Method for connecting in-situ growth whiskers with aluminum nitride ceramics

Abstract

The invention relates to a method for connecting aluminum nitride ceramics, in particular to a method for connecting aluminum nitride ceramics through in-situ growth of whiskers. The invention aims to solve the technical problems that the cost is higher, the process is complicated and the joint has larger residual stress when the aluminum nitride ceramic is connected by utilizing a metal intermediate layer in the prior art. The preparation method comprises the following steps: firstly, obtaining a thin aluminum oxide layer on the surface of aluminum nitride by adopting a pre-oxidation method, then changing boric acid into molten boron oxide at high temperature, and reacting the aluminum oxide layer on the surface of the aluminum nitride ceramic with the molten boron oxide in the presence of oxygen to generate aluminum borate whiskers; the aluminum borate whiskers simultaneously grow on the surfaces of the base materials on the two sides, one part of the whiskers grow into a whole, the other part of the whiskers are interlocked and staggered, and the aluminum nitride base materials on the two sides are connected. The aluminum borate whisker and aluminum nitride ceramic have similar physical and chemical properties, the mechanical property at high temperature is higher, the corrosion resistance is high, and a joint does not have a metal phase, so that the high-temperature service capability and higher corrosion resistance are realized.

Description

Technical Field

[0001] This invention relates to a method for joining aluminum nitride ceramics. Background Technology

[0002] Aluminum nitride ceramics possess excellent mechanical properties, thermal conductivity, and dielectric constant, making them promising candidates for applications in electronic packaging and other fields. In practical applications, the fabrication of complex-shaped or structurally complex aluminum nitride structures is required. Due to the hard and brittle nature of ceramics, traditional machining methods are challenging, making ceramic bonding a more viable option. Aluminum nitride ceramic bonding often employs a metal interlayer, with bonding performed in a specific atmosphere or vacuum. However, the metal interlayer is typically expensive, and the required equipment is complex. Furthermore, the significant difference in elastic modulus and coefficient of linear expansion between metals and ceramics leads to substantial residual stress at the joint. Additionally, ceramics generally maintain good mechanical properties at high temperatures, while the yield strength of metals decreases significantly at high temperatures. Moreover, the corrosion resistance of metals is generally lower than that of ceramics. These factors limit the application of metal interlayer bonding in ceramic structures.

[0003] Currently, alumina ceramics can achieve metal-free interlayer bonding by growing whiskers on the surface, generating aluminum borate whiskers through the reaction of alumina and boron oxide. However, this method has not yet been applied in the bonding of oxygen-free ceramics such as aluminum nitride. Summary of the Invention

[0004] The present invention aims to solve the problems of high cost, complex process and large residual stress in the joint of existing aluminum nitride ceramics using metal interlayers, and to provide a method for in-situ growth of whiskers to connect aluminum nitride ceramics.

[0005] The method for in-situ growth of whiskers to bond aluminum nitride ceramics according to the present invention is carried out according to the following steps:

[0006] 1. Pre-oxidation: Polish the aluminum nitride ceramic with sandpaper, then ultrasonically clean it with anhydrous ethanol and air dry it naturally; then place it in the air and raise it from room temperature to 800℃~1150℃ and keep it at that temperature for 20min~90min, then cool it to room temperature to obtain a micron-sized aluminum oxide layer on the surface of aluminum nitride.

[0007] II. Growth of whisker bonding: Boric acid is sandwiched between two aluminum nitride samples prepared in step one to form a sandwich structure. Then, a pressure of 0~2MPa is applied, and the sample is heated to 900℃~1150℃ in air and held for 30min~240min. The sample is then cooled to room temperature in the furnace and removed to obtain a whisker-bonded aluminum nitride ceramic joint.

[0008] The design principle of the invention:

[0009] The bonding of aluminum nitride ceramics requires interatomic bonding. In step one of this invention, a pre-oxidation method is used, where aluminum nitride reacts with oxygen in the air at high temperature to obtain a thin layer of alumina on the surface of aluminum nitride. The alumina layer has a high bonding strength with the aluminum nitride matrix. In step two, boric acid is converted into molten boron oxide at high temperature. The alumina layer on the surface of the aluminum nitride ceramic reacts with the molten boron oxide in the presence of oxygen to generate aluminum borate whiskers. Aluminum borate whiskers grow simultaneously on the surfaces of the two parent materials. Some whiskers grow into one piece, while others interlock and interweave, thus connecting the two aluminum nitride parent materials to form an "aluminum nitride / alumina / whisker / alumina / aluminum nitride" structure.

[0010] In addition, aluminum borate whiskers have similar physicochemical properties to aluminum nitride ceramics, exhibiting high mechanical properties at high temperatures and strong corrosion resistance. Therefore, the aluminum nitride connection structure obtained by this method has strong corrosion resistance and can operate at high temperatures.

[0011] The present invention has the following beneficial effects:

[0012] 1. The process of the present invention is simple and effective. By assembling pre-oxidized aluminum nitride ceramics and boric acid into a sandwich structure, aluminum borate whiskers can be generated in situ, thereby achieving the connection of aluminum nitride ceramics.

[0013] 2. The pre-oxidized layer of the present invention has strong bonding force with the substrate, and the whiskers grow in situ on the pre-oxidized layer, which also has good bonding performance, thus ensuring the excellent mechanical properties of the connection structure.

[0014] 3. Both the pre-oxidation method and the in-situ whisker growth method used in this invention can be carried out directly in air, without the need for complex and expensive equipment and atmosphere.

[0015] 4. The in-situ whisker growth connection method used in this invention has no metallic phase at the joint, thus it has high-temperature service capability and strong corrosion resistance. Attached Figure Description

[0016] Figure 1 The image shows the cross-sectional microstructure of the aluminum nitride ceramic connector obtained in step two of Experiment 1.

[0017] Figure 2 EDS image of the aluminum nitride ceramic joint obtained in step two of Experiment 1;

[0018] Figure 3 The XRD pattern of the aluminum nitride ceramic joint obtained in step two of Experiment 1. Detailed Implementation

[0019] Specific Implementation Method 1: This implementation method is a method for in-situ growth of whisker-connected aluminum nitride ceramics, specifically carried out according to the following steps:

[0020] 1. Pre-oxidation: Polish the aluminum nitride ceramic with sandpaper, then ultrasonically clean it with anhydrous ethanol and air dry it naturally; then place it in the air and raise it from room temperature to 800℃~1150℃ and keep it at that temperature for 20min~90min, then cool it to room temperature to obtain a micron-sized aluminum oxide layer on the surface of aluminum nitride.

[0021] II. Growth of whisker bonding: Boric acid is sandwiched between two aluminum nitride samples prepared in step one to form a sandwich structure. Then, a pressure of 0~2MPa is applied, and the sample is heated to 900℃~1150℃ in air and held for 30min~240min. The sample is then cooled to room temperature in the furnace and removed to obtain a whisker-bonded aluminum nitride ceramic joint.

[0022] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that, in step one, the aluminum nitride ceramic is successively polished with 400#, 800#, 1200#, 2000#, and 3000# sandpaper. Everything else is the same as in Specific Implementation Method One.

[0023] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that: in step 1, the device is ultrasonically cleaned with anhydrous ethanol for 5 to 15 minutes. Everything else is the same as in Specific Implementation Method 1 or 2.

[0024] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that: in step one, the temperature is increased from room temperature to 800℃ to 1150℃ in air at a heating rate of 5℃ / min to 15℃ / min and held for 20min to 90min. Everything else is the same as in Specific Implementation Methods One to Three.

[0025] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method Four in that, in step one, the aluminum is cooled to room temperature at a cooling rate of 5°C / min to 15°C / min, resulting in a micron-sized aluminum oxide layer on the aluminum nitride surface. Everything else is the same as in Specific Implementation Method Four.

[0026] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method Five in that, during the pre-oxidation process described in Step One, manganese oxide, potassium permanganate, hydrogen peroxide, or potassium persulfate, which can promote oxidation, are also placed on the surface of the aluminum nitride ceramic. Everything else is the same as in Specific Implementation Method Five.

[0027] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that the boric acid mentioned in step two is in granular form, powder form, aqueous solution of boric acid, organic solution of boric acid, or suspension of boric acid. Everything else is the same as in Specific Implementation Method Six.

[0028] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Method Seven in that a pressure of 0.1 MPa is applied in step two. Everything else is the same as in Specific Implementation Method Seven.

[0029] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Eight in that, in step two, the temperature is heated to 1050°C in an air environment. Everything else is the same as in Specific Implementation Method Eight.

[0030] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Method Nine in that, in step two, the temperature is heated to 1050°C in an air environment and maintained for 120 minutes. Everything else is the same as in Specific Implementation Method Nine.

[0031] The invention was verified using the following experiments:

[0032] Experiment 1: This experiment demonstrates a method for in-situ growth of whisker-bonded aluminum nitride ceramics, specifically carried out according to the following steps:

[0033] 1. Pre-oxidation: Aluminum nitride ceramics were polished sequentially with 400#, 800#, 1200#, 2000# and 3000# sandpaper, then ultrasonically cleaned with anhydrous ethanol for 10 min and air-dried. Then, the ceramics were placed in air and heated from room temperature to 950°C at a rate of 10°C / min and held at that temperature for 30 min. Finally, the ceramics were cooled to room temperature at a rate of 10°C / min to obtain a micron-sized aluminum oxide layer on the surface of aluminum nitride.

[0034] II. Growth of whisker bonding: Boric acid powder is sandwiched between two aluminum nitride samples prepared in step one to form a sandwich structure. Then, a pressure of 0.1 MPa is applied, and the mixture is heated to 1050°C in air and held for 120 min. The mixture is then cooled to room temperature in the furnace, and the sample is removed to obtain a whisker-bonded aluminum nitride ceramic joint.

[0035] Figure 1 Figure 1 shows the cross-sectional microstructure of the aluminum nitride ceramic connector obtained in step 2 of Experiment 1. Figure 2b is a magnified view of the red dashed box in Figure 2a. Figures 2a and 2b show that the two sides are aluminum nitride substrate and the middle is the grown whiskers.

[0036] Figure 2 The image shows the EDS diagram of the aluminum nitride ceramic joint obtained in step two of Experiment 1. The EDS results show that there is an Al2O3 layer between AlN and the whiskers, proving that the method successfully achieved the connection of aluminum nitride ceramics by in-situ growth of whiskers.

[0037] Figure 3The XRD pattern of the aluminum nitride ceramic joint obtained in step two of Experiment 1 shows that the main component of the ceramic is AlN, with the presence of Al4B2O9 (aluminum borate) and AlYO3 phases. Al4B2O9 is the main component of the whiskers growing on the surface of AlN ceramic, while AlYO3 is a small amount of impurity in AlN ceramic.

[0038] The aluminum nitride ceramic joint obtained in step two of Experiment 1 was subjected to mechanical property testing, and its room temperature shear strength was 72 MPa, proving that the aluminum nitride connection structure obtained by the in-situ growth of whiskers in this method has excellent mechanical properties.

Claims

1. A method for in-situ growth of whisker-bonded aluminum nitride ceramics, characterized in that... The method is performed according to the following steps:

1. Pre-oxidation: Polish the aluminum nitride ceramic with sandpaper, then ultrasonically clean it with anhydrous ethanol and air dry it naturally; then place it in the air and raise it from room temperature to 800℃~1150℃ and keep it at that temperature for 20min~90min, then cool it to room temperature to obtain a micron-sized aluminum oxide layer on the surface of aluminum nitride. II. Growth of whisker bonding: Boric acid is sandwiched between two aluminum nitride samples prepared in step one to form a sandwich structure. Then, a pressure of 0~2MPa is applied, and the sample is heated to 900℃~1150℃ in air and held for 30min~240min. The sample is then cooled to room temperature in the furnace and removed to obtain a whisker-bonded aluminum nitride ceramic joint.

2. The method for in-situ growth of whisker-linked aluminum nitride ceramics according to claim 1, characterized in that... In step one, the aluminum nitride ceramic is polished in sequence with sandpaper of 400#, 800#, 1200#, 2000# and 3000#.

3. The method for in-situ growth of whisker-linked aluminum nitride ceramics according to claim 1, characterized in that... In step one, use anhydrous ethanol for ultrasonic cleaning for 5 to 15 minutes.

4. The method for in-situ growth of whisker-linked aluminum nitride ceramics according to claim 1, characterized in that... In step one, the temperature is raised from room temperature to 800℃ to 1150℃ in air at a rate of 5℃ / min to 15℃ / min and held for 20min to 90min.

5. The method for in-situ growth of whisker-linked aluminum nitride ceramics according to claim 1, characterized in that... In step one, the aluminum is cooled to room temperature at a cooling rate of 5℃ / min to 15℃ / min to obtain a micron-sized aluminum oxide layer on the aluminum nitride surface.

6. The method for in-situ growth of whisker-linked aluminum nitride ceramics according to claim 1, characterized in that... In the pre-oxidation process described in step one, manganese oxide, potassium permanganate, hydrogen peroxide, or potassium persulfate are also placed on the surface of the aluminum nitride ceramic.

7. The method for in-situ growth of whisker-linked aluminum nitride ceramics according to claim 1, characterized in that... The boric acid mentioned in step two is in the form of granules, powder, aqueous solution, organic solution, or suspension.

8. The method for in-situ growth of whisker-linked aluminum nitride ceramics according to claim 1, characterized in that... In step two, a pressure of 0.1 MPa is applied.

9. The method for in-situ growth of whisker-linked aluminum nitride ceramics according to claim 1, characterized in that... In step two, heat the mixture to 1050°C in an air environment.

10. A method for in-situ growth of whisker-linked aluminum nitride ceramics according to claim 9, characterized in that... In step two, heat the mixture to 1050°C in air and hold it for 120 minutes.

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