Electret microphone back plate film coating device and film coating method

Abstract

The application belongs to the technical field of microphones and relates to a back plate film coating device and a film coating method for an electret microphone. The back plate film coating device comprises a film tension ring for continuously fixing an electret film with a certain tension; a back plate jig located below the film tension ring for mounting a back plate; a lifting platform located below the back plate jig for carrying the back plate jig and controlling the lifting of the back plate jig, and the maximum height that the back plate jig can reach is higher than the plane where the electret film fixed by the film tension ring is located; and a hot pressing component located above the film tension ring for implementing hot pressing to coat the electret film on the back plate. The application fixes the electret film through the film tension ring, continuously fixes the electret film with a certain tension, guarantees the film coating tension, and reduces the adverse effects of high-temperature hot pressing on the film coating effect.

Description

Technical Field

[0001] This invention belongs to the field of microphone technology, especially the preparation of electret condensers for the rear electrode plate, and particularly relates to a coating device and coating method for the rear electrode plate of an electret microphone. Background Technology

[0002] An electret microphone is a capacitive microphone based on electret materials. Its core principle is to utilize the permanent polarization properties of electret materials to achieve sound-to-electricity conversion without the need for an external polarization voltage. After being treated with a high-voltage electric field, the electret material (such as polytetrafluoroethylene) acquires a permanent electric charge on its surface, forming a fixed electric field. When sound waves cause the diaphragm to vibrate, the capacitance between the diaphragm and the back electrode changes accordingly, generating an alternating voltage signal synchronized with the sound waves.

[0003] In the manufacturing process of electret microphones, one step is to cover the upper surface of the rear electrode plate with an electret film, thereby forming a capacitor with the diaphragm.

[0004] The following is a partial disclosure of research on the preparation of electret thin films on the back electrode plate in the prior art.

[0005] CN116437278A discloses a method for attaching an FEP film to the rear electrode plate of an electret microphone and the electret microphone itself. The method includes corona treatment of the FEP film to be attached to the rear electrode plate; coating the rear electrode plate with a silica dispersion and baking it; contacting and attaching the FEP film to the rear electrode plate; performing a vacuum process to remove air bubbles between the FEP film and the rear electrode plate; placing it in an oven for heating; when the temperature reaches a set temperature, introducing compressed air to pressurize the molten FEP film and blow away the portion of the FEP film covering the damping holes of the rear electrode plate; stopping the compressed air supply; maintaining the temperature for a period of time; and allowing it to cool naturally to room temperature, thus completing the attachment of the electret microphone.

[0006] Invention CN115678360B discloses a method for preparing a composite electret and the resulting composite electret. This method involves forming two polymer layers on an electrode plate. The first layer is formed by high-temperature film deposition of a dispersion, with inorganic nanoparticles added to the dispersion. The second layer is formed by directly coating the first layer with a thin film. This method reduces the decomposition of the electret polymer, and the addition of inorganic nanoparticles to the first polymer dispersion significantly improves the charge performance of the electret. It also greatly simplifies the production process, achieving process stability and energy conservation and emission reduction.

[0007] In the preparation of the electret film on the rear electrode plate of the microphone, as described in the above patents, quality defects such as stripes, wrinkles, and bubbles often appear after the electret film is coated on the rear electrode plate. Summary of the Invention

[0008] This invention provides a coating device and method for the rear electrode plate of an electret microphone, which eliminates defects such as stripes, wrinkles, and bubbles in the electret film after coating, thereby achieving surface smoothness and production yield of the electret film in the electret microphone.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a rear electrode coating device for an electret microphone, comprising:

[0011] Thin film tensioning ring, used to continuously fix electret thin films under a certain tension;

[0012] A rear electrode plate fixture, located below the film tensioning ring, is used to install the rear electrode plate to be coated;

[0013] A lifting platform is located below the rear electrode plate fixture, used to support the rear electrode plate fixture and control the lifting of the rear electrode plate fixture. The maximum height that the rear electrode plate fixture can reach is higher than the plane where the film tensioning ring fixes the electret film.

[0014] A hot-pressing component, located above the film tensioning ring, is used to perform hot pressing to cover the electret film onto the rear electrode plate.

[0015] In existing technologies, electret thin films often exhibit quality defects such as streaks, wrinkles, and bubbles after being coated onto a back electrode. The reason for this is likely that current methods mostly involve directly coating the electret film onto the back electrode. However, electret films, such as FEP, PFA, and PTFE, typically require temperatures exceeding 280°C during the fusion bonding process with the back electrode. Normally, in the 100°C-200°C range, the electret film expands due to thermal expansion and contraction. Subsequently, as the temperature continues to rise, when the electret material approaches its melting point (e.g., FEP, 260°C), the crystalline regions of FEP begin to melt, disrupting the originally ordered crystal lattice structure and causing the molecular chains to change from a tightly packed state to a disordered state. This phase transition releases internal stress, leading to volume shrinkage.

[0016] In addition, the flatness error of the heating plate makes it difficult for the heating plate to completely flatten the 10-30 micrometer thick electret film; therefore, there will always be some space between the electret film and the heating plate, resulting in defects such as stripes, wrinkles, and bubbles after the electret film is coated on the back electrode plate.

[0017] In the above-described scheme of the present invention, the electret film is initially tensioned using a film tensioning ring. Then, a lifting platform is used to raise the rear electrode plate fixture, bringing the rear electrode plate into contact with the electret film and lifting it up. At this point, the film on the surface of the rear electrode plate is under tension. The electret film in this tensioned state has high flatness. Furthermore, when the electret film expands due to heat, the tension force exerted by the rear electrode plate on the electret film still helps maintain a continuously tensioned and flat state.

[0018] Preferably, the film tensioning ring includes a support ring and a clamping ring, and the electret film is clamped between the support ring and the clamping ring.

[0019] Preferably, the clamping ring and the support ring are arranged vertically, and the support ring and the clamping ring are locked or unlocked by a locking member.

[0020] Preferably, the support ring and the clamping ring are arranged inside and outside each other, and the clamping ring located on the outer side is locked or opened by a locking member.

[0021] Preferably, the film tensioning ring is installed via a tensioning ring positioning frame.

[0022] Preferably, the tension ring positioning frame includes a main body that forms an internal storage space, an opening at the top of the storage space, and tension ring positioning grooves for positioning the film tension ring on both sides of the main body. The lifting platform and the rear electrode plate fixture are placed in the storage space.

[0023] Preferably, the rear electrode coating device further includes a heat equalization buffer component, through which a heat equalization buffer film can be laid below the hot pressing component and above the film tensioning ring.

[0024] In this solution, a heat-spreading buffer film is added below the hot-pressing component and above the film tensioning ring. The heat-spreading buffer film uses a low thermal conductivity film material, such as a PI film (thermal conductivity approximately 0.2 W / m·K), to delay the instantaneous heat transfer from the hot-pressing plate to the film, preventing localized overheating and decomposition of the electret film (such as PTFE). This allows heat to penetrate evenly through the heat-spreading buffer film, reducing micro-wrinkles caused by thermal stress concentration. Simultaneously, the heat-spreading buffer film also forms a flexible transition layer between the hot-pressing component and the electret film, converting localized pressure points on the hot-pressing component into a uniformly distributed load, eliminating film depressions caused by micro-pits on the rear electrode surface. Furthermore, the heat-spreading buffer film also prevents adhesion between the electret film and the hot-pressing component. In summary, adding a heat-spreading buffer film to the rear electrode coating device further improves the flatness of the coating.

[0025] Preferably, the heat-spreading buffer component includes a feeding roller and a receiving roller, with the receiving roller driven to rotate by a drive structure. During the lamination process, the receiving roller rotates once after each lamination to roll up the used heat-spreading buffer film onto the receiving roller for replacement with new heat-spreading buffer film.

[0026] Secondly, the present invention provides a method for coating the rear electrode plate of an electret microphone, based on the coating device described above.

[0027] Specifically, the rear electrode coating method includes the following steps:

[0028] S1. Place the rear electrode plate neatly into the rear electrode plate fixture, and then place it on the platform of the lifting platform.

[0029] S2. Secure the electret film using a film tensioning ring;

[0030] S3. Place the film tensioning ring, which has been fixed to the electret film, into the tensioning ring positioning frame.

[0031] S4. Raise the rear electrode plate on the lifting platform until it contacts the electret film and lifts the electret film. At this time, the electret film is under tension in all directions.

[0032] S5. Press the hot-pressing component down to contact the electret film, and continue heating the electret film until the electret film begins to melt and bond with the back electrode plate.

[0033] S6. After hot pressing is completed, open the hot pressing table, wait for the rear electrode plate to cool down, remove the rear electrode plate and cut off the excess electret film at the edge of the rear electrode plate.

[0034] Preferably, in step S4, the electret film is lifted to a height of 5-10 mm. Here, the height refers to the height above the plane where the electret film is fixed by the film tensioning ring.

[0035] Preferably, after step S4, a heat-spreading buffer film, such as a PI film, is laid on the upper surface of the electret film. This further improves the flatness of the coating and prevents the electret film from sticking to the heating plate of the hot press during hot pressing.

[0036] Before fixing, the electret film is cut to the specified size, such as 100mm*10mm. Electret films such as FEP, PFA, PTFE and other films are cut to the specified size.

[0037] By implementing the above technical solution, compared with the prior art, the present invention has the following beneficial effects:

[0038] 1. The present invention fixes the electret film with a film tensioning ring, and continuously fixes the electret film with a certain tension to ensure the coating tension, so as to reduce the adverse effects of high temperature hot pressing on the coating effect.

[0039] 2. Based on the film tensioning ring, the rear electrode plate is raised by the lifting platform to lift the electret film, so that the electret film is in a tensioned state in all directions. The film is then coated in this state to further eliminate defects such as stripes, wrinkles, and bubbles in the coated electret film.

[0040] 3. The present invention adds a heat-spreading buffer film below the hot-pressing component and above the film tensioning ring by means of a heat-spreading buffer component, which can not only prevent the electret film from sticking to the hot-pressing component, but also further improve the flatness of the coating.

[0041] 4. This invention utilizes a tension ring positioning frame to rationally integrate the various parts of the device, making the device more compact, occupying less space, and facilitating more convenient and efficient film coating operations.

[0042] 5. By controlling the rising height of the rear electrode fixture and the hot pressing conditions during the coating process, the coating quality can be further guaranteed. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the structure of the rear electrode plate coating device shown in this invention;

[0044] Figure 2 This is a schematic diagram of the structure of a thin film tensioning ring according to one embodiment of the present invention;

[0045] Figure 3 This is a schematic diagram of the structure of a thin film tensioning ring according to another embodiment of the present invention;

[0046] Figure 4 This is a schematic diagram of the structure of the rear electrode plate fixture according to one embodiment of the present invention;

[0047] Figure 5 This is a schematic diagram of the rear electrode plate coating device according to another embodiment of the present invention;

[0048] Figure 6 The coated rear electrode plate obtained in Embodiment 2 of the present invention;

[0049] Figure 7 The coated rear electrode plate obtained in Embodiment 3 of the present invention;

[0050] Figure 8 This is the coated rear electrode plate obtained in Comparative Example 1 of the present invention;

[0051] Figure 9 This is the coated rear electrode plate obtained in Comparative Example 2 of the present invention. Detailed Implementation

[0052] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0053] It should be noted that the following embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0054] Example 1

[0055] This embodiment provides a rear electrode plate coating device for electret microphones, such as... Figure 1 As shown, the coating device includes the following core components: a film tensioning ring 10, a tensioning ring positioning frame 20, a rear electrode plate fixture 30, a lifting platform 40, and a hot pressing component 50.

[0056] The film tensioning ring 10 is used to fix the electret film and maintain a certain tension in all directions. The film tensioning ring 10 can be circular, square, or other shapes. In this embodiment, the film tensioning ring is circular, and the material can be wood, metal, or high-temperature resistant plastics such as PEEK, polytetrafluoroethylene, etc. It adopts an inner and outer double-ring structure, see [reference needed]. Figure 2 It includes a support ring 101 and a clamping ring 102, with the support ring 101 inside and the clamping ring 102 outside. A locking screw is provided on the clamping ring 102, and the electret film is clamped between the two rings and fixed by the locking screw. In another embodiment, the film tensioning ring 10 is square and adopts an upper and lower stacked structure, see [reference]. Figure 3 It can be quickly tightened using a wing nut and a screw.

[0057] The rear electrode plate fixture 30 is used to place the rear electrode plate 60. An array of grooves is provided on the surface of the rear electrode plate fixture 30 to position the rear electrode plate 60.

[0058] The lifting platform 40 carries the rear electrode plate fixture 30 and controls its lifting and lowering to perform the coating operation. The lifting platform 40 uses a precision lead screw for drive, resulting in better precision and stability. The specific lifting stroke is selected according to the specific situation, for example, a stroke of 0-50mm and an accuracy of ±0.01mm. The lifting platform 40 can raise the rear electrode plate fixture 30 to a maximum height higher than the plane where the electret film is fixed by the film tensioning ring 10. In other words, the lifting platform 40 enables the rear electrode plate 60 on the rear electrode plate fixture 30 to lift the electret film on the film tensioning ring 10 to a certain height.

[0059] The hot pressing component 50 is used to perform the hot pressing operation, bonding the electret film onto the rear electrode plate 60. The hot pressing component 50 includes a hot pressing platform 502 that can be raised and lowered along a lifting column 501, and a heating plate 503 disposed below the hot pressing platform 502. The heating plate 503 has a built-in PID temperature control system, and the temperature range can be controlled within room temperature to 400℃ with an accuracy of ±1℃. The hot pressing component 50 can also have its own pressure control system to control the pressure value during hot pressing.

[0060] The tension ring positioning frame 20 serves two purposes: firstly, to fix the membrane tension ring 10, and secondly, to integrate the various components of the entire device. The main body of the tension ring positioning frame 20 is a roughly U-shaped frame, which can be made of wood, plastic, or metal. In this embodiment, aluminum alloy is used. A storage space is formed in the middle of the U-shaped frame, and positioning grooves are provided on both sides of the top opening of the U-shaped frame to engage the outer edge of the membrane tension ring. The lifting platform is housed within the storage space, and the rear electrode plate fixture 30 is installed on top of the lifting platform 40, directly below the membrane tension ring 10.

[0061] The lifting column of the hot pressing component 50 is located on one side of the tension ring positioning frame 20. It can be fixed to the tension ring positioning frame 20 or operate independently of it. The heating plate is located directly above the thin film tension ring 10. The projected area of ​​the heating plate is slightly larger than the area of ​​the rear electrode fixture 30. The up-and-down movement of the hot pressing table of the hot pressing component 50 on the lifting column can be manual or implemented by a precision lead screw or other automatic means.

[0062] In another embodiment, a heat-spreading buffer component is also provided. This component is used to lay a heat-spreading buffer film 80 under the hot pressing table of the hot pressing component 50 to further improve the flatness of the coating and prevent the electret film from sticking to the upper heating plate after hot pressing and melting. See also Figure 5The heat-spreading buffer component 70 includes a feeding roller 701 and a receiving roller 702. The feeding roller is equipped with a heat-spreading buffer film 80, such as a PI film. The receiving roller 702 is driven by a drive motor. The feeding roller 701 can be a driven roller, rotating with the heat-spreading buffer film driven by the receiving roller 702, or it can be a driven roller, driven by a motor, rotating at the same frequency as the receiving roller 702 to ensure smooth movement of the heat-spreading buffer film 80. During the lamination process, the receiving roller 702 rotates once after each lamination to roll up the used heat-spreading buffer film 80 onto the receiving roller 702, replacing the heat-spreading buffer film 80 that has been heat-pressed below the hot-pressing platform with a new heat-spreading buffer film 80 on the feeding roller 701. The positions of the feeding roller 701 and the receiving roller 702 are such that the heat equalization buffer film 80 can pass through horizontally from above the tension ring positioning frame 20. For example, the two are located on both sides of the tension ring positioning frame 20. The tension ring positioning frame 20 is also provided with a through groove for the heat equalization buffer film 80 to pass through, located above the positioning groove, and penetrating the upper part of the tension ring positioning frame 20 in the horizontal direction.

[0063] Example 2

[0064] This embodiment provides a method for coating a rear electrode plate, based on the rear electrode plate coating device of Embodiment 1. In this embodiment, the rear electrode plate is a cylindrical stainless steel rear electrode plate with an upper surface diameter of 7mm and a height of 12mm, but this method is also applicable to other rear electrode plates. The method includes the following steps:

[0065] ① Insert the rear electrode plate into the groove of the rear electrode plate fixture, and place the rear electrode plate fixture on the lifting platform;

[0066] ② Cut the electret film (PTFE film) to a suitable size, place it on the support ring of the film tensioning ring, and tighten the clamping ring; the degree of fixation of the electret film should be based on the overall surface being flat and without wrinkles.

[0067] ③ The membrane tensioning ring is inserted into the groove of the tensioning ring positioning frame;

[0068] ④ The lifting platform is raised at a speed of 0.5 mm / s until the rear electrode plate contacts the film and is lifted by 5.5 mm (the electret film is fully tensioned).

[0069] ⑤ Press down the heating plate (pressure 0.5MPa, temperature 300℃) and hot press for 5 minutes to melt the PTFE and bond it to the back electrode plate;

[0070] ⑥ After cooling to room temperature, remove the rear electrode fixture and trim off any excess film from the edges.

[0071] Example 3

[0072] This embodiment provides a method for coating a rear electrode plate, based on the rear electrode plate coating device of Embodiment 1. In this embodiment, the rear electrode plate is a cylindrical stainless steel rear electrode plate with an upper surface diameter of 7mm and a height of 12mm, but this method is also applicable to other rear electrode plates. The method includes the following steps:

[0073] ① Insert the rear electrode plate into the groove of the rear electrode plate fixture, and place the rear electrode plate fixture on the lifting platform;

[0074] ② Cut the electret film (PTFE film) to a suitable size, place it on the support ring of the film tensioning ring, and tighten the clamping ring; the degree of fixation of the electret film should be based on the overall surface being flat and without wrinkles.

[0075] ③ The membrane tensioning ring is inserted into the groove of the tensioning ring positioning frame;

[0076] ④ The lifting platform is raised at a speed of 0.5 mm / s until the rear electrode plate contacts the film and is lifted by 5.5 mm (the electret film is fully tensioned).

[0077] ⑤ A PI release film (10 μm thick) is laid on the surface of the electret film using a heat-spreading buffer component;

[0078] ⑥ Press down the heating plate (pressure 0.5MPa, temperature 300℃) for 5 minutes to melt the PTFE and bond it to the back electrode plate;

[0079] ⑦ After cooling to room temperature, remove the rear electrode fixture and trim off any excess film from the edges.

[0080] Example 4

[0081] This embodiment provides a method for coating a rear electrode plate, based on the rear electrode plate coating device of Embodiment 1. The difference from Embodiment 3 lies in the heating method in step ⑥. In this embodiment, a three-stage gradient heating method is used. In the first stage, preheating is performed at 200°C for 1 minute to soften the electret film and eliminate thermal expansion stress. In the second stage, melting is performed at 320°C for 3 minutes to completely melt the PTFE and tightly cover the rear electrode plate. In the third stage, shaping is performed at 280°C for 1 minute to suppress cooling shrinkage wrinkles. After three-stage gradient hot pressing, the coating quality is superior.

[0082] Comparative Example 1

[0083] Traditional lamination method: the lamination method in CN116437278A.

[0084] 1) A 25-micron thick FEP film is preferred as the bonding material. Before bonding, the FEP film to be bonded to the back electrode is subjected to corona treatment (voltage -5kV to -15kV or 5kV to 15kV) to break and degrade the chemical bonds of the plastic molecules, increasing surface roughness and surface area, and improving adhesion to the back electrode. A 30% silica dispersion is coated on the electret back electrode, and then baked in a 100℃ oven for 30 minutes to remove the liquid components from the silica dispersion.

[0085] 2) During installation, first place the FEP film on the base plate, then place the rear electrode plate of the electret microphone into the middle plate, cover it with the top plate, and fix the FEP film, top plate, middle plate and base plate with fastening screws so that the rear electrode plate is in contact with the FEP film.

[0086] 3) Place the fixture containing the FEP film and the back electrode plate into a vacuum chamber for vacuum treatment (evacuate to 0.3 atm, vacuum treatment time is 20 minutes) to remove air bubbles between the FEP film and the back electrode plate. Place the fixture after the air bubble removal operation into an oven, the upper end of which is connected to compressed air, which can pressurize the molten FEP film to improve the adhesion and can also make the FEP on the damping hole of the back electrode plate through the hole.

[0087] 4) Set the oven temperature to 350℃. After heating to the specified temperature, turn on the compressed air (0.4 MPa pressure) switch to pressurize the molten FEP film and improve its adhesion. Since the damping orifice is a through hole, the pressure generated by the compressed air can blow away the FEP film covering the damping orifice, ensuring that the damping orifice is unobstructed. Apply compressed air for 5 minutes. After turning off the compressed air switch, continue to maintain 350℃ for 30 minutes, then turn off the oven heating and allow it to cool naturally to room temperature, completing the preparation of the electret.

[0088] Comparative Example 2

[0089] The difference from Example 3 is that the operation of step ④ is different. In step ④ of this comparative example, the lifting platform is raised at a speed of 0.5 mm / s until the rear electrode plate contacts the film, and the rear electrode plate does not continue to rise.

[0090] The flatness of the coating obtained by the coating methods of Examples 2-4 and Comparative Examples 1-2 was tested, and the results are shown in Tables 1-5.

[0091] Detection method:

[0092] Flatness testing was performed using a dial indicator. Six rear plates were selected for testing in each embodiment or comparative example. The center point of the rear plate was measured first and then zeroed. Then, four edge points on the rear plate were measured (one point every 90°).

[0093] Appearance inspection: Linglingxing HDMI high-definition 4K measuring electron microscope 4800-E, magnification 50x.

[0094] Table 1. Detection data of film smoothness using the method described in Example 2

[0095] Rear plate serial number Center point of the rear electrode (μm) Flatness (μm) of point 1 on the rear electrode plate from the center. Flatness (μm) of point 2 on the rear electrode plate from the center. Flatness (μm) of point 3 on the rear electrode plate from the center. Flatness (μm) of point 4 on the rear electrode plate from the center. 1 0 -0.6 0.8 -0.8 0.7 2 0 0.8 -1.0 -1.1 0.9 3 0 1.1 -1.0 0.9 -1.0 4 0 -0.8 0.9 1.1 0.8 5 0 0.9 -1.0 1.0 0.8 6 0 0.8 1.0 -1.2 1.1

[0096] Table 2. Test data on the flatness of the coating as described in Example 3

[0097] Rear plate serial number Center point of the rear electrode (μm) Flatness (μm) of point 1 on the rear electrode plate from the center. Flatness (μm) of point 2 on the rear electrode plate from the center. Flatness (μm) of point 3 on the rear electrode plate from the center. Flatness (μm) of point 4 on the rear electrode plate from the center. 1 0 -0.3 0.2 -0.2 0.6 2 0 0 -0.6 0.5 -0.1 3 0 0.4 0.3 0.2 -0.3 4 0 -0.4 -0.1 0.3 0.4 5 0 0.2 -0.1 0.3 0.6 6 0 0.2 0.4 -0.5 -0.2

[0098] Table 3. Test data on the flatness of the coating as described in Example 4

[0099] Rear plate serial number Center point of the rear electrode (μm) Flatness (μm) of point 1 on the rear electrode plate from the center. Flatness of point 2 on the rear electrode plate from the center (μm) Flatness (μm) of point 3 on the rear electrode plate from the center. Flatness (μm) of point 4 on the rear electrode plate from the center. 1 0 0.2 -0.2 -0.2 0.3 2 0 -0.1 -0.1 0.3 -0.1 3 0 0.2 0.1 -0.1 0.2 4 0 -0.3 -0.2 0.3 0.3 5 0 -0.2 -0.1 0.2 0.1 6 0 0.1 0.3 -0.2 -0.2

[0100] Table 4. Test data on the flatness of the coating produced by the method described in Comparative Example 1

[0101] Rear plate serial number Center point of the rear electrode (μm) Flatness (μm) of point 1 on the rear electrode plate from the center. Flatness of point 2 on the rear electrode plate from the center (μm) Flatness (μm) of point 3 on the rear electrode plate from the center. Flatness (μm) of point 4 on the rear electrode plate from the center. 1 0 10.1 11.2 -6.6 11.3 2 0 -5.7 -12.5 13.4 -6.6 3 0 12.2 10.3 9.1 3.7 4 0 -6.9 -6.1 -11.2 10.9 5 0 12.9 7.8 5.0 -11.1 6 0 -10.4 11.8 9.6 6.7

[0102] Table 5. Test data on the flatness of the coating produced by the method described in Comparative Example 2

[0103] Rear plate serial number Center point of the rear electrode (μm) Flatness (μm) of point 1 on the rear electrode plate from the center. Flatness of point 2 on the rear electrode plate from the center (μm) Flatness (μm) of point 3 on the rear electrode plate from the center. Flatness (μm) of point 4 on the rear electrode plate from the center. 1 0 12.2 13.2 10.1 -6.4 2 0 -15.3 -9.5 -16.2 -19.6 3 0 21.6 22.3 -5.6 10.9 4 0 8.9 -6.6 17.2 -11.2 5 0 -18.9 9.4 -11.9 10.2 6 0 19.2 12.3 9.1 4.9

[0104] As can be seen from the results shown in Tables 1-5, in Example 2, using the device of the present invention for coating the rear electrode plate, the results (Table 1) show that the maximum deviation was 1.2 μm, and the average deviation [Σ|deviation at each point| / 24 (6 samples × 4 detection points)] was 0.72 μm. Figure 6 The results showed virtually no air bubbles. In Example 3, compared to Example 2, a PI film was further used during the lamination process. The results (Table 2) showed a maximum deviation of 0.6 μm and an average deviation of 0.25 μm, both significantly lower than the deviation values ​​in Example 2. This indicates that using a PI film further improves the smoothness of the lamination. Figure 7 No bubbles were observed. In Example 4, compared to Example 3, gradient heating was further used during the lamination process. The results (Table 3) show a maximum deviation of 0.3 μm and an average deviation of 0.18 μm, both significantly lower than the deviation values ​​in Example 3. This indicates that using gradient heating during the lamination process is beneficial for further improving the smoothness of the lamination. Comparative Example 1 used a lamination method from the prior art. The results (Table 4) show a maximum deviation of 13.4 μm and an average deviation of 8.91 μm, significantly higher than the deviation values ​​in Examples 2-4. Figure 8The results show that there are many bubbles, and the bubbles are large in size. In Comparative Example 2, compared to Example 3, the rear electrode plate was not pushed out of the electret film during the coating process. The results (Table 5) show that the maximum deviation is 22.3 μm, and the average deviation is 19.78 μm, which are significantly higher than the deviation values ​​in Examples 2-4. Figure 9 The large number of bubbles indicates that the ejection step is crucial for the quality of the coating.

Claims

1. A device for coating the rear electrode plate of an electret microphone, characterized in that, include: Thin film tensioning ring, used to continuously fix electret thin films under a certain tension; A rear electrode plate fixture, located below the film tensioning ring, is used to install the rear electrode plate to be coated; A lifting platform is located below the rear electrode plate fixture, used to support the rear electrode plate fixture and control the lifting of the rear electrode plate fixture. The maximum height that the rear electrode plate fixture can reach is higher than the plane where the film tensioning ring fixes the electret film. A hot-pressing component, located above the film tensioning ring, is used to perform hot pressing to cover the electret film onto the rear electrode plate.

2. The rear electrode plate coating device for an electret microphone according to claim 1, characterized in that, The film tensioning ring includes a support ring and a clamping ring, and the electret film is clamped between the support ring and the clamping ring.

3. The rear electrode plate coating device for an electret microphone according to claim 2, characterized in that, The clamping ring and the support ring are arranged vertically, and the support ring and the clamping ring are locked or unlocked by a locking device.

4. The rear electrode plate coating device for an electret microphone according to claim 2, characterized in that, The support ring and the clamping ring are arranged inside and outside of each other, and the clamping ring located on the outer side is used to lock or open the support ring and the clamping ring through a locking member.

5. The rear electrode plate coating device for an electret microphone according to claim 1, characterized in that, The film tensioning ring is installed via a tensioning ring positioning frame.

6. The rear electrode plate coating device for an electret microphone according to claim 5, characterized in that, The tension ring positioning frame includes a main body that forms an internal storage space. The top of the storage space has an opening, and tension ring positioning grooves for positioning the film tension ring are provided on both sides of the main body. The lifting platform and the rear electrode plate fixture are placed in the storage space.

7. The rear electrode plate coating device for an electret microphone according to claim 1, characterized in that, The rear electrode plate coating device also includes a heat equalization buffer component, which is used to lay a heat equalization buffer film below the hot pressing component and above the film tensioning ring.

8. A method for coating the rear electrode plate of an electret microphone, characterized in that, The rear electrode coating device according to any one of claims 1-7 is used to implement this.

9. A method for coating the rear electrode plate of an electret microphone according to claim 8, characterized in that, Includes the following steps: S1. Place the rear electrode plate to be coated into the rear electrode plate fixture, and then place it on the platform of the lifting table. S2. Secure the electret film using a film tensioning ring; S3. Place the film tensioning ring, which has fixed the electret film, into the tensioning ring positioning frame; S4. Raise the rear electrode plate on the lifting platform until the rear electrode plate contacts the electret film and lifts the electret film. S5. Press the hot-pressing component down to contact the electret film, and continue to heat the electret film until the electret film begins to melt and bond with the back electrode plate. S6. After hot pressing is completed, open the hot pressing table, wait for the rear electrode plate to cool down, remove the rear electrode plate and cut off the excess electret film at the edge of the rear electrode plate.

10. A method for coating the rear electrode plate of an electret microphone according to claim 8, characterized in that, In step S4, the electret film is lifted to a height of 5-10 mm.

Images