Silver-coated copper particles, a method for preparing the same and use in sintering paste

Abstract

The application relates to a silver-coated copper particle, a preparation method thereof and application of the silver-coated copper particle in sintering paste, and belongs to the field of sintering materials. The application solves the problem of high sintering temperature of high-temperature solder in the prior art. The silver-coated copper particle is prepared by a multi-step chemical synthesis method, that is, silver-coated copper particle suspension is prepared first, and then a silver complex solution, a second chelating agent solution and a complexing agent solution are used to realize gradient structure evolution of the silver layer from compact to porous by controlling the release and reduction rate difference of silver ions, the surface of the silver-coated copper particle has a multi-stage pore structure, the contact resistance between particles can be effectively reduced, the sintering starting temperature can be effectively reduced, the poor oxidation performance of copper particles is solved, the silver consumption is reduced, the manufacturing cost is reduced, the ion migration path length and the electromigration life are increased, the silver-coated copper particle prepared by the application greatly meets the requirements of the electronic packaging field for new welding materials, and has remarkable social and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of sintering materials, specifically relating to a silver-coated copper particle, its preparation method, and its application in sintering slurry. Background Technology

[0002] With the widespread application of semiconductor materials, these materials have been extensively used in lasers, detectors, semiconductor lighting, radio frequency devices, and high-power devices. The advantages of semiconductors are mainly threefold: ① Wide bandgap provides excellent electrical performance, high temperature resistance, and high voltage resistance; ② The high saturated electron drift velocity and high electron mobility of wide bandgap semiconductors further improve the overall system transmission efficiency; ③ High thermal conductivity enables effective heat dissipation under high power conditions, reducing performance degradation and device failure caused by excessive temperature. All these advantages further increase the service temperature of semiconductor devices. This also places higher demands on soldering materials. In high-power semiconductor devices, soldering materials are crucial to ensuring the long-term stability of the devices. Traditional solders (such as Sn-Pb solder) have relatively low service temperatures and will melt at the peak operating temperature of high-power devices, leading to device failure. The choice of solder not only affects the thermal management of the entire electronic system but also directly relates to the device's operating efficiency and lifespan. Therefore, developing and using solders suitable for these new semiconductor materials has become key to improving the performance of electronic devices.

[0003] In recent years, new high-temperature soldering materials such as silver-based solder and copper-based solder have gradually become the preferred solders for semiconductor devices due to their excellent conductivity, high-temperature resistance, and good mechanical strength, meeting the requirements of low-temperature sintering and high-temperature service. These solders have the ability to sinter at low temperatures, and their thermal conductivity is typically 3 to 4 times that of tin-based solders. However, pure silver-based solders are expensive and have high electromigration. While copper-based solders can effectively solve these problems, their oxidation resistance is a major drawback. The silver-clad copper core-shell structure can encompass the advantages of both while overcoming their disadvantages, and is considered one of the conductive solid phases for new high-temperature soldering materials. However, to meet the requirements of high-temperature service, the low-temperature sintering requirement also necessitates a sintering temperature below 200℃ to reduce the accumulation of internal stress during the high-temperature sintering process. Furthermore, it is well known that due to the quantum size effect, the sintering temperature of nanomaterials is lower than that of micron-sized and larger particles. Therefore, developing a silver-clad copper particle solder that can meet the requirements of low-temperature sintering is of great significance to the quality of electronic device manufacturing. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of high sintering temperature in existing high-temperature solders. This invention provides silver-coated copper particles, their preparation method, and their application in sintering slurry.

[0005] The technical solution of the present invention is as follows:

[0006] One objective of this invention is to provide a method for preparing silver-coated copper particles, wherein the method includes:

[0007] S1: A copper precursor solution is prepared by mixing copper metal salt and dispersant 1;

[0008] S2: Add a reducing agent solution to the copper precursor solution obtained in S1, and react to obtain copper particles;

[0009] S3: Add the copper particles obtained in S2 and dispersant 2 to the solvent and stir ultrasonically to obtain a copper suspension;

[0010] S4: Prepare a silver metal salt solution with a concentration of 0.01-1 mol / L, and divide it into two portions for later use;

[0011] S5: Inject a portion of the silver metal salt solution from S4 into the copper suspension obtained in S3 to obtain a silver-coated copper particle suspension.

[0012] S6: Mix the first chelating agent with another part of the silver metal salt solution of S4 to obtain a silver complex solution;

[0013] S7: Prepare the second chelating agent into a second chelating agent solution;

[0014] S8: Prepare the complexing agent into a complexing agent solution;

[0015] S9: Under ultrasonic conditions, add the S6 silver complexing solution, the S7 second chelating agent solution and the S8 complexing agent solution to the S5 silver-coated copper particle suspension. After the reaction is completed, centrifuge, wash and dry to obtain silver-coated copper particles.

[0016] Further specified, the copper metal salt in S1 is one or more of copper formate, copper acetate, copper chloride, copper sulfate, copper carbonate, copper hydroxide, and copper iodide, the concentration of the copper metal salt in the copper precursor solution is 0.01-1 mol / L, and the molar ratio of copper metal salt to dispersant 1 is 1:0.001-0.1; the reducing agent in S2 is one or more of hydrazine hydrate, sodium borohydride, sodium hypophosphite, ascorbic acid, and glucose, the concentration of the reducing agent is 0.01-1 mol / L, and the volume ratio of copper precursor solution to reducing agent solution is 1:0.1-2.

[0017] Further specified, the reaction temperature is 0–80℃, the stirring speed is 100–2000 rpm, and the reaction time is 10–120 min.

[0018] Further specifying, dispersant 1 and dispersant 2 in S1 and S3 are one or more of Tween 20, Tween 80, polyethylene glycol 200, polyethylene glycol 2000, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, citrate, octadecylamine, maleate, fumarate, itaconic acid, and cyclodextrin compounds.

[0019] Further specified, in S3, the copper suspension has a copper particle concentration of 1–10 g / L, a copper particle to dispersant 2 mass ratio of 1:0.1–10, an ultrasonic power of 80–550 W, and a stirring speed of 100–2000 rpm; in S5, the copper suspension to silver metal salt solution volume ratio is 1:0.1–5; in S6, the first chelating agent to silver metal salt solution ratio is 0.5–5 g:50–200 mL, and the first chelating agent is a compound that forms chelates with metal ions with five or more coordinate bonds; in S7, the second chelating agent is a compound that forms chelates with metal ions with five or fewer coordinate bonds.

[0020] Further specifying, in S6, the first chelating agent is ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, 1,4,7-triazacyclononanetriacetic acid, ethylenediaminedisuccinic acid, diethylenetriaminepentamethylenephosphonic acid, deferoxamine, 8-hydroxyquinoline derivative, hydroxyethylethylenediaminetriacetic acid, or ethylene glycol diethyl ether diaminetetraacetic acid; in S7, the second chelating agent is sodium oxalate, ethylenediamine, o-phenanthroline, acetylacetone, sodium salicylate, glycine, dimethylglyoxime, cysteine, or N,N'-diphenylethylenediamine, with a solution concentration of 0.025–1 mol / L; in S8, the complexing agent is one or more of potassium ferrocyanide, sodium cyanide, ammonium acetate, sodium lactate, potassium malate, and potassium glycerophosphate. The concentration of the complexing agent solution is 0.025–1 mol / L; the ultrasonic power in S9 is 80–550 W, the stirring speed is 100–2000 rpm, the reaction time is 10–5000 s, and the volume ratio of the silver complexing solution, the second chelating agent solution, the complexing agent solution, and the silver-coated copper particle suspension is 1:0.1–5:0.1–5:0.1–5. The silver complexing solution is added at a rate of 400–800 mL / s, the second chelating agent solution is added at a rate of 300–500 mL / s, and the complexing agent solution is added at a rate of 100–200 mL / s. The order of addition is that the silver complexing solution is added last, or it is added last after being mixed with one or two of the first chelating agent solution and the complexing agent solution. The centrifugation speed is 1000–10000 rpm.

[0021] Further specifying, the solvent in S3 is one or more of the following: deionized water, ethanol, ethylene glycol, diethylene glycol, isopropanol, isopropanolamine, acetone, butanone, cyclohexanone, dimethyl ether, diethyl ether, methyl formate, ethyl acetate, vinyl chloride, and chloroform.

[0022] The second objective of this invention is to provide a silver-coated copper particle prepared by the above-described preparation method.

[0023] Further specifying, the copper molar content in the silver-coated copper particles is 10-90%, and the particle size is 500-3000 nm.

[0024] The third objective of this invention is to provide a sintering slurry, wherein the sintering slurry comprises, by mass percentage: 60-90% of the aforementioned silver-coated copper particles, 3-45% of organic solvent, 0.1-10% of dispersant 3, 0.1-10% of flux, and 0.1-10% of binder, for a total mass percentage of 100%.

[0025] Further specifying, the organic solution is one or more of ethanol, ethylene glycol, diethylene glycol, dipropylene glycol, butanediol, terpineol, glycerol, sorbitol, ethyl acetate, diethylene glycol diethyl ether, N-methylpyrrolidone, and dibutyl phthalate.

[0026] Further specifying, dispersant 2 is one or more of Tween 20, Tween 80, polyethylene glycol 200, polyethylene glycol 2000, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, citrate, octadecylamine, maleate, fumarate, itaconic acid, and cyclodextrin compounds.

[0027] Further specifying, the adhesive is one or more of phenolic resin, acrylic resin, N,N-dimethyloctyldecylamide, and polyethylene terephthalate.

[0028] Further specifying, the flux is one or more of rosin resin, phenolic resin, and epoxy resin.

[0029] The fourth objective of this invention is to provide a low-temperature sintering method for sintering slurry, wherein the method includes:

[0030] The above-mentioned sintering paste is transferred to the substrate pads by a scraping method, the chip is placed, and sintering is carried out for 15 to 150 minutes at a temperature of 150 to 200°C and a pressure of 0 to 30 MPa.

[0031] The fifth objective of this invention is to provide an application of the low-temperature sintering method for the above-mentioned sintering slurry in electronic devices.

[0032] Compared with the prior art, the specific advantages of the present invention are as follows:

[0033] (1) This invention employs a multi-step chemical synthesis method to prepare silver-coated copper particles. First, a copper precursor solution is prepared by mixing copper metal salt and a dispersant. Then, a reducing agent is injected, causing a large number of copper atoms to rapidly reduce and undergo nucleation, growth, and aggregation into micron-sized copper particles. Subsequently, a silver nitrate solution is introduced onto the surface of the copper particles. Utilizing the high redox properties of copper, a displacement reaction occurs, forming a dense silver seed layer on the surface of the copper particles. The structure of the silver seed layer provides high-density nucleation sites for the subsequent uniform growth of the silver layer, preventing the silver particles from self-nucleating and ensuring their continued growth on the silver-coated copper surface. Next, the silver metal salt solution is mixed with various complexing system solutions and chelating agent solutions. Due to the different coordination equilibrium constants between silver ions and different complexing agents, multiple complexing systems of silver ions are formed internally. Furthermore, the silver complexing system with the higher the equilibrium constant... The more stable the formed silver complex, the higher its proportion in the system. Complexes with low equilibrium constants exhibit weak reducing properties. This invention prioritizes the preparation of a silver complex solution, which preferentially combines with silver ions to form stable complexes, delaying the release rate of silver ions and ensuring dense growth of the silver layer. With the addition of a dispersant, a small amount of silver ions can be dynamically released, further slowly generating different surface morphologies on the surface of the silver-coated copper particles in the original silver-coated copper particle suspension. By controlling the difference between the release and reduction rates of silver ions, a gradient structure evolution of different morphologies of the silver layer is achieved. The specific surface nanostructure of the silver-coated copper particles can effectively reduce the contact resistance between particles, effectively reduce the sintering initiation temperature, solve the problem of poor oxidation performance of copper particles, reduce the amount of silver used, thereby reducing manufacturing costs, and also increase the ion migration path length and electromigration lifetime.

[0034] (2) This invention further prepares silver-coated copper particles into a sintering slurry. This slurry has a high solid content, and both silver and copper are excellent electrical and thermal conductive materials. Simultaneously, the nanostructure on the surface can effectively reduce the sintering initiation temperature to meet the requirements of low-temperature sintering and high-temperature service. Experiments have shown that the sintering initiation temperature of these nanoparticles can be reduced to below 130℃, the solder joint shear strength is 18–35 MPa, and the thermal conductivity is 100–200 W / (m·K). This demonstrates that the silver-coated copper particles prepared by this invention greatly meet the current requirements of the electronic packaging field for novel welding materials.

[0035] (3) The silver-coated copper particles prepared in this invention can impart nanoparticle sintering properties to micron-sized particles in sintering slurry. Nano-silver particles have high surface energy and reactivity, enabling sintering at lower temperatures, thereby improving sintering efficiency. The high activity and high sintering driving force of nano-silver can accelerate the sintering process, shorten sintering time, and improve production efficiency; the nano-silver coating can significantly improve the electrical and thermal conductivity of the material. During sintering, the silver coating can form a good electrical and thermal conductivity network, ensuring the stability and reliability of the material under high temperature and high current density; the high specific surface area and high activity of nano-silver particles enable them to fill the gaps between micron-sized copper particles during sintering, forming a dense sintered body. This dense structure can improve the mechanical strength and stability of the material, reducing porosity and microcrack generation; the low melting point of nano-silver allows sintering to be carried out at lower temperatures; the nano-silver coating can enhance the bonding force between particles, improving the mechanical strength of the sintered material. This enhancement allows the material to withstand greater stress and strain, thereby improving its reliability under high temperature and high stress environments. Attached Figure Description

[0036] Figure 1 This is a flowchart of the experimental process of the present invention;

[0037] Figure 2 A scanning electron microscope image of the silver-coated copper particles prepared in Example 1;

[0038] Figure 3 Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) images of the silver-coated copper particles prepared in Example 1;

[0039] Figure 4 This is a cross-sectional view of the weld joint after low-temperature sintering of the sintering slurry prepared in Example 1;

[0040] Figure 5 This is a scanning electron microscope image of the silver-coated copper particles prepared in Example 2;

[0041] Figure 6 Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) images of the silver-coated copper particles prepared in Example 2;

[0042] Figure 7 This is a cross-sectional view of the weld joint after low-temperature sintering of the sintering slurry prepared in Example 2;

[0043] Figure 8 The image shows a scanning electron microscope (SEM) image of the silver-coated copper particles prepared in Comparative Example 1.

[0044] Figure 9 Differential scanning calorimetry and thermogravimetric analysis images of the silver-coated copper particles prepared in Comparative Example 1.

[0045] Figure 10 The image shows a cross-sectional view of the weld joint after low-temperature sintering of the sintering slurry prepared in Comparative Example 1. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages 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.

[0047] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0048] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used in the following embodiments, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such a composition, step, method, article, or apparatus.

[0049] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range. In this specification and claims, range definitions may be combined and / or interchanged, unless otherwise stated, these ranges include all subranges contained therein.

[0050] The indefinite articles “a” and “an” preceding an element or component of this invention do not impose any limitation on the quantity (i.e., number of times) of the element or component. Therefore, “an” or “a” should be interpreted as including one or at least one, and the singular form of an element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0051] In this invention, "an embodiment" or "embodiment" refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments.

[0052] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0053] Example 1:

[0054] Preparation of silver-coated copper particles:

[0055] 0.1 mol copper acetate and 3.2 g polyvinylpyrrolidone were added to 150 mL ethylene glycol and stirred at 500 rpm at room temperature for 10 min to obtain a copper precursor solution. 0.2 mol ascorbic acid was mixed with 100 mL ethylene glycol and stirred and heated at 40 °C to dissolve the mixture. The completely dissolved reducing agent solution was added to the copper precursor solution, and the mixture was stirred at 500 rpm for 20 min. After that, the mixture was centrifuged at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate. This process was repeated three times. The mixture was then washed alternately with deionized water and ethanol three times to obtain pure copper particles.

[0056] Take 1g of the above copper particles and 0.1g of polyvinylpyrrolidone and add them to 100mL of deionized water. Disperse them at a stirring speed of 500rpm and an ultrasonic power of 450W to obtain a copper suspension. Take 2g of silver nitrate and place it in 200mL of deionized water to obtain 200mL of silver metal salt solution. Disperse it at a stirring speed of 500rpm until there is no precipitate. Then, take 100mL of silver metal salt solution and add it to the copper suspension. Maintain a stirring speed of 500rpm and an ultrasonic power of 450W throughout the process to obtain a silver-coated copper suspension.

[0057] Add 3.5g of EDTA to the remaining 100mL of silver metal salt solution to obtain a silver complex solution for later use.

[0058] Add 1.5g of sodium salicylate to 100mL of deionized water to obtain the second chelating agent solution, and set aside for later use;

[0059] Add 2.0 g of potassium ferrocyanide to 50 mL of deionized water to obtain a complexing agent solution for later use;

[0060] While maintaining a stirring rate of 500 rpm and an ultrasonic power of 450 W, a silver complexing solution, a second chelating agent solution, and a complexing agent solution were simultaneously added at rates of 400 mL / s, 400 mL / s, and 200 mL / s, respectively. The reaction was allowed to proceed for 3000 s. The resulting reaction solution was then centrifuged at 8000 rpm for 10 min to remove the supernatant and obtain a precipitate. This process was repeated three times. The precipitate was then washed alternately with deionized water and ethanol three times, followed by drying to obtain silver-coated copper particles with a nanosheet-like surface. Figure 2 As shown, the sintering performance is as follows Figure 3 As shown, from Figure 3 We can see that the sintering starting temperature of the nanosheet-shaped silver-coated copper particles is less than 150℃, and reaches its maximum at around 175℃. The overall curve shape shows obvious exothermic behavior, indicating that it has excellent sintering interconnect performance.

[0061] Preparation of sintering slurry:

[0062] 1g of the silver-coated copper particles prepared above, 0.3g of diethylene glycol, 0.15g of sodium citrate, 0.15g of rosin resin and 0.15g of polyethylene terephthalate were mixed to obtain a solder mixture. The mixture was thoroughly mixed using a planetary mixer with rotation speeds of 300rpm, 500rpm, 800rpm, 1200rpm and 1500rpm, and each rotation speed was mixed for 5 minutes to obtain a sintered slurry.

[0063] The sintering slurry obtained above was transferred onto the substrate (Cu pads) using a scraping method. The sample was then sintered at 150°C and 5 MPa for 60 minutes to obtain the final sintered sample. The cross-sectional view of the solder joints after sintering is shown below. Figure 4 As shown, from Figure 4 As can be seen, the cross-sectional particles are densely arranged, the sintered structure is relatively dense, there are no obvious defects, and there is no delamination at the interface, which proves that the silver-coated copper particles with nanosheet-like surfaces prepared in this embodiment have good low-temperature welding performance.

[0064] Example 2:

[0065] Preparation of silver-coated copper particles:

[0066] 0.1 mol of copper acetate and 3.2 g of polyvinylpyrrolidone were added to 150 mL of ethylene glycol and stirred at 500 rpm at room temperature for 10 min to obtain a copper precursor solution. 0.2 mol of reducing agent ascorbic acid was mixed with 100 mL of ethylene glycol and stirred and heated at 40 °C to dissolve the mixture. The completely dissolved reducing agent solution was added to the copper precursor solution, and the mixture was stirred at 500 rpm for 20 min. After that, it was centrifuged at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate. This process was repeated three times, and the mixture was then washed alternately with deionized water and ethanol three times to obtain pure copper particles.

[0067] Take 1g of the above copper particles and 0.1g of polyvinylpyrrolidone and add them to 100mL of deionized water. Disperse them at a stirring speed of 500rpm and an ultrasonic power of 450W to obtain a copper suspension. Take 2g of silver nitrate and place it in 200mL of deionized water to obtain 200mL of silver metal salt solution. Disperse it at a stirring speed of 500rpm until there is no precipitate. Then, take 100mL of silver metal salt solution and add it to the copper suspension. Maintain a stirring speed of 500rpm and an ultrasonic power of 450W throughout the process to obtain a silver-coated copper suspension.

[0068] Add 3.5g of EDTA to the remaining 100mL of silver metal salt solution to obtain a silver complex solution for later use.

[0069] Add 1.5g of sodium salicylate to 100mL of deionized water to obtain the second chelating agent solution, and set aside for later use;

[0070] Add 2.0 g of potassium ferrocyanide to 50 mL of deionized water to obtain a complexing agent solution for later use;

[0071] While maintaining a stirring speed of 500 rpm and an ultrasonic power of 450 W, the complexing agent solution was first added at a rate of 200 mL / s, followed by the simultaneous addition of the silver complexing solution and the second chelating agent solution at a rate of 400 mL / s. The reaction was allowed to proceed for 3000 s, and the resulting reaction solution was then centrifuged at 8000 rpm for 10 min. The supernatant was removed, and the precipitate was obtained. This process was repeated three times, followed by alternating washing with deionized water and ethanol three times. After drying, silver-coated copper particles with island-like surfaces were obtained. Figure 5 As shown, the sintering performance is as follows Figure 6 As shown, from Figure 6 We can see that the sintering peak of the silver-coated copper particles with island-like surfaces is around 150℃, which has a certain strength. The subsequent larger exothermic peak is caused by oxidation. Therefore, in order to ensure the sintering interconnect strength, the sintering should be carried out at a low temperature of around 150℃.

[0072] Preparation of sintering slurry:

[0073] 1g of the silver-coated copper particles prepared above, 0.3g of diethylene glycol, 0.15g of sodium citrate, 0.15g of rosin resin and 0.15g of polyethylene terephthalate were mixed to obtain a solder mixture. The mixture was thoroughly mixed using a planetary mixer with rotation speeds of 300rpm, 500rpm, 800rpm, 1200rpm and 1500rpm, and each rotation speed was mixed for 5 minutes to obtain a sintered slurry.

[0074] The sintering slurry obtained above was transferred onto the substrate (Cu pads) using a scraping method. The sample was then sintered at 150°C and 5 MPa for 60 minutes to obtain the final sintered sample. The cross-sectional view of the solder joints after sintering is shown below. Figure 7 As shown, from Figure 7 As can be seen, the cross-sectional particles are densely arranged, the sintered structure is dense, there are no obvious defects, and there is no delamination at the interface, which proves that the silver-coated copper particles with island-like surfaces prepared in this embodiment also have good low-temperature welding performance.

[0075] Example 3:

[0076] Preparation of silver-coated copper particles:

[0077] 0.1 mol of copper acetate and 3.2 g of polyvinylpyrrolidone were added to 150 mL of ethylene glycol and stirred at 500 rpm at room temperature for 10 min to obtain a copper precursor solution. 0.2 mol of reducing agent ascorbic acid was mixed with 100 mL of ethylene glycol and stirred and heated at 40 °C to dissolve the mixture. The completely dissolved reducing agent solution was added to the copper precursor solution, and the mixture was stirred at 500 rpm for 20 min. After that, it was centrifuged at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate. This process was repeated three times, and the mixture was then washed alternately with deionized water and ethanol three times to obtain pure copper particles.

[0078] Take 1g of the above copper particles and 0.1g of polyvinylpyrrolidone and add them to 100mL of deionized water. Disperse them at a stirring speed of 500rpm and an ultrasonic power of 450W to obtain a copper suspension. Take 2g of silver nitrate and place it in 200mL of deionized water to obtain 200mL of silver metal salt solution. Disperse it at a stirring speed of 500rpm until there is no precipitate. Then, take 100mL of silver metal salt solution and add it to the copper suspension. Maintain a stirring speed of 500rpm and an ultrasonic power of 450W throughout the process to obtain a silver-coated copper suspension.

[0079] Add 3.5g of EDTA to the remaining 100mL of silver metal salt solution to obtain a silver complex solution for later use.

[0080] Add 1.5g of sodium salicylate to 100mL of deionized water to obtain the second chelating agent solution, and set aside for later use;

[0081] Add 2.0 g of potassium ferrocyanide to 50 mL of deionized water to obtain a complexing agent solution for later use;

[0082] While maintaining a stirring rate of 500 rpm and an ultrasonic power of 450 W, a silver complexing solution, a second chelating agent solution, and a complexing agent solution were added simultaneously at rates of 800 mL / s, 500 mL / s, and 200 mL / s, respectively. The reaction was allowed to proceed for 3000 s. The resulting reaction solution was then centrifuged at 8000 rpm for 10 min to remove the supernatant and obtain a precipitate. This process was repeated three times. The precipitate was then washed alternately with deionized water and ethanol three times. After drying, silver-coated copper particles were obtained.

[0083] Preparation of sintering slurry:

[0084] 1g of the silver-coated copper particles prepared above, 0.3g of diethylene glycol, 0.15g of sodium citrate, 0.15g of rosin resin and 0.15g of polyethylene terephthalate were mixed to obtain a solder mixture. The mixture was thoroughly mixed using a planetary mixer with rotation speeds of 300rpm, 500rpm, 800rpm, 1200rpm and 1500rpm, and each rotation speed was mixed for 5 minutes to obtain a sintered slurry.

[0085] The sintering slurry obtained above was transferred to the substrate (Cu pad) by a scraping method, and the final sintered sample was obtained by sintering at 150°C and 5MPa for 60 minutes.

[0086] Comparative Example 1:

[0087] Preparation of silver-coated copper particles:

[0088] 0.1 mol of copper acetate and 3.2 g of polyvinylpyrrolidone were added to 150 mL of ethylene glycol and stirred at 500 rpm at room temperature for 10 min to obtain a copper precursor solution. 0.2 mol of reducing agent ascorbic acid was mixed with 100 mL of ethylene glycol and stirred and heated at 40 °C to dissolve the mixture. The completely dissolved reducing agent solution was added to the copper precursor solution, and the mixture was stirred at 500 rpm for 20 min. After that, it was centrifuged at 8000 rpm for 10 min to remove the supernatant and obtain the precipitate. This process was repeated three times, and the mixture was then washed alternately with deionized water and ethanol three times to obtain pure copper particles.

[0089] Take 1g of the above copper particles and 0.1g of polyvinylpyrrolidone and add them to 100mL of deionized water. Disperse them at a stirring speed of 500rpm and an ultrasonic power of 450W to obtain a copper suspension. Take 2g of silver nitrate and place it in 200mL of deionized water to obtain 200mL of silver metal salt solution. Disperse it at a stirring speed of 500rpm until there is no precipitate. Then, take 100mL of silver metal salt solution and add it to the copper suspension. Maintain a stirring speed of 500rpm and an ultrasonic power of 450W throughout the process to obtain a silver-coated copper suspension.

[0090] Add 3.5g of EDTA to the remaining 100mL of silver metal salt solution to obtain a silver complex solution for later use.

[0091] Add 1.5g of sodium salicylate to 100mL of deionized water to obtain the second chelating agent solution, and set aside for later use;

[0092] Add 2.0 g of potassium ferrocyanide to 50 mL of deionized water to obtain a complexing agent solution for later use;

[0093] While maintaining a stirring rate of 500 rpm and an ultrasonic power of 450 W, a silver complexing solution and a second chelating agent solution were added simultaneously at a rate of 400 mL / s. The reaction was allowed to proceed for 3000 s. The resulting reaction solution was then centrifuged at 8000 rpm for 10 min to remove the supernatant and obtain a precipitate. This process was repeated three times. The precipitate was then washed alternately with deionized water and ethanol three times, followed by drying to obtain silver-coated copper particles with a dendritic surface. Figure 8 As shown, the sintering performance is as follows Figure 9 As shown, Figure 9 Combination Figure 10 We can see that the surface of the silver-coated copper particles is dendritic. Although the exothermic peak is at a low temperature, it can only satisfy the interconnection between particles in low-temperature welding, and cannot guarantee the interconnection between the welding layer and the pad. Therefore, it is not suitable for use in the field of low-temperature welding.

[0094] Preparation of sintering slurry:

[0095] 1g of the silver-coated copper particles prepared above, 0.3g of diethylene glycol, 0.15g of sodium citrate, 0.15g of rosin resin and 0.15g of polyethylene terephthalate were mixed to obtain a solder mixture. The mixture was thoroughly mixed using a planetary mixer with rotation speeds of 300rpm, 500rpm, 800rpm, 1200rpm and 1500rpm, and each rotation speed was mixed for 5 minutes to obtain a sintered slurry.

[0096] The sintering slurry obtained above was transferred onto the substrate (Cu pads) using a scraping method. The sample was then sintered at 150°C and 5 MPa for 60 minutes to obtain the final sintered sample. The cross-sectional view of the solder joints after sintering is shown below. Figure 10 As shown, from Figure 10 As can be seen, the cross-sectional particles are densely arranged and the sintered structure is dense, but the weldability between the sintered slurry and the substrate is poor and the porosity is large, which proves that the silver-coated copper particles with dendritic surfaces prepared in this embodiment do not have low-temperature welding performance.

[0097] The shear strength of the final sintered samples prepared in Examples 1-2 and Comparative Example 1 was tested according to GB / T 4937.19 - Semiconductor devices, mechanical and climatic testing methods - Part 19: Chip shear strength method, as detailed in Table 1.

[0098] Thermal conductivity test:

[0099] The sintering slurries prepared in Examples 1-2 and Comparative Example 1 were placed in a metal cylinder with an internal height of 1 mm and a diameter of 6 mm, sintered for 60 min, and then placed in a laser thermal conductivity meter to test their thermal conductivity using the laser flash point method. See Table 1 for details.

[0100] Table 1 shows the shear strength of the final sintered samples prepared in Examples 1-2 and Comparative Example 1, and the thermal conductivity of the sintered slurry in Examples 1-2 and Comparative Example 1.

[0101]

[0102] The above description is merely a preferred embodiment of the present invention. These specific embodiments are different implementations based on the overall concept of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or 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. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing silver-coated copper particles, characterized in that, The method described: S1: A copper precursor solution is prepared by mixing copper metal salt and dispersant 1; S2: Add a reducing agent solution to the copper precursor solution obtained in S1, and react to obtain copper particles; S3: Add the copper particles obtained in S2 and dispersant 2 to the solvent and stir ultrasonically to obtain a copper suspension; S4: Prepare a silver metal salt solution with a concentration of 0.01~1mol / L, and divide it into two portions for later use; S5: Inject a portion of the silver metal salt solution from S4 into the copper suspension obtained in S3 to obtain a silver-coated copper particle suspension. S6: Mix the first chelating agent with another part of the silver metal salt solution of S4 to obtain a silver complex solution; S7: Prepare the second chelating agent into a second chelating agent solution; S8: Prepare the complexing agent into a complexing agent solution; S9: Under ultrasonic conditions, the silver complexing solution obtained in S6, the second chelating agent solution obtained in S7, and the complexing agent solution obtained in S8 are added to the silver-coated copper particle suspension obtained in S5. After the reaction is completed, the mixture is centrifuged, washed, and dried to obtain silver-coated copper particles. Among them, dispersant 1 and dispersant 2 in S1 and S3 are one or more of Tween 20, Tween 80, polyethylene glycol 200, polyethylene glycol 2000, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, citrate, octadecylamine, maleate, fumarate, itaconic acid, and cyclodextrin compounds. The first chelating agent in S6 is ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraaminehexaacetic acid, 1,4,7-triazacyclononanetriacetic acid, ethylenediaminedisuccinic acid, diethylenetriaminepentamethylenephosphonic acid, deferoxamine, 8-hydroxyquinoline derivatives, hydroxyethylethylenediaminetriacetic acid, or ethylene glycol diethyl ether diaminetetraacetic acid; the second chelating agent in S7 is sodium oxalate, ethylenediamine, o-phenanthroline, acetylacetone, sodium salicylate, glycine, dimethyl ethylenedioxime, cysteine, or N,N'-diphenylethylenediamine, with a solution concentration of 0.025~1 mol / L; the complexing agent in S8 is potassium ferrocyanide, sodium cyanide, ethyl... One or more of ammonium sulfate, sodium lactate, potassium malate, and potassium glycerophosphate are used; the concentration of the complexing agent solution is 0.025~1 mol / L; the ultrasonic power in S9 is 80~550W, the stirring speed is 100~2000rpm, the reaction time is 3000s, and the volume ratio of the silver complexing solution, the second chelating agent solution, the complexing agent solution, and the silver-coated copper particle suspension is 1:(0.1~5):(0.1~5):(0.1~5). The silver complexing solution is added last or mixed with one or two of the second chelating agent solution and the complexing agent solution before being added last. The centrifugation speed is 1000~10000rpm.

2. The method according to claim 1, characterized in that, In S1, the copper metal salt is one or more of copper formate, copper acetate, copper chloride, copper sulfate, copper carbonate, copper hydroxide, and copper iodide. The concentration of the copper metal salt in the copper precursor solution is 0.01~1 mol / L, and the molar ratio of copper metal salt to dispersant 1 is 1:(0.001~0.1). In S2, the reducing agent is one or more of hydrazine hydrate, sodium borohydride, sodium hypophosphite, ascorbic acid, and glucose. The concentration of the reducing agent is 0.01~1 mol / L, and the volume ratio of the copper precursor solution to the reducing agent solution is 1:(0.1~2).

3. The method according to claim 1, characterized in that, The copper suspension in S3 has a copper particle concentration of 1~10 g / L, a copper particle to dispersant 2 mass ratio of 1:(0.1~10), an ultrasonic power of 80~550W, and a stirring speed of 100~2000 rpm; the copper suspension to silver metal salt solution in S5 has a volume ratio of 1:(0.1~5); the first chelating agent in S6 has a mass ratio of (0.5~5) g to (50~200) mL of silver metal salt solution, and the first chelating agent is a compound that forms chelates with metal ions with more than five coordinate bonds; the second chelating agent in S7 is a compound that forms chelates with metal ions with fewer than five coordinate bonds.

4. The method according to claim 1, characterized in that, The silver complexing solution in S9 is added at a rate of 400-800 mL / s, the second chelating agent solution is added at a rate of 300-500 mL / s, and the complexing agent solution is added at a rate of 100-200 mL / s.

5. A silver-coated copper particle, characterized in that, It is prepared by any one of the preparation methods of claims 1 to 4.

6. The silver-coated copper particles according to claim 5, characterized in that, The copper molar content in silver-coated copper particles is 10-90%, and the particle size is 500-3000 nm.

7. A sintering slurry, characterized in that, The sintering slurry composition by mass percentage is as follows: 60-90% of the silver-coated copper particles as described in claim 5 or 6, 3-45% of the organic solution, 0.1-10% of the dispersant 3, 0.1-10% of the flux, and 0.1-10% of the binder, with a total mass percentage of 100%, and the dispersant 3 is sodium citrate.

8. A low-temperature sintering method for a sintering slurry, characterized in that, The method involves transferring the sintering paste described in claim 7 onto the substrate pads using a scraping method, placing the chip thereon, and sintering it for 15-150 minutes at a temperature of 150-200°C and a pressure of 0-30 MPa.

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