Silver paste and silver film for packaging power device and preparation method and application of silver paste and silver film

Abstract

The invention provides silver paste and a silver film for packaging a power device as well as a preparation method and application of the silver paste and the silver film. The silver paste for packaging the power device, provided by the invention, comprises the following components in parts by weight: 80-90 parts of nano-silver particles and 10-20 parts of an organic solvent system, the surfaces of the nano-silver particles are coated with at least one surfactant selected from lauryl sodium sulfate, Tween, polyvinylpyrrolidone, sodium citrate, sodium dodecyl benzene sulfonate and polyoxyethylene ether. The preparation method of the silver paste provided by the invention comprises the following steps: respectively preparing the nano-silver particles coated with the surfactant on the surfaces and the organic solvent system, and then mixing the nano-silver particles and the organic solvent system. According to the silver paste for packaging the power device, the powder on the surface does not fall off, a silver film adopting the silver paste is high in transfer printing quality and good in integrity, and high-quality connection can be achieved after the silver film is sintered for packaging the power device; the chip breaking risk is reduced, and cost reduction and efficiency improvement are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic packaging, and particularly relates to a silver paste, a silver film for power device packaging, and a preparation method and application thereof. Background Art

[0002] Power devices, also known as power semiconductor devices or power electronic devices (Power Electronic Device), are mainly used for power conversion and control circuits of power equipment, and are high-power electronic devices (usually referring to currents of dozens to thousands of amperes and voltages of more than several hundred volts). They are used in almost all electronic manufacturing industries, including laptops, PCs, servers, monitors, and various peripherals in the computer field; mobile phones, telephones, and other various terminals and central office equipment in the network communication field; traditional black and white household appliances and various digital products in the consumer electronics field; industrial PCs, various instruments, and various control devices in the industrial control category, etc.

[0003] With the increasingly wide application of the third-generation semiconductors represented by SiC and GaN in deep space exploration, rail transit, etc., higher requirements are put forward for packaging interconnect materials. In order to maximize their working performance, the packaging interconnect materials need to have the performance of low-temperature interconnection and high-temperature service. At present, the nano-silver sintering technology is one of the effective solutions, and sintered silver paste is the most widely used form at present, mainly including screen printing of silver paste, drying in an oven, then chip thermal bonding, and finally thermocompression sintering interconnection.

[0004] However, there are problems in the use of sintered silver paste, such as poor surface flatness leading to the risk of chip breakage, the printing area being larger than the chip area resulting in the risk of shedding of excess materials in subsequent process flows, a large amount of organic matter residue under large-area printing of sintered silver paste, and multiple process flows being unable to improve production efficiency. Sintered silver film is a very efficient and high-quality sintered silver interconnect material. The silver film can be transferred to the chip at a suitable temperature and pressure by using a transfer printing technology, avoiding the printing and drying processes of sintered silver paste, greatly shortening the process flow. The silver film transfer printing technology can perfectly adapt to the chip size and avoid the risk of shedding of excess materials.

[0005] At present, there are still problems with sintered silver films, such as poor surface flatness of the formed film, powder falling off the surface after film formation, and cracking after silver film transfer printing. Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems in the prior art to some extent. For this purpose, an object of the present invention is to provide a silver paste for power device packaging, which, by weight, comprises: 80-90 parts of nano silver particles and 10-20 parts of an organic solvent system; wherein, 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.

[0007] The silver paste for power device packaging provided by the present invention uses nano silver particles coated with a surfactant on the surface, which can effectively avoid the defect of powder falling off the surface of the silver film and achieve no powder 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. Thus, the problem of powder falling off the silver film prepared with the silver paste provided by the present invention can be more effectively solved, the silver film has high transfer quality and good integrity, and high-quality connection of the sintered silver film can be well achieved.

[0009] In some embodiments, the nano silver particles are in a flake shape with a particle size of 1000-2000 nm.

[0010] In some embodiments, the nano silver particles are in a spherical shape with a particle size of 100-800 nm, preferably 300-800 nm. Using such nano silver particles has the effect of reducing the sintering temperature.

[0011] In some embodiments, by weight, the organic solvent system comprises: 1.5-3 parts of a crosslinking coupling agent, 1-3 parts of a leveling agent, and 92.5-97 parts of an organic solvent; preferably, when the organic solvent system comprises: 1.5-2 parts of a crosslinking coupling agent, 1-2 parts of a leveling agent, and 95-97 parts of an 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 chrome alum, preferably a silane coupling agent or an epoxy resin. Using the above crosslinking coupling agent ensures the surface flatness of the sintered silver film and avoids the cracking phenomenon.

[0013] In some embodiments, the leveling agent is selected from one of acrylic acids, preferably fluorine-modified acrylic acid and phosphate-modified acrylic acid. Using the above leveling agent can further ensure the surface flatness of the sintered silver film and avoid the cracking phenomenon.

[0014] In some embodiments, the organic solvent is selected from at least one of alcohol-based 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 comprises 0.5 - 1.5 parts of a dispersant; when the organic solvent system further comprises a dispersant in the above content, the dispersion uniformity of the silver nanoparticles and the stability of the silver paste can be further promoted, thereby improving the performance of the silver film formed, such as no powder shedding, smooth surface, and good connection performance, etc.; in particular, when the organic solvent system comprises 0.5 - 1 part of the dispersant, the above effects are more obvious and prominent.

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

[0017] In the second aspect of the present invention, there is provided a method for preparing the silver paste, comprising: uniformly mixing silver nanoparticles coated with a surfactant and an organic solvent system, and stirring for 20 - 40 min.

[0018] Among them, the method for preparing the silver nanoparticles coated with a surfactant comprises: (1) Adding silver nanoparticles to ethanol for ultrasonic treatment, centrifuging to remove the supernatant, and drying under a nitrogen atmosphere to obtain pretreated silver nanoparticles; (2) Mixing the surfactant and absolute 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 silver particles and the ethanol solution of the surfactant according to a mass ratio of (0.1 - 3):(97 - 99.9), ultrasonicating for 10 - 40 min, and centrifuging to remove the supernatant; adding absolute ethanol, ultrasonicating for 5 - 20 min, and centrifuging to remove the supernatant to obtain coated silver nanoparticles.

[0019] Preferably, in step (1), the ultrasonic treatment time is 5 - 20 min, and the drying temperature is 30 - 70 °C.

[0020] Preferably, in step (2), the mixture of the surfactant and absolute ethanol is ultrasonically treated for at least 25 min.

[0021] In some embodiments, the method for preparing the organic solvent system comprises: weighing a crosslinking coupling agent, a dispersant, a leveling agent, and an organic solvent in proportion, and magnetically stirring at room temperature for 30 - 60 min to make them uniformly mixed.

[0022] The preparation method of the silver paste for power device packaging provided by the present invention first separately prepares nano silver particles with a surfactant coated on the surface and an organic solvent system, and then mixes them. The surfactant has a better coating effect on the surface of the nano silver particles, can more effectively improve the local agglomeration of the nano silver particles, thereby improving the stability of the silver paste and the coating bonding force, and preventing the powder from falling off after film formation. At the same time, adding a small amount of cross-linking coupling agent and leveling agent in the organic solvent system ensures the surface flatness of the sintered silver film and avoids cracking. It effectively solves the problems such as the uneven surface of the current sintered silver film, powder shedding, and cracking of the sintered silver film. In addition, pressure sintering is carried out in an inert atmosphere, which can achieve low-temperature sintering with a relatively high sintering strength, effectively meeting the usage requirements.

[0023] In the third aspect of the present invention, there is provided a silver film for power device packaging, which is formed by using the silver paste prepared by the aforementioned silver paste and / or the preparation method of the aforementioned silver paste.

[0024] In some embodiments, the thickness of the silver film is 50 - 300 μm. Using a silver film with this thickness, combined with the silver paste obtained by using the aforementioned silver paste or the preparation method of the aforementioned silver paste, the phenomenon of cracking of the silver film after sintering can be effectively avoided.

[0025] In the fourth aspect of the present invention, there is provided a preparation method of the silver film for power device packaging, including: forming a film of the silver paste obtained by using the aforementioned silver paste or the preparation method of the aforementioned silver paste on a carrier film and drying. In some embodiments, the carrier film is selected from a PI film (polyimide film). Selecting a PI film as the carrier film is beneficial to the separation of the silver film from the carrier film.

[0026] In some embodiments, the drying is carried out in an inert atmosphere at a temperature of 100 - 160 °C for 10 - 60 min. Drying at this temperature can achieve efficient drying and at the same time achieve the effect of anti-oxidation.

[0027] In some embodiments, the inert atmosphere is selected from at least one of a nitrogen atmosphere, a helium atmosphere, and an argon atmosphere. Drying in an inert atmosphere has the effect of anti-oxidation.

[0028] The silver film provided by the present invention and the silver film obtained by its preparation method achieve a high surface flatness after sintering of the silver film, avoiding the risk of chip breakage; the powder on the surface of the silver film does not fall off after sintering, and the connection performance is good; it does not crack after transfer printing, ensuring the integrity of the sintered silver film.

[0029] In the fifth aspect of the present invention, there is provided a power device packaging method, including: (a) Cutting the silver film and / or the silver film obtained by the preparation method with the same area as the back of the chip from the edge of the chip, detaching the silver film from the carrier film, and attaching it to the back of the chip. (b)Heat the copper-clad ceramic to 90 - 140 °C, and attach the chip and the silver film to the surface of the copper-clad ceramic under a pressure of 3 - 10 MPa; (c)Pressurized sintering of the chip-silver film-copper-clad ceramic substrate is carried out in an inert atmosphere; Among them, in step (c), the sintering conditions are: the sintering temperature is 190 - 250 °C, the sintering pressure is 5 - 20 MPa, and the sintering time is 1 - 15 min.

[0030] Performing pressure sintering in an inert atmosphere can achieve low-temperature sintering with relatively high sintering strength, effectively meeting the usage requirements. Using the aforementioned silver film or the silver film obtained by the preparation method, a high surface flatness of the silver film after sintering is achieved, avoiding the risk of chip breakage; the powder on the surface of the silver film does not fall off after sintering, and the connection performance is good; it does not crack after transfer printing, ensuring the integrity of the sintered silver film.

[0031] Compared with the prior art, 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 a surfactant on the surface or in its preparation method, first coats the surface of the nano-silver particles with a surfactant, and then jointly prepares a nano-silver paste with an organic solvent system, which can effectively prevent particle agglomeration, thereby improving the stability of the paste and the coating adhesion, so that no powder shedding occurs after film formation, and a small amount of cross-linking coupling agent and leveling agent are added to the organic solvent system to ensure the surface flatness of the sintered silver film and avoid cracking. The silver paste, silver film and their preparation methods for power device packaging provided by the present invention effectively solve the problems such as uneven surface, powder shedding, and cracking of the silver film after sintering. In addition, the power device packaging method provided by the present invention uses the aforementioned silver film and performs pressure sintering in an inert atmosphere, which can achieve low-temperature sintering with relatively high sintering strength, effectively meeting the usage requirements; at the same time, using the sintered silver film of the present invention can greatly reduce the sintering process flow, realize low-temperature sintering interconnection, reduce the risk of chip breakage, and achieve cost reduction and efficiency increase. Description of the Drawings

[0032] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0033] Figure 1 One of the preparation flowcharts of the preparation method of the silver paste for power device packaging provided by the present invention.

[0034] Figure 2 One of the preparation flowcharts of the preparation method of the silver film for power device packaging provided by the present invention.

[0035] Figure 3 One of the sintering flowcharts in the power device packaging method provided by the present invention.

[0036] Figure 4 One of the bar charts of the shear strength results after silver film sintering in the power device packaging method provided by the present invention.

[0037] Figure 5 One of the schematic diagrams of ultrasonic nondestructive testing after silver film sintering in the power device packaging method provided by the present invention.

[0038] Figure 6 One of the schematic diagrams of ultrasonic nondestructive testing after silver film sintering in the power device packaging method provided by the present invention.

[0039] Figure 7 One of the schematic diagrams of ultrasonic nondestructive testing after silver film sintering in the power device packaging method provided by the present invention.

[0040] Figure 8 One of the schematic diagrams of ultrasonic nondestructive testing after silver film sintering in the comparative example of the power device packaging method provided by the present invention. Specific embodiments

[0041] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of the present invention.

[0042] In order to overcome the problems existing in the existing sintered silver film, such as poor surface flatness of the formed film, powder falling off the surface after film formation, and cracking after silver film transfer.

[0043] In the first aspect of the present invention, a silver paste for power device packaging is proposed. By weight, it includes: 80-90 parts of nano-silver particles and 10-20 parts of an organic solvent system, preferably with a total amount of 100 parts.

[0044] Among them, 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 modification is one of sodium dodecylbenzenesulfonate and polyvinylpyrrolidone.

[0045] When the morphology of the nano-silver particles is flaky, its particle size is 1000-2000 nm, such as 1000 nm, 1500 nm, 2000 nm, etc. and the range composed thereof.

[0046] When the morphology of the silver nanoparticles is spherical, their particle size is 100 - 800 nm, preferably 300 - 800 nm, such as 300 nm, 400 nm, 500 nm, 800 nm, etc. and the ranges composed of them.

[0047] In some embodiments, by weight, the organic solvent system includes: 1.5 - 3 parts of a cross - linking coupling agent, 1 - 3 parts of a leveling agent, 0.5 - 1.5 parts of a dispersant, and 92.5 - 97 parts of an organic solvent. The total amount is preferably 100 parts.

[0048] In some embodiments, the organic solvent system includes: 1.5 - 2 parts of a cross - linking coupling agent, 1 - 2 parts of a leveling agent, 0.5 - 1 part of a dispersant, and 95 - 97 parts of an organic solvent. The total amount is preferably 100 parts.

[0049] Among them, the cross - linking coupling agent is selected from at least one of aldehyde compounds, silane coupling agents, titanate coupling agents, epoxy resins, polyurethanes, silicone resins, and chrome alum, preferably a silane coupling agent or an epoxy resin; the leveling agent is selected from one of acrylic acids, preferably fluorine - modified acrylic acid and phosphate - modified acrylic acid; the organic solvent is selected from at least one of alcohol - based 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.

[0050] The embodiment part of the present invention also provides a preparation method of the silver paste for power device packaging, as Figure 1 shown, including the following steps: (1) Add silver nanoparticles to ethanol and perform ultrasonic treatment for 5 - 20 min, preferably 5 - 15 min (such as 5 min, 10 min, 15 min, etc. and the time ranges composed of them), centrifuge to remove the supernatant, and dry under a nitrogen atmosphere at a temperature of 30 - 70 °C (preferably 40 - 60 °C, specifically 40 °C, 50 °C, 60 °C, etc. and the temperature ranges composed of them) to obtain pretreated silver nanoparticles; (2) Mix the surfactant and absolute ethanol according to a mass ratio of (0.5 - 5):(95:99.5) (such as 0.5:99.5, 1:99, 2:98, 3:97, 4:96, 5:95, etc. and the ratio ranges composed of them), the mixing method is not limited, just mix evenly, and the method includes but is not limited to ultrasonic treatment for at least 25 min; (3) Mix the pretreated silver particles obtained in step (1) with the ethanol solution of the surfactant obtained in step (2) at a mass ratio of (0.1 - 3):(97 - 99.9) (such as 0.1:99.9, 0.5:99.5, 1:99, 2:98, 3:97, etc. and the proportional ranges composed thereof), ultrasonicate for 10 - 40 min (such as 10 min, 20 min, 30 min, 40 min, etc. and the time ranges composed thereof), and centrifuge to remove the supernatant; add absolute ethanol, ultrasonicate for 5 - 20 min (such as 5 min, 10 min, 15 min, 20 min, etc. and the time ranges composed thereof), and centrifuge to remove the supernatant to obtain surfactant-coated silver nanoparticles; (4) Weigh the crosslinking coupling agent, dispersant, leveling agent, and organic solvent in proportion, and magnetically stir at room temperature for 30 - 60 min to mix them evenly to obtain the required organic solvent system; (5) Mix the coated silver nanoparticles obtained in step (3) with the organic solvent system obtained in step (4) evenly, and stir with a blender for 20 - 40 min to obtain the silver paste for power device packaging.

[0051] The silver paste for power device packaging provided by the present invention uses silver nanoparticles coated with a surfactant on the surface or in the preparation method, first coats the surface of the silver nanoparticles with a surfactant, and then jointly prepares a silver paste with an organic solvent system, which can effectively prevent particle aggregation, thereby improving the stability of the paste and the coating bonding force, so that no powder shedding phenomenon occurs after film formation, and a small amount of crosslinking coupling agent and leveling agent are added to the organic solvent system to ensure the surface flatness of the sintered silver film and avoid cracking.

[0052] The embodiment part of the present invention also provides a silver film for power device packaging, which is formed by using the silver paste described above or the silver paste obtained by the preparation method of the silver paste for power device packaging described above, and the thickness of the silver film is 50 - 300 μm.

[0053] The embodiment part of the present invention also provides a preparation method of the above silver film for power device packaging, which adopts a coating process and forms a film assisted by a nitrogen atmosphere, and its preparation process is as Figure 2 shown, and the specific steps are as follows: (1) Add the prepared silver nanoparticle paste into the storage tank, run the baseband, and make the carrier film level through the scraper, and control the thickness of the silver film to be 50 - 300 μm, such as 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, etc. and the thickness ranges composed thereof; (2) Introduce a nitrogen atmosphere into the drying chamber to make the interior an inert atmosphere. Control the temperature of the drying chamber at 100 - 160 °C, such as 100 °C, 120 °C, 140 °C, 150 °C, 160 °C, etc. and the temperature ranges composed of them; (3) Adjust the running speed of the baseband to keep the nano - silver paste in the drying furnace for 10 - 60 min, such as 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, etc. and the time ranges composed of them; (4) Obtain a sintered silver film after passing through the drying furnace.

[0054] In a specific embodiment, the carrier film can be selected from PI films; the inert atmosphere can be one of a nitrogen atmosphere, a helium atmosphere, and an argon atmosphere.

[0055] The silver paste, silver film, and their preparation method for power device packaging provided by the present invention effectively solve the problems such as the uneven surface, powder shedding, and cracking of the silver film after sintering.

[0056] The present invention also provides a power device packaging method, the process is as Figure 3 shown, and the specific steps are as follows: (1) Use a vacuum chuck that can apply pressure to suck the chip and apply a certain pressure. Cut a silver film with the same area as the back of the chip from the edge of the chip to make it separate from the PI film and attach it to the back of the chip; (2) Place the copper - clad ceramic on a heating table and heat it to 90 - 140 °C (such as 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, etc. and the temperature ranges composed of them), and attach the chip and the silver film to the surface of the copper - clad ceramic under a pressure of 3 - 10 MPa (such as 3 MPa, 5 MPa, 8 MPa, 10 MPa, etc. and the pressure ranges composed of them); (3) Press - sinter the chip - sintered silver film - copper - clad ceramic substrate in an inert atmosphere to obtain a power device packaging structure; Specifically, in step (3), the sintering conditions include: a sintering temperature of 190 - 250 °C (such as 190 °C, 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, etc. and the temperature ranges composed of them), a sintering pressure of 5 - 20 MPa (such as 5 MPa, 10 MPa, 15 MPa, 20 MPa, etc. and the pressure ranges composed of them), and a sintering time of 1 - 15 min (such as 1 min, 3 min, 5 min, 10 min, 12 min, 15 min, etc. and the time ranges composed of them). Specifically, for example, the sintering temperature is 250 °C, the sintering pressure is 20 MPa, and the sintering time is 3 min; or, the sintering temperature is 250 °C, the sintering pressure is 15 MPa, and the sintering time is 3 min; or, the sintering temperature is 250 °C, the sintering pressure is 10 MPa, and the sintering time is 3 min.

[0057] The power device packaging method provided by the present invention uses the aforementioned silver film and performs pressure sintering in an inert atmosphere, which can achieve low-temperature sintering with relatively high sintering strength and can effectively meet the usage requirements. At the same time, the sintered silver film of the present invention can greatly reduce the sintering process flow, achieve low-temperature sintering interconnection, reduce the risk of chip breakage, and achieve cost reduction and efficiency improvement.

[0058] The following describes the present invention 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.

[0059] Example 1 This example provides a silver paste for power device packaging, which consists of nano silver particles coated with a surface modifier and an organic solvent system. Among them, the particle size of the nano silver particles coated with the surface modifier is 800 nm, and the composition of the organic solvent system is cyclohexanol, epoxy resin, phosphate-modified acrylic acid, ethylene glycol, propylene glycol with a mass ratio of 1:1.5:2:30:30:35.5.

[0060] This example also provides a preparation method for the silver paste for power device packaging, and the steps are as follows: (1) Pretreatment of nano silver metal particles Mix the spherical nano silver particles (particle size 800 nm) with an ethanol solution and perform ultrasonic treatment for 10 min, then centrifuge to remove the supernatant to obtain pretreated silver particles.

[0061] (2) Coating treatment of nano silver metal particles Mix the above pretreated silver particles with a sodium dodecyl sulfate ethanol solution, where the mass ratio of sodium dodecyl sulfate to ethanol is 2:98, perform ultrasonic treatment for 30 min, centrifuge to remove the supernatant to obtain coated silver particles. After mixing the coated silver particles with the ethanol solution according to the dosage ratio, perform ultrasonic treatment for 40 min, and centrifuge to remove the supernatant to obtain coated silver particles.

[0062] (3) Preparation of organic solvent system Mix cyclohexanol, epoxy resin, phosphate-modified acrylic acid, ethylene glycol, and propylene glycol according to a mass ratio of 1:1.5:2:30:30:35.5 and stir magnetically for 1 h to obtain an organic solvent system.

[0063] (4) Preparation of nano silver paste Mix the coated metal particles in step (2) with the organic solvent system in step (3), and stir with a vacuum degassing machine for 20 min to obtain a nano silver paste.

[0064] Example 2 This example provides a silver film for power device packaging, and the film is formed using the silver paste provided in Example 1.

[0065] This embodiment also provides a method for preparing the silver film for power device packaging, including the following steps: (I) Coating Add the prepared nano-silver paste into the storage tank, run the baseband, and make the carrier film level by passing through the doctor blade, controlling the thickness of the sintered silver film to be 100 μm.

[0066] (II)Drying into film Adjust the running speed of the baseband, and keep the nano-silver paste in the nitrogen atmosphere of the drying furnace for 30 minutes to dry into a film, obtaining the silver film for power device packaging.

[0067] Example 3 This embodiment provides a power device packaging method, including the following steps: (a)Silver film transfer Use a vacuum suction head that can apply pressure to suck a 3×3 mm 2 chip, utilize the edge effect of the chip to suck the silver film in Example 2 of the corresponding size and apply 5 MPa to make the silver film separate from the PI film; (b)Heat the copper-clad ceramic to 140 °C, and transfer the chip and the silver film to the surface of the copper-clad ceramic substrate with a surface temperature of 140 °C, apply a pressure of 5 MPa for 2 s to make the silver film adhere to the surface of the copper-clad ceramic.

[0068] (c)Sintering Place the chip on the corresponding silver film to form a chip-sintered silver film-copper-clad ceramic substrate structure, and place it in a sintering furnace in a nitrogen atmosphere. Sinter for 3 minutes under the conditions of a sintering temperature of 250 °C and a sintering pressure of 20 MPa.

[0069] Example 4 This embodiment provides a power device packaging method, which is basically the same as Example 3, except that the nano-silver is in the form of flaky particles with a particle size of 1500 nm, and the sintering pressure is 10 MPa.

[0070] Example 5 This embodiment provides a power device packaging method, which is basically the same as Example 3, except that the sintering pressure is 15 MPa.

[0071] Comparative Example 1 This embodiment provides a power device packaging method, which is basically the same as Example 3, except that in the silver paste used to prepare the silver film, the nano-silver particles are not pretreated and coated with a surface modifier first, but are directly added together with the raw materials in the organic solvent system.

[0072] Test Example Test objects: Sintered silver films obtained in Example 3, Example 4, Example 5 and Comparative Example 1.

[0073] Test methods: (1) Test the shear strength of the sintered silver film; characterize the connection performance by the shear strength of the sintered silver film. The larger the numerical result, the better the connection performance. (2) Conduct ultrasonic non-destructive testing on the sintered silver film to observe the surface flatness, powder shedding and cracking of the sintered silver film. Among them, the frequency of the probe in the process of ultrasonic non-destructive testing is 15 HZ, the distance between the sample and the probe during scanning is 5 mm, and no special requirements are made for others. Take 4 parallel samples for each sample for testing.

[0074] Test results: (1) The shear strength of the sintered silver films in Examples 3-5 is as Figure 4 shown, and the ultrasonic non-destructive testing results are as Figures 5-7 shown.

[0075] (2) The ultrasonic non-destructive testing of the sintered silver film in Comparative Example 1 is as Figure 8 shown.

[0076] From Figure 4 it can be seen that for the silver film sintered in Example 3 (sintering pressure 20 MPa), its shear strength reaches more than 70 MPa; for the silver film sintered in Example 4 (sintering pressure 10 MPa), its shear strength reaches more than 50 MPa; for the silver film sintered in Example 5 (sintering pressure 15 MPa), its shear strength reaches more than 60 MPa. The above results show that by first coating the nano-silver particles with a surface modifier and then mixing with the raw materials in the organic solvent system, the shear strength of the silver film after sintering can be significantly improved when the obtained silver paste is used to form a silver film and for subsequent power device packaging. Further, it shows that by first coating the nano-silver particles with a surface modifier, the packaging performance can be significantly improved.

[0077] From Figures 5-7 it can be seen that the sintered silver films in Examples 3-5 show uniform surface color after ultrasonic non-destructive testing, indicating that the silver films have high surface flatness, uniform thickness and density, no powder shedding phenomenon, and no cracking phenomenon after transfer printing; Figure 8 The results show that the silver film obtained in Comparative Example 1 has uneven color, indicating that the sintered silver film in Comparative Example 1 may have defects such as uneven thickness, uneven flatness and uniform density; the above results show that compared with Comparative Example 1 (the surface modifier is directly added together with the raw materials in the organic solvent system), Examples 3-5 of the present invention (first pretreating and coating the nano-silver particles with a surface modifier) can significantly improve the performance of the silver film, especially the uniformity of thickness, flatness and density after transfer printing and sintering.

[0078] In summary, the power device packaging method proposed in the embodiments of the present invention can simplify the sintering process, improve the sintering quality, reduce the risk of chip breakage, and achieve cost reduction and efficiency improvement.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. However, such modifications or replacements 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 in that: The invention comprises, by weight, 80-90 parts of nano silver particles and 10-20 parts of an organic solvent system; wherein the surface of the nano silver particles is coated with at least one surface modifier selected from sodium dodecyl sulfate, Tween, polyvinyl pyrrolidone, sodium citrate, sodium dodecylbenzene sulfonate and polyoxyethylene ether.

2. The silver paste for power device packaging according to claim 1, characterized in that: The surface of the nano silver particles is coated with one of sodium dodecylbenzene sulfonate and polyvinyl pyrrolidone; Preferably, the nanosilver particles are in the form of flakes with a particle size of 1000-2000 nm; Preferably, the nanosilver particles are spherical in shape and have a particle size of 100-800 nm, preferably 300-800 nm.

3. The silver paste for power device packaging according to claim 1 or 2, characterized in that: In parts by weight, the organic solvent system comprises: 1.5-3 parts of a cross-linking coupling agent, 1-3 parts of a leveling agent, and 92.5-97 parts of an organic solvent; Preferably, the organic solvent system comprises: 1.5-2 parts of a cross-linking coupling agent, 1-2 parts of a leveling agent, and 95-97 parts of an organic solvent.

4. The silver paste for power device packaging according to claim 3, characterized in that: The cross-linking coupling agent is selected from at least one of aldehyde compounds, silane coupling agents, titanate coupling agents, epoxy resins, polyurethanes, silicone resins and chrome alum, preferably silane coupling agents or epoxy resins; And / or, the leveling agent is selected from one of acrylic acid, preferably fluorine-modified acrylic acid and phosphate-modified acrylic acid; And / or, the organic solvent is selected from at least one of alcohol organic substances, preferably at least one of ethylene glycol, propylene glycol, n-butanol, diethylene glycol, acetol and polyethylene glycol.

5. The silver paste for power device packaging according to claim 3 or 4, characterized in that: The organic solvent system also includes 0.5-1.5 parts of a dispersant; Preferably, the organic solvent system includes 0.5-1 part of a dispersant; Preferably, the dispersant is selected from at least one of fatty acids, n-decanol, methanol, cyclohexanol and ethanol.

6. The method for preparing the silver paste according to any one of claims 1 to 5, characterized in that: include: The silver nanoparticles coated with a surfactant and the organic solvent system are mixed evenly and stirred for 20-40 minutes; Preferably, the method for preparing the nanosilver particles coated with a surfactant comprises: (1) adding ethanol to the nanosilver particles for ultrasonic treatment, removing the supernatant by centrifugation, and drying under a nitrogen atmosphere to obtain pretreated nanosilver particles; (2) mixing the surfactant and anhydrous ethanol in a mass ratio of (0.5-5):(95:99.5) to obtain an ethanol solution of the surfactant; (3) mixing the pretreated silver particles with the ethanol solution of the surfactant in a mass ratio of (0.1-3): (97-99.9), ultrasonicating for 10-40 minutes, and removing the supernatant by centrifugation; adding anhydrous ethanol, ultrasonicating for 5-20 minutes, and removing the supernatant by centrifugation to obtain coated nanosilver particles; Preferably, in step (1), the ultrasonic treatment time is 5-20 min, and the drying temperature is 30-70 °C; Preferably, in step (2), the mixture of the surfactant and anhydrous ethanol is ultrasonicated for at least 25 minutes.

7. The preparation method according to claim 6, characterized in that: The preparation method of the organic solvent system comprises: weighing a cross-linking coupling agent, a dispersant, a leveling agent and an organic solvent in proportion, and magnetically stirring for 30-60 minutes at room temperature to mix them evenly.

8. A silver film for power device packaging, characterized in that: The silver paste according to claim 1 to 5 or the silver paste obtained by the preparation method according to claim 6 or 7 is used to form a film; Preferably, the thickness of the silver film is 50-300 μm.

9. The method for preparing the silver film for power device packaging according to claim 8, characterized in that: include: Forming a film on a carrier film using the silver paste described in claims 1 to 5 or the silver paste obtained by the preparation method described in claim 6, and drying; Preferably, the carrier film is selected from PI film; Preferably, the drying is carried out in an inert atmosphere at a temperature of 100-160° C. for 10-60 min; Preferably, the inert atmosphere is selected from at least one of a nitrogen atmosphere, a helium atmosphere, and an argon atmosphere.

10. A power device packaging method, characterized in that: include: (a) using the edge of the chip to cut the silver film of claim 8 and / or the silver film prepared by the method of claim 9 of the same area as the back of the chip, so that the silver film is separated from the carrier film and attached to the back of the chip; (b) heating the copper-clad ceramic to 90-140° C. and attaching the chip and the silver film to the surface of the copper-clad ceramic at a pressure of 3-10 MPa; (c) Pressurizing and sintering the chip-silver film-copper-clad ceramic substrate in an inert atmosphere; Wherein, in step (c), the sintering conditions are: sintering temperature is 190-250°C, sintering pressure is 5-20MPa, and sintering time is 1-15 min.

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