Film covering device and film covering method for rear polar plate of electret microphone

Abstract

The invention belongs to the technical field of microphones, and relates to a film covering device and method for a rear pole plate of an electret microphone, and the device comprises a film tensioning ring which is used for continuously fixing an electret film with a certain tension; the rear polar plate jig is positioned below the film tensioning ring and is used for mounting a rear polar plate; the lifting platform is positioned below the rear polar plate jig and is used for bearing the rear polar plate jig and controlling the lifting of the rear polar plate jig, and the maximum height that the rear polar plate jig can reach is higher than the plane where the electret film is fixed by the film tensioning ring; and the hot pressing part is positioned above the thin film tensioning ring and is used for implementing hot pressing to cover the electret thin film on the rear polar plate. The film tensioning ring is used for fixing the electret film, the electret film is continuously fixed with certain tension, the film laminating tension is guaranteed, and the adverse effect of high-temperature hot pressing on the film laminating effect is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of microphones, in particular to the preparation of a back plate electret, and particularly relates to a back plate coating device and a coating method for an electret microphone. Background Art

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

[0003] In the production process of electret microphones, one of the steps is to cover the electret film on the upper surface of the rear plate to form a capacitor with the diaphragm.

[0004] In the prior art, some research on preparing electret film on the back plate is disclosed as follows.

[0005] CN116437278A discloses a method for laminating an FEP film to the back plate of an electret microphone and a microphone electret. The method includes corona treatment of the side of the FEP film to be laminated to the back plate, coating the electret microphone back plate with a silica dispersion, and baking the film; placing the FEP film in contact with the electret microphone back plate and laminating the film; vacuuming the film to remove air bubbles between the film and the back plate; heating the film in an oven, and introducing compressed air when the temperature reaches a set temperature to pressurize the molten FEP film and blow away the portion of the FEP film covering the damping hole of the electret microphone back plate; and stopping the introduction of compressed air, maintaining the film for a period of time, and then cooling the film to room temperature, thereby completing the lamination of the electret.

[0006] Patent application CN115678360B describes a method for preparing a composite electret and the resulting composite electret. This method forms two polymer layers on an electrode plate. The first layer is formed by high-temperature film formation using a dispersion in which inorganic nanoparticles are added. The second layer is formed by directly overlaying a thin film on the first layer. This method reduces the decomposition of the electret polymer. The addition of inorganic nanoparticles to the first polymer dispersion significantly improves the electret's charge performance and significantly simplifies the production process, achieving process stability and energy conservation and emission reduction.

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

[0008] The present invention provides a laminating device and method for a rear plate of an electret microphone, which eliminate defects such as stripes, wrinkles, and bubbles in the electret film after lamination, thereby achieving surface smoothness and production yield of the electret film of the electret microphone.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

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

[0011] Film tensioning ring, used to continuously fix the electret film at a certain tension;

[0012] A rear plate jig, located below the film tensioning ring, for mounting the rear plate to be coated;

[0013] A lifting platform is located below the rear plate jig, and is used to carry the rear plate jig and control the lifting and lowering of the rear plate jig, and the maximum height that the rear plate jig can reach is higher than the plane where the film tensioning ring fixes the electret film;

[0014] The hot pressing component is located above the film tensioning ring and is used for hot pressing to cover the electret film on the rear plate.

[0015] In existing technology, electret film often exhibits quality defects such as streaks, wrinkles, and bubbles after being applied to the backplate. Analysis suggests that this may be due to the fact that existing methods typically involve directly applying the electret film to the backplate. However, electret films such as FEP, PFA, and PTFE typically require a maximum temperature of over 280°C during the fusion bonding process. Typically, in the 100°C-200°C range, the electret film expands slightly due to its thermal expansion and contraction properties. As the temperature continues to rise, when the electret material approaches its melting point (e.g., 260°C for FEP), the crystalline regions of the FEP begin to melt, disrupting the previously ordered lattice structure and transforming the tightly packed molecular chains into a disordered state. This phase transition releases internal stress, causing volume contraction.

[0016] In addition, the error in the flatness of the heating plate will make it difficult for the heating plate to completely flatten the 10-30 micron 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 on the electret film after it is coated on the rear plate.

[0017] In the above-mentioned solution of the present invention, the electret film is maintained in an initial tensioned state by means of a film tensioning ring. The rear plate fixture is then raised by means of a lifting platform, bringing the rear plate into contact with the electret film and lifting the electret film. At this point, the film on the surface of the rear plate is in a tensioned state. The electret film in this tensioned state has a high degree of flatness. Furthermore, when the electret film expands due to heat, the tensioning force exerted by the rear plate on the electret film can still help the electret film maintain a continuously tensioned and flat state.

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

[0019] Preferably, the clamping ring and the supporting ring are arranged one above the other, and the supporting ring and the clamping ring are locked or opened by a locking member.

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

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

[0022] Preferably, the tensioning ring positioning frame includes a main body with a storage space formed inside, an opening at the top of the storage space, and tensioning ring positioning grooves for positioning the film tensioning ring are opened on the main body on both sides of the opening, and the lifting platform and the rear plate fixture are placed in the storage space.

[0023] Preferably, the rear plate coating device further comprises a heat-equalizing buffer component, through which a layer of heat-equalizing buffer film can be laid below the hot pressing component and above the film tensioning ring.

[0024] In this solution, a heat-equalizing buffer film is added to the bottom of the hot pressing component and above the film tensioning ring through the heat-equalizing buffer component. The heat-equalizing buffer film uses a low thermal conductivity film material, such as a PI film (thermal conductivity coefficient of approximately 0.2 W / m·K) to delay the instantaneous heat transfer from the hot pressing plate to the film, avoid local overheating and decomposition of the electret film (such as PTFE), and allow heat to penetrate evenly through the heat-equalizing buffer film, reducing micro-wrinkles caused by thermal stress concentration. At the same time, the heat-equalizing buffer film also forms a flexible transition layer between the hot pressing component and the electret film, converting the local pressure points of the hot pressing component into a uniformly distributed load, eliminating the film depression caused by micro-pits on the surface of the rear plate. Moreover, the heat-equalizing buffer film can also prevent adhesion between the electret film and the hot pressing component. In summary, by adding a heat-equalizing buffer film to the rear plate coating device, the flatness of the coating can be further improved.

[0025] Preferably, the heat-scaling buffer component includes a feed roller and a take-up roller, which are driven to rotate by a drive structure. During the lamination process, the take-up roller rotates once each time the film is laminated to rewind the used heat-scaling buffer film onto the take-up roller and replace it with a new heat-scaling buffer film.

[0026] In a second aspect, the present invention provides a method for coating a rear plate of an electret microphone, based on the above-mentioned coating device.

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

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

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

[0030] S3. Place the film tensioning ring that fixes the electret film into the tensioning ring positioning frame.

[0031] S4. Raise the rear plate on the lifting platform until it contacts the electret film and lifts up the electret film. At this point, the electret film is in a tensioned state in all directions.

[0032] S5. Press the hot pressing component down until it contacts the electret film, and continue heating the electret film until the electret film begins to melt and adheres to the rear plate.

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

[0034] Preferably, in step S4, the electret film is lifted up to a height of 5-10 mm, where 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-saturating buffer film is laid on the upper surface of the electret film, such as a PI film, to further improve the flatness of the coating and prevent the electret film from sticking to the hot pressing plate during hot pressing.

[0036] Before fixing, the electret film is cut into a specified size, such as 100mm*10mm. Electret films such as FEP, PFA, PTFE, etc. are cut into a 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 by a film tensioning ring, continuously fixes the electret film with a certain tension, ensures the lamination tension, and reduces the adverse effects of high temperature hot pressing on the lamination effect.

[0039] 2. Based on the film tensioning ring, the rear plate is lifted 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 laminated in this state to further eliminate defects such as stripes, wrinkles, and bubbles in the electret film after lamination.

[0040] 3. The present invention adds a heat-equalizing buffer film below the hot pressing component and above the film tensioning ring through the heat-equalizing buffer component, which can not only prevent the adhesion between the electret film and the hot pressing component, but also further improve the flatness of the coating.

[0041] 4. The present invention uses a tensioning ring positioning frame to reasonably integrate various parts of the device, making the device more compact, occupying a smaller area, and making the laminating operation more convenient and efficient.

[0042] 5. By controlling the rising height of the rear plate fixture and the hot pressing conditions during the lamination process, the lamination quality can be further guaranteed. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the structure of the rear plate coating device shown in the present invention;

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

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

[0046] Figure 4 Schematic diagram of the structure of the rear plate fixture according to one embodiment of the present invention;

[0047] Figure 5 A schematic structural diagram of the rear plate coating device according to another embodiment of the present invention;

[0048] Figure 6 The back plate after coating obtained in Example 2 of the present invention;

[0049] Figure 7 The rear plate after coating obtained in Example 3 of the present invention;

[0050] Figure 8 The rear plate after coating obtained in Comparative Example 1 of the present invention;

[0051] Figure 9 This is the rear plate after coating obtained in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

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

[0053] It should be noted that the following implementation cases are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned implementation cases, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned implementation cases, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the implementation cases of the present invention.

[0054] Example 1

[0055] This embodiment provides a back plate coating device for an electret microphone, such as Figure 1 As shown, the laminating device includes the following core components: a film tensioning ring 10, a tensioning ring positioning frame 20, a rear 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 round, square or other shapes. In this embodiment, the film tensioning ring is set to be circular and can be made of wood, metal, or high-temperature resistant plastic such as PEEK, polytetrafluoroethylene, etc. It adopts an inner and outer double ring structure, see Figure 2 , including a support ring 101 and a clamping ring 102, the support ring 101 is inside and the clamping ring 102 is outside. A locking screw is provided on the clamping ring 102. The electret film is clamped between the two rings and fixed by the locking screw. In another embodiment, the film tensioning ring 10 is set in a square shape and adopts an upper and lower stacked structure. Figure 3 , quickly locked by butterfly nut and nut.

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

[0058] The lifting platform 40 supports the rear plate jig 30 and controls its elevation to perform the lamination operation. The platform 40 utilizes a precision lead screw to drive the platform, providing enhanced precision and stability. The specific lifting stroke is selected based on the specific situation, for example, a stroke of 0-50mm with an accuracy of ±0.01mm. The maximum height to which the lifting platform 40 can raise the rear plate jig 30 is higher than the plane where the film tensioning ring 10 secures the electret film. This means that the lifting platform 40 enables the rear plate 60 on the rear plate jig 30 to lift the electret film on the film tensioning ring 10 to a certain height.

[0059] The hot pressing unit 50 is used to perform hot pressing operations, hot pressing the electret film onto the back plate 60. This unit 50 comprises a hot pressing platform 502 that can be raised and lowered along a lifting column 501, and a heating plate 503 positioned below the hot pressing platform 502. The heating plate 503 has a built-in PID temperature control system that can control the temperature between room temperature and 400°C with an accuracy of ±1°C. The hot pressing unit 50 can also include a built-in pressure control system to control the pressure during hot pressing.

[0060] The tensioning ring positioning frame 20 is used to secure the film tensioning ring 10 and integrate the various components of the entire device. The main body of the tensioning 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. Positioning grooves are set on both sides of the top opening of the U-shaped frame to engage the outer edge of the film tensioning ring. The lifting platform is accommodated within the storage space, and the rear plate fixture 30 is mounted on the top of the lifting platform 40, directly below the film tensioning ring 10.

[0061] The lifting column of the hot-pressing unit 50 is located on one side of the tensioning ring positioning frame 20. It can be fixed to the tensioning ring positioning frame 20 or independent of the tensioning ring positioning frame 20. The heating plate is located directly above the film tensioning ring 10. The projected area of ​​the heating plate is slightly larger than the area of ​​the back plate jig 30. The hot-pressing table of the hot-pressing unit 50 moves up and down on the lifting column either manually or via a precision lead screw or other automated means.

[0062] In another embodiment, a heat-saturating buffer component is further provided, which is used to lay a heat-saturating buffer film 80 under the hot pressing platform 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 being melted by hot pressing. Figure 5The heat-saturating buffer component 70 includes a discharge roller 701 and a take-up roller 702. The discharge roller is equipped with a heat-saturating buffer film 80, such as a PI film. The take-up roller 702 is driven by a drive motor. The discharge roller 701 can be a driven roller, driven by the take-up roller 702 to rotate the heat-saturating buffer film, or it can be an active roller, driven by a motor and rotating at the same frequency as the take-up roller 702 to ensure smooth movement of the heat-saturating buffer film 80. During the lamination process, the take-up roller 702 rotates once after each lamination to rewind the used heat-saturating buffer film 80 onto the take-up roller 702, and the new heat-saturating buffer film 80 on the discharge roller 701 replaces the heat-saturating buffer film 80 under the hot pressing platform. The positions of the discharge roller 701 and the receiving roller 702 can enable the heat-equalizing buffer film 80 to pass across from above the tensioning ring positioning frame 20. For example, the two are respectively located on both sides of the tensioning ring positioning frame 20. The tensioning ring positioning frame 20 is also provided with a passing groove for the heat-equalizing buffer film 80 to pass through, which is located above the positioning groove and passes through the upper part of the tensioning ring positioning frame 20 in the horizontal direction.

[0063] Example 2

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

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

[0066] ② Cut the electret film (PTFE film) to the appropriate 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 wrinkle-free.

[0067] ③ The film 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 plate contacts the film and lifts up 5.5 mm (the electret film is fully tensioned);

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

[0070] ⑥ After cooling to room temperature, remove the rear plate fixture and cut off the excess film at the edge.

[0071] Example 3

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

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

[0074] ② Cut the electret film (PTFE film) to the appropriate 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 wrinkle-free.

[0075] ③ The film 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 plate contacts the film and lifts up 5.5 mm (the electret film is fully tensioned);

[0077] ⑤ Use a heat-saturating buffer component to lay a PI release film (thickness 10μm) on the surface of the electret film;

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

[0079] ⑦ After cooling to room temperature, remove the rear plate fixture and trim the excess film from the edge.

[0080] Example 4

[0081] This embodiment provides a method for laminating a rear plate. This method is based on the rear plate laminating apparatus of Example 1 and differs from Example 3 in that the heating method in step ⑥ is different. In this embodiment, heating employs a three-stage gradient heating method. The first stage is preheating at 200°C for 1 minute to soften the electret film and eliminate thermal expansion stress. The second stage is melting at 320°C for 3 minutes to completely melt the PTFE and tightly coat the rear plate. The third stage is setting at 280°C for 1 minute to suppress shrinkage wrinkles during cooling. This three-stage gradient hot pressing method results in superior lamination quality.

[0082] Comparative Example 1

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

[0084] 1) 25-micron-thick FEP film is the preferred lamination material. Before lamination, the side of the FEP film that will be bonded to the back plate is corona treated (voltage of -5kV to -15kV or 5kV to 15kV) to break the chemical bonds in the plastic molecules and degrade them, increasing surface roughness and surface area, and improving adhesion to the back plate. A 30% by mass silica dispersion is applied to the electret back plate and then baked in a 100°C oven for 30 minutes to remove the liquid component of the silica dispersion.

[0085] 2) During installation, first place the FEP film on the bottom plate, place the electret microphone rear plate into the middle plate, cover with the top plate, and fix the FEP film, top plate, middle plate, and bottom plate with screws so that the rear plate fits the FEP film.

[0086] 3) Place the tooling containing the FEP film and rear plate in a vacuum chamber and evacuate to 0.3 atm for 20 minutes to remove air bubbles between the FEP film and the rear plate. The tooling, after the air bubble removal process, is placed in an oven with compressed air connected to the top. This pressurizes the molten FEP film to enhance adhesion and allows for through-hole processing of the FEP film in the rear plate's damping hole.

[0087] 4) Set the oven temperature to 350°C. Once heated to the desired temperature, turn on the compressed air (0.4 mPa pressure) to pressurize the molten FEP film and improve adhesion. Because the damping hole is a through hole, the pressure generated by the compressed air can blow away the FEP film covering the damping hole, ensuring that the damping hole is unobstructed. Apply compressed air for 5 minutes. After turning off the compressed air, maintain the 350°C temperature for another 30 minutes, then turn off the oven and allow it to cool naturally to room temperature. This completes 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 lifted at a speed of 0.5 mm / s until the rear plate contacts the film, and the rear plate does not continue to move upward.

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

[0091] Detection method:

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

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

[0094] Table 1 Test data of film flatness of the method described in Example 2

[0095] Rear plate serial number Center point of rear plate (μm) Flatness of point 1 on the rear plate from the center (μm) Flatness of point 2 on the rear plate from the center (μm) Flatness of point 3 on the rear plate from the center (μm) Flatness of point 4 on the rear plate from the center (μm) 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 of film flatness of the method described in Example 3

[0097] Rear plate serial number Center point of rear plate (μm) Flatness of point 1 on the rear plate from the center (μm) Flatness of point 2 on the rear plate from the center (μm) Flatness of point 3 on the rear plate from the center (μm) Flatness of point 4 on the rear plate from the center (μm) 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 of film flatness of the method described in Example 4

[0099] Rear plate serial number Center point of rear plate (μm) Flatness of point 1 on the rear plate from the center (μm) Flatness of point 2 on the rear plate from the center (μm) Flatness of point 3 on the rear plate from the center (μm) Flatness of point 4 on the rear plate from the center (μm) 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 of film flatness of the method described in Comparative Example 1

[0101] Rear plate serial number Center point of rear plate (μm) Flatness of point 1 on the rear plate from the center (μm) Flatness of point 2 on the rear plate from the center (μm) Flatness of point 3 on the rear plate from the center (μm) Flatness of point 4 on the rear plate from the center (μm) 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 of film flatness of the method described in Comparative Example 2

[0103] Rear plate serial number Center point of rear plate (μm) Flatness of point 1 on the rear plate from the center (μm) Flatness of point 2 on the rear plate from the center (μm) Flatness of point 3 on the rear plate from the center (μm) Flatness of point 4 on the rear plate from the center (μm) 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] From the results shown in Tables 1 to 5, it can be seen that in Example 2, the device of the present invention was used to coat the rear plate. The results show (Table 1) that the maximum deviation is 1.2 μm, the average deviation [Σ|deviation of each point| / 24 (6 samples × 4 test points)] is 0.72 μm, and Figure 6 Compared with Example 2, Example 3 further uses PI film in the lamination process. The results show (Table 2) that the maximum deviation is 0.6μm and the average deviation is 0.25μm, which are significantly lower than the deviation values ​​of Example 2. This shows that the addition of PI film is beneficial to further improve the flatness of the lamination, and Figure 7 No bubbles are shown. Compared with Example 3, Example 4 further uses gradient heating during the coating process. The results show (Table 3) that the maximum deviation is 0.3μm and the average deviation is 0.18μm, which are significantly lower than the deviation values ​​of Example 3. This shows that the use of gradient heating during the coating process is conducive to further improving the flatness of the coating. Comparative Example 1 uses the coating method in the prior art. The results show (Table 4) that the maximum deviation is 13.4μm and the average deviation is 8.91μm, which are significantly higher than the deviation values ​​in Examples 2-4, and Figure 8The results show that the number of bubbles is large and the volume of bubbles is large. In Comparative Example 2, compared with Example 3, the rear plate was not pushed out of the electret film during the coating process. The results show (Table 5) that the maximum deviation is 22.3μm and the average deviation is 19.78μm, which is significantly higher than the deviation values ​​in Examples 2-4, and Figure 9 The results show that there are many bubbles, which means that the ejection step is crucial to the lamination quality.

Claims

1. A back plate coating device for an electret microphone, characterized in that: include: Film tensioning ring, used to continuously fix the electret film at a certain tension; A rear plate jig, located below the film tensioning ring, for mounting the rear plate to be coated; A lifting platform is located below the rear plate jig, and is used to carry the rear plate jig and control the lifting and lowering of the rear plate jig, and the maximum height that the rear plate jig can reach is higher than the plane where the film tensioning ring fixes the electret film; The hot pressing component is located above the film tensioning ring and is used for hot pressing to cover the electret film on the rear plate.

2. The back plate coating device of an electret microphone according to claim 1, characterized in that: The film tensioning ring comprises a supporting ring and a pressing ring, and the electret film is clamped between the supporting ring and the pressing ring.

3. The back plate coating device of an electret microphone according to claim 2, characterized in that: The clamping ring and the supporting ring are arranged up and down, and the supporting ring and the clamping ring are locked or opened by a locking member.

4. The back plate coating device of an electret microphone according to claim 2, characterized in that: The support ring and the clamping ring are arranged inside and outside, and the clamping ring located on the outside is locked or opened by a locking piece.

5. The back plate coating device of an electret microphone according to claim 1, characterized in that: The film tensioning ring is installed through a tensioning ring positioning frame.

6. The back plate coating device of an electret microphone according to claim 5, characterized in that: The tensioning ring positioning frame includes a main body with a storage space formed inside, an opening at the top of the storage space, and tensioning ring positioning grooves for positioning the film tensioning ring are opened on the main body on both sides of the opening. The lifting platform and the rear plate fixture are placed in the storage space.

7. The back plate coating device of an electret microphone according to claim 1, characterized in that: The rear plate coating device further includes a heat-equalizing buffer component, which is used to lay a heat-equalizing buffer film below the hot pressing component and above the film tensioning ring.

8. A method for coating the back plate of an electret microphone, characterized in that: The method is implemented by using the rear plate coating device described in any one of claims 1 to 7.

9. The method for coating the back plate of an electret microphone according to claim 8, characterized in that: The steps include: S1. Place the rear plate to be coated into the rear plate fixture and then place it on the table of the lifting platform; S2. Fix the electret film using a film tensioning ring; S3. The film tension ring of the electret film is fixed and placed into the tension ring positioning frame; S4. Raise the rear plate on the lifting platform until the rear plate contacts the electret film and lifts the electret film; S5. Pressing the hot pressing member down to contact the electret film, continuously heating the electret film until the electret film begins to melt and bond to the rear plate; S6. After the hot pressing is completed, open the hot pressing platform, wait for the rear plate to cool down, remove the rear plate and cut off the excess electret film at the edge of the rear plate.

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

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