Nanoscale silver paste, silver film, packaging structure for SiC semiconductor packaging, and preparation method thereof

Abstract

The present invention provides a nano silver paste, a silver film, a packaging structure and a preparation method thereof for SiC semiconductor packaging. The silver paste comprises 50-90 wt% of nano silver powder, 0.1-5 wt% of porous metal material, 5-45 wt% of organic carrier, and 0.01-0.5 wt% of inorganic nano mesoporous material. The nano silver powder comprises silver powders of two different sizes; the porous metal material is porous metal and / or metal organic framework material. By adopting nano silver powders of two different sizes, the present invention can increase the packing density and reduce the porosity after sintering of the nano silver paste. During the sintering process, silver atoms will diffuse and fill into the pores of the porous metal material and the inorganic nano mesoporous material, forming sintering necks in the pores, and the crystal nuclei will continuously grow, so that the porous metal material and the inorganic nano mesoporous material are interpenetrated and interconnected, improving the high-temperature service stability and long-term service reliability of the silver sintered joint.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor packaging. Specifically, it relates to a nano-silver paste for SiC semiconductor packaging, a nano-silver film for SiC semiconductor packaging prepared by using the nano-silver paste, a packaging structure of an SiC semiconductor power device prepared by using the nano-silver film, and preparation methods for the foregoing nano-silver paste, nano-silver film, and power device packaging structure. Background Art

[0002] With the progress of science and technology, semiconductor devices are constantly developing towards high power, high integration, and miniaturization, posing higher requirements for heat dissipation performance, electrical connection, and reliability. Especially in the application fields of high-power devices, such as aerospace, electronic communication, and power modules of new energy vehicles, the working environment of power devices is more severe, the load current density is greater, and they need to serve in a harsh environment for a long time and maintain the stability of performance.

[0003] With the wide application of power chips prepared from the third-generation wide-bandgap semiconductor materials represented by SiC in some high-power devices, and due to the dual requirements of lead-free and high-temperature resistance development, nano-silver paste solder and nano-silver sintering interconnect technology have developed. Due to its excellent performance of low-temperature sintering and high-temperature service, it has become an ideal chip welding technology and can replace traditional solder for high-temperature applications. However, the nano-silver paste printing and sintering technology has the disadvantages of poor surface flatness, residues of silver sintering materials around the chip, and inability to form large-area sintering interconnects, which limit its application and promotion in high-power devices.

[0004] Currently, nano-silver film products have been widely studied and applied. However, the nano-silver films in the prior art have the following disadvantages: 1. Due to the addition of a large amount of high-boiling organic additives, the performance of the welded joint is reduced; 2. The porosity of the nano-silver film is relatively large, and the connection strength and plasticity of the joint are generally poor, resulting in low reliability under conditions such as impact, vibration, and temperature cycling; 3. After conventional nano-silver films are sintered, the residual stress is relatively large, and the aging performance such as thermal shock is poor. Summary of the Invention

[0005] Aiming at the defects in the prior art, the purpose of the present invention is to provide a nano-silver paste for SiC semiconductor packaging, a nano-silver film for SiC semiconductor packaging prepared by using the nano-silver paste, a packaging structure of an SiC semiconductor power device prepared by using the nano-silver film, and preparation methods for the foregoing nano-silver paste, nano-silver film, and power device packaging structure. By adopting the technical solutions provided by the present invention, the porosity after sintering of the nano-silver paste can be reduced, the sintering stress can be reduced, the shear strength can be enhanced, and the high-temperature service stability and long-term service reliability of the interconnect joint can be improved.

[0006] To achieve the above-mentioned invention purpose, the present invention adopts the following technical solutions:

[0007] According to the first aspect of the present invention, there is provided a nano silver paste for SiC semiconductor packaging, which includes the following substance components in terms of mass percentage:

[0008] Nano silver powder: 50wt% - 90wt%;

[0009] Porous metal material: 0.1wt% - 5wt%;

[0010] Organic carrier: 5wt% - 45wt%;

[0011] Inorganic nano additive phase: 0.01wt% - 0.5wt%;

[0012] Wherein: the nano silver powder is composed of nano - scale first silver powder and second silver powder, the D50 of the first silver powder is 20 - 100nm, and the D50 of the second silver powder is 100 - 800nm; the porous metal material is porous metal and / or metal - organic framework material; the inorganic nano additive phase is inorganic nano - mesoporous material.

[0013] In this technical solution, two kinds of nano silver powders with different sizes are adopted, which can increase the packing density and reduce the porosity after sintering of the nano silver paste; by adding inorganic nano - mesoporous material, the sintering stress is reduced, the sintering structure is refined, and cracks are reduced; by adding porous metal material, the sintering degree is enhanced, the porosity is further reduced, and the plasticity of the silver sintered joint is improved by using the good ductility of the porous metal material, and the shear strength is improved; during the sintering process, silver atoms will diffuse and fill into the pores of the porous metal material and inorganic nano - mesoporous material, forming sintering necks in the pores, and the crystal nuclei continue to grow, so that the porous metal material and inorganic nano - mesoporous material are interpenetrated and interconnected, improving the high - temperature service stability and long - term service reliability of the silver sintered joint.

[0014] In this technical solution, the shape of the nano silver powder is not restricted, and it can be spherical, flaky, quasi - spherical, irregular, etc.; the porous metal in this technical solution is a lightweight structural material composed of a metal matrix framework and pores, with the advantages of low density, good ductility, good heat insulation performance, high porosity, and large specific surface area; metal - organic framework materials (English name: Metal Organic Framework, abbreviated as MOFs, also known as metal - organic framework compounds) are crystalline porous materials formed by the self - assembly connection of inorganic metal centers and bridging organic ligands, with the rigid characteristics of inorganic materials and the flexible characteristics of organic materials.

[0015] Preferably, based on the total amount of the nano silver powder, the content of the first silver powder is 30% - 80%, and the balance is the second silver powder.

[0016] Preferably, the porous metal is any one or more of the following substances: porous silver, porous copper, porous nickel, porous aluminum; the porosity of the porous metal is 60% - 95%, and the particle size is 10 - 150 μm.

[0017] Preferably, the metal-organic framework material is a porous material formed by self-assembly of an inorganic metal center and an organic ligand. The metal center is any one of Cu, Ag, Ni, Zn, Co, and the organic ligand is any one of imidazole and its derivatives, carboxylic acid-based compounds; the porosity of the metal-organic framework material is 50% - 80%, and the particle size is 1 - 15 μm.

[0018] Preferably, the inorganic nano-additive phase is any one or more of the following substances: nano-mesoporous Al2O3, nano-mesoporous SiO2, nano-mesoporous ZnO, nano-mesoporous TiC, nano-mesoporous SiC, nano-mesoporous AlN, nano-mesoporous BN; the particle size of the inorganic nano-additive phase is 200 - 800 nm.

[0019] Preferably, the organic carrier includes a solvent and a binder, and the mass ratio of the solvent to the binder is (2 - 4):0.04;

[0020] The solvent is any one or more of the following substances: terpineol, isopropanol, alcohol ester twelve, n-butanol; the binder is any one or more of the following substances: polyvinyl alcohol, cellulose acetate, polyurethane, acrylic resin, polyhydroxybutyrate.

[0021] In this technical solution, the selected binder can be decomposed below 250°C. During the low-temperature sintering process of the nano-silver film, the binder thermally decomposes into carbon dioxide and water, which can improve the contact bonding performance with the chip and the DBC substrate (i.e., direct copper clad ceramic substrate), further reduce the porosity, and reduce the resistivity of the silver sintered joint. In particular, the organic carrier is preferably a mixture of terpineol, isopropanol, and polyvinyl alcohol mixed in a mass ratio of 1:1.5:0.04.

[0022] According to the second aspect of the present invention, a preparation method of nano-silver paste for SiC semiconductor packaging is provided, including the following steps:

[0023] S 1a Weigh the nano-silver powder, organic carrier, and inorganic nano-additive phase, mix and roll them to obtain a uniform sample;

[0024] S 2a Add the weighed porous metal material to the uniform sample in S 1a , and mix evenly to prepare the nano-silver paste;

[0025] Step S 1aAmong them, the nano silver powder is composed of nano-scale first silver powder and second silver powder. The D50 of the first silver powder is 20 - 100 nm, and the D50 of the second silver powder is 100 - 800 nm. The inorganic nano-additive phase is an inorganic nano-mesoporous material; step S 2a Among them, the porous metal material is porous metal and / or metal-organic framework material;

[0026] Based on the total mass of the nano silver paste for SiC semiconductor packaging, the content of each substance is: nano silver powder 50wt% - 90wt%, porous metal material 0.1wt% - 5wt%, organic carrier 5wt% - 45wt%, inorganic nano-additive phase 0.01wt% - 0.5wt%.

[0027] In this technical solution, the porous metal material has good structural stability, can enhance the sintering degree, reduce the porosity, and improve the shear strength; the inorganic nano-mesoporous material can reduce the thermal expansion coefficient, reduce the sintering stress, and improve the bonding performance of low-temperature sintering interfaces such as Ag / Cu or Ag / Ni by refining the sintered structure. During the sintering process, silver atoms diffuse and fill into the pores of the porous metal material and the inorganic nano-mesoporous material, forming sintering necks in the pores, and the crystal nuclei continue to grow, making the porous metal material and the inorganic nano-mesoporous material interpenetrate and connect with each other. At the same time, due to the special pore structure and good ductility of the porous metal material, it can further disperse the sintering residual stress, reduce the generation and propagation of cracks, and improve the high-temperature service stability and long-term service reliability of the silver sintered joint. In the process of preparing the nano silver paste in this technical solution, after adding the porous metal material and the inorganic nano-mesoporous material at the same time, by using the synergistic effect of the two, the porosity is reduced, the sintered structure is refined, the sintering stress is reduced, the shear strength is improved, and the reliability and stability of the sintered joint are improved.

[0028] More specifically, in this technical solution, S 1a and S 2a The preparation steps are as follows:

[0029] S 1a First, put the weighed nano-scale first silver powder, nano-scale second silver powder, organic carrier, and inorganic nano-additive phase into the wide-mouth bottle of the planetary mixer, stir evenly with a spatula, and mix for 3 min at a speed of 800 rpm with the planetary mixer; then grind 4 times with a three-roll grinder, and test that its grinding fineness is less than 5 μm to obtain a uniformly mixed sample;

[0030] S 2a Add the porous metal material to the sample obtained in step S 1a and stir evenly with a spatula; then mix for 3 min at a speed of 800 rpm with the planetary mixer to obtain a nano silver paste with a Brookfield viscosity between 5 - 100 Pa·s.

[0031] According to the third aspect of the present invention, there is provided a nano silver film for SiC semiconductor packaging, which is prepared by using the nano silver paste for SiC semiconductor packaging according to any one of the first aspects of the present invention.

[0032] According to the fourth aspect of the present invention, there is provided a method for preparing a nano silver film for SiC semiconductor packaging, comprising the following steps:

[0033] S 1b Adsorb the plastic substrate on the platform by using a coating machine;

[0034] S 2b Flow the nano silver paste for SiC semiconductor packaging according to any one of the first aspects of the present invention onto the plastic substrate to form a wet silver film;

[0035] S 3b Dry the wet silver film to obtain a nano silver film for SiC semiconductor packaging with a preset thickness.

[0036] In this technical solution, the more specific preparation steps are as follows:

[0037] S 1b Vacuum-adsorb the plastic substrate on the platform by using a temperature-controlled coating machine to ensure that the surface of the plastic substrate is flat and free of bubbles;

[0038] S 2b After vacuum degassing the nano silver paste for SiC semiconductor packaging according to any one of the first aspects of the present invention, add it into the material bucket above the coating machine, adjust the pressure and flow rate of the coating head, so that the nano silver paste slowly flows onto the plastic substrate through the coating head, and use a scraper to scrape it into a wet silver film with regular shape and uniform thickness;

[0039] S 3b Adjust the running speed of the conveyor belt, enter the drying furnace under vacuum or N2 protection, dry at a temperature of 80-150 °C for 10-30 min to dry the wet silver film, and obtain a nano silver film for SiC semiconductor packaging with a thickness of 50-80 μm.

[0040] Preferably, in step S 1b Any one of the following plastic substrates is used: PET film, PI film, PTFE film, PFA film.

[0041] According to the fifth aspect of the present invention, there is provided a SiC semiconductor power device packaging structure, which is prepared by using the nano silver film for SiC semiconductor packaging according to any one of the third aspects of the present invention.

[0042] According to the sixth aspect of the present invention, there is provided a method for preparing a SiC semiconductor power device packaging structure, comprising the following steps:

[0043] S1c Attach the nano - silver film for SiC semiconductor packaging according to any one of the third aspects of the present invention to the back of the SiC chip, and the area of the nano - silver film is the same as the area of the back of the chip. A metal coating is plated on the surface of the SiC chip.

[0044] S 2c Attach the chip with the nano - silver film on its back obtained in step S 1c to the surface of the DBC board. After keeping warm for a preset time, rapidly raise the temperature for pressure sintering. The sintering temperature is 200°C to 250°C, and the sintering time is 1 min to 20 min, obtaining a SiC power device packaging structure with a chip on the upper layer, a sintered silver interconnection layer in the middle layer, and a DBC board on the lower layer.

[0045] In this technical solution, the more specific preparation steps are as follows:

[0046] S 1c Place the nano - silver film for SiC semiconductor packaging according to any one of the third aspects of the present invention with a bottom plastic substrate on a sampling table padded with a silica gel pad. Use a vacuum suction head that can apply pressure to suck the SiC chip with a metal coating on its surface, and apply a certain pressure at the same time. Cut a nano - silver film with the same area as the back of the chip from the edge of the chip, so that the nano - silver film detaches from the plastic substrate and attaches to the back of the chip.

[0047] S 2c Place the DBC board on a heating table, and the temperature of the heating table is 100 - 150°C. Attach the chip with the nano - silver film on its back obtained in step S 1c to the surface of the DBC board, and under vacuum or N2 protection, keep warm for 10 - 30 min, then rapidly raise the temperature for pressure sintering. The applied pressure is 10 MPa - 25 MPa, the sintering temperature is 200°C - 250°C, and the sintering time is 1 min - 20 min, obtaining a SiC power device packaging structure with a chip on the upper layer, a sintered silver interconnection layer in the middle layer, and a DBC board on the lower layer.

[0048] Preferably, in step S 1c , the metal coating on the surface of the SiC chip is any one or more of the following metals: Ag, Ni, Au, Pd.

[0049] Compared with the prior art, the present invention has the following beneficial effects:

[0050] The present invention uses two kinds of nano silver powders with different sizes, which can increase the packing density and reduce the porosity after sintering of the nano silver paste; by adding inorganic nano mesoporous materials, the sintering stress is reduced, the sintering structure is refined, and cracks are reduced; by adding porous metal materials, the sintering degree is enhanced, the porosity is further reduced, and the plasticity of the silver sintered joint is improved by using the good ductility of the porous metal materials, and the shear strength is improved; during the sintering process, silver atoms will diffuse and fill into the pores of the porous metal materials and inorganic nano mesoporous materials, forming sintering necks in the pores, and the crystal nuclei continue to grow, so that the porous metal materials and inorganic nano mesoporous materials are interpenetrated and interconnected, improving the high-temperature service stability and long-term service reliability of the silver sintered joint. Detailed implementation manners

[0051] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Apparently, the described embodiments are some, but not all, of the embodiments of the present application.

[0052] All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0053] Embodiment 1

[0054] (1) Preparation of nano silver paste

[0055] S 1a First, weigh 35 g of nano-sized first silver powder, 50 g of nano-sized second silver powder, 12 g of organic carrier, and 0.1 g of inorganic nano additive phase and put them into a wide-mouth bottle of a planetary mixer, stir evenly with a spatula, and mix them for 3 min at a speed of 800 rpm with the planetary mixer; then grind them 4 times with a three-roll grinder, and test that the grinding fineness is less than 5 μm to obtain a uniformly mixed sample;

[0056] S 2a Add 2.9 g of porous metal material to the sample obtained in step S 1a and stir evenly with a spatula; then mix them for 3 min at a speed of 800 rpm with the planetary mixer to obtain a nano silver paste with a Brookfield viscosity of 20 - 30 Pa·s.

[0057] Among them, in step S 1a , the D50 of the nano-sized first silver powder is 50 nm, and the D50 of the nano-sized second silver powder is 200 nm; in step S 2a , the porous metal material is porous nickel, its porosity is 90%, and D50 is 50 μm; in step S 1a , the inorganic nano additive phase is mesoporous Al2O3, its D50 is 300 nm; and in step S 1aAmong them, the organic carrier is a mixture of terpineol, isopropanol and polyvinyl alcohol in a mass ratio of 1:1.5:0.04.

[0058] (2)Preparation of the silver nanomembrane

[0059] S 1b 、Use a temperature-controlled film coater to vacuum-adsorb the plastic substrate on the platform to ensure that the surface of the plastic substrate is flat and bubble-free;

[0060] S 2b 、After vacuum degassing the silver nanoslurry prepared in the previous step of this example, add it to the material bucket above the film coater, adjust the pressure and flow rate of the coating head, and make the silver nanoslurry slowly flow through the coating head onto the plastic substrate, and use a squeegee to scrape it into a wet silver film with regular shape and uniform thickness;

[0061] S 3b 、Adjust the running speed of the conveyor belt, enter the drying furnace under a vacuum environment, and dry at a temperature of 120 °C for 10 min to dry the wet silver film and obtain a silver nanomembrane with a thickness of 60-70 μm;

[0062] Step S 1b In, the plastic substrate is a PET film.

[0063] (3)Preparation of the SiC power device packaging structure

[0064] S 1c 、Place the silver nanomembrane with the underlying plastic substrate on the sampling table padded with a silica gel pad, use a vacuum suction head that can apply pressure to suck the SiC chip plated with a metal coating on the surface, and apply a certain pressure at the same time. Cut a silver nanomembrane with the same area as the back of the chip from the edge of the chip to make the silver nanomembrane detach from the plastic substrate and attach to the back of the chip;

[0065] S 2c 、Place the direct copper clad ceramic substrate (referred to as DBC board) on the heating table, the temperature of the heating table is 100 °C, attach the chip with the silver nanomembrane on the back obtained in step S 1c to the surface of the DBC board, and keep it warm for 30 min under N2 protection, then quickly raise the temperature for pressure sintering. The applied pressure is 18 MPa, the sintering temperature is 250 °C, and the sintering time is 5 min to obtain an SiC power device packaging structure with a chip on the upper layer, a sintered silver interconnection layer in the middle layer, and a DBC board on the lower layer.

[0066] Among them, in step S 1c the metal coating on the surface of the SiC chip is a Ni coating.

[0067] Example 2

[0068] The SiC power device packaging structure was prepared by the same method as in Example 1, except that the porous metal material used in preparing the nano-silver paste in Example 1 was porous nickel, while the porous metal material in this example was porous silver.

[0069] Example 3

[0070] The SiC power device packaging structure was prepared by the same method as in Example 1, except that the porous metal material used in preparing the nano-silver paste in Example 1 was porous nickel, while the porous metal material in this example was porous copper.

[0071] Example 4

[0072] The SiC power device packaging structure was prepared by the same method as in Example 1, except that the porous metal material used in preparing the nano-silver paste in Example 1 was porous metal (specifically porous nickel), while the porous metal material in this example was a metal-organic framework material, specifically a porous material formed by the coordination self-assembly of Cu and 2-methylimidazole, with a porosity of 60% and a D50 of 3 μm.

[0073] Example 5

[0074] The SiC power device packaging structure was prepared by the same method as in Example 1, except that the inorganic nano-additive phase used in preparing the nano-silver paste in Example 1 was 0.1 g of mesoporous Al2O3, while the inorganic nano-additive phase in this example was 0.05 g of mesoporous Al2O3 and 0.05 g of mesoporous SiC, and the D50 of mesoporous SiC was 300 nm.

[0075] Example 6

[0076] The SiC power device packaging structure was prepared by the same method as in Example 1, except that the porous metal material used in preparing the nano-silver paste in Example 1 was 2.9 g of porous nickel, the inorganic nano-additive phase was 0.1 g of mesoporous Al2O3, and the mass of the organic carrier was 12 g; while the porous metal material in this example was 0.5 g of porous nickel, the inorganic nano-additive phase was 0.05 g of mesoporous Al2O3, and the mass of the organic carrier was 14.45 g.

[0077] Example 7

[0078] The SiC power device packaging structure was prepared by the same method as in Example 1, except that in Example 1, the porous metal material used in preparing the nano-silver paste was 2.9 g of porous nickel, the inorganic nano-additive phase was 0.1 g of mesoporous Al2O3, and the mass of the organic carrier was 12 g; while in this example, the porous metal material was 5 g of porous nickel, the inorganic nano-additive phase was 0.5 g of mesoporous Al2O3, and the mass of the organic carrier was 9.5 g.

[0079] Example 8

[0080] The SiC power device packaging structure was prepared by the same method as in Example 1, except that in Example 1, the pressure sintering condition in step S 2c was: after applying a pressure of 18 MPa, the sintering temperature was 250 °C for sintering; while in this example, the pressure sintering condition in step S 2c was: after applying a pressure of 18 MPa, the sintering temperature was 220 °C for sintering.

[0081] Example 9

[0082] The SiC power device packaging structure was prepared by the same method as in Example 1, except that in Example 1, the organic carrier used in preparing the nano-silver paste was a mixture of terpineol, isopropanol and polyvinyl alcohol in a mass ratio of 1:1.5:0.04, while in this example, the organic carrier was a mixture of terpineol, isopropanol and polyvinylpyrrolidone (PVP) in a mass ratio of 1:1.5:0.04, and the decomposition temperature of PVP was above 400 °C.

[0083] Table 1 shows the composition of the nano-silver powder, porous metal material, organic carrier, and inorganic nano-additive phase used in preparing the nano-silver paste in the above examples. The unit of each component is g, and the total mass of the prepared nano-silver paste is 100 g. Except for the nano-silver powder, porous metal carrier, and inorganic nano-additive phase, the balance is the organic carrier; in addition, Table 1 also shows the pressure sintering temperature used in the packaging process. It should be noted that for the sake of simplicity of the table, "Ex. 1" is used as the abbreviation of "Example 1", and the same applies to other examples.

[0084] Table 1

[0085]

[0086] Comparative Example 1

[0087] The SiC power device packaging structure was prepared by the same method as in Example 1, except that in this comparative example, the nano-silver paste was prepared only with nano-silver powder and an organic carrier. The preparation process was as follows: 85 g of nano-scale first silver powder and 15 g of organic carrier were placed in a wide-mouth bottle of a planetary mixer, stirred evenly with a spatula, mixed at 800 rpm for 3 min with the planetary mixer, and then ground 4 times with a three-roll mill. After testing that the grinding fineness was less than 5 μm, a uniformly mixed nano-silver paste was obtained. In this step, the D50 of the nano-scale first silver powder was 50 nm, and the organic carrier was a mixture of terpineol, isopropanol, and polyvinyl alcohol in a mass ratio of 1:1.5:0.04.

[0088] Comparative Example 2

[0089] The SiC power device packaging structure was prepared by the same method as in Example 1, except that in this comparative example, the nano-silver paste was prepared only with nano-silver powder and an organic carrier. The preparation process was as follows: 85 g of nano-scale second silver powder and 15 g of organic carrier were placed in a wide-mouth bottle of a planetary mixer, stirred evenly with a spatula, mixed at 800 rpm for 3 min with the planetary mixer, and then ground 4 times with a three-roll mill. After testing that the grinding fineness was less than 5 μm, a uniformly mixed nano-silver paste was obtained. In this step, the D50 of the nano-scale second silver powder was 200 nm, and the organic carrier was a mixture of terpineol, isopropanol, and polyvinyl alcohol in a mass ratio of 1:1.5:0.04.

[0090] Comparative Example 3

[0091] The SiC power device packaging structure was prepared by the same method as in Example 1, except that in this comparative example, the nano-silver paste was prepared only with nano-silver powder and an organic carrier. The preparation process was as follows: 35 g of nano-scale first silver powder, 50 g of nano-scale second silver powder, and 15 g of organic carrier were placed in a wide-mouth bottle of a planetary mixer, stirred evenly with a spatula, and mixed at 800 rpm for 3 min with the planetary mixer to obtain a uniformly mixed nano-silver paste. In this step, the D50 of the nano-scale first silver powder was 50 nm, the D50 of the nano-scale second silver powder was 200 nm, and the organic carrier was a mixture of terpineol, isopropanol, and polyvinyl alcohol in a mass ratio of 1:1.5:0.04.

[0092] Comparative Example 4

[0093] The SiC power device packaging structure was prepared by the same method as in Example 1, except that in this comparative example, porous metal materials were not used in the preparation of the nano-silver paste. The preparation process was as follows: First, 35 g of nano-sized first silver powder, 50 g of nano-sized second silver powder, 14.9 g of organic carrier, and 0.1 g of inorganic nano-additive were placed in a wide-mouth bottle of a planetary mixer, stirred evenly with a spatula, mixed at 800 rpm for 3 min with a planetary mixer, and then ground 4 times with a three-roll grinder. After testing that the grinding fineness was less than 5 μm, a uniformly mixed nano-silver paste was obtained. In this step, the D50 of the nano-sized first silver powder was 50 nm, the D50 of the nano-sized second silver powder was 200 nm, the organic carrier was a mixture of terpineol, isopropanol, and polyvinyl alcohol in a mass ratio of 1:1.5:0.04, and the inorganic nano-additive was mesoporous Al2O3.

[0094] Comparative Example 5

[0095] The SiC power device packaging structure was prepared by the same method as in Example 1, except that in this comparative example, inorganic nano-additives were not used in the preparation of the nano-silver paste. The preparation process was as follows:

[0096] S 1a First, 35 g of nano-sized first silver powder, 50 g of nano-sized second silver powder, and 12.1 g of organic carrier were placed in a wide-mouth bottle of a planetary mixer, stirred evenly with a spatula, mixed at 800 rpm for 3 min with a planetary mixer, and then ground 4 times with a three-roll grinder. After testing that the grinding fineness was less than 5 μm, a uniformly mixed sample was obtained;

[0097] S 2a 2.9 g of porous metal material was added to the sample obtained in step S 1a and stirred evenly with a spatula; then mixed at 800 rpm for 3 min with a planetary mixer to obtain a nano-silver paste with a Brookfield viscosity between 20 and 30 Pa·s.

[0098] Among them, in step S 1a , the D50 of the nano-sized first silver powder was 50 nm, and the D50 of the nano-sized second silver powder was 200 nm; in step S 2a , the porous metal material was porous nickel with a porosity of 90% and a D50 of 50 μm; in step S 1a , the organic carrier was a mixture of terpineol, isopropanol, and polyvinyl alcohol in a mass ratio of 1:1.5:0.04.

[0099] Comparative Example 6

[0100] The SiC power device packaging structure was prepared using the same method as in Example 1, except that in this comparative example, inorganic nano-mesoporous materials were not used in the preparation of the nano-silver paste, but inorganic nano-non-mesoporous materials were used. The preparation process was as follows:

[0101] S 1a First, 35 g of nano-scale first silver powder, 50 g of nano-scale second silver powder, 12 g of organic carrier, and 0.1 g of inorganic nano-additive phase were weighed and placed into a wide-mouth bottle of a planetary mixer. Stir evenly with a spatula, mix for 3 min at a speed of 800 rpm using the planetary mixer, and then grind 4 times with a three-roll grinder. Test that its grinding fineness is less than 5 μm to obtain a uniformly mixed sample;

[0102] S 2a 2.9 g of porous metal material was added to the sample obtained in step S 1a and stirred evenly with a spatula; then mix for 3 min at a speed of 800 rpm using the planetary mixer to obtain a nano-silver paste with a Brookfield viscosity between 20 and 30 Pa·s.

[0103] Among them, in step S 1a , the D50 of the nano-scale first silver powder was 50 nm, and the D50 of the nano-scale second silver powder was 200 nm; in step S 2a , the porous metal material was porous nickel with a porosity of 90% and a D50 of 50 μm; in step S 1a , the inorganic nano-additive phase was non-mesoporous Al2O3 with a D50 of 300 nm.

[0104] Comparative Example 7

[0105] The SiC power device packaging structure was prepared using the same method as in Example 1, except that in Example 1, 35 g of nano-scale first silver powder and 50 g of nano-scale second silver powder were used in the preparation of the nano-silver paste, while in this comparative example, only 85 g of nano-scale second silver powder was used. The preparation process was as follows:

[0106] S 1a First, 85 g of nano-scale second silver powder, 12 g of organic carrier, and 0.1 g of inorganic nano-additive phase were weighed and placed into a wide-mouth bottle of a planetary mixer. Stir evenly with a spatula, mix for 3 min at a speed of 800 rpm using the planetary mixer; then grind 4 times with a three-roll grinder. Test that its grinding fineness is less than 5 μm to obtain a uniformly mixed sample;

[0107] S 2a 2.9 g of porous metal material was added to the sample obtained in step S 1a and stirred evenly with a spatula; then mix for 3 min at a speed of 800 rpm using the planetary mixer to obtain a nano-silver paste with a Brookfield viscosity of 20 - 30 Pa·s.

[0108] Among them, in step S 1a , the D50 of the nanoscale second silver powder is 200 nm; in step S 2a , the porous metal material is porous nickel, its porosity is 90%, and D50 is 50 μm; in step S 1a , the inorganic nano-additive phase is mesoporous Al2O3, its D50 is 300 nm; and, in step S 1a , the organic carrier is a mixture of terpineol, isopropanol and polyvinyl alcohol in a mass ratio of 1:1.5:0.04.

[0109] Table 2 shows the compositions of the nano silver powder, porous metal material, organic carrier, and inorganic nano-additive phase used in preparing the nano silver paste in the above comparative examples. The unit of each component is g, and the total mass of the prepared nano silver paste is 100 g. Except for the nano silver powder, porous metal carrier, and inorganic nano-additive phase, the balance is the organic carrier; in addition, Table 2 also shows the pressure sintering temperature used in the encapsulation process. It should be noted that for the sake of simplicity of the table, "Dui 1" is used as the abbreviation of "Comparative Example 1", and the same applies to other comparative examples.

[0110] Table 2

[0111]

[0112] Test method:

[0113] (1) Shear strength test: Use a CONDOR150 type push-pull tester produced by XYZTEC Company. The shear speed of the push-pull machine is 100 μm / s, the shear height is 100 μm, the shear mode is the failure mode, and the unit is MPa;

[0114] (2) Thermal shock test: Use a two-chamber thermal shock test chamber produced by ACS Company. The thermal shock temperature range is -40°C to 175°C, cycle 1000 times, the temperature transition time is 15 s, and the heat preservation time is 15 min for both. Finally, perform a room temperature shear strength test on the samples after the shock;

[0115] (3) Porosity: Calculated through the Image Pro Plus image processing software for the SEM image. The specific operation is to convert the SEM photo into a grayscale image, adjust the threshold to select the pores, and the pore part will show a set color. When selecting the threshold, try to ensure that the pore part in the SEM photo is completely filled. Then, use the software to calculate the proportion of the pore part in the picture, that is, the porosity size of the SEM microstructure, and the unit is %;

[0116] (4)Thermal conductivity test: Test according to the ASTM-D5470 test standard using a DRL-III thermal conductivity tester purchased from Xiangtan Xiangyi Instrument Co., Ltd. Each sample is tested 5 times and the average value is taken, with the unit of W / m.K.

[0117] Table 3 shows the test data of the above embodiments. It should be noted that for the sake of table simplicity, "Ex. 1" is used as the abbreviation of "Example 1", and the same applies to other embodiments.

[0118] Table 3

[0119]

[0120] Table 4 shows the test data of the above comparative examples. It should be noted that for the sake of table simplicity, "Comp. 1" is used as the abbreviation of "Comparative Example 1", and the same applies to other comparative examples.

[0121] Table 4

[0122]

[0123] It can be seen from the above test data that:

[0124] All the data of the embodiments show excellent performance. The reason is that: all the embodiments use two different sizes of nano silver powder and are used in combination with porous metal materials and inorganic nano mesoporous materials. Those skilled in the art know that the driving force for sintering is the reduction of the total interfacial energy, and the sintering of nano silver mainly relies on the solid-state diffusion connection of silver particles. In the pressure sintering process of the nano silver film provided by the embodiments of the present invention, silver atoms will diffuse and fill into the pores of the porous metal material and the inorganic nano mesoporous material, forming sintering necks in the pores, and the crystal nuclei continue to grow, so that the porous metal material and the inorganic nano mesoporous material are interpenetrated and interconnected. Therefore, compared with the comparative examples, the embodiments of the present invention can reduce the porosity of the nano silver film after sintering, reduce the sintering stress, enhance the shear strength, and improve the high-temperature service stability and long-term service reliability of the interconnection joint.

[0125] By comparing the data of Comparative Examples 1 to 3, it can be seen that: the nano silver film provided by Comparative Example 3 shows better performance in terms of porosity, thermal conductivity, shear strength, etc. after sintering than Comparative Examples 1 and 2. The difference between Comparative Example 3 and Comparative Examples 1 and 2 is that Comparative Example 3 uses a mixture of two different sizes of nano silver powder, while Comparative Examples 1 and 2 only use one size of nano silver powder. The reason for the data difference among the three is that the mixture of two different sizes of nano silver powder in Comparative Example 3 can increase the packing density, reduce the porosity after sintering, and improve the performance such as thermal conductivity and shear strength.

[0126] Comparing Comparative Example 3 with Example 1, it can be seen that: the porosity of Comparative Example 3 is still relatively large, the densification after sintering is poor, the shear strength is small, the thermal conductivity is also small, and due to the large internal stress in the silver sintered joint, cracks are likely to be generated after thermal shock testing, resulting in poor reliability of the sintered joint.

[0127] The data of Comparative Examples 1-3 and Example 1 show that the use of two different-sized nano silver powders mixed is better than the use of one-sized nano silver powder. However, in the absence of the combined use of porous metal materials and inorganic nano mesoporous materials, their contribution to the technical effect is very limited.

[0128] Comparing the test data of Comparative Example 4 and Example 1, it can be seen that: all the data of Comparative Example 4 are worse than those of Example 1. On the basis of using two different-sized nano silver powders mixed, Comparative Example 4 uses inorganic nano mesoporous materials alone without using porous metal materials. Since the inorganic nano mesoporous materials have a large hardness, poor toughness and plasticity, it is easy to cause defects inside the sintered joint, with a large porosity and a reduced shear strength.

[0129] Comparing the test data of Comparative Example 5 and Example 1, it can be seen that: all the data of Comparative Example 5 are worse than those of Example 1. On the basis of using two different-sized nano silver powders mixed, Comparative Example 5 uses porous metal materials alone without using inorganic nano mesoporous materials. During the heating and pressure sintering process, due to the large sintering stress, cracks are likely to be generated after sintering, and due to low-temperature sintering, the interfacial bonding between different metals is poor, affecting the high-temperature service stability and long-term service reliability of the sintered joint.

[0130] The data of Comparative Examples 4-5 and Example 1 show that the use of inorganic nano mesoporous materials and porous metal materials alone cannot achieve good technical effects. Example 1 adds porous metal materials and inorganic nano mesoporous materials at the same time, using their synergistic effect to reduce the porosity, refine the sintered structure, reduce the sintering stress, increase the shear strength, and improve the reliability and stability of the sintered joint.

[0131] By comparing the test data of Comparative Example 6 with that of Example 1, it can be seen that all the data of Comparative Example 6 are worse than those of Example 1. The difference between Comparative Example 6 and Example 1 is that the inorganic nano-additive phase in Example 1 uses mesoporous nano-Al2O3, while that in Comparative Example 6 uses non-mesoporous nano-Al2O3. During the sintering process, silver atoms diffuse into the pores of mesoporous nano-Al2O3, improving the interfacial compatibility with nano-silver, and can better relieve the stress concentration caused by the mismatch of thermal expansion coefficients, reducing cracks. At the same time, due to its special structure, mesoporous nano-Al2O3 has a higher surface energy and stronger activity, and can effectively improve the interfacial bonding ability between different metals during low-temperature sintering, thereby improving the shear strength. However, the crystal structure of non-mesoporous nano-Al2O3 is relatively complete and has a high hardness. During low-temperature sintering, its interfacial compatibility with nano-silver is poor, which is prone to cracking during high-temperature service, affecting the service life of the chip.

[0132] By comparing the test data of Comparative Example 7 with that of Example 1, it can be seen that all the data of Comparative Example 7 are worse than those of Example 1. The difference between Comparative Example 7 and Example 1 is that Example 1 uses two different sizes of nano-scale silver powders to prepare nano-silver paste, while Comparative Example 7 only uses one nano-scale silver powder. This makes Comparative Example 7 also use inorganic nano-mesoporous materials and porous metal materials at the same time, but due to the low packing density of its silver powder, silver atoms cannot well fill the pores of the porous metal materials and inorganic nano-mesoporous materials, resulting in a higher porosity after sintering and a decrease in performance such as thermal conductivity and shear strength.

[0133] Furthermore, by comparing the test data of Examples 1 to 3, it can be seen that among Examples 1 to 3, although different porous metal materials are selected, they can all reduce the porosity, improve the shear strength, improve the thermal shock stability, and reduce the shear strength attenuation rate after thermal shock testing. And among them, the shear strength: Example 1 (porous nickel) > Example 3 (porous copper) > Example 2 (porous silver), and the shear strength attenuation rate: Example 2 (porous silver) > Example 3 (porous copper) > Example 1 (porous nickel). This is because the melting points of copper and nickel are higher than that of silver, which can prevent silver from further sintering, reduce stress, prevent cracks from generating inside the silver sintered joint, improve the shear strength, and reduce the attenuation rate. At the same time, due to the addition of inorganic mesoporous nano-Al2O3, the bonding performance of the Ni / Ag and Cu / Ag sintering interfaces during low-temperature sintering is improved, cracks are reduced, and the shear strength is increased.

[0134] By comparing the test data of Example 4 with that of Examples 1 to 3, it can be seen that the data performance of Example 4 is comparable to that of Examples 1 to 3. The difference between Example 4 and Examples 1 to 3 is that Example 4 uses a metal-organic framework material to replace the porous metal used in Examples 1 to 3. The metal-organic framework material can also produce a synergistic effect with inorganic mesoporous nano-Al2O3, reduce the porosity, refine the sintered structure, reduce the sintering stress, increase the shear strength, and improve the reliability and stability of the sintered joint.

[0135] By comparing the test data of Example 5 with that of Example 1, it can be seen that the data performance of Example 5 is comparable to that of Example 1 and slightly better than that of Example 1. The difference between Example 5 and Example 1 is that the inorganic nano-additive phase of Example 1 is only mesoporous Al2O3, while the inorganic nano-additive phase of Example 5 is a 1:1 mixture of mesoporous Al2O3 and mesoporous SiC. The comparable data of the two indicates that the porous metal material can also produce a synergistic effect with mesoporous nano-SiC, and the inorganic nano-mesoporous material is not limited to mesoporous Al2O3.

[0136] By comparing the test data of Examples 6 and 7 with that of Example 1, it can be seen that the data performance of Examples 6 and 7 is worse than that of Example 1. Compared with Example 1, the contents of the porous metal material and the inorganic nano-mesoporous material in Examples 6 and 7 are different. Among them, Example 6 reduces the use of the porous metal material and the inorganic nano-mesoporous material compared with Example 1, and Example 7 increases the use of the porous metal material and the inorganic nano-mesoporous material compared with Example 1. The performance of Example 1 is better than that of Examples 6 and 7, indicating that the appropriate addition of the porous metal material and the inorganic nano-mesoporous material can better reduce the porosity, increase the shear strength and the reliability of its sintered joint. Too little addition cannot meet the higher performance requirements, while too much addition will, to a certain extent, affect the hardness, thermal conductivity and high-temperature service reliability of the silver sintered joint.

[0137] By comparing the test data of Example 8 with that of Example 1, it can be seen that the thermal conductivity of Example 1 is better than that of Example 8. The pressure sintering temperature of Example 1 is 250 °C, and the pressure sintering temperature of Example 8 is 220 °C. Increasing the sintering temperature can increase the density and thickness of twins in the nano-silver sintered structure. The atomic arrangement at the twin boundaries is more regular, and the electron scattering ability is only one-tenth of that of the large-angle grain boundary, which can significantly improve the electrical and thermal conductivity of the material. The twin boundaries can also effectively hinder the movement of dislocations and increase the shear strength of the silver sintered joint.

[0138] By comparing the test data of Example 9 and Example 1, it can be seen that: the data of Example 1 is better than that of Example 9. The organic carrier in Example 1 is a mixture of terpineol, isopropanol and polyvinyl alcohol in a mass ratio of 1:1.5:0.04, and the organic carrier in Example 9 is a mixture of terpineol, isopropanol and PVP in a mass ratio of 1:1.5:0.04. The decomposition temperature of PVP is above 400°C, while the polyvinyl alcohol in Example 1 can be decomposed below 250°C. During the low-temperature sintering process, the polyvinyl alcohol thermally decomposes into carbon dioxide and water, which can improve the contact bonding performance with the chip and DBC substrate, further reduce the porosity, and reduce the resistivity of the silver sintered joint.

[0139] The specific embodiments of the present invention have been described above. Through the above description, relevant staff can make various changes and modifications within the scope not deviating from the technical idea of the present invention.

Claims

1. A nano silver paste for SiC semiconductor packaging, characterized in that: Calculated by mass percentage, it includes the following material components: Nano silver powder: 50wt%~90wt%; Porous metal materials: 0.1wt%~5wt%; Organic carrier: 5wt%~45wt%; Inorganic nano-additive phase: 0.01wt%~0.5wt%; Wherein: the nano silver powder is composed of a nano-scale first silver powder and a second silver powder, the D50 of the first silver powder is 20-100nm, and the D50 of the second silver powder is 100-800nm; the porous metal material is a porous metal and / or a metal organic framework material; and the inorganic nano added phase is an inorganic nano mesoporous material.

2. The nano silver paste for SiC semiconductor packaging according to claim 1, characterized in that: Based on the total amount of nano silver powder, the content of the first silver powder is 30% to 80%, and the remainder is the second silver powder.

3. The nano silver paste for SiC semiconductor packaging according to claim 1, characterized in that: The porous metal is any one or more of the following materials: porous silver, porous copper, porous nickel, porous aluminum; The porosity of porous metal is 60%~95% and the particle size is 10~150μm.

4. The nano silver paste for SiC semiconductor packaging according to claim 1, characterized in that: The metal organic framework material is a porous material formed by self-assembly of an inorganic metal center and an organic ligand, wherein the metal center is any one of Cu, Ag, Ni, Zn, and Co, and the organic ligand is any one of imidazole and its derivatives, and a carboxylic acid-based compound; The porosity of metal-organic framework materials is 50%~80% and the particle size is 1~15μm.

5. The nano silver paste for SiC semiconductor packaging according to claim 1, characterized in that: The inorganic nano-addition phase is any one or more of the following substances: nano-mesoporous Al2O3, nano-mesoporous SiO2, nano-mesoporous ZnO, nano-mesoporous TiC, nano-mesoporous SiC, nano-mesoporous AlN, nano-mesoporous BN; the particle size of the inorganic nano-addition phase is 200-800nm.

6. The nano silver paste for SiC semiconductor packaging according to claim 1, characterized in that: The organic carrier comprises a solvent and a binder, and the mass ratio of the solvent to the binder is (2-4):0.04; The solvent is any one or more of the following substances: pineol, isopropyl alcohol, alcohol ester dodecanol, n-butanol; the binder is any one or more of the following substances: polyvinyl alcohol, cellulose acetate, polyurethane, acrylic resin, polyhydroxybutyrate.

7. A method for preparing nano silver paste for SiC semiconductor packaging, characterized in that: The steps include: S 1a , mixing the weighed nano silver powder, organic carrier, and inorganic nano additive, and rolling to obtain a uniform sample; S 2a , to S 1a Add the weighed porous metal material into the uniform sample, mix well to obtain the nano silver paste; Step S 1a In the step S, the nano silver powder is composed of a nano-scale first silver powder and a second silver powder, the D50 of the first silver powder is 20-100 nm, the D50 of the second silver powder is 100-800 nm, and the inorganic nano added phase is an inorganic nano mesoporous material; 2a wherein the porous metal material is a porous metal and / or a metal organic framework material; Based on the total mass of the nano silver paste for SiC semiconductor packaging, the content of each substance is: nano silver powder 50wt%~90wt%, porous metal material 0.1wt%~5wt%, organic carrier 5wt%~45wt%, inorganic nano added phase 0.01wt%~0.5wt%.

8. A nanosilver film for SiC semiconductor packaging, characterized in that: The nano silver paste for SiC semiconductor packaging is prepared using the nano silver paste for SiC semiconductor packaging according to any one of claims 1 to 6.

9. A method for preparing a nanosilver film for SiC semiconductor packaging, characterized in that: The steps include: S 1b , using a coating machine to adsorb the plastic substrate onto the platform; S 2b , flowing the nano silver paste for SiC semiconductor packaging according to any one of claims 1 to 6 onto a plastic substrate to form a wet silver film; S 3b , drying the wet silver film to obtain a nano-silver film of preset thickness for SiC semiconductor packaging.

10. The method for preparing a nanosilver film for SiC semiconductor packaging according to claim 9, characterized in that: Step S 1b In the invention, any of the following plastic substrates is used: PET film, PI film, PTFE film, PFA film.

11. A SiC semiconductor power device packaging structure, characterized in that: The nano silver film for semiconductor packaging according to claim 8 is used for preparation.

12. A method for preparing a SiC semiconductor power device packaging structure, characterized in that: The steps include: S 1c , the nanosilver film for SiC semiconductor packaging as claimed in claim 8 is attached to the back of the SiC chip and the area of ​​the nanosilver film is the same as the area of ​​the back of the chip, and the surface of the SiC chip is plated with a metal coating; S 2c , step S 1c The obtained chip with a nanosilver film on the back is attached to the surface of the DBC board. After keeping warm for a preset time, the temperature is rapidly raised for pressure sintering. The sintering temperature is 200℃~250℃, and the sintering time is 1~20min. A SiC power device packaging structure is obtained with the upper layer being the chip, the middle layer being the sintered silver interconnect layer, and the lower layer being the DBC board.

13. The method for preparing a SiC semiconductor power device packaging structure according to claim 12, characterized in that: Step S 1c In the present invention, the metal coating on the surface of the SiC chip is any one or more of the following metals: Ag, Ni, Au, Pd.

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