furthermore, the average particle size of the nano-copper powder is 80~150nm.

[0013] Furthermore, the average diameter of the micron-sized copper powder is 1.2~5μm.

[0014] Furthermore, the average particle size of the flake copper powder is 8~20μm.

[0015] A method for preparing a high-adhesion atmospheric sintering type low-temperature copper paste as described in any one of claims 1 to 4, characterized in that it includes the following steps:

[0016] (1) The adhesive is added to the solvent, and a mixed solution is formed after heating and stirring;

[0017] (2) Add the dispersant and chemical bonding agent to the mixed solution formed in step (1), and then add nano copper powder, micron copper powder and flake copper powder to form a mixed slurry;

[0018] (3) The mixed slurry in step (2) is stirred and pre-dispersed to obtain a pre-dispersed mixed slurry;

[0019] (4) The pre-dispersed slurry in step (3) is dispersed a second time to obtain the finished product.

[0020] Furthermore, a planetary mixer is used for pre-dispersion in step (3).

[0021] Furthermore, a three-roll mill is used for the secondary dispersion in step (4).

[0022] The beneficial effects of this invention are:

[0023] 1. The low-temperature copper paste prepared by this invention is suitable for photonic sintering, with an applicable energy density range of 4.5 ~ 9.2 J / cm². 2 This method can achieve low-temperature sintering by adjusting the energy density to form sintering necks between copper powders without damaging the flexible substrate film. It is suitable for circuit printing, terminal electrode and electronic component fabrication in flexible devices.

[0024] 2. A key innovation of this invention lies in the introduction of a chemical bonding agent, which tightly bonds copper powder, resin, and substrate adhesive together. This chemical bonding agent can form stable covalent or coordinate bonds on the surface of copper particles, resin molecular chains, and substrate adhesive, constructing a high-strength interfacial bonding network. Even during high-energy photon sintering, where localized instantaneous temperatures are high, this chemical bonding agent maintains structural stability and does not undergo thermal decomposition, ensuring a tight bond between the copper powder, resin, and substrate. This design effectively overcomes the technical challenge of significant decrease in adhesion between the copper film and substrate due to the decomposition of resin inside the copper paste under traditional photon sintering conditions caused by intense thermal shock, significantly improving the bonding reliability between the sintered copper film and substrate.

[0025] 3. The low-temperature copper paste prepared by this invention can be sintered in an atmospheric environment and achieve good conductivity without the need for a nitrogen atmosphere or reducing atmosphere, and can be applied to the terminal electrodes of automotive chip resistors. Attached Figure Description

[0026] Figure 1 This is a SEM image of the low-temperature copper paste after photonic sintering in Example 1. Detailed Implementation

[0027] Example 1: A high-adhesion atmospheric sintering type low-temperature copper paste, comprising the following raw materials by mass percentage:

[0028] The composition comprises 10% nano-copper powder, 40% micron-sized copper powder, 10% flake-shaped copper powder, 3% binder, 30% solvent, 4% dispersant, and 3% chemical bonding agent. The average particle size of the nano-copper powder is 80 nm; the average diameter of the micron-sized copper powder is 1.2 μm; and the average particle size of the flake-shaped copper powder is 8 μm. The binder is polyvinyl butyral; the solvent is a diester; the dispersant is citric acid; and the chemical bonding agent is octyl sulfide.

[0029] Example 2: A high-adhesion atmospheric sintering type low-temperature copper paste, comprising the following raw materials by mass percentage:

[0030] The composition includes 8% nano-copper powder, 47% micron-sized copper powder, 7% flake-shaped copper powder, 4% binder, 28.45% solvent, 3.1% dispersant, and 2.45% chemical bonding agent. The average particle size of the nano-copper powder is 100 nm; the average diameter of the micron-sized copper powder is 2 μm; and the average particle size of the flake-shaped copper powder is 10 μm. The binder is ethyl cellulose; the solvent is diethylene glycol butyl ether acetate; the dispersant is polyvinylpyrrolidone; and the chemical bonding agent is hydroxythiophenol.

[0031] Example 3: A high-adhesion atmospheric sintering type low-temperature copper paste, comprising the following raw materials by mass percentage:

[0032] The composition includes 5% nano-copper powder, 55% micron-sized copper powder, 5% flake copper powder, 6% binder, 24.96% solvent, 2.4% dispersant, and 1.64% chemical bonding agent. The average particle size of the nano-copper powder is 110 nm; the average diameter of the micron-sized copper powder is 3 μm; and the average particle size of the flake copper powder is 12 μm. The binder is hydroxychlorovinyl acetate resin; the solvent is ethylene glycol; the dispersant is benzotriazole; and the chemical bonding agent is allyl mercaptan.

[0033] Example 4: A high-adhesion atmospheric sintering type low-temperature copper paste, comprising the following raw materials by mass percentage:

[0034] The composition includes 6% nano-copper powder, 61% micron-sized copper powder, 4% flake copper powder, 8% binder, 18.81% solvent, 1.2% dispersant, and 0.96% chemical bonding agent. The average particle size of the nano-copper powder is 120 nm; the average diameter of the micron-sized copper powder is 3.5 μm; and the average particle size of the flake copper powder is 15 μm. Polyimide is used as the binder; ethylene glycol is used as the solvent; citric acid is used as the dispersant; and octyl sulfide is used as the chemical bonding agent.

[0035] Example 5: A high-adhesion atmospheric sintering type low-temperature copper paste, comprising the following raw materials by mass percentage:

[0036] The composition includes 7% nano-copper powder, 68% micron-sized copper powder, 2% flake-shaped copper powder, 9% binder, 12.65% solvent, 0.7% dispersant, and 0.65% chemical bonding agent. The average particle size of the nano-copper powder is 140 nm; the average diameter of the micron-sized copper powder is 4 μm; and the average particle size of the flake-shaped copper powder is 16 μm. The binder is cyanate ester resin; the solvent is dipropylene glycol formate; the dispersant is ammonium formate; and the chemical bonding agent is hydroxythiophenol.

[0037] Example 6: A high-adhesion atmospheric sintering type low-temperature copper paste, comprising the following raw materials by mass percentage:

[0038] The composition includes 4.25% nano-copper powder, 70% micron-sized copper powder, 5% flake-shaped copper powder, 10% binder, 10% solvent, 0.2% dispersant, and 0.55% chemical bonding agent. The average particle size of the nano-copper powder is 150 nm; the average diameter of the micron-sized copper powder is 5 μm; and the average particle size of the flake-shaped copper powder is 20 μm. The binder is a cyanate ester resin; the solvent is a diester ester; the dispersant is a silane coupling agent; and the chemical bonding agent is hydroxythiophenol.

[0039] Example 7: Referring to Example 1, the binder is selected from at least one of ethyl cellulose, polyimide, polyvinyl butyral, benzoxazine resin, hydroxychloroacetic acid resin, and cyanate ester resin; the solvent is selected from at least one of ethylene glycol, diester, tripropylene glycol butyl ether, diethylene glycol butyl ether acetate, dimethyl sulfoxide, and dipropylene glycol formate; the dispersant is selected from at least one of benzotriazole, polyvinylpyrrolidone, citric acid, silane coupling agent, and ammonium formate; and the chemical bonding agent is selected from at least one of octyl thiophene, hydroxythiophenol, thioglycerol, and allyl mercaptan.

[0040] Example 8: A method for preparing an atmospheric sintering type low-temperature copper paste with high adhesion, comprising the following steps:

[0041] (1) The adhesive from Example 1 is added to the solvent, and a mixed solution is formed after heating and stirring;

[0042] (2) Add the dispersant and chemical bonding agent to the mixed solution formed in step (1), and then add nano copper powder, micron copper powder and flake copper powder to form a mixed slurry;

[0043] (3) The mixed slurry in step (2) is stirred and pre-dispersed to obtain a pre-dispersed mixed slurry. A planetary mixer is used for pre-dispersion.

[0044] (4) The pre-dispersed slurry in step (3) is dispersed a second time to obtain the finished product. Three rollers are used for the second dispersion.

[0045] Example 9: A method for preparing an atmospheric sintering type low-temperature copper paste with high adhesion, comprising the following steps:

[0046] (1) The adhesive from Example 2 was added to the solvent, and a mixed solution was formed after heating and stirring;

[0047] (2) Add the dispersant and chemical bonding agent to the mixed solution formed in step (1), and then add nano copper powder, micron copper powder and flake copper powder to form a mixed slurry;

[0048] (3) The mixed slurry in step (2) is stirred and pre-dispersed to obtain a pre-dispersed mixed slurry. A planetary mixer is used for pre-dispersion.

[0049] (4) The pre-dispersed slurry in step (3) is dispersed a second time to obtain the finished product. Three rollers are used for the second dispersion.

[0050] Example 10: A method for preparing an atmospheric sintering type low-temperature copper paste with high adhesion, comprising the following steps:

[0051] (1) The adhesive from Example 3 was added to the solvent and heated and stirred to form a mixed solution;

[0052] (2) Add the dispersant and chemical bonding agent to the mixed solution formed in step (1), and then add nano copper powder, micron copper powder and flake copper powder to form a mixed slurry;

[0053] (3) The mixed slurry in step (2) is stirred and pre-dispersed to obtain a pre-dispersed mixed slurry. A planetary mixer is used for pre-dispersion.

[0054] (4) The pre-dispersed slurry in step (3) is dispersed a second time to obtain the finished product. Three rollers are used for the second dispersion.

[0055] Example 11: A method for preparing an atmospheric sintering type low-temperature copper paste with high adhesion, comprising the following steps:

[0056] (1) The adhesive from Example 4 was added to the solvent and heated and stirred to form a mixed solution;

[0057] (2) Add the dispersant and chemical bonding agent to the mixed solution formed in step (1), and then add nano copper powder, micron copper powder and flake copper powder to form a mixed slurry;

[0058] (3) The mixed slurry in step (2) is stirred and pre-dispersed to obtain a pre-dispersed mixed slurry. A planetary mixer is used for pre-dispersion.

[0059] (4) The pre-dispersed slurry in step (3) is dispersed a second time to obtain the finished product. Three rollers are used for the second dispersion.

[0060] Example 12: A method for preparing an atmospheric sintering type low-temperature copper paste with high adhesion, comprising the following steps:

[0061] (1) The adhesive from Example 5 was added to the solvent, and a mixed solution was formed after heating and stirring;

[0062] (2) Add the dispersant and chemical bonding agent to the mixed solution formed in step (1), and then add nano copper powder, micron copper powder and flake copper powder to form a mixed slurry;

[0063] (3) The mixed slurry in step (2) is stirred and pre-dispersed to obtain a pre-dispersed mixed slurry. A planetary mixer is used for pre-dispersion.

[0064] (4) The pre-dispersed slurry in step (3) is dispersed a second time to obtain the finished product. Three rollers are used for the second dispersion.

[0065] Example 13: A method for preparing an atmospheric sintering type low-temperature copper paste with high adhesion, comprising the following steps:

[0066] (1) The adhesive from Example 6 was added to the solvent and heated and stirred to form a mixed solution;

[0067] (2) Add the dispersant and chemical bonding agent to the mixed solution formed in step (1), and then add nano copper powder, micron copper powder and flake copper powder to form a mixed slurry;

[0068] (3) The mixed slurry in step (2) is stirred and pre-dispersed to obtain a pre-dispersed mixed slurry. A planetary mixer is used for pre-dispersion.

[0069] (4) The pre-dispersed slurry in step (3) is dispersed a second time to obtain the finished product. Three rollers are used for the second dispersion.

[0070] The properties of the low-temperature copper pastes from Examples 1-6 after photonic sintering and curing are shown in the table below:

[0071]

[0072] Comparative Example 1: Conductive copper paste was prepared using the method of Example 1 in CN121483713A, as detailed below:

[0073] The conductive paste comprises 65 parts copper powder (D50=150 nm), 2 parts photothermal conversion aid, 2 parts ethanolamine, 0.8 parts antioxidant aid, 0.5 parts hydroxyethyl cellulose, 0.7 parts carboxymethyl cellulose, 0.3 parts polyvinylpyrrolidone, 12 parts ethylene glycol phenyl ether, and 6 parts terpineol. The average particle size of the copper powder is 50 nm. The photothermal conversion aid consists of acetylene black, titanium nitride nanoparticles, and carbon quantum dots in a mass ratio of 5:2:1. The antioxidant aid consists of imidazole phosphate and triethylphosphonate in a mass ratio of 3:1. The antioxidant aid (imidazole phosphate and triethylphosphonate) is dissolved in a mixed solvent of ethanol and isopropanol to obtain a coating solution; the volume ratio of ethanol to isopropanol is 1:1. The copper powder is added to the coating solution and stirred and dispersed for 30 min, then heated to 70 °C and stirred for 2 h, followed by drying under reduced pressure at 60 °C for 2 h to obtain modified copper powder. First, polyvinylpyrrolidone, hydroxyethyl cellulose, and carboxymethyl cellulose are dissolved in a mixed solvent of ethylene glycol phenyl ether and terpineol to form an organic carrier. Modified copper powder, photothermal conversion aid, and ethanolamine are added to the organic carrier, and the mixture is stirred at 2000 rpm for 30 minutes using a planetary mixer to remove bubbles, thus obtaining a conductive slurry.

[0074] In the above preparation method, Comparative Example 1 uses a photothermal conversion aid and blue light to enable copper powder to undergo low-temperature sintering. After irradiation for a certain time (30s), a conductive network is formed, which differs from the principle of this invention. This invention does not rely on a photothermal conversion aid. Instead, it uses a dispersant and generates high-energy light (not blue light) instantaneously (2ms). The copper particles themselves have excellent thermal conductivity, allowing for instantaneous photothermal conversion to form a good conductive network. Because the irradiation time is extremely short, the energy cannot be transferred to the substrate in time, thus preventing damage to the substrate. Furthermore, this invention enhances the adhesion between the copper film layer and the substrate through the addition of a chemical bonding agent, while Comparative Example 1 does not mention this method; therefore, the principle of enhancing adhesion is different.

[0075] Comparative Example 2: Conductive copper paste was prepared using the method of Example 1 in CN121748036A, as detailed below:

[0076] A low-temperature semi-sintered copper paste, sintered at 300℃ for 0.1 min, comprises the following raw material components by mass fraction: 85% copper powder conductive filler, 2% bisphenol A type epoxy resin, 5.5% activating solvent, 5.5% dispersing solvent, and 2% acid anhydride curing agent. The activating solvent consists of glycerol and PEG300 in a mass ratio of 3:7. The acid anhydride curing agent is methyl-5-norbornene-2,3-dicarboxylic anhydride (MNA). An organic solvent was prepared by adding 5.5% of an activating solvent (composed of glycerol and PEG300 in a mass ratio of 3:7) and 5.5% of a dispersing solvent, ethylene glycol, to a sample vial. A binder was prepared by mixing 2% of bisphenol A epoxy resin and 2% of anhydride curing agent, methyl-5-norbornene-2,3-dicarboxylic anhydride (MNA). The binder was then added to the organic solvent and stirred for 2 minutes at 2000 rpm using a planetary mixer to obtain a mixed solvent. 85% copper powder conductive filler was then added to the sample vial and stirred for 5 minutes at 1500 rpm using a planetary mixer to obtain a low-temperature semi-sintered copper paste.

[0077] In the above preparation method, Comparative Example 2 is similar to Comparative Example 1, using an activating solvent to lower the sintering temperature of the copper powder, which differs from the principle of this invention. This invention relies on instantaneous high-energy visible light for direct sintering via photothermal conversion, eliminating the need for additional agents to lower the sintering temperature. Secondly, the sintering temperature of Comparative Example 2 is 250~450℃, which may damage the flexible substrate. This invention, due to its extremely short sintering time, effectively protects the flexible substrate. Finally, Comparative Example 2 requires sintering in a nitrogen atmosphere, while the low-temperature copper paste of this invention can be directly sintered in air, also exhibiting good conductivity.

[0078] The present invention will be further described below with reference to embodiments. The description of the embodiments below is only for the purpose of helping to understand the present invention. It should be noted that those skilled in the art can make several modifications to the present invention without departing from the principle of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. An atmospheric sintering type low temperature copper paste having high adhesion, characterized by, Including the following percentages by weight of raw materials: Nano copper powder 4.25~10%, micron copper powder 40~70%, flake copper powder 5~10%, binder 3~10%, solvent 10~30%, dispersant 0.2~4%, chemical bonding agent 0.55~3%; The adhesive is selected from at least one of ethyl cellulose, polyimide, polyvinyl butyral, benzoxazine resin, hydroxychloroacetic acid resin, and cyanate ester resin; The solvent is selected from at least one of ethylene glycol, diester, tripropylene glycol butyl ether, diethylene glycol butyl ether acetate, dimethyl sulfoxide, and dipropylene glycol methyl ester; The dispersant is selected from at least one of benzotriazole, polyvinylpyrrolidone, citric acid, silane coupling agent, and ammonium formate; The chemical bonding agent is selected from at least one of octyl thiosulfate, hydroxythiophenol, thioglycerol, and allyl mercaptan.

2. The atmospheric sintering type low temperature copper paste with high adhesion according to claim 1, characterized in that, The average particle size of the nano-copper powder is 80~150nm.

3. The atmospheric sintering type low temperature copper paste with high adhesion according to claim 1, characterized in that, The average diameter of the micron-sized copper powder is 1.2~5μm.

4. The atmospheric sintering type low-temperature copper paste with high adhesion according to claim 1, characterized in that, The average particle size of the flaky copper powder is 8~20μm.

5. A method for preparing a high-adhesion atmospheric sintering type low-temperature copper paste as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) The adhesive is added to the solvent, and a mixed solution is formed after heating and stirring; (2) Add the dispersant and chemical bonding agent to the mixed solution formed in step (1), and then add nano copper powder, micron copper powder and flake copper powder to form a mixed slurry; (3) The mixed slurry in step (2) is stirred and pre-dispersed to obtain a pre-dispersed mixed slurry; (4) The pre-dispersed slurry in step (3) is dispersed a second time to obtain the finished product.

6. The method for preparing atmospheric sintering type low-temperature copper paste with high adhesion according to claim 5, characterized in that, A planetary mixer is used for pre-dispersion in step (3).

7. The method for preparing atmospheric sintering type low-temperature copper paste with high adhesion according to claim 5, characterized in that, In step (4), a three-roll mill is used for secondary dispersion.

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