Low-temperature curing silver-coated copper composite slurry and preparation method thereof

Abstract

The invention discloses low-temperature curing silver-coated copper composite slurry and a preparation method thereof. The conductive adhesive comprises the following raw material components in percentage by weight: 60-80% of conductive phase, 2-2.8% of adhesive, 5-10% of resin and 3-8% of additive, and 20%-30% of a solvent. Wherein the conductive phase is formed by compounding spherical silver-coated copper powder and flaky silver powder, and the silver content is reduced and the sheet resistance of the silver-coated copper composite conductive paste is below 25m omega / square through a copper matrix surface silver plating process. A step-by-step mixing technology is adopted in the preparation process, resin and a solvent are dispersed at a high speed at 60 DEG C, then conductive powder is introduced to avoid agglomeration, and a uniform and compact conductive network is finally formed after grinding. After being cured at the low temperature of 130-180 DEG C, the paste has excellent adhesive force and durability, can be applied to the fields of heterojunction solar cells, flexible circuits and the like, and remarkably improves the photoelectric conversion efficiency and the processing adaptability.

Description

Technical Field

[0001] The present invention relates to the technical field of conductive pastes, and in particular to a low-temperature curing silver-clad copper composite paste and a preparation method thereof. Background Art

[0002] With the rapid development of flexible electronic devices, thin-film photovoltaic cells and wearable devices, low-temperature conductive pastes, as core functional materials, need to achieve efficient curing at 150-200°C and have both excellent conductivity and substrate adhesion. Traditional high-temperature sintering conductive pastes are prone to thermal deformation of flexible substrates (such as polyimide and PET films) due to their high curing temperature (>300°C), and cannot meet the processing requirements of the new generation of electronic devices. Existing low-temperature conductive pastes mainly improve adhesion by adding adhesives such as epoxy resins, but the compatibility between resins and metal conductive phases is poor, which easily causes conductive particles to agglomerate, resulting in discontinuous conductive networks and significantly increased resistivity.

[0003] The current technology has the following bottlenecks: 1. The contradiction between conductivity and adhesion: Although high silver content can improve conductivity, excessive silver powder leads to insufficient resin wrapping, reduces the printability of the slurry, increases the brittleness of the film layer after curing, and reduces the interfacial bonding strength with the substrate. 2. Limitations of organic carriers: Existing adhesives such as epoxy resins and polyurethanes have insufficient shrinkage when cured at low temperatures, making it difficult to promote close contact between silver powder particles, and residual solvents easily form an insulating layer to block the conductive path. 3. Environmental protection and cost pressure: Silver-based materials are expensive, and copper-based slurries are prone to oxidation and deterioration. Additional antioxidants or silver coatings need to be added, which significantly increases the complexity of the process.

[0004] Therefore, developing a conductive paste that combines low-temperature processability, high conductivity and excellent interface bonding has become a technical problem that urgently needs to be overcome in this field. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to prepare a low-temperature conductive paste with excellent conductive properties, stable printability and good durability through multi-scale conductive phase compounding, gradient resin system design and green solvent development.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a low-temperature curing silver-clad copper composite paste, which includes the following raw material components, and each raw material component satisfies the following weight percentage: Conductive phase 60% to 80%; Resin 5% to 10%; Solvent 20% to 30%; Additives 3% to 8%.

[0008] The conductive phase is formed by compounding spherical silver-coated copper powder and flaky silver powder in a mass ratio of 0.5:1 to 3:1. The particle size of the spherical silver-coated copper powder is 1 to 3 μm, and the silver layer accounts for 10% to 20% of the total mass of the particles; the particle size of the flaky silver powder is 1 to 3 μm, and the tap density is 0.5 to 1.3 g / mL.

[0009] Preferably, the resin includes a combination of one or more of epoxy resin with an epoxy equivalent of 5000 to 6000, polyurethane resin and acrylic resin.

[0010] Preferably, the solvent includes any one or more combinations of terpineol, dibasic acid ester (DBE), diethylene glycol monoethyl ether acetate and cyclohexanone.

[0011] Preferably, the additive includes any one or more combinations of a curing agent, a leveling agent, a binder and a dispersant.

[0012] Preferably, the curing agent includes any one or a combination of at least two of dicyandiamide, blocked isocyanate, 2,4-dimethylimidazole, 2-methylbenzimidazole and 2-ethyl-4-methylimidazole.

[0013] Preferably, the leveling agent includes any one of polydimethylsiloxane (PDMS), polyether-modified siloxane (such as BYK-333), and fluorine-modified siloxane, or a combination of at least two thereof, to improve printing leveling.

[0014] Preferably, the binder includes any one of ethyl cellulose (EC100) and sodium carboxymethyl cellulose (CMC-Na) or a combination of at least two thereof to control the thixotropy of the slurry.

[0015] Preferably, the dispersant includes any one or a combination of at least two of polyvinyl pyrrolidone (PVP K30 / K90), polycarboxylate (such as BYK-110), cetyltrimethylammonium bromide (CTAB), silane coupling agent KH560 and YDC-2140.

[0016] In a second aspect, the present invention provides a low-temperature curing silver-clad copper composite slurry and a preparation method thereof, comprising the following steps:

[0017] Step 1: Mix the resin and solvent in steps, dispersing them at a high speed of 800-1200 r / min for 5-10 minutes to form a homogeneous carrier;

[0018] Step 2: Introduce the conductive phase by adding spherical silver-coated copper powder, flake silver powder and additives in sequence, with an interval of 5 minutes each time and mixing evenly;

[0019] Step 3: Grind the slurry in a mortar in a clockwise direction for 15 to 30 minutes to control the slurry fineness D50 ≤ 5 μm;

[0020] Step 4: Screen printing: the slurry is used to form a circuit pattern on the glass substrate through a screen printing process, with a line width of ≤1mm;

[0021] Step 5: Leveling treatment: let it stand at 25-30℃ for 10-30s to eliminate bubbles on the printing interface;

[0022] Step 6: Low temperature curing: Curing in a drying oven at 120-180°C for 10-20 minutes and then conducting a resistivity test.

[0023] In step 4, the mesh number of the screen is ≥ 400 mesh, the scraper angle is 60-75°, and the printing pressure is 0.2-0.5 MPa.

[0024] The numerical range described in the present invention includes not only the point values listed above, but also any point values between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values included in the range.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. The present invention adopts a composite system of spherical silver-coated copper powder (silver layer accounts for 10-20%) and flaky silver powder. Through the copper core silver-plated (Cu@Ag) structural design, it can reduce the amount of precious metal by 30-40%. At the same time, it can achieve the square resistance of the silver-coated copper composite conductive paste to below 25mΩ / □, achieving a leap in conductive performance while reducing costs, which is superior to the single conductive system in the existing technology.

[0027] 2. This invention utilizes a composite system of epoxy resin, polyurethane, and acrylic resin, using a step-by-step mixing process combined with a low-temperature curing process at 130-180°C to form a uniform, dense conductive network, achieving a balanced combination of resistivity and adhesion. A dicyandiamide / blocked isocyanate composite curing agent is used, curing at 120-180°C for 10-20 minutes, reducing energy consumption by over 40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments:

[0029] Figure 1 This is a microscope photograph of the edge of the printed pattern of Example 1;

[0030] Figure 2 This is a microscope photograph of the printed pattern of Comparative Example 1. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present application is further described below with reference to the following embodiments. The embodiments are merely illustrative, and any equivalent adjustments or substitutions made by those skilled in the art based on the core concept of the present invention are within the scope of protection.

[0032] Those skilled in the art should understand that the step numbers in the embodiments do not limit the execution order, and the execution sequence of each step can be adjusted according to actual needs.

[0033] The terms used in the embodiments of the present invention (such as "comprise" and "include") should be interpreted broadly, and the singular form includes the plural meaning.

[0034] Those skilled in the art will appreciate that the numerical ranges in the embodiments of the present invention should be considered to disclose all intermediate values and subranges between the upper and lower limits, and that the intervals may independently include or exclude the endpoints.

[0035] Unless otherwise specified, the meanings of the technical terms used herein shall be subject to conventional interpretations in the art. In the event of a conflict between a cited document and the present application, the content of the present application shall take precedence.

[0036] It should be noted that the raw materials and reagents used in the examples are all commercially available products or prepared by conventional methods in the art.

[0037] The technical method of the present invention will be further described below with reference to specific embodiments.

[0038] This embodiment provides a silver-coated copper composite conductive paste and a low-temperature preparation method thereof, comprising the following steps:

[0039] Example 1

[0040] A method for preparing a conductive paste comprises the following steps:

[0041] Components and ratio (weight percentage):

[0042] Conductive phase (75%): spherical silver-coated copper powder (average particle size 3 μm, silver layer proportion 15%) and flake silver powder (average particle size 2 μm, tap density 1.0 g / mL) are compounded in a mass ratio of 1:1;

[0043] Resin (8%): Bisphenol A epoxy resin (epoxy equivalent 5500) and polyurethane resin (molecular weight 38000) compounded in a mass ratio of 3:1;

[0044] Solvent (25%): terpineol and dibasic acid ester (DBE) were mixed in a mass ratio of 1:1;

[0045] Additives (8%): dicyandiamide curing agent (2%), BYK-333 leveling agent (1.5%), PVP K30 dispersant (3%), ethyl cellulose (EC100, 1.5%).

[0046] Preparation method:

[0047] (1) Stepwise mixing: The resin and solvent were dispersed at 1000 rpm for 8 min at 60°C to form a homogeneous carrier;

[0048] (2) Introduction of conductive phase: The conductive phase and additives were added in three batches, with an interval of 5 min between each addition (to avoid particle agglomeration);

[0049] (3) Grinding: Grind in a clockwise direction for 25 min in an agate mortar, and the slurry fineness D50 = 3.5 μm;

[0050] (4) Screen printing: Use a 400-mesh screen (squeegee angle 70°, pressure 0.3 MPa) to print a circuit with a line width of 0.8 mm on a glass substrate;

[0051] (5) Leveling treatment: Let it stand at 28℃ for 20s, and the surface tension will drop to 23mN / m;

[0052] (6) Low temperature curing: curing at 150℃ for 15 minutes.

[0053] Performance testing:

[0054] Conductivity: square resistance is 20mΩ / □;

[0055] Adhesion: ASTM D3359 test ≥5B (epoxy resin-polyurethane compounding improves interfacial bonding strength).

[0056] Example 2

[0057] A method for preparing a conductive paste comprises the following steps:

[0058] Components and ratio (weight percentage):

[0059] Conductive phase (68%): spherical silver-coated copper powder (particle size 3 μm, silver layer accounts for 18%) and flake silver powder (particle size 2 μm, tap density 0.8 g / mL) are compounded in a mass ratio of 1.5:1;

[0060] Resin (10%): acrylic resin and polyurethane resin (molecular weight 40,000) compounded in a mass ratio of 1:2;

[0061] Solvent (28%): diethylene glycol monoethyl ether acetate (boiling point 210°C, low volatility);

[0062] Additives (6%): blocked isocyanate (1.5%), PDMS leveling agent (1%), KH560 dispersant (2.5%), sodium carboxymethyl cellulose (CMC-Na, 1%).

[0063] Preparation method:

[0064] (1) Stepwise mixing: the resin and solvent were dispersed at a high speed of 1200 r / min at 70°C for 6 min;

[0065] (2) Introduction of conductive phase: The conductive phase was added twice with an interval of 5 min;

[0066] (3) Grinding: Grind in clockwise direction for 20 min using an agate mortar, and the slurry fineness D50 = 2.8 μm;

[0067] (4) Screen printing: 500 mesh screen printing line width 0.5mm circuit (PET substrate);

[0068] (5) Leveling treatment: let it stand at 30℃ for 15 seconds;

[0069] (6) Low temperature curing: curing at 180℃ for 10 minutes.

[0070] Performance testing:

[0071] Conductivity: Square resistance 35mΩ / □ (Flake silver powder filling improves the continuity of the conductive network);

[0072] Temperature resistance: No cracks after 50 cycles from -40°C to 200°C (gradient resin system relieves thermal stress);

[0073] Printing accuracy: Line width error ±0.05mm (KH560 dispersant inhibits silver powder agglomeration).

[0074] Comparative Example 1

[0075] Comparative Example 1 provides a method for preparing a conductive paste. The difference from Example 1 is that Comparative Example 1 is a single conductive phase and does not contain a compound conductive phase, as follows:

[0076] A method for preparing a conductive paste comprises the following steps:

[0077] Components and ratio (weight percentage):

[0078] Conductive phase (75%): pure flake silver powder (particle size 2.5 μm, tap density 1.2 g / mL);

[0079] Resin (8%): Bisphenol A epoxy resin (epoxy equivalent 5500) and polyurethane resin (molecular weight 38000) compounded in a mass ratio of 3:1;

[0080] Solvent (25%): terpineol and dibasic acid ester (DBE) were mixed in a mass ratio of 1:1;

[0081] Additives (8%): dicyandiamide curing agent (2%), BYK-333 leveling agent (1.5%), PVP K30 dispersant (3%), ethyl cellulose (EC100, 1.5%).

[0082] Preparation method:

[0083] (1) Stepwise mixing: The resin and solvent were dispersed at 1000 rpm for 8 min at 60°C to form a homogeneous carrier;

[0084] (2) Introduction of conductive phase: The conductive phase and additives were added three times, with an interval of 5 min between each addition (to avoid particle agglomeration);

[0085] (3) Grinding: Grind in a clockwise direction for 25 min in an agate mortar, and the slurry fineness D50 = 3.5 μm;

[0086] (4) Screen printing: Use a 400-mesh screen (squeegee angle 70°, pressure 0.3 MPa) to print a circuit with a line width of 0.8 mm on a glass substrate;

[0087] (5) Leveling treatment: Let it stand at 28℃ for 20s, and the surface tension will drop to 23mN / m;

[0088] (6) Low temperature curing: curing at 150℃ for 15 minutes.

[0089] The product prepared in this comparative example has a square resistance of 120 mΩ / □, an adhesion of ≤3B, and poor printability, with uneven edges of the printed pattern.

[0090] Comparative Example 2

[0091] Comparative Example 2 provides a method for preparing a conductive paste. The difference from Example 2 is that the conductive phase ratio in Comparative Example 2 is unbalanced, as follows:

[0092] A method for preparing a conductive paste comprises the following steps:

[0093] Components and ratio (weight percentage):

[0094] Conductive phase (68%): spherical silver-coated copper powder (particle size 3 μm, silver layer accounts for 18%) and flake silver powder (particle size 2 μm, tap density 0.8 g / mL) are compounded in a mass ratio of 5:1;

[0095] Resin (10%): acrylic resin and polyurethane resin (molecular weight 40,000) compounded in a mass ratio of 1:2;

[0096] Solvent (28%): diethylene glycol monoethyl ether acetate (boiling point 210°C, low volatility);

[0097] Additives (6%): blocked isocyanate (1.5%), PDMS leveling agent (1%), KH560 dispersant (2.5%), sodium carboxymethyl cellulose (CMC-Na, 1%).

[0098] Preparation method:

[0099] (1) Stepwise mixing: the resin and solvent were dispersed at a high speed of 1200 r / min at 70°C for 6 min;

[0100] (2) Introduction of conductive phase: The conductive phase was added twice with an interval of 5 min;

[0101] (3) Grinding: Grind in clockwise direction for 20 min using an agate mortar, and the slurry fineness D50 = 2.8 μm;

[0102] (4) Screen printing: 500 mesh screen printing line width 0.5mm circuit (PET substrate);

[0103] (5) Leveling treatment: let it stand at 30℃ for 15 seconds;

[0104] (6) Low temperature curing: curing at 180℃ for 10 minutes.

[0105] The product prepared in this comparative example has a large fluctuation in square resistance (120-260 mΩ / □, adhesion ≤ 3B) compared to the product provided in Example 2, and the excessive amount of spherical silver-coated copper powder causes particle sedimentation, resulting in poor printing uniformity and a line width error of ±0.3 mm.

Claims

1. A low-temperature curing silver-coated copper composite slurry and a preparation method thereof, characterized in that: Based on the total mass of the conductive paste being 100%, the low-temperature curing silver-clad copper composite paste is composed of the following components in percentage by weight: Conductive phase 60% to 80%; Resin 5% to 10%; Solvent 20% to 30%; Additives 3% to 8%. The conductive phase is compounded by mixing spherical silver-coated copper powder and flaky silver powder in a mass ratio of 0.5:1 to 3:1, wherein: The particle size of the spherical silver-coated copper powder is 1 to 3 μm, and the silver layer accounts for 10% to 20% of the total mass of the particles; The particle size of the flaky silver powder is 1 to 3 μm, and the tap density is 0.5 to 1.3 g / mL.

2. The low-temperature curing silver-clad copper composite slurry according to claim 1, characterized in that: The resin comprises a combination of one or more of epoxy resin with an epoxy equivalent of 5000 to 6000, polyurethane resin and acrylic resin.

3. The low-temperature curing silver-clad copper composite slurry according to claim 1, characterized in that: The solvent includes any one or more combinations of terpineol, dibasic acid ester (DBE), diethylene glycol monoethyl ether acetate and cyclohexanone.

4. The low-temperature curing silver-clad copper composite slurry according to claim 1, characterized in that: The additives include any one or more combinations of curing agents, leveling agents, adhesives and dispersants.

5. The low-temperature curing silver-clad copper composite slurry according to claim 1, characterized in that: The curing agent includes any one of dicyandiamide, blocked isocyanate, 2,4-dimethylimidazole, 2-methylbenzimidazole and 2-ethyl-4-methylimidazole, or a combination of at least two thereof.

6. The low-temperature curing silver-clad copper composite slurry according to claim 1, characterized in that: The leveling agent includes any one of polydimethylsiloxane (PDMS), polyether-modified siloxane (such as BYK-333), and fluorine-modified siloxane, or a combination of at least two thereof, to improve printing leveling.

7. The low-temperature curing silver-clad copper composite slurry according to claim 1, characterized in that: The binder includes any one of ethyl cellulose (EC100) and sodium carboxymethyl cellulose (CMC-Na) or a combination of at least two thereof to control the thixotropy of the slurry.

8. The low-temperature curing silver-clad copper composite slurry according to claim 1, characterized in that: The dispersant includes any one or a combination of at least two of polyvinyl pyrrolidone (PVP K30 / K90), polycarboxylate (such as BYK-110), cetyltrimethylammonium bromide (CTAB), silane coupling agent KH560 and YDC-2140.

9. The low-temperature curing silver-clad copper composite slurry and preparation method thereof according to claim 1, characterized in that: The following steps are involved: (1) Stepwise mixing: Disperse the resin and solvent at a high speed of 800-1200 r / min for 5-10 min to form a homogeneous carrier; (2) Introduction of conductive phase: add spherical silver-coated copper powder, flake silver powder and additives in sequence, with an interval of 5 minutes each time and mix well; (3) Grinding: Grind the slurry in a mortar in a clockwise direction for 15 to 30 minutes, and control the slurry fineness D50 ≤ 5 μm; (4) Screen printing: The slurry is used to form a circuit pattern on a glass substrate through a screen printing process, with a line width of ≤1mm; (5) Leveling treatment: Let it stand at 25-30°C for 10-30 seconds to eliminate bubbles on the printing interface; (6) Low temperature curing: Curing in a drying oven at 120-180°C for 10-20 minutes before conducting resistivity test.

10. The low-temperature curing silver-clad copper composite slurry and preparation method thereof according to claim 9, characterized in that: In step (4), the mesh number of the silk screen is ≥400 mesh, the scraper angle is 60-75°, and the printing pressure is 0.2-0.5 MPa.

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