A pressure-resistant packaging method suitable for deep-sea pH sensor

Abstract

A pressure-resistant encapsulation method for deep-sea pH sensors, belonging to the field of marine sensors, is disclosed. It employs a three-stage progressive pressure-resistant sealing system along the axial path of coastal water intrusion. The first stage involves a pressure-bearing seal for the probe, a second stage involves pressure-resistant buffering of the housing, and a third stage involves emergency water ingress protection, working in series to achieve triple protection: layered pressure relief, leakage warning, and self-repairing upon water ingress. The probe module uses an alumina ceramic-Kovar alloy-titanium alloy composite pressure-bearing electrode base with a double-layer potting structure, compatible with miniature ISFET chips. The main housing uses a three-section titanium alloy shell, with an elastic buffer sealing layer at the housing joint. The water ingress protection module integrates a polymer humidity-sensitive resistor and a sodium polyacrylate-nitrile rubber blend expansion component, enabling active warning and self-repair upon water contact. This invention can stably withstand 50MPa hydrostatic pressure, meeting the requirements for long-term in-situ monitoring in the 4000m deep sea, and is suitable for scenarios such as ocean acidification, deep-sea mining, and seabed carbon sequestration.

Description

Technical Field

[0001] This invention relates to the field of marine sensor technology, and in particular to a pressure-resistant packaging method for deep-sea pH sensors, suitable for long-term in-situ pH monitoring in extreme environments at depths of up to 4000 m. Background Technology

[0002] Deep-sea pH is a core environmental parameter for monitoring ocean acidification, studying the deep-sea carbon cycle, detecting hydrothermal activity on the seabed, and assessing deep-sea ecosystems. Its in-situ, long-term, and high-precision detection is of great significance for marine scientific research and marine engineering applications. However, the deep-sea environment has extreme conditions such as ultra-high hydrostatic pressure, highly corrosive seawater, low temperature, complex mechanical shocks, and biofouling, which place stringent requirements on the packaging structure of pH sensors.

[0003] Currently, ISFET (Ion Sensing Field-Effect Transistor) based pH sensors have become the mainstream technology for in-situ pH detection in deep seas due to their advantages such as fast response, high accuracy, and ease of miniaturization. However, existing packaging methods for ISFET-type deep-sea pH sensors still have the following prominent drawbacks:

[0004] 1. Insufficient reliability of pressure-resistant sealing. Traditional encapsulation often relies on a single O-ring seal or a single potting compound seal, which cannot effectively cope with the ultra-high hydrostatic pressure of the 4000m deep sea. During long-term high-pressure service, the single sealing structure is prone to stress relaxation, interface debonding, or permanent deformation of the elastomer, leading to seal failure, shell leakage, and direct damage to the core sensing element and circuit system after seawater intrusion. Currently reported ISFET-type pH sensors have reliable operating depths limited to shallower than 2000m, making it difficult to cover large areas of deep water such as the South my country Sea and the Northwest Pacific Ocean.

[0005] 2. Poor packaging compatibility and limited sensing accuracy. Current mainstream ISFET packaging architectures are designed for large-size dedicated chips with a width greater than 3.2 mm, neglecting adaptation designs for micro-sized chips with a width of 1.2 mm or less. This leads to multiple engineering and performance issues: First, micro-sized chips lack standardized matching sealing components, making it difficult to stably control assembly alignment accuracy; second, the manufacturing cost of large-size custom chips is approximately 20 times that of micro-sized chips, significantly increasing the overall material cost of the sensor. Regarding detection performance, traditional O-ring mechanical sealing solutions have inherent defects: the probe structure must include a seawater flow hole for hydrogen ion detection. To meet the requirements for sealing and preventing leakage, the inner diameter of the flow hole is significantly compressed, preventing efficient and sufficient contact between the seawater medium and the ISFET sensitive membrane. This directly causes sensor response lag and distortion of water pH measurement values, failing to meet the technical specifications for long-term, high-precision in-situ marine monitoring. In terms of electrical reliability, existing ISFET chip pads are mostly located on the upper surface of the chip. Traditional packaging and assembly processes easily cause mechanical damage to the solder points, significantly weakening the reliability of electrical connections during long-term underwater operation.

[0006] 3. Weak shock resistance and buffering capacity. Deep-sea sensors are subjected to severe impact acceleration during deployment and retrieval, as well as frequent external forces such as ocean currents and impacts from suspended objects. Existing packaging lacks effective buffering and isolation design, which can easily lead to loosening of internal circuitry, cracking of the potting layer, or breakage of leads, reducing service life.

[0007] 4. Lack of proactive water ingress warning and self-repair capabilities. Current packaging uses a passive protection mode; once even a small leak occurs, seawater will slowly corrode internal components, and the sensors cannot detect or alarm autonomously. By the time the abnormal signal is detected on the ground, the equipment is already completely damaged. Especially in deep-sea operations, where sensor retrieval cycles are long, complete failure will result in significant data gaps and economic losses.

[0008] In summary, developing a multi-level hermetically sealed packaging method that combines ultra-high pressure resistance, microchip adaptation, high sensing accuracy, shock resistance and buffering, and active warning and self-healing functions is of urgent engineering need and important application value. Summary of the Invention

[0009] The purpose of this invention is to provide a pressure-resistant packaging method suitable for deep-sea pH sensors, aiming to solve key technical problems such as insufficient pressure resistance, poor microchip packaging adaptability, low sensing accuracy, weak shock resistance, and lack of active water ingress protection in existing ISFET-type deep-sea pH sensors, so as to achieve long-term, stable, and accurate in-situ pH monitoring in a 4000 m deep-sea environment.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A pressure-resistant packaging structure suitable for deep-sea pH sensors, wherein the pressure-resistant packaging structure is provided with a three-stage progressive pressure-resistant sealing system along the axial path of coastal water intrusion. The three-stage progressive pressure-resistant sealing system consists of a probe sealing module (stage 1), a main body sealing module (stage 2), and a water ingress protection module (stage 3) arranged in series along the axial path.

[0012] The probe sealing module is equipped with a composite pressure-bearing electrode base, and the interior of the composite pressure-bearing electrode base forms a sealed micro-lead cavity. The sealed micro-lead cavity is provided with a double-layer layered potting structure to achieve pressure-bearing and sealing of the probe end.

[0013] The main body sealing module includes a titanium alloy shell, and the tank docking position of the titanium alloy shell is provided with an elastic buffer sealing layer to achieve buffer pressure resistance at the tank end.

[0014] The water ingress protection module integrates a humidity detection and early warning unit and a water-swellable sealing component; the humidity detection and early warning unit is used to detect water ingress into the cabin and output a leakage early warning signal, and the water-swellable sealing component is filled into each sealing gap for in-situ self-repair sealing when leakage occurs.

[0015] The probe sealing module, main cabin sealing module, and water ingress protection module work together in series to achieve triple protection of layered pressure relief, leakage early warning, and water ingress self-repair.

[0016] The composite pressure-bearing electrode base is an alumina ceramic-Kovar alloy-titanium alloy composite structure; the surface of the alumina ceramic is provided with a metallized sealing layer and a buffer coating layer, the alumina ceramic and Kovar alloy are thermally expanded and sealed, and the Kovar alloy and titanium alloy are low-temperature brazed to achieve metallurgical bonding; the alumina ceramic has a chip support groove for placing ISFET chips.

[0017] The width of the chip support groove is no greater than 1.2 mm; the ISFET chip is bonded to the alumina ceramic via gold wire bonding to form an electrical path; the ISFET chip, the alumina ceramic, and all gold wire bonding areas are covered with an epoxy resin protective layer, with only the hydrogen ion sensitive membrane exposed to the seawater environment; the thickness of the epoxy resin protective layer is 100~1000 μm.

[0018] The bottom layer of the double-layer potting structure is polyurethane potting compound, and the top layer is epoxy resin potting compound; the thickness of the polyurethane potting compound is 0.2~1.0 cm, and the thickness of the epoxy resin potting compound is 0.5~2.0 cm.

[0019] The probe sealing module also includes a probe base, a nitrile O-ring, and a copper integrated protective cover; the composite pressure-bearing electrode base and the probe base are axially sealed and locked together by fasteners and the nitrile O-ring; the copper integrated protective cover covers the outside of the composite pressure-bearing electrode base to prevent biofouling.

[0020] The titanium alloy shell is divided into a probe mounting end, a circuit compartment, and a communication mounting end along the axial direction; the main compartment sealing module also includes a PEEK engineering plastic support block and a watertight penetration component; the internal circuit system is fixed in the circuit compartment by the PEEK engineering plastic support block, and the watertight penetration component is used to achieve watertight electrical communication between the inside and outside of the compartment.

[0021] The elastic buffer sealing layer is a nitrile rubber buffer layer, which is laid at the docking position of each compartment; the thickness of the nitrile rubber buffer layer is 3~5 mm, and the Shore hardness is 60~70 HA, which is used to absorb hydrostatic pressure and mechanical impact stress.

[0022] The humidity detection and early warning unit is a polymer humidity-sensitive resistor, which is integrated inside the circuit compartment; the detection range of the polymer humidity-sensitive resistor is 0~100% RH, and the response time is no more than 5 s.

[0023] The water-swellable sealing component is made of sodium polyacrylate and nitrile rubber blend; the water-swellable sealing component adopts an expansion ring and / or expansion strip structure, with an expansion ratio of not less than 3 times when exposed to water, and completes gap sealing within 10 seconds when exposed to water.

[0024] A pressure-resistant packaging method for deep-sea pH sensors, employing the aforementioned pressure-resistant packaging structure, includes the following process steps:

[0025] S1. Integrated fabrication of composite pressure-bearing electrode base: A molybdenum-manganese metallization layer is prepared on the surface of alumina ceramic and a nickel buffer layer is electroplated. After matching and sealing the alumina ceramic with Kovar alloy, the Kovar alloy and titanium alloy are connected by low-temperature vacuum brazing. A chip support groove with a width ≤1.2 mm is processed on the alumina ceramic.

[0026] S2, ISFET chip insulation packaging and fixation: The ISFET chip is assembled into the chip support groove and electrical conduction is completed by gold wire bonding; an epoxy resin protective layer with a thickness of 100~1000 μm is deposited on the chip, ceramic substrate and all bonding line areas, leaving only the hydrogen ion sensitive film exposed.

[0027] S3. Probe sealing module assembly and sealing: The composite pressure-bearing electrode base and the probe base are axially locked and sealed with titanium alloy fasteners and nitrile O-rings; polyurethane potting compound is injected into the bottom layer of the micro lead cavity and cured at a constant temperature, then the upper layer of epoxy resin potting compound is injected and cured a second time, and finally a copper integrated protective cover is assembled on the outside of the electrode.

[0028] S4. Main hull pre-assembly and buffer sealing assembly: The circuit system is fixed to the circuit compartment of the titanium alloy shell through PEEK engineering plastic support blocks; a 3-5 mm thick nitrile rubber buffer layer with a Shore hardness of 60-70 HA is laid at all docking positions of the hull, and watertight penetrating components are assembled to complete the watertight electrical path construction of the hull.

[0029] S5. Water Ingress Protection System Integration Assembly: The assembled probe sealing module is sealed and connected to the titanium alloy shell; sodium polyacrylate-nitrile rubber blend expansion components are embedded in the sealing gaps of the cabin and around the watertight perforated parts; a polymer humidity-sensitive resistor humidity detection and early warning unit is installed inside the circuit cabin to complete the overall assembly of the axial three-level progressive pressure-resistant sealing system.

[0030] S6. Gradient pressure stabilization and leak detection process: After the whole machine is assembled, apply 0~50 MPa hydrostatic pressure in stages to stabilize the pressure and detect leaks, and verify the three-level seal's synergistic pressure bearing, leakage early warning, and self-repairing sealing performance.

[0031] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0032] 1. Synergistic Effect of Ultra-High Pressure Resistance and Staged Pressure Relief. This invention innovatively establishes a three-stage progressive sealing system: "Level 1 Probe Sealing - Level 2 Chamber Buffering - Level 3 Emergency Protection," which distributes the hydrostatic pressure step by step along the axial path to avoid stress concentration. The Level 1 seal, through a composite metal base and double-layer potting, initially bears pressure and attenuates pressure waves; the Level 2 seal utilizes the rigidity of the titanium alloy shell and the flexible deformation of the nitrile rubber buffer layer to further absorb pressure; the Level 3 seal initiates self-repair in extreme conditions. Tests have verified that this structure can stably withstand 50 MPa hydrostatic pressure (corresponding to a depth of 4000 m with a 1.25 times safety margin), maintaining pressure for 3 hours without pressure drop, leakage, or shell deformation, far exceeding the pressure resistance of existing single-seal structures.

[0033] 2. Achieving both microchip compatibility and high sensing accuracy. A support groove with a width ≤1.2 mm is created on the alumina ceramic substrate to precisely fit the micro ISFET chip, and reliable electrical connection is achieved through gold wire bonding, overcoming the challenge of finding suitable sealing components for microchips. Simultaneously, the limitation of traditional O-ring mechanical seals on seawater flow channels is eliminated. A thin layer of epoxy resin (only 100~1000 μm) covers the chip and bonding area, allowing only the sensing membrane to be directly exposed to seawater. This ensures sufficient and rapid exchange between seawater and the sensing membrane, eliminating response lag and measurement deviation caused by flow channels.

[0034] 3. Excellent impact resistance and vibration damping performance. The combination of PEEK engineering plastic support blocks and nitrile rubber buffer layers (thickness 3~5mm, hardness 60~70 HA) forms a flexible isolation zone between the circuit system and the rigid titanium alloy shell, effectively absorbing the impact of deployment and recovery, and greatly improving the mechanical reliability of the sensor under complex sea conditions.

[0035] 4. Active Leakage Warning and Instant Self-Repair. An integrated polymer humidity sensor (response time ≤ 5 s) monitors cabin humidity in real time. In the event of even a minor leak, the humidity sensor's resistance changes abruptly, triggering an early warning signal and giving operators time to respond. Simultaneously, a water-swellable sealing component (a blend of sodium polyacrylate and nitrile rubber, with an expansion ratio ≥ 3 times and sealing within 10 seconds) rapidly fills gaps in the early stages of leakage, achieving a closed-loop "detection-early warning-repair" system. This prevents irreversible damage to the circuitry from seawater, significantly extends sensor lifespan, and reduces maintenance costs. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the overall packaging structure used in the packaging method of the present invention.

[0037] Figure 2 This is a cross-sectional structural diagram of the probe sealing module of the present invention.

[0038] Figure 3 This is a cross-sectional schematic diagram of the composite pressure-bearing electrode base and the chip packaging module adapted to the chip of this invention.

[0039] Figure 4 This is a schematic diagram of the sensor element packaging module of the present invention.

[0040] Figure 5 This is the pressure resistance curve of the deep-sea pH sensor of the present invention.

[0041] Figure 6 This is a deep-sea pH profile from 0 to 4000 m obtained by the deep-sea pH sensor of this invention.

[0042] The component numbers and corresponding names in the diagram are as follows:

[0043] 1-Probe module, 11-Integral copper protective cover, 12-Electrode probe end, 121-Solid-state reference electrode, 1211-Reference electrode, 1212-Reference electrode lead, 122-Composite pressure-bearing electrode base, 1221-Titanium alloy support wall, 1222-Through hole, 1223-Nitrile O-ring, 1224-Kovar alloy, 123-Probe base, 124-ISFET chip, 1241-Chip sensitive film layer, 1242-Gold wire lead, 1243-Chip source and drain, 1244-ISFET chip silicon substrate, 1245- Ceramic substrate, 1246-Electrical connection pad, 1247-Chip support groove, 1248-ISFET chip packaging module lead, 125-Epoxy resin potting compound, 126-Polyurethane potting compound, 127-Watertight penetration component; 2-Main body sealing module, 211-Nitrile O-ring, 212-Nitrile O-ring, 22-PEEK engineering plastic support block, 23-Titanium alloy shell, 24-Circuit system, 25-Communication installation terminal, 26-Watertight plug-in; 3-Water ingress protection module, 31-Humidity detection and early warning unit, 32-Water-swelling sealing component. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Example 1: Construction of a pressure-resistant packaging structure for a deep-sea pH sensor

[0046] This embodiment details the specific construction process of the pressure-resistant packaging structure of the deep-sea pH sensor described in this invention. (Refer to...) Figure 1 The encapsulation structure, along the axial path of coastal water intrusion from the probe end to the communication end, sequentially includes a probe module 1 (primary seal), a main hull sealing module 2 (secondary seal), and a water ingress protection module 3 (tertiary seal). The construction process of each module is described in detail below.

[0047] I. Construction of the probe module

[0048] like Figures 2-4 As shown, the probe module 1 consists of a one-piece copper protective cover 11 and an electrode probe end 12. The electrode probe end 12 mainly includes a composite pressure-bearing electrode base 122, a probe base 123, a nitrile O-ring 1223, and an ISFET chip 124 and a solid reference electrode 121 encapsulated in the composite pressure-bearing electrode base 122.

[0049] (I) Integrated fabrication of composite pressure-bearing electrode base

[0050] The composite pressure-bearing electrode base is a three-layer composite structure of alumina ceramic, Kovar alloy, and titanium alloy, and its preparation process is as follows: Alumina ceramic is used as the substrate (corresponding to...). Figure 3 The ceramic substrate 1245 is treated with molybdenum-manganese metallization and then electroplated with a nickel buffer layer. Alumina ceramic and Kovar alloy 1224 are thermally matched and sealed under nitrogen protection, and then Kovar alloy 1224 is connected to the titanium alloy support wall 1221 by low-temperature vacuum brazing to form a composite pressure-bearing electrode base. The titanium alloy is TC4 titanium alloy.

[0051] A chip support groove 1247 with a width of 1.2 mm is fabricated on a ceramic substrate 1245. An ISFET chip 124 (1.0 mm wide and 2.0 mm long, with the sensitive film layer 1241 on the upper surface and the silicon substrate 1244 on the bottom) is placed into the chip support groove 1247. Using 25 μm diameter gold wires 1242, the source and drain electrodes 1243 of the chip are connected to the electrical connection pads 1246 on the ceramic substrate 1245 through wire bonding, forming an electrical path.

[0052] (ii) ISFET chip insulating package

[0053] Reference Figure 4 Using a precision dispensing process, an epoxy resin protective layer is coated on the surface of the ISFET chip 124, the gold wire bonding area, and the gap between the chip and the ceramic substrate. The thickness is controlled to 300 μm, leaving only the ISFET chip's sensitive film layer 1241 uncovered, allowing it to be directly exposed for contact with seawater. This epoxy resin protective layer serves both as insulation and seawater barrier functions.

[0054] (III) Probe end assembly and double-layer potting

[0055] The composite pressure-bearing electrode base 122 and the probe base 123 are fastened together by titanium alloy fasteners (passing through the through hole 1222), and a nitrile O-ring 1223 with a Shore hardness of 70 HA is installed between them to achieve axial sealing. After assembly, the composite pressure-bearing electrode base 122 and the probe base 123 together form a sealed micro lead cavity.

[0056] A polyurethane potting compound 126 with a thickness of 0.8 cm is injected into the bottom of the sealed micro lead cavity. After constant temperature curing, a flexible stress buffer bottom layer is formed. Then, an epoxy resin potting compound 125 with a thickness of 1.2 cm is injected on the polyurethane layer. After a second curing, a rigid sealing top layer is formed, thus obtaining a double-layer potting structure. This structure utilizes the low modulus characteristics of the bottom polyurethane to absorb the thermal mismatch stress between the chip and the metal substrate, and utilizes the high strength characteristics of the top epoxy resin to resist the compression deformation of the lead cavity by external water pressure.

[0057] Finally, a one-piece molded copper protective cover 11 with a wall thickness of 0.5 mm is fitted onto the outside of the electrode and fixed by interference fit. The one-piece molded copper protective cover utilizes its excellent ductility and corrosion resistance, and has both impact protection and anti-biofouling functions.

[0058] The probe sealing module also includes a solid-state reference electrode 121, which comprises a reference electrode 1211 and a reference electrode lead 1212, working in conjunction with the ISFET chip to achieve pH potential detection. The reference electrode lead 1212 and the ISFET chip packaging module lead 1248 are both connected to the watertight penetration chamber 127 at the probe end, through which the signal lead is sealed and passed through to the main chamber.

[0059] II. Construction of the Main Cabin Sealing Module

[0060] Reference Figure 1 The main body of the main compartment sealing module 2 is a titanium alloy shell 23, arranged in three sections: a probe mounting end, a circuit compartment, and a communication mounting end, arranged axially. The titanium alloy shell is precision machined and then anodized internally to improve corrosion resistance; the titanium alloy is TC4 titanium alloy. The circuit compartment has an outer diameter of 60 mm, a length of 140 mm, and a wall thickness of 6 mm.

[0061] The circuit system 24 (including signal conditioning circuitry, data acquisition module, and storage unit) is fixed to the center of the circuit compartment by a PEEK engineering plastic support block 22. The shape of the PEEK support block fits the inner wall of the compartment, creating a flexible isolation between the circuit system and the rigid titanium alloy shell, thus avoiding direct contact with the shell.

[0062] At the mating surfaces of the probe mounting end and the circuit compartment, and at the mating surfaces of the circuit compartment and the communication mounting end, 3mm thick nitrile rubber buffer layers with a Shore hardness of 70 HA are laid and tightened with titanium alloy flanges. The nitrile rubber buffer layers have a dual function: firstly, under static high pressure, they absorb part of the water pressure energy through their own compression deformation, reducing the peak stress transmitted to the docking surfaces of the compartments; secondly, under dynamic impacts (such as impacts during deployment and recovery), they absorb impact energy through a viscoelastic dissipation mechanism.

[0063] Nitrile O-rings 211 and 212 (Shore hardness 70 HA) are installed at the probe mounting end and communication end respectively as auxiliary radial seals. Watertight perforation components (rated pressure 50 MPa, leakage rate ≤1×10⁻⁶). -9 Pa·m 3 The probe mounting end is pressed into the through-hole between the probe mounting end and the circuit compartment to complete the sealed passage of the electrical leads through the compartment. The communication mounting end 25 and its watertight plug 26 are used to realize data communication and power supply connection between the inside and outside of the compartment.

[0064] III. Construction of the Water Ingress Protection Module

[0065] Reference Figure 1 The water ingress protection module 3 has a polymer humidity-sensitive resistor installed on the edge of the circuit board inside the circuit compartment as a humidity detection and early warning unit 31. Its detection range is 0~100% RH, and its response time is 5 s. The signal line is connected to the early warning input port of the circuit system 24. The polymer humidity-sensitive resistor utilizes the characteristic that the dielectric constant of the polymer moisture-sensitive material changes with humidity to convert changes in humidity inside the compartment into changes in resistance. When a sudden increase in humidity is detected, a leakage early warning signal is output.

[0066] A water-swellable sealing component 32 was prepared by blending sodium polyacrylate and nitrile rubber at a mass ratio of 30:70. The component was pre-molded into an expansion ring (with an outer diameter matching the sealing groove) and an expansion strip (2 mm × 3 mm cross-section). Sodium polyacrylate is a highly absorbent resin; its hydrophilic groups bind water molecules through hydrogen bonding upon contact with water, resulting in a three-dimensional network expansion with a volume expansion ratio exceeding 3 times. Nitrile rubber serves as the matrix material, providing elastic support and structural strength. The blend combines water-absorbing and swelling properties with mechanical strength.

[0067] During the final assembly of the machine, the expansion ring is embedded into the bottom of each sealing groove of the titanium alloy shell, and the expansion strip is filled around the watertight penetration chamber and in the gap between the probe module and the main body.

[0068] IV. Overall Assembly of the Three-Stage Progressive Pressure-Resistant Sealing System

[0069] Assemble the following components in axial order from the probe end to the communication end: probe sealing module, main cabin sealing module (including circuit system), and communication end cover. All connections are secured with threads and a predetermined torque is applied.

[0070] After assembly, the water pressure intrusion path from the probe end to the communication end undergoes three levels of sealing protection:

[0071] First stage: Electrode base pressure bearing + nitrile O-ring axial sealing + double-layer layered potting structure;

[0072] Second stage: rigid load-bearing titanium alloy shell + radial sealing with nitrile O-rings + energy absorption with nitrile rubber buffer layer;

[0073] Level 3: Active early warning from polymer humidity-sensitive resistor + self-healing water-swelling sealing component.

[0074] The three components are arranged in series along the axial path to form a complete progressive pressure-resistant sealing system.

[0075] Example 2: Pressure and Shock Resistance Test of Deep-Sea pH Sensor

[0076] The deep-sea pH sensor assembled using the method described in Example 1 was placed in a deep-sea high-pressure simulation test chamber and an electromagnetic vibration table for pressure resistance testing and mechanical shock testing, respectively.

[0077] (a) Pressure resistance test

[0078] The target hydrostatic pressure was set at 50 MPa (designed with a safety factor of 1.25, corresponding to a deep-sea environment of 4000 m). Gradual pressurization was used to reach the set value, followed by pressure holding for 3 hours. Pressure data inside the chamber was recorded in real time during the test, and pressure resistance curves were plotted (see...). Figure 5 ).

[0079] During the pressure holding period, the pressure monitoring curve remained stable without fluctuations or pressure drop (see...). Figure 5 The results indicate that the sensor packaging structure has no leakage or gas leaks. After the pressure holding period, the pressure was uniformly released to atmospheric pressure, and the sensor was removed for visual and structural inspection: the titanium alloy shell showed no plastic deformation or cracks; there were no wetting marks on the sealing surfaces, and the nitrile O-rings showed no extrusion deformation; after disassembling the sensor, the main body, circuit system, and probe module remained dry, with no signs of water ingress. The test results prove that the packaging structure of this invention can stably withstand 50 MPa of extreme hydrostatic pressure, meeting the pressure-resistant sealing requirements of 4000 m deep-sea environments.

[0080] (ii) Mechanical impact performance test

[0081] In accordance with the impact test standards for marine monitoring equipment, a peak acceleration of 100 m / s² was applied to the entire sensor. 2 A half-sine wave impact lasting 11 ms was applied, with the impact direction covering the ±X / ±Y / ±Z axes three times each.

[0082] After the impact, the encapsulation structure was found to be intact and all threaded fasteners were found to be free of looseness; the nitrile O-ring seals were found to be free of displacement; the double-layer potting structure was found to be free of cracks and debonding; the ISFET chip gold wire bonding nodes were found to be intact and the electrical continuity test was found to be normal; the test results proved that the encapsulation structure of the present invention has excellent impact resistance and shock absorption performance and can withstand the severe mechanical impact during deep-sea deployment and recovery.

[0083] In summary, the packaging structure of this invention can stably withstand 50 MPa extreme hydrostatic pressure, resist the impact of deep-sea deployment and operation machinery, and fully meet the requirements for reliable service in the 4000 m deep sea.

[0084] Example 3: In-situ pH profiling test of a deep-sea pH sensor at a depth of 4000 m.

[0085] The deep-sea pH sensor, which has been verified by pressure and shock resistance in Example 2, was mounted on a deep-sea temperature, salinity and depth profiler (CTD) and an in-situ marine test was conducted in the 4000 m deep-sea area of ​​the Northwest Pacific Ocean.

[0086] The sensor was lowered at a constant speed from the sea surface to a depth of 4000 m along with the profiler. After reaching the seabed at 4000 m, it was allowed to stand still for 10 minutes to record stable in-situ pH data. The profiler was then retrieved at a constant speed. pH values ​​were collected throughout the process, ranging from 0 to 4000 m in depth, and auxiliary parameters such as depth, temperature, and salinity were recorded simultaneously at a sampling frequency of 1 Hz.

[0087] Test results are as follows Figure 6 As shown. The sensor operates stably across the entire water depth range of 0~4000 m, with no signal interruption or abnormal drift. The pressure-resistant packaging structure remains reliably sealed under high pressure throughout the entire process.

[0088] The pH profile data is continuous and smooth: the pH of the surface seawater is about 8.05~8.15, and the pH decreases slowly with increasing depth. A pH transition occurs in the water layer of 800~1200 m. The pH of the deep seawater at 3000~4000 m is stable in the range of 7.75~7.85, which is consistent with the trend of historical observation data in this sea area. The noise level of the profile curve is low, which meets the requirements of high-precision in-situ pH monitoring in the deep sea.

[0089] After recovery, the sensor was inspected. The surface of the one-piece copper protective cover was free of biofouling, and the sensitive membrane area of ​​the probe was clean and free of biofouling, verifying the effectiveness of the anti-fouling function. Disassembly of the main chamber revealed it to be completely dry inside. The water-expansion sealing component did not activate (no warning was triggered), indicating that the primary and secondary seals performed fully in this test, and the tertiary seal was in standby mode. This embodiment fully demonstrates that the encapsulation method of the present invention can ensure high-precision and high-stability long-term in-situ pH monitoring of the pH sensor at a depth of 4000 m, making it suitable for long-term ocean acidification monitoring and deep-sea geochemical research.

[0090] In summary, this invention achieves multiple significant technological advancements compared to traditional single-seal packaging methods through a three-level progressive pressure-dividing packaging architecture, a composite metal-ceramic pressure-bearing packaging structure, a flexible buffer and shock-absorbing packaging, and an integrated packaging combination for early warning and self-repair. The specific comparison is shown in Table 1.

[0091] Table 1. Performance Comparison of Three-Stage Progressive Seal and Traditional Seal Technologies

[0092]

[0093] The above description represents a typical embodiment of the present invention, but the present invention should not be limited to the content disclosed in this embodiment. Therefore, any equivalent or modified versions made without departing from the spirit of the present invention fall within the scope of protection of the present invention.

Claims

1. A pressure-resistant packaging structure suitable for deep-sea pH sensors, characterized in that: The pressure-resistant encapsulation structure is equipped with a three-stage progressive pressure-resistant sealing system along the axial path of coastal water intrusion. The three-stage progressive pressure-resistant sealing system consists of a probe sealing module, a main body sealing module, and a water ingress protection module arranged in series along the axial path. The probe sealing module is equipped with a composite pressure-bearing electrode base, and the interior of the composite pressure-bearing electrode base forms a sealed micro-lead cavity. The sealed micro-lead cavity is provided with a double-layer layered potting structure to achieve pressure-bearing and sealing of the probe end. The main body sealing module includes a titanium alloy shell, and the tank docking position of the titanium alloy shell is provided with an elastic buffer sealing layer to achieve buffer pressure resistance at the tank end. The water ingress protection module integrates a humidity detection and early warning unit and a water-swellable sealing component; the humidity detection and early warning unit is used to detect water ingress into the cabin and output a leakage early warning signal, and the water-swellable sealing component is filled into each sealing gap for in-situ self-repair sealing when leakage occurs. The probe sealing module, main cabin sealing module, and water ingress protection module work together in series to achieve triple protection of layered pressure relief, leakage early warning, and water ingress self-repair.

2. The pressure-resistant packaging structure for a deep-sea pH sensor as described in claim 1, characterized in that: The composite pressure-bearing electrode base is an alumina ceramic-Kovar alloy-titanium alloy composite structure; the surface of the alumina ceramic is provided with a metallized sealing layer and a buffer coating layer, the alumina ceramic and Kovar alloy are thermally expanded and sealed, and the Kovar alloy and titanium alloy are low-temperature brazed to achieve metallurgical bonding; the alumina ceramic has a chip support groove for placing ISFET chips.

3. The pressure-resistant packaging structure for a deep-sea pH sensor as described in claim 2, characterized in that: The width of the chip support groove is no greater than 1.2 mm; the ISFET chip is bonded to the alumina ceramic via gold wire bonding to form an electrical path; the ISFET chip, the alumina ceramic, and all gold wire bonding areas are covered with an epoxy resin protective layer, with only the hydrogen ion sensitive membrane exposed to the seawater environment; the thickness of the epoxy resin protective layer is 100~1000 μm.

4. The pressure-resistant packaging structure for a deep-sea pH sensor as described in claim 1, characterized in that: The bottom layer of the double-layer potting structure is polyurethane potting compound, and the top layer is epoxy resin potting compound; the thickness of the polyurethane potting compound is 0.2~1.0 cm, and the thickness of the epoxy resin potting compound is 0.5~2.0 cm.

5. The pressure-resistant packaging structure for a deep-sea pH sensor as described in claim 1, characterized in that: The probe sealing module also includes a probe base, a nitrile O-ring, and a copper integrated protective cover; the composite pressure-bearing electrode base and the probe base are axially sealed and locked together by fasteners and the nitrile O-ring; the copper integrated protective cover covers the outside of the composite pressure-bearing electrode base to prevent biofouling.

6. The pressure-resistant packaging structure for a deep-sea pH sensor as described in claim 1, characterized in that: The titanium alloy shell is divided into a probe mounting end, a circuit compartment, and a communication mounting end along the axial direction; the main compartment sealing module also includes a PEEK engineering plastic support block and a watertight penetration component; the internal circuit system is fixed in the circuit compartment by the PEEK engineering plastic support block, and the watertight penetration component is used to achieve watertight electrical communication between the inside and outside of the compartment.

7. The pressure-resistant packaging structure for a deep-sea pH sensor as described in claim 1, characterized in that: The elastic buffer sealing layer is a nitrile rubber buffer layer, which is laid at the docking position of each compartment; the nitrile rubber buffer layer has a thickness of 3~5mm and a Shore hardness of 60~70 HA, and is used to absorb hydrostatic pressure and mechanical impact stress.

8. The pressure-resistant packaging structure for a deep-sea pH sensor as described in claim 1, characterized in that: The humidity detection and early warning unit is a polymer humidity-sensitive resistor, which is integrated inside the circuit compartment; the detection range of the polymer humidity-sensitive resistor is 0~100% RH, and the response time is no more than 5 s.

9. The pressure-resistant packaging structure for a deep-sea pH sensor as described in claim 1, characterized in that: The water-swellable sealing component is made of sodium polyacrylate and nitrile rubber blend; the water-swellable sealing component adopts an expansion ring and / or expansion strip structure, with an expansion ratio of not less than 3 times when exposed to water, and completes gap sealing within 10 seconds when exposed to water.

10. A pressure-resistant packaging method for a deep-sea pH sensor, characterized in that, The pressure-resistant packaging structure according to any one of claims 1 to 9 includes the following process steps: S1. Integrated fabrication of composite pressure-bearing electrode base: A molybdenum-manganese metallization layer is prepared on the surface of alumina ceramic and a nickel buffer layer is electroplated. After matching and sealing the alumina ceramic with Kovar alloy, the Kovar alloy and titanium alloy are connected by low-temperature vacuum brazing. A chip support groove with a width ≤1.2 mm is processed on the alumina ceramic. S2, ISFET chip insulation packaging and fixation: The ISFET chip is assembled into the chip support groove and electrical conduction is completed by gold wire bonding; an epoxy resin protective layer with a thickness of 100~1000 μm is deposited on the chip, ceramic substrate and all bonding line areas, leaving only the hydrogen ion sensitive film exposed. S3. Probe sealing module assembly and sealing: The composite pressure-bearing electrode base and the probe base are axially locked and sealed with titanium alloy fasteners and nitrile O-rings; polyurethane potting compound is injected into the bottom layer of the micro lead cavity and cured at a constant temperature, then the upper layer of epoxy resin potting compound is injected and cured a second time, and finally a copper integrated protective cover is assembled on the outside of the electrode. S4. Main hull pre-assembly and buffer sealing assembly: The circuit system is fixed to the circuit compartment of the titanium alloy shell through PEEK engineering plastic support blocks; a 3-5 mm thick nitrile rubber buffer layer with a Shore hardness of 60-70 HA is laid at all docking positions of the hull, and watertight penetrating components are assembled to complete the watertight electrical path construction of the hull. S5. Water Ingress Protection System Integration Assembly: The assembled probe sealing module is sealed and connected to the titanium alloy shell; sodium polyacrylate-nitrile rubber blend expansion components are embedded in the sealing gaps of the cabin and around the watertight perforated parts; a polymer humidity-sensitive resistor humidity detection and early warning unit is installed inside the circuit cabin to complete the overall assembly of the axial three-level progressive pressure-resistant sealing system. S6. Gradient pressure stabilization and leak detection process: After the whole machine is assembled, apply 0~50 MPa hydrostatic pressure in stages to stabilize the pressure and detect leaks, and verify the three-level seal's synergistic pressure bearing, leakage early warning, and self-repairing sealing performance.

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