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

Abstract

The invention provides low-temperature pressureless sintering type silver paste as well as a preparation method and application thereof. The low-temperature pressureless sintering type silver paste 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, and the binder is one or more of organic matters or aromatic compounds with long alkyl chains. According to the method, the silver particles are coated with the binder to form the steric hindrance effect, the stability of the silver particles can be improved, the silver paste has good flowability and storage performance, the activity of the silver particles can be improved, the sintering temperature is reduced, the requirement for low-temperature sintering is met, extra pressure does not need to be applied in the sintering process, and the cost is reduced. Hidden dangers caused by device compression are avoided; in addition, the cross-linking agent of the organic solvent system can generate a cross-linking effect with the silver particles coated with the binder, linear or branched polymer molecules are connected into a three-dimensional network structure, and the stability and activity of the silver particles are further improved.

Description

Technical Field

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

[0002] In recent years, with the rapid development of the electronics industry, the service conditions of electronic devices have become increasingly harsh, especially the third-generation semiconductor devices represented by silicon carbide and gallium nitride, which have broken the bottleneck of the second-generation semiconductor devices that are difficult to withstand high temperature and high pressure and handle high power. However, they have also posed greater challenges to the heat dissipation performance of the packaging structure.

[0003] As a new type of green packaging interconnect material, nano silver paste can improve the densification of the connection interface through pressure-assisted sintering, has high connection quality and reliability, and can achieve stable sintering at below 300°C. However, brittle chips and substrates may undergo passivation cracking during pressure sintering, which can easily cause power module failure. Pressure assistance poses challenges to the packaging process, the automation of the packaging process, and the yield rate of the product.

[0004] At present, there have been a certain number of studies on pressureless sintering silver paste, and some researchers have begun to focus on large-area pressureless sintering. However, the increase in the content of organic matter during large-area sintering, the limitation of solvent volatilization during pressureless sintering of the silver paste in the center area of ​​the connection layer, and how to effectively interconnect under low temperature conditions have become urgent problems to be solved.

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

[0006] The object of the present invention is to provide a low-temperature pressureless sintering silver paste and a preparation method and application thereof, wherein the silver paste can solve the problems raised in the above-mentioned background technology.

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

[0008] In the present invention, a binder is used to coat silver particles to form and utilize the steric hindrance effect. On the one hand, by adding the binder, a physical barrier is formed to affect the arrangement of the silver particles. Due to the existence of the "steric hindrance" effect, the stability of the silver particles is improved. On the other hand, when the steric hindrance is formed, the adjacent silver particles deviate from the angle they should originally 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 binder includes: one or more of n-heptane, n-octane, p-xylene, styrene, isopropylbenzene, and methyl cellulose.

[0010] Preferably, the morphology of the silver particles includes one or more of spherical, flaky or triangular.

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

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

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

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

[0015] Preferably, the crosslinking agent is a silane crosslinking agent; more preferably, the crosslinking agent includes: one or more of methyltrimethoxysilane, vinyltributylonoximesilane, vinyltriethoxysilane, γ-aminopropyltriethoxysilane, and γ-methacryloxypropyltrimethoxysilane.

[0016] Preferably, the solvent is an alcohol organic substance; more preferably, the solvent includes: one or more of benzyl alcohol, decanol, ethylene glycol, 1,2-propylene glycol, terpineol, n-butanol, tridecanol, and isomeric tridecanol.

[0017] In the present invention, the forming agent is used to ensure the post-patterning formability of the paste and ensure high uniformity during large-area mounting; the leveling agent can ensure uniform outflow of the paste during the dispensing process; the cross-linking agent can produce a cross-linking effect with the silver particle coating, and connect linear or branched polymer molecules into a three-dimensional network structure through a chemical reaction, 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, novolac epoxy resin, and cresol epoxy resin.

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

[0020] S1. adding silver particles into anhydrous ethanol, removing the supernatant by ultrasonic centrifugation, and dispersing the silver particles;

[0021] S2, mixing the silver particles with the binder, and removing the supernatant by ultrasonic centrifugation;

[0022] S3, adding anhydrous ethanol, removing the residue by ultrasonication, and removing the supernatant by centrifugation to obtain silver particles coated with a binder;

[0023] S4, mixing the organic solvent system and the resin to obtain an organic system;

[0024] S5, mixing the binder-coated silver particles obtained in step S3 with the organic system obtained in step S4 and degassing the mixture to obtain the silver paste.

[0025] Preferably, the method further comprises the following steps:

[0026] S6. The silver paste obtained in step S5 is filled into a syringe using a glue filling machine, ensuring that no bubbles are generated in the syringe, and the syringe is sealed and stored at low temperature.

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

[0028] In some specific embodiments, the method for preparing the low-temperature pressureless sintering silver paste comprises the following steps:

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

[0030] S2, mixing the silver particles with the ethanol solution of the binder, ultrasonicating for 10-30 min, centrifuging at 3000-6000 r / min, and removing the supernatant;

[0031] S3, adding anhydrous ethanol, ultrasonicating for 5-10 minutes to remove the residue, and centrifuging at 2000-4000 r / min to remove the supernatant to obtain silver particles coated with a binder;

[0032] S4, weighing the molding agent, leveling agent, cross-linking agent, solvent and resin in proportion and stirring them magnetically at 40-60° C. and 200-400 r / min for 60-90 min to ensure uniform mixing, to obtain an organic system;

[0033] S5, mixing the binder-coated silver particles obtained in step S3 and the organic system obtained in step S4 in proportion, and degassing in a vacuum degasser for 30-50 minutes to obtain a silver paste;

[0034] S6. Use a glue filling machine to fill the silver paste obtained in step S5 into a 5-20cc syringe, ensure that no bubbles are generated in the syringe, seal the syringe, and store it at ≤-20°C.

[0035] A third aspect of the present invention provides an application of a low-temperature pressureless sintering silver paste, which is applied in the packaging interconnection structure of a power device.

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

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

[0038] Preferably, the active metal welded ceramic substrate comprises: one or more of a bare copper active metal welded ceramic substrate, a silver-plated active metal welded ceramic substrate, and an 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 preparing a package interconnect structure of a power device, comprising the following steps:

[0041] P1. Remove dirt from the surface of active metal welding ceramic substrate;

[0042] P2, reheating the above-mentioned low-temperature pressureless sintering type silver paste at room temperature to restore the original fluidity of the silver paste;

[0043] P3, dispensing or printing silver paste on the surface of active metal welding ceramic substrate;

[0044] P4. Use the chip mounter to suck air and mount the chip at the dispensing or printing position to ensure 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 table, and continuously introduce argon / nitrogen / air into the sintering chamber;

[0046] P6. Drying is performed by using a gradient drying process and heat preservation to obtain the packaging interconnection structure of the power device.

[0047] In some specific embodiments, a method for preparing a package interconnect structure of a power device comprises the following steps:

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

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

[0050] P3. Use a dispensing machine to dispense or print pressureless sintering silver paste on the surface of the active metal welding ceramic substrate under a gas 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, the dispensing pattern is a cross or a cross; or, use a printer to print pressureless sintering silver paste on the surface of the active metal welding ceramic substrate, and the printing thickness is 60-90μm;

[0051] Preferably, the chip area is ≤25mm 2 The preferred dispensing shape is a cross (such as Figure 6 ), chip area ≥ 25mm 2 The preferred dispensing shape is a rice character (such as Figure 5 Preferably, the chip area is ≥49mm 2 , can be printed, the recommended printing thickness is 60-90μm;

[0052] P4. Use the chip mounter to suck air from the SiC / GaN chip and mount it at the dispensing or printing position. The chip mounting pressure is 0.1-0.3MPa to ensure that the entire chip is evenly pressed into the silver paste and the surrounding glue overflow is 20%-40% of the chip height.

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

[0054] P6. Use gradient drying process to volatilize the binder and cross-linking agent at 140-150℃, and then keep the temperature at 200-240℃ for 60-120min to complete sintering.

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

[0056] (1) The present invention uses organic matter or aromatic compounds with longer 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, improve the stability of the silver particles, and make the pressureless sintering type silver paste have better fluidity and storage properties; on the other hand, when the binder forms steric hindrance, it causes the adjacent silver particles to deviate from the normal bond angle. When using a specific process, the binder evaporates in large quantities, and the "steric hindrance" effect disappears. The intramolecular tension caused by the deviation of the normal bond angle of the adjacent silver particles improves the activity of the silver particles, and the previous sintering temperature of 260-300°C is reduced to 200-240°C, which can meet the needs of low-temperature sintering, and the pressureless process will not cause pressure on the brittle chip and bring hidden dangers.

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

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

[0059] (4) The present invention can be used in nitrogen / argon / air atmosphere, and there is no tailing during dispensing, which greatly improves the application range of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0061] Figure 1 A flow chart for preparing the low-temperature pressureless sintering silver paste provided by the present invention;

[0062] Figure 2A gradient drying process curve diagram provided in Example 1 of the present invention;

[0063] Figure 3 Ultrasonic non-destructive scanning image of the connection layer after sintering of the silver paste provided in Example 1 of the present invention (the selected size is 10 mm×10 mm);

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

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

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

[0067] Figure 7 A gradient drying process curve diagram provided in Example 2 of the present invention;

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

[0069] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0070] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form also includes the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates 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 in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0072] Example 1

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

[0074] in:

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

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

[0077] The binder is n-heptane;

[0078] The organic solvent system is composed of the following raw materials in percentage by weight: polyamide 2%; methyltrimethoxysilane 1%; organic modified polydimethylsiloxane 2%; benzyl alcohol, 1,2-propylene glycol, tridecanol 95%;

[0079] The resin is bisphenol F epoxy resin.

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

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

[0082] S2, mixing the silver particles with an ethanol solution of n-heptane (3% concentration), ultrasonicating for 20 min, centrifuging at 3000 r / min, and removing the supernatant;

[0083] S3, adding anhydrous ethanol, ultrasonicating for 10 min to remove the residue, and centrifuging at 3000 r / min to remove the supernatant to obtain silver particles coated with the binder;

[0084] S4, weighing the forming agent, leveling agent, cross-linking agent, solvent and resin in proportion and stirring them magnetically at 40° C. and 250 r / min for 70 min to ensure uniform mixing, to obtain an organic system;

[0085] S5, mixing the binder-coated silver particles obtained in step S3 with the organic system in proportion, and degassing in a vacuum degasser for 50 minutes to obtain a silver paste;

[0086] S6. Use a glue filling machine to fill the silver paste obtained in step S5 into a 20cc syringe, ensure that no bubbles are generated in the syringe, seal the syringe, and store it at ≤-20°C.

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

[0088] This embodiment also provides a method for preparing a packaging interconnection structure of a power device, and the specific steps are as follows:

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

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

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

[0092] P4. Use the placement machine to suck air from the silver-plated SiC / GaN chip and place it at the printing position. The placement pressure is 0.1MPa to ensure that the entire chip is evenly pressed into the silver paste and the surrounding glue overflow is 20% of the chip height.

[0093] P5. Place the active metal-welded ceramic substrate with the entire surface coated with silver, the silver paste, and the SiC / GaN chip with the surface coated with silver on a heating table, and continuously introduce the atmospheric atmosphere into the sintering chamber;

[0094] P6. Adoption Figure 2 The gradient drying process shown volatilizes the binder and the cross-linking agent at 140°C, thereby eliminating the steric hindrance, and then the sintering is completed by keeping the temperature at 200°C for 100 minutes.

[0095] After use test, the low-temperature pressureless sintering type silver paste prepared in this embodiment can well complete the sintering connection between the active metal welding ceramic substrate with silver-plated surface and the SiC / GaN chip with silver-plated surface. The connection layer is observed by ultrasonic scanning test, and the scanning image is as follows: Figure 3 As shown in the figure, it can be seen that the entire sintered structure is uniform and dense, and there are no void 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] The present embodiment provides a low-temperature pressureless sintering type silver paste, which is composed of the following raw materials in percentage by weight: 91% of silver particles coated with a binder; 8% of an organic solvent system; and 1% of a resin.

[0099] in:

[0100] The morphology of the silver particles is spherical, and the particle size is less than 600nm;

[0101] The binder is p-xylene;

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

[0103] The resin is phenolic epoxy resin.

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

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

[0106] S2, mixing the silver particles with an ethanol solution of p-xylene (5% concentration), ultrasonicating for 30 min, centrifuging at 3000 r / min, and removing the supernatant;

[0107] S3, adding anhydrous ethanol, ultrasonicating for 10 minutes to remove the residue, and centrifuging at 2000 r / min to remove the supernatant to obtain silver particles coated with a binder;

[0108] S4, weighing the forming agent, leveling agent, cross-linking agent, solvent and resin in proportion and stirring them magnetically at 40° C. and 400 r / min for 60 min to ensure uniform mixing, to obtain an organic system;

[0109] S5, mixing the binder-coated silver particles obtained in step S3 with the organic system in proportion, and degassing in a vacuum degasser for 50 minutes to obtain a silver paste;

[0110] S6. Use a glue filling machine to fill the silver paste obtained in step S5 into a 20cc syringe, ensure that no bubbles are generated in the syringe, seal the syringe, and store it at ≤-20°C.

[0111] The present embodiment also provides a packaging interconnection structure of a power device, comprising: a SiC / GaN chip with a gold-plated surface, a bare copper active metal welded ceramic substrate, and a connecting layer for connecting the SiC / GaN chip with a gold-plated surface and the bare copper active metal welded ceramic substrate, wherein the connecting layer is formed by sintering the low-temperature pressureless sintering silver paste prepared in the present embodiment.

[0112] This embodiment also provides a method for preparing a packaging interconnection structure of a power device, and the specific steps are as follows:

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

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

[0115] P3. Use a dispensing machine to dispense pressureless sintering silver paste on the surface of bare copper active metal welding ceramic substrate at a pressure of 0.3MPa. The dispensing width is 0.2mm and the dispensing pattern is a cross.

[0116] P4. Use the placement machine to suck air from the gold-plated SiC chip and mount it at the glue 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 surrounding glue overflow is 20% of the chip height.

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

[0118] P6. Adoption Figure 7 The gradient drying process shown volatilizes the binder and the cross-linking agent at 150°C, thereby eliminating the steric hindrance, and then the sintering is completed by keeping the temperature at 240°C for 100 minutes.

[0119] After use test, the low-temperature pressureless sintering type silver paste prepared in this embodiment can well complete the sintering connection between the bare copper active metal welding ceramic substrate and the gold-plated SiC / GaN chip. The ultrasonic scanning test observes the connection layer, and the scanning image is as follows: Figure 8 As shown, it can be seen from the figure that the entire connection layer is uniform and dense.

[0120] Comparative Example 1

[0121] This comparative example is basically the same as Example 1, except that: no gradient drying process is used, that is, the step of volatilizing the binder and the cross-linking agent at 140°C is removed, and the temperature is directly raised to 200°C and kept warm for 100 minutes. The remaining slurry formula and usage steps are basically the same as Example 1.

[0122] The measured sintering strength of the connection layer is still 35.2MPa, but much lower than 46.2MPa of Example 1. The lack of gradient drying means that the organic matter in the center of the chip cannot be completely volatilized, and some void defects appear in the center during ultrasonic nondestructive scanning, which seriously reduces reliability.

[0123] Comparative Example 2

[0124] This comparative example is basically the same as Example 2, except that no cross-linking agent that can form a three-dimensional network structure with the silver particle coating is used, and the rest of the slurry formula and the use method steps are basically the same as Example 2.

[0125] The measured sintering strength of the connecting layer is only 4.3MPa. The reason is that it is impossible to form a three-dimensional network structure with the silver particle coating. The silver paste is not stable enough. During the warming process, a large degree of agglomeration occurs, which makes the silver particles larger and reduces the activity of the silver particles. It is impossible to form effective interconnections at low temperatures, so that a sintering neck cannot be formed at the interface, and the sintering strength is low.

[0126] In summary, the present invention uses organic matter or aromatic compounds with longer alkyl chains as binders to coat silver particles. The silver particles coated with the binder used can produce a "steric hindrance" effect. On the one hand, the binder used can form a strong steric hindrance in space, improve the stability of the silver particles, and make the pressureless sintering type silver paste have better fluidity and storage; on the other hand, when the binder forms a steric hindrance, the adjacent silver particles deviate from the normal bond angle. When using a specific process, the binder evaporates in large quantities, and the "steric hindrance" effect disappears. The tension in the molecules of the adjacent silver particles caused by the deviation from the normal bond angle increases the activity of the silver particles, and the previous sintering temperature of 260-300°C is reduced to 200-240°C, which can meet the needs of low-temperature sintering, and the pressureless will not cause pressure to the brittle chip and bring hidden dangers. The cross-linking agent in the organic solvent system used in the present invention can produce a cross-linking effect with the silver particle coating, connect the linear or branched polymer molecules into a three-dimensional network structure through a chemical reaction, improve the stability of the silver paste, and further improve the activity of the silver particles. In order to further increase the sintering size, improve the sintering structure, optimize the design of the sintering process, the present invention adopts a gradient drying process to volatilize the organic matter in a gradient manner, and the internal structure after sintering is uniform and defect-free, thereby reducing the problem of organic matter volatilization during the pressureless sintering of the silver paste in the central area of ​​the connecting layer, and realizing large-area pressureless silver sintering. The present invention can be used in nitrogen / argon / air atmosphere, and there is no tailing in the dispensing, which greatly improves the application range of the product.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements 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 invention comprises the following raw materials in percentage by mass: 87-94% of silver particles coated with a binder, 4%-11% of an organic solvent system, and 1%-2% of a resin; the binder is one or more of organic substances with long alkyl chains or aromatic compounds.

2. The low-temperature pressureless sintering silver paste according to claim 1, characterized in that: The binder includes: one or more of n-heptane, n-octane, p-xylene, styrene, isopropylbenzene and methyl cellulose.

3. 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 spherical, flake or triangular.

4. The low-temperature pressureless sintering silver paste according to claim 1, characterized in that: The particle size of the silver particles ranges from 50 to 1200 nm.

5. The low-temperature pressureless sintering silver paste according to claim 1, characterized in that: In terms of mass percentage, the organic solvent system comprises: 2%-4% of a molding agent, 1%-3% of a leveling agent, 1%-2% of a cross-linking agent, and 91%-96% of a solvent.

6. The low-temperature pressureless sintering silver paste according to claim 5, 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, organic modified polydimethylsiloxane, polyether modified silicone, and modified polyacrylate; the crosslinking agent is a silane crosslinking agent; and the solvent is an alcohol organic matter.

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

8. The method for preparing the low-temperature pressureless sintering silver paste according to any one of claims 1 to 7, characterized in that: The steps include: S1. adding silver particles into anhydrous ethanol, removing the supernatant by ultrasonic centrifugation, and dispersing the silver particles; S2, mixing the silver particles with the binder, and removing the supernatant by ultrasonic centrifugation; S3, adding anhydrous ethanol, removing the residue by ultrasonication, and removing the supernatant by centrifugation to obtain silver particles coated with a binder; S4, mixing the organic solvent system and the resin to obtain an organic system; S5, mixing the binder-coated silver particles obtained in step S3 with the organic system obtained in step S4 and degassing the mixture to obtain the silver paste.

9. A packaging interconnection structure of a power device, characterized in that: include: A chip, an active metal welding ceramic substrate and a connection layer for connecting the chip and the active metal welding ceramic substrate, wherein the connection layer is formed by sintering the low-temperature pressureless sintering type silver paste according to any one of claims 1-8.

10. The method for preparing the packaging interconnection structure of a power device according to claim 9, characterized in that: The steps include: P1. Remove dirt from the surface of active metal welding ceramic substrate; P2. Reheating the low-temperature pressureless sintering silver paste according to any one of claims 1 to 8 at room temperature to restore the original fluidity of the silver paste; P3, dispensing or printing silver paste on the surface of active metal welding ceramic substrate; P4. Use the chip mounter to suck air and mount the chip at the dispensing or printing position to ensure 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 table, and continuously introduce argon / nitrogen / air into the sintering chamber; P6. Drying is performed by using a gradient drying process and heat preservation to obtain the packaging interconnection structure of the power device.

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