Microstructured micronic silver, low temperature sinterable solder paste and methods of making and using the same

Abstract

The application provides a mesostructure micron silver, a low-temperature sintering solder paste and a preparation method and application thereof. The mesostructure micron silver is prepared by the following steps: respectively configuring a precursor solution containing silver ions and a coating agent, a reducing solution containing a reducing agent; mixing the precursor solution and the reducing solution with each other, performing a redox reaction at 25-80 DEG C for a period of time, then adding a surface etching agent or a surface etching agent solution dropwise for reaction, performing centrifugation on the obtained solution, taking the precipitate, washing and drying to obtain micron silver particles with a mesostructure on the surface; the surface etching agent is at least one of ferric chloride, ferrous chloride and sodium chloride. The micron silver particle surface of the technical scheme of the application has a mesostructure shape structure, the obtained micron silver solder paste can be uniformly dispersed without additional additives, and low-temperature sintering and high-temperature service can be realized.

Description

Technical Field

[0001] This invention belongs to the field of electronic packaging materials technology, and particularly relates to a mesoscopic micron-sized silver, a low-temperature sinterable solder paste, its preparation method and application. Background Technology

[0002] Next-generation semiconductor materials, such as SiC and gallium nitride, can operate stably at higher temperatures and exhibit excellent performance. Meanwhile, as electronic components continue to evolve towards miniaturization and higher power, higher demands are placed on electronic packaging interconnect materials, requiring them to operate stably under more extreme operating environments, such as higher temperatures and higher current densities. While existing micron-sized silver solder paste can achieve sintering interconnects at certain temperatures, its performance still has room for improvement.

[0003] Meanwhile, existing micron-sized silver solder pastes, due to the micron-sized silver particles, have relatively lower sintering activity compared to nano- and submicron-sized silver particles. Therefore, higher temperatures or pressures are often required during actual sintering. However, micron-sized silver solder pastes, thanks to the steric hindrance effect of their micron-sized silver particles, can achieve excellent dispersibility. For nano-silver solder pastes, the high surface energy of the nano-silver particles makes them prone to agglomeration despite the presence of coating agents, and the thick coating layer is often detrimental to the actual sintering process. Therefore, it is particularly important to combine the advantages of nano- and submicron-sized silver solder pastes with those of micron-sized silver solder pastes to provide a silver solder paste preparation process that offers good dispersibility, is less prone to agglomeration, and possesses high sintering activity that can be sintered at lower temperatures or pressures. Summary of the Invention

[0004] To address the above technical problems, this invention discloses a mesoscopic micron-sized silver solder paste, a low-temperature sinterable solder paste, its preparation method, and its applications. The steric hindrance effect generated by the micron-sized silver particles in the solder paste effectively solves the problem of silver particle agglomeration, and the mesoscopic structure on the particle surface provides higher surface activity and higher sintering activity. Furthermore, this invention provides an application of a low-temperature sinterable micron-sized silver solder paste with a mesoscopic structure. This application enables the formation of dense sintered joints with excellent performance at low temperatures, without the need for additional binders.

[0005] The technical solution adopted by this invention is as follows:

[0006] A method for preparing mesoscopic micron-sized silver includes the following steps:

[0007] Step S1: Prepare a precursor solution containing silver ions and a coating agent, a reduction solution containing a reducing agent, and a surface etching solution containing a surface etchant, respectively. Step S2: Mix the precursor solution and the reduction solution together and carry out a redox reaction at 25℃~80℃ for a period of time. Then add the surface etchant or a surface etchant solution and carry out the reaction again. Centrifuge the resulting solution, collect the precipitate, wash and dry it to obtain micron-sized silver particles with a mesoscopic structure on the surface.

[0008] The surface etching agent is at least one of ferric chloride, ferrous chloride, and sodium chloride;

[0009] The molar ratio of silver ions to surface etchant is 10 to 50.

[0010] This technical solution involves adding a surface etchant after the precursor solution and the reducing solution have reacted. The surface etchant etches away the coating agent on the surface of the silver particles and reacts with some of the silver ions on the surface of the silver particles formed by the reaction, so that the surface of the resulting micron-sized silver particles forms a fractal structure with a mesoscopic size (100-150 nm). Micron-sized silver can provide higher surface activity, and the silver paste prepared using these micron-sized silver particles has higher sintering activity.

[0011] Furthermore, the average particle size of the obtained micron-sized silver particles is 1–2 μm.

[0012] Furthermore, in the precursor solution, the molar ratio of silver ions to coating agent is 0.5 to 2.5;

[0013] Furthermore, in step S2, after the precursor solution and the reducing solution are mixed, the molar ratio of silver ions to reducing agent is 0.1 to 1.5.

[0014] As a further improvement of the present invention, in the precursor solution, the silver ions are derived from one or more of silver nitrate, silver bromate, silver bromide, silver chloride, silver citrate, silver fluoride, silver iodate, silver iodide, silver nitrite, silver nitrite, silver phosphate, silver chlorate, silver perchlorate, and silver tetrafluoroborate; the coating agent is at least one of citric acid, sodium citrate, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, dodecyl mercaptan, polyethylene glycol, and polyacrylic acid.

[0015] As a further improvement of the present invention, the reducing agent is at least one selected from sodium borohydride, citric acid, formic acid, sodium citrate, disodium citrate, ferrous sulfate, ascorbic acid, sodium ascorbate, hydroxylamine, aniline, glucose, ethylene glycol, polyethylene glycol, glycerol, polyvinylpyrrolidone, and sodium sulfite.

[0016] As a further improvement of the present invention, step S1 further includes preparing a surface etchant solution, wherein the solvent of the surface etchant solution is one or a mixture of two or more of water, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, pentanol, isoamyl alcohol, and diethylene glycol.

[0017] As a further improvement of the present invention, the surface etching agent is at least one of ferric chloride and ferrous chloride.

[0018] As a further improvement of the present invention, in step S2, after the redox reaction, a surface etching agent solution is added dropwise to carry out the reaction.

[0019] As a further improvement of the present invention, in step S2, the rate of adding the surface etchant solution is 1-5 mL / min, and the reaction time is 0.5-1 h.

[0020] As a further improvement of the present invention, the solvent of the precursor solution includes at least one of water, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, pentanol, isoamyl alcohol, and diethylene glycol.

[0021] As a further improvement of the present invention, the solvent of the reducing solution includes at least one of water, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, pentanol, isoamyl alcohol, and diethylene glycol.

[0022] As a further improvement of the present invention, in step S2, the stirring rate during the redox reaction is 250 r / min to 1200 r / min, and the redox reaction time is 0.5 to 2.5 h.

[0023] As a further improvement of the present invention, in step S2, the cleaning includes washing with deionized water, anhydrous ethanol or acetone, and then centrifuging at 3000-4500 r / min at least 3 times.

[0024] Furthermore, after cleaning, the micron-sized silver particles were obtained by drying at 50°C for 10 hours under a vacuum of less than 0.01 MPa.

[0025] The present invention also discloses a mesoscopic micron-sized silver, which is prepared by the method for preparing mesoscopic micron-sized silver as described in any one of the above claims.

[0026] The present invention also discloses a low-temperature sinterable solder paste, which comprises micron-sized silver with a mesoscopic structure as described above and an organic solvent; the organic solvent is one or a mixture of at least two of ethanol, ethylene glycol, propylene glycol, terpineol, n-pentyl ether, and isopentyl ether.

[0027] As a further improvement of the present invention, the mass ratio of the mesoscopic micron-sized silver to the organic solvent is 8-9:1-2.

[0028] The present invention also discloses the application of the low-temperature sinterable solder paste as described above, which is used in the soldering interconnect packaging of electronic components.

[0029] As a further improvement to the present invention, the following steps are included:

[0030] The low-temperature sintering solder paste is applied to the material, substrate or part to be sealed by dispensing or printing, and then placed in an oven at 90-110°C for 20-40 minutes for descaling.

[0031] The chip to be connected is placed on a material or substrate that has been debonded, and then subjected to hot pressing sintering. The hot pressing sintering temperature is 150–250°C, and the hot pressing pressure is 5–20 MPa. Further, the sintering time is 10–30 minutes. Further, the debonding temperature is 100°C, and the time is 30 minutes.

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

[0033] Using the technical solution of this invention, micron-sized silver particles with a mesoscopic structure are prepared through a redox reaction. By adding a surface etchant, the etchant etches away organic matter and some silver ions on the surface of the silver particles. The chloride ions in the etchant combine with the silver ions to produce an etching effect, thereby growing and etching submicron-sized (mesoscopic) shape structures on the surface of the prepared micron-sized silver particles. Furthermore, the micron-sized silver particles are mixed with an organic solvent to obtain a low-temperature sinterable micron-sized silver solder paste with a mesoscopic structure, achieving uniform dispersion of the micron-sized silver particles without the need for additional additives. This micron-sized silver solder paste, due to its mesoscopic fractal structure on its surface, enhances sintering activity, allowing sintering to be achieved at a minimum of 160°C under pressure assistance. The resulting solder joints exhibit high shear strength, good oxidation resistance and conductivity, and stable operation at high temperatures, achieving "low-temperature sintering, high-temperature service." Simultaneously, the solder joints prepared using this micron-sized silver paste have excellent performance, with shear strength reaching over 50 MPa, making it well-suited for applications in electronic packaging. Attached Figure Description

[0034] Figure 1 This is a field emission scanning electron microscope (SEM, ×50000) image of the micron-sized silver particles in Embodiment 1 of the present invention.

[0035] Figure 2This is a field emission scanning electron microscope (SEM, ×5000) image of the micron-sized silver particles in Embodiment 1 of the present invention.

[0036] Figure 3 This is the XRD pattern of the micron-sized silver particles in Embodiment 1 of the present invention.

[0037] Figure 4 This is the DSC-TG image of the micron-sized silver solder paste in Embodiment 1 of the present invention.

[0038] Figure 5 This is a field emission scanning electron microscope (SEM, ×5000) image of the shear fracture surface of the sintered weld joint in Embodiment 1 of the present invention.

[0039] Figure 6 This is a field emission scanning electron microscope (SEM, ×50000) image of the micron-sized silver particles in Comparative Example 1 of this invention. Detailed Implementation

[0040] The preferred embodiments of the present invention will be described in further detail below.

[0041] Example 1

[0042] Micron-sized silver particles with a mesoscopic surface structure were prepared using the following steps:

[0043] 6.8 g of silver nitrate and 2.35 g of polyvinylpyrrolidone were dispersed in 150 mL of deionized water and stirred until homogeneous to obtain a precursor solution. 7.04 g of ascorbic acid was dispersed in 50 mL of deionized water and stirred until homogeneous to obtain a reducing solution. 0.20 g of ferric chloride solution was dissolved in 20 mL of deionized water to obtain a surface etchant solution—ferric chloride solution. The reducing solution was added dropwise to the precursor solution at a rate of 1 mL / s at 75 °C and a stirring speed of 500 r / min. After reacting for 45 min, the ferric chloride solution was added dropwise to the reaction solution at a rate of 2.5 mL / min, and the reaction was continued for 1 h. After the reaction was complete, the precipitate was collected by centrifugation, washed three times with deionized water at 3500 r / min, and then washed once with anhydrous ethanol. The precipitate was then dried at 50 °C for 10 h under a vacuum of less than 0.01 MPa to obtain micron-sized silver particles with a mesoscopic surface structure.

[0044] The above-mentioned micron-sized silver particles were calculated according to their mass parts. Eight parts of the micron-sized silver particles and two parts of terpineol were placed in a planetary mixer and stirred evenly to prepare a micron-sized silver solder paste that can be sintered at low temperature.

[0045] The micron-sized silver solder paste prepared by this method was subjected to interconnect welding tests. Interconnect joints were obtained by printing, debinding, and hot pressing sintering. When the sintering temperature was 175℃, the holding time was 10min, and the auxiliary pressure was 15MPa, the shear strength of the interconnect joints reached more than 50MPa.

[0046] The micron-sized silver particles with mesostructures obtained above were examined using field emission scanning electron microscopy (SEM) to observe their morphology. Phase mapping analysis was performed using X-ray diffraction (XRD). Thermogravimetric and differential thermal analyses were conducted on the obtained micron-sized silver solder paste using a simultaneous thermal analysis instrument. Finally, the cross-section of the interconnect joint obtained after shearing was observed using field emission scanning electron microscopy. The results are as follows: Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown. From Figure 1 As can be seen, the surface of the micron-sized silver particles contains a large number of mesoscopic structures, which are uniformly distributed on the surface of the micron-sized silver particles; from Figure 2 As can be seen, the micron-sized silver particles are well dispersed, with no obvious agglomeration, and exhibit uniform particle size and shape. Figure 3 Characteristic peaks of metallic silver can be observed, but there are no characteristic peaks of silver oxide or second-phase substances. From Figure 4 The thermogravimetric changes and heat absorption / release during the heating process of the micron-sized silver solder paste can be observed, showing that this type of micron-sized silver paste can sinter at a relatively low temperature of around 175℃. Figure 5 The cross-section of the interconnect joint after shearing test can be seen, and it can be seen that a certain sintering neck is formed between the particles under the action of low temperature hot pressing sintering.

[0047] Example 2

[0048] Micron-sized silver particles with a mesoscopic surface structure were prepared using the following steps:

[0049] Disperse 10g of silver nitrate and 7.0g of sodium citrate in 250mL of deionized water and stir until homogeneous to obtain a precursor solution. Disperse 10g of sodium ascorbate in 75mL of deionized water and stir until homogeneous to obtain a reducing solution. Dissolve 0.16g of ferrous chloride solution in 25mL of deionized water.

[0050] The reducing solution was added dropwise to the precursor solution at a rate of 1 mL / s at 60 °C and a stirring speed of 500 r / min. After reacting for 45 min, ferrous chloride solution was added dropwise to the reaction solution at a rate of 2.5 mL / min, and the reaction was continued for another 1 h. After the reaction was completed, the precipitate was collected by centrifugation, washed three times with deionized water at 3500 r / min, and then washed once with anhydrous ethanol. Subsequently, the precipitate was dried at 50 °C for 10 h under a vacuum of less than 0.01 MPa to obtain micron-sized silver particles with a mesoscopic structure on the surface.

[0051] The SEM image, XRD pattern and internal structure of the prepared micron-sized silver particles are similar to those in Example 1, indicating that the phase of the micron-sized silver particles is metallic silver, without other impurities, the particles do not agglomerate, are well dispersed, and have uniform particle size.

[0052] Comparative Example 1

[0053] The difference between this embodiment and Embodiment 1 is that the mass of ferric chloride added in Embodiment 1 is changed to 0.67g, while the other conditions are exactly the same as in Embodiment 1.

[0054] SEM images of the prepared micron-sized silver particles are shown below. Figure 6 As shown, in this comparative example, the excessive addition of surface etchant causes spherical particles to be completely etched into sheet-like particles.

[0055] Comparative Example 2

[0056] The difference between this embodiment and Embodiment 1 is that the mass of ferric chloride added in Embodiment 1 is changed to 0.12g, while the other conditions are exactly the same as in Embodiment 1.

[0057] The surface of the prepared silver particles was not etched, meaning that for this comparative example, the low content of the surface etchant was insufficient to produce an etching effect.

[0058] Example 3

[0059] A low-temperature sinterable micron silver solder paste is made of 8 parts by weight of micron silver particles and 2 parts by weight of ethylene glycol, wherein the micron silver particles are prepared in the same way as in Example 1.

[0060] The preparation method of the above-mentioned low-temperature sintering micron silver solder paste is the same as that in Example 1.

[0061] Example 4

[0062] A low-temperature sinterable micron silver solder paste is prepared by comprising 9 parts by weight of micron silver particles and 1 part by weight of n-pentyl ether, wherein the micron silver particles are prepared by the same method as in Example 1.

[0063] The preparation method of the above-mentioned low-temperature sintering micron silver solder paste is the same as that in Example 1.

[0064] Example 5

[0065] A low-temperature sinterable micron silver solder paste is prepared by comprising 9 parts by weight of micron silver particles and 2 parts by weight of glycerol, wherein the micron silver particles are prepared by the same method as in Example 1.

[0066] The preparation method of the above-mentioned low-temperature sintering micron silver solder paste is the same as that in Example 1.

[0067] Example 6

[0068] A low-temperature sinterable micron silver solder paste is prepared by comprising 8 parts by weight of micron silver particles and 1 part by weight of isopentyl ether, wherein the micron silver particles are prepared by the same method as in Example 1.

[0069] The preparation method of the above-mentioned low-temperature sintering micron silver solder paste is the same as that in Example 1.

[0070] Example 7

[0071] The preparation method of a low-temperature sinterable micron silver solder paste is the same as that in Example 1, except that the pressure of the hot pressing sintering process is 5 MPa.

[0072] Example 8

[0073] The preparation method of a low-temperature sinterable micron silver solder paste is the same as that in Example 1, except that the hot pressing sintering process takes 30 minutes.

[0074] Example 9

[0075] The preparation method of a low-temperature sinterable micron silver solder paste is the same as that in Example 1, except that the pressure of the hot pressing sintering process is 10 MPa.

[0076] Example 10

[0077] The preparation method of a low-temperature sinterable micron silver solder paste is the same as that in Example 1, except that the temperature of the hot pressing sintering process is 225°C.

[0078] The micron-sized silver solder paste prepared in each embodiment was placed between a silver-plated copper plate, a copper substrate, and a silver-plated silicon chip, and then hot-pressed and sintered. The specific sintering conditions are shown in Table 1 below:

[0079] Table 1 Application of micron-sized silver solder paste in each embodiment and comparative example

[0080] Sintering temperature (°C) Pressure (MPa) Sintering time (min) Example 1 175 15 10 Example 3 200 10 10 Example 4 225 5 10 Example 5 250 20 10 Example 6 160 20 10 Example 7 175 5 10 Example 8 175 15 30 Example 9 175 10 10 Example 10 225 15 10

[0081] The shear strength of the welded joint was tested at room temperature using a Try Precision MFM1200 push-pull testing machine at a shear rate of 300 μm / s. The test results are shown in Table 2.

[0082] Table 2. Application performance and test results of the micron-sized silver solder paste prepared in each embodiment and comparative example.

[0083] Shear strength (MPa) of welded joint Example 1 56.2 Example 3 63.3 Example 4 59.0 Example 5 112.5 Example 6 38.5 Example 7 21.7 Example 8 78.2 Example 9 40.7 Example 10 90.7

[0084] As shown in Table 2, the welded joints prepared by the micron-sized silver solder paste with a mesoscopic surface structure obtained by this method exhibit high shear strength after sintering at low temperatures, successfully achieving low-temperature connection and high-temperature service. This invention uses low-cost raw materials as reactants, employs low-consumption and environmentally friendly reaction conditions, and has a simple preparation process. Furthermore, the prepared micron-sized silver particles exhibit good dispersion, all with a consistent mesoscopic size structure on their surface, allowing for mass production and application in the field of electronic packaging materials.

[0085] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing mesoscopic micron-sized silver, characterized in that, Includes the following steps: Step S1: Prepare a precursor solution containing silver ions and a coating agent, and a reduction solution containing a reducing agent, respectively. Step S2: The precursor solution and the reducing solution are mixed and subjected to a redox reaction at 75℃~80℃ for 0.5-2.5h. Then, a surface etchant or a surface etchant solution is added and the reaction is carried out for 0.5-1h. The resulting solution is centrifuged, the precipitate is collected, washed, and dried to obtain micron-sized silver particles with a mesoscopic structure on the surface. The average particle size of the micron-sized silver particles is 1~2μm, and the surface of the mesoscopic silver particles forms a fractal structure with a mesoscopic size of 100~150 nm. The surface etching agent is at least one of ferric chloride, ferrous chloride, and sodium chloride; the coating agent is at least one of citric acid, sodium citrate, polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, dodecyl mercaptan, polyethylene glycol, and polyacrylic acid. The molar ratio of silver ions to surface etchant is 10 to 50.

2. The method for preparing mesoscopic micron-sized silver according to claim 1, characterized in that: In the precursor solution, the silver ions are derived from one or more of silver nitrate, silver bromate, silver bromide, silver chloride, silver citrate, silver fluoride, silver iodate, silver iodide, silver nitrite, silver phosphate, silver chlorate, silver perchlorate, and silver tetrafluoroborate; and the molar ratio of silver ions to coating agent in the precursor solution is 0.5 to 2.

5.

3. The method for preparing mesoscopic micron-sized silver according to claim 1, characterized in that: The reducing agent is at least one selected from sodium borohydride, citric acid, formic acid, sodium citrate, disodium citrate, ferrous sulfate, ascorbic acid, sodium ascorbate, hydroxylamine, aniline, glucose, ethylene glycol, polyethylene glycol, glycerol, polyvinylpyrrolidone, and sodium sulfite; in step S2, after the precursor solution and the reducing solution are mixed, the molar ratio of silver ions to reducing agent is 0.1 to 1.

5.

4. The method for preparing mesoscopic micron-sized silver according to claim 1, characterized in that: Step S1 further includes preparing a surface etchant solution, wherein the solvent of the surface etchant solution is one or a mixture of two or more of the following: water, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, pentanol, isoamyl alcohol, and diethylene glycol. The solvent of the precursor solution is at least one of water, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, pentanol, isoamyl alcohol, and diethylene glycol. The solvent of the reducing solution is at least one of water, methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, pentanol, isoamyl alcohol, and diethylene glycol.

5. The method for preparing mesoscopic micron-sized silver according to claim 1, characterized in that: In step S2, the stirring rate is 250 r / min to 1200 r / min during the redox reaction; in step S2, the cleaning includes washing with deionized water, anhydrous ethanol or acetone, followed by centrifugation at 3000 to 4500 r / min at least 3 times.

6. A mesoscopic structure of micron-sized silver, characterized in that: It was prepared using the method for preparing mesoscopic micron-sized silver as described in any one of claims 1 to 5.

7. A low-temperature sinterable solder paste, characterized in that: It comprises micron-sized silver with a mesoscopic structure as described in claim 6 and an organic solvent; said organic solvent is one or a mixture of at least two of ethanol, ethylene glycol, propylene glycol, terpineol, n-pentyl ether, and isopentyl ether.

8. The low-temperature sinterable solder paste according to claim 7, characterized in that: The mass ratio of the mesoscopic micron-sized silver to the organic solvent is 8-9:1-2.

9. The application of the low-temperature sinterable solder paste as described in claim 7, characterized in that: The low-temperature sinterable solder paste is used in the soldering, interconnection, and packaging of electronic components.

10. The application of the low-temperature sinterable solder paste according to claim 9, characterized in that, Includes the following steps: The low-temperature sintering solder paste is applied to the material, substrate or part to be sealed by dispensing or printing, and then placed in an oven at 90~110℃ for 20-40 minutes for descaling. The chip to be connected is placed on a material or substrate that has been de-adhesiveized, and then hot-pressed and sintered. The hot-pressing and sintering temperature is 150~250℃, and the hot-pressing pressure is 5~20 MPa.

Images