Preparation method of textured silicon nitride ceramic substrate

Abstract

The invention discloses a preparation method of a textured silicon nitride ceramic substrate, and belongs to the technical field of ceramic products. Beta-silicon nitride whiskers with the long diameter of 4-15 microns and the short diameter of 1-3 microns are added into silicon nitride ceramic slurry according to the design, and when the whiskers containing beta-silicon nitride pass through a scraper of a casting machine, the whiskers tend to be directionally arranged in the casting direction, so that a textured structure is generated in the silicon nitride ceramic substrate. The textured structure is beneficial to improving the three-point bending strength, the fracture toughness and the thermal conductivity in the horizontal direction of the ceramic substrate.

Description

Technical Field

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

[0002] As demand for energy-saving, high-efficiency, high-power, and intelligent devices continues to grow, the application scenarios of high-power modules are expanding. High-power devices, with their advantages of high performance, high reliability, high power density, and intelligence, perfectly meet the needs of human device development. Consequently, high-power modules are increasingly in demand in the communications, optoelectronics, consumer electronics, and industrial applications. For example, in recent years, IBGTs have been used in new energy vehicles and multi-mode, multi-frequency PA modules in consumer electronics. As transmission efficiency and energy levels increase, high-power devices have increasingly stringent heat dissipation requirements. According to statistics, thermal failure is the leading cause of device failure. High-power devices belong to the field of semiconductor circuits, where aluminum oxide (Al2O3), aluminum nitride (AlN), and silicon nitride (SiN) substrates are the most widely used. Aluminum oxide (Al2O3) substrates were the first to gain market acceptance due to their low cost, but with a thermal conductivity of only 30 W / m·K, ceramic performance cannot meet the high heat dissipation requirements of high-power devices. Aluminum nitride (AlN) substrates have a thermal conductivity of over 160W / m·k, fully meeting the high heat dissipation requirements of high-power devices. However, their three-point bending strength is typically below 400MPa, and this strength decreases significantly as thermal conductivity increases. Under complex operating conditions, cracking often occurs due to low strength, reducing reliability. Silicon nitride substrates have a thermal conductivity of over 70W / m·k and a bending strength of over 600MPa, offering the best overall performance in terms of thermal conductivity and reliability, making them the best match for the high heat dissipation and high reliability requirements of semiconductor circuit substrates. Summary of the Invention

[0003] The present invention incorporates a specific proportion of β-silicon nitride whiskers with a long diameter of 4-15 μm and a short diameter of 1-3 μm into a silicon nitride ceramic slurry. When the whiskers pass through the scraper of a tape casting machine, they tend to align along the casting direction, creating a textured structure within the silicon nitride ceramic substrate. This textured structure produces coarse A-type β-silicon nitride grains parallel to the ceramic substrate (with an angle of ±30° between the long diameter of the grains and the horizontal direction of the substrate), which improves the three-point bending strength, fracture toughness, and horizontal thermal conductivity of the ceramic substrate. In the perpendicular direction (with an angle of ±30° between the long diameter of the grains and the vertical direction of the substrate), densely packed shorter B-type β-silicon nitride ceramic grains are distributed above and below the A-type β-silicon nitride grains. The textured structure of the A-type grains shortens the distance heat travels along the B-type grains, improving vertical heat transfer and the overall thermal conductivity of the ceramic substrate.

[0004] A method for preparing a textured silicon nitride ceramic substrate, characterized in that the steps include: S1. Prepare silicon nitride powder with an α-phase content higher than 85%, wherein the oxygen content of the silicon nitride powder is ≤2% and the mass quantity is 80-95 parts; β-silicon nitride whiskers with a mass quantity of 3-15 parts; rare earth element compound A with a mass quantity of 3-15 parts; prepare rare earth element compound B with a mass quantity of 3-15 parts to obtain ceramic powder.

[0005] S2. Add one, two, or three organic solvents selected from ethanol, toluene, isopropanol, and acetone into a ball mill, then add a dispersant and ceramic powder, and perform ball milling for 4-48 hours. Then, add a binder and a plasticizer for two-step mixing, and perform ball milling for 4-48 hours. Ball mill the mixture until the particle size of the silicon nitride powder is 0.3-2 μm, the particle size of the rare earth element compound A is 0.05-0.5 μm, and the particle size of the rare earth element compound B is 0.8-1.5 μm, to obtain a mixed slurry.

[0006] S3. The mixed slurry is vacuum degassing and tape-cast to form a green tape of the ceramic substrate, which is then cut into specified sizes.

[0007] S4. Degreasing the raw porcelain strip.

[0008] S5. Place the degreased green porcelain strip into a sintering furnace for sintering at a temperature of 1600-1900° C., a holding time of 2-15 hours, and a heating rate of 1-15° C. / min.

[0009] Furthermore, in step S1, the rare earth element compound A may be one or more components of oxide, halogen compound, nitride or carbide; the rare earth element compound B may be one or more components of oxide, halogen compound, nitride or carbide.

[0010] Furthermore, in step S4, the degreasing temperature is between 400-800°C.

[0011] Furthermore, in step S4, the degreasing atmosphere may be air, nitrogen, argon, or vacuum.

[0012] Furthermore, in step S5, the sintering process may be gas pressure sintering, hot pressing sintering, or hot isostatic pressing sintering.

[0013] The grains of the silicon nitride ceramic substrate sintered body prepared by the present invention have a distinct textured structure. Specifically, in the direction parallel to the ceramic substrate (where the angle between the grains and the substrate is within ±30°), the A-type grains are significantly longer and thicker, with a long diameter of 8-25 μm and a short diameter of 2-4 μm. The A-type grains account for 25-65% of the area. The short diameter of the grains with a long diameter of 2-8 μm accounts for 35-75% of the area. In the direction perpendicular to the ceramic substrate (where the angle between the grains and the substrate is within ±30°), the B-type grains are significantly denser, with a long diameter of 3-10 μm and a short diameter of 1-3 μm. The grains account for 85-98% of the area, while the grains with a long diameter exceeding 10 μm account for 2-15% of the area. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the specific implementation or the description of the prior art.

[0015] Figure 1 The microscopic effect diagram under the embodiment process; B-type grains (1), A-type grains (2). DETAILED DESCRIPTION

[0016] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0017] In Example 1, the ceramic formulation consisted of 85% silicon nitride, 7% β-silicon nitride, 5% yttrium oxide, and 3% magnesium oxide. After 24 hours of mixing, organic materials such as PVB and DOP were added, followed by another 24 hours of mixing. The mixture was then vacuum degassed and tape-casted. The molded sample was degreased and sintered at 1850°C for 10 hours in a nitrogen atmosphere.

[0018] In Example 2, the ceramic formula is designed to be 90% silicon nitride, 2% β-silicon nitride, 5% yttrium oxide, and 3% magnesium oxide. Other processes are the same as in Example 1.

[0019] In Example 3, the ceramic formula is designed to be 82% silicon nitride, 10% β-silicon nitride, 5% yttrium oxide, and 3% magnesium oxide. Other processes are the same as in Example 1.

[0020] Comparative Example 1 The ceramic formula is designed to be 92% silicon nitride, 5% yttrium oxide, and 3% magnesium oxide. Other processes are the same as those in Example 1.

[0021] Comparative Example 2 The ceramic formula is designed to be 91.5% silicon nitride, 0.5% β-silicon nitride, 5% yttrium oxide, and 3% magnesium oxide. Other processes are the same as those in Example 1.

[0022] Comparative Example 3 The ceramic formula is designed to be 72% silicon nitride, 20% β-silicon nitride, 5% yttrium oxide, and 3% magnesium oxide. Other processes are the same as those in Example 1.

[0023] The physical indicators measured by the above 6 process technologies are as follows: From the above test results, it can be seen that after the introduction of long-grained β-phase silicon nitride whiskers, the proportion of long grains in the horizontal and vertical directions of the ceramic substrate has increased. Due to the directional pressure of the casting scraper, the distribution of long grains along the casting direction accounts for a higher proportion. This structure is obviously beneficial to the improvement of the toughness of the ceramic substrate. At the same time, after the formation of the textured structure of the horizontal type A long grains, the vertical type B grains and the type A grains form a bridge structure, which shortens the distance of heat transfer and improves the thermal conductivity of the product. However, when too many β-silicon nitride whiskers are introduced, the density of the ceramic product decreases, resulting in a decrease in both mechanical and thermal properties.

Claims

1. A method for preparing a textured silicon nitride ceramic substrate, The invention is characterized in that the steps are: S1. Prepare silicon nitride powder with an α-phase content greater than 85%, wherein the oxygen content of the silicon nitride powder is ≤2% and the weight amount is 80-95 parts; β-silicon nitride whiskers, the weight amount is 3-15 parts; and rare earth element compound A, the weight amount is 3-15 parts; Prepare 3-15 parts by weight of rare earth element compound B to obtain ceramic powder; S2. Add one, two, or three organic solvents selected from ethanol, toluene, isopropanol, and acetone to a ball mill, then add a dispersant and ceramic powder, and perform ball milling for 4-48 hours. Then, add a binder and a plasticizer for two-step mixing, and perform ball milling for 4-48 hours. Ball milling is performed until the silicon nitride powder has a particle size of 0.3-2 μm, the rare earth element compound A has a particle size of 0.05-0.5 μm, and the rare earth element compound B has a particle size of 0.8-1.5 μm, to obtain a mixed slurry. S3, the mixed slurry is vacuum degassing and tape-casting to form a green tape of the ceramic substrate, which is then cut into specified sizes; S4, degreasing the green porcelain strip; S5. Place the degreased green porcelain strip into a sintering furnace for sintering at a temperature of 1600-1900° C., a holding time of 2-15 hours, and a heating rate of 1-15° C. / min.

2. The method for preparing a textured silicon nitride ceramic substrate according to claim 1, wherein: In step S1, the rare earth element compound A may be one or more components of oxide, halogen compound, nitride or carbide; the rare earth element compound B may be one or more components of oxide, halogen compound, nitride or carbide.

3. The method for preparing a textured silicon nitride ceramic substrate according to claim 1, wherein: In step S4, the degreasing temperature is between 400-800°C.

4. The method for preparing a textured silicon nitride ceramic substrate according to claim 1, wherein: In step S4, the degreasing atmosphere may be air, nitrogen, argon or vacuum.

5. The method for preparing a textured silicon nitride ceramic substrate according to claim 1, wherein: In step S5, the sintering process may be gas pressure sintering, hot pressing sintering, or hot isostatic pressing sintering.

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