Medium and high temperature resistant silver-based conductive paste and preparation method thereof

Abstract

The preparation method specifically comprises the following steps: mixing silver-coated copper microspheres with spherical silver powder, flaky silver powder and dendritic silver powder to obtain mixed powder; adding rubber into a solvent, carrying out ultrasonic treatment to obtain a rubber liquid, slowly adding the rubber liquid into the binding phase, and uniformly stirring; and adding a curing agent, a catalyst and the mixed powder into the binding phase, uniformly stirring, and putting into vacuum defoaming equipment to remove bubbles generated in the mixing process to obtain the silver-based conductive paste. According to the preparation method disclosed by the invention, the rubber modified epoxy resin is used as a binding phase of the conductive paste, and the rubber can enhance the toughness and flexibility of the epoxy resin, reduce cracks and fractures caused in the use process and improve the adhesion performance of the epoxy resin, so that the conductive paste can be more firmly adhered to the surfaces of various substrates; and the modified epoxy resin shows better fatigue resistance, and the service life of the conductive paste is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of conductive paste preparation, and in particular relates to a method for preparing a medium- and high-temperature resistant silver-based conductive paste, and also relates to the medium- and high-temperature resistant silver-based conductive paste. Background Art

[0002] Conductive paste is a paste or liquid material mixed with conductive materials, binders and solvents, which can form a conductive coating or film structure under specific conditions. It is widely used in the manufacture of electronic components, printed circuit board preparation, solar cell electrodes and various functional films. Traditional conductive pastes often use metal powders (such as silver, gold, copper, etc.) as the conductive phase, and obtain good conductive properties through high-temperature sintering or curing treatment. With the development of the electronics industry, automobile industry and aerospace field, more and more application scenarios have put forward medium and high temperature resistance requirements for conductive pastes. For example, automotive sensors, engine control systems and conductive connection components in aerospace electronic equipment need to maintain good electrical properties and mechanical strength under high temperature conditions. Therefore, the development of a conductive paste that can maintain excellent conductive properties in medium and high temperature environments has become a hot spot for research and industrialization in related fields.

[0003] A Chinese patent (application number: 202210779926.X, publication number: CN115188519A, publication date: 2022.10.14) discloses a silver-coated copper-silver paste and a preparation method thereof, comprising: micron silver powder, nano silver powder, silver-coated copper powder, epoxy resin, epoxy curing accelerator, organic solvent and silane coupling agent; the silver-coated copper-silver paste can reduce the production cost of the silver paste and improve the conductivity of the silver paste; however, at high temperatures, it may induce an interfacial reaction between the metal (silver powder and silver-coated copper powder) and the organic components (epoxy resin, silane coupling agent), and the chemical bonds will break at high temperatures, resulting in a decrease in the bonding performance and stability of the silver paste.

[0004] Chinese patent (application number: 202111111878.9, publication number: CN 113555145 B, publication date: 2022.03.25) discloses a flexible high temperature resistant conductive paste, comprising: conductive powder, high heat resistant resin, epoxy resin, amine curing agent, imidazole curing accelerator, amino silicone oil modified epoxy resin, solvent, coupling agent and rheological additive; the cured film of the conductive paste has good flexibility and can be applied to flexible substrates such as PEEK and PI, and the cured film has excellent high temperature resistance. However, the high temperature performance of the conductive paste has certain defects. The synergy between the high heat resistant resin and other resins is uncertain, and the improper proportion or poor compatibility may not effectively improve the high temperature resistance; the curing system may over-react or fail at high temperature, produce by-products that affect the performance, and even the self-structure is damaged and cannot be cured normally, thereby comprehensively affecting the conductive, mechanical and other properties of the conductive paste in a high temperature environment. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a silver-based conductive paste resistant to medium and high temperatures, thereby solving the problems of poor thermal stability and low conductivity of the existing conductive paste.

[0006] Another object of the present invention is to provide a silver-based conductive paste that is resistant to medium and high temperatures.

[0007] The technical solution adopted by the present invention is a method for preparing a silver-based conductive paste resistant to medium and high temperatures, which is specifically implemented according to the following steps: Step 1, mixing silver-coated copper microspheres with spherical silver powder, flaky silver powder, and dendritic silver powder to obtain a mixed powder; Step 2, adding rubber into a solvent and performing ultrasonic treatment to obtain a rubber liquid; Step 3, slowly add the rubber liquid into the bonding phase and stir evenly; Step 4, adding a curing agent, a catalyst, and a mixed powder to the adhesive phase obtained in step 3, stirring evenly, and placing the mixture in a vacuum degassing device to remove bubbles generated during the mixing process to obtain a silver-based conductive paste.

[0008] The present invention is also characterized in that: In step 1, the mass ratio of silver-coated copper microspheres, spherical silver powder, flaky silver powder, and dendritic silver powder is 1:0.05-0.4:0.25-2.4:0.0025-0.2.

[0009] In step 2, the rubber is silicone rubber, the solvent is ethanol, the ultrasonic treatment temperature is 40° C., and the ultrasonic treatment time is 30 min.

[0010] In step 3, bisphenol A epoxy resin is selected as the bonding phase; the mass ratio of the bonding phase to the rubber liquid is 1:0.2, the stirring speed is 300 r / min; and the stirring time is 15 min.

[0011] In step 4, imidazole is selected as the curing agent and acrylic acid is selected as the catalyst; the added amount of the curing agent is 30-50% by weight of the bisphenol A epoxy resin, and the added amount of the catalyst is 0.5-1% by weight of the bisphenol A epoxy resin.

[0012] In step 4, the stirring speed is 300 r / min; the stirring time is 30 min; and the defoaming time is 20 min.

[0013] Another technical solution adopted by the present invention is a medium-high temperature resistant silver-based conductive paste prepared by a method for preparing a medium-high temperature resistant silver-based conductive paste.

[0014] The beneficial effects of the present invention are: (1) The method for preparing the medium- and high-temperature resistant silver-based conductive paste of the present invention uses rubber-modified epoxy resin as the bonding phase of the conductive paste, wherein the rubber can enhance the toughness and flexibility of the epoxy resin, reduce cracks and fractures caused during use, and improve the adhesion performance of the epoxy resin, so that the conductive paste can be more firmly adhered to various substrate surfaces, and the modified epoxy resin exhibits better fatigue resistance, thereby extending the service life of the conductive paste; (2) The method for preparing the medium- and high-temperature resistant silver-based conductive paste of the present invention uses a mixture of flaky silver-coated copper and silver powder as the conductive phase, which does not affect its conductive properties and can reduce the cost of preparing the conductive paste; (3) The method for preparing the medium- and high-temperature resistant silver-based conductive paste of the present invention uses imidazole and acrylic acid as a curing agent and a catalyst, which can efficiently cure the conductive paste at a lower temperature, thereby improving the curing speed and efficiency. The cured conductive paste has good thermal stability and can maintain its performance at a higher temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a graph of the square resistance change rate of the medium- and high-temperature resistant silver-based conductive paste prepared in Example 1; Figure 2 This is a graph of the square resistance change rate of the medium- and high-temperature resistant silver-based conductive paste prepared in Example 2; Figure 3 This is a graph of the square resistance change rate of the medium- and high-temperature resistant silver-based conductive paste prepared in Example 3; Figure 4 This is a graph of the square resistance change rate of the medium- and high-temperature resistant silver-based conductive paste prepared in Example 4. DETAILED DESCRIPTION

[0016] The present invention is described in detail below in conjunction with specific implementation modes and accompanying drawings.

[0017] The method for preparing the medium- and high-temperature resistant silver-based conductive paste of the present invention is specifically implemented according to the following steps: Step 1, mixing silver-coated copper microspheres with a particle size of 10 μm-15 μm with spherical silver powder, flaky silver powder, and dendritic silver powder to obtain a mixed powder; The mass ratio of silver-coated copper microspheres, spherical silver powder, flaky silver powder and dendritic silver powder is 1: 0.05-0.4: 0.25-2.4: 0.0025-0.2: Step 2, adding rubber into a solvent and performing ultrasonic treatment to obtain a rubber liquid; The rubber is silicone rubber, and the solvent is ethanol; The concentration of rubber liquid is 10%; The ultrasonic treatment temperature was 40 °C and the ultrasonic treatment time was 30 min; Step 3, slowly add the rubber liquid into the bonding phase and stir evenly; The bonding phase uses bisphenol A epoxy resin; The mass ratio of the adhesive phase to the rubber liquid is 1:0.2, the stirring speed is 300r / min, and the stirring time is 15min; Step 4, adding a curing agent, a catalyst, and a mixed powder to the binder phase obtained in step 3, stirring evenly, and placing in a vacuum degassing device to remove bubbles generated during the mixing process to obtain a silver-based conductive paste; Imidazole is used as curing agent and acrylic acid is used as catalyst; The amount of curing agent added is 30-50% of the weight of bisphenol A epoxy resin, and the amount of catalyst added is 0.5-1% of the weight of bisphenol A epoxy resin; The mass ratio of the binder phase to the mixed powder is 10:5-7; The stirring speed is 300r / min; the stirring time is 30min; the degassing time is 20min; The medium- and high-temperature resistant conductive paste of the present invention can maintain excellent conductive performance for a long time in a working environment of 200° C. to 800° C., thereby greatly improving the service life and reliability of the conductive layer.

[0018] The medium- and high-temperature resistant silver-based conductive paste prepared by the preparation method of the present invention has a very wide range of applications, covering multiple industrial fields from electronic components to new energy storage equipment, and its superior conductive properties make it an important material that is indispensable to modern technology.

[0019] Example 1 The method for preparing the medium- and high-temperature resistant silver-based conductive paste of the present invention is specifically implemented according to the following steps: Step 1, 10 g of silver-coated copper microspheres with a particle size of 10 μm are mixed evenly with 0.5 g of spherical, 2.3 g of flake, and 0.2 g of dendritic silver powder to obtain a mixed powder; Step 2, add 5.2 g of silicone rubber to 5.2 g of ethanol and perform ultrasonic treatment for 30 minutes to ensure that the silicone rubber is evenly dispersed; Step 3, pour the silicone rubber liquid dispersed in step 2 into 26g of bisphenol A epoxy resin, and stir with a stirrer at a stirring speed of 300r / min for 15min.

[0020] Step 4, adding 7.8 g imidazole, 0.13 g acrylic acid, and the mixed powder of step 1 to the mixed adhesive phase obtained in step 3, using a stirrer with a stirring speed of 300 r / min and a stirring time of 30 min to ensure that the conductive filler is evenly dispersed in the resin, and placing the mixed slurry into a vacuum degassing device to remove bubbles generated during the mixing process to obtain a silver-based conductive slurry; like Figure 1 As shown in the figure, after 100 hours and 200 hours of testing, the square resistance change rate of the silver-based conductive paste prepared in this embodiment gradually increases with the increase of temperature. In the medium and high temperature range, the square resistance change rate is always kept below 10% and 20%, showing its excellent conductive performance and stability in this temperature range.

[0021] Example 2 The method for preparing the medium- and high-temperature resistant silver-based conductive paste of the present invention is specifically implemented according to the following steps: Step 1, 10 g of silver-coated copper microspheres with a particle size of 15 μm are mixed evenly with 0.7 g of spherical, 4 g of flake, and 0.3 g of dendritic silver powder to obtain a mixed powder; Step 2, add 6 g of silicone rubber to 6 g of ethanol and perform ultrasonic treatment for 30 minutes to ensure that the silicone rubber is evenly dispersed; Step 3, pour the silicone rubber liquid dispersed in step 2 into 30g of bisphenol A epoxy resin, and stir with a stirrer at a stirring speed of 300r / min for 15min.

[0022] Step 4, add 15g imidazole, 0.3g acrylic acid, and the mixed powder of step 1 to the mixed adhesive phase in step 3, use a stirrer with a stirring speed of 300r / min and a stirring time of 30min to ensure that the conductive filler is evenly dispersed in the resin, and place the mixed slurry into a vacuum degassing device to remove bubbles generated during the mixing process. The degassing time is 20 minutes.

[0023] like Figure 2 As shown, after 100 hours and 200 hours of testing, the square resistance change rate of the silver-based conductive paste prepared in this embodiment is always maintained below 10% and 20% in the medium and high temperature range, reflecting the excellent conductive performance and stability of the conductive paste in this temperature range.

[0024] Example 3 The method for preparing the medium- and high-temperature resistant silver-based conductive paste of the present invention is specifically implemented according to the following steps.

[0025] Step 1, 10 g of silver-coated copper microspheres with a particle size of 15 μm are mixed evenly with 0.5 g of spherical, 2.3 g of flake, and 0.2 g of dendritic silver powder to obtain a mixed powder; Step 2, add 3.72 g of silicone rubber to 3.72 g of ethanol and perform ultrasonic treatment for 30 minutes to ensure that the silicone rubber is evenly dispersed; Step 3, pour the silicone rubber liquid dispersed in step 2 into 18.6 g of bisphenol A epoxy resin, and stir with a stirrer at a stirring speed of 300 r / min for 15 min.

[0026] Step 4, add 5.58g imidazole, 0.093g acrylic acid, and the mixed powder of step 1 to the mixed adhesive phase of step 3, use a stirrer with a stirring speed of 300r / min and a stirring time of 30min to ensure that the conductive filler is evenly dispersed in the resin, and put the mixed slurry into a vacuum degassing device to remove bubbles generated during the mixing process. The degassing time is usually 20 minutes.

[0027] like Figure 3 As shown in the figure, after 100 hours and 200 hours of testing, the square resistance change rate of the silver-based conductive paste prepared in this embodiment gradually increases with the increase of temperature. In the medium and high temperature range, the square resistance change rate is always controlled below 10% and 15%, showing the excellent conductivity stability of the conductive paste in this range.

[0028] Example 4 The method for preparing the medium- and high-temperature resistant silver-based conductive paste of the present invention is specifically implemented according to the following steps: Step 1: 10 g of silver-coated copper microspheres with a particle size of 10 μm are uniformly mixed with 0.7 g of spherical, 4 g of flake, and 0.3 g of dendritic silver powder.

[0029] Step 2, add 4.28 g of silicone rubber to 4.28 g of ethanol and perform ultrasonic treatment for 30 minutes to ensure that the silicone rubber is evenly dispersed; Step 3, pour the silicone rubber liquid dispersed in step 2 into 21.4 g of bisphenol A epoxy resin, and stir with a stirrer at a stirring speed of 300 r / min for 15 min.

[0030] Step 4, add 6.42g imidazole, 0.214g acrylic acid, and the mixed powder of step 1 to the mixed adhesive phase of step 3, use a stirrer with a stirring speed of 300r / min and a stirring time of 30min to ensure that the conductive filler is evenly dispersed in the resin, and put the mixed slurry into a vacuum degassing device to remove bubbles generated during the mixing process. The degassing time is usually 20 minutes.

[0031] like Figure 4 As shown in the figure, after 100 hours and 200 hours of testing, the square resistance change rate of the silver-based conductive paste prepared in this embodiment gradually increases with the increase of temperature. As the temperature slowly rises from 25°C (room temperature) to 200°C, the square resistance change rate shows an upward trend. However, in the medium and high temperature range, the square resistance change rate always remains below 15% and 10%, indicating that the conductive paste has good conductivity stability in this temperature range.

Claims

1. A method for preparing a medium- and high-temperature resistant silver-based conductive paste, characterized in that: Follow the steps below to implement it: Step 1, mixing silver-coated copper microspheres with spherical silver powder, flaky silver powder, and dendritic silver powder to obtain a mixed powder; Step 2, adding rubber into a solvent and performing ultrasonic treatment to obtain a rubber liquid; Step 3, slowly add the rubber liquid into the bonding phase and stir evenly; Step 4, adding a curing agent, a catalyst, and a mixed powder to the adhesive phase obtained in step 3, stirring evenly, and placing the mixture in a vacuum degassing device to remove bubbles generated during the mixing process to obtain a silver-based conductive paste.

2. The method for preparing the medium- and high-temperature resistant silver-based conductive paste according to claim 1, characterized in that: In the step 1, the mass ratio of the silver-coated copper microspheres, the spherical silver powder, the flaky silver powder, and the dendritic silver powder is 1:0.05-0.4:0.25-2.4:0.0025-0.

2.

3. The method for preparing the medium- and high-temperature resistant silver-based conductive paste according to claim 1, characterized in that: In the step 2, the rubber is silicone rubber, the solvent is ethanol, the ultrasonic treatment temperature is 40° C., and the ultrasonic treatment time is 30 min.

4. The method for preparing the medium- and high-temperature resistant silver-based conductive paste according to claim 1, characterized in that: In the step 3, the adhesive phase is bisphenol A epoxy resin; the mass ratio of the adhesive phase to the rubber liquid is 1:0.2, the stirring speed is 300 r / min; and the stirring time is 15 min.

5. The method for preparing the medium- and high-temperature resistant silver-based conductive paste according to claim 4, characterized in that: In step 4, imidazole is selected as the curing agent, and acrylic acid is selected as the catalyst; the added amount of the curing agent is 30-50% of the weight of the bisphenol A epoxy resin, and the added amount of the catalyst is 0.5-1% of the weight of the bisphenol A epoxy resin.

6. The method for preparing the medium- and high-temperature resistant silver-based conductive paste according to claim 1, characterized in that: In step 4, the stirring speed is 300 r / min; the stirring time is 30 min; and the degassing time is 20 min.

7. The medium-high temperature resistant silver-based conductive paste prepared by the method for preparing the medium-high temperature resistant silver-based conductive paste according to any one of claims 1 to 6.

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