A prestress-reinforced Si3N4 ceramic substrate and its preparation method

Abstract

This invention discloses a method for preparing a prestressed reinforced Si3N4 ceramic substrate. The specific steps are as follows: Si3N4 raw material is divided into two grinding processes with different particle sizes; a metal oxide sintering aid is mixed with one type of Si3N4 to form a Si3N4 ceramic substrate; a fine hole array is punched onto the Si3N4 ceramic substrate; a metal mesh is laid on the upper surface of the perforated Si3N4 ceramic substrate; a metal oxide sintering aid is mixed with another type of Si3N4 and laid at the bottom of the Si3N4 ceramic substrate in a mold box; multiple Si3N4 ceramic substrates with metal mesh are stacked sequentially and sintered to form a reinforced Si3N4 ceramic substrate. The prestressed reinforced Si3N4 ceramic substrate is thus prepared using the above method. This invention further increases the overall strength of the Si3N4 ceramic substrate, and due to the stacking process to form the substrate, the occurrence of cracks and fissures is greatly reduced. The added metal mesh provides prestress, and the addition of mixture B forms a coating, enhancing the design and increasing the strength of the Si3N4 ceramic substrate by more than double. The tested bending strength can reach 700-800MPa, enabling mass production.

Description

Technical Field

[0001] This invention relates to the field of ceramic substrate technology, and in particular to a prestress-reinforced Si3N4 ceramic substrate and its preparation method. Background Technology

[0002] Si3N4 ceramics possess excellent properties such as high temperature resistance, corrosion resistance, and wear resistance, but they also suffer from fatal weaknesses such as high brittleness and poor reliability, which severely restricts the development of ceramic materials in many fields such as aerospace, energy, machinery, and automobiles.

[0003] By optimizing the surface prestressing design, a layer of high compressive stress can be formed on the surface of ceramic components, thereby preventing crack propagation and offsetting applied tensile stress, thus improving the strength and damage tolerance of ceramics. This prestressing design theory and procedure can be applied to different fields such as structural ceramics, building ceramics, and daily-use ceramics, and has obvious versatility and wide applicability. It is also simple, economical, and not limited by the size and shape of the components, thus showing great application potential.

[0004] Ceramics are typical brittle materials, characterized by high compressive strength but low tensile strength. In practical applications, ceramic materials often undergo brittle fracture at low stress levels, and the fracture strength is several orders of magnitude lower than the theoretical strength. For example, the flexural strength of ordinary silicon nitride is 400-500 MPa.

[0005] Most ceramic fractures originate from the propagation of surface main cracks. Therefore, the key to improving the strength and damage tolerance of ceramic materials is to enhance their resistance to crack propagation and reduce stress concentration at crack tips, especially surface microcracks. Methods to improve ceramic strength include grain refinement, high density and purity, and prestressing reinforcement. Even so, ceramic plates still cannot overcome the fact that their toughness is inferior to that of metal plates. However, metal plates are heavier and unsuitable for the aforementioned applications because their weight, poor thermal insulation, and high electrical conductivity determine their inferior performance compared to ceramic plates. Therefore, improving ceramic plates to possess ceramic properties while also incorporating the prestressing and compressive strength of metal plates is the key area for improvement. Summary of the Invention

[0006] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one objective of this invention is to provide a prestress-reinforced Si3N4 ceramic substrate and its preparation method, thereby solving problems such as weak tensile strength, high brittleness, and easy fracture of the ceramic substrate.

[0007] The preparation method of a prestress-reinforced Si3N4 ceramic substrate according to the present invention comprises the following steps:

[0008] S1: Divide the Si3N4 raw material into two portions, put them into grinding jars respectively, and grind them into two different grades of fine grains with particle sizes of 30-40nm and 90-100nm respectively.

[0009] S2: Mix the metal oxide sintering aid with 90-100nm modified Si3N4, place it in a ball mill jar, ball mill for 3-5 hours, dry it, and sieve it through a 40-mesh sieve to obtain mixture A. Put it into a mold and press it under a vacuum of 70-80 MPa to obtain Si3N4 blocks. Heat it in a N2 atmosphere to 1500-1600℃ and hold it for 2-3 hours to obtain Si3N4 ceramic substrates.

[0010] S3: Punch out a matrix-distributed array of fine holes on the Si3N4 ceramic substrate prepared in step S2 using a punch press;

[0011] S4: A metal mesh is laid on the upper surface of the porous Si3N4 ceramic substrate prepared in step S3;

[0012] S5: Mix the metal oxide sintering aid with 30-40nm modified Si3N4, put it into a ball mill jar, ball mill for 3-5 hours, dry it, and sieve it through a 60-mesh sieve to obtain mixture B, which is ready for use.

[0013] S6: Place a Si3N4 ceramic substrate with metal mesh prepared in step S4 at the bottom of a mold box, apply mixture B to the Si3N4 ceramic substrate with metal mesh, cover it with another Si3N4 ceramic substrate with metal mesh and press it firmly, continue to apply mixture B to the newly laid substrate, and complete the stacking of multiple Si3N4 ceramic substrates with metal mesh in sequence.

[0014] S7: Press the ceramic substrate stacked in the mold in step S6 under a vacuum of 70-80 MPa to form a Si3N4 laminate; heat it in a N2 atmosphere to 1800-1950℃ and hold for 2-3 hours to obtain an enhanced Si3N4 ceramic substrate.

[0015] In some embodiments of the present invention, the thickness of the Si3N4 ceramic substrate is 2-3 times the coating thickness of the mixture B.

[0016] In some other embodiments of the present invention, the lower surface of the Si3N4 ceramic substrate is first sanded before being laid in step S6.

[0017] In other embodiments of the present invention, the metal oxide sintering aid comprises metal oxide, polynitrosilane fiber, polyethylene glycol butyral, and polyethylene glycol in a ratio of 1-1.1: 0.1-0.2: 0.1-0.15: 2.0-3.0.

[0018] In some other embodiments of the present invention, the preparation steps of the metal oxide sintering aid are as follows: metal oxide, polynitrosilane fiber, polyethylene glycol butyral and polyethylene glycol are mixed and mixed into a slurry under a water bath. The slurry is then placed in a ball mill and ground. After ball milling, the slurry is sieved to remove bubbles and then dried to obtain a casting slurry. Finally, the slurry is ground into powder.

[0019] In some other embodiments of the present invention, in step S2, the temperature is heated to 1500-1600°C in a N2 atmosphere by a stepwise heating method, with the heating rate being: 10-15°C / minute for 0-800°C, holding at 800°C for 1-2 hours, and 5-8°C / minute for temperatures above 800°C.

[0020] In some other embodiments of the present invention, in step S7, the temperature is heated to 1800-1950°C in an N2 atmosphere using a stepwise heating method. The heating rate is as follows: 10-15°C / minute for 0-1600°C, holding at 1600°C for 1-2 hours, and 3-5°C / minute for temperatures above 1600°C.

[0021] A prestress-reinforced Si3N4 ceramic substrate is prepared using the aforementioned method for preparing a prestress-reinforced Si3N4 ceramic substrate.

[0022] In other embodiments of the present invention, the thickness of the Si3N4 ceramic substrate is 1.5-2.0 cm, and the thickness of each Si3N4 ceramic substrate is 3.0-4.0 mm. Three to five Si3N4 ceramic substrates are provided.

[0023] In this invention, a metal mesh is laid in the interlayer to enhance the toughness of the ceramic plate. The spaces between Si3N4 ceramic substrates and the pores within the Si3N4 ceramic substrates are filled with a mixture B. After secondary heating and sintering at temperatures above 1800℃, it transforms into rod-shaped β-Si3N4. β-Si3N4 exhibits excellent mechanical properties, further increasing the overall strength of the Si3N4 ceramic substrate. The stacked substrate significantly reduces the occurrence of cracks and fissures. The added metal mesh increases prestress, and the addition of mixture B forms a coating, reinforcing the design and more than doubling the strength of the Si3N4 ceramic substrate. The tested bending strength can reach 700-800 MPa, enabling mass production. Attached Figure Description

[0024] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0025] Figure 1 This is a schematic diagram of a prestress-reinforced Si3N4 ceramic substrate structure layer proposed in this invention.

[0026] In the figure: 1. Si3N4 ceramic substrate; 11. Fine-pore internal column; 2. Metal mesh; 3. Mixed material B layer plate. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0028] The present invention proposes a method for preparing a prestressed reinforced Si3N4 ceramic substrate, the specific steps of which are as follows:

[0029] S1: Divide the Si3N4 raw material into two portions, put them into grinding jars respectively, and grind them into two different grades of fine grains with particle sizes of 30-40nm and 90-100nm respectively.

[0030] S2: Mix the metal oxide sintering aid with 90-100nm modified Si3N4, place it in a ball mill jar, ball mill for 3-5 hours, dry it, and sieve it through a 40-mesh sieve to obtain mixture A. Put it into a mold and press it under a vacuum of 70-80 MPa to obtain Si3N4 blocks. Heat it in a N2 atmosphere to 1500-1600℃ and hold it for 2-3 hours to obtain Si3N4 ceramic substrates.

[0031] S3: Punch out a matrix-distributed array of fine holes on the Si3N4 ceramic substrate prepared in step S2 using a punch press;

[0032] S4: A metal mesh is laid on the upper surface of the porous Si3N4 ceramic substrate prepared in step S3;

[0033] S5: Mix the metal oxide sintering aid with 30-40nm modified Si3N4, put it into a ball mill jar, ball mill for 3-5 hours, dry it, and sieve it through a 60-mesh sieve to obtain mixture B, which is ready for use.

[0034] S6: Place a Si3N4 ceramic substrate with metal mesh prepared in step S4 at the bottom of a mold box, apply mixture B to the Si3N4 ceramic substrate with metal mesh, cover it with another Si3N4 ceramic substrate with metal mesh and press it firmly, continue to apply mixture B to the newly laid substrate, and complete the stacking of multiple Si3N4 ceramic substrates with metal mesh in sequence.

[0035] S7: Press the ceramic substrate stacked in the mold in step S6 under a vacuum of 70-80 MPa to form a Si3N4 laminate; heat it in a N2 atmosphere to 1800-1950℃ and hold for 2-3 hours to obtain an enhanced Si3N4 ceramic substrate.

[0036] The Si3N4 raw material was divided into two parts and ground into powders with different particle sizes. The powder with the larger particle size was first used to make Si3N4 ceramic substrates to facilitate the subsequent installation of a metal mesh. The metal mesh was made of stainless steel, and the diameter of the metal strips was no more than 1 / 3 of the diameter of the Si3N4 ceramic substrate. The Si3N4 ceramic substrates were perforated to increase the bonding strength between mixture B and the Si3N4 raw material (mixture A). The metal mesh was then coated with mixture B, which enveloped the mesh and penetrated into the pores. During the sintering process, mixture B agglomerated into layers, while the mixture B within the pores formed pillars firmly inserted into the pores, achieving a strong connection with the Si3N4 ceramic substrate. The entire structure was as follows: Figure 1 As shown, mixture B forms a multilayer board with microporous internal pillars connecting the boards to clamp the Si3N4 ceramic substrate. The metal mesh greatly increases the prestress and the toughness of the substrate. In addition, the two different layers formed by mixture A and mixture B effectively buffer the pressure from external forces, preventing the board from cracking.

[0037] During the sintering process, after sintering at temperatures above 1800℃, it transforms into rod-shaped β-Si3N4, greatly increasing the strength of the sheet and enhancing the stability of the fine porous structure. When Si3N4 is heated to 1500-1600℃ in a N2 atmosphere, it forms α-Si3N4. α-Si3N4 has relatively better toughness, while β-Si3N4 has a certain degree of brittleness. The combination of the two greatly improves the toughness and rigidity of the sheet, making it more resistant to external pressure and preventing cracking.

[0038] The thickness of the Si3N4 ceramic substrate is 2-3 times the coating thickness of mixture B. Mixture B is brittle and prone to cracking under pressure, but the Si3N4 ceramic substrate made with the tougher mixture A, and due to the greater thickness of the Si3N4 ceramic substrate, greatly increases the overall toughness of the substrate. This improves the performance of the substrate, and when combined with the metal mesh, it is less prone to cracking and the formation of fissures.

[0039] The lower surface of the Si3N4 ceramic substrate is sanded before being laid in step S6. Sanding facilitates the adhesion of the mixture B to the Si3N4 ceramic substrate during sintering.

[0040] The metal oxide sintering aid comprises metal oxide, polynitrosilane fiber, polyethylene glycol butyral, and polyethylene glycol in a ratio of 1-1.1:0.1-0.2:0.1-0.15:2.0-3.0. Based on actual needs, a ratio obtained through experimentation was determined, making the performance of the metal oxide sintering aid more suitable for the sintering process of this application.

[0041] The preparation steps of the metal oxide sintering aid are as follows: metal oxide, polynitrosilane fiber, polyethylene glycol butyral, and polyethylene glycol are mixed and ground in a water bath to obtain a slurry. The slurry is then milled in a ball mill. After milling, the slurry is sieved to remove bubbles to obtain a casting slurry, which is then dried and ground into powder. This is a relatively conventional manufacturing process, and its application here also meets the manufacturing requirements of this application.

[0042] In step S2, the temperature is raised to 1500-1600℃ in an N2 atmosphere using a stepwise heating method. The heating rate is as follows: 10-15℃ / minute for 0-800℃, holding at 800℃ for 1-2 hours, and 5-8℃ / minute for temperatures above 800℃. The main purpose is to raise the temperature slowly to prevent excessively rapid sintering and cracking.

[0043] In step S7, heating to 1800-1950℃ in an N2 atmosphere using a stepwise heating method is employed. The heating rate is as follows: 10-15℃ / min for 0-1600℃, holding at 1600℃ for 1-2 hours, and 3-5℃ / min for temperatures above 1600℃. Similarly, to prevent cracking due to excessively rapid sintering, and considering the different powder particle sizes, the heating conditions differ slightly from the above.

[0044] A prestress-reinforced Si3N4 ceramic substrate is prepared using the aforementioned method. After sintering, edge sealing adhesive or other edge sealing materials are applied to one perimeter, which is a conventional edge sealing technique and will not be elaborated upon further.

[0045] The thickness of the Si3N4 ceramic substrate is 1.5-2.0 cm, and the thickness of each Si3N4 ceramic substrate is 3.0-4.0 mm. Three to five Si3N4 ceramic substrates are used. The overall substrate thickness can also be increased as needed.

[0046] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a prestress-reinforced Si3N4 ceramic substrate, characterized in that: The specific steps are as follows: S1: Divide the Si3N4 raw material into two portions, put them into grinding jars respectively, and grind them into two different grades of fine grains with particle sizes of 30-40nm and 90-100nm respectively. S2: Mix the metal oxide sintering aid with 90-100nm modified Si3N4, place it in a ball mill jar, ball mill for 3-5 hours, dry it, and sieve it through a 40-mesh sieve to obtain mixture A. Put it into a mold and press it under a vacuum of 70-80 MPa to obtain Si3N4 blocks. Heat it in a N2 atmosphere to 1500-1600℃ and hold it for 2-3 hours to obtain Si3N4 ceramic substrates. S3: Punch out a matrix-distributed array of fine holes on the Si3N4 ceramic substrate prepared in step S2 using a punch press; S4: A metal mesh is laid on the upper surface of the porous Si3N4 ceramic substrate prepared in step S3; S5: Mix the metal oxide sintering aid with 30-40nm modified Si3N4, put it into a ball mill jar, ball mill for 3-5 hours, dry it, and sieve it through a 60-mesh sieve to obtain mixture B, which is ready for use. S6: Place a Si3N4 ceramic substrate with metal mesh prepared in step S4 at the bottom of a mold box, apply mixture B to the Si3N4 ceramic substrate with metal mesh, cover it with another Si3N4 ceramic substrate with metal mesh and press it firmly, continue to apply mixture B to the newly laid substrate, and complete the stacking of multiple Si3N4 ceramic substrates with metal mesh in sequence. S7: Press the ceramic substrate stacked in the mold in step S6 under a vacuum of 70-80 MPa to form a Si3N4 laminate; heat it in N2 atmosphere to 1800-1950℃ and hold for 2-3 hours to obtain an enhanced Si3N4 ceramic substrate. In step S7, the temperature is heated to 1800-1950℃ in a N2 atmosphere using a stepwise heating method. The heating rate is as follows: 10-15℃ / minute for 0-1600℃, holding at 1600℃ for 1-2 hours, and 3-5℃ / minute for temperatures above 1600℃.

2. The method for preparing a prestressed reinforced Si3N4 ceramic substrate according to claim 1, characterized in that: The thickness of the Si3N4 ceramic substrate is 2-3 times the coating thickness of the mixture B.

3. The method for preparing a prestressed reinforced Si3N4 ceramic substrate according to claim 1, characterized in that: The lower surface of the Si3N4 ceramic substrate is first sanded before being laid in step S6.

4. The method for preparing a prestressed reinforced Si3N4 ceramic substrate according to claim 1, characterized in that: The metal oxide sintering aid comprises metal oxide, polynitrosilane fiber, polyethylene glycol butyral, and polyethylene glycol in a ratio of 1-1.1: 0.1-0.2: 0.1-0.15: 2.0-3.

0.

5. The method for preparing a prestressed reinforced Si3N4 ceramic substrate according to claim 4, characterized in that: The preparation steps of the metal oxide sintering aid are as follows: metal oxide, polynitrosilane fiber, polyethylene glycol butyral and polyethylene glycol are mixed and mixed into a slurry under water bath. The slurry is then placed in a ball mill and ground. After ball milling, the slurry is sieved to remove bubbles and then dried and ground into powder.

6. The method for preparing a prestressed reinforced Si3N4 ceramic substrate according to claim 1, characterized in that: In step S2, the temperature is raised to 1500-1600℃ in an N2 atmosphere using a stepwise heating method. The heating rate is as follows: 10-15℃ / minute for 0-800℃, holding at 800℃ for 1-2 hours, and 5-8℃ / minute for temperatures above 800℃.

7. A prestress-reinforced Si3N4 ceramic substrate, characterized in that: It is prepared by the method for preparing a prestressed reinforced Si3N4 ceramic substrate according to any one of claims 1-6.

8. A prestressed reinforced material according to claim 7 The ceramic substrate is characterized by: The The thickness of the ceramic substrate is 1.5-2.0 cm, and each piece is described as follows. The thickness of the ceramic substrate is 3.0-4.0 mm.

Images