Process for forming a profiled aluminum nitride ceramic structural component

Abstract

The application discloses a forming process of a special-shaped aluminum nitride ceramic structural member, and the process comprises the following steps: ball milling of aluminum nitride ceramic powder, preparation of ceramic slurry, preparation of wax cakes from the ceramic slurry, fermentation of the wax cakes, melting of the wax cakes into ceramic slurry again, hot-pressing injection of the ceramic slurry, high-temperature degreasing and sintering, and obtaining of the densified special-shaped aluminum nitride ceramic structural member. The application is suitable for various complex and irregular ceramic structural members, the product prepared by the method has higher density and thermal conductivity, the prepared aluminum nitride ceramic has a density of 3.32 g / cm 3 , a thermal conductivity greater than 170 W / (m*K), and high qualified product yield. The process makes the aluminum nitride material adopt hot-pressing injection forming, the whole production process has simple molds, short production cycle, low cost, high efficiency, is suitable for multi-variety and small-batch production, meanwhile, the problem of easy moisture absorption and hydrolysis of the aluminum nitride raw material is avoided, and long-term storage of the aluminum nitride raw material is realized.

Description

Technical Field

[0001] This invention relates to the field of advanced ceramic forming and processing technology, and in particular to a hot pressing injection molding process for irregularly shaped aluminum nitride ceramic structural parts. Background Technology

[0002] Aluminum nitride ceramics possess excellent properties such as high thermal conductivity, low dielectric constant, low coefficient of linear expansion, low density, non-toxicity, high mechanical strength, and good insulation performance, making them widely used in high-power integrated circuits, modular circuits, microelectronics, optics, communications, electrical devices, and intelligent manufacturing. Given their superior performance and wide applications, they are poised to become a mainstream new material for high thermal conductivity, high strength, and insulation in the 21st century, possessing broad market prospects and attracting widespread attention. Research has found that the theoretical thermal conductivity of aluminum nitride is 320 W / (m·K), but due to the incorporation of oxygen and impurities in the crystal lattice during the preparation of aluminum nitride ceramics, its thermal conductivity is reduced. Currently, the thermal conductivity of commercially available products generally does not exceed 170 W / (m·K). Furthermore, the prepared aluminum nitride ceramics have low density and are easily deformed, resulting in uneven surfaces. These factors all affect the widespread application of aluminum nitride ceramics.

[0003] Traditional forming processes for aluminum nitride ceramics include dry pressing, isostatic pressing, hot pressing, and die molding. These processes are suitable for preparing bulk aluminum nitride materials. Dry pressing has the advantages of simple operation, fewer process steps, and high efficiency. Its disadvantages include low strength of the formed green body and inability to press green bodies with complex geometries. Therefore, dry pressing is mainly used for the forming of simple, regular sheet and block ceramics. Isostatic pressing is an improvement on dry pressing, requiring relatively complex isostatic pressing equipment. The price of the equipment increases with the size of the ceramic, and the green body usually needs to be trimmed after isostatic pressing. For irregularly shaped aluminum nitride structural parts, the method of first pressing the powder into shape and then machining it to form complex shapes suffers from high wear and high cost due to the inherent brittleness and high hardness of ceramic materials. It is also difficult to produce small, complex, and dimensionally accurate aluminum nitride ceramic parts. Because aluminum nitride is prone to moisture absorption and hydrolysis in the atmosphere, traditional slip casting processes for ceramics cannot be used.

[0004] To meet the demand for aluminum nitride ceramics in the electronics industry, a tape casting process for forming aluminum nitride ceramic substrates was developed. Tape casting is a crucial ceramic substrate forming process with high production efficiency, but it can only be used for producing simple sheet materials and cannot meet the requirements for forming complex-shaped aluminum nitride ceramic green bodies. Therefore, powder injection molding emerged as a solution.

[0005] Powder injection molding (PIM) is a process that introduces plastic injection molding technology into the field of powder metallurgy. Ceramic powder, with the addition of a certain amount of polymer and additives, is heated slightly and then injected into a metal mold under pressure. After cooling, the preform is removed to obtain the blank. PIM offers advantages such as the ability to mold complex shapes in a single step, high dimensional accuracy, no need for machining, and ease of achieving highly efficient automated production. However, due to its long development cycle and high cost, it is more suitable for mass production and lacks flexibility for multi-variety, small-batch products. Furthermore, the debinding process for aluminum nitride ceramic green bodies produced by PIM requires a long time, sometimes several days to tens of days, during subsequent sintering, and is prone to defects such as blistering, deformation, and cracking, leading to quality problems. Due to debinding limitations, it is difficult to produce thick-walled products.

[0006] With the development of the semiconductor industry, the demand for complex, high-precision, and high-thermal-conductivity ceramic parts is constantly increasing, leading to a trend of multi-variety, small-batch customized production with the advantage of rapid delivery. Existing processing methods struggle to produce high-thermal-conductivity aluminum nitride ceramics with the required shape and dimensional accuracy. While powder injection molding can achieve complex-shaped parts, its development cycle is long and costly, and it lacks the flexibility for multi-variety, small-batch products, failing to meet current market demands. The problem this application aims to solve is to provide a method for the rapid, customized production of irregularly shaped aluminum nitride ceramics. Summary of the Invention

[0007] To address the existing technical problems, the purpose of this invention is to provide a simple and easy-to-implement molding process for irregularly shaped aluminum nitride ceramic structural components, suitable for small-batch customized production, and especially suitable for the production of irregularly shaped aluminum nitride ceramic structural components. Irregular shapes refer to complex shapes, typically with variable cross-sections, such as variable cross-section circular or square tubes, unlike simple long sheet-like, cylindrical, circular, or block-like regular shapes; it also includes combinations of complex curved surfaces, such as heating tiles with a semi-circular arc configuration and serrated grooves on the outside, impeller shapes, gear shapes, etc.

[0008] This invention provides a hot-press casting process for irregularly shaped aluminum nitride ceramic structural parts, comprising the following steps:

[0009] (1) Preparation of porcelain powder

[0010] Weigh aluminum nitride powder and yttrium oxide powder in a certain proportion, pour them into a ball mill and mix and ball mill. After ball milling for a period of time, add grinding aid and mix evenly to form ceramic powder.

[0011] (2) Making aluminum nitride wax cake

[0012] Add the first binder and the second binder to the ceramic powder prepared in step (1), and simultaneously use a high-speed mixer to quickly stir to obtain a ceramic slurry. Pour the ceramic slurry into a mold, cool and solidify it, and then remove it to obtain an aluminum nitride wax cake. The prepared aluminum nitride wax cake is aged and fermented under constant temperature and humidity conditions. The first binder is paraffin wax at a ceramic powder mass ratio of 1:0.135-0.142, and the second binder is polyvinyl alcohol weighed at a ceramic powder mass ratio of 1:0.005-0.006.

[0013] (3) Hot pressing grouting molding

[0014] Break the aluminum nitride wax cake after aging and fermentation in step (2) and put it into a container. Slowly heat it to make the aluminum nitride wax cake melt and flow, turning it back into a porcelain slurry. While it is hot, add a dispersant and stir to make the porcelain slurry uniform. Then pour the porcelain slurry into a hot press injection equipment and press it into various shapes of aluminum nitride green blanks through a mold.

[0015] (4) Degreasing and sintering of green body

[0016] Add adsorbent to the sagger, which is about 1 / 3 of the sagger volume. Arrange the aluminum nitride green blanks at intervals of 10-25 mm. After the blanks are arranged, add adsorbent to the sagger until the product is completely covered. Degrease the blanks in a high-temperature degreasing furnace. After degreasing, place the blanks in a vacuum sintering furnace for high-temperature sintering and allow them to cool naturally to produce aluminum nitride ceramic structural parts.

[0017] Furthermore, in step (1), the aluminum nitride powder is 95.5 wt% and the yttrium oxide powder is 4.5 wt% by mass fraction.

[0018] Preferably, the aluminum nitride powder in step (1) has a particle size of 2 to 4.5 micrometers.

[0019] Furthermore, the grinding aid mentioned in step (1) is preferably oleic acid, and the amount added is 0.3wt%-0.6wt% of the powder weight.

[0020] Furthermore, the viscosity of the ceramic slurry in step (2) is 18000-26000 mPa·s.

[0021] Preferably, the aging and fermentation in step (2) is carried out at a temperature of 16-22℃ and a relative humidity of 30-80%, and the fermentation time is more than 3 days.

[0022] Preferably, the dispersant in step (3) is ammonium polyacrylate, and the amount added is 0.2-0.38 wt%.

[0023] Preferably, the adsorbent in step (4) is β-Al2O3 powder.

[0024] Furthermore, the degreasing temperature in step (4) is 1000-1100℃, and the sintering temperature is 1800-2000℃.

[0025] This invention can mold complex-shaped aluminum nitride products with high dimensional accuracy, requiring no subsequent processing and being unrestricted by size, especially suitable for thick-walled products. It can be used for various complex-shaped high thermal conductivity ceramic structural parts or components. The resulting aluminum nitride structural parts can achieve a density of up to 3.32 g / cm³. 3 Its thermal conductivity is greater than 170 W / (m·K), and even reaches 200 W / (m·K).

[0026] This invention involves preparing aluminum nitride ceramic slurry into aluminum nitride wax cakes, followed by aging and fermentation. This allows the cakes to be molded using a hot-press casting process. The entire production process and equipment are simple, with low production costs and high efficiency, making it suitable for customized production. Furthermore, the aluminum nitride wax cakes are easy to store and do not easily absorb moisture or hydrolyze.

[0027] This invention features simple and quick mold making, convenient production process, short development cycle, ability to mold various irregular parts, and suitability for multi-variety, small-batch production. Implementation

[0028] The present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand the technical solution of the present invention.

[0029] Example 1: A hot-press casting method for irregularly shaped aluminum nitride ceramic structural parts, comprising the following steps:

[0030] (1) Preparation of porcelain powder

[0031] Weigh the following raw materials by weight percentage: 95.5 wt% aluminum nitride powder with a particle size of 2~4.5 micrometers and 4.5 wt% yttrium oxide powder. Pour them into a ball mill for mixing and ball milling. After ball milling for six hours, add 0.3 wt%-0.6 wt% of grinding aid by weight of the powder. Oleic acid is preferred as the grinding aid. Mix evenly to form ceramic powder.

[0032] (2) Making aluminum nitride wax cakes

[0033] Add a binder to the ceramic powder. Specifically, weigh out analytical grade paraffin wax at a ceramic powder mass ratio of 1:0.135 and analytical grade polyvinyl alcohol at a ceramic powder mass ratio of 1:0.005, and add them to the ceramic powder prepared in step (1). At the same time, use a high-speed mixer to stir rapidly. The temperature of the high-speed mixer is 80℃±5℃ and the speed is 1400 rpm. After stirring for one hour, the material is in the form of a slurry. Test its viscosity. Viscosity is an important indicator for measuring the dispersibility and flowability of fluids. If the viscosity reaches 18000-26000 mPa·s, stop stirring; pour the ceramic slurry into a mold, cool and solidify it, and then take it out to obtain aluminum nitride wax cake. The binder can change the rheological properties of the ceramic slurry and also has the function of maintaining the shape, so that the product can maintain its shape without change from the formation of the green body to debinding and sintering. The selected binder should be easy to demold, have high debinding efficiency, and good adhesion. If the binder is not selected well, it may cause the green body to deform or produce defects during the debinding process. Polyvinyl alcohol has good adhesion and flammability, and is easily discharged at high temperatures.

[0034] The prepared aluminum nitride wax cake is aged and fermented at a temperature of 16-22℃ and a humidity of 30-80% for at least 3 days. This aging process allows the auxiliary materials and ceramic powder to react, making the subsequent wax removal process smoother.

[0035] The primary purpose of making wax cakes is to enable the use of slip casting for aluminum nitride structural components. It also solves the problem of aluminum nitride powder's susceptibility to moisture absorption and hydrolysis, allowing for long-term storage of the raw material. The solid particles remain suspended for extended periods without stratification or sedimentation, preventing uneven composition in the finished product and facilitating storage and transportation. Furthermore, the aging and fermentation process of the wax cakes volatilizes moisture and some additives, maximizing the removal of ineffective components under constant temperature and humidity conditions, thus improving the success rate of subsequent pressing and molding.

[0036] (3) Hot pressing grouting molding

[0037] The aluminum nitride wax cake after aging and fermentation in step (2) is broken up and placed in a container. The mixture is slowly heated until it melts and becomes fluid, transforming back into a porcelain slurry. While still hot, 0.2-0.38 wt% of a dispersant (preferably ammonium polyacrylate) is added, and the mixture is stirred until the slurry is homogeneous. The dispersant, acting on the surface of the porcelain powder particles in the suspension, prevents agglomeration and improves the fluidity of the slurry, ensuring that it fills all parts of the mold during casting. After thorough mixing, the slurry is poured into a hot press casting machine. The air pressure is set to 0.6-0.7 MPa, and the holding time is 3-4 seconds. The mold is then removed, and the aluminum nitride green blank is extracted. Various shapes of aluminum nitride green blanks are then formed by pressing through the mold.

[0038] (4) Degreasing and sintering of green body

[0039] Add adsorbent, preferably β-Al₂O₃ powder, to the sagger, filling approximately 1 / 3 of its volume. Arrange the aluminum nitride green blanks at 10-25 mm intervals. After arrangement, add adsorbent to the sagger until the product is completely covered. Degrease the product in a high-temperature degreasing furnace above 800°C. After degreasing, sinter the product in a vacuum sintering furnace at high temperature, and allow it to cool naturally to produce aluminum nitride ceramic structural parts. If the degreasing temperature is too high, the product is prone to depressions; if the temperature is too low, the product is prone to patterns. Preferably, the degreasing temperature is 1000-1100°C, and sintering is carried out in a vacuum sintering furnace at 1800-2000°C.

[0040] Example 2 differs from Example 1 in that the grinding aid is 0.5 wt% oleic acid of the powder weight, the amount of paraffin added in step (2) is weighed according to the ceramic powder mass ratio of 1:0.142, and the amount of polyvinyl alcohol added is weighed according to the ceramic powder mass ratio of 1:0.006.

[0041] Example 3 differs from Example 1 in that the grinding aid is 0.35 wt% oleic acid of the powder, the amount of paraffin added in step (2) is weighed according to the ceramic powder mass ratio of 1:0.138, and the amount of polyvinyl alcohol added is weighed according to the ceramic powder mass ratio of 1:0.005.

[0042] The aluminum nitride ceramic structural components prepared in the examples have smooth surfaces and are free of cracks. Performance test data for the aluminum nitride ceramic structural components: density 3.32 g / cm³. 3 Thermal conductivity greater than 170 W / (m·K), flexural strength greater than 350 MPa, volume resistivity greater than 10¹⁴ Ω·cm, and breakdown strength greater than 15 KV / mm.

[0043] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A process for forming a shaped aluminum nitride ceramic structure, comprising: The method comprises the following steps: Step (1), preparing porcelain powder: taking aluminum nitride powder and yttrium oxide powder by weight percentage, mixing and ball milling, then adding grinding aid and mixing uniformly to form porcelain powder; Step (2), preparing aluminum nitride wax cake: adding first binder and second binder into the porcelain powder prepared in step (1), and stirring rapidly to obtain porcelain slurry; pouring the porcelain slurry into a mold, taking out after cooling and solidification, and obtaining aluminum nitride wax cake; the prepared aluminum nitride wax cake is subjected to aging fermentation; the first binder is paraffin with a mass ratio of 1:0.135-0.142 to the porcelain powder, and the second binder is polyvinyl alcohol with a mass ratio of 1:0.005-0.006 to the porcelain powder; wherein the aging fermentation is carried out at a temperature of 16-22℃ and a relative humidity of 30-80%, and the placing time is at least 3 days; Step (3), hot-pressing injection molding: crushing the aluminum nitride wax cake subjected to aging fermentation in step (2) and putting it into a container, heating to become porcelain slurry again; adding dispersant and stirring to make the porcelain slurry uniform; pouring the porcelain slurry into a hot-pressing injection molding equipment, and pressing and injecting through a mold to form an aluminum nitride green body; Step (4), green body degreasing and sintering: adding adsorbent into a sagger, arranging the aluminum nitride green body, adding adsorbent into the sagger until the product is completely covered, degreasing in a high-temperature degreasing furnace; after degreasing, putting it into a vacuum sintering furnace for high-temperature sintering, and naturally cooling to obtain an aluminum nitride ceramic.

2. The forming process of claim 1, wherein: The particle size of the aluminum nitride powder in step (1) is 2-4.5 microns.

3. The forming process of claim 1, wherein: In step (1), the aluminum nitride powder is taken by mass fraction of 95.5wt%, and the yttrium oxide powder is taken by mass fraction of 4.5wt%.

4. The forming process of claim 1, wherein: The grinding aid in step (1) is oleic acid, and the addition amount is 0.3wt%-0.6wt% of the weight of the powder.

5. The forming process of claim 1, wherein: The viscosity of the porcelain slurry in step (2) is 18000-26000 mPa·s.

6. The forming process of claim 1, wherein: The dispersant in step (3) is polyacrylammonium, and the addition amount is 0.2-0.38wt%.

7. The forming process of claim 1, wherein: The adsorbent in step (4) is β-Al2O3 powder.

8. The forming process of claim 1, wherein: The degreasing temperature in step (4) is 1000-1100℃, and the sintering temperature is 1800-2000℃.