Preparation method of high-reliability aluminum nitride applied to IGBT

Abstract

The application relates to the field of aluminum nitride materials, and provides a preparation method of high-reliability aluminum nitride applied to IGBT, solves the defects that the bending strength of an aluminum nitride substrate in the prior art is not high and the heat shock resistance is poor, and comprises the following preparation steps: (1) powder pretreatment; (2) flow casting; (3) glue removal; (4) sintering; and (5) post-treatment.

Description

Technical Field

[0001] This invention relates to the field of aluminum nitride materials, and more particularly to a method for preparing high-reliability aluminum nitride for use in IGBTs. Background Technology

[0002] Aluminum nitride ceramics have become a key substrate material for high-power insulated-gate bipolar transistor (IGBT) module packaging due to their excellent high thermal conductivity, thermal expansion coefficient matching that of silicon, and good electrical insulation. As power electronic equipment develops towards high voltage and high power density, the specifications of IGBT modules are constantly increasing, placing higher demands on the size and reliability of aluminum nitride substrates, necessitating the development of large-size substrates with areas reaching 140mm × 190mm.

[0003] However, due to defects in the raw materials and manufacturing processes used in existing large-size substrates, the resulting bending strength and thermal shock resistance are not high.

[0004] Chinese Patent Publication No. CN112142474A discloses a method for preparing a water-based cast aluminum nitride ceramic substrate with high thermal conductivity, comprising the following preparation steps: (1) surface modification of aluminum nitride powder with aluminum dihydrogen phosphate; (2) weighing the modified aluminum nitride powder, dispersant, plasticizer, and binder and mixing them evenly; (3) vacuum degassing; (4) preparation of the green body, using a combination of cast aluminum tinning and cold isostatic pressing; (5) debinding, and holding at 180℃-460℃ for 2-3 hours; (6) sintering at 1600℃-1750℃ for 4-6 hours under a nitrogen atmosphere. The solvent used in this application is water, which is safe, green, and environmentally friendly. The slurry has good stability, and the ceramic substrate obtained is claimed to have high thermal conductivity. The process is simple and the production cost is low, making it suitable for high power density circuits, IGBTs, and other fields. However, its surface modification of aluminum nitride powder is only conventional ball milling, which makes it difficult to ensure that the sintering aids achieve a relatively uniform coating on the aluminum nitride powder. The forming process adopts tape casting and cold isostatic pressing. For large-size thin blanks, cold isostatic pressing is prone to introducing new stress and density gradients, increasing the risk of blank deformation and delamination. Therefore, it is not suitable for the preparation of large-scale aluminum nitride substrates. Summary of the Invention

[0005] Therefore, in view of the above problems, the present invention provides a method for preparing high-reliability aluminum nitride for IGBTs, which solves the defects of low bending strength and poor thermal shock resistance of aluminum nitride substrates in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for preparing high-reliability aluminum nitride for IGBTs, comprising the following preparation steps:

[0007] (1) Powder pretreatment: Select aluminum nitride powder with a purity of ≥99.9%, add it to the integrated solution dispersion, stir at a speed of 1500rpm-3000rpm to form a uniform slurry, pump the slurry into a ball mill, and ball mill for 1h-2h. Use zirconia beads with a diameter of 0.3mm-0.8mm during ball milling. Then transfer the slurry into a storage tank with a speed of 200rpm-300rpm for later use. Then pump the slurry into a spray drying tower for drying to obtain pretreated powder. Finally, calcine the pretreated powder in a nitrogen atmosphere at 450℃-550℃ for 1h-2h to obtain composite powder.

[0008] (2) Casting: The composite powder obtained in step (1) is mixed with an organic carrier and a solvent to prepare a casting slurry with a solid content of 30wt%-45wt%. After vacuum degassing, it is formed on a casting machine to obtain a green strip with a thickness of 0.5mm-1.2mm, and then cut into a size of 140mm×190mm.

[0009] (3) Debinding: The green body is heated to 500℃-600℃ at a heating rate of 0.5℃ / min-2℃ / min under the protection of flowing nitrogen atmosphere, and kept at the temperature for 1h-3h;

[0010] (4) Sintering: The debinding blank is placed in a high-temperature sintering furnace and sintered under a flowing high-purity nitrogen atmosphere. The sintering regime is as follows: the temperature is raised to 1300℃-1500℃ at a rate of 3℃ / min-8℃ / min, and then raised to the final sintering temperature of 1750℃-1850℃ at a rate of 1℃ / min-3℃ / min. The temperature is held at this temperature for 2h-5h, and then cooled with the furnace.

[0011] (5) Post-processing: The sintered aluminum nitride substrate is ground and polished on both sides to make its surface roughness Ra≤0.4μm. Then, a copper layer is coated on the substrate surface by active metal brazing to complete the metallization.

[0012] Furthermore, the integrated solution dispersion is made from the following raw materials in parts by weight: 100 parts deionized water, 40-50 parts anhydrous ethanol, 0.5-1.5 parts inorganic dispersant, 2-5 parts yttrium nitrate, 0.5-1.5 parts calcium nitrate, and an appropriate amount of pH adjuster to adjust the pH to 9-10.

[0013] Furthermore, the preparation process of the integrated solution dispersion is as follows: under stirring, the inorganic dispersant is added to the mixed solvent of deionized water and anhydrous ethanol and fully dissolved. Then, yttrium nitrate and calcium nitrate are added in sequence and stirred until completely dissolved and mixed evenly. Finally, the pH adjuster is added to adjust the pH value of the solution to 9-10, thereby obtaining the integrated solution dispersion.

[0014] Furthermore, the inorganic dispersant is any one of sodium hexametaphosphate, ammonium polyacrylate, and ammonium polymethacrylate.

[0015] Furthermore, the pH adjuster is any one of ammonia, tetramethylammonium hydroxide, or organic amine.

[0016] Furthermore, the inlet air temperature of the spray drying tower is 200℃-250℃, and the outlet air temperature is 90℃-110℃.

[0017] Furthermore, the composite powder obtained in step (1) is a spherical or near-spherical granulated powder with an average particle size D50 between 50 μm and 150 μm.

[0018] Furthermore, the organic carrier in step (2) is a mixture of 8-12 parts by weight of polyvinyl butyral, 3-8 parts by weight of polyethylene glycol, and 0.3-1.0 parts by weight of phosphate ester.

[0019] Furthermore, the solvent in step (2) is anhydrous ethanol.

[0020] By adopting the aforementioned technical solution, the beneficial effects of the present invention are as follows:

[0021] 1. This application obtains an aluminum nitride substrate with a size of 140mm*190mm by pre-treating the powder and using specific casting, debinding and sintering processes. The substrate has a three-point bending strength of more than 500MPa and can withstand more than 240 severe thermal shock cycles, meeting the requirements of high-end IGBT modules for packaging substrates.

[0022] 2. An integrated solution dispersion with a specific formulation is used to disperse aluminum nitride powder. The precise content of yttrium nitrate and calcium nitrate ensures that the sintering aid can fully form a liquid phase to promote densification without leaving excessive residue that would impair thermal conductivity. Adjusting the pH value to 9-10 enables the powder surface to carry a strong negative charge, achieving better dispersion stability of the slurry through electrostatic repulsion, laying the foundation for obtaining a uniform microstructure in the subsequent process.

[0023] 3. This application specifies the preparation sequence of the integrated dispersion. This preparation process ensures that the inorganic dispersant preferentially and fully dissolves and adsorbs onto the powder surface, forming a stable steric hindrance layer. Subsequently added auxiliary precursor salts can be uniformly distributed in the solution, and finally, the pH value is adjusted to fix the dispersion state. This sequence avoids possible ineffective reactions or flocculation between components, ensuring the long-term stability and homogeneity of the solution.

[0024] 4. This application specifies the inlet and outlet air temperatures for spray drying. An inlet air temperature of 200-250℃ ensures that the slurry droplets are dried and shaped instantly, forming spherical particles with a loose structure and good flowability. At the same time, controlling the outlet air temperature at 90-110℃ can avoid the organic dispersant or additive salt decomposition and denaturation due to excessively high temperature, or incomplete drying and particle adhesion due to excessively low temperature.

[0025] 5. During the preparation of the integrated solution dispersion, the pH is adjusted and stabilized within the alkaline range of 9-10, which can optimize the absolute value of the Zeta potential on the powder surface, enhance the electrostatic stabilization effect, and also inhibit the hydrolysis side reaction of aluminum nitride powder, ensuring the chemical stability of the slurry. Detailed Implementation

[0026] Example 1

[0027] A method for preparing high-reliability aluminum nitride for IGBTs includes the following preparation steps:

[0028] (1) Powder pretreatment: Aluminum nitride powder with a purity of 99.9% is selected and added to the integrated solution dispersion. The mixture is stirred at a speed of 1500 rpm to form a uniform slurry. The slurry is pumped into a ball mill and ball milled for 1 hour. Zirconia beads with a diameter of 0.3 mm are used during ball milling. The slurry is then transferred to a storage tank with a speed of 200 rpm for later use. The slurry is then pumped into a spray drying tower for drying. The inlet air temperature of the spray drying tower is 200℃ and the outlet air temperature is 90℃ to obtain pretreated powder. Finally, the pretreated powder is calcined at 450℃ for 1 hour in a nitrogen atmosphere to obtain composite powder. The composite powder is a spherical granulated powder with an average particle size D50 of 50 μm.

[0029] The integrated solution dispersion is made from the following raw materials in parts by weight: 100 parts deionized water, 40 parts anhydrous ethanol, 0.5 parts sodium hexametaphosphate, 2 parts yttrium nitrate, 0.5 parts calcium nitrate, and an appropriate amount of ammonia water to adjust the pH to 9. The preparation process of the integrated solution dispersion is as follows: under stirring, the inorganic dispersant is added to the mixed solvent of deionized water and anhydrous ethanol and fully dissolved. Then, yttrium nitrate and calcium nitrate are added in sequence and stirred until completely dissolved and mixed evenly. Finally, the ammonia water is added to adjust the pH of the solution to 9, thus obtaining the integrated solution dispersion.

[0030] (2) Casting: The composite powder obtained in step (1) is mixed with an organic carrier and anhydrous ethanol to prepare a casting slurry with a solid content of 30wt%. After vacuum degassing, it is formed on a casting machine to obtain a green strip with a thickness of 0.5mm, and then cut into a size of 140mm×190mm.

[0031] The organic carrier is a mixture of 8 parts by weight of polyvinyl butyral, 3 parts by weight of polyethylene glycol, and 0.3 parts by weight of phosphate ester.

[0032] (3) Debinding: The green body is heated to 500°C at a heating rate of 0.5°C / min under the protection of flowing nitrogen atmosphere, and kept at the temperature for 1 hour;

[0033] (4) Sintering: The blank after debinding is placed in a high-temperature sintering furnace and sintered under the protection of a flowing high-purity nitrogen atmosphere. The sintering regime is as follows: the temperature is raised to 1300℃ at a rate of 3℃ / min, and then raised to the final sintering temperature of 1750℃ at a rate of 1℃ / min. The temperature is held at this temperature for 2 hours, and then cooled with the furnace.

[0034] (5) Post-processing: The sintered aluminum nitride substrate is ground and polished on both sides to make its surface roughness Ra=0.4μm. Then, a copper layer is coated on the substrate surface by active metal brazing to complete the metallization.

[0035] Example 2

[0036] A method for preparing high-reliability aluminum nitride for IGBTs includes the following preparation steps:

[0037] (1) Powder pretreatment: Aluminum nitride powder with a purity of 99.95% is selected and added to the integrated solution dispersion. The mixture is stirred at a speed of 2250 rpm to form a uniform slurry. The slurry is pumped into a ball mill and ball milled for 1.5 h. Zirconia beads with a diameter of 0.55 mm are used during ball milling. The slurry is then transferred to a storage tank with a speed of 250 rpm for later use. The slurry is then pumped into a spray drying tower for drying. The inlet air temperature of the spray drying tower is 225℃ and the outlet air temperature is 100℃ to obtain pretreated powder. Finally, the pretreated powder is calcined at 500℃ for 1.5 h in a nitrogen atmosphere to obtain composite powder. The composite powder is a spherical granulated powder with an average particle size D50 of 100 μm.

[0038] The integrated solution dispersion is made from the following raw materials in parts by weight: 100 parts deionized water, 45 parts anhydrous ethanol, 1 part ammonium polyacrylate, 3.5 parts yttrium nitrate, 1 part calcium nitrate, and an appropriate amount of tetramethylammonium hydroxide to adjust the pH to 9.5. The preparation process of the integrated solution dispersion is as follows: under stirring, the ammonium polyacrylate is added to the mixed solvent of deionized water and anhydrous ethanol and fully dissolved. Then, yttrium nitrate and calcium nitrate are added in sequence and stirred until completely dissolved and mixed evenly. Finally, the tetramethylammonium hydroxide is added to adjust the pH of the solution to 9.5, thus obtaining the integrated solution dispersion.

[0039] (2) Casting: The composite powder obtained in step (1) is mixed with an organic carrier and anhydrous ethanol to prepare a casting slurry with a solid content of 37.5wt%. After vacuum degassing, it is formed on a casting machine to obtain a green strip with a thickness of 0.9mm, and then cut into a size of 140mm×190mm.

[0040] The organic carrier is a mixture of 10 parts by weight of polyvinyl butyral, 5.5 parts by weight of polyethylene glycol, and 0.65 parts by weight of phosphate ester.

[0041] (3) Debinding: The green body is heated to 550°C at a heating rate of 1.3°C / min under the protection of flowing nitrogen atmosphere, and held at the temperature for 2 hours;

[0042] (4) Sintering: The blank after debinding is placed in a high-temperature sintering furnace and sintered under the protection of a flowing high-purity nitrogen atmosphere. The sintering regime is as follows: the temperature is raised to 1400℃ at a rate of 5.5℃ / min, and then raised to the final sintering temperature of 1800℃ at a rate of 2℃ / min. The temperature is held at this temperature for 3.5h, and then cooled with the furnace.

[0043] (5) Post-processing: The sintered aluminum nitride substrate is ground and polished on both sides to make its surface roughness Ra 0.35μm. Then, a copper layer is coated on the substrate surface by active metal brazing to complete the metallization.

[0044] Example 3

[0045] A method for preparing high-reliability aluminum nitride for IGBTs includes the following preparation steps:

[0046] (1) Powder pretreatment: Aluminum nitride powder with a purity of 99.98% is selected and added to the integrated solution dispersion. The mixture is stirred at a speed of 3000 rpm to form a uniform slurry. The slurry is pumped into a ball mill and ball milled for 2 hours. Zirconia beads with a diameter of 0.8 mm are used during ball milling. The slurry is then transferred to a storage tank with a speed of 300 rpm for later use. The slurry is then pumped into a spray drying tower for drying. The inlet air temperature of the spray drying tower is 250℃ and the outlet air temperature is 110℃ to obtain pretreated powder. Finally, the pretreated powder is calcined at 550℃ for 2 hours in a nitrogen atmosphere to obtain composite powder. The composite powder is spherical or near-spherical granulated powder with an average particle size D50 between 150 μm.

[0047] The integrated solution dispersion is made from the following raw materials in parts by weight: 100 parts deionized water, 50 parts anhydrous ethanol, 1.5 parts ammonium polymethacrylate, 5 parts yttrium nitrate, 1.5 parts calcium nitrate, and an appropriate amount of organic amine to adjust the pH to 10. The preparation process of the integrated solution dispersion is as follows: under stirring, the inorganic dispersant is added to the mixed solvent of deionized water and anhydrous ethanol and fully dissolved. Then, yttrium nitrate and calcium nitrate are added sequentially and stirred until completely dissolved and mixed evenly. Finally, the organic amine is added to adjust the pH of the solution to 10, thus obtaining the integrated solution dispersion.

[0048] (2) Casting: The composite powder obtained in step (1) is mixed with an organic carrier and anhydrous ethanol to prepare a casting slurry with a solid content of 45wt%. After vacuum degassing, it is formed on a casting machine to obtain a green strip with a thickness of 1.2mm, and then cut into a size of 140mm×190mm.

[0049] The organic carrier is a mixture of 12 parts by weight of polyvinyl butyral, 8 parts by weight of polyethylene glycol, and 1.0 part by weight of phosphate ester.

[0050] (3) Debinding: The green body is heated to 600°C at a heating rate of 2°C / min under the protection of flowing nitrogen atmosphere, and kept at the temperature for 3h;

[0051] (4) Sintering: The blank after debinding is placed in a high-temperature sintering furnace and sintered under the protection of a flowing high-purity nitrogen atmosphere. The sintering regime is as follows: the temperature is raised to 1500℃ at a rate of 8℃ / min, and then raised to the final sintering temperature of 1850℃ at a rate of 3℃ / min. The temperature is held at this temperature for 5 hours, and then cooled with the furnace.

[0052] (5) Post-processing: The sintered aluminum nitride substrate is ground and polished on both sides to make its surface roughness Ra=0.3μm. Then, a copper layer is coated on the substrate surface by active metal brazing to complete the metallization.

[0053] Comparative Example 1

[0054] Referring to Example 1, this comparative example does not have a powder pretreatment step. The aluminum nitride powder is directly mixed with an organic carrier and anhydrous ethanol to prepare a casting slurry. The other steps are the same as in Example 1.

[0055] Comparative Example 2

[0056] Referring to Example 1, in this comparative example, the sintering process was changed to a heating rate of 5℃ / min to 1800℃ and a holding time of 4h. Other techniques were the same as in Example 1.

[0057] The aluminum nitride substrates obtained by the preparation methods of Examples 1 to 3 and Comparative Examples 1 and 3 of this application were subjected to performance testing, and the results are shown in the table below:

[0058]

[0059] The flexural strength test standard is based on GB / T 6569-2006, the thermal shock cycle test standard is based on MIL-STD-883G 1010.9, and the thermal conductivity test standard is based on ASTM E1461.

[0060] The tests show that the aluminum nitride substrate prepared by the method of this application has a higher bending strength than Comparative Example 1 and Comparative Example 2, and better thermal shock resistance and thermal conductivity.

[0061] Although the invention has been specifically shown and described in conjunction with preferred embodiments, those skilled in the art should understand that various changes in form and detail may be made to the invention without departing from the spirit and scope of the invention as defined in the appended claims, all of which shall be within the scope of protection of the invention.

Claims

1. A method for preparing high-reliability aluminum nitride for IGBTs, characterized in that, The preparation steps include the following: (1) Powder pretreatment: Select aluminum nitride powder with a purity of ≥99.9%, add it to the integrated solution dispersion, stir at a speed of 1500rpm-3000rpm to form a uniform slurry, pump the slurry into a ball mill, and ball mill for 1h-2h. Use zirconia beads with a diameter of 0.3mm-0.8mm during ball milling. Then transfer the slurry into a storage tank with a speed of 200rpm-300rpm for later use. Then pump the slurry into a spray drying tower for drying to obtain pretreated powder. Finally, calcine the pretreated powder in a nitrogen atmosphere at 450℃-550℃ for 1h-2h to obtain composite powder. The integrated solution dispersion is made from the following raw materials in parts by weight: 100 parts deionized water, 40-50 parts anhydrous ethanol, 0.5-1.5 parts inorganic dispersant, 2-5 parts yttrium nitrate, 0.5-1.5 parts calcium nitrate, and an appropriate amount of pH adjuster to adjust the pH to 9-10. The preparation process of the integrated solution dispersion is as follows: under stirring, the inorganic dispersant is added to the mixed solvent of deionized water and anhydrous ethanol and fully dissolved. Then, yttrium nitrate and calcium nitrate are added in sequence and stirred until completely dissolved and mixed evenly. Finally, the pH adjuster is added to adjust the pH value of the solution to 9-10, thereby obtaining the integrated solution dispersion. (2) Casting: The composite powder obtained in step (1) is mixed with an organic carrier and a solvent to prepare a casting slurry with a solid content of 30wt%-45wt%. After vacuum degassing, it is formed on a casting machine to obtain a green strip with a thickness of 0.5mm-1.2mm, and then cut into a size of 140mm×190mm. (3) Debinding: The green body is heated to 500℃-600℃ at a heating rate of 0.5℃ / min-2℃ / min under the protection of flowing nitrogen atmosphere, and kept at the temperature for 1h-3h; (4) Sintering: The debinding blank is placed in a high-temperature sintering furnace and sintered under a flowing high-purity nitrogen atmosphere. The sintering regime is as follows: the temperature is raised to 1300℃-1500℃ at a rate of 3℃ / min-8℃ / min, and then raised to the final sintering temperature of 1750℃-1850℃ at a rate of 1℃ / min-3℃ / min. The temperature is held at this temperature for 2h-5h, and then cooled with the furnace. (5) Post-processing: The sintered aluminum nitride substrate is ground and polished on both sides to make its surface roughness Ra≤0.4μm. Then, a copper layer is coated on the substrate surface to complete the metallization.

2. The method for preparing high-reliability aluminum nitride for IGBTs according to claim 1, characterized in that: The inorganic dispersant is any one of sodium hexametaphosphate, ammonium polyacrylate, and ammonium polymethacrylate.

3. The method for preparing high-reliability aluminum nitride for IGBTs according to claim 1, characterized in that: The pH adjuster is any one of ammonia, tetramethylammonium hydroxide, or organic amine.

4. The method for preparing high-reliability aluminum nitride for IGBTs according to claim 1, characterized in that: The inlet air temperature of the spray drying tower is 200℃-250℃, and the outlet air temperature is 90℃-110℃.

5. The method for preparing high-reliability aluminum nitride for IGBTs according to claim 1, characterized in that: The composite powder obtained in step (1) is a spherical or near-spherical granulated powder with an average particle size D50 between 50 μm and 150 μm.

6. The method for preparing high-reliability aluminum nitride for IGBTs according to claim 1, characterized in that: The organic carrier in step (2) is a mixture of 8-12 parts by weight of polyvinyl butyral, 3-8 parts by weight of polyethylene glycol, and 0.3-1.0 parts by weight of phosphate ester.

7. The method for preparing high-reliability aluminum nitride for IGBTs according to claim 1, characterized in that: The solvent in step (2) is anhydrous ethanol.

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