Method for casting slurry on silicon nitride substrate and silicon nitride substrate

Abstract

The invention belongs to the field of electronic ceramic materials, and particularly relates to a method for preparing tape-casting slurry of a silicon nitride substrate, a stirring mill instead of a traditional ball mill is adopted in the early stage of preparing the tape-casting slurry, the dispersion effect of silicon nitride powder and a sintering aid can be effectively improved, the grinding time of the silicon nitride powder is effectively shortened, and the production cost is reduced. The phenomenon that the casting effect is affected due to the fact that the main powder is ground too fine is avoided, and it can be guaranteed that the sintering aid can be evenly distributed in the main powder; a small amount of a high-boiling-point solvent is added into a solvent system, so that the phenomenon that in the tape casting process, due to the fact that the surface of the slurry volatilizes too fast and peels, volatilization of the solvent in the lower layer of the slurry is hindered and uneven is avoided.

Description

Technical Field

[0001] The invention belongs to the field of electronic ceramic materials, and in particular relates to a method for casting slurry on a silicon nitride substrate and a silicon nitride substrate. Background Art

[0002] The commercially mass-produced high thermal conductivity silicon nitride ceramic substrate blank is obtained by mixing powder and various additives through ball milling to make slurry, and then drying it through tape casting. Since silicon nitride powder has fine particle size and large specific surface area, it is easy to crack during the tape casting process, resulting in a low pass rate for blank production. Currently, the strength of the wet blank is mainly improved by adding a large amount of binder, and the tape casting speed is reduced to prevent cracking during the drying process. The increase in the amount of binder directly affects the pass rate of low-temperature degreasing of the blank, and the blank is more easily deformed during the later processing, affecting (reducing) the pass rate of the final product, and the reduction in the tape casting speed leads to the production efficiency of the tape casting process.

[0003] After searching, CN202410132393.5 discloses a silicon nitride substrate and a preparation method thereof, which solves the problem that the silicon nitride substrate produced by the prior art has poor thermal conductivity and cannot be mass-produced industrially; the silicon nitride substrate includes the following raw materials in parts by weight: 90-95 parts of raw material powder, 8-15 parts of composite sintering aid, 2-5 parts of dispersant, 2-5 parts of organic solvent, 2-5 parts of binder, and 2-5 parts of plasticizer.

[0004] CN202211540656.3 discloses a high thermal conductivity silicon nitride substrate and a preparation method thereof. The substrate of the invention is made of a silicon nitride green ceramic sheet after tape casting, which is sequentially subjected to a debinding process and a sintering process, and the oxygen atomic percentage in the substrate is 0 to 0.01%. The carbon atomic percentage in the debinding process is accurately controlled by changing the debinding process, and the phase transition and oxygen atomic percentage composition are accurately controlled by the pressure change during the sintering process, thereby realizing the preparation of a high thermal conductivity and high strength silicon nitride substrate.

[0005] The above solutions do not solve the problem of the reduction of casting speed leading to the production efficiency of the casting process. Therefore, a method for casting slurry for silicon nitride substrate is invented to solve the problem of increasing the strength of the wet blank and cracking during the drying process by adding a large amount of binder, which has great economic significance and market value in actual production. Summary of the invention

[0006] The present invention aims at the deficiencies of the prior art and provides a method for tape-casting slurry for silicon nitride substrates. By adjusting the ball milling slurry making process and the slurry solvent formula, the qualified rate and production efficiency of the tape-casting blanks are improved without adding a binder.

[0007] To achieve the above object, the present invention provides the following technical solutions: A method for tape casting slurry on a silicon nitride substrate is disclosed, comprising the following steps: S1. Ingredient preparation stage: silicon nitride powder, magnesium oxide and yttrium oxide are placed in a stirred mill, a solvent and a dispersant are added, stirred and ground to obtain a suspension; Pour the binder and plasticizer solvent into a sol tank, add solvent 2 and solvent 3, dissolve them, and obtain a glue solution; S2. Mixing stage: Pour the suspension and the glue solution into the ball mill at the same time, perform bonding ball milling, and obtain a casting slurry to improve the uniformity and stability of the slurry; S3. Degassing and aging the casting slurry in step S2, drying and forming by a casting machine, cutting and rolling to obtain a silicon nitride membrane green body; S4. The silicon nitride membrane is subjected to low-temperature debinding in the air. The debinding process is as follows: the temperature is increased to 250°C at 1°C / min, kept at this temperature for 10 hours, then the temperature is increased to 350°C at 2°C / min, kept at this temperature for 8 hours, then the temperature is increased to 700°C at 3°C / min, kept at this temperature for 2 hours, and then naturally cooled to room temperature with the furnace. After debinding, the silicon nitride membrane is placed in a high-temperature air pressure furnace for sintering. The sintering process is as follows: the temperature is increased to 800°C at 5°C / min under vacuum, the pressure is increased to 1.5MPa, the temperature is increased to 1800°C at 2°C / min, kept at this temperature for 4 hours, the temperature is decreased to 1350°C at 1.5°C / min, and then rapidly cooled to obtain a silicon nitride substrate.

[0008] The present invention adopts a stirred mill instead of a traditional ball mill in the early stage of preparing the casting slurry, which can effectively improve the dispersion effect of silicon nitride powder and sintering aids (magnesium oxide and yttrium oxide), effectively reduce the grinding time of silicon nitride powder, avoid grinding the main powder particle size too finely, affect the casting effect, and ensure that the sintering aid can be evenly distributed in the main powder; by adding a small amount of high-boiling point solvent to the solvent system, it is prevented from peeling off due to too fast volatilization of the slurry surface during the casting process, resulting in obstruction of volatilization of the lower layer of solvent in the slurry and uneven volatilization.

[0009] Furthermore, the mass ratio of silicon nitride, magnesium oxide and yttrium oxide is 100: (2-6): (4-8); the dispersant is a mixture of one or more of castor oil, SC-0505K, and KD-1, and its amount is 0.1%-2% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide. Silicon nitride is a material with high hardness, high wear resistance and excellent corrosion resistance. Silicon nitride is a strong covalent bond compound with a low self-diffusion coefficient, and it is difficult to achieve densification through conventional solid phase sintering; sintering aids need to be added to promote its densification and performance improvement. The addition of magnesium oxide can effectively improve the mechanical strength of silicon nitride ceramics. Magnesium oxide forms a good bond with silicon nitride, and the density of the material is enhanced by filling the tiny pores inside the ceramic. This enhanced density makes silicon nitride ceramics stronger and less prone to cracking when subjected to external forces. In a high temperature environment, magnesium oxide can stabilize the structure of the ceramic and reduce damage caused by thermal expansion and thermal shock. Yttrium oxide is also a commonly used rare earth oxide sintering aid, which can reduce the sintering temperature of silicon nitride and improve the bending strength and fracture toughness of the material. The addition of yttrium oxide has a significant effect on the densification behavior and mechanical properties of sintered ceramic materials.

[0010] Furthermore, the solvent 1 in step S1 is a mixture of one or more of toluene, isopropanol, anhydrous ethanol, and ethyl acetate in a certain proportion, and its usage is 20%-40% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide.

[0011] Further, in step S1, the second solvent is a mixture of one or more of toluene, isopropanol, anhydrous ethanol, and ethyl acetate in proportion, and its usage is 20%-40% of the total mass of silicon nitride powder, magnesium oxide, and yttrium oxide, and the third solvent is at least one of n-butanol and cyclohexanone, and its usage is 1%-15% of the total amount of the first and second solvents. By adding a small amount of high-boiling-point solvents to the solvent system, it is prevented from peeling off due to the rapid evaporation of the slurry surface during the casting process, resulting in the obstruction of the evaporation of the lower layer of the slurry and uneven evaporation.

[0012] Furthermore, the process of the stirred mill is to put grinding balls (silicon nitride balls, zirconium oxide balls, one or a mixture of the two) into the stirred mill, the amount of which is 2-6 times the total mass of the planned silicon nitride powder, magnesium oxide and yttrium oxide, the ball diameter is 5mm-10mm, silicon nitride, magnesium oxide and yttrium oxide are put into the stirred mill, solvent and dispersant are added, the stirring speed is set to 30r / min-50r / min, and the stirring time is set to 2h-8h.

[0013] Furthermore, the binder in step S1 is polyvinyl butyral, and the amount used is 6%-20% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide; the plasticizer is dibutyl phthalate, and the amount used is 3%-10% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide.

[0014] Furthermore, the original particle size of the silicon nitride powder is 0.7-1.2 μm, the original particle size of the magnesium oxide powder is 0.1-0.6 μm, and the original particle size of the yttrium oxide powder is 0.3-1.0 μm.

[0015] Furthermore, in step S2, the maximum temperature of the drying and molding is 100°C.

[0016] Further, the low-temperature debinding process and high-temperature sintering process described in step S4 are as follows: the debinding process is: heating to 250°C at 1°C / min, keeping warm for 10 hours, then heating to 350°C at 2°C / min, keeping warm for 8 hours, then heating to 700°C at 3°C / min, keeping warm for 2 hours, and then naturally cooling to room temperature with the furnace, and sintering in a high-temperature gas pressure furnace after debinding; The sintering process is as follows: under vacuum, heat to 800°C at 5°C / min, increase the pressure to 1.5 MPa, heat to 1800°C at 2°C / min, keep warm for 4 hours, cool to 1350°C at 1.5°C / min, and then cool rapidly.

[0017] Another object of the present invention is to prepare a silicon nitride substrate using the above-mentioned method of casting slurry for silicon nitride substrate.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The method for casting slurry of silicon nitride substrate of the present invention improves the qualified rate and production efficiency of casting blanks without adding a binder by adjusting the ball milling slurry making process and the slurry solvent formula.

[0019] The present invention is the first time that a stirring mill is used to replace a ball mill to grind and disperse silicon nitride powder and a sintering aid in the method of preparing silicon nitride substrate tape casting slurry. Combined with adding a small amount of high boiling point solvent to the solvent system, the method effectively prevents the slurry surface from peeling off due to excessive volatilization during the tape casting process, thereby preventing the volatilization of the lower layer of the slurry from being blocked and volatilizing unevenly. This provides a new technical idea for the preparation of silicon nitride substrate tape casting slurry. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a physical picture of a silicon nitride casting film prepared in Example 1 of the method for casting slurry for a silicon nitride substrate of the present invention.

[0021] Figure 2 This is a physical picture of a silicon nitride casting film prepared in Example 2 of the method for casting slurry for a silicon nitride substrate of the present invention.

[0022] Figure 3 This is a physical picture of a silicon nitride casting film prepared in Example 3 of the method for casting slurry for a silicon nitride substrate of the present invention.

[0023] Figure 4This is a physical picture of a silicon nitride casting film prepared in Example 4 of the method for casting slurry for a silicon nitride substrate of the present invention.

[0024] Figure 5 This is a physical picture of a silicon nitride casting film prepared in Example 5 of the method for casting slurry for a silicon nitride substrate of the present invention.

[0025] Figure 6 This is a physical picture of the silicon nitride cast membrane prepared in Comparative Example 1.

[0026] Figure 7 This is a physical picture of the silicon nitride cast membrane prepared in Comparative Example 2. DETAILED DESCRIPTION

[0027] The present invention is further described below.

[0028] The method for casting slurry on silicon nitride substrate of the present invention has the following process flow: Figure 1 As shown. The following steps are included: S1. Ingredient preparation stage: put silicon nitride powder, magnesium oxide and yttrium oxide into a stirred mill, add solvent 1 and dispersant, stir and grind to obtain a suspension; the original particle size of silicon nitride powder is 0.7-1.2μm, the original particle size of magnesium oxide is 0.1-0.6μm and the original particle size of yttrium oxide powder is 0.3-1.0μm.

[0029] Pour the binder and plasticizer solvent into a sol tank, add solvent 2 and solvent 3, dissolve them, and obtain a glue solution; S2. Mixing stage: Pour the suspension and the glue solution into the ball mill at the same time, perform bonding ball milling, and obtain a casting slurry to improve the uniformity and stability of the slurry; S3. Degassing and aging the casting slurry in step S2, drying and forming by a casting machine, cutting and rolling to obtain a silicon nitride membrane green body; S4. Debind the silicon nitride membrane in the air at low temperature, and after debinding, place it in a high-temperature pressure furnace for sintering to obtain a silicon nitride substrate. This process can choose normal debinding process parameters. For the convenience of description and comparison, the debinding process of this embodiment is fixed as follows: heating to 250°C at 1°C / min, keeping warm for 10 hours, then heating to 350°C at 2°C / min, keeping warm for 8 hours, then heating to 700°C at 3°C / min, keeping warm for 2 hours, and then naturally cooling to room temperature with the furnace, and after debinding, placing it in a high-temperature pressure furnace for sintering; The sintering process is: in a vacuum state, the temperature is raised to 800°C at 5°C / min, the pressure is raised to 1.5MPa, the temperature is raised to 1800°C at 2°C / min, the temperature is kept at that temperature for 4 hours, the temperature is lowered to 1350°C at 1.5°C / min, and then the temperature is rapidly cooled. The specific implementation is as follows. Example 1

[0030] The method for tape-casting slurry for silicon nitride substrate disclosed in this embodiment includes the following steps.

[0031] S1. Ingredient preparation stage: silicon nitride powder, magnesium oxide and yttrium oxide are placed in a stirred mill, the original particle size of the powder is 0.7564 μm (D50), solvent 1 and dispersant are added, stirred and ground to obtain a suspension; as shown in Table 1, in this embodiment, the mass ratio of silicon nitride, magnesium oxide and yttrium oxide is 100:3:6; the dispersant is SC-0505k, and its usage is 0.8% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide.

[0032] The first solvent is ethanol, and its usage is 30% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide.

[0033] Pour the binder and plasticizer solvent into the sol tank, add solvent 2 and solvent 3, dissolve and obtain a glue solution; in this embodiment, the binder is polyvinyl butyral, and the amount is 8% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide, and the plasticizer is dibutyl phthalate, and the amount is 4% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide. Solvent 2 is a mixture of toluene and isopropanol in a mass ratio of 4:3, and its amount is 20% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide, and solvent 3 is n-butanol, and its amount is 1% of the total amount of solvent 1 and solvent 2. By adding a small amount of high boiling point solvent to the solvent system, it is prevented from peeling off due to the rapid volatilization of the slurry surface during the casting process, resulting in the obstruction of the volatilization of the lower layer of the slurry solvent and uneven volatilization.

[0034] In this embodiment, the process of the stirred mill is to put grinding ball silicon nitride balls into the stirred mill, and the amount is 3 times the total mass of the planned silicon nitride powder, magnesium oxide and yttrium oxide. The ball diameter is 5mm. Silicon nitride, magnesium oxide and yttrium oxide are put into the stirred mill, and solvents and dispersants are added. The speed is set to 35r / min and the time is set to 4h.

[0035] S2. Mixing stage: Pour the suspension and the glue solution into the ball mill at the same time, with a ball-to-material ratio of 1:3 and a ball milling speed of 30 r / min for bonding ball milling to obtain a casting slurry with a particle size of 0.6585 μm (D50) to improve the uniformity and stability of the slurry; the discharge viscosity is 2547 CPS.

[0036] S3. The casting slurry of step S2 is cast to degas, mature, and dried by a casting machine. The casting speed is 150 mm / min, the maximum drying temperature is 85°C, and the rolls are cut into pieces to obtain silicon nitride membrane green sheets. No cracks are observed in the casting drying condition. Figure 1 shown.

[0037] S4. Debind the silicon nitride membrane in the air at low temperature, and then sinter it in a high-temperature gas pressure furnace to obtain a silicon nitride substrate. The sintered density is 3.1986g / cm 3 , thermal conductivity is 75.87wm -1 .k -1 , flexural strength 723MPa. Example 2

[0038] The method for tape-casting slurry for silicon nitride substrate disclosed in this embodiment includes the following steps.

[0039] S1. Ingredient preparation stage: put silicon nitride powder, magnesium oxide and yttrium oxide into a stirred mill, the original particle size of the powder is 0.7564μm (D50), add solvent 1 and dispersant, stir and grind to obtain a suspension; as shown in Table 1, in this embodiment, the mass ratio of silicon nitride, magnesium oxide and yttrium oxide is 100:2:4; the dispersant is KD-1, and its amount is 2% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide.

[0040] The first solvent is toluene, and its usage is 30% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide.

[0041] Pour the binder and plasticizer solvent into the sol tank, add solvent 2 and solvent 3, dissolve and obtain a glue solution; in this embodiment, the binder is polyvinyl butyral, and the amount is 10% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide, and the plasticizer is dibutyl phthalate, and the amount is 10% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide. Solvent 2 is a mixture of toluene and isopropanol in a mass ratio of 1:1, and its amount is 20% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide, and solvent 3 is n-butanol, and its amount is 2.5% of the total amount of solvent 1 and solvent 2.

[0042] In this embodiment, the process of the stirred mill is to put grinding ball silicon nitride balls into the stirred mill, and the amount is 6 times the total mass of the planned silicon nitride powder, magnesium oxide and yttrium oxide. The ball diameter is 5mm. Silicon nitride, magnesium oxide and yttrium oxide are put into the stirred mill, and solvents and dispersants are added. The speed is set to 35r / min and the time is set to 4h.

[0043] S2. Mixing stage: Pour the suspension and the glue solution into the ball mill at the same time, with a ball-to-material ratio of 1:3 and a ball milling speed of 30 r / min for bonding ball milling to obtain a casting slurry with a particle size of 0.6617 μm (D50) to improve the uniformity and stability of the slurry; the discharge viscosity is 2378 CPS.

[0044] S3. The casting slurry of step S2 is cast to degas, mature, and dried by a casting machine. The casting speed is 150 mm / min, the maximum drying temperature is 95°C, and the rolls are cut into pieces to obtain silicon nitride membrane green sheets. No cracks are observed during the casting and drying process. Figure 2 shown.

[0045] S4. Debind the silicon nitride diaphragm in air at low temperature and sinter it to a density of 3.2207g / cm 3 , thermal conductivity is 85.17wm -1 .k -1 , flexural strength 759MPa. Example 3

[0046] The method for casting slurry for silicon nitride substrate in this embodiment is similar to that in Example 2, except that, as shown in Table 1, in the preparation of the glue solution in stage S1, the dispersant is castor oil, and its amount is 0.1% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide. Solvent 1 is isopropanol, and its amount is 20% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide.

[0047] Pour the binder and plasticizer solvent into the sol tank, add solvent 2 and solvent 3, dissolve and obtain a glue solution; in this embodiment, the binder is polyvinyl butyral, and the amount is 6% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide, and the plasticizer is dibutyl phthalate, and the amount is 3% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide. Solvent 2 is a mixture of isopropanol and anhydrous ethanol in a mass ratio of 2:1, and its amount is 40% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide, and solvent 3 is n-butanol, and its amount is 5% of the total amount of solvent 1 and solvent 2. Set the speed to 35r / min and the time to 4h.

[0048] S2. Mixing stage: Pour the suspension and the glue solution into the ball mill at the same time, with a ball-to-material ratio of 1:2, and a ball milling speed of 30r / min for bonding ball milling. The casting speed is 150mm / min, and the particle size of the casting slurry is 0.6678 (D50) to improve the uniformity and stability of the slurry; the discharge viscosity is 2566CPS.

[0049] S3. The casting slurry of step S2 is cast to degas, mature, and dried by a casting machine. The casting speed is 220 mm / min, the maximum drying temperature is 95°C, and the rolls are cut into pieces to obtain silicon nitride membrane green sheets. No cracks are observed in the casting drying condition. Figure 3 shown.

[0050] S4. Debind the silicon nitride membrane in the air at low temperature, and then sinter it in a high-temperature gas pressure furnace to obtain a silicon nitride substrate. The sintered density is 3.2389g / cm3 , thermal conductivity is 84.87wm -1 .k -1 , flexural strength 756MPa. Example 4

[0051] The method for casting slurry for silicon nitride substrate in this embodiment is similar to that in Example 2, except that, as shown in Table 1, solvent 1 is toluene, and its amount is 40% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide. The speed is set to 50r / min, and the stirring time is set to 2h.

[0052] The mass ratio of silicon nitride, magnesium oxide and yttrium oxide is 100:6:8. In this embodiment, the binder is polyvinyl butyral, and the amount used is 20% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide. The plasticizer is dibutyl phthalate, and the amount used is 6% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide. The amount of solvent tri-n-butyl alcohol is 15% of the total mass of solvent one and solvent two.

[0053] S2. Mixing stage: Pour the suspension and the glue solution into the ball mill at the same time, with a ball-to-material ratio of 1:3 and a ball milling speed of 30 r / min for bonding ball milling to obtain a casting slurry with a particle size of 0.6498 μm to improve the uniformity and stability of the slurry; the discharge viscosity is 2479 CPS.

[0054] S3. The casting slurry of step S2 is cast to degas, mature, and dried by a casting machine. The casting speed is 220 mm / min, the maximum drying temperature is 95°C, and the rolls are cut into pieces to obtain silicon nitride membrane green sheets. No cracks are observed in the casting drying condition, and the membrane is moderately dry. Figure 4 shown.

[0055] S4. Debind the silicon nitride membrane in the air at low temperature, and then sinter it in a high-temperature gas pressure furnace to obtain a silicon nitride substrate. The sintered density is 3.2205g / cm 3 , thermal conductivity is 83.07wm -1 .k -1 , flexural strength 805MPa. Example 5

[0056] The method for casting slurry for silicon nitride substrate in this embodiment is similar to that in Example 3, except that, as shown in Table 1, solvent 3 is cyclohexanone, and its amount is 9% of the total mass of solvent 1 and solvent 2. The speed is set to 30r / min, and the stirring time is set to 8h.

[0057] S2. Mixing stage: Pour the suspension and the glue solution into the ball mill at the same time, with a ball-to-material ratio of 1:3 and a ball milling speed of 30 r / min for bonding ball milling to obtain a casting slurry with a particle size of 0.6698 μm to improve the uniformity and stability of the slurry; the discharge viscosity is 2469 CPS.

[0058] S3. The casting slurry of step S2 is cast to degas, mature, and dried by a casting machine. The casting speed is 220 mm / min, the maximum drying temperature is 95°C, and the rolls are cut into pieces to obtain silicon nitride membrane green sheets. No cracks are observed in the casting drying condition, and the membrane is moderately dry. Figure 5 shown.

[0059] S4. Debind the silicon nitride membrane in the air at low temperature, and then sinter it in a high-temperature gas pressure furnace to obtain a silicon nitride substrate. The sintered density is 3.2298g / cm 3 , thermal conductivity is 84.26wm -1 .k -1 , flexural strength 784MPa. Comparative Example 1

[0060] The method of casting slurry for silicon nitride substrate used in this comparative example is similar to that in Example 1, except that, in the S1 stage, as shown in Table 1, the suspension is prepared by ball milling, the ball-to-material ratio is 1:3, and the ball milling speed is 25 r / min for bonding ball milling for 24 hours. The particle size of the slurry in the S2 stage is 0.5017 μm, and the discharge viscosity is 3089 cps.

[0061] S3. The casting slurry of step S2 is cast to degas, mature, and dried by a casting machine. The casting speed is 150mm / min, the maximum drying temperature is 95°C, and the rolls are cut into pieces to obtain silicon nitride membrane green pieces. The casting drying condition is severe cracking. Figure 6 As shown. Sintered density 3.2203g / cm 3 , thermal conductivity is 82.78wm -1 .k -1 , flexural strength 790MPa. Comparative Example 2

[0062] The method of casting slurry for silicon nitride substrate used in this comparative example is similar to that of Example 2, except that solvent three is not added during the preparation of the gel solution in stage S1, the particle size of the slurry in stage S2 is 0.6417 μm, and the discharge viscosity is 2579 cps.

[0063] S3. The casting slurry of step S2 is cast to degas, mature, and dried by a casting machine. The casting speed is 150mm / min, the maximum drying temperature is 95°C, and the rolls are cut into pieces to obtain silicon nitride membrane green pieces. The casting drying condition is a small amount of cracking. Figure 7 As shown. Sintered density 3.2123g / cm 3 , thermal conductivity is 81.74wm -1 .k -1 , flexural strength 760MPa.

[0064]

[0065] In Examples 1 to 5, a stirred mill is used instead of a ball mill to grind and disperse silicon nitride powder as a sintering aid, and a small amount of high-boiling point solvent is added to the solvent system. The combination of the two completely avoids the cracking of the cast film. In Comparative Example 1, ball milling is used to achieve good dispersion, which takes a relatively long time, resulting in the material being too fine in particle size and prone to cracking in the subsequent casting process. In Comparative Example 2, a stirred mill is used but no high-boiling point solvent is used. As a result, the cast film has a small amount of cracking.

[0066] The above are only embodiments of the present invention. The invention is not limited to the field involved in this implementation case. The common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the content of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for tape casting slurry on a silicon nitride substrate, characterized in that: The following steps are involved: S1. Ingredient preparation stage: silicon nitride powder, magnesium oxide and yttrium oxide are placed in a stirred mill, a solvent and a dispersant are added, stirred and ground to obtain a suspension; Pour the binder and plasticizer solvent into a sol tank, add solvent 2 and solvent 3, dissolve them, and obtain a glue solution; S2. Mixing stage: Pour the suspension and the glue solution into the ball mill at the same time, perform bonding ball milling, and obtain a casting slurry to improve the uniformity and stability of the slurry; S3. Degassing and aging the casting slurry in step S2, drying and forming by a casting machine, cutting and rolling to obtain a silicon nitride membrane green body; S4. Debinding the silicon nitride membrane in air at low temperature, and then sintering it in a high-temperature air pressure furnace to obtain a silicon nitride substrate.

2. The method for tape casting slurry on a silicon nitride substrate according to claim 1, characterized in that: The mass ratio of silicon nitride, magnesium oxide and yttrium oxide is 100:(2-6):(4-8); the dispersant is a mixture of one or more of castor oil, SC-0505K and KD-1, and its usage is 0.1%-2% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide.

3. The method for tape casting slurry on a silicon nitride substrate according to claim 1, characterized in that: The solvent 1 in step S1 is a mixture of one or more of toluene, isopropanol, anhydrous ethanol, and ethyl acetate in a certain proportion, and its usage is 20%-40% of the total mass of silicon nitride powder, magnesium oxide, and yttrium oxide.

4. The method for tape casting slurry on a silicon nitride substrate according to claim 3, characterized in that: The second solvent is a mixture of one or more of toluene, isopropanol, anhydrous ethanol, and ethyl acetate in proportion, and its usage is 20%-40% of the total mass of silicon nitride powder, magnesium oxide, and yttrium oxide. The third solvent is at least one of n-butanol and cyclohexanone, and its usage is 1%-15% of the total amount of solvent one and solvent two.

5. The method for tape casting slurry on a silicon nitride substrate according to claim 1, characterized in that: The process of the stirred mill is to put grinding balls into the stirred mill, the amount of which is 2-6 times the total mass of the planned silicon nitride powder, magnesium oxide and yttrium oxide, the diameter of the balls is 5mm-10mm, silicon nitride, magnesium oxide and yttrium oxide are put into the stirred mill, solvent and dispersant are added, the stirring speed is 30r / min-50r / min, and the stirring time is set to 2h-8h.

6. The method for tape casting slurry on a silicon nitride substrate according to claim 1, characterized in that: The binder in step S1 is polyvinyl butyral, and the amount used is 6%-20% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide.

7. The method for tape casting slurry on a silicon nitride substrate according to claim 1, characterized in that: The plasticizer is dibutyl phthalate, and the amount used is 3%-10% of the total mass of silicon nitride powder, magnesium oxide and yttrium oxide.

8. The method for tape casting slurry on a silicon nitride substrate according to any one of claims 1 to 7, characterized in that: The original particle size of the silicon nitride powder is 0.7-1.2 μm, the original particle size of the magnesium oxide is 0.1-0.6 μm, and the original particle size of the yttrium oxide powder is 0.3-1.0 μm.

9. The method for tape casting slurry on a silicon nitride substrate according to claim 1, characterized in that: In step S2, the maximum temperature of the drying and molding is 100°C.

10. A silicon nitride substrate prepared by the method of using the silicon nitride substrate casting slurry according to any one of claims 1 to 9.

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