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

Abstract

The invention provides silver paste for a power device, a silver film, a packaging veneer and a preparation method and application thereof. The silver paste for 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% of an organic solvent system, wherein the organic solvent system comprises 0.5-1 part of a diluent, 0.5-1 part of a dispersant, 1-2 parts of a binder, 1-2 parts of a rheological agent and 94-97 parts of an organic solvent; the nano-silver particles are selected from spherical nano-silver particles with the particle size of 100 to 800 nm and / or flaky nano-silver particles with the particle size of 1000 to 2000 nm. The silver paste is favorable for forming a silver film with a flat surface. The performance of the silver film adopting the silver paste is also improved. A silver film is prefabricated on a packaging single plate, no residual colloid exists in sintered silver, the integrity and connection performance of the sintered silver are guaranteed, and no damage and no pollution are achieved in the prefabricated process of the sintered silver; the method is used for packaging the power device, successfully expands the application scene of the sintered silver film, prolongs the service life of the power device, is simple to operate, and is beneficial to reducing the cost and improving the efficiency.

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, a packaging single board for power devices, and a preparation method and application thereof. Background Art

[0002] 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 interconnect and high-temperature service. At present, the nano-silver sintering technology is one of the effective solutions, and related nano-silver pastes and sintered silver films have been widely studied and applied, and have been applied commercially. The sintered silver film transfer technology is a technology that transfers the sintered silver film on a thin film carrier to a chip at a suitable temperature and pressure. When using the sintered silver film, the printing and drying processes are avoided, and the chip can be directly transferred onto the silver film, and then pasted and sintered. Therefore, the sintered silver film is a very efficient and high-quality silver sintering interconnect material.

[0003] Currently, the sintered silver film transfer utilizes the chip edge effect to absorb the silver film of the corresponding size, which limits the application scenario of the silver film to the sintering of the chip and the copper-clad ceramic substrate. In the entire power device, the application of sintered silver in the top interconnect of the chip and system-level packaging will greatly improve the service life of the power device. Therefore, in order to realize the multi-sintering scenario application of the sintered silver film, the surface flatness and prefabrication method of the sintered silver are particularly important. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems in the prior art to some extent. For this reason, an object of the present invention is to provide a silver paste for power devices, which, by weight, comprises: 80-90 parts of nano-silver particles and 10-20% of an organic solvent system; wherein, the organic solvent system comprises: 0.5-1 part of a diluent, 0.5-1 part of a dispersant, 1-2 parts of a binder, 1-2 parts of a rheological agent, and 94-97 parts of an organic solvent; the nano-silver particles are selected from spherical nano-silver particles with a particle size of 100-800 nm and / or flaky nano-silver particles with a particle size of 1000-2000 nm. The silver paste for power devices provided by the present invention uses nano-silver particles as raw materials, and by adding a rheological agent and a diluent, it is beneficial to obtain a silver film with high surface flatness and good integrity by using the silver paste, providing a basis for high-quality packaging and improving the service life of power devices; furthermore, the other components and their dosages are optimized to ensure the flatness and integrity of the silver paste when forming a silver film.

[0005] In some embodiments, the silver nanoparticles are spherical silver nanoparticles with a particle size of 300 - 800 nm. Using spherical silver nanoparticles with a particle size of 300 - 800 nm has the effects of high sintering strength and low sintering temperature.

[0006] In some embodiments, the silver nanoparticles are flaky silver nanoparticles with a particle size of 1200 - 1600 nm. Using flaky silver nanoparticles with a particle size of 1200 - 1600 nm has the effect of good printing performance.

[0007] In some embodiments, the diluent is selected from at least one of ester alcohol, tributyl citrate, cyclohexyl isobornyl acetate, methanol, and propylene glycol. Preferably, it is ester alcohol or propylene glycol.

[0008] In some embodiments, the dispersant is selected from at least one of sodium citrate, n-decyl polyacrylate, methanol, cyclohexanol, and ethanol. Preferably, it is sodium citrate or cyclohexanol.

[0009] In some embodiments, the binder is selected from at least one of polyvinyl alcohol, polyacrylate, polyvinylpyrrolidone, diethylene glycol monoethyl ether acetate, acrylic resin, methylcellulose, and ethylcellulose. Preferably, it is ethylcellulose, acrylic resin, and polyvinylpyrrolidone.

[0010] In some embodiments, the rheological agent is selected from at least one of terpineol, ethyl acrylate, ethyl methacrylate, divinylbenzene, and ethylene glycol dimethacrylate. Preferably, it is terpineol and ethyl acrylate.

[0011] In some embodiments, the solvent is selected from at least one of alcohol organic compounds. Preferably, it is at least one of ethylene glycol, diethylene glycol, glycol, glycerol, and polyethylene glycol. More preferably, it is a mixture of ethylene glycol, polyethylene glycol, and diethylene glycol.

[0012] The second aspect of the present invention provides a silver film for power devices, which is formed by forming a film with the aforementioned silver paste. The silver film for power devices provided by the present invention has high flatness and is used for the encapsulation of power devices, which can effectively improve the service life of power devices.

[0013] In some embodiments, the thickness of the silver film for power devices is 50 - 300 μm.

[0014] In the third aspect of the present invention, a method for preparing the silver film for power devices is provided. The aforementioned silver paste is used and coated on a release film by a coating process and then dried. The silver film preparation method provided by the present invention obtains a silver-release film integrated structure after drying. Among them, the thickness of the release film is 25 - 100 μm, and its release force is 40 - 150 g / 25 mm. The release film has a certain adhesiveness, which is manifested as the release force. Using the release film as the carrier film enables the silver film to adhere to the release film, forming a silver-release film integrated structure.

[0015] In some embodiments, the release film is one of a PET film and a PE film; preferably, it is pre-cleaned with ethanol.

[0016] In some embodiments, the drying temperature is 100 - 160 °C, and the drying time is 10 - 60 min; preferably, the drying is carried out in an inert atmosphere.

[0017] In the fourth aspect of the present invention, a packaging substrate is provided, which is used as an application of the aforementioned silver film, and the aforementioned silver film is prefabricated on the surface of the packaging substrate. Prefabricating a sintered silver film on the packaging substrate is beneficial to improving production efficiency, reducing operation difficulty, etc., and helps to reduce costs.

[0018] In some embodiments, the packaging substrate is selected from at least one of a ceramic substrate and a lead frame.

[0019] In the fifth aspect, a method for preparing the packaging substrate is provided, including: A. Cutting the silver-release film integrated structure into different sizes; B. Selecting a silver-release film integrated structure with a suitable size and transferring it to the original packaging substrate, and separating the silver film from the release film.

[0020] In some embodiments, in step A, laser cutting is used; preferably, the pulse width of the laser cutting is picosecond and / or femtosecond, the laser wavelength is 355 nm and 1064 nm, the power is 0 - 200 W, and the frequency is 0 - 400 kHz; preferably, the pulse width of the laser cutting is femtosecond, the laser wavelength is 355 nm, the laser power is 10 - 60 W, and the frequency is 100 kHz - 200 kHz. Using laser cutting can realize customized sizes of the sintered silver-release film integrated structure and its application in multiple sintering scenarios of sintered silver. Especially when the cutting parameters are within the above range, it has the effects of neat cutting edges and no black edges.

[0021] In some embodiments, in step B, the surface of the original packaging substrate is heated to 100 - 200 °C, the pressure of the vacuum chuck is 0 - 10 MPa, and it is maintained for 0 - 2 s; preferably, in step B, the temperature of the surface of the original packaging substrate is 140 - 180 °C, the pressure of the vacuum chuck is 1 - 5 MPa, and it is maintained for 100 ms - 500 ms. Applying temperature and pressure simultaneously during the prefabrication process can realize the separation of the release film from the sintered silver, and there is no residual colloid on the sintered silver, ensuring the integrity and connection performance of the sintered silver, and realizing no damage and no pollution during the prefabrication process of the sintered silver.

[0022] The sixth aspect provides a power device packaging method, which adopts the packaging substrate or the packaging substrate obtained by the preparation method. The power device packaging method provided by the present invention adopts a packaging substrate prefabricated with a silver film, which can significantly improve the efficiency, reduce the requirements for the operation level of workers, and contribute to cost reduction and efficiency improvement.

[0023] In some embodiments, during sintering, the temperature is 190 - 250 °C, the sintering pressure is 5 - 20 MPa, and the sintering time is 1 - 15 min. Preferably, during sintering, the temperature is 200 - 220 °C, the sintering pressure is 5 - 15 MPa, and the sintering time is 1 - 5 min. Pressure sintering under an air / inert atmosphere can achieve low-temperature sintering with relatively high sintering strength, effectively meeting the usage requirements.

[0024] The present invention formulates a nano silver paste by designing the silver paste components and component contents and adopts a coating process for film formation. Coating the nano silver paste on the release film and applying temperature and pressure simultaneously during the prefabrication process can separate the release film from the sintered silver, and there is no residual colloid in the sintered silver, ensuring the integrity and connection performance of the sintered silver, and realizing non-damage and non-pollution during the prefabrication process of the sintered silver; at the same time, the laser cutting method is used to realize the customized size of the sintered silver-release film integrated structure and the application of the sintered silver in multiple sintering scenarios. In addition, pressure sintering under an air / inert atmosphere can achieve low-temperature sintering with relatively high sintering strength, effectively meeting the usage requirements.

[0025] The present invention effectively solves the limitations of the current application scenarios of sintered silver and provides a new method for the application of sintered silver in multiple sintering scenarios of power devices. Description of the Drawings

[0026] 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, without creative efforts, other drawings can also be obtained based on these drawings.

[0027] Figure 1 is one of the flowcharts of the preparation method of the silver film for power devices provided by the present invention.

[0028] Figure 2 is one of the flowcharts of the preparation of the nano silver paste for power devices provided by the present invention.

[0029] Figure 3 is one of the flowcharts of the preparation method of the packaging substrate provided by the present invention.

[0030] Figure 4 is one of the schematic diagrams of the connection between the chip and the ceramic substrate involved in the power device packaging method provided by the present invention.

[0031] Figure 5 It is the second flowchart of the preparation method of the packaging substrate provided by the present invention.

[0032] Figure 6 It is one of the schematic diagrams of the top interconnection of the chip involved in the power device packaging method provided by the present invention. Detailed implementation manners

[0033] 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 protection scope of the present invention.

[0034] In the first aspect of the present invention, a silver paste for power devices 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.

[0035] Among them, the organic solvent system includes: 0.5-1 part of a diluent, 0.5-1 part of a dispersant, 1-2 parts of a binder, 1-2 parts of a rheological agent, and 94-97 parts of an organic solvent; preferably with a total amount of 100 parts.

[0036] In some embodiments, 1 part of the above weight parts is equal to 1 g.

[0037] Among them, the nano-silver particles are selected from spherical nano-silver particles with a particle size of 100-800 nm (such as 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, etc. and other particle sizes and the particle size ranges composed thereof, preferably 300-800 nm) and / or flaky nano-silver particles with a particle size of 1000-2000 nm (such as 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm, 2000 nm, etc. and other particle sizes and the particle size ranges composed thereof, preferably 1200-1600 nm).

[0038] In some embodiments, the diluent is selected from at least one of ester alcohol, tributyl citrate, cyclohexyl isobornyl acetate, methanol, and propylene glycol.

[0039] In some embodiments, the dispersant is selected from at least one of sodium citrate, n-decyl polyacrylate, methanol, cyclohexanol, and ethanol, especially sodium citrate or cyclohexanol.

[0040] In some embodiments, the binder is selected from at least one of polyvinyl alcohol, polyacrylate, polyvinylpyrrolidone, diethylene glycol monoethyl ether acetate, acrylic resin, methylcellulose, and ethylcellulose, especially the binder is selected from ethylcellulose, acrylic resin, and polyvinylpyrrolidone.

[0041] In some embodiments, the rheological agent is selected from at least one of terpineol, ethyl acrylate, ethyl methacrylate, divinylbenzene, and ethylene glycol dimethacrylate, and has the effect of low drying temperature; especially terpineol and ethyl acrylate.

[0042] In some embodiments, the solvent is selected from at least one of organic alcohols, preferably at least one of ethylene glycol, diethylene glycol, glycol, glycerol, and polyethylene glycol, and more preferably a variety of ethylene glycol, polyethylene glycol, and diethylene glycol.

[0043] The embodiment of the present invention also provides a silver film for a power device, which is formed by forming a film with the aforementioned silver paste.

[0044] In some embodiments, the thickness of the silver film for the power device is 50 - 300 μm. When the thickness of the silver film is 50 - 300 μm, it has a better flatness effect. The thickness of the silver film can be 50 μm, 100 μm, 150 μm, 200 μm, 300 μm, etc., and other thicknesses and the thickness ranges composed thereof.

[0045] The embodiment of the present invention also provides a method for preparing the silver film for the power device. Using the aforementioned silver paste, it is coated on a release film by a coating process and then dried. Specifically, it includes the following steps: (1) Add the prepared nano - silver paste to the storage tank, run the base belt, and make the release film level through the doctor blade, controlling the thickness of the sintered silver to be 50 - 300 μm; (2) Introduce a nitrogen atmosphere into the drying chamber to make the inside an inert atmosphere, and control the temperature of the drying chamber to be 100 - 160 °C; (3) Adjust the running speed of the base belt to keep the nano - silver paste in the drying furnace for 10 - 60 min; (4) Obtain a sintered silver - release film integrated structure after passing through the drying furnace.

[0046] The method for preparing the silver film provided by the present invention obtains a silver - release film integrated structure after drying. Among them, the thickness of the release film is 25 - 100 μm (such as 25 μm, 50 μm, 75 μm, 100 μm, etc., and other thicknesses and the thickness ranges composed thereof, preferably 50 - 70 μm), and its release force is 40 - 150 g / 25 mm (such as 40 g / 25 mm, 50 g / 25 mm, 60 g / 25 mm, 75 g / 25 mm, 100 g / 25 mm, 125 g / 25 mm, 150 g / 25 mm, etc., and other thicknesses and the release force ranges composed thereof, preferably 45 - 80 g / 25 mm).

[0047] In some embodiments, the release film is one of a PET film and a PE film. For example, the release film is a PET film with a thickness of 50 - 70 μm and a release force of 45 - 80 g / 25 mm; in certain specific embodiments, the release film is a PET film with a release force of 50 g / 25 mm and a thickness of 70 μm. Preferably, the surface of the release film is pre-cleaned with ethanol to remove dust particles and avoid forming pores, thereby improving the thermal conductivity.

[0048] In some embodiments, the drying temperature is 100 - 160 °C and the drying time is 10 - 60 min; preferably, the drying is carried out in an inert atmosphere, which has a good antioxidant effect.

[0049] The embodiment of the present invention also provides a packaging substrate, as an application of the aforementioned silver film, and the silver film is prefabricated on the surface of the packaging substrate.

[0050] In the prior art, the top interconnection of chips generally has problems such as troublesome operation, difficult precision control, and poor packaging quality. In this application, by prefabricating a silver film on the packaging substrate, during packaging, the operation is simple, the technical level requirements for operators are low, which is beneficial to improving efficiency and reducing costs.

[0051] In some embodiments, the packaging substrate is selected from at least one of a ceramic substrate and a lead frame. Prefabricating the silver film on the ceramic substrate and the lead frame can achieve top interconnection of chips, thereby realizing system-level packaging and improving the service life of power devices; it can also realize the connection between the chip and the ceramic substrate and the connection between the ceramic substrate and the heat sink, expanding the application scenarios of sintered silver.

[0052] The embodiment of the present invention also provides a preparation method of the packaging substrate, including: A. Cutting the silver-release film integrated structure into different sizes; B. Selecting a silver-release film integrated structure with a suitable size and transferring it to the original packaging substrate, and separating the silver film from the release film.

[0053] In some embodiments, the preparation method of the packaging substrate includes: (1) Placing the dried sintered silver under a laser cutting machine, and according to the sintering scenario, using certain process parameters to customize the size of the sintered silver with a laser while ensuring a good cutting effect, and the sintered silver-release film integrated structure is cut and dropped; (2) Inverting the cut sintered silver-release film integrated structure and placing it in a waffle box, and using a vacuum suction head to suck the sintered silver-release film integrated structure according to the size required by the sintering scenario and transfer it to the sintering scenario; (3) During the prefabrication process, under the action of heating the vacuum suction head and applying a certain pressure, the release film overcomes the release force and separates from the silver film, and there is no residual colloid on the surface of the silver film.

[0054] In step A, laser cutting is used; preferably, the pulse width of the laser cutting is picosecond and / or femtosecond, the laser wavelength is 355nm, 1064nm, the power is 0 - 200W, and the frequency is 0 - 400kHz; preferably, the pulse width of the laser cutting is femtosecond, the laser wavelength is 355nm, the laser power is 10 - 60W, and the frequency is 100kHz - 200kHz. Using laser cutting can achieve customized dimensions of the sintered silver - release film integrated structure and realize the application of sintered silver in multiple sintering scenarios.

[0055] In step B, heat the surface of the original packaging substrate to 100 - 200 °C (such as 100 °C, 120 °C, 140 °C, 160 °C, 180 °C, etc. and other temperatures and their temperature ranges, preferably 140 - 180 °C), the pressure of the vacuum suction head is 0 - 10MPa (such as 1MPa, 2MPa, 3MPa, 4MPa, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa, 10MPa, etc. and other pressures and their pressure ranges, preferably the pressure of the vacuum suction head is 1 - 5MPa), and keep it for 0 - 2s (such as 100ms, 200ms, 300ms, 400ms, 500ms, 700ms, 800ms, 1000ms, etc. and other times and their time ranges, preferably 100 - 500ms). Applying temperature and pressure simultaneously during the prefabrication process can achieve the separation of the release film from the sintered silver, and there is no residual colloid on the sintered silver, ensuring the integrity and connection performance of the sintered silver, and realizing no damage and no pollution during the prefabrication process of the sintered silver.

[0056] The embodiment part of the present invention also provides a power device packaging method, which uses the packaging substrate or the packaging substrate obtained by the preparation method.

[0057] In some embodiments, sintering is carried out in an air / inert atmosphere; during sintering, the temperature is 190 - 250 °C, the sintering pressure is 5 - 20MPa, and the sintering time is 1 - 15 min. Preferably, during sintering, the temperature is 200 - 220 °C, the sintering pressure is 5 - 15MPa, and the sintering time is 1 - 5min.

[0058] In the embodiments, the information of each raw material is shown in the following table.

[0059] For those not specifying specific techniques or conditions in the embodiments, follow the techniques or conditions described in the literature in this field or according to the product specifications. For reagents or instruments not indicating the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0060] The present invention will be described below with reference to specific embodiments. It should be noted that these embodiments are merely illustrative and do not limit the present invention in any way.

[0061] Embodiment 1 This embodiment provides a nano silver paste for power devices, with ester alcohol, sodium citrate, terpineol, polyvinyl alcohol, and ethylene glycol in a mass ratio of 1:1:1:1:96; among them, the nano silver particles are spherical in shape and have a particle size of 800 nm.

[0062] This embodiment also provides a preparation method for the nano silver paste, and its flowchart is as Figure 2 shown: Mix ester alcohol, sodium citrate, terpineol, polyvinyl alcohol, and ethylene glycol in a mass ratio of 1:1:1:1:96 and stir magnetically for 1 h to obtain an organic solution. After mixing with spherical nano silver particles (800 nm), stir with a vacuum degassing machine for 20 min to obtain the nano silver paste.

[0063] Embodiment 2 This embodiment provides a silver film for power devices, which is formed using the nano silver paste provided in Embodiment 1.

[0064] This embodiment also provides a preparation method for the silver film for power devices, and its flowchart is as Figure 1 shown: Select a PET film with a release force of 50 g / 25 mm and a thickness of 70 μm as the release film (the surface is pre-cleaned with ethanol). Pour the prepared nano silver paste into the storage tank, run the baseband, and make the release film pass through the doctor blade to level it, controlling the thickness of the sintered silver to be 100 μm. Adjust the running speed of the baseband so that the nano silver paste is kept in the nitrogen atmosphere of the drying oven for 30 min to dry into a sintered silver-release film integrated structure.

[0065] Embodiment 3 This embodiment provides a packaging substrate, specifically, a copper-clad ceramic substrate, on the surface of which the silver film provided in Embodiment 2 is prefabricated.

[0066] This embodiment also provides a preparation method for the packaging substrate, as Figure 3 shown: Place the dried sintered silver-release film integrated structure under a laser cutting machine. According to the chip sizes of 3×3 mm 2 , 5×5 mm 2 , select 60 W, 200 kHz, 355 nm picosecond laser to prefabricate the sintered silver-release film integrated structure into the chip size, while ensuring good cutting effect, and the sintered silver and the release film are cut and dropped. Invert the cut sintered silver-release film integrated structure and place it in a waffle box, and use a vacuum suction head to suck 3×3 mm 2 , 5×5 mm 2The sintered silver - release film integrated structure is applied with a pressure of 5 MPa and placed on a copper - clad ceramic substrate with a surface temperature of 140 °C. Under the action of temperature and pressure, the release film is separated from the sintered silver, and the sintered silver is pre - formed on the copper - clad ceramic substrate.

[0067] Example 4 This example provides a method for packaging power devices. As Figure 4 shown, nano - silver paste is coated on the release film to form a silver - release film integrated structure, which is pre - formed on the packaging substrate and then sintered: The chip is placed on the sintered silver to form a chip - sintered silver - copper - clad ceramic substrate sandwich structure, which is placed in a heating and pressurizing device under N2 atmosphere protection and sintered under the conditions of 250 °C - 5 MPa - 3 min.

[0068] Example 5 This example provides a packaging substrate for a silver film, which is basically the same as Example 3. The difference is only that, as Figure 5 shown, the packaging substrate is a lead frame, that is, specifically, the lead frame provided in Example 2 is pre - formed in this example.

[0069] Example 6 This example provides a method for packaging power devices, which is basically the same as Example 4. The difference is only that the packaging substrate provided in Example 5 is used for sintering and packaging, as Figure 6 shown.

[0070] Chip sintering The lead frame coated with sintered silver is placed on the chip surface and placed in a heating and pressurizing device under N2 atmosphere protection and sintered under the conditions of 250 °C - 5 MPa - 3 min. At the same time, this method can achieve one - time sintering for chip top interconnection and copper - clad ceramic substrate interconnection.

[0071] Finally, it should be noted that: The above examples 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 examples, those of ordinary skill in the art should understand that: They can still modify the technical solutions recorded in the foregoing examples, or perform equivalent replacements for some of the technical features; And these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A silver paste for power devices, characterized in that: The invention comprises, by weight, 80-90 parts of nano silver particles and 10-20% of an organic solvent system; wherein the organic solvent system comprises 0.5-1 parts of a diluent, 0.5-1 parts of a dispersant, 1-2 parts of a binder, 1-2 parts of a rheological agent, and 94-97 parts of an organic solvent; and the nano silver particles are selected from spherical nano silver particles with a particle size of 100-800 nm and / or flaky nano silver particles with a particle size of 1000-2000 nm.

2. The silver paste according to claim 1, characterized in that: The nano silver particles are spherical nano silver particles with a particle size of 300-800 nm; And / or, the nano silver particles are flaky nano silver particles with a particle size of 1200-1600 nm.

3. The silver paste according to claim 1 or 2, characterized in that: The diluent is selected from at least one of ester alcohol, tributyl citrate, cyclohexyl isoborneol, methanol, and propylene glycol, preferably ester alcohol or propylene glycol; and / or, the dispersant is selected from at least one of sodium citrate, polyacrylic acid n-decanol, methanol, cyclohexanol and ethanol, preferably sodium citrate or cyclohexanol; and / or, the binder is selected from at least one of polyvinyl alcohol, polyacrylate, polyvinyl pyrrolidone, diethylene glycol monoethyl ether acetate, acrylic resin, methyl cellulose and ethyl cellulose, preferably ethyl cellulose, acrylic resin, polyvinyl pyrrolidone; and / or, the rheological agent is selected from at least one of terpineol, ethyl acrylate, ethyl methacrylate, divinylbenzene, and ethylene glycol dimethacrylate, preferably terpineol and ethyl acrylate; And / or, the solvent is selected from at least one of alcohol organic substances, preferably at least one of ethylene glycol, diethylene glycol, glycol, glycerol, and polyethylene glycol, and more preferably multiple of ethylene glycol, polyethylene glycol, and diethylene glycol.

4. A silver film for power devices, characterized in that: Obtained by forming a film using the silver paste described in any one of claims 1 to 3; Preferably, the thickness of the silver film for power devices is 50-300 μm.

5. The method for preparing the silver film according to claim 4, characterized in that: include: The silver paste according to any one of claims 1 to 3 is coated on a release film and dried to obtain a silver-release film integrated structure; The release film has a thickness of 25-100 μm and a release force of 40-150 g / 25 mm.

6. The preparation method according to claim 5, characterized in that: The release film has a thickness of 50-70 μm and a release force of 40-80 g / 25 mm; Preferably, the release film is one of a PET film and a PE film; Preferably, the release film is cleaned in advance with ethanol.

7. The preparation method according to claim 6, characterized in that: The drying temperature is 100-160°C and the drying time is 10-60min; Preferably, the drying is performed under an inert atmosphere.

8. A packaging substrate, characterized in that: The silver film according to any one of claims 5 to 7 is prefabricated on its surface; Preferably, the packaging substrate is selected from at least one of a ceramic substrate and a lead frame.

9. The method for preparing a packaging substrate according to claim 8, characterized in that: include: A. Cutting the silver film according to any one of claims 5 to 7 into different sizes; B. Select a silver film of suitable size and transfer it to the original packaging substrate, and separate the silver film from the release film; Preferably, in step A, laser cutting is used; Preferably, the pulse width of laser cutting is picosecond and / or femtosecond, the laser wavelength is 355nm, 1064nm, the power is 0-200W, and the frequency is 0-400kHz; Preferably, the pulse width of laser cutting is femtosecond, the laser wavelength is 355nm, the laser power is 10-60W, and the frequency is 100kHz-200kHz. Preferably, in step B, the surface of the original packaging substrate is heated to 100-200° C., the pressure of the vacuum suction head is 0-10 MPa, and maintained for 0-2 seconds; Preferably, in step B, the temperature of the surface of the packaging substrate original plate is 140-180° C., the pressure of the vacuum suction head is 1-5 MPa, and is maintained for 100 ms-500 ms.

10. A power device packaging method, characterized in that: A packaging substrate according to claim 8 or a packaging substrate obtained by the preparation method according to claim 9; Preferably, during sintering, the temperature is 190-250°C, the sintering pressure is 5-20MPa, and the sintering time is 1-15 min; Preferably, during sintering, the temperature is 200-220° C., the sintering pressure is 5-15 MPa, and the sintering time is 1-5 min.

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