Flexible calorimetric vector flow rate sensor and method of making same

Abstract

The application discloses a flexible calorimetric vector flow velocity sensor and relates to the technical field of flow velocity sensors.The flexible calorimetric vector flow velocity sensor comprises a flexible substrate, a signal transmission assembly and a temperature measurement assembly, a groove communicating with the outside is arranged on one side surface of the flexible substrate, the signal transmission assembly is fixedly arranged on the flexible substrate, the temperature measurement assembly is fixedly arranged on the open side of the groove, and a gap is formed between the temperature measurement assembly and the bottom wall of the groove; the temperature measurement assembly is connected with the signal transmission assembly and is electrically connected to a processing circuit through the signal transmission assembly; and the temperature measurement assembly is used for changing temperature under the action of a flow field and causing resistance change of the processing circuit. The flexible calorimetric vector flow velocity sensor can improve the sensitivity of flow velocity sensing. The application further provides a preparation method of the flexible calorimetric vector flow velocity sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flow rate sensor, in particular to a flexible calorimetric vector flow rate sensor and a preparation method thereof. BACKGROUND

[0002] Air flow velocity is an important flow field parameter, and the accurate perception of air flow velocity vector is of great significance in many fields such as environmental monitoring, air flow regulation, unmanned aerial vehicle flight control, etc. With the development of industry, many small devices such as portable airspeed meters and micro unmanned aerial vehicles have higher requirements for accurate detection of flow velocity vector. Traditional flow rate measurement techniques such as paddle type anemometer, ultrasonic anemometer and pitot tube are difficult to be flexibly installed on small devices due to their large size and non-flexibility. Therefore, thermal flow rate sensors based on MEMS technology have become the mainstream of flow rate sensor research in recent years due to their small size, high stability, portability, high sensitivity and good product consistency. For example, a flexible MEMS flow rate sensor based on self-heating amorphous germanium thermal resistance is provided in patent CN112730945A. The flow rate is measured by measuring the change of the temperature of the suspended membrane temperature measuring thermal resistance located above the heat insulation cavity and the change of the flow rate. However, in the use process of the flow rate sensor, the fluid can only flow through the outer surface of the insulating protective layer, i.e. the flow rate sensitive surface, to realize heat exchange with the temperature measuring thermal resistance, and the heat exchange effect is poor, which affects the sensitivity of flow rate perception. SUMMARY

[0003] The purpose of the present application is to provide a flexible calorimetric vector flow rate sensor and a preparation method thereof to solve the problems existing in the prior art and improve the sensitivity of flow rate perception.

[0004] To achieve the above-mentioned purpose, the present application provides the following solutions.

[0005] The present application provides a flexible calorimetric vector flow rate sensor, which comprises a flexible substrate, a signal transmission assembly and a temperature measuring assembly. The flexible substrate is provided with a groove communicating with the outside on one side. The signal transmission assembly is fixedly arranged on the flexible substrate. The temperature measuring assembly is fixedly arranged on the open side of the groove, and there is a gap between the temperature measuring assembly and the bottom wall of the groove. The temperature measuring assembly is connected with the signal transmission assembly and is electrically connected to a processing circuit through the signal transmission assembly. The temperature measuring assembly is used to change temperature under the action of flow field and cause resistance change of the processing circuit.

[0006] Preferably, the temperature measuring component includes a heating element and a plurality of temperature-sensing resistor elements arranged around the heating element. The heating element and each of the temperature-sensing resistor elements are fixedly disposed on the open side of the groove, and each has a gap between itself and the bottom wall of the groove. The heating element is connected to the signal transmission component and is used to be electrically connected to an external circuit through the signal transmission component to heat the surrounding fluid. Each of the temperature-sensing resistor elements is connected to the signal transmission component and is used to be electrically connected to the processing circuit through the signal transmission component. Each temperature-sensing resistor element is used to undergo temperature changes and resistance changes due to heat exchange with the fluid heated by the heating element under the action of the flow field.

[0007] Preferably, the flexible substrate includes a flexible circuit board and a flexible film fixedly covered on one side of the flexible circuit board, the signal transmission component is fixedly disposed on the flexible film, and the temperature measuring component is disposed on the open side of the groove and fixedly connected to the flexible film.

[0008] Preferably, the groove includes a first groove and a second groove arranged in a cross pattern, and the heating component is disposed at the intersection of the first groove and the second groove; two temperature-sensing resistors are fixedly disposed on the open side of the first groove, respectively located on both sides of the heating component, and two temperature-sensing resistors are fixedly disposed on the open side of the second groove, respectively located on both sides of the heating component.

[0009] Preferably, the first groove and the second groove are perpendicular to each other, and the aspect ratio of the first groove and the second groove is greater than 5; the plurality of temperature sensing resistors are symmetrically distributed about the center of the heating element.

[0010] Preferably, each of the temperature-sensing resistors is a vanadium oxide semiconductor, and the heating element is made of metal.

[0011] Preferably, the signal transmission component includes a plurality of signal wires and pads fixedly disposed on the flexible substrate, the heating component is connected to one end of two of the signal wires, each of the temperature sensing resistors is connected to one end of two of the signal wires, and one end of each of the signal wires is connected to a pad.

[0012] Preferably, it further includes a waterproof protective layer, which covers the exposed portions of the flexible substrate, the signal transmission component, and the temperature measurement component.

[0013] The present invention also provides a method for fabricating the above-mentioned flexible calorimetric vector flow sensor, comprising processing a signal transmission component and a temperature measurement component on a flexible substrate, connecting the temperature measurement component to the signal transmission component; processing a groove on the flexible substrate, fixing the temperature measurement component to the open side of the groove, and creating a gap between the temperature measurement component and the bottom wall of the groove.

[0014] Preferably, the method further includes the steps of: curing a flexible thin film on the flexible circuit board to form the flexible substrate; and processing the signal transmission component and the temperature measuring component on the surface of the flexible thin film; first, opening a window in the flexible thin film, and then etching the copper layer of the flexible circuit board to form the groove.

[0015] The present invention achieves the following technical effects compared to the prior art:

[0016] The flexible calorimetric vector flow velocity sensor provided by this invention is configured with a flexible substrate. Its flexibility meets the requirements for lightweight and curved surface flow velocity sensing. The temperature sensing component undergoes temperature changes under the influence of the flow field, causing a change in the resistance of the connected processing circuit. The processing circuit then senses the resistance change through a signal transmission component and processes it to obtain the current temperature change of the temperature sensing component, thereby obtaining fluid information such as flow velocity. Furthermore, a groove communicating with the outside is provided on the flexible substrate, and the temperature sensing component is positioned on the open side of the groove. A gap exists between the temperature sensing component and the bottom wall of the groove. When the fluid moves, it can enter the groove and flow through the gap between the temperature sensing component and the groove. The fluid can also flow through the open side of the groove and contact the temperature sensing component. Therefore, the fluid can contact multiple sides of the temperature sensing component. Compared to the method of setting up a heat-insulating cavity, this increases the heat exchange area between the fluid and the temperature sensing component, thereby enhancing convective heat transfer, improving temperature response, and increasing the sensitivity of flow velocity sensing.

[0017] The method for fabricating a flexible calorimetric vector flow velocity sensor provided by this invention involves processing a groove on a flexible substrate and fixing a temperature sensing component to the open side of the groove, with a gap between the component and the bottom wall of the groove. When fluid moves, the fluid can enter the groove and flow through the gap between the temperature sensing component and the groove. The fluid can also flow through the open side of the groove and contact the temperature sensing component. Therefore, the fluid can contact multiple sides of the temperature sensing component. Compared with the setting of heat-insulating cavities and solid structures, this method can increase the heat exchange area between the fluid and the temperature sensing component, thereby enhancing convective heat transfer, improving temperature response, and increasing the sensitivity of flow velocity sensing. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A schematic diagram of the isometric structure of the flexible calorimetric vector flow sensor provided in Embodiment 1;

[0020] Figure 2 for Figure 1 A top view of the provided flexible calorimetric vector flow sensor;

[0021] Figure 3 for Figure 2 Schematic diagram of the cross section at point AA;

[0022] Figure 4 for Figure 2 A schematic diagram of the cross-section at point AA after the waterproof protective layer has been applied;

[0023] Figure 5 A schematic diagram comparing the flow velocity-temperature difference of the flexible calorimetric vector flow velocity sensor provided in Example 1 with flow velocity sensors with heat-insulated cavity structure and solid structure.

[0024] Figure 6 This is a schematic flowchart of the preparation method provided in Example 2.

[0025] Icons: 1-Flexible calorimetric vector flow sensor; 10-Flexible substrate; 11-Flexible circuit board; 12-Flexible film; 20-Groove; 21-First groove; 22-Second groove; 30-Signal transmission component; 31-Signal wire; 32-Pad; 40-Temperature measuring component; 41-Heating component; 42-Temperature sensing resistor component; 50-Waterproof protective layer. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] The purpose of this invention is to provide a flexible calorimetric vector flow velocity sensor and its fabrication method, so as to solve the problems existing in the prior art and improve the sensitivity of flow velocity sensing.

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Example 1

[0030] This embodiment provides a flexible calorimetric vector flow sensor 1. Please refer to [link to relevant documentation]. Figures 1-3 The system includes a flexible substrate 10, a signal transmission component 30, and a temperature measuring component 40. A groove 20 communicating with the outside is provided on one side of the flexible substrate 10. The signal transmission component 30 is fixedly disposed on the flexible substrate 10. The temperature measuring component 40 is fixedly disposed on the open side of the groove 20, and there is a gap between the temperature measuring component 40 and the bottom wall of the groove 20. The temperature measuring component 40 is connected to the signal transmission component 30 and is used to be electrically connected to the processing circuit through the signal transmission component 30. The temperature measuring component 40 is used to cause a temperature change under the action of the flow field and cause a change in the resistance connected to the processing circuit.

[0031] The substrate 10 is designed as a flexible substrate, which meets the requirements of lightweight design and curved surface flow velocity sensing. The temperature sensing component 40 can change temperature under the action of the flow field, causing a change in resistance of the circuit connected to the processing circuit. The processing circuit senses the resistance change through the signal transmission component 30 and processes it to obtain the current temperature change of the temperature sensing component 40, thereby obtaining fluid information such as flow velocity. In addition, a groove 20 connected to the outside is provided on the flexible substrate 10, and the temperature sensing component 40 is placed on the open side of the groove 20. There is a gap between the temperature sensing component 40 and the bottom wall of the groove 20. When the fluid moves, the fluid can enter the groove 20 and flow through the gap between the temperature sensing component 40 and the groove 20. The fluid can also flow through the open side of the groove 20 and come into contact with the temperature sensing component 40. Therefore, the fluid can come into contact with multiple sides of the temperature sensing component 40. Compared with the setting of heat insulation cavity and solid structure, this can increase the heat exchange area between the fluid and the temperature sensing component 40, thereby enhancing convective heat transfer, improving temperature response, and improving the sensitivity of flow velocity sensing.

[0032] In the optional solutions of this embodiment, a more preferred option is described in the following description: Figure 2The temperature sensing component 40 includes a heating component 41 and a plurality of temperature-sensing resistor components 42 arranged around the heating component 41. The heating component 41 and each temperature-sensing resistor component 42 are fixedly arranged on the open side of the groove 20, and there is a gap between them and the bottom wall of the groove 20. The plurality of temperature-sensing resistor components 42 can sense the flow velocity and direction of the fluid in different directions. The heating component 41 is connected to the signal transmission component 30 and is used to be electrically connected to an external circuit through the signal transmission component 30 to heat the surrounding fluid. Each temperature-sensing resistor component 42 is connected to the signal transmission component 30 and is used to be electrically connected to a processing circuit through the signal transmission component 30. Each temperature-sensing resistor component 42 is used to exchange heat with the fluid heated by the heating component 41 under the action of the flow field, resulting in a temperature change and a change in resistance.

[0033] Specifically, the heat generated by the heating element 41 heats the surrounding fluid. If an airflow blows across the sensor surface, the hot fluid will flow downstream with the airflow, causing a temperature difference between the temperature sensing resistors 42 on both sides of the heating element 41 in the flow direction. Consequently, the resistance values ​​of the temperature sensing resistors 42 on both sides change. By acquiring the output signal of the temperature sensing resistors 42, the temperature difference between the temperature sensing resistors 42 on both sides of the heating element 41 in the flow direction can be obtained, and thus the flow velocity information in that direction can be obtained.

[0034] More preferably, each temperature-sensing resistor component 42 is configured as a vanadium oxide semiconductor, which has a very high temperature coefficient of resistance. Its resistance change is very sensitive to temperature, which is beneficial to improving the sensitivity of the sensor.

[0035] In the optional embodiments of this example, more preferably, the flexible substrate 10 includes a flexible circuit board 11 and a flexible film 12 fixedly covered on one side of the flexible circuit board 11. The signal transmission component 30 is fixedly disposed on the flexible film 12, and the temperature measuring component 40 is disposed on the open side of the groove 20 and fixedly connected to the flexible film 12. Specifically, when the flexible film 12 forms the groove 20, it can retain a portion to support and fix the temperature measuring component 40, thereby realizing the fixation of the temperature measuring component 40. Moreover, the signal transmission component 30 is designed according to the wiring specifications of the flexible circuit board 11, which facilitates electrical integration and improves circuit stability.

[0036] In a preferred embodiment, the groove 20 includes a first groove 21 and a second groove 22 arranged in a cross configuration, with the heating component 41 disposed at the intersection of the first groove 21 and the second groove 22. Two temperature-sensing resistors 42 are fixedly disposed on the open side of the first groove 21, respectively located on both sides of the heating component 41, and two temperature-sensing resistors 42 are fixedly disposed on the open side of the second groove 22, respectively located on both sides of the heating component 41. Specifically, the first groove 21 and the second groove 22 are perpendicular to each other, and the plurality of temperature-sensing resistors 42 are symmetrically distributed about the center of the heating component 41. With the length direction of the first groove 21 as the transverse direction and the length direction of the second groove 22 as the longitudinal direction, the heating component... The heat generated by component 41 is transferred to the air to heat the fluid. If an airflow blows laterally across the sensor surface, the hot fluid will flow downstream with the wind, causing a temperature difference in the fluid at the positions of the two temperature-sensing resistor components 42 in the lateral direction. This, in turn, causes a change in the resistance value of the two temperature-sensing resistor components 42. By acquiring the output signals of the two temperature-sensing resistor components 42, the temperature difference can be obtained, and thus the lateral wind speed information can be obtained. Similarly, when the airflow blows longitudinally across the sensor surface, the temperature difference can be obtained by acquiring the output signals of the two temperature-sensing resistor components 42 in the longitudinal direction, and thus the longitudinal wind speed information can be obtained. By simultaneously acquiring the lateral and longitudinal temperature difference information, the current flow velocity and direction can be obtained.

[0037] More preferably, the aspect ratio of the first groove 21 and the second groove 22 is greater than 5. The first groove 21 and the second groove 22 can guide the fluid to prevent the fluid temperature from spreading to the surroundings, effectively reduce the heat dissipation inside the sensor, enhance convective heat transfer, and thus improve the sensor sensitivity.

[0038] Further preferred, please refer to Figure 5 The suspended structure temperature measuring component 40 of the flexible calorimetric vector flow sensor 1 provided in this embodiment, compared with flow sensors with a heat-insulating cavity structure (i.e., the groove 20 is closed, and fluid cannot enter the groove 20) and a solid structure (the flexible substrate 10 is a solid structure, and the temperature measuring component 40 is directly disposed on the flexible substrate 10), under the same conditions, the suspended structure ( Figure 5 The temperature difference between the temperature sensing resistors 42 on both sides of the heating component 41 (as shown by the uppermost curve) and the temperature difference between the insulation cavity structure ( Figure 5 The highest values ​​are shown in the middle curve (as shown in the middle curve) and the solid structure (as shown in the lower curve in 5), indicating that under the condition of using the same temperature sensing component 40, the suspended structure temperature sensing component 40 provided in this embodiment has the greatest flow rate sensing sensitivity.

[0039] In an optional embodiment, more preferably, the signal transmission component 30 includes a plurality of signal wires 31 and pads 32 fixedly disposed on the flexible substrate 10. The heating component 41 is connected to one end of two signal wires 31, and each temperature sensing resistor component 42 is connected to one end of two signal wires 31. Each signal wire 31 is connected to a pad 32 at one end. Specifically, the materials of the heating component 41, signal wires 31 and pads 32 are metals, including but not limited to: chromium (Cr), copper (Cu) or gold (Au).

[0040] In the optional solutions of this embodiment, a more preferred option is described in the following description: Figure 5 The flexible calorimetric vector flow sensor 1 provided in this embodiment also includes a waterproof protective layer 50. The waterproof protective layer 50 is applied to the exposed parts of the flexible substrate 10, the signal transmission component 30 and the temperature measuring component 40, and can be used for underwater flow velocity measurement. The waterproof protective layer 50 serves to protect the temperature measuring component 40, the signal transmission component 30 and the flexible substrate 10.

[0041] Example 2

[0042] This embodiment provides a method for fabricating a flexible calorimetric vector flow sensor 1 as provided in Embodiment 1, including the following steps: processing a signal transmission component 30 and a temperature sensing component 40 on a flexible substrate 10, connecting the temperature sensing component 40 to the signal transmission component 30; processing a groove 20 on the flexible substrate 10, fixing the temperature sensing component 40 within the groove 20, and creating a gap between the temperature sensing component 40 and the bottom wall of the groove 20; by processing the groove 20 on the flexible substrate 10 and fixing the temperature sensing component 40 on the open side of the groove 20, creating a gap between the temperature sensing component 40 and the bottom wall of the groove 20, when fluid moves, the fluid can enter the groove 20 and flow through the gap between the temperature sensing component 40 and the groove 20, and the fluid can also flow from the open side of the groove 20 to contact the temperature sensing component 40. Therefore, the fluid can contact multiple sides of the temperature sensing component 40. Compared with the arrangement of heat-insulating cavities and solid structures, this method can increase the heat exchange area between the fluid and the temperature sensing component 40, thereby enhancing convective heat transfer, improving temperature response, and increasing the sensitivity of flow velocity sensing.

[0043] Further preferred, please refer to Figure 6 The specific steps of the preparation method include:

[0044] S1: A flexible thin film 12 is pre-cured on the flexible circuit board 11 to form a flexible substrate 10, such as... Figure 6 As shown in a;

[0045] S2: Heating components 41, signal wires 31, and pads 32 are formed on the surface of the flexible thin film 12 using methods such as photolithography and sputtering. Figure 6As shown in b, the heating component 41, signal wire 31 and solder pad 32 are made of the same metal material and are manufactured at the same time, which simplifies the manufacturing process.

[0046] S3: The temperature-sensing resistor component 42 is formed using methods such as photolithography, sputtering, and annealing, for example... Figure 6 As shown in c;

[0047] S4: A window for a groove 20 is formed on the flexible thin film 12 using methods such as photolithography and etching, for example... Figure 6 As shown in d;

[0048] S5: The copper layer of the flexible circuit board 11 is etched using a wet etching method to form a groove 20, as shown in the figure. Figure 6 As shown in e.

[0049] The process is simple, and the processing methods used are all conventional MEMS processing techniques, which do not involve complex structures, thus helping to improve sensor lifespan and enhance consistency.

[0050] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A flexible calorimetric vector velocity sensor, characterized in that: include: A flexible substrate (10) has a groove (20) on one side surface that communicates with the outside world. The signal transmission component (30) is fixedly disposed on the flexible substrate (10); and A temperature measuring component (40) is fixedly disposed on the surface of the flexible substrate (10) and placed on the open side of the groove (20), and there is a gap between the temperature measuring component (40) and the bottom wall of the groove (20); fluid can enter the groove (20) and flow through the gap between the temperature measuring component (40) and the groove (20), and the fluid can also flow from the open side of the groove (20) and contact the temperature measuring component (40), so that the fluid can contact multiple sides of the temperature measuring component (40); the temperature measuring component (40) is connected to the signal transmission component (30) and is used to be electrically connected to the processing circuit through the signal transmission component (30); the temperature measuring component (40) is used to cause temperature change under the action of the flow field and cause resistance change connected to the processing circuit.

2. The flexible calorimetric vector velocity sensor according to claim 1, characterized in that: The temperature measuring component (40) includes a heating component (41) and a plurality of temperature-sensing resistor components (42) arranged around the heating component (41). The heating component (41) and each of the temperature-sensing resistor components (42) are fixedly arranged on the open side of the groove (20) and have the gap between them and the bottom wall of the groove (20). The heating component (41) is connected to the signal transmission component (30) and is used to be electrically connected to an external circuit through the signal transmission component (30) to heat the surrounding fluid. Each of the temperature-sensing resistor components (42) is connected to the signal transmission component (30) and is used to be electrically connected to the processing circuit through the signal transmission component (30). Each of the temperature-sensing resistor components (42) is used to exchange heat with the fluid heated by the heating component (41) under the action of the flow field, causing a temperature change and a resistance change.

3. The flexible calorimetric vector velocity sensor according to claim 1, characterized in that: The flexible substrate (10) includes a flexible circuit board (11) and a flexible film (12) fixedly covered on one side of the flexible circuit board (11). The signal transmission component (30) is fixedly disposed on the flexible film (12), and the temperature measuring component (40) is disposed on the open side of the groove (20) and fixedly connected to the flexible film (12).

4. The flexible calorimetric vector velocity sensor according to claim 2, characterized in that: The groove (20) includes a first groove (21) and a second groove (22) arranged in a cross pattern. The heating element (41) is disposed at the intersection of the first groove (21) and the second groove (22). Two temperature-sensing resistors (42) are fixedly disposed on the open side of the first groove (21) and respectively located on both sides of the heating element (41). Two temperature-sensing resistors (42) are fixedly disposed on the open side of the second groove (22) and respectively located on both sides of the heating element (41).

5. The flexible calorimetric vector velocity sensor according to claim 4, characterized in that: The first groove (21) and the second groove (22) are perpendicular to each other, and the aspect ratio of the first groove (21) and the second groove (22) is greater than 5; the multiple temperature-sensing resistor components (42) are symmetrically distributed about the heating component (41).

6. The flexible calorimetric vector velocity sensor according to claim 2, characterized in that: Each of the temperature-sensing resistor components (42) is configured as vanadium oxide semiconductor, and the heating component (41) is configured as a metal material.

7. The flexible calorimetric vector velocity sensor according to claim 2, characterized in that: The signal transmission component (30) includes multiple signal wires (31) and pads (32) fixedly disposed on the flexible substrate (10). The heating component (41) is connected to one end of two of the signal wires (31), and each of the temperature sensing resistors (42) is connected to one end of two of the signal wires (31). Each of the signal wires (31) is connected to one of the pads (32).

8. The flexible calorimetric vector velocity sensor according to claim 1, characterized in that: It also includes a waterproof protective layer (50) that covers the exposed portions of the flexible substrate (10), the signal transmission component (30), and the temperature measuring component (40).

9. A method for fabricating a flexible calorimetric vector flow sensor as described in any one of claims 1-8, characterized in that: Including the following steps: A signal transmission component (30) and a temperature measurement component (40) are fabricated on a flexible substrate (10), and the temperature measurement component (40) is connected to the signal transmission component (30). A groove (20) is processed on the flexible substrate (10) so that the temperature measuring component (40) is fixedly disposed on the open side of the groove (20) and there is a gap between the temperature measuring component (40) and the bottom wall of the groove (20).

10. The preparation method according to claim 9, characterized in that: It also includes the step of: curing a flexible film (12) on the flexible circuit board (11) to form the flexible substrate (10). The signal transmission component (30) and the temperature measuring component (40) are processed on the surface of the flexible film (12). First, a window is made in the flexible film (12), and then the copper layer of the flexible circuit board (11) is etched to form the groove (20).

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