High-conductivity low-temperature cured carbon nanotube enhanced conductive silver adhesive and preparation method thereof

Abstract

The invention relates to a high-conductivity low-temperature cured carbon nanotube enhanced conductive silver adhesive and a preparation method thereof. The conductive silver adhesive comprises 75%-80% of silver powder, 15%-20% of epoxy resin, 3%-5% of a curing agent, 0.1%-1% of carbon nanotubes, 0.5%-1% of a coupling agent and 1%-3% of a diluent. Through a special preparation process, the conductive silver adhesive has remarkable advantages. In the aspect of conductivity, the high-content silver powder is matched with the carbon nanotubes to form an efficient conductive network, so that high conductivity and low resistance stability are achieved; in the aspect of mechanical properties, the epoxy resin and the coupling agent ensure strong binding power, and the carbon nanotubes enhance the mechanical stability; and in terms of processing property, low-temperature curing can be realized, and good flowability and coating property are achieved. The conductive silver adhesive can effectively solve the problems of conductive connection of high-precision electronic devices, packaging of temperature-sensitive devices, reliability of electronic equipment in a complex environment and the like, and can be widely applied to the fields of integrated circuit chips, micro electro mechanical systems, aerospace and the like.

Description

Technical Field

[0001] The present invention relates to the field of conductive silver paste, and in particular to a high-conductivity, low-temperature curing carbon nanotube-enhanced conductive silver paste and a preparation method thereof. Background Art

[0002] In the development of the electronics industry, there are many problems with commonly used conductive connection materials in the early days, such as lead-tin solder. Lead is a toxic heavy metal, and its use can cause serious harm to the environment and human health, and does not meet environmental protection requirements. With increasingly stringent environmental regulations, the trend of restricting the use of lead is becoming more and more obvious. For example, the EU's "Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment Directive" (RoHS) explicitly restricts the use of hazardous substances such as lead. At the same time, the welding process of traditional solders usually requires higher temperatures, which may cause damage to some electronic components that are not resistant to high temperatures, affecting their performance and reliability. Moreover, in the connection of some delicate electronic components and micro-nano structures, traditional solders are difficult to meet the high-precision and high-reliability connection requirements.

[0003] As electronic devices evolve towards miniaturization, higher performance, and greater multifunctionality, the performance requirements for conductive interconnect materials are becoming increasingly stringent. Conductive silver paste, a new type of conductive interconnect material, offers advantages such as low-temperature curing, precise coating, and good compatibility with a wide range of materials. It has become a research hotspot in the electronic packaging and interconnection fields. It can be used for connecting chips to substrates, soldering components on printed circuit boards, and manufacturing flexible electronic devices. However, current commercially available conductive silver pastes still have limitations in terms of conductivity, mechanical properties, and processability, failing to fully meet the demands of the rapidly developing electronics industry. Summary of the Invention

[0004] The first object of the present invention is to provide a high-conductivity, low-temperature curing carbon nanotube-enhanced conductive silver paste, which has high conductivity, good mechanical properties and processability, and can meet the demand of the rapid development of the electronics industry for high-performance conductive connection materials.

[0005] The technical solution for achieving the first object of the present invention is as follows: the high-conductivity, low-temperature curing carbon nanotube-enhanced conductive silver paste of the present invention comprises the following components by weight: 75%-80% silver powder, 15%-20% epoxy resin, 3%-5% curing agent, 0.1%-1% carbon nanotubes, 0.5%-1% coupling agent, and 1%-3% diluent; the silver powder is a mixture of flaky silver powder and spherical silver powder, wherein the flaky silver powder has a particle size of 5-10 μm and the spherical silver powder has a particle size of 1-3 μm; the epoxy resin is bisphenol A epoxy resin; the curing agent is an aliphatic amine curing agent; the carbon nanotubes are multi-walled carbon nanotubes that have been acidified; the coupling agent is a silane coupling agent; and the diluent is active butyl glycidyl ether.

[0006] As an optimized design, the following components are included in weight percentage: silver powder content is 80%, epoxy resin content is 15%, curing agent content is 3%, carbon nanotube content is 0.5%, coupling agent content is 0.5%, and diluent content is 1%; among which, the particle size of the flaky silver powder in the silver powder is 5-10μm, and the particle size of the spherical silver powder is 1-3μm.

[0007] The design of the conductive silver paste in the present invention is optimized and improved in the following aspects:

[0008] Conductive filler: Flake silver powder and spherical silver powder are mixed in a certain proportion as the conductive filler. Flake silver powder has a large specific surface area and a unique planar structure, which can form abundant conductive channels. Spherical silver powder has good fluidity and filling properties, which can fill the gaps in the flake silver powder and increase the packing density.

[0009] Resin matrix: Select a resin with good bonding properties and chemical stability as the matrix material, such as epoxy resin. The resin matrix plays the role of bonding the silver powder and the connected material, and can provide a certain degree of mechanical support.

[0010] Additives: Add appropriate amounts of additives to improve the performance of conductive silver paste, such as dispersants used to improve the dispersion of silver powder in the resin matrix and prevent silver powder agglomeration; curing agents used to promote the curing reaction of the resin matrix, so that the conductive silver paste can be quickly cured under certain conditions; coupling agents used to enhance the interfacial bonding between silver powder and the resin matrix, and improve the comprehensive performance of the conductive silver paste.

[0011] The second object of the present invention is to provide a method for preparing the above-mentioned high-conductivity low-temperature curing carbon nanotube-enhanced conductive silver paste.

[0012] The technical solution for achieving the second object of the present invention is: the method for preparing the above-mentioned high-conductivity, low-temperature curing carbon nanotube-enhanced conductive silver paste in the present invention comprises the following steps:

[0013] S1. Mixing flaky silver powder and spherical silver powder in a ratio of 2:1, adding acidified multi-walled carbon nanotubes, placing in a high-speed blender, and stirring at a speed of 1000-3000 rpm for 15-30 minutes to obtain a pretreated mixture;

[0014] S2. Add bisphenol A epoxy resin, aliphatic amine curing agent, silane coupling agent and active butyl glycidyl ether into a stirring container according to the formula ratio, and stir at a low speed of 200-500 rpm for 10-15 minutes at room temperature of 20-30° C. to obtain a resin mixture;

[0015] S3, the pre-treated mixture is gradually added to the resin mixture in small amounts and repeatedly, stirred at a speed of 300-800 rpm while adding, and then ground using a three-roll mill, the grinding pressure is controlled at 5-10MPa, and the number of grindings is 3-5 times to obtain a mixed material;

[0016] S4. Put the mixed material into a vacuum degassing device, set the vacuum degree to -0.09 MPa to -0.1 MPa, and degas for 10-30 minutes to obtain the conductive silver paste.

[0017] Among them, the reason why silver powder is a mixture of flake silver powder and spherical silver powder is that the conductive silver paste prepared by such a proportion of silver powder can not only significantly improve the conductivity, but also make the conductive grid more perfect.

[0018] Furthermore, in the above step S3, the roller gap of the three-roll mill decreases from the feed end to the discharge end, the roller gap at the feed end is 50-100 μm, and the roller gap at the discharge end is 10-30 μm.

[0019] Since the silver powder content is 80%, adding a large amount of silver powder mixture at one time may cause agglomeration or uneven dispersion or too high viscosity, affecting the performance of the conductive adhesive. Therefore, the silver powder mixture is added gradually in small amounts and multiple times and the pressure is controlled to grind multiple times.

[0020] Furthermore, in the above step S4, in the degassing step, the mixed material is slowly stirred at a speed of 100-200 rpm during the degassing process.

[0021] The present invention has positive effects: (1) The conductive silver glue in the present invention can be applied to integrated circuit chip packaging to ensure stable electrical signal transmission and mechanical fixation, and is also suitable for micro-electromechanical system packaging to meet low-temperature curing and electrical connection and protection requirements.

[0022] (2) High conductivity: By rationally adjusting the ratio of flaky silver powder and spherical silver powder and adding acid-treated multi-walled carbon nanotubes, the advantages of the two silver powders are fully utilized. The flaky silver powder can form more conductive contact points, the spherical silver powder fills the gaps, and the carbon nanotubes build additional conductive bridges between the silver powders. They are evenly dispersed through high-speed stirring to form an efficient and continuous conductive network, which greatly improves the conductivity and stability of the conductive silver paste and reduces the resistance.

[0023] (3) Good mechanical properties: The reasonable selection of resin matrix and additives and the optimized preparation process make the conductive silver glue have good bonding strength and mechanical stability, which can withstand certain external forces and ensure the reliability of electronic component connection.

[0024] (4) Excellent process performance: Conductive silver glue has good fluidity and coating properties, making it easy to process through printing, dispensing and other processes, and can adapt to different production processes and application scenarios. At the same time, the low-temperature curing process can reduce thermal damage to electronic components, improving production efficiency and product quality.

[0025] (5) Environmental protection: Compared with traditional lead-tin solder, conductive silver glue does not contain toxic heavy metal lead, meets environmental protection requirements, and is conducive to the sustainable development of the electronics industry. DETAILED DESCRIPTION

[0026] (Example 1)

[0027] The conductive silver paste of the present invention includes metal powder, bisphenol A epoxy resin, dispersant, curing agent, and coupling agent; the metal powder is silver powder, the bisphenol A epoxy resin is E-51, the dispersant is BYK-110, the curing agent is D230 (diethylenetriamine), the carbon nanotubes are single-walled carbon nanotubes, and the coupling agent is KH-560 (propyltrimethoxysilane); in terms of weight percentage, the silver powder content is 80%, the epoxy resin content is 15%, the curing agent content is 3%, the carbon nanotube content is 0.5%, the coupling agent content is 0.5%, and the diluent content is 1%.

[0028] The preparation of the conductive silver paste in the present invention comprises the following steps:

[0029] S1. Prepare silver powder: prepare flaky silver powder with an average particle size of 3-5 μm and a purity of 99.9%; prepare spherical silver powder with an average particle size of 1-3 μm and a purity of 99.9%.

[0030] S2. Mix flaky silver powder and spherical silver powder in a proportion of 80% silver powder; wherein the ratio of flaky silver powder to spherical silver powder is 2:1, add acidified multi-walled carbon nanotubes, place in a high-speed blender, and stir at a speed of 3000 rpm for 20 minutes;

[0031] S3. Add E-51, BYK-110, and D230 into a stirring container according to the formula ratio, and stir at a low speed of 500 rpm for 15 minutes at room temperature (20-30°C) to obtain a resin mixture;

[0032] S4. Slowly add the weighed silver powder to the resin mixture in batches. After adding each portion of silver powder, stir at a speed of 800r / min for 10 minutes. After all the silver powder is added, grind it using a three-roll mill with a grinding pressure of 10MPa for 3 times to ensure that the silver powder, carbon nanotubes and epoxy resin are fully mixed.

[0033] S5. Place the mixed conductive silver paste into a vacuum degassing machine and degas at a vacuum degree of -0.1 MPa for 30 minutes to remove bubbles in the system.

[0034] (Comparative Example 1)

[0035] In this comparative example, the content of silver powder is 80%, the content of epoxy resin is 15%, the content of curing agent is 3%, the content of coupling agent is 1%, and the content of diluent is 1% by weight.

[0036] S1. Prepare metallic silver powder, flake silver powder, average particle size is 3-5μm, purity is 99.9%, spherical silver powder: average particle size is 1μm, purity is 99.9%,

[0037] S2. Mix flaky silver powder and spherical silver powder in a proportion of 80% silver powder, wherein the ratio of flaky silver powder to spherical silver powder is 2:1, put into a high-speed blender, and stir at a speed of 3000 rpm for 20 minutes;

[0038] The preparation methods are the same as those in Example 1.

[0039] (Comparative Example 2)

[0040] In this comparative example, the content of silver powder is 80%, the content of epoxy resin is 15%, the content of curing agent is 3%, the content of carbon nanotubes is 0.5%, the content of coupling agent is 0.5%, and the content of diluent is 1% by weight.

[0041] S1. Prepare metallic silver powder, flake silver powder, average particle size 3-5μm, purity 99.9%,

[0042] S2, silver powder content is 80%; add acidified multi-walled carbon nanotubes, put into a high-speed blender, and stir at 3000 rpm for 20 minutes;

[0043] The preparation methods are the same as those in Example 1.

[0044]

[0045] in conclusion:

[0046] A comparative analysis of the formulations, preparation methods, and performance of Example 1, Comparative Example 1, and Comparative Example 2 reveals the following: Example 1 exhibits the best overall performance. In terms of conductivity, due to the optimal combination of spherical and flaky silver powders and the addition of carbon nanotubes, it achieves the lowest volume resistivity and the best conductivity. In terms of mechanical properties, it exhibits high bonding strength, demonstrating good cohesion and stability. In terms of process performance, it exhibits uniform mixing and excellent degassing. Comparative Example 1 lacks carbon nanotubes, and Comparative Example 2 lacks spherical silver powder, resulting in deficiencies in conductivity, mechanical properties, and process performance, respectively. This demonstrates that the synergistic effect of spherical and flaky silver powders with carbon nanotubes significantly enhances the performance of the conductive silver paste.

[0047] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A high-conductivity, low-temperature curing carbon nanotube-enhanced conductive silver paste; characterized by: The invention comprises the following components in weight percentage: 75%-80% silver powder, 15%-20% epoxy resin, 3%-5% curing agent, 0.1%-1% carbon nanotubes, 0.5%-1% coupling agent, and 1%-3% diluent; the silver powder is a mixture of flaky silver powder and spherical silver powder, wherein the particle size of the flaky silver powder is 5-10 μm, and the particle size of the spherical silver powder is 1-3 μm; the epoxy resin is bisphenol A epoxy resin; the curing agent is an aliphatic amine curing agent; the carbon nanotubes are multi-walled carbon nanotubes that have been acidified; the coupling agent is a silane coupling agent; and the diluent is active butyl glycidyl ether.

2. The high-conductivity, low-temperature curing carbon nanotube-enhanced conductive silver paste according to claim 1, characterized in that: The invention comprises the following components in weight percentage: 80% silver powder, 15% epoxy resin, 3% curing agent, 0.5% carbon nanotube, 0.5% coupling agent and 1% diluent; wherein, the particle size of the flaky silver powder in the silver powder is 5-10 μm, and the particle size of the spherical silver powder is 1-3 μm.

3. A method for preparing the high-conductivity, low-temperature curing carbon nanotube-enhanced conductive silver paste according to claim 1 or 2, characterized in that The following steps are involved: S1. Mixing flaky silver powder and spherical silver powder in a ratio of 2:1, adding acidified multi-walled carbon nanotubes, placing in a high-speed blender, and stirring at a speed of 1000-3000 rpm for 15-30 minutes to obtain a pretreated mixture; S2. Add bisphenol A epoxy resin, aliphatic amine curing agent, silane coupling agent and active butyl glycidyl ether into a stirring container according to the formula ratio, and stir at a low speed of 200-500 rpm for 10-15 minutes at room temperature of 20-30° C. to obtain a resin mixture; S3, the pre-treated mixture is gradually added to the resin mixture in small amounts and repeatedly, stirred at a speed of 300-800 rpm while adding, and then ground using a three-roll mill, the grinding pressure is controlled at 5-10MPa, and the number of grindings is 3-5 times to obtain a mixed material; S4. Put the mixed material into a vacuum degassing device, set the vacuum degree to -0.09 MPa to -0.1 MPa, and degas for 10-30 minutes to obtain the conductive silver paste.

4. The preparation method according to claim 3, wherein: In step S3, the roller gap of the three-roller mill decreases from the feed end to the discharge end, with the roller gap at the feed end being 50-100 μm and the roller gap at the discharge end being 10-30 μm.

5. The preparation method according to claim 3, wherein: In the step S4, in the degassing step, the mixed material is slowly stirred at a speed of 100-200 rpm during the degassing process.

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