A sintered copper paste for power device packaging and its preparation method and application

Abstract

This invention provides a sintering copper paste for power device packaging, its preparation method, and its application. The paste comprises: 75%-85% copper particles coated with a binder, and 15%-25% an organic solvent system; the organic solvent system includes rare earth antioxidants; it also includes one or more of a forming agent, leveling agent, thickener, crosslinking agent, surfactant, solvent, and resin. This invention utilizes a variety of organic components and an adhesive-enhancing binder system to give the copper paste excellent antioxidant capacity, adhesion, and long-term reliability. Simultaneously, it ensures good dispersibility, formability, and thickness uniformity during sintering, meeting the reliability requirements of high-temperature packaging. This invention employs a double-sided copper paste coating and pressure-assisted sintering process, achieving reliable interconnection and high-strength adhesion of the copper paste at high temperatures. Furthermore, the double-sided coated copper paste can effectively suppress oxide diffusion at the interface at high temperatures, thereby significantly improving the antioxidant performance of the packaging structure.

Description

Technical Field

[0001] This invention relates to the field of third-generation semiconductor power device packaging, and in particular to a sintered copper paste for power device packaging, its preparation method, and its application. Background Technology

[0002] With the rapid development of aerospace, electric vehicles, and other fields, the performance requirements for core power devices are constantly increasing. Especially in high-power applications, third-generation wide-bandgap semiconductor materials (such as silicon carbide and gallium nitride) have gained widespread attention due to their high thermal conductivity and high-temperature resistance. These materials can operate normally at temperatures of 350°C or even higher, meeting reliability requirements under extreme conditions. However, if the interconnect materials in the device package cannot match the high-temperature performance of the semiconductor materials, it will become a bottleneck for system reliability.

[0003] The thermal conductivity and reliability of packaging materials directly determine the heat dissipation capacity and overall performance of power modules. Currently, devices such as silicon carbide typically use tin-based solder to connect to active metal-ceramic substrates and heat sinks. However, tin-based solder has poor high-temperature performance; its low melting point and thermal conductivity are insufficient to meet the requirements of high-temperature semiconductors, especially during long-term high-temperature service, where the packaging may experience fatigue failure and decreased thermal efficiency. Therefore, sintered copper materials with good thermal conductivity and high-temperature resistance are considered a potential alternative to tin-based solder.

[0004] However, large-area sintered copper materials still face many bottlenecks in practical applications. On the one hand, during the sintering process, the high reactivity of copper easily leads to surface oxidation, which weakens the interfacial adhesion and long-term stability of the solder layer. On the other hand, in large-area printing of copper paste, it is difficult to control the thickness uniformity, which may lead to localized weak areas. In addition, the copper layer often warps during cooling, which not only affects the flatness of the package but also further deteriorates the thermal conductivity and mechanical properties of the solder layer. These problems severely limit the practical application of sintered copper materials in large-area high-temperature interconnects. Therefore, effectively suppressing oxidation diffusion while ensuring thickness uniformity has become a key technological breakthrough for improving the performance of the packaging structure.

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

[0006] The purpose of this invention is to provide a sintered copper paste for power device packaging, its preparation method, and its application. This copper paste can solve the problems mentioned in the background art.

[0007] In a first aspect, the present invention provides a sintered copper paste for power device packaging, comprising the following raw materials by weight percentage: 75%-85% copper particles coated with binder, and 15%-25% organic solvent system; wherein the organic solvent system includes rare earth antioxidants; and further comprising one or more of the following: molding agent, leveling agent, thickener, crosslinking agent, surfactant, solvent, and resin.

[0008] In this invention, rare earth antioxidants effectively inhibit oxidation on the surface of nano-copper particles by forming a stable rare earth oxide barrier layer during high-temperature sintering, and further slow down the oxidation reaction by capturing free oxygen through redox behavior. A forming agent ensures the formability of the copper paste after printing, thereby achieving large-area printing and uniform thickness. A leveling agent ensures uniform thickness during double-sided brush printing, effectively guaranteeing uniform paste thickness during printing. The thickness difference between different positions of the bonding layer after pre-sintering is less than 20 μm, avoiding performance loss caused by uneven thickness. A thickener controls the viscosity of the copper paste, ensuring it maintains appropriate thickness and shape during printing. A crosslinking agent enhances the adhesion between sintered copper layers. The combination of antioxidants and high-temperature stable crosslinking agents effectively controls oxidation during sintering, ensuring the reliability of the bonding layer during long-term high-temperature service. This invention is particularly suitable for designs involving double-sided copper paste interconnects. Surfactants improve the dispersibility of copper particles in solution, reduce particle agglomeration, and ensure uniform copper paste. Surfactants also help improve the stability of the copper paste and reduce particle sedimentation. Solvents are used to adjust the viscosity of the copper paste, improve its flowability, ensure uniform dispersion of copper particles during printing, and prevent particle sedimentation. Resin provides adhesion between copper particles, enhancing the adhesion and mechanical strength of the sintered copper layer. The organic solvent system ensures good formability, oxidation resistance, and thickness uniformity of the copper paste at high temperatures, and improves the dispersibility of copper particles, reducing particle agglomeration.

[0009] Preferably, the adhesive comprises one or more of the following: polyvinylpyrrolidone (PVP), methylcellulose, ethylcellulose, epoxy acrylate, acrylate, and cellulose acetate.

[0010] Preferably, by mass percentage, the organic solvent system comprises: 1%-5% molding agent, 0.5%-2% leveling agent, 0.5%-1% thickener, 1%-3% rare earth antioxidant, 1%-3% crosslinking agent, 1%-2% surfactant, 85%-90% solvent, and 1%-2% resin.

[0011] Preferably, the rare earth antioxidant comprises one or more of cerium oxide (CeO2), lanthanum oxide (La2O3), cerium chloride (CeCl3), and lanthanum nitrate (La(NO3)3). Cerium oxide captures free oxygen to delay the diffusion of oxides, thereby improving the oxidation resistance, mechanical properties, and high-temperature adhesion of the solder layer; lanthanum oxide is used to inhibit the oxidation reaction of copper particles by forming a stable oxide barrier layer during high-temperature sintering.

[0012] Preferably, the morphology of the copper particles includes one or more of the following: spherical, plate-like, or triangular.

[0013] Preferably, the copper particles have a particle size range of 50-2000 nm; more preferably, the copper particles have a particle size range of 100-1500 nm; further, the copper particles have a particle size of 100 nm, 300 nm, 500 nm, 800 nm, 1000 nm, 1200 nm, or 1500 nm.

[0014] Preferably, the molding agent includes one or more of polyvinylidene fluoride, polyacrylate, and styrene-butadiene copolymer.

[0015] Preferably, the leveling agent includes one or more of sodium polyacrylate, ethoxylated modified silicone oil, and polyethylene glycol.

[0016] Preferably, the thickener includes one or more of carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose (HPMC), and sodium polyacrylate.

[0017] Preferably, the crosslinking agent includes one or more of butyl methacrylate, butyl acrylate, and polyethyleneimine.

[0018] Preferably, the surfactant comprises one or more of polyvinyl alcohol (PVA), polyoxyethylene octylphenol ether, and sodium dodecylbenzene sulfonate.

[0019] Preferably, the solvent is an alcoholic organic compound; more preferably, the solvent includes one or more of isopropanol, diisopropanol, triethylene glycol, terpineol, and α-terpineol.

[0020] Preferably, the resin includes one or more of polyimide resin, amino resin, and polyurethane resin; more preferably, the resin includes one or more of bisphenol A type polyimide resin, bisphenol F type polyurethane resin, or amino resin.

[0021] A second aspect of the present invention provides a method for preparing a sintered copper paste for power device packaging, comprising the following steps:

[0022] S1. Treat the copper particles with a complex to ensure that there is no oxide layer on the surface of the copper particles;

[0023] S2. Mix the copper particles treated with the complex with the binder, remove the supernatant by ultrasonic centrifugation, add anhydrous ethanol to wash, centrifuge to remove the supernatant, and obtain copper particles coated with binder.

[0024] S3. Mix the molding agent, leveling agent, thickener, rare earth antioxidant, crosslinking agent, surfactant, solvent and resin, and stir evenly to obtain an organic solvent system;

[0025] S4. Mix the copper particles coated with the binder obtained in step S2 with the organic solvent system obtained in step S3 to obtain the copper paste.

[0026] Preferably, step S1 includes the following steps:

[0027] S11. Dissolve the complexing agent in deionized water to obtain a complexing agent solution;

[0028] S12. Add copper particles to the complexing agent solution obtained in step S11, so that the oxide on the surface of the copper particles reacts with the complexing agent to generate a soluble complex.

[0029] S13. Centrifuge the mixture obtained in step S12 to remove the supernatant, then wash with anhydrous ethanol and centrifuge to remove the supernatant.

[0030] S14. Dry the cleaned copper particles to obtain copper particles with no oxide on the surface.

[0031] Preferably, the complexing agent comprises one or more of ethylenediaminetetraacetic acid (EDTA), aminotriacetic acid (NTA), citric acid, malic acid, oxalic acid, or aminopolycarboxylic acid compounds; more preferably, ethylenediaminetetraacetic acid and / or citric acid.

[0032] Preferably, the concentration of the complexing agent is 0.5%-2%, more preferably 0.8%-1.5%.

[0033] In some specific embodiments, step S1 includes the following steps:

[0034] S11. Dissolve the complexing agent in deionized water and stir magnetically until completely dissolved to obtain a complexing agent solution.

[0035] S12. Add copper particles to the complexing agent solution obtained in step S11, mix them at a solid-liquid mass ratio of 1:10-1:20, and stir magnetically for 10-30 minutes to allow the oxides on the surface of the copper particles to react with the complexing agent and generate a soluble complex.

[0036] S13. Place the mixture obtained in step S12 into a centrifuge, control the centrifugation speed at 5000-8000 r / min, and centrifuge for 5-15 minutes. Remove the supernatant and wash with anhydrous ethanol 2-3 times. After each wash, centrifuge at 2000-4000 r / min for 5-10 minutes and remove the supernatant to remove the complex and other residues.

[0037] S14. Place the cleaned copper particles in a vacuum drying oven at 60℃-80℃ and dry for 30-60 minutes to obtain pure copper particles with no oxide residue on the surface.

[0038] Preferably, step S2 includes the following steps:

[0039] The copper particles treated with the complex were mixed with an ethanol solution of the binder, sonicated for 20-30 minutes, centrifuged at 4000-6000 r / min to remove the supernatant, and then washed with anhydrous ethanol for 5-10 minutes. After centrifugation at 2000-4000 r / min, the supernatant was removed to obtain copper particles coated with the binder.

[0040] Preferably, step S3 includes the following steps:

[0041] S31. Dissolve the rare earth material in deionized water or alcohol solvent and stir magnetically for 20-40 minutes to form a uniformly dispersed rare earth antioxidant.

[0042] Preferably, the concentration range of the rare earth antioxidant is 0.1%-2%, more preferably 0.5%-1%;

[0043] S32. Add each component to the solvent in the following proportions: rare earth antioxidant 1%-3%, molding agent 1%-5%, leveling agent 0.5%-2%, thickener 0.5%-1%, crosslinking agent 1%-3%, surfactant 1%-2%, solvent 85%-90%, and resin 1%-2%. Stir with a magnetic stirrer to ensure uniform dispersion of the solution and obtain an organic solvent system.

[0044] Preferably, step S4 includes the following steps:

[0045] S41. Add the binder-coated copper particles to the organic solvent system and stir with a magnetic stirrer for 20-30 minutes to make the rare earth antioxidants and other organic components in the organic solvent system evenly distributed on the surface of the copper particles, and achieve preliminary antioxidant treatment through chemical adsorption and physical coating.

[0046] S42. Place the mixture from step S41 in an ultrasonic bath and ultrasonically disperse it at a temperature of 20-30°C for 10-15 minutes to further enhance the adhesion and dispersion of rare earth antioxidants and organic components on the surface of copper particles.

[0047] S43. Place the mixture processed in step S42 into a centrifuge, control the centrifugation speed at 5000-8000 r / min, and centrifuge for 5-15 minutes. Remove the supernatant and retain the copper paste with rare earth antioxidants and organic components attached.

[0048] A third aspect of the present invention provides an application of a sintered copper paste for power device packaging, which is applied to the packaging interconnect structure of power devices.

[0049] Preferably, it is used in the sintering connection process between the substrate and the heat sink.

[0050] A fourth aspect of the present invention provides a package interconnect structure for a power device, comprising: a substrate, a heat sink, and a connection layer for connecting the substrate and the heat sink, wherein the connection layer is formed by pressure-assisted sintering of the aforementioned copper paste coated on both sides to ensure complete interconnection of the copper paste on both sides. This structure prevents oxide diffusion to the interface under high-temperature conditions, thereby enhancing the overall structural reliability.

[0051] Preferably, the substrate is a DBC substrate, more preferably an active metal substrate with a metallized surface, specifically including: bare copper active metal welded ceramic substrate, silver-plated active metal welded ceramic substrate, and nickel-gold plated active metal welded ceramic substrate, etc.

[0052] Preferably, the heat sink can be a copper plate, an aluminum plate, a nickel-plated copper plate, or a nickel-plated steel plate to meet the thermal conductivity and high temperature resistance requirements of different packaging needs.

[0053] A fifth aspect of the present invention provides a method for fabricating a packaged interconnect structure for a power device, comprising the following steps:

[0054] P1. Remove contaminants from the surface of the substrate and heat sink;

[0055] P2. Apply the copper paste to the connection surfaces of the substrate and the heat sink respectively, and pre-dry the coated substrate and the heat sink.

[0056] P3. Align and stack the pre-dried substrate and heat sink, place the stacked assembly in the sintering equipment, heat the sintering equipment and apply pressure to complete the sintering connection process, so that a dense and high-strength connection layer is formed between the substrate and the heat sink.

[0057] P4. Gradually reduce the temperature of the sintering equipment to cool the stacked components to room temperature, thereby obtaining the packaged interconnect structure of the power device.

[0058] In some specific embodiments, the fabrication method of the package interconnect structure of the power device includes the following steps:

[0059] P1. Clean the surfaces of the DBC substrate and heat sink to be interconnected with a lint-free cloth to remove all contaminants and ensure the adhesion of the copper paste.

[0060] P2. Apply copper paste to the connection surfaces of the DBC substrate and the heat sink, respectively. The coating thickness should be controlled within the range of 50-200μm to ensure the uniformity of the double-sided interconnect structure. Place the coated DBC substrate and heat sink in a drying oven for pre-drying. Purge with nitrogen / argon / hydrogen / formic acid atmosphere to avoid oxidation. Control the drying temperature at 100-120℃ and maintain for 30-60 minutes to achieve preliminary curing.

[0061] P3. Align and stack the pre-dried DBC substrate and heat sink tightly. Place the stacked components in a sintering equipment, heat to 200-250℃, and apply a pressure of 5-20MPa for 2-8 minutes to complete the sintering connection process, so as to ensure the complete curing and tight bonding of the double-sided copper paste connection layer.

[0062] P4. Gradually reduce the equipment temperature and slowly cool the sintered stacked components to room temperature to ensure that the connection layer does not crack or warp during the cooling process, thus obtaining the packaged interconnect structure of the power device.

[0063] The present invention has at least the following beneficial effects:

[0064] (1) By using an adhesive to coat copper particles, the present invention can significantly enhance the adhesion and interface stability of copper paste. Moreover, the adhesive has excellent stability in high temperature environment, which can ensure that the connection layer coated with double-sided copper paste maintains excellent adhesion and long-term reliability under high temperature extreme conditions, thereby effectively improving the high temperature service performance of the packaged interconnect structure.

[0065] (2) The present invention enables copper particles to have excellent antioxidant capacity through the synergistic effect of rare earth antioxidants and other organic components, while ensuring that the copper paste has good dispersibility, formability and thickness uniformity during sintering, thus meeting the reliability requirements of high-temperature packaging.

[0066] (3) The various organic components and adhesive system used in this invention enable the copper paste to remain stable under extreme conditions, the bonding layer is not easy to crack, it has high high temperature resistance and excellent mechanical strength, and is suitable for high temperature packaging applications of DBC substrates and heat sinks.

[0067] (5) In the preparation method of the present invention, the copper particles are treated with complexes, which greatly improves the shear strength of the bonding layer after the copper paste is sintered.

[0068] (6) The present invention adopts double-sided copper paste coating and pressure-assisted sintering process to achieve reliable interconnection and high-strength adhesion of copper paste at high temperature. Moreover, the double-sided coated copper paste design can effectively suppress the diffusion of oxides at the interface under high temperature conditions, thereby significantly improving the anti-oxidation performance of the packaging structure. Attached Figure Description

[0069] 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.

[0070] Figure 1 A schematic diagram of the preparation method of sintered copper paste for power device packaging provided by the present invention.

[0071] Figure 2 The diagram shows the power device's package interconnect structure before and after sintering, as provided by this invention.

[0072] Figure 3 This diagram shows the selection of test points for the uniformity of copper paste coating thickness provided by the present invention.

[0073] Figure 4 The diagram shows the test results of the shear strength of the connecting layer provided by the present invention under different temperatures and pressures.

[0074] Figure 5 The images are ultrascan images of the sintered bonding layer provided by the present invention; wherein, (a) is the bonding layer of Example 1, and (b) is the bonding layer of Example 2.

[0075] Figure 6 The diagram shows a comparative test of the antioxidant properties of the bonding layer provided by the present invention under high temperature conditions; wherein, (ab) is a cross-sectional SEM image of the copper paste after sintering on one side and aging at high temperature; (c) is an EDS image of the copper paste after sintering on one side and aging at high temperature; (de) is a cross-sectional SEM image of the copper paste after sintering on both sides and aging at high temperature; and (f) is an EDS image of the copper paste after sintering on both sides and aging at high temperature.

[0076] Figure 7 The diagram shows a comparison of the shear strength of the bonding layers after aging at 250°C for different times under conditions of rare earth oxidant treatment and no rare earth oxidant treatment, as provided by this invention.

[0077] Figure 8 The graph shows the shear strength test results of the connecting layer treated with and without complexation, as provided by this invention. Detailed Implementation

[0078] 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.

[0079] 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.

[0080] 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.

[0081] Example 1

[0082] This embodiment provides a sintered copper paste for power device packaging, comprising the following raw materials by weight percentage: 82% copper particles coated with binder and 18% organic solvent system.

[0083] in:

[0084] The copper particles are a mixture of spherical and flaky particles, with spherical particles accounting for about 30% and flaky particles accounting for about 70%.

[0085] The particle size of spherical copper particles is 300-500nm, and the particle size of flake copper particles is 1000-1200nm.

[0086] The binder is a mixture of polyvinylpyrrolidone (PVP) and ethyl cellulose to enhance the surface adhesion of the copper particles;

[0087] The organic solvent system consists of the following mass percentages: 1% cerium oxide (CeO2) rare earth antioxidant; 3% polyvinylidene fluoride (PVDF) molding agent; 1.5% polyethylene glycol (PEG) leveling agent; 0.8% carboxymethyl cellulose thickener; 2% butyl methacrylate crosslinking agent; 1% polyvinyl alcohol surfactant; 88.7% diisopropanol solvent; and 2% polyurethane resin.

[0088] like Figure 1 As shown, this embodiment also provides a method for preparing sintered copper paste for power device packaging, including the following steps:

[0089] S1. Mix copper particles with ethylenediaminetetraacetic acid (EDTA, 1%) and citric acid (0.5%) solutions at a solid-liquid mass ratio of 1:15. Stir magnetically for 20 minutes to allow the oxides on the surface of the copper particles to react with the complexing agent and form a soluble complex. Centrifuge at 6000 r / min for 10 minutes, remove the supernatant, and then add anhydrous ethanol for ultrasonic cleaning twice, 5 minutes each time. After each cleaning, centrifuge at 3000 r / min for 5 minutes to remove the supernatant, in order to remove the complex and other residues and ensure that there is no oxide layer on the surface of the copper particles. Place the cleaned copper particles in a vacuum drying oven at 70℃ and dry for 40 minutes to obtain pure copper particles with no oxide residue on the surface.

[0090] S2. The copper particles after complexation treatment are mixed with an ethanol solution of 0.5% polyvinylpyrrolidone and 0.5% ethyl cellulose, sonicated for 20 minutes, centrifuged at 5000 r / min to remove the supernatant, then washed with anhydrous ethanol for 5 minutes, centrifuged at 3000 r / min, and the supernatant is removed to obtain copper particles coated with binder.

[0091] S3. Dissolve cerium oxide in an alcohol solvent at a concentration of 1% and stir magnetically for 30 minutes to form a uniformly dispersed rare earth antioxidant. Weigh the molding agent, rare earth antioxidant, leveling agent, thickener, crosslinking agent, surfactant and resin in proportion, add them to the solvent, and stir magnetically for 70 minutes to ensure uniform mixing, thus preparing an organic solvent system.

[0092] S4. Add the binder-coated copper particles to the organic solvent system and stir with a magnetic stirrer for 20 minutes to ensure that the rare earth antioxidants and other organic components in the organic solvent system are evenly distributed on the surface of the copper particles, and achieve preliminary antioxidant treatment through chemical adsorption and physical coating. Place the mixture in an ultrasonic bath and ultrasonically disperse it at 25°C for 10 minutes to further enhance the adhesion and dispersion effect of the rare earth antioxidants and organic components on the surface of the copper particles. Place the treated mixture in a centrifuge, control the centrifugation speed at 6000 r / min, and centrifuge for 10 minutes. Remove the supernatant and degas it in a vacuum degassing machine for 15 minutes to obtain a uniform copper paste.

[0093] like Figure 2 As shown, this embodiment also provides a power device packaging interconnection structure, including: a silver-plated active metal welded ceramic substrate, a pure copper heat sink, and a connection layer for connecting the silver-plated active metal welded ceramic substrate and the pure copper heat sink, wherein the connection layer is formed by double-sided coated copper paste under pressure-assisted sintering.

[0094] This embodiment also provides a method for fabricating a packaged interconnect structure for a power device, comprising the following steps:

[0095] P1. Use a lint-free cloth to clean the surface of the silver-plated active metal welding ceramic substrate and the pure copper heat sink to remove surface dirt and ensure that the surface is free of grease, oxides and other contaminants in order to improve the adhesion of copper paste.

[0096] P2. Copper paste is applied to the connecting surfaces of the silver-plated active metal welding ceramic substrate and the pure copper heat sink, respectively. The coating thickness is controlled within the range of 150-200μm to ensure uniform coating and provide a good foundation for subsequent sintering. The coated silver-plated active metal welding ceramic substrate and the pure copper heat sink are placed in a drying oven for pre-drying. A nitrogen / argon / hydrogen / formic acid atmosphere is introduced to avoid oxidation. The drying temperature is controlled at 100-120℃ and maintained for 40 minutes to achieve preliminary curing.

[0097] P3. Following the order from top to bottom, align and tightly stack the silver-plated active metal welding ceramic substrate coated with copper paste with the pure copper heat sink coated with copper paste. Place the stacked assembly on the heating table of the sintering equipment and continuously introduce nitrogen atmosphere to prevent the copper paste from undergoing oxidation reaction during heating. Heat the equipment to 200-275℃ and apply a pressure of 20MPa for 5 minutes to complete the sintering connection process, so that a dense and high-strength connection layer is formed between the silver-plated active metal welding ceramic substrate and the pure copper heat sink.

[0098] P4. Gradually reduce the equipment temperature and slowly cool the sintered stacked components to room temperature to ensure that the connection layer does not crack or warp during the cooling process, thus obtaining the packaged interconnect structure of the power device.

[0099] After testing, the sintering copper paste for power device packaging prepared in this embodiment can successfully complete the sintering connection between the silver-plated active metal welding ceramic substrate and the pure copper heat sink. Tests show that the thickness uniformity of the pre-sintered connection layer is good. Figure 3 The method shown was used to test the thickness at different locations, and the maximum thickness difference was less than 20 μm.

[0100] The sintered interconnect layer exhibits high strength and stability. The strength of the interconnect layer after chip mounting is as follows: Figure 4 As shown in the figure, the shear strength reaches 38.7 MPa under conditions of 200℃ and 20 MPa pressure; and 59.8 MPa under conditions of 250℃ and 20 MPa pressure. The quality of the bonding layer was measured by ultrasonic scanning, and the scanned images are shown below. Figure 5 As shown in (a) of the figure, it can be seen from the figure that the internal structure of the connecting layer is uniform and there are no obvious defects or voids, which verifies the reliability and practicality of the copper paste of the present invention.

[0101] Example 2

[0102] This embodiment provides a sintered copper paste for power device packaging, comprising the following raw materials by weight percentage: 83% copper particles coated with binder; 17% organic solvent system.

[0103] in:

[0104] The morphology of the copper particles is a mixture of spherical and plate-like particles, with spherical particles accounting for about 40% and plate-like particles accounting for about 60%.

[0105] The particle size of copper particles ranges from 200 to 1200 nm, with spherical particles having a particle size of 400 to 600 nm and plate-like particles having a particle size of 800 to 1200 nm.

[0106] The binder is a mixture of methylcellulose and epoxy acrylate to further enhance the adhesion properties and high-temperature stability of the particles.

[0107] The organic solvent system comprises the following components by mass percentage: 1.5% lanthanum oxide (La2O3) rare earth antioxidant; 3% polyacrylate molding agent; 1% ethoxylated modified silicone oil leveling agent; 1% hydroxypropyl methylcellulose thickener; 1% butyl acrylate crosslinking agent; 1% polyoxyethylene octylphenol ether surfactant; 89.5% triethylene glycol solvent; and 2% amino resin.

[0108] This embodiment also provides a method for preparing sintered copper paste for power device packaging, including the following steps:

[0109] S1. Mix copper particles with aminotriacetic acid (NTA, 1% concentration) and malic acid (0.5% concentration) solution at a solid-liquid mass ratio of 1:10. Stir magnetically for 15 minutes to allow the oxides on the surface of the copper particles to react with the complexing agent and form a soluble complex. Centrifuge at 5000 r / min for 15 minutes, remove the supernatant, and then add anhydrous ethanol for ultrasonic cleaning 3 times, 5 minutes each time. After each cleaning, centrifuge at 4000 r / min for 5 minutes to remove the supernatant to remove the complex and other residues, ensuring that there is no oxide layer on the surface of the copper particles. Place the cleaned copper particles in a vacuum drying oven at 60℃ and dry for 50 minutes to obtain pure copper particles with no oxide residue on the surface.

[0110] S2. The copper particles treated with the complex were mixed with a 1% methylcellulose solution, sonicated for 25 minutes, centrifuged at 5000 r / min to remove the supernatant, and then washed with anhydrous ethanol for 10 minutes. After centrifugation at 3000 r / min, the supernatant was removed to obtain copper particles uniformly coated with binder.

[0111] S3. Dissolve lanthanum oxide in an alcohol solvent at a concentration of 1% and stir magnetically for 40 minutes to form a uniformly dispersed rare earth antioxidant. Add the molding agent, rare earth antioxidant, leveling agent, thickener, crosslinking agent, surfactant and epoxy resin to the solvent in proportion and stir magnetically for 60 minutes to ensure uniform mixing to prepare an organic solvent system.

[0112] S4. Add the binder-coated copper particles to the organic solvent system and stir with a magnetic stirrer for 30 minutes to ensure that the rare earth antioxidants and other organic components in the organic solvent system are evenly distributed on the surface of the copper particles, and achieve preliminary antioxidant treatment through chemical adsorption and physical coating. Place the mixture in an ultrasonic bath and ultrasonically disperse it at 26°C for 15 minutes to further enhance the adhesion and dispersion effect of the rare earth antioxidants and organic components on the surface of the copper particles. Place the treated mixture in a centrifuge, control the centrifugation speed at 5000 r / min, and centrifuge for 15 minutes. Remove the supernatant and degas it in a vacuum degassing machine for 15 minutes to obtain a uniform copper paste.

[0113] This embodiment also provides a package interconnection structure for a power device, including: a nickel-gold active metal welded ceramic substrate, a nickel-copper heat sink, and a connecting layer for connecting the nickel-gold active metal welded ceramic substrate and the nickel-copper heat sink, wherein the connecting layer is formed by double-sided coated copper paste under pressure-assisted sintering.

[0114] This embodiment also provides a method for fabricating a packaged interconnect structure for a power device, comprising the following steps:

[0115] P1. Use a lint-free cloth to clean the surface of the nickel-gold active metal welding ceramic substrate and the nickel-copper heat sink to remove surface dirt and ensure that the surface is free of grease, oxides and other contaminants in order to improve the adhesion of copper paste.

[0116] P2. Copper paste is applied to the connecting surfaces of the nickel-gold active metal welding ceramic substrate and the nickel-copper heat sink, respectively. The coating thickness is controlled within the range of 150-200μm to ensure uniform coating and provide a good foundation for subsequent sintering. The coated nickel-gold active metal welding ceramic substrate and the nickel-copper heat sink are placed in a drying oven for pre-drying. A nitrogen / argon / hydrogen / formic acid atmosphere is introduced to avoid oxidation. The drying temperature is controlled at 100-120℃ and maintained for 50 minutes to achieve preliminary curing.

[0117] P3. Following the order from top to bottom, align and tightly stack the surface of the nickel-plated gold active metal welding ceramic substrate coated with copper paste and the nickel-plated copper heat sink coated with copper paste. Place the stacked assembly on the heating table of the sintering equipment and continuously introduce a nitrogen-hydrogen mixed atmosphere to prevent the copper paste from undergoing an oxidation reaction during heating. Heat the equipment to 200-275°C and apply a pressure of 10MPa for 5 minutes to complete the sintering connection process, so that a dense and high-strength connection layer is formed between the silver-plated active metal welding ceramic substrate and the nickel-plated copper heat sink.

[0118] P4. Gradually reduce the equipment temperature and slowly cool the sintered stacked components to room temperature to ensure that the connection layer does not crack or warp during the cooling process, thus obtaining the packaged interconnect structure of the power device.

[0119] After testing, the sintered copper paste for power device packaging prepared in this embodiment exhibited excellent reliability in the connection between the nickel-gold plated active metal welding ceramic substrate and the nickel-copper plated heat sink. The connection layer thickness uniformity was good, with tests showing a maximum thickness difference of less than 18 μm. The sintered stacked structure exhibited high strength and significant high-temperature resistance. The connection layer strength after chip mounting was as follows: Figure 4 As shown in the figure, the shear strength reaches 32.4 MPa under conditions of 200℃ and 10 MPa pressure; and 54.1 MPa under conditions of 250℃ and 10 MPa pressure. The ultrasonic scanning results are as follows... Figure 5 As shown in (b) of the figure, it can be seen that the internal structure of the connection layer is defect-free and has good density, which verifies its application value in high-reliability packaging.

[0120] Example 3

[0121] This embodiment is basically the same as Embodiment 1, except that: in this embodiment, a pressure of 5 MPa is applied, while the other raw materials and preparation methods are basically the same as in Embodiment 1.

[0122] The strength of the bonding layer after chip mounting is as follows Figure 4 As shown in the figure, the shear strength reaches 30.2 MPa under the conditions of 200℃ and 5 MPa pressure; and the shear strength reaches 50.3 MPa under the conditions of 250℃ and 5 MPa pressure.

[0123] Comparative Example 1

[0124] This comparative example is basically the same as Example 1, except that: in this comparative example, copper paste is only coated on one side of the copper paste-plated silver active metal welding ceramic substrate connection surface, and the other raw materials and preparation methods are basically the same as in Example 1.

[0125] A thermal aging test at 500℃ for 200 hours revealed a significant increase in oxides at the interface of the bonding layer in the single-sided coating design. Figure 6 As shown in (ac), the oxides mainly accumulate at the interface between the substrate and the interconnect layer, and the distribution of the oxides is uneven, with more severe oxidation in the edge areas, leading to a decrease in the interfacial adhesion of the interconnect layer. In subsequent mechanical strength tests, the shear strength of the interconnect layer decreased from the initial 30 MPa to 15 MPa, indicating that interfacial oxidation has a significant impact on the strength of the interconnect layer.

[0126] In contrast, Example 1 employs a double-sided copper paste coating design, which effectively prevents the formation and accumulation of oxides at the interface by simultaneously coating the copper paste on the interface between the substrate and the heat sink. Figure 6 The (df) values ​​indicate that the bonding layer hinders the diffusion of oxides into the interior at the interface after the aging test, resulting in a uniform internal structure and good interfacial adhesion. Under the same testing conditions, its shear strength remains above 30 MPa, demonstrating significantly better reliability than the single-sided coating design.

[0127] This invention, through an innovative design of double-sided copper paste coating, significantly improves the oxidation resistance of the bonding layer, effectively preventing the formation and accumulation of oxides at the interface during high-temperature aging, thereby enhancing the strength of the bonding layer and its long-term service reliability. In contrast, single-sided coating designs fail to suppress the formation of interface oxides, resulting in a significant decrease in bonding layer strength and failing to meet the requirements of high-temperature, high-reliability packaging.

[0128] Comparative Example 2

[0129] This comparative example is basically the same as Example 1, except that: no rare earth antioxidants were added to the organic solvent system of this comparative example, and the other raw materials and preparation methods are basically the same as those in Example 1.

[0130] The comparison of shear strength at different times after high-temperature aging at 250°C under rare earth oxidant treatment in Example 1 and Comparative Example 2 without rare earth oxidant treatment is shown in the figure. Figure 7 As can be seen from the figure, the shear strength of copper paste treated with rare earth oxidant during the aging process is significantly higher than that of untreated copper paste. Rare earth oxidant effectively inhibits the generation and diffusion of oxides under high temperature environment by forming a stable anti-oxidation barrier layer on the surface of copper particles, which significantly improves the mechanical properties and long-term reliability of the bonding layer.

[0131] Comparative Example 3

[0132] This comparative example is basically the same as Example 1, except that the copper particles in this comparative example did not undergo a complexation treatment step, while the other raw materials and preparation methods are basically the same as in Example 1.

[0133] The shear strength test results of the connecting layer in Example 1 treated with a complex and in Comparative Example 3 not treated with a complex are shown in the figure. Figure 8 As can be seen from the figure, the use of complex treatment technology makes it easier for copper particles to achieve densification during sintering, thereby enhancing shear strength.

[0134] 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 above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above 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 sintering-type copper paste for power device packaging, characterized in that, The raw materials comprise the following percentages by weight: 75%-85% copper particles coated with binder, and 15%-25% organic solvent system; the organic solvent system includes rare earth antioxidants; it also includes: molding agents, leveling agents, thickeners, crosslinking agents, surfactants, solvents, and resins; the binder includes one or more of polyvinylpyrrolidone, methylcellulose, ethylcellulose, epoxy acrylate, acrylate, and cellulose acetate; the rare earth antioxidants include one or more of cerium oxide, lanthanum oxide, cerium chloride, and lanthanum nitrate; the crosslinking agents include one or more of butyl methacrylate, butyl acrylate, and polyethyleneimine.

2. The sintered copper paste for power device packaging according to claim 1, characterized in that, The organic solvent system comprises, by mass percentage: 1%-5% molding agent, 0.5%-2% leveling agent, 0.5%-1% thickener, 1%-3% rare earth antioxidant, 1%-3% crosslinking agent, 1%-2% surfactant, 85%-90% solvent and 1%-2% resin.

3. The sintered copper paste for power device packaging according to claim 1, characterized in that, The morphology of the copper particles includes one or more of the following: spherical, plate-like, or triangular; the particle size range of the copper particles is 50-2000 nm.

4. The sintered copper paste for power device packaging according to claim 1, characterized in that, The molding agent includes one or more of polyvinylidene fluoride, polyacrylate, and styrene-butadiene copolymer; the leveling agent includes one or more of sodium polyacrylate, ethoxylated modified silicone oil, and polyethylene glycol; the thickener includes one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, and sodium polyacrylate; the surfactant includes one or more of polyvinyl alcohol, polyoxyethylene octylphenol ether, and sodium dodecylbenzene sulfonate; the solvent is an alcoholic organic compound; and the resin includes one or more of polyimide resin, amino resin, and polyurethane resin.

5. The method for preparing sintered copper paste for power device packaging according to any one of claims 1-4, characterized in that, The steps include: S1. Treat the copper particles with a complex to ensure that there is no oxide layer on the surface of the copper particles; S2. Mix the copper particles treated with the complex with the binder, remove the supernatant by ultrasonic centrifugation, add anhydrous ethanol to wash, centrifuge to remove the supernatant, and obtain copper particles coated with binder. S3. Mix the molding agent, leveling agent, thickener, rare earth antioxidant, crosslinking agent, surfactant, solvent and resin, and stir evenly to obtain an organic solvent system; S4. Mix the copper particles coated with the binder obtained in step S2 with the organic solvent system obtained in step S3 to obtain the copper paste.

6. The method for preparing the sintered copper paste for power device packaging according to claim 5, characterized in that, Step S1 includes the following steps: S11. Dissolve the complexing agent in deionized water to obtain a complexing agent solution; S12. Add copper particles to the complexing agent solution obtained in step S11, so that the oxide on the surface of the copper particles reacts with the complexing agent to generate a soluble complex. S13. Centrifuge the mixture obtained in step S12 to remove the supernatant, then wash with anhydrous ethanol and centrifuge to remove the supernatant. S14. Dry the cleaned copper particles to obtain copper particles with no oxide on the surface.

7. A package interconnect structure for a power device, characterized in that, include: A substrate, a heat sink, and a connecting layer for connecting the substrate and the heat sink, the connecting layer being formed by pressure-assisted sintering of copper paste as described in any one of claims 1-4, applied on both sides.

8. The method for fabricating the packaged interconnect structure of the power device according to claim 7, characterized in that, The steps include: P1. Remove contaminants from the surface of the substrate and heat sink; P2. Apply the copper paste according to any one of claims 1-4 to the connection surface of the substrate and the heat sink, and pre-dry the coated substrate and the heat sink. P3. Align and stack the pre-dried substrate and heat sink, place the stacked assembly in the sintering equipment, heat the sintering equipment and apply pressure to complete the sintering connection process, so that a dense and high-strength connection layer is formed between the substrate and the heat sink. P4. Gradually reduce the temperature of the sintering equipment to cool the stacked components to room temperature, thereby obtaining the packaged interconnect structure of the power device.

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