Low-activity sintering-resistant silver powder and preparation method thereof

Abstract

The invention discloses low-activity sintering-resistant silver powder and a preparation method thereof, and belongs to the technical field of precious metal powder materials. The preparation method comprises the following steps: S1, dissolving a reducing agent and a dispersing agent in water, adding a silver nitrate solution, and reacting to obtain a seed crystal solution; s2, adding the seed crystal solution into a dispersing agent solution, and adding a silver nitrate solution and a reducing agent solution at the same time to obtain a reaction mixture; and S3, the reaction mixture is subjected to impurity removal, drying, crushing and sieving, and the low-activity sintering-resistant silver powder is obtained. The prepared silver powder is large in particle size, high in tap density, small in specific surface area and low in burning loss, and is mainly applied to silver-palladium resistance paste or silver-palladium-platinum resistance paste of a thick film heating module.

Description

Technical Field

[0001] This invention belongs to the field of precious metal powder materials technology, specifically relating to a low-activity sintering-resistant silver powder and its preparation method. Background Technology

[0002] Silver has excellent electrical and thermal conductivity. Among precious metals, silver is relatively inexpensive. Therefore, silver powder is widely used in electronic pastes, conductive inks, conductive ceramics and other fields.

[0003] Currently, methods for preparing silver powder include electrolysis, atomization, and chemical reduction. Among these, liquid-phase chemical reduction is the most widely used due to its advantages such as low cost, high stability, and suitability for mass production.

[0004] With the rapid iteration of 5G communication, artificial intelligence, the Internet of Things, and wearable electronic products, electronic components are racing towards "high speed, high frequency, high density, and thinness and miniaturization." As a key interconnect material in passive components, RF antennas, flexible circuits, and system-in-package (SiP), electronic paste directly determines the conductivity, resolution, and long-term reliability of circuits. In screen printing or stencil printing processes, the task assigned to the paste is no longer "simply connecting a conductive path," but rather to construct "tall and narrow, steep-edge, rectangular-section" three-dimensional conductors within a linewidth scale of tens or even several micrometers to achieve the largest possible aspect ratio. An improved aspect ratio means that within a limited wiring area, the conductor cross-sectional area can be increased, thereby significantly reducing resistance, increasing current carrying capacity, and reducing signal transmission loss. At the same time, the tall and narrow line shape can also reduce parasitic capacitance and crosstalk between adjacent lines, providing a cleaner electromagnetic environment for high-speed signals in the millimeter-wave band.

[0005] Silver possesses excellent intrinsic electrical conductivity (1.6 × 10⁻⁶) due to its face-centered cubic crystal structure. -8With its high Ω·m (dimethyl methacrylate) content, chemical stability, and antioxidant capacity, silver powder has become the preferred functional phase for high-end electronic pastes. To obtain fine silver lines with clear edges, flat tops, and an aspect ratio greater than 0.5 after printing, the silver powder particle size is generally reduced during preparation. When the silver powder particle size is reduced from the traditional 1μm-3μm to submicron (100 nm-500 nm) or even nanoscale (<100 nm), the number of particles at the same mass fraction increases cubically, significantly reducing the packing gaps between particles. This allows the ink to form a denser wet film after solvent evaporation. Simultaneously, smaller particle size silver powder requires lower activation energy during sintering, enabling surface diffusion and grain boundary migration at lower temperatures, thus achieving low-temperature rapid sintering and avoiding thermal damage to low-cost flexible substrates such as PET, PI, and PC. Furthermore, reducing the particle size increases the specific surface area of ​​the silver powder, increasing its surface activity, which can lead to significant shrinkage, blistering, and overheating during high-temperature sintering.

[0006] Therefore, preparing a low-activity, sintering-resistant silver powder has become the key to solving the above problems. Summary of the Invention

[0007] In response to the problem that reducing the particle size in existing technologies increases the specific surface area of ​​silver powder, thereby increasing its surface activity and causing significant shrinkage, bubbling, and overheating during high-temperature sintering, this invention provides a low-activity, sinter-resistant silver powder and its preparation method, which can produce a silver powder with large particle size, small specific surface area, and low burn-off.

[0008] The technical solution of the present invention is as follows: This invention discloses a method for preparing low-activity sintering-resistant silver powder. The preparation method includes the following steps: dissolving a reducing agent and a dispersant in water and then adding silver nitrate solution to react and obtain a seed solution; adding the seed solution to the dispersant solution, and simultaneously adding silver nitrate solution and reducing agent solution to obtain a reaction mixture; removing impurities from the reaction mixture, drying, crushing, and sieving to obtain low-activity sintering-resistant silver powder.

[0009] The silver powder prepared by this invention has a large particle size, high tap density, small specific surface area, and low burn-off, and is mainly used in silver-palladium or silver-palladium-platinum resistance pastes for thick film heating modules.

[0010] The objective of this invention is achieved through the following technical solution: A method for preparing low-activity, sintering-resistant silver powder includes the following steps: S1. Dissolve the reducing agent and dispersant in water, add silver nitrate solution, stir, and react to obtain a seed crystal solution; The mass ratio of the reducing agent to the dispersant is 1:(1~100), and the mass ratio of silver nitrate to the reducing agent is (0.1~1.1):1; the volume ratio of the mixed aqueous solution of the reducing agent and the dispersant to the silver nitrate solution is (5~10):1. S2. Add the seed crystal solution to the dispersant solution and stir. At the same time, add the silver nitrate solution and the reducing agent solution to obtain the reaction mixture. The mass ratio of the dispersant, silver nitrate, and reducing agent is 1:(5~20):(5~10), and the volume ratio of the seed solution to the dispersant solution is 1:(300~800); the volume ratio of the silver nitrate solution, the reducing agent solution, and the dispersant solution is 1:1:(1~5). S3. The reaction mixture is purified, dried, crushed, and sieved to obtain a low-activity, sinterable silver powder. This low-activity, sinterable silver powder has the following performance parameters: D 50 The micrometer diameter is 5.0 μm to 7.0 μm, and the tap density is >5.0 g / cm³. 3 Specific surface area < 0.16 m² 2 / g, burn loss <0.11%.

[0011] Furthermore, in S1, the concentration of the silver nitrate solution is 0.1 mol / L to 0.8 mol / L.

[0012] Furthermore, in S1, the reaction temperature is 20℃~70℃, the reaction time is 60min~90min, and the stirring speed is 200 r / min~500 r / min.

[0013] Furthermore, in S2, the reaction temperature is 20℃~70℃, the reaction time is 30min~60min, and the stirring speed is 200 r / min~500 r / min.

[0014] Furthermore, the dispersant described in S1 and S2 is selected from one or more of gelatin, gum arabic, polyvinyl alcohol, magnesium stearate, zinc stearate, polyvinylpyrrolidone, and N-methylpyrrolidone, or any mixture thereof.

[0015] Furthermore, the reducing agent described in S1 and S2 is selected from one or more of ascorbic acid, glucose, sodium borohydride, formaldehyde, hydrazine hydrate, hydrogen peroxide, hydroquinone, catechol, triethanolamine, diethanolamine, and sodium hydroxide, or any mixture thereof.

[0016] Furthermore, the impurity removal, drying, crushing, and sieving described in S3 involves washing away impurities with deionized water, baking in an oven at 60°C for 10 hours, drying, dispersing with a crusher, and sieving through a 200-mesh sieve.

[0017] This invention also relates to a low-activity, sinter-resistant silver powder, obtained by the above-mentioned preparation method for a low-activity, sinter-resistant silver powder. The prepared low-activity, sinter-resistant silver powder has the following performance parameters: D 50 The micrometer diameter is 5.0 μm to 7.0 μm, and the tap density is >5.0 g / cm³. 3 Specific surface area < 0.16 m² 2 / g, burn loss <0.11%.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention discloses a method for preparing low-activity sintering-resistant silver powder, wherein seed crystals are introduced during the preparation process, and the number of seed crystals in the second redox reaction process is controlled, thereby regulating the particle size of silver powder particles and reducing the specific surface area.

[0019] 2. The method for preparing low-activity sintering-resistant silver powder described in this invention reduces the probability of free silver generating new seed crystals in the second reaction and avoids the possibility of silver powder agglomeration by introducing a dispersant.

[0020] 3. The method for preparing low-activity sintering-resistant silver powder described in this invention has the characteristics of simple operation, stability and high efficiency. The silver powder obtained has a high yield (99.92%~99.95%), is easy to clean, and is suitable for mass production. Attached Figure Description

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0022] Figure 1 Electron micrograph of silver powder prepared by a method for preparing low-activity sintering-resistant silver powder according to Example 1 of the present invention; Figure 2 Electron micrograph of silver powder prepared by a method for preparing low-activity sintering-resistant silver powder according to Embodiment 2 of the present invention; Figure 3 The image shows an electron microscope (EM) image of silver powder prepared by a method for preparing low-activity, sinter-resistant silver powder according to Example 3 of the present invention. Detailed Implementation

[0023] To make the objectives, technical solutions, and key points of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0024] The following detailed implementation method further illustrates this solution.

[0025] Example 1: A method for preparing low-activity, sintering-resistant silver powder includes the following steps: S1. Weigh 55g of ascorbic acid and 55g of polyvinylpyrrolidone, dissolve them in 3L of deionized water, set the stirring speed to 400r / min, add 100g of 0.5mol / L silver nitrate deionized water solution to react and obtain a seed solution. S2. Measure 100ml of seed crystal solution and add it to 35L of aqueous solution containing 300g of gelatin. Set the stirring speed to 500r / min. After stirring thoroughly, add 30L of deionized aqueous solution containing 1700g of silver nitrate and 30L of deionized aqueous solution containing 900g of ascorbic acid to obtain the reaction mixture. S3. The reaction mixture is purified, dried, crushed, and sieved to obtain low-activity sintering resistant silver powder.

[0026] The yield of the low-activity sintering-resistant silver powder in this embodiment is 99.94%, and the electron micrograph of the low-activity sintering-resistant silver powder is shown below. Figure 1 As shown.

[0027] Example 2: A method for preparing low-activity, sintering-resistant silver powder includes the following steps: S1. Weigh 2.68g of sodium hydroxide and 55g of gelatin and dissolve them in 3L of deionized water. Set the stirring speed to 300r / min and add 10g of 0.5mol / L silver nitrate deionized water solution to react and obtain a seed solution. S2. Measure 50 ml of seed crystal solution and add it to 25 L of aqueous solution containing 200 g of gum arabic. Set the stirring speed to 500 r / min. After stirring thoroughly, keep the temperature constant at 60℃. At the same time, add 25 L of deionized aqueous solution containing 1700 g of silver nitrate and 25 L of deionized aqueous solution containing 2000 g of triethanolamine to obtain the reaction mixture. S3. The reaction mixture is purified, dried, crushed, and sieved to obtain low-activity sintering resistant silver powder.

[0028] The yield of the low-activity sintering-resistant silver powder in this embodiment is 99.95%. The electron micrograph of this low-activity sintering-resistant silver powder is shown below. Figure 2 As shown.

[0029] Example 3: A method for preparing low-activity, sintering-resistant silver powder includes the following steps: S1. Weigh 1.1g sodium borohydride and 100g gum arabic and dissolve them in 3L deionized water. Set the stirring speed to 400r / min and add 10g of 0.5mol / L silver nitrate deionized water solution to react and obtain a seed solution. S2. Measure 100ml of seed crystal solution and add it to 30L of aqueous solution containing 100g of gelatin. Set the stirring speed to 500r / min and the temperature to 60℃. After stirring thoroughly, add 20L of deionized aqueous solution containing 1700g of silver nitrate and 20L of deionized aqueous solution containing 900g of ascorbic acid to obtain the reaction mixture. S3. The reaction mixture is purified, dried, crushed, and sieved to obtain low-activity sintering resistant silver powder.

[0030] The yield of the low-activity sintering-resistant silver powder in this embodiment is 99.92%, and the electron micrograph of the low-activity sintering-resistant silver powder is shown below. Figure 3 As shown.

[0031] Comparative Example 1: A method for preparing micron-sized silver powder is the same as in Example 1, except that the seed solution reaction in step S1 is not performed, and the reaction in step S2 is performed directly.

[0032] Comparative Example 2: A method for preparing micron-sized silver powder, which is otherwise the same as in Example 1, except that no dispersant is added.

[0033] Results and discussion: Table 1. Particle size D of silver powder obtained in the examples and comparative examples 50 Tap density, specific surface area and burn loss

[0034] 1. By comparing Examples 1-3 and Comparative Example 1, it can be seen that the silver powder of Comparative Example 1 has a smaller particle size D compared to the silver powder of the Examples. 50 The size of the crystals is significantly smaller, and the specific surface area is also decreasing. This indicates that the S1 step seed solution reaction was not carried out. Directly carrying out the S2 step reaction will lead to higher surface activity and agglomeration of the silver powder. As a result, the silver powder produced by this reaction will shrink significantly at a higher sintering temperature.

[0035] 2. By comparing Examples 1-3 and Comparative Example 2, it can be seen that no dispersant was added in Comparative Example 2, which resulted in severe silver powder agglomeration during the reaction, a larger specific surface area, and higher sintering activity.

[0036] 3. As can be seen, the low-activity sintering-resistant silver powder prepared by this invention has a large particle size, small specific surface area, high tap density and low burn-off, which is beneficial to reducing its surface activity and can significantly improve its sintering performance in high-temperature environments. The silver powder prepared by this invention through liquid-phase reduction method and secondary reaction by adding seed crystals has stable performance and very small batch-to-batch fluctuations in indicators.

[0037] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations and substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing low-activity, sintering-resistant silver powder, characterized in that, Includes the following steps: S1. Dissolve the reducing agent and dispersant in water, add silver nitrate solution, stir, and react to obtain a seed crystal solution; The mass ratio of the reducing agent to the dispersant is 1:(1~100), and the mass ratio of silver nitrate to the reducing agent is (0.1~1.1):1; the volume ratio of the mixed aqueous solution of the reducing agent and the dispersant to the silver nitrate solution is (5~10):

1. S2. Add the seed crystal solution to the dispersant solution and stir. At the same time, add the silver nitrate solution and the reducing agent solution to obtain the reaction mixture. The mass ratio of the dispersant, silver nitrate, and reducing agent is 1:(5~20):(5~10), and the volume ratio of the seed solution to the dispersant solution is 1:(300~800); the volume ratio of the silver nitrate solution, the reducing agent solution, and the dispersant solution is 1:1:(1~5). S3. The reaction mixture is purified, dried, crushed, and sieved to obtain a low-activity, sinterable silver powder. This low-activity, sinterable silver powder has the following performance parameters: D 50 The micrometer diameter is 5.0 μm to 7.0 μm, and the tap density is >5.0 g / cm³. 3 Specific surface area < 0.16 m² 2 / g, burn loss <0.11%.

2. The method for preparing a low-activity, sintering-resistant silver powder according to claim 1, characterized in that, In S1, the concentration of the silver nitrate solution is 0.1 mol / L to 0.8 mol / L.

3. The method for preparing a low-activity, sintering-resistant silver powder according to claim 1, characterized in that, In S1, the reaction temperature is 20℃~70℃, the reaction time is 60min~90min, and the stirring speed is 200 r / min~500 r / min.

4. The method for preparing low-activity sintering-resistant silver powder according to claim 1, characterized in that, In S2, the reaction temperature is 20℃~70℃, the reaction time is 30min~60min, and the stirring speed is 200 r / min~500 r / min.

5. The method for preparing a low-activity, sintering-resistant silver powder according to claim 1, characterized in that, The dispersant described in S1 and S2 is selected from one or more of gelatin, gum arabic, polyvinyl alcohol, magnesium stearate, zinc stearate, polyvinylpyrrolidone, and N-methylpyrrolidone, or any mixture thereof.

6. The method for preparing a low-activity, sintering-resistant silver powder according to claim 1, characterized in that, The reducing agent described in S1 and S2 is selected from one or more of the following: ascorbic acid, glucose, sodium borohydride, formaldehyde, hydrazine hydrate, hydrogen peroxide, hydroquinone, catechol, triethanolamine, diethanolamine, and sodium hydroxide, or any mixture thereof.

7. The method for preparing a low-activity, sintering-resistant silver powder according to claim 1, characterized in that, The impurity removal, drying, crushing, and sieving processes described in S3 involve washing away impurities with deionized water, baking in an oven at 60°C for 10 hours, drying, dispersing with a crusher, and then sieving through a 200-mesh sieve.

8. A low-activity, sintering-resistant silver powder, characterized in that, The low-activity sintering-resistant silver powder prepared according to any one of claims 1-7 has the following performance parameters: D 50 The micrometer diameter is 5.0 μm to 7.0 μm, and the tap density is >5.0 g / cm³. 3 Specific surface area < 0.16 m² 2 / g, burn loss <0.11%.

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