Low-temperature pressureless sintering silver paste, preparation method and application thereof

Abstract

The application provides a low-temperature pressureless sintering type silver paste, a preparation method and application thereof, and comprises the following raw materials in percentage by mass: 87-94% of binder-coated silver particles, 4-11% of an organic solvent system, and 1-2% of resin; the binder is one or more of long-alkyl-chain organic substances or aromatic compounds. The binder is used to coat the silver particles to form a steric hindrance effect, which can improve the stability of the silver particles, make the silver paste have good fluidity and storage property, improve the activity of the silver particles, thereby reduce the sintering temperature, meet the need of low-temperature sintering, and avoid hidden dangers caused by pressure on the device in the sintering process without applying additional pressure; in addition, the crosslinking agent of the organic solvent system can crosslink with the binder-coated silver particles, connect linear or branched polymer molecules into a three-dimensional network structure, and further improve the stability and activity of the silver particles.

Description

Technical Field

[0001] This invention relates to the field of third-generation semiconductor power device packaging, and in particular to a low-temperature pressureless sintering silver paste, its preparation method, and its application. Background Technology

[0002] In recent years, with the rapid development of the electronics industry, the service conditions of electronic devices have become increasingly demanding. In particular, third-generation semiconductor devices, represented by silicon carbide and gallium nitride, have broken through the bottlenecks of second-generation semiconductor devices, which were unable to withstand high temperatures and pressures and handle high power. However, they have also posed greater challenges to the heat dissipation performance of the packaging structure.

[0003] Nano-silver paste, as a novel green packaging interconnect material, can improve the densification of the connection interface through pressure-assisted sintering, resulting in high connection quality and reliability, and achieving stable sintering at temperatures below 300°C. However, brittle chips and substrates may undergo passivation cracking during pressure sintering, easily leading to power module failure. Pressure-assisted sintering poses challenges to packaging processes, automation, and product yield.

[0004] Currently, there has been a certain amount of research on pressureless sintering silver paste, and some researchers have begun to focus on pressureless large-area sintering. However, the increased organic content during large-area sintering, the limitation on solvent evaporation in the central region of the bonding layer during pressureless sintering, and how to achieve effective interconnection under low-temperature conditions are urgent problems to be solved.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a low-temperature pressureless sintering silver paste, its preparation method, and its application, which can solve the problems mentioned in the background art.

[0007] In a first aspect, the present invention provides a low-temperature pressureless sintering silver paste comprising the following raw materials by weight percentage: 87-94% silver particles coated with binder, 4%-11% organic solvent system, and 1%-2% resin; wherein the binder is one or more of a long alkyl chain organic compound or an aromatic compound.

[0008] In this invention, a binder is used to coat silver particles to form and utilize the steric hindrance effect. On the one hand, by adding this binder, a physical barrier is formed, affecting the arrangement of the silver particles. Due to the presence of the steric hindrance effect, the stability of the silver particles is improved. On the other hand, when steric hindrance is formed, neighboring silver particles deviate from the angle they should occupy due to the steric hindrance effect. As the binder evaporates, the original steric hindrance gradually disappears. Due to the deviation caused by the previous steric hindrance effect, after the steric hindrance disappears, the activity of the silver particles is improved due to the internal tension.

[0009] Preferably, the adhesive comprises one or more of the following: n-heptane, n-octane, p-xylene, styrene, cumene, and methylcellulose.

[0010] Preferably, the morphology of the silver particles includes one or more of the following: spherical, flake-shaped, or triangular.

[0011] Preferably, the silver particles have a particle size range of 50-1200 nm; more preferably, the silver particles have a particle size range of 100-1000 nm; further, the silver particles have a particle size of 200 nm, 300 nm, 400 nm, 500 nm, or 800 nm.

[0012] Preferably, the organic solvent system comprises, by mass percentage: 2%-4% molding agent, 1%-3% leveling agent, 1%-2% crosslinking agent, and 91%-96% solvent; for example: 2% molding agent, 1.5% leveling agent, 1% crosslinking agent, and 95.5% solvent; or, 3% molding agent, 2% leveling agent, 1% crosslinking agent, and 94% solvent.

[0013] Preferably, the molding agent includes one or more of polyamide, polyimide, polyamide wax, and polyacrylic acid.

[0014] Preferably, the leveling agent comprises one or more of the following: dimethylsiloxane, polymethylphenylsiloxane, organically modified polydimethylsiloxane, polyether-modified organosilicon, and modified polyacrylate.

[0015] Preferably, the crosslinking agent is a silane-based crosslinking agent; more preferably, the crosslinking agent includes one or more of the following: methyltrimethoxysilane, vinyltributylone oxime silane, vinyltriethoxysilane, γ-aminopropyltriethoxysilane, and γ-methacryloyloxypropyltrimethoxysilane.

[0016] Preferably, the solvent is an alcoholic organic compound; more preferably, the solvent includes one or more of benzyl alcohol, decanol, ethylene glycol, 1,2-propanediol, terpineol, n-butanol, tridecanol, and isotrimetrol.

[0017] In this invention, the molding agent is used to ensure the moldability of the paste after patching and to ensure high uniformity during large-area patching; the leveling agent can ensure that the paste flows out uniformly during dispensing; the crosslinking agent can crosslink with the silver particle coating, and through chemical reaction, connect linear or branched polymer molecules into a three-dimensional network structure, thereby improving the stability of the pressureless sintering silver paste; the solvent is used to adjust the viscosity of the paste.

[0018] Preferably, the resin includes one or more of bisphenol F epoxy resin, bisphenol A epoxy resin, phenolic epoxy resin, and cresol epoxy resin.

[0019] A second aspect of the present invention provides a method for preparing a low-temperature pressureless sintering type silver paste, comprising the following steps:

[0020] S1. Add silver particles to anhydrous ethanol, remove the supernatant by ultrasonic centrifugation, and disperse the silver particles.

[0021] S2. Mix the silver particles with the binder and remove the supernatant by ultrasonic centrifugation;

[0022] S3. Add anhydrous ethanol, sonicate to remove residue, centrifuge to remove supernatant, and obtain silver particles coated with binder.

[0023] S4. Mix the organic solvent system and the resin to obtain an organic system;

[0024] S5. Mix the silver particles coated with the binder obtained in step S3 with the organic system obtained in step S4 and degas to obtain the silver paste.

[0025] Preferably, the following steps are also included:

[0026] S6. Fill the syringe with the silver paste obtained in step S5 using a dispensing machine, ensuring that no air bubbles are generated in the syringe, seal the syringe, and store it at low temperature.

[0027] Preferably, the mass ratio of the silver particles coated with the adhesive, the organic solvent system, and the resin is (87-94):(4-11):(1-2).

[0028] In some specific embodiments, the preparation method of low-temperature pressureless sintering type silver paste includes the following steps:

[0029] S1. Add anhydrous ethanol to the silver particles, sonicate for 5-10 min, centrifuge at 2000-4000 r / min, remove the supernatant, and disperse the silver particles.

[0030] S2. Mix the silver particles with the ethanol solution of the binder, sonicate for 10-30 min, centrifuge at 3000-6000 r / min, and remove the supernatant;

[0031] S3. Add anhydrous ethanol, sonicate for 5-10 min to remove residue, centrifuge at 2000-4000 r / min to remove supernatant, and obtain silver particles coated with binder.

[0032] S4. Weigh the molding agent, leveling agent, crosslinking agent, solvent and resin according to the proportion and stir magnetically at 40-60℃ and 200-400r / min for 60-90min to ensure uniform mixing and obtain an organic system.

[0033] S5. Mix the silver particles coated with binder obtained in step S3 with the organic system obtained in step S4 in a certain proportion, and degas in a vacuum degassing machine for 30-50 minutes to obtain silver paste.

[0034] S6. Fill the silver paste obtained in step S5 into a 5-20cc syringe using a dispensing machine, ensuring that no air bubbles are generated in the syringe, seal the syringe, and store it at ≤-20℃.

[0035] A third aspect of the present invention provides an application of a low-temperature pressureless sintering silver paste in the packaging interconnect structure of power devices.

[0036] Preferably, it is used in the sintering connection process of chip and active metal welding ceramic substrate.

[0037] A fourth aspect of the present invention provides a packaged interconnect structure for a power device, comprising: a chip, an active metal-bonded ceramic substrate, and a connection layer for connecting the chip and the active metal-bonded ceramic substrate, wherein the connection layer is formed by sintering the aforementioned low-temperature pressureless sintering silver paste.

[0038] Preferably, the active metal-welded ceramic substrate includes one or more of the following: bare copper active metal-welded ceramic substrate, silver-plated active metal-welded ceramic substrate, and ENIG active metal-welded ceramic substrate.

[0039] Preferably, the chip is a SiC / GaN chip, more preferably a silver-plated SiC / GaN chip or a gold-plated SiC / GaN chip.

[0040] A fifth aspect of the present invention provides a method for fabricating a packaged interconnect structure for a power device, comprising the following steps:

[0041] P1. Remove contaminants from the surface of active metal-welded ceramic substrates;

[0042] P2. The above-mentioned low-temperature pressureless sintered silver paste is warmed at room temperature to restore its original fluidity.

[0043] P3. Apply silver paste by dispensing or printing onto the surface of an active metal-welded ceramic substrate.

[0044] P4. Use a pick-and-place machine to remove air from the chip and place it at the dispensing or printing position, ensuring that the chip is evenly pressed into the silver paste.

[0045] P5. Place the active metal welding ceramic substrate, silver paste and chip on the heating stage, and continuously introduce argon / nitrogen / atmosphere into the sintering chamber.

[0046] P6. The power device is dried using a gradient drying process and kept warm to obtain the packaged interconnect structure.

[0047] In some specific embodiments, the fabrication method of the package interconnect structure of the power device includes the following steps:

[0048] P1. Wipe the surface of the active metal-welded ceramic substrate with a lint-free cloth to remove surface dirt;

[0049] P2. Take out the above-mentioned low-temperature pressureless sintering silver paste needle and warm it at room temperature for 60-120 minutes to restore the original fluidity of the silver paste.

[0050] P3. Use a dispensing machine to apply or print pressureless sintering silver paste onto the surface of the active metal-bonded ceramic substrate under an air pressure of 0.2-0.4MPa; the dispensing width is 0.1-0.3mm, and the dispensing pattern is related to the chip size, preferably a cross or star pattern; or, use a printing machine to print pressureless sintering silver paste onto the surface of the active metal-bonded ceramic substrate, with a printing thickness of 60-90μm;

[0051] Preferably, the chip area is ≤25mm². 2 The preferred dispensing shape is a cross (e.g.) Figure 6 Chip area ≥ 25mm² 2 The preferred dispensing shape is a star pattern (e.g., a cross shape). Figure 5 (as shown); preferably, the chip area is ≥49mm². 2 It can be printed, with a recommended printing thickness of 60-90μm;

[0052] P4. Use a pick-and-place machine to suction air from the SiC / GaN chip and place it at the dispensing or printing position. The placement pressure is 0.1-0.3MPa to ensure that the entire chip is evenly pressed into the silver paste, and the amount of adhesive overflow around it is 20%-40% of the chip height.

[0053] P5. Place the entire active metal welded ceramic substrate, silver paste and SiC / GaN chip on the heating stage, and continuously introduce nitrogen / argon / atmosphere into the sintering chamber; preferably, nitrogen / argon atmosphere is used when the active metal welded ceramic substrate is a bare copper active metal welded ceramic substrate.

[0054] P6. Using a gradient drying process, the binder and crosslinking agent are volatilized at 140-150℃, and then held at 200-240℃ for 60-120 minutes to complete sintering.

[0055] The present invention has at least the following beneficial effects:

[0056] (1) This invention uses organic or aromatic compounds with long alkyl chains as binders to coat silver particles. The silver particles coated with the binder can produce a "steric hindrance" effect. On the one hand, the binder can form strong steric hindrance in space, which improves the stability of silver particles and makes the pressureless sintering silver paste have good fluidity and storage properties. On the other hand, when the binder forms steric hindrance, it causes adjacent silver particles to deviate from the normal bond angle. When using a specific process, the binder volatilizes in large quantities, and the "steric hindrance" effect disappears. The intramolecular tension caused by the deviation of adjacent silver particles from the normal bond angle improves the activity of silver particles, reducing the previous sintering temperature of 260-300℃ to 200-240℃, which can meet the needs of low-temperature sintering. Moreover, the pressureless process will not cause pressure on brittle chips and bring hidden dangers.

[0057] (2) The crosslinking agent in the organic solvent system used in this invention can crosslink with the silver particle coating, and connect linear or branched polymer molecules into a three-dimensional network structure through chemical reaction, thereby improving the stability of the silver paste and further improving the activity of the silver particles.

[0058] (3) In order to further improve the sintering size and sintering structure, the present invention optimizes the sintering process by using a gradient drying process to allow the organic matter to volatilize in a gradient manner. After sintering, the internal structure is uniform and defect-free, reducing the problem of organic matter volatilization in the pressureless sintering process of the silver paste in the central area of ​​the connecting layer, and realizing large-area pressureless silver sintering.

[0059] (4) This invention can be used in nitrogen / argon / atmospheric atmospheres and there is no tailing during dispensing, which greatly improves the application range of the product. Attached Figure Description

[0060] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0061] Figure 1 This invention provides a flow chart for the preparation of low-temperature pressureless sintering silver paste.

[0062] Figure 2This is a gradient drying process curve provided in Embodiment 1 of the present invention;

[0063] Figure 3 The image is an ultrasonic non-destructive scanning image of the bonding layer after sintering of silver paste provided in Embodiment 1 of the present invention (selected size is 10mm×10mm).

[0064] Figure 4 The sintering strength diagram of the silver paste provided in Embodiment 1 of the present invention at different temperatures (selected size is 10mm×10mm);

[0065] Figure 5 A schematic diagram of the low-temperature pressureless sintering silver paste dispensing (dispensing shape is a star shape) provided by the present invention;

[0066] Figure 6 This is a schematic diagram of the low-temperature pressureless sintering silver paste dispensing (dispensing shape is cross) provided by the present invention;

[0067] Figure 7 This is a gradient drying process curve provided in Embodiment 2 of the present invention;

[0068] Figure 8 This is an ultrasonic non-destructive scanning image of the bonding layer after sintering of silver paste provided in Embodiment 2 of the present invention (selected size is 10mm×10mm). Detailed Implementation

[0069] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0070] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form includes the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0071] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0072] Example 1

[0073] This embodiment provides a low-temperature pressureless sintering silver paste, which is composed of the following raw materials by weight percentage: 89% silver particles coated with binder; 9.5% organic solvent system; and 1.5% resin.

[0074] in:

[0075] The silver particles are spherical and flake-shaped, specifically a mixture of 20%-40% spherical silver particles and 60%-80% flake-shaped silver particles;

[0076] The particle size of spherical silver particles is 200-500 nm, and the particle size of plate-shaped silver particles is 800-1000 nm.

[0077] The binder is n-heptane;

[0078] The organic solvent system consists of the following raw materials in the following mass percentages: polyamide 2%; methyltrimethoxysilane 1%; organically modified polydimethylsiloxane 2%; benzyl alcohol, 1,2-propanediol, and tridecanol 95%;

[0079] The resin is bisphenol F type epoxy resin.

[0080] like Figure 1 As shown, this embodiment also provides a method for preparing a low-temperature pressureless sintering type silver paste, including the following steps:

[0081] S1. Add anhydrous ethanol to the silver particles, sonicate for 10 min, centrifuge at 3000 r / min, remove the supernatant, and perform preliminary dispersion treatment on the silver particles.

[0082] S2. Mix the silver particles with an ethanol solution of n-heptane (3% concentration), sonicate for 20 min, centrifuge at 3000 r / min, and remove the supernatant.

[0083] S3. Add anhydrous ethanol, sonicate for 10 min to remove residue, centrifuge at 3000 r / min to remove supernatant, and obtain silver particles coated with binder.

[0084] S4. Weigh the molding agent, leveling agent, crosslinking agent, solvent and resin according to the proportion and stir magnetically at 250 r / min for 70 min at 40℃ to ensure uniform mixing and obtain an organic system.

[0085] S5. Mix the silver particles coated with binder obtained in step S3 with the organic system in a certain proportion, and degas in a vacuum degassing machine for 50 minutes to obtain silver paste.

[0086] S6. Fill the silver paste obtained in step S5 into a 20cc syringe using a dispensing machine, ensuring that no air bubbles are generated in the syringe, seal the syringe, and store it at ≤-20℃.

[0087] This embodiment also provides a package interconnection structure for a power device, including: a SiC / GaN chip with a silver-plated surface, an active metal-welded ceramic substrate with a silver-plated surface, and a connection layer for connecting the SiC / GaN chip with a silver-plated surface and the active metal-welded ceramic substrate with a silver-plated surface. The connection layer is formed by sintering a low-temperature pressureless sintering silver paste prepared in this embodiment.

[0088] This embodiment also provides a method for fabricating a packaged interconnect structure for a power device, the specific steps of which are as follows:

[0089] P1. Wipe the surface of the silver-plated active metal-welded ceramic substrate with a lint-free cloth to remove surface dirt;

[0090] P2. Take out the prepared silver paste syringe and allow it to warm up at room temperature for 80 minutes to restore the original fluidity of the silver paste.

[0091] P3. Use a printing press to print pressureless sintering silver paste on the surface of the silver-plated active metal welding ceramic substrate, with a printing thickness of 70μm.

[0092] P4. Use a pick-and-place machine to suction air from the silver-plated SiC / GaN chip and mount it at the printed position. The mounting pressure is 0.1MPa to ensure that the entire chip is evenly pressed into the silver paste, and the amount of adhesive overflow around it is 20% of the chip height.

[0093] P5. Place the silver-plated active metal welding ceramic substrate, silver paste, and silver-plated SiC / GaN chip on the heating stage, and continuously introduce atmospheric atmosphere into the sintering chamber.

[0094] P6, Adopt Figure 2 The gradient drying process shown causes the binder and crosslinking agent to volatilize at 140°C, eliminating steric hindrance, and then sintering is completed by holding at 200°C for 100 minutes.

[0095] After testing, the low-temperature pressureless sintering silver paste prepared in this embodiment can successfully complete the sintering connection between the silver-plated active metal welding ceramic substrate and the silver-plated SiC / GaN chip. The connection layer was observed using ultrasonic scanning, and the scanning image is shown below. Figure 3 As shown in the figure, the entire sintered structure is uniform and dense, and there are no voids or delamination defects.

[0096] The sintering strength of the low-temperature pressureless sintering silver paste provided in this embodiment at different temperatures is as follows: Figure 4 As shown (the selected size is 10mm × 10mm).

[0097] Example 2

[0098] This embodiment provides a low-temperature pressureless sintering silver paste, which is composed of the following raw materials by weight percentage: 91% silver particles coated with binder; 8% organic solvent system; and 1% resin.

[0099] in:

[0100] The silver particles are spherical in shape with a particle size of less than 600 nm.

[0101] The adhesive is p-xylene;

[0102] The organic solvent system is composed of the following raw materials in the following mass percentages: polyimide 4%; γ-aminopropyltriethoxysilane 2%; dimethylsiloxane 2%; decanol, ethylene glycol, and isotridecyl alcohol 92%;

[0103] The resin is a phenolic epoxy resin.

[0104] This embodiment also provides a method for preparing a low-temperature pressureless sintering type silver paste, including the following steps:

[0105] S1. Add anhydrous ethanol to the silver particles, sonicate for 5 min, centrifuge at 2000 r / min, remove the supernatant, and perform preliminary dispersion treatment on the silver particles.

[0106] S2. Mix the silver particles with an ethanol solution of p-xylene (5% concentration), sonicate for 30 min, centrifuge at 3000 r / min, and remove the supernatant.

[0107] S3. Add anhydrous ethanol, sonicate for 10 min to remove residue, centrifuge at 2000 r / min to remove supernatant, and obtain silver particles coated with binder.

[0108] S4. Weigh the molding agent, leveling agent, crosslinking agent, solvent and resin according to the proportion and stir magnetically at 400 r / min for 60 min at 40℃ to ensure uniform mixing, and obtain an organic system.

[0109] S5. Mix the silver particles coated with binder obtained in step S3 with the organic system in a certain proportion, and degas in a vacuum degassing machine for 50 minutes to obtain silver paste.

[0110] S6. Fill the silver paste obtained in step S5 into a 20cc syringe using a dispensing machine, ensuring that no air bubbles are generated in the syringe, seal the syringe, and store it at ≤-20℃.

[0111] This embodiment also provides a package interconnect structure for a power device, including: a gold-plated SiC / GaN chip, a bare copper active metal welded ceramic substrate, and a connection layer for connecting the gold-plated SiC / GaN chip and the bare copper active metal welded ceramic substrate. The connection layer is formed by sintering a low-temperature pressureless sintering silver paste prepared in this embodiment.

[0112] This embodiment also provides a method for fabricating a packaged interconnect structure for a power device, the specific steps of which are as follows:

[0113] P1. Wipe the surface of the bare copper active metal welded ceramic substrate with a lint-free cloth to remove surface dirt;

[0114] P2. Take out the prepared silver paste syringe and allow it to warm up at room temperature for 90 minutes to restore the original fluidity of the silver paste.

[0115] P3. Using a dispensing machine, pressureless sintering silver paste is applied to the surface of a bare copper active metal welding ceramic substrate under an air pressure of 0.3MPa. The dispensing width is 0.2mm and the dispensing pattern is a star shape.

[0116] P4. Use a pick-and-place machine to suction air from the gold-plated SiC chip and place it at the dispensing position. The placement pressure is 0.1MPa to ensure that the entire chip is evenly pressed into the pressureless sintering silver paste, and the amount of adhesive overflow around it is 20% of the chip height.

[0117] P5. Place the entire bare copper active metal welded ceramic substrate, silver paste, and gold-plated SiC / GaN chip on the heating stage, and continuously introduce nitrogen atmosphere into the sintering chamber.

[0118] P6, Adopt Figure 7 The gradient drying process shown causes the binder and crosslinking agent to volatilize at 150°C, eliminating steric hindrance, and then sintering is completed by holding at 240°C for 100 minutes.

[0119] After testing, the low-temperature pressureless sintering silver paste prepared in this embodiment can successfully complete the sintering connection between the bare copper active metal welding ceramic substrate and the gold-plated SiC / GaN chip. Ultrasonic scanning tests were conducted to observe the connection layer; the scanned images are shown below. Figure 8 As shown in the figure, the entire connecting layer is uniform and dense.

[0120] Comparative Example 1

[0121] This comparative example is basically the same as Example 1, except that the gradient drying process was not used, that is, the step of evaporating the binder and crosslinking agent at 140°C was removed, and the temperature was directly raised to 200°C and kept at 100 min. The rest of the slurry formulation and usage method are basically the same as in Example 1.

[0122] The measured bonding layer still had a sintering strength of 35.2 MPa, but this was significantly lower than the 46.2 MPa of Example 1. The lack of a gradient drying method prevented the complete volatilization of organic matter in the chip's center, resulting in some voids in the center during ultrasonic non-destructive scanning, severely reducing reliability.

[0123] Comparative Example 2

[0124] This comparative example is basically the same as Example 2, except that: no crosslinking agent that can form a three-dimensional network structure with the silver particle coating was used. The rest of the slurry formulation and application method are basically the same as in Example 2.

[0125] The measured sintering strength of the bonding layer was only 4.3 MPa. This was because it could not form a three-dimensional network structure with the silver particle coating. The silver paste was not stable enough and agglomerated to a large extent during the warming process, which increased the size of the silver particles and reduced their activity. It could not form an effective interconnection at low temperature, so a sintering neck could not be formed at the interface, resulting in low sintering strength.

[0126] In summary, this invention uses organic or aromatic compounds with relatively long alkyl chains as binders to coat silver particles. The silver particles coated with the binder can generate a "steric hindrance" effect. On the one hand, the binder can form strong steric hindrance in space, improving the stability of the silver particles and giving the pressureless sintered silver paste good flowability and storage properties. On the other hand, when the binder forms steric hindrance, it causes adjacent silver particles to deviate from normal bond angles. When using specific processes, a large amount of binder volatilizes, and the "steric hindrance" effect disappears. The intramolecular tension caused by the deviation of adjacent silver particles from normal bond angles increases the activity of the silver particles, reducing the previous sintering temperature of 260-300℃ to 200-240℃, which can meet the needs of low-temperature sintering, and the pressureless process will not cause pressure hazards to brittle chips. The crosslinking agent in the organic solvent system used in this invention can crosslink with the silver particle coating, connecting linear or branched polymer molecules into a three-dimensional network structure through chemical reaction, improving the stability of the silver paste and further enhancing the activity of the silver particles. To further improve sintering dimensions and microstructure, this invention optimizes the sintering process by employing a gradient drying process to allow for the gradual volatilization of organic matter. This results in a uniform and defect-free internal structure after sintering, reducing the volatilization of organic matter in the central region of the bonding layer during pressureless sintering and achieving large-area pressureless silver sintering. Furthermore, this invention can be used in nitrogen, argon, or atmospheric atmospheres, and exhibits no tailing during dispensing, significantly expanding the product's application range.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-temperature pressureless sintering silver paste, characterized in that, The raw materials comprise the following percentages by weight: 87-94% silver particles coated with binder, 4%-11% organic solvent system, and 1%-2% resin; the binder comprises one or more of n-heptane, n-octane, p-xylene, styrene, and cumene; the organic solvent system comprises, by weight percentage: 2%-4% molding agent, 1%-3% leveling agent, 1%-2% crosslinking agent, and 91%-96% solvent; The preparation method of the low-temperature pressureless sintering type silver paste includes the following steps: S1. Add silver particles to anhydrous ethanol, remove the supernatant by ultrasonic centrifugation, and disperse the silver particles. S2. Mix the silver particles with the binder and remove the supernatant by ultrasonic centrifugation; S3. Add anhydrous ethanol, sonicate to remove residue, centrifuge to remove supernatant, and obtain silver particles coated with binder. S4. Mix the organic solvent system and the resin to obtain an organic system; S5. Mix the silver particles coated with the binder obtained in step S3 with the organic system obtained in step S4 and degas to obtain the silver paste.

2. The low-temperature pressureless sintering silver paste according to claim 1, characterized in that, The morphology of the silver particles includes one or more of the following: spherical, flake-shaped, or triangular.

3. The low-temperature pressureless sintering silver paste according to claim 1, characterized in that, The silver particles have a particle size range of 50-1200 nm.

4. The low-temperature pressureless sintering silver paste according to claim 1, characterized in that, The molding agent includes one or more of polyamide, polyimide, polyamide wax, and polyacrylic acid; the leveling agent includes one or more of dimethylsiloxane, polymethylphenylsiloxane, organically modified polydimethylsiloxane, polyether-modified organosilicon, and modified polyacrylate; the crosslinking agent is a silane crosslinking agent; and the solvent is an alcohol-based organic compound.

5. The low-temperature pressureless sintering silver paste according to claim 1, characterized in that, The resin includes one or more of the following: bisphenol F type epoxy resin, bisphenol A type epoxy resin, phenolic epoxy resin, and cresol epoxy resin.

6. A package interconnect structure for a power device, characterized in that, include: A chip, an active metal-bonded ceramic substrate, and a connecting layer for connecting the chip and the active metal-bonded ceramic substrate, wherein the connecting layer is formed by sintering a low-temperature pressureless sintering silver paste as described in any one of claims 1-5.

7. The method for fabricating the packaged interconnect structure of the power device according to claim 6, characterized in that, Includes the following steps: P1. Remove contaminants from the surface of active metal-welded ceramic substrates; P2. The low-temperature pressureless sintering silver paste according to any one of claims 1-5 is warmed at room temperature to restore the original fluidity of the silver paste; P3. Apply silver paste by dispensing or printing onto the surface of an active metal-welded ceramic substrate. P4. Use a pick-and-place machine to remove air from the chip and place it at the dispensing or printing position, ensuring that the chip is evenly pressed into the silver paste. P5. Place the active metal welding ceramic substrate, silver paste and chip on the heating stage, and continuously introduce argon / nitrogen / atmosphere into the sintering chamber. P6. The power device is dried using a gradient drying process and kept warm to obtain the packaged interconnect structure.

Images