Silver paste for power device package, silver film, and preparation method and application thereof

Abstract

The application provides a silver paste for power device packaging, a silver film and a preparation method and application thereof. The silver paste for power device packaging comprises, by weight, 80-90 parts of nano silver particles and 10-20 parts of an organic solvent system; the surface of the nano silver particles is coated with a surfactant selected from at least one of sodium dodecyl sulfate, Tween, polyvinylpyrrolidone, sodium citrate, sodium dodecyl benzene sulfonate and polyoxyethylene ether. The preparation method of the silver paste comprises separately preparing the nano silver particles coated with the surfactant and the organic solvent system, and then mixing. The silver paste for power device packaging has the advantages that the surface powder does not fall off, the silver film adopting the silver paste has high transfer printing quality and good integrity, the packaging of the power device can realize high-quality connection after sintering of the silver film, the risk of chip breakage is reduced, and cost reduction and efficiency increase are realized.

Description

Technical Field

[0001] This invention relates to the field of electronic packaging technology, specifically to a silver paste and silver film for power device packaging, their preparation methods, and applications. Background Technology

[0002] Power devices, also known as power semiconductor devices or power electronic devices, are high-power electronic devices (typically referring to currents ranging from tens to thousands of amperes and voltages of hundreds of volts or more) mainly used in the power conversion and control circuits of power equipment. They are used in almost all electronics manufacturing industries, including laptops, PCs, servers, monitors, and various peripherals in the computer field; mobile phones, telephones, and other terminals and central office equipment in the network communication field; traditional black and white home appliances and various digital products in the consumer electronics field; and industrial PCs, various instruments and meters, and various control equipment in the industrial control field.

[0003] With the increasing application of third-generation semiconductors, represented by SiC and GaN, in fields such as deep space exploration and rail transportation, higher demands are being placed on packaging interconnect materials. To maximize their performance, these materials need to be capable of low-temperature interconnection and high-temperature operation. Currently, nano-silver sintering technology is one effective solution, with sintered silver paste being the most widely used method. This process mainly involves silver paste stencil printing, oven drying, followed by chip thermal bonding, and finally, hot-pressing sintering for interconnection.

[0004] However, sintered silver paste presents several challenges during use, including poor surface smoothness leading to chip breakage, a printing area larger than the chip area causing excess material to detach in subsequent processes, significant organic residue from large-area printing, and complex process flows that hinder production efficiency. Sintered silver film, on the other hand, is a highly efficient and high-quality sintered silver interconnect material. Transfer technology allows the silver film to be transferred to the chip at appropriate temperature and pressure, eliminating the need for sintered silver paste printing and drying processes, greatly shortening the process time. This silver film transfer technology perfectly adapts to chip size, avoiding the risk of excess material detachment.

[0005] Currently, sintered silver films still have problems such as poor surface smoothness, powder falling off the surface after film formation, and cracking after silver film transfer. Summary of the Invention

[0006] The present invention aims to at least partially solve one of the technical problems in the prior art. To this end, one object of the present invention is to provide a silver paste for power device packaging, comprising, by weight: 80-90 parts of silver nanoparticles and 10-20 parts of an organic solvent system; wherein the surface of the silver nanoparticles is coated with a surface modifier selected from at least one of sodium dodecyl sulfate, Tween, polyvinylpyrrolidone, sodium citrate, sodium dodecylbenzenesulfonate, and polyoxyethylene ether.

[0007] The silver paste for power device packaging provided by this invention uses nano-silver particles coated with surfactants, which can effectively avoid the defect of powder falling off the surface of the silver film and achieve powder non-falling off the surface of the silver film.

[0008] In some embodiments, the surface of the nano-silver particles is coated with one of sodium dodecylbenzenesulfonate and polyvinylpyrrolidone. As a result, the problem of silver film powder falling off prepared by the silver paste provided by the present invention can be more effectively solved, the silver film transfer quality is high, the integrity is good, and the high-quality connection of sintered silver film can be well achieved.

[0009] In some embodiments, the silver nanoparticles are in the form of flakes with a particle size of 1000-2000 nm.

[0010] In some embodiments, the silver nanoparticles are spherical in shape with a particle size of 100-800 nm, preferably 300-800 nm. Using these silver nanoparticles reduces the sintering temperature.

[0011] In some embodiments, the organic solvent system comprises, by weight, 1.5-3 parts of crosslinking coupling agent, 1-3 parts of leveling agent, and 92.5-97 parts of organic solvent; preferably, the organic solvent system comprises 1.5-2 parts of crosslinking coupling agent, 1-2 parts of leveling agent, and 95-97 parts of organic solvent.

[0012] In some embodiments, the crosslinking coupling agent is selected from at least one of aldehyde compounds, silane coupling agents, titanate coupling agents, epoxy resins, polyurethanes, silicone resins, and chromium sulfate, preferably silane coupling agents or epoxy resins. Using the above-mentioned crosslinking coupling agent ensures the surface smoothness of the sintered silver film and avoids cracking.

[0013] In some embodiments, the leveling agent is selected from acrylics, preferably fluorinated acrylics and phosphate-modified acrylics. Using the above-mentioned leveling agent can further ensure the surface smoothness of the sintered silver film and prevent cracking.

[0014] In some embodiments, the organic solvent is selected from at least one of alcoholic organic compounds, preferably at least one of ethylene glycol, propylene glycol, n-butanol, diethylene glycol, acetone alcohol, and polyethylene glycol.

[0015] In some embodiments, the organic solvent system further includes 0.5-1.5 parts of a dispersant; when the organic solvent system includes the above-mentioned amount of dispersant, it can further promote the uniform dispersion of the silver nanoparticles and the stability of the silver paste, thereby improving the performance of the silver film, such as no powder shedding, smooth surface and good bonding performance; in particular, when the organic solvent system includes 0.5-1 parts of dispersant, the above effects are more obvious and prominent.

[0016] In some embodiments, the dispersant is selected from at least one of fatty acids, n-decaol, methanol, cyclohexanol, and ethanol.

[0017] In a second aspect, the present invention provides a method for preparing the silver paste, comprising: mixing nano-silver particles coated with surfactants on their surface with an organic solvent system until homogeneous, and stirring for 20-40 minutes.

[0018] The method for preparing the silver nanoparticles coated with surfactants includes:

[0019] (1) Add the nano-silver particles to ethanol for ultrasonic treatment, centrifuge to remove the supernatant, and dry under nitrogen atmosphere to obtain pretreated nano-silver particles.

[0020] (2) The surfactant and anhydrous ethanol are mixed evenly at a mass ratio of (0.5-5):(95:99.5) to obtain an ethanol solution of the surfactant;

[0021] (3) The pretreated silver particles and the ethanol solution of the surfactant are mixed at a mass ratio of (0.1-3): (97-99.9), sonicated for 10-40 min, and the supernatant is removed by centrifugation; anhydrous ethanol is added, sonicated for 5-20 min, and the supernatant is removed by centrifugation to obtain coated silver nanoparticles.

[0022] Preferably, the ultrasonic treatment time in step (1) is 5-20 min, and the drying temperature is 30-70 ℃.

[0023] Preferably, in step (2), the mixture of the surfactant and anhydrous ethanol is sonicated for at least 25 minutes.

[0024] In some embodiments, the preparation method of the organic solvent system includes: weighing the crosslinking coupling agent, dispersant, leveling agent and organic solvent in proportion, and magnetically stirring at room temperature for 30-60 minutes to make them uniformly mixed.

[0025] The present invention provides a method for preparing silver paste for power device packaging. First, nano-silver particles coated with surfactants and an organic solvent system are prepared separately, then mixed. The surfactants provide better coating on the surface of the nano-silver particles, effectively reducing local agglomeration and improving the stability and adhesion of the silver paste, preventing powder detachment after film formation. Simultaneously, the addition of a small amount of crosslinking coupling agent and leveling agent to the organic solvent system ensures the surface smoothness of the sintered silver film and prevents cracking. This effectively solves the problems of uneven surface, powder detachment, and cracking in current sintered silver films. Furthermore, pressure sintering under an inert atmosphere enables low-temperature sintering with high sintering strength, effectively meeting application requirements.

[0026] In a third aspect, the present invention provides a silver film for power device packaging, wherein the silver film is formed by using the aforementioned silver paste and / or the aforementioned silver paste preparation method.

[0027] In some embodiments, the thickness of the silver film is 50-300 μm. Using a silver film of this thickness, combined with silver paste prepared by the aforementioned silver paste preparation method, can effectively prevent the phenomenon of cracking after the silver film is partially cut.

[0028] In a fourth aspect, the present invention provides a method for preparing the silver film for power device packaging, comprising: forming a film on a carrier film using the silver paste or the silver paste preparation method, and drying it;

[0029] In some embodiments, the carrier membrane is selected from PI membranes (polyimide films). Using PI membranes as carrier membranes facilitates the separation of the silver film from the carrier membrane.

[0030] In some embodiments, the drying is carried out in an inert atmosphere at a temperature of 100-160°C for 10-60 minutes. Drying at this temperature achieves efficient drying while also providing an anti-oxidation effect.

[0031] In some embodiments, the inert atmosphere is selected from at least one of nitrogen, helium, and argon atmospheres. Drying in an inert atmosphere has an anti-oxidation effect.

[0032] The silver film provided by this invention, prepared by a method that achieves high surface flatness after sintering, avoiding the risk of chip breakage; the powder on the surface of the silver film does not fall off after sintering, resulting in good bonding performance; and it does not crack after transfer, ensuring the integrity of the sintered silver film.

[0033] A fifth aspect of the present invention provides a power device packaging method, comprising:

[0034] (a) Using the edge of the chip, cut out a silver film of the same area as the back of the chip and / or a silver film obtained by the preparation method, so that the silver film is detached from the carrier film and attached to the back of the chip;

[0035] (b) Heat the copper-clad ceramic to 90-140°C, and attach the chip and silver film to the surface of the copper-clad ceramic with a pressure of 3-10 MPa;

[0036] (c) The chip-silver film-copper-clad ceramic substrate is pressure-sintered in an inert atmosphere;

[0037] In step (c), the sintering conditions are: sintering temperature of 190-250 ℃, sintering pressure of 5-20 MPa, and sintering time of 1-15 min.

[0038] Pressure sintering under an inert atmosphere enables low-temperature sintering with high sintering strength, effectively meeting application requirements. Silver films prepared using the aforementioned methods achieve high surface smoothness after sintering, avoiding the risk of chip breakage; the powder on the sintered silver film does not detach, resulting in good adhesion; and it does not crack after transfer, ensuring the integrity of the sintered silver film.

[0039] Compared with existing technologies, the present invention has at least the following advantages: The silver paste for power device packaging provided by the present invention uses nano-silver particles coated with surfactants, or its preparation method first uses surfactants to coat the surface of nano-silver particles, and then prepares the nano-silver paste with an organic solvent system. This effectively prevents particle agglomeration, thereby improving the stability of the paste and the coating adhesion, preventing powder detachment after film formation. Furthermore, the addition of a small amount of crosslinking coupling agent and leveling agent to the organic solvent system ensures the surface smoothness of the sintered silver film and avoids cracking. The silver paste, silver film, and their preparation method for power device packaging provided by the present invention effectively solve the problems of uneven surface, powder detachment, and cracking after silver film sintering. In addition, the power device packaging method provided by the present invention uses the aforementioned silver film and performs pressure sintering under an inert atmosphere, achieving low-temperature sintering with high sintering strength, effectively meeting usage requirements. Simultaneously, using the sintered silver film of the present invention can greatly reduce the sintering process, achieve low-temperature sintering interconnection, reduce the risk of chip breakage, and achieve cost reduction and efficiency improvement. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0041] Figure 1 One of the preparation flowcharts of the silver paste for power device packaging provided by the present invention.

[0042] Figure 2 One of the process flow diagrams for preparing a silver film for power device packaging provided by the present invention.

[0043] Figure 3 One of the sintering flowcharts in the power device packaging method provided by the present invention.

[0044] Figure 4 One of the bar charts showing the shear strength results of the silver film after sintering in the power device packaging method provided by this invention.

[0045] Figure 5 One of the schematic diagrams of ultrasonic non-destructive testing after silver film sintering in the power device packaging method provided by the present invention.

[0046] Figure 6 The second schematic diagram of ultrasonic non-destructive testing after silver film sintering in the power device packaging method provided by this invention.

[0047] Figure 7 The third schematic diagram of ultrasonic non-destructive testing after silver film sintering in the power device packaging method provided by this invention.

[0048] Figure 8 One of the schematic diagrams of ultrasonic non-destructive testing after silver film sintering in the comparative example of the power device packaging method provided by the present invention. Detailed Implementation

[0049] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0050] In order to overcome the problems that still exist in existing sintered silver films, such as poor surface smoothness, powder falling off the surface after film formation, and cracking after silver film transfer.

[0051] In a first aspect, the present invention provides a silver paste for power device packaging, comprising, by weight: 80-90 parts of nano-silver particles and 10-20 parts of an organic solvent system, preferably a total of 100 parts.

[0052] The surface of the nano-silver particles is coated with a surface modifier selected from at least one of sodium dodecyl sulfate, Tween, polyvinylpyrrolidone, sodium citrate, sodium dodecylbenzenesulfonate, and polyoxyethylene ether. Preferably, the surface modifier is sodium dodecylbenzenesulfonate or polyvinylpyrrolidone.

[0053] The nano-silver particles are in the form of flakes, with a particle size of 1000-2000 nm, such as 1000 nm, 1500 nm, 2000 nm, etc., and the range of their composition.

[0054] The nano-silver particles are spherical in shape and have a particle size of 100-800 nm, preferably 300-800 nm, such as 300 nm, 400 nm, 500 nm, 800 nm, etc., and the range of their composition.

[0055] In some embodiments, the organic solvent system comprises, by weight: 1.5-3 parts crosslinking coupling agent, 1-3 parts leveling agent, 0.5-1.5 parts dispersant, and 92.5-97 parts organic solvent. Preferably, the total amount is 100 parts.

[0056] In some embodiments, the organic solvent system comprises: 1.5-2 parts of crosslinking coupling agent, 1-2 parts of leveling agent, 0.5-1 parts of dispersant, and 95-97 parts of organic solvent. Preferably, the total amount is 100 parts.

[0057] The crosslinking coupling agent is selected from at least one of aldehyde compounds, silane coupling agents, titanate coupling agents, epoxy resins, polyurethanes, silicone resins, and chromium sulfate, preferably silane coupling agents or epoxy resins; the leveling agent is selected from one of acrylic acids, preferably fluorinated acrylic acid and phosphate-modified acrylic acid; the organic solvent is selected from at least one of alcoholic organic compounds, preferably at least one of ethylene glycol, propylene glycol, n-butanol, diethylene glycol, acetone alcohol, and polyethylene glycol; the dispersant is selected from at least one of fatty acids, n-decanol, methanol, cyclohexanol, and ethanol.

[0058] The embodiments of this invention also provide a method for preparing the above-mentioned silver paste for power device packaging, such as... Figure 1 As shown, it includes the following steps:

[0059] (1) Add the nano-silver particles to ethanol and sonicate for 5-20 min, preferably 5-15 min (such as 5 min, 10 min, 15 min, etc. and the time range thereof), centrifuge to remove the supernatant, and dry under nitrogen atmosphere at a temperature of 30-70℃ (preferably 40-60℃, specifically 40℃, 50℃, 60, etc. and the temperature range thereof) to obtain pretreated nano-silver particles;

[0060] (2) Mix the surfactant with anhydrous ethanol at a mass ratio of (0.5-5): (95:99.5) (e.g., 0.5:99.5, 1:99, 2:98, 3:97, 4:96, 5:95, etc. and the range of their composition). The mixing method is not limited. Mix until the mixture is homogeneous. The method includes, but is not limited to, sonication for at least 25 minutes.

[0061] (3) The pretreated silver particles obtained in step (1) are mixed with the ethanol solution of the surfactant obtained in step (2) at a mass ratio of (0.1-3):(97-99.9) (e.g., 0.1:99.9, 0.5:99.5, 1:99, 2:98, 3:97, etc. and their composition ranges), and ultrasonicated for 10-40 min (e.g., 10 min, 20 min, 30 min, 40 min, etc. and their composition ranges), and the supernatant is removed by centrifugation; anhydrous ethanol is added, and ultrasonicated for 5-20 min (e.g., 5 min, 10 min, 15 min, 20 min, etc. and their composition ranges), and the supernatant is removed by centrifugation to obtain surfactant-coated silver nanoparticles;

[0062] (4) Weigh the crosslinking coupling agent, dispersant, leveling agent and organic solvent according to the proportion, and stir magnetically at room temperature for 30-60 minutes to make them evenly mixed to obtain the required organic solvent system;

[0063] (5) Mix the coated silver nanoparticles obtained in step (3) with the organic solvent system obtained in step (4) and stir for 20-40 minutes to obtain the silver paste for power device packaging.

[0064] The silver paste for power device packaging provided by this invention uses nano-silver particles coated with surfactants, or a preparation method in which surfactants are first used to coat the surface of nano-silver particles, and then the nano-silver paste is prepared together with an organic solvent system. This can effectively prevent particle agglomeration, thereby improving the stability of the paste and the coating adhesion, so that no powder falls off after film formation. In addition, the addition of a small amount of crosslinking coupling agent and leveling agent to the organic solvent system ensures the surface smoothness of the sintered silver film and avoids cracking.

[0065] The present invention also provides a silver film for power device packaging, which is formed by using the silver paste for power device packaging or the silver paste obtained by the aforementioned preparation method of silver paste for power device packaging, and the thickness of the silver film is 50-300μm.

[0066] The present invention also provides a method for preparing the above-mentioned silver film for power device packaging, which employs a coating process and nitrogen atmosphere-assisted film formation, and the preparation process is as follows: Figure 2 As shown, the specific steps are as follows:

[0067] (1) Add the prepared nano silver paste to the storage tank, run the base belt, and make the carrier film flow through the scraper to level it. Control the thickness of the silver film to be 50-300μm, such as 50μm, 100μm, 150μm, 200μm, 250μm, 300μm, etc. and the thickness range of their composition.

[0068] (2) Introduce nitrogen atmosphere into the drying chamber to make it an inert atmosphere. Control the temperature of the drying chamber to 100-160℃, such as 100℃, 120℃, 140℃, 150℃, 160℃, etc. and the temperature ranges they form.

[0069] (3) Adjust the baseband running speed so that the nano silver paste is kept in the drying oven for 10-60 minutes, such as 10 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, etc., and the time range of their composition;

[0070] (4) A sintered silver film is obtained after passing through a drying oven.

[0071] In a specific embodiment, the carrier film can be selected from PI film; the inert atmosphere can be one of nitrogen atmosphere, helium atmosphere, and argon atmosphere.

[0072] The silver paste, silver film and preparation method for power device packaging provided by the present invention effectively solve the problems of uneven surface, powder fall-off and cracking after sintering of silver film.

[0073] This invention also provides a power device packaging method, the process of which is as follows: Figure 3 As shown, the specific steps are as follows:

[0074] (1) Use a vacuum pick-up head that can apply pressure to pick up the chip and apply a certain pressure. Use the chip edge to cut out a silver film with the same area as the back of the chip, so that it is separated from the PI film and attached to the back of the chip.

[0075] (2) Place the copper-clad ceramic on a heating table and heat it to 90-140℃ (such as 90℃, 100℃, 110℃, 120℃, 130℃, 140℃ and other temperature ranges). Then attach the chip and silver film to the surface of the copper-clad ceramic with a pressure of 3-10MPa (such as 3MPa, 5MPa, 8MPa, 10MPa and other pressure ranges).

[0076] (3) The chip-sintered silver film-copper-clad ceramic substrate is pressurized and sintered in an inert atmosphere to obtain the power device packaging structure;

[0077] Specifically, in step (3), the sintering conditions include: a sintering temperature of 190-250℃ (such as 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, etc., and temperature ranges thereof), a sintering pressure of 5-20MPa (such as 5MPa, 10MPa, 15MPa, 20MPa, etc., and pressure ranges thereof), and a sintering time of 1-15 min (such as 1min, 3min, 5min, 10min, 12min, 15min, etc., and time ranges thereof). For example, the sintering temperature is 250℃, the sintering pressure is 20MPa, and the sintering time is 3min; or, the sintering temperature is 250℃, the sintering pressure is 15MPa, and the sintering time is 3min; or, the sintering temperature is 250℃, the sintering pressure is 10MPa, and the sintering time is 3min.

[0078] The power device packaging method provided by this invention uses the aforementioned silver film and performs pressure sintering in an inert atmosphere, which can achieve low-temperature sintering and high sintering strength, effectively meeting the application requirements. At the same time, using the sintered silver film of this invention can greatly reduce the sintering process, achieve low-temperature sintering interconnection, reduce the risk of chip breakage, and achieve cost reduction and efficiency improvement.

[0079] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0080] Example 1

[0081] This embodiment provides a silver paste for power device packaging, which is composed of silver nanoparticles coated with a surface modifier and an organic solvent system; wherein, the silver nanoparticles coated with the surface modifier have a particle size of 800 nm, and the organic solvent system is composed of cyclohexanol, epoxy resin, phosphate-modified acrylic acid, ethylene glycol, and propylene glycol in a mass ratio of 1:1.5:2:30:30:35.5.

[0082] This embodiment also provides a method for preparing the silver paste for packaging the power device, the steps of which are as follows:

[0083] (1) Pretreatment of nano-silver metal particles

[0084] The nano-silver spherical particles (800 nm in diameter) were mixed with an ethanol solution and ultrasonically treated for 10 min. The supernatant was removed by centrifugation to obtain pretreated silver particles.

[0085] (2) Coating treatment with nano-silver metal particles

[0086] The pretreated silver particles were mixed with a sodium dodecyl sulfate ethanol solution at a mass ratio of 2:98. The mixture was ultrasonically treated for 30 minutes, and the supernatant was removed by centrifugation to obtain coated silver particles. The coated silver particles were then mixed with the ethanol solution according to the specified proportions, ultrasonically treated for 40 minutes, and the supernatant was removed by centrifugation to obtain the coated silver particles again.

[0087] (3) Preparation of organic solvent system

[0088] Cyclohexanol, epoxy resin, phosphate-modified acrylic acid, ethylene glycol, and propylene glycol were mixed in a mass ratio of 1:1.5:2:30:30:35.5 and then magnetically stirred for 1 hour to obtain an organic solvent system.

[0089] (4) Preparation of nano silver paste

[0090] After mixing the coated metal particles from step (2) with the organic solvent system from step (3), the mixture was stirred in a vacuum degassing machine for 20 minutes to obtain nano silver paste.

[0091] Example 2

[0092] This embodiment provides a silver film for power device packaging, which is formed using the silver paste provided in Embodiment 1.

[0093] This embodiment also provides a method for preparing the silver film for power device packaging, including the following steps:

[0094] (a) Coating

[0095] Add the prepared nano-silver paste to the storage tank, rotate the substrate to make the carrier film flow level as it passes through the scraper, and control the thickness of the sintered silver film to be 100 μm.

[0096] (ii) Drying and film formation

[0097] Adjust the baseband running speed to keep the nano-silver paste in a nitrogen atmosphere in a drying oven for 30 minutes, then dry it to form a film, thus obtaining a silver film for power device packaging.

[0098] Example 3

[0099] This embodiment provides a power device packaging method, including the following steps:

[0100] (a) Silver film transfer

[0101] Use a pressure-applying vacuum tip to pick up 3×3mm 2 The chip utilizes the chip edge effect to pick up the silver film of the corresponding size in Example 2 and applies 5MPa to make the silver film detach from the PI film.

[0102] (b) Heat the copper-clad ceramic to 140°C and transfer the chip and silver film to the surface of the copper-clad ceramic substrate at 140°C. Apply a pressure of 5 MPa for 2 seconds to allow the silver film to adhere to the surface of the copper-clad ceramic.

[0103] (c) Sintering

[0104] The chip is placed on the corresponding silver film to form a chip-sintered silver film-copper-clad ceramic substrate structure. The structure is placed in a sintering machine under a nitrogen atmosphere and sintered for 3 minutes at a sintering temperature of 250℃ and a sintering pressure of 20MPa.

[0105] Example 4

[0106] This embodiment provides a power device packaging method, which is basically the same as that in Embodiment 3, except that the nano-silver is in the form of sheet-like particles with a particle size of 1500nm and a sintering pressure of 10MPa.

[0107] Example 5

[0108] This embodiment provides a power device packaging method, which is basically the same as that in embodiment 3, except that the sintering pressure is 15MPa.

[0109] Comparative Example 1

[0110] This embodiment provides a power device packaging method, which is basically the same as that in Embodiment 3. The only difference is that the silver paste used to prepare the silver film is not pre-treated with a surface modifier to coat the nano-silver particles, but is directly added together with the raw materials in the organic solvent system.

[0111] Test case

[0112] Test subjects: sintered silver films obtained from Examples 3, 4, 5 and Comparative Example 1.

[0113] Test method:

[0114] (1) The shear strength of the sintered silver film was tested; the shear strength of the sintered silver film was used to characterize the bonding performance. The larger the value, the better the bonding performance.

[0115] (2) Ultrasonic non-destructive testing was performed on the sintered silver film to observe the surface flatness, powder shedding and cracking of the sintered silver film. The frequency of the ultrasonic non-destructive testing probe was 15 Hz, and the distance between the sample and the probe was 5 mm during scanning. No other special requirements were made. Four parallel samples were taken for each sample for testing.

[0116] Experimental results:

[0117] (1) The shear strength of the sintered silver films in Examples 3-5 is as follows: Figure 4As shown, the results of ultrasonic non-destructive testing are as follows: Figure 5-7 As shown.

[0118] (2) Ultrasonic non-destructive testing of the sintered silver film in Comparative Example 1 Figure 8 As shown.

[0119] from Figure 4 As can be seen, the silver film sintered (sintering pressure 20 MPa) in Example 3 has a shear strength of over 70 MPa, the silver film sintered (sintering pressure 10 MPa) in Example 4 has a shear strength of over 50 MPa, and the silver film sintered (sintering pressure 15 MPa) in Example 5 has a shear strength of over 60 MPa. These results demonstrate that coating the silver nanoparticles with a surface modifier before mixing them with raw materials in an organic solvent system, and then using the resulting silver paste to form silver films for subsequent power device packaging, significantly improves the shear strength of the sintered silver film. This further illustrates that coating the silver nanoparticles with a surface modifier significantly improves packaging performance.

[0120] from Figure 5-7 As can be seen from the results, the silver films sintered in Examples 3-5 showed uniform surface color after ultrasonic non-destructive testing, indicating that the silver film had high surface flatness, uniform thickness and density, no powder shedding, and no cracking after transfer. Figure 8 The results show that the silver film obtained in Comparative Example 1 has an uneven color, indicating that the sintered silver film in Comparative Example 1 may have defects such as uneven thickness, uneven flatness, and uneven density. The above results show that compared with Comparative Example 1 (the surface modifier and raw materials are added together with the organic solvent system), Examples 3-5 of the present invention (pre-treating and coating the nano-silver particles with the surface modifier first) can significantly improve the performance of the silver film, especially the uniformity of thickness, flatness, and density after transfer and sintering.

[0121] In summary, the power device packaging method proposed in this embodiment of the invention can simplify the sintering process, improve sintering quality, reduce the risk of chip breakage, and achieve cost reduction and efficiency improvement.

[0122] 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 of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silver paste for power device packaging, characterized by, According to weight parts, it comprises: nano silver particles 80-90 parts and organic solvent system 10-20 parts; wherein, the surface of the nano silver particles is coated with sodium dodecyl sulfate; According to weight parts, the organic solvent system comprises: cross-linking coupling agent 1.5-3 parts, leveling agent 1-3 parts, dispersing agent 0.5-1.5 parts, and organic solvent 92.5-97 parts; The cross-linking coupling agent is epoxy resin; The leveling agent is phosphate modified acrylic acid; The dispersing agent is cyclohexanol.

2. The silver paste for power device packaging according to claim 1, wherein The morphology of the nano silver particles is flaky, and the particle size is 1000-2000 nm.

3. The silver paste for power device packaging according to claim 1, wherein The morphology of the nano silver particles is spherical, and the particle size is 100-800 nm.

4. The silver paste for power device packaging according to claim 3, wherein The particle size of the nano silver particles is 300-800 nm.

5. The silver paste for power device encapsulation according to any one of claims 1 to 4, wherein The organic solvent system comprises: cross-linking coupling agent 1.5-2 parts, leveling agent 1-2 parts, and organic solvent 95-97 parts.

6. The silver paste for power device encapsulation according to claim 1, wherein The organic solvent is selected from at least one of the alcohol organic substances.

7. The silver paste for power device encapsulation according to claim 6, wherein The organic solvent is at least one of ethylene glycol, propylene glycol, n-butanol, diethylene glycol, acetone alcohol and polyethylene glycol.

8. A method for the preparation of the silver paste according to any one of claims 1 to 7, characterized in that, It comprises: Mixing the nano silver particles coated with surfactant and the organic solvent system uniformly, stirring for 20-40 min; The preparation method of the nano silver particles coated with surfactant comprises: (1) adding nano silver particles into ethanol for ultrasonic treatment, centrifuging to remove supernatant, and drying under nitrogen atmosphere to obtain pretreated nano silver particles; (2) mixing the surfactant and anhydrous ethanol uniformly according to a mass ratio of (0.5-5):(95:99.5) to obtain an ethanol solution of the surfactant; (3) mixing the pretreated nano silver particles and the ethanol solution of the surfactant according to a mass ratio of (0.1-3):(97-99.9), ultrasonic treatment for 10-40 min, centrifuging to remove supernatant, adding anhydrous ethanol, ultrasonic treatment for 5-20 min, centrifuging to remove supernatant, and obtaining coated nano silver particles; In step (1), the ultrasonic treatment time is 5-20 min, and the drying temperature is 30-70 ℃; In step (2), the mixture of the surfactant and anhydrous ethanol is ultrasonic treated for at least 25 min.

9. The preparation method according to claim 8, characterized in that, The preparation method of the organic solvent system comprises: weighing the cross-linking coupling agent, the dispersing agent, the leveling agent and the organic solvent according to the proportion, magnetically stirring at room temperature for 30-60 min, and mixing uniformly.

10. A silver film for power device packaging, characterized by, The silver paste obtained by the preparation method of any one of claims 1-7 or claim 8 or 9 is formed into a film.

11. The silver film for power device packaging according to claim 10, wherein The thickness of the silver film is 50-300 μm.

12. The method of claim 10 or 11, wherein the silver film for power device packaging is prepared by a process comprising: It comprises: The silver paste obtained by the preparation method of any one of claims 1-7 or claim 8 is formed into a film on a carrier film and dried.

13. The method for preparing a silver film for power device packaging according to claim 12, characterized in that, The carrier film is selected from a PI film.

14. The method for preparing a silver film for power device packaging according to claim 12, characterized in that, The drying is performed in an inert atmosphere at a temperature of 100-160 ℃ for 10-60 min.

15. The method for preparing a silver film for power device packaging according to claim 14, characterized in that, The inert atmosphere is selected from at least one of a nitrogen atmosphere, a helium atmosphere and an argon atmosphere.

16. A method of packaging a power device, comprising: It comprises: (a) cutting a silver film with the same area as the back of the chip from the edge of the chip, removing the silver film from the carrier film, and attaching the silver film to the back of the chip; the silver film is the silver film of claim 10 or 11 or the silver film obtained by the preparation method of any one of claims 12-15; (b) heating the copper-coated ceramic to 90-140℃, and attaching the chip and the silver film to the surface of the copper-coated ceramic at a pressure of 3-10 MPa; (c) pressure sintering the chip-silver film-copper-coated ceramic substrate in an inert atmosphere; wherein in step (c), the sintering conditions are: a sintering temperature of 190-250℃, a sintering pressure of 5-20 MPa, and a sintering time of 1-15 min.

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