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

Abstract

The invention provides nano silver paste for SiC semiconductor packaging, a silver film, a packaging structure and a preparation method thereof. The silver paste comprises 50-90 wt% of nano silver powder, 0.1-5 wt% of a porous metal material, 5-45 wt% of an organic carrier and 0.01-0.5 wt% of an inorganic nano mesoporous material, and the nano silver powder comprises two kinds of silver powder with different sizes; the porous metal material is porous metal and / or a metal organic framework material. Two kinds of nano silver powder with different sizes are adopted, the stacking density can be increased, the porosity of the nano silver paste after sintering can be reduced, in the sintering process, silver atoms can be diffused and filled into holes of the porous metal material and the inorganic nano mesoporous material, sintering necks are formed in the holes, crystal nucleuses continuously grow up, and the porosity of the nano silver paste is reduced. The porous metal material and the inorganic nano mesoporous material are interspersed and interactively connected, so that the high-temperature service stability and long-term service reliability of a silver sintered joint are improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor packaging technology, and in particular, to a nano-silver paste for SiC semiconductor packaging, a nano-silver film for SiC semiconductor packaging prepared using the nano-silver paste, a SiC semiconductor power device packaging structure prepared using the nano-silver film, and a preparation method for the aforementioned nano-silver paste, nano-silver film, and power device packaging structure. Background Art

[0002] With the advancement of science and technology, semiconductor devices are constantly developing towards high power, high integration, and miniaturization, which puts forward higher requirements for heat dissipation performance, electrical connection, and reliability. Especially in the application fields of high-power devices, such as aerospace, electronic communications, 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 harsh environments for a long time and maintain performance stability.

[0003] As power chips made of third-generation wide-bandgap semiconductor materials represented by SiC are widely used in some high-power devices, and based on the dual requirements of lead-free and high-temperature resistant development, nano silver paste solder and nano silver sintering interconnection technology have developed accordingly. 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, residual silver sintering materials around the chip, and the inability to form large-area sintering interconnections, which limits its application and promotion in high-power devices.

[0004] At present, nanosilver film products have been widely studied and applied. However, the nanosilver film in the prior art has the following disadvantages: 1. The performance of the welding joint is reduced due to the addition of a large amount of high-boiling point organic additives; 2. The porosity of the nanosilver film is large, and the connection strength and plasticity of the joint are generally poor, and the reliability is low under conditions such as impact, vibration, and temperature cycling; 3. The conventional nanosilver film has a large residual stress after sintering, and has poor aging performance such as cold and hot shock. Summary of the invention

[0005] In view of 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 SiC semiconductor power device packaging structure prepared by using the nano-silver film, and a preparation method of the aforementioned nano-silver paste, nano-silver film, and power device packaging structure. By adopting the technical scheme provided by the present invention, the porosity of the nano-silver paste after sintering 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 interconnection joint can be improved.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solution:

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

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

[0009] Porous metal materials: 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 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.

[0013] In the present technical scheme, two nano silver powders of different sizes are used to increase the packing density and reduce the porosity of the nano silver paste after sintering; 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 good ductility of the porous metal materials is utilized to improve the plasticity of the silver sintered joints and the shear strength; during the sintering process, silver atoms will diffuse and fill into the pores of the porous metal materials and the inorganic nano mesoporous materials, forming sintering necks in the pores, and the crystal nuclei will continue to grow, so that the porous metal materials and the inorganic nano mesoporous materials are interlaced and interconnected, thereby improving the high temperature service stability and long-term service reliability of the silver sintered joints.

[0014] The technical solution does not limit the shape of the nano silver powder, which can be spherical, flaky, quasi-spherical, irregular, etc. The porous metal in the technical solution is a lightweight structural material composed of a metal matrix skeleton and pores, and has the advantages of low density, good ductility, good thermal insulation, high porosity, and large specific surface area. Metal organic framework materials (MOFs, also known as metal organic framework compounds) are crystalline porous materials with a periodic network structure formed by self-assembly of inorganic metal centers and bridging organic ligands, and have both the rigidity of inorganic materials and the flexibility of organic materials.

[0015] Preferably, 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.

[0016] Preferably, the porous metal is any one or more of the following materials: porous silver, porous copper, porous nickel, porous aluminum; the porosity of the porous metal is 60% to 95%, and the particle size is 10 to 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, and Co, and the organic ligand is any one of imidazole and its derivatives, and carboxylic acid-based compounds; the porosity of the metal-organic framework material is 50% to 80%, and the particle size is 1 to 15 μm.

[0018] Preferably, the inorganic nano-added 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-added phase is 200~800nm.

[0019] Preferably, the organic carrier comprises 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: 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.

[0021] In the technical solution, the selected binder can be decomposed below 250°C. During the low-temperature sintering process of the nanosilver film, the binder is thermally decomposed into carbon dioxide and water, which can improve the contact and 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 pine alcohol, isopropyl alcohol and polyvinyl alcohol in a mass ratio of 1:1.5:0.04.

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

[0023] S 1a , mixing the weighed nano silver powder, organic carrier, and inorganic nano additive, and rolling to obtain a uniform sample;

[0024] S 2a , to S 1a Add the weighed porous metal material into the uniform sample, mix well to obtain the nano silver paste;

[0025] Step S 1aIn 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;

[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 added phase 0.01wt%~0.5wt%.

[0027] In this technical solution, the porous metal material has good structural stability, can enhance the degree of sintering, reduce porosity, and improve shear strength; the inorganic nano-mesoporous material can reduce the thermal expansion coefficient, reduce sintering stress, and improve the bonding performance of low-temperature sintering interfaces such as Ag / Cu or Ag / Ni by refining the sintering 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 a sintering neck in the pores, and the crystal nucleus continues to grow, so that the porous metal material and the inorganic nano-mesoporous material are interlaced and interconnected. At the same time, due to the special pore structure and good ductility of the porous metal material, the sintering residual stress can be further dispersed, the generation and expansion of cracks can be reduced, and the high-temperature service stability and long-term service reliability of the silver sintered joint can be improved. In the process of preparing nano-silver paste, this technical solution simultaneously adds porous metal materials and inorganic nano-mesoporous materials, and utilizes the synergistic effect of the two to reduce porosity, refine sintering structure, reduce sintering stress, improve shear strength, and improve the reliability and stability of the sintered joint.

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

[0029] S 1a 1. First, weigh the first nanometer silver powder, the second nanometer silver powder, the organic carrier, and the inorganic nanometer additive phase into a wide-mouth bottle of a planetary mixer, stir them evenly with a scraper, and mix them at 800 rpm for 3 minutes 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;

[0030] S 2a , adding porous metal material to step S 1a The obtained sample was stirred evenly with a spatula; then mixed with a planetary mixer at a speed of 800 rpm for 3 minutes to obtain a nano silver paste with a Brookfield viscosity between 5 and 100 Pa.s.

[0031] According to a third aspect of the present invention, there is provided a nanosilver film for SiC semiconductor packaging, which is prepared using the nanosilver paste for SiC semiconductor packaging as described in any one of the first aspect of the present invention.

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

[0033] S 1b , using a coating machine to adsorb the plastic substrate onto the platform;

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

[0035] S 3b , drying the wet silver film to obtain a nano-silver film of preset thickness for SiC semiconductor packaging.

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

[0037] S 1b 1. Use a temperature-controlled coating machine to vacuum-absorb the plastic substrate onto the platform to ensure that the surface of the plastic substrate is flat and free of bubbles;

[0038] S 2b , adding the nano silver paste for SiC semiconductor packaging described in any one of the first aspects of the present invention into the material barrel above the coating machine after vacuum degassing, adjusting the pressure and flow rate of the coating head so that the nano silver paste slowly flows through the coating head onto the plastic substrate, and using a scraper to scrape and coat it into a wet silver film with a regular shape and uniform thickness;

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

[0040] Preferably, step S 1b In the invention, any of the following plastic substrates is used: PET film, PI film, PTFE film, PFA film.

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

[0042] According to a 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 , the nanosilver film for SiC semiconductor packaging as described in any one of the third aspects of the present invention 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;

[0044] 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 1min~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.

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

[0046] S 1c , placing the nanosilver film for SiC semiconductor packaging as described in any one of the third aspects of the present invention with an underlying plastic substrate on a sampling table padded with a silicone pad, using a vacuum suction head capable of applying pressure to suck up a SiC chip with a metal coating on its surface, and applying a certain pressure at the same time, using the edge of the chip to cut off the nanosilver film of the same area as the back of the chip, so that the nanosilver film is separated from the plastic substrate and attached to the back of the chip;

[0047] S 2c , place the DBC plate on a heating platform at a temperature of 100-150°C, and 1c The obtained chip with a nanosilver film on the back is attached to the surface of the DBC board, and is kept warm for 10 to 30 minutes under vacuum or N2 protection, and then the temperature is rapidly increased for pressure sintering. The applied pressure is 10MPa to 25MPa, the sintering temperature is 200℃ to 250℃, and the sintering time is 1min to 20min, thereby obtaining a SiC power device packaging structure with the upper layer being the chip, the middle layer being the sintered silver interconnect layer, and the lower layer being the DBC board.

[0048] Preferably, 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.

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

[0050] The present invention adopts two nano silver powders of different sizes, which can increase the packing density and reduce the porosity of the nano silver paste after sintering; 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 good ductility of the porous metal materials is utilized to improve the plasticity of the silver sintered joint and the shear strength; during the sintering process, silver atoms diffuse and fill into the pores of the porous metal materials and the inorganic nano mesoporous materials, forming sintering necks in the pores, and the crystal nuclei continue to grow, so that the porous metal materials and the inorganic nano mesoporous materials are interlaced and interconnected, thereby improving the high temperature service stability and long-term service reliability of the silver sintered joint. DETAILED DESCRIPTION

[0051] In order to make the purpose, 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. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0052] Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of this application.

[0053] Example 1

[0054] (1) Preparation of nano silver paste

[0055] S 1a 1. First, 35 g of the first nanometer silver powder, 50 g of the second nanometer silver powder, 12 g of the organic carrier, and 0.1 g of the inorganic nanometer additive phase were put into a wide-mouth bottle of a planetary mixer, stirred evenly with a scraper, and mixed with the planetary mixer at a speed of 800 rpm for 3 min; then ground with a three-roll grinder for 4 times, and the grinding fineness was tested to be less than 5 μm, to obtain a uniformly mixed sample;

[0056] S 2a , add 2.9g of porous metal material to step S 1a The obtained sample was stirred evenly with a spatula; then mixed with a planetary mixer at a speed of 800 rpm for 3 minutes to obtain a nano silver paste with a Brookfield viscosity of 20-30 Pa.s.

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

[0058] (2) Preparation of nanosilver film

[0059] S 1b 1. Use a temperature-controlled coating machine to vacuum-absorb the plastic substrate onto the platform to ensure that the surface of the plastic substrate is flat and free of bubbles;

[0060] S 2b 2. After vacuum degassing, add the nano silver paste prepared in the above embodiment into the material barrel above the coating machine, adjust the pressure and flow rate of the coating head so that the nano silver paste slowly flows through the coating head onto the plastic substrate, and use a scraper to scrape and coat it into a wet silver film with regular shape and uniform thickness;

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

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

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

[0064] S 1c 1. Place the nanosilver film with the bottom plastic substrate on a sampling table padded with a silicone pad, use a vacuum suction head that can apply pressure to suck up the SiC chip with a metal coating on the surface, and apply a certain amount of pressure at the same time, use the edge of the chip to cut the nanosilver film with the same area as the back of the chip, so that the nanosilver film is separated from the plastic substrate and attached to the back of the chip;

[0065] S 2c , place the direct copper-clad ceramic substrate (DBC substrate) on a heating platform at a temperature of 100°C, and 1c The obtained chip with a nanosilver film on the back is attached to the surface of the DBC board and kept warm for 30 minutes under N2 protection. The temperature is then rapidly raised for pressure sintering. The applied pressure is 18 MPa, the sintering temperature is 250°C, and the sintering time is 5 minutes. 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.

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

[0067] Example 2

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

[0069] Example 3

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

[0071] Example 4

[0072] The SiC power device packaging structure is prepared by the same method as in Example 1, with the only difference being that the porous metal material used in preparing the nano-silver paste in Example 1 is a porous metal (specifically porous nickel), while the porous metal material in this embodiment is a metal organic framework material, specifically a porous material self-assembled by coordination 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 is prepared by the same method as in Example 1, with the only difference being that the inorganic nano-added phase used in preparing the nano-silver paste in Example 1 is 0.1 g of mesoporous Al2O3, while the inorganic nano-added phase in this example is 0.05 g of mesoporous Al2O3 and 0.05 g of mesoporous SiC, and the D50 of the mesoporous SiC is 300 nm.

[0075] Example 6

[0076] The SiC power device packaging structure was prepared by the same method as in Example 1, with the only difference being 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-added 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 embodiment was 0.5 g of porous nickel, the inorganic nano-added 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, with the only difference being 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-added 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 5 g of porous nickel, the inorganic nano-added 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 is prepared by the same method as in Example 1, except that in step S 2c The pressure sintering conditions are: after applying a pressure of 18 MPa, the sintering temperature is set at 250°C for sintering; and in this embodiment, step S 2c The pressure sintering conditions are: sintering at a temperature of 220° C. after applying a pressure of 18 MPa.

[0081] Example 9

[0082] The SiC power device packaging structure was prepared by the same method as in Example 1, with the only difference being that the organic carrier used in preparing the nano-silver paste in Example 1 was a mixture of pinene alcohol, isopropyl alcohol and polyvinyl alcohol in a mass ratio of 1:1.5:0.04, while the organic carrier in this embodiment was a mixture of pinene alcohol, isopropyl alcohol and polyvinyl pyrrolidone (PVP) in a mass ratio of 1:1.5:0.04, wherein 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 the preparation of the nano silver paste in the above embodiments. The unit of each component is g. The total mass of the prepared nano silver paste is 100g. In addition to 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 based on the simplicity of the table, "Example 1" is used as the abbreviation of "Example 1", and the other embodiments are similar.

[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 the nano-silver paste in this comparative example was prepared using only nano-silver powder and an organic carrier, and the preparation process was as follows: 85 g of the weighed first nano-scale silver powder and 15 g of the organic carrier were put into a wide-mouth bottle of a planetary mixer, stirred evenly with a scraper, mixed at 800 rpm for 3 min with a planetary mixer, and then ground 4 times with a three-roll grinder. The grinding fineness was tested to be less than 5 μm, and a uniformly mixed nano-silver paste was obtained; in this step, the D50 of the first nano-scale silver powder was 50 nm, and the organic carrier was a mixture of pine alcohol, isopropyl alcohol 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 the nano-silver paste in this comparative example was prepared using only nano-silver powder and an organic carrier, and the preparation process was as follows: 85 g of the weighed nano-grade second silver powder and 15 g of the organic carrier were put into a wide-mouth bottle of a planetary mixer, stirred evenly with a scraper, mixed at 800 rpm for 3 min with a planetary mixer, and then ground 4 times with a three-roll grinder. The grinding fineness was tested to be less than 5 μm, and a uniformly mixed nano-silver paste was obtained; in this step, the D50 of the nano-grade second silver powder was 200 nm, and the organic carrier was a mixture of pine alcohol, isopropyl alcohol 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, with the only difference being that, in this comparative example, the nano-silver paste was prepared using only nano-silver powder and an organic carrier, and the preparation process was as follows: 35 g of a first nano-scale silver powder, 50 g of a second nano-scale silver powder, and 15 g of an organic carrier were weighed and put into a wide-mouth bottle of a planetary mixer, stirred evenly with a scraper, and mixed with a planetary mixer at a speed of 800 rpm for 3 min to obtain a uniformly mixed nano-silver paste; in this step, the D50 of the first nano-scale silver powder was 50 nm, the D50 of the second nano-scale silver powder was 200 nm, and the organic carrier was a mixture of pine alcohol, isopropyl alcohol, and polyvinyl alcohol in a mass ratio of 1:1.5:0.04.

[0092] Comparative Example 4

[0093] The SiC power device packaging structure is prepared by the same method as in Example 1, with the only difference being that, in this comparative example, porous metal material is not used in the preparation of nano silver paste, and the preparation process is as follows: first, 35 g of the weighed first nano silver powder, 50 g of the second nano silver powder, 14.9 g of the organic carrier, and 0.1 g of the inorganic nano added phase are put into a wide-mouth bottle of a planetary mixer, stirred evenly with a scraper, mixed at 800 rpm for 3 min with a planetary mixer, and then ground 4 times with a three-roll grinder. The grinding fineness is tested to be less than 5 μm, and a uniformly mixed nano silver paste is obtained. In this step, the D50 of the first nano silver powder is 50 nm, the D50 of the second nano silver powder is 200 nm, the organic carrier is a mixture of pine oil, isopropyl alcohol and polyvinyl alcohol in a mass ratio of 1:1.5:0.04, and the inorganic nano added phase is 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, the nano silver paste was prepared without using an inorganic nano additive phase, and the preparation process was as follows:

[0096] S 1a , firstly put 35g of the first nano-scale silver powder, 50g of the second nano-scale silver powder, and 12.1g of the organic carrier into a wide-mouth bottle of a planetary mixer, stir them evenly with a scraper, mix them at 800rpm for 3min with a planetary mixer, and then grind them 4 times with a three-roll grinder, and test the grinding fineness to be less than 5μm, to obtain a uniformly mixed sample;

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

[0098] Among them, step S 1a In step S, the D50 of the first nanometer-sized silver powder is 50 nm, and the D50 of the second nanometer-sized silver powder is 200 nm; 2a In the step S, the porous metal material is porous nickel, the porosity of which is 90%, and D50 is 50 μm; 1a The organic carrier is a mixture of terpineol, isopropyl alcohol 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 by the same method as in Example 1, except that in this comparative example, inorganic nano-mesoporous material was not used in the preparation of the nano-silver paste, but inorganic nano-non-mesoporous material was used. The preparation process was as follows:

[0101] S 1a 1. First, 35 g of the first nano-scale silver powder, 50 g of the second nano-scale silver powder, 12 g of the organic carrier, and 0.1 g of the inorganic nano-additive phase were weighed and put into a wide-mouth bottle of a planetary mixer, and stirred evenly with a scraper. The mixture was mixed at 800 rpm for 3 min with a planetary mixer, and then ground with a three-roll grinder for 4 times. The grinding fineness was tested to be less than 5 μm, and a uniformly mixed sample was obtained.

[0102] S 2a , add 2.9g of porous metal material to step S 1a The obtained sample was stirred evenly with a spatula; then mixed with a planetary mixer at a speed of 800 rpm for 3 minutes to obtain a nano silver paste with a Brookfield viscosity between 20 and 30 Pa.s.

[0103] Among them, step S 1a In step S, the D50 of the first nanometer-sized silver powder is 50 nm, and the D50 of the second nanometer-sized silver powder is 200 nm; 2a In the step S, the porous metal material is porous nickel, the porosity of which is 90%, and D50 is 50 μm; 1a In the nanostructured composite, the inorganic nanoparticle phase is non-mesoporous Al2O3, and its D50 is 300nm.

[0104] Comparative Example 7

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

[0106] S 1a 1. First, 85 g of the weighed nano-grade second silver powder, 12 g of the organic carrier, and 0.1 g of the inorganic nano-additive phase were put into a wide-mouth bottle of a planetary mixer, stirred evenly with a scraper, and mixed at 800 rpm with a planetary mixer for 3 min; then ground with a three-roll grinder for 4 times, and the grinding fineness was tested to be less than 5 μm, to obtain a uniformly mixed sample;

[0107] S 2a , add 2.9g of porous metal material to step S 1a The obtained sample was stirred evenly with a spatula; then mixed with a planetary mixer at a speed of 800 rpm for 3 minutes to obtain a nano silver paste with a Brookfield viscosity of 20-30 Pa.s.

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

[0109] Table 2 shows the composition of the nano silver powder, porous metal material, organic carrier, and inorganic nano additive phase used in the preparation of the nano silver paste in the above comparative examples. The unit of each component is g. The total mass of the prepared nano silver paste is 100g. In addition to 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 packaging process. It should be noted that based on the simplicity of the table, "Comparative Example 1" is used as the abbreviation of "Comparative Example 1", and the other comparative examples are similar.

[0110] Table 2

[0111]

[0112] Test method:

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

[0114] (2) Hot and cold shock test: A two-chamber hot and cold shock test chamber produced by ACS was used. The hot and cold shock temperature range was -40°C to 175°C, and the cycle was 1000 cycles. The temperature transition time was 15s, and the insulation time was 15min. Finally, the samples after impact were subjected to room temperature shear strength test.

[0115] (3) Porosity: Calculated by Image Pro Plus image processing software on SEM images. 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 appear in the 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 image, that is, the porosity of the SEM microstructure, in units of %;

[0116] (4) Thermal conductivity test: According to the ASTM-D5470 test standard, the DRL-III thermal conductivity tester purchased from Xiangtan Xiangyi Instrument Co., Ltd. was used for testing. Each sample was tested 5 times and the average value was taken in W / mK.

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

[0121] Table 4

[0122]

[0123] From the above test data we can see that:

[0124] The data performance of all embodiments is relatively good, because: all embodiments use two nano silver powders of different sizes, and use porous metal materials and inorganic nano mesoporous materials in combination. Those skilled in the art know that the driving force of sintering is the reduction of total interfacial energy, and nano silver sintering mainly relies on the solid diffusion connection of silver particles. In the process of pressurized sintering of the nano silver film provided by the embodiment 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 a sintering neck in the pores, and the crystal nucleus will continue to grow, so that the porous metal material and the inorganic nano mesoporous material are interspersed and interconnected. Therefore, compared with the comparative example, the embodiment 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 after sintering, the porosity, thermal conductivity, shear strength and other data of the nanosilver film provided by Comparative Example 3 are better than those of 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 nanosilver powders of different sizes, while Comparative Examples 1 and 2 only use one size of nanosilver powder. The reason for the difference in the data among the three is that the mixture of two nanosilver powders of different sizes in Comparative Example 3 can increase the packing density, reduce the porosity after sintering, and improve the thermal conductivity and shear strength and other performances.

[0126] By comparing Comparative Example 3 with Example 1, it can be seen that the porosity of Comparative Example 3 is still relatively large, the density after sintering is relatively poor, the shear strength is relatively small, the thermal conductivity is also relatively small, and due to the large internal stress of the silver sintered joint, cracks are easily generated after the hot and cold shock test, resulting in poor reliability of the sintered joint.

[0127] The data of Comparative Examples 1-3 and Example 1 show that the mixed use of two nano-silver powders of different sizes is better than the use of nano-silver powder of one size, but in the absence of the use of porous metal materials and inorganic nano-mesoporous materials, its 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 the data of Comparative Example 4 are all worse than those of Example 1. Comparative Example 4 uses two nano-silver powders of different sizes mixed together, and uses inorganic nano-mesoporous materials alone without using porous metal materials. Since the inorganic nano-mesoporous materials have high hardness, poor toughness and plasticity, they are prone to defects inside the sintered joint, high porosity, and reduced shear strength.

[0129] Comparing the test data of Comparative Example 5 and Example 1, it can be seen that the data of Comparative Example 5 are all worse than those of Example 1. Comparative Example 5 uses two nano silver powders of different sizes mixed together, and uses porous metal materials alone without using inorganic nano mesoporous materials. During the heating and pressurizing sintering process, due to the large sintering stress, cracks are easily generated after sintering, and due to the low temperature sintering, the interface bonding between different metals is poor, which affects 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, and utilizes the synergistic effect of the two to reduce porosity, refine sintering structure, reduce sintering stress, increase shear strength, and improve the reliability and stability of sintered joints.

[0131] Comparing the test data of Comparative Example 6 with that of Example 1, it can be seen that the performance of each data of Comparative Example 6 is worse than that of Example 1. The difference between Comparative Example 6 and Example 1 is that the inorganic nano-additive phase of Example 1 adopts mesoporous nano-Al2O3, while the inorganic nano-additive phase adopted in Comparative Example 6 is non-mesoporous nano-Al2O3. During the sintering process, silver atoms diffuse into the pores of mesoporous nano-Al2O3, which improves the interface compatibility with nano-silver, can better alleviate the stress concentration caused by the mismatch of thermal expansion coefficient, and reduce cracks. At the same time, mesoporous nano-Al2O3 has a special structure, higher surface energy, and stronger activity, which can effectively improve the interface bonding ability between different metals during low-temperature sintering, thereby improving the shear strength. The non-mesoporous nano-Al2O3 has a relatively complete crystal structure and high hardness. During low-temperature sintering, the interface compatibility with nano-silver is poor, which is easy to cause cracking during high-temperature service, affecting the service life of the chip.

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

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

[0134] Comparing the test data of Example 4 with those 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, and the metal organic framework material can also produce a synergistic effect with the inorganic mesoporous nano-Al2O3 to reduce the porosity, refine the sintering structure, reduce the sintering stress, increase the shear strength, and improve the reliability and stability of the sintered joint.

[0135] 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 and slightly better than that of Example 1. The difference between Example 5 and Example 1 is that the inorganic nano-addition phase of Example 1 is only mesoporous Al2O3, while the inorganic nano-addition phase of Example 5 is a mixture of mesoporous Al2O3 and mesoporous SiC in a ratio of 1:1. The comparable data of the two indicate that porous metal materials can also produce synergistic effects with mesoporous nano-SiC, and inorganic nano-mesoporous materials are not limited to mesoporous Al2O3.

[0136] 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 content of porous metal materials and inorganic nano-mesoporous materials in Examples 6 and 7 is different, among which Example 6 reduces the use of porous metal materials and inorganic nano-mesoporous materials compared with Example 1, and Example 7 increases the use of porous metal materials and inorganic nano-mesoporous materials compared with Example 1. The performance of Example 1 is better than that of Examples 6 and 7, indicating that the appropriate addition of porous metal materials and inorganic nano-mesoporous materials can better reduce the porosity, improve the shear strength and the reliability of the sintered joint. Too little addition will not meet the higher performance requirements, and too much addition will affect the hardness, thermal conductivity and high-temperature service reliability of the silver sintered joint to a certain extent.

[0137] Comparing the test data of Example 8 and 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 nanosilver sintered structure. The atomic arrangement at the twins 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 dislocation movement and improve 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 of Example 1 is a mixture of pinene alcohol, isopropyl alcohol and polyvinyl alcohol in a mass ratio of 1:1.5:0.04, and the organic carrier of Example 9 is a mixture of pinene alcohol, isopropyl alcohol and PVP in a mass ratio of 1:1.5:0.04, wherein 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, polyvinyl alcohol is thermally decomposed into carbon dioxide and water, which can improve the contact and bonding performance with the chip and DBC substrate, further reduce the porosity, and reduce the resistivity of the silver sintered joint.

[0139] The above describes the specific embodiments of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical concept 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.

Images