Online sampling detection device for tensile elongation of copper foil

Abstract

The invention discloses a copper foil tensile elongation online sampling detection device, and belongs to the technical field of copper foil production, the copper foil tensile elongation online sampling detection device comprises a connecting box, a first guide roller and a second guide roller are arranged in the connecting box, a detection mechanism is arranged between the first guide roller and the second guide roller, and the detection mechanism comprises a connecting roller slidably connected in the connecting box; a first sliding groove and a second sliding groove are formed in the two sides of the connecting box correspondingly, the connecting roller is slidably connected with the first sliding groove and the second sliding groove correspondingly, and a first driving part is arranged between the connecting roller and the first sliding groove. The copper foil is guided into the connecting box through the first guide roller and the second guide roller, the connecting roller in the detection mechanism slides in the first sliding groove and the second sliding groove to adjust the position, the cutting part triggers cutting in the movement of the copper foil, and the cut sample is automatically received by the detection part and subjected to a tensile test. Continuous sampling detection of the copper foil production line can be achieved, shutdown sampling is not needed, the detection efficiency is greatly improved, and manual intervention is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of copper foil production, and in particular relates to an online sampling detection device for tensile elongation of copper foil. Background Art

[0002] Currently, in the copper foil production process, tensile strength, an indicator of resistance to plastic fracture, and elongation, a parameter reflecting the material's plasticity, are crucial indicators for copper foil production and application. Therefore, in actual production, the foil production process requires the tensile strength to be controlled between 330 and 380 MPa, and the elongation to be ≥3.3%. However, during foil production, tensile strength and elongation can only be tested during the coiling and uncoiling phases; testing during the intermediate phases is not possible. This makes it impossible to monitor and adjust the tensile strength and elongation in real time, which can easily result in the entire roll of copper foil failing to meet quality standards and increase manufacturing costs. Summary of the Invention

[0003] The purpose of the present invention is to provide an online sampling detection device for tensile elongation of copper foil to solve the problems existing in the above-mentioned prior art.

[0004] To achieve the above-mentioned purpose, the present invention provides the following scheme: The present invention provides an online sampling and detection device for the tensile elongation of copper foil, comprising a connecting box, wherein a first guide roller and a second guide roller are respectively provided in the connecting box, and a detection mechanism is provided between the first guide roller and the second guide roller, and the detection mechanism comprises a connecting roller slidably connected to the connecting box, a first slide groove and a second slide groove are respectively provided on both sides of the connecting box, the connecting roller is slidably connected to the first slide groove and the second slide groove respectively, a first driving part is provided between the connecting roller and the first slide groove, a second driving part is provided between the connecting roller and the second slide groove, the first driving part and the second driving part are respectively fixed to the connecting box, a cutting part is provided on the connecting roller, a detection part is provided in the connecting box, and the detection part is located below the cutting part.

[0005] Preferably, the first driving part includes a first connecting plate fixedly connected to the outside of the first slide groove, the top surface of the first connecting plate is fixedly connected to the first motor, the output shaft of the first motor is fixedly connected to the first screw, the end of the connecting roller close to the first slide groove is fixedly connected to the first connecting shaft, the first connecting shaft is located in the first slide groove, the end of the first connecting shaft away from the connecting roller extends to the outside of the first slide groove and is fixedly connected to the second motor, the second motor is slidably connected to the outer wall of the connecting box, the second motor is fixedly connected to the second connecting plate away from the side wall of the connecting box, and the first screw is threadedly connected to the second connecting plate.

[0006] Preferably, the second driving part includes a third motor fixedly connected to the top surface of the second slide groove, the output shaft of the third motor is fixedly connected to the second lead screw, the end of the connecting roller close to the second slide groove is rotatably connected to the second connecting shaft, the end of the second connecting shaft away from the connecting roller is rotatably connected to the first slider, the first slider is slidably connected in the second slide groove, and the second lead screw is threadedly connected to the first slider.

[0007] Preferably, a first groove is provided on the connecting roller, the cutting portion is provided in the first groove, the cutting portion comprises a first electric telescopic rod fixedly connected in the first groove, and a cutting knife is fixedly connected to the output end of the first electric telescopic rod.

[0008] Preferably, the detection part includes a first connecting seat fixedly connected in the connecting box, the first connecting seat is located below the connecting roller, a second groove is provided on the top surface of the first connecting seat, a first cavity is provided in the first connecting seat, the first cavity is connected to the second groove, an adsorption part is provided in the first cavity, and a detection part is provided in the second groove.

[0009] Preferably, the adsorption component includes a second electric telescopic rod fixedly connected to the first cavity, and a vacuum adsorption head is fixedly connected to the top surface of the second electric telescopic rod.

[0010] Preferably, the detection component includes a third electric telescopic rod symmetrically fixed to both sides of the second groove, the output end of the third electric telescopic rod is fixed with a clamping head, and a pressure sensor is provided in the clamping head.

[0011] Preferably, a third guide roller is provided between the first guide roller and the connecting roller, the third guide roller is rotatably connected in the connecting box, and the third guide roller is located below the first guide roller and the connecting roller.

[0012] Preferably, a collecting tank is provided in the first cavity.

[0013] Preferably, the first guide roller, the connecting roller and the second guide roller are respectively located above the copper foil, and the third guide roller is located below the copper foil.

[0014] The present invention discloses the following technical effects: copper foil is guided into a connection box via first and second guide rollers. The connection roller in the detection mechanism slides within first and second chutes to adjust its position. The cutting unit triggers shearing during the movement of the copper foil. The sheared sample is automatically received by the detection unit and subjected to tensile testing. This invention enables continuous sampling and testing of the copper foil production line without stopping the machine for sampling, significantly improving detection efficiency and reducing manual intervention. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0016] Figure 1 This is a structural schematic diagram of one side of the on-line sampling detection device for tensile elongation of copper foil according to the present invention;

[0017] Figure 2 This is a structural schematic diagram of the other side of the on-line sampling detection device for tensile elongation of copper foil according to the present invention;

[0018] Figure 3 This is a schematic diagram of the internal structure of the connection box of the present invention;

[0019] Figure 4 Schematic diagram of the internal structure of the first connecting socket of the present invention.

[0020] In the figure: 1. connecting box; 2. first guide roller; 3. second guide roller; 4. connecting roller; 5. first slide; 6. second slide; 7. first connecting plate; 8. first motor; 9. first lead screw; 10. first connecting shaft; 11. second motor; 12. second connecting plate; 13. third motor; 14. second lead screw; 15. second connecting shaft; 16. first slider; 17. first groove; 18. first electric telescopic rod; 19. first connecting seat; 20. cutting knife; 21. second groove; 22. first cavity; 23. second electric telescopic rod; 24. vacuum adsorption head; 25. third electric telescopic rod; 26. clamping head; 27. third guide roller. DETAILED DESCRIPTION

[0021] The evolution of copper foil tensile strength and elongation testing technology is closely related to the increasing requirements for material performance in the electronic information industry. Early copper foil testing relied on offline sampling and was performed using universal material testing machines (such as the ASTM E345 standard), but this was inefficient and unable to provide real-time feedback on production fluctuations. As electronic devices develop towards lighter weight and higher performance, the thickness of copper foil has evolved from micron level to ultra-thin (such as 4.5μm lithium battery copper foil). Its tensile strength (needed to reach 330-380MPa) and elongation (≥3.3%) have become core indicators, driving a surge in demand for online testing technology.

[0022] The current mainstream technical solution is centered on the integrated design of "winding-detection-cutting", covering three major modules: mechanical structure, control logic and data processing.

[0023] 1. Mechanical structure design

[0024] Winding mechanism:

[0025] The system utilizes a circular rotating platform with multiple winding rollers, each station equipped with an independent drive motor and snap-in mechanism. The snap-in rods are made of carbide and hard chrome-plated, with adjustable spacing (6-10mm) to accommodate copper foils of varying thicknesses (5-100μm).

[0026] Testing agency:

[0027] The test fixture is driven by a hydraulic cylinder and features a micro-serrated silicone coating on the gripping surface, with a coefficient of friction of ≥0.8 to prevent slippage. The tension sensor has a range of 0-500N and an accuracy of 0.1N, meeting the requirements for ultra-thin copper foil testing.

[0028] Shearing and pulling:

[0029] The automatic shearing module uses an ultrasonic cutting blade with a diamond-coated blade and a lifespan of 100,000 cuts. After shearing, a pneumatically driven clamp pulls the copper foil to the reel. The pulling force is automatically adjusted using a PID control algorithm to prevent breakage.

[0030] 2. Control logic

[0031] Workstation switching:

[0032] The positioning sensor senses the positioning sensor plate and triggers the rotary drive mechanism. The station switching time is ≤0.5 seconds.

[0033] Tension control:

[0034] The tension buffer mechanism drives the swing-arm tensioner through a servo motor to compensate for tension fluctuations in real time and ensure stable tension in the detection section.

[0035] Data collection:

[0036] The tension sensor and displacement sensor collect data synchronously with a sampling frequency of 1000 Hz. The data is transmitted to the PLC via the CAN bus to achieve closed-loop control.

[0037] 3. Technical Characteristics and Limitations

[0038] Advantages:

[0039] Integrate scrap recycling and online inspection to reduce material waste.

[0040] The detection cycle is short (8-10 seconds / time), suitable for high-speed production lines (30-100m / min).

[0041] Limitations:

[0042] Mechanical clamping may cause local deformation of the copper foil and affect the test results.

[0043] Surface defects (such as scratches and oxidation spots) may cause stress concentration and need to be combined with a visual inspection system to eliminate interference.

[0044] Although existing technologies have achieved efficient online detection, they still face the following bottlenecks:

[0045] 1. Detection accuracy and stability

[0046] Mechanical clamping deformation:

[0047] Traditional fixtures can easily cause irreversible deformation of ultra-thin copper foil (≤12μm), resulting in low tensile strength test values.

[0048] Sensor response speed:

[0049] In a high-speed production environment, sensors need to meet a 1000Hz sampling frequency, but dynamic response lag may cause data distortion.

[0050] 2. Surface defect interference

[0051] Surface defects in copper foil (such as pinholes and copper particles) can cause stress concentration, causing test results to deviate from the true value. For example, a pinhole with a diameter of 0.1 mm can reduce the local tensile strength by 20-30%.

[0052] 3. Environmental adaptability

[0053] Lighting changes:

[0054] Fluctuations in light intensity (500-5000 Lux) at the production site may affect the imaging quality of visual inspection systems (such as CCD cameras).

[0055] Temperature fluctuations:

[0056] Ambient temperature changes (±5°C) may cause thermal expansion of the copper foil, affecting detection accuracy.

[0057] 4. Data processing efficiency

[0058] High-speed production generates massive amounts of data (e.g., 1GWh of lithium battery copper foil generates terabytes of data), requiring optimized algorithms for real-time analysis. Traditional methods (such as Fourier transforms) are computationally complex and struggle to meet real-time requirements.

[0059] To break through existing bottlenecks, technological development presents the following trends:

[0060] 1. Non-contact detection technology

[0061] Laser vision collaborative detection:

[0062] Integrating a laser displacement sensor with an industrial camera enables non-contact deformation monitoring. The laser sensor measures longitudinal deformation, while the camera captures transverse necking. Combined with a binocular vision algorithm, the 3D deformation field is reconstructed to reduce mechanical clamping interference.

[0063] Infrared thermal imaging:

[0064] The temperature distribution of the copper foil is monitored by infrared sensors, and the detection results are corrected in combination with the thermal stress model to improve environmental adaptability.

[0065] 2. Intelligent control

[0066] AI algorithm optimization:

[0067] The LSTM network is introduced to predict quality fluctuations and optimize detection parameters (such as stretching rate and sampling frequency). For example, by training the model with historical data, it can provide an early warning of tension anomalies 0.5 seconds in advance.

[0068] Adaptive Control:

[0069] The detection parameters (such as clamping force and stretching rate) are automatically adjusted according to the copper foil specifications (thickness and width), realizing "one machine with multiple functions".

[0070] 3. Modular design

[0071] Expandable detection modules:

[0072] Reserved interfaces support online testing of multiple parameters such as resistivity and roughness. For example, the bus-based architecture design allows for plug-and-play addition of new modules without modifying the main control program.

[0073] Standardized interface:

[0074] Adopt industrial protocols such as OPC UA and Modbus TCP to achieve seamless integration with MES and ERP systems and improve data utilization.

[0075] 4. Energy saving and environmental protection

[0076] Energy Recovery System:

[0077] The winding mechanism uses a permanent magnet synchronous motor and is equipped with a supercapacitor energy storage module to recycle mechanical energy for the next inspection, reducing energy consumption by more than 30%.

[0078] Lightweight design:

[0079] The detection mechanism is manufactured using carbon fiber composite materials, which reduces weight by 40%, reduces inertia, and improves dynamic response speed.

[0080] Online sampling testing technology for copper foil tensile elongation has evolved from offline to online, and from a single function to multi-parameter integration. Existing technologies, such as circular rotary tables and hydraulically driven testing, achieve efficient and accurate testing, but still face challenges such as mechanical deformation and interference from surface defects. In the future, non-contact testing, intelligent control, and modular design will become key technological breakthroughs, driving the copper foil industry towards higher performance, lower costs, and greater environmental friendliness.

[0081] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0082] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0083] Reference Figure 1-Figure 4 As shown, this embodiment provides an online sampling and detection device for tensile elongation of copper foil, including a connecting box 1, in which a first guide roller 2 and a second guide roller 3 are respectively provided, and a detection mechanism is provided between the first guide roller 2 and the second guide roller 3, and the detection mechanism includes a connecting roller 4 slidably connected to the connecting box 1, and a first chute 5 and a second chute 6 are respectively provided on both sides of the connecting box 1, and the connecting roller 4 is slidably connected to the first chute 5 and the second chute 6 respectively, and a first driving part is provided between the connecting roller 4 and the first chute 5, and a second driving part is provided between the connecting roller 4 and the second chute 6, and the first driving part and the second driving part are respectively fixed to the connecting box 1, and a cutting part is provided on the connecting roller 4, and a detection part is provided in the connecting box 1, and the detection part is located below the cutting part.

[0084] The copper foil is introduced into the connection box 1 via first and second guide rollers 2 and 3. The connection roller 4 in the detection mechanism slides within first and second chutes 5 and 6 to adjust its position. The cutting unit triggers shearing during the copper foil's movement. The sheared sample is automatically received by the detection unit and subjected to a tensile test. This invention enables continuous sampling and testing of the copper foil production line without stopping the machine for sampling, significantly improving detection efficiency and reducing manual intervention.

[0085] A further optimized solution is that the first driving part includes a first connecting plate 7 fixedly connected to the outside of the first slide groove 5, the top surface of the first connecting plate 7 is fixedly connected to the first motor 8, the output shaft of the first motor 8 is fixedly connected to the first screw 9, the end of the connecting roller 4 close to the first slide groove 5 is fixedly connected to the first connecting shaft 10, the first connecting shaft 10 is located in the first slide groove 5, the end of the first connecting shaft 10 away from the connecting roller 4 extends to the outside of the first slide groove 5 and is fixedly connected to the second motor 11, the second motor 11 is slidably connected to the outer wall of the connecting box 1, the second motor 11 is fixedly connected to the second connecting plate 12 away from the side wall of the connecting box 1, and the first screw 9 is threadedly connected to the second connecting plate 12.

[0086] The first motor 8 drives the first lead screw 9 to rotate, driving the second connecting plate 12 to move, so that the second motor 11 pushes the first connecting shaft 10 to slide along the first sliding groove 5, thereby accurately adjusting the horizontal position of the connecting roller 4.

[0087] To further optimize the solution, the second driving part includes a third motor 13 fixedly connected to the top surface of the second slide groove 6, the output shaft of the third motor 13 is fixedly connected to the second lead screw 14, the end of the connecting roller 4 close to the second slide groove 6 is rotatably connected to the second connecting shaft 15, the end of the second connecting shaft 15 away from the connecting roller 4 is rotatably connected to the first slider 16, the first slider 16 is slidably connected in the second slide groove 6, and the second lead screw 14 is threadedly connected to the first slider 16.

[0088] The third motor 13 drives the second lead screw 14 to rotate, driving the first slider 16 to slide in the second slide groove 6 , and adjusting the vertical height of the connecting roller 4 through the second connecting shaft 15 .

[0089] A further optimized solution is that a first groove 17 is provided on the connecting roller 4 , a cutting portion is provided in the first groove 17 , the cutting portion includes a first electric telescopic rod 18 fixedly connected in the first groove 17 , and a cutting knife 20 is fixedly connected to the output end of the first electric telescopic rod 18 .

[0090] The first electric telescopic rod 18 extends in response to the control signal, pushing the cutting knife 20 to pop out from the first groove 17, and horizontally cutting the copper foil passing through to generate a standard sample.

[0091] To further optimize the solution, the detection part includes a first connecting seat 19 fixedly connected to the connecting box 1, the first connecting seat 19 is located below the connecting roller 4, the top surface of the first connecting seat 19 is provided with a second groove 21, and the first connecting seat 19 is provided with a first cavity 22, the first cavity 22 is connected to the second groove 21, the first cavity 22 is provided with an adsorption part, and the second groove 21 is provided with a detection part.

[0092] The sheared sample falls into the second groove 21, where the adsorption element secures it. The detection element then applies tension and measures deformation. This combined adsorption and stretching function allows for automatic sample positioning and testing, avoiding damage caused by manual transfer.

[0093] According to a further optimized solution, the adsorption component includes a second electric telescopic rod 23 fixedly connected to the first cavity 22 , and a vacuum adsorption head 24 is fixedly connected to the top surface of the second electric telescopic rod 23 .

[0094] The second electric telescopic rod 23 adjusts the height of the vacuum adsorption head 24 so that the vacuum adsorption head 24 is in contact with the surface of the sample and then starts negative pressure adsorption.

[0095] According to a further optimized solution, the detection component includes a third electric telescopic rod 25 symmetrically fixed on both sides of the second groove 21 , and an output end of the third electric telescopic rod 25 is fixed with a clamping head 26 , in which a pressure sensor is provided.

[0096] The third electric telescopic rod 25 pushes the clamping head 26 to clamp the two ends of the sample. The pressure sensor monitors the clamping force in real time and calculates the elongation during the stretching process.

[0097] To further optimize the solution, a third guide roller 27 is provided between the first guide roller 2 and the connecting roller 4 . The third guide roller 27 is rotatably connected in the connecting box 1 . The third guide roller 27 is located below the first guide roller 2 and the connecting roller 4 .

[0098] As a further optimization solution, a collecting trough is provided in the first cavity 22. The waste or debris generated by shearing falls into the collecting trough of the first cavity 22 through the second groove 21 and is centrally stored.

[0099] In a further optimized solution, the first guide roller 2, connecting roller 4, and second guide roller 3 are located above the copper foil, while the third guide roller 27 is located below the copper foil. The first guide roller 2, connecting roller 4, and second guide roller 3 exert pressure above the copper foil, while the third guide roller 27 provides support from below, forming a stable transmission path.

[0100] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0101] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. An online sampling detection device for tensile elongation of copper foil, characterized by: The invention comprises a connecting box (1), wherein a first guide roller (2) and a second guide roller (3) are respectively provided in the connecting box (1), a detection mechanism is provided between the first guide roller (2) and the second guide roller (3), the detection mechanism comprises a connecting roller (4) slidably connected to the connecting box (1), a first slide groove (5) and a second slide groove (6) are respectively provided on both sides of the connecting box (1), the connecting roller (4) is slidably connected to the first slide groove (5) and the second slide groove (6), a first driving part is provided between the connecting roller (4) and the first slide groove (5), a second driving part is provided between the connecting roller (4) and the second slide groove (6), the first driving part and the second driving part are respectively fixed to the connecting box (1), a cutting part is provided on the connecting roller (4), a detection part is provided in the connecting box (1), and the detection part is located below the cutting part.

2. The copper foil tensile elongation online sampling detection device according to claim 1, characterized in that: The first driving part includes a first connecting plate (7) fixedly connected to the outside of the first slide groove (5), a first motor (8) is fixedly connected to the top surface of the first connecting plate (7), an output shaft of the first motor (8) is fixedly connected to a first lead screw (9), an end of the connecting roller (4) close to the first slide groove (5) is fixedly connected to a first connecting shaft (10), the first connecting shaft (10) is located in the first slide groove (5), an end of the first connecting shaft (10) away from the connecting roller (4) extends to the outside of the first slide groove (5) and is fixedly connected to a second motor (11), the second motor (11) is slidably connected to the outer wall of the connecting box (1), the second motor (11) is fixedly connected to the second connecting plate (12) away from the side wall of the connecting box (1), and the first lead screw (9) is threadedly connected to the second connecting plate (12).

3. The on-line sampling detection device for tensile elongation of copper foil according to claim 1, characterized in that: The second driving part includes a third motor (13) fixedly connected to the top surface of the second slide groove (6), the output shaft of the third motor (13) is fixedly connected to the second lead screw (14), the end of the connecting roller (4) close to the second slide groove (6) is rotatably connected to the second connecting shaft (15), the end of the second connecting shaft (15) away from the connecting roller (4) is rotatably connected to the first slider (16), the first slider (16) is slidably connected in the second slide groove (6), and the second lead screw (14) is threadedly connected to the first slider (16).

4. The on-line sampling detection device for tensile elongation of copper foil according to claim 1, characterized in that: The connecting roller (4) is provided with a first groove (17), the cutting portion is provided in the first groove (17), the cutting portion comprises a first electric telescopic rod (18) fixedly connected in the first groove (17), and a cutting knife (20) is fixedly connected to the output end of the first electric telescopic rod (18).

5. The on-line sampling detection device for tensile elongation of copper foil according to claim 4, characterized in that: The detection portion includes a first connection seat (19) fixedly connected to the connection box (1), the first connection seat (19) is located below the connection roller (4), a second groove (21) is provided on the top surface of the first connection seat (19), a first cavity (22) is provided in the first connection seat (19), the first cavity (22) is communicated with the second groove (21), an adsorption component is provided in the first cavity (22), and a detection component is provided in the second groove (21).

6. The on-line sampling detection device for tensile elongation of copper foil according to claim 5, characterized in that: The adsorption component comprises a second electric telescopic rod (23) fixedly connected in the first cavity (22), and a vacuum adsorption head (24) is fixedly connected to the top surface of the second electric telescopic rod (23).

7. The on-line sampling detection device for tensile elongation of copper foil according to claim 5, characterized in that: The detection component comprises a third electric telescopic rod (25) symmetrically fixed on both sides of the second groove (21); an output end of the third electric telescopic rod (25) is fixedly connected to a clamping head (26); and a pressure sensor is provided in the clamping head (26).

8. The on-line sampling detection device for tensile elongation of copper foil according to claim 1, characterized in that: A third guide roller (27) is provided between the first guide roller (2) and the connecting roller (4); the third guide roller (27) is rotatably connected in the connecting box (1); and the third guide roller (27) is located below the first guide roller (2) and the connecting roller (4).

9. The on-line sampling detection device for tensile elongation of copper foil according to claim 5, characterized in that: A collecting tank is provided in the first cavity (22).

10. The on-line sampling detection device for tensile elongation of copper foil according to claim 8, characterized in that: The first guide roller (2), the connecting roller (4) and the second guide roller (3) are respectively located above the copper foil, and the third guide roller (27) is located below the copper foil.

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