Method for preparing silicon nitride substrate by adopting water-based tape casting silicon powder slurry

Abstract

The invention discloses a preparation method for preparing a silicon nitride substrate by adopting water-based tape casting silicon powder slurry in the technical field. The preparation method comprises the following steps: step 1) preparation of tape casting slurry: weighing silicon powder, an inorganic sintering aid, a dispersing agent, a water-based binder and a plasticizer; the preparation method comprises the following steps: adding a water solvent into silicon powder, carrying out ball milling, adding a water-based binder and a plasticizer into a ball milling tank, and defoaming slurry obtained after ball milling at a set vacuum degree to obtain slurry; (2) preparing a green body: carrying out tape casting on the adjusted slurry; and (3) degreasing: spraying and coating powder on the cut green body sheets of the silicon powder, stacking the green body sheets and then putting the green body sheets into a glue discharging furnace for degreasing to obtain a uniform and consistent degreased green body. And 4) sintering: transferring the degreased green body into a sintering furnace, raising the temperature to a nitriding temperature, firstly nitriding, then raising the temperature to a sintering temperature, carrying out heat preservation, and then carrying out furnace cooling to obtain the silicon nitride substrate. According to the invention, the cost is reduced on the premise of ensuring environmental protection.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic materials, and in particular to a method for preparing a silicon nitride substrate. Background Art

[0002] At present, the preparation method of silicon nitride substrate is mainly to make a green body by tape casting, and then sinter it into a dense ceramic. Among them, tape casting needs to be prepared into a ceramic slurry first, and then filtered and degassed for tape casting. The raw materials for preparing ceramic slurry are silicon nitride powder and organic solvents. Due to the relatively high cost of silicon nitride powder. This leads to a higher final cost of silicon nitride substrates. At the same time, the use of organic solvents will bring safety and environmental troubles. Organic solvents are flammable, explosive and toxic. Explosion-proof design and fire protection design are required for the workshop. At the same time, the exhaust gas of organic solvents needs to use environmental protection equipment, which increases the total investment cost of the project. The toxicity of solvents has an adverse effect on the health of employees, causing greater pressure on enterprises. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present invention provides a method for preparing a silicon nitride substrate by using a water-based cast silicon powder slurry, which reduces the cost while ensuring environmental protection.

[0004] The object of the present invention is achieved by: a method for preparing a silicon nitride substrate using a water-based cast silicon powder slurry, characterized in that it comprises the following steps: Step 1) Preparation of tape casting slurry: weigh silicon powder, inorganic sintering aid, dispersant, water-based binder and plasticizer; add water solvent to silicon powder, use zirconium oxide grinding balls as ball milling media, perform mixed ball milling for a set time, add water-based binder and plasticizer to the ball milling tank, and degas the slurry obtained after ball milling under a set vacuum degree to obtain slurry; Step 2) Preparation of green body: tape casting the adjusted slurry; Step 3) Degreasing: The cut green silicon powder sheets are sprayed with powder, stacked and loaded into a debinding furnace for degreasing to obtain a uniform and consistent degreased green body.

[0005] Step 4) Sintering: The degreased green body is transferred into a sintering furnace, heated and sintered, and then cooled in the furnace to obtain a silicon nitride substrate.

[0006] Furthermore, in step 1), the ratio of dispersant to silicon powder is 1:100-1:20; the molar ratio of inorganic sintering aid to silicon powder is 5:95; the weight of the aqueous solvent is 0.8 times the sum of the weights of silicon powder and the inorganic sintering aid; the ratio of aqueous binder to silicon powder is 1:5-1:10; the ratio of plasticizer to silicon powder is 1:30-1:10, and ball milling is performed for 24 hours.

[0007] Furthermore, the inorganic sintering aid is a mixture of magnesium carbonate and yttrium oxide.

[0008] Furthermore, the dispersant is an acrylate polymer.

[0009] Furthermore, the water-based adhesive is water-based acrylic latex, and the solid content of the adhesive is 35%.

[0010] Furthermore, the plasticizer is glycerol.

[0011] Furthermore, the slurry obtained after ball milling in step 1) is degassed under a vacuum degree of -0.1 MPA to obtain a slurry with a viscosity of about 5000 cps.

[0012] Furthermore, in step 2), the scraper height of the casting machine is set to 1 mm, the PET film tape adopts a thickness of 125 μm, the casting speed is set to 0.5 m / min, and a five-stage drying oven is used, and the temperatures are set to 60°C, 45°C, 50°C, 60°C, and 80°C respectively. After drying, the green sheet is cut and wound, and then a die-cutting machine is used to punch out green sheets of the required size.

[0013] Furthermore, in step 3), the stacking process is as follows: 10 layers of green sheets are stacked into a stack, the degreasing temperature is set to 600°C, and 500L / min of compressed air is passed through, and after about 72 hours of degreasing, Furthermore, the sintering process in step 4) is specifically as follows: the temperature is raised to 1380°C at a heating rate of 20°C / min and kept at this temperature for 2 hours (nitridation), then the temperature is raised to 1830°C at a heating rate of 5°C / min, and after being kept at this temperature for 6 hours, the temperature is lowered to 1500°C at a cooling rate of 1°C / min, and the sintering atmosphere is 20atm of nitrogen to obtain a silicon nitride substrate.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention adopts silicon powder instead of silicon nitride powder as the main raw material for preparing substrates, which can greatly reduce the production cost of silicon nitride substrates, and the source of silicon powder is relatively stable, and the quality reliability is good. The use of silicon powder can improve the batch stability of silicon nitride substrate products. However, if the expensive silicon powder is simply selected, it will increase the environmental pressure. Therefore, the use of a water-based solvent formula to prepare the slurry can greatly reduce the environmental pressure. The water-based formula slurry has no explosion-proof requirements and is more friendly to the health of employees. Employees do not have the risk of occupational diseases. At the same time, the water-based slurry is easy to handle and has low environmental damage. DETAILED DESCRIPTION

[0015] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0016] Example 1 A method for preparing a silicon nitride substrate by using a water-based tape-cast silicon powder slurry comprises the following steps: (1) Preparation of tape casting slurry: ① Weigh silicon powder (D50=5μm), inorganic sintering aid, dispersant, and water-based adhesive according to the ratio; the inorganic sintering aid is a mixture of magnesium carbonate and yttrium oxide. The ratio of dispersant to silicon powder is 1:20. The molar ratio of inorganic sintering aid to silicon powder is 5:95; add a water solvent with a weight of 0.8 times that of the inorganic substance (silicon powder, inorganic sintering aid), use zirconium oxide grinding balls as ball milling media, and mix and ball mill for 24 hours. ② Add water-based binder and environmentally friendly plasticizer to the ball mill, wherein the binder is water-based acrylic latex, the plasticizer is glycerol, the solid content of the binder is 35%, the ratio of binder to silicon powder is 1:5; the ratio of plasticizer to binder is 1:3, and ball mill for 24 hours. ③ Degas the slurry obtained after ball milling at a vacuum degree of -0.1MPA to obtain a slurry with a viscosity of about 5000cps.

[0017] (2) Preparation of green sheets: The adjusted slurry is subjected to tape casting, wherein the scraper height of the tape casting machine is set to 1 mm, the PET film tape is 125 μm thick, the tape casting speed is set to 0.5 m / min, and the length of the five drying ovens is 6 meters; the temperatures are set to 60°C, 45°C, 50°C, 60°C, and 80°C respectively. After drying, the green sheets are cut and wound, and then die-cut into green sheets of the required size using a die-cutting machine.

[0018] (3) Degreasing: Spray the cut silicon powder green sheets with powder. Then stack 10 layers of green sheets into a stack and put them into the debinding furnace for degreasing. The degreasing temperature is set to 600℃ and 500L / min of compressed air is passed. After about 72 hours of degreasing, a uniform degreased green body is obtained.

[0019] (4) Sintering: The degreased green body is transferred to a sintering furnace, and the temperature is raised to 1380°C at a heating rate of 20°C / min and kept at this temperature for 2 hours (nitriding). Then, the temperature is raised to 1830°C at a heating rate of 5°C / min. After being kept at this temperature for 6 hours, the temperature is lowered to 1500°C at a cooling rate of 1°C / min. The green body is then cooled in the furnace. The sintering atmosphere is 20 atm of nitrogen. The thermal conductivity of the Si3N4 ceramic substrate obtained is greater than 105 W·m-1·K-1, the fracture toughness reaches 6.8 MPa·m1 / 2, and the bending strength is 830 MPa.

[0020] Comparative Example 1 A method for preparing a silicon nitride substrate by using an organic solvent to cast silicon nitride powder slurry comprises the following steps: (1) Preparation of tape casting slurry: ① Weigh silicon nitride powder (D50 = 0.7 μm), inorganic sintering aid, dispersant, and organic adhesive according to the ratio; wherein the inorganic sintering aid is a mixture of magnesium oxide and yttrium oxide. The ratio of dispersant to silicon nitride powder is 1:20. The molar ratio of inorganic sintering aid to silicon nitride is 10:90; add a solvent with a weight of 0.8 times that of the inorganic substance (silicon nitride powder, inorganic sintering aid), wherein isopropanol is 0.4 times and propyl acetate is 0.4 times, and zirconium oxide grinding balls are used as ball milling media, and the mixture is ball milled for 24 hours. ② Add organic binder and plasticizer to the ball mill, wherein the binder is polyvinyl butyral, the plasticizer is polyethylene glycol, the solid content of the binder is 20%, the ratio of the binder to the silicon nitride powder is 18%, and the ratio of the plasticizer to the binder is 1:2, and the ball milling is carried out for 24 hours. ③ The slurry obtained after ball milling was degassed under a vacuum degree of -0.1 MPA to obtain a slurry with a viscosity of about 9000 cps.

[0021] (2) Preparation of green sheets: The adjusted slurry is subjected to tape casting, wherein the scraper height of the tape casting machine is set to 1 mm, the PET film tape is 125 μm thick, the tape casting speed is set to 0.5 m / min, and the length of the five drying ovens is 6 meters; the temperatures are set to 60°C, 45°C, 50°C, 60°C, and 80°C respectively. After drying, the green sheets are cut and wound, and then die-cut into green sheets of the required size using a die-cutting machine.

[0022] (3) Degreasing: Spray the cut green sheets of silicon nitride powder. Then stack 10 layers of green sheets into a stack and put them into a debinding furnace for degreasing. The degreasing temperature is set to 600°C and 500L / min of compressed air is passed. After about 72 hours of degreasing, a uniform degreased green body is obtained.

[0023] (4) Sintering: The degreased green body is transferred to a sintering furnace and the temperature is raised to 1380°C at a heating rate of 20°C / min, then raised to 1830°C at a heating rate of 5°C / min. After 6 hours of heat preservation, the temperature is lowered to 1500°C at a cooling rate of 1°C / min, and then cooled in the furnace. The sintering atmosphere is 20atm of nitrogen. The thermal conductivity of the obtained Si3N4 ceramic substrate is greater than 82W·m-1·K-1, the fracture toughness reaches 6.3MPa·m1 / 2, and the flexural strength is greater than 850MPa.

[0024] Comparative Example 2 A method for preparing a silicon nitride substrate by using an organic solvent to cast silicon powder slurry comprises the following steps: (1) Preparation of tape casting slurry: ① Weigh silicon powder (D50 = 5 μm), inorganic sintering aid, dispersant, and organic adhesive according to the ratio; the inorganic sintering aid is a mixture of magnesium oxide and yttrium oxide. The ratio of dispersant to silicon powder is 1:20. The molar ratio of inorganic sintering aid to silicon nitride is 5:95; add a solvent with a weight of 0.8 times that of the inorganic substance (silicon powder, inorganic sintering aid), of which 0.4 times isopropanol and 0.4 times propyl acetate, use zirconium oxide grinding balls as ball milling media, and mix and ball mill for 24 hours. ② Add organic binder and plasticizer to the ball mill, of which the binder is polyvinyl butyral, the plasticizer is polyethylene glycol, the solid content of the binder is 20%, the ratio of the binder to the silicon nitride powder is 18%, and the ratio of the plasticizer to the binder is 1:2, and ball mill for 24 hours. ③ The slurry obtained after ball milling was degassed under a vacuum degree of -0.1 MPA to obtain a slurry with a viscosity of about 9000 cps.

[0025] (2) Preparation of green sheets: The adjusted slurry is subjected to tape casting, wherein the scraper height of the tape casting machine is set to 1 mm, the PET film tape is 125 μm thick, the tape casting speed is set to 0.5 m / min, and the length of the five drying ovens is 6 meters; the temperatures are set to 60°C, 45°C, 50°C, 60°C, and 80°C respectively. After drying, the green sheets are cut and wound, and then die-cut into green sheets of the required size using a die-cutting machine.

[0026] (3) Degreasing: Spray the cut silicon powder green sheets with powder. Then stack 10 layers of green sheets into a stack and put them into the debinding furnace for degreasing. The degreasing temperature is set to 600℃ and 500L / min of compressed air is passed. After about 72 hours of degreasing, a uniform degreased green body is obtained.

[0027] (4) Sintering: The degreased green body is transferred to a sintering furnace, and the temperature is raised to 1380°C at a heating rate of 20°C / min and kept at this temperature for 2 hours (nitriding). Then, the temperature is raised to 1830°C at a heating rate of 5°C / min. After being kept at this temperature for 6 hours, the temperature is lowered to 1500°C at a cooling rate of 1°C / min. The green body is then cooled in the furnace. The sintering atmosphere is 20 atm of nitrogen. The thermal conductivity of the Si3N4 ceramic substrate obtained is greater than 105 W·m-1·K-1, the fracture toughness reaches 6.8 MPa·m1 / 2, and the bending strength is 830 MPa.

[0028] The above Comparative Examples 1 and 2 are existing production methods. Compared with Comparative Examples 1 and 2, the present invention uses silicon powder to replace silicon nitride powder as the main raw material for preparing the substrate. Due to the low oxygen content of silicon powder, the grain size produced is a bimodal distribution. Therefore, the substrate cast by silicon powder in the present invention has better thermal conductivity and toughness than the substrate cast by silicon nitride powder. In addition, compared with silicon nitride, the cost of substrate production can be greatly reduced, and the source of silicon powder is relatively stable, and the quality reliability is good. The use of silicon powder can improve the batch stability of silicon nitride substrate products. However, if the silicon powder is simply used, it will increase the environmental pressure. Therefore, the slurry is prepared by using a water-based solvent formula, which can greatly reduce the environmental pressure. The slurry with a water-based formula has no explosion-proof requirements and is more friendly to the health of employees. Employees do not have the risk of occupational diseases. At the same time, the water-based slurry is easy to handle and has low environmental harm.

[0029] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a silicon nitride substrate using water-based tape-cast silicon powder slurry, characterized in that: The following steps are involved: Step 1) Preparation of tape casting slurry: weigh silicon powder, inorganic sintering aid, dispersant, water-based binder and plasticizer; add water solvent to silicon powder, use zirconium oxide grinding balls as ball milling media, perform mixed ball milling for a set time, add water-based binder and plasticizer to the ball milling tank, and degas the slurry obtained after ball milling under a set vacuum degree to obtain slurry; Step 2) Preparation of green body: tape casting the adjusted slurry; Step 3) Degreasing: The cut green silicon powder sheets are sprayed with powder, stacked and loaded into a debinding furnace for degreasing to obtain a uniform and consistent degreased green body.

2. Step 4) Sintering: The degreased green body is transferred into a sintering furnace, heated to the nitriding temperature, first nitrided, then heated to the sintering temperature, kept warm, and then cooled with the furnace to obtain a silicon nitride substrate.

3. The method for preparing a silicon nitride substrate using water-based tape-cast silicon powder slurry according to claim 1, characterized in that: In step 1), the ratio of dispersant to silicon powder is 1:100-1:20; the molar ratio of inorganic sintering aid to silicon powder is 5:95; the weight of water solvent is 0.8 times the sum of the weight of silicon powder and inorganic sintering aid; the ratio of water-based binder to silicon powder is 1:5-1:10; the ratio of plasticizer to silicon powder is 1:30-1:10, and ball milling is performed for 24 hours.

4. A method for preparing a silicon nitride substrate using water-based tape-cast silicon powder slurry according to claim 1 or 2, characterized in that: The inorganic sintering aid is a mixture of magnesium carbonate and yttrium oxide.

5. A method for preparing a silicon nitride substrate using water-based tape-cast silicon powder slurry according to claim 1 or 2, characterized in that: The dispersant is an acrylate polymer.

6. A method for preparing a silicon nitride substrate using water-based tape-cast silicon powder slurry according to claim 1 or 2, characterized in that: The water-based adhesive is water-based acrylic latex, and the solid content of the adhesive is 35%.

7. A method for preparing a silicon nitride substrate using water-based tape-cast silicon powder slurry according to claim 1 or 2, characterized in that: The plasticizer is glycerol.

8. A method for preparing a silicon nitride substrate using water-based tape-cast silicon powder slurry according to claim 1 or 2, characterized in that: The slurry obtained after ball milling in step 1) is degassed under a vacuum degree of -0.1 MPA to obtain a slurry with a viscosity of about 5000 cps.

9. A method for preparing a silicon nitride substrate using water-based tape-cast silicon powder slurry according to claim 1 or 2, characterized in that: In step 2), the scraper height of the casting machine is set to 1 mm, the PET film tape adopts a thickness of 125 μm, the casting speed is set to 0.5 m / min, and a five-stage drying oven is used. The temperatures are set to 60°C, 45°C, 50°C, 60°C, and 80°C respectively. After drying, the green sheet is cut and wound, and then a die-cutting machine is used to punch out green sheets of the required size.

10. A method for preparing a silicon nitride substrate using water-based tape-cast silicon powder slurry according to claim 1 or 2, characterized in that: In step 3), the stacking process is as follows: 10 layers of green sheets are stacked into a stack, the degreasing temperature is set to 600°C, and 500L / min of compressed air is passed through. After about 72 hours of degreasing, The method for preparing a silicon nitride substrate using water-based tape-cast silicon powder slurry according to claim 1 or 2 is characterized in that: The sintering process in step 4) is specifically as follows: the temperature is raised to 1380°C at a heating rate of 20°C / min and kept at this temperature for 2 hours (nitridation), then the temperature is raised to 1830°C at a heating rate of 5°C / min, and after being kept at this temperature for 6 hours, the temperature is lowered to 1500°C at a cooling rate of 1°C / min, and the sintering atmosphere is 20atm of nitrogen to obtain a silicon nitride substrate.