Low-temperature curing copper-based conductive paste as well as preparation method and application thereof

Abstract

The invention discloses a low-temperature curing copper-based conductive paste and a preparation method and application thereof, and belongs to the technical field of conductive pastes.The low-temperature curing copper-based conductive paste is prepared from, by mass, 45-90% of copper powder, 3-40% of composite copper powder and 5-30% of organic carrier; the granularity of the copper powder is 0.2-5 microns; the composite copper powder is nano copper powder pre-wrapped by low-melting-point alloy powder, the melting point of the low-melting-point alloy powder is smaller than or equal to 250 DEG C, and the particle size of the composite copper powder is 0.5-5 microns; the organic carrier comprises resin, a curing agent, an antioxidant, a soldering flux and a solvent, and in the organic carrier, the content of the resin is 2wt%-20wt%, the content of the curing agent is 0.5 wt%-10wt%, the content of the antioxidant is 0.1 wt%-8wt%, and the content of the soldering flux is 0.1 wt%-1wt%. The low-temperature curing copper-based conductive paste has a good application prospect in the aspect of electronic product preparation.

Description

Technical Field

[0001] The present invention belongs to the technical field of conductive pastes, and particularly relates to a low-temperature curing copper-based conductive paste, a preparation method thereof, and an application thereof. Background Art

[0002] Conductive paste is one of the core materials in high-tech and advanced manufacturing fields such as integrated circuits, aerospace, communications, and automobiles. With the development of the photovoltaic industry and flexible electronic products, the demand for conductive paste is increasing, and at the same time, the requirements for its performance are also getting higher and higher.

[0003] Conductive paste mainly consists of three parts: a conductive phase, a binder phase, and an organic carrier. The conductive phase determines the electrical properties of the conductive paste. Generally, metals or alloys with good conductivity are selected as the conductive phase materials. Silver has excellent conductivity and oxidation resistance and is the most ideal conductive phase material. However, the reserves of silver are scarce and the price is relatively expensive. Copper has abundant reserves and a low price. Its conductivity is second only to silver, and it does not cause electromigration phenomena. It has now been widely used in the preparation of conductive pastes. For example, the Chinese patent document with the publication number CN103056383A discloses a preparation method of a high-performance conductive copper paste. In this invention, a copper precursor and a surface protective agent are first dissolved in an organic solvent to obtain reaction solution A, and then a reducing agent is dissolved in an organic solvent to obtain reaction solution B. Reaction solution A and reaction solution B are mixed to react, and then a precipitating agent is added to separate the precipitate. After the precipitate is washed, it is dispersed with a non-polar or weakly polar solvent to obtain a high-performance conductive copper paste. The Chinese patent document with the publication number CN118748098A discloses an antioxidant conductive copper paste and a preparation method thereof. First, copper powder is washed with an acid solution, and then it is added to a coating solution made of a first thermoplastic resin and a first organic solvent. After removing the first organic solvent, antioxidant copper powder is obtained. The antioxidant copper powder is mixed with a thermosetting resin, a second thermoplastic resin, an auxiliary conductive agent, a curing agent, a coupling agent, and a second organic solvent, and then ground to obtain an antioxidant copper paste.

[0004] Copper has poor stability and is easily oxidized in air. After an oxide film layer is formed on the copper surface, its conductivity will be greatly reduced. In view of this, researchers usually add antioxidants with high boiling points and high stability to form a dense protective film on the surface of copper particles to isolate the contact between oxygen and the copper surface and improve its antioxidant performance. However, for the copper paste prepared by the corresponding method, the heat treatment temperature needs to be increased to remove the influence of the antioxidant. Currently, the prepared copper conductive paste requires a heat treatment temperature above 200°C after printing, which limits its use in heterojunction solar cells and flexible electronic products.

[0005] Therefore, it is necessary to develop a copper paste that can be cured below 200°C so that it can meet the low-temperature curing requirements of heterojunction solar cells and flexible substrates. Summary of the Invention

[0006] The present invention provides a low-temperature curable copper-based conductive paste, which is added with composite copper powder - nano copper powder pre-coated with low-melting-point alloy powder, and has the advantages of low curing temperature, fast curing speed and high stability.

[0007] The specific technical solution adopted is as follows:

[0008] A low-temperature curable copper-based conductive paste, by mass percentage, comprises 45wt%-90wt% copper powder, 3wt%-40wt% composite copper powder and 5wt%-30wt% organic carrier;

[0009] The particle size of the copper powder is 0.2 - 5μm;

[0010] The composite copper powder is nano copper powder pre-coated with low-melting-point alloy powder, the melting point of the low-melting-point alloy powder ≤ 250°C, and the particle size of the composite copper powder is 0.5 - 5μm;

[0011] The organic carrier includes resin, curing agent, antioxidant, soldering flux and solvent. In the organic carrier, the content of resin is 2wt%-20wt%, the content of curing agent is 0.5wt%-10wt%, the content of antioxidant is 0.1wt%-8wt%, and the content of soldering flux is 0.1wt%-1wt%.

[0012] The present invention adds composite copper powder - nano copper powder pre-coated with low-melting-point alloy powder to the copper-based conductive paste. The addition of the composite copper powder can reduce the curing temperature of the copper-based conductive paste. At the same time, during the curing process, the low-melting-point alloy forms a liquid phase between the copper particles, promoting the rapid densification of the film layer and effectively filling the gaps between the copper particles to form a good conductive path.

[0013] Preferably, the low-temperature curable copper-based conductive paste, by mass percentage, comprises 55wt%-90wt% copper powder, 5wt%-30wt% composite copper powder and 5wt%-15wt% organic carrier.

[0014] Specifically, the composite copper powder is prepared by the following method: Mix nano copper powder and low-melting-point alloy powder according to a mass ratio of 1 - 5:1. Under the protection of nitrogen atmosphere, place the mixed powder at a constant temperature of 150 - 250°C for 15 - 60 minutes. After cooling, ball mill it to 0.5 - 5μm to obtain the composite copper powder.

[0015] Further, the low melting point alloy powder is Sn-Zn-Ag alloy, Bi-Sn alloy, Sn-Bi-Ag alloy, Sn-Bi-Cu alloy, In-Sn alloy, Bi-Sn-Zn alloy, Pb-Sn alloy or Bi-Pb-Sn alloy (under the condition of permitted use, lead-containing alloys can also be applied); the particle size of the nano copper powder is 20-300 nm. The low melting point alloy powder has low cost and good industrial application prospects.

[0016] Most preferably, the low melting point alloy powder is Sn-Bi-Ag or Sn-Bi-Cu series low melting point alloy powder with a melting point lower than 200 °C, such as Sn 69.5 Bi 30 Cu 0.5 、Sn 42 Bi 57 Ag1、Sn 42 Bi 57.6 Ag 0.4 etc.

[0017] Optionally, the resin is at least one of acrylic resin, acrylic modified epoxy resin, bisphenol A type epoxy resin, aliphatic epoxy resin, polyester modified epoxy resin, and polyurethane modified epoxy resin.

[0018] Optionally, the curing agent is at least one of silane coupling agent, imidazole, modified imidazole, dicyandiamide, modified dicyandiamide, and ethylenediamine.

[0019] Optionally, the antioxidant is at least one of benzimidazole, 2-mercaptobenzimidazole, benzothiazole, aminotrimethylphosphonic acid, and hydroxyethylidene diphosphonic acid. The antioxidant can modify and passivate the surface of the copper powder to improve the antioxidant ability.

[0020] Optionally, the soldering flux is at least one of ethylene glycol, polyethylene glycol, ethyl acetate, and butyl acetate. Polyethylene glycol includes, but is not limited to, polyethylene glycol 200, polyethylene glycol 400, etc. The soldering flux can remove the oxide film on the surface of the copper powder during the curing process, form a good contact interface between the copper particles. At the same time, the soldering flux can also reduce the surface tension of the liquid phase to improve the wetting performance of the liquid phase and the copper powder, effectively reduce the interfacial contact resistance and improve the electrical conductivity.

[0021] Optionally, the solvent is at least four of terpineol, alcohol ester twelve, butyl carbitol, butyl carbitol acetate, and dibutyl phthalate. The combination of the four solvents can ensure good rheological properties of the slurry during the printing process and the initial stage of curing.

[0022] The present invention also provides a preparation method of the low-temperature curing copper-based conductive paste, including the following steps:

[0023] (1) Prepare a mixed solvent which, by mass percentage, includes 5 wt% - 50 wt% terpineol, 30 wt% - 85 wt% lauryl alcohol phthalate, 1 wt% - 20 wt% butyl carbitol, 1 wt% - 5 wt% butyl carbitol acetate, and 0 wt% - 3 wt% dibutyl phthalate;

[0024] (2) Mix the mixed solvent from step (1) with resin, curing agent, antioxidant, and flux in proportion, and place it under stirring and mixing at a temperature of 50 - 80 °C to obtain an organic carrier;

[0025] (3) Mix copper powder, composite copper powder, and the organic carrier in proportion, fully premix and then grind, further defoam and filter to obtain the low-temperature curing copper-based conductive paste.

[0026] The present invention also provides the application of the low-temperature curing copper-based conductive paste in the field of electronic product preparation. Specifically, after coating the low-temperature curing copper-based conductive paste and heating and curing, a conductive material layer can be obtained on the surface of the substrate.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) By adding composite copper powder - nano copper powder pre-coated with low-melting-point alloy powder, the present invention effectively reduces the curing temperature of the copper-based conductive paste. The low-melting-point alloy forms a liquid phase during the curing process, which can promote the rapid densification of copper powder and form a well-connected conductive path.

[0029] (2) The curing temperature of the low-temperature curing copper-based conductive paste provided by the present invention is as low as below 200 °C, the curing time is shortened to within 15 minutes, and the volume resistance is less than 10 μΩ·cm.

[0030] (3) The organic carrier of the present invention includes flux. The flux can remove the oxide film on the surface of copper powder during the curing process, enabling a good contact interface to be formed between copper particles. At the same time, adding flux can also reduce the surface tension of the liquid phase, improve the wetting performance of the liquid phase with copper powder, and effectively reduce the interface contact resistance to improve the conductive characteristics. Description of the Drawings

[0031] Figure 1 It is a scanning electron microscope picture of copper powder raw material, where the scale bar is 10 μm.

[0032] Figure 2 It is a scanning electron microscope picture of the composite copper powder prepared in Example 1, where the scale bar is 10 μm.

[0033] Figure 3 It is a scanning electron microscope picture of the cured conductive paste prepared in Example 1. Detailed Embodiments

[0034] To make the objectives, features, and advantages of the present invention more apparent and understandable, the following provides a detailed description through specific embodiments. A number of specific details are set forth in the following description in order to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the spirit of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined accordingly without conflict.

[0035] For the operating methods without specific conditions noted in the following embodiments, they are generally in accordance with conventional conditions or the conditions recommended by the manufacturer. The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art. The experimental materials used in the following embodiments can be obtained from conventional biochemical reagent companies without special instructions.

[0036] A representative SEM image of the raw material copper powder used in the embodiments is as Figure 1 shown.

[0037] Example 1

[0038] (1) Take 15 g of terpineol, 75 g of lauryl acetate, 6 g of butyl carbitol, 3 g of butyl carbitol acetate, and 1 g of dibutyl phthalate. After mixing the solvents, a mixed solvent is obtained;

[0039] (2) Mix 85.5 g of the mixed solvent with 8 g of acrylic resin, 3 g of silane coupling agent, 3 g of benzimidazole, and 0.5 g of polyethylene glycol 400, and stir and mix for 1 h to obtain an organic carrier;

[0040] (3) Weigh 16 g of nano copper powder with a particle size of 50 nm, weigh 8 g of Sn 42 Bi 57 Ag1 alloy powder. In a glove box under nitrogen atmosphere protection, thoroughly grind and mix them with a mortar. Then, under nitrogen atmosphere protection, keep them at a constant temperature of 200 °C for 30 min. After cooling, ball mill them until the particle size ≤ 5 μm to obtain composite copper powder. The scanning electron microscope image of the composite copper powder is as Figure 2 shown;

[0041] (4) Thoroughly premix 60 g of copper powder with a particle size of 1 μm, 25 g of the composite copper powder prepared in step (3), and 15 g of the organic carrier prepared in step (2). After thoroughly grinding with a three-roll mill, further perform vacuum defoaming and sieving to obtain the low-temperature curing copper-based conductive paste.

[0042] Example 2

[0043] (1) 35 g of terpineol, 55 g of alcohol ester dodecanol, 5 g of butyl carbitol, 4 g of butyl carbitol acetate and 1 g of dibutyl phthalate were mixed to obtain a mixed solvent;

[0044] (2) 83 g of the mixed solvent was mixed with 11 g of acrylic modified epoxy resin, 2 g of imidazole, 3.5 g of benzimidazole, and 0.5 g of polyethylene glycol 400, and the mixture was stirred for 1 h to obtain an organic carrier;

[0045] (3) Weigh 21 g of nano copper powder with a particle size of 100 nm and 7 g of Sn with a melting point of 140 °C. 42 Bi 57 Ag1 alloy powder was fully ground and mixed in a mortar in a glove box protected by a nitrogen atmosphere, and then kept at a constant temperature of 200°C for 30 minutes under the protection of a nitrogen atmosphere. After cooling, it was ball-milled to a particle size of ≤5 μm to obtain a composite copper powder;

[0046] (4) 60 g of copper powder with a particle size of 1 μm, 25 g of the composite copper powder obtained in step (3) and 15 g of the organic carrier obtained in step (2) are fully premixed, and then fully ground using a three-roll mill, and then further subjected to vacuum degassing and sieving to obtain the low-temperature curing copper-based conductive paste.

[0047] Example 3

[0048] (1) In this embodiment, the organic carrier used is the same as that in Example 2;

[0049] (2) Weigh 20 g of nano copper powder with a particle size of 100 nm and 5 g of Sn with a melting point of 140 °C. 42 Bi 57 Ag1 alloy powder was fully ground and mixed in a mortar in a glove box protected by a nitrogen atmosphere, and then kept at a constant temperature of 180°C for 30 minutes under the protection of a nitrogen atmosphere. After cooling, the powder was ball-milled to a particle size of ≤5 μm to obtain a composite copper powder;

[0050] (3) 60 g of copper powder with a particle size of 1 μm, 25 g of the composite copper powder obtained in step (2) and 15 g of the organic carrier in Example 2 were fully premixed, and then fully ground using a three-roll mill, and then further vacuum-defoamed and sieved to obtain the low-temperature curing copper-based conductive paste.

[0051] Comparative Example 1

[0052] (1) In this comparative example, the organic carrier used is the same as that in Example 2;

[0053] (2) 85 g of copper powder with a particle size of 1 μm and 15 g of an organic carrier were fully premixed, and then fully ground using a three-roll mill, and then further vacuum-defoamed and sieved to obtain a copper-based conductive paste.

[0054] Comparative Example 2

[0055] (1) In this comparative example, the mixed solvent used is the same as that in Example 2;

[0056] (2) 83.5 g of the mixed solvent, 11 g of acrylic acid-modified epoxy resin, 2 g of imidazole, and 3.5 g of benzimidazole were stirred and mixed for 1 h to obtain an organic carrier;

[0057] (3) 85 g of copper powder with a particle size of 1 μm and 15 g of the organic carrier were sufficiently premixed, then thoroughly ground using a three-roll mill, and further subjected to vacuum degassing and sieving to obtain a copper-based conductive paste.

[0058] Comparative Example 3

[0059] (1) In this comparative example, the mixed solvent used is the same as that in Example 2;

[0060] (2) 83.5 g of the mixed solvent, 11 g of acrylic acid-modified epoxy resin, 2 g of imidazole, and 3.5 g of benzimidazole were stirred and mixed for 1 h to obtain an organic carrier;

[0061] (3) 60 g of copper powder with a particle size of 1 μm, 25 g of nano-copper powder with a particle size of 100 nm, and 15 g of the organic carrier were sufficiently premixed, then thoroughly ground using a three-roll mill, and further subjected to vacuum degassing and sieving to obtain a copper-based conductive paste.

[0062] Sample Analysis

[0063] Taking the copper-based conductive pastes of Examples 1 - 3 and Comparative Examples 1 - 3 as samples, each sample was printed on the same substrate for conductive performance testing, electrical performance, and adhesion testing. The scanning electron microscope image of the conductive paste prepared in Example 1 after curing is as Figure 3 shown.

[0064] Sheet resistance test: Tested according to the standard of GB / T 17473.3 - 2008.

[0065] Adhesion test: Tested according to the method of ISO 2409 - 2020.

[0066] Table 1 Results of curing methods, sheet resistance, and adhesion tests

[0067] Number Sheet Resistance (mΩ / □) Curing Temperature and Time Adhesion Example 1 5.32 190°C, 30 min 1 Example 2 6.1 180°C, 30 min 0 Example 3 5.56 180°C, 30 min 0 Comparative Example 1 15.33 190°C, 30 min 1 Comparative Example 2 18.16 190°C, 30 min 1 Comparative Example 3 25.36 190°C, 30 min 1

[0068] It can be seen from the results in Table 1 that it is fully proved that the low-temperature curing copper-based conductive paste provided by the present invention has excellent performance and has broad application prospects in the fields of solar cells and flexible electronic devices, etc.

[0069] The embodiments described above have elaborated on the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and do not limit the present invention. Any modifications, supplements, or substitutions in a similar manner within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-temperature curable copper-based conductive paste, characterized in that, By mass percentage, it includes 45wt%-90wt% copper powder, 3wt%-40wt% composite copper powder and 5wt%-30wt% organic carrier; The particle size of the copper powder is 0.2 - 5μm; The composite copper powder is nano copper powder pre-coated with low melting point alloy powder, the melting point of the low melting point alloy powder ≤ 250°C, and the particle size of the composite copper powder is 0.5 - 5μm; The organic carrier includes resin, curing agent, antioxidant, soldering flux and solvent. In the organic carrier, the content of resin is 2wt%-20wt%, the content of curing agent is 0.5wt%-10wt%, the content of antioxidant is 0.1wt%-8wt%, and the content of soldering flux is 0.1wt%-1wt%.

2. The low-temperature curing copper-based conductive paste according to claim 1, wherein The low-temperature curing copper-based conductive paste, by mass percentage, includes 55wt%-90wt% copper powder, 5wt%-30wt% composite copper powder and 5wt%-15wt% organic carrier.

3. The low-temperature curing copper-based conductive paste according to claim 1, wherein The composite copper powder is prepared by the following method: Mix nano copper powder and low melting point alloy powder according to a mass ratio of 1 - 5:

1. Under the protection of nitrogen atmosphere, place the mixed powder at a constant temperature of 150 - 250°C for 15 - 60 minutes. After cooling, ball mill it to 0.5 - 5μm to obtain the composite copper powder.

4. The low-temperature curable copper-based conductive paste according to claim 1, characterized in that, The low melting point alloy powder is Sn-Zn-Ag alloy, Bi-Sn alloy, Sn-Bi-Ag alloy, Sn-Bi-Cu alloy, In-Sn alloy, Bi-Sn-Zn alloy, Pb-Sn alloy or Bi-Pb-Sn alloy; the particle size of the nano copper powder is 20 - 300nm.

5. The low-temperature curing copper-based conductive paste according to claim 1, wherein, The resin is at least one of acrylic resin, acrylic modified epoxy resin, bisphenol A type epoxy resin, aliphatic epoxy resin, polyester modified epoxy resin, polyurethane modified epoxy resin.

6. The low-temperature curable copper-based conductive paste according to claim 1, wherein The curing agent is at least one of silane coupling agent, imidazole, modified imidazole, dicyandiamide, modified dicyandiamide, ethylenediamine.

7. The low-temperature curable copper-based conductive paste according to claim 1, wherein, The antioxidant is at least one of benzimidazole, 2-mercaptobenzimidazole, benzothiazole, aminotrimethylenephosphonic acid, hydroxyethylidene diphosphonic acid.

8. The low-temperature curable copper-based conductive paste according to claim 1, characterized in that, The soldering flux is at least one of ethylene glycol, polyethylene glycol, ethyl acetate, butyl acetate; The solvent is at least four of terpineol, ethyl lactate 12, butyl carbitol, butyl carbitol acetate, dibutyl phthalate.

9. The preparation method of the low-temperature curable copper-based conductive paste according to any one of claims 1-8, characterized in that, It includes the following steps: (1) Prepare a mixed solvent. In this mixed solvent, by mass percentage, it includes 5wt%-50wt% terpineol, 30wt%-85wt% ethyl lactate 12, 1wt%-20wt% butyl carbitol, 1wt%-5wt% butyl carbitol acetate, 0wt%-3wt% dibutyl phthalate; (2) Mix the mixed solvent in step (1) with resin, curing agent, antioxidant and soldering flux in proportion, and stir and mix evenly at a temperature of 50 - 80°C to obtain the organic carrier; (3) Mix copper powder, composite copper powder and organic carrier in proportion, fully premix and grind, and further defoam and filter to obtain the low-temperature curing copper-based conductive paste.

10. Use of the low-temperature curing copper-based conductive paste according to any one of claims 1-8 in the field of electronic product preparation.

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