High-temperature-resistant airtight packaging process for piezoresistive pressure sensor

Abstract

The present application relates to the technical field of high-temperature pressure sensor packaging, and in particular to a high-temperature-resistant airtight packaging process for a piezoresistive pressure sensor, which comprises the following steps: firstly, molybdenum-manganese activated metallization is performed on 95 alumina ceramic beads, and 4J29 Kovar pins are plated with nickel; twice vacuum brazing is performed using Ag72Cu28 silver-copper solder; and finally, an integrated airtight insulation package is formed by matching a Kovar assembly ring with a shell. According to the scheme, thermal matching is achieved by using the same Kovar alloy structure, and the interface thermal stress caused by the thermal expansion mismatch of heterogeneous metals is eliminated; the alumina ceramic is used to replace the traditional glass sintered body, and the problems of high-temperature insulation failure and interface cracking and air leakage are solved. Tests show that the pin insulation resistance of the product is more than 10 8 Ω at 400 DEG C, the leakage rate is less than 1.97 x 10⁻ 6 Pa m3 / s after 24 hours of high-temperature and high-pressure pressure maintaining, and the performance is much better than that of the traditional scheme. The structure is integrated with multiple functions, is compact and strong, and has good vibration resistance; the raw materials and equipment are common in the industry, the process is easy to operate, and is suitable for application scenarios such as aerospace and ultra-deep well drilling.

Description

Technical Field

[0001] This invention relates to the field of high-temperature pressure sensor packaging technology, and in particular to a high-temperature resistant and airtight packaging process for a piezoresistive pressure sensor. Background Technology

[0002] High-temperature pressure sensors are currently core sensing devices used in extreme operating conditions such as aero-engines, ultra-deep well drilling, heavy-duty gas turbines, and nuclear power equipment. They are key basic units for in-situ monitoring of high-temperature environmental parameters in high-end equipment. As high-end equipment develops towards higher parameters, higher reliability, and longer service life, the combined extreme operating conditions of temperatures above 400°C, pressures above 20MPa, and strong vibrations place extremely stringent requirements on the high-temperature stability, airtight protection capabilities, and long-term service reliability of sensor packaging. Packaging technology has become the core bottleneck restricting the transition of piezoresistive high-temperature pressure sensors from laboratory research and development to engineering mass application.

[0003] High-temperature resistance, airtightness, and insulation performance are two core indicators of sensor packaging reliability under high-temperature environments. Packaging failure or performance degradation often directly manifests as airtightness failure and decreased insulation performance under high temperature and pressure. Existing high-temperature pressure sensor packaging processes still have significant shortcomings: Firstly, most current solutions employ low-temperature glass powder sintering to achieve insulation sealing. In high-temperature environments above 300℃, the intrinsic carrier concentration of the glass sintered body increases exponentially with temperature, leading to a sharp increase in bulk conductivity and a dramatic drop in insulation resistance from the 10¹²Ω range at room temperature to 10Ω. 6 Below Ω, long-term stable electrical isolation between pins cannot be maintained, resulting in an inherent high-temperature insulation failure defect. Secondly, existing packages often use a combination of multiple dissimilar materials such as stainless steel, Kovar alloy, and glass, leading to a significant mismatch in the coefficient of thermal expansion (CTE) between these materials (e.g., 4J29 Kovar alloy has a CTE of approximately 5.0 × 10⁻⁶). -6 / ℃, while the CTE of low-temperature glass is approximately 9×10 -6 / ℃). Under cyclic conditions at 400℃, accumulated thermal stress is generated at the interface, which can easily lead to the propagation of microcracks in the glass sintered body, debonding of the sintered interface, and failure of airtightness, resulting in leakage failure of the sensor in a high-pressure medium environment.

[0004] In summary, existing packaging processes cannot simultaneously guarantee long-term stable airtightness and insulation performance under high-temperature and high-pressure coupling environments of 400℃ / 20MPa. This is the fundamental problem restricting the engineering application of high-temperature pressure sensors. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention is proposed.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a high-temperature resistant and hermetic packaging process for a piezoresistive pressure sensor, comprising the following steps: Pretreatment was performed on 95% alumina ceramic beads, and a metallization layer was formed on their inner and outer walls by the activated molybdenum-manganese method. The 4J29 Kovar alloy pins are pretreated and a nickel plating layer is formed on their surface; The nickel-plated pin is inserted into the center hole of the metallized ceramic bead, and the first brazing is performed under vacuum brazing conditions using Ag72Cu28 silver-copper solder to form a ceramic bead-pin assembly. The 4J29 Kovar alloy component ring is coaxially placed on the stepped limiting platform inside the 4J29 Kovar alloy shell, and multiple ceramic bead-pin assemblies are placed on the limiting platforms that are evenly distributed around the component ring. Ag72Cu28 silver-copper solder is filled between the outer wall of the ceramic bead and the limiting stage of the component ring, and between the component ring and the outer shell. A second brazing is performed under vacuum brazing conditions to form an integrated hermetically sealed insulating package.

[0007] As a preferred embodiment of the high-temperature resistant and airtight packaging process for the piezoresistive pressure sensor of the present invention, the ceramic bead is a 95% alumina ceramic bead, and its pretreatment steps include ultrasonic cleaning with acetone for 10 min, ultrasonic cleaning with anhydrous ethanol for 10 min, rinsing with deionized water, and drying in a vacuum oven at 100°C for 1 h.

[0008] As a preferred embodiment of the high-temperature resistant and hermetic packaging process for the piezoresistive pressure sensor described in this invention, the activated molybdenum-manganese method includes screen printing a molybdenum-manganese metallizing paste on the inner and outer walls of a ceramic bead, followed by high-temperature sintering in a humid hydrogen atmosphere at 1300℃~1500℃ to form a Mo-Mn metallization layer with a thickness of 10μm~20μm.

[0009] As a preferred embodiment of the high-temperature resistant and hermetic packaging process for the piezoresistive pressure sensor described in this invention, the surface of the metallization layer of the ceramic bead is further deposited with a 2μm~5μm nickel plating layer by chemical nickel plating or electroplating.

[0010] As a preferred embodiment of the high-temperature resistant and hermetic packaging process for the piezoresistive pressure sensor described in this invention, the pretreatment steps of the 4J29 Kovar alloy pin include mechanical polishing to remove the surface oxide layer, ultrasonic cleaning with acetone, and electroplating a nickel layer with a thickness of 3μm~5μm.

[0011] As a preferred embodiment of the high-temperature resistant and hermetic packaging process for the piezoresistive pressure sensor described in this invention, the process conditions for the first brazing are: temperature 780℃~820℃, vacuum degree ≤10. -2 Pa, heat preservation time 10min~20min.

[0012] As a preferred embodiment of the high-temperature resistant and airtight packaging process for the piezoresistive pressure sensor of the present invention, the fitting gap between the component ring and the housing limiting stage is controlled within 0.02mm~0.05mm, and the fitting gap between the ceramic bead and the component ring limiting stage is controlled within 0.03mm~0.06mm.

[0013] As a preferred embodiment of the high-temperature resistant and hermetic packaging process for the piezoresistive pressure sensor described in this invention, the second brazing process conditions are: temperature 780℃~820℃, vacuum degree ≤10. -2 Pa, heat preservation time 15min~25min.

[0014] As a preferred embodiment of the high-temperature resistant and hermetic packaging process for the piezoresistive pressure sensor of the present invention, wherein the integrated hermetic insulating package has an insulation resistance between pins greater than 156MΩ at a high temperature of 400℃.

[0015] As a preferred embodiment of the high-temperature resistant, hermetic packaging process for the piezoresistive pressure sensor described in this invention, the integrated hermetic insulating package exhibits a leakage rate of less than 1.97 × 10⁻⁶ after being pressurized for 24 hours at 400°C and 20 MPa coupling. - 6 Pa·m³ / s.

[0016] The beneficial effects of this invention are as follows: This invention addresses the core packaging pain point of piezoresistive high-temperature pressure sensors under extreme conditions of 400℃ / 20MPa. By using an integrated thermal matching design of the same 4J29 Kovar alloy shell, component ring, and pin, it fundamentally eliminates the interfacial thermal stress caused by thermal expansion mismatch between dissimilar metals. It uses 95% alumina ceramic beads instead of traditional glass sintered bodies as the insulating medium, and achieves high-airtightness metallurgical sealing between ceramic and metal by metallization using activated molybdenum-manganese method and brazing with Ag72Cu28 silver-copper solder. This effectively solves key problems such as glass sintering insulation failure and interfacial cracking and leakage at 400℃, and significantly improves the reliability of the sensor under extreme operating conditions.

[0017] The packaged sensor prepared by this invention, after undergoing a high-temperature insulation test at 400℃, exhibits a stable insulation resistance between the pins greater than 10. 8 Ω; After airtightness testing in a 400℃ / 20MPa coupled environment for 24 hours, the leakage rate was less than 1.97×10. -6 With a pressure of Pa·m³ / s, its high-temperature insulation and airtightness are far superior to traditional glass sintering packaging solutions, meeting the stringent requirements for long-term stability of high-temperature pressure sensors in aerospace, ultra-deep well drilling and other fields.

[0018] The packaging process of this invention is clear and controllable. The raw materials used, such as 4J29 Kovar alloy, 95% alumina ceramic, Ag72Cu28 silver-copper solder, Mo-Mn metallizing paste, and high-temperature inorganic adhesive, are all industry-standard. The equipment used for vacuum brazing and electroplating is conventional equipment in the semiconductor / sensor industry. No complex and precision special equipment is required. The operation is convenient, highly repeatable, and has a high product yield. It can be directly adapted to existing sensor production lines for large-scale production and has broad engineering application prospects in the field of high-temperature and high-pressure sensing.

[0019] This invention achieves multi-functional integration of mechanical support, electrical insulation lead-out, and high-voltage airtight protection for sensitive chips through an integrated structural design of a component ring central platform and circumferentially distributed ceramic beads. The package structure is compact, with a short axial dimension, high mechanical strength, and excellent vibration resistance, making it suitable for extreme working environments with limited space and strong vibration coupling. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the pressure sensor manufacturing process of the present invention; Figure 2 This is a schematic diagram of the high-temperature insulation and airtightness testing system of the present invention; Figure 3 This is a graph showing the change in insulation resistance of the sensor pin as a function of temperature. Figure 4 This is a high-temperature airtightness data diagram of the integrated sensor of the present invention. Detailed Implementation

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0024] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments. Example 1

[0025] This is the first embodiment of the present invention, which provides a high-temperature resistant and hermetic packaging process for a piezoresistive pressure sensor.

[0026] Its preparation method is as follows: Step 1: Ceramic bead pretreatment and metallization First, the 95% alumina ceramic beads were pretreated: acetone was used for ultrasonic cleaning for 10 minutes to remove organic contaminants, followed by anhydrous ethanol for ultrasonic cleaning for 10 minutes. After rinsing with deionized water, they were dried in a vacuum oven at 100℃ for 1 hour. The dried ceramic beads underwent ceramic metallization treatment using the activated molybdenum-manganese (Mo-Mn) method—molybdenum-manganese metallization paste was screen-printed onto the inner and outer walls of the ceramic beads, and then sintered at high temperature in a humid hydrogen atmosphere at 1300℃~1500℃ to form a Mo-Mn metallization layer with a thickness of approximately 10μm~20μm. Subsequently, a nickel plating layer of approximately 2μm~5μm was deposited on the surface of the metallization layer using electroless nickel plating or electroplating to improve surface solderability and high-temperature oxidation resistance.

[0027] Step 2: Pin Pre-processing Meanwhile, the 4J29 Kovar alloy pins are pretreated by mechanical polishing to remove the surface oxide layer, followed by ultrasonic cleaning with acetone and electroplating of a nickel layer with a thickness of approximately 3μm~5μm.

[0028] Step 3: First brazing Insert the nickel-plated pin into the center hole of the metallized ceramic bead, fill the space between the pin and the inner wall of the ceramic bead with Ag72Cu28 silver-copper solder foil or solder paste, and place it in a vacuum brazing furnace at 780℃~820℃ and a vacuum degree ≤10. -2 The brazing was completed by holding the material at Pa for 10-20 minutes. During the brazing process, the silver-copper solder reacted with the Mo-Mn metallization layer of the ceramic bead and the nickel plating layer of the insert, forming a strong metal-ceramic seal. This seal maintained excellent shear strength and airtightness even at 400℃.

[0029] Step 4: Pre-treatment of the outer casing and component rings After machining, the 4J29 Kovar alloy housing and component ring undergo burr removal and surface finishing to ensure that the clearance between the component ring and the housing retaining platform is controlled within 0.02mm~0.05mm, and the clearance between the ceramic bead and the component ring retaining platform is controlled within 0.03mm~0.06mm. Following pretreatment, the inner wall of the housing, the surface of the component ring, and the retaining platform are electroplated with nickel to a thickness of approximately 3μm~5μm to improve solder wettability and sealing reliability during subsequent brazing.

[0030] Step 5: Second brazing The nickel-plated component ring is coaxially placed on the stepped limiting platform inside the outer casing, ensuring complete contact between the bottom surface of the component ring and the limiting platform. The ceramic bead-pin assemblies prepared in step one are then placed on five evenly distributed limiting platforms around the circumference of the component ring, with Ag72Cu28 silver-copper solder filling the gap between the outer wall of the ceramic beads and the limiting platforms. The assembled structure is then placed in a vacuum brazing furnace at 780℃~820℃ and a vacuum degree ≤10. -2 Under Pa conditions, the secondary brazing is completed after holding at a temperature of 15-25 minutes. After the secondary brazing, a high-strength metallurgical seal is formed between the outer wall of the ceramic bead and the component ring, and between the component ring and the outer shell, forming a front-end hermetically sealed insulated package.

[0031] The above preparation process is as follows: Figure 1 As shown.

[0032] Test and verification: The sensor probe was placed in a high-temperature oven, and the insulation resistance between the pins at the sensor's tail end was continuously monitored using an insulation resistance tester. The temperature was maintained at 400℃, and the changes in insulation resistance between the pins were recorded in real time to verify the high-temperature insulation performance. The airtightness testing platform employed a high-pressure gas loading and high-temperature coupling method. After the sensor and gas pipeline were sealed and assembled, part of the gas pipeline and the sensor probe were placed in a 400℃ high-temperature furnace for constant temperature stabilization. High-pressure gas exceeding 20MPa was introduced into the sensor and maintained at that pressure for 24 hours. The leakage amount and leakage rate of the pipeline and the encapsulation shell were monitored. The testing platform... Figure 2 As shown.

[0033] Insulation performance test results: Continuous testing at a high temperature of 400℃ showed that the insulation resistance between the pins remained greater than 156MΩ under this condition. Figure 3 As shown, it meets the requirements for high-temperature insulation performance.

[0034] Air tightness test results: After assembly, the airtightness of the entire machine was tested at 400℃. Figure 4As shown. The assembled sensor was installed at the outlet of the pressure pump, and pressurized to 20 MPa at 300℃, 400℃, and 500℃ respectively, and held at the pressure for 24 hours. The leakage rate at the three test temperatures was approximately 1.62 × 10⁻⁶. -6 Pa·m³ / s, 1.97×10 -6 Pa·m³ / s, 2.14×10 -6 Pa·m³ / s, the overall airtightness meets the requirements for sensor airtightness in the national metrological verification procedure "JJG860-2015 Static Pressure Sensor".

[0035] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high-temperature resistant, hermetic packaging process for a piezoresistive pressure sensor, characterized in that, Includes the following steps: Pretreatment was performed on 95% alumina ceramic beads, and a metallization layer was formed on their inner and outer walls by the activated molybdenum-manganese method. The 4J29 Kovar alloy pins are pretreated and a nickel plating layer is formed on their surface; The nickel-plated pin is inserted into the center hole of the metallized ceramic bead, and the first brazing is performed under vacuum brazing conditions using Ag72Cu28 silver-copper solder to form a ceramic bead-pin assembly. The 4J29 Kovar alloy component ring is coaxially placed on the stepped limiting platform inside the 4J29 Kovar alloy shell, and multiple ceramic bead-pin assemblies are placed on the limiting platforms that are evenly distributed around the component ring. Ag72Cu28 silver-copper solder is filled between the outer wall of the ceramic bead and the limiting stage of the component ring, and between the component ring and the outer shell. A second brazing is performed under vacuum brazing conditions to form an integrated hermetically sealed insulating package.

2. The high-temperature resistant, hermetic packaging process for the piezoresistive pressure sensor as described in claim 1, characterized in that: The ceramic beads are 95% alumina ceramic beads, and their pretreatment steps include ultrasonic cleaning with acetone for 10 min, ultrasonic cleaning with anhydrous ethanol for 10 min, rinsing with deionized water, and drying in a vacuum oven at 100℃ for 1 h.

3. The high-temperature resistant and hermetic packaging process for the piezoresistive pressure sensor as described in claim 2, characterized in that: The activated molybdenum-manganese method includes screen printing a molybdenum-manganese metallizing paste on the inner and outer walls of ceramic beads, followed by high-temperature sintering in a humid hydrogen atmosphere at 1300℃~1500℃ to form a Mo-Mn metallization layer with a thickness of 10μm~20μm.

4. The high-temperature resistant and hermetic packaging process for the piezoresistive pressure sensor as described in claim 3, characterized in that: The surface of the metallized layer of the ceramic bead is also deposited with a nickel plating layer of 2μm to 5μm through chemical nickel plating or electroplating.

5. The high-temperature resistant and hermetic packaging process for the piezoresistive pressure sensor as described in claim 4, characterized in that: The pretreatment steps of the 4J29 Kovar alloy pin include mechanical polishing to remove the surface oxide layer, ultrasonic cleaning with acetone, and electroplating a nickel layer with a thickness of 3μm~5μm.

6. The high-temperature resistant, hermetic packaging process for the piezoresistive pressure sensor as described in claim 5, characterized in that: The process conditions for the first brazing were a temperature of 780℃~820℃ and a vacuum degree of ≤10. -2 Pa, heat preservation time 10min~20min.

7. The high-temperature resistant and hermetic packaging process for the piezoresistive pressure sensor as described in claim 6, characterized in that: The clearance between the component ring and the outer shell limiting platform is controlled within 0.02mm to 0.05mm, and the clearance between the ceramic bead and the component ring limiting platform is controlled within 0.03mm to 0.06mm.

8. The high-temperature resistant and hermetic packaging process for the piezoresistive pressure sensor as described in claim 7, characterized in that: The process conditions for the second brazing are a temperature of 780℃~820℃ and a vacuum degree of ≤10. -2 Pa, heat preservation time 15min~25min.

9. The high-temperature resistant, hermetic packaging process for the piezoresistive pressure sensor as described in claim 8, characterized in that: The integrated hermetic insulating package exhibits an insulation resistance greater than 156 MΩ between pins at a high temperature of 400°C.

10. The high-temperature resistant, hermetic packaging process for the piezoresistive pressure sensor as described in claim 9, characterized in that: The integrated hermetic insulating package exhibits a leakage rate of less than 1.97 × 10⁻⁶ after being pressure-held at 400°C and 20 MPa for 24 hours. -6 Pa·m³ / s.

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