A Deep-Sea Flexible Temperature Sensor Based on Modified Packaging and Its Packaging Method

Abstract

This invention discloses a deep-sea flexible temperature sensor based on modified encapsulation and its encapsulation method, belonging to the field of marine environmental monitoring technology. The sensor includes a flexible circuit board, a first encapsulation layer covering the component surface, a chemical bonding interface formed between the two, and a hydrophobic and antifouling layer disposed on the outer surface of the first encapsulation layer; the hydrophobic and antifouling layer comprises a micro / nano rough structure and a low surface energy modified layer. The encapsulation method involves first pre-curing the first encapsulation layer, then activating it with plasma and modifying it with a silane coupling agent before chemically bonding it to the flexible circuit board. Next, nanoparticles are sprayed onto the outer surface to construct the micro / nano rough structure, and finally, a low surface energy modified layer is grafted. This invention achieves deep-sea pressure-resistant encapsulation through interface chemical enhancement, flexible mechanical buffering through low-modulus PDMS, antifouling stability through a nano-hydrophobic coating, and high-precision deep-sea temperature measurement through a ratio-based temperature measurement structure.

Description

Technical Field

[0001] This invention relates to the field of marine environmental monitoring technology, and more specifically to a deep-sea flexible temperature sensor based on modified packaging and its packaging method. Background Technology

[0002] Ocean temperature is one of the most important parameters in deep-sea observation, playing a crucial role in understanding changes in the marine environment and ecological status. Currently used deep-sea temperature sensors are mostly rigid structures, which, although able to withstand extremely high pressures, are difficult to conform to curved surfaces and are not suitable for conformal monitoring or high-density deployment scenarios.

[0003] Current flexible temperature sensors are generally encapsulated using polydimethylsiloxane (PDMS), thermoplastic polyurethane (TPU), or other flexible polymer materials, bonded to flexible circuit boards via physical adhesion at the interface. While this type of encapsulation structure offers a degree of flexibility, it exhibits significant drawbacks in the high-pressure environment of the deep sea. First, under extremely high hydrostatic pressure in the deep sea, the encapsulation undergoes significant deformation, leading to uneven mechanical compression of internal components and a sharp increase in interfacial stress between circuit solder joints, component pads, and sensing units. Under continuous pressure, the polymer encapsulation material may develop microcracks, closure of voids, and structural deformation, even altering the overall morphology of the encapsulation layer, resulting in a substantial decrease in the long-term stability of the sensor.

[0004] Secondly, existing flexible packaging generally relies on the physical adhesion between PDMS and flexible printed circuit boards (FPCs), resulting in low interfacial bonding energy. Under the high pressure and continuous immersion conditions of the deep sea, delamination and debonding are highly likely to occur. Ions, dissolved oxygen, and microorganisms in seawater further weaken the adhesion upon entering the interface, leading to gradual peeling and ultimately water vapor penetration into the device. Once microcracks or interfacial peeling occur in the packaging, seawater under the high pressure of the deep sea can rapidly infiltrate the circuit layer, causing short circuits or corrosion of sensitive resistors, wire pads, and amplification circuits, rendering the sensor completely ineffective. Because existing packaging typically lacks chemical bonding structures, its interfacial durability is insufficient, and the adhesion continuously weakens during pressure cycling, making it difficult to meet the engineering requirements for long-term continuous deep-sea observation.

[0005] Furthermore, deep-sea environments are rife with contaminants such as suspended particulate matter, inorganic salt ions, and microbial colonies. Traditional flexible packaging surfaces are relatively smooth and lack resistance to contamination. A layer of contaminants gradually forms an uneven thickness, reducing the thermal conductivity of the outer surface and making temperature measurement lag more pronounced. Long-term deposits of contaminants can also lead to uneven stress distribution on the packaging surface, accelerating material aging and further reducing packaging reliability.

[0006] Overall, existing flexible temperature sensors face a series of problems when encapsulated in deep-sea environments, including severe compression deformation, insufficient interfacial adhesion, susceptibility to water seepage and failure, water absorption and swelling leading to aging, and weak antifouling capabilities. These challenges make it difficult to guarantee structural stability and measurement accuracy during long-term deployment. Therefore, achieving stable, reliable, and high-precision flexible temperature measurement in high-pressure seawater environments is a pressing issue that needs to be addressed in current deep-sea monitoring technologies. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a deep-sea flexible temperature sensor based on modified packaging and its packaging method. By constructing a stable chemical bonding interface between the flexible circuit board and the packaging material, and forming an anti-fouling and hydrophobic structure on the outer surface of the packaging layer, the flexible temperature sensor can maintain long-term stable structural integrity and temperature measurement accuracy in a high-pressure seawater environment.

[0008] The technical solution adopted by this invention to solve the technical problem is: a deep-sea flexible temperature sensor based on modified packaging, comprising: A flexible circuit board on which components are integrated; The first encapsulation layer covers the side of the flexible circuit board on which the components are disposed, and the first encapsulation layer is composed of a flexible polymer encapsulation material; A chemical bonding interface is formed between the flexible circuit board and the first encapsulation layer to achieve a chemical bonding connection between the flexible circuit board and the first encapsulation layer. A hydrophobic and antifouling layer is formed on the outer surface of the first encapsulation layer. The hydrophobic and antifouling layer includes, from the inside to the outside, a micro-nano rough structure and a low surface energy modified layer.

[0009] Furthermore, the chemical bonding interface between the flexible circuit board and the first encapsulation layer is formed through surface activation treatment and the introduction of a silane coupling agent.

[0010] Furthermore, the silane coupling agent is selected from one or more of the following: a compound system of 3-aminopropyltriethoxysilane and 3-glycidyl etheroxypropyltrimethoxysilane, mercaptosilane coupling agents, vinylsilane coupling agents, or silane coupling agents containing epoxy groups.

[0011] Furthermore, the sensor also includes a second encapsulation layer, which covers the other side of the flexible circuit board and is made of a flexible polymer encapsulation material.

[0012] Furthermore, the flexible polymer encapsulation material is polydimethylsiloxane, wherein the mass ratio of the prepolymer to the curing agent is 15:1.

[0013] Furthermore, the thickness of the first encapsulation layer is 1.5~2 mm, and the thickness of the second encapsulation layer is 0.5~1 mm.

[0014] Furthermore, the hydrophobic and antifouling layer includes a micro-nano rough structure formed by nanoparticles on the outer surface of the first encapsulation layer, and a low surface energy modified layer containing fluorine groups grafted onto the surface of the micro-nano rough structure by chemical bonding.

[0015] Furthermore, the flexible circuit board integrates a temperature-sensitive element and a reference resistor matched with the temperature-sensitive element to construct a ratio-based dual-channel temperature measurement structure; the temperature-sensitive element is a positive temperature coefficient thermistor, a negative temperature coefficient thermistor, or a thin-film platinum resistance thermometer.

[0016] This invention also discloses a packaging method for a deep-sea flexible temperature sensor based on modified packaging, comprising the following steps: Step a: Provide a flexible circuit board with integrated components; Step b: Cover the side of the flexible circuit board where the components are disposed with a first encapsulation layer made of flexible polymer encapsulation material; Specifically, the process involves first pre-curing to obtain a first encapsulation layer; then activating the surface of the flexible circuit board and the surface of the first encapsulation layer; finally introducing a silane coupling agent into the activated surface, allowing the two to form a covalent bond connection through a chemical reaction between the silane coupling agents. Step c: Construct a hydrophobic and antifouling layer on the outer surface of the first encapsulation layer; Specifically, a micro-nano rough structure is first formed on the outer surface of the first encapsulation layer. After the micro-nano rough structure is activated, a hydrophobic low surface energy modified layer containing fluorine groups is introduced, so that the surface of the micro-nano rough structure forms a low surface energy modified layer containing fluorine groups through chemical bonding.

[0017] Furthermore, the packaging method further includes covering the other side of the flexible circuit board with a second packaging layer; the edge of the second packaging layer is combined with the edge of the first packaging layer to form an overall seal.

[0018] The beneficial effects of this invention are that, compared with the prior art, the deep-sea flexible temperature sensor based on modified packaging and its packaging method provided by this invention have the following advantages: 1) This invention achieves a stable chemical bond structure between the encapsulation layer and the flexible circuit board through surface activation treatment and the introduction of silane coupling agent, effectively overcoming the defects of traditional physical attachment encapsulation such as peeling, cracking and water seepage under deep-sea pressure; it significantly improves the peel strength of the encapsulation layer, enabling the sensor to maintain structural integrity and reliability under deep-sea pressure cycling and long-term immersion conditions.

[0019] 2) By optimizing the curing ratio of the polymer encapsulation material (the mass ratio of prepolymer to curing agent is 15:1), the encapsulation layer can maintain low modulus and moderate flexibility in a high-pressure environment. This can effectively disperse the concentrated stress on the internal components caused by deep-sea pressure, reduce the impact of encapsulation compression deformation on the internal components, and ensure that the temperature output of the sensor does not drift significantly under pressure cycling conditions. This significantly improves the measurement stability and service life during long-term deployment in the deep sea.

[0020] 3) By forming a hydrophobic and antifouling composite coating on the outer surface of the encapsulation layer, the contact angle of the outer surface of the encapsulation layer is increased to more than 130°, which enables the sensor to effectively inhibit the accumulation of microorganisms and fouling layers under long-term seawater immersion conditions, avoid the thermal conductivity decay caused by the fouling layer, and improve the speed and long-term stability of the sensor's temperature response in the deep sea environment.

[0021] 4) This invention adopts a dual-channel temperature measurement structure with a ratio of the thermistor to the reference resistor, which can effectively suppress errors caused by pressure coupling, contact resistance changes and power supply fluctuations, and achieve anti-interference temperature reading under deep-sea pressure and power supply fluctuation conditions.

[0022] 5) The present invention has a flexible and thin overall structure, stable packaging, and strong water resistance. It can be conformally attached to the outer shell of the submersible, the seabed structure, or the cylindrical curved surface. It is suitable for various scenarios such as deep-sea temperature monitoring, seabed pipeline leak detection, and thermal field assessment of the submersible surface, and has good engineering application prospects. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall packaging structure of the present invention.

[0024] Among them, 1 - flexible circuit board; 2 - first encapsulation layer; 3 - second encapsulation layer; 4 - micro-nano rough structure; 5 - low surface energy modified layer; 6 - silane coupling agent.

[0025] Figure 2 This is a flowchart of the packaging process of the present invention.

[0026] Figure 3 This is a schematic diagram illustrating the chemical bonding principle of silane coupling agents.

[0027] Figure 4 The figure shows the test results of the bonding strength between PDMS and PI and components.

[0028] Figure 5 The image shows contact angle measurements after different processing methods were used to treat the sensor surface.

[0029] Figure 6 The results show the measurement of the contact angle of the sensor surface after immersion in seawater for different times.

[0030] Figure 7 This is a comparison chart of the sensor's measurement results in a real-world test at a depth of 4300 meters with those of the RBR commercial sensor.

[0031] Figure 8 The results are the high-pressure reliability test results of the sensor. (a) Stability of the sensor output ratio k under pressure of 0~45 MPa; (b) Change rate of the sensor measurement before and after pressure testing for unoptimized and optimized packaged sensors. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0033] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. All directional indications (such as upper, lower, outer, surface, one side, another side, etc.) in the embodiments of this application are only used to explain the relative spatial positions and movements of the components in a specific orientation (as shown in the drawings). If the specific orientation changes, the directional indications will change accordingly. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or devices.

[0034] Figure 1 This is a schematic diagram of the overall packaging structure of the present invention. (See diagram below.) Figure 1 As shown, the sensor includes: a flexible circuit board 1 on which components are integrated; a first encapsulation layer 2 covering the side of the flexible circuit board 1 on which the components are disposed, the first encapsulation layer 2 being composed of a flexible polymer encapsulation material; a chemical bonding interface formed between the flexible circuit board 1 and the first encapsulation layer 2, used to realize the chemical bonding connection between the flexible circuit board 1 and the first encapsulation layer 2; and a hydrophobic and antifouling layer formed on the outer surface of the first encapsulation layer 2, the hydrophobic and antifouling layer comprising, from the inside out, a micro-nano rough structure 4 and a low surface energy modified layer 5.

[0035] The formation of the chemical bonding interface between the flexible circuit board 1 and the first encapsulation layer 2 is achieved through surface activation treatment and the introduction of a silane coupling agent 6. Activation treatment is performed on the surfaces of both the flexible circuit board 1 and the first encapsulation layer 2 to expose reactive groups. Then, the activated surfaces are modified with the silane coupling agent 6 to form a stable covalent bond structure between the first encapsulation layer 2 and the flexible circuit board 1, thereby significantly improving the adhesion and peel resistance of the interface.

[0036] The surface activation treatment is plasma activation, including oxygen plasma, nitrogen plasma, argon plasma, etc. This embodiment uses oxygen plasma as an example to illustrate the activation principle. An oxygen plasma treatment device (e.g., 30 W power, 1 min processing time) is used to activate the two opposing surfaces of the flexible circuit board 1 and the first encapsulation layer 2. The high-energy plasma particles break the C / C and CH bonds on the material surface, generating a large number of hydroxyl (-OH) active sites, providing a reaction basis for the subsequent formation of chemical bonds with the silane coupling agent. In addition to plasma, other surface activation methods include ultraviolet ozone (UV-O3), wet chemical activation, etc. Any process that can generate sufficient active groups on the surface to achieve covalent bonding can be considered an equivalent technical solution of this invention.

[0037] The silane coupling agent is selected from one or more of the following: a compound system of 3-aminopropyltriethoxysilane and 3-glycidyl etheroxypropyltrimethoxysilane, a mercaptosilane coupling agent, a vinylsilane coupling agent, or a silane coupling agent containing an epoxy group. The silane system can also be replaced with interfacial molecules containing functional groups such as mercapto, epoxy, or allyl groups to achieve different interfacial bonding forms according to application requirements.

[0038] This embodiment uses a compound system of 3-aminopropyltriethoxysilane (APTES) and 3-glycidyl etheroxypropyltrimethoxysilane (GPTMS) as an example for illustration. Both APTES and GPTMS were prepared as 2 vol% solutions in anhydrous isopropanol. APTES underwent a hydrolysis reaction on the surface of the first encapsulation layer 2 (PDMS as an example of the encapsulation material) after surface activation treatment, grafting functional groups with amino (-NH2) groups. Similarly, GPTMS underwent hydrolysis on the surface of the flexible circuit board 1 (FPC), grafting functional groups with epoxy (-CH-O-CH-) groups. Ultimately, the amino and epoxy groups underwent a typical addition reaction to form a stable covalent bond structure, thereby constructing a tight and strong interfacial connection between the first encapsulation layer 2 and the flexible circuit board 1. The bonding mechanism is as follows: Figure 3As shown, this covalent bonding method significantly improves the adhesion strength between the two, effectively solving the problem of easy peeling of traditional physical bonding under high pressure, and laying a key structural foundation for the long-term stable operation of the sensor in the high-pressure environment of the deep sea.

[0039] The flexible polymer encapsulation material used is polydimethylsiloxane (PDMS). PDMS is a widely used silicon-based organic polymer elastomer. Its main advantages include: excellent chemical stability and weather resistance, suitable for underwater and corrosive environments; a wide range of tunable Young's modulus, allowing control of flexibility by changing the degree of crosslinking (curing ratio); excellent tensile properties; good biocompatibility; easy casting and curing; and relatively low cost. PDMS is typically supplied in a two-component form: a prepolymer and a curing agent, which are mixed and cured under specific temperature conditions.

[0040] To verify the bonding performance of PDMS to FPC interface after APTES and GPTMS bonding, a series of tests were conducted, wherein the substrate material of the flexible circuit board (FPC) was polyimide (PI). A universal testing machine was used to test the peel strength of PDMS-PI samples, and T-shaped peel tests were performed on samples with and without chemical bonding. The results showed that the peel strength of the PDMS-PI interface without chemical bonding was almost 0; however, after modification with APTES and GPTMS bonding, the peel strength between PDMS and PI, and between PDMS and components, was significantly improved. Specifically, the peel strength between PDMS and PI increased to 83.27 N / m, and the peel strength between PDMS and components increased to 102.57 N / m.

[0041] To further test the effect of PDMS curing ratio on interfacial adhesion performance, a T-type peel test was conducted to measure the change in peel strength of the PDMS–PI interface under different PDMS curing agent to prepolymer ratios (1:5, 1:10, 1:15). The results are as follows: Figure 4 As shown in a, when the ratio of curing agent to prepolymer in PDMS is adjusted to 1:15, the interfacial peel strength further increases from 63.15 N / m (peel strength between PDMS and PI at a 1:10 ratio) to 83.27 N / m, an increase of 31.86%. This result indicates that the PDMS network structure formed by a lower curing agent ratio is more conducive to interfacial bonding and load mitigation. It should be noted that the flexible circuit board 1 typically uses polyimide (PI) as a substrate, on which various components are integrated, and these components are typically encapsulated with epoxy resin. Therefore, the PI substrate is the supporting material and insulating layer of the entire flexible circuit board.

[0042] Furthermore, considering the various contact interfaces between components and PDMS on the FPC, and that the interfacial adhesion performance between these components and PDMS directly affects the packaging reliability of the entire flexible circuit system, this embodiment further conducted peel strength tests on PDMS with different curing ratios (curing agent to prepolymer ratios of 1:5, 1:10, and 1:15) and the main components (epoxy resin encapsulation). The test results are as follows: Figure 4 As shown in b, when the ratio of curing agent to prepolymer in PDMS is adjusted to 1:15, the peel strength between PDMS and components with this ratio further increases from 74.95 N / m (peel strength between PDMS and components with a 1:10 ratio) to 102.57 N / m, an increase of 36.85%. This result indicates that PDMS with a curing agent to prepolymer ratio of 1:15 can not only form a strong interfacial bond with the PI substrate, but also has good adhesion and compatibility with the surface of epoxy-encapsulated components in FPC, which is beneficial to improving the overall stability and reliability of flexible packaging systems in complex deep-sea service environments.

[0043] In summary, in the embodiments of the present invention, the preferred mass ratio of PDMS prepolymer to curing agent is 15:1. This curing ratio will also be used for the samples used in subsequent performance tests.

[0044] In another embodiment, the sensor further includes a second encapsulation layer 3, which covers the other side of the flexible circuit board 1, forming the bottom of the sensor after encapsulation. The second encapsulation layer 3 uses the same flexible polymer encapsulation material as the first encapsulation layer 2, which will not be described in detail here.

[0045] In use, since the bottom of the sensor needs to be in contact with a fixed surface, and the forces mainly fall on the other five surfaces in the deep-sea environment, the second encapsulation layer and the FPC typically do not need to be chemically bonded; physical contact encapsulation is sufficient to ensure stability. In actual operation, after injecting PDMS solution through potting, it can form a good bond with the existing PDMS solid on the upper surface (the first encapsulation layer), ensuring the stability and sealing of the overall encapsulation.

[0046] Regarding the thickness of the encapsulation layer, the thickness of the first encapsulation layer 2 can be selected between 1.5mm and 2.0mm. The lower limit of 1.5mm is chosen because the overall thickness of the FPC is approximately 0.75mm, requiring a certain thickness to ensure mechanical reliability and waterproof sealing performance. An excessively thin encapsulation layer would suffer physical damage under the high pressure of deep sea conditions. The upper limit of 2.0mm is chosen to consider heat transfer efficiency; an excessively thick first encapsulation layer would lead to a slower thermal response time. In this embodiment, the thickness of the first encapsulation layer 2 is 2.0mm.

[0047] Furthermore, the thickness of the second encapsulation layer 3 can be selected to be between 0.5 and 1 mm. The thickness of the second encapsulation layer 3 is thinner than that of the first encapsulation layer 2 because the bottom of the sensor is fixed to the surface of an object during use, and only waterproof performance needs to be considered; its mechanical performance requirements are not high. In this embodiment, the thickness of the second encapsulation layer 3 is 1.0 mm.

[0048] Furthermore, to enable the sensor to resist the adhesion of microorganisms, biofilms, and inorganic particles in a long-term seawater immersion environment, and to maintain stable thermal conductivity and external surface integrity, a hydrophobic and antifouling layer is further provided on the outer surface of the first encapsulation layer 2. The hydrophobic and antifouling layer comprises two parts: a micro / nano rough structure formed by nanoparticles, and a low surface energy modified layer 5 chemically bonded to the surface of the micro / nano rough structure 4. The low surface energy modified layer is typically a fluorine-containing low surface energy modified layer.

[0049] The micro / nano rough structure 4 is obtained by attaching hydrophobic nanoparticles to the outer surface of the first encapsulation layer 2. It should be noted that a micro / nano rough structure refers to a surface structure that simultaneously possesses micrometer-scale (1-100 μm) and nanometer-scale (1-1000 nm) morphological features, such as a composite morphology formed by the accumulation of nanoparticles, where micrometer-scale protrusions and nanometer-scale depressions coexist. The hydrophobic nanoparticles can be nanoscale SiO2, TiO2, ZnO, Al2O3, SiC, silicon nitride, or other nanoparticles that meet the hydrophobic requirements. In this embodiment, nano-SiO2 with a particle size of 10-20 nm is preferred, and the thickness of the formed micro / nano rough structure 4 is controlled at 20-30 μm.

[0050] The low surface energy modified layer 5 is constructed on the basis of the micro / nano rough structure 4, creating a "low surface energy" surface to achieve superhydrophobicity and antifouling properties. The fluorinated low surface energy modified layer with low surface energy is typically formed by a fluorinated silane coupling agent, selected from one or more of perfluorooctyltriethoxysilane (FAS) and perfluorodecyltriethoxysilane (PFDTES). Alternatively, the fluorinated low surface energy modified layer can also be formed from polytetrafluoroethylene (PTFE), PDMS, fluoroacrylate copolymers, etc. In this embodiment, FAS is preferred as the forming material for the fluorinated low surface energy modified layer; when grafted onto the surface of the micro / nano rough structure, it can significantly improve the contact angle of the encapsulation surface.

[0051] To further verify the effect of the hydrophobic and antifouling layer on the contact angle change of the encapsulation surface, this embodiment measures the contact angle of each surface treated with different methods (untreated, nano-SiO2 treated, FAS treated, and nano-SiO2+FAS treated) using a contact angle measuring instrument. Figure 5As shown. Test results show that the contact angle after treatment with nano-SiO2 alone is approximately 101°; the contact angle after treatment with FAS alone is approximately 117°; and the contact angle of the encapsulation surface can be increased to over 130° after treatment with nano-SiO2 + FAS. Figure 6 As shown, after immersion in seawater for 15 days, the contact angle can still be maintained above 120°, significantly reducing surface aging caused by marine fouling. It should be noted that the specific process of the above-mentioned "isolated nano-SiO2 treatment" is consistent with the micro-nano rough structure formation method in the examples; the specific process of the "isolated FAS treatment" is consistent with the formation method of the fluorine-containing low surface energy modified layer in the examples.

[0052] This result demonstrates a synergistic effect between nano-SiO2 treatment and hydrophobic FAS treatment. Nano-SiO2 particles are used to form a micro-nano rough structure on the outer surface of the first encapsulation layer. This structure can trap an air layer between the encapsulation layer and seawater, significantly reducing the actual liquid-solid contact area and making the encapsulation surface hydrophobic. At the same time, through the synergistic grafting of fluorine-containing groups on its surface, stable superhydrophobic properties with a contact angle greater than 130° are ultimately achieved, and the encapsulation surface is endowed with self-cleaning and anti-biofouling capabilities, thereby maintaining the cleanliness of the sensor's outer surface and stable thermal response performance during long-term immersion in deep sea.

[0053] The flexible circuit board integrates a temperature-sensitive element and a reference resistor matched with the temperature-sensitive element to construct a ratio-based dual-channel temperature measurement structure; wherein, the temperature-sensitive element is used to sense the ambient temperature and convert it into an electrical signal, and the reference resistor is used to provide a stable reference signal independent of temperature.

[0054] The temperature-sensitive element can be selected from positive temperature coefficient (PTC) thermistors, negative temperature coefficient (PTC) thermistors, or thin-film platinum resistance thermometers, with consistent ratio calculation methods. This embodiment uses a high-stability PTC thermistor as an example, with a temperature measurement accuracy of ±0.1%. To eliminate the influence of wire resistance, contact resistance, and power supply voltage fluctuations on the measurement results, a thin-film metal reference resistor is placed on the flexible circuit board, adjacent to the temperature-sensitive element. This reference resistor is made of a low-temperature-coefficient metal material (such as nickel-chromium alloy or platinum), and its resistance remains essentially unchanged with temperature within the measurement range.

[0055] The temperature-sensitive element and the reference resistor are powered by the same excitation source (such as the same constant voltage source or constant current source), and the voltage signal V across the temperature-sensitive element is synchronously acquired through a 24-bit multi-channel analog-to-digital converter (ADC). PTC The voltage signal V across the reference resistor ref During data processing, the ratio R=V is calculated. PTC / Vref Temperature is characterized by the shared excitation source and signal link between the temperature sensing element and the reference resistor. The effects of power supply voltage fluctuations, changes in wire resistance, and contact resistance drift on the two signals are common-mode and cancel each other out in the ratio calculation, thus significantly improving the anti-interference capability and long-term stability of temperature measurement.

[0056] Figure 2 This is a flowchart illustrating the packaging process for a modified, flexible temperature sensor for deep-sea applications. Figure 2 As shown, the packaging method of this sensor includes the following steps: Step a: Provide a flexible circuit board with integrated components. The board, measuring 15×15mm, is provided by Shenzhen JLCPCB Co., Ltd. 2 A flexible circuit board is constructed, integrating a PTC thermistor with an accuracy of ±0.1%. A thin-film metal reference resistor is positioned adjacent to the PTC thermistor for subsequent ratiometric acquisition. The flexible circuit board is then ultrasonically cleaned in anhydrous ethanol and deionized water for 5 minutes each, and subsequently dried with nitrogen gas for later use.

[0057] Step b: Cover the side of the flexible circuit board where the components are located with a first encapsulation layer made of flexible polymer encapsulation material; this step specifically includes the following sub-steps: b1. First, pre-curing is performed to obtain the first encapsulation layer. Specifically, a clean glass plate is taken, and it is cleaned and dried sequentially with anhydrous ethanol and deionized water. The FPC treated in step a is placed flat on the glass plate, with the component side facing up, ensuring that the bottom of the FPC is tightly fitted to the glass plate without gaps. A nano-adhesive tape is used to surround the FPC to form an encapsulation area with encapsulation dimensions of 40×30×2mm. 3 The prepolymer of the flexible polymer encapsulation material—polydimethylsiloxane (PDMS, Dow Corning Sylgard 184)—was thoroughly mixed with a curing agent at a mass ratio of 15:1 and poured into the area enclosed by nano-adhesive tape, with a pouring thickness of 2 mm. After vacuum degassing for 10 min, it was cured in a constant temperature drying oven at 80 ℃ for 1 h. After curing, the PDMS was peeled off from the FPC surface to obtain the pre-cured first encapsulation layer. At this point, the side of the first encapsulation layer in contact with the component forms a recessed structure that matches the shape of the component.

[0058] b2. Activate the surfaces of the flexible circuit board and the first encapsulation layer. Specifically, place the pre-cured first encapsulation layer and the FPC with components in an oxygen plasma treatment device for 60 seconds at a power of 30 W. High-energy particles in the plasma bombard the material surface, breaking the C-C and CH bonds and generating a large number of hydroxyl (-OH) active groups, providing chemical binding sites for the subsequent silane coupling reaction.

[0059] b3. Introduce a silane coupling agent into the activated surface, allowing covalent bonds to form between the two through a chemical reaction between the silane coupling agent and the surface. Specifically: First, prepare the silane coupling agent solution: Mix APTES and GPTMS at a volume ratio of 1:1, and dilute with isopropanol to a total volume concentration of 2 vol%. Immerse the activated first encapsulation layer and FPC separately in this composite silane coupling agent solution for 1 h. After removal, place them in a clean fume hood to air dry naturally for 30 min to remove residual solvent from the surface. Align and bond the dried first encapsulation layer with the FPC (the two activated surfaces are bonded together), and apply a pressure of 30 kPa using a custom-made fixture to ensure tight contact and no interfacial gaps. Let it stand at a constant temperature of 25 ℃ for 8 h to allow the amino groups of APTES and the epoxy groups of GPTMS to undergo a ring-opening addition reaction, forming a stable covalent bond network, thereby achieving chemical bonding between the first encapsulation layer and the FPC.

[0060] Then, flip the semi-encapsulated PDMS-FPC over and place it into a 40×30×3 mm 4 ... 3 A 1mm thick layer of PDMS is cast inside the nano-adhesive tape, placed in a vacuum drying oven, and after 10 minutes of defoaming treatment, transferred to an 80°C constant temperature drying oven for 1 hour of curing to form the second encapsulation layer. The edge of the second encapsulation layer naturally combines with the edge of the first encapsulation layer on the side of the FPC, realizing a "sandwich" encapsulation structure of PDMS-FPC-PDMS. Step c: Construct a hydrophobic and antifouling layer on the outer surface of the first encapsulation layer; this step specifically includes the following sub-steps: c1. A micro-nano rough structure is formed on the outer surface of the first encapsulation layer.

[0061] First, prepare the nano-SiO2-PDMS composite solution: Weigh 0.5 g of nano-SiO2 particles (approximately 15 nm in diameter) and add them to 50 mL of ethyl acetate. Disperse the particles using a 100 W ultrasonic disperser for 30 min to obtain a uniform and stable suspension. Add 1 g of PDMS prepolymer to the suspension and continue ultrasonic dispersion for 30 min. Then add 0.1 g of PDMS curing agent and magnetically stir at room temperature for 30 min to obtain a uniformly dispersed, non-agglomerated nanocomposite solution.

[0062] The encapsulation structure obtained in step b was placed in anhydrous ethanol and ultrasonically cleaned (100 W, 5 min). It was then rinsed twice with deionized water and dried with nitrogen (3 L / min, 3 min) to ensure no impurities remained on the surface, thus avoiding any impact on coating adhesion. A 0.5 mm nozzle was used, with the nozzle 15 cm from the outer surface of the first encapsulation layer and a moving speed of approximately 1 cm / s. Two coats were applied using a horizontal-to-vertical cross-spraying method. After each coat, the coating was allowed to air dry at room temperature for 15 min to allow the ethyl acetate to completely evaporate. After spraying, nano-SiO2 particles formed a continuous and uniform micro-nano rough structure on the surface of the first encapsulation layer, with a coating thickness controlled at 20–30 μm.

[0063] In the nano-SiO2-PDMS composite solution, the PDMS prepolymer binds to the SiO2 particles through hydrogen bonds, which can enhance the stability of the SiO2 solution and improve its dispersibility. The addition of PDMS curing agent enables the SiO2 layer to adhere more firmly after the mixed solution is sprayed onto the outer surface of the first encapsulation layer, preventing it from falling off or peeling off.

[0064] c2. Activate the micro / nano roughened structure. The package containing the micro / nano roughened structure is subjected to oxygen plasma treatment again, with the same parameters as in step b2 (power 30 W, time 60 s), so that the surface of the micro / nano roughened structure is exposed to abundant hydroxyl active groups.

[0065] c3. Introduce a hydrophobic, low-surface-energy modified layer containing fluorinated groups. Solution preparation: Dilute FAS in anhydrous isopropanol to prepare a 2 vol% fluorosilane solution. Immerse the encapsulated body activated in step c2 in this fluorosilane solution for 1 hour. After removal, place it in a fume hood to air dry naturally, and then heat-treat it in an oven at 80°C for 30 minutes. This allows the fluorosilane molecules to chemically bond to the surface of the micro / nano rough structure through a silanol condensation reaction, forming a low-surface-energy modified layer containing fluorinated groups.

[0066] To verify the overall pressure resistance and water resistance of the encapsulation structure, the encapsulated sample was placed in a 45 MPa high-pressure chamber for 10 pressure cycles, each lasting 10 minutes. The sensor output signal was monitored during the test. After the test, ultrasonic testing and optical microscopy revealed no peeling or voids at the interface, and no corrosion was observed in the internal circuitry. The test results are as follows: Figure 8 As shown, these results fully demonstrate that the covalent bonding of APTES and GPTMS effectively enhances the interface reliability of PDMS and FPC, enabling it to work stably for a long time in the high-pressure and corrosive environment of the deep sea, providing strong support for the performance assurance of the sensor.

[0067] The above-mentioned hyperbaric chamber experiment maintained a constant ambient temperature of approximately 27°C. Figure 8As shown in Figure a, under the condition of ratiometric dual-channel measurement, the rate of change of the sensor's output k during the pressure loading process is relatively small. To evaluate the changes in the sensor's working performance before and after high-pressure loading, the temperature measurement results before and after pressurization were compared and analyzed, and the results are as follows. Figure 8 As shown in b, the sensor without optimized encapsulation (no chemical bonding) exhibits a measurement change rate of 1.1317, indicating a non-negligible change in its electrical parameters after high voltage application. In contrast, the sensor with optimized encapsulation using the AG interface enhancement method (covalent bonding of APTES and GPTMS) shows a change rate of 0.9995, with the measured values ​​remaining essentially consistent. These test results demonstrate that the covalently bonded encapsulation strategy improves the bonding strength between the first encapsulation layer and the flexible circuit board. The enhanced stability of the encapsulation structure significantly strengthens the sensor system's pressure resistance, providing a structural foundation for its long-term reliable operation in the high-pressure environment of the deep sea.

[0068] To verify the measurement accuracy and calibration stability of the flexible temperature sensor of this invention, the sensor and a commercial RBR sensor were placed together in a constant temperature water bath. Multiple stable temperature points were set at 2.5°C intervals within the range of 0–35°C, and the ratio-based measurement signal of the sensor and the corresponding reference temperature were recorded at each temperature. A calibration model for the sensor was established by fitting the ratio-based output of the thermistor to the temperature data of the RBR, and temperature calibration parameters for deep-sea environments were obtained. The fitting results show a linear correspondence between the ratio-based measurement signal and the temperature value. A linear function calibration model was established with the ratio-based measurement signal as the independent variable and the temperature value as the dependent variable. The fitting formula can be expressed as T = ak + b, where T is the temperature value, and coefficient ak is the temperature conversion coefficient obtained from linear calibration. This is the voltage ratio. The linear fitting intercept is given. In this embodiment, the specific fitting formula is: T = 167.04k - 141.31. It should be noted that the above calibration parameters are related to the individual characteristics of the specific batch of thermistors used. In practical applications, the corresponding parameters should be obtained through independent calibration of each sensor. The sensor of this invention maintains a fitting error within 0.04 °C across the entire calibration range, and its output remains stable under repeated temperature increases and decreases without significant drift.

[0069] To verify the long-term stability and engineering usability of the sensor in a real deep-sea environment, the sensor was installed on a deep-sea lander and subjected to a live-fire test at a depth of 4300 m. Temperature data were recorded throughout the descent, landing, and ascent processes, and compared with those of a commercial RBR sensor. The test results are as follows: Figure 7 As shown, the results indicate that the sensor of the present invention performs stably under full pressure and immersion conditions, with an average error of 0.03 °C.

[0070] In summary, the key technical aspects of this invention lie in the deep-sea pressure-resistant encapsulation achieved through interface chemical enhancement, the flexible mechanical cushioning achieved through low-modulus PDMS, the anti-fouling stability achieved through a nano-hydrophobic coating, and the high-precision deep-sea temperature measurement achieved through a ratio-based temperature sensing structure. These synergistic technologies constitute the core innovation of this invention and should be protected by law.

[0071] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A deep-sea flexible temperature sensor based on modified packaging, characterized in that, include: A flexible circuit board on which components are integrated; The first encapsulation layer covers the side of the flexible circuit board on which the components are disposed, and the first encapsulation layer is composed of a flexible polymer encapsulation material; A chemical bonding interface is formed between the flexible circuit board and the first encapsulation layer. The formation of the chemical bonding interface is achieved by surface activation treatment and the introduction of a silane coupling agent, which is used to realize the chemical bonding connection between the flexible circuit board and the first encapsulation layer. A hydrophobic and antifouling layer is formed on the outer surface of the first encapsulation layer. The hydrophobic and antifouling layer includes, from the inside to the outside, a micro-nano rough structure and a low surface energy modified layer.

2. The deep-sea flexible temperature sensor based on modified packaging as described in claim 1, characterized in that, The silane coupling agent is selected from one or more of the following: a compound system of 3-aminopropyltriethoxysilane and 3-glycidyl etheroxypropyltrimethoxysilane, a mercaptosilane coupling agent, a vinylsilane coupling agent, or a silane coupling agent containing an epoxy group.

3. The deep-sea flexible temperature sensor based on modified packaging as described in claim 1, characterized in that, The sensor also includes a second encapsulation layer, which covers the other side of the flexible circuit board and is made of a flexible polymer encapsulation material.

4. A deep-sea flexible temperature sensor based on modified packaging as described in claim 1, characterized in that, The flexible polymer encapsulation material is polydimethylsiloxane, wherein the mass ratio of prepolymer to curing agent is 15:

1.

5. A deep-sea flexible temperature sensor based on modified packaging as described in claim 3, characterized in that, The thickness of the first encapsulation layer is 1.5~2 mm, and the thickness of the second encapsulation layer is 0.5~1 mm.

6. A deep-sea flexible temperature sensor based on modified packaging as described in claim 1, characterized in that, The hydrophobic and antifouling layer includes a micro-nano rough structure formed by nanoparticles on the outer surface of the first encapsulation layer, and a low surface energy modified layer containing fluorine groups grafted onto the surface of the micro-nano rough structure by chemical bonding.

7. A deep-sea flexible temperature sensor based on modified packaging as described in claim 1, characterized in that, The flexible circuit board integrates a temperature-sensitive element and a reference resistor matched with the temperature-sensitive element to construct a ratio-based dual-channel temperature measurement structure; the temperature-sensitive element is a positive temperature coefficient thermistor, a negative temperature coefficient thermistor, or a thin-film platinum resistance thermometer.

8. A packaging method for a deep-sea flexible temperature sensor based on modified packaging as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step a: Provide a flexible circuit board with integrated components; Step b: Cover the side of the flexible circuit board where the components are disposed with a first encapsulation layer made of flexible polymer encapsulation material; Specifically, the process involves first pre-curing to obtain a first encapsulation layer; then activating the surface of the flexible circuit board and the surface of the first encapsulation layer; finally introducing a silane coupling agent into the activated surface, allowing the two to form a covalent bond connection through a chemical reaction between the silane coupling agents. Step c: Construct a hydrophobic and antifouling layer on the outer surface of the first encapsulation layer; Specifically, a micro-nano rough structure is first formed on the outer surface of the first encapsulation layer. After the micro-nano rough structure is activated, a hydrophobic low surface energy modified layer containing fluorine groups is introduced, so that the surface of the micro-nano rough structure forms a low surface energy modified layer containing fluorine groups through chemical bonding.

9. The packaging method for a deep-sea flexible temperature sensor based on modified packaging as described in claim 8, characterized in that, The encapsulation method further includes covering the other side of the flexible circuit board with a second encapsulation layer; the edge of the second encapsulation layer is combined with the edge of the first encapsulation layer to form an overall seal.

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