Low-temperature sintered silver paste resistant to electrochemical migration and its preparation method

Abstract

This disclosure relates to a low-temperature sintered silver paste with resistance to electrochemical migration and its preparation method, belonging to the field of chemical paste technology. The low-temperature sintered silver paste comprises: 60-90 parts by weight of compounded silver powder, 10-30 parts by weight of organic carrier, 0.1-3 parts by weight of functional additives, and 0.05-0.3 parts by weight of hydrophobic SiO2 nanoparticles; wherein, the compounded silver powder includes modified silver powder and composite silver powder; the modified silver powder is obtained by adding surface loading to the composite silver powder; in the modified silver powder, the surface loading has a mass part of 0.2-0.8 parts by weight; in the compounded silver powder, the modified silver powder has a mass part of 20-100 parts by weight. This achieves the construction of a dual protection mechanism of physical barrier and chemical passivation in the obtained silver paste, which is expected to significantly improve its resistance to electrochemical migration and long-term reliability while maintaining the excellent electrical and thermal conductivity of the silver paste.

Description

Technical Field

[0001] This disclosure relates to the field of chemical paste technology, and more specifically, to a low-temperature sintering silver paste resistant to electrochemical migration and a method for preparing such a paste. Background Technology

[0002] In some related solutions, the existing technologies mainly adopt the following methods to improve the anti-migration performance of silver paste: on the one hand, noble metal doping; that is, suppressing anion dissolution by forming an inert layer on the silver surface, but the cost is high; on the other hand, low melting point metal alloying; that is, achieving surface passivation by generating intermetallic compounds, but this method will reduce the conductivity of silver paste.

[0003] It should be noted that the information in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] The purpose of this disclosure is to provide a low-temperature sintered silver paste resistant to electrochemical migration and a method for preparing such a paste, thereby overcoming, to at least some extent, the problems of high preparation cost and low conductivity caused by limitations and defects in related technologies.

[0005] According to one aspect of this disclosure, a low-temperature sintering silver paste resistant to electrochemical migration is provided, comprising: 60-90 parts by weight of a compounded silver powder, 10-30 parts by weight of an organic carrier, 0.1-3 parts by weight of a functional additive, and 0.05-0.3 parts by weight of hydrophobic SiO2 nanoparticles; wherein the compounded silver powder comprises modified silver powder and composite silver powder; the modified silver powder is obtained by adding a surface load to the composite silver powder; in the modified silver powder, the surface load is 0.2-0.8 parts by weight relative to the modified silver powder; in the compounded silver powder, the modified silver powder is 20-100 parts by weight relative to the compounded silver powder.

[0006] In an exemplary embodiment of this disclosure, the surface loading is rare earth oxide nanoparticles, the rare earth oxide nanoparticles are CeO2; the D50 particle size of the hydrophobic SiO2 nanoparticles is 15~30 nm; the D50 particle size of the rare earth oxide nanoparticles is 10~50 nm.

[0007] In an exemplary embodiment of this disclosure, the modified silver powder is prepared by the following steps: Step S101, composite silver powder is added to anhydrous ethanol and stirred and washed 1-2 times. After solid-liquid separation, it is vacuum dried at 60-80°C to obtain pretreated silver powder; Step S102, a nonionic dispersant is added to anhydrous ethanol, and the pretreated silver powder is dispersed in the ethanol with the added nonionic dispersant to form a silver powder dispersion slurry; Step S103, a cerium salt solution is added to the silver powder dispersion slurry, and ammonia is added to the silver powder dispersion slurry with the added cerium salt solution to adjust the pH to 8.5-9.0 and maintain the reaction for 30-90 minutes. Step S104 involves solid-liquid separation of the silver powder deposit, followed by washing with anhydrous ethanol and drying the washed silver powder deposit to obtain a silver powder intermediate loaded with cerium oxygen-containing precursor on the silver powder surface. Step S105 involves heat-treating the silver powder intermediate at 180–220 °C for 10–120 min in an air atmosphere to convert the cerium oxygen-containing precursor in the silver powder intermediate into CeO2 and obtain the modified silver powder.

[0008] In one exemplary embodiment of this disclosure, the organic carrier includes an organic solvent and a modified resin;

[0009] The organic solvent includes one or more of the following: mixed diesters, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, dibutyl diacid, and isoflurane; the modified resin includes one or more of the following: polyurethane-modified epoxy resin, polyurethane resin, acrylic resin, and epoxy-modified acrylic resin.

[0010] In an exemplary embodiment of this disclosure, the composite silver powder comprises a mixture of nano-silver powder, submicron silver powder, and micron silver powder; in the composite silver powder, the nano-silver powder comprises 10-15 parts by weight, the submicron silver powder comprises 40-50 parts by weight, and the micron silver powder comprises 35-50 parts by weight; in the compound silver powder, the nano-silver powder is spherical nanoparticles, the submicron silver powder is spherical submicron powder, and the micron silver powder is flake-shaped micron powder.

[0011] In one exemplary embodiment of this disclosure, the D50 particle size range of the nano silver powder is 30~60 nm; the D50 particle size range of the submicron silver powder is 300~500 nm; and the D50 particle size range of the micron silver powder is 1~3 μm.

[0012] In one exemplary embodiment of this disclosure, the functional additive includes one or more of a silane coupling agent, an antioxidant, a dispersant, a leveling agent, a thixotropic agent, and a defoamer; the silane coupling agent includes KH550 type silane coupling agent or KH560 silane coupling agent; the antioxidant includes 2,6-di-tert-butyl-p-cresol and / or pentaerythritol ester; the dispersant includes BYK110; the leveling agent includes at least one of BK-333, diacetone alcohol, Solvesso 150, and a fluorocarbon compound; the thixotropic agent includes BYK410; and the defoamer includes polyether-modified organosilicon BYK-024 or TEGO931.

[0013] According to one aspect of this disclosure, a method for preparing a low-temperature sintered silver paste resistant to electrochemical migration is provided, comprising: step S201, preparation of an organic carrier containing hydrophobic SiO2 nanoparticles: adding an organic solvent to a dry and sealed stirring tank, starting stirring and slowly adding a modified resin until the modified resin is completely dissolved to form a transparent and homogeneous resin solution; adding functional additives and hydrophobic SiO2 nanoparticles to the resin solution and performing high-shear dispersion for 5-15 min to obtain an organic carrier containing hydrophobic SiO2 nanoparticles; step S202, preparation of composite silver powder: adding nano silver powder, submicron silver powder, and micron silver powder in a mass ratio of 2:3:5 into a high-speed mixer for premixing until the silver powder mixture is free of visible lumps and has a uniform color to obtain composite silver powder; adding a surface load to the composite silver powder to obtain composite silver powder; step S203, preparation of silver paste: mixing and stirring the organic carrier with the composite silver powder; during the mixing and stirring process, adding the composite silver powder in 3 portions, stirring for 10 minutes after each addition. After the compounded silver powder is completely wetted, the next batch is added and mixed evenly. Then, a scraper fineness meter is used to detect the fineness. When the fineness is ≤10 μm, stirring is stopped to obtain the low-temperature sintered silver paste that resists electrochemical migration.

[0014] In an exemplary embodiment of this disclosure, the method for preparing the low-temperature sintering silver paste with anti-electrochemical migration further includes: step S204, three-roll milling: the silver paste is added at a uniform speed above the rear roller, so that the slurry of the silver paste flows along the roller surface and passes through the gap between the rollers, and the slurry scraped off by the front roller is collected; the roller gap is gradually reduced, and the fineness is checked after each rolling pass, and stopped when the fineness is ≤5 μm, so as to obtain the three-roll milling slurry; step S50, coating and sintering: the three-roll milling slurry is coated on the target substrate using a screen printing process; then, the coated substrate is placed in a hot press sintering furnace to obtain the packaged substrate.

[0015] In an exemplary embodiment of this disclosure, the thickness of the three-roll mill slurry coated on the target substrate is 10-50 μm; the temperature in the hot pressing sintering furnace is 200 ℃, the pressure is 5 MPa, and the holding time is 20 min; in the preparation process of the SiO2-containing organic carrier, the weight of the nano-additive is 1 part by weight.

[0016] This disclosure provides a low-temperature sintered silver paste with resistance to electrochemical migration. The silver paste comprises: 60-90 parts by weight of compounded silver powder, 10-30 parts by weight of organic carrier, 0.1-3 parts by weight of functional additives, and 0.05-0.3 parts by weight of hydrophobic SiO2 nanoparticles. The compounded silver powder includes modified silver powder and composite silver powder. The modified silver powder is obtained by adding a surface load to the composite silver powder. In the modified silver powder, the surface load is 0.2-0.8 parts by weight relative to the modified silver powder. In the compounded silver powder, the modified silver powder is 20-100 parts by weight relative to the compounded silver powder. This achieves a dual protection mechanism in the obtained silver paste, namely, physical barrier (which can be achieved through hydrophobic SiO2 nanoparticles to reduce hygroscopicity) and chemical passivation (which can be achieved through the formation of a stable passivation film through surface loading to inhibit the generation and migration of silver ions). This is expected to significantly improve the resistance to electrochemical migration and long-term reliability of the silver paste while maintaining its excellent electrical and thermal conductivity.

[0017] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and are not intended to limit this disclosure. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0019] Figure 1 The diagram schematically illustrates the mechanism of a silver paste without the addition of a barrier / interface control phase according to an exemplary embodiment of the present disclosure.

[0020] Figure 2 The diagram schematically illustrates the mechanism of a silver paste containing only hydrophobic silica according to an exemplary embodiment of the present disclosure.

[0021] Figure 3 The diagram schematically illustrates the mechanism of a silver paste using only cerium oxide-modified silver powder according to an example embodiment of the present disclosure.

[0022] Figure 4The diagram schematically illustrates the mechanism of synergistic effect of modified silver powder with added hydrophobic silica and cerium oxide according to an exemplary embodiment of the present disclosure.

[0023] Figure 5 The illustration shows a SEM image of a low-temperature silver paste sintered film without the addition of a nanophase according to an exemplary embodiment of the present disclosure.

[0024] Figure 6 The diagram illustrates a SEM image of a low-temperature silver paste sintered film with only SiO2 nanoparticles (0.2 parts by weight) added, according to an exemplary embodiment of the present disclosure.

[0025] Figure 7 The diagram illustrates a SEM image of a low-temperature silver paste sintered film with only CeO2 nanoparticles (0.2 parts by weight) added, according to an exemplary embodiment of the present disclosure.

[0026] Figure 8 The diagram illustrates a SEM image of a low-temperature silver paste sintered film with a physically mixed addition of SiO2+CeO2 total nanophase (1.0 parts by weight) according to an exemplary embodiment of the present disclosure.

[0027] Figure 9 The diagram illustrates a SEM image of a low-temperature silver paste sintered film with hydrophobic SiO2 and CeO2 modified silver powder (total nanophase 0.2 parts by weight) added according to an exemplary embodiment of the present disclosure.

[0028] Figure 10 The diagram illustrates a SEM image of a low-temperature silver paste sintered film with hydrophobic SiO2 and CeO2 modified silver powder (total nanophase 1.0 parts by weight) added according to an exemplary embodiment of the present disclosure.

[0029] Figure 11 The diagram illustrates a SEM image of a low-temperature silver paste sintered film with hydrophobic SiO2 and CeO2 modified silver powder (total nanophase 2.0 parts by weight) added according to an exemplary embodiment of the present disclosure.

[0030] Figure 12 The diagram illustrates a SEM image of a low-temperature silver paste sintered film containing 100% CeO2-modified silver powder (total nanophase 1.0 parts by weight) according to an exemplary embodiment of the present disclosure.

[0031] Figure 13 The diagram illustrates a SEM image of a low-temperature silver paste sintered film containing 20% ​​CeO2-modified silver powder (total nanophase 1.0 parts by weight) according to an exemplary embodiment of the present disclosure. Detailed Implementation

[0032] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided to make this disclosure more comprehensive and complete, and to fully convey the concept of the example embodiments to those skilled in the art. The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced with one or more of the specific details omitted, or other methods, components, apparatus, steps, etc., can be employed. In other instances, well-known technical solutions are not shown or described in detail to avoid obscuring various aspects of this disclosure.

[0033] Furthermore, the accompanying drawings are merely illustrative of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities. These functional entities may be implemented in software, in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0034] With the widespread application of wide-bandgap semiconductor devices, such as silicon carbide (SiC) and gallium nitride (GaN), in fields like new energy vehicles, industrial control, and aerospace, electronic packaging materials are facing increasingly demanding operating environments. In practical applications, power chips can operate at temperatures exceeding 200°C, with heat flux densities several times higher than traditional silicon-based devices. This places higher demands on the thermal conductivity, electrical conductivity, and high-temperature reliability of interconnect materials. Meanwhile, traditional high-lead solders, due to their excellent high-temperature stability, were once widely used in power device packaging. However, because they contain harmful substances, they are subject to strict environmental regulations and are gradually being phased out of the market. Existing lead-free solder systems (such as Sn-Ag-Cu and Sn-Bi) meet environmental requirements, but generally suffer from low melting points and insufficient thermal conductivity, making them unsuitable for high-temperature, high-power applications.

[0035] Against this backdrop, low-temperature sintering silver technology has attracted widespread attention due to its superior comprehensive performance. This technology enables solid-state sintering of silver particles at low temperatures of 160-300 °C, forming a dense metallic bonding layer. Simultaneously, the sintered silver layer exhibits high electrical conductivity approaching that of bulk silver (approximately 6 × 10⁻⁶). 7 (S / m) and excellent thermal conductivity (typically exceeding 200 W·m). -1·K -1 While maintaining stable mechanical properties at high temperatures, it is currently widely used in power module chip mounting and ceramic substrate circuit interconnection. However, low-temperature sintered silver paste faces a serious challenge of electrochemical migration in practical applications; specifically, under humid and hot environments or applied bias conditions, silver undergoes anodizing (Ag→Ag) reaction. + + e - Under this premise, silver ions generated by anodic oxidation migrate to the cathode through the water film or electrolyte under the action of an electric field, and are reduced and deposited on the cathode to form silver dendrites. At the same time, the growth of these dendrites may eventually lead to short circuits between electrodes, decreased insulation performance, and even thermal failure. Furthermore, related studies have shown that this failure process is significantly accelerated under humid and hot environments (e.g., 85°C / 85%RH) or bias test conditions.

[0036] It should be noted that the main factors affecting the electrochemical migration performance of silver paste include: on the one hand, the pores and microcracks in the sintered layer provide channels for moisture and ion migration; on the other hand, incomplete sintering or residual organic matter forms ion-rich areas; and the lack of an effective passivation layer on the silver surface leads to Ag... + Ag is easily dissolved and migrates. Therefore, to improve its anti-migration performance, existing technologies mainly employ the following methods: The first method is noble metal doping (such as Pd, Pt, etc.); that is, suppressing Ag by forming an inert layer on the silver surface. + The first method involves dissolution, but this is costly and may cause interfacial embrittlement. The second method is alloying with low-melting-point metals (such as In, Bi, Sn), i.e., surface modification through the formation of intermetallic compounds, but this reduces conductivity and may increase sintering temperature. The third method is organic coating and interfacial modification; i.e., amines or carboxylic acids can be used to form a protective layer on the surface of silver particles, but these organic layers are prone to decomposition under high temperatures or electric fields. The fourth method is structural control strategies; i.e., bimodal silver powder or core-shell structures can be used to increase density, but it is still difficult to completely block Ag. + Migration channel.

[0037] Based on this, the exemplary embodiments of this disclosure first provide a low-temperature sintered silver paste resistant to electrochemical migration. This solution can solve the problem that low-temperature sintered silver paste is prone to electrochemical migration and dendrite growth under humid and hot bias conditions, leading to short circuits / insulation degradation. At the same time, the low-temperature sintered silver paste provided by this disclosure achieves the goal of synergistically improving the anti-electrochemical migration ability of the silver paste through hydrophobic SiO2 physical barrier + CeO2 modified silver powder interface regulation. The silver paste provided by this disclosure can significantly improve the reliability of the basic life service under temperature and humidity bias (THB) while maintaining the electrical and thermal conductivity. Furthermore, the low-temperature sintering silver paste with anti-electrochemical migration described in the exemplary embodiments of this disclosure may include the following components: 60-90 parts by weight of compounded silver powder, 10-30 parts by weight of organic carrier, 0.1-3 parts by weight of functional additives, and 0.05-0.3 parts by weight of hydrophobic SiO2 nanoparticles; wherein the compounded silver powder includes modified silver powder and composite silver powder; the modified silver powder is obtained by adding surface loading to the composite silver powder; in the modified silver powder, the surface loading is 0.2-0.8 parts by weight relative to the modified silver powder; in the compounded silver powder, the modified silver powder is 20-100 parts by weight relative to the compounded silver powder. In other words, at least a portion of the compounded silver powder needs to be Ag@CeO2, a silver powder coated with CeO2 on a surface (i.e., modified silver powder), where the CeO2 content is 0.2–0.8 parts by weight based on the weight of the silver powder, and the Ag@CeO2 coated silver powder accounts for 20–100 parts by weight of the compounded silver powder. It should be further noted that this composite system of silver powder can simultaneously achieve low-temperature densification, conductive network construction, and printing rheology. Micron-sized flake silver powder, with its high aspect ratio, more easily builds a continuous main conductive framework and reduces particle contact resistance; submicron-sized spherical silver powder effectively fills the gaps created by the stacking of flake particles, increases packing density, and improves the flow and printing of the paste at high solids content; nano-sized spherical silver powder, due to its high surface energy, more easily forms sintering necks and bridges large particles at lower temperatures, further reducing porosity and contact resistance, thereby achieving lower sheet resistance, higher adhesion, and better film reliability at lower sintering temperatures.

[0038] In one exemplary embodiment, the surface loading described above is rare earth oxide nanoparticles, wherein the rare earth oxide nanoparticles are CeO2; the D50 particle size of the hydrophobic SiO2 nanoparticles is 15~30 nm; and the D50 particle size of the rare earth oxide nanoparticles is 10~50 nm.

[0039] In an exemplary embodiment, the modified silver powder described above is prepared by the following method: Step S101, composite silver powder is added to anhydrous ethanol and stirred and washed 1-2 times. After solid-liquid separation, it is vacuum dried at 60-80°C to obtain pretreated silver powder; Step S102, a nonionic dispersant is added to anhydrous ethanol, and the pretreated silver powder is dispersed in the ethanol with the added nonionic dispersant to form a silver powder dispersion slurry; Step S103, a cerium salt solution is added to the silver powder dispersion slurry, and ammonia is added to the silver powder dispersion slurry with the added cerium salt solution to adjust the pH to 8.5-9.0 and maintain the reaction for 30-90 minutes. Step S104 involves solid-liquid separation of the silver powder deposit, followed by washing with anhydrous ethanol and drying the washed silver powder deposit to obtain a silver powder intermediate loaded with cerium oxygen-containing precursor on the silver powder surface. Step S105 involves heat-treating the silver powder intermediate at 180–220 °C for 10–120 min in an air atmosphere to convert the cerium oxygen-containing precursor in the silver powder intermediate into CeO2 and obtain the modified silver powder.

[0040] In one example embodiment, during the preparation of modified silver powder, composite silver powder is added to anhydrous ethanol and stirred and washed 1-2 times. After solid-liquid separation, it is vacuum dried at 60-80°C. The pretreated silver powder is dispersed in ethanol to form a silver powder dispersion slurry with a silver powder mass fraction of 10-30 parts by weight. 0-0.2 parts by weight (relative to the silver powder) of nonionic dispersant can be added. A cerium salt solution (cerium salt is cerium nitrate Ce(NO3)3·6H2O, solvent is ethanol / water = 95 / 5 (volume ratio)) is prepared and added dropwise to the silver powder dispersion slurry under stirring conditions for 20-30 minutes. Subsequently, diluted ammonia water is used to adjust the pH to 8.5-9.0 and the reaction is maintained for 30-90 minutes. The process involves depositing cerium-oxygen precursors heterogeneously on the surface of silver powder to obtain a silver powder deposit containing cerium-oxygen precursors. After solid-liquid separation, the silver powder is washed 2-3 times with ethanol and then washed once with ethanol:water at a ratio of 99:1 to reduce residual nitrate. The silver powder is dried to obtain an intermediate with cerium-oxygen precursors loaded on its surface. The silver powder is then heat-treated at 180-220℃ for 10-120 min in air to convert the cerium-oxygen precursors into CeO2 and obtain Ag@CeO2 coated silver powder.

[0041] In one exemplary embodiment, the organic carrier described above includes an organic solvent and a modified resin; wherein the organic solvent includes mixed diesters (DBE), diethylene glycol butyl ether (DGBE), diethylene glycol butyl ether acetate (DGBEA), dibutyl diacid (DBA), isoflurane, etc.; and the modified resin includes polyurethane-modified epoxy resin, polyurethane resin, acrylic resin, and epoxy-modified acrylic resin, etc.

[0042] In one exemplary embodiment, the composite silver powder described above comprises a mixture of nano-silver powder, submicron silver powder, and micron silver powder; in the composite silver powder, the nano-silver powder accounts for 10 to 15 parts by weight of the composite silver powder, the submicron silver powder accounts for 40 to 50 parts by weight of the composite silver powder, and the micron silver powder accounts for 35 to 50 parts by weight of the composite silver powder; in the composite silver powder, the nano-silver powder is spherical nanoparticles, the submicron silver powder is spherical submicron powder, and the micron silver powder is flake-shaped micron powder.

[0043] In one exemplary embodiment, the D50 particle size range of the described nano-silver powder is 30~60 nm; the D50 particle size range of the submicron silver powder is 300~500 nm; and the D50 particle size range of the micron silver powder is 1~3 μm.

[0044] In one exemplary embodiment of this disclosure, the functional additives described above include silane coupling agents, antioxidants, dispersants, leveling agents, thixotropic agents, and defoamers, etc.; wherein, the silane coupling agent is KH550 type silane coupling agent or KH560 silane coupling agent; the antioxidant is one or more of 2,6-di-tert-butyl-p-cresol (BHT) and pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (1010); the dispersant is BYK110; the leveling agent is one or more of BK-333, diacetone alcohol, Solvesso 150, and fluorocarbon compounds; the thixotropic agent is BYK410; and the defoamer is polyether-modified organosilicon BYK-024 or TEGO 931.

[0045] This disclosure also provides an example embodiment of a method for preparing a low-temperature sintering silver paste resistant to electrochemical migration, which can be used to prepare the aforementioned low-temperature silver paste, comprising the following steps: Step S201, preparation of an organic carrier containing hydrophobic SiO2 nanoparticles: adding an organic solvent to a dry and sealed stirring tank, turning on the stirring and slowly adding a modified resin until the modified resin is completely dissolved, forming a transparent and homogeneous resin solution; adding functional additives and hydrophobic SiO2 nanoparticles to the resin solution and performing high-shear dispersion for 5-15 minutes. In step S202, the organic carrier containing hydrophobic SiO2 nanoparticles was prepared. In step S203, the composite silver powder was prepared by mixing nano-silver powder, submicron silver powder, and micron silver powder in a mass ratio of 2:3:5 using a high-speed mixer until the mixture was free of visible lumps and had a uniform color. A surface loading agent was added to the composite silver powder to obtain the composite silver powder. In step S204, the silver paste was prepared by mixing the organic carrier with the composite silver powder. During the mixing process, the composite silver powder was added in three batches, stirring for 10 minutes after each addition. The next batch was added only after the composite silver powder was completely wetted and mixed thoroughly. Then, a scraper fineness meter was used to check the fineness. When the fineness was ≤10... Stirring is stopped when the particle size reaches μm to obtain the low-temperature sintered silver paste resistant to electrochemical migration; Step S204, three-roll milling: the silver paste is added uniformly above the rear roller, so that the silver paste flows along the roller surface and passes through the gap between the rollers, and the paste scraped off by the front roller is collected; the roller gap is gradually reduced, and the fineness is checked after each rolling pass, and stopped when the fineness is ≤5 μm to obtain the three-roll milling paste; Step S205, coating and sintering: the three-roll milling paste is coated on the target substrate using a screen printing process; then, the coated substrate is placed in a hot press sintering furnace to obtain the packaged substrate.

[0046] In one example embodiment, the preparation process of the organic carrier containing hydrophobic SiO2 nanoparticles is as follows: a solvent is added to a dry and sealed stirring tank, stirring is started and the resin is slowly added until the resin is completely dissolved to form a transparent and homogeneous resin solution; then, functional additives such as dispersant, leveling agent, defoamer, antioxidant, and silane coupling agent are added in sequence; hydrophobic SiO2 nanoparticles are added and high-shear dispersion is performed for 5-15 min to obtain the organic carrier containing hydrophobic SiO2, which is then sealed for later use.

[0047] In one example embodiment, the silver paste preparation process is as follows: the organic carrier and the compounded silver powder are mixed and stirred, the silver powder is added in 3 batches, and the mixture is stirred until it is completely wetted after each addition, wherein the compounded silver powder includes Ag@CeO2 coated silver powder (i.e. modified silver powder); the mixture of organic carrier and silver powder is mixed and stirred, and the fineness is detected by a scraper fineness meter. When the fineness is ≤10 μm, the stirring is stopped to obtain the preliminary silver paste.

[0048] In one example embodiment, the three-roll milling process is as follows: silver paste is added at a uniform speed and the roller gap is gradually reduced. The fineness is checked after each rolling pass and stopped when the fineness is ≤5 μm. The silver paste after the three rolls is vacuum degassed for 2~5 min to obtain the final silver paste.

[0049] In one example embodiment, the coating and sintering process is as follows: the silver paste is coated onto the target substrate using a screen printing process, and the coating thickness is controlled to be 10-50 μm; the coated substrate is placed in a hot press sintering furnace at a temperature of 200°C, a pressure of 5 MPa, and a holding time of 20 min.

[0050] Thus, the low-temperature sintered silver paste and its preparation method for resisting electrochemical migration described in the exemplary embodiments of this disclosure have been fully realized. Based on the foregoing description, it can be understood that the low-temperature sintered silver paste and its preparation method for resisting electrochemical migration described in the exemplary embodiments of this disclosure construct a dual synergistic protection mechanism of "physical barrier-interface regulation," the mechanism of which can be found by referring to... Figure 1-4 As shown. Among them, Figure 1 This is a mechanism diagram without the addition of a barrier / interface control phase. Ag loses electrons at the anode to generate Ag under humid and hot bias conditions. + Ag + The silver migrates along the water film (arrow direction) toward the cathode, where it gains electrons and is reduced to Ag, gradually forming silver dendrites. The silver paste becomes ineffective due to electrochemical migration. Figure 2 This is a mechanism diagram showing the addition of only hydrophobic SiO2. During the silver paste sintering process, the hydrophobic SiO2 nanoparticles form a dispersed barrier phase inside the silver layer, which can reduce pore connectivity and water film continuity. This not only improves the density of the sintered layer and reduces hygroscopicity, but more importantly, it significantly increases the tortuosity of the ion / moisture diffusion path, physically hindering Ag. + Vertical migration reduces the formation of silver dendrites; among which, Figure 2 (a) in the diagram represents the mechanism without the addition of a barrier / interface control phase. Figure 2 (b) in the diagram represents the mechanism of adding only hydrophobic SiO2. Figure 3 This is a mechanism diagram of CeO2-modified silver powder. CeO2 adheres to the surface or near-surface region of the silver powder in a finely dispersed state. It is more likely to participate in interface / microstructure regulation at grain boundaries, pore walls, and defect regions of the sintered layer, thereby reducing the anodic dissolution of silver and the tendency of silver ion generation / migration, and slowing down dendrite growth. Figure 3 (a) in the diagram represents the mechanism without the addition of a barrier / interface control phase. Figure 3 (b) in the diagram represents the mechanism diagram of silver powder modified by adding only CeO2. Figure 4This diagram illustrates the synergistic effect of hydrophobic SiO2 and CeO2-modified silver powder. Hydrophobic SiO2 reduces water ingress and ion channel formation, while CeO2-modified silver powder lowers the effective source term and migration driving force of silver ions. Together, they achieve highly efficient suppression of electrochemical migration through two mechanisms: "channel control" and "source term reduction." Simultaneously, the three-peak composite silver powder enhances densification and the continuity of the conductive network, achieving a balance between electrical / thermal conductivity and anti-migration reliability. Figure 4 (a) in the diagram represents the mechanism without the addition of a barrier / interface control phase. Figure 4 (b) in the diagram represents the mechanism of the synergistic effect of the simultaneous addition of hydrophobic SiO2 and CeO2 modified silver powder.

[0051] The following will provide a detailed explanation and description of the low-temperature sintering silver paste with anti-electrochemical migration and its preparation method as described in the exemplary embodiments of this disclosure, with reference to specific examples.

[0052] Example 1

[0053] A low-temperature sintering silver paste resistant to electrochemical migration is provided, comprising the following components and weight percentages: 80 parts by weight of compounded silver powder, 17 parts by weight of organic carrier, 3 parts by weight of functional additives, and 0.2 parts by weight of total nanophase. The compounded silver powder employs a three-peak compounding system, with Ag@CeO2-coated silver powder (i.e., modified silver powder) comprising 50 parts by weight, and the CeO2 loading in the Ag@CeO2 is 0.25 parts by weight based on the mass of the coated silver powder. The content of hydrophobic SiO2 nanoparticles is 0.10 parts by weight. In this embodiment, the total nanophase consists of hydrophobic SiO2 and the effective CeO2 content converted to the silver paste, totaling 0.2 parts by weight.

[0054] Example 2

[0055] A low-temperature sintering silver paste resistant to electrochemical migration is provided, comprising the following components and weight percentages: 80 parts by weight of compounded silver powder, 17 parts by weight of organic carrier, 3 parts by weight of functional additives, and 1.0 part by weight of total nanophase. Of the compounded silver powder, Ag@CeO2-coated silver powder accounts for 50 parts by weight, and the CeO2 loading in Ag@CeO2 is 0.5 parts by weight based on the mass of the coated silver powder. The content of hydrophobic SiO2 nanoparticles is 0.80 parts by weight. In this embodiment, the total nanophase consists of hydrophobic SiO2 and the effective CeO2 content converted to the silver paste, totaling 1.0 parts by weight.

[0056] Example 3

[0057] A low-temperature sintering silver paste resistant to electrochemical migration has the following composition: 80 parts by weight of compounded silver powder, 17 parts by weight of organic carrier, 3 parts by weight of functional additives, and 2.0 parts by weight of total nanophase. In the compounded silver powder, Ag@CeO2-coated silver powder (i.e., modified silver powder) accounts for 50 parts by weight, and the CeO2 loading in Ag@CeO2 is 0.5 parts by weight; the hydrophobic SiO2 content is 1.8 parts by weight.

[0058] Example 4

[0059] A low-temperature sintered silver paste resistant to electrochemical migration has the following composition: 80 parts by weight of compounded silver powder, 17 parts by weight of organic carrier, 3 parts by weight of functional additives, and 1.0 parts by weight of total nanophase. The compounded silver powder contains 100 parts by weight of Ag@CeO2-coated silver powder, with a CeO2 loading of 0.5 parts by weight in the Ag@CeO2; the hydrophobic SiO2 content is 0.6 parts by weight.

[0060] Example 5

[0061] A low-temperature sintered silver paste resistant to electrochemical migration has the following composition: 80 parts by weight of compounded silver powder, 17 parts by weight of organic carrier, 3 parts by weight of functional additives, and 1.0 parts by weight of total nanophase. The compounded silver powder contains 20 parts by weight of Ag@CeO2-coated silver powder, with a CeO2 loading of 0.5 parts by weight in the Ag@CeO2; the hydrophobic SiO2 content is 0.92 parts by weight.

[0062] Comparative Example 1 (Control Group: No SiO2, No CeO2)

[0063] A silver paste, comprising the following components and weight percentages: 80 parts by weight of compounded silver powder, 17 parts by weight of organic carrier, and 3 parts by weight of functional additives. The resin is a polyurethane-modified epoxy resin with a molecular weight >100,000 g / mol and a viscosity of 17,500 cP; the solvent is DBE and isoflurane in a weight ratio of 7:3; the silane coupling agent is KH550, with a content of 1 part by weight; the antioxidant is 1010, with a content of 0.3 parts by weight; the dispersant is BYK110, with a content of 0.2 parts by weight; the leveling agent is BK-333, with a content of 0.2 parts by weight; the thixotropic agent is BYK410, with a content of 1 part by weight; and the defoamer is TEGO 931, with a content of 0.3 parts by weight.

[0064] A method for preparing silver paste may be adopted by the following steps: (1) Preparation of organic carrier: The solvent (DBE 0.97 g, isoflurone 0.42 g) is added to a dry and sealed stirring tank, stirring is started (500 rpm) and the resin (polyurethane modified epoxy resin 1.16 g) is slowly added, stirring for 40 min, controlling the temperature inside the tank to ≤40 ℃, until the resin is completely dissolved and a transparent and uniform resin solution is formed; then dispersant BYK110 (0.03 g), leveling agent BK-333 (0.03 g), defoamer TEGO 931 (0.045 g), antioxidant 1010 (0.045 g) are added in sequence; finally, silane coupling agent KH550 (0.15 g) is added, mixed evenly, and the organic carrier is obtained and sealed for later use. (2) Preparation of silver powder mixture (i.e., composite silver powder): The nano silver powder (1.50 g), submicron silver powder (5.40 g), and micron silver powder (5.10 g) are put into a high-speed mixer for premixing. The mixer is stopped every 5 minutes for observation. The mixture is transferred to a sealed container for later use until there are no visible lumps and the color is uniform. (3) Preparation of silver paste: The organic carrier and the silver powder mixture are mixed and stirred. The silver powder mixture is added in 3 batches. After each addition, the mixture is stirred for 10 minutes. The next batch is added and mixed evenly after the silver powder is completely wetted. The fineness is measured by a scraper fineness meter. When the fineness is ≤10 μm, stirring is stopped to obtain silver paste. (4) Three-roll milling: The silver paste is added at a uniform speed above the rear roller, so that the paste flows along the roller surface and passes through the gap between the rollers. The paste scraped off by the front roller is collected. The roller gap is gradually reduced. The fineness is measured after each rolling pass. The process is stopped when the fineness is ≤5 μm. (5) Coating and sintering: The silver paste is coated onto the target substrate using screen printing process, and the coating thickness is controlled to be 10-50 μm; the coated substrate is placed in a hot press sintering furnace at a temperature of 200 ℃, a pressure of 5 MPa, and a holding time of 20 min.

[0065] Comparative Example 2 (Hydrophobic SiO2 only: 0.2 parts by weight)

[0066] A silver paste, comprising the following components and weight percentages: 80 parts by weight of compounded silver powder, 17 parts by weight of organic carrier, 3 parts by weight of functional additives, and 0.2 parts by weight of hydrophobic SiO2 nanoparticles. The resin is a polyurethane-modified epoxy resin with a molecular weight >100,000 g / mol and a viscosity of 17,500 cP; the solvent is DBE and isoflurane in a weight ratio of 7:3; the silane coupling agent is KH550, with a content of 1 part by weight; the antioxidant is 1010, with a content of 0.3 parts by weight; the dispersant is BYK110, with a content of 0.2 parts by weight; the leveling agent is BK-333, with a content of 0.2 parts by weight; the thixotropic agent is BYK410, with a content of 1 part by weight; the defoamer is TEGO 931, with a content of 0.3 parts by weight; and the hydrophobic SiO2 nanoparticles are 0.2 parts by weight.

[0067] The preparation method of silver paste adopts the following steps: (1) Preparation of organic carrier: The solvent (DBE 0.97 g, isoflurone 0.42 g) is added to a dry and sealed stirring tank, stirring is started (500 rpm) and the resin (polyurethane modified epoxy resin 1.16 g) is slowly added, stirring for 40 min, controlling the temperature inside the tank ≤40 ℃, until the resin is completely dissolved and a transparent and uniform resin solution is formed; then dispersant BYK110 (0.03 g), leveling agent BK-333 (0.03 g), defoamer TEGO931 (0.045 g), antioxidant 1010 (0.045 g) are added in sequence; then silane coupling agent KH550 (0.15 g) is added, and finally hydrophobic SiO2 nanoparticles (0.03 g) are added and high shear dispersion is carried out for 5-15 min to obtain an organic carrier containing hydrophobic SiO2, which is sealed for later use. (2) Preparation of silver powder mixture (i.e., composite silver powder): The nano silver powder (1.50 g), submicron silver powder (5.40 g), and micron silver powder (5.10 g) are put into a high-speed mixer for premixing. The mixer is stopped every 5 minutes to observe the mixture until there are no visible lumps and the color is uniform. The mixture is then transferred to a sealed container for later use. (3) Preparation of silver paste: The organic carrier is mixed and stirred with the silver powder mixture. The silver powder mixture is added in 3 batches. After each addition, the mixture is stirred for 10 minutes. The next batch is added and mixed evenly after the silver powder is completely wetted. The fineness is measured with a scraper fineness meter. When the fineness is ≤10 μm, stirring is stopped to obtain silver paste. (4) Three-roll milling: The silver paste is added at a uniform speed above the rear roller, so that the paste flows along the roller surface and passes through the gap between the rollers. The paste scraped off by the front roller is collected. The roller gap is gradually reduced. The fineness is measured after each rolling pass. The process is stopped when the fineness is ≤5 μm. (5) Coating and sintering: The silver paste is coated onto the target substrate using screen printing process, and the coating thickness is controlled to be 10-50 μm; the coated substrate is placed in a hot press sintering furnace at a temperature of 200 ℃, a pressure of 5 MPa, and a holding time of 20 min.

[0068] Comparative Example 3 (Physical mixing of CeO2 only: 0.2 parts by weight)

[0069] A silver paste, comprising the following components and weight percentages: 80 parts by weight of compounded silver powder, 17 parts by weight of organic carrier, 3 parts by weight of functional additives, and 0.2 parts by weight of CeO2 nanoparticles. The resin is a polyurethane-modified epoxy resin with a molecular weight >100,000 g / mol and a viscosity of 17,500 cP; the solvent is DBE and isoflurane in a weight ratio of 7:3; the silane coupling agent is KH550, with a content of 1 part by weight; the antioxidant is 1010, with a content of 0.3 parts by weight; the dispersant is BYK110, with a content of 0.2 parts by weight; the leveling agent is BK-333, with a content of 0.2 parts by weight; the thixotropic agent is BYK410, with a content of 1 part by weight; the defoamer is TEGO 931, with a content of 0.3 parts by weight; and the CeO2 nanoparticles content is 0.2 parts by weight.

[0070] A method for preparing silver paste includes the following steps: (1) Preparation of organic carrier: The solvent (DBE 0.97 g, isoflurone 0.42 g) is added to a dry and sealed stirring tank, stirring is started (500 rpm) and the resin (polyurethane modified epoxy resin 1.16 g) is slowly added, stirring for 40 min, controlling the temperature inside the tank to ≤40 ℃, until the resin is completely dissolved and a transparent and uniform resin solution is formed; then the dispersant BYK110 (0.03 g), leveling agent BK-333 (0.03 g), and defoamer TEGO 931 (0.045 g) are added in sequence and mixed evenly to obtain the organic carrier, which is then sealed for later use. (2) Preparation of silver powder mixture (i.e., composite silver powder): The nano silver powder (2.40 g), submicron silver powder (3.60 g), and micron silver powder (6.0 g) are added to a high-speed mixer in a mass ratio of 2:3:5 for premixing. The mixer is stopped every 5 minutes for observation until the silver powder mixture is free of visible lumps and has a uniform color. The mixture is then transferred to a sealed container for later use. (3) Preparation of silver paste: The organic carrier is mixed and stirred with the silver powder mixture. The silver powder mixture is added in 3 batches, and stirred for 10 minutes after each addition. The next batch is added and mixed evenly after the silver powder is completely wetted. Then CeO2 (0.03 g) is added and mixed evenly. The fineness is measured with a scraper fineness meter. When the fineness is ≤10 μm, stirring is stopped to obtain silver paste. (4) Three-roll milling: The silver paste is added at a uniform speed above the rear roller, so that the paste flows along the roller surface and passes through the gap between the rollers. The paste scraped off by the front roller is collected. The roller gap is gradually reduced. The fineness is measured after each rolling pass. The process is stopped when the fineness is ≤5 μm. (5) Coating and sintering: The silver paste is coated onto the target substrate using screen printing process, and the coating thickness is controlled to be 10-50 μm; the coated substrate is placed in a hot press sintering furnace at a temperature of 200 ℃, a pressure of 5 MPa, and a holding time of 20 min.

[0071] Comparative Example 4 (physically mixed hydrophobic SiO2 + CeO2, total nanophase 1.0 parts by weight)

[0072] A silver paste, comprising the following components and weight percentages: 80 parts by weight of compounded silver powder, 17 parts by weight of organic carrier, 3 parts by weight of functional additives, and 1.0 part by weight of nano-additives. The nano-additives consist of hydrophobic SiO2 nanoparticles and CeO2 nanoparticles in a 1:1 mass ratio, with a total addition of 1.0 part by weight (i.e., 0.5 parts by weight of hydrophobic SiO2 and 0.5 parts by weight of CeO2). The resin is a polyurethane-modified epoxy resin with a molecular weight >100,000 g / mol and a viscosity of 17,500 cP; the solvent is DBE and isoflurane in a weight ratio of 7:3; the silane coupling agent is KH550, with a content of 1 part by weight; the antioxidant is 1010, with a content of 0.3 parts by weight; the dispersant is BYK110, with a content of 0.2 parts by weight; the leveling agent is BK-333, with a content of 0.2 parts by weight; the thixotropic agent is BYK410, with a content of 1 part by weight; the defoamer is TEGO 931, with a content of 0.3 parts by weight; and the total content of hydrophobic SiO2 nanoparticles and CeO2 nanoparticles is 1.0 part by weight.

[0073] A method for preparing silver paste, comprising the following steps: (1) Preparation of organic carrier: The solvent (DBE 0.97g, isoflurane 0.42g) is added to a dry and sealed stirring tank, the stirring is turned on (500 rpm) and the resin (polyurethane modified epoxy resin 1.16g) is slowly added, the stirring is carried out for 40 min, the temperature inside the tank is controlled to be ≤40 ℃, until the resin is completely dissolved and a transparent and uniform resin solution is formed; then the dispersant BYK110 (0.03g), the leveling agent BK-333 (0.03g), the defoamer TEGO 931 (0.045g), and the antioxidant 1010 (0.045g) are added in sequence; then the silane coupling agent KH550 (0.15g) is added, and finally the hydrophobic SiO2 nanoparticles (0.075g) are added and high shear dispersion is carried out for 5-15 min to obtain an organic carrier containing hydrophobic SiO2, which is then sealed for later use. (2) Preparation of silver powder mixture: Nano silver powder (2.40g), submicron silver powder (3.60g), and micron silver powder (6.0g) are added to a high-speed mixer in a mass ratio of 2:3:5 for premixing. The mixer is stopped every 5 minutes for observation. The mixture is transferred to a sealed container for later use until there are no visible lumps and the color is uniform. (3) Preparation of silver paste: The organic carrier is mixed with the silver powder mixture. The silver powder mixture is added in 3 batches. After each addition, the mixture is stirred for 10 minutes. The next batch is added and mixed evenly after the silver powder is completely wetted. Then CeO2 (0.075g) is added and mixed evenly. The fineness is measured with a scraper fineness meter. When the fineness is ≤10 μm, stirring is stopped to obtain silver paste. (4) Three-roll milling: The silver paste is added at a uniform speed above the rear roller, so that the paste flows along the roller surface and passes through the gap between the rollers. The paste scraped off by the front roller is collected. The roller gap is gradually reduced. The fineness is measured after each rolling pass. The process is stopped when the fineness is ≤5 μm. (5) Coating and sintering: The silver paste is coated onto the target substrate using screen printing process, and the coating thickness is controlled to be 10-50 μm; the coated substrate is placed in a hot press sintering furnace at a temperature of 200 ℃, a pressure of 5 MPa, and a holding time of 20 min.

[0074] Furthermore, the performance of silver pastes corresponding to different total nanophase contents and introduction methods can be referenced in Table 1 below:

[0075] Table 1

[0076]

[0077] Comparative Example 4 and Example 1 of the present invention have the same total nanophase content (1.0 parts by weight) and the same sintering process (200℃, 5 MPa, 20 min), differing only in the introduction method and distribution state of CeO2: In Comparative Example 4, CeO2 is a physically mixed particle, which is prone to random distribution or local agglomeration during slurry preparation and sintering, and its effect on the interface / defect region is greatly affected by the dispersion state; while in the present invention, Ag@CeO2 modifies silver powder, making CeO2 more inclined to enter the conductive framework and interface region with silver particles, and synergizes with the low hygroscopicity and high tortuosity migration channel constructed by hydrophobic SiO2, thereby obtaining a longer lifetime and smaller contact resistance drift under humid heat bias conditions such as THB. This comparative example is used to highlight the significant technical difference between the "structured design" of the present invention and "simple co-doping".

[0078] from Figures 5-13 The SEM image of the low-temperature silver paste sintered film shows that... Figure 5 This is a SEM image of a low-temperature silver paste sintered film without added nano-additives; by Figure 5 It can be seen that it has high porosity, which will interrupt the conductive path between silver particles, resulting in high sheet resistance and poor conductivity. At the same time, the pores become the migration channels for water vapor and silver ions, which can easily accelerate electrochemical migration failure. In addition, the effective contact area between the film and the substrate is small, which can easily lead to stress concentration and insufficient adhesion. In a humid and hot environment, water vapor is more likely to penetrate, which will accelerate the oxidation of silver particles and the aging of the film. Figure 6 , Figure 7 as well as Figure 8 Silver paste sintered films with 0.2 parts by weight, 1 part by weight, and 2 parts by weight of nano-additives added, respectively; from Figure 6 , Figure 7 as well as Figure 8 As can be seen, with the introduction of nano-additives, the porosity is significantly reduced. The film is most smooth and dense when the addition amount is 1 w%. When the addition amount reaches 2 parts by weight, the dispersion is slightly uneven due to excessive additives, and the porosity increases slightly but is still lower than that without additives. Figure 7 (1 part by weight) Due to its optimal density and conductivity, the dense structure can physically block electron migration and greatly enhance its resistance to electrochemical migration; the film layer is more firmly bonded to the substrate, the adhesion is adapted to the needs of electronic packaging, and the resistance to damp heat stability is also significantly improved.

[0079] Furthermore, combining the data in Table 1 below with... Figures 5-13 The SEM images show that the total nanophase (effective content of hydrophobic SiO2 and CeO2) exhibits a "moderate amount optimizes, excessive amount slightly degrades" effect on the silver paste performance. Without the addition of nanophase (Comparative Example 1), the sintered layer has a porosity of 10.5%, a volume resistivity of 3.20 μΩ·cm, and a conductivity of 3.13 × 10⁻⁶. 7The S / m and shear strength were 10 MPa, the temperature and humidity bias (THB) lifetime was 90 h, and the contact resistance change rate was +15%. Adding only 0.2 parts by weight of hydrophobic SiO2 (Comparative Example 2) or only 0.2 parts by weight of physically mixed CeO2 powder (Comparative Example 3) could reduce porosity and improve THB lifetime to some extent, but the improvement was limited. When hydrophobic SiO2 and CeO2 were added simultaneously in a physically mixed manner, with a total amount of 1.0 parts by weight (Comparative Example 4), the porosity was further reduced to 5.4%, and the THB lifetime was increased to 480 h. In contrast, the example embodiment of this disclosure, using CeO2-modified silver powder (Ag@CeO2) combined with a hydrophobic SiO2 structuring scheme (Example 2, total nanophase 1.0 parts by weight), obtained a denser and more uniform sintered layer (porosity 4.6%), with a volume resistivity reduced to 1.90 μΩ·cm and a conductivity increased to 5.26 × 10⁻⁶. 7 The sample exhibited a shear strength of 15 MPa (S / m), a THB lifetime of 720 h, and a contact resistance change rate ≤3%. When the total nanophase content was further increased to 2.0 parts by weight (Example 3), the porosity rebounded to 6.8% due to dispersion difficulties and localized air traps. While the electrical properties and reliability slightly decreased, they remained superior to the unadded sample. These results indicate that hydrophobic SiO2 reduces pore connectivity and water film continuity, while CeO2-modified silver powder promotes interface / defect region regulation. A better balance between channel control and interface regulation is achieved around 1.0 parts by weight.

[0080] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention described herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not invented by this disclosure. The specification and embodiments are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the claims.

Claims

1. A low-temperature sintered silver paste resistant to electrochemical migration, characterized in that, include: 60-90 parts by weight of compound silver powder, 10-30 parts by weight of organic carrier, 0.1-3 parts by weight of functional additives and 0.05-0.3 parts by weight of SiO2 nanoparticles; The compounded silver powder includes modified silver powder and composite silver powder; the composite silver powder is composed of nano silver powder, submicron silver powder and micron silver powder; in the composite silver powder, the nano silver powder accounts for 10 to 15 parts by weight of the composite silver powder, the submicron silver powder accounts for 40 to 50 parts by weight of the composite silver powder, and the micron silver powder accounts for 35 to 50 parts by weight of the composite silver powder. The modified silver powder is obtained by adding a surface load to the composite silver powder; the surface load is rare earth oxide nanoparticles, the rare earth oxide nanoparticles are CeO2, and the SiO2 nanoparticles are hydrophobic SiO2. In the modified silver powder, the surface load is 0.2-0.8 parts by weight relative to the mass of the modified silver powder; In the compound silver powder, the modified silver powder accounts for 20-100 parts by weight relative to the compound silver powder.

2. The low-temperature sintered silver paste with anti-electrochemical migration according to claim 1, characterized in that, The D50 particle size of the hydrophobic SiO2 nanoparticles is 15~30nm; The rare earth oxide nanoparticles have a D50 particle size of 10~50 nm.

3. The low-temperature sintered silver paste with anti-electrochemical migration according to claim 2, characterized in that, The modified silver powder is prepared by the following method: Step S101: Add composite silver powder to anhydrous ethanol and stir and wash 1 to 2 times. After solid-liquid separation, dry under vacuum at 60 to 80°C to obtain pretreated silver powder. Step S102: Add a nonionic dispersant to anhydrous ethanol and disperse the pretreated silver powder in the ethanol with added nonionic dispersant to form a silver powder dispersion slurry. Step S103: Add cerium salt solution to the silver powder dispersion slurry, and add ammonia water to the silver powder dispersion slurry with added cerium salt solution to adjust the pH to 8.5-9.0 and maintain the reaction for 30-90 min, so that the cerium oxygen-containing precursor is heterogeneously deposited on the surface of the silver powder to obtain a silver powder deposit containing the cerium oxygen-containing precursor. Step S104: The silver powder deposit is subjected to solid-liquid separation, and anhydrous ethanol is added to the silver powder deposit after solid-liquid separation for washing. The washed silver powder deposit is then dried to obtain a silver powder intermediate with cerium oxygen-containing precursor loaded on the surface of the silver powder. Step S105: The silver powder intermediate is heat-treated at 180-220°C for 10-120 min in an air atmosphere to convert the cerium-containing oxygen precursor in the silver powder intermediate into CeO2 and obtain the modified silver powder.

4. The low-temperature sintered silver paste with anti-electrochemical migration according to claim 1, characterized in that, The organic carrier includes an organic solvent and a modified resin; The organic solvent includes one or more of the following: mixed diesters, diethylene glycol butyl ether, diethylene glycol butyl ether acetate, dibutyl diacid, and isoflurane; The modified resin includes one or more of polyurethane-modified epoxy resin, polyurethane resin, acrylic resin, and epoxy-modified acrylic resin.

5. The low-temperature sintering silver paste with anti-electrochemical migration according to claim 1, characterized in that, In the compound silver powder, the nano silver powder is spherical nano powder, the submicron silver powder is spherical submicron powder, and the micron silver powder is flake-shaped micron powder.

6. The low-temperature sintering silver paste with anti-electrochemical migration according to claim 5, characterized in that, The D50 particle size range of the silver nanoparticles is 30~60 nm; The D50 particle size range of the submicron silver powder is 300~500 nm; The D50 particle size range of the micron-sized silver powder is 1~3 μm.

7. The low-temperature sintering silver paste with anti-electrochemical migration according to claim 1, characterized in that, The functional additives include one or more of the following: silane coupling agents, antioxidants, dispersants, leveling agents, thixotropic agents, and defoamers; The silane coupling agent includes KH550 or KH560 silane coupling agent; the antioxidant includes 2,6-di-tert-butyl-p-cresol and / or pentaerythritol ester; the dispersant includes BYK110; the leveling agent includes at least one of BK-333, diacetone alcohol, Solvesso 150, and fluorocarbon compounds; the thixotropic agent includes BYK410; and the defoamer includes polyether-modified silicone BYK-024 or TEGO 931.

8. A method for preparing a low-temperature sintered silver paste resistant to electrochemical migration according to claim 1, characterized in that, include: Step S201, Preparation of organic carrier containing hydrophobic SiO2 nanoparticles: Add organic solvent to a dry and sealed stirring tank, turn on the stirring and slowly add modified resin until the modified resin is completely dissolved to form a transparent and homogeneous resin solution; add functional additives and hydrophobic SiO2 nanoparticles to the resin solution and perform high shear dispersion for 5-15 min to obtain organic carrier containing hydrophobic SiO2 nanoparticles. Step S202, preparation of composite silver powder: nano silver powder, submicron silver powder and micron silver powder are added to a high-speed mixer at a mass ratio of 2:3:5 and premixed until the silver powder mixture is free of visible lumps and has a uniform color to obtain composite silver powder; surface loading is added to the composite silver powder to obtain composite silver powder. Step S203, preparation of silver paste: The organic carrier is mixed and stirred with the compound silver powder; during the mixing and stirring process, the compound silver powder is added in 3 batches, and stirred for 10 min after each addition. The next batch is added and mixed evenly after the compound silver powder is completely wetted; then, the fineness is detected by a scraper fineness meter, and stirring is stopped when the fineness is ≤10 μm, so as to obtain the low-temperature sintering silver paste with anti-electrochemical migration.

9. The method for preparing low-temperature sintered silver paste resistant to electrochemical migration according to claim 8, characterized in that, The method for preparing the low-temperature sintered silver paste resistant to electrochemical migration further includes: Step S204, Three-roll grinding: Add silver paste at a uniform speed above the rear roller, so that the silver paste flows along the roller surface and passes through the gap between the rollers, and collect the paste scraped off by the front roller; gradually reduce the roller gap, check the fineness after each rolling pass, and stop when the fineness is ≤5 μm to obtain three-roll grinding paste; Step S205, Coating and Sintering: The three-roll grinding slurry is coated onto the target substrate using a screen printing process; then, the coated substrate is placed into a hot press sintering furnace to obtain the packaged substrate.

10. The method for preparing low-temperature sintered silver paste resistant to electrochemical migration according to claim 9, characterized in that, The thickness of the three-roll polishing slurry coated on the target substrate is 10-50 μm; The temperature in the hot-press sintering furnace is 200 ℃, the pressure is 5 MPa, and the holding time is 20 min.

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