Battery temperature and pressure integrated FPC sensor and manufacturing method thereof

Abstract

This invention relates to the technical fields of sensor design, and provides an integrated battery temperature and pressure FPC sensor and its manufacturing method. The FPC sensor includes a substrate, a copper foil layer disposed on one side of the substrate, and a constantan layer disposed on the other side of the substrate via an insulating pure adhesive layer. The copper foil layer, substrate, insulating pure adhesive layer, and constantan layer are stacked to form a composite structure substrate, with signal lines formed on the copper foil surface and constantan surface, respectively. Multiple vias penetrate the composite structure substrate, and electroplating ensures electrical connection between the constantan layer and the copper foil layer at the penetration points, forming a detection circuit. The copper foil layer converts pressure changes into pressure detection signals through the piezoresistive effect, and the constantan layer converts temperature changes into temperature detection signals through the thermoelectric effect, achieving simultaneous temperature and pressure detection within a single flexible thin unit. The manufacturing method includes setting the copper foil, hot-pressing and kneading the constantan, drilling, pattern electroplating, film coating, and die-cutting. This invention offers high temperature measurement accuracy and reliable structure, suitable for large-scale deployment within batteries.

Description

Technical Field

[0001] This invention belongs to the technical fields of battery safety monitoring and sensor design, specifically relating to a composite sensing unit for use inside a battery that can simultaneously detect temperature and pressure and its manufacturing process, which is particularly suitable for safety early warning systems for power batteries of new energy vehicles and industrial and commercial energy storage batteries. Background Technology

[0002] In battery applications (especially lithium-ion batteries), real-time monitoring of internal temperature and pressure changes is crucial for preventing safety accidents such as thermal runaway and fires. Current technologies often rely on sensing units that can only detect temperature or pressure individually, making it difficult to achieve integrated temperature and pressure monitoring within a single, thin, flexible structure.

[0003] A common existing technology involves embedding the thermistor in a hole drilled in a rigid circuit board to detect temperature. This approach has the following drawbacks: the thermistor is prone to failure when subjected to pressure from the expanding battery pack; and the overall surface is uneven, making it difficult to achieve a good fit with the battery pack surface. Furthermore, the inherent limitations of the structure make it difficult to integrate pressure detection functions and achieve large-scale, consistent mass production.

[0004] Existing technology includes a flexible array-type integrated sensor that uses copper foil and constantan foil respectively fabricated on both sides of a polyimide (PI) substrate. Electrical connections between the upper and lower layers are achieved at the temperature sensing junction using a via-plating process, forming a T-type thermocouple for array-type temperature detection. However, this solution only addresses temperature measurement and does not include pressure detection functionality, nor does it provide structural adaptation for internal battery applications.

[0005] Existing technology also includes a thin-film sensor for monitoring the pressure and temperature of lithium batteries based on a flexible printed circuit anode current collector. This sensor uses PVDF-TrFE (polyvinylidene fluoride-trifluoroethylene) as the piezoelectric and pyroelectric sensing material layer, enabling simultaneous monitoring of internal battery pressure and temperature. This approach relies on a piezoelectric / pyroelectric polymer material system. However, this approach only addresses temperature measurement, not pressure detection, and lacks structural adaptation for specific battery internal applications.

[0006] There is another copper current collector with temperature sensing function in the existing technology, which adopts a sandwich structure of electroplated copper layer, copper foil and film, but it only involves temperature measurement function.

[0007] In summary, existing battery monitoring solutions suffer from technical problems such as limited sensor functionality, low integration, and poor mass production feasibility. Summary of the Invention

[0008] To address the shortcomings of the existing technology, the present invention provides the following technical solution: In a first aspect, the present invention provides an integrated battery temperature and pressure FPC sensor, comprising: A copper foil layer is disposed on one side of a flexible insulating substrate, and signal lines are formed on its copper foil surface. The copper foil layer is configured to convert pressure changes into pressure detection signals and serves as both a conductive layer and a pressure-sensitive layer. A constantan layer is disposed on the other side of the flexible insulating substrate through an insulating pure adhesive layer, such that the copper foil layer, the flexible insulating substrate, the insulating pure adhesive layer and the constantan layer are stacked to form a composite structure substrate; a signal line is formed on the constantan surface of the constantan layer, and the constantan layer is configured to convert temperature changes into temperature detection signals through its thermoelectric effect, and is used as a temperature sensitive layer. Multiple vias penetrate the composite structure substrate. The vias are electroplated to make the constantan layer and the copper foil layer electrically connected at the penetration points, so as to connect the signal lines on the constantan side and the signal lines on the copper foil side and form a detection circuit, so as to realize temperature detection and pressure detection simultaneously in a single FPC sensor.

[0009] Furthermore, the through hole is made by laser drilling or mechanical drilling.

[0010] Furthermore, the electroplating process selectively electroplats only the preset line area on the inner wall of the via to form a metallized layer.

[0011] Furthermore, the metallization layer on the inner wall of the via is made of electroplated copper.

[0012] Furthermore, the constantan layer is configured to be directly attached to the surface of the battery pack under test during use, and the battery pack temperature is sensed through contact thermal conduction.

[0013] Furthermore, the temperature detection signal and the pressure detection signal are respectively transmitted to a signal acquisition point located at one end of the FPC sensor via corresponding signal lines. The signal acquisition point is configured to be pluggably connected to an external signal acquisition device via a connector.

[0014] Furthermore, the composite structure substrate is in the shape of a flexible sheet, and the plurality of through holes are arranged at intervals along the length direction of the composite structure substrate.

[0015] Furthermore, among the plurality of through holes arranged at intervals along the length direction of the composite structure substrate, each through hole corresponds to an independent temperature detection point and a pressure detection point, forming a multi-point, multi-channel detection array.

[0016] Furthermore, the outermost surfaces of the constantan layer and the copper foil layer are covered with an insulating protective film; the conductive position of the via is spatially separated from the position of the signal acquisition point, and the signal acquisition point is concentrated at one end of the composite structure substrate along the length direction.

[0017] Secondly, the present invention provides a method for manufacturing an integrated battery temperature and pressure FPC sensor, the method being used to manufacture the aforementioned integrated FPC sensor, the method comprising the following steps: A copper foil material is set on one side of a flexible insulating substrate to form a copper foil layer, and constantan material is hot-pressed and kneaded with insulating pure adhesive on the other side of the flexible insulating substrate to form a composite structure substrate with a constantan layer on one side and a copper foil layer on the other side. Multiple through holes are fabricated at predetermined positions on the composite structure substrate. Copper is selectively electroplated onto the walls of the through holes using a pattern electroplating process to form a metallized copper layer on the inner wall of the through holes, thereby achieving electrical connection between the constantan layer and the copper foil layer at predetermined points. Copper is selectively electroplated onto the constantan surface of the constantan layer and the copper foil surface of the copper foil layer to form a constantan surface signal circuit pattern and a copper foil surface signal circuit pattern, respectively. After electroplating, the composite structure substrate is covered with an insulating protective film on both sides. The film-coated substrate is then punched into a strip-shaped sensing unit that matches the size of the target battery pack through a die-cutting process.

[0018] Compared with the prior art, the beneficial effects of this invention are as follows: Compared with the prior art, the technical solution of the present invention has the following beneficial effects: 1. Integrated Functionality: By coordinating the copper foil layer (piezoresistive pressure measurement) and the constantan layer (thermoelectric temperature measurement) in the same double-sided composite structure supported by a flexible insulating substrate, the temperature detection function and pressure detection function inside the battery are realized simultaneously within a single thin flexible unit. This eliminates the need to deploy two independent sensors inside the battery, significantly improving the utilization rate of the limited space inside the battery.

[0019] 2. Stable structure and reliable dimensions: The flexible insulating substrate serves as the intermediate support layer, with the copper foil layer and constantan layer attached to both sides of the flexible insulating substrate. This avoids problems such as interlayer misalignment and warping that may occur when metal foils are directly stacked, giving the composite structure substrate good mechanical strength and dimensional stability. The flexible insulating substrate also serves as an electrical isolation layer, working in conjunction with the insulating pure adhesive layer to achieve reliable insulation of the copper foil layer and constantan layer.

[0020] 3. High temperature sensitivity and accuracy: Constantan (nickel-copper alloy) is used as a special temperature-sensitive layer material. Its thermoelectric effect (Seebeck effect) is used for temperature measurement. Its temperature sensitivity is higher than that of ordinary copper foil. Combined with the structural design of constantan layer directly attached to battery pack, industrial-grade high-precision temperature measurement can be achieved.

[0021] 4. Reliable structure and suitable for mass production: Avoiding the unreliable structure of traditional thermistors with hole-embedded design, it adopts a fully laminated structure and a patterned electroplating selective conduction process. The upper and lower metal layers are stably laminated with flexible insulating substrate and insulating pure glue, with no solder joints or cavities. The product has good consistency and strong resistance to battery pack expansion and extrusion. It is also fully compatible with roll-to-roll continuous production process and is suitable for large-scale industrial mass production.

[0022] 5. Flexible design and wide application: The external dimensions, spacing and number of through holes of the FPC sensor can be customized according to the specific battery model, and it can be adapted to various battery pack forms such as square batteries, cylindrical batteries and pouch batteries.

[0023] 6. Outstanding thermal runaway early warning capability: By synchronously collecting two key safety parameters, temperature and pressure, inside the battery in real time, it can detect abnormal changes in temperature and / or pressure and issue an alarm signal before thermal runaway occurs (for example, about half an hour in advance). This provides a critical time window for the battery management system to take proactive safety measures, effectively preventing battery safety accidents. Attached Figure Description

[0024] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. Some specific embodiments of the invention will be described in detail below with reference to the accompanying drawings in an exemplary and non-limiting manner. The same reference numerals in the drawings designate the same or similar parts or components. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale. In the drawings: Figure 1 This is a schematic flowchart of a method for manufacturing an integrated battery temperature and pressure FPC sensor according to an embodiment of the present invention; Figure 2 This is a schematic diagram of a battery temperature and pressure integrated FPC sensor according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the battery temperature and pressure integrated FPC sensor in one usage state according to an embodiment of the present invention.

[0025] Explanation of reference numerals in the attached figures: 1. Flexible insulating substrate; 2. Copper foil layer; 3. Insulating pure adhesive layer; 4. Constantan layer; 5. Insulating protective film; 6. Through hole. Detailed Implementation

[0026] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are merely 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 should fall within the scope of protection of the present invention.

[0027] In the description of the embodiments of this invention, the term "flexible insulating substrate" refers to a known carrier substrate in the field of flexible printed circuit boards (FPCs), used to carry metal circuits and provide insulation, and can be selected from polyimide (PI) film, polyester (PET) film, or liquid crystal polymer (LCP) film, etc. The term "constantan" refers to a nickel-copper alloy with a nickel content of approximately 40% to 45% (mass percentage), possessing high resistivity and a moderate temperature coefficient of resistance, and is a well-known thermocouple material in the sensor field. The term "insulating pure adhesive" refers to a pure resin film layer without reinforcing fibers or fabrics, possessing both adhesive and insulating functions under heating and pressure. The term "patterned electroplating" refers to a process of selectively forming an electroplating layer on the surface of a substrate, using a photoresist (dry film) to form a mask in non-electroplated areas, exposing only the holes and circuit areas to be electroplated, as opposed to whole-board electroplating.

[0028] Example 1 See Figures 1-3 This embodiment provides an integrated FPC sensor for battery temperature and pressure used in power batteries of new energy vehicles and its manufacturing method. The manufacturing method of the integrated FPC sensor includes the following steps: Step S1: Fabrication of the composite structure substrate: A polyimide (PI) base film (25 μm thick) is provided as the substrate. On one side of the substrate, an electrolytic copper foil (18 μm thick) is deposited using a copper cladding process to form a copper foil layer, thus obtaining a single-sided copper-clad flexible substrate. On the other side of the substrate, an acrylic insulating pure adhesive film (25 μm thick) is placed between the substrate and constantan foil (nickel-copper alloy, approximately 43% nickel content, 12 μm thick, temperature coefficient of resistance approximately 40 × 10⁻⁶). -6 Between / K), a hot press kneading machine is used to hot press and knead the constantan foil to the other side of the substrate under the conditions of temperature 120℃~150℃ and pressure 0.5MPa~2MPa, and then the constantan foil is bonded to the other side of the substrate through an insulating pure adhesive layer. This forms a composite substrate with a copper foil layer on one side, a constantan layer on the other side, and a substrate and an insulating pure adhesive layer in the middle. The stacking order from top to bottom is: copper foil layer, substrate, insulating pure adhesive layer and constantan layer.

[0029] Step S2: Fabrication of vias and pattern electroplating: Based on the preset monitoring point layout, mark multiple via positions at equal intervals (e.g., 50mm interval) along the length of the composite substrate. Use an ultraviolet laser drilling machine (wavelength 355nm) to drill vias penetrating the copper foil layer, substrate, insulating pure adhesive layer, and constantan layer at the marked positions, with a hole diameter of 100μm to 200μm. Following this, pattern electroplating is performed: a photoresist dry film is laminated to both sides of the substrate, and a photolithography process is used to expose the copper surfaces to be electroplated in the via and pre-defined circuit areas. The substrate is then immersed in an acidic copper plating solution (copper sulfate-sulfuric acid system) and electroplated for 15-30 minutes at a current density of 1.5A / dm² to 3A / dm², depositing a 5μm-15μm thick metallized copper layer on the inner wall of the vias. This reliably electrically connects the pre-defined circuit nodes of the constantan layer with the corresponding circuit nodes of the copper foil layer. Simultaneously, copper is selectively electroplated in the pre-defined circuit areas on both the constantan and copper foil surfaces to form signal circuit patterns on the constantan and copper foil surfaces, respectively. This pattern electroplating process selectively electroplats only the vias and circuit areas, avoiding the risk of short circuits between circuits caused by plating the entire board.

[0030] Step S3: Applying Protective Film and Punching: Polyimide (PI) insulating protective films (12.5 μm thick) are applied to both sides of the electroplated composite substrate, and then hot-pressed to ensure tight adhesion. Subsequently, a precision die-cutting process is used to punch the film-coated substrate into elongated sensing units that match the size of the target battery pack. For example, for a square aluminum-cased power battery with dimensions of 148 mm × 102 mm × 27 mm, the FPC sensor can be punched into a slender strip with a length of 140 mm and a width of 8 mm, allowing it to adhere to the surface of the battery pack along its length.

[0031] In use, the FPC sensor prepared in this embodiment is sandwiched between adjacent battery packs or attached to the surface of the battery pack. During the charge-discharge cycle, when the battery pack temperature rises, the constantan layer rapidly senses the temperature change. The copper-constantan thermocouple junction formed by the constantan layer and the copper foil layer at the via generates a temperature-related thermoelectric potential. The temperature detection signal is transmitted to the acquisition point via the constantan surface signal line and the via loop. Simultaneously, when the battery pack expands in volume due to lithium ion insertion / extraction, the resulting pressure acts on the copper foil layer, causing a change in the resistance value under the piezoresistive effect of the copper foil layer, thereby generating a pressure detection signal, which is transmitted to the acquisition point via the copper foil surface signal line. Both signals are transmitted to the battery management system (BMS) via a connector for processing and analysis. When the BMS detects an abnormal rate of temperature rise or a pressure value exceeding a preset safety threshold, the system issues a warning before thermal runaway occurs.

[0032] Example 2 The difference between this embodiment and Embodiment 1 is that mechanical drilling (micro-drilling) is used instead of laser drilling to create the via in step S2. Specifically, a 150μm diameter micro-carbide drill bit is used to drill the via at a preset position on the substrate at high speed (over 100,000 rpm). After drilling, plasma cleaning can be used to remove drill chips and pure adhesive residue from the hole walls to ensure the adhesion of subsequent copper electroplating. The remaining steps are the same as in Embodiment 1.

[0033] Example 3 The difference between this embodiment and Embodiment 1 lies in the choice of substrate material: In this embodiment, a liquid crystal polymer (LCP) film (25 μm thick) is used as the substrate to improve the temperature resistance and dimensional stability of the composite structure substrate. Because LCP has lower moisture absorption and superior dimensional stability, the FPC sensor in this embodiment is particularly suitable for power battery modules with stringent temperature and humidity requirements. The remaining steps are the same as in Embodiment 1.

[0034] In addition, as an alternative, polyester (PET) film can be used as the substrate to reduce manufacturing costs and is suitable for energy storage battery scenarios with relatively low temperature resistance requirements.

[0035] Example 4 This embodiment provides a multi-channel, long-size array-type FPC sensor for distributed temperature and pressure monitoring of multiple areas of a large prismatic battery. The difference from Embodiment 1 is that in step S2, 32 vias are arranged at 30mm intervals along the length of the substrate, forming a 32-channel temperature and pressure detection array. The total length of the substrate is approximately 1000mm (1 meter). In step S3, the shape is punched into an ultra-long, thin strip with a length of 960mm and a width of 6mm. The temperature and pressure signal lines of each channel are led to the corresponding acquisition points using an alternating finger-like pattern. This multi-point, multi-channel array design enables three-dimensional, grid-like real-time temperature and pressure monitoring of large-size battery packs or battery modules composed of multiple battery packs, improving the accuracy and lead time of thermal runaway warnings.

[0036] Example 5 The difference between this embodiment and Embodiment 1 lies in the application scenario: the FPC sensor in this embodiment is used for temperature and pressure monitoring of lithium iron phosphate (LFP) battery packs in commercial and industrial energy storage battery systems (ESS). Accordingly, in step S3 of this embodiment, the FPC sensor is punched to fit the size of a 280Ah battery pack (e.g., 205mm long and 8mm wide), and the through-hole spacing is adjusted to 80mm to increase the coverage area of ​​a single channel. Furthermore, the protective film in step S3 is a fluoropolymer film with better weather resistance to adapt to the long-term operating environment in outdoor or semi-outdoor cabinets of energy storage power stations.

[0037] Example 6 The difference between this embodiment and Embodiment 1 lies in the form of the battery pack to be monitored: this embodiment targets cylindrical batteries (e.g., 18650 or 21700 type cylindrical lithium-ion batteries). In step S3, the FPC sensor after being punched is not a long strip, but a thin, curved sheet with a radius of curvature matching the curvature of the outer circumferential surface of the target cylindrical battery pack, so as to fit tightly against the outer circumferential surface of the cylindrical battery pack. In step S1, thinner constantan foil (8μm thick) and copper foil (12μm thick) are selected to enhance the flexibility and fit of the FPC sensor in the circumferential direction. The vias can be arranged on the curved substrate at circumferential angles of 90° or 120° to realize multi-point temperature and pressure monitoring of the cylindrical battery pack in the circumferential direction.

[0038] Example 7 This embodiment focuses on the design and technical advantages of separating the signal acquisition points from the conduction positions. In the overall layout of the FPC sensor of this invention, the through holes (i.e., the positions where the constantan layer and the copper foil layer are electrically connected) are distributed in the sensing functional area of ​​the substrate, while the signal acquisition points (i.e., the lead-out ends of the temperature signal lines and pressure signal lines) are concentrated at one end of the substrate in the length direction (e.g., within a 15mm wide extension area at the end), and the two are clearly separated in space. The advantages of this separation design are: (1) avoiding the mechanical stress of external connector insertion from being transmitted to the sensing functional area, and preventing fatigue damage to the copper plating layer of the through holes; (2) the signal acquisition points are concentrated at one end, which facilitates standardized insertion with FFC / FPC connectors and simplifies the electrical connection operation in the battery module assembly process; (3) the sensing area can maintain a uniform thickness (e.g., total thickness ≤ 0.2mm), ensuring good adhesion to the surface of the battery pack.

[0039] It should be noted that the above embodiments are merely preferred embodiments of the present invention, and the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention, and the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A battery temperature and pressure integrated FPC sensor, characterized in that, include: A copper foil layer is disposed on one side of a flexible insulating substrate, and signal lines are formed on its copper foil surface. The copper foil layer is configured to convert pressure changes into pressure detection signals and serves as both a conductive layer and a pressure-sensitive layer. A constantan layer is disposed on the other side of the flexible insulating substrate through an insulating pure adhesive layer, such that the copper foil layer, the flexible insulating substrate, the insulating pure adhesive layer and the constantan layer are stacked to form a composite structure substrate; a signal line is formed on the constantan surface of the constantan layer, and the constantan layer is configured to convert temperature changes into temperature detection signals through its thermoelectric effect, and is used as a temperature sensitive layer. Multiple vias penetrate the composite structure substrate. The vias are electroplated to make the constantan layer and the copper foil layer electrically connected at the penetration points, so as to connect the signal lines on the constantan side and the signal lines on the copper foil side and form a detection circuit, so as to realize temperature detection and pressure detection simultaneously in a single FPC sensor.

2. The battery temperature and pressure integrated FPC sensor according to claim 1, characterized in that, The through holes are made by laser drilling or mechanical drilling.

3. The battery temperature and pressure integrated FPC sensor according to claim 1, characterized in that, The electroplating process selectively electroplats only the preset line area on the inner wall of the through hole to form a metallized layer.

4. The battery temperature and pressure integrated FPC sensor according to claim 3, characterized in that, The metallization layer on the inner wall of the through hole is made of electroplated copper.

5. The battery temperature and pressure integrated FPC sensor according to claim 1, characterized in that, The constantan layer is configured to be directly attached to the surface of the battery pack under test during use, and the battery pack temperature is sensed through contact thermal conduction.

6. The battery temperature and pressure integrated FPC sensor according to claim 1, characterized in that, The temperature detection signal and the pressure detection signal are respectively transmitted to a signal acquisition point located at one end of the FPC sensor via corresponding signal lines. The signal acquisition point is configured to be pluggably connected to an external signal acquisition device via a connector.

7. The battery temperature and pressure integrated FPC sensor according to claim 1, characterized in that, The composite structure substrate is in the shape of a flexible sheet, and the plurality of through holes are arranged at intervals along the length direction of the composite structure substrate.

8. The battery temperature and pressure integrated FPC sensor according to claim 1, characterized in that, The plurality of through holes arranged at intervals along the length of the composite structure substrate correspond to independent temperature detection points and pressure detection points, forming a multi-point, multi-channel detection array.

9. The battery temperature and pressure integrated FPC sensor according to claim 6, characterized in that, The outermost surfaces of the constantan layer and the copper foil layer are covered with an insulating protective film; the conductive position of the via is spatially separated from the position of the signal acquisition point, and the signal acquisition point is concentrated at one end of the composite structure substrate along the length direction.

10. A method for manufacturing an integrated battery temperature and pressure FPC sensor, characterized in that, The method is used to manufacture the integrated FPC sensor as described in any one of claims 1-9, and the method includes the following steps: A copper foil material is set on one side of a flexible insulating substrate to form a copper foil layer, and constantan material is hot-pressed and kneaded with insulating pure adhesive on the other side of the flexible insulating substrate to form a composite structure substrate with a constantan layer on one side and a copper foil layer on the other side. Multiple through holes are fabricated at predetermined positions on the composite structure substrate. Copper is selectively electroplated onto the walls of the through holes using a pattern electroplating process to form a metallized copper layer on the inner wall of the through holes, thereby achieving electrical connection between the constantan layer and the copper foil layer at predetermined points. Copper is selectively electroplated onto the constantan surface of the constantan layer and the copper foil surface of the copper foil layer to form a constantan surface signal line pattern and a copper foil surface signal line pattern, respectively. After electroplating, the composite structure substrate is covered with an insulating protective film on both sides. The film-coated substrate is then punched into a strip-shaped sensing unit that matches the size of the target battery pack through a die-cutting process.

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