CN114822983A - Preparation method of fast-curing conductive paste - Google Patents
Preparation method of fast-curing conductive paste Download PDFInfo
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- CN114822983A CN114822983A CN202210286553.2A CN202210286553A CN114822983A CN 114822983 A CN114822983 A CN 114822983A CN 202210286553 A CN202210286553 A CN 202210286553A CN 114822983 A CN114822983 A CN 114822983A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/20—Conductive material dispersed in non-conductive organic material
- H01B1/22—Conductive material dispersed in non-conductive organic material the conductive material comprising metals or alloys
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K1/00—Printed circuits
- H05K1/02—Details
- H05K1/09—Use of materials for the conductive, e.g. metallic pattern
- H05K1/092—Dispersed materials, e.g. conductive pastes or inks
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/10—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern
- H05K3/12—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns
- H05K3/1216—Apparatus or processes for manufacturing printed circuits in which conductive material is applied to the insulating support in such a manner as to form the desired conductive pattern using thick film techniques, e.g. printing techniques to apply the conductive material or similar techniques for applying conductive paste or ink patterns by screen printing or stencil printing
Abstract
The application provides a preparation method of a fast-curing conductive paste for a printed circuit. The conductive slurry is prepared from conductive powder, high-molecular resin, a curing agent, a solvent, carbon nanotubes and other functional auxiliaries. After the conductive paste is subjected to screen printing, the conductive paste can be cured at the temperature of 90-150 ℃ for 5 minutes.
Description
Technical Field
The present invention relates to a curable conductive paste, and more particularly, to a formulation and a preparation method of a conductive paste that can be cured rapidly at a temperature of 90 ℃ to 150 ℃.
Background
The cured conductive paste has good conductivity, stability and reliability, and is widely applied to the electronic industry, including membrane switches, keyboards, touch screens, flexible sensors, blood glucose testers, electromagnetic shielding and other subdivided fields. The main components of the curing type conductive slurry comprise conductive metal powder, high polymer resin, a curing agent, a solvent, a functional auxiliary agent and the like. In the process of heating and curing, the solvent in the slurry system volatilizes under the action of temperature, and meanwhile, the polymer resin, the curing agent and part of the auxiliary agent undergo a crosslinking reaction to form a three-dimensional network structure. The crosslinking reaction enables the cured thick film paste to have excellent performances such as conductivity, hardness, adhesion and the like.
The curing type conductive silver paste is a common conductive paste and has great market potential. However, most conductive silver pastes on the market generally require longer curing times (20 minutes or even longer). Longer cure times have two major adverse effects on production: (1) the production efficiency is low, and the number of products produced in unit time is greatly less than that of the rapidly solidified silver paste. A fast curing silver paste (cure in 5 minutes) may be more than 3 times more efficient at downstream client production than a non-fast curing silver paste (e.g., 20 minutes cure). (2) The energy consumption of unit products is high, a tunnel furnace is usually used in the production process of silver paste solidification, the tunnel furnace belongs to high-power and high-energy consumption products, and the power of the tunnel furnace can reach dozens of kilowatts. The non-fast curing silver paste will result in high electricity cost for unit finished product and no carbon neutralization requirement. Therefore, the quick-curing silver paste has important economic, production efficiency and environmental protection significance.
The curing reaction refers to a chemical reaction in which the monomer/oligomer is crosslinked under specific conditions (e.g., temperature, humidity, light, etc.) and forms a coating with higher hardness. Curing agents play a crucial role in the curing reaction, and generally contain functional groups that can cross-link with the monomers/oligomers and irreversibly change the thermosetting resin by chemical reactions such as condensation, ring closure, addition, or catalysis. The curing agent is widely used, and the curing agent can be classified into aliphatic amine, aromatic amine, modified amine, low molecular polyamide, imidazole curing agent, acid anhydride curing agent, latent curing agent, and the like, taking a common epoxy resin as an example. The latent curing agent can be mixed with corresponding resin and has certain storage stability at room temperature, so that the latent curing agent is commonly used as a single-component electronic paste curing agent.
Disclosure of Invention
In view of the advantages of the fast curing electronic paste in the aspects of production efficiency, energy conservation and the like, the application provides a preparation method of the fast curing electronic paste, which comprises the following steps: 20-90 wt% of conductive powder, 1-20 wt% of polymer resin, 0.1-10 wt% of curing agent, 0.1-10 wt% of Carbon Nano Tube (CNT), 5-50 wt% of solvent and 0.1-15 wt% of auxiliary agent. The electronic paste can be rapidly cured within 5 minutes at a temperature range of 90-150 ℃ to form a thick film material with good electrical, mechanical and thermal properties.
The conductive powder is a novel functional material, and can be used as a filler in electronic paste to endow the paste with the functions of conductivity, static resistance, electromagnetic shielding and the like. The conductive powder is various, and commonly used are metal-based powder and carbon-based powder. The basic properties of the powder include:
particle size distribution: the composition of the particle size in the powder system is divided into frequency distribution and cumulative distribution. Typical parameters are D10 (cumulative particle distribution of 10% particle size), D50 (cumulative particle distribution of 50% particle size, also known as median or median particle size) and D90 (cumulative particle distribution of 90% particle size).
The appearance is as follows: the shape of the particles in the powder is commonly spherical, flaky, dendritic, rod-like, linear, etc.
Tap density: the powder can reach the limit stacking density after external force such as vibration and the like is applied.
Specific surface area: total area per unit mass of material.
The metal powder is the most important conductive powder material, and commonly used materials include gold powder, silver powder, platinum powder, nickel powder, aluminum powder, copper powder, silver-coated copper powder and the like. The gold, silver and platinum are noble metals, the nickel, aluminum and copper are base metals, and the silver-coated copper is a noble metal-coated base metal material. The conductive silver paste is widely applied to the fields of photovoltaics, microelectronic packaging, sensors and the like, is large in market scale, and also drives the upstream silver powder industry. The conductive silver powder for the electronic paste is usually prepared by a chemical reduction method, and the method has the advantages of controllable particle size and morphology, high purity and the like. Silver powder is expensive, so that cost reduction by coating base metal with silver has been promoted in recent years, and alloy powder such as silver-coated copper, silver-coated aluminum, silver-coated nickel and the like is also receiving more and more market attention.
The carbon-based powder may be further classified into conductive carbon black, carbon fiber, carbon nanotube, graphene, and the like. The conductive carbon black is the most commonly used carbon powder, has the advantages of low resistance, small particle size, large and rough specific surface area, clean surface and the like, and can be widely applied to the fields of conductive ink, lithium batteries, supercapacitors, cables, tires and the like. The carbon fiber is a fiber made of carbon materials, has the characteristics of high temperature resistance, friction resistance, electric conduction, heat conduction, corrosion resistance and the like, and can be used for improving the electric conduction and the mechanical strength of a base material. Carbon nanotubes and graphene are new carbon materials, have electrical, thermal and mechanical properties greatly superior to those of traditional conductive carbon black, and are receiving wide attention in recent years.
Carbon nanotubes (abbreviated CNTs) are round tubes formed of Carbon atoms arranged in a hexagonal shape, and are representative of advanced Carbon materials. The CNT has excellent electrical, thermal and mechanical properties, and the application field of the CNT is wider and wider along with the deep research and development. CNTs exhibit a one-dimensional linear structure with a diameter of 2-20 nanometers and a length of several hundred micrometers. CNTs can be classified into single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) according to the number of wall layers. The carbon atoms of the CNTs taking the SP 2 Hybridization with SP 3 Carbon materials have higher mechanical strength than carbon materials. The theoretical tensile strength of the CNT reaches 50-200 GPa, which is close to 100 times of that of steel, but the density of the CNT is only 1/6 of the steel. Meanwhile, the CNT has the same structure as the graphite lamellar structure, so the CNT also has good conductivity. Based on the above properties, the electronic paste of the present application uses CNTs to improve its mechanical and electrical properties.
Unlike the high-temperature electronic paste using glass powder, the low-temperature electronic paste uses polymer resin as a matrix material. The polymer resin is a compound having a relatively high molecular weight of thousands to millions, and its structure is formed by connecting simple structural units in a repetitive manner. Resins commonly used in electronic pastes include epoxy resins, vinyl chloride-vinyl acetate resins, polyester resins, polyurethane and silicone resins, among others. The choice of resin is determined based on the specific application scenario, for example, polyurethane is generally used as the electronic paste for flexible circuits, and epoxy resin is used as the HJT silver paste due to the requirements of high conductivity and high mechanical strength.
The curing agent reacts with the specific functional group of the high molecular resin to realize molecular chain crosslinking, thereby playing a hardening role on the thick film material. Isocyanates are a commonly used curing agent, whose functional groups (-N ═ C ═ O) can undergo a crosslinking reaction with the hydroxyl functional groups (-OH) of the polymer itself under specific conditions (e.g. temperature). Isocyanates can be divided into monoisocyanates, diisocyanates and polyisocyanates. Diisocyanates are often used as curing agents, and two functional groups (-N ═ C ═ O) contained in a single diisocyanate molecule can react with two polyol-containing monomer/oligomer molecules, respectively, to effect crosslinking of the molecular chain. Commonly used diisocyanates include Toluene Diisocyanate (TDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), Hexamethylene Diisocyanate (HDI), Lysine Diisocyanate (LDI). The electronic paste adopts diisocyanate ester curing agent.
The specific preparation method of the electronic paste comprises the following steps: (1) mixing, stirring and dissolving a high-molecular resin and a solvent in a specific ratio, (2) weighing and mixing conductive powder, a resin solution, a curing agent, a carbon nano tube, the solvent and an auxiliary agent in a specific mass ratio, (3) stirring the mixed materials to be uniform and fully infiltrated (the rotating speed is 30-100 rpm) by using a double-planet stirrer, (4) dispersing the electronic slurry to the fineness of less than 10 microns by using a three-roll grinder, collecting the electronic slurry and marking.
Screen printing and curing: printing the electronic paste into a film by using a screen printer (printing speed is 100mm/s, pressure is 30kPa, and the thickness of a base material is 125 mu m of PET); and (3) placing the printed circuit in a blast oven for drying and curing, and testing the square resistance (numerical value calculated by the thickness of 25.4 mu m) of the thick film material, the pencil hardness and the adhesive force after curing.
Drawings
FIG. 1: scanning electron microscope picture of conductive silver powder
FIG. 2: carbon nanotube scanning electron microscopy
FIG. 3: conductive silver paste and printed circuit
FIG. 4: conductive silver paste curing temperature test
FIG. 5 is a schematic view of: conductive silver paste curing time test
FIG. 6: scanning electron microscope picture of conductive silver coated copper powder
Detailed Description
In order to illustrate the invention more clearly, the invention is further described below with reference to specific examples of implementation and the accompanying drawings, which are not intended to limit the scope of protection of the invention.
Example 1
The formula and the preparation method of the fast curing electronic paste comprise the following steps:
weighing thermoplastic polyurethane (weight average molecular weight (M) w ): 60000-100000) 6.80 g and 35.70 g of dibasic ester solvent are added into a round-bottom flask. The above mixed solution was heated to 70 ℃ and stirring was continued for several hours until the resin was dissolved. After the resin was completely dissolved, the resin solution was cooled to room temperature and transferred to a slurry tank. Thereafter, 54.50 g of plate-like silver powder (FIG. 1), 0.50 g of carbon nanotube powder (FIG. 2), 0.80 g of diisocyanate latent curing agent (deblocking temperature about 80 ℃ C.) and 1.7 g of paste aids (mainly dispersant, adhesion promoter and thixotropic agent) were added to the resin solution. The paste formula is used for preparing low-temperature curing conductive silver paste through processes of stirring, three-roll grinding and the like, and a conductive thick film material is obtained through screen printing and baking in a hot air box. Fig. 3(a) shows the conductive silver paste prepared by the above formulation and process, and fig. 3(b) is a silver paste screen printed circuit.
In order to study the curing temperature of the silver paste, the prepared silver paste printed circuit was baked at 90 ℃, 110 ℃, 130 ℃ and 150 ℃ respectively, and the baking time was set to 5 minutes. After baking is finished, the performances of square resistance, hardness, adhesive force and the like of the cured silver paste under different temperature conditions are respectively tested to examine the curing degree of the paste. As shown in FIG. 4, the sheet resistance of the silver paste printed circuit decreased with increasing temperature from 71.77 m.OMEGA/□ (90 ℃) to 45.77 m.OMEGA/□ (150 ℃). At the same time, the hardness increased from H (90 ℃ C.) to 3H (150 ℃ C.). Under the four test temperature conditions, the adhesion force of the cured slurry on PET is 5B. From the above results, it can be seen that: (1) under the baking condition of 90 ℃, partial curing of the silver paste is realized, so that a circuit with the hardness of H (the hardness of the uncured silver paste is obviously lower than H) and the square resistance of 71.77m omega/□ can be obtained; (2) with the temperature rise, the silver paste solidification is further improved, mainly represented by hardness increase and square resistance decrease; (3) the slurry can realize rapid curing (curing time 5 minutes) under the baking condition of 90-150 ℃.
And (3) testing curing time: the baking temperature was set to a constant temperature of 130 ℃ and the printed circuits were tested for sheet resistance, hardness and adhesion after curing for 1 minute, 3 minutes, 5 minutes, 10 minutes, 20 minutes, respectively. As shown in fig. 5, the sheet resistance of the printed circuit decreased with increasing cure time; the hardness increases with time; the adhesive force is 5B. From the above data, one can conclude: (1) the slurry can be cured in as little as 1 minute at 130 ℃; (2) the degree of cure increases with time; (3) under the condition of curing for 5 minutes, the hardness of the silver paste rises to 3H and is stable, indicating that the curing is nearly completed.
In summary, the conductive silver paste prepared in example 1 can be rapidly cured at a temperature ranging from 90 ℃ to 150 ℃.
Example 2
The formula and the preparation method of the fast curing electronic paste comprise the following steps:
polyester resin (weight average molecular weight (M) was weighed w ) About 50000)7.60 grams, 30.40 grams of carbitol acetate were added to the round bottom flask. The above mixed solution was heated to 60 ℃ and stirring was continued for several hours until the resin was dissolved. After the resin was completely dissolved, the resin solution was cooled to room temperature and transferred to a slurry tank. Thereafter, 60.00 g of silver-coated copper powder (FIG. 6), 0.30 g of carbon nanotube powder (FIG. 2), 0.90 g of latent diisocyanate curing agent (deblocking temperature about 80 ℃ C.), and 0.8 g of paste aids (mainly adhesion promoters and thixotropic agents) were added to the resin solution. The low-temperature cured conductive silver-copper paste is prepared by the paste formula through processes of stirring, three-roll grinding and the like, and a conductive thick film material is obtained through screen printing and baking in a hot air box. Tests show that after the silver-coated copper paste is cured at 130 ℃ for 5 minutes, the square resistance is 561.22m omega/□, the hardness is 3H, the adhesive force is 5B, and low-temperature rapid curing can be realized.
Claims (13)
1. A preparation method of fast curing conductive paste is characterized by comprising the following steps: the conductive paste can realize rapid curing at the temperature range of 90-150 ℃,
a fast-curing conductive paste, comprising:
20-90 wt% of conductive powder;
1-20 wt% of polymer resin;
0.1-10 wt% of a curing agent;
0.1-10 wt% of Carbon Nanotube (CNT);
5-50 wt% of a solvent;
0.1-15 wt% of an auxiliary agent;
wherein, the polymer resin, the curing agent and part of the auxiliary agent can complete the cross-linking reaction and realize the rapid curing at the temperature range of 90 ℃ to 150 ℃.
2. The method for preparing a fast-curing conductive paste according to claim 1, wherein: the conductive powder is one or more of silver powder, silver-coated copper powder or copper powder.
3. The method for preparing a fast-curing conductive paste according to any one of claims 1 to 2, wherein: the conductive powder is in one or more of a flake shape, a spherical shape or an irregular shape.
4. The fast-curing conductive paste according to claims 1-2, wherein: the particle size distribution of the conductive powder is D100.5-3 μm, D501-8 μm, and D905-30 μm.
5. The method for preparing a fast-curing conductive paste according to claim 1, wherein; the polymer resin is one or more of polyurethane, polyester resin or vinyl chloride-vinyl acetate resin with molecular chain containing hydroxyl (-OH) functional group.
6. The method for preparing a fast-curing conductive paste according to claim 1, wherein: the curing agent is diisocyanate (-N ═ C ═ O) curing agent.
7. The method for preparing a fast-curing conductive paste according to any one of claims 1 or 6, wherein: the diisocyanate curing agent is a latent curing agent, and the gel temperature of the diisocyanate curing agent and the hydroxyl functional group-containing thermoplastic resin is between 40 ℃ and 90 ℃.
8. The fast-curing conductive paste according to claim 1, wherein: the carbon nanotubes may be single-walled carbon nanotubes or multi-walled carbon nanotubes.
9. The method for preparing a fast-curing conductive paste according to any one of claims 1 or 8, wherein: the diameter of the carbon nano tube is between 1 nanometer and 100 nanometers, and the length of the carbon nano tube is between 0.1 micrometer and 100 micrometers.
10. The method for preparing a fast-curing conductive paste according to claim 1, wherein: the solvent is one or more of high boiling point alcohols, ethers, alcohol ethers or ester solvents.
11. The method for preparing a fast-curing conductive paste according to claim 1, wherein: the auxiliary agent comprises one or more of a wetting dispersant, a thickening agent, a defoaming agent, a leveling agent and an antioxidant.
12. The method for preparing a fast-curing conductive paste according to any one of claims 1 or 11, wherein: the auxiliary agent may contain an organic metal complex catalyst and accelerate the reaction rate of the resin and the curing agent in the conductive paste.
13. The method for preparing a fast-curing conductive paste according to any one of claims 1 to 12, wherein: the conductive paste may form a conductive line through a screen printing process and a baking process.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116130142A (en) * | 2022-12-28 | 2023-05-16 | 北京交通大学 | High-conductivity, anti-corrosion and anti-aging electric power composite grease and preparation method thereof |
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- 2022-03-22 CN CN202210286553.2A patent/CN114822983A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116130142A (en) * | 2022-12-28 | 2023-05-16 | 北京交通大学 | High-conductivity, anti-corrosion and anti-aging electric power composite grease and preparation method thereof |
| CN116130142B (en) * | 2022-12-28 | 2023-09-22 | 北京交通大学 | Preparation method of high-conductivity, anti-corrosion and anti-aging electric power composite grease |
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