Silver-coated copper particles, preparation method thereof and application of silver-coated copper particles in sintering slurry

Abstract

The invention discloses silver-coated copper particles, a preparation method thereof and application of the silver-coated copper particles in sintering slurry. The invention belongs to the field of sintered materials. The problem that in the prior art, the sintering temperature of high-temperature welding flux is high is solved. According to the silver-coated copper particles, a multi-step chemical synthesis method is adopted, firstly, silver-coated copper particle suspension is prepared, and then a silver complexing solution, a second chelating agent solution and a complexing agent solution are used for regulating and controlling the release and reduction rate difference of silver ions, so that gradient structure evolution of a silver layer from a compact structure to a porous structure is achieved; the surfaces of the silver-coated copper particles have multistage pore structures, so that the contact resistance among the particles can be effectively reduced, the sintering initial temperature is effectively reduced, the problem of poor oxidation performance of the copper particles is solved, the use amount of silver is reduced, the manufacturing cost is reduced, the ion migration path length is increased, and the electromigration life is prolonged; the prepared silver-coated copper particles greatly meet the requirements of the current electronic packaging field for novel welding materials, and have remarkable social benefits and economic benefits.

Description

Technical Field

[0001] The invention belongs to the field of sintered materials, and in particular relates to silver-coated copper particles, a preparation method thereof, and application of the silver-coated copper particles in sintering slurry. Background Art

[0002] With the widespread application of semiconductor materials, these materials have been widely adopted in fields such as lasers, detectors, semiconductor lighting, radio frequency devices, and high-power devices. Semiconductors offer three key advantages: ① Wide bandgap semiconductors provide 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 overall system transmission efficiency; and ③ High thermal conductivity enables effective heat dissipation under high-power conditions, reducing performance degradation and device failure caused by excessive temperatures. These advantages have further increased the operating temperature of semiconductor devices. This also places higher demands on solder materials. In high-power semiconductor devices, solder materials are critical to ensuring long-term device stability. Traditional solders (such as Sn-Pb solder) have relatively low operating temperatures and melt at the peak operating temperatures 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 affects the operating efficiency and service life of the device. Therefore, the development and use of solders suitable for these new semiconductor materials has become crucial for improving the performance of electronic devices.

[0003] In recent years, new high-temperature solder materials such as silver- and copper-based solders have become the preferred solders for semiconductor devices due to their excellent electrical conductivity, high-temperature resistance, and mechanical strength, meeting the requirements of low-temperature sintering and high-temperature service. These solders possess low-temperature sintering capabilities and typically have thermal conductivity three to four times that of tin-based solders. However, pure silver-based solder is expensive and has high electromigration. While copper-based solder can effectively address these issues, its oxidation resistance is a major drawback. Silver-coated copper core-shell structures combine the advantages of both while mitigating their disadvantages, and are considered a new conductive solid phase for high-temperature soldering. However, to meet high-temperature service requirements and achieve low-temperature sintering, the sintering temperature must be below 200°C to reduce internal stress accumulation during the high-temperature sintering process. Furthermore, due to quantum size effects, the sintering temperature of nanomaterials must be lower than that of micron-sized and larger particles. Therefore, developing a silver-coated copper particle solder that can sinter at low temperatures is crucial for the quality of electronic device production. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem of high sintering temperature of high-temperature solder in the prior art. The present invention provides a silver-coated copper particle and a preparation method thereof and an application in a sintering slurry.

[0005] The technical solutions of the present invention are as follows:

[0006] One of the objects of the present invention is to provide a method for preparing silver-coated copper particles, the method comprising:

[0007] S1: preparing a copper metal salt and a dispersant 1 to obtain a copper precursor solution;

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

[0009] S3: adding the copper particles obtained in S2 and dispersant 2 to the solvent, stirring with ultrasound, to obtain a copper suspension;

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

[0011] S5: injecting a portion of the silver metal salt solution obtained in S4 into the copper suspension obtained in S3 to obtain a suspension of silver-coated copper particles;

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

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

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

[0015] S9: adding the silver complex solution S6, the second chelating agent solution S7 and the complexing agent solution S8 to the silver-coated copper particle suspension S5 under ultrasonic conditions; after the reaction is completed, centrifuging, washing and drying to obtain silver-coated copper particles.

[0016] It is further defined that 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 to 1 mol / L, and the molar ratio of the copper metal salt to the dispersant 1 is 1:0.001 to 0.1; the reducing agent in S2 is one or more of hydrazine hydrate, sodium borohydride, sodium hypophosphite, ascorbic acid, and glucose, the reducing agent concentration is 0.01 to 1 mol / L, and the volume ratio of the copper precursor solution to the reducing agent solution is 1:0.1 to 2.

[0017] It is further defined that the reaction temperature is 0-80° C., the stirring speed is 100-2000 rpm, and the reaction time is 10-120 min.

[0018] It is further defined that dispersant 1 and dispersant 2 in S1 and S3 are one or more of Tween 20, Tween 80, polyethylene glycol 200, polyethylene glycol 2000, polyvinyl pyrrolidone, cetyltrimethylammonium bromide, citrate, octadecylamine, maleate, fumarate, itaconate, and cyclodextrin compounds.

[0019] It is further defined that the concentration of copper particles in the copper suspension of S3 is 1-10 g / L, the mass ratio of copper particles to dispersant 2 is 1:0.1-10, the ultrasonic power is 80-550 W, and the stirring speed is 100-2000 rpm; the volume ratio of the copper suspension to the silver metal salt solution in S5 is 1:0.1-5; the ratio of the first chelating agent to the silver metal salt solution in S6 is 0.5-5 g:50-200 mL, the first chelating agent is a compound that forms a chelate with more than five coordination bonds with the metal ion; the second chelating agent of S7 is a compound that forms a chelate with less than five coordination bonds with the metal ion.

[0020] Further defined, the first chelating agent in S6 is ethylenediaminetetraacetic acid (EDTA), 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, dimethylglyoxime, cysteine or N,N'-diphenylethylenediamine, and the concentration of the second chelating agent solution is 0.025-1 mol / L; the complexing agent in S8 is one or more of potassium ferrocyanide, sodium cyanide, ammonium acetate, sodium lactate, potassium malate, and potassium hydrogen 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 rate is 100-2000 rpm, the reaction time is 10-5000 s, 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 speed of 400-800 mL / s, the second chelating agent solution is added at a speed of 300-500 mL / s, and the complexing agent solution is added at a speed of 100-200 mL / s. The addition order is that the silver complexing solution is added last or mixed with one or both of the first chelating agent solution and the complexing agent solution and then added last. The centrifugal rate is 1000-10000 rpm.

[0021] It is further defined that the solvent in S3 is one or more of deionized water, ethanol, ethylene glycol, diethylene glycol, isopropyl alcohol, isopropylamine, acetone, butanone, cyclohexanone, dimethyl ether, ethyl ether, methyl formate, ethyl acetate, ethylene chloride, and chloroform.

[0022] A second object of the present invention is to provide silver-coated copper particles prepared by the above preparation method.

[0023] It is further defined that the molar content of copper element in the silver-coated copper particles is 10 to 90%, and the particle size is 500 to 3000 nm.

[0024] The third object of the present invention is to provide a sintering slurry, wherein the components of the sintering slurry are as follows by mass percentage: 60-90% of the above-mentioned silver-coated copper particles, 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 the total mass percentage being 100%.

[0025] It is further defined that the organic solvent is one or more of ethanol, ethylene glycol, diethylene glycol, dipropylene glycol, butylene glycol, terpineol, glycerol, sorbitol, ethyl acetate, diethylene glycol diethyl ether, N-methylpyrrolidone, and dibutyl phthalate.

[0026] It is further defined that the dispersant 2 is one or more of Tween 20, Tween 80, polyethylene glycol 200, polyethylene glycol 2000, polyvinyl pyrrolidone, cetyltrimethylammonium bromide, citrate, octadecylamine, maleate, fumarate, itaconate, and cyclodextrin compounds.

[0027] It is further defined that the binder is one or more of phenolic resin, acrylic resin, N,N-dimethyloctanamide, and polyethylene terephthalate.

[0028] It is further defined that the soldering flux is one or more of rosin resin, phenolic resin, and epoxy resin.

[0029] A fourth object of the present invention is to provide a low-temperature sintering method for sintering slurry, wherein:

[0030] The sintering slurry is transferred to the substrate pad by a doctor blade method, a chip is placed, and sintering is performed for 15 to 150 minutes at a temperature of 150 to 200° C. and a pressure of 0 to 30 MPa.

[0031] A fifth object of the present invention is to provide a low-temperature sintering method for the sintering slurry and its application in electronic devices.

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

[0033] (1) The present invention adopts a multi-step chemical synthesis method when preparing silver-coated copper particles. First, copper metal salt and dispersant are configured to obtain a copper precursor solution, and then a reducing agent is injected. At this time, a large number of copper atoms are quickly reduced and undergo nucleation, growth and agglomeration to form micron-sized copper particles. Then, a silver nitrate solution is introduced on the surface of the copper particles, and a replacement reaction occurs by utilizing the higher redox property of copper to form a dense silver seed crystal layer on the surface of the copper particles. The structure of the silver seed crystal layer provides a high-density nucleation site for the uniform growth of the subsequent silver layer, thereby preventing the self-nucleation growth of silver particles and ensuring their continued growth on the silver-coated copper surface. Next, the silver metal salt solution is mixed with a plurality of complex system solutions and chelating agent solutions. Due to the different coordination equilibrium constants between silver ions and different complexing agents, a multi-complex system of silver ions is formed internally, and the silver complex system with a higher equilibrium constant is more soluble in water. The more stable the silver complex substance formed, the higher its proportion in the system, while the complex substance with a low equilibrium constant shows its weak reducing property. The present invention preferentially configures a silver complex solution, which preferentially combines with silver ions to form a stable complex, delays the release rate of silver ions, and ensures the dense growth of the silver layer. In combination with a dispersant, a small amount of silver ions can be dynamically released, and different surface morphologies are further slowly generated on the surface of the silver-coated copper particles in the original silver-coated copper particle suspension. By regulating the difference in the release and reduction rates of silver ions, the gradient structural evolution of different morphologies of the silver layer is achieved. The surface of the silver-coated copper particles has a specific surface nanostructure, which can effectively reduce the contact resistance between particles and effectively reduce the sintering starting temperature, thereby solving the poor oxidation performance of copper particles, reducing the amount of silver used and thus reducing manufacturing costs, and also increasing the length of the ion migration path and the electromigration life.

[0034] (2) The present 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 materials for electrical and thermal conductivity. At the same time, the surface nanostructure can effectively reduce the sintering starting temperature to meet the needs of low-temperature sintering and high-temperature service. Experiments have shown that the sintering starting temperature of the nanoparticles can be reduced to below 130°C, the solder joint shear strength is 18 to 35 MPa, and the thermal conductivity is 100 to 200 W / (m·K). It is proved that the silver-coated copper particles prepared by the present invention greatly meet the current requirements for new welding materials in the field of electronic packaging.

[0035] (3) The silver-coated copper particles prepared by the present invention can give micron-sized particles the sintering properties of nanoparticles in the sintering slurry. Nanosilver particles have high surface energy and reactivity, and can be sintered at a lower temperature, thereby improving the sintering efficiency. The high activity and high sintering driving force of nanosilver can accelerate the sintering process, shorten the sintering time, and improve production efficiency; the nanosilver coating can significantly improve the electrical conductivity and thermal conductivity of the material. During the sintering process, 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 the nanosilver particles enable them to fill the gaps between the micron copper particles during the sintering process to form a dense sintered body. This dense structure can improve the mechanical strength and stability of the material and reduce the porosity and the generation of microcracks; the low melting point of nanosilver allows sintering to be carried out at a lower temperature; the nanosilver coating can enhance the bonding force between the particles and improve the mechanical strength of the sintered material. This enhancement enables the material to withstand greater stress and strain, thereby improving its reliability in high temperature and high stress environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is the experimental flow chart of the present invention;

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

[0038] Figure 3 The differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA) test images of the silver-coated copper particles prepared in Example 1;

[0039] Figure 4 This is a cross-sectional view of the solder 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 These are the differential scanning calorimeter and thermogravimetric analyzer test images of the silver-coated copper particles prepared in Example 2;

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

[0043] Figure 8 This is a scanning electron microscope image of the silver-coated copper particles prepared in Comparative Example 1;

[0044] Figure 9 The differential scanning calorimeter and thermogravimetric analyzer test images of the silver-coated copper particles prepared in Comparative Example 1;

[0045] Figure 10 This is a cross-sectional view of the solder joint after low-temperature sintering of the sintering slurry prepared in Comparative Example 1. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

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

[0048] As used in the following examples, the terms "comprising," "including," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises the listed elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0049] When amount, concentration or other value or parameter are represented with the range of scope, preferred range or a series of upper preferred value and lower preferred value limit, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, and no matter whether this scope is disclosed separately.For example, when disclosing scope "1 to 5", described scope should be interpreted as including scope "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc.When numerical range is described in this article, unless otherwise stated, otherwise this scope is intended to include its end value and all integers and fractions within the scope.In this application specification and claims, range limitation can be combined and / or interchanged, and if these ranges are not otherwise stated, include all subranges contained therein.

[0050] The indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirement (i.e. the number of times they appear). Therefore, "a" or "an" should be interpreted as including one or at least one, and elements or components in the singular also include plural forms, unless the quantity clearly refers to only the singular form.

[0051] The term "one embodiment" or "embodiment" of the present invention refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in various places throughout this specification does not necessarily refer to the same embodiment, nor does it necessarily refer to a separate or selective embodiment that is mutually exclusive of other embodiments.

[0052] The endpoints of the ranges and any values disclosed in the present 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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0053] Example 1:

[0054] Preparation of silver-coated copper particles:

[0055] 0.1 mol of copper acetate and 3.2 g of polyvinyl pyrrolidone were added to 150 mL of ethylene glycol, stirred at room temperature at a speed of 500 rpm for 10 minutes to obtain a copper precursor solution; 0.2 mol of ascorbic acid was mixed with 100 mL of ethylene glycol, and stirred and heated at 40°C to dissolve, and the completely dissolved reducing agent solution was added to the copper precursor solution, maintaining a stirring rate of 500 rpm. After reacting for 20 minutes, the mixture was centrifuged at a speed of 8000 rpm for 10 minutes, the upper solution was removed and a precipitate was obtained, which was repeated three times. The mixture was then washed alternately with deionized water and ethanol, alternately three times, to obtain pure copper particles.

[0056] 1 g of the copper particles and 0.1 g of polyvinyl pyrrolidone were added to 100 mL of deionized water and dispersed at a stirring rate of 500 rpm and an ultrasonic power of 450 W to obtain a copper suspension; 2 g of silver nitrate was placed in 200 mL of deionized water to obtain 200 mL of a silver metal salt solution, and dispersed at a stirring rate of 500 rpm until no precipitation was observed. 100 mL of the silver metal salt solution was then added to the copper suspension, and a stirring rate of 500 rpm and an ultrasonic power of 450 W were maintained throughout the process to obtain a silver-coated copper suspension;

[0057] Take 3.5g EDTA and add it to the remaining 100mL silver metal salt solution to obtain a silver complex solution for later use;

[0058] Add 1.5 g of sodium salicylate to 100 mL of deionized water to obtain a second chelating agent solution 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 complex solution, a second chelating agent solution, and a complexing agent solution were added simultaneously. The addition rates of the three solutions were 400 mL / s, 400 mL / s, and 200 mL / s, respectively. The reaction was carried out for 3000 s, and then the obtained reaction solution was centrifuged at a speed of 8000 rpm for 10 min. The upper solution was removed and a precipitate was obtained. This was repeated three times, and then the mixture was washed alternately with deionized water and ethanol, alternately three times, and dried to obtain silver-coated copper particles with nano-sheet surfaces. Figure 2 As shown, the sintering performance is Figure 3 As shown, from Figure 3 We can see that the sintering starting temperature of the nano-sheet silver-coated copper particles is less than 150°C and reaches a maximum at around 175°C. The overall curve shape releases heat significantly, indicating that it has excellent sintering interconnection performance.

[0061] Preparation of sintering slurry:

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

[0063] The sintered slurry obtained above was transferred to the substrate (Cu pad) by the doctor blade method, and sintered at 150°C and 5 MPa pressure for 60 minutes to obtain the final sintered sample. The cross-sectional view of the solder joint after sintering is shown in FIG. Figure 4 As shown, from Figure 4 It can be seen that the cross-sectional particles are closely arranged, the sintered structure is relatively dense, there are no obvious defects, and there is no stratification at the interface, which proves that the silver-coated copper particles with nano-sheet 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 polyvinyl pyrrolidone were added to 150 mL of ethylene glycol, stirred at room temperature at a speed of 500 rpm for 10 minutes to obtain a copper precursor solution; 0.2 mol of the reducing agent ascorbic acid was mixed with 100 mL of ethylene glycol, and stirred and heated at 40°C to dissolve, and the completely dissolved reducing agent solution was added to the copper precursor solution, maintaining a stirring rate of 500 rpm. After reacting for 20 minutes, the mixture was centrifuged at a speed of 8000 rpm for 10 minutes, the upper solution was removed and a precipitate was obtained, which was repeated three times. The mixture was then washed alternately with deionized water and ethanol, alternately three times, to obtain pure copper particles.

[0067] 1 g of the copper particles and 0.1 g of polyvinyl pyrrolidone were added to 100 mL of deionized water and dispersed at a stirring rate of 500 rpm and an ultrasonic power of 450 W to obtain a copper suspension; 2 g of silver nitrate was placed in 200 mL of deionized water to obtain 200 mL of a silver metal salt solution, and dispersed at a stirring rate of 500 rpm until no precipitation was observed. 100 mL of the silver metal salt solution was then added to the copper suspension, and a stirring rate of 500 rpm and an ultrasonic power of 450 W were maintained throughout the process to obtain a silver-coated copper suspension;

[0068] Take 3.5g EDTA and add it to the remaining 100mL silver metal salt solution to obtain a silver complex solution for later use;

[0069] Add 1.5 g of sodium salicylate to 100 mL of deionized water to obtain a second chelating agent solution 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 rate of 500 rpm and an ultrasonic power of 450 W, the complexing agent solution was first added at a rate of 200 mL / s, and then the silver complexing solution and the second chelating agent solution were added simultaneously, the addition rate of the silver complexing solution and the second chelating agent solution was 400 mL / s, the reaction was carried out for 3000 s, and then the obtained reaction solution was centrifuged at a speed of 8000 rpm for 10 min, the upper solution was removed and a precipitate was obtained, and the reaction was repeated three times. The mixture was then washed alternately with deionized water and ethanol, alternately three times, and dried to obtain silver-coated copper particles with island-like surfaces, such as Figure 5 As shown, the sintering performance is Figure 6 As shown, from Figure 6 We can see that the sintering peak of the island-shaped silver-coated copper particles on the surface is around 150°C, with a certain strength. The subsequent larger exothermic peak is caused by oxidation. Therefore, in order to ensure the sintering interconnection strength, low-temperature sintering at around 150°C should be ensured.

[0072] Preparation of sintering slurry:

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

[0074] The sintered slurry obtained above was transferred to the substrate (Cu pad) by the doctor blade method, and sintered at 150°C and 5 MPa pressure for 60 minutes to obtain the final sintered sample. The cross-sectional view of the solder joint after sintering is shown in FIG. Figure 7 As shown, from Figure 7 It can be seen that the cross-sectional particles are closely arranged, the sintered structure is dense, there are no obvious defects, and there is no stratification at the interface, which proves that the silver-clad copper particles with island-shaped 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 polyvinyl pyrrolidone were added to 150 mL of ethylene glycol, stirred at room temperature at a speed of 500 rpm for 10 minutes to obtain a copper precursor solution; 0.2 mol of the reducing agent ascorbic acid was mixed with 100 mL of ethylene glycol, and stirred and heated at 40°C to dissolve, and the completely dissolved reducing agent solution was added to the copper precursor solution, maintaining a stirring rate of 500 rpm. After reacting for 20 minutes, the mixture was centrifuged at a speed of 8000 rpm for 10 minutes, the upper solution was removed and a precipitate was obtained, which was repeated three times. The mixture was then washed alternately with deionized water and ethanol, alternately three times, to obtain pure copper particles.

[0078] 1 g of the copper particles and 0.1 g of polyvinyl pyrrolidone were added to 100 mL of deionized water and dispersed at a stirring rate of 500 rpm and an ultrasonic power of 450 W to obtain a copper suspension; 2 g of silver nitrate was placed in 200 mL of deionized water to obtain 200 mL of a silver metal salt solution, and dispersed at a stirring rate of 500 rpm until no precipitation was observed. 100 mL of the silver metal salt solution was then added to the copper suspension, and a stirring rate of 500 rpm and an ultrasonic power of 450 W were maintained throughout the process to obtain a silver-coated copper suspension;

[0079] Take 3.5g EDTA and add it to the remaining 100mL silver metal salt solution to obtain a silver complex solution for later use;

[0080] Add 1.5 g of sodium salicylate to 100 mL of deionized water to obtain a second chelating agent solution 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 complex solution, a second chelating agent solution and a complexing agent solution were added simultaneously, with the addition rates of the three solutions being 800 mL / s, 500 mL / s and 200 mL / s, respectively. The reaction was carried out for 3000 s, and then the obtained reaction solution was centrifuged at a speed of 8000 rpm for 10 min, the upper solution was removed and a precipitate was obtained, which was repeated three times. The mixture was then washed alternately with deionized water and ethanol, alternately three times, and dried to obtain silver-coated copper particles.

[0083] Preparation of sintering slurry:

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

[0085] The sintered slurry obtained above was transferred to a substrate (Cu pad) by a doctor blade method, and sintered at 150° C. and a pressure of 5 MPa for 60 min to obtain a final sintered sample.

[0086] Comparative Example 1:

[0087] Preparation of silver-coated copper particles:

[0088] 0.1 mol of copper acetate and 3.2 g of polyvinyl pyrrolidone were added to 150 mL of ethylene glycol, stirred at room temperature at a speed of 500 rpm for 10 minutes to obtain a copper precursor solution; 0.2 mol of the reducing agent ascorbic acid was mixed with 100 mL of ethylene glycol, and stirred and heated at 40°C to dissolve, and the completely dissolved reducing agent solution was added to the copper precursor solution, maintaining a stirring rate of 500 rpm. After reacting for 20 minutes, the mixture was centrifuged at a speed of 8000 rpm for 10 minutes, the upper solution was removed and a precipitate was obtained, which was repeated three times. The mixture was then washed alternately with deionized water and ethanol, alternately three times, to obtain pure copper particles.

[0089] 1 g of the copper particles and 0.1 g of polyvinyl pyrrolidone were added to 100 mL of deionized water and dispersed at a stirring rate of 500 rpm and an ultrasonic power of 450 W to obtain a copper suspension; 2 g of silver nitrate was placed in 200 mL of deionized water to obtain 200 mL of a silver metal salt solution, and dispersed at a stirring rate of 500 rpm until no precipitation was observed. 100 mL of the silver metal salt solution was then added to the copper suspension, and a stirring rate of 500 rpm and an ultrasonic power of 450 W were maintained throughout the process to obtain a silver-coated copper suspension;

[0090] Take 3.5g EDTA and add it to the remaining 100mL silver metal salt solution to obtain a silver complex solution for later use;

[0091] Add 1.5 g of sodium salicylate to 100 mL of deionized water to obtain a second chelating agent solution 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, the silver complex solution and the second chelating agent solution were added simultaneously, the addition rate of the two solutions was 400 mL / s, the reaction was carried out for 3000 s, and then the obtained reaction solution was centrifuged at a speed of 8000 rpm for 10 min, the upper solution was removed and a precipitate was obtained, and the reaction was repeated three times. The mixture was then washed alternately with deionized water and ethanol, alternately three times, and dried to obtain silver-coated copper particles with a dendritic surface, such as Figure 8 As shown, the sintering performance is Figure 9 As shown, Figure 9 Combine Figure 10 We can see that the silver-coated copper particles with dendritic surfaces have a relatively low exothermic peak temperature, but in low-temperature welding, they can only meet the interconnection between particles and cannot guarantee the interconnection between the welding layer and the pad. Therefore, they are not suitable for use in the field of low-temperature welding.

[0094] Preparation of sintering slurry:

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

[0096] The sintered slurry obtained above was transferred to the substrate (Cu pad) by the doctor blade method, and sintered at 150°C and 5 MPa pressure for 60 minutes to obtain the final sintered sample. The cross-sectional view of the solder joint after sintering is shown in FIG. Figure 10 As shown, from Figure 10 It can be seen that the cross-section particles are closely 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-clad 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 to 2 and Comparative Example 1 was tested according to the method of GB / T 4937.19-Semiconductor Devices, Mechanical and Climatic Test Methods Part 19: Chip Shear Strength. See Table 1 for details.

[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 inner 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 its 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 tests of the sintered slurries of Examples 1-2 and Comparative Example 1.

[0101]

[0102] The foregoing are merely preferred embodiments of the present invention. These embodiments are all different implementations based on the overall concept of the present invention. The scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope 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 based on the scope of protection of the claims.

Claims

1. A method for preparing silver-coated copper particles, characterized in that: The method: S1: preparing a copper metal salt and a dispersant 1 to obtain a copper precursor solution; S2: adding a reducing agent solution to the copper precursor solution obtained in S1 to react and obtain copper particles; S3: adding the copper particles obtained in S2 and dispersant 2 to the solvent, stirring with ultrasound, to obtain a copper suspension; S4: Prepare a silver metal salt solution with a concentration of 0.01 to 1 mol / L and divide it into two parts for later use; S5: injecting a portion of the silver metal salt solution obtained in S4 into the copper suspension obtained in S3 to obtain a suspension of silver-coated copper particles; S6: mixing the first chelating agent with another portion of the silver metal salt solution of S4 to obtain a silver complex solution; S7: preparing a second chelating agent into a second chelating agent solution; S8: preparing the complexing agent into a complexing agent solution; S9: adding the silver complex solution S6, the second chelating agent solution S7 and the complexing agent solution S8 to the silver-coated copper particle suspension S5 under ultrasonic conditions; after the reaction is completed, centrifuging, washing and drying to obtain silver-coated copper particles.

2. The method according to claim 1, characterized in that 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 to 1 mol / L, and the molar ratio of the copper metal salt to the dispersant is 1:0.001 to 0.1; the reducing agent in S2 is one or more of hydrazine hydrate, sodium borohydride, sodium hypophosphite, ascorbic acid, and glucose, the reducing agent concentration is 0.01 to 1 mol / L, and the volume ratio of the copper precursor solution to the reducing agent solution is 1:0.1 to 2.

3. The method according to claim 1, characterized in that Dispersant 1 and dispersant 2 in S1 and S3 are one or more of Tween 20, Tween 80, polyethylene glycol 200, polyethylene glycol 2000, polyvinyl pyrrolidone, cetyltrimethylammonium bromide, citrate, octadecylamine, maleate, fumarate, itaconate, and cyclodextrin compounds.

4. The method according to claim 1, wherein The copper particle concentration in the copper suspension of S3 is 1-10 g / L, the mass ratio of copper particles to dispersant 2 is 1:0.1-10, the ultrasonic power is 80-550 W, and the stirring speed is 100-2000 rpm; the volume ratio of the copper suspension to the silver metal salt solution in S5 is 1:0.1-5; the ratio of the first chelating agent to the silver metal salt solution in S6 is 0.5-5 g:50-200 mL, the first chelating agent is a compound that forms a chelate with more than five coordination bonds with the metal ion; the second chelating agent of S7 is a compound that forms a chelate with less than five coordination bonds with the metal ion.

5. The method according to claim 1 or 4, characterized in that 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, dimethylglyoxime, cysteine or N,N'-diphenylethylenediamine, and the concentration of the second chelating agent solution is 0.025-1 mol / L; the complexing agent in S8 is one or more of potassium ferrocyanide, sodium cyanide, ammonium acetate, sodium lactate, potassium malate and potassium hydrogen glycerophosphate, and the concentration of the complexing agent solution is 0.025-1 mol / L. The concentration is 0.025-1 mol / L; the ultrasonic power in S9 is 80-550 W, the stirring rate is 100-2000 rpm, the reaction time is 10-5000 s, the volume ratio of the silver complex 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 complex solution is added at a speed of 400-800 mL / s, the second chelating agent solution is added at a speed of 300-500 mL / s, and the complexing agent solution is added at a speed of 100-200 mL / s. The order of addition is that the silver complex solution is added last or mixed with one or both of the second chelating agent solution and the complexing agent solution and then added last. The centrifugal rate is 1000-10000 rpm.

6. A silver-coated copper particle, characterized in that: Prepared by the preparation method according to any one of claims 1 to 5.

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

8. A sintering slurry, characterized in that: The sintering slurry components are as follows by mass percentage: 60-90% of the silver-coated copper particles according to claim 6 or 7, 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 the total mass percentage being 100%.

9. A low-temperature sintering method for sintering slurry, characterized in that: The method comprises the following steps: transferring the sintering slurry according to claim 8 to a substrate pad by a scraping method, placing a chip thereon, and sintering the slurry at a temperature of 150 to 200° C. and a pressure of 0 to 30 MPa for 15 to 150 minutes.

10. Use of the low-temperature sintering method of the sintering slurry according to claim 9 in electronic devices.

Images