A metal-free gradient bonding paste for aluminum nitride ceramic heaters and method

Abstract

This invention discloses a metal-free gradient bonding slurry and method for aluminum nitride ceramic heaters, belonging to the field of ceramic heater bonding technology. The bonding slurry includes a first slurry and a second slurry. The first slurry comprises 50-70 wt% aluminum nitride ceramic powder, 5-20 wt% alumina ceramic powder, 0-5 wt% magnesium fluoride powder, and 1-10 wt% yttrium oxide powder. The second slurry comprises 50-70 wt% aluminum nitride ceramic powder, 5-20 wt% alumina ceramic powder, 5-15 wt% magnesium fluoride powder, and 1-10 wt% yttrium oxide powder. The slurry of this application avoids the formation of brittle intermetallic compounds, maintains good thermal conductivity and electrical insulation in the joint area, and improves high-temperature stability. The gradient transition layer design solves the problem of thermal expansion mismatch caused by the difference in microstructure between the ceramic plate and the ceramic shaft, significantly improving the thermal shock fatigue resistance of the joint.

Description

Technical Field

[0001] This invention relates to the field of ceramic heater bonding technology, and particularly to a metal gradient-free bonding slurry and method for aluminum nitride ceramic heaters. Background Technology

[0002] Aluminum nitride (AlN) ceramics have been widely used in many fields such as heating substrates and heat sinks due to their high thermal conductivity, low dielectric constant, high-temperature dissipation and corrosion resistance. Their coefficient of thermal expansion is similar to that of silicon wafers, which can reduce stress problems caused by different thermal expansion.

[0003] However, the connection between the AlN ceramic plate and the ceramic shaft is crucial. Existing common methods include brazing, glass bonding, and solid-liquid bonding. Brazing cannot wet the ceramic surface, and the high welding temperature can cause product deformation and abnormal grain growth, which in turn affects volume resistivity and temperature distribution uniformity. Glass bonding has low strength and poor corrosion resistance, making it unsuitable for operation in plasma environments.

[0004] In the prior art, Chinese patent CN 117447223A describes a method where four oxide raw materials (Li2O, MgO, Al2O3, and SiO2) are mixed together by low-speed ball milling to obtain a uniformly mixed oxide powder. The resulting joint, obtained by holding the uniformly mixed oxide powder at 1380℃ for 10 minutes, exhibits a maximum room-temperature shear strength of 57 MPa. This solid-liquid bond exhibits good airtightness and high connection strength, and is widely used.

[0005] However, due to existing process issues, the thermal expansion coefficients of the aluminum nitride heater plate and the shaft are different, resulting in large residual stress in the bonding process, leading to cracks and detachment at the joint. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a metal gradient bonding slurry and method for aluminum nitride ceramic heaters, which can reduce the residual stress in the bonding of aluminum nitride heater plates and shafts.

[0007] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0008] The present invention provides a metal-free gradient bonding slurry for an aluminum nitride ceramic heater, comprising a first slurry and a second slurry. The first slurry comprises 50-70 wt% aluminum nitride ceramic powder, 5-20 wt% alumina ceramic powder, 0-5 wt% magnesium fluoride powder, and 1-10 wt% yttrium oxide powder. The second slurry comprises 50-70 wt% aluminum nitride ceramic powder, 5-20 wt% alumina ceramic powder, 5-15 wt% magnesium fluoride powder, and 1-10 wt% yttrium oxide powder.

[0009] Preferably, the preparation method of the first slurry and the second slurry includes: first weighing aluminum nitride ceramic powder, alumina ceramic powder, magnesium fluoride powder and yttrium oxide powder according to their respective mass percentages, mixing the powders after weighing, then adding solvent, binder and dispersant to each and mixing them together, and grinding and dispersing them respectively through a pounder and a three-roll mill to prepare the first slurry and the second slurry.

[0010] Preferably, the solvent is terpineol, the binder is at least one of polyvinyl alcohol, polyvinyl butyral, and polymethyl methacrylate, and the dispersant is an acrylic polymer.

[0011] Preferably, the aluminum nitride ceramic powder is first ball-milled before mixing, with a ball-to-material ratio of 5 to 8:1, and then oxidized in an atmospheric furnace to increase its oxygen content to 2 to 4%.

[0012] Another aspect of the present invention discloses a bonding method using the above-mentioned aluminum nitride ceramic heater metal-free gradient bonding slurry, the bonding method comprising:

[0013] First, clean the aluminum nitride plate and aluminum nitride shaft of the aluminum nitride ceramic heater that need to be joined, using alcohol as the cleaning agent, and perform ultrasonic cleaning for 30-60 minutes.

[0014] The first paste is printed at the location where the aluminum nitride shaft is connected, and the first paste is printed first at the location where the aluminum nitride plate is connected, followed by the second paste, and then dried.

[0015] Finally, the aluminum nitride shaft and the aluminum nitride plate are placed in the furnace for bonding, and a pressure of 3-4 MPa is applied. Nitrogen gas is introduced at 900°C for atmosphere protection. The bonding temperature is 1400-1600°C, and the bonding time is 2-2.5 hours.

[0016] After bonding is completed, the sample is cooled and removed, the bonding strength is tested, and a helium leak detector is used to check for helium leaks in the product.

[0017] Preferably, the total printing thickness of the first paste and the second paste printed on the aluminum nitride plate is 30-80 μm; the printing thickness of the first paste printed on the aluminum nitride plate is 30-40 μm.

[0018] Preferably, the bonding strength between the aluminum nitride plate and the aluminum nitride shaft is between 150 and 300 MPa, and the helium leakage is less than 1 × 10⁻⁶ MPa. -9 Pa•m 3 / s or less.

[0019] The above technical solution has the following beneficial effects:

[0020] Metal-free connection: avoids the formation of brittle intermetallic compounds, maintains good thermal conductivity and electrical insulation in the joint area, and improves high-temperature stability.

[0021] Excellent stress mitigation capability: The gradient transition layer design solves the problem of thermal expansion mismatch caused by the difference in microstructure between ceramic plate and ceramic shaft, and greatly improves the joint's resistance to thermal shock fatigue. Detailed Implementation

[0022] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] This invention provides a metal-free gradient bonding slurry and bonding method for aluminum nitride ceramic heaters to solve the problems mentioned in the background art, and can reduce residual stress and achieve a connection method that matches thermal expansion.

[0024] A metal-free gradient bonding slurry for an aluminum nitride ceramic heater includes a first slurry and a second slurry. The first slurry comprises 50-70 wt% aluminum nitride ceramic powder, 5-20 wt% alumina ceramic powder, 0-5 wt% magnesium fluoride powder, and 1-10 wt% yttrium oxide powder. The second slurry comprises 50-70 wt% aluminum nitride ceramic powder, 5-20 wt% alumina ceramic powder, 5-15 wt% magnesium fluoride powder, and 1-10 wt% yttrium oxide powder.

[0025] Specifically, the first slurry comprises aluminum nitride ceramic powder, alumina ceramic powder, magnesium fluoride powder, yttrium oxide powder, binder, and dispersant, with a total weight percentage of 100 wt%. The sum of the weight percentages of binder and dispersant can be 5 wt%, specifically 2 wt% binder and 3 wt% dispersant. Other weight percentages can be: 70 wt% aluminum nitride ceramic powder, 15 wt% alumina ceramic powder, 0 wt% magnesium fluoride powder, and 10 wt% yttrium oxide powder; or 65 wt% aluminum nitride ceramic powder, 20 wt% alumina ceramic powder, 5 wt% magnesium fluoride powder, and 5 wt% yttrium oxide powder. Furthermore, the first slurry is a screen printing slurry and also includes a solvent. The amount of solvent added is sufficient to form a printable slurry after mixing. After mixing and grinding and dispersing with a mortar and a three-roll mill, the first slurry is formed.

[0026] Specifically, the second slurry comprises 100 wt% aluminum nitride ceramic powder, alumina ceramic powder, magnesium fluoride powder, yttrium oxide powder, binder, and dispersant. The sum of the weight percentages of binder and dispersant can be 5 wt%, specifically 2 wt% binder and 3 wt% dispersant. More specifically, the second slurry may include: 55 wt% aluminum nitride ceramic powder, 20 wt% alumina ceramic powder, 15 wt% magnesium fluoride powder, 5 wt% yttrium oxide powder, and 5 wt% binder and dispersant. The first slurry may also include: 65 wt% aluminum nitride ceramic powder, 15 wt% alumina ceramic powder, 10 wt% magnesium fluoride powder, 5 wt% yttrium oxide powder, and 5 wt% binder and dispersant. In addition, the first slurry is a screen-printable slurry and also includes a solvent. The amount of solvent added is sufficient to prepare a printable slurry. After mixing and grinding and dispersing with a mortar and a three-roll mill, the second slurry is formed. The prepared first and second slurries are used to bond aluminum nitride plates and aluminum nitride shafts of aluminum nitride ceramic heaters.

[0027] In some embodiments, the preparation methods of the first slurry and the second slurry include: first weighing aluminum nitride ceramic powder, alumina ceramic powder, magnesium fluoride powder and yttrium oxide powder according to their respective mass percentages, mixing the powders after weighing, then adding solvent, binder and dispersant to each and mixing them together, and grinding and dispersing them respectively through a pounder and a three-roll mill to prepare the first slurry and the second slurry;

[0028] Specifically, the preparation methods of the first and second slurries are similar. First, aluminum nitride ceramic powder, alumina ceramic powder, magnesium fluoride powder, and yttrium oxide powder are weighed according to their respective percentages. After weighing, the powders are mixed. The mixing medium can be isopropanol. After the powders of the first and second slurries are mixed separately, solvents, binders, and dispersants are added to each slurry and mixed together. The solvent is added as needed. The first and second slurries prepared in the end only need to be suitable for screen printing. Using the first and second slurries of this application to join aluminum nitride ceramic heaters completely avoids the formation of brittle intermetallic compounds, maintains good thermal conductivity and electrical insulation in the joint area, and improves high-temperature stability.

[0029] In some embodiments, the solvent is specifically terpineol, the binder is specifically at least one of polyvinyl alcohol, polyvinyl butyral and polymethyl methacrylate, or a mixture of any two of the three, wherein the weight percentage of the two mixtures is 1:1, or the three mixtures are mixed, wherein the weight percentage of the three mixtures is 1:1:1, and the dispersant is specifically an acrylic polymer.

[0030] In some embodiments, the aluminum nitride ceramic powder is first ball-milled before mixing, with a ball-to-powder ratio of 5 to 8:1. Then, it is oxidized in an atmospheric furnace to increase its oxygen content to 2 to 4%. Specifically, the ball-to-powder ratio of the aluminum nitride ceramic powder during ball milling is 5:1 or 8:1. After ball milling, it is oxidized in an atmospheric furnace to increase its oxygen content to 2% or 4%. The oxidation treatment of the aluminum nitride ceramic powder causes its surface to oxidize and form amorphous alumina, which is then used to prepare a bonding slurry. During the bonding process, a liquid phase is formed, reducing thermal expansion and making the sintering more compact.

[0031] A bonding method using the above-mentioned aluminum nitride ceramic heater metal-free gradient bonding paste, the bonding method specifically includes the following steps:

[0032] First, clean the aluminum nitride plate and aluminum nitride shaft of the aluminum nitride ceramic heater that need to be joined. Use alcohol as the cleaning agent and perform ultrasonic cleaning for 30 to 60 minutes. Specifically, at least the joint area of ​​the aluminum nitride plate and aluminum nitride shaft needs to be cleaned. During operation, the cleaning area can be larger for easier cleaning. Specifically, use alcohol as the cleaning agent and perform ultrasonic cleaning for 30 or 60 minutes to clean the joint area of ​​the aluminum nitride plate and aluminum nitride shaft, so as to facilitate the next step of joining.

[0033] The first paste is printed at the connection point of the aluminum nitride shaft, and the second paste is printed at the connection point of the aluminum nitride plates, followed by drying. Specifically, the paste is printed onto the joint points of the aluminum nitride shaft and the aluminum nitride plates using screen printing. Specifically, the first paste is printed at the joint point of the aluminum nitride shaft, and the second paste is printed at the joint point of the aluminum nitride plates. The total printing thickness of the first and second pastes on the aluminum nitride plates is 30–80 μm. The specific total printing thickness of the first and second pastes can be further specified. The thickness can be 30μm, 80μm, or even 60μm. Specifically, the thickness of the first and second slurries can be equal. The printing thickness of the first slurry on the aluminum nitride shaft is 30-40μm. The printing thickness of the first slurry brushed onto the aluminum nitride shaft can be 30μm or 40μm. During bonding, a gradient bond is formed between the first slurry layer, the second slurry layer, and the first slurry layer. The design of the gradient transition layer fundamentally solves the problem of thermal expansion mismatch caused by the difference in microstructure between the ceramic plate and the ceramic shaft, and greatly improves the thermal shock fatigue resistance of the joint.

[0034] Finally, the aluminum nitride shaft and aluminum nitride plate are placed in the furnace for bonding, and a pressure of 3-4 MPa is applied. Nitrogen gas is introduced at 900°C for atmosphere protection. The bonding temperature is 1400-1600°C, and the bonding time is 2-2.5 hours. Specifically, after printing the paste, the aluminum nitride shaft and aluminum nitride plate are aligned and placed in the sintering furnace. Pressure is applied from the axial direction of the aluminum nitride shaft, specifically 3 MPa or 4 MPa. The furnace temperature is raised to 1400-1600°C, specifically 1400°C, 1600°C, or 1500°C. During the heating process, nitrogen gas is introduced at 900°C for atmosphere protection. At the bonding temperature of 1400-1600°C, this temperature is maintained for 2-2.5 hours to complete the bonding. Specifically, the bonding temperature is maintained for 2 hours or 2.5 hours. After bonding, the material is allowed to cool naturally to room temperature.

[0035] After cooling following the bonding process, the assembled aluminum nitride ceramic heater is removed. The bonding strength between the aluminum nitride plate and the aluminum nitride shaft is tested, and a helium leak detector is used to check for helium leakage in the aluminum nitride ceramic heater. Specifically, the bonding strength between the aluminum nitride plate and the aluminum nitride shaft is between 150 and 300 MPa, and the helium leakage is within 1 × 10⁻⁶ MPa. -9 Pa•m 3 Below / s, it can meet the requirements of aluminum nitride ceramic heater products.

[0036] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A metal gradient bonding slurry for aluminum nitride ceramic heaters, characterized in that, The slurry comprises a first slurry and a second slurry. The first slurry comprises 50-70 wt% aluminum nitride ceramic powder, 5-20 wt% alumina ceramic powder, 0-5 wt% magnesium fluoride powder, and 1-10 wt% yttrium oxide powder. The second slurry comprises 50-70 wt% aluminum nitride ceramic powder, 5-20 wt% alumina ceramic powder, 5-15 wt% magnesium fluoride powder, and 1-10 wt% yttrium oxide powder.

2. The metal gradient bonding slurry for an aluminum nitride ceramic heater according to claim 1, characterized in that, The preparation methods of the first slurry and the second slurry include: firstly, weighing aluminum nitride ceramic powder, alumina ceramic powder, magnesium fluoride powder, and yttrium oxide powder according to their respective mass percentages, mixing the powders after weighing, then adding solvent, binder, and dispersant to each powder and mixing them together, and then grinding and dispersing them separately through a pulverizer and a three-roll mill to prepare the first slurry and the second slurry.

3. The metal-free gradient bonding slurry and method for an aluminum nitride ceramic heater according to claim 1, characterized in that, The solvent is terpineol, the binder is at least one of polyvinyl alcohol, polyvinyl butyral and polymethyl methacrylate, and the dispersant is an acrylic polymer.

4. The metal-free gradient bonding slurry and method for an aluminum nitride ceramic heater according to claim 1, characterized in that, The aluminum nitride ceramic powder is first ball-milled before mixing, with a ball-to-material ratio of 5 to 8:1, and then oxidized in an atmospheric furnace to increase its oxygen content to 2 to 4%.

5. A bonding method using a metal-free gradient bonding slurry for an aluminum nitride ceramic heater as described in any one of claims 1-4, characterized in that, The bonding method includes: First, clean the aluminum nitride plate and aluminum nitride shaft of the aluminum nitride ceramic heater that need to be joined, using alcohol as the cleaning agent, and perform ultrasonic cleaning for 30-60 minutes. The first paste is printed at the location where the aluminum nitride shaft is connected, and the first paste is printed first at the location where the aluminum nitride plate is connected, followed by the second paste, and then dried. Finally, the aluminum nitride shaft and the aluminum nitride plate are placed in the furnace for bonding, and a pressure of 3-4 MPa is applied. Nitrogen gas is introduced at 900°C for atmosphere protection. The bonding temperature is 1400-1600°C, and the bonding time is 2-2.5 hours. After bonding is completed, the sample is cooled and removed, the bonding strength is tested, and a helium leak detector is used to check for helium leaks in the product.

6. The bonding method according to claim 5, characterized in that, The total printing thickness of the first and second pastes printed on the aluminum nitride plate is 30-80 μm; the printing thickness of the first paste printed on the aluminum nitride shaft is 30-40 μm.

7. The bonding method according to claim 5, characterized in that, The bonding strength between the aluminum nitride plate and the aluminum nitride shaft is between 150 and 300 MPa, and the helium leakage is less than 1 × 10⁻⁶. -9 Pa•m 3 / s or less.