A stepped sintering method for a dual-hole ceramic pedestal

Abstract

This invention discloses a stepped sintering method for a dual-hole ceramic base, involving radial glass-sealed NTC thermistor encapsulation. It aims to solve the problems of existing alumina ceramic bases, which suffer from insufficient tensile strength, low density, and mismatch in thermal expansion coefficients with the Dummes wires and encapsulation glass, making it difficult to meet wide-temperature-range reliability requirements. The method sequentially includes hot pressing, pretreatment of the blank, stepped heating and debinding, gradient high-temperature sintering, and gradient cooling processes. This invention achieves ceramic densification and thermal expansion coefficient control through gradient temperature regulation combined with the synergistic effect of the atmosphere, eliminating thermal stress cracks in the glass during cooling. The resulting ceramic base matches the thermal expansion coefficients of the Dummes wires and encapsulation glass, significantly enhancing the stability and long-term reliability of the radial glass-sealed NTC thermistor over a wide temperature range of -55 to 350 °C.

Description

Technical Field

[0001] This invention belongs to the field of ceramic sintering technology and relates to the preparation process of ceramic bases for NTC thermistors, specifically to a stepped sintering method for a dual-hole ceramic base. Background Technology

[0002] Radial ceramic-base glass-sealed NTC thermistors, as a high-reliability temperature sensing element, are characterized by a dual-hole ceramic base installed at the root of the encapsulation glass of the traditional radial glass-sealed NTC thermistor. This improves the product's reliability and lifespan. The ceramic base serves multiple functions, including electrical insulation, mechanical support, and hermetic matching with the Dummes leads and glass encapsulation.

[0003] In existing technologies, ceramic bases are mostly made of alumina. However, in practical applications, it is often difficult to simultaneously achieve the desired tensile strength, density, and compatibility with the thermal expansion coefficients of the Dummex leads and encapsulation glass over a wide temperature range of -55 to 350 °C. Insufficient tensile strength or density can easily lead to a decrease in product consistency and reliability; mismatch in thermal expansion coefficients can generate significant thermal stress at the encapsulation interface, causing microcracks to form in the glass at the junction of the ceramic base and the glass, affecting the long-term reliability of the product.

[0004] Therefore, in order to ensure the performance of radial ceramic base glass-sealed NTC thermistors, it is necessary to improve the slurry of the ceramic base and to develop a ceramic base sintering method adapted to radial ceramic base glass-sealed NTC thermistors based on the slurry. Summary of the Invention

[0005] To address the aforementioned problems, the main objective of this invention is to design a stepped sintering method for a dual-hole ceramic base. This method combines steps such as stepped heating debonding, stepped high-temperature sintering, and gradient cooling to solve the problems of insufficient tensile strength, low density, and mismatch in thermal expansion coefficients with Dummes wires and encapsulation glass in existing alumina ceramic bases, which makes it difficult to meet the reliability requirements of a wide temperature range of -55 to 350 ℃.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A stepped sintering method for a double-hole ceramic base, comprising the following steps: S1. Hot pressing: The uniformly mixed slurry is placed in a mold and hot-pressed under set conditions to form a double-hole ceramic base blank that matches the NTC thermistor leads; S2. Green body pretreatment: Place the ceramic base green body in a drying oven, dry it at a constant temperature, and then let it cool naturally to room temperature; S3. Stepwise heating debonding: The pretreated green body is placed in a sintering furnace and debonded at multiple heat preservation nodes at room temperature to 900~1100 ℃ for a total time of 3~7 days to remove the binder in the green body and cool to room temperature with the furnace. S4. Gradient high-temperature sintering: After degumming, the green body is placed in a high-temperature sintering furnace. The sintering furnace is kept sealed and the temperature is raised to 1000-1200 ℃ at a rate of 30-50 ℃ / h, held at the temperature for 1.5-3 h, and then raised to 1500-1650 ℃ at a rate of 50-80 ℃ / h, held at the temperature for 3-6 h to complete the densification sintering of the ceramic base. S5. Gradient cooling: After sintering, the sintering furnace stops heating and cools down to 1000℃ at a rate of 30~80℃ / h, and then naturally cools to room temperature to obtain the finished product.

[0007] As a further description of the present invention, in step S1, the slurry is hot-pressed at 50~80 ℃ and 5~10 MPa.

[0008] As a further description of the present invention, in step S2, the drying oven is used for constant temperature drying at 80±10 ℃ for 2~4 h.

[0009] As a further description of the present invention, in step S3, the insulation nodes are set to 200 ℃, 400 ℃, 600 ℃, 800 ℃, and 900~1100 ℃. Each insulation node is heated at a rate of 30~50 ℃ / h, and each insulation node is kept at a constant temperature for 8~24 h before being heated to the next insulation node.

[0010] As a further description of the present invention, in step S4, the sintering furnace is kept sealed and argon gas is introduced for sintering. The argon gas flow rate is 0.5~1.0 L / min, and the time for replacing the air in the furnace is ≥30 min, so that the oxygen content in the furnace is ≤0.01%, avoiding the reaction of functional additives such as B2O3 with oxygen at high temperature and resulting in volatilization.

[0011] As a further description of the present invention, in step S5, the sintering furnace stops heating and keeps argon gas continuously supplied, and the argon gas is turned off when the temperature drops to ≤200 ℃; in this step S5, 1000 ℃ is used as the switching critical point of the cooling rate to release the temperature stress on the inner wall of the ceramic base and avoid the generation of microcracks.

[0012] A dual-hole ceramic base, prepared by the above sintering method, is used for radial glass-sealed NTC thermistors, including a ceramic body and two through holes formed on the ceramic body. The ceramic body includes a top surface and a bottom surface, which are parallel to each other. The through holes are vertically opened from the top surface to the bottom surface, and the two through holes are arranged in parallel. The through holes are fitted outside the Dummel wire leads of the radial glass-sealed NTC thermistor. The top surface or bottom surface of the ceramic body is attached to the root of the encapsulation glass of the radial glass-sealed NTC thermistor.

[0013] Compared with the prior art, the technical advantages of the present invention are as follows: This invention provides a stepped sintering method for a dual-hole ceramic base. The method includes hot pressing, pretreatment of the green body, stepped heating and debinding, gradient high-temperature sintering, and gradient cooling. It is suitable for preparing dual-hole ceramic bases for radially glass-sealed NTC thermistors under a wide temperature range of -55 to 350 °C, significantly enhancing the product's stability and long-term reliability. Specifically, through gradient temperature control and an isothermal stage protected by an argon atmosphere, oxygen is effectively isolated, suppressing the volatilization of functional additives such as B2O3 during the ceramic base sintering process. This achieves sufficient densification of the ceramic material and control of its thermal expansion coefficient, eliminating or suppressing thermal stress cracks during the cooling process, increasing the yield of the prepared ceramic base to over 98%. Simultaneously, the resulting ceramic base matches the thermal expansion coefficient of the Dummex leads and encapsulation glass, significantly enhancing the stability and long-term reliability of the radially glass-sealed NTC thermistor within a wide temperature range of -55 to 350 °C. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the preparation method of the present invention; Figure 2 A view of a ceramic base manufactured using the method of the present invention.

[0015] In the diagram, 1. Ceramic body, 2. Through hole. Detailed Implementation

[0016] The present invention will now be described in detail with reference to the accompanying drawings: Example 1

[0017] A stepped sintering method for a double-hole ceramic base is disclosed. This method is suitable for preparing ceramic bases with an outer diameter of 1.45 mm, a height of 1.2 mm, a double-hole diameter of 0.45 mm, and a center-to-center distance of 0.18 mm. During the preparation of the ceramic base, a ceramic slurry containing a binder is typically used; specifically, a binder such as paraffin wax is added to the raw materials, and the mixture is ball-milled to prepare a ceramic slurry with uniform particle size.

[0018] like Figure 1 As shown in this embodiment, the preparation method includes the following steps: S1. Hot pressing: The uniformly mixed slurry is placed in a mold and hot-pressed at 50~80 ℃ and 5~10 MPa to form a double-hole ceramic base blank that matches the radial glass-sealed NTC thermistor leads; the blank dimensions are: cylindrical outer diameter 1.45 mm, height 1.2 mm, double hole diameter 0.45 mm, center distance 0.18 mm.

[0019] S2. Pretreatment of the green body: Place the ceramic base green body in a drying oven and dry it at a constant temperature of 80±10 ℃ for 2~4 h. After drying, let it cool naturally to room temperature to remove moisture and residual organic solvents from the inside of the green body.

[0020] S3. Stepped Heating Debonding: The pretreated green body is placed in a tubular sintering furnace and subjected to multi-temperature-holding step debonding at temperatures ranging from room temperature to 900~1100 ℃ for a total duration of 3~7 days. This process removes the paraffin wax and other binders from the green body, which is then cooled to room temperature with the furnace. Specifically, in this embodiment, the temperature-holding nodes are set at 200 ℃, 400 ℃, 600 ℃, 800 ℃, and 900~1100 ℃. Each temperature-holding node is heated at a rate of 30~50 ℃ / h, and each temperature-holding node is held at a constant temperature for 8~24 h before moving to the next temperature-holding node. This ensures that the paraffin wax and other binders are completely removed, and that the green body is free from blistering, cracking, and deformation, maintaining its complete shape and structure.

[0021] S4. Gradient High-Temperature Sintering: After degumming, the green body is cooled to room temperature in the furnace. The sintering furnace is kept sealed, and argon gas (purity ≥99.999%) is introduced into the furnace to replace the air inside. Specifically, the argon flow rate is 0.5~1.0 L / min, and the time for replacing the air in the furnace is ≥30 min, ensuring that the oxygen content in the furnace is ≤0.01% to prevent functional additives such as B2O3 from reacting with oxygen at high temperatures and volatilizing. The sintering furnace is heated to 1000~1200 ℃ at a rate of 30~50 ℃ / h, held at that temperature for 1.5~3 h, and then heated to 1500~1650 ℃ at a rate of 50~80 ℃ / h, held at that temperature for 3~6 h to complete the densification sintering of the ceramic base.

[0022] S5. Gradient cooling: After sintering, the sintering furnace stops heating and keeps argon gas continuously supplied; the sintering furnace is cooled to 1000 ℃ at a rate of 30~80℃ / h, and the argon gas is turned off when the temperature drops to ≤200 ℃, and then naturally cooled to room temperature to obtain the finished product.

[0023] In step S5 above, 1000 ℃ is used as the critical point for switching the cooling rate to release the temperature stress on the inner wall of the ceramic base and avoid the generation of microcracks.

[0024] To better illustrate Embodiment 1 above, it will be described in detail using three sub-implementations, as follows: Example 1-1: A stepped sintering method for a double-hole ceramic base, the method comprising: Hot pressing at 1.50 ℃ and 5 MPa; Dry at 2.80 ℃ for 3 hours, then allow to cool naturally to room temperature; S3. The sintering furnace is heated to 1000 ℃ at a rate of 50 ℃ / h, and the temperature is maintained at each insulation node for 20 h for 5 days to remove the glue. S4. The sintering furnace is purged with 99.999% high-purity argon gas at a flow rate of 0.8 L / min for 30 min; the temperature is increased to 1000 ℃ at 50 ℃ / h and held for 3 h; the temperature is increased to 1500 ℃ at 50 ℃ / h and held for 3 h. S5. Stop heating the sintering furnace while keeping argon gas flowing in, and cool down to 1000 ℃ at a rate of 30 ℃ / h; when the temperature drops to 200 ℃, turn off the argon gas and let the furnace cool down to room temperature.

[0025] Performance testing: B2O3 retention rate 96.2%, ceramic density 96.5%, coefficient of thermal expansion 8.8×10⁻⁶. -6 / ℃, no microcracks on the inner wall, yield rate 98.5%.

[0026] Examples 1-2: A stepped sintering method for a double-hole ceramic base, the method comprising: Hot pressing at 1.80 ℃ and 10 MPa; Dry at 2.90 ℃ for 1 h, then allow to cool naturally to room temperature; S3. The sintering furnace is heated to 900 ℃ at a rate of 30 ℃ / h, and the heat is maintained for 5 days for debonding. Each heat-insulating node is kept at a constant temperature for 18 hours. S4. The sintering furnace is purged with 99.999% high-purity argon gas at a flow rate of 0.5 L / min for 30 min; the temperature is increased to 1100 ℃ at 40 ℃ / h and held for 2 h; the temperature is increased to 1600 ℃ at 60 ℃ / h and held for 4 h. S5. Stop heating the sintering furnace while keeping argon gas flowing through, and cool down to 1000 ℃ at a rate of 50 ℃ / h; when the temperature drops to 200 ℃, turn off the argon gas and let the furnace cool down to room temperature.

[0027] Performance testing: B2O3 retention rate 95.5%, ceramic density 95.8%, coefficient of thermal expansion 9.8×10⁻⁶ -6 / ℃, no microcracks on the inner wall, yield rate 98.2%.

[0028] Examples 1-3: A stepped sintering method for a double-hole ceramic base, the method comprising: Hot pressing at 1.60 ℃ and 8 MPa; Dry at 2.70 ℃ for 3 hours, then allow to cool naturally to room temperature; S3. The sintering furnace is heated to 1000 ℃ at a rate of 40 ℃ / h, and the temperature is maintained at a constant temperature for 3 days with stepped heat preservation and debonding. Each heat preservation node is kept at a constant temperature for 9.5 h. S4. The sintering furnace is purged with 99.999% high-purity argon gas at a flow rate of 1.0 L / min for 30 min; the temperature is increased to 1000 ℃ at 30 ℃ / h and held for 1.5 h; the temperature is increased to 1650 ℃ at 80 ℃ / h and held for 5 h. S5. Stop heating the sintering furnace while keeping argon gas flowing in, and cool down to 1000 ℃ at a rate of 80 ℃ / h; when the temperature drops to 200 ℃, turn off the argon gas and let the furnace cool down to room temperature.

[0029] Performance testing: B2O3 retention rate 95.8%, ceramic density 95.2%, coefficient of thermal expansion 8.2×10⁻⁶. -6 / ℃, no microcracks on the inner wall, yield rate 98.1%.

[0030] As can be seen from Examples 1-1, 1-2, and 1-3 above, the ceramic base obtained by the above preparation method can increase the yield from 85% to over 98.0%. Furthermore, the densification sintering of the ceramic base effectively improves the overall bonding strength, and it exhibits no cracking or deformation after 100 temperature cycles in a wide temperature range of -55 to 350 ℃. The coefficient of thermal expansion of the obtained ceramic base is controlled within (8~10) × 10⁻⁶. -6 / ℃, the difference in thermal expansion coefficient between the glass encapsulation and the Dummes wire leads is ≤1.5×10 -6 / ℃, excellent matching. Example 2

[0031] A dual-hole ceramic base, prepared using the above-described method, is used for radially glass-sealed NTC thermistors, such as... Figure 2 As shown, it includes a ceramic body 1 and two through holes 2 formed on the ceramic body 1; The ceramic body 1 includes a top surface and a bottom surface, which are parallel to each other. The through hole 2 is vertically opened from the top surface to the bottom surface, and the two through holes 2 are arranged in parallel. The through hole 2 is fitted outside the Dumme wire lead of the radial glass-sealed NTC thermistor. The top surface or bottom surface of the ceramic body 1 is attached to the root of the encapsulation glass of the radial glass-sealed NTC thermistor.

[0032] This invention discloses, through embodiments, the ceramic base of the present invention and a method for preparing the ceramic base. This method has the following advantages compared to the prior art: 1. This invention employs a combination of processes such as stepped heating debonding, gradient high-temperature sintering, and gradient cooling to ensure that the ceramic base is fully densified without the need for additional equipment, thereby improving the yield of ceramic bases, reducing production costs, and making it suitable for large-scale mass production. 2. In the gradient high-temperature sintering and gradient cooling process, this invention adds an argon atmosphere protection isothermal stage, effectively isolating oxygen, reducing the loss of volatile functional additives such as B2O3, ensuring the effectiveness of the ceramic slurry formulation, and maintaining a thermal expansion coefficient fluctuation ≤0.2×10⁻⁶. -6 / ℃, to avoid mismatch in thermal expansion coefficients between the ceramic base and the Dumex leads and encapsulation glass; 3. This invention adopts a gradient cooling method that combines high-temperature rapid cooling with natural cooling. Rapid cooling above 1000 ℃ improves production efficiency, while natural cooling below 1000 ℃ releases the temperature stress on the inner hole wall, eliminates micro-cracks in the inner hole wall, and improves the crack-free rate of the ceramic base.

[0033] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the direction and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A stepped sintering method for a double-hole ceramic base, characterized in that, The method includes the following steps: S1. Hot pressing: The uniformly mixed slurry is placed in a mold and hot-pressed under set conditions to form a double-hole ceramic base blank that matches the NTC thermistor leads; S2. Green body pretreatment: Place the ceramic base green body in a drying oven, dry it at a constant temperature, and then let it cool naturally to room temperature; S3. Stepwise heating debonding: The pretreated green body is placed in a sintering furnace and debonded at multiple heat preservation nodes at room temperature to 900~1100 ℃ for a total time of 3~7 days to remove the binder in the green body and cool to room temperature with the furnace. S4. Gradient high-temperature sintering: After degumming, the green body is placed in a high-temperature sintering furnace. The sintering furnace is kept sealed and the temperature is increased to 1000-1200 ℃ at a rate of 30-50℃ / h, and held at the temperature for 1.5-3 h. Then, the temperature is increased to 1500-1650℃ at a rate of 50-80 ℃ / h, and held at the temperature for 3-6 h to complete the densification sintering of the ceramic base. S5. Gradient cooling: After sintering, the sintering furnace stops heating and cools down to 1000 ℃ at a rate of 30~80 ℃ / h, and then naturally cools to room temperature to obtain the finished product.

2. The stepped sintering method for a double-hole ceramic base according to claim 1, characterized in that: In step S1, the slurry is hot-pressed at 50~80 ℃ and 5~10 MPa.

3. The stepped sintering method for a double-hole ceramic base according to claim 1, characterized in that: In step S2, the product is dried at a constant temperature of 80±10 ℃ in a drying oven for 2~4 h.

4. The stepped sintering method for a double-hole ceramic base according to claim 1, characterized in that: In step S3, the insulation nodes are set to 200 ℃, 400 ℃, 600 ℃, 800 ℃, and 900~1100 ℃. Each insulation node is heated at a rate of 30~50℃ / h, and each insulation node is kept at a constant temperature for 8~24 h before being heated to the next insulation node.

5. The stepped sintering method for a double-hole ceramic base according to claim 1, characterized in that: In step S4, the sintering furnace is kept sealed and argon gas is introduced for sintering. The argon gas flow rate is 0.5~1.0 L / min, and the time for replacing the air in the furnace is ≥30 min, so that the oxygen content in the sintering furnace is ≤0.01%.

6. The stepped sintering method for a double-hole ceramic base according to claim 1, characterized in that: In step S5, the sintering furnace stops heating and argon gas is continuously supplied. When the temperature drops to ≤200 ℃, the argon gas is turned off.

7. A double-hole ceramic base prepared by any one of claims 1-6, characterized in that: The ceramic base is used for radial glass-sealed NTC thermistors and includes a ceramic body and two through holes formed on the ceramic body; The ceramic body includes a top surface and a bottom surface, which are parallel to each other. The through holes are vertically opened from the top surface to the bottom surface, and the two through holes are arranged in parallel. The through holes are fitted outside the Dummel wire leads of the radial glass-sealed NTC thermistor. The top surface or bottom surface of the ceramic body is attached to the root of the encapsulation glass of the radial glass-sealed NTC thermistor.

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